Paper coating agent

Abstract

To provide a paper coating agent that enables production of coated paper having superior water repellency and oil resistance, a manufacturing method for the paper coating agent, coated paper obtained using the paper coating agent, and a manufacturing method for such coated paper.SOLUTION: A paper coating agent comprises resin particles that contain an amorphous polyester resin and silica particles, the resin particles having a polydispersity index of 0.20 or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a paper coating agent and a method for producing the paper coating agent, as well as coated paper using the paper coating agent and a method for producing the coated paper. [Background technology]

[0002] Conventionally, paper laminated with plastic films such as polyethylene film and polypropylene has been used as a paper material that can be used for paper labels, packaging, and containers that require water repellency and oil resistance. However, because paper laminated with plastic films is difficult to recycle, with the recent increase in environmental awareness, polymer coating technology has been investigated as a technology that can impart water repellency and oil resistance as an alternative to lamination.

[0003] For example, Patent Document 1 describes a water-repellent composition for paper that maintains water-repellent performance and provides excellent slip resistance, the water-repellent composition comprising a film-forming resin (A) and a wax (B), wherein the solubility parameter SPA of the film-forming resin (A) is in the range of 8.3 to 9.1, the softening point of the wax (B) is in the range of 40 to 95°C, and the solids mass ratio (A):(B) of the film-forming resin (A) to the wax (B) is in the range of 99:1 to 85:15. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-52397 Summary of the Invention [Problem to be solved by the invention]

[0005] From the viewpoint of environmental impact, there is a strong demand for polymer coatings that are more recyclable than conventional lamination technology in order to improve the functionality of paper materials. However, while the water-repellent composition for paper described in Patent Document 1 exhibits water repellency, it does not sufficiently achieve oil resistance. An object of the present invention is to provide a paper coating agent capable of producing coated paper with excellent water repellency and oil resistance, a method for producing the paper coating agent, and coated paper using the paper coating agent and a method for producing the coated paper. [Means for solving the problem]

[0006] The inventors focused on providing a coating layer that suppresses contact between the paper substrate and water and / or oil, and discovered that a paper coating agent for forming the coating layer containing resin particles that contain an amorphous polyester resin and silica particles, with the polydispersity index of the resin particles being within a specific range, can solve the above-mentioned problems. The present invention relates to the following [1] to [4]. [1] A paper coating agent containing resin particles containing an amorphous polyester resin and silica particles, The polydispersity index of the resin particles is 0.20 or less. Paper coating agent. [2] A method for producing a paper coating agent, comprising the step of mixing and coalescing particles of an amorphous polyester resin with silica particles to prepare resin particles, The polydispersity index of the resin particles is 0.20 or less. A method for manufacturing paper coating agents. [3] Coated paper having a coating layer derived from the paper coating agent described in [1] on at least one side of a paper substrate. [4] A method for producing coated paper, comprising: Step I, in which the paper coating agent according to [1] is applied to at least one side of a paper substrate to form a layer of the paper coating agent; and Step II, in which the layer of the paper coating agent on the paper substrate coated in Step I is heated and dried to form a resin coating layer. [Effects of the Invention]

[0007] The present invention provides a paper coating agent that can produce coated paper with excellent water repellency and oil resistance, a method for producing the paper coating agent, and coated paper using the paper coating agent and a method for producing the coated paper. DETAILED DESCRIPTION OF THE INVENTION

[0008] The paper coating agent of the present invention is a paper coating agent containing resin particles containing an amorphous polyester resin and silica particles, and the resin particles have a polydispersity index of 0.20 or less.

[0009] [Paper coating agent] The paper coating agent of the present invention contains resin particles containing an amorphous polyester resin and silica particles, and the resin particles have a polydispersity index of 0.20 or less.

[0010] Here, the "polydispersity index" is an index that represents the width of the particle size distribution, and a smaller value indicates a narrower width of the particle size distribution. The polydispersity index of the particles in the paper coating agent is 0.20 or less, preferably 0.15 or less, and more preferably 0.12 or less, from the viewpoint of improving the water repellency and oil resistance of the resulting coated paper. The polydispersity index of the resin particles is measured by the method described in the Examples.

[0011] Furthermore, "aqueous" means that water accounts for the largest proportion of the medium. As the water in the aqueous medium, deionized water or distilled water is preferably used. The aqueous medium may further contain an organic solvent, such as aliphatic alcohols having from 1 to 4 carbon atoms, such as methanol, ethanol, and 2-propanol; ketones having from 3 to 5 carbon atoms, such as acetone and methyl ethyl ketone; and ethers, such as diethyl ether and tetrahydrofuran. From the viewpoint of environmental friendliness, 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.

[0012] The definitions of various terms used in this specification are shown below. The crystallinity of a resin is expressed by the ratio of the softening point to the maximum endothermic peak temperature measured by a differential scanning calorimeter (DSC), i.e., the crystallinity index defined as "softening point (°C) / maximum endothermic peak temperature (°C)". The term "crystalline resin" refers to a resin having a crystallinity index of 0.6 or more and 1.4 or less. The term "amorphous resin" refers to a resin in which no endothermic peak is observed by differential scanning calorimetry (DSC), or, if an endothermic peak is observed, the resin has a crystallinity index of less than 0.6 or more 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 types and ratios of raw material monomers, and production conditions (e.g., reaction temperature, reaction time, cooling rate), etc. The term "carboxylic acid component" includes not only carboxylic acids but also their anhydrides and alkyl esters having 1 to 3 carbon atoms.

[0013] According to the present invention, it is possible to provide a paper coating agent that can impart water repellency and oil resistance to paper by coating the paper. The detailed reason why the paper coating agent can simultaneously impart water repellency and oil resistance to paper is not clear, but it is thought to be as follows. Coatings made from aqueous dispersions of resins have water-repellent and oil-resistant properties, but when applied to paper, the resin is absorbed into the gaps between the paper fibers, preventing the formation of a resin coating of sufficient thickness on the paper surface. The paper coating agent of the present invention contains resin particles containing an amorphous polyester resin and silica particles, with a polydispersity index of 0.20 or less, in which the silica particles and the amorphous polyester resin are present (coalesced) within the same particle. Therefore, when the resin coating agent is applied to a paper substrate to form a resin particle coating layer, the silica particles can be uniformly distributed throughout the coating layer without uneven distribution. Therefore, the silica particles uniformly present throughout the coating layer exert a filler effect on the amorphous polyester resin, rapidly increasing the viscosity of the coating layer during heat drying, thereby suppressing the absorption of the resin into the gaps between the paper fibers and forming a coating of sufficient thickness on the paper surface. From the above, it is believed that the paper coating agent of the present invention can impart water-repellent and oil-resistant properties to paper.

[0014] [Amorphous polyester resin] The amorphous polyester resin is a resin containing a polyester resin segment that is a polycondensate of an alcohol component containing a dihydric or higher alcohol and a carboxylic acid component containing a dihydric or higher carboxylic acid, from the viewpoint of improving the water repellency and oil resistance of the resulting coated paper, and may be an unmodified polyester resin or a modified polyester resin. Examples of modified polyester resins include composite resins containing a polyester resin segment and an addition polymerization resin segment, urethane-modified polyester resins, epoxy-modified polyester resins, and silicone-modified polyester resins. Among these, the amorphous polyester resin is preferably an amorphous polyester resin or a composite resin containing a polyester resin segment and an addition polymerization resin segment.

[0015] (alcohol content) Examples of dihydric or higher alcohols include diols and trihydric or higher polyhydric alcohols. The diol includes an aromatic diol, an aliphatic diol, and an alicyclic diol. The alcohol component may be used alone or in combination of two or more.

[0016] 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).

[0017] [ka]

[0018] In the general formula (I), OR 1 , and R 2 Each O is an alkyleneoxy group, preferably each independently an alkyleneoxy group having 1 to 4 carbon atoms, more preferably an ethyleneoxy group or a propyleneoxy group, and even more preferably a propyleneoxy 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, and preferably 7 or less, more preferably 5 or less, and even more preferably 3 or less. x ORs 1 and y R 2 Each O may be the same or different.

[0019] The alkylene oxide adducts of bisphenol A may be used alone or in combination of two or more. The alkylene oxide adduct of bisphenol A is preferably at least one selected from a propylene oxide adduct of bisphenol A and an ethylene oxide adduct of bisphenol A, and more preferably a propylene oxide adduct of bisphenol A.

[0020] The aliphatic diol preferably has 2 or more carbon atoms and preferably 16 or less, more preferably 14 or less, and even more preferably 10 or less. 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, and 2,5- Examples of the 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.

[0021] Examples of alicyclic diols include cyclohexanediol, cyclohexanedimethanol, and hydrogenated bisphenol A. Examples of trihydric or higher polyhydric alcohols include glycerin, pentaerythritol, trimethylolpropane, sorbitol, and sorbitan.

[0022] Of these, from the viewpoint of improving the water repellency and oil resistance of the resulting coated paper, the alcohol component preferably contains one or more selected from aliphatic diols and aromatic diols, more preferably one or more selected from aliphatic diols having from 2 to 16 carbon atoms and alkylene oxide adducts of bisphenol A, and even more preferably one or more selected from 1,2-propanediol, ethylene oxide adducts of bisphenol A, and propylene oxide adducts of bisphenol A.

[0023] From the viewpoint of improving the water repellency and oil resistance of the resulting 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.

[0024] (carboxylic acid component) Examples of the carboxylic acid component include aromatic dicarboxylic acids, aliphatic dicarboxylic acids, alicyclic aliphatic dicarboxylic acids, and trivalent or higher polycarboxylic acids. Examples of aromatic dicarboxylic acids include phthalic acid, isophthalic acid, terephthalic acid, etc. Among these, from the viewpoint of improving the water repellency and oil resistance of the resulting coated paper, the aromatic dicarboxylic acid is preferably isophthalic acid or terephthalic acid, more preferably terephthalic acid. Examples of aliphatic dicarboxylic acids include fumaric acid, adipic acid, sebacic acid, maleic acid, azelaic acid, succinic acid, and succinic acid substituted with a hydrocarbon group having from 1 to 20 carbon atoms. Specific examples of succinic acid substituted with a hydrocarbon group having from 1 to 20 carbon atoms include dodecylsuccinic acid, dodecenylsuccinic acid, and octenylsuccinic acid. Of these, preferred aliphatic dicarboxylic acids are succinic acid, adipic acid, and fumaric acid, from the viewpoint of improving the water repellency and oil resistance of the resulting coated paper. Examples of alicyclic aliphatic dicarboxylic acids include cyclohexanedicarboxylic acid. Examples of trivalent or higher polycarboxylic acids include trimellitic acid, 2,5,7-naphthalenetricarboxylic acid, pyromellitic acid, and aconitic acid. Of these, trimellitic acid is preferred as the trivalent or higher polycarboxylic acid, from the viewpoint of improving the water repellency and oil resistance of the resulting coated paper. Of these, from the viewpoint of improving the water repellency and oil resistance of the resulting coated paper, the carboxylic acid component preferably contains an aromatic dicarboxylic acid, more preferably contains an aromatic dicarboxylic acid and one or more selected from aliphatic dicarboxylic acids and trivalent or higher polycarboxylic acids, and even more preferably contains terephthalic acid and one or more selected from succinic acid, adipic acid, and fumaric acid.

[0025] From the viewpoint of improving the water repellency and oil resistance of the resulting coated paper, the content of aromatic dicarboxylic acid in the carboxylic acid component is preferably 25 mol% or more, more preferably 30 mol% or more, even more preferably 33 mol% or more, and is preferably 100 mol% or less, more preferably 97 mol% or less, even more preferably 95 mol% or less.

[0026] From the viewpoint of improving the water repellency and oil resistance of the resulting coated paper, the total content of aromatic dicarboxylic acids and aliphatic dicarboxylic acids in the carboxylic acid component is preferably 60 mol% or more, more preferably 65 mol% or more, even more preferably 70 mol% or more, and preferably 100 mol% or less.

[0027] When the carboxylic acid component contains a trivalent or higher polycarboxylic acid, the content of the trivalent or higher 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, from the viewpoint of improving the water repellency and oil resistance of the resulting coated paper, and is preferably 35 mol% or less, more preferably 30 mol% or less, even more preferably 28 mol% or less.

[0028] The equivalent ratio (COOH groups / OH groups) of the carboxyl groups (COOH groups) of the carboxylic acid component to the hydroxyl groups (OH groups) of the alcohol component is preferably 0.7 or more, more preferably 0.8 or more, and is preferably 1.3 or less, more preferably 1.2 or less.

[0029] [Composite resin] The 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 the raw material monomer as an addition polymerized resin segment. The alcohol component and the carboxylic acid component can be the same as those described above, and preferred examples thereof are also the same.

[0030] (raw material monomer) Examples of raw material monomers for the addition polymerization resin segment include styrene-based compounds. The term "styrene-based compound" refers to unsubstituted or substituted styrene. Examples of the substituent substituted on styrene include an alkyl group having 1 to 5 carbon atoms, a halogen atom, an alkoxy group having 1 to 5 carbon atoms, a sulfonic acid group, or a salt thereof. Examples of styrene compounds include styrene, methylstyrene, α-methylstyrene, β-methylstyrene, tert-butylstyrene, chlorostyrene, chloromethylstyrene, methoxystyrene, styrenesulfonic acid, and 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 50% by mass or more, more preferably 65% ​​by mass or more, even more preferably 75% by mass or more, and preferably 100% by mass or less, more preferably 95% by mass or less, even more preferably 90% by mass or less, and still more preferably 85% by mass or less.

[0031] Examples of raw material monomers other than styrene-based compounds include (meth)acrylic acid esters such as alkyl (meth)acrylate, benzyl (meth)acrylate, and dimethylaminoethyl (meth)acrylate; olefins such as ethylene, propylene, and butadiene; halovinyl compounds 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 more preferred.

[0032] The number of carbon atoms in the alkyl group in the alkyl (meth)acrylate is preferably 1 or more, more preferably 4 or more, even more preferably 6 or more, and is preferably 24 or less, more preferably 22 or less, even more preferably 20 or less. Examples of alkyl (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, (iso)propyl (meth)acrylate, (iso- or tertiary)butyl (meth)acrylate, (iso)amyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, (iso)octyl (meth)acrylate, (iso)decyl (meth)acrylate, (iso)dodecyl (meth)acrylate, (iso)palmityl (meth)acrylate, (iso)stearyl (meth)acrylate, (iso)behenyl (meth)acrylate, etc. Among these, preferred are 2-ethylhexyl (meth)acrylate or stearyl (meth)acrylate, more preferred are 2-ethylhexyl (meth)acrylate, and even more preferred are 2-ethylhexyl acrylate. In addition, "(iso or tertiary)" and "(iso)" refer to both the presence and absence of these prefixes, and the absence of these prefixes indicates normal. In addition, "(meth)acrylic acid" refers to acrylic acid or methacrylic acid. The content of alkyl (meth)acrylate in the raw material monomers of the addition polymerization resin segment is preferably 0% by mass or more, more preferably 5% by mass or more, even more preferably 10% by mass or more, still more preferably 15% by mass or more, and preferably 50% by mass or less, more preferably 35% by mass or less, even more preferably 25% by mass or less.

[0033] The total content of the styrene compound and the (meth)acrylic acid ester 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.

[0034] The polyester resin containing the addition polymerization resin segment preferably has a polyester resin segment and a constitutional unit derived from a bireactive monomer bonded to the addition polymerization resin segment via a covalent bond. The term "structural unit derived from a bireactive monomer" refers to a unit formed by reaction of a functional group and an addition-polymerizable group of a bireactive monomer. An example of the addition polymerizable group is a carbon-carbon unsaturated bond (ethylenically unsaturated bond). Examples of the bireactive monomer include addition-polymerizable monomers having at least one functional group selected from a hydroxyl group, a carboxyl group, an epoxy group, a primary amino group, and a secondary amino group in the molecule. Among these, from the viewpoint of reactivity, the bireactive monomer is preferably an addition-polymerizable monomer having at least one functional group selected from a hydroxyl group and a carboxyl group, and more preferably an addition-polymerizable monomer having a carboxyl group. Examples of addition-polymerizable monomers having a carboxy group include acrylic acid, methacrylic acid, fumaric acid, and maleic acid. Among these, from the viewpoint of reactivity in both polycondensation reactions and addition polymerization reactions, one or more selected from acrylic acid and methacrylic acid is preferred, and acrylic acid is more preferred. When the bireactive monomer is an addition-polymerizable monomer having a carboxy group, the amount of the constitutional unit derived from the bireactive monomer is preferably 1 molar part or more, more preferably 3 molar parts or more, and preferably 15 molar parts or less, more preferably 10 molar parts or less, relative to 100 molar parts of the alcohol component of the polyester resin segment of the polyester resin containing the addition-polymerized resin segment.

[0035] The content of polyester resin segments in the polyester-based resin containing addition polymerization resin segments 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 92% by mass or less, even more preferably 90% by mass or less. The content of the addition polymerization resin segment in the polyester resin containing the addition polymerization resin segment is preferably 5% by mass or more, more preferably 8% by mass or more, even more preferably 10% by mass or more, and is preferably 35% by mass or less, more preferably 30% by mass or less, even more preferably 25% by mass or less. The content of structural units derived from bireactive monomers in a polyester resin containing an addition polymerization resin segment is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, even more preferably 0.3% by mass or more, and is preferably 2% by mass or less, more preferably 1.5% by mass or less, even more preferably 1% by mass or less. In the polyester resin containing an addition polymerization resin segment, the total content of the polyester resin segment, the addition polymerization resin segment, and the structural unit derived from a bireactive monomer 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 amounts are calculated based on the ratio of the amounts of raw material monomers, bireactive monomers, and radical polymerization initiator for the polyester resin segment and addition polymerization resin segment, and are based on the mass excluding the amount of water produced by polycondensation in the polyester resin segment, etc. When a radical polymerization initiator is used, the mass of the radical polymerization initiator is calculated by including it in the addition polymerization resin segment.

[0036] (Method for producing amorphous polyester resin) The amorphous polyester resin is preferably produced by a method including, for example, step A of polycondensing an alcohol component and a carboxylic acid component. When the amorphous polyester resin is a composite resin, it may be produced by a method including step A and step B of addition-polymerizing raw material monomers of the addition-polymerized resin segment and a bireactive monomer. In this case, step B may be performed after step A, or step A may be performed after step B, or step A and step B may be performed simultaneously. A preferred method is to subject a part of the carboxylic acid component to a polycondensation reaction in step A, then carry out step B, and then add the remainder of the carboxylic acid component, an esterification catalyst, and the like to the polymerization system to further promote the polycondensation reaction of step A and the polycondensation reaction with the carboxy group of the bireactive monomer or the constituent moiety derived from the bireactive monomer.

[0037] In step A, for example, the polycondensation of an alcohol component and a carboxylic acid component can be carried out in an inert gas atmosphere at a temperature of 120°C or higher and 250°C or lower, using an esterification catalyst, an esterification promoter, and a radical polymerization inhibitor as required.

[0038] Examples of the esterification catalyst include tin compounds such as dibutyltin oxide and tin(II) di(2-ethylhexanoate), and titanium compounds such as titanium diisopropoxybis(triethanolaminate). Examples of the esterification promoter that can be used together with the esterification catalyst include gallic acid. The amount of the esterification catalyst used is preferably 0.01 to 10 parts by mass relative to 100 parts by mass of the total amount of the alcohol component and the carboxylic acid component, which are raw material monomers for the amorphous polyester resin. The amount of the esterification promoter used is preferably 0.001 part by mass or more and 1 part by mass or less relative to 100 parts by mass of the total amount of the alcohol component and the carboxylic acid component, which are raw material monomers for the amorphous polyester resin. Furthermore, examples of the radical polymerization inhibitor include 4-tert-butylcatechol and the like. When a radical polymerization inhibitor is used, the amount of the radical polymerization inhibitor used is preferably 0.001 part by mass or more and 1 part by mass or less per 100 parts by mass of the total amount of the alcohol component and the carboxylic acid component, which are raw material monomers of the amorphous polyester resin.

[0039] A polymerization initiator such as a radical polymerization initiator may be used in the addition polymerization reaction of step B. Examples of the radical polymerization initiator include peroxides such as di-tert-butyl peroxide, persulfates such as sodium persulfate, and azo compounds such as 2,2'-azobis(2,4-dimethylvaleronitrile). When a radical polymerization initiator is used, the amount of the radical polymerization initiator used is preferably 1 part by mass or more and 20 parts by mass or less relative to 100 parts by mass of the raw material monomers of the addition polymerization resin segment. When a radical polymerization initiator is used, the temperature of the addition polymerization 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.

[0040] (Physical properties of amorphous polyester resin) From the viewpoint of improving the water repellency and oil resistance of the resulting coated paper, the softening point of the amorphous polyester resin is preferably 90°C or higher, more preferably 100°C or higher, even more preferably 105°C or higher, and is preferably 135°C or lower, more preferably 130°C or lower, even more preferably 125°C or lower. The softening point is measured by the method described in the examples. From the viewpoint of improving the water repellency and oil resistance of the resulting coated paper, the glass transition temperature of the amorphous polyester resin is preferably 40°C or higher, more preferably 45°C or higher, even more preferably 50°C or higher, and is preferably 85°C or lower, more preferably 80°C or lower, even more preferably 75°C or lower. The glass transition temperature is measured using a differential scanning calorimeter, specifically by the method described in the examples. The number average molecular weight of the amorphous polyester resin is preferably 1,000 or more, more preferably 2,000 or more, even more preferably 2,300 or more, and is preferably 4,500 or less, more preferably 4,000 or less, even more preferably 3,500 or less. The weight average molecular weight of the amorphous polyester resin is preferably 5,000 or more, more preferably 5,600 or more, even more preferably 6,000 or more, and preferably 50,000 or less, more preferably 40,000 or less, even more preferably 35,000 or less. The number average molecular weight and weight average molecular weight are measured by the method described in the Examples. From the viewpoint of improving the water repellency and oil resistance of the resulting coated paper, the acid value of the amorphous polyester resin is preferably 5 mgKOH / g or more, more preferably 10 mgKOH / g or more, even more preferably 15 mgKOH / g or more, and is preferably 45 mgKOH / g or less, more preferably 40 mgKOH / g or less, even more preferably 35 mgKOH / g or less. The acid value is measured by the method described in the Examples.

[0041] The amorphous polyester resins may be used alone or in combination of two or more. The softening point, glass transition temperature, number average molecular weight, weight average molecular weight, and acid value of the amorphous polyester resin can be appropriately adjusted by adjusting the types and amounts of raw material monomers used, as well as production conditions such as reaction temperature, reaction time, and cooling rate, and these values ​​can be determined by the methods described in the examples. When two or more amorphous polyester resins are used in combination, the softening point, glass transition temperature and acid value of the resulting mixture are preferably within the above-mentioned ranges.

[0042] In the present invention, the amorphous polyester resin is preferably substantially 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 applying the paper coating agent to the paper substrate becomes water-insoluble, thereby improving the water repellency and oil resistance. Here, "substantially water-insoluble" means that when an amorphous polyester resin that has been vacuum dried at 40°C for 12 hours and has reached a constant weight is dissolved in 100 g of water at 25°C until saturated, the amount of dissolution is less than 1 g. When the amorphous polyester resin contains acid groups, the amount of dissolution is the amount of dissolution when 100 mol % of the acid groups of the amorphous polyester resin are neutralized with sodium hydroxide. In addition, the solubility parameter (SP(cal / cm)) of amorphous polyester resins by the Fedors method was 3 ) 1 / 2 ) is 10.5 (cal / cm 3 )1 / 2 More than 12.0(cal / cm 3 ) 1 / 2 If the viscosity is less than this, the amorphous polyester resin becomes substantially water-insoluble, which is preferable.

[0043] [Silica particles] From the viewpoint of improving the water repellency and oil resistance of the resulting coated paper, the silica particles preferably have a volume average particle size (Dv) of 5 nm or more, more preferably 10 nm or more, even more preferably 15 nm or more, and even more preferably 20 nm or more, and preferably 100 nm or less, more preferably 80 nm or less, and even more preferably 50 nm or less. When two or more types of silica particles are used in combination, it is preferable that the volume average particle size (Dv) of each silica particle falls within the above range. The volume average particle size (Dv) of the silica particles is measured by the method described in the Examples. When a commercially available product is used, the value listed in the catalog may be used.

[0044] The silica particles may be silica particles derived from colloidal silica or fumed silica particles. However, from the viewpoint of achieving a volume average particle diameter (Dv) within the above range and making the volume average particle diameter (Dv) relatively uniform, silica particles derived from colloidal silica are preferred, silica particles derived from neutral and alkaline stable colloidal silica are more preferred, and silica particles derived from sodium-dispersed colloidal silica, ammonium ion-stabilized colloidal silica, and neutral stable colloidal silica are even more preferred.

[0045] Colloidal silica can be obtained by a method of obtaining an aqueous dispersion by hydrolysis of alkoxysilane, or by a method of polymerizing silica in the presence of an alkaline catalyst such as sodium hydroxide. Alternatively, commercially available colloidal silica may be used. Specific examples of commercially available colloidal silica include "CATALOID (registered trademark) SI-50" and "CATALOID (registered trademark) SI-500" manufactured by JGC Catalysts and Chemicals Co., Ltd., and "SNOWTEC (registered trademark) ST-N-40" and "SNOWTEC (registered trademark) ST-CM" manufactured by Nissan Chemical Industries, Ltd.

[0046] The silica particles may be hydrophobic silica that has been subjected to a hydrophobic treatment in order to improve the affinity with the amorphous polyester resin. Examples of hydrophobic treatment agents that hydrophobize the surfaces of silica particles include silane coupling agents and silicone oils. Examples of silane coupling agents include disilazanes such as hexamethyldisilazane (HMDS); cyclic silazanes; trimethylsilane; trimethylchlorosilane; dimethyldichlorosilane, methyltrichlorosilane, allyldimethylchlorosilane, benzyldimethylchlorosilane, methyltrimethoxysilane, methyltriethoxysilane, isobutyltrimethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, trimethylmethoxysilane, octyltriethoxysilane, hydroxypropyltrimethoxysilane, phenyltrimethoxysilane, n-octadecyltrimethoxysilane, vinyltrimethoxysilane, and vinyltrimethoxysilane. alkylsilane compounds such as 2-(2-methyl-2-phenyl)-2-methyl-1,2-dimethyl-2,3-dimethyl-1,3-dimethyl-2,4-dimethyl-1 ... Examples of the silicone oil include polydimethylsiloxane, polymethylhydrogensiloxane, polymethylphenylsiloxane, and amino-modified silicone oil. Among these, hexamethyldisilazane (HMDS), dimethyldichlorosilane (DMDS), polydimethylsiloxane, and octyltriethoxysilane (OTES) are preferred. These may be used alone or in combination of two or more.

[0047] [Resin particles] The resin particles contain an amorphous polyester resin and silica particles. Specifically, the resin particles are preferably composed of an amorphous polyester resin and silica particles, and the resin particles are preferably dispersed in an aqueous medium. Here, the form of the resin particles is not particularly limited as long as they contain at least an amorphous polyester resin and silica particles. Examples of the form of the resin particles include a particle form in which silica particles are encapsulated in an amorphous polyester resin, a particle form in which silica particles are coated on an amorphous polyester resin, and a form in which an amorphous polyester resin is adsorbed to silica particles, and mixtures of these are also included. From the viewpoint of improving the water repellency and oil resistance of the resulting coated paper, the content of the amorphous polyester resin contained in the resin particles is preferably 20% by mass or more, more preferably 25% by mass or more, even more preferably 30% by mass or more, and is preferably 80% by mass or less, more preferably 70% by mass or less, even more preferably 65% ​​by mass or less.

[0048] From the viewpoint of improving the water repellency and oil resistance of the resulting coated paper, the resin particles preferably contain 20 parts by mass or more, more preferably 30 parts by mass or more, even more preferably 40 parts by mass or more of silica particles per 100 parts by mass of amorphous polyester resin, and preferably 300 parts by mass or less, more preferably 250 parts by mass or less, even more preferably 200 parts by mass or less.

[0049] Furthermore, the resin particles may contain resins other than amorphous polyester-based resins, such as crystalline polyester-based resins, acrylic resins such as styrene-acrylic copolymers, and polyurethane resins, as long as the effects of the present invention are not impaired.

[0050] From the viewpoint of improving the water repellency and oil resistance of the resulting coated paper, the total content of the amorphous polyester resin and silica particles in the resin particles according to the present invention is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and even more preferably 95% by mass or more, and is preferably 100% by mass or less, more preferably 100% by mass.

[0051] From the viewpoint of improving the water repellency and oil resistance of the resulting coated paper, the volume average particle size (Dv) of the resin particles is preferably 20 nm or more, more preferably 40 nm or more, even more preferably 50 nm or more, still more preferably 60 nm or more, and is preferably 400 nm or less, more preferably 300 nm or less, even more preferably 200 nm or less, still more preferably 150 nm or less. The volume average particle diameter (Dv) is measured by the method described in the examples.

[0052] The difference between the volume average particle size (Dv) of the resin particles and the volume average particle size (Dv) of the silica particles is preferably 10 nm or more, more preferably 15 nm or more, even more preferably 20 nm or more, still more preferably 25 nm or more, and is preferably 350 nm or less, more preferably 300 nm or less, even more preferably 250 nm or less, and still more preferably 200 nm or less.

[0053] [Manufacturing method of paper coating agent] The method for producing a paper coating agent of the present invention includes a step of combining an amorphous polyester resin and silica particles to form resin particles. Examples of the mixing and coalescence of the amorphous polyester resin and the silica particles include a method of phase inversion emulsifying the amorphous polyester resin in an aqueous medium in the presence of silica particles, a method of mixing the amorphous polyester resin and the silica particles in an aqueous medium and irradiating them with ultrasonic waves to coalesce the amorphous polyester resin and the silica particles, etc. Among these, a method of mixing the amorphous polyester resin and the silica particles in an aqueous medium and irradiating them with ultrasonic waves to coalesce the amorphous polyester resin and the silica particles is preferred. It is also preferable to include a step of mixing the amorphous polyester resin and silica particles before coalescence. When the amorphous polyester resin and silica particles are mixed in an aqueous medium, it is preferable to mix an aqueous dispersion of the amorphous polyester resin with an aqueous dispersion of silica particles, from the viewpoint of operability and improving the water repellency and oil resistance of the resulting coated paper.

[0054] (Aqueous dispersion of amorphous polyester resin) Methods for dispersing an amorphous polyester resin in an aqueous medium include a method in which a resin containing an amorphous polyester resin is added to an aqueous medium and then subjected to a dispersion treatment using a disperser or the like, and a method in which an aqueous medium is gradually added to a solution of a resin containing an amorphous polyester resin to perform phase inversion emulsification, etc. From the viewpoint of improving the water repellency and oil resistance of the resulting coated paper, the method for dispersing an amorphous polyester resin in an aqueous medium is preferably a phase inversion emulsification method.

[0055] A preferred phase inversion emulsification method is to first dissolve a resin containing an amorphous polyester resin in an organic solvent to obtain a resin solution, then add an aqueous medium to the solution to cause phase inversion, and then remove the organic solvent. Examples of organic solvents for dissolving resins including amorphous polyester resins include ketone-based solvents such as dialkyl ketones having an alkyl group with 1 to 3 carbon atoms, such as acetone and methyl ethyl ketone; ether-based solvents such as dibutyl ether and tetrahydrofuran; ester-based solvents such as ethyl acetate and isopropyl acetate; and alkyl halide solvents such as dichloromethane and chloroform. Among these, from the viewpoint of dissolving resins including amorphous polyester resins and facilitating their removal from emulsions, preferred are dialkyl ketones having an alkyl group with 1 to 3 carbon atoms, such as acetone and methyl ethyl ketone, and more preferred is methyl ethyl ketone.

[0056] From the viewpoint of improving productivity, the mass ratio of the organic solvent to the resin including the amorphous polyester resin (organic solvent / resin) is preferably 50 parts by mass or more, more preferably 70 parts by mass or more, and even more preferably 100 parts by mass or more, per 100 parts by mass of the amorphous polyester resin, and is 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.

[0057] When the amorphous polyester resin contains an acid group, it is preferable to add an aqueous solution of a basic compound to neutralize the resin, from the viewpoint of improving the dispersion stability of the amorphous polyester resin particles in an aqueous medium and the dispersion stability of the resin particles in a paper coating agent. The basic compound includes a metal basic compound and a non-metal basic compound. Examples of the metal basic compound include alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, and potassium hydroxide. Examples of the non-metallic basic compound include ammonia and organic amine compounds. The organic amine compound contains at least one primary amino group, secondary amino group, or tertiary amino group. The organic amine compound may contain a functional group other than these amino groups. Examples of such functional groups include a hydroxyl group. Examples of the organic amine compound include primary, secondary, or tertiary aliphatic amines, and amino alcohols having at least one amino group and at least one hydroxy group, and specific examples include trimethylamine, ethylamine, diethylamine, triethylamine, and triethanolamine. The basic compounds can be used alone or in combination of two or more.

[0058] The amount of the 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. The equivalent amount of the basic compound used can be calculated by the following calculation formula (1): When the equivalent amount of the basic compound used is 100 mol % or less, it is synonymous with the degree of neutralization, and when the equivalent amount of the basic compound used in the following formula exceeds 100 mol %, 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 (mg KOH / g) × mass of amorphous polyester resin (g)] / (56.1 × 1000 (mg KOH / mol))]} × 100 (1)

[0059] The dissolution of the resin containing the amorphous polyester resin in the organic solvent and the subsequent addition of the aqueous solution of the basic compound are usually carried out at a temperature not higher than the boiling point of the organic solvent.

[0060] The temperature when adding an aqueous medium to a resin solution containing an amorphous polyester resin is preferably 10°C or higher, more preferably 20°C or higher, even more preferably 25°C or higher, and is preferably 80°C or lower, more preferably 75°C or lower.

[0061] The addition rate of the aqueous medium is preferably 0.5 parts by mass / min or more, more preferably 1 part by mass or more, and even more preferably 3 parts by mass or more, relative to 100 parts by mass of the amorphous polyester resin until the phase inversion is completed, and is 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. After the phase inversion and the amorphous polyester resin particles are obtained, there is no limitation on the addition rate of the aqueous medium. From the viewpoint of improving productivity, the amount of the aqueous medium added is preferably 50 parts by mass or more, more preferably 100 parts by mass or more, even more preferably 200 parts by mass or more, relative to 100 parts by mass of the amorphous polyester resin, and is preferably 1000 parts by mass or less, more preferably 800 parts by mass or less, even more preferably 700 parts by mass or less.

[0062] After the phase inversion emulsification, it is preferable to remove the organic solvent from the aqueous dispersion obtained by the phase inversion emulsification. The method for removing the organic solvent is not particularly limited, and any method can be used. The obtained aqueous dispersion of the amorphous polyester resin is preferably filtered through a wire mesh or the like to remove coarse particles, etc. When the organic solvent is removed, water is also reduced azeotropically together with the organic solvent, and therefore, it is preferable to add water to adjust the solids concentration.

[0063] From the viewpoint of improving the water repellency and oil resistance of the resulting coated paper, the volume average particle size (Dv) of the amorphous polyester resin particles in the aqueous dispersion of the amorphous polyester resin is preferably 20 nm or more, more preferably 40 nm or more, even more preferably 50 nm or more, and even more preferably 60 nm or more, and is preferably 400 nm or less, more preferably 300 nm or less, and even more preferably 200 nm or less. The volume average particle diameter (Dv) is measured by the method described in the examples.

[0064] From the viewpoint of dispersion stability of the aqueous dispersion of the amorphous polyester resin, the pH of the aqueous dispersion of the amorphous polyester resin is preferably 6.0 or more, more preferably 6.5 or more, even more preferably 7.0 or more, and is preferably 9.0 or less, more preferably 8.5 or less, even more preferably 8.3 or less.

[0065] From the viewpoints of dispersion stability and manufacturability of the aqueous dispersion of the amorphous polyester resin, the solids concentration of the aqueous dispersion of the amorphous polyester resin is preferably 40% by mass or less, more preferably 35% by mass or less, and is preferably 20% by mass or more, more preferably 25% by mass or more.

[0066] (Aqueous dispersion of silica particles) As the aqueous dispersion of silica particles, colloidal silica is preferred, silica particles derived from neutral and alkaline stable colloidal silica are more preferred, and silica particles derived from sodium-dispersed colloidal silica, ammonium ion-stabilized colloidal silica, and neutral stable colloidal silica are even more preferred.

[0067] The colloidal silica may be the same as those listed above in the section "Silica particles."

[0068] The solid content concentration of the colloidal silica is preferably 10% by mass or more, more preferably 15% by mass or more, and is preferably 60% by mass or less, more preferably 50% by mass or less.

[0069] The difference between the volume average particle size (Dv) of the amorphous polyester resin particles and the volume average particle size (Dv) of the silica particles is preferably 150 nm or less, more preferably 120 nm or less, even more preferably 100 nm or less, and still more preferably 85 nm or less.

[0070] 〔mixture〕 The mixing can be carried out by mixing the aqueous dispersion of the amorphous polyester resin and the aqueous dispersion of the silica particles and stirring them together. The stirring may be carried out using a dispersing machine, such as a homomixer or a ball mill.

[0071] From the viewpoint of improving the water repellency and oil resistance of the resulting coated paper, the solids concentration in the mixture of amorphous polyester resin and silica particles after mixing is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and is preferably 50% by mass or less, more preferably 40% by mass or less, even more preferably 30% by mass or less. The solid content concentration is measured by the method described in the Examples.

[0072] [Union] Coalescence of the amorphous polyester resin with the silica particles means that the amorphous polyester resin adheres to the entire or part of the surface of the silica particles. Coalescence can be achieved by subjecting an aqueous dispersion of the amorphous polyester resin and the silica particles to high-pressure dispersion, ultrasonic irradiation, or the like. From the viewpoint of improving the water repellency and oil resistance of the resulting coated paper, it is preferable to coalesce the amorphous polyester resin with the silica particles by ultrasonic irradiation.

[0073] The ultrasonic irradiation can be carried out using an ultrasonic disperser, and examples of the ultrasonic disperser include an ultrasonic homogenizer.

[0074] As the ultrasonic homogenizer, commercially available products such as "US-150T", "US-300T", and "US-600T" (manufactured by Nippon Seiki Seisakusho Co., Ltd.), SONI=FIER4020-400, and SONIFIER4020-800 (manufactured by Branson) can be used.

[0075] From the viewpoint of improving the water repellency and oil resistance of the resulting coated paper, the frequency of the ultrasonic waves is preferably 5 kHz or more, more preferably 10 kHz or more, even more preferably 15 kHz or more, and is preferably 35 kHz or less, more preferably 30 kHz or less, even more preferably 25 kHz or less. From the viewpoint of improving the water repellency and oil resistance of the resulting coated paper, the temperature during ultrasonic irradiation is preferably higher than the glass transition temperature of the amorphous polyester resin, more preferably at least 10°C higher than the glass transition temperature of the amorphous polyester resin, and even more preferably at least 20°C higher than the glass transition temperature of the amorphous polyester resin, and is preferably lower than 100°C, which is the boiling point of water. The ultrasonic irradiation time can be appropriately set depending on the ultrasonic irradiation conditions.

[0076] The coalescence of the amorphous polyester resin and the silica particles can be confirmed by analyzing the obtained resin particles using X-ray photoelectric spectroscopy (XPS, ESCA) or the like. Furthermore, the coalescence is continued until the polydispersity index of the resin particles obtained after coalescence of the amorphous polyester resin and silica particles becomes 0.20 or less, preferably 0.15 or less, and more preferably 0.12 or less. By coalescing the resin particles until the polydispersity index falls within the above range, all or almost all of the amorphous polyester resin and silica particles in the aqueous dispersion of amorphous polyester resin and silica particles coalesce to form resin particles.

[0077] After combining the amorphous polyester resin and the silica particles, the solid content concentration of the resin particles in the paper coating agent may be adjusted by adding water or the like. From the viewpoint of improving the water repellency and oil resistance of the resulting coated paper, the solid content concentration of the resin particles in 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 is preferably 50% by mass or less, more preferably 40% by mass or less, even more preferably 30% by mass or less.

[0078] The paper coating agent may contain, in addition to resin particles, particles of an amorphous polyester resin and / or silica particles. The paper coating agent may also contain various additives, such as organic solvents, humectants, wetting agents, penetrating agents, viscosity modifiers, antifoaming agents, preservatives, antifungal agents, rust inhibitors, pH adjusters, antioxidants, and ultraviolet absorbers, as needed.

[0079] From the viewpoint of improving the water repellency of the resulting coated paper, the paper coating agent preferably contains substantially no surfactant. If the paper coating agent contains substantially no surfactant, the coating layer formed by applying the paper coating agent to the paper substrate will have a low affinity for water, thereby further improving the water repellency. Here, "substantially free" means that no surfactant is intentionally added, and does not exclude the presence of a small amount of surfactant as an impurity. For example, even if the paper coating agent of the present invention contains a surfactant, the content of the surfactant is preferably 0.1% by mass or less, more preferably 0.01% by mass or less, and even more preferably 0.001% by mass or less.

[0080] The pH of the paper coating agent is preferably 6.5 or higher, more preferably 7.0 or higher, and preferably 9.5 or lower, more preferably 9.0 or lower. If necessary, a pH adjuster may be added during the production of the paper coating agent so that the pH of the paper coating agent falls within this range.

[0081] [Coated paper] The coated paper of the present invention has a coating layer derived from the above-mentioned paper coating agent containing an amorphous polyester resin and silica particles on at least one side of a paper substrate. Examples of paper substrates for coated paper include uncoated paper such as fine paper, medium-quality paper, and wood-burning paper; printing paper such as art paper, coated paper, and matte-coated paper; information paper such as PPC paper; packaging paper such as kraft paper; cardboard base paper; and paperboard such as paper container board. The basis weight of the paper substrate is not particularly limited, but from the viewpoint of the ease of handling the coated paper and the ease of applying the coating liquid to the paper substrate, it is preferably 10 g / m 2 More preferably, 30 g / m 2 More preferably, 50 g / m 2 and preferably 200 g / m 2 or less, more preferably 150 g / m 2 More preferably 120 g / m or less 2 The following is the result.

[0082] [Manufacturing method of coated paper] The method for producing coated paper of the present invention includes step I of applying the paper coating agent to at least one surface of a paper substrate to form a layer of the paper coating agent, with the aim of obtaining coated paper with excellent water repellency and oil resistance. Examples of the paper substrate include the paper substrates described above.

[0083] The amount of the paper coating agent applied in step I is preferably 1.0 g / m2 in terms of solid content, from the viewpoint of obtaining coated paper with excellent water repellency and oil resistance. 2 More preferably, 1.5 g / m 2 More preferably, 2.0 g / m 2 The amount of the paper coating agent to be applied is not particularly limited, but from the viewpoint of productivity, it is preferably 20 g / m2 Less than 15 g / m, more preferably 2 More preferably, 10 g / m or less 2 The following is the result. The method for applying the paper coating agent to the paper substrate in step I is not particularly limited, and examples include methods 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.

[0084] In order to obtain coated paper with excellent water repellency and oil resistance, the present invention further comprises a step II of heating and drying the layer of paper coating agent on the paper substrate coated in step I. This makes it possible to obtain coated paper having a resin coating layer. Examples of the heating and drying method in Step II include a method of heating by applying hot air to the surface of the paper coating agent layer on the paper substrate, a method of heating by bringing a heater close to the surface of the paper coating agent layer on the paper substrate, a method of heating by bringing a heater into contact with the side of the paper substrate opposite to the side on which the paper coating agent layer is coated, and a method of 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 coated paper with excellent water repellency and oil resistance, and is preferably 200°C or lower from the viewpoint of suppressing deformation of the paper base material due to heat and reducing energy consumption. The drying time is preferably 3 minutes or more from the viewpoint of obtaining coated paper with excellent water repellency and oil resistance, and is preferably 15 minutes or less, more preferably 10 minutes or less, from the viewpoint of suppressing deformation of the paper base due to heat and reducing energy consumption. [Example]

[0085] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. Each property value was measured and evaluated by the following methods. In the examples, room temperature means a temperature of 20°C or higher and 25°C or lower.

[0086] [Measurement method] [Softening point of resin] Using a flow tester "CFT-500D" (Shimadzu Corporation), 1 g of sample was heated at a temperature increase rate of 6°C / min, while a load of 1.96 MPa was applied by the plunger, and the sample was extruded from a nozzle 1 mm in diameter and 1 mm in length. The plunger depression distance of the flow tester was plotted against the temperature, and the temperature at which half of the sample flowed out was taken as the softening point.

[0087] [Glass transition temperature of amorphous polyester resin] Using a differential scanning calorimeter "Q-100" (manufactured by TA Instruments Japan Co., Ltd.), 0.01 to 0.02 g of sample was weighed into an aluminum pan, heated to 200 °C, and cooled to 0 °C at a rate of 10 °C / min to prepare a sample for measurement. The sample was then heated at a rate of 10 °C / min, and the calorific value was measured. The peak temperature with the largest peak area among the observed endothermic peaks was defined as the endothermic maximum peak temperature (1), and the temperature at the intersection of the extension of the baseline below the endothermic maximum peak temperature (1) and the tangent line representing the maximum slope from the rising part of the peak to the peak apex was defined as the glass transition temperature.

[0088] [Number-average molecular weight and weight-average molecular weight of amorphous polyester resin] The molecular weight distribution was measured by gel permeation chromatography (GPC) obtained by the following method, and the number average molecular weight and weight average molecular weight were determined. (1) Preparation of sample solution The sample was dissolved in tetrahydrofuran (for amorphous resins) or chloroform (for crystalline resins) at 25° C. to a concentration of 0.5 g / 100 mL. Next, this solution was filtered using a fluororesin filter "DISMIC-25JP" (manufactured by ADVANTEC) with a pore size of 0.2 μm to remove insoluble matter, and a sample solution was obtained. (2) Molecular weight measurement The following measurement equipment and analytical column were used, and tetrahydrofuran (amorphous resin) or chloroform (crystalline resin) was used as the eluent at a flow rate of 1 mL per minute. The column was stabilized in a thermostatic bath at 40°C. 100 μL of sample solution was injected into the column and the measurement was performed. The molecular weight of the sample was calculated based on a calibration curve prepared in advance. The calibration curve used here included several types of monodisperse polystyrene "A-500" (5.0 × 10 2 ), "A-1000" (1.01 x 10 3 ), "A-2500" (2.63 x 10 3 ), "A-5000" (5.97 x 10 3 ), "F-1" (1.02 x 10 3 ), "F-2" (1.81 x 10 4 ), "F-4" (3.97 x 10 4 ), "F-10" (9.64 x 10 4 ), "F-20" (1.90 x 10 5 ), "F-40" (4.27 x 10 5 ), "F-80" (7.06 x 10 5 ), "F-128" (1.09 x 10 6 ) (all manufactured by Tosoh Corporation) were used as standard samples. Measuring device: "HLC-8220CPC" (Tosoh Corporation) Analytical column: "GMHXL" + "G3000HXL" (manufactured by Tosoh Corporation)

[0089] [Acid value of amorphous polyester resin] Measurement was performed in accordance with JIS K0070, except that the measurement solvent was a mixed solvent of acetone and toluene (acetone:toluene=1:1 (volume ratio)).

[0090] [Crystallinity index of amorphous polyester resin] Using a differential scanning calorimeter "Q-100" (TA Instruments Japan), 0.01-0.02 g of sample was weighed into an aluminum pan and cooled to 0°C at a rate of 10°C / min. The sample was then left to stand for 1 minute, after which it was heated to 180°C at a rate of 10°C / min and the calorific value was measured. The temperature of the peak with the largest area among the observed endothermic peaks was taken as the endothermic maximum peak temperature (2), and the crystallinity index was calculated according to the following formula: Crystallinity index = softening point (°C) / maximum endothermic peak temperature (2) (°C)

[0091] [Volume average particle size (Dv) of silica particles and resin particles, and polydispersity index of resin particles in paper coating agent] The volume average particle diameter Dv was measured using the following measuring device and under the following measuring conditions. Measurement equipment: Zeta potential and particle size measurement system "ELSZ-2" (Otsuka Electronics Co., Ltd.) Measurement conditions: Cumulant analysis. The particle concentration to be measured is approximately 5 × 10 -3 An aqueous dispersion diluted with water to a mass % was placed in a measurement cell, and the temperature was 25°C, the number of accumulations was 100, and the refractive index of water (1.333) was entered as the refractive index of the dispersion solvent.

[0092] [Solid content concentration] Using a heat-drying moisture meter "FD-230" (Kett Electric Laboratory Co., Ltd.), 5 g of the measurement sample was dried at a drying temperature of 150°C (monitoring time 2.5 minutes / fluctuation range 0.05%), and the moisture content (mass%) of the aqueous dispersion was measured. The solid content was calculated according to the following formula. Solid content concentration (mass%) = 100-moisture (mass%)

[0093] [Resin manufacturing] Production Example 1-1 (Production of amorphous polyester resin A-1) A four-neck flask equipped with a nitrogen inlet tube, a dehydration tube, a stirrer, and a thermocouple was purged with nitrogen. 4828 g of propylene oxide (2.2) adduct of bisphenol A, 1374 g of terephthalic acid, 35 g of tin(II) di(2-ethylhexanoate), and 3.5 g of gallic acid were added. The mixture was heated to 235°C under a nitrogen atmosphere with stirring. After maintaining the temperature at 235°C for 5 hours, the pressure in the flask was further reduced and the reaction was carried out at 8.3 kPa for 1 hour. After returning the pressure to atmospheric pressure, the mixture was cooled to 180°C. 480 g of fumaric acid, 318 g of trimellitic anhydride, and 3.5 g of 4-tert-butylcatechol were added. The mixture was then heated in steps of 10°C per hour to 210°C. After the temperature reached 210°C, the reaction was continued for 2 hours, and then the pressure inside the flask was further reduced to 8.3 kPa and the reaction was continued until the softening point reached the temperature shown in Table 1, thereby obtaining amorphous polyester resin A-1. The physical properties of the obtained amorphous polyester resin A-1 are shown in Table 1.

[0094] Production Example 1-2 (Production of amorphous polyester resin A-2) A four-neck flask equipped with a nitrogen inlet tube, a dehydration tube, a stirrer, a rectification column containing 95°C hot water, and a thermocouple was purged with nitrogen. 2290 g of 1,2-propanediol, 4501 g of terephthalic acid, and 35 g of tin(II) di(2-ethylhexanoate) were added. The mixture was heated in steps of 10°C every 2 hours from 180°C to 230°C under a nitrogen atmosphere with stirring. After reaching 230°C, the reaction was continued for 2 hours. The pressure in the flask was then further reduced and the reaction continued for 1 hour at 8.3 kPa. The mixture was cooled to 180°C, the rectification column was removed, and 210 g of fumaric acid and 3.5 g of 4-tert-butylcatechol were added. The mixture was then heated in steps of 10°C every 1 hour to 210°C. After the temperature reached 210°C, the reaction was continued for 2 hours, and then the pressure inside the flask was further reduced to 8.3 kPa and the reaction was continued until the softening point reached the temperature shown in Table 1, thereby obtaining amorphous polyester resin A-2. The physical properties of the obtained amorphous polyester resin A-2 are shown in Table 1.

[0095] Production Example 1-3 (Production of amorphous polyester resin A-3) The inside of a four-neck flask equipped with a nitrogen inlet tube, a dehydration tube, a stirrer, and a thermocouple was replaced with nitrogen, and 3128 g of a propylene oxide (2.2) adduct of bisphenol A, 726 g of an ethylene oxide (2.2) adduct of bisphenol A, 1539 g of terephthalic acid, and 158 g of succinic acid were added, and the temperature was raised to 160°C with stirring under a nitrogen atmosphere. Thereafter, the temperature was maintained at 160°C, and a mixture of 976 g of styrene, 214 g of 2-ethylhexyl acrylate, 48 g of acrylic acid, and 119 g of di-tert-butyl peroxide was added dropwise to the flask to carry out a reaction. Thereafter, 28 g of tin(II) di(2-ethylhexanoate) was added, and the temperature was raised to 235°C over 8 hours. After maintaining the temperature at 235°C for 10 hours, the pressure inside the flask was further reduced and the reaction was continued at 8.3 kPa 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.

[0096] Production Example 1-4 (Production of amorphous polyester resin A-4) A four-neck flask equipped with a nitrogen inlet, dehydration tube, stirrer, and thermocouple was purged with nitrogen. 4819 g of propylene oxide (2.2) adduct of bisphenol A, 686 g of terephthalic acid, 13.6 g of tin(II) di(2-ethylhexanoate), and 1.4 g of gall were added. The mixture was heated to 235°C under a nitrogen atmosphere with stirring. After maintaining the temperature at 235°C for 3 hours, the pressure inside the flask was further reduced and the reaction was continued at 8.3 kPa for 1 hour. The pressure was then returned to atmospheric pressure, cooled to 180°C, and 704 g of adipic acid and 582 g of trimellitic anhydride were added. The temperature was then increased in steps of 10°C per hour to 210°C. After reaching 210°C, the reaction was continued for 2 hours. The pressure inside the flask was further reduced and the reaction continued at 8.3 kPa until the softening point reached the temperature shown in Table 1, yielding amorphous polyester resin A-4. The physical properties of the obtained amorphous polyester resin A-4 are shown in Table 1.

[0097] [Table 1]

[0098] [Production of aqueous dispersion of amorphous polyester resin] Production Example 2-1 (Aqueous Dispersion E-1 of Amorphous Polyester Resin) 100 g of amorphous polyester resin A-1 was placed in a four-neck flask equipped with a reflux condenser, a stirrer (Three-One Motor BL300, manufactured by Shinto Scientific Co., Ltd.), and a thermocouple, and mixed with 200 g of methyl ethyl ketone at 30°C to dissolve the resin. Next, 6.3 g of a 5N aqueous solution of sodium hydroxide was added, and the mixture was stirred for 60 minutes. Next, 600 g of deionized water was added dropwise at a rate of 20 mL / min while stirring at 30°C, resulting in phase inversion emulsification of the amorphous polyester resin A-1. The temperature was then raised to 65°C, and while maintaining the temperature at 65°C, the pressure was gradually reduced from 80 kPa to 30 kPa to distill off the methyl ethyl ketone, and then some of the water was distilled off. After cooling to room temperature, the mixture was filtered through a 150-mesh wire screen and the solids concentration was adjusted to 30% by mass with deionized water to obtain an aqueous dispersion of the amorphous polyester resin E-1. The volume-average particle size (Dv) of the polyester resin particles in the resulting aqueous dispersion and the pH of the aqueous dispersion are shown in Table 2.

[0099] Production Examples 2-2 to 2-8 (Aqueous Dispersions E-2 to E-8 of Amorphous Polyester Resin) Aqueous dispersions E-2 to E-8 of amorphous polyester resins were produced in the same manner as in Production Example 2-1, except that the types and amounts of the amorphous polyester resins and basic compounds were changed as shown in Table 2.

[0100] [Table 2]

[0101] Example 1 (Production of Paper Coating Agent 1) Colloidal silica (JGC Catalysts and Chemicals Co., Ltd., Cataloid SI-50, solids content 48% by mass, silica particle volume average particle diameter (Dv) 25 nm, sodium-dispersed colloidal silica) was added to a 1-L beaker so that the silica particle mass was 100 g, and then aqueous dispersion E-5 of amorphous polyester resin was added to the mixture so that the amorphous polyester resin A-4 mass was 100 g. Deionized water was then added to the mixture so that the solids content was 20%. The mixture was stirred while maintaining the temperature at 95-100°C to mix the amorphous polyester resin and silica particles. The polydispersity index of the mixture of amorphous polyester resin and silica particles was measured and found to be 0.30. The mixture was then dispersed for 60 minutes using an ultrasonic homogenizer "US-600T" (Nippon Seiki Seisakusho Co., Ltd.) while maintaining the temperature at 95-100°C to combine the amorphous polyester resin and silica particles, and then cooled to room temperature. Deionized water was added to the resulting dispersion to adjust the solid concentration to 20% by mass, thereby obtaining paper coating agent 1. The volume average particle size (Dv) of the resin particles in the resulting paper coating agent 1 is shown in Table 3. The polydispersity index of the particles in Paper Coating Agent 1 was measured and found to be 0.07, which suggests that the amorphous polyester resin and silica particles in the mixture had almost completely coalesced.

[0102] Examples 2 to 21 (Paper Coating Agents 2 to 21) Paper coating agents 2 to 21 were obtained in the same manner as in Example 1, except that the type of aqueous dispersion of amorphous polyester resin and the type and amount of silica particles were changed as shown in Table 3. The volume average particle size (Dv) and polydispersity index of the resin particles in the obtained paper coating agents 2 to 21 are shown in Table 3.

[0103] Comparative Example 1 (Paper Coating Agent C1) The process up to mixing the amorphous polyester resin and silica particles was carried out in the same manner as in Example 1, and the resulting mixture was designated as paper coating agent C1. The volume average particle size (Dv) and polydispersity index of the particles in the resulting paper coating agent C1 are shown in Table 3.

[0104] The colloidal silica used in Examples 1 to 21 and Comparative Example 1 is as follows. SI-550: Sodium-dispersed alkaline colloidal silica "Cataloid SI-550" (solid content 20% by mass, silica particle volume average diameter (Dv) 5 nm, manufactured by JGC Catalysts and Chemicals Co., Ltd.) SI-30: Sodium-dispersed alkaline colloidal silica "Cataloid SI-30" (solid content 30% by mass, silica particle volume average diameter (Dv) 11 nm, manufactured by JGC Catalysts and Chemicals Co., Ltd.) SI-40: Sodium-dispersed alkaline colloidal silica "Cataloid SI-40" (solid content 40% by mass, silica particle volume average diameter (Dv) 18 nm, manufactured by JGC Catalysts and Chemicals Co., Ltd.) SI-50: Sodium-dispersed alkaline colloidal silica "Cataloid SI-50" (solid content 48% by mass, silica particle volume average diameter (Dv) 25 nm, manufactured by JGC Catalysts and Chemicals Co., Ltd.) SI-45P: Sodium-dispersed alkaline colloidal silica "Cataloid SI-45P" (solid content 40% by mass, silica particle volume average particle size (Dv) 45 nm, manufactured by JGC Catalysts and Chemicals Co., Ltd.) SI-80P: Sodium-dispersed alkaline colloidal silica "Cataloid SI-80P" (solid content 40% by mass, silica particle volume average diameter (Dv) 80 nm, manufactured by JGC Catalysts and Chemicals Co., Ltd.) SI-20L: Sodium-dispersed alkaline colloidal silica "Cataloid SI-20L" (solid content 20% by mass, silica particle volume average particle size (Dv) 15 nm, manufactured by JGC Catalysts and Chemicals Co., Ltd.) SI-30H: Sodium-dispersed alkaline colloidal silica "Cataloid SI-30H" (solid content 30% by mass, silica particle volume average diameter (Dv) 15 nm, manufactured by JGC Catalysts and Chemicals Co., Ltd.) ST-N-40: Ammonia ion-stabilized alkaline colloidal silica "Snowtec ST-N-40" (solid content 40% by mass, silica particle volume average diameter (Dv) 22 nm, manufactured by Nissan Chemical Industries, Ltd.) ST-CM: Neutral stable colloidal silica "Snowtec ST-CM" (solid content 30% by mass, silica particle volume average diameter (Dv) 22 nm, manufactured by Nissan Chemical Industries, Ltd.)

[0105] [Table 3-1]

[0106] [Table 3-2]

[0107] <Manufacturing of coated paper> (Process 1) The paper coating agents produced in the examples and comparative examples were applied to PPC paper "J paper" (basis weight 82 g / m) using a bar coater (No. 6). 2 The coating was applied to a paper substrate at a solid content of 3 g / m2. 2 It was done so that it would be like this. (Process 2) The paper coating layer on the paper substrate was then dried in a dryer at 80°C for 5 minutes to obtain coated papers with a layer of resin particles on one side of the paper substrate. The water repellency and oil resistance of each of the resulting coated papers were evaluated using the following methods. The evaluation results are shown in Table 4.

[0108] [Water repellency evaluation] Water repellency was evaluated in accordance with JAPAN TAPPI Paper and Pulp Testing Method No. 68:2000. At room temperature, coated paper was tilted at a 45° angle, and a droplet of deionized water was dropped from 10 mm above the coated paper. The appearance of the coated paper after the droplet had passed over it was visually inspected and the water repellency rating was determined as follows: R0 to R10, where R10 is the highest water repellency rating and R0 is the lowest. [Water repellency] R10: Completely rolls down R9: Small spherical droplets scattered here and there R8: More than 1 / 4 of the mark is made up of scattered spherical droplets R7: 1 / 4 of the mark is wetted by elongated water droplets R6: Half of the mark is wet R4: A continuous mark that is broken in places and clearly shows a width narrower than that of a water droplet R2: A continuous mark with a width slightly narrower than that of a water droplet R0: Continuous marks of uniform width

[0109] [Evaluation of oil resistance] Coated paper was placed on a horizontal table, and a drop of castor oil was dropped from 10 mm above the paper and allowed to stand for 30 seconds. The oil drop was then wiped off, and the condition of the paper after wiping was visually inspected and oil resistance was assessed using the following criteria. L5 was rated as the highest oil resistance, and L1 was rated as the lowest. 〔Judgment criteria〕 L5: No oil stains are visible on the paper. L4: Slight oil stains are visible. L3: Oil stains are visible, but the size of the stains is smaller than an oil droplet. L2: A stain the same size as an oil droplet is observed. L1: Stains larger than oil droplets are observed.

[0110] [Table 4]

[0111] Table 4 shows that the paper coating agents of Examples 1 to 21 can provide coated paper with excellent water repellency and oil resistance. On the other hand, the coated paper obtained using the paper coating agent of Comparative Example 1, which was a mixture of only amorphous polyester resin and silica particles, did not have water repellency and was poor in oil resistance. [Industrial Applicability]

[0112] According to the present invention, coated paper having a coating layer with excellent water and oil repellency can be obtained, and can be used for paper labels, packaging paper, paper containers, etc. that require resistance to water and oil.

Claims

1. A paper coating agent containing resin particles containing an amorphous polyester resin and silica particles, The polydispersity index of the resin particles is 0.20 or less. Paper coating agent.

2. 2. The paper coating agent according to claim 1, wherein the resin particles contain 20 parts by mass or more and 300 parts by mass or less of the silica particles per 100 parts by mass of the amorphous polyester resin.

3. 3. The paper coating agent according to claim 1, wherein the surfactant content is 0.1% by mass or less.

4. 3. The paper coating agent according to claim 1, wherein the amorphous polyester resin is water-insoluble.

5. A method for producing a paper coating agent, comprising a step of combining particles of an amorphous polyester resin and silica particles to form resin particles, The polydispersity index of the resin particles is 0.20 or less. A method for manufacturing paper coating agents.

6. The method for producing a paper coating agent according to claim 5, wherein the coalescence is carried out by irradiation with ultrasonic waves.

7. 7. The method for producing a paper coating agent according to claim 5, wherein the silica particles are neutral and alkaline stable colloidal silica particles.

8. a step of mixing an aqueous dispersion of amorphous polyester resin particles and an aqueous dispersion of silica particles before the coalescence; 7. The method for producing a paper coating agent according to claim 5, wherein the difference between the volume average particle size (Dv) of the amorphous polyester resin particles and the volume average particle size (Dv) of the silica particles is 150 nm or less.

9. A coated paper having a coating layer made from the paper coating agent according to claim 1 on at least one side of a paper substrate.

10. 3. A method for producing coated paper, comprising: Step I: applying the paper coating agent according to claim 1 or 2 to at least one side of a paper substrate to form a layer of the paper coating agent; and Step II: heating and drying the layer of the paper coating agent on the paper substrate coated in Step I to form a resin coating layer.