Paper coating agent

Abstract

This invention relates to a paper coating agent that can produce coated paper with excellent water repellency and oil resistance. [Solution] A paper coating agent comprising resin particles containing an amorphous polyester resin and an alkyl ketene dimer, wherein the content of the alkyl ketene dimer is 40 parts by mass or more and 280 parts by mass or less per 100 parts by mass of the amorphous polyester resin.

Description

[Technical Field]

[0001] The present invention relates to a paper coating agent, a method for producing the 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 in areas requiring water and oil repellency have been paper laminated with plastic films such as polyethylene or polypropylene to provide these properties. However, paper laminated with plastic films is difficult to recycle. Therefore, with the growing environmental awareness in recent years, there has been a demand for and research into alternative technologies to lamination that can provide water and oil repellency.

[0003] While fluorine-based paper coatings are known as a technology for imparting water repellency and oil resistance, there is a growing demand for paper coatings made from non-fluorine-based materials from the perspectives of safety and environmental considerations.

[0004] Patent Document 1 discloses an oil-resistant paper comprising a paper substrate, an intermediate layer, and a surface layer, with the aim of providing an oil-resistant paper that combines high oil resistance and high air permeability, wherein the intermediate layer is provided on at least one surface of the paper substrate, and the surface layer is provided on the surface of the intermediate layer opposite to the side on which the paper substrate is provided, the intermediate layer contains polyvinyl alcohol, and the surface layer contains styrene-(meth)acrylic copolymer resin and a sizing agent. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2022-85465 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] However, the oil-resistant paper described in the prior art document 1 may have insufficient water repellency and oil resistance. The present invention relates to a paper coating agent capable of obtaining a coated paper excellent in water repellency and oil resistance, a method for producing the paper coating agent, and a coated paper using the paper coating agent.

Means for Solving the Problems

[0007] The inventors of the present invention focused on providing a coating layer that suppresses the contact between paper and water and oil, and found that the above problems can be solved by a paper coating agent containing resin particles containing an amorphous polyester resin and an alkyl ketene dimer. The present invention relates to the following [1] to [3]. [1] A paper coating agent containing resin particles containing an amorphous polyester resin and an alkyl ketene dimer, wherein the content of the alkyl ketene dimer is 40 parts by mass or more and 280 parts by mass or less with respect to 100 parts by mass of the amorphous polyester resin. [2] A coated paper having a coating layer containing an amorphous polyester resin and an alkyl ketene dimer, wherein the content of the alkyl ketene dimer is 40 parts by mass or more and 280 parts by mass or less with respect to 100 parts by mass of the amorphous polyester resin. [3] A method for producing the paper coating agent according to [1], having the following steps 1 to 3 in this order. Step 1: Dissolving the amorphous polyester resin in an organic solvent, adding an aqueous medium to perform phase inversion emulsification, and distilling off the organic solvent to obtain an aqueous dispersion of particles of the amorphous polyester resin. Step 2: Adding and mixing the alkyl ketene dimer to the aqueous dispersion of particles of the amorphous polyester resin to obtain a mixed liquid. Step 3: Dispersing the mixed liquid at a temperature not lower than the melting point of the alkyl ketene dimer to obtain the resin particles containing the amorphous polyester resin and the alkyl ketene dimer. [Advantages of the Invention]

[0008] According to the present invention, it is possible to provide a paper coating agent capable of obtaining a coated paper excellent in water repellency and oil resistance, a method for producing the paper coating agent, and a coated paper using the paper coating agent. [Embodiments for Carrying Out the Invention]

[0009] [Paper Coating Agent] The paper coating agent of the present invention contains resin particles containing an amorphous polyester resin and an alkyl ketene dimer.

[0010] The paper coating agent of the present invention is preferably one in which the resin particles are dispersed in an aqueous medium. In the present invention, "aqueous" means that water occupies the largest proportion in the medium. As the water of the aqueous medium, distilled water is preferably used. The aqueous medium may further contain an organic solvent. Examples of the organic solvent include water-soluble organic solvents soluble in water such as aliphatic alcohols having 1 to 4 carbon atoms such as methanol, ethanol, and 2-propanol; ketones having 3 to 8 carbon atoms such as acetone and methyl ethyl ketone; and ethers such as diethyl ether and tetrahydrofuran. From the viewpoint of environmental properties, the content of water in the aqueous medium is preferably 60% by mass or more, more preferably 70% by mass or more, still more preferably 90% by mass or more, even more preferably 95% by mass or more, and preferably 100% by mass or less, even more preferably 100% by mass.

[0011] The definitions of various terms in this specification are shown below. The crystallinity of the resin is represented by a crystallinity index defined as the ratio of the softening point to the maximum peak temperature of endotherm measured by a differential scanning calorimeter (DSC), that is, "softening point (°C) / maximum peak temperature of endotherm (°C)". "Crystalline resin" refers to a resin having a crystallinity index of 0.6 or more and 1.4 or less. "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.

[0012] According to the present invention, a paper coating agent can be obtained that can produce coated paper with excellent water repellency and oil resistance. The reason for this is not entirely clear, but it is thought to be as follows. The inventors have found that when a paper coating agent containing a sizing agent is applied to a paper substrate, the sizing agent dispersed by a general emulsifier penetrates into the interior of the paper substrate. As a result, the amount of sizing agent present on the surface of the paper substrate is small, and the resulting coated paper has difficulty exhibiting water repellency and oil resistance based on the sizing agent. The paper coating agent of the present invention is thought to contain resin particles in which an amorphous polyester resin and an alkyl ketene dimer are dispersed in an amorphous polyester resin, and the alkyl ketene dimer partially reacts with the hydroxyl groups of the amorphous polyester resin to form a composite. Therefore, in coated paper obtained by coating a paper substrate with the paper coating agent of the present invention, a coating layer containing resin particles is formed on the surface of the paper substrate. The resulting coated paper exhibits oil resistance due to the effect of the relatively hydrophilic amorphous polyester resin and alkyl ketene dimer contained in the resin particles, and exhibits water repellency due to the effect of the alkyl group, which is a hydrophobic group of the alkyl ketene dimer.

[0013] [Amorphous polyester resin] In the present invention, the resin particles include an amorphous polyester resin. The amorphous polyester resin is not particularly limited as long as it contains a polycondensate of the alcohol component and the carboxylic acid component described later. Examples include polyester resins made from polycondensates of the alcohol component and the carboxylic acid component, and modified polyester resins. Examples of modified polyester resins include amorphous composite resins containing polyester resin segments and addition polymerization resin segments, silicone-modified polyester resins modified with modified silicone, urethane-modified polyester resins, epoxy-modified polyester resins, and the like. Among these, the amorphous polyester resin is preferably one or more selected from amorphous polyester resins and amorphous composite resins.

[0014] In the present invention, the amorphous polyester resin is preferably water-insoluble from the viewpoint of improving the water repellency and oil resistance of the resulting coated paper. When the amorphous polyester resin is water-insoluble, the coating layer formed by coating the paper substrate with the paper coating agent becomes water-insoluble, thereby improving water repellency and oil resistance. Here, "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 resin contains acidic groups, the amount dissolved is the amount dissolved when the acidic groups are neutralized by 100 mol% with sodium hydroxide.

[0015] (Alcohol content) The alcohol component constituting the amorphous polyester resin (hereinafter also simply referred to as "alcohol component") includes alcohols of dihydride or higher. Alcohol components can be used individually or in combination of two or more types. Examples of alcohols with a valency of 2 or higher include diols and polyhydric alcohols with a valency of 3 or higher. Examples of diols include aromatic diols, aliphatic diols, and alicyclic diols.

[0016] Examples of aromatic diols include alkylene oxide adducts of bisphenol A. In the present invention, "alkylene oxide adduct of bisphenol A" refers to the entire structure obtained by adding an alkylene oxide to 2,2-bis(4-hydroxyphenyl)propane. From the viewpoint of improving the water repellency and oil resistance of the resulting coated paper, the alkylene oxide adduct of bisphenol A is preferably a compound represented by the following formula (I).

[0017] [ka]

[0018] In the above formula (I), OR 1 , and R 2 In all cases, O is an alkylene oxy group, and from the viewpoint of improving the water repellency and oil resistance of the resulting coated paper, preferably each is an alkylene oxy group having 1 to 4 carbon atoms, 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. Furthermore, from the viewpoint of reactivity with the carboxylic acid component, the average value of the sum of x and y is preferably 2 or more. Also, from the same viewpoint, the average value of the sum of x and y is preferably 7 or less, more preferably 5 or less, and even more preferably 3 or less. x pieces OR 1 and y R 2 The oxygen atoms may be the same or different, but it is preferable that they be the same from the viewpoint of improving the adhesion of the coating layer to the paper. One type of alkylene oxide adduct of bisphenol A may be used alone or two or more types may be used. From the viewpoint of improving the water repellency and oil resistance of the resulting coated paper, the alkylene oxide adduct of bisphenol A is preferably one or more selected from propylene oxide adduct of bisphenol A and ethylene oxide adduct of bisphenol A, and more preferably propylene oxide adduct of bisphenol A.

[0019] Examples of aliphatic diols include aliphatic diols with 2 to 16 carbon atoms and alicyclic aliphatic diols. 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, 2,4-pentanediol, 1,2-hexanediol, 1,5-hexanediol, 2,5-hexanediol, 1,6-hexanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,12-dodecanediol, 1,14-tetradecanediol, 1,16-hexadecanediol, and 3,3-dimethyl-1,2-butanediol. From the viewpoint of improving the water repellency and oil resistance of the resulting coated paper, 1,2-propanediol is preferred as the aliphatic diol.

[0020] Examples of alicyclic diols include cyclohexanediol and hydrogenated bisphenol A.

[0021] Examples of polyhydric alcohols with a valency of 3 or higher include aliphatic polyols, such as glycerin, pentaerythritol, trimethylolpropane, sorbitol, and sorbitan.

[0022] Among these, the alcohol component constituting the amorphous polyester resin preferably includes one or more selected from aromatic diols and aliphatic diols, and more preferably includes one or more selected from alkylene oxide adducts of bisphenol A and 1,2-propanediols, from the viewpoint of improving the water repellency and oil resistance of the resulting coated paper.

[0023] The content of diol in the alcohol component constituting the amorphous polyester resin is preferably 60 mol% or more, more preferably 80 mol% or more, even more preferably 90 mol% or more, even more preferably 95 mol% or more, and preferably 100 mol% or less, from the viewpoint of improving the water repellency and oil resistance of the resulting coated paper.

[0024] (Carboxylic acid component) Examples of carboxylic acid components that make up amorphous polyester resins (hereinafter also simply referred to as "carboxylic acid components") include dicarboxylic acids and polycarboxylic acids with a valency of three or more. The carboxylic acid component includes not only the compound itself, but also anhydrides that decompose during the reaction to produce acid, and alkyl esters of each carboxylic acid with 1 to 3 carbon atoms. The carboxylic acid component may be used individually or in combination of two or more types.

[0025] Examples of dicarboxylic acids include aromatic dicarboxylic acids and aliphatic dicarboxylic acids. Examples of aromatic dicarboxylic acids include phthalic acid, isophthalic acid, and terephthalic acid. Among these, terephthalic acid is preferred as the aromatic dicarboxylic acid from the viewpoint of improving the water repellency and oil resistance of the resulting coated paper. 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 fumaric acid and succinic acid, from the viewpoint of improving the water repellency and oil resistance of the resulting coated paper.

[0026] The total content of dicarboxylic acids in the carboxylic acid components constituting the amorphous polyester resin is preferably 40 mol% or more, more preferably 45 mol% or more, even more preferably 50 mol% or more, and preferably 100 mol% or less, and more preferably 95 mol% or less, from the viewpoint of improving the water repellency and oil resistance of the resulting coated paper.

[0027] Examples of polycarboxylic acids with a valency of three or more include aromatic polycarboxylic acids with a valency of three or more. Examples of trivalent or higher aromatic polycarboxylic acids include trimellitic acid, 2,5,7-naphthalentricarboxylic acid, and pyromellitic acid. Among these, trimellitic acid is preferred from the viewpoint of improving the water repellency and oil resistance of the resulting coated paper.

[0028] In the present invention, from the viewpoint of improving the water repellency and oil resistance of the resulting coated paper, it is preferable to use a combination of a dicarboxylic acid and a trivalent or higher aromatic carboxylic acid as the carboxylic acid component. When the carboxylic acid component contains a trivalent or higher aromatic carboxylic acid, the content of the trivalent or higher aromatic polycarboxylic acid in the carboxylic acid component is preferably 3 mol% or more, more preferably 5 mol% or more, even more preferably 10 mol% or more, and preferably 60 mol% or less, more preferably 55 mol% or less, and even more preferably 50 mol% or less, from the viewpoint of improving the water repellency and oil resistance of the resulting coated paper.

[0029] (Amorphous composite resin) When the amorphous polyester resin is an amorphous composite resin, it is preferable that the amorphous composite resin contains a polycondensate of the alcohol component and the carboxylic acid component as a polyester resin segment, and further contains an addition polymer of a raw material monomer containing a styrene compound as an addition polymerization resin segment. Examples of styrene compounds include unsubstituted or substituted styrene. Examples of substituents that can be substituted for styrene include alkyl groups having 1 to 5 carbon atoms, halogen atoms, alkoxy groups having 1 to 5 carbon atoms, sulfonic acid groups, or salts thereof. Examples of styrene-based compounds include styrene, methylstyrene, α-methylstyrene, β-methylstyrene, tert-butylstyrene, chlorostyrene, chloromethylstyrene, methoxystyrene, styrene sulfonic acid, or salts thereof. Among these, styrene is preferred. The content of styrene compounds in the raw material monomers of the addition polymerization resin segment is preferably 65% ​​by mass or more, more preferably 70% by mass or more, even more preferably 75% by mass or more, and preferably 95% by mass or less, more preferably 90% by mass or less, and even more preferably 85% by mass or less.

[0030] Other raw material monomers besides styrene compounds include, for example, (meth)acrylic acid esters such as alkyl (meth)acrylate, benzyl (meth)acrylate, and dimethylaminoethyl (meth)acrylate; olefins such as ethylene, propylene, and butadiene; halovinyls such as vinyl chloride; vinyl esters such as vinyl acetate and vinyl propionate; vinyl ethers such as methyl vinyl ether; vinylidene halides such as vinylidene chloride; and N-vinyl compounds such as N-vinylpyrrolidone. Among these, (meth)acrylic acid esters are preferred, and alkyl (meth)acrylates are preferred.

[0031] The number of carbon atoms in the alkyl group of (meth)acrylate is preferably 1 or more, more preferably 4 or more, even more preferably 6 or more, and preferably 24 or less, more preferably 22 or less, and even more preferably 20 or less. Examples of alkyl (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, isopropyl (meth)acrylate, iso(or tertiary)butyl (meth)acrylate, isoamyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, isodecyl (meth)acrylate, isododecyl (meth)acrylate, isopalmityl (meth)acrylate, isostearyl (meth)acrylate, and isobehenyl (meth)acrylate. Among these, 2-ethylhexyl (meth)acrylate or stearyl (meth)acrylate is preferred, more preferably 2-ethylhexyl (meth)acrylate, and even more preferably 2-ethylhexyl acrylate. Note that "(iso or tertiary)" and "(iso)" refer to both cases where these prefixes are present and where they are not, and the absence of these prefixes indicates the normal form. Also, "(meth)acrylic acid" refers to acrylic acid or methacrylic acid. The content of alkyl (meth)acrylate in the raw material monomer of the addition polymerization resin segment is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and preferably 35% by mass or less, more preferably 30% by mass or less, and even more preferably 25% by mass or less.

[0032] The total content of styrene compounds and (meth)acrylic acid esters in the raw material monomers of the addition polymerization resin segment is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and preferably 100% by mass or less, and even more preferably 100% by mass.

[0033] When the amorphous polyester resin is an amorphous composite resin, it is preferable that the amorphous polyester resin has constituent units derived from both reactive monomers that are covalently bonded to the polyester resin segment and the addition polymerization resin segment. "Constituent units derived from both reactive monomers" refers to units formed by the reaction of the functional groups and addition polymerizable groups of both reactive monomers. Examples of addition polymerizable groups include carbon-carbon unsaturated bonds (ethylenically unsaturated bonds). Examples of both reactive monomers include addition polymerizable monomers having at least one functional group selected from hydroxyl groups, carboxyl groups, epoxy groups, primary amino groups, and secondary amino groups within the molecule. Among these, from the viewpoint of reactivity, both reactive monomers are preferably addition polymerizable monomers having at least one functional group selected from hydroxyl groups and carboxyl groups, and more preferably addition polymerizable monomers having carboxyl groups. Examples of addition polymerizable monomers having a carboxyl group include acrylic acid, methacrylic acid, fumaric acid, and maleic acid. Among these, from the viewpoint of reactivity in both polycondensation and addition polymerization reactions, one or more selected from acrylic acid and methacrylic acid are preferred, and acrylic acid is more preferred.

[0034] When both reactive monomers are addition polymerizable monomers having a carboxyl group, the amount of constituent units derived from both reactive monomers is preferably 1 mole or more, more preferably 3 moles or more, even more preferably 5 moles or more, and preferably 30 moles or less, more preferably 20 moles or less, even more preferably 15 moles or less, and even more preferably 10 moles or less, based on 100 moles of the alcohol component of the polyester resin segment of the amorphous polyester resin.

[0035] When the amorphous polyester resin is an amorphous composite resin, the content of polyester resin segments in the amorphous composite resin is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, and preferably 90% by mass or less, more preferably 85% by mass or less, and even more preferably 80% by mass or less. When the amorphous polyester resin is an amorphous composite resin, the content of the addition polymerization resin segment in the amorphous composite resin is preferably 8% by mass or more, more preferably 15% by mass or more, even more preferably 20% by mass or more, and preferably 40% by mass or less, more preferably 35% by mass or less, and even more preferably 30% by mass or less. When the amorphous polyester resin is an amorphous composite resin, the content of constituent units derived from both reactive monomers in the amorphous composite resin is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, even more preferably 0.5% by mass or more, and preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 2% by mass or less. When the amorphous polyester resin is an amorphous composite resin, the total content of the polyester resin segment, the addition polymerization resin segment, and the constituent units derived from both reactive monomers in the amorphous composite resin is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and preferably 100% by mass or less, and even more preferably 100% by mass. The above quantities are calculated based on the ratio of the raw material monomers, both reactive monomers, and radical polymerization initiators for the polyester resin segment and the addition polymerization resin segment. The mass of the polyester resin segment, etc., is based on the mass excluding the mass of water produced by polycondensation. When a radical polymerization initiator is used, the mass of the radical polymerization initiator is included in the calculation of the addition polymerization resin segment.

[0036] Amorphous polyester resins can be produced, for example, by polycondensing an alcohol component and a carboxylic acid component in an inert gas atmosphere, using an esterification catalyst as needed, at a temperature of 150°C to 250°C. Examples of esterification catalysts include tin compounds such as di(2-ethylhexanoate)tin(II) and dibutyltin oxide; and titanium compounds such as titanium diisopropylate bistriethanolamine. Furthermore, if necessary, esterification co-catalysts such as 3,4,5-trihydroxybenzoic acid (gallic acid) and radical polymerization inhibitors such as 4-tert-butylcatechol may be used.

[0037] Furthermore, if the amorphous polyester resin is an amorphous composite resin, it may be produced by a method including, for example, step A, which involves polycondensation of an alcohol component and a carboxylic acid component, and step B, which involves addition polymerization of the raw material monomers of the addition polymerization resin segment and both reactive monomers. Process A may be performed after process B, or process B may be performed after process A, or process A and process B may be performed simultaneously. In step A, a portion of the carboxylic acid component is subjected to a polycondensation reaction, and then step B is carried out. After that, the remaining carboxylic acid component is added to the polymerization system to further advance the polycondensation reaction in step A and the polycondensation reaction with the carboxyl groups of both reactive monomers or constituent parts derived from both reactive monomers.

[0038] In step A, for example, it is preferable to produce the product by polycondensing an alcohol component and a carboxylic acid component in an inert gas atmosphere at a temperature of 150°C to 250°C, using the above-mentioned esterification catalyst, esterification co-catalyst, and radical polymerization inhibitor as needed. Examples of radical polymerization initiators for the addition polymerization in step B include peroxides such as di-tert-butyl peroxide, persulfates such as sodium persulfate, and azo compounds such as 2,2'-azobis(2,4-dimethylvaleronitrile). The amount of radical polymerization initiator used is preferably 1 to 20 parts by mass per 100 parts by mass of raw material monomers of the addition polymerization resin segment. The addition polymerization temperature is preferably 110°C or higher, more preferably 130°C or higher, and preferably 230°C or lower, more preferably 220°C or lower, and even more preferably 210°C or lower.

[0039] The softening point of the amorphous polyester resin is preferably 90°C or higher, more preferably 95°C or higher, even more preferably 100°C or higher, and preferably 170°C or lower, more preferably 150°C or lower, and even more preferably 130°C or lower, from the viewpoint of improving the water repellency and oil resistance of the resulting coated paper.

[0040] The glass transition temperature of the amorphous polyester resin is preferably 30°C or higher, more preferably 35°C or higher, even more preferably 40°C or higher, and preferably 90°C or lower, more preferably 80°C or lower, and even more preferably 75°C or lower, from the viewpoint of improving the water repellency and oil resistance of the resulting coated paper.

[0041] 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 40 mg KOH / g or less, more preferably 37 mg KOH / g or less, and even more preferably 35 mg KOH / g or less, from the viewpoint of improving the dispersibility of resin particles in the paper coating agent and improving the water repellency and oil resistance of the resulting coated paper.

[0042] The hydroxyl value of the amorphous polyester resin is preferably 1 mg KOH / g or more, more preferably 3 mg KOH / g or more, even more preferably 5 mg KOH / g or more, and preferably 50 mg KOH / g or less, more preferably 47 mg KOH / g or less, and even more preferably 45 mg KOH / g or less, from the viewpoint of forming a composite between the amorphous polyester resin and the alkyl ketene dimer, and from the viewpoint of improving the water repellency and oil resistance of the resulting coated paper.

[0043] The number-average molecular weight of the amorphous polyester resin is preferably 1,000 or more, more preferably 1,500 or more, even more preferably 2,000 or more, and preferably 10,000 or less, more preferably 8,000 or less, and even more preferably 5,000 or less, from the viewpoint of improving the water repellency and oil resistance of the resulting coated paper. Furthermore, the weight-average molecular weight of the amorphous polyester resin is preferably 3,000 or more, more preferably 4,000 or more, even more preferably 5,000 or more, and preferably 50,000 or less, more preferably 45,000 or less, and even more preferably 40,000 or less, from the viewpoint of improving the water repellency and oil resistance of the resulting coated paper.

[0044] Amorphous polyester resins may be used individually or in combination of two or more types. The softening point, glass transition temperature, acid value, hydroxyl value, number-average molecular weight, and weight-average molecular weight 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, acid value, hydroxyl value, number average molecular weight, and weight average molecular weight obtained from the mixture thereof are all within the above ranges.

[0045] <Alkyl ketene dimer> In the present invention, the resin particles include an amorphous polyester resin in addition to an alkyl ketene dimer. Alkyl ketene dimers are compounds represented by the following formula (1), and can be prepared from acid chlorides by methods described, for example, R. Adams, Org. Reactions Vol. III, p 129 John Wiley & Sons Inc. NY 1946 or JCSaner; J. Am. Chem. Soc., Vol. 69, p. 2444 (1947).

[0046] [ka]

[0047] In formula (1), R 1 and R 2is, independently of each other, a linear, branched, or alicyclic alkyl group, R 1 The bond with the double bond may be in either the E or Z configuration.

[0048] R 1 and R 2 The number of carbon atoms in the alkyl group represented by is preferably 14 or more, more preferably 15 or more, still more preferably 16 or more, and preferably 24 or less, more preferably 22 or less, still more preferably 20 or less, from the viewpoint of improving the water repellency and oil resistance of the resulting coated paper. Here, for example, an alkyl ketene dimer having 18 carbon atoms means that in the compound represented by the above formula (1), R 1 and R 2 both represent an alkyl ketene dimer having 18 carbon atoms.

[0049] When the alkyl ketene dimer is a mixture, the content of the compound represented by the formula (1) in which the number of carbon atoms in the alkyl group represented by R 1 and R 2 is 14 or more and 24 or less is preferably 30% by mass or more, more preferably 35% by mass or more, still more preferably 38% by mass or more, from the viewpoint of improving the water repellency and oil resistance of the resulting coated paper.

[0050] The melting point of the alkyl ketene dimer is preferably 40°C or higher, more preferably 43°C or higher, still more preferably 45°C or higher, and preferably 80°C or lower, more preferably 75°C or lower, still more preferably 70°C or lower, from the viewpoint of improving the dispersibility of resin particles in the paper coating agent and the water repellency and oil resistance of the resulting coated paper. When a mixture of alkyl ketene dimers is used, the melting point of the alkyl ketene dimer is the melting point of the mixture. The melting point of the alkyl ketene dimer can be measured, for example, by the method described in the examples, and when it is a commercially available product, the catalog value may be used.

[0051] From the viewpoint of improving the water repellency and oil resistance of the resulting coated paper, the content of alkyl ketene dimer in the resin particles is 40 parts by mass or more, preferably 45 parts by mass or more, more preferably 48 parts by mass or more, and 280 parts by mass or less, preferably 270 parts by mass or less, more preferably 260 parts by mass or less, per 100 parts by mass of amorphous polyester resin.

[0052] (Resin particles) In the resin particles of the present invention, from the viewpoint of improving the dispersion stability of the resin particles in the paper coating agent, the amorphous polyester resin is preferably a neutralized product with a basic compound. 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. Among these, the basic compound is preferably one or more selected from metallic basic compounds and nonmetallic basic compounds, and more preferably one or more selected from sodium hydroxide and ammonia.

[0053] The equivalent amount of basic compound used is preferably 30 mol% or more, more preferably 35 mol% or more, even more preferably 40 mol% or more, and preferably 100 mol% or less, more preferably 98 mol% or less, and even more preferably 96 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 × 1000 (mgKOH / mol))]} × 100 (1)

[0054] Furthermore, in the present invention, the resin particles may contain resins other than amorphous polyester resins, such as styrene-acrylic copolymers, epoxy resins, polycarbonates, polyurethanes, etc., to the extent that they do not impair the effects of the present invention. Furthermore, the resin particles according to the present invention 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 alkyl ketene dimer in the resin particles according to the present invention is preferably 80% by mass or more, more preferably 85% 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 improving the water repellency and oil resistance of the resulting coated paper.

[0055] <Method for manufacturing paper coating agent> In the present invention, the paper coating agent is preferably produced by dispersing an amorphous polyester resin and an alkyl ketene dimer in an aqueous medium. Methods for dispersing the amorphous polyester resin and alkyl ketene dimer in an aqueous medium include adding the amorphous polyester resin and alkyl ketene dimer to an aqueous medium and performing dispersion treatment using a disperser or the like, and gradually adding the aqueous medium to a solution containing the amorphous polyester resin and alkyl ketene dimer to perform phase inversion emulsification. Among these, the method of performing dispersion treatment is preferred.

[0056] In other words, the method for producing the paper coating agent of the present invention preferably comprises the following steps 1 to 3 in this order. Step 1: Dissolve the amorphous polyester resin in an organic solvent, add a basic compound to neutralize the amorphous polyester resin, add an aqueous medium to perform phase inversion emulsification, distill off the organic solvent to obtain an aqueous dispersion of amorphous polyester resin particles. Step 2: Adding and mixing an alkyl ketene dimer to an aqueous dispersion of amorphous polyester resin particles obtained in Step 1 to obtain a mixed solution. Step 3: Disperse the mixture obtained in Step 2 at a temperature above the melting point of the alkyl ketene dimer to obtain resin particles containing amorphous polyester resin and alkyl ketene dimer.

[0057] [Process 1] Step 1 is the step of obtaining an aqueous dispersion of amorphous polyester resin particles. As a method for obtaining an aqueous dispersion of amorphous polyester resin particles, a phase inversion emulsification method is preferred from the viewpoint of being able to disperse the resin particles in an aqueous medium without using a surfactant and improving the water repellency and oil resistance of the resulting coated paper.

[0058] Phase inversion emulsification is preferably performed by first dissolving an amorphous polyester resin in an organic solvent to obtain a solution of the amorphous polyester resin, then adding an aqueous medium to the solution to perform phase inversion, and then removing the organic solvent. Organic solvents for dissolving amorphous polyester resins include ketone solvents such as acetone and dialkylketones having an alkyl group with 1 to 3 carbon atoms, 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 resins and being easily removed from emulsions, dialkylketones having an alkyl group with 1 to 3 carbon atoms, such as acetone and methyl ethyl ketone, are preferred, and methyl ethyl ketone is more preferred.

[0059] If the amorphous polyester resin contains multiple types of amorphous polyester resins, the multiple types of amorphous polyester resins, or the amorphous polyester resins themselves, may be mixed beforehand before dissolving them in an organic solvent. Alternatively, these resins may be added to the organic solvent simultaneously and dissolved to obtain a solution of amorphous polyester resin. The mass ratio of the organic solvent to the amorphous polyester resin [organic solvent / 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, even more preferably 300 / 100 or less, and even more preferably 250 / 100 or less, from the viewpoint of dissolving the resin and facilitating phase inversion to an aqueous medium, and from the viewpoint of further improving the dispersion stability of the resin particle dispersion.

[0060] In the present invention, the amorphous polyester resin is preferably 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. The preferred types and amounts of basic compounds used are the same as those described for the paper coating agent.

[0061] The temperature at which an aqueous medium is added to a solution of amorphous polyester resin is preferably 10°C or higher, more preferably 15°C or higher, even more preferably 20°C or higher, and preferably 40°C or lower, more preferably 35°C or lower, and even more preferably 25°C or lower, from the viewpoint of improving the dispersion stability of the resin particle dispersion. From the viewpoint of improving the dispersion stability of the resin particle dispersion, 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 100 parts by mass / min or less, more preferably 50 parts by mass / min or less, and even more preferably 30 parts by mass / min or less, per 100 parts by mass of the resin component constituting the resin particles, until the phase inversion is completed. After the phase inversion, there are no restrictions on the addition rate of the aqueous medium after the resin particles have been obtained. From the viewpoint of improving the productivity of the resin particle dispersion, the amount of aqueous medium added is preferably 50 parts by mass or more, more preferably 100 parts by mass or more, even more preferably 150 parts by mass or more, and preferably 500 parts by mass or less, more preferably 400 parts by mass or less, and even more preferably 300 parts by mass or less, per 100 parts by mass of the resin component constituting the resin particles.

[0062] After phase inversion emulsification, it is preferable to remove the organic solvent from the aqueous dispersion obtained by phase inversion emulsification in order to improve the dispersion stability of the amorphous polyester resin particles. The removal of organic solvents is not particularly limited, and any method can be used. The resulting aqueous dispersion of amorphous polyester resin particles 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.

[0063] The solid content concentration of the aqueous dispersion of amorphous polyester resin particles 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, from the viewpoint of stabilizing the dispersibility of the particles. The solid content concentration of the aqueous dispersion is measured by the method described in the examples.

[0064] The volume median particle size (D) of amorphous polyester resin particles in an aqueous dispersion of amorphous polyester resin particles. 50 From the viewpoint of efficiently forming resin particles with alkyl ketene dimers, the particle size is preferably 50 μm or more, more preferably 60 μm or more, even more preferably 70 μm or more, and preferably 120 μm or less, more preferably 110 μm or less, and even more preferably 100 nm or less. Volume median particle size (D) of amorphous polyester resins 50 ) is measured by the method described in the examples.

[0065] [Process 2] Step 2 is a step in which an alkyl ketene dimer is added to and mixed with the aqueous dispersion of amorphous polyester resin particles obtained in Step 1 to obtain a mixed solution. From the viewpoint of improving the water repellency and oil resistance of the resulting coated paper, the alkyl ketene dimer is added in an amount of preferably 40 parts by mass or more, more preferably 45 parts by mass or more, even more preferably 48 parts by mass or more, and preferably 280 parts by mass or less, more preferably 270 parts by mass or less, and even more preferably 260 parts by mass or less, per 100 parts by mass of amorphous polyester resin.

[0066] It is preferable to add an alkyl ketene dimer to an aqueous dispersion of amorphous polyester resin particles, mix it, and then add water to the mixture to adjust the solid content concentration. The solid content concentration of the mixture is preferably 10% by mass or more, more preferably 15% by mass or more, even more preferably 18% by mass or more, and preferably 35% by mass or less, more preferably 30% by mass or less, and even more preferably 25% by mass or less, from the viewpoint of obtaining resin particles containing amorphous polyester resin and alkyl ketene dimer in the dispersion treatment of step 3.

[0067] [Step 3] Step 3 is a step in which the mixture obtained in Step 2 is dispersed at a temperature above the melting point of the alkyl ketene dimer to obtain resin particles containing amorphous polyester resin and alkyl ketene dimer. In the resin particles after dispersion, amorphous polyester resin is attached to at least a portion of the surface of the alkyl ketene dimer. In the resin particles formed by the dispersion treatment in which the hydroxyl groups of the amorphous polyester resin react with the alkyl ketene dimer, the portion derived from the amorphous polyester resin is present on the surface of the resin particles, and the portion derived from the alkyl ketene dimer is present inside the resin particles. In addition, amorphous polyester resin may be attached to the portion derived from the alkyl ketene dimer that is present near the surface of the resin particles formed by the reaction of the hydroxyl groups of the amorphous polyester resin with the alkyl ketene dimer.

[0068] From the viewpoint of improving the dispersibility of alkyl ketene dimers in the paper coating agent, homogenizers, high-pressure dispersers, and ultrasonic dispersers are preferred as dispersers used in the dispersion process, with ultrasonic dispersers being more preferred. The distribution time can be set appropriately depending on the distribution machine being used. Examples of ultrasonic dispersion machines include ultrasonic homogenizers. Commercially available models include the "US-150T," "US-300T," and "US-600T" (manufactured by Nippon Seiki Seisakusho Co., Ltd.), and the "SONIFIER4020-400" and "SONIFIER4020-800" (manufactured by Branson). Furthermore, in the present invention, the paper coating agent may be pre-dispersed in a mixing machine such as a homomixer or ball mill before using the disperser.

[0069] The temperature at which the alkyl ketene dimer and resin particles are dispersed in an aqueous medium is preferably above the melting point of the alkyl ketene dimer and 80°C or higher, more preferably 85°C or higher, even more preferably 90°C or higher, and preferably 100°C or lower.

[0070] The median particle size (D) of resin particles containing amorphous polyester resin and alkyl ketene dimer in a paper coating agent. 50 From the viewpoint of improving the water repellency and oil resistance of the resulting coated paper, the wavelength is preferably 400 nm or more, more preferably 430 nm or more, even more preferably 450 nm or more, and preferably 600 nm or less, more preferably 580 nm or less, and even more preferably 550 nm or less. The medium particle size (D) of resin particles 50 ) is measured by the method described in the examples.

[0071] The solid content concentration of the paper coating agent is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and preferably 35% by mass or less, more preferably 30% by mass or less, and even more preferably 25% by mass or less, from the viewpoint of improving the dispersibility of resin particles and facilitating handling.

[0072] The paper coating agent of the present invention may optionally contain various additives such as organic solvents, humectants, wetting agents, penetrating agents, viscosity modifiers, defoaming agents, preservatives, fungicides, rust inhibitors, pH adjusters, antioxidants, and ultraviolet absorbers. Furthermore, because surfactants have a very high affinity for water, their presence in the paper coating agent results in their inclusion in the coating layer formed when the coating is applied to the paper, leading to a decrease in water repellency. Therefore, from the viewpoint of improving the water repellency and oil resistance of the resulting coated paper, the paper coating agent of the present invention substantially does not contain surfactants. Here, "substantially contained" means that surfactants are not intentionally added, and does not exclude the possibility of small amounts of surfactants being present as impurities.

[0073] [Coated paper] The coated paper of the present invention has a coating layer containing an amorphous polyester resin and an alkyl ketene dimer. Here, the content of the alkyl ketene dimer in the coating layer is 40 parts by mass or more, preferably 45 parts by mass or more, more preferably 48 parts by mass or more, and 280 parts by mass or less, preferably 270 parts by mass or less, more preferably 260 parts by mass or less, per 100 parts by mass of amorphous polyester resin, from the viewpoint of improving the water repellency and oil resistance of the resulting coated paper. Furthermore, it is preferable that the coated paper of the present invention has a coating layer formed by the paper coating agent described above.

[0074] [Paper base material] Examples of paper substrates include uncoated papers such as fine paper, medium-quality paper, and newsprint; coated papers such as art paper, coated paper, and matte coated paper; information paper such as PPC paper; packaging paper 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 coating the paper substrate, it is preferably 10 g / m². 2 The above applies, and preferably 200 g / m². 2 More preferably, 150 g / m² 2More preferably 120 g / m² 2 The following applies:

[0075] [Amorphous polyester resin] The amorphous polyester resin contained in the coating layer can be any of the amorphous polyester resins listed above for paper coating agents, and the same applies to preferred examples. Furthermore, the coating layer may also contain other polyester resins.

[0076] [Alkylketene dimer] The alkyl ketene dimers contained in the coating layer can be those listed above for paper coating agents, and the preferred examples are similar.

[0077] [Manufacturing method for coated paper] From the viewpoint of improving the water repellency and oil resistance of the resulting coated paper, the method for manufacturing coated paper of the present invention preferably includes a step I of applying a coating liquid to at least one side of a paper substrate, and preferably includes a step II of drying the layer of coating liquid on the paper substrate coated in step I. As the paper substrate, the paper substrates listed above for coated paper can be used, and the preferred examples are the same.

[0078] [Process I] Step I is a step of applying a paper coating agent to at least one side of a paper substrate to form a layer of coating liquid. In step I, the amount of paper coating agent applied is preferably 1 g / m² in solid content, from the viewpoint of improving the water repellency and water resistance of the resulting coated paper. 2 Above, a comfortable 3g / m 2 More preferably 5 g / m 2 The above, and preferably 20 g / m² 2 More preferably 15g / m 2 More preferably 10 g / m 2 The following applies: There are no particular restrictions on the method of applying the paper coating agent to the paper substrate in step I. 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.

[0079] [Process II] Step II is the process of drying the coating liquid layer on the paper substrate coated in Step I. Examples of 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, at least one selected from forced-air drying and heat drying is preferred, and heat drying is more preferred. Heat drying methods include applying hot air to the surface of the coating liquid layer on a paper substrate to heat it, bringing a heater close to the surface of the coating liquid layer on a paper substrate to heat it, contacting a heater with the surface of the paper substrate opposite to the surface on which the coating liquid layer is formed to heat it, and heating by steam curing using high-temperature steam at normal or high pressure. The drying temperature is preferably 30°C or higher, more preferably 40°C or higher, even more preferably 50°C or higher, and even more preferably 70°C or higher, from the viewpoint of improving the water repellency and water resistance of the resulting coated paper, and preferably 150°C or lower, more preferably 120°C or lower, and even more preferably 100°C or lower, from the viewpoint of suppressing deformation of the paper substrate due to heat and reducing energy. The drying time is preferably 3 minutes or more, more preferably 5 minutes or more, from the viewpoint of improving the water repellency and water resistance of the resulting coated paper, and preferably 30 minutes or less, more preferably 15 minutes or less, from the viewpoint of suppressing deformation of the paper substrate due to heat and reducing energy. [Examples]

[0080] The present invention will be described in more detail below with reference to examples. The present invention is not limited in any way by these examples. In the following examples, each physical property was measured by the following method.

[0081] [Softening point of amorphous polyester resins] 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 extruded through a nozzle with a diameter of 1 mm and a length of 1 mm. The volume below the plunger 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.

[0082] [Glass transition temperature of amorphous polyester 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.

[0083] [Crystallization index of amorphous polyester 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 taken as the maximum endothermic peak temperature, and the crystallinity index was calculated according to the following formula. Crystallinity index = softening point (°C) / maximum endothermic peak temperature (°C)

[0084] [Acid value and hydroxyl value of amorphous polyester resins] The acid value and hydroxyl value of amorphous polyester resins were measured in accordance with JIS K0070:1992. However, the solvent used for measuring the acid value was changed from a mixed solvent of ethanol and ether to a mixed solvent of acetone and toluene [acetone:toluene = 1:1 (volume ratio)]. In addition, the solvent used for measuring the hydroxyl value was changed from a mixed solvent of ethanol and ether to tetrahydrofuran.

[0085] [Amorphous polyester resin particles and resin particle mid-volume particle size (D 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.

[0086] [Solid content concentration of amorphous polyester resin particles and paper coating agents] 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%) of the dispersion was measured. The solid content concentration was calculated according to the following formula. Solid concentration (mass%) = 100-moisture (mass%)

[0087] [Number-average molecular weight and weight-average molecular weight of amorphous polyester resins] A polyester resin was dissolved in tetrahydrofuran to a concentration of 0.5 g / 100 mL. This solution was then filtered using a fluoropolymer filter "FP-200" (manufactured by Sumitomo Electric Industries, Ltd.) with a pore size of 2 μm to remove insoluble components, and the sample solution was obtained. The column was stabilized in a 40°C constant temperature bath by flowing tetrahydrofuran as the eluent at a flow rate of 1 mL / min. 100 μL of the sample solution was then injected and measurements were performed. The number-average molecular weight and weight-average molecular weight of the sample were calculated based on a pre-prepared calibration curve. The calibration curve was based on several types of monodisperse polystyrene [monodisperse polystyrene manufactured by Tosoh Corporation; 2.63 × 10⁻⁶]. 3 , 2.06×10 4 , 1.02 × 10 5 (Weight-average molecular weight (Mw)), monodisperse polystyrene manufactured by GL Sciences Co., Ltd.; 2.10 × 10 3 , 7.00×10 3 , 5.04×10 4 It was prepared using (weight-average molecular weight (Mw)) as a standard sample. Measuring device: "CO-8010" (manufactured by Tosoh Corporation) Analysis columns: "GMHXL" + "G3000HXL" (manufactured by Tosoh Corporation)

[0088] [Melting point of alkyl ketene dimers] Using a differential scanning calorimeter "Q-100" (manufactured by T.A. Instruments Japan Co., Ltd.), 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. The peak temperature of the obtained endothermic reaction was defined as the melting point.

[0089] [Manufacturing of amorphous polyester resins] Manufacturing Example 1-1 (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. 4828 g of bisphenol A propylene oxide (2.2) adduct, 1374 g of terephthalic acid, 35 g of tin di(2-ethylhexanoate), and 3.5 g of gallic acid were added, and the mixture was heated to 235°C over 1 hour under a nitrogen atmosphere. After holding at 235°C for 5 hours, the reaction was carried out at 8.3 kPa for 1 hour. After returning to atmospheric pressure, the mixture was cooled to 180°C, and 480 g of fumaric acid, 318 g of trimellitic anhydride, and 3.5 g of 4-tert-butylcatechol were added. The mixture was then gradually heated to 210°C in 10°C increments every hour. After the reaction was carried out at 210°C for 2 hours, the mixture was further reacted at 8.3 kPa until the softening point reached the temperature shown in Table 1, yielding amorphous polyester resin A-1. The physical properties of the obtained amorphous polyester resin A-1 are shown in Table 1.

[0090] Manufacturing Example 1-2 (Manufacturing of Amorphous Polyester Resin A-2) A four-necked flask equipped with a nitrogen inlet tube, dehydration tube, stirrer, and thermocouple was purged with nitrogen. 4595 g of bisphenol A propylene oxide (2.2) adduct, 1308 g of terephthalic acid, 35 g of tin(II) di(2-ethylhexanoate), and 3.5 g of gallic acid were added, and the mixture was heated to 235°C over 1 hour under a nitrogen atmosphere. After holding at 235°C for 6 hours, the reaction was carried out at 8.3 kPa for 1 hour. After returning to atmospheric pressure, the mixture was cooled to 180°C, and 796 g of sebacic acid and 303 g of trimellitic anhydride were added. The mixture was then gradually heated to 210°C in 10°C increments every hour. After the reaction was carried out at 210°C for 1 hour, the mixture was further reacted at 13.3 kPa until the softening point reached the temperature shown in Table 1, yielding amorphous polyester resin A-2. The physical properties of the obtained amorphous polyester resin A-2 are shown in Table 1.

[0091] Manufacturing Example 1-3 (Manufacturing of Amorphous Polyester Resin A-3) The inside of a four-necked flask equipped with a nitrogen inlet tube, dehydration tube, stirrer, rectification column into which 95°C hot water was introduced, and thermocouple was purged with nitrogen. 2290g of 1,2-propanediol (1,2-PD), 4501g of terephthalic acid, 35g of tin(II) di(2-ethylhexanoate), and 3.5g of gallic acid were added, and the temperature was gradually increased from 180°C to 230°C in 10°C increments every 2 hours while stirring under a nitrogen atmosphere. After reaching 230°C, the reaction was allowed to continue for 2 hours, followed by a further reaction at 8.3kPa for 1 hour. After returning to atmospheric pressure, the reaction vessel was set to 180°C, the rectification column was removed, and 210g of fumaric acid and 3.5g of 4-tert-butylcatechol were added, and the temperature was gradually increased to 210°C in 10°C increments every 1 hour. After reacting at 210°C for 2 hours, the reaction was further carried out at 8.3 kPa until the softening point reached the temperature shown in Table 1 to obtain amorphous polyester resin A-3. The physical properties of the obtained amorphous polyester resin A-3 are shown in Table 1.

[0092] Manufacturing Example 1-4 (Manufacturing of Amorphous Polyester Resin A-4) A four-necked flask equipped with a nitrogen inlet tube, a dehydration tube, a stirrer, and a thermocouple contained 3128 g of bisphenol A propylene oxide (2.2) adduct, 726 g of bisphenol A ethylene oxide (2.2) adduct, 1539 g of terephthalic acid, and 158 g of succinic acid. The mixture was heated to 160°C over 1 hour while stirring under a nitrogen atmosphere. The mixture was then maintained at 160°C and the reaction was carried out by dropwise adding a mixture of 48 g of acrylic acid, 976 g of styrene, 214 g of 2-ethylhexyl acrylate, and 119 g of di-tert-butyl peroxide. Subsequently, 28 g of tin(II) di(2-ethylhexanoate) and 2.8 g of gallic acid were added, and the temperature was raised to 235°C over 1 hour. After holding at 235°C for 10 hours, the pressure in the flask was further reduced, and the reaction was carried out at 8.3 kPa until the softening point shown in Table 1 was reached, yielding amorphous polyester resin A-4. The physical properties of the obtained amorphous polyester resin A-4 are shown in Table 1.

[0093] Manufacturing Example 1-5 (Manufacturing of Amorphous Polyester Resin A-5) A four-necked flask equipped with a nitrogen inlet tube, dehydration tube, stirrer, and thermocouple was purged with nitrogen. 4577 g of bisphenol A propylene oxide (2.2) adduct, 977 g of terephthalic acid, 35 g of tin(II) di(2-ethylhexanoate), and 3.5 g of gallic acid were added, and the mixture was heated to 235°C over 1 hour under a nitrogen atmosphere. After holding at 235°C for 6 hours, the reaction was carried out at 8.3 kPa for 1 hour. After returning to atmospheric pressure, the mixture was cooled to 180°C, and 317 g of sebacic acid and 1130 g of trimellitic anhydride were added. The mixture was then gradually heated to 210°C in 10°C increments every hour. After the reaction was carried out at 210°C for 1 hour, the mixture was further reacted at 13.3 kPa until the softening point reached the temperature shown in Table 1, yielding amorphous polyester resin A-5. The physical properties of the obtained amorphous polyester resin A-5 are shown in Table 1.

[0094] [Table 1]

[0095] [Production of aqueous dispersions of amorphous polyester resin particles] Manufacturing Example 2-1 (Manufacturing of Dispersion E-1) In a 2L four-necked flask equipped with a reflux condenser, stirrer, and thermocouple, 100g of amorphous polyester resin A-1 was placed and mixed with 200g of methyl ethyl ketone at room temperature. The mixture was then heated to 65°C to dissolve. Next, it was cooled to room temperature, and 6.3g of 5N sodium hydroxide aqueous solution was added at room temperature and stirred for 60 minutes. Then, at room temperature, 600g of distilled water was added dropwise at a rate of 20mL / min while stirring to induce phase inversion emulsification. After that, the mixture was heated to 65°C, and the methyl ethyl ketone was removed by distillation while gradually reducing the pressure from 80kPa to 30kPa, and some of the water was further removed by distillation. After cooling to room temperature, the mixture was filtered through a 150-mesh wire mesh, and the solid content concentration was adjusted to 30% by mass with distilled water to obtain an aqueous dispersion of amorphous polyester resin particles E-1. The volume median particle size (D) of the obtained aqueous dispersion of amorphous polyester resin particles E-1 was measured. 50 ) are shown in Table 2.

[0096] Manufacturing Examples 2-2 to 2-5 (Manufacturing of aqueous dispersions E-2 to E-5 of amorphous polyester resin particles) Aqueous dispersions of amorphous polyester resin particles E-2 to E-5 were obtained in the same manner as in Production Example 2-1, except that the type and amount of amorphous polyester resin and the amount of 5N sodium hydroxide aqueous solution were changed to those shown in Table 2. The median particle size (D) of amorphous polyester resin particles in the obtained aqueous dispersions of amorphous polyester resin particles E-2 to E-5 was determined. 50 ) are shown in Table 2.

[0097] [Table 2]

[0098] Example 1 (Manufacturing of paper coating agent W-1) In a 1L beaker, 333g (100g as solid content) of aqueous particle dispersion E-1 of amorphous polyester resin particles and 250g of alkyl ketene dimer (AKD1, Solenis, AKD1840) were added. Distilled water was added to achieve a solid content concentration of 20% by mass. The mixture was then heated and stirred while maintaining the temperature at 95-100°C to melt the alkyl ketene dimer, obtaining a molten mixture. Subsequently, while maintaining the temperature at 95-100°C, the mixture was dispersed for 30 minutes using an ultrasonic homogenizer "US-600T" (Nippon Seiki Seisakusho Co., Ltd.), and then cooled to room temperature. Distilled water was added to the obtained dispersion, and the solid content concentration was adjusted again to 20% by mass to obtain paper coating agent W-1. The median particle size (D) of the resin particles in paper coating agent W-1 was measured. 50 ) are shown in Table 3.

[0099] Examples 2-10, Comparative Example 1 (Manufacturing of paper coating agents W-2-W-11) Paper coating agents W-2 to W-11 were obtained in the same manner as in Example 1, except that the type of resin particle dispersion and the type and amount of alkyl ketene dimer were changed as shown in Table 3. The median particle size (D) of the resin particles in paper coating agents W-2 to W-11 50 ) are shown in Table 3.

[0100] Comparative Example 2 (Manufacturing of paper coating agent W-12) Distilled water was added to an aqueous particle dispersion of amorphous polyester resin particles, E-1, to obtain a paper coating agent W-12, so that the solid content concentration was 20% by mass.

[0101] Comparative Example 3 (Manufacturing of Paper Coating Agent W-13) 100 g of alkyl ketene dimer (AKD1, Solenis, AKD1840) was placed in a 500 mL beaker, and 6.7 g of Neoperex G-15 (Kao Corporation) as a surfactant and 394 g of distilled water were added. The mixture was then dispersed for 30 minutes using an ultrasonic homogenizer "US-600T" (Nippon Seiki Seisakusho Co., Ltd.) while maintaining the temperature at 95-100°C, and then cooled to room temperature. Distilled water was added to the resulting dispersion, and the solid content concentration was adjusted again to 20% by mass to obtain paper coating agent W-13.

[0102] The alkyl ketene dimers shown in Table 3 are as follows: AKD1: A compound represented by formula (1), manufactured by Solenis, AKD1840, with 18 carbon atoms (catalog value), in which R 1 and R 2 Alkyl ketene dimers whose main component is an alkyl group with 18 carbon atoms and whose melting point is 47°C (catalog value). AKD2: A compound represented by formula (1), manufactured by Wilmer, AKD1865, with 18 carbon atoms (catalog value), in which R 1 and R 2 Alkyl ketene dimers whose main component is an alkyl group with 18 carbon atoms and whose melting point is 50°C (catalog value).

[0103] [Evaluation of water repellency] The paper coating agent manufactured above was applied to PPC paper "J paper" (basis weight 82 g / m²) using a bar coater (NO. 12). 2 Coated paper was produced by applying a coating amount (manufactured by Fujifilm Business Innovation Co., Ltd.) to the paper substrate and drying it in an 80°C dryer for 5 minutes. The coating amount of the paper coating agent to the paper substrate was 8 g / m² as solid content. 2 It was done in such a way. Water repellency was evaluated in accordance with JAPAN TAPPI Paper and Pulp Test Method No. 68:2000. At room temperature, a sample was tilted at a 45° angle, and a droplet of distilled water was dropped from 10 mm above the coated paper. The degree of water repellency R0 to R10 was determined by observing the state of the sample after the droplet passed over it. R0: A continuous trace showing a uniform width. R2: A continuous trace that is slightly narrower than a water droplet. R4 A continuous pattern, but broken in places, clearly showing a width narrower than a water droplet. R6: Half of the mark is wet. R7 One-quarter of the traces are wet with long, elongated water droplets. More than a quarter of the R8 traces consist of scattered spherical droplets. R9: A substance with small, spherical water droplets scattered throughout. R10 Something that rolls down completely

[0104] [Evaluation of oil resistance] Coated paper was manufactured using the same method as described above for [Evaluation of Water Repellency]. The manufactured coated paper was placed on a level surface, and a drop of castor oil was dropped onto it from 10 mm above, allowing it to stand for 3 minutes. After that, the oil drop was wiped off the coated paper, and the oil resistance level L1 to L5 was determined by observing the condition of the coated paper after wiping. L1: A stain larger than an oil droplet is visible. L2: A stain the same size as an oil droplet is visible. L3: Oil stains are visible, but they are smaller than oil droplets. L4 Slight oil stains are visible. L5 No oil stains are visible on the paper.

[0105] [Table 3]

[0106] The results in Table 3 show that the paper coating agents of Examples 1 to 10 produced coated paper with superior water repellency and oil resistance compared to the paper coating agents of Comparative Examples 1 to 3.

Claims

1. A paper coating agent comprising resin particles containing an amorphous polyester resin and an alkyl ketene dimer, A paper coating agent wherein the content of the alkyl ketene dimer is 40 parts by mass or more and 280 parts by mass or less per 100 parts by mass of the amorphous polyester resin.

2. The paper coating agent according to claim 1, wherein the hydroxyl value of the amorphous polyester resin is 1 mg KOH / g or more and 50 mg KOH / g or less.

3. The paper coating agent according to claim 1, wherein the melting point of the alkyl ketene dimer is 40°C or higher and 80°C or lower.

4. The paper coating agent according to claim 1, wherein the resin particles are dispersed in an aqueous medium.

5. Coated paper having a coating layer containing an amorphous polyester resin and an alkyl ketene dimer, Coated paper wherein the content of the alkyl ketene dimer is 40 parts by mass or more and 280 parts by mass or less per 100 parts by mass of the amorphous polyester resin.

6. A method for producing a paper coating agent according to any one of claims 1 to 4, comprising the following steps 1 to 3 in this order. Step 1: Dissolve the amorphous polyester resin in an organic solvent, add a basic compound to neutralize the amorphous polyester resin, add an aqueous medium to perform phase inversion emulsification, distill off the organic solvent to obtain an aqueous dispersion of amorphous polyester resin particles. Step 2: Adding and mixing the alkyl ketene dimer to the aqueous dispersion of amorphous polyester resin particles to obtain a mixed solution. Step 3: Disperse the mixture at a temperature above the melting point of the alkyl ketene dimer to obtain resin particles containing the amorphous polyester resin and the alkyl ketene dimer.

7. The manufacturing method according to claim 6, wherein 40 to 280 parts by mass of the alkyl ketene dimer is used with respect to 100 parts by mass of the amorphous polyester resin.

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