JPS6153959B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a heat-sensitive recording medium with improved continuous recording properties and high recording sensitivity. Conventionally, heat-sensitive recording materials that utilize a coloring reaction between a coloring agent and a coloring agent that can develop a color when brought into contact with the coloring agent, and obtain a colored image by bringing both coloring materials into contact with heat, have been well-known. Are known. There are various heat transfer means for putting such heat-sensitive recording materials into practical use, and each method is suitable for the purpose. One type of heat transfer means is a thermal head (an assembly of dot-shaped electrical resistance heating elements). A method of obtaining a colored recorded image is carried out by transmitting the Joule heat generated by passing a current pulse corresponding to a recording signal to the surface of a heat-sensitive recording medium that is placed in close contact with a thermal head. However, one of the difficulties in putting this type of system into practice is that the coloring material, which is in a molten state when heated, transfers and adheres to the thermal head. This so-called "scum adhesion" gradually accumulates during continuous recording, and as a result, the heat conduction from the thermal head to the heat-sensitive recording medium decreases, which not only significantly impairs the recording speed but also reduces the recorded image quality and density. It will bring about. Furthermore, another difficulty in putting such a system into practice is that the surfaces of the thermal head and the heat-sensitive recording material become sticky or sticky when heat is applied. This so-called "state king" not only prevents the smooth feeding of the recording medium, but also causes the line spacing to become short during recording and the recorded image to be blurred, making continuous recording impossible and sometimes even causing damage to the thermal head. . In order to improve the above-mentioned difficulties, proposals have been made such as adding general clay, talc, calcium carbonate, titanium oxide, etc. to the coloring layer, or increasing the amount of adhesive in the coloring layer. (Unexamined Japanese Patent Publication 1973)
−33832, USP3859112). However, in order to improve dust adhesion and staining on the thermal head with this method, it is necessary to add an extremely large amount of general pigment, and as the improvement is made, it is unavoidable that the density of the recorded image will decrease, and the color development Similar drawbacks are associated with increasing the amount of adhesive in the layer. In view of the current situation, the inventors of the present invention have conducted intensive research on heat-sensitive recording materials with improved continuous recording properties, and have developed a color-forming layer containing pigments with extremely high oil absorption properties that efficiently absorb color-forming substances that are in a molten state when heated. It was discovered that the above-mentioned drawbacks could be effectively improved by including the
Proposed as No. 86229. The continuous recording properties of heat-sensitive recording media have been significantly improved by incorporating oil-absorbing pigments, but recently, information equipment such as facsimiles, computers, and telex that use such heat-sensitive recording media as recording media have become faster. Along with this, the application time in the thermal head during recording has become extremely short, so that continuous recording tends to be insufficient even when such oil-absorbing pigments are incorporated. Significantly increasing the blended amount of oil-absorbing pigments naturally causes a decrease in recorded image density, so it is important to apply it to high-speed information equipment without a decrease in image density and with stable continuous recording performance. It is desired to develop a heat-sensitive recording material that obtains the following. Therefore, the main object of the present invention is to provide a heat-sensitive recording medium that has excellent continuous recording properties, high recording sensitivity, and can be stably applied to high-speed information equipment. The object of the present invention is to provide (a) a color former, (b) a color former capable of forming a color upon contact with the color former when heated, and (c) a melting point of
In a heat-sensitive recording material provided with a color-forming layer containing a thermofusible substance having a temperature of 60 to 200°C, the surface of a pigment whose oil absorption amount is 80 ml/100 g or more as measured based on JISK5101 is colored by the above (a). (b) coloring agent and (c)
This is achieved by including in the color forming layer a pigment coated with at least one type of thermofusible substance (excluding a combination of a color former and a color former). In the present invention, the (a) coloring agent and (b) coloring agent contained in the coloring layer include, for example, a combination of a basic colorless dye and an inorganic or organic acidic substance, ferric stearate, ferric myristic acid, etc. Examples include combinations of metal salts of long-chain fatty acids such as iron and phenols such as tannic acid and gallic acid. Various types of basic colorless dyes are known, and examples include the following. 3,3-bis(p-dimethylaminophenyl)
-6-dimethylaminophthalide, 3,3-bis(p-dimethylaminophenyl)phthalide, 3-
(p-dimethylaminophenyl)-3-(1,2-
Triallylmethane dyes such as dimethylindol-3-yl) phthalide, 4,4'-bis-dimethylaminobenzhydrylbenzyl ether, N-halophenyl-leucoauramine, N-2,4,5-
Diphenylmethane dyes such as trichlorophenyl leuco auramine, 7-dimethylamino-3-chlorofluoran, 7-diethylamino-3-chloro-2-methylfluoran, 2-phelamino-
Fluorane dyes such as 3-methyl-6-(N-ethyl-N-p-tolyl)aminofluorane, thiazine dyes such as benzoylleucomethylene blue, p-nitrobenzylleucomethylene blue,
Spiro dyes such as 3-methyl-spiro-dinaphthopyran, 3-ethyl-spiro-dinaphthopyran, 3-propyl-spiro-dibenzopyran, etc. In addition, various inorganic or organic acidic substances that change color when they come into contact with basic colorless dyes are known.
For example, the following are exemplified. Inorganic acidic substances such as activated clay, acid clay, attapulgite, bentonite, colloidal silica, aluminum silicate, 4-tertiarybutylphenol, 4-hydroxydiphenoxide, α-naphthol, β-naphthol, 4-hydroxyacetophenol, 4-tert-octylcatechol, 2.2'-dihydroxydiphenol, 2.
2'-methylenebis(4-methyl-6-tert-isobutylphenol), 4,4'-isopropridene bis(2-tert-butylphenol), 4,4'-secondary-butylidenephenol, 4-phenyl Phenol, 4,4'isopropylidenediphenol, 2,2'-methylenebis(4
-chlorphenol), hydroquinone, 4.
Phenolic compounds such as 4' cyclohexylidine diphenol, novolac type phenolic resin, phenolic polymer, benzoic acid, paratertiarybuterbenzoic 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-tertiarybutylsalicylic acid, 3-benzylsalicylic acid, 3-(α-methylbenzyl)salicylic acid, 3-chloro-5-(α-methylbenzyl)
Aromatic carboxylic acids such as salicylic acid, 3,5-dithyabutylsalicylic acid, 3-phenyl-5-(α,α-dimethylbenzyl)salicylic acid, 3,5-di-α-methylbenzylsalicylic acid, and these phenolic acids compounds, organic acidic substances such as salts of aromatic carboxylic acids and polyvalent metals such as magnesium, aluminum, calcium, titanium, manganese, tin, nickel, etc.; In the heat-sensitive recording material of the present invention, the ratio of the color former and color former in the color forming layer is appropriately selected depending on the type of color former and color former used, and is not particularly limited. For example, when using a basic colorless dye and an acidic substance, generally 1 to 50 parts by weight, preferably 4 to 10 parts by weight of the acidic substance are used per 1 part by weight of the basic colorless dye. In the present invention, the (c) thermofusible substance contained in the coloring layer is preferably 60 to 200°C, more preferably 65 to 120°C.
has a melting point of at least one of a color former and a color former.
It is preferable to use a substance that has the property of dissolving the color former and the color forming agent, and that does not exhibit a practical color forming function with the color forming agent. Examples of such substances include the following. mp 2,6-diisopropyl-naphthalene 68 °C 1,4,5-trimethyl-naphthalene 63 °C 2,3,5-trimethyl-naphthalene 146 °C 2,3,6-trimethyl-naphthalene 102 °C 1,5-dimethylnaphthalene 82 °C 1,8-dimethylnaphthalene 65 °C 2,3-dimethylnaphthalene 105 °C 2,6-dimethylnaphthalene 113 °C 2,7-dimethylnaphthalene 98.5 °C 1,2,3,4-tetramethylnaphthalene
106℃ mp 1,3,6,8-tetramethylnaphthalene
85℃ 1,4,5,8-tetramethylnaphthalene
121 °C 1,2,6,7-tetramethyl-4-isopropylnaphthalene 103 °C 1,3,6,7-tetramethyl-4-isopropylnaphthalene 97 °C 2,7-di-tertiarybutylnaphthalene
104 °C 1,2-di-O-tolylethane 66 °C α-methyl-4,4'-di-tert-butyl-
Diphenylmethane 94 °C 1,2-di-p-tolylethane 82 °C 1,2-bis(4ethylphenyl)ethane
69.8℃ 1,1,2,2-tetramethyl 1,2, di-p
-Tolylethane 159°C α・βbis(tert-butylphenyl)ethane 149°C 2,3-di-m-tolylbutane 97°C 2,3-dimethyl-2,3-di-p-tolylbutane 158°C Diphenyl-p-tolylmethane 72 °C Diphenyl-O-tolylmethane 83 °C 1,2-dibenzylbenzene 78 °C 1,3-dibenzylbenzene 59 °C 1,4-dibenzylbenzene 86 °C Diphenyl O-tolylmethane 83 °C 3,4-diphenyl Enylhexane 92 ℃ 1,2bis[2,3dimethylphenyl]ethane
112 ℃ 1.2bis[2.4dimethylphenyl]ethane
72 ℃ 1.2bis[3.5dimethylphenyl]ethane
86 ℃ 4'-Methyl-4'-α-methyl-p-methylbenzyl-1,1-diphenylethane 85 ℃ Bis-[2,4,5-trimethylphenyl]methane 98 ℃ Bis-[2,4,6 -Trimethylphenyl]methane 135 °C 1,2bis-[2,4,6-trimethylphenyl]ethane 118 °C [2,3,5,6-tetramethylphenyl]-[4
-tertiarybutylphenyl]methane 117℃ 1.6bis[2.4.6trimethylphenyl]
Hexane 74 °C Bis-[2,6-dimethyl-4tertiarybutylphenyl]methane 135 °C 1,18-diphenyl-octadecane 61 °C 4,4'-dimethylbiphenyl 121 °C 2,4,6,2'4',6'-Hexamethylbiphenyl 101℃ 4,4'-Di-tertiarybutylbiphenyl
128 °C 2,6,2',6'-tetramethylbiphenyl
67 ℃ 1,3-terphenyl 87 ℃ mp Stearamide 99 ℃ Stearic acid methylene bisamide 140 ℃ Oleic acid amide 68-74 ℃ Palmitic acid amide 95-100 ℃ Matcha oleic acid amide 65-72 ℃ Coconut fatty acid amide 85-90 ℃ Other examples include N-methylamide, anilide, β-naphthylamide, N-(2-hydroxyethyl)amide, N-(mercaptoethyl)amide, N-octadecylamide, and phenylhydrazide. The amount of such a thermofusible substance to be used is not limited as the appropriate amount varies depending on the type of thermofusible substance used, the coloring agent, the type of coloring agent, etc., but usually the coloring agent It is used in an amount of 0.1 to 30 parts by weight, preferably 0.5 to 10 parts by weight per 1 part by weight. In the present invention, two or more of the coloring agent, coloring agent, and thermofusible substance may be used in combination. In the heat-sensitive recording material of the present invention, the coloring agent as described above,
In the coloring layer containing a coloring agent and a thermofusible substance,
It contains a pigment whose surface has been coated with at least one of such a coloring agent, a coloring agent, and a thermofusible substance, but the pigment before coating is JISK5101.
If the oil absorption amount measured based on is less than 80ml/100g, the desired improvement effect cannot be obtained.
80ml/100g or more, preferably 100-400ml/100g
A pigment having an oil absorption amount of .
Examples of pigments that have such a specific oil absorption amount and are useful in the present invention are as follows. Diatomaceous earth Oil absorption (ml/100g) 100-120 Calcined diatomaceous earth Oil absorption (ml/100g)
130-140 Flux calcined diatomaceous earth Oil absorption (ml/100g)
120～160 Fine particulate anhydrous aluminum oxide oil absorption (ml/100
g) 80-250 Particulate titanium oxide oil absorption (ml/100g)
80～120 White carbon oil absorption (ml/100g)
80～300 Particulate silicon oxide oil absorption (ml/100g)
100～300 Magnesium aluminosilicate oil absorption (ml/100
g) 300 to 400 Among these, pigments that have -OH groups on the pigment surface, such as fine particulate silicon oxide, are used as coloring agents,
When the surface is treated with a thermofusible substance, it is more preferably used because it also exhibits the effect of preventing paint fogging and preventing the coloring layer from fading over time. Incidentally, since the oil absorption amount of a pigment changes depending on factors such as particle shape and particle size, various pigments that have been made to maintain a specific oil absorption amount as described above through physical and chemical treatments are also used. It can be used as an effective pigment. The surface of the specific oil-absorbing pigment as mentioned above is
Examples of the method of coating with a treatment agent consisting of at least one of a coloring agent and a thermofusible substance include the following method. 1. A method in which an oil-absorbing pigment is mixed into a heat-molten treatment agent, coated by cooling and solidifying, and then pulverized using a suitable pulverizer such as an attritor, sand mill, or ball mill. 2. A method of coating by mixing an oil-absorbing pigment into a heat-molten treatment agent, stirring and dispersing it in water, and cooling it. 3. A method of coating by dissolving the treatment agent in a suitable solvent, mixing the oil-absorbing pigment therein, and then evaporating the solvent. 4. A method in which a treatment agent with a low melting point is dissolved in warm water, an oil-absorbing pigment is mixed therein to adhere the treatment agent to the surface, and the coating is then cooled. As mentioned above, the coating treatment on the surface of the pigment is carried out using at least one of a coloring agent, a coloring agent, and a thermofusible substance, but when a coating treatment is performed using a combination of a coloring agent and a coloring agent, Naturally, such a combination is excluded because both react and develop color during the coating process. In the present invention, as a treatment agent consisting of at least one of a coloring agent, a coloring agent, and a thermofusible substance to be coated on the surface of an oil-absorbing pigment, various substances as described above are used. The coloring agent, coloring agent, and thermofusible substance to be contained in the layer can also be used as they are as a processing agent. Furthermore, if the amount of such a treatment agent applied to the oil-absorbing pigment is too small, the desired effect of the present invention cannot be obtained, so it is preferably 5 to 500 parts by weight per 100 parts by weight of the pigment. It is desirable to apply 10 to 400 parts by weight of the treatment agent. In the present invention, the proportion of the specific pigment whose surface has been coated in the coloring layer is generally about 5 to 80% by weight (dry weight), preferably about 10 to 65% by weight. be done. In addition, the coating liquid for forming the coloring layer contains starches, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, styrene, maleic anhydride copolymer salt, styrene-butadiene, as is well known in the conventional art. Various binders such as copolymer emulsions, stearic acid, anti-staking agents such as normal paraffin wax emulsions, various dispersants such as dioctyl sulfosuccinates, fatty acid metal salts, etc.
Ultraviolet absorbers such as benzophenone type and triazole type, ester type, ether type, alcohol type,
Various auxiliary agents such as silicone-based antifoaming agents, fluorescent dyes, and colored dyes, as well as general pigments such as calcium carbonate, zinc oxide, titanium oxide, kaolin, and clay, and one type of normal oil-absorbing pigment. The above components can be blended as needed within a range that does not impair the desired effects of the present invention. Note that the method of forming the coloring layer is not particularly limited, and may be formed according to conventionally known and commonly used techniques. The heat-sensitive recording material of the present invention obtained in this way has high-speed processing, probably because the specific surface-treated pigment contained in the color-forming layer absorbs the color-forming substance in a molten state very efficiently in a short period of time during recording. Even when applied to information equipment, stable continuous recording can be performed without a decrease in image density. The present invention will be described in more detail with reference to Examples below, but it is of course not limited thereto. Further, unless otherwise specified, parts and % in the examples indicate parts by weight and % by weight, respectively. Example 1 Preparation of liquid A 2-phenylamino-3-methyl-6-(N-
Ethyl-P-tolyl)aminofluorane 100 parts Stearamide (mp 99°C) 200 parts Methyl cellulose 5% aqueous solution 100 parts Water 600 parts This composition was ground with a sand grinder until the average particle size was 3 μm. Preparation of liquid B: 100 parts of finely divided silicon oxide having an oil absorption of 300 ml/100 g were added and mixed into 200 parts of bisphenol A which had been heated and dissolved at 160°C. When both were thoroughly mixed, they were added to 1200 parts of water, and cooled while being pulverized with a homomixer. The average particle size after crushing is
It was 10 μm. Formation of coloring layer: 1000 parts of liquid A, 1500 parts of liquid B, oil absorption 300ml/
100g of microparticulate silicon oxide, 200 parts, 650 parts of 15% polyvinyl alcohol aqueous solution, 200 parts of styrene-butadiene copolymer latex (solid content 50%)
part, zinc stearate emulsion (solid content 20
%) and an appropriate amount of antifoaming agent were mixed to prepare a coating liquid. This coating liquid was applied to a base paper of 49 g/m ² with a dry weight of 7
g/m ² and treated with a super calender to obtain thermal recording paper. Example 2 Preparation of liquid A 2-phenylamino-3-methyl-6-(N-
Ethyl-P-tolyl) aminofluorane 100 parts Styrene/acrylic acid copolymer sodium salt 30
% aqueous solution 10 parts water 300 parts This composition was ground with a sand grinder until the average particle size was 2 μm. Preparation of Solution B 200 parts of bisphenol A and 200 parts of stearic acid amide were mixed and then heated and melted at 120°C. 300 parts of silicon oxide having an oil absorption of 200 ml/100 g were added to this mixed melt, and when the three components were sufficiently mixed, it was added to 2,800 parts of water, and cooled while being pulverized with a homomixer. The average particle size after pulverization was 8 μm. Formation of coloring layer Mix and disperse 410 parts of liquid A, 3500 parts of liquid B, 650 parts of 15% polyvinyl alcohol aqueous solution, 100 parts of styrene-butadiene copolymer latex (solid content 50%) and 50 parts of zinc stearate to make a coating liquid. And so. This coating liquid was coated onto a base paper weighing 49 g/m ² to give a dry weight of 6 g/m ² and subjected to supercalender treatment to obtain heat-sensitive recording paper. Example 3 Preparation of liquid A 2-phenylamino-3-methyl-6-(N
-ethyl-P-tolyl)aminofluorane 100
150 parts of finely divided titanium oxide having an oil absorption of 85 ml/100 g were added thereto, and after uniform mixing, the chloroform was evaporated. The obtained treated pigment was added to 1000 parts of water and ground with a homomixer until the average particle size was 4 μm. B-solution preparation Bisphenol A 200 parts Stearamide 200 parts Styrene/acrylic acid copolymer sodium salt 30
% aqueous solution 10 parts water 960 parts This composition was ground with a sand grinder until the average particle size was 3 μm. Formation of coloring layer: 1250 parts of liquid A, 1360 parts of liquid B, oil absorption 300ml/
100g of finely divided silicon oxide, 100 parts of styrene.
Butadiene copolymer latex (50% solids)
200 parts, polyvinyl alcohol 15% aqueous solution 650
100 parts of zinc stearate and 30 parts of an antifoaming agent were mixed and dispersed to prepare a coating liquid. This coating liquid is 49g/m ²
The mixture was coated on base paper to a dry weight of 5 g/m ² and subjected to supercalender treatment to obtain thermosensitive recording paper. Example 4 Preparation of Solution A 100 parts of 3-(N-cyclohexyl-N-methylamino)-6-methyl-7anilinofluorane and methylene bisstearylamide (mp130
℃）200 parts, heated and melted at 150℃, and 300 parts of silicon oxide with an oil absorption of 200ml/100g when melted.
part was added and mixed. Gradually add this mixture to 2400 parts of water with high speed stirring to obtain an average particle size of 12 μm.
A treated pigment dispersion was obtained. B-solution preparation Bisphenol A 200 parts Styrene/acrylic acid copolymer sodium salt 30
% aqueous solution 10 parts water 960 parts
It was ground to 1.5 μm. Formation of coloring layer: 3000 parts of liquid A, 800 parts of liquid B, 200 parts of styrene-butadiene copolymer latex (solid content 50%)
parts, 650 parts of 15% polyvinyl alcohol aqueous solution,
A coating solution obtained by mixing and dispersing 50 parts of zinc stearate was applied to a base paper weighing 49 g/m ² to a dry weight of 6 g/m ² and subjected to supercalender treatment to obtain heat-sensitive recording paper. Example 5 200 parts of stearamide was heated and dissolved at 110°C, and at the same time, 250 parts of anhydrous aluminum oxide having an oil absorption of 125 ml/100 g were added and mixed. When both were well mixed, the mixture was ground in 1800 parts of water using a homomixer and cooled. The average particle size was 10 μm. To 2250 parts of this dispersion, 410 parts of liquid A used in Example 2, 810 parts of liquid B used in Example 4, 650 parts of a 15% polyvinyl alcohol aqueous solution, and 100 parts of zinc stearate were added and mixed, and further an antifoaming agent was added. 30 parts were added to prepare a coating liquid. This coating liquid was applied to base paper of 49 g/m ² with a dry weight of 7
g/m ² and treated with a super calender to obtain thermal recording paper. Example 6 1000 parts of 20% emulsion of stearic acid amide and fine particulate silicon oxide with an oil absorption of 300 ml/100 g
350 parts were mixed and heated at 90° C. for 2 hours while stirring, and then naturally cooled. 2750 parts of this dispersion, 410 parts of liquid A used in Example 2, 810 parts of liquid B used in Example 4, and a 15% polyvinyl alcohol aqueous solution.
A coating liquid was prepared by adding and mixing 650 parts of 50% styrene-butadiene copolymer latex, 200 parts, and 100 parts of zinc stearate. Apply this coating liquid to 49g/ ^m2 base paper with a dry weight of 7g/ ^m2.
A thermal recording paper was obtained by coating with a supercalender treatment. Comparative example 1 Preparation of liquid A 2-phenylamino-3-methyl-6-(N-
Ethyl-p-tolyl)aminofluorane 100 parts Stearamide 100 parts Dispersant 5 parts Water 480 parts This composition was ground with a sand grinder until the average particle size was 2.8 μm. Preparation of Part B Bisphenol A 200 parts Stearamide 100 parts Dispersant 5 parts Water 710 parts This composition was ground with a sand grinder until the average particle size was 2.4 μm. Formation of coloring layer: 685 parts of liquid A, 1015 parts of liquid B, zinc stearate
500 parts of 20% emulsion, oil absorption 200ml/100
A coating liquid was prepared by mixing and dispersing 300 parts of silicon oxide (g), 650 parts of a 15% aqueous polyvinyl alcohol solution, and 200 parts of a 50% styrene-butadiene copolymer latex. This coating liquid was applied to a base paper weighing 49 g/m ² to give a dry weight of 7 g/m ² and subjected to supercalender treatment to obtain heat-sensitive recording paper. Comparative Example 2 200 parts of stearic acid amide was heated and dissolved at 110°C, and kaolin 220 with an oil absorption of 40 ml/100 g was added to the solution.
part was added and mixed. Once both are thoroughly mixed
The mixture was added to 1200 parts of water and cooled while being crushed with a homomixer. The average particle size after pulverization was 5 μm. Part A used in Example 2 was added to 1400 parts of this dispersion.
410 parts, 810 parts of B liquid used in Example 4, 650 parts of 15% polyvinyl alcohol aqueous solution, 50% styrene.
200 parts of butadiene copolymer latex was added and mixed to prepare a coating liquid. This coating liquid was applied to a base paper weighing 49 g/m ² to give a dry weight of 6 g/m ² and subjected to supercalender treatment to obtain heat-sensitive recording paper. In order to confirm the properties of the eight types of heat-sensitive recording materials obtained in this way, all marks were recorded for 2 minutes using a practical heat-sensitive fax (Model EF-11 manufactured by Matsushita Electric Transmission Co., Ltd.), and the film was placed on the thermal head. The state of adhesion was visually determined. In addition, the density of the obtained recorded image and the density of the background area other than the recorded image were measured using a Macbeth reflection densitometer RD-100R model (manufactured by Macbeth Co., Ltd.) using an amber filter, and the results were used in the first test.
Shown in the table.

[Table] As is clear from the results in Table 1, the thermal recording paper obtained in each example of the present invention has improved adhesion of debris on the thermal head without any decrease in recording sensitivity, and has excellent continuity. It had recordability.

Claims (1)

[Claims] 1. A coloring layer containing (a) a coloring agent, (b) a coloring agent capable of forming a color when heated in contact with the coloring agent, and (c) a thermofusible substance having a melting point of 60 to 200°C is provided. In the heat-sensitive recording medium, the surface of the pigment whose oil absorption amount is 80 ml/100 g or more as measured based on JISK5101 is referred to as (a) above.
The coloring layer contains a pigment coated with at least one of a coloring agent, (b) a coloring agent, and (c) a thermofusible substance (excluding a combination of a coloring agent and a coloring agent). A heat-sensitive recording medium characterized by the following.