JPH0222091A - Thermal recording material - Google Patents

Abstract

PURPOSE:To improve the reproducibility of a printing pixel in any region from low density to high density and to obtain a recording image of high image quality by providing an intermediate layer containing a basic dye and a coupler capable of forming color upon contact with said dye on a support and further providing a thermal recording layer on said intermediate layer. CONSTITUTION:An intermediate layer containing pigment having apparent specific gravity of 0.7g/cm<3> or less, a colorless or light-colored basic dye and a coupler capable of forming a color upon the contact with said dye is provided on a support and a thermal recording layer is further provided on said intermediate layer to prepare a thermal recording material. Since the dye is contained in the intermediate layer as mentioned above, the color development of the thermal recording layer is supplied by the color development of the intermediate layer at the time of recording and the reproducibility of a printing pixel can be improved in any region from low density to high density and a recording image of high image quality can be obtained.

Description

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

"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 heat-sensitive recording media are relatively inexpensive, and the recording equipment is compact and relatively easy to maintain.
It is used not only as a recording medium for facsimiles and various computers, but also in a wide range of fields.

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

Since the surface of the base paper used as the support of the heat-sensitive recording material has irregularities due to fibers, the surface of the heat-sensitive recording layer formed thereon also has fine irregularities. Therefore, the surface of the recording layer is not necessarily in perfect contact with the thermal head of the recording device, making it difficult to obtain excellent print pixel reproducibility. The base paper has irregularities of 10 to 15 μm, and improvements have been attempted in the past, such as providing an intermediate layer to eliminate the irregularities, performing a super calender treatment after forming the intermediate layer, and providing an intermediate layer with a multilayer structure. This was insufficient to completely eliminate unevenness on the base paper.

For example, in order to obtain a heat-sensitive recording medium with high image quality and high sensitivity, an intermediate layer made of a film-forming polymer material with a glass transition temperature of 60°C or less may be provided between the support and the recording layer (especially JP-A-54-92263), an intermediate layer made of an oil-absorbing pigment was provided (JP-A-59-155097, JP-A-61-4).
No. 4683), and a method of combining these layers into multiple layers to improve smoothness and heat insulation (Japanese Patent Laid-Open No. 61-11
No. 286, No. 61-193880), etc. have been proposed.

However, none of these methods provide sufficient print pixel reproducibility or sensitivity. In addition, the inventors have determined that the thickness of the heat-sensitive recording layer itself is 2.
Although attempts were made to increase the thickness to 0 to 40 μm, sufficient printed pixel reproducibility was still not obtained.

``Problems to be Solved by the Invention'' The present invention solves the above problems, and provides thermal recording that provides excellent reproducibility of printed pixels in all areas from low density to high density, and that provides high-quality recorded images. The purpose is to provide the body.

"Means for Solving the Problems" The present invention provides a method for disposing a material on a support with an apparent specific gravity of 0.7 g/cm3.
A heat-sensitive recording material comprising an intermediate layer containing the following pigment, a colorless or light-colored basic dye, and a coloring agent capable of forming a color when it comes into contact with the dye, and further a heat-sensitive recording layer provided on the intermediate layer. be.

"Function" Since the intermediate layer of the heat-sensitive recording material of the present invention contains a color-forming material, the color development of the intermediate layer supplements the color development of the heat-sensitive recording layer during recording, enabling excellent printed pixel reproducibility and recording density. be.

Incidentally, if the coating amount of the heat-sensitive recording layer provided on the support is simply increased, the unevenness existing on the support cannot be completely eliminated and sufficient printed pixel reproducibility cannot be obtained. Additionally, it has the disadvantage that dregs tend to accumulate in the thermal head. In addition, if two heat-sensitive recording layers are simply provided, the oil absorption of the first heat-sensitive recording layer provided on the support is insufficient, so the heat-melted wax and the like become dregs on the thermal head of the recording device. There are drawbacks that can accumulate.

In the present invention, the intermediate layer has an apparent specific gravity of 0.7 g/cm3 or less,
This problem is solved by containing a pigment, preferably 0.3 g/cm' or less, as a main component, and in the present invention, such a pigment is contained in an amount of preferably 13 to 98 g/cm' or less in the total solid content of the intermediate layer. % by weight, more preferably 35-92% by weight, most preferably 50-90% by weight. When a pigment with a large apparent specific gravity is used or when the content of the pigment is low, dregs tend to accumulate in the thermal head, and conversely, when the content of the pigment is high, it is difficult to obtain sufficient printed pixel reproducibility.

Various inorganic and organic pigments are known as pigments with an apparent specific gravity of 0.7 g/cm3 or less that can be used in the intermediate layer, such as calcined kaolin, talc, light calcium carbonate, amorphous silica, Examples include fine polystyrene powder and fine urea-formalin resin powder.

Among these various pigments, calcined kaolin and amorphous silica are particularly preferably used because they have excellent heat insulating properties and have the effect of further improving recording sensitivity.

As the colorless or light-colored basic dye contained in the intermediate layer, the same dye as that contained in the recording layer or a different dye may be used, or both may be used in combination.

Examples of basic dyes include the following.

3.3-bis(p-dimethylaminophenyl) 6-dimethylaminophthalide, 3.3-bis(p-dimethylaminophenyl) phthalide, 3-(p-dimethylaminophenyl)-3-(1,2-dimethylindole) -3-yl)phthalide, 3-(p-dimethylaminophenyl)-3-(
2-methylindol-3-yl)phthalide, 3,3-
Bis(1,2-dimethylindol-3-yl)5-dimethylaminophthalide, 3.3-bis(1゜2-dimethylindol-3-yl)-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
-Triallylmethane dyes such as -methylpyrrol-3-yl)-6-dimethylaminophthalide, 4,4'bis-dimethylaminobenzhydrylbenzyl ether, N-halophenyl-leucoolamine, N-2,4 ,5-'M
Diphenylmethane dyes such as J-chlorophenylleucoolamine, thiazine dyes such as benzoylleucomethylene blue, p-nitrobenzoylleucomethylene blue,
3-Methyl-spiro-dinaphthopyran, 3-ethyl-spiro-dinaphthopyran, 3-phenyl-spiro-dinaphthopyran, 3-benzyl-spiro-dinaphthopyran, 3-
Spiro dyes such as methyl-naphtho-(6'-methoxybenzo)spiropyran, 3-propyl-spirodibenzopyran, rhodamine B anilinolactam, rhodamine (p
- Lactam dyes such as nitroanilino)lactam, rhodamine (0-chloroanilino)lactam, 3-dimethylamino-7-methoxyfluorane, 3-diethylamino-6-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-dibenzylaminofluorane, 3-diethylamino-7 -N-methyl-N-hensylaminofluorane, 3-diethylamino-7-N-chloroethyl-N-methylaminofluorane, 3-diethylamino-7-N-diethylaminofluorane, 3-(N-ethyl p-toluidino) )-6-methyl-7-phenylaminofluorane,
3-(N-cyclopentyl-N-ethylamino)-6-methyl-7-anilinofluorane, 3-(N-ethyl-p
-toluidino)6-methyl-7-(p-)luidino)fluorane, 3-diethylamino-6-methyl-7-phenylaminofluorane, 3-diethylamino-7(2-
Carbomethoxy-phenylamino)fluorane, 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 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-p- Butylphenylaminofluorane, 3-N-methyl-N-
Fluoran dyes such as tetrahydrofurfurylamino-6-methyl-7-anilinofluorane and 3-N-ethyl-N-tetrahydrofurfurylamino-6-methyl-7-anilinofluorane.

Further, as the coloring agent contained in the intermediate layer, it is possible to use the same coloring agent as that contained in the recording layer, a different coloring agent, or a combination of both.

Examples of coloring agents include the following.

4-tert-butylphenol, α-naphthol, β
-naphthol, 4-acetylphenol, 4tert
-octylphenol, 4.4'-5ec-butylidene diphenol, 4-phenylphenol, 4.4'-
Dihydroxy-diphenylmethane, 44'-isopropylidene diphenol, hydroquinone, 44'-cyclohexylidene diphenol, 4,4'-(1,3-dimethylbutylidene)bisphenol, 4,4'-dihydroxydiphenyl sulfide, 4 ,4'-thiobis(6
tert-butyl-3-methylphenol), 4°4'
-dihydroxydiphenylsulfone, 4-hydroxy-
4'-methyldiphenylsulfone, 4hydroxy-4'
-methoxydiphenylsulfone, 4-hydroxy-4'
-isopropoxydiphenyl sulfone, 4-hydroxy-3'4' trimethylene diphenyl sulfone, 4-
Hydroxy-3'4'-tetramethylenediphenylsulfone,34-dihydroxy-4'-methyldiphenylsulfone, bis(3-allyl-4-hydroxyphenyl)sulfone, 1,3-di(2-(4hydroxyphenyl)) -2-propyl]benzene, 1-[α-methyl-α
-(4'-hydroxyphenyl)ethyl)-4-[α'
, α'-bis(4'-hydroxyphenyl)ethyl]benzene, hydroquinone monobenzyl ether, bis(4
hydroxyphenyl) acetic acid butyl ester, 4-hydroxybenzophenone, 2,4-dihydroxybenzophenone, 2,4,4'-trihydroxybenzophenone,
2.2'4.4' -Tetrahydroxybenzophenone, dimethyl 4-hydroxyphthalate, methyl 4-hydroxybenzoate, ethyl 4-hydroxybenzoate,
Propyl 4-hydroxybenzoate, 5ec-butyl 4-hydroxybenzoate, pentyl 4-hydroxybenzoate, phenyl 4-hydroxybenzoate, hensyl 4-hydroxybenzoate, tolyl 4-hydroxybenzoate, chlorophenyl 4-hydroxybenzoate, Phenylpropyl 4-hydroxybenzoate, phenethyl 4-hydroxybenzoate, p-chlorobenzyl 4-hydroxybenzoate, 4
-Hydroxybenzoic acid - Phenolic compounds such as p-methoxybenzyl, novolak type phenolic resin, phenol polymer, benzoic acid, p-tert-butylbenzoic acid, trichlorobenzoic acid, terephthalic acid, 3-5ecbutyl-4-hydroxy Benzoic acid, 3-cyclohexyl-
4-Hydroxybenzoic acid, 3.5-dimethyl-4-hydroxybenzoic acid, salicylic acid, 3-isopropylsalicylic acid, 37tert-butylsalicylic acid, 3.5-ditert-butylsalicylic acid, 3-hensylsalicylic acid, 3-( α-Methylbenzyl) salicylic acid, 3-chloro1m1-5- (7 volumes methylbenzyl) salicylic acid, 3-phenyl-5 (α,
α-dimethylbenzyl)salicylic acid, 3゜5-di-α-
Aromatic carboxylic acids such as methylbenzyl salicylic acid, and these phenolic compounds, aromatic carboxylic acids such as zinc, magnesium, aluminum, calcium,
Organic acidic substances such as salts with polyvalent metals such as titanium, manganese, tin, and nickel. Incidentally, it is of course possible to use two or more of these coloring agents in combination as necessary.

Among them, 4.4'-isopropylidenediphenol, 4
．． 4'-(1,3-dimethylbutylidene)bisphenol, 4-hydroxy-4'-isopropoxydiphenylsulfone, etc. are preferably used because they do not cause background fog in the resulting recording material.

In the present invention, the total weight of the basic dye and coloring agent (i.e., color-forming material) contained in the intermediate layer is 1 to 10% of the total solid content of the intermediate layer.
40% by weight, and the weight ratio of dye and coloring agent is t
ri to 1:50 is preferred.

If the amount of color-forming material is small, it will be difficult to obtain sufficient print pixel reproducibility.
If there is too much, lees tend to accumulate on the thermal head.

A binder, which will be described later in connection with the heat-sensitive recording layer, is usually added to the coating solution for the intermediate layer in an amount of about 1 to 30% by weight based on the total solid content of the intermediate layer.

The coating solution for the intermediate layer is generally prepared by using water as a dispersion medium and dispersing pigments, basic dyes, coloring agents, etc. together or separately using a ball mill, attritor, Santo mill, etc., stirring or grinding machine. .

The dry coating weight of the intermediate layer is usually 5 to 40 g 7 m2.

It is also possible to provide multiple intermediate layers in order to further increase the oil absorption of the intermediate layer and reduce the amount of debris in the thermal head, or to further improve the recording density by increasing the heat insulation effect. When the intermediate layer has a multilayer structure, it is also possible to provide a first intermediate layer without a color-forming material on the support, and then provide a second intermediate layer containing the color-forming material.

A heat-sensitive recording layer is coated on the intermediate layer thus formed and dried to produce the heat-sensitive recording material of the present invention. There are no particular limitations on the combination of the coloring agent and the coloring agent contained in the heat-sensitive recording layer, and any combination can be used as long as the two come into contact with each other due to heat and cause a coloring reaction. Examples include combinations of colorless or 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 can be applied to various heat-sensitive recording materials in which a recorded image is obtained by heat, such as a heat-sensitive recording layer containing a combination of a diazonium compound, a coupler, and a basic substance.

However, the recording medium of the present invention exhibits an excellent effect particularly in a combination of a colorless or light-colored basic dye and an acidic substance as a coloring agent, and is therefore particularly preferably applied to such a combination.

Various colorless to light-colored basic dyes are known and can be selected from those listed above in the description of the intermediate layer.

In addition, various inorganic or organic coloring agents that develop color upon contact with colorless or light-colored basic dyes are also known, and can be selected from the coloring agents mentioned above as a component of the intermediate layer.

In the present invention, the ratio of the coloring agent to the coloring agent used 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 an acidic substance as a coloring agent,
Generally, 1 to 50 parts by weight, preferably 1 to 10 parts by weight of acidic substance are used per part by weight of basic dye.

The coating solution for the heat-sensitive recording layer containing these substances is generally prepared by using water as a dispersion medium and dispersing the coloring agent and the coloring agent together or separately using a ball mill, attritor, sand mill, or other stirring or pulverizing machine. This is done by

Such coating liquids usually contain starches and binders as binders.
Hydroxyethylcellulose, methylcellulose, carboxymethylcellulose, gelatin, casein, gum arabic, polyvinyl alcohol, diisobutylene/maleic anhydride copolymer salt, styrene/maleic anhydride copolymer salt, ethylene/acrylic acid copolymer salt, styrene/
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, ethylene/hinyl acetate Total solid content of emulsions etc. is 10~
It is added in an amount of 70% by weight, preferably 15 to 50% by weight.

Furthermore, various auxiliary agents can be added to the coating liquid for the heat-sensitive recording layer, such as sodium dioctyl sulfosuccinate, sodium dodecylbenzenesulfonate, sodium lauryl alcohol sulfate, alginate, fatty acid metal. Dispersants such as salt, benzophenone,
Examples include triazole-based ultraviolet absorbers, other antifoaming agents, fluorescent dyes, and colored dyes.

In addition, lubricants such as zinc stearate, calcium stearate, polyethylene wax, carnauba wax, paraffin wax, and ester wax, calcium carbonate, zinc oxide, aluminum oxide, titanium dioxide, silicon dioxide, aluminum hydroxide, barium sulfate, and sulfuric acid may also be used as necessary. Inorganic pigments such as zinc, talc, kaolin, clay, fired clay, colloidal silica, styrene micropol,
Nylon powder, polyethylene powder, urea/formalin resin filler, organic pigments such as raw starch, fatty acid amides such as stearic acid amide, stearic acid methylene bisamide, oleic acid amide, palmitic acid amide, coconut fatty acid amide, dibenzyl terephthalate, ■ , 2-
Di(3-methylphenoxy)ethane, 1.2-diphenoxyethane, 44'-ethylenedioxy-bis-benzoic acid diphenylmethyl ester, 1. 1. 3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)phthane, 2,2'-methylenebis(4methyl-5-tert-butylphenol), 4,4'-butylidenebis(6-tert-butyl) Hindered phenols such as -3-methylphenol and various known thermofusible substances can also be added.

When an inorganic or organic pigment is contained in the heat-sensitive recording layer, it is preferable to use a pigment with a particle size as small as possible, and it is particularly desirable to use a pigment with an average particle size of 2 μm or less.

There is no particular limitation on the amount of coating liquid for heat-sensitive recording material.
Usually 2-12 g/rrf in dry weight, preferably 3-12 g/rrf
It is in the range of about 10 g/rd.

There are no particular limitations on the method of forming the intermediate layer and the heat-sensitive recording layer, for example, by using a coating device equipped with a suitable coater head such as an air knife coater or a blade coater
It is formed by applying each coating liquid onto a support or an intermediate layer and drying it.

Supports include high-quality paper, base paper made with a Yankee machine, single-sided glossy base paper, double-sided glossy base paper, cast coated paper, art paper, coated paper, medium-quality coated paper, synthetic fiber paper, and synthetic resin film. etc. are used as appropriate.

Incidentally, after coating and drying the intermediate layer and the recording layer, smoothing treatment such as super calendering may be performed as necessary. Furthermore, it is possible to provide an overcoat layer on the recording layer for the purpose of protecting the recording layer, etc., and various known techniques in the field of heat-sensitive recording materials can be added, such as providing a backing layer on the support. .

The thus obtained heat-sensitive recording material of the present invention has an intermediate layer having a specific composition between the support and the heat-sensitive recording layer, so that pixel reproducibility is improved in any range from low density to high density. It is a heat-sensitive recording material with excellent recording density and high recording density.

"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 [Preparation of intermediate layer coating liquid] ■ Preparation of liquid A 3-(N-ethyl-N-iso-amyl)amino-6-methyl-7-phenylaminofluorane
10 parts methylcellulose 5% aqueous solution
15 parts water
50 parts of this composition was ground in a sand mill to an average particle size of 2 μm.

■ Preparation of Solution B 4. 4'-isopropylidenediphenol 30 parts Methylcellulose 5% aqueous solution 30 parts water
80 parts of this composition was ground in a sand mill until the average particle size was 2 μm.

[Intermediate layer coating liquid-1] Baked clay (apparent specific gravity 0.22 g/cm3) 1
00 parts SBR (glass transition point -20"C1 solid content = 50%)
20 parts polyvinyl alcohol 10% zlJ solution 20 parts A solution
60 parts B liquid 100 parts water
Intermediate layer coating liquid-1 was prepared by mixing 50 parts of the above composition.

[Formation of Intermediate Layer] The obtained Intermediate Layer Coating Solution-1 was coated and dried on a high-quality paper with a basis weight of 50 g/rd so that the coating amount after drying was 10 g/n (20 g/n) to form an intermediate layer.

[Preparation of coating liquid for recording layer]

125 parts of liquid A, 130 parts of liquid B, 30 parts of silicon oxide, 20 parts
A recording layer coating liquid was prepared by stirring and mixing 150 parts of % oxidized starch aqueous solution and 55 parts of water.

[Formation of recording layer] The obtained recording layer coating liquid was applied onto the intermediate layer so that the coating amount after drying was 5 g/n (drying), and supercalender treatment was performed to form a heat-sensitive recording material. Obtained.

Example 2 [Intermediate layer coating liquid-2] Amorphous silica (apparent specific gravity 0.18 g/cm3) 1
00 parts SBR (glass transition point -20'C, solid content: 50%)
20 parts 10% aqueous solution of polyvinyl alcohol 20 parts Solution A
10 parts B liquid 10 parts water 5
Intermediate layer coating liquid-2 was prepared by mixing 0 parts of the above composition.

A heat-sensitive recording material was obtained in the same manner as in Example 1 except that Intermediate layer coating liquid-2 was used instead of Intermediate layer coating liquid-1.

Example 3 However, 3-dibutylamino-6-methyl-7phenylaminofluoran manufactured by M 10 parts Methyl cellulose 5% aqueous solution 15 parts water
50 parts of the above composition was ground in a sand mill until the average particle size was 2 μm.

■ 4-Hydroxy-4'-isopropoxydiphenylsulfone made by Natsutada 30 parts Methylcellulose 5% aqueous solution 30 parts water
80 parts of this composition was ground in a sand mill until the average particle size was 2 μm.

[Intermediate layer coating liquid-3] Baked clay (apparent specific gravity 0.22 g/cm3) 10
0 parts SBR (glass transition point -20°C1 solid content: 50%)
20 parts 10% aqueous solution of polyvinyl alcohol 20 parts Solution C
60 parts stock solution 100 parts water 50
Intermediate layer coating liquid-3 was prepared by mixing the above compositions.

A heat-sensitive recording material was obtained in the same manner as in Example 1 except that Intermediate layer coating liquid-3 was used instead of Intermediate layer coating liquid-1.

Example 4 [Preparation of intermediate N coating liquid-4] Baked clay (apparent specific gravity 0.22 g/cm3) 10
0 parts SBR (glass transition point -20'C, solid content: 50%)
20 parts 10% aqueous solution of polyvinyl alcohol 20 parts water
Intermediate layer coating liquid-4 was prepared by mixing 50 parts of the above composition.

[Formation of intermediate layer]

The obtained intermediate layer coating liquid-4 was applied to a high-quality paper with a basis weight of 50 g/rrf so that the coating amount after drying was Log/rrf, and dried to form a first intermediate layer. Intermediate layer coating liquid-1 was coated and dried on the first intermediate layer so that the dry coating amount was 5 g/i to obtain a multilayer intermediate layer.

A thermosensitive recording material was obtained in the same manner as in Example 1 except for using the above intermediate layer.

Example 5 [Preparation of intermediate layer coating liquid-5] Baked clay (apparent specific gravity 0.22 g/cm3) 40
Part SBR (glass transition point -20°C2 solid content = 50%)
20 parts 10% aqueous solution of polyvinyl alcohol 20 parts Solution A 100 parts Solution B
100 parts water
Intermediate layer coating liquid-5 was prepared by mixing 50 parts of the above composition.

A heat-sensitive recording material was obtained in the same manner as in Example 1, except that Intermediate layer coating liquid-5 was used instead of Intermediate layer coating liquid-1.

Example 6 In the preparation of intermediate layer coating liquid-5 of Example 5, baking sheet 4
A thermosensitive recording material was obtained in the same manner except that 0 parts were changed to 10 parts.

Comparative Example 1 A thermosensitive recording material was obtained in the same manner as in Example 1 except that Intermediate Layer Coating Liquid-4 was used instead of Intermediate Layer Coating Liquid-1.

Comparative Example 2 A thermosensitive recording material was obtained in the same manner as in Example 4, except that Intermediate Layer Coating Liquid-4 was used instead of Intermediate Layer Coating Liquid-1.

Comparative Example 3 A thermosensitive recording material was obtained in the same manner as in Example 1 except that 10 parts of 3-(N-ethyl N-isoamyl)amino-6-methyl-7-phenylaminofluorane was not added in the preparation of lacquer A. Ta.

Each heat-sensitive recording medium thus obtained was printed on a heat-sensitive printer (S
ONY UP-701 model, video printer) was used to record printing pulse times of 3 ms and 8 ms, and the color density was measured with a Macbeth densitometer (RD-100R model, using an amber filter), and the results were reported in the It is shown in Table 1. We also evaluated the reproducibility of printed pixels and used the results as the first
Also listed in the table.

The reproducibility of printed pixels was evaluated by the ratio of the area of a printed dot to the area of one dot of the thermal head (double 1 to reproduction rate), and the evaluation criteria were as follows.

◎・・・86% or more○・・・76-85% △・・・70-75% ×・・・74% or less Head dregs test facsimile (NEFAX-27, NEC 10 sheets of A4 size recording charts (printing rate: 50%) were recorded, and the state of the scum adhering to the thermal head was visually observed.

Head dregs evaluation ◎・・・・・・No head dregs observed ○・・・・・・
Head lees can be seen slightly.

△・・・・・・Head residue can be confirmed.

Table 1 "Effects" As is clear from the results in Table 1, the heat-sensitive recording material of the present invention has excellent reproducibility of printed pixels in any region from low density to high density, and has a high recording density. It was an excellent thermosensitive recording medium.

Claims (2)

[Claims] (1) An intermediate layer containing a pigment with an apparent specific gravity of 0.7 g/cm^3 or less, a colorless or light-colored basic dye, and a coloring agent capable of forming a color upon contact with the dye is provided on the support. , a heat-sensitive recording material further comprising a heat-sensitive recording layer provided on the intermediate layer. (2) The total weight of the colorless or light-colored basic dye and the coloring agent that can develop color when in contact with the dye is 1 to 40% of the total solid content of the intermediate layer.
The heat-sensitive recording material according to claim 1, wherein the amount is % by weight.