JPH05318928A - Thermal recording material - Google Patents

Abstract

PURPOSE:To provide a thermal recording material having high sensitivity and good dot reproducibility and reduced in the fading of an image due to a chemical agent such as a plasticizer. CONSTITUTION:In a thermal recording material wherein an undercoat layer, a thermal color forming layer containing a leuco dye and a developer allowing the leuco dye to form a color at the time of heating as main components and an overcoat layer are successively laminated on a support, the undercoat layer contains non-foamable plastic hollow fine particles with a mean particle size of 2-10mum and hollowness of 90% or more and the overcoat layer contains aluminum hydroxide with a mean particle size of 0.1-1.5mum.

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 material, and more specifically, it has a high dynamic sensitivity, good dot reproducibility, and an underlayer, a heat-sensitive color-developing layer, and an overlayer which are sequentially laminated on a support. The present invention relates to a heat-sensitive recording material that causes less fading of an image with respect to chemicals such as a plasticizer.

[0002]

2. Description of the Related Art Recently, various recording materials have been researched, developed, and put into practical use in the information recording field in response to social demands such as diversification and increase of information, resource saving, and pollution-free. Above all, the heat-sensitive recording material was further obtained, (1) a color image was recorded by simply heating and a complicated developing process was not required, and (2) recording was possible using a relatively simple and compact device. The recording material is easy to handle and the maintenance cost is low. (3) In many cases, paper is used as the support. In this case, not only the support cost is low, but also the recording material obtained is Because it has the advantage that it feels like plain paper, it is used in the fields of computer output, printers such as calculators, low and high-speed facsimile fields, automatic ticket vending machines, thermal copying fields, and POS system label fields. Oite widely used.

The thermal recording material is usually paper, synthetic paper,
Alternatively, it is produced by coating a support such as a synthetic resin film with a thermosensitive color developing layer liquid containing a color-forming component capable of causing a color-developing reaction by heating and drying it. The thermosensitive recording material thus obtained A colored image is formed by heating with a hot pen or a thermal head. A conventional example of such a thermal recording material is, for example, Japanese Patent Publication No. 43-41.
Examples of the heat-sensitive recording materials disclosed in JP-B No. 60 or JP-B No. 45-14039 include such conventional heat-sensitive recording materials, which have slow thermal responsiveness and cannot provide sufficient color density during high-speed recording. It was

As a method for improving such drawbacks, for example, JP-B-49-38424 discloses a nitrogen-containing compound such as acetamide, stearamide, m-nitroaniline and dinitrile phthalate in JP-A-52-106746. Acetoacetic acid anilide is disclosed in JP-A-53-11036, N, N-diphenylamine derivative, benzamide derivative and carbazole derivative are disclosed in JP-A-53-11036, and alkylated biphenyl and biphenylalkane are disclosed in JP-A-53-39139. Japanese Patent Application Laid-Open No. 56-144193 discloses a method for increasing the speed and increasing the sensitivity by adding a p-hydroxybenzoic acid ester derivative, respectively, but any method is sufficiently satisfactory. The current situation is that the results have not been satisfactory. As another method, a method of lowering the melting point and increasing the sensitivity by making a leuco dye having a high melting point amorphous is disclosed in JP-A-56-164890. However, since the surface of the amorphized dye is activated and is highly reactive, liquid fog or background fog of the heat-sensitive color-developing coating liquid or the heat-sensitive recording material is large, resulting in poor whiteness.

Therefore, in order to suppress the background fog and enhance the dynamic color development sensitivity, the thermal conductivity of the support is set to 0.04 Kcal / mh ° C.
In the following (JP-A-55-164192), or by providing a layer containing fine hollow spherical particles as a main component on a support (JP-A-59-5093 and JP-A-59-225987). It is proposed.

However, the heat-sensitive recording materials proposed in the above-mentioned JP-A-55-164192, JP-A-59-5093, etc. have insufficient foaming property and the wall material is not flexible, or the heat insulation In some cases, the properties are not sufficient, or the contact between the thermal head and the heat-sensitive recording material is insufficient, and so satisfactory results have not been obtained. Further, in order to improve the fading of the image with a chemical such as a plasticizer, which is one of the drawbacks of the thermosensitive recording material, an overlayer may be provided on the thermosensitive coloring layer, but the kinetic sensitivity is lowered or the dot is reduced. There is a problem that the reproducibility of is deteriorated.

[0007]

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a heat-sensitive recording material having high sensitivity and good dot reproducibility, and less fading of an image with a chemical such as a plasticizer.

[0008]

The above object of the present invention is to:
In a heat-sensitive recording material comprising a support, an under layer, a leuco dye, and a heat-sensitive color-developing layer whose main component is a color developer that develops a color when the leuco dye is heated, and an over-layer, which are successively laminated, in which the under layer has an average grain size. Diameter 2-10 μm, hollowness 90
% Of non-expandable plastic hollow particles, and the above overlayer was achieved by a heat-sensitive recording material containing aluminum hydroxide having an average particle size of 0.1 to 1.5 μm.
That is, the thermosensitive recording material of the present invention has high dynamic color development sensitivity, good dot reproducibility, and less fading of an image with a chemical such as a plasticizer because of the above-mentioned constitution.

The non-expandable plastic hollow fine particles having an average particle diameter and hollowness of 2 to 10 μm on average and a hollowness of 90% or more have high dynamic sensitivity and good dot reproducibility.

More specifically, in this case, the non-foamable plastic hollow particles in the under layer act as low density hollow particles, that is, low thermal conductivity hollow particles, and have the effect of making the entire under layer a heat insulating layer. Therefore, by providing the under layer, the heat energy applied for image recording can be effectively utilized in the heat-sensitive color forming layer, and a heat-sensitive recording material having high heat sensitivity can be obtained. In particular, non-foaming plastic hollow fine particles having an average of 2 to 10 μm and a hollowness of 90% or more have a large effect.

Further, the average particle diameter in the overlayer is 0.1 to
Since 1.5 μm of aluminum hydroxide exists as fine particles, it has the effect of making the entire overlayer a highly smooth layer and a high barrier layer. Therefore, by providing the over layer, the heat sensitivity is high due to the high smoothness and the high barrier property, the dot reproducibility is good, and the image fading by the chemicals such as the plasticizer is small.

In the present invention, the under layer containing the non-expandable plastic hollow fine particles is provided. In this case, the hollow fine particles have a shell made of a thermoplastic material, and the inside is liquid or gas, and even if heated. Although not foamed, at least a part of the inside of the hollow particles is hollow fine particles in the state of being formed as a heat-sensitive recording material by a method such as drying. The average particle size is 2 to 10 μm, and the hollowness is 90% or more. In addition,
The hollowness referred to here is the ratio of the outer diameter to the inner diameter of the hollow particles and is represented by the following equation.

[0013]

[Equation 1] Hollowness = (hollow particle inner diameter / hollow particle outer diameter)
× 100 (%)

As the thermoplastic resin which is the shell of the non-expandable plastic hollow fine particles, polystyrene, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, polyacrylic acid ester, polyacrylonitrile, polybutadiene or a copolymer thereof is used. Can be mentioned.

The aluminum hydroxide used in the overlayer of the present invention has an average particle size of 0.1 to 1.5 μm. The proportion of the binder resin and aluminum hydroxide used is 0.3 to 3 parts by weight, preferably 0.5 to 2.
5 parts by weight, the amount of aluminum hydroxide is 0.5-3.5 g / m ²
Is.

When forming the under layer of the present invention, the binder resin is appropriately selected from conventionally known water-soluble polymers and / or aqueous polymer emulsions. Specific examples thereof include water-soluble polymer resins such as polyvinyl alcohol, starch and derivatives thereof, methoxycellulose, hydroxyethylcellulose, carboxymethylcellulose, methylcellulose, cellulose derivatives such as ethylcellulose, sodium polyacrylate, polyvinylpyrrolidone, and acrylamide. / Acrylic acid ester copolymer, acrylamide / acrylic acid ester / methacrylic acid terpolymer, styrene / maleic anhydride copolymer alkali salt, isobutylene / maleic anhydride copolymer alkali salt, polyacrylamide, sodium alginate, Examples include gelatin and casein. As the aqueous polymer emulsion, a styrene / butadiene copolymer,
Examples include latexes such as styrene / butadiene / acrylic copolymers, emulsions such as vinyl acetate resins, vinyl acetate / acrylic copolymers, styrene / acrylic ester copolymers, acrylic ester resins and polyurethane resins. ..

In the undercoat layer of the present invention, together with the plastic spherical hollow particles and the binder resin, auxiliary additives, such as a filler and a heat fusible agent, which are commonly used in this type of heat-sensitive recording material, may be added if necessary. It is possible to use together a substance and a surfactant. In this case, as the specific examples of the filler and the heat-fusible substance, various ones mentioned below in connection with the components of the thermosensitive color developing layer can be mentioned.

Further, in order to make the surface of the undercoat layer formed on the support as described above smoother, the flat surface may be smoothed by a calendering treatment after the formation of the undercoat layer.

The leuco dyes used in the thermosensitive coloring layer of the present invention may be used alone or in admixture of two or more, and as such leuco dyes, those applied to this type of thermosensitive recording material are arbitrary. And leuco compounds of dyes such as triphenylmethane type, fluorane type, phenothiazine type, auramine type, spiropyran type and indolinophtalide type dyes are preferably used. Specific examples of such leuco dyes include those shown below.

3,3-bis (p-dimethylaminophenyl) -phthalide, 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide (also known as crystal violet lactone), 3,3-bis ( p-Dimethylaminophenyl) -6-diethylaminophthalide, 3,3-bis (p-dimethylaminophenyl) -6-chlorophthalide, 3,3bis (p-dibutylaminophenyl) phthalide, 3-cyclohexylamino-6 -Chlorofluorane, 3-dimethylamino-5,7-dimethylfluorane, 3
-Diethylamino-7-chlorofluorane, 3-diethylamino-7-methylfluorane, 3-diethylamino-
7,8-benzfluorane, 3-diethylamino-6-methyl-7-chlorofluorane, 3- (Np-tolyl-N-ethylamino) -6-methyl-7-anilinofluorane,
3-pyrrolidino-6-methyl-7-anilinofluorane, 2
-{N- (3'-trifluoromethylphenyl) amino}
-6-diethylaminofluorane, 2- {3,6-bis (diethylamino) -9- (o-chloroanilino) xanthyl benzoate lactam}, 3-diethylamino-6-methyl-7
-(M-trichloromethylanilino) fluorane, 3-diethylamino-7- (o-chloroanilino) fluorane,
3-dibutylamino-7- (o-chloroanilino) fluorane, 3-N-methyl-N-amylamino-6-methyl-7
-Anilinofluorane, 3-N-methyl-N-cyclohexylamino-6-methyl-7-anilinofluorane, 3-
Diethylamino-6-methyl-7-anilinofluorane,
3- (N, N-diethylamino) -5-methyl-7- (N, N
-Dibenzylamino) fluorane, benzoylleuco methylene bull-, 6'-chloro-8'-methoxy-benzoindolino-pyrrilospirane, 6'-bromo-3'-methoxy-
Benzindolino-pyrrilospirane, 3- (2'-hydroxy-4'-dimethylaminophenyl) -3- (2'-methoxy-5'-chlorophenyl) phthalide, 3- (2'-hydroxy-4'-dimethylamino Phenyl) -3- (2'-methoxy-5'-nitrophenyl) phthalide, 3- (2'-hydroxy-4'-diethylaminophenyl) -3- (2'-
Methoxy-5'-methylphenyl) phthalide, 3- (2'-
Methoxy-4'-dimethylaminophenyl) -3- (2'-
Hydroxy-4'-chloro-5'-methylphenyl) phthalide, 3-N-ethyl-N-tetrahydrofurfurylamino-6-methyl-7-anilinofluorane, 3-N-ethyl-
N-(-2-ethoxypropyl) amino-6-methyl-7-
Anilinofluorane, 3- (N-methyl-N-isobutylamino) -6-methyl-7-anilinofluorane, 3-morpholino-7- (N-propyl-trifluoromethylanilino) fluorane, 3- Pyrrolidino-7-trifluoromethylanilinofluorane, 3-diethylamino-5-chloro-7- (N-benzyl-trifluoromethylanilino)
Fluorane, 3-pyrrolidino-7- (di-p-chlorophenyl) methylaminofluorane, 3-diethylamino-5
-Chloro-7- (α-phenylethylamino) fluorane, 3- (N-ethyl-p-toluidino) -7- (α-phenylethylamino) fluorane, 3-diethylamino-7
-(O-Methoxycarbonylphenylamino) fluorane, 3-diethylamino-5-methyl-7- (α-phenylethylamino) fluorane, 3-diethylamino-7-
Piperidinofluorane, 2-chloro-3- (N-methyltoluidino) -7- (pn-butylanilino) fluorane, 3-di-n-butylamino-6-methyl-7-anilinofluorane, 3 , 6-Bis (dimethylamino) fluorene spiro (9,3 ')-6-dimethylaminophthalide, 3- (N-benzyl-N-cyclohexylamino) -5,6-benzo-7
-Α-naphthylamino-4'-bromofluorane, 3-diethylamino-6-chloro-7-anilinofluorane, 3
-Diethylamino-6-methyl-7-mesitidino-4 ', 5'
-Benzofluorane, 3-N-methyl-N-isopropylamino-6-methyl-7-anilinofluorane, 3- (N-
Ethyl-N-isoamylamino) -6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7-
(2 ', 4'-Dimethylanilino) fluorane etc.

As the color developer used in the thermosensitive color developing layer of the present invention, various electron-accepting compounds that cause the leuco dye to develop color upon contact, or oxidizing agents are applied. Such a material is conventionally known, and specific examples thereof include the following.

4,4'-isopropylidene bisphenol,
4,4'-isopropylidene bis (o-methylphenol),
4,4'-Secondary butylidene bisphenol 4,4'-isopropylidene bis (2-tert-butylphenol), zinc p-nitrobenzoate, 1,3,5-tris (4
-Tert-butyl-3-hydroxy-2,6-dimethylbenzyl) isocyanuric acid, 2,2- (3,4-dihydroxydiphenyl) propane, bis (4-hydroxy-3-methylphenyl) sulfide, 4- [β -(p-Methoxyphenoxy) ethoxy] salicylic acid, 1,7-bis (4-hydroxyphenylthio) -3,5-dioxaheptane, phthalic acid monobenzyl ester monocarboxylic acid, 4,4'-cyclohexylidenepheno -L, 4,4'-isopropylidene bis (2-chlorophen-
), 2,2'-methylenebis (4-methyl-6-tert-butylphenol), 2,2'-methylenebis (4-ethyl-6)
-Tert-butylphenol), 4,4'-butylidenebis (6-tert-butyl-2-methyl) phenol,
1,1,3-Tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 1,1,3-Tris (2-methyl-4-)
Hydroxy-5-cyclohexylphenyl) butane, 4,4 '
-Thiobis (6-tert-butyl-2-methyl) phenol, 4,4'-diphenolsulfone, 4-isopropoxy
-4'-hydroxydiphenyl sulfone, 4-benzyloxy-
4'-hydroxydiphenyl sulfone, 4,4'-diphenol sulfoxide, isopropyl P-hydroxybenzoate,
Benzyl P-hydroxybenzoate, benzyl protocatechuate, stearyl gallate, lauryl gallate, octyl gallate, 1,3-bis (4-hydroxyphenylthio)-
Propane, 1,3-bis (4-hydroxyphenylthio) -2-
Hydroxypropane, N, N'-diphenylthiourea, N,
N'-di (m-chlorophenyl) thiourea, salicylanilide, 5-chloro-salicylanilide, bis (4-hydroxyphenyl) acetic acid methyl ester, bis (4-hydroxyphenyl) acetic acid benzyl ester, 1,3-bis ( 4-hydroxycumyl) benzene, 1,4-bis (4-hydroxycumyl)
Benzene, 2,4'-diphenol sulfone, 2,2'-diallyl
-4,4'-diphenolsulfone, 3,4-dihydroxy-4'-methyldiphenylsulfone, zinc 1-acetyloxy-2-naphthoate, zinc 2-acetyloxy-1-naphthoate, 2-acetyloxy- Zinc 3-naphthoate, α, α-bis (4-hydroxyphenyl) -α-methyltoluene, zinc thiocyanate antipyrine complex, tetrabromobisphenol A, tetrabromobisphenol S 4,4′-thiobis (2-methylphenol ), 4,4'-thiobis
(2-chlorophenol) etc.

In the heat-sensitive color developing layer of the present invention, various conventional binder resins can be appropriately used for coating the above leuco base and the color developer on the undercoat layer. Are the same as those exemplified in the above undercoat layer coating.

In the heat-sensitive color developing layer of the present invention, the above-mentioned leuco dye and developer may be added, if necessary, and further auxiliary additives commonly used in heat-sensitive recording materials of this type, such as pigments, heat-soluble substances and interfaces. An activator or the like can be used in combination. In this case, examples of the pigment include calcium carbonate, silica, zinc oxide, titanium oxide, aluminum hydroxide, zinc hydroxide, barium sulfate, clay, talc, inorganic fine powder such as surface-treated calcium and silica, and urea. -Organic fine powders such as formalin resin, styrene / methacrylic acid copolymer, and polystyrene resin can be mentioned. Examples of the heat-fusible substance include higher fatty acids or esters, amides or metal salts thereof, various waxes, condensates of aromatic carboxylic acids and amines, benzoic acid phenyl esters, higher linear glycols. , 3,4-epoxy-dialkyl hexahydrophthalate, higher ketones, other heat-fusible organic compounds, etc.
One having a melting point of about 200 ° C is mentioned.

In the present invention, a layer containing a pigment, a binder resin, a heat-soluble substance or the like may be provided as another intermediate layer between the under layer and the thermosensitive coloring layer, if necessary. In this case, specific examples of the pigment, the binder resin, and the heat-soluble substance include those similar to those exemplified in connection with the thermosensitive coloring layer or the underlayer.

Further, the present invention is characterized in that the overlayer contains aluminum hydroxide.
A pigment other than aluminum hydroxide having an average particle diameter of 0.1 to 0.5 μm can be used in combination therewith, and a binder resin, a thermoplastic substance and the like are further contained. In this case, the pigment,
Specific examples of the binder resin and the thermoplastic substance include the same as those exemplified in connection with the thermosensitive coloring layer or the underlayer.

The heat-sensitive recording material of the present invention is produced, for example, by coating the above-mentioned coating liquid for forming each layer on a suitable support such as paper, synthetic paper, plastic film and drying, and various heat-sensitive recording fields. Applied to.

[0028]

EXAMPLES Next, the present invention will be described in more detail by way of examples. The parts and% shown below are based on weight.

Example 1 [Solution A] 20 parts of 3- (N-methyl-3-N-cyclohexyl) amino 6-methyl-7-anilinofluorane Polyvinyl alcohol 10% aqueous solution 20 parts Water 60 parts

[Solution B] 1,5 bis- (4-hydroxyphenylthio) -3-oxapentane 10 parts Polyvinyl alcohol 10% aqueous solution 25 parts Calcium carbonate 15 parts Water 60 parts

The mixture consisting of the above composition was dispersed using a sand mill so that the average particle diameter was 2 μm or less and 2.5 μm or less, to prepare [solution A] and [solution B]. [Liquid C] Aluminum hydroxide powder 6 parts (manufactured by Showa Denko KK; Hydilite, average particle size 0.6 μm) Polyvinyl alcohol 10% aqueous solution 40 parts Zinc stearate 0.3 parts Water 44.7 parts Was used to disperse and prepare [C liquid].

[Liquid D] Micro hollow particles (copolymer resin mainly composed of vinylidene chloride and 30 parts of acrylonitol) (solid content concentration 32%, average particle size 5 μm, hollowness 92%) Styrene / butadiene copolymer latex 10 parts (solid concentration 47.5%) Water 60 parts

A mixture having the above composition was stirred and dispersed to prepare an under layer forming liquid, which was prepared with a commercially available high quality paper (basis weight 52
The under layer coated paper was obtained by coating and drying on a surface of g / m ² ) so that the weight after drying was 5 g / m ² .

Next, the above-mentioned [solution A] and [solution B] are mixed and stirred in a weight ratio of 1:10 to prepare a thermosensitive color forming layer-forming liquid, which is dried on the surface of the underlayer coated paper. The coating amount was adjusted to 5 g / m ² and dried to obtain a thermosensitive coloring layer-coated paper.

Next, the above [C liquid] is applied to the surface of the above-mentioned thermosensitive color-developing layer-coated paper so as to have a dry amount of 2 g / m ² and dried to form an overlayer, and then the peck degree is 2000 to 30.
Supercalendering was performed for 00 seconds to obtain a heat-sensitive recording material of the present invention.

Example 2 Instead of the fine hollow particle dispersion in [D liquid] of Example 1, another fine hollow particle dispersion (copolymer resin mainly containing liquefied vinylidene and acrylonitrile; solid content concentration 30%) A heat-sensitive recording material of the present invention was obtained in the same manner as in Example 1 except that the average particle diameter was 9 μm and the hollowness was 93%).

Example 3 An aluminum hydroxide powder having an average particle diameter of 0.35 μm (manufactured by Nippon Light Metal Co., Ltd., B-700) was used in place of the aluminum hydroxide powder in [C liquid] of Example 1. A thermal recording material of the present invention was obtained in the same manner as in Example 1.

Comparative Example 1 Instead of the fine hollow particles in [D liquid] of Example 1,
The thermosensitive recording of the present invention was carried out in the same manner as in Example 1 except that fine hollow particles having a hollowness of 75% and an average particle diameter of 0.4 μm (Rohm and Haas Co .; OP-62, solid content concentration 37.5%) were used. Got the material.

Comparative Example 2 Instead of the aluminum hydroxide powder in [C liquid] of Example 1, aluminum hydroxide powder having an average particle diameter of 8.0 μm (Showa Denko KK; Hydilite, H-32) was used. A heat-sensitive recording material for comparison was obtained in the same manner as in Example 1 except that it was used.

Comparative Example 3 Instead of the fine hollow particles in [D liquid] of Example 1,
Plastic spherical non-hollow particles (Mitsui Toatsu Co., Ltd .; SPMM-H
A thermal recording material for comparison was obtained in the same manner as in Example 1 except that S and solid content concentration of 47%) were used.

Comparative Example 4 Example 4 was repeated except that kaolin powder having an average particle diameter of 0.8 μm (Georgia Kaolin Co .; Hydra Sparse) was used in place of the aluminum hydroxide powder in [C liquid] of Example 1. 1
A thermal recording material for comparison was obtained in the same manner as in.

With respect to each of the heat-sensitive recording materials obtained as described above, the fading of images in dynamic color development sensitivity, dot reproducibility and plasticity was evaluated by the following test methods. The results are shown in Table 1.

Dynamic color density: In a thermal printing experimental device having a thin film head manufactured by Matsushita Electronic Components Co., Ltd., head power 0.45 w / dot, 1 line recording time 20 msec / l, scanning line density 8 × 3.8.
Pulse width 0.3, 0.4, 0.5 and 0.6 ms under 5 dots / mm condition
Print with ec, and print the density with Macbeth Densitometer RD-914
It was measured at. Dot reproducibility: The dot reproducibility of the image used in the dynamic color density test method was visually evaluated. ◎ Very good ○ Good △ Normal × Poor Plasticizer test: 150 ° C using a thermal inclinometer with a built-in thermal head (manufactured by Toyo Seiki), crimping time 1.0 second, crimping pressure 2kg
/ cm plasticizer color unit of printing under the conditions of ² polyvinyl chloride sheet containing the applied overlay, a load of 100 g / cm ²
Measure the concentration after storing at 40 ℃ for 15 hours.

[0044]

[Table 1] Table 1

From the results shown in Table 1, it can be seen that the thermosensitive recording material of the present invention has high sensitivity and good dot reproducibility, and has little image fading to chemicals such as a plasticizer.

[0046]

The heat-sensitive recording material of the present invention comprises an underlayer, a leuco dye, and a heat-sensitive coloring layer mainly composed of a color developer capable of coloring the leuco dye when heated, and an overlayer which are successively laminated on a support. In the heat-sensitive recording material, the under layer contains hollow non-expandable plastic particles having an average particle size of 2 to 10 μm and a hollowness of 90% or more, and the over layer contains aluminum hydroxide having an average particle size of 0.1 to 0.5 μm. Since it is contained, the dynamic color development sensitivity is high, the dot reproducibility is good, and the fading of the image is small with a chemical such as a plasticizer.

Claims (2)

[Claims] 1. A heat-sensitive recording material comprising a support, an underlayer, a leuco dye, and a thermosensitive coloring layer containing a color developer that develops a color when the leuco dye is heated as a main component, and an overlayer, which are successively laminated. Underlayer has an average particle size of 2-10μ
m, a non-foaming plastic hollow fine particle having a hollowness of 90% or more, and the over layer contains aluminum hydroxide having an average particle diameter of 0.1 to 1.5 μm. 2. The heat-sensitive recording material according to claim 1, wherein the amount of aluminum hydroxide contained in the overlayer is 0.5 to 3.0 g / m ² .