JPH07304260A - Thermal recording material - Google Patents

Abstract

PURPOSE:To provide a thermal recording material capable of erasing a color image developed by heating being the important technical element of a multicolor thermal recording material. CONSTITUTION:In a thermal recording material forming a developed color image on a support by the reaction of a leuco dye and a coupler, at least one or more kind of the leuco dye is added to the polymer of a vinyl polymer suspension prepared by emulsion or suspension polymerization.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermosensitive recording medium capable of erasing an image formed by heating, which is an important technical element of a multicolor thermosensitive recording medium.

[0002]

2. Description of the Related Art Conventionally, a method of combining a leuco dye and a color developer and bringing both substances into contact with each other by heat to obtain a color image is well known. Since such a thermal recording material is easy to reduce the size and cost of a printing machine and is overwhelmingly advantageous in use and maintenance as compared with other image forming methods such as ink jet, thermal transfer or electrophotography,
It is used as a thermal recording material in a wide range of fields such as facsimiles, labels and various industrial recorders.

Along with the expansion of applications, the performance and quality required for a thermal recording material have been diversified, and for example, sensitization, image stabilization or multicolor has been diversified. Especially multicolor
It has been said that the most weak point of the thermal recording method so far, and if it can be overcome, it can be expected to broaden the range of application of the thermal recording material as an image forming method.

In the conventional multicolor thermosensitive recording method, as described in Japanese Patent Publication No. 49-69, first, a color forming layer having different color forming temperatures is provided, and the first color forming layer is formed at a low temperature. There is a method in which a single color is obtained by color development, and then a second or more color development layer is sequentially developed at a high temperature to obtain a mixed color. However, in this method, since it is a color-added type, it is theoretically impossible to clearly develop three colors such as red, blue and black.

In the second multicolor thermosensitive recording method, the first coloring layer is colored at a low temperature to obtain a single color, and the second coloring of the second layer is obtained at a higher temperature. The layer is decolorized by using a decoloring agent to obtain only the second color, and this method is repeated to obtain multiple colors. JP-A-48-8251 discloses that a once colored leuco dye is decolorized by using an alcohol, and JP-B-54-36864 describes that it is decolorized by using an amine derivative. With the devising of such an erasable type multicolor heat-sensitive recording method, a concept capable of vividly producing multicolors was completed in principle.

This decolorizing type multicolor thermosensitive recording medium is composed of at least a leuco dye which develops color, a developer and a decoloring agent, and the decoloring agent is in the same layer or in JP-A-55-39.
As disclosed in Japanese Patent No. 13, there is a method in which a specific intermediate layer is provided and contained therein so that the upper color-forming layer is decolored when heated.
In this way, for example, if a color forming layer and a decoloring layer are sequentially combined, it should be possible to form a multicolor heat sensitive material by utilizing the difference in heating temperature.However, due to the combination of decoloring agents and the multilayer structure, high image density can be obtained. However, there were many problems such as not being able to obtain a clear image and increasing the coating cost due to the complicated layer structure.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a thermosensitive recording medium which can form a clear image as a recorded image and can be erased.

[0008]

As a result of repeated studies to solve the above-mentioned problems, the present inventor has emulsified or suspended the leuco dye in a heat-sensitive recording material that develops color by the reaction of a leuco dye and a developer. It has been found that a thermosensitive recording medium capable of forming a clear image and decoloring can be obtained by incorporating the vinyl polymer suspension produced by the turbid polymerization in the polymer.

That is, the present invention relates to a heat-sensitive recording material for forming a color image by the reaction of a leuco dye and a color developer on a support, wherein the leuco dye is a vinyl polymer suspension prepared by emulsion or suspension polymerization. A thermosensitive recording material characterized by being contained in the polymer, wherein the color is developed by heating and is erased by heating at a higher temperature.

The normally colorless or light-colored leuco dye used in the present invention is typically represented by those used for pressure-sensitive recording paper, heat-sensitive recording paper, light-sensitive pressure-sensitive paper, electric heat-sensitive recording paper, heat-sensitive transfer paper, etc. It is not particularly limited. A typical leuco dye is “Coloring Materials Association Magazine” 54 (6) 355.
(Published by the Coloring Materials Association, 1981). Specific examples include the followings, but the present invention is not limited thereto.

(1) Triarylmethane compound 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide (crystal violet lactone), 3,3-bis (p-dimethylaminophenyl) phthalide, 3- (p-dimethylaminophenyl) -3-
(1,2-dimethylindol-3-yl) phthalide,
3- (p-dimethylaminophenyl) -3- (2-methylindol-3-yl) phthalide, 3- (p-dimethylaminophenyl) -3- (2-phenylindole-
3-yl) phthalide, 3,3-bis (1,2-dimethylindol-3-yl) -5-dimethylaminophthalide, 3,3-bis (1,2-dimethylindole-3-)
Yl) -6-dimethylaminophthalide, 3- (p-diethylamino-o-ethoxyphenyl) -3- (1-ethyl-2-methylindol-3-yl) phthalide, 3,
3-bis (1-n-butyl-2-methylindole-3
-Yl) phthalide, 3,3-bis (1-n-octyl-)
2-Methylindol-3-yl) phthalide, 3- (p
-Diethylamino-o-ethoxyphenyl) -3- (1
-N-octyl-2-methylindol-3-yl) phthalide, 3,3-bis (9-ethylcarbazole-3-
Yl) -5-dimethylaminophthalide, 3,3-bis (2-phenylindol-3-yl) -5-dimethylaminophthalide, 3-p-dimethylaminophenyl-3
-(1-Methylpyrrol-2-yl) -6-dimethylaminophthalide, 3- (p-diethylamino-o-ethoxyphenyl) -3- (1-ethyl-2-methylindol-3-yl) azaphthalide, etc. ,

(2) Diphenylmethane compound 4,4'-bis (dimethylaminophenyl) benzhydryl benzyl ether, N-chlorophenyl leuco auramine, N-2,4,5-trichlorophenyl leuco auramine, etc.

(3) Xanthene compound Rhodamine B anilinolactam, rhodamine B p-chloroanilinolactam, 3-diethylamino-6-methyl-7-aminofluorane, 3-dibutylamino-6-
Methyl-7-aminofluorane, 3-diethylamino-
6-methyl-7-xylinofluorane, 3-diethylamino-7-chloroanilinofluorane, 3-diethylamino-7,8-benzofluorane, 3,6-diethoxyfluorane, 3-dimethylamino-6 -Methoxy-7-
Anilinofluorane, 3-diethylamino-7-n-octylaminofluorane, 3-diethylamino-7-dibenzylaminofluorane, 3- (N-ethyl-Nn)
-Hexyl) amino-7-phenylaminofluorane,
3-Diethylamino-7- (N-benzyl-N-cyclohexyl) aminofluorane, 3-diethylamino-6
-Methyl-7-chlorofluorane, 3-cyclohexylamino-6-chlorofluorane, 3-diethylamino-
7-chlorofluorane, 3-diethylamino-7-methylfluorane, 3-diethylamino-7- (3,4-dichloroanilino) fluorane,

3- (N-ethyl-N-tolyl) amino-
6-methyl-7-anilinofluorane, 3-piperidino-6-methyl-7-anilinofluorane, 3- (N-ethyl-N-tolyl) amino-6-methyl-7-phenethylfluorane, 3 -Diethylamino-7- (4-nitroanilino) fluorane, 3-dibutylamino-6-methyl-7-anilinofluorane, 3- (N-methyl-N-)
Propyl) amino-6-methyl-7-anilinofluorane, 3- (N-ethyl-N-isoamyl) amino-6-
Methyl-7-anilinofluorane, 3- (N-methyl-
N-cyclohexyl) amino-6-methyl-7-anilinofluorane, 3- (N-ethyl-N-tetrahydrofuryl) amino-6-methyl-7-anilinofluorane, and the like.

(4) Thiazine-based compound benzoyl leuco methylene blue, p-nitrobenzoyl leuco methylene blue, etc.

(5) Spiro compound 3-methylspirodinaphthopyran, 3-ethylspirodinaphthopyran, 3,3'-dichlorospirodinaphthopyran, 3-benzylspirodinaphthopyran, 3-methylnaphtho- (3 -Methoxybenzo) spiropyran, 3-propylspirobenzopyran, etc.,

The usually colorless to light-colored leuco dyes used in the present invention may be used either individually or in combination of two or more.

At least one of the leuco dyes used in the present invention
One or more species can be decolorized with a decoloring agent, and the leuco dye used in such a case is preferably a triarylmethane compound or a xanthene compound. These are described in "Pulp and Paper Technology Times" (September 1982, p. 99, published by Tech Times Co., Ltd.).

The color developer used in the present invention includes the following materials, but is not limited thereto.

Inorganic acidic substances such as activated clay, attapulgite, colloidal silica, aluminum silicate, 1,1-
Bis (4-hydroxyphenyl) cyclohexane, 2,
2-bis (4-hydroxyphenyl) propane, bis (4-hydroxyphenyl) sulfide, bis (4-
Hydroxyphenyl) sulfone, 1,4-bis (3-
Hydroxyphenoxy) benzene, 1,3-bis (4-
Hydroxyphenoxy) benzene, 2,2-bis (4-
Hydroxyphenyl) butane, 1,1-bis (4-hydroxyphenyl) ethane, bis (4-hydroxyphenyl) ether, α, α′-tris (4-hydroxyphenyl) -1-ethyl-4-isopropylbenzene, 2 ，
2-bis (4-hydroxyphenyl) hexafluoropropane, 1,1-bis (4-hydroxyphenyl) -1
-Phenylethane, α, α'-bis (4-hydroxyphenyl) -1,4-diisopropylbenzene, 4-benzoyl-3-methyl-1-phenyl-5-pyrazolone,
Benzoic acid resorcinol ester, gallic acid-n-octyl ester, 4-hydroxybenzoic acid benzyl ester, 2-hydroxy-4-n-octyloxybenzophenone, 4-hydroxybiphenyl, 4-cyclohexylphenol, 4-n-dodecylphenol, 4'-hydroxy-n-heptadecane anilide, Nn-octadecyl-4-hydroxybenzamide, 4- (N-octadecylsulfonylamino) phenol, N- (4-hydroxyphenyl) -N'-n-octadecylurea , P-
Phenolic compounds such as octyl ester of hydroxyphenylpyruvic acid.

4-Phenylbenzoic acid, phthalic acid mono-2
-Aromatic carboxylic acids such as ethylhexyl ester, phthalic acid mono-n-butyl ester, phthalic acid monocholesterol ester, isophthalic acid monooctyl ester, nonanoylaminosalicylic acid, salicylate salicylate, and zinc, magnesium and aluminum of these aromatic carboxylic acids Salts with polyvalent metals such as calcium, manganese, tin, nickel, iron and copper, and other organic acidic substances can be used.

These color developing agents are leuco dyes and, although not particularly limited, generally 0.1% by weight per 1 part by weight of the leuco dye.
It is used in a proportion of about 2 to 10 parts by weight, preferably about 0.5 to 5 parts by weight. Of course, two or more kinds may be used together.

Various binders may be added to the heat-sensitive recording material of the present invention in order to improve the strength of the heat-sensitive recording layer. Specific examples of the binder used include starches, hydroxyethyl cellulose, methyl cellulose,
Carboxymethyl cellulose, gelatin, casein, polyvinyl alcohol, modified polyvinyl alcohol, sodium polyacrylate, acrylic acid amide / acrylic acid ester copolymer, acrylic acid amide / acrylic acid ester / methacrylic acid terpolymer, styrene / maleic anhydride Water-soluble polymer such as alkali salt of acid copolymer, alkali salt of ethylene / maleic anhydride copolymer, polyvinyl acetate, polyurethane, polyacrylic ester, styrene / butadiene copolymer, acrylonitrile / butadiene copolymer Examples thereof include latex such as methyl acrylate / butadiene copolymer and ethylene / vinyl acetate copolymer, but are not limited thereto.

A heat-fusible substance may be contained in the heat-sensitive recording layer as an additive for controlling the color developing sensitivity and the decoloring temperature of the heat-sensitive recording layer of the heat-sensitive recording material of the present invention. As the heat-fusible substance used in the present invention, those having a melting point of 40 ° C to 260 ° C are preferable, and those having a melting point of 60 ° C to 220 ° C are particularly preferable. Further, a sensitizer used in general thermal recording paper can also be used. Specific examples of the heat-fusible substance used in the present invention include waxes such as N-hydroxymethylstearic acid amide, stearic acid amide and palmitic acid amide, naphthol derivatives such as 2-benzyloxynaphthalene, p-benzylbiphenyl, Biphenyl derivatives such as 4-allyloxybiphenyl, 1,2-bis (3-methylphenoxy) ethane,
Polyether compounds such as 2,2′-bis (4-methoxyphenoxy) diethyl ether and bis (4-methoxyphenyl) ether; carbonic acid such as diphenyl carbonate, dibenzyl oxalate and bis (p-methylbenzyl) oxalate. Examples include oxalic acid diester derivatives, 2
It is also possible to use them in combination of one or more species.

Furthermore, thermoplastic polymers can also be used. For example, polyolefins such as polystyrene and polypropylene, polyesters, polyvinyl butyral, polyethers, acrylic resins, polyamides such as nylon,
Examples thereof include polyacrylamides, polyvinyl acetate and polyethylene vinyl acetate copolymers. Two or more of these thermoplastic substances may be used in combination, or may be contained in the polymer of the polymer suspension.

As the support used in the thermosensitive recording medium of the present invention, paper, various non-woven fabrics, woven fabrics, synthetic resin films, synthetic resin laminated papers, synthetic papers, metal foils, glass, etc., or a composite sheet combining these is used. It can be optionally used depending on the purpose, but is not limited thereto. When a support such as paper is used, an anti-curl layer or an antistatic layer can be formed on the side opposite to the surface forming the thermosensitive recording layer.

The heat-sensitive recording material of the present invention can be used as a multicolor heat-sensitive recording material. In this case, it may have a multi-layered structure or may be combined with other leuco dyes if necessary. Further, a layer structure capable of recording electrical, magnetic and optical information may be provided. When the thermosensitive recording medium of the present invention is used as one component of the multicolor thermosensitive recording medium, other leuco dyes may be decolorized with a decoloring agent within the range where the object of the present invention is achieved. Further, a surface protective layer or an intermediate layer may be provided.

The heat-sensitive recording material of the present invention can be decolored after color development, and since the decolored portion does not recolor, it can be used for anti-counterfeiting applications.

As the decolorizing agent, aliphatic amines, amides, piperidines, piperazines, pyridines, imidazoles, imidazolines, morpholines, guanidines, amidines, polyesters, polyethers,
There are glycols and the like, but the glycols are not particularly limited thereto. Specifically, the following compounds are described in various known documents.

Alkylene oxide compounds of bisphenols (JP-A-54-13941), ethylene oxide adducts of terephthalic acid (JP-A-55-25306),
Long-chain 1,2-glycol (JP-A-55-27217), glycerin aliphatic ester (JP-A-55-152)
094), urea derivatives (JP-A-55-13929).
No. 0), alkylene oxide adducts of long-chain glycols (JP-A-55-152094), morpholine derivatives (JP-A-56-40588), polyether and polyethylene glycol derivatives (JP-B-50-178).
67, Japanese Patent Publication No. 50-17868), guanidine derivatives (Japanese Patent Publication No. 51-29024), amines or quaternary ammonium salts (Japanese Patent Publication No. 50-18048), nitrogen-containing crystalline organic compounds ( Japanese Patent Publication 51-199
No. 91).

These decoloring agents are used in the range of 10 to 1000% by weight, preferably 30 to 300% by weight, based on the total amount of the leuco dye and the color developer in the layer to be decolored. . Further, two or more kinds of decoloring agents may be combined.

Further, the heat-sensitive recording layer, the protective layer and the intermediate layer include
Diatomaceous earth, talc, kaolin, calcined kaolin, calcium carbonate, magnesium carbonate, titanium oxide, zinc oxide,
Pigments such as silicon oxide, aluminum hydroxide, and urea-formalin resin, and zinc stearate for the purpose of preventing head wear and sticking in the surface protective layer.
Higher fatty acid metal salts such as calcium stearate, waxes such as paraffin, oxidized paraffin, polyethylene, oxidized polyethylene, stearamide, castor wax, dispersants such as sodium dioctylsulfosuccinate, surfactants, fluorescent dyes, etc. Can also be included.

As a method for producing a vinyl polymer suspension in which a leuco dye is contained in a vinyl polymer, a solid polymer is dissolved in a solvent, mixed with a leuco dye, the solvent is removed, and emulsification and dispersion are carried out again to produce an artificial mixture. There are a method of obtaining a latex, a method of emulsion-polymerizing a monomer together with a leuco dye to obtain a synthetic latex, and a method of obtaining a polymer suspension by suspension polymerization with the leuco dye contained in the monomer.

On the other hand, the leuco dye is contained and dispersed in microcapsules when it is used as a pressure-sensitive color former, and microcapsules containing leuco dyes are also being studied for heat-sensitive use. Copied in 1990, pp. 257 (Electrophotographic Society of Japan), it was developed as a method for producing a transparent heat-sensitive layer. In microcapsules, only the surface of particles dispersed in water or the like separates the inner and outer phases. The polymer suspension is different from the above-mentioned polymer suspension in that it is coated with a polymer for the purpose of and the purpose is to clearly retain the contents.

Generally, artificial latex and synthetic latex are described in detail in "Introduction to Polymer Latex" (published by Kobunsha, 1st edition, 1983), including the differences. A method of forming a leuco dye into an artificial latex and mixing it in the polymer fine particles is described in JP-A-5-270127. First, an organic solvent is used to dissolve both the leuco dye and the polymer. Dry to remove solvent and redisperse. With this method, it is necessary to dry and remove the organic solvent, but in general, special equipment is required to recover or incinerate the vaporized organic solvent,
In addition, there is a concern about environmental pollution such as leakage to the atmosphere even in part. Further, the number of steps for dissolving, drying and dispersing and manufacturing increases, which causes a cost increase, and if the solvent remains in the heat-sensitive recording layer, it causes fogging, which causes many problems. In addition, the shape of the particles after dispersion is generally uneven, which causes uneven coloring density, uneven sensitivity, and uneven decoloring.

In order to form a synthetic latex by emulsion polymerization, first, a leuco dye is dissolved in a monomer, and polymerization is carried out in an emulsifier in the presence of a polymerization initiator soluble in an aqueous phase to form a spherical leuco dye and a vinyl polymer. Get the particles.

To obtain a polymer suspension by suspension polymerization, a leuco dye and a polymerization initiator are dissolved in a monomer, emulsified in the presence of an emulsifier and polymerized in water. Suspension polymerization is also called granular polymerization or pearl polymerization, but the details thereof are described in "Chemical Encyclopedia 3", page 456 (first published in 1960 by Kyoritsu Shuppan), including points different from emulsion polymerization. Also, "surface" vol. 31 No. 1 (1993, published by Koushinsha Co., Ltd.), page 56 describes the synthesis of functional fine particles by the suspension polymerization method. The term "polymer suspension" in the present invention means a general term for water-dispersed systems in which a polymer containing a leuco dye and produced by a polymerization reaction becomes spherical particles.

As the monomer which can be used for such polymerization, various vinyl monomers such as styrene derivative, acrylic acid derivative, methacrylic acid derivative, acrylamide derivative, methacrylamide derivative and crotonic acid derivative can be used. These may be polymerized alone or may be used by being copolymerized with two or more kinds of monomers. A specific example is given below.

Methacrylic acid, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, dodecyl methacrylate, cyclohexyl methacrylate, benzyl methacrylate, methacrylic acid. Glycidyl, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, dimethylaminoethyl methylmethacrylate chloride salt, tetrahydrofurfuryl methacrylate, isobornyl methacrylate, phenyl methacrylate, 2-succinooyloxyethyl methacrylate, methacryl Acid 2-hexahydrophthaloyloxyethyl, acrylic acid, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, isobutyl acrylate, Acrylic acid t- butyl, stearyl acrylate, tetrahydrofurfuryl acrylate, carbitol acrylate tall, benzyl acrylate, N, N- dimethylacrylamide, acryloyl morpholine, N-
Isopropylacrylamide, styrene, methylstyrene, ethylstyrene, p-octadecylstyrene, chlorostyrene, p-methoxystyrene, p-vinylbenzylpropyl ether, methyl p-vinylbenzoate, crotonic acid, n-octyl crotonic acid, vinyl acetate, Maleic anhydride, vinyl chloride, ethylene, acrylonitrile,
Examples include t-butyl acrylamide and n-octyl methacrylamide.

When forming the heat-sensitive recording layer, the leuco dye is encapsulated in the polymer particles, and at this time, the particles are fused to each other and phase-separated with other dispersed particles such as a color developer or a binder. In order not to cause this, it is desirable that the particles formed by these monomers have a glass transition temperature of room temperature or higher. There is a method of crosslinking the particles to prevent fusion of the particles, and in this case, a monomer having a bifunctional or higher functional vinyl group is used. Specifically, the following monomers can be used.

Divinylbenzene, diacrylic acid 1,4-
Examples thereof include butanediol, neopentyl glycol diacrylate, trimethylolpropane triacrylate, pentaerythritol tetraacrylate, allyl acrylate, ethylene glycol dimethacrylate, triethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, and the like.

As the polymerization initiator for polymerizing these monomers, azo compounds and oxides can be used in addition to ammonium persulfate, and specifically, the following compounds can be used.

Benzoyl peroxide, octanoyl peroxide,
Decanoyl peroxide, 3,5,5-trimethylhexanoyl peroxide, m-toluoyl peroxide, diisopropylperoxydicarbonite, di (3-methyl-3-methoxyvinyl) peroxydicarbonite, t-butylperoxide Oxyisobutyrate, t-butylperoxy neodecanoate, t-butylperoxybenzoate, 2,2 '
-Azobis (4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobis (2-cyclopropylpropionitrile), 2,2'-azobis (2,4-dimethylvaleronitrile), 2, 2'-azobisisobutyronitrile, 2,2'-azobis (2-methylbutyronitrile) 2,2'-azobis (2-methyl-N-phenylpropionamidine) dihydrochloride, 2,2 '
-Azobis (2-methylpropionamidine) dihydrochloride, 2,2'-azobis (N, N'-dimethyleneisobutylamidine) dihydrochloride, 2,
2'-azobis (2-methylpropionate) and the like.

In addition to these, various emulsifiers and protective colloids can be used in order to control dispersion stability and particle size. In suspension polymerization, various devices can be used when emulsifying the oil phase. The polymer suspension produced in this manner is spherical and has a size of about 0.01 to 20 μm. When it is used as a thermal recording medium, particles having a size of about 0.1 to 5 μm are used. Is preferred.

[0045]

In the thermosensitive recording material of the present invention, the coloring and decoloring behaviors and the effectiveness of the resulting image sharpness are considered as follows. When such a polymer contains a leuco dye, in order to develop the color of the leuco dye, it is necessary that the heat-melted developer penetrates into the polymer and associates with the leuco dye. For the penetration of the color developer, not only the heating to the melting point of itself or more but also the glass transition temperature of the polymer and the compatibility with the polymer become important. For example, when the heat-sensitive recording layer is heated to a temperature not lower than the melting point of the developer but not higher than the glass transition temperature of the polymer, the low molecular weight type developer penetrates into the polymer to develop the leuco dye, but it is a high molecular weight type. In the case of a color developer that is not compatible with the polymer, the penetration speed into the polymer becomes extremely slow, and the color cannot be apparently developed. In the crosslinked polymer matrix, the penetration of the color developer into the polymer can be suppressed even at the glass transition temperature of the polymer or higher, depending on the crosslink density.

However, in order to control the color developability by permeation of the color developer into the polymer particles in this way, the permeation amount and permeation distance are important. Will be strongly received. In the polymer suspension having a glass transition temperature of room temperature or higher, which is produced by the method for producing an artificial latex, the particles are not spherical but the surface morphology is diversified, and therefore, the surface area is relatively larger than that of the spherical particles produced by the present invention. Since the amount increases and there is variation, it is difficult to control the color forming property and the vividness deteriorates.

After the reaction with the color developer to develop a color, further heating causes a phase change in the polymer matrix in which the dye is present, and thermal fusion starts. At this time, the compatibility of the developer reacting with the dye becomes more important with the polymer, and some of them are separated from the dye in the polymer matrix apart from the dye.
This state means that the dye has returned to the state of Leuco,
As a result, the developed color is erased. However, in order to control such coloring and decoloring, it is necessary to consider penetration and redetachment of the color developer into the polymer. Therefore, spherical and uniform particle size is an important factor.

The leuco dye contained in such a polymer must penetrate into the polymer, as described above, because the leuco dye does not develop color only when the developer is melted by heat.
For this reason, there is a selection system for the color developer that develops the leuco dye. As a result that the decolorizing agent has the same selectivity as the color developing agent, it is possible to form a clear image that is not affected by these.

For example, leuco dye A, developer A, decolorizer, leuco dye B, and developer B are prepared. Leuco dye A
Is a leuco dye contained in the polymer described in the present invention. First, at a low temperature (temperature A), the developer A acts on the leuco dye A to develop a color. At a higher temperature, the decoloring agent acts to restore the color developing body to the leuco body, and the developing agent B acts on the leuco dye B near this temperature or at a higher temperature (temperature B) to develop the second color. At this time, if the leuco dye A cannot associate with the color developer B due to the influence of the polymer matrix, color development on the low temperature side when heating at high temperature, that is, color mixing can be prevented. Further, due to the influence of the polymer matrix, if the decoloring agent does not exist in the vicinity of the leuco dye B, it is possible to prevent the color density of the leuco dye B from decreasing due to the decoloring agent. Such a phenomenon becomes an even more important technique in the case of color thermosensitive recording that attempts to develop three or more colors.

Further, a temperature gradient is generated by thermal diffusion during color development or color erasing, but this temperature gradient usually causes a phenomenon of image bleeding around the color image area and the color erasing area. However, the permeation rate of the color developer or the color erasing agent into the polymer matrix is adjusted from the viewpoint of compatibility with the polymer, and for example, it occurs around the high temperature color-developing portion (leuco dye B and the color developing agent B) or the color-erasing portion. The coloring of the leuco dye A and the color developer A can be solved by speeding up the penetration of the decoloring agent into the latter.

Furthermore, if there are two leuco dyes described in the present invention, and they develop and decolor at different temperatures, it is possible to develop and decolor in two layers and two colors, and one layer and two colors.
A simple multicolor thermosensitive recording medium having a layer structure can be obtained.

[0052]

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

(A-1) Synthesis of Polymer Suspension Containing Leuco Dye by Suspension Polymerization 40 parts of styrene was mixed with 3- (p-diethylamino-o-ethoxyphenyl) -3- (1-n-octyl-2-methyl). 8.0 parts of indole-3-yl) phthalide and 1.2 parts of azobisisobutyronitrile (ABIN) were dissolved. Separately, in 120 parts of distilled water, sodium dodecyl sulfate of 0.
08 parts and polyvinyl alcohol (PVA224 manufactured by Kuraray Co., Ltd.) 2.4 parts were dissolved. Mix these two liquids,
A homomixer manufactured by Tokushu Kika Kogyo Co., Ltd. was used to disperse the mixture at 8000 rpm for 3 minutes for emulsification. This emulsion is placed under a nitrogen atmosphere for 8
Polymer Suspension Liquid A-1 by heating at 0 degrees for 8 hours
Got The polymer obtained had a spherical particle size and a size with a distribution of 3 to 5 microns.

(A-2) Synthesis of Polymer Suspension Containing Leuco Dye by Suspension Polymerization 40 parts of styrene was mixed with 3,3-bis (1-n-octyl-2).
-Methylindol-3-yl) phthalide 8.0 parts, dimethyl oxalate 15 parts and azobisisobutyronitrile (ABIN) 1.2 parts were dissolved. Separately distilled water 120
0.08 parts of sodium dodecyl sulfate and 2.4 parts of polyvinyl alcohol (PVA224 manufactured by Kuraray) were dissolved in the parts. The two kinds of liquids were mixed and dispersed by a homomixer manufactured by Tokushu Kika Kogyo at 8000 rpm for 3 minutes for emulsification. This emulsion was heated at 80 ° C. for 8 hours in a nitrogen atmosphere to obtain a polymer suspension liquid A-2. The polymer obtained had a spherical particle size and a size with a distribution of 2 to 3.5 microns.

(A-3) Synthesis of polymer suspension containing leuco dye by emulsion polymerization 10 parts of t-butyl methacrylate, 6 parts of n-butyl methacrylate and 4 parts of diethylaminoethyl methacrylate 3,3-bis (1-n-) 8.0 parts of octyl-2-methylindol-3-yl) phthalide were dissolved. Separately, 120 parts of distilled water, emulsifier (newcol-707sf
5 parts of Nippon Emulsifier) and 1.2 parts of a polymerization initiator 2,2'-azobis (2-methylpropionamidine) dihydrochloride were dissolved and heated to 60 ° C under a nitrogen atmosphere. To this heated aqueous solution, 20 parts of t-butyl methacrylate in which 4 parts of the dye was dissolved was gradually added dropwise over 4 hours. Then, the mixture was heated for 3 hours to obtain a polymer suspension liquid A-3. The obtained polymer is spherical particles,
The size had a distribution of 0.5 to 1 micron.

(A-4) Synthesis of Polymer Suspension Containing Leuco Dye by Emulsion Polymerization 38 parts of styrene and 2 parts of dimethylaminomethylstyrene were mixed with 3-di-n-pentylamino-6-methyl-7-anilinofluorane. Two parts were dissolved. Separately, in 120 parts of distilled water, an emulsifier (newcol-707sf made by Nippon Emulsifier)
5.4 parts and 2,2'-azobis (2-
Methylpropionamidine) dihydrochloride 0.
8 parts was dissolved and heated under a nitrogen atmosphere at 60 ° C. for 10 hours to obtain a polymer suspension liquid A-4. The resulting polymer was spherical and had a size distribution of 0.2 to 0.5 microns.

(B-1) Preparation of Leuco Dye Dispersion Liquid 40 parts of 3-diethylamino-6-methyl-7-chlorofluorane and sulfonic acid-modified polyvinyl alcohol (L3
266 (Nippon Gosei Kagaku KK) 2.8 parts and distilled water 57.2
Parts with glass beads in a paint shaker (manufactured by Red Devil Co.) for 12 hours to give a leuco dye dispersion B.
-1 was obtained.

(B-2) Preparation of leuco dye dispersion 40 parts of 3-di-n-butyl-6-methyl-7-anilinofluorane and sulfonic acid-modified polyvinyl alcohol (L
3266 (Nippon Gosei Kagaku KK) 2.8 parts and distilled water 57.
Two parts were dispersed together with glass beads in a paint shaker (manufactured by Red Devil Co.) for 12 hours to obtain a leuco dye dispersion B-2.

(B-3) Preparation of Leuco Dye Dispersion Liquid 40 parts of 3,3-bis (p-dimethylaminophenyl) phthalide and sulfonic acid-modified polyvinyl alcohol (L32)
66 Nippon Synthetic Chemical Industry Co., Ltd.) 2.8 parts and distilled water 57.2 parts were dispersed together with glass beads in a paint shaker (manufactured by Red Devil Co.) for 12 hours to obtain a leuco dye dispersion B-.
Got 3.

(C-1) Preparation of color developer dispersion 40 parts of 1,1-bis (4-hydroxyphenyl) cyclohexane and sulfonic acid-modified polyvinyl alcohol (L3
266 (Nippon Gosei Kagaku KK) 2.8 parts and distilled water 57.2
Part was dispersed for 12 hours with a glass shaker in a paint shaker (manufactured by Red Devil Co.) to obtain a developer dispersion C-1.
Got

(C-2) Preparation of developer dispersion 40 parts of 4-hydroxyphenyl-4-n-dodecyloxyphenyl sulfone, 2.8 parts of sulfonic acid modified polyvinyl alcohol (L3266 manufactured by Nippon Synthetic Chemical Industry) and distillation 57.2 parts of water was dispersed together with glass beads for 12 hours with a paint shaker (manufactured by Red Devil Co.) to obtain a developer dispersion C-2.

(D) Preparation of Discoloring Agent Dispersion Liquid 40 parts of 1,3-dicyclohexyl-2-dimethylphenylguanidine, 2.8 parts of sulfonic acid modified polyvinyl alcohol (L3266 manufactured by Nippon Synthetic Chemical Industry) and 5 parts of distilled water
7.2 parts were dispersed together with glass beads in a paint shaker (manufactured by Red Devil Co.) for 12 hours to obtain a decolorizer dispersion liquid D.

(E) Preparation of Binder Solution Polyvinyl alcohol (NM-11 manufactured by Nippon Synthetic Chemical Industry)
Binder solution E was obtained by dissolving 20 parts in 200 parts of distilled water.

(F) Preparation of White Pigment Dispersion Calcium carbonate (Brilliant 15 manufactured by Shiraishi Kogyo) 40
Parts, 2 parts of sodium hexametaphosphate and 38 parts of distilled water,
Pigment dispersion F was obtained by dispersing together with glass beads for 3 hours with a paint shaker (manufactured by Red Devil).

Example 1 15 parts of binder solution E and 1 part of developer dispersion C-1
0.7 parts, polymer suspension containing leuco dye A
-4 was mixed with 27 parts and 15 parts of distilled water to obtain a coating liquid.
This coating liquid is applied on foamed PET having a basis weight of 60 g / m ² ,
It was dried at 60 ° C. for 5 minutes to obtain a thermal recording material having a coating amount of 5 g / m ² . This recording medium is used as a thermal print head (KJT-2
56-8MGF1 1670 ohm (Kyocera) was used to set a pulse width of 0.4 to 1.1 milliseconds at 26 volts, and when color printing was performed, it developed to a density of 1.0 in 0.6 milliseconds. However, the density dropped to 0.3 in 1.1 milliseconds. When the area where the density was reduced was printed for 0.6 milliseconds, no recoloring occurred.

Example 2 (1) Preparation of coating liquid for first thermosensitive recording layer (magenta color development) 15 parts of binder solution E and 1 part of developer dispersion C-1
0.7 parts, 27 parts of leuco dye dispersion liquid B-1, 1.6 parts of pigment dispersion liquid F and 15 parts of distilled water were mixed to prepare a coating liquid.

(2) Preparation of coating liquid for intermediate layer (decoloring layer) Mixing 30 parts of binder solution E, 9 parts of decolorizer dispersion D, 2.5 parts of pigment dispersion F and 40 parts of distilled water To prepare a coating solution.

(3) Preparation of Second Thermosensitive Recording Layer (Cyan Coloring) Coating Solution 15 parts of binder solution E and 1 part of developer dispersion C-2
2.5 parts, polymer suspension liquid A containing leuco dye
-1 to 2.5 parts, pigment dispersion F to 1.7 parts and distilled water 4
0 part was mixed to prepare a coating liquid.

(4) Formation of heat-sensitive recording layer A second heat-sensitive recording layer coating liquid, an intermediate layer coating liquid and a first heat-sensitive recording layer coating liquid were applied in this order on a synthetic paper having a basis weight of 60 g / m ² , dried and laminated. Then, a multicolor thermosensitive recording medium was produced by applying a calendar.
The applied amount after drying is 5 g / m ² and 2.5 g / m ² , respectively.
It was m ² and 2.5 g / m ² .

Example 3 (1) Preparation of First Thermosensitive Recording Layer (Magenta Coloring) Coating Solution 15 parts of binder solution E and 1 part of developer dispersion C-1
0.7 parts, polymer suspension containing leuco dye A
-32 parts, pigment dispersion F 1.2 parts and distilled water 10
The parts were mixed to obtain a coating liquid.

(2) Preparation of Second Thermosensitive Recording Layer (Black Coloring) Coating Solution 15 parts of Binder solution E and 8. Dispersion of color developer C-1.
5 parts, polymer suspension containing leuco dye A-4
Of 45 parts and 1.2 parts of pigment dispersion liquid F were mixed to prepare a coating liquid.

(3) Preparation of Third Thermosensitive Recording Layer (Cyan Coloring) Coating Solution 15 parts of Binder Solution E and 15 parts of Developer Dispersion C-2
Parts, 2.5 parts of the leuco dye-containing polymer suspension liquid A-1, 1.8 parts of the pigment dispersion liquid F, and 40 parts of distilled water were mixed to prepare a coating liquid.

(4) Formation of Thermosensitive Recording Layer Each coating solution was applied on a synthetic paper having a basis weight of 60 g / m ^{2 in} the order of the third thermosensitive recording layer, the second thermosensitive recording layer and the first thermosensitive recording layer, and dried. The layers were laminated and calendered to prepare a multicolor thermosensitive recording medium. The coating amount after drying is 5 g and 3 g per m ^2, respectively.
It was 3 g.

Comparative Example 1 (1) Preparation of First Thermosensitive Recording Layer (Magenta Coloring) Coating Solution 15 parts of Binder Solution E and 6. Dispersion of Developer Dispersion C-1.
3 parts, leuco dye dispersion B-1 2.5 parts, pigment dispersion F 1.2 parts and distilled water 40 parts were mixed to prepare a coating liquid.

(3) Preparation of Second Thermosensitive Recording Layer (Cyan Coloring) Coating Solution 15 parts of Binder Solution E and 1 part of Developer Dispersion C-2
2.5 parts, leuco dye dispersion B-3 2.5 parts, pigment dispersion F 1.2 parts and distilled water 34 parts were mixed to prepare a coating liquid.

(4) Formation of thermosensitive recording layer Each coating solution was applied in the order of the second thermosensitive recording layer, the intermediate layer and the first thermosensitive recording layer on a synthetic paper having a basis weight of 60 g / m ² , dried and laminated, A multicolor thermosensitive recording medium was prepared by calendering. The intermediate layer in this case is the same as in Example 2. The coating amounts after drying were 3 g, 1 g, and 1.5 g per m ^2, respectively.

Comparative Example 2 (1) Preparation of First Thermosensitive Recording Layer (Magenta Coloring) Coating Solution 15 parts of Binder solution E and 6.
3 parts, leuco dye dispersion B-1 2.5 parts, pigment dispersion F 1.2 parts and distilled water 40 parts were mixed to prepare a coating liquid.

(2) Preparation of Second Thermosensitive Recording Layer (Black Coloring) Coating Solution Binder solution E (15 parts) and developer dispersion C-1 (8)
5 parts, 45 parts of leuco dye dispersion B-2, pigment dispersion F
Was mixed with 1.2 parts of distilled water and 40 parts of distilled water to prepare a coating liquid.

(3) Preparation of Third Thermosensitive Recording Layer (Cyan Coloring) Coating Solution 15 parts of Binder Solution E and 1 part of Developer Dispersion C-2
2.5 parts, leuco dye dispersion B-3 2.5 parts, pigment dispersion F 1.8 parts and distilled water 40 parts were mixed to prepare a coating liquid.

(4) Formation of heat-sensitive recording layer Each coating solution was formed on a synthetic paper having a basis weight of 60 g / m ^{2 in} the order of the third heat-sensitive recording layer, the intermediate layer, the second heat-sensitive recording layer, the intermediate layer and the first heat-sensitive recording layer. Was applied, dried and laminated, and a calendar was applied to prepare a multicolor thermosensitive recording medium. The intermediate layers in this case are the same as in Example 2. The coating amounts after drying were 5 g, 1.5 g, 3 g, 1.5 g and 3 g per m ^2, respectively.

The four kinds of multicolor thermosensitive recording media of Examples 2 and 3 and Comparative Examples 1 and 2 thus obtained were applied with a thermal printing head (KJT-256-8MGF1 1670 ohm Kyocera) at 26 volts. Pulse width 0.4 to 1.1
Color printing was performed by setting the time to be millisecond, and color mixture and bleeding were visually judged. The results are given in Table 1.

[0082]

[Table 1]

[0083]

Industrial Applicability As shown in Table 1, a thermosensitive recording material which can be decolored after color development by incorporating a leuco dye into the polymer by emulsion polymerization or suspension polymerization, and is a clear recording material using this It was possible to obtain a multicolor thermosensitive recording layer from which an image was obtained.

[Brief description of drawings]

FIG. 1 is an electron micrograph of (A-1) polystyrene particles containing a leuco dye prepared by synthesizing a polymer suspension containing a leuco dye by (A-1) suspension polymerization.

Claims (2)

[Claims] 1. A heat-sensitive recording material for forming a color image by a reaction between a leuco dye and a color developer, wherein the leuco dye is contained in the polymer of a vinyl polymer suspension produced by emulsion or suspension polymerization. A heat-sensitive recording material characterized by the following. 2. The heat-sensitive recording material according to claim 1, which develops color when heated and is decolorized when heated at a higher temperature.