Transparent agent, manufacturing method thereof, transparent paper and manufacturing method thereof

Abstract

Provided is a transparentizing agent for obtaining a transparentized paper having excellent transparency and long-term stability, said transparentizing agent using a raw material derived from organisms. Provided is a transparentizing agent comprising a polyester resin component which is a reaction product of raw material components comprising (A) a rosin, (B) a polycarboxylic acid, (C) a polyol, and (D) an aliphatic monocarboxylic acid, the polyester resin component having an acid value of 100 mgKOH / g or less and a weight-average molecular weight of 1,000,000 or less, the refractive index of the polyester resin component is from 1.40 to 1.60 (inclusive).

Description

Technical Field

[0001] This invention relates to a transparentizing agent and its manufacturing method, and a transparent paper and its manufacturing method.

[0002] This application claims priority based on Japanese Patent Application No. 2023-176632, filed in Japan on October 12, 2023, the contents of which are incorporated herein by reference. Background Technology

[0003] Methods for manufacturing paper with high transparency include, for example, using pulp fibers with improved beating degree for papermaking, and methods that allow resin or the like to impregnate the spaces between the fibers of the paper after papermaking.

[0004] The method of papermaking using pulp fibers with improved beating degree is used in the manufacture of cellophane, tracing paper, etc. Paper made from pulp fibers with improved beating degree is used as packaging paper for things like the windows of envelopes. However, because the pulp fibers are ground and cut due to the high beating degree, such paper is usually difficult to use for applications requiring strength, such as packaging bags.

[0005] On the other hand, methods for impregnating resins or the like into the spaces between the fibers of papermaking base paper are used in the manufacture of oil paper, coated paper, and the like. For example, Patent Document 1 discloses a technique for obtaining transparent paper by hot-melting and coating or impregnating a transparent agent containing resin and paraffin onto base paper. Patent Document 2 discloses a technique for 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 discloses a technique for obtaining a windowed packaging bag by coating a portion of base paper with a rosin-based aqueous transparent agent and heating it. Patent Document 4 discloses a technique for making opaque paper transparent by printing and impregnating a transparent agent with vegetable oil as the main component onto a specific surface of opaque paper and forming an oil protective film on both sides.

[0006] Existing technical documents Patent documents Patent Document 1: Japanese Patent Application Publication No. 61-132698 Patent Document 2: Japanese Patent Application Publication No. 61-132699 Patent Document 3: Japanese Patent Application Publication No. 2011-63286 Patent Document 4: Japanese Patent Application Publication No. 62-15395 Summary of the Invention The problem that the invention aims to solve In recent years, as part of the transition to sustainable and recyclable materials, research is underway to replace plastic films with paper. For example, the replacement of plastic films with paper is also underway in the field of packaging materials. It is believed that if paper could be given the transparency of plastic films, its applications would be further expanded.

[0007] In the technologies of Patent Documents 1 to 4, by impregnating the transparent agent into the gaps between the cellulose fibers of the paper, the transparency of the translucent area impregnated with the transparent agent can be improved.

[0008] However, the paraffin used in Patent Document 1 is a mixture of solid hydrocarbons made from petroleum, and does not use raw materials derived from biological sources.

[0009] The liquid diene polymer used in Patent Document 2 is also a petroleum-derived resin, and no biological-derived raw materials were used.

[0010] The rosin-based water-based transparentizing agent used in Patent Document 3 cannot achieve sufficient transparency.

[0011] In Patent Document 4, an oil protective layer is required to prevent the impregnated vegetable oil from seeping to the outside. Without the oil protective layer, the vegetable oil will seep out over time or dry out, causing the paper to become cloudy.

[0012] The purpose of this invention is to provide a transparentizing agent that uses biologically derived raw materials to obtain transparent paper with excellent transparency and stability over time, and a method for manufacturing the same, as well as transparent paper that uses a transparentizing agent that uses biologically derived raw materials to obtain transparent paper with excellent transparency and stability over time, and a method for manufacturing the same.

[0013] Methods for solving problems The inventors investigated the use of rosin-based and aliphatic carboxylic acid-based transparentizing agents. Rosin-based and aliphatic carboxylic acids are substances with refractive indices close to those of cellulose pulp. By using these substances together, the refractive index of the paper becomes closer to that of the cellulose pulp than its individual refractive indices. However, in this state, similar to Patent Document 4, the aliphatic carboxylic acid leaches or dries, causing the paper to become cloudy. Therefore, after further and repeated research, it was discovered that by introducing rosin-based and aliphatic carboxylic acids into a polyester resin, the above-mentioned problem can be solved, thus completing the present invention.

[0014] The present invention has the following aspects.

[0015] [1] A transparentizing agent, wherein the transparentizing agent comprises a polyester resin component, the polyester resin component being a reaction product comprising (A) rosin, (B) polycarboxylic acid, (C) polyol and (D) aliphatic monocarboxylic acid, wherein the acid value of the polyester resin component is less than 100 mg KOH / g, the weight-average molecular weight of the polyester resin component is less than 1 million, and the refractive index of the polyester resin component is more than 1.40 and less than 1.60.

[0016] [2] According to the transparentizing agent of [1], wherein the iodine value of the polyester resin component is more than 10g / 100g and less than 140g / 100g.

[0017] [3] A method for manufacturing a transparentizing agent, wherein a raw material component comprising (A) rosin, (B) polycarboxylic acid, (C) polyol and (D) aliphatic monocarboxylic acid is reacted to obtain a polyester resin component with an acid value of less than 100 mg KOH / g, a weight-average molecular weight of less than 1 million, and a refractive index of more than 1.40 and less than 1.60.

[0018] [4] According to the method for manufacturing the transparentizing agent described in [3], wherein the iodine value of the polyester resin component is 10g / 100g or more and 140g / 100g or less.

[0019] [5] The method for manufacturing a transparentizing agent according to [3] or [4], wherein the (B) polycarboxylic acid comprises α,β-unsaturated dicarboxylic acid, 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, the (C) polyol, and the (D) aliphatic monocarboxylic acid are reacted.

[0020] [6] The method for manufacturing a transparentizing agent according to [3] or [4], wherein the (B) polycarboxylic acid comprises α,β-unsaturated dicarboxylic acid, 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 an oil containing the (D) aliphatic monocarboxylic acid as a fatty acid to obtain a modified product. The first product is then reacted with the modified product.

[0021] [7] A transparent paper, wherein a transparentizing agent is contained at least within the paper substrate. The transparentizing agent comprises a polyester resin component, which is a reaction product comprising (A) rosin, (B) polycarboxylic acid, (C) polyol and (D) aliphatic monocarboxylic acid. The polyester resin component has an acid value of less than 100 mg KOH / g, a weight-average molecular weight of less than 1 million, and a refractive index of more than 1.40 and less than 1.60.

[0022] [8] The transparent paper according to [7], wherein the iodine value of the polyester resin component is 10g / 100g or more and 140g / 100g or less.

[0023] [9] The transparent paper according to [7] or [8], wherein the paper substrate comprises softwood chemical pulp and hardwood chemical pulp.

[0024]

[10] A method for manufacturing transparent paper involves coating or impregnating a liquid composition containing a transparent agent and a liquid medium onto a paper substrate and then drying it to manufacture transparent paper. The transparentizing agent comprises a polyester resin component, which is a reaction product comprising (A) rosin, (B) polycarboxylic acid, (C) polyol and (D) aliphatic monocarboxylic acid. The polyester resin component has an acid value of less than 100 mg KOH / g, a weight-average molecular weight of less than 1 million, and a refractive index of more than 1.40 and less than 1.60.

[0025]

[11] According to the method for manufacturing transparent paper as described in

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

[0026]

[12] The method for manufacturing transparent paper according to

[10] or

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

[0027] Invention Effects According to the present invention, a transparentizing agent and a method thereof for manufacturing transparent paper using biologically derived raw materials are provided, as well as transparent paper using biologically derived raw materials and exhibiting excellent transparency and stability over time, and a method thereof for manufacturing transparent paper using biologically derived raw materials and exhibiting excellent transparency and stability over time. Detailed Implementation

[0028] In this specification, the "~" sign indicating a numerical range means that the values ​​before and after it are included as the lower limit and the upper limit.

[0029] The lower and upper limits of the numerical ranges disclosed in this specification can be arbitrarily combined to create new numerical ranges.

[0030] "Transparenting agent" The transparentizing agent of the present invention comprises a polyester resin component, which is a reaction product comprising (A) rosin, (B) polycarboxylic acid, (C) polyol, and (D) aliphatic monocarboxylic acid. The polyester resin component has an acid value of 100 mg KOH / g or less, a weight-average molecular weight of 1 million 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.

[0031] Because the acid value of the polyester resin component is below 100 mg KOH / g, it exhibits excellent transparency properties. The acid value of the polyester resin component is preferably below 70 mg KOH / g, more preferably below 60 mg KOH / g, and even more preferably below 50 mg KOH / g. Furthermore, from the viewpoint of adaptability to transparency, the acid value of the polyester resin component is, for example, 0 mg KOH / g or more, preferably 5 mg KOH / g or more, more preferably 10 mg KOH / g or more, and even more preferably 20 mg KOH / g or more.

[0032] The acid value was determined according to JIS K 5601-2-1 (1999).

[0033] Because the weight-average molecular weight (Mw) of the polyester resin component is less than 1 million, it exhibits excellent transparency properties. The weight-average molecular weight of the polyester resin component is preferably less than 900,000, more preferably less than 800,000. There is no particular limitation on the lower limit of the weight-average molecular weight of the polyester resin component; for example, it is preferably 5,000 or more, more preferably 10,000 or more.

[0034] The weight-average molecular weight of the polyester resin component was determined by gel permeation chromatography (GPC) and is a value converted from standard polystyrene.

[0035] By ensuring that the refractive index of the polyester resin component is 1.40 or higher and 1.60 or lower, the transparency effect is excellent for sheets, such as paper, where the transparent agent is mainly composed of cellulose. This is because the refractive index of cellulose fibers is typically in the range of 1.4 to 1.6. By setting the refractive index of the polyester resin component to a value close to that of the cellulose fibers, light refraction at the interface between the transparent 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 higher and 1.58 or lower, more preferably 1.47 or higher and 1.57 or lower, and even more preferably 1.48 or higher and 1.56 or lower.

[0036] The refractive index was determined according to JIS K 7142 (2014).

[0037] From the viewpoint of dryness, the iodine value of the polyester resin component is, for example, 5 g / 100g or more, preferably 10 g / 100g or more, more preferably 20 g / 100g or more, and even more preferably 40 g / 100g or more. Furthermore, from the viewpoint of transparency adaptability, the iodine value of the polyester resin component is, for example, 160 g / 100g or less, preferably 140 g / 100g or less, more preferably 120 g / 100g or less, and even more preferably 100 g / 100g or less.

[0038] Iodine value was determined according to JIS K 0070 (1992).

[0039] From the viewpoint of film-forming properties and anti-sticking properties, 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. Furthermore, from the viewpoint of film-forming properties and anti-sticking properties, 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.

[0040] The softening point was determined by the methanol method.

[0041] (Raw material components of polyester resin) (A) Rosin is a plant-derived component. Therefore, polyester resin components can contribute to carbon neutrality. More specifically, (A) rosin is a compound derived from pine. There are no particular restrictions on the type of pine; examples include Norfolk pine, slash pine, and Masson pine. They can be used alone or in combination of two or more.

[0042] As for (A) rosin, there are no particular limitations, and well-known unmodified rosin and its derivatives can be cited. Examples of unmodified rosin include crude rosin and refined rosin. Examples of crude rosin include resin rosin, top-oil 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. They can be used alone or in combination of two or more. Furthermore, there are no particular limitations on the origin of rosin; examples include China, Vietnam, Indonesia, and Brazil. They can be used alone or in combination of two or more.

[0043] As for (A) rosin, from the viewpoint of film-forming properties and water resistance, unmodified rosin is preferred, and resin rosin is even more preferred.

[0044] The content ratio of rosin (A) relative to the total amount of raw material components is not particularly limited as long as the refractive index of the obtained polyester resin component is 1.40 or more and 1.60 or less. From the viewpoints of transparency adaptability, film-forming properties, water resistance, and tack resistance, the content ratio of rosin (A) 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. Furthermore, from the viewpoints of film-forming properties, water resistance, and tack resistance, the content ratio of rosin (A) 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.

[0045] (B) Polycarboxylic acids refer to compounds with two or more carboxyl groups and their anhydrides. (B) Polycarboxylic acids are components used to adjust the molecular weight of polyester resins. Examples of (B) polycarboxylic acids include oxalic acid, malonic acid, succinic acid, fumaric acid, maleic acid, itaconic acid, citraconic acid, glutaric acid, adipic acid, octanoic acid, azelaic acid, sebacic acid, dodecanoic acid, tetradecanoic acid, hexadecanoic 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, diethylene glycol, 1,3-propanone dicarboxylic acid, ketoglutaric acid, cyclopropane-1,1-dicarboxylic acid, cyclobutane-1,1-dicarboxylic acid, cyclohexane-1,1-dicarboxylic acid, 2-oxoadipic acid, 4-oxoheptanoic acid, 5-oxoazelaic acid, phenylene dioxydiacetic acid, indane-2,2-dicarboxylic acid, and naphthalene-2, 6-Dicarboxylic acid, naphthalene-2,7-dicarboxylic acid, cyclohexanedicarboxylic acid, ethylenediaminetetraacetic acid, and their anhydrides. They can be used alone or in combination of two or more.

[0046] From the perspective of adjusting molecular weight, dicarboxylic acids are preferred as (B) polycarboxylic acids.

[0047] As a polycarboxylic acid (B), it is preferable to include an α,β-unsaturated dicarboxylic acid. Since the α,β-unsaturated dicarboxylic acid reacts with (A) rosin, transparency adaptability is improved by including an α,β-unsaturated dicarboxylic acid in the polycarboxylic acid (B).

[0048] Examples of α,β-unsaturated dicarboxylic acids include fumaric acid, maleic acid, itaconic acid, citraconic acid, and their anhydrides. Examples of acid anhydrides include maleic anhydride, itaconic anhydride, and citraconic anhydride. They can be used alone or in combination of two or more. Furthermore, α,β-unsaturated dicarboxylic acids can be used in combination with other dicarboxylic acids.

[0049] As for (B) polycarboxylic acid, from the viewpoint of adjusting the molecular weight, it is preferable to include at least one selected from the group consisting of succinic acid, fumaric acid, maleic anhydride and adipic acid, and more preferably to include fumaric acid.

[0050] From the viewpoint of the molecular weight of the polyester resin components, the content of (B) polycarboxylic acid relative to the total amount of the raw material components is, 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, from the viewpoint of the molecular weight of the polyester resin, the content of (B) polycarboxylic acid relative to the total amount of the raw material components is, 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.

[0051] From the viewpoint of the molecular weight of the polyester resin component, the content ratio of (B) polycarboxylic acid to 100 moles of (A) rosin is, 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 ratio of (B) polycarboxylic acid to 100 moles of (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.

[0052] When the content of (B) polycarboxylic acid is above the lower limit of the above range, there is less unreacted (A) rosin, which can increase the molecular weight of the polyester resin component. Furthermore, when the content of (B) polycarboxylic acid is below the upper limit of the above range, there is less unreacted (B) polycarboxylic acid, making it easier to adjust the molecular weight of the polyester resin component, resulting in less likelihood of gelation.

[0053] Examples of (C) polyols include diols, triols, and alcohols with four or more ions.

[0054] Examples of diols include straight-chain alkyl glycols, branched-chain alkyl glycols, and ether glycols. Examples of straight-chain alkyl glycols include ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol. Examples of branched-chain alkyl glycols include propylene glycol, 1,3-butanediol, 1,2-butanediol, 3-methyl-1,5-pentanediol, and 2,6-dimethyl-1-octene-3,8-diol. Examples of ether glycols include diethylene glycol, triethylene glycol, and dipropylene glycol. In addition, examples of diols include 1,4-dihydroxy-2-butene, isosorbide, cyclohexanediethanol, cyclohexanediol, tricyclodecanedimethylol, bisphenol A, hydrogenated bisphenol A, hydrogenated bisphenol F, hydrogenated bisphenol S, hydrogenated catechol, hydrogenated resorcinol, hydrogenated hydroquinone, and dicyclopentadiene-2-allyl alcohol copolymer.

[0055] Examples of triols include glycerol, trimethylolethane, trimethylolpropane, trimethylolhexane, and trimethyloloctane.

[0056] Examples of alcohols with four or more nucleotides include 4- to 8-nucleotide alcohols. Examples of 4- to 8-nucleotide alcohols include pentaerythritol, diglycerides, di- and trimethylolpropane, sorbitol, sorbitol, dipentaerythritol, inositol, and tripentaerythritol.

[0057] They can be used individually or in combination of two or more.

[0058] As for (C) polyol, from the viewpoint of adjusting the molecular weight of the polyester resin component, it is preferable to include at least one selected from the group consisting of triols and alcohols with four or more ions, more preferably triols, and even more preferably at least one selected from the group consisting of trimethylolpropane, glycerol and pentaerythritol, and particularly preferably glycerol.

[0059] (C) The polyol has 2 or more carbon atoms, preferably 3 or more. Additionally, the polyol has 30 or fewer carbon atoms, preferably 20 or fewer, more preferably 10 or fewer, and even more preferably 8 or fewer.

[0060] From the viewpoint of the molecular weight of the polyester resin components, the content of (C) polyol relative to the total amount of the raw material components is, for example, 5% by mass or more, preferably 8% by mass or more, more preferably 12% by mass or more, further preferably 13% by mass or more, and especially preferably 15% by mass or more. Furthermore, from the viewpoint of the molecular weight of the polyester resin, the content of (C) polyol relative to the total amount of the raw material components is, for example, 40% by mass or less, preferably 30% by mass or less, more preferably 25% by mass or less, and further preferably 20% by mass or less.

[0061] Examples of (D) aliphatic monocarboxylic acids include formic acid, acetic acid, trifluoroacetic acid, propionic acid, acrylic acid, methacrylic acid, neopentanoic acid, mercaptoacetic acid, and sorbic acid.

[0062] As (D) aliphatic monocarboxylic acids, examples can also be found of fatty acids derived from oils and fats. More specifically, examples include linseed oil fatty acids, grapefruit 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 seed oil fatty acids, sunflower seed oil fatty acids, cactus oil fatty acids, sesame oil fatty acids, walnut oil fatty acids, tung oil fatty acids, clove oil fatty acids, and castor oil fatty acids. They can be used alone or in combination of two or more.

[0063] (D) The refractive index of the aliphatic monocarboxylic acid is, for example, 1.35 to 1.65, preferably 1.40 to 1.60.

[0064] From the viewpoint of transparency adaptability, (D) aliphatic monocarboxylic acids with a specified iodine value are preferred as (D) aliphatic monocarboxylic acids. From the viewpoint of transparency adaptability, the iodine value of the (D) aliphatic monocarboxylic acid 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.

[0065] From the viewpoint of transparency adaptability, (D) aliphatic monocarboxylic acids preferably contain aliphatic monocarboxylic acids with an iodine value of 20 g / 100 g or more as the main component. Furthermore, the main component is shown to be 80% by mass or more, preferably 90% by mass or more, and more preferably 95% by mass or more. That is, relative to the total amount of (D) aliphatic monocarboxylic acids, the content of aliphatic monocarboxylic acids with an iodine value of 20 g / 100 g or more is, for example, 80% by mass or more, preferably 90% by mass or more, and more preferably 95% by mass or more. It is particularly preferred that (D) aliphatic monocarboxylic acids consist of aliphatic monocarboxylic acids with an iodine value of 20 g / 100 g or more.

[0066] Examples of aliphatic monocarboxylic acids with an iodine value of 20g / 100g or higher include linseed oil fatty acids, grapefruit 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, malic acid fatty acids, sunflower seed oil fatty acids, cactus oil fatty acids, sesame oil fatty acids, walnut oil fatty acids, tung oil fatty acids, clove oil fatty acids, and castor oil fatty acids.

[0067] The content ratio of (D) aliphatic monocarboxylic acids (the total amount of which is used in combination) relative to the total amount of the raw material components is not particularly limited as long as the refractive index of the obtained polyester resin component is 1.40 or more and 1.60 or less. From the viewpoint of transparency adaptability, softness, water resistance, etc., the content ratio of (D) aliphatic monocarboxylic acids 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, further preferably 20% by mass or more, and especially preferably 25% by mass or more. In addition, from the viewpoint of transparency adaptability, softness, water resistance, etc., the content ratio of (D) aliphatic monocarboxylic acids 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 further preferably 35% by mass or less.

[0068] (Manufacturing of polyester resin components) Polyester resin components can be manufactured by reacting the aforementioned raw material components.

[0069] In addition, in order to adjust the acid value and molecular weight of the polyester resin components to the above-mentioned range, for example, the proportion of raw material components is adjusted to the above-mentioned preferred ratio, and the reaction temperature and reaction time are adjusted.

[0070] In order to adjust the refractive index of the polyester resin components to the above range, for example, the content ratio of (A) rosin and (D) aliphatic monocarboxylic acids can be adjusted.

[0071] In order to adjust the iodine value of the polyester resin component to the above range, for example, the iodine value and content ratio of (D) aliphatic monocarboxylic acid can be adjusted.

[0072] When reacting raw material components, the raw material components can react all at once or in multiple stages.

[0073] In a combined reaction, the aforementioned 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°C to 300°C and a reaction time of approximately 2 to 20 hours.

[0074] In the case where (B) the polycarboxylic acid includes α,β-unsaturated dicarboxylic acid, a multi-stage reaction is preferred.

[0075] Specifically, firstly, (A) rosin is reacted with α,β-unsaturated dicarboxylic acid to obtain a first product. Next, the first product, (C) polyol, and (D) aliphatic monocarboxylic acid are reacted to obtain a second product containing polyester resin components.

[0076] In the process of obtaining the first product, the unsaturated bonds of (A) rosin are subjected to an addition reaction with the unsaturated bonds of α,β-unsaturated dicarboxylic acids.

[0077] From the viewpoint of adjusting the acid value and molecular weight of the polyester resin components, the reaction temperature in the process of obtaining the first product is, for example, 150°C or higher, preferably 170°C or higher, and more preferably 180°C or higher. Furthermore, from the viewpoint of adjusting the acid value and molecular weight of the polyester resin components, the reaction temperature in the process of obtaining the first product is, for example, 230°C or lower, preferably 220°C or lower, and more preferably 200°C or lower.

[0078] From the viewpoint of adjusting the acid value and molecular weight of the polyester resin components, the reaction time in the process of obtaining the first product is, for example, 0.1 hours or more, preferably 0.5 hours or more. Furthermore, from the viewpoint of adjusting the acid value and molecular weight of the polyester resin components, the reaction time in the process of obtaining the first product is, for example, 5 hours or less, preferably 3 hours or less.

[0079] Furthermore, in the process of obtaining the first component, a known reaction catalyst can be added in an appropriate proportion as needed. Additionally, in the process of obtaining the first product, the raw material components can react in a solvent-free environment or in the presence of a known solvent.

[0080] In the process of obtaining the second product, the carboxyl group of the first product or the (D) aliphatic monocarboxylic acid is subjected to an esterification reaction with the hydroxyl group of the (C) polyol. The first product, the (C) polyol, and the (D) aliphatic monocarboxylic acid can react simultaneously or in multiple stages. From the viewpoint of adjusting the acid value and hydroxyl value of the polyester resin composition, the reaction temperature in the process of obtaining the second product is, 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. Furthermore, from the viewpoint of adjusting the acid value and molecular weight of the polyester resin composition, the reaction temperature in the process of obtaining the second product is, 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.

[0081] From the viewpoint of adjusting the acid value and molecular weight of the polyester resin components, the reaction time in the process of obtaining the second product is, for example, 1 hour or more, preferably 3 hours or more. Furthermore, from the viewpoint of adjusting the acid value and molecular weight of the polyester resin components, the reaction time in the process of obtaining the second product is, for example, 48 hours or less, preferably 24 hours or less. Additionally, in this reaction, if necessary, the condensation water generated by the esterification reaction can be removed by distillation using known methods.

[0082] Furthermore, in the process of obtaining the second product, a known reaction catalyst can be added in an appropriate proportion as needed. Additionally, in the process of obtaining the second product, the starting materials can react in a solvent-free environment, or in the presence of a known solvent.

[0083] In the case where (D) aliphatic monocarboxylic acid contains fatty acids derived from oils, (C) polyols can be modified using oils whose constituent fatty acids are (D) aliphatic monocarboxylic acid before obtaining the aforementioned second product.

[0084] When the (C) polyol is modified using the oil, a modified product containing an ester (fatty acid ester) of the (C) polyol and a fatty acid derived from the oil can be obtained through transesterification. This fatty acid ester is then hydrolyzed to produce the (C) polyol and fatty acid. Therefore, the modified product can replace both the (C) polyol and the (D) aliphatic monocarboxylic acid.

[0085] Specifically, as described above, (A) rosin is reacted with α,β-unsaturated dicarboxylic acids to obtain a first product. Then, (C) polyol is modified using an oil whose fatty acids are composed of (D) aliphatic monocarboxylic acids to obtain a modified product. Next, the first product is reacted with the modified product to obtain a second product containing polyester resin components.

[0086] In the process of obtaining the second component, the first product undergoes an esterification reaction with the modified product. This yields the second product.

[0087] Examples of oils whose fatty acids are composed of (D) aliphatic monocarboxylic acids include flaxseed oil, grapefruit oil, pistachio oil, rice oil, safflower oil, apricot oil, cottonseed oil, sesame oil, corn oil, watermelon oil, soybean oil, poppy seed oil, apple seed oil, sunflower seed oil, cactus oil, sesame oil, walnut oil, tung oil, clove oil, and castor oil.

[0088] The proportions in the process of obtaining the modified product can be set appropriately. For example, relative to 1 mole of oil, the hydroxyl groups of (C) polyol are, for example, 3 moles or more, preferably 10 moles or more, for example 50 moles or less, preferably 40 moles or less.

[0089] From the viewpoint of film-forming properties, the reaction temperature in the process of obtaining the modified material is, 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 properties, the reaction temperature in the process of obtaining the modified material is, for example, 300°C or lower, preferably 280°C or lower, and more preferably 270°C or lower. If the reaction temperature is too low, the reaction in the process of obtaining the modified material may sometimes not occur, and (D) aliphatic monocarboxylic acid may not enter the polyester resin. Therefore, film-forming properties may sometimes decrease. Additionally, if the reaction temperature is too high, a decomposition reaction may sometimes occur, leading to an increase in low molecular weight components. Therefore, film-forming properties may sometimes decrease.

[0090] From the viewpoint of film-forming properties, the reaction time in the process of obtaining the modified material is, for example, 0.5 hours or more, preferably 1 hour or more. Furthermore, from the viewpoint of film-forming properties, the reaction time in the process of obtaining the modified material is, for example, 20 hours or less, preferably 10 hours or less.

[0091] Furthermore, in the process of obtaining the modified product, a known reaction catalyst can be added in an appropriate proportion as needed. Additionally, in the process of obtaining the modified product, the raw material components can be reacted in a solvent-free environment, or in the presence of a known solvent.

[0092] The resulting second product is a resin composition comprising (A) rosin and a polyester resin modified with (D) aliphatic monocarboxylic acid (hereinafter also referred to as rosin-modified polyester resin). The second product can be used as a polyester resin component for use as a transparentizing agent.

[0093] In addition to rosin-modified polyester resin, the second product may also contain unreacted raw material components. Examples of unreacted raw material components include: unreacted (A) rosin derivatives, unreacted (B) polydicarboxylic acids, unreacted (C) polyols, and unreacted (D) aliphatic monocarboxylic acids. Unreacted raw material components are removed from the second product as needed.

[0094] The proportion of rosin-modified polyester resin relative to the total amount of polyester resin is, for example, 25% by mass or more, preferably 30% by mass or more. Furthermore, the proportion of rosin-modified polyester resin relative to the total amount of polyester resin is, for example, 100% by mass or less, preferably 90% by mass or less.

[0095] (Other ingredients) Depending on the requirements, the transparentizing agent may further contain other components besides the aforementioned polyester resin components.

[0096] For example, a transparent agent can contain a liquid medium.

[0097] Examples of liquid media include organic solvents, water, and mixtures thereof. Preferably, a liquid media capable of dissolving or dispersing the polyester resin components is preferred.

[0098] As a liquid medium, organic solvents are preferred from the viewpoints of excellent permeability to paper substrates, no fluctuations that occur when water is used, and excellent drying properties.

[0099] Examples of organic solvents include alcohols, ethers, esters, and nonpolar solvents.

[0100] Examples of alcohols include methanol, ethanol, n-propanol, isopropanol, n-butanol, n-pentanol, and n-hexanol, which have 1 to 6 carbon atoms.

[0101] 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 monoisobutyl ether, tetraethylene glycol monoisobutyl ether, ethylene glycol monotert-butyl ether, di ... Diethylene glycol monotert-butyl ether, triethylene glycol monotert-butyl ether, tetraethylene glycol monotert-butyl ether, propylene glycol monomethyl ether, dipropylene 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 monoisobutyl ether, propylene glycol monoisobutyl ether, dipropylene glycol monoisobutyl ether, tripropylene glycol monoisobutyl ether, propylene glycol monotert-butyl ether, dipropylene glycol monotert-butyl ether, tripropylene glycol monotert-butyl ether, etc.

[0102] Examples of esters include diethylene glycol monoethyl ether and diethylene glycol monobutyl ether.

[0103] Examples of nonpolar solvents include pentane, hexane, heptane, octane, nonane, decane, dodecane, and other alkanes; isoalkanes such as isohexane, isooctane, and isododecane; alkylcycloalkanes such as liquid paraffin; aromatic hydrocarbons such as benzene, toluene, xylene, alkylbenzene, and solvent naphtha; and silicone oil.

[0104] The content of the liquid medium is appropriately set according to the purpose and application. For example, relative to the total amount of the liquid medium and polyester resin components, the liquid medium is, for example, 5% by mass or more, preferably 10% by mass or more. Furthermore, relative to the total amount of the liquid medium and polyester resin components, the liquid medium is, for example, 80% by mass or less, preferably 70% by mass or less. Furthermore, relative to the total amount of the liquid medium and polyester resin components, the polyester resin component is, for example, 20% by mass or more, preferably 30% by mass or more. Furthermore, relative to the total amount of the liquid medium and polyester resin components, the polyester resin component is, for example, 95% by mass or less, preferably 90% by mass or less. When the ratio of the liquid medium to the polyester resin component is within the above range, a sharp increase in viscosity can be suppressed, and the productivity, coatability, and drying properties of the transparentizing agent can be improved.

[0105] The transparentizing agent may contain other resins. Other resins are resins other than the polyester resin component mentioned above.

[0106] 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, polyurethane resins, urea resins, melamine resins, and cellulose resins. These can be used alone or in combination of two or more.

[0107] Transparent agents can contain wax. By containing wax, they can inhibit adhesion when used on paper substrates.

[0108] Examples of waxes include fatty acid amide waxes, carnauba wax, rice bran wax, polyolefin waxes, paraffin wax, Fischer-Tropsch wax, beeswax, microcrystalline wax, polyethylene oxide wax, and amide waxes. They can be used alone or in combination of two or more.

[0109] As waxes, preferred examples include fatty acid amide waxes, carnauba waxes, polyolefin waxes, paraffin waxes, and microcrystalline waxes, with more preferred examples including carnauba waxes, polyolefin waxes, and paraffin waxes.

[0110] More specifically, examples of fatty acid amide waxes include nonanoic acid amide, decanoic acid amide, undecanoic acid amide, lauryl acid amide, tridecanoic acid amide, myristoic acid amide, pentadecanoic acid amide, palmitic acid amide, heptadecanoic acid amide, stearic acid amide, nonadecanoic acid amide, arachidic acid amide, behenic acid amide, tetracosanoic acid amide, oleic acid amide, cetylene amide, linoleic acid amide, linolenic acid amide, and mixtures thereof. Additionally, examples of fatty acid amide waxes include fatty acid amides from animal and vegetable oils. These can be used alone or in combination of two or more.

[0111] As for carnauba wax, more specifically, examples include MICROKLEAR 418 (manufactured by Micro Powders, Inc.) and refined carnauba wax No. 1 powder (Nippon Wax Co., Ltd.). They can be used alone or in combination of two or more.

[0112] Examples of olefin waxes, more specifically, include polyethylene wax, polypropylene wax, MPP-635 VF (MicroPowders, Inc.), and MP-620 VF XF (Micro Powders, Inc.). They can be used alone or in combination of two or more.

[0113] As paraffin waxes, more specifically, examples include MP-28C, MP-22XF, and MP-28C (all from MicroPowders, Inc.). They can be used alone or in combination of two or more.

[0114] From the perspective of heat resistance, the melting point of wax is, for example, above 60°C or below 130°C.

[0115] The proportion of wax in the transparentizing agent is appropriately set according to the purpose and application. For example, relative to 100 parts by weight of polyester resin, the wax content is, for example, 0 parts by weight or more, preferably 1 part by weight or more, and more preferably 3 parts by weight or more. In addition, relative to 100 parts by weight of polyester resin, the wax content is, for example, 50 parts by weight or less, preferably 30 parts by weight or less.

[0116] Transparent agents 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 octanoate and cobalt naphthenate. They may be used alone or in combination of two or more.

[0117] The transparentizing agent can be manufactured by producing the polyester resin component as described above and by mixing other components as needed.

[0118] Although the transparentizing agent of this invention uses biologically derived raw materials ((A) rosin, (D) aliphatic monocarboxylic acids, etc.), it yields transparent paper with excellent transparency and long-term stability. The polyester resin component in the transparentizing agent has a refractive index close to that of pulp (cellulose), the main component of the paper substrate. Therefore, the porous portions of the paper substrate are filled by the polyester resin component, thereby reducing the refraction of light within the paper substrate and achieving excellent transparency. Furthermore, the transparentizing agent of this invention ensures transparency through single-sided coating, thus exhibiting excellent recyclability.

[0119] Furthermore, the transparentizing agent of the present invention is not limited to paper substrates, but can also be applied to substrates made of materials having the same refractive index as cellulose, such as woven fabrics, nonwoven fabrics, films, synthetic paper, etc.

[0120] "Transparent paper" The transparent paper of the present invention contains a transparentizing agent at least internally within a paper substrate. The transparentizing agent comprises a polyester resin component, which is a reaction product comprising (A) rosin, (B) a polycarboxylic acid, (C) a polyol, and (D) an aliphatic monocarboxylic acid. The polyester resin component has an acid value of 100 mg KOH / g or less, a weight-average molecular weight of 1 million or less, and a refractive index of 1.40 or more and 1.60 or less.

[0121] (Transparenting agent) The above-mentioned transparent agent can be used as a transparent agent.

[0122] (Paper substrate) Paper substrates contain pulp.

[0123] Pulp, which constitutes the paper substrate, can be categorized into chemical pulp, mechanical pulp, waste paper pulp, and non-wood pulp. One type of pulp can be used alone, or two or more can be used in combination. Chemical pulp is preferred.

[0124] As chemical pulp, there are coniferous chemical pulp and hardwood chemical pulp, and as paper substrate, it is preferred to include coniferous chemical pulp and hardwood chemical pulp.

[0125] Hardwood chemical pulp has a shorter and finer fiber structure than softwood chemical pulp. Using hardwood chemical pulp results in a short and fine fiber structure, leading to excellent paper substrate quality. If the paper substrate quality is poor, even with impregnation of a clearing agent, uneven penetration due to the unevenness caused by the texture can sometimes impair transparency. Therefore, a high-quality paper substrate is preferred for obtaining excellent transparent paper. However, while hardwood chemical pulp with its fine and short fiber structure has good quality, the smaller gaps and voids can create areas where the clearing agent cannot penetrate. Furthermore, the increased number of interfaces tends to reduce the refraction of transmitted light, thus decreasing transparency. Moreover, because it is easily covered by the clearing agent, its defiberization properties during recycling tend to be worse compared to softwood chemical pulp. Therefore, by using both hardwood and softwood chemical pulps as the paper substrate, both transparency and recyclability of the transparent paper can be achieved.

[0126] 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 perspective of balancing the transparency and strength of transparent paper.

[0127] The Canadian Standard Freeness (CSF) of the softwood chemical pulp is preferably 400 mL to 700 mL, more preferably 420 mL to 650 mL, and even more preferably 450 mL to 600 mL. When the CSF of the softwood chemical pulp is above the lower limit of the above range, the porosity of the paper substrate can be maintained, thus resulting in excellent impregnation of the transparent material. When the CSF of the softwood chemical pulp is below the upper limit of the above range, the texture of the paper substrate can be improved, and transparent paper with transparent areas exhibiting excellent transparency and visual recognizability can be easily obtained.

[0128] Examples of hardwood chemical pulps include unbleached hardwood kraft pulp (LUKP), bleached hardwood kraft pulp (LBKP), semi-bleached hardwood kraft pulp (LBKP), and hardwood sulfite pulp (LSP). Among these, bleached hardwood kraft pulp (LBKP) and hardwood sulfite pulp (LSP) are preferred from the perspective of balancing the transparency and strength of transparent paper.

[0129] The Canadian Standard Freeness (CSF) of the hardwood chemical pulp is preferably 350 mL to 650 mL, more preferably 370 mL to 630 mL, and even more preferably 400 mL to 600 mL. When the CSF of the hardwood chemical pulp is above the lower limit of the above range, the strength of the paper substrate can be improved. When the CSF of the hardwood chemical pulp is below the upper limit of the above range, the texture of the paper substrate can be improved, and transparent paper with transparent areas that have excellent transparency and visual recognizability can be easily obtained.

[0130] 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.

[0131] When the paper substrate contains both softwood chemical pulp and hardwood chemical pulp, it may also contain other pulps in addition to these chemical pulps, such as mechanical pulp, waste paper pulp, non-wood pulp, etc.

[0132] Examples of mechanical pulps include stone-refined pulp (SGP), pressurized stone-refined pulp (PGW), refined pulp (RGP), thermomechanical pulp (TGP), chemically refined pulp (CGP), wood chip pulp (GP), and thermomechanical pulp (TMP).

[0133] Examples of waste paper pulp include leached waste paper pulp, leached deinked waste paper pulp, and leached deinked bleached waste paper pulp. Examples of waste paper that can be used as raw material for waste paper pulp include tea paper waste paper, kraft paper envelope waste paper, magazine waste paper, newspaper waste paper, flyer waste paper, office waste paper, corrugated paper waste paper, high-quality white paper waste paper, Kent paper waste paper, counterfeit waste paper, and land certificate waste paper.

[0134] As non-wood pulp, examples include various types of pulp made chemically or mechanically from non-wood fibers such as kenaf, cotton, hemp, and reeds.

[0135] These pulps can be used alone or in combination with two or more types.

[0136] When waste paper pulp is used as pulp, the content of waste paper pulp relative to the total mass of the pulp constituting the paper substrate is preferably 10% by mass or less, more preferably 5% by mass or less. When the content of waste paper pulp is below the above-mentioned upper limit, transparent paper can be appropriately applied to packaging materials for food and beverages. The lower limit for the content of waste paper pulp is 0% by mass.

[0137] The opacity of the paper substrate is, for example, 45% to 95%.

[0138] Opacity was measured according to JIS P 8149 (2000).

[0139] The preferred basis weight of the paper substrate is 35 g / m³. 2 ~150g / m 2 More preferably 40g / m 2 ~100g / m 2 Further preferred is 43g / m 2 ~80g / m 2 When the basis weight is above the lower limit of the above range, the paper strength is achieved, making it a transparent paper suitable for applications such as packaging paper and printing paper. When the basis weight is below the upper limit of the above range, the transparency of the transparent paper can be improved.

[0140] Basis weight was determined according to JIS P 8124.

[0141] 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 above the lower limit of the above range, the paper strength is obtained, making it a transparent paper suitable for packaging paper, printing paper, and other applications. When the air permeability is below the upper limit of the above range, the penetration of the transparentizing agent is excellent, which can improve the transparency of the transparent paper.

[0142] The air permeability is measured according to the Wang Yan type air permeability based on J.TAPPI-5-2000.

[0143] The preferred density of the paper substrate is 0.5 g / cm³. 3 ~0.90g / cm 3 More preferably 0.6 g / cm³ 3 ~0.8 g / cm³. When the density is above the lower limit of the above range, the paper strength is obtained, making it a transparent paper suitable for packaging, printing, and other applications. When the density is below the upper limit of the above range, the transparent material exhibits excellent permeability, which can improve the transparency of the transparent paper.

[0144] Density was determined according to JIS P 8118.

[0145] 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 above the lower limit of the above range, it is easy to improve the transparency of the transparent area. When the porosity of the paper substrate is below the upper limit of the above range, it is difficult to reduce the physical strength of the sheet.

[0146] The porosity of the paper substrate is the value obtained by dividing the density measured according to JIS P 8118 by the true density of cellulose, which is 1.50.

[0147] The smoothness of the Parker-printed surface of at least one side of the paper substrate is preferably 7 μm or less, more preferably 5 μm or less. There is no particular limitation on the lower limit value. Generally speaking, the smaller the value, the smoother the surface. The smoothness of the Parker-printed surface can evaluate the smoothness of fine details; the smaller the value, the less light scattering occurs on the paper surface, thus improving visual visibility through the transparent areas.

[0148] The smoothness of the Parker printed surface is determined according to ISO 8791-4:1992 (soft backing / clamping pressure 500kPa).

[0149] In addition to pulp, paper substrates may also contain known papermaking additives such as paper strength enhancers, sizing agents, fillers, and colorants.

[0150] The addition of fillers such as talc and calcium carbonate improves the smoothness and whiteness of the paper substrate. However, while they enhance the paper's opacity, they are less likely to impart transparency. Therefore, the filler content in the paper substrate is preferably kept within a range that does not impair transparency and visual legibility; more preferably, the paper substrate is filler-free.

[0151] There is no particular limitation on the manufacturing method of paper substrate. For example, the following methods can be included: a process of pulping the pulp that will become the raw material for paper substrate, a process of forming paper from the pulp containing the pulped pulp, and a process of drying the wet sheet obtained from the papermaking.

[0152] In the pulping process, it is preferable to pulp the raw material pulp to achieve the aforementioned Canadian standard freeness. There are no particular limitations on the pulping machine. For example, well-known pulping machines such as the twin-disc refiner can be cited.

[0153] There are no particular limitations on the papermaking machines used in papermaking. For example, there are long-wire papermaking machines, short-wire papermaking machines, and cylinder papermaking machines.

[0154] There are no particular restrictions on the drying process. For example, a dryer attached to a paper machine can be used.

[0155] The paper substrate can also be smoothed. By performing a smoothing treatment, the scattering of light on the paper surface can be reduced, thus improving the visual visibility of the transparent parts.

[0156] As a smoothing process, examples include density pressing, mechanical calendering, gloss calendering, soft calendering, and supercalendering. However, since these devices increase the paper density, care must be taken to reduce the linear pressure to prevent the density from becoming excessively high. On the other hand, transfer methods that involve pasting the paper to a smooth surface while it is still wet and then removing it from the smooth surface after drying are preferred because the paper density does not increase. For example, Yankee cylinders, casting cylinders, and film transfer techniques can be used. Among these, Yankee drying cylinders using Yankee cylinders are preferred because they are attached to the paper machine and offer excellent productivity.

[0157] Commercially available papers can also be used as the paper substrate, such as kraft paper, single-sided glossy kraft paper, premium paper, electronic photographic paper, inkjet recording paper, thermal recording paper, laser thermal paper, thermal transfer recording paper, coated paper, coated paper, cast-coated paper, whiteboard paper, colored paperboard, corrugated boxboard, cellophane, rice bran paper, dictionary paper, and Japanese paper. Among these, premium paper, electronic photographic paper, kraft paper, and single-sided glossy kraft paper with lower pigment content are preferred due to the excellent visual visibility of the transparent areas based on the transparentizing agent.

[0158] (Transparent paper) By including a transparentizing agent at least inside the paper substrate, transparency is improved compared to cases without a transparentizing agent.

[0159] The area of ​​the paper substrate that has been made transparent by the transparentizing agent (the transparent area) can be the entire surface of the paper substrate or a part of it when viewed from above.

[0160] 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.

[0161] As a method to make the paper substrate contain at least the transparent agent, it can also be added during the papermaking process. However, if productivity is important, it is preferable to coat or impregnate the paper substrate with the transparent agent as shown in the manufacturing method described later.

[0162] In transparent paper, the transparentizing agent does not need to be entirely present inside the paper substrate.

[0163] If a portion of the transparentizing agent covers the surface of the paper substrate, it can suppress diffuse reflection of light caused by the paper substrate surface, thereby further improving transparency. Furthermore, the coating on the surface of the paper substrate based on the transparentizing agent has heat-sealable properties, and therefore can also be used as a sealing layer.

[0164] The content of the transparentizing agent varies depending on the type of paper substrate used (porosity, etc.) and cannot be generalized. Optimally, it is 10 g / m², calculated as the mass of solid polyester resin per unit area of ​​the transparent region.2 ~80g / m 2 More preferably 20g / m 2 ~70g / m 2 More preferably 30g / m 2 ~60g / m 2 When the content of the transparent agent is above the lower limit of the above range, the transparency of the transparent area is easily improved. When the content of the transparent agent is below the upper limit of the above range, the recyclability is improved.

[0165] As described above, the transparent paper of the present invention fills the voids inside the paper substrate by including a transparentizing agent containing a polyester resin component having a refractive index close to that of the pulp, which is the main component of the paper substrate. This reduces the refraction of light inside the paper substrate, thus resulting in excellent transparency. In addition, it also exhibits excellent stability over time and recyclability.

[0166] The transparent paper of this invention can be used as packaging paper with transparent areas for purposes such as boxes, bags, envelopes, and transparent folders. Furthermore, because it achieves unprecedented transparency and visual legibility, it can be used not only for packaging paper but also for various applications in printing paper, book paper, photocopying paper, information paper, label paper, and household paper, for visually recognizing images (text, symbols, images, objects, etc.) on the opposite side of the paper through the paper substrate.

[0167] "Methods for manufacturing transparent paper" The method for manufacturing transparent paper according to the present invention involves coating or impregnating a liquid composition comprising a transparent agent and a liquid medium onto a paper substrate and then drying it. The transparent agent comprises a polyester resin component, which is a reaction product comprising (A) rosin, (B) polycarboxylic acid, (C) polyol, and (D) aliphatic monocarboxylic acid. The polyester resin component has an acid value of 100 mg KOH / g or less, a weight-average molecular weight of 1 million or less, and a refractive index of 1.40 or more and 1.60 or less.

[0168] (Liquid composition) The above-mentioned transparent agent can be used as a transparent agent.

[0169] The liquid medium only needs to be able to dissolve or disperse the transparentizing agent.

[0170] As a liquid medium, examples include liquid media similar to those used in transparent agents, with organic solvents being preferred. Using organic solvents offers advantages such as rapid penetration of the transparent agent into the paper substrate, suppression of fluctuations in the paper substrate, and rapid drying. One type of liquid medium can be used alone, or two or more can be used in combination.

[0171] The content of the liquid medium can be appropriately set considering the ease of coating or impregnation on the paper substrate. For example, the content of the liquid medium is 30% to 50% by mass relative to the total mass of the liquid composition.

[0172] The viscosity of the liquid composition is preferably 50 mPa·s to 5000 mPa·s, more preferably 50 mPa·s to 4000 mPa·s, and even more preferably 50 mPa·s to 3000 mPa·s. When the viscosity is below the upper limit of the above range, the liquid composition easily penetrates into the interior of the paper substrate, easily improving the transparency of the transparent area. When the viscosity is above the lower limit of the above range, when a portion of the paper substrate is used as the transparent area, the boundary between the transparent area and other areas is clear.

[0173] Viscosity was measured using a Blookfield viscometer at 30°C and 60 rpm.

[0174] (Paper substrate) The aforementioned paper substrate can be used as a paper substrate.

[0175] The coating or impregnation of liquid compositions can be carried out by known methods. Examples include: flexographic printing, inkjet printing, gravure printing, offset printing, gravure-offset printing, screen printing, spray coating machines, roller coating machines, gravure coating machines, bar coating machines, doctor blade coating machines, curtain coating machines, flow coating machines, comma coating machines, brush coating, and dipping methods.

[0176] The coating or impregnation of the liquid composition can be performed on the entire surface of the paper substrate or on a partial surface. Additionally, during the coating or impregnation of the liquid composition, a portion of the paper substrate may be formed on the opposite side of the surface from which the transparent agent did not reach the impregnated coating.

[0177] The liquid composition can be coated or impregnated on only one side of the paper substrate, or it can be coated or impregnated on one side and the other side of the paper substrate respectively.

[0178] The coating or impregnation of the liquid composition can be performed in one step or in multiple steps. When performed in multiple steps, the composition and combination of the transparent material used in each step can be the same or different.

[0179] The coating or impregnation amount of the liquid composition varies depending on the type of paper substrate used (porosity, etc.). It is preferably 10 g / m², calculated as the mass of the solid component of the polyester resin in the transparentizing agent per unit area of ​​the area coated or impregnated with the liquid composition (transparent area). 2 ~80g / m2 More preferably 20g / m 2 ~70g / m 2 More preferably 30g / m 2 ~60g / m 2 When the coating or impregnation amount is above the lower limit of the above range, the transparency of the transparent area is easily improved. When the coating or impregnation amount is below the upper limit of the above range, the recyclability is improved.

[0180] The liquid medium is removed by drying a paper substrate coated or impregnated with a liquid composition, resulting in transparent paper containing a transparentizing agent at least inside the paper substrate.

[0181] Drying after coating or impregnation can be carried out using known methods. Drying conditions can be natural drying at room temperature or heated drying. Heated drying is preferred. The drying temperature during heated drying is, for example, 40°C or higher, preferably 50°C or higher. Furthermore, the drying temperature is, for example, 150°C or lower, preferably 130°C or lower. Furthermore, the drying time is, for example, 1 second or higher, preferably 5 seconds or higher. Furthermore, the drying time is, for example, 600 seconds or lower, preferably 500 seconds or lower.

[0182] After drying, humidity control can be performed to adjust the moisture content. Humidity control conditions, for example, include a temperature of 23°C and a relative humidity of 50%.

[0183] Example Next, the present invention will be described based on embodiments and comparative examples, but the present invention is not limited to the following embodiments. Unless otherwise stated, "parts" and "%" are mass measurements.

[0184] Furthermore, the specific values ​​of proportions (including proportions), physical property values, parameters, etc. used in the following description can be replaced with the corresponding upper limit values ​​(defined as "below" or "less than") or lower limit values ​​(defined as "above" or "exceeding") of the proportions (including proportions), physical property values, parameters, etc. recorded in the "Specific Embodiments" above.

[0185] <Determination Method> (1) Acid value The acid value of the polyester resin components was determined according to JIS K 5601-2-1 (1999).

[0186] (2) Iodine value The iodine value of the polyester resin component was determined according to JIS K 0070 (1992).

[0187] (3) Molecular weight The polyester resin component was dissolved in tetrahydrofuran to obtain a 1.0 g / L sample. Next, the sample was determined by gel permeation chromatography (GPC) equipped with a differential refractive index detector (RID), and the weight-average molecular weight (Mw) was calculated from the obtained chromatogram (chart). The apparatus and conditions for determination are shown below.

[0188] Device: Shodex GPC-101 (manufactured by Showa Denko Corporation) Detector: RI detector Columns used: Shodex Column GPC KF-802, 803, 804, 806 (manufactured by Shodex Science & Technology Co., Ltd.) Elution buffer: THF Column rate: 1.0 mL / min. Measurement temperature: 40℃ Molecular weight marker: Standard polystyrene (using Agilent's EasiCal Polystyrene Standards PS-1). (4) Refractive index The refractive index was measured using a multi-wavelength Abbe DR-M4 refractometer (manufactured by Atago) according to JIS K 7142 (2014).

[0189] <Manufacturing Example 1> In a four-necked flask equipped with a stirrer, a reflux condenser with a water separator, and a thermometer, 27.8 parts of rosin were added while nitrogen was being purged, and the temperature was raised to 210°C. Next, 9.8 parts of fumaric acid were added, and the mixture was stirred at 210°C for approximately 90 minutes. This yielded the first product.

[0190] In a separate four-necked flask equipped with a reflux condenser with a water separator and a thermometer, 73.4 parts of linseed oil and 15.5 parts of glycerin were added, and the mixture was stirred at 250°C for approximately 90 minutes. Next, the first product was mixed in, and the mixture was cooled to 190°C. Then, a dehydration condensation reaction was carried out at 190°C for 8 hours to obtain the polyester resin component (resin 1) as the second product. Resin 1 has an acid value of 10 mg KOH / g, an iodine value of 109 g / 100 g, a weight-average molecular weight of 82,000, and a refractive index of 1.49.

[0191] In addition, the refractive index of flaxseed oil fatty acids is 1.49.

[0192] <Manufacturing Examples 2, 3, 5, 8, 10> Except for changing the ratio of raw material components to the ratio shown in Table 1, polyester resin components (resins 2, 3, 5, 8, and 10) were obtained in the same manner as in Manufacturing Example 1. The physical properties of each resin are shown in Table 1.

[0193] <Manufacturing Example 4> In a four-necked flask equipped with a stirrer, a reflux condenser with a water separator, and a thermometer, 46.9 parts of rosin were added while nitrogen was being purged, and the temperature was raised to 210°C. Next, 16.5 parts of fumaric acid were added, and the mixture was stirred at 210°C for approximately 90 minutes. This yielded the first product.

[0194] In a separate four-necked flask equipped with a reflux condenser with a water separator and a thermometer, 56.8 parts of linseed oil and 25 parts of pentaerythritol were added, and the mixture was stirred at 250°C for approximately 90 minutes. Next, the first product was mixed in, and the mixture was cooled to 190°C. Then, a dehydration condensation reaction was carried out at 190°C for 7 hours to obtain the polyester resin component (resin 4). Resin 4 has an acid value of 8 mg KOH / g, an iodine value of 74 g / 100 g, a weight-average molecular weight of 618,000, and a refractive index of 1.50.

[0195] <Manufacturing Example 6> Except for replacing linseed oil with tung oil, the polyester resin component (resin 6) was obtained by the same method as in manufacturing example 1. The resin 6 has 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.

[0196] In addition, the refractive index of tung oil fatty acids is 1.52.

[0197] <Manufacturing Example 7> In a four-necked flask equipped with a stirrer, a reflux condenser with a water separator, and a thermometer, 18.5 parts of rosin were added while nitrogen was being purged, and the temperature was raised to 210°C. Next, 6.5 parts of fumaric acid were added, and the mixture was stirred at 210°C for approximately 90 minutes. After the reaction, the mixture was cooled to 190°C, and 25.0 parts of glycerol and 77.9 parts of oleic acid were added. A dehydration condensation reaction was then carried out at 190°C for 10 hours to obtain the polyester resin component (Resin 7). Resin 7 has an acid value of 10 mg KOH / g, an iodine value of 55 g / 100 g, a weight-average molecular weight of 122,000, and a refractive index of 1.40.

[0198] In addition, oleic acid has a refractive index of 1.37.

[0199] <Manufacturing Example 9> In a four-necked flask equipped with a stirrer, a reflux condenser with a water separator, and a thermometer, 27.8 parts of rosin were added while nitrogen was being purged, and the temperature was raised to 210°C. Next, 9.8 parts of fumaric acid were added, and the mixture was stirred at 210°C for approximately 90 minutes. This yielded the first product.

[0200] In a separate four-necked flask equipped with a reflux condenser with a water separator and a thermometer, 73.4 parts coconut oil and 15.5 parts glycerol were added and stirred at 250°C for approximately 90 minutes. The first product was then mixed in and cooled to 190°C. A dehydration condensation reaction was then carried out at 190°C for 8 hours to obtain the polyester resin component (Resin 9). Resin 9 has an acid value of 8 mg KOH / g, an iodine value of 9 g / 100 g, a weight-average molecular weight of 86,000, and a refractive index of 1.47.

[0201] In addition, the refractive index of coconut oil fatty acids is 1.45.

[0202] <Manufacturing Example 11> Except that the time for the dehydration condensation reaction to obtain the second product was extended to 12 hours, the polyester resin component (resin 11) was obtained by the same method as in manufacturing example 1. The resin 11 has 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.

[0203] <Manufacturing Example 12> In a four-necked flask equipped with a stirrer, a reflux condenser with a water separator, and a thermometer, 35.2 parts of rosin were added while nitrogen was being purged, and the temperature was raised to 210°C. Next, 12.4 parts of fumaric acid were added, and the mixture was stirred at 210°C for approximately 90 minutes. This yielded the first product.

[0204] In a separate four-necked flask equipped with a reflux condenser with a water separator and a thermometer, 64.3 parts of clove oil and 19.1 parts of glycerol were added, and the mixture was stirred at 250°C for approximately 90 minutes. Next, the first product was mixed in, and the mixture was cooled to 190°C. Then, a dehydration condensation reaction was carried out at 190°C for 8 hours to obtain the polyester resin component (resin 12) as the second product. Resin 12 has an acid value of 9 mg KOH / g, an iodine value of 45 g / 100 g, a weight-average molecular weight of 72,000, and a refractive index of 1.61.

[0205] In addition, the refractive index of clove oil fatty acids is 1.56.

[0206] <Manufacturing Example 13> In a four-necked flask equipped with a stirrer, a reflux condenser with a water separator, and a thermometer, 13.7 parts of rosin were added while nitrogen was being purged, and the temperature was raised to 210°C. Next, 4.7 parts of fumaric acid were added, and the mixture was stirred at 210°C for approximately 90 minutes. After the reaction, the mixture was cooled to 190°C, and 18.2 parts of glycerol and 75.6 parts of oleic acid were added. A dehydration condensation reaction was then carried out at 190°C for 10 hours to obtain the polyester resin component (Resin 13). Resin 13 has an acid value of 10 mg KOH / g, an iodine value of 61 g / 100 g, a weight-average molecular weight of 102,000, and a refractive index of 1.38.

[0207] In addition, oleic acid has a refractive index of 1.37.

[0208] <Examples 1-9, Comparative Examples 1-4> (Preparation of liquid compositions) Add 50 parts of the polyester resin component and 50 parts of isopropanol as shown in Table 2 to an Erlenmeyer flask equipped with a reflux duct, and stir at 50°C for approximately 1 hour. This yields a liquid composition.

[0209] (The production and evaluation of transparent paper) As a paper substrate, a basis weight of 50 g / m³ is prepared. 2 This is a single-sided glossy kraft paper. The pulp constituting this single-sided glossy kraft paper consists of 40% hardwood bleached kraft pulp and 60% softwood bleached kraft pulp. The paper has an opacity of 68.5% and a density of 0.72 g / cm³. 3 The thickness is 70μm.

[0210] The liquid composition, adjusted to 25°C, was applied to the non-gloss surface of a paper substrate using a rod coater No. 36 with a winding mechanism to obtain coated paper. The coating weight of the liquid composition at this point, calculated based on the resin solids content, was 30 g / m². 2 Then, the coated paper was dried at 120°C for 2 minutes. After drying, it was conditioned for 12 hours in a constant temperature and humidity environment (23°C, 50% relative humidity). This yielded a transparent paper.

[0211] <Comparative Example 5> 50 parts of rosin and 50 parts of isopropanol were mixed to obtain a rosin solution. 50 parts of linseed oil and 50 parts of isopropanol 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. The liquid composition of Comparative Example 7 was thus obtained.

[0212] <Comparative Example 6> 50 parts of rosin and 50 parts of isopropanol were mixed to obtain a rosin solution. 50 parts of linseed oil and 50 parts of isopropanol were mixed to obtain a linseed oil solution. Next, 44 parts of the rosin solution and 56 parts of the linseed oil solution were mixed. Thus, the liquid composition of Comparative Example 8 was obtained.

[0213] <Comparative Example 7> 50 parts of rosin and 50 parts of isopropanol were mixed to obtain a rosin solution. 50 parts of linseed oil and 50 parts of isopropanol 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. Thus, the liquid composition of Comparative Example 9 was obtained.

[0214] <Evaluation> The resulting transparent paper was evaluated as follows. The results are shown in Table 2.

[0215] (Transparency) The opacity of transparent paper after conditioning was determined according to JIS P 8149 (2000). Opacity below 16% is marked with ◎, above 16% but below 20% with ○, above 20% but below 30% with △, and above 30% with ×.

[0216] (Total transmittance) The total transmittance of the transparent paper was measured immediately after conditioned (total transmittance immediately after conditioned). Then, the transparent paper was left to stand for 7 days at 22°C and 50% relative humidity, and the total transmittance was measured again (total transmittance after 7 days). The total transmittance was measured using a haze meter NDH 5000 (manufactured by Nippon Denshoku Kogyo Co., Ltd.) according to JIS K 7361-1 (1997).

[0217] However, in Comparative Example 4, the viscosity of the liquid composition exceeded 10,000 mPa·s, making it difficult to coat or impregnate onto the paper substrate. Therefore, the production and evaluation of transparent paper were not carried out.

[0218] [Table 1]

[0219] [Table 2]

[0220] As shown in the results above, the transparent papers of Examples 1 to 9 exhibit a small difference between their total light transmittance immediately after conditioned and after 7 days, demonstrating excellent long-term stability. Specifically, the transparent papers of Examples 1 to 7 show total light transmittance of over 58% immediately after conditioned and after 7 days, indicating excellent transparency. Furthermore, the transparent papers of Examples 1 to 5 show the same total light transmittance immediately after conditioned and after 7 days, demonstrating particularly excellent long-term stability of transparency.

[0221] On the other hand, Comparative Example 1, with an acid value exceeding 100 mg KOH / g, exhibited poor transparency. The production of Comparative Example 2, with a weight-average molecular weight exceeding 1 million, was discontinued due to thickening. Comparative Examples 3 and 4, which used polyester resin components with a refractive index not exceeding 1.40 but not exceeding 1.60, also exhibited poor transparency. In Comparative Examples 5 to 7, which used a mixture of rosin and linseed oil to replace the polyester resin component, the total light transmittance after 7 days was lower than the total light transmittance immediately after conditioned, indicating poor long-term stability, such as whitening over time.

Claims

1. A transparentizing agent, wherein, The transparentizing agent comprises a polyester resin component, which is a reaction product comprising (A) rosin, (B) polycarboxylic acid, (C) polyol and (D) aliphatic monocarboxylic acid. The polyester resin component has an acid value of less than 100 mg KOH / g, a weight-average molecular weight of less than 1 million, and a refractive index of more than 1.40 and less than 1.

60.

2. The transparentizing agent according to claim 1, wherein, The iodine value of the polyester resin component is above 10g / 100g and below 140g / 100g.

3. A method for manufacturing a transparentizing agent, wherein, The raw material components containing (A) rosin, (B) polycarboxylic acid, (C) polyol and (D) aliphatic monocarboxylic acid are reacted to obtain a polyester resin component with an acid value of less than 100 mg KOH / g, a weight-average molecular weight of less than 1 million, and a refractive index of more than 1.40 and less than 1.

60.

4. The method for manufacturing the transparentizing agent according to claim 3, wherein, The iodine value of the polyester resin component is above 10g / 100g and below 140g / 100g.

5. The method for manufacturing the transparentizing agent according to claim 3 or 4, wherein, The (B) polycarboxylic acid comprises α,β-unsaturated dicarboxylic acids. 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, the (C) polyol, and the (D) aliphatic monocarboxylic acid are reacted.

6. The method for manufacturing the transparentizing agent according to claim 3 or 4, wherein, The (B) polycarboxylic acid comprises α,β-unsaturated dicarboxylic acids. 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 an oil containing the (D) aliphatic monocarboxylic acid as a fatty acid to obtain a modified product. The first product is then reacted with the modified product.

7. A transparent paper, wherein, A transparentizing agent is contained at least inside the paper substrate. The transparentizing agent comprises a polyester resin component, which is a reaction product comprising (A) rosin, (B) polycarboxylic acid, (C) polyol and (D) aliphatic monocarboxylic acid. The polyester resin component has an acid value of less than 100 mg KOH / g, a weight-average molecular weight of less than 1 million, and a refractive index of more than 1.40 and less than 1.

60.

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

9. The transparent paper according to claim 7 or 8, wherein, The paper substrate comprises coniferous chemical pulp and broadleaf chemical pulp.

10. A method for manufacturing transparent paper, comprising coating or impregnating a liquid composition containing a transparent agent and a liquid medium onto a paper substrate and then drying it to manufacture transparent paper, wherein... The transparentizing agent comprises a polyester resin component, which is a reaction product comprising (A) rosin, (B) polycarboxylic acid, (C) polyol and (D) aliphatic monocarboxylic acid. The polyester resin component has an acid value of less than 100 mg KOH / g, a weight-average molecular weight of less than 1 million, and a refractive index of more than 1.40 and less than 1.

60.

11. The method for manufacturing transparent paper according to claim 10, wherein, The iodine value of the polyester resin component is above 10g / 100g and below 140g / 100g.

12. The method for manufacturing transparent paper according to claim 10 or 11, wherein, The paper substrate comprises coniferous chemical pulp and broadleaf chemical pulp.

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