GOLF BALL

Description

FIELD OF THE DISCLOSURE

The present disclosure relates to a golf ball having improved durability.

DESCRIPTION OF THE RELATED ART

Examples of the construction of a golf ball include a two-piece golf ball composed of a core and a cover, a three-piece golf ball composed of a core, one intermediate layer covering the core and a cover covering the intermediate layer, and a multi-piece golf ball composed of a core, at least two intermediate layers covering the core and a cover covering the intermediate layers. As a material constituting each layer of the golf ball, an ionomer resin is used. The ionomer resin has high stiffness, and if it is used as the constituent member of the golf ball, a golf ball travelling a great flight distance can be obtained. Thus, the ionomer resin is widely used as the material for the intermediate layer or the cover of the golf ball.

For example, JP 2004-524418 A discloses a composition comprising a thermoplastic composition that is melt processible consisting essentially of: (a) a thermoplastic composition comprising an E/X/Y copolymer (where E is ethylene, X is an α,β ethylenically unsaturated carboxylic acid having C3 to C8, and Y is a softening comonomer selected from an alkyl acrylate and an alkyl methacrylate wherein the alkyl group has 1 to 8 carbon atoms), wherein a, the E/X/Y copolymer has a melt index of at least 75 grams per 10 minutes measured in accordance with condition E, ASTM D-1238 at a temperature of 190° C. using a weight of 2160 grams, b. X is about 2 to 30 wt % of the E/X/Y copolymer and Y is about 17 to 40 wt % of the E/X/Y copolymer, and c. at least 55% of X is neutralized by one or more cations of an alkaline metal, a transition metal or an alkaline earth metal; and (b) one or more aliphatic mono-functional organic acids having less than 36 carbon atoms or salts thereof in an amount of about 5 to 50 weight % based on total of (a) and (b), wherein greater than 80% of all the acids of (a) and (b) is neutralized by one or more cations of an alkaline metal, a transition metal or an alkaline earth metal.

JP 2002-219195 A discloses a golf ball material that is a mixture comprising, as essential components, 100 parts by mass of a resin component comprising a base resin and (e) a non-ionomer thermoplastic elastomer in a mass ratio of 100:0 to 50:50, (c) 5 to 80 parts by mass of a fatty acid having a molecular weight of 280 to 1500 and/or a derivative thereof, and (d) 0.1 to 10 parts by mass of a basic inorganic metal compound capable of neutralizing acidic groups left unneutralized in the base resin and the component (c), wherein the base resin comprises (a) an olefin-unsaturated carboxylic acid binary random copolymer and/or a metal ion-neutralized product of an olefin-unsaturated carboxylic acid binary random copolymer, and (b) an olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester ternary random copolymer and/or a metal ion-neutralized product of an olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester ternary random copolymer in a mass ratio of 100:0 to 25:75.

JP 2004-180725 A discloses a golf ball comprising a core and two or more cover layers covering the core, wherein the first cover layer is formed mainly from (a) a non-ionomer thermoplastic elastomer and (b) a mixture of (b-1) an isocyanate compound and (b2) a thermoplastic resin which does not substantially react with an isocyanate, the second cover layer is formed mainly from a mixture of a resin component containing (c) one or at least two base resins selected from (c-1) an olefin-unsaturated carboxylic acid binary random copolymer and a metal ion-neutralized product of an olefin-unsaturated carboxylic acid binary random copolymer, and (c-2) an olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester ternary random copolymer and a metal ion-neutralized product of an olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester ternary random copolymer, and (d) a non-ionomer thermoplastic elastomer in a weight ratio ranging from 100:0 to 50:50, (e) a fatty acid having 18 to 80 carbon atoms and/or a derivative thereof, (f) a metal ion source capable of neutralizing unneutralized acidic groups in the components (c) and (e), and (g) a compound having a molecular weight of 20,000 or less and having two or more reactive functional groups, and the first cover layer is adjacent to the second cover layer.

JP 2001-348467 A discloses a golf ball resin composition containing 100 parts by mass of (A) at least one thermoplastic resin component selected from (a-1) an olefin-unsaturated carboxylic acid random copolymer and/or an olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester ternary copolymer, (a-2) a metal ion-neutralized product of an olefin-unsaturated carboxylic acid random copolymer and/or a metal ion-neutralized product of an olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester ternary copolymer, and (a-3) a thermoplastic elastomer, and 0.1 to 10 parts by mass of (B) at least one wax component selected from (b-1) a fatty acid having 20 to 80 carbon atoms and/or a derivative thereof and (b-2) a natural wax oxide and/or natural wax derivative having a neutralization value ranging from 60 to 190 mgKOH/g.

JP 2013-78563 A discloses a golf ball resin composition comprising (A) at least one member selected from the group consisting of (a-1) a binary copolymer composed of an olefin and an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms, (a-2) a metal ion-neutralized product of a binary copolymer composed of an olefin and an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms, (a-3) a ternary copolymer composed of an olefin, an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and an α,β-unsaturated carboxylic acid ester, and (a-4) a metal ion-neutralized product of a ternary copolymer composed of an olefin, an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and an α,β-unsaturated carboxylic acid ester, and (B) a compound having a hydrocarbon chain, a cationic moiety and an anionic moiety in its molecule.

SUMMARY OF THE DISCLOSURE

Although the golf ball using an ionomer resin has high resilience and travels a great distance, the durability of the golf ball is not always sufficient.

The present disclosure has been made in view of the above circumstances, and an object of the present disclosure is to provide a golf ball having improved durability without substantially lowering resilience.

The present disclosure that has solved the above problem provides a golf ball comprising a core and at least one cover layer positioned outside the core, wherein the at least one cover layer is formed from a cover composition containing one or more ionomer resins, the ionomer resin comprises a copolymer (P) having a structural unit (A) derived from ethylene and/or an α-olefin having 3 to 20 carbon atoms and a structural unit (B) having a carboxyl group and/or a dicarboxylic anhydride group as an essential constitutional unit, and at least a part of the carboxyl group and/or the dicarboxylic anhydride group in the copolymer (P) is neutralized with at least one kind of metal ion selected from Group 1, Group 2 and Group 12 in the periodic table, and a loss modulus E″ at a temperature of 0° C. is 3.40×10⁷ Pa or less, wherein the loss modulus E″ at the temperature of 0° C. is determined by measuring a dynamic viscoelasticity of the cover composition under the following conditions.

• • <measuring conditions>
  • measuring mode: sine wave tensile mode
  • measuring temperature range: −100° C. to 100° C.
  • temperature increasing rate: 4° C./min
  • oscillation frequency: 10 Hz
  • measuring strain: 0.05%

According to the present disclosure, the durability of the golf ball is significantly improved without substantially lowering the resilience of the golf ball.

BRIEF DESCRIPTION OF THE DRAWINGS

The FIGURE is a partially cutaway cross-sectional view showing a golf ball according to one embodiment of the present disclosure.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present disclosure provides a golf ball comprising a core and at least one cover layer positioned outside the core, wherein the at least one cover layer is formed from a cover composition containing one or more ionomer resins, the ionomer resin comprises a copolymer (P) having a structural unit (A) derived from ethylene and/or an α-olefin having 3 to 20 carbon atoms and a structural unit (B) having a carboxyl group and/or a dicarboxylic anhydride group as an essential constitutional unit, and at least a part of the carboxyl group and/or the dicarboxylic anhydride group in the copolymer (P) is neutralized with at least one kind of metal ion selected from Group 1, Group 2 and Group 12 in the periodic table, and a loss modulus E″ at a temperature of 0° C. is 3.40×10⁷ Pa or less, wherein the loss modulus E″ at the temperature of 0° C. is determined by measuring a dynamic viscoelasticity of the cover composition under the following conditions. The ionomer resin contained in the cover composition preferably has a phase angle δ in a range from 50 degrees to 75 degrees at an absolute value G*=0.1 MPa of a complex modulus of elasticity measured by a rotary rheometer described later to make the loss modulus E″ of the cover composition at the temperature of 0° C. 3.40×10⁷ Pa or less.

• • <measuring conditions>
  • measuring mode: sine wave tensile mode
  • measuring temperature range: −100° C. to 100° C.
  • temperature increasing rate: 4° C./min
  • oscillation frequency: 10 Hz
  • measuring strain: 0.05%

First, the ionomer resin used in the present disclosure will be explained. The ionomer resin used in the present disclosure comprises, as a base resin, a copolymer (P) having a structural unit (A) derived from ethylene and/or an α-olefin having 3 to 20 carbon atoms and a structural unit (B) having a carboxyl group and/or a dicarboxylic anhydride group as an essential constitutional unit. These structural units (A) and (B) are substantially linearly random copolymerized. At least a part of the carboxyl group and/or the dicarboxylic anhydride group of the structural unit (B) are neutralized with at least one kind of metal ion selected from Group 1, Group 2 and Group 12 in the periodic table.

(1) Structural Unit (A)

The structural unit (A) is at least one structural unit selected from the group consisting of a structural unit derived from ethylene and a structural unit derived from the α-olefin having 3 to 20 carbon atoms. In other words, the structural unit (A) is a structural unit in the copolymer (P) formed by polymerizing ethylene and/or the α-olefin having 3 to 20 carbon atoms. The α-olefin in the present disclosure is an α-olefin having 3 to 20 carbon atoms represented by the structural formula: CH₂═CHR¹⁸ (R¹⁸ is a hydrocarbon group having 1 to 18 carbon atoms, and may be a linear structure or may have a branch). The α-olefin more preferably has 3 to 12 carbon atoms.

Specific examples of ethylene and/or the α-olefin having 3 to 20 carbon atoms for providing the structural unit (A) include ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-decene, 3-methyl-1-butene, and 4-methyl-1-pentene, and ethylene is preferable. Ethylene derived from a non-petroleum raw material such as a plant raw material as well as ethylene derived from a petroleum raw material can be used.

Ethylene and/or the α-olefin having 3 to 20 carbon atoms for forming the structural unit (A) may be one, or may be plural. Examples of a combination of two kinds include ethylene-propylene, ethylene-1-butene, ethylene-1-hexene, ethylene-1-octene, propylene-1-butene, propylene-1-hexene, and propylene-1-octene. Examples of a combination of three kinds include ethylene-propylene-1-butene, ethylene-propylene-1-hexene, ethylene-propylene-1-octene, propylene-1-butene-hexene, and propylene-1-butene-1-octene.

In the present disclosure, it is preferable that the structural unit (A) essentially includes the unit derived from ethylene, and optionally further includes one or more units derived from the α-olefin having 3 to 20 carbon atoms where necessary. The unit derived from ethylene in the structural unit (A) may range from 65 mol % to 100 mol % or may range from 70 mol % to 100 mol % with respect to the total mole of the structural unit (A). From the viewpoint of impact resistance, the structural unit (A) may consist of the structural unit derived from ethylene.

(2) Structural Unit (B)

The structural unit (B) is a structural unit having a carboxyl group and/or a dicarboxylic anhydride group, and is preferably, for example, a structural unit derived from a monomer having a carboxyl group and/or a structural unit derived from a monomer having a dicarboxylic anhydride group. It is noted that the structural unit (B) has the same structure as the structural unit derived from the monomer having the carboxyl group and/or the dicarboxylic anhydride group, but the structural unit (B) is not necessarily formed by using the monomer having the carboxyl group and/or the dicarboxylic anhydride group as described in the production method mentioned later.

Examples of the monomer having the carboxyl group for providing the structural unit (B) include an unsaturated carboxylic acid such as acrylic acid, methacrylic acid, maleic acid, fumaric acid, tetrahydrophthalic acid, itaconic acid, citraconic acid, crotonic acid, isocrotonic acid, norbornenedicarboxylic acid, and bicyclo[2,2,1]hept-2-ene-5,6-dicarboxylic acid.

Examples of the monomer having the dicarboxylic anhydride group for providing the structural unit (B) include an unsaturated dicarboxylic anhydride such as maleic anhydride, itaconic anhydride, citraconic anhydride, tetrahydrophthalic anhydride, 5-norbornene-2,3-dicarboxylic anhydride, 3,6-epoxy-1,2,3,6-tetrahydrophthalic anhydride, tetracyclo[6.2.1.1^3,6.0^2,7]dodeca-9-ene-4,5-dicarboxylic anhydride, and 2,7-octadiene-1-ylsuccinic anhydride.

Preferable examples of the structural unit (B) derived from the monomer having the carboxyl group and/or the dicarboxylic anhydride group include structural units derived from acrylic acid, methacrylic acid, or 5-norbornene-2,3-dicarboxylic anhydride from the viewpoint of industrial availability, and in particular, the structural unit (B) may be the structural unit derived from acrylic acid. In addition, the structural unit derived from the monomer having the carboxyl group and/or the dicarboxylic anhydride group may be one kind, or may be plural kinds.

It is noted that the dicarboxylic anhydride group may react with moisture in the air to open a ring and partially become a dicarboxylic acid. The dicarboxylic anhydride group may be ring-opened in a context without deviating from the gist of the present disclosure.

(3) Other Structural Units (C)

The copolymer (P) may include a structural unit (C) other than the structural units represented by the structural unit (A) and the structural unit (B). As the monomer for providing the structural unit (C), any monomer can be used, as long as the monomer is not included in the monomers for providing the structural unit (A) and the structural unit (B). The monomer for providing the structural unit (C) is not limited, as long as the monomer for providing the structural unit (C) is a compound having one or more carbon-carbon double bonds in the molecular structure, and examples thereof include a non-cyclic monomer represented by the following general formula (1) and a cyclic monomer represented by the following general formula (2).

Non-Cyclic Monomer

[In the general formula (1), T¹ to T³ are each independently a substituent selected from the group consisting of a hydrogen atom, a hydrocarbon group having 1 to 20 carbon atoms, a hydrocarbon group having 1 to 20 carbon atoms substituted with a hydroxyl group, a hydrocarbon group having 2 to 20 carbon atoms substituted with an alkoxy group having 1 to 20 carbon atoms, a hydrocarbon group having 3 to 20 carbon atoms substituted with an ester group having 2 to 20 carbon atoms, a hydrocarbon group having 1 to 20 carbon atoms substituted with a halogen atom, an alkoxy group having 1 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms, an ester group having 2 to 20 carbon atoms, a silyl group having 3 to 20 carbon atoms, a halogen atom, and a cyano group.

T⁴ is a substituent selected from the group consisting of a hydrocarbon group having 1 to 20 carbon atoms substituted with a hydroxyl group, a hydrocarbon group having 2 to 20 carbon atoms substituted with an alkoxy group having 1 to 20 carbon atoms, a hydrocarbon group having 3 to 20 carbon atoms substituted with an ester group having 2 to 20 carbon atoms, a hydrocarbon group having 1 to 20 carbon atoms substituted with a halogen atom, an alkoxy group having 1 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms, an ester group having 2 to 20 carbon atoms, a silyl group having 3 to 20 carbon atoms, a halogen atom, and a cyano group.]

The carbon backbone of the hydrocarbon group, the substituting alkoxy group, the substituting ester group, the alkoxy group, the aryl group, the ester group and the silyl group with regard to T¹ to T⁴ may have a branch, a ring and/or an unsaturated bond.

Regarding the number of carbon atoms of the hydrocarbon group with regard to T¹ to T⁴, the lower limit thereof is 1 or more, and the upper limit thereof is 20 or less, and may be 10 or less.

Regarding the number of carbon atoms of the substituting alkoxy group with regard to T¹ to T⁴, the lower limit thereof is 1 or more, and the upper limit thereof is 20 or less, and may be 10 or less.

Regarding the number of carbon atoms of the substituting ester group with regard to T¹ to T⁴, the lower limit thereof is 2 or more, and the upper limit thereof is 20 or less, and may be 10 or less.

Regarding the number of carbon atoms of the alkoxy group with regard to T¹ to T⁴, the lower limit thereof is 1 or more, and the upper limit thereof is 20 or less, and may be 10 or less.

Regarding the number of carbon atoms of the aryl group with regard to T¹ to T⁴, the lower limit thereof is 6 or more, and the upper limit thereof is 20 or less, and may be 11 or less.

Regarding the number of carbon atoms of the ester group with regard to T¹ to T⁴, the lower limit thereof is 2 or more, and the upper limit thereof is 20 or less, and may be 10 or less.

Regarding the number of carbon atoms of the silyl group with regard to T¹ to T⁴, the lower limit thereof is 3 or more, and the upper limit thereof is 18 or less, and may be 12 or less. Examples of the silyl group include a trimethylsilyl group, a triethylsilyl group, a trin-propylsilyl group, a triisopropylsilyl group, a dimethylphenylsilyl group, a methyldiphenylsilyl group and a triphenylsilyl group.

In the ionomer resin, T¹ and T² may be a hydrogen atom, T³ may be a hydrogen atom or a methyl group, and each of T¹ to T³ may be a hydrogen atom, from the viewpoint of easiness in production. In addition, T⁴ may be an ester group having 2 to 20 carbon atoms from the viewpoint of impact resistance.

Specific examples of the non-cyclic monomer include the case where T⁴ is an ester group having 2 to 20 carbon atoms, such as (meth)acrylic acid ester.

When T⁴ is an ester group having 2 to 20 carbon atoms, examples of the non-cyclic monomer include a compound represented by the structural formula: CH₂═C(R²¹)CO₂(R²²). Herein, R²¹ is a hydrogen atom or a hydrocarbon group having 1 to 10 carbon atoms, and may have a branch, a ring and/or an unsaturated bond. R²² is a hydrocarbon group having 1 to 20 carbon atoms, and may have a branch, a ring and/or an unsaturated bond. In addition, a hetero atom may be included at any position in R²².

Examples of the compound represented by the structural formula: CH₂═C(R²¹)CO₂ (R²²) include a compound in which R²¹ is a hydrogen atom or a hydrocarbon group having 1 to 5 carbon atoms, an acrylic acid ester in which R²¹ is a hydrogen atom, and a methacrylic acid ester in which R²¹ is a methyl group.

Specific examples of the compound represented by the structural formula: CH₂═C(R²¹)CO₂(R²²) include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, dodecyl (meth)acrylate, octadecyl (meth)acrylate, phenyl (meth)acrylate, toluyl (meth)acrylate, and benzyl (meth)acrylate.

It is noted that in the present disclosure, “(meth)acrylic acid” means “acrylic acid and/or methacrylic acid”.

Specific examples of the compound include methyl acrylate, ethyl acrylate, n-butyl (nBA) acrylate, isobutyl (iBA) acrylate, t-butyl ((BA) acrylate and 2-ethylhexyl acrylate, in particular, the compound may be n-butyl (nBA) acrylate, isobutyl (iBA) acrylate and t-butyl (tBA) acrylate.

It is noted that the non-cyclic monomer may be one kind, or may be plural kinds.

Cyclic Monomer

[In the general formula (2), R¹ to R¹² may be identical to or different from each other, and are selected from the group consisting of a hydrogen atom, a halogen atom and a hydrocarbon group having 1 to 20 carbon atoms, R⁹ and R¹⁰, or R¹¹ and R¹² may be integrated to form a divalent organic group, and R⁹ or R¹⁰ and R¹¹ or R¹² may form a ring with each other. In addition, n represents 0 or a positive integer, and when n is 2 or more, R⁵ to R⁸ may be identical to or different from each other in each repeating unit.]

Examples of the cyclic monomer include a norbornene-based olefin, and include a compound having a backbone of a cyclic olefin such as norbornene, vinyl norbornene, ethylidene norbornene, norbornadiene, tetracyclododecene, and tricyclo[4.3.0.12,5] deca-3-ene. The cyclic monomer may be 2-norbornene (NB), tetracyclo[6.2.1.13,6.02,7]dodeca-4-ene, or the like.

(4) Metal Ion

Examples of the metal ion of the salt of the carboxylic acid group in the ionomer resin include monovalent or divalent metal ions selected from the group consisting of the Group 1, the Group 2 and the Group 12 in the periodic table, and specific examples thereof include lithium (Li) ion, sodium (Na) ion, potassium (K) ion, rubidium (Rb) ion, magnesium (Mg) ion, calcium (Ca) ion and zinc (Zn) ion. In particular, sodium (Na) ion or zinc (Zn) ion is preferable from the viewpoint of easy handling.

The salt of the carboxylic acid group can be obtained, for example, by a reaction between the copolymer and a compound including a metal ion of Group 1, Group 2 or Group 12 in the periodic table after hydrolyzing or thermally decomposing an ester group of the copolymer, or while hydrolyzing or thermally decomposing an ester group of the copolymer. It is noted that the metal ion may be one kind, or may be plural kinds.

(5) Copolymer (P)

The copolymer (P) which is the base resin of the ionomer resin used in the present disclosure includes the structural unit (A) derived from ethylene and/or the α-olefin having 3 to 20 carbon atoms and the structural unit (B) having the carboxy group and/or the dicarboxylic anhydride group as essential constitutional units, and the optional structural unit (C) where necessary, and these structural units are substantially linearly copolymerized, preferably random copolymerized.

“Substantially linearly” refers to a state that the copolymer has no branch, or frequency of appearing branched structure is low such that the copolymer can be regarded as a linear copolymer. Specifically, as described later, it refers to a state that the copolymer has a phase angle δ of 50 degrees or more.

The copolymer (P) is required to include the structural units derived from two or more monomers in total, i.e. one or more structural units (A) and one or more structural units (B), and may further include another structural unit (C). Next, the structural units and the amount of the structural units of the copolymer (P) will be explained.

A structure derived from each one molecule of ethylene and/or the α-olefin having 3 to 20 carbon atoms, the monomer having the carboxy group and/or the dicarboxylic anhydride group, and the optional monomer is defined to be one structural unit in the copolymer. Further, when the total structural units in the copolymer is 100 mol %, the ratio of each structural unit is expressed in mol %, which is the amount of the structural unit.

Amount of the Structural Unit (A) Derived from Ethylene and/or the α-Olefin Having 3 to 20 Carbon Atoms:

• • The lower limit of the amount of the structural unit (A) is 60.0 mol % or more, preferably 70.0 mol % or more, more preferably 80.0 mol % or more, even more preferably 85.0 mol % or more, further more preferably 90.0 mol % or more, and particularly preferably 91.2 mol % or more, and the upper limit of the amount of the structural unit (A) is 97.9 mol % or less, preferably 97.5 mol % or less, more preferably 97.0 mol % or less, and even more preferably 96.5 mol % or less.

If the amount of the structural unit (A) derived from ethylene and/or the α-olefin having 3 to 20 carbon atoms is 60.0 mol % or more, the copolymer has better toughness, and if the amount of the structural unit (A) derived from ethylene and/or the α-olefin having 3 to 20 carbon atoms is 97.9 mol % or less, the crystallinity is lower and the transparency is higher.

Amount of the Structural Unit (B) Having the Carboxy Group and/or the Dicarboxylic Anhydride Group:

• • The lower limit of the amount of the structural unit (B) is 2.0 mol % or more, preferably 2.9 mol % or more, more preferably 3.5 mol % or more, and even more preferably 6.0 mol % or more, and the upper limit of the amount of the structural unit (B) is 20.0 mol % or less, preferably 18.0 mol % or less, more preferably 15.0 mol % or less, and even more preferably 10.0 mol % or less.

If the amount of the structural unit (B) having the carboxy group and/or the dicarboxylic anhydride group is 2.0 mol % or more, the copolymer has better adhesiveness with a different material having high polarity, and if the amount of the structural unit (B) having the carboxy group and/or the dicarboxylic anhydride group is 20.0 mol % or less, the copolymer has better mechanical properties. If the amount of the structural unit (B) is 6.0 mol % or more, the coefficient of restitution is greatly enhanced and thus it is preferable. Further, the monomer having the carboxy group and/or the dicarboxylic anhydride group to be used may be alone, or two or more of them may be used in combination.

Amount of the Structural Unit (C) Derived from the Other Monomer:

• • The upper limit of the amount of the structural unit (C) is 20.0 mol % or less, preferably 15.0 mol % or less, more preferably 10.0 mol % or less, even more preferably 5.0 mol % or less, and particularly preferably 3.6 mol % or less, and the lower limit of the amount of the structural unit (C) is not particularly limited, and may be 0 mol %. If the amount of the optional structural unit (C) derived from the other monomer is 20.0 mol % or less, the copolymer easily has sufficient mechanical properties.

Further, the optional monomer to be used may be alone, or two or more of them may be used in combination.

Number of Branches of the Copolymer (P) Per 1,000 Carbon Atoms:

• • In the copolymer (P), from the viewpoint of increasing elastic modulus and obtaining sufficient mechanical properties, the upper limit of the number of methyl branches calculated by ¹³C-NMR per 1,000 carbon atoms may be 50 or less, may be 5.0 or less, may be 1.0 or less, and may be 0.5 or less, and the lower limit of the number of methyl branches calculated by ¹³C-NMR per 1,000 carbon atoms is not particularly limited, and it is better when the number is as little as possible. In addition, the upper limit of the number of ethyl branches per 1,000 carbon atoms may be 3.0 or less, may be 2.0 or less, may be 1.0 or less, and may be 0.5 or less, and the lower limit of the number of ethyl branches per 1,000 carbon atoms is not particularly limited, and it is better when the number is as little as possible. In addition, the upper limit of the number of butyl branches per 1,000 carbon atoms may be 7.0 or less, may be 5.0 or less, may be 3.0 or less, and may be 0.5 or less, and the lower limit of the number of butyl branches per 1,000 carbon atoms is not particularly limited, and it is better when the number is as little as possible.
    Method for Measuring the Amount of the Structural Units Derived from the Monomer Having the Carboxy Group and/or the Dicarboxylic Anhydride Group and the Non-Cyclic Monomer, and the Number of Branches in the Copolymer (P):

The amount of the structural units derived from the monomer having the carboxy group and/or the dicarboxylic anhydride group and the non-cyclic monomer, and the number of branches per 1,000 carbon atoms in the copolymer (P) can be obtained by using ¹³C-NMR spectrum. ¹³C-NMR is measured by the following method.

A sample in an amount of 200 mg to 300 mg together with 2.4 ml of a mixed solvent of o-dichlorobenzene (C₆H₄Cl₂) and deuterated benzene bromide (C₆D₅Br) (C₆H₄Cl₂/C₆D₅Br=2/1 (volume ratio)) and hexamethyldisiloxane which is a standard substance of chemical shift are added in an NMR sample tube having an inner diameter of 10 mmφ. After nitrogen replacement, the tube is sealed and the mixture is dissolved under heating to form a uniform solution, which is used as the NMR measurement sample.

The NMR measurement is carried out at a temperature of 120° C. by using an AV400M type NMR apparatus available from Brucker Japan Co., Ltd. equipped with a 10 mmφ cryoprobe. ¹³C-NMR is measured by a reverse gate decoupling method under conditions of: a sample temperature: 120° C., a pulse angle: 90°, a pulse interval: 51.5 seconds, and a number of integrations: 512 times or more.

The chemical shift of the ¹³C signal of hexamethyldisiloxane is set to 1.98 ppm, and the chemical shift of the signal by the other ¹³C is based on this. The amount of the structural units derived from the monomers and the number of the branches in the copolymer can be analyzed by identifying the signals specific to the monomers or branches of the copolymer in the obtained ¹³C-NMR, and comparing the strength thereof. The position of the signals specific to the monomers or branches can be obtained by referring to the publicly known documents, or can be uniquely identified depending on the sample. Such the analytical method can be generally carried out by the person skilled in the art.

Weight Average Molecular Weight (Mw) and Molecular Weight Distribution (Mw/Mn):

• • The lower limit of the weight average molecular weight (Mw) of the copolymer (P) is generally 1,000 or more, preferably 6,000 or more, and more preferably 10,000 or more, and the upper limit of the weight average molecular weight (Mw) of the copolymer (P) is generally 2,000,000 or less, preferably 1,500,000 or less, more preferably 1,000,000 or less, particularly preferably 800,000 or less, and most preferably 100,000 or less.

If Mw is 1,000 or more, the copolymer has better properties such as mechanical strength and impact resistance, and if Mw is 2,000,000 or less, the copolymer has lower melt viscosity and thus better processability.

The ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the copolymer (P) generally ranges from 1.5 to 4.0, preferably ranges from 1.6 to 3.5, and more preferably ranges from 1.9 to 2.3. If Mw/Mn is 1.5 or more, the copolymer has better processability, and if Mw/Mn is 4.0 or less, the copolymer has better mechanical properties. In the present disclosure, (Mw/Mn) is sometimes expressed as a molecular weight distribution parameter. The measuring method of the weight average molecular weight (Mw) and the number average molecular weight (Mn) will be described later.

Melting Point (Tm, ° C.):

The melting point of the copolymer (P) is indicated by a maximum peak temperature in an endothermic curve measured with a differential scanning calorimeter (DSC). The maximum peak temperature indicates a temperature of the peak having the maximum height from the baseline when multiple peaks are shown in the endothermic curve, and indicates a temperature of the peak when the peak is one, in the DSC measurement where a vertical axis shows a heat flow (mW) and a horizontal axis shows a temperature (° C.).

The melting point of the copolymer (P) preferably ranges from 50° C. to 140° C., more preferably ranges from 60° C. to 138° C., and most preferably ranges from 70° C. to 135° C. If the melting point of the copolymer (P) falls within the above range, heat resistance and adhesiveness are better.

In the present disclosure, the melting point can be obtained, for example, from an absorption curve obtained by using DSC (DSC7020) available from SII Nano Technology Co., Ltd, and charging about 5.0 mg of the sample in an aluminum pan, elevating the temperature to 200° C. at 10° C./min, maintaining the temperature at 200° C. for 5 minutes, lowering the temperature to 20° C. at 10° C./min, maintaining the temperature at 20° C. for 5 minutes, and elevating the temperature to 200° C. at 10° C./min again.

Crystallinity (%):

• • The crystallinity of the copolymer (P) observed by the differential scanning calorimetry measurement (DSC) is not particularly limited, and is preferably more than 0%, more preferably more than 5%, and even more preferably 7% or more. If the crystallinity is more than 0%, the copolymer easily exhibits toughness. The crystallinity also represents an index of transparency. The copolymer (P) is preferably transparent, but the upper limit of the crystallinity is not particularly limited.

In the present disclosure, the crystallinity can be obtained, for example, by obtaining the heat of fusion (ΔH) from the area of the melting endothermic peak obtained by the DSC measurement in the same procedure as that in the measurement of the above-mentioned melting point, and dividing the heat of fusion by the heat of fusion 293 J/g of the perfect crystal of the high density polyethylene (HDPE).

Molecular Structure of the Copolymer (P):

The molecular chain terminal of the copolymer (P) may be the structural unit (A) derived from ethylene and/or the α-olefin having 3 to 20 carbon atoms, may be the structural unit (B) having the carboxy group and/or the dicarboxylic anhydride group, or may be the optional structural unit (C) derived from the other monomer.

In addition, examples of the copolymer (P) include a random copolymer, a block copolymer or a graft copolymer of the structural unit (A) derived from ethylene and/or the α-olefin having 3 to 20 carbon atoms, the structural unit (B) having the carboxy group and/or the dicarboxylic anhydride group and the optional structural unit (C) derived from the other monomer. Among them, the random copolymer capable of including a large amount of the structural unit (B) is preferable.

A molecular structure example (1) of a general ternary copolymer is shown below.

The random copolymer means a copolymer where the probability to find each structural unit of the structural unit (A) derived from ethylene and/or the α-olefin having 3 to 20 carbon atoms, the structural unit (B) having the carboxy group and/or the dicarboxylic anhydride group and the optional structural unit (C) derived from the other monomer at a position in an arbitrary molecular chain of the molecular structure example (1) shown below is irrelevant to the kind of the adjacent structural unit. As shown below, in the molecular structure example (1) of the copolymer (P), the structural unit (A) derived from ethylene and/or the α-olefin having 3 to 20 carbon atoms, the structural unit (B) having the carboxy group and/or the dicarboxylic anhydride group and the optional structural unit (C) derived from the other monomer form a random copolymer.

Molecular Structure Example (1)

A molecular structure example (2) shows the copolymer where the structural unit (B) having the carboxyl group and/or the dicarboxylic anhydride group is introduced by graft modification for reference. The structural unit (A) derived from ethylene and/or the α-olefin having 3 to 20 carbon atoms and the optional structural unit (C) derived from the other monomer are copolymerized to form a copolymer and a part of the copolymer is graft modified by the structural unit (B) having the carboxy group and/or the dicarboxylic anhydride group.

Molecular Structure Example (2)

In addition, it is possible to confirm the random copolymerizability of the copolymer by various methods, and a method of judging the random copolymerizability from the relationship between the comonomer amount and melting point of the copolymer is described in detail in JP 2015-163691 A and JP 2016-079408. From the above-mentioned documents, it can be judged that the randomness is low when the melting point (Tm, ° C.) of the copolymer is higher than −3.74×[Z]+130 (where [Z] is a comonomer amount/mol %).

In the copolymer (P) that is a random copolymer, the melting point (Tm, ° C.) observed by the differential scanning calorimetry measurement (DSC) and the total amount [Z] (mol %) of the structural unit (B) having the carboxy group and/or the dicarboxylic anhydride group and the optional structural unit (C) derived from the other monomer preferably satisfy the following formula (I).

5 ⁢ 0 < T ⁢ m < - 3 . 7 ⁢ 4 × [ Z ] + 130 ( I )

When the melting point (Tm, ° C.) of the copolymer is higher than −3.74×[Z]+130 (° C.), the random copolymerizability is low, and thus the mechanical properties such as impact strength are inferior, and when the melting point is lower than 50° C., the stiffness may be inferior.

In addition, the copolymer (P) is preferably produced in the presence of a transition metal catalyst from the viewpoint of making its molecular structure linear. It has been known that the molecular structure of a copolymer differs depending on the production method such as polymerization by a high pressure radical polymerization method process, polymerization using a metal catalyst, etc. The difference in the molecular structure can be controlled by selecting the production method, and the molecular structure can also be estimated, for example, by the complex modulus of elasticity measured with a rotary rheometer as described in JP 2010-150532 A.

Phase Angle δ at the Absolute Value G*=0.1 MPa of the Complex Modulus of Elasticity:

In the copolymer (P) according to the present disclosure, the lower limit of the phase angle δ at the absolute value G*=0.1 MPa of the complex modulus of elasticity measured with the rotary rheometer may be 50 degrees or more, may be 51 degrees or more, may be 54 degrees or more, may be 56 degrees or more, and may be 58 degrees or more, and the upper limit of the phase angle δ at the absolute value G*=0.1 MPa of the complex modulus of elasticity measured with the rotary rheometer may be 75 degrees or less, and may be 70 degrees or less.

More specifically, when the phase angle δ (G*=0.1 MPa) at the absolute value G*=0.1 MPa of the complex modulus of elasticity measured with the rotary rheometer is 50 degrees or more, the molecular structure of the copolymer shows a linear structure without any long chain branch, or a structure that includes such a small amount of a long chain branch that does not affect the mechanical strength.

In addition, when the phase angle δ (G*=0.1 MPa) at the absolute value G*=0.1 MPa of the complex modulus of elasticity measured with the rotary rheometer is lower than 50 degrees, the molecular structure of the copolymer shows a structure that excessively includes a long chain branch, and is inferior in the mechanical strength.

The phase angle δ at the absolute value G*=0.1 MPa of the complex modulus of elasticity measured with the rotary rheometer is affected by both of the molecular weight distribution and the long chain branch. However, with respect to a copolymer having Mw/Mn≤4, more preferably Mw/Mn≤3, the phase angle δ becomes an index of the amount of the long chain branch, and as the amount of the long chain branch included in the molecular structure is greater, the δ (G*=0.1 MPa) value is smaller. It is noted that if Mw/Mn of the copolymer is 1.5 or more, the δ (G*=0.1 MPa) value never exceeds 75 degrees even if the molecular structure is a structure including no long chain branch.

The measurement method of the complex modulus of elasticity is as follows.

The sample is charged in a mold for heat press with a thickness of 1.0 mm, and preheated for 5 minutes in a hot press machine with a surface temperature of 180° C. Then, the residual gas in the molten resin is degassed by repeating pressurization and depressurization, and the sample is further pressurized at 4.9 MPa and kept for 5 minutes. Then, the sample is transferred to a press machine with a surface temperature of 25° C. and held at a pressure of 4.9 MPa for 3 minutes for cooling, to prepare a press plate formed of the sample with a thickness of about 1.0 mm. The press plate formed of the sample is processed into a circle shape with a diameter of 25 mm, which is used as a sample, and the dynamic viscoelasticity thereof is measured using an ARES type rotary rheometer available from Rheometrics Ltd. as a measurement apparatus for the dynamic viscoelasticity characteristics under the following conditions in a nitrogen atmosphere.

• • Plate: φ25 mm parallel plate
  • Temperature: 160° C.
  • Strain amount: 10%
  • Measurement angular frequency range: 1.0×10-2 to 1.0×102 rad/s
  • Measurement interval: 5 points/decade

The phase angle δ is plotted to the common logarithm log G* of the absolute value G* (Pa) of the complex modulus of elasticity, and the δ (degrees) value at the point corresponding to log G*=5.0 is adopted as δ (G*=0.1 MPa). When there is no point corresponding to log G*=5.0 in the measurement points, the δ value at log G*=5.0 is obtained by linear interpolation using two points around log G*=5.0. In addition, when all the measurement points are log G*<5, the δ value at log G*=5.0 is obtained by extrapolating the δ value at log G*=5.0 using the three points from the largest log G* value with a quadratic curve.

Regarding the Production of the Copolymer (P)

The copolymer (P) according to the present disclosure is preferably produced in the presence of a transition metal catalyst from the viewpoint of making its molecular structure linear.

Polymerization Catalyst

The kind of the polymerization catalyst used for the production of the copolymer (P) is not particularly limited, as long as it is capable of copolymerizing the structural unit (A), the structural unit (B) and the optional structural unit (C), and for example, a transition metal compound of Group 5 to Group 11 having a chelating ligand is preferable, and a transition metal complex of Group 5 to Group 11 having a chelating ligand is more preferable.

Specific examples of the preferable transition metal include a vanadium atom, niobium atom, a tantalum atom, a chromium atom, a molybdenum atom, a tungsten atom, a manganese atom, an iron atom, a platinum atom, a ruthenium atom, a cobalt atom, a rhodium atom, a nickel atom, a palladium atom, and a copper atom. Among them, the transition metal of Group 8 to Group 11 is preferable, the transition metal of Group 10 is more preferable, and nickel (Ni) or palladium (Pd) is particularly preferable. These metals may be used alone, or a plurality of them may be used in combination.

The chelating ligand has at least two atoms selected from the group consisting of P, N, O and S, includes a ligand which is bidentate or multidentate, and is electrically neutral or anionic. In a review by Brookhart et al., the structure of chelating ligands is exemplified (Chem. Rev., 2000, 100, 1169).

Preferable examples of the chelating ligand include a bidentate anionic P and O ligand. Examples of the bidentate anionic P and O ligand include phosphorus sulfonic acid, phosphorus carboxylic acid, phosphorus phenol and phosphorus enolate. Examples of the chelating ligand further include a bidentate anionic N and O ligand. Examples of the bidentate anionic N and O ligand include salicylamide iminate and pyridine carboxylic acid. Examples of the chelating ligand also include diimine ligand, diphenoxide ligand and diamide ligand.

The structure of the metal complex obtained from the chelating ligand is represented by the following structural formula (a) or (b) in which an arylphosphine compound, an arylarsine compound or an arylantimony compound, each optionally having a substituent, is coordinated.

[In the structural formula (a) and the structural formula (b),

• • M represents a transition metal belonging to any one of Group 5 to Group 11 in the periodic table, i.e. various transition metals as mentioned above.
  • X¹ represents oxygen, sulfur, —SO₃—, or —CO₂—.
  • Y¹ represents carbon or silicon.
  • n represents an integer of 0 or 1.
  • E¹ represents phosphorus, arsenic or antimony.
  • R⁵³ and R⁵⁴ each independently represent a hydrogen, or a hydrocarbon group having 1 to 30 carbon atoms and optionally having a hetero atom.
  • R⁵⁵ each independently represents a hydrogen, a halogen, or a hydrocarbon group having 1 to 30 carbon atoms and optionally having a hetero atom.
  • R⁵⁶ and R⁵⁷ each independently represent a hydrogen, a halogen, a hydrocarbon group having 1 to 30 carbon atoms and optionally having a hetero atom, OR⁵², CO₂R⁵², CO₂M′, C(O)N(R⁵¹)₂, C(O)R⁵², SR⁵², SO₂R⁵², SOR⁵², OSO₂R⁵², P(O)(OR⁵²)_2-y(R⁵¹)_y, CN, NHR⁵², N(R⁵²)₂, Si(OR⁵¹)_3-x(R⁵¹)_x, OSi(OR⁵¹)_3-x(R⁵¹)_x, NO₂, SO₃M′, PO₃M′₂, P(O)(OR⁵²)₂M′, or an epoxy-containing group.
  • R⁵¹ represents a hydrogen or a hydrocarbon group having 1 to 20 carbon atoms.
  • R⁵² represents a hydrocarbon group having 1 to 20 carbon atoms.
  • M′ represents an alkali metal, an alkaline earth metal, ammonium, quaternary ammonium or phosphonium, x represents an integer of 0 to 3, and y represents an integer of 0 to 2.

It is noted that R⁵⁶ and R⁵⁷ may be bonded to each other to form an alicyclic ring, an aromatic ring or a heterocyclic ring including a hetero atom selected from oxygen, nitrogen or sulfur. In this case, a number of the ring member is 5 to 8, and the ring may have or may not have a substituent.

• • L¹ represents a ligand coordinated to M.

In addition, R⁵³ and L¹ may be bonded to each other to form a ring.]

The transition metal complex having the chelating ligand is more preferably a transition metal complex represented by the following structural formula (c).

[In the structural formula (c),

• • M represents a transition metal belonging to any one of Group 5 to Group 11 in the periodic table, i.e. various transition metals as mentioned above.
  • X¹ represents oxygen, sulfur, —SO₃—, or —CO₂—.
  • Y¹ represents carbon or silicon.
  • n represents an integer of 0 or 1.
  • E¹ represents phosphorus, arsenic or antimony.
  • R⁵³ and R⁵⁴ each independently represent a hydrogen, or a hydrocarbon group having 1 to 30 carbon atoms and optionally having a hetero atom.
  • R⁵⁵ each independently represents a hydrogen, a halogen, or a hydrocarbon group having 1 to 30 carbon atoms and optionally having a hetero atom.
  • R⁵⁸, R⁵⁹, R⁶⁰ and R⁶¹ each independently represent a hydrogen, a halogen, a hydrocarbon group having 1 to 30 carbon atoms and optionally having a hetero atom, OR⁵², CO₂R⁵², CO₂M′, C(O)N(R⁵¹)₂, C(O)R⁵², SR⁵², SO₂R⁵², SOR⁵², OSO₂R⁵², P(O)(OR⁵²)_2-y(R⁵¹)_y, CN, NHR⁵², N(R⁵²)₂, Si(OR⁵¹)_3-x(R⁵¹)_x, OSi(OR⁵¹)_3-x(R⁵¹)_x, NO₂, SO₃M′, PO₃M′₂, P(O)(OR⁵²)₂M′, or an epoxy-containing group.
  • R⁵¹ represents a hydrogen or a hydrocarbon group having 1 to 20 carbon atoms.
  • R⁵² represents a hydrocarbon group having 1 to 20 carbon atoms.
  • M′ represents an alkali metal, an alkaline earth metal, ammonium, quaternary ammonium or phosphonium, x represents an integer of 0 to 3, and y represents an integer of 0 to 2.
  • It is noted that a plurality of groups appropriately selected from R⁵⁸ to R⁶¹ may be bonded to each other to form an alicyclic ring, an aromatic ring or a heterocyclic ring including a hetero atom selected from oxygen, nitrogen or sulfur. In this case, a number of the ring member is 5 to 8, and the ring may have or may not have a substituent.
  • L¹ represents a ligand coordinated to M.
  • In addition, R⁵³ and L¹ may be bonded to each other to form a ring.]

Herein, as the representative catalyst of the transition metal compound of Group 5 to Group 11 having the chelating ligand, a catalyst such as the so-called SHOP-based catalyst and Drent-based catalyst has been known.

The SHOP-based catalyst is a catalyst in which a phosphorus-based ligand having an aryl group which may have a substituent is coordinated to a nickel metal (for example, refer to WO2010-050256).

In addition, the Drent-based catalyst is a catalyst in which a phosphorus-based ligand having an aryl group which may have a substituent is coordinated to a palladium metal (for example, refer to JP 2010-202647 A).

Polymerization Method of the Copolymer (P):

The polymerization method of the copolymer (P) is not limited.

Examples of the polymerization method include a slurry polymerization in which at least a part of the formed polymer becomes a slurry in a medium, a bulk polymerization in which the liquefied monomer itself is used as a medium, a vapor phase polymerization carried out in a vaporized monomer, and a high pressure ion polymerization in which at least a part of the formed polymer is dissolved in the monomer liquefied at a high temperature and high pressure.

The polymerization type may be any type of a batch polymerization, a semi-batch polymerization and a continuous polymerization.

In addition, a living polymerization may be carried out, or the polymerization may be carried out while simultaneously causing a chain transfer. Further, at the time of the polymerization, a chain shuttling reaction or coordinative chain transfer polymerization (CCTP) may be carried out by using a so-called chain shuttling agent (CSA) in combination. The specific producing process and conditions are disclosed, for example, in JP 2010-260913 A and JP 2010-202647 A.

Introducing Method of the Carboxyl Group and/or the Dicarboxylic Anhydride Group into the Copolymer:

• • The introducing method of the carboxyl group and/or the dicarboxylic anhydride group into the copolymer according to the present disclosure is not particularly limited.
  • The carboxyl group and/or the dicarboxylic anhydride group can be introduced by various methods in a context without deviating from the gist of the present disclosure.
  • Examples of the introducing method of the carboxyl group and/or the dicarboxylic anhydride group include a method in which the comonomer having the carboxyl group and/or the dicarboxylic anhydride group is directly copolymerized, and a method in which the carboxyl group and/or the dicarboxylic anhydride group is introduced by modification after the other monomer is copolymerized.

For example, when introducing a carboxylic acid, examples of the method for introducing the carboxyl group and/or the dicarboxylic anhydride group by modification include a method in which an acrylic acid ester is copolymerized and then hydrolyzed to form a carboxylic acid, and a method in which t-butyl acrylate is copolymerized and then thermally decomposed to form a carboxylic acid.

When the above-mentioned hydrolysis or thermal decomposition is carried out, a conventionally known acidic or basic catalyst may be used as an additive for promoting the reaction. The acidic or basic catalyst is not particularly limited, and for example, a hydroxide of an alkali metal or alkaline earth metal such as sodium hydroxide, potassium hydroxide and lithium hydroxide, a carbonate of an alkali metal or alkaline earth metal such as sodium hydrogen carbonate and sodium carbonate, a solid acid such as montmorillonite, an inorganic acid such as hydrochloric acid, nitric acid and sulfuric acid, and an organic acid such as formic acid, acetic acid, benzoic acid, citric acid, para-toluenesulfonic acid, trifluoroacetic acid and trifluoromethanesulfonic acid can be suitably used.

From the viewpoint of reaction promoting effect, price, equipment corrosivity, etc., sodium hydroxide, potassium hydroxide, sodium carbonate, para-toluenesulfonic acid and trifluoroacetic acid are preferable, and para-toluenesulfonic acid and trifluoroacetic acid are more preferable.

(6) Ionomer Resin

The ionomer resin used in the present disclosure is not particularly limited, as long as it is a product obtained by neutralizing at least a part of the carboxyl group and/or the dicarboxylic anhydride group of the structural unit (B) of the copolymer (P) with at least one kind of metal ion selected from Group 1, Group 2 or Group 12 in the periodic table.

Structure of the Ionomer Resin

The ionomer resin used in the present disclosure has a substantially linear structure, thus the phase angle δ thereof at the absolute value G*=0.1 MPa of the complex modulus of elasticity measured with the rotary rheometer is preferably in a range from 50 degrees to 75 degrees. If the phase angle δ (G*=0.1 MPa) is lower than 50 degrees, the molecular structure of the ionomer indicates a structure excessively including the long chain branch, and the mechanical strength is inferior. In addition, the δ (G*=0.1 MPa) value never exceeds 75 degrees even if the molecular structure is a structure including no long chain branch.

From the viewpoint of increasing the mechanical strength, the lower limit of the phase angle δ of the ionomer resin used in the present disclosure is preferably 51 degrees or more, more preferably 54 degrees or more, even more preferably 56 degrees or more, and further even more preferably 58 degrees or more. The upper limit of the phase angle δ of the ionomer resin used in the present disclosure is not particularly limited, but it is preferable that the upper limit of the phase angle δ is as close to 75 degrees as possible.

The measurement method of the complex modulus of elasticity is as follows.

The sample is charged in a mold for heat press with a thickness of 1.0 mm, and preheated at a surface temperature of 180° C. for 5 minutes in a hot press machine. Then, the residual gas in the molten resin is degassed by repeating pressurization and depressurization, and the sample is further pressurized at 4.9 MPa and kept for 5 minutes. Then, the sample is transferred to a press machine with a surface temperature of 25° C. and held at a pressure of 4.9 MPa for 3 minutes for cooling, to prepare a press plate formed of the sample with a thickness of about 1.0 mm. The press plate formed of the sample is processed into a circle shape with a diameter of 25 mm, which is used as a sample, and the dynamic viscoelasticity thereof is measured using an ARES type rotary rheometer available from Rheometrics Ltd. as a measurement apparatus for the dynamic viscoelasticity characteristics under the following conditions in a nitrogen atmosphere.

• • Plate: ¢25 mm parallel plate
  • Temperature: 160° C.
  • Strain amount: 10%
  • Measurement angular frequency range: 1.0×10-2 to 1.0×102 rad/s
  • Measurement interval: 5 points/decade

The phase angle δ is plotted to the common logarithm log G* of the absolute value G* (Pa) of the complex modulus of elasticity, and the δ (degrees) value at the point corresponding to log G*=5.0 is adopted as δ (G*=0.1 MPa). When there is no point corresponding to log G*-5.0 in the measurement points, the δ value at log G*=5.0 is obtained by linear interpolation using two points around log G*=5.0. In addition, when all the measurement points are log G*<5, the δ value at log G*=5.0 is obtained by extrapolating the δ value at log G*=5.0 using the three points from the largest log G* value with a quadratic curve.

Metal Ion

The metal ion included in the ionomer resin used in the present disclosure is not particularly limited, and a metal ion used for the conventionally known ionomer can be included. As the metal ion, among them, a metal ion of Group 1, Group 2 or Group 12 in the periodic table is preferable, at least one member selected from the group consisting of Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺ and Zn²⁺ is more preferable, at least one member selected from the group consisting of Lit, Na⁺, K⁺, Mg²⁺, Ca²⁺ and Zn²⁺ is particularly preferable, and at least one member selected from the group consisting of Na⁺ and Zn²⁺ is even more preferable. Among them, from the viewpoint of an excellent balance between the strength, durability or resilience performance and the processability, the ionomer resin used in the present disclosure preferably includes two or more of these metal ions. When two metal ions are used in combination, they are preferably used in a weight ratio ranging from 20/80 to 80/20, and more preferably used in a weight ratio ranging from 30/70 to 70/30.

Neutralization Degree (Mol %)

The amount of the metal ion preferably includes an amount that neutralizes at least a part of or all the carboxy group and/or the dicarboxylic anhydride group in the copolymer that is the base polymer, and the neutralization degree (average neutralization degree) preferably ranges from 5 mol % to 95 mol %, more preferably ranges from 10 mol % to 90 mol %, and even more preferably ranges from 10 mol % to 80 mol %.

It is noted that the neutralization degree can be obtained from a ratio of a total molar amount of the valence×molar amount of the metal ion, to a total molar amount of the carboxyl group in the copolymer and/or the carboxyl group that may be included in the dicarboxylic anhydride group.

Since the dicarboxylic anhydride group becomes a dicarboxylic acid by ring-opening at the time of forming a carboxylic acid salt, the total molar amount of the carboxyl group is obtained assuming that 1 mol of the dicarboxylic anhydride group provides 2 mol of the carboxyl group. In addition, for example, with regard to the divalent metal ion such as Zn²⁺, the total molar amount of the molecule for the neutralization degree is calculated by 2×molar amount assuming that 1 mol of the divalent metal ion such as Zn²⁺ can form a salt with 2 mol of carboxyl group.

When the neutralization degree is high, the ionomer has high tensile strength and tensile fracture stress and low tensile fracture strain, but the ionomer tends to have a low melt flow rate (MFR). On the other hand, when the neutralization degree is low, the obtained ionomer has a suitable MFR, but the ionomer tends to have low tensile modulus of elasticity and tensile fracture stress and high tensile fracture strain.

Production Method of the Ionomer Resin

The ionomer resin can be obtained by neutralizing a copolymer of ethylene and/or the α-olefin having 3 to 20 carbon atoms/unsaturated carboxylic acid obtained by the method of introducing the carboxy group and/or the dicarboxylic anhydride group into the above-mentioned copolymer, with at least one metal ion selected from Group 1, Group 2 or Group 12 in the periodic table. In addition, the ionomer resin can also be obtained by a heating-converting process of heating a copolymer of ethylene and/or the α-olefin having 3 to 20 carbon atoms/unsaturated carboxylic acid ester, thereby converting at least a part of the ester group in the copolymer into a metal-containing carboxylic acid salt containing at least one metal ion selected from Group 1, Group 2 or Group 12 in the periodic table.

The temperature for heating the copolymer of ethylene and/or the α-olefin having 3 to 20 carbon atoms/unsaturated carboxylic acid ester is high enough for the ester to become a carboxylic acid. If the heating temperature is excessively low, the ester is not converted into a carboxylic acid, and if the heating temperature is excessively high, decarbonylation or decomposition of the copolymer proceeds. Therefore, the heating temperature in the present disclosure preferably ranges from 80° C. to 350° C., more preferably ranges from 100° C. to 340° C., even more preferably ranges from 150° C. to 330° C., and further even more preferably ranges from 200° C. to 320° C.

The reaction time varies depending on the heating temperature, the reactivity of the ester group moiety, etc., and generally ranges from 1 minutes to 50 hours, more preferably ranges from 2 minutes to 30 hours, even more preferably ranges from 2 minutes to 10 hours, further even more preferably ranges from 2 minutes to 3 hours, and particularly preferably ranges from 3 minutes to 2 hours.

In the above-mentioned process, the reaction atmosphere is not particularly limited, and generally the reaction is preferably carried out under an inert gas stream. Examples of the inert gas include nitrogen, argon and carbon dioxide. A small amount of oxygen or air may be mixed therein.

The reactor used in the above-mentioned process is not particularly limited, as long as the reactor is capable of substantially uniformly stirring the copolymer. A glass container equipped with a stirrer or an autoclave (AC) may be used, and any conventionally known kneader such as Brabender Plastograph, a single-screw or twin-screw extruder, a high-power screw kneader, a Banbury mixer, a kneader, a roll, etc., may also be used.

The metal ion supply source for the neutralization may be an oxide, a hydroxide, a carbonate, a bicarbonate, an acetate, a formate, etc., of the metal of Group 1, Group 2 or Group 12 in the periodic table. The metal ion supply source may be supplied to the reaction system in a form of granule or fine powder, may be supplied to the reaction system after dissolving or dispersing the metal ion supply source in water or an organic solvent, or may be supplied to the reaction system in a form of a master batch in which an ethylene/unsaturated carboxylic acid copolymer or olefin copolymer is used as a base polymer. In order to proceed the reaction smoothly, the method of preparing the master batch and supplying it to the reaction system is preferable.

The reaction with the metal ion supply source may be carried out by melting and kneading with various apparatus such as a vent extruder, a Banbury mixer and a roll mill, and the reaction may be carried out by a batch method or a continuous method. The reaction is preferably continuously carried out using an extruder equipped with a degassing apparatus such as a vent extruder. Water and carbon dioxide gas produced as a by-product of the reaction are discharged by the deaerator so that the reaction can be smoothly carried out. When reacting with the compound containing the metal ion, a small amount of water may be injected to promote the reaction.

Whether or not the metal ion has been introduced into the copolymer (P) that is the base resin to form the ionomer can be confirmed by measuring the IR spectrum of the obtained resin and examining the decrease in the peak derived from the carbonyl group of the carboxylic acid (dimer). Similarly, the neutralization degree can be confirmed by examining the decrease in the peak derived from the carbonyl group of the carboxylic acid (dimer) and the increase in the peak derived from the carbonyl group of the salt of the carboxylic acid group, in addition to the calculation from the above-mentioned molar ratio.

Additives

The conventionally known additives such as an antioxidant, an ultraviolet absorber, a lubricant, an antistatic agent, a colorant, a pigment, a crosslinking agent, a foaming agent, a nucleating agent, a flame retardant, a conductive material and a filler may be added in the ionomer resin used in the present disclosure in a context without deviating from the gist of the present disclosure.

The bending stiffness (M) of the ionomer resin used in the present disclosure is preferably 10 MPa or more, more preferably 20 MPa or more, and even more preferably 50 MPa or more, and is preferably 3000 MPa or less, more preferably 2000 MPa or less, and even more preferably 1000 MPa or less. If the bending stiffness (M) of the ionomer resin is 10 MPa or more, the resilience is higher, and if the bending stiffness (M) of the ionomer resin is 3000 MPa or less, the golf ball has better shot feeling. Herein, the bending stiffness of the ionomer resin is obtained by molding the ionomer resin into a sheet and measuring the bending stiffness of the sheet by the measuring method described later.

The slab hardness of the ionomer resin is preferably 10 or more, more preferably 20 or more, and even more preferably 30 or more, and is preferably 95 or less, more preferably 90 or less, and even more preferably 85 or less in Shore D hardness. If the slab hardness of the ionomer resin falls within the above range, a golf ball having high resilience performance and good shot feeling can be provided. Herein, the Shore D hardness of the ionomer resin is obtained by molding the ionomer resin into a sheet and measuring the Shore D hardness of the sheet by the measuring method described later.

The melt flow rate (190° C., 2.16 kgf) of the ionomer resin is preferably 0.01 g/10 min or more, more preferably 0.05 g/10 min or more, and even more preferably 0.1 g/10 min or more, and is preferably 500 g/10 min or less, more preferably 200 g/10 min or less, and even more preferably 100 g/10 min or less. If the melt flow rate (190° C., 2.16 kgf) of the ionomer resin is 0.01 g/10 min or more, the cover composition has better fluidity, and for example, a thinner constituent member can be obtained.

The cover composition for forming the cover of the golf ball according to the present disclosure preferably contains, as the ionomer resin, a first ionomer resin neutralized with a first metal ion and having a phase angle δ in a range from 50 degrees to 75 degrees at an absolute value G*=0.1 MPa of a complex modulus of elasticity measured by a rotary rheometer, and a second ionomer resin neutralized with a second metal ion that is different from the first metal ion and having a phase angle δ in a range from 50 degrees to 75 degrees at an absolute value G*=0.1 MPa of a complex modulus of elasticity measured by a rotary rheometer.

For example, the first metal ion and the second metal ion are preferably the metal ion of Group 1, Group 2 or Group 12 in the periodic table, more preferably at least one member selected from the group consisting of Li⁺, Na⁺, K⁺, Rb⁺, Be²⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Ra²⁺ and Zn²⁺, even more preferably at least one member selected from the group consisting of Lit, Na⁺, K⁺, Ca²⁺ and Zn²⁺, and particularly preferably at least one member selected from the group consisting of Na⁺ and Zn²⁺. It is preferable that one of the first metal ion and the second metal ion is Nat, and the other one is Zn²⁺.

The amount of the structural unit (B) in each of the first ionomer resin and the second ionomer resin is preferably 2.0 mole % or more, more preferably 2.9 mole % or more, even more preferably 3.5 mole % or more, and even more preferably 6.0 mole % or more, and is preferably 20.0 mole % or less, more preferably 18.0 mole % or less, even more preferably 15.0 mole % or less, and even more preferably 10.0 mole % or less.

The neutralization degree of each of the first ionomer resin and the second ionomer resin by the metal ion is preferably 5 mole % or more, more preferably 10 mole % or more, and is preferably 95 mole % or less, more preferably 90 mole % or less, and even more preferably 80 mole % or less.

The melt flow rate (190° C., 2.16 kgf) of the first ionomer resin and the second ionomer resin is preferably 100 g/10 min or less, respectively.

Examples of the combination of the first ionomer resin and the second ionomer resin contained in the cover composition include an embodiment containing a first ionomer resin having a neutralization degree of 50 mole % or less and a second ionomer resin having a neutralization degree of 50 mole % or less (more preferably an embodiment containing a first ionomer resin having a neutralization degree of less than 50 mole % and a second ionomer resin having a neutralization degree of less than 50 mole %); an embodiment containing a first ionomer resin having a neutralization degree of 50 mole % or more and a second ionomer resin having a neutralization degree of more than 50 mole % (more preferably an embodiment containing a first ionomer resin having a neutralization degree of more than 50 mole % and a second ionomer resin having a neutralization degree of more than 50 mole %); and an embodiment containing a first ionomer resin having a neutralization degree of 50 mole % or less and a second ionomer resin having a neutralization degree of more than 50 mole % (more preferably an embodiment containing a first ionomer resin having a neutralization degree of less than 50 mole % and a second ionomer resin having a neutralization degree of more than 50 mole %).

The blending ratio (mass ratio) of the first ionomer resin to the second ionomer resin is preferably 10/90 or more, and is preferably 90/10 or less.

The cover composition for forming the cover of the golf ball according to the present disclosure may contain other resins in addition to the ionomer resin as the resin component.

Specific examples of the other resins include an ionomer resin having a trade name of “Himilan (registered trademark)” available from Dow-Mitsui Polychemicals Co., Ltd., a thermoplastic polyurethane elastomer having a trade name of “Elastollan (registered trademark)” available from BASF Japan Ltd., a thermoplastic polyamide elastomer having a trade name of “Pebax (registered trademark)” available from Arkema K. K., a thermoplastic polyester elastomer having a trade name of “Hytrel (registered trademark)” available from Toray Celanese Co., Ltd., and a thermoplastic styrene elastomer or thermoplastic polyester elastomer having a trade name of “TEFABLOC (registered trademark)” available from Mitsubishi Chemical Corporation. The cover material may be used solely, or two or more of them may be used in combination.

The cover composition according to the present disclosure contains the ionomer resin as the resin component. The amount of the ionomer resin component in the resin component is preferably 50 mass % or more, more preferably 75 mass % or more, and even more preferably 90 mass % or more. It is also preferable that the resin component consists of the ionomer resin.

The cover composition may further contain a fluidity modifier. If the fluidity modifier is contained, the constituent member of the golf ball can be easily formed. Examples of the fluidity modifier include a fatty acid and/or a metal salt thereof.

The fatty acid is not particularly limited, and examples thereof include a saturated fatty acid such as butyric acid, valeric acid, hexanoic acid, heptanoic acid, octanoic acid, pelargonic acid, decanoic acid, lauric acid, myristic acid, palmitic acid, heptadecanoic acid, stearic acid, eicosanoic acid, behenic acid, lignoceric acid and cerotic acid; and an unsaturated fatty acid such as palmitoleic acid, oleic acid, linoleic acid, α-linolenic acid, y-linolenic acid and arachidonic acid.

The fatty acid metal salt is not particularly limited, and examples thereof include a monovalent metal salt such as a fatty acid sodium salt, a fatty acid potassium salt and a fatty acid lithium salt; a divalent metal salt such as a fatty acid magnesium salt, a fatty acid calcium salt, a fatty acid zinc salt, a fatty acid barium salt and a fatty acid cadmium salt; and a trivalent metal salt such as a fatty acid aluminum salt. Among them, as the fatty acid metal salt, the divalent metal salt of the saturated fatty acid such as magnesium stearate, calcium stearate, zinc stearate, barium stearate and copper stearate are preferable.

The amount of the fluidity modifier is preferably 0.5 part by mass or more, more preferably 1.5 parts by mass or more, and is preferably 30 parts by mass or less, more preferably 25 parts by mass or less, with respect to 100 parts by mass of the resin component of the cover composition. If the amount of the fluidity modifier falls within the above range, the fluidity of the golf ball resin composition is improved. Thus, a thin constituent member can be molded.

The cover composition may further contain a pigment component such as a white pigment (e.g. titanium oxide), a blue pigment and a red pigment, a weight adjusting agent such as calcium carbonate and barium sulfate, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent material or fluorescent brightener, or the like, as long as they do not impair the performance of the cover.

The amount of the white pigment (e.g. titanium oxide) is preferably 0.5 part by mass or more, more preferably 1 part by mass or more, and is preferably 10 parts by mass or less, more preferably 8 parts by mass or less, with respect to 100 parts by mass of the ionomer resin component included in the cover composition. If the amount of the white pigment is 0.5 part by mass or more, it is possible to impart the opacity to the cover, and if the amount of the white pigment is 10 parts by mass or less, the shot feeling is enhanced.

In the golf ball according to the present disclosure, the loss modulus E″ at the temperature of 0° C. obtained by measuring the dynamic viscoelasticity of the cover composition containing the above-mentioned ionomer resin under the following conditions is 3.40×10⁷ Pa or less. The loss modulus E″ at the temperature of 0° C. is preferably 3.00×10⁷ Pa or less, more preferably 2.80×10⁷ Pa or less, and even more preferably 2.60×10⁷ Pa or less. If the loss modulus E″ at the temperature of 0° C. is 3.40×10⁷ Pa or less, the durability of the golf ball can be significantly improved without substantially lowering the resilience of the golf ball. It is noted that the loss modulus E″ at the temperature of 0° C. is not particularly limited, and is preferably 1.00×10⁶ Pa or more, more preferably 1.20×10⁶ Pa or more, and even more preferably 1.40×10⁶ Pa or more.

• • <measuring conditions>
  • measuring mode: sine wave tensile mode
  • measuring temperature range: −100° C. to 100° C.
  • temperature increasing rate: 4° C./min
  • oscillation frequency: 10 Hz
  • measuring strain: 0.05%

In the golf ball according to the present disclosure, the slab hardness (D) and the bending stiffness (M) of the cover composition containing the above-mentioned ionomer resin preferably satisfy M/D²≥0.070. The M/D² is preferably 0.070 or more, more preferably 0.071 or more, and is preferably 0.200 or less, more preferably 0.150 or less. If the M/D² falls within the above range, the golf ball has better durability or shot feeling without lowering resilience performance.

The bending stiffness (M) of the cover composition is preferably 50 MPa or more, more preferably 60 MPa or more, and even more preferably 70 MPa or more, and is preferably 1000 MPa or less, more preferably 900 MPa or less, and even more preferably 800 MPa or less. If the bending stiffness (M) of the cover composition is 50 MPa or more, the resilience is higher, and if the bending stiffness (M) of the cover composition is 1000 MPa or less, the golf ball has better durability or shot feeling. Herein, the bending stiffness of the cover composition is obtained by molding the cover composition into a sheet and measuring the bending stiffness of the sheet by the measuring method described later. The bending stiffness (M) of the cover composition can be adjusted, for example, by controlling the amount of the structural units (A) and (B), the type of the metal ion, the neutralization degree, etc. of the ionomer resin blended therein. In addition, the bending stiffness (M) of the cover composition can be adjusted by varying the amount of a filler added in the cover composition.

The slab hardness (D) of the cover composition is preferably 30 or more, more preferably 35 or more, and even more preferably 40 or more, and is preferably 90 or less, more preferably 85 or less, and even more preferably 80 or less in Shore D hardness. If the slab hardness is 30 or more in Shore D hardness, the resilience is higher, and if the slab hardness is 90 or less in Shore D hardness, the durability or shot feeling is better. Herein, the slab hardness of the cover composition is obtained by molding the cover composition into a sheet and measuring the slab hardness of the sheet by the measuring method described later. The slab hardness of the cover composition can be adjusted, for example, by controlling the amount of the structural units (A) and (B), the type of the metal ion, the neutralization degree, etc. of the ionomer resin blended therein. In addition, the slab hardness of the cover composition can be adjusted by varying the amount of an anisotropic filler added in the cover composition.

The cover composition for forming the cover may be obtained, for example, by dry blending the ionomer resin and the additives that are blended where necessary, or by melting and mixing the ionomer resin and the additives. The melting and mixing can be carried out by using a kneader or an extruder (e.g. a single-screw extruder, a twin-screw extruder, and a twin-screw/single-screw extruder).

[Golf Ball]

The golf ball according to the present disclosure comprises a core and at least one cover layer positioned outside the core, wherein the at least one cover layer is formed from the cover composition containing the above-mentioned ionomer resin. The construction of the golf ball is not particularly limited, and examples thereof include a two-piece golf ball having a single layered core and a cover covering the core; and a multi-piece golf ball (e.g. a three-piece golf ball, a four-piece golf ball, and a five-piece golf ball) having a core and two or more cover layers covering the core It is noted that in a case of a multiple-layered cover, a cover layer other than an outermost cover layer is sometimes referred to as an intermediate layer, inner cover layer or outer core.

Examples of the golf ball according to the present disclosure include a two-piece golf ball having a single layered core and a cover covering the single layered core, wherein the cover is formed from the cover composition containing the above-mentioned ionomer resin; a multi-piece golf ball having a core and two or more cover layers covering the core, wherein an outermost cover layer is formed from the cover composition containing the above-mentioned ionomer resin; a golf ball having a single layered core, an inner cover layer covering the core and composed of at least one layer, and an outermost cover layer covering the inner cover layer, wherein at least one layer of the inner cover layer is formed from the cover composition containing the above-mentioned ionomer resin; and a golf ball having a single layered core, an inner cover layer covering the core and composed of at least one layer, and an outermost cover layer covering the inner cover layer, wherein at least one layer of the inner cover layer and the outermost cover layer are formed from the cover composition containing the above-mentioned ionomer resin. In the embodiment that at least one layer of the inner cover layer is formed from the cover composition containing the above-mentioned ionomer resin, the inner cover layer adjacent to the outermost cover layer is preferably formed from the cover composition containing the above-mentioned ionomer resin.

The core can be formed from a conventional rubber composition (hereinafter sometimes simply referred to as “core rubber composition”). For example, the core can be molded by heat pressing a rubber composition containing a base rubber, a co-crosslinking agent and a crosslinking initiator.

As the base rubber, a high-cis polybutadiene having a cis bond in an amount of 40 mass % or more, preferably 70 mass % or more, and more preferably 90 mass % or more is particularly preferably used in view of its superior resilience. As the co-crosslinking agent, an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms or a metal salt thereof is preferable, a metal salt of acrylic acid or a metal salt of methacrylic acid is more preferable. As the metal of the metal salt, zinc, magnesium, calcium, aluminum or sodium is preferable, and zinc is more preferable. The amount of the co-crosslinking agent is preferably 20 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the base rubber. As the crosslinking initiator, an organic peroxide is preferably used. Specific examples of the organic peroxide include dicumyl peroxide, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di(t-butylperoxy) hexane, and di-t-butyl peroxide. Among them, dicumyl peroxide is preferably used. The amount of the crosslinking initiator is preferably 0.2 part by mass or more, more preferably 0.3 part by mass or more, and is preferably 3 parts by mass or less, more preferably 2 parts by mass or less, with respect to 100 parts by mass of the base rubber.

In addition, the core rubber composition may further contain an organic sulfur compound. Examples of the organic sulfur compound include compounds belonging to diphenyl disulfides, thiophenols or thionaphthols. The amount of the organic sulfur compound is preferably 0.1 part by mass or more, more preferably 0.3 part by mass or more, and is preferably 5.0 parts by mass or less, more preferably 3.0 parts by mass or less, with respect to 100 parts by mass of the base rubber. The core rubber composition may further contain a carboxylic acid and/or a salt thereof. As the carboxylic acid and/or the salt thereof, a carboxylic acid having 1 to 30 carbon atoms and/or a salt thereof is preferable. The amount of the carboxylic acid and/or the salt thereof is preferably 1 part by mass or more and 40 parts by mass or less with respect to 100 parts by mass of the base rubber.

The core rubber composition may further appropriately contain a weight adjusting agent such as zinc oxide and barium sulfate, an antioxidant, a colored powder, or the like in addition to the base rubber, the co-crosslinking agent, the crosslinking initiator, and the organic sulfur compound. The molding conditions for heat pressing the core rubber composition may be determined appropriately depending on the rubber formulation. Generally, the heat pressing is preferably carried out at a temperature of 130° C. to 200° C. for 10 minutes to 60 minutes, or carried out in a two-step heating of heating at a temperature of 130° C. to 150° C. for 20 minutes to 40 minutes followed by heating at a temperature of 160° C. to 180° C. for 5 minutes to 15 minutes. The shape of the core is not particularly limited, and the spherical shape is preferable.

The embodiment for molding the cover from the cover composition is not particularly limited, and examples thereof include an embodiment comprising injection molding the cover composition directly onto the core; and an embodiment comprising molding the cover composition into hollow shells, covering the core with a plurality of the shells and compression molding the core with a plurality of the shells (preferably an embodiment comprising molding the cover composition into half hollow-shells, covering the core with two of the half shells and compression molding the core with two of the half shells). The golf ball body having the cover formed thereon is ejected from the mold, and as necessary, the golf ball body is preferably subjected to surface treatments such as deburring, cleaning, and sandblast. If desired, a mark may be formed.

The thickness of the cover is preferably 4.0 mm or less, more preferably 3.0 mm or less, and even more preferably 2.0 mm or less. If the thickness of the cover is 4.0 mm or less, the obtained golf ball has better resilience or shot feeling. The thickness of the cover is preferably 0.3 mm or more, more preferably 0.5 mm or more, even more preferably 0.8 mm or more, and particularly preferably 1.0 mm or more. If the thickness of the cover is less than 0.3 mm, the wear resistance of the cover may be lowered.

The total number of dimples formed on the cover is preferably 200 or more and 500 or less. If the total number of dimples is less than 200, the dimple effect is hardly obtained. On the other hand, if the total number of dimples exceeds 500, the dimple effect is hardly obtained because the size of the respective dimples is small. The shape (shape in a plan view) of the formed dimples includes, but is not particularly limited to, a circle, a polygonal shape such as a roughly triangular shape, a roughly quadrangular shape, a roughly pentagonal shape and a roughly hexagonal shape, and other irregular shapes. The shape of dimples can be employed solely or at least two of them may be used in combination.

The golf ball having the cover formed thereon is ejected from the mold, and as necessary, the golf ball body is preferably subjected to surface treatments such as deburring, cleaning, and sandblast. In addition, if desired, a paint film or a mark may be formed. The thickness of the paint film is not particularly limited, and is preferably 5 μm or more, more preferably 7 μm or more, and is preferably 50 μm or less, more preferably 40 μm or less, and even more preferably 30 μm or less. If the thickness of the paint film is less than 5 μm, the paint film is easy to wear off by the continuous use, and if the thickness of the paint film is more than 50 μm, the dimple effect is lowered and thus the flight performance of the golf ball is lowered.

The golf ball according to the present disclosure preferably has a diameter ranging from 40 mm to 45 mm. In light of satisfying the regulation of US Golf Association (USGA), the diameter is particularly preferably 42.67 mm or more. In light of prevention of air resistance, the diameter is more preferably 44 mm or less, and particularly preferably 42.80 mm or less. In addition, the golf ball preferably has a mass of 40 g or more and 50 g or less. In light of obtaining greater inertia, the mass is more preferably 44 g or more, and particularly preferably 45.00 g or more. In light of satisfying the regulation of USGA, the mass is particularly preferably 45.93 g or less.

When the golf ball according to the present disclosure has a diameter in the range from 40 mm to 45 mm, the compression deformation amount (shrinking amount along the compression direction) of the golf ball when applying a load from an initial load of 98 N to a final load of 1275 N to the golf ball is preferably 2.0 mm or more, more preferably 2.4 mm or more, and even more preferably 2.5 mm or more, and is preferably 5.0 mm or less, more preferably 4.5 mm or less, and even more preferably 4.0 mm or less. If the compression deformation amount is 2.0 mm or more, the golf ball is not excessively hard and thus has better shot feeling. On the other hand, if the compression deformation amount is 5.0 mm or less, the resilience is greater.

The FIGURE is a partially cutaway cross-sectional view of a golf ball 1 according to one embodiment of the present disclosure. The golf ball 1 comprises a spherical core 2, and a cover 3 disposed outside the spherical core 2. A plurality of dimples 31 are formed on the surface of the cover 3. Other portions than the dimples 31 on the surface of the cover 3 are lands 32. The cover 3 is formed from the cover composition containing the ionomer resin.

EXAMPLES

Next, the present disclosure will be described in detail by way of examples. However, the present disclosure is not limited to the examples described below. Various changes and modifications without departing from the spirit of the present disclosure are included in the scope of the present disclosure.

[Evaluation Method]

(1) Measurement of Phase Angle δ (G*=0.1 MPa) at Absolute Value G*=0.1 MPa of Complex Modulus

1) Preparation and Measurement of Sample

The sample was charged in a mold for heat press with a thickness of 1.0 mm, and preheated for 5 minutes in a hot press machine with a surface temperature of 180° C. Then, the residual gas in the molten resin was degassed by repeating pressurization and depressurization, and the sample was further pressurized at 4.9 MPa and kept for 5 minutes. Then, the sample was transferred to a press machine with a surface temperature of 25° C. and held at a pressure of 4.9 MPa for 3 minutes for cooling, to prepare a press plate formed of the sample with a thickness of about 1.0 mm. The press plate formed of the sample was processed into a circle shape with a diameter of 25 mm, which was used as a sample, and the dynamic viscoelasticity thereof was measured using an ARES type rotary rheometer available from Rheometrics Ltd. as a measurement apparatus for the dynamic viscoelasticity characteristics under the following conditions in a nitrogen atmosphere.

• • Plate: φ25 mm (diameter) parallel plate
  • Temperature: 160° C.
  • Strain amount: 10%
  • Measurement angular frequency range: 1.0×10-2 to 1.0×102 rad/s
  • Measurement interval: 5 points/decade

The phase angle δ was plotted to the common logarithm log G* of the absolute value G* (Pa) of the complex modulus of elasticity, and the 0 (degrees) value at the point corresponding to log G*=5.0 was adopted as δ (G*=0.1 MPa). When there was no point corresponding to log G*=5.0 in the measurement points, the δ value at log G*=5.0 was obtained by linear interpolation using two points around log G*=5.0. In addition, when all the measurement points were log G*<5, the δ value at log G*=5.0 was obtained by extrapolating the δ value at log G*=5.0 using the three points from the largest log G* value with a quadratic curve.

(2) Measurement of Weight Average Molecular Weight (Mw) and Molecular Weight Distribution Parameter (Mw/Mn)

The weight average molecular weight (Mw) was obtained by gel permeation chromatography (GPC). In addition, the molecular weight distribution parameter (Mw/Mn) was calculated from the ratio of Mw to Mn, i.e. Mw/Mn by further obtaining the number average molecular weight (Mn) by gel permeation chromatography (GPC).

The measurement was carried out according to the following procedure and conditions.

1) Pretreatment of Sample

When the sample had a carboxylic acid group, for example, esterification treatment such as methyl esterification using diazomethane or trimethylsilyl (TMS) diazomethane, was carried out and used for the measurement. In addition, when the sample had a salt of carboxylic acid group, an acid treatment was carried out to modify the salt of the carboxylic acid group into a carboxylic acid group, and then the above-mentioned esterification treatment was carried out and used for the measurement.

2) Preparation of Sample Solution

In a vial bottle with a volume of 4 mL, 3 mg of the sample and 3 mL of o-dichlorobenzene were weighed, and the vial bottle was sealed with a screw cap and a septum made of Teflon (registered trademark) and then shaken at a temperature of 150° C. for 2 hours with an SSC-7300 type high temperature shaking device available from Senshu Scientific Co., Ltd. After the shaking was completed, it was visually confirmed that there were no insoluble components.

3) Measurement

One high temperature GPC column Showdex HT-G and two high temperature GPC columns HT-806M, both available from SHOWA DENKO K.K., were connected to Alliance GPCV2000 type available from Waters Corp., and o-dichlorobenzene was used as an eluent to carry out the measurement at a temperature of 145° C. and a flow rate of 1.0 mL/min.

4) Calibration Curve

Calibration of the column was carried out by subjecting to measurements of monodispersed polystyrenes (each 0.07 mg/ml solution of S-7300, S-3900, S-1950, S-1460, S-1010, S-565, S-152, S-66.0, S-28.5 and S-5.05) available from SHOWA DENKO K.K., n-eicosane and n-tetracontane under the same conditions as mentioned above, and the elution time and the logarithmic value of the molecular weight were approximated by a quaternary equation. It is noted that the following formula was used for the conversion of the molecular weight of polystyrene (MPS) to the molecular weight of polyethylene (MPE).

MPE = 0.468 × MPS

(3) Melt Flow Rate (MFR)

MFR was measured under the conditions of a temperature of 190° C. and a load of 21.18 N (=2.16 kgf) in accordance with Table 1-Condition 7 of JIS K-7210 (2018).

(4) Melting Point and Crystallinity

The melting point is indicated by a peak temperature in an endothermic curve measured with a differential scanning calorimeter (DSC). The measurement was carried out with DSC (DSC7020) available from SII NanoTechnology Co., Ltd. under the following measurement conditions.

About 5.0 mg of the sample was put in an aluminum pan, and the temperature thereof was raised to 200° C. at 10° C./min, maintained at 200° C. for 5 minutes, and then lowered to 30° C. at 10° C./min. The temperature was maintained at 30° C. for 5 minutes, and raised at 10° C./min again to obtain an absorption curve. In the absorption curve, the maximum peak temperature was adopted as the melting point Tm, and the heat of fusion (ΔH) was obtained from the area of the melting endothermic peak and divided by the heat of fusion 293 J/g of the perfect crystal of the high density polyethylene (HDPE) to obtain the crystallinity (%).

(5) Bending Stiffness (MPa)

Test pieces with a thickness of about 2 mm, a width of 20 mm and a length of 100 mm were produced by injection molding the ionomer resin or cover composition. The test pieces were stored at a temperature of 23° C. plus or minus 2° C. and a relative humidity of 50% plus or minus 5% for 14 days. Load scales of the obtained test piece at bending angles of 3°, 6°, 9° and 12° were measured with an Olsen stiffness tester (available from Toyo Seiki Seisaku-sho, Ltd.), the bending angles (°) were plotted in the horizontal axis and the load scale readings were plotted in the vertical axis to obtain a linear approximation curve, and the slope of the linear approximation curve was calculated. Measurement was carried out under conditions of a temperature of 23° C. plus or minus 2° C., a relative humidity of 50% plus or minus 5%, a bending speed of 60°/min, and a distance between fulcrums of 50 mm. The bending stiffness was calculated by multiplying the above slope value by 8.7078 and then dividing the obtained product by the cube of thickness (cm) of the test piece. In the present disclosure, the unit of the bending stiffness has been converted into MPa from kgf/cm².

(6) Slab Hardness (Shore D Hardness)

Sheets with a thickness of about 2 mm were prepared by injection molding the ionomer resin or cover composition. The sheets were stored at a temperature of 23° C. for two weeks. At least three of these sheets were stacked on one another so as not to be affected by the measuring substrate on which the sheets were placed, and the hardness of the stack was measured with an automatic hardness tester (Digitest II available from Bareiss company) using a detector of “Shore D”.

(7) Measurement of Loss Modulus E″ at Temperature of 0° C.

The loss modulus E″ of the cover layer at the temperature of 0° C. was measured under the following conditions.

Apparatus: dynamic viscoelasticity measuring apparatus Rheogel-E4000 available from UBM CO., Ltd.

Measuring sample: a sheet with a thickness of about 0.5 mm was prepared by press molding the cover composition, and a sample piece was cut from the sheet such that the sample piece had a width of 4 mm and a distance between clamps of 20 mm.

• • measuring mode: sine wave tensile mode
  • measuring temperature range: −100° C. to 100° C.
  • temperature elevating rate: 4° C./min
  • Measurement data acquisition interval: 4° C.
  • oscillation frequency: 10 Hz
  • measuring strain: 0.05%

(8) Measurement of Compression Deformation Amount

The compression deformation amount was measured with a YAMADA type compression tester “SCH”. The golf ball was placed on a metal rigid plate of the tester. A metal cylinder slowly fell toward the golf ball. The golf ball sandwiched between the bottom of the cylinder and the rigid plate deformed. The travelling distance of the cylinder was measured when applying a load from an initial load of 98 N to a final load of 1275 N to the golf ball. The compression deformation amount (mm) was the travelling distance. The travelling speed of the cylinder before applying the initial load was 0.83 mm/s. The travelling speed of the cylinder when applying the load from the initial load to the final load was 1.67 mm/s.

(9) Coefficient of Restitution

A metal cylindrical object having a mass of 198.4 g was allowed to collide with each golf ball at a speed of 45 m/see, and the speeds of the cylindrical object and the golf ball before and after the collision were measured. The coefficient of resilience of each golf ball was calculated based on the respective speeds and mass of the golf ball and the cylindrical object. The measurement was conducted using twelve samples for each golf ball, and the average value thereof was adopted as the coefficient of resilience of the golf ball.

(10) Durability

A W #1 driver provided with a metal head (XXIO S, loft angel: 11°, available from Sumitomo Rubber Industries, Ltd.) was installed on a swing robot M/C available from Golf Laboratories, Inc. Each golf ball was hit repeatedly at a head speed of 45 m/see until the golf ball was broken, and the hitting times when the golf ball was broken were counted. The hitting times of the golf ball No. 1 were defined as 100 for the golf ball No. 2, the hitting times of the golf ball No. 3 were defined as 100 for the golf balls No. 4 to No. 8, the hitting times of the golf ball No. 9 were defined as 100 for the golf balls No. 10 to No. 14, and the durability of each golf ball was represented by converting the hitting times of each golf ball into the index. The golf ball having a greater indexed value has more excellent durability.

[Production of Ionomer]

<Synthesis of Metal Complex>

(1) Synthesis of B-27DM/Ni Complex

For the B-27DM/Ni complex, the following 2-bis(2,6-dimethoxyphenyl)phosphano-6-pentafluorophenylphenol ligand (B-27DM) was used in accordance with Synthetic Example 4 described in WO 2010/050256. In accordance with Example 1 described in WO 2010/050256, bis(1,5-cyclooctadiene) nickel (0) (referred to as Ni(COD)₂) was used to synthesize the nickel complex (B-27DM/Ni) which is a reaction product between B-27DM and Ni(COD)₂ in a ratio of 1:1.

(2) Synthesis of B-423/Ni Complex

For the B-423/Ni complex, the following 2-bis(2,6-dimethoxyphenyl)phosphano-6-(2,6-diisopropylphenyl) phenol ligand (B-423) in accordance with Synthetic Example 1 described in JP 6913051 B was used. In accordance with Example 1 described in JP 6913051 B, bis(1,5-cyclooctadiene) nickel (0) (referred to as Ni(COD)₂) was used to synthesize the nickel complex (B-423/Ni) which is a reaction product between B-423 and Ni(COD)₂ in a ratio of 1:1.

< (Production Examples 1 to 3): Production of Ionomer Base Resin Precursor>

The transition metal complex (B-27DM/Ni complex or B-423/Ni complex) was used to produce ethylene/tBu acrylate copolymers. The ionomer base resin precursors were produced with reference to the production example 1 described in JP 6750936 B. The type of the metal complex, the amount of the metal complex, the amount of trioctyl aluminum (TNOA), the amount of toluene, the type of the comonomer, the amount of the comonomer, the partial pressure of ethylene, the polymerization temperature, the polymerization time, etc. were changed in accordance with the conditions shown in Table 1, and the physical properties of the obtained ionomer base resin precursors were shown in Table 2.

TABLE 1
Ionomer base resin	Production	Production	Production
precursor	Example 1	Example 2	Example 3
Type of	B-423/Ni	B-27DM/Ni	B-27DM/Ni
Metal complex
Amount of Metal complex	910	1060	860
(mmol)
Trioctyl aluminum	320	1110	274
(TNOA) (mmol)
Toluene (L)	750	750	750
Comonomer 1	t-butyl	t-butyl	t-butyl
	acrylate	acrylate	acrylate
Comonomer 1	347	394	444
Concentration
mmol/L

Polymerization	Partial	0.7	0.7	0.7
Conditions	Pressure of
	Ethylene (MPa)
	Temperature	95	100	93
	(° C.)
	Time (min.)	390	210	260

Yield (g)	139000	166200	134290
Catalytic efficiency	1.5E+05	1.6E+05	1.6E+05
(g/mol)

TABLE 2
Ionomer base resin	Production	Production	Production
precursor	Example 1	Example 2	Example 3
Structural Unit (B)	t-butyl acrylate	t-butyl acrylate	t-butyl acrylate
Amount of Structural	5.2	4.9	7.5
Unit (B) (mol %)
Melting point Tm	93.8	97.6	85.9
(° C.)
Crystallinity(%)	22	25	16
Weight average	3.6	1.9	2.1
molecular weight
(MW*10−4)
Molecular weight	2.3	3.0	2.2
distribution parameter
(Mw/Mn)
Number of Methyl	1.0	1.2	0.6
Branches
(branches/1000 C)
Number of Ethyl	Not detected	Not detected	Not detected
Branches
(branches/1000 C)
Number of butyl	Not detected	Not detected	Not detected
Branches
(branches/1000 C)
“Not detected” means less than detection limit.

<(Resins 1 to 3): Production of Ionomer Base Resin (Copolymer (P))>

In a SUS316L-made autoclave with an internal volume of 1.6 m³ equipped with a stirring blade, 100 kg of one of the copolymers obtained in the production examples 1 to 3, 2.0 kg of para-toluenesulfonic acid monohydrate and 173 L of toluene were charged, and stirred at 105° C. for 4 hours. After 173 L of ion exchange water was charged, and the mixture was stirred and allowed to stand, the aqueous layer was removed. Thereafter, ion exchange water was charged and removed repeatedly until pH of the removed aqueous layer became 5 or more. The remaining solution was charged into a twin-screw extruder (L/D=45.5) equipped with a 42 mmφ vent device, and the solvent was distilled off by evacuating the vent. Further, the resin in the form of strands extruded continuously from the die at the tip of the extruder was cooled in water and cut with a cutter to obtain resin pellets.

Disappearance of the peak near 850 cm⁻¹ attributed to the t-Bu group, decrease of the peak near 1730 cm⁻¹ attributed to the carbonyl group of the ester, and increase of the peak near 1700 cm⁻¹ attributed to the carbonyl group of the carboxylic acid (dimer) in the IR spectra of the obtained resins were observed.

According to this, decomposition of the t-Bu ester and formation of the carboxylic acid were confirmed, and the ionomer base resins 1 to 3 were obtained. The physical properties of the obtained resins were shown in Table 3. It is noted that “not detected” in the table means “lower than the detection limit”.

TABLE 3
Ionomer base resin
(copolymer)	Resin 1	Resin 2	Resin 3
Base resin Precursor	Production	Production	Production
	Example 1	Example 2	Example 3
Resin composition	E/AA =	E/AA =	E/AA =
A/B (mol/mol)	94.8/5.2	95.1/4.9	92.5/7.5
MFR (190° C., 2.16 kgf)	11	85	70
(g/10 min)
Melting point Tm	99	102	92
(° C.)
Crystallinity(%)	28	32	23
Amount of Structural	5.2	4.9	7.5
Unit [Z] [B] (mol %)
−3.74 X [Z] + 130	111	112	102
Phase angle δ	58	59	67
(G* = 0.1 MPa)
(Degree)

Example 1 to Example 11: Production of Ionomer Resin

1) Preparation of Na Ion Supply Source

An ethylene/methacrylic acid (MAA) copolymer (available from Dow-Mitsui Polychemicals Co., Ltd., Brand name: Nucrel N1050H) and sodium carbonate in a blending ratio of 55 wt %: 45 wt % were charged continuously into a twin-screw extruder (L/D=64) equipped with a 26 mmφ vent device available from Toshiba Machine Co. Ltd., and the mixture was kneaded under kneading conditions of a barrel set temperature of 150° C. and a screw rotational speed of 150 rpm while removing gas and water produced during the kneading from the bent part with a vacuum pump. Further, the resin in the form of strands extruded continuously from the die at the tip of the extruder was cooled in water and cut with a cutter to obtain Na ion supply source pellets.

2) Preparation of Zn Ion Supply Source

An ethylene/methacrylic acid (MAA) copolymer (available from Mitsui-Du Pont Chemical Co., Ltd., Brand name: Nucrel M1050H), zinc oxide and zinc stearate were continuously charged into a twin-screw extruder (L/D=64) equipped with a 26 mmφ vent device available from Toshiba Machine Co. Ltd. in a blending ratio of 54.5 wt %: 45 wt %: 0.5 wt %, and the mixture was kneaded under kneading conditions of a barrel set temperature of 150° C. and a screw rotational speed of 150 rpm while removing gas and water produced during the kneading from the vent part with a vacuum pump. Further, the resin was extruded continuously from the die at the tip of the extruder in the form of strands and was cooled in water and cut with a cutter to obtain Zn ion supply source pellets.

3) Preparation of Ionomer

One of the resins 1 to 3 and the Na ion supply source or Zn ion supply source were charged continuously into a twin-screw extruder (L/D=65) equipped with a 26 mmφ vent device available from Toshiba Machine Co. Ltd. in a blending ratio to obtain a predetermined neutralization degree, and the mixture was kneaded under kneading conditions of a barrel set temperature of 200° C. and a screw rotational speed of 150 rpm while injecting water in an amount of 4 parts with respect to 100 parts of the charged resin and removing gas and water produced during the kneading from the vent part with a vacuum pump. Further, the resin was extruded continuously from the die at the tip of the extruder in the form of strands and cooled in water and cut with a cutter to obtain ionomer pellets.

The peak near 1700 cm⁻¹ attributed to the carbonyl group of the carboxylic acid (dimer) decreased, and the peak near 1560 cm⁻¹ attributed to the carbonyl group of the salt of the carboxylic acid group increased in the IR spectra of the obtained resins. It was confirmed that an ionomer with a desired neutralization degree was produced based on the decreased amount of the peak near 1,700 cm⁻¹ attributed to the carbonyl group of the carboxylic acid (dimer). The physical properties of the obtained ionomers were shown in Table 4.

TABLE 4
Ionomer resin	IO-1	IO-2	IO-3	IO-4
Ionomer Base resin	Resin 1	Resin 1	Resin 2	Resin 2
Resin composition	E/AA =	E/AA =	E/AA =	E/AA =
A/B (mol %/mol %)	94.8/5.2	94.8/5.2	95.1/4.9	95.1/4.9
Metal ion type	Na	Zn	Na	Na
Neutralization degree	20	20	50	60
(n × Mn+/AA)
(mol %)
MFR	1.7	1.5	3.0	1.1
(190° C., 2.16 kgf)
(g/10 min)
Shore D	63	63	62	61
Bending stiffness	372	298	282	261
(MPa)
Phase angle δ	57	57	56	55
(G* = 0.1 MPa)
(Degree)
Ionomer resin	IO-5	IO-6	IO-7	IO-8
Ionomer Base resin	Resin 2	Resin 2	Resin 2	Resin 3
Resin composition	E/AA =	E/AA =	E/AA =	E/AA =
A/B (mol %/mol %)	95.1/4.9	95.1/4.9	95.1/4.9	92.5/7.5
Metal ion type	Na	Zn	Zn	Na
Neutralization degree	80	40	60	41
(n × Mn+/AA)
(mol %)
MFR	0.3	3.4	1.0	3.2
(190° C., 2.16 kgf)
(g/10 min)
Shore D	61	63	63	65
Bending stiffness	229	382	334	318
(MPa)
Phase angle δ	53	56	54	73
(G* = 0.1 MPa)
(Degree)

	Ionomer resin	IO-9	IO-10	IO-11
	Ionomer Base resin	Resin 3	Resin 3	Resin 3
	Resin composition	E/AA =	E/AA =	E/AA =
	A/B (mol %/mol %)	92.5/7.5	92.5/7.5	92.5/7.5
	Metal ion type	Na	Zn	Zn
	Neutralization degree	54	29	41
	(n × Mn+/AA)
	(mol %)
	MFR	1.1	4.4	1.5
	(190° C., 2.16 kgf)
	(g/10 min)
	Shore D	65	65	65
	Bending stiffness	279	320	323
	(MPa)
	Phase angle δ	68	74	70
	(G* = 0.1 MPa)
	(Degree)

[Production of Golf Ball]

(1) Production of Core

According to the formulations shown in Table 5, the rubber compositions were kneaded, and heat-pressed at a temperature of 170° C. for 30 min in upper and lower molds, each having a hemispherical cavity, to obtain spherical cores.

TABLE 5
Core composition	A	B	C

Polybutadiene	100	100	100
Zinc acrylate	28.5	30.6	28.5
Zinc oxide	5	5	5
Barium sulfate	Appropriate	Appropriate	Appropriate
	amount*1)	amount*1)	amount*1)
Diphenyl disulfide	—	0.5	0.5
Dicumyl peroxide	0.6	0.7	0.6
*1)The amount of barium sulfate was adjusted such that the ball had a mass of 45.3 g.

• • Polybutadiene rubber: “BR730 (high-cis polybutadiene)” available from ENEOS Materials Corporation
  • Zinc acrylate: “ZNDA-90S” available from Nisshoku Techno Fine Chemical Co., Ltd.
  • Zinc oxide: “Ginrei R” available from Toho Zinc Co., Ltd.
  • Barium sulfate: “Barium Sulfate BD” available from Sakai Chemical Industry Co., Ltd.
  • Dicumyl peroxide: “Percumyl (register trademark) D (dicumyl peroxide)” available from NOF Corporation
  • Diphenyl disulfide: available from Sumitomo Seika Chemicals Co., Ltd.

(2) Production of Cover

According to the formulations shown in Table 6, the materials were extruded with a twin-screw kneading extruder to prepare the cover composition in a pellet form. The extruding conditions were a screw diameter of 30 mm, a screw rotational speed of 200 rpm, and a screw L/D=30, and the cover composition was heated to a temperature of 220° C. to 250° C. at the die position of the extruder.

The cover composition was injection molded onto the core obtained as above to form the cover layer (thickness: 1.5 mm). The surface of the obtained golf ball bodies was treated with sandblast and marked. Then, a clear paint was applied thereon, and dried in an oven at a temperature of 40° C. to obtain golf balls having a diameter of 42.7 mm and a mass of 45.3 g. The evaluation results regarding the obtained golf balls are shown in Table 6.

TABLE 6
Golf ball No.	1	2	3	4
Core formulation	A	A	B	B

Cover	Resin	Himilan 1605 (Na)	50	—	50	—
composition	component	Himilan AM7329 (Zn)	50	—	50	—
(parts		Surlyn 8150 (Na, acid amount: 5.8 mole % or more)	—	—	—	—
by mass)		Surlyn 9150 (Zn, acid amount: 5.8 mole % or more)	—	—	—	—
		IO-1 (Na, acid amount: 5.2 mole %, neutralization	—	50	—	—
		degree: 20 mole %)
		IO-2 (Zn, acid amount: 5.2 mole %, neutralization	—	50	—	—
		degree: 20 mole %)
		IO-3 (Na, acid amount: 4.9 mole %, neutralization	—	—	—	50
		degree: 50 mole %)
		IO-4 (Na, acid amount: 4.9 mole %, neutralization	—	—	—	—
		degree: 60 mole %)
		IO-5 (Na, acid amount: 4.9 mole %, neutralization	—	—	—	—
		degree: 80 mole %)
		IO-6 (Zn, acid amount: 4.9 mole %, neutralization	—	—	—	—
		degree: 40 mole %)
		IO-7 (Zn, acid amount: 4.9 mole %, neutralization	—	—	—	50
		degree: 60 mole %)
		IO-8 (Na, acid amount: 7.5 mole %, neutralization	—	—	—	—
		degree: 41 mole %)
		IO-9 (Na, acid amount: 7.5 mole %, neutralization	—	—	—	—
		degree: 54 mole %)
		IO-10 (Zn, acid amount: 7.5 mole %, neutralization	—	—	—	—
		degree: 29 mole %)
		IO-11 (Zn, acid amount: 7.5 mole %, neutralization	—	—	—	—
		degree: 41 mole %)
		UMEX 1010	—	—	—	—

	Melt flow rate (190° C., 2.16 kgf)	4.1	2.3	4.1	3.0
	Slab hardness D (Shore D)	64.0	63.5	64.6	64.0
	Bending stiffness M (MPa)	283	398	270	329
	M/D2	0.069	0.099	0.065	0.080
	Loss modulus E″ at 0° C. (×107 Pa)	3.80	3.28	3.80	3.12

Ball	Compression deformation amount (mm)	2.61	2.62	2.75	2.77
performance	Coefficient of restitution	0.789	0.786	0.789	0.786

	Durability (index)	100	346	100	321

Golf ball No.	5	6	7	8
Core formulation	B	B	B	B

Cover	Resin	Himilan 1605 (Na)	—	—	—	50
composition	component	Himilan AM7329 (Zn)	—	—	—	50
(parts		Surlyn 8150 (Na, acid amount: 5.8 mole % or more)	—	—	—	—
by mass)		Surlyn 9150 (Zn, acid amount: 5.8 mole % or more)	—	—	—	—
		IO-1 (Na, acid amount: 5.2 mole %, neutralization	—	—	—	—
		degree: 20 mole %)
		IO-2 (Zn, acid amount: 5.2 mole %, neutralization	—	—	—	—
		degree: 20 mole %)
		IO-3 (Na, acid amount: 4.9 mole %, neutralization	—	—	—	—
		degree: 50 mole %)
		IO-4 (Na, acid amount: 4.9 mole %, neutralization	50	—	—	—
		degree: 60 mole %)
		IO-5 (Na, acid amount: 4.9 mole %, neutralization	—	50	50	—
		degree: 80 mole %)
		IO-6 (Zn, acid amount: 4.9 mole %, neutralization	50	50	—	—
		degree: 40 mole %)
		IO-7 (Zn, acid amount: 4.9 mole %, neutralization	—	—	50	—
		degree: 60 mole %)
		IO-8 (Na, acid amount: 7.5 mole %, neutralization	—	—	—	—
		degree: 41 mole %)
		IO-9 (Na, acid amount: 7.5 mole %, neutralization	—	—	—	—
		degree: 54 mole %)
		IO-10 (Zn, acid amount: 7.5 mole %, neutralization	—	—	—	—
		degree: 29 mole %)
		IO-11 (Zn, acid amount: 7.5 mole %, neutralization	—	—	—	—
		degree: 41 mole %)
		UMEX 1010	—	——	—	2

	Melt flow rate (190° C., 2.16 kgf)	4.5	1.9	0.9	4.5
	Slab hardness D (Shore D)	64.3	63.1	62.6	64.3
	Bending stiffness M (MPa)	334	293	278	275
	M/D2	0.081	0.074	0.071	0.067
	Loss modulus E″ at 0° C. (×107 Pa)	3.32	3.14	2.28	3.80

Ball	Compression deformation amount (mm)	2.74	2.74	2.75	2.75
performance	Coefficient of restitution	0.787	0.787	0.784	0.788

	Durability (index)	306	325	375	135

Golf ball No.	9	10	11	12
Core formulation	C	C	C	C

Cover	Resin	Himilan 1605 (Na)	—	—	—	—
composition	component	Himilan AM7329 (Zn)	—	—	—	—
(parts		Surlyn 8150 (Na, acid amount: 5.8 mole % or more)	50	—	—	—
by mass)		Surlyn 9150 (Zn, acid amount: 5.8 mole % or more)	50	—	—	—
		IO-1 (Na, acid amount: 5.2 mole %, neutralization	—	—	—	—
		degree: 20 mole %)
		IO-2 (Zn, acid amount: 5.2 mole %, neutralization	—	—	—	—
		degree: 20 mole %)
		IO-3 (Na, acid amount: 4.9 mole %, neutralization	—	—	—	—
		degree: 50 mole %)
		IO-4 (Na, acid amount: 4.9 mole %, neutralization	—	—	—	—
		degree: 60 mole %)
		IO-5 (Na, acid amount: 4.9 mole %, neutralization	—	—	—	—
		degree: 80 mole %)
		IO-6 (Zn, acid amount: 4.9 mole %, neutralization	—	—	—	—
		degree: 40 mole %)
		IO-7 (Zn, acid amount: 4.9 mole %, neutralization	—	—	—	—
		degree: 60 mole %)
		IO-8 (Na, acid amount: 7.5 mole %, neutralization	—	25	50	75
		degree: 41 mole %)
		IO-9 (Na, acid amount: 7.5 mole %, neutralization	—	—	—	—
		degree: 54 mole %)
		IO-10 (Zn, acid amount: 7.5 mole %, neutralization	—	75	50	25
		degree: 29 mole %)
		IO-11 (Zn, acid amount: 7.5 mole %, neutralization	—	—	—	—
		degree: 41 mole %)
		UMEX 1010	—	——	—	—

	Melt flow rate (190° C., 2.16 kgf)	6.9	4.0	5.3	3.9
	Slab hardness D (Shore D)	65.9	64.7	65.7	64.8
	Bending stiffness M (MPa)	334	329	395	323
	M/D2	0.077	0.079	0.091	0.077
	Loss modulus E″ at 0° C. (×107 Pa)	3.45	2.57	2.13	2.49

Ball	Compression deformation amount (mm)	2.77	2.68	2.66	2.67
performance	Coefficient of restitution	0.795	0.798	0.799	0.799

	Durability (index)	100	318	322	320

Golf ball No.	13	14
Core formulation	C	C

Cover	Resin	Himilan 1605 (Na)	—	—
composition	component	Himilan AM7329 (Zn)	—	—
(parts		Surlyn 8150 (Na, acid amount: 5.8 mole % or more)	—	—
by mass)		Surlyn 9150 (Zn, acid amount: 5.8 mole % or more)	—	—
		IO-1 (Na, acid amount: 5.2 mole %, neutralization		—
		degree: 20 mole %)
		IO-2 (Zn, acid amount: 5.2 mole %, neutralization	—	—
		degree: 20 mole %)
		IO-3 (Na, acid amount: 4.9 mole %, neutralization	—	—
		degree: 50 mole %)
		IO-4 (Na, acid amount: 4.9 mole %, neutralization	—	—
		degree: 60 mole %)
		IO-5 (Na, acid amount: 4.9 mole %, neutralization	—	—
		degree: 80 mole %)
		IO-6 (Zn, acid amount: 4.9 mole %, neutralization	—	—
		degree: 40 mole %)
		IO-7 (Zn, acid amount: 4.9 mole %, neutralization	—	—
		degree: 60 mole %)
		IO-8 (Na, acid amount: 7.5 mole %, neutralization	—	—
		degree: 41 mole %)
		IO-9 (Na, acid amount: 7.5 mole %, neutralization	50	50
		degree: 54 mole %)
		IO-10 (Zn, acid amount: 7.5 mole %, neutralization	50	—
		degree: 29 mole %)
		IO-11 (Zn, acid amount: 7.5 mole %, neutralization	—	50
		degree: 41 mole %)
		UMEX 1010	—	—

	Melt flow rate (190° C., 2.16 kgf)	3.4	1.7
	Slab hardness D (Shore D)	65.3	63.5
	Bending stiffness M (MPa)	374	354
	M/D2	0.088	0.088
	Loss modulus E″ at 0° C. (×107 Pa)	1.90	2.08

Ball	Compression deformation amount (mm)	2.69	2.68
performance	Coefficient of restitution	0.798	0.797

	Durability (index)	390	439

The materials shown below were used in Table 6.

• • Himilan 1605: sodium ion-neutralized ethylene-methacrylic acid copolymer ionomer resin (Shore D hardness: 64, bending stiffness: 226 MPa) available from Dow-Mitsui Polychemicals Co., Ltd.
  • Himilan AM7329: zinc ion-neutralized ethylene-methacrylic acid copolymer ionomer resin (Shore D hardness: 62, bending stiffness: 187 MPa) available from Dow-Mitsui Polychemicals Co., Ltd.
  • Surlyn 8150: sodium ion-neutralized ethylene-methacrylic acid copolymer ionomer resin (Shore D hardness: 68) available from Dow Chemical Company
  • Surlyn 9150: zinc ion-neutralized ethylene-methacrylic acid copolymer ionomer resin (Shore D hardness: 64) available from Dow Chemical Company
  • UMEX 1010: acid-modified polypropylene resin available from Sanyo Chemical Industries, Ltd.

It is apparent from the results shown in Table 6 that the golf ball according to the present disclosure that comprises a core and at least one cover layer positioned outside the core, wherein the at least one cover layer is formed from a cover composition containing one or more ionomer resins, the ionomer resin comprises a copolymer (P) having a structural unit (A) derived from ethylene and/or an α-olefin having 3 to 20 carbon atoms and a structural unit (B) having a carboxyl group and/or a dicarboxylic anhydride group as an essential constitutional unit, and at least a part of the carboxyl group and/or the dicarboxylic anhydride group in the copolymer (P) is neutralized with at least one kind of metal ion selected from Group 1, Group 2 and Group 12 in the periodic table, and a loss modulus E″ at a temperature of 0° C. is 3.40×10⁷ Pa or less, wherein the loss modulus E″ at the temperature of 0° C. is obtained by measuring a dynamic viscoelasticity of the cover composition under the following conditions, has remarkedly improved durability without substantially lowering resilience. On the other hand, the golf ball No. 1 has a loss modulus E″ of more than 3.40×10⁷ Pa and thus has more inferior durability than the golf ball No. 2, if comparing the golf balls No. 1 and No. 2 where the same core formulation A is used. The golf balls No. 3 and No. 8 have a loss modulus E″ of more than 3.40×10⁷ Pa and thus have more inferior durability than the golf balls No. 4 to 7, if comparing the golf balls No. 3 to No. 8 where the same core formulation B is used. The golf ball No. 9 has a loss modulus E″ of more than 3.40×10⁷ Pa and thus have more inferior durability than the golf balls No. 10 to 14, if comparing the golf balls No. 9 to No. 14 where the same core formulation C is used.

The preferable embodiment (1) according to the present disclosure is a golf ball comprising a core and at least one cover layer positioned outside the core, wherein the at least one cover layer is formed from a cover composition containing one or more ionomer resins, the ionomer resin comprises a copolymer (P) having a structural unit (A) derived from ethylene and/or an α-olefin having 3 to 20 carbon atoms and a structural unit (B) having a carboxyl group and/or a dicarboxylic anhydride group as an essential constitutional unit, and at least a part of the carboxyl group and/or the dicarboxylic anhydride group in the copolymer (P) is neutralized with at least one kind of metal ion selected from Group 1, Group 2 and Group 12 in the periodic table, and a loss modulus E″ at a temperature of 0° C. is 3.40×10⁷ Pa or less, wherein the loss modulus E″ at the temperature of 0° C. is determined by measuring a dynamic viscoelasticity of the cover composition under the following conditions.

• • <measuring conditions>
  • measuring mode: sine wave tensile mode
  • measuring temperature range: −100° C. to 100° C.
  • temperature increasing rate: 4° C./min
  • oscillation frequency: 10 Hz
  • measuring strain: 0.05%

The preferable embodiment (2) according to the present disclosure is the golf ball according to the embodiment (1), wherein the metal ion includes two or more metal ions selected from lithium, sodium, potassium, calcium and zinc.

The preferable embodiment (3) according to the present disclosure is the golf ball according to the embodiment (1) or (2), wherein the cover composition contains, as the ionomer resin, an ionomer resin having a phase angle δ in a range from 50 degrees to 75 degrees at an absolute value G*=0.1 MPa of a complex modulus of elasticity measured by a rotary rheometer.

The preferable embodiment (4) according to the present disclosure is the golf ball according to any one of the embodiments (1) to (3), wherein the cover composition contains, as the ionomer resin, a first ionomer resin neutralized with a first metal ion and having a phase angle δ in a range from 50 degrees to 75 degrees at an absolute value G*=0.1 MPa of a complex modulus of elasticity measured by a rotary rheometer, and a second ionomer resin neutralized with a second metal ion and having a phase angle δ in a range from 50 degrees to 75 degrees at an absolute value G*=0.1 MPa of a complex modulus of elasticity measured by a rotary rheometer.

The preferable embodiment (5) according to the present disclosure is the golf ball according to the embodiment (4), wherein the first ionomer resin includes the structural unit (B) in an amount ranging from 2.0 mole % to 20.0 mole %, and has a neutralization degree ranging from 5 mole % to 95 mole %.

The preferable embodiment (6) according to the present disclosure is the golf ball according to the embodiment (4) or (5), wherein the second ionomer resin includes the structural unit (B) in an amount ranging from 2.0 mole % to 20.0 mole %, and has a neutralization degree ranging from 5 mole % to 95 mole %.

The preferable embodiment (7) according to the present disclosure is the golf ball according to any one of the embodiments (4) to (6), wherein the first ionomer resin and the second ionomer resin have a melt flow rate (190° C., 2.16 kgf) of 100 g/10 min or less.

The preferable embodiment (8) according to the present disclosure is the golf ball according to any one of the embodiments (4) to (7), wherein the cover composition contains a first ionomer resin having a neutralization degree of 50 mole % or less and a second ionomer resin having a neutralization degree of 50 mole % or less.

The preferable embodiment (9) according to the present disclosure is the golf ball according to any one of the embodiments (4) to (7), wherein the cover composition contains a first ionomer resin having a neutralization degree of 50 mole % or more and a second ionomer resin having a neutralization degree of more than 50 mole %.

The preferable embodiment (10) according to the present disclosure is the golf ball according to any one of the embodiments (4) to (7), wherein the cover composition contains a first ionomer resin having a neutralization degree of 50 mole % or less and a second ionomer resin having a neutralization degree of more than 50 mole %.

The preferable embodiment (11) according to the present disclosure is the golf ball according to any one of the embodiments (4) to (10), wherein a blending ratio (mass ratio) of the first ionomer resin to the second ionomer resin is 10/90 or more and 90/10 or less.

The preferable embodiment (12) according to the present disclosure is the golf ball according to any one of the embodiments (4) to (11), wherein one of the first metal ion and the second metal ion is sodium ion, and the other one of the first metal ion and the second metal ion is zinc ion.

The preferable embodiment (13) according to the present disclosure is the golf ball according to any one of the embodiments (4) to (12), wherein the loss modulus E″ at the temperature of 0° C. is 3.00×10⁷ Pa or less.

The preferable embodiment (14) according to the present disclosure is the golf ball according to any one of the embodiments (4) to (13), wherein the cover composition has a slab hardness (D: Shore D) and a bending stiffness (M: MPa) satisfying M/D²≥0.070.

This application is based on Japanese patent application No. 2024-067758 filed on Apr. 18, 2024 and Japanese patent application No. 2025-005342 filed on Jan. 15, 2025, the contents of which are hereby incorporated by reference.