JP2003103937A - Dye precursor compound fine particle and multicolor heat sensitive recording body employing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multicolor heat sensitive recording body excellent in recorded image clarity and color separability. SOLUTION: In the multicolor heat sensitive recorded body, a heat sensitive recording layer containing dye precursor compound fine particles including a colorless or light-colored dye precursor, the polymer of multivalent isocyanate compounds and a resin having a softening temperature of 50 to 150 deg.C, at least one or more kinds of dye precursors developing color tones different from those of the dye precursors including in the dye precursor compound fine particles and an organic developer developing color through the reaction with these dye precursors is provided on a support.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to composite fine particles of a dye precursor and a resin, which can be used for heat-sensitive recording materials, pressure-sensitive copying paper and the like.

[0002]

2. Description of the Related Art A heat-sensitive recording system is provided with a heat-sensitive recording layer mainly composed of an electron-donating, usually colorless or light-colored dye precursor and an electron-accepting developer on a support. By heating with a pen, laser light, or the like, the dye precursor and the developer are allowed to react instantaneously to obtain a recorded image. JP-B-43-4160 and 45-1.
No. 4039 is disclosed. Such a thermosensitive recording medium does not require developing and fixing, and a very clear image can be obtained with a relatively simple device. In addition, the equipment is relatively inexpensive and compact, has the advantages of easy maintenance, noise generation, etc., and is used in a wide range of fields such as facsimiles, printers, measurement recorders, labels, ticket vending machines, etc. It is used in. With respect to the thermosensitive recording medium, the required quality has been diversified with the expansion of its applications, and examples thereof include high sensitivity, image stabilization, and multicolor recording. In particular, with regard to multicoloring, it is possible to record a character or figure to be emphasized in a color tone different from that of other portions, and thus there are advantages such as excellent visual effects. As a multicolor thermosensitive recording medium, a plurality of coloring layers each of which develops a different color tone are provided on a support, and a laminated type in which a recording image is formed by utilizing a difference in heating temperature or thermal energy and in the same coloring layer A single layer type is known which contains two or more dye precursors that develop different color tones. In the multi-layer type, a high-temperature color-developing layer and a low-temperature color-developing layer that develops color in a temperature range lower than that of the high-temperature color-developing layer or heat energy are laminated, and multicolored by erasing or adding colors. In the decoloring type, only the low temperature coloring layer develops color when heated at low temperature, and when heating at high temperature, the decoloring agent that has a decoloring effect on the coloring system of the low temperature coloring layer acts, and only the high temperature coloring layer develops color. Is to do. This method has an advantage that the color tone can be freely selected, but it is necessary to add a large amount of a decoloring agent to obtain a sufficient decoloring effect for the low temperature color developing layer, which deteriorates the storage stability of the recorded image. In addition, since a large amount of heat energy is consumed for melting the decoloring agent, there is a problem that recording sensitivity is lowered.

In the additive type, the low temperature coloring layer is colored by low temperature heating, and the high temperature coloring layer is further colored by high temperature heating so that both coloring layers are colored. At that time, the colors of both layers are mixed to obtain. To
Substantially, it was essential to make the high-temperature color-developing layer a black color-developing system. In addition, since the black image of the high-temperature color-developing layer is obtained by mixing with the color-developing system of the low-temperature color-developing layer, the color of the low-temperature color-developing layer is fogged on the black image, and the difference in the color-developing color tone is unclear, especially in the peripheral area The mixed color is extremely hard to produce a clear black color. Further, when exposed to a high-temperature atmosphere such as on the dashboard of a car, the high-temperature color-developing layer develops color, causing a problem such as fogging of the low-temperature color-tone or blackening. Also, recently
The heat-sensitive recording material is also used for many purposes such as receipts, and at the present time, no one having sufficient storability of recorded images has been obtained. The use of microcapsules is known for a single-layer type multicolor thermosensitive recording medium. JP-A-60-244594 describes that the wall of a microcapsule containing a basic colorless dye and an organic solvent in its core becomes impermeable by heating so that the dye can penetrate. . In JP-A-4-101885, a solution of a dye precursor and a microcapsule wall material dissolved in a water-insoluble or insoluble organic solvent is emulsified and dispersed in a hydrophilic colloid solution, and then the temperature of the system is increased. A production method is described in which the pressure inside the reaction vessel is reduced to distill off the organic solvent and form the walls of the microcapsules. However, in the case of the above-mentioned JP-A-60-242093, when the dyes which develop different color tones are separately encapsulated in microcapsules, the coloration sensitivity is lowered because they are completely isolated from the capsule wall, resulting in poor color separation. There is a problem. Further, the microcapsules obtained by the method described in JP-A-4-101885 are easily broken by pressure. The microcapsule of JP-A-9-76634 is a method in which an oil solution containing a dye as a solute and an organic solvent as a solvent is emulsified and dispersed in an aqueous liquid to form a wall film composed of a polymer substance around the oil droplets. However, in the case of microcapsules using an organic solvent, the color reaction between the leuco dye and the color developer is caused via the organic solvent, and the background color is deteriorated or friction is generated. There is a problem that it easily gets dirty. Also, Japanese Patent Laid-Open No. 2000-17725
The No. 1 microcapsules are easily broken, and the multicolor heat-sensitive recording material of sufficient quality cannot be obtained because of poor background color and scratch resistance. In order to make up for the drawbacks of such microcapsules, JP-A-9-142025 and JP-A-9-290 have been proposed.
No. 565 and the like disclose the use of composite fine particles obtained by compositing a dye precursor with a polymer substance composed of polyurea or polyurethane. However, although this method is improved in terms of capsule destruction, high-temperature color development is still insufficient.

[0004]

In view of the above circumstances, the present invention provides a clear color tone in each of low temperature color development and high temperature color development, and is excellent in color separation without fog between the low temperature color development color and the high temperature color development color. It is an object to provide a color heat-sensitive recording material.

[0005]

Means for Solving the Problems As a result of intensive studies for solving the above problems, the present inventors have accomplished the present invention by using specific dye precursor composite fine particles. That is, the present invention is a colorless to light-colored dye precursor,
The present invention relates to a dye precursor composite fine particle containing a polymer of a polyvalent isocyanate compound and a resin having a melting point or a softening temperature in the range of 50 to 150 ° C. Furthermore, the multicolor heat-sensitive recording material of the present invention has at least one kind of dye precursor complex fine particles and a dye precursor contained in the dye precursor complex fine particles, which develops a different color tone on the support. The present invention is characterized in that a thermosensitive coloring layer containing the dye precursor of (1) and an organic developer which reacts with these dye precursors to develop a color is provided. Dye precursor composite fine particles of the present invention (hereinafter,
It may be simply referred to as "composite fine particles"), which is suitable for a coloring material having a high-temperature color tone, and has a melting point or a softening temperature of 50 in addition to a dye precursor and a polymer of a polyvalent isocyanate compound.
It contains a resin in the range of 150 ° C. With such a structure, the color development of the composite fine particles is suppressed in the recording in the low temperature or low energy region, and a clear low temperature color tone is obtained, and the composite fine particles are contained in the recording in the high temperature or the high energy region. A heat-sensitive recording material having a clear color tone of the dye precursor is obtained. The reason for this is not clear, but it is considered as follows. The conventional composite fine particles of a dye precursor and a polymer substance are in a solid solution state in which the dye precursor and the polymer substance are uniformly mixed at the molecular level, and a large amount is required for melting and coloring the polymer substance. Energy is needed. Therefore, it is considered that ordinary coloring energy cannot provide sufficient coloring property. On the other hand, the present invention, by the action of the resin having a specific melting point or softening temperature, compared to the case where it is composed only of a dye precursor and a polymer of a polyvalent isocyanate compound, melting point drop occurs in the composite fine particles It will be easier to do.
However, the degree of easiness of melting is higher than the temperature at which the dye precursor, which is not contained in the composite fine particles, develops color, and does not easily melt up to the recording temperature or recording energy of the high-color color tone, so that it does not come into contact with the recording temperature. It is desirable to be able to melt instantly when doing. The present invention, by further containing a resin having a melting point or a softening temperature in a specific range in the composite fine particles of the dye precursor and the polyvalent isocyanate polymer, it is possible to obtain such composite fine particles having excellent thermal responsiveness. It has been made that it is done.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below. First, a method for producing the dye precursor composite fine particles used in the present invention will be described below. As the dye precursor contained in the composite fine particles, various known ones can be used,
For example: <Black color-forming dye precursor> 3-diethylamino-6-methyl-7-anilinofluorane 3-diethylamino-6-methyl-7- (o, p-dimethylanilino) fluorane 3-diethylamino-6-methyl- 7- (m-trifluoromethylanilino) fluorane 3-diethylamino-6-methyl-7- (o-chloroanilino) fluorane 3-diethylamino-6-methyl-7- (p-chloroanilino) fluorane 3-diethylamino-6- Methyl-7- (o-fluoroanilino) fluorane 3-diethylamino-6-methyl-7- (m-methylanilino) fluorane 3-diethylamino-6-methyl-7-n-octylanilinofluorane 3-diethylamino-6 -Methyl-7-benzylaminofluorane 3-diethylamino-6-methyl-7 -Dibenzylaminofluorane 3-diethylamino-6-ethoxyethyl-7-anilinofluorane 3-diethylamino-7- (m-trifluoromethylanilino) fluorane 3-diethylamino-7- (o-chloroanilino) fluorane 3 -Diethylamino-7- (p-chloroanilino) fluorane 3-diethylamino-7- (o-fluoroanilino) fluorane 3-dibutylamino-6-methyl-7-anilinofluorane 3-dibutylamino-6-methyl-7 -(O, p-dimethylanilino) fluorane

3-dibutylamino-6-methyl-7-
(O-Chloroanilino) fluorane 3-dibutylamino-6-methyl-7- (p-chloroanilino) fluorane 3-dibutylamino-6-methyl-7- (o-fluoroanilino) fluorane 3-dibutylamino-6-methyl -7- (m-Trifluoromethylanilino) fluorane 3-dibutylamino-6-ethoxyethyl-7-anilinofluorane 3-dibutylamino-6-methyl-7- (p-methylanilino) fluorane 3-dibutylamino -7- (o-Chloroanilino) fluorane 3-dibutylamino-7- (o-fluoroanilino) fluorane 3-di-n-pentylamino-6-methyl-7-anilinofluorane 3-di-n-pentyl Amino-6-methyl-7- (p-
Chloroanilino) fluorane 3-di-n-pentylamino-7- (m-trifluoromethylanilino) fluorane 3-di-n-pentylamino-6-chloro-7-anilinofluorane 3-di-n-pentyl Amino-7- (p-chloroanilino) fluorane 3-pyrrolidino-6-methyl-7-anilinofluorane 3-piperidino-6-methyl-7-anilinofluorane 3- (N-methyl-N-propylamino) -6-Methyl-7-anilinofluorane 3- (N-methyl-N-cyclohexylamino) -6-
Methyl-7-anilinofluorane 3- (N-ethyl-N-cyclohexylamino) -6-
Methyl-7-anilinofluorane 3- (N-ethyl-N-xylamino) -6-methyl-
7- (p-chloroanilino) fluorane 3- (N-ethyl-p-toluidino) -6-methyl-
7-anilinofluorane 3- (N-ethyl-N-isoamylamino) -6-methyl-7-anilinofluorane

3- (N-Ethyl-N-tetrahydrofurfurylamino) -6-methyl-7-anilinofluorane 3- (N-ethyl-N-isobutylamino) -6-methyl-7-anilinoflu Oran 3- (N-ethyl-N-ethoxypropylamino) -6
-Methyl-7-anilinofluorane 2-chloro-3-methyl-6- [p- (p-phenylaminophenyl) aminoanilino] fluorane 2-chloro-6- [p- (p-dimethylaminophenyl) aminoanilino] Fluoran 3,3-bis [2- (p-dimethylaminophenyl)-
2- (p-methoxyphenyl) ethenyl] -4,5,
6,7-Tetrabromophthalide 3,3-bis [2- (p-dimethylaminophenyl)-
2- (p-methoxyphenyl) ethenyl] -4,5,
6,7-Tetrachlorophthalide 3,3-bis [1,1-bis (4-pyrrolidinophenyl) ethylene-2-yl] -4,5,6,7-tetrabromophthalide 3,3-bis [1- (4-methoxyphenyl) -1-
(4-Pyrrolidinophenyl) ethylene-2-yl]-
4,5,6,7-Tetrachlorophthalide 3-diethylamino-6-chloro-7-anilinofluorane 3-diethylamino-6-chloro-7-p-methylanilinofluorane 3-dibutylamino-6- Chloro-7-anilinofluorane 3- (N-ethyl-N-isoamylamino) -6-chloro-7-anilinofluorane 3-diethylamino-7-methylaminofluorane

<Blue Coloring Dye Precursor> 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide 3,3-bis (p-dimethylaminophenyl) phthalide 3,3-bis (p -Diethylaminophenyl) -6-dimethylaminophthalide 3,3-bis (p-dimethylaminophenyl) -6-di-n-propylaminophthalide tris (4-dimethylaminophenyl) methane 3-diethylamino-6-methyl -7-n-octylaminofluorane 3-diethylamino-6-methyl-7-benzylaminofluorane 3-diethylamino-7-benzylaminofluorane 3-diethylamino-6-methyl-7-diphenylmethylaminofluorane 3- Diethylamino-7-dinaphthylmethylaminofluorane 3- (4-diethylamino -2-Ethoxyphenyl)-
3- (1-ethyl-2-methylindol-3-yl)
-4-azaphthalide 3- (4-diethylamino-2-ethoxyphenyl)-
3- (1-octyl-2-methylindol-3-yl) -4-azaphthalide 3- (4-cyclohexylethylamino-2-methoxyphenyl) -3- (1-ethyl-2-methylindol-3-yl) ) -4-Azaphthalide 3- (4-cyclohexylmethylamino-2-methoxyphenyl) -3- (1-ethyl-2-methylindol-3-yl) -4-azaphthalide 3- (4-diethylamino-2-n -Hexyloxyphenyl) -3- (1-ethyl-2-methylindole-
3-yl) -4-azaphthalide <green color developing dye precursor> 3-diethylamino-7-anilinofluorane 3-diethylamino-6-methyl-7-dibenzylaminofluorane 3-diethylamino-5-methyl-7 -Dibenzylaminofluorane 3- (N-ethyl-N-hexylamino) -7-anilinofluorane 3-pyrrolidino-7-cyclohexylaminofluorane 3-diethylamino-7-cyclohexylaminofluorane 3- (N- p-toluyl-N-ethylamino) -7-
(N-Methyl-N-phenylamino) fluorane 3-diethylamino-7- (N-methyl-N-phenylamino) fluorane 3-diethylamino-7-n-octylaminofluorane 3-diethylamino-7- (N-cyclohexyl -N-
Benzylamino) fluorane 3-diethylamino-7- (di-p-chlorobenzylamino) fluorane 3- (N-ethyl-N-hexylamino) -7- (N-
Methyl-N-phenylamino) fluorane 3-pyrrolidyl-7-dibenzylaminofluorane 3-dibutylamino-7- (o-chlorobenzylamino) fluorane 3-diethylamino-6-ethoxyethyl-7-anilinofluorane

<Red color forming dye precursor> 3-diethylamino-6-methyl-7-chlorofluorane 3-diethylamino-7-chlorofluorane 3-diethylamino-6-methylfluorane 3-diethylamino-7-methylfluor Olane 3-diethylamino-benzo [a] fluorane 10-diethylamino-4-dimethylaminobenzo [a] fluorane 3-diethylamino-7- (di-p-methylbenzylamino) fluorane 3-diethylamino-6-methyl-7-di Benzylaminofluorane 3-diethylamino-7-methylfluorane 3- (N-ethyl-N-isoamylamino) -benzo [a] fluorane 3- (N-ethyl-N-p-toluylamino) -7-methylfluor Oran 3-diethylamino-6-chloro-7-methylfluorane 3-di Ethylamino-7-methylfluorane 3-dibutylamino-6-methylfluorane 3-dibutylamino-6-methyl-7-chlorofluorane 3-cyclohexylamino-6-chlorofluorane 3-diethylamino-6,8- Dimethylfluorane 3-dibutylamino-6-methyl-7-bromofluorane 3,6-bis (diethylamino) fluorane-γ-
(4'-Nitro) anilinolactam 3,3-bis (1-ethyl-2-methylindole-3)
-Yl) phthalide 3,3-bis (1-n-butyl-2-methylindol-3-yl) phthalide 3,6-bis (diethylamino) fluorane-γ-anilinolactam These dye precursors are used alone. Alternatively, two or more kinds may be mixed and used. In the present invention, a black color recording material is preferably used because a multicolor thermosensitive recording material having good color developability can be obtained.

The polyvalent isocyanate compound used in the present invention is a compound which forms a polyurea or a polyurethane-polyurea by reacting with water, and may be a polyvalent isocyanate compound alone or a polyvalent isocyanate compound. Also, it may be a mixture with a polyol that reacts with it, or an adduct of a polyvalent isocyanate compound with a polyol, and a multimer such as a biuret body or an isocyanurate body. For example, as the polyvalent isocyanate compound, m-phenylene diisocyanate, p-phenylene diisocyanate, 2,6-tolylene diisocyanate, 2,4-tolylene diisocyanate, naphthalene-1,4-diisocyanate, diphenylmethane-
4,4'-diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, 5-isocyanato-1
-(Isocyanatomethyl) -1,3,3-trimethylcyclohexane, 1,3-bis (isocyanatomethyl) cyclohexane, tetramethylxylylene diisocyanate, 3,3'-dimethyldiphenylmethane-4,4'-
Diisocyanate, xylylene-1,4-diisocyanate, 4,4'-diphenylpropane diisocyanate, trimethylene diisocyanate, hexamethylene diisocyanate, propylene-1,2-diisocyanate, butylene-1,2-diisocyanate, cyclohexylene-1,2- Diisocyanates such as diisocyanate and cyclohexylene-1,4-diisocyanate,
Triisocyanates such as 4,4 ', 4 "-triphenylmethane triisocyanate and toluene-2,4,6-triisocyanate, 4,4'-dimethyldiphenylmethane-2,2', 5,5'-tetraisocyanate And the like, etc. Examples of adducts of polyvalent isocyanate compounds and polyols include trimethylolpropane adduct of hexamethylene diisocyanate, trimethylolpropane adduct of 2,4-tolylene diisocyanate, and xylylenediene. Isocyanate prepolymers such as trimethylolpropane adduct of isocyanate and hexanetriol adduct of tolylene diisocyanate can be used, and polyvalent isocyanate compounds such as biuret of hexamethylene diisocyanate, A multimer such as a socyanurate body can also be used in the present invention. These may be used alone or in a mixture of two or more kinds, among which xylylene diisocyanate and xylylene diisocyanate may be used. It is preferable to contain at least one polyvalent isocyanate compound selected from trimethylolpropane adduct, hexamethylene diisocyanate, trimethylolpropane adduct of hexamethylene diisocyanate, and dicyclohexylmethane diisocyanate.

Examples of the polyol compound 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-dihydroxybutane, 1,2-dihydroxybutane, 1,3-dihydroxybutane, 2,2-dimethyl-1,3-propanediol, 2,4-pentanediol, 2,5-hexanediol, 3- Methyl-1,5-
Fats such as pentanediol, 1,4-cyclohexanedimethanol, dihydroxycyclohexane, diethylene glycol, 1,2,6-trihydroxyhexane, phenylethylene glycol, 1,1,1-trimethylolpropane, hexanetriol, pentaerythritol and glycerin Group polyols, 1,4-di (2-hydroxyethoxy) benzene, 1,3-di (2-hydroxyethoxy) benzene and other aromatic polyhydric alcohols, condensation products of alkylene oxides, p-xylylene glycol, m-xylylene glycol, α, α′-dihydroxy-p-diisopropylbenzene, 4,4′-dihydroxydiphenylmethane, 2- (p, p′-dihydroxydiphenylmethyl) benzyl alcohol, 4,4′-
Isopropylidene diphenol, 4,4'-dihydroxydiphenyl sulfone, 4,4'-dihydroxydiphenyl sulfide, 4,4'-isopropylidenediphenol ethylene oxide adduct, 4,4'-isopropylidenediphenol propylene oxide Adjunct,
Examples thereof include acrylates having a hydroxy group in the molecule such as 2-hydroxyacrylate.

As the polyamine compound, for example, ethylenediamine, trimethylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, p-phenylenediamine, m-phenylenediamine, piperazine, 2-methylpiperazine, 2,5.
-Dimethylpiperazine, 2-hydroxytrimethylenediamine, diethylenetriamine, triethylenetriamine, triethylenetetramine, diethylaminopropylamine, tetraethylenepentamine, amine adducts of epoxy compounds, and the like. Of course, these polyol compounds and polyamine compounds are not limited to the above compounds, and two or more kinds may be used in combination as required. Further, as the resin having a melting point or softening temperature in the range of 50 to 150 ° C. used in the present invention, a thermoplastic resin can be used, and examples thereof include polystyrene, polyethylene, polypropylene, polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymer. Resin, ethylene-vinyl chloride copolymer resin, ethylene / vinyl acetate-vinyl chloride graft copolymer resin, vinylidene chloride resin, vinyl chloride resin, chlorinated vinyl chloride resin, chlorinated polyethylene, chlorinated polypropylene, phenoxy resin, fluorine resin, polyacetal resin , Polyamide resin, polyamideimide, polyarylate, thermoplastic polyimide resin, polyetherimide resin, polyetheretherketone, polyethylene terephthalate, polybutylene terephthalate, polycarbonate resin, polysulfone resin, polyparamethyl Styrene resins, polyphenylene ether, polyphenylene sulfide resin, a methacrylic resin, ionomer resin, AAS resin, AES resin, AS resin, ABS resin, ACS resin, MBS resin and the like. Among these, especially the softening temperature is 80 to 1.
Those having a temperature of 20 ° C. are highly effective and are preferably used. Of these, polystyrene is most preferably used because it has high solubility of the dye precursor and excellent thermal responsiveness of the composite fine particles. In addition, in the present invention, the softening temperature means a remarkable fluidity when the temperature exceeds an increasing temperature, which is described in "Physical Chemistry Dictionary" (Iwanami Shinsho, Fourth Edition, July 5, 1998). It is the temperature at which a softened state occurs. The content ratio of the resin having the melting point or the softening temperature in the range of 50 to 150 ° C. can be adjusted according to the required performance level, but if the content is too small, the action of the resin is difficult to be exhibited. If too much, it becomes difficult to form composite fine particles having an appropriate particle size. In the present invention, the amount is preferably 10% by weight or more, preferably 25% by weight or more, and 400% by weight or less, preferably 100% by weight or less, based on 1 part of the polyvalent isocyanate compound.
Next, as a solvent for dissolving these materials, ethyl acetate, methyl acetate, butyl acetate, methylene chloride, butyl chloride, propyl chloride and the like can be mentioned. It is preferable that the solvent sufficiently dissolves the dye precursor, the polyvalent isocyanate compound, and the resin having a melting point or a softening temperature in a specific range. The dye precursor composite fine particles of the present invention include n-butanol, alcohols such as ethylene glycol, benzotriazole-based, benzophenone-based,
It is also possible to contain a salicylic acid-based or benzoxazinone-based ultraviolet absorber, or a hindered amine-based or hindered phenol-based antioxidant. Further, in order to increase the color development sensitivity, a sensitizer as known in heat-sensitive recording materials can be added. Using the above materials,
The dye precursor composite fine particles of the present invention are, for example, a dye precursor,
A polyisocyanate compound and a resin having a melting point or a softening temperature in the range of 50 to 150 ° C. are dissolved in a low boiling point water-insoluble organic solvent, and this solution is then dissolved in a water-dispersible medium containing a protective colloid substance. It can be produced by polymerizing these polymer-forming materials by emulsifying and dispersing in, and optionally mixing a reactive substance such as polyamine, and then heating the emulsified dispersion. it can.

Specifically, as an example, first, a dye precursor, a polyvalent isocyanate compound, a melting point or a softening temperature is 50 to 150 in an organic solvent having a boiling point of 100 ° C. or less.
The resin in the range of 0 ° C is dissolved between 30 ° C and 100 ° C, and then emulsified and dispersed using an emulsifier. At that time, the emulsification is performed at a rotation speed of 10,000 rotations for 10 minutes or less. As the emulsifier to be used, a known dispersant is used, but polyvinyl alcohol is particularly preferable. Then, 50 ℃ ~ 1
The organic solvent is evaporated by heating at 00 ° C for 1 to 3 hours,
Further, the polyvalent isocyanate compound is polymerized by reacting at that temperature for 1 to 3 hours. Then, it is cooled to room temperature to prepare a dispersion liquid of composite fine particles. In addition,
Using a polyvalent isocyanate compound as a solvent, dissolving a solute containing a dye precursor therein, and emulsifying and dispersing the resulting solution in a hydrophilic colloid aqueous solution to participate in the polymerization reaction of the polyvalent isocyanate compound. There is also a method.
The obtained composite fine particles have an average particle diameter of 0.1 μm to 10.0.
It is desirable that the particles are atomized to a particle size of μm, preferably 1 μm or less, because the coloring sensitivity is further improved. In the present invention, the use of the above-mentioned composite fine particles makes it possible to obtain a multicolor heat-sensitive recording material having excellent thermal response. The melting point or softening temperature of the composite fine particles is 100 ° C. or higher, more preferably 110 ° C. or higher, lower than 150 ° C., and further 13
It is preferably 0 ° C. or lower. Further, in the present invention, the ratio of the dye precursor contained in the composite fine particles can be appropriately adjusted according to the desired performance, but is preferably 20 to 80% by weight of the total weight of the composite fine particles, and more preferably 4
It is 0 to 70% by weight. The multicolor thermosensitive recording medium of the present invention further contains, in the thermosensitive recording layer, at least one dye precursor which develops a color tone different from that of the dye precursor contained in the dye precursor composite fine particles. These can be appropriately selected from various known dye precursors such as the above-mentioned dye precursors, but those that develop color at a lower temperature than the composite fine particles are desirable. Further, these are dispersed and used in a form used in a general thermal recording material, that is, in a solid fine particle state.

Further, an organic microparticle that causes color formation by reacting with the dye precursor composite fine particles and the dye precursor which is colored at a temperature different from that of the dye precursor contained in the composite fine particles and which is colored at a temperature lower than that of the composite fine particles. As the colorant, activated clay, attapulgite, colloidal silica, inorganic acid substances such as aluminum silicate, benzyl 4-hydroxybenzoate, ethyl 4-hydroxybenzoate, normal propyl 4-hydroxybenzoate, isopropyl 4-hydroxybenzoate, 4-Hydroxybenzoic acid such as butyl 4-
Hydroxybenzoates, dimethyl 4-hydroxyphthalate, diisopropyl 4-hydroxyphthalate,
4-hydroxyphthalic acid diesters such as 4-hydroxyphthalic acid dibenzyl and 4-hydroxyphthalic acid dihexyl, phthalic acid such as phthalic acid monobenzyl ester, phthalic acid monocyclohexyl ester, phthalic acid monophenyl ester and phthalic acid monomethylphenyl ester Monoesters, bis (4-hydroxy-3-tert-
Butyl-6-methylphenyl) sulfide, bis (4-
Hydroxy-2,5-dimethylphenyl) sulfide,
Bishydroxyphenyl sulfides such as bis (4-hydroxy-5-ethyl-2-methylphenyl) sulfide, 3,4-bisphenol A, 1,1-bis (4-
Hydroxyphenyl) ethane, 2,2-bis (4-hydroxyphenyl) propane <bisphenol A>, bis (4-hydroxyphenyl) methane <bisphenol F
>, 2,2-bis (4-hydroxyphenyl) hexane, tetramethylbisphenol A, 1,1-bis (4
-Hydroxyphenyl) -1-phenylethane, 1,4
-Bis (2- (4-hydroxyphenyl) propyl) benzene, 1,3-bis (2- (4-hydroxyphenyl) propyl) benzene, 1,4-bis (4-hydroxyphenyl) cyclohexane, 2,2 ' -Bis- (4-
Hydroxy-3-isopropylphenyl) propane,
Bisphenols such as 1,4-bis (1- (4- (2- (4-hydroxyphenyl) -2-propyl) phenyl) ethyl) benzene, 4-hydroxy-4′-isopropoxydiphenyl sulfone <D-8 >, 4-hydroxy-4′-methoxydiphenyl sulfone, 4-hydroxy-4′-normal propoxydiphenyl sulfone and other 4-hydroxyphenyl aryl sulfones, bis (4-hydroxyphenyl) sulfone <bisphenol S>, tetramethylbisphenol S, bis (3-ethyl-4-hydroxyphenyl) sulfone, bis (3-propyl-4-hydroxyphenyl) sulfone, bis (3
-Isopropyl-4-hydroxyphenyl) sulfone,
Bis (3-tert-butyl-4-hydroxy-6-methylphenyl) sulfone, bis (3-chloro-4-hydroxyphenyl) sulfone, bis (3-bromo-4-hydroxyphenyl) sulfone, 2-hydroxyphenyl-
Bishydroxyphenyl sulfones such as 4′-hydroxyphenyl sulfone, 4-hydroxybenzenesulfonate, 4-hydroxyphenyl-p-tolylsulfonate, 4-hydroxyphenylarylsulfo such as 4-hydroxyphenyl-p-chlorobenzenesulfonate Naates, benzyl 4-hydroxybenzoyloxybenzoate, ethyl 4-hydroxybenzoyloxybenzoate, normal propyl 4-hydroxybenzoyloxybenzoate, isopropyl 4-hydroxybenzoyloxybenzoate, butyl 4-hydroxybenzoyloxybenzoate, etc. 4-hydroxybenzoyloxybenzoic acid esters, 2,4-dihydroxybenzophenone,
α, α′-bis- (3-methyl-4-hydroxyphenyl) -m-diisopropylbenzophenone, 2,3
Benzophenones such as 4,4′-tetrahydroxybenzophenone, N-stearyl-p-aminophenol, 4-hydroxysalicylanilide, 4,4′-dihydroxydiphenyl ether, n-butylbis (hydroxyphenyl) acetate, α, α ′, α ″ -tris (4-hydroxyphenyl) -1,3,5-triisopropylbenzene, stearyl gallate, 4,4′-thiobis (6-t-butyl-m-cresol), 2,2-bis (3 -Allyl-4-hydroxyphenyl) sulfone,
Bis (4-hydroxyphenyl) sulfide, bis (4-hydroxy-3-methylphenyl) sulfide, p-tert-butylphenol, p-phenylphenol, p-benzylphenol, 1-naphthol,
Phenolic compounds such as 2-naphthol, thiourea compounds such as N, N′-di-m-chlorophenylthiourea,
Benzoic acid, p-tert-butylbenzoic acid, trichlorobenzoic acid, 3-sec-butyl-4-hydroxybenzoic acid,
3-cyclohexyl-4-hydroxybenzoic acid, 3,5
-Dimethyl-4-hydroxybenzoic acid, terephthalic acid,
Salicylic acid, 3-isopropylsalicylic acid, 3-tert-
Butyl salicylic acid, 4- (2- (p-methoxyphenoxy) ethyloxy) salicylic acid, 4- (3- (p-tolylsulfonyl) propyloxy) salicylic acid, 5- (p
Aromatic carboxylic acids such as-(2- (p-methoxyphenoxy) ethoxy) cumyl) salicylic acid, and zinc, magnesium, aluminum of these aromatic carboxylic acids;
Salts with polyvalent metals such as calcium, titanium, manganese, tin and nickel, and further organic acid substances such as antipyrine complex of zinc thiocyanate, complex zinc salt of terephthalaldehyde acid and other aromatic carboxylic acids, etc. However,
It is not limited to these. Moreover, you may mix 2 or more types.

Further, in a thermosensitive recording medium, a sensitizer is usually used for the purpose of improving sensitivity. Also in the present invention, a sensitizer may be added to the heat-sensitive recording layer depending on the purpose. Specific examples thereof are shown below, but the present invention is not limited to these, and two or more kinds may be mixed and used. Stearic acid amide, methoxycarbonyl-N
-Stearic acid benzamide, N-benzoylstearic acid amide, N-eicosanoic acid amide, ethylenebisstearic acid amide, behenic acid amide, methylenebisstearic acid amide, methylolamide, N-methylolstearic acid amide, dibenzyl terephthalate, terephthalic acid Dimethyl, dioctyl terephthalate, benzyl p-benzyloxybenzoate, phenyl 1-hydroxy-2-naphthoate, dibenzyl oxalate, oxalic acid-di-
p-methylbenzyl, oxalic acid-di-p-chlorobenzyl, 2-naphthylbenzyl ether, m-terphenyl, p-benzylbiphenyl, 1,2-bis (phenoxymethyl) benzene <PMB-2>, tolylbiphenyl ether. , Di (p-methoxyphenoxyethyl) ether, 1,2-di (3-methylphenoxy) ethane, 1,
2-di (4-methylphenoxy) ethane, 1,2-di (4-methoxyphenoxy) ethane, 1,2-di (4-
Chlorophenoxy) ethane, 1,2-diphenoxyethane, 1- (4-methoxyphenoxy) -2- (2-methylphenoxy) ethane, p-methylthiophenylbenzyl ether, 1,4-di (phenylthio) butane, p −
Acetotoluidide, p-acetophenetidide, N-acetoacetyl-p-toluidine, di (-biphenylethoxy) benzene, p-di (vinyloxyethoxy) benzene, 1-isopropylphenyl-2-phenylethane and the like are exemplified. . These sensitizers are usually used in an amount of 0.1 to 10 parts by weight based on 1 part by weight of the total amount of the dye precursor contained as composite fine particles and solid fine particles.

Further, a storage stabilizer may be used in the multicolor thermosensitive recording medium of the present invention to stabilize it during storage. Specific examples include 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) ) Butane, 4,4′-butylidene bis (2-tert-butyl-5-methylphenol), 4,4′-thiobis (2-tert-butyl-5-methylphenol), 2,2′-thiobis (6-tert- Butyl-4-methylphenol), 2,2′-methylenebis (6-tert-butyl-4-methylphenol) and other hindered phenol compounds, 4-benzyloxy-4 ′
-(2-Methylglycidyloxy) diphenyl sulfone, sodium 2,2'-methylenebis (4,6-di-
tert-butylphenyl) phosphate, etc., and these storage stabilizers are used in an amount of 0.1 to 10 parts by weight per 1 part by weight of the total amount of the dye precursor contained as the composite fine particles and the solid fine particles. It Specific examples of the binder used in the multicolor thermosensitive recording medium of the present invention include starches, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin,
Casein, gum arabic, polyvinyl alcohol, carboxy modified polyvinyl alcohol, acetoacetyl group modified polyvinyl alcohol, silicon modified polyvinyl alcohol, isobutylene-maleic anhydride copolymer alkali salt, styrene-maleic anhydride copolymer alkali salt, ethylene-anhydrous Maleic acid copolymer alkali salt, water-soluble binder such as styrene-acrylic acid copolymer alkali salt, styrene-butadiene copolymer, acrylonitrile-butadiene copolymer, latexes such as methyl acrylate-butadiene copolymer, Examples thereof include water-dispersible binders such as urea resin, melamine resin, amide resin and polyurethane resin.

Further, as the filler, activated clay, clay,
Calcined clay, diatomaceous earth, talc, kaolin, calcined kaolin, calcium carbonate, magnesium carbonate, barium carbonate, titanium oxide, zinc oxide, silicon oxide, inorganic filler such as aluminum hydroxide, urea-formalin resin, polystyrene resin, phenol resin, etc. Organic fillers are used. Further, a dispersant such as sodium dioctylsulfosuccinate, a surfactant, an antifoaming agent, a fluorescent brightening agent, a water resistant agent, a lubricant, an ultraviolet absorber, an antioxidant and the like are used as desired. As the support, paper such as high-quality paper, medium-quality paper, recycled paper, coated paper is mainly used, but various non-woven fabrics, plastic films, synthetic papers, metal foils, etc. or composite sheets combining these are optional. Used for. Further, an overcoat layer of a polymer substance or the like is provided on the heat-sensitive recording layer for the purpose of improving storage stability, and an undercoat layer of a polymer substance or the like containing a filler is provided under the heat-sensitive recording layer for the purpose of enhancing color development sensitivity. You can also An intermediate layer may be provided between the thermal recording layer and the overcoat layer.

The multicolor thermosensitive recording medium of the present invention can be manufactured by a conventionally known method using various materials as described above. The method for preparing the coating liquid for each layer of the thermosensitive recording medium is not particularly limited, and generally, water is used as a dispersion medium, the dye precursor composite fine particles, and the dye precursor in the form of solid fine particles having a different color tone from this, and an organic material. In addition to the color developer
It is prepared by mixing and stirring a binder, a filler, a lubricant, etc., which are added if necessary. Usually, these materials are separately pulverized in a water system by a sand grinder, an attritor, a ball mill, etc., and then mixed to obtain a water-based coating material. The use ratio of the dye precursor and the developer is not particularly limited and is appropriately selected depending on the type of the dye precursor or the developer to be used, but the dye precursor contained as composite fine particles and solid fine particles 1 to 50 parts by weight, preferably 2 to 1 part by weight of the total amount
About 10 parts by weight of the developer is used. The binder is used in the range of 15 to 80 parts by weight based on the total solid amount of each layer. Furthermore, the ratio of the dye precursor in the form of solid fine particles to the dye precursor in the composite fine particles is not particularly limited, but is preferably 50% by weight to 300% by weight.

The method for forming each layer is not particularly limited, and air knife coating, varibar blade coating, pure blade coating, rod blade coating, short dwell coating, curtain coating, die coating and the like can be appropriately selected. The coating liquid for heat-sensitive recording layer is applied onto the support and dried, and then the coating liquid for overcoat layer is applied onto the heat-sensitive recording layer and dried. The coating amount of the thermal recording layer coating liquid is 2 to 12 g as a dry weight.
/ M ² , preferably about 3 to 10 g / m ² , and the coating amount of the coating liquid for the undercoat layer, the intermediate layer or the overcoat layer is about 0.1 to 15 g / m ² , preferably about 0. It is adjusted within the range of about 5 to 7 g / m ² . In addition,
If necessary, provide a back coat layer on the back side of the support,
It is also possible to further improve storability. Further, smoothing treatment such as super calendering can be performed after forming each layer. The multicolor thermosensitive recording medium of the present invention is used for commercial or household facsimile paper, POS, physical distribution, industrial label paper, word processor printer paper, supermarket or cash register printer paper, medical measurement printer paper. , Printer paper for industrial measurement, bank ATM paper,
The present invention can be applied to fields in which thermal recording materials are generally used, such as ticket paper.

[0021]

EXAMPLES The present invention will be described in detail below with reference to specific examples. However, the present invention is not limited to this embodiment. In addition, "part" and "%" show "part by weight" and "% by weight", respectively, unless otherwise specified. [Synthesis of Dye Precursor Composite Fine Particles A] 18 parts of 3-dibutylamino-6-methyl-7-anilinofluorane <ODB-2> and polystyrene (melting point 95
C., 3 parts of Hymer ST95 manufactured by Sanyo Kasei Co., Ltd. were dissolved in 80 parts of methylene chloride at 40 to 50.degree. C., and a 3: 1 molar ratio of xylylene diisocyanate and trimethylolpropane was added to this solution (Takenate D110 manufactured by Mitsui Takeda Chemical Co., Ltd.).
16 parts of N, 75 wt% ethyl acetate solution) was added and mixed uniformly. Next, this mixed solution is mixed with a homogenizer to obtain 10
It was gradually added to 250 parts of a 5% aqueous solution of polyvinyl alcohol (PVA-217C manufactured by Kuraray Co., Ltd.) rotated at 000 rpm and emulsified. This dispersion was heated at 55 ° C. for 2 hours to remove methylene chloride, and then stirred at 80 ° C. for 3 hours to polymerize the isocyanate to obtain an average particle size of 0.5.
A dispersion liquid of black dye precursor composite fine particles A having a size of μm was prepared. [Synthesis of Dye Precursor Composite Fine Particle B] 6 parts of polystyrene,
A dispersion of black dye precursor composite fine particles B having an average particle size of 0.5 μm was prepared in the same manner as for the composite fine particles A except that the xylylene diisocyanate and the trimethylolpropane molar ratio of 3: 1 were added to 8 parts. . [Synthesis of Dye Precursor Composite Fine Particle C] Polystyrene 12
Parts, xylylene diisocyanate and trimethylol propane molar ratio 3: 1 adduct 4 parts in the same manner as the composite fine particles A, except that the dispersion liquid of the black dye precursor composite fine particles C having an average particle diameter of 0.5 μm. Prepared.

[Synthesis of Dye Precursor Composite Fine Particles D] 3- (N-isobutyl-N-ethylamino) -6-methyl-7-anilinofluorane <PSD-
A dispersion of black dye precursor composite fine particles D having an average particle diameter of 0.5 μm was prepared in the same manner as for the composite fine particles A except that 184> 18 parts was used and 30 parts of ethyl acetate was used as a solvent. [Synthesis of Dye Precursor Composite Fine Particles E] Polystyrene 6 parts, xylylene diisocyanate and trimethylol propane molar ratio 3: 1 adduct Instead of 16 parts, hexamethylene diisocyanate and trimethylol propane molar ratio 3: 1 adduct (Mitsui Takeda Chemical Takenate D16
A dispersion of black dye precursor composite fine particles E having an average particle diameter of 0.5 μm was prepared in the same manner as for the composite fine particles A except that 8 parts of 0N, 75 wt% ethyl acetate solution) was used. [Synthesis of Dye Precursor Composite Fine Particles F] 3- (N-isobutyl-N-ethylamino) -6-methyl-7-anilinofluorane <PSD-184> 18 as a black dye precursor
Parts, 30 parts of ethyl acetate as a solvent, 6 parts of polystyrene, 3: 1 molar ratio of xylylene diisocyanate and trimethylolpropane, and 16 parts of adduct instead of 16 parts of hexamethylene diisocyanate and 3: 1 molar ratio of trimethylolpropane. A dispersion of black dye precursor composite particles F having an average particle diameter of 0.5 μm was prepared in the same manner as for the composite particles A except that 8 parts of 1 addition product was used.

[Synthesis of Dye Precursor Composite Fine Particles G] Melting Point 9
The same as the fine composite particles A except that 6 parts of polystyrene having a melting point of 120 ° C. (Haimer ST120 manufactured by Sanyo Kasei Co., Ltd.) and 8 parts of a 3: 1 adduct of xylylene diisocyanate and trimethylolpropane were used instead of 5 ° C. polystyrene. By the method, a dispersion liquid of the black dye precursor composite fine particles G having an average particle diameter of 0.5 μm was prepared. [Synthesis of Dye Precursor Composite Fine Particles H] From the synthesis of the dye precursor composite fine particles A, 3 parts of polystyrene were removed, and the other processes were the same as those for the composite fine particle A, and a black dye precursor having an average particle diameter of 0.5 μm. A dispersion liquid of the composite fine particles H was prepared. [Synthesis of Dye Precursor Composite Fine Particles I] 6 parts of 3-dibutylamino-6-methyl-7-anilinofluorane <ODB-2> was used as a black dye precursor, 3 parts of polystyrene was removed, and other than that, A dispersion of black dye precursor composite particles I having an average particle size of 0.5 μm was prepared in the same manner as for the composite particles A. [Synthesis of Dye Precursor Composite Fine Particles J] 6 parts of 3- (N-isobutyl-N-ethylamino) -6-methyl-7-anilinofluorane <PSD-184> was used as a black dye precursor, and polystyrene 3 was used. Except for this, the same procedure as that for the composite fine particles A was performed to prepare a dispersion liquid of the black dye precursor composite fine particles J having an average particle diameter of 0.5 μm. [Synthesis of Dye Precursor Composite Fine Particles K] Polystyrene 12
Dispersion of black dye precursor composite fine particles K having an average particle diameter of 0.5 μm in the same manner as for the composite fine particles A, except that xylene diisocyanate and trimethylolpropane in a molar ratio of 3: 1 are not used. Was prepared.

[Example 1] Liquid (blue dye precursor dispersion liquid) 3,3-bis-dimethylaminophenyl-6-dimethylaminophthalide <CVL> 30.0 parts 10% polyvinyl alcohol aqueous solution 50.0 parts water 20.0 parts A mixed solution of the above composition was ground with a sand grinder to an average particle size of 1 micron. Liquid (developer dispersion liquid) 2,4′-dihydroxydiphenyl sulfone 30.0 parts 10% polyvinyl alcohol aqueous solution 20.0 parts water 10.0 parts Mixture of the above composition is sand grinder with an average particle diameter of 1 micron Ground up. Next, the dispersion liquids were mixed at the following ratios to prepare coating liquids. Black dye precursor composite fine particle A dispersion liquid 10.0 parts liquid (blue dye precursor dispersion liquid) 10.0 parts liquid (developer dispersion liquid) 20.0 parts Silica 30% dispersion liquid 40.0 parts The above coating liquid Was applied to one side of 60 g / m ² paper using a Meyer bar so that the coating amount was 6.0 g / m ² and dried to prepare a thermosensitive recording medium.

Example 2 A thermosensitive recording medium was prepared in the same manner as in Example 1 except that the black dye precursor composite fine particle A dispersion liquid of Example 1 was used in place of the black dye precursor composite fine particle B dispersion liquid. It was created. Example 3 A thermosensitive recording medium was prepared in the same manner as in Example 1 except that the black dye precursor composite fine particle A dispersion liquid was used in place of the black dye precursor composite fine particle A dispersion liquid of Example 1. . [Example 4] A thermosensitive recording medium was prepared in the same manner as in Example 1 except that the black dye precursor composite fine particle A dispersion liquid of Example 1 was used in place of the black dye precursor composite fine particle D dispersion liquid. . [Example 5] A thermosensitive recording medium was prepared in the same manner as in Example 1 except that the black dye precursor composite fine particle E dispersion liquid was used in place of the black dye precursor composite fine particle A dispersion liquid of Example 1. . Example 6 A thermal recording medium was prepared in the same manner as in Example 1 except that the black dye precursor composite fine particle A dispersion liquid of Example 1 was used in place of the black dye precursor composite fine particle F dispersion liquid. . [Example 7] A thermosensitive recording medium was prepared in the same manner as in Example 1 except that the black dye precursor composite fine particle A dispersion liquid of Example 1 was used instead of the black dye precursor composite fine particle A dispersion liquid. .

Comparative Example 1 Liquid (black dye precursor dispersion liquid) 3-dibutylamino-6-methyl-7-anilinofluorane <ODB-2> 20.0 parts 10% polyvinyl alcohol aqueous solution 20.0 parts 20.0 parts of water A mixed solution of the above composition was ground with a sand grinder to an average particle size of 1 micron. A thermosensitive recording medium was prepared in the same manner as in Example 1 except that the liquid was used instead of the black dye precursor composite fine particle A dispersion liquid of Example 1. Comparative Example 2 A thermosensitive recording medium was prepared in the same manner as in Example 1 except that the black dye precursor composite fine particle A dispersion liquid in Example 1 was used in place of the black dye precursor composite fine particle A dispersion liquid. . Comparative Example 3 A thermosensitive recording medium was prepared in the same manner as in Example 1 except that the black dye precursor composite fine particle A dispersion liquid of Example 1 was used in place of the black dye precursor composite fine particle I dispersion liquid. . Comparative Example 4 A thermosensitive recording medium was prepared in the same manner as in Example 1 except that the black dye precursor composite fine particle A dispersion liquid in Example 1 was used in place of the black dye precursor composite fine particle J dispersion liquid. . Comparative Example 5 A thermosensitive recording medium was prepared in the same manner as in Example 1 except that the black dye precursor composite fine particle A dispersion liquid in Example 1 was used in place of the black dye precursor composite fine particle A dispersion liquid. .

[Evaluation Test] The multicolor heat-sensitive recording material obtained as described above was tested as follows, and the results are shown in Table 1. The softening temperature of the composite fine particles was measured with a melting point measuring device manufactured by Buchi.・ Coloring property MARKPOINT thermal printer (equipped with ROHN thermal head KM2004-A3) was used for low-temperature color development. Four
Position (applied energy 0.076 mj / dot), and No. as high temperature color development. 11 positions (applied energy 0.
219 mj / dot), and the obtained image was measured using a Macbeth densitometer (RD-914). The black color image (high temperature color image) is the density using a yellow filter, and the blue color image (low temperature color image) is the density obtained by subtracting the value using the yellow filter from the value using the cyan filter. The developed color tone was visually determined. Color tone of color-developed part ◯: Vivid color development ×: Color development with other colors mixed, or low-density color development / color separation property The thermosensitive recording materials obtained in Examples and Comparative Examples are the same as the surface provided with the thermosensitive recording layer. From the surface, the state of the central portion and the peripheral portion of the color-developed portion which spreads in a round and irregular shape was visually judged by burning with a lighter. Since the central portion of the color-developing portion has a high temperature, it has a high-temperature coloring color tone, and the peripheral portion has a low temperature, and thus has a low-temperature coloring color tone. Color separation ∘: The boundary between black, which is a high-temperature color tone, and blue, which is a low-temperature color tone, is clear. ×: The boundary is blurred, bleeding, or difficult to distinguish.

[0028]

[Table 1]

[0029]

INDUSTRIAL APPLICABILITY As described above, by using the dye precursor composite fine particles of the present invention, clear color tones can be obtained in each of low temperature color development and high temperature color development, and fogging between low temperature color development color tone and high temperature color development color tone. It is possible to obtain a very useful multicolor heat-sensitive recording material having no color separation property.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Daisuke Imai             5-21-1 Oji, Kita-ku, Tokyo Nippon Paper Industries             Product Research Institute Co., Ltd. (72) Inventor Naomi Sumikawa             5-21-1 Oji, Kita-ku, Tokyo Nippon Paper Industries             Product Research Institute Co., Ltd. (72) Inventor Takashi Sasaki             5-21-1 Oji, Kita-ku, Tokyo Nippon Paper Industries             Product Research Institute Co., Ltd. F term (reference) 2H026 AA07 AA11 BB02 BB24 FF05                       FF07

Claims (3)

[Claims] 1. Dye precursor composite fine particles comprising a colorless or light-colored dye precursor, a polymer of a polyvalent isocyanate compound, and a resin having a melting point or a softening temperature in the range of 50 to 150 ° C. . 2. The dye precursor composite fine particles according to claim 1, wherein the resin having a softening temperature in the range of 50 to 150 ° C. is polystyrene. 3. A dye precursor composite fine particles according to claim 1 or 2 and at least one or more dyes which develop a different color tone from the dye precursor contained in the dye precursor composite fine particles on a support. A multicolor thermosensitive recording medium comprising a thermosensitive recording layer containing a precursor and an organic developer which reacts with these dye precursors to develop a color.