Heat seal paper and packaging material, container, or straw using the heat seal paper

Abstract

To provide heat seal paper that can be used as a substitute for plastic film-laminated paper since being a paper laminate having high water resistance and oil resistance, and heat sealability, and heat seal paper that can be used for various purposes and can contribute to paper recycling efficiency.SOLUTION: Heat seal paper includes: a paper base material; a resin layer provided on at least a part of the paper base material; and a heat seal layer provided in contact with the resin layer. The resin layer includes a polymer having a constituent unit derived from (meth)acrylic acid ester, and the heat seal layer includes olefin-α,β-unsaturated carboxylic acid copolymer.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to heat-sealing paper, and a packaging material, container or straw using the heat-sealing paper.

Background Art

[0002] Paper packaging materials such as paper bags, cardboard boxes, and paper cups have been conventionally used according to various applications and purposes. In recent years, as the problem of marine plastic waste, including microplastics, has come to the fore, there has been an increasing trend to use "paper" made from the renewable resource "wood" as one of the materials with functions such as "reusable" and "biodegradable" instead of plastic materials.

[0003] One of the currently widely used paper containers is paper cups used as containers for beverages, ice cream, yogurt, etc. Paper cups are given water resistance by using a polyethylene film as part of the raw material although they are made of paper. Such paper cups are obtained by laminating a polyethylene film or a polypropylene film, which is obtained by extruding a heat-melted polyethylene resin, a polypropylene resin, etc. into a film shape, onto a paper base material. When the polyethylene film is used for forming a paper cup, it serves as an adhesive under indirect heating by a burner or hot air, etc., and since the polyethylene film is present inside the paper cup, waterproofness, moisture resistance, and strength are imparted without the paper base material coming into direct contact with the contents.

[0004] However, the laminated polyethylene film needs to be physically removed because it does not dissolve in the alkaline solution used in the paper recycling process during paper recycling, leading to a decrease in recycling efficiency. In addition, marine pollution caused by the outflow of plastic waste into the ocean has become a global problem. As a target of the Sustainable Development Goals (SDGs), there is a goal to "prevent and significantly reduce all types of marine pollution, especially pollution caused by land-based activities, including marine litter and eutrophication, by 2025", and it has become an important global theme such as the summit (G20 summit) also agreeing to strengthen efforts. Therefore, there is a need for a polyethylene film substitute that is applicable to these uses and does not reduce paper recycling efficiency.

[0005] On the other hand, an aqueous heat-sealing agent is known as a material that serves as an adhesive during the molding of bags, boxes, paper cups, etc. For example, Patent Document 1 discloses that an ethylene-based resin aqueous dispersion in which an olefin-α,β-unsaturated carboxylic acid copolymer neutralized with ammonia or an amine and another olefin-based thermoplastic resin are mixed and dispersed at a specific ratio can be applied as a heat-sealing agent.

[0006] Also, Patent Document 2 discloses that an aqueous dispersion containing a polyolefin resin composed of an unsaturated carboxylic acid unit, an ethylene-based hydrocarbon, and an acrylate or methacrylate, a natural wax, and an aqueous medium in a specific ratio can be applied as a heat-sealing agent.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] However, as an alternative to plastic packaging materials that are heat-sealable, excellent in packaging material design, and also excellent in oil and water resistance, there are still many problems in using paper packaging materials. Heat-sealing agents for paper such as Patent Document 1 and Patent Document 2 have existed so far, but these documents disclose only the performance as a so-called heat-sealing agent such as heat-sealing strength and blocking resistance, and there is no description at all about the water resistance and oil resistance desired as an alternative to polyethylene film. That is, since there is no heat-sealing agent having oil resistance and water resistance, improvement in oil and water resistance is required when converting various plastic packages to paper packaging materials.

Means for Solving the Problems

[0009] That is, the present invention has a paper substrate, a resin layer provided on at least a part of the paper substrate, and a heat-sealing layer provided in contact with the resin layer. The resin layer contains a polymer having a structural unit derived from (meth)acrylate, and the heat-sealing layer is a heat-sealing paper containing an olefin-α,β-unsaturated carboxylic acid copolymer.

[0010] Further, the present invention provides a package, a container, or a straw using the above heat-sealing paper.

Effects of the Invention

[0011] The heat-sealing paper of the present invention is a paper laminate having excellent water resistance, oil resistance, and heat-sealing properties, and is useful as an alternative to paper laminated with a plastic film. Since it is useful for various applications, it can contribute to paper recycling efficiency. Further, the heat-sealing paper of the present invention can easily obtain a laminate having excellent water resistance, oil resistance, and heat-sealing properties with respect to paper only by coating, and further has excellent blocking resistance, so that it is possible to improve productivity and the quality of products after heat-sealing.

Modes for Carrying Out the Invention

[0012] The heat-sealing paper of the present invention has at least a paper base material, a resin layer provided on at least a part of the paper base material, and a heat-sealing layer provided in contact with the resin layer. In the heat-sealing paper of the present invention, the resin layer contains a polymer having a structural unit derived from (meth)acrylate, and the heat-sealing layer contains an olefin-α,β-unsaturated carboxylic acid copolymer. The heat-sealing paper of the present invention has a layer in which the resin layer and the heat-sealing layer are laminated, and the order of these layers is not particularly limited, but it is preferably laminated in the order of paper / resin layer / heat-sealing layer.

[0013] In the present invention, (meth)acrylate represents the general term for acrylate and methacrylate, and (meth)acrylic acid represents the general term for acrylic acid and methacrylic acid.

[0014] [Resin layer] The resin layer of the present invention contains a polymer having a structural unit derived from (meth)acrylate. The polymer having a structural unit derived from (meth)acrylate is not particularly limited, and it may be a homopolymer of methacrylate or a copolymer. Examples of the copolymer include a copolymer obtained by copolymerizing a vinyl monomer copolymerizable with (meth)acrylate. Further, it is preferably a copolymer having an acid value for the purpose of imparting water dispersibility or water solubility.

[0015] (Meth)acrylates used as a constituent of a homopolymer or copolymer of (meth)acrylates are not particularly limited, but among them, acrylates having an alkyl group with 1 to 20 carbon atoms are preferably used. Since homopolymers having acrylates exhibit a lower glass transition temperature, it is preferable to use acrylates having an alkyl group with 1 to 20 carbon atoms as the main component, and it is more preferably to use acrylates having an alkyl group with 1 to 12 carbon atoms as the main component. Examples of such acrylates having an alkyl group with 1 to 12 carbon atoms include methyl acrylate, ethyl acrylate, iso-propyl acrylate, allyl acrylate, n-butyl acrylate, iso-butyl acrylate, sec-butyl (meth)acrylate, tert-butyl acrylate, n-amyl acrylate, iso-amyl acrylate, n-hexyl acrylate, n-octyl acrylate, 2-ethylhexyl acrylate, n-lauryl (meth)acrylate, and the like.

[0016] Examples of other (meth)acrylates and vinyl monomers copolymerizable with (meth)acrylates include aromatic (meth)acrylates such as benzyl (meth)acrylate; hydroxyl group-containing monomers such as 2-hydroxyethyl (meth)acrylate and 2-hydroxypropyl (meth)acrylate; alkyl polyalkylene glycol mono(meth)acrylates such as methoxypolyethylene glycol mono(meth)acrylate and methoxypolypropylene glycol mono(meth)acrylate; fluorine-based (meth)acrylates such as perfluoroalkyl ethyl (meth)acrylate; aromatic vinyl compounds such as styrene, styrene derivatives (p-dimethylsilylstyrene, (p-vinylphenyl)methyl sulfide, p-hexynylstyrene, p-methoxystyrene, p-tert-butyldimethylsiloxystyrene, o-methylstyrene, p-methylstyrene, p-tert-butylstyrene, α-methylstyrene, etc.), vinylnaphthalene, vinylanthracene, 1,1-diphenylethylene; (meth)acrylate compounds such as glycidyl (meth)acrylate, epoxy (meth)acrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, tetramethylene glycol tetra(meth)acrylate, 2-hydroxy-1,3-diacryloxypropane, 2,2-bis[4-(acryloxymethoxy)phenyl]propane, 2,2-bis[4-(acryloxyethoxy)phenyl]propane, dicyclopentenyl (meth)acrylate tricyclodecanyl (meth)acrylate, tris(acryloxyethyl) isocyanurate, urethane (meth)acrylate; (meth)acrylates having an alkylamino group such as dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, dimethylaminopropyl (meth)acrylate; vinylpyridine compounds such as 2-vinylpyridine, 4-vinylpyridine, naphthylvinylpyridine; conjugated dienes such as 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene, 1,3-cyclohexadiene, etc.These monomers can be used alone or in combination of two or more kinds.

[0017] Also, for the purpose of introducing one or more acidic groups selected from the group consisting of a carboxyl group and a carboxylate group in which the carboxyl group is neutralized by a basic compound, (meth)acrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, β-(meth)acryloyloxyethyl hydrogen succinate, β-(meth)acryloyloxyethyl hydrogen phthalate, etc. A copolymer having an acid value can be obtained by copolymerizing a (meth)acrylic monomer having a carboxyl group. When introducing an acidic group, it is preferable to appropriately adjust the monomer amount so that the acid value falls within a desired range.

[0018] The homopolymer or copolymer of (meth)acrylate can be produced, for example, by polymerizing one or more monomers in a temperature range of 50°C to 180°C in the presence of a polymerization initiator, and a temperature range of 80°C to 150°C is more preferable. Examples of the polymerization method include bulk polymerization method, solution polymerization method, suspension polymerization method, emulsion polymerization method, etc. Examples of the polymerization mode include random copolymer, block copolymer, graft copolymer, etc. The copolymer may also be of a core-shell type.

[0019] As the homopolymer or copolymer of (meth)acrylate, commercially available products may be used. Examples of commercially available products include Hylos-XPE-2273 (manufactured by Starlight PMC Co., Ltd.), Hylos-XNE-2260 (manufactured by Starlight PMC Co., Ltd.), JONCRYL DFC3030 (manufactured by BASF Co., Ltd.), JONCRYL DFC3040 (manufactured by BASF Co., Ltd.), JONCRYL DFC3050 (manufactured by BASF Co., Ltd.), SEIKOAT NE-2260 (manufactured by Starlight PMC Co., Ltd.), Hylos-X·NE-2273 (manufactured by Starlight PMC Co., Ltd.), NEOCRYL A-2091 (manufactured by Covestro AG), etc.

[0020] The resin layer of the present invention can be formed by applying an aqueous resin composition (emulsion) containing a homopolymer or copolymer of (meth)acrylate.

[0021] The emulsion containing a homopolymer or copolymer of (meth)acrylate preferably has a minimum film-forming temperature in the range of 0°C to 100°C, more preferably in the range of 0°C to 60°C, and even more preferably in the range of 0 to 30°C. In the present invention, the minimum film-forming temperature is the minimum temperature required for forming a continuous film when the water in the synthetic rubber latex evaporates and dries, and is obtained by the temperature gradient plate method.

[0022] The glass transition temperature (hereinafter sometimes referred to as Tg) of the emulsion containing a homopolymer or copolymer of (meth)acrylate is preferably in the range of -30°C to 100°C, more preferably in the range of -30 to 80°C, and even more preferably in the range of 15 to 65°C. In the present invention, the glass transition temperature is obtained by measurement using a differential scanning calorimeter.

[0023] Also, the acid value of the emulsion is preferably in the range of 10 to 150 mgKOH / g, preferably in the range of 30 to 80 mgKOH / g, more preferably in the range of 40 to 80 mgKOH / g, and even more preferably in the range of 45 to 70 mgKOH / g. In the present invention, the acid value is obtained by a measurement method conforming to the JIS test method K0070-1992.

[0024] The aqueous resin composition containing the emulsion containing a homopolymer or copolymer of (meth)acrylate has a dense film-forming property without defects such as pinholes, and thus is excellent in water resistance and oil resistance. Therefore, the water resistance and oil resistance of the laminate can be improved. In addition, since the aqueous resin composition also has adhesiveness, it is excellent in adhesiveness to the heat-sealing coat layer and / or the paper substrate, and does not impair the function of the heat-sealing layer, so it has excellent compatibility when used in combination with the heat-sealing layer.

[0025] In addition, since the composition of the present invention contains a homopolymer or copolymer of (meth)acrylate, its heat resistance is improved. Therefore, it can be applied even when the contained substance is at a high temperature such as heated food.

[0026] Hereinafter, an aqueous resin composition containing a styrene-acrylic copolymer as a copolymer of (meth)acrylate will be described as an example.

[0027] Among them, as the copolymer of (meth)acrylate, for example, it is preferable to use a styrene-acrylic copolymer of styrene, α-methylstyrene, and (meth)acrylate.

[0028] <Aqueous resin composition containing a styrene-acrylic copolymer> (Emulsion containing a styrene-acrylic copolymer) As an example of the aqueous resin composition of the present invention, first, an emulsion containing a styrene-acrylic copolymer (A) of styrene, α-methylstyrene, and (meth)acrylate will be described.

[0029] In the present invention, α-methylstyrene in the styrene-acrylic copolymer (A) represents any one or a mixture of o-methylstyrene, m-methylstyrene, and p-methylstyrene.

[0030] In addition, the styrene-acrylic copolymer (A) may partially use styrene derivatives other than the styrene and α-methylstyrene (p-dimethylsilylstyrylstylene, p-tert-butyldimethylsiloxystyrene, p-tert-butylstyrene), vinylnaphthalene, vinylanthracene, 1,1-diphenylethylene, etc. within the range not impairing the scope of the present invention.

[0031] (Meth)acrylates are not particularly limited. For example, methyl (meth)acrylate, ethyl (meth)acrylate, iso-propyl (meth)acrylate, allyl (meth)acrylate, n-butyl (meth)acrylate, iso-butyl (meth)acrylate, sec-butyl (meth)acrylate, tert-butyl (meth)acrylate, n-amyl (meth)acrylate, iso-amyl (meth)acrylate, n-hexyl (meth)acrylate, n-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-lauryl (meth)acrylate, n-tridecyl (meth)acrylate, n-stearyl (meth)acrylate, phenyl (meth)acrylate, benzyl (meth)acrylate, cyclohexyl (meth)acrylate, 4-tert-butylcyclohexyl (meth)acrylate, isobornyl (meth)acrylate, tricyclodecanyl (meth)acrylate, dicyclopentadienyl (meth)acrylate, adamantyl (meth)acrylate, glycidyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, trifluoroethyl methacrylate, tetrafluoropropyl methacrylate, pentafluoropropyl methacrylate, octafluoropentyl methacrylate, pentadecafluorooctyl methacrylate, heptadecafluorodecyl methacrylate, N,General (meth)acrylates such as N-dimethyl(meth)acrylamide, acryloylmorpholine, (meth)acrylonitrile, polyethylene glycol (meth)acrylate, polypropylene glycol (meth)acrylate, polyethylene glycol-polypropylene glycol (meth)acrylate, polyethylene glycol-polybutylene glycol (meth)acrylate, polypropylene glycol-polybutylene glycol (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, ethoxypolyethylene glycol (meth)acrylate, butoxypolyethylene glycol (meth)acrylate, octoxypolyethylene glycol (meth)acrylate, lauroxypolyethylene glycol (meth)acrylate, stearoxypolyethylene glycol (meth)acrylate, phenoxypolyethylene glycol (meth)acrylate, methoxypolypropylene glycol (meth)acrylate, octoxypolyethylene glycol-polypropylene glycol (meth)acrylate and other polyalkylene oxide group-containing (meth)acrylic monomers can be used. Among them, homopolymers having acrylate exhibit a lower glass transition temperature, so they are preferred. It is preferable to use acrylate having an alkyl group with 1 to 20 carbon atoms as the main component, and it is more preferable to use acrylate having an alkyl group with 1 to 12 carbon atoms as the main component. Examples of such acrylate having an alkyl group with 1 to 12 carbon atoms include methyl acrylate, ethyl acrylate, iso-propyl acrylate, allyl acrylate, n-butyl acrylate, iso-butyl acrylate, (meth)sec-butyl acrylate, tert-butyl acrylate, n-amyl acrylate, iso-amyl acrylate, n-hexyl acrylate, n-octyl acrylate, 2-ethylhexyl acrylate, (meth)n-lauryl acrylate, etc.

[0032] The (meth)acrylate used as a constituent of the styrene-acrylic copolymer (A) of the present invention may be one kind or two or more kinds, but it is preferable to use two or more kinds of (meth)acrylates. Among them, it is preferable to use two or more kinds of acrylates having an alkyl group with 1 to 12 carbon atoms as the main component.

[0033] The emulsion containing the styrene-acrylic copolymer (A) preferably further contains a copolymer of (meth)acrylic acid and (meth)acrylate. The copolymer of (meth)acrylic acid and (meth)acrylate is a copolymer of (meth)acrylic acid and the above-mentioned (meth)acrylate (hereinafter sometimes referred to as acrylic copolymer (B)). The (meth)acrylate is not particularly limited, but among them, it is preferably an acrylate having an alkyl group with 1 to 20 carbon atoms. Since a homopolymer having an acrylate exhibits a lower glass transition temperature, it is preferable, and it is preferable to use an acrylate having an alkyl group with 1 to 20 carbon atoms as the main component, and it is preferable to use an acrylate having an alkyl group with 1 to 12 carbon atoms as the main component. Examples of such acrylates having an alkyl group with 1 to 12 carbon atoms include methyl acrylate, ethyl acrylate, iso-propyl acrylate, allyl acrylate, n-butyl acrylate, iso-butyl acrylate, (meth)sec-butyl acrylate, tert-butyl acrylate, n-amyl acrylate, iso-amyl acrylate, n-hexyl acrylate, n-octyl acrylate, 2-ethylhexyl acrylate, (meth)n-lauryl acrylate and the like.

[0034] The emulsion containing the styrene-acrylic copolymer (A) preferably contains the styrene-acrylic copolymer (A) and the acrylic copolymer (B). This may be an emulsion obtained by appropriately mixing an emulsion of the styrene-acrylic copolymer (A) polymerized by a polymerization method using a known aqueous medium such as emulsion polymerization or transfer emulsion, and an emulsion of the acrylic copolymer (B) polymerized by a polymerization method using a known aqueous medium such as emulsion polymerization or transfer emulsion, or may be an emulsion of a resin in which the styrene-acrylic copolymer (A) and the acrylic copolymer (B) form a core-shell structure. Note that the "resin containing the styrene-acrylic copolymer (A)" may be a resin composed of the styrene-acrylic copolymer (A), or may be a resin in which the styrene-acrylic copolymer (A) and the acrylic copolymer (B) form a core-shell structure.

[0035] The core-shell structure is formed by having a region where a large amount of the "styrene-acrylic copolymer (A)" exists and a region where a large amount of the "acrylic copolymer (B)" exists. In this core-shell structure, for example, the "acrylic copolymer (B)" may exist in the region where a large amount of the "styrene-acrylic copolymer (A)" exists, or these copolymers may be polymerized with each other.

[0036] (Method for producing an emulsion containing a styrene-acrylic copolymer) In the present invention, the emulsion can be obtained by polymerization using a known polymerization method such as emulsion polymerization or transfer emulsion using a known aqueous medium without particular limitation. Also, there are various expressions for the form in which the polymer is dispersed in the aqueous medium, such as emulsion, dispersion, suspension, etc., but in the present invention, it is unified as an emulsion.

[0037] For example, a monomer mixture is supplied into an aqueous medium, and in the presence of an initiator, this monomer mixture is polymerized to polymerize the emulsion.

[0038] In the case of an emulsion obtained by appropriately mixing the emulsion of the styrene-acrylic copolymer (A) and the emulsion of the acrylic copolymer (B), it is obtained by mixing emulsions obtained by polymerizing the respective monomer mixtures.

[0039] In the case of an emulsion forming a core-shell structure, it is obtained by a step (1) of supplying a monomer mixture forming a core polymer and polymerizing this monomer mixture in the presence of an initiator to form a core polymer, and a step (2) of supplying a monomer mixture forming a shell polymer to the core polymer of step (1) and polymerizing this monomer mixture in the presence of an initiator to form a shell on the core polymer. Also, it is obtained by a step (i) of supplying a monomer mixture forming a shell polymer and polymerizing this monomer mixture in the presence of an initiator to form a shell polymer, and a step (ii) of supplying a monomer mixture forming a core polymer to the shell polymer of step (i) and polymerizing this monomer mixture in the presence of an initiator to form a shell on the core polymer.

[0040] As the initiator, there is no particular limitation, and peroxides, persulfates, azo compounds, redox systems, or mixtures thereof used in emulsion polymerization methods or the like may be used. Examples of peroxides include hydrogen peroxide, ammonium peroxide, sodium peroxide, or potassium peroxide, t-butyl peroxide, t-butyl hydroperoxide, cumene hydroperoxide, and benzene peroxide. Examples of persulfates include ammonium persulfate, sodium persulfate, or potassium persulfate. Examples of azo compounds include 2,2-azobisisobutyronitrile and 4,4'-(4-cyanovaleric acid). The redox system consists of an oxidizing agent and a reducing agent. Examples of the oxidizing agent include one of the peroxides, persulfates, or azo compounds mentioned above, or sodium chloride or potassium chloride, or sodium bromide or potassium bromide. Examples of the reducing agent include ascorbic acid, glucose, or ammonium, sodium hydrogen sulfate or potassium hydrogen sulfate, sodium bisulfite or potassium bisulfite, sodium thiosulfate or potassium thiosulfate, or sodium sulfide or potassium sulfide, or iron(II) ammonium sulfate. Among them, persulfates, more preferably ammonium persulfate, are preferred.

[0041] The polymerization of the monomer mixture can be carried out, for example, in the presence of additives such as surfactants, chain transfer agents, chelating agents, etc., for example, in the presence of surfactants and chain transfer agents. These additives may be added in advance to the aqueous medium used in step (1), or may be mixed with the monomer mixture supplied in step (1) or step (2).

[0042] The surfactant is not particularly limited, and examples thereof include disodium dodecyldiphenyloxide, disulfonate, and the like. The chain transfer agent is also not particularly limited, and examples thereof include α-methylstyrene dimer, thioglycolic acid, sodium hydrogen phosphite, 2-mercaptoethanol, N-dodecyl mercaptan, and t-dodecyl mercaptan. The chelating agent is not particularly limited, and examples thereof include ethylenediaminetetraacetic acid.

[0043] When forming a core-shell structure, in order to enhance the stability in an aqueous medium, it is preferable that the acrylic copolymer (B) having an acidic group forms the shell. However, an emulsion having a structure in which not all of the acrylic copolymer (B) forms the shell during synthesis and a part of the styrene acrylic copolymer (A) forms the shell is also acceptable.

[0044] When neutralization is required, bases such as ammonia, triethylamine, aminomethylpropanol, monoethanolamine, diethylaminoethanol, sodium hydroxide, and potassium hydroxide can be used as the neutralizing agent.

[0045] (Other resins) The aqueous resin composition of the present invention may contain other resins other than the polymer having a structural unit derived from (meth)acrylate. The material of the other resin is not particularly limited, but it is preferably selected from materials that do not impair the properties such as oil resistance and heat resistance of the aqueous resin composition of the present invention. Further, the content of the other resin can be appropriately adjusted within a range that does not impair the effects of the present invention. However, the weight ratio of the polymer having a structural unit derived from (meth)acrylate to the other resin ((meth)acrylate-derived structural unit-containing polymer / other resin) is preferably 100 / 0 to 50 / 50, and more preferably 100 / 0 to 60 / 40.

[0046] (Aqueous solvent) The aqueous resin composition preferably contains water. As the water, pure water such as ion-exchanged water, ultrafiltration water, reverse osmosis permeated water, distilled water, or ultrapure water can be used. Also, as the water, it is preferable to use water sterilized by ultraviolet irradiation or hydrogen peroxide addition or the like when storing the composition for a long time because it can prevent the generation of mold or bacteria. Among them, it is most preferable to use water.

[0047] Water-soluble organic solvents such as alcohols dissolved in water may be mixed and used. Examples of the alcohols include methanol, ethanol, isopropyl alcohol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, butyl alcohol, pentyl alcohol, and the like. These alcohols can be used alone or in combination of two or more.

[0048] (Other additives) The aqueous resin composition can also be blended with other silica, alumina, polyethylene wax, defoaming agent, leveling agent, tackifier, preservative, antibacterial agent, rust inhibitor, etc.

[0049] The aqueous resin composition may contain wax. Examples of the wax include fatty acid amide wax, carnauba wax, polyolefin wax, paraffin wax, Fischer-Tropsch wax, beeswax, microcrystalline wax, oxidized polyethylene wax, amide wax, and the like. These can be used alone or in combination.

[0050] Among them, it is preferable to use fatty acid amide wax, carnauba wax, Fischer-Tropsch wax, polyolefin wax, paraffin wax, and particularly it is preferable to use carnauba wax, polyolefin wax, paraffin wax.

[0051] Specific examples of fatty acid amide waxes include, for example, pelargonic acid amide, capric acid amide, undecyl acid amide, lauric acid amide, tridecyl acid amide, myristic acid amide, pentadecyl acid amide, palmitic acid amide, heptadecyl acid amide, stearic acid amide, nonadecanoic acid amide, arachidic acid amide, behenic acid amide, lignoceric acid amide, oleic acid amide, cetoleic acid amide, linoleic acid amide, linolenic acid amide, mixtures thereof, and fatty acid amides of animal and vegetable oils and fats, etc.

[0052] Specific examples of the carnauba wax include MICROKLEAR 418 (manufactured by Micro Powders, Inc.), refined carnauba wax No. 1 powder (Nippon Wax Co., Ltd.), etc.

[0053] Specific examples of the olefin wax include polyethylene wax and polypropylene wax, and for example, MPP-635VF (MicroPowders, Inc.), MP-620VF XF (Micro Powders, Inc.), etc.

[0054] Specific examples of the paraffin wax include, for example, MP-28C, MP-22XF, MP-28C (Micro Powders, Inc.), etc.

[0055] The blending amount of the wax is preferably 1.5 to 20% by mass based on 100% by mass of the total solid content in the aqueous resin composition. If the total amount of the wax is 3% by mass or more based on 100% of the total solid content in the coating composition, the blocking resistance tends to be maintained, and if the total amount of the wax is 15% by mass or less based on 100% of the total solid content of the aqueous resin composition, the heat sealability tends to be maintained.

[0056] Also, from the viewpoints of oil resistance and heat resistance, the melting point of the wax is preferably in the range of 80°C to 130°C. The wax may be directly added to and mixed and dispersed in an emulsion of a resin containing a polymer having a structural unit derived from (meth)acrylic acid ester, or after preparing a dispersion of the wax, it may be mixed with the emulsion. As the dispersion method, known methods can be used. For example, as a dispersion device using media, a paint shaker, ball mill, attritor, basket mill, sand mill, sand grinder, dyno mill, dispermat, SC mill, spike mill, agitator mill, etc. can be used, and without using media, an ultrasonic homogenizer, high-pressure homogenizer, nanomizer, desolver, disper, high-speed impeller disperser, etc. can be used for dispersion.

[0057] When using powdered wax, in order to uniformly disperse the wax, it is preferable to knead using media or to perform compounding after preparing a dispersion of the wax. The kneading method can be carried out by a known method.

[0058] When using a combination of multiple types of waxes, the multiple types of waxes may be added simultaneously or added in multiple steps.

[0059] Also, when coating the aqueous resin composition using various coaters, in order to prevent the composition from foaming, polymer-based antifoaming agents, silicone-based antifoaming agents, and fluorine-based antifoaming agents are preferably used. As these antifoaming agents, any of emulsion dispersion type and solubilization type can be used. Among them, polymer-based antifoaming agents are preferable.

[0060] As the addition amount of the antifoaming agent, 0.005% by weight to 0.1% by weight of the total amount of the aqueous resin composition is preferable.

[0061] The resin layer used in the present invention, in addition to the aqueous resin composition containing an emulsion containing a polymer having a structural unit derived from (meth)acrylic acid ester and an aqueous medium as described above, preferably contains at least one or more other resins such as vinyl chloride-vinyl acetate copolymer resins and various synthetic latexes.

[0062] The vinyl chloride-vinyl acetate copolymer resin is not particularly limited as long as it is a copolymer of vinyl chloride and vinyl acetate. From the viewpoint of improving heat sealability, it is preferably a vinyl chloride-vinyl acetate copolymer containing an acid group, and more preferably an acid-modified vinyl chloride-vinyl acetate copolymer resin. As the acid group, those using maleic acid or fumaric acid are preferred.

[0063] Examples of various synthetic latexes include styrene-butadiene copolymer latex, acrylonitrile-butadiene copolymer latex, (meth)acrylate-butadiene copolymer latex, and the like. These latexes may or may not be crosslinked.

[0064] In addition, when the resin layer used in the present invention is directly applied onto a paper substrate, for example, it is also preferable to use a surface treatment agent or a surface sizing agent that covers the surface of the paper substrate. As these surface treatment agents or surface sizing agents, those generally used as surface treatment agents or surface sizing agents for paper can be used, and mixtures thereof can also be used.

[0065] The type of binder used in the surface treatment agent is not particularly limited, and starches such as native starch, oxidized starch, esterified starch, cationized starch, and modified starch made from acetylated tapioca starch, modified starches such as aldehyde starch and hydroxyethylated starch, cellulose derivatives such as carboxymethyl cellulose, hydroxyethyl cellulose, methyl cellulose, and cellulose nanofibers, modified alcohols such as polyacrylamide, carboxyl-modified polyvinyl alcohol, and acetoacetylated polyvinyl alcohol, styrene-butadiene copolymers, polyvinyl acetate, vinyl chloride-vinyl acetate copolymers, polyvinyl chloride, polyvinylidene chloride, polyacrylate esters, etc. can be used alone or in combination.

[0066] Also, the surface sizing agent is not particularly limited as long as it can hydrophobize the surface of paper (cellulose) with the sizing agent to suppress the penetration of water, oil, etc. For example, styrene-based sizing agents, olefin-based sizing agents, acrylate-based sizing agents, styrene-acrylic sizing agents, styrene-maleic sizing agents, cationic sizing agents, rosin-based sizing agents, AKD (alkyl ketene dimer) emulsion type sizing agents, ASA (alkenyl succinic anhydride) emulsion type sizing agents, etc. can be mentioned.

[0067] The surface sizing agent is preferably used in combination with the surface treatment agent. When used in combination, the solid content concentration in the surface treatment agent is preferably 0.05 to 5% by weight, and more preferably 0.05 to 1% by weight.

[0068] When using the surface treatment agent, it may be made into a mixture of the aqueous resin composition and the surface treatment agent to form a resin layer, or the aqueous resin composition and the surface treatment agent may be coated in sequence and used as a resin layer.

[0069] In order to improve the coating performance, the aqueous resin composition for forming the resin layer of the present invention is preferably used by dissolving the above-described resin, surface treatment agent, or sizing agent in an aqueous solvent or various organic solvents. It is preferable to use an aqueous solvent using an emulsion or latex. As the aqueous solvent, the same solvents as those used in the emulsion containing a polymer having a structural unit derived from the above-mentioned (meth)acrylate can be used. Among them, it is preferable to use water.

[0070] When using a vinyl chloride-vinyl acetate copolymer resin, a polyester resin, etc., it is preferable to use an organic solvent.

[0071] The organic solvent is not particularly limited. For example, aromatic hydrocarbon-based solvents such as toluene, xylene, Solvesso #100, and Solvesso #150; aliphatic hydrocarbon-based solvents such as hexane, heptane, octane, and decane; various ester-based organic solvents such as methyl acetate, ethyl acetate, isopropyl acetate, butyl acetate, amyl acetate, ethyl formate, and butyl propionate. Also, alcohol-based solvents such as methanol, ethanol, propanol, and butanol; ketone-based solvents such as acetone, methyl ethyl ketone, and cyclohexanone; glycol ether-based solvents such as ethylene glycol (mono, di) methyl ether, ethylene glycol (mono, di) ethyl ether, ethylene glycol monopropyl ether, ethylene glycol monoisopropyl ether, monobutyl ether, diethylene glycol (mono, di) methyl ether, diethylene glycol (mono, di) ethyl ether, diethylene glycol monoisopropyl ether, diethylene glycol monobutyl ether, triethylene glycol (mono, di) methyl ether, propylene glycol (mono, di) methyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, and dipropylene glycol (mono, di) methyl ether; and various organic solvents such as amide-based solvents like N,N-dimethylformamide, N,N-diethylformamide, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone, which are good solvents. Among these, toluene, methyl ethyl ketone, ethyl acetate, which usually have a fast drying rate, or a mixture thereof are preferably used.

[0072] [Heat seal layer] The heat seal paper of the present invention has a heat seal layer in contact with the resin layer. The heat seal layer contains an olefin-α,β-unsaturated carboxylic acid copolymer resin system. Hereinafter, a composition example of the heat sealant will be described.

[0073] <Heat sealant (HS)> The heat sealant (HS) contains at least an olefin-α,β-unsaturated carboxylic acid copolymer resin system in order to improve water resistance.

[0074] Examples of the olefin-α,β-unsaturated carboxylic acid copolymer resin include copolymers of an olefin and at least one monomer selected from the group consisting of an α,β-unsaturated carboxylic acid, a metal salt of an α,β-unsaturated carboxylic acid, and an α,β-unsaturated carboxylic acid ester. Specifically, they are copolymers of an α,β-unsaturated carboxylic acid, a metal salt of an α,β-unsaturated carboxylic acid, or an α,β-unsaturated carboxylic acid ester and an olefin, such as olefin-α,β-unsaturated carboxylic acid copolymers, ethylene-acrylic acid ester copolymers, ethylene-methacrylic acid copolymers, ethylene-methacrylic acid ester copolymers, ethylene-acrylic acid-maleic anhydride copolymers, ethylene-acrylic acid ester-maleic anhydride copolymers, ethylene-methacrylic acid-maleic anhydride copolymers, ethylene-methacrylic acid ester-maleic anhydride copolymers, and metal salts thereof. These copolymers may be used alone or as a mixture of two or more. Among them, olefin-α,β-unsaturated carboxylic acid copolymers are preferred. Examples of the olefin-α,β-unsaturated carboxylic acid copolymer include random copolymers or block copolymers of ethylene and an α,β-unsaturated carboxylic acid.

[0075] Examples of the olefin include ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-decene, 4-methyl-1-pentene, butadiene, dicyclopentadiene, 5-ethylidene-2-norbornene, etc. Among them, ethylene is preferred. Examples of the α,β-unsaturated carboxylic acid include acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid, etc. Among these, acrylic acid and methacrylic acid are preferably used. These α,β-unsaturated carboxylic acids may be used alone or as a mixture of two or more.

[0076] As the α,β-unsaturated carboxylic acid ester, known alkyl esters, hydroxyalkyl esters, alkoxyalkyl esters, etc. of acrylic acid or methacrylic acid can be used without particular limitation. For example, specifically, acrylic acid esters such as methyl acrylate, ethyl acrylate, isopropyl acrylate, n-propyl acrylate, n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate, n-octyl acrylate, 2-hydroxyethyl acrylate, 2-methoxyethyl acrylate, and methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, n-lauryl methacrylate, 2-hydroxyethyl methacrylate, 2-ethoxyethyl methacrylate can be exemplified. These can be used alone or in combination of two or more.

[0077] As a method for producing the olefin-α,β-unsaturated carboxylic acid copolymer, it can be obtained by a known method, for example, radical copolymerization under high temperature and high pressure.

[0078] The content of the α,β-unsaturated carboxylic acid in the above olefin-α,β-unsaturated carboxylic acid copolymer is desirably 8 to 24% by weight, preferably 18 to 23% by weight. When the content of the α,β-unsaturated carboxylic acid is less than 8% by weight, due to the non-polar nature derived from the ethylene unit, the dispersibility in the aqueous dispersion medium is poor, and it may be difficult to obtain an excellent aqueous dispersion of the olefin-α,β-unsaturated carboxylic acid copolymer resin. Also, when the content of the α,β-unsaturated carboxylic acid exceeds 24% by weight, the blocking resistance of the obtained film may deteriorate.

[0079] As the olefin-α,β-unsaturated carboxylic acid copolymer, commercially available products may be used.

[0080] The olefin-α,β-unsaturated carboxylic acid copolymer used in the heat-sealing agent is preferably used as an aqueous dispersion dispersed in an aqueous solvent. The method of dispersing in an aqueous solvent is not particularly limited and may be carried out by a known method. For example, a method of emulsifying with a surfactant and dispersing in an aqueous solvent, a method of neutralizing the olefin-α,β-unsaturated carboxylic acid copolymer with a basic compound and then dispersing in an aqueous solvent, etc. may be mentioned.

[0081] As the surfactant used in the emulsification, various known anionic, cationic, nonionic surfactants, or various water-soluble polymers can be used in appropriate combination.

[0082] Examples of the basic compound used in the neutralization include organic amines such as ammonia, methylamine, ethylamine, diethylamine, dimethylethanolamine, diethanolamine, triethanolamine, and alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, and lithium hydroxide. These basic compounds may be used alone or in combination of two or more.

[0083] The degree of neutralization with the basic compound may be the degree of neutralization at which the olefin-α,β-unsaturated carboxylic acid copolymer exists stably in the aqueous solvent. For example, it may be 30 to 100 mol% of the carboxyl groups of the copolymer, and more preferably 40 to 90 mol%.

[0084] As the dispersion method, known methods can be used. For example, as a dispersion device using media, a paint shaker, ball mill, attritor, basket mill, sand mill, sand grinder, dyno mill, dispermat, SC mill, spike mill, agitator mill, etc. can be used, and as those not using media, an ultrasonic homogenizer, high-pressure homogenizer, nanomizer, desolver, disper, high-speed impeller disperser, etc. can be used for dispersion.

[0085] The solid content of the aqueous dispersion of the olefin-α,β-unsaturated carboxylic acid copolymer used in the present invention is not particularly limited and may be appropriately determined depending on the desired viscosity when applied as a heat-sealing agent, the drying conditions after application of the heat-sealing agent, the film thickness of the film, and the like. Generally, it is often applied in the range of 10 to 40% by mass of the solid content concentration.

[0086] (Solvent) In order to improve the coating performance, the heat-sealing agent (HS) is preferably used by dissolving the above-mentioned resin in an aqueous solvent. As the aqueous solvent, the same solvents as those used in the above-mentioned coating composition (CS) can be used. Among them, it is preferable to use water.

[0087] (Wax) The heat-sealing agent (HS) preferably contains wax. By containing wax, blocking resistance can be maintained. Examples of the wax include fatty acid amide wax, carnauba wax, polyolefin wax, paraffin wax, Fischer-Tropsch wax, beeswax, microcrystalline wax, oxidized polyethylene wax, amide wax and other waxes, coconut oil fatty acid, soybean oil fatty acid, and the like. These may be used alone or in combination.

[0088] Among them, it is preferable to use fatty acid amide wax, carnauba wax, Fischer-Tropsch wax, polyolefin wax, paraffin wax, and particularly preferably fatty acid amide wax and carnauba wax.

[0089] Specific examples of fatty acid amide waxes include, for example, pelargonic acid amide, capric acid amide, undecylic acid amide, lauric acid amide, tridecylic acid amide, myristic acid amide, pentadecylic acid amide, palmitic acid amide, heptadecylic acid amide, stearic acid amide, nonadecanoic acid amide, arachidic acid amide, behenic acid amide, lignoceric acid amide, oleic acid amide, cetoleic acid amide, linoleic acid amide, linolenic acid amide, mixtures thereof, and fatty acid amides of animal and vegetable oils and fats, etc. Specific examples of the carnauba wax include MICROKLEAR 418 (manufactured by Micro Powders, Inc.), refined carnauba wax No. 1 powder (manufactured by Nippon Wax Co., Ltd.), etc.

[0090] The blending amount of the wax is preferably such that the total amount of the wax is 1.5 to 20% by mass based on 100% by mass of the solid content of the heat sealant (HS). If the total amount of the wax is 3% by mass or more based on 100% by mass of the solid content of the heat sealant (HS), the blocking resistance tends to be maintained, and if the total amount of the wax is 15% by mass or less based on 100% by mass of the solid content of the heat sealant (HS), the heat sealability tends to be maintained.

[0091] Among the waxes, it is more preferable to use the fatty acid amide wax and the carnauba wax in combination, as the blocking resistance is further improved. When used in combination, the ratio is not particularly limited, but preferably, the ratio of fatty acid amide wax: the carnauba wax = 1:1 to 1:10 is preferable, and the range of 1:1 to 1:5 is still more preferable.

[0092] Also, among the waxes, it is more preferable to use the polyolefin wax and the paraffin wax in combination, as the blocking resistance is further improved. When used in combination, the ratio is not particularly limited, but preferably, the ratio of polyolefin wax: paraffin wax = 1:1 to 10:1 is preferable, and the range of 1:1 to 5:1 is still more preferable.

[0093] When using an aqueous solvent, it is preferable to further use wax, and among them, it is preferably used in combination with the olefin-α,β-unsaturated carboxylic acid copolymer or (meth)acrylic resin. In this case, the wax may be directly added to and mixed and dispersed in the aqueous dispersion of the olefin-α,β-unsaturated carboxylic acid copolymer or (meth)acrylic resin, or may be added and mixed and dispersed simultaneously when dispersing the olefin-α,β-unsaturated carboxylic acid copolymer or (meth)acrylic resin in an aqueous solvent. As the dispersion method, the method used in the above-mentioned dispersion method of the olefin-α,β-unsaturated carboxylic acid copolymer in an aqueous solvent can be appropriately used.

[0094] When using a plurality of types of waxes in combination, the plurality of types of waxes may be added simultaneously or may be added in divided steps. For example, after adding the first wax when dispersing it in the aqueous solvent of the olefin-α,β-unsaturated carboxylic acid copolymer or (meth)acrylic resin, the second wax is further added to the obtained aqueous dispersion of the first wax and the olefin-α,β-unsaturated carboxylic acid copolymer or (meth)acrylic resin, and a heat sealant (HS) can be obtained.

[0095] The heat sealant (HS) may contain additives such as silica, alumina, defoaming agents, viscosity modifiers, leveling agents, tackifiers, preservatives, antibacterial agents, rust preventives, antioxidants, silicone oil, etc. in addition to the above components as long as the object of the present invention is not inhibited.

[0096] In addition, in the heat sealant (HS), in order to prevent foaming when coating using various coaters, polymer-based defoaming agents, silicone-based defoaming agents, and fluorine-based defoaming agents are preferably used. Any of these defoaming agents such as emulsion dispersion type and solubilization type can be used. Among them, polymer-based defoaming agents are preferred. The addition amount of the defoaming agent is preferably 0.005% by weight to 0.1% by weight of the total amount of the aqueous heat sealant.

[0097] The heat sealant (HS) can be used as a heat sealant when manufacturing paper packaging materials and paper containers such as bags and boxes. For the coated parts other than the seal (adhesive) part, the water resistance of the laminate can be further improved by laminating with a styrene-acrylic copolymer coat layer. By bonding the heat seal parts, various packaging materials such as bags, boxes, and containers can be manufactured according to the application, and it has excellent processability.

[0098] [Heat Seal Paper] The heat seal paper of the present invention has at least a resin layer on a paper substrate and a heat seal layer provided in contact with the resin layer.

[0099] As the paper substrate, it is manufactured by a known paper-making machine using natural fibers for papermaking such as wood pulp, but the papermaking conditions are not particularly specified. Examples of natural fibers for papermaking include wood pulp such as softwood pulp and hardwood pulp, non-wood pulp such as Manila hemp pulp, sisal hemp pulp, and flax pulp, and pulp obtained by chemically modifying these pulps. As the type of pulp, chemical pulp such as kraft sulfate pulping method, acidic / neutral / alkaline sulfite pulping method, and soda salt pulping method, ground pulp, chemiground pulp, thermomechanical pulp, etc. can be used. In addition, various commercially available high-quality papers, coated papers, backing papers, impregnated papers, cardboard papers, and paperboards can also be used.

[0100] The paper substrate can be sequentially selected according to the purpose, such as the type and thickness of the paper. For example, for burger wrap, it is about 20 g / m corresponding to the Japanese tatami mat size, for paper cups, it is 200 - 300 g / m corresponding to the Japanese tatami mat size, 2 for paper plates, paper spoons, paper ladles, etc., food base paper such as cup base paper of 50 - 500 g / m corresponding to the Japanese tatami mat size is preferred. These papers are preferably not laminated with polyethylene film, aluminum, etc. from the viewpoints of recycling efficiency and cost reduction. The paper substrate may have a printing layer. Also, many commercially available papers have already been treated with the aforementioned surface treatment agent, but such papers can also be used in the present invention. 2 for paper plates, paper spoons, paper ladles, etc., food base paper such as cup base paper of 50 - 500 g / m corresponding to the Japanese tatami mat size is preferred. 2 These papers are preferably not laminated with polyethylene film, aluminum, etc. from the viewpoints of recycling efficiency and cost reduction. The paper substrate may have a printing layer. Also, many commercially available papers have already been treated with the aforementioned surface treatment agent, but such papers can also be used in the present invention.

[0101] The resin layer is preferably provided between the paper substrate and the second layer. The coating amount of the resin layer is 0.5 to 10.0 g / m 2 and more preferably 1.0 to 5.0 g / m 2 .

[0102] The heat-sealing layer is preferably provided on the resin layer. The coating amount of the heat-sealing layer is preferably 0.5 to 8.0 g / m 2 and more preferably 1.0 to 5.0 g / m 2 . In the case of the paper substrate / resin layer / heat-sealing layer configuration, due to the blocking function of the resin layer, the coating amount of the heat-sealing layer can be reduced compared to the case where the resin layer is not provided.

[0103] The heat-sealing paper may further have another coating layer on the surface of the paper substrate where the resin layer and the heat-sealing layer are not provided. For the other coating layer, it is preferable to appropriately select and use various coating agents according to the performance to be imparted to the heat-sealing paper. For example, as the other coating layer, the above-described styrene-acrylic copolymer coating layer may be provided. Further, when it is desired to further improve the water resistance, it is more preferable to use a water-resistant coating layer containing at least a styrene-acrylic copolymer and wax. Further, as the other coating layer, the above-described layer of the surface treatment agent may be provided, or paper that has already been subjected to the surface treatment agent may be used.

[0104] 〔When providing a water-resistant coating layer as the other coating layer〕 The water-resistant coating layer provided as the other coating layer is preferably formed from a water-resistant coating composition containing at least an aqueous solvent, a styrene-acrylic copolymer, and wax. The film thickness of the water-resistant coating layer depends on the application, but for example, it is preferably in the range of 1 to 10 g / m 2 and more preferably in the range of 1 to 5 g / m 2 .

[0105] (Aqueous solvent) As the aqueous solvent, the same solvents as those used in the above-mentioned heat-sealing agent (HS) can be used.

[0106] (Styrene-acrylic copolymer) It is preferable that the styrene-acrylic copolymer forms a core-shell structure with a copolymer of styrenes and (meth)acrylate, and it is more preferable that a copolymer of styrenes and (meth)acrylate and a copolymer of styrenes, (meth)acrylate, and (meth)acrylic acid form a core-shell structure.

[0107] As the styrenes and (meth)acrylate used as the components of the styrene-acrylic copolymer, the same ones as those used in the styrene-acrylic copolymer (A) of the styrene-acrylic copolymer coat layer described above can be used.

[0108] As components of the styrene-acrylic copolymer, other known polymerizable compounds other than styrenes, (meth)acrylate, and (meth)acrylic acid may be contained.

[0109] The styrene-acrylic copolymer (A) may contain a wax described below. By containing a wax in the styrene-acrylic copolymer (A), the water resistance can be further improved. The wax may be present in the core part or the shell part. It may also be present on the surface of the styrene-acrylic copolymer.

[0110] In the styrene-acrylic copolymer (A), the ratio of "the copolymer of styrenes and (meth)acrylate" to "the copolymer of styrenes, (meth)acrylate, and (meth)acrylic acid" is preferably in the range of 20:80 to 95:5 by mass ratio, more preferably in the range of 30:70 to 92:8, and most preferably in the range of 40:60 to 90:10.

[0111] In the copolymer of styrenes and (meth)acrylate, the ratio of styrenes to (meth)acrylate is preferably in the range of 20:80 to 80:20 by mass, more preferably in the range of 30:70 to 70:30, and most preferably in the range of 40:60 to 60:40.

[0112] In the copolymer of styrenes, (meth)acrylate and (meth)acrylic acid, the proportion of styrenes is preferably 10 to 90% by mass, more preferably 20 to 80% by mass, and most preferably 30 to 70% by mass. Also, in the copolymer of styrenes, (meth)acrylate and (meth)acrylic acid, the proportion of (meth)acrylate is preferably 10 to 80% by mass, more preferably 15 to 70% by mass, and most preferably 20 to 60% by mass. Also, in the copolymer of styrenes, (meth)acrylate and (meth)acrylic acid, the proportion of (meth)acrylic acid is preferably 10 to 70% by mass, more preferably 15 to 60% by mass, and most preferably 20 to 50% by mass.

[0113] When the styrene acrylic copolymer (A) contains other known polymerizable compounds other than styrenes, (meth)acrylate, and (meth)acrylic acid, the proportion of the other polymerizable compounds in the styrene acrylic copolymer (A) is preferably 10% by mass or less, and preferably 5% by mass or less.

[0114] The glass transition temperature (hereinafter sometimes referred to as Tg) of the styrene acrylic copolymer (A) is in the range of -30°C to 10°C, preferably in the range of -25°C to 5°C, and more preferably in the range of -20°C to 0°C. In the present invention, the glass transition temperature is obtained by measurement with a differential scanning calorimeter.

[0115] Styrene-acrylic copolymers can be produced by known methods. Among them, it is preferable to carry out the polymerization of the monomer mixture in the presence of wax. That is, by previously adding wax to an aqueous medium or mixing it with the monomer mixture, a core-shell structure in which wax is incorporated into the styrene-acrylic copolymer can be formed.

[0116] (wax) The water-resistant coating composition can further improve its water resistance by containing wax. The wax is preferably at least one wax selected from paraffin wax, microcrystalline wax, polyethylene oxide wax, and amide wax, and paraffin wax or microcrystalline wax is more preferable. These can be used alone or in combination.

[0117] The melting point of the wax is preferably in the range of 30°C to 130°C, and more preferably in the range of 50°C to 100°C. The blending amount of the wax is preferably 0.5 to 20% by mass, and preferably 1 to 15% by mass, based on 100% by mass of the styrene-acrylic copolymer.

[0118] The wax only needs to be dispersed and present in the water-resistant coating layer. However, as described above, it is preferably present in the core part and / or shell part of the styrene-acrylic copolymer and exists integrally with the styrene-acrylic copolymer. In the water-resistant coating layer, the wax may be present in a form contained in the styrene-acrylic copolymer and may be present without being contained in the styrene-acrylic copolymer.

[0119] (Other additives) The water-resistant coating composition may further contain additives such as silica, alumina, wax, defoaming agent, leveling agent, tackifier, preservative, antibacterial agent, rust preventive agent, etc., as long as the object of the present invention is not inhibited. Further, resins other than the styrene-acrylic copolymer may be blended. Among them, it is preferable that a leveling agent and / or wax is further blended.

[0120] [Method for manufacturing heat-sealing paper] The heat-sealing paper of the present invention can be obtained by sequentially applying a composition for forming a resin layer and a composition for forming a heat-sealing layer on a paper substrate, and further applying a composition for forming a third layer if necessary.

[0121] As a method for applying the coating composition on the paper substrate, comma coater, roll coater, reverse roll coater, direct gravure coater, reverse gravure coater, offset gravure coater, roll kiss coater, reverse kiss coater, kiss gravure coater, reverse kiss gravure coater, air doctor coater, knife coater, bar coater, wire bar coater, die coater, lip coater, dip coater, blade coater, brush coater, curtain coater, die slot coater, flexo coater, impregnation coater, cast coater, spray coater, offset printing press, screen printing press, etc. Any one or a combination of two or more coating methods can be used.

[0122] Alternatively, a resin layer may be provided on the paper substrate by impregnating the paper substrate into the composition. Further, a drying step may be provided in an oven or the like after coating.

[0123] [Package, container or straw] Since the heat-sealing paper of the present invention has a heat-sealing layer containing an olefin-α,β-unsaturated carboxylic acid copolymer, it can be processed into boxes, bags, containers, straws, etc. by heat-sealing using the heat-sealing coat layer.

[0124] Examples of the packaging body include bags for packaging, paper bags, cardboard boxes, corrugated cardboard, wrapping paper, envelopes, cup sleeves, lids, and the like. Examples of the container include paper containers, paper plates, trays, cup holders, paper cups, and the like. Since the present invention is excellent in water resistance and oil resistance, it is preferably used as a packaging material for foods, fertilizers, etc. that require water resistance and oil resistance. For example, cups or lids for desserts such as cup noodles, ice cream, pudding, jelly, etc., bags or boxes for storing confectioneries, grains, beans, powders, pet hoods, fertilizers, etc., wrapping paper for hamburgers and hot dogs, takeout containers for pizza, etc., containers for hot snacks such as fried chicken and potatoes, paper food containers or packaging materials such as cups for prepared dishes such as natto, and bags or boxes for sanitary products such as detergents and sanitary supplies.

[0125] For example, when manufacturing a paper cup using the heat-sealing paper of the present invention, a heat-sealing layer can be provided on the inner surface of the container and the bonding part when assembling the container, and the bonding part can be bonded by overlapping and adhering through the heat-sealing layer. That is, the paper cup has a body member (1) obtained by bonding the bonding surfaces at both ends where the paper base material of the laminate of the present invention is rolled and overlapped, and a plate-shaped bottom member (2) bonded to the lower end of the body member (1). The resin layer and the heat-sealing layer provided at the bonding part are bonded by the heat-sealing function, and the resin layer and the heat-sealing layer provided at parts other than the bonding part can exhibit the functions of water resistance and oil resistance. Since the resin layer and the heat-sealing layer provided at parts other than the bonding part are highly safe for the human body and the environment, they can also be directly in contact with food for storage. Furthermore, by providing a water-resistant coating layer as a third layer on the outside of the paper cup, excellent water resistance can be obtained even when used for a long time.

[0126] Similarly, cardboard boxes, paper bags, etc. can also be manufactured by heat-sealing using the laminate of the present invention.

[0127] As for the specific method of heat sealing, after applying the first layer and the second layer to at least one of the two parts of the paper substrate (both parts may be applicable), the two parts are overlapped and softened by heating. The heat-sealing agent can be easily softened by heating with a burner or hot air, and can bond paper to paper or paper to other materials. Then, by cooling, the bonded part solidifies, and paper can be firmly sealed to paper or paper to other materials.

[0128] As the heating method, conventionally known means such as a heat source like a burner, hot air, electrothermal, infrared rays, and electron beams can be used. Specifically, methods of heating with a burner or hot air, or depending on the form of molding, a heat welding seal method, an ultrasonic seal method, or a high-frequency seal method is preferable. The heating temperature at this time is preferably 200 to 500 °C, and the heating time is preferably 0.1 to 3 seconds.

[0129] In addition, besides the method of melting the heat-sealing agent (HS) by contacting it with a direct heat source such as a heat-sealing bar, it can be easily heated and softened by non-contact heating, and the heat-sealing function can persist for a certain period of time even after being separated from the heat source. When the substrate is paper, there is a possibility that the paper will burn if it is in contact with a direct heat source. However, since the heat-sealing agent of the present invention exhibits the heat-sealing function by non-contact heating and the function persists, it is particularly useful as a heat-sealing agent for the industrial production of paper containers that require a high line speed.

[0130] After applying the heat-sealing agent (HS) and heating and softening the coated part, it can be used as a heat-sealing agent by pressing in a state where the coated part and another part are overlapped. The pressing method is not particularly limited, and it can be performed by a hot plate method, an ultrasonic seal, or a high-frequency seal method.

[0131] Hereinafter, the present invention will be described in detail based on examples, but the technical scope of the present invention is not limited to these embodiments.

Examples

[0132] In the following examples, "parts" represents "parts by mass", and "%" represents "% by mass".

[0133] (Preparation of Aqueous Resin Composition 1 Containing Styrene-Acrylic Copolymer (A)) 100 parts of isopropyl alcohol was charged into a four-necked flask purged with nitrogen gas, and the temperature was raised to 80 - 82°C. Then, a mixture of 1 part of myristyl acrylate, 30 parts of styrene, 10 parts of acrylic acid, 5 parts of methyl methacrylate, and 1 part of benzoyl peroxide charged in a dropping funnel was added dropwise over 2 hours. After the addition was completed, 0.5 part of benzoyl peroxide was added, and the reaction was continued for another 2 hours. The temperature was lowered to 40°C, and dimethylethanolamine and ion-exchanged water were added. Then, the temperature of the reaction flask was raised to 80 - 82°C, and stripping was performed to finally obtain a water-soluble resin with a solid content of 30%.

[0134] 10 parts of ion-exchanged water was charged into the reaction flask with the water-soluble resin obtained above, and the temperature was raised to 80°C - 82°C. Then, 2 parts of potassium persulfate was added, and a mixture of 15 parts of styrene, 5 parts of α-methylstyrene, 24 parts of 2-ethylhexyl acrylate, and 10 parts of butyl acrylate was added dropwise over 2 hours. After the addition was completed, 0.2 part of potassium persulfate was added, and the reaction was carried out for 2 hours. The solid content of the acrylic emulsion (Resin 1) thus obtained was 47%, the minimum film-forming temperature was 1°C, the glass transition point was -27°C, and the acid value of the solid content was 64 mgKOH / g.

[0135] A total of 100 parts, consisting of 77 parts of the acrylic emulsion (Resin 1) and 23 parts of ion-exchanged water, was thoroughly stirred with a disperser at 25°C for 15 minutes to prepare Aqueous Resin Composition 1.

[0136] (Preparation of Aqueous Resin Compositions 2 - 7) The acrylic emulsions (Resins 2 - 7) and ion-exchanged water were mixed at the blending ratios shown in Table 1 and thoroughly stirred with a disperser at 25°C for 15 minutes to prepare Aqueous Resin Compositions 2 - 7.

[0137]

Table 1

[0138] In Table 1, for Resins 2 to 8, commercially available acrylic emulsions having the acid value, glass transition point, and minimum film-forming temperature shown in Table 1 were used.

[0139] Also, Resin 8 was adjusted as follows.

[0140] (Adjustment of Resin 8 used for the heat-sealing agent (HS1)) 77.8 parts of ethylene, 11.1 parts of ethyl acrylate, and 11.2 parts of acrylic acid were synthesized by a conventional method to obtain an ethylene-ethyl acrylate-acrylic acid copolymer.

[0141] 25 parts of the obtained copolymer, ammonia with a neutralization rate of 100% with respect to the acid value of the copolymer, water as an aqueous solvent, and 1.5 parts of fatty acid amide wax as a wax were charged and stirred to obtain an aqueous dispersion (Resin 8) of an olefin-α,β-unsaturated carboxylic acid copolymer and fatty acid amide wax.

[0142] (Preparation of heat-sealing paper) (Examples 1 to 7) A paper substrate (kraft paper: basis weight 70 g / m 2 (manufactured by Maruizumi Paper Co., Ltd.)) was prepared, and the aqueous resin compositions 1 to 7 described in Table 1 were each applied to one surface of the paper substrate so that the film thickness was 3 g / m when dry 2 and dried to form a resin layer. Subsequently, the HS agent described in Table 1 was applied on the resin layer so that the film thickness was 3 g / m when dry 2 and dried at 100 °C for 30 seconds using a dryer to produce the heat-sealing papers of Examples 1 to 7.

[0143] (Comparative Examples 1 to 8) The aqueous resin compositions 1 to 7 and the HS agent described in Table 1 were each applied to one surface of the same paper substrate as in the examples so that the film thickness was 3 g / m when dry 2 and dried to form a resin layer or a heat-sealing layer.

[0144] (Evaluation) (Heat sealability) In the heat-sealing papers of the prepared examples and comparative examples, the coated surfaces of the aqueous resin composition and the heat-sealing agent were overlapped with the coated surfaces (surface / surface), heated in the temperature range of 100°C to 200°C, and immediately pressurized at 0.2 MPa. A heat-sealing part was provided by using a heat-sealing machine under the condition of 1-second adhesion. Note that the heat-sealed and adhered part has a width of 1.5 cm.

[0145] Similarly, in the heat-sealing papers of the examples and comparative examples, the coated surface of the aqueous resin composition and the heat-sealing agent was overlapped with the uncoated surface (surface / back), heated in the temperature range of 100°C to 200°C, and immediately pressurized at 0.2 MPa. A heat-sealing part was provided by using a heat-sealing machine under the condition of 1-second adhesion.

[0146] The adhesion situation was evaluated for the adhesion strength from the occurrence situation of the sites where peeling and destruction occurred by peeling the heat-sealing part. Between the coating films, between the coating film and the base paper, and between the papers were the sites where peeling occurred respectively. As the heat-sealing strength, it was coating film / coating film < coating film / base paper < paper / paper. The peeling between the papers means that the heat-sealing strength was strong and substrate destruction occurred. Also, adhesion NG represents those that did not adhere.

[0147] (Blocking resistance 1) The prepared heat-sealing papers were overlapped so that the coated surfaces contacted each other, a load of 5 kgf / cm 2 was applied, and left for 24 hours in an environment of 50°C. After taking out, the adhesion condition of the coated surface and the non-coated surface was evaluated as follows from the surface change and the peeling resistance. (Evaluation criteria for surface change by visual inspection) 〇: No blocking is seen at all. 〇△: Slight blocking is seen partially. △: Blocking is seen partially. ×: Blocking is seen over the entire surface Also, the adhesion condition of the coated surface and the non-coated surface was visually evaluated in the following 4 grades. (Evaluation criteria for peeling resistance) 〇: No resistance 〇△: Slightly resistant △: Resistant overall but peelable ×: Resistant and non - peelable (Blocking resistance 2) The heat - seal paper produced was overlapped so that the coated surfaces were in contact, and a load of 5 kgf / cm 2 was applied, and it was left for 24 hours in an environment of 50°C and 75% humidity. After taking it out, the adhesion between the coated surface and the non - coated surface was evaluated in the same way as blocking resistance 1 from the surface change and peel resistance.

[0148] (Oil resistance) Using the produced heat - seal paper, the oil repellency was evaluated using the JAPAN TAPPI paper pulp test method No. 41 kit method. The maximum value of the oil repellency degree is 16.

[0149] (Water resistance) Tap water was collected with a dropper, and 0.1 ml was dropped onto the surface of the heat - seal paper test piece for evaluation where the resin layer and the heat - seal layer were provided. After dropping, it was left at 25°C. After 5 minutes, 15 minutes, 30 minutes, 1 hour, and 2 hours, the tap water was wiped off, and the front and back surfaces were visually evaluated according to the following evaluation criteria.

[0150] ○: There are no traces of dripping or swelling due to water on the surface, and there is no penetration to the back surface. △: There are traces of dripping on the surface, but there is no penetration to the back surface.

[0151] ×: There are traces of dripping or swelling due to water on the surface, and there is penetration to the back surface. The evaluation results are shown in the following table.

[0152]

Table 2

[0153]

Table 3

[0154]

Table 4

[0155]

Table 5

Claims

1. A paper substrate, a resin layer provided on at least a part of the paper substrate, and a heat-sealing layer provided in contact with the resin layer, wherein the resin layer contains a polymer having a structural unit derived from (meth)acrylic acid ester, and the heat-sealing layer contains an olefin-α,β-unsaturated carboxylic acid copolymer characterized heat-sealing paper.

2. The polymer having a structural unit derived from (meth)acrylic acid ester contained in the resin layer has an acid value of 10 mgKOH / g or more and 80 mgKOH / g or less, and a glass transition temperature of -30°C to 100°C The heat-sealing paper according to Claim 1.

3. The polymer having a structural unit derived from (meth)acrylic acid ester contained in the resin layer contains a styrene-acrylic copolymer composed of a copolymer of styrenes and (meth)acrylate The heat-sealing paper according to Claim 1 or 2.

4. The resin layer further contains wax The heat-sealing paper according to Claim 1 or 2.

5. The heat-sealing layer contains wax and / or a leveling agent The heat-sealing paper according to Claim 1 or 2.

6. The coating amount of the heat-sealing layer during drying is 1.0 to 8.0 g / m ２ The heat-sealing paper according to claim 1 or 2, wherein the heat-sealing paper is as described above.

7. 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8. A packaging material, container or straw in which the heat-sealing paper according to Claim 1 is adhered to another paper substrate or plastic film via the heat-sealing layer.

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