Resin particle aqueous dispersion for paper coating

Abstract

To provide a resin particle aqueous dispersion for paper coating that can produce coated paper with excellent water repellency and oil resistance, a coating solution for paper containing the aqueous resin particle dispersion, and coated paper using the coating solution.SOLUTION: This invention relates to a resin particle aqueous dispersion for paper coating which contains an amorphous polyester resin and polyvinyl alcohol, wherein the mass ratio of the amorphous polyester resin to the polyvinyl alcohol in the aqueous resin particle dispersion (amorphous polyester resin / polyvinyl alcohol) is 50 / 50 or more and 90 / 10 or less. The present invention also provides a method for manufacturing the resin particle aqueous dispersion, a paper coating solution containing the resin particle aqueous dispersion, coated paper having a coating layer formed by the paper coating solution, and a method for manufacturing the coated paper.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an aqueous resin particle dispersion for paper coating, a paper coating fluid containing the aqueous resin particle dispersion, coated paper using the coating fluid, and a method for producing the coated paper. [Background technology]

[0002] Conventionally, paper materials that can be used for paper labels, wrapping paper, paper containers, etc. that require resistance to water and oil have been made by laminating plastic films such as polyethylene films and polypropylene films to impart water resistance, water repellency, and oil resistance. However, paper laminated with plastic films is difficult to recycle. Therefore, with the recent increase in environmental awareness, there has been a demand for and has been studied to develop a technology to impart water resistance, water repellency, and oil resistance as an alternative to lamination.

[0003] For example, Patent Document 1 describes an oil-resistant film that provides an oil-resistant substrate with excellent oil resistance not only in the flat part of a packaging body but also in the folded part, the oil-resistant film comprising polymer particles containing a polyvinyl alcohol-based polymer and a polymer having a glass transition temperature of 40° C. or lower, the content of the polymer particles being 1 part by mass or more and less than 150 parts by mass per 100 parts by mass of the polyvinyl alcohol-based polymer. Patent Document 2 describes a waterproof paper that can achieve moisture conditioning by being coated with resin and can prevent water droplets from accumulating even when packaging moist items. The waterproof paper comprises a paper base material and a resin layer formed by coating on the paper base material, and the resin layer contains a water-resistant agent made of a polyester-based resin and a moisture-conditioning agent made of inorganic particles and / or a water-absorbent resin. Patent Document 3 describes a non-fluorine-based grease-resistant paper for food that has good printability, little food sticking, and excellent oil resistance on both sides, and is characterized in that the paper has oil-resistant layers on both sides of a pulp-based base material and has a pattern printed on one side of the oil-resistant layer, the oil-resistant layer containing a water-soluble resin and a water-insoluble resin, and the oil-resistant layer provided on the side opposite the side with the pattern printed contains a water-repellent agent. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2020 / 130131 [Patent Document 2] JP 2005-113283 A [Patent Document 3] JP 2014-136840 A Summary of the Invention [Problem to be solved by the invention]

[0005] As an alternative to plastic film lamination treatment, a treatment using a fluorine-based coating liquid is known as a technique for imparting water repellency and oil resistance to paper, but in recent years, from the viewpoint of safety and environmental consideration, a non-fluorine-based coating liquid has been required. However, the techniques of Patent Documents 1 to 3 could not obtain sufficient water repellency and oil resistance like paper laminated with a plastic film. An object of the present invention is to provide an aqueous dispersion of resin particles for paper coating, which can provide coated paper having excellent water repellency and oil resistance, a paper coating fluid containing the aqueous dispersion of resin particles, and coated paper using the coating fluid. [Means for solving the problem]

[0006] The inventors focused on providing a coating layer that suppresses contact between paper and water, and discovered that the above-mentioned problem can be solved by using an aqueous resin particle dispersion containing an amorphous polyester resin and polyvinyl alcohol as the aqueous resin particle dispersion for forming the coating layer, and by setting the mass ratio of the amorphous polyester resin to the polyvinyl alcohol within a specific range. The present invention relates to the following [1] to [5]. [1] An aqueous dispersion of resin particles for paper coating, comprising an amorphous polyester resin and polyvinyl alcohol, wherein the mass ratio of the amorphous polyester resin to the polyvinyl alcohol (amorphous polyester resin / polyvinyl alcohol) in the aqueous dispersion of resin particles is 50 / 50 or more and 90 / 10 or less. [2] A method for producing the aqueous dispersion of resin particles for paper coating according to the above [1], comprising either the following method (i) or method (ii): Method (i): A method in which a resin containing an amorphous polyester resin is dispersed in an aqueous medium and then mixed with polyvinyl alcohol. Method (ii): A method in which polyvinyl alcohol is dissolved in an aqueous medium, and then a resin containing an amorphous polyester resin is dispersed in the aqueous medium. [3] A paper coating liquid containing the resin particle aqueous dispersion according to [1] above. [4] A coated paper having a coating layer formed from the paper coating liquid described in [3] above. [5] A method for producing coated paper, comprising step 1 of coating at least one side of a paper substrate with the paper coating liquid described in [3] above, and step 2 of drying the paper coating liquid on the paper substrate coated in step 1. Effect of the Invention

[0007] The present invention can provide an aqueous resin particle dispersion for paper coating that can produce coated paper with excellent water repellency and oil resistance, a paper coating fluid containing the aqueous resin particle dispersion, and coated paper using the coating fluid. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] [Resin particle water dispersion for paper coating] The aqueous dispersion of resin particles for paper coating of the present invention (hereinafter also simply referred to as "aqueous dispersion of resin particles") is an aqueous dispersion of resin particles for paper coating containing an amorphous polyester resin and polyvinyl alcohol, in which the mass ratio of the amorphous polyester resin to the polyvinyl alcohol (amorphous polyester resin / polyvinyl alcohol) in the aqueous dispersion of resin particles is 50 / 50 or more and 90 / 10 or less.

[0009] The resin particle aqueous dispersion of the present invention contains an amorphous polyester resin and polyvinyl alcohol. The resin particle aqueous dispersion of the present invention preferably contains an amorphous polyester resin as resin particles, and polyvinyl alcohol is preferably dissolved in an aqueous medium. Furthermore, the resin particle aqueous dispersion of the present invention is more preferably such that resin particles containing a polyester resin are dispersed in an aqueous medium in which polyvinyl alcohol is dissolved. Here, "aqueous-based" means that water accounts for the largest proportion of the medium. As the water in the aqueous medium, deionized water, ion-exchanged water or distilled water is preferably used. The aqueous medium may further contain an organic solvent, such as aliphatic alcohols having 1 to 4 carbon atoms, such as methanol, ethanol, and 2-propanol, ketones having 3 to 5 carbon atoms, such as acetone and methyl ethyl ketone, and ethers, such as diethyl ether and tetrahydrofuran, which are water-soluble. 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, further preferably 80% by mass or more, and preferably 100% by mass or less.

[0010] The definitions of various terms used in this specification are given below. The crystallinity of a resin is represented 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 endothermic 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 the raw material monomers, and the 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 their alkyl esters having from 1 to 3 carbon atoms. In other words, when only the name of a carboxylic acid is mentioned in this specification, it is understood that the description also includes the anhydrides and alkyl esters of the carboxylic acid having from 1 to 3 carbon atoms.

[0011] According to the present invention, it is possible to provide a resin particle aqueous dispersion that can impart water repellency and oil resistance to paper by coating the paper. Although the detailed reason why the water repellency and oil resistance can be simultaneously imparted to the paper by this is not clear, it is thought to be as follows. Generally, as an aqueous dispersion capable of imparting water repellency to paper, an aqueous dispersion in which a hydrophobic material having crystallinity, such as an acrylic resin, a polyurethane resin, or wax, is dispersed is known. However, although these materials can impart water repellency to paper, it is not sufficient, and in addition, since they are hydrophobic, they have affinity for oil, so it is difficult to impart oil resistance to paper. On the other hand, as a method for imparting oil resistance to paper, it is known to treat paper with a water-soluble substance such as starch. However, since these materials are hydrophilic, they can impart oil resistance, but they cannot impart water repellency. The present invention has realized both water repellency and oil resistance by forming a resin particle aqueous dispersion containing a relatively polar but non-water-soluble amorphous polyester resin as the main component and further containing water-soluble polyvinyl alcohol. In the coating layer formed by applying the resin particle aqueous dispersion of the present invention to paper, the polyvinyl alcohol having a large number of hydroxyl groups is oriented on the interface side with the paper, and the relatively hydrophobic amorphous polyester resin is oriented on the surface side to form a coating layer. This coating layer is strong because the relatively polar amorphous polyester resin and the polyvinyl alcohol have high affinity, and it is believed that the coating layer can be maintained on the paper surface without dissolving each resin in water and oil. From the above, it is believed that the resin particle aqueous dispersion of the present invention can impart both water repellency and oil resistance to paper.

[0012] In the present invention, the mass ratio of the amorphous polyester resin to the polyvinyl alcohol in the resin particle aqueous dispersion (amorphous polyester resin / polyvinyl alcohol) is from 50 / 50 to 90 / 10. By having the mass ratio within the above range, a stronger coating layer can be formed, and the resulting coated paper can be endowed with both water repellency and oil resistance. From the viewpoint of improving the water repellency and oil resistance of the resulting coated paper, the mass ratio (amorphous polyester resin / polyvinyl alcohol) is preferably 55 / 45 or more, more preferably 60 / 40 or more, and is preferably 85 / 15 or less, more preferably 80 / 20 or less.

[0013] (Amorphous polyester resin) The amorphous polyester resin contains 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. There is no particular limitation as long as it contains a polycondensate of an alcohol component containing a dihydric or higher alcohol and a carboxylic acid component containing a dihydric or higher carboxylic acid, and examples of the resin include a polyester resin made of a polycondensate and a modified polyester resin. Examples of the modified polyester resin include a composite resin containing a polyester resin segment and an addition polymerization resin segment, a urethane modified polyester resin, and an epoxy modified polyester resin. Among these, the amorphous polyester resin is preferably an amorphous polyester resin 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.

[0014] [Alcohol content] The dihydric or higher alcohol includes diols and trihydric or higher polyhydric alcohols. The diol includes an aliphatic diol, an aromatic diol, and an alicyclic diol. The alcohol component may be used alone or in combination of two or more.

[0015] The aliphatic diol preferably has 2 or more carbon atoms, and preferably has 16 or less, more preferably 14 or less, and further preferably 10 or less. Examples of the aliphatic diol include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 2,3-butanediol, 1,4-butanediol, 1,2-pentanediol, 1,4-pentanediol, 1,5-pentanediol, 2,4-pentanediol, 1,2-hexanediol, 1,5-hexanediol, 2,5- Examples of aliphatic diols include hexanediol, 1,6-hexanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,12-dodecanediol, 1,14-tetradecanediol, 1,16-hexadecanediol, 3,3-dimethyl-1,2-butanediol, 2,2-dimethyl-1,3-propanediol, and 3-methyl-1,5-pentanediol.

[0016] The aromatic diol may, for example, be an alkylene oxide adduct 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 is 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 is preferably 7 or less, more preferably 5 or less, and further preferably 3 or less. x ORs 1 and y R 2Each O may be the same or different, but is preferably the same from the viewpoint of improving the adhesion of the coating layer to the paper substrate to be formed.

[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] Examples of the alicyclic diol include cyclohexanediol, cyclohexanedimethanol, and hydrogenated bisphenol A. Examples of the trihydric or higher polyhydric alcohol include glycerin, pentaerythritol, trimethylolpropane, sorbitol, and sorbitan.

[0021] 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 contains 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 contains one or more selected from 1,2-propanediol and propylene oxide adducts of bisphenol A.

[0022] From the viewpoint of improving the water repellency and oil resistance of the resulting coated paper, the diol content in the alcohol component is preferably 60 mol% or more, more preferably 80 mol% or more, even more preferably 90 mol% or more, still more preferably 95 mol% or more, and preferably 100 mol% or less.

[0023] [Carboxylic Acid Component] Examples of the carboxylic acid component include aromatic dicarboxylic acids, aliphatic dicarboxylic acids, and polycarboxylic acids having three or more carboxylic 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, and more preferably terephthalic acid. Examples of the aliphatic dicarboxylic acid include linear, branched, or alicyclic aliphatic dicarboxylic acids such as fumaric acid, adipic acid, sebacic acid, maleic acid, azelaic acid, succinic acid, succinic acid substituted with a hydrocarbon group having from 1 to 20 carbon atoms, and cyclohexanedicarboxylic acid. 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, the aliphatic dicarboxylic acid is preferably fumaric acid from the viewpoint of improving the water repellency and oil resistance of the resulting coated paper. Examples of trivalent or higher polyvalent carboxylic acids include trimellitic acid, 2,5,7-naphthalenetricarboxylic acid, pyromellitic acid, and aconitic acid. Of these, the trivalent or higher polyvalent carboxylic acid is preferably trimellitic 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 one or more selected from an aromatic dicarboxylic acid, an aliphatic dicarboxylic acid, and a polyvalent carboxylic acid having three or more carboxylic acids, and even more preferably contains one or more selected from terephthalic acid, fumaric acid, and trimellitic acid.

[0024] 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 45 mol% or more, more preferably 50 mol% or more, even more preferably 55 mol% or more, and is preferably 100 mol% or less, more preferably 85 mol% or less, even more preferably 70 mol% or less.

[0025] From the viewpoint of improving the water repellency and oil resistance of the resulting coated paper, the total content of aromatic dicarboxylic acid and aliphatic dicarboxylic acid in the carboxylic acid component is preferably at least 60 mol%, more preferably at least 70 mol%, even more preferably at least 80 mol%, and preferably at most 100 mol%.

[0026] When the carboxylic acid component contains a trivalent or higher polyvalent carboxylic acid, the content of the trivalent or higher polyvalent carboxylic acid in the carboxylic acid component is, from the viewpoint of improving water repellency and oil resistance, preferably 3 mol % or more, more preferably 5 mol % or more, even more preferably 10 mol % or more, and preferably 35 mol % or less, more preferably 28 mol % or less, even more preferably 20 mol % or less.

[0027] (Method for producing amorphous polyester resin) The amorphous polyester resin is preferably produced, for example, by a method of polycondensing an alcohol component and a carboxylic acid component.

[0028] The polycondensation of an alcohol component and a carboxylic acid component can be carried out, for example, by polycondensing an alcohol component and a carboxylic acid component 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 described below as necessary.

[0029] 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 parts by mass or more and 10 parts by mass or less based on 100 parts by mass in total 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 based on 100 parts by mass in total of the alcohol component and the carboxylic acid component which are raw material monomers for the amorphous polyester resin. Furthermore, examples of the polymerization inhibitor include radical polymerization inhibitors such as 4-tert-butylcatechol. When a polymerization inhibitor is used, the amount of the 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.

[0030] (Physical properties of amorphous polyester resin) From the viewpoint of improving water repellency and oil resistance, the softening point of the amorphous polyester resin is preferably 80°C or higher, more preferably 90°C or higher, and even more preferably 100°C or higher, and is preferably 140°C or lower, more preferably 130°C or lower, and even more preferably 125°C or lower. The softening point is measured by the method described in the Examples.

[0031] From the viewpoint of improving water repellency and oil resistance, the glass transition temperature of the amorphous polyester resin is preferably 40° C. or higher, more preferably 45° C. or higher, and even more preferably 50° C. or higher, and is preferably 85° C. or lower, more preferably 80° C. or lower, and even more preferably 75° C. or lower. The glass transition temperature is measured by using a differential scanning calorimeter, specifically, by the method described in the examples.

[0032] From the viewpoint of improving water repellency and oil resistance, 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.

[0033] The amorphous polyester resins may be used alone or in combination of two or more. The softening point, glass transition temperature and acid value of the amorphous polyester resin can be appropriately adjusted by 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 kinds of amorphous polyester resins are used in combination, the softening point, glass transition temperature and acid value of the mixture are preferably within the above-mentioned ranges.

[0034] In the present invention, the amorphous polyester resin is preferably substantially water-insoluble from the viewpoint of improving water repellency and oil resistance. When the amorphous polyester resin is water-insoluble, the coating layer formed by applying the resin particle aqueous dispersion to the paper substrate becomes water-insoluble, and the water repellency and oil resistance can be improved. 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 to saturation in 100 g of water at 25° C., the amount of dissolution is 1 g or less. 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.

[0035] In the present invention, when the amorphous polyester resin contains an acid group, the amorphous polyester resin is preferably a product neutralized with a basic compound, from the viewpoint of improving the dispersion stability of the resin particles in an aqueous medium. The basic compound includes metal basic compounds and non-metal basic compounds. 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 functional groups other than these amino groups. Examples of such functional groups include hydroxyl groups. 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 thereof include trimethylamine, ethylamine, diethylamine, triethylamine, and triethanolamine. The basic compounds can be used alone or in combination of two or more.

[0036] The amount of the basic compound used is preferably 50 mol % or more, more preferably 55 mol % or more, further preferably 60 mol % or more, and preferably 100 mol % or less. The equivalent amount of the basic compound used can be calculated by the following 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 (mgKOH / g)×mass of amorphous polyester resin (g)] / (56.1×1000(mgKOH / mol))]}×100 (1)

[0037] <Resin particles> In the present invention, it is preferable to contain an amorphous polyester resin as resin particles. That is, the resin particle aqueous dispersion of the present invention preferably contains resin particles containing an amorphous polyester resin. By containing an amorphous polyester resin as resin particles, the coating film when applied to paper can be made to have a uniform thickness, and a stronger coating layer can be formed, so that the water repellency and oil resistance of the resulting coated paper can be improved.

[0038] Furthermore, the resin particles in the present invention may contain resins other than the amorphous polyester resin, for example, acrylic resins such as styrene-acrylic copolymers, polyurethane resins, etc., within the scope of not impairing the effects of the present invention. Furthermore, the resin particles in the present invention may contain, as optional components, reinforcing fillers such as fibrous substances, additives such as antioxidants, and the like, within the scope of not impairing the effects of the present invention. From the viewpoint of improving the water repellency and oil resistance of the resulting coated paper, the content of the amorphous polyester resin 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, still more preferably 95% by mass or more, and preferably 100% by mass or less.

[0039] <Polyvinyl alcohol> The resin particle aqueous dispersion of the present invention contains polyvinyl alcohol. By containing polyvinyl alcohol, a stronger coating layer can be formed, and the resulting coated paper can be endowed with both water repellency and oil resistance.

[0040] From the viewpoint of improving the water repellency and oil resistance of the resulting coated paper, the degree of polymerization of polyvinyl alcohol is preferably 200 or more, more preferably 250 or more, even more preferably 300 or more, and is preferably 2000 or less, more preferably 1500 or less, even more preferably 1200 or less. From the viewpoint of improving the water repellency and oil resistance of the resulting coated paper, the degree of saponification of the polyvinyl alcohol is preferably 70% or more, more preferably 80% or more, even more preferably 85% or more, and is preferably 100% or less.

[0041] The polyvinyl alcohol used in the present invention is preferably not modified. That is, in the present invention, the polyvinyl alcohol is preferably unmodified polyvinyl alcohol. Generally, polyvinyl alcohol is obtained by saponifying polyvinyl acetate, and therefore has hydroxyl groups and residual acetyl groups in the structure, but it is preferable from the viewpoint of water repellency and oil resistance that it is not modified with other hydrophobic functional groups such as ethylene. Furthermore, since the polyvinyl alcohol is not modified, it is possible to increase the affinity with the above-mentioned amorphous polyester resin and form a stronger coating layer, which makes it easier to improve the water repellency and oil resistance of the resulting coated paper.

[0042] (Production of resin particle aqueous dispersion) The method for producing the resin particle aqueous dispersion of the present invention includes the following method (i) or method (ii), etc. Method (i): A method in which a resin containing an amorphous polyester resin is dispersed in an aqueous medium and then mixed with polyvinyl alcohol Method (ii): A method in which polyvinyl alcohol is dissolved in an aqueous medium, and then a resin containing an amorphous polyester resin is dispersed in the aqueous medium. The method for producing a resin particle aqueous dispersion of the present invention preferably includes any one of the methods (i) and (ii) described above, from the viewpoint of improving the dispersibility of resin particles in the resulting resin particle aqueous dispersion, and more preferably includes the method (i).

[0043] [Method (i)] In the above method (i), examples of the method for dispersing the 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 a dispersion treatment is carried out using a dispersing machine 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 carry out phase inversion emulsification. The aqueous dispersion of the resin particles of the present invention can be produced by mixing polyvinyl alcohol with the aqueous dispersion of the amorphous polyester resin thus obtained. The polyvinyl alcohol can be used alone or dissolved in an aqueous medium.

[0044] When producing the resin particle aqueous dispersion of the present invention by the above method (i), from the viewpoint of improving the water repellency and oil resistance of the resulting coated paper, the method for dispersing the amorphous polyester resin in an aqueous medium is preferably a phase inversion emulsification method.

[0045] A preferred phase inversion emulsification method is to first dissolve a resin including an amorphous polyester resin in an organic solvent to obtain a resin solution, then add an aqueous medium to the solution to invert the phase, 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 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.

[0046] The mass ratio of the organic solvent to the resin including the amorphous polyester resin [organic solvent / resin] is preferably 50 / 100 or more, more preferably 70 / 100 or more, even more preferably 100 / 100 or more, from the viewpoint of dissolving the resin and facilitating phase transfer to the aqueous medium and further improving the dispersion stability of the resin particle aqueous dispersion, and is preferably 500 / 100 or less, more preferably 400 / 100 or less, even more preferably 300 / 100 or less.

[0047] When the amorphous polyester resin is neutralized with a basic compound, it is preferable to obtain a resin solution containing the amorphous polyester resin, and then add an aqueous solution of the basic compound to the resin solution to neutralize the resin. The operation of dissolving the resin including 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 equal to or lower than the boiling point of the organic solvent.

[0048] The temperature when adding an aqueous medium to a resin solution containing an amorphous polyester resin is, from the viewpoint of improving the dispersion stability of the resin particle aqueous dispersion, 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.

[0049] From the viewpoint of improving the dispersion stability of the resin particle aqueous 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, and even more preferably 3 parts by mass / min or more, relative to 100 parts by mass of the resin component constituting the resin particles, 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. There is no restriction on the addition rate of the aqueous medium after the phase inversion and the resin particles are obtained. From the viewpoint of improving the productivity of the resin particle aqueous dispersion, the amount of the aqueous medium added is preferably 50 parts by mass or more, more preferably 100 parts by mass or more, and even more preferably 200 parts by mass or more, relative to 100 parts by mass of the resin component constituting the resin particles, and is preferably 900 parts by mass or less, more preferably 500 parts by mass or less, and even more preferably 400 parts by mass or less.

[0050] In the above method (i), from the viewpoint of improving the dispersion stability of the resin particle aqueous dispersion, it is preferable to remove the organic solvent from the aqueous dispersion obtained by phase inversion emulsification after the phase inversion emulsification. The method for removing the organic solvent is not particularly limited, and any method can be used. The obtained resin particle aqueous dispersion 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 by azeotropy together with the organic solvent, so that it is preferable to add water to adjust the solid content concentration.

[0051] [Method (ii)] In the above method (ii), examples of the method for obtaining the aqueous dispersion of resin particles of the present invention include a method in which a resin containing an amorphous polyester resin is added to an aqueous medium in which polyvinyl alcohol has been dissolved, and then a dispersion treatment is carried out using a dispersing machine or the like, and a method in which an aqueous medium in which polyvinyl alcohol has been dissolved is gradually added to a solution of a resin containing an amorphous polyester resin, and then phase inversion emulsification is carried out. In the above method (ii), in the method of gradually adding an aqueous medium in which polyvinyl alcohol has been dissolved to a resin solution containing an amorphous polyester resin to carry out phase inversion emulsification, the temperature, addition rate, addition amount, etc., when adding the aqueous medium in which polyvinyl alcohol has been dissolved are preferably the same conditions as those in the above method (i).

[0052] From the viewpoint of improving the water repellency and oil resistance of the resulting coated paper, the solid content concentration of the resin particle aqueous dispersion of the present invention 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 of the aqueous dispersion is measured by the method described in the Examples.

[0053] From the viewpoint of improving the water repellency and oil resistance of the resulting coated paper, the volume average particle diameter Dv of the resin particles in the resin particle aqueous dispersion of the present invention 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.

[0054] The resin particle aqueous dispersion of the present invention may contain various additives, such as organic solvents, moisturizers, wetting agents, penetrants, viscosity adjusters, defoamers, preservatives, antifungal agents, rust inhibitors, pH adjusters, antioxidants, and ultraviolet absorbers, if necessary. In addition, since surfactants have a very high affinity for water, the presence of a surfactant in the resin particle aqueous dispersion results in the surfactant being contained in the coating layer formed when the resin particle aqueous dispersion is applied to a paper substrate, resulting in a decrease in the water repellency of the coated paper. Therefore, from the viewpoint of improving the water repellency of the resulting coated paper, it is preferable that the resin particle aqueous dispersion of the present invention does not substantially contain a surfactant. 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. Furthermore, in the present invention, when producing an aqueous dispersion of resin particles, a method of adding a resin containing the above-mentioned amorphous polyester-based resin to an aqueous medium and carrying out a dispersion treatment using a disperser or the like, or a method of gradually adding an aqueous medium to a solution of a resin containing an amorphous polyester-based resin to carry out phase inversion emulsification can be used, whereby the resin particles can be dispersed in an aqueous medium without using a surfactant, and an aqueous dispersion of resin particles that is substantially free of surfactant can be obtained.

[0055] [Paper coating fluid] The above-mentioned resin particle aqueous dispersion can be used as a paper coating liquid as it is, but the resin particle aqueous dispersion can also be used by adding and mixing various additives used in paper coating liquids as necessary. That is, the paper coating liquid of the present invention (hereinafter also simply referred to as "coating liquid") preferably contains the above-mentioned resin particle aqueous dispersion. As mentioned above, surfactants have very high affinity for water, and therefore, from the viewpoint of improving the water repellency and oil resistance of the resulting coated paper, it is preferable that the coating fluid of the present invention also contains substantially no surfactants.

[0056] [Coated paper] The coated paper of the present invention is a coated paper having a coating layer containing an amorphous polyester resin and polyvinyl alcohol, in which the mass ratio of the amorphous polyester resin to the polyvinyl alcohol (amorphous polyester resin / polyvinyl alcohol) is 50 / 50 or more and 90 / 10 or less. The coated paper of the present invention preferably has a coating layer formed from the above-mentioned paper coating fluid. The coated paper of the present invention can be obtained by applying the above-mentioned paper coating liquid to a paper substrate to form a coating layer on the paper substrate containing an amorphous polyester resin and polyvinyl alcohol in the above-mentioned mass ratio. Examples of paper base materials for coated paper include uncoated papers such as fine paper, medium quality paper, and sawdust paper; printing papers such as art paper, coated paper, and matte coated paper; information papers such as PPC paper; packaging papers such as kraft paper; cardboard base paper; and paperboards such as paper container boards. The basis weight of the paper substrate is not particularly limited, but from the viewpoints of handling the coated paper and 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 Less than 150 g / m 2 More preferably, 120 g / m 2 The following is the result.

[0057] [Manufacturing method of coated paper] From the viewpoint of obtaining coated paper with excellent water repellency and oil resistance, the method for producing coated paper of the present invention preferably comprises step 1 of coating the coating liquid on at least one surface of a paper substrate. This makes it possible to obtain a coated paper having a coating layer formed by coating at least one side of a paper substrate with the coating liquid. Examples of the paper substrate include the paper substrates described above.

[0058] The amount of the coating liquid in step 1 is preferably 1 g / m2 in terms of solid content, from the viewpoint of obtaining a coated paper having excellent water repellency and oil resistance. 2 More preferably, 3 g / m 2 More preferably, 5 g / m 2 More preferably, 10 g / m 2 and preferably 30 g / m 2 Less than or equal to 25 g / m 2More preferably, 20 g / m 2 The following is the result. The method for applying the coating liquid to the paper substrate in step 1 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.

[0059] In the present invention, from the viewpoint of obtaining coated paper having excellent water repellency and oil resistance, it is preferable to further include a step 2 of drying the coating liquid on the paper substrate coated in the step 1. Examples of the drying method in step 2 include static drying, air drying, heat drying, vacuum drying, infrared drying, etc. One or more of the drying methods may be used in combination. Among these, from the viewpoint of ease of operation, at least one selected from air drying and heat drying is preferred, and heat drying is more preferred. Examples of heat drying include a method of heating the surface of the coating liquid on the paper substrate by applying hot air to it, a method of heating the surface of the coating liquid on the paper substrate by bringing a heater close to it, a method of heating the surface of the paper substrate by bringing a heater into contact with the side of the paper substrate opposite to the side on which the coating liquid is applied, 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 a 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 material due to heat and reducing energy. EXAMPLES

[0060] 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 method. In the examples, room temperature means a temperature of 20°C or higher and 25°C or lower.

[0061] [Measurement method] The properties of the amorphous polyester resin, resin particles, etc. were measured and evaluated by the following methods.

[0062] [Softening point of resin] Using a flow tester "CFT-500EX" (Shimadzu Corporation), 1 g of the sample was heated at a temperature increase rate of 6°C / min, while applying a load of 1.96 MPa with the plunger, and extruding the sample from a nozzle with a diameter of 1 mm and a length of 1 mm. The plunger descent amount 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.

[0063] [Resin Crystallinity Index] Using a differential scanning calorimeter "Q-20" (manufactured by TA Instruments Japan Co., Ltd.), 0.01 to 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 peak area among the observed endothermic peaks was taken as the maximum endothermic peak temperature, and the crystallinity index was calculated by (softening point (°C)) / (maximum endothermic peak temperature (°C)).

[0064] [Glass transition temperature of resin] Using a differential scanning calorimeter "Q-20" (manufactured by TA Instruments Japan Co., Ltd.), 0.01 to 0.02 g of the 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 temperature was then increased at a rate of 10°C / min to measure the amount of heat. The peak temperature with the largest peak area among the observed endothermic peaks was taken as the maximum endothermic peak temperature. In the case of a crystalline resin, the peak temperature was taken as the melting point. In the case of an amorphous resin, the temperature at the intersection of the extension line of the baseline below the maximum endothermic peak temperature and the tangent line showing the maximum slope from the rising part of the peak to the apex of the peak was taken as the glass transition temperature.

[0065] [Acid value of resin] The 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)].

[0066] [Volume average particle size (Dv) of resin particles] The volume average particle diameter Dv was measured using the following measuring device and under the following measuring conditions. Measurement equipment: Zeta potential / particle size measurement system "ELSZ-2" (Otsuka Electronics Co., Ltd.) Measurement conditions: Cumulant analysis method. The particle concentration to be measured is about 5×10 -3 An aqueous dispersion diluted with water to a mass % was placed in a measurement cell, the temperature was 25° C., the number of accumulated measurements was 100, and the refractive index of water (1.333) was entered as the refractive index of the dispersion solvent.

[0067] [Solids Concentration of Resin Particle Aqueous Dispersion] Using a heat-drying moisture meter "MX-50" (manufactured by A&D Co., Ltd.), 5 g of the measurement sample was dried at a drying temperature of 150°C, in standard measurement mode, with standard heating pattern and ACCURACY: LO, and the moisture content (mass%) of the aqueous dispersion was measured. The solid content was calculated according to the following formula. Solid concentration (mass%) = 100-moisture (mass%)

[0068] [Resin manufacturing] Production Example A1 (Production of amorphous polyester resin X-1) 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 5518 g of propylene oxide (2.2) adduct of bisphenol A, 1570 g of terephthalic acid, 40 g of tin (II) di(2-ethylhexanoate), and 2 g of gallic acid were added, and the mixture was heated to 235°C under a nitrogen atmosphere while stirring, and after maintaining the temperature for 6 hours, the pressure in the flask was further reduced and maintained at 8.3 kPa for 1 hour. After that, the pressure was returned to atmospheric pressure, and the mixture was cooled to 190°C, and 549 g of fumaric acid, 4 g of tert-butylcatechol, and 363 g of trimellitic anhydride were added, and the mixture was heated to 210°C over 2 hours, and maintained at 210°C for 1 hour, and the pressure in the flask was further reduced and maintained at 8.3 kPa to react until the softening point reached the temperature shown in Table 1, and amorphous polyester resin X-1 was obtained. Various physical properties of the resin are shown in Table 1.

[0069] Production Example A2 (Production of amorphous polyester resin X-2) 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 2708 g of 1,2-propanediol, 3845 g of terephthalic acid, 40 g of tin (II) di(2-ethylhexanoate), and 0.8 g of gallic acid were added, and the mixture was heated to 180°C under nitrogen atmosphere while stirring and held for 1 hour, and then heated to 210°C over 6 hours. After holding at 210°C for 1 hour, the pressure in the flask was further reduced and held at 8.3 kPa for 1 hour. After that, the mixture was returned to atmospheric pressure, cooled to 180°C, 1447 g of fumaric acid and 4 g of tert-butylcatechol were added, heated to 210°C over 3 hours, held at 210°C for 1 hour, and then the pressure in the flask was further reduced and held at 8.3 kPa to react until the softening point reached the temperature shown in Table 1, and amorphous polyester resin X-2 was obtained. Various physical properties of the resin are shown in Table 1.

[0070] [Table 1]

[0071] Example 1 (Preparation of Resin Particle Water Dispersion E-1) In a 2L four-neck flask equipped with a reflux condenser, a stirrer "Three-One Motor BL300" (manufactured by Shinto Scientific Co., Ltd.) and a thermocouple, 200 g of amorphous polyester resin X-1 was placed as an amorphous polyester resin, and mixed with 200 g of methyl ethyl ketone (hereinafter referred to as "MEK") at room temperature to dissolve the resin. Next, a 5 mass% aqueous sodium hydroxide solution was added so that the degree of neutralization with respect to the acid value of the amorphous polyester resin X-1 was 60 mol%, and the mixture was stirred for 60 minutes. Next, 600g of deionized water was added dropwise at a rate of 10mL / min under stirring at room temperature to cause phase inversion emulsification. After that, the temperature was raised to 65°C, and while maintaining 65°C, the pressure was gradually reduced from 80kPa to 30kPa to distill off MEK, and further a part of the water was distilled off. After cooling to room temperature, an aqueous medium containing polyvinyl alcohol was added under stirring, in which 67g of polyvinyl alcohol with a polymerization degree of 1000 and a saponification degree of 99% was dissolved in 412g of deionized water. After stirring for 5 minutes, the mixture was filtered through a 150-mesh wire net, and the solid content concentration was adjusted to 20% by mass with deionized water to obtain a resin particle aqueous dispersion E-1. Table 2 shows the volume average particle size (Dv) of the resin particles in the obtained resin particle aqueous dispersion.

[0072] Examples 2 to 7 and 9 and Comparative Example 1 (Production of Resin Particle Aqueous Dispersions E-2 to E-7, E-9, and CE-1) Each resin particle aqueous dispersion was obtained in the same manner as in Example 1, except that the type and amount of the amorphous polyester resin, the type and amount of polyvinyl alcohol in the aqueous medium containing polyvinyl alcohol, and the amount of deionized water were changed to those shown in Table 2. The volume average particle size (Dv) of the resin particles in the obtained resin particle aqueous dispersion is shown in Table 2.

[0073] Example 8 (Preparation of Resin Particle Water Dispersion E-8) 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, 200 g of amorphous polyester resin X-1 was placed as an amorphous polyester resin, and mixed with 200 g of MEK at room temperature to dissolve the resin. Next, a 5% by mass aqueous solution of sodium hydroxide was added so that the degree of neutralization with respect to the acid value of the amorphous polyester resin X-1 was 65 mol%, and the mixture was stirred for 60 minutes. Next, under stirring at room temperature, 67 g of polyvinyl alcohol with a degree of polymerization of 1000 and a degree of saponification of 99% was dissolved in 800 g of deionized water, and the aqueous medium containing polyvinyl alcohol was dropped at a rate of 9 mL / min to cause phase inversion emulsification. After that, the temperature was 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 MEK, and further, some water was distilled off. After cooling to room temperature, the mixture was filtered through a 150 mesh wire net, and the solid content concentration was adjusted to 20 mass% with deionized water to obtain a resin particle aqueous dispersion E-8. The volume average particle size (Dv) of the resin particles in the obtained resin particle aqueous dispersion is shown in Table 2.

[0074] Comparative Example 2 (Production of Resin Particle Aqueous Dispersion CE-2) A resin particle aqueous dispersion CE-2 was obtained in the same manner as in Example 1, except that the aqueous medium containing polyvinyl alcohol was not added in Example 1. The volume average particle size (Dv) of the resin particles in the obtained resin particle aqueous dispersion is shown in Table 2.

[0075] Comparative Example 3 (Preparation of Aqueous Polyvinyl Alcohol Solution CE-3) 67 g of polyvinyl alcohol with a degree of polymerization of 1000 and a degree of saponification of 99% was dissolved in 268 g of deionized water to prepare an aqueous medium containing polyvinyl alcohol, and a polyvinyl alcohol aqueous solution CE-3 with a solid content of 20 mass% was obtained. Note that the polyvinyl alcohol aqueous solution CE-3 is a comparative example that does not contain resin particles, and the volume average particle size (Dv) of the resin particles could not be measured.

[0076] The polyvinyl alcohols used in the examples and comparative examples shown in Table 2 are as follows: Y-1 to Y-4 are manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., and Y-5 is manufactured by Nippon Vacuum Acetate & Poval Corporation. Y-1: "Polyvinyl alcohol 1,000, fully saponified type: Product code 162-16325", polymerization degree: 1000, saponification degree: 99% Y-2: "Polyvinyl alcohol 500, fully saponified type: Product code 165-16315", polymerization degree: 500, saponification degree: 99% Y-3: "Polyvinyl alcohol (degree of polymerization approximately 500): Product code 163-03045", degree of polymerization: 500, degree of saponification: 88% Y-4: "Polyvinyl alcohol: Product code 165-17915", polymerization degree: 1500, saponification degree: 80% Y-5: "J-Poval JF-03", fully saponified polyvinyl alcohol, polymerization degree: 300, saponification degree: 99%

[0077] <Preparation of coated paper> (Process 1) The resin particle aqueous dispersions obtained in Examples 1 to 9 and Comparative Examples 1 to 3 were used as coating liquids as they were, and PPC paper "J paper" (basis weight 82 g / m) was used as a paper substrate. 2 The coating was performed on a paper substrate with a bar coater (No. 40, manufactured by Fujifilm Business Innovation Co., Ltd.). The coating amount on the paper substrate was 18 g / m2 in terms of solid content. 2 It was carried out so that it became. (Process 2) The resin particle aqueous dispersion on the paper substrate was then dried for 5 minutes in a dryer at 100°C to obtain coated papers having a coating layer on the paper substrate, which was formed using the resin particle aqueous dispersion obtained in Examples 1 to 9 and Comparative Examples 1 to 3. The water repellency and oil resistance of each of the obtained coated papers were evaluated by the following methods. The evaluation results are shown in Table 2.

[0078] [Water repellency evaluation] Water repellency was evaluated according to JAPAN TAPPI Paper and Pulp Test Method No. 68:2000. At room temperature, coated paper was tilted at 45° and a droplet of ion-exchanged water was dropped from 10 mm above the coated paper. The state of the coated paper after the droplet had passed over it was observed and the water repellency was judged as follows: R0 to R10 is the highest water repellency rating, and R0 is the lowest water repellency rating. [Water repellency] R0: A continuous mark of uniform width R2: A continuous mark with a width slightly narrower than that of a water drop R4: A continuous mark that is broken in places and clearly has a width narrower than that of a water drop. R6: Half of the mark is wet R7: 1 / 4 of the mark is wetted by elongated water droplets R8: More than 1 / 4 of the mark is made up of scattered spherical droplets. R9: Small spherical droplets scattered here and there R10: Completely rolls down

[0079] [Evaluation of oil resistance] The coated paper was placed on a horizontal table, and a drop of castor oil was dropped from 10 mm above the coated paper and left to stand for 1 minute. The oil drop on the coated paper was then wiped off, and the condition of the paper after wiping was checked and the oil resistance was evaluated according to the following criteria. L5 is the highest rating for oil resistance, and L1 is the lowest rating for oil resistance. 〔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: Stains the same size as oil droplets are observed. L1: Stains larger than oil droplets are observed.

[0080] [Table 2]

[0081] From Table 2, it can be seen that the resin particle aqueous dispersions of Examples 1 to 9 can produce coated papers with superior water repellency and oil resistance compared to the resin particle aqueous dispersions of Comparative Examples 1 and 2 or the polyvinyl alcohol aqueous solution of Comparative Example 3. [Industrial Applicability]

[0082] 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, wrapping paper, paper containers, etc. that require resistance to water and oil.

Claims

1. An aqueous dispersion of resin particles for paper coating, comprising an amorphous polyester resin and polyvinyl alcohol, The resin particle aqueous dispersion for paper coating, wherein the mass ratio of the amorphous polyester resin to the polyvinyl alcohol (amorphous polyester resin / polyvinyl alcohol) in the resin particle aqueous dispersion is 50 / 50 or more and 90 / 10 or less.

2. 2. The aqueous dispersion of resin particles for paper coating according to claim 1, wherein the degree of polymerization of the polyvinyl alcohol is 250 or more and 2,000 or less.

3. 2. The aqueous dispersion of resin particles for paper coating according to claim 1, wherein the degree of saponification of the polyvinyl alcohol is 70% or more and 100% or less.

4. 2. The aqueous dispersion of resin particles for paper coating according to claim 1, wherein the amorphous polyester resin has a glass transition temperature of 45°C or higher.

5. The aqueous resin particle dispersion for paper coating according to claim 1 , which contains the amorphous polyester resin as resin particles.

6. 6. A method for producing the aqueous dispersion of resin particles for paper coating according to claim 1, comprising any one of the following methods (i) and (ii): Method (i): A method in which a resin containing an amorphous polyester resin is dispersed in an aqueous medium and then mixed with polyvinyl alcohol. Method (ii): A method in which polyvinyl alcohol is dissolved in an aqueous medium, and then a resin containing an amorphous polyester resin is dispersed in the aqueous medium.

7. A paper coating liquid comprising the resin particle aqueous dispersion according to any one of claims 1 to 5.

8. Coated paper having a coating layer formed with the paper coating liquid according to claim 7.

9. A coated paper having a coating layer containing an amorphous polyester resin and polyvinyl alcohol, The coated paper has a mass ratio of the amorphous polyester resin to the polyvinyl alcohol (amorphous polyester resin / polyvinyl alcohol) of 50 / 50 or more and 90 / 10 or less.

10. A method for producing coated paper, comprising step 1 of applying the paper coating liquid according to claim 7 to at least one surface of a paper substrate, and step 2 of drying the paper coating liquid on the paper substrate coated in step 1.