JPH05139035A - Thermal recording material - Google Patents

Abstract

PURPOSE:To obtain a thermal recording material excellent in the coating properties of an undercoat layer and having high sensitivity by adding a thickener composed of acrylic modified polyether or acrylic modified polyether and a montmorillonite type clay substance to the undercoat layer. CONSTITUTION:In a thermal recording material produced by successively laminating an undercoat layer containing plastic spherical hollow particles and a thermal color forming layer based on a leuco base and a developer allowing the leuco base to form a color at the time of heating to a support, a thickener is added to the undercoat layer. Herein, the thickener is composed of acrylic modified polyether or acrylic modified polyether and a montmorillonite type clay substance. By this method, color forming sensitivity becomes extremely excellent and coating properties are improved.

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 particularly to a heat-sensitive recording material having various properties improved by providing an undercoat layer between a support and a heat-sensitive color forming layer.

[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 heat-sensitive recording material is, for example, Japanese Patent Publication No. 43-41.
Examples of the heat-sensitive recording material 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 anilide in JP-A No. 53-11036, N, N-diphenylamine derivatives, benzamide derivatives, and carbazole derivatives in JP-A No. 53-11036, and alkylated biphenyls, biphenylalkanes in JP-A No. 53-39139. JP-A-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 sufficient. The current situation is that satisfactory results have not been obtained. Also, as another method,
JP-A-56-164890 discloses a method in which a leuco dye having a high melting point is made amorphous to lower the melting point to increase the sensitivity. 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 increase the dynamic color development sensitivity, the thermal conductivity of the support is 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). However, these have insufficient foamability and lack flexibility in the wall material, insufficient heat insulation, or insufficient adhesion between the thermal head and the thermal recording material. There are cases in which there are cases where it cannot be said that satisfactory results can be obtained, and it is made of thermoplastic resin.
A method (Japanese Patent Laid-Open No. 62-5886) in which non-expandable fine hollow spherical particles of 5 μm or less are used for the intermediate layer has been proposed.

[0005]

However, the heat-sensitive recording materials proposed in the above-mentioned JP-A-55-164192 and JP-A-59-5093 have insufficient foamability and are soft to the wall material. In some cases, there is a lack of heat resistance, insufficient heat insulation, or insufficient contact between the thermal head and the heat-sensitive recording material. Cannot be said, and the above-mentioned JP-A-62-58
The heat-sensitive recording material proposed in Japanese Patent Publication No. 86 does not give sufficiently satisfactory results. Therefore, an object of the present invention is to provide a heat-sensitive recording material having excellent coatability of the undercoat layer and having high sensitivity.

[0006]

According to the present invention, an undercoat layer containing plastic spherical hollow particles on a support, a leuco dye, and a color developing agent capable of coloring the leuco dye under heat are the main components. In a heat-sensitive recording material in which a heat-sensitive color forming layer is sequentially laminated, a thickener is contained in the undercoat layer. Further, the thickening agent is acrylic modified polyether, or acrylic modified polyether and a montmorillonite clay material.

The acrylic modified polyether is a copolymer mainly composed of alkylene oxide and acrylic acid and / or methacrylic acid, in which a part of carboxylic acid is neutralized with sodium or ammonia.

Further montmorillonite clay material is part cationic substitution of colloidal hydrous aluminum silicate, and _{Al 2 O 3 · 4SiO 2 ·} H 2 O · nH 2 O of Al Mg, Si is Al It has been partially replaced with. For example, magnesium bentonite partially replaced with Mg is called calcium bentonite, Ca replaced with calcium bentonite, and all adsorbed ions replaced with H are called hydrogen bentonite. Natural bentonite also contains a large amount of montmorillonite clay minerals.

The undercoat layer containing the hollow microparticles of the present invention and the above-mentioned thickener acts as a heat insulating layer, and the thermal energy supplied from a thermal head or the like is efficiently utilized to obtain a coloring sensitivity. Bring about an improvement. Further, the addition of the above-mentioned thickener improves the liquidity of the undercoat layer forming liquid containing the spherical hollow particles.

The plastic spherical hollow particles used in the present invention have a thermoplastic polymer as a shell and contain air or other gas inside, and are fine hollow particles which have already been foamed, and have an average particle diameter. Is 0.2 to 20 μm. If the average particle size (particle outer diameter) is smaller than 0.2 μm, there is a production problem such as difficulty in achieving an arbitrary hollowness, which is difficult in terms of cost. Conversely, if it is larger than 20 μm, Since the smoothness of the surface after coating and drying decreases, the contact property with the thermal head decreases and the sensitivity improving effect cannot be exhibited. Further, it is desirable that the particles have a particle diameter within the above range and have a small variation in size.

Further, the plastic spherical hollow particles used in the present invention have a hollowness of 40% or more, but those having a hollowness of less than 40% have a low heat insulating property, so that the thermal energy from the thermal head is reduced. Are released to the outside of the heat-sensitive recording material through the support, and the effect of improving the sensitivity becomes insufficient. 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 formula. Hollowness = (inner diameter of hollow particles / outer diameter of hollow particles) x 100
(%)

The plastic spherical hollow particles used in the present invention can be easily and inexpensively produced from an acrylic resin such as acrylic acid ester or acrylonitrile, a styrene resin such as styrene, or a copolymer resin thereof.

The thickener used in the present invention is an acrylic modified polyether, which is a copolymer of vinyl alkyl ether and acrylic acid and / or methacrylic acid as a main component, and a part of carboxylic acid is sodium or ammonium. It is hydrated, dissolves in water, behaves as a polymer electrolyte, raises clay, and imparts water retention. The thickeners of the present invention include other thickeners such as polyacrylic acid, sodium polyacrylate, ammonium polyacrylate, sodium alginate, ammonium alginate, carboxymethyl cellulose, poval,
Compared with methyl cellulose and the like, when the plastic spherical hollow particles are contained in the undercoat layer as the main component, the effect of improving the stability of the liquid with a low viscosity is large. In addition, montmorillonite clay minerals have a structural viscosity such that when they absorb water, their crystal lattice swells and the volume increases up to about 16 times, and they have reversible thixotropic flow characteristics with respect to shear stress. Therefore, it is presumed that the addition of this property can provide a coating liquid having a low viscosity and good liquid stability.

By the way, the liquid for forming the undercoat layer containing the spherical hollow particles tends to float and aggregate because the specific gravity of the spherical hollow particles is small, and the layers are easily separated in a short time, and the surface of the formed undercoat layer is formed. Also tends to be rough.

However, when the thickener of the present invention is added to such an undercoat layer forming liquid, the floating agglomeration of spherical hollow particles is prevented, and the surface of the undercoat layer formed during coating is dense. Therefore, the thermal recording material obtained by applying the undercoat layer-forming liquid has extremely improved sensitivity.

The weight ratio of the spherical hollow particles to the thickener of the present invention is preferably 0.5 to 0.005 with respect to 1 of the spherical hollow particles, and is 0.1.
~ 0.01 is more preferred. If this weight ratio exceeds 0.5, the heat insulating effect becomes insufficient, and conversely, if it is less than 0.005, the liquidity improving effect is lost.

In order to form the undercoat layer on the support, the plastic spherical hollow particles are dispersed in water together with a known water-soluble polymer or a binder resin such as an aqueous polymer emulsion, and this is dispersed on the surface of the support. It is obtained by coating and drying. In this case, the coating amount of the plastic spherical hollow particles is at least 1 g, preferably 2 g / m ² of the support.
Approximately 15 g, and the coating amount of the binder resin may be such that the undercoat layer is strongly bonded to the support,
Usually, it is 2 to 50% by weight based on the total amount of the spherical plastic hollow particles and the binder resin.

In the present invention, the binder resin used when forming the undercoat layer is appropriately selected from conventionally known water-soluble polymers and / or aqueous polymer emulsions. Specific examples thereof include water-soluble polymers such as polyvinyl alcohol, starch and derivatives thereof, methoxycellulose, hydroxyethyl cellulose, carboxymethyl cellulose, methyl cellulose,
Cellulose derivatives such as ethyl cellulose, sodium polyacrylate, polyvinylpyrrolidone, acrylamide /
Acrylic ester copolymer, acrylamide / acrylic acid ester / methacrylic acid terpolymer, styrene /
Examples thereof include maleic anhydride copolymer alkali salt, isobutylene / maleic anhydride copolymer alkali salt, polyacrylamide, sodium alginate, gelatin, and casein. Examples of the aqueous polymer emulsion include latexes such as styrene / butadiene copolymer, styrene / butadiene / acrylic copolymer, vinyl acetate resin, vinyl acetate / acrylic copolymer, styrene / acrylic ester copolymer. Examples include coalesce, acrylic ester resin, polyurethane resin, and other emulsions.

In the undercoat layer of the present invention, together with the plastic spherical hollow particles and the binder resin, auxiliary additives, such as fillers and heat-fusible fillers, which are commonly used in heat-sensitive recording materials of this kind, may be added, if necessary. It is possible to use together a substance and a surfactant. In this case, as specific examples of the filler and the heat-fusible substance, various ones shown in relation to the components of the thermosensitive color developing layer will 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 calendering after the formation of the undercoat layer.

The leuco dyes used in the thermosensitive color developing 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 bisphenol (o-methylphenol), 4,4'-Secondary butylidene bisphenol 4,4'-Isopropylidene bis (2-tertiary butylpheno- ), Zinc p-nitrobenzoate, 1,3,5-tris (4-
Tertiary 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, Four'-
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, P-
Benzyl 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'-diphenol sulfone, 3,4-dihydroxy-4'-methyldiphenyl sulfone, zinc 1-acetyloxy-2-naphthoate, zinc 2-acetyloxy-1-naphthoate, 2-acetyloxy-3-naphthoate Zinc acid, α, α-bis (4-hydroxyphenyl) -α-methyltoluene, antipyrine complex of zinc thiocyanate, tetrabromobisphenol A,
Tetrabromobisphenol S 4,4'-thiobis (2-methylphenol), 4,4'-thiobis
(2-chlorophenol) etc.

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

In addition to the leuco base and the color developer, if necessary, an auxiliary additive component such as a filler, a heat-soluble substance, or a surfactant which is commonly used in this type of heat-sensitive recording material may be used in combination. You can In this case, as the filler, for example, calcium carbonate, silica, zinc oxide, titanium oxide, aluminum hydroxide, zinc hydroxide, barium sulfate, clay, talc, other inorganic fine powder such as surface-treated calcium or silica, Urea-formalin resin,
Examples include organic fine powders such as styrene / methacrylic acid copolymers and polystyrene resins. 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, and other heat-fusible organic compounds having a melting point of about 50 to 200 ° C.

In the present invention, a filler may be provided as an intermediate layer between the undercoat layer and the thermosensitive color developing layer, if necessary.
It is also possible to provide a layer containing a binder resin, a heat-soluble substance and the like. In this case, specific examples of the filler, the binder resin and the heat-soluble substance include the same as those exemplified in connection with the thermosensitive coloring layer or the undercoat layer.

Further, in the heat-sensitive recording material of the present invention, a protective layer may be provided on the heat-sensitive color developing layer for the purpose of improving the matching property with a thermal head or the like and further improving the storability of recorded images. In this case, the above-mentioned filler, binder resin, and heat-soluble substance can also be used as components constituting the protective layer.

The heat-sensitive recording material of the present invention is produced, for example, by applying 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.

[0029]

[Liquid A]

 3- (N-methyl-3-N-cyclohexyl) amino 20 parts -6-Methyl-7-anilinofluorane Polyvinyl alcohol 10% aqueous solution 20 parts Water 60 parts

[Solution B] Benzyl P-hydroxybenzoate 10 parts Polyvinyl alcohol 10% aqueous solution 25 parts Calcium carbonate 15 parts Water 50 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, to prepare [solution A] and [solution B].

[C liquid] Plastic spherical hollow particle dispersion (solid content concentration 31%) 30 parts (average particle size 7 μm hollowness 95%) Acrylic modified polyether aqueous solution 6 parts (Sannopco Thickener 613 solid content 5%) Styrene / Butadiene copolymer latex (solid content 47%) 10 parts Water 54 parts

An undercoat liquid was prepared by stirring and dispersing the mixture having the above composition with a disper, and the undercoat liquid was dried on a surface of commercially available high-quality paper (basis weight: 52 g / m ² ) with a weight of 6 g / m ² after drying.
Was coated and dried to obtain an undercoat paper.

Next, the above [Liquid A] and [Liquid B] were mixed and stirred in a weight ratio of 1: 8 to prepare a thermosensitive color forming layer-forming liquid, which was applied to the surface of the above undercoated paper. After drying, a thermosensitive coloring layer is provided by coating and drying so that the weight becomes 7 g / m ^2, and then supercalendering is performed so that the Beck smoothness becomes 500 to 600 seconds to obtain the thermosensitive recording material of the present invention. It was

Example 2 A thermosensitive recording material was obtained in the same manner as in Example 1 except that 5 parts of a sodium montmorillonite dispersion (solid content 5%, Kunimine Koguni Kunipia F) was added to [C liquid].

Comparative Example 1 A thermosensitive recording material for comparison was obtained in the same manner as in Example 1 except that the aqueous solution of acrylic modified polyether of [C liquid] was omitted.

Comparative Example 2 In Comparative Example 1, instead of the plastic spherical hollow particles, plastic spherical non-hollow particles (Mitsui Toatsu Co., Ltd .: SPMM-
A thermal recording material for comparison was obtained in the same manner as in Comparative Example 1 except that HS and solid content concentration 40%) were used.

Each of the heat-sensitive recording materials obtained as described above was tested for dynamic color development sensitivity. The results are shown in Table 1. The test was conducted as follows.

Dynamic color development: Head thermal power of 0.45 W / in a thermal printing experimental apparatus having a thin film head manufactured by Matsushita Electronic Components Co., Ltd.
Dot, recording time 20msec / l line, scanning line density 8 × 3.8
Pulse width 0.3, 0.4, 0.5 and 0 under 5 dots / mm.
It prints in 6msec and the print density is Macbeth densitometer RD-914.
It was measured at.

Further, with respect to each of the above-mentioned undercoat layer forming liquids, a test regarding coating liquid properties was conducted. The results are shown in Table 2. This test was conducted as follows. Coating liquid properties ... After adjusting each undercoat layer forming liquid, the liquid was allowed to stand for 24 hours and the liquid state was observed. The viscosity at 25 ° C was measured with an E-type viscometer (manufactured by Tokyo Keiki Co., Ltd.).

[0041]

[Table 1]

[0042]

[Table 2]

From the results shown in Tables 1 and 2, it can be seen that the heat-sensitive recording material of the present invention has high sensitivity and the liquidity of the undercoat forming liquid is improved.

[0044]

The heat-sensitive recording material of the present invention comprises a support, a thermo-sensitive coloring material containing an undercoat layer containing spherical plastic hollow particles and a leuco base, and a color developer capable of coloring the leuco base under heat. In the heat-sensitive recording material in which layers are sequentially laminated, since the undercoat layer contains a specific thickener, the color developing sensitivity is very excellent. Further, since the undercoat layer forming liquid used in the present invention has a constitution in which a specific thickening agent is blended with the plastic spherical hollow particles, the coating liquid property is improved.

Claims (3)

[Claims] 1. An undercoat layer containing spherical plastic hollow particles on a support, and a thermosensitive coloring layer mainly containing a leuco base and a color developer capable of coloring the leuco base when heated, are sequentially laminated. A heat-sensitive recording material, characterized in that a thickener is contained in the undercoat layer. 2. The thermal recording material according to claim 1, wherein the thickener is an acrylic modified polyether. 3. The thermal recording material according to claim 1, wherein the thickener is an acrylic modified polyether and a montmorillonite clay material.