JPH06312580A - Thermal recording medium - Google Patents

Abstract

PURPOSE:To provide a thermal recording medium having excellent recording sensitivity and small skin fog due to temperature, humidity, etc. CONSTITUTION:A thermal recording medium comprises a recording layer containing colorless or pale basic dye and developer on a support, wherein as the developer, 2,4'-dihydroxydiphenylsulfone is used, and further emulsion of amide stearate is contained in the recording layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-sensitive recording material, and more particularly to a heat-sensitive recording material having excellent recording sensitivity and less background fog due to temperature and humidity.

[0002]

2. Description of the Related Art Heretofore, a heat-sensitive recording material has been well known which uses a heat energy of a heat-sensitive head or the like to develop a colorless or light-colored basic dye and a color developer. Since such a thermal recording material is relatively inexpensive and the recording equipment 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 such as thermal labels. .

In recent years, recording speeds of 10 seconds or less for A4 size heat-sensitive fax and 120 characters / second or more for heat-sensitive printers have become possible. With the speeding up of such recording equipment, excellent recording sensitivity has been achieved. There is an increasing demand for thermosensitive recording media. In response to such requirements, various proposals have been made, such as a method of using a heat-fusible substance in combination with a color former and a color developer, but new defects such as a decrease in whiteness are accompanied, The present situation is that the effect is not always satisfactory enough.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a thermosensitive recording medium which is excellent in recording sensitivity and has less background fog due to the influence of temperature and humidity.

[0005]

SUMMARY OF THE INVENTION The present invention comprises:
In a thermosensitive recording medium provided with a recording layer containing a colorless or light-colored basic dye and a developer, 2,4'-
It has been found that the above object can be achieved by using dihydroxydiphenyl sulfone and further containing an emulsion of stearic acid amide in the recording layer, and completed the present invention.

[0006]

The heat-sensitive recording material using 2,4'-dihydroxydiphenyl sulfone as the color developer has a characteristic that the background fog is small and the white portion does not develop even when it is touched with an oil-based pen. It had the drawback of low sensitivity. Therefore, various sensitizers have been studied in order to increase the recording sensitivity of the heat-sensitive recording material using 2,4'-dihydroxydiphenyl sulfone, but a new defect that the background fog is likely to occur occurs. . However, when 2,4′-dihydroxydiphenyl sulfone is used in combination with an emulsion type stearic acid amide emulsion, particularly a stearic acid amide emulsion having an average particle size of 0.5 μm or less, the recording sensitivity can be improved without lowering the whiteness. found. Further, since the recording sensitivity is increased, the amount of conventional sensitizer used can be reduced. It is speculated that the emulsion type stearic acid amide has a sharper particle size distribution than a dispersion product obtained by mechanical dispersion, and therefore there are few coarse particles, and therefore exhibits an extremely sharp melting behavior during heat printing.

In the present invention, the use ratio of the emulsion of 2,4'-dihydroxydiphenyl sulfone and stearic acid amide varies depending on the basic dye and the like to be used, but it cannot be said unconditionally, but 2,4'-dihydroxydiphenyl sulfone 1 It is desirable to adjust the emulsion of stearic acid amide to about 0.5 to 5 parts by weight, preferably 1 to 3 parts by weight based on parts by weight.

In the heat-sensitive recording material of the present invention, the colorless or light-colored basic dye contained in the heat-sensitive recording layer is
Various known compounds can be used, and the following are exemplified. 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-dimethylindole-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-methylpyrrol-3-yl) -6
-Triallylmethane dyes such as dimethylaminophthalide, 4,4'-bis-dimethylaminobenzhydrylbenzyl ether, N-halophenyl-leukoauramine, N-2,4,5-trichlorophenylleucoaamine, etc. Diphenylmethane dyes, benzoyl leuco methylene blue, p-nitrobenzoyl leuco methylene blue and other thiazine dyes, 3-methyl-spiro-dinaphthopyran, 3-ethyl-spiro-dinaphthopyran, 3-
Phenyl-spiro-dinaphthopyran, 3-benzyl-spiro-dinaphthopyran, 3-methyl-naphtho- (6'-
Methoxybenzo) spiropyran, spiro dyes such as 3-propyl-spiro-dibenzopyran, rhodamine-B-
Anilinolactam, Rhodamine (p-nitroanilino)
Lactam, lactam dyes such as rhodamine (o-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-benzylaminofluorane, 3-diethylamino-7-N-chloroethyl-N-methylaminofluorane, 3-diethylamino-7-N-diethylaminofluorane, 3- (N-ethyl-p-toluidino) )
-6-Methyl-7-phenylaminofluorane, 3-
(N-ethyl-p-toluidino) -6-methyl-7-
(P-Toluidino) fluorane, 3-dimethylamino-
6-methyl-7-phenylaminofluorane, 3-diethylamino-6-methyl-7-phenylaminofluorane, 3-diethylamino-7- (2-carbomethoxy-
Phenylamino) fluorane, 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) fluorane, 3-dibutylamino-7- (o-chlorophenylamino) ) Fluoran, 3-pyrrolidino-6-methyl-7-
p-Butylphenylaminofluorane, 3-diethylamino-7- (o-fluorophenylamino) fluorane, 3-dibutylamino-7- (o-fluorophenylamino) fluorane, 3-dibutylamino-7- (m-
Trifluoromethylphenylamino) fluorane, 3-
Di (n-butyl) amino-6-methyl-7-phenylaminofluorane, 3-di (N-pentyl) amino-6-
Methyl-7-phenylaminofluorane, 3- (N-
Methyl-Nn-amyl) amino-6-methyl-7-phenylaminofluorane, 3- (N-ethyl-Nn-)
Amyl) amino-6-methyl-7-phenylaminofluorane, 3- (N-ethyl-N-iso-amyl) amino-6-methyl-7-phenylaminofluorane, 3-
(N-methyl-Nn-hexyl) amino-6-methyl-7-phenylaminofluorane, 3- (N-ethyl-
N-n-hexyl) amino-6-methyl-7-phenylaminofluorane, 3- (N-ethyl-N-β-ethylhexyl) amino-6-methyl-7-phenylaminofluorane, 3- (N- Ethyl-N-tetrahydrofurfuryl) amino-6-methyl-7-phenylaminofluorane, 3- (N-ethyl-N-cyclopentyl) amino-6-methyl-7-phenylaminofluorane, 3-
Examples thereof include fluorane dyes such as (N-ethyl-N-ethoxypropylamino) -6-methyl-7-phenylaminofluorane. Of course, the dyes are not limited to these dyes, and two or more dyes can be used in combination as required.

In the heat-sensitive recording material of the present invention, the use ratio of the basic dye and the color developer contained in the recording layer is not particularly limited, but the basic dye 1 is generally used.
0.5-50 parts by weight, preferably 1-1
It is desirable to use about 0 parts by weight of the developer.

The present invention is characterized in that 2,4'-dihydroxydiphenyl sulfone is used as a developer, but within the range that does not impair the effects of the present invention, for example, the following known developers It is also possible to use together. Activated clay, attapulgite, colloidal silica,
Inorganic acidic substances such as aluminum silicate, 4-tert-butylphenol, 4-hydroxydiphenoxide, α-naphthol, β-naphthol, 4-hydroxyacetophenol, 4-tert-octylcatechol, 2,2′-dihydroxydiphenol, 4,4'-isopropylidene bis (2-tert-butylphenol), 4,4'-sec-
Butylidene diphenol, 4-phenylphenol,
4,4'-isopropylidenediphenol, 2,2-bis (4-hydroxyphenyl) -4-methylpentane,
2,2'-methylenebis (4-chlorophenol), hydroquinone, 4,4'-cyclohexylidene diphenol, 4,4'-dihydroxydiphenyl sulfide, hydroquinone monobenzyl ether, 4-hydroxybenzophenone, 2,4-dihydroxybenzophenone , 2,4,4'-trihydroxybenzophenone,
2,2 ', 4,4'-tetrahydroxybenzophenone, dimethyl 4-hydroxyphthalate, methyl 4-hydroxybenzoate, propyl 4-hydroxybenzoate, 4
-Hydroxybenzoic acid-sec-butyl, 4-hydroxybenzoic acid pentyl, 4-hydroxybenzoic acid phenyl,
Benzyl 4-hydroxybenzoate, tolyl 4-hydroxybenzoate, chlorophenyl 4-hydroxybenzoate,
Phenylpropyl 4-hydroxybenzoate, phenethyl 4-hydroxybenzoate, 4-hydroxybenzoic acid-p
-Chlorobenzyl, 4-hydroxybenzoic acid-p-methoxybenzyl, novolac type phenolic resin, phenolic compounds such as phenolic 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, 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-methylbenzylsalicylic acid and other aromatic carboxylic acids , 3,4-dihydroxydiphenyl sulfone, 3,4-dihydroxy-4'-methyldiphenyl sulfone and other diphenyl sulfone derivatives,
Sulfide derivatives such as bis (3-tert-butyl-4-hydroxy-6-methylphenyl) sulfide and bis (2-methyl-4-hydroxy-6-tert-butylphenyl) sulfide, as well as these phenolic compounds and aromatic compounds Group carboxylic acids and the like and salts of polyvalent metals such as zinc, magnesium, aluminum, calcium, titanium, manganese, tin and nickel, and organic acid substances such as antipyrine complexes of zinc thiocyanate, bis- (4 -Hydroxyphenyl) sulfone, bis- (3-allyl-
4-hydroxyphenyl) sulfone, 2-hydroxy-5-tert-butylphenyl-4'-hydroxyphenyl sulfone, 2-hydroxy-5-tert-amylphenyl-4'-hydroxyphenyl sulfone, 2-hydroxy-5-isopropyl Phenyl-4'-hydroxyphenyl sulfone, 2-hydroxy-5-tert-butylphenyl-3'-methyl-4'-hydroxyphenyl sulfone, 2-hydroxy-5-tert-butylphenyl-3'-isopropyl-4 ' -Hydroxyphenyl sulfone, 2-hydroxy-5-tert-butylphenyl-2'-methyl-4'-hydroxyphenyl sulfone, 4-hydroxy-4'-isopropoxydiphenyl sulfone, 4-hydroxy-4'-methoxydiphenyl sulfone , 4-hydro 4'-methyl diphenyl sulfone, and the like.

The present invention improves the recording sensitivity by using an emulsion of stearic acid amide in the recording layer. However, known sensitizers such as those described below are used in combination within the range that does not impair the effects of the present invention. It is also possible to do so. Methoxycarbonyl-N-stearic acid benzamide, N-benzoylstearic acid amide, N-eicoic acid amide, ethylenebisstearic acid amide, behenic acid amide, methylenebisstearic acid amide, N-methylolstearic acid amide, 2,2 ′ -Methylenebis (4
-Methyl-6-tert-butylphenol), 4,4'-
Butylidene bis (6-tert-butyl-3-methylphenol), 2,2'-methylenebis (4-ethyl-6-te)
rt-butylphenol), 2,4-di-tert-butyl-
Hindered phenols such as 3-methylphenol, 2
UV absorbers such as-(2'-hydroxy-5'-methylphenyl) benzotriazole and 2-hydroxy-4-benzyloxybenzophenone, p-benzylbiphenyl, 1,2-di (3-methylphenoxy) ethane, 1 ，
2-diphenoxyethane, 1- (2-methylphenoxy) -2- (4-methoxyphenoxy) ethane, 1-phenoxy-2- (4-methylphenoxy) ethane, parabenzyl biphenyl, naphthylbenzyl ether, benzyl-4 -Methylthiophenyl ether, oxalic acid dibenzyl ester, oxalic acid-di-p-methyl-benzyl ester, oxalic acid-di-p-chloro-benzyl ester, terephthalic acid dimethyl ester, terephthalic acid dibutyl ester, terephthalic acid dibenzyl ester , Isophthalic acid dibutyl ester, 1-hydroxynaphthoic acid phenyl ester, benzyl-4-methylthiophenyl ether, and various known heat-fusible substances.
The amount of these sensitizers used is not particularly limited, but it is generally preferable to adjust the amount within a range of about 0.5 to 5 parts by weight with respect to 1 part by weight of the color developer.

Further, a preservative improving agent may be used in combination so as to further enhance the preservability of the recorded image depending on the purpose as long as the effect is not impaired. Examples of such storage improvers include, for example, 1,4-diglycidyloxybenzene, 4,4'-diglycidyloxydiphenyl sulfone, 4-benzyloxy-4 '-(2-methyl-2,3.
-Epoxypropyloxy) diphenyl sulfone, diglycidyl terephthalate, epoxy compounds such as bisphenol A type epoxy resin, 2,2'-methylenebis (4-
Methyl-6-tert-butylphenol), 2,2'-methylenebis (4-ethyl-6-tert-butylphenol), 2,2'-ethylidenebis- (4,6-di-tert)
-Butylphenol), 4,4'-thiobis (3-methyl-6-tert-butylphenol), 4,4'-thiobis (2-methyl-6-tert-butylphenol), 4,
4'-butylidene bis (6-tert-butyl-m-cresol), 1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane, 1,1,
3-tris (2-methyl-4-hydroxy-5-tert-
Butylphenyl) butane, 4,4'-thiobis (3-methylphenol), 4,4'-dihydroxy-3,
3 ', 5,5'-tetrabromodiphenyl sulfone,
4,4'-dihydroxy-3,3 ', 5,5'-tetramethyldiphenyl sulfone, 2,2-bis (4-hydroxy-3,5-dibromophenyl) propane, 2,2-
Hindered phenol compounds such as bis (4-hydroxy-3,5-dichlorophenyl) propane and 2,2-bis (4-hydroxy-3,5-dimethylphenyl) propane, 1- [α-methyl-α- (4 '-Hydroxyphenyl) ethyl] -4- [α', α'-bis (4 "-hydroxyphenyl) ethyl] benzene, N, N'-di-2-
Examples thereof include naphthyl-p-phenylenediamine and 2,2'-methylenebis (4,6-di-tert-butylphenyl) sodium phosphate. Among the above compounds, 4-benzyloxy-4 '-(2-methyl-
2,3-epoxypropyloxy) diphenyl sulfone is most preferably used because it is excellent in the preservability of recorded images and the effect of background fog.

In order to prepare a coating liquid for a recording layer containing these substances, water is generally used as a dispersion medium, for example, it is dissolved by heat and a solvent, and then dispersed in water to form an emulsion, or an attritor. A wet pulverization method in which dispersion is performed using a ball mill, a sand mill, or the like.

In the case of the wet pulverization method, for example, polyvinyl alcohol, methyl cellulose,
Carboxymethyl cellulose, hydroxyethyl cellulose, vinyl acetate resin containing sulfonic acid group, starch, sodium polyacrylate, sodium polysulfonate, sodium dioctylsulfosuccinate, sodium dodecylbenzenesulfonate, sodium lauryl alcohol sulfate, sodium fatty acid salt Various dispersants such as

In the coating liquid for the recording layer, starch, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin, casein, gum arabic, polyvinyl alcohol, acetoacetyl group-modified polyvinyl alcohol, carboxyl group-modified polyvinyl alcohol are used as adhesives. , Silicon-modified polyvinyl alcohol, diisobutylene / maleic anhydride copolymer salt,
Styrene / maleic anhydride copolymer salt, ethylene / acrylic acid copolymer salt, styrene / acrylic acid copolymer salt,
A styrene / butadiene copolymer emulsion, urea resin, melamine resin, amide resin, or the like is used in an amount of 5 to 40% by weight, preferably 10 to 30% by weight, based on the total solid content of the recording layer.

It is also possible to use various pigments in combination in the coating liquid. For example, magnesium carbonate, calcium carbonate, calcium sulfamate, aluminum hydroxide, alkali-modified silica, kaolin, clay, talc,
Inorganic pigments such as calcined kaolin, titanium oxide, diatomaceous earth, particulate anhydrous silica, activated clay, styrene microballs, nylon powder, polyethylene powder, urea
Examples include formalin resin fillers and organic pigments such as raw starch particles. Further, if necessary, waxes such as zinc stearate, calcium stearate, polyethylene wax, carnauba wax, paraffin wax, ester wax and the like can be added.

Further, various auxiliary agents can be added to the coating liquid, if necessary. For example, dioctylsulfosuccinic acid sodium salt, dodecylbenzenesulfonic acid.
A dispersant such as sodium salt, lauryl alcohol sulfate / sodium salt, fatty acid metal salt or the like, a UV absorber such as benzophenone type, an antifoaming agent, a fluorescent dye, a coloring dye and the like are appropriately added.

In the present invention, the method for forming the recording layer is not particularly limited, and the coating solution is supported by a suitable coating method such as air knife coating, varibar blade coating, pure blade coating, short dwell coating, curtain coating and the like. It can be formed by a method such as coating on a body and drying. The coating amount of the coating liquid is not particularly limited, and is usually adjusted in the range of ² to 12 g / m ² , preferably about 3 to 10 g / m ^{2 in} dry weight. As the support, paper, synthetic paper, plastic film or the like can be appropriately selected and used.

In the present invention, it is possible to further improve the storability of a recorded image by providing a resin layer on the thermosensitive recording medium and on the back side thereof, if necessary. further,
Provide an undercoat layer on the support, improve the image quality and image density by applying a smoothing process such as supercalendering after coating each layer, or apply an adhesive treatment on the back of the recording material to process it into an adhesive label, If necessary, various known techniques in the field of manufacturing a thermal recording medium, such as providing a magnetic layer on the back surface of the body, can be added. Further, the image quality and the image density can be improved by performing a super calendering process after forming the recording layer.

[0020]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. In addition, "part" and "%" in an example show "weight part" and "weight%", respectively, unless there is particular notice.

Example 1 [Preparation of solution A] A composition consisting of 10 parts of 3-di (n-butyl) amino-6-methyl-7-phenylaminofluorane, 5 parts of a 5% methylcellulose aqueous solution, and 40 parts of water was prepared. It was pulverized with a sand mill until the average particle size became 2.0 μm. [Preparation of solution B] A composition comprising 30 parts of 2,4'-dihydroxydiphenyl sulfone, 5 parts of a 5% aqueous solution of methyl cellulose, and 80 parts of water was sand milled to have an average particle size of 2.
It was pulverized to 0 μm.

[Formation of Recording Layer] Liquid A 55 parts, liquid B 115
Parts, stearic acid amide emulsion 21.5% liquid [trade name: Himicron G-270, manufactured by Chukyo Yushi Co., Ltd., average particle size: 0.4 μm] 80 parts, 10% polyvinyl alcohol aqueous solution 160 parts, calcium carbonate 35 parts the recording layer coating liquid obtained are stirred together, coating amount after drying base paper of 45 g / m ² was obtained a heat-sensitive recording material by coating and drying so that 4.5 g / m ^2.

Example 2 In the preparation of solution A of Example 1, 3- (N-ethyl-N-ethoxypropylamino) was used instead of 3-di (n-butyl) amino-6-methyl-7-phenylaminofluorane. ) A thermosensitive recording medium was obtained in the same manner as in Example 1 except that 6-methyl-7-phenylaminofluorane was used.

Example 3 A stearamide amide emulsion having an average particle size of 0.9 μm was used instead of the stearamide amide emulsion (average particle size: 0.4 μm) in the formation of the recording layer of Example 1. A thermal recording material was obtained in the same manner as in Example 1.

Example 4 [Preparation of liquid C] A composition consisting of 20 parts of 1,2-di (3-methylphenoxy) ethane, 5 parts of a 5% aqueous solution of methylcellulose, and 55 parts of water having a mean particle diameter of 2.
It was pulverized to 0 μm.

[Formation of Recording Layer] Liquid A 55 parts, liquid B 115
Part, C solution 30 parts, stearic acid amide emulsion 2
1.5% liquid [trade name: Himicron G-270, manufactured by Chukyo Yushi Co., Ltd., average particle size: 0.4 μm] 60 parts, 10% polyvinyl alcohol aqueous solution 160 parts, calcium carbonate 35
45 g / m of the coating liquid for recording layer obtained by mixing and stirring parts
The coating amount after drying ² of the base paper was obtained heat-sensitive recording material by coating and drying so that 4.5 g / m ^2.

Example 5 [Preparation of solution D] 10 parts of 4-benzyloxy-4 '-(2-methyl-2,3-epoxypropyloxy) diphenylsulfone, 5 parts of 5% methylcellulose aqueous solution, and 40 parts of water. The composition was ground with a sand mill until the average particle size was 2.0 μm.

[Formation of Recording Layer] Liquid A 55 parts, liquid B 115
Part, D solution 80 parts, stearic acid amide emulsion 2
1.5% liquid [trade name: High Micron G-270, manufactured by Chukyo Yushi Co., Ltd., average particle size: 0.4 μm] 80 parts, 10% polyvinyl alcohol aqueous solution 160 parts, calcium carbonate 35
45 g / m of the coating liquid for recording layer obtained by mixing and stirring parts
The coating amount after drying ² of the base paper was obtained heat-sensitive recording material by coating and drying so that 4.5 g / m ^2.

Example 6 [Preparation of solution E] Calcined clay [Product name: Ansilex, E
Manufactured by MC, oil absorption: 110 ml / 100 g] 100 parts,
A composition consisting of 100 parts of a 10% aqueous polyvinyl alcohol solution and 200 parts of water was mixed and stirred to obtain a coating liquid for the undercoat layer.

[Formation of recording layer] ^On a base paper of 45 g / m ² ,
^{3. The} solution E was applied and dried so that the coating amount after drying was 8 g / m ² to form an undercoat layer, and then the coating material for heat-sensitive layer prepared in the same manner as in Example 3 had a coating amount after drying of 4. After coating and drying so as to be 5 g / m ² , super calendering treatment was carried out to obtain a thermosensitive recording medium.

Comparative Example 1 [Preparation of Solution F] A composition comprising 20 parts of stearic acid amide, 5 parts of a 5% aqueous solution of methyl cellulose, and 75 parts of water was pulverized by a sand mill until the average particle size became 1.5 μm. [Formation of Recording Layer] The thermosensitive recording medium was prepared in the same manner as in Example 1 except that 80 parts of the F liquid was used instead of 80 parts of the 21.5% stearic acid emulsion in the formation of the recording layer of Example 1. Got

Comparative Example 2 Comparative Example 1 except that 20 parts of parabenzyl biphenyl was used instead of 20 parts of stearic acid amide in the preparation of solution F.
A thermosensitive recording medium was obtained in the same manner as described above.

Comparative Example 3 A thermosensitive recording medium was prepared in the same manner as in Example 1 except that 30 parts of 4,4'-isopropylidenediphenol was used in place of 30 parts of 2,4'-dihydroxydiphenylsulfone in the preparation of solution B. Obtained.

The following 9 evaluation tests were conducted on the 9 types of thermal recording materials thus obtained, and the results are shown in Table 1. [Whiteness] The whiteness of the recording layer was measured with a Hunter whiteness meter immediately after the recording medium was formed. [Color density] Thermal recording material evaluation machine (Product name: TH-PM
D, manufactured by Okura Electric Co., Ltd.), the above-mentioned thermosensitive recording medium is colored with an applied voltage of 24 V and a pulse time of 2 ms, and the color density of the obtained recorded image is measured by a Macbeth densitometer (RD-914 type, manufactured by Macbeth). Measured in visual mode.

[Heat Resistance] As a background fog acceleration test, a thermal recording material before printing was treated under a drying condition of 60 ° C. for 24 hours, and then the degree of fog was visually evaluated. [Moisture resistance] The thermal recording material before printing was processed for 24 hours under the conditions of 40 ° C and 90% RH, and then the degree of fogging was visually evaluated.

[Plasticizer resistance] polypropylene pipe (4
A vinyl chloride wrap film (manufactured by Mitsui Toatsu Chemical Co., Inc.) is wound three times on a 0 mmφ tube, and the heat-sensitive recording material on which the print color is formed is sandwiched so that the print color surface is on the outside, and further chlorinated. Wrap the vinyl wrap film in three layers,
The plasticizer resistance was evaluated from the print density after standing at 25 ° C. for 12 hours. [Solvent resistance] The color development of the background after writing with an oil-based marker on the heat-sensitive recording material before printing was visually evaluated.

[Evaluation Criteria] Evaluation criteria for heat resistance, moisture resistance, plasticizer resistance and solvent resistance are as follows. ◎ ・ ・ ・ ・ ○ ・ ・ ・ ・ △ ・ ・ ・ ・ × Excellent Excellent

[0038]

[Table 1]

[0039]

As is clear from the results of Table 1, all of the thermosensitive recording materials of the present invention were excellent in storage stability and recording sensitivity of recorded images and had little thermal fog.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Keiichi Inubushi 4-3-1, Jokoji, Amakosaki-shi, Hyogo Kanzaki Paper Mill Kanzaki Mill

Claims (2)

[Claims] 1. A thermosensitive recording medium comprising a support and a recording layer containing a colorless or light-colored basic dye and a developer, wherein 2,4'-dihydroxydiphenyl sulfone is used as the developer. A heat-sensitive recording material comprising a stearic acid amide emulsion in the recording layer. 2. The thermosensitive recording medium according to claim 1, wherein the emulsion of stearic acid amide has an average particle diameter of 0.5 μm or less.