JP2022016065A - Coating agent for food packaging sheet and food packaging sheet - Google Patents

Abstract

To provide a food packaging sheet which has good stability of a coating agent, is excellent in blocking properties and heat sealability, and is also excellent in food product resistance such as seasoning resistance such as catsup and sauce, and microwave oven resistance.SOLUTION: A coating agent for a food packaging sheet contains resin fine particles (A) that are a polymer of an ethylenically unsaturated monomer (a), in which the resin fine particles (A) have glass transition temperatures in each range of -40 to 30°C and 40 to 140°C, and an acid value of 20-40 mgKOH/g, and contain 85-97 mass% of an ethylenically unsaturated monomer (a-1) having a straight-chain alkyl group having 1 to 4 carbon atoms based on the total mass of the ethylenically unsaturated monomer (a).SELECTED DRAWING: Figure 1

Description

The present invention relates to a coating agent for food packaging sheets and food packaging sheets.

Conventionally, as a food packaging sheet, a laminated sheet in which a resin film such as polyethylene is laminated on a base sheet such as thin paper, paperboard, or non-woven fabric has been used. The laminated resin film has a function of preventing oil stains on the base material sheet and a decrease in the strength of the base material due to oil derived from food. On the other hand, in recent years, the recycling of paper has been accelerating due to the global trend of reducing environmental load. However, the above-mentioned laminated sheet has a high degree of difficulty in recycling paper and requires an expensive capital investment in the process of removing the laminated resin film layer, which has been an obstacle to promoting recycling. Against this background, coating agent-type food packaging sheets that are easier to recycle are being actively studied. Also in this resin coating agent, a material having a low environmental load is required, and for example, a styrene-free material containing no styrene is required.
However, when the resin fine particles contained in the food packaging coating agent are made styrene-free, the dispersion stability of the particles deteriorates, and the stability of the coating agent also deteriorates accordingly. The precipitates and aggregates generated by the deterioration of the stability of the coating agent adversely affect the coatability and film-forming property of the coating agent.

As such a styrene-free type food packaging sheet, for example, in Patent Document 1, for the purpose of imparting oil resistance and water resistance to a paper substrate, 2-ethylhexyl acrylate is the main component, and the acid value is high and the molecular weight is low. A coating agent using acrylic resin fine particles containing a large amount of the above components and a food packaging sheet coated with the coating agent are disclosed.

However, such a coating agent exhibits a certain level of oil resistance to fats and oils contained in foods at room temperature such as snack foods, and although water resistance also exhibits a certain effect if water alone is used, ketchup and sauces are used. When packaging foods that contain multiple components such as oil, salt, acid, and amino acids and have a high water content, such as seasonings, the stability of the coating agent and the resin composition have an effect. As a result, there is a problem that the seasoning component permeates the base material sheet and exudes to the outer surface, resulting in poor appearance (hereinafter, abbreviated as seasoning resistance). Furthermore, assuming that the packaged food is heated in a microwave oven, oil resistance and water resistance for a certain period of time or longer are required at high temperatures, but with conventional food packaging sheets, food generated when heated in a microwave oven is required. Since it is not resistant to steam from the oven, it causes the problem that water and oil easily permeate into the base sheet and seep out to the outside, blocking the food and the sheet (hereinafter,). Microwave oven resistant and abbreviated).

In addition, due to poor coating and film-forming properties due to poor stability of the coating agent, heat-sealing properties may deteriorate, or the food packaging sheet may be rolled into a roll and stored, and then rewound with a resin. The coat layer may cause blocking.

Japanese Unexamined Patent Publication No. 2001-303475

INDUSTRIAL APPLICABILITY The present invention provides a food packaging sheet having good stability of a coating agent, excellent blocking property and heat-sealing property, and also excellent food resistance such as seasoning resistance such as ketchup and sauce, and microwave oven resistance. The purpose is to provide.

The present inventors have reached the present invention as a result of repeated diligent studies to solve the above problems.
That is, the present invention contains the resin fine particles (A) which are polymers of the ethylenically unsaturated monomer (a), and the resin fine particles (A) are at −40 to 30 ° C. and 40 to 140 ° C., respectively. A linear alkyl group having a glass transition temperature in the range of 1 to 4, having an acid value of 20 to 40 mgKOH / g, and having 1 to 4 carbon atoms based on the total mass of the ethylenically unsaturated monomer (a). The present invention relates to a coating agent for a food packaging sheet containing 85 to 97% by mass of an ethylenically unsaturated monomer (a-1) having.

Ｒは炭素数８～１６の直鎖又は分岐アルキル基である。 The present invention relates to the coating agent for a food packaging sheet, wherein the polymer of the ethylenically unsaturated monomer (a) contains a polymer having a structure represented by the general formula (1) at one end.

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

The present invention relates to the coating agent for food packaging sheets, wherein the ethylenically unsaturated monomer (a) contains methacrylic acid.

The present invention relates to the coating agent for food packaging sheets, wherein the resin fine particles (A) have an average particle size of 30 to 300 nm.

The present invention contains at least one of lauryl sulfate and dioctylsulfosuccinate, and the total amount of the ethylenically unsaturated monomer (a) is 100 parts by mass as a reference, and both are 0.1 to 2% by mass in total. The present invention relates to a coating agent for a food packaging sheet, including a portion.

The present invention relates to the coating agent for food packaging sheets, wherein the resin fine particles (A) have a mass average molecular weight of 100,000 or more.

The present invention relates to a food packaging sheet having a base sheet and a coating layer formed of the coating agent for a food packaging sheet on the base sheet.

The present invention relates to the above-mentioned food packaging sheet in which the base sheet is paper.

The coating agent for food packaging sheets of the present invention has good stability, and is not only food resistant to seasonings such as ketchup and sauces and microwave heating, but also good blocking resistance and heat sealing resistance. We can provide packaging sheets.

The schematic diagram for demonstrating the glass transition temperature of the resin fine particle (A) by DSC.

Hereinafter, the present invention will be described in detail. Needless to say, other embodiments are also included in the scope of the present invention as long as they are in line with the gist of the present invention. In addition, the numerical range specified by using "-" in the present specification shall include the numerical values before and after "-" as the range of the lower limit value and the upper limit value. Further, in the present specification, "film" and "sheet" are not distinguished by thickness. In other words, the "sheet" in the present specification includes a thin film-like material, and the "film" in the present specification includes a thick sheet-like material.
Unless otherwise noted, the various components mentioned in the present specification may be used independently or in combination of two or more.

Further, in the present specification, the terms "(meth) acrylic acid" and "(meth) acrylate" are used to represent "acrylic acid or methacrylic acid", respectively, unless otherwise specified. Further, the "(meth) acrylic acid ester monomer" is a general term for "acrylic acid ester monomer" and "methacrylic acid ester monomer". The monomer means an ethylenically unsaturated double bond-containing monomer.

In the present specification, the ethylenically unsaturated monomer (a-1) having a linear alkyl group having 1 to 4 carbon atoms, the ethylenically unsaturated monomer (a-2) having a carboxy group, and the like. The other ethylenically unsaturated monomers (a-3) that can be copolymerized with the ethylenically unsaturated monomers (a-1) and (a-2) are added to the ethylenically unsaturated monomers (a-), respectively. 1), ethylenically unsaturated monomer (a-2), and ethylenically unsaturated monomer (a-3) may be abbreviated.

In the present specification, "Mw" is a polystyrene-equivalent mass average molecular weight determined by gel permeation chromatography (GPC) measurement. "Mn" is a polystyrene-equivalent number average molecular weight obtained by GPC measurement. These can be measured by the method described in the section of [Example].

≪Coating agent for food packaging sheet≫
The coating agent for a food packaging sheet of the present invention is applied on a base sheet such as paper or non-woven fabric and dried to form a coating layer, and is a sheet for packaging food (hereinafter referred to as food). It can be suitably used for forming a packaging sheet (abbreviated as a packaging sheet). Further, the food packaging sheet of the present invention is not only excellent in oil resistance and water resistance for snack foods and the like, but also excellent in seasoning resistance and microwave oven resistance, so that it can be used for direct contact between the coat layer and food. It can be suitably used.

The coating agent for a food packaging sheet of the present invention contains resin fine particles (A) which are polymers of the ethylenically unsaturated monomer (a), and the resin fine particles (A) are at −40 to 30 ° C. and 40. It has a glass transition temperature Tg in each range of about 140 ° C., has an acid value of 20 to 40 mgKOH / g, and has 1 to 4 carbon atoms based on the total mass of the ethylenically unsaturated monomer (a). It is a coating agent for a food packaging sheet containing 85 to 97% by mass of an ethylenically unsaturated monomer (a-1) having a linear alkyl group. A coating agent for a food packaging sheet containing such resin fine particles (A) has excellent stability, and a food packaging sheet prepared using this coating agent has food resistance, which was difficult with conventional water-based coating agents. It exhibits excellent performance in (seasoning resistance, microwave oven resistance), blocking resistance, and heat sealability.

<Resin fine particles (A)>
First, the resin fine particles (A) used in the present invention will be described.
The resin fine particles (A) are polymers of the ethylenically unsaturated monomer (a), and the ethylenically unsaturated monomer (a) is ethylenically having a linear alkyl group having 1 to 4 carbon atoms. Copolymerization with an unsaturated monomer (a-1), an ethylenically unsaturated monomer (a-2) having a carboxy group, and the above-mentioned ethylenically unsaturated monomers (a-1) and (a-2). It is classified into other possible ethylenically unsaturated monomers (a-3).
The resin fine particles (A) have a structure represented by the general formula (1) at one end by polymerizing the ethylenically unsaturated monomer (a) in the presence of the chain transfer agent (X) described later. It can contain a polymer. Such resin fine particles (A) are extremely excellent in dispersion stability, and the wettability and coatability of the coating agent are also significantly improved. Therefore, it is preferable because the food resistance (seasoning resistance, microwave oven resistance) and heat sealability of the food packaging sheet are further improved.

Ｒは炭素数８～１６の直鎖又は分岐アルキル基である。

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

The resin fine particles (A) are ethylenically unsaturated monomer (a-) having a linear alkyl group having 1 to 4 carbon atoms based on 100% by mass of the total mass of the ethylenically unsaturated monomer (a). 1) is contained in an amount of 85 to 97% by mass, more preferably in the range of 90 to 96% by mass.
By containing it in the above range, the dispersion stability of the resin fine particles at the time of synthesis is significantly improved, and a coating agent having excellent coatability and film-forming property can be obtained. The coat layer formed by this coating agent is tough, and even if it is exposed to a food component containing a plurality of components such as water, oil, salt and acid, the coat layer is not easily attacked. In addition, even under the heating conditions of a microwave oven, the penetration of food components is suppressed, and there is no risk of blocking between the sheet and the food. Therefore, the food packaging sheet exhibits excellent food resistance (seasoning resistance, microwave oven resistance), blocking resistance, and heat sealability.

[Ethylene unsaturated monomer (a-1)]
The ethylenically unsaturated monomer (a-1) is an ethylenically unsaturated monomer having a linear alkyl group having 1 to 4 carbon atoms, and is a methyl (meth) acrylate, an ethyl (meth) acrylate, or n. -Propyl (meth) acrylate, n-butyl (meth) acrylate can be mentioned.

[Ethylene unsaturated monomer (a-2)]
The ethylenically unsaturated monomer (a-2) is an ethylenically unsaturated monomer having a carboxy group, which improves the dispersion stability of the resin fine particles (A) and controls the rheology at the time of coating the coating agent. A carboxy group is introduced on the surface of the resin fine particles for the purpose of promoting film formation and the like. The carboxy group can be introduced by copolymerizing the ethylenically unsaturated monomer (a-2) having a carboxy group in the ethylenically unsaturated monomer (a). The acid value of the resin fine particles (A) depends on the amount of the ethylenically unsaturated monomer (a-2) having a carboxy group introduced.

The acid value of the resin fine particles (A) used in the present invention is in the range of 20 to 40 mgKOH / g, more preferably in the range of 25 to 40 mgKOH / g. When the acid value is 20 mgKOH / g or more, the dispersion stability of the resin fine particles at the time of synthesis is improved. The coating agent containing the resin fine particles has excellent stability, good coatability and film-forming property, and thus forms a tough and highly resistant coating layer. Therefore, the food packaging sheet exhibits excellent food resistance (seasoning resistance, microwave oven resistance). In addition, the interaction between the carboxy groups of the resin becomes stronger, so that the heat sealability is also improved. On the other hand, when the acid value is 40 mgKOH / g or less, the coating film resistance to food components containing water, oil, salt, acid, etc. is improved, and the steam emitted from the food when heated in a microwave oven is applied to the coat layer. Penetration can be suppressed and blocking between the sheet and food does not occur. Therefore, the food packaging sheet exhibits excellent food resistance (seasoning resistance, microwave oven resistance). In addition, since the interaction between the carboxy groups between the coat layers is reduced, the blocking resistance of the food packaging sheet is improved.

Examples of the ethylenically saturated monomer (a-2) having a carboxy group include acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid and cinnamic acid. , The resin fine particles (A) having more excellent stability can be obtained, and the ethylenic saturated monomer having a carboxy group is good in terms of the coatability of the coating agent and the coating resistance of the coating layer to food-derived components. (A-2) preferably contains methacrylic acid. By containing methacrylic acid, the dispersion stability of the resin fine particles is further improved, and the stability of the coating agent is further improved. In addition, the food resistance (seasoning resistance, microwave oven resistance) of the food packaging sheet is further improved.

Based on the total mass of the ethylenically unsaturated monomer (a), the above-mentioned ethylenically saturated monomer (a-2) having a carboxy group is preferably contained in an amount of 2 to 5% by mass, more preferably 4 It is in the range of ~ 4.9% by mass. By containing the resin fine particles (A) in the above range, the dispersion stability of the resin fine particles (A) is improved, and the coatability and film-forming property of the coating agent are improved. Therefore, a food packaging sheet having excellent food resistance (seasoning resistance, microwave oven resistance) and heat sealability can be obtained.

[Ethylene unsaturated monomer (a-3)]
The ethylenically unsaturated monomer (a-3) is an ethylenically unsaturated monomer (a-1) having a linear alkyl group having 1 to 4 carbon atoms and an ethylenically unsaturated monomer having a carboxy group. It is another ethylenically unsaturated monomer copolymerizable with the saturated monomer (a-2).
Further required for the ethylenically unsaturated monomer (a-1) and the ethylenically unsaturated monomer (a-2) in order to control the mass average molecular weight, the average particle size, etc. of the resin fine particles (A). Accordingly, the ethylenically unsaturated monomer (a-3) can be copolymerized.

The ethylenically unsaturated monomer (a-3) is preferably contained in an amount of 0 to 13% by mass, more preferably 0.5 to 10 based on the total mass of the ethylenically unsaturated monomer (a). It is in the range of% by mass. By containing the resin fine particles (A) in the above range, the dispersion stability of the resin fine particles (A) is improved, and the coatability and film-forming property of the coating agent are improved. Therefore, a food packaging sheet having excellent food resistance (seasoning resistance, microwave oven resistance) and heat sealability can be obtained.

Examples of the other ethylenically unsaturated monomer (a-3) include vinylnaphthalene, benzyl (meth) acrylate, phenoxyethyl (meth) acrylate, phenoxydiethylene glycol (meth) acrylate, and phenoxytetraethylene glycol (meth). Aromatic ethylenically unsaturated substances such as acrylate, phenoxyhexaethylene glycol (meth) acrylate, phenoxyhexaethylene glycol (meth) acrylate, and phenyl (meth) acrylate; pentyl (meth) acrylate, heptyl (meth) acrylate, hexyl ( Meta) acrylate, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, nonyl (meth) acrylate, decyl (meth) acrylate, undecyl (meth) acrylate, lauryl (meth) acrylate, tridecyl (meth) acrylate, tetradecyl (meth) acrylate Linear or linear having 5 or more carbon atoms such as meta) acrylate, pentadecyl (meth) acrylate, hexadecyl (meth) acrylate, heptadecyl (meth) acrylate, stearyl (meth) acrylate, isostearyl (meth) acrylate, and behenyl (meth) acrylate. Branched alkyl group-containing ethylenically unsaturated monomer; Acrylic alkyl group-containing ethylenically unsaturated monomer such as cyclohexyl (meth) acrylate and isobonyl (meth) acrylate; trifluoroethyl (meth) acrylate, heptadecafluoro Fluorinated alkyl group-containing ethylenically unsaturated monomers such as decyl (meth) acrylate; sodium 2-acrylamide 2-methylpropanesulfonate, methallylsulfonic acid, methallylsulfonic acid, sodium methallylsulfonic acid, allylsulfonic acid , Sodium allyl sulfonate, ammonium allyl sulfonate, vinyl sulfonic acid and other sulfo group-containing ethylenically unsaturated monomers; (meth) acrylamide, N-methoxymethyl- (meth) acrylamide, N-ethoxymethyl- (meth) Acrylate, 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) metaacrylamide, N, N-di (butoxymethyl) acrylamide, N-butoxymethyl-N- (methoxymethyl) metaacrylamide , N, N-di (pentoxymethyl) acrylamide, N-methoxymethyl-N- (pentoxymethyl) metaacrylamide, N, N-dimethylaminopropylacrylamide, N, N-diethylaminopropylacrylamide, N, N-dimethyl Amid group-containing ethylenically unsaturated monomers such as acrylamide, N, N-diethylacrylamide and diacetone acrylamide; 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) Hydroxyl group-containing ethylenically unsaturated monomers such as acrylate, glycerol mono (meth) acrylate, 4-hydroxyvinylbenzene, 1-ethynyl-1-cyclohexanol, and allyl alcohol; methoxypolyethylene glycol (meth) acrylate, polyethylene glycol (meth). ) Polyoxyethylene group-containing ethylenically unsaturated monomer such as acrylate; dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, methylethylaminoethyl (meth) acrylate, dimethylaminostyrene, diethylaminostyrene and the like. Amino group-containing ethylenically unsaturated monomers such as dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, and methylethylaminoethyl (meth) acrylate; glycidyl (meth) acrylate, 3,4-epoxycyclohexyl. Epoxy group-containing ethylenically unsaturated monomer such as (meth) acrylate; Ketone group-containing ethylenically unsaturated monomer such as diacetone (meth) acrylamide and acetoacetoxy (meth) acrylate; allyl (meth) acrylate, 1- Methylallyl (meth) acrylate, 2-methylallyl (meth) acrylate, 1-butenyl (meth) acrylate, 2-butenyl (meth) acrylate, 3-butenyl (meth) acrylate, 1,3-methyl-3-butenyl (meth) Acrylate, 2-Chlorallyl (meth) acrylate, 3-Chlorallyl (meth) acrylate, o-allylphenyl (meth) acrylate, 2- (allyloxy) ethyl (meth) acrylate, allyl Lactyl (meth) acrylate, citronellyl (meth) acrylate, geranyl (meth) acrylate, loginyl (meth) acrylate, cinnamyl (meth) acrylate, diallyl maleate, diallyl itaconic acid, vinyl (meth) acrylate, vinyl crotonate, oleic acid Vinyl, vinyl linolenate, 2- (2'-vinyloxyethoxy) ethyl (meth) acrylate, ethylene glycol di (meth) acrylate, triethylene glycol (meth) acrylate, tetraethylene glycol (meth) acrylate, trimethyl propantri (Meta) acrylate, pentaerythritol tri (meth) acrylate, 1,1,1-trishydroxymethylethanediacrylate, 1,1,1-trishydroxymethylethanetriacrylate, 1,1,1-trishydroxymethylpropanetri Ethyl unsaturated monomer having two or more ethylenically unsaturated groups such as acrylate, divinylbenzene, divinyl adipate, diallyl isophthalate, diallyl phthalate, diallyl maleate; γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropyltriethoxysilane, γ-methacryloxypropyltributoxysilane, γ-methacryloxypropylmethyldimethoxysilane, γ-methacryloxypropylmethyldiethoxysilane, γ-acryloxypropyltrimethoxysilane, γ-acryloxy Propyltriethoxysilane, γ-acryloxypropylmethyldimethoxysilane, γ-methacryloxymethyltrimethoxysilane, γ-acryloxymethyltrimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltributoxysilane, vinylmethyldimethoxy Ekoxysilyl group-containing ethylenically unsaturated monomer such as silane; methylol group-containing ethylenic such as N-methylol (meth) acrylamide, N, N-dimethylol (meth) acrylamide, and alkyl etherified N-methylol (meth) acrylamide. Unsaturated monomers; but are not particularly limited thereto.

In addition, styrenes such as styrene, α-methylstyrene, o-methylstyrene, p-methylstyrene, and m-methylstyrene may be used as long as they do not interfere with the effect, but they are not included in terms of environmental friendliness. Is preferable.

Among the ethylenically unsaturated monomers (a-3) exemplified above, the ethylenically unsaturated monomer (a) is used from the viewpoint of improving the stability of the resin fine particles (A) and improving the physical properties of the coating agent by increasing the molecular weight. -3) is more preferably acrylamide, glycidyl methacrylate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, or N-methylolacrylamide.

[Manufacturing method of resin fine particles (A)]
The method for polymerizing the resin fine particles (A) is not particularly limited, but emulsion polymerization is preferable because a high-molecular-weight, low-viscosity, high-solid resin fine particle dispersion can be easily obtained in an aqueous medium. As a method for preparing resin fine particles having different Tg, the dropping tank is divided into multiple stages at the time of emulsion polymerization, and the composition of the ethylenically unsaturated monomer is changed so that the Tg of each polymer produced is different. Acrylic resin is synthesized in advance by multi-stage polymerization, bulk polymerization or solution polymerization, and after dissolving or dispersing it in the aqueous phase, it is ethylenically so that a polymer having Tg different from that of the previous acrylic resin is produced. A method of dropping a monomer to polymerize can be mentioned, but the resin fine particles (A) should be synthesized by multi-stage polymerization in consideration of the fact that the process is not complicated and the dispersion stability of the generated resin fine particles is good. Is more preferable.

In the resin fine particles (A), the mass ratio of the total amount of the polymer having Tg in the range of −40 to 30 ° C. and the total amount of the polymer having Tg in the range of 40 to 140 ° C. is 70/30 to 50/50. It is preferably in the range, more preferably in the range of 60/40 to 55/45. When the mass ratio of the polymer is in the above range, the coating agent has excellent film-forming properties, while excessive fusion and thermal motion of the formed coat layer are suppressed, and the resistance of various coating films is improved. .. Therefore, the food packaging sheet exhibits more excellent food resistance (seasoning resistance, microwave oven resistance), blocking resistance, and heat sealability. The total amount of the polymer is the total amount of ethylenically unsaturated monomers constituting the polymer.

In the resin fine particles (A), the polymer having Tg in the range of −40 to 30 ° C. and the polymer having Tg in the range of 40 to 140 ° C. are incompatible with each other, and the particles have a core-shell structure or sea islands. Although it can have a deformed particle structure such as a structure and a raspberry type, it is preferable to have a core-shell structure from the viewpoint of better development of coating material properties, and the core portion has Tg in the range of -40 to 30 ° C. It is more preferable that the polymer has a core-shell structure in which the shell portion is composed of a polymer having Tg in the range of 40 to 140 ° C. Due to the core-shell structure, the film-forming property of the resin fine particles is significantly improved, and the coating agent forms a dense and tough coating film even under low-temperature drying conditions. Therefore, the food packaging sheet made of the coating agent exhibits more excellent food resistance (seasoning resistance, microwave oven resistance).

(Radical polymerization initiator)
As the radical polymerization initiator used in the polymerization reaction of the ethylenically unsaturated monomer (a), known oil-soluble polymerization initiators and water-soluble polymerization initiators can be used, and these may be used alone. It may be used, or two or more kinds may be mixed and used.
The radical polymerization initiator is preferably 0.1 to 4 parts by mass, more preferably 0.2 to 2 parts by mass, based on 100 parts by mass of the total amount of the ethylenically unsaturated monomer (a). ..

The oil-soluble polymerization initiator is not particularly limited, and is, for example, benzoyl peroxide, tert-butylperoxybenzoate, tert-butylhydroperoxide, tert-butylperoxy (2-ethylhexanoate), tert-butylper. Organic peroxides such as oxy-3,5,5-trimethylhexanoate, di-tert-butyl peroxide; 2,2'-azobisisobutyronitrile, 2,2'-azobis-2,4- Azobis compounds such as dimethylvaleronitrile, 2,2'-azobis (4-methoxy-2,4-dimethylvaleronitrile), 1,1'-azobis-cyclohexane-1-carbonitrile; can be mentioned.

In emulsion polymerization, it is preferable to use a water-soluble polymerization initiator, and examples of the water-soluble polymerization initiator include ammonium persulfate (APS), potassium persulfate (KPS), hydrogen peroxide, and 2,2'-azobis (). 2-Methylpropion amidin) Conventionally known substances such as dihydrochloride can be preferably used.

(Reducing agent)
Further, in emulsion polymerization, a reducing agent may be used in combination with the polymerization initiator. By using a reducing agent in combination, the emulsion polymerization rate can be promoted and the emulsion polymerization at a low temperature can be facilitated. Examples of the reducing agent include reducing organic compounds such as metal salts such as ascorbic acid, elsorbic acid, tartrate acid, citric acid, glucose and formaldehyde sulfoxylate; sodium thiosulfate, sodium sulfite, sodium bisulfate and sodium metabisulfate. Reducing inorganic compounds such as: ferrous chloride, longalit, thiourea dioxide and the like.
It is preferable to use 0.05 to 5 parts by mass of these reducing agents based on 100 parts by mass of the total amount of the ethylenically unsaturated monomer (a).

The polymerization temperature may be equal to or higher than the polymerization start temperature of the polymerization initiator. For example, in the case of a peroxide-based polymerization initiator, it is usually about 80 ° C. The polymerization time is not particularly limited, but is usually 2 to 24 hours. The ethylenically unsaturated monomer (a) may be polymerized by a photochemical reaction or irradiation without using the above-mentioned polymerization initiator.

(Buffering agent or chain transfer agent)
In the polymerization of the ethylenically unsaturated monomer (a), a buffering agent or a chain transfer agent may be further used, if necessary. Examples of the buffer include sodium acetate, sodium citrate, and sodium bicarbonate. The chain transfer agent is, for example, 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, t-tetra Decyl mercaptan, n-heptadecyl mercaptan, t-heptadecyl mercaptan, t-hexadecyl mercaptan, n-hexadecyl mercaptan, n-heptadecyl mercaptan, n-octadecyl mercaptan, t-heptadecyl mercaptan, t-octadecyl Examples thereof include mercaptan, mercaptan mercaptoacetate 2-ethylhexyl, mercaptoacetate octyl, mercaptopropionate methoxybutyl, mercaptopropionate 2-ethylhexyl, mercaptopropionate octyl, mercaptopropionate stearyl and the like.
The buffer is preferably used in the range of 0 to 1 part by mass, more preferably 0.05 to 0.5 part by mass, based on 100 parts by mass of the total amount of the ethylenically unsaturated monomer (a). It is a range.
The chain transfer agent is preferably used in the range of 0.4 to 3 parts by mass, more preferably 0.6 to 2 parts, based on 100 parts by mass of the total amount of the ethylenically unsaturated monomer (a). It is in the range of parts by mass.

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

Ｒは炭素数８～１６の直鎖又は分岐アルキル基である。

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

By using the chain transfer agent (X) at the time of polymerization, the structure represented by the general formula (1) can be introduced into one end of the polymer of the ethylenically unsaturated monomer (a). In a polymer having a structure represented by the general formula (1) at one end, an appropriate polar contrast is generated between the terminal alkyl group R, which is a low polar moiety, and the highly polar acrylic resin bonded thereto. Therefore, the surface active ability is exhibited, and the dispersion stability of the resin fine particles (A) is further improved. Therefore, the stability of the coating agent is also improved, and the formation of sediments and agglomerates leading to poor coating and film formation is significantly reduced. It also has the effect of improving the wettability of the resin with respect to the substrate. As a result, the coating agent component firmly permeates and binds to the base material, so that the binding at the interface between the base material and the resin becomes stronger. Therefore, even if the coat layer comes into contact with the food component, the risk of the food component invading the base material side is reduced, and the food resistance (seasoning resistance, microwave oven resistance) and heat sealability of the food packaging sheet are further improved. do. The polymer having the structure represented by the above general formula (1) is contained in the polymer having Tg in the range of 40 to 140 ° C. from the viewpoint of more effective film forming property and improving wettability of the resin. Is more preferable.

Examples of the chain transfer agent (X) include n-octyl mercaptan, t-octyl mercaptan, n-nonyl mercaptan, t-nonyl mercaptan, n-decyl mercaptan, t-decyl mercaptan, n-undecyl mercaptan, and t-un. Decyl 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, Examples thereof include t-hexadecyl mercaptan and n-hexadecyl mercaptan.

The chain transfer agent (X) is preferably used in the range of 0.4 to 3 parts by mass, more preferably 0.6 to 3 parts by mass, based on a total amount of 100 parts by mass of the ethylenically unsaturated monomer (a). It is in the range of 2 parts by mass. By using it in the above range, the effect of introducing an alkyl group at one end of the above-mentioned polymer can be sufficiently obtained, and at the same time, there is no possibility of adversely affecting other physical characteristics. Therefore, it is possible to obtain a food packaging sheet exhibiting more excellent food resistance (seasoning resistance, microwave oven resistance) and heat sealability. The introduction rate of the chain transfer agent of the general formula (2) into the polymer is 100%.

(Basic compound)
When the ethylenically unsaturated monomer (a) is polymerized, a basic compound may be used as a neutralizing agent in order to enhance the dispersion stability of the resin fine particles (A). Examples of the basic compound include various organic amines such as aqueous ammonia, dimethylaminoethanol, diethanolamine and triethanolamine; and inorganic alkaline agents such as hydroxides of alkali metals such as sodium hydroxide, lithium hydroxide and potassium hydroxide. Can be mentioned. The basic compound may be added after the completion of the first-stage dropping, or may be added after the completion of the reaction.
The basic compound is preferably used in the range of 0.75 to 1.2 mol based on 1 mol of the carboxy group in the resin fine particles (A).

(Surfactant)
Further, when obtaining the resin fine particles (A), a surfactant may be used for the purpose of improving the dispersion stability of the resin fine particles as long as the coating agent and the food packaging sheet are not adversely affected. can. Examples of the surfactant include anionic surfactants, cationic surfactants, nonionic surfactants, amphoteric surfactants, etc., and anionic surfactants from the viewpoint of safety and good appearance of coating material properties. Alternatively, it is preferably a nonionic surfactant. Since the adverse effect on food resistance (seasoning resistance, microwave oven resistance) is unlikely to occur, the surfactant is 0.1 to 2. based on 100 parts by mass of the total amount of the ethylenically unsaturated monomer (a). It is preferably contained in the range of 0 parts by mass, and more preferably 0.4 to 1.0 part by mass. The surfactant may be used alone or in combination of two or more.

Examples of anionic surfactants that can be used include higher fatty acid salts such as sodium oleate, alkylaryl sulfonates such as dodecylbenzenesulfonic acid, alkyl sulfates such as sodium lauryl sulfate, and sodium polyoxyethylene lauryl ether sulfate. Polyoxyethylene alkyl ether sulfate ester salts, alkyl sulfosuccinic acid ester salts such as monooctyl sulfosuccinate sodium, dioctyl sulfosuccinate sodium, polyoxyethylene lauryl sulfosuccinate sodium and derivatives thereof, polyoxyethylene distyrene phenyl ether sulfate ester salts. However, among the above, the surfactant is an alkyl sulfate ester salt or an alkyl sulfosuccinic acid ester salt because it is unlikely to adversely affect the food resistance (seasoning resistance, microwave resistance) of the food packaging sheet. Further, it is more preferable that the alkyl sulfate ester salt is a lauryl sulfate salt and the alkyl sulfosuccinic acid ester salt is a dioctyl sulfosuccinate.

Nonionic surfactants include, for example, polyoxyethylene alkyl ethers such as polyoxyethylene lauryl ether and polyoxyethylene stearyl ether, and polyoxyethylene alkyl phenyl ethers such as polyoxyethylene octylphenyl ether and polyoxyethylene nonylphenyl ether. Solbitan higher fatty acid esters such as sorbitan monolaurate, sorbitan monostearate, sorbitan trioleate, polyoxyethylene sorbitan higher fatty acid esters such as polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monostearate, polyoxyethylene monolaurate. Polyoxyethylene higher fatty acid esters such as rates, polyoxyethylene monostearate, glycerin higher fatty acid esters such as oleic acid monoglyceride, stearate monoglyceride, polyoxyethylene polyoxypropylene block copolymers, polyvinyl alcohol, polyvinylpyrrolidone, polyoxy Examples thereof include ethylene distyrene phenyl ether.

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

As the polymerizable surfactant, a polymerizable anionic surfactant and a polymerizable nonionic surfactant are preferable.

Examples of the polymerizable anionic surfactant include sulfosuccinic acid esters, alkyl ethers, alkyl phenyl ethers, alkyl phenyl esters, (meth) acrylate sulfate esters, and phosphoric acid esters having a main skeleton.
Examples of the polymerizable nonionic surfactant include alkyl ethers, alkyl phenyl ethers, and alkyl phenyl esters having a main skeleton.

Among the above-exemplified surfactants, the surfactant contains at least one of lauryl sulfate and dioctylsulfosuccinate, and the total amount of the ethylenically unsaturated monomer (a) is 0 based on 100 parts by mass. It is preferably contained in an amount of 1 to 2.0 parts by mass, and more preferably 0.4 to 1.0 part by mass. By containing lauryl sulfate or dioctyl sulfosuccinate in the above range, the physical properties of the food packaging sheet are not adversely affected, the dispersion stability of the resin fine particles (A) is improved, and the film-forming of the coating agent is formed. Sexuality also improves. In addition, since the wetting of the coating agent with respect to the substrate is improved, uneven coating is reduced, and the coating agent firmly penetrates into the substrate and binds to the substrate. Therefore, it is preferable because the food resistance (seasoning resistance, microwave oven resistance) and heat sealability of the food packaging sheet are further improved.

[Glass transition temperature (Tg)]
The resin fine particles (A) have a glass transition temperature Tg in the low temperature side range of −40 to 30 ° C. and in the high temperature side range of 40 to 140 ° C., respectively. As described above, the resin fine particles (A) of the present invention are characterized by having at least two glass transition temperatures Tg obtained by DSC within a specific temperature range, and further outside these temperature ranges. It may have a glass transition temperature Tg.
The Tg on the low temperature side is more preferably in the range of −20 to 10 ° C., and the Tg on the high temperature side is more preferably in the range of 70 to 140 ° C.
When Tg is in the range of −40 to 30 ° C., the film-forming property of the coating agent is improved and a dense coating film having no gaps or cracks is formed, so that there is no possibility that food components permeate into the coating layer. Further, when heated in a microwave oven, there is no risk that the resin component of the heated coat layer will swell or elute due to steam or oil from the food. Further, at the time of heat sealing, the coating layers are firmly fused to each other to form a strong entanglement between the resins. Therefore, the food packaging sheet exhibits excellent food resistance (seasoning resistance, microwave oven resistance) and heat sealability.
When Tg is in the range of 40 to 140 ° C., there is no possibility that the coat layer is excessively fused and blocking occurs between the coat layers. In addition, in order to suppress the motility of the polymer on the low temperature side (Tg is -40 to 30 ° C) coexisting in the coat layer, when heated in a microwave oven, the resin component of the heated coat layer is vaporized from food. Suppresses swelling with oil. On the other hand, the film-forming property at the time of coating the coating agent does not deteriorate. Therefore, the food packaging sheet exhibits excellent food resistance (seasoning resistance, microwave oven resistance) and blocking resistance.
Since the resin fine particles (A) have Tg in the low temperature side range of -40 to 30 ° C. and the high temperature side range of 40 to 140 ° C., their synergistic effect also works, and food resistance (seasoning resistance, electron electron resistance) It is possible to obtain a food packaging sheet having excellent range resistance), blocking resistance, and heat sealability. The glass transition temperature of the resin fine particles (A) can be appropriately adjusted by the combination of the ethylenically unsaturated monomer (a) constituting the resin fine particles (A).

The glass transition temperature of the resin fine particles (A) can be determined by performing DSC measurement on the solid obtained by drying the dispersion of the resin fine particles (A). When DSC is measured under the temperature rising condition, the glass transition of the resin is observed as an endothermic phenomenon. The temperature at the intersection of the baseline on the low temperature side and the tangent of the inflection is defined as the glass transition temperature of the resin. In the resin fine particles (A), for example, as shown in FIG. 1, Tg can be confirmed on the low temperature side of −40 to 30 ° C. and on the high temperature side of 40 to 140 ° C., respectively.

[Mass average molecular weight]
The mass average molecular weight of the resin fine particles (A) is preferably 100,000 or more. More preferably, it is 200,000 or more. When the mass average molecular weight is 100,000 or more, the coat layer forms a tough coating film, so that swelling and elution of the resin are suppressed even when exposed to food components containing water, oil, salt, acid, etc. And the coat layer is less likely to be invaded. In addition, even under the heating conditions of a microwave oven, the coat layer is less likely to be damaged by steam or oil from food. Therefore, the food resistance (seasoning resistance, microwave oven resistance) of the food packaging sheet is further improved. In addition, since excessive fusion between the coat layers is suppressed, the blocking resistance of the food packaging sheet is also improved. Since a tough coat layer is formed of a high molecular weight resin, the resins are firmly fused and entangled with each other during heat sealing, and the heat sealing property is greatly improved. The mass average molecular weight of the resin fine particles (A) can be appropriately adjusted depending on the amount of the initiator and the amount of the chain transfer agent at the time of polymerization.
Preferably, it is 3 million or less.
The mass average molecular weight is a polystyrene-equivalent value measured by GPC (gel permeation chromatography).

[Average particle size]
The average particle size of the resin fine particles (A) is preferably in the range of 30 to 300 nm. More preferably, it is 35 to 200 nm. When the particle size is in the above range, the particle size is too small and the coating agent penetrates into the base material too much to sufficiently develop the heat sealability. On the contrary, the particle size is too large to coat the base material. It is possible to prevent problems such as insufficient heat sealability and food resistance due to insufficient penetration of the agent, which makes it impossible to firmly bond between the base material and the coat layer, and the coating agent causes poor film formation. can. Therefore, it becomes a coating agent having excellent coatability and film-forming property, and a food packaging sheet having excellent food resistance (seasoning resistance, microwave oven resistance) and heat sealability can be obtained.

<Arbitrary ingredient>
The coating agent for food packaging sheets of the present invention may contain additives such as extender pigments, antifoaming agents, leveling agents, preservatives, solvents and waxes as optional components. It is preferable that the optional component does not adversely affect the health when it remains on the food packaging sheet after coating.

As the extender pigment, those approved as foods or food additives are preferably used. Specific examples thereof include talc, silica, calcium carbonate, barium sulfate, titanium oxide, diatomaceous earth (white carbon), cellulose powder and the like.

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

The wax may be, for example, carnauba wax, mitsuro, paraffin wax, modified paraffin wax, polyethylene wax, polyethylene oxide wax, modified polyethylene wax, polypropylene wax, polypropylene oxide wax, modified polypropylene wax, ethylene vinyl acetate copolymer wax, modified ethylene vinyl acetate. Examples thereof include copolymer wax, fatty acid amide, microcrystallin wax, Fishertropush wax, polytetrafluoroethylene and the like.

≪Food packaging sheet≫
The food packaging sheet of the present invention has a coating layer formed from the coating agent for food packaging sheets on the base sheet.

The base material sheet is a sheet having a porous surface state for paper, non-woven fabric, and woven fabric, but paper is preferable. Since the base material is a paper base material, the coating agent sufficiently wets the base material and penetrates into the base material, so that the base material and the coat layer are more firmly bonded. Therefore, the food packaging sheet can exhibit more excellent food resistance (seasoning resistance, microwave oven resistance) and heat sealability.
By further applying the coating agent for food packaging sheets a plurality of times after forming the coating layer, the food resistance (seasoning resistance, microwave oven resistance) and heat sealability can be improved. Further, the coat layer may be impregnated in the base material sheet, and an embodiment in which the coating layer is not impregnated can also be used.

A known coating method can be used for the coating, but a flexographic method and a gravure method are preferable. The flexographic method is a method in which the coating agent is once transferred from the intaglio plate called on the anilox roll to the resin plate or the rubber plate, and the coating agent on the resin plate or the rubber plate is picked up by the original fabric. It is also possible to pattern a resin plate or a rubber plate. The gravure method includes a method of transferring the coating agent directly from the intaglio plate to the original fabric, and a so-called gravure offset method of transferring the coating agent from the intaglio plate to the planographic plate and then transferring it to the original fabric. It is also possible to pattern the intaglio. In the case of the gravure method, it is preferable to press the surface with a smoothing roll after coating.

The food packaging sheet of the present invention includes not only sweets such as popcorn, chocolate and caramel, fruits and vegetables such as vegetables and fruits, but also burgers such as hamburgers, hot dogs, hamburgers and rice burgers, fried chicken, fried potatoes and tangs. It can be used for packaging fried foods such as fried, tempura, fried bread, grilled chicken, grilled chicken, sama and other meat and seafood, meat buns, anman, dumplings, shumai, spring rolls, etc. It can also be used for foods containing multiple components such as salt, acid and amino acids, and having a large amount of water such as ketchup, sauce, and sauce. It can also be used for sheets for wrapping various foods such as frozen foods and paper trays for lunch boxes, and can be used for heating in a microwave oven from the packaged state. The food packaging sheet of the present invention is preferably used for applications such that the coat layer is in direct contact with various foods as described above.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the following Examples do not limit the scope of rights of the present invention at all. In addition, "part" in an Example represents "part by mass", "%" represents "mass%", the numerical value in a table is a solid content mass, and a blank is not used.
The methods for measuring the glass transition temperature, acid value, average particle size, and mass average molecular weight of the resin fine particles are as follows.

<Glass transition temperature>
The glass transition temperature of the resin fine particles was measured using a DSC (differential scanning calorimeter manufactured by TA Instrument). Specifically, an aluminum pan containing about 3 mg of dried resin precisely and put in it and an empty aluminum pan as a reference are set in a DSC measurement holder and measured under a temperature rise condition of 10 ° C./min. The temperature at the intersection of the baseline on the low temperature side of the heat absorption phenomenon and the tangent at the inflection in the obtained DSC curve was defined as the glass transition temperature (Tg).

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

<Average particle size>
The average particle size was measured by diluting the resin fine particle dispersion 500 times with water and measuring about 5 ml of the diluted solution by a dynamic light scattering measurement method (measurement device was manufactured by Nanotrack 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.

<Mass average molecular weight>
The mass average molecular weight of the resin is determined by dissolving the dried resin in tetrahydrofuran, preparing a 0.2% solution, and further filtering with a membrane filter (13HP045AN pore diameter 0.45 μm manufactured by ADVANTEC), and the following equipment and the following equipment. It was measured according to the measurement conditions. The resin that does not completely dissolve in THF or that dissolves but does not pass through the filter is considered to have a sufficiently high molecular weight, and the molecular weight is set to 2 million or more.
Equipment: HLC-8320-GPC system (manufactured by Tosoh Corporation)
Column: TSKgel-Super Multipole HZ-M0021488 4.6 mm I. D. × 15 cm × 3 (molecular weight measurement range 20 to about 2 million)
Elution solvent: Tetrahydrofuran Standard substance: Polystyrene (manufactured by Tosoh)
Flow rate: 0.6 mL / min Sample solution usage: 10 μL
Column temperature: 40 ° C

<Preparation of coating agent for food packaging sheet>
[Example 1]
83.6 parts of water and 0.35 parts of Emar 0 (100% active ingredient of sodium lauryl sulfate manufactured by Kao Corporation) were charged in a reaction vessel (reaction tank) equipped with a stirrer, a thermometer, a dropping funnel, and a refluxer. 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 part of Emar, 52 parts of water. .9 parts were mixed and stirred in advance to prepare an emulsion of ethylenically unsaturated monomer (first-stage dropping tank) to be dropped into the first stage. After raising the internal temperature of the reaction vessel to 80 ° C. and sufficiently performing nitrogen substitution, 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., 5.5 parts of an emulsion of an ethylenically unsaturated monomer and a 5% aqueous solution of potassium persulfate to be dropped in the first stage was dropped over 2 hours.
After completing the dropping of the first-stage ethylenically unsaturated monomer emulsion, leave it for 30 minutes, and leave it for 30 minutes, 30.0 parts of ethyl acrylate, 50.0 parts of methyl methacrylate, 10.0 parts of n-butyl methacrylate, 20 parts of n-butyl acrylate. .0 parts, acrylic acid 2.0 parts, 2-ethylhexyl acrylate 15.0 parts, cyclohexyl acrylate 2.0 parts, glycidyl methacrylate 1.0 parts, diethylene glycol dimethacrylate 1.0 parts, t-dodecyl mercaptan 0.1 parts , Emar 0 1.20 parts and water 160.8 parts were mixed in advance and stirred to prepare a second-stage ethylenically unsaturated monomer emulsion (second-stage dropping tank) and 10% of ammonium persulfate. 11.1 part of the aqueous solution was added dropwise over 2 hours. After the dropping was completed, the reaction was carried out at 80 ° C. for another 3 hours. After the reaction was completed, 9.8 parts of 25% aqueous ammonia was added with stirring to neutralize the mixture to obtain an aqueous dispersion of resin fine particles.
The Tg of the obtained resin fine particles was 8.4 ° C and 56.4 ° C, the acid value was 33.8 mgKOH / g, and the average particle size was 200 nm. Moreover, since the resin was insoluble in THF, the mass average molecular weight was set to 2 million or more. Water was further added to the resin fine particle water dispersion to adjust the non-volatile content to 40% to obtain the desired coating agent for food packaging sheets.

[Examples 2 to 12, Comparative Examples 1 to 6]
An aqueous dispersion of resin fine particles was prepared by the same method as in Example 1 with the compounding compositions shown in Tables 1 and 2. Regarding Example 6 and Comparative Example 3, the amount of water charged in the second-stage dropping tank was changed from 160.8 parts to 250.8 parts, Examples 7, 8, 11, 12 and Comparative Examples 4 to 6. Was changed to 130.8 copies. After the reaction was completed, 25% aqueous ammonia was added to the carboxy group in the resin so as to be in the molar amount to neutralize the carboxy group. For the obtained resin fine particles, Tg, acid value, average particle size, and mass average molecular weight were measured in the same manner as in Example 1. Water was further added to the resin fine particle aqueous dispersion to adjust the non-volatile content to 40%, and the desired coating agent for a food packaging sheet was obtained.

[Example 13]
237.8 parts of water, 0.86 parts of Perex OT-P (70% active ingredient of sodium dioctylsulfosuccinate manufactured by Kao Corporation) in a reaction vessel (reaction tank) equipped with a stirrer, thermometer, dropping funnel, and reflux device. Was prepared. Separately, 69.5 parts of methyl methacrylate, 18.0 parts of n-butyl acrylate, 12.5 parts of methacrylic acid, 3.0 parts of t-dodecyl mercaptan, 2.01 parts of Perex OT-P, 65.8 parts of water. An emulsified solution of an ethylenically unsaturated monomer (first-stage dropping tank) to be dropped in the first stage by mixing and stirring in advance was prepared. After raising the internal temperature of the reaction vessel to 80 ° C. and sufficiently performing nitrogen substitution, 12.1 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., 5.5 parts of an emulsion of an ethylenically unsaturated monomer and a 5% aqueous solution of potassium persulfate to be dropped in the first stage was dropped over 2 hours.
After the dropping was completed, the reaction was carried out for 2 hours, and 9.9 parts of 25% aqueous ammonia was added to neutralize the mixture while maintaining the temperature at 80 ° C. Subsequently, 50.0 parts of methyl acrylate and 102.0 parts of n-butyl acrylate were mixed in advance to prepare a second-stage ethylenically unsaturated monomer solution (second-stage dropping tank) and 10 of ammonium persulfate. 24.2 parts of the aqueous solution was added dropwise over 2 hours. After the dropping was completed, the reaction was carried out at 80 ° C. for another 3 hours to obtain an aqueous dispersion of resin fine particles.
The Tg of the obtained resin fine particles was -18.8 ° C. and 70.6 ° C., the acid value was 31.2 mgKOH / g, and the average particle size was 35 nm. Moreover, since the resin was insoluble in THF, the mass average molecular weight was set to 2 million or more. Water was further added to the resin fine particle aqueous dispersion to adjust the non-volatile content to 40%, and the desired coating agent for a food packaging sheet was obtained.

[Examples 13 to 20, Comparative Examples 7 and 8]
An aqueous dispersion of resin fine particles was prepared by the same method as in Example 13 with the compounding composition shown in Table 3. 25% aqueous ammonia was added to the carboxy group in the resin so as to be in the molar amount and neutralized. For the obtained resin fine particles, Tg, acid value, average particle size, and mass average molecular weight were measured in the same manner as in Example 13. Water was further added to the resin fine particle aqueous dispersion to adjust the non-volatile content to 40%, and the desired coating agent for a food packaging sheet was obtained.

The abbreviations in the table are as follows.
<Surfactant>
Emar 0: Sodium lauryl sulfate (manufactured by Kao Corporation, 100% by mass of active ingredient)
Perex O-TP: Sodium dioctylsulfosuccinate (manufactured by Kao Corporation, 70% by mass of active ingredient)
Neugen TDS-120: Polyoxyethylene tridodecyl ether (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., 100% by mass of active ingredient)

[Example 21]
143.0 parts of n-propanol was charged in a reaction vessel (reaction tank) equipped with a stirrer, a thermometer, a dropping funnel, and a refluxer. Separately, 71.0 parts of methyl methacrylate, 15.0 parts of n-butyl acrylate, and 14.0 parts of methacrylic acid were mixed in advance to prepare a mixed solution of ethylenically unsaturated monomers to be added dropwise. After raising the internal temperature of the reaction vessel to 90 ° C. and sufficiently performing nitrogen substitution, 6.0 parts of azobisisobutyronitrile (AIBN) as an initiator was added to initiate radical polymerization. While maintaining the internal temperature at 90 ° C., the mixed solution of the ethylenically unsaturated monomer was added dropwise over 2 hours. Then, the reaction was carried out for another 4 hours while maintaining the temperature at 90 ° C. After the reaction was completed, 11.5 parts of 25% aqueous ammonia and 660 parts of water were added and stirred. From there, solvent removal treatment was carried out under reduced pressure conditions to obtain an aqueous acrylic resin solution having a non-volatile component adjusted to 22.0%.
Subsequently, the internal temperature of the reaction vessel was raised to 80 ° C. again to sufficiently perform nitrogen substitution, and then 70.0 parts of methyl acrylate, 82.0 parts of n-butyl acrylate, and a 10% aqueous solution of ammonium persulfate as an initiator. 15.0 parts were added dropwise over 2 hours. After the dropping was completed, the reaction was carried out at 80 ° C. for another 3 hours to obtain an aqueous dispersion of resin fine particles. The content of the ethylenically unsaturated monomer (a-1) in the obtained resin fine particles was 94.4% by mass. The content of the surfactant per 100 parts by mass of the ethylenically unsaturated monomer (a) is 0 parts, and the content of the chain transfer agent per 100 parts by mass of the ethylenically unsaturated monomer (a) is 0. It is a department.
Further, when Tg, acid value, average particle size, and mass average molecular weight were measured in the same manner as in Example 13, the Tg of the resin fine particles was -10.4 ° C and 78.8 ° C, and the acid value was 35.4 mgKOH / g. The average particle size was 102 nm and the mass average molecular weight was 900,000. Water was further added to the resin fine particle aqueous dispersion to adjust the non-volatile content to 40%, and the desired coating agent for a food packaging sheet was obtained.

<< Evaluation items and evaluation methods >>
The evaluation items and evaluation methods for the food packaging sheet coating agent and the food packaging sheet are as follows.
<Stability of coating agent for food packaging sheet>
The coating agent for food packaging sheets obtained above was placed in a screw bottle and allowed to stand at 50 ° C. for 1 month to confirm the presence or absence of sediment generation and the rate of change in average particle size over time. The average particle size of the coating agent before and after aging was measured by the same method as the above-mentioned measurement of the average particle size of the resin fine particles.
[Evaluation criteria]
S: No sediment is generated and the average particle size has not changed (extremely good).
A: No sediment is generated, but the average particle size has changed slightly (change rate is less than ± 20%) (good).
B: No sediment is generated, but the average particle size is changing (change rate is ± 20% or more and less than ± 50%) (usable)
C: Precipitates are generated or the average particle size has changed significantly (change rate is ± 50% or more) (cannot be used)

<Making food packaging sheets>
(Food packaging sheet 1)
The obtained coating agent for food packaging sheets was applied to the glossy surface of commercially available sanitary paper (weighing 21 g, one-sided gloss treatment) using bar coater # 4. After coating, the food packaging sheet 1 was obtained by drying in a hot air oven at 80 ° C. for 30 seconds.
(Food packaging sheet 2)
The obtained coating agent for a food packaging sheet was applied to one side of a commercially available thick paper (weighing 300 g) using a bar coater # 8. After coating, the food packaging sheet 2 for contact with frozen food was obtained by drying in a hot air oven at 100 ° C. for 60 seconds.

<Blocking resistance test>
The coated surface and the non-coated surface of the obtained food packaging sheet 1 were overlapped with each other, and the blocking resistance was measured by the following equipment and measurement conditions.
Equipment: CO-201 permanent strain tester (manufactured by Tester Sangyo Co., Ltd., heating of upper and lower plates)
Conditions: ² kg / cm 2-40 ° C-24hr
[Evaluation criteria]
S: There is no resistance when peeling, and the sanitary paper is not damaged (extremely good).
A: There is some resistance when peeling, but the sanitary paper is not damaged (good).
B: There is a feeling of resistance when peeling, but the sanitary paper is not damaged (usable)
C: There is a feeling of resistance when peeling, and the sanitary paper is also missing (cannot be used).

<Heat sealability>
The obtained food packaging sheet 1 was cut into a width of 15 mm, and the heat seal strength was measured using the test piece as a test piece according to the following equipment and measurement conditions.
(Heat seal)
Equipment: HEATSHEEL & IMPULSE TESTER (manufactured by Nihon Rikagaku Kogyo Co., Ltd., heating of upper and lower plates)
Heat seal conditions: 130 ° C- ² kgf / cm 2-1 seconds (peeling)
Equipment: Tensile tester (manufactured by Tester Sangyo Co., Ltd.)
Peeling conditions: 180 ° peeling, 300 mm / min [evaluation criteria]
S: 2N or more (extremely good)
A: 1.5N or more and less than 2N (good)
B: 1N or more, less than 1.5N (usable)
C: Less than 1N (cannot be used)

<Food resistance>
(Seasoning resistance test)
In an environment of 23 ° C, one drop of a mixed solution of ketchup / vinegar / salad oil = 1/1/1 was dropped on the coated surface of the obtained food packaging sheet 1, and the droplets on the surface passed through the sanitary paper. The time to reach the back surface was measured.
[Evaluation criteria]
S: 90 minutes or more (extremely good)
A: 60 minutes or more, less than 90 minutes (good)
B: 30 minutes or more, less than 60 minutes (usable)
C: Less than 30 minutes (extremely bad)

(Microwave oven resistance test)
Place one "Tokukara Young Chicken Fried Chicken" manufactured by Nichirei Foods Inc. on the coated surface of the obtained food packaging sheet 2, heat it at 500 W for 180 seconds in a microwave oven, and leave it for 20 minutes at room temperature. While returning and removing the fried chicken, the state of penetration of oil and water on the surface of the fried chicken and the presence or absence of sticking to the fried chicken sheet (blocking between the food and the sheet) were confirmed.
[Evaluation criteria]
S: Oil and water have not penetrated the sheet, and the fried chicken does not stick to the sheet. (Very good)
A: Some oil and water have penetrated, but they have not penetrated to the back side, and the fried chicken does not stick to the sheet. (Good)
B: Oil and water have penetrated, but they have not penetrated to the back side, and the fried chicken does not stick to the sheet. (Available)
C: Oil or water has penetrated to the back side, or fried chicken is stuck to the sheet. (Usage prohibited)

As can be seen from Tables 4 to 6, the coating agents for food packaging sheets obtained in Examples 1 to 21 have good stability, and the food packaging sheets produced using them have food resistance (seasoning resistance, seasoning resistance, It is extremely excellent in microwave oven resistance), blocking resistance, and heat sealability, and has developed performance that sufficiently meets the practical level. On the other hand, the coating agents for food packaging of Comparative Examples 1, 5 and 6 were remarkably inferior in stability, and the physical characteristics of the food packaging sheet produced using the coating agents were also remarkably inferior. Further, even in the food packaging coating agents of Comparative Examples 2 to 4, 7, and 8, the physical characteristics of any of the food packaging sheets were extremely inferior, and it was difficult to say that the results met the practical level.

Claims (8)

It contains resin fine particles (A) which are polymers of the ethylenically unsaturated monomer (a).
The resin fine particles (A) are
It has a glass transition temperature in the range of -40 to 30 ° C and 40 to 140 ° C, respectively.
And the acid value is 20-40 mgKOH / g,
Based on the total mass of the ethylenically unsaturated monomer (a), it contains 85 to 97% by mass of the ethylenically unsaturated monomer (a-1) having a linear alkyl group having 1 to 4 carbon atoms. Coating agent for food packaging sheets. The coating agent for a food packaging sheet according to claim 1, wherein the polymer of the ethylenically unsaturated monomer (a) contains a polymer having a structure represented by the general formula (1) at one end.

R is a linear or branched alkyl group having 8 to 16 carbon atoms. The coating agent for a food packaging sheet according to claim 1 or 2, wherein the ethylenically unsaturated monomer (a) contains methacrylic acid. The coating agent for a food packaging sheet according to any one of claims 1 to 3, wherein the resin fine particles (A) have an average particle size of 30 to 300 nm. It contains at least one of lauryl sulfate and dioctylsulfosuccinate, and contains 0.1 to 2.0 parts by mass in total based on 100 parts by mass of the total amount of the ethylenically unsaturated monomer (a). , The coating agent for a food packaging sheet according to any one of claims 1 to 4. The coating agent for a food packaging sheet according to any one of claims 1 to 5, wherein the resin fine particles (A) have a mass average molecular weight of 100,000 or more. A food packaging sheet having a base material sheet and a coat layer formed on the base material sheet from the coating agent for a food packaging sheet according to any one of claims 1 to 6. The food packaging sheet according to claim 7, wherein the base sheet is paper.

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