JPH11267495A - Microcapsule and thermosensitive recording body using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a microcapsule encapsulating a hydrophobic core material and having narrow particle size distribution and a thermosensitive recording body having excellent recording image quality, light resistance and water resistance. SOLUTION: The microcapsule encapsulates the hydrophobic core material emulsified or dispersed by a emulsifying agent. As a means for obtaining the microcapsule having narrow particle size distribution, a polyvinyl alcohol containing a monomer having diacetone group is used as the emulsifying agent. In the thermosensitive recording body successively having a thermosensitive recording layer containing an electron donative compound and an electron accepting compound and a protective layer on a supporting body, the microcapsule encapsulating an ultraviolet absorbent as the hydrophobia core material is incorporated in the protective layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microcapsule containing a hydrophobic core substance, and more particularly to a microcapsule having a uniform particle diameter.
The present invention also relates to a microcapsule having excellent water resistance and a thermosensitive recording medium containing the microcapsule.

[0002]

2. Description of the Related Art As an emulsifier for microcapsules containing a hydrophobic core material emulsified or dispersed by an emulsifier,
For example, microcapsules using a polyvinyl alcohol having a saponification degree of 80 mol% or more are used as a pressure-sensitive recording material, a heat-sensitive recording material, or an adhesive. For example, heat-sensitive recording media containing microcapsules containing an electron-donating compound and a hydrophobic core substance such as an ultraviolet absorber in a heat-sensitive recording layer or a protective layer are disclosed in JP-A-60-244594 and JP-A-5-184909. As described in Japanese Patent Application Laid-Open Publication No. H10-157, microcapsules having an average particle diameter of 3 μm or less and a narrow particle size distribution width are demanded in order to obtain uniform recording image quality.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a microcapsule containing a hydrophobic core substance and having a narrow particle size distribution, and a heat-sensitive recording material having excellent recording image quality, light resistance and water resistance. It is in.

[0004]

As one means for obtaining a microcapsule having a narrow particle size distribution in a microcapsule containing a hydrophobic core material emulsified or dispersed by an emulsifier, the present invention uses diacetone as an emulsifier. A polyvinyl alcohol containing a monomer having a group is used. Further, on a support, on a heat-sensitive recording layer containing an electron-donating compound and an electron-accepting compound, and a heat-sensitive recording material sequentially having a protective layer, the protective layer contains an ultraviolet absorber as a hydrophobic core substance. The microcapsules are contained.

[0005]

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a polyvinyl alcohol containing a diacetone group-containing monomer (hereinafter referred to as a specific polyvinyl alcohol) as an emulsifier for a microcapsule containing a hydrophobic core material emulsified or dispersed by an emulsifier. ), And the amount of the specific polyvinyl alcohol to be used is not particularly limited, but is 1 to the total of the hydrophobic core substance and the wall film material.
About 50% by weight, more preferably about 3 to 30% by weight.

As the hydrophobic core substance, a liquid or solid substance is used, and a specific polyvinyl alcohol can provide an emulsion having a particularly narrow particle size distribution with respect to the liquid hydrophobic core substance. The liquid hydrophobic core substance also includes a solution in which a liquid or solid solute is dissolved in a liquid hydrophobic solvent.

Examples of the hydrophobic solvent include acetates such as ethyl acetate and butyl acetate, phosphates such as tricresyl phosphate and octyl diphenyl phosphate, and phthalate esters such as dibutyl phthalate and dioctyl phthalate. Carboxylic acid esters such as butyl oleate, various fatty acid amides, alkylated naphthalenes such as diethylene glycol dibenzoate, monoisopropyl naphthalene, diisopropyl naphthalene, toluene, xylene, 1-methyl-1-phenyl-1-tolylmethane, 1 Alkylated benzenes such as -methyl-1-phenyl-1-xylylmethane and 1-phenyl-1-tolylmethane; alkylated biphenyls such as isopropylbiphenyl; xenoxy alka such as o-phenylphenol glycidyl ether Class, acrylic acid esters such as trimethylolpropane triacrylate, esters of polyhydric alcohols and unsaturated carboxylic acids, chlorinated paraffin, and kerosene, vegetable oil, and the like.

The solid hydrophobic core substance includes, for example, antioxidants, ultraviolet absorbers, leuco dyes, colorants, fragrances,
Coloring dyes, fluorescent pigments and the like.

The degree of saponification of the specific polyvinyl alcohol is not particularly limited as long as the specific polyvinyl alcohol is water-soluble when used as an emulsifier.
About 98 mol% is preferable. Good protective colloid performance is exhibited, probably because a monomer having a diacetone group of an appropriate size is bonded to the main chain, side chain and terminal of a specific polyvinyl alcohol. Therefore, the degree of saponification is 90%
Bubbling at the time of emulsification or dispersion, such as the following partially saponified polyvinyl alcohol, hardly occurs, and the use of a cross-linking agent such as a dihydrazide compound has an effect of easily achieving water resistance. Although the degree of polymerization of the specific polyvinyl alcohol is not particularly limited, it is about 300 to 3000, preferably about 400 to 2000.

The specific polyvinyl alcohol is a partially or completely saponified product of a copolymer of a monomer having a diacetone group and a vinyl ester, and is obtained by copolymerizing a monomer having a diacetone group with a vinyl ester. It is produced by saponifying the obtained resin. Examples of the vinyl ester include vinyl formate, vinyl acetate, vinyl propionate, vinyl pivalate, and vinyl versatate. Among them, vinyl acetate is industrially preferable.

The monomer having a diacetone group is not particularly limited, and examples thereof include diacetone acrylamide, diacetone acrylate, and diacetone methacrylate. Of these, diacetone acrylamide is preferred.

As a method for copolymerizing the above-mentioned monomer having a diacetone group with a vinyl ester, various polymerization methods such as bulk polymerization, solution polymerization, suspension polymerization and emulsion polymerization which are conventionally known are possible. Solution polymerization using methanol as a solvent is industrially preferred. As a method for saponifying a resin obtained by copolymerizing a monomer having a diacetone group and a vinyl ester, conventionally known alkali saponification and acid saponification can be applied, and among them, water saponification in methanol is preferable. Alcohol decomposition using alkali oxide is preferred.

The specific polyvinyl alcohol is a monomer copolymerizable with a monomer having a vinyl ester or diacetone group (for example, unsaturated monomers such as crotonic acid, acrylic acid and methacrylic acid) as long as the effects of the present invention are not impaired. Monocarboxylic acids and their alkyl esters such as methyl and ethyl).

In the specific polyvinyl alcohol, the content of the monomer having a diacetone group is not particularly limited, but is preferably about 0.5 to 10 mol%, more preferably about all the monomers of the specific polyvinyl alcohol. Is about 1.0 to 7.0 mol%. When the content of the diacetone group is less than 0.5 mol%, the protective colloid ability decreases, and when the content exceeds 10 mol%, not only the solubility in water decreases, but also the imparting of water resistance may decrease. .

The present invention is characterized in that a specific polyvinyl alcohol is used as an emulsifier for microcapsules containing a hydrophobic core substance, but other emulsifiers are used in combination as long as the effects of the present invention are not impaired. You can also. Specific examples of such an emulsifier include the following. Water-soluble polymers such as completely saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, carboxy-modified polyvinyl alcohol, sulfone-modified polyvinyl alcohol, acetoacetyl-modified polyvinyl alcohol, silicon-modified polyvinyl alcohol, hydroxyethylcellulose, methylcellulose, carboxymethylcellulose, gelatin, and casein And surfactants such as polyacrylates and alkylbenzenesulfonates

The wall film material of the microcapsule is not particularly limited. However, microcapsules having a polyurea resin or a polyurethane / polyurea resin as the wall film material are excellent in heat resistance. It has an excellent attendant effect of also functioning as an inorganic pigment added for the purpose of preventing sticking to, and has a lower refractive index than microcapsules or other pigments composed of other wall films, and Since it is spherical in shape, even if it is incorporated in a large amount in the protective layer, the density of a recorded image does not decrease (so-called whitening phenomenon) due to irregular reflection of light, so that it is preferably used.

The microcapsules having a wall material made of polyurea or polyurethane / polyurea resin should encapsulate a capsule wall material such as a polyvalent isocyanate and a polyol reacting with the polyisocyanate, or an adduct of a polyvalent isocyanate and a polyol. It is manufactured by mixing in a hydrophobic core substance, emulsifying and dispersing in an aqueous medium in which a specific polyvinyl alcohol is dissolved, and raising the liquid temperature to cause a polymer forming reaction at an oil droplet interface.

Examples of the polyvalent isocyanate compound include m-phenylene diisocyanate, p-phenylene diisocyanate, 2,4-tolylene diisocyanate,
Naphthalene-1,4-diisocyanate, xylylene-
1,4-diisocyanate, 4,4′-diphenylpropane diisocyanate, trimethylene diisocyanate, hexamethylene diisocyanate, propylene
Diisocyanates such as 1,2-diisocyanate, butylene-1,2-diisocyanate, cyclohexylene-1,2-diisocyanate, and cyclohexylene-1,4-diisocyanate; 4,4 ′, 4 ″ -triphenylmethane triisocyanate; Triisocyanates such as toluene-2,4,6-triisocyanate, 4,4 ′
Tetradimethylisocyanates such as -dimethyldiphenylmethane-2,2 ', 5,5'-tetraisocyanate, adducts of hexamethylene diisocyanate with trimethylolpropane, adducts of 2,4-tolylenediisocyanate with trimethylolpropane, Adducts of xylylene diisocyanate and trimethylolpropane, adducts of triresin isocyanate and hexanetriol, isocyanate prepolymers such as trimers of hexamethylene diisocyanate, and the like are included.

Furthermore, the aliphatic isocyanate derivative whose wall film itself does not turn yellow upon exposure to light becomes less compatible with an ultraviolet absorber, an electron-donating compound, or an electron-accepting compound as its viscosity increases. There is a possibility that sufficient wall strength of the microcapsules cannot be obtained, and problems such as leakage of the core substance contained in the microcapsules may occur. Therefore, as the aliphatic isocyanate derivative,
Viscosity at 25 ° C by B-type viscometer is 1000 mPa · s
The following are preferred. In particular, the viscosity is 1000 mPa.
s or less of a hexamethylene diisocyanate derivative such as isocyanurate-type hexamethylene diisocyanate (a trimer of hexamethylene diisocyanate), a mixture of a trimer and a pentamer or more of hexamethylene diisocyanate, and a buret-type hexamer Methylene diisocyanate (trimer). Among them, isocyanurate-type hexamethylene diisocyanate is preferable because the obtained microcapsules have excellent durability. Further, in order to further increase the compatibility with an ultraviolet absorber, an electron donating compound, or an electron accepting compound, it is more preferable to use a reactant of an isocyanurate compound and a monoalcohol together in the wall film material.

In particular, a xylylene diisocyanate derivative having a property between an aromatic isocyanate and an aliphatic isocyanate generally requires a diluting solvent because of its high viscosity and has a problem in terms of environment and disaster prevention. Since the wall film itself has almost no tendency to yellow, it is preferably used as the wall film material of the present invention.

As the polyol compound, for example, ethylene glycol, 1,3-propanediol, 1,1,
6-hexanediol, 1,7-heptanediol, propylene glycol, 2,3-dihydroxybutane,
1,2-dihydroxybutane, 1,3-dihydroxybutane, 2,2-dimethyl-1,3-propanonediol, 2,4-pentanediol, 2,5-hexanediol, 1,4-cyclohexanedimethanol, Diethylene glycol, 1,2,6-trihydroxyhexane,
Aliphatic polyols such as phenylethylene glycol, 1,1,1-trimethylolpropane, hexanetriol, pentaerythritol, and glycerin, 1,4-di (2-hydroxyethoxy) benzene, 1,3-di (2
A condensation product of an aromatic polyhydric alcohol such as -hydroxyethoxy) benzene and an alkylene oxide, p-xylylene glycol, m-xylylene glycol, α,
α'-dihydroxy-p-diisopropylbenzene,
4,4'-isopropylidene diphenol, 4,4'-
Dihydroxydiphenylsulfone, ethylene oxide adduct of 4,4′-isopropylidenediphenol,
Propylene oxide adducts of 4,4′-isopropylidene diphenol and the like can be mentioned.

Of course, the polyvalent isocyanate compound and the polyol compound are not limited to the above compounds, and two or more kinds can be used in combination as needed.

In the present invention, the use ratio of the wall film material of the microcapsules to the hydrophobic core material is not particularly limited, but generally, the wall film material is used in an amount of 1 to 1000 wt. Parts, preferably about 5 to 500 parts by weight.

When an ultraviolet absorber is used as a hydrophobic core substance of a specific microcapsule, various known ultraviolet absorbers can be used, and among them, a benzotriazole-based ultraviolet absorber is particularly suitable for ultraviolet absorption efficiency. In particular, those which are liquid at normal temperature can be encapsulated at a high concentration in microcapsules because it is not necessary to dissolve the ultraviolet absorber in an organic solvent when synthesizing oil-in-water microcapsules. It is more preferably used because the ultraviolet absorbing ability is also remarkably improved. Specific examples of the benzotriazole-based ultraviolet absorber which is liquid at ordinary temperature include, for example, the following.

2- (2'-hydroxy-3'-dodecyl-5'-methylphenyl) benzotriazole, 2-
[2'-hydroxy-4 '-(2 "-ethylhexyl)
Oxyphenyl] benzotriazole, methyl-3-
Condensation product with [3-tert-butyl-5- (2H-benzotriazol-2-yl) -4-hydroxyphenyl] propionate-polyethylene glycol (molecular weight: about 300), 5-tert-butyl-3- (5- Chloro-2H-benzotriazol-2-yl) -4-hydroxybenzene-octyl propionate, 2- (2'-hydroxy-
3'-sec-butyl-5'-tert-butylphenyl)-
5-tert-butylbenzotriazole and the like.

The benzotriazole which is solid at room temperature includes 2- (2'-hydroxyphenyl) benzotriazole, 2- (2'-hydroxy-5'-methylphenyl) benzotriazole, 2- (2'-hydroxyphenyl) benzotriazole. −
5′-tert-butylphenyl) benzotriazole, 2
-(2'-hydroxy-3 ', 5'-di-tert-butylphenyl) benzotriazole, 2- (2'-hydroxy-3'-tert-butyl-5'-methylphenyl) -5
-Chlorobenzotriazole, 2- (2'-hydroxy-3 ', 5'-di-tert-butylphenyl) -5-chlorobenzotriazole, 2- (2'-hydroxy-
3 ', 5'-di-tert-amylphenyl) benzotriazole, 2- (2'-hydroxy-3', 5'-di-te
rt-butylphenyl) -5-tert-butylbenzotriazole, 2- (2′-hydroxy-3′-sec-butyl-5′-tert-butylphenyl) -5-tert-butylbenzotriazole, 2- (2 '-Hydroxy-3',
5'-di-tert-amylphenyl) -5-tert-amylbenzotriazole, 2- [2'-hydroxy-3'-
(3 ", 4", 5 ", 6" -tetrahydrophthalimide-methyl) -5'-methylphenyl] benzotriazole, 2- (2'-hydroxy-5'-tert-octylphenyl) benzotriazole and the like. .

Other ultraviolet absorbers include salicylic acid-based ultraviolet absorbers such as phenyl salicylate, p-tert-butylphenyl salicylate and p-octylphenyl salicylate, 2,4-dihydroxybenzophenone and 2-hydroxy-4-methoxybenzophenone. , 2
-Hydroxy-4-octyloxybenzophenone, 2
-Hydroxy-4-dodecyloxybenzophenone,
Benzophenone ultraviolet absorbers such as 2,2'-dihydroxy-4-methoxybenzophenone, 2,2'-dihydroxy-4,4'-dimethoxybenzophenone, 2-hydroxy-4-methoxy-5-sulfobenzophenone, 2-ethylhexyl -2-cyano-3,3'-diphenylacrylate, ethyl-2-cyano-3,3'-
A cyanoacrylate-based ultraviolet absorber such as diphenyl acrylate, bis (2,2,6,6-tetramethyl-4-
Piperidyl) sebacate, bis-succinate-bis (2,2,
6,6-tetramethyl-4-piperidyl) ester, 2
-(3,5-di-tert-butyl) malonic acid-bis (1,
Hindered amine-based ultraviolet absorbers such as (2,2,6,6-pentamethyl-4-piperidyl) ester and the like.

When a specific microcapsule containing an ultraviolet absorber is contained in the protective layer of the thermosensitive recording medium, the amount of the ultraviolet absorber used is 0.1 to 3.
Preferably cause 0 g / m ² is present, more preferably about 0.2 to 2.0 g / m ^2. When the amount of the ultraviolet absorbent in the protective layer is less than 0.1 g / m ² , the effect of preventing the background portion of the thermosensitive recording medium from yellowing is reduced, and is 3.0 g / m ^2.
If it exceeds, the protective layer is inevitably thickened, and the recording sensitivity is lowered. Further, when the amount of the ultraviolet absorber is less than 10% by weight based on the total amount of the ultraviolet absorber, the microcapsule wall film material and the organic solvent used as required, the effect of preventing the background portion of the heat-sensitive recording material from yellowing can be prevented. In order to exert the effect, the coating amount of the microcapsule must be increased, so that the protective layer is inevitably thickened and the recording sensitivity is reduced.

At the time of microencapsulation, a tin compound, a polyamide compound, an epoxy compound, a polyamine compound and the like can be added to the microcapsules or the emulsion as a reaction accelerator.

When a specific microcapsule is used for the thermosensitive recording medium, the average particle diameter of the microcapsule is 0.1 to 3 μm, preferably 0.1 to 3 μm, in consideration of the strength for smoothing the surface and the quality of the recorded image. It is desirable to adjust so as to be about 3 to 2.5 μm.

Specific microcapsules containing an electron-donating compound or an electron-accepting compound as a color-forming component can be contained in the heat-sensitive recording layer of the heat-sensitive recording medium.

When a specific microcapsule containing an ultraviolet absorber is contained in the protective layer, the specific polyvinyl alcohol used as an emulsifier can also provide an effect as an adhesive for the protective layer, but the protective layer contains Also, certain polyvinyl alcohols or other adhesives can be used.

Specific examples of other adhesives include starches, hydroxyethylcellulose, methylcellulose, carboxymethylcellulose, gelatin, casein, gum arabic, polyvinyl alcohol, carboxy-modified polyvinyl alcohol, acetoacetyl-modified polyvinyl alcohol, and silicon-modified polyvinyl alcohol. , Diisobutylene / maleic anhydride copolymer salt, styrene
Maleic anhydride copolymer salt, ethylene / acrylic acid copolymer salt, styrene / acrylic acid copolymer salt, urea resin,
Melamine resins, amide resins, styrene / butadiene-based latex, acrylic latex, urethane-based latex, and the like are included. Among them, acetoacetyl-modified polyvinyl alcohol and a specific polyvinyl alcohol are particularly preferably used because they can form a strong film.

The protective layer further contains calcium carbonate, zinc oxide, titanium dioxide, amorphous silica, aluminum hydroxide, barium sulfate, talc, kaolin, calcined kaolin,
Pigments such as urea / formalin resin fillers, lubricants such as zinc stearate, calcium stearate, polyethylene wax, carnauba wax, paraffin wax, ester wax, surfactants such as sodium alkylbenzene sulfonate, sodium dioctyl sulfosuccinate, glyoxal, Auxiliary agents such as crosslinkers such as boric acid, dialdehyde starch, methylol urea, epoxy compounds and hydrazide compounds can also be added.
Among them, hydrazide compounds are preferable because an effect having particularly excellent water resistance can be obtained. In order not to shorten the pot life of the coating liquid for the protective layer, it is desirable to add a crosslinking agent to the heat-sensitive recording layer or to the intermediate layer adjacent to the protective layer.

Specific examples of the hydrazide compound include, for example, benzoic hydrazide, formic hydrazide, acetic hydrazide, propionic hydrazide, n-butyric hydrazide,
Isobutyric acid hydrazide, n-valeric acid hydrazide, isovaleric acid hydrazide, activated valeric acid hydrazide, monocarboxylic acid hydrazides such as pivalic acid hydrazide, phthalic acid dihydrazide, isophthalic acid dihydrazide, terephthalic acid dihydrazide, oxalic acid dihydrazide, malonic acid , Succinic dihydrazide, glutaric dihydrazide, adipic dihydrazide, sebacic dihydrazide, maleic dihydrazide, fumaric dihydrazide,
Dicarboxylic acid dihydrazides such as itaconic acid dihydrazide; and polyacrylic acid hydrazide. Among them, dicarboxylic acid dihydrazide is preferable,
Considering the effect of imparting water resistance, solubility in water, and safety, adipic dihydrazide is most preferred.

When the above-mentioned hydrazide compound is added to the heat-sensitive recording layer, its use amount is not particularly limited, but it is generally 0.1 to 2% in the total solid of the heat-sensitive recording layer.
0% by weight, preferably about 0.5 to 10% by weight.

When a specific polyvinyl alcohol is used as an adhesive in the protective layer coating solution for forming the protective layer, crosslinking is carried out together with the crosslinking agent to further increase the water resistance of the protective layer. Oxalic acid, acetic acid,
It is preferable to use an organic acid such as lactic acid and citric acid or an inorganic acid such as hydrochloric acid, phosphoric acid and sulfuric acid in combination. In particular, the pH of the coating solution
Is preferably adjusted to 2 to 6, preferably about 3 to 5. Conversely, a crosslinking inhibitor such as ammonia or monoethanolamine may be added to the coating liquid to suppress crosslinking.

Examples of the combination of a color-forming component comprising an electron-donating compound and an electron-accepting compound include a leuco dye and a developer, a diazonium salt and a coupler, a transition element such as copper, cobalt, iron and the like, a chito compound, and an aromatic compound. Examples include a combination of an isocyanate compound and an imino compound. Among them, a combination of a leuco dye and a color former is preferably used because of its excellent color density.

As the leuco dye and the color former, various known ones can be used. Specific examples of leuco dyes include:
For example, 3- (N-ethyl-N-isoamyl) amino-6
-Methyl-7-anilinofluoran, 3- (N-methyl-N-cyclohexyl) amino-6-methyl-7-anilinofluoran, 3-diethylamino-6-methyl-7
-Anilinofluoran, 3-di (n-butyl) amino-
6-methyl-7-anilinofluoran, 3-di (n-pentyl) amino-6-methyl-7-anilinofluoran, 3-di (n-butyl) amino-7- (o-chlorophenylamino) Fluoran, 3-diethylamino-7-
(O-fluorophenylamino) fluoran, 3- (N
-Ethyl-p-toluidino) -6-methyl-7-anilinofluoran, 3- (N-methyl-NN-propylamino) -6-methyl-7-anilinofluoran, 3-diethylamino-6 -Methyl-7-p-ethoxyanilinofluoran, 3-pyrrolidino-6-methyl-7-anilinofluoran, 3-piperidino-6-methyl-7-anilinofluoran, 3,3-bis (p -Dimethylaminophenyl) -6-dimethylaminophthalide, 3-cyclohexylamino-6-chlorofluorane, 3-diethylamino-6-methyl-7-chlorofluorane, 3-diethylamino-6,8-dimethylfluoran, 3,3-bis [1- (4-methoxyphenyl) -1- (4-dimethylaminophenyl) ethylene-2-yl] -4,5,6
7-tetrachlorophthalide, 3- [p- (p-anilinoanilino) anilino] -6-methyl-7-chlorofluoran, 3-p- (p-chloroanilino) anilino-6
Methyl-7-chlorofluoran. The amount of these leuco dyes to be used cannot be limited because it differs depending on the color former used, but it is 5 to 3 times the total solids of the heat-sensitive recording layer.
It is about 0% by weight.

Specific examples of the coloring agent include, for example, 4,4 ′
-Isopropylidene diphenol, 1,1-bis (4-
(Hydroxyphenyl) cyclohexane, 2,2-bis (4-hydroxyphenyl) -4-methylpentane, hydroquinone monobenzyl ether, benzyl 4-hydroxybenzoate, 4,4′-dihydroxydiphenylsulfone, 2,4′-dihydroxydiphenyl Sulfone, 4
-Hydroxy-4'-isopropoxydiphenylsulfone, bis (3-allyl-4-hydroxyphenyl) sulfone, 4-hydroxy-4'-methyldiphenylsulfone, 4-hydroxyphenyl-4'-benzyloxyphenylsulfone, 3, 4-dihydroxyphenyl-4 '
Phenolic compounds such as -methylphenylsulfone and 1,1-bis (4-hydroxyphenyl) -1-phenylethane, thiourea compounds such as N, N'-di-m-chlorophenylthiourea, N- (p-tolyl Sulfonyl) carbamoyl acid p-cumylphenyl ester, N- (p-
Toluenesulfonyl) -N ′-(p-tolyl) urea,
In a molecule such as 4,4 ′-(Np-tolylsulfonylaminocarbonylamino) diphenylmethane, —SO ₂ NH
Having a bond, zinc p-chlorobenzoate, 4-
[2- (p-methoxyphenoxy) ethyloxy] zinc salicylate, 4- [3- (p-tolylsulfonyl) propyloxy] zinc salicylate, 5- [p- (2-p-methoxyphenoxyethoxy) cumyl] zinc salicylate, etc. And zinc salts of aromatic carboxylic acids. Among them, 4-hydroxy-4′-isopropoxydiphenylsulfone and bis (3-allyl-4-hydroxyphenyl) sulfone are preferably used because of their excellent general preservability of recorded images.

The ratio of the leuco dye to the colorant is appropriately selected according to the type of the leuco dye and the colorant used, and is not particularly limited. 1 to 10 parts by weight, preferably 1 to
About 5 parts by weight of a coloring agent is used.

The heat-sensitive recording layer has an average particle diameter of 0.2 to 3.
A heat-sensitive recording layer coating liquid prepared by mixing and stirring a leuco dye, a coloring agent, an adhesive, and, if necessary, an auxiliary agent finely dispersed to about 0 μm, is used as a high-quality paper (neutral paper, acidic paper), film The amount of coating after drying on a support such as synthetic paper is 2 to 8 g /
It is formed by coating and drying so as to have a thickness of about m ² . The leuco dye or color former may be included in a specific microcapsule. As the adhesive and auxiliary contained in the heat-sensitive recording layer, those contained in the above-mentioned protective layer are used.

Further, the heat-sensitive recording layer may contain a sensitizer for improving the recording sensitivity and a storability improving agent for improving the storage stability of the recorded image over time. Specific examples of the sensitizer include, for example, stearic acid amide, ethylene bis stearic acid amide, methylene bis stearic acid amide, N-methylol stearic acid amide, dibenzyl terephthalate, dimethyl terephthalate, benzyl p-benzyloxybenzoate, -Naphthylbenzyl ether, m-terphenyl, dibenzyl oxalate, di-p-methylbenzyl oxalate, di-p-chlorobenzyl oxalate, 1,2-di (3-methylphenoxy) ethane,
1,2-di (4-methylphenoxy) ethane, 1,2-
Di (4-methoxyphenoxy) ethane, 1,2-diphenoxyethane, 1- (2-naphthyloxy) -2-phenoxyethane, 1,3-di (2-naphthyloxy) propane, 1-isopropylphenyl-2 -Phenylethane and the like.

Specific examples of the preservability improver include, for example, 2,2'-methylenebis (4-methyl-6-tert-butylphenol) and 2,2'-ethylidenebis (4,6-
Di-tert-butylphenol), 2-tert-butyl-6
-(3-tert-butyl-2-hydroxy-5-methylbenzyl) -4-methylphenyl acrylate), 4,
4′-thiobis (2-methyl-6-tert-butylphenol), 1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane, 1,1,
3-tris (2-methyl-4-hydroxy-5-tert-
Hindered phenol compounds such as butylphenyl) butane, 1,4-diglycidyloxybenzene, 4,4′-
Diglycidyloxydiphenylsulfone, 4-benzyloxy-4 ′-(2-methylglycidyloxy) diphenylsulfone, phenol novolak type epoxy resin,
Epoxy compounds such as bisphenol A type epoxy resin,
Bis (4-ethyleneiminocarbonylaminophenyl)
Methane and the like can be mentioned.

The method for forming the protective layer and the heat-sensitive recording layer is not particularly limited. For example, an appropriate method such as air knife coating, variver blade coating, pure blade coating, rod blade coating, short dwell coating, curtain coating, and die coating can be used. After the coating solution for the heat-sensitive recording layer is coated on the support by a coating method and dried, the coating amount after the coating solution for the protective layer is further dried on the heat-sensitive recording layer is about 0.5 to 6 g / m ^2. It is formed by a method such as coating and drying.

If necessary, a protective layer may be provided on the back side of the heat-sensitive recording medium to further improve the storability. Furthermore, an organic or inorganic oil-absorbing pigment, or an intermediate layer containing hollow particles as a main component is provided between the support and the heat-sensitive recording layer to improve the sensitivity and image quality of the recorded image, or to form a super calendar after forming each layer. It is also possible to perform a smoothing process. Various other known techniques in the field of heat-sensitive recording medium production can be added as necessary.

[0047]

The present invention will be described in more detail with reference to the following Examples, but it should be understood that the present invention is by no means restricted to such specific Examples. In the examples, "parts" and "%" indicate "parts by weight" and "% by weight", respectively, unless otherwise specified.

Example 1 Preparation of coating liquid for undercoat layer 100 parts of calcined clay [oil absorption: 90 ml / 100 g]
A composition comprising 200 parts of a 10% aqueous solution of polyvinyl alcohol and 100 parts of water was mixed and stirred to obtain a paint for an undercoat layer.

Preparation of Solution A A composition comprising 10 parts of 3-di- (n-butyl) amino-6-methyl-7-anilinofluoran, 5 parts of a 5% aqueous solution of methylcellulose and 40 parts of water was subjected to sand milling to obtain an average particle size. The solution A was obtained by crushing until the diameter became 1.0 μm.

Solution B Preparation A composition comprising 30 parts of 4-hydroxy-4′-isopropoxydiphenylsulfone, 5 parts of a 5% aqueous solution of methylcellulose and 80 parts of water is pulverized by a sand mill until the average particle diameter becomes 1.0 μm. Liquid B was obtained.

Solution C Preparation A composition comprising 20 parts of 1,2-di (3-methylphenoxy) ethane, 5 parts of a 5% aqueous solution of methylcellulose, and 55 parts of water is pulverized by a sand mill until the average particle diameter becomes 1.0 μm. Thus, solution C was obtained.

Preparation of Coating Solution for Thermosensitive Recording Layer 55 parts of solution A, 115 parts of solution B, 80 parts of solution C, 160 parts of 10% aqueous polyvinyl alcohol solution, 20 parts of 50% SBR latex and 17 parts of calcium carbonate, 5% adipic acid 110 parts of dihydrazide was mixed and stirred to obtain a coating solution for a heat-sensitive recording layer.

Synthesis of polyvinyl alcohol containing monomer having diacetone group In a flask equipped with a stirrer, thermometer, dropping funnel and reflux condenser, 670 parts of vinyl acetate, 10 parts of diacetone acrylamide and 172 parts of methanol Was charged and the system was purged with nitrogen, and then the temperature of the system was raised to 60 ° C. In this system, a solution prepared by dissolving 1 part of 2,2-azobisisobutyronitrile in 50 parts of methanol was started. A solution of 59 parts of diacetone acrylamide dissolved in 39 parts of methanol was added dropwise at a constant rate over 5 hours after the start of the polymerization, and the polymerization was stopped for 6 hours. The polymerization yield was 78%. The remaining vinyl acetate was distilled off while adding methanol vapor to the obtained reaction mixture, to obtain a 50% methanol solution of a vinyl acetate polymer containing a diacetone acrylamide copolymer component. To 500 parts of this solution, 50 parts of methanol and 10 parts of a 4% methanol solution of sodium hydroxide were added, mixed and stirred, and a saponification reaction was performed at 40 ° C. The obtained gel was pulverized, washed well with methanol, and then dried to obtain a polyvinyl alcohol containing a diacetone acrylamide group. Its diacetone acrylamide group content was 6.5 mol%,
The degree of polymerization was 1780, and the degree of saponification was 99 mol%.

Preparation of Microcapsules Enclosing Ultraviolet Absorber In a stirring and mixing vessel equipped with a heating device, 220 parts of an 8% aqueous solution of polyvinyl alcohol containing a diacetone acrylamide group obtained above was added, and an aqueous medium for producing capsules was added. And Separately, 2- (2'-hydroxy-3'-
Dodecyl-5'-methylphenyl) benzotriazole 77 parts, hexamethylene diisocyanate trimer (isocyanurate type) [trade name: Takenate D-170
HN, Takeda Pharmaceutical Co., Ltd.] 33 parts of the solution obtained by heating, mixing and stirring up to 40 ° C. in the aqueous medium for capsule production using a TK homomixer (Model HV-M, manufactured by Tokushu Kika Kogyo Co., Ltd.). And emulsified while cooling so that the average particle size became 1.5 μm. Then, 175 of water was added to this emulsified dispersion.
The resulting mixture was reacted at 90 ° C. for 5 hours while stirring to prepare a microcapsule dispersion having a wall film made of a polyurethane / polyurea resin containing an ultraviolet absorbent. The average particle size after the reaction was 1.6 μm, and the standard deviation was 0.3.
20.

Preparation of Coating Solution for Protective Layer: Microcapsule Dispersion Liquid 220 Enclosing Ultraviolet Absorbent Obtained with 240 Parts of 8% Aqueous Solution of 8% Polyvinyl Alcohol Containing Diacetoneacrylamide Group Obtained in
Part, kaolin (trade name: UW-90, manufactured by EC) 50
% Aqueous dispersion and 6 parts of a 30% aqueous solution of zinc stearate by mixing and stirring a dispersion obtained.
Lactic acid was added to adjust the pH value to 4 to obtain a protective layer coating liquid.

Preparation of Thermosensitive Recording Material A coating solution for an undercoat layer was applied on one side of a high-quality paper of 60 g / m ^{2 at} a rate of 7 g / m ^2.
After m ² coating, the surface was smoothed by a super calender, heat-sensitive layer coating solution thereon, the coating amount after drying a protective layer coating solution is 6 g / m ^2, 5 g / m ^2, respectively After coating and drying as described above to form a heat-sensitive recording layer and a protective layer in that order, the surface was smoothed with a super calender to obtain a heat-sensitive recording material.

Example 2 In the synthesis of the polyvinyl alcohol containing a monomer having a diacetone group in Example 1, the content of the diacetone acrylamide group was 4.0 mol%, and the degree of polymerization was 100.
A polyvinyl alcohol containing a diacetone acrylamide group was obtained in the same manner as in Example 1 except that the saponification degree was adjusted to 95 mol%. A microcapsule dispersion was obtained by using 220 parts of this 12% aqueous solution of polyvinyl alcohol as an aqueous medium for preparing capsules for the preparation of microcapsules containing an ultraviolet absorber. The average particle diameter of the obtained microcapsules containing the ultraviolet absorbent after the reaction was 1.2 μm, and the standard deviation was 0.16. In addition, 220 parts of this microcapsule dispersion, 150 parts of a 10% aqueous solution of polyvinyl alcohol used as an aqueous medium for capsule production, kaolin (trade name: UW-90, manufactured by EC Company)
Of a 50% aqueous dispersion of 30 parts of water and 6 parts of a 30% aqueous solution of zinc stearate were mixed and stirred to obtain a dispersion, to which a lactic acid was added to adjust the pH to 4. A thermosensitive recording medium was obtained in the same manner as in Example 1 except that a coating liquid for a protective layer was obtained.

Example 3 In the synthesis of the polyvinyl alcohol containing a monomer having a diacetone group of Example 1, the content of the diacetone acrylamide group was 0.3 mol% and the degree of polymerization was 110.
A polyvinyl alcohol containing a diacetone acrylamide group was obtained in the same manner as in Example 1 except that the saponification degree was adjusted to 95 mol%. A microcapsule dispersion was obtained by using 220 parts of this 12% aqueous solution of polyvinyl alcohol as an aqueous medium for preparing capsules for the preparation of microcapsules containing an ultraviolet absorber. The average particle diameter of the obtained microcapsules containing the ultraviolet absorbent after the reaction was 1.2 μm, and the standard deviation was 0.31. In the preparation of the coating liquid for the protective layer in Example 1, the above-mentioned polyvinyl alcohol was used in place of the polyvinyl alcohol containing a diacetone group-containing monomer obtained in Example 1 using the microcapsule dispersion liquid. A heat-sensitive recording material was obtained in the same manner as in Example 1 except for using.

Example 4 In the synthesis of the polyvinyl alcohol containing a diacetone group-containing monomer of Example 1, the content of the diacetone acrylamide group was 12 mol%, and the degree of polymerization was 110.
A polyvinyl alcohol containing a diacetone acrylamide group was obtained in the same manner as in Example 1 except that the saponification degree was adjusted to 95 mol%. A microcapsule dispersion was obtained by using 220 parts of this 12% aqueous solution of polyvinyl alcohol as an aqueous medium for preparing capsules for the preparation of microcapsules containing an ultraviolet absorber. The average particle size of the obtained microcapsules containing the ultraviolet absorbent after the reaction was 1.2 μm, and the standard deviation was 0.18. In the preparation of the coating liquid for the protective layer in Example 1, the above-mentioned polyvinyl alcohol was used in place of the polyvinyl alcohol containing a diacetone group-containing monomer obtained in Example 1 using the microcapsule dispersion liquid. A heat-sensitive recording material was obtained in the same manner as in Example 1 except for using.

Comparative Example 1 In the preparation of the microcapsules encapsulating the ultraviolet absorbent of Example 1, a completely saponified polyvinyl alcohol [trade name: PVA] was used instead of the diacetone acrylamide group-containing polyvinyl alcohol as the aqueous medium for capsule production.
-117, manufactured by Kuraray Co., Ltd., degree of saponification: 99 mol%, degree of polymerization: 1750] was used to prepare microcapsules encapsulating an ultraviolet absorbent. The average particle size after the reaction was 5 μm, and the standard deviation was 0.42. 220 parts of this microcapsule dispersion, 240 parts of an 8% aqueous solution of completely saponified polyvinyl alcohol (trade name: PVA-117, manufactured by Kuraray), kaolin [trade name: UW
-90, manufactured by EC Co.] and a mixture comprising 30 parts of a 30% aqueous dispersion of zinc stearate and 6 parts of a 30% aqueous dispersion of zinc stearate. A heat-sensitive recording material was obtained in the same manner as in Example 1 except that lactic acid was added as described above to obtain a coating liquid for a protective layer. At the time of the surface smoothing treatment for forming the thermal recording medium, the surface of the chilled roll of the super calender was stained due to the destruction of the microcapsules.

Comparative Example 2 In the preparation of the microcapsules encapsulating the ultraviolet absorbent of Example 1, a partially saponified polyvinyl alcohol [trade name: PVA] was used instead of the diacetone acrylamide group-containing polyvinyl alcohol as the aqueous medium for capsule production.
-217, manufactured by Kuraray Co., Ltd., a saponification degree: 88 mol%, a polymerization degree: 1750], and an ultraviolet absorbent-encapsulated microcapsule was prepared using 220 parts of an 8% aqueous solution. The average particle size after the reaction is. 2.1 μm, standard deviation was 0.26. In addition, 220 parts of this microcapsule dispersion, partially saponified polyvinyl alcohol [trade name: PVA-21]
7, Kuraray Co., Ltd.] 240 parts of 8% aqueous solution, kaolin [trade name: UW-90, manufactured by EC Co.] 30 parts of 50% aqueous dispersion,
A dispersion obtained by mixing and stirring a composition comprising 6 parts of a 30% aqueous dispersion of zinc stearate was added to lactic acid so that the pH value of the dispersion was adjusted to 4 to obtain a coating liquid for a protective layer. A heat-sensitive recording material was obtained in the same manner as in Example 1 except for the above.

The following evaluation tests were conducted on the thus obtained heat-sensitive recording medium, and the results are shown in Table 1.

[Coloring Property] Thermal Recording Evaluation Machine [Product Name: TH]
-PMD, manufactured by Okura Electric Co., Ltd.] and applied energy:
Each thermosensitive recording medium was colored at 0.45 mJ / dot, and the obtained recorded image was measured in a visual mode using a Macbeth densitometer (RD-914, manufactured by Macbeth). The unrecorded portion was measured with a blue filter.

[Light Resistance] The unrecorded portion of the obtained heat-sensitive recording medium after being exposed to direct sunlight for 10 days was measured with a Macbeth densitometer (using a blue filter).

[Water resistance 1] Each thermosensitive recording medium colored in the same manner as in the above-described color development test was immersed in tap water at 20 ° C. for 15 hours, allowed to dry naturally, and the optical density of the recorded image was determined by the Macbeth density. The measurement was performed in a visual mode using a total [RD-914, manufactured by Macbeth Co., Ltd.] to evaluate the whitening of the recorded image.

[Water resistance 2] The recording surface of each heat-sensitive recording material colored in the same manner as in the above-described color development test was wet with tap water, attached to a cardboard, and air-dried. The surface water resistance was evaluated by the degree of sticking. A: The recording body naturally separates from the cardboard. ：: No surface peeling was observed even when the recording medium was peeled from the cardboard. Δ: When the recording medium was peeled off from the cardboard, slight surface peeling was observed. D: Most of the surface was peeled off when the recording medium was peeled off the cardboard. Or the recording medium does not come off.

[0067]

[Table 1]

[0068]

As is clear from the results shown in Table 1, the microcapsules of the present invention were able to easily control the particle size and to have a good particle size distribution by using polyvinyl alcohol as an emulsifier. . The heat-sensitive recording material using the microcapsules was an excellent heat-sensitive recording material having good coloring properties, preservability, and particularly good water resistance.

Claims (7)

[Claims] 1. A microcapsule containing a hydrophobic core material emulsified or dispersed by an emulsifier, wherein the emulsifier is polyvinyl alcohol containing a monomer having a diacetone group. 2. The microcapsule according to claim 1, wherein the amount of the monomer having a diacetone group is 0.5 to 10 mol% based on all monomers in the polyvinyl alcohol. 3. The microcapsule according to claim 1, wherein the degree of saponification of polyvinyl alcohol containing a monomer having a diacetone group is 92 to 98 mol%. 4. The microcapsule according to claim 1, wherein the wall film material of the microcapsule is polyurea or polyurethane / polyurea. 5. The microcapsule according to claim 1, wherein the hydrophobic core substance is an ultraviolet absorber. 6. The ultraviolet absorbent is liquid at room temperature.
The microcapsule as described. 7. A thermosensitive recording medium having a thermosensitive recording layer containing an electron donating compound and an electron accepting compound on a support, and a protective layer in order, wherein the microlayer according to claim 5 or 6 is provided in the protective layer. A heat-sensitive recording material comprising a capsule.