JPH09328628A - Composite fine particles and thermal recording material - Google Patents

Abstract

(57) [Abstract] [Problem] High recording sensitivity, discoloration of white paper due to pressure,
Provided is a heat-sensitive recording material in which discoloration of a white paper portion due to heat or humidity is extremely small. SOLUTION: An oxidative coloring leuco dye and a polymer-forming raw material for forming polyurea or polyurethane-polyurea by polymerization are dissolved and mixed in a water-insoluble organic solvent having a boiling point of 100 ° C. or lower, and this organic solvent solution is mixed with an aqueous medium. Emulsified and dispersed in, the emulsified dispersion is heated to volatilize and remove the organic solvent, and thereafter, the polymer-forming raw material is prepared by polymerizing the composite fine particles and polyurea by polymerization Polyurethane-Polyurea-forming polymer-forming raw material is used as a solvent, a solution containing an oxidative coloring leuco dye as a solute is emulsified and dispersed in an aqueous medium, and the emulsified dispersion is heated to increase the polymer-forming raw material. Thermosensitive recording material having composite fine particles prepared by molecularization and a thermosensitive coloring layer containing the composite fine particles and an oxidizing agent

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to composite fine particles and a heat-sensitive recording material. Especially high recording sensitivity,
The present invention relates to composite fine particles capable of providing a thermosensitive recording material in which discoloration of a white paper portion due to pressure and discoloration of a white paper portion due to heat or humidity are extremely small, and a thermosensitive recording material having a thermosensitive coloring layer containing the composite fine particles. . Further, the present invention has high recording sensitivity and can be fixed by irradiation with light, and the discoloration of the white paper portion at the time of optical fixing and the discoloration of the white paper portion due to pressure,
The present invention relates to a heat-sensitive recording material in which discoloration of a white paper portion due to heat and humidity is extremely small.

[0002]

2. Description of the Related Art A heat-sensitive recording material generally comprises a support made of paper, synthetic paper, plastic film or the like and a heat-sensitive coloring layer containing a color-developing substance, a developer and an adhesive as main components. It is possible to obtain a color-recorded image by reacting these color-forming substances and the color developer with heat energy. Such a thermal recording method has the advantages that the recording apparatus is compact, inexpensive, and easy to maintain, and not only as a recording medium for facsimiles, automatic ticket vending machines, and scientific measuring instruments, It is also widely used as an output medium for various printers and plotters for POS labels, CAD and CRT medical images.

As a combination of the color-forming substance and the color developer used in these heat-sensitive recording layers, a combination of an electron-donating dye precursor and an electron-accepting substance is most widely used. Since the color development reaction is a reversible reaction, there is a drawback that the reverse reaction occurs due to the influence of humidity, a plasticizer and the like to erase the color. For this reason, it was difficult to apply it to the documents that require preservation. It is also known to utilize a dye precursor encapsulated in a microcapsule in a thermal recording paper in order to improve such a defect.
No. 4960, Japanese Patent Publication No. 4-37796, Japanese Patent Publication No. 4-37797, Japanese Patent Publication No. 5-63315. However, when microcapsules containing an oily liquid in which these dye precursors are dissolved are applied to a recording material, rubbing and pressure fog increase,
There was a problem that the background was colored. In addition, since it cannot be fixed, the defect that the uncolored part will be colored if it gets too close to the heat source after recording, making it impossible to read the record, cannot be forged. Could not be applied to the cards.

Examples of such a thermal recording material having a permanent image which can be fixed by improving the defects caused by the constitution of the thermal recording material include, for example, a thermal recording material comprising a combination of a diazo compound and a coupling component. Is mentioned. This is so-called fixing by forming an image on a recording material by heating and then irradiating the entire surface with ultraviolet rays to decompose the unreacted diazo compound and eliminate the color forming ability. However, the heat-sensitive recording material obtained by combining the diazo compound and the coupling component is
At the time of light fixing, not only the diazo compound is decomposed but also coupling between the diazo compounds occurs, which tends to cause so-called stain which causes the white paper portion to develop a light color.

Further, Japanese Patent Publication No. 54-1453 discloses that an oxidative coloring type leuco dye is colored by a latent developer which liberates an oxidant by heating such as nitrate, and fixing including a photoreducing agent as a photofixing agent is possible. However, there is a problem that the color development sensitivity is low and the fixing property is not sufficient because extra energy is required to release the oxidant.

[0006]

DISCLOSURE OF THE INVENTION The present invention solves the above problems of conventional thermal recording materials and has a high color developing sensitivity.
It is intended to provide a heat-sensitive recording material in which the discoloration of the white paper portion due to pressure and the discoloration of the white paper portion due to heat or humidity are extremely small. Further, the present invention has a high color development sensitivity and can be fixed by irradiation with light, and the color change of the white paper portion at the time of light fixation, the color change of the white paper portion due to pressure, and the color change of the white paper portion due to heat or humidity are extremely small. It provides the material.

[0007]

The present invention provides an oxidative coloring leuco dye and a polymer-forming raw material which forms a polyurea or a polyurethane-polyurea by polymerization.
It is dissolved and mixed in a water-insoluble organic solvent having a boiling point of 0 ° C. or lower, the organic solvent solution is emulsified and dispersed in an aqueous medium, and the emulsified dispersion is heated to volatilize and remove the organic solvent, and then the polymer. The composite fine particles are prepared by polymerizing the forming raw material. Furthermore, the present invention uses a polymer-forming raw material forming a polyurea or polyurethane-polyurea by polymerization as a solvent, and emulsifies and disperses a solution containing an oxidative coloring leuco dye as a solute in an aqueous medium, and heats the emulsified dispersion. Then, the composite fine particles are prepared by polymerizing the polymer-forming raw material.

Further, the present invention provides a heat-sensitive recording material comprising a support and a heat-sensitive color-forming layer which develops a color when heated, wherein the heat-sensitive color-forming layer contains the composite fine particles and an oxidizing agent. It depends on the material. Furthermore, the present invention resides in the heat-sensitive recording material, wherein the heat-sensitive color forming layer contains a photo-reducing substance.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The heat-sensitive recording material of the present invention comprises a support, a composite fine particle in which an oxidative coloring leuco dye is contained in a base material made of polyurea or polyurethane-polyurea, and an oxidative coloring leuco dye is oxidized. The heat-sensitive color forming layer contains an oxidant that develops a color when exposed to light and a photo-reducing agent that is activated by light and exhibits a reducing property in the case of a light-fixing type heat-sensitive recording material. When this heat-sensitive recording material is heated, the intermolecular network of the polymer base material of the composite fine particles loosens, and the oxidative coloring leuco dye comes into contact with the oxidant and is oxidized to develop a color. In the case of a light-fixing type heat-sensitive recording material, when the heat-sensitive coloring layer is irradiated with light, the photo-reducing agent is activated and exhibits a reducing property. For this reason, even if this is further heated after the light irradiation, the color formation due to the oxidation of the oxidative coloring type leuco dye does not occur, and the optical fixing is possible. Activation of the photoreducing agent of the heat-sensitive recording material of the present invention by light irradiation does not cause a side reaction accompanied by coloration upon light irradiation as seen in the combination of diazo and a coupler, and discoloration of an uncolored portion at the time of light fixing. I can't see it.

Further, the oxidative color-forming leuco dye used in the present invention is highly isolated from the outside because it is present in the form of composite fine particles contained in the matrix of the polymeric substance consisting of polyurea or polyurethane-polyurea. Therefore, discoloration of the white paper portion due to heat and humidity is extremely small. Further, since the composite fine particles do not substantially contain a solvent, the physical strength thereof is high, and the heat-sensitive recording material of the present invention is excellent in pressure resistance and abrasion resistance. It is considered that the composite fine particles are present in a solid solution state by mixing the oxidative coloring leuco dye and the polymer substance at the molecular level. The appearance of the composite fine particles is almost spherical when observed with an electron microscope, or is hemoglobin-like with a hollow center, and when a cross section is observed, a solid solid without voids and a large number of pores are observed in the cross section. It is an existing porous solid or a hollow solid having a hollow portion having a diameter of ⅕ or more of the particle diameter. Further, in the heat-sensitive recording material of the present invention, the oxidant which is a color-developing substance develops color immediately upon contact with the oxidative color-forming leuco dye contained in the composite fine particles upon heating, and therefore a compound such as a nitrate compound which liberates the oxidant by heating. The color development sensitivity is remarkably higher than that produced by.

The oxidative coloring type leuco dye used in the present invention is
Usually, it is a colorless or light-colored compound, and is a compound that forms a colored body by oxidation. Examples of the oxidative coloring leuco dye include, for example, Japanese Examined Patent Publication No. 2-14353 and JP-A-62-1.
Aminotriarylmethanes, aminoxanthenes, aminothioxanthenes, amino-9,10 described in Japanese Patent Publication No. 98494, US Pat. No. 3,445,234, etc.
-Dihydroacridine, aminophenoxazine, aminophenothiazine, aminodihydrophenazine, aminodiphenylmethane, leuco damamine, aminohydrocinnamic acid, hydrazine, leucoindigoid, amino-2,3-dihydroanthraquinone, tetrahalo-p,
p'-biphenol, 2- (p-hydroxyphenyl)
Examples thereof include compounds such as 4,5-diphenylimidazole and phenethylaniline, alkoxyxanthene compounds, and the like, all of which are compounds having a coloring structure by losing one or two hydrogen atoms. Among these, aminotriarylmethane, aminodiphenylmethane, aminoxanthene, aminophenothiazine, aminophenoxazine, alkoxyxanthene and the like are preferably used from the viewpoints of color development sensitivity, fixability and the like.

Specific examples thereof include 3,7-bis (dimethylamino) -10-benzoylphenothiazine and 3,7-bis (dimethylamino) -10-benzoylphenothiazine
7-bis (dimethylamino) -10- (p-toluoyl) phenothiazine, 3,7-bis (dimethylamino)
-10-pivaloylphenothiazine, 3,7-bis (diethylamino) -10-benzoylphenothiazine,
3,7-bis (diethylamino) -10- (p-toluoyl) phenoxazine, tris (4-dimethylaminophenyl) methane, bis (4-dimethylaminophenyl)
Methane, tris (4-diethylaminophenyl) methane, tris (4-dimethylamino-2-methylphenyl) methane, tris (4-diethylamino-2-methylphenyl) methane, bis (4-dimethylaminophenyl)-(4- Diethylaminophenyl) methane, bis (4-diethylamino-2-methylphenyl)-(4-
Diethylaminophenyl) methane, bis (4-dimethylamino-2-methylphenyl)-(4-dimethylaminophenyl) methane, bis (4-dimethylaminophenyl)-(2-methoxycarbonylphenyl) methane, bis (4-dimethyl Aminophenyl)-(4-dimethylamino-2-methoxycarbonylphenyl) methane, (4
-Dimethylaminophenyl)-(4-diethylamino-
2-Methylphenyl)-(4-dimethylamino-2-methoxycarbonylphenyl) methane, bis (1-ethyl-2-methylindol-3-yl)-(2-methoxycarbonylphenyl) methane, bis (1-methyl -2-
Phenylindol-3-yl)-(2-methoxycarbonylphenyl) methane and the like.

Further, (2-methyl-4-dimethylaminophenyl)-(1-ethyl-2-methylindole-3)
-Yl)-(2-methoxycarbonylphenyl) methane, (2-methyl-4-dimethylaminophenyl)-
(1-Ethyl-2-methylindol-3-yl)-
(2-Butoxycarbonylphenyl) methane, (2-methyl-4-diethylaminophenyl)-(1-ethyl-
2-Methylindol-3-yl)-(2-methoxycarbonylphenyl) methane, (2-methoxy-4-dimethylaminophenyl)-(1-ethyl-2-methylindol-3-yl)-(2-methoxy Carbonylphenyl) methane, (2-methyl-4-dimethylaminophenyl)-(1-methyl-2-phenylindol-3-yl)-(2-methoxycarbonylphenyl) methane and the like.

Further, (2-methyl-4-dimethylaminophenyl)-(1-ethyl-2-methylindole-
3-yl)-(3-methoxycarbonyl-2-pyridyl) methane, (2-methyl-4-dimethylaminophenyl)-(1-ethyl-2-methylindol-3-yl)-(3-butoxycarbonyl- 2-pyridyl) methane, (2-methyl-4-diethylaminophenyl)-
(1-Ethyl-2-methylindol-3-yl)-
(3-methoxycarbonyl-2-pyridyl) methane,
(2-Methyl-4-diethylaminophenyl)-(1-
Ethyl-2-methylindol-3-yl)-(3-ethoxycarbonyl-2-pyridyl) methane, (2-methoxy-4-dimethylaminophenyl)-(1-ethyl-
2-Methylindol-3-yl)-(3-methoxycarbonyl-2-pyridyl) methane, (2-methyl-4-
Dimethylaminophenyl)-(1-methyl-2-phenylindol-3-yl)-(2-methoxycarbonyl-4-methoxyphenyl) methane, (2-methyl-4-)
Dimethylaminophenyl)-(1-ethyl-2-methylindol-3-yl)-(2-methoxycarbonyl-
3,4,5,6-tetrabromophenyl) methane and the like.

Further, 3,6-dimethoxy-9- (2-methoxycarbonylphenyl) xanthene, 3,6-dimethoxy-9- (2-ethoxycarbonylphenyl) xanthene, 3,6-dimethoxy-9- (2-butoxy). Carbonylphenyl) xanthene, 3,6-dibutoxy-9
-(2-butoxycarbonylphenyl) xanthene, 8
-Diethylamino-11- (2-methoxycarbonylphenyl) -benzo [a] xanthene, 8-diethylamino-11- (2-phenoxycarbonylphenyl) -benzo [a] xanthene, 8-diethylamino-11-
(2-Ethoxycarbonylphenyl) -benzo [a] xanthene, 8-dibutylamino-11- (2-methoxycarbonylphenyl) -benzo [a] xanthene, 8-
Examples thereof include dibutylamino-11- (2-ethoxycarbonylphenyl) -benzo [a] xanthene and 8-dibutylamino-11- (2-butoxycarbonylphenyl) -benzo [a] xanthene.

Further, 3-dibutylamino-6-methyl-
7-anilino-9- (2-methoxycarbonylphenyl) xanthene, 3-diethylamino-6-methyl-7
-Anilino-9- (2-methoxycarbonylphenyl)
Xanthene, 3-dibutylamino-6-methyl-7-anilino-9- (2-ethoxycarbonylphenyl) xanthene, 3- (N-isoamyl-N-ethylamino)-
6-methyl-7-anilino-9- (2-methoxycarbonylphenyl) xanthene, 3-dibutylamino-7-
(O-chloroanilino) -9- (2-methoxycarbonylphenyl) xanthene, 3-dimethylamino-7-
(M-Trifluoromethylanilino) -9- (2-methoxycarbonylphenyl) xanthene, 3-pyrrolidino-6-methyl-7-anilino-9- (2-methoxycarbonylphenyl) xanthene, 3-piperidino-6- Methyl-7-anilino-9- (2-methoxycarbonylphenyl) xanthene, 3-dimethylamino-7-dibenzylamino-9- (2-methoxycarbonylphenyl)
There are xanthene and the like.

Further, 3-diethylamino-6-methyl-7-chloro-9- (2-methoxycarbonylphenyl) xanthene, 3-diethylamino-7-chloro-9.
-(2-Methoxycarbonylphenyl) xanthene, 3
-Dibutylamino-6-methyl-7-chloro-9- (2
-Ethoxycarbonylphenyl) xanthene, 3-diethylamino-6,7-dimethyl-9- (2-methoxycarbonylphenyl) xanthene, 3- (N-ethyl-N)
-P-toluidino) -7-methyl-9- (2-methoxycarbonylphenyl) xanthene, 3-dibutylamino-6-methyl-7-anilino-9- (2-methoxycarbonyl-4-methoxyphenyl) xanthene, 3 -Dibutylamino-6-methyl-7-anilino-9- (2-methoxycarbonyl-3,4,5,6-tetrachlorophenyl) xanthene, 3,6-bis (dimethylamino)-
9- (2-methoxycarbonylphenyl) xanthene,
3,6-bis (diphenylamino) -9- (2-methoxycarbonylphenyl) xanthene and the like can be mentioned. Two or more kinds of these oxidative coloring leuco dyes may be used in combination.

The polymer-forming raw material used for forming the composite fine particles in the present invention may be a polyvalent isocyanate compound alone, or a mixture of a polyvalent isocyanate compound and a polyol which reacts with it, or a polyvalent isocyanate compound. It may be an addition product of an isocyanate compound and a polyol, or a multimer such as a biuret body or an isocyanurate body.

The polyvalent isocyanate compound used as the polymer-forming raw material is, for example, m-phenylene diisocyanate, p-phenylene diisocyanate,
2,6-Tolylene diisocyanate, 2,4-Tolylene diisocyanate, Naphthalene-1,4-diisocyanate, Diphenylmethane-4,4'-diisocyanate, 3,3'-Dimethyldiphenylmethane-4,4'-
Diisocyanate, p-xylylene diisocyanate,
m-xylylene diisocyanate, 4,4'-diphenylpropane diisocyanate, trimethylene diisocyanate, hexamethylene diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, 5-isocyanato-1- (isocyanatomethyl) -1,3,3 −
Trimethylcyclohexane, propylene-1,2-diisocyanate, butylene-1,2-diisocyanate,
Diisocyanates such as cyclohexylene-1,2-diisocyanate and cyclohexylene-1,4-diisocyanate, triisocyanates such as 4,4 ′, 4 ″ -triphenylmethane triisocyanate and toluene-2,4,6-triisocyanate And tetraisocyanates such as 4,4′-dimethyldiphenylmethane-2,2 ′, 5,5′-tetraisocyanate.

Examples of adducts of polyvalent isocyanates and polyols include trimethylolpropane adduct of hexamethylene diisocyanate, trimethylolpropane adduct of 2,4-tolylene diisocyanate, trimethylolpropane adduct of xylylene diisocyanate, Isocyanate prepolymers such as hexanetriol adducts of tolylene diisocyanate can be used. Further, a multimer of a polyvalent isocyanate compound, for example, a biuret body of hexamethylene diisocyanate, an isocyanurate body of hexamethylene diisocyanate, or the like can also be used as the polymer-forming raw material of the present invention.

Examples of the polyol compound used as the polymer-forming raw material include ethylene glycol, 1,
3-propanediol, 1,4-butanediol, 1,
5-pentanediol, 1,6-hexanediol,
1,7-heptanediol, 1,8-octanediol, propylene glycol, 2,3-butanediol,
1,2-butanediol, 1,3-butanediol,
2,2-dimethyl-1,3-propanediol, 2,4
-Pentanediol, 2,5-hexanediol, 3-
Methyl-1,5-pentanediol, 1,4-cyclohexanedimethanol, dihydroxycyclohexane, diethylene glycol, 1,2,6-trihydroxyhexane, phenylethylene glycol, 1,1,1-trimethylolpropane, hexanetriol, penta Aliphatic polyols such as erythritol and glycerin, 1,4
-Bis (2-hydroxyethoxy) benzene, 1,3-
A condensation product of an aromatic polyhydric alcohol such as bis (2-hydroxyethoxy) benzene and an alkylene oxide,
p-xylylene glycol, m-xylylene glycol, α, α′-dihydroxy-p-diisopropylbenzene, 4,4′-dihydroxydiphenylmethane, 2-
(P, p'-dihydroxydiphenylmethyl) benzyl alcohol, 4,4'-isopropylidenediphenol, 4,4'-dihydroxydiphenylsulfone, 4,
4'-dihydroxydiphenyl sulfide, 4,4'-
Examples thereof include ethylene oxide adduct of isopropylidene diphenol, propylene oxide adduct of 4,4′-isopropylidene diphenol, and acrylate having a hydroxyl group in the molecule such as 2-hydroxyacrylate.

Of course, the polyisocyanate compound, the adduct of polyisocyanate and polyol, the polyol compound and the like are not limited to the above compounds, and if necessary, two or more kinds may be used in combination.

The weight ratio of the oxidative coloring leuco dye to the polymer substance in the composite fine particles is such that the content of the oxidative coloring leuco dye is 5 to 80% by weight based on the total weight of the composite fine particles from the viewpoint of color development sensitivity. Preferably 20 to 50
More preferably, it is wt%.

As a method for preparing composite fine particles comprising a polymeric substance selected from the polyurea and polyurethane-polyurea of the present invention and an oxidative coloring leuco dye, for example, an oxidative coloring leuco dye having a boiling point of 100 ° C. or lower is used. Dissolved in a low boiling water-insoluble organic solvent, a polymer-forming raw material, for example, a polyvalent isocyanate compound alone, or a mixture of a polyvalent isocyanate and a polyol that reacts with it, or an adduct of a polyvalent isocyanate and a polyol, A biuret form of a polyvalent isocyanate, a multimer such as an isocyanurate form is added, and this mixed solution is emulsified and dispersed in an aqueous medium containing a protective colloid substance such as polyvinyl alcohol dissolved therein. After mixing the reactive substances, the organic solvent is volatilized by heating this emulsion dispersion. Removed, by polymerizing By subsequently polymerizing the polymer forming material, whereby there is a method of forming a composite fine particles comprising the oxidative coloring type leuco dye and a polymer material.

In this method, in order to sufficiently volatilize and remove the organic solvent, the conditions are experimentally set in consideration of the kind of the solvent, the emulsification and dispersion conditions, the mixing ratio of the oxidative coloring leuco dye and the solvent and the like. Just keep it. Generally, the boiling point is 5
When a solvent of 0 ° C. or lower is used, an open container is used and the dispersion after emulsification and dispersion is kept under stirring conditions at a temperature 5 to 10 ° C. lower than the boiling point of the solvent for 2 hours or more, more preferably 5 hours or more. As a result, the organic solvent can be volatilized and removed. After removing the organic solvent, the dispersion liquid is heated to 80 ° C. to 95 ° C. in order to polymerize the polymerizing raw material, and this temperature is maintained for 1 hour or more, more preferably 2 hours or more to form the composite fine particles. It can be manufactured.

The organic solvent used for preparing the composite fine particles has a boiling point of 100 ° C. or less, more preferably a boiling point of 80 ° C.
It is preferably below and hydrophobic. For example, such low boiling point hydrophobic (water insoluble) organic solvents include butyl chloride (boiling point 78 ° C.), ethylidene chloride (57 ° C. same), propyl chloride (46 ° C. same), methylene chloride (42 ° C. same). ,
It can be selected from ethyl acetate (at 77 ° C. at the same temperature), methyl acetate (at 57 ° C. at the same temperature) and the like. Acetone (at 56 ° C. at the same temperature) and methanol (at 65 ° C. at the same temperature) are compatible with water, and thus the emulsified state of the obtained emulsion may be unstable, which is not preferable.

As another method for preparing the composite fine particles composed of a polyurea used in the present invention and a polymer substance selected from polyurethane-polyurea and an oxidative coloring leuco dye, an oxidative coloring leuco dye is used to form a polymer. Dissolved only in the polyvalent isocyanate compound as a raw material, or a mixture of polyvalent isocyanate and a polyol that reacts with it, or an adduct of polyvalent isocyanate and polyol, a biuret body of polyvalent isocyanate, and a multimer such as isocyanurate body Then, this solution is emulsified and dispersed in an aqueous medium containing a protective colloid substance such as polyvinyl alcohol dissolved therein, and further, if necessary, a reactive substance such as polyamine is mixed, and then the emulsified dispersion liquid is heated. The polymer-forming raw material is polymerized to polymerize it, which causes oxidation. It can be produced by a method of forming a composite fine particles comprising a mold leuco dye and a polymer material. Since this method does not use a low boiling point solvent, it has an advantage that the evaporation step is not necessary, and also has the feature that composite fine particles excellent in isolation can be obtained.

In the present invention, the emulsifier (protective colloid agent) used for preparing the composite fine particles includes polyacrylamide, polyvinylpyrrolidone, polyvinyl alcohol, modified polyvinyl alcohol such as sulfo group-modified polyvinyl alcohol, methyl cellulose, carboxymethyl cellulose, styrene- Water-soluble synthetic polymer compounds such as maleic anhydride copolymer salts and their derivatives can be used. At the same time, a surfactant, a defoaming agent or the like may be used. The amount of the emulsifier used in the preparation of the composite fine particles is not particularly limited, but it is generally preferably 1 to 50 parts by weight, preferably 3 to 30 parts by weight, based on 100 parts by weight of the solid content of the composite fine particle dispersion. More preferably.

In the composite fine particles used in the present invention, an ultraviolet absorber, an antioxidant, an oil-soluble fluorescent dye, a release agent and the like are added, if necessary, in addition to the oxidative coloring type leuco dye. Good. Such an additive substance is preferably solid at room temperature, but may be liquid. The oxidative coloring leuco dye may be a mixture of two or more oxidative coloring leuco dyes.

The inclusion of an ultraviolet absorber in the composite fine particles used in the thermosensitive coloring layer of the present invention is preferable from the viewpoint of light resistance, and particularly 2- (2-hydroxy-5-methylphenyl) -2H-benzotriazole. The benzotriazole-based UV absorbers such as ## STR3 ## have not only the effect of improving the light resistance of the color image but also the effect of improving the color developing sensitivity, and are preferably used. In addition, a tin compound, a polyamide compound, an epoxy compound, a polyamine compound or the like may be used in combination as a reaction accelerator when polymerizing the composite fine particles. In addition, when using a polyamine compound, it is preferable to use an aliphatic polyamine compound from the viewpoint that light resistance is not deteriorated. The average particle diameter of the composite fine particles used in the present invention is preferably adjusted to be in the range of 0.1 to 5.0 μm, preferably 0.3 to 3.0 μm in consideration of color development sensitivity.

By using the composite fine particles of the present invention, it is possible to suppress the background color development due to the pressing force and the background fogging when the white paper is stored for a long period of time. Decolorization due to oil and oil can also be significantly suppressed.

Examples of the oxidizing agent that can be used in the present invention include triarylmethyl compounds and quinone compounds substituted with electron withdrawing groups. Examples of the triarylmethyl compound include triphenylmethyl chloride,
Examples include triphenylmethyl bromide. The quinone compound substituted with an electron-withdrawing group is 2,5-
Dibromo-1,4-benzoquinone-3,6-dicarboxylic acid-di-n-hexyl ester, 2,5-dichloro-
2,4-Dihalogen-1,4-benzoquinone-3,6-dicarboxylic acid esters such as 1,4-benzoquinone-3,6-dicarboxylic acid-diisobutyl ester, 2-p-
Monosulfonylquinones such as toluenesulfonyl-1,4-benzoquinone, disubstituted quinones such as 2,5-dibenzoyl-1,4-benzoquinone and 1,4-benzoquinone-2,5-dicarboxylic acid dicyclohexyl ester,
o-chloranil, chloranil, bromanil, 1,4-
4-Substituted quinones such as ethyl benzoquinone tetracarboxylate, 2,5-di-p-toluenesulfonyl-1,4-benzoquinone-3,6-dicarboxylic acid diisobutyl ester, 2,5-dibutylsulfonyl-1,4-benzoquinone Examples include disulfonylquinone dicarboxylic acid ester such as -3,6-dicarboxylic acid diethyl ester, monosulfonylquinone dicarboxylic acid diester such as 2-p-toluenesulfonyl-1,4-benzoquinone-3,6-dicarboxylic acid dicyclohexyl ester, and the like. To be of course,
It is not limited to these, and if necessary, one kind,
Alternatively, two or more kinds of compounds can be used in combination. The amount of the oxidant used is not particularly limited, but the oxidant is 1 to 500 parts by weight with respect to 100 parts by weight of the oxidative coloring leuco dye.
It is preferable to mix and use them in a ratio of parts by weight. More preferably, it is used in a proportion of 5 to 200 parts by weight.

Examples of the photoreducing agent used in the present invention include quinone, disulfide, diazoanthrone, diazonium salt, diazophenanthrone, aromatic azide, acyloin and aroma described in JP-A No. 50-139724. Group ketones, aromatic carbazides, diazo sulfonates, compounds such as 2H-benzimidazole, and compounds such as anthrone and phenazine can be used. Specific examples thereof include 1,4-naphthoquinone and 2-methyl-
1,4-naphthoquinone, p-quinone, 2-amylanthraquinone, 2-tert-butylanthraquinone, phenanthrenequinone, bilenquinone, 1,2-benzanthraquinone, 1-naphthyldisulfide, 10-diazoanthrone, benzophenone, benzoin, Examples thereof include benzoin isobutyl ether, 2,2-dimethyl-2H-benzimidazole, benzanthron, phenazine and the like. Of course, it is not limited to these,
If necessary, one kind or two or more kinds of compounds can be used in combination. In this case, each photoreducing agent can be activated with light having a different wavelength by utilizing the difference in the wavelength of photoactivation of each compound. The amount of photoreducing agent used is
Although not particularly limited, it is preferable to mix and use the photoreducing agent in an amount of 5 to 2000 parts by weight with respect to 100 parts by weight of the oxidative coloring leuco dye. More preferably 20-5
It is used in a proportion of 00 parts by weight.

In the present invention, a reducing agent may be added to the thermosensitive color developing layer in order to improve the photofixability. Examples of these reducing agents include p-hydroquinone, 4-methoxy-1-naphthol, 4-methoxyphenol, 2-methoxyphenol, 4-hydroxydiphenyl ether, 4-methyl-4′-hydroxydiphenylthioether and the like. Of course, the present invention is not limited to these, and if necessary, one kind or two or more kinds of compounds can be used in combination.

In the present invention, the photoreducing agent is preferably made into composite fine particles or encapsulated in microcapsules in order to increase the efficiency of photoactivation. Further, for the purpose of further improving the efficiency of photo-fixing, it is possible to include an oxidizing agent and a photo-reducing agent in the same composite fine particles or encapsulate them in microcapsules. The composite fine particles can be prepared by the same method as that containing the oxidative coloring leuco dye. The microcapsules can be prepared by various known methods. Generally, a solution (oil-soluble) obtained by dissolving a solute containing an oxidizing agent or a photo-reducing agent as a main component as described above in a high-boiling-point solvent is emulsified and dispersed in an aqueous medium to form a high concentration around the oil-based droplets. It is prepared by a method of forming a wall film made of a molecular substance. As a wall material for such microcapsules, polyurethane, polyurea, polyester, polycarbonate, urea-formaldehyde resin, melamine resin, polystyrene, styrene methacrylate copolymer, gelatin, polyvinylpyrrolidone, polyvinyl alcohol, etc. There are materials. Also, two or more of these polymers can be used in combination. Among these wall materials, polyurea or polyurethane-polyurea is preferable.

The microcapsules having a wall film made of polyurea or polyurethane-polyurea contain a capsule wall film material such as an isocyanate compound alone, or a polyvalent isocyanate and a polyol that reacts therewith, or an adduct of a polyvalent isocyanate and a polyol. It is produced by mixing in a core substance to be encapsulated, emulsifying and dispersing it in an aqueous medium in which a protective colloid substance such as polyvinyl alcohol is dissolved, and raising the liquid temperature to cause a polymer forming reaction at the oil droplet interface.

As the polyvalent isocyanate compound, the addition product of the polyvalent isocyanate and the polyol, and the polyol compound for microencapsulation, the same ones as those used for the production of the composite fine particles can be used.

As an emulsifier (protective colloidal agent) used for microencapsulation, various anions, nonions, cations or amphoteric water-soluble polymers are used. Of these, partially saponified polyvinyl alcohol has high emulsion stability and is preferably used. Further, modified polyvinyl alcohol (acetoacetyl group-modified, carboxyl group-modified, silicon-modified, etc.) can impart water resistance and is preferably used for the heat-sensitive recording material of the present invention.

The high boiling point solvent used for the microencapsulation is not particularly limited, and can be appropriately selected from various high boiling point hydrophobic media used in the field of pressure-sensitive copying paper and used. Examples of the phosphonates include tricresyl phosphate, octyldiphenyl phosphate, and other phosphoric acid esters, dibutyl phthalate, dioctyl phthalate, and other phthalic acid esters, butyl oleate, and other carboxylic acid esters, various fatty acid amides, and diethylene glycol diethylene. Benzoate, monoisopropyl naphthalene,
Alkylated naphthalenes such as diisopropylnaphthalene, 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 isopropyl biphenyl,
Examples thereof include xenoxyalkanes such as o-phenylphenol glycidyl ether, acrylic acid esters such as trimethylolpropane triacrylate, esters of polyhydric alcohol and unsaturated carboxylic acid, chlorinated paraffin, and kerosene. Of course, these may be used in combination of two or more kinds. The amount of the capsule wall membrane material used is not particularly limited, either, but the ratio of the wall membrane material to the entire microcapsule is 5 to 70% by weight, preferably 10 to 50% by weight. It is desirable to select.

The amount of the emulsifier used is not particularly limited, but it is generally 1 to 50 parts by weight, preferably 3 to 30 parts by weight per 100 parts by weight of the wall membrane material. Good.

In the microcapsules, an ultraviolet absorber, an antioxidant, an oil-soluble fluorescent dye, a release agent and the like can be added, if necessary, in addition to the oxidizing agent and the photoreducing agent. Further, at the time of microencapsulation, a tin compound, a polyamide compound, an epoxy compound, a polyamine compound or the like can be used together as a reaction accelerator. When a polyamine compound is used, it is desirable to use an aliphatic polyamine compound from the viewpoint of light resistance.

The average particle size of the microcapsules is 0.1 to 0.1
It is desirable to adjust the thickness to be in the range of 5.0 μm, preferably 0.3 to 3.0 μm.

The oxidizing agent and the photoreducing agent used in the present invention are
It can be used as a solid dispersion with a water-soluble polymer by a sand mill or the like. As the water-soluble polymer, various anions, nonions, cations or amphoteric water-soluble polymers are used. Of these, partially saponified polyvinyl alcohol has high emulsion stability and is preferably used. Further, modified polyvinyl alcohol (acetoacetyl group-modified, carboxyl group-modified, silicon-modified, etc.) can be crosslinked to impart water resistance, and is preferably used for the application of the heat-sensitive recording material of the present invention. The dispersed particle size is 0.3μ
The thickness is preferably 10 to 10 μm.

The oxidizing agent and photoreducing agent used in the present invention can be dissolved in a non-aqueous medium and used as an emulsion together with a suitable emulsifier (water-soluble polymer). Examples of preferable high-boiling point non-aqueous medium and emulsifier used in this case include the same ones as those used for preparing the microcapsules. The average particle size of the emulsion used in the present invention is preferably adjusted to be in the range of 0.1 to 3 μm, preferably 0.3 to 2.5 μm in consideration of color development sensitivity.

The oxidizing agent and the photoreducing agent used in the present invention can be used by dissolving them in a non-aqueous medium together with a suitable non-water-soluble resin such as an acrylic resin. Preferred non-aqueous media used in this case include xylene, toluene, ethyl acetate, butyl acetate, methyl ethyl ketone, cyclohexanone, methyl cellosolve, butyl cellosolve and the like.

The heat-sensitive recording material of the present invention can be applied to heat-sensitive recording materials that develop different color tones. In this case, it is desirable that two or more thermosensitive coloring layers that develop different colors are laminated on the support. It is also possible to laminate a thermosensitive coloring layer of a coloring system different from the thermosensitive coloring layer of the present invention containing an oxidative coloring leuco dye and an oxidizing agent. Further, the photo-fixing type thermosensitive coloring layer may contain another coloring thermosensitive coloring material. As such other coloring system,
It can be selected from a combination of an electron-donating dye precursor and an electron-accepting compound used in a conventional heat-sensitive recording material, or a combination of a diazo compound and a coupling component.

In the present invention, as the adhesive contained in the thermosensitive coloring layer, any of water-soluble resin, water-dispersible resin and water-insoluble resin can be used. For example, polyvinyl alcohol
, Starch, modified starch, gum arabic, gelatin, casein, chitosan, methyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, polyvinylpyrrolidone, polyacrylic acid salt, polyacrylic amide,
Polyester resin, styrene-acrylic acid ester copolymer resin, styrene-maleic anhydride copolymer resin, methyl vinyl ether-maleic anhydride copolymer resin, water-soluble resin such as isopropylene-maleic anhydride copolymer resin and polyvinyl acetate, An emulsified dispersion of a water-insoluble resin such as polyacrylic acid ester, polymethacrylic acid ester, polyurethane, polyvinyl chloride, polystyrene butadiene, and polymethylmethacrylate butadiene in an aqueous medium and a non-aqueous medium solution of these water-insoluble resins are prepared. I can give you. Further, these adhesives can be used in combination of two or more kinds.

However, when such an adhesive is mixed with the dispersion liquid of the oxidative coloring leuco dye, the oxidizing agent and the photoreducing agent component, or the solution, the mixed liquid develops color or aggregates,
Alternatively, it is necessary that the viscosity does not become high, and that the formed heat-sensitive recording layer film is tough and has no desensitizing effect. The compounding amount of the adhesive in the thermosensitive coloring layer is 5 to 80 relative to 100 parts by weight of the solid content of the thermosensitive coloring layer.
If the amount is less than 5 parts by weight, the coating film strength is weak, and if it exceeds 80 parts by weight, the sensitivity is lowered.

Further, in order to improve the water resistance of the thermosensitive coloring layer, a crosslinking agent for curing the resin can be used. For example, aldehyde compounds such as glyoxal, polyamine compounds such as polyethyleneimine, epoxy compounds, polyamide resins, melamine resins, dimethylolurea compounds, aziridine compounds, block isocyanate compounds, and ammonium persulfate and ferric chloride, And an inorganic compound such as magnesium chloride, sodium tetraborate, potassium tetraborate or the like, or boric acid, boric acid triester, or boron-based polymer is used in the range of 1 to 10 parts by weight with respect to 100 parts by weight of the solid content of the thermosensitive coloring layer. Is desirable.

In the present invention, a fine particle pigment having a high whiteness and an average particle diameter of 10 μm or less can be used in order to improve the whiteness of the thermosensitive coloring layer and the uniformity of the image. For example, calcium carbonate, magnesium carbonate, kaolin, clay, talc, calcined clay, silica, diatomaceous earth, synthetic aluminum silicate, zinc oxide, titanium oxide,
Inorganic pigments such as aluminum hydroxide, barium sulfate, surface-treated calcium carbonate and silica, and organic pigments such as urea-formalin resin, styrene-methacrylic acid copolymer resin and polystyrene resin can be used. The blending amount of the pigment is preferably 40% by weight or less based on the total solid content of the thermosensitive coloring layer in order not to reduce the coloring density.

In the present invention, various heat fusible substances can be used. As the heat fusible substance, for example,
Stearic acid amide, stearic acid bisamide, oleic acid amide, palmitic acid amide, coconut fatty acid amide,
Fatty acid amides such as behenic acid amide, zinc stearate, calcium stearate, polyethylene wax,
Waxes (or lubricants) such as carnauba wax, paraffin wax, ester wax, terephthalic acid dimethyl ester, terephthalic acid dibutyl ester, terephthalic acid dibenzyl ester, isophthalic acid dibutyl ester, 1-hydroxynaphthoic acid phenyl ester, 1,
2-bis (3-methylphenoxy) ethane, 1,2-diphenoxyethane, 1-phenoxy-2- (4-methylphenoxy) ethane, diphenyl carbonate, p-benzylbiphenyl, 2,2'-methylenebis (4- Methyl-6-
t-butylphenol), 4,4'-butylidenebis (6-t-butyl-3-methylphenol), 1,1,
3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane, 2,2'-methylenebis (4-
Ethyl-6-t-butylphenol), 2,4-di-t
-Butyl-3-methylphenol, hindered phenols such as 4,4'-thiobis (3-methyl-6-t-butylphenol), 2- (2'-hydroxy-5'-methylphenyl) ) -Benzotriazole, 2-hydroxy-4-benzyloxybenzophenone and other sensitizers, antioxidants and UV absorbers.

The heat-fusible substance is preferably contained in the thermosensitive coloring layer in a proportion of 400 parts by weight or less based on 100 parts by weight of the oxidation coloring leuco dye. Further, in order to improve the wetting of the heat-sensitive color developing layer coating and eliminate cissing, it is necessary to add a wetting improver such as acetylene glycol or dialkylsulfosuccinate, a pigment dispersant, a defoaming agent, a fluorescent dye, etc. You can

The support used in the present invention is obtained by heat-kneading a polyolefin resin and a white inorganic pigment, extruding from a die, and stretching in the machine direction. ~ 2
Layered, synthetic paper produced by stretching in the transverse direction to make it semi-transparent or opaque, and thermoplastic resin such as polyethylene, polypropylene, ethylene-vinyl acetate copolymer resin, polyvinyl chloride, polystyrene, polyester alone or Films obtained by biaxially stretching the mixture by heating and kneading the mixture, and opaque films obtained by mixing these resins with a white inorganic pigment and biaxially stretching it, as well as high-quality paper (acidic paper, neutral paper) , Those produced from pulp fibers such as medium-quality paper, recycled paper and coated paper can be used. In order to improve the uniformity of the image on the support made of pulp fibers, it is desirable to apply a heat-sensitive layer after forming a coating layer as an undercoat layer in advance. In this case, the sensitivity can be increased by incorporating an inorganic or organic pigment having a large oil absorption amount or a small apparent specific gravity into the undercoat layer. Further, a conventionally known protective layer may be provided on the heat-sensitive layer to improve sticking to the thermal head, adhesion of lees, and the like.

The coating amount of the heat-sensitive color forming layer is generally preferably 3 to 15 g / m ^{2 in} terms of color forming sensitivity and color forming density. The coating method is air knife method, Mayer bar method, blade method,
Conventional methods used by those skilled in the art, such as a reverse roll method, a slit die method, a multi-slide method, and a curtain coating method can be used. Further, by smoothing the surface of the thermosensitive coloring layer with a super calender, gloss calender, machine calender, etc., the surface property can be enhanced and the recording density and sensitivity can be improved.

In the present invention, so-called tack such as release label processing in which a release paper is provided on the surface opposite to the recording layer of the support through an adhesive layer, and delayed tack processing in which an adhesive layer that develops tackiness by heating is provided. It can also be processed. Furthermore, the back side of this recording sheet can be used as a magnetic recording sheet, thermal transfer sheet, ink jet sheet, xerographic sheet, carbonless sheet, and electrostatic recording sheet, so that it can be used for recording on both front and back sides. You can Of course, a double-sided heat-sensitive recording material can also be used. As the light source for activating the photo-reducing agent when the heat-sensitive recording material of the present invention is optically fixed, various light sources that emit light of a desired wavelength can be used, for example, a fluorescent lamp, a xenon lamp,
Examples include a xenon flash lamp, a mercury lamp, a photographic flash, and a flash.

[0056]

The present invention will be described in more detail with reference to the following examples, but the scope of the present invention is not limited thereto. Unless otherwise specified, parts and% indicate parts by weight and% by weight, respectively.

Example 1 [Preparation of Dispersion Liquid of Composite Fine Particles Containing Oxidative Coloring Type Leuco Dye] 8-diethylamino-11- (2-methoxycarbonylphenyl) -benzo [a] xanthene 5 was used as an oxidative coloring type leuco dye. Part was dissolved in 18 parts of dicyclohexylmethane-4,4′-diisocyanate heated to 100 ° C., and this solution was cooled to 35 ° C., and then 8% polyvinyl alcohol (trade name: Gohsenol GM-, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) at the same temperature. 14 L) 250 parts of an aqueous solution is gradually added, and a homogenizer is used to rotate at 10,000 rpm.
After emulsifying and dispersing by stirring, water 1 is added to the emulsified dispersion.
00 parts was added to homogenize. This emulsified dispersion was heated to 90 ° C. and cured for 10 hours to prepare a dispersion of composite fine particles containing an oxidative coloring leuco dye having an average particle diameter of 1.3 μm.

[Preparation of Microcapsule Liquid Containing Oxidizing Agent] 1 part of chloranil as an oxidizing agent was dissolved in 50 parts of tricresyl phosphate. Furthermore, to this, as a capsule wall material, 25 parts of a 1: 3 adduct of trimethylolpropane and xylylene diisocyanate (trade name: Takenate D-110N manufactured by Takeda Pharmaceutical Co., Ltd.) was added and mixed uniformly.
An aqueous solution of 8% polyvinyl alcohol (trade name: Gohsenol GM-14L, manufactured by Nippon Synthetic Chemical Industry) 1%
It was gradually added to 00 parts, and was emulsified and dispersed at a rotation speed of 10000 rpm using a homogenizer, and then 100 parts of water was added to homogenize. Next, while stirring this emulsion dispersion, the temperature was raised to 60 ° C. and a curing reaction was performed for 3 hours to obtain a microcapsule liquid having an average particle diameter of 1.0 μm.

[Preparation of Thermosensitive Recording Material] Composite fine particle dispersion containing the above-mentioned oxidative coloring leuco dye, microcapsule liquid containing an oxidizing agent and 5% polyvinyl alcohol (trade name: Gohsenol NH manufactured by Nippon Synthetic Chemical Industry Co., Ltd.). −
17) The aqueous solution was dried and then mixed so that the weight ratio was 40:15:15 to obtain a coating liquid. Using a Mayer bar, this coating solution was coated on a commercially available polyethylene terephthalate film having a thickness of 75 μm (trade name: Lumirror E manufactured by Toray) so that the dry weight was 8 g / m ^2, and a heat-sensitive recording material was obtained. It was made.

Example 2 [Preparation of microcapsule liquid containing photoreducing agent] As a photoreducing agent, 5 parts of 2-methyl-1,4-naphthoquinone was dissolved in 50 parts of tricresyl phosphate. Furthermore, as a capsule wall material, 15 parts of a 1: 3 adduct of trimethylolpropane and xylylene diisocyanate (Takenate D-110N, manufactured by Takeda Pharmaceutical Co., Ltd.) was added,
Mix evenly, and mix this mixture with 8% polyvinyl alcohol (Nippon Gosei Kagaku Kogyo, trademark: Gohsenol GM-1).
4 L) was gradually added to 100 parts of the aqueous solution and emulsified and dispersed at a rotation speed of 10,000 rpm using a homogenizer,
100 parts of water was added and homogenized. Next, while stirring this emulsion dispersion, the temperature was raised to 60 ° C. and a curing reaction was performed for 3 hours to obtain a microcapsule liquid having an average particle diameter of 1.0 μm.

[Preparation of Thermosensitive Recording Material] Composite fine particle dispersion containing the oxidative coloring leuco dye used in Example 1,
The weight ratio after drying the microcapsule liquid containing an oxidizing agent, the microcapsule liquid containing the above-mentioned photoreducing agent and a 5% polyvinyl alcohol (manufactured by Nippon Synthetic Chemical Industry, trademark: Gohsenol NH-17) aqueous solution was 40: 15:
The mixture was mixed at 30:15 to obtain a coating liquid. Using a Mayer bar, this coating solution was coated on a commercially available polyethylene terephthalate film having a thickness of 75 μm (trade name: Lumirror E manufactured by Toray) so that the dry weight was 8 g / m ^2, and a heat-sensitive recording material was obtained. It was made.

Example 3 [Preparation of Microcapsule Solution Containing Oxidizing Agent and Photoreducing Agent] 0.5 part of chloranil as an oxidizing agent and 5 parts of 2-methyl-1,4-naphthoquinone as a photoreducing agent and 25 methylene chloride. Parts, then 30 parts tricresyl phosphate were added. Furthermore, as a capsule wall material, a 1: 3 adduct of trimethylolpropane and xylylene diisocyanate (trade name: Takenate D-, manufactured by Takeda Pharmaceutical Co., Ltd.)
110N) 30 parts were added and mixed uniformly, and this mixture was mixed with 8% polyvinyl alcohol (manufactured by Nippon Synthetic Chemical Industry,
Trademark: Gohsenol GM-14L) Gradually added to 56.5 parts of an aqueous solution, and using a homogenizer, the rotation speed is 1000.
After emulsifying and dispersing at 0 rpm, 56.5 parts of water was added to homogenize. Then, while stirring this emulsion dispersion,
The temperature is raised to 0 ° C., the curing reaction is performed for 3 hours, and the average particle size is 1.
A 0 μm microcapsule solution was obtained. [Preparation of Thermosensitive Recording Material] Microcapsule liquid containing the above-mentioned oxidizing agent and photo-reducing agent mixture, composite fine particle dispersion liquid containing the oxidative coloring leuco dye used in Example 1 and 5
% Polyvinyl alcohol (Nippon Gosei Kagaku Kogyo, trade name: Gohsenol NH-17) aqueous solution was mixed so that the weight ratio after drying was 45:30:15 to prepare a coating solution. Using a Mayer bar, apply this coating solution to a commercially available thickness of 7
A 5 μm polyethylene terephthalate film (trade name: Lumirror E, manufactured by Toray Industries, Inc.) was coated so as to have a dry weight of 8 g / m ² , to prepare a heat-sensitive recording material.

Example 4 Instead of 8-diethylamino-11- (2-methoxycarbonylphenyl) -benzo [a] xanthene used in Example 3, bis (2-methyl-4-diethylaminophenyl)-(4-diethylamino). A thermosensitive recording material was prepared in the same procedure as in Example 3 except that phenyl) methane was used.

Example 5 A thermosensitive recording material was prepared in the same manner as in Example 3 except that the dispersion liquid of the composite fine particles containing the oxidative coloring leuco dye was prepared by the following method. [Preparation of Dispersion Liquid of Composite Fine Particles Containing Oxidative Coloring Leuco Dye] As an oxidative coloring leuco dye, 5 parts of 8-diethylamino-11- (2-methoxycarbonylphenyl) -benzo [a] xanthene and methylene chloride 30 were used. And then added to this solution with a molar ratio of trimethylolpropane and hexamethylene diisocyanate of 1: 3 (Takeda Yakuhin Kogyo, trademark: Takenate D-160N, diluting solvent: ethyl acetate, concentration 75%). ) 20 parts were added and mixed uniformly, and this mixed solution was mixed with 5% polyvinyl alcohol (trade name: Gohsenol GM-14, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.).
L) 250 parts of the aqueous solution was gradually added, and the mixture was emulsified and dispersed by stirring with a homogenizer at a rotation speed of 8000 rpm, and then 100 parts of water was added to the emulsion for homogenization. This emulsified dispersion was heated to 45 ° C., and stirring was continued for 7 hours to evaporate and remove methylene chloride and ethyl acetate. Thereafter, the mixed solution was heated to 80 ° C. and a curing reaction was carried out for 6 hours to prepare a dispersion liquid of oxidative coloring leuco dye-containing composite fine particles having an average particle diameter of 1.3 μm.

Example 6 A coating solution prepared in Example 4 was applied onto a thermosensitive recording material prepared in the same manner as in Example 3 so that the dry weight was 8 g / m ^2, and a two-color thermosensitive material was developed. A recording material was prepared.

Comparative Example 1 Example 1 was repeated except that a microcapsule solution containing an oxidative coloring leuco dye prepared by the following method was used in place of the dispersion liquid of the composite fine particles containing an oxidative coloring leuco dye used in Example 1. A thermal recording material was prepared in the same manner as in Example 1. [Preparation of Microcapsule Liquid Containing Oxidative Coloring Type Leuco Dye] As an oxidative coloring type leuco dye, 5 parts of 8-diethylamino-11- (2-methoxycarbonylphenyl) -benzo [a] xanthene was dissolved in 30 parts of methylene chloride. Then, 6 parts of tricresyl phosphate was added. Furthermore, as a capsule wall material, a molar ratio of trimethylolpropane to hexamethylene diisocyanate is 1:
Addendum 3 (Takenate D-1 manufactured by Takeda Pharmaceutical Co., Ltd.)
24 parts of 60N, diluted solvent: ethyl acetate, concentration 75%) were added and mixed uniformly, and this mixed solution was 65 parts of 8% polyvinyl alcohol (Nippon Gosei Kagaku Kogyo KK, trademark: Gohsenol GM-14L) aqueous solution. Was gradually added, and the mixture was emulsified and dispersed at a rotation speed of 10,000 rpm using a homogenizer, and then 100 parts of water was added to homogenize. Next, while stirring this emulsion dispersion, the temperature was raised to 90 ° C. and a curing reaction was performed for 3 hours to obtain a microcapsule liquid having an average particle diameter of 1.2 μm.

Comparative Example 2 The microcapsule liquid containing the oxidative coloring leuco dye used in Comparative Example 1 was used in place of the dispersion liquid of the composite fine particles containing the oxidative coloring leuco dye used in Example 3. A thermal recording material was prepared in the same manner as in Example 3.

Comparative Example 3 The oxidative coloring leuco dye 8-diethylamino-11- (2-methoxycarbonylphenyl) -benzo [a] xanthene used in Example 3 was replaced by a diazo compound 2,5-diethoxy- ( Examples except that p-tolylthio) benzenediazonium hexafluorophosphate, a photoreducing agent 2-methyl-1,4-naphthoquinone, and a coupler 4-pyrazolic acid were used in place of the oxidizing agent. A thermosensitive recording material was prepared in the same procedure as in 3.

[Evaluation of Normal Thermal Paper] (Coloring Test) Using the thermal head (manufactured by Kyocera Corp.), the thermal recording materials prepared in Example 1 and Comparative Example 1 were adjusted to 30 mJ / mm ² per unit area. Image recording was performed by adjusting the applied voltage and pulse width. Macbeth densitometer (made by Macbeth, model number: RD-91
It was measured in 4).

(Preservation test) In order to evaluate the preservability of a blank sheet, the heat-sensitive recording material after the above-mentioned color development / fixing discoloration test was allowed to stand at 60 ° C. and 90% for 100 hours, and then the whiteness of the background part ( Hunter whiteness, JIS P8123) was measured.

(Pressure resistance test) In order to evaluate the pressure resistance, the whiteness was measured after applying a pressure of 50 kg / m ² to the thermal recording material for 30 seconds.

[Evaluation of Light-Fixing Thermal Paper] (Coloring / Fixing Discoloration Test) The thermal recording materials prepared in Examples 2 to 5 and Comparative Examples 2 to 3 were used in a unit area by using a thermal head (manufactured by Kyocera Corporation). 30mJ / mm ²
The image was recorded by adjusting the applied voltage and the pulse width so that After printing, using a 420 nm UV lamp, irradiate UV light for 30 seconds from a distance of 2 cm between the light source and the heat-sensitive surface,
The image was fixed, and the density of the colored portion and the whiteness of the background portion were measured.

(Fixing Property Test) After fixing, printing was further performed on the uncolored part under the same conditions as above, and the density of the colored part was measured and used as an index of fixing property.

(Storability test) In order to evaluate the storability of a blank sheet, the heat-sensitive recording material after the color-forming / fixing discoloration test was tested under the same conditions as the storability test of the normal heat-sensitive paper.

(Pressure Resistance Test) In order to evaluate the pressure resistance, an uncolored and unfixed thermal recording material was tested under the same conditions as the pressure resistance test of the normal thermal paper.

[Evaluation of two-color thermal paper] 2 prepared in Example 6
Using a thermal head (manufactured by Kyocera Co., Ltd.) for the color-developing recording material, the applied voltage and pulse width were adjusted so as to be 20 mJ / mm ² per unit area, and image recording of the first color was performed. After printing, 420 nm UV light was irradiated for 30 seconds to fix the first color image, and the applied voltage and pulse width were adjusted so that the unit area was 40 mJ / mm ^2, and the second color image was recorded. After the printing of the second color, UV irradiation is further performed for 2 minutes to fix the image of the second color, and the density of the first and second colors in the color-developed portion of the first color and the background with a Macbeth densitometer (Macbeth RD-914). Whiteness (Hunter whiteness, JI
S P8123) was measured. In addition, in order to evaluate the storability of the blank portion, after leaving the heat-sensitive recording material after the above-mentioned color development / fixing discoloration test at 60 ° C. and 90% for 100 hours,
The whiteness of the background part was measured. Further, in order to evaluate the pressure resistance, the whiteness was measured after applying a pressure of 50 kg / m ² to the thermal recording material for 30 seconds.

The above results are summarized in Tables 1, 2 and 3 below. In the color development / light discoloration test, if the color density is 1.20 or more, the whiteness is 75 or more, which is a level having no practical problem. In the fixing property test, the color density is 0.20 or less, and the storage property has a whiteness of 70 or more, which is a level with no practical problem, and 75 or more is a sufficient whiteness with good appearance. Regarding the pressure resistance, if the whiteness is 70 or higher, there is no problem in practical use, and if the whiteness is 75 or higher, the whiteness is good and looks good.

[0078]

[Table 1]

[0079]

[Table 2]

[0080]

[Table 3]

[0081]

As is clear from Tables 1, 2, and 3, the heat-sensitive recording material of the present invention has high recording sensitivity and has very little discoloration of the white paper portion due to pressure and heat or humidity. Yes, it is extremely useful in practice.

Claims (4)

[Claims] 1. An oxidative coloring leuco dye and a polymer-forming raw material for forming polyurea or polyurethane-polyurea by polymerization are dissolved and mixed in a water-insoluble organic solvent having a boiling point of 100 ° C. or lower, and this organic solvent solution is aqueous. Composite fine particles prepared by emulsifying and dispersing in a medium, heating the emulsion dispersion to volatilize and remove the organic solvent, and then polymerizing the polymer-forming raw material. 2. A polymer-forming raw material for forming polyurea or polyurethane-polyurea by polymerization is used as a solvent, and a solution containing an oxidative coloring leuco dye as a solute is emulsified and dispersed in an aqueous medium, and the emulsified dispersion is heated. Composite fine particles prepared by polymerizing the polymer-forming raw material. 3. A thermosensitive recording material comprising a support and a thermosensitive coloring layer which develops a color when heated, wherein the thermosensitive coloring layer contains the composite fine particles according to claim 1 and an oxidizing agent. Heat sensitive recording material 4. The thermosensitive recording material according to claim 3, wherein the thermosensitive coloring layer contains a photoreducing substance.