STRUCTURE, METHOD FOR PRODUCING STRUCTURE, GREASEPROOF PAPER, GAS BARRIER PAPER, FLAVOR BARRIER PAPER, AND PACKAGING MATERIAL

Description

TECHNICAL FIELD

The present invention relates to a structure, a method for producing a structure, greaseproof paper, gas barrier paper, flavor barrier paper, and a packaging material.

DISCUSSION OF THE BACKGROUND

For packaging foods, medical products, electronic components, and the like, packaging materials in which water vapor barrier properties and gas barrier properties (particularly, oxygen barrier properties) are imparted to a paper base material have been conventionally used. Patent Documents 1 and 2 each disclose a packaging material in which a water vapor barrier layer, a gas barrier layer, and a heat-sealing layer are provided in this order on a paper base material. Patent Documents 1 and 2 each also disclose, as such a packaging material, a packaging material in which a vinyl alcohol polymer is used in a gas barrier layer.

PRIOR ART DOCUMENTS

Patent Documents

• • Patent Document 1: Japanese Unexamined Patent Application, Publication No. 2020-163675
  • Patent Document 2: Japanese Unexamined Patent Application, Publication No. 2021-20398

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

In a packaging material like those disclosed in Patent Documents 1 and 2, each layer is typically provided by coating a paper base material therewith. However, in a case in which a heat-sealing layer is provided on a surface of a gas barrier layer containing a vinyl alcohol polymer, for example, a crack may occur in the formed film, and thus, uniform heat-sealing properties may not be obtained. Furthermore, the inventors have also found that a crack in the heat-sealing layer causes a decrease in water vapor barrier properties.

An object of the present invention is to provide: a structure in which a layer having heat-sealing properties has few cracks and which is superior in water vapor barrier properties, heat-sealing properties, and oxygen barrier properties: a method for producing such a structure; and greaseproof paper, gas barrier paper, flavor barrier paper, and a packaging material each including such a structure.

Means for Solving the Problems

The foregoing problems can be solved by providing any of the followings:

• • (1) a structure in which an A layer, a B layer, and a C layer are laminated in this order on at least one face of a paper base material, wherein the A layer contains at least one selected from the group consisting of an olefin polymer, a styrene polymer, and a polyester polymer, the B layer contains a vinyl alcohol polymer, and the C layer contains a polymer having a glass transition temperature of −100° C. or more and 5° C. or less;
  • (2) the structure according to (1), wherein the C layer has a melting point of 120° C. or less;
  • (3) the structure according to (1) or (2), wherein the A layer contains the olefin polymer, and the olefin polymer contains an olefin-unsaturated carboxylic acid polymer;
  • (4) the structure according to any one of (1) to (3), wherein the A layer further contains talc;
  • (5) the structure according to (4), wherein a content of the talc in the A layer is 1% by mass or more and 80% by mass or less;
  • (6) the structure according to any one of (1) to (5), wherein the vinyl alcohol polymer is an ethylene-modified vinyl alcohol polymer;
  • (7) the structure according to any one of (1) to (6), wherein the polymer having a glass transition temperature of −100° C. or more and 5° C. or less is a styrene-acrylic copolymer;
  • (8) the structure according to any one of (1) to (7), wherein the C layer further contains wax;
  • (9) the structure according to (8), wherein a content of the wax in the C layer is 0.1% by mass or more and 30% by mass or less;
  • (10) the structure according to (8) or (9), wherein the wax contains paraffin wax;
  • (11) the structure according to (10), wherein a content of the paraffin wax in the C layer is 1% by mass or more and 30% by mass or less;
  • (12) the structure according to any one of (1) to (11), wherein the vinyl alcohol polymer consists of two or more types of vinyl alcohol polymers having different degrees of polymerization;
  • (13) the structure according to any one of (1) to (12), wherein the A layer contains at least two selected from the group consisting of the olefin polymer, the styrene polymer, and the polyester polymer;
  • (14) the structure according to any one of (1) to (13), wherein the C layer contains two or more types of polymers;
  • (15) a method for producing the structure according to any one of (1) to (14), the method including: providing at least one of the A layer, the B layer, or the C layer by using a curtain coater;
  • (16) greaseproof paper including the structure according to any one of (1) to (14);
  • (17) gas barrier paper including the structure according to any one of (1) to (14);
  • (18) flavor barrier paper including the structure according to any one of (1) to (14); and
  • (19) a packaging material including at least one selected from the group consisting of the greaseproof paper according to (16), the gas barrier paper according to (17), and the flavor barrier paper according to (18).

Effects of the Invention

According to the present invention, a structure in which a layer having heat-sealing properties has few cracks and which is superior in water vapor barrier properties, heat-sealing properties, and oxygen barrier properties; a method for producing such a structure; and greaseproof paper, gas barrier paper, flavor barrier paper, and a packaging material each including such a structure can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view illustrating a structure according to one embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

Structure

One embodiment of the present invention is a structure in which an A layer, a B layer, and a C layer are laminated in this order on at least one face of a paper base material, wherein the A layer contains at least one selected from the group consisting of an olefin polymer, a styrene polymer, and a polyester polymer, the B layer contains a vinyl alcohol polymer, and the C layer contains a polymer having a glass transition temperature of −100° C. or more and 5° C. or less.

In the structure, the layer having heat-sealing properties has few cracks, and the structure is superior in water vapor barrier properties, heat-sealing properties, and oxygen barrier properties. Although the reason why the structure has such effects is not certain, the following reason can be presumed. The oxygen barrier properties can be improved by using, in the B layer, a vinyl alcohol resin having superior oxygen barrier properties. However, the vinyl alcohol polymer is a resin which changes relatively significantly owing to swelling and shrinkage; therefore, in the case in which the C layer is provided on the B layer containing the vinyl alcohol polymer, the C layer cannot follow the swelling and shrinkage of the B layer and may crack. Therefore, by using, in the C layer, the polymer having a glass transition temperature of −100° C. or more and 5° C. or less, i.e., a polymer having a low glass transition temperature, the C layer can sufficiently follow the swelling and shrinkage of the B layer. As a result, in the structure, cracks in the C layer can be inhibited, and the water vapor barrier properties can be improved.

As illustrated in FIG. 1, a structure 10 according to one embodiment of the present invention includes a paper base material 11, an A layer 12, a B layer 13, and a C layer 14. The structure 10 is a laminate in which the A layer 12, the B layer 13, and the C layer 14 are laminated in this order on one face of the paper base material 11. In the structure 10, the paper base material 11 and the A layer 12, the A layer 12 and the B layer 13, and the B layer 13 and the C layer 14 are respectively directly laminated. Furthermore, in the structure 10, the C layer 14 is an outermost layer. The structure 10 may be coated paper.

In an embodiment different from that of the structure 10 in FIG. 1, the A layer, the B layer, and the C layer may be laminated in this order on both faces of the paper base material. The A layer, the B layer, and the C layer may be laminated in this order on one face of the paper base material, while one or more of the A layer, the B layer, the C layer, and other layer(s) may be laminated on the other face of the paper base material. Other layer(s) may be present between the paper base material and the A layer and/or between the A layer and the B layer and/or between the B layer and the C layer and/or on a surface of the C layer. Hereinafter, each constituent member of the structure will be described in detail.

Paper Base Material

As the paper base material, general paper containing a plant-based pulp as a principal component may be used. It is to be noted that the “principal component” as referred to herein means a component having the highest content on the mass basis. The paper base material may contain, besides the pulp, a sizing agent, a filler, a paper-strengthening agent, a yield-improving agent, a pH modifier, a drainage-improving agent, a water-proofing agent, a softener, an antistatic agent, a defoaming agent, a slime-controlling agent, a dye, a pigment, and/or the like.

Examples of the paper base material include kraft paper, woodfree paper, mechanical paper, alkaline paper, a paperboard, glassine paper, semi-glassine paper, parchment paper, and the like, and woodfree paper is preferred.

A basis weight (mass per unit area) of the paper base material is preferably 20 g/m² or more and 500 g/m² or less, more preferably 30 g/m² or more and 300 g/m² or less, still more preferably 40 g/m² or more and 200 g/m² or less, and even more preferably 50 g/m² or more 100 g/m² or less.

A density of the paper base material is preferably 0.5 g/cm³ or more and 1.2 g/cm³ or less, and more preferably 0.6 g/cm³ or more and 1.0 g/cm³ or less.

The paper base material can be produced by a known method. Furthermore, a commercial product may be used as the paper base material.

A Layer

The A layer is a layer which is present between the paper base material and the B layer. The A layer may be directly laminated on the paper base material.

Polymer (a)

The A layer contains at least one selected from the group consisting of an olefin polymer, a styrene polymer, and a polyester polymer (hereinafter, may be also referred to as “polymer (a)”). When the A layer thus contains the polymer (a) having relatively high hydrophobic properties, the A layer can exert favorable water vapor barrier properties and the like. The polymer (a) is preferably a principal component of the A layer. As the polymer (a), one type or two or more types of polymers may be used.

Olefin Polymer

The olefin polymer is a polymer containing an olefin as a monomer. The olefin polymer may be a polyolefin, which is a polymer of one type or two or more types of olefins, or may be a copolymer of one type or two or more types of olefins and one type or two or more types of other monomers than olefins.

Examples of the olefin include α-olefins such as ethylene, propylene, n-butene, isobutylene, and the like.

Examples of the other monomer(s) than olefins, the other monomer(s) constituting the olefin polymer, include an unsaturated carboxylic acid compound, a diene compound, vinyl ether, a vinyl halide, a vinylidene halide, an allyl compound, and the like, and an unsaturated carboxylic acid compound is preferred.

The unsaturated carboxylic acid compound refers to an unsaturated carboxylic acid and a compound in which a hydrogen atom of a carboxy group constituting an unsaturated carboxylic acid is substituted by another atom or another group. That is to say, the unsaturated carboxylic acid compound includes, besides unsaturated carboxylic acids, unsaturated carboxylic acid ester, unsaturated carboxylic acid salts, and the like. The unsaturated carboxylic acid compound is preferably a monomer having a carboxy group or a salt thereof.

Examples of the unsaturated carboxylic acid compound include unsaturated carboxylic acids such as (meth)acrylic acid, crotonic acid, cinnamic acid, itaconic acid, fumaric acid, maleic acid, and butene tricarboxylic acid; unsaturated carboxylic acid ester such as methyl (meth)acrylate, ethyl (meth)acrylate, itaconic acid monoethyl ester, and fumaric acid monobutyl ester; unsaturated carboxylic acid salts such as sodium (meth)acrylate; and the like. It is to be noted that the “(meth)acrylic acid” means acrylic acid and methacrylic acid.

As the olefin polymer, a polyolefin and an olefin-unsaturated carboxylic acid copolymer are preferred, and an olefin-unsaturated carboxylic acid copolymer is more preferred. The olefin-unsaturated carboxylic acid copolymer refers to a copolymer of one type or two or more types of olefins and one type or two or more types of unsaturated carboxylic acid compounds. Of olefin-unsaturated carboxylic acid copolymers, an olefin-unsaturated carboxylic acid copolymer which is a copolymer of one type or two or more types of olefins and one type or two or more types of unsaturated carboxylic acids is preferred.

Examples of the olefin-unsaturated carboxylic acid copolymer include an ethylene-(meth)acrylic acid copolymer, an ethylene-methyl (meth)acrylate copolymer, an ethylene-ethyl (meth)acrylate copolymer, an ethylene-butyl (meth)acrylate copolymer, and the like; of these, an ethylene-(meth)acrylic acid copolymer is preferred. Furthermore, a copolymer of ethylene and an unsaturated carboxylic acid compound is also preferred. Such a copolymer may be further copolymerized with another monomer which can be copolymerized with the olefin and the unsaturated carboxylic acid compound.

Styrene Polymer

The styrene polymer is a polymer containing a styrene compound as a monomer. The styrene compound refers to styrene and a compound in which a hydrogen atom included in styrene is substituted by another atom or another group. Examples of the styrene compound include styrene, α-methyl styrene, vinyl toluene, chlorostyrene, and the like, and styrene is preferred.

Examples of a styrene copolymer include polystyrene, a styrene-acrylic copolymer, a styrene-butadiene copolymer, and the like.

The styrene-acrylic copolymer is a copolymer of the above-mentioned styrene compound and an acrylic compound. The acrylic compound refers to a (meth)acrylic acid and a compound in which a hydrogen atom of a carboxy group constituting a (meth)acrylic acid is substituted by another atom or another group. Examples of the acrylic compound include a (meth)acrylic acid, (meth)acrylic acid ester, a (meth)acrylate, and the like. Examples of the (meth)acrylic acid ester include (meth)acrylic acid alkyl ester such as methyl (meth)acrylate, ethyl (meth)acrylate, and the like. Examples of the (meth)acrylate include sodium (meth)acrylate and the like.

Examples of the styrene-acrylic copolymer include a styrene-(meth)acrylic acid copolymer, a styrene-(meth)acrylic acid ester copolymer, a styrene-(meth)acrylate copolymer, and the like. The styrene-acrylic copolymer may be further copolymerized with another monomer.

The styrene-butadiene copolymer is a copolymer of the above-mentioned styrene compound and a butadiene compound. The butadiene compound refers to butadiene and a compound in which a hydrogen atom included in butadiene is substituted by another atom or another group. Examples of the butadiene compound include 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene), 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, and the like, and 1,3-butadiene is preferred.

As the styrene-butadiene copolymer, a styrene-butadiene copolymer is preferred. The styrene-butadiene copolymer may be further copolymerized with another monomer.

As the styrene polymer, a styrene-acrylic copolymer and a styrene-butadiene copolymer are preferred.

Polyester Polymer

The polyester polymer is a polymer in which one type or two or more types of monomers are polymerized through an ester bond. Examples of the polyester polymer include polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, polyethylene naphthalate, polyglycolic acid, aromatic liquid crystalline polyester, and the like.

Of the examples of the polymer (a), in light of the water vapor barrier properties and the like, an olefin polymer and a styrene polymer are preferred, and an olefin polymer is more preferred.

The lower limit of a content of the polymer (a) in the A layer is preferably 20% by mass, more preferably 40% by mass, and may be 60% by mass, 70% by mass, 80% by mass, or 90% by mass. On the other hand, the upper limit of this content may be 100% by mass or may be 99% by mass, 90% by mass, 80% by mass, or 60% by mass.

Other Component(s) etc. in A Layer

The A layer preferably contains a layered inorganic compound. When the A layer contains the layered inorganic compound, the water vapor barrier properties and the like of the structure can be further improved.

Examples of the layered inorganic compound include micas, talc, montmorillonite, kaolinite, vermiculite, smectite, hectorite, taeniolite, acid clay, and the like. In light of the water vapor barrier properties and the like, talc is preferred as the layered inorganic compound used in the A layer. One type or two or more types of layered inorganic compounds may be used.

In the case in which the A layer contains the layered inorganic compound such as talc or the like, the lower limit of a content of the layered inorganic compound in the A layer is preferably 1% by mass, more preferably 5% by mass, and still more preferably 10% by mass, 20% by mass, or 30% by mass. On the other hand, the upper limit of this content is preferably 80% by mass, more preferably 70% by mass, and still more preferably 60% by mass, 50% by mass, or 40% by mass. By setting the content of the layered inorganic compound in the A layer within the above range, the water vapor barrier properties and the like can be further improved.

The A layer may further contain other component(s) than the polymer (a) and the layered inorganic compound. Examples of the other component(s) include a resin other than the polymer (a), a dispersant, a surfactant, a defoaming agent, a dye, a thickening agent, and the like. It is to be noted that a total content of the polymer (a) and the optional layered inorganic compound in the A layer is preferably 90% by mass or more, and more preferably 95% by mass or more or 99% by mass or more. Furthermore, a content of a cationic resin in the A layer may be preferably 10% by mass or less and may be more preferably 5% by mass or less, 1% by mass or less, or 0.5% by mass or less.

A mass per unit area of one layer of the A layer is preferably 1 g/m² or more and 100 g/m² or less, more preferably 3 g/m² or more and 50 g/m² or less, still more preferably 5 g/m² or more and 30 g/m² or less, even more preferably 7 g/m² or more and 20 g/m² or less, and particularly preferably 9 g/m² or more and 15 g/m² or less. When the mass per unit area of one layer of the A layer is greater than or equal to the lower limit, the water vapor barrier properties and the like can be further improved. On the other hand, when the mass per unit area of one layer of the A layer is less than or equal to the upper limit, for example, the thickness of the structure can be reduced.

B Layer

The B layer is a layer which is present between the A layer and the C layer. The B layer may be a layer directly laminated on the A layer.

Polymer (b)

The B layer contains a vinyl alcohol polymer (hereinafter, may be also referred to as “polymer (b)”). When the structure includes the B layer containing the polymer (b), superior oxygen barrier properties can be exerted. The polymer (b) is preferably a principal component of the B layer. The polymer (b) is a polymer having a vinyl alcohol unit (—CH₂—CHOH—). The polymer (b) is typically obtained by saponifying a vinyl ester polymer. One type or two or more types of polymers (b) may be used.

The lower limit of a degree of saponification of the polymer (b) is preferably 80 mol %, more preferably 90 mol %, and may be still more preferably 95 mol %, 97 mol %, 98 mol %, or 99 mol %. When the degree of saponification is greater than or equal to the lower limit, the oxygen barrier properties and the like can be further improved. On the other hand, the upper limit of the degree of saponification may be 100 mol % or 99.9 mol %. The degree of saponification of the polymer (b) is measured according to JIS K 6726:1994.

A viscosity average degree of polymerization of the polymer (b) is preferably 200 or more and 3,000 or less. The lower limit of the viscosity average degree of polymerization may be 300, 500, or 800. On the other hand, the upper limit of the viscosity average degree of polymerization may be 2,500, 2,000, 1,200, or 800. When the viscosity average degree of polymerization of the polymer (b) falls within the above range, the oxygen barrier properties and the like can be further improved, and the coatability at the time of providing the B layer by coating, the strength of the B layer, and the like can also be optimized.

The viscosity average degree of polymerization of the polymer (b) is measured according to JIS K 6726:1994. Specifically, a limiting viscosity [η] (L/g) of the polymer (b) is measured in water at 30° C., and the value of the limiting viscosity [η] is used to calculate a viscosity average degree of polymerization P according to the following formula. It is to be noted that in a case in which the degree of saponification of the polymer (b) is less than 99.5 mol %, the limiting viscosity [η] is measured after saponifying the polymer until the degree of saponification reaches 99.5 mol % or more.

P = ( [ η ] × 10 4 / 8.29 ) ( 1 / 0.62 )

The polymer (b) may have a monomer unit derived from an other monomer than the vinyl alcohol unit and a vinyl ester unit. Examples of the other monomer include α-olefins such as ethylene, propylene, n-butene, and isobutylene; (meth)acrylic acids and salts thereof; (meth)acrylic acid ester; (meth)acrylamides; (meth)acrylamide derivatives such as N-methyl (meth)acrylamides, N-ethyl (meth)acrylamides, N,N-dimethyl (meth)acrylamides, diacetone (meth)acrylamides, (meth)acrylamide propane sulfonic acids and salts thereof, (meth)acrylamide propyl dimethyl amines and salts or quaternary salts thereof, and N-methylol (meth)acrylamides and derivatives thereof; vinyl ether such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, and stearyl vinyl ether; nitriles such as acrylonitrile and methacrylonitrile; vinyl halides such as vinyl chloride and vinyl fluoride; vinylidene halides such as vinylidene chloride and vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; unsaturated dicarboxylic acids such as maleic acid, itaconic acid, and fumaric acid and salts or ester thereof; vinylsilyl compounds such as vinyltrimethoxysilane; isopropenyl acetate; and the like.

The other monomer is preferably an α-olefin and more preferably ethylene. That is to say, the polymer (b) is preferably an α-olefin-modified vinyl alcohol polymer and more preferably an ethylene-modified vinyl alcohol polymer. By using such a modified vinyl alcohol polymer, the oxygen barrier properties and the like can be further improved.

The lower limit of a content percentage of an α-olefin unit with respect to all the monomer units in the α-olefin-modified vinyl alcohol polymer is preferably 0.1 mol %, more preferably 1 mol %, and may be 2 mol %, 5 mol %, or 7 mol %. On the other hand, the upper limit of this content percentage may be 30 mol % or may be 20 mol %, 15 mol %, or 12 mol %. It is to be noted that the content percentage of the α-olefin unit with respect to all the monomer units is also referred to as an amount of α-olefin modification. For example, a content percentage of an ethylene unit with respect to all the monomer units is also referred to as an amount of ethylene modification.

A total content percentage of the vinyl alcohol unit, the vinyl ester unit, and the optional α-olefin unit with respect to all the monomer units in the polymer (b) is preferably 95 mol % or more, more preferably 99 mol % or more, and may be 100 mol %.

A mixture of two or more types of polymers (b) may be used. For example, the polymer (b) may consist of two or more types of vinyl alcohol polymers having different degrees of polymerization. A vinyl alcohol polymer having a low degree of polymerization has low viscosity and superior coatability. On the other hand, a vinyl alcohol polymer having a high degree of polymerization has superior strength and the like. Accordingly, by using a mixture of two or more types of vinyl alcohol polymers having different degrees of polymerization, these properties can be well balanced. It is to be noted that the mixture consisting of two or more types of vinyl alcohol polymers having different degrees of polymerization may have two or more peaks in a molecular weight distribution curve obtained by GPC (gel permeation chromatography) analysis.

The lower limit of a content of the polymer (b) in the B layer is preferably 70% by mass, more preferably 80% by mass, and still more preferably 90% by mass. By setting the content of the polymer (b) in the B layer to be greater than or equal to the lower limit, the oxygen barrier properties and the like can be further improved. On the other hand, the upper limit of this content may be 100% by mass, 99% by mass, or 97% by mass.

Other Component(s) etc. in B Layer

The B layer preferably contains a layered inorganic compound. When the B layer contains the layered inorganic compound, the oxygen barrier properties and the like of the structure can be further improved.

Examples of the layered inorganic compound are similar to those listed in the description of the A layer. In light of the oxygen barrier properties and the like, a mica is preferred as the layered inorganic compound used in the B layer. One type or two or more types of layered inorganic compounds may be used.

In the case in which the B layer contains the layered inorganic compound such as a mica or the like, the lower limit of a content of the layered inorganic compound in the B layer is preferably 1% by mass and more preferably 3% by mass. On the other hand, the upper limit of this content is preferably 30% by mass, more preferably 20% by mass, and still more preferably 10% by mass. By setting the content of the layered inorganic compound in the B layer within the above range, the oxygen barrier properties and the like can be further improved.

The B layer may further contain other component(s) than the polymer (b) and the layered inorganic compound. Examples of the other component(s) include a resin other than the polymer (b), a dispersant, a surfactant, a defoaming agent, a dye, a thickening agent, and the like. It is to be noted that a total content of the polymer (b) and the optional layered inorganic compound in the B layer is preferably 90% by mass or more, and more preferably 95% by mass or more or 99% by mass or more.

A mass per unit area of one layer of the B layer is preferably 0.3 g/m² or more and 20 g/m² or less, more preferably 0.5 g/m² or more and 10 g/m² or less, still more preferably 1 g/m² or more and 7 g/m² or less, and even more preferably 2 g/m² or more and 5 g/m² or less. When the mass per unit area of one layer of the B layer is greater than or equal to the lower limit, the oxygen barrier properties and the like can be further improved. On the other hand, when the mass per unit area of one layer of the B layer is less than or equal to the upper limit, for example, the thickness of the structure can be reduced.

C Layer

The C layer is a layer which is present opposite to the A layer with respect to the B layer. The C layer may be a layer directly laminated on the B layer. Furthermore, the C layer may be an outermost layer.

Polymer (c)

The C layer contains a polymer having a glass transition temperature of −100° C. or more and 5° C. or less (hereinafter, may be also referred to as “polymer (c)”). The polymer (c) is preferably a principal component of the C layer. One type or two or more types of polymers (c) may be used.

The upper limit of the glass transition temperature of the polymer (c) is 5° C., preferably 3° C., more preferably 2° C., and still more preferably 1° C., 0° C., −1° C., −3° C., −5° C., or −10° C. When the glass transition temperature of the polymer (c) is less than or equal to the upper limit, cracks in the C layer can be inhibited, and the water vapor barrier properties can be improved. On the other hand, the lower limit of this glass transition temperature is −100° C., may be −80° C., or may be −60° C., −50° C., or −40° C.

The upper limit of a melting point of the polymer (c) may be 120° C. and is preferably 100° C., more preferably 85° C., still more preferably 80° C., and even more preferably 75° C., 70° C., or 65° C. When the melting point of the polymer (c) is less than or equal to the upper limit, the heat-sealing properties can be improved. The melting point of the polymer (c) may be less than 80° C. On the other hand, the lower limit of this melting point is preferably 30° C., more preferably 40° C., and still more preferably 50° C.

The glass transition temperature and the melting point of the polymer (c) are measured by differential scanning calorimetry (DSC). Specifically, they can be measured by a procedure described in EXAMPLES.

The polymer (c) is not particularly limited as long as it is a polymer having a glass transition temperature of −100° C. or more and 5° C. or less. As the polymer (c), for example, of the olefin polymer, the styrene polymer, and the polyester polymer in the description of the polymer (a), a polymer or the like having a glass transition temperature of −100° C. or more and 5° C. or less may be used.

As the polymer (c), an olefin polymer and a styrene polymer are preferred, a styrene polymer is more preferred, a styrene-acrylic copolymer and a styrene-butadiene copolymer are still more preferred, a styrene-acrylic copolymer is even more preferred, and a styrene-(meth)acrylic acid ester copolymer is particularly preferred. Furthermore, of olefin polymers, an olefin-unsaturated carboxylic acid copolymer is preferred, an olefin-unsaturated carboxylic acid copolymer is more preferred, and an ethylene-(meth)acrylic acid copolymer is still more preferred. As the polymer (c), a copolymer of a hydrocarbon monomer and an acrylic compound is also preferred. Examples of the hydrocarbon monomer include the above-described olefins, styrene compounds, and the like. By using such a polymer as the polymer (c), the water vapor barrier properties, the heat-sealing properties, and the like can be further improved. Specific modes of the olefin polymer and the styrene polymer used as the polymer (c) are similar to those of the olefin polymer and the styrene polymer in the polymer (a) described above.

In one embodiment of the present invention, the polymer (a) and the polymer (c) may be polymers of the same type or different types of polymers. For example, to optimize the functions of the A layer and the C layer, different types of polymers may be used as the polymer (a) and the polymer (c).

The lower limit of a content of the polymer (c) in the C layer is preferably 50% by mass, more preferably 60% by mass, still more preferably 70% by mass, and even more preferably 80% by mass, 85% by mass, or 90% by mass. On the other hand, the upper limit of this content is preferably 100% by mass, more preferably 99% by mass, and still more preferably 95% by mass.

Other Component(s) etc. in C Layer

The C layer preferably contains wax. When the C layer contains the wax, for example, the water vapor barrier properties can be further improved. Furthermore, when the C layer contains the wax, the grease resistance and the like tend to be improved.

The wax preferably contains paraffin wax. As the paraffin wax, for example, paraffin wax containing, as a principal component, normal paraffin having 20 or more and 40 or less carbon atoms and a molecular weight of 300 or more and 500 or less may be used. A commercial product may be used as the paraffin wax.

In the case in which the C layer contains the wax, the lower limit of a content of the wax in the C layer may be, for example, 0.1% by mass and is preferably 1% by mass, more preferably 3% by mass, and still more preferably 5% by mass. On the other hand, the upper limit of this content may be, for example, 30% by mass and is preferably 20% by mass, more preferably 15% by mass, and still more preferably 12% by mass. By setting the content of the wax in the C layer within the above range, the water vapor barrier properties and the like can be further improved. Furthermore, in the case in which the C layer contains the paraffin wax, the lower limit of a content of the paraffin wax in the C layer may be, for example, 0.1% by mass and is preferably 1% by mass, more preferably 3% by mass, and still more preferably 5% by mass. On the other hand, the upper limit of this content may be, for example, 30% by mass and is preferably 20% by mass, more preferably 15% by mass, and still more preferably 12% by mass. By setting the content of the paraffin wax in the C layer within the above range, the water vapor barrier properties and the like can be further improved.

The C layer may further contain other component(s) than the polymer (c) and the wax. Examples of the other component(s) include a resin other than the polymer (c), a dispersant, a surfactant, a defoaming agent, a dye, a thickening agent, and the like. The C layer may contain two or more types of polymers. The two or more types of polymers which may be contained in the C layer may be a combination of the polymer (c) and other polymer(s) or may be two or more types of polymers (c). It is to be noted that a total content of the polymer (c) and the optional wax in the C layer is preferably 90% by mass or more, and more preferably 95% by mass or more or 99% by mass or more.

In particular, it is preferred that the C layer contains substantially no vinyl alcohol polymer. A content of the vinyl alcohol polymer in the C layer is preferably 10% by mass or less, more preferably 3% by mass or less, still more preferably 1% by mass or less, and even more preferably 0.1% by mass or less. By thus reducing the content of the vinyl alcohol polymer in the C layer, an increase in the viscosity of a C layer-forming coating liquid at the time of providing the C layer by coating can be inhibited, and the C layer can be efficiently formed.

The C layer preferably has a melting point of 120° C. or less. The upper limit of the melting point of the C layer is preferably 100° C., more preferably 85° C., still more preferably 80° C., and even more preferably 75° C., 70° C., or 65° C. When the melting point of the C layer is less than or equal to the upper limit, the heat-sealing properties can be improved. The melting point of the C layer may be less than 80° C. On the other hand, the lower limit of this melting point is preferably 30° C., more preferably 40° C., and still more preferably 50° C. The melting point of the C layer is measured by differential scanning calorimetry (DSC). It is to be noted that in a case in which one of the components (polymer (c) and other optional component(s)) of the C layer has a predetermined melting point T, typically, the C layer also has the predetermined melting point T.

A mass per unit area of one layer of the C layer is preferably 1 g/m² or more and 100 g/m² or less, more preferably 3 g/m² or more and 50 g/m² or less, still more preferably 5 g/m² or more and 30 g/m² or less, even more preferably 7 g/m² or more and 20 g/m² or less, and particularly preferably 9 g/m² or more and 15 g/m² or less. When the mass per unit area of one layer of the C layer is greater than or equal to the lower limit, the water vapor barrier properties and the like can be further improved. On the other hand, when the mass per unit area of one layer of the C layer is less than or equal to the upper limit, for example, the thickness of the structure can be reduced.

The structure can be suitably used as greaseproof paper, gas barrier paper, flavor barrier paper, a packaging material, or the like. The structure can also be used in a state in which the structure is formed into a predetermined shape (for example, a bag shape) by heat-sealing the C layers together. A heat-sealing method is not particularly limited and may be a known method: for example, the heat sealing may be performed using a heat plate type heat sealer, an impulse sealer, an ultrasonic sealer, a friction heat sealer, a dielectric heat sealer, or the like.

Method for Producing Structure

A method for producing the structure according to one embodiment of the present invention is not particularly limited, and the structure can be typically produced in such a manner that the A layer, the B layer, and the C layer are provided in this order on the paper base material by coating. Specifically, for example, the A layer is provided in such a manner that a surface of the paper base material is coated with an A layer-forming coating liquid and then drying is performed. Next, the B layer is provided in such a manner that a surface of the A layer is coated with a B layer-forming coating liquid and then drying is performed. Next, the C layer is provided in such a manner that a surface of the B layer is coated with a C layer-forming coating liquid and then drying is performed; thus, the structure can be obtained. The drying does not necessarily need to be performed after the coating with each coating liquid, and a simultaneous multilayer coating method may be employed.

The coating with each coating liquid may be performed by a conventionally known method. For example, the coating may be performed using a blade coater, a bar coater, an air knife coater, a slit die coater, a gravure coater, a micro gravure coater, a gate roll coater, a curtain coater, or the like. Of these, a curtain coater is preferably used.

That is to say, the method for producing the structure according to one embodiment of the present invention includes a step of providing at least one of the A layer, the B layer, or the C layer by using a curtain coater. In the production method, all of the A layer, the B layer, and the C layer are preferably provided using a curtain coater.

A method for drying each coating liquid which has been applied is not particularly limited, and for example, a hot-air dryer, an infrared dryer, a gas burner, a heat plate, or the like may be used.

A solvent or a dispersion medium of the coating liquid for forming each layer is not particularly limited; water or an organic solvent (ethanol, isopropyl alcohol, methyl ethyl ketone, toluene, or the like) may be used, and water is preferred.

A solid content (solid content concentration) in the coating liquid for forming each layer is not particularly limited and may be, for example, 3% by mass or more and 70% by mass or less, may be 5% by mass or more and 60% by mass or less, or may be 10% by mass or more and 50% by mass or less.

Greaseproof Paper

Greaseproof paper according to one embodiment of the present invention includes the structure according to one embodiment of the present invention. The greaseproof paper according to one embodiment of the present invention may consist of the structure according to one embodiment of the present invention.

The greaseproof paper is superior in water vapor barrier properties and oxygen barrier properties, and in the case of including a heat-sealed portion, the adhesiveness thereof is also favorable. The greaseproof paper is suitably used, for example, as a packaging material used at the time of serving oily foods such as French fries, fried chicken, etc., as a packaging material for wrapping butter etc., or as cooking paper used at the time of baking a bread, a cake, etc.

A grease resistance (KIT value) of the greaseproof paper is preferably the fifth grade or higher, and more preferably the sixth or seventh grade or higher. This grease resistance is defined to be a value obtained when the surface of the C layer is measured by a TAPPI UM-557 method (kit test).

Gas Barrier Paper

Gas barrier paper according to one embodiment of the present invention includes the structure according to one embodiment of the present invention. The gas barrier paper according to one embodiment of the present invention may consist of the structure according to one embodiment of the present invention.

The gas barrier paper is superior in both oxygen barrier properties and water vapor barrier properties, and in the case of including a heat-sealed portion, the adhesiveness thereof is also favorable. The gas barrier paper is suitably used, for example, as packaging materials for foods, agrichemicals, chemicals, cosmetics, medical products, electronic components, clothing items, etc.

An oxygen transmission rate of the gas barrier paper is preferably 10 cc/m²·24 h or less, more preferably 5 cc/m²·24 h or less, and still more preferably 3 cc/m²·24 h or less. The oxygen transmission rate is defined to be a value measured under conditions including 23° C./65% RH.

Flavor Barrier Paper

Flavor barrier paper according to one embodiment of the present invention includes the structure according to one embodiment of the present invention. The flavor barrier paper according to one embodiment of the present invention may consist of the structure according to one embodiment of the present invention.

The flavor barrier paper is superior in both oxygen barrier properties and water vapor barrier properties, and in the case of including a heat-sealed portion, the adhesiveness thereof is also favorable. The flavor barrier paper is suitably used, for example, as packaging materials for items with flavors such as sweets, tea leaves, coffee, spices, tobacco, cosmetics, perfumes, etc. The flavor barrier paper is also useful as packaging materials or the like for other foods, agrichemicals, chemicals, clothing items, etc.

In general, in a case in which the oxygen transmission rate is low, the flavor blocking properties also tend to be improved. An oxygen transmission rate of the flavor barrier paper is preferably 10 cc/m²·24 h or less, more preferably 5 cc/m²·24 h or less, and still more preferably 3 cc/m²·24 h or less.

Packaging Material

A packaging material according to one embodiment of the present invention includes at least one selected from the group consisting of the greaseproof paper according to one embodiment of the present invention, the gas barrier paper according to one embodiment of the present invention, and the flavor barrier paper according to one embodiment of the present invention. The packaging material according to one embodiment of the present invention may include the structure according to one embodiment of the present invention.

The packaging material is superior in water vapor barrier properties and oxygen barrier properties, and in the case of including a heat-sealed portion, the adhesiveness thereof is also favorable. The packaging material is suitably used, for example, as packaging materials for foods, agrichemicals, chemicals, cosmetics, medical products, electronic components, clothing items, etc.

EXAMPLES

Hereinafter, the present invention is more specifically described by way of Examples, and the present invention is not limited to the Examples.

Production Example 1: Production of PVA-1

Into a reaction tank equipped with a stirrer, a nitrogen introduction port, and an initiator addition port, 1,050 g of vinyl acetate and 1,950 g of methanol were charged and heated to 60° C., and then, the inside of the system was replaced with nitrogen by nitrogen bubbling for 30 min. After the temperature in the reaction tank was adjusted to 60° C., 1.6 g of azobisisobutyronitrile (AIBN) was charged as a polymerization initiator to start polymerization. At the point of time when the polymerization rate reached 50% in 3 hrs., cooling was performed to stop the polymerization. Unreacted vinyl acetate monomers were removed, and methanol was added to obtain a polyvinyl acetate (PVAc) solution in methanol (concentration: 30% by mass). To 400 g of the PVAc solution in methanol (PVAc in the solution: 120 g), 55.8 g of a 10% NaOH solution in methanol (molar ratio [MR] of the amount of NaOH with respect to the vinyl acetate unit in the PVAc: 0.10) was added, and saponification was performed at 40° C. After the addition of the NaOH solution in methanol, the resulting gel was crushed in a crusher and subjected to a saponification reaction for 1 hr. in total. After that, 1,000 g of methyl acetate was added to neutralize the remaining alkali. A phenolphthalein indicator was used to confirm that the neutralization had been finished, 1,000 g of methanol was then added to a white solid obtained by filtration, and the resulting mixture was left at room temperature for 3 hrs. and then washed. After the washing operation was repeated three times, a solid obtained by centrifugal liquid removal was left and dried in a dryer at 70° C. for 2 days to obtain a vinyl alcohol polymer (PVA-1).

Production Example 2: Production of PVA-2

Into a 5 L-pressure reaction tank equipped with a stirrer, a nitrogen introduction port, an ethylene introduction port, and an initiator addition port, 1,440 g of vinyl acetate and 1,560 g of methanol were charged and heated to 60° C., and then, the inside of the system was replaced with nitrogen by nitrogen bubbling for 30 min. Next, ethylene was introduced such that the reaction tank pressure was 7.8 kg/cm². After the temperature in the reaction tank was adjusted to 60° C., 2.0 g of AIBN was charged as a polymerization initiator to start polymerization. During the polymerization, ethylene was introduced to maintain the reaction tank pressure at 7.8 kg/cm² and the polymerization temperature at 60° C. At the point of time when the polymerization rate reached 50% in 3 hrs., cooling was performed to stop the polymerization. After the reaction tank was opened to release ethylene, bubbling with a nitrogen gas was further performed. Next, unreacted vinyl acetate monomers were removed under reduced pressure, and methanol was added to obtain an ethylene-vinyl acetate copolymer solution in methanol (concentration: 30% by mass). To 400 g of the ethylene-vinyl acetate copolymer solution in methanol (ethylene-vinyl acetate copolymer in the solution: 120 g), 55.8 g of a 10% NaOH solution in methanol (molar ratio [MR] of the amount of NaOH with respect to the vinyl acetate unit in the ethylene-vinyl acetate copolymer: 0.10) was added, and saponification was performed at 40° C. After the addition of the NaOH solution in methanol, the resulting gel was crushed in a crusher, and a saponification reaction was performed for 1 hr. in total. After that, 1,000 g of methyl acetate was added to neutralize the remaining alkali. A phenolphthalein indicator was used to confirm that the neutralization had been finished, 1,000 g of methanol was then added to a white solid obtained by filtration, and the resulting mixture was left at room temperature for 3 hrs. and then washed. After the washing operation was repeated three times, a solid obtained by centrifugal liquid removal was left in a dryer at 70° C. for 2 days to obtain an ethylene-modified vinyl alcohol polymer (PVA-2).

Production Examples 3 to 5: Production of PVA-3 to PVA-5

Each ethylene-modified vinyl alcohol polymer (PVA-3 to PVA-5) was produced by the same procedure as in Production Example 2, except that the polymerization conditions and the saponification conditions were as shown in Table 1.

The viscosity average degree of polymerization, the degree of saponification, and the amount of ethylene modification (ethylene unit content) of each of the obtained PVA-1 to PVA-5 were measured. The measurement results are shown in Table 1.

Besides the PVA-1 to PVA-5, polymers used in Examples and Comparative Examples are shown below.

Polymer (a)

• • Polymer a1: “MFP1883” (produced by Michelman, Inc.), an olefin-acrylic acid copolymer emulsion having a solid content of 27% by mass
  • Polymer a2: “OP-671” (produced by Lion Corporation), a styrene-acrylic acid ester copolymer emulsion having a solid content of 48% by mass
  • Polymer a3: “CHEMIPEARL S-100” (produced by Mitsui Chemicals, Inc.), an ethylene-methacrylic acid copolymer emulsion having a solid content of 27% by mass
  • Polymer a4: “Tykote 1004” (produced by Mallard Creek Polymers, Inc.), a styrene-butadiene copolymer emulsion

Polymer (b)

• • PU-1: “TAKELAC WPB-341” (produced by Mitsui Chemicals, Inc.), a polyurethane emulsion having a solid content of 30% by mass

Polymer (c)

• • Polymer c1: “VAPCT2200” (produced by Michelman, Inc.), a styrene-acrylic acid ester copolymer emulsion having a solid content of 48% by mass, a glass transition temperature of −32.3° C., and a melting point of 60.4° C.
  • Polymer c2: “498340R” (produced by Michelman, Inc.), an ethylene-acrylic acid copolymer emulsion having a solid content of 40% by mass, a glass transition temperature of −0.5° C., and a melting point of 78.7° C.
  • Polymer c3: “OP-671” (produced by Lion Corporation), a styrene-butadiene copolymer emulsion having a solid content of 48% by mass, a glass transition temperature of 2.8° C., and a melting point of 47.0° C.
  • Polymer c4: “CHEMIPEARL S-100” (produced by Mitsui Chemicals, Inc.), an ethylene-methacrylic acid copolymer emulsion having a solid content of 27% by mass, a glass transition temperature of 23.9° C., and a melting point of 86.9° C.

Procedure for Measuring Glass Transition Temperature and Melting Point

The glass transition temperature and the melting point of the polymer (c) were measured by the following procedure.

About 3 mg of a measurement sample was charged in a sample pan, and the glass transition point and the melting point of the sample were measured using a DSC Q2000 apparatus (produced by TA Instruments, Inc.). The temperature of the sample was increased from 30° C. to 200° C., then decreased to −90° C. and maintained for 5 min, and then increased to 200° C. Both the increase and decrease in temperature were conducted at 10° C./min.

Example 1: Production of Structure

Woodfree paper having a basis weight of 70.5 g/m² was prepared as the paper base material. The A layer was provided in such a manner that one face of the paper base material was coated, at a coating amount of 10.0 g/m² by dry mass, with the emulsion “MFP1883” of the polymer a1 as the A layer-forming coating liquid and then drying was performed. Next, the B layer was provided in such a manner that a surface of the A layer was coated, at a coating amount of 3.0 g/m² by dry mass, with an aqueous solution of the PVA-1 (solid content: 10% by mass) as the B layer-forming coating liquid and then drying was performed. Next, the C layer was provided in such a manner that a surface of the B layer was coated, at a coating amount of 10.0 g/m² by dry mass, with the emulsion “VAPCT2200” of the polymer c1 as the C layer-forming coating liquid and then drying was performed. In the above-described manner, a structure of Example 1 was obtained. The A layer, the B layer, and the C layer were all applied using a wire bar. The obtained structure and the C layer-forming coating liquid used were subjected to the following evaluation. The evaluation results are shown in Table 3.

Evaluation

(1) Viscosity of the C Layer-Forming Coating Liquid

After the temperature of the C layer-forming coating liquid was regulated in a chamber at 20° C., the viscosity of the C layer-forming coating liquid was measured using a B-type viscometer under conditions including 60 rpm.

(2) Viscosity Stability of the C Layer-Forming Coating Liquid

The solid content of the C layer-forming coating liquid was adjusted to 22% by mass, and the fluidity of the coating liquid during stirring was evaluated according to the following criteria:

• • A: fluid without thickening;
  • B: thickened but fluid; and
  • C: not fluid (creamy).

(3) Oxygen Transmission Rate (Gas Barrier Properties)

The oxygen transmission rate of the structure was measured using “OX-TRAN2/21,” produced by MOCON, Inc., under conditions including 23° C./65% RH.

(4) Water Vapor Transmission Rate (Water Vapor Barrier Properties)

The water vapor transmission rate of the structure was measured based on JIS Z 2080 by a dish method under conditions including a temperature of 40±0.5° C. and a relative humidity difference of 90±2%.

(5) Cracks in the C Layer

The presence or absence of cracks in the C layer of the structure and the degree thereof were visually evaluated according to the following criteria:

• • A⁺: no cracks;
  • A: cracks observed partly;
  • B: continuous cracks observed partly; and
  • C: continuous cracks observed entirely.

(6) Heat-Sealing Properties

The C layers of the structure were superimposed on each other and sealed together by heating using a heat gradient tester under conditions including 160° C., 0.3 MPa, and 1 sec. After that, a 180° peeling test was conducted using an autograph, and a portion where breakage occurred was evaluated according to the following criteria:

• • A: breakage of the paper base material (the strength between the C layers was greater than or equal to that of the paper base material and was sufficiently high):
  • B: interlayer peeling (the C layers were sealed, but the strength therebetween was lower than that of the paper base material); and
  • C: natural peeling (unsealed state).

Example 2

A structure of Example 2 was obtained by the same operation as in Example 1, except that instead of the PVA-1, the PVA-2 was used in the B layer-forming coating liquid and that the emulsion “498340R” of the polymer c2 was used as the C layer-forming coating liquid. Evaluation was performed by the same procedures as in Example 1. The evaluation results are shown in Table 3.

Example 3

A structure of Example 3 was obtained by the same operation as in Example 2, except that the emulsion “OP-671” of the polymer c3 was used as the C layer-forming coating liquid. Evaluation was performed by the same procedures as in Example 1. The evaluation results are shown in Table 3.

Example 4

A paraffin wax emulsion “Haricoat RT” (produced by Harima Chemicals Group, Inc.) was added to the emulsion “VAPCT2200” of the polymer c1 to prepare a mixture in which the content of “Haricoat RT” with respect to the polymer c1 (100 parts by mass) was 0.5 parts by mass in terms of solid content. A structure of Example 4 was obtained by the same operation as in Example 2, except that this mixture was used as the C layer-forming coating liquid. Evaluation was performed by the same procedures as in Example 1. The evaluation results are shown in Table 3.

Example 5

A structure of Example 5 was obtained by the same operation as in Example 4, except that the content of “Haricoat RT” with respect to the polymer c1 (100 parts by mass) in the C layer-forming coating liquid was set to 10 parts by mass in terms of solid content. Evaluation was performed by the same procedures as in Example 1. The evaluation results are shown in Table 3.

Example 6

A structure of Example 6 was obtained by the same operation as in Example 4, except that the content of “Haricoat RT” with respect to the polymer c1 (100 parts by mass) in the C layer-forming coating liquid was set to 22 parts by mass in terms of solid content. Evaluation was performed by the same procedures as in Example 1. The evaluation results are shown in Table 3.

Example 7

A structure of Example 7 was obtained by the same operation as in Example 5, except that the emulsion “OP-671” of the polymer a2 was used as the A layer-forming coating liquid. Evaluation was performed by the same procedures as in Example 1. The evaluation results are shown in Table 3.

Example 8

A structure of Example 8 was obtained by the same operation as in Example 5, except that the emulsion “CHEMIPEARL S-100” of the polymer a3 was used as the A layer-forming coating liquid. Evaluation was performed by the same procedures as in Example 1. The evaluation results are shown in Table 3.

Example 9

A structure of Example 9 was obtained by the same operation as in Example 5, except that the emulsion “Tykote 1004” of the polymer a4 was used as the A layer-forming coating liquid. Evaluation was performed by the same procedures as in Example 1. The evaluation results are shown in Table 3.

Example 10

A talc dispersion “Finntalc C10B” (produced by Elementis plc) was added to the emulsion “MFP1883” of the polymer a1 to prepare a mixture in which the content of the talc with respect to the polymer a1 (100 parts by mass) was 50 parts by mass. A structure of Example 10 was obtained by the same operation as in Example 5, except that this mixture was used as the A layer-forming coating liquid. Evaluation was performed by the same procedures as in Example 1. The evaluation results are shown in Table 3.

Example 11

A mica dispersion “ME-100” (produced by Katakura & Co-op Agri Corporation) was added to an aqueous solution of the PVA-2 (solid content: 10% by mass) to prepare a mixture in which the content of the mica with respect to the PVA-2 (100 parts by mass) was 5 parts by mass. A structure of Example 11 was obtained by the same operation as in Example 5, except that this mixture was used as the B layer-forming coating liquid. Evaluation was performed by the same procedures as in Example 1. The evaluation results are shown in Table 3.

Example 12

A structure of Example 12 was obtained by the same operation as in Example 5, except that instead of the PVA-2, the PVA-3 was used in the B layer-forming coating liquid. Evaluation was performed by the same procedures as in Example 1. The evaluation results are shown in Table 3.

Example 13

A structure of Example 13 was obtained by the same operation as in Example 5, except that instead of the PVA-2, the PVA-4 was used in the B layer-forming coating liquid. Evaluation was performed by the same procedures as in Example 1. The evaluation results are shown in Table 3.

Example 14

A mica dispersion “ME-100” (produced by Katakura & Co-op Agri Corporation) was added to an aqueous solution of the PVA-2 (solid content: 10% by mass) to prepare a mixture in which the content of the mica with respect to the PVA-2 (100 parts by mass) was 5 parts by mass. A structure of Example 14 was obtained by the same operation as in Example 10, except that this mixture was used as the B layer-forming coating liquid. Evaluation was performed by the same procedures as in Example 1. The evaluation results are shown in Table 3.

Comparative Example 1

A structure of Comparative Example 1 was obtained by the same operation as in Example 5, except that the emulsion “CHEMIPEARL S-100” of the polymer c4 was used as the C layer-forming coating liquid. Evaluation was performed by the same procedures as in Example 1. The evaluation results are shown in Table 3.

Comparative Example 2

A structure of Comparative Example 2 was obtained by the same operation as in Example 2, except that the emulsion “CHEMIPEARL S-100” of the polymer c4 was used as the C layer-forming coating liquid. Evaluation was performed by the same procedures as in Example 1. The evaluation results are shown in Table 3.

Comparative Example 3

The PVA-5 was added to the emulsion “CHEMIPEARL S-100” of the polymer c4 to prepare a mixture in which the content of the PVA-5 with respect to the polymer c4 (100 parts by mass) was 5 parts by mass. A structure of Comparative Example 3 was obtained by the same operation as in Comparative Example 2, except that this mixture was used as the C layer-forming coating liquid. Evaluation was performed by the same procedures as in Example 1. The evaluation results are shown in Table 3.

Comparative Example 4

A structure of Comparative Example 4 was obtained by the same operation as in Comparative Example 2, except that the emulsion “TAKELAC WPB-341” of the PU-1 was used as the B layer-forming coating liquid. Evaluation was performed by the same procedures as in Example 1. The evaluation results are shown in Table 3.

	TABLE 1
	Analysis results

Polymerization conditions

Saponification conditions

viscosity

polymer-

amount

average

amount

polymer-

vi-

polymer-

ization

of

saponifi-

degree

degree

of

ization

nyl

ization

initiator

polymer-

polymer-

PVAc

added

cation

of

of sa-

ethylene

temper-

ace-

meth-

ethylene

charging

ization

ization

concen-

NaOH

temper-

polymeri-

ponifi-

modifi-

ature

tate

anol

pressure

amount

time

rate

tration

molar

ature

zation

cation

cation

PVA

° C.

g

g

kg/cm2

g

h

%

%

ratio

° C.

—

mol %

mol %

PVA-1	60	1,050	1,950	—	1.6	3	50	30	0.10	40	400	99.3	0
PVA-2	60	1,440	1,560	7.8	2.0	3	50	30	0.10	40	400	99.2	10
PVA-3	60	2,550	450	2.9	1.0	3	20	20	0.04	40	1,700	98.4	2
PVA-4	60	2,640	360	7.3	0.8	3	20	20	0.04	40	2,000	98.2	6
PVA-5	60	2,550	450	2.9	1.0	3	20	20	0.01	40	1,700	93.1	2

	TABLE 2
	A layer	B layer	C layer

talc

mica

polymer (c)

Haricoat RT

		content		content		glass transition	melting	content
	polymer (a)	(parts by	polymer (b)	(parts by		temperature	point	(parts by
	type	mass)	type	mass)	type	(° C.)	(° C.)	mass)

Example 1	a1	0	PVA-1	0	c1	−32.3	60.4	0
Example 2	a1	0	PVA-2	0	c2	−0.5	78.7	0
Example 3	a1	0	PVA-2	0	c3	2.8	47.0	0
Example 4	a1	0	PVA-2	0	cl	−32.3	60.4	0.5
Example 5	a1	0	PVA-2	0	c1	−32.3	60.4	10
Example 6	a1	0	PVA-2	0	cl	−32.3	60.4	22
Example 7	a2	0	PVA-2	0	cl	−32.3	60.4	10
Example 8	a3	0	PVA-2	0	cl	−32.3	60.4	10
Example 9	a4	0	PVA-2	0	c1	−32.3	60.4	10
Example 10	a1	50	PVA-2	0	cl	−32.3	60.4	10
Example 11	a1	0	PVA-2	5	cl	−32.3	60.4	10
Example 12	a1	0	PVA-3	0	cl	−32.3	60.4	10
Example 13	a1	0	PVA-4	0	c1	−32.3	60.4	10
Example 14	a1	50	PVA-2	5	cl	−32.3	60.4	10
Comparative	a1	0	PVA-2	0	c4	23.9	86.9	10
Example 1
Comparative	a1	0	PVA-2	0	c4	23.9	86.9	0
Example 2
Comparative	a1	0	PVA-2	0	c4/PVA-5 =	23.9*1	86.9	0
Example 3					100/5 (mass
					ratio)
Comparative	a1	0	PU-1	0	c4	23.9	86.9	0
Example 4
*1The glass transition temperature of the polymer c4, which is the principal-component polymer

	TABLE 3
	C layer-forming coating liquid	Structure

		viscosity	oxygen transmission	water vapor		heat-sealing
	viscosity	stability	rate	transmission rate	cracks	properties
	mPa · s	—	cc/m2 · 24 h	g/m2 · 24 h	—	—

Example 1	200	A	5	30	A+	A
Example 2	1,200	A	3	45	A	A
Example 3	110	A	3	60	B	A
Example 4	190	A	3	25	A+	A
Example 5	160	A	3	15	A+	A
Example 6	130	A	3	20	A+	A
Example 7	160	A	3	35	A+	A
Example 8	160	A	3	30	A+	A
Example 9	160	A	3	35	A+	A
Example 10	160	A	3	10	A+	A
Example 11	160	A	1	30	A+	A
Example 12	160	A	5	30	A+	A
Example 13	160	A	5	30	A+	A
Example 14	160	A	1	10	A+	A
Comparative	320	A	3	100	C	B
Example 1
Comparative	400	A	3	100	C	B
Example 2
Comparative	not measurable	C	3	75	A	B
Example 3
Comparative	400	A	10	45	A	B
Example 4

The results indicate that the structures of Examples 1 to 14, in each of which the B layer contains the vinyl alcohol polymer (PVA-1 to PVA-4) and the C layer contains the polymer having a glass transition temperature of −100° C. or more and 5° C. or less (polymers c1 to c3), include few cracks in the C layer and are superior in water vapor barrier properties, heat-sealing properties, and oxygen barrier properties. In particular, for example, according to comparison between Examples 2 and 3 and Comparative Example 2, which are different only in the type of the polymer (c), it can be confirmed that the glass transition temperature of the polymer (c) constituting the C layer significantly influences the occurrence of cracks in the C layer and the water vapor barrier properties.

It is to be noted that in the case in which the B layer contains no vinyl alcohol polymer as in Comparative Example 4, the oxygen barrier properties were low, whereas cracks in the C layer were less likely to occur even when the glass transition temperature of the polymer contained in the C layer was high. In contrast, in the case in which the B layer contains the vinyl alcohol polymer as in Comparative Examples 1 and 2, cracks occurred in the C layer depending on the glass transition temperature of the polymer contained in the C layer, and the water vapor barrier properties were deteriorated. Thus, it can be confirmed that the cracks in the C layer are a phenomenon which prominently occurs when the B layer contains the vinyl alcohol polymer. In other words, in each of the structures of Examples 1 to 14, the vinyl alcohol polymer having particularly high oxygen barrier properties is used in the B layer, and the polymer which is less likely to cause cracks is used in the C layer, whereby both superior oxygen barrier properties and superior water vapor barrier properties can be achieved.

Furthermore, in the case in which the C layer-forming coating liquid contains the vinyl alcohol polymer as in Comparative Example 3, it is found that the viscosity increases and the viscosity stability decreases, leading to a deterioration in coatability.

INDUSTRIAL APPLICABILITY

The structure of the present invention can be suitably used as a packaging material such as greaseproof paper, gas barrier paper, flavor barrier paper, or the like.

EXPLANATION OF REFERENCE SYMBOLS

• • 10: Structure
  • 11: Paper base material
  • 12: A layer
  • 13: B layer
  • 14: C layer