JPH0272992A - Thermal recording material - Google Patents

Abstract

PURPOSE:To enhance printed image reproduction properties and record images with high quality by incorporating a synthetic hectorite clay into at least one of layers constituting a recording material which layer comprises a pigment having an apparent specific gravity not more than a specified value. CONSTITUTION:A thermal recording material comprises a thermal color forming layer, a support layer and, optionally, a protective layer, an intermediate layer or the like, with a synthetic hectorite clay incorporated in at least one of those layers which comprise a pigment having an apparent specific gravity of not more than 0.7g/cm<3>. A desired effect can be easily obtained when the synthetic hectorite clay is incorporated in the intermediate layer comprising the pigment. With the synthetic clay incorporated in the intermediate layer, the amount of a binder necessary for obtaining a certain adhesion is reduced to about 60% of an initial value, enabling a reduction in the amount of an adhesive, whereby an enhancing effect on heat insulating properties is developed, recorded density is enhanced, end adhesion of refuse to a thermal head is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION "Industrial Application Field" The present invention relates to a heat-sensitive recording medium, and particularly to a heat-sensitive recording medium that has excellent print pixel reproducibility, high recording density, and excellent workability in production.

"Prior Art" Conventionally, heat-sensitive recording utilizes a coloring reaction between a coloring agent and a coloring agent that develops color when it comes into contact with the coloring agent, and brings a recoloring substance into contact with heat to obtain a colored image. The body is well known. Such a thermal recording medium is relatively inexpensive, and the recording device is compact and its maintenance is relatively easy.
It is used not only as a recording medium for facsimiles and various computers, but also in a wide range of fields.

In addition, with the diversification of uses, thermal recording materials have been developed that have excellent reproducibility of printed pixels even in areas ranging from low density to high density, and that can obtain recorded images of high image quality comparable to silver halide photography. It is expected that it will appear. On the other hand, as the speed of recording equipment increases, the demand for heat-sensitive recording materials with excellent dynamic recording sensitivity is also increasing.

In order to obtain a heat-sensitive recording medium with high image quality and high sensitivity as described above, for example, the glass transition temperature between the support and the recording layer must be 60°C.
An intermediate layer made of a film-forming polymeric substance as shown below (Japanese Patent Application Laid-Open No. 54-92263) or an intermediate layer made of an oil-absorbing pigment (Japanese Patent Application Laid-Open No. 59-155097, 61)
-44683), and a method of combining these layers into multiple layers to improve smoothness and heat insulation (Japanese Patent Application Laid-open No. 61-4468).
No. 11286, No. 61-193880) have been proposed.

However, as improvements come with new difficulties,
Satisfactory results have not always been obtained. For example, with the method of providing an intermediate layer made of a film-forming polymer material, dot reproducibility improves as the smoothness improves, but the adhesion of scum to the thermal head increases and there are fewer voids in the intermediate layer. As a result, the heat insulation properties deteriorate and satisfactory recording sensitivity cannot be obtained. In addition, in the method of providing an intermediate layer mainly composed of oil-absorbing pigments, the adhesion of scum to the thermal head is difficult and the recording sensitivity is good, but on the other hand, the adhesive strength of the intermediate layer is weak and the process of manufacturing a thermal recording medium That is, in the super calendering process performed for smoothing treatment, there is a problem that the coating layer peels off from the intermediate layer and adheres to the roll.

"Problems to be Solved by the Invention" In light of the above-mentioned circumstances, the inventors of the present invention have conducted extensive research and have found a solution that incorporates pigments with high heat insulation properties and synthetic hectorite clay into the layer constituting the heat-sensitive recording material. Accordingly, there is provided a heat-sensitive recording medium which has excellent reproducibility of printed pixels in a region ranging from low density to high density, and which can obtain a recorded image of high image quality.

"Means for Solving the Problems" The present invention provides a heat-sensitive recording material in which a heat-sensitive recording layer is provided on a support, in which each layer constituting the recording material has an apparent specific gravity of 0.
．． This heat-sensitive recording material is characterized in that at least one of the layers containing 7 g/cm' or less of pigment contains synthetic hectorite clay.

"Function" As described above, in the heat-sensitive recording material of the present invention, among the layers constituting the recording material, at least one of the layers containing a pigment with an apparent specific gravity of 0.7 g/cm' or less contains synthetic hectorite. It is characterized by containing clay.

Here, synthetic hectorite clay has the same structural formula as natural hectorite clay, specifically, for example, the following structural formula, ((Srs (Mgs, :+4Lio, 66)02
゜(OH,F)4) Gate゛. , 66 (flooded, almost all N
Laporte Industries L represented by a')
Laponite B, S manufactured by TD, or the following structural formula in which all the central layers are hydroxyl groups, namely [(Sis(Mgs, :+4Lio, bb)Oz.

(Of()43 M'., 6° (M is always Na"
) Laporte Industries L
Examples include Laponite RD, RDS, XLG, and XLS manufactured by TD. All of these products are white powders and are mixed with water for 1
Laponite B, RD, and XLG form a gel, and Laponite S, RDS, and XLS form a sol.

Various inorganic pigments and amorphous pigments are known as pigments with an apparent specific gravity of 0.7 g/m3 or less, such as calcined kaolin, talc, light calcium carbonate, amorphous silica,
Preferred specific examples include polystyrene fine powder and urea-formalin resin fine powder. Among these various pigments, calcined kaolin (for example, trade name Ansilex/manufactured by EMC, apparent specific gravity 0.22 g/cm')
or amorphous silica (for example, product name Mizuriki Seal P-52)
7/Made by Suikagakusha, apparent specific gravity 0.1.8g/cm3)
Since pigments have an apparent specific gravity lower than other pigments, the layer formed using them has a high porosity and, as a result, has excellent heat insulation properties, so they are particularly preferred in the present invention from the standpoint of improving recording sensitivity. It is a pigment.

The heat-sensitive recording material of the present invention has an apparent specific gravity of 0.7 g / cta”
It is characterized by containing a synthetic hectorite clay in at least one layer of the following pigment-containing layers, but especially an intermediate layer containing a pigment with an apparent specific gravity of 0-1 g/cm' or less. It is easier to obtain the desired effect when it is mixed into the layer.

Conventionally, when providing an intermediate layer consisting of an oil-absorbing pigment, the solid content ratio of the oil-absorbing pigment and binder, which are the main components of the intermediate layer, is in the range of 100:8 to 100:30 (parts by weight). It is said that it is preferable to mix it as follows,
Even within this range, it has been difficult to obtain a thermal recording material that can exhibit sufficient adhesive strength and satisfactory recording sensitivity, and can suppress the adhesion of residue to the thermal head.

In the case of the present invention, when synthetic hectorite clay is contained in the intermediate layer containing a pigment with an apparent specific gravity of 0.7 g/cm' or less, compared to the case where the intermediate layer does not contain synthetic hectorite clay, , the former has the advantage that the amount of binder required to obtain the same adhesive strength as the latter is about 60% of the latter, and the amount of organic adhesive can be reduced, improving insulation properties. The present invention was finally completed after discovering the fact that the present invention is effective, improves the recording fH degree, and furthermore improves the adhesion of lees to the thermal head.

The reason why such excellent effects are obtained is not necessarily clear, but due to the structural charge specificity of the tabular particles unique to synthetic hectorite clay, the difference between synthetic hectorite clay, oil-absorbing pigment, and binder is It is presumed that this is achieved through the development of a unique interaction.

In the present invention, the amount of synthetic hectorite clay added to the oil-absorbing pigment is not particularly limited;
It is desirable to add 0.1 to 10 parts by weight per 00 parts by weight.

In order to form a specific intermediate layer as described above on a support, an aqueous coating solution is generally prepared by mixing an oil-absorbing pigment, a synthetic hectorite clay, and a water-soluble binder, and the resulting coating is A method is adopted in which a liquid is applied to a support and dried.

The method of applying the coating liquid is not particularly limited, and the coating liquid is applied and dried using a coating device equipped with a suitable coater head such as an air knife coater, a gravure coater, a roll coater-bar coater, or the like.

In the case of the present invention, it is desirable that the intermediate layer having the above-mentioned specific composition be coated on the support so that the thickness after coating and drying is about 4 to 20 μm.

Incidentally, if it is less than 4 μm, a sufficient improvement effect cannot be obtained, and if it exceeds 20 μm, the effect becomes saturated, which is not preferable from an economical and drying point of view.

The coating liquid for the intermediate layer usually contains starches, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin, etc. as water-soluble binders.
casein, gum arabic, polyvinyl alcohol, diisobutylene-maleic anhydride copolymer salt, styrene-maleic anhydride copolymer salt, ethylene-acrylic acid copolymer salt, natural rubber emulsion, styrene-butadiene copolymer emulsion, Acrylonitrile-butadiene copolymer emulsion, methyl methacrylate-butadiene copolymer emulsion, polychloroprene emulsion, vinyl acetate emulsion, etc. have a total solid content of 5 to 70.
Added in wt% wt% box size.

A heat-sensitive recording layer is coated on the intermediate layer thus formed and dried to produce a heat-sensitive recording material. Incidentally, various auxiliary agents as described below are also appropriately added to the coating liquid for forming the heat-sensitive recording layer.

There are no particular restrictions on the combination of the coloring agent and coloring agent contained in the recording layer, but any combination that causes a coloring reaction when the two come into contact with each other due to heat can be used. Examples include combinations of colorless to light-colored basic dyes and inorganic or organic acidic substances, and combinations of higher fatty acid metal salts such as ferric stearate and phenols such as gallic acid. Furthermore, it is also possible to apply the present invention to various heat-sensitive recording bodies in which a recorded image is obtained by heat, such as a heat-sensitive recording body in which a diazonium compound, a coupler, and a basic substance are combined.

However, since the effects of the present invention are particularly exhibited in combinations of basic dyes and acidic substances,
It is preferably applied to such combinations. Various colorless to light-colored basic dyes are known, including the following.

3.3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide, 3.3-bis(p-dimethylaminophenyl)phthalide, 3-(p-dimethylaminophenyl)-3-(1, 2-dimethylindol-3-yl)phthalide, 3-(p-dimethylaminophenyl)-
3-(2-methylindole)phthalide, 3.3-bis(1,2-dimethylindol-3-yl)-5-dimethylaminophthalide, 3.3-bis(1,2-dimethylindol-3yl) )-6-dimethylaminophthalide,
3,3-bis(9-ethylcarbazol-3-yl)-
6-dimethylaminophthalide, 3,3-bis(2-phenylindol-3-yl)-6-dimethylaminophthalide, 3-p dimethylaminophenyl-3-(1-methylpyrrol-3yl)-6 -Triarylmethane dyes such as dimethylaminophthalide, 4.4''-bis-dimethylaminobenzhydrylbenzyl ether, N-halophenyl-leucoauramine, N-2,4,5-1-lichlorophenylleucoaura diphenylmethane dyes such as amine, thiazine dyes such as hendiylleucomethylene blue, p-nitrohendiylleucomethylene blue, 3-
Methyl-spiro-dinaphthopyran, 3-ethyl-spiro-dinaphthopyran, 3-phenyl-spiro-dinaphthopyran, 3-benzyl-spirodinaphthopyran, 3-methyl-naphtho-(6゛-methoxybenzo)-spiropyran,
Spiro dyes such as 3-propyl-spiro-dibenzopyran, rhodamine-B alininolactam, rhodamine (p
- Lactam dyes such as nitroanilino)lactam and rhodamine(0-chloroanilino)lactam, 3-dimethylamino-7-methoxyfluorane, 3-diethylamino-7-methoxyfluorane, 3-diethylamino-7-
Chlorofluorane, 3-diethylamino-6-methyl-
7-chlorofluorane, 3-diethylamino-6,7-
Dimethylfluorane, 3-(N-ethyl-p-toluidino)-7-methylfluorane, 3-diethylamino-7
-N-acetyl-N-methylaminofluorane, 3-diethylamino-7-N-methylaminofluorane, 3-
Diethylamino-7-dibenzylaminofluoran-N-benzylaminofluoran, 3-diethylamino-7-N-chloroethyl-N-methylaminofluoran, 3-diethylamine-7-N-diethylaminofluoran, 3-( N-ethyl-p-toluidino)-6methyl-7-phenylaminofluorane, 3-(N-cyclopentyl-N-ethylamino)-6-methyl-7-anilinofluorane, 3-(N-ethyl- p-)luidino)-6-methyl-7-(p-)luidino)fluoran, 3-diethylamino-6-methyl-7-phenylaminofluoran, 3-diethylamino-7-(2-carbomethoxy-phenylamino)fluoran , 3-(N-ethyl-N-isoamylamino)-6-methyl-7-phenylaminofluorane, 3-(N-cyclohexyl-N
-methylamino)-6-methyl-7-phenylaminofluorane, 3-pyrrolidino-6-methyl-7-phenylaminofluorane, 3-piperidino-6-methyl-7phenylaminofluorane, 3-diethylamino 6 -Methyl-7-xylidinofluorane, 3-diethylamino-
7-(o-chlorophenylamino)fluorane, 3-pyrrolidino-6-methyl-7-p-butylphenylaminofluorane, 3-N-methyl-N-tetrahydrofurfurylamino-6-methyl-7-anilinoflu Oran, 3
-N-ethyl-N-tetrahydrofurfurylamino-6
-Fluoran dyes such as methyl-7-anilinofluorane, etc.

Furthermore, various types of inorganic or organic acidic substances that develop color upon contact with basic dyes are known, for example, the following are exemplified.

Inorganic acidic substances such as activated clay, acid clay, acpulgite, bentonite, colloidal silica, aluminum silicate, 4-tert-butylnol, 4-hydroxydiphenol, α-naphthol, β-naphthol, 4-hydroxyacetophenol, 4- tert-octylcatechol, 212'-dihydroxydiphenol, 2.2'
-methylenebis(4-methyl6-tert-butyllaenol), 4,4"-isopropylidenebis(2-t
ert-butylphenol), 4.4'-sec-butylidene diphenyl, 4-phenylphenol, 4,
4'-isopropylidenediphenol (bisphenol A), 2,2°-methylenebis(4-chlorophenol), hydroquinone, 4,4'-cyclohexylidenediphenol, benzyl 4-hydroxybenzoate, 4-hydroxyphthalic acid Phenolic compounds such as dimethyl, hydroquinone monobenzyl ether, novolac type phenolic resin, phenol polymer, benzoic acid, p-tert
-Butylbenzoic acid, trichlorobenzoic acid, terephthalic acid, 3-sec-butyl-4-hydroxybenzoic acid, 3-
Cyclohexyl-4-hydroxybenzoic acid, 3,5-dimethyl-4-hydroxybenzoic acid, salicylic acid, 3-isopropylsalicylic acid, 3-tert-butylsalicylic acid, 3-benzylsalicylic acid, 3-(α-methylbenzyl)salicylic acid , 3-chloro-5-(α-methylbenzyl)salicylic acid, 3,5-di-tert-butylsalicylic acid, 3-phenyl-5-(α,α-dimethylbenzyl)salicylic acid, 3,5-di-α- Aromatic carboxylic acids such as methylbenzyl salicylic acid, and their phenolic compounds; organic acidic substances such as aromatic carboxylic acids and polyvalent metal salts such as zinc, magnesium, aluminum, calcium, titanium, manganese, tin, and nickel; .

In the present invention, the usage ratio of the coloring agent and coloring agent in the recording layer is appropriately selected depending on the type of coloring agent and coloring agent used, and is not particularly limited. When using a colorless dye and an acidic substance, the acidic substance is generally used in an amount of about 1 to 50 parts by weight, more preferably about 1 to 10 parts by weight, per 1 part by weight of the basic colorless dye.

To prepare a coating liquid containing these substances, the coloring agent and the coloring agent are usually dispersed together or separately using water as a dispersion medium, stirring with a ball mill, attritor sand mill, etc., or dispersing the coloring agent separately. Prepared as a coating solution.

In such a coating liquid, usually one or a combination of binders used in the intermediate layer as described above is added as a binder. In that case, the amount added is preferably about 10 to 70% by weight of the total solids.

Furthermore, various auxiliary agents can be added to the coating liquid as necessary, such as sodium dioctyl sulfosuccinate, sodium dodecylbenzenesulfonate, sodium lauryl alcohol sulfate, alginate, Examples include dispersants such as fatty acid metal salts, ultraviolet absorbers such as benzophenone type and triazole type, other foaming agents, fluorescent dyes, and coloring dyes.

In addition, lubricants such as zinc stearate, calcium stearate, polyethylene wax, carnauba wax, paraffin wax, calcium carbonate, zinc oxide,
Inorganic pigments such as aluminum oxide, titanium dioxide, silicon dioxide, aluminum hydroxide, barium sulfate, zinc sulfate, talc, kaolin, clay fired resin, colloidal silica, styrene micropol, nylon powder, polyethylene powder, urea formalin resin filler raw material Organic pigments such as starch, fatty acid amides such as stearic acid methylene bisamide, oleic acid amide, valmitic acid amide, coconut fatty acid amide, dibenzyl terephthalate, 1,
2-di(3-methylphenoxy)ethane, 1,2-diphenoxyethane, 4,4”-ethylenedioxy-bis-benzoic acid diphenylmethyl ester, 1,1,3-)lis(2-methyl-4- Hydroxy-5-tert-butylphenyl)butane, 2,2°-methylenebis(4-methyl-5-tert-butylphenol), 4,4′-butylidenebis(6-tert-butyl-3-methylphenol), etc. Hindered phenols and various known thermofusible substances can be added.

Further, the support used in the present invention is not particularly limited, and includes wood-free paper, base paper made with a Yankee machine, single-sided gloss base paper, double-sided gloss base paper, cast coated paper, art paper, coated paper, Paper such as medium quality coated paper, synthetic fiber paper, synthetic fiber film, etc. are used as appropriate.

The method of forming the recording layer is not particularly limited either, and for example, a method may be used in which a coating liquid is applied onto the intermediate layer using a coating device equipped with a suitable coater head such as an air knife coater or a blade coater, and then dried. . The coating amount of the coating liquid is not particularly limited, and the dry weight is usually 2 to 1.
2g/n? , more preferably 3 to 10 g/rrl
It is adjusted within a range of degrees.

As mentioned above, the heat-sensitive recording material obtained by applying the present invention to the intermediate layer provided between the support and the heat-sensitive recording layer has excellent pixel reproducibility in the region from low density to high density, and It has excellent manufacturing operability.

"Example" The present invention will be described in more detail with reference to Examples below, but the present invention is of course not limited to these.

In addition, unless otherwise specified, parts and % in the examples indicate parts by weight and % by weight, respectively.

Example 1 [Formation of intermediate layer] 97 parts synthetic hectorite clay (product name: Labonite RD/La)
porte Industries I, TD) 3
48% styrene-butadiene copolymer emulsion
20 parts polyvinyl alcohol 10% aqueous solution 15 parts water
250 parts of the above composition were mixed and stirred to prepare a coating liquid for an intermediate layer. The obtained coating liquid was coated on high-quality paper with a basis weight of 50 g and the coating amount after drying was 10 g/
r+? (Thickness=12μ111) and dried to form an intermediate layer.

[Formation of recording layer]

■ 3-(N-cyclohexyl-N-methylamino)-
6-Methyl-7-phenylaminofluorane 10 parts Dibenzyl terephthalate 20 parts Methylcellulose 5% aqueous solution 15 parts Water
80 parts of this composition was ground in a sand mill until the average particle size was 3 μm.

■ 4.4゛-Isopropylidenephenol 30 parts Methylcellulose 5%zk? g't & 15 parts Water 70 parts This composition was ground in a sand mill until the average particle diameter was 3 μm.

■125 parts of liquid, ■130 parts of liquid, silicon oxide pigment (oil absorption 1
80 ml/100 g), 150 parts of a 20% oxidized starch aqueous solution, and 55 parts of water were stirred and mixed to obtain a coating liquid for a recording layer.

The obtained coating liquid was applied onto the intermediate layer so that the coating amount after drying was 5.
A heat-sensitive recording paper was obtained by coating and drying to give a ratio of g/a.

Example 2 [Formation of the intermediate layer] Calcined clay (same product as used in Example 1) 97 parts synthetic hectorite clay (same product as used in Example I) 3 parts 48% styrene-butadiene polymer emulsion
12 parts polyvinyl alcohol 10% aqueous solution 9 parts water
A coating solution for an intermediate layer was prepared by mixing 260 parts of the above composition. The obtained coating liquid was coated on high-quality paper with a weight of 50 g/rd after drying.
og/rd (thickness: 12 μm) and dried to form an intermediate layer.

A recording layer coating liquid was coated on this intermediate layer in the same manner as in Example I and dried to obtain a heat-sensitive recording paper.

Example 3 [Formation of intermediate layer] Amorphous silica (product name: Mizuriki Seal P-527/manufactured by Mizusawa Chemical Co., Ltd., apparent specific gravity 0.18 g/cm3)
97 parts synthetic hectorite clay (same product used in Example 1) 3 parts 48% styrene-butadiene copolymer emulsion
20 parts polyvinyl alcohol 1
0% aqueous solution 15 parts water
A coating solution for an intermediate layer was prepared by mixing 250 parts of the above composition. The resulting coating liquid was applied to a weight of 50 g/m2.
The coating amount after drying is Log/resistant (thickness: 12μ) on high-quality paper.
m) and dried to form an intermediate layer.

A recording layer coating liquid was coated on this intermediate layer in the same manner as in Example 1 and dried to obtain a heat-sensitive recording paper.

Example 4 [Formation of intermediate layer] Amorphous silica (same product as used in Example 3) 97
3 parts synthetic hectorite clay (same product used in Example 1) 3 parts 48% styrene-butadiene copolymer emulsion
12 parts polyvinyl alcohol 1
0% water r8? fi 9 part water
A coating solution for an intermediate layer was prepared by mixing 260 parts of the above composition. The obtained coating liquid was
An intermediate layer was formed by coating and drying on a high-quality paper of g/m so that the coating amount after drying was log/m (thickness: 212 μm).

A recording layer coating liquid was coated on this intermediate layer in the same manner as in Example 1 and dried to obtain a heat-sensitive recording paper.

Comparative Example 1 [Formation of intermediate layer] Baked resin (same product as used in Example 1) 100
48% styrene-butadiene copolymer emulsion
20 parts polyvinyl alcohol 10% aqueous solution 15 parts water
A coating solution for an intermediate layer was prepared by mixing 250 parts of the above composition. The obtained coating liquid was coated on a high-quality paper with a weight of 50 g/m so that the coated amount after drying was 10 g/m (thickness: 212 μm) and dried to form an intermediate layer.

A recording layer coating liquid was coated on this intermediate layer in the same manner as in Example 1 and dried to obtain a heat-sensitive recording paper.

Comparative Example 2 [Formation of intermediate layer] Amorphous silica (same product as used in Example 3) 10
0 parts 48% styrene-butadiene copolymer emulsion
20 parts polyvinyl alcohol 1
0% aqueous solution 15 parts water
A coating solution for an intermediate layer was prepared by mixing 250 parts of the above composition. The obtained coating liquid was applied to a high-quality paper with a weight of 50 g/m, and the coating amount after drying was 10 g/rrf (thickness: 12 μm).
) and dried to form an intermediate layer.

A recording layer coating liquid was coated on this intermediate layer in the same manner as in Example 1 and dried to obtain a heat-sensitive recording paper.

The six types of thermal recording paper obtained in this way were recorded using a thermal printer (SONY UP-701 model, TV printer) at printing pulse times of 3ms and 8ms, and the color density at that time was measured using a Maches densitometer (RD). -100R type,
The results are shown in Table 1. Note that the higher the evaluation value, the higher the concentration.

In addition, the reproducibility of printed pixels and the adhesion strength of the coated surface were also evaluated using the following methods.

The printed pixel reproducibility was evaluated by the ratio of the area of a printed dot to the area of one dot of the thermal head (dot reproduction rate). The evaluation criteria are as follows.

◎：86% or more The condition of the printed surface at the time of printing was visually judged. The evaluation criteria are as follows.

◎; No peeling of coated surface at all ○: There is slight peeling on the coated surface, but There is no practical problem.

×: Severe peeling of the coated surface Table 1 "Effect" As is clear from the results in Table 1, the heat-sensitive recording material obtained in the example of the present invention was effective in any range from low density to high density. Also, the reproducibility of printed pixels was excellent, and the operability in manufacturing the recording medium was also excellent.

Claims (2)

[Claims] (1) In a heat-sensitive recording material in which a heat-sensitive recording layer is provided on a support, the apparent specific gravity of each layer constituting the recording layer is 0.7.
A heat-sensitive recording material, characterized in that at least one of the layers containing a pigment of g/cm^3 or less contains synthetic hectorite clay. (2) The heat-sensitive recording material according to claim 1, wherein the synthetic hectorite clay is a white powder having the following composition and easily forms a sol or gel when added to water. [(Si_8(Mg_5_._3_4Li_0_._6
_6) O_2_0(OH)_4]Na^+_0_. ＿６
＿６