JPH106652A - Thermosensitive recording sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermosensitive recording sheet which has outstanding surface characteristics and preservability, and further, the excellent adhesive properties of a protecting layer. SOLUTION: This thermosensitive recording sheet 10 includes a sheet base material 12, and on one of the main faces of the sheet base material 12, a thermosensitive color developing layer 14 is formed. On the thermosensitive color developing layer 14, an intermediate protecting layer 16 is formed by applying a product obtained by compatibilizing colloidal silica with an acrylic emulsion of the core shell structure to the surface of a thermosensitive color developing layer 14. Further, surface protecting layer 18 is formed on the intermediate protecting layer 16 by applying a solution containing a binder and/or wax to the surface of the intermediate protecting layer 16 and drying the solution.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-sensitive recording sheet, and more particularly, to a heat-sensitive recording sheet in which a protective layer having a multilayer structure is provided on a heat-sensitive recording layer.

[0002]

2. Description of the Related Art Conventional thermal recording sheets are widely used for recording in, for example, thermal facsimile machines, thermal printers, automatic ticket vending machines and the like. Among such heat-sensitive recording sheets, there is a heat-sensitive recording sheet in which a heat-sensitive recording layer is provided on a sheet substrate and a protective layer having a multilayer structure is provided on the heat-sensitive recording layer. For example, Japanese Patent Publication No. 2-2439 discloses that a protective layer has a two-layer structure, and a first protective layer as an intermediate protective layer provided on a heat-sensitive recording layer is a layer having excellent storage stability such as water resistance and solvent resistance. A second protective layer provided thereon as a surface protective layer is disclosed as a layer having excellent surface characteristics capable of preventing sticking of a thermal head, preventing adhesion of scum, and preventing abrasion of a thermal head. I have. In order to impart such a surface property to the surface protective layer which comes into contact with the thermal head, conventionally, a pigment and / or a wax is contained in a binder of the surface protective layer.

[0003]

However, if pigments and / or waxes are added to the surface protective layer in order to improve the surface properties, there is a disadvantage that the adhesion of the surface protective layer is reduced. In this case, the surface protective layer is easily peeled off during use of the heat-sensitive recording sheet, and sticking of the thermal head, adhesion of scum, head wear, and the like are apt to occur, which is not preferable.

[0004] Therefore, a main object of the present invention is to provide a heat-sensitive recording sheet having good surface characteristics and preservability, and also having good adhesion of a protective layer.

[0005]

A heat-sensitive recording sheet according to the present invention comprises a sheet base, a heat-sensitive recording layer formed on the sheet base, and a binder formed on the heat-sensitive recording layer and containing a binder. A heat-sensitive recording sheet comprising an intermediate protective layer and a surface protective layer formed on the intermediate protective layer and containing a binder, a pigment and / or a wax, wherein the intermediate protective layer has a colloidal shape to improve adhesion. A heat-sensitive recording sheet characterized by containing silica.

It is preferable to use an acrylic emulsion as a binder. Further, it is preferable to use an acrylic emulsion having a core-shell structure. Further, it is preferable to use ammonium zirconium carbonate as a crosslinking agent for the acrylic emulsion.

[0007]

The thermosensitive recording sheet according to the present invention has improved adhesion between the intermediate protective layer, the surface protective layer and the thermosensitive recording layer by including colloidal silica in the intermediate protective layer. Therefore, the heat-sensitive recording sheet according to the present invention does not decrease the adhesion of the surface protective layer even when a pigment and / or wax is blended into the surface protective layer in order to improve the surface characteristics, and the heat-sensitive recording sheet is compared with the conventional one. And the surface protective layer is not easily peeled off. Therefore, the heat-sensitive recording sheet according to the present invention is excellent in surface properties such as sticking prevention, scum adhesion prevention, and head abrasion prevention. Further, in the present invention, when an acrylic emulsion is used as a binder and the acrylic emulsion is cross-linked with a cross-linking agent to form a surface protective layer and an intermediate protective layer, a synergistic effect with containing colloidal silica is provided. In addition, the adhesion of the surface protective layer is further improved. In particular, by using an acrylic emulsion having a core-shell structure, a surface protective layer having good adhesion can be obtained. Furthermore, by using zirconium ammonium carbonate as a cross-linking agent, a surface protective layer having good adhesion can be obtained. Further, since the heat-sensitive recording sheet according to the present invention has an intermediate protective layer between the surface protective layer and the heat-sensitive recording layer, it has good storage stability such as solvent resistance and plasticizer resistance.

[0008]

According to the present invention, it is possible to obtain a heat-sensitive recording sheet having good surface characteristics and preservability and also having good adhesion of the protective layer.

The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description of embodiments of the present invention with reference to the accompanying drawings.

[0010]

FIG. 1 is an illustrative sectional view showing an embodiment of the invention according to the present invention. The heat-sensitive recording sheet 10 according to the present invention includes a sheet-like sheet substrate 12. As the sheet substrate 12, for example, paper, synthetic paper, synthetic resin, or the like can be selected. On one main surface of the sheet substrate 12, a heat-sensitive recording layer 14 that is colored by heating is formed. The heat-sensitive recording layer 14 is formed by applying a solution containing a color former, a developer, a binder, and the like to the surface of the sheet substrate 12 and drying the solution. The mixture used as the material of the heat-sensitive recording layer 14 may include additives such as pigments, waxes, and antifoaming agents, if necessary, a filler for coloring the heat-sensitive recording layer 14 with any color, and a heat-sensitive recording layer. A sensitizer for increasing the sensitivity to heat of No. 14 and a stabilizer for improving the storage stability may be added.
Further, the mixture used as the material of the heat-sensitive recording layer 14 may include a crosslinking agent for crosslinking the binder in the mixture, a lubricant, and the like.

As the color former, known colorless or pale leuco dyes and the like are used. For example, (1) 3,3
-Bis (p-dimethylaminophenyl) -6-dimethylaminophthalide, 3- (p-dimethylaminophenyl)
-3- (2-phenyl-3-indolyl) phthalide, 3
-(P-dimethylaminophenyl) -3- (1,2-dimethyl-3-indolyl) phthalide, 3,3-bis (9
Triethylmethane-based compounds such as -ethyl-3-carbazolyl) -5-dimethylaminophthalide and 3,3-bis (2-phenyl-3-indolyl) -5-dimethylaminophthalide; (2) 4,4 Diphenylmethane compounds such as -bis (dimethylamino) benzhydrin benzyl ether, N-2,4,5-trichlorophenylleuco auramine; (3) rhodamine-β-anilinolactam;
-Methyl-N-cyclohexylamino) -6-methyl-
7-anilinofluoran, 3-diethylamino-7-octylaminofluoran, 3-diethylamino-7-
(2-chloroanilino) fluoran, 3-diethylamino-6-methyl-7-anilinofluoran, 3-diethylamino-6-methyl-7- (2,4-dimethylanilino) fluoran, 3-diethylamino-7-di Benzylaminofluoran, 3-diethylamino-6-chloro-
7- (β-ethoxyethylamino) fluoran, 3-diethylamino-6-chloro-7- (γ-chloropropylamino) fluoran, 3- (N-ethyl-N-isoamylamino) -6-methyl-7-ani Linofluoran, 3
-(N-ethyl-N-ethoxyethylamino) -6-methyl-7-anilinofluoran, 3- (N-ethyl-N
-Tetrahydrofurfurylamino) -6-methyl-7-
Anilinofluoran, 3- (N-ethyl-N-tolylamino) -6-methyl-7-anilinofluoran, 3-dibutylamino-6-methyl-7-anilinofluoran,
3-dibutylamino-7- (2-chloroanilino) fluoran, 3-dipentylamino-6-methyl-7-anilinofluoran, 3-piperidino-6-methyl-7-anilinofluoran, 3- (4- Anilino) Anilino-6
Xanthene compounds such as -methyl-7-chlorofluorane; (4) thiazine compounds such as benzoylleucomethylene ble-, p-nitrobenzoyl leucomethylene ble; and (5) 3-methylspirodinaphthopyran, 3- Spiro compounds such as ethylspirodinaphthopyran, 3-benzylspirodinaphthopyran, and 3-methylnaphtho- (3-methoxybenzo) spiropyran; (6) others, 3,5 ', 6-tris (dimethylamino) -spiro [9H-fluorene-9,1 '(3'H)
-Isobenzofuran] -3'-one, 1,1-bis [2
-(4-dimethylaminophenyl) -2- (4-methoxyphenyl) ethenyl] -4,5,6,7-tetrachloro (3H) isobenzofuran-3-one and the like. Alternatively, two or more kinds can be used as a mixture.

Examples of the color developing agent include, for example, p-octylphenol, p-tert-butylphenol, p-phenylphenol, p-hydroxyacetophenone, α
-Naphthol, β-naphthol, p-tert-octylcatechol, 2,2'-dihydroxybiphenyl, bisphenol-A, 1,1-bis (p-hydroxyphenyl)
Butane, 2,2-bis (4-hydroxyphenyl) heptane, 2,2-bis- (3-methyl-4-hydroxyphenyl) propane, 2,2-bis (3,5-dimethyl-
4-hydroxyphenyl) propane, 2,2-bis (3,5-dichloro-4-hydroxyphenyl) propane, bis (4-hydroxyphenyl) sulfone, bis (3-allyl-4-hydroxyphenyl) sulfone, bis ( 3,4-dihydroxyphenyl) sulfone, 2,
4'-dihydroxyphenylsulfone, 1,1-bis (4-hydroxyphenyl) cyclohexane, bis (4
-Hydroxyphenyl) ether, bis [2- (4-hydroxyphenylthio) ethoxy] methane, 4- (4-
Isopropoxybenzenesulfonyl) phenol, 4-
Phenols such as dimethyl hydroxyphthalate, butyl bis (4-hydroxyphenyl) acetate, benzyl p-hydroxybenzoate and 3,5-ditert-butylsalicylic acid; organic carboxylic acids such as benzoic acid; metals such as zinc salicylate A color developing agent such as an anilide derivative system such as 2,4-dihydroxy-N-2'-methoxybenzanilide;
These developers can be used alone or in combination of two or more.

Further, as the binder, for example, acrylic emulsion, polyvinyl alcohol, methyl cellulose, methoxy cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, starch, polyvinyl pyrrolidone, acrylate, polyacrylamide polymer, styrene-maleic anhydride A copolymer, a vinyl acetate-maleic anhydride copolymer, a styrene-butadiene copolymer or a modified product thereof can be selected.

[0014] Examples of the fine particles include aluminum hydroxide, heavy calcium carbonate, light calcium carbonate, titanium oxide, barium sulfate, silica gel, activated clay, talc, clay, kaolinite, diatomaceous earth, magnesium carbonate, and alumina. For example, inorganic materials such as aluminum oxide and organic materials such as polystyrene resin particles, urea-formalin resin particles, and polyolefin particles can be selected.

Examples of the sensitizer include zinc acetate, zinc octylate, zinc laurate, zinc stearate, zinc oleate, zinc behenate, zinc benzoate, and the like.
Metal salts of organic acids such as salicylic acid dodecyl ester zinc salt, calcium stearate, magnesium stearate and aluminum stearate; stearic acid amide,
Amide compounds such as methylolamide stearate, stearoyl urea, acetanilide, acetotoluide, stearylamide benzoate, ethylenebisstearic acid amide, hexamethylenebisoctylamide;
-Bis (3,4-dimethylphenyl) ethane, m-terphenyl, 1,2-diphenoxyethane, 1,2-bis (3-methylphenoxy) ethane, p-benzylbiphenyl, p-benzyloxybiphenyl, diphenyl Carbonate, bis (4-methylphenyl) carbonate, dibenzyl oxalate, bis (4-methylbenzyl) oxalate, bis (4-chlorobenzyl) oxalate, phenyl 1-hydroxy-2-naphthalenecarboxylate, 1-hydroxy- Benzyl 2-naphthalenecarboxylate, phenyl 3-hydroxy-2-naphthalenecarboxylate, methylenedibenzoate, 1,4-bis (2-vinyloxyethoxy) benzene, 2-benzyloxynaphthalene, benzyl 4-benzyloxybenzoate, dimethyl Phthalate, terephthal Dibenzyl, dibenzoylmethane and 4-methylphenoxy -p- biphenyl. These sensitizers may be used alone or in combination. Examples of the storage stabilizer include 1,1,3-tris (2-methyl-4hydroxy-5-tert-butylphenyl) butane and 1,1,3-tris (2-methyl-4-hydroxy-). 5-cyclohexylphenyl) butane, 4,4'-butylidenebis (2-tert-butyl-5-methylphenol), 4,4'-thiobis (2-tert-butyl-5-methylphenol), 2,
2'-thiobis (6-tert-butyl-4-methylphenol), 2,2'-methylenebis (6-tert-butyl-4-
Hindered phenol compounds such as methylphenol), 4-benzyloxy-4 '-(2-methylglycidyloxy) diphenylsulfone, sodium-2,2'
-Methylenebis (4,6-di-tert-butylphenyl) phosphate; and these storage stabilizers can be used alone or as a mixture of two or more.

Further, on the heat-sensitive recording layer 14, an intermediate protective layer 16 is formed. The intermediate protective layer 16 contains a binder.

Examples of the binder for the intermediate protective layer 16 include acrylic emulsion, polyvinyl alcohol, modified polyvinyl alcohol, starch, modified starch, casein, gelatin, glue, polyamide, polyacrylamide, hydroxyethylcellulose, methylcellulose, polyvinyl acetate and polyvinyl acetate. Acrylic ester, styrene-maleic anhydride copolymer, vinyl acetate-maleic anhydride copolymer, styrene-butadiene copolymer, polyvinyl chloride,
At least one of polyvinylidene chloride and polyurethane can be used. In particular, it is preferable to use an acrylic emulsion as the binder, and it is more preferable to use an acrylic emulsion having a core-shell structure. Further, it is preferable to use ammonium zirconium carbonate as a crosslinking agent for crosslinking the acrylic emulsion.

The acrylic emulsion having a core-shell structure is a copolymer emulsion obtained by copolymerizing a monomer component containing acrylamide as a main component in the presence of a seed emulsion as core particles. Examples of the seed emulsion include acrylic ester, styrene / acrylate ester, acrylonitrile, styrene-butadiene, acrylonitrile-butadiene,
General polymer emulsions such as acrylate-butadiene, vinyl chloride, and vinyl acetate can be used, and they can be used alone or in combination of two or more. The monomer component contains an unsaturated monomer copolymerizable with acrylamide, if necessary. Examples of the unsaturated monomer include methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, and acrylic acid 2
-Aminoethyl, 2- (N-methylamino) acrylate
Acrylates such as ethyl, 2- (N, N-dimethylamino) ethyl acrylate and glycidyl acrylate; vinyl esters such as vinyl acetate and vinyl propionate; and nitrile group-containing monomers such as acrylonitrile;
Unsaturated carboxylic acids such as acrylic acid, maleic anhydride, fumaric acid, itaconic acid, crotonic acid, styrene, α
Aromatic vinyl monomers such as -methylstyrene and divinylbenzene; N-substituted unsaturated carboxylic acid amides such as N-methylolacrylamide; In particular, among these, it is preferable to use an unsaturated monomer having a functional group such as a carboxyl group, a hydroxyl group, an amino group, a methylol group, and a glycidyl group. This acrylic emulsion having a core-shell structure is produced by a known polymerization technique using a polymerization initiator and a chain transfer agent together with the above-mentioned materials.

The acrylic emulsion having the core-shell structure can be used as a binder for the intermediate protective layer 16 and the surface protective layer 18. The binder may be an acrylic emulsion alone, or may be used in combination with the above-mentioned known binder as needed. Further, it is preferable to crosslink the acrylic emulsion in combination with a water-soluble or water-dispersible epoxy compound, melamine, glyoxal, polyaldehyde, amino-formaldehyde compound, or a water-resistant agent (crosslinking agent) such as zirconium salt. In this case, the water resistance, the solvent resistance, and the like of the intermediate protective layer 16 can be further improved. Further, if necessary, an antifoaming agent, a dispersing agent, a leveling agent and the like may be contained.

The binder of the intermediate protective layer 16 contains colloidal silica in order to improve the adhesion. Colloidal silica is a colloidal solution in which ultrafine particles of silicic anhydride are dispersed in water using water as a dispersion medium, and becomes a dry gel solid when dried. In addition, colloidal silica is a colloidal solution in which negatively charged amorphous silica particles are dispersed in water to form a colloidal form. , Aggregation and the like occur. The particle size of silicic anhydride in colloidal silica is 10 to 50 n.
m, more preferably 10 to 20 n
m is preferred. Further, the content of silicic anhydride in water at the time of the colloidal solution is preferably 20 to 41% by weight, more preferably 20 to 21% by weight. Further, the colloid solution may be stabilized with ammonia. The colloidal silica can be made compatible with the one having the same pH and charge in the colloid solution. Therefore, colloidal silica can be compatible with an acrylic emulsion as a binder. In this embodiment, the content of colloidal silica is 5 parts per 100 parts by weight of the binder.
-40 parts by weight, preferably 25-35 parts by weight.
The intermediate protective layer 16 of the present invention is formed by coating a core-shell structure acrylic emulsion with colloidal silica compatible on the heat-sensitive recording layer 14 and then crosslinking the acrylic emulsion.

Further, on the intermediate protective layer 16, a surface protective layer 18 is formed. The surface protective layer 18 is formed by applying a solution containing a binder, a pigment and / or a wax to the intermediate protective layer 1.
6 is formed by applying the composition to the surface and drying it.
As the binder for forming the surface protective layer 18, the same binder as that for forming the intermediate protective layer 16 can be used. In particular, an acrylic emulsion is preferably used. It is preferable to use a core-shell structure emulsion. Further, it is preferable to use ammonium zirconium carbonate as a crosslinking agent for crosslinking the acrylic emulsion.
Further, pigments to be contained in the surface protective layer 18 to improve surface properties such as anti-sticking property, anti-adhesion property, and anti-abrasion property include calcium carbonate,
At least one of clay, talc, titanium oxide, magnesium carbonate, kaolin, zinc oxide, aluminum silicate and the like can be used. As the waxes, fatty acids such as oleic acid, polyolefins such as paraffin wax, metal soaps, and other oils such as silicone oil and whale oil can also be used.

[0022]

【Example】

Example: 7 parts by weight of 3-dibutylamino-6-methyl-7-anilinofluoran, 10 parts by weight of clay and 3 parts by weight of stearamide powder in 100 parts by weight of a 5% aqueous solution of polyvinyl alcohol, a water-soluble binder. The parts were mixed and dispersed by a centrifugal rotary ball mill to prepare a liquid A. Further, 7 parts by weight of bisphenol A, 10 parts by weight of clay, and 3 parts by weight of stearic acid amide powder were mixed with 100 parts by weight of a 5% aqueous solution of a water-soluble binder polyvinyl alcohol, and dispersed by a centrifugal rotary ball mill to prepare a liquid B. Was. And A
The solution B and the solution B were mixed and stirred at a ratio of 1: 3 to obtain a uniform dispersion paint for forming a heat-sensitive recording layer. This dispersion paint was applied on one main surface of high-quality paper of 64 g / m ² with a wire bar so that the dry coating amount was 8 g / m ² ,
Blow dry for minutes. Thus, a heat-sensitive recording layer was formed on the high-quality paper. Next, in order to form an intermediate protective layer, 3.96 parts by weight of ammonium zirconium carbonate (AC-7, manufactured by Daiichi Kagaku Kagaku Kogyo Co., Ltd.) and colloidal silica (Nissan) were used in 66.04 parts by weight of an acrylic emulsion having a core-shell structure. 30.00 parts by weight of Snowtex N) (manufactured by Chemical Industry Co., Ltd.) were added, and the mixture was stirred with a homomixer to obtain a coating for an intermediate protective layer. In addition, Snowtex N as colloidal silica is a colloid solution containing 20 to 21% by weight of silicic anhydride having a particle diameter of 10 to 20 nm in water, and is stabilized with ammonia. Then, this intermediate protective layer coating was applied onto the above-mentioned heat-sensitive recording layer so that the dry weight was 5 g / m ² , and dried at 60 ° C. for 3 minutes to form an intermediate protective layer. Next, in order to form a surface protective layer, 5.89 parts by weight of zirconium ammonium carbonate (AC-7 manufactured by Daiichi Kagaku Kagaku Kogyo Co., Ltd.) and calcium carbonate (Shiraishi) were added to 45.11 parts by weight of an acrylic emulsion having a core-shell structure. Industrial Br-15) 30.0
0 parts by weight and zinc stearate (Z-8-3 manufactured by Chukyo Yushi)
6) 15.00 parts by weight and stirring with a homomixer to obtain a coating for a surface protective layer. Then, the coating for the surface protective layer was applied onto the above-mentioned heat-sensitive recording layer by a dry weight of 5 g / m
² and dried at 60 ° C. for 3 minutes to form a surface protective layer.

Comparative Example In a comparative example, an acrylic emulsion 9 having a core-shell structure was used to form an intermediate protective layer.
5.66 parts by weight of zirconium ammonium carbonate (AC-7, manufactured by Daiichi Kagaku Kagaku Kogyo Co., Ltd.) was added to 4.34 parts by weight, and the mixture was stirred with a homomixer to obtain a coating for an intermediate protective layer. Then, this intermediate protective layer coating material was applied on the heat-sensitive recording layer formed in the same manner as in the above-mentioned example so that the dry weight was 5 g / m ² , and dried at 60 ° C. for 3 minutes to form the intermediate protective layer. Formed. Further, on the intermediate protective layer, a surface protective layer similar to that of the above-described embodiment was formed.

(Evaluation Test) The heat-sensitive recording sheets obtained in the above Examples and Comparative Examples were each subjected to a temperature gradient of 130 ° C. and a pressure of 2 using a thermal gradient tester (manufactured by Toyo Seiki Seisaku-sho, Ltd.).
The mixture was heated at kg / cm ² for 1 second to form a black colored portion.
Then, various evaluation tests were performed on the heat-sensitive recording sheets of Examples and Comparative Examples under the following conditions. The results of the evaluation test are shown in Table 1 below. In each evaluation test, the color density was measured with a Macbeth reflection densitometer RD-914. The residual ratio of the coloring density was calculated by dividing the reflection density after the test by the reflection density before the test. When the residual ratio is 100, it indicates that there is no change in the color density of the heat-sensitive recording sheet.
This indicates that the color density of the heat-sensitive recording sheet has been reduced.
When it is larger than 00, it indicates that the glossiness of the surface of the thermal recording sheet has increased.

(1) Adhesion test A black ink was offset-printed on the surface protective layer of the heat-sensitive recording sheet, dried and then a cellophane tape was stuck thereon and rubbed several times with a finger. Then, the degree of peeling of the ink after the cellophane tape was peeled off at a stretch was observed and compared. (2) Water resistance adhesion test A black ink was offset-printed on the surface protective layer of the heat-sensitive recording sheet, dried, and then 200 cc of the heat-sensitive recording sheet was dried.
For 24 hours in tap water. Then, the degree of peeling of the ink after rubbing the printing surface with a finger was observed and compared. (3) Water resistance test The heat-sensitive recording sheet was immersed in 200 cc of tap water for 24 hours. Then, the coloring density of the black coloring portion of the thermosensitive recording sheet before and after the test was measured, and the residual ratio of the coloring density was calculated. Then, the embodiment and the comparative example were compared with respect to the residual ratio of the coloring density. In addition, the appearance of water swelling after immersion was observed and compared. (4) Corrosion resistance test Salad oil was dropped on the surface of the thermal recording sheet with a dropper. Then, the color density of the black color portion before and after the test was measured, and the residual ratio of the color density was calculated. Then, the embodiment and the comparative example were compared with respect to the residual ratio of the coloring density. (5) Plasticizer resistance test A thermosensitive recording sheet was placed on a polyester film,
On top of that, vinyl chloride wrap (Mitsubishi Chemical Dia Wrap M
SA) were stacked three times, and 300 g /
15 hours in an atmosphere of 40 ° C. while applying a pressure of ² cm ²
r was left. Thereafter, the coloring density of the black coloring portion before and after the test was measured, and the residual ratio of the coloring density was calculated. Then, the embodiment and the comparative example were compared with respect to the residual ratio of the coloring density.

[0026]

[Table 1]

As can be seen from Table 1, the heat-sensitive recording sheet of this example was prepared by adding colloidal silica to the intermediate protective layer so that the intermediate protective layer and the heat-sensitive recording medium were mixed with pigments and waxes. Adhesion with the recording layer and the surface protective layer is improved. Therefore, when the heat-sensitive recording sheet is used, the surface protective layer is less likely to be peeled off as compared with the conventional recording sheet, and is excellent in surface properties such as anti-sticking property, anti-adhesion property and anti-head abrasion property. Further, as is apparent from Table 1, the heat-sensitive recording sheet of this example has excellent water resistance, corrosion resistance, and plasticizer resistance.

[Brief description of the drawings]

FIG. 1 is an illustrative sectional view showing one embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Thermal recording sheet 12 Substrate 14 Thermal recording layer 16 Intermediate protective layer 18 Surface protective layer

Claims (4)

[Claims] 1. A sheet base, a heat-sensitive recording layer formed on the sheet base and colored by heating, an intermediate protective layer formed on the heat-sensitive recording layer and containing a binder, and the intermediate A heat-sensitive recording sheet formed on a protective layer and including a surface protective layer containing a binder, a pigment and / or a wax, wherein the intermediate protective layer contains colloidal silica to improve adhesion. Characteristic thermal recording sheet. 2. The thermal recording sheet according to claim 1, wherein an acrylic emulsion is used as the binder. 3. The thermosensitive recording sheet according to claim 2, wherein the acrylic emulsion has a core-shell structure. 4. The heat-sensitive recording sheet according to claim 2, wherein zirconium ammonium carbonate is used as a crosslinking agent for the acrylic emulsion.