JPH07137442A - Thermal recording sheet - Google Patents

Abstract

(57) [Summary] [Purpose] To provide a thermal recording sheet having good printability and sticking property, and excellent storage stability such as plasticizer resistance and water resistance. [Structure] A heat-sensitive recording sheet having a heat-sensitive recording layer provided on a support and a protective layer on the surface thereof is mainly composed of a water-dispersible polymer as a protective layer, and a higher fatty acid metal salt and a water-soluble modified polyamine resin. By using zinc stearate and a carboxyl-modified polyamine resin having a nitrogen content of 12 to 30% by weight, a water-dispersible polymer having a specific core-shell structure is used as a main component. use. [Effect] According to the present invention, a thermal recording sheet having excellent printability, matching property with a color-developing device, and good storage stability is obtained.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a thermal recording sheet,
More specifically, the present invention relates to a heat-sensitive recording sheet which has good printability, excellent matching properties with color-developing devices, and good storability of white paper and recording areas.

[0002]

2. Description of the Related Art In recent years, heat-sensitive recording sheets that develop color by heat have been widely used for facsimiles, word processors, plotters, labels and the like. The reason is that the printing method obtains a colored image by an instantaneous chemical reaction due to heat,
This is because the device is small, the recording speed is fast, there is little noise and environmental pollution, and the cost is low. However, in a heat-sensitive recording method using a dye precursor or an acidic substance that is commonly used as a coloring component, the white paper portion is colored with an organic solvent such as toluene or methyl ethyl ketone, and it is also used as a plasticizer for an eraser or a synthetic resin such as vinyl chloride. There is a case where the colored portion disappears due to the existing dibutyl phthalate, dioctyl phthalate or the like or a hair styling material, or the colored portion disappears due to the rubbing of the wetted portion. In addition, when using a magic ink, a highlighter pen, etc., problems such as discoloration of the color development part and color development of the white paper part occur, or the sticking phenomenon between the thermal head and the heat-sensitive recording layer when developing the color or the residue on the thermal head. In some cases, defective coloring may occur due to the accumulation of. Furthermore, for labels, ATM / CD, etc., it is often printed on the surface layer,
Printability such as surface strength and ink adhesion is required.

Among these drawbacks, in order to improve the storage stability against organic solvents, chemicals, etc., an aromatic isocyanate is used instead of the recording method using a dye precursor and an acidic substance which are usually used in a thermosensitive recording layer as a color forming component. The heat-sensitive recording method using the coloring component of the imino compound has also come to be used.
(JP-A-58-38733, JP-A-58-104
959 publication)

In addition, a water-soluble high molecular polymer on the heat-sensitive recording layer,
Various proposals have been made to improve the above-mentioned drawbacks by providing a protective layer containing a water-dispersible polymer as a main component. (JP-A-55-95593, JP-A-57-188392)
JP-A-58-122892, JP-A-59
-1797, JP 59-45191, JP 60-115484, JP 62-4288.
No. 4, etc.).

However, even when these water-soluble high-molecular-weight polymers are provided in the protective layer, a small amount cannot provide sufficient chemical resistance, so that the amount of the protective layer needs to be increased. Satisfactory heat-sensitive recording sheet having drawbacks such as a decrease in coloration and unclearness of the color image, chemical resistance but poor water resistance, poor printability, and problems during thermal coloring. Was not obtained.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a heat-sensitive recording sheet having good printability, good matching with color-developing equipment and excellent whiteness, plasticizer resistance, chemical resistance and water resistance. To do.

[0007]

Means for Solving the Problems As a result of intensive studies to solve these problems, the present inventors have found that a protective layer of a heat-sensitive recording sheet contains a water-dispersible polymer as a main component and a higher fatty acid metal salt. By containing a water-soluble modified polyamine resin, preferably the higher fatty acid metal salt is zinc stearate, the water-soluble modified polyamine resin is a carboxyl modified polyamine resin, and the nitrogen content is 12 to 30% by weight. Resin is used.

More preferably, by using a polymer having a core-shell structure in which the water-dispersible polymer has a polymer latex as a core and a water-soluble vinyl polymer as a main component of a shell, printability, It has been found that a thermosensitive recording sheet having good color-matching device matching properties and improved storability such as chemical resistance can be obtained.

Although the reason is not clear, the thermal recording sheet containing the higher fatty acid metal salt in the protective layer has a poor affinity between the printing ink and the protective layer when printed after being left in a high humidity state. If you rub it with your fingernail, the ink will come off easily. Probably, when it is placed in a high humidity state, the affinity of the sheet surface with the ink becomes poor due to migration of the hydrophobic substance to the surface of the thermal recording sheet, etc.
It is expected that the addition of the water-soluble modified polyamine resin will suppress migration, and that a heat-sensitive recording sheet can be obtained in which the surface property hardly changes even after passing through a high humidity environment.

Especially, the nitrogen content is 1 by carboxyl modification.
The effect of the water-soluble modified polyamine resin of 2 to 30% by weight is great. When a highly viscous water-soluble polymer (for example, various polyvinyl alcohol, starch, etc.) is used for the protective layer,
Although it has the effect of suppressing migration, it becomes inferior in smearing suitability of the coating liquid, water resistance, chemical resistance, and matching property with color-developing equipment.

A water-dispersible polymer, particularly a polymer latex in the core portion and a water-soluble vinyl polymer in the shell portion, has a core-shell structure, and a relatively soft latex is used for the core portion. When a relatively hard polymer is used for the shell, the core has an effect of improving chemical resistance, plasticizer resistance, adhesive strength, and water resistance, and the shell has improved sticking resistance and resistance. Since it also has the effect of improving chemical resistance and plasticizer resistance, a good heat-sensitive recording sheet can be obtained. Furthermore, if the protective layer is composed of two or more layers, it is considered that the properties can be harmonized by properly using the polymers having a softening point within a specific range for the uppermost layer and the lower layer. In particular, if the softening point of the polymer used for the uppermost protective layer is low, sticking will occur during color development, and if it is too high, the adhesive strength will be poor and printability will be a problem. When the protective layer is one layer, a water-dispersible high molecular weight polymer having a softening point of 200 to 350 ° C., preferably a core-shell structure, can be used as a main component, and when the protective layer is two or more layers, it is the uppermost layer. As the main component of the above, a conventionally known water-dispersible polymer or water-soluble polymer having a softening point in the range of 200 to 350 ° C. can be used, but preferably the core used when the uppermost layer also has one layer -Use of a specific water-dispersible polymer having a shell structure improves plasticizer resistance, chemical resistance and the like.

Examples of the water-dispersible polymer or the polymer latex of the core used in the present invention include styrene-
Butadiene copolymer, methyl methacrylate-butadiene copolymer, methyl methacrylate-styrene-butadiene copolymer, acrylonitrile-butadiene copolymer, styrene polymer, isoprene polymer, butadiene polymer,
A vinyl acetate-acrylic acid ester copolymer, an acrylic acid ester polymer, a vinyl acetate-ethylene copolymer, a vinyl chloride polymer, a vinylidene chloride polymer and the like and derivatives thereof are used. As the shell part, the above-mentioned hydrophobic high molecular polymer can be used together with the water-soluble vinyl polymer. The following water-soluble vinyl monomers may be preliminarily copolymerized with the polymer latex used at the time of polymerization of the water-dispersible polymer having a core-shell structure, or may be used for polymerization of the shell part. I can.

Examples of the water-soluble vinyl monomer include acrylamide, methacrylamide, acrylic acid, methacrylic acid, dimethylaminoethyl methacrylate, dimethylaminopropyl methacrylamide and the like.

The water-dispersible polymer having a core-shell structure can be obtained by a conventionally known polymerization method. Examples thereof include radical polymerization using a peroxide such as ammonium persulfate and potassium persulfate, and a redox method performed by using a peroxide and a reducing agent such as sodium thiosulfate together.

The higher fatty acid metal salt for preventing sticking used in the present invention has a carbon number of 1 such as zinc stearate, calcium stearate, barium stearate, zinc palmitate and aluminum palmitate.
Metallic salts of 6 or more fatty acids are mentioned. The usage is
About 1% to 40% by weight of the total solid content of the protective layer is preferable.
If it is too large, the preservability such as the plasticizer resistance becomes poor.

The water-soluble modified polyamine resin used in the present invention includes carboxyl modified, hydroxyl modified,
Examples thereof include polyamine resins such as imino-modified, which are carboxyl-modified polyamines and have a nitrogen content of 12 to 30.
Weight percent is preferred. A 60 wt% aqueous solution having a B-type viscosity at 60 rpm of 25 ° C. of 50 cps to 500 cps is used. The amount used is from 1% of the total solid content of the protective layer to
It is 40% by weight. If it is too large, the effect of improving printability becomes small. The nitrogen content is measured by a total nitrogen analyzer.

In the protective layer of the heat-sensitive recording sheet of the present invention, in addition to the water-dispersible polymer, a conventionally used water-soluble polymer is used in combination to the extent that the effect of the present invention is not impaired. However, it is preferably about 30% by weight or less of the total protective layer. Other materials for the protective layer include kaolin, calcined kaolin, aluminum silicate, aluminum hydroxide,
Inorganic pigments such as calcium carbonate, silicon oxide, talc, magnesium carbonate and titanium oxide, organic pigments such as polystyrene, urea-formalin and polyacrylic, dialdehyde-based, epoxy-based, diglycidyl-based, dimethylol urea, ferric chloride , Metal salts such as zirconium salt, crosslinking agents such as ammonium chloride, waxes such as paraffin and polyethylene, defoaming agents, surfactants, and ultraviolet absorbers are appropriately added and used in combination.

The coating amount of the protective layer is adjusted so as to have almost no effect on the color developability, but generally 1 to 10 g /
m ^2, preferably separately 1 to 6 g / m ² in one layer or several layers applied.

As the colorless or light-colored dye precursor, the acidic substance, the aromatic isocyanate compound, the imino compound and the binder used in the heat-sensitive recording layer of the present invention, conventionally known ones are used.

Dye precursors include crystal violet lactone, 3-indolino-3-p-dimethylaminophenyl-6-dimethylaminophthalide, 3-diethylamino-7-chlorofluorane, 3-diethylamino-7-cyclohexylamino. Fluorane, 3-diethylamino-5-methyl-7-t-butylfluorane, 3-
Diethylamino-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7-p-butylanilinofluorane, 2- (N-phenyl-N-ethyl) aminofluorane, 3-diethylamino- 7-dibenzylaminofluorane, 3-cyclohexylamino-
6-chlorofluorane, 3-diethylamino-6-methyl-7-xylidinofluorane, 2-anilino-3-methyl-6- (N-ethyl-p-toluidino) fluorane, 3-pyrrolidino-6-methyl- 7-anilinofluorane, 3-pyrrolidino-7-cyclohexylaminofluorane, 3-piperidino-6-methyl-7-toluidinofluorane, 3-piperidino-6-methyl-7-anilinofluorane, 3 -(N-methylcyclohexylamino) -6-methyl-7-anilino) fluorane, 3-diethylamino-6-methyl-7-chlorofluorane, 3
-Dibutylamino-6-methyl-7-anilinofluorane is used.

As the acidic substance, 4,4'-isopropylidenediphenol, 4,4'-isopropylidenebis (2-chlorophenol), 4,4'-isopropylidenebis (2-tert-butylphenol), 4 ，
4'-Secondary butylidene diphenol, 4,4 '
-(1-Methyl-normalhexylidene) diphenol, 4-phenylphenol, 4-hydroxydiphenol, methyl-4-hydroxybenzoate, phenyl-4-hydroxybenzoate, 4-hydroxyacetophenone, salicylic acid anilide, 4,4 '-Cyclohexylidenediphenol, 4,4'-cyclohexylidenebis (2-methylphenol), 4,4'-benzylidenediphenol, 4,4'-thiobis (6-tercarybutyl-3-methylphenol) ,, 4,4'-isopropylidene bis (2-methylphenol), 4,4 '
-Ethylenebis (2-methylphenol), 4,4'-
Cyclohexylidene bis (2-isopropylphenol), 2,2'-dihydroxydiphenyl, 2,2'-
Methylenebis (4-chlorophenol), 2,2'-methylenebis (4-methyl-6-t-butylphenol), 1,1'-bis (4-hydroxyphenol)-
Cyclohexane, 2,2'-bis (4'-hydroxyphenyl) propane, novolac type phenol resin, halogenated novolac type phenol resin, α-naphthol,
β-naphthol, 3,5-di-t-butylsalicylic acid,
3,5-di-α-methylbenzylsalicylic acid, 3-methyl-5-t-butylsalicylic acid, monoanilide paraethoxybenzoic acid phthalate, bis (4-hydroxyphenyl) sulfone, 4-hydroxy-4′-isopropyloxy Diphenyl sulfone, di- (3-allyl-4-
Hydroxyphenyl) sulfone, 2,4′-dihydroxydiphenylsulfone, parabenzyloxybenzoic acid, parahydroxybenzoic acid benzyl ester are used.

As the aromatic isocyanate compound,
2,6-dichlorophenyl isocyanate, p-chlorophenyl isocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, 1,
3-dimethylbenzene-4,6-diisocyanate,
1,4-dimethylbenzene-2,5-diisocyanate, 1-methoxybenzene-2,4-diisocyanate, 1-methoxybenzene-2,5-diisocyanate, 1-ethoxybenzene-2,4-diisocyanate, diphenylether- 4,4'-diisocyanate, naphthalene-1,4-diisocyanate, naphthalene-1,5-diisocyanate, naphthalene-1,3
7-triisocyanate, biphenyl-2,4,4'-
There are triisocyanate, 4,4 ′, 4 ″ -triisocyanate-2,5-dimethoxytriphenylamine, p-dimethylaminophenylisocyanate, etc. These isocyanate groups may be phenols, lactams, oximes as necessary. The compound may be used in the form of a so-called blocked isocyanate or a diisocyanate which is an addition compound with, etc., but when all the isocyanate groups are blocked, the effect may not be exhibited.

The imino compounds include 3-iminoindoline-1-one, 3-imino-4,5,6,7-tetrachloroisoindoline-1-one, 3-imino-4,
5,6,7-Tetrabromoindoline-1-one, 3-
Imino-4,5,6,7-tetrafluoroisoindoline-1-one, 3-imino-5,6-dichloroisoindoline-1-one, 3-imino-4,5,7-trichloro-6-methoxy -Isoindoline-1-one, 1-ethoxy-3-iminoisoindoline, 1,3-diiminoisoindoline, 1,3-diimino-4,5,6,7-
Tetrachloroindoline, 1,3-Diimino-6-methoxyisoindoline, 1,3-Diimino-6-cyanoisoindoline, 1,3-Diimino-4,7-dithiazolyl-5,5,6,6-tetrahiu Droisoindoline,
1-iminonaphthalimide, 1-iminodiphenimide, 1- (5 ', 6'-dichlorobenzothiazolyl-
2'-imino) -3-iminoisoindoline, 1-
(6'-methylbenzothiazolyl-2'-imino) -3
-Iminoisoindoline, 3-imino-1-sulfobenzoic acid imide, 3-imino-1-sulfo-6-chlorobenzoic acid imide, 3-imino-1-sulfo-5-bromonaphthoic acid imide, 3-imino-2 -Methyl-4,5,6
7-tetrachloroisoindoline-1-one and the like.

For the purpose of improving sensitivity, the melting point is 80 to 14
Organic substances at about 0 ° C., for example, benzoic acid or terephthalic acid esters, naphthalene sulfonic acid esters, naphthyl ether derivatives, anthryl ether derivatives, aliphatic ethers, and other sensitizers such as phenanthrene and fluorene can be used. .

Examples of the binder include starches such as oxidized starch, phosphoric acid esterified starch and etherified starch, hydroxyethyl cellulose, methylene cellulose, polyvinyl alcohol, styrene-acryl, polyacrylamide, carboxymethyl cellulose, gum arabic and casein. Water-soluble binders or derivatives thereof, and latexes such as styrene-butadiene latex are used.

Examples of pigments used in the heat-sensitive recording layer include diatomaceous earth, talc, kaolin, calcined kaolin, calcium carbonate, magnesium carbonate, titanium oxide, zinc oxide, silicon oxide, aluminum hydroxide and urea-formalin resin. . Other additives include higher fatty acid metal salts such as zinc stearate and calcium stearate,
Waxes such as paraffin, oxidized paraffin, polyethylene and polyethylene oxide, wetting agents such as dioctyl sulfosuccinate, UV absorbers such as benzophenone and benzotriazole, surfactants, fluorescent dyes and the like are used.

When an intermediate layer is provided between the support of the present invention and the heat-sensitive recording layer for the purpose of improving color developability, an inorganic or organic pigment used in the heat-sensitive recording layer, a hollow organic pigment or a binder is used. . In addition, a dispersant for pigments, a viscosity modifier, an antifoaming agent and the like are also added as appropriate.

As the support used in the present invention, paper is used, but synthetic paper, metal foil, laminated paper of polyethylene or the like, film of polyethylene terephthalate or the like may be used alone or in combination. . As an apparatus used for coating the intermediate layer, the heat-sensitive recording layer and the protective layer, an air knife coater, a gravure coater, a roll coater, a rod coater, a curtain coater, a die coater, a lip coater, a blade coater and the like are used. In particular, when an intermediate layer is provided below the heat-sensitive recording layer, a size press device, a gate roll device, etc. used in the paper making process of paper are also used. Also, printing methods such as offset and silk screen are used. Further, in order to improve the surface smoothness of the coated product, machine calender, super calender, gloss calender, brushing, etc. are used.

[0029]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.
The parts and% in the examples mean parts by weight and% by weight.

Example 1 [Preparation of coating liquid for thermosensitive recording layer] Liquid (A) 3-dibutylamino-6-methyl-7-anilinofluorane (solid) 12 parts 10% aqueous solution of polyvinyl alcohol (Nippon Gosei Kagaku KK: NM11 ) (Solid 1.8 parts) 18 parts Water 30 parts (B) Liquid 4,4'-isopropylidenediphenol (solid) 40 parts 2-Benzyloxynaphthalene (solid) 40 parts Zinc stearate (solid) 20 parts 10 % Polyvinyl alcohol aqueous solution (NM11) (solid 5 parts) 50 parts water 100 parts

The liquids (A) and (B) were separately dispersed with a sand grinder until the average particle size became about 2 μ, and the heat-sensitive layer coating liquid was prepared by the following formulation. Calcium carbonate (manufactured by Shiraishi Industry, Brt15) (solid) 8 parts (B) liquid 30 parts 10% polyvinyl alcohol aqueous solution (NM11) 40 parts (A) liquid 12 parts water 100 parts

[Preparation of protective layer coating liquid (C)] Acrylonitrile was polymerized mainly by acrylamide in the presence of a polymer latex of methyl methacrylate-styrene-butadiene (glass transition temperature, 10 ° C) to obtain high water dispersibility. A molecular polymer (L) was obtained. (The softening point of the polymer (L) is 235 ° C.).
The protective layer coating liquid (C) was prepared with the following formulation. 20% polymer (L) aqueous dispersion 100 parts Calcium carbonate (Brt15) (solid) 2 parts 20% zinc stearate dispersion 5 parts 70% modified polyamine resin aqueous solution (PA-622 manufactured by Japan PMC, nitrogen content is 22% by weight, 60% of 25% liquid at 25 ° C, 60 rpm B-type viscosity is 80 cps) 5 parts Epoxy cross-linking agent (solid content 20%) 2 parts Water 50 parts A thermosensitive recording layer coating liquid on one side of a paper having a basis weight of 60 g / m ^2. 6 g / m ² solid coating, 3 g solid after coating the protective layer coating liquid (C)
/ M ² coating and drying and super calendar processing to obtain a heat-sensitive recording sheet of the present invention.

Example 2 [Preparation of coating solution (D) for protective layer] Methyl methacrylate-acrylonitrile water-dispersible polymer (M, softening point = 2
The protective layer coating liquid (D) was prepared by the following formulation using 20 ° C.). 20% polymer (M) aqueous dispersion 100 parts Epoxy cross-linking agent (solid content 20%) 2 parts Calcium carbonate (Brt15) (solid) 2 parts 20% zinc stearate dispersion 5 parts 70% modified polyamine resin aqueous solution ( PA-622 manufactured by Japan PMC Co., Ltd. 8 parts Water 50 parts As in Example 1, the thermosensitive recording layer coating liquid was solid at 6 g / m 2.
^{After 2} coatings were dried, the protective layer coating liquid (D) was applied as a solid at 3 g / m ^{2 and} dried, and then supercalendered to obtain a heat-sensitive recording sheet of the present invention.

Example 3 A thermosensitive recording sheet of the present invention was obtained in the same manner as in Example 1 except that calcium stearate was used instead of zinc stearate used in the protective layer coating liquid (C).

Example 4 Instead of PA-622 which is the water-soluble modified polyamine resin used in the coating solution (C) for protective layer in Example 1, PA-625 (manufactured by Japan PMC, nitrogen content 13% by weight, 60%). A thermosensitive recording sheet of the present invention was obtained in the same manner except that a 25 rpm liquid of 60 rpm B type viscosity of 300 cps) was used.

Example 5 After providing a heat-sensitive recording layer in the same manner as in Example 1, 1.5 g / m ² of the following protective layer coating liquid (E) was applied and dried to give the protective layer coating liquid (C) 1 After the coating was dried at 0.5 g / m ^2, it was subjected to a super calendar treatment to obtain a heat-sensitive recording sheet of the present invention. [Preparation of coating liquid (E) for protective layer] 10% aqueous solution of polyvinyl alcohol (NM-11, manufactured by Nippon Synthetic Chemical Industry) 100 parts Calcium carbonate (Brt15) (solid) 5 parts Water 20 parts

Example 6 A thermosensitive recording sheet was obtained in the same manner as in Example 5 except that the polymer (L) was used in place of polyvinyl alcohol in the preparation of the lower protective layer coating liquid (E) in Example 5. .

Comparative Example 1 A thermosensitive recording sheet was obtained in the same manner except that the water-soluble modified polyamine resin of the protective layer coating liquid (C) of Example 1 was omitted.

Comparative Example 2 A thermosensitive recording sheet was obtained in the same manner as in Example 1 except that the zinc stearate of the protective layer coating liquid (C) of Example 1 was omitted.

Comparative Example 3 A thermosensitive recording sheet was obtained in the same manner except that polyvinyl alcohol (NM-11) was used in place of the polymer (L) in the production of the protective layer (C) of Example 1.

The thermal recording sheets obtained in Examples 1 to 6 and Comparative Examples 1 to 3 were evaluated by the following methods. The evaluation results are shown in Table 1. The softening point was measured by a differential thermal analyzer and a differential scanning calorimeter. The unit in the table is ° C.

(Thermal Coloring Property) Using a thermal tester manufactured by Okura Electric Co., Ltd., a thermal head having a head resistance of 2800 ohms was used to develop color with a pulse width of 1.2 msec, and the density was measured with a Macbeth type reflection densitometer. The higher the number, the higher the concentration.

(Printability) A thermosensitive recording sheet was placed at 40 ° C. for 9 minutes.
After being left in an environment of 0% RH for 24 hours, dried, and then printed by an RI printer (manufactured by Meisei Seisakusho) using an ultraviolet curable ink and cured, the surface was scratched with a metal spatula to evaluate the degree of peeling.

(Stickability) Sound at the time of thermal color development evaluation with a color tester manufactured by Okura Electric Co., Ltd. and white spots in the colored part,
It was evaluated by the bleeding of the color development part. ○: No sticking, △: Some sticking but can be used, ×: Sticking is too large to use

(Plasticizer resistance) Three sheets of wrap film are placed on a sheet which has been subjected to heat color development, and a load is applied to the sheet at 50 ° C. and 90% R.
Leave for 24 hours under the condition of H. The colored portion after the treatment was visually evaluated. ○: No difference before and after treatment, △: Some difference before and after treatment, ×: Large difference before and after treatment

(Water resistance) Heat-color-developed sheet was immersed in pure water at room temperature for 3 minutes, and the white paper part and the color-developed part were rubbed three times with fingers to decrease the color density and to visually check the color density when the white paper part was colored. Evaluated by. ◯: Almost no decrease in density, Δ: Can be used although there is some decrease in density, ×: Significant decrease in density.

[0047]

[Table 1]

[0048]

The heat-sensitive recording sheet of the present invention has good printability, good matching with color-developing equipment, and excellent storage stability such as plasticizer resistance and water resistance.

Claims (5)

[Claims] 1. A thermosensitive recording sheet in which a thermosensitive recording layer and a protective layer are sequentially laminated on a support, wherein the protective layer composition comprises
A heat-sensitive recording sheet comprising a water-dispersible polymer as a main component and a higher fatty acid metal salt and a water-soluble modified polyamine resin. 2. The heat-sensitive recording sheet according to claim 1, wherein the higher fatty acid metal salt is zinc stearate. 3. The heat-sensitive recording sheet according to claim 1, wherein the water-soluble modified polyamine resin is a carboxyl-modified polyamine resin. 4. The water-soluble modified polyamine resin is 12 to 3
The heat-sensitive recording sheet according to claim 1, which is a resin having a nitrogen content of 0% by weight. 5. The water-dispersible polymer is a polymer having a core-shell structure in which a polymer latex is a core and a water-soluble vinyl polymer is a main component of a shell. The heat-sensitive recording sheet according to any one of 1 to 4.