JPH0199875A - Thermal recording material - Google Patents

Abstract

PURPOSE:To prevent the formation of aggregates in a thermal recording material, by forming on a support a thermal recording layer comprising microcapsules containing a basic dye precursor and a developer dispersed in an organic solvent with the aid of a specified surfactant. CONSTITUTION:A coating solution comprising a dipersion is prepared by emulsifying microcapsules containing a colorless or light-colored basic dye precursor and a developer, which is dissolved in a difficulty water-soluble or water- insoluble solvent, by using an emulsification aid. Said emulsification aid is a surfactant having an -SO3<->M<+> or -OSO3<->M<+> group (wherein M<+> represents K<+>, Na<+> or NH4<+>). The obtained solution is applied onto a support and dried to form a thermal recording layer, thus preparing a thermal recording material. Since the emulsion is stable, it is possible to conduct stable coating and to obtain a thermal recording material free from aggregates and excellent in transparency.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a heat-sensitive recording material, and particularly to a heat-sensitive recording material suitable as a second original.

(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 the applications of thermal recording are also expanding. are doing.

Against this background, in recent years, in order to adapt to multicolor, overhead projectors (
With the desire to develop a transparent heat-sensitive recording material that can be directly recorded with a thermal head for use in OHP (abbreviated as OHP), the present inventors filed a patent application in 1983-
No. 121875 discloses a coating solution consisting of an emulsified dispersion of microcapsules containing a colorless or light-colored basic dye precursor and a color developer dissolved in Ili or an insoluble organic solvent in water. We proposed transparent heat-sensitive recording materials coated on polyesters such as polyethylene terephthalate and polybutylene terephthalate, cellulose derivative films such as cellulose triacetate, polyolefin films such as polystyrene, polypropylene, and polyethylene, or transparent supports laminated with these films. .

(Problem to be solved by the invention) However, the emulsified dispersion obtained by emulsifying and dispersing a color developer dissolved in an organic solvent that is sparingly soluble or insoluble in water cannot be used as an emulsifying dispersion that is used in general industry. Because they are unstable compared to dispersions, stable coating is not possible, and the coating surface often contains aggregates, which often impairs transparency. This was an extremely serious problem in obtaining transparent heat-sensitive recording materials.

As a result of intensive studies aimed at resolving these conventional drawbacks, the present inventors have found that when a certain type of surfactant is used as an emulsification aid, the emulsified dispersion is extremely stable and stable coating is possible. The present invention was achieved by discovering that this can be done.

Therefore, a first object of the present invention is to provide a transparent heat-sensitive recording material that does not contain LiE aggregates and has a heat-sensitive layer with good transparency.

A second object of the present invention is to provide a stable color developer emulsion that can efficiently produce a heat-sensitive recording material with good transparency.

A third object of the present invention is to provide a method for efficiently producing a heat-sensitive recording material with good transparency.

(Means for Solving the Problem) The above aspects of the present invention include microcapsules containing a colorless or light-colored basic dye precursor, and a color developer dissolved in an organic solvent that is sparingly soluble or insoluble in water. emulsifying and dispersing the agent,
In a heat-sensitive recording material having a heat-sensitive layer formed by coating and drying a coating solution containing the obtained emulsified dispersion, -303-M ten groups or -0303 is used as an emulsification aid for a color developer emulsion.
This was achieved by a heat-sensitive recording material characterized by using a surfactant having -M+ (where M+ represents Ni+, Na+, or NH4+) group.

As the basic dye precursor used in the present invention, a colorless or light-colored one is appropriately selected from known compounds that develop color by donating electrons or accepting protons such as acids. Such compounds have partial skeletons such as lactones, lactams, sultones, spiropyrans, esters, and amides, and these partial skeletons are ring-opened or cleaved upon contact with a color developer. Preferred compounds include Examples include 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 alkoxyalkyl group or a tetrahydrofurfuryl group, and R3 is a hydrogen atom or an alkyl group having 1 to 15 carbon atoms. Alkyl group or halogen atom, R4 is substituted or unsubstituted with 6 to 20 carbon atoms.
represents a group.

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.

In the present invention, by encapsulating the above-mentioned coloring agent in microcapsules, it is possible to prevent capri 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. can. 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 color former used is preferably 0.05 to 5.0 g/m.

The wall materials of the microcapsules include polyurethane, polyurea, polyester, polycarbonate, urea-formaldehyde), melamine resin, polystyrene,
Examples include styrene methacrylate copolymer, styrene-acrylate copolymer, gelatin, polyvinylpyrrolidone, polyvinyl alcohol, and the like. 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 coloring 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 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 oil droplets can be appropriately selected from those generally used as pressure-sensitive oils, but among them, preferred oils include the following -(1) formula (1) to ( 1) and triallylmethane (e.g., tritolylmethane, tolyldiphenylmethane), terphenyl compounds (e.g., terphenyl), alkylated diphenyl ethers (e.g., 7'-pyldiphenyl ether), hydrogenated Examples include terphenyl (eg, hexahydroterphenyl), diphenyl ether chlorinated paraffin, and the like.

In the formula, R1 is hydrogen or an alkyl group having 1 to 18 carbon atoms,
R2 represents an alkyl group having 1 to 18 carbon atoms. pl, q
1 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.

(n) (R3)R2(R4)q2 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.

R2 and q2 represent integers of 1 to 4. When n=1, the total number of alkyl groups is 4 or less, and when n=2, the total number of alkyl groups is 6 or less.

([I[) (R5)R3(R'')q3 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 q3 represent an integer of 1 to 3, and the total number of alkyl groups is 3 or less.

The alkyl group of Nao, R5, and R6 is particularly preferably an alkyl group having 2 to 4 carbon atoms.

Examples of the compound represented by formula (1) include dimethylnaphthalene, diethylnaphthalene, diisopropylnaphthalene, and the like.

Examples of the compound represented by formula (n) include dimethylbiphenyl, diethylbiphenyl, diisopropylbiphenyl, diisobutylbipheyl, and the like.

As an example of a compound represented by formula (III), °ζ is l-methyl-1-dimethylphenyl-1-phenylmethane, l-
ethyl-1-dimethylphenyl-1-phenylmethane,
Examples include 1-propyl-1-dimethylphenyl-1-phenylmethane.

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

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

The preferred microcapsules produced as described above are not ruptured by heat or pressure as is used in conventional recording materials, and the reactive substances contained in the core and outside of the microcapsules are not destroyed by the microcapsule walls. can pass through and react.

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 1986-
119862) to prepare microcapsules consisting of walls with different glass transition points, and by selecting combinations of basic colorless dye precursors with different hues and their color developers. It is possible to achieve intermediate colors. Therefore, the present invention is not limited to single-color thermal paper, but can also be applied to two-color or multi-color thermal paper and thermal paper that has been subjected to gradation image recording.

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.

As a color developer that causes a color-forming reaction when melted with the basic colorless dye used in the present invention, any known color developer can be used as appropriate. For example, color developers for leuco dyes include phenolic compounds, sulfur-containing phenolic compounds, carboxylic acid compounds, sulfone compounds, urea or thiourea compounds, etc. Times (1985) 49-54
and pages 65-70. Among these, those having a melting point of 50°C to 250°C are particularly preferable, and especially those having a melting point of 60°C to 200°C, Ni-based phenol and
A acid is preferred. 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 (IV) to (■).

(TV) m=O~2, n=2~11 (V) \H R7 is an alkyl group, an aryl group, an aryloxyalkyl group, or an aralkyl group, and a methyl group, an ethyl group, and a butyl group are particularly preferred.

(Vl) Ro is a hydrogen atom or a methyl group, and n is O-2.

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

[■]

R9 is an alkyl group, an aralkyl group or an aryloxyalkyl 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 in the form of a dispersion.

Particularly from the viewpoint of heat sensitivity, it is preferable to use a low boiling point organic solvent having a boiling point of 150° C. or lower. this.

Examples of such low-boiling organic solvents include ethyl acetate, isopropyl acetate, butyl acetate, and methylene chloride.

These low-boiling point organic solvents may be used alone or in combination of two or more types, but other high-boiling point organic solvents that dissolve the color developer may be added as appropriate.

The high boiling point organic solvent that dissolves the color developer can be appropriately selected from high boiling point oils. Among them, preferable oils include esters and oils having the general formulas ([) to ([
1) and triallylmethane (for example,
tritolylmethane, tolyl diphenylmethane),
Examples include terphenyl compounds (eg, terphenyl), alkylated diphenyl ethers (eg, propyl diphenyl ether, hydrogenated terphenyl (eg, hexahydroterphenyl), diphenyl ether, salted paraffin, 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.

Examples of esters include phosphoric acid esters (for example, triphenyl phosphate, tricresyl phosphate, butyl v4 acid, octyl phosphate, cresyl diphenyl phosphate), latalic acid esters (dibutyl phthalate, 2-ethylhexyl phthalate,
ethyl phthalate, octyl phthalate, benzyl butyl phthalate) dioctyl tetrahydrophthalate, benzoic acid ester (ethyl benzoate, propyl benzoate, butyl benzoate, isopentyl benzoate, hensyl benzoate),
Abietate ester (ethyl abietate, benzyl abietate), dioctyl adipate, isodecyl succinate, dioctyl azelaate, oxalate ester (
Diptyl oxalate, dipentyl oxalate), diethyl malonate, maleate esters (dimethyl maleate, diethyl maleate, dibutyl maleate), tributyl citrate, sorbate esters (methyl sorbate, ethyl sorbate, butyl sorbate) , sebacate ester (dibutyl sebacate, dioctyl sebacate),
Ethylene glycol esters (formic acid monoesters and diesters, butyric acid monoesters and diesters, lauric acid monoesters and diesters, palmitic acid monoesters and diesters, stearic acid heptanoesters and diesters, oleic acid monoesters and diesters)
, triacetin, diethyl carbonate, diphenyl carbonate, ethylene carbonate, J#, propylene acid, borate esters (tributyl borate, tripentyl borate), and the like.

Among these, when tricresyl phosphate is used in combination, the emulsion dispersion stability of the color developer is particularly good and is therefore preferred.

\7゛'/' / , / / / The water-soluble polymer to be contained as a protective colloid in the aqueous phase mixed with the oil phase in which the color developer is dissolved may be a known anionic polymer, nonionic polymer, or amphoteric polymer. Although it can be appropriately selected from polymers, polyvinyl alcohol, gelatin, cellulose derivatives, etc. are preferred.

In this case, the stability of the emulsion can be significantly increased by using a surfactant having a -3O3'-M+ or -0303-M+ group as an emulsification aid. Such surfactants are represented by the following general formulas (i) to (iii).

R1-X-3O3-M+ (i) R1-X
-03O3-M” (ii) In the general formula, X is a divalent group having 1 to 18 carbon atoms, and R1 is a divalent group having 1 to 18 carbon atoms.
an alkyl group having 1 to 18 carbon atoms, a phenyl group optionally having a substituent having 1 to 18 carbon atoms, R2
and R3 is an alkyl group having 4 to IO carbon atoms (R2 and RY may be the same or different), M+ is Ni+, Na
Represents 10 or NH, s+.

Among the surfactants represented by the above general formula, a suitable surfactant is Cl2H25SO3Na.

C> 7 H35CON [(CH2CH2S 03
Na, 9H19 / Ki\ 〆cl (tq / * \ も9H19 / Outside\ Ri♂ (CH2CH20) 3 (CH2) As03Na (
t) c5H++ / kon〇 (CH2)3 SO3Na C12H250SO3Na CaH+70SO3Na Clf3. Examples include R35oso3 Na and those substituted for the above metal ions Crab+ and N HJ+. In addition, when two or more types are used together,
In particular, Cl2H250SO3
The emulsified dispersion of Na and the color developer in the present invention is prepared by combining an oil phase containing the color developer and an aqueous phase containing a protective colloid and a surfactant using conventional fine particle emulsification methods such as high-speed stirring and ultrasonic dispersion. Mixing and dispersion can be easily obtained using the following 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. Examples of such compounds include hydroxy compounds, carbamate ester compounds, sulfonamide compounds, and aromatic methoxy compounds, the details of which are described in, for example, Japanese Patent Application No. 59-244190.

These melting point depressants can be appropriately used in the range of 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 that the color developer and the color developer whose melting point is lowered thereby are used at 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 contains pigments such as silica, barium sulfate, titanium oxide, aluminum hydroxide, zinc oxide, and calcium carbonate, styrene beads, and urea-melamine for the purpose of preventing sticking to a heat head and improving writing properties. Fine powder such as resin, silicone oil, paraffin wax, etc. can be added, but in order to maintain the transparency of the heat-sensitive layer, protection mainly for the purpose of preservation and stability is added on top of the heat-sensitive layer. Preferably, the layer is applied by known methods and added to this protective layer. Details about the protective layer are described, for example, in "Paper and Pulp Technology Times" (September issue, 1985), pages 2-4.

Similarly, metal stones can also be added to prevent sticking. The amount used is 0.2g to 7g.
/m2.

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/m2 as solid content.

The heat-sensitive recording material of the present invention is produced by preparing a coating liquid containing microcapsules containing a color former, main components of a dispersion in which at least a color developer is emulsified and dispersed, and other additives such as a binder. Bar coating, blade coating, air knife coating, gravure coating,
Apply by coating methods such as roll coating, spray coating, dip coating, etc. and dry to a solid content of 2.5 to 25%.
It is manufactured by providing a heat sensitive layer of g/d.

The heat-sensitive layer of the heat-sensitive material produced in this way has extremely good transparency because the developer emulsion dispersion has good stability.

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 pH-sized paper 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 the paper and to improve the contact between the thermal recording head and the thermal recording layer, Japanese Patent Laid-Open No. 57-1166
The paper described in No. 87 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/cm3 or less and an optical contact ratio of 15% or more, JP-A-58-69
Canadian standard freeness described in No. 097 (JIS P
8121) paper made from pulp beaten to 400 cc or more to prevent penetration of coating liquid, JP-A-58
-65695, which improves the color density and resolution by using the glossy side of paper made by a Yankee machine as the coating surface, and JP-A-59-35985, which applies corona discharge treatment to base paper. Papers etc. which have been coated to improve their coatability can 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.

A transparent support can also be used in the heat-sensitive recording material of the present invention. By using a transparent support, the recorded matter can be used on an OHP sheet or the like.

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.

In the present invention, an undercoat layer can be provided between the transparent support and the heat-sensitive layer in order to improve the adhesion between the two layers. Materials for the undercoat layer include gelatin, synthetic polymer latex,
Nitrocellulose and the like are used. The coating amount of the undercoat layer is 0
．． 1g/n? ~2. It is preferably in the range of Og/rd, especially 0. 2g/rd~1. A range of Og/rrr is preferred.

If it is less than 0.1g/rrr, the adhesion between the support and the heat-sensitive layer will not be sufficient, and even if it is increased to 2.0g/rrr or more, the adhesion between the support and the heat-sensitive layer will reach saturation, so it is cost-effective. It will be disadvantageous.

A hardening agent is used for the undercoat layer, since 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 applied thereon. It is desirable to make it effective.

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

■Divinylsulfone N,N'-ethylenebis(bitylsulfonylacetamide), 1,3-bis(vinylsulfonyl)-2-propatol, methylenebismaleimide, 5-acetyl-1,3-diacryloyl- xahydro-5-) riazine, ■.

Active vinyl compounds such as 3.5-triacryloyl-hexahydro-3-triazine, 1,3.5-)rivinylsulfonyl-hexahydro-S-trizidine.

■2.4-dichloro-6-hydroxy-5-triazine sodium salt, 2.4-dichloro-6=methoxy-5
-) riazine, 2.4-dichloro-6-(4-sulfoanilino)-s-triazine sodium salt, 2.4-dichloro-6-(2-sulfoethylamino)-S-) riazine, N, No- Active halogen compounds such as bis(2-chloroethylcarbamyl)piperazine.

■Bis(2,3-epoxypropyl)methylbusbylammonium p-1-luenesulfonate, 1,4-bis(2°,3'-epoxypropyloxy)butane,
1,3.5-1-liglycidyl isocyanurate, 1.
Epoxy compounds such as 3-diglycidyl-5-(γ-acetoxyβ-oxypropyl)isocyanurate.

■2.4.6-) lyethylene-5-) 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 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, 5.5'=(paraphenylene)bisisoxazole.

■Inorganic compounds such as chromium alum, chromium acetate, zirconium salts, 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.

[Phase] Toluene-2,4-diisocyanate, l.

Isocyanates such as 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.
0. ．． An appropriate addition amount can be selected in the range of 20% by weight to 3.0% by weight depending on the coating method and desired degree of curing.

Added? If it is less than 0.203] iQ%, 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. When the amount is too high, the degree of curing progresses too much, the adhesion between the undercoat layer and the support deteriorates, and the undercoat layer becomes film-like and peels off from the support.

Depending on the hardening agent used, if necessary, the pH of the liquid can be made alkaline by adding caustic soda or the like, or 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 undercoat layer, it is desirable to activate the surface of the support by a known method.

Activation treatment methods include acid etching treatment,
Flame treatment using a gas burner, corona treatment, glow discharge treatment, etc. are used, but from the point of view of cost or simplicity, U.S. Pat.
No. 846,727, No. 3,549,406, No. 3
, No. 590.107 is most preferably used.

The heat-sensitive recording material of the present invention may have the above-described substantially transparent heat-sensitive layer formed on at least one side of the support.
In addition to providing one layer of the heat-sensitive layer on one side of a transparent or opaque support, a double-sided heat-sensitive recording material may be prepared by providing one heat-sensitive layer of the same structure on both sides of an opaque support, and The substantially transparent heat-sensitive layers described herein that can be colored in different colors may be provided on both sides of the transparent support, and one layer may be provided on each side. Various embodiments are possible depending on the use and purpose, such as the ability to laminate a transparent heat-sensitive layer.

(Effects of the Invention) According to the present invention, by appropriately selecting an emulsifying agent for the color developer emulsion, which is a coating liquid component, the emulsion becomes stable, allowing stable coating without agglomerates. A heat-sensitive recording material with excellent transparency can be obtained.

(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] 14 g of crystal violet lactone (leuco pigment)
, 60 g of Takenate D-11ON (capsule wall material manufactured by Narita Pharmaceutical Co., Ltd.) and 2 g of Sumithorp 200 (ultraviolet absorber manufactured by Sumitomo Chemical ■) were added to a mixed solvent of 55 g of 1-phenyl-1-xylylethane and 55 g of methylene chloride. , 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 (dispersant), and mixed with an ace homogenizer manufactured by Nippon Seiki (R4). The mixture was emulsified at 10,000 γpm for 5 minutes, 150 g of water was added, and the mixture was reacted at 40° C. for 3 hours to produce a capsule liquid with a capsule size of 0.7 tt.

[Preparation of color developer emulsion dispersion]

Color developers represented by the following structural formulas (a) 8 g, (b) 4 g and (c) 30 g; Ir: dissolved in 8.0 g of 1-phenyl-1-xylylethane and 30 g of ethyl acetate. The infused developer solution was mixed with an aqueous solution of 100 g of 8% polyvinyl alcohol aqueous solution, 150 g of water, and 0.5 g of sodium dodecylbenzenesulfonate, and was mixed with an aqueous solution of 10,000 γ pm using an Ace homogenizer manufactured by Nippon Seiki. The mixture was emulsified at room temperature for 5 minutes to obtain an emulsified dispersion with a particle size of 0.5μ.

This emulsified dispersion did not cause clot even after being left at 25°C for 3 days and was normal.

[Preparation of heat-sensitive material]

5.0 g of the above capsule liquid, 10.0 g of color developer emulsion dispersion
, and 5.0 g of water were stirred and mixed, and the mixture was coated on one side of a transparent polyethylene terephthalate (PET) support with a thickness of 75 μm.
Solid content is 15g/n? The heat-sensitive recording material of Example 1 was obtained by coating and drying to form a heat-sensitive layer.

(The smoothness of the coating film surface of the cracked heat-sensitive recording material was good, and after applying a coating liquid with the following composition to form a protective layer with a thickness of 2 μm, a hazemeter (manufactured by Nippon Seimitsu Kogyo @, integral The haze measured using a ball method (HTR meter) was 11%, and the transparency of the coating film was extremely good.

[Composition of protective layer]

Silica-modified poval...1 part by weight (solid content) (PVA R2105 manufactured by Kuraray@) Coroiglusilicity...1.5 parts by weight (solid content) (Snowtex 30 manufactured by Nissan Chemical @) Paraffin wax...0. 02 weight 1 part (solid content) (Middle East oil (Explosive Hydrin Z-7) The same procedure as in Example 1 was carried out except that the color developer emulsion dispersion was used, and the stability of the developer emulsion dispersion was as good as in Example 1, and the smoothness of the heat-sensitive layer was also good. Further, the haze after coating the protective layer was 9%, which was extremely good.

Example 3 The developer was prepared in the same manner as in Example 1, except that Cl2H250SO3Na was used instead of the sodium dodecylbenzenesulfonate used as a surfactant when preparing the color developer emulsion dispersion in Example 1. The stability of the colorant emulsion dispersion was good as in Example 1, and the smoothness of the heat-sensitive layer was also good. Further, the haze after coating the protective layer was 9%, which was extremely good.

Example 4゜Same as Example 1 except that o and zsg of Cl2H250SO3Na were used in place of the sodium dodecylbenzenesulfonate used as a surfactant when preparing the developer emulsion dispersion in Example 1. When the same procedure was carried out, the stability of the developer emulsion dispersion was as good as in Example 1,
The smoothness of the heat-sensitive layer was also good. Further, the haze after coating the protective layer was 8%, which was extremely good.

Comparative Example 1゜Smoothness of the coating film was determined in the same manner as in Example 1, except that sodium dodecylbenzene sulfonate, which was used as a surfactant when preparing the color developer emulsion dispersion in Example 1, was not used. When observing the transparency, it was found that no coating film aggregates were observed and the coating was smooth and smooth, but the haze level was 16%, which was worse than in Example 1. Also, 25°
C. After 13 days, agglutination occurred in the color developer emulsion dispersion, which did not appear to be in a normal state.

Comparative Example 2゜8. of the developer emulsified dispersion of Example 1. When the coating surface of the heat-sensitive layer was observed in the same manner as in Example 1, except that ONa/ was used instead of the sodium dodecylbenzenesulfonate used as a surfactant during the preparation, a slight amount of aggregates were observed. It was observed that the smoothness was poor. Transparency after applying the protective layer is haze 1
8%, worse than any of Examples 1 to 4, and 2
Aggregates were observed in the emulsified dispersion after 3 days at 5°C, and the stability of the emulsified dispersion was poor.

Comparative Example 3 The same procedure as Comparative Example was used except that C12H250 (CH2CH20) H was used instead of Na / Cl2H250P 11\ONa used in Comparative Example 2, but the transparency of the heat-sensitive recording material was slightly lower than the haze of 15%. The results were exactly the same as in Comparative Example 2, except that the results were better than in Comparative Example 2.

Comparative Example 4゜The coating surface of the heat-sensitive layer was observed in the same manner as in Comparative Example 3 except that C1211250 (CH2CH20)H used in Comparative Example 3 was used, and it was found that there were many aggregates and the smoothness was poor. Ta. or,
The transparency after coating the protective layer also deteriorated further with a haze of 24%. In addition, there were many aggregates in the emulsified dispersion after 3 days at 25°C.
The stability of the emulsified dispersion was t.

COMPARATIVE EXAMPLE 5 Exactly the same results were obtained in the same manner as in Comparative Example 4, except that 5° was used in place of that used in Comparative Example 4.

As is clear from the above results, it has been demonstrated that the stability of the color developer emulsion dispersion used in the present invention is good, and the smoothness of the heat-sensitive layer coating and the transparency of the heat-sensitive recording material are also very good. Ta.

Claims (1)

[Claims] 1) Coating containing the emulsified dispersion obtained by emulsifying and dispersing microcapsules containing a colorless or light-colored basic dye precursor and a color developer dissolved in an organic solvent that is sparingly soluble or insoluble in water. In a heat-sensitive recording material having a heat-sensitive layer formed by coating and drying a liquid, as an emulsification aid for a color developer emulsion,
-SO_3^-M^+ group or -OSO_3^-M^+(
A thermosensitive recording material characterized in that a surfactant having a group (M^+ represents K^+, Na^+ or NH_4^+) is used.