Coating agents, sheets, and molded articles

Abstract

To provide a coating agent which is excellent in oil resistance and water resistance, and is also excellent in low extractability when used at high coating amount, and a sheet and a molded body each obtained using the coating agent.SOLUTION: A coating agent is provided, including resin particles including a resin (A) which is a polymer of an ethylenic unsaturated monomer (a) and a resin (B) (except for the resin (A)) which is a polymer of an ethylenic unsaturated monomer (b), and aliphatic monoalcohol having 6 or more and 12 or less carbon atoms, wherein the ethylenic unsaturated monomer (a) includes an aromatic ethylenic unsaturated monomer (a-1) and a carboxy group-containing ethylenic unsaturated monomer (a-2), the ethylenic unsaturated monomer (b) includes an aromatic ethylenic unsaturated monomer (b-1) and an alkyl group-containing ethylenic unsaturated monomer (b-2) having an alkyl group having 6 or more and 12 or less carbon atoms, and 100 ppm or more and 20,000 ppm or less of aliphatic monoalcohol having 6 or more and 12 or less carbon atoms is included based on the resin particles.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a coating agent, a sheet, and a molded body.

Background Art

[0002] Conventionally, for food packaging sheets, laminated sheets obtained by laminating a resin film such as polyethylene on a base sheet such as paper or non-woven fabric have been used. The laminated sheet has functions such as preventing oil stain on the base sheet due to oil components derived from food and reducing the decrease in the strength of the base sheet. On the other hand, in recent years, due to the global trend of reducing environmental impact, the recycling of paper has been accelerating. However, when attempting to recycle paper in a laminated sheet where the base sheet is paper, a process for separating the base sheet and the resin film laminated thereon is required, but the technical difficulty of separating and recovering the paper without imposing a large economic burden is high, which has been an obstacle to promoting recycling. Against this background, coating agent-type food packaging sheets that are more easily recyclable have been actively studied.

[0003] As such a food packaging sheet, for example, in Patent Document 1, when packaging foods containing animal fats such as meat, a coating agent using a core-shell type acrylic emulsion for the purpose of imparting oil resistance and a food packaging sheet obtained by coating it are disclosed.

[0004] However, such a coating agent shows a certain level of oil resistance against foods containing animal fats such as meat, but has insufficient water resistance against foods with a high moisture content. There was a problem that the molded body packaged by the food packaging sheet using such a coating agent swelled and the moisture leaked out.

[0005] Furthermore, from the perspective of food packaging applications, it is required to make the amount of substances oxidized by potassium permanganate present in substances migrating from the molded body to water below a certain value (hereinafter abbreviated as "low extractability"). However, when increasing the coating amount of the coating agent to improve water resistance, there was a problem that the low extractability deteriorated. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2014-214250 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] The problem that this invention aims to solve is to provide a coating agent that has good oil and water resistance and excellent low extractability even when applied in large quantities, as well as sheets and molded articles using the same. [Means for solving the problem]

[0008] The inventors of this invention have diligently conducted research to solve the above-mentioned problems, and as a result, have arrived at this invention. In other words, the present invention relates to a coating agent comprising resin particles comprising a resin (A) which is a polymer of an ethylenically unsaturated monomer (a) and a resin (B) which is a polymer of an ethylenically unsaturated monomer (b) (excluding the above resin (A)), and an aliphatic monoalcohol having 6 to 12 carbon atoms, wherein the ethylenically unsaturated monomer (a) comprises an aromatic ethylenically unsaturated monomer (a-1) and a carboxyl group-containing ethylenically unsaturated monomer (a-2), and the ethylenically unsaturated monomer (b) comprises an aromatic ethylenically unsaturated monomer (b-1) and an alkyl group-containing ethylenically unsaturated monomer (b-2) having an alkyl group with 6 to 12 carbon atoms, and the coating agent contains 100 ppm to 20,000 ppm of the aliphatic monoalcohol having 6 to 12 carbon atoms based on the above resin particles.

[0009] Furthermore, the present invention relates to the coating agent, which contains, based on the above ethylenically unsaturated monomer (a), 51% by mass or more and 90% by mass or less of the above aromatic ethylenically unsaturated monomer (a-1), and 10% by mass or more and 40% by mass or less of the above carboxyl group-containing ethylenically unsaturated monomer (a-2).

[0010] Furthermore, the present invention relates to the coating agent described above, wherein the coating agent contains 10% by mass or more and 50% by mass or less of the aromatic ethylenically unsaturated monomer (b-1) and 51% by mass or more and 90% by mass or less of an alkyl group-containing ethylenically unsaturated monomer (b-2) having 6 to 12 carbon atoms in the alkyl group, based on the ethylenically unsaturated monomer (b) described above.

[0011] Furthermore, the present invention relates to the coating agent comprising 60 to 400 parts by mass of resin (B) with respect to 100 parts by mass of resin (A).

[0012] Furthermore, the present invention relates to a coating agent in which the resin particles are core-shell type resin particles, the shell resin is made of the above-mentioned resin (A), and the core resin is made of the above-mentioned resin (B).

[0013] Furthermore, the present invention relates to the above-mentioned coating agent for food packaging.

[0014] Furthermore, the present invention relates to a sheet having a coating layer of the above-mentioned coating agent on at least one side of a substrate.

[0015] Furthermore, the present invention relates to a molded article obtained by molding the above-mentioned sheet.

[0016] Furthermore, the present invention relates to a molded body in which the coating layer of the coating agent is molded so as to be on the side of the contents, and the contents are food. [Effects of the Invention]

[0017] The present invention provides a coating agent that has good oil and water resistance and excellent low extractability even at high application rates, as well as sheets and molded articles using the same. [Modes for carrying out the invention]

[0018] Hereinafter, the present invention will be described in detail. In this specification, a numerical range specified using "~" shall include the numerical values described before and after "~" as the range of the lower limit value and the upper limit value. Each of the various components appearing in this specification shall be construed to be either alone or in combination of two or more, unless otherwise noted.

[0019] Also, in this specification, when expressed as "(meth)acrylic acid" and "(meth)acrylate", unless otherwise specified, they shall represent "acrylic acid or methacrylic acid" and "acrylate or methacrylate", respectively. Further, "(meth)acrylate monomer" refers to the general term for "acrylate monomer" and "methacrylate monomer". Monomer means a monomer containing an ethylenically unsaturated double bond.

[0020] In addition, in this specification, the aromatic ethylenically unsaturated monomer (a-1), the carboxy group-containing ethylenically unsaturated monomer (a-2), the other ethylenically unsaturated monomer (a-3) copolymerizable with the above ethylenically unsaturated monomers (a-1) and (a-2), the aromatic ethylenically unsaturated monomer (b-1), the alkyl group-containing ethylenically unsaturated monomer (b-2) having 6 to 12 carbon atoms in the alkyl group, and the other ethylenically unsaturated monomer (b-3) copolymerizable with the above ethylenically unsaturated monomers (b-1) and (b-2) may be abbreviated as ethylenically unsaturated monomer (a-1), ethylenically unsaturated monomer (a-2), ethylenically unsaturated monomer (a-3), ethylenically unsaturated monomer (b-1), ethylenically unsaturated monomer (b-2), and ethylenically unsaturated monomer (b-3), respectively.

[0021] In this specification, "Mw" is the mass average molecular weight in terms of polystyrene determined by gel permeation chromatography (GPC) measurement. "Mn" is the number average molecular weight in terms of polystyrene determined by GPC measurement. These can be measured by the method described in the section of [Examples].

[0022] ≪Coating agent≫ The coating agent of the present invention is suitable for coating on a substrate such as paper or non-woven fabric to form a coating layer of the coating agent (hereinafter sometimes abbreviated as "coating layer") to form a sheet, and is particularly suitable for forming a sheet for packaging food (hereinafter abbreviated as food packaging sheet). Further, the sheet of the present invention not only has excellent oil resistance against foods containing animal fats such as meats, but also has excellent water resistance against more moist foods, so it can also be suitably used for applications where the coating layer and the food are in direct contact.

[0023] The coating agent of the present invention comprises resin particles comprising a resin (A) which is a polymer of an ethylenically unsaturated monomer (a) and a resin (B) which is a polymer of an ethylenically unsaturated monomer (b) (excluding the above resin (A)), and an aliphatic monoalcohol having 6 to 12 carbon atoms, wherein the ethylenically unsaturated monomer (a) comprises an aromatic ethylenically unsaturated monomer (a-1) and a carboxyl group-containing ethylenically unsaturated monomer (a-2), and the ethylenically unsaturated monomer (b) comprises an aromatic ethylenically unsaturated monomer (b-1) and an alkyl group-containing ethylenically unsaturated monomer (b-2) having 6 to 12 carbon atoms in the alkyl group, and contains 100 ppm or more and 20,000 ppm or less of an aliphatic monoalcohol having 6 to 12 carbon atoms based on the resin particles. Such a coating agent is excellent in film-forming properties, and the sheet and molded body using this coating agent exhibit excellent performance in oil resistance, water resistance, and low extractability, which were difficult with conventional aqueous coating agents of resins.

[0024] <Resin (A)> First, the resin (A) will be described. The resin (A) is a polymer of an ethylenically unsaturated monomer (a). The ethylenically unsaturated monomer (a) which is a constituent unit of the resin (A) is classified into an aromatic ethylenically unsaturated monomer (a-1), a carboxyl group-containing ethylenically unsaturated monomer (a-2), and other ethylenically unsaturated monomers (a-3) copolymerizable with the above ethylenically unsaturated monomers (a-1) and (a-2).

[0025] Resin (A) preferably contains 51% to 90% by mass of ethylenically unsaturated monomer (a-1) and 10% to 40% by mass of ethylenically unsaturated monomer (a-2), based on 100% by mass of the total mass of ethylenically unsaturated monomer (a). More preferably, it contains 61% to 80% by mass of ethylenically unsaturated monomer (a-1) and 20% to 39% by mass of ethylenically unsaturated monomer (a-2). By keeping the resin within the above range, the dispersion stability of the resin particles is improved, and the wettability and coating properties of the coating agent are also greatly improved. Therefore, this is preferable because it further improves the oil resistance and water resistance of the sheet.

[0026] <Resin (B)> Next, resin (B) will be described. Resin (B) is preferably composed of 10% to 50% by mass of ethylenically unsaturated monomer (b-1) and 51% to 90% by mass of ethylenically unsaturated monomer (b-2), based on 100% by mass of the total mass of ethylenically unsaturated monomer (b). More preferably, it is composed of 15% to 45% by mass of ethylenically unsaturated monomer (a-1) and 55% to 80% by mass of ethylenically unsaturated monomer (a-2). This range is preferable because it improves the film-forming properties of the resin particles and further improves the oil resistance, water resistance, and low extractability of the sheet.

[0027] <Aliphatic monoalcohols with 6-12 carbon atoms> Next, we will describe aliphatic monoalcohols having 6 to 12 carbon atoms. The aliphatic monoalcohols having 6 to 12 carbon atoms are present in an amount of 100 ppm to 20,000 ppm, and more preferably 300 ppm to 10,000 ppm, based on the resin particles. This range is preferable because it prevents excessive residue in the coating film after drying, improves the film-forming properties of the resin particles, and further improves the oil resistance, water resistance, and low extractability of the sheet.

[0028] [Ethylene-unsaturated monomer (a-1)] Examples of aromatic ethylenically unsaturated monomers (a-1) include styrene, α-methylstyrene, o-methylstyrene, p-methylstyrene, m-methylstyrene, vinylnaphthalene, benzyl acrylate, benzyl methacrylate, phenoxyethyl acrylate, phenoxyethyl methacrylate, phenoxydiethylene glycol acrylate, phenoxydiethylene glycol methacrylate, phenoxytetraethylene glycol acrylate, phenoxytetraethylene glycol methacrylate, phenoxyhexaethylene glycol acrylate, phenoxyhexaethylene glycol methacrylate, phenyl acrylate, and phenyl methacrylate, but it is preferable that the mixture contains styrene and α-methylstyrene.

[0029] [Ethylene-unsaturated monomers (a-2)] Examples of carboxyl group-containing ethylenically saturated monomers (a-2) include acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, and cinnamic acid. However, it is preferable that the carboxyl group-containing ethylenically saturated monomer (a-2) contains acrylic acid and / or methacrylic acid, as this yields resin particles with superior stability and improves the coatability of the coating agent and the coating film's resistance to food-derived components in the coating layer. The inclusion of acrylic acid and methacrylic acid further improves the dispersion stability of the resin particles and significantly improves the wettability and coatability of the coating agent. Therefore, it is preferable as it further improves the oil resistance and water resistance of the sheet.

[0030] [Ethylene-unsaturated monomers (a-3)] Other ethylenically unsaturated monomers (a-3) include, for example, methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, iso-butyl (meth)acrylate, pentyl (meth)acrylate, tert-butyl (meth)acrylate, pentyl (meth)acrylate, isoamyl (meth)acrylate, heptyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate. ethylenically unsaturated monomers containing linear or branched alkyl groups, such as acrylate, nonyl(meth)acrylate, decyl(meth)acrylate, undecyl(meth)acrylate, lauryl(meth)acrylate, tridecyl(meth)acrylate, tetradecyl(meth)acrylate, pentadecyl(meth)acrylate, hexadecyl(meth)acrylate, heptadecyl(meth)acrylate, stearyl(meth)acrylate, isostearyl(meth)acrylate, and behenyl(meth)acrylate; Alicyclic alkyl group-containing ethylenically unsaturated monomers such as cyclohexyl (meth)acrylate and isobornyl (meth)acrylate; Fluorinated alkyl group-containing ethylenically unsaturated monomers such as trifluoroethyl (meth)acrylate and heptadecafluorodecyl (meth)acrylate; Sulfo-containing ethylenically unsaturated monomers such as sodium 2-methylpropanesulfonate, methallyl sulfonic acid, sodium methallyl sulfonic acid, allyl sulfonic acid, sodium allyl sulfonate, ammonium allyl sulfonate, and vinyl sulfonic 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, Amide group-containing ethylenically unsaturated monomers such as N-butoxymethyl-N-(propoxymethyl)methacrylamide, N,N-di(butoxymethyl)acrylamide, N-butoxymethyl-N-(methoxymethyl)methacrylamide, N,N-di(pentoxymethyl)acrylamide, N-methoxymethyl-N-(pentoxymethyl)methacrylamide, N,N-dimethylaminopropylacrylamide, N,N-diethylaminopropylacrylamide, N,N-dimethylacrylamide, N,N-diethylacrylamide, and diacetoneacrylamide; 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; Polyoxyethylene group-containing ethylenically unsaturated monomers such as methoxypolyethylene glycol (meth)acrylate and polyethylene glycol (meth)acrylate; Examples include dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, methylethylaminoethyl (meth)acrylate, dimethylaminostyrene, diethylaminostyrene, etc., and amino group-containing ethylenically unsaturated monomers such as dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, and methylethylaminoethyl (meth)acrylate; Epoxy group-containing ethylenically unsaturated monomers such as glycidyl (meth)acrylate and 3,4-epoxycyclohexyl (meth)acrylate; Ketone group-containing ethylenically unsaturated monomers such as diacetone(meth)acrylamide and acetoseacetoxy(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, allyllactyl (meth)acrylate, citronellyl (meth)acrylate, geranyl (meth)acrylate, rhodinyl (meth)acrylate, cinnamyl (meth)acrylate, diallyl maleate, diaryllutaconic acid, vinyl (meth)acrylate, crotonic acid Ethylene-unsaturated monomers having two or more ethylenically unsaturated groups, such as Nyl, vinyl oleate, vinyl linolenate, 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, etc.; Alkoxysilyl group-containing ethylenically unsaturated monomers such as γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropyltriethoxysilane, γ-methacryloxypropyltributoxysilane, γ-methacryloxypropylmethyldimethoxysilane, γ-methacryloxypropylmethyldiethoxysilane, γ-acryloxypropyltrimethoxysilane, γ-acryloxypropyltriethoxysilane, γ-acryloxypropylmethyldimethoxysilane, γ-methacryloxymethyltrimethoxysilane, γ-acryloxymethyltrimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltributoxysilane, vinylmethyldimethoxysilane; Methylol group-containing ethylenically unsaturated monomers such as N-methylol(meth)acrylamide, N,N-dimethylol(meth)acrylamide, and alkyl etherified N-methylol(meth)acrylamide; These are some examples, but are not limited to them.

[0031] [Ethylene-unsaturated monomer (b-1)] The aromatic ethylenically unsaturated monomer (b-1) may be the same monomer as the aromatic ethylenically unsaturated monomer (a-1). It is preferable that it contains styrene and α-methylstyrene, similar to (a-1).

[0032] [Ethylene-unsaturated monomers (b-2)] Examples of alkyl-containing ethylenically unsaturated monomers (b-2) having 6 to 12 carbon atoms in the alkyl group include hexyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, octyl(meth)acrylate, nonyl(meth)acrylate, decyl(meth)acrylate, undecyl(meth)acrylate, and lauryl(meth)acrylate. However, due to the balance of hydrophilicity and hydrophobicity, it is preferable to include 2-ethylhexyl(meth)acrylate.

[0033] [Ethylene-unsaturated monomers (b-3)] Other ethylenically unsaturated monomers and (b-3) can be any ethylenically unsaturated monomer other than ethylenically unsaturated monomer (b-1) and ethylenically unsaturated monomer (b-2). However, from the viewpoint of improving the stability of resin particles (A) and improving the properties of the coating agent by increasing molecular weight, it is preferable to include methyl methacrylate, butyl methacrylate, butyl acrylate, glycidyl methacrylate, ethylene glycol dimethacrylate, and diethylene glycol dimethacrylate.

[0034] [Aliphatic monoalcohols with 6 to 12 carbon atoms] Examples of aliphatic monoalcohols having 6 to 12 carbon atoms include hexyl alcohol, pentyl alcohol, octyl alcohol, 2-ethylhexyl alcohol, nonyl alcohol, decyl alcohol, undecyl alcohol, and lauryl alcohol. However, from the viewpoint of improving film formation, it is preferable to include 2-ethylhexyl alcohol. Furthermore, in both coating agents containing an aliphatic monoalcohol with 6 to 12 carbon atoms as a hydrolysis product of an ethylenically unsaturated monomer (b-2), and coating agents containing an aliphatic monoalcohol with 6 to 12 carbon atoms by intentional addition, film formation is improved, and the oil resistance and water resistance of the sheet can be enhanced.

[0035] [Resin particles] The resin particles contain the above-mentioned resin (A) and resin (B), and it is preferable that the resin (B) is present in an amount of 60 to 400 parts by mass, and more preferably 100 to 300 parts by mass, of resin (A) per 100 parts by mass. By keeping the range within the above limits, the coating agent will have good film-forming properties, and its oil and water resistance will be improved.

[0036] Furthermore, it is preferable that the resin particles are core-shell type resin particles, where the shell portion is made of the above-mentioned resin (A) and the core portion is made of the above-mentioned resin (B). By designing the resin particles as core-shell type, dispersion stability is further improved, and the wettability and coatability of the coating agent are also greatly improved. Therefore, this is preferable because it further improves the oil resistance and water resistance of the sheet.

[0037] [Synthesis of resin (A)] The polymerization method for resin (A) is not particularly limited, but it is preferable to synthesize it by bulk polymerization or solution polymerization from the viewpoint of molecular weight control.

[0038] (Polymerization initiator) As the polymerization initiator used in the polymerization reaction of the ethylenically unsaturated monomer (a), known polymerization initiators can be used, and oil-soluble polymerization initiators are preferred. One type may be used alone, or two or more types may be used in mixture. The polymerization initiator is preferably used in amounts of 0.1 to 5 parts by mass, and more preferably 0.2 to 4 parts by mass, based on 100 parts by mass of the total amount of ethylenically unsaturated monomer (a).

[0039] The oil-soluble polymerization initiator is not particularly limited and includes, for example, organic peroxides such as benzoyl peroxide, tert-butyl peroxybenzoate, tert-butyl hydroperoxide, tert-butyl peroxy(2-ethylhexanoate), tert-butyl peroxy-3,5,5-trimethylhexanoate, and di-tert-butyl peroxide; 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; One could list these:

[0040] (Chain transfer agent) In the polymerization of ethylenically unsaturated monomers (a), chain transfer agents may be used as needed. 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. Lucaptan, n-tridecyl mercaptan, t-tridecyl mercaptan, n-tetradecyl mercaptan, t-tetradecyl 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, mer Examples include 2-ethylhexyl mercaptoacetate, octyl mercaptoacetate, methoxybutyl mercaptopropionate, 2-ethylhexyl mercaptopropionate, octyl mercaptopropionate, stearyl mercaptopropionate, etc., but also n-octyl mercaptan, t-octyl mercaptan, n-nonyl mercaptan, t-nonyl mercaptan, n-decyl mercaptan, t-decyl mercaptan It is preferable to use tan, n-undecylmercaptan, t-undecylmercaptan, n-dodecylmercaptan, t-dodecylmercaptan, n-tridecylmercaptan, t-tridecylmercaptan, n-tetradecylmercaptan, t-tetradecylmercaptan, n-heptadecylmercaptan, t-heptadecylmercaptan, t-hexadecylmercaptan, or n-hexadecylmercaptan.

[0041] (Basic compounds) During the polymerization of the ethylenically unsaturated monomer (a), a basic compound may be used as a neutralizing agent to improve the dispersion stability of the resin particles. Examples of basic compounds include organic bases such as dimethylaminoethanol, diethanolamine, and triethanolamine. Examples of inorganic alkalis include alkaline hydroxides such as sodium hydroxide, lithium hydroxide, and potassium hydroxide, as well as inorganic bases such as ammonia. However, ammonia is preferred from the viewpoint of water resistance. The basic compound is preferably used in a range of 0.75 to 1.5 mol, based on 1 mol of carboxyl groups in resin (A).

[0042] [Glass transition temperature (Tg) of resin (A)] Resin (A) preferably has a Tg in the range of 60 to 140°C. Having a Tg within this range improves the water resistance of the coating agent.

[0043] [Mass-average molecular weight of resin (A)] The mass-average molecular weight of resin (A) is preferably 4,000 to 30,000, and more preferably 5,000 to 20,000. This range of mass-average molecular weight improves dispersion stability and significantly enhances the wettability and coatability of the coating agent. Therefore, it is preferable for further improving the oil and water resistance of the sheet. The mass-average molecular weight of resin (A) can be adjusted as appropriate by varying the amount of initiator and chain transfer agent used during polymerization. In this specification, the mass-average molecular weight refers to the standard polystyrene equivalent value measured by GPC (gel permeation chromatography).

[0044] [Synthesis of resin particles] While there are no particular limitations on the polymerization method for resin particles, emulsion polymerization is preferred because it allows for easy acquisition of high molecular weight, low viscosity, and high solids content resin particle dispersions in an aqueous medium. Furthermore, it is preferable to synthesize resin particles containing resin (A) and resin (B) by neutralizing resin (A) with a basic compound and polymerizing the ethylenically unsaturated monomer (b) in the presence of the water-soluble resin (A). Synthesizing resin particles containing resin (B) in the presence of resin (A) and a basic compound makes it easier to obtain aliphatic monoalcohols having 6 to 12 carbon atoms as hydrolysis products of the ethylenically unsaturated monomer (b-2), improving the film-forming properties of the resin particles and further improving the oil resistance, water resistance, and low extractability of the sheet.

[0045] (Radical polymerization initiator) As the radical polymerization initiator used in the polymerization reaction of the ethylenically unsaturated monomer (b), known oil-soluble polymerization initiators and water-soluble polymerization initiators can be used. These may be used individually or in mixtures 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 monomer (b).

[0046] The oil-soluble polymerization initiator is not particularly limited, and the same polymerization initiator used in the synthesis of resin (A) can be used.

[0047] In emulsion polymerization, it is preferable to use a water-soluble polymerization initiator. 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.

[0048] (Reducing agent) Furthermore, in emulsion polymerization, a reducing agent may be used in combination with the polymerization initiator. Using a reducing agent in combination accelerates the emulsion polymerization rate and facilitates emulsion polymerization at low temperatures. Examples of reducing agents include reducing organic compounds such as ascorbic acid, erythorbic acid, tartaric acid, citric acid, glucose, and metal salts such as formaldehyde sulfoxylate; reducing inorganic compounds such as sodium thiosulfate, sodium sulfite, sodium bisulfite, and sodium metabisulfite; ferrous chloride, rongalit, and thiourea dioxide. 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 ethylenically unsaturated monomer (a).

[0049] (Chain transfer agent) In the polymerization of the ethylenically unsaturated monomer (b), a chain transfer agent may be used as needed, and the same chain transfer agent as used in the synthesis of resin (A) can be used.

[0050] (buffering agent) In the polymerization of the ethylenically unsaturated monomer (b), a buffer may be used as needed. Examples of buffers include sodium acetate, sodium citrate, and sodium bicarbonate.

[0051] (Surfactants) Furthermore, when obtaining resin particles, surfactants can be used to improve the dispersion stability of the resin particles, provided that they do not adversely affect the properties of the coating agent or the sheet. Examples of surfactants include anionic surfactants, cationic surfactants, nonionic surfactants, and amphoteric surfactants, but anionic or nonionic surfactants are preferred from the viewpoint of safety and good coating film properties. To avoid adverse effects on the water resistance and low extractability of the sheet, the surfactant is preferably included in an amount of 0.1 to 5 parts by mass, and more preferably 0.2 to 4 parts by mass, based on 100 parts by mass of the total amount of ethylenically unsaturated monomer (b). Surfactants can be used alone or in combination of two or more types.

[0052] Examples of anionic surfactants that can be used include higher fatty acid salts such as sodium oleate, alkylaryl sulfonates such as dodecylbenzenesulfonic acid, alkyl sulfate esters such as sodium lauryl sulfate, polyoxyethylene alkyl ether sulfate esters such as sodium polyoxyethylene lauryl ether sulfate, alkyl sulfosuccinate esters and their derivatives such as sodium monooctyl sulfosuccinate, sodium dioctyl sulfosuccinate, and sodium polyoxyethylene lauryl sulfosuccinate, and polyoxyethylene distyleninated phenyl ether sulfate. However, among the above, alkyl sulfate esters or alkyl sulfosuccinate esters are preferred as surfactants because they do not adversely affect the water resistance and low extractability of the sheet, and more preferably the alkyl sulfate ester is lauryl sulfate, and the alkyl sulfosuccinate ester is dioctyl sulfosuccinate.

[0053] Examples of nonionic surfactants include polyoxyethylene alkyl ethers such as polyoxyethylene lauryl ether and polyoxyethylene stearyl ether, polyoxyethylene alkylphenyl 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 stearate monoglyceride, polyoxyethylene polyoxypropylene block copolymer, polyvinyl alcohol, polyvinylpyrrolidone, and polyoxyethylene distyleninated phenyl ether.

[0054] The above-mentioned surfactant can be a polymerizable surfactant having one or more ethylenically unsaturated double bonds capable of radical polymerization within its molecule. Polymerizable anionic surfactants and polymerizable nonionic surfactants are preferred.

[0055] Examples of the polymerizable anionic surfactants mentioned above include those whose main skeletons are sulfosuccinate esters, alkyl ethers, alkylphenyl ethers, alkylphenyl esters, (meth)acrylate sulfate esters, and phosphate esters. Examples of the polymerizable nonionic surfactants mentioned above include those whose main skeleton is an alkyl ether, alkylphenyl ether, or alkylphenyl ester.

[0056] Among the examples given above, the surfactant preferably contains at least one of lauryl sulfate or diotyl sulfosuccinate, and preferably contains a total of 0.1 to 5 parts by mass of both, and more preferably 0.2 to 4 parts by mass, based on 100 parts by mass of the total amount of ethylenically unsaturated monomer (b). By including lauryl sulfate or diotyl sulfosuccinate within the above range, the various physical properties of the sheet are not adversely affected, the dispersion stability of the resin particles is improved, and the film-forming ability of the coating agent is also improved. Furthermore, the wetting of the coating agent to the substrate is improved, reducing uneven coating and allowing the coating agent to penetrate and adhere firmly to the substrate. Therefore, it exhibits superior oil resistance, water resistance, and low extractability.

[0057] [Tg of resin (B)] Resin (B) preferably has a Tg in the range of -40 to 20°C. Setting the Tg within this range improves the film-forming properties of the coating agent, and even under low-temperature drying conditions, the coating agent forms a dense and tough coating film, thereby improving oil resistance, water resistance, and low extractability.

[0058] [Average particle size of resin particles] The average particle size of the resin particles is preferably in the range of 30 to 300 nm. This particle size range allows the coating agent to penetrate the substrate appropriately while maintaining good film-forming properties, resulting in a dense and tough coating that improves oil resistance, water resistance, and low extractability.

[0059] The coating agent of the present invention is preferable for use as a coating agent for food packaging because it has excellent oil resistance, water resistance, and low extractability.

[0060] <Optional ingredients> The coating agent of the present invention may contain additives such as extender pigments, defoamers, leveling agents, preservatives, solvents, and waxes as optional components. When used as a coating agent for food packaging, it is preferable that the optional components do not have adverse health effects if they remain on the sheet after coating.

[0061] It is preferable to use extender pigments that are approved as food or food additives. Specifically, examples include talc, kaolin, silica, calcium carbonate, barium sulfate, titanium dioxide, diatomaceous earth (white carbon), and cellulose powder.

[0062] Examples of defoaming agents include mineral oil-based, polyether-based, and silicone-based agents, but silicone-based agents are preferred from the viewpoint of defoaming properties.

[0063] Leveling agents include acrylic, vinyl, silicone, fluorine, and acetylene glycol-based agents, but acetylene glycol-based agents are preferred from the viewpoint of oral safety.

[0064] Preservatives that are isothiazolinoline-based are preferred. Specifically, examples include 2-methyl-4-isothiazolin-3-one, 5-chloro-2-methyl-4-isothiazolin-3-one, 1,2-benzisothiazolin-3-one, and 4,5-dichloro-2-octyl-4-isothiazolin-3-one.

[0065] From the perspective of oral safety, suitable solvents include ethanol, isopropyl alcohol, propylene glycol, and glycerin.

[0066] 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 amides, microcrystalline wax, Fischer-Tropsch wax, and polytetrafluoroethylene. However, from the viewpoint of improving water resistance, paraffin wax, modified paraffin wax, polyethylene wax, and oxidized polyethylene wax are preferred.

[0067] ≪Sheet≫ The sheet of the present invention has a coating layer formed from the coating agent of the present invention on a substrate.

[0068] The substrate is not particularly limited, but it is preferably paper, nonwoven fabric, or other substrates having a porous surface, and more preferably paper. This is because when the coating agent sufficiently wets the substrate and penetrates into the substrate, the substrate and the coating layer bond more firmly.

[0069] For applying the coating agent to the substrate to form the coating layer, known coating methods can be used, but knife coating, dipping, flexographic coating, and gravure coating are preferred. The flexographic coating method involves transferring the coating agent from an intaglio plate called an anilox roll to a resin or rubber plate, and then transferring the coating agent from the resin or rubber plate to the base material. The resin or rubber plate can also be patterned. The gravure coating method includes a method in which the coating agent is transferred directly from the intaglio plate to the base material, and the so-called gravure offset method in which the coating agent is transferred from the intaglio plate to a planar plate before being transferred to the base material. The intaglio plate can also be patterned. In the case of the gravure coating method, it is preferable to press the coating with a smoothing roll after application.

[0070] Molded body The molded article of the present invention is formed by molding the sheet of the present invention. Because the molded article has excellent oil resistance, water resistance, and low extractability, it can be used in applications where the coated surface comes into direct contact with food. For example, it can be used to package confectionery such as popcorn, chocolate, and caramel, as well as fresh produce such as vegetables and fruits, and burgers such as hamburgers, hot dogs, rice burgers, fried foods such as fried chicken, french fries, karaage, tempura, and fried bread, grilled meat and seafood such as grilled chicken, yakitori, and saury, and foods such as steamed buns, sweet bean paste buns, dumplings, shumai, and spring rolls. It can also be used for foods to which ketchup, sauces, and dips containing multiple components such as oil, salt, acid, and amino acids, and which have a high moisture content, are attached. Furthermore, because of its excellent low extractability, it is possible to make molded articles with high coating amounts, and it can be used as a sheet for packaging various foods such as frozen foods and paper trays for lunch boxes, where high oil and water resistance is required. [Examples]

[0071] The present invention will be described in more detail below with reference to examples, but the following examples do not limit the technical scope of the present invention in any way. In the examples, "parts" refers to "parts by mass," and "%" refers to "mass%." The numerical values ​​in the table represent the solid content mass, and blank spaces indicate that the material was not used.

[0072] <Glass transition temperature (Tg)> Tg was measured using a DSC (Differential Scanning Calorimeter, TA Instruments). Specifically, approximately 3 mg of dried sample was accurately weighed and placed in an aluminum pan, along with an empty aluminum pan used as a reference. These pans were then placed in a DSC measuring holder, and the temperature at the intersection of the low-temperature baseline of the endothermic phenomenon and the tangent line at the inflection point in the resulting DSC curve was defined as Tg.

[0073] <Acid value> The acid value was determined by potentiometric titration using a potassium hydroxide-ethanol solution as specified in JIS K2501.

[0074] <Mass average molecular weight> The mass-average molecular weight was measured by dissolving the dried sample in tetrahydrofuran to prepare a 0.2% solution, which was then filtered through a membrane filter (ADVANTEC 13HP045AN, pore size 0.45 μm) and measured using the following apparatus and measurement conditions. Equipment: HLC-8320-GPC system (manufactured by Tosoh Corporation) Column: TSKgel-Super Multipore HZ-M0021488 4.6 mm I.D. × 15 cm × 3 tubes (molecular weight measurement range 2,000 to approximately 2,000,000) Elution solvent: tetrahydrofuran Standard material: Polystyrene (manufactured by Tosoh Corporation) Flow rate: 0.6mL / min Sample solution volume: 10 μL Column temperature: 40℃

[0075] <Average particle size> The average particle size was determined by diluting a dispersion of resin particles 500 times with water, and measuring approximately 5 ml of the resulting diluted solution using dynamic light scattering (measurement device: NanoTrack UPA Co., Ltd., MicroTrack Bell). The peak of the volume particle size distribution data (histogram) obtained at this time was defined as the average particle size.

[0076] <Quantitative determination of aliphatic monoalcohols with 6 to 12 carbon atoms> Approximately 1 g of the coating agent was diluted 10-fold with water, and 1 ml of the resulting diluted solution was analyzed by gas chromatography (GC) to quantify aliphatic monoalcohols with 6 to 12 carbon atoms. The measurement conditions for the GC analysis were as follows: (Measurement conditions) Measuring device: GC-4000 (manufactured by GL Sciences Co., Ltd.) Column: AQUATEC-2 0.25mm ID × 60m, df = 1.4μm (GL Sciences Co., Ltd.) Temperature increase program: 80°C (3 minutes) → 3°C / minute → 200°C (7 minutes) Carrier gas: He Detector: FID

[0077] <Preparation of resin (A)> [Synthesis Example 1] In a reaction vessel (reaction tank) equipped with a stirrer, thermometer, dropping funnel, and reflux apparatus, 60 parts of butyl alcohol were charged, and the internal temperature of the reaction vessel was raised to 110°C while purging with nitrogen. Next, 35 parts of styrene, 40 parts of α-methylstyrene, and 25 parts of acrylic acid were charged into the dropping funnel, and then 4 parts of azoisobutyronitrile were added and dissolved, and added dropwise over 2 hours. After the addition was complete, the reaction was carried out under reflux for 4 hours. After the reaction, the mixture was cooled to 80°C, neutralized with 23.6 parts of 25% aqueous ammonia, diluted with 210 parts of water, and the butyl alcohol was removed by distillation to adjust the non-volatile content to 30% to obtain an aqueous solution of resin (A). The obtained resin had a Tg of 126°C, an acid value of 187 mgKOH / g, and a mass-average molecular weight of 12000.

[0078] [Synthesis Examples 2-11] An aqueous solution of resin (A) was prepared using the same method as in Synthesis Example 1, with the formulation shown in Table 1. The 25% aqueous ammonia was added to neutralize the resin by adding it in an equimolar amount relative to the carboxyl groups in the resin. The Tg, acid value, and mass-average molecular weight of the obtained resin (A) were measured in the same manner as in Example 1.

[0079] [Table 1]

[0080] <Preparation of coating agent> [Example 1] In a reaction vessel (reaction tank) equipped with a stirrer, thermometer, dropping funnel, and refluxer, 333.3 parts of an aqueous solution of resin (A) obtained in Synthesis Example 1 and 175 parts of water were charged, and the internal temperature of the reaction vessel was raised to 80°C while purging with nitrogen. Next, 85 parts of styrene, 140 parts of 2-ethylhexyl acrylate, and 10 parts of methyl methacrylate were charged into the dropping funnel. After raising the internal temperature of the reaction vessel to 80°C and thoroughly purging with nitrogen, 20 parts of a 10% aqueous solution of ammonium persulfate were added, and after 5 minutes, the mixture of ethylenically unsaturated monomers charged into the dropping funnel was added dropwise over 2 hours to carry out the reaction. After the dropwise addition was complete, the reaction was continued for another 3 hours at 80°C. After the reaction was complete, an aqueous dispersion of resin particles was obtained. The Tg of the resin (B) portion of the obtained resin particles was -24°C, and the average particle size was 80 nm. 2-ethylhexyl alcohol and water were added to the obtained resin particle aqueous dispersion to adjust the non-volatile content to 40.0% and obtain the desired coating agent. The amount of 2-ethylhexyl alcohol added was adjusted to 2000 ppm based on the amount of resin particles in the coating agent.

[0081] [Examples 2-29, Comparative Examples 1-6] Aqueous dispersions of resin particles were prepared using the same method as in Example 1, with the formulations shown in Tables 2-4. The Tg and average particle size were measured in the same manner as in Example 1. An aliphatic monoalcohol with 6 to 12 carbon atoms and water were added to the resin particle aqueous dispersion to adjust the non-volatile content to 40.0% and obtain the desired coating agent. The amount of aliphatic monoalcohol with 6 to 12 carbon atoms added was determined based on the resin particles in the coating agent to achieve the content shown in Tables 2-4.

[0082] Evaluation items and evaluation methods The evaluation items and methods for the coating agent and sheet are as follows:

[0083] <Creating the sheet> (Sheet) The obtained coating agent was applied to one side of a commercially available cardboard sheet (weighing 300g) using a bar coater #18. After coating, a sheet was obtained by drying in a hot air oven at 80°C for 60 seconds.

[0084] <Oil resistance> To evaluate the oil resistance of the obtained sheets, a few drops of salad oil heated to 80°C were dropped onto the coated surface, and the state of staining on the surface and the state of oil seepage to the back were observed. [Evaluation Criteria] S: No stains after 30 minutes (extremely good) A: After 30 minutes, a stain is visible, but there is no bleed-through (good condition). B: After 10 minutes, no leakage was observed, but after 30 minutes, leakage occurred (usable). C: A gap was created in less than 10 minutes (unusable).

[0085] <Water resistance> The coated surface of the obtained sheet was subjected to a water resistance test based on JIS P8140 (Water absorption test method: Cobb method). For a more rigorous evaluation, the test was performed using water heated to 80°C for a test period of 30 minutes. [Evaluation Criteria] S: Water absorption rate after 30 minutes is 10g / m 2 Less than (Excellent) A: The water absorption rate after 30 minutes is 10g / m 2 More than 20g / m 2 Less than (good) B: Water absorption rate after 30 minutes is 20g / m 2 More than 30g / m 2 Less than (usable) C: Water absorption after 30 minutes is 30g / m² 2 or more (unusable)

[0086] <Low extractability> To eliminate the influence of the substrate, a coating agent was applied to one side of aluminum foil using a bar coater #18, and dried at 80°C for 60 seconds to create a coated aluminum foil sheet. The prepared coated aluminum foil sheet was cut to a size of 6 cm wide and 16 cm long, placed in a cleaned glass container, immersed in 96 mL of deionized water, sealed, and retorted in a retort kettle at 95°C for 30 minutes. The water after retorting was analyzed to quantify the total organic carbon (TOC) content. TOC is the total amount of organic matter present in water, expressed as the amount of carbon in the organic matter. The measurement conditions for TOC analysis are as follows. (Measurement conditions) Measuring device: Total organic carbon meter TOC-L CPH (manufactured by Shimadzu Corporation) [Evaluation Criteria] S: Less than 10 ppm (Excellent) A: 10 ppm to less than 15 ppm (good) B: 15 ppm or more but less than 20 ppm (usable) C: 20ppm or more (unusable)

[0087] As can be seen from Tables 2 to 4, the coatings obtained in Examples 1 to 30 exhibited excellent oil resistance, water resistance, and low extractability of the sheets, demonstrating performance that fully met practical requirements. On the other hand, the coatings in Comparative Examples 1 to 7 had extremely poor physical properties in oil resistance, water resistance, or low extractability, and the results were not satisfactory for practical use.

[0088] [Table 2]

[0089] [Table 3]

[0090] [Table 4]

Claims

1. Resin particles comprising resin (A), which is a polymer of ethylenically unsaturated monomer (a), and resin (B), which is a polymer of ethylenically unsaturated monomer (b) (excluding resin (A)); and an aliphatic monoalcohol having 6 to 12 carbon atoms. The ethylenically unsaturated monomer (a) comprises an aromatic ethylenically unsaturated monomer (a-1) and a carboxyl group-containing ethylenically unsaturated monomer (a-2). The ethylenically unsaturated monomer (b) comprises an aromatic ethylenically unsaturated monomer (b-1) and an alkyl group-containing ethylenically unsaturated monomer (b-2) having 6 to 12 carbon atoms in the alkyl group. A coating agent comprising, based on the aforementioned resin particles, 100 ppm to 20,000 ppm of an aliphatic monoalcohol having 6 to 12 carbon atoms.

2. The coating agent according to claim 1, wherein, based on the ethylenically unsaturated monomer (a), it contains 51% by mass or more and 90% by mass or less of the aromatic ethylenically unsaturated monomer (a-1), and 10% by mass or more and 40% by mass or less of the carboxyl group-containing ethylenically unsaturated monomer (a-2).

3. The coating agent according to claim 1, wherein, based on the ethylenically unsaturated monomer (b), it contains 10% by mass or more and 50% by mass or less of the aromatic ethylenically unsaturated monomer (b-1), and 51% by mass or more and 90% by mass or less of an alkyl group-containing ethylenically unsaturated monomer (b-2) having 6 to 12 carbon atoms in the alkyl group.

4. The coating agent according to claim 1, comprising 60 to 400 parts by mass of resin (B) per 100 parts by mass of resin (A).

5. The coating agent according to claim 1, wherein the resin particles are core-shell type resin particles, the shell resin is made of resin (A), and the core resin is made of resin (B).

6. A coating agent according to claim 1, for use in food packaging.

7. A sheet having a coating layer of the coating agent according to any one of claims 1 to 6 on at least one side of a substrate.

8. A molded body obtained by molding the sheet described in claim 7.

9. The molded body according to claim 8, wherein the coating layer of the coating agent is molded so that it faces the contents side, and the contents are food.

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