JP3107864B2 - Manufacturing method of thermal recording material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a heat-sensitive recording material having high sensitivity and excellent image storability.

[0002]

2. Description of the Related Art In recent years, heat-sensitive recording materials have been widely used in printers for measuring instruments, printers for computers, facsimile machines, etc. because of the simplicity of the apparatus and the need for almost no maintenance. In general,
A heat-sensitive recording material is a heat-sensitive recording layer containing an electron-donating dye precursor and an electron-accepting color developer provided on a support, and by heating it, the dye precursor reacts with the color developer to form an image. It is to get. However, the reaction between the dye precursor and the developer is a reversible reaction, and the color is easily erased by contact with cosmetics, stationery, an organic solvent or the like. As a heat-sensitive recording material in which such disadvantages are improved, a heat-sensitive recording material comprising an aromatic isocyanate compound and an imino compound is disclosed in
8-38733, JP-A-58-54085, and JP-A-58-104959. Regarding the wet grinding method of the aromatic isocyanate compound, for example, Japanese Patent Application Laid-Open No.
55986 and JP-A-3-150190.
JP-A-3-155986 aims to improve sensitivity by simultaneously pulverizing and dispersing an aromatic isocyanate compound and an alcoholic compound. Further, Japanese Patent Application Laid-Open No. 3-150190 aims to keep the average particle diameter of the aromatic isocyanate compound at 0.7 μm to 3.0 μm as a preferable particle diameter by wet pulverization. However, at present, the sensitivity is not yet sufficient even if the above-mentioned method is used, and further higher sensitivity is required.

[0003]

SUMMARY OF THE INVENTION The present applicant has disclosed Japanese Patent Application Laid-Open
The invention relating to the wet pulverization of an aromatic isocyanate compound described in JP-A No. 155986 and JP-A-3-150190 has already been filed. According to these inventions, the aromatic isocyanate compound can be wet-pulverized, but the sensitivity is insufficient. When the aromatic isocyanate compound is wet-pulverized, an intense reaction between the aromatic isocyanate compound and water occurs, and the heat generation is extremely large.
It is considered that the reaction between the aromatic isocyanate compound and water is further accelerated, and the number of isocyanate groups which form a color by reacting with the imino group when heated is drastically reduced. For example, in Comparative Example 1, cooling was continued with tap water to prevent the temperature from becoming high. However, since the calorific value was extremely large, even though such measures were taken, the temperature greatly exceeded 40 ° C. and reached 50 ° C. It has become. Therefore, the present inventors have found that cooling with tap water is not sufficient, and the liquid temperature of the cooling aqueous medium is changed to 5 to 35 in place of tap water.
Cooling was continued sufficiently to maintain the temperature in the range of ° C. Liquid temperature 5
By maintaining the temperature in the range of ~ 35 ° C, the number of isocyanate groups was prevented from drastically decreasing, and the aim was to further increase the sensitivity.

[0004]

SUMMARY OF THE INVENTION The present invention relates to a method for producing a heat-sensitive recording material comprising an aromatic isocyanate compound and an imino compound as a color-forming component, wherein the aromatic isocyanate compound is wet-ground in an aqueous medium. A method for producing a heat-sensitive recording material, characterized in that the temperature of the aqueous medium is maintained in the range of 5 to 35 ° C. By maintaining the liquid temperature of the aqueous medium in the range of 5 to 35 ° C., the hydrolysis of the aromatic isocyanate compound during wet pulverization is more effectively prevented.

[0005]

It is known that isocyanate compounds generally have high reactivity and react with amines, acid amides, phenols, carboxylic acids, thiols, active methylene compounds, water and the like. Even when the aromatic isocyanate compound used in the present invention is wet-pulverized, the isocyanate group on the particle surface of the aromatic isocyanate compound is brought into contact with water, so that hydrolysis proceeds and the aromatic amine and Generates carbon dioxide. Since the hydrolysis of the isocyanate group is an exothermic reaction, if wet pulverization is continued, an increase in the liquid temperature is observed due to the progress of hydrolysis. As the liquid temperature increases, hydrolysis is further promoted. As described above, the rise in the liquid temperature proceeds at an accelerated rate, and is accompanied by significantly more exothermic heat than when other compounds are pulverized in an aqueous medium. When wet pulverization is carried out by a normal method without taking any measures, the liquid temperature rises to 50 ° C. or higher, and the liquid temperature becomes 50 ° C. even when cooling with tap water is continued as in Comparative Example 1. When the liquid temperature rises to 50 ° C. or higher, a large amount of the aromatic isocyanate compound is hydrolyzed. The present inventors have observed that the sensitivity is significantly reduced in such a case. In order to prevent such a phenomenon, when the aromatic isocyanate compound is wet-pulverized, it is constantly cooled,
It was found that maintaining the solution temperature in the range of 5 to 35 ° C was effective. If the aqueous medium does not coagulate even at 0 ° C. or lower, the effect appears. However, when the aqueous medium is only water, it is not preferable because it coagulates at 0 ° C. or lower. In this way, by suppressing the hydrolysis rate of the aromatic isocyanate compound, pulverization can be performed while maintaining the activity of the aromatic isocyanate compound. A clear increase in sensitivity was observed compared to those without temperature control and those with continued cooling with tap water.

In the wet pulverization, the aromatic isocyanate according to the present invention has an average particle size of 0.7 to 3.0.
0 μm is preferred. It is a well-known fact that in a heat-sensitive recording material, sensitivity can be improved by reducing the particle size of each material. However, when the average particle size of the aromatic isocyanate compound is reduced, the surface area of the particles increases, and the contact area with water increases, whereby the hydrolysis of the aromatic isocyanate compound is promoted. . For these reasons, the above range of the average particle size is preferable.

[0008] As a wet grinding method of the aromatic isocyanate compound according to the present invention, a general wet grinding method can be used. For example, one or more of the aromatic isocyanate compounds are preliminarily dispersed in an aqueous solution containing a compound having a dispersing ability such as a water-soluble polymer, a polymer emulsion, and a surfactant. Is wet-pulverized using a pulverizer such as a ball mill, a sand mill, a dyno mill, an attritor, and a colloid mill. At this time, cooling is performed by circulating cooling water or the like inside or outside the pulverizer, and the liquid temperature of the dispersion during wet pulverization is maintained in the range of 5 to 35 ° C. The cooling can be performed by a method such as using a cooling jacket or circulating a refrigerant in a crusher. As the refrigerant, low-temperature air, ice, dry ice, liquid nitrogen, or the like can be used.

The aromatic isocyanate compound used in the present invention is a colorless or pale-colored aromatic isocyanate compound or a heterocyclic isocyanate compound which is solid at room temperature. For example, at least one of the following isocyanate compounds is used. Used. 2,6-dichlorophenyl isocyanate, p-chlorophenyl isocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, 1,3-dimethylbenzene-4,6-diisocyanate, 1,4 -Dimethylbenzene-2,5-diisocyanate, 1-methoxybenzene-2,4-diisocyanate, 1-methoxybenzene-2,5-diisocyanate, 1-ethoxybenzene-2,4-diisocyanate 2,5-dimethoxybenzene-1,4-diisocyanate, 2,5-diethoxybenzene-1,4-diisocyanate, 2,5-dibutoxybenzene-1,4
-Diisoanato, azobenzene-4,4'-diisocyanate, diphenylether-4,4'-diisocyanate, naphthalene-1,4-diisocyanate, naphthalene-1,5-diisocyanate, naphthalene-2,6
-Diisocyanate, naphthalene-2,7-diisocyanate, 3,3'-dimethylbiphenyl-4,4'-diisocyanate, 3,3'-dimethoxybiphenyl-
4,4'-diisocyanate, diphenylmethane-4,
4'-diisocyanate, diphenyldimethylmethane-
4,4′-diisocyanate, benzophenone-3,
3'-diisocyanate, fluorene-2,7-diisocyanate, anthraquinone-2,6-diisocyanate, 9-ethylcarbazole-3,6-diisocyanate, pyrene-3,8-diisocyanate , Naphthalene-
1,3,7-triisocyanate, biphenyl-2,2
4,4′-triisocyanate, 4,4 ′, 4 ″ -triisocyanate-2,5-dimethoxytriphenylamine, p-dimethylaminophenyl isocyanate, tris (4-phenylisocyanate) thiophosphate and the like There is.

If necessary, these isocyanate compounds may be used in the form of so-called block isocyanates, which are addition compounds with phenols, lactams, oximes, etc., and diisocyanate dimers. For example, it may be used in the form of 1-methylbenzene-2,4-diisocyanate dimer and trimer isocyanurate, or used as a polyisocyanate adducted with various polyols and the like. It is also possible.

The imino compound used in the present invention is a compound represented by the following chemical formula 1 (φ is a residue of an aromatic compound capable of forming a conjugated system with adjacent C） N), and is a colorless solid at room temperature. Or it is a light-colored compound. Specific examples are shown below. Two or more imino compounds can be used in combination depending on the purpose.

[0012]

Embedded image

3-iminoisoindoline-1-one, 3
-Imino-4,5,6,7-tetrachloroisoindoline-1-one, 3-imino-4,5,6,7-tetrabromoisoindoline-1-one, 3-imino-4,5
6,7-tetrafluoroisoindoline-1-one, 3
-Imino-5,6-dichloroisoindoline-1-one, 3-imino-4,5,7-trichloro-6-methoxyisoindoline-1-one, 3-imino-4,5,7
-Trichloro-6-methylmercapto-isoindoline-1-one, 3-imino-6-nitroisoindoline-
1-one, 3-imino-isoindoline-1-spiro-
Dioxolan, 1,1-dimethoxy-3-iminoisoindoline, 1,1-diethoxy-3-imino-4,5,
6,7-tetrachloroisoindoline, 1-ethoxy-
3-iminoisoindoline, 1,3-diiminoisoindoline, 1,3-diimino-4,5,6,7-tetrachloroisoindoline, 1,3-diimino-6-methoxyisoindoline, 1,3- Diimino-6-cyanoisoindoline, 1,3-diimino-4,7-dithia-5,
5,6,6-tetrahydroisoindoline, 7-amino-2,3-dimethyl-5-oxopyrrolo [3,4b] pyrazine, 7-amino-2,3-diphenyl-5-oxopyrrolo [3,4b] pyrazine, 1-iminonaphthalimide, 1-iminodiphenimide, 1-phenylimino-3-iminoisoindoline, 1- (3'-chlorophenylimino) -3-iminoisoindoline, 1-
(2 ′, 5′-dichlorophenylimino) -3-iminoisoindoline, 1- (2 ′, 4 ′, 5′-trichlorophenylimino) -3-iminoisoindoline, 1-
(2'-cyano-4'-nitrophenylimino) -3-
Iminoisoindoline, 1- (2'-chloro-5'-cyanophenylimino) -3-iminoisoindoline, 1
-(2 ', 6'-dichloro-4'-nitrophenylimino) -3-iminoisoindoline, 1- (2', 5'-
Dimethoxyphenylimino) -3-iminoisoindoline, 1- (2 ', 5'-diethoxyphenylimino)-
3-iminoisoindoline, 1- (2'-methyl-4 '
-Nitrophenylimino) -3-iminoisoindoline, 1- (5'-chloro-2'-phenoxyphenylimino) -3-iminoisoindoline, 1- (4'-N,
N-dimethylaminophenylimino) -3-iminoisoindoline, 1- (3'-N, N-dimethylamino-
4'-methoxyphenylimino) -3-iminoisoindoline, 1- (2'-methoxy-5'-N-phenylcarbamoylphenylimino) -3-iminoisoindoline, 1- (2'-chloro-5'-) (Trifluoromethylphenylimino) -3-iminoisoindoline, 1-
(5 ′, 6′-dichlorobenzothiazolyl-2′-imino) -3-iminoisoindoline, 1- (6′-methylbenzothiazolyl-2′-imino) -3-iminoisoindoline, 1 -(4'-phenylaminophenylimino) -3-iminoisoindoline, 1- (p-phenylazophenylimino) -3-iminoisoindoline, 1
-(Naphthyl-1'-imino) -3-iminoisoindoline, 1- (anthraquinone-1'-imino) -3-iminoisoindoline, 1- (5'-chloroanthraquinone-1'-imino)- 3-iminoisoindoline, 1-
(N-ethylcarbazolyl-3′-imino) -3-iminoisoindoline, 1- (naphthoquinone-1′-imino) -3-iminoisoindoline, 1- (pyridyl-
4'-imino) -3-iminoisoindoline, 1- (benzimidazolone-6'-imino) -3-iminoisoindoline, 1- (1'-methylbenzimidazolone-
6'-imino) -3-iminoisoindoline, 1-
(7'-chlorobenzimidazolone-5'-imino)-
3-iminoisoindoline, 1- (benzimidazolyl-2′-imino) -3-iminoisoindoline, 1-
(Benzimidazolyl-2'-imino) -3-imino-
4,5,6,7-tetrachloroisoindoline, 1-
(2 ′, 4′-dinitrophenylhydrazone) -3-iminoisoindoline, 1- (indazolyl-3′-imino) -3-iminoisoindoline, 1- (indazolyl-3′-imino) -3-imino- 4,5,6,7-tetrabromoisoindoline, 1- (indazolyl-3′-
Imino) -3-imino-4,5,6,7-tetrafluoroisoindoline, 1- (benzimidazolyl-2'-
Imino) -3-imino-4,7-dithiatetrahydroisoindoline, 1- (4 ', 5'-dicyanoimidazolyl-2'-imino) -3-imino-5,6-dimethyl-
4,7-pyradioisoindoline, 1- (cyanobenzoylmethylene) -3-iminoisoindoline, 1- (cyanocarbonamidomethylene) -3-iminoisoindoline, 1- (cyanocarbomethoxymethylene) -3-imino Isoindoline, 1- (cyanocarbethoxymethylene) -3-iminoisoindoline, 1- (cyano-N-
Phenylcarbamoylmethylene) -3-iminoisoindoline, 1- [cyano-N- (3'-methylphenyl)
-Carbamoylmethylene] -3-iminoisoindoline, 1- [cyano-N- (4'-chlorophenyl) -carbamoylmethylene] -3-iminoisoindoline, 1
-[Cyano-N- (4'-methoxyphenyl) -carbamoylmethylene] -3-iminoisoindoline, 1-
[Cyano-N- (3'-chloro-4'-methylphenyl) -carbamoylmethylene] -3-iminoisoindoline, 1- (cyano-p-nitrophenylmethylene)-
3-iminoisoindoline, 1- (dicyanomethylene)
-3-iminoisoindoline, 1- (cyano-1 ',
2 ′, 4′-Triazolyl- (3 ′)-carbamoylmethylene) -3-iminoisoindoline, 1- (cyanothiazoyl- (2 ′) carbamoylmethylene) -3-iminoisoindoline, 1- (cyanobenzimidazolyl-
(2 ′)-carbamoylmethylene) -3-iminoisoindoline, 1- (cyanobenzothiazolyl- (2 ′)-
Carbamoylmethylene) -3-iminoisoindoline,
1-[(cyanobenzimidazolyl-2 ′) methylene]
-3-iminoisoindoline, 1-[(cyanobenzimidazolyl-2 ')-methylene] -3-imino-4,
5,6,7-tetrachloroisoindoline, 1-[(cyanobenzimidazolyl-2 ′)-methylene] -3-imino-5-methoxyisoindoline, 1-[(cyanobenzimidazolyl-2 ′)-methylene] -3-imino-
6-chloroisoindoline, 1-[(1′-phenyl-
3'-methyl-5-oxo) -pyrazolidene-4 ']-
3-iminoisoindoline, 1-[(cyanobenzimidazolyl-2 ')-methylene] -3-imino-4,7-
Dithiatetrahydroisoindoline, 1-[(cyanobenzimidazolyl-2 ′) methylene] -3-imino-
5,6-dimethyl-4,7-pyradiisoindoline, 1
-[(1'-methyl-3'-n-butyl) -barbituric acid-5 ']-3-iminoisoindoline, 3-imino-
1-sulfobenzoic acid imide, 3-imino-1-sulfo-
6-chlorobenzoic imide, 3-imino-1-sulfo-
5,6-dichlorobenzoic imide, 3-imino-1-sulfo-4,5,6,7-tetrachlorobenzoic imide,
3-imino-1-sulfo-4,5,6,7-tetrabromobenzoic imide, 3-imino-1-sulfo-4,5,
6,7-tetrafluorobenzoic imide, 3-imino-
1-sulfo-6-nitrobenzoic acid imide, 3-imino-
1-sulfo-6-methoxybenzoic imide, 3-imino-1-sulfo-4,5,7-trichloro-6-methylmercaptobenzoic imide, 3-imino-1-sulfonaphthoic imide, 3-imino-1 -Sulfo-5-bromonaphthoic imide, 3-imino-2-methyl-4,5,
6,7-tetrachloroisoindoline-1-one and the like.

The heat-sensitive recording material according to the present invention can contain a heat-fusible substance in order to improve its thermal response. In this case, those having a melting point of 60 ° C to 180 ° C are preferable, and those having a melting point of 80 ° C to 140 ° C are more preferable. Specific examples of the heat-fusible substance (sensitizer) for improving such thermal responsiveness include N-hydroxymethylstearic amide, stearic amide, palmitic amide, oleic amide, and ethylene. -Bisstearic acid amide, ricinoleic acid amide, paraffin wax, microcrystalline wax, polyethylene wax, rice wax,
Waxes such as carnauba wax, naphthol derivatives such as 2-benzyloxynaphthalene, biphenyl derivatives such as p-benzylbiphenyl and 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 di (p-chlorobenzyl) oxalate; Oxalic acid diester derivatives and the like can be mentioned. These sensitizers can be used alone or in combination of two or more. Further, in order to obtain a sufficient thermal responsiveness, the aromatic isocyanate compound should be used in an amount of 10 to 30.
It is preferably used at 0% by weight, and more preferably used at 20 to 250% by weight.

Furthermore, the heat-sensitive recording material according to the present invention may contain an aniline derivative having at least one amino group, which is disclosed in International Application WO 87/06885 filed by the present applicant. These aniline derivatives are effective in preventing background fog. These compounds include methyl p-aminobenzoate, ethyl p-aminobenzoate, n-propyl p-aminobenzoate, iso-propyl p-aminobenzoate, butyl p-aminobenzoate, p-aminobutyl Dodecyl benzoate, benzyl p-aminobenzoate, o-aminobenzophenone, m-aminoacetophenone, p-aminoacetophenone, m-aminobenzamide, o-aminobenzamide, p-aminobenzamide, p-amino-N-methylbenzamide, 3-
Amino-4-methylbenzamide, 3-amino-4-methoxybenzamide, 3-amino-4-chlorobenzamide, p- (N-phenylcarbamoyl) aniline, p
-[N- (4-chlorophenyl) carbamoyl] aniline, p- [N- (4-aminophenyl) carbamoyl]
Aniline, 2-methoxy-5- (N-phenylcarbamoyl) aniline, 2-methoxy-5- [N- (2′-methyl-3′-chlorophenyl) carbamoyl] aniline, 2-methoxy-5- [N- ( 2'-chlorophenyl) carbamoyl] aniline, 5-acetylamino-2
-Methoxyaniline, 4-acetylaminoaniline, 4
-(N-methyl-N-acetylamino) aniline, 2,
5-dimethoxy-4- (N-benzoylamino) aniline, 2,5-diethoxy-4- (N-benzoylamino) aniline, 2-methoxy-4- (N-benzoylamino) -5-methylaniline, 4- Sulfamoylaniline, 3-sulfamoylaniline, 2- (N-ethyl-N-phenylaminosulfonyl) aniline, 4-dimethylaminosulfonylaniline, 4-diethylaminosulfonylaniline, sulfathiazole, 4-aminodiphenylsulfone, 2-chloro-5-N-phenylsulfamoylaniline, 2-methoxy-5-N, N-diethylsulfamoylaniline, 2,5-dimethoxy-4
-N-phenylsulfamoylaniline, 2-methoxy-5-benzylsulfonylaniline, 2-phenoxysulfonylaniline, 2- (2'-chlorophenoxy)
Sulfonylaniline, 3-anilinosulfonyl-4-methylaniline, bis [4- (m-aminophenoxy) phenyl] sulfone, bis [4- (p-aminophenoxy) phenyl] sulfone, bis [3-methyl-4- (P
-Aminophenoxy) phenyl] sulfone, 3,3'-
Dimethoxy-4,4'-diaminobiphenyl, 3,3 '
-Dimethyl-4,4'-diaminobiphenyl, 2,2 '
-Dichloro-4,4'-diamino-5,5'-dimethoxybiphenyl, 2,2 ', 5,5'-tetrachloro-
4,4′-diaminobiphenyl, ortho-tolysine sulfone, 2,4′-diaminobiphenyl, 2,2′-diaminobiphenyl, 4,4′-diaminobiphenyl, 2,
2'-dichloro-4,4'-diaminobiphenyl, 3,
3'-dichloro-4,4'-diaminobiphenyl, 2,
2′-dimethyl-4,4′-diaminobiphenyl, 4,
4′-thiodianiline, 2,2′-dithiodianiline,
4,4'-dithiodianiline, 4,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4 '
-Diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, bis (3-amino-4-chlorophenyl) sulfone, bis (3,4-diaminophenyl) sulfone, bis (3-aminophenyl) sulfone, bis (4
-Aminophenyl) sulfone, 3,4'-diaminodiphenylsulfone, 3,3'-diaminodiphenylmethane, 4,4'-ethylenedianiline, 4,4'-diamino-2,2'-dimethyldibenzyl, 4, 4'-diamino-3,3'-dichlorodiphenylmethane, 3,3'-
Diaminobenzophenone, 4,4′-diaminobenzophenone, 1,4-bis (4-aminophenoxy) benzene, 1,3-bis (4-aminophenoxy) benzene,
1,3-bis (3-aminophenoxy) benzene, 9,
9-bis (4-aminophenoxy) fluoran, 2,2
-Bis (4-aminophenoxyphenyl) propane,
4,4′-bis (4-aminophenoxy) diphenyl,
3,3 ', 4,4'-tetraaminodiphenyl ether, 3,3', 4,4'-tetraaminodiphenylsulfone, 3,3 ', 4,4'-tetraaminobenzophenone, and the like.

Further, in order to improve the fog resistance and thermal response of the uncolored portion, N-stearyl-N '-(2-hydroxyphenyl) urea and N-stearyl-N'-(3-
(Hydroxyphenyl) urea, N-stearyl-N′-
(4-hydroxyphenyl) urea, p-stearoylaminophenol, o-stearoylaminophenol, p-lauroylaminophenol, p-butyrylaminophenol, m-acetylaminophenol, o-
Acetylaminophenol, p-acetylaminophenol, o-butylaminocarbonylphenol, o-stearylaminocarbonylphenol, p-stearylaminocarbonylphenol, 1,1,3-tris (3
-Tert. -Butyl-4-hydroxy-6-methylphenyl) butane, 1,1,3-tris (3-tert.
-Butyl-4-hydroxy-6-ethylphenyl) butane, 1,1,3-tris (3,5-di-tert.-butyl-4-hydroxyphenyl) butane, 1,1,3-
Tris (3-tert.-butyl-4-hydroxy-6
-Methylphenyl) propane, 1,2,3-tris (3
-Tert. -Butyl-4-hydroxy-6-methylphenyl) butane, 1,1,3-tris (3-phenyl-
4-hydroxyphenyl) butane, 1,1,3-tris (3-cyclohexyl-4-hydroxy-5-methylphenyl) butane, 1,1,3-tris (3-cyclohexyl-4-hydroxy-6-methylphenyl )butane,
1,1,3,3-tetra (3-phenyl-4-hydroxyphenyl) propane, 1,1,3,3-tetra (3-
Cyclohexyl-4-hydroxy-6-methylphenyl) propane, 1,1-bis (3-tert.-butyl-4-hydroxy-6-methylphenyl) butane, 1,
1-bis (3-cyclohexyl-4-hydroxy-6-
It is also possible to add a phenol compound such as methylphenyl) butane.

[0017] In addition, diatomaceous earth, talc, kaolin, calcined kaolin, calcium carbonate, magnesium carbonate, titanium oxide,
Zinc oxide, silicon oxide, aluminum hydroxide, urea-formalin resin and the like are used. Also, for the purpose of preventing head abrasion and preventing sticking, higher fatty acid metal salts such as zinc stearate and calcium stearate, waxes such as paraffin, paraffin oxide, polyethylene, polyethylene oxide, stearic acid amide, caster wax, and dioctyl. A dispersant such as sodium sulfosuccinate, a benzophenone-based or benzotriazole-based ultraviolet absorber, a surfactant, a fluorescent dye, and the like are added as necessary.

As the binder used in the heat-sensitive recording material according to the present invention, various binders which are usually used can be used. For example, starches, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin, casein, polyvinyl alcohol, modified polyvinyl alcohol, sodium polyacrylate, acrylamide / acrylate copolymer, acrylamide / acrylate / methacrylic acid ternary copolymer Water-soluble binders such as coalescables, alkali salts of styrene / maleic anhydride copolymers, alkali salts of ethylene / maleic anhydride copolymers, and styrene / butadiene copolymers, acrylonitrile / butadiene copolymers, and methyl acrylate / Latex-based water-insoluble binders such as butadiene copolymers.

The heat-sensitive recording material according to the present invention comprises a support and a heat-sensitive recording layer which is colored by heating. As the support, paper is mainly used, but in addition to paper, various woven fabrics, nonwoven fabrics, synthetic resin films, laminated paper, synthetic paper, metal foil, or composite sheets obtained by combining these are optionally used according to the purpose. be able to. The structure of the heat-sensitive recording layer may be a single layer or a multi-layer structure. For example, each coloring component is contained one by one,
It may have a multilayer structure. Further, a protective layer may be provided on the heat-sensitive recording layer. This heat-sensitive recording layer can be obtained by mixing each aqueous dispersion obtained by finely pulverizing each color-forming component or other components, a binder and the like, applying the mixture on a support, and drying. Further, a support coated with an undercoat layer made of a pigment or the like can also be used as the support.

[0020]

The aromatic isocyanate compound according to the present invention reacts with water to cause hydrolysis of the isocyanate group. Since this hydrolysis is an exothermic reaction, when the aromatic isocyanate compound is dispersed in an aqueous medium, the temperature of the liquid increases. When the liquid temperature rises, the hydrolysis of the isocyanate group is accelerated. It is considered that the isocyanate group on the particle surface is reduced by hydrolysis. Thus, when the absolute amount of the active group possessed by the aromatic isocyanate compound decreases, by the reaction with the imino group during printing,
Since the amount of the aromatic isocyanate compound that forms color is substantially reduced, the sensitivity is reduced. In the present invention, cooling is performed during wet milling, and by controlling the temperature of the dispersion of the aromatic isocyanate compound, the decomposition of the aromatic isocyanate compound is reduced.As a result, the sensitivity is improved. Obtained.

[0021]

The present invention will be described in more detail with reference to the following examples. Example 1 [Liquid A] Dispersion of aromatic isocyanate compound Preliminary dispersion of 100 g of 4,4 ′, 4 ″ -triisocyanato-2,5-dimethoxytriphenylamine together with 400 g of a 2.5% aqueous polyvinyl alcohol solution was carried out. This was dispersed in a small dyno mill in which glass beads having a diameter of 1 mm were sealed. At that time, cooling with cooling water was performed, and the liquid temperature was kept at 5 ° C. Further, while measuring the particle size of the dispersion using Microtrac SRA manufactured by Leeds & Northrop Co., the dispersion time was adjusted so that the average particle size became about 0.9 μm. [Liquid B] Dispersion of imino compound 150 g of 1,3-diimino-4,5,6,7-tetrachloroisoindoline was dispersed in a small bead mill together with 350 g of an 8.5% aqueous polyvinyl alcohol solution to obtain a dispersion. [Liquid C] Dispersion of sensitizer 200 g of 2-benzyloxynaphthalene was similarly dispersed together with 800 g of a 2.5% aqueous polyvinyl alcohol solution,
A dispersion was obtained.

These three dispersions are mixed and sufficiently stirred, and 375 g of a 40% dispersion of zinc stearate, 1250 g of a 40% dispersion of calcium carbonate, and 1500 g of a 5% aqueous solution of polyvinyl alcohol are added until uniform. The mixture was stirred to obtain a coating liquid for a heat-sensitive recording material.

This coating solution is applied on a base paper having a basis weight of 50 g / m ² ,
The coating was applied to a solid content of 5.0 g / m ² , dried, and treated with a super calender to obtain a heat-sensitive recording material. This heat-sensitive recording material was applied with an applied energy of 0.65 mJ and 0.92 m using a heat-sensitive facsimile printing tester.
Printing was performed under the conditions of mJ, and the optical density of the obtained color image was measured using a densitometer Macbeth RD-918. As a result, optical densities of 0.58 and 1.17 were obtained, respectively.

Example 2 A solution was prepared in the same manner as in Example 1. However, the liquid temperature was kept at 10 ° C. during the dispersion. The dispersion time was adjusted in the same manner as in Example 1 so that the average particle diameter became about 0.9 μm. The same liquid as in Example 1 was used as the liquid B and the liquid C. Using these three kinds of dispersion liquids, a coating liquid was prepared in the same manner as in Example 1, applied to a base paper, and subjected to a super calender treatment to obtain a heat-sensitive recording material. This thermosensitive recording material was printed in the same manner as in Example 1, and the optical density of the developed image was measured to obtain densities of 0.57 and 1.15.

Example 3 A solution A was prepared in the same manner as in Example 1. However, the liquid temperature was kept at 20 ° C. during the dispersion. The dispersion time was adjusted in the same manner as in Example 1 so that the average particle diameter became about 0.9 μm. The same liquid as in Example 1 was used as the liquid B and the liquid C. Using these three kinds of dispersion liquids, a coating liquid was prepared in the same manner as in Example 1, applied to a base paper, and subjected to a super calender treatment to obtain a heat-sensitive recording material. This thermosensitive recording material was printed in the same manner as in Example 1, and the optical density of the developed image was measured to obtain densities of 0.56 and 1.12.

Example 4 A solution was prepared in the same manner as in Example 1. However, the liquid temperature was kept at 35 ° C. during the dispersion. The dispersion time was adjusted in the same manner as in Example 1 so that the average particle diameter became about 0.9 μm. The same liquid as in Example 1 was used as the liquid B and the liquid C. Using these three kinds of dispersion liquids, a coating liquid was prepared in the same manner as in Example 1, applied to a base paper, and subjected to a super calender treatment to obtain a heat-sensitive recording material. This thermosensitive recording material was printed in the same manner as in Example 1, and the optical density of the developed image was measured to obtain densities of 0.58 and 1.13.

Reference Example 1 A solution was prepared in the same manner as in Example 1. However, the liquid temperature was kept at 40 ° C. during the dispersion. The dispersion time was adjusted in the same manner as in Example 1 so that the average particle diameter became about 0.9 μm. The same liquid as in Example 1 was used as the liquid B and the liquid C. Using these three kinds of dispersion liquids, a coating liquid was prepared in the same manner as in Example 1, applied to a base paper, and subjected to a super calender treatment to obtain a heat-sensitive recording material. This thermosensitive recording material was printed in the same manner as in Example 1, and the optical density of the developed image was measured to obtain densities of 0.56 and 1.06.

Comparative Example 1 Liquid A was prepared in the same manner as in Example 1. However, the liquid temperature was kept at 50 ° C. during the dispersion. The dispersion time was adjusted in the same manner as in Example 1 so that the average particle diameter became about 0.9 μm. The same liquid as in Example 1 was used as the liquid B and the liquid C. Using these three kinds of dispersion liquids, a coating liquid was prepared in the same manner as in Example 1, applied to a base paper, and subjected to a super calender treatment to obtain a heat-sensitive recording material. This thermosensitive recording material was printed in the same manner as in Example 1, and the optical density of the developed image was measured to obtain densities of 0.49 and 0.97.

The results of measuring the optical densities of the color images obtained in Examples 1 to 4, Comparative Example 1 and Reference Example 1 are summarized in Table 1.

[0030]

[Table 1]

Evaluation In Examples 1-4, the liquid temperature at the time of wet pulverization of the present invention was 5-3.
Since the temperature is in the range of 5 ° C., hydrolysis of the aromatic isocyanate compound is suppressed, and a high optical density is exhibited. On the other hand, Comparative Example 1 is a case where the liquid temperature is out of the range of the present invention, and the optical density also shows a low value because the isocyanate group is hydrolyzed.

[0032]

According to the present invention, in a method for producing a heat-sensitive recording material comprising an aromatic isocyanate compound and an imino compound as a color-forming component, when the aromatic isocyanate compound is wet-pulverized in an aqueous medium, Medium temperature
By maintaining the temperature in the range of 35 ° C., an aromatic isocyanate compound having high reactivity can be wet-pulverized, and as a result, a thermosensitive recording material having high sensitivity and excellent image storability can be obtained. Was.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B41M 5/28-5/34 B02C 17/16-17/18

Claims (1)

(57) [Claims] In a method for producing a heat-sensitive recording material comprising an aromatic isocyanate compound and an imino compound as a color-forming component, when the aromatic isocyanate compound is wet-pulverized in an aqueous medium, the liquid temperature of the aqueous medium is set to 5 or less. A method for producing a heat-sensitive recording material, wherein the temperature is maintained in a range of from 35 to 35 ° C.