JPH1111016A - Thermal recording medium - Google Patents

Abstract

(57) [Problem] To provide a thermosensitive recording medium which is excellent in recording image quality and has little heat shrinkage curl after recording. SOLUTION: An unstretched polystyrene film is used as a support, and its thickness is 20 to 2
Those having a size of about 00 μm are used. By using such an unstretched 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 curl after recording is reduced.

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). Undesired distortion) and heat-shrinkage curl in applications requiring heat resistance such as a microwave oven.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a thermosensitive recording medium which is excellent in recording image quality and has little heat shrinkage after recording.

[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 having a smaller heat shrinkability than a stretched film as a support.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is characterized in that an unstretched polystyrene film is used as a support, and its thickness 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.

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.

Various known leuco dyes and coloring agents can be used in the heat-sensitive recording layer. Specific examples of the leuco dye include the following.
3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide, 3- (4-diethylamino-2
-Methylphenyl) -3- (4-dimethylaminophenyl) -6-dimethylaminophthalide, 3-diethylamino-7-dibenzylamino-benzo [a] fluoran, and other blue-coloring dyes: 3- (N-ethyl) -Np-tolyl) amino-7-N-methylanilinofluoran, 3-
Green chromogenic dyes such as diethylamino-7-anilinofluoran: 3-diethylamino-7-methylfluoran,
3-diethylamino-6-methyl-7-chlorofluorane, 3-diethylamino-7-chlorofluorane, rhodamine (p-chloroanilino) lactam, 3- (N-ethyl-p-toluidino) -7-methylfluoran, 3,
3'-bis (1-n-butyl-2-methylindole-
Red-coloring dyes such as 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-butyl) amino- 6-methyl-7-anilinofluoran, 3-di (n-amyl) amino-6-methyl-7
-Anilinofluoran, 3-diethylamino-7- (o
-Chloroanilino) fluoran, 3-di (n-butyl)
Amino-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
Black color-forming dyes such as methyl-7-anilinofluoran;

Specific examples of the color former include, for example, 4,4 ′
-Isopropylidene diphenol, 1,1-bis (4-
Hydroxyphenyl) cyclohexane, 2,2-bis (4-hydroxyphenyl) -4-methylpentane,
-Benzyl benzoate, 4,4'-dihydroxydiphenylsulfone, 2,4'-dihydroxydiphenylsulfone, 4-hydroxy-4'-isopropyloxydiphenylsulfone, bis (3-allyl-4-hydroxyphenyl) sulfone, -Hydroxy-4'-methyldiphenylsulfone, 4-hydroxyphenyl-
4′-benzyloxyphenyl sulfone, 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- Phenolic compounds such as hydroxy-3-methylphenyl) sulfide, 2,2′-thiobis (3-tert-octylphenol), and 2,4-dihydroxy-2′-methoxybenzanilide: 4,4′-bis (p- Toluylsulfonylaminocarbonylamino) diphenylmethane, N-p-tolylsulfonyl-N'-phenylurea, and other sulfourea-based compounds: zinc p-chlorobenzoate, zinc 4- [2- (p-methoxyphenoxy) ethyloxy] salicylate, Zinc 4- [3- (p-tolylsulfonyl) propyloxy] salicylate, 5- [p
-(2-p-methoxyphenoxyethoxy) cumyl] and zinc salts of aromatic carboxylic acids such as zinc salicylate. The use ratio of the leuco dye to the color former in the heat-sensitive recording layer is not particularly limited.
A coloring agent is used in an amount of 1 to 7 parts by weight, preferably about 1 to 4 parts by weight based on parts by weight.

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 p-benzylbiphenyl, dibenzyl terephthalate, dibenzyl oxalate, and di-p oxalate.
-Chlorobenzyl, di-p-methylbenzyl oxalate,
Dibutyl terephthalate, di-o-chlorobenzyl adipate, 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, Examples include 1'-biphenyl, diphenyl sulfone, diphenyl carbonate, stearic acid amide, ethylenebisstearic acid amide, methylolbehenic acid amide, oleic acid amide, and palmitic acid amide.

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′-methylenebi (4,6-di-tert (Butylphenyl) phosphoric acid metal salt, etc. The amount of the sensitizer and the preservability improver is 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,
The average particle diameter becomes about 0.1 to 3 μm by a pulverizer such as a ball mill, an attritor, and a sand mill separately or together with a leuco dye, a color former, and if necessary, a sensitizer, a preservability improver, and the like. After finely dispersing as described above, a coating solution for a heat-sensitive recording layer prepared by adding the following adhesive while mixing and stirring with a stirrer is applied to an unstretched polystyrene film and dried.

Specific examples of the adhesive contained in the heat-sensitive recording layer include water-dispersible 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.

Further, 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 , A nylon filler, a pigment such as a urea formalin resin filler, an antifoaming agent, a fluorescent dye, a coloring dye, a crosslinking agent, and the like.

The method for forming the heat-sensitive recording layer is not particularly limited. For example, bar coating, air knife coating, rod blade coating, pure blade coating, short duel coating, 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 terms 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 cross-linking agent such as glyoxal, methylol melamine, potassium persulfate, ammonium persulfate, sodium persulfate, ammonium zirconium carbonate, boric acid, borax, polyamide epichlorohydrin, stearin Zinc acid, calcium stearate, stearamide, potassium stearyl phosphate,
Lubricants such as polyethylene wax, carnauba wax, paraffin wax and ester wax, surfactants such as sodium dioctyl sulfosuccinate, sodium dodecylbenzene sulfonate, sodium lauryl alcohol sulfate and sodium alginate, defoamers, fluorescent dyes, coloring dyes Various auxiliaries such as can be added as appropriate.

If necessary, after forming the heat-sensitive recording layer and the protective layer, the heat-sensitive recording medium may be subjected to a smoothing treatment with a super calender or the like, a conductive treatment may be applied to the back surface of the heat-sensitive recording material, or an adhesive treatment may be applied to 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.

[0024]

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.

Preparation of Solution B As a coloring agent, 1,1-bis (4-hydroxyphenyl)
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.

Preparation of Solution C A composition comprising 30 parts of 1,2-di (3-methylphenoxy) ethane as a sensitizer, 5 parts of a 5% aqueous solution of methylcellulose, and 65 parts of water was subjected to sand milling to give an average particle diameter of 1 μm.
m was obtained to obtain a liquid C.

Preparation of Coating Solution for Thermal 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 Co., Ltd.)
% Aqueous solution 20 parts, styrene-butadiene latex having a solid concentration of 48% (trade name: Polylac 750K, manufactured by Mitsui Toatsu Chemicals, Inc.) 60 parts, 5% aqueous solution of sodium di-2-ethylhexylsulfosuccinate 5 parts and water 80 parts Was mixed and stirred to obtain a coating liquid for a heat-sensitive recording layer.

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 GH)
-8300, HIPS, manufactured by Dainippon Ink and Chemicals, Inc.) 8
0 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 (namely, 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 heat-sensitive recording layer The coating solution for heat-sensitive recording layer obtained on the above-mentioned unstretched polystyrene film was 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 value of 6.0 kg-cm / cm (trade names: 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.

Example 3 In the production of the unstretched polystyrene film of Example 1, a transparent 65% polystyrene compound was used without using a polystyrene compound containing 50% by weight of titanium oxide.
μ of unstretched polystyrene film was obtained. Other than that,
A thermosensitive recording medium was obtained in the same manner as in Example 1.

Example 4 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 of 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.

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

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

[Adhesion of Thermosensitive Recording Layer Coating Solution to Polystyrene Film] A cellophane tape is pressed onto the surface of the thermosensitive recording layer coated on the polystyrene film, and the cellophane tape is peeled off to remove the thermosensitive recording layer from the polystyrene film. This was visually determined as follows. Judgment criteria ◎: Cannot be obtained at all ○: Can be partially obtained

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

[Recording image quality] The recording image quality of the recording image obtained by the above-described color development evaluation test was visually judged as follows. Judgment criteria ◎: Very good recording quality ○: Excellent recording quality

[Curl After Recording] The curl state of the recorded thermosensitive recording medium obtained by the above-described color development evaluation test was visually determined as follows. Criteria ◎: No curl after recording ×: Strong curl after recording

[0042]

[Table 1]

[0043]

As is clear from the results shown in Table 1, the thermosensitive recording medium of the present invention has excellent recording image quality and less curl after recording.

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.
A thermosensitive recording medium, wherein the support is an unstretched polystyrene film. 2. The polystyrene resin used for the unstretched polystyrene film has an Izod impact strength of 6.0 kg.
The thermal recording medium according to claim 1, wherein the thermal recording medium has a density of -cm / cm or more. 3. The heat-sensitive recording material according to claim 1, wherein a pigment is contained in the unstretched polystyrene film.