JPH01204785A - Thermal recording material - Google Patents

Abstract

PURPOSE:To contrive higher raw preservability of a transparent thermal recording film and contrive prevention of sticking of a thermal head, by providing a protective layer consisting mainly of a silicon-modified polyvinyl alcohol and colloidal silica, on a thermal recording layer. CONSTITUTION:A coating liquid comprising an emulsified dispersion and microcapsules containing a decoloring agent therein is applied to a base, followed by drying to provide a thermal recording layer. Then, a protective layer consisting mainly of a silicon-modified polyvinyl alcohol and colloidal silica is provided on the thermal recording layer by coating. It is generally preferable that the silicon-modified polyvinyl alcohol has a structure wherein a silicon atom contained in the molecule thereof has a reactive substituent group, e.g., an alkoxyl, an acyloxyl, a hydroxyl obtained by hydrolysis or the like or an alkali metal salt thereof. The colloidal silica is used in the form of a colloidal solution obtained by dispersing ultrafine particles of silicic anhydride in water used as a dispersant. It is suitable and preferable that the amount of the colloidal silica used is 0.5-3 pts.wt. per 1 pts.wt. of the silicon-modified polyvinyl alcohol.

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 in recent years negative type images, such as ``white-out images in the previous section'', have been particularly prized in the field of slides because they reduce eye fatigue. ) (P films are not common, especially negative-type OHP heat-sensitive films that can be easily recorded with thermal heads widely used in facsimile printers and the like.

Therefore, the present inventors investigated to develop a negative type 01 (P heat-sensitive film), and as a result, we used a dye and a decoloring agent, which had been colored by contacting a leuco dye and an acidic compound in advance.
It has been discovered that the above-mentioned negative type OHP heat-sensitive film can be produced by coating it on a transparent film support, and this has already been proposed (Japanese Patent Application No. 60,646/1982).

(Problem to be Solved by the Invention) However, when a protective layer is provided on the heat-sensitive layer in order to improve the shelf life of the transparent heat-sensitive film or prevent sticking of the thermal head, the protective layer The disadvantage was that the image quality deteriorated due to poor transparency.

As a result of intensive studies aimed at solving the above-mentioned drawbacks, the present inventors have found that a protective layer mainly composed of silicon-modified polyvinyl alcohol and colloidal silica is extremely convenient as it has excellent transparency and anti-sticking properties. We have arrived at the present invention.

Therefore, a first object of the present invention is to provide a negative type OHP film which has good storage stability and recordability, and which can be easily recorded with a thermal head.

A second object of the present invention is to provide a protective layer made of a heat-sensitive film for OHP and having good transparency.

(Means for Solving the Problems) The above aspects of the present invention are characterized in that a colorless or light-colored basic dye precursor and a color developer are dissolved in an organic solvent that is sparingly soluble or insoluble in water, and then emulsified and dispersed. A coating solution containing microcapsules containing a dispersion and a decolorizing agent is coated on a support and dried to form a heat-sensitive layer, and then a protective layer consisting mainly of silicon-modified polyvinyl alcohol and colloidal silica is placed on the heat-sensitive layer. This was achieved using a heat-sensitive recording material coated with

In the heat-sensitive recording material according to the present invention, the unheated part is colored by a reaction product of a colorless or light-colored basic dye precursor pair and a color developer, and the heated part is colored by a reaction product of a colorless or light-colored basic dye precursor pair and a color developer. Since the above-mentioned coloring is bleached by the agent, when an overhead projector is used, the background is colored and the image portion appears 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 , for example, triarylmethane compounds, diphenylmethane compounds, gysanthene compounds, thiazine compounds, spiropyran compounds, and the like.

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, R8 is an alkyl group having 4 to 18 carbon atoms, an alkoxyl group, or a tetrahydrofurfuryl group, and R1 is a hydrogen atom, an alkyl group having 1 to 15 carbon atoms, or halogen atom,
R1 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) 49- pages 54 and 6
It is described on pages 5-70.

Among these, those having a melting point of 50'C to 250''C are particularly preferable, and phenols and organic acids that are sparingly soluble in water and having a melting point of 60'C to 200''C are particularly desirable. It is preferable to use two or more color developers in combination because the solubility increases.

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

(1) C, H, □.

m=o~2, n=2~11 (II) R+ 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) (V) Rs 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 dissolved in an organic solvent that is sparingly soluble or insoluble in water, 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 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 general formulas (Vl) 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,
Rz represents an alkyl group having 1 to 1 carbon atoms. p+
, q + represents an integer of 1 to 4, and the total number of alkyl groups is 4 or less.

In addition, the alkyl group of R1 and R2 is preferably an alkyl group 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'' and 'q' represent integers 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, R5 and R6 represent a hydrogen atom or the same or different alkyl groups having 1 to 18 carbon atoms.

m represents an integer from 1 to 13. R3 and q'' represent an integer of 1 to 3, and the total number of alkyl groups is 3 or less.

Note that the alkyl group of R55R& is particularly preferably an alkyl group having 2 to 4 carbon atoms.

Examples of the compound represented by formula (VI) 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 1-methyl-
Dimethylphenyl-1-phenylmethane, 1-ethyl-1-dimethylphenyl-1-phenylmethane, 1-
Propyl-1-dimethylphenyl-1-phenylmethane is mentioned.

Examples of esters include phosphate esters (for example, triphenyl phosphate, tricresyl phosphate, butyl phosphate, octyl phosphate, cresyl diphenyl phosphate), phthalate esters (
Diptyl phthalate 1, 2-ethylhexyl phthalate,
ethyl phthalate, octyl phthalate, butyl benzyl phthalate), dioctyl tetrahydrophthalate, benzoic acid ester (ethyl benzoate, propyl benzoate, butyl benzoate, isopentyl benzoate, benzyl benzoate)
, abietate ester (ethyl abietate, benzyl abietate), dioctyl adipate) Lt, isodecyl succinate, dioctyl azelaate, oxalate ester (dibutyl sherate, dipentyl oxalate), diethyl malonate, maleate ester (maleic acid) dimethyl acid, diethyl maleate, diptyl maleate), tributyl citrate, sorbate esters (methyl sorbate, ethyl sorbate, butyl sorbate), sebacate esters (diptyll 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 ± noesters 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 methylene chloride.

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. Such compounds include, for example.

There are hydroxy compounds, carbamate ester compounds, sulfonamide compounds, aromatic methoxy compounds, etc., and details thereof are described, for example, in Japanese Patent Application No. 59-244190.

These compounds can be used appropriately in the range of 0.1 to 2 parts by weight, preferably 0.5 to 1 part by weight, per 1 part by weight of the color developer, but they may be used as melting point depressants and thereby reduce the melting point. It is preferable to use the color developer and the like that fall at the same location. When adding to different locations, it is preferable to add 1 to 3 times the above amount.

Color developer: 0.05-8g/m2, 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!, 0) , l H 0-(C, Ht*O), ' -H where A is methylene or alkylidene, b) Melting point 11
0°C or higher 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 〇-17865 Publication) f) Polyoxydecamethylene, polyoxymethylene, polyethylene oxide, trimethylene oxide polymer,
1. Polyethers such as 3-dioxolane polymers, polyoxyethylene alkylamine, sorbitan monostearate, polyoxyethylene oleyl ether, polyethylene glycol monostearate, polyoxyethylene alkylamide, oxydiethylene alkylamine, or Polyethylene glycol derivatives (Special Publication of 1970)
-17867 and Japanese Patent Publication No. 17868) g) Acetamide, stearamide, phthalonitrile,
m-Nitroaniline, β-naphthylamine (Special Publication No. 1983
-19991 publication) h'') 1,3-dicyclohexyl-2-phenylguanidine, 1,3-dicyclohexyl-2-naphthylguanidine, 2,3-dicyclohexyl-1-phenylguanidine, 1.2 .3-) Guanidine derivatives such as liphenylguanidine (Japanese Patent Publication No. 51-29024) i) Hexadecylamine, tribenzylamine, N, N
, N', N'-tetrabenzyl ethylenediamine, tricyclohexylamine, dioctadecylamine,
Amine or quaternary ammonium salt such as 2-aminobenzoxazole, dodecyltrimethylammonium chloride, hexadecyltrimethylammonium chloride (Japanese Unexamined Patent Publication No. 18048/1983) A decoloring agent is used to erase pigments generated from basic dyes. It is sufficient to experimentally determine and apply a sufficient amount, 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. 0 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, a reactant forming a polymeric substance is added inside the oil droplet and/or outside the oil droplet. 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.

Binders include polyvinyl alcohol, methylcellulose, carboxymethylcellulose, sodium alginate, hydroxypropylcellulose, gum arabic, gelatin, polyvinylpyrrolidone, 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 0.0 as solid content.
It is 5 to 5 g/nf.

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 solids content of 2.5 to 25 g/m.

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.

In the present invention, in order to protect the surface of the heat-sensitive layer, which has good transparency, it is preferable to provide a transparent protective layer of 1711 or more, which has 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.

The silicon-modified polyvinyl alcohol used in the present invention is not particularly limited as long as it contains a silicon atom in the molecule, but usually the silicon atom contained in the molecule is an alkoxyl group, an acyloxyl group, or a hydrolyzed polyvinyl alcohol. It is preferable to use those having a reactive substituent such as a hydroxyl group or an alkali metal base thereof obtained by the above method.

Details of the method for producing modified polyvinyl alcohol containing silicon atoms in the molecule are disclosed in JP-A-58-193189.
The modified polyvinyl alcohol containing silicon atoms in the molecule used in the present invention described in the above publication can also be produced by these known methods.

The colloidal silica used in the present invention is used as a colloidal solution in which ultrafine particles of silicic anhydride are dispersed in water using water as a dispersion medium. The particle size of colloidal silica is 1
Those having a specific gravity of 0 mμ to 100 mμ and a specific gravity of 1.1 to 1.3 are preferable. The pH value of the colloidal solution in this case is about 4 to about 10.
are preferably used.

(Function) When a protective layer made of at least the above silicon-modified polyvinyl alcohol and colloidal silica is provided on the surface of the heat-sensitive recording material, the sticking and transparency of the heat-sensitive recording material can be significantly improved.

A suitable blending ratio of silicon-modified polyvinyl alcohol and colloidal silica in the present invention is 0.5 parts by weight of colloidal silica to 1 part by weight of silicon-modified polyvinyl alcohol.
~3 parts by weight, more preferably 1 to 2 parts by weight. If the amount of colloidal silica used is less than 0.5 parts by weight, the effect of improving transparency will be small, and if it is used more than 3 parts by weight, cracks will occur in the protective layer, and the transparency will be reduced.

The protective layer may further contain one or more polymers. Specific examples of polymers that can be used in combination include methylcellulose, carboxymethylcellulose, hydroxymethylcellulose, starches, gelatin, gum arabic, casein, and styrene-maleic anhydride. Water-soluble polymers such as acid copolymer hydrolyzate, styrene-maleic anhydride copolymer half ester hydrolyzate, polyvinyl alcohol, carboxy-modified polyvinyl alcohol, polyacrylamide derivatives, polyvinylpyrrolidone, sodium polystyrene sulfonate, sodium alginate, etc. and water-insoluble polymers such as styrene-butadiene rubber latex, acrylonitrile-butadiene rubber latex, methyl acrylate-butadiene rubber latex, and polyvinyl acetate emulsion. The amount used in combination is 0.01 to 0 per 1 part by weight of silicon-modified polyvinyl alcohol.
．． 5 parts by weight is preferred.

Protect! Pigments,
Metal soaps, waxes, crosslinking agents, etc. are added.

Pigments include zinc oxide, calcium carbonate, barium sulfate, titanium oxide, lithopone, talc, Rouseki, kaolin, aluminum hydroxide, amorphous silica, etc., and the amount added is 0.05 to 2.0% of the total weight of the polymer. The amount is particularly preferably 0.1 to 0.5 times. 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 0.5 to 20% by weight, preferably 1 to 10% by weight of the total weight of the protective layer. added in quantity. Waxes include emulsions such as paraffin wax, microcrystalline wax, carnauba wax, methylol stearamide, stearic acid amide, polyethylene wax, and silicone.
．． It is added in an amount of 5 to 40% by weight or 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 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.

Also, keep it! A surfactant, a polymer electrolyte, etc. may be added to the layer to prevent charging of the heat-sensitive recording material.The solid content coating amount of the protective layer is usually 0. It is preferably 2 to 5 g/rrf, more preferably 1 g to 3 g/rrf.

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 a thermally extracted paper sized with a neutral sizing agent such as an alkyl ketene dimer.
Use of neutral paper No. 6 to No. 9 (described in JP-A-55-14281) 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
Paper having a (meter basis weight) of 2 and 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/cm' or less and an optical contact ratio of 15% or more, described in JP-A No. 8-69097, JP-A-58-69
Canadian Standard Freeness (JIS P81) described in No. 097
21) Paper made from pulp beaten to 400 cc or more to prevent penetration of coating liquid, JP-A-58-6
5695, the glossy side of base paper made by a Yankee machine is used as the coating surface to improve the color density and resolution, and the method described in JP-A-59-35985.
Papers whose base paper has been subjected to corona discharge treatment to improve coating suitability can also be used in the present invention and give 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, it is not only possible to use the recorded matter on an OHP sheet, etc., but also by providing heat-sensitive layers that develop different hues on both sides of the transparent support. It is also easy to use multiple colors.

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.
It is preferably in the range of Ig/m" to 2.0 g/m", particularly preferably in the range of 0.2 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.

The undercoat layer is coated with a hardening agent because 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 when the heat-sensitive layer is coated on top of it. It is desirable to cure it.

As hardeners that can be used in the present invention, the following can be mentioned.

■Divinylsulfone-N,N'-ethylenebis(vinylsulfonylacetamide), 1,3-bis(vinylsulfonyl)-2-propatol, methylenebismaleimide, 5-acetyl-1,3-'; to acryloyl Active vinyl compounds such as hexahydro-5-) liazine, 1,3.5-)lyacryloyl-hexahydro-5-1 lyazine, 1,3,5-)rivinylsulfonyl-hexahydro-5-1 lyazine. .

■2.4-dichloro-6-hydroxy-3-triazine sodium salt, 2.4-dichloro-6-medoxy S
-) Riazine, 2.4-dichloro-6-(4-sulfoanilino)-s-triazine sodium salt, 2.4-dichloro-6-(2-sulfoethylamino)-S-triazine, N-N'- Bis(2-chloroethylcarbamyl)
Active halogen compounds such as piperazine.

■Bis(2,3-epoxypropyl)methylpropylammonium p-toluenesulfonate, 1,4-bis(2°,3°-epoxypropyloxy)butane, 1,
Epoxy compounds such as 3.5-) diglycidyl isocyanurate and 1,3-diglycidyl-5-(T-acetoxy-β-oxypropyl isocyanurate).

■2.4.6-) Liethylene-s-) Reazine 1.6-
Ethyleneimino compounds such as hexamethylene-N,N'-bisethyleneurea and bis-β-ethyleneiminoethylthioether.

■1.2-di(methanesulfonoxy)ethane, 1.4
- Methanesulfonic acid ester compounds such as di(methanesulfonoxy)butane and 1°5-di(methanesulfonoxy)pentane.

■Dicyclohexylcarbodiimide, 1-cyclohexyl-3-(3-)dimethylaminopropyl)carbodiimide-p-)rienesulfonate, 1-ethyl-3-(
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)
Dehydrated condensed peptide reagents such as -4-methylpyridinium chloride, active ester compounds such as N,N'-aziboyldioxydisuccinimide, 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-')oxane.

Among these, dialdehydes such as glutaraldehyde and 2°3-dihydroxy-1,4-dioxane, and boric acid are particularly preferred.

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 applying the lower tell, 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, U.S. Pat.
No. 846,727, No. 3,549,406, No. 3
．． Corona discharge treatment, such as that described in No. 590.107, 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 the support, the content received by facsimile or the like can be directly printed on a negative OHP. In particular, since it has a highly transparent Wi-retention layer on the heat-sensitive layer, not only the raw storage life of the heat-sensitive recording material and the storage stability of the recorded image are good, but also the sticking performance to the thermal head is significantly improved. can do.

(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 developer emulsified dispersion] 14 g of crystal violet lactone (leuco dye), 60 g of Takena D-11ON (capsule wall material manufactured by Takeda Pharmaceutical ■) and Sumisorb 200 (ultraviolet absorber manufactured by Sumitomo Chemical ■) 2g
was added to a mixed solvent of 55 g of 1-phenyl-1-xylylethane and 55 g of methylene chloride and dissolved. This leuco dye solution was mixed with an aqueous solution of 100 g of 8% polyvinyl alcohol aqueous solution, 40 g of water, and 1.4 g of 2% sodium salt of dioctyl sulfosuccinate (dispersing agent), and mixed with an Ace homogenizer manufactured by Nippon Seiki ■ for 10 minutes. ．．
Emulsify at 00 rpm for 5 minutes, add 150 g of water, and react at 40°C for 3 hours to obtain a capsule size of 0.7μ.
A capsule liquid was prepared.

[Preparation of developer emulsion dispersion]

Color developer represented by the following structural formula (a) 2 g, (b)
1 g, (c) 8 g, and basic dye precursor (d) 2
g was dissolved in 5 g of diethyl maleate and 10 g of ethyl acetate.

The resulting solution was mixed with 8% polyvinyl alcohol (PVA
217E manufactured by Kuraray Co., Ltd.), mixed with an aqueous solution of 50 g of water and 0.5 g of sodium dodecylbenzenesulfonate,
Using Nippon Seiki's Ace homogenizer, io, o
ooγpm, emulsified for 5 minutes at room temperature, particle size 0.5μ
An emulsified dispersion was obtained.

Color developer (a) Color developer (b) Color developer (a) H Basic dye (d) Color eraser (e) However, a + b + c + d -12 [Preparation of color eraser capsule liquid ] 10 g of the following decolorizer (e), 20 g of 1-phenyl-1-xylylethane, 10 g of ethyl acetate, 1 Takenate D-1
A solution containing 25 g of 1ON (capsule wall agent manufactured by Takeda Pharmaceutical ■) was mixed with 8% polyvinylflu:1-/L, PVA.
Mix 60 g of 217 E in an aqueous solution of 20 g of water,
11000 Or with Nippon Seiki's Ace homogenizer
Emulsify with p for 5 minutes, add 150g of water, and heat at 40°C.
After reacting for 3 hours, a capsule liquid having a capsule size of 0.7 μm was mixed.

(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,
70μ thick transparent polyethylene terephthalate (PE)
T) A transparent heat-sensitive film was prepared by coating and drying the coating on a support so that the solid content was 15 g/m'', and then providing a 2μ thick protective layer with the following composition.

[Composition of protective layer]

Silica-modified polyvinyl alcohol 1 part by weight (PVA R2105 manufactured by Kuraray ■) (Solid content) Colloidal silica 1.5 parts by weight (Nissan Chemical ■
Snowtex 30) (solid content) Zinc stearate
0.02 parts by weight (Hydrin Z manufactured by Middle East Oil Co., Ltd.)
-7) (Solid content) Paraffin wax 0.0
1 part by weight (Hydrin P-7 manufactured by Middle East Oil & Fat ■) (solid content)
Example 2 A sample was prepared in the same manner as in Example 1 except that the composition of the protective layer was changed as follows.

Silica-modified polyvinyl alcohol 1 part by weight (PVA R210 manufactured by Kuraray ■) (Solid content) Colloidal silica 1.8 parts by weight (Nissan Chemical ■
Snowtex 30) (solid content) amorphous silica
0.1 part by weight (P-832 manufactured by Mizusawa Chemical Co., Ltd.)
(Solid content) Zinc stearate
0.02 parts by weight (Hydrin Z-7 manufactured by Middle East Oil Co., Ltd.) (
Solid content) Comparative Example 1 Comparative sample 1 was prepared in the same manner as in Example 1, except that polyvinyl alcohol (PVA217 manufactured by Kuraray ■) was used instead of silica-modified polyvinyl alcohol in the composition of the protective layer in Example 1. .

Comparative Example 2゜Holding in Example 1! ! Comparative sample 2 was prepared in the same manner as in Example 1 except that colloidal silica was not used in the composition of the layer.

Comparative Example 3 Comparative sample 3 was prepared in the same manner as in Example 1 except that colloidal silica was not used in the composition of the protective layer and oxidized starch (MS3800 manufactured by Nikko ■) was used instead of silica-modified polyvinyl alcohol. was created.

Comparative Example 4 Comparative sample 4 was prepared in the same manner as in Example 2 except that colloidal silica was not used in the composition of the protective layer in Example 2.
was created.

Comparative Example 5゜ Preservation 1 in Example 2! In the composition of the layer, styrene-maleic acid copolymer half ester salt (Polymaron 38 manufactured by Arayo Kagaku ■) was used instead of silica-modified polyvinyl alcohol.
Comparative sample 5 was prepared in the same manner as in Example 2, except that Example 5) was used.

Comparative Example 6 In the composition of the protective layer in Example 2, colloidal silica was not used, and polyvinyl alcohol (PVA217 manufactured by Kuraray ■) was used instead of silica-modified polyvinyl alcohol.
) Comparative sample 6 was prepared in the same manner as in Example 2, except that the sample 6 was used.

The haze (%) of the sample prepared as described above was measured using an integrating sphere HTR meter manufactured by Nippon Seimitsu Koshu ■, and the results are shown in the following table.

2 Haze 0 Example 1 16 Comparative Example 1 40 The above results demonstrate that the heat-sensitive recording material of the present invention exhibits excellent transparency.

Further, when the film after printing was subjected to OHP, a good white image was obtained.

Claims (1)

[Claims] Supports a coating solution containing microcapsules containing an emulsified dispersion and a color erasing agent, which are obtained by dissolving a colorless or light-colored basic dye precursor and a color developer in an organic solvent that is sparingly soluble or insoluble in water, and then emulsifying and dispersing the mixture. 1. A heat-sensitive recording material characterized in that a heat-sensitive layer is formed by coating and drying on a body, and then a protective layer consisting mainly of silicon-modified polyvinyl alcohol and colloidal silica is coated on the heat-sensitive layer.