GOLF BALL

Description

FIELD OF THE PRESENT DISCLOSURE

The present disclosure relates to a golf ball, and particularly relates to a technology for improving formability of a polyurethane cover.

DESCRIPTION OF THE RELATED ART

Conventionally, as a resin component constituting a cover of a golf ball, an ionomer resin or a polyurethane is used. A cover using an ionomer resin tends to have excellent resilience, durability, processability and the like. A cover using a polyurethane tends to have improved shot feeling or spin performance. In addition, a cover material using an ionomer resin and a polyurethane in combination has also been proposed.

For example, JP H11-128402 A discloses a golf ball cover material containing a thermoplastic polyurethane elastomer, an ethylene-acrylate-glycidyl methacrylate ternary copolymer, and magnesium stearate.

JP 2003-180878 A discloses a cover composition primarily containing a heated mixture of 60 to 95 wt % of (a) a polyurethane thermoplastic elastomer and 5 to 40 wt % of (b) an ethylene-(meth)acrylic acid-(meth)acrylate ternary copolymer ionomer resin.

In addition, JP 2007-125377 A discloses a golf ball comprising a cover, wherein the cover is formed from a cover material primarily containing a heated mixture of 60 to 90 mass % of (A) a metal ion neutralized product of an olefin-unsaturated carboxylic acid copolymer and/or a metal ion neutralized product of an olefin-unsaturated carboxylic acid-unsaturated carboxylate copolymer (wherein 40 to 80 mass % of the component (A) is an ionomer neutralized with an alkaline metal ion.), 5 to 20 mass % of (B) at least one member selected from an olefin-unsaturated carboxylic acid copolymer and/or an olefin-unsaturated carboxylic acid-unsaturated carboxylate copolymer, and 2 to 30 mass % of (C) a thermoplastic polyurethane elastomer.

SUMMARY OF THE DISCLOSURE

When a polyurethane is primarily used as a resin component of a cover composition, the cover composition tends to have lowered fluidity, and there is a problem that the cover is hard to be formed. Here, if an ionomer resin is added into the cover composition containing the polyurethane, the fluidity of the cover composition can be improved. However, if the ionomer resin is added into the polyurethane, there is a problem that the formed cover has lowered scratch resistance.

The present disclosure has been made in view of the above circumstances, and an object of the present disclosure is, with respect to a golf ball comprising a cover containing a polyurethane as a resin component, to improve formability of the cover and enhance productivity of the golf ball while inhibiting lowering of scratch resistance of the cover.

The present disclosure that has solved the above problem provides a golf ball comprising a spherical core and a cover covering the spherical core, wherein the cover contains (A) a thermoplastic polyurethane as a resin component, and a difference Δv (v1−v2) between a wave number (v1) of an absorption peak attributed to an N—H group not forming a hydrogen bond in (A) the thermoplastic polyurethane and a wave number (v2) of an absorption peak attributed to an N—H group forming a hydrogen bond with a carbonyl oxygen of a urethane group in (A) the thermoplastic polyurethane ranges from 100.0 cm⁻¹ to 109.0 cm⁻¹ when the cover is measured with a Fourier transform infrared spectrometer under the following measuring conditions:

<Measuring Conditions>

• • measuring method: single-reflection ATR (Attenuated Total Reflection) method
  • measuring range: 400 cm⁻¹ to 4000 cm⁻¹
  • resolution: 4 cm⁻¹
  • cumulative number: 32 times
  • crystal: diamond
  • temperature rising rate: 10° C./min
  • measuring temperature: 190° C.

According to the present disclosure, with respect to a golf ball comprising a cover containing a polyurethane as a resin component, formability of the cover can be improved and productivity of the golf ball can be enhanced while inhibiting lowering of scratch resistance of the cover.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially cutaway cross-sectional view showing a golf ball according to one embodiment of the present disclosure; and

FIG. 2 is an IR spectrum of the cover compositions No. 1, 4, 6.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present disclosure provides a golf ball comprising a spherical core and a cover covering the spherical core, wherein the cover contains (A) a thermoplastic polyurethane as a resin component, and a difference Δv (v1−v2) between a wave number (v1) of an absorption peak attributed to an N—H group not forming a hydrogen bond in (A) the thermoplastic polyurethane and a wave number (v2) of an absorption peak attributed to an N—H group forming a hydrogen bond with a carbonyl oxygen of a urethane group in (A) the thermoplastic polyurethane ranges from 100.0 cm⁻¹ to 109.0 cm⁻¹ when the cover is measured with a Fourier transform infrared spectrometer under the measuring conditions described later.

The polyurethane has a plurality of urethane bonds (—NH—COO—) in the molecule, and a part of the NH groups in the polyurethane forms a hydrogen bond with the carbonyl bond (CO group) of the urethane group. In the Fourier transform infrared spectroscopic analysis, the absorption attributed to the NH group that does not form the hydrogen bond appears around 3450 cm⁻¹, and the absorption attributed to the NH group that forms the hydrogen bond with the carbonyl bond of the urethane group appears between 3355 cm⁻¹ and 3300 cm⁻¹. Here, the absorption wave number of stretching vibration of the NH group that forms the hydrogen bond depends on the intensity of the hydrogen bond, the absorption peak shifts toward the low wave number side if the bond is strong, and the absorption peak shifts toward the high wave number side if the bond is weak.

Therefore, if the difference Δv (v1−v2) is controlled within the range from 100.0 cm⁻¹ to 109.0 cm⁻¹, the intensity of the hydrogen bond is weakened, and the formability of the cover can be improved while inhibiting lowering of the scratch resistance of the cover.

The difference Δv (v1−v2) is preferably 100.0 cm⁻¹ or more, more preferably 100.5 cm⁻¹ or more, and even more preferably 101.0 cm⁻¹ or more, and is preferably 109.0 cm⁻¹ or less, more preferably 108.0 cm⁻¹ or less, and even more preferably 107.0 cm⁻¹ or less.

The thickness of the cover is preferably 0.3 mm or more, more preferably 0.4 mm or more, and even more preferably 0.5 mm or more, and is preferably 2.0 mm or less, more preferably 1.8 mm or less, and even more preferably 1.6 mm or less. If the thickness of the cover is 0.3 mm or more, the cover is more easily molded, and if the thickness of the cover is 2.0 mm or less, the core has a relatively large diameter and thus the golf ball has enhanced resilience performance.

[Cover Composition]

The cover can be formed from a cover composition. Next, the cover composition used in the golf ball according to the present disclosure will be explained.

((A) Thermoplastic Polyurethane)

The cover composition contains (A) a thermoplastic polyurethane as a resin component.

(A) The thermoplastic polyurethane is a material having a plurality of urethane bonds in the molecule and exhibiting thermoplasticity. The thermoplastic polyurethane is a polyurethane exhibiting plasticity by heating and generally means a polyurethane having a linear chain structure of a high molecular weight to a certain extent. Examples of (A) the thermoplastic polyurethane include a product having urethane bonds formed in the molecule by a reaction between a polyisocyanate and a polyol.

The polyisocyanate constituting (A) the thermoplastic polyurethane is not particularly limited, as long as the polyisocyanate is a compound having at least two isocyanate groups in the molecule. The polyisocyanate may be used solely, or at least two of them may be used in combination. The polyisocyanate is preferably a diisocyanate having two isocyanate groups in the molecule.

Examples of the polyisocyanate include an aromatic polyisocyanate such as 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, a mixture of 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate (TDI), 4,4′-diphenylmethane diisocyanate (MDI), 1,5-naphthylene diisocyanate (NDI), 3,3′-bitolylene-4,4′-diisocyanate (TODI), xylylene diisocyanate (XDI), tetramethylxylylene diisocyanate (TMXDI), and para-phenylene diisocyanate (PPDI); and an alicyclic or aliphatic polyisocyanate such as 4,4′-dicyclohexylmethane diisocyanate (H12MDI), 1,3-bis(isocyanatomethyl) cyclohexane (H₆XDI), hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), trans-1,4-cyclohexane diisocyanate (CHDI), and norbornene diisocyanate (NBDI). Among these, as the polyisocyanate, the alicyclic diisocyanate and/or the aromatic diisocyanate is preferable. If the alicyclic diisocyanate and/or the aromatic diisocyanate is used, the obtained polyurethane has enhanced mechanical properties, and the obtained cover has further enhanced scratch resistance.

As the polyisocyanate of (A) the thermoplastic polyurethane, at least one diisocyanate selected from the group consisting of 4,4′-dicyclohexylmethane diisocyanate (H₁₂MDI), 1,3-bis(isocyanatomethyl)cyclohexane (H₆XDI), isophorone diisocyanate (IPDI), trans-1,4-cyclohexane diisocyanate (CHDI), 4,4′-diphenylmethane diisocyanate (MDI) and tolylene diisocyanate (TDI) is particularly preferable. If the above diisocyanate is used, the obtained polyurethane has enhanced mechanical properties, and the obtained cover has further enhanced scratch resistance.

The polyol constituting (A) the thermoplastic polyurethane is not particularly limited, as long as the polyol is a compound having at least two hydroxy groups in the molecule, and examples thereof include a high molecular weight polyol. The high molecular weight polyol may be used solely, or at least two of them may be used in combination. As the polyol, a diol having two hydroxy groups in the molecule is preferable.

Examples of the high molecular weight polyol include a polyether polyol such as polyoxyethylene glycol (PEG), polyoxypropylene glycol (PPG), polytrimethylene ether glycol (PO3G) and polyoxytetramethylene glycol (PTMG); a condensed polyester polyol such as polyethylene adipate (PEA), polybutylene adipate (PBA) and polyhexamethylene adipate (PHMA); a lactone polyester polyol such as poly-ε-caprolactone (PCL); a polycarbonate polyol such as polyhexamethylene carbonate; and an acrylic polyol. The high molecular weight polyol may be derived from a petroleum resource or a biomass resource.

The number average molecular weight of the high molecular weight polyol is not particularly limited, and for example, is preferably 400 or more, more preferably 1,000 or more, and is preferably 10,000 or less, more preferably 8,000 or less.

(A) The thermoplastic polyurethane may include a chain extender as the constituent component. As the chain extender component, a low molecular weight polyol, a low molecular weight polyamine or the like can be used.

Examples of the low molecular weight polyol include a diol such as ethylene glycol, diethylene glycol, triethylene glycol, propane diol (e.g. 1,2-propane diol, 1,3-propane diol, 2-methyl-1,3-propane diol), dipropylene glycol, butane diol (e.g. 1,2-butane diol, 1,3-butane diol, 1,4-butane diol, 2,3-butane diol, 2,3-dimethyl-2,3-butane diol), neopentyl glycol, pentane diol, hexane diol, heptane diol, octane diol, 1,6-cyclohexane dimethylol, aniline diol, and bisphenol A diol; a triol such as glycerin, trimethylolpropane, and hexane triol; and a tetraol or hexaol such as pentaerythritol, and sorbitol.

In addition, the low molecular weight polyamine used as the chain extender component is not particularly limited, as long as the polyamine has at least two amino groups. Examples of the polyamine include an aliphatic polyamine such as ethylene diamine, propylene diamine, butylene diamine, and hexamethylene diamine; an alicyclic polyamine such as isophorone diamine and piperazine; and an aromatic polyamine.

The aromatic polyamine is not particularly limited, as long as the aromatic polyamine has at least two amino groups directly or indirectly bonded to an aromatic ring. Herein, the “indirectly bonded” means that the amino group is bonded to the aromatic ring via, for example, a lower alkylene bond. The aromatic polyamine may be, for example, a monocyclic aromatic polyamine having at least two amino groups bonded to one aromatic ring, or a polycyclic aromatic polyamine having at least two aminophenyl groups each having at least one amino group bonded to one aromatic ring.

Examples of the monocyclic aromatic polyamine include a type having the amino groups directly bonded to the aromatic ring, such as phenylene diamine, toluene diamine, diethyltoluene diamine, and dimethylthiotoluene diamine; and a type having the amino groups bonded to the aromatic ring via the lower alkylene bond, such as xylylene diamine.

In addition, the polycyclic aromatic polyamine may be a poly(aminobenzene) having at least two aminophenyl groups directly bonded to each other, or a compound having at least two aminophenyl groups bonded to each other via a lower alkylene group or an alkylene oxide group. Among them, a diaminodiphenyl alkane having two aminophenyl groups bonded to each other via a lower alkylene group is preferable. Particularly, 4,4′-diaminodiphenyl methane or the derivative thereof is preferable.

The molecular weight of the chain extender is preferably less than 400, more preferably 350 or less, and even more preferably 200 or less, and is preferably 30 or more, more preferably 40 or more, and even more preferably 45 or more.

The constitution embodiment of (A) the thermoplastic polyurethane is not particularly limited, and examples thereof include an embodiment that (A) the thermoplastic polyurethane is composed of the polyisocyanate and the high molecular weight polyol; an embodiment that (A) the thermoplastic polyurethane is composed of the polyisocyanate, the high molecular weight polyol and the low molecular weight polyol; an embodiment that (A) the thermoplastic polyurethane is composed of the polyisocyanate, the high molecular weight polyol, the low molecular weight polyol and the polyamine; and an embodiment that (A) the thermoplastic polyurethane is composed of the polyisocyanate, the high molecular weight polyol and the polyamine. As the constitution embodiment of (A) the thermoplastic polyurethane, in particular, an embodiment that (A) the thermoplastic polyurethane is composed of the diisocyanate and the diol is preferable, and an embodiment that (A) the thermoplastic polyurethane is composed of the diisocyanate, the high molecular weight diol and the low molecular weight diol is more preferable.

The amount of the polyol in 100 mass % of (A) the thermoplastic polyurethane is preferably 10 mass % or more, more preferably 15 mass % or more, and even more preferably 20 mass % or more, and is preferably 90 mass % or less, more preferably 85 mass % or less, and even more preferably 80 mass % or less.

The amount of the polyisocyanate in 100 mass % of (A) the thermoplastic polyurethane is preferably 10 mass % or more, more preferably 15 mass % or more, and even more preferably 20 mass % or more, and is preferably 90 mass % or less, more preferably 85 mass % or less, and even more preferably 80 mass % or less.

The slab hardness of (A) the thermoplastic polyurethane is preferably 80.0 or more, more preferably 85.0 or more, and even more preferably 90.0 or more, and is preferably 97.0 or less, more preferably 96.0 or less, and even more preferably 95.0 or less in Shore A hardness. If the hardness of (A) the thermoplastic polyurethane is 80.0 or more in Shore A hardness, the spin rate on driver shots can be lowered, and if the hardness of (A) the thermoplastic polyurethane is 97.0 or less in Shore A hardness, the spin rate on approach shots increases.

The amount of (A) the thermoplastic polyurethane in the resin component is preferably 50 mass % or more, more preferably 55 mass % or more, even more preferably 60 mass % or more, and most preferably 80 mass % or more, and is preferably 99.9 mass % or less, more preferably 99 mass % or less, even more preferably 98 mass % or less, and most preferably 95 mass % or less. If the amount of the component (A) is 50 mass % or more, the cover has better scratch resistance, and if the amount of the component (A) is 99.9 mass % or less, the cover composition has higher formability.

((B) Olefin-Unsaturated Carboxylic Acid Copolymer and/or the Olefin-Unsaturated Carboxylic Acid-Unsaturated Carboxylate Copolymer)

The cover composition preferably contains (B) the olefin-unsaturated carboxylic acid copolymer and/or the olefin-unsaturated carboxylic acid-unsaturated carboxylate copolymer as the resin component. (B) The olefin-unsaturated carboxylic acid copolymer and/or the olefin-unsaturated carboxylic acid-unsaturated carboxylate copolymer may be used solely, or two or more of them may be used in combination.

If (B) the olefin-unsaturated carboxylic acid copolymer and/or the olefin-unsaturated carboxylic acid-unsaturated carboxylate copolymer is added as the resin component of the cover composition, the aggregation force of the urethane group constituting the hard segment in (A) the thermoplastic polyurethane can be lowered.

The olefin-unsaturated carboxylic acid copolymer is a binary copolymer (hereinafter, sometimes referred to as “(B1) the binary copolymer”) of an olefin and an unsaturated carboxylic acid. The olefin-unsaturated carboxylic acid-unsaturated carboxylate copolymer is a ternary copolymer (hereinafter, sometimes referred to as “(B2) the ternary copolymer”) of an olefin, an unsaturated carboxylic acid and an unsaturated carboxylate. (B) The olefin-unsaturated carboxylic acid copolymer and/or the olefin-unsaturated carboxylic acid-unsaturated carboxylate copolymer may consist of (B1) the binary copolymer, or may consist of (B2) the ternary copolymer. In addition, (B1) the binary copolymer and (B2) the ternary copolymer may be used in combination.

The olefin is preferably an olefin having 2 to 8 carbon atoms, more preferably an olefin having 2 to 4 carbon atoms. Examples of the olefin include ethylene, propylene, butene, pentene, hexene, heptene and octene, and ethylene is particularly preferred.

The unsaturated carboxylic acid is preferably an α,β-unsaturated carboxylic acid, more preferably an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms. Examples of the unsaturated carboxylic acid include acrylic acid, methacrylic acid, fumaric acid, maleic acid and crotonic acid, and acrylic acid or methacrylic acid is particularly preferred.

The unsaturated carboxylate is preferably an α,β-unsaturated carboxylate, more preferably an alkyl ester of an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms. As the unsaturated carboxylate, the alkyl ester of acrylic acid, methacrylic acid, fumaric acid or maleic acid is more preferable, the alkyl ester of acrylic acid or the alkyl ester of methacrylic acid is particularly preferable. Examples of the alkyl group constituting the ester include a methyl group, an ethyl group, a propyl group, an n-butyl group, and an isobutyl group. As the unsaturated carboxylate, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, or isobutyl (meth)acrylate is preferable. It is noted that (meth)acrylic acid means acrylic acid and/or methacrylic acid in the present disclosure.

(B1) The binary copolymer is preferably a binary copolymer of ethylene and the α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms, more preferably an ethylene-(meth)acrylic acid binary copolymer.

(B2) The ternary copolymer is preferably a ternary copolymer of ethylene, the α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and the alkyl ester of the α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms, more preferably an ethylene-(meth)acrylic acid-alkyl (meth)acrylate ternary copolymer.

The amount of the unsaturated carboxylic acid component in (B1) the binary copolymer is preferably 1 mass % or more, more preferably 3 mass % or more, and even more preferably 5 mass % or more, and is preferably 50 mass % or less, more preferably 45 mass % or less, and even more preferably 40 mass % or less. If the amount of the unsaturated carboxylic acid component falls within the above range, the compatibility with (A) the thermoplastic polyurethane is better.

The amount of the unsaturated carboxylic acid component in (B2) the ternary copolymer is preferably 1 mass % or more, more preferably 3 mass % or more, and even more preferably 5 mass % or more, and is preferably 50 mass % or less, more preferably 45 mass % or less, and even more preferably 40 mass % or less. If the amount of the unsaturated carboxylic acid component falls within the above range, the compatibility with (A) the thermoplastic polyurethane is better.

The melt flow rate (MFR) (190° C., 2.16 kgf) of (B) the olefin-unsaturated carboxylic acid copolymer and/or the olefin-unsaturated carboxylic acid-unsaturated carboxylate copolymer is preferably 10 g/10 min or more, more preferably 15 g/10 min or more, and even more preferably 25 g/10 min or more, and is preferably 1000 g/10 min or less, more preferably 900 g/10 min or less, and even more preferably 800 g/10 min or less. If the MFR (190° C., 2.16 kgf) of the component (B) is 10 g/10 min or more, the cover composition has better fluidity. In addition, if the MFR (190° C., 2.16 kgf) of the component (B) is 1000 g/10 min or less, the obtained cover has better impact durability. The MFR is measured with a flow tester according to JIS K7210. When a plurality of the components (B) are used in combination, the MFR of their mixture is measured.

The melting point of (B) the olefin-unsaturated carboxylic acid copolymer and/or the olefin-unsaturated carboxylic acid-unsaturated carboxylate copolymer is preferably 120° C. or less, more preferably 118° C. or less, and even more preferably 115° C. or less. The melting point of the component (B) is preferably 75° C. or more.

Examples of the component (B) include Nucrel (registered trademark) N2050H, N2060, N1050H, N1560, N1525, AN4221C, AN4213C, N1110H, AN4229C, N11081C, N1108C, N1035, N035C, N0908C, AN42012C, N0903HC, N0823, AN42115C, AN4228C, AN4214C, N0200H, AN4233C (available from Dow-Mitsui Polychemicals Co., Ltd.); and Primacor (registered trademark) 1321, 1410, 1430, 3002, 3003, 3004, 3330, 3340, 3440, 3460 (available from SK Geo Centric).

The amount of (B) the olefin-unsaturated carboxylic acid copolymer and the olefin-unsaturated carboxylic acid-unsaturated carboxylate copolymer in the resin component is preferably 0.1 mass % or more, more preferably 0.5 mass % or more, even more preferably 1 mass % or more, particularly preferably 3 mass % or more, and most preferably 5 mass % or more, and is preferably 50 mass % or less, more preferably 45 mass % or less, even more preferably 40 mass % or less, and particularly preferably 20 mass % or less. If the amount of the component (B) is 0.1 mass % or more, the cover composition has further enhanced formability, and if the amount of the component (B) is 50 mass % or less, lowering of the scratch resistance of the obtained cover can be inhibited.

The mass ratio ((A)/(B)) of (A) the thermoplastic polyurethane to (B) the olefin-unsaturated carboxylic acid copolymer and the olefin-unsaturated carboxylic acid-unsaturated carboxylate copolymer in the resin component is preferably 80.0/20.0 or more, more preferably 82.0/18.0 or more, and even more preferably 85.0/15.0 or more, and is preferably 97.0/3.0 or less, more preferably 96.0/4.0 or less, and even more preferably 95.0/5.0 or less. If the mass ratio ((A)/(B)) is 80.0/20.0 or more, lowering of the scratch resistance of the obtained cover can be inhibited, and if the mass ratio ((A)/(B)) is 97.0/3.0 or less, the cover composition has further enhanced formability.

(Other Resin Components)

The resin component of the cover composition may consist of (A) the thermoplastic polyurethane and (B) the olefin-unsaturated carboxylic acid copolymer and/or the olefin-unsaturated carboxylic acid-unsaturated carboxylate copolymer, or may further include other resin components in addition to these components (A) and (B).

Examples of the other resin components include a thermoplastic elastomer.

Specific examples of thermoplastic elastomer include a thermoplastic polyamide elastomer such as “Pebax (registered trademark) (e.g. “Pebax 2533”)” available from Arkema Inc.; a thermoplastic polyester elastomer such as “Hytrel (registered trademark) (e.g. “Hytrel 3548”, “Hytrel 4047”)” available from Toray Celanese Co., Ltd.; and a thermoplastic polystyrene elastomer such as “Tefabloc (registered trademark)” available from Mitsubishi Chemical Corporation.

When the resin component other than the component (A) and the component (B) is contained, the total amount of the component (A) and the component (B) in the resin component is preferably 85 mass % or more, more preferably 90 mass % or more, even more preferably 95 mass % or more, and most preferably 99 mass % or more.

(Additives)

The cover composition may further contain a pigment component such as titanium oxide and a blue 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 resin component in the cover composition is preferably 90 mass % or more, more preferably 92 mass % or more, and even more preferably 94 mass % or more.

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 even more preferably 1.5 parts by mass or more, and is preferably 10 parts by mass or less, more preferably 8 parts by mass or less, and even more preferably 6 parts by mass or less, with respect to 100 parts by mass of the resin component. 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, lowering of the durability of the cover can be inhibited.

The cover composition preferably does not contain a basic metal compound for neutralizing the carboxy group included in (B) the olefin-unsaturated carboxylic acid copolymer and/or the olefin-unsaturated carboxylic acid-unsaturated carboxylate copolymer. Examples of the metal included in the basic metal compound include lithium, sodium, potassium, calcium, magnesium, zinc, aluminum, nickel, iron, copper, manganese, tin, lead, and cobalt. Examples of the basic metal compound include magnesium oxide, magnesium hydroxide, magnesium carbonate, zinc oxide, sodium hydroxide, sodium carbonate, calcium oxide, calcium hydroxide, lithium hydroxide, lithium carbonate, and magnesium stearate.

The cover composition can be obtained, for example, by dry blending the component (A), the component (B), and the optional other additives or the like. In addition, the dry blended mixture may be extruded into a pellet form. In the dry blending, for example, a mixer that can mix materials in a pellet form is preferably used, and a tumbler mixer is more preferably used. In the extrusion, a conventional extruder such as a single-screw extruder, a twin-screw extruder, and a twin screw-single screw extruder can be used.

The slab hardness of the cover composition is preferably 80.0 or more, more preferably 85.0 or more, and even more preferably 90.0 or more, and is preferably 97.0 or less, more preferably 96.0 or less, and even more preferably 95.0 or less in Shore A hardness. If the slab hardness is 80.0 or more in Shore A hardness, the spin rate on driver shots can be lowered, and if the slab hardness is 97.0 or less in Shore A hardness, the spin rate on approach shots increases.

The melt viscosity (190° C.) of the cover composition is preferably 1100.0 Pa·s or less, more preferably 1070.0 Pa·s or less, and even more preferably 1050.0 Pa·s or less. If the melt viscosity (190° C.) is 1100.0 Pas or less, the cover composition has further enhanced formability. It is noted that the lower limit of the melt viscosity (190° C.) is not particularly limited, and the melt viscosity (190° C.) is preferably 10 Pa·s or more. The measurement method of the melt viscosity (190° C.) will be described later.

The flow beginning temperature of the cover composition is preferably 173.0° C. or less, more preferably 172.5° C. or less, and even more preferably 172.0° C. or less. If the flow beginning temperature is 173.0° C. or less, the cover composition has further enhanced formability. It is noted that the lower limit of the flow beginning temperature is not particularly limited, and is preferably 70° C. or more. The measuring method of the flow beginning temperature will be described later.

[Golf Ball]

The golf ball according to the present disclosure comprises a spherical core and a cover covering the spherical core. The cover constitutes the outermost layer of the golf ball body. It is noted that the present disclosure relates to the formability and scratch resistance of the cover, and the constitution or the like of the spherical core is not limited.

(Spherical Core)

Examples of the spherical core include a single layered spherical core; a spherical core composed of a center and one intermediate layer covering the center; and a spherical core composed of a center and two or more intermediate layers covering the center.

A conventionally known rubber composition (hereinafter sometimes simply referred to as “core rubber composition”) may be used for the spherical core or center, and the spherical core or center may be formed by heat pressing, for example, a rubber composition containing a base rubber, a co-crosslinking agent and a crosslinking initiator.

As the base rubber, particularly preferred is 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 in view of its advantageous 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, and acrylic acid or a metal salt thereof, methacrylic acid or a metal salt thereof is more preferable. As the metal constituting 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. When the α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms is used as the co-crosslinking agent, a metal compound (e.g. magnesium oxide) is preferably used in combination.

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 even more preferably 0.4 part by mass or more, and is preferably 5 parts by mass or less, more preferably 4 parts by mass or less, and even more preferably 3 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. As the organic sulfur compound, diphenyl disulfides, thiophenols or thionaphthols are preferably used. 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 even more preferably 0.5 part by mass or more, and is preferably 5.0 parts by mass or less, more preferably 4.0 parts by mass or less, and even more preferably 2.0 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 preferred. As the carboxylic acid, an aliphatic carboxylic acid or an aromatic carboxylic acid (e.g. benzoic acid) may be used. 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 contain a weight adjusting agent such as zinc oxide and barium sulfate, an antioxidant, or a colored powder, 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 ranging from 130° C. to 200° C. for 10 to 60 minutes, or carried out in a two-step heating of heating at a temperature ranging from 130° C. to 150° C. for 20 to 40 minutes followed by heating at a temperature ranging from 160° C. to 180° C. for 5 to 15 minutes.

When the spherical core comprises an intermediate layer, examples of the intermediate layer material include a thermoplastic resin such as a polyurethane resin, an ionomer resin, a polyamide resin, and polyethylene; a thermoplastic elastomer such as a styrene elastomer, a polyolefin elastomer, a polyurethane elastomer, a polyamide elastomer, and a polyester elastomer; and a cured product of a rubber composition. Herein, examples of the ionomer resin include a product obtained by neutralizing at least a part of carboxyl groups in a copolymer composed of ethylene and an α,β-unsaturated carboxylic acid with a metal ion; and a product obtained by neutralizing at least a part of carboxyl groups in a terpolymer composed of ethylene, an α,β-unsaturated carboxylic acid and an α,β-unsaturated carboxylic acid ester with a metal ion. The intermediate layer may further contain a weight adjusting agent such as barium sulfate and tungsten, an antioxidant, and a pigment.

The method for molding the intermediate layer is not particularly limited, and examples thereof include a method which comprises molding the intermediate layer composition into a half shell in advance, covering the spherical body with two of the half shells, and performing compression molding; and a method which comprises injection molding the intermediate layer composition directly onto the spherical body to cover the spherical body.

In case of injection molding the intermediate layer composition onto the spherical body to form the intermediate layer, it is preferred to use upper and lower molds, each having a hemispherical cavity. When molding the intermediate layer by the injection molding method, the hold pin is protruded to hold the spherical body to be covered, and the intermediate layer composition which has been heated and melted is charged and then cooled to form the intermediate layer.

When molding the intermediate layer by the compression molding method, the molding of the half shell may be performed by either a compression molding method or an injection molding method, and the compression molding method is preferable. Compression molding the intermediate layer composition into the half shell may be carried out, for example, under a pressure of 1 MPa or more and 20 MPa or less at a molding temperature of −20° C. or more and +70° C. or less relative to the flow beginning temperature of the intermediate layer composition. If the molding is carried out under the above conditions, the half shell having a uniform thickness can be formed. Examples of the method for molding the intermediate layer by using the half shell include a method which comprises covering the spherical body with two of the half shells and performing compression molding. Compression molding the half shells into the intermediate layer may be carried out, for example, under a pressure of 0.5 MPa or more and 25 MPa or less at a molding temperature of −20° C. or more and +70° C. or less relative to the flow beginning temperature of the intermediate layer composition. If the molding is carried out under the above conditions, the intermediate layer having a uniform thickness can be formed.

It is noted that the molding temperature means the highest temperature where the temperature at the surface of the concave portion of the lower mold reaches from closing the mold to opening the mold. In addition, the flow beginning temperature of the composition can be measured using thermoplastic resin composition in a pellet form under the following conditions with “Flow Tester CFT-500” available from Shimadzu Corporation.

Measuring conditions: Plunger area: 1 cm², Die length: 1 mm, Die diameter: 1 mm, Load: 588.399 N, Starting temperature: 30° C., and Temperature rising rate: 3° C./min.

The diameter of the spherical core is preferably 34.8 mm or more, more preferably 35.7 mm or more, and even more preferably 36.6 mm or more, and is preferably 42.2 mm or less, more preferably 41.8 mm or less, even more preferably 41.2 mm or less, and most preferably 40.8 mm or less. If the diameter of the spherical core is 34.8 mm or more, the cover is not excessively thick and thus the resilience is better. On the other hand, if the diameter of the spherical core is 42.2 mm or less, the cover is not excessively thin and thus the cover functions better.

(Construction of Golf Ball)

The construction of the golf ball is not particularly limited, as long as the golf ball comprises a spherical core and a cover covering the spherical core. Examples of the construction of the golf ball include a two-piece golf ball having a single layered spherical core and a cover covering the spherical core; a three-piece golf ball having a spherical core composed of a center and one intermediate layer covering the center, and a cover covering the spherical core; and a multi-piece golf ball having a spherical core composed of a center and two of more intermediate layers covering the center, and a cover covering the spherical core.

The method for forming the cover from the cover composition is not particularly limited, and examples thereof include a method which comprises injection molding the cover composition directly onto the spherical core; and a method which comprises molding the cover composition into a hollow shell, covering the spherical core with a plurality of the shells and performing compression molding (preferably a method which comprises molding the cover composition into a hollow half-shell, covering the spherical core with two of the half-shells and performing compression molding). From the viewpoint of the productivity of the golf ball, the embodiment that the cover composition is directly injection molded on the spherical core is preferable.

When the cover composition is directly injection molded on the spherical core, the molding temperature is preferably 180° C. or more, more preferably 185° C. or more, and even more preferably 190° C. or more, and is preferably 250° C. or less, more preferably 245° C. or less, and even more preferably 240° C. or less. If the molding temperature is 180° C. or more, the cover composition has further enhanced formability, and if the molding temperature is 250° C. or less, lowering in the scratch resistance of the obtained cover can be suppressed.

The golf ball body having the cover formed thereon is ejected from the mold, and is preferably subjected to surface treatments such as deburring, cleaning and sandblast where necessary. In addition, if desired, a mark may be formed.

The total number of the dimples formed on the cover is preferably 200 or more and 500 or less. If the total number of the dimples is less than 200, the dimple effect is hardly obtained. In addition, if the total number of the 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, without limitation, 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 shape. These shapes may be employed solely, or at least two of them may be employed in combination.

The golf ball body having the cover formed thereon is ejected from the mold, and is preferably subjected to surface treatments such as deburring, cleaning and sandblast where necessary. 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 even more preferably 9 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 5 μm or more, the paint film is hard to wear off even if the golf ball is used continuously, and if the thickness of the paint film is 50 μm or less, the dimple effect is fully obtained.

The golf ball 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 according to the present disclosure 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 44.00 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 of 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 higher.

FIG. 1 is a partially cutaway cross-sectional view showing 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 land 32. The cover 3 is formed from the above-described cover material.

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) Slab Hardness (Shore A Hardness)

Sheets with a thickness of about 2 mm were produced by injection molding the 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 testing device of “Shore A”.

(2) Measurement of Fourier Transform Infrared Spectroscopy (FT-IR)

The materials of the cover composition were kneaded and extruded with a twin-screw extruder and then cut into pellets to prepare a measuring sample.

The FT-IR analysis was conducted for the obtained measuring sample under the following measuring conditions. The difference Δv (v1−v2) between the wave number (v1) of the absorption peak attributed to the N—H group that did not form the hydrogen bond in (A) the thermoplastic polyurethane and the wave number (v2) of the absorption peak attributed to the N—H group that formed the hydrogen bond with the carbonyl oxygen of the urethane group in (A) the thermoplastic polyurethane was determined based on the obtained spectrum.

<Measuring Conditions>

• • Apparatus: Fourier transform infrared spectrometer (“Cary 670 FTIR” available from Agilent Technologies Co., Ltd.), Diamond ATR apparatus (Golden Gate available from Specac Ltd.)
  • Measuring method: single-reflection Attenuated Total Reflection measuring method (ATR method)
  • Measuring range: 400 cm⁻¹ to 4000 cm⁻¹
  • Resolution: 4 cm⁻¹
  • Cumulative number: 32 times
  • Crystal: diamond
  • Temperature rising rate: 10° C./min
  • Measuring temperature: 190° C.

(3) Melt Viscosity

The melt viscosity of the cover composition in a pellet form was measured with a flow characteristic evaluation apparatus (Flow Tester CFT-500D available from Shimadzu Corporation), and evaluated according to the following evaluation standard. The measuring conditions were a die length of 10 mm, a die hole diameter of 1 mm, a cylinder pressure of 3 MPa, and a temperature of 190° C.

• • E (Excellent): less than 900 Pa·s
  • G (Good): 900 Pa·s or more and less than 1100 Pa·s
  • F (Fair): 1100 Pa·s or more and less than 1200 Pa·s
  • P (Poor): 1200 Pa·s or more

(4) Flow Beginning Temperature

The flow beginning temperature of the cover composition in a pellet form was measured with a flow characteristic evaluation apparatus (Flow Tester CFT-500D available from Shimadzu Corporation) under the following conditions, and evaluated according to the following evaluation standard.

Measuring conditions: Plunger area: 1 cm², Die length: 1 mm, Load: 588.399 N, Starting temperature: 30° C., and Temperature rising rate: 3° C./min.

• • E (Excellent): less than 168.0° C.
  • G (Good): 168.0° C. or more and less than 175.0° C.
  • P (Poor): 175.0° C. or more

(5) Thickness of Cover

The golf ball having the cover formed was cut through each pole and perpendicular to the seam line for evaluating the formability of the cover. Specifically, the cut ball was stored at a temperature of 23° C. plus or minus 1° C. for at least 2 hours. Then, the cover thickness at each pole, the cover thickness at two locations slightly above the seam and the cover thickness at two locations slightly below the seam on the cut surface were measured, and the average value of the thickness at the six locations was adopted as the cover thickness. It is noted that the pole is an apex of an upper hemisphere or an apex of a lower hemisphere when the golf ball is equally divided into upper and lower parts along the seam line.

(6) Formability

The golf ball having the cover formed was cut through each pole and perpendicular to the seam line, and the formability of the cover was evaluated. Specifically, the cut ball was stored at a temperature of 23° C. plus or minus 1° C. for at least 2 hours, and then on the cut surface, the cover thickness at each pole was measured and the difference (d1) between them was calculated, the cover thickness at two locations slightly above the seam was measured and the difference (d2) between them was calculated, the cover thickness at two locations slightly below the seam was measured and the difference (d3) between them was calculated, and the maximum value among these differences (d1), (d2) and (d3) was adopted as the thickness unevenness value. The formability was evaluated based on the thickness unevenness value according to the following standard.

• • E (Excellent): The cover was uniformly formed (The thickness unevenness value was less than 0.1 mm).
  • G (Good): The cover was formed with slight unevenness of thickness (The thickness unevenness value was from 0.1 mm to 0.4 mm).
  • F (Fair): The cover was formed with great unevenness of thickness (The thickness unevenness value was more than 0.4 mm).
  • P (Poor): The cover failed to be formed.

(7) Scratch Resistance

A commercially available pitching wedge was installed on a swing robot, and two different locations of the golf ball were each hit once at a head speed of 36 m/s, and the golf balls were hit twice in total. The two hit locations were visually observed and evaluated into 5 grades according to the following standard, and the poorest point was adopted as the evaluation result. It is noted that when the cover with the predetermined thickness failed to be formed so that the scratch resistance failed to be evaluated, it was indicated as “P”.

5 points: substantially no damage was recognized.

4 points: there was no visually recognizable damage, but slight damage was recognized when the golf ball was carefully observed on the hand.

3 points: there was visually confirmable damage.

2 points: there was conspicuous damage.

1 point: there was damage in such an extent that the golf ball cannot be reused.

[Production of Golf Ball]

(1) Preparation of Rubber Composition

According to the formulation shown in Table 1, the materials were kneaded with a kneading roll to prepare the rubber composition.

TABLE 1
Rubber composition

	Formulation	BR730	100
	(parts by mass)	ZN-DA90S	33
		Zinc oxide	3
		Barium sulfate	Appropriate amount *1)
		Dicumyl peroxide	0.7
	*1) The amount of barium sulfate was adjusted such that the golf ball had a mass of 45.6 g.

The diameter of the core was adjusted such that the golf ball had a diameter of 42.7 mm.

The materials used in Table 1 are shown as follows.

BR730: high-cis polybutadiene rubber (cis-1,4 bond amount=95 mass %, 1,2-vinyl bond amount=1.3 mass %, Moony viscosity (ML₁₊₄ (100° C.))=55, molecular weight distribution (Mw/Mn)=3) available from JSR Corporation

ZN-DA90S: Zinc acrylate (containing zinc stearate in an amount of 10%) 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: available from Tokyo Chemical Industry Co., Ltd.

(2) Preparation of Cover Composition

According to the formulations shown in Table 2, the materials were extruded with a twin-screw kneading extruder to prepare the cover compositions in a pellet form. The evaluation results of the obtained cover compositions are shown in Table 2. In addition, the IR spectrum of the cover compositions No. 1, 4, 6 is shown in FIG. 2.

TABLE 2
Cover composition No.	1	2	3	4	5	6	7

Formulation	Resin	(A)	100	99	97	95	90	80	70
(parts by	component	Elastollan
mass)		1195ATR
		(B)	—	1	3	5	10	20	30
		N2050H

	Titanium dioxide	4	4	4	4	4	4	4
Property	Δv of resin component (cm−1)	109.9	109.5	106.0	106.1	102.7	100.3	99.5
data	Slab hardness (Shore A)	92.2	92.3	92.3	92.4	92.5	92.6	93.0
	Melt viscosity (Pa · S)	1189.9	1186.0	1015.2	899.3	567.9	286.2	190.5
	Melt viscosity evaluation	F	F	G	E	E	E	E
	Flow beginning	174	173	173	171	167	149	143
	temperature (° C.)
	Flow beginning	G	G	G	G	E	E	E
	temperature evaluation

The materials used in Table 2 are shown as follows.

Elastollan (registered trademark) 1195ATR: thermoplastic polyurethane elastomer (polyisocyanate: 4,4′-diphenylmethane diisocyanate) (Slab hardness (Shore A): 95) available from BASF Japan Ltd.

Titanium dioxide: A-220 available from Ishihara Sangyo Kaisha, Ltd.

As shown in Table 2, when Δv of the resin component is small, the hydrogen bond is alleviated, the melt viscosity is low, and the flow beginning temperature decreases. Thus, when the resin component has small Av, the cover has high fluidity, a cover with a thin thickness can be formed even by an injection molding method, and the flow beginning temperature deceases, so that the molding temperature can be set to a low value.

(3) Formation of Cover

The cover composition was injection molded on the spherical core to obtain golf balls.

The spherical core was charged into a final mold provided with a plurality of pimples on the cavity surface. The cover composition was injection molded on the spherical core to obtain golf balls having a plurality of dimples with an inverted shape of the pimples on the cavity surface formed on the cover. The evaluation results of the obtained golf balls are shown in Tables 3 and 4.

TABLE 3
Golf ball No.	1	2	3	4	5	6	7

Cover	No.	3	4	5	6	1	2	7
composition	Δv of resin component (cm−1)	106.0	106.1	102.7	100.3	109.9	109.5	99.5
	Slab hardness (Shore A)	92.3	92.4	92.5	92.6	92.2	92.3	93.0
	Melt viscosity (Pa · S)	1015.2	899.3	567.9	286.2	1189.9	1186.0	190.5
	Flow beginning temperature	173	171	167	149	173	173	143
	(° C.)
Cover	Thickness (mm)	1.6	1.6	1.6	1.6	1.6	1.6	1.6
	Molding temperature (° C.)	230	230	230	230	230	230	230
	Formability evaluation	E	E	E	E	G	G	E
	Scratch resistance	3	3	3	3	3	3	2

The golf balls No. 1 to 7 shown in Table 3 are the cases that the cover has a thickness of 1.6 mm, and the molding temperature of the cover is 230° C.

The covers of the golf balls No. 1 to 4 were formed from the cover compositions No. 3 to 6 whose resin component had Δv of 100.0 cm⁻¹ to 109.0 cm⁻¹. The covers of these golf balls No. 1 to 4 had good formability and excellent scratch resistance.

The covers of the golf balls No. 5 and 6 were formed from the cover compositions No. 1 and 2 whose resin component had Δv of more than 109.0 cm⁻¹. The formed covers of these golf balls had excellent scratch resistance, but the formability thereof was inferior to that of the covers of the golf balls No. 1 to 4.

The cover of the golf ball No. 7 was formed from the cover composition No. 7 whose resin component had Δv of less than 100.0 cm⁻¹. The cover of the golf ball No. 7 had good formability, but the scratch resistance thereof was inferior.

TABLE 4
Golf ball No.	8	9	10	11	12	13	14

Cover	No.	3	4	1	2	3	1	2
composition	Δv of resin component (cm−1)	106.0	106.1	109.9	109.5	106.0	109.9	109.5
	Slab hardness (Shore A)	92.3	92.4	92.2	92.3	92.3	92.2	92.3
	Melt viscosity (Pa · S)	1015.2	899.3	1189.9	1186.0	1015.2	1189.9	1186.0
	Flow beginning	173	171	173	173	173	173	173
	temperature (° C.)
Cover	Thickness (mm)	1.4	1.4	1.4	1.4	1.4	1.4	1.4
	Molding temperature (° C.)	230	230	230	230	250	250	250
	Formability evaluation	F	G	P	P	G	G	G
	Scratch resistance	3	3	—	—	2	1	1

The golf balls No. 8 to 11 shown in Table 4 are the cases that the cover has a thickness of 1.4 mm, and the molding temperature of the cover is 230° C.

The covers of the golf balls No. 8 and 9 were formed from the cover compositions No. 3 and 4 whose resin component had Δv of 100.0 cm⁻¹ to 109.0 cm⁻¹. The covers of these golf balls No. 8 and 9 were successfully formed at the molding temperature of 230° C. and had excellent scratch resistance even though they had a thin thickness of 1.4 mm.

The covers of the golf balls No. 10 and 11 were formed from the cover compositions No. 1 and 2 whose resin component had Δv of more than 109.0 cm⁻¹. The covers of these golf balls could not be formed at the molding temperature of 230° C.

The golf balls No. 12 to 14 shown in Table 4 are the cases that the cover has a thickness of 1.4 mm, and the molding temperature of the cover is 250° C.

The covers with the thickness of 1.4 mm of the golf balls No. 12 to 14 were successfully formed at the molding temperature of 250° C., but the covers of the golf balls No. 13 and 14 had greatly lowered scratch resistance. The golf ball No. 12 had more excellent scratch resistance than the golf balls No. 13 and 14.

The present disclosure (1) is a golf ball comprising a spherical core and a cover covering the spherical core, wherein the cover contains (A) a thermoplastic polyurethane as a resin component, and a difference Δv (v1−v2) between a wave number (v1) of an absorption peak attributed to an N—H group not forming a hydrogen bond in (A) the thermoplastic polyurethane and a wave number (v2) of an absorption peak attributed to an N—H group forming a hydrogen bond with a carbonyl oxygen of a urethane group in (A) the thermoplastic polyurethane ranges from 100.0 cm⁻¹ to 109.0 cm⁻¹ when the cover is measured with a Fourier transform infrared spectrometer under the following measuring conditions:

<Measuring Conditions>

• • measuring method: single-reflection ATR (Attenuated Total Reflection) method
  • measuring range: 400 cm⁻¹ to 4000 cm⁻¹
  • resolution: 4 cm⁻¹
  • cumulative number: 32 times
  • crystal: diamond
  • temperature rising rate: 10° C./min
  • measuring temperature: 190° C.

The preferable embodiment (2) of the present disclosure is the golf ball according to the present disclosure (1), wherein the cover is formed from a cover composition containing (A) the thermoplastic polyurethane and (B) an olefin-unsaturated carboxylic acid copolymer and/or an olefin-unsaturated carboxylic acid-unsaturated carboxylate copolymer as the resin component.

The preferable embodiment (3) of the present disclosure is the golf ball of the preferable embodiment (2), wherein a mass ratio ((A)/(B)) of (A) the thermoplastic polyurethane to (B) the olefin-unsaturated carboxylic acid copolymer and the olefin-unsaturated carboxylic acid-unsaturated carboxylate copolymer in the resin component ranges from 80.0/20.0 to 97.0/3.0.

The preferable embodiment (4) of the present disclosure is the golf ball of any one of the preferable embodiments (1) to (3), wherein a polyisocyanate constituting (A) the thermoplastic polyurethane includes an alicyclic diisocyanate and/or an aromatic diisocyanate.

The present disclosure (5) is the golf ball of the preferable embodiment (4), wherein the polyisocyanate includes at least one diisocyanate selected from the group consisting of 4,4′-dicyclohexylmethane diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, isophorone diisocyanate, trans-1,4-cyclohexane diisocyanate, 4,4′-diphenylmethane diisocyanate and tolylene diisocyanate.

This application is based on Japanese patent application No. 2024-229113 filed on Dec. 25, 2024, the content of which is hereby incorporated by reference.