JP2019001921A - Dispersion liquid and thermosensitive recording material - Google Patents

Abstract

To provide a dispersion liquid which has dispersed particles having a small diameter, is excellent in dispersion stability and hardly causes liquid fogging and to provide a thermosensitive recording material which is prepared using the dispersion liquid and is excellent in color developing sensitivity and the whiteness of a texture.SOLUTION: There is provided a dispersion liquid which contains a vinyl alcohol-based copolymer obtained by saponification of a copolymer of vinyl acetate and a polyfunctional monomer, wherein the polyfunctional monomer contains two or more ethylenic double bonds in the molecule, the vinyl alcohol-based copolymer contains ethylenic double bonds in the side chain and has a saponification degree of 65.0 to 98.0 mol% and an aqueous solution viscosity at a concentration of 4 mass % at 20°C of 2.0 to 10.0 mPa s, the content (S) of the structural unit derived from the polyfunctional monomer in the total structural units constituting the vinyl alcohol-based copolymer is 0.05 to 1.5 mol% and the ratio Y/S of the content (Y) of the ethylenic double bonds to the content (S) is 0.10 to 0.90.SELECTED DRAWING: None

Description

  The present invention relates to a dispersion having a small dispersed particle size, excellent dispersion stability, and less liquid fog, and a thermosensitive recording material produced using the dispersion and excellent in color development sensitivity and background whiteness. .

  In recent years, with the diversification of information and the expansion of needs, various recording materials have been put into practical use through research and development in the field of information recording. Among them, the heat-sensitive recording materials are (1) simple image recording by only the heating process, (2) the necessary device mechanism is simple and easy to make compact, and the recording material is easy to handle and inexpensive. Information processing field (desktop computer, computer output, etc.), medical measurement recorder field, facsimile field, automatic ticket machine field (passenger ticket, admission ticket, etc.), thermal copying machine field, POS system It is used in a wide variety of label fields.

  In the production process of a thermal recording material, a dispersion containing a thermal dye or a developer is prepared, but as a further means for increasing the sensitivity of the thermal recording material, various proposals for making leuco dye fine particles have been made. . For example, polyvinyl alcohol having a sulfonic acid group (Patent Document 1), polyvinyl alcohol having a carboxyl group (Patent Document 2), polyvinyl alcohol having a carboxyl group and an olefin The use of a maleic acid copolymer resin composition (Patent Document 3) has been proposed. In addition, for the purpose of improving whiteness and fog-resistant skin fog, it has been proposed that a urethane urea compound dispersion and a dye precursor dispersion be heat-treated at 40 ° C. or more for 3 hours or more (Patent Document 4).

  However, some problems remain in these conventional proposals. As a specific problem, in a dispersion containing a dye, as the dye particles become smaller, the liquid fog of the dispersion becomes intense, and when the dispersion is heat-treated for the purpose of improving whiteness and moisture-resistant fog, the dispersion state is changed. It becomes unstable, and re-aggregation, viscosity increase and gelation occur. The liquid fog refers to a phenomenon in which the dispersion liquid darkens as the dye particles become smaller, and the background fog refers to a phenomenon in which the coated surface coated with the dispersion liquid darkens. That is, in the prior art, a dispersion having a small dispersed particle size, excellent dispersion stability, and less liquid fog has not been obtained.

Japanese Patent Laid-Open No. 58-179691 JP-A-8-48076 JP 11-321103 A JP 2004-359802 A

  An object of the present invention is to provide a dispersion having a small dispersed particle size, excellent dispersion stability, and less liquid fog, and to provide a heat-sensitive recording material excellent in color development sensitivity and background whiteness. And

  The above-mentioned problem is a dispersion containing a vinyl alcohol copolymer obtained by saponifying a copolymer of vinyl acetate and a polyfunctional monomer, the polyfunctional monomer having ethylene in the molecule. 2 or more, and the vinyl alcohol copolymer contains an ethylenic double bond in the side chain and has a saponification degree of 65.0 to 98.0 mol% at 20 ° C. The aqueous solution viscosity of 4% by mass is 2.0 to 10.0 mPa · s, and the content (S) of the structural unit derived from the polyfunctional monomer in all the structural units constituting the vinyl alcohol copolymer is Provided is a dispersion having a content Y (S) of 0.05 to 1.5 mol% and a ratio Y / S of the ethylenic double bond (Y) of 0.10 to 0.90. It is solved by doing.

  At this time, it is preferable that the side chain contains a vinyl ether group or an allyl group.

  The dispersion preferably further contains a dye, a developer or a sensitizer.

  A coated product obtained by coating the above dispersion on a substrate is a preferred embodiment of the present invention.

  The above-mentioned problem is a coating liquid containing a vinyl alcohol copolymer obtained by saponifying a copolymer of vinyl acetate and a polyfunctional monomer, a dye, a color developer and a sensitizer; The alcohol-based copolymer contains an ethylenic double bond in the side chain, has a saponification degree of 65.0 to 98.0 mol%, and a 4% by mass aqueous solution viscosity at 20 ° C of 2.0 to 10. 0 mPa · s, the content (S) of the structural unit derived from the polyfunctional monomer in all structural units constituting the vinyl alcohol copolymer is 0.05 to 1.5 mol%, The problem can also be solved by a coating solution in which the ratio Y / S between the amount (S) and the content (Y) of the ethylenic double bond is 0.10 to 0.90.

  A heat-sensitive recording material obtained by coating the substrate with the coating solution is a preferred embodiment of the present invention.

  The above-mentioned problem is a thermosensitive recording material having a base material and a thermosensitive coloring layer, wherein the thermosensitive coloring layer is obtained by saponifying a copolymer of vinyl acetate and a polyfunctional monomer. A dye, a developer, and a sensitizer, the vinyl alcohol copolymer contains an ethylenic double bond in the side chain, and the degree of saponification is 65.0 to 98.0 mol%, 4 mass% aqueous solution viscosity at 20 ° C. is 2.0 to 10.0 mPa · s, and the content of structural units derived from the polyfunctional monomer in all structural units constituting the vinyl alcohol copolymer ( S) is 0.05 to 1.5 mol%, and the ratio Y / S between the content (S) and the content (Y) of the ethylenic double bond is 0.10 to 0.90. It is also solved by recording materials.

  The dispersion of the present invention can efficiently disperse dispersed particles such as a dye, a developer and a sensitizer by using a modified PVA containing an ethylenic double bond in the side chain, and has excellent dispersion stability. Furthermore, there is little liquid fog. Furthermore, the heat-sensitive recording material produced using the dispersion is excellent in color development sensitivity and background whiteness.

  The present invention is a dispersion containing a vinyl alcohol copolymer (hereinafter sometimes abbreviated as “modified PVA”) obtained by saponifying a copolymer of vinyl acetate and a polyfunctional monomer. The polyfunctional monomer contains two or more ethylenic double bonds in the molecule, the modified PVA contains an ethylenic double bond in the side chain, and the degree of saponification is 65.0 to 98. 0 mol%, 4% by mass aqueous solution viscosity at 20 ° C. is 2.0 to 10.0 mPa · s, derived from the polyfunctional monomer in all structural units constituting the vinyl alcohol copolymer The content (S) of the structural unit is 0.05 to 1.5 mol%, and the ratio Y / S between the content (S) and the content (Y) of the ethylenic double bond is 0.10 to 0.10. Relates to a dispersion of 0.90.

  As the polyfunctional monomer used in the present invention, various monomers can be used as long as they contain two or more ethylenic double bonds in the molecule. However, it must be capable of introducing a necessary amount of double bonds without causing excessive crosslinking reaction during the copolymerization with vinyl acetate to cause gelation. Select a polyfunctional monomer with appropriate reactivity while considering various factors such as blending ratio of polyfunctional monomer to vinyl acetate, polymerization temperature, monomer concentration, polymerization rate, viscosity average polymerization degree, etc. There is a need to. From the viewpoint of suppressing an excessive crosslinking reaction, the number of ethylenic double bonds contained in the polyfunctional monomer is preferably two.

  Among them, ethanediol divinyl ether, propanediol divinyl ether, butanediol divinyl ether, ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, polyethylene glycol divinyl ether, propylene glycol divinyl ether, A polyfunctional monomer containing a vinyl ether group such as a divinyl ether compound such as polypropylene glycol divinyl ether is preferable.

  A polyfunctional monomer containing an allyl group is also suitable. Examples of polyfunctional monomers containing allyl groups include diene compounds such as pentadiene, hexadiene, heptadiene, octadiene, nonadiene, decadiene; glycerin diallyl ether, diethylene glycol diallyl ether, ethylene glycol diallyl ether, triethylene glycol diallyl ether, polyethylene glycol Diallyl ether compounds such as diallyl ether, trimethylolpropane diallyl ether, pentaerythritol diallyl ether, triallyl ether compounds such as glyceryl triallyl ether, trimethylolpropane triallyl ether, pentaerythritol triallyl ether, pentaerythritol tetraallyl ether, etc. Contains allyl ether groups such as tetraallyl ether compounds. Monomers containing allyl ester groups such as diallyl carboxylate such as diallyl phthalate, diallyl maleate, diallyl itaconate, diallyl terephthalate, diallyl adipate; diallylamine compounds such as diallylamine and diallylmethylamine Monomers containing an allylamino group such as triallylamine; monomers containing an allylammonium group such as diallylammonium salt such as diallyldimethylammonium chloride; triallyl isocyanurate; 1,3-diallylurea; triallyl phosphate Diallyl disulfide and the like are exemplified. Especially, the monomer containing an allyl ether group is easy to control the degree of polymerization and the double bond content, and is more preferably used.

  In addition to the polyfunctional monomers described above, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, propylene glycol di (meth) ) Acrylate, polypropylene glycol di (meth) acrylate, glycerin di (meth) acrylate, glycerin tri (meth) acrylate, pentaerythritol tri (meth) acrylate, trimethylolpropane tri (meth) acrylate, ditrimethylolpropane tetra (meth) acrylate , Pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, isocyanuric acid tri (meth) acrylate ( A) Monomers having acrylic acid; monomers having (meth) acrylamide such as N, N′-methylenebis (meth) acrylamide, N, N′-ethylenebis (meth) acrylamide, divinylbenzene, trivinylbenzene And so on.

  The method for producing the modified PVA is not particularly limited. For example, a method of copolymerizing vinyl acetate and the polyfunctional monomer to obtain a vinyl ester copolymer and then saponifying the vinyl ester copolymer is preferable.

  In the said manufacturing method, it is preferable to copolymerize content of the said polyfunctional monomer with respect to vinyl acetate as 0.1-5 mol%. When the content of the polyfunctional monomer is less than 0.1 mol%, it tends to be difficult to introduce an ethylenic double bond into the side chain. The content of the polyfunctional monomer is more preferably 0.15 mol% or more, and further preferably 0.2 mol% or more. On the other hand, when the content of the polyfunctional monomer exceeds 5 mol%, it tends to be difficult to control the degree of polymerization of the vinyl ester copolymer. Further, the modified PVA obtained by saponifying the vinyl ester copolymer tends not to dissolve in water. The content of the polyfunctional monomer is more preferably 3 mol% or less, and further preferably 2 mol% or less.

  As a copolymerization method, any polymerization method such as a bulk polymerization method, a solution polymerization method, a suspension polymerization method, and an emulsion polymerization method can be employed. The copolymerization can be carried out without solvent or in the presence of an alcohol solvent. Among these, a solvent-free bulk polymerization method and a solution polymerization method using an alcohol solvent can be suitably employed. The alcohol solvent is not particularly limited, and for example, methanol, ethanol, propanol and the like can be used alone or in admixture of two or more. The copolymerization method is not particularly limited, and any of batch polymerization, semi-batch polymerization, continuous polymerization, and semi-continuous polymerization can be employed.

  Although the temperature (copolymerization temperature) at the time of polymerizing vinyl acetate and a polyfunctional monomer is not particularly limited, it is preferably 0 to 200 ° C and more preferably 30 to 140 ° C. When the temperature is lower than 0 ° C., a sufficient polymerization rate may not be obtained. When the said temperature is higher than 200 degreeC, there exists a concern about decomposition | disassembly of the vinyl acetate and polyfunctional monomer to be used.

  The method for controlling the copolymerization temperature is not particularly limited, and examples thereof include a method for balancing the heat generated by the polymerization and the heat radiation from the surface of the polymerization vessel by controlling the polymerization rate. Moreover, the method of controlling by the external jacket using a suitable heat medium is also mentioned. The latter method is preferable from the viewpoint of safety.

  The polymerization initiator used when copolymerizing vinyl acetate and a polyfunctional monomer can be selected from known initiators (for example, azo initiators, peroxide initiators, redox initiators, etc.). . Examples of the azo initiator include 2,2′-azobisisobutyronitrile, 2,2′-azobis (2,4-dimethylvaleronitrile), 2,2′-azobis (4-methoxy-2, 4-dimethylvaleronitrile). Examples of the peroxide-based initiator include percarbonate compounds such as diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, and diethoxyethyl peroxydicarbonate; t-butyl peroxyneodecanate, α -Perester compounds such as cumylperoxyneodecanate and t-butylperoxydecanate; acetylcyclohexylsulfonyl peroxide; 2,4,4-trimethylpentyl-2-peroxyphenoxyacetate and the like. These initiators may be combined with potassium persulfate, ammonium persulfate, hydrogen peroxide, or the like as an initiator. Examples of the redox initiator include an initiator in which the peroxide is combined with a reducing agent such as sodium hydrogen sulfite, sodium hydrogen carbonate, tartaric acid, L-ascorbic acid, or longalite. When the copolymerization is performed at a high temperature, coloring due to decomposition of vinyl acetate may be observed. In that case, for the purpose of preventing coloring, an antioxidant such as tartaric acid may be added to the polymerization system in an amount of about 1 to 100 ppm based on vinyl acetate.

  In the copolymerization of vinyl acetate and a polyfunctional monomer, other monomers may be copolymerized within a range not impairing the gist of the present invention. Examples of the other monomers include α-olefins such as ethylene and propylene; (meth) acrylic acid and salts thereof; methyl (meth) acrylate, ethyl (meth) acrylate, and n- (meth) acrylate. Propyl, i-propyl (meth) acrylate, n-butyl (meth) acrylate, i-butyl (meth) acrylate, t-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, (meth) (Meth) acrylic acid esters such as dodecyl acrylate and octadecyl (meth) acrylate; (meth) acrylamide; N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide , Diacetone (meth) acrylamide, (meth) acrylamide propanesulfonic acid and its salts, (meta (Meth) acrylamide derivatives such as acrylamidopropyldimethylamine and salts thereof or quaternary salts thereof, N-methylol (meth) acrylamide and derivatives thereof; methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl Vinyl ethers such as vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether and stearyl vinyl ether; Nitriles such as acrylonitrile and methacrylonitrile; Vinyl halides such as vinyl chloride and vinyl fluoride; Vinylidene chloride and fluoride Vinylidene halides such as vinylidene; allyl compounds such as allyl acetate and allyl chloride; unsaturated dicarboxylic acids such as maleic acid, itaconic acid and fumaric acid; Examples thereof include salts thereof and esters thereof; vinylsilyl compounds such as vinyltrimethoxysilane; and isopropenyl acetate. When such other monomers are copolymerized, the copolymerization amount is usually 5 mol% or less.

  The copolymerization of vinyl acetate and a polyfunctional monomer is carried out in the presence of a chain transfer agent for the purpose of adjusting the degree of polymerization of the obtained copolymer and the like within the range not impairing the gist of the present invention. Also good. Examples of the chain transfer agent include aldehydes such as acetaldehyde and propionaldehyde; ketones such as acetone and methyl ethyl ketone; mercaptans such as 2-hydroxyethanethiol; and halogenated hydrocarbons such as trichloroethylene and perchloroethylene. . Of these, aldehydes and ketones are preferably used. The addition amount of the chain transfer agent can be determined according to the chain transfer constant of the chain transfer agent to be added and the degree of polymerization of the target modified PVA, but usually about 0.1 to 10% by mass with respect to vinyl acetate. preferable.

  Moreover, it is preferable that the polymerization rate of vinyl acetate is 20 to 85%. If the polymerization rate is less than 20%, the amount of vinyl ester copolymer that can be produced per unit time tends to decrease, and the production efficiency tends to decrease, and the cost for recovering vinyl acetate tends to increase. It becomes. From the viewpoint of production efficiency and cost, the polymerization rate is more preferably 30% or more, and further preferably 40% or more. On the other hand, when the polymerization rate exceeds 85%, the crosslinking reaction proceeds excessively, and the water solubility of the resulting modified PVA (A) tends to decrease. In light of suppression of the crosslinking reaction, the polymerization rate is more preferably 80% or less, and even more preferably 70% or less.

  The saponification method of the vinyl ester copolymer obtained by copolymerizing vinyl acetate and a polyfunctional monomer is not particularly limited, and a known saponification method can be employed. For example, an alcoholysis reaction or a hydrolysis reaction using a basic catalyst such as sodium hydroxide, potassium hydroxide or sodium methoxide or an acidic catalyst such as p-toluenesulfonic acid can be mentioned. Examples of the solvent that can be used in this reaction include alcohols such as methanol and ethanol; esters such as methyl acetate and ethyl acetate; ketones such as acetone and methyl ethyl ketone: aromatic hydrocarbons such as benzene and toluene. . These solvents can be used alone or in combination of two or more. Of these, saponification using methanol or methanol / methyl acetate mixed solution as a solvent and sodium hydroxide as a catalyst is simple and preferable.

  The saponification degree of the modified PVA needs to be 65.0 to 98.0 mol%, preferably 75.0 to 96.0 mol%, and more preferably 80.0 to 90.0 mol%. When the degree of saponification is less than 65.0 mol%, the water solubility of the modified PVA is lowered, the particle size of the dispersed particles is increased in the resulting dispersion, or the color sensitivity of the resulting thermal recording material is insufficient. Become. On the other hand, when the degree of saponification exceeds 98.0 mol%, the liquid fog of the resulting dispersion becomes a problem.

  The saponification degree is a value measured by the saponification degree measurement method described in JIS-K6726 (1994). At this time, units other than the vinyl alcohol unit, the vinyl acetate unit and the polyfunctional monomer unit are negligible even if they are contained.

  The viscosity of the 4% by weight aqueous solution of the modified PVA at 20 ° C. needs to be 2.0 to 10.0 mPa · s, preferably 2.2 to 8.0 mPa · s, and preferably 2.4 to 4.0 mPa · s. More preferred. When the viscosity of the aqueous solution is less than 2.0 mPa · s, the particle diameter of the dispersed particles is increased in the obtained dispersion liquid, and the color development sensitivity of the obtained heat-sensitive recording material becomes insufficient. On the other hand, when the viscosity of the aqueous solution exceeds 10.0 mPa · s, the viscosity of the resulting dispersion increases, resulting in insufficient dispersion stability, and insufficient color development sensitivity of the obtained thermal recording material.

  The viscosity of a 4% by mass aqueous solution of the modified PVA is, for example, TOKIMEC INC. It can be measured at a rotor rotation speed of 60 rpm and a temperature of 20 ° C. using a manufactured B-type viscometer.

  The content (S) of the structural unit derived from the polyfunctional monomer in all the monomer units constituting the modified PVA needs to be 0.05 to 1.5 mol%, and 0.1 to 1.3 mol % Is preferable, and 0.2 to 1.0 mol% is more preferable. When the content (S) is less than 0.05 mol%, the liquid fog of the resulting dispersion becomes a problem. On the other hand, when the content (S) exceeds 1.5 mol%, it becomes very difficult to control the degree of polymerization of the vinyl ester copolymer.

  It is preferable that the side chain of the modified PVA contains an ethylenic double bond such as a vinyl ether group or an allyl group. Moreover, as an allyl group, an allyl ether group is more preferable. The ratio Y / S between the content (Y) of such a side chain ethylenic double bond and the content (S) of the structural unit derived from the polyfunctional monomer is 0.10 to 0.90. It is important that 0.10 to 0.50 is preferred. When the ratio Y / S is less than 0.10, the overall evaluation of the performance required for the heat-sensitive recording material becomes insufficient. On the other hand, when the ratio Y / S exceeds 0.90, the particle diameter of the dispersed particles is increased in the obtained dispersion.

The content (S) of the structural unit derived from the polyfunctional monomer and the content (Y) of the side chain ethylenic double bond may be abbreviated as a vinyl ester copolymer (hereinafter referred to as “PVAc”) before saponification. A) from a ¹ H-NMR spectrum in a deuterated chloroform solvent. Specifically, after reprecipitation purification of PVAc is sufficiently performed three times or more with n-hexane / acetone, drying is performed under reduced pressure at 50 ° C. for 2 days to prepare a PVAc sample for analysis. The sample is dissolved in deuterated chloroform and measured at room temperature using ¹ H-NMR (JEOL GX-500) at 500 MHz. Peak α (4.7 to 5.1 ppm) derived from vinyl ester main chain methine and proton peak β (5.8 to 6.0 ppm) bonded to the side chain of ethylenic double bond main chain carbon And the content (S) of the structural unit derived from the polyfunctional monomer and the side chain ethylenicity from the peak γ (0.7 to 0.9 ppm) derived from the methyl group derived from the polyfunctional monomer using the following formula: The double bond content (Y) is calculated (when the polyfunctional monomer is trimethylolpropane diallyl ether).
(1) Content (S) mol% = (number of protons of γ / 3) / (number of protons of α + number of protons of γ / 3) × 100
(2) Double bond content (Y) (mol%) = (number of protons of β) / (number of protons of α + number of protons of γ / 3) × 100

  The dispersion of the present invention preferably uses the above modified PVA as a dispersant and various agents such as dyes, developers, and sensitizers as dispersoids. As the dispersion medium at this time, water is mainly used.

  The dye is not particularly limited as long as it is used for general pressure-sensitive recording materials or heat-sensitive recording materials. For example, 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide (crystal violet lactone), 3- (p-dimethylaminophenyl) -3- (1,2-dimethylindole-3) -Yl) phthalide, 3- (p-dimethylaminophenyl) -3- (2-phenylindol-3-yl) phthalide, 3,3-bis- (9-ethylcarbazol-3-yl) -5-dimethylamino Triarylmethane compounds such as phthalide; Diphenylmethane compounds such as 4,4′-bisdimethylaminobenzhydrin benzyl ether and N-halophenylleucooramine; Rhodamine B-anilinolactam, 3-diethylamino-7- Benzylaminofluorane, 3-diethylamino-7-butylaminofluorane, 3-diethy Amino-7- (chloroanilino) fluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3-piperidino-6-methyl-7-anilinofluorane, 3-ethyl-tolylamino-6-methyl-7 -Anilinofluorane, 3-cyclohexyl-methylamino-6-methyl-7-anilinofluorane, 3-diethylamino-6-chloro-7- (β-ethoxyethyl) aminofluorane, 3-diethylamino-6- Chloro-7- (γ-chloropropyl) aminofluorane, 3- (N-ethyl-N-isoamyl) -6-methyl-7-phenylaminofluorane, 3-dibutylamino-6-methyl-7-anilino Xanthene compounds such as fluorane; benzoyl leucomethylene blue, p-nitrobenzoyl leucomethylene blue, etc. Azine compounds; spiro compounds such as 3-methyl-spiro-dinaphthopyran, 3-ethyl-spiro-dinaphthopyran, 3-benzylsulfo-dinaphthopyran, 3-methylnaphtho- (3-methoxy-benzo) -spiropyran, etc. . Such dye can be used individually by 1 type or in combination of 2 or more types.

  The developer is not particularly limited as long as it is used for general pressure-sensitive recording materials or heat-sensitive recording materials, but phenols and aromatic carboxylic acid derivatives are preferable, and bisphenols are particularly preferable. For example, phenols such as p-octylphenol, p-tert-butylphenol, p-phenylphenol; 1,1-bis (p-hydroxyphenyl) propane, 2,2-bis (p-hydroxyphenyl) propane, 1,1 -Bis (p-hydroxyphenyl) pentane, 1,1-bis (p-hydroxyphenyl) hexane, 2,2-bis (p-hydroxyphenyl) hexane, 1,1-bis (p-hydroxyphenyl) -2- Bisphenols such as ethyl-hexane and 2,2-bis (4-hydroxy-3,5-dichlorophenyl) propane; and dihydroxydiphenyl ether. Examples of aromatic carboxylic acid derivatives include p-hydroxybenzoic acid, ethyl p-hydroxybenzoate, butyl p-hydroxybenzoate, 3,5-di-tert-butylsalicylic acid, 3,5-di-α-methylbenzylsalicylic acid And polyvalent metal salts of the above carboxylic acids. Such developers can be used singly or in combination of two or more.

  The sensitizer is not particularly limited as long as it is used for general pressure-sensitive recording materials or heat-sensitive recording materials. For example, benzyl-2-naphthyl ether, stearamide, methylenebis stearamide, benzyl p-benzyloxybenzoate, 1,2-di (3-methylphenoxy) ethane, 1,2-di (4-methylphenoxy) ) Ethane, 1,2-di (4-methoxyphenoxy) ethane, 1,2-di (4-chlorophenoxy) ethane, 1,2-diphenoxyethane, 1- (4-methoxyphenoxy) -2- (3 -Methylphenoxy) ethane, p-methylthiophenylbenzyl ether, 1,4-di (phenylthio) butane, p-benzylbiphenyl, p-tolylbiphenyl ether, di (p-methoxyphenoxyethyl) ether, m-terphenyl, benzyl -4-methylthiophenyl ether, phenyl ester of 1-hydroxy-2-naphthoic acid Terephthalic acid dibenzyl ester, oxalic acid-di-p-methylbenzyl ester, oxalic acid-di-p-chlorobenzyl ester, terephthalic acid dibutyl ester, terephthalic acid dibenzyl ester, isophthalic acid dibutyl ester, p-acetoluizide, Examples include p-acetophenetide, N-acetoacetyl-p-toluidine, di (β-biphenylethoxy) benzene and the like. Such sensitizers can be used alone or in combination of two or more.

  In addition to the modified PVA, a dispersant used for a general pressure-sensitive recording material or a heat-sensitive recording material can be used in combination as a dispersant used for the dispersion liquid of the present invention. For example, polyvinyl alcohols other than the modified PVA, sulfonated celluloses, sulfonated starches, carboxyethyl cellulose, hydroxyethyl cellulose, polyacrylic acids, ethylene-maleic anhydride copolymers, methyl vinyl ether-maleic anhydride copolymers, Vinyl acetate-maleic anhydride copolymer, isobutylene-maleic anhydride copolymer, styrene-maleic anhydride copolymer, higher alcohol sulfate ester, alkyl polyether sulfate ester, alkyl sulfonic acid, aryl sulfonic acid Salts, phosphates, aliphatic phosphates, aromatic phosphates, polyoxyethylene alkyl sulfates, polyoxyethylene aryl sulfates, polyoxyethylene alkyl aryl Esters, dialkyl sulfosuccinic acid esters, alkylbenzenesulfonic acid salts, polyoxyalkylene alkyl ether phosphoric acid esters, polyoxyalkylene alkyl aryl ether phosphate esters.

  In general, the dispersant contained in the dye dispersion is preferably 5 to 50 parts by mass, more preferably 8 to 30 parts by mass, and still more preferably 10 to 20 parts by mass with respect to 100 parts by mass of the dye. When the content of the dispersant is less than 5 parts by mass, the dispersion state of the dye is poor, and the color development sensitivity and image storability of the resulting thermal recording material tend to be lowered. On the other hand, when the content of the dispersant exceeds 50 parts by mass, the viscosity of the dispersion becomes high, and the handleability tends to decrease.

  Usually, the dispersant contained in the developer dispersion is preferably 5 to 50 parts by mass, more preferably 8 to 30 parts by mass, and further 10 to 20 parts by mass with respect to 100 parts by mass of the developer. preferable. When the content of the dispersant is less than 5 parts by mass, the colorant is poorly dispersed and the color development sensitivity and image storage stability of the resulting heat-sensitive recording material tend to be lowered. On the other hand, when the content of the dispersant exceeds 50 parts by mass, the viscosity of the dispersion becomes high, and the handleability tends to decrease.

  Usually, the dispersant contained in the sensitizer dispersion is preferably 5 to 50 parts by mass, more preferably 8 to 30 parts by mass, and further 10 to 20 parts by mass with respect to 100 parts by mass of the sensitizer. preferable. When the content of the dispersant is less than 5 parts by mass, the dispersion state of the sensitizer is poor, and the color development sensitivity and image storage stability of the resulting heat-sensitive recording material tend to be lowered. On the other hand, when the content of the dispersant exceeds 50 parts by mass, the viscosity of the dispersion becomes high, and the handleability tends to decrease.

  The coated product of the present invention is obtained by coating the above dispersion on a substrate. There is no restriction | limiting in particular as a base material, For example, paper, a synthetic fiber paper, a synthetic resin film etc. can be used. Among these, it is preferable to use paper.

  Another aspect of the present invention is a coating liquid containing the modified PVA, a dye, a developer, and a sensitizer. A heat-sensitive recording material can be obtained by applying this coating solution to a substrate. That is, the thermosensitive recording material has a base material and a thermosensitive coloring layer, and the thermosensitive coloring layer contains the modified PVA, the dye, the developer and the sensitizer.

  For the dispersion of the dye, developer and / or sensitizer, a ball mill, attritor, sand mill, SC mill, ring mill, spike mill, coball mill, dyno mill and the like can be usually used. Using the modified PVA as a dispersant, a dye, developer or sensitizer having a particle size of 0.1 to 1.0 μm (preferably 0.2 to 0.7 μm, more preferably 0.3 to 0.5 μm). A coating liquid containing a dispersion containing an agent as a dispersoid and a modified PVA, a dye, a developer and a sensitizer can be obtained.

Although the solid content concentration in the said dispersion liquid and coating liquid is not specifically limited, From points, such as coating property, 5-50 mass% is preferable and 10-45 mass% is more preferable. There is no particular limitation on the method for obtaining the coated product by applying the dispersion liquid to the substrate, or the coating method for obtaining the heat-sensitive recording material by applying the coating solution to the substrate, and a known method is used. Can be adopted. As the coating method, for example, an air knife method, a plate method, a gravure method, a roll coater method, a spray method, a dip method, a bar method, an extrusion method, or the like can be adopted. Application amount of the dispersion or coating liquid is not particularly limited, but is preferably 1 to 10 g / ^{m 2} in terms of solid content, and more preferably 2 to 8 g / ^{m 2.}

  In addition to dyes, developers and sensitizers, the above thermosensitive coloring layer is an aqueous binder, filler, surfactant, lubricant to further improve coating suitability, whiteness, coloring sensitivity, dispersion stability, etc. , Antifoaming agents, wetting agents, pressure coloring agents, etc. can be used in combination.

  A water-based binder is not specifically limited, A well-known thing can be used. For example, starch and derivatives thereof, cellulose derivatives such as hydroxymethylcellulose, hydroxyethylcellulose, carboxymethylcellulose, methylcellulose, ethylcellulose; modified polyvinyl alcohol, polyvinyl alcohol, sodium polyacrylate, polyvinylpyrrolidone, acrylamide / acrylate ester copolymer, acrylamide / Water-soluble polymers such as acrylic acid ester / methacrylic acid terpolymer, styrene / maleic anhydride copolymer alkali salt, isobutylene / maleic anhydride copolymer alkali metal salt, polyacrylamide, sodium alginate, gelatin, casein Polyvinyl acetate, polyurethane, polyacrylic acid, polyacrylate, vinyl chloride / vinyl acetate copolymer, polybutyl methacrylate, Emulsions, such as Ren / vinyl acetate copolymers; styrene / butadiene copolymer, latexes such as styrene / butadiene / acrylic copolymer. It is preferable that the addition amount of an aqueous binder is 1-20 mass parts with respect to 100 mass parts of total amounts of dye, a color developer, and a sensitizer.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples. In the following Examples and Comparative Examples, “part” and “%” mean mass basis unless otherwise specified.

[Production Example 1 (Production of PVA1)]
(Synthesis of vinyl alcohol copolymer having ethylenic double bond in the side chain)
A 6-liter reaction vessel equipped with a stirrer, nitrogen inlet, additive inlet and initiator inlet was charged with 600 g of vinyl acetate, 2400 g of methanol, and 9.3 g of trimethylolpropane diallyl ether as a polyfunctional monomer at 60 ° C. Then, the system was purged with nitrogen by nitrogen bubbling for 30 minutes. Subsequently, 2.5 g of 2,2′-azobis (isobutyronitrile) was added to initiate polymerization. The polymerization temperature was maintained at 60 ° C. during the polymerization. After 4 hours, when the polymerization rate reached 75%, the polymerization was stopped by cooling. Next, unreacted vinyl acetate was removed under reduced pressure to obtain a methanol solution of polyvinyl acetate (hereinafter sometimes abbreviated as “PVAc”). Using the obtained PVAc, the content (S) of the structural unit derived from the polyfunctional monomer (trimethylolpropane diallyl ether) and the content (Y) of the side chain ethylenic double bond were determined by the method described later. . The concentration of the PVAc methanol solution was adjusted to 30%, and the NaOH methanol solution (10% concentration) was adjusted so that the alkali molar ratio (number of moles of NaOH / number of moles of vinyl ester units in PVAc) was 0.008. Added and saponified. The obtained vinyl alcohol copolymer was washed with methanol. By the above operation, modified PVA having a saponification degree of 87.0 mol% was obtained. The obtained modified PVA was dissolved in water at 90 ° C. to prepare a 4 mass% aqueous solution, and the viscosity at 20 ° C. was measured with a B-type viscometer (60 rotations), which was 3.0 mPa · s. .

(Measurement of content (S) and (Y))
After reprecipitation purification of PVAc obtained with n-hexane / acetone was sufficiently performed three times or more, drying was performed for 2 days under reduced pressure at 50 ° C. Thereafter, the obtained purified PVAc was dissolved in deuterated chloroform and subjected to ¹ H-NMR measurement. From the obtained spectrum, the content (S) of the structural unit derived from trimethylolpropane diallyl ether was 0.7 mol%. The side chain allyl ether group content (Y) was calculated to be 0.18 mol%.

[Production Examples 2 to 15 (Production of PVA 2 to 15)]
Table 1 shows the saponification conditions such as the amount of vinyl acetate and methanol, the polymerization conditions such as the type and amount of polyfunctional monomer used during polymerization, and the molar ratio of sodium hydroxide to vinyl ester units during saponification. Various PVA (PVA2-15) was manufactured like manufacture example 1 except having changed.

[Example 1]
(1) Preparation of dye dispersion and evaluation Preparation of dye dispersion (concentration 35%)
Dye: Leuco dye (manufactured by Yamamoto Kasei Co., Ltd., trade name: ODB-2) 100 parts PVA1 10 parts 2,4,7,9-tetramethyl-5-decyne-4,7-diol 0.2 parts (Air Products (Product name: Surfynol 104E, surfactant)
204 parts distilled water

The dye, PVA1, Surfynol 104E and distilled water were pre-stirred in a beaker for 60 minutes, then transferred to a bead mill (AIMEX, Ready-mill type NVM-03 type) and glass beads (diameter 0.5 mm). (Soda quartz glass) was added (filling rate 82%), and the amount of discharge was 55 cc / min, high rotation speed (3400 rpm), and dispersion was performed for 30 minutes under cooling (circulation frequency: 8 times).

Next, the physical properties of the obtained dye dispersion were evaluated by the following methods.
Particle size of dye dispersion: The particle size after dispersion was measured with a laser diffraction particle size distribution analyzer (manufactured by Shimadzu Corporation, model: SALD-2200). The average particle size was 0.35 μm. Rank 5 was determined using the criteria.
Rank 5: Less than 0.40 μm Rank 4: 0.40 μm or more and less than 0.50 μm Rank 3: 0.50 μm or more and less than 0.70 μm Rank 2: 0.70 μm or more and less than 1.00 μm Rank 1: 1.00 μm or more

Solution viscosity of the dye dispersion: The viscosity of the dye dispersion after dispersion was measured using a B-type viscometer (manufactured by TOKIMEC INC.) At a rotor speed of 60 rpm and a temperature of 20 ° C., and it was 44 mPa · s. Therefore, it was determined as Rank 5 using the following criteria.
Rank 5: Less than 50 mPa · s Rank 4: 50 mPa · s or more and less than 100 mPa · s Rank 3: 100 mPa · s or more and less than 400 mPa · s Rank 2: 400 mPa · s or more and less than 700 mPa · s Rank 1: 700 mPa · s or more

Whiteness of the dye dispersion solution: About 1 hour after the dispersion was completed, the dye dispersion solution was hand-coated on a commercially available thermal paper (manufactured by KOKUYO; Thailand-2010) (the coating amount was about 5 g / m ² ). When the ISO whiteness of this coated paper was measured with PF-10 (Nippon Denshoku), it was whiteness 84, and therefore it was determined as Rank 5 using the following criteria.
Rank 5: 82 or more Rank 4: 79 or more and less than 82 Rank 3: 75 or more and less than 79 Rank 2: 72 or more and 75 or less Rank 1: Less than 72

(2) Preparation of developer dispersion and sensitizer dispersion and evaluation thereof Preparation of developer dispersion (concentration: 34%)
Developer: Bisphenol S (trade name: D-8, manufactured by Nippon Soda Co., Ltd.) 100 parts PVA1 10 parts 2,4,7,9-tetramethyl-5-decyne-4,7-diol 0.2 parts ( (Product name: Surfynol 104E, surfactant, manufactured by Air Products)
Distilled water 210 parts Preparation of sensitizer dispersion (concentration 40%)
Sensitizer: Benzyl-2-naphthyl ether 100 parts PVA1 10 parts 2,4,7,9-Tetramethyl-5-decyne-4,7-diol 0.2 part (product name: Surfynol 104E, manufactured by Air Products) , Surfactant)
165 parts of distilled water As a result of producing a developer dispersion and a sensitizer dispersion under the same conditions as the above dye dispersion and measuring the particle diameter thereof, the particle diameter of the developer dispersion is 0.6 μm. The particle size of the sensitizer dispersion was 0.5 μm.

(3) Preparation and evaluation of heat-sensitive recording material After mixing and stirring 50 parts of a dye dispersion, 120 parts of a developer dispersion, and 75 parts of a sensitizer dispersion (in terms of solid content), a base paper (basis weight: 60 g / weight) After coating the above coating liquid at 3 g / m ² (solid content conversion) on the surface of a high-quality paper of m ² by a bar method using a Mayer bar, it was dried using a dryer, and further super calendar (line A heat-sensitive recording paper was produced by surface treatment at a pressure of 30 kg / cm).

Color development sensitivity measurement of thermal recording paper: Color development test was performed using a thermal inclination tester (TYPE HG-100, press pressure 0.6 kg / cm ² , press time 5 seconds, press temperature 120 ° C., manufactured by Toyo Seiki Seisakusho) When the color density was measured (GretagMacbeth reflection densitometer RD-19), it was 1.28, so it was determined to be rank 5 using the following criteria.
Rank 5: 1.25 or more Rank 4: 1.20 or more but less than 1.25 Rank 3: 1.10 or more but less than 1.20 Rank 2: 1.00 or more but less than 1.10 Rank 1: Less than 1.00

Comprehensive evaluation of the thermal recording material: For the above four evaluation items, the determined rank is read as it is, and the graded score is given as shown below for the physical properties that greatly affect the thermal paper performance. When comprehensive evaluation was carried out, the thermal recording material using PVA1 scored 50 points. Those with a score of 35 or more were judged as acceptable and those with less than 35 were judged as unacceptable.

Comprehensive evaluation = dispersed particle diameter score + dye dispersion viscosity score × 2 + dye dispersion whiteness score × 2 + thermal paper coloring sensitivity score × 5

[Examples 2 to 8, Comparative Examples 1 to 7]
A dye dispersion, a developer dispersion, a sensitizer dispersion, and a heat-sensitive recording material were prepared and evaluated in the same manner as in Example 1 except that PVA2 to 15 were used instead of PVA1. The results are shown in Table 2.

As the above examples show, the dispersion liquid of the present invention uses a specific modified PVA, so that the particle diameter of the dispersed particles is small, the dispersion stability is excellent, and the liquid fog is small. In addition, the heat-sensitive recording material obtained from the dispersion is excellent not only in color development sensitivity and background whiteness, but also in high-speed printability and image resolution. It is particularly preferably used in the field.

Claims (9)

A dispersion containing a vinyl alcohol copolymer obtained by saponifying a copolymer of vinyl acetate and a polyfunctional monomer;
The polyfunctional monomer contains two or more ethylenic double bonds in the molecule;
The vinyl alcohol copolymer contains an ethylenic double bond in the side chain, has a saponification degree of 65.0 to 98.0 mol%, and a 4% by mass aqueous solution viscosity at 20 ° C. of 2.0 to 10.0 mPa · s, the content (S) of the structural unit derived from the polyfunctional monomer is 0.05 to 1.5 mol%, and all the structural units constituting the vinyl alcohol copolymer Dispersion liquid in which the ratio Y / S of the content (S) and the ethylenic double bond content (Y) is 0.10 to 0.90.   The dispersion according to claim 1, wherein the side chain contains a vinyl ether group or an allyl group.   Furthermore, the dispersion liquid of Claim 1 or 2 containing a dye.   The dispersion according to claim 1 or 2, further comprising a developer.   Furthermore, the dispersion liquid of Claim 1 or 2 containing a sensitizer.   The coated material formed by coating the dispersion liquid in any one of Claims 3-5 on a base material. A coating solution containing a vinyl alcohol copolymer obtained by saponifying a copolymer of vinyl acetate and a polyfunctional monomer, a dye, a developer and a sensitizer;
The vinyl alcohol copolymer contains an ethylenic double bond in the side chain, has a saponification degree of 65.0 to 98.0 mol%, and a 4% by mass aqueous solution viscosity at 20 ° C. of 2.0 to 10.0 mPa · s, and the content (S) of the structural unit derived from the polyfunctional monomer in all structural units constituting the vinyl alcohol copolymer is 0.05 to 1.5 mol%. The coating liquid whose ratio Y / S of content (S) and content (Y) of this ethylenic double bond is 0.10-0.90.   A heat-sensitive recording material obtained by coating the coating liquid according to claim 7 on a substrate. A thermal recording material having a substrate and a thermal coloring layer,
The thermosensitive coloring layer contains a vinyl alcohol copolymer obtained by saponifying a copolymer of vinyl acetate and a polyfunctional monomer, a dye, a developer, and a sensitizer.
The vinyl alcohol copolymer contains an ethylenic double bond in the side chain, has a saponification degree of 65.0 to 98.0 mol%, and a 4% by mass aqueous solution viscosity at 20 ° C. of 2.0 to 10.0 mPa · s, and the content (S) of the structural unit derived from the polyfunctional monomer in all structural units constituting the vinyl alcohol copolymer is 0.05 to 1.5 mol%. A heat-sensitive recording material in which the ratio Y / S of the content (S) and the content (Y) of the ethylenic double bond is 0.10 to 0.90.