JPH1111017A - Thermal recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermal recording medium having a polystyrene film of small occurrence of skin fog of a thermal recording layer with elapse of time as a support with small curl after recording. SOLUTION: The thermal recording medium comprises a thermal recording layer containing leuco dye, colorant and adhesive and a protective layer containing pigment and aqueous resin as main components to be sequentially provided on a support. In this case, as the support, a non-oriented polystyrene film is used. As the dye, 3-di(n-butyl)amino-6-methyl-7-anilinofluoran or 3-di(n- butyl)amino-7-(o-chloroanilino)fluoran is used.

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 utilizing a color-forming reaction between a leuco dye and a color former, and more particularly to a heat-sensitive recording material using a film as a support.

[0002]

2. Description of the Related Art Hitherto, a heat-sensitive recording medium which utilizes a color-forming reaction between a leuco dye and a color former to contact both color-forming substances by heat to obtain a color-formed image is well known. Such a thermosensitive recording medium is relatively inexpensive, and its recording equipment is compact and its maintenance is relatively easy. Therefore, it is used not only as a recording medium such as a facsimile and various computers but also in a wide field such as a thermosensitive label. I have. Among them, those using a plastic film or synthetic paper as a support are particularly excellent in terms of water resistance and image quality, and thus the use amount thereof has been remarkably increased.

On the other hand, in recent years, there has been a demand for recycling of plastic containers due to environmental problems. For example, a label to be attached to a polystyrene container also requires a label using a polystyrene film that can be recycled at the same time as the container. However, a heat-sensitive recording material using a general stretched polystyrene film as a support is described in Japanese Patent Application Laid-Open No. Hei 7-242061, and in such a heat-sensitive recording material, the recording portion shrinks and curls (recording due to heat). Unnecessarily distorted) or the background fog is likely to occur over time.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a heat-sensitive recording material using a polystyrene film as a support, which has little heat-shrinkage curl after recording, and has less occurrence of background fogging of the heat-sensitive recording layer over time. Is to do.

[0005]

Means for Solving the Problems In a heat-sensitive recording medium in which a heat-sensitive recording layer containing a leuco dye, a coloring agent and an adhesive, and a protective layer containing a pigment and an aqueous resin as main components are sequentially provided on a support. As one means for solving the above problems, the present invention uses an unstretched polystyrene film as a support and 3-di (n-butyl) as a leuco dye.
Amino-6-methyl-7-anilinofluoran or 3
-Di (n-butyl) amino-7- (o-chloroanilino) fluoran.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention uses an unstretched polystyrene film as a support, and further uses 3 leuco dye as a support.
-Di (n-butyl) amino-6-methyl-7-anilinofluoran or 3-di (n-butyl) amino-7-
It is characterized by using a specific leuco dye of (o-chloroanilino) fluoran, and the thickness of the non-stretched polystyrene film is about 20 to 200 μm. By using such a non-stretched polystyrene film as a support, it is possible to obtain an effect that recording quality is superior to that of a generally stretched polystyrene film, and that heat shrinkage after recording is reduced. Further, by using a specific leuco dye, even if a polystyrene film is used for the support, the effect of less generation of background fog on the heat-sensitive recording layer over time can be obtained.

As the polystyrene resin for the unstretched polystyrene film, a polystyrene resin (GPPS), an impact-resistant polystyrene resin (H) obtained by adding a synthetic rubber at the time of polymerization or graft copolymerizing styrene to the synthetic rubber.
IPS), impact polystyrene resin (MIPS) blending GPPS and HIPS, or styrene
Acrylonitrile copolymer resin (AS resin), styrene / methyl methacrylate copolymer resin, styrene / butadiene / acrylonitrile copolymer resin (ABS resin), and the like. Among them, a polystyrene resin generally has an Izod impact strength value of 1.0 to 2.0 kg-cm / cm, and a film made of the resin is brittle, and there is a possibility that the recording image quality may be deteriorated. Izod impact strength value of 6.0 kg-cm
/ Cm or more impact-resistant polystyrene resin (MIPS) is more preferred. In particular, 8.0 kg-cm / cm or more (HIPS) is preferable. The synthetic rubber to be added to polystyrene includes styrene-butadiene rubber, polybutadiene rubber and the like. Particularly, styrene butadiene rubber is preferred. The addition amount is 5 to 40% by weight based on the polystyrene resin.
Is preferred. More preferably, it is 25 to 35% by weight.

[0008] The production of an unstretched film employs an inflation method. The inflation method has a feature that the heat shrinkage of the film is smaller than the T-die method for producing a stretched film.

Further, by applying a corona discharge treatment to the surface of an unstretched polystyrene film, providing an anchor coat layer on the surface, or incorporating a pigment in the film, the coating properties of the coating solution for the heat-sensitive recording layer are improved. An excellent effect on the adhesion between the polystyrene film and the heat-sensitive recording layer can be obtained. The amount of the pigment to be used is preferably 5 to 20% by weight, more preferably 1 to 20% by weight, based on the total solid content of the polystyrene film.
0 to 15% by weight. Specific examples of such pigments include:
Examples include calcium carbonate, titanium oxide, amorphous silica, and aluminum hydroxide. Titanium oxide is more preferable in order to secure film hiding properties.

In the heat-sensitive recording layer, 3-di (n-butyl) amino-6-methyl-7-anilinofluoran or 3-di (n-butyl) amino-7- (o-
Although it contains chloroanilino) fluorane, various other known leuco dyes can be contained as long as the desired effects of the present invention are not impaired. Specific examples of such leuco dyes include, for example, the following.

3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide, 3- (4-diethylamino-2-methylphenyl) -3- (4-dimethylaminophenyl) -6-dimethylamino Phthalide, 3-
Diethylamino-7-dibenzylamino-benzo [a]
Blue coloring dye such as fluoran: 3- (N-ethyl-N
Green-coloring dyes such as -p-tolyl) amino-7-N-methylanilinofluoran and 3-diethylamino-7-anilinofluoran: 3-diethylamino-7-methylfluoran, 3-diethylamino-6 Methyl-7-chlorofluorane, 3-diethylamino-7-chlorofluorane, rhodamine (p-chloroanilino) lactam, 3
Red-coloring dyes such as-(N-ethyl-p-toluidino) -7-methylfluoran, 3,3'-bis (1-n-butyl-2-methylindol-3-yl) phthalide: 3
-(N-ethyl-N-isoamyl) amino-6-methyl-7-anilinofluoran, 3- (N-cyclohexyl-N-methyl) amino-6-methyl-7-anilinofluoran, 3- ( N-ethyl-N-ethoxypropylamino) -6-methyl-7-anilinofluoran, 3-dimethylamino-6-methyl-7-anilinofluoran, 3
-Diethylamino-6-methyl-7-anilinofluoran, 3-di (n-amyl) amino-6-methyl-7-anilinofluoran, 3-diethylamino-7- (o-chloroanilino) fluoran, 3- Diethylamino-7-
(O-fluoroanilino) fluoran, 3-di (n-butyl) amino-7- (o-fluoroanilino) fluoran, 3-diethylamino-7- (m-trifluoromethylanilino) fluoran, 3- ( N-ethyl-p-toluidino) -6-methyl-7-anilinofluoran, 3-
(N-ethyl-p-toluidino) -6-methyl-7-
(P-toluidino) fluoran, 3-diethylamino-
6-chloro-7-anilinofluoran, 3-di (n-butyl) amino-6-methyl-7-m-toluidinofluoran, 3-piperidino-6-methyl-7-anilinofluoran and the like Black coloring dyes.

As the color former used in combination with the above-mentioned leuco dye, various known ones can be used.

4,4'-isopropylidene diphenol, 1,1-bis (4-hydroxyphenyl) cyclohexane, 2,2-bis (4-hydroxyphenyl) -4
-Methylpentane, benzyl 4-hydroxybenzoate,
4,4′-dihydroxydiphenyl sulfone, 2,4 ′
-Dihydroxydiphenylsulfone, 4-hydroxy-
4'-isopropyloxydiphenyl sulfone, bis (3-allyl-4-hydroxyphenyl) sulfone, 4
-Hydroxy-4'-methyldiphenylsulfone, 4-
Hydroxyphenyl-4′-benzyloxyphenylsulfone, 1,1-bis (4-hydroxyphenyl) -1
-Phenylethane, 1,4-bis [α-methyl-α-
(4'-hydroxyphenyl) ethyl] benzene, 1,
3-bis [α-methyl-α- (4′-hydroxyphenyl) ethyl] benzene, di (4-hydroxy-3-methylphenyl) sulfide, 2,2′-thiobis (3-t
phenolic compounds such as tert-octylphenol) and 2,4-dihydroxy-2'-methoxybenzanilide: 4,4'-bis (p-tolylsulfonylaminocarbonylamino) diphenylmethane, Np-tolylsulfonyl-N'- Sulfourea compounds such as phenylurea: zinc p-chlorobenzoate, zinc 4- [2- (p-methoxyphenoxy) ethyloxy] salicylate, 4-
Zinc salts of aromatic carboxylic acids such as [3- (p-tolylsulfonyl) propyloxy] zinc salicylate and 5- [p- (2-p-methoxyphenoxyethoxy) cumyl] zinc salicylate. Among these, especially bis (3-
(Allyl-4-hydroxyphenyl) sulfone or 1,
1-bis (4-hydroxyphenyl) -1-phenylethane is excellent in the preservability of a recorded image.

The ratio of the specific leuco dye to the color former in the heat-sensitive recording layer is not particularly limited, but is generally from 1 to 1 part by weight of the total leuco dye containing the specific leuco dye.
7 parts by weight, preferably about 1 to 4 parts by weight of a color former is used.

If necessary, a sensitizer for improving the recording sensitivity and a storability improving agent for improving the storability of the recorded image can be used in the heat-sensitive recording layer.

Specific examples of the sensitizer include, for example, p-benzylbiphenyl, dibenzyl terephthalate, dibenzyl oxalate, di-p-chlorobenzyl oxalate, di-p-methylbenzyl oxalate, dibutyl terephthalate, adipic acid Di-o-chlorobenzyl, 1,2-diphenoxyethane, 1,2-di (3-methylphenoxy) ethane, 1-phenoxy-2- (4-methylphenoxy) ethane, 1,2-bis (3, 4-dimethylphenyl) ethane, p-xylene glycol bis (p-tolyloxymethyl) ether, 1,4-bis (p-tolyloxy) benzene, 1,2-di (3-methylphenoxy) ethane,
3-phenyl-1,1′-biphenyl, diphenylsulfone, diphenyl carbonate, stearamide, ethylenebisstearic acid amide, methylolbehenamide,
Oleic acid amide, palmitic acid amide and the like can be mentioned.

Specific examples of the preservability improver include, for example, 1,4-diglycidyloxybenzene, 4,4'-diglycidyloxydiphenylsulfone, 4-benzyloxy-4 '-(2-methyl-2,3 Epoxy compounds such as -epoxypropyloxy) diphenyl sulfone and 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'-butylidenebis (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'-
Tetrabromodiphenylsulfone, 4,4'-dihydroxy-3,3 ', 5,5'-tetramethyldiphenylsulfone, 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-naphthyl-p-phenylenediamine, 2,2′-methylenebis (4,6-
And metal salts of di-tert-butylphenyl) phosphoric acid. The amounts of the sensitizer and the preservability improver are 4 parts by weight or less for 1 part by weight of the leuco dye.

The heat-sensitive recording layer is formed, for example, by using water as a dispersion medium,
Certain leuco dyes, color formers and, if necessary, sensitizers,
Ball mill, separately or together with preservative improver,
After finely dispersing by an attritor, a pulverizer such as a sand mill so that the average particle diameter is about 0.1 to 3 μm,
A thermosensitive recording layer coating solution prepared by adding the following adhesive with a stirrer while mixing and stirring is coated on a non-stretched polystyrene film and dried.

Specific examples of the adhesive contained in the heat-sensitive recording layer include water-dispersible materials such as styrene-butadiene latex, vinyl acetate-vinyl chloride-ethylene copolymer latex, and methyl methacrylate-butadiene copolymer latex. Resins, starches, hydroxyethylcellulose, methylcellulose, carboxymethylcellulose, gelatin, casein, gum arabic,
Completely (partially) saponified polyvinyl alcohol, acetoacetyl group-modified polyvinyl alcohol, silicon-modified polyvinyl alcohol, carboxyl group-modified polyvinyl alcohol, diisobutylene-maleic anhydride copolymer salt, styrene-maleic anhydride copolymer salt, ethylene- Water-soluble resins such as acrylic acid copolymer salts and styrene-acrylic acid copolymer salts are exemplified. The amount of the adhesive used is about 5 to 40% by weight based on the total solid content of the heat-sensitive recording layer.

Furthermore, various auxiliaries can be appropriately added to the coating solution for the heat-sensitive recording layer, if necessary, for example, sodium dioctyl sulfosuccinate, sodium dodecylbenzene sulfonate, sodium polystyrene sulfonate, lauryl. Surfactants such as alcohol sulfate-sodium salt, alginate, fatty acid metal salt, calcium carbonate, zinc oxide, aluminum oxide, titanium dioxide, amorphous silica, aluminum hydroxide, barium sulfate, talc, kaolin, clay, calcined clay , Nylon fillers, pigments such as urea formalin resin fillers, defoamers, fluorescent dyes, coloring dyes, cross-linking agents and the like.

The method for forming the heat-sensitive recording layer is not particularly limited, and may be, for example, a bar coating, an air knife coating, a rod blade coating, a pure blade coating, a short dwell coating, a gravure coating, etc. It is formed by a coating method. The coating amount of the coating solution for the heat-sensitive recording layer is not particularly limited, but is usually ² to 20 g / m ² , preferably 3 to ²⁰ g / m ² in terms of dry weight.
１５15 g / m ² .

In the heat-sensitive recording medium of the present invention, a protective layer containing a film-forming aqueous adhesive is provided on the heat-sensitive recording layer thus obtained. For example, completely (partially) saponified polyvinyl alcohol, acetoacetyl group-modified polyvinyl alcohol,
Carboxyl group-modified polyvinyl alcohol, olefin-modified polyvinyl alcohol, amide-modified polyvinyl alcohol, pyrrolidone-modified polyvinyl alcohol, cellulose derivatives such as methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, casein, gum arabic, oxidized starch, etherified starch, dialdehyde starch , Starches such as esterified starch,
Examples include acrylic latex, polyester-polyurethane latex, and polyether-polyurethane latex.

Among these aqueous adhesives, various modified polyvinyl alcohols, cellulose derivatives and casein are preferred, and acetoacetylated polyvinyl alcohol and carboxy modified polyvinyl alcohol are more preferred in view of heat resistance and barrier properties.

The amount of the aqueous adhesive used is not particularly limited, but may be 10 to the solid content of the protective layer.
The content is about 90 to 90% by weight, preferably about 20 to 60% by weight.

The protective layer may contain a pigment for improving the recording running property. Specific examples of the pigment include, for example, calcium carbonate, zinc oxide, aluminum oxide, titanium dioxide, amorphous silica, aluminum hydroxide, barium sulfate, talc, kaolin, clay, calcined clay, nylon filler, urea-formalin resin filler and the like. Pigments. In addition, about the usage-amount, 5-80 weight% with respect to the total solid content of a protective layer, Preferably it is 30-80%.
It is about 70% by weight.

The protective layer is generally formed by using water as a dispersion medium, a propeller stirrer, a mixer, an attritor, a ball mill,
The coating amount of the protective layer coating liquid in which the adhesive and the pigment are mixed and stirred as required by a mixing / stirring machine such as a roll mill is applied onto the heat-sensitive recording layer by a coating method similar to that of the above-mentioned heat-sensitive recording layer so that the coating amount after drying is 0.1%. -10 g / m ² , preferably 0.5-6 g
/ M ² by coating and drying. After the application, the curability of the adhesive can be increased by irradiating ultraviolet rays or electron beams.

Further, in the coating liquid for the protective layer, a crosslinking agent such as glyoxal, methylol melamine, potassium persulfate, ammonium persulfate, sodium persulfate, boric acid, borax, polyamide epichlorohydrin, zinc stearate, stearic acid, etc. Lubricants such as calcium phosphate, stearic acid amide, potassium stearyl phosphate, polyethylene wax, carnauba wax, paraffin wax, ester wax, etc., surface activities such as sodium dioctyl sulfosuccinate, sodium dodecylbenzene sulfonate, sodium lauryl alcohol sulfate and sodium alginate Various auxiliaries such as an agent, an antifoaming agent, a fluorescent dye, and a coloring dye can be appropriately added.

If necessary, after forming the heat-sensitive recording layer and the protective layer, they may be smoothed by a super calender or the like, conductive treatment may be performed on the back surface of the heat-sensitive recording material, or adhesive treatment may be performed on the back surface of the heat-sensitive recording material. And various known techniques in the field of heat-sensitive recording medium production, such as processing into an adhesive label.

[0029]

The present invention will be described in more detail with reference to the following Examples, but it should be understood that the present invention is by no means restricted thereto. In the examples, "parts" and "%" indicate "parts by weight" and "% by weight", respectively, unless otherwise specified.

[Example 1] Preparation of solution A: 30 parts of 3-di (n-butyl) amino-6-methyl-7-anilinofluoran as a leuco dye, 5 parts of a 5% aqueous solution of methylcellulose and 65 parts of water. The composition was pulverized with a sand mill until the average particle diameter became 1 μm to obtain a liquid A.

Solution B Preparation 1,1-bis (4-hydroxyphenyl) as a coloring agent
30 parts of -1-phenylethane, 5% of methylcellulose
A composition comprising 5 parts of an aqueous solution and 65 parts of water was pulverized with a sand mill until the average particle diameter became 1 μm to obtain a liquid B.

Solution C Preparation 30 parts of di-p-chlorobenzyl oxalate as a sensitizer,
A composition comprising 5 parts of a 5% aqueous solution of methylcellulose and 65 parts of water was pulverized with a sand mill until the average particle diameter became 1 μm to obtain a liquid C.

Preparation of Coating Solution for Thermosensitive Recording Layer 50 parts of solution A, 150 parts of solution B, 50 parts of solution C, and 15 parts of polyvinyl alcohol (trade name: PVA105, manufactured by Kuraray)
% Aqueous solution 20 parts, solid content 48% styrene-butadiene latex (trade name: Polylac 750K, manufactured by Mitsui Toatsu Chemicals, Inc.) 60 parts, 30% dispersion of zinc stearate 20%, di-2-ethylhexyl sulfosuccinic acid A composition comprising 5 parts of a 5% aqueous solution of sodium and 80 parts of water was mixed and stirred to obtain a coating liquid for a heat-sensitive recording layer obtained.

Production of Unstretched Polystyrene Film Impact-resistant polystyrene resin having an Izod impact strength value of 8.0 kg-cm / cm (trade name: Dick Styrene G
H-8300, HIPS, manufactured by Dainippon Ink and Chemicals, Inc.)
A composition comprising 80 parts and 20 parts of a polystyrene compound (trade name: Plamaster White SH, manufactured by Dainippon Ink and Chemicals, Inc.) containing 50% by weight of titanium oxide (ie, 10% by weight of titanium oxide based on the total solid content) ) Was obtained by inflation method to obtain a white 65 μm non-oriented polystyrene film.

Formation of the heat-sensitive recording layer The coating solution for the heat-sensitive recording layer obtained on the above-mentioned unstretched polystyrene film is coated with a gravure coating method at 25 g / m 2.
⁽²⁾ After coating, the coated surface was smoothed with a bar so that the coated amount after drying was 5 g / m ^2, and dried by coating to form a heat-sensitive recording layer. Formation of protective layer Acetoacetyl group-modified polyvinyl alcohol (trade name:
100 parts of a 10% aqueous solution of Gosefimer Z-200, manufactured by Nippon Synthetic Chemical Industry Co., Ltd., kaolin (trade name: UW)
-90, 30 parts of a 60% dispersion of Engelhard Co.)
A coating solution for a protective layer obtained by mixing and stirring a composition comprising 2 parts of a 5% aqueous solution of glyoxal and 40 parts of water was applied onto the above-mentioned thermosensitive recording layer so that the coating amount after drying was 3 g / m ^2. After coating and drying to form a protective layer, a super calender treatment was performed to obtain a thermosensitive recording medium.

Example 2 In the production of the unstretched polystyrene film of Example 1, an impact-resistant polystyrene resin having an Izod impact strength of 6.0 kg-cm / cm (trade name: Dick Styrene MH-6100, MIP
S, manufactured by Dainippon Ink and Chemicals, Inc.)
Was obtained. Otherwise in the same manner as in Example 1, a thermosensitive recording medium was obtained.

Examples 3 to 5 In the preparation of solution B of Example 1, 1,1-bis (4-hydroxyphenyl) -1-
A heat-sensitive recording material was obtained in the same manner as in Example 1 except that the following colorant was used instead of phenylethane.

Example 3: bis (3-allyl-4-hydroxyphenyl) sulfone Example 4: 4-hydroxy-4'-isopropoxydiphenylsulfone Example 5: 4,4'-dihydroxydiphenylsulfone

Example 6 In the preparation of solution A of Example 1, 3-di (n-butyl) amino was used instead of 3-di (n-butyl) amino-6-methyl-7-anilinofluoran. A thermosensitive recording medium was obtained in the same manner as in Example 1, except that -6-methyl-7- (o-chloroanilino) fluoran was used.

Example 7 In the production of the unstretched polystyrene film of Example 1, a polystyrene resin having an Izod impact strength value of 1.5 kg-cm / cm (trade name: Dick Styrene CR-3500, GPPS; Using Nippon Ink Chemical Industry Co., Ltd.), a white 65 μm unstretched polystyrene film was obtained. Otherwise in the same manner as in Example 1, a thermosensitive recording medium was obtained.

Comparative Example 1 In forming a non-stretched polystyrene film in Example 1, a white biaxially stretched polystyrene film of 65 μm was obtained not by the inflation method but by the T-die method. Otherwise in the same manner as in Example 1, a thermosensitive recording medium was obtained.

[Comparative Examples 2-3] In the preparation of solution A of Example 1, 3-di (n-butyl) amino-6-methyl-7-
A heat-sensitive recording material was obtained in the same manner as in Example 1 except that the following leuco dye was used instead of anilinofluoran.

Comparative Example 2: 3- (N-ethyl-N-isoamyl) amino-6-methyl-7-anilinofluorane Comparative Example 3: 3- (N-cyclohexyl-N-methyl)
Amino-6-methyl-7-anilinofluoran

The following evaluation tests were performed on the thus obtained heat-sensitive recording medium, and the results are shown in Tables 1 and 2. [Film brittleness] Tear a polystyrene film by hand.
The criteria are as follows.

◎: very difficult to tear ○: hard to tear △: slightly easy to tear

[Coloring Property] An applied energy of 0.4 mJ / d was applied to each thermosensitive recording medium of 15 cm × 15 cm by using a thermosensitive recording evaluator (trade name: TM-PMD type, manufactured by Okura Electric Co., Ltd.).
The recording density of the obtained recorded image was recorded using a Macbeth densitometer (trade name: RD-914,
Macbeth)).

[Preservation of Recorded Image] The recording density of the recorded image after leaving the heat-sensitive recording material obtained in the above-described color development evaluation test under the conditions of 40 ° C. and 90% RH for 24 hours was measured by a Macbeth densitometer. (Product name: RD-914, manufactured by Macbeth Co., Ltd.) was measured in the visual mode.

[Surface fog]
After treatment for 24 hours under the condition of 0% RH, the degree of background fog in the unrecorded portion was measured for whiteness (based on JIS P 8123 method).

[Curl After Recording] The curl state of the heat-sensitive recording medium after recording obtained in the above-described color development evaluation test was visually judged as follows.

A: no curl after recording x: strong curl after recording

[0051]

[Table 1]

[0052]

[Table 2]

The following are indicated by abbreviations in Tables 1 and 2.
"PS" is polystyrene. “A” is 1,1-bis (4-
(Hydroxyphenyl) -1-phenylethane. "B"
Is bis (3-allyl-4-hydroxyphenyl) sulfone. "C" is 4-hydroxy-4'-isopropoxydiphenyl sulfone. "D" is 4,4'-dihydroxydiphenyl sulfone. "A" is 3-di (n-butyl) amino-6-methyl-7-anilinofluoran. "B" is 3
-Di (n-butyl) amino-6-methyl-7- (o-chloroanilino) fluoran. "C" is 3- (N-ethyl-N-isoamyl) amino-6-methyl-7-anilinofluoran. "D" is 3- (N-cyclohexyl-N-
Methyl) amino-6-methyl-7-anilinofluoran.

[0054]

As is clear from the results shown in Tables 1 and 2, the heat-sensitive recording material of the present invention has less curl after recording and has less background fogging of the heat-sensitive recording layer over time.

Claims (3)

[Claims] 1. A thermosensitive recording medium comprising: a thermosensitive recording layer containing a leuco dye, a coloring agent and an adhesive; and a protective layer containing a pigment and an aqueous resin as main components.
The support is an unstretched polystyrene film, and the leuco dye is 3-di (n-butyl) amino-6-methyl-7-anilinofluoran or 3-di (n-butyl) amino-
A heat-sensitive recording material, which is 7- (o-chloroanilino) fluoran. 2. The polystyrene resin used for the unstretched polystyrene film has an Izod impact strength of 6.0 kg.
2. The heat-sensitive recording medium according to claim 1, which has a density of -cm / cm or more. 3. The color former is bis (3-allyl-4-hydroxyphenyl) sulfone or 1,1-bis (4-hydroxyphenyl) -1-phenylethane.
Or the heat-sensitive recording material according to 2.