Resin composition and use thereof, and method for producing resin composition

Abstract

Provided is a resin composition containing a PVA-based resin containing a sulfonic acid or a salt group thereof, in which coloring (yellowing) of the aforementioned PVA-based resin at high temperatures is inhibited, whereby a resin composition in which coloring (yellowing) can be reduced even when exposed to high temperatures is obtained. The resin composition of the present invention contains: a polyvinyl alcohol-based resin containing a sulfonic acid or a salt group thereof (A), and a chlorine component (B), the content of the chlorine component (B) being 0.1 parts by mass or less, calculated as chlorine atoms, relative to 100 parts by mass of the polyvinyl alcohol-based resin containing a sulfonic acid or a salt group thereof (A).

Description

Technical Field

[0001] The present invention relates to resin compositions comprising polyvinyl alcohol resins containing sulfonic acid or its salts, and more specifically, to resin compositions particularly suitable for use as dispersants and coating liquids, and to dispersants and coating liquids for thermosensitive color development containing the resin compositions. Background Technology

[0002] Polyvinyl alcohol resins (hereinafter referred to as PVA resins) are widely used as dispersants, emulsifiers, suspending agents, fiber processing agents, paper processing agents, adhesives, bonding agents, and films due to their excellent water solubility, interfacial properties (dispersibility, protective colloid properties), and film coating properties (film-forming properties, strength, oil resistance, etc.).

[0003] In addition, PVA resins are widely used as solvent-free aqueous coatings, taking advantage of their water solubility, for protective layers of thermal recorders, coatings for thermal recording layers, and coatings for ink receiving layers of inkjet recording media.

[0004] Among them, PVA-based resins containing sulfonic acid or its salts have excellent dispersing properties due to their negative charge, and are used in various emulsifiers, suspending agents, and dispersants.

[0005] Furthermore, it is also used as a coating solution for the thermal color development layer of thermal recording media, and is suitable as a coating solution containing color developers and colorless dyes.

[0006] The thermal recording medium has a thermal color developing layer, which is formed by coating an aqueous dispersion containing a colorless dye, a color developer, and a dispersant onto a support substrate and then drying it. When heated, the colorless dye and the color developer melt and mix, reacting to produce color.

[0007] For example, Patent Document 1 proposes the following scheme: using a polyvinyl alcohol derivative containing sulfonic acid groups as a dispersant.

[0008] In addition, in recent years, for the purpose of improving ultraviolet absorption, for example, Patent Document 2 has proposed the following scheme: using PVA-based resins with acetyl acetyl groups and sulfonic acid groups.

[0009] Existing technical documents

[0010] Patent documents

[0011] Patent Document 1: Japanese Patent Application Publication No. 58-102794

[0012] Patent Document 2: Japanese Patent Application Publication No. 2014-139000 Summary of the Invention

[0013] The problem the invention aims to solve

[0014] However, PVA-based resins containing sulfonic acid or its salts have the problem of yellowing due to heating. The aforementioned patent documents 1 and 2 did not take any consideration into account for this problem, and no detailed study has been conducted to date.

[0015] Therefore, in this context, the object of the present invention is to provide a resin composition in which the coloring (yellowing) of the aforementioned PVA-based resin at high temperatures is suppressed, thereby reducing coloring (yellowing) when exposed to high temperatures (specifically, 50 to 200°C).

[0016] Solution for solving the problem

[0017] Therefore, the inventors conducted repeated and in-depth research in view of the above situation, and as a result, focusing on the chlorine content in PVA resins containing sulfonic acid or its salts, which had not been given much attention until now, they found that by reducing the chlorine content to a certain level, the yellowing of PVA resins containing sulfonic acid or its salts could be reduced, thus completing the present invention.

[0018] That is, the present invention relates to the following (1) to (6).

[0019] (1) A resin composition comprising: a polyvinyl alcohol resin (A) containing sulfonic acid or its salt base and a chlorine component (B), wherein the content of the chlorine component (B) is 0.1 parts by mass or less per 100 parts by mass of the polyvinyl alcohol resin (A) containing sulfonic acid or its salt base, calculated in chlorine atom conversion.

[0020] (2) The resin composition according to (1) above, wherein the content of sulfonic acid or its salt in the aforementioned polyvinyl alcohol resin (A) containing sulfonic acid or its salt is 0.01 to 10 mol.

[0021] (3) The resin composition according to (1) or (2) above, wherein the chlorine component (B) is sodium chloride.

[0022] (4) A dispersant formed from any one of the resin compositions described in (1) to (3) above.

[0023] (5) A coating liquid for a thermosensitive color developing layer, comprising: the resin composition of any one of (1) to (3) above, a colorless dye, a color developer and water.

[0024] (6) A method for manufacturing a resin composition, which is a method for manufacturing the resin composition described in any one of (1) to (3) above, the method comprising the following steps: copolymerizing a vinyl ester monomer with an unsaturated monomer containing sulfonic acid or its salt to obtain a polymer, saponifying the obtained polymer, and further comprising at least one of the following steps: removing the chlorine component of the aforementioned unsaturated monomer containing sulfonic acid or its salt before saponification; and removing the chlorine component of the saponified polyvinyl alcohol resin (A) containing sulfonic acid or its salt.

[0025] The effects of the invention

[0026] The resin composition of the present invention exhibits minimal coloration (yellowing) even at high temperatures, making it useful in applications requiring whiteness and transparency, such as coating solutions for color development layers of thermal recording media. For example, it is also useful as a dispersant for color developers used in thermal color development layers of thermal recording media.

[0027] It should be noted that chlorine acts as a catalyst for the formation of double bonds, which is the cause of coloring (yellowing). Therefore, in order to further suppress the formation of double bonds, it is also important to have a resin composition with less chlorine. However, in this invention, in the context of requiring color suppression at higher temperatures, a resin composition with less coloring (yellowing) can be obtained by reducing the chlorine content, which has not been of much concern until now, to a level above this. Detailed Implementation

[0028] The present invention will now be described in detail.

[0029] It should be noted that the following description of the technical features is an example (representative example) of an embodiment of the present invention and is not limited to these contents.

[0030] In this specification, (meth)allyl refers to allyl or methylallyl, (meth)acrylic acid refers to acrylic acid or methacrylic acid, and (meth)acrylate refers to acrylate or methacrylate.

[0031] In addition, in this specification, the percentages and parts indicated by mass are the same as those indicated by weight.

[0032] The resin composition of the present invention is a resin composition comprising a PVA-based resin (A) containing sulfonic acid or its salts and a chlorine component (B). First, the PVA-based resin (A) containing sulfonic acid or its salts will be described.

[0033] [PVA-based resins containing sulfonic acid or its salts (A)]

[0034] The PVA-based resin (A) containing sulfonic acid or its salts used in this invention has sulfonic acid or its salts directly on the main chain of the PVA-based resin, or has sulfonic acid or its salts by means of a bonded chain. For example, sulfonic acid or its salts are represented by the following general formula (1).

[0035]

[0036] (In formula (1), X represents a single bond or a bonded chain, and M represents a hydrogen atom, an alkali metal, or an ammonium group.)

[0037] As the bonding chain of X, there are no particular limitations as long as it is a divalent linking group. For example, in addition to straight-chain or branched alkylene groups with 1 to 20 carbon atoms, straight-chain or branched alkenyl groups with 1 to 20 carbon atoms, straight-chain or branched alkyneyl groups with 1 to 20 carbon atoms, phenylene groups, naphthyl groups, etc. (these hydrocarbon groups may be substituted by halogens such as fluorine, chlorine, and bromine), examples include: -O-, -(CH2O). m -、-(OCH2) m -、-(CH2O) m CH2-, -CO-, -COCO-, -CO(CH2) m CO-, -CO(C6H4)CO-, -S-, -CS-, -SO-, -SO2-, -NR-, -CONR-, -NRCO-, -CSNR-, -NRCS-, -NRNR-, -HPO4-, -Si(OR)2-, -OSi(OR)2-, -OSi(OR)2O-, -Ti(OR)2-, -OTi(OR)2-, -OTi(OR)2O-, -Al(OR)-, -OAl(OR)-, -OAl(OR)O-, etc. (R is independently any substituent, preferably a hydrogen atom, an alkyl group having 1 to 15 carbon atoms, and m is an integer from 1 to 5). These bonded chains can be single or a combination of two or more bonded chains. From the perspective of stability during manufacturing or use, single bonds, straight-chain or branched alkylene groups having 1 to 6 carbon atoms are preferred.

[0038] Examples of alkali metals that can be represented by M include lithium, sodium, potassium, rubidium, and cesium.

[0039] The degree of saponification (determined according to JIS K 6726) of the PVA-based resin (A) containing sulfonic acid or its salts of the present invention is preferably 75 to 100 mol%, particularly preferably 80 to 95 mol%, and especially preferably 85 to 90 mol%. If the above degree of saponification is too low, there is a tendency for the water solubility to decrease.

[0040] The average degree of polymerization (as determined according to JIS K 6726) of the PVA-based resin (A) containing sulfonic acid or its salts of the present invention is preferably 100 to 4000, particularly preferably 150 to 3000, and especially preferably 200 to 1500.

[0041] If the average degree of polymerization is too low, the coating film is prone to cracking; if it is too high, the coating and other workability will be reduced.

[0042] The sulfonic acid or its salt content in the PVA-based resin (A) of the present invention is preferably 0.01 to 10 mol%, particularly preferably 0.1 to 7 mol%, and especially preferably 1 to 5 mol%. If the above content is too low, the chargeability of the resin tends to decrease or the protective colloidal properties decrease; if it is too high, the manufacturing tends to become more difficult.

[0043] As a method for manufacturing the PVA-based resin (A) containing sulfonic acid or its salts according to the present invention, examples include the following methods: Method (1), copolymerizing and saponifying a vinyl ester monomer with an unsaturated monomer containing sulfonic acid or its salts; Method (2), coexisting a compound with a functional group such as an alcohol, aldehyde, or thiol having sulfonic acid or its salts as a chain transfer agent, and polymerizing and saponifying the vinyl ester monomer; Method (3), treating the PVA-based resin with bromine, iodine, etc., and then heating it in an acidic sodium sulfite aqueous solution; Method (4), heating the PVA-based resin in a concentrated sulfuric acid aqueous solution; Method (5), acetalizing the PVA-based resin with an aldehyde compound having sulfonic acid or its salts; etc. In the methods (1) and (2) above, the carboxylic acid can be reduced by washing with an alcohol solvent such as methanol after saponification.

[0044] From the perspective of safety and workability during manufacturing, it is preferable that (1) the vinyl ester monomer is copolymerized with an unsaturated monomer containing sulfonic acid or its salt group to obtain a polymer, and the obtained polymer is saponified to obtain the product.

[0045] Examples of vinyl ester monomers include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl butyrate, vinyl isobutyrate, vinyl neovalerate, vinyl decanoate, vinyl laurate, vinyl stearate, vinyl benzoate, and vinyl tert-carbonate. From an economic perspective, vinyl acetate is preferred.

[0046] Examples of unsaturated monomers containing sulfonic acid or its salt group include (i) olefin sulfonic acid or its salt represented by general formula (2) below, (ii) sulfoalkyl maleate represented by general formula (3) or (4) below, (iii) sulfoalkyl (meth)acrylamide represented by general formula (5), (6) or (7) below, and (iv) sulfoalkyl (meth)acrylate represented by general formula (8) below.

[0047] CH2=CH-R1-SO3M (2)

[0048] [In formula (2), R1 represents an alkylene group having 1 to 4 carbon atoms, and M represents a hydrogen atom, an alkali metal, or an ammonium group.]

[0049]

[0050] [In formula (3), R2 represents an alkyl group with 1 to 3 carbon atoms, n represents an integer from 2 to 4, and M represents a hydrogen atom, an alkali metal, or an ammonium group.]

[0051]

[0052] [In equation (4), n represents an integer from 2 to 4, and M represents a hydrogen atom, an alkali metal, or an ammonium group.]

[0053]

[0054] [In formula (5), R3 and R4 each independently represent a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, n represents an integer of 2 to 4, and M represents a hydrogen atom, an alkali metal, or an ammonium group.]

[0055]

[0056] [In formula (6), R5 represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, n represents an integer of 2 to 4, and M represents a hydrogen atom, an alkali metal, or an ammonium group.]

[0057]

[0058] [In formula (7), R6 represents an alkyl group with 1 to 3 carbon atoms, R7, R8, R9 and R10 each independently represent a hydrogen atom or an alkyl group with 1 to 3 carbon atoms, and M represents a hydrogen atom, an alkali metal or an ammonium group.]

[0059]

[0060] [In formula (8), R11 represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, n represents an integer of 2 to 4, and M represents a hydrogen atom, an alkali metal, or an ammonium group.]

[0061] Specific examples of the above-mentioned olefin sulfonic acids or their salts include, for example, vinyl sulfonic acid, allyl sulfonic acid, methyl allyl sulfonic acid, and other olefin sulfonic acids or their salts.

[0062] In addition, specific examples of the aforementioned sulfoalkyl maleates include sodium sulfopropyl-2-ethylhexyl maleate, sodium sulfopropyl-tetrate maleate, and sodium sulfopropyl-eicosyl maleate.

[0063] In addition, specific examples of the aforementioned sulfoalkyl (meth)acrylamides include sodium sulfomethacrylamide, sodium sulfo-tert-butylacrylamide, sodium sulfo-sec-butylacrylamide, sodium sulfo-tert-butylacrylamide, etc.

[0064] Furthermore, specific examples of the aforementioned sulfoalkyl (meth)acrylates include, for instance, sodium sulfoethyl acrylate.

[0065] In the case of copolymerization introduction, among the unsaturated monomers containing sulfonic acid or its salt group, olefin sulfonic acid or its salt is suitable for use.

[0066] In addition, in this invention, besides the aforementioned copolymerizing components, other monomers of approximately 0.1 to 10 mol% may be copolymerized without hindering the purpose of this invention. Examples of other monomers include, for instance, α-olefins such as ethylene, propylene, isobutylene, α-octene, α-dodecene, and α-octadecene; unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, maleic anhydride, and itaconic acid, or their salts or mono- or dialkyl esters; nitriles such as acrylonitrile and methacrylonitrile; amides such as diacetone acrylamide, acrylamide, and methacrylamide; alkyl vinyl ethers; dimethyl allyl vinyl ketone; N-vinylpyrrolidone; vinyl chloride; vinylidene chloride; polyoxyethylene (methyl) allyl ether, poly... Polyoxyalkylene (meth)allyl ethers, etc.; polyoxyethylene (meth)acrylates, polyoxypropylene (meth)acrylates, etc.; polyoxyalkylene (meth)acrylamides, polyoxypropylene (meth)acrylamides, etc.; polyoxyethylene (1-(meth)acrylamide-1,1-dimethylpropyl) ester; polyoxyethylene ethylene ethers; polyoxypropylene ethylene ethers; polyoxyethylene allylamine; polyoxypropylene allylamine; polyoxyethylene ethyleneamine; polyoxypropylene ethyleneamine, etc.

[0067] Furthermore, examples include monomers containing cationic groups such as N-acrylamidomethyltrimethylammonium chloride, N-acrylamidoethyltrimethylammonium chloride, N-acrylamidopropyltrimethylammonium chloride, 2-acryloyloxyethyltrimethylammonium chloride, 2-methacryloyloxyethyltrimethylammonium chloride, 2-hydroxy-3-methacryloyloxypropyltrimethylammonium chloride, allyltrimethylammonium chloride, methylallyltrimethylammonium chloride, 3-butenetrimethylammonium chloride, dimethyldiallylammonium chloride, and diethyldiallylammonium chloride; monomers containing acetylacetyl groups; 3,4-diacetoxy-1-butene; 1,4-diacetoxy-2-butene; ethylene carbonate; vinyl ethylene carbonate; glycerol monoallyl ether; isopropyl acetate; and 1-methoxyvinyl acetate.

[0068] From the perspective of improving emulsifying power and viscosity stability of aqueous solutions, α-olefin-vinyl alcohol copolymers obtained by using α-olefins such as ethylene, propylene, isobutylene, α-octene, α-dodecene, and α-octadecene as copolymerizing components are preferred, and the preferred content of the above-mentioned α-olefins is 0.1 to 10 mol.

[0069] There are no particular limitations on the method for copolymerizing the above-mentioned vinyl ester monomers with unsaturated monomers containing sulfonic acid or its salt groups. Known methods such as bulk polymerization, solution polymerization, suspension polymerization, dispersion polymerization, or emulsion polymerization can be used, with solution polymerization being the most common method.

[0070] There are no particular restrictions on the method of adding monomer components during copolymerization; any method can be used, such as simultaneous addition, batch addition, or continuous addition.

[0071] Solvents used in the above copolymerization typically include lower alcohols such as methanol, ethanol, isopropanol, n-propanol, and butanol, as well as ketones such as acetone and methyl ethyl ketone. Industrially, alcohols with 1 to 3 carbon atoms are suitable, and methanol is particularly suitable.

[0072] The amount of solvent can be appropriately selected based on the degree of polymerization of the target copolymer and the chain transfer constant of the solvent. For example, when the solvent is methanol, it can be selected from a range of S (solvent) / M (monomer) = 0.01 to 10 (mass ratio), preferably 0.05 to 3 (mass ratio).

[0073] During copolymerization, a polymerization catalyst can be used. Examples of such catalysts include well-known free radical polymerization catalysts such as azobisisobutyronitrile, acetyl peroxide, benzoyl peroxide, and lauroyl peroxide, as well as low-temperature active free radical polymerization catalysts such as azobis(dimethyl)pentadionitrile and azobis(methoxy)dimethylpentadionitrile. The amount of polymerization catalyst used varies depending on the type of catalyst and cannot be fixed in a general sense; it can be arbitrarily selected based on the polymerization rate. For example, when using azobisisobutyronitrile or acetyl peroxide, the amount relative to the vinyl ester monomer is preferably 0.01–1.0 mol%, and particularly preferably 0.02–0.5 mol%.

[0074] In addition, the copolymerization reaction is carried out at a temperature of around 30°C to the boiling point, depending on the solvent and pressure used. More specifically, it is carried out in the range of 35°C to 150°C, preferably 40°C to 75°C.

[0075] The resulting copolymer is then saponified. The saponification is carried out as follows: the copolymer obtained above is dissolved in an alcohol or aqueous alcohol, using a base catalyst or an acid catalyst.

[0076] Examples of alcohols include lower alcohols such as methanol, ethanol, propanol, and tert-butanol, with alcohols having 1 to 3 carbon atoms being preferred, and methanol being particularly preferred. The concentration of the copolymer in the alcohol can be appropriately selected based on the viscosity of the system, typically ranging from 10 to 60% by mass. Examples of catalysts used in saponification include alkaline catalysts such as hydroxides and alcohols of alkali metals such as sodium hydroxide, potassium hydroxide, sodium methoxide, sodium ethoxide, potassium methoxide, and lithium methoxide; and acid catalysts such as sulfuric acid, hydrochloric acid, nitric acid, methanesulfonic acid, zeolites, and cation exchange resins.

[0077] The amount of the above-mentioned saponification catalyst can be appropriately selected according to the saponification method, the target degree of saponification, etc. When using an alkaline catalyst, it is generally appropriate to use a ratio of 0.1 to 30 mmol, preferably 2 to 15 mmol, relative to the total stoichiometry of the vinyl ester monomer and the compound shown in general formulas (2) to (8) for 1 mol.

[0078] In addition, there is no particular limitation on the reaction temperature of the saponification reaction, but 10 to 60°C is preferred, and 20 to 50°C is particularly preferred.

[0079] Thus, the PVA-based resin (A) containing sulfonic acid or its salt groups used in this invention can be obtained.

[0080] Next, the resin composition of the present invention will be described.

[0081] [Resin Composition]

[0082] The resin composition of the present invention comprises: a PVA-based resin (A) containing sulfonic acid or its salts and a chlorine component (B), wherein the chlorine component (B) is presumably derived from the raw materials used in manufacturing the PVA-based resin (A) containing sulfonic acid or its salts. For example, if the PVA-based resin (A) containing sulfonic acid or its salts is manufactured by the method described in (1) above, in which a vinyl ester monomer is copolymerized with an unsaturated monomer containing sulfonic acid or its salts and then saponified, it is presumably that chlorine mixed in as an impurity in the unsaturated monomer containing sulfonic acid or its salts reacts with a saponification catalyst (e.g., sodium hydroxide) and exists in the PVA-based resin (A) containing sulfonic acid or its salts as a chloride (e.g., sodium chloride).

[0083] Therefore, the chlorine component (B) exists in the resin composition in the form of chlorides such as sodium chloride (NaCl), potassium chloride (KCl), and magnesium chloride (MgCl2).

[0084] For the resin composition of the present invention, the content of chlorine component (B) relative to 100 parts by mass of the PVA-based resin (A) containing sulfonic acid or its salts, calculated in chlorine atom conversion, is 0.1 parts by mass or less, preferably 0.075 parts by mass or less, and particularly preferably 0.05 parts by mass or less. Excessive amounts will result in coloring. Furthermore, the lower limit is typically around 0.001 parts by mass, preferably 0.005 parts by mass.

[0085] As for the specific content of chlorine component (B), for example, it is preferably 0.001 to 0.1 parts by mass relative to 100 parts by mass of PVA resin (A) containing sulfonic acid or its salts, calculated in terms of chlorine atoms.

[0086] It should be noted that the method for determining the chlorine component (B) can be the method using fluorescent X-rays.

[0087] As a method for making the chlorine component (B) in the resin composition less than 0.1 parts by mass relative to 100 parts by mass of the PVA-based resin (A) containing sulfonic acid or its salt, a preferred method is one that includes the following steps: copolymerizing a vinyl ester monomer with an unsaturated monomer containing sulfonic acid or its salt to obtain a polymer; saponifying the obtained polymer; and further including at least one of the following steps: removing the chlorine component of the aforementioned unsaturated monomer containing sulfonic acid or its salt before saponification; and removing the chlorine component of the saponified PVA-based resin (A) containing sulfonic acid or its salt. Specifically, for example, the following methods can be cited: Method (i) removing or reducing the chlorine content of an unsaturated monomer containing sulfonic acid or its salt (e.g., the chlorine content is 0.3 parts by weight or less relative to 100 parts by weight of the unsaturated monomer), copolymerizing with a vinyl ester monomer and saponifying; Method (ii) manufacturing a PVA-based resin (A) containing sulfonic acid or its salt, and then removing or reducing the chlorine content contained in the PVA-based resin (A) containing sulfonic acid or its salt. From the perspective of easily controlling the chlorine content, method (i) is preferred.

[0088] (i) can be detailed as follows: a method of washing and filtering an unsaturated monomer containing sulfonic acid or its base with a solvent (water and / or alcohol, etc.); a method of concentrating and drying an unsaturated monomer containing sulfonic acid or its base synthesized in a solvent and extracting it with an alcohol; a method of washing and filtering a copolymer of a vinyl ester monomer before saponification and an unsaturated monomer containing sulfonic acid or its base, wherein, from the perspective of purity, the method of washing and filtering an unsaturated monomer containing sulfonic acid or its base with a solvent (water and / or alcohol, etc.) is preferred.

[0089] Thus, the resin composition of the present invention can be obtained.

[0090] The resin composition of the present invention exhibits minimal coloring (yellowing) even when exposed to high temperatures, and can be effectively used for a variety of applications.

[0091] As for the use of the resin composition of the present invention, various uses can be described, for example, as shown in (1) to (10) below.

[0092] (1) Relationship of molded products: fibers, films, sheets, pipes, conduits, leak-proof membranes, temporary coverings, water-soluble lace, water-soluble fibers, etc.

[0093] (2) Adhesives: adhesives, binders, rewetting agents, non-woven fabric adhesives, adhesives for various building materials such as gypsum board and fiberboard, adhesives for various powder granulation, cement and mortar additives, hot melt adhesives, pressure-sensitive adhesives, and fixatives for anionic coatings.

[0094] (3) Coating agents: transparent coating agents for paper, pigment coating agents for paper, internal sizing agents for paper, sizing agents for fiber products, warp paste, fiber processing agents, leather processing agents, coatings, antifogging agents, metal corrosion inhibitors, galvanizing brighteners, antistatic agents, conductive agents, temporary coatings, etc.

[0095] (4) Relationship of blending agents for hydrophobic resins: antistatic agents and hydrophilic agents for hydrophobic resins, additives for composite fibers, films and other molded products, etc.

[0096] (5) Relationship between suspension and dispersion stabilizers: dispersants for color development liquids used in thermosensitive color development layers, pigment dispersion stabilizers for coatings, inks, water-based pigments, adhesives, etc., dispersion stabilizers for suspension polymerization of various vinyl compounds such as vinyl chloride, vinylidene chloride, styrene, (meth)acrylate, vinyl acetate, etc.

[0097] (6) Emulsifying, dispersing and stabilizing agents: emulsifiers for emulsifying and polymerizing various acrylic monomers, olefinic unsaturated compounds, butadiene compounds, hydrophobic resins such as polyolefins and polyester resins, epoxy resins, paraffin wax, asphalt and other post-emulsifiers, etc.

[0098] (7) Thickener relationship: Thickeners for various aqueous solutions, emulsions, and oil drilling fluids, etc.

[0099] (8) Flocculant relationship: flocculants for suspended solids and dissolved solids in water, pulp, slurry drainage, etc.

[0100] (9) Relationships of exchange resins: ion exchange resins, chelate exchange resins, ion exchange membranes, etc.

[0101] (10) Others: soil conditioners, photosensitizers, photosensitive corrosion-resistant resins, etc.

[0102] In particular, the resin composition of the present invention is useful as a dispersant for various dispersions, and especially as a dispersant for a color developer in a coating liquid for a thermally sensitive recording medium.

[0103] [Coating solution for thermosensitive colorimetric layer]

[0104] Next, the coating solution for the thermosensitive color development layer of the present invention will be described.

[0105] The coating liquid for thermal recording color development layer of the present invention comprises: a resin composition containing the above-mentioned PVA-based resin (A) containing sulfonic acid or its salt group and chlorine component (B), a colorless dye, a color developer, and water, wherein the PVA-based resin (A) containing sulfonic acid or its salt group serves as a dispersant for dispersing the colorless dye and the color developer.

[0106] The pH of the coating solution for the thermosensitive color development layer of the present invention is 6.4 to 8, preferably 6.4 to 7.5, and particularly preferably 6.5 to 7. Both excessively low and excessively high pH values ​​tend to cause thickening. Methods for adjusting the pH include: method (1), controlling the amount of carboxylate generated during the manufacture of the PVA-based resin (A) containing sulfonic acid or its base when cleaning it with a solvent such as alcohol; method (2), adding a pH adjuster to the coating solution; method (3), adding an alkali to the PVA-based resin (A) containing sulfonic acid or its base; etc. From the perspective of less work and simplicity, method (1) is preferred.

[0107] In addition, in the method of (1), the content of carboxylate in the PVA-based resin (A) containing sulfonic acid or its salt is usually 2.5 to 8% by mass, preferably 3 to 5% by mass. Usually, the PVA-based resin (A) containing sulfonic acid or its salt that has undergone saponification is washed once or several times with a solvent to reduce the carboxylate content (usually 0.1 to 2.4% by mass). In order to make the carboxylate content 2.5% by mass or more, the following methods can be used: reducing the number of washing times, or not washing; or adding carboxylate after washing, etc.

[0108] Examples of carboxylic acids that can be used as carboxylates include formic acid, acetic acid, butyric acid, and benzoic acid. Examples of salts that can be used as salts include alkali metal salts and alkaline earth metal salts. Among these, acetic acid is preferred as a carboxylic acid, and alkali metal salts, particularly sodium salts, are preferred as salts, specifically sodium acetate.

[0109] The method for manufacturing the coating liquid for the thermosensitive color developing layer of the present invention is generally as follows: a dispersion containing a colorless dye and a dispersion containing a color developing agent are prepared separately, and the two are mixed to manufacture the coating liquid.

[0110] To prepare a dispersion containing a colorless dye or a dispersion containing a color developer, a resin composition containing the aforementioned PVA-based resin (A) containing sulfonic acid or its salt and a chlorine component (B) is used as the dispersant to disperse the colorless dye and the color developer. It should be noted that the use of the resin composition of the present invention as the dispersant is not limited to the dispersion containing the colorless dye or the dispersion containing the color developer; the resin composition of the present invention can be used in at least one of the dispersions. In the above case, the resin composition of the present invention is preferably used in the dispersion containing at least the color developer.

[0111] The amount of resin composition used in this invention is not particularly limited, but is typically 1 to 40 parts by weight, particularly preferably 1 to 10 parts by weight, and even more preferably 1 to 5 parts by weight, relative to 100 parts by weight of the color developer. If the above amount is too small, it tends to cause poor dispersion; if the amount is too large, it tends to increase the foaming of the coating liquid.

[0112] Dispersions containing colorless dyes and dispersions containing color developers can be prepared by dispersion using known dispersers such as sand mills, ultrafine pulverizers, bead mills, ball mills, viscous mills, three-roll mills, extruders, kneaders, and homogenizers. The dispersed particle size in the dispersions containing colorless dyes and color developers is typically 0.1–10 μm, preferably 0.2–2 μm, and more preferably 0.3–1 μm. If the dispersed particle size is too large, it tends to cause a decrease in resolution and poor color development; if the dispersed particle size is too small, it tends to cause color development of the substrate, a decrease in image density, and poor color development. It should be noted that the dispersed particle size can be appropriately adjusted according to dispersion conditions such as dispersion time.

[0113] The concentration of solids in the coating solution, which is a mixture of a dispersion containing a colorless dye and a dispersion containing a color developer, is typically 20–70% by mass, preferably 30–60% by mass, and more preferably 40–50% by mass. If the solids content is too low, the image tends to become less sharp; if the solids content is too high, the coating tends to be poor.

[0114] The coating liquid for the thermosensitive color developing layer of the present invention may further contain, as needed, auxiliary additives, such as fillers, surfactants, heat-soluble substances (or lubricants), pressure color developing inhibitors, etc.

[0115] Example

[0116] The following examples illustrate the present invention in further detail, but the present invention is not limited to the following examples as long as it does not deviate from its spirit. It should be noted that, in the following, "%" and "parts" refer to mass standards.

[0117] (Example 1)

[0118] [Preparation of unsaturated monomers containing sulfonic acid or its salts]

[0119] Sodium allyl sulfonate was prepared using conventional methods as an unsaturated monomer containing sulfonic acid or its salts. The mixture was washed with a water / alcohol mixture (5 / 5 ratio) and then hot-filtered (at 50°C) to obtain sodium allyl sulfonate 1. The chlorine content in sodium allyl sulfonate 1 was determined using fluorescent X-rays. The results showed that the chlorine content in 62 parts of sodium allyl sulfonate was 0.16 parts.

[0120] [Preparation of Resin Composition 1]

[0121] In a reaction vessel equipped with a reflux condenser, a dropping funnel, and a stirrer, 1000 parts of vinyl acetate, 422 parts of methanol, 162 parts of sodium allyl sulfonate obtained above, and 1.4 parts of azobisisobutyronitrile were added. The mixture was stirred while the temperature was increased under a nitrogen gas flow, and polymerization was carried out under reflux.

[0122] Midway through the polymerization process, 1.4 parts of azobisisobutyronitrile (AIBN) were added in four separate additions. When the polymerization rate of vinyl acetate reached 96.4% of the total vinyl acetate monomer input, 0.1 parts of m-dinitrobenzene were added to terminate the polymerization, yielding a copolymer of vinyl acetate and sodium allyl sulfonate. Subsequently, unreacted vinyl acetate monomers were removed from the system by blowing in methanol vapor, resulting in a methanol solution of the copolymer.

[0123] Next, the solution was diluted with methanol, and the solid content concentration of the methanol solution of the copolymer of vinyl acetate and sodium allyl sulfonate 1 obtained above was adjusted to 55%. This solution was then fed into a kneader, and while maintaining the solution temperature at 35°C, a methanol solution of sodium hydroxide (sodium concentration 2% of the total sodium hydroxide methanol solution) was added at a ratio of 8 mmol / L relative to 1 mole of vinyl acetate structural unit in the copolymer, to carry out saponification. During saponification, the saponified product precipitated, and when it became granular, it was filtered out, washed with methanol, and dried in a hot air dryer to obtain resin composition 1 containing a PVA-based resin containing sulfonic acid or its salts and a chlorine component.

[0124] The chlorine content is 0.092 parts per 100 parts of PVA resin containing sulfonic acid or its salts, calculated using chlorine atoms.

[0125] The degree of saponification of the obtained PVA-based resin containing sulfonic acid or its salts was analyzed based on the amount of alkali required for the hydrolysis of the residual vinyl acetate units, and the result was 87.3 mol%. The average degree of polymerization was determined according to JIS K 6726, and the result was 200. Furthermore, the sulfonic acid or salt content (modification rate) in the PVA-based resin containing sulfonic acid or its salts was calculated by NMR determination, and the result was 2.7 mol%.

[0126] [Coloring Evaluation]

[0127] A 10% aqueous solution of the resin composition 1 obtained above was poured into a mold frame to make the film thickness 100 μm. The film was then dried at 23°C and 50% RH for 3 days to produce a cast film. The resulting cast film was heat-treated at 150°C for 5 hours, and the YI value was determined by transmission method using a spectrophotometer CM-2600d (manufactured by Konica Minolta Sensing Co., Ltd.). The results are shown in Table 1.

[0128] (Example 2)

[0129] [Preparation of Resin Composition 2]

[0130] In a reaction vessel equipped with a reflux condenser, a dropping funnel, and a stirrer, 1000 parts of vinyl acetate, 422 parts of methanol, 1116 parts of sodium allyl sulfonate obtained above, and 1.4 parts of azobisisobutyronitrile were added. The mixture was stirred while the temperature was increased under a nitrogen gas flow, and polymerization was carried out under reflux.

[0131] Midway through the polymerization process, 1.4 parts of azobisisobutyronitrile (AIBN) were added in four separate additions. When the polymerization rate of vinyl acetate reached 96.4% of the total amount of vinyl acetate monomers added, 0.1 parts of m-dinitrobenzene were added to terminate the polymerization, yielding a copolymer of vinyl acetate and sodium allyl sulfonate 1. Subsequently, unreacted vinyl acetate monomers were removed from the system by blowing in methanol vapor, resulting in a methanol solution of the copolymer.

[0132] Next, the solution was diluted with methanol, and the solid content concentration of the methanol solution of the copolymer of vinyl acetate and sodium allyl sulfonate 1 obtained above was adjusted to 55%. This solution was then fed into a kneader, and while maintaining the solution temperature at 35°C, a methanol solution of sodium hydroxide (sodium concentration 2% of the total sodium hydroxide methanol solution) was added at a ratio of 8 mmol / L relative to 1 mol of vinyl acetate structural unit in the copolymer, to carry out saponification. During saponification, the saponified product precipitated, and when it became granular, it was filtered out, washed with methanol, filtered again, washed with methanol, and dried in a hot air dryer to obtain a resin composition containing a PVA-based resin containing sulfonic acid or its salts and a chlorine component.

[0133] The chlorine content is 0.005 parts per 100 parts of PVA resin containing sulfonic acid or its salts, calculated using chlorine atoms.

[0134] The degree of saponification of the obtained PVA-based resin containing sulfonic acid or its salts was analyzed based on the amount of alkali required for the hydrolysis of the residual vinyl acetate units, and the result was 86.5 mol%. The average degree of polymerization was determined according to JIS K 6726, and the result was 200. Furthermore, the content of sulfonic acid or its salts and the content of sulfovinyl groups (modification rate) in the PVA-based resin containing sulfonic acid or its salts were calculated by NMR determination, and the result was 3.9 mol%.

[0135] The resin composition 2 obtained above was evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0136] (Comparative Example 1)

[0137] In Example 1, 62 parts of sodium allyl sulfonate 3 containing 0.28 parts of chlorine were used instead of sodium allyl sulfonate 1. Otherwise, the process was carried out in the same manner to obtain resin composition 3. The resin composition 3 was evaluated in the same manner as in Example 1.

[0138] The chlorine content of the obtained resin composition 3 is 0.241 parts per chlorine atom relative to 100 parts of PVA-based resin containing sulfonic acid or its salts.

[0139] (Comparative Example 2)

[0140] In Example 1, 62 parts of sodium allyl sulfonate 4 containing 0.31 parts of chlorine were used instead of sodium allyl sulfonate 1. Otherwise, the process was carried out in the same manner to obtain resin composition 4. The resin composition 4 was evaluated in the same manner as in Example 1.

[0141] The chlorine content of the obtained resin composition 4 is 0.225 parts per chlorine atom relative to 100 parts of PVA-based resin containing sulfonic acid or its salts.

[0142] (Refer to Example 1)

[0143] In Example 1, resin composition 5 containing unmodified PVA (88 mol% saponification, 300 degree of polymerization) and chlorine was used instead of resin composition 1. Otherwise, the color evaluation was performed in the same manner. The results are shown in Table 1.

[0144] The chlorine content of the obtained resin composition 5 is 0.062 parts per chlorine atom relative to 100 parts of PVA.

[0145] (See Example 2 for reference)

[0146] In Example 1, resin composition 6 containing unmodified PVA (88 mol% saponification, 300 degree of polymerization) and chlorine was used instead of resin composition 1. Otherwise, the color evaluation was performed in the same manner. The results are shown in Table 1.

[0147] The chlorine content of the obtained resin composition 6 is 0.207 parts per chlorine atom relative to 100 parts of PVA.

[0148] [Table 1]

[0149] Table 1

[0150]

[0151] According to the results in Table 1 above, the resin compositions of Examples 1 and 2 have low YI values ​​and less yellowing, while Comparative Examples 1 and 2, which have high chlorine content, show greater yellowing at high temperatures.

[0152] In addition, for unmodified PVA, the chlorine content does not affect the coloring.

[0153] The present invention has been described in detail with reference to specific embodiments; however, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the concept and scope of the invention. This application is based on Japanese Patent Application No. 2016-149369, filed on July 29, 2016, the contents of which are incorporated herein by reference.

[0154] Industrial availability

[0155] The resin composition of the present invention exhibits minimal coloration (yellowing), and therefore is useful as a dispersant for various coatings and dispersions, particularly as a dispersant for the color developer of coating solutions for thermal recording media.

Claims

1. A resin composition comprising: a polyvinyl alcohol resin (A) containing sulfonic acid or its salts, and a chlorine component (B), wherein the chlorine component (B) is sodium chloride. The content of the chlorine component (B) relative to 100 parts by mass of the polyvinyl alcohol resin (A) containing sulfonic acid or its salts is less than 0.1 parts by mass (based on chlorine atom conversion). The polyvinyl alcohol resin (A) containing sulfonic acid or its salts has a sulfonic acid or its salt content of 1 to 5 mol.

2. A dispersant formed from the resin composition of claim 1.

3. A coating liquid for a thermosensitive color developing layer, comprising: the resin composition of claim 1, a colorless dye, a color developer, and water.

4. A method for manufacturing a resin composition, comprising the method for manufacturing the resin composition of claim 1. The manufacturing method includes the following steps: copolymerizing a vinyl ester monomer with an unsaturated monomer containing sulfonic acid or its salt group to obtain a polymer, and saponifying the obtained polymer. Furthermore, it includes at least one of the following steps: a step of removing the chlorine component of the unsaturated monomer containing sulfonic acid or its salt before saponification; and a step of removing the chlorine component of the polyvinyl alcohol resin (A) containing sulfonic acid or its salt after saponification.

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