JPH03244592A - Manufacture of thermal recording material - Google Patents

Abstract

PURPOSE:To obtain a thermal recording material which has excellent resistance against scratch, and high blocking and sticking prevention capability as well as a transparent recording layer by limitting the pH value of at least either of a thermally sensitive layer or a protecting layer application liquid applied to a support and dried for layer formation, to a specific range. CONSTITUTION:An application liquid is prepared by adding a microcapsule containing an electron-donative dye precursor, a dispersed product containing at least, emulsified, dispersed developer, binder and other ingredients. This liquid is applied to a support such as paper or synthetic resin film using bar application or other technique, and then is dried to form a thermally sensitive layer. Next, single or more protecting layers are formed on a top thermally sensitive layer. The recommended polymers used for the protecting layer are water-soluble polymers such as methylcellulose and starch, and water-insoluble polymers such as styrene-butadiene rubber latex and polyvinylacetate emulsion. A surfactant is added to an application liquid for the formation of a protecting layer. If the pH value of at least either of the application liquid of the thermally sensitive layer or the protecting layer is set to 2 to 7, it is possible to improve the resistance against scratch and the ability to prevent blocking and sticking of the recording material without impairing its transparency.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a method for producing a heat-sensitive recording material.

More specifically, the present invention relates to a method for producing a heat-sensitive recording material with excellent transparency.

(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, transparent heat-sensitive recording materials that can be directly recorded with a thermal head have been developed in order to adapt to multicolor printing or to be used in overhead projectors (abbreviated as OHP). (For example, Japanese Patent Application Laid-open Nos. 63-92489, 63-252783, and 63-265682).

(Problem to be Solved by the Invention) However, if such a transparent heat-sensitive layer is scratched and opaque areas are created, not only will the image quality deteriorate when used as an OHP, but it will also be inconvenient when forming multicolor images. be. Therefore, at least one protective layer is usually provided on the heat-sensitive layer, but it is not easy to create a protective layer that improves scratch resistance without impairing the transparency of the heat-sensitive layer. It is not easy to provide a protective layer that can also help prevent adhesion. As a result of intensive studies to solve the above problems, the present inventors have found that by maintaining the pH of at least one of the coating liquids for the heat-sensitive layer and the protective layer at pH 2 to pH 7, transparency, scratch resistance, The present invention was achieved by discovering that very good results can be obtained in anti-blocking ability and anti-sticking ability.

Accordingly, a first object of the present invention is to provide a heat-sensitive recording material having excellent scratch resistance, anti-blocking ability and anti-sticking ability, and having a transparent recording layer.

A second object of the present invention is to provide a protective layer that has excellent scratch resistance, anti-blocking ability, anti-sticking ability, and excellent transparency.

(Means for Solving the Problems) The above-mentioned objects of the present invention are to provide microcapsules containing a colorless or light-colored electron-donating dye precursor and a dye precursor dissolved in an organic solvent that is sparingly soluble or insoluble in water. At least one heat-sensitive layer formed by coating and drying a coating solution containing an emulsified dispersion obtained by emulsifying and dispersing a colorant on a support, and at least one protective layer provided on the heat-sensitive layer. This was achieved by a method for producing a heat-sensitive recording material, characterized in that the pH of at least one of the coating solutions for the heat-sensitive layer and the protective layer is adjusted to 2 to 7.

In the present invention, the substance for adjusting the pH of the coating liquid can be appropriately selected from among the substances that can adjust the coating liquid to pH 2 to pH 7, but it is particularly preferable to adjust the pH using an acid. is preferred, and it is more preferred to use a volatile acid such as hydrochloric acid or acetic acid.

Surprisingly, the heat-sensitive recording material produced by coating the heat-sensitive layer and protective layer coating liquids in the pHeJl range has significantly improved scratch resistance, anti-blocking ability, and anti-sticking ability without impairing the transparency of the recording material. If the ePH that can be improved is 2 or less, transparency will deteriorate, and if the pH is 7 or more, blocking prevention ability and sticking prevention ability will deteriorate.
A range of 6 is preferred.

Specific examples of polymers used in the protective layer include methylcellulose, carboxymethylcellulose, hydroxymethylcellulose, starches, gelatin, gum arabic, casein, styrene-maleic anhydride copolymer hydrolyzate,
Water-soluble polymers such as styrene-maleic anhydride copolymer half ester hydrolyzate, polyvinyl alcohol, carboxy-modified polyvinyl alcohol, silicon-modified polyvinyl alcohol, polyacrylamide derivatives, polyvinylpyrrolidone, sodium polystyrene sulfonate, sodium alginate, and styrene- Butadiene rubber latex, acrylonitrile-butadiene rubber latex,
Examples include water-insoluble polymers such as methyl acrylate-butadiene rubber latex and polyvinyl acetate emulsion.

Pigments, metal soaps, wax, crosslinking agents, and the like are added to the protective layer for the purpose of improving matching with a thermal head during thermal printing and improving the water resistance of the protective layer.

Pigments include organic substances such as zinc oxide, calcium carbonate, barium sulfate, titanium oxide, lithopone, talc, stone, kaolin, aluminum hydroxide, amorphous silica, styrene resin, formalin condensate, fluorinated ethylene resin, and urea resin. The amount added is 0.05 to 0.05 of the total weight of the polymer.
The amount is 2 times, particularly preferably 001 to 0.5 times. 0
．． If the amount is less than 0.05 times, it is ineffective in improving the matching property with the head, and if the amount is more than 2 times, the transparency and sensitivity of the heat-sensitive recording material will be significantly reduced, impairing its commercial value.

Metal soaps include emulsions of higher fatty acid metal salts such as zinc stearate, calcium stearate, and argonium stearate, and the proportion thereof is 0.5 to 20% by weight, preferably 1 to 10% by weight of the total weight of the protective layer. is added in an amount of Waxes include emulsions such as paraffin wax, microcrystalline wax, carnauba wax, methylol stearamide, polyethylene wax, silicone, etc., and the amount thereof is 0.5 to 40% by weight, preferably 1 to 20% by weight of the total weight of the protective layer. Added in proportion.

Further, in order to uniformly form a protective layer on the heat-sensitive layer, a surfactant is added to the coating solution for forming the protective layer. Surfactants include sulfosuccinic acid-based alkali metal salts, fluorine-containing surfactants, etc. Specifically, sodium salts of di(2-ethylhexyl)sulfosuccinic acid, di(n-hexyl)sulfosuccinic acid, etc. Or ammonium salt etc.

In addition, a surfactant, a polymer electrolyte, etc. may be added to the protective layer to prevent charging of the heat-sensitive recording material.The solid content coating amount of the protective layer is usually 0.2 to 5 g/%. Preferably,
More preferably Ig to 3g/bo.

One or more hardening agents may be added to the heat-sensitive layer and protective layer of the present invention, and all hardening agents other than those that rapidly react at pH 2 to pH 7 and cause liquid coagulation may be added. agents can be used. The amount of the hardening agent added is preferably in the range of 0.20% to 50% by weight based on the weight of the binder, and dialdehydes and boric acid are particularly preferred as the hardening agent.

As the electron-donating dye precursor used in the heat-sensitive layer of 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 include lactones, lactams,
It has a partial skeleton such as sultone, spiropyran, ester, amide, etc., 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.

A particularly preferred compound is a compound represented by the following general formula.

In the formula, R3 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 R8 is a hydrogen atom or an alkyl group having 1 to 15 carbon atoms. Alternatively, the halogen atom and R4 represent a substituted or unsubstituted aryl group having 6 to 20 carbon atoms.

As the substituent for R4, an alkyl group having 1 to 5 carbon atoms, an alkoxy group, a halogenated alkyl group, and a halogen atom are preferable.

In the present invention, by encapsulating the above-mentioned electron-donating dye precursor 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. 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/ryf.

The wall materials of the microcapsules include polyurethane, polyurea, polyester, polycarbonate, urea-formaldehyde resin, melamine resin, polystyrene, styrene-methacrylate copolymer, styrene-acrylate.
Examples include F copolymer, gelatin, polyvinylpyrrolidone, polyvinyl alcohol, etc. 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 produced by emulsifying a core material containing a reactive substance such as an electron-donating dye precursor, and then
It is preferable to form a wall of a polymeric substance around the oil liquid for microencapsulation, in which case a reactant forming a polymeric substance is added inside and/or outside the oil droplet.

Details of microcapsules that can be preferably used in the present invention, such as a preferred method for producing microcapsules, are described in, for example, JP-A-59-222716.

Here, the organic solvent for forming the oil droplets can be appropriately selected from those generally used as pressure-sensitive oils, but in particular, an organic solvent suitable for dissolving the color developer described below is used. In this case, it is preferable because it has excellent solubility in leuco dyes, increases the color density and speed of color development during thermal printing, and reduces fogging.

When the preferred microcapsules produced as described above are used, during thermal printing, the reactive substances contained in the core and outside of the microcapsules permeate through the microcapsule walls 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 a combination of electron-donating colorless dye precursors and their color developers with different hues. It is possible to realize multiple intermediate colors. Therefore, the present invention is not limited to monochrome heat-sensitive recording materials, but can also be applied to two-color or multi-color heat-sensitive paper and heat-sensitive recording materials suitable for recording images with gradation.

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.

The color developer that causes a color-forming reaction upon thermal melting with the electron-donating colorless dye precursor used in the present invention can be appropriately selected from known ones and used. For example, color developers for leuco dyes include phenolic compounds, triphenylmethane compounds, sulfur-containing phenolic compounds, carboxylic acid compounds, sulfone compounds, urea or thiourea compounds, etc. , for example, Paper Valve Technology Times (1985) pp. 49-54 and 65.
- described on page 70. 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 to 250°C.
A phenol and an organic acid that are soluble in water at 00° C. are preferable, and it is preferable to use two or more a-coloring agents in combination because the solubility increases.

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

(I) C, H! □.

(II) R1 is an alkyl group, an aryl group, an aryloxyalkyl group or an aralkyl group, with methyl, ethyl and butyl groups being particularly preferred.

(III) 3 m=! O~2.11="=2~1 1 Rg is an alkyl group, especially a butyl group, a pentyl group,
Heptyl and octyl groups are preferred.

R1 is a hydrogen atom or a methyl group, and n is O-2.

(IV) R4 is an alkyl group, an aryloxyalkyl 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 in the form of a dispersion.

The organic solvent for dissolving the color developer can be appropriately selected from those commonly used as pressure-sensitive oils.
In particular, oils having two or more benzene rings and the number of heteroatoms equal to or less than the group constant are preferred. Such oils include compounds represented by the following general formulas (V) to (■) and triallylmethane. (e.g. tritolylmethane, tolyldiphenylmethane), terphenyl compounds (e.g.
terphenyl), alkylated diphenyl ether (eg, propyl diphenyl ether), hydrogenated terphenyl (eg, hexahydroterphenyl), diphenyl ether, and the like.

(V) In the formula, R1 represents a hydrogen atom or an alkyl group having 1 to 18 carbon atoms, and R8 represents an alkyl group having 1 to 18 carbon atoms, p'
and ql represent an integer of 1 to 4, and the total number of alkyl groups is 4 or less.

Note that the alkyl groups of R1 and R2 preferably have 1 to 8 carbon atoms.

(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.

pt and q! represents an integer from 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.

(■) (R')R3 (R')q'' In the formula, R5 and R' represent a hydrogen atom or the same or different alkyl groups having 1 to 18 carbon atoms.

m represents an integer of 1 to 13, R3 and q3 represent integers of 1 to 3, and the total number of alkyl groups is 3 or less.

Note that the alkyl groups of R5 and R6 are particularly preferably those having 2 to 4 carbon atoms.

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

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

Examples of compounds represented by formula (■) include 1-methyl-
1-dimethylphenyl-1-phenylmethane, l-ethyl-1-dimethylphenyl-1-phenylmethane and 1
-propyl-1-dimethylphenyl-1-phenylmethane and the like.

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

In the present invention, an auxiliary solvent may be added to the above-mentioned 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.

Further, as the surfactant to be contained in the aqueous phase, one can be appropriately selected from anionic or nonionic surfactants that do not cause precipitation or aggregation by interacting with the above-mentioned protective colloid. .

Preferred surfactants include sodium alkylbenzenesulfonate (eg, sodium lauryl sulfate), dioctyl sodium sulfosuccinate, polyalkylene glycol (eg, polyoxyethylene nonylphenyl ether), and the like.

The emulsified dispersion of a color developer in the present invention is produced by mixing an oil phase containing a color developer and an aqueous phase containing a protective colloid and a surfactant by means commonly used for fine particle emulsification, such as high-speed stirring and ultrasonic dispersion. It can be easily mixed and dispersed using.

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 are used in an amount of 0.0% per part by weight of the color developer that lowers the melting point. 1-2 parts by weight, preferably 0.5-1
The melting point depressant and the color developer that lowers the melting point are preferably used at the same location.If they are added at different locations, please use the above-mentioned methods. It is preferable to add 1 to 3 times the amount added.

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 20 g/m8 as solid content, preferably 0.2 to 5 g/m8.

The heat-sensitive layer provided as described above surprisingly has extremely good transparency.

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, and then applying the coating solution to paper or synthetic resin. A heat-sensitive layer having a solid content of 2.5 to 25 g/rd is formed by coating and drying on a support such as a film by a coating method such as bar coating, and then one or more of the above-mentioned layers is coated on the outermost heat-sensitive layer. It is manufactured by forming a protective layer of.

In this case, the pH of the coating solution for the heat-sensitive layer (the pH of the color developer emulsion dispersion) should also be set to 2 to 7 to improve the transparency, scratch resistance, and anti-blocking ability of the entire recording layer including the protective layer. This is preferable in terms of good anti-sticking ability.

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 the paper and to improve the contact between the recording heat head and the heat-sensitive recording layer, Japanese Patent Application Laid-Open No. 57-1166
The paper described in No. 87 and having a Bekk smoothness of 90 seconds or more is advantageous.

Also, 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.
Density 0.-69097. Paper with an optical contact rate of 9 g/cm' or less and an optical contact rate of 15% or more, JP-A-58-690
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-58-65
695, the glossy side of base paper made by a Yankee machine is used as the coated surface to improve the color density and resolution, and the method described in JP-A-59-35985.
Papers whose base paper has been subjected to corona discharge treatment to improve coating suitability can also be used in the present invention and give good results. In addition to these, any support commonly used in the field of heat-sensitive recording paper can be used as the support of the present invention.

The synthetic resin film used as a support in the present invention has excellent abrasion resistance, water resistance, and chemical resistance, and has a thickness and/or rigidity that does not cause curling when the heat-sensitive layer is applied.
Any material can be selected from known materials that are dimensionally stable and do not deform even when heated during the development process. Examples of such films include polyester films such as polyethylene terephthalate and polybutylene terephthalate, cellulose derivative films such as cellulose triacetate films, polystyrene films, polypropylene films, and polyolefin films such as polyethylene. It can be used as

The thickness of the 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 synthetic resin film 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 preferably in the range of 0.1 g/m" to 2.0 g7 m", particularly preferably in the range of 0.2 g/m" to 1.0 g/m", from O.1 g7 m" If the amount is too small, the adhesion between the film and the heat-sensitive layer will not be sufficient, and even if it is increased to 2.0 g/m'' or more, the adhesion between the film and the heat-sensitive layer will reach saturation, which is disadvantageous in terms of cost.

The undercoat layer may swell due to the water contained in the heat-sensitive layer when the heat-sensitive layer is applied thereon.
It is desirable to harden using a hardening agent.

As the hardening agent, dialdehydes such as glutaraldehyde and 2,3-dihydroxy-1,4-dioxane, and boric acid are 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.

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.

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 film by a known method. As the method of activation treatment, etching treatment with acid, flame treatment with gas burner, corona treatment, glow discharge treatment, etc. are used, but from the point of view of cost or simplicity,
U.S. Patent No. 2.715.075, U.S. Pat. No. 2.846.7
No. 27, No. 3,549.406, No. 3.590,
The corona discharge treatment described in No. 107 and the like is most preferably used.

The coating according to the present invention can be carried out using generally well-known coating methods, such as dip coating, air knife coating, curtain coating, roller coating, doctor coating, etc.
Coating can be performed by a wire barcode method, a slide coating method, a gravure coating method, or an extrusion coating method using a hopper as described in US Pat. No. 2,681,294. U.S. Pat. No. 2,761,791 and U.S. Pat. No. 3,508,947 as appropriate.
No. 2,941.898, and No. 3゜526.
Specification No. 528, Yuji Harasaki, "Coating Engineering" 25
31 (published by Asakura Shoten, 1973), etc., it is also possible to coat two or more layers at the same time, and an appropriate method can be selected depending on the coating amount, coating speed, etc.

In the present invention, in addition to the above materials, citric acid, tartaric acid, oxalic acid, boric acid, phosphoric acid, pyrophosphoric acid, etc. can be added as acid stabilizers.

In the present invention, a back layer may be provided on the back surface of the support for the purpose of curl correction, antistatic, and improved slipperiness.As the structural acid content of the back layer, the same acid content as that of the protective layer is used. Things are good.

(Effects of the Invention) The heat-sensitive recording material of the present invention has high thermal sensitivity, so the factor ξ
It is possible to form images using a thermal head such as a printer. In particular, it has a protective layer with excellent scratch resistance, anti-blocking ability, and anti-sticking ability, so it is easy to handle, and the recording layer can be transparent, so
By using a transparent film as a support, it is possible to use OHP immediately after receiving the image by a factor ξ.

(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 ■) and 2 g of Suten Soap 200 (ultraviolet absorber manufactured by Sumitomo Chemical ■) were mixed with 55 g of 1-phenyl-1-xylylethane.
and 55 g of methylene chloride were added to a mixed solvent and dissolved. This leuco dye solution was mixed with an aqueous solution of 100 g of 8% polyvinyl alcohol aqueous solution (Kuraray PVA217E), 40 g of water, and 1.4 g of 2% sodium salt of dioctyl sulfosuccinate (dispersant).
10 with Ace Homogenizer, 5 with OOOypm
The mixture was emulsified for a minute, 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 0.7a.

[Preparation of developer emulsion dispersion]

Color developer represented by the following structural formula (a) 8g, (b) 4g
Reach? :30 g of F(c) was dissolved in 8.0 g of 1-phenyl-1-xylylethane and 30 g of ethyl acetate. The obtained developer solution was mixed with an aqueous solution of 100 g of an 8% polyvinyl alcohol aqueous solution, 150 g of water, and 5 g of sodium dodecylbenzenesulfonate Q, and heated at 10.00 rpm using an Ace homogenizer manufactured by Nippon Seiki ■. Emulsification was carried out for 5 minutes at room temperature to obtain an emulsified dispersion with a particle size of 0.5 μm.

Color developer (breeding color developer (b) Color developer (C) H [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 water were stirred and mixed, and then the pH of the coating solution was adjusted to 5.0 with hydrochloric acid. I applied it and let it dry.

(Composition of protective layer) Silica-modified polyvinyl alcohol (PVA R2105 manufactured by Kuraray ■) 2 parts by weight (solid content) Colloidal silica (Snowtex O manufactured by Nissan Chemical ■) 3 parts by weight (solid content) Zinc stearate (manufactured by Chukyo Yushi Co., Ltd.) Hydrin Z7) 20.1 parts by weight (solid content) Paraffin wax (Cellosol 428 manufactured by Chukyo Yushi Co., Ltd.) 1 part by weight (solid content) Boric acid: 0.06 parts by weight (solid content) Glyoxal = 0.2 parts by weight ( Solid content) Adjust the pH of the aqueous solution providing the protective layer with the above composition to 5.0 with hydrochloric acid, and apply it on the heat-sensitive layer so that the thickness after drying is 2μ,
A transparent thermosensitive film was produced.

In order to examine the ability of the obtained heat-sensitive recording material to prevent bronking, the heat-sensitive recording material was left under high temperature and humidity conditions (40°C, 90% relative humidity) for 3 days, and the blocking resistance was good and the scratch resistance was also good. It was almost satisfactory.

Example 2゜p)I of both the coating liquids of the heat-sensitive layer coating liquid and the protective layer coating liquid
When the same procedure as in Example 1 was carried out except that the value was adjusted to 4.0 with hydrochloric acid, the same results as in Example 1 were obtained.

Example 3: The pH of both the heat-sensitive layer coating solution and the protective layer coating solution was adjusted to 7 with acetic acid! Il! When the same procedure as in Example (2) was carried out except that ff was used, the same results as in Example 1 were obtained.

Example 4 The same procedure as in Example 1 was performed except that the pH of both the heat-sensitive layer coating solution and the protective layer coating solution was adjusted to 2.0 with acetic acid. The same results as in Example 1 were obtained. Obtained.

Comparative Example 1゜The same procedure as in Example 1 was carried out except that the pH of both the coating liquid for the heat-sensitive layer and the coating liquid for the protective layer was adjusted to 8. However, blocking such as sticking between sheets of heat-sensitive recording material was observed. A phenomenon has occurred.

Comparative Example 2 The same procedure as in Example 1 was carried out, except that the pH of both the heat-sensitive layer coating solution and the protective layer coating solution was adjusted to 1.5.
Transparency has deteriorated significantly.

Example 5 Same as Example 1, except that only the pH of the heat-sensitive layer coating solution was adjusted to pH 5 with acetic acid, and the pH of the protective layer coating solution was left to take its course without adjusting. The results were obtained.

Example 6゜ Only the pH of the coating solution for the protective layer was adjusted to pH 5 by tI with hydrochloric acid.
i! The same results as in Example 1 were obtained by carrying out the same procedure as in Example 1, except that the pH of the heat-sensitive layer coating solution was not adjusted and left as it was.

The results of Examples 1 to 6 and Comparative Examples 1 to 2 are summarized in Table 1.

The results shown in Table 1 demonstrate that adjusting the pH of the coating liquid is extremely effective in improving the anti-blocking ability, anti-sticking ability and scratch resistance of the heat-sensitive recording material.

Claims (1)

[Claims] A coating liquid containing an emulsified dispersion obtained by emulsifying and dispersing 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 method for producing a heat-sensitive recording material comprising at least one heat-sensitive layer formed by coating and drying on a support, and at least one protective layer provided on the heat-sensitive layer, comprising: a coating solution for the heat-sensitive layer and the protective layer; A method for producing a heat-sensitive recording material, characterized in that the pH of at least one of the coating liquids is set to 2 to 7.