JPH0437588A - Thermal recording material - Google Patents

Abstract

PURPOSE:To obtain a thermal recording material excellent in the transparency of a heat-sensitive layer, in heat sensitivity and blocking resistance by forming a weak-adhesive transparent heat-sensitive layer through applying and drying a coating liquid including microcapsules containing electron donative dye precursor and the emulsion dispersant of specific quantity and less. CONSTITUTION:This thermal recording material is composed of a support, at least one transparent heat-sensitive layer applying and drying a coating liquid including microcapsules containing colorless or light-colored electron donative dye precursor and an emulsion dispersant obtained by emulsion- dispersing a developer dissolved in an organic solvent slightly soluble or insoluble in water, and a weak-adhesive transparent heat-sensitive layer provided on the transparent heat-sensitive layer. The two adhesive transparent heat- sensitive layer is formed by applying and drying the coating liquid including microcapsules containing the electron donative dye precursor and 20wt.% and less emulsion dispersant. Because the weak-adhesive transparent heat-sensitive layer including only 20wt.% and less developed emulsion dispersant is provided, blocking resistance is improved without deteriorating the transparency and heat sensitivity of the transparent heat-sensitive recording material layer.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a heat-sensitive recording material, and more particularly to a heat-sensitive recording material that has a heat-sensitive layer that is excellent in sensitivity and transparency, and that does not easily cause profking.

(Prior art) The thermal recording method has three advantages: (1) no development is required; (2) when the support is paper, the quality of the paper is similar to that of ordinary paper; (3) it is easy to handle; and (4) color density is high. (5) The recording device is simple and inexpensive, and (6) There is no noise during recording, so it has rapidly become popular in the field of facsimiles and printers in recent years, and has become popular in the field of labels such as PO3 etc. , the use of thermal recording is also expanding.

Against this background, in recent years, in order to adapt to multicolorization, overhead flow projectors (
It is desired to develop a transparent heat-sensitive recording material that can be directly recorded with a thermal head for use in OHP.

Therefore, the present inventors first prepared microcapsules containing a colorless or light-colored electron-donating dye precursor on a support, and a color developer dissolved in an organic solvent that is sparingly soluble or insoluble in water. proposed a heat-sensitive recording material having a substantially transparent heat-sensitive layer formed by coating and drying a coating liquid consisting of an emulsified dispersion of .

(Problem to be Solved by the Invention) However, the above-mentioned transparent heat-sensitive layer is prone to adhesion, and when heat-sensitive recording materials are stacked and placed in a high-temperature and humid environment, blocking may occur and the heat-sensitive recording materials may be destroyed. , it has disadvantages such as being unsightly when applied to OHP.

As a result of intensive studies to solve the above-mentioned drawbacks, the inventors of the present invention found that simply providing a thick protective layer would result in a new drawback of reduced thermal sensitivity. When a transparent heat-sensitive layer containing a color developer emulsion dispersion of 20% by weight or less is provided, and a protective layer is further provided as necessary, the adhesiveness of the surface of the heat-sensitive recording material can be improved without reducing the heat sensitivity. The present invention has been achieved based on the discovery that blocking can be prevented.

Accordingly, an object of the present invention is to provide a heat-sensitive recording material that has a heat-sensitive layer that has excellent transparency, and also has excellent heat sensitivity and blocking resistance.

(Means for Solving the Problems) The above-mentioned object of the present invention is to provide at least a support and a microcapsule containing a colorless or light-colored electron-donating dye precursor, which is dissolved in an organic solvent that is sparingly soluble or insoluble in water. at least one transparent heat-sensitive layer formed by coating and drying a coating solution containing an emulsified dispersion obtained by emulsifying and dispersing a color developer, and a low-adhesion transparent heat-sensitive layer provided on the transparent layer. A heat-sensitive recording material comprising: the low-adhesion transparent heat-sensitive layer;
This was achieved by a heat-sensitive recording material formed by coating and drying a coating solution containing microcapsules containing the electron-donating dye precursor and 20% by weight or less of the emulsified dispersion.

As the electron-donating 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 triarylmethane 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 R5 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. The substituent for R4 is preferably an alkyl group having 1 to 5 carbon atoms, an alkoxy group, a halogenated alkyl group, or a halogen atom.

In the present invention, by encapsulating the above-mentioned electron-donating dye precursor in microcapsules, fogging can be prevented during the production of heat-sensitive recording materials, and at the same time, the heat-sensitive recording materials can have good raw storage properties and archival properties. It can be done. In this case, by selecting the wall material and manufacturing method of the microcapsules, it is possible to increase the image density during recording. The amount of electron donating dye precursor used is 0.05
It is preferable that it is 5.0 g/rrf.

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 an electron-donating dye precursor and then forming a wall of a polymer material around the oil droplets. A polymeric material or actant is added to the interior of the oil droplet and/or to the exterior of 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.

Here, the organic solvent for forming the oil droplets can be appropriately selected from known ones, but especially when an organic solvent suitable for dissolving the color developer described below is used, It is preferable because it has excellent solubility in the electron-donating dye precursor, increases color density during thermal printing, and reduces fogging.

The preferred microcapsules produced as described above are not ruptured by heat or pressure as is used in conventional recording materials (the reactive components contained in the core and outside of the microcapsules are It can penetrate through the capsule wall and react.

In the present invention, the wall material of the microcapsule is selected,
If necessary, a glass transition point adjusting agent (for example,
277490) to prepare microcapsules consisting of walls with different glass transition points, and by selecting combinations of electron-donating dye precursors and their color developers with different hues. It is possible to achieve intermediate colors. Therefore, the present invention is not limited to single-color heat-sensitive sheets, but can also be applied to two-color or multi-color heat-sensitive sheets and heat-sensitive sheets subjected to gradation image recording.

Further, if necessary, a photofading inhibitor described in, for example, JP-A-61-283589, JP-A-61-283590, and JP-A-61-283591 can be appropriately added.

As the color developer that causes a color-forming reaction when thermally melted with the electron-donating dye precursor used in the present invention, any known color developer can be used as appropriate. For example, as color developers for leuco dyes, phenolic compounds, triphenylmethane compounds, synthetic phenolic compounds,
Examples include carboxylic acid compounds, sulfone compounds, urea or thiourea compounds, and details thereof can be found, for example, in Paper Valve Technology Times (1985), pp. 49-54 and 6.
It is described in 5-70 shellfish. Among these, those with a melting point of 50°C to 250°C are particularly preferable, especially those with a melting point of 60°C.
C to 200''C, phenols and organic acids that are poorly soluble in water are preferable, and it is preferable to use two or more color developers in combination because the solubility increases.

The amount of color developer used is usually 1.0 to 10 g/m''.

Among the color developers used in the present invention, particularly preferred ones are represented by the following formulas CI3 to (■).

C1m HZ II * 1 m-0~2, n-2~11 (II) R1 is an alkyl group, an aryl group, or an aralkyl group, and a methyl group, an ethyl group, and a butyl group are particularly preferred.

CII[)H R8 is an alkyl group, especially a butyl group, a pentyl group,
Heptyl and octyl groups are preferred.

(IV) R8 is an alkyl group or an aralkyl group.

In the present invention, a color developer is dissolved in an organic solvent that is sparingly soluble or insoluble in water, and then mixed with an aqueous phase containing a surfactant and having a water-soluble polymer as a protective colloid to emulsify and disperse it. Use a dispersion.

The organic solvent for dissolving the color developer can be appropriately selected from high boiling point oils. Among these, preferable oils include, in addition to esters, compounds represented by the following formulas (V) to (■), triallylmethane (e.g., tritolylmethane, tolyldiphenylmethane), and terphenyl compounds (e.g., terlylmethane). phenyl), alkylated diphenyl ether (9'4 eva, propyl diphenyl ether, hydrogenated terphenyl (eg, hexahydroterphenyl), diphenyl ether, etc.).

In the present invention, among these, it is particularly preferable to use esters from the viewpoint of the solubility of the color developer and the emulsion stability of the emulsified dispersion of the color developer.

(V) In the formula, R1 is hydrogen or an alkyl group having 1 to 18 carbon atoms,
R8 represents an alkyl group having 1 to 18 carbon atoms; eP' and ql represent integers of 1 to 4; and the total number of alkyl groups is 4.
No more than 100 pieces.

In addition, it is preferable that the alkyl group of R' and R8 is a C1-C8 alkyl group.

(Vl) 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.

p3 and q2 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, Rs and R- represent a hydrogen atom or a same or different alkyl group having 1 to 18 carbon atoms, and 0m represents 1 to 1
p3 and q3 represent an integer of 3, and the total number of alkyl groups is 3 or less.

In addition, it is particularly preferable that the alkyl group of RS and R6 is a C2-C4 alkyl group.

Examples of the compound represented by formula (V) include dimethylnaphthalene, diethylnaphthalene, and diisopropylnaphthalene.

Examples of the compound represented by formula (Vl) include dimethylbiphenyl, diethylbiphenyl, diisopropylbiphenyl, and diisobutylbiphenyl.

Examples of compounds represented by formula (■) include 1-methyl-
1-dimethylphenyl-1-phenylmethane, 1-ethyl-1-dimethylphenyl-phenylmethane, and 1-propyl-1-dimethylphenyl-1-phenylmethane are used early.

Examples of esters include phosphoric acid esters (e.g., rev, triphenyl phosphate, tricrezi J phosphate, ethyl phosphate, octyl phosphate, tallysyl diphenyl phosphate), phthalic esters (dibutyl phthalate, 2-ethylhexyl phthalate, Ethyl phthalate, octyl phthalate, butyl phthalate, dioctyl tetrahydrophthalate, ester benzoate, ethyl benzoate, propyl benzoate,
Phytyl benzoate, isopentyl benzoate, benzyl benzoate), abietate ester (ethyl abietate)
benzyl abietate), dioctyl adipate,
Isodecyl succinate, dioctyl azelaate, oxalate esters (cyphytyl oxalate, dipentyl oxalate), diethyl malonate, maleate esters (dimethyl maleate, diethyl maleate, dibutyl maleate), tributyl citrate, sorbic acid Esters (methyl sorbate, ethyl sorbate, butyl sorbate)
, cenominic acid ester (dibutyl sebacate, dioctyl sebacate), ethylene glycol ester It (
Formic acid monoesters and diesters, butyric acid monoesters and diesters, lauric acid monoesters and diesters, valmitic 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 ester (tributyl borate, tripentyl borate)
etc. Among these, when tricresyl phosphate is used alone or in combination, the emulsion dispersion stability of the color developer is particularly good, and therefore it is preferable.

In the present invention, an auxiliary solvent may be added to the above organic solvent as a low boiling point dissolution aid. Particularly preferred examples of such co-solvents 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 to be mixed with the oil phase in which the color developer is dissolved can be appropriately selected from known anionic polymers, nonionic polymers, and amphoteric polymers. However, polyvinyl alcohol, gelatin, cellulose derivatives, etc. are preferred.

In addition, as the surfactant to be included in the aqueous phase, one should be appropriately selected from anionic, nonionic, or amphoteric surfactants that do not interact with the protective colloid to cause precipitation or aggregation. I can do it. Preferred surfactants include sodium alkylbenzenesulfonate (e.g., sodium dodecylbenzenesulfonate), sodium alkylsulfate, dioctyl sodium sulfosuccinate,
Examples include polyalkylene glycol (eg, polyoxyethylene nonylphenyl ether).

The emulsified dispersion of a color developer in the present invention can be prepared by mixing an oil phase containing a color developer and an aqueous phase containing a protective colloid and a surfactant using conventional microparticle emulsification methods such as high-speed stirring and ultrasonic dispersion. Mixing and dispersion can be easily obtained using means.

A melting point depressant for a color developer may be added to this emulsified dispersion as appropriate. Some of these melting point depressants are
It also functions as a glass transition point regulator for the capsule wall. Examples of such compounds include hydroxy compounds, carbamate ester compounds, sulfonamide compounds, aromatic methoxy compounds, etc. For details, see
For example, it is described in Japanese Patent Application No. 59-244190.

These melting point depressants can be used in an amount 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 that lowers the melting point. It is preferable to use the color developer, etc., which lowers the melting point, in the same location. When adding to different locations, it is preferable to add 1 to 3 times the above amount.

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

Binders include polyvinyl alcohol, methylcellulose, carboxymethylcellulose, hydroxypropylcellulose, gum arabic, gelatin, polyvinylpyrrolidone, casein, styrene-butadiene latex, acrylonitrile-butadiene latex, polyvinyl acetate, polyacrylic acid ester, ethylene-vinyl acetate, etc. Various emulsions such as polymers can be used. The amount used is 0.5 to 5 g/rrr as solid content.

The heat-sensitive recording material of the present invention is produced by preparing a coating liquid containing microcapsules containing an electron-donating dye precursor, a dispersion in which at least a color developer is emulsified and dispersed, and other additives such as a binder. It is coated and dried on a support such as bar coating, blade coating, air knife coating, gravure coating, roll coating, spray coating, dip coating, etc. to a solid content of 2.5 to 2.
Manufactured by providing a heat sensitive layer of 5g/r+f.

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

In the present invention, at least the electron-donating dye precursor used in the heat-sensitive layer is added on top of the transparent heat-sensitive layer (the uppermost transparent heat-sensitive layer when there are two or more transparent heat-sensitive layers). A low adhesion transparent thermosensitive layer is provided which contains microcapsules containing bodies. In this case, a color developer emulsified dispersion may be further included if necessary, but the amount thereof must be 20% by weight or less of the total weight of the layer. By providing a layer containing a small amount of color developer emulsified dispersion in this way, it is possible to reduce the adhesion between the heat-sensitive recording materials when the heat-sensitive recording materials of the present invention are stacked, and also to reduce the adhesion between the heat-sensitive recording materials. The contained electron-donating dye precursor can also contribute to color development by reacting with the color developer diffused from the underlying transparent heat-sensitive layer, so the provision of this layer does not reduce the heat sensitivity.

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,
8-69097, paper with a density of 0°9 g/cm" or less and an optical contact ratio of 15% or more, JP-A-5S=s90
Canadian standard freeness described in No. 97 (JIS P812
Paper made from valves beaten to 400 cc or more in 1) to prevent penetration of coating liquid, JP-A-58-656
No. 95, the glossy side of base paper made by a Yankee machine is used as the coating surface to improve color density and resolution, and JP-A No. 59-35985 describes a method 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.

In the present invention, pigments such as silica, barium sulfate, titanium oxide, aluminum hydroxide, zinc oxide, calcium carbonate, etc., and styrene beads are added to the heat-sensitive layer for the purpose of preventing sticking to the heat head and improving writing properties. ,
Fine powder such as urea-melamine resin can be added, but in order to maintain the transparency of the heat-sensitive layer, a protective layer is provided on the heat-sensitive layer by a known method mainly for the purpose of preservation and safety. Details of the protective layer, which is preferably added to this protective layer, are described, for example, in [Paper Valve Technology Times J (September issue, 1985), pages 2 to 4.

In particular, when a protective layer containing a combination of silicon-modified polyvinyl alcohol and coro or idal silica is used as a main component, the transparency of the protective layer becomes extremely good, and as a result, the transparency of the heat-sensitive recording material can be significantly improved. Therefore, it is preferable.

Similarly, waxes or metal soaps may be added to prevent sticking. The usage of these is 0
．． 2~7g/rr? It is.

If necessary, a layer having the same composition as the protective layer may be provided as a back layer on the back surface of the support for the purpose of preventing curling of the heat-sensitive recording material or improving writing properties on the back surface.

In the present invention, in order to allow the heat-sensitive recording material to be conveyed smoothly within the recording apparatus, the following formula (I) is used in the protective layer and/or the back layer provided as necessary.
Alternatively, a compound represented by (n) may be added.

General formula (I) R"O(CH, cHz O), -H - Formula (II) R"O(CH2), 11-3O3 In the formula, R1. represents an alkyl group having 5 to 20 carbon atoms, R
111 is an aryl group having 6 to 30 carbon atoms, M is an alkali metal or ammonium group, m and n are each 1
Represents an integer between ~20.

- Specific examples of compounds represented by formula (1) include the following compounds: Cs H+ IO4CHz CHt O)
l 2 H compound ■ CsH+? O(CHgCH□o
), -H compound■ C+gH1sO(CH! CHgo
) 1゜-H compound■ Ctd(zqO(CHiCH
tO)+x H compound ■ CI? Hs s O(
CHz CHt O) + z H compound ■ C, I
There are H3,O(CHICH□0)1□-H, etc.

Furthermore, as the compound represented by the formula (II), a compound represented by the following formula (l[) is particularly preferred.

General Formula (II[) In the formula, R'' represents an alkyl group having 1 to 20 carbon atoms, M represents an alkali metal or ammonium group, and n represents an integer of 1 to 20, respectively.

Among the compounds represented by the above-mentioned formula (III),
More preferred are those in which R311 is substituted at the para position with respect to the sulfoalkyloxy group.In the present invention, these compounds represented by the formula (1) and the formula (n) At least one kind of compounds represented by is used.

These compounds are usually added at a concentration of 0°000 per mz of support.
By using it in an amount of about 1 to 0.5 g, preferably about 0.05 to 0.2 g, antistatic properties can be imparted to the heat-sensitive recording material 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 on an OHP sheet etc., but also both sides of the transparent support can be used. By providing a heat-sensitive layer that develops colors in different hues, it becomes easy to create 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.

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 1 g/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-diacryloyl- Active vinyl compounds such as hexahydro-5-) liazine, 1.3.5-)+J acryloyl-hexahydro-5-) liazine, and 1,3.5-trivinylsulfonyl-hexahydro-5-1 riazine.

■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-1 luenesulfonate, 1,4-bis(2',3'-epoxypropyloxy)butane,
1,3.5-triglycidyl isocyanurate, 1.3
-Epoxy compounds such as diglycidyl-5-(T-acetoxy-β-oxypropyl)isocyanurate.

■2,4.6-) Liethylene-3-1 riazine, 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 15-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 boric acid.

■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.

■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.

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 acidic by adding 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.

Before applying the undercoat layer, it is desirable to activate the surface of the support by a known method. As the activation treatment method, etching treatment with acid, flame treatment with gas burner, corona discharge treatment, glow discharge treatment, etc. are used, but from the point of view of cost or simplicity, U.S. Patent No. 2,715.075 The corona discharge treatment described in No. 2,846.727, No. 3,549.406, No. 3,590,107, etc. is most preferably used.

(Effects of the Invention) As detailed above, in the present invention, although the transparent heat-sensitive layer contains an electron-donating dye precursor, the color developer emulsified dispersion is contained in a low adhesion layer containing only 20% or less. Since the transparent heat-sensitive layer is provided, the blocking resistance is improved without deteriorating the transparency and heat sensitivity of the transparent heat-sensitive recording material layer.

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

Example 1 [Preparation of capsule liquid] Leuco dye Takenate D-11ON represented by the following structural formula (Capsule 9H manufactured by Narita Pharmaceutical ■)
t) 20g to 12g of 1-phenyl-1-xylylethane
and 20 g of methylene chloride were added to a mixed solvent and dissolved. This leuco dye solution was mixed with 60 g of an 8% polyvinyl alcohol aqueous solution using PVA217E (manufactured by Kuraray ■) and 20 g of water, and the solution was mixed with an aqueous solution of 20 g of water using an Ace homogenizer manufactured by Nippon Seiki ■. Emulsify at OOOrpm for 5 minutes, add 120g of water, and react at 40°C for 3 hours until the capsule size is 1. A capsule liquid of 0μ was produced.

[Preparation of color developer emulsion dispersion] Color developer represented by the following structural formula (a) 5g, (b) 2g
and (C) 8g to 1-phenyl-1-xylylethane 1
g and 7 g of ethyl acetate. The obtained developer solution was mixed with 8% polyvinyl alcohol water using PVA217E (manufactured by Kuraray ■). 31 g of gH, 35 g of water, and 0.2 g of sodium dodecylbenzenesulfonate (surfactant)
Mixed with an aqueous solution of and emulsified for 5 minutes at room temperature using an Ace homogenizer manufactured by Nippon Seiki ■,
An emulsified dispersion with a particle size of 1.5μ was obtained.

Color developer (a) Color developer (C) Color developer (b) [Preparation of heat-sensitive recording material] 5.0 g of the above capsule liquid, 10.0 g of color developer emulsion dispersion
, and 5.0 g of ion-exchanged water were stirred and mixed to a thickness of 75 μm.
A transparent polyethylene terephthalate (PET) substrate was coated on one side with a solid content of 5.5 g/m'' and dried to form a heat-sensitive layer.Next, 6 g of the above capsule solution and color developer were added. 3g of emulsified dispersion and 6% by weight of PVAI24
(manufactured by Kuraray ■) were stirred and mixed, and the mixture was coated and dried on the heat-sensitive layer to a solid content of 0.5 g/m'' to form a second heat-sensitive layer.

Next, a protective layer having the composition shown below was coated on the leisurely recording layer so that the solid content was 2.5 g/m''.

Polyvinyl alcohol 2 parts by weight (PVA-124 manufactured by Kuraray ■) Kaobrite (Thiele) 4 parts by weight Boric acid 0.1 parts by weight Zn stearate dispersion 0. 2 parts by weight (Middle East oil) Sodium lauryl sulfate 0.05 parts by weight Example 2
A heat-sensitive recording material was prepared in exactly the same manner as in Example 1, except that the coating liquid composition of the second heat-sensitive layer in Example 1 was changed as follows.

Coating liquid composition: Capsule liquid 3g Color developer emulsion dispersion 6g 6% PVA124 (
(manufactured by Kuraray FM) 200g Example 3 A heat-sensitive recording material was prepared in exactly the same manner as in Example 1, except that the coating liquid composition of the second heat-sensitive layer provided in Example 1 was changed as follows.

Coating liquid composition: Capsule liquid 12μ Color developer emulsion dispersion 6g 6% PVA124 (manufactured by Kuraray ■) 200g Example 4゜The coating liquid composition of the second heat-sensitive layer provided in Example 1 was changed to the following keyaki. A heat-sensitive recording material was prepared in exactly the same manner as in Example 1.

Coating liquid composition: Capsule liquid 12g 6% PVA
124 (manufactured by Kuraray ■) 200g Comparative Example 1゜A heat-sensitive recording material was prepared in the same manner as in Example 1, except that the coating liquid composition of the second heat-sensitive layer provided in Example 1 was changed as follows. .

Coating liquid composition: Capsule liquid 6g Color developer emulsion dispersion 12g 6% PVA124 (manufactured by Kuraray ■) 100g Comparative example 2゜The first heat-sensitive layer provided in Example 1 had a solid content of 6g/m''
The second heat-sensitive layer was not provided.

A heat-sensitive recording material was produced in the same manner as in Example 1 in other respects.

The prepared heat-sensitive recording materials were stacked so that the front and back sides were in contact, and a pressure of 5 kg/m was applied to the temperature at 35°C and a relative humidity of 85°C.
% environment for 7 days, and the adhesion was evaluated. The results are shown in the table below.

Further, the color density and transparency when printed with a thermal head were almost the same between Examples 1-4 and Comparative Examples 1-2.

Claims (1)

[Claims] An emulsified dispersion obtained by emulsifying and dispersing at least a support, microcapsules containing a colorless or light-colored electron-donating dye precursor, and a color developer dissolved in an organic solvent that is sparingly soluble or insoluble in water. A heat-sensitive recording material comprising at least one transparent heat-sensitive layer formed by applying and drying a coating solution containing the low-adhesion transparent heat-sensitive layer, and a low-adhesion transparent heat-sensitive layer provided on the transparent heat-sensitive layer. A heat-sensitive recording material, wherein the layer is formed by applying and drying a coating solution containing microcapsules containing the electron-donating dye precursor and 20% by weight or less of the emulsified dispersion.