Clarity agents, methods of production, transparent paper and methods of production

Abstract

The invention proposes a transparent material which uses bio-derived raw materials and is capable of producing transparent paper with excellent transparency and stability over time. The invention proposes a transparent material comprising a polyester resin component which is the reaction product of a raw material component comprising (A) rosin, (B) polycarboxylic acid, (C) polyol and (D) fatty monocarboxylic acid, wherein the polyester resin component has an acid value of 100 mg KOH / g or less, a bulk mean molecular weight of 1,000,000 or less and a refractive index of 1.40 or more and 1.60 or less.

Description

Clarifying agent, its manufacturing method, transparent paper and its manufacturing method

[0001] This application claims priority to Japanese Patent Application No. 2023-176632, filed on October 12, 2023, the contents of which are incorporated herein by reference.

[0002] Common methods for producing highly transparent paper include, for example, a method of making paper using pulp fibers with a high degree of beating, and a method of impregnating the spaces between the fibers of a made base paper with a resin or the like. The method of making paper using pulp fibers with a high degree of beating is used to make glassine paper, tracing paper, etc. Paper made using pulp fibers with a high degree of beating is used as packaging paper for windows in envelopes, etc. However, such paper is generally difficult to apply to applications such as packaging bags that require strength, because the pulp fibers are crushed and cut by the high beating.

[0003] On the other hand, a method of impregnating the spaces between fibers of a paper-made base paper with a resin or the like is used in the production of oil paper, wax paper, etc. For example, Patent Document 1 proposes obtaining transparent paper by thermally melting and coating or impregnating a transparent agent containing a resin and paraffin wax onto a base paper. Patent Document 2 proposes obtaining transparent paper by coating or impregnating paper with a composition containing a liquid diene polymer and irradiating it with ultraviolet light. Patent Document 3 proposes applying a rosin-based aqueous transparent agent to a portion of base paper and heating it to obtain a windowed packaging bag. Patent Document 4 proposes printing and impregnating a transparent agent mainly composed of vegetable oil onto a specific surface of opaque paper, and forming oil layer protective films on both sides to make the opaque paper transparent.

[0004] Japanese Patent Laid-Open No. 61-132698 Japanese Patent Laid-Open No. 61-132699 Japanese Patent Laid-Open No. 2011-63286 Japanese Patent Laid-Open No. 62-15395

[0005] In recent years, the replacement of plastic films with paper has been considered as a sustainable and recyclable material. For example, the replacement of packaging materials with paper is also progressing. If the transparency of plastic films could be imparted to paper, it is expected that its applications would be further expanded.

[0006] The techniques of Patent Documents 1 to 4 can increase the transparency of the translucent regions impregnated with the clarifying agent by impregnating the voids between the cellulose fibers of paper with a clarifying agent. However, the paraffin wax used in Patent Document 1 is a mixture of solid hydrocarbons made from petroleum, and is not a bio-based raw material. The liquid diene-based polymer used in Patent Document 2 is also a petroleum-derived resin, and is not a bio-based raw material.

[0007] The rosin-based aqueous clarifying agent used in Patent Document 3 is unable to achieve sufficient transparency. Patent Document 4 requires an oil layer protection layer to prevent the impregnated vegetable oil from seeping out. If an oil layer protection layer is not provided, the vegetable oil will seep out or dry over time, causing the paper to become cloudy.

[0008] The present invention aims to provide a clarifying agent using bio-derived raw materials that can produce transparent paper that is excellent in transparency and stability over time, and a method for producing the same, as well as transparent paper that is excellent in transparency and stability over time and uses a clarifying agent using bio-derived raw materials, and a method for producing the same.

[0009] The inventors investigated a clarifying agent that uses a combination of rosins and aliphatic carboxylic acids. While rosins and aliphatic carboxylic acids each exhibit a refractive index close to that of cellulose pulp, using them together brings the refractive index closer to that of cellulose pulp than that of either of them. However, as in Patent Document 4, if used alone, the aliphatic carboxylic acid will leach out or dry, causing the paper to become cloudy. After further investigation, the inventors discovered that the above-mentioned problems can be solved by incorporating rosins and aliphatic carboxylic acids into polyester resins, leading to the completion of the present invention.

[0010] The present invention has the following aspects. [1] A clarifying agent comprising a polyester resin component that is a reaction product of raw material components including (A) a rosin, (B) a polycarboxylic acid, (C) a polyol, and (D) an aliphatic monocarboxylic acid, wherein the polyester resin component has an acid value of 100 mgKOH / g or less, a weight-average molecular weight of 1,000,000 or less, and a refractive index of 1.40 to 1.60. [2] The clarifying agent according to [1], wherein the polyester resin component has an iodine value of 10 g / 100 g or more and 140 g / 100 g or less. [3] A method for producing a clarifying agent, comprising reacting raw material components including (A) a rosin, (B) a polycarboxylic acid, (C) a polyol, and (D) an aliphatic monocarboxylic acid to obtain a polyester resin component having an acid value of 100 mgKOH / g or less, a weight-average molecular weight of 1,000,000 or less, and a refractive index of 1.40 to 1.60. [4] The method for producing a clarifying agent according to [3], wherein the polyester resin component has an iodine value of 10 g / 100 g or more and 140 g / 100 g or less. [5] The method for producing a clarifying agent according to [3] or [4], wherein the (B) polycarboxylic acid contains an α,β-unsaturated dicarboxylic acid, and the polyester resin component is produced by reacting the (A) rosin with the α,β-unsaturated dicarboxylic acid to obtain a first product, and then reacting the first product with the (C) polyol and the (D) aliphatic monocarboxylic acid. [6] The method for producing a clarifying agent according to [3] or [4], wherein the (B) polycarboxylic acid contains an α,β-unsaturated dicarboxylic acid, and the polyester resin component is produced by reacting the (A) rosin with the α,β-unsaturated dicarboxylic acid to obtain a first product, modifying the (C) polyol with an oil or fat having the (D) aliphatic monocarboxylic acid as a constituent fatty acid to obtain a modified product, and then reacting the first product with the modified product.[7] Transparent paper comprising a clarifying agent at least inside the paper base material, the clarifying agent comprising a polyester resin component which is a reaction product of raw material components including (A) rosins, (B) polycarboxylic acids, (C) polyols, and (D) aliphatic monocarboxylic acids, the polyester resin component having an acid value of 100 mgKOH / g or less, a weight-average molecular weight of 1,000,000 or less, and a refractive index of 1.40 or more and 1.60 or less. [8] Transparent paper according to [7], wherein the polyester resin component has an iodine value of 10 g / 100 g or more and 140 g / 100 g or less. [9] Transparent paper according to [7] or [8], wherein the paper base material comprises softwood chemical pulp and hardwood chemical pulp.

[10] A method for producing transparent paper by coating or impregnating a paper substrate with a liquid composition containing a clarifying agent and a liquid medium, and drying the resulting mixture, wherein the clarifying agent contains a polyester resin component that is a reaction product of raw material components containing (A) rosins, (B) polycarboxylic acids, (C) polyols, and (D) aliphatic monocarboxylic acids, and the polyester resin component has an acid value of 100 mgKOH / g or less, a weight-average molecular weight of 1,000,000 or less, and a refractive index of 1.40 or more and 1.60 or less.

[11] A method for producing transparent paper according to

[10] , wherein the polyester resin component has an iodine value of 10 g / 100 g or more and 140 g / 100 g or less.

[12] A method for producing transparent paper according to

[10] or

[11] , wherein the paper substrate contains softwood chemical pulp and hardwood chemical pulp.

[0011] The present invention can provide a clarifying agent using bio-derived raw materials that can produce transparent paper that is excellent in transparency and stability over time, and a method for producing the same, as well as transparent paper that is excellent in transparency and stability over time and uses a clarifying agent using bio-derived raw materials, and a method for producing the same.

[0012] In this specification, the term "to" indicating a range of values ​​means that the values ​​before and after it are included as the lower and upper limits. The lower and upper limits of the ranges disclosed in this specification can be arbitrarily combined to form new ranges.

[0013] "Clarifying Agent" The clarifying agent of the present invention contains a polyester resin component which is a reaction product of raw material components including (A) rosins, (B) polycarboxylic acids, (C) polyols, and (D) aliphatic monocarboxylic acids. The polyester resin component has an acid value of 100 mg KOH / g or less, a weight-average molecular weight of 1,000,000 or less, and a refractive index of 1.40 or more and 1.60 or less. The raw material components will be described in detail later.

[0014] When the acid value of the polyester resin component is 100 mgKOH / g or less, excellent transparency properties are obtained. The acid value of the polyester resin component is preferably 70 mgKOH / g or less, more preferably 60 mgKOH / g or less, and even more preferably 50 mgKOH / g or less. Furthermore, from the viewpoint of transparency suitability, the acid value of the polyester resin component is, for example, 0 mgKOH / g or more, preferably 5 mgKOH / g or more, more preferably 10 mgKOH / g or more, and even more preferably 20 mgKOH / g or more. The acid value is measured in accordance with JIS K 5601-2-1 (1999).

[0015] When the weight average molecular weight (Mw) of the polyester resin component is 1,000,000 or less, excellent transparency properties are obtained. The weight average molecular weight of the polyester resin component is preferably 900,000 or less, more preferably 800,000 or less. The lower limit of the weight average molecular weight of the polyester resin component is not particularly limited, and is, for example, preferably 5,000 or more, more preferably 10,000 or more. The weight average molecular weight of the polyester resin component is a value measured by gel permeation chromatography (GPC) in terms of standard polystyrene.

[0016] When the refractive index of the polyester resin component is 1.40 or more and 1.60 or less, the clarifying agent has an excellent effect of clarifying a sheet whose main component is cellulose, such as paper. This is because the refractive index of cellulose fibers is generally in the range of 1.4 to 1.6. By adjusting the refractive index of the polyester resin component to a value close to the refractive index of cellulose fibers, the refraction of light at the interface between the clarifying agent and the pulp fibers in the paper substrate can be reduced. The refractive index of the polyester resin component is preferably 1.45 or more and 1.58 or less, more preferably 1.47 or more and 1.57 or less, and even more preferably 1.48 or more and 1.56 or less. The refractive index is measured in accordance with JIS K 7142 (2014).

[0017] The iodine value of the polyester resin component is, from the viewpoint of drying property, for example, 5 g / 100 g or more, preferably 10 g / 100 g or more, more preferably 20 g / 100 g or more, and even more preferably 40 g / 100 g or more. Furthermore, from the viewpoint of suitability for transparency, the iodine value of the polyester resin component is, for example, 160 g / 100 g or less, preferably 140 g / 100 g or less, more preferably 120 g / 100 g or less, and even more preferably 100 g / 100 g or less. The iodine value is measured in accordance with JIS K 0070 (1992).

[0018] From the viewpoints of film-forming ability and tack resistance, the softening point of the polyester resin component is, for example, 70° C. or higher, preferably 75° C. or higher, and more preferably 80° C. or higher. From the viewpoints of film-forming ability and tack resistance, the softening point of the polyester resin component is, for example, 150° C. or lower, preferably 130° C. or lower, and more preferably 120° C. or lower. The softening point is measured by the Mettler method.

[0019] (Raw material components of polyester resin component) (A) Rosins are plant-derived components. Therefore, the polyester resin component can contribute to carbon neutrality. More specifically, (A) Rosins are compounds derived from pine. The pine is not particularly limited, and examples thereof include Merkus pine, slash pine, and Masson pine. These can be used alone or in combination of two or more types.

[0020] (A) Rosins are not particularly limited, and examples thereof include known unmodified rosins and derivatives thereof. 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 rosins 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 types. The origin of the rosin is not particularly limited, and examples include China, Vietnam, Indonesia, and Brazil. These can be used alone or in combination of two or more types. As (A) Rosins, unmodified rosin is preferred, and gum rosin is more preferred, from the viewpoints of film-forming ability and water resistance.

[0021] The content ratio of the (A) rosins relative to the total amount of raw material components is not particularly limited as long as the refractive index of the resulting polyester resin component satisfies 1.40 or more and 1.60 or less. From the viewpoints of clarifying suitability, film-forming ability, water resistance, and tack resistance, the content ratio of the (A) rosins relative to the total amount of raw material components is, for example, 10% by mass or more, preferably 15% by mass or more, more preferably 20% by mass or more, and even more preferably 25% by mass or more. From the viewpoints of film-forming ability, water resistance, and tack resistance, the content ratio of the (A) rosins relative to the total amount of raw material components is, for example, 80% by mass or less, preferably 70% by mass or less, more preferably 65% ​​by mass or less, and even more preferably 60% by mass or less.

[0022] The (B) polycarboxylic acid refers to a compound having two or more carboxy groups and anhydrides thereof. The (B) polycarboxylic acid is a component that adjusts the molecular weight of the polyester resin component. Examples of the (B) polycarboxylic acid 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, dodecanedioic acid, tetradecanedioic acid, hexadecanedioic acid, phthalic acid, isophthalic acid, terephthalic acid, tetrahydrophthalic acid, oxaloacetic acid, methylmalonic acid, dimethylmalonic acid, methylsuccinic acid, 2,2-dimethylsuccinic acid, methylglutaric acid, dimethylglutaric acid, diglycolic acid, 1,2-dimethyl-2,3-dimethyl-2,4-dimethyl-2,5-dimethyl-2,6 ... ,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 anhydrides thereof. These may be used alone or in combination of two or more. As the (B) polycarboxylic acid, dicarboxylic acids are preferred from the viewpoint of molecular weight adjustment.

[0023] The (B) polycarboxylic acid preferably contains an α,β-unsaturated dicarboxylic acid. Because the α,β-unsaturated dicarboxylic acid reacts with the (A) rosin, the inclusion of the α,β-unsaturated dicarboxylic acid in the (B) polycarboxylic acid improves the clarifying suitability. Examples of the α,β-unsaturated dicarboxylic acid include fumaric acid, maleic acid, itaconic acid, citraconic acid, and anhydrides thereof. Examples of the anhydrides include maleic anhydride, itaconic anhydride, and citraconic anhydride. These can be used alone or in combination of two or more. The α,β-unsaturated dicarboxylic acid can also be used in combination with other dicarboxylic acids.

[0024] From the viewpoint of adjusting the molecular weight, the (B) polyvalent carboxylic acid preferably includes at least one selected from the group consisting of succinic acid, fumaric acid, maleic anhydride, and adipic acid, and more preferably includes fumaric acid.

[0025] The content of the (B) polycarboxylic acid relative to the total amount of raw material components is, from the viewpoint of the molecular weight of the polyester resin component, for example, 3% by mass or more, preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 12% by mass or more. Furthermore, the content of the (B) polycarboxylic acid relative to the total amount of raw material components is, from the viewpoint of the molecular weight of the polyester resin, for example, 40% by mass or less, preferably 30% by mass or less, more preferably 25% by mass or less, and even more preferably 20% by mass or less. From the viewpoint of the molecular weight of the polyester resin component, the content of the (B) polycarboxylic acid relative to 100 moles of the (A) rosin is, from the viewpoint of the molecular weight of the polyester resin component, for example, 20 moles or more, preferably 30 moles or more, more preferably 35 moles or more, and even more preferably 40 moles or more. Furthermore, the content of the (B) polycarboxylic acid relative to 100 moles of the (A) rosin is, for example, 150 moles or less, preferably 120 moles or less, more preferably 110 moles or less, and even more preferably 100 moles or less. When the content of the (B) polycarboxylic acid is equal to or greater than the lower limit of the above range, the amount of unreacted (A) rosin is relatively small, allowing the molecular weight of the polyester resin component to be increased. When the content of the (B) polycarboxylic acid is equal to or less than the upper limit of the above range, the amount of unreacted (B) polycarboxylic acid is relatively small, making it easier to adjust the molecular weight of the polyester resin component, and as a result, gelation is less likely to occur.

[0026] (C) Polyols include, for example, dihydric alcohols, trihydric alcohols, and tetrahydric or higher alcohols. Dihydric alcohols include, for example, linear alkyl diols, branched alkyl diols, and ether diols. Linear alkyl diols include, for example, ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol. Branched alkyl diols include, for example, propylene glycol, 1,3-butanediol, 1,2-butanediol, 3-methyl-1,5-pentanediol, and 2,6-dimethyl-1-octene-3,8-diol. Ether diols include, for example, 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 tetrahydric or higher alcohols 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 alone or in combination of two or more.

[0027] From the viewpoint of adjusting the molecular weight of the polyester resin component, the (C) polyol preferably contains at least one selected from the group consisting of trihydric alcohols and tetrahydric or higher alcohols, more preferably contains a trihydric alcohol, still more preferably contains at least one selected from the group consisting of trimethylolpropane, glycerin, and pentaerythritol, and particularly preferably contains glycerin.

[0028] The polyol (C) has a carbon number of, for example, 2 or more, preferably 3 or more. The polyol (C) has a carbon number of, for example, 30 or less, preferably 20 or less, more preferably 10 or less, and still more preferably 8 or less.

[0029] The content of the polyol (C) relative to the total amount of the raw material components is, from the viewpoint of the molecular weight of the polyester resin component, for example, 5% by mass or more, preferably 8% by mass or more, more preferably 12% by mass or more, even more preferably 13% by mass or more, and particularly preferably 15% by mass or more. Also, the content of the polyol (C) relative to the total amount of the raw material components is, from the viewpoint of the molecular weight of the polyester resin, for example, 40% by mass or less, preferably 30% by mass or less, more preferably 25% by mass or less, and even more preferably 20% by mass or less.

[0030] Examples of (D) aliphatic monocarboxylic acids include formic acid, acetic acid, trifluoroacetic acid, propionic acid, acrylic acid, methacrylic acid, pivalic acid, mercaptoacetic acid, and sorbic acid. Further examples of (D) aliphatic monocarboxylic acids include fatty acids derived from fats and oils. More specifically, examples include linseed oil fatty acids, yuzu oil fatty acids, pistachio oil fatty acids, rice oil fatty acids, safflower oil fatty acids, apricot 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 alone or in combination of two or more.

[0031] The refractive index of the aliphatic monocarboxylic acid (D) is, for example, 1.35 to 1.65, or preferably 1.40 to 1.60.

[0032] From the viewpoint of suitability for clarifying, the aliphatic monocarboxylic acid (D) preferably has a predetermined iodine value. From the viewpoint of suitability for clarifying, the iodine value of the aliphatic monocarboxylic acid (D) 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.

[0033] From the viewpoint of clarifying suitability, the aliphatic monocarboxylic acid (D) preferably contains an aliphatic monocarboxylic acid having an iodine value of 20 g / 100 g or more as a main component. The term "main component" refers to 80% by mass or more, preferably 90% by mass or more, and more preferably 95% by mass or more. That is, the content of the aliphatic monocarboxylic acid having an iodine value of 20 g / 100 g or more relative to the total amount of the aliphatic monocarboxylic acid (D) is, for example, 80% by mass or more, preferably 90% by mass or more, and more preferably 95% by mass or more. Particularly preferably, the aliphatic monocarboxylic acid (D) is an aliphatic monocarboxylic acid having an iodine value of 20 g / 100 g or more.

[0034] Examples of aliphatic monocarboxylic acids having an iodine value of 20 g / 100 g or more include linseed oil fatty acids, yuzu oil fatty acids, pistachio oil fatty acids, rice oil fatty acids, safflower oil fatty acids, apricot 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.

[0035] The content ratio of the (D) aliphatic monocarboxylic acid (when used in combination, their total amount) relative to the total amount of the raw material components is not particularly limited, as long as the refractive index of the resulting polyester resin component satisfies 1.40 to 1.60. From the viewpoints of suitability for making transparent, flexibility, water resistance, and the like, the content ratio of the (D) aliphatic monocarboxylic acid relative to the total amount of the raw material components is, for example, 5% by mass or more, preferably 10% by mass or more, more preferably 15% by mass or more, even more preferably 20% by mass or more, and particularly preferably 25% by mass or more. From the viewpoints of suitability for making transparent, flexibility, water resistance, and the like, the content ratio of the (D) aliphatic monocarboxylic acid relative to the total amount of the raw material components is, for example, 60% by mass or less, preferably 55% by mass or less, more preferably 40% by mass or less, and even more preferably 35% by mass or less.

[0036] (Production of Polyester Resin Component) The polyester resin component can be produced by reacting the above-mentioned raw material components. The acid value and molecular weight of the polyester resin component can be adjusted to the above-mentioned ranges by, for example, adjusting the blending amounts of the raw material components to the preferred ratios described above, and adjusting the reaction temperature and reaction time. The refractive index of the polyester resin component can be adjusted to the above-mentioned ranges by, for example, adjusting the content ratios of (A) rosins and (D) aliphatic monocarboxylic acids. The iodine value of the polyester resin component can be adjusted to the above-mentioned ranges by, for example, adjusting the iodine value and content ratio of (D) aliphatic monocarboxylic acid.

[0037] When reacting the raw material components, the raw material components may be reacted in one batch or in multiple stages. In the batch reaction, the polyester resin component can be produced by a known dehydration condensation reaction of an acid and an alcohol. Suitable conditions for the dehydration condensation reaction are approximately 150 to 300°C and a reaction time of approximately 2 to 20 hours.

[0038] When the polycarboxylic acid (B) contains an α,β-unsaturated dicarboxylic acid, a multi-stage reaction is preferred. Specifically, first, a rosin (A) is reacted with an α,β-unsaturated dicarboxylic acid to obtain a first product. Next, the first product is reacted with a polyol (C) and an aliphatic monocarboxylic acid (D) to obtain a second product containing a polyester resin component.

[0039] In the step of obtaining a first product, an unsaturated bond in the rosin (A) and an unsaturated bond in the α,β-unsaturated dicarboxylic acid are subjected to an addition reaction. The reaction temperature in the step of obtaining a first product is, from the viewpoint of adjusting the acid value and molecular weight of the polyester resin component, for example, 150°C or higher, preferably 170°C or higher, and more preferably 180°C or higher. The reaction temperature in the step of obtaining a first product is, from the viewpoint of adjusting the acid value and molecular weight of the polyester resin component, for example, 230°C or lower, preferably 220°C or lower, and more preferably 200°C or lower. The reaction time in the step of obtaining a first product is, from the viewpoint of adjusting the acid value and molecular weight of the polyester resin component, for example, 0.1 hours or higher, preferably 0.5 hours or higher. The reaction time in the step of obtaining a first product is, from the viewpoint of adjusting the acid value and molecular weight of the polyester resin component, for example, 5 hours or lower, preferably 3 hours or lower. In addition, in the step of obtaining a first component, a known reaction catalyst can be added at an appropriate ratio, if necessary. In the step of obtaining the first product, the raw material components may be reacted in the absence of a solvent, or in the presence of a known solvent.

[0040] In the step of obtaining the second product, the carboxy group of the first product or the (D) aliphatic monocarboxylic acid is esterified with the hydroxyl group of the (C) polyol. The first product, the (C) polyol, and the (D) aliphatic monocarboxylic acid may be reacted in one step or in multiple steps. The reaction temperature in the step of obtaining the second product is, from the viewpoint of adjusting the acid value and hydroxyl value of the polyester resin component, for example, 150°C or higher, preferably 160°C or higher, more preferably 170°C or higher, and even more preferably 180°C or higher. In addition, the reaction temperature in the step of obtaining the second product is, from the viewpoint of adjusting the acid value and molecular weight of the polyester resin component, for example, 230°C or lower, preferably 220°C or lower, more preferably 210°C or lower, and even more preferably 200°C or lower. The reaction time in the step of obtaining the second product is, from the viewpoint of adjusting the acid value and molecular weight of the polyester resin component, for example, 1 hour or higher, preferably 3 hours or higher. The reaction time in the step of obtaining the second product is, for example, 48 hours or less, preferably 24 hours or less, from the viewpoint of adjusting the acid value and molecular weight of the polyester resin component. In this reaction, if necessary, condensation water generated by the esterification reaction can be distilled off by a known method. If necessary, a known reaction catalyst can be added in an appropriate ratio in the step of obtaining the second product. In the step of obtaining the second product, the raw material components may be reacted in the absence of a solvent, or may be reacted in the presence of a known solvent.

[0041] When the (D) aliphatic monocarboxylic acid contains a fatty acid derived from a fat or oil, the (C) polyol can be modified with a fat or oil containing the (D) aliphatic monocarboxylic acid as a constituent fatty acid before obtaining the second product. Modifying the (C) polyol with the fat or oil results in a transesterification reaction, yielding a modified product containing an ester (fatty acid ester) of the (C) polyol and a fatty acid derived from the fat or oil. This fatty acid ester generates the (C) polyol and a fatty acid upon hydrolysis. Therefore, the modified product can be used in place of the (C) polyol and the (D) aliphatic monocarboxylic acid. Specifically, as described above, the (A) rosin is reacted with an α,β-unsaturated dicarboxylic acid to obtain the first product. Separately, the (C) polyol is modified with a fat or oil containing the (D) aliphatic monocarboxylic acid as a constituent fatty acid to obtain a modified product. The first product is then reacted with the modified product to obtain a second product containing a polyester resin component. In the step of obtaining the second component, the first product and the modified product undergo an esterification reaction. This results in the second product.

[0042] (D) Examples of fats and oils having an aliphatic monocarboxylic acid as a constituent fatty acid 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 seed oil, apple oil, sunflower oil, cactus oil, tall oil, walnut oil, tung oil, clove oil, and castor oil.

[0043] The blending ratio in the step of obtaining the modified product is set as appropriate, but for example, the amount of hydroxyl groups in the polyol (C) relative to 1 mole of the fat or 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.

[0044] The reaction temperature in the step of obtaining the modified product is, from the viewpoint of film-forming ability, for example, 230°C or higher, preferably 240°C or higher, and more preferably 250°C or higher. Furthermore, from the viewpoint of film-forming ability, the reaction temperature in the step of obtaining the modified product is, for example, 300°C or lower, preferably 280°C or lower, and more preferably 270°C or lower. If the reaction temperature is excessively low, the reaction in the step of obtaining the modified product may not proceed, and the aliphatic monocarboxylic acid (D) may not be incorporated into the polyester resin. This may result in a decrease in film-forming ability. Furthermore, if the reaction temperature is excessively high, a decomposition reaction may occur, causing an increase in low-molecular-weight components. This may result in a decrease in film-forming ability. The reaction time in the step of obtaining the modified product is, from the viewpoint of film-forming ability, for example, 0.5 hours or higher, preferably 1 hour or higher. Furthermore, from the viewpoint of film-forming ability, the reaction time in the step of obtaining the modified product is, from the viewpoint of film-forming ability, for example, 20 hours or lower, preferably 10 hours or lower. If necessary, a known reaction catalyst may be added in an appropriate ratio in the step of obtaining the modified product. In the step of obtaining the modified product, the raw material components may be reacted in the absence of a solvent, or in the presence of a known solvent.

[0045] The second product thus obtained is a resin composition containing (A) rosins and (D) a polyester resin modified with an aliphatic monocarboxylic acid (hereinafter also referred to as a rosin-modified polyester resin). The second product can be used as the polyester resin component of a clarifying agent. In addition to the rosin-modified polyester resin, the second product may also contain unreacted raw material components. Examples of unreacted raw material components include unreacted (A) rosins, unreacted (B) polydicarboxylic acid, unreacted (C) polyol, and unreacted (D) aliphatic monocarboxylic acid. The unreacted raw material components are removed from the second product as necessary.

[0046] The content of the rosin-modified polyester resin relative to the total amount of the polyester resin components is, for example, 25% by mass or more, or preferably 30% by mass or more, and for example, 100% by mass or less, or preferably 90% by mass or less, relative to the total amount of the polyester resin components.

[0047] (Other Components) The clarifying agent may further contain other components in addition to the polyester resin component, as needed.

[0048] For example, the clarifying agent can contain a liquid medium. Examples of the liquid medium include organic solvents, water, and mixtures thereof. The liquid medium is preferably one that can dissolve or disperse the polyester resin component. As the liquid medium, an organic solvent is preferred from the viewpoints of excellent penetration into the paper substrate, no lumps that occur when water is used, and excellent drying properties.

[0049] Examples of organic solvents include alcohols, ethers, esters, and non-polar solvents. Examples of alcohols include alcohols having 1 to 6 carbon atoms, such as methanol, ethanol, n-propanol, isopropanol, n-butanol, n-pentanol, and n-hexanol.

[0050] 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 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 of glycol ethers include dipropylene glycol monoisobutyl ether, tripropylene glycol monoisobutyl ether, propylene glycol monotertiary butyl ether, dipropylene glycol monotertiary butyl ether, and tripropylene glycol monotertiary butyl ether.

[0051] Examples of esters include diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, etc. Examples of non-polar 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; silicone oil, etc.

[0052] The content of the liquid medium is appropriately set depending on 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 the polyester resin component. Furthermore, 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 the polyester resin component. Furthermore, the polyester resin component is, for example, 20% by mass or more, preferably 30% by mass or more, relative to the total amount of the liquid medium and the polyester resin component. Furthermore, the polyester resin component is, for example, 95% by mass or less, preferably 90% by mass or less, relative to the total amount of the liquid medium and the polyester resin component. When the ratio of the liquid medium to the polyester resin component is within the above range, a sudden increase in viscosity can be suppressed, and the productivity, coatability, and drying properties of the clarifying agent can be improved.

[0053] The clarifying agent can contain other resins. The other resins are resins other than the polyester resin component. Examples of the other resins include acrylic resins, styrene-modified acrylic resins, silicone acrylic resins, modified silicone acrylic resins, rosin phenolic resins, rosin ester resins, terpene phenolic 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 alone or in combination of two or more.

[0054] The clarifying agent can contain a wax. By containing a wax, blocking can be suppressed when used on a paper substrate. Examples of waxes include fatty acid amide wax, carnauba wax, rice wax, polyolefin wax, paraffin wax, Fischer-Tropsch wax, beeswax, microcrystalline wax, oxidized polyethylene wax, and amide wax. These can be used alone or in combination of two or more. Preferred examples of waxes include fatty acid amide wax, carnauba wax, polyolefin wax, paraffin wax, and microcrystalline wax, and more preferred examples include carnauba wax, polyolefin wax, and paraffin wax.

[0055] More specifically, examples of fatty acid amide waxes include pelargonic acid amide, capric acid amide, undecylic acid amide, lauric acid amide, tridecylic acid amide, myristic acid amide, pentadecylic acid amide, palmitic acid amide, heptadecylic 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 amide waxes also include animal and vegetable oil fatty acid amides. These may be used alone or in combination of two or more.

[0056] More specific examples of carnauba waxes include MICROKLEAR 418 (manufactured by Micro Powders, Inc.) and Refined Carnauba Wax No. 1 Powder (Nippon Wax Co., Ltd.). These can be used alone or in combination of two or more. More specific 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 alone or in combination of two or more. More specific examples of paraffin waxes include MP-28C, MP-22XF, and MP-28C (all Micro Powders, Inc.). These can be used alone or in combination of two or more.

[0057] From the viewpoint of heat resistance, the melting point of the wax is, for example, 60°C or higher and, for example, 130°C or lower.

[0058] The wax content in the clarifying agent is appropriately set depending on the purpose and application. For example, the wax content is, for example, 0 part by mass or more, preferably 1 part by mass or more, more preferably 3 parts by mass or more, per 100 parts by mass of the polyester resin component. Furthermore, the wax content is, for example, 50 parts by mass or less, preferably 30 parts by mass or less, per 100 parts by mass of the polyester resin component.

[0059] The clarifying agent may contain additives in an appropriate ratio. 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 may be used alone or in combination of two or more.

[0060] The clarifying agent can be produced by producing the polyester resin component as described above and mixing other components as required.

[0061] The clarifying agent of the present invention uses bio-derived raw materials (e.g., (A) rosins, (D) aliphatic monocarboxylic acids), yet can produce transparent paper with excellent transparency and stability over time. The polyester resin component in the clarifying agent has a refractive index close to that of pulp (cellulose), the main component of the paper substrate. Therefore, the polyester resin component fills the voids inside the paper substrate, reducing the refraction of light inside the paper substrate and resulting in excellent transparency. Furthermore, the transparency of the clarifying agent of the present invention can be ensured by single-sided coating, resulting in excellent recyclability. The clarifying agent of the present invention can be applied not only to paper substrates, but also to substrates made of materials with a refractive index similar to that of cellulose, such as woven fabrics, nonwoven fabrics, films, synthetic paper, etc.

[0062] "Transparent Paper" The transparent paper of the present invention contains a clarifying agent at least inside the paper substrate. The clarifying agent contains a polyester resin component that is a reaction product of raw material components including (A) rosin, (B) polycarboxylic acid, (C) polyol, and (D) aliphatic monocarboxylic acid. The polyester resin component has an acid value of 100 mgKOH / g or less, a weight-average molecular weight of 1,000,000 or less, and a refractive index of 1.40 to 1.60.

[0063] (Clarifying Agent) As the clarifying agent, the above-mentioned clarifying agents can be used.

[0064] (Paper base material) The paper base material contains pulp. Examples of pulp constituting the paper base material include chemical pulp, mechanical pulp, recycled paper pulp, and non-wood pulp. These pulps may be used alone or in combination of two or more. Among these, chemical pulp is preferred.

[0065] Chemical pulp includes softwood chemical pulp and hardwood chemical pulp, and it is preferable that the paper base material contain both softwood chemical pulp and hardwood chemical pulp. Hardwood chemical pulp has a shorter and thinner fiber structure than softwood chemical pulp. The short and thin fiber structure of hardwood chemical pulp results in superior paper base material formation. Poor paper base material formation can lead to uneven penetration of the clarifying agent due to the non-uniformity caused by the formation, even when the paper is impregnated with a clarifying agent, resulting in a loss of transparency. To obtain excellent transparent paper, it is preferable that the paper base material have excellent formation. However, hardwood chemical pulp, with its thin and short fiber structure, has good formation, but small gaps and voids, making it prone to areas where the clarifying agent is difficult to penetrate. Furthermore, the increased number of interfaces tends to result in refracted and attenuated transmitted light, resulting in reduced transparency. Furthermore, because it is easily coated with the clarifying agent, its defibration ability when recycled as waste paper tends to be inferior to that of softwood chemical pulp. Therefore, by using both hardwood chemical pulp and softwood chemical pulp as the paper base material, it is possible to achieve both transparency and recyclability of the transparent paper.

[0066] Examples of softwood chemical pulp include unbleached softwood kraft pulp (NUKP), bleached softwood kraft pulp (NBKP), semi-bleached softwood kraft pulp (NSBKP), softwood sulfite pulp (NSP), etc. Among these, bleached softwood kraft pulp (NBKP) and softwood sulfite pulp (NSP) are preferred from the viewpoint of achieving both transparency and strength in the transparent paper.

[0067] The Canadian Standard Freeness (CSF) of the softwood chemical pulp is preferably 400 to 700 mL, more preferably 420 to 650 mL, and even more preferably 450 to 600 mL. When the CSF of the softwood chemical pulp is at or above the lower limit of the above range, the voids in the paper base material can be maintained, resulting in excellent impregnation of the transparentizing material. When the CSF of the softwood chemical pulp is at or below the upper limit of the above range, the formation of the paper base material can be improved, making it easier to obtain transparent paper with transparent regions that are excellent in transparency and visibility.

[0068] Examples of hardwood chemical pulp include unbleached hardwood kraft pulp (LUKP), bleached hardwood kraft pulp (LBKP), semi-bleached hardwood kraft pulp (LSBKP), and hardwood sulfite pulp (LSP). Among these, bleached hardwood kraft pulp (LBKP) and hardwood sulfite pulp (LSP) are preferred from the viewpoint of achieving both transparency and strength in the transparent paper.

[0069] The Canadian Standard Freeness (CSF) of the hardwood chemical pulp is preferably 350 to 650 mL, more preferably 370 to 630 mL, and even more preferably 400 to 600 mL. When the CSF of the hardwood chemical pulp is equal to or greater than the lower limit of the above range, the strength of the paper base material can be increased. When the CSF of the hardwood chemical pulp is equal to or less than the upper limit of the above range, the formation of the paper base material can be improved, and it is easy to obtain transparent paper with a transparent region that is excellent in transparency and visibility.

[0070] The mass ratio of softwood chemical pulp to hardwood chemical pulp (softwood 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.

[0071] When the paper base material contains softwood chemical pulp and hardwood chemical pulp, the paper base material may contain, in addition to these chemical pulps, other pulps such as mechanical pulp, recycled paper pulp, non-wood pulp, etc. Examples of mechanical pulp include stone ground pulp (SGP), pressurized stone ground pulp (PGW), refiner ground pulp (RGP), thermoground pulp (TGP), chemiground pulp (CGP), groundwood 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 that can be used as a 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, cardboard recycled paper, white recycled paper, Kent recycled paper, imitation recycled paper, and land-based recycled paper. Examples of non-wood pulp include various pulps such as pulp produced chemically or mechanically from non-wood fibers such as kenaf, cotton, hemp, reed, etc. These pulps may be used alone or in combination of two or more.

[0072] When recycled paper pulp is used as the pulp, the recycled paper pulp content is preferably 10% by mass or less, more preferably 5% by mass or less, based on the total mass of the pulp constituting the paper base material. When the recycled paper pulp content is equal to or less than the upper limit, the transparent paper can be suitably used as a packaging material for food and beverages. The lower limit of the recycled paper pulp content is 0% by mass.

[0073] The opacity of the paper substrate is, for example, 45 to 95% and is measured in accordance with JIS P 8149 (2000).

[0074] The basis weight of the paper base material is 35 to 150 g / m ２ is preferred, and 40 to 100 g / m ２ More preferably, 43 to 80 g / m ２ is more preferable. When the basis weight is equal to or greater than the lower limit of the above range, the paper strength is obtained, and the transparent paper is suitable for applications such as packaging paper and printing paper. When the basis weight is equal to or less than the upper limit of the above range, the transparency of the transparent paper can be increased. The basis weight is measured in accordance with JIS P8124.

[0075] 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. When the air permeability is at or above the lower limit of the above range, the paper strength is obtained, and the transparent paper is suitable for applications such as packaging paper and printing paper. When the air permeability is at or below the upper limit of the above numerical range, the permeability of the clarifying agent is excellent, and the transparency of the transparent paper can be increased. The air permeability is the Oken air permeability measured in accordance with J. TAPPI-5-2:2000.

[0076] The density of the paper substrate is 0.5 to 0.90 g / cm ３ is preferred, and 0.6 to 0.8 g / cm ３ It is more preferable that the density is equal to or greater than the lower limit of the above range, the paper strength is sufficient, and the transparent paper is suitable for applications such as packaging paper and printing paper. If the density is equal to or less than the upper limit of the above range, the permeability of the transparent material is excellent, and the transparency of the transparent paper can be increased. The density is measured in accordance with JIS P8118.

[0077] The porosity of the paper substrate is preferably 30 to 80%, more preferably 40 to 70%, and even more preferably 50 to 70%. When the porosity of the paper substrate is equal to or greater than the lower limit of the above range, the transparency of the transparent region is easily increased. When the porosity of the paper substrate is equal to or less than 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, 1.50.

[0078] The Parker Print Surf smoothness of at least one surface of the paper substrate is preferably 7 μm or less, more preferably 5 μm or less. There is no particular lower limit. The smaller the value, the smoother the paper. The Parker Print Surf smoothness can evaluate the smoothness of fine details, and the smaller this value, the more light scattering on the paper surface can be reduced, thereby improving visibility through transparent parts. The Parker Print Surf smoothness is determined in accordance with ISO 8791-4:1992 (soft backing / clamp pressure 500 kPa).

[0079] In addition to pulp, the paper base material may contain known papermaking aids such as paper strength agents, sizing agents, fillers, and colorants. The incorporation of fillers such as talc and calcium carbonate improves the smoothness and whiteness of the paper base material, but also acts to increase the paper's hiding power, making it difficult to impart transparency. Therefore, it is preferable to keep the filler content in the paper base material within a range that does not impair transparency and visibility, and it is more preferable that the paper base material does not contain any fillers.

[0080] The method for producing the paper base material is not particularly limited, and examples thereof include a method including a step of beating pulp, which is the raw material for the paper base material, a step of making a pulp slurry containing the beaten pulp, and a step of drying the wet sheet obtained by papermaking.

[0081] In the beating step, it is preferable to beat the raw pulp so as to obtain the Canadian Standard Freeness. The beating machine is not particularly limited. For example, known beating machines such as a double-disc refiner can be used. The paper machine used for papermaking is not particularly limited. For example, a fourdrinier paper machine, a short wire paper machine, a cylinder paper machine, etc. can be used. The drying step is also not particularly limited. For example, a dryer attached to the paper machine can be used.

[0082] The paper substrate may be subjected to a smoothing treatment. Smoothing treatment can reduce light scattering on the paper surface, thereby improving visibility through the transparent portion. Examples of smoothing treatments include a tight press, machine calender, gloss calender, soft nip calender, and super calender. However, these devices increase the density of the paper, so care must be taken to reduce the linear pressure and prevent the density from becoming too high. On the other hand, a transfer method, in which paper is attached to a smooth surface while still wet and then dried to transfer the smooth surface, is preferred because it does not increase the paper density. For example, techniques such as Yankee cylinder, cast drum, and film transfer can be used. Among these, Yankee dryers using Yankee cylinders are preferred because they are attached to papermaking machines and offer excellent productivity.

[0083] The paper substrate can also be commercially available paper, such as kraft paper, one-side gloss 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 paperboard, colored paperboard, cardboard liner, glassine paper, rice paper, India paper, Japanese paper, etc. Among these, fine paper, electrophotographic paper, kraft paper, and one-side gloss kraft paper with low pigment content are preferred because they provide excellent visibility of the transparent region due to the clarifying agent.

[0084] (Transparent Paper) By including a transparent agent at least inside the paper substrate, transparency is increased compared to when no transparent agent is included. The area of ​​the paper substrate that is made transparent by the transparent agent (transparent area) may be the entire surface or a part of the paper substrate in a plan view. The opacity of the transparent area is preferably 30% or less, more preferably 20% or less, and even more preferably 16% or less. The lower the opacity, the better the transparency.

[0085] As a method for incorporating a clarifying agent into at least the interior of a paper base material, it is possible to add the agent when making paper, but when productivity is important, it is preferable to coat or impregnate the paper base material with the clarifying agent, as shown in the manufacturing method described below.

[0086] In transparent paper, it is not necessary for all of the clarifying agent to be present inside the paper substrate. If a portion of the clarifying agent covers the surface of the paper substrate, diffuse reflection of light by the surface of the paper substrate can be suppressed, and transparency can be further improved. In addition, since the coating film of the clarifying agent on the surface of the paper substrate has heat-sealing properties, it can also be used as a sealant layer.

[0087] The content of the clarifying agent cannot be generally determined depending on the type of paper substrate used (void volume, etc.), but it is generally 10 to 80 g / m as the mass of the polyester resin component converted to solid content per unit area of ​​the transparent region. ２ is preferred, and 20 to 70 g / m ２ More preferably, 30 to 60 g / m ２When the content of the clarifying agent is equal to or greater than the lower limit of the above range, the transparency of the transparent region is easily increased. When the content of the clarifying agent is equal to or less than the upper limit of the above range, the recyclability can be improved.

[0088] As described above, the transparent paper of the present invention has excellent transparency because the voids inside the paper base are filled with a clarifying agent containing a polyester resin component with a refractive index close to that of pulp, the main component of the paper base, thereby reducing the refraction of light inside the paper base.In addition, the transparent paper of the present invention has excellent stability over time and recyclability.

[0089] The transparent paper of the present invention can be used as packaging paper having a transparent region for applications such as boxes, bags, envelopes, clear files, etc. Furthermore, because it can achieve unprecedented transparency and visibility, it can be used not only for packaging paper but also for various applications such as printing paper, book paper, copying paper, information paper, label paper, and household paper, in which images (characters, symbols, pictures, objects, etc.) on the opposite side of the paper can be seen through the paper base.

[0090] "Method for Producing Transparent Paper" The method for producing transparent paper of the present invention involves coating or impregnating a paper substrate with a liquid composition containing a transparentizing agent and a liquid medium, followed by drying to produce transparent paper. The transparentizing agent contains a polyester resin component that is a reaction product of raw material components including (A) rosin, (B) polycarboxylic acid, (C) polyol, and (D) aliphatic monocarboxylic acid. The polyester resin component has an acid value of 100 mgKOH / g or less, a weight-average molecular weight of 1,000,000 or less, and a refractive index of 1.40 to 1.60.

[0091] (Liquid Composition) As the clarifying agent, the above-mentioned clarifying agents can be used.

[0092] The liquid medium may be any liquid medium capable of dissolving or dispersing the clarifying agent. Examples of the liquid medium include the same liquid medium as that for the clarifying agent, and organic solvents are preferred. The use of an organic solvent has the advantages of allowing the clarifying agent to quickly penetrate into the paper substrate, suppressing the occurrence of lumps in the paper substrate, and allowing for rapid drying. The liquid medium may be used alone or in combination of two or more.

[0093] The content of the liquid medium can be appropriately set taking into consideration the ease of application or impregnation to the paper substrate, and is, for example, 30 to 50% by mass relative to the total mass of the liquid composition.

[0094] The viscosity of the liquid composition is preferably 50 to 5,000 mPa·s, more preferably 50 to 4,000 mPa·s, and even more preferably 50 to 3,000 mPa·s. When the viscosity is equal to or less than the upper limit of the above range, the liquid composition easily penetrates into the paper substrate, making it easier to increase the transparency of the transparent region. When the viscosity is equal to or greater than the lower limit of the above range, when a portion of the paper substrate is made into a transparent region, the boundary between the transparent region and other regions becomes clear. The viscosity is measured using a Brookfield viscometer at 30°C and 60 rpm.

[0095] (Paper substrate) As the paper substrate, the above-mentioned paper substrates can be used.

[0096] The application or impregnation of the liquid composition can be carried out by a known method, for example, a coating method, an impregnation method, or a printing method such as flexographic printing, inkjet printing, gravure printing, offset printing, gravure offset printing, silk screen printing, a spray coater, a roll coater, a gravure coater, a bar coater, a blade coater, a curtain coater, a flow coater, a comma coater, brush coating, or a dipping method.

[0097] The application or impregnation of the liquid composition may be carried out over the entire surface of the paper substrate, or may be carried out partially. Furthermore, during the application or impregnation of the liquid composition, a portion may be formed in the cross section of the paper substrate in which the clarifying agent does not reach part of the surface opposite the impregnated surface. The liquid composition may be applied to or impregnated onto only one surface of the paper substrate, or the liquid composition may be applied to or impregnated onto both one surface and the other surface of the paper substrate. The application or impregnation of the liquid composition may be carried out in one step, or in multiple steps. When the application or impregnation is carried out in multiple steps, the constituent components and composition of the clarifying material used in each of the multiple steps may be the same or different from each other.

[0098] The amount of the liquid composition to be applied or impregnated depends on the type of paper substrate used (void volume, etc.), but it is generally 10 to 80 g / m as the mass of the polyester resin component in the transparentizing agent converted into the solid content per unit area of ​​the region to be applied or impregnated with the liquid composition (transparentized region). ２ is preferred, and 20 to 70 g / m ２ More preferably, 30 to 60 g / m ２ When the amount of coating or impregnation is equal to or greater than the lower limit of the above range, the transparency of the transparent region is easily increased. When the amount of coating or impregnation is equal to or less than the upper limit of the above range, the recyclability can be improved.

[0099] By drying the paper substrate coated or impregnated with the liquid composition, the liquid medium is removed, and transparent paper containing the clarifying agent at least inside the paper substrate is obtained. Drying after coating or impregnation can be carried out by a known method. The drying conditions may be natural drying at room temperature or heated drying. Heat 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, 150°C or lower, preferably 130°C or lower. The drying time is, for example, 1 second or longer, preferably 5 seconds or longer. The drying time is, for example, 600 seconds or shorter, preferably 500 seconds or shorter. After drying, humidity control may be performed to adjust the moisture content. The humidity control conditions are, for example, a temperature of 23°C and a relative humidity of 50%.

[0100] Next, the present invention will be described based on examples and comparative examples, but the present invention is not limited to the following examples. "Parts" and "%" are by mass unless otherwise specified. Note that specific numerical values ​​such as blending ratios (content ratios), physical property values, parameters, etc. used in the following description can be replaced with the upper limit values ​​(numeric values ​​defined as "equal to or less than") or lower limit values ​​(numeric values ​​defined as "equal to or more than" or "exceeding") of the corresponding blending ratios (content ratios), physical property values, parameters, etc. described in the above "Modes for Carrying Out the Invention."

[0101] <Measurement Method> (1) Acid Value The acid value of the polyester resin component was measured in accordance with JIS K 5601-2-1 (1999).

[0102] (2) Iodine Value The iodine value of the polyester resin component was measured in accordance with JIS K 0070 (1992).

[0103] (3) Molecular Weight The polyester resin component was dissolved in tetrahydrofuran to obtain a 1.0 g / L sample. The molecular weight was then measured using a gel permeation chromatograph (GPC) equipped with a refractive index detector (RID), and the weight-average molecular weight (Mw) of the sample was calculated from the resulting chromatogram (chart). The measurement device and measurement conditions are as follows: Device: Shodex GPC-101 (manufactured by Showa Denko K.K.) Detector: RI detector Column used: Shodex Column GPC KF-802, 803, 804, 806 (manufactured by Shoko Science Co., Ltd.) Eluent: THF Column speed: 1.0 mL / min Measurement temperature: 40°C Molecular weight marker: Standard polystyrene (EasiCal Polystyrene Standards PS-1 manufactured by Agilent was used).

[0104] (4) Refractive Index The refractive index was measured using a multi-wavelength Abbe refractometer DR-M4 (manufactured by Atago Co., Ltd.) in accordance with JIS K 7142 (2014).

[0105] <Production Example 1> 27.8 parts of gum rosin were placed in a four-neck flask equipped with a stirrer, a reflux condenser with a water separator, and a thermometer, and heated to 210°C while nitrogen gas was blown in. Next, 9.8 parts of fumaric acid were added and stirred at 210°C for approximately 90 minutes. This resulted in a first product. 73.4 parts of linseed oil and 15.5 parts of glycerin were added to another four-neck flask equipped with a reflux condenser with a water separator and a thermometer, and stirred at 250°C for approximately 90 minutes. Next, the first product was mixed therein, and the mixture was cooled to 190°C after mixing. A dehydration condensation reaction was then carried out at 190°C for 8 hours to obtain a second product, a polyester resin component (Resin 1). This Resin 1 had an acid value of 10 mgKOH / g, an iodine value of 109 g / 100 g, a weight-average molecular weight of 82,000, and a refractive index of 1.49. The refractive index of linseed oil fatty acid was 1.49.

[0106] <Production Examples 2, 3, 5, 8, 10> Polyester resin components (resins 2, 3, 5, 8, 10) were obtained in the same manner as in Production Example 1, except that the ratio of raw material components was changed to the ratio shown in Table 1. The physical properties of each resin are shown in Table 1.

[0107] <Production Example 4> 46.9 parts of gum rosin was placed in a four-neck flask equipped with a stirrer, a reflux condenser with a water separator, and a thermometer, and heated to 210°C while nitrogen gas was blown in. Next, 16.5 parts of fumaric acid was added and stirred at 210°C for approximately 90 minutes. This resulted in a first product. 56.8 parts of linseed oil and 25 parts of pentaerythritol were added to another four-neck flask equipped with a reflux condenser with a water separator and a thermometer, and stirred at 250°C for approximately 90 minutes. Next, the first product was mixed therein, and the mixture was cooled to 190°C after mixing. A dehydration condensation reaction was then carried out at 190°C for 7 hours to obtain a polyester resin component (Resin 4). This Resin 4 had an acid value of 8 mgKOH / g, an iodine value of 74 g / 100 g, a weight-average molecular weight of 618,000, and a refractive index of 1.50.

[0108] Production Example 6: A polyester resin component (Resin 6) was obtained in the same manner as Production Example 1, except that linseed oil was replaced with tung oil. Resin 6 had an acid value of 8 mg KOH / g, an iodine value of 98 g / 100 g, a weight-average molecular weight of 98,000, and a refractive index of 1.56. The refractive index of tung oil fatty acid was 1.52.

[0109] <Production Example 7> 18.5 parts of gum rosin were placed in a four-neck flask equipped with a stirrer, a reflux condenser with a water separator, and a thermometer, and heated to 210°C while nitrogen gas was blown in. Next, 6.5 parts of fumaric acid were added and stirred at 210°C for approximately 90 minutes. After the reaction, the mixture was cooled to 190°C, and 25.0 parts of glycerin and 77.9 parts of oleic acid were added. A dehydration condensation reaction was carried out at 190°C for 10 hours to obtain a polyester resin component (Resin 7). Resin 7 had an acid value of 10 mgKOH / g, an iodine value of 55 g / 100 g, a weight-average molecular weight of 122,000, and a refractive index of 1.40. The refractive index of oleic acid was 1.37.

[0110] <Production Example 9> 27.8 parts of gum rosin were placed in a four-neck flask equipped with a stirrer, a reflux condenser with a water separator, and a thermometer, and heated to 210°C while nitrogen gas was blown in. Next, 9.8 parts of fumaric acid were added and stirred at 210°C for approximately 90 minutes. This resulted in a first product. 73.4 parts of coconut oil and 15.5 parts of glycerin were added to another four-neck flask equipped with a reflux condenser with a water separator and a thermometer, and stirred at 250°C for approximately 90 minutes. Next, the first product was mixed therein, and the mixture was cooled to 190°C after mixing. A dehydration condensation reaction was then carried out at 190°C for 8 hours to obtain a polyester resin component (Resin 9). This Resin 9 had an acid value of 8 mgKOH / g, an iodine value of 9 g / 100 g, a weight-average molecular weight of 86,000, and a refractive index of 1.47. The refractive index of coconut oil fatty acid was 1.45.

[0111] Production Example 11 A polyester resin component (Resin 11) was obtained in the same manner as in Production Example 1, except that the time for the dehydration condensation reaction to obtain the second product was extended to 12 hours. This Resin 11 had an acid value of 2 mg KOH / g, an iodine value of 109 g / 100 g, a weight-average molecular weight of 11,000,000, and a refractive index of 1.49.

[0112] <Production Example 12> 35.2 parts of gum rosin was placed in a four-neck flask equipped with a stirrer, a reflux condenser with a water separator, and a thermometer, and heated to 210°C while nitrogen gas was blown in. Next, 12.4 parts of fumaric acid was added and stirred at 210°C for approximately 90 minutes. This resulted in a first product. 64.3 parts of clove oil and 19.1 parts of glycerin were added to another four-neck flask equipped with a reflux condenser with a water separator and a thermometer, and stirred at 250°C for approximately 90 minutes. Next, the first product was mixed therein, and the mixture was cooled to 190°C after mixing. A dehydration condensation reaction was then carried out at 190°C for 8 hours to obtain a second product, a polyester resin component (Resin 12). This Resin 12 had an acid value of 9 mgKOH / g, an iodine value of 45 g / 100 g, a weight-average molecular weight of 72,000, and a refractive index of 1.61. The refractive index of clove oil fatty acid was 1.56.

[0113] <Production Example 13> 13.7 parts of gum rosin was placed in a four-neck flask equipped with a stirrer, a reflux condenser with a water separator, and a thermometer, and heated to 210°C while nitrogen gas was blown in. Next, 4.7 parts of fumaric acid was added and stirred at 210°C for approximately 90 minutes. After the reaction, the mixture was cooled to 190°C, and 18.2 parts of glycerin and 75.6 parts of oleic acid were added. A dehydration condensation reaction was carried out at 190°C for 10 hours to obtain a polyester resin component (Resin 13). This Resin 13 had an acid value of 10 mgKOH / g, an iodine value of 61 g / 100 g, a weight-average molecular weight of 102,000, and a refractive index of 1.38. The refractive index of oleic acid was 1.37.

[0114] Examples 1 to 9 and Comparative Examples 1 to 4 (Preparation of Liquid Compositions) 50 parts of the polyester resin component shown in Table 2 and 50 parts of isopropyl alcohol were placed in an Erlenmeyer flask equipped with a reflux condenser and stirred for about 1 hour at 50° C. This gave liquid compositions.

[0115] (Preparation and Evaluation of Transparent Paper) As a paper substrate, a paper having a basis weight of 50 g / m ２The pulp constituting this one-sided glossy kraft paper was 40% hardwood bleached kraft pulp and 60% softwood bleached kraft pulp, and the opacity of this one-sided glossy kraft paper was 68.5% and the density was 0.72 g / cm ３ The liquid composition adjusted to 25°C was applied to the non-glossy side of the paper substrate using a wire-wound bar coater No. 36 to obtain coated paper. The amount of the liquid composition applied was 30 g / m2 in terms of resin solid content. ２ The obtained coated paper was then dried at 120°C for 2 minutes. After drying, the paper was conditioned in a constant temperature and humidity environment (23°C, relative humidity 50%) for 12 hours. This resulted in a transparent paper.

[0116] Comparative Example 5: 50 parts of gum rosin and 50 parts of isopropyl alcohol were mixed to obtain a gum rosin solution. 50 parts of linseed oil and 50 parts of isopropyl alcohol were mixed to obtain a linseed oil solution. Next, 90 parts of the rosin solution and 10 parts of the linseed oil solution were mixed. This gave the liquid composition of Comparative Example 7.

[0117] Comparative Example 6: A rosin solution was obtained by mixing 50 parts of gum rosin and 50 parts of isopropyl alcohol. A linseed oil solution was obtained by mixing 50 parts of linseed oil and 50 parts of isopropyl alcohol. Next, 44 parts of the rosin solution and 56 parts of the linseed oil solution were mixed. This gave the liquid composition of Comparative Example 8.

[0118] Comparative Example 7: 50 parts of gum rosin and 50 parts of isopropyl alcohol were mixed to obtain a rosin solution. 50 parts of linseed oil and 50 parts of isopropyl alcohol were mixed to obtain a linseed oil solution. Next, 20 parts of the rosin solution and 80 parts of the linseed oil solution were mixed. This gave the liquid composition of Comparative Example 9.

[0119] <Evaluation> The obtained transparent paper was evaluated as follows. The results are shown in Table 2.

[0120] (Transparency) The opacity of the transparentized paper immediately after humidity conditioning was measured in accordance with JIS P 8149 (2000). An opacity of 16% or less was evaluated as ⊚, 16% to 20% or less was evaluated as ○, 20% to 30% or less was evaluated as △, and more than 30% was evaluated as ×.

[0121] (Total Light Transmittance) The total light transmittance of the transparentized paper immediately after humidity conditioning (total light transmittance immediately after conditioning) was measured. Thereafter, the transparentized paper was left to stand for 7 days in an environment of 22 ° C. and 50% relative humidity, and the total light transmittance (total light transmittance after 7 days) was measured again. The total light transmittance was measured using a haze meter NDH5000 type (manufactured by Nippon Denshoku Industries Co., Ltd.) in accordance with JIS K 7361-1 (1997). However, in Comparative Example 4, the viscosity of the liquid composition exceeded 10,000 mPa s, making it difficult to apply or impregnate the paper substrate, so the preparation and evaluation of transparentized paper were not performed.

[0122]

[0123]

[0124] As shown in the above results, the transparentized papers of Examples 1 to 9 were transparentized papers with excellent stability over time, with a small difference between the total light transmittance immediately after application and the total light transmittance after 7 days. Among them, the transparentized papers of Examples 1 to 7 had total light transmittances of 58% or higher immediately after application and after 7 days, demonstrating excellent transparency. Furthermore, the transparentized papers of Examples 1 to 5 had the same total light transmittance immediately after application and after 7 days, demonstrating particularly excellent stability of transparency over time. On the other hand, Comparative Example 1, which had an acid value exceeding 100 mg KOH / g, exhibited poor transparency. Comparative Example 2, which had a weight-average molecular weight exceeding 1,000,000, exhibited increased viscosity, and production of the transparentized paper was discontinued. The transparentized papers of Comparative Examples 3 and 4, which used polyester resin components with refractive indices not satisfying the refractive index of 1.40 or higher and 1.60, exhibited poor transparency. Comparative Examples 5 to 7, in which a mixture of rosin and linseed oil was used instead of the polyester resin component, had poor stability over time, such as a lower total light transmittance after 7 days than the total light transmittance immediately after use and whitening over time.

Claims

1. A clarifying agent comprising a polyester resin component which is a reaction product of raw material components including (A) rosins, (B) polycarboxylic acids, (C) polyols, and (D) aliphatic monocarboxylic acids, wherein the acid value of the polyester resin component is 100 mg KOH / g or less, the weight average molecular weight of the polyester resin component is 1,000,000 or less, and the refractive index of the polyester resin component is 1.40 or more and 1.60 or less.

2. The clarifying agent according to claim 1, wherein the iodine value of the polyester resin component is from 10 g / 100 g to 140 g / 100 g.

3. A method for producing a clarifying agent, comprising reacting raw material components including (A) rosins, (B) polycarboxylic acids, (C) polyols, and (D) aliphatic monocarboxylic acids to obtain a polyester resin component having an acid value of 100 mg KOH / g or less, a weight average molecular weight of 1,000,000 or less, and a refractive index of 1.40 or more and 1.60 or less.

4. The method for producing a clarifying agent according to claim 3, wherein the iodine value of the polyester resin component is 10 g / 100 g or more and 140 g / 100 g or less.

5. The method for producing a clarifying agent according to claim 3 or 4, wherein the (B) polyvalent carboxylic acid contains an α,β-unsaturated dicarboxylic acid, and when obtaining the polyester resin component, the (A) rosin is reacted with the α,β-unsaturated dicarboxylic acid to obtain a first product, and the first product is reacted with the (C) polyol and the (D) aliphatic monocarboxylic acid.

6. A method for producing a clarifying agent according to claim 3 or 4, wherein the (B) polyvalent carboxylic acid contains an α,β-unsaturated dicarboxylic acid, and when obtaining the polyester resin component, the (A) rosin is reacted with the α,β-unsaturated dicarboxylic acid to obtain a first product, the (C) polyol is modified with the (D) oil or fat having an aliphatic monocarboxylic acid as a constituent fatty acid to obtain a modified product, and the first product is reacted with the modified product.

7. A transparent paper comprising a transparent agent at least inside a paper base material, the transparent agent comprising a polyester resin component which is a reaction product of raw material components including (A) rosins, (B) polycarboxylic acids, (C) polyols, and (D) aliphatic monocarboxylic acids, the polyester resin component having an acid value of 100 mg KOH / g or less, a weight average molecular weight of 1,000,000 or less, and a refractive index of 1.40 or more and 1.60 or less.

8. The transparent paper according to claim 7, wherein the iodine value of the polyester resin component is 10 g / 100 g or more and 140 g / 100 g or less.

9. The transparent paper according to claim 7 or 8, wherein the paper base material comprises softwood chemical pulp and hardwood chemical pulp.

10. A method for producing transparent paper by applying or impregnating a liquid composition containing a clarifying agent and a liquid medium to or on a paper substrate and drying the composition, wherein the clarifying agent contains a polyester resin component which is a reaction product of raw material components containing (A) rosins, (B) polycarboxylic acids, (C) polyols, and (D) aliphatic monocarboxylic acids, and the acid value of the polyester resin component is 100 mg KOH / g or less, the weight average molecular weight of the polyester resin component is 1,000,000 or less, and the refractive index of the polyester resin component is 1.40 or more and 1.60 or less.

11. The method for producing transparent paper according to claim 10, wherein the iodine value of the polyester resin component is 10 g / 100 g or more and 140 g / 100 g or less.

12. The method for producing transparent paper according to claim 10 or 11, wherein the paper base material comprises softwood chemical pulp and hardwood chemical pulp.