JPH01216883A - Thermal recording material - Google Patents

Abstract

PURPOSE:To obtain a film which can be recorded easily by a thermal head and is free of the problem that the transparency of a recording layer itself is spoiled upon adhesion of a water droplet to a recording surface, by applying a coating liquid comprising an emulsified or dispersed material, obtained by dissolving a colorless or light-colored basic dye precursor and a color developer in an organic solvent insoluble or difficultly soluble in water followed by emulsification or dispersion, microcapsules containing a decoloring agent therein and a specified amount of a hardener, to a base, followed by drying. CONSTITUTION:A thermal recording layer is provided by applying a coating liquid comprising an emulsified or dispersed material, obtained by dissolving a colorless or light-colored basic dye precursor and a color developer in an organic solvent insoluble or difficultly soluble in water followed by emulsification or dispersion, microcapsules containing a decoloring agent therein end 0.1-10wt.% (on a dried basis) of a hardener, to a base, followed by drying, in a thermal recording material comprising at least the thermal recording layer on the base. Unheated parts of the thermal recording layer are colored with a reaction product of the dye precursor with the color developer, whereas heated parts of the layer are decolored by the decoloring agent permitted to penetrate through heat-responsive capsule walls. Therefore, when the recorded recording material is set on an overheat projector, a colorless or light-colored image against a colored background is projected on a white screen.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a heat-sensitive recording material, and particularly to a heat-sensitive recording material useful as an image-forming film sheet for an overhead projector (hereinafter abbreviated as OHP).

(Prior art) Conventional OHP film sheets used to be of a thermal copying method using a heat-reactive substance, but more recently, the film itself or a resin layer coated on the film is distorted by heat. There are methods in which a colored powder is fixed on a transparent support by xerography, and methods in which a facsimile printer (thermal transfer type using an ink sheet) is used.

However, all of the images produced by these conventional thermal methods are positive type, and negative type OHPs such as ``white-out images in the previous section'' have been particularly prized in the field of slides in recent years because they reduce eye fatigue. This film is not common, especially negative-type OHP heat-sensitive film that can be easily recorded with thermal heads widely used in facsimile printers and the like.

Therefore, the inventors of the present invention investigated the possibility of developing a negative-type OHP heat-sensitive film, and found that a leuco dye and an acidic compound were brought into contact with each other to form a color, and a coloring agent and a decoloring agent were coated on a transparent film support. It has been found that the above-mentioned negative-type heat-sensitive heat-sensitive film for OHP can be produced by this method, and has already been proposed (Japanese Patent Application No. 62-60646).

On the other hand, a protective layer is usually provided on these heat-sensitive layers for the purpose of improving scratch resistance.

(Problems to be Solved by the Invention) However, when water droplets are mistakenly attached to the surface of the heat-sensitive recording material as described above, there is a drawback that the area becomes opaque.

The present inventors have solved the above-mentioned drawbacks (as a result of intensive studies), and have found that the influence of water droplets can be overcome by increasing the hardness of the heat-sensitive layer, and have arrived at the present invention.

Therefore, an object of the present invention is to provide a negative type OHP film which can be easily recorded with a thermal head and which does not impair the transparency of the recording layer itself even if water droplets adhere to the recording surface. It is in.

(Means for Solving the Problems) The above object of the present invention is to provide a heat-sensitive recording material having at least a heat-sensitive layer on a support, in which the heat-sensitive layer contains a colorless or light-colored basic dye precursor and a color developer. An emulsified dispersion obtained by dissolving in an organic solvent that is sparingly soluble or insoluble in water, and then emulsifying and dispersing it, a microcapsule containing a decoloring agent, and a dry weight of 0.1~
This was achieved using a heat-sensitive recording material characterized by a heat-sensitive layer formed by coating a coating solution containing 10% by weight of a hardening agent on a support and drying it.

In the heat-sensitive recording material according to the present invention, the unheated portion is colored by a reaction product of a colorless or light-colored basic dye precursor and a color developer, and the heated portion is colored by the reaction product that passes through the thermoresponsive capsule wall. Since the above-mentioned coloring is bleached by the agent, when an overhead projector is used, the background is colored and the image area is colorless or light-colored on a white screen.

The transparent film support used is polyester,
Acrylic resins, styrene/acrylic copolymers, cellulose acetate, and the like are suitable, but are not particularly limited. or,
Application of the coating of the present invention on a paper support results in a negative-working thermal paper.

Next, the heat-sensitive layer of the heat-sensitive material of the present invention will be explained in detail.

As the basic dye precursor used in the present invention, a colorless or light-colored one is appropriately selected from known compounds that develop color by donating electrons or accepting protons such as acids. Such compounds have partial skeletons such as lactones, lactams, sultones, spiropyrans, esters, and amides, and these partial skeletons are ring-opened or cleaved upon contact with a color developer. Preferred compounds include Examples include triarynylmethane compounds, diphenylmethane compounds, xanthine compounds, thiazine compounds, and spiropyran compounds.

Particularly preferred compounds are those represented by the following general formula.

In the formula, R1 is an alkyl group having 1 to 8 carbon atoms, R2 is an alkyl group having 4 to 18 carbon atoms, an alkoxyl group, or a tetrahydrofurfuryl group, and R8 is a hydrogen atom, an alkyl group having 1 to 15 carbon atoms, or halogen atom,
R4 represents a substituted or unsubstituted aryl group having 6 to 20 carbon atoms. As the substituent for R4, an alkyl group having 1 to 5 carbon atoms, an alkoxy group, a halogenated alkyl group, and a halogen atom are preferable.

As a color developer that causes a color-forming reaction with the basic colorless dye used in the present invention, any known color developer can be used as appropriate. For example, as a color developer for leuco dye,
Examples include phenolic compounds, sulfur-containing phenolic compounds, carboxylic acid compounds, sulfone compounds, urea-based or thiourea-based compounds, etc. For details, see, for example, Paper and Pulp Technology Times (1985), pp. 49-54 and 65. -70
It is written on the page. Among these, especially those with a melting point of 50
°C to 250 °C is preferable, especially 60 °C to 2
00'C, phenols and organic acids that are sparingly soluble in water are preferred. It is preferable to use two or more color developers in combination, as this increases solubility.

Among the color developers used in the present invention, particularly preferred ones are represented by the following formulas (1) to (V).

(It) R1 is an alkyl group, an aryl group or an aralkyl group, with methyl, ethyl and butyl groups being particularly preferred.

R2 is an alkyl group, especially a butyl group, a pentyl group,
Heptyl and octyl groups are preferred.

(IV) R3 is an alkyl group or an aralkyl group.

(v) Ra and Rs represent hydrogen, halogen, hydroxyl group, nitro group, alkyl group, allyl group, aralyl group, and alkylaryl group.

Further, if necessary, a photofading inhibitor described in, for example, Japanese Patent Application No. 60-125470, Japanese Patent Application No. 60-125471, and Japanese Patent Application No. 60-125472 can be appropriately added.

In the present invention, a basic dye precursor and a color developer are added to water.
After dissolving it in a soluble or insoluble organic solvent, it is mixed with an aqueous phase containing a surfactant and a water-soluble polymer as a protective colloid, and used in the form of an emulsified dispersion! The organic solvent for dissolving the basic dye precursor and the color developer can be appropriately selected from esters and those commonly used as pressure-sensitive oils, but in particular, esters and organic solvents containing two or more benzene rings can be used. and the number of heteroatoms is equal to or less than the group constant, compounds represented by the following formulas (VI) to [■], triallylmethane (e.g. tritolylmethane, tolyldiphenylmethane), terphenyl compounds ( terphenyl), alkylated diphenyl ethers (e.g. propyl diphenyl ether)
, hydrogenated terphenyl (eg, hexahydroterphenyl), diphenyl ether, and the like are preferred.

(Vl) In the formula, R1 is hydrogen or an alkyl group having 1 to 18 carbon atoms,
R1 represents an alkyl group having 1 to 18 carbon atoms e Pl
, q' represents an integer of 1 to 4, and the total number of alkyl groups is 4 or less.

Note that the alkyl groups for R' and R'' are preferably alkyl groups having 1 to 8 carbon atoms.

[■]

In the formula, R3 represents a hydrogen atom or an alkyl group having 1 to 12 carbon atoms, R4 represents an alkyl group having 1 to 12 carbon atoms, and n represents 1 or 2.

P"Sq" represents an integer from 1 to 4; when n=1, the total number of alkyl groups is 4 or less; when n=2, the total number of alkyl groups is 6 or less.

[■]

In the formula, RS and R'' represent a hydrogen atom or a same or different alkyl group having 1 to 18 carbon atoms.

m represents an integer from 1 to 13. p3 and q3 represent integers of 1 to 3, and the total number of alkyl groups is 3 or less.

In addition, the alkyl group of R' and Rh is particularly preferably an alkyl group having 2 to 4 carbon atoms.

Examples of compounds represented by the formula ('l) include dimethylnaphthalene, diethylnaphthalene, and diisopropylnaphthalene.

Examples of the compound represented by formula [■] include dimethylbiphenyl, diethylbiphenyl, diisopropylbiphenyl, and diisobutylbiphenyl.

Examples of compounds represented by formula [■] include l-methyl-
1-dimethylphenyl-1-phenylmethane, 1-ethyl-1-dimethylphenyl-1-phenylmethane, 1-
Propyl-1-dimethylphenyl-1-phenylmethane is mentioned.

Examples of esters include phosphate esters (e.g., triphenyl phosphate, tricresyl phosphate, butyl phosphate, octyl phosphate, talesyl diphenyl phosphate), phthalate esters (
Dibutyl phthalate, 2-ethylhexyl phthalate, ethyl phthalate, octyl phthalate, butylbenzyl phthalate), dioctyl tetrahydrophthalate, benzoate ester (ethyl benzoate, propyl benzoate, butyl benzoate, isopentyl benzoate, benzyl benzoate),
Abietate ester (ethyl abietate, benzyl abietate), dioctyl adipate, isodecyl succinate, dioctyl azelaate, oxalate ester (
dibutyl oxalate, dipentyl oxalate), diethyl malonate, maleate esters (dimethyl maleate, diethyl maleate, dibutyl maleate), tributyl citrate, sorbate esters (methyl sorbate, ethyl sorbate, butyl sorbate) , sebacate ester (dibutyl sebacate, dioctyl sebacate),
Ethylene glycol esters (formic acid monoesters and diesters, butyric acid monoesters and diesters, lauric acid monoesters and diesters, palmitic acid monoesters and diesters, stearic acid monoesters and diesters, oleic acid monoesters and diesters)
, triacetin, diethyl carbonate, diphenyl carbonate, ethylene carbonate, propylene carbonate, boric acid esters (tributyl borate, tripentyl borate), and the like.

It is also possible to use the above oils together or with other oils.

In the present invention, a low boiling point auxiliary solvent may be added to the above-mentioned organic solvent as a solubilizing agent. Preferred examples of such co-solvents include ethyl acetate, isopropyl acetate, butyl acetate, and methyl phthalolide.

The water-soluble polymer is contained as a protective colloid in the aqueous phase that is mixed with the oil phase in which the basic dye precursor and color developer are dissolved.
Although it can be appropriately selected from known anionic polymers, nonionic polymers, and amphoteric polymers, polyvinyl alcohol, gelatin, cellulose derivatives, etc. are preferable.

Further, as the surfactant to be contained in the aqueous phase, one can be appropriately selected from anionic or nonionic surfactants that do not cause precipitation or aggregation by interacting with the above-mentioned protective colloid. .

Preferred surfactants include sodium alkylbenzenesulfonate (e.g., sodium dodecylbenzenesulfonate), sodium alkylsulfate, dioctyl sodium sulfosuccinate, polyalkylene glycol (e.g., polyoxyethylene nonylphenyl ether), and the like. .

The emulsified dispersion of a basic dye precursor and a color developer in the present invention is produced by mixing an oil phase containing a basic dye precursor and a color developer and an aqueous phase containing a protective colloid and a surfactant with high-speed stirring and ultraviolet stirring. It can be easily obtained by mixing and dispersing the particles using a method commonly used for fine particle emulsification, such as sonic dispersion.

A compound having the function of a glass transition point regulator for the capsule wall can be added to this emulsified dispersion. Examples of such compounds include hydroxy compounds,
Carbamate ester compounds, sulfonamide compounds,
There are aromatic methoxy compounds and the like, the details of which are described in, for example, Japanese Patent Application No. 59-244190.

These compounds are added in an amount of 0.01 to 2 parts by weight, preferably 0.001 to 2 parts by weight, per 1 part by weight of the color developer. It can be used appropriately in a range of 5 to 1 part by weight.

Color developer: 0.05-8g/m", basic dye precursor: 0.
．． It is applied in a range of 0.02 to 4 g/m''.

The color erasing agent in the present invention has a color erasing effect on the coloring system of a basic dye and a color developer, and examples thereof are shown below.

a) Alkylene oxide adduct of bisphenols (Japanese Patent Publication No. 53-46689) 0- (C, H,, O) fi-H where A is methylene or alkylidene, b) Melting point 11
0'C or more methylolamide and bisamide (Japanese Patent Application No. 53-80557), C) long chain 1,2-glycol (
d) Ethylene oxide adduct of terephthalic acid (Japanese Patent Application No. 53-99563), d) Ethylene oxide adduct of terephthalic acid
9666), e) Solid alcohols such as stearyl alcohol, tripropyl carbinol, polyethylene glycol, polypropylene glycol, 1,8-octanediol, dimethylpentaglycerin, 1,2,3,4-tetraoxybutane -17865 Publication) ") Polyoxydecamethylene, polyoxymethylene, polyethylene oxide, trimethylene oxide polymer,
1. Polyethers or polyethylene glycol derivatives such as 3-dioxolane polymers, polyoxyethylene alkylamine, sorbitan monostearate, polyoxyethylene oleyl ether, polyethylene glycol monostearate, polyoxyethylene alkylamide, oxyethylene alkylamine, etc. (Tokuko Showa 50-1
7867 and Japanese Patent Publication No. 50-17868) ") Acetamide, stearamide, phthalonitrile,
m-Nitroaniline, β-naphthylamine (Special Publication No. 1983
h) 1,3-dicyclohexyl-2-phenylguanidine, 1,3-dicyclohexyl-2-naphthylguanidine, 2,3-dicyclohexyl-1-phenylguanidine, 1,2 .3-1-Riphenylguanidine and other guanidine derivatives (Japanese Patent Publication No. 51-29024) i) Hexadecylamine, tribenzylamine, N, N
, N', N'-tetrabenzylethylenediamine,
Tricyclohexylamine, dioctadecylamine, 2
-Amine or quaternary ammonium salt such as aminobenzoxazole, dodecyltrimethylammonium chloride, hexadecyltrimethylammonium chloride (Japanese Patent Application Laid-Open No. 18048/1983) A decoloring agent is sufficient to erase the pigment generated from the basic dye. The appropriate amount can be determined experimentally, but it is usually 0.05 to 8.
It is preferable to use it within the range of "g/m".

In the present invention, by encapsulating the above color erasing agent in microcapsules, it is possible to prevent color erasure during the production of heat-sensitive recording materials, and at the same time, to improve the shelf life and archival properties of heat-sensitive recording materials. be able to. In this case, by selecting the wall material and manufacturing method of the microcapsules, it is possible to increase the image density during recording.

Examples of the wall material of the microcapsule include polyurethane, polyurea, polyester, polycarbonate, urea-formaldehyde resin, melamine resin, polystyrene, styrene methacrylate copolymer, styrene-acrylate copolymer, gelatin, polyvinylpyrrolidone, polyvinyl alcohol, etc. . In the present invention, two or more of these polymeric substances can also be used in combination.

In the present invention, among the above-mentioned polymeric substances, polyurethane, polyurea, polyamide, polyester, polycarbonate, etc. are preferable, and polyurethane and polyurea are particularly preferable.

The microcapsules used in the present invention are preferably microencapsulated by emulsifying a core material containing a reactive substance such as a decolorizing agent, and then forming a wall of a polymer material around the oil droplets. In this case, polymeric substances or actants are added to the interior of the oil droplets and/or to the exterior of the oil droplets. Details of microcapsules that can be preferably used in the present invention, such as a preferred method for producing microcapsules, are described in, for example, JP-A-59-222716.

In addition to the decolorizing agent, an organic solvent can be added to the core material of the microcapsule. The organic solvent used is the same as that used to dissolve the basic dye precursor and the color developer.

In addition, in order to make the thermal printing part highly transparent, the refractive index of the core material of the microcapsules should be close to the refractive index of the oil phase in which the basic dye precursor and color developer are dissolved. preferable.

In the present invention, the size of the microcapsules is preferably 4 microns or less, as measured by the volume average particle size measured, for example, by the measurement method described in JP-A No. 60-214990.

The preferred microcapsules produced as described above are not destroyed by heat or pressure as used in conventional recording materials, and the reactive substances contained in the core and outside of the microcapsules are Can react by penetrating walls.

The heat-sensitive recording material of the present invention can be coated using a suitable binder.

As a binder, polyvinyl alcohol, methylcellulose, carboxymethylcellulose, sodium alginate, hydroxypropylcellulose, gum arabic, gelatin, polyvinylpyrrolidone, casein, styrene-butadiene latex, acrylonitrile-butadiene latex, polyvinyl acetate, polyacrylic acid ester, ethylene- Various emulsions such as vinyl acetate copolymers can be used. The amount used is 0.0 as solid content.
It is 5 to 5 g/rrf.

The heat-sensitive recording material of the present invention comprises a coating liquid containing microcapsules containing a decolorizing agent, a main component of a dispersion in which at least a basic dye precursor and a color developer are emulsified and dispersed, and other additives such as a binder. It is then coated onto a support such as paper or synthetic resin film using a coating method such as bar coating, blade coating, air knife coating, gravure coating, roll coating, spray coating, dip coating, etc. and dried.
It is manufactured by providing a heat sensitive layer with a solid content of 2.5 to 25 g/rrf.

The heat-sensitive layer of the heat-sensitive recording material produced in this manner surprisingly has extremely good transparency, although the reason is not clear.

Further, in the present invention, a hardening agent is added to the heat-sensitive layer in order to prevent the above-mentioned highly transparent heat-sensitive layer from becoming opaque due to water droplets. The hardening agent used in this case must be appropriately selected depending on the type of polymer used in the heat-sensitive layer.

/ Examples of hardening agents that can be used in the present invention include the following.

■Divinylsulfone-N,N'-ethylenebis(vinylsulfonylacetamide), l,3-bis(vinylsulfonyl)-2-propatol, methylenebismaleimide, 5-acetyl-1,3-diacryloyl- xahydro-5-) liazine, 1.3.5-) lyacryloyl-
Active vinyl compounds such as hexahydro-s-triazine, 1,3.5-)rivinylsulfonyl-hexahydro-5-1-riazine.

■2.4-dichloro-6-hydroxy-8-triazine sodium salt, 2.4-dichloro-6-medoxy 5
-1-Riazine, 2,4-dichloro-6-(4-sulfoanilino)-S ~ triazine sodium salt, 2,4-
Active halogen compounds such as dichloro-6-(2-sulfoethylamino)-s-triazine and N-N'-bis(2-chloroethylcarbamyl)piperazine.

■Bis(2,3-epoxypropyl)methylpropylammonium p-toluenesulfonate, 1.4-bis(2',3°-epoxypropyloxy)butane, 1.
Epoxy compounds such as 3.5-triglycidyl isocyanurate and 1.3-diglycidyl-5-(T-acetoxy β-oxypropyl) isocyanurate.

■2,4.6-doriethylene-5-1-riazine, 1.
6-hexamethylene-N,N'-bisethyleneurea,
Ethylenimino compounds such as bis-β-ethyleneiminoethylthioether.

■l, 2-di(methanesulfonoxy)ethane, 1.4
-di(methanesulfonoxy)butane, l.

Methanesulfonic acid ester compounds such as 5-di(methanesulfonoxy)pentane.

■Dicyclohexylcarbodiimide, ■-cyclohexyl-3-(3-)dimethylaminopropyl)carbodiimide-P-trienesulfonate, 1-ethyl-3
- Carbodiimide compounds such as (3-dimethylaminopropyl)carbodiimide hydrochloride.

■2,5~dimethylisoxazole/perchlorate, 2
Isoxazole compounds such as -ethyl-5-phenylisoxazole-3'-sulfonate and 5.5'-(paraphenylene)bisisoxazole.

■Inorganic compounds such as chromium alum, chromium acetate, and zirconium borate.

■N-carboethoxy-2-isopropoxy-1,2-
Dihydroquinoline, N-(1-morpholinocarboxy)
Dehydration condensation type peptide reagents such as -4-methylpyridinium chloride; active ester compounds such as N,N''-aziboyldioxydisuccinimide and N,N'-terephthaloyldioxydisuccinimide.

[Phase] Toluene-2.4-diisocyanate, 1°6-
Isocyanates such as hexamethylene diisocyanate.

■Dialdehydes such as glutaraldehyde, glyoxal, dimethoxyurea, and 2,3-dihydroxy-1,4-dioxane.

Among these, glutaraldehyde, 2゜3-
Dialdehydes such as dihydroxy-1,4-dioxane and boric acid are preferred.

The amount of these hardeners to be added is 0.00% based on the weight of the heat-sensitive layer.
01. An appropriate addition amount can be selected from a range of 10% by weight depending on the coating method and desired degree of curing.

If the amount added is less than 0.01% by weight, the effect will not be sufficient, and if it is more than 10% by weight, the heat sensitivity and image density will decrease, which is not preferable.

In the present invention, details about the protective layer that can be provided as necessary are described in, for example, "Paper and Pulp Technology Times" (September issue, 1985), pages 2 to 4.

In the present invention, in order to protect the surface of the heat-sensitive layer with good transparency, it is preferable to provide one or more transparent protective layers that have good transparency and can improve sticking to a thermal head. . Such a protective layer can be composed mainly of silica-modified polyvinyl alcohol and colloidal silica.

Pigments, metal soaps, wax, crosslinking agents, and the like are added to the protective layer for the purpose of improving matching with a thermal head during thermal printing and improving the water resistance of the protective layer.

Pigments include zinc oxide, calcium carbonate, barium sulfate, titanium oxide, lithopone, talc, Rouseki, kaolin, aluminum hydroxide, amorphous silica, styrene beads, urea-melamine resin, etc., and the amount of these added depends on the total amount of the polymer. The amount is 0.05 to 2 times the weight, particularly preferably 0.1 to 0.5 times the weight. If the amount is less than 0.05 times, it is ineffective in improving the matching property with the head, and if the amount is more than 2 times, the transparency and sensitivity of the heat-sensitive recording material will be significantly reduced, impairing its commercial value.

Metal soaps include emulsions of higher fatty acid metal salts such as zinc stearate, calcium stearate, and aluminum stearate, and contain 065 to 2Of the total weight of the protective layer.
It is added in an amount of % fi, preferably 1 to 10% by weight. Waxes include emulsions such as paraffin wax, microcrystalline wax, carnauba wax, methylol stearamide, stearamide, polyethylene wax, and silicone, and the amount thereof is 0.5 to 40% by weight, preferably 1 to 20% by weight of the total weight of the protective layer. It is added in a proportion of % by weight. Further, a hardening agent of the same type as that added to the heat-sensitive layer may be added to the protective layer.

Further, in order to uniformly form a protective layer on the heat-sensitive layer, a surfactant is added to the coating solution for forming the protective layer. Surfactants include sulfosuccinic acid-based alkali metal salts, fluorine-containing surfactants, etc. Specifically, sodium salts of di(2-ethylhexyl)sulfosuccinic acid, di(n-hexyl)sulfosuccinic acid, etc. Or ammonium salt etc.

Furthermore, a surfactant, a polymer electrolyte, etc. may be added to the protective layer to prevent charging of the heat-sensitive recording material. The solid content coating amount of the protective layer is usually preferably 0.2 to 5 g/m, more preferably Ig to 3 g/m.

As the support for the heat-sensitive recording material of the present invention, both a transparent support and an opaque support such as paper can be used depending on the purpose and use.

The paper used for the support is heat extracted pH 6 sized with a neutral sizing agent such as an alkyl ketene dimer.
~9 Neutral paper (described in JP-A-55-14281)
The use of is advantageous in terms of storage stability over time.

In order to prevent the coating liquid from penetrating into the paper and improve the contact between the thermal recording head and the thermal recording layer, Japanese Patent Application Laid-Open No. 57-116687
The paper described in the above-mentioned issue and having a Bekk smoothness of 90 seconds or more is advantageous.

In addition, paper having an optical surface roughness of 8μ or less and a thickness of 40 to 75μ described in JP-A-58-136492, JP-A-58-136492,
Paper with a density of 0°9 g/cm3 or less and an optical contact rate of 5% or more per month as described in No. 8-69097, JP-A-58-690
Canadian standard freeness described in No. 97 (JIS P812
Paper making from the pulp beaten to 400cc or more in 1)
Paper that prevents coating liquid from seeping in, JP-A-58-65
695, the glossy side of base paper made by a Yankee machine is used as the coated surface to improve the color density and resolution, and the method described in JP-A-59-35985, in which the base paper is subjected to corona discharge treatment. Papers with improved coating suitability may also be used in the present invention with good results. In addition to these, any support commonly used in the field of heat-sensitive recording paper can be used as the support of the present invention.

It is preferable to use a transparent support in the heat-sensitive recording material of the present invention. By using this transparent support, not only can the recorded matter be used for OHP sheets, etc., but also by providing heat-sensitive layers that develop different hues on both sides of the transparent support, it is possible to Coloring is also facilitated.

The transparent supports mentioned here include polyester films such as polyethylene terephthalate and polybutylene terephthalate, cellulose derivative films such as cellulose triacetate films, polystyrene films, polypropylene films, polyolefin films such as polyethylene, etc. It can be used alone or in combination.

The thickness of the transparent support used is 20 to 200 .mu.m, particularly preferably 50 to 100 .mu.m.

The support may be provided with perforations so that the support can be conveyed with high precision during printing.

In the present invention, an undercoat layer can be provided between the transparent support and the heat-sensitive layer in order to enhance adhesion between the two layers. Gelatin, synthetic polymer latex, nitrocellulose, etc. are used as the material for the undercoat layer. The coating amount of the undercoat layer is 0.
The range is preferably from 1 g/m" to 2.0 g/m", particularly preferably from 0.62 g/m" to 1.0 g/m".

If it is less than 0.1 g/m", the adhesion between the support and the heat-sensitive layer will not be sufficient, and even if it is increased to more than 2.0 g/m", the adhesion between the support and the heat-sensitive layer will reach saturation. This is disadvantageous in terms of cost.

If the undercoat layer is coated on top of the heat-sensitive layer, the image quality of the heat-sensitive layer may deteriorate if the undercoat layer swells due to the water contained in the heat-sensitive layer. It is desirable to harden using a similar hardening agent.

The amount of these hardeners added is based on the weight of the base coat material.
An appropriate addition amount can be selected in the range of 0.20% by weight to 3.0% by weight depending on the coating method and desired degree of curing.

If the amount added is less than 0.20% by weight, the degree of curing will be insufficient no matter how long it is allowed to last, and the undercoat layer will swell when applying the heat-sensitive layer, and conversely, if it is more than 3.0% by weight. The problem is that the degree of curing progresses too much, the adhesion between the undercoat layer and the support worsens, and the undercoat layer becomes film-like and peels off from the support.

Depending on the curing agent used, if necessary, the pH of the solution can be made alkaline by adding caustic soda, or the pH of the solution can be made acidic by using citric acid or the like.

It is also possible to add an antifoaming agent to eliminate foam generated during coating, or to add an activator to improve liquid leveling and prevent coating streaks. .

Moreover, it is also possible to add an antistatic agent if necessary.

Furthermore, before coating the second layer, it is desirable to activate the surface of the support by a known method.

Activation treatment methods include acid etching treatment,
Flame treatment using a gas burner, corona treatment, glow discharge treatment, etc. are used, but from the point of view of cost or simplicity, US Pat. No. 2.715.075, US Pat.
No. 846.727, No. 3,549,406, No. 3
, 590, 107, etc., is most preferably used.

The heat-sensitive recording material of the present invention only needs to have the above-described substantially transparent heat-sensitive layer formed on at least one side of the support,
It is also possible to prepare a double-sided heat-sensitive recording material by providing one heat-sensitive layer for each layer.

(Effects of the Invention) In the heat-sensitive recording material of the present invention, especially when a transparent film is used as a support, the content received by facsimile etc. can be directly applied to an OHP to view a negative image. In particular, since the hardness of the heat-sensitive layer is sufficiently high, even if water adheres to the recording surface, the heat-sensitive layer will not become opaque, and the image will not deteriorate.

(Examples) Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited thereto.

[Preparation of basic dye and color developer emulsion dispersion] [Preparation of color developer emulsion dispersion] Color developer (a) 2 g, (b) 1 represented by the following structural formula
g, (cJ8g, and 2g of basic dye precursor (d) were dissolved in 5g of diethyl maleate and log of ethyl acetate.

The resulting solution was mixed with 8% polyvinyl alcohol (PVA
217E (manufactured by Kuraray Co., Ltd.) 40g, water 50g, and sodium dodecylbenzenesulfonate 0. Mix it with 5g of aqueous solution and use Nippon Seiki's Ace homogenizer for 10 minutes.
．． OOOrpm, emulsify for 5 minutes at room temperature, particle size 0.
A 5μ emulsified dispersion was obtained.

Color developer (a) Color developer (b) Color developer (C) H Basic dye precursor (d) CH3Ct-13 [Preparation of decolorizer capsule liquid] Decolorizer (e) below 10 g, 1- 20 g of phenyl-1-xylylethane 10 g of ethyl acetate, Takenate DL
A solution containing 25 g of ION (capsule wall agent manufactured by Takeda Pharmaceutical ■) was mixed with 8% polyvinyl alcohol PVA217.
Mix 60 g of E and 20 g of water (7) in an aqueous solution, and mix with an Ace homogenizer manufactured by Nippon Seiki ■ at 11,000 Orp.
The mixture was emulsified for a minute, then 150 g of water was added, and the mixture was reacted at 40°C for 3 hours to mix a capsule liquid with a capsule size of 0.7μ.

Erasing agent (e) (Preparation of heat-sensitive material) 5.0 g of the above capsule liquid, 10.0 g of basic dye precursor and color developer emulsified dispersion, and 5.0 g of water were stirred and mixed to form a transparent material with a thickness of 70 μm. The mixture was coated and dried on a polyethylene terephthalate (PET) support to a solid content of 10 g and 7 m'', and then a 2μ thick protective layer having the following composition was provided to prepare a transparent heat-sensitive film.

[Composition of protective layer]

1 part by weight of silica-modified polyvinyl alcohol (Cura L
[PVA R2105 manufactured by 3] (solid content) Colloidal silica 1.5 parts by weight (Snowtex 30 manufactured by Nissan Chemical ■) (solid content) Zinc stearate 0.02 parts by weight (Hydrin Z-7 manufactured by Middle East Oil & Fats ■) (solid content) min) Paraffin Wanks o,
ouiit part (Hydrin P-7 manufactured by Middle East Oil Co., Ltd.) (solid content) After dropping one drop of water with a dropper on the surface of the obtained heat-sensitive recording material, it was dried in an open air at 50°C, and almost no water droplets remained. First, it was difficult to see water droplets even when projected using an OHP.

Example 2 A heat-sensitive recording material was prepared in the same manner as in Example 1 except that 0.2 g of glutaraldehyde was added instead of the hardening agent used in Example 1.

The obtained heat-sensitive recording material was subjected to the same test as in Example 1, and similar results were obtained.

Comparative Example 1 A heat-sensitive recording material was prepared in the same manner as in Example 2, except that 0.2 g of glutaraldehyde used in Example 2 was not used, and the same tests as in Example 2 were conducted. Water droplets remained on the surface, and when administered at 0 HP, the image became cloudy and deteriorated in image quality.

As is clear from the results of the above examples, it was demonstrated that it is effective to include a hardening agent in the heat-sensitive layer even when a protective layer is provided above the heat-sensitive layer.

Claims (1)

[Claims] In a heat-sensitive recording material having at least a heat-sensitive layer on a support, the heat-sensitive layer comprises a colorless or light-colored basic dye precursor and a color developer that are dissolved in an organic solvent that is sparingly soluble or insoluble in water and then emulsified and dispersed. A heat-sensitive layer comprising an emulsified dispersion, microcapsules containing a decolorizing agent, and a coating solution containing a hardening agent of 0.1 to 10% by dry weight, coated on a support and dried. Recording materials.