JPH085248B2 - Thermal recording material - Google Patents

Description

TECHNICAL FIELD The present invention relates to a negative-type heat-sensitive recording material, and more particularly to a negative-type heat-sensitive recording material having a high heat-sensitive layer film strength and high transparency.

<< Prior Art >> In the heat-sensitive recording method, (1) development is unnecessary, (2) when the support is paper, the paper quality is close to the general formula, and (3) easy handling. (4) High color density, (5) Simple and inexpensive recording device, (6) No noise during recording, etc., which has led to rapid spread in the field of facsimiles and printers in recent years, resulting in heat sensitivity. The use of recording is expanding.

Against such a background, in recent years, in order to adapt to multiple colors or to be used for an overhead projector (abbreviated as OHP), a transparent thermal recording material that can be directly recorded by a thermal head. Is desired to be developed. Therefore, in recent years, on a support, a microcapsule containing a colorless or light-colored basic dye precursor, and a color developer dissolved in an organic solvent hardly soluble or insoluble in water from an emulsion dispersion A heat-sensitive recording material having a substantially transparent heat-sensitive layer obtained by coating and drying the following coating liquid has been proposed.

However, all of the images obtained by these conventional thermal methods are of a positive type, and since the fatigue of the eyes is reduced, a negative type image such as “white image on blue background” which has recently been especially prized in the field of slides is used. OHP films are not common, and there are no known negative type OHP thermal films that can be easily recorded with a thermal head that is widely used especially in facsimile printers.

Therefore, the present inventors have studied to develop a negative-type heat-sensitive film for OHP, as a result, a leuco dye and an acidic compound are preliminarily brought into contact with each other to develop a color and a decoloring agent, which are coated on a transparent film support. It has been found that the above-mentioned negative type heat-sensitive film for OHP can be obtained, and it 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, the surface of the heat-sensitive layer of the above-mentioned transparent heat-sensitive recording material has a weak film strength and is easily scratched when scratched by a hard object such as a nail.

Therefore, it is an object of the present invention to provide a heat-sensitive recording material having a transparent heat-sensitive layer with improved scratch resistance.

<< Means for Solving the Problems >> The above object of the present invention is to provide a thermosensitive recording material having at least a thermosensitive layer on a support, wherein the thermosensitive layer is a colorless or pale basic dye precursor and a developer. On a support, an emulsified dispersion obtained by dissolving in an organic solvent hardly soluble or insoluble in water and then emulsified and dispersed, microcapsules containing a decoloring agent, and a filler having an average particle size of 3 μ or less are provided on a support. A heat-sensitive layer that has been applied and dried, wherein the ratio of the refractive index of the filler to the refractive index of the organic solvent solution in which the basic dye precursor and the color developer are dissolved is 0.95 to 1.05. And a heat-sensitive recording material.

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

Polyester, acrylic resin, styrene / acrylic copolymer, cellulose acetate and the like are suitable as the transparent film support to be used, but are not particularly limited.
When the coating material of the present invention is applied to a paper support, a negative type thermal paper is obtained.

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

As the basic dye precursor used in the present invention, a colorless or light-colored one is appropriately selected from known compounds which develop a color by donating an electron or accepting a proton such as an acid.
Such compounds include lactones, lactams, sultones,
Has a partial skeleton such as spiropyran, ester, amide,
These partial skeletons are ring-opened or cleaved by contact with a color developer, and preferable compounds include, for example, triarylmethane compounds and diphenylmethane compounds,
Examples thereof include xanthene compounds, thiazine compounds, spiropyran compounds and the like.

As the color developing agent that causes a color reaction with the basic colorless dye used in the present invention, any of known ones can be appropriately used. For example, as a developer for a leuco dye, a phenol compound, a sulfur-containing phenolic compound, a carboxylic acid compound, a sulfone compound, a urea compound or a thiourea compound, and the like can be mentioned. The details are, for example, paper pulp technology. Times (1985), pages 49-54 and 65-70. Among these, especially the melting point is 50 ℃ ~ 250 ℃
Are preferred, and among them, phenol and organic acids having a poor water solubility of 60 ° C to 200 ° C are desirable. When two or more developers are used in combination, the solubility increases, which is preferable.

Particularly preferred among the developers used in the present invention are:
It is represented by the following general formulas [I] to [v].

R ₁ is an alkyl group, an aryl group or an aralkyl group, and a methyl group, an ethyl group and a butyl group are particularly preferable.

R ₂ is an alkyl group, especially a butyl group, a pentyl group,
Heptyl and octyl are preferred.

R ₃ is an alkyl group or an aralkyl group.

R ₄ and R ₅ represent hydrogen, halogen, a hydroxyl group, a nitro group, an alkyl group, an allyl group, an araryl group and an alkylallyl group.

In addition, if necessary, for example, JP-A-61-283589 and 61
The photobleaching inhibitors described in JP-A Nos. 283590 and 61-283591 can be appropriately added.

In the present invention, the basic dye precursor and the color developer are dissolved in a water-insoluble or insoluble organic solvent, and then 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 that dissolves the basic dye precursor and the color developer can be appropriately selected from those commonly used as esters or pressure-sensitive oils, and particularly, the ester and two or more benzene rings are used. And the number of heteroatoms is equal to or less than the group constant, compounds represented by the following general formulas [VI] to [VIII] and triallylmethane (for example, tritoluylmethane, toluyldiphenylmethane), terphenyl compounds ( For example, terphenyl), alkylated diphenyl ether (eg propyl diphenyl ether), hydrogenated terphenyl (eg hexahydroterphenyl), diphenyl ether and the like are preferable.

In the formula, R ¹ represents hydrogen or an alkyl group having 1 to 18 carbon atoms, R ²
Represents an alkyl group having 1 to 18 carbon atoms. p ¹ and q ¹ are 1 to 4
The total number of alkyl groups is 4 or less.

The alkyl group of R ¹ and R ² is preferably an alkyl group having 1 to 8 carbon atoms.

In the formula, R ³ is a hydrogen atom or an alkyl group having 1 to 12 carbon atoms,
R ⁴ represents an alkyl group having 1 to 12 carbon atoms, and n represents 1 or 2.

p ² and q ² represent an integer of 1 to 4. If n = 1,
The total number of alkyl groups is 4 or less, and when n = 2, the total number of alkyl groups is 6 or less.

In the formula, R ⁵ and R ⁶ represent a hydrogen atom or the same or different alkyl group having 1 to 18 carbon atoms. m represents an integer of 1 to 13. p ³ and q ³ represent an integer of 1 to 3, and the total sum of alkyl groups is 3 or less.

In addition, the alkyl group of R ⁵ and R ⁶ is particularly preferably an alkyl group having 2 to 4 carbon atoms.

Examples of the compound represented by the formula [VI] include dimethylnaphthalene, diethylnaphthalene and diisopropylnaphthalene.

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

Examples of the compound represented by the formula [VIII] include 1-methyl-1-dimethylphenyl-1-phenylmethane, 1-
Ethyl-1-dimethylphenyl-1-phenylmethane,
1-propyl-1-dimethylphenyl-1-phenylmethane may be mentioned.

Examples of the esters include phosphates (eg, triphenyl phosphate, tricresyl phosphate, butyl phosphate, octyl phosphate, cresyl diphenyl phosphate), phthalates (dibutyl phthalate, 2-ethylhexyl phthalate,
Ethyl phthalate, octyl phthalate, butylbenzyl phthalate), dioctyl tetrahydrophthalate, benzoic acid ester (ethyl benzoate, propyl benzoate, butyl benzoate, isopentyl benzoate, benzyl benzoate), abietic acid ester (abietic acid) Ethyl, benzyl abietic acid), dioctyl adipate, isodecyl succinate, dioctyl azelate, oxalate ester (dibutyl oxalate, dipentyl oxalate), diethyl malonate, maleate ester (dimethyl maleate, diethyl maleate, maleic acid) Dibutyl), tributyl citrate, sorbate (methyl sorbate, ethyl sorbate, butyl sorbate), sebacate (dibutyl sebacate, dioctyl sebacate), ethylene glycol Glycol ester compounds (formic acid monoesters and diesters, butyric acid monoesters and diesters,
Lauric acid monoester and diester, palmitic acid monoester and diester, stearic acid monoester and diester, oleic acid monoester and diester), triacetin, diethyl carbonate, diphenyl carbonate, ethylene carbonate, propylene carbonate, borate ester (tributyl borate) , Tripentyl borate) and the like.

The above oils can be used together or with other oils.

In the present invention, an auxiliary solvent having a low boiling point can be added to the above organic solvent as a solvent aid. Preferable examples of such an auxiliary solvent include ethyl acetate, isopropyl acetate, butyl acetate and methylene chloride.

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

As the surfactant to be contained in the aqueous phase, it is possible to appropriately select and use anionic or nonionic surfactants that do not cause precipitation or aggregation by acting on the protective colloid. . Preferred surfactants include sodium alkylbenzene sulfonate (eg, sodium dodecylbenzene sulfonate), sodium alkyl sulfate, dioctyl sodium sulfosuccinate, polyalkylene glycol (eg, polyoxyethylene nonylphenyl ether), and the like. .

The emulsion dispersion of the basic dye precursor and the developer in the present invention is a high-speed stirring of an oil phase containing the basic dye precursor and the developer, an aqueous phase containing a protective colloid and a surfactant,
It can be easily obtained by mixing and dispersing by using a means generally used for emulsification of fine particles such as ultrasonic dispersion.

A compound having a function of a glass transition point regulator of the capsule wall can be added to the emulsified dispersion.
Examples of such a compound include a hydroxy compound, a carbamic acid ester compound, a sulfonamide compound, an aromatic methoxy compound, and the like.
For example, it is described in Japanese Patent Application No. 59-244190.

These compounds can be appropriately used in the range of 0.1 to 2 parts by weight, preferably 0.5 to 1 part by weight, based on 1 part by weight of the color developer.

Developer is 0.05 to 8 g / m ² , basic dye precursor is 0.02 to 4 g / m ² .
It is applied in the range of m ² .

The decolorizing agent in the present invention has a decoloring effect on the coloring system of the basic dye and the color developing agent, and this is exemplified below.

a) Alkylene oxide adduct of bisphenols
53-46689) Here, A is methylene or alkylidene, b) methylolamide and bisamide having a melting point of 110 ° C. or higher (Japanese Patent Application No. 53-80557), c) long-chain 1,2-glycol (Japanese Patent Application No. 53-99563), d) Ethylene oxide adduct of terephthalic acid (Japanese Patent Application No. 53-96
66), e) solid alcohols such as stearyl alcohol, tripropylcarbinol, polyethylene glycol, polypropylene glycol, 1,8-octanediol, dimethylpentaglycerin, 1,2,3,4-tetraoxybutane (Japanese Patent Publication No. -17865).

f) a polymer of polyoxydecamethylene, polyoxymethylene, polyethylene oxide, trimethylene oxide,
Polyether or polyethylene glycol derivative such as 1,3-dioxolane polymer, polyoxyethylene alkylamine, sorbitan monostearate, polyoxyethylene oleyl ether, polyethylene glycol monostearate, polyoxyethylene alkyl amide, oxyethylene alkylamine (Japanese Patent Publication 50-1786
7 and Japanese Patent Publication No. 50-17868).

g) acetamide, stearamide, phthalonitrile,
m-nitroaniline, β-naphthylamine (Japanese Patent Publication No. 51-
19991 publication).

h) Guanidine derivatives such as 1,3-dicyclohexyl-2-phenylguanidine, 1,3-dicyclohexyl-2-naphthylguanidine, 2,3-dicyclohexyl-1-phenylguanidine and 1,2,3-triphenylguanidine (specifically Japanese Patent Publication No. 51-29024).

i) hexadecylamine, tribenzylamine, N, N,
N ', N'-tetrabenzylethylenediamine, tricyclohexylamine, dioctadecylamine, 2-aminobenzoxazole, dodecyltrimethylammonium chloride, hexadecyltrimethylammonium chloride, and other amines or quaternary ammonium salts (Patent Document 1)
50-18048 publication).

The decolorizer may be experimentally determined and applied in an amount sufficient to erase the pigment produced from the basic dye, but usually 0.05 to 8 g / m
^It is preferably used in the range of ² .

In the present invention, by encapsulating the above decolorizing agent in a microcapsule, it is possible to prevent decoloring at the time of manufacturing the heat-sensitive recording material, and at the same time, to improve the raw storage stability and the record storage stability of the heat-sensitive recording material. You can In this case, the image density during recording can be increased by selecting the wall material and manufacturing method of the microcapsules.

The wall material of the microcapsule is polyurethane,
Polyurea, polyester, polycarbonate, urea-
Formaldehyde resin, melamine resin, polystyrene,
Examples thereof include styrene methacrylate copolymer, styrene-acrylate copolymer, gelatin, polyvinylpyrrolidone, polyvinyl alcohol and the like. In the present invention, two or more of these polymer substances may be used in combination.

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

Microcapsules used in the present invention, after emulsifying a core substance containing a reactive substance such as a decolorizing agent, it is preferable to form a wall of a polymer substance around the oil droplets for microencapsulation, In this case, a reactant forming a polymer substance is added inside the oil droplet and / or outside the oil droplet.
Details of the microcapsules that can be preferably used in the present invention, such as the preferred method for producing the microcapsules, are described in, for example, JP-A-59-222716.

In addition to the decoloring agent, an organic solvent can be added to the core material of the microcapsules. As the organic solvent, those similar to those used for dissolving the basic dye precursor and the color developer can be used.

Further, in order to make the heat-printed portion highly transparent, the refractive index of the core substance of the microcapsules is close to the refractive index of the oil phase in which the basic dye precursor and the color developer are dissolved. preferable.

In the present invention, the size of the microcapsules is preferably 4 μm or less as the volume average particle size according to the measuring method described in JP-A-60-214990.

The preferred microcapsules produced as described above are:
It is not destroyed by heat or pressure as used in conventional recording materials, and the reactive substance contained in the core and outside of the microcapsule can permeate and react with the microcapsule wall.

A filler is added to the heat-sensitive layer of the heat-sensitive recording material of the present invention in order to increase the film strength or prevent sticking. This filler has a refractive index range of 0.95 to 1.05 times the refractive index of the organic solvent solution in which the basic dye precursor and the color developer are dissolved so as not to reduce the transparency of the heat-sensitive layer. It is necessary to be a proper filler.

Examples of such fillers include inorganic pigments such as zinc oxide, calcium carbonate, barium sulfate, titanium oxide, lithopone, talc, rouxite, kaolin, aluminum hydroxide, amorphous silica and colloidal silica, and polystyrene,
Vinyl acetate resin, polystyrene methacrylate, styrene-methacrylate copolymer, vinylidene chloride, polystyrene, polyurea, melamine-formaldehyde and other organic pigments, zinc stearate, calcium stearate, aluminum stearate and other metallic soaps and paraffin wax, micro Waxes such as crystallin wax, carnauba wax, methylol stearamide, polyethylene wax and silicone can be mentioned.

In order not to reduce the transparency, the particle size of these fillers needs to be 3 μm or less, and more preferably 1.5 μm or less.

These fillers may be used alone or in combination of two or more kinds.

The total amount of these fillers added is usually 0.1 to 100%, preferably 10 to 50% based on the weight of the heat-sensitive layer.

<< Function >> In the present invention, the addition of the filler to the heat-sensitive layer improves the film strength and scratch resistance of the heat-sensitive layer, but as described above, the refractive index of the filler and the developer The ratio of the refractive index to the solution is 0.95 to 1.05, and the particle size of the filler is 3μ or less, which is extremely fine, so even if the filler is added, light scattering hardly occurs, and the transparency of the heat-sensitive layer is filled. It is hardly damaged by the addition of the agent.

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

As the binder, polyvinyl alcohol, methyl cellulose, carboxymethyl cellulose, sodium alginate, idoxypropyl cellulose, arabic gum, gelatin, polyvinyl pyrrolidone, casein, styrene-butadiene latex, acrylonitrile-butadiene latex, polyvinyl acetate, polyacrylic acid ester, ethylene-acetic acid. Various emulsions such as vinyl copolymers can be used. The amount used is 0 as solid content.
It is 5 to 5 g / m ² .

The heat-sensitive recording material of the present invention comprises a microcapsule containing a decoloring agent, a dispersion in which at least a basic dye precursor and a color developer are emulsified and dispersed, and a coating solution containing other additives such as a binder, It is coated and dried by a coating method such as bar coating, blade coating, air knife coating, gravure coating, roll coating coating, spray coating, or dip coating on a support such as paper or synthetic resin film, and the solid content is 2.5 to 25 g / It is manufactured by providing a heat-sensitive layer of m ² .

The heat-sensitive layer of the heat-sensitive recording material produced in this manner has extremely good transparency.

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

In order to improve the matching property with the thermal head during thermal printing and the water resistance of the protective layer, a pigment,
Metal soap, wax, crosslinking agent, etc. are added.

Pigments include zinc oxide, calcium carbonate, barium sulfate,
Titanium oxide, lithopone, talc, sekiseki, kaolin, aluminum hydroxide, amorphous silica, styrene beads, urea melamine resin, etc. are present, and the addition amount thereof is 0.05 to 2 times the total weight of the polymer, particularly preferably 0.1 to 0.5 times the amount. When the amount is 0.05 times or less, it is ineffective for improving the matching property with the head, and when the amount is 2 times or more, the transparency and sensitivity of the heat-sensitive recording material are remarkably lowered and the commercial value thereof is impaired.

Metal soaps include emulsions of higher fatty acid metal salts such as zinc stearate, calcium stearate and aluminum stearate, and are added in an amount of 0.5 to 20% by weight, preferably 1 to 10% by weight based on the total weight of the protective layer. To be done.
The wax includes paraffin wax, microcrystalline wax, carnauba wax, methylol stearamide, stearic acid amide, polyethylene wax, emulsions of silicone, etc., and the total weight of the protective layer is 0.5-4.
It is added in an amount of 0% by weight, preferably 1 to 20% by weight.

Further, in order to uniformly form a protective layer on the heat sensitive layer, a surfactant is added to the protective layer forming coating liquid. Surfactants include sulfosuccinic acid-based alkali metal salts, fluorine-containing surfactants, and the like, and specific examples thereof include di- (2-ethylhexyl) sulfosuccinic acid and di- (n-hexyl) sulfosuccinic acid. There are sodium salt, ammonium salt and the like.

Further, in the protective layer, a surfactant, a polymer electrolyte or the like for preventing the heat-sensitive recording material from being charged may be added. The solid coating amount of the protective layer is usually preferably 0.2-5 g / m ^2, more preferably from 1g~3g / m ^2.

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

The paper used for the support is heat-extracted pH 6 sized with a neutral sizing agent such as alkyl ketene dimer.
It is advantageous to use a neutral paper of Nos. 9 to 9 (described in JP-A-55-14281) 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, it is described in JP-A-57-116687. Moreover, paper having a Bekk smoothness of 90 seconds or more is advantageous.

Further, the optical surface roughness described in JP-A-58-136492 is 8
Paper having a thickness of 40 μm or less and a thickness of 40 to 75 μm, a paper having a density of 0.9 g / cm ³ or less and an optical contact ratio of 15% or more described in JP-A-58-69097, and described in JP-A-58-69097. Canadian Standard Freeness (J
Paper made from pulp that has been beaten to 400 cc or more with IS P8121) to prevent the impregnation of the coating liquid, JP-A-58-65695
In order to improve the color density and resolution by using the glossy surface of the base paper produced by the Yankee machine as the coating surface,
The paper described in JP-A-59-35985, which has been subjected to corona discharge treatment on the base paper to improve the coating suitability, is also used in the present invention and gives good results. Any of these other supports used in the field of ordinary thermosensitive recording paper can be used as the support of the present invention.

A transparent support is preferably used in the heat-sensitive recording material of the present invention. By using this transparent support, not only the recorded matter after recording can be used for an OHP sheet or the like, but also by providing heat-sensitive layers that develop different hues on both sides of the transparent support, Colorization becomes easy.

Examples of the transparent support include polyester films such as polyethylene terephthalate and polybutylene terephthalate, films of cellulose derivatives such as cellulose triacetate film, polystyrene films, polypropylene films, and polyolefin films such as polyethylene. It can be used alone or by pasting.

The thickness of the transparent support is 20 to 200 μm, and preferably 50 to 100 μm.

The support may be provided with a perforation so that the support can be accurately conveyed during printing.

In the present invention, an undercoat layer may be provided between the transparent support and the heat-sensitive layer in order to enhance the adhesion between the two layers. As the material for the undercoat layer, gelatin or synthetic polymer latex,
Nitrocellulose or the like is used. The coating amount of the undercoat layer is 0.
It is preferably in the range of ^{1g / m 2 ~2.0g / m 2} , especially 0.2g
The range of / m ^{2 to} 1.0 g / m ² is preferred.

If it is less than 0.1 g / m ² , the adhesion between the support and the heat-sensitive layer is not sufficient, and even if it is increased to 2.0 g / m ² or more, the adhesive force between the support and the heat-sensitive layer reaches saturation, which is cost effective. Will be at a disadvantage.

Since the undercoat layer may deteriorate the image quality of the heat-sensitive layer when the undercoat layer swells due to the water contained in the heat-sensitive layer when the heat-sensitive layer is coated thereon, it is used as the heat-sensitive layer. It is desirable to cure using the same hardening agent as described above.

The following hardeners can be used in the present invention.

Divinylsulfone-N, N'-ethylenebis (vinylsulfonylacetamide), 1,3-bis (vinylsulfonyl) -2-propanol, methylenebismaleimide, 5
-Acetyl-1,3-diacryloyl-hexahydro-s
-Triazine, 1,3,5-triacryloyl-hexahydro-s-triazine, 1,3,5-trivinylsulfonyl-
Active vinyl compounds such as hexahydro-s-triazine.

2,4-dichloro-6-hydroxy-s-triazine
Sodium salt, 2,4-dichloro-6-methoxy-s-triazine, 2,4-dichloro-6- (4-sulfoanilino) -s-triazine sodium salt, 2,4-dichloro-6- (2-sulfo Ethylamino) -s-triazine,
Active halogen compounds such as NN'-bis (2-chloroethylcarbamyl) piperazine.

Bis (2,3-epoxypropyl) methylpropylammonium.p-toluenesulfonate, 1,4-bis (2 ', 3'-epoxypropyloxy) butane, 1,3,5
An epoxy compound such as triglycidyl isocyanurate, 1,3-diglycidyl-5- (γ-acetoxy-β-oxypropyl) isocyanurate.

Ethyleneimino compounds such as 2,4,6-triethylene-s-triazine, 1,6-hexamethylene-N, N'-bisethyleneurea and bis-β-ethyleneiminoethylthioether.

Methanesulfonic acid ester compounds such as 1,2-di (methanesulfonoxy) ethane, 1,4-di (methanesulfonoxy) butane, and 1,5-di (methanesulfonoxy) pentane.

Dicyclohexylcarbodiimide, 1-cyclohexyl-3- (3-trimethylaminopropyl) 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, zirconium borate.

N-carbethoxy-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'-adipoyldioxydisuccinimide and N, N'-terephthaloyldioxydisuccinimide.

Isocyanates such as toluene-2,4-diisocyanate and 1,6-hexamethylene diisocyanate.

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

Of these, glutaraldehyde, dialdehydes such as 2,3-dihydroxy-1,4-dioxane, and boric acid are particularly preferable.

The amount of these hardeners added is 0 with respect to the weight of the heat-sensitive layer.
In the range of 01% by weight to 10% by weight, an appropriate addition amount can be selected according to the coating method and the desired degree of curing. If the addition amount is less than 0.01% by weight, the effect is not sufficient, and 10% by weight
If the amount is larger than the above range, the heat sensitivity and the image density are lowered, which is not preferable.

The amount of these hardeners added is in the range of 0.20% to 3.0% by weight based on the weight of the undercoat material, and an appropriate amount can be selected according to the coating method and the desired degree of curing.

If the amount added is less than 0.20% by weight, the degree of curing will be insufficient regardless of the time, and the undercoat layer will swell when the heat-sensitive layer is applied. Conversely, if it is more than 3.0% by weight, the degree of curing will be poor. If it proceeds too much, the adhesion between the undercoat layer and the support deteriorates, and the undercoat layer becomes a film and peels from the support.

Depending on the curing agent used, if necessary, caustic soda may be added to bring the pH of the solution to the alkaline side, or the pH of the solution may be brought to the acidic side with citric acid or the like.

It is also possible to add an antifoaming agent in order to eliminate bubbles generated during coating, or to add an activator to improve the leveling of the liquid and prevent the generation of coating streaks. .

Further, if necessary, an antistatic agent can be added.

Further, it is desirable to activate the surface of the support by a known method before applying the undercoat layer. As the method of activation treatment, etching treatment with acid, flame treatment with gas burner, corona treatment, glow discharge treatment or the like is used, but from the viewpoint of cost or simplicity,
U.S. Pat.Nos. 2,715,075, 2,846,727, 3,549,
The corona discharge treatment described in No. 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-mentioned substantially transparent heat-sensitive layer formed on at least one surface of the support, and a double-sided heat-sensitive recording material can be prepared by providing one heat-sensitive layer each.

<< Effect of the Invention >> In the heat-sensitive recording material of the present invention, when a transparent film is used as the support, the contents received by a facsimile or the like can be directly subjected to OHP to see a negative image. In particular, since a special filler is added to the heat sensitive layer, the heat sensitive layer has good transparency and heat resistance.

<< Examples >> The present invention will be described in more detail below with reference to Examples, but the present invention is not limited thereto.

[Preparation of Emulsion Dispersion of Basic Dye Precursor and Developer]

Developer (a) 2g, (b) 1g represented by the following structural formula,
8 g of (c) and 2 g of the basic dye precursor (d) were dissolved in 5 g of diethyl maleate and 10 g of ethyl acetate. The resulting solution was added with 40% of 8% polyvinyl alcohol (PVA217E Kuraray Co., Ltd.), 50 g of water, and sodium dodecylbenzenesulfonate.
Mix with 0.5 g of aqueous solution and emulsify for 5 minutes at 10,000 rpm at room temperature using Ace Homogenizer manufactured by Nippon Seiki Co., Ltd.
An emulsified dispersion with a particle size of 0.5μ was obtained.

[Preparation of Decoloring Agent Capsule Liquid] The following decoloring agent (e) (10 g), 1-phenyl-1-xylylethane (20 g), ethyl acetate (10 g) and Takenate D-110N (Takeda Yakuhin Co., Ltd. capsule wall agent) were mixed. The solution
Mix with 60 g of 8% polyvinyl alcohol PVA217E and 20 g of water, emulsify with Ace Homogenizer manufactured by Nippon Seiki Co., Ltd. for 5 minutes at 10,000 rpm, and add 150 g of water to 40 ° C.
The mixture was allowed to react for 3 hours, and a capsule liquid having a capsule size of 0.7 μ was mixed.

(Preparation of thermosensitive recording material) 5.0 g of the above-mentioned capsule liquid, 10.0 g of an emulsified dispersion of a basic dye precursor and a developer, and 20% dispersion liquid of the filler shown in Table 1 4.5.
g and 5.0 g of water are mixed by stirring, and the solid content is 10 g / m on a transparent polyethylene terephthalate (PET) support with a thickness of 70 μm.
^It was applied and dried so as to have a thickness of 2, and then a protective layer of 2 μm having the following composition was provided to prepare a transparent heat-sensitive film.

[Composition of protective layer]

Silica modified polyvinyl alcohol 1 part by weight (Kuraray Co., Ltd. PVA R 2105) (solid content) Colloidal silica 1.5 parts by weight (Nissan Chemical Co., Ltd. Snowtex 30) (solid content) Zinc stearate 0.02 parts by weight (Chukyo Yushi Co., Ltd.) Hydrin Z-7 manufactured by Co., Ltd. (solid content) 0.01 part by weight of paraffin wax (Hydrin Z-7 manufactured by Chukyo Yushi Co., Ltd.) (solid content) The transparency of the heat-sensitive recording material thus obtained was measured with an integrating sphere photometer (haze meter). Further, the surface of the film was lightly rubbed with a nail, and the film strength was evaluated from the ease of scratching. The results are as shown in Table 2.

From the results shown in Table 2, it was verified that the heat-sensitive layer of the heat-sensitive recording material of the present invention had good transparency and scratch resistance.

Claims (1)

[Claims] 1. A heat-sensitive recording material having at least a heat-sensitive layer on a support, wherein the heat-sensitive layer comprises a colorless or light-colored basic dye precursor and a developer which are dissolved in a water-insoluble or insoluble organic solvent. A heat-sensitive layer obtained by coating and drying on a support a coating solution containing an emulsified dispersion that has been emulsified and dispersed, a microcapsule containing a decoloring agent, and a filler having an average particle size of 3 μm or less. A heat-sensitive recording material, characterized in that the ratio of the refractive index of the agent to the refractive index of the organic solvent solution in which the basic dye precursor and the color developer are dissolved is 0.95 to 1.05.