Paper coating agent, method for manufacturing coated paper, and coated paper

Abstract

To provide a paper coating agent that yields coated paper with excellent transparency and drying properties during manufacturing. [Solution] A coating agent for paper comprising a polyester resin and a curing agent, wherein the polyester resin is a reaction product of at least one selected from the group consisting of polycarboxylic acids (A) and aliphatic monocarboxylic acids (B), rosins (C), and polyols (D), and has hydroxyl groups, and the curing agent comprises an isocyanate compound.

Description

[Technical Field]

[0001] This invention relates to a coating agent for paper, a method for manufacturing coated paper, and coated paper. [Background technology]

[0002] Common methods for producing highly transparent paper include using pulp fibers with a high degree of beating during the papermaking process, and impregnating the spaces between the fibers of the paper with resin or other substances. The method using pulp fibers with a high degree of beating during the papermaking process is used in the production of glassine paper, tracing paper, etc. The method of impregnating the spaces between the fibers of the paper with resin or other substances is used in the production of oil paper, wax paper, etc.

[0003] In recent years, as a shift towards sustainable and recyclable materials, the replacement of plastic film with paper has been explored. For example, the replacement of plastic film with paper is progressing in the field of packaging materials. If the transparency of plastic film can be imparted to paper, its applications are expected to expand even further.

[0004] Patent Document 1 proposes applying a rosin-based aqueous clearing agent to a portion of the base paper and heating it to obtain a windowed packaging bag. Patent Document 2 proposes making opaque paper transparent by printing and impregnating a transparent agent mainly composed of vegetable oil onto a specific surface of the opaque paper, thereby forming an oily protective film on both surfaces. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2011-63286 [Patent Document 2] Japanese Patent Application Publication No. 15395 / 1983 [Overview of the project] [Problems that the invention aims to solve]

[0006] The technologies described in Patent Documents 1 and 2 involve impregnating the voids between the cellulose fibers of paper with a clearing agent, thereby increasing the transparency of the translucent areas impregnated with the clearing agent. However, the rosin-based aqueous clearing agent used in Patent Document 1 does not provide sufficient transparency. Patent Document 2 requires an oil layer protection layer to prevent the impregnated vegetable oil from leaching out. If an oil layer protection layer is not provided, the vegetable oil will leach out or dry out over time, causing the paper to become cloudy.

[0007] The inventors, after extensive research, have found that a polyester resin incorporating rosins and aliphatic carboxylic acids is useful as a clearing agent. Rosins and aliphatic carboxylic acids each exhibit refractive indices close to those of cellulose pulp, but using them together brings the refractive index closer to that of cellulose pulp than the refractive indices of each substance alone. However, as described in Patent Document 2, the aliphatic carboxylic acids leach out or dry out, causing the paper to become cloudy. By resinifying these substances, the clouding of the paper can be suppressed. Further investigation into practical application revealed that achieving both transparency and good drying properties during manufacturing is difficult with the polyester resins described above. Poor drying properties result in stickiness remaining after drying during high-speed coating, preventing the next process from being carried out and reducing productivity.

[0008] The present invention aims to provide a paper coating agent and a method for producing the same, as well as coated paper with excellent transparency and drying properties during manufacturing. [Means for solving the problem]

[0009] The present invention has the following aspects. [1] comprising polyester resin and a curing agent, The polyester resin is a reaction product of at least one selected from the group consisting of polycarboxylic acids (A) and aliphatic monocarboxylic acids (B), rosins (C), and polyols (D), and having hydroxyl groups. The curing agent is a paper coating agent containing an isocyanate compound. [2] The paper coating agent according to [1], wherein the refractive index of the polyester resin is 1.4 to 1.6. [3] The paper coating agent according to [1] or [2], wherein the molar ratio (NCO / OH) of isocyanate groups of the isocyanate compound to the hydroxyl groups of the polyester resin is 0.5 to 5. [4] The paper coating agent according to any one of [1] to [3], wherein the hydroxyl value of the polyester resin is 10 to 180 mg KOH / g. [5] A method for manufacturing coated paper, comprising applying a paper coating agent described in any of [1] to [4] above to at least one surface of a paper substrate. [6] Coated paper having at least one surface of a paper substrate coated with any of the paper coating agents described in [1] to [4] above. [Effects of the Invention]

[0010] According to the present invention, a paper coating agent and a method for producing the same can be obtained, which yield coated paper with excellent transparency and drying properties during manufacturing. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic cross-sectional view showing an example of coated paper. [Modes for carrying out the invention]

[0012] In this specification, the "~" symbol indicating a numerical range means that the numbers before and after it are included as the lower and upper limits. The lower and upper limits of the numerical ranges disclosed herein can be arbitrarily combined to form new numerical ranges. "Polycarboxylic acid" refers to compounds having two or more carboxyl groups and their anhydrides. The refractive index is measured in accordance with JIS K 7142 (2014). The "hydroxyl value" is measured in accordance with JIS K 0070 (1992). "Acid value" is measured in accordance with JIS K 5601-2-1 (1999).

[0013] The coated paper of the present embodiment is a coated paper obtained by applying a coating agent onto at least one surface of a paper base material. The coating agent contains a polyester resin and a curing agent. The coating agent will be described in detail later.

[0014] By applying the coating agent onto at least one surface of the paper base material, at least a part of the coating agent impregnates the interior of the paper base material, and the paper base material is made transparent. The region made transparent (transparent region) may be the entire surface or a part of the paper base material in a plan view. At least a part of the coating agent may be positioned on at least one surface of the paper base material. In this case, diffuse reflection of light by the surface of the paper base material can be suppressed, and the transparency can be further enhanced. Further, the resin contained in the coating agent may have heat sealability. When a resin having heat sealability is used, the coating agent positioned on at least one surface of the paper base material can also be used as a sealant layer.

[0015] Figure 1 is a schematic cross-sectional view showing an example of the coated paper. The coated paper 1 of this example is obtained by applying a coating agent 12 onto one surface of a paper base material 11. In Figure 1, the upper surface is the coated surface 1a. For convenience of explanation, the dimensions and the like in Figure 1 are made different from the actual ones. Although an example in which the coating agent 12 is applied onto one surface of the paper base material 11 is shown here, the coating agent 12 may be applied onto each of one surface of the paper base material 11 and the other surface opposite thereto.

[0016] In the coated paper, the visible light transmittance of the transparent region is preferably 40% or more, more preferably 50% or more, and even more preferably 60% or more. The visible light transmittance is measured using a transmission meter. The details are as described in the Examples below.

[0017] The amount of coating agent to be applied cannot be stated definitively as it depends on the type of paper substrate (void amount, etc.), but as the mass of polyester resin per unit area of ​​the transparent region, it is approximately 10-80 g / m². 2 Preferably, 20-70 g / m 2 More preferably, 30-60 g / m 2 This is even more preferable. If the amount of coating agent applied is above the lower limit of the range, the transparency of the transparent region is more easily enhanced. If the amount of coating agent applied is below the upper limit of the range, the recyclability can be improved. The mass of the polyester resin is calculated on a solids basis, and the same applies below. Solids refer to non-volatile components, which are the components excluding the liquid medium described later.

[0018] <Coating agent> The coating agent of this embodiment comprises a polyester resin and a curing agent.

[0019] [Polyester resin] The polyester resin is a reaction product of at least one selected from the group consisting of polycarboxylic acids (A) and aliphatic monocarboxylic acids (B), rosins (C), and a polyol (D), and has a hydroxyl group. By using at least one carboxylic acid component selected from the group consisting of polycarboxylic acids (A) and aliphatic monocarboxylic acids (B) in combination with rosin (C) as the carboxylic acid component of the polyester resin, the refractive index of the polyester resin becomes close to that of the paper substrate, resulting in an excellent transparency effect. Furthermore, since rosin (C) is a plant-derived component, using rosin (C) as a raw material for polyester resin contributes to carbon neutrality.

[0020] Polycarboxylic acid (A) and aliphatic monocarboxylic acid (B) may be used individually or in combination. From the viewpoint of transparency effect, it is preferable to use at least aliphatic monocarboxylic acid (B) among polycarboxylic acid (A) and aliphatic monocarboxylic acid (B), and it is particularly preferable to use both polycarboxylic acid (A) and aliphatic monocarboxylic acid (B). Therefore, it is particularly preferable that the polyester resin is a reaction product of polycarboxylic acid (A), aliphatic monocarboxylic acid (B), rosins (C), and polyol (D).

[0021] "Polycarboxylic acid (A)" Polycarboxylic acid (A) is a component that adjusts the molecular weight of polyester resins. Examples of polycarboxylic acids (A) include oxalic acid, malonic acid, succinic acid, fumaric acid, maleic acid, itaconic acid, citraconic acid, glutaric acid, adipic acid, suberic acid, azelaic acid, sebacic acid, dodecanediic acid, tetradecanediic acid, hexadecanedioic acid, phthalic acid, isophthalic acid, terephthalic acid, tetrahydrophthalic acid, oxaloacetate, methylmalonic acid, dimethylmalonic acid, methylsuccinic acid, 2,2-dimethylsuccinic acid, methylglutaric acid, dimethylglutaric acid, diglycolic acid, 1 Examples include 3-acetonedicarboxylic acid, ketoglutaric acid, cyclopropane-1,1-dicarboxylic acid, cyclobutane-1,1-dicarboxylic acid, cyclohexane-1,1-dicarboxylic acid, 2-oxoadipic acid, 4-oxoheptanedioic acid, 5-oxoazelaic acid, phenylenedioxydiacetic acid, indan-2,2-dicarboxylic acid, naphthalene-2,6-dicarboxylic acid, naphthalene-2,7-dicarboxylic acid, cyclohexanedicarboxylic acid, ethylenediaminetetraacetic acid, and their anhydrides. These can be used individually or in combination of two or more types. As for the polycarboxylic acid (A), a dicarboxylic acid is preferred from the viewpoint of adjusting the molecular weight.

[0022] The polycarboxylic acid (A) preferably contains an α,β-unsaturated dicarboxylic acid. Since α,β-unsaturated dicarboxylic acids react with rosins (C), the presence of an α,β-unsaturated dicarboxylic acid in the polycarboxylic acid (A) improves its transparency properties. Examples of α,β-unsaturated dicarboxylic acids include fumaric acid, maleic acid, itaconic acid, citraconic acid, and their anhydrides. Examples of anhydrides include maleic anhydride, itaconic anhydride, and citraconic anhydride. These can be used individually or in combination of two or more. In addition, α,β-unsaturated dicarboxylic acids can be used in combination with other dicarboxylic acids.

[0023] From the viewpoint of adjusting the molecular weight, the polycarboxylic acid (A) preferably contains at least one selected from the group consisting of succinic acid, fumaric acid, maleic anhydride, and adipic acid, and more preferably contains fumaric acid.

[0024] "Aliphatic monocarboxylic acid (B)" Examples of aliphatic monocarboxylic acids (B) include formic acid, acetic acid, trifluoroacetic acid, propionic acid, acrylic acid, methacrylic acid, vivalic acid, mercaptoacetic acid, and sorbic acid. Examples of aliphatic monocarboxylic acids (B) include fatty acids derived from oils and fats. More specifically, these include linseed oil fatty acids, yuzu oil fatty acids, pistachio oil fatty acids, rice bran oil fatty acids, safflower oil fatty acids, apricot kernel oil fatty acids, cottonseed oil fatty acids, sesame oil fatty acids, corn oil fatty acids, watermelon oil fatty acids, soybean oil fatty acids, poppy seed oil fatty acids, apple oil fatty acids, sunflower oil fatty acids, cactus oil fatty acids, tall oil fatty acids, walnut oil fatty acids, tung oil fatty acids, clove oil fatty acids, and castor oil fatty acids. These can be used individually or in combination of two or more types.

[0025] The refractive index of the aliphatic monocarboxylic acid (B) is, for example, 1.35 to 1.65, preferably 1.40 to 1.60.

[0026] As the aliphatic monocarboxylic acid (B), a hydroxyl group-containing aliphatic monocarboxylic acid is preferred from the viewpoint of introducing hydroxyl groups into the polyester resin. Examples of hydroxyl-containing aliphatic monocarboxylic acids include ricinoleic acid and 12-hydroxystearic acid derived from castor oil. Furthermore, hydroxylated unsaturated fatty acids such as oleic acid and linoleic acid, extracted from soybean oil, flaxseed oil, olive oil, rice bran oil, palm oil, and tall oil, can also be used. These can be used individually or in combination of two or more types. A hydroxyl-containing aliphatic monocarboxylic acid and a hydroxyl-free aliphatic monocarboxylic acid may be used in combination. The content ratio of hydroxyl group-containing aliphatic monocarboxylic acid to the total mass of aliphatic monocarboxylic acid (B) is preferably 10% by mass or more, and more preferably 20% by mass or more.

[0027] From the viewpoint of suitability for transparency, the aliphatic monocarboxylic acid (B) is preferably one having a predetermined iodine value. From the viewpoint of suitability for transparency, the iodine value of the aliphatic monocarboxylic acid (B) is, for example, 0 mg / 100 mg or more, preferably 70 mg / 100 mg or more, and more preferably 100 mg / 100 mg or more.

[0028] From the viewpoint of suitability for transparency, the aliphatic monocarboxylic acid (B) preferably contains as a main component an aliphatic monocarboxylic acid with an iodine value of 20 g / 100 g or more. The main component refers to 80% by mass or more, preferably 90% by mass or more, and more preferably 95% by mass or more. Therefore, the content ratio of the aliphatic monocarboxylic acid with an iodine value of 20 g / 100 g or more relative to the total amount of the aliphatic monocarboxylic acid (B) is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more. It is particularly preferable that the aliphatic monocarboxylic acid (B) consists of an aliphatic monocarboxylic acid with an iodine value of 20 g / 100 g or more.

[0029] Examples of aliphatic monocarboxylic acids with an iodine value of 20g / 100g or more include linseed oil fatty acids, yuzu oil fatty acids, pistachio oil fatty acids, rice bran oil fatty acids, safflower oil fatty acids, apricot kernel oil fatty acids, cottonseed oil fatty acids, sesame oil fatty acids, corn oil fatty acids, watermelon oil fatty acids, soybean oil fatty acids, poppy seed oil fatty acids, apple oil fatty acids, sunflower oil fatty acids, cactus oil fatty acids, tall oil fatty acids, walnut oil fatty acids, tung oil fatty acids, clove oil fatty acids, and castor oil fatty acids. These can be used individually or in combination of two or more types.

[0030] "Rosins (C)" Rosins (C) are plant-derived components, more specifically, compounds derived from pine. The type of pine is not particularly limited; examples include Merkus pine, slash pine, and horsehair pine. These can be used individually or in combination of two or more types.

[0031] Rosins (C) are not particularly limited and include known unmodified rosins and their derivatives. Examples of unmodified rosins include crude rosin and refined rosin. Examples of crude rosins include gum rosin, tall rosin, and wood rosin. Examples of refined rosin include refined products of crude rosin. Examples of rosin derivatives include hydrogenated rosin, disproportionated rosin, and polymerized rosin. These can be used alone or in combination of two or more. The origin of the rosin is not particularly limited and includes, for example, China, Vietnam, Indonesia, and Brazil. These can be used alone or in combination of two or more. As for rosin(C), unmodified rosin is preferred from the viewpoint of film-forming properties and water resistance, and gum rosin is more preferred.

[0032] [Polyol (D)] Examples of polyols (D) include dihydric alcohols, trihydric alcohols, and tetrahydric or higher alcohols. Examples of dihydric alcohols include linear alkyldiols, branched alkyldiols, and etherdiols. Examples of linear alkyldiols include ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol. Examples of branched alkyldiols include propylene glycol, 1,3-butanediol, 1,2-butanediol, 3-methyl-1,5-pentanediol, and 2,6-dimethyl-1-octen-3,8-diol. Examples of etherdiols include diethylene glycol, triethylene glycol, and dipropylene glycol. Examples of dihydric alcohols include 1,4-dihydroxy-2-butene, isosorbide, cyclohexanedimethanol, cyclohexanediol, tricyclodecanedimethylol, bisphenol A, hydrogenated bisphenol A, hydrogenated bisphenol F, hydrogenated bisphenol S, hydrogenated catechol, hydrogenated resorcinol, hydrogenated hydroquinone, and dicyclopentadiene diallyl alcohol copolymer. Examples of trihydric alcohols include glycerin, trimethylolethane, trimethylolpropane, trimethylolhexane, and trimethyloloctane. Examples of alcohols with a tetrahydric or higher hydric value include tetrahydric to octahydric alcohols. Examples of tetrahydric to octahydric alcohols include pentaerythritol, diglycerin, ditrimethylolpropane, sorbitan, sorbitol, dipentaerythritol, inositol, and tripentaerythritol. These can be used individually or in combination of two or more types.

[0033] From the viewpoint of adjusting the molecular weight of the polyester resin, polyol (D) preferably contains at least one selected from the group consisting of trihydric alcohols and tetrahydric or higher alcohols, more preferably contains a trihydric alcohol, even more preferably contains at least one selected from the group consisting of trimethylolpropane, glycerin, and pentaerythritol, and particularly preferably contains glycerin.

[0034] The number of carbon atoms in polyol (D) is, for example, 2 or more, preferably 3 or more, and also, for example, 30 or less, preferably 20 or less, more preferably 10 or less, and even more preferably 8 or less.

[0035] "Properties of polyester resin" The refractive index of the polyester resin is preferably 1.4 to 1.6, more preferably 1.45 to 1.58, even more preferably 1.47 to 1.57, and particularly preferably 1.48 to 1.56. When the refractive index of the polyester resin is within the above range, the transparency of the coated paper is better. This is because the refractive index of cellulose fibers is generally in the range of 1.4 to 1.6. By making the refractive index of the polyester resin close to the refractive index of the cellulose fibers, the refraction of light at the interface between the coating agent and the pulp fibers in the paper substrate can be reduced.

[0036] The hydroxyl value of the polyester resin is preferably 10 to 180 mg KOH / g, more preferably 10 to 150 mg KOH / g, and particularly preferably 10 to 120 mg KOH / g. If the refractive index of the polyester resin is above the lower limit, the reaction with the isocyanate compound described later increases, which tends to improve drying properties. If it is below the upper limit, the polyester resin does not become too soft, which tends to improve drying properties.

[0037] The acid value of the polyester resin is preferably 5 to 100 mg KOH / g, more preferably 10 to 70 mg KOH / g, and particularly preferably 20 to 50 mg KOH / g. When the acid value of the polyester resin is above the lower limit, it tends to have better drying properties. When it is below the upper limit, it tends to have better transparency.

[0038] "Method for manufacturing polyester resin" Polyester resins can be produced by reacting at least one selected from the group consisting of polycarboxylic acids (A) and aliphatic monocarboxylic acids (B) with rosins (C) and polyols (D). To adjust the refractive index of the polyester resin to the above range, for example, the content ratio of aliphatic monocarboxylic acids (B) and rosins (C) can be adjusted. To adjust the hydroxyl value of the polyester resin to the above range, for example, the types and proportions of polycarboxylic acids (A), aliphatic monocarboxylic acids (B), rosins (C), and polyols (D), as well as the ratio of carboxyl groups to hydroxyl groups, can be adjusted. To adjust the acid value of the polyester resin to the above range, for example, the time of the dehydration condensation reaction can be adjusted.

[0039] When reacting the raw materials, they may be reacted all at once or in a multi-stage reaction. In a single reaction, polyester resin can be produced by a dehydration condensation reaction of a known acid and alcohol. Suitable conditions for the dehydration condensation reaction are approximately 150-300°C and 2-20 hours.

[0040] If the polycarboxylic acid (A) includes an α,β-unsaturated dicarboxylic acid, a multi-step reaction is preferred. Specifically, first, an α,β-unsaturated dicarboxylic acid is reacted with rosins (C) to obtain a primary product. Then, the primary product is reacted with an aliphatic monocarboxylic acid (B) and a polyol (D) to obtain a polyester resin.

[0041] In the step to obtain the first product, an addition reaction is carried out between the unsaturated bond of the α,β-unsaturated dicarboxylic acid and the unsaturated bond of the rosin (C). The reaction temperature in the step of obtaining the first product is, for example, 150°C or higher, preferably 170°C or higher, more preferably 180°C or higher, and also, for example, 230°C or lower, preferably 220°C or lower, more preferably 200°C or lower. The reaction time in the step of obtaining the first product is, for example, 0.1 hours or more, preferably 0.5 hours or more, and also, for example, 5 hours or less, preferably 3 hours or less. In the step of obtaining the first component, a known reaction catalyst may be added in an appropriate proportion as needed. Furthermore, in the step of obtaining the first product, the raw material components may be reacted without a solvent, or in the presence of a known solvent.

[0042] In the step of reacting the first product with an aliphatic monocarboxylic acid (B) and a polyol (D), the carboxyl group of the first product or the aliphatic monocarboxylic acid (B) is esterified with the hydroxyl group of the polyol (D). The first product may be reacted with the aliphatic monocarboxylic acid (B) and the polyol (D) in a single reaction, or in a multi-step reaction. The reaction temperature in the step of reacting the first product with an aliphatic monocarboxylic acid (B) and a polyol (D) is, for example, 150°C or higher, preferably 160°C or higher, more preferably 170°C or higher, even more preferably 180°C or higher, and also, for example, 230°C or lower, preferably 220°C or lower, more preferably 210°C or lower, even more preferably 200°C or lower. The reaction time in the step of reacting the first product with the aliphatic monocarboxylic acid (B) and the polyol (D) is, for example, 1 hour or more, preferably 3 hours or more, and also, for example, 48 hours or less, preferably 24 hours or less. In this reaction, if necessary, the condensed water produced by the esterification reaction can be removed by known distillation method. In the step of reacting the first product with the aliphatic monocarboxylic acid (B) and the polyol (D), a known reaction catalyst may be added in an appropriate proportion as needed. Furthermore, in the step of reacting the first product with the aliphatic monocarboxylic acid (B) and the polyol (D), the starting materials may be reacted without a solvent, or in the presence of a known solvent.

[0043] If the aliphatic monocarboxylic acid (B) contains fatty acids derived from oils and fats, a polyester resin may be obtained by reacting an oil or fat containing the aliphatic monocarboxylic acid (B) as a constituent fatty acid with a polyol (D) to obtain a second product containing a modified product in which the polyol (D) has been modified with the oil or fat, and then reacting this second product with the first product. When the aforementioned oil and fat are reacted with polyol (D), a modified product containing an ester (fatty acid ester) of polyol (D) and a fatty acid derived from the oil and fat is obtained by transesterification. This fatty acid ester is hydrolyzed to produce polyol (D) and fatty acid. Therefore, the modified product can be used in place of aliphatic monocarboxylic acid (B) and polyol (D). Specifically, as described above, an α,β-unsaturated dicarboxylic acid is reacted with rosins (C) to obtain the first product. Separately, an oil containing an aliphatic monocarboxylic acid (B) as a constituent fatty acid is reacted with a polyol (D) to obtain the second product. Then, the first product and the second product are reacted to obtain a polyester resin.

[0044] Examples of oils and fats whose constituent fatty acids are aliphatic monocarboxylic acids (B) include linseed oil, yuzu oil, pistachio oil, rice bran oil, safflower oil, apricot oil, cottonseed oil, sesame oil, corn oil, watermelon oil, soybean oil, poppy oil, apple oil, sunflower oil, cactus oil, tall oil, walnut oil, tung oil, clove oil, and castor oil.

[0045] The blending ratio in the process of obtaining the second product is set as appropriate, but for example, the amount of hydroxyl groups of polyol(D) per mole of oil is, for example, 3 moles or more, preferably 10 moles or more, and for example, 50 moles or less, preferably 40 moles or less.

[0046] The reaction temperature in the step to obtain the second product is, for example, 230°C or higher, preferably 240°C or higher, more preferably 250°C or higher, and also, for example, 300°C or lower, preferably 280°C or lower, more preferably 270°C or lower. If the reaction temperature is excessively low, the reaction in the step to obtain the modified product may not proceed, and the aliphatic monocarboxylic acid (B) may not be incorporated into the polyester resin. If the reaction temperature is excessively high, a decomposition reaction may occur, leading to an increase in low molecular weight components. The reaction time in the step of obtaining the second product is, for example, 0.5 hours or more, preferably 1 hour or more, and also, for example, 20 hours or less, preferably 10 hours or less. In the step to obtain the second product, a known reaction catalyst may be added in an appropriate proportion as needed. Furthermore, in the step to obtain the second product, the starting material components may be reacted without a solvent, or in the presence of a known solvent.

[0047] The reactant obtained in this manner contains a polyester resin. In addition to the polyester resin, the reactant may also contain unreacted raw material components. Unreacted raw material components are removed from the reactant as needed.

[0048] [Hardening agent] The curing agent contains an isocyanate compound. The isocyanate compound reacts with the hydroxyl groups of the polyester resin. Typically, the isocyanate compound has two or more isocyanate groups (-NCO) in one molecule.

[0049] Examples of isocyanate compounds include aliphatic isocyanate compounds, isocyanate compounds having an alicyclic structure, and modified forms of these isocyanate compounds. Isocyanate compounds may be used alone or in combination of two or more types.

[0050] Examples of aliphatic isocyanate compounds include ethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, dodecamethylene diisocyanate, 1,6,11-undecane triisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,6-diisocyanatomethyl caproate, bis(2-isocyanatoethyl) fumarate, bis(2-isocyanatoethyl) carbonate, and 2-isocyanatoethyl-2,6-diisocyanatohexanoate. Among these, hexamethylene diisocyanate is preferred.

[0051] Examples of isocyanate compounds having an alicyclic structure include 4,4'-dicyclohexylmethane diisocyanate (hydrogenated MDI), isophorone diisocyanate, methylcyclohexylene diisocyanate (hydrogenated TDI), and 1,3-bis(isocyanatomethyl)cyclohexane (hydrogenated m-XDI).

[0052] Modified forms include isocyanurates, biuretes, and adducts. Three molecules of an isocyanate compound can form an isocyanurate or biuret. In addition, a trimer adduct is formed by the reaction of three molecules of trimethylolpropane with a polyisocyanate.

[0053] Examples of modified organisms include the following: Biuret and isocyanurate derivatives of isocyanate compounds such as ethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, and dodecamethylene diisocyanate; Biuret and isocyanurate derivatives of alicyclic isocyanate compounds such as 4,4'-dicyclohexylmethane diisocyanate (hydrogenated MDI), isophorone diisocyanate, methylcyclohexylene diisocyanate (hydrogenated TDI), and 1,3-bis(isocyanatomethyl)cyclohexane (hydrogenated m-XDI); Trimeric adduct of trimethylolpropane (TMP) and hydrogenated MDI; A trimer adduct of 3 moles of one isocyanate compound such as isophorone diisocyanate, methylcyclohexylene diisocyanate (hydrogenated TDI), or 1,3-bis(isocyanatomethyl)cyclohexane (hydrogenated m-XDI) and 1 mole of trimethylolpropane (TMP); Adducts of trimethylolpropane (TMP), 2 moles of isophorone diisocyanate, and 1 mole of hexamethylene diisocyanate (HDI); and A bifunctional polyurethane diisocyanate obtained by the addition reaction of a diol with an aliphatic diisocyanate such as ethylene diisocyanate, tetramethylene diisocyanate, or hexamethylene diisocyanate.

[0054] As for the isocyanate compound, from the viewpoint of reactivity with polyester resin, an isocyanate compound having three or more isocyanate groups in one molecule is preferred, the biuret and isocyanurate forms of the isocyanate compound are more preferred, the isocyanurate form of the isocyanate compound is even more preferred, and the isocyanurate form of an aliphatic isocyanate compound is particularly preferred.

[0055] The total content of polyester resin and curing agent in the coating agent is preferably 20% by mass or more, more preferably 40% by mass or more, even more preferably 60% by mass or more, particularly preferably 80% by mass or more, and may also be 100% by mass, based on the total solid content of the coating agent.

[0056] The molar ratio (NCO / OH) of isocyanate groups of the isocyanate compound to the hydroxyl groups of the polyester resin is preferably 0.5 to 5, more preferably 0.3 to 4, and even more preferably 1 to 3. If NCO / OH is above the lower limit, the reaction between the polyester resin and the isocyanate compound increases, improving drying properties. If it is below the upper limit, even if the isocyanate compound is liquid at room temperature, the amount of isocyanate compound in the coating agent is sufficiently small, improving drying properties.

[0057] [Other ingredients] The coating agent may further contain other components besides polyester resin and curing agent, as needed.

[0058] The coating agent may contain, for example, a liquid medium. The liquid medium in the coating agent is removed by drying during the manufacturing of the coated paper. Examples of liquid media include organic solvents, water, and mixtures thereof. Preferably, the liquid media is capable of dissolving or dispersing the polyester resin. As a liquid medium, an organic solvent is preferred because it has excellent penetration into the paper substrate, does not produce the lumps that occur when water is used, and has excellent drying properties.

[0059] Examples of organic solvents include alcohols, ethers, esters, and non-polar solvents. Examples of alcohols include methanol, ethanol, n-propanol, isopropanol, n-butanol, n-pentanol, n-hexanol, and other alcohols having 1 to 6 carbon atoms.

[0060] Examples of ethers include ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, tetraethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, tetraethylene glycol monoethyl ether, ethylene glycol monopropyl ether, diethylene glycol monopropyl ether, triethylene glycol monopropyl ether, tetraethylene glycol monopropyl ether, ethylene glycol monoisopropyl ether, diethylene glycol monoisopropyl ether, triethylene glycol monoisopropyl ether, tetraethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monobutyl ether, ethylene glycol monoisobutyl ether, diethylene glycol monoisobutyl ether, triethylene glycol Polyethylene glycol monoisobutyl ether, tetraethylene glycol monoisobutyl ether, ethylene glycol monotertiary butyl ether, diethylene glycol monotertiary butyl ether, triethylene glycol monotertiary butyl ether, tetraethylene glycol monotertiary butyl ether, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, tripropylene glycol monomethyl ether, propylene glycol monoethyl ether, dipropylene glycol monoethyl ether, tripropylene glycol monoethyl ether, tetrapropylene glycol monoethyl ether, propylene glycol monopropyl ether, dipropylene glycol monopropyl ether, tripropylene glycol monopropyl ether, propylene glycol monoisopropyl ether, dipropylene glycol monoisopropyl ether, tripropylene glycol monoisopropyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monobutyl ether, propylene glycol monoisobutyl ether,Examples include glycol ethers such as dipropylene glycol monoisobutyl ether, tripropylene glycol monoisobutyl ether, propylene glycol monotertiary butyl ether, dipropylene glycol monotertiary butyl ether, and tripropylene glycol monotertiary butyl ether.

[0061] Examples of esters include ethyl acetate, n-butyl acetate, isobutyl acetate, n-amyl acetate, diethylene glycol monoethyl ether acetate, and diethylene glycol monobutyl ether acetate. Examples of nonpolar solvents include paraffinic hydrocarbons such as pentane, hexane, heptane, octane, nonane, decane, and dodecane; isoparaffinic hydrocarbons such as isohexane, isooctane, and isododecane; alkylnaphthenic hydrocarbons such as liquid paraffin; aromatic hydrocarbons such as benzene, toluene, xylene, alkylbenzene, and solvent naphtha; and silicone oil.

[0062] The liquid medium content is set appropriately according to the purpose and application. For example, the liquid medium is, for example, 5% by mass or more, preferably 10% by mass or more, relative to the total amount of the liquid medium and polyester resin. Alternatively, the liquid medium is, for example, 80% by mass or less, preferably 70% by mass or less, relative to the total amount of the liquid medium and polyester resin. Alternatively, the polyester resin may be, for example, 20% by mass or more, preferably 30% by mass or more, relative to the total amount of the liquid medium and polyester resin. Furthermore, the polyester resin may be, for example, 95% by mass or less, preferably 90% by mass or less, relative to the total amount of the liquid medium and polyester resin. If the liquid medium or polyester resin is within the aforementioned range relative to the total amount of the liquid medium and polyester resin, a rapid increase in viscosity can be suppressed, and the productivity, coatability, and drying properties of the coating agent can be improved.

[0063] The coating agent may contain, for example, other resins besides the polyester resin mentioned above. Other resins include, for example, acrylic resins, styrene-modified acrylic resins, silicone acrylic resins, modified silicone acrylic resins, rosin phenol resins, rosin ester resins, terpene phenol resins, coumarone indene resins, petroleum resins, epoxy resins, modified epoxy resins, polyester resins, vinyl acetate resins, ethylene-vinyl acetate resins, urethane resins, urea resins, melamine resins, and cellulose resins. These can be used individually or in combination of two or more types. In coating agents, the proportion of other resins is set appropriately according to the purpose and application. For example, with respect to 100 parts by mass of polyester resin, the other resin may be 0 parts by mass or more, or 20 parts by mass or more, or 80 parts by mass or less, or 60 parts by mass or less.

[0064] The coating agent may contain, for example, wax. The inclusion of wax can suppress blocking when used on paper substrates. Examples of waxes include fatty acid amide waxes, carnauba wax, rice wax, polyolefin wax, paraffin wax, Fischer-Tropsch wax, beeswax, microcrystalline wax, polyethylene oxide wax, and amide waxes. These can be used individually or in combination of two or more types. Preferred waxes include fatty acid amide waxes, carnauba waxes, polyolefin waxes, paraffin waxes, and microcrystalline waxes, and more preferably carnauba waxes, polyolefin waxes, and paraffin waxes.

[0065] More specifically, fatty acid amide waxes include, for example, pelargonic acid amide, capric acid amide, undecylic acid amide, lauric acid amide, tridecyl acid amide, myristic acid amide, pentadecyl acid amide, palmitic acid amide, heptadecyl acid amide, stearic acid amide, nonadecanoic acid amide, arachidic acid amide, behenic acid amide, lignoceric acid amide, oleic acid amide, cetoleic acid amide, linoleic acid amide, linolenic acid amide, and mixtures thereof. Fatty acid amides from animal and vegetable oils are also included as fatty acid amide waxes. These can be used individually or in combination of two or more types.

[0066] More specifically, examples of carnauba wax include MICROKLEAR 418 (manufactured by Micro Powders, Inc.) and refined carnauba wax No. 1 powder (Nippon Wax Co., Ltd.). These can be used individually or in combination of two or more types. More specifically, examples of olefin waxes include polyethylene wax, polypropylene wax, MPP-635VF (Micro Powders, Inc.), and MP-620VF XF (Micro Powders, Inc.). These can be used individually or in combination of two or more types. More specifically, examples of paraffin waxes include MP-28C, MP-22XF, and MP-28C (all from Micro Powders, Inc.). These can be used individually or in combination of two or more types.

[0067] From the standpoint of heat resistance, the melting point of wax is, for example, 60°C or higher and, for example, 130°C or lower.

[0068] In coating agents, the proportion of wax is set appropriately according to the purpose and application. For example, per 100 parts by mass of polyester resin, the amount of wax is, for example, 0 parts by mass or more, preferably 1 part by mass or more, more preferably 3 parts by mass or more, or, for example, 50 parts by mass or less, preferably 30 parts by mass or less.

[0069] The coating agent may contain additives in appropriate proportions. Examples of additives include fillers, thickeners, foaming agents, antioxidants, light stabilizers, heat stabilizers, flame retardants, color adjusters, and drying accelerators such as cobalt octylate and cobalt naphthenate. These can be used individually or in combination of two or more types.

[0070] The coating agent can be manufactured by mixing a polyester resin, a curing agent, and other components as needed. It is preferable to mix the polyester resin and curing agent immediately before applying the coating agent to the paper substrate. The other components may be mixed at the same time as the polyester resin and curing agent, or they may be mixed with the polyester resin or curing agent before the polyester resin and curing agent are mixed.

[0071] <Paper base material> The paper substrate contains pulp. Examples of pulps that make up the paper substrate include chemical pulp, mechanical pulp, recycled paper pulp, and non-wood pulp. These pulps may be used individually or in combination of two or more. Chemical pulp is preferred among these.

[0072] Chemical pulps include coniferous chemical pulp and hardwood chemical pulp, but it is preferable that the paper substrate contains both coniferous and hardwood chemical pulp. Hardwood chemical pulp has a shorter and finer fiber structure than softwood chemical pulp. When using hardwood chemical pulp, the short and fine fiber structure results in superior paper substrate structure. If the paper substrate structure is poor, even if the coating agent is impregnated, the heterogeneity caused by the structure can lead to uneven penetration of the coating agent, which can impair transparency. To obtain coated paper with excellent transparency, it is preferable to have a good paper substrate structure. However, while hardwood chemical pulp with its fine and short fiber structure has good structure, the voids and air spaces are small, making it easy for the coating agent to not penetrate. Also, because there are more interfaces, transmitted light is refracted and attenuated, which tends to reduce transparency. Furthermore, because it is easily coated with the coating agent, its defibration properties when recycled as waste paper tend to be inferior to those of softwood chemical pulp. For this reason, by using a combination of hardwood chemical pulp and softwood chemical pulp as the paper substrate, it is possible to achieve both transparency and recyclability in coated paper.

[0073] Examples of softwood chemical pulps include unbleached softwood kraft pulp (NUKP), bleached softwood kraft pulp (NBKP), semi-bleached softwood kraft pulp (NSBKP), and softwood sulfite pulp (NSP). Among these, bleached softwood kraft pulp (NBKP) and softwood sulfite pulp (NSP) are preferred from the viewpoint of achieving both transparency and strength in coated paper.

[0074] The Canadian standard filtration efficiency (CSF) of softwood chemical pulp is preferably 300-700 mL, more preferably 400-680 mL, even more preferably 420-650 mL, and particularly preferably 450-600 mL. When the CSF of the softwood chemical pulp is above the lower limit of the above range, the voids in the paper substrate can be retained, resulting in excellent impregnation of the coating agent. When the CSF of the softwood chemical pulp is below the upper limit of the above range, the form of the paper substrate can be improved, making it easier to obtain coated paper with a transparent region that has excellent transparency and visibility.

[0075] Examples of hardwood chemical pulps include unbleached hardwood kraft pulp (LUKP), bleached hardwood kraft pulp (LBKP), semi-bleached hardwood kraft pulp (LSBKP), and sulfite hardwood pulp (LSP). Among these, bleached hardwood kraft pulp (LBKP) and sulfite hardwood pulp (LSP) are preferred from the viewpoint of achieving both transparency and strength in coated paper.

[0076] The Canadian standard filtration efficiency (CSF) of hardwood chemical pulp is preferably 250 to 680 mL, more preferably 350 to 650 mL, even more preferably 370 to 630 mL, and particularly preferably 400 to 600 mL. If the CSF of the hardwood chemical pulp is above the lower limit of the above range, the strength of the paper substrate can be increased. If the CSF of the hardwood chemical pulp is below the upper limit of the above range, the form of the paper substrate can be improved, and coated paper with a transparent area that is excellent in transparency and visibility can be easily obtained.

[0077] The mass ratio of coniferous chemical pulp to hardwood chemical pulp (coniferous chemical pulp:hardwood chemical pulp) is preferably 80:20 to 20:80, more preferably 75:25 to 25:75, and even more preferably 70:30 to 30:70.

[0078] If the paper substrate contains softwood chemical pulp and hardwood chemical pulp, the paper substrate may also contain other pulps in addition to these chemical pulps, such as mechanical pulp, recycled paper pulp, non-wood pulp, etc. Examples of mechanical pulps include stonegland pulp (SGP), pressure stonegland pulp (PGW), refinergland pulp (RGP), thermogland pulp (TGP), chemigland pulp (CGP), wood pulp (GP), and thermomechanical pulp (TMP). Examples of recycled paper pulp include disintegrated recycled paper pulp, disintegrated and deinked recycled paper pulp, and disintegrated, deinked and bleached recycled paper pulp. Examples of recycled paper used as raw material for recycled paper pulp include brown recycled paper, kraft envelope recycled paper, magazine recycled paper, newspaper recycled paper, flyer recycled paper, office recycled paper, corrugated cardboard recycled paper, white recycled paper, Kent recycled paper, imitation recycled paper, and land deed recycled paper. Examples of non-wood pulps include various types of pulps, such as pulps chemically or mechanically produced from non-wood fibers like kenaf, cotton, hemp, and reeds. These pulps may be used individually or in combination of two or more types.

[0079] The recycled pulp content is preferably 10% by mass or less, and more preferably 5% by mass or less, relative to the total mass of pulp constituting the paper base material. When the recycled pulp content is below the above upper limit, the coated paper can be suitably applied as packaging material for food and beverages. The lower limit for the recycled pulp content is 0% by mass.

[0080] The visible light transmittance of paper substrates is, for example, 10-20%.

[0081] The basis weight of the paper substrate is 35-150 g / m². 2 Preferably, 40-100 g / m² 2 More preferably, 43-80 g / m 2 This is even more preferable. If the basis weight is above the lower limit of the above range, the paper will have sufficient strength and become a coated paper suitable for use as packaging paper, printing paper, etc. If the basis weight is below the upper limit of the above range, the transparency of the coated paper can be increased. Basis weight is measured in accordance with JIS P8124.

[0082] The air permeability of the paper substrate is preferably 10 to 40 seconds, more preferably 12 to 35 seconds, and even more preferably 15 to 33 seconds. If the air permeability is above the lower limit of the above range, the paper will have sufficient strength and will be a coated paper suitable for applications such as packaging paper and printing paper. If the air permeability is below the upper limit of the above numerical range, the penetration of the coating agent will be excellent and the transparency of the coated paper can be increased. The air permeability is measured using the Wangyan method, in accordance with J.TAPPI-5-2:2000.

[0083] The density of the paper substrate is 0.5 to 0.90 g / cm³. 3 Preferably, 0.6-0.8 g / cm³ 3This is more preferable. If the density is above the lower limit of the range, the paper strength is obtained, resulting in coated paper suitable for applications such as packaging paper and printing paper. If the density is below the upper limit of the range, the penetration of the coating agent is excellent, and the transparency of the coated paper can be increased. Density is measured in accordance with JIS P8118.

[0084] The porosity of the paper substrate is preferably 30-80%, more preferably 40-70%, and even more preferably 50-70%. If the porosity of the paper substrate is above the lower limit of the above range, the transparency of the transparent area is easily enhanced. If the porosity of the paper substrate is below the upper limit of the above range, the physical strength of the sheet is less likely to decrease. The porosity of the paper substrate is the value obtained by dividing the density, measured in accordance with JIS P8118, by the true density of cellulose, which is 1.50.

[0085] The ParkerPrintSurf smoothness of at least one surface of the paper substrate is preferably 7 μm or less, and more preferably 5 μm or less. There is no particular lower limit. The smaller the value, the smoother the surface. ParkerPrintSurf smoothness can evaluate the smoothness of fine details, and the smaller this value, the less light scattering on the paper surface can be reduced, thereby improving visibility through the transparent portion. The smoothness of Parker Print Surf is determined in accordance with ISO 8791-4:1992 (soft backing / clamping pressure 500kPa).

[0086] In addition to pulp, the paper substrate may contain known papermaking aids such as paper strength enhancers, sizing agents, fillers, and colorants. The inclusion of fillers such as talc and calcium carbonate improves the smoothness and whiteness of the paper substrate, but it also increases the opacity of the paper, making it difficult to impart transparency. Therefore, it is preferable to keep the filler content in the paper substrate within a range that does not impair transparency and visibility, and it is even preferable that the paper substrate does not contain any fillers.

[0087] The method for manufacturing paper substrates is not particularly limited. For example, one method may include a step of beating pulp which will be the raw material for the paper substrate, a step of papermaking from a pulp slurry containing the beated pulp, and a step of drying the wet sheet obtained by papermaking.

[0088] In the beating process, it is preferable to beating the raw pulp so that it achieves the Canadian standard water content. The beating machine is not particularly limited. For example, known beating machines such as double disc refiners can be used. The papermaking machines used are not particularly limited. Examples include screenprint machines, short screenprint machines, and cylinder screenprint machines. The drying process is not particularly limited. For example, a dryer attached to the paper machine can be used.

[0089] The paper substrate may be subjected to a smoothing treatment. By applying a smoothing treatment, light scattering on the paper surface can be reduced, thereby improving visibility through the transparent portion. Examples of smoothing processes include compression presses, machine calenders, gloss calenders, soft nip calenders, and supercalenders. However, these devices increase the density of the paper, so care must be taken to reduce the linear pressure to prevent excessive density. On the other hand, transfer methods, in which the paper is attached to a smooth surface while still wet and then dried to transfer the smooth surface, are preferable because they do not increase the density of the paper. For example, technologies such as Yankee cylinders, cast drums, and film transfers can be used. Among these, Yankee dryers using Yankee cylinders are preferable because they are attached to the paper machine, resulting in superior productivity.

[0090] As a paper substrate, commercially available papers such as kraft paper, glossy kraft paper, fine paper, electrophotographic paper, inkjet recording paper, thermal recording paper, laser thermal paper, thermal transfer recording paper, art paper, coated paper, cast coated paper, white cardboard, colored cardboard, corrugated cardboard liner, glassine paper, rice paper, India paper, and Japanese paper can also be used. Among these, fine paper, electrophotographic paper, kraft paper, and glossy kraft paper, which have a low pigment content, are preferred because they provide excellent visibility of the transparent areas due to the coating agent.

[0091] <Method of manufacturing coated paper> The coated paper of this embodiment can be manufactured by applying the above-mentioned coating agent to at least one surface of a paper substrate.

[0092] The coating agent can be applied by known methods. Examples include spray coaters, roll coaters, gravure coaters, nip coaters, bar coaters, blade coaters, lip coaters, fountain coaters, curtain coaters, flow coaters, comma coaters, dip coaters, brush coating, immersion methods, flexographic printing, inkjet printing, gravure printing, offset printing, gravure offset printing, and silkscreen printing. Among these, methods that apply, impregnate, and print using rolls and roll nibs are preferred because they efficiently push the coating agent into the paper substrate, resulting in high transparency. Examples of such methods include roll coaters, gravure coaters, nip coaters, bar coaters, blade coaters, etc., which combine rolls such as backup rolls and backing rolls with applicator rolls, and gravure printing, gravure offset printing, and offset printing, which combine an impression cylinder with a plate cylinder or blanket cylinder.

[0093] The coating agent may be applied to the entire surface of the paper substrate or to a portion of it. Furthermore, during the application of the coating agent, there may be areas in the cross-section of the paper substrate where the coating agent does not reach a portion of the surface opposite the coated surface. The coating agent may be applied to only one side of the paper substrate, or it may be applied to both one side and the other side of the paper substrate. The coating agent may be applied in a single application or in multiple applications. If applied in multiple applications, the components and composition of the coating agent used in each application may be the same or different.

[0094] After applying the coating agent, allow it to dry and remove the liquid medium as needed. Drying can be carried out by known methods. Drying conditions may be natural drying at room temperature or heated drying. Heated drying is preferred. The drying temperature in heated drying is, for example, 40°C or higher, preferably 50°C or higher. The drying temperature is, for example, 190°C or lower, preferably 160°C or lower. The drying time is, for example, 1 second or more, preferably 5 seconds or more. The drying time is, for example, 600 seconds or less, preferably 300 seconds or less. After drying, humidity control may be performed to adjust the moisture content. For example, the humidity control conditions are a temperature of 23°C and a relative humidity of 50%.

[0095] <Application> The coated paper of this embodiment can be used as packaging paper with a transparent area for applications such as boxes, bags, envelopes, and clear files. In addition to packaging paper, it can also be used for various applications in printing paper, book paper, copy paper, information paper, label paper, household paper, etc., to allow visibility of images (characters, symbols, images, objects, etc.) on the opposite side of the paper through the paper substrate. [Examples]

[0096] Next, the present invention will be described based on examples and comparative examples, but the present invention is not limited to the following examples. Unless otherwise specified, "parts" and "%" are based on mass. Furthermore, the specific numerical values ​​such as the blending ratio (content), physical properties, and parameters used in the following description may be replaced with the corresponding upper limits (numerical values ​​defined as "less than or equal to" or "less than") or lower limits (numerical values ​​defined as "greater than or equal to" or "greater than") of the blending ratio (content), physical properties, and parameters described in the "Modes for Carrying Out the Invention" above.

[0097] <Method for measuring the properties of polyester resin> (1) Refractive index The refractive index was measured using a multi-wavelength Abbe refractometer DR-M4 (manufactured by Atago Corporation) in accordance with JIS K 7142 (2014).

[0098] (2) Hydroxyl value The hydroxyl value was measured in accordance with JIS K 0070 (1992).

[0099] (3) Acid value The acid value was measured in accordance with JIS K 5601-2-1 (1999).

[0100] <Manufacturing of polyester resin> (Manufacturing Example 1) A four-necked flask equipped with a stirrer, a reflux condenser with a water separator, and a thermometer was filled with 46.6 parts of gum rosin while blowing nitrogen gas into it, and the temperature was raised to 210°C. Next, 6.5 parts of fumaric acid were added to the flask and stirred at 210°C for approximately 90 minutes. This yielded the first product. In another four-necked flask equipped with a reflux condenser with a water separator and a thermometer, 41.3 parts of linseed oil and 8.7 parts of glycerin were added and stirred at 250°C for approximately 90 minutes. This yielded the second product. The first product was mixed into a four-necked flask containing the second product, and the mixture was cooled to 190°C. A dehydration condensation reaction was then carried out at 190°C for 8 hours to obtain rosin-modified polyester resin (resin 1). The properties of the obtained resin 1 are shown in Table 1.

[0101] (Manufacturing examples 2 and 3) Rosin-modified polyester resins (Resins 2 and 3) were obtained in the same manner as in Production Example 1, except that the raw material components and ratios were changed as shown in Table 1. The physical properties of the obtained Resins 2 and 3 are shown in Table 1.

[0102] (Production Example 4) While blowing nitrogen gas into a four-necked flask equipped with a stirrer, a reflux condenser with a water separator, and a thermometer, 92.5 parts of oleic acid was charged, and the temperature was raised to 210°C. Next, 12.1 parts of pentaerythritol was added to the flask, and the temperature was raised to 250°C. Thereafter, a dehydration condensation reaction was carried out at 250°C for about 8 hours to obtain a pentaerythritol ester of oleic acid (Resin 4). The physical properties of the obtained Resin 4 are shown in Table 1.

[0103]

Table 1

[0104] <Example 1> (Preparation of coating liquid) 70 parts of Resin 1 and 30 parts of toluene were mixed to obtain a toluene solution of Resin 1 having a solid content of 70%. Next, 5.2 parts of Duranate TPA-100 (manufactured by Asahi Kasei Corporation, isocyanurate form of hexamethylene diisocyanate) was added to 100 parts of the toluene solution of Resin 1, and the mixture was diluted with toluene to a solid content of 70% to obtain the coating liquid of Example 1.

[0105] (Preparation of coated paper) A one-side glossy kraft paper having a basis weight of 50 g / m 2 was prepared as the paper base material. The pulp constituting this paper base material was 40% bleached hardwood kraft pulp and 60% bleached softwood kraft pulp. Further, this paper base material had a visible light transmittance of 15% and a density of 0.72 g / cm 3 and a thickness of 70 μm. The above coating liquid adjusted to 25°C was applied to one side of the above paper base material using a wire-wound bar coater No. 36, and dried at 110°C for 1 minute to obtain a coated paper. The resin solid adhesion amount at this time was 30 g / m 2 .

[0106] <Examples 2-7, Comparative Example 1> The coating solution was prepared in the same manner as in Example 1, except that the types of resin and solvent, and the ratio of resin to hardener were changed as shown in Table 2. The coated paper was prepared in the same manner as in Example 1, except that this coating solution was used. "IPA" is 2-propanol.

[0107] <Comparative Example 2> 70 parts of resin 2 and 30 parts of toluene were mixed to obtain a toluene solution of resin 2 with a solid content of 70%. This solution was used as the coating solution for Comparative Example 6. Coated paper was prepared in the same manner as in Example 1, except that this coating solution was used.

[0108] <Rating> The following evaluations were performed for each case. The results are shown in Table 2.

[0109] (dryness) After drying at 110°C for 1 minute, the coated surface was touched with a finger to check for stickiness. ○ indicated no stickiness, △ indicated slight stickiness but no practical problems, and × indicated stickiness where the coated surface adhered to the finger.

[0110] (transmittance) The obtained coated paper was conditioned for 12 hours in a constant temperature and humidity environment (22°C, 50% relative humidity), and then its visible light transmittance was measured. Visible light transmittance was measured using a transmission meter LS160 (manufactured by ZHELLY) with visible light at a wavelength of 530 nm.

[0111] [Table 2]

[0112] As shown in the results above, the coated papers of Examples 1 to 7 exhibited excellent drying properties and transparency. On the other hand, Comparative Example 1, which did not use rosin as a raw material component of the polyester resin, had low visible light transmittance and poor transparency. Comparative Example 2, which did not contain isocyanate compounds, had poor drying properties. [Explanation of Symbols]

[0113] 1 Coated paper 1a Coated surface 11 Paper base material 12 Coating agents

Claims

1. It contains polyester resin and a hardening agent. The polyester resin is a reaction product of at least one selected from the group consisting of polycarboxylic acids (A) and aliphatic monocarboxylic acids (B), rosins (C), and polyols (D), and has hydroxyl groups. The curing agent is a paper coating agent containing an isocyanate compound.

2. The paper coating agent according to claim 1, wherein the refractive index of the polyester resin is 1.4 to 1.

6.

3. The paper coating agent according to claim 1, wherein the molar ratio (NCO / OH) of isocyanate groups of the isocyanate compound to the hydroxyl groups of the polyester resin is 0.5 to 5.

4. The paper coating agent according to claim 1, wherein the hydroxyl value of the polyester resin is 10 to 180 mg KOH / g.

5. A method for manufacturing coated paper, comprising applying a paper coating agent according to any one of claims 1 to 4 to at least one surface of a paper substrate.

6. Coated paper having a paper coating agent according to any one of claims 1 to 4 applied to at least one surface of a paper substrate.

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