JP7735770B2 - Laminate, coating liquid, food packaging sheet, and method for manufacturing laminate - Google Patents

Description

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 manufacturing the laminate.

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 liquid materials is also increasing year by year. Biomass-derived materials are materials made from biological resources. From the perspective of carbon neutrality, even if a material is incinerated, the amount of _CO2 emitted is the same as the amount absorbed by the plants used as raw materials. Consequently, it is believed that there is no impact on the increase or decrease of _CO2 in the atmosphere, and therefore the environmental impact is smaller than that of petroleum-derived products. Biodegradable materials are known to have a 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 film properties compared to conventional coating liquid types, and there is a demand for laminates suitable for food packaging sheets with good coating film properties, such as oil resistance, water resistance, heat sealability, and blocking properties.

In contrast, for example, Patent Document 1 produces 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 is biodegradable, it can be said to be a laminate with a low environmental impact. However, the laminate obtained using the production method of Patent Document 1 has poor water resistance because it is primarily composed of starch alone, and even the addition of wax is not sufficient to impart water resistance. Many prepared foods and fast foods that use laminates with excellent oil resistance and air permeability contain more water than oil, and there is a risk that water will seep into the laminate. Furthermore, from the perspective of processing the laminate, heat sealability is required of the laminate, and heat sealability cannot be achieved with a composition consisting only of starch and wax.

In Patent Document 2, a laminate with excellent oil resistance is created using a coating liquid that mixes starch or PVA with polylactic acid. However, as with Patent Document 1, the starch or PVA, which has poor water resistance, is present on the film surface, allowing water to penetrate, resulting in insufficient water resistance. Furthermore, mixing starch or PVA with polylactic acid also reduces film-forming properties, adversely affecting oil resistance and heat sealability.

Patent Document 3 describes the creation of a laminate with excellent water and oil resistance, which has a first layer of starch and a second layer of a fluoropolymer. However, when fluorine-based compositions are heated, the fluorine compounds present in the paper undergo thermal decomposition, generating fluorine-based hydrocarbons that are difficult to decompose in nature, and this has been pointed out as causing problems such as environmental pollution. As a shift from laminate films to liquid coating 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.

JP 2018-53374 A Japanese Patent Application Laid-Open No. 2020-128616 JP 2016-29220 A

The present invention aims to provide a laminate, a coating liquid for forming the laminate, a food packaging sheet including the laminate, and a method for manufacturing the laminate, which are made using biomass-derived and biodegradable materials but do not use fluorine compounds and have excellent oil resistance, water resistance, heat sealability, and anti-blocking properties.

The present inventors have conducted extensive research to solve the above problems and have arrived at the present invention.
That is, the present invention relates to 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), the total coating weight of the first coating layer (A) and the second coating layer (B) is 0.5 to 10 g/ ^m2 , and the air barrier property is 20 kPa or less.

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)

The present invention relates to the above coating liquid, which is characterized by having a solids content of 5 to 40% and a viscosity at 25°C specified in JIS Z8803 of 5 to 500 mPa·s.

The present invention relates to the above-mentioned laminate having a first coating layer (A) formed from the above-described coating liquid.

The present invention relates to the above laminate, in which the water-insoluble resin (b) includes at least one of an acrylic resin (c), a polyester resin (d), and a urethane resin (e).

The present invention relates to the laminate described above, in which 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.

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

The present invention relates to the laminate described above, in which the modified starch (a) is a modified starch obtained by hydroxyalkylating or oxidizing raw starch.

The present invention relates to a food packaging sheet for containing food, comprising the laminate described above.

The present invention provides a laminate that uses biomass-derived and biodegradable materials and has excellent oil resistance, water resistance, heat sealability, and blocking properties without using fluorine compounds, a coating liquid for forming the laminate, a food packaging sheet that includes the laminate, and a method for manufacturing the laminate.

1 is a front view of an air barrier property measuring device according to the present invention. FIG. 2 is a plan view of a glass filter in the air barrier property measuring device of the present invention.

The present invention is described in detail below. Needless to say, other embodiments are also included within the scope of the present invention as long as they conform to the spirit of the present invention. Furthermore, in this specification, numerical ranges specified using "to" include the numerical values written before and after "to" as the range's lower and upper limits. Unless otherwise noted, the various components appearing in this specification may be used independently, either alone or in combination of two or more types.

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 term "monomer" refers to a monomer containing an ethylenically unsaturated double bond.

<Laminate>
The laminate of the present invention is formed by applying a coating liquid to a paper substrate and drying the applied coating liquid to form a coating layer. The laminate 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 in applications where the coating layer comes into direct contact with food.

<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.

<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 coating suitability, allowing the production of a coating film that uniformly covers the substrate without gaps, and by overlaying the second coating layer on top of this, a laminate with good oil resistance and water resistance can be obtained. In addition, the inclusion of modified starch (a) improves biodegradability.

(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 type of raw starch is not particularly limited, 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.

The modified starch (a) can be modified by, for example, 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.

Oxidized starch can be obtained by oxidizing starch with sodium hypochlorite. When the amorphous portions 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.).

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, resulting in excellent coating suitability. It is possible to form a uniform coating film, thereby imparting 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. A DS of 0.01 or more improves the solubility in water and stability after dissolution in water due to sufficient modification of the raw starch. A DS of 1.0 or less improves water resistance when a laminate is produced.

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), details of which are described in the Examples section.

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.

<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.

(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 the water-insoluble resin (b) is dispersed in water, the solution becomes cloudy, and its dispersion can be determined by transmittance measurement. Specifically, transmittance measurements are performed on samples prepared to have 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 a water-insoluble resin (b). A resin that exhibits a transmittance of 80% or more at 660 nm can be considered a water-soluble resin. Even if a portion of the resin dissolves in water, the present invention defines the resin as a water-insoluble resin (b) if the above conditions are met. The form of the water-insoluble resin (b) in water may be dispersed in particulate form in water, or it may exist in an amorphous form without being completely dissolved in water. 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 resins (c), polyester resins (d), and urethane resins (e) are preferred in terms of oil resistance and water resistance. In addition, an organic solvent that is miscible with water may be included.

[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 having 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.

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 acrylic resin (c) has excellent dispersion stability and significantly improves the wettability and coatability of the coating liquid.

R is a linear or branched alkyl group having 8 to 16 carbon atoms.

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.

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%, based on 100 mass% of the total 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.

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. It is preferable that the ethylenically saturated monomer (c-2) having a carboxy group contains methacrylic acid, as this results in 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.

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 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 content of the ethylenically unsaturated monomer (c-2) is preferably 0 to 13% by mass, more preferably 0.5 to 10% by mass, of 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 the 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. An acid value of 20 mgKOH/g or higher improves the dispersion stability of the acrylic resin (c) during synthesis. A coating liquid containing this acrylic resin (c) has excellent stability and good coatability and film-forming properties, allowing the formation of a coating layer that is strong and durable. Therefore, the laminate exhibits excellent oil resistance. Furthermore, the interaction between the carboxy groups of the resin is strengthened, improving heat-sealability. On the other hand, an acid value of 40 mgKOH/g or lower reduces the interaction between the carboxy groups between coating films, improving the blocking resistance of the laminate.

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 having 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), if necessary, other ethylenically unsaturated monomer (c-3) may be copolymerized, thereby making it possible to control the mass average molecular weight, average particle size, etc. of the acrylic resin (c).

Examples of the other ethylenically unsaturated monomers (c-3) include aromatic ethylenically unsaturated monomers 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, and tridecyl ( ethylenically unsaturated monomers containing a straight or branched alkyl group having 5 or more carbon atoms, such as methyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (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; 2-acrylamido-2-methylpropanesulfonate, sodium methallylsulfonic acid, methallylsulfonic acid, sodium methallylsulfonate, allylsulfonic acid, methyl methallyls ... Sulfo group-containing ethylenically unsaturated monomers such as 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-butoxymethyl-N-(propoxymethyl)methacrylamide, and N,N-di(butoxymethyl)acrylamide Amide group-containing ethylenically unsaturated monomers such as 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, and diacetone acrylamide; hydroxyl 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, and allyl alcohol; methoxypolyethylene glycol (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxyvinyl acrylate, 2-hydroxypropyl (meth) ... ) acrylate, polyethylene glycol (meth)acrylate, and other polyoxyethylene group-containing ethylenically unsaturated monomers; dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, methylethylaminoethyl (meth)acrylate, dimethylaminostyrene, diethylaminostyrene, and other amino group-containing ethylenically unsaturated monomers; epoxy group-containing ethylenically unsaturated monomers such as glycidyl (meth)acrylate, 3,4-epoxycyclohexyl (meth)acrylate; ketone group-containing ethylenically unsaturated monomers such as diacetone (meth)acrylamide, acetoacetoxy (meth)acrylate; allyl (meth)acrylate 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, diaryl 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, diallyl maleate, and other ethylenically unsaturated monomers having two or more ethylenically unsaturated groups; γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropyltriethoxysilane, γ-methacryloxypropyltribut ... Examples of suitable ethylenically unsaturated monomers include, but are not limited to, alkoxysilyl group-containing ethylenically unsaturated monomers such as silane, 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.

Styrene derivatives such as styrene, α-methylstyrene, o-methylstyrene, p-methylstyrene, and m-methylstyrene may also be used as long as they do not impair the effect, but it is preferable not to include them from an environmental perspective.

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 through higher molecular weight, it is more preferable that the other ethylenically unsaturated monomer (c-3) be acrylamide, glycidyl methacrylate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, or N-methylolacrylamide.

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. A content of 10% or less improves the dispersion stability of the synthesized acrylic resin (c), making it possible to obtain a coating liquid with excellent coatability and film-forming properties, and as a result, a laminate with excellent oil resistance and water resistance can be produced.

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 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 multi-stage polymerization, in which the emulsion polymerization is performed using a dropping tank divided into multiple stages and different ethylenically unsaturated monomer compositions are dropped into each stage so that the resulting polymers have different Tgs, and methods in which the acrylic resin (c) is synthesized in advance by bulk polymerization or solution polymerization, dissolved or dispersed in an aqueous phase, and then an ethylenic monomer is dropped to polymerize the resulting polymer with a different Tg from the previous acrylic resin (c). However, considering that the process is not complicated and the resulting acrylic resin (c) has good dispersion stability, it is more preferred to synthesize acrylic resins (c) with two or more different glass transition temperatures by multi-stage 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, the average value of these 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 fully 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 soak in even when exposed to moisture or oil.
The glass transition temperature of the acrylic resin can be determined by subjecting a solid obtained by drying the resin to differential scanning calorimetry (DSC measurement). Details will be described in the Examples section.

The radical polymerization initiator used in the polymerization reaction of ethylenically unsaturated monomers can be a known oil-soluble or water-soluble polymerization initiator. These can 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, and more preferably 0.2 to 2 parts by mass, based on 100 parts by mass of the total amount of ethylenically unsaturated monomers.

The oil-soluble polymerization initiator is not particularly limited, and examples 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.

In emulsion polymerization, it is preferable to use a water-soluble polymerization initiator. Examples of suitable water-soluble polymerization initiators include conventionally known ones such as ammonium persulfate (APS), potassium persulfate (KPS), hydrogen peroxide, and 2,2'-azobis(2-methylpropionamidine) dihydrochloride.

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 metal salts of ascorbic acid, erythorbic acid, tartaric acid, citric acid, glucose, and formaldehyde sulfoxylate; reducing inorganic compounds such as sodium thiosulfate, sodium sulfite, sodium bisulfite, and sodium metabisulfite; ferrous chloride, Rongalit, and thiourea dioxide.
The reducing agent is preferably used in an amount of 0.05 to 5 parts by mass based on 100 parts by mass of the total amount of the ethylenically unsaturated monomers.

The polymerization temperature should be equal to or higher than the polymerization initiation temperature of the polymerization initiator; for example, for peroxide polymerization initiators, it is usually around 80°C. The polymerization time is not particularly limited, but is usually 2 to 24 hours. Furthermore, ethylenically unsaturated monomers may also be polymerized by photochemical reaction or radiation exposure, without using the polymerization initiators described above.

When polymerizing ethylenically unsaturated monomers, a buffer or chain transfer agent may be used as needed. 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 mercaptan 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, 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. Furthermore, the chain transfer agent is preferably used in an amount of 0.4 to 3 parts by mass, and more preferably 0.6 to 2 parts by mass, based on 100 parts by mass of the total amount of ethylenically unsaturated monomers.

Among the chain transfer agents listed above, it is preferable to use chain transfer agent (X), which is a chain transfer agent represented by the following general formula (2):

R is a linear or branched alkyl group having 8 to 16 carbon atoms.

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 appropriate 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 liquid and significantly reduces the formation of sediments and aggregates that can lead to coating defects and film formation defects. It also has the effect of improving the wettability of the resin to the substrate. This allows the coating liquid to firmly penetrate and bond to the substrate, resulting in stronger bonding at the interface between the substrate and the resin.

Examples of chain transfer agents (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.

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 alkalis such as alkali metal hydroxides such as sodium hydroxide, lithium hydroxide, and potassium hydroxide. The basic compound may be added after the first dropwise addition is complete, or after the reaction is complete.

When obtaining acrylic resin (c), a surfactant can be used to improve the dispersion stability of acrylic resin (c), as long as it does not adversely affect the physical properties of the coating liquid or 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 standpoints of safety and the development of good coating film properties. One or more types of surfactants can be used.

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 and derivatives thereof such as sodium monooctyl sulfosuccinate, sodium dioctyl sulfosuccinate, and sodium polyoxyethylene lauryl sulfosuccinate, and polyoxyethylene distyrenated phenyl ether sulfates. Among the above, alkyl sulfates or alkyl sulfosuccinates are preferred, and it is more preferred that the alkyl sulfates are lauryl sulfates and the alkyl sulfosuccinates are dioctyl sulfosuccinates.

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.

The surfactant can be a polymerizable surfactant having one or more radically polymerizable ethylenically unsaturated double bonds in the molecule.

The polymerizable surfactant is preferably a polymerizable anionic surfactant or a polymerizable nonionic surfactant.

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.

[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 resulting mixture with a 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.

Specific examples of polybasic acid components include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, phthalic anhydride, naphthalenedicarboxylic acid, and biphenyldicarboxylic acid, oxalic acid, succinic acid, succinic anhydride, adipic acid, azelaic acid, sebacic acid, dodecanedioic acid, and hydrogenated dimer acids, fumaric acid, maleic acid, maleic anhydride, and itaconic acid,
Examples of suitable dicarboxylic acids include saturated or unsaturated aliphatic dicarboxylic acids such as itaconic anhydride, citraconic acid, citraconic anhydride, and dimer acid, unsaturated dicarboxylic acids and anhydrides thereof such as 1,4-cyclohexanedicarboxylic acid and terpene-maleic acid adducts, and 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 anhydride. Furthermore, a small amount of 5-sodium sulfoisophthalic acid or 5-hydroxyisophthalic acid can be used as needed.

Polybasic acids having 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 also be included.

In addition, 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 as the polybasic acid.

Examples of the polyhydric alcohol component include aliphatic glycols, alicyclic glycols, and ether bond-containing glycols. Specific examples of the aliphatic glycols include:
For example, ethylene glycol, 1,2-propanediol, 1,3-propanediol,
Examples of suitable glycols include 1,4-butanediol, 2-methyl-1,3-propanediol, 1,5-pentanediol, 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, and dipropylene glycol, as well as 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 having a molecular weight of 500 or more.

Examples of trifunctional or higher polyhydric alcohols that may be included include glycerin, trimethylolethane, trimethylolpropane, pentaerythritol, diglycerin, polyglycerin, xylitol, sorbitol, glucose, fructose, mannose, etc. Also, a portion of the polyhydric alcohol components described above may be modified before use.

Polyester resin (d) may optionally be copolymerized with fatty acids such as lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, and linolenic acid, or their ester-forming derivatives; 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 their ester-forming derivatives.

Polylactic acid polyesters can be easily obtained by ring-opening addition polymerization of lactides and lactones using a polyol as an initiator. The polyol may be one of the polyhydric alcohols mentioned above, 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 have to be used alone; multiple types can also be copolymerized. Of these, ε-caprolactone and lactide are preferred due to their excellent biodegradability and ease of polymerization.

When polymerizing polyester resin (d), it is effective to add various antioxidants. If the polymerization temperature is high or the polymerization time is long, the polylactic acid segments may undergo oxidative degradation and discoloration due to their low heat resistance. Furthermore, copolymerization with segments with low heat resistance, such as polyethers, can make the resin even more susceptible to oxidative degradation. In such cases, the addition of an antioxidant is particularly effective. Examples of antioxidants include well-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.

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 a 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 tri- or higher-functional polybasic acid to introduce carboxyl groups into the polymer side chain. Alternatively, a water-based dispersion can be obtained by introducing a sulfonate salt as a functional group. Examples of methods for introducing sulfonate salts include the use of a sulfonic acid group-containing polybasic acid such as 5-sodium sulfoisophthalic acid.

Basic compounds used to neutralize the acid groups introduced into polyester resin (d) include ammonia, organic amine compounds, inorganic basic compounds, etc.

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.

Specific examples of the inorganic basic compound 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. Polyvalent metal basic compounds may form salts that are poorly soluble in water with the multiple carboxy groups contained in the polyester resin (d), potentially worsening dispersibility. Therefore, when used, it is preferable that the neutralization rate of the carboxy groups is 50% or less.

[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.
Further, 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; 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, and 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 sulfonate 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.

Examples of polyisocyanates that can be used to synthesize 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 Examples of suitable polyisocyanates include aromatic polyisocyanates such as 1,5-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.

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, dimethylol acetic acid, dimethylolpropionic acid, dimethylolbutanoic acid, 2,2-dimethylolbutyric acid, 2,2-dimethylolpentanoic acid, and other dimethylolalkanoic acids, dihydroxysuccinic acid, dihydroxypropionic acid, and dihydroxybenzoic acid.

The urethane resin (e) may be terminally modified or chain-extended.
Examples of compounds that can be used for the terminal modification or chain extension reaction 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.

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

Aqueous dispersions of urethane resin (e) may be commercially available. Examples of commercially available products 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.

<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/ ^m² , more preferably 1.5 to 4 g/ ^m² . A total coating weight of 0.5 g/m² or ^more ensures that the coating layers sufficiently cover the paper substrate, preventing uneven coating and improving oil resistance, water resistance, and heat sealability. A total coating weight of 10 g/m² ^{or less} prevents blocking that occurs when the coated and uncoated surfaces are superimposed. The coating weight of each of the first coating layer (A) and the second coating layer (B) is preferably 0.1 to 8 g/ ^m² , more preferably 0.3 to 3.2 g/ ^m² . Within this range, a smooth, uniform film can be formed on the paper substrate, resulting in a laminate with excellent oil resistance, water resistance, and blocking properties.

In the laminate, the mass ratio per unit area of the first coating layer (A) to the second coating layer (B) ((A)/(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 satisfying both oil resistance and water resistance can be obtained.

<Air barrier properties>
The airtightness in this application refers to the value of the degree of vacuum measured using a vacuum device under conditions where the degree of vacuum is 70 kPa when copy paper is placed in the opening. Specifically, the measurement can be performed by placing a laminate in the opening using a vacuum device 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 an opening with a diameter of 4 cm and an area of 12.56 cm2. A smaller value indicates a higher degree of airtightness, meaning that a film is formed on the paper substrate without any gaps.

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. A laminate with an air barrier property of 20 kPa or less forms a uniform, even coating film on the paper substrate, improving oil resistance and water resistance.

Air barrier properties are measured using the device shown in Figure 1. A glass filter 2 is placed on top of glass container 1, and a rubber tube 3 is attached to the side of the glass container, to which a hydraulic pump 4 and vacuum gauge 5 are connected. The hydraulic pump 4 is used to reduce the pressure, and the degree of pressure reduction is measured using vacuum gauge 5. Only the filter section 6 at the top of the device is designed to allow air to pass through, with the rest of the device being completely sealed. The filter section 6 is circular and has a diameter of 4 cm. The glass filter section is flat relative to the glass section surrounding the glass filter, and is neither protruding nor recessed. If the glass filter section is not flat, it will be impossible to accurately measure the degree of pressure reduction 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 taken as the air barrier properties.

<Coating liquid>
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 also include additives such as extender pigments, 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.

Hydrophilic solvents include, for example, 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; 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 may be used alone or in combination of two or more.

It is preferable to use extender pigments that are approved as foods or food additives. Specific examples include talc, silica, calcium carbonate, barium sulfate, titanium oxide, diatomaceous earth (white carbon), cellulose powder, etc.

Solvents that are considered safe for oral use include ethanol, isopropyl alcohol, propylene glycol, and glycerin.

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.

The coating liquid for preparing the first coating layer (A) preferably has a solids content of 5 to 40% and a viscosity at 25°C of 5 to 500 mPa·s as specified in JIS Z8803. Having the 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 of 30 to 300 mPa·s as specified in JIS Z8803.
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.

The coating liquid for preparing the first coating layer (A) preferably has viscosities V ₁ and V ₂ measured using a rheometer that satisfy the condition shown in formula (1).
Formula (1)
_V2 ≦1.5× _V1
(V ₁ : viscosity 5 seconds after applying a shear rate of 2000 (l/s), V ₂ : 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.

The surface of a paper substrate is not completely uniform, and some unevenness is known to exist, although the degree varies depending on whether or not the surface is treated. In the present invention, it is important to coat the first coating layer on the paper substrate as tightly as possible. When thixotropy is high, the coating fluid has good fluidity 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 layer without gaps on the paper substrate. If there are uncoated surfaces on the paper substrate, water and oil can penetrate through these areas, reducing the 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 coating layer on top of the first coating layer coated tightly on the paper substrate, a laminate can be obtained that combines water resistance, oil resistance, and heat sealability.

<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 provided on the second coating layer. The number of coatings required to form the first coating layer (A) and the second coating layer (B) is not particularly limited; each layer may be coated at once, or multiple layers may be applied.

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.

<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.

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 version can also be used.

The food packaging sheet can be used to package not only confectioneries such as popcorn, chocolate, and caramel, and produce such as vegetables and fruits, but also burgers such as hamburgers, hot dogs, hamburgers, and rice burgers, deep-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, as well as meat buns, red bean buns, dumplings, shumai, and spring rolls. It can also be used for foods that contain multiple ingredients such as oil, salt, acid, and amino acids, and that are high in moisture and coated with ketchup, sauce, or dressing. 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 for 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.

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.

<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 a precisely weighed amount of about 3 mg of dried resin and an empty aluminum pan serving as a reference were set in a DSC measurement holder, and measurement was performed at a temperature increase rate of 10°C/min. 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 was taken as the glass transition temperature (Tg).

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

<Average particle diameter>
The average particle size was measured by diluting the resin aqueous dispersion with water 500 times 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.

<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) using the following equipment and measurement 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 2,000,000 or more.
Apparatus: HLC-8320-GPC system (manufactured by Tosoh Corporation)
Column: TSKgel-Super Multipore HZ-M0021488 4.6 mm I.D. x 15 cm x 3 (molecular weight measurement range: 2,000 to approximately 2,000,000)
Elution solvent: tetrahydrofuran Standard material: polystyrene (manufactured by Tosoh Corporation)
Flow rate: 0.6 mL/min Amount of sample solution used: 10 μL
Column temperature: 40°C

<Viscosity at 25°C as specified in JIS Z8803>
Measurement was carried out in accordance with JIS Z8803 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.

<Viscosity V ₁ , Viscosity V ₂ >
The viscosity _V1 and the viscosity _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.

<Transmittance>
The transmittance of the resin was measured using an ultraviolet-visible-near-infrared spectrophotometer (V-770D manufactured by JASCO Corporation). A resin solution prepared by diluting the resin with water to a solids content of 5% was added to a glass cell, and the transmittance at a wavelength of 660 nm was measured. 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 waxes.

<Production of Water-Insoluble Resin Aqueous Dispersions (b1 to b6)>
[Water-insoluble resin (polyester resin) aqueous dispersion (b1)]
A mixture of 2,492 g of terephthalic acid, 415 g of isophthalic acid, 1,516 g of sebacic acid, 1,210 g of ethylene glycol, and 1,484 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 temperature of the system was raised to 275°C. The pressure of the system was gradually reduced to 13 Pa after 1.5 hours. Under these conditions, the polycondensation reaction was continued for another 4 hours, the system was returned to atmospheric pressure with nitrogen gas, the temperature of the system was lowered, and when the temperature reached 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. Thereafter, the system was pressurized with nitrogen gas, and the resin was discharged in the form of a sheet. After cooling at room temperature, a sheet-like polyester resin 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 about 60°C while stirring using 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 adding water at a rate of 100 g/min, to obtain a water dispersion (b1) of polyester resin with a non-volatile content of 35%. The obtained (b1) was adjusted with water to a non-volatile content of 5%, and the transmittance was measured, and the transmittance was found to be 10%.

[Water dispersion (b2) of water-insoluble resin (acrylic resin)]
A reaction vessel (reaction tank) 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 pre-mixed and stirred to prepare an emulsion of ethylenically unsaturated monomers to be added dropwise to the first stage (first-stage dropping tank). The internal temperature of the reaction vessel was raised to 80°C and thoroughly purged with nitrogen, after which 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 completion of the dropwise addition of the first-stage ethylenically unsaturated monomer emulsion, 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 Emal 0, and 160.8 parts of water were mixed and stirred in advance to prepare a second-stage ethylenically unsaturated monomer emulsion (second-stage dropping tank), and 11.1 parts of a 10% aqueous solution of ammonium persulfate. After completion of the dropwise addition, the mixture was allowed to react for another 3 hours at 80°C. After the reaction was completed, 9.8 parts of 25% aqueous ammonia was added under stirring to neutralize the mixture, and the acrylic resin was dispersed in water. Further water was added to adjust the nonvolatile content to 35%, thereby obtaining the target aqueous dispersion (b2) of the acrylic resin. The obtained (b2) was adjusted to a nonvolatile content of 5% with water, and the transmittance was measured, which was 8%. The Tg of the obtained acrylic resin was 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, since the acrylic resin was insoluble in THF, the mass average molecular weight was set to 2 million or more.

[Water dispersion (b3) of water-insoluble resin (acrylic-modified urethane resin)]
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 mgKOH/g) as a polyol, 20.2 parts of polyester polyol (P-2011 manufactured by Kuraray Co., Ltd., functionality 2, hydroxyl value 56.0 mgKOH/g), 48.6 parts of polycarbonate polyol (C-2090 manufactured by Kuraray Co., Ltd., functionality 2, hydroxyl value 56.3 mgKOH/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, and then the temperature was lowered to 80° C. The weight average molecular weight of the urethane prepolymer produced at this time 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 confirmed by FT-IR by the disappearance of the peak (near 2270 cm ^- 1) derived from the isocyanato group. Further, methyl ethyl ketone was added to adjust the solids concentration to 70%, and a solution of urethane resin U1 having sulfanyl groups at both ends was obtained. Next, a reaction vessel equipped with a stirrer, thermometer, dropping funnel, and reflux condenser was added to the above-obtained urethane resin U1 solution 50 parts, 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 Adeka STAB LA-82, and 35.0 parts of n-propanol, and the mixture was heated to 75°C while stirring under a nitrogen atmosphere. A dropping funnel was charged with 20.0 parts of methyl ethyl ketone and 0.35 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) as an initiator, and the mixture was added dropwise to the reaction vessel over 5 hours. The reaction was allowed to proceed at 78°C for 8 hours, completing the graft reaction of the acrylic resin (c) portion. After the reaction, 10 parts of water was added, and 25% aqueous ammonia was added to the resin in an equimolar amount 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%.

[Water-insoluble resin (polylactic acid polyester resin) aqueous dispersion (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, a stirrer, and a 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 the mixture was stirred for 1 hour. The contents were then removed and cooled to obtain the target aqueous dispersion (b4) of polylactic acid polyester resin. The resulting (b4) was adjusted to a nonvolatile content of 5% with water, and the transmittance was measured, revealing a transmittance of 13%.

[Water-insoluble resin (polylactic acid polyester resin) aqueous dispersion (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, a stirrer, and a Liebig condenser was charged with 25 parts of polylactic acid polyester resin, 1.0 part of TEA, and 75 parts of water, and the temperature was raised 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 a transmittance of 15%.

[Water dispersion (b6) of water-insoluble resin (polylactic acid-containing urethane resin)]
A 1 L glass flask equipped with a thermometer, a stirrer, and a 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 thereafter until it reached 230°C. After confirming the completion of methanol distillation at 230°C, the temperature was raised to 250°C, stirred under reduced pressure for 10 minutes, and the reaction mixture was 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 charged into 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 at room temperature for 30 minutes, and the contents were further dried. The reaction system was again heated to 180°C under a nitrogen gas flow, and the flask was stirred for 3 hours.
Next, 0.10 parts of phosphoric acid was added, and after stirring for 30 minutes, the system was depressurized 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, a stirrer, and a 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 reacting at 70°C for 4 hours, 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 the contents were maintained 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%.

[Water-insoluble resin (acrylic resin) water dispersion (b7)]
A reaction vessel (reaction tank) 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 pre-mixed and stirred to prepare an emulsion of ethylenically unsaturated monomers to be added dropwise to the first stage (first-stage dropping tank). The internal temperature of the reaction vessel was raised to 80°C and thoroughly purged with nitrogen, after which 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 completion of the dropwise addition of the first-stage ethylenically unsaturated monomer emulsion, 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 Emal 0, and 160.8 parts of water were mixed and stirred in advance to prepare a second-stage ethylenically unsaturated monomer emulsion (second-stage dropping tank), and 11.1 parts of a 10% aqueous solution of ammonium persulfate. After completion of the dropwise addition, the mixture was allowed to react for another 3 hours at 80°C. After the reaction was completed, 9.8 parts of 25% aqueous ammonia was added while stirring to neutralize the mixture and disperse it in water. Further water was added to adjust the nonvolatile content to 35%, thereby obtaining the target aqueous dispersion of acrylic resin (b7). The obtained (b7) was adjusted to a nonvolatile content of 5% with water, and the transmittance was measured, resulting in a transmittance of 10%. The Tg of the obtained resin was 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, since the resin was insoluble in THF, the mass average molecular weight was set to 2 million or more.

The materials in Table 1 are as follows:
Modified starch (a);
Pyostarch LV (manufactured by 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 (manufactured by Nippon Starch Chemical Co., Ltd., starch phosphate, Mw 5600, transmittance 88%)
Polyvinyl alcohol;
Exeval RS2117 (manufactured by Kuraray Co., Ltd., modified polyvinyl alcohol, Mw 74800, transmittance 90%)
A water dispersion of a water-insoluble resin (b);
Superflex SF-170 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., urethane resin water dispersion, pH 7-9, average particle size 10 μm, transmittance 45%, non-volatile content 33%)

<Production of Coating Liquid>
[Production Example 1]
70 parts of water and 30 parts of Pyostarch LV (manufactured by 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 prepared by stirring for 2 hours. Next, 5 parts of IPA was added and stirred for 10 minutes to obtain the desired coating liquid. The viscosity of the obtained coating liquid was measured using a Brookfield viscometer and was 100 mPa·s. The nonvolatile content was 29%. Viscosity measurements were performed using a rheometer, and the viscosity _V1 was 90 mPa·s and the viscosity _V2 was 120 mPa·s.

[Production 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 obtained coating liquids, viscosity measurement was carried out using a Brookfield viscometer, viscosity measurement was carried out using a rheometer, and non-volatile content measurement was carried out.
[Production Example 12]
100 parts of a water-insoluble resin (polyester resin) aqueous 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. Then, a mixture of 15 parts of water and 0.5 parts of IPA was added while stirring to obtain a coating liquid. The viscosity of the obtained coating liquid was measured using a Brookfield viscometer and was 150 mPa·s. The nonvolatile content was 30%. Viscosity measurements were performed using a rheometer, and the viscosity _V1 was 120 mPa·s and the viscosity _V2 was 300 mPa·s.
[Production 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 obtained coating liquids, viscosity measurement was carried out using a Brookfield viscometer, viscosity measurement was carried out using a rheometer, and non-volatile content measurement was carried out.

<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, followed by the coating liquid of Production Example 11, using a Windmiller & Hoelscher "SOLOFLEX" central impression (CI) 6-color flexographic printing press. 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 paper was then dried in an oven at 80°C to obtain a laminate. The coating amount of the laminate was measured to be 2 g/ ^m² .

[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.

[Example 23]
The coating liquid 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 liquid of Production Example 12 was applied onto the first layer and 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/ ^m2 .

[Example 24]
The coating liquid 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. Then, the coating liquid of Production Example 11 was applied onto the first layer and 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/ ^m2 .

[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.

The laminate was evaluated as follows:

<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 completely adhered to each other so that the laminate would not bend or wrinkle. After placing the laminate at the measurement location, the value of the vacuum level was read after the value on the vacuum gauge stabilized, and this was used as the value of air barrier properties. The measurement was carried out in a constant temperature and humidity room at a temperature of 25°C and a humidity of 60%.

<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 (manufactured by Tester Sangyo Co., Ltd., upper and lower plate heating)
Conditions: 2kg/cm2 ^-40 ℃-24hr
[Evaluation criteria]
S: No resistance is felt when peeling off, and the paper is not damaged (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 off, and the paper is damaged (unusable)

<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°C - 2 kgf/cm ² - 1 second (peel)
Equipment: Tensile testing machine (manufactured by Tester Sangyo Co., Ltd.)
Peeling conditions: 180° peeling, 300 mm/min [Evaluation criteria]
S: 2N or more (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)

<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 has soaked (good)
B: The area soaked is between 10% and 50% (usable)
C: The area soaked is 50% or more (very poor)

<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 confirmed 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 has soaked (good)
B: The area soaked is between 10% and 50% (usable)
C: The area soaked is 50% or more (very poor)

<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 60% to less than 70% (good)
B: Residue visible to the naked eye is 70% to less than 90% (usable)
C: 90% or more of the residue can be visually confirmed (very poor)

The results in Tables 2 and 3 show that the coatings of the present invention, which were prepared using modified starch in the first coating layer and a water-insoluble resin in the second coating layer, exhibited excellent oil resistance, water resistance, heat seal strength, and anti-blocking properties. In particular, Example 1, which used hydroxypropylated starch in the first coating layer, exhibited superior oil resistance and water resistance compared to Example 9, which used phosphorylated 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.

1 Glass container 2 Glass filter 3 Rubber tube 4 Hydraulic pump 5 Vacuum gauge 6 Filter part 7 Laminate (measurement sample)

Claims (8)

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/ ^m2 , and
A laminate for food packaging sheets, characterized in that the air barrier property is 20 kPa or less. 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)
_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) The coating liquid according to claim 2, characterized in that the solids content is 5 to 40% and the viscosity at 25°C specified in JIS Z8803 is 5 to 500 mPa·s. The laminate for food packaging sheets according to claim 1, having a first coating layer (A) formed from the coating liquid according to claim 2 or 3. The laminate for food packaging sheets according to claim 1 or 4, 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. The method for producing a laminate for food packaging sheets according to any one of claims 1, 4 and 5, wherein the first coating layer (A) and the second coating layer (B) are formed by gravure printing or flexographic printing. The laminate for food packaging sheets according to any one of claims 1, 4 and 5, wherein the modified starch (a) is a modified starch obtained by hydroxyalkylating or oxidizing raw starch. 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.