JPH0225380A - Thermal recording material - Google Patents

Abstract

PURPOSE:To enhance recording sensitivity and printing picture element reproduction properties, without causing ground fogging, and prevent the adhesion of scum to a thermal head by providing a thermal recording layer on two kinds of undercoat layers comprising respective constituents having specified oil absorptions and provided on a support. CONSTITUTION:An undercoat layer comprising silica having an oil absorption according to the method of JIS K-5101 of at least 110ml/100g, an undercoat layer comprising an inorganic or organic oil-absorptive pigment (exclusive of solid acid) having an oil absorption of at least 80ml/100g, and a thermal recording layer are sequentially provided on a support. The undercoat layer provided directly on the support functions as both a heat-insulating layer and a cushioning layer, and provides high degrees of recording sensitivity characteristics and picture element reproduction properties. The next undercoat layer improves a refuse adhesion phenomenon, without causing ground fogging. Particularly preferable examples of the oil-absorptive pigment to be incorporated in the next undercoat layer are calcined kaolin and alkali-treated silica.

Description

Detailed Description of the Invention "Industrial Application Field" The present invention relates to a thermal recording medium, and in particular to a thermal recording medium that has excellent recording sensitivity and printed pixel reproducibility, has little adhesion of residue to the thermal head, and has extremely low background fog. It is related to recording bodies.

``Prior art'' Conventionally, thermosensitive technology utilizes a color reaction between a color former and a color former that develops color when it comes into contact with the color former, and brings both photochromic substances into contact with each other using heat to obtain a colored image. Records are well known.

Such thermal recording media are relatively inexpensive, the recording device is compact, and maintenance is relatively easy, so they are used not only as recording media for facsimiles and various computers, but also in a wide range of fields.

With the diversification of applications, there is a need for thermal recording materials that have excellent reproducibility of printed pixels in all areas from low density to high density, and that can produce recorded images of high quality comparable to silver halide photography. Demand is increasing. Furthermore, as recording equipment becomes faster, there is an increasing demand for heat-sensitive recording materials with excellent dynamic recording sensitivity.

Methods have been proposed in which an intermediate layer containing various oil-absorbing pigments is provided between the support and the heat-sensitive recording layer for the purpose of improving the adhesion of residue to the heat-sensitive head or increasing the recording sensitivity. . However, although the heat-sensitive recording materials obtained by these methods do improve the adhesion of residue, they do not necessarily have sufficient recording sensitivity characteristics or image quality characteristics, and depending on the oil-absorbing pigment used, they may cause background fog, etc. with new flaws.

In addition, for the purpose of improving recording sensitivity and dot reproducibility,
A method of providing a plurality of intermediate layers between the support and the heat-sensitive recording layer has been proposed (JP-A-61-11286, JP-A-61-193880, etc.).

For example, JP-A No. 61-11286 discloses that an intermediate layer mainly composed of a film-forming polymer is formed on a support, an intermediate layer mainly composed of a pigment having an apparent specific gravity of 0.5 g/cf or less, A heat-sensitive recording material in which heat-sensitive coloring layers are sequentially provided has been proposed, but the darkening heat-sensitive recording material cannot obtain satisfactory recording sensitivity characteristics and dot reproducibility, and depending on the selection of pigments, It also has the disadvantage of causing background fog. On the other hand, JP-A-61-193880 discloses a method of sequentially providing on a support an intermediate layer containing an inorganic pigment with an oil absorption of 100 ml/100 g or more, a film-forming polymer layer, and a thermosensitive coloring layer. Although this method has been proposed, it is still not possible to obtain a thermosensitive recording medium having satisfactory recording sensitivity characteristics and dot reproducibility.

"Problems to be Solved by the Invention" In view of the current situation, the present inventors have conducted extensive studies on the composition and structure of the under two layers provided between the support and the heat-sensitive recording layer, and have found that the At least one undercoat layer containing silica having a specific oil absorption amount is provided on the undercoat layer, and an undercoat layer containing an inorganic or organic oil absorbing pigment (however, excluding solid acids) having a specific oil absorption amount is further provided on the undercoat layer. By forming a heat-sensitive recording layer on top of a coating layer, recording sensitivity and printed pixel reproducibility can be significantly improved without causing background fog, and a heat-sensitive recording medium that does not adhere to the thermal head can be obtained. This discovery led to the completion of the present invention.

"Means for Solving the Problems" The present invention provides at least one undercoat layer containing silica with an oil absorption of 110 ml/100 g or more according to JIS K-5101 method, and an oil absorption of 80 ml/100 g on a support.
l/100 g or more of inorganic or organic oil-absorbing pigment (
However, this is a heat-sensitive recording material characterized by sequentially providing an undercoat layer containing a solid acid (excluding solid acid) and a heat-sensitive recording layer.

"Function" In the present invention, the undercoat layer formed directly on the support contains silica having an oil absorption of 110 ml/100 g or more according to the JIS K-5101 method, as described above. The coating layer functions not only as a heat insulating layer but also as a cushion layer, and as a result provides high recording sensitivity characteristics and pixel reproducibility. Furthermore, this undercoat layer functions to supplement the scum adhesion improving effect of the undercoat layer formed thereon, and to exhibit a sufficient scum adhesion improving effect as a whole.

By the way, even if the oil absorption amount is 110ml/100g or more, pigments other than silica may be used, or the oil absorption amount may be 110ml/100g or more.
If less than 100 g of silica is used, desired recording sensitivity characteristics and pixel reproducibility cannot be obtained. Furthermore, with pigments other than silica, it may not be possible to form a uniform layer on the support depending on the type of pigment. Furthermore, silica with low oil absorption does not have the ability to supplement the improvement of scum adhesion. Therefore, in the present invention, silica having an oil absorption capacity of 10 ml/100 g or more is selectively used.

Note that the undercoat layer containing silica can be formed into two or more layers, if necessary.

In the present invention, the oil absorption amount according to JIS L5101 method is 80 m on the undercoat layer containing silica as described above.
The undercoat layer contains an inorganic or organic oil-absorbing pigment of 1/100 g or more, and this undercoat layer improves the phenomenon of residue adhesion without causing background fog, and at the same time, the undercoat layer contains an undercoat containing silica. It also exhibits the effect of further enhancing the recording sensitivity characteristics and pixel reproducibility of the coating layer.

Such inorganic or organic oil-absorbing pigments having an oil absorption amount of 80 ml/100 g or more may be used to prevent color fogging (
It is necessary to select pigments other than pigments that function as solid acids to avoid causing (background fog), and specifically, inorganic pigments such as calcined kaolin, alkali-treated silica, aggregates of fine particulate light calcium carbonate, and urea. Examples include organic pigments such as formaldehyde resin powder and cellulose powder.

Among these pigments, calcined kaolin and alkali-treated silica have particularly excellent recording sensitivity characteristics and pixel reproducibility when combined with the undercoat layer formed directly on the above-mentioned support. In addition, it is particularly preferably used because a heat-sensitive recording material excellent in terms of background fog and residue adhesion can be obtained.

The above-mentioned silica having a specific oil absorption amount and inorganic or organic oil-absorbing pigment having a specific oil absorption amount are generally prepared using water as a dispersion medium as a coating liquid for an undercoat. The following binders are added to the coating liquid in an amount of 2 to 40% by weight, preferably 5 to 20% by weight based on the total solid content of the coating liquid.

Specific examples of the binder include starches such as oxidized starch, enzyme-modified starch, cationic starch, esterified starch, and etherified starch; cellulose derivatives such as methyl cellulose, ethyl cellulose, carboxymethyl cellulose, methoxy cellulose, and hydroxyethyl cellulose; (or incompletely) saponified polyvinyl alcohol, carboxy-modified polyvinyl alcohol, polyvinyl alcohols such as acelylated polyvinyl alcohol, sodium polyacrylate, polyacrylamide, polyvinylpyrrolidone, acrylic amide/acrylic ester copolymer, acrylic acid Amide/Acrylic ester/
Water-soluble polymers such as methacrylic acid ternary copolymer, styrene/maleic anhydride copolymer alkali salt, isobutylene/maleic anhydride copolymer alkali salt, sodium alginate, gelatin, casein; polyvinyl acetate, polyurethane, polyester, etc. Latex such as acrylic acid, nistyl polyacrylate, polybutyl methacrylate, styrene/butadiene copolymer, vinyl chloride/vinyl acetate copolymer, ethylene/vinyl acetate copolymer, styrene/butadiene/acrylic copolymer, etc. Can be mentioned.

In addition, various auxiliary agents such as a dispersant, an antifoaming agent, a coloring dye, a fluorescent dye, and an ultraviolet absorber can be added to the undercoat coating liquid as required.

Furthermore, it is also possible to add a decolorizing agent to a coating solution containing silica that requires an undercoat for the purpose of preventing background fogging, and such an embodiment is particularly preferable when using highly acidic silica. .

Such decolorizing agents are not particularly limited, but include:
Ethylene oxide adducts of terephthalic acid, ethylene glycol derivatives, glycerin fatty acid esters, N,N'-dithio-di-ε-caprolactam, morpholine compounds, disubstituted amides of aromatic dihydric carboxylic acids, piperidine derivatives, piperidine derivatives, etc. can be mentioned.

The amount of decolorizing agent to be used should be selected as appropriate, depending on the acidity of the silica used and the type of decolorizing agent, so long as it does not inhibit the color development of the recording layer.
．． It is blended in an amount of 1 to 40% by weight, preferably 0.5 to 20% by weight.

Note that when a plurality of undercoat layers containing silica are provided, the silica may be added to each undercoat layer or only to the undercoat layer closest to the recording layer.

There are no particular limitations on the method of applying the coating liquid required for undercoating, such as air knife coating,
Known coating methods such as blade coating, bar coating, gravure coating, and curtain coating can be applied.

Furthermore, there is no particular limitation on the coating amount of each undercoat layer, and both the layer containing silica and the layer containing an inorganic or organic oil-absorbing pigment have a dry weight of 2.
~20 g/n (adjusted in the range).

The heat-sensitive recording material of the present invention can record without causing background fog by arranging two types of undercoat layers containing the above-mentioned specific pigments at specific positions and forming a heat-sensitive recording layer thereon. The present invention provides a heat-sensitive recording material with significantly improved sensitivity characteristics and dot reproducibility, and with improved dust adhesion.

As a combination of a coloring agent and a coloring agent constituting such a heat-sensitive recording layer, a combination of a colorless or light-colored basic dye and an acidic substance is used.

Various types of colorless to light-colored basic dyes are known, and examples include the following.

3.3-bis(p-dimethylaminophenyl)6-cyphthylaminophthalide, 3,3-bis(p-dimethylaminophenyl)phthalide, 3-(Pdimethylaminophenyl)-3-(1,2-dimethyl indol-3-yl)phthalide, 3-(P-dimethylaminophenyl)-3-
(2-methylindole-3-ylphthalide, 3,3-
Bis(1,2-dimethylindol-3-yl)-5dimethylaminophthalide, 3,3-bis(12-dimethylindol-3-yl)-6-cyphthylaminophthalide, 3,3-bis( 9-ethylcarbazol-3-yl)
-6-Cyphtylaminophthalide, 3,3-bis(2-phenylindol-3-yl)-6-cyphtylaminophthalide, 3-P-dimethylaminophenyl-3-(1-methylpyrrole-3 triallylmethane dyes such as -yl)-6-cyphthylaminophthalide, 4,4'bis-dimethylaminohenzhydrylhenzyl ether, N-halophenyl-leucoauramine, N-2,4,5-) Diphenylmethane dyes such as lychlorophenyl leuco auramine, thiazine dyes such as hendiyl leucomethylene blue, p-nitrohenyl leucomethylene blue, 3-
Methyl-spiro-dinaphthopyran, 3-ethyl-spiro-dinaphthopyran, 3-phenyl-spiro-dinaphthopyran, 3-hensyl-spiro-dinaphthopyran, 3-methyl-naphtho(6'-methoxybenzo)spiropyran, 3
- Spiro dyes such as propyl-spirodibenzopyran,
Lactam dyes such as rhodamine B-anilinolactam, rhodamine (p-nitroanilino) lactam, rhodamine (0-chloroanilino) lactam, 3-dimethylamino-7-methoxyfluorane, 3-diethylamine-6
-Methoxyfluorane, 3-diethylamino-7-methoxyfluorane, 3-diethylamine-7-chlorofluorane, 3-diethylamino-6-methyl-7-chlorofluorane, 3-diethylamino-6,7-siftylfluoran Oran, 3-(N-ethyl-p-)luidino)-7methylfluorane, 3-diethylamino-7-N-acetyl-N-methylaminofluorane, 3-diethylamine-7
-N-methylaminofluorane, 3-diethylamino-
7-dibenzylaminofluorane, 3-diethylamino-7-N-methyl-N-benzylaminofluorane, 3
-diethylamino-7-N-chloroethyl-N-methylaminofluorane, 3-diethylamino-7-diethylaminofluorane, 3-(N-ethyl-p-toluidino)
-6-methyl-7-phenylaminofluorane, 3-(
N-ethyl-P-)luidino)6-methyl-7-(p-
) luidino) fluoran, 3-diethylamino-6-methyl-7-phenylaminofluoran, 3-dibutylamino-6methyl-7-phenylaminofluoran, 3-diethylamino-7-(2-carbomethoxy-phenylamino)fluoran , 3-(N-cyclohexyl-N-methylamino)-6-methyl-7phenylaminofluorane, 3-pyrrolidino-6methyl-7-phenylaminofluorane, 3piperidino-6-methyl-7- Phenylaminofluorane, 3-diethylamino-6-methyl-7
Xylidinofluorane, 3-diethylamino 7-(o-
chlorophenylamino)fluoran, 3-dibutylamino-7-(0-chlorophenylamino)fluoran, 3
-pyrrolidino-6-methyl-7-T)-butylphenylaminofluorane, 3-(N-methyl-N-n-amyl)amino-6methyl-7-phenylaminofluorane,
3(N-ethyl-N-n-amyl)amino-6-methyl-7-phenylaminofluorane, 3-(N-ethyl-N
-isoamyl)amino-6-methyltwophenylaminofluorane, 3-(N-methyl-Nn-hexyl)amino-6-methyltwophenylaminofluorane, 3-
(N-ethyl-N-n-hexyl)amino-6-methyl-7phenylaminofluorane, 3-(N-ethyl N-
Examples include fluoran dyes such as β-ethylhexyl)amino-6-methyltophenylaminofluoran. Of course, the dyes are not limited to these dyes, and two or more types of dyes can be used in combination.

Furthermore, various compounds are known as acidic substances to be used in combination with the above-mentioned basic dyes, for example, the following are exemplified.

4-tert-butylphenol, α-naphthol, β
-naphthol, 4-acetylphenol, 4tert
-octylphenol, 4,4'-5ec-phthylidene diphenol, 4-phenylphenol, hydroquinone, 4,4'-dihydroxy-diphenylmethane, 4,
4'-isopropylidenediphenol, 2,2-bis(
4-hydroxyphenyl)-4-methylpentane, 44
'-Cyclohexylidene diphenol, 4,4'-dihydroxydiphenyl sulfide, 44'-thiobis(
6-tert-butyl-3-methylphenol), 44
'-dihydroxydiphenylsulfone, 4hydroxy-
4'-methyldiphenylsulfone, 4-hydroxy-4
'-Methyldiphenylsulfone, 4-hydroxy-4'
-isopropoxydiphenyl sulfone, hydroquinone monobenzyl ether, 4-hydroxyhensiphenone,
2.4dihydroxybenzophenone, 244'trihydroxyhensiphenone, 22'44'-tetrahydroxyhensiphenone, 2,2'methylenebis(4-chlorophenol), 1°3-di(2-(4- hydroxyphenyl)-2propyl] Hensen, bis(3-allyl-4-hydroxyphenyl)sulfone, dimethyl 4-hydroxyphthalate, methyl 4-hydroxybenzoate, 4
-ethyl hydroxybenzoate, propyl 4-hydroxybenzoate, -5ec butyl 4-hydroxybenzoate, 4
-pentyl hydroxybenzoate, phenyl 4-hydroxybenzoate, benzyl 4-hydroxybenzoate, tolyl 4-hydroxybenzoate, chlorophenyl 4-hydroxybenzoate, phenylpropyl 4-hydroxybenzoate, 4
-Phenethyl hydroxybenzoate, p-chlorobenzyl 4-hydroxybenzoate, 4-hydroxybenzoic acid-
p-methoxybenzyl, novolac type phenolic resin,
Phenolic compounds such as phenol polymers, benzoic acid,
p-tert-butylbenzoic acid, trichlorobenzoic acid, terephthalic acid, 3-5ecbutyl-4-hydroxybenzoic acid, 3-cyclohexyl-4-hydroxybenzoic acid, 3,5-dimethyl-4-hydroxybenzoic acid, Salicylic acid, 3-isopropylsalicylic acid, 3-tert-butylsalicylic acid, 3.5-di-tert-butylsalicylic acid, 3-benzylsalicylic acid, l-(α-methylbenzyl)salicylic acid, 3-chloro-5-(α-methylhensyl) Aromatic carboxylic acids such as salicylic acid, 3-phenyl-5-(α,α-dimethylhensyl)salicylic acid, 35-diα-methylhensylsalicylic acid, and these phenolic compounds, aromatic carboxylic acids such as zinc, magnesium, Organic acidic substances such as salts with polyvalent metals such as aluminum, calcium, titanium, manganese, tin, and nickel. Note that, of course, two or more of these coloring agents can be used in combination as necessary.

The ratio of the basic dye and coloring agent to be used is appropriately selected depending on the type of basic dye and coloring agent used, and is not particularly limited, but is generally based on 100 parts by weight of the basic dye. 100-700 parts by weight, preferably 150-4
About 0.00 parts by weight of coloring agent is used.

Thermal coating liquids containing these are generally prepared by using water as a dispersion medium and dispersing the dye and coloring agent together or separately using a stirring/pulverizing machine such as a ball mill, attritor, or sand grinder. be done.

Such coating liquids usually contain starches and binders as binders.
Hydroxyethylcellulose, methylcellulose, carboxymethylcellulose, gelatin, casein, gum arabic, polyvinyl alcohol, styrene/maleic anhydride copolymer salt, styrene/acrylic acid copolymer salt, styrene/butadiene copolymer emulsion, etc. have a total solid content. It is blended in an amount of about 2 to 40% by weight, preferably about 5 to 30% by weight.

Furthermore, various auxiliary agents can be added to the coating liquid.
Examples include dispersants such as dioctyl sulfosuccinate, dodecylhenzenesulfonate, sodium salt of lauryl alcohol sulfate, fatty acid metal salts, other antifoaming agents, fluorescent dyes, and coloring dyes. Further, a dispersion or emulsion of stearic acid, polyethylene, carnauba wax, paraffin wax, zinc stearate, calcium stearate, ester wax, etc. may be added to prevent sticking from contact with a recording device or a recording head.

Further, fatty acid amides such as stearic acid amide, stearic acid methylene bisamide, oleic acid amide, palmitic acid amide, coconut fatty acid amide, 22'-methylene bis(4-
methyl-5-tertbutylphenol), 4.4'-
Butylidenephthylidene bis(5-tert-butyl-3
-methylphenol), hindered phenols such as 1,1.3-)lis(2-methyl4-hydroxy-5-tert-butylphenyl)butane, p-hensylbiphenyl, 12-bis(phenoxy)ethane, 12-bis(
Ethers such as 4-methylphenoxy)ethane, 1,2-bis(3-methylphenoxy)ethane, 2-naphtholhensyl ether, dihenzyl terephthalate, 1-
Esters such as hydroxy-2 naphthoic acid phenyl ester, 2(2'-hydroxy-5'-methylphenyl)
Ultraviolet absorbers such as hensitriazole and 2-hydroxy-4-hensyloxybenzophenone, and various known thermofusible substances can also be added as sensitizers.

In addition, inorganic pigments such as kaolin, clay, talc, calcium carbonate, calcined clay, titanium oxide, diatomaceous earth, fine particulate anhydrous silica, and activated clay may be added to further improve the adhesion of debris to the recording head. can.

In the present invention, the method of forming the heat-sensitive recording layer is not particularly limited, and it can be formed according to conventionally well-known and commonly used techniques, such as an air knife coater, a blade coater, a no-coater, a gravure coater, and a curtain coater. A suitable coating device such as the following may be used. Further, the amount of the coating liquid to be applied is not particularly limited, and is generally adjusted in the range of 2 to 12 g/n (and preferably 3 to 10 g/rtl) in terms of dry weight.

Further, as the support, paper, plastic film, synthetic paper, etc. can be used, but paper is most preferably used in terms of cost, coating suitability, etc.

In addition, it is also possible to provide an overcoat layer on the recording layer for the purpose of protecting the recording layer, etc., and it is also possible to provide a protective layer on the back side of the support, or even apply adhesive processing, etc. in the heat-sensitive recording material manufacturing field. Various known techniques can be added.

"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.

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

Example 1 [Formation of undercoat layer] (1) Preparation of coating liquid (1) for undercoat layer Oil absorption: 150
ml/100g silica (product name: Fine Seal CM
F, manufactured by Tokuyama Soda Co., Ltd.), 7 parts of SBR latex (in terms of solid content), and 3 parts of polyvinyl alcohol aqueous solution (in terms of solid content) were uniformly mixed to make an undercoat wear coating liquid with a solid content concentration of 25% ( 1) was obtained.

■ Preparation of undercoat wear coating liquid (II) Oil absorption amount 11
0ml/100g of calcined kaolin (trade name: Ansilex, manufactured by Engel Hard), 100 parts, SBR latex 7 parts (solid content equivalent), and polyvinyl alcohol aqueous solution 3 parts (solid content equivalent) were mixed uniformly, and a solid Min concentration 3
A 0% undercoat coating fluid (II) was obtained.

■ Formation of undercoat layer Coating liquid for undercoat layer (1
) with a Mayer bar so that the coating amount after drying is 8 g/nf, and drying, and on top of that, apply the undercoat coating liquid (n) with a Meyer bar so that the coating amount after drying is 7 g/rrf. An undercoated paper was obtained by coating and drying.

[Preparation of coating liquid for recording layer]

■ Preparation of liquid A 3-(N-cyclohexyl-N-methylamino)-6-
Methyl-7-phenylaminofluorane
Part 10 Jihenzil Terephthalate
20 parts 5% methylcellulose aqueous solution 15 parts water 80 parts This composition was ground with a sand mill until the average particle size was 2 μm.

■ Solution B" Shusei 44'-isopropylidene diphenol 30 parts methylcellulose 5% water? 9? Fl 30 part water 70
This composition was ground in a sand mill until the average particle size was 2 μm.

125 parts of liquid A, 130 parts of liquid B, silicon oxide pigment (oil absorption 1
A recording layer coating liquid was prepared by stirring and mixing 30 parts of 20% oxidized starch aqueous solution (80 ml/100 g), 150 parts of 20% oxidized starch aqueous solution, and 55 parts of water.

[Formation of recording layer]

The obtained recording layer coating liquid was coated onto the undercoat paper using a Muco Meyer bar so that the coated amount after drying was 5 g/n, and dried to obtain a heat-sensitive recording paper.

Example 2 [Formation of undercoat layer] ■ Preparation of undercoat coating liquid (I[l) Oil absorption amount 1
60 ml/100 g of 100 parts of silica (trade name: Mizuka Seal P-527, manufactured by Mizusawa Chemical Co., Ltd.), 7 parts of SBR latex (in terms of solid content), and 3 parts of polyvinyl alcohol aqueous solution (in terms of solid content) were mixed uniformly, Solid content concentration 25
% undercoat coating liquid (III) was obtained.

(2) Formation of Undercoat Layer An undercoat paper was obtained in the same manner as in Example 1, except that the above-mentioned undercoat coating liquid (III) was used instead of the undercoat coating liquid (1).

[Formation of recording layer]

A thermosensitive recording paper was obtained in the same manner as in Example 1 except that the above-mentioned undercoated paper was used.

Example 3 [Formation of undercoat layer] ■ Preparation of undercoat coating liquid (TV) Oil absorption amount 13
5ml/100g alkali-treated silica (product name:
Mizuriki Seal P-832 (manufactured by Mizusawa Chemical Co., Ltd.) 100 copies, SB
7 parts of R latex (in terms of solid content) and 3 parts of polyvinyl alcohol aqueous solution (in terms of solid content) were uniformly mixed to obtain an underyo 1-layer coating liquid (TV) with a solid content concentration of 25%.

(2) Formation of Undercoat Layer An undercoat paper was obtained in the same manner as in Example 1 except that the above undercoat coating liquid (TV) was used instead of the undercoat coating liquid (II).

[Formation of Recording Layer] A thermosensitive recording paper was obtained in the same manner as in Example 1 except that the above-mentioned undercoat paper was used.

Example 4 [Formation of undercoat layer] ■ Preparation of decolorizing agent dispersion Tetrakis (2°2.6.
6-tetramethyl-4-piperidyl) 123.10 parts of 4-butanetetracarpoxylate, 1 part of polyvinyl alcohol aqueous solution (in terms of solid content), and 0.05 part of sodium dodecylhenzenesulfonate were mixed and averaged using a sand mill. The particles were pulverized to a particle size of 2 μm to obtain a decolorizing agent dispersion having a solid content concentration of 25%.

■ Preparation of coating liquid (V) required for undercoat Oil absorption: 200
ml/100g silica (product name: Nip Seal E15
0, Nippon Silica Co., Ltd.) 100 parts, SBR latex 7 parts (solid content equivalent), polyvinyl alcohol aqueous solution 3
(in terms of solid content) and 11.05 parts (in terms of solid content) of the decolorizing agent dispersion were uniformly mixed to obtain a coating liquid (V) requiring undercoat having a solid content concentration of 25%.

(2) Formation of Undercoat Layer An undercoat paper was obtained in the same manner as in Example 1, except that the above coating liquid (V) for undercoat was used instead of coating liquid (I) for undercoat.

[Formation of recording layer]

A thermosensitive recording paper was obtained in the same manner as in Example 1 except that the above-mentioned undercoated paper was used.

Example 5 [Formation of undercoat layer] ■ Preparation of coating liquid (Vl) required for undercoat Oil absorption amount 20
0ml/100g silica (product name: Nip Seal E1
50, 100 parts of Nippon Silica Co., Ltd.), 7 parts of SBR latex (in terms of solid content), and 3 parts of polyvinyl alcohol aqueous solution (in terms of solid content) were uniformly mixed to obtain a solid content concentration of 2.
A 5% undercoat required coating liquid (Vl) was obtained.

(2) Formation of Undercoat Layer An undercoat paper was obtained in the same manner as in Example 1, except that the above coating liquid (Vl) for undercoat was used instead of coating liquid (1) for undercoat.

[Formation of recording layer]

A thermosensitive recording paper was obtained in the same manner as in Example 1 except that the above-mentioned undercoated paper was used.

Comparative Example 1 The same procedure as in Example 1 was conducted except that the undercoat-required coating liquid (n) was used instead of the undercoat-required coating liquid (1) in the formation of the undercoat layer in Example 1. I got the recording paper.

Comparative Example 2 [Formation of undercoat layer] ■ Preparation of coating liquid requiring undercoat (■) Oil absorption: 130
ml/100 g of kaolin (product name: Samton 471
．． 100 parts (manufactured by Hüber), 7 parts SBR latex (
(converted to solid content), and 3 parts of polyvinyl alcohol aqueous solution (
(in terms of solid content) were mixed uniformly to obtain a coating liquid (■) requiring undercoating with a solid content concentration of 25%.

(2) Formation of undercoat layer An undercoat paper was obtained in the same manner as in Example 1, except that the above-mentioned undercoat required coating liquid (■) was used instead of undercoat required coating liquid N).

[Formation of recording layer]

A thermosensitive recording paper was obtained in the same manner as in Example 1 except that the above-mentioned undercoated paper was used.

Comparative Example 3 [Formation of undercoat layer] ■ Preparation of coating liquid for undercoat (■) Oil absorption: 95 m
1/100 g of silica (trade name: Thyroid 63, manufactured by Fuji Davison), 100 parts, SBR latex 7 parts (in terms of solid content), and 3 parts of polyvinyl alcohol aqueous solution (in terms of solid content) were uniformly mixed to reduce the solid content. A coating solution (■) requiring an undercoat with a concentration of 25% was obtained.

(2) Formation of undercoat layer An undercoat paper was obtained in the same manner as in Example 1 except that the above-mentioned undercoat required coating liquid (■) was used instead of the undercoat required coating liquid (1).

[Formation of recording layer]

A thermosensitive recording paper was obtained in the same manner as in Example 1 except that the above-mentioned undercoated paper was used.

Comparative Example 4 [Formation of undercoat layer] ■ Preparation of coating liquid (IX) required for undercoat Oil absorption: 80
ml/100g of light calcilum carbonate (trade name: Callite SA, manufactured by Shiroishi Calcium Co., Ltd.) 100 parts, SBR latex 7 parts (solid content equivalent), and polyvinyl alcohol aqueous solution 3 parts (solid content equivalent) were mixed uniformly, and a solid A coating liquid (IX) requiring undercoat having a concentration of 25% was obtained.

(2) Formation of undercoat layer Undercoat paper was obtained in the same manner as in Example 1, except that the above-mentioned undercoat required coating liquid (IX) was used instead of undercoat required coating liquid (1).

[Formation of recording layer]

A thermosensitive recording paper was obtained in the same manner as in Example 1 except that the above-mentioned undercoated paper was used.

Comparative Example 5 In the formation of the undercoat layer in Example 1, the undercoat required coating (Vl) prepared in the same manner as in Example 5 was used instead of the undercoat required coating liquid (II). A thermosensitive recording paper was obtained in the same manner as in Example 1.

Comparative Example 6 Except that in Example 1, instead of applying the undercoat required coating liquid (II) of 1 g/nl in terms of dry weight, a polyvinyl alcohol aqueous solution was applied and dried to have a dry weight of 1.5 g/rrf. A thermosensitive recording paper was obtained in the same manner as in Example 1.

Comparative Example 7 In Example 1, instead of applying the undercoat-required coating liquid (1) at a dry weight of 8 g/nf, a carboxymethyl cellulose aqueous solution was applied and dried at a dry weight of 0.3 g/nf. A thermosensitive recording paper was obtained in the same manner as in Example 1.

The 12 types of thermal recording papers obtained in this way were recorded using a thermal printer (SONY VP-103, video printer) at printing pulse times of 3 m5 ec and 8 m5 ec, and the color density of each was measured using a Macbeth densitometer (RD-100).
The results are shown in Table 1.

Furthermore, the printed pixel (dot) reproducibility of the recorded image obtained above is evaluated by evaluating the ratio of the area of a printed dot to the area of one dot of the thermal head (dot reproduction rate) using the following criteria. It is also listed in Table 1.

◎: Dot reproduction rate 86% or more ○: Dot reproduction rate 71-85% △: Dot reproduction rate 61-70% ×: Dot reproduction rate 60% or less Each thermal recording paper was recorded using a thermal facsimile (Canon Canofax 520) The degree of adhesion of residue to the heat-sensitive head and head was visually evaluated, and the results are shown in Table 1. Note that the evaluation criteria for head residue adhesion are as follows.

◎: No head residue adhesion is observed.

○: Slight adhesion of head residue is observed, but there is no problem in practical use.

△: There was considerable adhesion of head residue, which may cause printing problems.

×: There is a large amount of shedding residue, causing printing problems.

Furthermore, the whiteness of the recording layer (background part) was measured using a Hunter whiteness meter, and the results are listed in Table 1.

Table 1 "Effects" As is clear from Table 1, the thermal recording material of the present invention has excellent printed pixel reproducibility in all regions from low density to high density, and also has good recording sensitivity characteristics. It was an excellent thermal recording medium with no residue adhering to the thermal head or background fog.

Claims (3)

[Claims] (1) On the support, at least one undercoat layer containing silica with an oil absorption of 110 ml/100 g or more according to JISK-5101 method, an oil absorption of 80 ml/10
A heat-sensitive recording material, characterized in that an undercoat layer containing 0 g or more of an inorganic or organic oil-absorbing pigment (excluding solid acids) and a heat-sensitive recording layer are sequentially provided. (2) Claim (1) wherein the pigment with an oil absorption of 80 ml/100 g or more is calcined kaolin or alkali-treated silica.
The heat-sensitive recording medium described above. (3) The heat-sensitive recording material according to claim (1), wherein at least one of the undercoat layers containing silica further contains a decoloring agent.