Paper coating agent

Abstract

To provide a paper coating agent that forms a coating layer with excellent oil resistance even after folding, and coated paper using the paper coating agent. [Solution] A paper coating agent and coated paper using the paper coating agent, comprising an amorphous polyester resin, a hydrophobic compound A consisting of one or more selected from wax and silicone, polyvinyl alcohol, and an aqueous medium.

Description

[Technical Field]

[0001] This invention relates to a paper coating agent and coated paper using the paper coating agent. [Background technology]

[0002] Traditionally, paper materials used for paper labels, packaging paper, and paper containers requiring water resistance have been paper laminated with plastic films such as polyethylene or polypropylene to provide water and oil resistance. However, paper laminated with plastic films is difficult to recycle, and with the growing environmental awareness in recent years, paper coating agents containing resin components have been investigated as an alternative technology to lamination to provide water and oil resistance. Furthermore, while fluorine-based paper coatings are known as an alternative to laminating plastic films onto paper materials to impart water-repellent and oil-resistant properties, non-fluorine-based paper coatings are in demand from the perspectives of safety and environmental considerations.

[0003] For example, Patent Document 1 describes a non-fluorine-based oil-resistant paper for food use that has good printability, less food sticking, and excellent oil resistance on both sides, comprising a pulp-based substrate with oil-resistant layers on both sides, and a pattern printed on one side of the oil-resistant layer, characterized in that the oil-resistant layer contains a water-soluble resin and a water-insoluble resin, and the oil-resistant layer on the side opposite to the side with the pattern printing contains a water-repellent agent. Patent Document 2 describes an oil-resistant paper that satisfies oil resistance and is free from coating defects, characterized in that an oil-resistant layer is formed on at least one side of the base paper, the oil-resistant layer mainly consists of a polyvinyl alcohol-based resin and a styrene-acrylic copolymer resin, and the content of the polyvinyl alcohol-based resin is 15 to 50 parts by mass per 100 parts by mass of the styrene-acrylic copolymer resin. [Prior art documents] [Patent Documents]

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] Among the applications where a paper material having water repellency and oil resistance is used, in the case of wrapping paper and containers, it is necessary to fold the paper in order to process it into a container such as a paper bag. However, in the oil-resistant paper described in Patent Documents 1 and 2, there is a problem that the resistance to physical forces such as folding of the resin layer derived from the paper coating agent formed on the paper surface is not sufficient. Since the resistance of the resin layer to physical forces is not sufficient, the oil resistance imparted by the treatment with the paper coating agent is impaired. Therefore, a paper coating agent that forms a resin layer strong against physical forces such as folding is desired. The present invention relates to a paper coating agent that forms a coating layer having excellent oil resistance even in the coated paper after folding, and a coated paper using the paper coating agent.

Means for Solving the Problems

[0006] The present inventors focused on providing a coating layer that suppresses the contact between the paper substrate and water and oil, and found that the above problems can be solved by a paper coating agent containing an amorphous polyester resin, a hydrophobic compound A composed of one or more selected from wax and silicone, polyvinyl alcohol, and an aqueous medium. The present invention relates to the following [1] to [4]. 〔1〕A paper coating agent containing an amorphous polyester resin, a hydrophobic compound A composed of one or more selected from wax and silicone, polyvinyl alcohol, and an aqueous medium. 〔2〕A coated paper having a coating layer formed by the paper coating agent according to [1]. [3] Coated paper having a coating layer formed by the paper coating agent described in [1]. A method for producing coated paper, comprising: step I, applying the paper coating agent described in [1] to at least one side of a paper substrate to form a coating liquid layer; and step II, drying the coating layer on the paper substrate coated in step I. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a paper coating agent that forms a coating layer having excellent oil resistance even after the coated paper has been folded, and coated paper using the paper coating agent. [Modes for carrying out the invention]

[0008] [Paper coating agent] The paper coating agent of the present invention contains an amorphous polyester resin, a hydrophobic compound A consisting of one or more selected from waxes and silicones, polyvinyl alcohol, and an aqueous medium. Here, "aqueous medium" refers to a medium in which water makes up the largest proportion. Deionized water or distilled water is preferably used as the water in the aqueous medium. The aqueous medium may further contain an organic solvent. Examples of such organic solvents include aliphatic alcohols having 1 to 4 carbon atoms, such as methanol, ethanol, and 2-propanol; ketones having 3 to 5 carbon atoms, such as acetone and methyl ethyl ketone; and water-soluble organic solvents such as ethers, such as diethyl ether and tetrahydrofuran. From an environmental standpoint, the water content in the aqueous medium is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and preferably 100% by mass or less.

[0009] The definitions of various terms used in this specification are shown below. The crystallinity of a resin is expressed by the crystallinity index, which is defined as the ratio of the softening point to the maximum endothermic peak temperature measured by differential scanning calorimeter (DSC), i.e., "softening point (°C) / maximum endothermic peak temperature (°C)". "Crystalline resin" refers to a resin whose crystallinity index is between 0.6 and 1.4. "Amorphous resin" refers to a resin in which no endothermic peak is observed by differential scanning calorimeter (DSC), or, if an endothermic peak is observed, the crystallinity index is less than 0.6 or greater than 1.4. The maximum endothermic peak temperature refers to the temperature of the peak with the largest peak area among the endothermic peaks observed under the conditions of the measurement method described in the examples. The crystallinity of the resin can be adjusted by the type and ratio of raw material monomers, and the manufacturing conditions (e.g., reaction temperature, reaction time, cooling rate). The term "carboxylic acid component" includes not only carboxylic acids but also their anhydrides and alkyl esters having 1 to 3 carbon atoms. In other words, in this specification, when only the name of a carboxylic acid is mentioned, it is assumed that the anhydrides and alkyl esters having 1 to 3 carbon atoms of that carboxylic acid are also included.

[0010] According to the paper coating agent of the present invention, oil resistance can be imparted to paper by coating, and coated paper can be obtained that is strong against bending and has excellent oil resistance even at the bent parts. The detailed reason for this is not clear, but it is thought to be as follows. The amorphous polyester resin contained in the paper coating agent is highly polar due to the presence of numerous highly polar ester bonds, resulting in low affinity for oil and high affinity for cellulose, the main component of paper substrates. Therefore, it can adhere to the paper substrate and impart oil resistance to it. Furthermore, if the paper coating agent contains hydrophobic components that are even less polar than oils, such as wax or silicone, when the paper coating agent is applied to the paper substrate, the hydrophobic components can be fixed to the surface of the paper substrate via the amorphous polyester, and it is believed that a coating layer with superior water repellency and oil resistance can be formed on the surface of the paper substrate. However, the inventors of this invention have discovered that when a coating layer with excellent water-repellent and oil-resistant properties is formed on the surface of a paper substrate, and a large physical force such as bending is applied when the coated paper is processed, the coating layer may partially detach from the paper surface or break down, resulting in a decrease in the oil resistance of the coated paper. The paper coating agent of the present invention further contains polyvinyl alcohol in addition to an amorphous polyester resin and hydrophobic compound A, and it is believed that the polyvinyl alcohol dissolved in the aqueous medium adheres to the particles containing the amorphous polyester resin by hydrogen bonding or the like. Therefore, when the paper coating agent is applied to a paper substrate, it is believed that the polyvinyl alcohol is not absorbed by the paper substrate, and a coating layer containing the amorphous polyester resin, hydrophobic compound A, and polyvinyl alcohol is formed on the surface of the paper substrate. In this coating layer, the hydroxyl groups of polyvinyl alcohol, which are more polar than the amorphous polyester resin, adhere to the paper substrate, and it is believed that the amorphous polyester resin and hydrophobic compound A are present in this order on the main chain side of the polyvinyl alcohol. Even if large physical forces such as bending are applied when processing coated paper, polyvinyl alcohol is more flexible than amorphous polyester resin, so the polyvinyl alcohol layer in the coating is less likely to break than the amorphous polyester resin layer. Therefore, even if the amorphous polyester resin in the coating is broken by large physical forces, the amorphous polyester resin suppresses detachment and chipping from the coating through interaction with polyvinyl alcohol, so it is thought that the coated paper can still have excellent oil resistance even when large physical forces such as bending are applied.

[0011] [Amorphous polyester resin] Amorphous polyester resins contain a polycondensate of an alcohol component containing a divalent or higher alcohol and a carboxylic acid component containing a divalent or higher carboxylic acid, from the viewpoint of obtaining a coating layer that has excellent oil resistance even in coated paper after bending. There are no particular limitations as long as the resin contains a polycondensate of an alcohol component containing a divalent or higher alcohol and a carboxylic acid component containing a divalent or higher carboxylic acid, and examples include polyester resins made from polycondensates and modified polyester resins. Examples of modified polyester resins include composite resins containing polyester resin segments and addition polymerization resin segments, urethane-modified polyester resins, and epoxy-modified polyester resins. Among these, amorphous polyester resins are preferably amorphous polyester resins that are polycondensates of an alcohol component containing a divalent or higher alcohol and a carboxylic acid component containing a divalent or higher carboxylic acid.

[0012] (Alcohol content) The alcohol component includes alcohols with a hydride of 2 or more. The alcohol component can be used individually or in combination of two or more. Examples of alcohols with a hydride of 2 or more include diols and polyhydric alcohols with a hydride of 3 or more. Examples of diols include aliphatic diols, aromatic diols, and alicyclic diols.

[0013] The aliphatic diol has two or more carbon atoms, preferably 16 or fewer, more preferably 14 or fewer, and even more preferably 10 or fewer. Examples of aliphatic diols include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 2,3-butanediol, 1,4-butanediol, 1,2-pentanediol, 1,4-pentanediol, 1,5-pentanediol, 2,4-pentanediol, 1,2-hexanediol, 1,5-hexanediol, 2,5- Examples of aliphatic diols include hexanediol, 1,6-hexanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,12-dodecanediol, 1,14-tetradecanediol, 1,16-hexadecanediol, 3,3-dimethyl-1,2-butanediol, 2,2-dimethyl-1,3-propanediol, and 3-methyl-1,5-pentanediol.

[0014] Examples of aromatic diols include alkylene oxide adducts of bisphenol A. The alkylene oxide adduct of bisphenol A is preferably a compound represented by the following general formula (I).

[0015] [ka]

[0016] In general formula (I), OR 1 , and R 2 Each of the O groups is an alkylene oxy group, preferably an alkylene oxy group having 1 to 4 carbon atoms independently, more preferably an ethylene oxy group or a propylene oxy group, and even more preferably a propylene oxy group. x and y correspond to the number of moles of alkylene oxide added. The average value of the sum of x and y is preferably 2 or more, preferably 7 or less, more preferably 5 or less, and even more preferably 3 or less. x pieces OR 1 and y R 2 O may be the same or different in each case, but from the standpoint of availability, it is preferable that they be the same.

[0017] The alkylene oxide adduct of bisphenol A may be used individually or in combination of two or more types. The alkylene oxide adduct of bisphenol A is preferably one or more selected from propylene oxide adducts of bisphenol A and ethylene oxide adducts of bisphenol A, and more preferably propylene oxide adducts of bisphenol A.

[0018] Examples of alicyclic diols include cyclohexanediol, cyclohexanedimethanol, and hydrogenated bisphenol A. Examples of polyhydric alcohols with a valency of 3 or higher include glycerin, pentaerythritol, trimethylolpropane, sorbitol, and sorbitan.

[0019] Among these, the alcohol component preferably includes one or more selected from aliphatic diols and aromatic diols, from the viewpoint of obtaining a coating layer that has excellent oil resistance even in the coated paper after folding, more preferably includes one or more selected from aliphatic diols having 2 to 16 carbon atoms and alkylene oxide adducts of bisphenol A, and even more preferably includes one or more selected from 1,2-propanediol and propylene oxide adducts of bisphenol A.

[0020] From the viewpoint of obtaining a coating layer that has excellent oil resistance even after folding the coated paper, the content of diol in the alcohol component is preferably 60 mol% or more, more preferably 80 mol% or more, even more preferably 90 mol% or more, and even more preferably 95 mol% or more, and preferably 100 mol% or less, and more preferably 100 mol%.

[0021] (Carboxylic acid component) Examples of carboxylic acid components include dicarboxylic acids and polycarboxylic acids with a valency of three or more. Examples of dicarboxylic acids include aromatic dicarboxylic acids, aliphatic dicarboxylic acids, and alicyclic dicarboxylic acids.

[0022] Examples of aromatic dicarboxylic acids include phthalic acid, isophthalic acid, and terephthalic acid. Among these, isophthalic acid and terephthalic acid are preferred, and more preferably terephthalic acid, from the viewpoint of obtaining a coating layer that has excellent oil resistance even in coated paper after folding. Examples of aliphatic dicarboxylic acids include straight-chain, branched-chain, or alicyclic aliphatic dicarboxylic acids such as fumaric acid, adipic acid, sebacic acid, maleic acid, azelaic acid, succinic acid, succinic acid substituted with hydrocarbon groups having 1 to 20 carbon atoms, and cyclohexanedicarboxylic acid. Specific examples of succinic acid substituted with hydrocarbon groups having 1 to 20 carbon atoms include dodecyl succinic acid, dodecenyl succinic acid, and octenyl succinic acid. Among these, the aliphatic dicarboxylic acid is preferably one or more selected from succinic acid and sebacic acid, from the viewpoint of obtaining a coating layer with excellent oil resistance even in coated paper after folding. Examples of polycarboxylic acids with a valency of three or higher include trimellitic acid, 2,5,7-naphthalentricarboxylic acid, pyromellitic acid, and aconitic acid. Among these, trimellitic acid is preferred from the viewpoint of obtaining a coating layer that has excellent oil resistance even in coated paper after folding. Among these, the carboxylic acid component preferably includes an aromatic dicarboxylic acid, more preferably an aromatic dicarboxylic acid, and one or more selected from aliphatic dicarboxylic acids and polycarboxylic acids of trivalent or higher, and even more preferably one or more selected from terephthalic acid, succinic acid, and sebacic acid, and trimellitic acid.

[0023] From the viewpoint of obtaining a coating layer that has excellent oil resistance even after folding the coated paper, the content of aromatic dicarboxylic acid in the carboxylic acid component is preferably 50 mol% or more, more preferably 55 mol% or more, even more preferably 60 mol% or more, and preferably 88 mol% or less, more preferably 85 mol% or less, and even more preferably 83 mol% or less. From the viewpoint of obtaining a coating layer that has excellent oil resistance even after folding the coated paper, the content of aliphatic dicarboxylic acid in the carboxylic acid component is preferably 5 mol% or more, more preferably 6 mol% or more, even more preferably 7 mol% or more, and preferably 30 mol% or less, more preferably 25 mol% or less, and even more preferably 22 mol% or less. When the carboxylic acid component contains a polycarboxylic acid of trivalent or higher, the content of the polycarboxylic acid of trivalent or higher in the carboxylic acid component is preferably 5 mol% or more, more preferably 7 mol% or more, even more preferably 9 mol% or more, and preferably 20 mol% or less, more preferably 18 mol% or less, and even more preferably 16 mol% or less, from the viewpoint of obtaining a coating layer that has excellent oil resistance even in the coated paper after folding.

[0024] (Method for producing amorphous polyester resin) Amorphous polyester resins are preferably produced, for example, by a method of polycondensation of an alcohol component and a carboxylic acid component.

[0025] Polycondensation of an alcohol component and a carboxylic acid component can be produced, for example, by polycondensing the alcohol component and the carboxylic acid component in an inert gas atmosphere, using the esterification catalyst and esterification co-catalyst described below as necessary, at a temperature of 160°C to 250°C.

[0026] Examples of esterification catalysts include tin compounds such as dibutyltin oxide and tin(II) di(2-ethylhexanoate), and titanium compounds such as titanium diisopropoxybis(triethanolamine). Examples of esterification co-catalysts that can be used together with the esterification catalyst include gallic acid. The amount of esterification catalyst used is preferably 0.01 parts by mass or more and 10 parts by mass or less, based on 100 parts by mass of the total amount of alcohol and carboxylic acid components, which are raw material monomers for the amorphous polyester resin. The amount of esterification co-catalyst used is preferably 0.001 parts by mass or more and 1 part by mass or less, based on 100 parts by mass of the total amount of alcohol and carboxylic acid components, which are raw material monomers of the amorphous polyester resin. Furthermore, when using a carboxylic acid containing multiple bonds, such as fumaric acid, as the carboxylic acid component, a polymerization inhibitor may be used. Examples of polymerization inhibitors include radical polymerization inhibitors such as 4-tert-butylcatechol. When a polymerization inhibitor is used, the amount of polymerization inhibitor used is preferably 0.001 parts by mass or more and 1 part by mass or less, based on 100 parts by mass of the total amount of alcohol and carboxylic acid components which are raw material monomers of the amorphous polyester resin.

[0027] (Physical properties of amorphous polyester resins) From the viewpoint of obtaining a coating layer that has excellent oil resistance even in the coated paper after bending, the softening point of the amorphous polyester resin is preferably 80°C or higher, more preferably 90°C or higher, even more preferably 100°C or higher, and preferably 140°C or lower, more preferably 135°C or lower, and even more preferably 130°C or lower. The aforementioned softening point is measured by the method described in the examples.

[0028] The glass transition temperature of amorphous polyester resin is preferably 45°C or higher, more preferably 47°C or higher, even more preferably 49°C or higher, and preferably 75°C or lower, more preferably 72°C or lower, and even more preferably 70°C or lower, from the viewpoint of obtaining a coating layer that has excellent oil resistance even in coated paper after bending. The glass transition temperature is measured by the method described in the examples.

[0029] From the viewpoint of improving the dispersion stability of resin particles containing amorphous polyester resin in the paper coating agent, the acid value of the amorphous polyester resin is preferably 5 mg KOH / g or more, more preferably 10 mg KOH / g or more, even more preferably 15 mg KOH / g or more, and preferably 45 mg KOH / g or less, more preferably 40 mg KOH / g or less, and even more preferably 35 mg KOH / g or less. The acid value is measured by the method described in the examples.

[0030] Amorphous polyester resins may be used individually or in combination of two or more types. The softening point, glass transition temperature, and acid value of amorphous polyester resins can be appropriately adjusted depending on the type and amount of raw material monomers used, as well as manufacturing conditions such as reaction temperature, reaction time, and cooling rate. These values ​​can be determined by the method described in the examples. Furthermore, when using two or more amorphous polyester resins in combination, it is preferable that the softening point, glass transition temperature, and acid value obtained from the mixture are all within the aforementioned ranges.

[0031] In the present invention, the amorphous polyester resin is preferably substantially water-insoluble from the viewpoint of obtaining a coating layer that has excellent oil resistance even in coated paper after bending. When the amorphous polyester resin is water-insoluble, the coating layer formed by applying the paper coating agent to the paper substrate becomes water-insoluble, which can improve water repellency and oil resistance. Here, "substantially water-insoluble" means that when an amorphous polyester resin, which has been vacuum-dried at 40°C for 12 hours and reached a constant weight, is dissolved in 100g of water at 25°C until saturated, the amount dissolved is 1g or less. If the amorphous polyester resin contains acidic groups, the amount dissolved is the amount dissolved when the acidic groups of the amorphous polyester resin are neutralized by 100 mol% with sodium hydroxide.

[0032] In the present invention, when the amorphous polyester resin contains acidic groups, it is preferable that the amorphous polyester resin is a neutralized product of a basic compound, from the viewpoint of improving the dispersion stability of resin particles containing the amorphous polyester resin in the paper coating agent. Basic compounds include metallic basic compounds and non-metallic basic compounds. Examples of metal-based compounds include alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, and potassium hydroxide. Examples of nonmetallic basic compounds include ammonia and organic amine compounds. Basic compounds can be used individually or in combination of two or more.

[0033] The equivalent amount of basic compound used is preferably 50 mol% or more, more preferably 55 mol% or more, even more preferably 60 mol% or more, and preferably 100 mol% or less, more preferably 90 mol% or less, and even more preferably 80 mol% or less. The equivalent amount of basic compound used can be determined by the following formula (1). If the equivalent amount of basic compound used is 100 mol% or less, it is equivalent to the degree of neutralization. If the equivalent amount of basic compound used exceeds 100 mol% in the following formula, it means that the basic compound is in excess of the acid groups of the amorphous polyester resin, and in this case, the degree of neutralization of the amorphous polyester resin is considered to be 100 mol%. Equivalent amount of basic compound used (mol%) = {[Mass of basic compound added (g) / Equivalent amount of basic compound (g / mol)] / [[Acid value of amorphous polyester resin (mgKOH / g) × Mass of amorphous polyester resin (g)] / (56.1 × 1,000 (mgKOH / mol))]} × 100 (1)

[0034] From the viewpoint of obtaining a coating layer that has excellent oil resistance even after the coated paper has been folded, the content of amorphous polyester resin in the paper coating agent is preferably 5% by mass or more, more preferably 6% by mass or more, even more preferably 8% by mass or more, and preferably 20% by mass or less, more preferably 18% by mass or less, and even more preferably 16% by mass or less.

[0035] [Hydrophobic compound A] Hydrophobic compound A consists of one or more selected from waxes and silicones.

[0036] (wax) Examples of waxes include petroleum-based waxes, synthetic waxes, fatty acid amides, plant-based waxes, and animal-based waxes.

[0037] Examples of petroleum-based waxes include Montan wax, paraffin wax, and Fischer-Tropsch wax. Examples of synthetic waxes include olefin waxes such as synthetic ester wax, polyethylene wax, polypropylene wax, polybutene wax, and polyethyleneimide wax. Examples of fatty acid amides include oleic acid amide and stearic acid amide. Examples of plant-based waxes include carnauba wax, rice wax, and candelilla wax. An example of an animal-derived wax is beeswax.

[0038] Among these, one or more selected from petroleum-based waxes, synthetic waxes, and plant-based waxes are preferred, one or more selected from paraffin wax, olefin wax, synthetic ester wax, and carnauba wax are more preferred, and one or more selected from paraffin wax, synthetic ester wax, and polyethylene wax are even more preferred.

[0039] From the viewpoint of the manufacturability of the paper coating agent, the melting point of the wax is preferably less than 100°C, more preferably 95°C or lower, even more preferably 90°C or lower, and preferably 60°C or higher, more preferably 65°C or higher, and even more preferably 70°C or higher.

[0040] (silicone) Examples of silicones include general dimethyl silicone, methylphenyl silicone obtained by replacing at least one methyl group in dimethyl silicone with a phenyl group, and modified silicones with introduced reactive functional groups. From the viewpoint of obtaining a coating layer that has excellent oil resistance even in coated paper after bending, modified silicones are preferred.

[0041] The modified silicone is preferably a modified silicone having one or more groups selected from amino groups, epoxy groups, ester groups, hydroxyl groups, and carboxyl groups in its side chains, one end, or both ends. More preferably, it is a modified silicone having one or more groups selected from amino groups, epoxy groups, ester groups, and hydroxyl groups in its side chains, even more preferably, it is a modified silicone having one or more groups selected from amino groups, hydroxyl groups, and carboxyl groups in its side chains, and even more preferably, it is a modified silicone having an amino group in its side chains.

[0042] The modified silicone includes at least one selected from a modified silicone having repeating units represented by formula (1) and formula (2), a modified silicone having repeating units represented by formula (1) and the structure represented by formula (3), and a modified silicone having repeating units represented by formula (1) and formula (4). The modified silicone is a modified silicone having repeating units represented by formula (1) and formula (2), wherein X in formula (2) is preferably a group containing an amino group.

[0043] [ka] [In formula (1), R is independently a hydrocarbon group having 1 to 6 carbon atoms, and * is a bonding site.]

[0044] [ka] [In formula (2), R is independently a hydrocarbon group having 1 to 6 carbon atoms, R' is independently an alkylene group having 1 to 10 carbon atoms, a is 1 or 0, X is independently a group containing an amino group, an epoxy group, an ester group, a hydroxyl group, or a carboxyl group, and * is a bonding site.]

[0045] *-SiR 3-b (R''-X) b (3) [In formula (3), R is independently a hydrocarbon group having 1 to 6 carbon atoms, R'' is independently an alkylene group having 1 to 10 carbon atoms, b is an integer between 1 and 3, X is independently a group containing an amino group, an epoxy group, an ester group, a hydroxyl group, or a carboxyl group, and * is a bonding site to the repeating unit represented by formula (1) and / or formula (2).]

[0046] *-(R'''-O) c -* (4) [In formula (4), each R''' is independently an alkylene group having 2 to 4 carbon atoms, c is an integer between 30 and 60, and * is a bonding site to the repeating unit represented by formula (1) and / or formula (2).]

[0047] The repeating units represented by equation (1), equation (2), and equation (4) may be random or block-based, and are not particularly limited.

[0048] In formulas (1) to (3), the number of carbon atoms in the hydrocarbon group R is 6 or less, preferably 4 or less, more preferably 3 or less, even more preferably 2 or less, and even more preferably 1. Examples of hydrocarbon groups for R include methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, pentyl, and phenyl groups. Among these, the methyl group is preferred.

[0049] In formulas (2) and (3), the number of carbon atoms in the alkylene groups R' and R'' is 10 or less, preferably 8 or less, more preferably 5 or less, even more preferably 4 or less, even more preferably 3 or less, and preferably 1 or more. Examples of alkylene groups for R' and R'' include methanediyl group, ethane-1,2-diyl group, ethane-1,1-diyl group, propane-1,3-diyl group, and propane-1,2-diyl group. Among these, the methanediyl group is preferred.

[0050] In formula (4), examples of the alkylene group R''' include ethane-1,2-diyl group, propane-1,3-diyl group, propane-1,2-diyl group, butane-1,4-diyl group, butane-1,3-diyl group, butane-1,2-diyl group, and butane-2,3-diyl group. Among these, ethane-1,2-diyl group, propane-1,3-diyl group, and propane-1,2-diyl group are preferred.

[0051] Each of X is independently a group containing an amino group, an epoxy group, an ester group, a hydroxyl group, or a carboxyl group. When a is 0, X may have an ether bond. That is, X may be an aliphatic hydrocarbon group which may contain an ether bond and is substituted with one or more amino groups, epoxy groups, ester groups, hydroxyl groups, or carboxyl groups, and the total number of carbon atoms of X is preferably 10 or less, more preferably 9 or less, and preferably 1 or more, more preferably 2 or more. Furthermore, an aliphatic hydrocarbon group containing an ether bond refers to a group that has an ether bond (-O-) between carbon-carbon bonds.

[0052] When the modified silicone is a silicone having an amino group in the side chain, X is a group containing an amino group. In this case, in the above formula (2), a is 1 or 0, X is, independently of each other, -NH2 or -R''''-NH-R''''-NH2, and R'''' is preferably an alkylene group having 1 to 10 carbon atoms, more preferably when a is 1, X is -NH2, and when a is 0, X is -R''''-NH-R''''-NH2, still more preferably a is 1, X is -NH2, and R'''' is an alkylene group having 1 to 10 carbon atoms.

[0053] The modified silicone contains 500 or less, preferably 450 or less, more preferably 400 or less of the repeating units represented by the formula (1), and preferably contains 10 or more, preferably 30 or more, more preferably 50 or more. Also, the repeating unit represented by the formula (2) is preferably 40 or less, more preferably 20 or less, still more preferably 10 or less, and preferably contains 1 or more.

[0054] When the modified silicone has one or more functional groups selected from an amino group, an epoxy group, an ester group, a hydroxy group, or a carboxy group, the functional group equivalent of the modified silicone is preferably 300 g / mol or more, more preferably 500 g / mol or more, still more preferably 1,000 g / mol or more, still more preferably 2,000 g / mol or more, and preferably 10,000 g / mol or less, more preferably 8,000 g / mol or less, still more preferably 6,000 g / mol or less. The functional group equivalent means the mass of the modified silicone per mole of the functional group.

[0055] When the modified silicone is liquid at 25°C, the kinematic viscosity of the modified silicone is preferably 100 mm 2 / s or more, more preferably 200 mm 2 / s or more, still more preferably 500 mm 2It is 10,000 mm or more 2 / s or less, more preferably 5,000 mm 2 / s or less, more preferably 2,000 mm 2 It is less than or equal to / s. The kinematic viscosity of modified silicone can be determined using catalog values, or it can be measured using, for example, a fully automated micro-kinematic viscometer (manufactured by Viscotec Co., Ltd.).

[0056] Examples of the modified silicones mentioned above include: modified silicones having amino groups in the side chain (commercial products include, for example, "KF-864", "KF-865" (manufactured by Shin-Etsu Chemical Co., Ltd.), "WT-1650", "WT-1270" (manufactured by Asahi Kasei Wacker Silicone Co., Ltd.)); modified silicones having amino groups at both ends (commercial products include, for example, "KF-8008" (manufactured by Shin-Etsu Chemical Co., Ltd.), "DOWSIL BY16-871" (manufactured by Dow Toray Industries, Inc.)); modified silicones having an amino group at one end; and modified silicones having carboxyl groups in the side chain (commercial products include, for example, "X-22-3701E" (manufactured by Shin-Etsu Chemical Co., Ltd.), "DOWSIL BY16-880 (manufactured by Dow Toray Industries, Inc.), modified silicones having epoxy groups in their side chains (commercially available examples include "KF-101", "KF-1001", "X-22-343" (manufactured by Shin-Etsu Chemical Co., Ltd.), "DOWSIL SF8413 (manufactured by Dow Toray Industries, Inc.), modified silicones having epoxy groups at both ends (commercial products include, for example, "KF-105", "X-22-163A", "X-22-163B", "X-22-163C", "X-22-169AS", "X-22-169B" (manufactured by Shin-Etsu Chemical Co., Ltd.)), modified silicones having epoxy groups at one end (commercial products include, for example, "X-22-173BX", "X-22-173DX" (both manufactured by Shin-Etsu Chemical Co., Ltd.)), modified silicones having ester groups in the side chain (commercial products include, for example, "X-22-715" (manufactured by Shin-Etsu Chemical Co., Ltd.), etc.) Modified silicones having ster groups at both ends, modified silicones having an ester group at one end, modified silicones having hydroxyl groups at both ends (commercially available examples include "KF-6003" (manufactured by Shin-Etsu Chemical Co., Ltd.)), modified silicones having a hydroxyl group at one end (commercially available examples include "X-22-170BX" (manufactured by Shin-Etsu Chemical Co., Ltd.)), modified silicones having carboxyl groups at both ends (commercially available examples include "X-22-162C" (manufactured by Shin-Etsu Chemical Co., Ltd.)), and modified silicones having a carboxyl group at one end (commercially available examples include "X-22-3710" (manufactured by Shin-Etsu Chemical Co., Ltd.)).Modified silicones having hydroxyl groups in their side chains (commercially available examples include "X-22-4015" (manufactured by Shin-Etsu Chemical Co., Ltd.)).

[0057] From the viewpoint of obtaining a coating layer that has excellent oil resistance even after the coated paper has been folded, the content of hydrophobic compound A in the paper coating agent is preferably 2% by mass or more, more preferably 3% by mass or more, even more preferably 4% by mass or more, and preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 12% by mass or less.

[0058] The mass ratio of amorphous polyester resin to hydrophobic compound A in the paper coating agent (amorphous polyester resin / hydrophobic compound A) is preferably 45 / 55 or more, more preferably 47 / 53 or more, even more preferably 50 / 50 or more, and preferably 90 / 10 or less, more preferably 85 / 15 or less, and even more preferably 80 / 20 or less, from the viewpoint of obtaining a coating layer that has excellent oil resistance even in coated paper after folding.

[0059] [Polyvinyl alcohol] The paper coating agent of the present invention contains polyvinyl alcohol. From the viewpoint of obtaining a coating layer with excellent oil resistance even in the coated paper after folding, the degree of polymerization of polyvinyl alcohol is preferably 150 or higher, more preferably 170 or higher, and even more preferably 190 or higher. From the viewpoint of the coating properties of the paper coating agent, it is preferably 2,000 or lower, more preferably 1,500 or lower, and even more preferably 1,200 or lower. From the viewpoint of obtaining a coating layer that has excellent oil resistance even in the coated paper after bending, the degree of saponification of polyvinyl alcohol is preferably 70% or more, more preferably 80% or more, even more preferably 85% or more, and preferably 100% or less.

[0060] The polyvinyl alcohol used in the present invention is preferably unmodified. That is, the polyvinyl alcohol is preferably unmodified.

[0061] From the viewpoint of obtaining a coating layer that has excellent oil resistance even after the coated paper has been folded, the polyvinyl alcohol content in the paper coating agent is preferably 0.4% by mass or more, more preferably 0.7% by mass or more, even more preferably 1.0% by mass or more, and preferably 8% by mass or less, more preferably 7.5% by mass or less, and even more preferably 7% by mass or less.

[0062] The mass ratio of the total amount of amorphous polyester resin and hydrophobic compound A in the paper coating agent to polyvinyl alcohol (total amount of amorphous polyester resin and hydrophobic compound A / polyvinyl alcohol) is preferably 70 / 30 or more, more preferably 72 / 28 or more, even more preferably 74 / 26 or more, and preferably 99 / 1 or less, more preferably 97 / 3 or less, and even more preferably 96 / 4 or less, from the viewpoint of obtaining a coating layer that has excellent oil resistance even in coated paper after folding.

[0063] The paper coating agent may contain hydrophobic compounds other than hydrophobic compound A, as long as it does not impair the effects of the present invention.

[0064] <Resin particles> The paper coating agent may contain amorphous polyester resin and hydrophobic compound A in the same particle, or in separate particles. That is, the paper coating agent may be a paper coating agent containing resin particles containing amorphous polyester resin and hydrophobic compound A, and polyvinyl alcohol, or a paper coating agent containing resin particles containing amorphous polyester resin, particles containing hydrophobic compound A, and polyvinyl alcohol. In the following, when the term "resin particles" is used, it includes resin particles containing amorphous polyester resin and hydrophobic compound A, as well as resin particles containing amorphous polyester resin.

[0065] Furthermore, the resin particles may contain resins other than amorphous polyester resins, such as acrylic resins like styrene-acrylic copolymers or polyurethane resins, to the extent that they do not impair the effects of the present invention. Furthermore, the resin particles may contain reinforcing fillers such as fibrous materials, additives such as antioxidants, etc., as optional components, to the extent that they do not impair the effects of the present invention. The total content of amorphous polyester resin and hydrophobic compound A in resin particles containing amorphous polyester resin and hydrophobic compound A is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, and preferably 100% by mass or less, from the viewpoint of obtaining a coating layer that has excellent oil resistance even in coated paper after folding. Furthermore, the content of amorphous polyester resin in the resin particles containing amorphous polyester resin is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, and preferably 100% by mass or less, from the viewpoint of obtaining a coating layer that has excellent oil resistance even in the coated paper after bending.

[0066] [Manufacturing of paper coating agents] If the paper coating agent of the present invention is a paper coating agent comprising resin particles containing an amorphous polyester resin and hydrophobic compound A, and polyvinyl alcohol, it is preferable that the method for producing the paper coating agent includes a method for obtaining an aqueous dispersion of resin particles containing an amorphous polyester resin and hydrophobic compound A. Furthermore, if the paper coating agent of the present invention is a paper coating agent comprising resin particles containing an amorphous polyester resin, particles containing hydrophobic compound A, and polyvinyl alcohol, it is preferable that the method for producing the paper coating agent includes a method for mixing an aqueous dispersion of the amorphous polyester resin with an aqueous dispersion of hydrophobic compound A.

[0067] Methods for obtaining an aqueous dispersion of resin particles containing amorphous polyester resin and hydrophobic compound A include a method of gradually adding an aqueous medium to a solution containing amorphous polyester resin and hydrophobic compound A to perform phase inversion emulsification, and a method of adding amorphous polyester resin and hydrophobic compound A to an aqueous medium and performing dispersion treatment using a disperser or the like. In the phase inversion emulsification process, it is preferable to first dissolve the polyester resin and hydrophobic compound A in an organic solvent to obtain a solution of the polyester resin and hydrophobic compound A, then add an aqueous medium to the solution to perform phase inversion emulsification, and then remove the organic solvent.

[0068] If the method for producing the paper coating agent of the present invention includes a method for obtaining an aqueous dispersion of resin particles containing an amorphous polyester resin and hydrophobic compound A by phase inversion emulsification, the method for producing the paper coating agent preferably has the following steps 1-1 to 1-5 in this order. Step 1-1: Step of dissolving amorphous polyester resin and hydrophobic compound A in an organic solvent. Step 1-2: A step to neutralize the amorphous polyester resin by adding a basic compound. Steps 1-3: Adding an aqueous medium and performing phase inversion emulsification. Steps 1-4: Steps to remove organic solvents by distillation. Steps 1-5: Adding polyvinyl alcohol

[0069] [Step 1-1] Step 1-1 is a step of dissolving an amorphous polyester resin and hydrophobic compound A in an organic solvent. Organic solvents for dissolving amorphous polyester resin and hydrophobic compound A include ketone solvents such as acetone and dialkylketones having 1 to 3 C1 alkyl groups, such as methyl ethyl ketone; ether solvents such as dibutyl ether and tetrahydrofuran; ester solvents such as ethyl acetate and isopropyl acetate; and alkyl halide solvents such as dichloromethane and chloroform. Among these, from the viewpoint of dissolving amorphous polyester resin and hydrophobic compound A and easily removing them from the emulsion, dialkylketones having 1 to 3 C1 alkyl groups, such as acetone and methyl ethyl ketone, are preferred, and methyl ethyl ketone is more preferred.

[0070] The amorphous polyester resin and hydrophobic compound A may be dissolved in the organic solvent one at a time, or both may be dissolved in the organic solvent simultaneously. If the amorphous polyester resin contains multiple types of amorphous polyester resins, the multiple types of amorphous polyester resins may be mixed beforehand before dissolving in the organic solvent. Similarly, if the hydrophobic compound A contains multiple types of hydrophobic compound A, the multiple types of hydrophobic compound A may be mixed beforehand before dissolving in the organic solvent.

[0071] The mass ratio of amorphous polyester resin to hydrophobic compound A [amorphous polyester resin / hydrophobic compound A] is the same as the mass ratio [amorphous polyester resin / hydrophobic compound A] in the paper coating agent described above.

[0072] The mass ratio of the organic solvent to the total mass of the amorphous polyester resin and hydrophobic compound A [organic solvent / total mass of amorphous polyester resin and hydrophobic compound A] is preferably 50 / 100 or more, more preferably 100 / 100 or more, even more preferably 150 / 100 or more, and preferably 500 / 100 or less, more preferably 400 / 100 or less, and even more preferably 300 / 100 or less, from the viewpoint of dissolving the amorphous polyester resin and hydrophobic compound A and facilitating phase inversion to an aqueous medium.

[0073] [Step 1-2] Steps 1-2 involve adding a basic compound to neutralize the amorphous polyester resin. Specifically, in step 1-1, after obtaining a solution of amorphous polyester resin and hydrophobic compound A, an aqueous solution of a basic compound is added to neutralize it. The addition of the aqueous solution of the basic compound is usually carried out at a temperature below the boiling point of the organic solvent. The preferred types and amounts of basic compounds used are the same as those described above.

[0074] [Step 1-3] Steps 1-3 involve adding an aqueous medium and performing phase inversion emulsification to obtain resin particles containing an amorphous polyester resin and hydrophobic compound A. The preferred aqueous medium and the water content within the aqueous medium are the same as those described above.

[0075] When adding an aqueous medium, the temperature of the solution of amorphous polyester resin and hydrophobic compound A is preferably 10°C or higher, more preferably 20°C or higher, and preferably 40°C or lower, more preferably 30°C or lower, from the viewpoint of improving the dispersion stability of the resin particles containing amorphous polyester resin and hydrophobic compound A in the aqueous medium. From the viewpoint of improving the dispersion stability of resin particles containing amorphous polyester resin and hydrophobic compound A in the aqueous medium by phase inversion emulsification, the addition rate of the aqueous medium is preferably 0.5 parts by mass / min or more, more preferably 1 part by mass / min or more, even more preferably 3 parts by mass / min or more, and preferably 20 parts by mass / min or less, more preferably 15 parts by mass / min or less, and even more preferably 10 parts by mass / min or less, based on 100 parts by mass of the total mass of amorphous polyester resin and hydrophobic compound A constituting the resin particles, until the phase inversion is completed. After phase inversion, there are no restrictions on the addition rate of the aqueous medium after resin particles containing amorphous polyester resin and hydrophobic compound A have been obtained by phase inversion emulsification.

[0076] [Step 1-4] Steps 1-4 are steps for removing organic solvents by distillation. In steps 1-3, after performing phase inversion emulsification, it is preferable to remove the organic solvent from the aqueous dispersion of resin particles containing amorphous polyester resin and hydrophobic compound A obtained by phase inversion emulsification, from the viewpoint of obtaining a coating layer that has excellent oil resistance even in the coated paper after folding. The removal of organic solvents is not particularly limited and any method can be used, but it is preferable to carry it out under heating and reduced pressure. The resulting aqueous dispersion of amorphous polyester resin and resin particles containing hydrophobic compound A is preferably filtered through a wire mesh or the like to remove coarse particles and the like.

[0077] [Step 1-5] Steps 1-5 involve adding polyvinyl alcohol to the aqueous dispersion of resin particles containing amorphous polyester resin and hydrophobic compound A, which was prepared in Steps 1-4. The method for adding polyvinyl alcohol is not particularly limited. Polyvinyl alcohol may be added to the aqueous dispersion of resin particles containing amorphous polyester resin and hydrophobic compound A by phase inversion emulsification obtained in steps 1-4, or the aqueous dispersion of resin particles containing amorphous polyester resin and hydrophobic compound A may be added to polyvinyl alcohol. It is preferable to use the polyvinyl alcohol dissolved in water. Furthermore, it is preferable to adjust the concentration of non-volatile components when adding polyvinyl alcohol or after adding it.

[0078] The mass ratio of the total amount of amorphous polyester resin and hydrophobic compound A to polyvinyl alcohol (total amount of amorphous polyester resin and hydrophobic compound A / polyvinyl alcohol) is the same as the mass ratio in the paper coating agent described above (total amount of amorphous polyester resin and hydrophobic compound A / polyvinyl alcohol).

[0079] The median particle size (D) of the resin particles containing amorphous polyester resin and hydrophobic compound A in a paper coating agent containing polyvinyl alcohol. 50 From the viewpoint of obtaining a coating layer that has excellent oil resistance even in the coated paper after folding, the thickness of the coating is preferably 0.08 μm or more, more preferably 0.09 μm or more, even more preferably 0.10 μm or more, and preferably 0.40 μm or less, more preferably 0.35 μm or less, and even more preferably 0.30 μm or less.

[0080] The above manufacturing method is applied to a hydrophobic compound A that is preferably a liquid at room temperature, and more preferably a silicone that is a liquid at room temperature.

[0081] If the method for producing the paper coating agent of the present invention includes a method of adding an amorphous polyester resin and a hydrophobic compound A to an aqueous medium and performing a dispersion treatment using a disperser or the like, the method for producing the paper coating agent preferably has the following steps 2-1 to 2-3 in this order. Step 2-1: Step to obtain an aqueous dispersion of amorphous polyester resin. Step 2-2: Add hydrophobic compound A and perform dispersion treatment. Step 2-3: Adding polyvinyl alcohol

[0082] [Step 2-1] Step 2-1 is a step to obtain an aqueous dispersion of an amorphous polyester resin. Step 2-1 is the same as the steps in [Steps 1-1] to [Steps 1-4] above, except that hydrophobic compound A is not used.

[0083] In step 2-1, the mass ratio of the organic solvent to the amorphous polyester resin [organic solvent / amorphous polyester resin] is preferably 50 / 100 or more, more preferably 100 / 100 or more, even more preferably 150 / 100 or more, and preferably 500 / 100 or less, more preferably 400 / 100 or less, and even more preferably 300 / 100 or less, from the viewpoint of dissolving the amorphous polyester resin and hydrophobic compound A and facilitating phase inversion to an aqueous medium.

[0084] In step 2-1, the equivalent amount of the basic compound used is preferably 45 mol% or more, more preferably 50 mol% or more, even more preferably 55 mol% or more, and preferably 100 mol% or less, relative to the acid value of the amorphous polyester resin.

[0085] The resulting aqueous dispersion of amorphous polyester resin is preferably filtered through a wire mesh or the like to remove coarse particles. Furthermore, if the organic solvent is removed, water is also reduced by azeotropic formation along with the organic solvent; therefore, it is preferable to add water to adjust the solid content concentration.

[0086] From the viewpoint of improving the efficiency of the dispersion process in step 2-2, the solid content concentration of the aqueous dispersion of amorphous polyester resin is preferably 10% by mass or more, more preferably 15% by mass or more, even more preferably 20% by mass or more, and preferably 50% by mass or less, more preferably 45% by mass or less, and even more preferably 40% by mass or less. The solid content concentration of the aqueous dispersion is measured by the method described in the examples.

[0087] The median particle size (D) of resin particles containing amorphous polyester resin in an aqueous dispersion of amorphous polyester resin. 50 The volume median particle size (D) is preferably 0.08 μm or larger, more preferably 0.30 μm or smaller, more preferably 0.20 μm or smaller, and even more preferably 0.15 μm or smaller, from the viewpoint of improving the dispersibility of hydrophobic compound A in step 2-2. 50 ) is measured by the method described in the examples.

[0088] [Step 2-2] Step 2-2 is a step in which hydrophobic compound A is added to the aqueous dispersion of amorphous polyester resin obtained in step 2-1 and subjected to a dispersion treatment to obtain an aqueous dispersion of resin particles containing amorphous polyester resin and hydrophobic compound A.

[0089] The dispersion treatment is preferably carried out by adding hydrophobic compound A to an aqueous dispersion of amorphous polyester resin, then heating it to a temperature above the melting point of hydrophobic compound A to obtain a mixture of molten hydrophobic compound A and amorphous polyester resin (hereinafter also referred to as the "molten mixture"), and then dispersing the molten mixture in an aqueous medium. The dispersion treatment can be carried out, for example, with a homogenizer, ultrasonic disperser, or high-pressure disperser. The temperature at which the dispersion treatment is performed is not particularly limited as long as it is above the melting point of hydrophobic compound A, but is preferably, for example, 90°C to 100°C.

[0090] The mass ratio of amorphous polyester resin to hydrophobic compound A [amorphous polyester resin / hydrophobic compound A] is the same as the mass ratio [amorphous polyester resin / hydrophobic compound A] in the paper coating agent described above.

[0091] The mass ratio of the aqueous medium to the total amount of amorphous polyester resin and hydrophobic compound A [aqueous medium / total amount of amorphous polyester resin and hydrophobic compound A] is preferably 50 / 50 or more, more preferably 60 / 40 or more, and even more preferably 65 / 35 or more, from the viewpoint of dispersion stability of resin particles containing amorphous polyester resin and hydrophobic compound A, and from the viewpoint of dispersion efficiency, it is preferably 90 / 10 or less, more preferably 85 / 15 or less, and even more preferably 80 / 20 or less.

[0092] [Step 2-3] Step 2-3 is the process of adding polyvinyl alcohol to an aqueous dispersion of resin particles containing the amorphous polyester resin and hydrophobic compound A obtained in Step 2-2, and is the same process as in Step 1-5 above.

[0093] The mass ratio of the total amount of amorphous polyester resin and hydrophobic compound A to polyvinyl alcohol (total amount of amorphous polyester resin and hydrophobic compound A / polyvinyl alcohol) is the same as the mass ratio in the paper coating agent described above (total amount of amorphous polyester resin and hydrophobic compound A / polyvinyl alcohol).

[0094] The median particle size (D) of the resin particles containing amorphous polyester resin and hydrophobic compound A in a paper coating agent containing polyvinyl alcohol. 50 From the viewpoint of obtaining a coating layer that has excellent oil resistance even in the coated paper after folding, the thickness of the coating is preferably 0.08 μm or more, more preferably 0.09 μm or more, even more preferably 0.10 μm or more, and preferably 0.40 μm or less, more preferably 0.35 μm or less, and even more preferably 0.30 μm or less. The aforementioned volume median particle size (D 50) is measured by the method described in the examples.

[0095] The above manufacturing method is applied to a hydrophobic compound A which is preferably a solid at room temperature, and more preferably a wax which is solid at room temperature.

[0096] When the paper coating agent of the present invention is a paper coating agent comprising resin particles containing an amorphous polyester resin, particles containing hydrophobic compound A, and polyvinyl alcohol, the method for producing the paper coating agent preferably comprises the following steps 3-1 to 3-3 in this order. Step 3-1: Step to obtain an aqueous dispersion of amorphous polyester resin and an aqueous dispersion of hydrophobic compound A. Step 3-2: Step of mixing an aqueous dispersion of amorphous polyester resin with an aqueous dispersion of hydrophobic compound A. Step 3-3: Adding polyvinyl alcohol

[0097] [Step 3-1] An aqueous dispersion of amorphous polyester resin can be obtained, for example, by the method described in [Step 2-1] above. The median particle size (D) of the amorphous polyester resin contained in the aqueous dispersion of amorphous polyester resin. 50 ) is the same as the range described in [Step 2-1] above.

[0098] An aqueous dispersion of hydrophobic compound A can be obtained by dispersing the hydrophobic compound A, which has been melted in an aqueous medium, using a disperser such as a homogenizer or ultrasonic disperser in the presence of a dispersant such as a surfactant. Known surfactants can be used as the surfactant when dispersing hydrophobic compound A in an aqueous medium. Examples of surfactants include nonionic surfactants, anionic surfactants, and cationic surfactants, with nonionic and anionic surfactants being preferred, and anionic surfactants being more preferred. Examples of anionic surfactants include sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, and sodium alkyl ether sulfate. Examples of nonionic surfactants include polyoxyethylene alkylaryl ethers, polyoxyethylene alkyl ethers, polyoxyethylene fatty acid esters, and oxyethylene / oxypropylene block copolymers.

[0099] The volume-median particle size (D) of particles containing hydrophobic compound A in an aqueous dispersion of hydrophobic compound A 50 From the viewpoint of obtaining a coating layer that has excellent oil resistance even in coated paper after bending, the thickness of the coating layer is preferably 0.10 μm or more, more preferably 0.14 μm or more, even more preferably 0.17 μm or more, and preferably 0.35 μm or less, more preferably 0.32 μm or less, and even more preferably 0.30 μm or less. Medium volume particle size (D 50 ) is measured by the method described in the examples.

[0100] [Step 3-2] Step 3-2 is a step in which the aqueous dispersion of amorphous polyester resin obtained in step 3-1 is mixed with the aqueous dispersion of hydrophobic compound A to obtain an aqueous dispersion containing amorphous polyester resin and hydrophobic compound A.

[0101] The mixing temperature is preferably 10°C or higher, more preferably 20°C or higher, and preferably 40°C or lower, more preferably 30°C or lower.

[0102] The mass ratio of amorphous polyester resin to hydrophobic compound A [amorphous polyester resin / hydrophobic compound A] is the same as the mass ratio [amorphous polyester resin / hydrophobic compound A] in the paper coating agent described above.

[0103] The mass ratio of the aqueous medium to the total amount of amorphous polyester resin and hydrophobic compound A [aqueous medium / total amount of amorphous polyester resin and hydrophobic compound A] is preferably 50 / 50 or more, more preferably 60 / 40 or more, even more preferably 65 / 35 or more, and from the viewpoint of dispersion efficiency, it is preferably 90 / 10 or less, more preferably 85 / 15 or less, and even more preferably 80 / 20 or less.

[0104] [Step 3-3] Step 3-3 is the process of adding polyvinyl alcohol to a mixture of a dispersion of resin particles containing amorphous polyester resin obtained in Step 3-2 and a dispersion of particles containing hydrophobic compound A, and is the same process as in Step 1-5 above.

[0105] The mass ratio of the total amount of amorphous polyester resin and hydrophobic compound A to polyvinyl alcohol (total amount of amorphous polyester resin and hydrophobic compound A / polyvinyl alcohol) is the same as the mass ratio in the paper coating agent described above (total amount of amorphous polyester resin and hydrophobic compound A / polyvinyl alcohol).

[0106] The above manufacturing method is applied to a hydrophobic compound A which is preferably a solid at room temperature, and more preferably a wax which is solid at room temperature.

[0107] From the viewpoint of obtaining a coating layer that has excellent oil resistance even after folding the coated paper, the concentration of non-volatile components in the paper coating agent of the present invention is preferably 10% by mass or more, more preferably 15% by mass or more, even more preferably 20% by mass or more, and preferably 50% by mass or less, more preferably 45% by mass or less, and even more preferably 40% by mass or less. The concentration of non-volatile components is measured by the method described in the examples.

[0108] The paper coating agent of the present invention can also be used by adding and mixing various additives used in paper coating agents as needed. Examples of such additives include organic solvents, humectants, wetting agents, penetrating agents, viscosity modifiers, defoaming agents, preservatives, fungicides, rust inhibitors, pH adjusters, antioxidants, and UV absorbers. Furthermore, the paper coating agent of the present invention may contain hydrophobic substances other than hydrophobic compound A, to an extent that does not impair the effect of the paper coating agent of the present invention.

[0109] [Coated paper] The coated paper of the present invention has a coating layer formed by the above-mentioned paper coating agent. Examples of paper substrates in coated paper include uncoated papers such as fine paper, medium-quality paper, and newsprint; printing papers such as art paper, coated paper, and matte coated paper; information papers such as PPC paper; packaging papers such as kraft paper; base paper for corrugated cardboard; and cardboard such as paperboard for paper packaging. The basis weight of the paper substrate is not particularly limited, but from the viewpoint of handling the coated paper and ease of applying the coating liquid to the paper substrate, it is preferably 10 g / m². 2 Above, a comfortable 30g / m 2 More preferably 50 g / m 2 The above applies, and preferably 200 g / m². 2 More preferably, 150 g / m² 2 More preferably 120 g / m² 2 The following applies:

[0110] [Manufacturing method for coated paper] From the viewpoint of obtaining a coating layer that has excellent oil resistance even after the coated paper has been folded, the method for manufacturing coated paper of the present invention preferably includes a step I of applying the coating liquid to at least one side of a paper substrate. This makes it possible to obtain coated paper having a coated layer formed by applying the coating liquid to at least one side of a paper substrate. Examples of paper substrates include the aforementioned paper substrates.

[0111] In step I, the amount of coating liquid applied is preferably 1 g / m² in terms of non-volatile content, from the viewpoint of obtaining a coating layer that has excellent oil resistance even in the coated paper after bending. 2 Above, a comfortable 3g / m 2 More preferably 5 g / m2 More preferably 8 g / m 2 The above is true, and preferably 30 g / m² 2 More preferably 20 g / m 2 More preferably, 15 g / m 2 The following applies: The method for applying the coating liquid to the paper substrate in step I is not particularly limited, and examples include using a roll coater, gravure coater, die coater, curtain coater, spray coater, blade coater, wire bar coater, bar coater, rod bar coater, impregnation coater, cast coater, air knife coater, reverse coater, lip coater, kiss coater, etc.

[0112] In the present invention, from the viewpoint of obtaining a coating layer that has excellent oil resistance even after the coated paper has been folded, it is preferable to further include a step II in which the coating liquid applied in step I is dried on the paper substrate. Drying methods in step II include static drying, forced-air drying, heat drying, vacuum drying, and infrared drying. One or more drying methods may be used. Among these, from the viewpoint of ease of operation, one or more selected from forced-air drying and heat drying are preferred, and heat drying is more preferred. Examples of heating and drying methods include heating by applying hot air to the surface of the coating liquid on the paper substrate, heating by bringing a heater close to the surface of the coating liquid on the paper substrate, heating by bringing a heater into contact with the surface of the paper substrate opposite to the surface to which the coating liquid is applied, and heating by steam curing using high-temperature steam at normal or high pressure. The drying temperature is preferably 30°C or higher from the viewpoint of obtaining a coating layer that has excellent oil resistance even in the coated paper after folding, and preferably 200°C or lower from the viewpoint of suppressing deformation of the paper substrate due to heat and reducing energy. The drying time is preferably 1 minute or more, more preferably 3 minutes or more, from the viewpoint of obtaining a coating layer that has excellent oil resistance even in the coated paper after folding, and preferably 15 minutes or less, more preferably 10 minutes or less, from the viewpoint of suppressing deformation of the paper substrate due to heat and reducing energy. [Examples]

[0113] The present invention will be specifically described below with reference to examples, but the present invention is not limited in any way by these examples. In the examples, room temperature means a temperature of 20°C or higher and 25°C or lower.

[0114] [Measurement method] The properties of amorphous polyester resins, resin particles, etc., were measured and evaluated using the following methods.

[0115] [Softening point of resin] Using a flow tester "CFT-500EX" (manufactured by Shimadzu Corporation), 1 g of sample was heated at a heating rate of 6°C / min while a load of 1.96 MPa was applied by a plunger, and the sample was extruded from a nozzle with a diameter of 1 mm and a length of 1 mm. The amount of plunger descent of the flow tester was plotted against temperature, and the temperature at which half of the sample flowed out was defined as the softening point.

[0116] [Crystallization index of resins] Using a differential scanning calorimeter "Q-20" (manufactured by T.A. Instruments Japan Co., Ltd.), 0.01 to 0.02 g of the sample was weighed into an aluminum pan and cooled to 0°C at a cooling rate of 10°C / min. The sample was then left to stand still for 1 minute, and then heated to 180°C at a heating rate of 10°C / min, and the amount of heat was measured. Among the observed endothermic peaks, the temperature of the peak with the largest peak area was defined as the maximum endothermic peak temperature, and the crystallinity index was determined by the formula (softening point (°C)) / (maximum endothermic peak temperature (°C)).

[0117] [Glass transition temperature of resins] Using a differential scanning calorimeter "Q-20" (manufactured by T.A. Instruments Japan Co., Ltd.), 0.01 to 0.02 g of the sample was weighed into an aluminum pan, heated to 200°C, and then cooled to 0°C at a rate of 10°C / min to prepare the sample for measurement. Subsequently, the temperature was increased at a rate of 10°C / min and the heat quantity was measured. If a peak was observed, that peak temperature was recorded. If no peak was observed but a step was observed, the temperature at the intersection of the tangent line showing the maximum slope of the curve at the step and the extension of the baseline on the low-temperature side of the step was recorded as the glass transition temperature.

[0118] [Acid value of resins] The measurement was performed according to the neutralization titration method described in JIS K0070:1992. However, in this method, only the measurement solvent was changed from a mixed solvent of ethanol and ether to a mixed solvent of acetone and toluene [acetone:toluene = 1:1 (volume ratio)].

[0119] [Medium particle size (D) of resin particles 50 )〕 The volume median particle size (D) was measured using the following measuring device and conditions. 50 ) was measured. (1) Measuring device: Laser diffraction / scattering particle size distribution analyzer "LA-960V2" (manufactured by Horiba, Ltd.) (2) Measurement conditions: A flow cell is used as the measurement cell, deionized water is used as the dispersion medium, and the sample to be measured is added so that the absorbance is within an appropriate range, and the volume median particle size (D 50 ) was measured.

[0120] [Concentration of non-volatile content and concentration of solid content] Using a heat-drying type moisture meter "MX-50" (manufactured by A&D Co., Ltd.), 5g of the sample was dried at a drying temperature of 150°C, in standard measurement mode, standard heating pattern, and with ACCURACY:LO, and the moisture content (mass%) was measured. The concentrations of non-volatile components and solids were calculated according to the following formulas. Non-volatile content concentration and solid content concentration (mass%) = 100 - water content (mass%)

[0121] [Evaluation of oil resistance of coated paper after folding] The coated paper to be evaluated was folded in half so that the coated surfaces faced each other, and a 500g weight was placed on top and the paper was moved back and forth once to create a crease. The coated paper was unfolded and placed on a level surface, and at room temperature, a drop of castor oil was dropped onto the crease of the coated paper from 10mm above the paper and left to stand for 30 seconds. After that, the oil drop was quickly wiped off, and the condition of the paper after wiping was checked. The oil resistance of the coated paper after folding was evaluated according to the following criteria. L5 indicates the highest oil resistance of the coated paper after folding. (Judgment criteria) L5: There are almost no oil stains visible on the folds of the paper. L4: A slight oil stain is visible in the area where the oil droplet was dropped along the fold. L3: Oil stains are visible along the folds, but the size of the stains is smaller than oil droplets. L2: Along the fold, there are stains the same size as or slightly larger than oil droplets. L1: A stain considerably larger than an oil droplet is visible along the fold.

[0122] [Manufacturing of amorphous polyester resins] Manufacturing Example A1 (Manufacturing of amorphous polyester resin A-1) A four-necked flask equipped with a nitrogen inlet tube, dehydration tube, stirrer, and thermocouple was purged with nitrogen. 2561 g of 1,2-propanediol (1,2-PD), 4474 g of terephthalic acid, and 40 g of tin(II) di(2-ethylhexanoate) were added. Under a nitrogen atmosphere, the mixture was heated to 180°C with stirring and held for 1 hour, then heated to 220°C over 8 hours. After holding the reaction system at 220°C for 1 hour, the pressure inside the flask was reduced to 8.3 kPa and held for 1 hour. After returning to atmospheric pressure, the mixture was cooled to 210°C, and 318 g of succinic acid and 647 g of trimellitic anhydride were added. The reaction system was held at 210°C for 1 hour, then the pressure inside the flask was reduced to 8.3 kPa and the reaction was carried out until the softening point shown in Table 1 was reached, yielding amorphous polyester resin A-1. The physical properties of the obtained amorphous polyester resin A-1 are shown in Table 1.

[0123] Manufacturing Example A2 (Manufacturing of Amorphous Polyester Resin A-2) Amorphous polyester resin A-2 was obtained in the same manner as in production example A1, except that the raw material monomers were changed as shown in Table 1. The physical properties of the obtained amorphous polyester resin A-2 are shown in Table 1.

[0124] Manufacturing Example A3 (Manufacturing of Amorphous Polyester Resin A-3) A four-necked flask equipped with a nitrogen inlet tube, dehydration tube, stirrer, and thermocouple was purged with nitrogen. 5487g of bisphenol A propylene oxide (2.2) adduct, 1692g of terephthalic acid, 370g of succinic acid, 40g of tin di(2-ethylhexanoate), and 0.8g of gallic acid were added. Under a nitrogen atmosphere, the mixture was heated to 235°C with stirring and maintained for 6 hours. The pressure inside the flask was then reduced and maintained at 8.3kPa for 1 hour. After returning to atmospheric pressure, the mixture was cooled to 210°C, and 452g of trimellitic anhydride was added. The reaction system was maintained at 210°C for 1 hour, then the pressure inside the flask was reduced to 8.3kPa and the reaction was carried out until the softening point shown in Table 1 was reached, yielding amorphous polyester resin A-3. The physical properties of the obtained amorphous polyester resin A-3 are shown in Table 1.

[0125] [Table 1]

[0126] Manufacturing Example E1 (Manufacturing of Resin Particle Dispersion E-1) 200 g of amorphous polyester resin A-1 was placed in a 2 L four-necked flask equipped with a reflux condenser, stirrer, and thermocouple. 400 g of methyl ethyl ketone was added at room temperature and mixed and stirred until dissolved. Then, at room temperature, a 5% by mass aqueous sodium hydroxide solution was added to achieve a degree of neutralization of 60 mol% relative to the acid value of amorphous polyester resin A-1, and the mixture was stirred for 60 minutes. Next, under stirring at room temperature, 467 g of deionized water was added dropwise at a rate of 10 mL / min to emulsify the methyl ethyl ketone solution of amorphous polyester resin A-1 in phase inversion. Then, the temperature was raised to 65°C, and while maintaining 65°C, the methyl ethyl ketone was removed by gradually reducing the pressure from 80 kPa to 30 kPa, and some of the water was further removed by distillation. After cooling to room temperature, the solution was filtered through a 150-mesh wire mesh, and the solid content concentration was adjusted to 30% by mass with deionized water to obtain resin particle dispersion E-1. The median particle size (D) of the amorphous polyester resin A-1 particles in the obtained resin particle dispersion E-1 was measured. 50 ) are shown in Table 2.

[0127] Manufacturing Examples E2 and E3 (Manufacturing of Resin Particle Dispersions E-2 and E-3) Resin particle dispersions E-2 and E-3 were obtained in the same manner as in production example E1, except that the amorphous polyester resin used was changed to the one shown in Table 2. The median particle size (D) of the amorphous polyester resin A-2 and amorphous polyester resin A-3 particles in the obtained resin particle dispersions E-2 and E-3 was determined. 50 These are shown in Table 2.

[0128] [Table 2]

[0129] Manufacturing Example H1 (Manufacturing of hydrophobic particle dispersion H-1) In a 1L beaker, 227g of deionized water, 13.3g of the anionic surfactant Neoperex G-15 (sodium dodecylbenzenesulfonate, manufactured by Kao Corporation), and 100g of HNP-9 (W-1, paraffin wax, manufactured by Nippon Seiro Co., Ltd.) were added. The mixture was heated while stirring, and the temperature was maintained at 95-100°C to melt the wax and obtain a molten mixture. Next, while maintaining the temperature at 95-100°C, the mixture was dispersed for 30 minutes using an ultrasonic homogenizer "US-600AT" (manufactured by Nippon Seiki Seisakusho Co., Ltd.), then cooled to room temperature. After filtration through a 150-mesh wire mesh, deionized water was added to adjust the solid content concentration to 25% by mass to obtain a hydrophobic particle dispersion H-1 containing wax. The median particle size (D) of the hydrophobic compound A particles in the obtained hydrophobic particle dispersion H-1 was measured. 50 ) are shown in Table 3.

[0130] Manufacturing Examples H2 and H3 (Manufacturing of hydrophobic particle dispersions H-2 and H-3) Hydrophobic particle dispersions H-2 and H-3 were obtained in the same manner as in production example H1, except that the wax used was changed to W-2 and W-3 ​​as shown in Table 3. The median particle size (D) of the hydrophobic compound A particles in the obtained hydrophobic particle dispersions H-2 and H-3 was determined. 50 These are shown in Table 3.

[0131] In Table 3, waxes W-1 to W-3 refer to the following: W-1: HNP-9 (Paraffin wax, melting point 75℃, manufactured by Nippon Seiro Co., Ltd.) W-2: POLYWAX500 (Polyethylene wax, melting point 88℃, manufactured by Toyo Chem Co., Ltd.) W-3:WE14 (ester wax, melting point 78℃, NOF Corporation)

[0132] [Table 3]

[0133] Example 1 (Manufacturing of paper coating agent 1) In a 2L four-necked flask equipped with a reflux condenser, stirrer, and thermocouple, 150g of amorphous polyester resin A-1 and 50g of silicone (S1, amino-modified silicone, Shin-Etsu Chemical Co., Ltd. "KF-864") as hydrophobic compound A were placed and mixed with 400g of methyl ethyl ketone at room temperature. The mixture was then heated to 65°C and dissolved. Next, it was cooled to room temperature, and a 5% by mass aqueous sodium hydroxide solution was added at room temperature to achieve a degree of neutralization of 70 mol% relative to the acid value of amorphous polyester resin A-1, and the mixture was stirred for 60 minutes. Next, under stirring at room temperature, 467 g of deionized water was added dropwise at a rate of 10 mL / min to emulsify the amorphous polyester resin A-1 and the methyl ketone solution of silicone by phase inversion. Then, the temperature was raised to 65°C, and while maintaining 65°C, the methyl ethyl ketone was removed by gradually reducing the pressure from 80 kPa to 30 kPa, and some of the water was further removed by distillation. After cooling to room temperature, under stirring, an aqueous solution of polyvinyl alcohol (V1, "JP-03" manufactured by Nippon Vinegar & Polyvinyl Alcohol Co., Ltd.) was dissolved in 198 g of deionized water and added. After stirring for 5 minutes, the mixture was filtered through a 150 mesh wire mesh, and the concentration of non-volatile matter was adjusted to 20% by mass with deionized water to obtain paper coating agent 1. The median particle size (D) of the resin particles in the obtained paper coating agent 1 was measured. 50 The results are shown in Table 4.

[0134] (Manufacturing and evaluation of coated paper) PPC paper "J paper" (basis weight 82g / m²) is used as the paper base material. 2 Using a bar coater (No. 12) manufactured by Fujifilm Business Innovation Co., Ltd., paper coating agent 1 was applied at a rate of 10 g / m² (non-volatile content). 2 It was painted in such a way. Next, the paper coating layer on the paper substrate was dried in a 110°C dryer for 5 minutes to obtain coated paper having a coating layer on the paper substrate. The oil resistance of the obtained coated paper was evaluated as described above. The results are shown in Table 4.

[0135] Examples 2, 3, 5-7 Paper coating agents 2, 3, and 5-7 were obtained in the same manner as in Example 1, except that the types and amounts of amorphous polyester resin, silicone, and polyvinyl alcohol were changed as shown in Table 4. The median particle size (D) of the resin particles in the obtained paper coating agents was determined. 50 The results are shown in Table 4. Next, the oil resistance of the coated paper obtained in the same manner as in Example 1 was evaluated after folding. The results are shown in Table 4.

[0136] Example 4 In Example 1, the polyvinyl alcohol aqueous solution was changed to a polyvinyl alcohol aqueous solution prepared by dissolving 67 g of polyvinyl alcohol (V1, "JP-03" manufactured by Nippon Vi-Poval Co., Ltd.) in 380 g of deionized water. Paper coating agent 4 was obtained in the same manner as in Example 1. The median particle size (D) of the resin particles in the obtained paper coating agent 4 was determined. 50 The results are shown in Table 4. Next, the oil resistance of the coated paper obtained in the same manner as in Example 1 was evaluated after folding. The results are shown in Table 4.

[0137] Example 8 In Example 1, the polyvinyl alcohol aqueous solution was changed to a polyvinyl alcohol aqueous solution prepared by dissolving 11 g of polyvinyl alcohol (V1, "JP-03" manufactured by Nippon Vi-Poval Co., Ltd.) in 99 g of deionized water. Paper coating agent 8 was obtained in the same manner as in Example 1. The median particle size (D) of the resin particles in the obtained paper coating agent 8 was determined. 50 The results are shown in Table 4. Next, the oil resistance of the coated paper obtained in the same manner as in Example 1 was evaluated after folding. The results are shown in Table 4.

[0138] Comparative Example 1 In Example 1, paper coating agent C1 was obtained in the same manner except that an aqueous polyvinyl alcohol solution was not used. The median particle size (D) of the resin particles in the obtained paper coating agent C1 was determined. 50 The results are shown in Table 4. Next, the oil resistance of the coated paper obtained in the same manner as in Example 1 was evaluated after folding. The results are shown in Table 4.

[0139] Comparative Example 2 (Manufacturing of paper coating agent C2) Deionized water was added to paper coating agent C1 prepared in Comparative Example 1 to adjust the concentration of non-volatile components to 19% by mass, thereby obtaining paper coating agent C2.

[0140] (Manufacturing and evaluation of coated paper) PPC paper "J paper" (basis weight 82g / m²) is used as the paper base material. 2 (Manufactured by Fujifilm Business Innovation Co., Ltd.) The coating amount of polyvinyl alcohol is 0.5 g / m². 2 To achieve this, a 4% by mass aqueous solution of polyvinyl alcohol (V1, "JP-03" manufactured by Nippon Vinegar Vinegar Co., Ltd.) was applied using a bar coater (No. 3) and dried in a 110°C dryer for 5 minutes. Next, the paper substrate coated with polyvinyl alcohol, which had been removed from the dryer and cooled to room temperature, was further coated with paper coating agent C2 using a bar coater (No. 12) at a rate of 9.5 g / m² (non-volatile content) on top of the polyvinyl alcohol coating. 2 The paper was coated in the manner described above. The paper coating layer on the paper substrate was dried in a 110°C dryer for 5 minutes to obtain coated paper having a coating layer on the paper substrate. The above-described evaluation of the oil resistance of the coated paper after folding was performed on the obtained coated paper. The results are shown in Table 4.

[0141] In Table 4, silicones S1 and S2, and polyvinyl alcohols V1 and V2 have the following meanings, respectively. S1: KF-864 (amino-modified silicone, viscosity 1700 mm) 2 (Manufactured by Shin-Etsu Chemical Co., Ltd.) S2:WT-1650 (amino-modified silicone, viscosity 1000 mm) 2 (Manufactured by Asahi Kasei Wacker Silicone Co., Ltd.) V1:JP-03 (Partially saponified polyvinyl alcohol, degree of polymerization 300, degree of saponification 88%, manufactured by Nippon Vi-Poval Co., Ltd.) V2: JF-02 (Fully saponified polyvinyl alcohol, degree of polymerization 200, degree of saponification 98%, manufactured by Nippon Vi-Poval Co., Ltd.)

[0142] [Table 4]

[0143] Table 4 shows that the paper coating agents of Examples 1 to 8 can produce coated paper with superior oil resistance even after folding, compared to the paper coating agents of Comparative Examples 1 and 2. Furthermore, as in Comparative Example 2, coated paper, which was coated and dried with a paper coating agent consisting of an aqueous dispersion of resin particles containing amorphous polyester resin and silicone after applying polyvinyl alcohol to a paper substrate, was found to have poor oil resistance after bending. This is thought to be because most of the polyvinyl alcohol penetrated into the paper substrate, resulting in weak interaction between the amorphous polyester resin and polyvinyl alcohol in the coating layer, and causing the amorphous polyester resin to detach or break off from the coating layer upon bending.

[0144] Example 11 In a 1L beaker, 165g of deionized water, 150g of resin particle dispersion E-1, and 45g of wax (W1, paraffin wax, "HNP-9" manufactured by Nippon Seiro Co., Ltd.) as hydrophobic compound A were added. The mixture was heated while stirring, and the temperature was maintained at 95-100°C to melt the wax and obtain a molten mixture. Next, while maintaining the temperature at 95-100°C, the mixture was dispersed using an ultrasonic homogenizer "US-600AT" (manufactured by Nippon Seiki Seisakusho Co., Ltd.) for 30 minutes, then cooled to room temperature and filtered through a 150-mesh wire mesh. An aqueous polyvinyl alcohol solution, prepared by dissolving 5g of polyvinyl alcohol (V1, "JP-03" manufactured by Nippon Vi-Poval Co., Ltd.) in 95g of deionized water, was added. Deionized water was added to adjust the concentration of non-volatile components to 20% by mass to obtain paper coating agent 11. The median particle size (D) of the resin particles in the obtained paper coating agent 11 was measured. 50 ) are shown in Table 5. Next, the oil resistance of the coated paper obtained in the same manner as in Example 1 was evaluated after folding. The results are shown in Table 5.

[0145] Examples 12, 13, 16, and 17 In Example 11, paper coating agents 12, 13, 16, and 17 were obtained in the same manner, except that the types and amounts of amorphous polyester resin particle dispersion, wax, and polyvinyl alcohol were changed as shown in Table 5. The median particle size (D) of the resin particles in the obtained paper coating agents was determined. 50 ) are shown in Table 5. Next, the oil resistance of the coated paper obtained in the same manner as in Example 1 was evaluated after folding. The results are shown in Table 5.

[0146] Example 14 In Example 11, the amounts of resin particle dispersion and wax were changed as shown in Table 5, and the amount of deionized water obtained when the molten mixture was obtained was changed to 130 g, otherwise the paper coating agent 14 was obtained in the same manner. The median particle size (D) of the resin particles in the obtained paper coating agent 14 50 ) are shown in Table 5. Next, the oil resistance of the coated paper obtained in the same manner as in Example 1 was evaluated after folding. The results are shown in Table 5.

[0147] Example 15 In Example 11, the amount of deionized water obtained when the molten mixture was obtained was changed to 130 g, and the polyvinyl alcohol aqueous solution was changed to a polyvinyl alcohol aqueous solution obtained by dissolving 23 g of polyvinyl alcohol (V1, "JP-03" manufactured by Nippon Vi-Poval Co., Ltd.) in 130 g of deionized water. Otherwise, the paper coating agent 15 was obtained in the same manner. The median particle size (D) of the resin particles in the obtained paper coating agent 15 was determined. 50 ) are shown in Table 5. Next, the oil resistance of the coated paper obtained in the same manner as in Example 1 was evaluated after folding. The results are shown in Table 5.

[0148] Comparative Example 3 In Example 11, paper coating agent C3 was obtained in the same manner except that an aqueous polyvinyl alcohol solution was not used. The median particle size (D) of the resin particles in the obtained paper coating agent C3 was determined. 50 ) are shown in Table 5. Next, the oil resistance of the coated paper obtained in the same manner as in Example 1 was evaluated after folding. The results are shown in Table 5.

[0149] Note that waxes W1 and W2 in Table 5 are the same as waxes W-1 and W-2 shown in Table 3. Also, polyvinyl alcohols V1 and V2 are the same as polyvinyl alcohols V1 and V2 shown in Table 4.

[0150] [Table 5]

[0151] Table 5 shows that the paper coating agents of Examples 11 to 17 can produce coated paper with superior oil resistance even after folding, compared to the paper coating agent of Comparative Example 3.

[0152] Example 21 200g of resin particle dispersion E-1 and 240g of hydrophobic particle dispersion H-1 were placed in a 1L beaker and stirred with a magnetic stirrer at room temperature. Next, while stirring, an aqueous polyvinyl alcohol solution was added, prepared by dissolving 6g of polyvinyl alcohol (V1, "JP-03" manufactured by Nippon Vi-Poval Co., Ltd.) in 94g of deionized water. The mixture was then stirred with a magnetic stirrer for 5 minutes, and deionized water was added to adjust the concentration of non-volatile components to 20% by mass to obtain paper coating agent 21. Next, the oil resistance of the coated paper obtained in the same manner as in Example 1 was evaluated after folding. The results are shown in Table 6.

[0153] Examples 22-26 and 28 In Example 21, paper coating agents 22-26 and 28 were obtained in the same manner, except that the types and amounts of the resin particle dispersion, hydrophobic particle dispersion, and polyvinyl alcohol were changed as shown in Table 6. Next, the oil resistance of the coated paper obtained in the same manner as in Example 1 was evaluated after folding. The results are shown in Table 6.

[0154] Example 27 In Example 21, the polyvinyl alcohol aqueous solution was changed to a polyvinyl alcohol aqueous solution obtained by dissolving 24 g of polyvinyl alcohol (V1, "JP-03" manufactured by Nippon Vinegar Bi-Poval Co., Ltd.) in 216 g of deionized water, and the paper coating agent 27 was obtained in the same manner. Next, the oil resistance of the coated paper obtained in the same manner as in Example 1 was evaluated after folding. The results are shown in Table 6.

[0155] Comparative Example 4 Paper coating agent C4 was obtained in the same manner as in Example 21, except that an aqueous polyvinyl alcohol solution was not used. Next, the oil resistance of the coated paper obtained in the same manner as in Example 1 was evaluated after folding. The results are shown in Table 6.

[0156] Note that waxes W1 and W2 in Table 6 are the same as waxes W-1 and W-2 shown in Table 3. Also, polyvinyl alcohols V1 and V2 are the same as polyvinyl alcohols V1 and V2 shown in Table 4.

[0157] [Table 6]

[0158] Table 6 shows that the paper coating agents of Examples 21 to 28 can produce coated paper with superior oil resistance even after folding, compared to the paper coating agent of Comparative Example 4. [Industrial applicability]

[0159] According to the paper coating agent of the present invention, coated paper with excellent oil resistance even after folding can be obtained, and can be used for paper labels, packaging paper, paper containers, etc., where resistance to water and oil is required.

Claims

1. A paper coating agent comprising an amorphous polyester resin, a hydrophobic compound A consisting of one or more selected from waxes and silicones, polyvinyl alcohol, and an aqueous medium.

2. The paper coating agent according to claim 1, wherein the mass ratio of the total amount of the amorphous polyester resin and the hydrophobic compound A to the polyvinyl alcohol (total amount of amorphous polyester resin and the hydrophobic compound A / polyvinyl alcohol) is 70 / 30 or more and 99 / 1 or less.

3. The paper coating agent according to claim 1, wherein the glass transition temperature of the amorphous polyester resin is 45°C or higher and 75°C or lower.

4. The paper coating agent according to claim 1, wherein the mass ratio of the amorphous polyester resin to the hydrophobic compound A (amorphous polyester resin / hydrophobic compound A) is 45 / 55 or more and 90 / 10 or less.

5. The paper coating agent according to claim 1, comprising the amorphous polyester resin and resin particles containing the hydrophobic compound A, and the polyvinyl alcohol.

6. The paper coating agent according to claim 1, comprising resin particles containing the amorphous polyester resin, particles containing the hydrophobic compound A, and the polyvinyl alcohol.

7. Coated paper having a coating layer formed by the paper coating agent described in any one of claims 1 to 6.

8. A method for producing coated paper, comprising: step I, applying a paper coating agent according to any one of claims 1 to 6 to at least one side of a paper substrate to form a coating liquid layer; and step II, drying the coating layer on the paper substrate coated in step I.

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