Laminate, coating liquid, food packaging sheet, and method for manufacturing laminate

Abstract

To provide a laminate which is excellent in oil resistance, water resistance, heat sealability and blocking property without using a fluorine compound even when a biomass-derived material having biodegradability is used, a coating liquid for forming a laminate, a food packaging sheet having the laminate, and a method for manufacturing a laminate.SOLUTION: A laminate has a first coating layer (A) containing modified starch on at least one paper base material, and a second coating layer (B) composed of a non-water soluble resin on the first coating layer, wherein the total of coating amounts of the first coating layer (A) and the second coating layer (B) is 0.5-10 g / m2, and air shielding property is 20 kPa or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a laminate, a coating liquid for forming the laminate, a food packaging sheet including the laminate, and a method for producing the laminate. [Background technology]

[0002] Conventionally, food packaging sheets have been made by laminating a resin film such as polyethylene onto a base sheet such as tissue paper, paperboard, or nonwoven fabric. The laminated resin film has functions such as preventing oil stains on the base sheet caused by food-derived oils and reducing the strength of the base sheet. Meanwhile, in recent years, paper recycling has accelerated due to the global trend toward reducing environmental impact. However, the above-mentioned laminated sheets are difficult to recycle, and the process of removing the laminated resin film layer requires expensive capital investment, which has been an obstacle to promoting recycling. Against this background, active research is being conducted into coating-type food packaging sheets that are easier to recycle. Furthermore, in recent years, there has been a demand for food packaging sheets to further reduce their environmental impact by using biomass-derived and biodegradable materials. Demand for biomass-derived and biodegradable coating materials is also increasing year by year. Biomass-derived materials are materials made from biological resources. From the perspective of carbon neutrality, even if they are incinerated, the amount of CO2 emitted is the same as the amount absorbed by the plants used as raw materials. Consequently, they are considered to have no effect on the increase or decrease of CO2 in the atmosphere, resulting in a smaller environmental impact than petroleum-derived products. Biodegradable materials are known for their low environmental impact because microorganisms in soil and oceans break them down into water and carbon dioxide. However, food packaging sheets made from biomass-derived and biodegradable materials often have inferior coating properties compared to conventional coating liquid types, and there is a demand for laminates suitable for food packaging sheets with good coating properties, such as oil resistance, water resistance, heat sealability, and blocking resistance.

[0003] In contrast, for example, Patent Document 1 discloses a laminate with excellent oil resistance and air permeability by providing a coating layer of starch containing wax on a paper substrate. Because starch is a biomass-derived material and biodegradable, it can be said that this laminate has a low environmental impact. However, the laminate obtained by the method of Patent Document 1 has poor water resistance because it is mainly composed of starch alone, and even the addition of wax is not sufficient to impart water resistance. Many prepared foods and fast foods, which use laminates with excellent oil resistance and air permeability, contain more water than oil, which may lead to the moisture seeping into the laminate. Furthermore, from the perspective of processing the laminate, heat sealability is required for the laminate, and heat sealability cannot be achieved with a composition consisting only of starch and wax.

[0004] In Patent Document 2, a laminate with excellent oil resistance is produced using a coating liquid that is a mixture of starch or PVA and polylactic acid, but as in Patent Document 1, the starch or PVA, which has poor water resistance, is present on the film surface, allowing water to soak in, resulting in insufficient water resistance. Furthermore, mixing starch or PVA with polylactic acid also deteriorates film-forming properties, which has a negative effect on oil resistance and heat sealability.

[0005] Patent Document 3 describes a laminate having excellent water and oil resistance, which has a first layer of starch and a second layer of a fluoropolymer. However, when a fluorine-based composition is heated, the fluorine compounds present in the paper are thermally decomposed, generating fluorine-based hydrocarbons that are difficult to decompose in nature, which has been pointed out as causing problems such as environmental pollution. As a shift from laminate films to coating liquid types is being considered to reduce the environmental burden, it is necessary to avoid using substances that may have a negative impact on the environment. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2018-53374 [Patent Document 2] Japanese Patent Application Publication No. 2020-128616 [Patent Document 3] Japanese Patent Application Laid-Open No. 2016-29220 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention aims to provide a laminate that is excellent in oil resistance, water resistance, heat sealability, and anti-blocking properties even when made from biomass-derived and biodegradable materials, without using a fluorine compound; a coating liquid for forming the laminate; a food packaging sheet including the laminate; and a method for producing the laminate. [Means for solving the problem]

[0008] The present inventors have conducted extensive research to solve the above problems and have arrived at the present invention. That is, the present invention provides a laminate having a first coating layer (A) on at least one side of a paper substrate, and further having a second coating layer (B) on the first coating layer, wherein the first coating layer (A) contains at least one type of modified starch (a), and the second coating layer (B) contains at least one type of water-insoluble resin (b), and the total coating weight of the first coating layer (A) and the second coating layer (B) is 0.5 to 10 g / m 2 and the laminate has an air barrier property of 20 kPa or less.

[0009] The present invention relates to a coating liquid for forming the first coating layer (A), which is characterized by satisfying the following formula (1): Formula (1) V2≦1.5×V1 (V1: Viscosity 5 seconds after applying a shear rate of 2000 (l / s) to the coating liquid, V2: Viscosity 5 seconds after applying a shear rate of 50 (l / s) to the coating liquid)

[0010] The present invention relates to the above coating liquid, which is characterized in that the solid content is 5 to 40% and the viscosity at 25° C. specified in JIS Z8803 is 5 to 500 mPa·s.

[0011] The present invention relates to the above laminate having a first coating layer (A) formed from the above coating liquid.

[0012] The present invention relates to the above laminate, wherein the water-insoluble resin (b) contains at least one of an acrylic resin (c), a polyester resin (d), and a urethane resin (e).

[0013] The present invention relates to the laminate described above, wherein the mass ratio per unit area of ​​the first coating layer (A) to the second coating layer (B) ((A) / (B)) is 2 / 8 to 8 / 2.

[0014] The present invention relates to a method for producing the above-described laminate, wherein the first coating layer (A) and the second coating layer (B) are formed by gravure printing or flexographic printing.

[0015] The present invention relates to the laminate described above, wherein the modified starch (a) is a modified starch obtained by hydroxyalkylating or oxidizing a raw starch.

[0016] The present invention relates to a food packaging sheet for containing food, which comprises the above-described laminate. [Effects of the Invention]

[0017] The present invention can provide a laminate that has good oil resistance, water resistance, heat sealability, and blocking properties even when using a biomass-derived and biodegradable material without using a fluorine compound, a coating liquid for forming the laminate, a food packaging sheet including the laminate, and a method for producing the laminate. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a front view of an air barrier property measuring device according to the present invention. [Figure 2]FIG. 2 is a plan view of a glass filter in the air barrier property measuring device of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0019] The present invention will be described in detail below. Needless to say, other embodiments are also included within the scope of the present invention as long as they are consistent with the spirit of the present invention. Furthermore, in this specification, a numerical range specified using "to" includes the numerical values ​​before and after "to" as the lower and upper limit values ​​of the range. Unless otherwise noted, the various components appearing in this specification may be used independently, either singly or in combination of two or more.

[0020] In this specification, unless otherwise specified, the terms "(meth)acrylic acid" and "(meth)acrylate" refer to "acrylic acid or methacrylic acid" and "acrylate or methacrylate," respectively. Furthermore, "(meth)acrylic acid ester monomer" is a general term for "acrylic acid ester monomer" and "methacrylic acid ester monomer." The monomer refers to an ethylenically unsaturated double bond-containing monomer.

[0021] <Laminate> The laminate of the present invention is formed by applying a coating liquid to a paper substrate and drying the applied coating, and has a first coating layer (A) on at least one side of the paper substrate, and a second coating layer (B) on the first coating layer. By forming such a laminate, the paper substrate can be endowed with resistance properties such as oil resistance and water resistance. The laminate of the present application is particularly suitable for use in forming sheets for packaging food (hereinafter referred to as food packaging sheets). Furthermore, because it has excellent heat sealability, blocking properties, oil resistance, and water resistance, it can also be used favorably in applications where the coating layer comes into direct contact with food.

[0022] <Paper base material> The paper base material is obtained by papermaking a paper stock containing pulp, fillers, various auxiliaries, etc. That is, the paper support used in the present invention is not particularly limited, and examples include bleached or unbleached kraft paper (acid paper or neutral paper), fine paper, medium-quality paper, lightly coated paper, coated paper, paperboard, white paperboard, liner, semi-glassine paper, glassine paper, one-side glazed paper, parchment paper, etc. Any type of paper commercially available for food packaging can be used.

[0023] <First coating layer (A)> The first coating layer (A) contains at least one type of modified starch (a). The inclusion of at least one type of modified starch (a) improves coatability, allowing the production of a coating film that uniformly covers the substrate without gaps. By overlaying the second coating layer on top of this, a laminate with good oil and water resistance can be obtained. The inclusion of modified starch (a) also improves biodegradability.

[0024] (Modified starch (a)) The modified starch (a) is preferably a starch modified by chemically modifying raw starch using some method. In this specification, raw starch refers to unprocessed starch, i.e., starch extracted from plants and purified. The raw starch is not particularly limited in type, and can be appropriately selected from various known starches. For example, starches made from corn, potato, wheat, rice, tapioca, sweet potato, etc. can be used. Two or more of these starches can also be used in combination. Furthermore, the modified starch (a) in the present invention is preferably water-soluble. Because it is water-soluble, it can be completely dissolved in water by stirring in water at any temperature.

[0025] Examples of the method for modifying the modified starch (a) include oxidation, urea phosphate esterification, acetate esterification, hydroxyethylation, cationization, enzyme treatment, roasting, etc. The modified starch (a) modified by these methods can be used alone or in combination of two or more kinds. Specific examples of the modified starch (a) include oxidized starch, hydrophobized starch, starch acetate, phosphated starch, acetylated starch, etherified starch, cationized starch, carbamate starch, hydroxyalkylated starch, etc. Among these, hydroxyalkylated starch and oxidized starch are preferably used in terms of stability when dissolved in water.

[0026] Oxidized starch can be obtained by oxidizing starch with sodium hypochlorite. When the amorphous parts of starch particles are oxidized, the molecules are depolymerized and carboxyl groups are generated, making them less susceptible to oxidation, resulting in oxidized starch with excellent viscosity stability and transparency. Oxidized starch is chemically stable and has excellent oil resistance, so when coated on a paper substrate, it can impart excellent oil resistance to the paper substrate. Commercially available oxidized starch includes Cornstarch SK-20 (manufactured by Japan Cornstarch Co., Ltd.).

[0027] Hydroxyalkylated starch refers to modified starch (a) in which the hydroxyl groups of raw starch have been modified with hydroxyalkyl groups. The hydroxyalkyl groups preferably have 2 to 7 carbon atoms, more preferably 2 to 4 carbon atoms. The hydroxyalkyl groups contained in the hydroxyalkylated starch may contain two or more types of hydroxyalkyl groups. Preferred are hydroxyethyl groups, hydroxypropyl groups, hydroxybutyl groups, hydroxyhexyl groups, or combinations thereof, and more preferably hydroxypropyl groups. Examples of substances used for hydroxyalkylation include etherifying agents such as alkylene oxides, such as ethylene oxide, propylene oxide, and butylene oxide, and alkylene chlorohydrins, such as ethylene chlorohydrin, with propylene oxide being particularly preferred. Hydroxyalkylated starch has excellent stability in aqueous solution and can maintain low viscosity even at low temperatures, making it suitable for coating. It is possible to form a uniform coating film, which can impart excellent oil resistance. Commercially available hydroxyalkylated starch includes Piostarch LV (manufactured by Nippon Starch Chemical Co., Ltd.). The degree of substitution (DS) of the modified starch is preferably 0.01 to 1.5, more preferably 0.05 to 1.0. When the DS is 0.01 or more, the raw starch is sufficiently modified, improving solubility in water and improving stability after dissolving in water. When the DS is 1.0 or less, water resistance is improved when a laminate is produced.

[0028] The weight-average molecular weight of the modified starch (a) is preferably 50,000 to 300,000, and more preferably 70,000 to 200,000. A weight-average molecular weight of 50,000 or more allows a tough resin coating to be obtained, thereby improving oil resistance. A weight-average molecular weight of 300,000 or less allows the viscosity of the solution after dissolving the starch in water to be kept low. Maintaining a low viscosity improves coatability, allowing a uniform coating film to be produced, and eliminates unevenness when applying a second coating layer, improving water resistance. The weight-average molecular weight is a value measured using GPC (gel permeation chromatography), and details are described in the Examples section.

[0029] The modified starch (a) may be crosslinked with a crosslinking agent. By crosslinking the modified starch (a) with a crosslinking agent, the oil resistance and water resistance of the laminate can be further improved. The crosslinking agent that can be used for the modified starch (a) is not particularly limited. Examples of crosslinking agents include isocyanate resins, aminoaldehyde resins, glyoxal resins, epoxy resins, carbodiimide resins, inorganic metal salts, phenol resins, melamine resins, urea resins, and epichlorohydrin compounds. Among these, epichlorohydrin compounds are preferred from the viewpoint of reactivity, and polyamide epichlorohydrin resins are particularly preferred. The amount of crosslinking agent added varies depending on the type of crosslinking agent, the number of reactive groups, and the reaction rate, but may be about 1 to 25 parts by mass per 100 parts by mass of the solid content of the starch.

[0030] <Second coating layer (B)> The second coating layer (B) contains at least one water-insoluble resin (b), which blocks moisture from penetrating from the outside of the laminate, improving the water resistance of the laminate.

[0031] (Water-insoluble resin (b)) The water-insoluble resin (b) is a resin that does not completely dissolve in water and exists in a dispersed state in water. When water-insoluble resin (b) is dispersed in water, the solution becomes cloudy, allowing for the determination of whether it has been dispersed by transmittance measurement. Specifically, transmittance measurements are performed on samples prepared to a nonvolatile content of 5% using an ultraviolet-visible-near-infrared spectrophotometer (V-770, manufactured by JASCO Corporation). In the present invention, a resin that exhibits a transmittance of less than 80% at 660 nm when dispersed in water is defined as water-insoluble resin (b). A resin that exhibits a transmittance of 80% or more at 660 nm can be considered water-soluble. Even if a resin is partially dissolved in water, it is defined as water-insoluble resin (b) in the present invention if the above conditions are met. The water-insoluble resin (b) may be dispersed in water in particulate form or may not be completely dissolved in water and exist in an amorphous form. Furthermore, the water-insoluble resin (b) used in the present invention is not particularly limited as long as it meets the above definition. Among these, acrylic resin (c), polyester resin (d), and urethane resin (e) are preferred in terms of oil resistance and water resistance. In addition, an organic solvent that is miscible with water may be included.

[0032] [Acrylic resin (c)] The acrylic resin (c) is a polymer of an ethylenically unsaturated monomer. The ethylenically unsaturated monomer is classified into an ethylenically unsaturated monomer (c-1) having a linear alkyl group with 1 to 4 carbon atoms, an ethylenically unsaturated monomer (c-2) having a carboxy group, and another ethylenically unsaturated monomer (c-3) copolymerizable with the ethylenically unsaturated monomers (c-1) and (c-2). In this specification, the ethylenically unsaturated monomer (c-1) having a linear alkyl group having 1 to 4 carbon atoms, the ethylenically unsaturated monomer (c-2) having a carboxy group, and the other ethylenically unsaturated monomer (c-3) copolymerizable with the ethylenically unsaturated monomers (c-1) and (c-2) may be abbreviated as the ethylenically unsaturated monomer (c-1), the ethylenically unsaturated monomer (c-2), and the ethylenically unsaturated monomer (c-3), respectively.

[0033] The acrylic resin (c) can contain a polymer having a structure represented by general formula (1) at one end by polymerizing an ethylenically unsaturated monomer in the presence of a chain transfer agent (X) described below. Such an acrylic resin (c) has excellent dispersion stability and significantly improves the wettability and coatability of the coating liquid.

[0034] [ka] R is a linear or branched alkyl group having 8 to 16 carbon atoms.

[0035] Examples of the ethylenically unsaturated monomer (c-1) having a linear alkyl group having 1 to 4 carbon atoms include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, and n-butyl (meth)acrylate.

[0036] The content of the ethylenically unsaturated monomer (c-1) having a linear alkyl group having 1 to 4 carbon atoms is preferably 85 to 97 mass%, more preferably 90 to 96 mass%, of the total mass (100 mass%) of the ethylenically unsaturated monomers. By including the component (B) in the above range, the dispersion stability of the resin during synthesis is significantly improved, and a coating liquid having excellent coatability and film-forming properties can be obtained.

[0037] Examples of the ethylenically saturated monomer (c-2) having a carboxy group include acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, and cinnamic acid. The ethylenically saturated monomer (c-2) having a carboxy group preferably contains methacrylic acid, because this provides an acrylic resin (c) with superior stability and provides good coating properties of the coating liquid and good coating film resistance of the coating layer to food-derived components. The inclusion of methacrylic acid further improves the dispersion stability of the acrylic resin (c) and further improves the stability of the coating liquid.

[0038] By including an ethylenically unsaturated monomer (c-2) having a carboxy group as the ethylenically unsaturated monomer, a carboxy group can be introduced into the acrylic resin (c). From the viewpoints of improving the dispersion stability of the acrylic resin (c), controlling the rheology during application of the coating liquid, and promoting film formation, it is preferable that a carboxy group be introduced into the acrylic resin (c). The acid value of the acrylic resin (c) depends on the amount of the ethylenically unsaturated monomer (c-2) having a carboxy group introduced. The ethylenically unsaturated monomer (c-2) is preferably contained in an amount of 0 to 13% by mass, more preferably 0.5 to 10% by mass, based on the total mass (100% by mass) of the ethylenically unsaturated monomers. By containing the ethylenically unsaturated monomer (c-2) in the above range, the dispersion stability of the acrylic resin (c) is improved, and the coatability and film-forming properties of the coating agent are improved, thereby improving oil resistance and water resistance. The acid value of the acrylic resin (c) is preferably in the range of 20 to 40 mgKOH / g, more preferably in the range of 30 to 40 mgKOH / g. When the acid value is 20 mgKOH / g or more, the dispersion stability of the acrylic resin (c) during synthesis is improved. A coating liquid containing this acrylic resin (c) has excellent stability and good coatability and film-forming properties, making it possible to form a coating layer that is strong and has excellent durability. Therefore, the laminate exhibits excellent oil resistance. Furthermore, the interaction between the carboxy groups of the resin is strengthened, thereby improving heat-sealability. On the other hand, when the acid value is 40 mgKOH / g or less, the interaction between the carboxy groups between coating films is also reduced, thereby improving the blocking resistance of the laminate.

[0039] The other ethylenically unsaturated monomer (c-3) is an ethylenically unsaturated monomer copolymerizable with (c-1) and (c-2), other than the ethylenically unsaturated monomer (c-1) having a linear alkyl group with 1 to 4 carbon atoms and the ethylenically unsaturated monomer (c-2) having a carboxy group. In addition to the ethylenically unsaturated monomer (c-1) and the ethylenically unsaturated monomer (c-2), other ethylenically unsaturated monomer (c-3) may be copolymerized as needed to control the mass average molecular weight, average particle size, etc. of the acrylic resin (c).

[0040] Examples of the other ethylenically unsaturated monomer (c-3) include aromatic ethylenically unsaturated compounds such as vinylnaphthalene, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, phenoxydiethylene glycol (meth)acrylate, phenoxytetraethylene glycol (meth)acrylate, phenoxyhexaethylene glycol (meth)acrylate, phenoxyhexaethylene glycol (meth)acrylate, and phenyl (meth)acrylate; pentyl (meth)acrylate, heptyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, undecyl (meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, and phenyl (meth)acrylate. Ethylenically unsaturated monomers containing a straight or branched alkyl group having 5 or more carbon atoms, such as pentadecadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, and behenyl (meth)acrylate; ethylenically unsaturated monomers containing an alicyclic alkyl group, such as cyclohexyl (meth)acrylate and isobornyl (meth)acrylate; ethylenically unsaturated monomers containing a fluorinated alkyl group, such as trifluoroethyl (meth)acrylate and heptadecafluorodecyl (meth)acrylate; sulfo group-containing ethylenically unsaturated monomers, such as sodium 2-acrylamido-2-methylpropanesulfonate, methallylsulfonic acid, methallylsulfonic acid, sodium methallylsulfonate, allylsulfonic acid, sodium allylsulfonate, ammonium allylsulfonate, and vinylsulfonic acid;(Meth)acrylamide, N-methoxymethyl-(meth)acrylamide, N-ethoxymethyl-(meth)acrylamide, N-propoxymethyl-(meth)acrylamide, N-butoxymethyl-(meth)acrylamide, N-pentoxymethyl-(meth)acrylamide, N,N-di(methoxymethyl)acrylamide, N-ethoxymethyl-N-methoxymethylmethacrylamide, N,N-di(ethoxymethyl)acrylamide, N-ethoxymethyl-N-propoxymethylmethacrylamide, N,N-di(propoxymethyl)acrylamide N-butyl)acrylamide, N-butoxymethyl-N-(propoxymethyl)methacrylamide, N,N-di(butoxymethyl)acrylamide, N-butoxymethyl-N-(methoxymethyl)methacrylamide, N,N-di(pentoxymethyl)acrylamide, N-methoxymethyl-N-(pentoxymethyl)methacrylamide, N,N-dimethylaminopropylacrylamide, N,N-diethylaminopropylacrylamide, N,N-dimethylacrylamide, N,N-diethylacrylamide, diacetone acrylamide amide group-containing ethylenically unsaturated monomers such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, glycerol mono(meth)acrylate, 4-hydroxyvinylbenzene, 1-ethynyl-1-cyclohexanol, allyl alcohol, and other hydroxyl group-containing ethylenically unsaturated monomers; methoxypolyethylene glycol (meth)acrylate, polyethylene glycol (meth)acrylate, and other polyoxyethylene group-containing ethylenically unsaturated monomers; di Examples thereof include methylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, methylethylaminoethyl (meth)acrylate, dimethylaminostyrene, and diethylaminostyrene, and amino group-containing ethylenically unsaturated monomers such as dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, and methylethylaminoethyl (meth)acrylate; epoxy group-containing ethylenically unsaturated monomers such as glycidyl (meth)acrylate and 3,4-epoxycyclohexyl (meth)acrylate;Ketone group-containing ethylenically unsaturated monomers such as diacetone (meth)acrylamide and acetoacetoxy (meth)acrylate; allyl (meth)acrylate, 1-methylallyl (meth)acrylate, 2-methylallyl (meth)acrylate, 1-butenyl (meth)acrylate, 2-butenyl (meth)acrylate, 3-butenyl (meth)acrylate, 1,3-methyl-3-butenyl (meth)acrylate, 2-chloroallyl (meth)acrylate, 3-chloroallyl (meth)acrylate, o-allylphenyl (meth)acrylate, 2-(allyloxy)ethyl (meth)acrylate, allyl lactyl (meth)acrylate, citronellyl (meth)acrylate, geranyl (meth)acrylate, rosinyl (meth)acrylate, cinnamyl (meth)acrylate, diallyl maleate, Ethylenically unsaturated monomers having two or more ethylenically unsaturated groups, such as lyl itaconic acid, vinyl (meth)acrylate, vinyl crotonate, vinyl oleate, vinyl linoleate, 2-(2'-vinyloxyethoxy)ethyl (meth)acrylate, ethylene glycol di(meth)acrylate, triethylene glycol (meth)acrylate, tetraethylene glycol (meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, 1,1,1-trishydroxymethylethane diacrylate, 1,1,1-trishydroxymethylethane triacrylate, 1,1,1-trishydroxymethylpropane triacrylate, divinylbenzene, divinyl adipate, diallyl isophthalate, diallyl phthalate, and diallyl maleate;Examples of the alkoxysilyl group-containing ethylenically unsaturated monomer include γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropyltriethoxysilane, γ-methacryloxypropyltributoxysilane, γ-methacryloxypropylmethyldimethoxysilane, γ-methacryloxypropylmethyldiethoxysilane, γ-acryloxypropyltrimethoxysilane, γ-acryloxypropyltriethoxysilane, γ-acryloxypropylmethyldimethoxysilane, γ-methacryloxymethyltrimethoxysilane, γ-acryloxymethyltrimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltributoxysilane, and vinylmethyldimethoxysilane; and methylol group-containing ethylenically unsaturated monomers such as N-methylol(meth)acrylamide, N,N-dimethylol(meth)acrylamide, and alkyl-etherified N-methylol(meth)acrylamide, but are not limited to these.

[0041] Furthermore, styrenes such as styrene, α-methylstyrene, o-methylstyrene, p-methylstyrene, and m-methylstyrene may be used to the extent that the effect is not impaired, but it is preferable that they are not included from the viewpoint of environmental friendliness.

[0042] Among the other ethylenically unsaturated monomers (c-3) exemplified above, from the viewpoint of improving the stability of the acrylic resin (c) and improving the physical properties of the coating liquid by increasing the molecular weight, the other ethylenically unsaturated monomer (c-3) is more preferably acrylamide, glycidyl methacrylate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, or N-methylolacrylamide.

[0043] The content of the other ethylenically unsaturated monomer (c-3) is preferably 0 to 10% based on 100% by mass of the total mass of the ethylenically unsaturated monomers. When the content is 10% or less, the dispersion stability of the synthesized acrylic resin (c) is good, so that a coating liquid with excellent coatability and film-forming properties can be obtained, and as a result, a laminate with excellent oil resistance and water resistance can be produced.

[0044] The polymerization method for the acrylic resin (c) is not particularly limited, but emulsion polymerization is preferred because it allows for the easy production of a resin dispersion with a high molecular weight, low viscosity, and high solids content in an aqueous medium. The acrylic resin (c) synthesized using emulsion polymerization may have only one glass transition temperature, or it may have two or more different glass transition temperatures. Methods for preparing acrylic resins (c) with different glass transition temperatures (hereinafter referred to as Tg) include multistage polymerization, in which emulsion polymerization is performed using a multiple-stage dropping tank and different ethylenically unsaturated monomer compositions are dropped into each tank so that the resulting polymers have different Tg values, and methods in which acrylic resin (c) is first synthesized by bulk polymerization or solution polymerization, dissolved or dispersed in an aqueous phase, and then ethylenic monomers are dropped to produce a polymer with a different Tg from the previous acrylic resin (c) and polymerized. However, considering the simplicity of the process and the good dispersion stability of the resulting acrylic resin (c), it is more preferred to synthesize acrylic resins (c) with two or more different glass transition temperatures by multistage polymerization. The glass transition temperature Tg is preferably 0 to 100°C, and more preferably 15 to 80°C. When there are two or more Tg's, their average value is used. The average particle size is preferably in the range of 30 to 300 nm. By having a particle size in the above range, heat sealing properties and oil resistance can be sufficiently exhibited. The weight average molecular weight is preferably 100,000 or more. By having a weight average molecular weight of 100,000 or more, the coating layer forms a tough coating film, making it possible to obtain a laminate that does not penetrate even when exposed to moisture or oil. The glass transition temperature of the acrylic resin can be determined by subjecting the solid obtained by drying the resin to differential scanning calorimetry (DSC measurement). Details are given in the Examples section.

[0045] As the radical polymerization initiator used in the polymerization reaction of the ethylenically unsaturated monomer, a known oil-soluble polymerization initiator or water-soluble polymerization initiator can be used, and these may be used alone or in combination of two or more. The radical polymerization initiator is preferably used in an amount of 0.1 to 4 parts by mass, more preferably 0.2 to 2 parts by mass, based on 100 parts by mass of the total amount of the ethylenically unsaturated monomer.

[0046] The oil-soluble polymerization initiator is not particularly limited, and examples thereof include organic peroxides such as benzoyl peroxide, tert-butyl peroxybenzoate, tert-butyl hydroperoxide, tert-butylperoxy(2-ethylhexanoate), tert-butylperoxy-3,5,5-trimethylhexanoate, and di-tert-butyl peroxide; and azobis compounds such as 2,2'-azobisisobutyronitrile, 2,2'-azobis-2,4-dimethylvaleronitrile, 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), and 1,1'-azobis-cyclohexane-1-carbonitrile.

[0047] In emulsion polymerization, it is preferable to use a water-soluble polymerization initiator. As the water-soluble polymerization initiator, for example, conventionally known ones such as ammonium persulfate (APS), potassium persulfate (KPS), hydrogen peroxide, and 2,2'-azobis(2-methylpropionamidine) dihydrochloride can be suitably used.

[0048] In emulsion polymerization, a reducing agent may be used in combination with the polymerization initiator. The use of a reducing agent in combination accelerates the emulsion polymerization rate and facilitates emulsion polymerization at low temperatures. Examples of reducing agents include reducing organic compounds such as ascorbic acid, erythorbic acid, tartaric acid, citric acid, glucose, and metal salts of formaldehyde sulfoxylate; reducing inorganic compounds such as sodium thiosulfate, sodium sulfite, sodium bisulfite, and sodium metabisulfite; ferrous chloride, Rongalit, and thiourea dioxide. These reducing agents are preferably used in an amount of 0.05 to 5 parts by mass based on 100 parts by mass of the total amount of ethylenically unsaturated monomers.

[0049] The polymerization temperature may be equal to or higher than the polymerization initiation temperature of the polymerization initiator, and for example, in the case of a peroxide-based polymerization initiator, the polymerization temperature is usually about 80°C. The polymerization time is not particularly limited, but is usually 2 to 24 hours. The ethylenically unsaturated monomer may be polymerized by a photochemical reaction or radiation exposure, without using the above-mentioned polymerization initiator.

[0050] In the polymerization of ethylenically unsaturated monomers, a buffer or chain transfer agent may be further used as necessary. Examples of buffers include sodium acetate, sodium citrate, and sodium bicarbonate. Examples of chain transfer agents include n-hexyl mercaptan, n-heptyl mercaptan, t-hexyl mercaptan, t-heptyl mercaptan, n-octyl mercaptan, t-octyl mercaptan, n-nonyl mercaptan, t-nonyl mercaptan, n-decyl mercaptan, t-decyl mercaptan, n-undecyl mercaptan, t-undecyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, n-tridecyl mercaptan, t-tridecyl mercaptan, n-tetradecyl mercaptan, and t-tetradecyl mercaptan. Examples of the ethylenically unsaturated monomer include mercaptan, n-heptadecyl mercaptan, t-heptadecyl mercaptan, t-hexadecyl mercaptan, n-hexadecyl mercaptan, n-heptadecyl mercaptan, n-octadecyl mercaptan, t-heptadecyl mercaptan, t-octadecyl mercaptan, 2-ethylhexyl mercaptoacetate, octyl mercaptoacetate, methoxybutyl mercaptopropionate, 2-ethylhexyl mercaptopropionate, octyl mercaptopropionate, and stearyl mercaptopropionate. The buffer is preferably used in an amount of 0 to 1 part by mass, more preferably 0.05 to 0.5 parts by mass, based on 100 parts by mass of the total amount of the ethylenically unsaturated monomers. The chain transfer agent is preferably used in an amount of 0.4 to 3 parts by mass, more preferably 0.6 to 2 parts by mass, based on 100 parts by mass of the total amount of ethylenically unsaturated monomers.

[0051] Among the above chain transfer agents, it is preferable to use a chain transfer agent (X) represented by the following general formula (2).

[0052] [ka] R is a linear or branched alkyl group having 8 to 16 carbon atoms.

[0053] By using a chain transfer agent (X) during polymerization, a structure represented by general formula (1) can be introduced at one end of a polymer of an ethylenically unsaturated monomer. A polymer having a structure represented by general formula (1) at one end exhibits surface activity due to the moderate polarity contrast between the terminal alkyl group R, which is a low-polarity moiety, and the highly polar acrylic resin (c) bonded thereto, further improving the dispersion stability of the acrylic resin (c). This improves the stability of the coating solution and significantly reduces the formation of sediments and aggregates that can lead to coating defects and film formation failures. It also has the effect of improving the wettability of the resin to the substrate. This allows the coating solution to penetrate and bond firmly to the substrate, resulting in stronger bonding at the interface between the substrate and the resin.

[0054] Examples of the chain transfer agent (X) include n-octyl mercaptan, t-octyl mercaptan, n-nonyl mercaptan, t-nonyl mercaptan, n-decyl mercaptan, t-decyl mercaptan, n-undecyl mercaptan, t-undecyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, n-tridecyl mercaptan, t-tridecyl mercaptan, n-tetradecyl mercaptan, t-tetradecyl mercaptan, n-heptadecyl mercaptan, t-heptadecyl mercaptan, t-hexadecyl mercaptan, and n-hexadecyl mercaptan.

[0055] During polymerization of the ethylenically unsaturated monomer, a basic compound may be used as a neutralizing agent to enhance the dispersion stability of the acrylic resin (c). Examples of basic compounds include various organic amines such as aqueous ammonia, dimethylaminoethanol, diethanolamine, and triethanolamine; and inorganic alkali agents such as alkali metal hydroxides such as sodium hydroxide, lithium hydroxide, and potassium hydroxide. The basic compound may be added after the completion of the first dropwise addition or after the completion of the reaction.

[0056] Furthermore, when obtaining the acrylic resin (c), a surfactant can be used to improve the dispersion stability of the acrylic resin (c) as long as it does not adversely affect the properties of the coating liquid or the food packaging sheet. Examples of surfactants include anionic surfactants, cationic surfactants, nonionic surfactants, and amphoteric surfactants, but anionic surfactants or nonionic surfactants are preferred from the viewpoints of safety and the expression of good coating film properties. The surfactants can be used alone or in combination of two or more.

[0057] Examples of anionic surfactants that can be used include higher fatty acid salts such as sodium oleate, alkylarylsulfonates such as dodecylbenzenesulfonic acid, alkyl sulfates such as sodium lauryl sulfate, polyoxyethylene alkyl ether sulfates such as sodium polyoxyethylene lauryl ether sulfate, alkyl sulfosuccinates such as sodium monooctyl sulfosuccinate, sodium dioctyl sulfosuccinate, and sodium polyoxyethylene lauryl sulfosuccinate, and derivatives thereof, polyoxyethylene distyrenated phenyl ether sulfates, etc. Among the above, the surfactant is preferably an alkyl sulfate or an alkyl sulfosuccinate, and more preferably the alkyl sulfate is lauryl sulfate and the alkyl sulfosuccinate is dioctyl sulfosuccinate.

[0058] Examples of nonionic surfactants include polyoxyethylene alkyl ethers such as polyoxyethylene lauryl ether and polyoxyethylene stearyl ether, polyoxyethylene alkyl phenyl ethers such as polyoxyethylene octylphenyl ether and polyoxyethylene nonylphenyl ether, sorbitan higher fatty acid esters such as sorbitan monolaurate, sorbitan monostearate, and sorbitan trioleate, polyoxyethylene sorbitan higher fatty acid esters such as polyoxyethylene sorbitan monolaurate and polyoxyethylene sorbitan monostearate, polyoxyethylene higher fatty acid esters such as polyoxyethylene monolaurate and polyoxyethylene monostearate, glycerin higher fatty acid esters such as oleic acid monoglyceride and stearic acid monoglyceride, polyoxyethylene-polyoxypropylene block copolymers, polyvinyl alcohol, polyvinylpyrrolidone, and polyoxyethylene distyrenated phenyl ether.

[0059] The surfactant may be a polymerizable surfactant having one or more radically polymerizable ethylenically unsaturated double bonds in the molecule.

[0060] The polymerizable surfactant is preferably a polymerizable anionic surfactant or a polymerizable nonionic surfactant.

[0061] Examples of the polymerizable anionic surfactant include those having a main skeleton such as sulfosuccinate ester, alkyl ether, alkylphenyl ether, alkylphenyl ester, (meth)acrylate sulfate ester, and phosphate ester. Examples of the polymerizable nonionic surfactant include those whose main skeleton is alkyl ether, alkyl phenyl ether, or alkyl phenyl ester.

[0062] [Polyester resin (d)] The polyester resin (d) can be produced by a known method, such as polycondensing one or more polybasic acid components with one or more polyhydric alcohol components, depolymerizing the polybasic acid component after polycondensation, or adding an acid anhydride after polycondensation. The polyester resin (d) also includes polylactic acid-based resins produced by using lactic acid or caprolactone alone or both.

[0063] Specific examples of the polybasic acid component include terephthalic acid, isophthalic acid, phthalic acid, and inorganic acid. Aromatic dicarboxylic acids such as phthalic acid, naphthalenedicarboxylic acid, and biphenyldicarboxylic acid Acid, oxalic acid, succinic acid, succinic anhydride, adipic acid, azelaic acid, sebacic acid, dodecyl alcohol Candioic acid, hydrogenated dimer acid, fumaric acid, maleic acid, maleic anhydride, itaconic acid, Saturated or unsaturated acids such as itaconic anhydride, citraconic acid, citraconic anhydride, and dimer acids Examples of suitable dicarboxylic acids include aliphatic dicarboxylic acids, unsaturated dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid and terpene-maleic acid adducts, and anhydrides thereof, as well as alicyclic dicarboxylic acids such as 1,3-cyclohexanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, 2,5-norbornenedicarboxylic acid, 2,5-norbornenedicarboxylic acid anhydride, tetrahydrophthalic acid, and tetrahydrophthalic acid anhydride. A small amount of 5-sodium sulfoisophthalic acid or 5-hydroxyisophthalic acid can also be used as needed.

[0064] Polybasic acids with three or more functional groups can also be used, such as trimellitic acid, pyromellitic acid, Benzophenone tetracarboxylic acid, trimesic acid, ethylene glycol bis(anhydrotrimellitate), glycerol tris(anhydrotrimellitate), 1,2,3,4-butane tetracarboxylic acid, and the like may be included.

[0065] In addition, as the polybasic acid, acid dianhydrides such as pyromellitic anhydride (PMDA), oxydiphthalic dianhydride (ODPA), 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), 3,3',4,4'-diphenyltetracarboxylic dianhydride (BPDA), ethylene glycol bisanhydrotrimellitate (TMEG), 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride (DSDA), 4,4'-(hexafluoroisopropylidene)diphthalic dianhydride (6FDA), 2,2'-bis[(dicarboxyphenoxy)phenyl]propane dianhydride (BSAA), and glycerin trisanhydrotrimellitate can also be used.

[0066] Examples of the polyhydric alcohol component include aliphatic glycols, alicyclic glycols, ethers, and the like. Specific examples of the aliphatic glycol include: For example, ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 2-methyl-1,3-propanediol, 1,5-pentanediol Examples of suitable glycols include ethanol, neopentyl glycol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, 1,9-nonanediol, and 2-ethyl-2-butylpropanediol. Specific examples of alicyclic glycols include 1,4-cyclohexanedimethanol. Specific examples of ether bond-containing glycols include diethylene glycol, triethylene glycol, dipropylene glycol, and ethylene oxide adducts of bisphenols (bisphenol A) such as 2,2-bis[4-(hydroxyethoxy)phenyl]propane, ethylene oxide adducts of bisphenols (bisphenol S) such as bis[4-(hydroxyethoxy)phenyl]sulfone, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol. Among these, examples of long-chain ether bond-containing glycols include polyethylene glycol, polypropylene glycol, and polytetramethylene glycol with a molecular weight of 500 or more.

[0067] Examples of polyhydric alcohols with three or more functional groups include glycerin, trimethylolethane, trimethylolethane, and trimethylolethane. It may contain methylolpropane, pentaerythritol, diglycerin, polyglycerin, xylitol, sorbitol, glucose, fructose, mannose, etc. Furthermore, the polyhydric alcohol components described above may be partially modified before use.

[0068] The polyester resin (d) may be copolymerized with, as needed, fatty acids such as lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, and linolenic acid, or ester-forming derivatives thereof; monocarboxylic acids such as benzoic acid, p-tert-butylbenzoic acid, cyclohexanoic acid, and 4-hydroxyphenylstearic acid; monoalcohols such as stearyl alcohol and 2-phenoxyethanol; hydroxycarboxylic acids such as ε-caprolactone, lactic acid, β-hydroxybutyric acid, and p-hydroxybenzoic acid, or ester-forming derivatives thereof.

[0069] Polylactic acid-based polyesters can be easily obtained by ring-opening addition polymerization of lactides and lactones using a polyol as an initiator. The polyol may be the aforementioned polyhydric alcohol, or a polyester polyol having an ester bond. Examples of lactides that can be used include lactide (a cyclic dimer of lactic acid) and glycolide (a cyclic dimer of glycolic acid). Examples of lactones that can be used include β-propionolactone, β-butyrolactone, pivalolactone, γ-butyrolactone, γ-valerolactone, δ-valerolactone, and ε-caprolactone. These compounds do not necessarily need to be used alone; multiple types can be copolymerized. Of these, ε-caprolactone and lactide are preferred because of their excellent biodegradability and ease of polymerization.

[0070] When polymerizing polyester resin (d), it is effective to add various antioxidants. When the polymerization temperature is high or the polymerization time is long, the polylactic acid segment may be subject to oxidative degradation and discoloration due to its low heat resistance. Furthermore, if a segment with low heat resistance, such as polyether, is copolymerized, the polylactic acid may be even more susceptible to oxidative degradation, and in this case, the addition of an antioxidant is particularly effective. Examples of antioxidants include known ones such as phenol-based antioxidants, phosphorus-based antioxidants, amine-based antioxidants, sulfur-based antioxidants, nitro compound-based antioxidants, and inorganic compound-based antioxidants.

[0071] The polyester resin (d) can be made into an aqueous dispersion by introducing acid groups such as carboxyl groups into the resin skeleton and neutralizing all or part of the acid groups with a basic compound. Carboxy groups can be introduced by adjusting the amount of polybasic acid introduced so that the polyester resin has a carboxyl group at its terminal, or by using a polybasic acid with three or more functionalities to introduce carboxyl groups into the polymer side chain. Alternatively, sulfonates can be introduced as functional groups to produce aqueous dispersions. Examples of sulfonate introduction methods include the use of sulfonic acid group-containing polybasic acids such as 5-sodium sulfoisophthalic acid.

[0072] Examples of the basic compound used to neutralize the acid groups introduced into the polyester resin (d) include ammonia, organic amine compounds, and inorganic basic compounds.

[0073] Specific examples of the organic amine compound include alkylamines such as triethylamine, isopropylamine, ethylamine, diethylamine, and sec-butylamine; alkoxyamines such as 3-ethoxypropylamine, propylamine, N,N-dimethylethanolamine, and 3-methoxypropylamine; alkanolamines such as N,N-diethylethanolamine, aminoethanolamine, N-methyl-N,N-diethanolamine, monoethanolamine, diethanolamine, and triethanolamine; and morpholines such as morpholine, N-methylmorpholine, and N-ethylmorpholine.

[0074] Specific examples of the inorganic basic compound that can be used include alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, and potassium hydroxide, alkali metal carbonates such as sodium bicarbonate and sodium carbonate, bicarbonates, and ammonium carbonate. Since polyvalent metal basic compounds may form salts that are poorly soluble in water with the multiple carboxy groups contained in the polyester resin (d) and may deteriorate dispersibility, when used, it is preferable that the neutralization rate of the carboxy groups is 50% or less.

[0075] [Urethane resin (e)] The urethane resin (e) is a reaction product of a polyol and a polyisocyanate. Examples of polyols that can be used in the synthesis of the urethane resin (e) include polyether polyols such as polyethylene glycol, polypropylene glycol, poly(ethylene / propylene) glycol, and polytetramethylene glycol; ethylene glycol, propylene glycol, dipropylene glycol, diethylene glycol, triethylene glycol, butylene glycol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, 3,3'-dimethylolheptane, polyoxyethylene glycol, polyoxypropylene glycol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, octanediol, butylethylpentanediol, 2-ethyl-1,3-hexanediol, cyclohexanediol, and bisphenols. Polyester polyols obtained by reacting a difunctional diol such as A and / or a trifunctional diol such as glycerin, trimethylolpropane, or pentaerythritol with a dibasic acid such as terephthalic acid, adipic acid, azelaic acid, sebacic acid, dimer acid, hydrogenated dimer acid, phthalic anhydride, isophthalic acid, or trimellitic acid; polycarbonate polyols obtained by reacting the above-mentioned difunctional diols with a dialkyl carbonate, alkylene carbonate, or diaryl carbonate; polyolefin polyols such as hydroxyl group-containing polybutadiene, acid group-containing hydrogenated polybutadiene, hydroxyl group-containing polyisoprene, hydroxyl group-containing hydrogenated polyisoprene, hydroxyl group-containing chlorinated polypropylene, and hydroxyl group-containing chlorinated polyethylene; and castor oil polyols made from plant-derived oils. Additionally, ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butylene glycol, 1,3-butylene glycol, 2,3-butylene glycol, 1,4-butylene glycol, 2-methyl-1,3-propylene glycol, neopentyl glycol, 3-methyl-1,5-pentanediol, 2,2,4-trimethyl-1,3-pentanediol, 2,4-diethyl-1,5-pentanediol, and 2-ethyl-1,3-hexanediol. Aliphatic diols such as 2,2-dimethyl-3-hydroxypropyl-2',2'-dimethyl-3'-hydroxypropanate, 2-n-butyl-2-ethyl-1,3-propanediol, 3-ethyl-1,5-pentanediol, 3-propyl-1,5-pentanediol, 2,2-diethyl-1,3-propanediol, and 3-octyl-1,5-pentanediol, as well as 1,3-bis(hydroxymethyl)cyclohexane, 1,4-bis(hydroxymethyl)cyclohexane, and 1,4- Polyester polyols obtained by condensing one or more polyols selected from alicyclic glycols such as bis(hydroxyethyl)cyclohexane, 1,4-bis(hydroxypropyl)cyclohexane, 1,4-bis(hydroxymethoxy)cyclohexane, 1,4-bis(hydroxyethoxy)cyclohexane, 2,2-bis(4-hydroxymethoxycyclohexyl)propane, 2,2-bis(4-hydroxyethoxycyclohexyl)propane, bis(4-hydroxycyclohexyl)methane, 2,2-bis(4-hydroxycyclohexyl)propane, 3(4),8(9)-tricyclo[5.2.1.0]decanedimethanol, or aromatic glycols such as ethylene oxide or propylene oxide adducts to both terminal hydroxyl groups of bisphenol A, with 5-sodium sulfoisophthalic acid, 3-sodium sulfoterephthalic acid, or 4-potassium sulfo-1,8-naphthalenedicarboxylic anhydride, which are dibasic acids having a sulfonic acid metal salt group, may also be used. It is also possible to use a polyol (polylactic acid diol) having a hydroxyl group at the end of the polylactic acid polyester described above, and a urethane resin (e) containing a polylactic acid moiety can be obtained.

[0076] Examples of polyisocyanates that can be used in the synthesis of the urethane resin (e) include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, 4,4'-diphenylmethane diisocyanate, xylylene diisocyanate, lysine diisocyanate, 3,3'-dimethyl-4,4'-biphenylene diisocyanate, 3,3'-dimethoxy-4,4'-biphenylene diisocyanate, and 3,3'-dichloro-4,4 aromatic polyisocyanates such as 1,4-biphenylene diisocyanate, 1,5-naphthalene diisocyanate, and 1,5-tetrahydronaphthalene diisocyanate; aliphatic polyisocyanates such as tetramethylene diisocyanate, hexamethylene diisocyanate, and trimethylhexamethylene diisocyanate; and alicyclic polyisocyanates such as isophorone diisocyanate, 1,4-cyclohexylene diisocyanate, and 4,4'-dicyclohexylmethane diisocyanate.

[0077] In the synthesis of the urethane resin (e), a low molecular weight diol may be used in combination for the purpose of adjusting the urethane bond concentration or introducing various functional groups. The low-molecular-weight diol is preferably a diol having a molecular weight of 500 or less. Examples of such diols include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, pentanediol, hexanediol, octanediol, 2-butyl-2-ethyl-1,3-propanediol, 1,4-butylenediol, dipropylene glycol, glycerin, trimethylolpropane, trimethylolethane, 1,2,6-butanetriol, pentaerythritol, sorbitol, N,N-bis(2-hydroxypropyl)aniline, dimethylolalkanoic acids such as dimethylolacetic acid, dimethylolpropionic acid, dimethylolbutanoic acid, 2,2-dimethylolbutyric acid, and 2,2-dimethylolpentanoic acid, as well as dihydroxysuccinic acid, dihydroxypropionic acid, and dihydroxybenzoic acid.

[0078] The urethane resin (e) may be terminally modified or chain-extended. Examples of compounds that can be used for terminal modification and chain extension reactions include diamines such as hydrazine, ethylenediamine, propylenediamine, hexamethylenediamine, nonamethylenediamine, xylylenediamine, isophoronediamine, piperazine and its derivatives, phenylenediamine, tolylenediamine, xylenediamine, and N-(β-aminoethyl)ethanolamine; and dihydrazides such as adipic acid dihydrazide and isophthalic acid dihydrazide.

[0079] In the synthesis of urethane resin (e), a chain transfer agent may be used for molecular weight adjustment and terminal modification.As the chain transfer agent, a compound having a sulfanyl group is preferably used, for example, hydroxyalkanethiols such as 2-hydroxyethanethiol, 3-hydroxypropyl-1-thiol, 1-hydroxypropyl-2-thiol, 4-hydroxy-1-butanethiol; dithiols such as 1,2-ethanedithiol, 1,3-propanedithiol, 1,4-butanedithiol, 1,5-pentanedithiol, 1,6-hexanedithiol; aminoalkanethiols such as 2-aminoethanethiol, 3-aminopropyl-1-thiol, 1-aminopropyl-2-thiol, 4-amino-1-butanethiol; aminobenzenethiols such as 2-aminothiophenol, 3-aminothiophenol, 4-aminothiophenol. The urethane resin (e) whose terminals are modified with sulfanyl groups can be used to synthesize an acrylic-modified urethane resin by using the above-described ethylenically unsaturated monomer and a polymerization initiator. The acrylic-modified urethane resin can be suitably used as one type of urethane resin (e).

[0080] A commercially available product may be used as the aqueous dispersion of urethane resin (e). Examples of the commercially available product include the Superflex series (SF-170, SF-210, etc.) manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., the U-coat and Permarin series (UX-310, UX-3945, etc.) manufactured by Sanyo Chemical Industries, Ltd., the Juliano series (W-600, W-321, etc.) manufactured by Arakawa Chemical Industry Co., Ltd., the Adeka Pontitor series (HUX-420A, HUX-386) manufactured by ADEKA, the UW series (UW-5002, UW-5020, etc.) manufactured by Ube Industries, Ltd., and the Acrit series (WBR2000U, WBR2101, WEM-200U, etc.) manufactured by Taisei Fine Chemical Co., Ltd.

[0081] <Coating amount in laminate> The total coating weight of the first coating layer (A) and the second coating layer (B) in the laminate is 0.5 to 10 g / m 2 and 1.5 to 4 g / m 2 It is more preferable that the total coating amount is 0.5 g / m 2 If the total coating weight is 10 g / m or more, the coating layer will be sufficient to cover the paper substrate, preventing uneven coating and improving oil resistance, water resistance and heat sealability. 2 By keeping the coating weight of each of the first coating layer (A) and the second coating layer (B) within the range of 0.1 to 8 g / m, it is possible to prevent blocking that occurs when the coated surface and the uncoated surface are overlapped. 2 It is preferable that the density is 0.3 to 3.2 g / m 2 When the content is within this range, a smooth and even film can be formed on the paper substrate, and a laminate having good oil resistance, water resistance and blocking properties can be obtained.

[0082] In the laminate, the mass ratio ((A) / (B)) per unit area of ​​the first coating layer (A) to the second coating layer (B) is preferably 2 / 8 to 8 / 2, and more preferably 4 / 6 to 6 / 4. The first coating layer (A) is water-soluble and has low resistance to water but high resistance to oil. The second coating layer (B) is a water-insoluble resin (b) and has high resistance to water but low resistance to oil. By having the mass ratio per unit area within this range, a laminate that satisfies both oil resistance and water resistance can be obtained.

[0083] <Air barrier properties> The air barrier property in this application is the value of the degree of vacuum measured using a vacuum device under conditions where the degree of vacuum is 70 kPa when a copy paper is placed in the opening. 2 The measurement can be performed by placing a laminate in the opening under conditions where the hydraulic pump is set so that the degree of vacuum is 70 kPa when copy paper (product name: Multi Paper Super White+, manufactured by Askul Corporation) is placed in the opening. The smaller the value, the higher the degree of airtightness, meaning that a film is formed on the paper substrate without any gaps.

[0084] The laminate of the present invention has an air barrier property of 20 kPa or less. More preferably, the air barrier property is 5 kPa or less. When the laminate has an air barrier property of 20 kPa or less, a uniform coating film with little unevenness is formed on the paper substrate, and oil resistance and water resistance are improved.

[0085] The air barrier property is measured using the apparatus shown in Figure 1. A glass filter 2 is installed on top of a glass container 1, and a rubber tube 3 is attached to the side of the glass container, to which a hydraulic pump 4 and a vacuum gauge 5 are connected. The hydraulic pump 4 is used to reduce the pressure, and the degree of pressure reduction is measured using the vacuum gauge 5. Only the filter section 6 at the top of the device is allowed to pass air; the rest of the device is completely sealed. The filter section 6 is circular and 4 cm in diameter, and the glass filter section is flat relative to the glass section around the glass filter, with no protrusions or dents. If the glass filter section is not flat, an accurate degree of pressure reduction cannot be measured when the laminate is placed. The laminate 7 is placed on the glass filter section with the coated side facing down, and the degree of pressure reduction is measured; the value obtained is the air barrier property.

[0086] <Coating fluid> The coating liquid used to prepare the laminate will now be described. The coating liquid for forming the first coating layer is prepared using the modified starch (a) and the water-insoluble resin (b). Each coating liquid can be prepared by mixing the modified starch (a) and the water-insoluble resin (b) with water or a hydrophilic organic solvent in any desired ratio. Alternatively, they can be used alone without being mixed with water or a hydrophilic organic solvent. The modified starch (a) and the water-insoluble resin (b) used in this case can be used alone or in combination of two or more. Optional components can include additives such as extenders, antifoaming agents, leveling agents, preservatives, solvents, and waxes. It is preferable that the optional components do not pose a health risk if they remain in the laminate after coating.

[0087] Examples of hydrophilic solvents include monohydric alcohol solvents such as ethanol, 1-propanol, 2-propanol, 1-butanol, 2-methyl-1-propanol, 2-butanol, and 2-methyl-2-propanol; glycol solvents such as ethylene glycol, 1,3-propanediol, propylene glycol, 1,2-butanediol, 1,4-butanediol, pentylene glycol, 1,2-hexanediol, 1,6-hexanediol, diethylene glycol, triethylene glycol, and tetraethylene glycol; ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, triethylene glycol monoethyl ether, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, ethylene glycol monoisopropyl ether, diethylene glycol monoisopropyl ether, triethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, and diethylene glycol monoisopropyl ether. Examples of suitable solvents include glycol ether solvents such as glycol monobutyl ether, triethylene glycol monobutyl ether, ethylene glycol monoisobutyl ether, diethylene glycol monoisobutyl ether, triethylene glycol monoisobutyl ether, ethylene glycol monohexyl ether, diethylene glycol monohexyl ether, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol dimethyl ether, and tripropylene glycol monomethyl ether; lactam solvents such as N-methyl-2-pyrrolidone, N-hydroxyethyl-2-pyrrolidone, 2-pyrrolidone, and ε-caprolactam; and amide solvents such as formamide, N-methylformamide, N,N-dimethylformamide, and Idemitsu's Equamide M-100 and Equamide B-100. These solvents can be used alone or in combination of two or more.

[0088] The extender pigment is preferably one approved as a food or food additive, such as talc, silica, calcium carbonate, barium sulfate, titanium oxide, diatomaceous earth (white carbon), or cellulose powder.

[0089] Examples of the solvent include ethanol, isopropyl alcohol, propylene glycol, and glycerin from the viewpoint of oral safety.

[0090] Examples of waxes include carnauba wax, beeswax, paraffin wax, modified paraffin wax, polyethylene wax, oxidized polyethylene wax, modified polyethylene wax, polypropylene wax, oxidized polypropylene wax, modified polypropylene wax, ethylene-vinyl acetate copolymer wax, modified ethylene-vinyl acetate copolymer wax, fatty acid amide, microcrystalline wax, Fischer-Tropsch wax, and polytetrafluoroethylene.

[0091] The coating liquid for producing the first coating layer (A) preferably has a solids content of 5 to 40% and a viscosity at 25°C, as specified in JIS Z8803, of 5 to 500 mPa·s. Having a viscosity and solids content within these ranges allows for the formation of a uniform coating film on the substrate, and improves oil resistance, water resistance, and heat sealability. More preferably, the solids content is 15 to 35% and the viscosity at 25°C, as specified in JIS Z8803, is 30 to 300 mPa·s. The viscosity of the coating liquid is a value measured using a Brookfield viscometer at a temperature of 25° C. Details will be described in the Examples section.

[0092] The coating liquid for preparing the first coating layer (A) preferably has viscosities V1 and V2 measured using a rheometer that satisfy the condition shown in formula (1). Formula (1) V2≦1.5×V1 (V1: Viscosity 5 seconds after applying a shear rate of 2000 (l / s), V2: Viscosity 5 seconds after applying a shear rate of 50 (l / s)) When the coating liquid for preparing the first coating layer (A) satisfies the condition shown in formula (1), it is possible to reduce the thixotropy of the coating liquid.

[0093] It is known that the surface of a paper substrate is not completely uniform, and some unevenness exists, although the degree varies depending on whether or not the surface is treated. In the present invention, it is important to coat the first layer of coating film on the paper substrate as tightly as possible. When thixotropy is high, the fluidity of the coating liquid is good when force is applied from the plate to the substrate during gravure or flexographic printing, but the viscosity increases the moment it is transferred to the paper substrate. This results in poor wetting and spreading on the paper substrate, making it impossible to create a coating film without gaps on the paper substrate. If there are uncoated surfaces on the paper substrate, water and oil can penetrate through these areas, resulting in poor water and oil resistance of the laminate. However, by satisfying the viscosity condition defined by the above formula (1), thixotropy is reduced, enabling the paper substrate to be covered without gaps. Then, by coating a water-insoluble resin (b) with excellent water resistance as a second layer of coating film on top of the first layer of coating film coated tightly on the paper substrate, a laminate that combines water resistance, oil resistance, and heat sealability can be obtained.

[0094] <Method of manufacturing laminate> A laminate is formed by coating at least one side of a paper substrate with a first coating layer (A) and a second coating layer (B) in that order. An additional layer may be formed on the second coating layer. There are no particular restrictions on the number of coatings used to form the first coating layer (A) and the second coating layer (B); each layer may be coated once, or multiple layers may be coated.

[0095] When preparing a laminate, known coating methods such as offset gravure coaters, gravure coaters, doctor coaters, bar coaters, blade coaters, flexo coaters, and roll coaters can be used, but flexographic and gravure methods are preferred. The flexographic method involves transferring the coating liquid from an intaglio plate, known as an anilox roll, to a resin or rubber plate, and then transferring the coating liquid from the resin or rubber plate to a base sheet. It is also possible to pattern the resin or rubber plate. The gravure method includes a method in which the coating liquid is transferred directly from the intaglio plate to the base sheet, and a so-called gravure offset method in which the coating liquid is transferred from the intaglio plate to a planographic plate and then transferred to the base sheet. It is also possible to pattern the intaglio plate. In the gravure method, it is preferable to perform a press treatment with a smoothing roll after coating. By using the flexographic or gravure method, it is possible to create a smooth and even coating film even when the amount of coating is small, and to obtain a laminate with good oil resistance, water resistance and heat sealability.

[0096] <Food packaging sheet> The laminate of the present invention can be used as a food packaging sheet in applications where the laminate comes into direct contact with food. When used as a food packaging sheet, it is desirable that it be composed only of substances that comply with regulations in each country.

[0097] By applying the coating liquid multiple times after forming the coating layer, water resistance, oil resistance, and heat sealability can be improved. The coating layer may be impregnated into the substrate sheet, or a non-impregnated embodiment can also be used.

[0098] The food packaging sheet can be used to package not only confectioneries such as popcorn, chocolate, and caramel, and fruits and vegetables, but also burgers such as hamburgers, hot dogs, hamburgers, and rice burgers, fried foods such as fried chicken, French fries, fried chicken, tempura, and fried bread, grilled meat and seafood foods such as grilled chicken, yakitori, and saury, meat buns, red bean buns, dumplings, shumai, and spring rolls. It can also be used to package foods containing multiple ingredients such as oil, salt, acid, and amino acids, and high-moisture foods such as ketchup, sauces, and dressings. It can also be used as a sheet to package various foods such as frozen foods and paper trays for lunch boxes, and can be used in applications where the packaged food is heated in a microwave oven. The food packaging sheet of the present invention is suitable for applications in which the coating layer comes into direct contact with the various foods mentioned above. [Example]

[0099] The present invention will be described in more detail below with reference to examples, but the following examples do not limit the scope of the invention in any way. In the examples, "parts" means "parts by mass," "%" means "% by mass," and the values ​​in the tables are solid content masses, and blank spaces indicate empty spaces. The glass transition temperature, acid value, average particle size, and weight average molecular weight of the resin are measured as follows.

[0100] <Glass transition temperature> The glass transition temperature of the resin was measured using a DSC (differential scanning calorimeter, manufactured by TA Instruments). Specifically, an aluminum pan containing approximately 3 mg of dried resin was precisely weighed and placed in it, and an empty aluminum pan serving as a reference was set in a DSC measurement holder. Measurement was performed at a temperature increase rate of 10°C / min. The glass transition temperature (Tg) was determined as the temperature at the intersection of the baseline on the low-temperature side of the endothermic phenomenon and the tangent line at the inflection point in the DSC curve obtained.

[0101] <Acid value> The acid value of a resin is the number of milligrams of potassium hydroxide required to neutralize the acidic components contained in 1 g of dried resin. It was calculated by potentiometric titration of the dried water-soluble resin with a potassium hydroxide-ethanol solution according to the method specified in JIS K2501.

[0102] <Average particle size> The average particle size was measured by diluting the resin aqueous dispersion 500 times with water and measuring approximately 5 ml of the diluted solution using a dynamic light scattering measurement method (measuring device manufactured by Nanotrac UPA Co., Ltd., Microtrac Bell Co., Ltd.). The peak of the volume particle size distribution data (histogram) obtained at this time was taken as the average particle size.

[0103] <Weight average molecular weight> The weight-average molecular weight of the resin was measured by dissolving the dried resin in tetrahydrofuran (THF) to prepare a 0.2% solution, filtering the solution through a membrane filter (13HP045AN, manufactured by ADVANTEC, pore size 0.45 μm), and measuring the solution using the following equipment and conditions. Note that resins that do not completely dissolve in THF, or that dissolve but do not pass through the filter, were considered to have a sufficiently high molecular weight, and their molecular weight was set to 2 million or more. Apparatus: HLC-8320-GPC system (Tosoh Corporation) Column: TSKgel-Super Multipore HZ-M0021488 4.6 mm I.D. x 15 cm x 3 (molecular weight measurement range: 2000 to approximately 2,000,000) Elution solvent: tetrahydrofuran Standard material: Polystyrene (manufactured by Tosoh Corporation) Flow rate: 0.6mL / min Amount of sample solution used: 10 μL Column temperature: 40℃

[0104] <Viscosity at 25°C as specified in JIS Z8803> Based on JIS Z8803, measurements were carried out using a rotational viscometer (Toki Sangyo B-type viscometer: TVB-10, measurement conditions: rotor No. 2, rotor rotation speed 60 rpm) at a measurement temperature of 25°C.

[0105] <Viscosity V1, Viscosity V2> The viscosities V1 and V2 were measured using a rheometer, MCR302 manufactured by Anton Paar, Inc. The measurements were carried out using a cone plate (60 mm, 1°) at a measurement temperature of 25°C.

[0106] <Transmittance> The transmittance of the resin was measured using an ultraviolet-visible-near-infrared spectrophotometer (JASCO V-770D). The resin solution was diluted with water to a solids content of 5%, and then placed in a glass cell to measure the transmittance at a wavelength of 660 nm. When measuring transmittance, it is necessary to use a resin solution prepared by diluting a single resin with water, and the resin must not contain any other substances that would change the transmittance, such as inorganic fillers or wax.

[0107] <Production of Water-insoluble Resin Aqueous Dispersions (b1 to b6)> [Water dispersion of water-insoluble resin (polyester resin) (b1)] A mixture of 2492 g of terephthalic acid, 415 g of isophthalic acid, 1516 g of sebacic acid, 1210 g of ethylene glycol, and 1484 g of neopentyl glycol was heated in an autoclave at 250°C for 5 hours to carry out an esterification reaction. Next, 3.3 g of zinc acetate dihydrate was added as a catalyst, and the system temperature was raised to 275°C. The system pressure was gradually reduced to 13 Pa after 1.5 hours. The polycondensation reaction continued under these conditions for an additional 4 hours, and the system was then returned to atmospheric pressure with nitrogen gas. The system temperature was then lowered. At 265°C, 29 g of trimellitic anhydride was added, and the mixture was stirred at 265°C for 2 hours to carry out a depolymerization reaction. The system was then pressurized with nitrogen gas, and the resin was discharged in the form of a sheet. After cooling at room temperature, a polyester resin sheet was obtained. 400 g of the obtained sheet-like polyester resin and 600 g of methyl ethyl ketone (MEK) were placed in a 3 L polyethylene container, and the container was heated with warm water at approximately 60°C while stirring with a stirrer, thereby completely dissolving the polyester resin in the MEK and obtaining a polyester resin solution with a solids concentration of 40 mass%. Next, 500 g of the polyester resin solution was placed in a jacketed glass vessel, and the system temperature was maintained at 13°C by running cold water through the jacket, followed by stirring with a stirrer. Next, while stirring, 23.3 g of triethylamine was added as a basic compound, followed by water at a rate of 100 g / min, to obtain a water dispersion (b1) of polyester resin with a nonvolatile content of 35%. The resulting (b1) was adjusted with water to a nonvolatile content of 5%, and the transmittance was measured, revealing a transmittance of 10%.

[0108] [Water dispersion of non-water-soluble resin (acrylic resin) (b2)] A reaction vessel (reactor) equipped with a stirrer, thermometer, dropping funnel, and reflux condenser was charged with 83.6 parts of water and 0.35 parts of Emal 0 (Kao Corporation, sodium lauryl sulfate, active ingredient 100%). Separately, 30.0 parts of ethyl acrylate, 53.0 parts of methyl methacrylate, 7.0 parts of n-butyl acrylate, 10.0 parts of methacrylic acid, 3.9 parts of t-dodecyl mercaptan, 0.80 parts of Emal 0, and 52.9 parts of water were premixed and stirred to prepare an emulsion of ethylenically unsaturated monomers (first-stage dropping vessel) to be added dropwise to the first stage. The internal temperature of the reaction vessel was raised to 80 °C and thoroughly purged with nitrogen. Then, 5.5 parts of a 5% aqueous solution of potassium persulfate was added as an initiator to initiate emulsion polymerization. While maintaining the internal temperature at 80°C, the emulsion of the ethylenically unsaturated monomer to be added dropwise in the first stage and 5.5 parts of a 5% aqueous solution of potassium persulfate were added dropwise over 2 hours. After the first stage of the ethylenically unsaturated monomer emulsion was completed, 30 minutes were allowed to pass, and then the second stage of the ethylenically unsaturated monomer emulsion (second stage dropping tank) was prepared by mixing and stirring 30.0 parts of ethyl acrylate, 50.0 parts of methyl methacrylate, 10.0 parts of n-butyl methacrylate, 20.0 parts of n-butyl acrylate, 2.0 parts of acrylic acid, 15.0 parts of 2-ethylhexyl acrylate, 2.0 parts of cyclohexyl acrylate, 1.0 parts of glycidyl methacrylate, 1.0 parts of diethylene glycol dimethacrylate, 0.1 parts of t-dodecyl mercaptan, 1.20 parts of EMAIL 0, and 160.8 parts of water. 11.1 parts of a 10% aqueous solution of ammonium persulfate was added dropwise over 2 hours. After the completion of the dropwise addition, the mixture was allowed to react for another 3 hours at 80 ° C. After the reaction was complete, 9.8 parts of 25% aqueous ammonia was added with stirring to neutralize the mixture, and the acrylic resin was dispersed in water. Further water was added to adjust the nonvolatile content to 35%, yielding the target aqueous dispersion of acrylic resin (b2). The resulting (b2) was adjusted to a nonvolatile content of 5% with water, and the transmittance was measured, resulting in a transmittance of 8%. The Tg values ​​of the resulting acrylic resin were 8.4°C and 56.4°C, the acid value was 33.8 mg KOH / g, and the average particle size was 200 nm. Furthermore, because the acrylic resin was insoluble in THF, the mass-average molecular weight was set to 2 million or more.

[0109] [Water dispersion of non-water-soluble resin (acrylic-modified urethane resin) (b3)] First, a reaction vessel equipped with a stirrer, a thermometer, and a reflux condenser was charged with 14.6 parts of polytetramethylene glycol (PTG-2000SN manufactured by Hodogaya Chemical Co., Ltd., functionality 2, hydroxyl value 57.0 mg KOH / g) as a polyol, 20.2 parts of polyester polyol (P-2011 manufactured by Kuraray Co., Ltd., functionality 2, hydroxyl value 56.0 mg KOH / g), 48.6 parts of polycarbonate polyol (C-2090 manufactured by Kuraray Co., Ltd., functionality 2, hydroxyl value 56.3 mg KOH / g), 4.3 parts of dimethylol butanoic acid, 0.1 parts of neopentyl glycol, and 9.7 parts of isophorone diisocyanate as a polyisocyanate, and the mixture was heated to 80°C with stirring under a nitrogen atmosphere. Next, 0.02 parts of titanium diisopropoxybiz(ethyl acetoacetate) was added, and the mixture was heated to 110° C. and reacted for 5 hours, after which the temperature was lowered to 80° C. At this time, the weight average molecular weight of the produced urethane prepolymer was 32,100. Next, 40.0 parts of methyl ethyl ketone and 2.4 parts of 2-aminoethanethiol were added, and the mixture was allowed to react at 75° C. for 2 hours. The end point of the reaction was determined by FT-IR when a peak (2270 cm ) derived from an isocyanato group was detected. -1The disappearance of the solids (around 1000 ppm) was confirmed. Further, methyl ethyl ketone was added to adjust the solids concentration to 70%, yielding a solution of urethane resin U1 having sulfanyl groups at both ends. Next, 50 parts of the urethane resin U1 solution obtained above, 5.0 parts of styrene, 13.0 parts of methyl methacrylate, 9.0 parts of n-butyl acrylate, 2.0 parts of methacrylic acid, 1.0 parts of diacetone acrylamide, 18.0 parts of RUVA-093, 2.0 parts of ADK STAB LA-82, and 35.0 parts of n-propanol were added to a reaction vessel equipped with a stirrer, thermometer, dropping funnel, and reflux condenser, and the mixture was heated to 75°C while stirring under a nitrogen atmosphere. 20.0 parts of methyl ethyl ketone and 0.35 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) as an initiator were charged to the dropping funnel, and the mixture was added dropwise to the reaction vessel over 5 hours. The reaction was carried out at 78°C for 8 hours to complete the graft reaction of the acrylic resin (c). After the reaction, 10 parts of water was added, and 25% ammonia water was added to the resin to make an equimolar amount relative to the carboxyl groups, followed by neutralization and a solvent removal treatment. Water was added to the resulting aqueous dispersion to adjust the nonvolatile content to 35%, yielding the target aqueous dispersion of acrylic-modified urethane resin (b3). The resulting (b3) was adjusted with water to a nonvolatile content of 5%, and the transmittance was measured; the transmittance was 5%.

[0110] [Water dispersion of non-water-soluble resin (polylactic acid polyester resin) (b4)] A 500 ml glass flask equipped with a thermometer, stirrer, and Liebig condenser was charged with 8.7 parts of polyglycerol ethylene oxide adduct (number average molecular weight 1000), 67.3 parts of L-lactide, 16.8 parts of D-lactide, and 0.028 parts of tin octoate as a catalyst, and nitrogen gas was passed through at 60°C for 30 minutes. The pressure was then reduced to 60°C for 30 minutes, and the contents were further dried. The polymerization system was again heated to 180°C while passing nitrogen gas through, and after reaching 180°C, the system was stirred for 3 hours. Next, 0.018 parts of phosphoric acid was added, and after stirring for 20 minutes, the system was reduced in pressure and unreacted lactide and caprolactone were distilled off. After approximately 20 minutes, when the distillation of unreacted materials had ceased, 5.5 parts of succinic anhydride was added, and the mixture was stirred at 180°C for 2 hours. The contents were then removed and cooled. A 500 ml glass flask equipped with a thermometer, stirrer, and Liebig condenser was charged with 25 parts of polylactic acid polyester resin and 1.0 part of TEA, and ion-exchanged water was added to adjust the nonvolatile content to 35%. The temperature was then raised to 70°C and stirred for 1 hour. The contents were then removed and cooled to obtain the target aqueous dispersion of polylactic acid polyester resin (b4). The resulting (b4) was adjusted with water to a nonvolatile content of 5% and the transmittance was measured, which was 13%.

[0111] [Water dispersion of non-water-soluble resin (polylactic acid polyester resin) (b5)] A 500 ml glass flask equipped with a thermometer, stirrer, and Liebig condenser was charged with 8.7 parts of polyglycerol ethylene oxide adduct (number average molecular weight 1000), 74.4 parts of L-lactide, 15.2 parts of ε-caprolactone, and 0.028 parts of tin octoate as a catalyst, and nitrogen gas was passed through at 60°C for 30 minutes. The pressure was then reduced to 60°C for 30 minutes, and the contents were further dried. The polymerization system was again heated to 180°C while passing nitrogen gas through, and after reaching 180°C, the system was stirred for 3 hours. Next, 0.018 parts of phosphoric acid was added, and after stirring for 20 minutes, the system was reduced in pressure and unreacted lactide and caprolactone were distilled off. After approximately 20 minutes, when the distillation of unreacted materials had ceased, 5.5 parts of succinic anhydride was added, and the mixture was stirred at 180°C for 2 hours. The contents were then removed and cooled. A 500 ml glass flask equipped with a thermometer, stirrer, and Liebig condenser was charged with 25 parts of polylactic acid polyester resin, 1.0 part of TEA, and 75 parts of water, and the mixture was heated to 70°C and stirred for 1 hour. The contents were then removed and cooled, and water was added to the resulting aqueous dispersion to adjust the nonvolatile content to 35%, producing the target aqueous dispersion (b5) of polylactic acid polyester resin. The resulting (b5) was adjusted with water to a nonvolatile content of 5%, and the transmittance was measured, finding it to be 15%.

[0112] [Water dispersion of non-water-soluble resin (polylactic acid-containing urethane resin) (b6)] A 1 L glass flask equipped with a thermometer, stirrer, and Liebig condenser was charged with 408 parts of 2,2-dimethyl-3-hydroxypropyl-2',2'-dimethyl-3'-hydroxypropanate, 197 parts of 5-sodium dimethyl sulfoisophthalate, and 0.1 parts of tetrabutyl titanate (TBT) catalyst. After stirring and reacting for 1 hour while distilling off the methanol distilled at 190°C, the temperature was raised by 10°C every hour until it reached 230°C. After confirming completion of methanol distillation at 230°C, the temperature was raised to 250°C, stirred under reduced pressure for 10 minutes, and then cooled to 100°C. 141 parts of toluene was added and the mixture was dissolved uniformly to obtain a sulfonic acid-containing diol. Next, 18 parts of NPG, 400 parts of L-lactide, 100 parts of D-lactide, and 0.15 parts of tin octoate as a catalyst were placed in a 1 L glass flask equipped with a thermometer, a stirrer, and a Liebig condenser, and the flask was left under a nitrogen gas flow at room temperature for 30 minutes. The pressure was then reduced for 30 minutes at room temperature to further dry the contents. The reaction system was again heated to 180°C under a nitrogen gas flow and stirred for 3 hours. Next, 0.10 parts of phosphoric acid was added, and after stirring for 30 minutes, the system was decompressed and the unreacted residual lactide was distilled off. After approximately 20 minutes, when the distillation of unreacted lactide had ceased, the contents were removed and cooled to obtain polylactic acid diol. In a 1-L glass flask equipped with a thermometer, stirrer, and condenser, 100 parts of the polylactic acid diol and 62.5 parts of the sodium sulfonate salt group-containing diol (80 wt % toluene solution) were dissolved in 200 parts of MEK and heated to 50°C. Next, 38 parts of MDI were dissolved, and 0.4 parts of dibutyltin laurate was added as a catalyst. After 4 hours of reaction at 70°C, the mixture was diluted with 238 parts of MEK. The mixture was then heated to 50°C, and deionized water was gradually added with stirring to achieve uniform mixing. Next, MEK was distilled off under reduced pressure while maintaining the contents at 50°C, and the MEK / water mixture was removed. Thereafter, the dispersion was diluted with deionized water to a non-volatile content of 35%, thereby obtaining an aqueous dispersion of polylactic acid-containing urethane resin ((b6)). The obtained (b6) was adjusted with water to a non-volatile content of 5%, and the transmittance was measured, and the transmittance was found to be 30%.

[0113] [Water dispersion of non-water-soluble resin (acrylic resin) (b7)] A reaction vessel (reactor) equipped with a stirrer, thermometer, dropping funnel, and reflux condenser was charged with 83.6 parts of water and 0.35 parts of Emal 0 (Kao Corporation, sodium lauryl sulfate, active ingredient 100%). Separately, 30.0 parts of ethyl acrylate, 46.0 parts of methyl methacrylate, 7.0 parts of n-butyl acrylate, 17.0 parts of methacrylic acid, 3.9 parts of t-dodecyl mercaptan, 0.80 parts of Emal 0, and 52.9 parts of water were premixed and stirred to prepare an emulsion of ethylenically unsaturated monomers (first-stage dropping vessel) to be added dropwise to the first stage. The internal temperature of the reaction vessel was raised to 80 °C and thoroughly purged with nitrogen. Then, 5.5 parts of a 5% aqueous solution of potassium persulfate was added as an initiator to initiate emulsion polymerization. While maintaining the internal temperature at 80°C, the emulsion of the ethylenically unsaturated monomer to be added dropwise in the first stage and 5.5 parts of a 5% aqueous solution of potassium persulfate were added dropwise over 2 hours. After the first stage of the ethylenically unsaturated monomer emulsion was completed, 30 minutes were allowed to pass, and then the second stage of the ethylenically unsaturated monomer emulsion (second stage dropping tank) was prepared by mixing and stirring 30.0 parts of ethyl acrylate, 50.0 parts of methyl methacrylate, 10.0 parts of n-butyl methacrylate, 20.0 parts of n-butyl acrylate, 2.0 parts of acrylic acid, 15.0 parts of 2-ethylhexyl acrylate, 2.0 parts of cyclohexyl acrylate, 1.0 parts of glycidyl methacrylate, 1.0 parts of diethylene glycol dimethacrylate, 0.1 parts of t-dodecyl mercaptan, 1.20 parts of EMAIL 0, and 160.8 parts of water. 11.1 parts of a 10% aqueous solution of ammonium persulfate was added dropwise over 2 hours. After the completion of the dropwise addition, the mixture was allowed to react for another 3 hours at 80 ° C. After the reaction was complete, 9.8 parts of 25% aqueous ammonia was added with stirring to neutralize the mixture and disperse it in water. Further water was added to adjust the nonvolatile content to 35%, yielding the target acrylic resin aqueous dispersion (b7). The resulting (b7) was adjusted to a nonvolatile content of 5% with water, and the transmittance was measured; it was 10%. The Tg values ​​of the resulting resin were 8.4°C and 46.2°C, the acid value was 43.4 mg KOH / g, and the average particle size was 180 nm. Furthermore, because the resin was insoluble in THF, the mass-average molecular weight was set to 2 million or more.

[0114] The materials in Table 1 are as follows: Modified starch (a); Pyostarch LV (Nippon Starch Chemical Co., Ltd., hydroxypropylated starch, Mw 100,000, degree of substitution 0.1, transmittance 96%) SK-20 (manufactured by Japan Cornstarch Co., Ltd., oxidized starch, transmittance 85%) Brivine P-63 (Nippon Starch Chemical Co., Ltd., starch phosphate, Mw 5600, transmittance 88%) Polyvinyl alcohol; Exeval RS2117 (Kuraray Co., Ltd., modified polyvinyl alcohol, Mw 74800, transmittance 90%) an aqueous dispersion of a water-insoluble resin (b); Superflex SF-170 (Dai-ichi Kogyo Seiyaku Co., Ltd., polyurethane resin water dispersion, pH 7-9, average particle size 10 μm, transmittance 45%, non-volatile content 33%)

[0115] <Production of coating fluid> [Manufacturing Example 1] 70 parts of water and 30 parts of Pyostarch LV (Nippon Starch Chemical Co., Ltd.) were added to a reaction vessel (reaction tank) equipped with a stirrer, thermometer, dropping funnel, and reflux condenser, and the temperature of the reaction vessel was raised to 85°C while stirring. A solution was then created by stirring for 2 hours. Next, 5 parts of IPA was added and stirred for 10 minutes to obtain the desired coating solution. The viscosity of the resulting coating solution was measured using a Brookfield viscometer and found to be 100 mPa·s. The nonvolatile content was 29%. Viscosity measurements using a rheometer revealed a viscosity V1 of 90 mPa·s and a viscosity V2 of 120 mPa·s.

[0116] [Manufacturing Examples 2 to 11] Coating liquids were obtained in the same manner as in Production Example 1, except that the blending compositions were changed to those shown in Table 1. For each of the resulting coating liquids, viscosity measurements were carried out using a Brookfield viscometer, viscosity measurements using a rheometer, and non-volatile content measurements. [Manufacturing Example 12] 100 parts of a water-insoluble resin (polyester resin) dispersion (b1) was added to a reaction vessel (reaction tank) equipped with a stirrer, thermometer, dropping funnel, and reflux condenser, and stirred at room temperature. A mixture of 15 parts water and 0.5 parts IPA was then added while stirring to obtain a coating solution. The viscosity of the resulting coating solution was measured using a Brookfield viscometer and found to be 150 mPa·s. The nonvolatile content was 30%. Viscosity measurements using a rheometer revealed a viscosity V1 of 120 mPa·s and a viscosity V2 of 300 mPa·s. [Manufacturing Examples 13 to 19] Coating liquids were obtained in the same manner as in Production Example 12, except that the blending compositions were changed to those shown in Table 1. For each of the resulting coating liquids, viscosity measurements were carried out using a Brookfield viscometer, viscosity measurements using a rheometer, and non-volatile content measurements were carried out.

[0117] [Table 1]

[0118] <Preparation of laminate> [Example 1] The glossy side of commercially available sanitary paper (21 g, gloss-treated on one side) was first coated with the coating liquid of Production Example 1, and then with the coating liquid of Production Example 11, using a "SOLOFLEX" central impression (CI) 6-color flexographic printing press manufactured by Windmiller & Hoelscher. The coating amounts were adjusted so that the coating weight ratio after drying would be 5:5 for the first layer and the second layer. The product was then dried in an oven at 80°C to obtain a laminate. The coating amount of the laminate was measured and found to be 2 g / m 2 It was.

[0119] [Examples 2 to 22, 25] Each laminate was produced in the same manner as in Example 1, except that the blending compositions, coating amounts, and ratios of the first layer and the second layer were changed to those shown in Tables 2 and 3.

[0120] [Example 23] The coating solution of Production Example 1 was applied to the glossy side of commercially available sanitary paper (weighing 21 g, gloss-treated on one side) using a simple gravure coater (GRAVO-PROOF MINI manufactured by Nissho Gravure Corporation) and dried in an oven at 80°C. Thereafter, the coating solution of Production Example 12 was applied on top of the first layer and dried in an oven at 80°C. The coating amount was adjusted so that the coating weight ratio of the first layer to the second layer after drying was 5:5. The coating amount of the laminate was measured and found to be 2 g / m 2 It was.

[0121] [Example 24] The coating solution of Production Example 1 was applied to the glossy side of commercially available sanitary paper (weighing 21 g, gloss-treated on one side) using a bar coater, and then dried in an oven at 80°C. Thereafter, the coating solution of Production Example 11 was applied on top of the first layer, and then dried in an oven at 80°C. The coating amounts were adjusted so that the coating weight ratio of the first layer to the second layer after drying was 5:5. The coating amount of the laminate was measured and found to be 2 g / m 2 It was.

[0122] [Comparative Examples 1 to 10] Each laminate was produced in the same manner as in Example 1, except that the blending composition, coating amount, and ratio of the first layer to the second layer were changed as shown in Table 3.

[0123] The laminate was evaluated as follows.

[0124] <Air barrier properties> The air barrier property in the present invention was measured by the method described in the section on air barrier property above. The obtained laminate was cut into a piece of 5 cm x 5 cm. The laminate was placed under reduced pressure so that the coated surface was aligned with the glass filter surface. At this time, the laminate and the glass filter surface were brought into complete contact to prevent the laminate from folding and wrinkling. After placing the laminate in the measurement location, the vacuum level was read once the reading on the vacuum gauge had stabilized, and this was used as the air barrier value. The measurement was carried out in a constant temperature and humidity chamber at a temperature of 25°C and a humidity of 60%.

[0125] <Blocking property test> The coated surface and the uncoated surface of the resulting laminate were placed together, and the blocking resistance was measured using the following equipment and under the following measurement conditions. Equipment: CO-201 permanent strain tester (Tester Sangyo Co., Ltd., upper and lower plate heating) Condition: 2kg / cm 2 -40℃-24 hours [Evaluation criteria] S: No resistance when peeled off, and no damage to the paper (very good) A: There is some resistance when peeling, but the paper is not damaged (good) B: There is some resistance when peeling, but the paper is not damaged (usable) C: There is resistance when peeling and the paper is damaged (unusable)

[0126] <Heat sealability> The resulting laminate was cut into a 15 mm wide piece, which was used as a test piece to measure the heat seal strength using the following equipment and measurement conditions. (heat seal) Equipment: HEATSHEEL&IMPULSE TESTER (manufactured by Nichiri Kagaku Kogyo Co., Ltd., upper and lower plate heating) Heat sealing conditions: 130℃-2kgf / cm 2 -1 second (peeling) Equipment: Tensile testing machine (manufactured by Tester Sangyo Co., Ltd.) Peeling conditions: 180° peel, 300 mm / min [Evaluation criteria] S: 2N or better (very good) A: 1.5N or more, less than 2N (good) B: 1N or more, less than 1.5N (usable) C: Less than 1N (unusable)

[0127] <Oil resistance> A drop of castor oil was dropped onto the coated surface of the resulting laminate in an environment of 23°C, and after 30 seconds, it was confirmed whether the castor oil had soaked into the laminate. Evaluation was made based on the percentage of the area onto which the castor oil had soaked and discolored the paper. [Evaluation criteria] S: No penetration observed (very good) A: Less than 10% of the area is soaked (good) B: The area soaked is between 10% and 50% (usable). C: Over 50% of the surface area is soaked (very poor)

[0128] <Water resistance> A drop of water was dropped onto the coated surface of the resulting laminate in an environment of 23°C, and after 30 seconds, it was checked whether the water had soaked into the laminate. Evaluation was made based on the percentage of the area onto which the water had soaked and discolored the paper. [Evaluation criteria] S: No penetration observed (very good) A: Less than 10% of the area is soaked (good) B: The area soaked is between 10% and 50% (usable). C: Over 50% of the surface area is soaked (very poor)

[0129] <Biodegradability test> The coating liquid used to prepare the laminate was dried to prepare a film 0.5 mm thick, 10 cm long, and 10 cm wide, which was then buried in compost for one month. The film prepared with the coating liquid used to prepare the first coating layer was designated test piece α, and the film prepared with the coating liquid used for the second coating layer was designated test piece β. When the total volume of test piece α and test piece β was taken as 100%, evaluation was performed based on the percentage of residue that could be visually confirmed after the test. [Evaluation criteria] S: Less than 60% of the residue is visible to the naked eye (very good) A: Residue visible to the naked eye is between 60% and 70% (good) B: Residue visible to the naked eye is between 70% and 90% (usable) C: More than 90% of the residue is visible to the naked eye (very poor)

[0130] [Table 2]

[0131] [Table 3]

[0132] According to the results in Tables 2 and 3, the coated products prepared using modified starch in the first coating layer and a water-insoluble resin in the second coating layer of the present invention had excellent oil resistance, water resistance, heat seal strength, and blocking resistance. In particular, Example 1, which used hydroxypropylated starch in the first coating layer, showed superior oil resistance and water resistance compared to Example 9, which used phosphated starch in the first coating layer. On the other hand, in Comparative Examples 1 and 2, polyvinyl alcohol was used in the first coating layer, but the oil resistance and water resistance were significantly reduced. In Comparative Example 8, polyester resin was used in the first layer, and no biodegradability was observed at all. [Explanation of symbols]

[0133] 1 glass container 2 glass filters 3 rubber tubes 4 Hydraulic pump 5 Vacuum gauge 6 Filter part 7 Laminate (measurement sample)

Claims

1. A paper substrate has a first coating layer (A) on at least one side thereof, A laminate further having a second coating layer (B) on the first coating layer, the first coating layer (A) comprises at least one modified starch (a); and, the second coating layer (B) contains at least one water-insoluble resin (b) as a main component; the water-insoluble resin (b) is at least one selected from the group consisting of an acrylic resin (c), a polyester resin (d), and a urethane resin (e) (excluding polyurethanes having a hydroxyl group); The total coating weight of the first coating layer (A) and the second coating layer (B) is 0.5 to 10 g / m ２ and A laminate for food packaging sheets, characterized in that the air barrier property is 20 kPa or less.

2. 2. A coating liquid for forming the first coating layer (A) of the laminate for food packaging sheets according to claim 1, which satisfies the following formula (1): Formula (1) V ２ ≦1.5×V １ (V １ : Viscosity 5 seconds after applying a shear rate of 2000 (l / s) to the coating liquid, V ２ : Viscosity 5 seconds after applying a shear rate of 50 (l / s) to the coating liquid

3. 3. The coating liquid according to claim 2, wherein the solid content is 5 to 40% and the viscosity at 25° C. as specified in JIS Z8803 is 5 to 500 mPa·s.

4. 4. The laminate for food packaging sheets according to claim 1, which has a first coating layer (A) formed from the coating liquid according to claim 2 or 3.

5. 5. The laminate for food packaging sheets according to claim 1, wherein the mass ratio per unit area of ​​the first coating layer (A) to the second coating layer (B) ((A) / (B)) is 2 / 8 to 8 / 2.

6. 6. The method for producing a laminate for food packaging sheets according to claim 1, wherein the first coating layer (A) and the second coating layer (B) are formed by gravure printing or flexographic printing.

7. 6. The laminate for food packaging sheets according to claim 1, wherein the modified starch (a) is a modified starch obtained by hydroxyalkylating or oxidizing raw starch.

8. A food packaging sheet for containing food, comprising the laminate for food packaging sheets according to any one of claims 1, 4, 5 and 7.

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