JPH06104382B2 - Thermal recording material - Google Patents

Description

TECHNICAL FIELD The present invention relates to a heat-sensitive recording material in which a heat-sensitive layer is provided on a support. More specifically, the present invention relates to a heat-sensitive recording material having a heat-sensitive layer having excellent transparency.

<< Prior Art >> In the thermal recording method, (1) development is not necessary, (2) when the support is paper, the quality of the paper is close to that of ordinary paper, (3) easy handling, (4) color density It has the advantages of high cost, (5) simple and inexpensive recording device, and (6) no noise at the time of recording. is doing.

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. It came to be desired to develop.

However, the conventional transparent heat-sensitive recording material, by radiating light in close contact with the manuscript, absorbs infrared rays in the image part of the manuscript to raise the temperature of the image part, whereby the heat-sensitive recording film is colored. It is a so-called transparent heat-sensitive film, and does not have the heat sensitivity directly obtained by a thermal head used in a facsimile or the like.

Further, the heat-sensitive layer of the heat-sensitive recording material which can be heat-recorded by the thermal head is devitrified, and it was not possible to realize the desired transparency simply by coating it on the transparent support.

The present inventors have adopted a combination of a colorless or light-colored basic dye precursor and a color developer as a color-developing system as a heat-sensitive recording material capable of solving the above conventional drawbacks, and the former is contained in a microcapsule. Disclosed is a novel transparent heat-sensitive material which can be obtained by dissolving the latter in an organic solvent that is hardly soluble or insoluble in water, emulsifying and dispersing them, and then mixing the two and coating the mixture on a support (Japanese Patent Application Laid-Open Publication No. 2000-242242). 62-88197
issue).

<< Problems to be Solved by the Invention >> However, it has been found that the transparency of the heat-sensitive recording material is significantly affected by the emulsion stabilizer of the emulsion of the heat-sensitive layer. Therefore, the present inventors have conducted extensive studies to improve the emulsion stability of the above emulsion, and as a result, found that it is effective to add a partial saponified product of polyvinyl alcohol to the coating solution, and arrived at the present invention. did.

Accordingly, a first object of the present invention is to provide a heat sensitive recording material having an improved transparent heat sensitive layer.

A second object of the present invention is to provide a heat-sensitive recording material which has high sensitivity and can be used for OHP.

Furthermore, a third object of the present invention is to provide a method for producing a heat-sensitive recording material having a transparent heat-sensitive layer with good stability.

<< Means for Solving the Problem >> The above-mentioned various objects of the present invention are directed to a thermosensitive recording material in which a thermosensitive layer having a microcapsule containing at least a color former and a developer is provided on a support, As a colorless or light-colored basic dye precursor is used as, and at least the developer is dissolved or sparingly soluble in water and has a boiling point of 150 ° C. or less, which is emulsified and dispersed, and then partially saponified polyvinyl alcohol. It was achieved by a heat-sensitive recording material characterized in that a coating liquid comprising the emulsified dispersion containing the microcapsules was prepared, and then coated on a support and dried.

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 a compound has a partial skeleton such as lactone, lactam, sultone, spiropyran, ester, amide, etc., and these partial skeletons are ring-opened or cleaved upon contact with a color developing agent. Examples thereof include triarylmethane compounds, diphenylmethane compounds, xanthene compounds, thiazine compounds, spiropyran compounds, and the like.

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

In the formula, R ₁ is an alkyl group having 1 to 8 carbon atoms, R ₂ is an alkyl group having 4 to 18 carbon atoms, an alkoxyalkyl group or a tetrahydrofurfuryl group, and R ₃ is a hydrogen atom or 1 to 15 carbon atoms. Is an alkyl group or a halogen atom, and R ₄ is a substituted or unsubstituted aryl group having 6 to 20 carbon atoms.
As the substituent of R ₄ , an alkyl group having 1 to 5 carbon atoms,
Alkoxy groups, halogenated alkyl groups and halogen atoms are preferred.

In the present invention, by encapsulating the above-mentioned color former in microcapsules, it is possible to prevent fogging during the production of the heat-sensitive material, and at the same time improve the raw storage stability and the record storage stability of the heat-sensitive material. In this case, the image density during recording can be increased by selecting the wall material and manufacturing method of the microcapsules. The amount of the color former used is preferably 0.05 to 5.0 g / m ² .

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 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.

The microcapsules used in the present invention are preferably microencapsulated by emulsifying a core substance containing a reactive substance such as a color former, and then forming a wall of a polymer substance around the oil droplets. In this case, the 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.

Here, the organic solvent for forming the oil droplets can be appropriately selected from those generally used as pressure sensitive oils. Among them, preferable oils include compounds represented by the following general formulas (I) to (III) and triallylmethane (eg, tritoluylmethane, toluyldiphenylmethane), terphenyl compounds (eg, terphenyl), alkylated Diphenyl ether (eg,
Examples thereof include propyl diphenyl ether, hydrogenated terphenyl (eg hexahydroterphenyl), diphenyl ether, chlorinated paraffin and the like.

In the formula, R ¹ represents hydrogen or an alkyl group having 1 to 18 carbon atoms, and R ² represents an alkyl group having 1 to 18 carbon atoms. p ¹ and q ¹ represent an integer of ¹ to 4, and the total sum 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. When n = 1, the total number of alkyl groups is 4 or less, and when n = 1, 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 (I) include dimethylnaphthalene, diethylnaphthalene and diisopropylnaphthalene.

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

Examples of the compound represented by the formula (III) include 1-methyl-1-dimethylphenyl-1-phenylmethane, 1-ethyl-1-dimethylphenyl-1-phenylmethane, and 1-methyl-1-dimethylphenyl-1-phenylmethane.
-Propyl-1-dimethylphenyl-1-phenylmethane.

It is also possible to use the above oils in combination, or to use in combination with other oils.

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 not destroyed by heat or pressure as used in conventional recording materials, and the reactive substance contained in the core and outside of the microcapsules is microcapsules. It can penetrate and react through walls.

In the present invention, the wall material of the microcapsule is selected,
If necessary, a glass transition point adjusting agent (for example, Japanese Patent Application No. 60-11
No. 9862), microcapsules composed of walls having different glass transition points are prepared, and a combination of basic colorless dye precursors having different hues and their developers can be used to increase the It is possible to realize intermediate colors. Therefore, the present invention is not limited to a monochromatic thermal paper, but can be applied to a bicolor or multicolor thermal paper and a thermal paper suitable for image recording with gradation.

In addition, if necessary, for example, Japanese Patent Application Nos. 60-125470 and 60-
The photobleaching inhibitors described in 125471 and 60-125472 can be added as appropriate.

As the color developing agent which causes a color developing reaction in the heat application with the basic colorless dye used in the present invention, a known developer can be appropriately used. For example, as a developer for a leuco dye, a phenol compound, a triphenylmethane compound, a sulfur-containing phenol compound, a carboxylic acid compound, a sulfone compound, a urea compound or a thiourea compound, and the like can be mentioned. , Pulp and Paper Technical Times (1985), pages 49-54 and 65-70. Among these, those having a melting point of 50 ° C. to 250 ° C. are particularly preferable, and among them, phenol and an organic acid having a low water solubility of 60 ° C. to 200 ° C. are preferable. When two or more developers are used in combination, the solubility increases, which is preferable.

Among the developers used in the present invention, particularly preferable ones are represented by the following general formulas [IV] to [VII].

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, particularly preferably a butyl group, a pentyl group, a heptyl group and an octyl group.

R ₃ is an alkyl group or an aralkyl group.

In the present invention, after the developer is dissolved in a poorly water-soluble or insoluble organic solvent, it is mixed with an aqueous phase containing a surfactant and having a water-soluble polymer as a protective colloid, and emulsified and dispersed. Used in the form of a dispersion.

The organic solvent that dissolves the developer can be appropriately selected from organic solvents that are sparingly soluble or insoluble in water, but from the viewpoint of improving thermal sensitivity, the boiling point is particularly 150 ° C in the present invention.
The following organic solvents are used. Examples of these organic solvents include ethyl acetate, isopropyl acetate, butyl acetate and methylene chloride.

In the present invention, esters having a high boiling point and these pressure-sensitive oils can be appropriately mixed with these organic solvents and used, but in particular, esters are used from the viewpoint of the stability of the color developer emulsion dispersion. It is preferable.

Examples of the high boiling point esters include phosphoric acid esters (eg, triphenyl phosphate, tricresyl phosphate, butyl phosphate, octyl phosphate, cresyl diphenyl phosphate), phthalic acid esters (dibutyl phthalate, 2-ethylhexyl phthalate, phthalic acid). Ethyl, octyl phthalate, butylbenzyl phthalate) dioctyl tetrahydrophthalate,
Benzoic acid esters (ethyl benzoate, propyl benzoate, butyl benzoate, isopentyl benzoate, benzyl benzoate), abietic acid esters (ethyl abietic acid, benzyl abietic acid), dioctyl adipate,
Isodecyl succinate, dioctyl azelate, oxalate (dibutyl oxalate, dipentyl oxalate), diethyl malonate, maleate (dimethyl maleate, diethyl maleate, dibutyl maleate), tributyl citrate, sorbate ( Methyl sorbate, ethyl sorbate, butyl sorbate), sebacate ester (dibutyl sebacate, dioctyl sebacate), ethylene glycol esters (formic acid monoester and diester, butyric acid monoester and diester, lauric acid monoester and diester, Palmitic acid monoesters and diesters, stearic acid monoesters and diesters, oleic acid monoesters and diesters), triacetin, diethyl carbonate, diphenyl carbonate, ethyl carbonate. Emissions, propylene carbonate,
Examples thereof include boric acid esters (tributyl borate, tripentyl borate) and the like.

The water-soluble polymer to be contained as a protective colloid in the aqueous phase in which the developer is mixed with the dissolved oil phase can be appropriately selected from known anionic polymers, nonionic polymers and amphoteric polymers. However, polyvinyl alcohol, gelatin, cellulose derivatives and the like are preferable. Of these, polyvinyl alcohol partially saponified products, particularly those having a saponification degree of 75 to 90% are preferable.

<< Action >> Especially, when a partially saponified product of polyvinyl alcohol is used as a protective colloid, the reason is not clear, but as a result of stabilizing the developer emulsion dispersion, the heat-sensitive recording material phase when used as a heat-sensitive recording material. The transparency of can be extremely improved. In order to obtain the most effective results of this polyvinyl alcohol partially saponified product, it is preferable to use it at the time of emulsification, but it is also possible to add the polyvinyl alcohol partially saponified product after emulsifying with another protective colloid.

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 developer of the present invention, a polyvinyl alcohol partially saponified emulsion-containing dispersion, an oil phase containing a developer and an aqueous phase containing a protective colloid and a surfactant are rapidly stirred,
It can be easily obtained by mixing and dispersing using a means generally used for emulsification of fine particles such as ultrasonic dispersion.

To this emulsified dispersion, a melting point depressant for a color developer can be added as appropriate. Some of these melting point depressants are
It also has the function of a glass transition point regulator of the capsule wall. Examples of such a compound include a hydroxy compound, a carbamic acid ester compound, a sulfonamide compound, an aromatic methoxy compound, and the details thereof are described, for example, in Japanese Patent Application No. 59-244190.

These melting point depressants can be appropriately used in the range of 0.1 to 2 parts by weight, preferably 0.5 to 1 part by weight, relative to 1 part by weight of the color-developing agent that lowers the melting point. It is preferable to use the color developing agent and the like that drop in the same place at the same place. When adding to different places, it is preferable to add 1 to 3 times the above addition amount.

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, hydroxypropyl cellulose, arabic rubber, gelatin, polyvinyl pyrrolidone, casein, styrene-butadiene latex, acrylonitrile-butadiene latex, polyvinyl acetate, polyacrylic acid ester, ethylene-vinyl acetate copolymer. It is possible to use various emulsions such as The amount used is 0.5 to 5 g / m ² as solid content.

The heat-sensitive recording material of the present invention is a microcapsule containing a color-forming agent and at least a color-developing agent emulsified and dispersed, a partially saponified product-containing dispersion of polyvinyl alcohol, and a coating solution containing other additives such as a binder, It is manufactured by coating and drying on a support such as paper or synthetic resin film by a coating method as described below to provide a heat-sensitive layer having a solid content of 2.5 to 25 g / m ² . The heat-sensitive layer of the heat-sensitive material produced in this way surprisingly has very good transparency, for reasons which are not clear.

The transparency referred to here is the integrating sphere method manufactured by Nippon Seimitsu Kogyo Co., Ltd.
It can be expressed by the haze (%) measured with an HTR meter. However, the actual transparency of the heat-sensitive layer test sample is greatly affected by light scattering due to fine irregularities on the surface of the heat-sensitive layer. Therefore, the transparency peculiar to the heat-sensitive layer to be a problem in the present invention, that is, when the transparency inside the heat-sensitive layer is measured with a haze meter, a transparent adhesive tape is attached onto the heat-sensitive layer as a simple method, Evaluation is made with the value measured with scattering almost excluded.

The heat-sensitive recording material of the present invention contains silica, barium sulfate, titanium oxide, aluminum hydroxide, zinc oxide, for the purpose of preventing sticking to a thermal head and improving writability.
Pigments such as calcium carbonate and fine powders such as styrene beads and urea-melamine resin can be added, but in order to maintain the transparency of the heat-sensitive layer, preserving and stability are mainly required on the heat-sensitive layer. It is preferable to provide a desired protective layer by a known method and add it to this protective layer. For details of the protective layer, see “Pulp and Paper Technology Times” (19
1985, September issue) 2-4.

Similarly, metal soaps may be added to prevent sticking. The amount of these used is 0.2 to 7 g / m ² .

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

The optical surface roughness described in JP-A-58-136492 is 8 μm.
Paper having a thickness of 40 to 75μ, 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, described in JP-A-58-69097. Canadian Standard Freeness (JIS
P8121) paper made from pulp that has been beaten to 400 cc or more 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. In addition to these, any of the supports generally used in the field of heat-sensitive recording paper can be used as the support of the present invention.

When the transparent support is used as the support, the heat-sensitive material of the present invention can be seen as a transmission image or an opposite image from one side of the transparent support. When the back side becomes transparent and the image is not clear, a white pigment may be added to the heat-sensitive layer in order to make it appear white, or a layer containing a white pigment may be additionally applied. In any case, it is effective to perform the process for the outermost layer on the side opposite to the side where the recorded image is viewed. Examples of preferable white pigments include talc, calcium carbonate, calcium sulfate, magnesium carbonate, magnesium hydroxide, alumina, synthetic silica, titanium oxide, barium sulfate, kaolin, calcium silicate, urea resin and the like.

The dispersed particle size is preferably 10 μm or less.

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.

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 a material for the undercoat layer, gelatin, synthetic polymer latex, nitrocellulose or the like is used. The coating amount of the undercoat layer is 0.1 g
/ m ^{2 to} 2.0 g / m ² is preferable, especially 0.2 g / m
The range of ^{2 to} 1.0 g / m ² is preferable.

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 image quality of the heat-sensitive layer may be deteriorated when the heat-sensitive layer is swelled by water contained in the heat-sensitive layer when the heat-sensitive layer is coated thereon, a hardener is used. It is desirable to cure.

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, boric acid, zirconium salts.

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 based on the weight of the base coating material.
In the range of 0.20% by weight to 3.0% by weight, an appropriate addition 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 a method of activation treatment, etching treatment with acid, flame treatment with a gas burner, or corona treatment, glow discharge treatment or the like is used, but from the viewpoint of cost or simplicity, U.S. Pat.No. 2,715,075, the same. No. 2,846,727, No. 3,549,40
The corona discharge treatment described in No. 6, No. 3,590,107, etc. is most preferably used.

The heat-sensitive recording material of the present invention can be designed not only for OHP but of course, two or more heat-sensitive layers capable of developing different colors directly on the support or via the above-mentioned protective layer or undercoat layer. It may be provided, and further, one layer selected from a known photosensitive layer, a heat-sensitive layer and a light- and heat-sensitive layer may be provided on the support, and further a layer different in color from this layer may be formed thereon as described above. Various modes are possible depending on the application and purpose, such as the provision of a substantially transparent heat-sensitive layer.

The coating liquid according to the present invention is a generally well-known coating method,
For example, dip coating method, air knife coating method, curtain coating method, roller coating method, doctor coating method,
It can be applied by a wire bar coating method, a slide coating method, a gravure coating method, or an extrusion coating method using a hopper described in US Pat. No. 2,681,294. US Patent No. 2,
No. 761,791, No. 3,508,947, No. 2,941,898, and No. 3,526,528, Yuji Harasaki, "Coating Engineering", page 253 (issued by Asakura Shoten in 1973) It is also possible to divide and apply simultaneously, and an appropriate method can be selected according to the application amount, the application speed, and the like.

In the coating liquid used in the present invention, a pigment dispersant, a thickener, a flow modifier, a defoaming agent, a foam suppressor, a release agent, and a colorant may be appropriately added as needed as long as the characteristics are not impaired. It doesn't matter.

<< Effects of the Invention >> According to the present invention, the dispersion stability of the color developer emulsified dispersion can be remarkably enhanced, so that a thermosensitive recording material having a transparent thermosensitive layer can be produced reproducibly and efficiently. In addition, the transparency of the obtained heat-sensitive recording material is also very good.

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

Example 1. [Preparation of capsule liquid] Crystal violet lactone 14 g (leuco dye),
Takenate D-110N (Takeda Pharmaceutical Co., Ltd. capsule wall material)
60 g and 2 g of Sumisorb 200 (UV absorber manufactured by Sumitomo Chemical Co., Ltd.) were 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 100 g of an 8% aqueous solution of polyvinyl alcohol, 40 g of water and 1.4 g of a 2% sodium salt of dioctyl sulfosuccinate (dispersant) and mixed with an ace homogenizer manufactured by Nippon Seiki Co., Ltd. 10,000γpm
Was emulsified for 5 minutes, 150 g of water was further added, and the mixture was reacted at 40 ° C. for 3 hours to prepare a capsule liquid having a capsule size of 0.7 μm.

[Preparation of color developer emulsion]

2.0 g of 1-phenyl-1-xylylethane, 8 g of (a), 4 g of (b) and 30 g of (c) represented by the following structural formula,
It was dissolved in 6.0 g of dibutyl phthalate and 30 g of ethyl acetate.
The resulting developer solution was used as a 100% aqueous solution of 8% polyvinyl alcohol (Kuraray Co., Ltd. PVA205: saponification degree 87-89%).
g and 150 g of water, and sodium dodecylbenzene sulfonate 0.5
It was mixed with an aqueous solution of g and emulsified for 5 minutes at room temperature of 10,000 rpm using an ace homogenizer manufactured by Nippon Seiki Co., Ltd. to obtain an emulsified dispersion having a particle size of 0.5μ.

[Preparation of heat-sensitive material] 5.0 g of the above capsule liquid, 10.0 g of a color developer emulsion, and water
5.0 g was mixed with stirring to prepare a coating liquid. Then, the coating liquid was allowed to stand for 1 hour and the state of the coating liquid was observed. As a result, the stability of the coating liquid was confirmed. As described above, the coating liquid after standing for 1 hour was made of transparent polyethylene terephthalate (PE
T) Apply it to the film so that the solid content is 15 g / m ² ,
After drying, the transparency of this film was measured by an integrating sphere method HTR meter manufactured by Nippon Seimitsu Kogyo Co., Ltd. The haze was 8%, and it was proved that the film had very good transparency.

Example 2. Polyvinyl alcohol manufactured by Kuraray Co., Ltd. (PVA205; saponification degree 87-89%) used in Example 1 when preparing the developer emulsion dispersion, instead of polyvinyl alcohol manufactured by Kuraray Co., Ltd. (PVA217E: Saponification degree 87-89%) was used, and the same tests as in Example 1 were carried out, and the stability of the coating solution and the transparency of the coating film were extremely good as in Example 1. there were.

Example 3. Polyvinyl alcohol produced by Kuraray Co., Ltd. (PVA205; saponification degree 87-89%) used in Example 1 to prepare the developer emulsion dispersion, instead of polyvinyl alcohol produced by Kuraray Co., Ltd. (PVA420: The same test as in Example 1 was carried out except that a saponification degree of 79.5 to 83.5% was used. The stability of the coating solution and the transparency of the coating film were extremely good as in Example 1. It was

Comparative Example 1. In Example 1, polyacrylamide was used instead of polyvinyl alcohol (PVA205; saponification degree 87-89%) manufactured by Kuraray Co., Ltd., which was used when preparing the developer emulsion dispersion. The test was conducted in exactly the same manner as in Example 1. As a result, the coating solution was unstable enough to separate, and even if it was applied to the transparent film before separation, the film became opaque in the drying step.

Comparative Examples 2-5. Instead of the polyacrylamide used in Comparative Example 1,
Maleic anhydride / styrene copolymer (Comparative example 2), Maleic anhydride / isobutylene copolymer (Comparative example 3),
Completely saponified Poval (Kuraray Co., Ltd. PVA105: Saponification degree 9
8 to 99%) (Comparative Example 4) and fully saponified Poval (Kuraray Co., Ltd. PVA117: Saponification degree 98 to 99%) (Comparative Example 5)
The same results as in the case of Comparative Example 1 were also obtained when each of the above was used.

These results demonstrate that the partially saponified product of polyvinyl alcohol is particularly effective for the dispersion stability of the color developer emulsion.

Claims (2)

[Claims] 1. A thermosensitive recording material comprising a support and microcapsules containing at least a color-forming agent and a thermosensitive layer containing a color-developing agent, wherein a colorless or light-colored basic dye precursor is used as the color-developing agent. Together with a coating solution consisting of a polyvinyl alcohol partially saponified emulsion-containing emulsion and the microcapsules, which are sparingly soluble or insoluble in water and have a boiling point of 150 ° C. or less and are emulsified and dispersed after dissolving at least the developer. A heat-sensitive recording material which is prepared and then coated and dried on a support. 2. A heat-sensitive recording material according to claim 1, wherein the degree of saponification of the partially saponified polyvinyl alcohol is 75 to 90%.