Multilayer structure, roll-shaped structure, and packaging material

Abstract

Provided are a multilayer structure and a roll-shaped structure in which adhesion of a pigment to a resin layer is suppressed and which have good barrier properties, and a packaging material obtained using such a multilayer structure. A multilayer structure having a paper substrate, a layer A laminated on one surface side of the paper substrate, and a layer B laminated on the other surface side of the paper substrate, the layer A containing a pigment, the layer B containing a polymer (a) having a glass transition temperature of 25 DEG C or less and a polymer (b) having a glass transition temperature of 30 DEG C or more, the content of the polymer (b) is from 1 part by mass to 50 parts by mass (inclusive) per 100 parts by mass of the polymer (a).

Description

Technical Field

[0001] This invention relates to multi-layer structures, roll structures, and packaging materials. Background Technology

[0002] In food packaging, packaging materials that impart water vapor barrier, gas barrier, and oil resistance to paper substrates have been used for a long time. Patent Document 1 describes a packaging material obtained by sequentially layering a water vapor barrier layer, a gas barrier layer, and a heat-sealing layer on at least one side of a paper substrate.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2021-20398 Summary of the Invention

[0006] The problem that the invention aims to solve

[0007] In packaging materials for food and other products, various printing processes are typically applied to their surfaces. Therefore, to improve printability, aesthetics, and smoothness, a pigment layer is sometimes applied to at least one side of the paper substrate.

[0008] When one or more resin layers are applied to the other side of a paper substrate with a pigment layer on one side by coating or other methods, the long strip of multilayer structure produced during the manufacturing process is sometimes rolled into a roll each time a resin layer is applied. Furthermore, the completed long strip of multilayer structure is usually stored in a roll. When an unfinished or completed multilayer structure is rolled into such a roll, defects sometimes occur on the surface of the resin layer. Besides resulting in a poor appearance, these surface defects can also lead to a reduction in desired barrier properties. The inventors believe that the main reason for these surface defects is that adhesion occurs between the pigment layer and the resin layer when they come into contact, with pigment from the pigment layer adhering to the resin layer. This pigment adhesion is particularly pronounced when resin layers obtained using polymers with low glass transition temperatures, such as those used in heat-sealing layers.

[0009] The object of the present invention is to provide a multilayer structure and a roll structure that inhibit the adhesion of pigments to the resin layer and have good barrier properties, as well as packaging materials obtained using such multilayer structures.

[0010] means for solving problems

[0011] The above problem can be solved by providing any of the following solutions.

[0012] [1] A multilayer structure having a paper substrate, an A layer, and a B layer, wherein the A layer is stacked on one side of the paper substrate and the B layer is stacked on the other side of the paper substrate.

[0013] The aforementioned layer A contains pigments, and the aforementioned layer B contains a polymer (a) with a glass transition temperature of 25°C or less and a polymer (b) with a glass transition temperature of 30°C or more, wherein the content of the aforementioned polymer (b) is more than 1 part by mass and less than 50 parts by mass relative to 100 parts by mass of the aforementioned polymer (a).

[0014] [2] According to the multilayer structure of [1], wherein both the polymer (a) and the polymer (b) are water-soluble or water-dispersible;

[0015] [3] According to the multilayer structure of [1] or [2], wherein the total content of the polymer (a) and the polymer (b) in the B layer is 20% by mass or more and 100% by mass or less;

[0016] [4] According to any one of [1] to [3], the multilayer structure, wherein the polymer (b) is a vinyl alcohol polymer;

[0017] [5] According to the multilayer structure of [4], wherein the degree of saponification of the above-mentioned vinyl alcohol polymer is 80 mol% or more and 100 mol% or less;

[0018] [6] According to the multilayer structure of [4], wherein the degree of saponification of the above-mentioned vinyl alcohol polymer exceeds 96 mol% and is less than 100 mol%;

[0019] [7] According to any one of [4] to [6], the viscosity-average degree of polymerization of the above-mentioned vinyl alcohol polymer is 200 or more and 3,000 or less;

[0020] [8] A multilayer structure according to any one of [1] to [7], wherein the polymer (a) comprises at least one selected from styrene polymers, modified olefin polymers and ester polymers;

[0021] [9] The multilayer structure according to any one of [1] to [8] has, in sequence, the above-mentioned layer A, the above-mentioned paper substrate, the pre-coating layer, the barrier layer and the heat-sealing layer, wherein the above-mentioned pre-coating layer is the above-mentioned layer B;

[0022]

[10] According to any one of [1] to [8], the multilayer structure has the above-mentioned layer A, the above-mentioned paper substrate, the pre-coating layer, the barrier layer and the heat-sealing layer in sequence, wherein the above-mentioned heat-sealing layer is the above-mentioned layer B;

[0023]

[11] The multilayer structure according to any one of [1] to [8] has, in sequence, the above-mentioned A layer, the above-mentioned paper substrate, the pre-coating layer, the barrier layer and the heat-sealing layer, wherein the above-mentioned pre-coating layer and the above-mentioned heat-sealing layer are the above-mentioned B layer;

[0024]

[12] A multilayer structure according to any one of [9] to

[11] , wherein the barrier layer comprises a vinyl alcohol polymer;

[0025]

[13] A roll structure is a roll structure formed by winding any one of the multi-layer structures of [1] to [8] and

[10] to

[12] , wherein the above-mentioned layer A is in direct contact with the above-mentioned layer B;

[0026]

[14] Packaging material, which comprises a multilayer structure of any one of [1] to

[12] .

[0027] Invention Effects

[0028] According to the present invention, multilayer structures and roll structures with good barrier properties that suppress pigment adhesion to resin layers can be provided, as well as packaging materials obtained using such multilayer structures. Attached Figure Description

[0029] Figure 1 This is a schematic cross-sectional view showing a multi-layer structure according to one embodiment of the present invention. Detailed Implementation

[0030] <Multi-layer structure>

[0031] According to one embodiment of the present invention, the multilayer structure is a multilayer structure having a paper substrate, an A layer, and a B layer. The A layer is stacked on one side of the paper substrate, and the B layer is stacked on the other side of the paper substrate. The A layer contains pigment, and the B layer contains a polymer (a) with a glass transition temperature of 25°C or less and a polymer (b) with a glass transition temperature of 30°C or more. The content of the polymer (b) is more than 1 part by mass and less than 50 parts by mass relative to 100 parts by mass of the polymer (a).

[0032] In this multilayer structure, the adhesion of pigments to the resin layer (i.e., layer B) is suppressed, resulting in excellent barrier properties. The reason for this effect is not yet certain, but it can be speculated that it is due to the following: By simultaneously containing a predetermined amount of polymer (a) with a glass transition temperature below 25°C and polymer (b) with a glass transition temperature above 30°C in layer B, which serves as the resin layer, the adhesion of the layer B surface to the pigment is reduced at temperatures near room temperature. Therefore, when the incomplete or completed multilayer structure is wound with layer A and layer B in direct contact, adhesion between layer A and layer B can be suppressed, and the adhesion of pigments to layer B can be inhibited. With the adhesion of pigments to layer B suppressed, surface roughness of layer B caused by pigments can also be suppressed, thus exhibiting excellent barrier properties based on layer B. On the other hand, when the content of polymer (b) in layer B is excessive relative to polymer (a), the barrier properties based on polymer (a) that should have been exhibited are sometimes hindered by polymer (b). In a multilayer structure where the content of polymer (b) in layer B is more than 1 part by mass and less than 50 parts by mass relative to 100 parts by mass of polymer (a), the roughness of the surface of layer B can be suppressed, and the effect of polymer (a) can be fully utilized. Therefore, sufficient barrier properties based on layer B can be achieved.

[0033] Figure 1 The multilayer structure 10 shown in one embodiment of the present invention sequentially comprises a layer A 11, a paper substrate 12, a pre-coating layer 13, a barrier layer 14, and a heat-sealing layer 15. In this embodiment of the multilayer structure 10, at least one of the pre-coating layer 13 and the heat-sealing layer 15 is the aforementioned layer B. Both the pre-coating layer 13 and the heat-sealing layer 15 may be layers B. The pre-coating layer 13 and the heat-sealing layer 15 may be layers of the same composition or layers of different compositions.

[0034] Figure 1 The multilayer structure 10 in one embodiment is a five-layer structure consisting only of layer A 11, paper substrate 12, pre-coating layer 13, barrier layer 14, and heat-sealing layer 15. In other embodiments, the multilayer structure may further have other layers. For example, a resin layer, such as an overcoat layer, may be provided between the barrier layer 14 and the heat-sealing layer 15. A pigment layer may be provided between the paper substrate 12 and the pre-coating layer 13. One embodiment of the multilayer structure may be a three-layer structure consisting of layer A, paper substrate, and layer B. For example, in... Figure 1 In the multilayer structure 10, when the pre-coating layer 13 is layer B, the multilayer structure consisting of three layers—layer A 11, paper substrate 12, and pre-coating layer 13—during the manufacturing process of the multilayer structure 10 is also an embodiment of the present invention. Furthermore, the multilayer structure of the present invention may have three or more layers B, for example, it may have a metal layer.

[0035] In one embodiment of the multilayer structure described in this invention, both layer A and layer B may be the outermost layers with one side exposed. For example, other layers may be further laminated on a portion of the surface (exposed surface) of layer A, and printing may also be performed on this layer. Similarly, other layers may be further laminated on a portion of the surface (exposed surface) of layer B, and printing may also be performed on this layer. Hereinafter, each layer of the multilayer structure will be described in detail.

[0036] (Paper substrate)

[0037] The paper substrate can be ordinary paper with plant-derived pulp as the main component. It should be noted that, in this specification, "main component" refers to the component with the highest content by weight. In addition to pulp, the paper substrate may also contain sizing agents, fillers, paper strength enhancers, yield improvers, pH adjusters, water permeability improvers, water-resistant agents, softeners, antistatic agents, defoamers, sludge control agents, dyes, pigments, etc.

[0038] Examples of paper substrates include kraft paper, premium paper, medium-quality paper, alkaline paper, paperboard, cellophane, semi-cellophane, and parchment.

[0039] The basis weight (mass per unit area) of the paper substrate is not particularly limited, but is preferably 20 g / m². 2 Above and 500g / m 2 The following is more preferably 30g / m 2 Above and 300g / m 2 The following is a further preferred value: 40g / m 2 Above and 200g / m 2 the following.

[0040] The preferred density for the paper substrate is 0.5 g / cm³. 3 Above and 1.2g / cm 3 The following is more preferably 0.6 g / cm³ 3 Above and 1.0 g / cm 3 the following.

[0041] Paper substrates can be manufactured using known methods. Alternatively, commercially available products can be used as paper substrates.

[0042] (A floor)

[0043] Layer A is a layer that is laminated to one side of the paper substrate. Layer A can be laminated directly onto the paper substrate or laminated in between other layers.

[0044] Layer A contains pigment. There are no particular limitations on the pigment; known pigments used in coated paper, for example, can be used. The pigment can be organic or inorganic, but inorganic pigments are preferred. Examples of pigments include light calcium carbonate, heavy calcium carbonate, kaolin, calcined kaolin, engineered kaolin, clay, talc, silica, colloidal silica, calcium sulfate, barium sulfate, titanium dioxide, zinc oxide, zinc sulfide, zinc carbonate, satin white, aluminum silicate, calcium silicate, magnesium silicate, aluminum hydroxide, aluminum oxide, magnesium carbonate, magnesium hydroxide, kaolinite, serpentine, montmorillonite, vermiculite, mica, etc. Among these, clay is preferred. One or more pigments can be used.

[0045] The pigment content in layer A is preferably 60% by mass or more and 99% by mass or less, more preferably 70% by mass or more and 95% by mass or less, and can be 75% by mass or more and 90% by mass or less.

[0046] Layer A typically includes both pigments and binders. As the binder, known binders used in coated paper, for example, can be used. Examples of binders include vinyl alcohol polymers, acrylic polymers, cellulose derivatives, starches, styrene polymers, ester polymers, olefin polymers, fluoropolymers, silicone resins, polyvinyl chloride, polyvinyl acetate, polyacrylamide, polyacrylate, polyvinyl butyral, polystyrene, and polyamides. One or more binders can be used.

[0047] The content of the binder in layer A is preferably 1% or more and 40% or less by mass, more preferably 5% or more and 30% or less by mass, and can be 10% or more and 25% or less by mass. The total content of pigment and binder in layer A is preferably 80% or more and 100% or less by mass, and can be 90% or more and 100% or less by mass.

[0048] Layer A may also contain dispersants, viscosity modifiers, water-retaining agents, defoamers, water-resistant agents, fluorescent dyes, coloring dyes, surfactants, pH adjusters, ultraviolet absorbers, metal salts, and other components other than pigments and binders.

[0049] (Level B)

[0050] Layer B is a layer laminated on the side of the paper substrate opposite to the side where layer A is laminated. Layer B can be laminated directly onto the paper substrate or with the aid of other layers. For example, as mentioned above, layer B can be a pre-coating layer disposed between the paper substrate and the barrier layer, or it can be a heat-sealing layer. Layer B can be a single layer or two or more layers.

[0051] Layer B comprises polymers (a) with a glass transition temperature below 25°C and polymers (b) with a glass transition temperature above 30°C. When polymer (a) is composed of two or more polymers, each polymer has a glass transition temperature below 25°C. Similarly, when polymer (b) is composed of two or more polymers, each polymer has a glass transition temperature above 30°C. In other words, all polymers contained in Layer B are classified as polymers (a) with a glass transition temperature below 25°C, polymers (b) with a glass transition temperature above 30°C, and polymers with a glass transition temperature exceeding 25°C but below 30°C. It should be noted that polymers with a glass transition temperature exceeding 25°C but below 30°C are arbitrary components.

[0052] The glass transition temperature of the polymer was determined by differential scanning calorimetry (DSC). Specifically, it was determined by the method described in the examples.

[0053] (Polymer(a))

[0054] The upper limit of the glass transition temperature of polymer (a) is 25°C, preferably 20°C, more preferably 15°C, further preferably 10°C, and even more preferably 5°C. By setting the glass transition temperature of polymer (a) below the above-mentioned upper limit, layer B can exhibit good flexural strength, interlayer adhesion, etc. In addition, when layer B is a heat-sealing layer, it can also exhibit good heat-sealing properties. The lower limit of the glass transition temperature of polymer (a) is not particularly limited, and for example, it can be -150°C, -100°C, -50°C, or -15°C.

[0055] As for polymer (a), there is no particular limitation as long as it is a polymer with a glass transition temperature of 25°C or below. Preferably, it includes at least one selected from styrene-based polymers, modified olefin polymers, and ester polymers. More preferably, it includes at least one selected from styrene-based polymers, modified olefin polymers, and ester polymers. By using such polymer as polymer (a), layer B can exhibit good water vapor barrier properties, etc. One or more polymers (a) can be used.

[0056] (Styrene-based polymers)

[0057] Styrene-based polymers are polymers containing styrene-based compounds as monomers. Styrene-based compounds refer to styrene and compounds in which the hydrogen atoms of styrene are replaced by other atoms or other groups. Examples of styrene-based compounds include styrene, α-methylstyrene, vinyltoluene, and chlorostyrene, with styrene being preferred.

[0058] Examples of styrene-based polymers include polystyrene, styrene-acrylic copolymers, and styrene-butadiene copolymers.

[0059] Styrene-acrylic copolymers are copolymers of the aforementioned styrene compounds and acrylic compounds. Acrylic compounds refer to (meth)acrylic acid and compounds in which the hydrogen atoms of the carboxyl groups constituting (meth)acrylic acid are replaced by other atoms or other groups. Examples of acrylic compounds include (meth)acrylic acid, (meth)acrylates, and (meth)acrylate salts. Examples of (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, and other alkyl (meth)acrylates. Examples of (meth)acrylate salts include sodium (meth)acrylate. It should be noted that "(meth)acrylic acid" refers to both acrylic acid and methacrylic acid.

[0060] Examples of styrene-acrylic acid copolymers include styrene-(meth)acrylic acid copolymers, styrene-(meth)acrylate copolymers, and styrene-(meth)acrylate copolymers. Styrene-acrylic acid copolymers can be further copolymerized with other monomers.

[0061] Styrene-butadiene copolymers are copolymers of the aforementioned styrene compounds and butadiene compounds. Butadiene compounds refer to butadiene and compounds in which the hydrogen atoms of butadiene are replaced by other atoms or other groups. Examples of butadiene compounds include 1,3-butadiene, 2-methyl-1,3-butadiene (i.e., isoprene), 2,3-dimethyl-1,3-butadiene, and 1,3-pentadiene, with 1,3-butadiene being preferred.

[0062] As a styrene-butadiene copolymer, a styrene-butadiene copolymer is preferred. The styrene-butadiene copolymer may be further copolymerized with other monomers.

[0063] As a styrene-based polymer, a styrene-butanediene copolymer is preferred.

[0064] (Modified olefin polymers)

[0065] Modified olefin polymers are polymers containing olefins and other monomers as monomers. Modified olefin polymers can be copolymers of olefins and other monomers, or substances obtained by post-modifying polyolefins with other monomers. Modified olefin polymers are preferably copolymers of olefins and other monomers.

[0066] Examples of olefins include ethylene, propylene, n-butene, isobutene, and other α-olefins, with ethylene being the preferred choice.

[0067] Other monomers besides olefins that constitute the modified olefin polymer can include unsaturated carboxylic acid compounds, diene compounds, vinyl esters, vinyl ethers, halogenated ethylene, unsymmetrical dihalogenated ethylene, allyl compounds, etc., preferably unsaturated carboxylic acid compounds or vinyl esters, more preferably unsaturated carboxylic acid compounds.

[0068] Unsaturated carboxylic acid compounds refer to compounds in which the hydrogen atoms of the unsaturated carboxylic acid and the carboxyl group constituting the unsaturated carboxylic acid are replaced by other atoms or other groups. That is, unsaturated carboxylic acid compounds include not only unsaturated carboxylic acids but also unsaturated carboxylic acid esters, unsaturated carboxylates, and unsaturated carboxylic anhydrides. Unsaturated carboxylic acid compounds are preferably monomers or salts containing a carboxyl group.

[0069] As unsaturated carboxylic acid compounds, examples 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 esters such as (meth)acrylate, (meth)acrylate, (meth)acrylate monoethyl ester, itaconic acid monobutyl ester, and fumarate monobutyl ester; unsaturated carboxylic acid salts such as (meth)acrylate sodium; and unsaturated carboxylic anhydrides such as maleic anhydride.

[0070] Examples of vinyl esters include vinyl acetate, vinyl formate, vinyl propionate, vinyl valerate, vinyl decanoate, vinyl laurate, vinyl stearate, vinyl neovalerate, and vinyl tert-carbonate, with vinyl acetate being the preferred choice.

[0071] As modified olefin polymers, olefin-unsaturated carboxylic acid copolymers or olefin-vinyl ester copolymers are preferred, with olefin-unsaturated carboxylic acid copolymers being more preferred. An olefin-unsaturated carboxylic acid copolymer refers to a copolymer of one or more olefins with one or more unsaturated carboxylic acid compounds. An olefin-vinyl ester copolymer refers to a copolymer of one or more olefins with one or more vinyl esters. Olefin-unsaturated carboxylic acid copolymers can also be called carboxylic acid-modified polyolefins. Carboxylic acid-modified polyolefins can be polyolefins with carboxyl groups introduced. As modified olefin polymers, saponifications of olefin-vinyl ester copolymers can also be used.

[0072] As an olefin-unsaturated carboxylic acid copolymer, a copolymer of ethylene and an unsaturated carboxylic acid compound is preferred, and a copolymer of ethylene and an unsaturated carboxylic acid or an unsaturated carboxylic anhydride is more preferred. The copolymer of ethylene and an unsaturated carboxylic acid or an unsaturated carboxylic anhydride can be called carboxylic acid-modified polyethylene. Carboxylic acid-modified polyethylene can be polyethylene with carboxyl groups introduced into it.

[0073] As an olefin-vinyl ester copolymer, it is preferably an ethylene-vinyl acetate copolymer.

[0074] The content of olefin units in modified olefin polymers relative to all monomer units can be more than 10 mol% and less than 99 mol%, or more than 30 mol% and less than 95 mol%.

[0075] (Ester polymers)

[0076] Ester polymers are polymers formed by the polymerization of one or more monomers via ester bonds. Examples of ester polymers include polyethylene terephthalate, polybutylene terephthalate, polypropylene terephthalate, polyethylene naphthalate, polyglycolic acid, and aromatic liquid crystal polyesters. Additionally, ester polymers can be biodegradable. Examples of biodegradable ester polymers include polyethylene succinate, polybutylene succinate, polybutylene adipate succinate, polybutylene lactate succinate, polybutylene adipate terephthalate, poly-3-hydroxybutyric acid, and poly-3-hydroxybutyrate-3-hydroxyhexanoate.

[0077] From the viewpoint of water vapor barrier properties and anti-blocking properties, the polymer (a) is preferably a styrene-based polymer or a modified olefin-based polymer, more preferably a styrene-based polymer, even more preferably a styrene-butadiene copolymer, and particularly preferably a styrene-butadiene copolymer.

[0078] Polymer (a) is preferably a water-soluble or water-dispersible polymer. In this case, a coating solution using water as a solvent or dispersion medium can be used to efficiently form layer B. Examples of water-soluble or water-dispersible polymers include styrene-acrylic acid copolymers, styrene-butadiene copolymers, olefin-unsaturated carboxylic acid copolymers, and olefin-vinyl ester copolymers. Alternatively, known polymers sold in the form of water-soluble or water-dispersible polymers can be used.

[0079] The lower limit for the content of polymer (a) in layer B is preferably 20% by mass, more preferably 40% by mass, even more preferably 60% by mass, and even more preferably 65% ​​by mass. It can be 70% by mass, 75% by mass, or 80% by mass. By setting the content of polymer (a) to the above-mentioned lower limit or above, barrier properties (e.g., water vapor barrier properties), flexural strength, etc., can be improved. In addition, when layer B is a heat-sealing layer, heat-sealing properties can also be improved. On the other hand, the upper limit for this content is preferably 99% by mass, more preferably 95% by mass, even more preferably 92% by mass, and even more preferably 85% by mass.

[0080] (Polymer(b))

[0081] The lower limit of the glass transition temperature of polymer (b) is 30°C, preferably 40°C, more preferably 50°C, and even more preferably 60°C. By setting the glass transition temperature of polymer (b) to a value above the aforementioned lower limit, the adhesion between layer B and layer A under normal temperature conditions is reduced, and the adhesion between layer A and layer B is suppressed. As a result, the adhesion of pigment to layer B can be suppressed. The upper limit of the glass transition temperature of polymer (b) is not particularly limited, and can be, for example, 200°C, 150°C, or 100°C.

[0082] Polymer (b) is preferably a water-soluble or water-dispersible polymer, more preferably a water-soluble polymer. It is particularly preferred that both polymer (a) and polymer (b) are water-soluble or water-dispersible polymers. In this case, the B layer can be formed efficiently using a coating solution with water as a solvent or dispersion medium. Examples of water-soluble polymers (b) include vinyl alcohol-based polymers and starch-based polymers.

[0083] As for polymer (b), there are no particular limitations as long as it is a polymer with a glass transition temperature of 30°C or higher. As mentioned above, a polymer that is water-soluble or water-dispersible is preferred, and a vinyl alcohol-based polymer is more preferred. By using a vinyl alcohol-based polymer as polymer (b), advantages such as improved film-forming properties and imparted toughness are achieved. One or more polymers (b) can be used.

[0084] (Vinyl alcohol polymers)

[0085] Vinyl alcohol polymers are polymers having vinyl alcohol units (-CH2-CHOH-). Vinyl alcohol polymers are typically obtained by saponification of vinyl ester polymers. Examples of vinyl esters constituting vinyl ester polymers include various vinyl esters described above that are monomers other than olefins constituting modified olefin polymers, with vinyl acetate being preferred.

[0086] The lower limit of the degree of saponification of the vinyl alcohol polymer can be, for example, 60 mol%, preferably 80 mol%, more preferably 90 mol%, and even more preferably 95 mol%. The degree of saponification of the vinyl alcohol polymer is further preferably greater than 96 mol%, more preferably greater than 97.0 mol%, greater than 97.5 mol%, or greater than 98.0 mol%. By setting the degree of saponification of the vinyl alcohol polymer to or above the above lower limit, the hygroscopicity is reduced, and adhesion between layer A and layer B under high humidity can be effectively suppressed. The upper limit of the degree of saponification of the vinyl alcohol polymer can be 100 mol%, or 99.9 mol%. The degree of saponification of the vinyl alcohol polymer is determined according to JIS K 6726:1994.

[0087] The lower limit of the viscosity-uniform polymerization degree of the vinyl alcohol-based polymer is preferably 200, more preferably 300, further preferably 500, and even more preferably 800. The upper limit of the viscosity-uniform polymerization degree is preferably 3,000, more preferably 2,500, and even more preferably 2,000. By making the viscosity-uniform polymerization degree of the vinyl alcohol-based polymer above or above the above lower limit, the adhesion resistance of the B layer is improved, the adhesion of pigments to the B layer is further suppressed, and the film-forming properties are improved, thus imparting toughness. By making the viscosity-uniform polymerization degree of the vinyl alcohol-based copolymer below or below the above upper limit, molding processability is imparted, for example, when prepared as an aqueous solution and coated onto a paper substrate, coating can be performed at a suitable viscosity.

[0088] The viscosity-uniform degree of polymerization of vinyl alcohol polymers was determined according to JIS K 6726:1994. Specifically, the intrinsic viscosity [η] (L / g) of the vinyl alcohol polymer was measured in water at 30°C, and the viscosity-uniform degree of polymerization P was calculated using the following formula based on the intrinsic viscosity [η]. It should be noted that when the degree of saponification of the vinyl alcohol polymer is less than 99.5 mol%, the intrinsic viscosity [η] was measured after saponification to a degree of saponification of 99.5 mol% or higher.

[0089] P=([η]×10 4 / 8.29) (1 / 0.62)

[0090] Vinyl alcohol polymers can have monomer units derived from other monomers besides vinyl alcohol and vinyl ester units. Examples of other monomers include α-olefins such as ethylene, propylene, n-butene, and isobutene; (meth)acrylic acid and its salts; (meth)acrylates; (meth)acrylamide; N-methyl (meth)acrylamide, N-ethyl (meth)acrylamide, N,N-dimethyl (meth)acrylamide, diacetone (meth)acrylamide, (meth)acrylamide propane sulfonic acid and its salts, (meth)acrylamide propyl dimethylamine and its salts or quaternary salts, N-hydroxymethyl (meth)acrylamide and its derivatives, and other (meth)acrylamide derivatives; methyl vinyl ethers. Vinyl ethers such as ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, tert-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether, etc.; nitriles such as acrylonitrile and methacrylonitrile; halogenated vinylides such as vinyl chloride and fluorovinyl chloride; vinylidene halogenated vinylides such as vinylidene chloride and vinylidene fluoride; allyl acetate, allyl chloride, and other allyl compounds; unsaturated dicarboxylic acids such as maleic acid, itaconic acid, fumaric acid, and their salts or esters; vinyl silyl compounds such as vinyltrimethoxysilane; isopropyl acetate, etc.

[0091] The other monomers optionally included in the vinyl alcohol polymer can be α-olefins or ethylene. When the vinyl alcohol polymer contains α-olefin units, the lower limit of the content of α-olefin units relative to all monomer units in the vinyl alcohol polymer can be 0.1 mol%, or 0.5 mol%, 1 mol%, 2 mol%, 3 mol%, or 4 mol%. On the other hand, the upper limit of this content can be 20 mol%, or 15 mol%, 12 mol%, 10 mol%, 5 mol%, or 3 mol%. It should be noted that the content of α-olefin units relative to all monomer units is also referred to as the α-olefin modification amount. For example, the content of ethylene units relative to all monomer units is also referred to as the ethylene modification amount.

[0092] The total content of vinyl alcohol units and vinyl ester units in the vinyl alcohol-based polymer relative to all monomer units is preferably 80 mol% or more, more preferably 90 mol% or more, and can be 95 mol% or more, 98 mol% or more, 99 mol% or more, or 100 mol%. The total content of vinyl alcohol units, vinyl ester units, and any α-olefin units in the vinyl alcohol-based polymer relative to all monomer units is preferably 95 mol% or more, more preferably 99 mol% or more, and can be 100 mol%.

[0093] The lower limit of the content of polymer (b) relative to polymer (a) per 100 parts by mass is 1 part by mass, preferably 5 parts by mass, more preferably 10 parts by mass, even more preferably 20 parts by mass, and can be 30 parts by mass. By setting the content of polymer (b) relative to polymer (a) to the above-mentioned lower limit or above, the adhesion of pigment to layer B is suppressed, resulting in good barrier properties. The upper limit of the content of polymer (b) relative to polymer (a) per 100 parts by mass is 50 parts by mass, and can be 45 parts by mass, 40 parts by mass, 35 parts by mass, or 30 parts by mass. By setting the content of polymer (b) relative to polymer (a) to the above-mentioned upper limit or below, barrier properties (e.g., water vapor barrier properties) can be improved.

[0094] The lower limit for the content of polymer (b) in layer B is preferably 1% by mass, more preferably 5% by mass, even more preferably 8% by mass, even more preferably 10% by mass, even more preferably 12% by mass, and can be 15% by mass or 20% by mass. By setting the content of polymer (b) in layer B to the above-mentioned lower limit or above, the adhesion of pigment to layer B is further suppressed, and as a result, the barrier properties can also be improved. On the other hand, the upper limit for this content is preferably 33% by mass, more preferably 30% by mass, and can be 25% by mass or 20% by mass. By setting the content of polymer (b) in layer B to the above-mentioned upper limit or below, the barrier properties (e.g., water vapor barrier properties) can be improved.

[0095] The lower limit for the total content of polymer (a) and polymer (b) in layer B is sometimes preferably 20% by mass, more preferably 40% by mass, even more preferably 60% by mass, and even more preferably 80% by mass, 90% by mass, 95% by mass, 98% by mass, or 99% by mass. By making the total content of polymer (a) and polymer (b) in layer B above the above-mentioned lower limit, there is a tendency to particularly effectively utilize the advantages of using polymer (a) and polymer (b) in layer B, and to achieve excellent bending resistance and barrier properties. The upper limit for the total content of polymer (a) and polymer (b) in layer B can be 100% by mass, or 99.9% by mass or 99% by mass.

[0096] Layer B may also contain other components besides polymer (a) and polymer (b). Examples of such other components include polymers other than polymer (a) and polymer (b), layered inorganic compounds, surfactants, wetting agents, oil repellents, defoamers, dyes, thickeners, etc. Surfactants can be emulsifiers.

[0097] For example, when layer B contains layered inorganic compounds, the barrier properties of the multilayer structure are sometimes further improved. Examples of layered inorganic compounds include mica, talc, montmorillonite, kaolinite, vermiculite, montmorillonite, lithium montmorillonite, mica-bearing clay, etc. When layer B contains layered inorganic compounds, the content of these compounds in layer B can be set to, for example, 1% by mass or more and 80% by mass or less. However, a high content of layered inorganic compounds in layer B can sometimes reduce flexural strength, causing cracking in layer B itself or other layers (e.g., barrier layers) in direct contact with layer B due to bending. Therefore, the upper limit of the content of layered inorganic compounds in layer B is sometimes preferably 50% by mass, 30% by mass, 10% by mass, 5% by mass, or 1% by mass. In one embodiment of the present invention, layer B may not contain layered inorganic compounds.

[0098] The lower limit of the mass per unit area of ​​layer B is preferably 1 g / m². 2 More preferably 2g / m 2 Further preferred is 3g / m 2 A further preferred value is 5g / m 2 By ensuring that the mass per unit area of ​​the first B layer is at or above the aforementioned lower limit, barrier properties and heat-sealing properties when used as a heat-sealing layer can be improved. The preferred upper limit for the mass per unit area of ​​the first B layer is 100 g / m². 2 More preferably 50g / m 2 More preferably 30g / m 2 A further preferred value is 20g / m 2By keeping the mass per unit area of ​​layer B below the aforementioned upper limit, it is possible to achieve thin-film and lightweight multilayer structures.

[0099] (Pre-coating)

[0100] The pre-coating layer can be layer B as described above. Alternatively, if other layers such as the heat-sealing layer are layer B, the pre-coating layer may not be layer B. When the pre-coating layer is not layer B, it can be made into a layer composed, for example, of polymer (a) and other optional components. In the pre-coating layer that is not layer B, polymer (a) can be the main component. The specific and suitable forms of the polymer (a) included in the pre-coating layer that is not layer B are the same as the specific and suitable forms of the polymer (a) included in layer B.

[0101] The preferred lower limit for the mass per unit area of ​​the pre-coating is 1 g / m². 2 More preferably 2g / m 2 Further preferred is 3g / m 2 A further preferred value is 5g / m 2 By ensuring that the mass per unit area of ​​the pre-coating is at or above the aforementioned lower limit, barrier properties can be improved. The preferred upper limit for the mass per unit area of ​​the pre-coating is 100 g / m². 2 More preferably 50g / m 2 More preferably 30g / m 2 A further preferred value is 20g / m 2 By keeping the mass per unit area of ​​the pre-coated layer below the aforementioned upper limit, it is possible to achieve thin-film and lightweighting of multilayer structures.

[0102] (Barrier layer)

[0103] The barrier layer is typically a layer that inhibits the permeation of gases and water vapor, and preferably a layer that inhibits the permeation of oxygen and water vapor. That is, the barrier layer is preferably an oxygen barrier layer or a water vapor barrier layer. Examples of barrier layers include metal films such as aluminum; inorganic oxide films such as alumina and silicon oxide; and polymer films. Metal films and inorganic oxide films can be vapor-deposited films or foils. The barrier layer may contain one of these layers or two or more layers of different types. Polymer films preferably contain a water-soluble polymer, and more preferably contain a water-soluble polymer as a main component.

[0104] Examples of water-soluble polymers include vinyl alcohol polymers, starches, cellulose derivatives, polyvinylpyrrolidone, urethane resins, polyacrylic acid and its salts, casein, and polyethyleneimine. Among these, the polymer used as the barrier layer is preferably a vinyl alcohol polymer or a urethane resin, and more preferably a vinyl alcohol polymer. The specific and suitable forms of the vinyl alcohol polymers that can be used in the barrier layer are the same as those of the vinyl alcohol polymers listed as an example of polymer (b) in layer B.

[0105] The lower limit for the content of water-soluble polymer in the polymer membrane is preferably 70% by mass, more preferably 80% by mass, and even more preferably 90% by mass. The upper limit for this content can be 100% by mass.

[0106] Polymer membranes may also contain other components besides water-soluble polymers. Examples of such other components include polymers other than water-soluble polymers, layered inorganic compounds, dispersants, surfactants, defoamers, dyes, thickeners, etc.

[0107] The lower limit of the mass per unit area of ​​the barrier layer is preferably 0.3 g / m². 2 More preferably 0.5 g / m 2 Further preferred is 1g / m 2 By ensuring that the mass per unit area of ​​the barrier layer is above the aforementioned lower limit, barrier properties can be improved. The upper limit of the mass per unit area of ​​the barrier layer is sometimes preferably 20 g / m². 2 More preferably 10g / m 2 Further preferred is 5g / m 2 A further preferred value is 3g / m 2 By keeping the mass per unit area of ​​the barrier layer below the aforementioned upper limit, it is possible to achieve thinner multilayer structures, etc.

[0108] (Heat-sealing layer)

[0109] The heat-sealing layer can be layer B as described above. It should be noted that when the heat-sealing layer contains a vinyl alcohol-based polymer as polymer (b), it offers a further advantage in suppressing heat-sealing layer breakage. This can be attributed to the increased affinity between the barrier layer and the heat-sealing layer when a water-soluble polymer is included, reducing the likelihood of rejection of the coating liquid used to apply the heat-sealing layer. With heat-sealing layer breakage suppressed, heat-sealing properties and barrier properties are further improved. Furthermore, in the reuse of multilayer structures, the paper substrate and resin layer are sometimes separated. When peeling the heat-sealing layer from the multilayer structure, fewer breakages in the heat-sealing layer also offer the advantages of easy peeling and improved reusability.

[0110] When other layers, such as the pre-coating layer, are layer B, the heat-sealing layer may not be layer B. As a heat-sealing layer that is not layer B, it can be made into a layer composed, for example, of polymer (a) and other optional components. In a heat-sealing layer that is not layer B, polymer (a) can be the main component. The specific and suitable forms of the polymer (a) included in the heat-sealing layer that is not layer B are the same as the specific and suitable forms of the polymer (a) included in layer B.

[0111] The lower limit of the mass per unit area of ​​the heat-sealing layer is preferably 1 g / m². 2 More preferably 2g / m 2 Further preferred is 3g / m 2 A further preferred value is 5g / m 2 By ensuring that the mass per unit area of ​​the heat-sealing layer is above the aforementioned lower limit, heat-sealing properties and barrier properties can be improved. The preferred upper limit for the mass per unit area of ​​the heat-sealing layer is 100 g / m². 2 More preferably 50g / m 2 More preferably 30g / m 2 A further preferred value is 20g / m 2 By keeping the mass per unit area of ​​the heat-sealing layer below the aforementioned upper limit, it is possible to achieve thin-film and lightweight multilayer structures.

[0112] (Uses, etc.)

[0113] The multi-layer structure described in one embodiment of the present invention can be suitable for use as packaging material, etc.

[0114] The shape and size of the multilayer structure described in one embodiment of the present invention are not particularly limited. The multilayer structure can be sheet-like or molded into a predetermined shape. The multilayer structure can be a long strip. For example, the lower limit of the length of the multilayer structure can be 5m, 10m, 50m, or 100m. The upper limit of the length can be, for example, 1,000,000m or 100,000m. The lower limit of the width of the multilayer structure can be, for example, 30cm or 50cm. The upper limit of the width can be, for example, 10m or 5m. Generally, the longer the multilayer structure, the easier it is for the surfaces in contact during winding to adhere tightly, and the easier it is for pigment to adhere to the resin layer during winding when the pigment layer and resin layer are in contact. Therefore, when the present invention is applied to such a long strip multilayer structure, the advantages of inhibiting pigment adhesion to the resin layer and having good barrier properties can be obtained particularly effectively.

[0115] When the multi-layer structure has heat-sealing layers, it can also be used in a state where the heat-sealing layers are heat-sealed together to form a predetermined shape (e.g., a bag). There are no particular limitations on the heat-sealing method; known methods can be used, such as hot plate heat sealers, pulse sealers, ultrasonic sealers, friction heat sealers, dielectric heating sealers, etc.

[0116] (Manufacturing method for multi-layered structures)

[0117] The method for manufacturing a multilayer structure according to one embodiment of the present invention is not particularly limited, and can be manufactured, for example, by applying coatings to a paper substrate to form each layer. Alternatively, commercially available coated paper with layer A on one side of the paper substrate can be purchased and used. By applying layer B, etc., to such coated paper, a multilayer structure can also be manufactured. As an example, Figure 1 The manufacturing of the multilayer structure 10 can be performed according to the following steps. For a coated paper consisting of layer A 11 and paper substrate 12, a pre-coating liquid for forming a pre-coating layer is applied to the exposed surface of the paper substrate 12 and dried to form a pre-coating layer 13. Next, a barrier layer 14 is formed by applying a barrier layer forming liquid to the surface of the pre-coating layer 13 and drying it. Next, a heat-sealing layer 15 is formed by applying a heat-sealing layer forming liquid to the surface of the barrier layer 14 and drying it. After each layer is formed, a process can be performed to roll up the unfinished or completed strip of the multilayer structure to form a roll. In addition, drying may not be performed during each application of the coating liquid, and a simultaneous multilayer coating method can be used.

[0118] The coating of each coating liquid can be carried out using existing known methods. Coating can be carried out using, for example, scraper coating machines, bar coating machines, air knife coating machines, slot die coating machines, gravure coating machines, micro-gravure coating machines, roller coating machines, curtain coating machines, offset coating machines, comma coating machines, etc.

[0119] There are no particular limitations on the method for drying the applied coating liquid; for example, a hot air dryer, an infrared dryer, a gas spray gun, or a heating plate can be used.

[0120] There are no particular limitations on the solvent or dispersion medium used to form the coating liquid for each layer; water, organic solvents (ethanol, isopropanol, methyl ethyl ketone, toluene, etc.) can be used, with water being preferred.

[0121] There is no particular limitation on the amount of solid components (solid component concentration) used in the coating liquid to form each layer. For example, it can be set to 3% or more by mass and 70% or less by mass, or 5% or more by mass and 60% or less by mass, or 10% or more by mass and 50% or less by mass.

[0122] <Roll-shaped structure>

[0123] The rolled structure described in one embodiment of the present invention is a rolled structure formed by winding the multi-layer structure described in one embodiment of the present invention, with layer A and layer B in direct contact. Unfinished or completed long strips of multi-layer structures are sometimes also stored in a rolled state. For example, […]. Figure 1 When the multi-layer structure 10 shown is wound into a roll structure, layer A 11, which is the outermost layer, is in direct contact with the heat-sealing layer 15, which is the other outermost layer. When the heat-sealing layer 15 is layer B, layer A and layer B are in direct contact. Furthermore, ... Figure 1 During the manufacturing process of the multilayer structure shown, when the multilayer structure consisting of layer A 11, paper substrate 12, and pre-coating layer 13 is wound into a roll structure, layer A 11, which is the outermost layer, is in direct contact with the pre-coating layer 13, which is the other outermost layer. When the pre-coating layer 13 is layer B, layer A and layer B are in direct contact.

[0124] In one embodiment of the present invention, the roll-shaped structure, even though layer A, which is the pigment layer, is in direct contact with layer B, which is the resin layer, still inhibits the adhesion of pigment to the resin layer (i.e., layer B), and the multilayer structure has good barrier properties. Therefore, by employing this roll-shaped structure, multilayer structures can be manufactured and stored efficiently.

[0125] Packaging Materials

[0126] The packaging material described in one embodiment of the present invention may comprise or be composed of the multi-layer structure described in one embodiment of the present invention.

[0127] This packaging material inhibits pigment adhesion to the resin layer, thus providing a good appearance and excellent barrier properties. It is typically used with the A-layer side (based on the paper substrate) as the outermost side. The material can be formed into a specified shape through heat sealing or similar methods. It is suitable for use as packaging for products such as food, pesticides, pharmaceuticals, cosmetics, medical products, electronic components, and clothing.

[0128] Example

[0129] The present invention will be described in more detail below using examples, but the present invention is not limited to these examples at all.

[0130] (Method for determining glass transition temperature (Tg))

[0131] The glass transition temperature of the polymer was determined by the following method.

[0132] Approximately 3 mg of the sample was filled into a sample dish, and the glass transition temperature and melting point were determined using a DSC Q2000 instrument (manufactured by TA Instruments, Inc.). The sample was heated from 30°C to 200°C, then cooled to -90°C and held for 5 minutes before being heated back to 200°C. Both heating and cooling were performed at a rate of 10°C / minute.

[0133] [Manufacturing Example 1] Manufacturing of PVA-1

[0134] 1,050 g of vinyl acetate and 1,950 g of methanol were added to a reaction vessel equipped with a stirrer, a nitrogen inlet, and an initiator addition port. After heating to 60°C, the system was purged with nitrogen by bubbling for 30 minutes. The temperature in the reaction vessel was then adjusted to 60°C, and 1.6 g of azobisisobutyronitrile (AIBN) as a polymerization initiator was added to begin polymerization. After 3 hours, when the polymerization rate reached 50%, the polymerization was stopped by cooling. Unreacted vinyl acetate monomers were removed, and methanol was added to obtain a methanol solution of polyvinyl acetate (PVAc) (concentration 30% by mass). 55.8 g of a 10% methanol solution of NaOH was added to 400 g of this PVAc methanol solution (containing 120 g of PVAc in the solution), with the molar ratio of NaOH to vinyl acetate units in the PVAc [MR] being 0.10, and saponification was carried out at 40°C. After adding NaOH methanol solution, gelation was performed, and the resulting substance was pulverized and subjected to a saponification reaction for a total of 1 hour. Subsequently, 1,000 g of methyl acetate was added to neutralize the residual alkali. Phenolphthalein indicator was used to confirm the completion of neutralization, followed by filtration. 1,000 g of methanol was added to the resulting white solid, and the mixture was left to wash at room temperature for 3 hours. This washing process was repeated three times, followed by centrifugation to remove the liquid. The resulting solid was dried in a dryer at 70°C for 2 days to obtain the vinyl alcohol polymer (PVA-1).

[0135] [Manufacturing Example 2] Manufacturing of PVA-2

[0136] 2,550 g of vinyl acetate and 450 g of methanol were added to a 5 L pressurized reactor equipped with a stirrer, nitrogen inlet, ethylene inlet, and initiator addition port. After heating to 60 °C, the system was purged with nitrogen by bubbling for 30 minutes. Then, the reactor pressure was adjusted to 2.9 kg / cm³. 2 Ethylene was introduced in the following manner. After adjusting the temperature in the reaction tank to 60°C, 1.0 g of AIBN as a polymerization initiator was added to begin polymerization. Ethylene was introduced during polymerization, and the pressure in the reaction tank was maintained at 2.9 kg / cm². 2The polymerization temperature was maintained at 60°C. After 3 hours, when the polymerization rate reached 20%, the polymerization was stopped by cooling. After removing ethylene by opening the reaction tank, nitrogen gas was further purged. Then, unreacted vinyl acetate monomers were removed under reduced pressure, and methanol was added to obtain a methanol solution of ethylene-vinyl acetate copolymer (concentration 20% by mass). 14.9 g of a 10% methanol solution of NaOH was added to 400 g of this methanol solution of ethylene-vinyl acetate copolymer (80 g of ethylene-vinyl acetate copolymer in the solution) (the molar ratio of NaOH to vinyl acetate units in the ethylene-vinyl acetate copolymer [MR] was 0.04), and saponification was carried out at 40°C. After adding the NaOH methanol solution, gelation was performed, and the resulting material was pulverized and subjected to a saponification reaction for a total of 1 hour. Subsequently, 1,000 g of methyl acetate was added to neutralize the residual alkali. After confirming the neutralization was complete using phenolphthalein indicator, the mixture was filtered, and 1,000 g of methanol was added to the resulting white solid, which was then washed at room temperature for 3 hours. After repeating the above cleaning operation three times, centrifugation was performed to remove the liquid. The resulting solid was placed in a dryer at 70°C for 2 days to obtain ethylene-modified vinyl alcohol polymer (PVA-2).

[0137] [Manufacturing Examples 3-4] Manufacturing of PVA-3 to PVA-4

[0138] Regarding the polymerization and saponification conditions listed in Table 1, they are set as shown in Table 1. Except for this, each ethylene-modified vinyl alcohol polymer (PVA-3 to PVA-4) is manufactured by the same method as in Manufacturing Example 2.

[0139] The viscosity-uniform polymerization degree, saponification degree, ethylene modification amount (ethylene unit content), and glass transition temperature (Tg) of PVA-1 to PVA-4 were determined. The results are shown in Table 1.

[0140]

[0141] (Evaluation of anti-adhesion properties) [Example 1]

[0142] A coating liquid was prepared comprising 90% by mass of styrene-based polymer-1 (styrene-butadiene copolymer with Tg of 3°C) as polymer (a) and 10% by mass of PVA-1 as polymer (b) as solid components. Additionally, clay-coated paper (Bladepak, manufactured by Twin Rivers Paper Company) was prepared, on one side of a paper substrate having a clay coating layer as layer A. The exposed surface of the clay-coated paper on the paper substrate was dried to a weight of 10 g / m². 2The above coating liquid was applied in a certain amount and dried to form layer B, thus obtaining a multilayer structure. The adhesion resistance after overlapping the clay-coated surface (layer A) with the surface of layer B and applying pressure of 1 MPa was evaluated according to the following criteria. The results are shown in Table 2.

[0143] A: The layers are easy to peel off.

[0144] B: Slight adhesion between layers, but peeling occurs.

[0145] C: The layers are slightly difficult to peel off.

[0146] D: No delamination occurs between layers, and the paper substrate is damaged.

[0147] [Examples 2-8, Comparative Examples 1 and 2]

[0148] As described in Table 2, the types and amounts of polymers used as solid components in the coating liquid were set. Otherwise, the same procedure as in Example 1 was followed to obtain multilayer structures, and their anti-blocking properties were evaluated. The results are shown in Table 2. It should be noted that the polymers(a) listed in Table 2 and Table 3 (described later) are all commercially available products.

[0149] Styrene-based polymer-1: Styrene-butadiene copolymer with a Tg of 3℃

[0150] Modified olefin polymer-1: Carboxylic acid modified polyethylene with a Tg of -23℃

[0151] Modified olefin polymer-2: Carboxylic acid modified polyethylene with a Tg of -46℃

[0152]

[0153] [Example 9]

[0154] A clay-coated paper ("Bladepak" manufactured by Twin Rivers Paper Company) is prepared, with a clay coating layer as layer A on one side of the paper substrate.

[0155] A pre-coating forming coating liquid was prepared, comprising 190% by mass of a styrene-based polymer (a) and 110% by mass of PVA (b) as solid components. Using a gravure coating machine, the coating was applied to the exposed surface of a clay-coated paper substrate with a dry weight of 10 g / m². 2A coating liquid for forming a pre-coating layer is applied and dried to establish a pre-coating layer, which serves as layer B. The resulting multilayer structure (layer A / paper substrate / pre-coating layer) is then wound into a roll. Subsequently, the multilayer structure is extracted from the roll, and the surface of the pre-coating layer is observed using SEM (scanning electron microscopy). No pigment adhesion was confirmed.

[0156] A coating solution for forming a barrier layer, containing only PVA-1 as a solid component, was prepared. Using a gravure coating machine, the solution was applied to the pre-coated surface at a dry mass of 2 g / m². 2 The coating liquid for forming the barrier layer is applied in a certain amount and then dried to form the barrier layer. The resulting multilayer structure (A layer / paper substrate / pre-coating layer / barrier layer) is wound up and formed into a roll structure, and then the multilayer structure is extracted from the roll structure.

[0157] A coating liquid for heat-sealing layer formation was prepared, comprising 190% by mass of a styrene-based polymer (a) and 110% by mass of PVA (b) as solid components. A gravure coating machine was used to coat the surface of the barrier layer with a dry mass of 10 g / m². 2 A coating liquid for forming the heat-seal layer is applied in a certain amount and allowed to dry, thereby setting the heat-seal layer as layer B. The resulting multilayer structure (layer A / paper substrate / pre-coating / barrier layer / heat-seal layer) is wound up to form a roll structure. Subsequently, the multilayer structure is extracted from the roll structure, and the surface of the heat-seal layer is observed using SEM (scanning electron microscope). No pigment adhesion was confirmed.

[0158] For the multilayer structure (layer A / paper substrate / pre-coating / barrier layer / heat-sealing layer) of Example 9, the moisture permeability was measured at 23°C and 85% RH, and the result was 58 cc / (m²). 2 •day). It should be noted that, in addition to setting the temperature and humidity to the conditions mentioned above, the permeability and humidity should be measured according to the cup method described in JIS Z 2080:1976.

[0159] [Compare Examples 3 and 4]

[0160] As shown in Table 3, the types and contents of polymers used as solid components in the coating liquid for forming the pre-coating layer and the coating liquid for forming the heat-sealing layer were set. Otherwise, the same procedure as in Example 9 was followed to obtain the multilayer structures of Comparative Examples 3 and 4.

[0161] The observation of the pre-coated surface in the multilayer structure during manufacturing, the observation of the heat-sealing layer surface in the resulting multilayer structure, and the measurement of the moisture permeability of the resulting multilayer structure were performed in the same manner as in Example 9. The results are shown in Table 3.

[0162] It should be noted that the appearance evaluation based on surface observation of the pre-coating and heat-sealing layers, including Example 9, is set as the following benchmark.

[0163] A: No pigment adhesion was observed.

[0164] B: Pigment adhesion was observed, and the surface was rough.

[0165]

[0166] As shown in Table 3, in the multilayer structure of Example 9, which forms a pre-coating and a heat-sealing layer by including a polymer (a) with a glass transition temperature of 25°C or less and a polymer (b) with a glass transition temperature of 30°C or more, and where the content of polymer (b) is 1 part by mass or more and 50 parts by mass or less per 100 parts by mass of polymer (a), the adhesion of pigments to the pre-coating and heat-sealing layer is suppressed, and good barrier properties (water vapor barrier properties) can be confirmed. In the multilayer structure of Comparative Example 3, which forms a pre-coating and heat-sealing layer without polymer (b) with a glass transition temperature of 30°C or more, pigments adhere to the pre-coating and heat-sealing layer, and the gas barrier properties are insufficient. In addition, in the multilayer structure of Comparative Example 4, which forms a pre-coating and heat-sealing layer with an excessive amount of polymer (b) with a glass transition temperature of 30°C or more, although the adhesion of pigments to the pre-coating and heat-sealing layer is suppressed, the gas barrier properties are insufficient.

[0167] The pre-coating solution and heat-sealing solution used in Example 9 were the same as those used in Example 1. Furthermore, the pre-coating solution and heat-sealing solution used in Comparative Example 3 were the same as those used in Comparative Example 2. As shown in Table 2, the B layers of Examples 1-8, formed by including a polymer (a) with a glass transition temperature of 25°C or less and a polymer (b) with a glass transition temperature of 30°C or more, and wherein the content of polymer (b) is 1 part by mass or more and 50 parts by mass or less relative to 100 parts by mass of polymer (a), exhibited good anti-adhesion properties to the A layer (evaluations A-C). On the other hand, the B layers of Comparative Examples 1 and 2, which did not contain a specified amount of polymer (b), showed poor anti-adhesion properties to the A layer (evaluation D). It can be inferred that when the B layer exhibits good anti-adhesion properties relative to the A layer, there is a correlation between the inhibition of pigment adhesion to the B layer.

[0168] Industrial utilization

[0169] The multi-layer structure of the present invention can be suitable for use as packaging material.

[0170] Explanation of reference numerals in the attached figures

[0171] 10+ layers of structure

[0172] 11A Floor

[0173] 12 paper substrate

[0174] 13 Pre-coating

[0175] 14 barrier layers

[0176] 15 heat seal layers

Claims

1. A multilayer structure having a paper substrate, a layer A, and a layer B, wherein layer A is stacked on one side of the paper substrate, and layer B is stacked on the other side of the paper substrate. Layer A contains pigment. The B layer comprises a polymer (a) with a glass transition temperature of less than 25°C and a polymer (b) with a glass transition temperature of more than 30°C, wherein the content of the polymer (b) is more than 1 part by mass and less than 50 parts by mass relative to 100 parts by mass of the polymer (a).

2. The multi-layer structure according to claim 1, wherein, Both polymer (a) and polymer (b) are water-soluble or water-dispersible.

3. The multi-layer structure according to claim 1, wherein, The total content of polymer (a) and polymer (b) in layer B is more than 20% by mass and less than 100% by mass.

4. The multi-layer structure according to claim 1, wherein, The polymer (b) is a vinyl alcohol-based polymer.

5. The multi-layer structure according to claim 4, wherein, The degree of saponification of the vinyl alcohol polymer is above 80 mol% and below 100 mol%.

6. The multi-layer structure according to claim 4, wherein, The degree of saponification of the vinyl alcohol polymer is greater than 96 mol% and less than 100 mol%.

7. The multi-layer structure according to claim 4, wherein, The viscosity-average degree of polymerization of the vinyl alcohol polymer is above 200 and below 3,000.

8. The multi-layer structure according to claim 1, wherein, The polymer (a) comprises at least one selected from styrene-based polymers, modified olefin-based polymers, and ester-based polymers.

9. The multi-layer structure according to claim 1, wherein, It sequentially comprises layer A, the paper substrate, a pre-coating layer, a barrier layer, and a heat-sealing layer. The pre-coating layer is layer B.

10. The multilayer structure according to claim 1, comprising, in sequence, the A layer, the paper substrate, the pre-coating layer, the barrier layer, and the heat-sealing layer. The heat-sealing layer is layer B.

11. The multilayer structure according to claim 1, comprising, in sequence, the A layer, the paper substrate, the pre-coating layer, the barrier layer, and the heat-sealing layer. The pre-coating layer and the heat-sealing layer are the B layer.

12. The multilayer structure according to any one of claims 9 to 11, wherein, The barrier layer comprises a vinyl alcohol-based polymer.

13. A roll-shaped structure, which is a roll-shaped structure formed by winding the multi-layer structure according to any one of claims 1-8, 10 and 11. Layer A is in direct contact with Layer B.

14. Packaging material comprising a multilayer structure as described in any one of claims 1 to 11.

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