JP3177542B2 - Thermal recording sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-sensitive recording sheet, and more particularly, to a heat-sensitive recording sheet provided between a support and a heat-sensitive recording layer.
An intermediate layer mainly composed of an inorganic pigment and a binder having an oil absorption of 50 ml / 100 g or more according to the SK5101 method is provided, and a water-soluble polymer compound or a water-dispersible resin is mainly formed on the heat-sensitive recording layer. The present invention relates to a heat-sensitive recording sheet provided with an overcoat layer.

[0002]

2. Description of the Related Art Conventionally, many types of thermal recording are known. For example, a heat-sensitive recording material using an electron-donating colorless dye and an electron-accepting compound is disclosed in JP-B-43-41.
No. 60, JP-B-45-14039, etc., and in recent years, these thermal recording systems have been applied to various fields such as facsimile machines, printers, word processors, labels, and the like, and their needs are expanding. The properties required for this type of heat-sensitive recording paper are, of course, that it has the sensitivity appropriate for various uses, that the background is white, that the color image is stable for a long time, and that Does not occur, and does not adhere to the thermal head during recording (sticking).

In order to increase the sensitivity, a low-melting-point compound having good compatibility between an electron-donating colorless dye and an electron-accepting compound, a so-called sensitizer (JP-A-60-82382, JP-B-63-42590). JP-B-57-52915), and the use of an intermediate layer of a pigment having high oil absorption.
A colorless electron-donating dye and an electron-accepting compound are atomized (Japanese Patent Application Laid-Open No. 58-76293), but generally the higher the sensitivity is, the more scum adheres. In order to improve the adhesion of the scum, a method such as addition of an inorganic pigment to the intermediate layer or the heat-sensitive layer has been carried out. Also,
There is also a method of calendering the surface by applying a strong pressure to smooth the surface.However, the gloss of the surface of the heat-sensitive layer is increased more than necessary, and fogging due to pressure tends to occur, and the appearance of the impression tends to worsen. At present, satisfactory results have not been obtained.

[0004] Further, in practical handling after recording, physical action from outside, that is, pressure coloring by friction or impact,
And chemical action, i.e., when it comes into contact with bags made of various chemicals, for example, an eraser or a vinyl chloride bag containing a large amount of a plasticizer, when it is touched by hand with oil for hand cream or hair styling, When superimposed on diazo photosensitive paper, there is a drawback that the image disappears or the background develops color fogging when writing underline or the like with a highlighter, making it difficult to read the recorded image.

[0005] This decoloring phenomenon occurs, for example, in that the lactone ring of a color-forming lactone compound opened with an acidic developer is closed in the presence of a plasticizer such as dibutyl phthalate, dioctyl phthalate or dioctyl adipate. It is thought to be. The fogging phenomenon is considered to be due to the fact that the developer contained in the developing solution of the diazo photosensitive paper or the solvent contained in the fluorescent pen dissolves the color developing agent and comes into contact with the dye precursor to cause a color development reaction. Therefore, it has been proposed that such a phenomenon does not occur if a film for preventing the penetration of the plasticizer is formed on the thermal recording paper (Japanese Patent Laid-Open No. 54-128347).
No., JP-A-54-3549). Also, for the purpose of improving the protection efficiency against water and oil, addition of various curing agents, water-resistant agents and oil-repellents to the overcoat layer has been attempted.

[0006] However, when these additives are used in the overcoat layer, it is necessary to keep the color development sensitivity and the amount within a range that does not adversely affect the fog of the background. It is practically impossible to provide a temperature that allows the reaction between the water-soluble polymer compound of the coating layer and the water-proofing agent to proceed promptly. There is a limit, and fading or background fogging easily occurs over time, which is not satisfactory at present.

As a method for preventing the color erasing phenomenon, a heat-sensitive recording material which reacts when two components are heated to obtain a recorded image having good storability is disclosed in, for example, Japanese Patent Application Laid-Open No. 58-1983.
JP-A-38733, JP-A-58-54085, JP-A-58-54085
8-104959, JP-A-58-149388, JP-A-59-11587, and JP-A-59-115888.
No. 4,521,793 disclose thermosensitive recording materials comprising two components consisting of an imino compound and an isocyanate compound, but these thermosensitive recording materials have excellent storage stability of recorded images. However, the thermal responsiveness was insufficient, and it was difficult to obtain a recorded image having a sufficient density with a high-speed printing apparatus.

The inventors of the present invention have conducted intensive studies on a heat-sensitive recording sheet having good press quality without pressure inhibition, water resistance and chemical resistance, without inhibiting color formation and sensitivity and without fogging of the background. The invention has been reached.

SUMMARY OF THE INVENTION An object of the present invention is to provide a heat-sensitive recording sheet having high sensitivity, low background fog, and excellent pressure resistance, water resistance and chemical resistance.

[0009]

Means for Solving the Problems The present inventors have intensively studied to improve these disadvantages. The resulting heat-sensitive recording sheet is as follows. JIS on the support
An intermediate layer mainly composed of an inorganic pigment and a binder having an oil absorption of 50 ml / 100 g or more according to the K5101 method is provided, and an electron-donating colorless or light-colored dye and an electron-accepting colorant are formed on the intermediate layer by heating the dye. A heat-sensitive recording sheet comprising a color-forming layer containing a compound and a binder as main components, and an overcoat layer mainly comprising a water-soluble polymer compound or a water-dispersible resin provided on the color-forming layer; An aromatic isocyanate compound and an imino compound having at least one> C = NH group are contained in the coat layer, and an aromatic isocyanate compound is added to the water-soluble polymer compound or the water-dispersible resin in the overcoat layer. A heat-sensitive recording sheet containing a total of 1 to 30% by weight of a water-soluble isocyanate compound and at least one imino compound having> C = NH group. Further, in the heat-sensitive recording sheet, an aromatic isocyanate compound and an imino compound having at least one> C = NH group in the overcoat layer are contained in a weight ratio of 1:20 to 20: 1. Heat sensitive recording sheet.

The total amount of the aromatic isocyanate compound and the at least one imino compound having at least one> C = NH group in the overcoat layer is from 1 to the amount of the water-soluble polymer compound or the water-dispersible resin in the overcoat layer. 30% by weight
In the overcoat layer, the amount of the aromatic isocyanate compound and at least one imino compound having at least one> C = NH group is most efficiently in the range of 1:20 to 20: 1 by weight%. The effect of improving the storability of the background can be exhibited. The total amount of the aromatic isocyanate compound and at least one imino compound having> C = NH group in the overcoat layer is less than 1% by weight based on the water-soluble polymer compound or the water-dispersible resin in the overcoat layer. The effect is not clear, and if it exceeds 30% by weight, the film properties are reduced and the color forming layer is adversely affected.

As the pigment for the intermediate layer, JIS K5101 which is porous and has high heat insulation from the viewpoint of improving sensitivity and adhesion of scum.
Inorganic powder having an oil absorption of 50 ml / 100 g or more according to the method is used. For example, calcined kaolin, activated clay, silica, calcium carbonate, diatomaceous earth and the like are mainly used, and kaolin and talc can be used in combination. Examples of the water-soluble adhesive include styrene-butadiene latex, acrylic resin emulsion, styrene-maleic anhydride polymer, polyvinyl alcohol, hydroxyethylcellulose, starch, starch derivatives, casein, gelatin and the like, and other dispersants, defoamers , A lubricant and the like can be added, and those used for general coated paper can be used.

The heat-sensitive coloring layer provided on the support mainly comprises an electron-donating colorless dye, an electron-accepting compound and a sensitizer (sensitizer).
Metallic soaps, ultraviolet absorbers and the like may be added, and further pigments and the like may be mixed.

The colorless electron-donating dye used in the present invention is not particularly limited as long as it is used for general pressure-sensitive recording paper, heat-sensitive recording paper and the like. Specific examples include (1) 3,3 as a triarylmethane compound.
-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, 3,3-bis- (9-ethylcarbazol-3-yl) -5-dimethylaminophthalide, 3,3-bis- (2-phenylindol-3-yl) ) -5-Dimethylaminothalide, 3-
p-dimethylaminophenyl-3- (1-methylpyrrol-2-yl) -6-dimethyl-aminophthalide and the like.
(2) As a diphenylmethane compound, 4,4′-
Bis-dimethylaminobenzhydrin benzyl ether, N-halophenylleuco auramine, N-2,4,
5-trichlorophenylleuco auramine and the like. (3)
As xanthene compounds, rhodamine B-anilinolactam, rhodamine B-p-nitroanilinolactam,
Rhodamine B-p-chloroanilinolactam, 3-diethylamino-7-dibenzylaminofluoran, 3-diethylamino-7-octylaminofluoran, 3-diethylamino-7-phenylfluoran, 3-diethylamino-7-3 , 4-Dichloroanilinofluoran, 3
-Diethylamino-7- (2-chloroanilino) fluoran, 3-diethylamino-6-methyl-7-anilinofluoran, 3-piperidino-6-methyl-7-anilinofluoran, 3-ethyl-tolylamino-6- Methyl-7-anilinofluoran, 3-ethyl-tolylamino-6-methyl-7-phenyltylfluoran, 3-diethylamino-7- (4-nitroanilino) fluoran, 3
-Dibutylamino-6-methyl-7-anilinofluoran and the like. (4) As thiazine-based compounds, benzoyl leucomethylene blue, p-nitrobenzoyl leucomethylene blue and the like. (5) As spiro compounds, 3-methyl-spiro-dinaphthopyran, 3-ethyl-spiro-
Dinaphthopyran, 3,3'-dichloro-spiro-dinaphthopyran, 3-benzylspiro-dinaphthopyran, 3-
Examples thereof include methylnaphtho- (3-methoxy-benzo) -spiropyran, 3-propyl-spiro-dibenzopyran and the like, or a mixture thereof. These are determined by the application and desired properties.

As the electron-accepting compound used in the present invention, phenol derivatives and aromatic carboxylic acid derivatives are preferable, and bisphenols are particularly preferable. Specifically, as phenols, p-octylphenol, p
-Tert-butylphenol, p-phenylphenol,
1,1-bis (p-hydroxyphenyl) propane,
2,2-bis (p-hydroxyphenyl) propane,
1,1-bis (p-hydroxyphenyl) pentane,
1,1-bis (p-hydroxyphenyl) hexane,
2,2-bis (p-hydroxyphenyl) hexane,
1,1-bis (p-hydroxyphenyl) -2-ethyl-hexane, 2,2-bis (4-hydroxy-3,5-
Dichlorophenyl) propane and the like. As aromatic carboxylic acid derivatives, p-hydroxybenzoic acid,
ethyl p-hydroxybenzoate, butyl p-hydroxybenzoate, 3,5-di-tert-butylsalicylic acid, 3,
Examples of 5-di-α-methylbenzyl salicylic acid and carboxylic acid include polyvalent metal salts thereof. Further, a sulfone compound and a sulfide compound can also be used. For example, bis (4-hydroxyphenyl) sulfone, 4-hydroxy-4'-methyldiphenylsulfone, 4-hydroxy-4'-isopropyloxydiphenylsulfone, bis (3-allyl-4-hydroxyphenyl) sulfone, bis (3- Methyl-4-hydroxyphenyl) sulfone, bis (3-butyl-4-hydroxyphenyl) sulfone, bis (3,5-diallyl-4-hydroxyphenyl) sulfone, bis (3-chloro-4-)
(Hydroxyphenyl) sulfone, 3-allyl-4,4 '
-Dihydroxydiphenylsulfone, bis (2-ethyl-4-hydroxyphenyl) sulfone, 3-isopropyl-4,4'-dihydroxydiphenylsulfone, bis (2,5-dimethyl-4-hydroxyphenyl) sulfone, bis (2 5-dichloro-4-hydroxyphenyl) sulfone, 4,4'-thiobis (2,5-dichlorophenol), 4,4'-thiodiphenol, 2,2 '
-Thiobis (4-chlorophenol), 2,2'-thiobis (4,6-dichlorophenol), 4,4'-thiobis (2,6-dimethylphenol), 4,4'-thiobis (2,5- Dimethylphenol), 4,4'-thiobis (2-isopropyl-5-methylphenol),
4,4'-thiobis (2-cyclohexylphenol), 4,4'-thiobis (2-isopropylphenol), 4,4'-thiobis (3-ethylphenol),
4,4'-thiobis (2-t-butyl-5-methylphenol) and the like.

The waxes include paraffin wax, kauna wax, microcrystalline wax, polyethylene wax, higher fatty acid amide,
For example, stearic acid amide, ethylenebisstearamide, higher fatty acid ester and the like can be mentioned.

Examples of the metal soap include polyvalent metal salts of higher fatty acids, that is, zinc stearate, aluminum stearate, calcium stearate, zinc oleate and the like.

As a sensitizer for improving the sensitivity, a sensitizer having a melting point of 80 to 140 ° C., a relatively sharp melting range and good heat responsiveness is preferred. Specifically, 2- (p-methylbenzyloxy) is used. ) Naphthalene, bis (p-methylbenzyl) oxalate, esters of benzoic acid and terephthalic acid,
Sensitizers such as naphthalenesulfonic acid esters, naphthyl ether derivatives, anthryl ether derivatives, aliphatic ethers, and other phenanthrenes and fluorenes may be used in combination. Further, the above-mentioned waxes can be used in combination as a sensitizer.

Examples of the pigment include diatomaceous earth, talc, kaolin, calcined kaolin, calcium carbonate, basic magnesium carbonate, titanium oxide, zinc oxide, silicon oxide, aluminum hydroxide, and urea-formalin resin.

These are dispersed and applied in a binder (adhesive). Water-soluble binders are generally used, and polyvinyl alcohol, modified polyvinyl alcohol, hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, carboxymethyl cellulose, ethylene-maleic anhydride copolymer, styrene-maleic anhydride copolymer, Isobutylene-maleic anhydride copolymer, polyacrylamide copolymer,
Examples include polyacrylic acid, starch derivatives, casein, and gelatin. For the purpose of imparting water resistance to these binders, a water resistant agent (crosslinking agent, curing agent) is added, or an emulsion of a hydrophobic polymer, specifically, a styrene-butadiene rubber latex, an acrylic resin emulsion, or the like is added. You can also.

Next, as a water-soluble polymer compound or a water-dispersible resin which is a film-forming agent used for the overcoat layer of the present invention, polyvinyl alcohol, polyethylene oxide, polyvinyl methyl ether, vinyl methyl ether-maleic anhydride are used. Polymer, sodium polyacrylate,
Synthetic polymer binders such as polysodium methacrylate, polyacrylamide, isobutylene-maleic anhydride copolymer, styrene-maleic anhydride copolymer, polyethyleneimine, polyvinylpyrrolidone, etc., oxidized starch, dextrin, dialdehyde starch, enzyme treatment Starch, aminated starch, phosphorylated starch, hydroxyethylated starch, carboxyethylated starch, methylcellulose, ethylcellulose, hydroxyethylcellulose,
Carboxymethylcellulose, hydroxypropylcellulose, gelatin, casein, natural binders such as phosphorylated guar gum, and polyvinyl acetate, vinyl acetate-acrylate copolymer, vinyl acetate-ethylene copolymer, polyacrylate, Latexes such as a styrene-butadiene copolymer, a butadiene-acrylonitrile copolymer, a butadiene-methyl methacrylate copolymer, and emulsions may be used alone or in combination of two or more.

The above-mentioned film-forming agent such as a water-soluble polymer can be crosslinked or cured by using an inorganic peroxide, an organic silicon peroxide, an organic peroxide, a phenol resin, an amino resin, or the like.
Quinones, halogen compounds, isocyanate compounds, carboxylic acids and acid anhydrides, aldehyde compounds, alcohols, epoxy compounds, boric acid, silane compounds can be used. In addition, metal soaps, waxes, wetting agents, ultraviolet absorbers, fluorescent whitening agents, used in thermosensitive coloring layers,
Various surfactants are used.

Next, the aromatic isocyanate compound used in the present invention is a colorless or pale-colored aromatic isocyanate or heterocyclic isocyanate which is a solid at room temperature. For example, one or more of the following are 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 Nato, 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'-diisoanato, 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 Nath, 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-2,4,4'-triisocyanate, 4,4 ', 4''-Triisocyanate-2,5-
Dimethoxytriphenylamine, p-dimethylaminophenyl isocyanate, tris (4-phenyl isocyanate) thiophosphate and the like.

The imino compound of the present invention has at least one> C = NH group, and has the general formula 1 (φ is an aromatic compound residue capable of forming a conjugated system with an adjacent C = N). Base)
Is a colorless or pale-colored compound which is solid at ordinary temperature. Hereinafter, specific examples of the imino compound of the present invention are shown. In addition, two or more kinds of imino compounds can be used in combination depending on the purpose.

[0024]

(Equation 1)

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.

As the support, paper is generally used, but it is also possible to use resin film, synthetic paper, cloth or the like. As an apparatus used for coating the intermediate layer and the heat-sensitive recording layer, a coater head such as a blade coater, an air knife coater, a roll coater, a rod coater, and a curtain coater can be used.

Further, in order to improve the surface smoothness of the coated product, an apparatus such as a machine calender, a super calender, a gloss calender, and brushing can be used.

The coating amount of the intermediate layer is not particularly limited, but if the amount is too small, the effect is small, and if the paper thickness is considered constant, if the amount is too large, the strength of the paper becomes weak. 3 to 20 g / m ^2, preferably 5 to 1
0 g / m ² is appropriate. The coating amount of the heat-sensitive recording layer on the support is not limited, but is usually 3 to 3% by dry weight.
It is in the range of 15 g / m ² , preferably 4 to 10 g / m ² .

The coating amount of the overcoat layer is not particularly limited either. However, if the amount is too small, the effect of preventing physical and chemical influences from the outside is reduced. If the amount is too large, the heat energy from the heating element is too small. Is difficult to be transmitted to the color-forming layer, leading to a decrease in color-forming sensitivity.
5.0 g / m ^2, preferably, 1.0 to 3.0 g / m ² are suitable.

[0030]

The heat-sensitive recording sheet obtained by the method of the present invention has an intermediate layer mainly composed of an inorganic pigment having an oil absorption of 50 ml / 100 g or more according to JIS K5101 and a binder as described above. On the layer, a color-forming layer mainly composed of an electron-donating dye and an electron-accepting compound for causing the dye to develop color by heating and a binder is provided, and a water-soluble polymer compound or a water-dispersible resin is mainly formed on the color-forming layer. The overcoat layer contains an aromatic isocyanate compound and an imino compound having at least one> C = NH group, and the total amount of both is adjusted to the water-soluble polymer compound or water dispersion in the overcoat layer. Of an aromatic isocyanate compound and an imino compound having at least one> C = NH group in a ratio of 1% to 30% by weight based on the weight of the hydrophilic resin. Then, by adding the compound in the range of 1:20 to 20: 1, a heat-sensitive recording sheet having high sensitivity at the time of heat-sensitive recording, little background fog, and good pressure resistance, water resistance and chemical resistance was obtained. .

The reason why the effect is exhibited is that the physical action, that is, the color formation due to the pressurization of the background can be prevented by the presence of the overcoat layer on the color formation layer. Further, it is possible to prevent the image obtained from the reaction between the electron-donating dye and the electron-accepting compound from decoloring very quickly by a chemical action, that is, water or various chemicals, to some extent. However, considering the penetration of chemicals into the overcoat layer, it is necessary to add a large amount of a curing agent or an oil repellent, or to increase the thickness of the overcoat layer,
There was a tendency to lower the sensitivity. However, by including a specific amount of the aromatic isocyanate compound and the imino compound of the present invention in the overcoat layer with respect to the water-soluble polymer compound or the water-dispersible resin in the layer, the image by chemical action can be obtained. For the addition amount and thickness of the curing agent and oil repellent in the overcoat layer in order to significantly improve the degree of decolorization, it can be minimized,
It is considered that a heat-sensitive recording sheet having high sensitivity, low background fog, and excellent pressure resistance, water resistance, and chemical resistance can be obtained by fully utilizing the effect of the intermediate layer for the purpose of improving sensitivity.

[0032]

Next, the present invention will be described in more detail by way of examples. All parts and percentages shown below are based on weight. Unless otherwise specified, the value indicating the amount of smear indicates the amount of smear after drying.

Example 1 Preparation of Intermediate Layer Ansilex (fired kaolin manufactured by Engelhard Co., Ltd., oil absorption according to JIS K5101 80 ml / 100 g) 100 parts 10% sodium hexametaphosphate 4 parts 20% MS4600 (phosphorylated starch manufactured by Nippon Shokuhin) 30 parts 48% styrene-butadiene copolymer latex 40 parts 80 parts of water was stirred and dispersed to prepare a coating liquid for the intermediate layer. A base coat of 40 g / m ^{2 was} coated with a coat amount of 8.5 g / m ² using a blade coater to form an intermediate layer. did.

Preparation of Color-Forming Layer (1) Preparation of Solution A 35 parts of 3-dibutylamino-6-methyl-7-anilinofluoran 105 parts of 5% PVA 105 parts of Solution A using Dynomill (manufactured by Shinmaru Enterprises) It was pulverized to a volume average diameter of 0.5 μm. (2) Preparation of solution B 40 parts of 2,2-bis (p-hydroxyphenyl) propane 55 parts of 2-benzyloxynaphthalene 5 parts of PVA 100 parts 40% of zinc stearate dispersion 20 parts The solution B was dynomill (Shinmaru Enterprise) (Pulverized) to a volume average diameter of 1.1 μm. (3) Preparation of liquid C 35 parts of light calcium carbonate 3.5 parts of 10% sodium hexametaphosphate 3.5 parts of water 63 parts of liquids A, B and C are mixed, and the 10% PVA liquid is further solidified to be 20% of the total solid. To form a coloring layer coating solution.

This color forming layer coating solution was applied to the above-mentioned intermediate layer by an air knife coater so as to have a coating amount of 3 g / m ² , and a calendered finish thermosensitive recording sheet was obtained with a Beck smoothness of 550 to 650 seconds. .

Preparation of Overcoat Layer (4) Preparation of Solution D 15% Polyvinyl Alcohol / Acrylamide Copolymer Aqueous Solution (Papyrol, manufactured by Showa Denko) 400 parts 40% zinc stearate dispersion 25 parts (5) Solution E Preparation 4,4 ', 4''-triisocyanato-2,5-dimethoxytriphenylamine 6 parts 5% PVA 6 parts Water 3 parts The solution E was subjected to volume average particle diameter using Dynomill (manufactured by Shinmaru Enterprises). It was pulverized to 1.0 μm. (6) Preparation of Solution F 1,3-diimino-4,5,6,7-tetrachloroisoindoline 6 parts 5% PVA 6 parts Water 3 parts The volume of the solution F was measured using a Dynomill (manufactured by Shinmaru Enterprises). It was pulverized to an average particle size of 1.0 μm. D, E, F
The liquids were mixed, and the solid content was adjusted to 12% with water to obtain an overcoat layer coating liquid.

Example 2 A heat-sensitive recording sheet was prepared in the same manner as in Example 1 except that 2,2-bis (p-hydroxyphenyl) propane of Solution B was replaced with 4-hydroxy-4'-isopropyloxydiphenylsulfone. Obtained.

Example 3 A thermosensitive recording sheet was obtained in the same manner as in Example 2 except that the amounts of the solution E and the solution F in the overcoat layer were changed to 1 part of the solution E and 29 parts of the solution F, respectively.

Example 4 A thermosensitive recording sheet was obtained in the same manner as in Example 2 except that the amounts of the solution E and the solution F in the overcoat layer were changed to 29 parts of the solution E and 1 part of the solution F, respectively.

Reference Example 1 A heat-sensitive recording sheet was prepared in the same manner as in Example 2 except that the amounts of the solution E and the solution F in the overcoat layer were changed to 0.38 part of the solution E and 0.38 part of the solution F, respectively. Obtained.

Reference Example 2 A heat-sensitive recording sheet was prepared in the same manner as in Example 2 except that the amounts of the solution E and the solution F in the overcoat layer were changed to 37.5 parts of the solution E and 37.5 parts of the solution F, respectively. Obtained.

Comparative Example 1 A heat-sensitive recording sheet was obtained in the same manner as in Example 2 except that the solution E and the solution F in the overcoat layer were removed.

Comparative Example 2 A thermosensitive recording sheet was obtained in the same manner as in Example 2 except that the solution E in the overcoat layer was removed.

Comparative Example 3 A thermosensitive recording sheet was obtained in the same manner as in Example 2 except that the solution F in the overcoat layer was removed.

Comparative Example 4 The procedure of Comparative Example 1 was repeated, except that 15 parts of a 40% glyoxal solution was added as a curing agent to the overcoat layer.
A heat-sensitive recording sheet was obtained.

Next, the thermal recording sheets of Examples 1 to 4, Reference Examples 1 and 2, and Comparative Examples 1 to 4 were evaluated for print density, pressure resistance, water resistance, and chemical resistance. It was shown to. At the time of sheet preparation, only the case of Comparative Example 4 caused background fog.

[0047]

[Table 1]

The print density was measured at 10 ms / Li using a tester manufactured by Okura Electric Co., Ltd. and using a head having a head resistance of 2816 Ω.
Ne was printed at an energy of 0.2 w / dot and evaluated at a pulse width of 2.5 ms. The print density is measured with a Macbeth densitometer, and the higher the numerical value, the higher the density, indicating a good evaluation.

The pressure resistance was measured using a dyeing fastness tester (Gakushin type) manufactured by Daiei Kagaku Seiki Laboratory, and the test conditions were as follows: pendulum weight: 300 g, speed: 30 reciprocations / minute, stroke: 12
cm, the front and back surfaces of the sample were rubbed, and the change in optical density at that portion was measured with a Macbeth densitometer.

For water resistance, a sample colored by Panafax UF-7 manufactured by Matsushita Electric Transmission Co., Ltd. was immersed in a beaker filled with tap water at 20 ° C., taken out after 4 hours, allowed to dry naturally at room temperature, and developed. The change in the optical density of each part was examined.

The chemical resistance was determined by coloring each sample with Panafax UF-7 manufactured by Matsushita Electric Transmission Co., Ltd., applying 0.05 to 1.0 ml / m ^{2 of} ethylene glycol, and after 3 days, The change in the optical density of the printed portion was examined.

As is clear from the examples, the heat-sensitive recording sheet obtained by the present invention was high in sensitivity, excellent in pressure resistance, water resistance and chemical resistance.

Claims (2)

(57) [Claims] 1. An intermediate layer mainly composed of an inorganic pigment and a binder having an oil absorption of 50 ml / 100 g or more according to JIS K5101 method on a support, and an electron-donating colorless or light-colored dye is further provided on the intermediate layer. A color-forming layer containing an electron-accepting compound and a binder as main components for coloring the dye by heating is provided, and an overcoat layer mainly containing a water-soluble polymer compound or a water-dispersible resin is provided on the color-forming layer. In the heat-sensitive recording sheet provided, in the overcoat layer,
Aromatic isocyanate compound and at least one of>
An imino compound having a C = NH group is contained, and an aromatic isocyanate compound and an imino compound having at least one> C = NH group are added to the water-soluble polymer compound or the water-dispersible resin in the overcoat layer. A heat-sensitive recording sheet comprising 1 to 30% by weight of the total amount of compounds. 2. The weight ratio of the aromatic isocyanate compound and at least one imino compound having at least one> C ＝ NH group in the overcoat layer from 1:20 to 20:
2. The heat-sensitive recording sheet according to claim 1, wherein said heat-sensitive recording sheet is contained in the range of 1.