JPH09254544A - Production of thermal recording material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a thermal recording material excellent in recording density, recording sensitivity and recording image quality. SOLUTION: This thermal recording material is constituted by successively providing an undercoat layer, a thermal recording layer containing a leuco dye and a coupler and, if necessary, a protective layer. In this case, a mechanically foamed coating soln. for the undercoat layer is applied to a support and the coating surface of the support is dried while brought into contact with the surface of a heated metal drum under pressure to provide the undercoat layer or the mechanically foamed coating soln. for the undercoat layer is applied to the surface of the heated metal drum and the coating surface is dried while the support is brought into contact with the coating surface under pressure to provide the undercoat 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 utilizing a color-forming reaction between a leuco dye and a coloring agent, and more particularly to a method for producing a heat-sensitive recording material having excellent recording sensitivity and recording image quality.

[0002]

2. Description of the Related Art Conventionally, a heat-sensitive recording material is well known in which a coloring image of a leuco dye and a coloring agent is utilized to bring both coloring materials into contact with each other by heat to obtain a recorded image. Since such a thermosensitive recording medium is relatively inexpensive, the recording device is compact and the 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.

In recent years, with the progress of the information society, the amount of information has increased and the processing speed of information has been increased. Also for the thermosensitive recording medium, there is a demand for high sensitivity capable of withstanding high-speed recording and high image quality satisfying high density of information. As a technique for improving image quality, there is a method for smoothing the heat-sensitive recording layer by providing an undercoat layer having a specific composition on the surface of the support as described in JP-A-59-204594. However, this technology has a drawback that the thermal energy efficiency is poor because the undercoat layer is dense and the heat insulation is low, and sufficient thermal energy cannot be given at high-speed recording, so that sufficient printing density cannot be obtained. is there.

Further, in order to improve thermal energy efficiency as a technique for increasing sensitivity, it is disclosed in JP-A-49-133113 that a porous undercoat layer is provided on the surface of a support, and JP-A-59-5093. In JP-A-59-225987 and JP-A-59-171685, there is a method in which an organic foaming pigment is blended in the undercoat layer to increase the heat insulating property of the support to improve the heat energy efficiency. However, these techniques have problems in that a heat treatment step is required for foaming and that a uniform surface cannot be obtained, and thus sufficient quality has not yet been achieved.

Further, in order to solve these problems, in JP-A-1-275184, an aqueous resin coating liquid which is mechanically foamed together with a foam stabilizer is provided between the support and the heat-sensitive recording layer. A thermosensitive recording medium is described. However, even with this method, it is difficult to obtain a uniform image quality, and in particular, there is a possibility that the recording sensitivity is lowered and the storability of a recorded image is lowered due to the thermal recording layer penetrating into the foamed resin layer.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing a thermosensitive recording medium which is particularly excellent in recording density, recording sensitivity and recording image quality.

[0007]

[Means for Solving the Problems] An undercoat layer on a support,
As a means for solving the above-mentioned problems in a method for producing a heat-sensitive recording medium in which a heat-sensitive recording layer containing a leuco dye and a color former, and optionally a protective layer are sequentially provided, the present invention includes: 1) a support After applying a mechanically foamed coating liquid for the undercoat layer on the above, the undercoat layer is provided by drying while pressing the coated surface against the heated metal drum surface, and as another means, 2) The undercoat layer is formed by applying a mechanically foamed coating liquid for the undercoat layer on the heated metal drum surface and then drying the support while pressing the support against the coated surface. Further, as means, there is a method of 3) adjusting the apparent specific gravity of the undercoat layer to 0.1 to 0.5, 4) a method of further containing lecithin in the undercoat layer coating solution, and 5) undercoat layer coating. There is a method in which a liquid contains a colloidal silica-containing acrylic resin latex as an aqueous resin.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention provides a means for providing an undercoat layer by applying a mechanically foamed coating liquid for an undercoat layer and then drying the coated surface while pressing it against a heated metal drum surface.

Alternatively, a means for applying a mechanically foamed undercoat layer coating solution onto a heated metal drum surface, and then drying the substrate while pressing the support against the coated surface to provide an undercoat layer, The undercoat layer is formed by peeling between the metal drum surface and the undercoat layer surface.

The apparent specific gravity of the undercoat layer is 0.
1 to 0.5 is preferable. The apparent specific gravity of the undercoat layer is 0.1
When it is less than 0.2, the formed undercoat layer is likely to be broken, and when it exceeds 0.5, the heat insulating property of the undercoat layer may be deteriorated to lower the recording sensitivity. .

The undercoat layer coating liquid generally contains an aqueous resin, and is prepared by mechanically foaming with water as a dispersion medium so that the apparent specific gravity is 0.7 or less. As a method of mechanically foaming the coating liquid for the undercoat layer, various known techniques such as a homomixer and a double cylindrical continuous foaming machine for stirring and foaming while mixing air into the coating liquid can be used.
The average particle size of bubbles is 20 μm or less, preferably 10 μm
m or less, more preferably 5 μm or less. 20μ
If it exceeds m, the recording image quality may be deteriorated.

Specific examples of such an aqueous resin include completely (partially) saponified polyvinyl alcohol, silicon-modified polyvinyl alcohol, acetoacetyl group-modified polyvinyl alcohol, sodium polyacrylate, carboxymethyl cellulose, polyvinylpyrrolidone, casein, styrene-maleic acid. Water-soluble resin such as alkali salt of copolymer, sodium alginate, alkali salt of acrylic acid amide / acrylic acid ester / methacrylic acid copolymer, acrylic resin latex, acrylic resin latex containing colloidal silica, polyester polyurethane latex, Polyether polyurethane latex, styrene / butadiene copolymer latex, vinyl chloride / vinyl acetate copolymer latex, ethylene / vinyl acetate copolymer latex Which water-dispersible resin.
Of course, two or more of such water-based resins can be used in combination. Although the content of the aqueous resin is not particularly limited, it is preferably 50% by weight or more based on the total solid content of the undercoat layer.

Of these, colloidal silica-containing acrylic resin latex is preferable. What is colloidal silica-containing acrylic resin latex? Silica is contained in the resin component such as acrylic acid / methyl (meth) acrylate / butyl (meth) acrylate copolymer, methyl (meth) acrylate / butyl (meth) acrylate / styrene copolymer. Is a latex internally added in an amount of 20 to 70% by weight based on the total solid amount of the latex. By including such a latex in the coating liquid for the undercoat layer, the releasability of the undercoat layer surface from the metal drum surface and the water resistance of the undercoat surface are improved.
The amount of the colloidal silica-containing acrylic resin latex used is not particularly limited, but is preferably about 10 to 50% by weight based on the total solid amount of the undercoat layer. If it is less than 10% by weight, the releasability of the undercoat layer from the metal drum is deteriorated. On the other hand, if it exceeds 50% by weight, the heat insulating property may be lowered and the recording sensitivity may be lowered, so that 20 to 40% by weight is particularly preferable.

In the coating liquid for the undercoat layer, if necessary, inorganic pigments such as kaolin, calcium carbonate, aluminum hydroxide, titanium oxide, talc, amorphous silica, calcined kaolin, urea-formalin resin filler, melamine resin filler, etc. Organic pigments, ammonium stearate, ammonium oleate, sodium stearate, di (2
-Ethylhexyl) Surfactants such as sodium sulfosuccinate, sodium styrenesulfonate, polyoxyethylene alkyl ether, sorbitan fatty acid ester, glycerin fatty acid ester, and polyoxyethylene fatty acid ester are added.

By further containing lecithin in the undercoat layer coating liquid, the releasability of the undercoat layer surface from the metal drum surface is improved and a uniform undercoat surface is formed. The amount of lecithin used is not particularly limited, but is preferably about 0.5 to 10% by weight based on the total solid amount of the undercoat layer. 0.
If it is less than 5% by weight, the effect of improving the releasability is small, and 10
If the content is more than 5% by weight, the strength of the layer may be lowered, or coating defects may occur when the heat-sensitive recording layer is applied, so 1 to 5% by weight is particularly preferable.

For the undercoat layer, a curtain coater, a slit die coater (extrusion coating machine) or the like is used to dry the undercoat layer coating solution on a support or a metal drum in an amount of 1 to 1 by dry weight.
20 g / m ^2, preferably transferring a cast surface is coated with a metal drum about 3 to 15 g / m ^2, is formed and dried.
If it is less than 1 g / m ² , a uniform coated surface cannot be obtained, and problems such as insufficient heat insulating effect occur. 20g / m
^If it exceeds ² , the surface strength may deteriorate and printing may not be possible. The method of applying the undercoat layer coating liquid onto the metal drum is preferable because the surface of the undercoat layer is denser than the method of applying onto the support. It is preferable that the surface of the metal drum is mirror-finished because an undercoat layer having excellent smoothness can be obtained.

The surface temperature of the metal drum is 60 to 8
About 0 ° C. is preferable. If the temperature is lower than 60 ° C., the mold may not be sufficiently dried and a problem such as so-called blocking may occur. Also, 8
If the temperature exceeds 0 ° C., bubbles may coalesce or expand before the surface is hardened and become large, so that a uniform coated surface may not be obtained.

In the heat-sensitive recording material of the present invention, the material to be used for the support is not particularly limited as long as the support has air permeability. For example, fine paper (including neutral paper), art paper, coated paper, etc. Paper, non-woven fabric, etc. are used.

A thermal recording layer containing a leuco dye and a colorant is provided on the thus obtained undercoat layer.
Various known leuco dyes can be used, and specific examples thereof include the following. Three,
3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide, 3- (4-diethylamino-2-methylphenyl) -3- (4-dimethylaminophenyl)
-6-Dimethylaminophthalide, 3-diethylamino-
7-dibenzylamino-benzo [a] fluorane, 3-
(N-ethyl-N-p-tolyl) amino-7-N-methylanilinofluorane, 3-diethylamino-7-anilinofluorane, 3-cyclohexylamino-6-chlorofluorane, 3-diethylamino-6 -Methyl-7-
Chlorofluorane, 3-diethylamino-7-chlorofluorane, 3- (N-ethyl-N-isoamyl) amino-6-methyl-7-anilinofluorane, 3-diethylamino-7- (m-trifluoromethyl) Anilino) fluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3-di (n-butyl) amino-6-methyl-7-anilinofluorane, 3-di (n-pentyl)
Amino-6-methyl-7-anilinofluorane, 3-diethylami-7- (o-chloroanilino) fluorane,
3-di (n-butyl) amino-7- (o-chloroanilino) fluorane, 3-diethylamino-7- (o-fluoroanilino) fluorane, 3- (N-ethyl-p-toluidino) -6-methyl- 7-anilinofluoran, 3
-Diethylamino-6-chloro-7-anilinofluorane, 3,3-bis [1- (4-methoxyphenyl) -1
-(4-Pyrrolidinophenyl) ethylene-2-yl]-
4,5,6,7-tetraclophthalide, 3-p- (p-
Anilinoanilino) anilino-6-methyl-7-chlorofluorane, 2,2-bis {4- [6 '-(N-cyclohexyl-N-methylamino) -3'-methylspiro (phthalide-3,9'-xanthene ) -2'-ylamino] phenyl} propane, 3,6-bis (dimethylamino) fluorene-9-spiro-3 '-(6'-dimethylamino) phthalide and the like. Of course, it is not limited to these, and if necessary, two or more kinds may be used in combination. The leuco dye is used in an amount of about 5 to 40% by weight based on the total solid amount of the thermosensitive recording layer.

As the coloring agent used together with the leuco dye, various known coloring agents can be used, for example, 4-cumylphenol, hydroquinone monobenzyl ether, 4,4 '.
-Isopropylidenediphenol, 1,1-bis (4-
Hydroxyphenyl) cyclohexane, 4,4'-dihydroxydiphenyl sulfide, bis (4-hydroxy-3-methylphenyl) sulfide, 4,4'-dihydroxydiphenyl sulfone, 2,4'-dihydroxydiphenyl sulfone, 4-hydroxy -4'-methyldiphenyl sulfone, 4-hydroxy-4'-isopropoxydiphenyl sulfone, bis (3-allyl-4-hydroxyphenyl) sulfone, 4-hydroxyphenyl-
4'-benzyloxyphenyl sulfone, 4-hydroxy-3 ', 4'-tetramethylene biphenyl sulfone,
3,4-dihydroxyphenyl-p-tolyl sulfone,
4-Hydroxybenzoic acid benzyl ester, N, N'-
Di-m-chlorophenyl thiourea, zinc 4- [2- (p-methoxyphenoxy) ethyloxy] salicylate, 4
Zinc [-(3- (p-tolylsulfonyl) propyloxy] salicylate, Zinc 5- [p- (2-p-methoxyphenoxyethoxy) cumyl] salicylate, 4,4'-bis (p-tolylsulfonylaminocarbonylamino) Examples include diphenylmethane.

The use ratio of the leuco dye and the color former in the heat-sensitive recording layer is appropriately selected according to the type of the leuco dye and the color former used, and is not particularly limited.
Generally, 1 to 10 parts by weight, and preferably 1 to 5 parts by weight, of a coloring agent are used with respect to 1 part by weight of a colorless or pale leuco dye.

Preparation of the coating liquid for the heat-sensitive recording layer containing these leuco dyes and color formers generally uses water as a dispersion medium,
It is prepared by finely dispersing the leuco dye and the coloring agent together or separately with a stirring / crushing machine such as a ball mill, attritor, or sand grinder, and then adding the adhesive while mixing and stirring.

Specific examples of the adhesive include fully (partially) saponified polyvinyl alcohol, silicon-modified polyvinyl alcohol, acetoacetyl group-modified polyvinyl alcohol, methyl cellulose, carboxymethyl cellulose, starches, gelatin, casein, gum arabic,
Styrene / maleic anhydride copolymer alkali salt, ethylene / acrylic acid copolymer alkali salt, styrene / acrylic acid copolymer alkali salt, natural rubber latex, styrene / butadiene copolymer latex, acrylonitrile / butadiene Examples thereof include copolymer latex, acrylic resin latex and vinyl acetate resin latex. The amount of the adhesive used is about 5 to 40% by weight of the total solid content of the thermosensitive recording layer.

If desired, various additives may be used in combination in the heat-sensitive recording layer coating liquid. For example, lubricants such as zinc stearate, calcium stearate, polyethylene wax, carnauba wax, paraffin wax, and ester wax; calcium carbonate, zinc oxide, aluminum oxide, titanium dioxide, amorphous silica, aluminum hydroxide, barium sulfate, talc, kaolin, Inorganic pigments such as clay, calcined clay, colloidal silica; organic pigments such as styrene microballs, nylon powder, polyethylene powder, urea / formalin resin fillers;
Stearic acid amide, N-methylstearic acid amide,
Fatty acid amides such as benzanilide, stearic acid methylene bisamide, oleic acid amide, baltimic acid amide, scented oleic acid amide, and coconut fatty acid amide;

4,4'-butylidene bis (6-tert
-Butyl-3-methylphenol), 2,2'-methylenebis (4-ethyl-6-tert-butylphenol), 2,4-di-tert-butyl-3-methylphenol, 1,1,3-tris ( 2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 1,
1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane, 1,3,5-tris (5-tert-butyl-3-hydroxy-2,6-dimethylbenzyl) isocyanuric acid, etc. Hindered phenols; 4- (2-methyl-1,2-epoxyethyl) diphenyl sulfone, 4- (2-ethyl-1,2)
Diphenyl sulfone derivatives such as epoxyethyl) diphenyl sulfone and 4-benzyloxy-4 ′-(2,3-glycidyloxy) diphenyl sulfone; 2-
UV absorbers such as (2'-hydroxy-5'-methylphenyl) benzotriazole and 2-hydroxy-4-benzyloxybenzophenone;

1,2-di (3-methylphenoxy) ethane, 1,2-diphenoxyethane, parabenzyl biphenyl, naphthylbenzyl ether, benzyl-4-methylthiophenyl ether, 1-hydroxy-2-naphthoic acid phenyl ester , Oxalic acid dibenzyl ester,
Recording sensitivity improver (sensitizer) such as oxalic acid di-p-methylbenzyl ester, oxalic acid di-p-chlorobenzyl ester, terephthalic acid dibutyl ester, terephthalic acid dibenzyl ester, and isophthalic acid dibutyl ester
And the like.

Further, glyoxal, methylolmelamine, ammonium persulfate, sodium persulfate, ferric chloride,
Water resistant agents such as magnesium chloride, boric acid, ammonium chloride, ammonium zirconium carbonate; dispersants such as sodium dioctyl sulfosuccinate, sodium dodecylbenzene sulfonate, lauryl alcohol sulfate / sodium salt, alginate, fatty acid metal salt;
A defoaming agent; a fluorescent dye; a coloring dye or the like can be added as necessary.

In the heat-sensitive recording material of the present invention, a protective layer is optionally provided on the heat-sensitive recording layer thus obtained. The protective layer contains an aqueous resin and, if necessary, a pigment. Specific examples of the aqueous resin include, for example, completely (partially) saponified polyvinyl alcohol, acetoacetyl group-modified polyvinyl alcohol, carboxyl group-modified polyvinyl alcohol, silicon-modified polyvinyl alcohol,
Cellulose derivatives such as methylcellulose, ethylcellulose, hydroxyethylcellulose, carboxymethylcellulose, water-soluble resins such as casein, gum arabic, oxidized starch, ether starch, dialdehyde starch, esterified starch, self-crosslinking acrylic resin latex, polyester polyurethane latex Water-dispersible resins such as Among these aqueous resins, acetoacetyl group-modified polyvinyl alcohol and silicon-modified polyvinyl alcohol are more preferable. The amount of the aqueous resin used is not particularly limited, but it is used in an amount of 20 to 100% by weight, preferably 30 to 80% by weight, based on the total solid amount of the protective layer.

Specific examples of the pigment include calcium carbonate,
Inorganic pigments such as zinc oxide, aluminum oxide, titanium dioxide, amorphous silica, aluminum hydroxide, barium sulfate, talc, kaolin, clay, calcined clay, colloidal silica, styrene microballs, nylon powder, polyethylene powder, urea / formalin resin Examples include fillers and organic pigments such as raw starch granules. The amount used is generally 5 to 500 parts by weight, preferably 7 parts by weight, based on 100 parts by weight of the aqueous resin component forming the protective layer.
About 0 to 350 parts by weight is desirable.

Further, in the protective layer, glyoxal, methylolmelamine, ammonium persulfate, sodium persulfate,
Water-resistant agents such as ferric chloride, magnesium chloride, boric acid, ammonium chloride, ammonium zirconium carbonate, zinc stearate, calcium stearate, stearamide, polyethylene wax, carnauba wax, paraffin wax, ester wax and other lubricants, dioctyl sulfo. Surfactants such as sodium succinate, sodium dodecylbenzene sulfonate, sodium lauryl alcohol sulfate / sodium salt, alginate, fatty acid metal salt, UV absorbers such as benzophenone-based and triazole-based, antifoaming agents, fluorescent dyes, coloring dyes It is also possible to appropriately add various auxiliaries such as.

The method for forming the heat-sensitive recording layer and the protective layer is not particularly limited, and examples thereof include air knife coating, varibar blade coating,
It is formed by a method in which the coating liquids for the heat-sensitive recording layer and the protective layer are sequentially coated and dried on the undercoat layer by pure blade coating, short dwell coating, or the like. Although there is no particular limitation on the coating amount of each coating solution, 2~12g / m ² at normal dry weight in the heat-sensitive recording layer, preferably 3 to 10 g / m ² approximately, and in the protective layer It is about 0.5 to 10 g / m ² , preferably about 1 to 6 g / m ² .

In the heat-sensitive recording material of the present invention, for the purpose of improving the recording image quality, it is possible to perform smoothing treatment with a super calender or the like after forming each layer. Furthermore, on the protective layer,
After applying a coating liquid containing electron beam curable resin or UV curable resin as the main component, irradiate it with electron beams or ultraviolet rays to give it gloss, or to store it further by providing a protective layer on the back side of the thermosensitive recording medium. If necessary, various publicly known techniques in the field of heat-sensitive recording material production can be added, such as improving the property or treating the back surface of the heat-sensitive recording material with an adhesive to process it into an adhesive label.

[0033]

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, unless otherwise specified, parts and% in the examples indicate parts by weight and% by weight, respectively.

Example 1 Preparation of Coating Liquid for Undercoat Layer Styrene / butadiene copolymer latex (trade name:
L-1571, solid concentration 48%, manufactured by Asahi Kasei) 250
Parts, 60% aqueous solution of carboxymethyl cellulose 60
Parts, ammonium stearate 10 parts, colloidal silica-containing acrylic resin latex (trade name: Movinyl 8050, solid concentration 44%, Hoechst Synthetic Co., Ltd.) 180
Part, lecithin (trade name: Separ 380, solid concentration 20)
%, Manufactured by Chukyo Yushi Co., Ltd.) 15 parts, di (2-ethylhexyl)
A composition consisting of 5 parts of a 5% aqueous solution of sodium sulfosuccinate and 10 parts of water was stirred with a homomixer until the apparent specific gravity became 0.32 to obtain a coating liquid for undercoat layer.

Preparation of Solution A A composition consisting of 20 parts of 4-hydroxy-4′-isopropoxydiphenyl sulfone, 5 parts of a 5% aqueous solution of methylcellulose, and 55 parts of water was ground by a sand mill until the average particle size became 0.8 μm. Then, A solution was obtained.

Solution B preparation 3-di (n-butyl) amino-6-methyl-7-anilinofluorane 10 parts, oxalic acid di-p-methylbenzyl ester 10 parts, oxalic acid di-p-chlorobenzyl ester A composition consisting of 10 parts, 10 parts of a 5% aqueous solution of methyl cellulose, and 60 parts of water was pulverized by a sand mill until the average particle size became 1.0 μm, to obtain a liquid B.

Formation of Undercoat Layer A coating liquid for undercoat layer was applied to a mirror-finished metal drum surface (surface temperature: 70 ° C.) using a slit die coater so that the coating amount after drying was 10 g / m ^2, and the coated surface was coated. Basis weight 50g / m
^{The high-} quality paper of No. ² was pressed, dried, and then peeled off between the mirror-finished metal drum surface and the undercoat layer surface, and the undercoat layer was dried with hot air at 120 ° C. to form an undercoat layer having an apparent specific gravity of 0.39.

Formation of Thermosensitive Recording Layer 80 parts of solution A, 100 parts of solution B, 10% aqueous solution of polyvinyl alcohol (saponification degree 99%, polymerization degree 1000) 200
Parts, 10 parts of light calcium carbonate, and 65 parts of water are mixed and stirred to obtain a coating liquid, which is applied to the above-mentioned undercoat layer so that the coating amount after drying is 5 g / m ^2. Then, a thermosensitive recording layer was formed.

Formation of Protective Layer Acetoacetyl group-modified polyvinyl alcohol (trade name:
Gocefimer Z-200, 400 parts of 10% aqueous solution of Nippon Synthetic Chemical Industry Co., Ltd., kaolin (trade name: UW)
-90, manufactured by Engelhart) 60 parts, 2 parts 20% aqueous solution of sodium polyacrylate, 10 glyoxal
% 3% aqueous solution and 100 parts of water are mixed and stirred to obtain a coating solution for a protective layer, which is applied onto the thermosensitive recording layer so that the coating amount after drying is 3 g / m ^2. After drying to form a protective layer, a super calendering treatment was carried out so that the surface Bekk smoothness of the protective layer was 1000 seconds to obtain a heat-sensitive recording material.

Example 2 A thermosensitive recording medium was obtained in the same manner as in Example 1 except that the undercoat layer was formed by using the following undercoat layer coating liquid in the formation of the undercoat layer in Example 1.

Preparation of Coating Liquid for Undercoat Layer Acetoacetyl group-modified polyvinyl alcohol (trade name:
Gocefimer Z-200, manufactured by Nippon Synthetic Chemical Industry Co., Ltd., 800 parts of 15% aqueous solution, 30 parts of 10% aqueous solution of carboxymethyl cellulose, 10 parts of ammonium stearate, colloidal silica-containing acrylic resin latex (trade name: Movinyl 8050, A composition comprising 180 parts of solid concentration 44%, Hoechst Synthetic Co., Ltd.), lecithin (trade name: Separ 380, solid concentration 20%, Chukyo Yushi Co., Ltd.), and 10 parts of water has an apparent specific gravity with a homomixer. The mixture was stirred until it reached 0.42 to obtain a coating liquid for undercoat layer.

Formation of Undercoat Layer A coating liquid for undercoat layer was applied on the mirror-finished metal drum surface (surface temperature 60 ° C.) so that the coating amount after drying was 10 g / m ² .
Press the high-quality paper of basis weight 50 g / m ² against the coated surface, and after drying,
Peel between the mirror surface metal drum surface and the undercoat layer surface, and
The apparent specific gravity is 0.4 after drying the undercoat layer with hot air at 20 ° C.
7 undercoat layer was formed.

Example 3 A thermosensitive recording medium was obtained in the same manner as in Example 1 except that the undercoat layer was formed by using the following undercoat layer coating liquid in the formation of the undercoat layer in Example 1.

Preparation of Coating Liquid for Undercoat Layer Polyester polyurethane latex (trade name: Hydran AP30, solid concentration 30%, manufactured by Dainippon Ink and Chemicals, Inc.)
400 parts, 60 parts of 10% aqueous solution of carboxymethyl cellulose, 10 parts of ammonium stearate, colloidal silica-containing acrylic resin latex (trade name: Movinyl LX8201, solid concentration 45%, Hoechst Synthetic Co., Ltd.) 180 parts, lecithin (trade name: A composition comprising 15 parts of Separ 380, a solid concentration of 20%, manufactured by Chukyo Yushi Co., Ltd.), and 10 parts of water has an apparent specific gravity of 0.2 with a homomixer.
The mixture was stirred until it became 4, to obtain a coating liquid for undercoat layer.

Formation of Undercoat Layer A coating liquid for undercoat layer was applied to the mirror-finished metal drum surface (surface temperature 80 ° C.) so that the coating amount after drying was 10 g / m ² .
Press the high-quality paper of basis weight 50 g / m ² against the coated surface, and after drying,
Peel between the mirror surface metal drum surface and the undercoat layer surface, and
The apparent specific gravity is 0.3 after drying the undercoat layer with hot air at 20 ° C.
1 undercoat layer was formed.

Example 4 In the preparation of the undercoat layer coating solution and the formation of the undercoat layer of Example 1, instead of stirring until the apparent specific gravity reached 0.32, the mixture was stirred until the apparent specific gravity reached 0.24, and the apparent specific gravity reached 0.24. Example 1 except that an undercoat layer having a specific gravity of 0.27 was formed.
A thermosensitive recording medium was obtained in the same manner as described above.

Example 5 In the preparation of the undercoat layer coating solution of Example 1 and the formation of the undercoat layer, stirring was carried out until the apparent specific gravity became 0.59, and the undercoat layer having an apparent specific gravity of 0.71 was formed. A thermosensitive recording medium was obtained in the same manner as in Example 1 except that the thermosensitive recording medium was formed.

Example 6 In the formation of the undercoat layer of Example 1, instead of applying the coating liquid for undercoat layer at a coating amount after drying of 10 g / m ² , the coating liquid was coated at 15 g / m ^2. A thermosensitive recording medium was obtained in the same manner as in Example 1 except that the above was carried out.

Example 7 Formation of Undercoat Layer The undercoat layer coating solution obtained in the preparation of the undercoat layer coating solution of Example 1 was dried on a woodfree paper having a basis weight of 50 g / m ² using a slit die coater. The coating amount is 10 g / m ^2, and the coating surface is a mirror surface metal drum (surface temperature 7
(0 ° C.) surface, and after drying, the mirror-finished metal drum surface and the undercoat layer surface were peeled off, and the undercoat layer was dried with hot air at 120 ° C. to form an undercoat layer having an apparent specific gravity of 0.42.

Example 8 In the formation of the undercoat layer of Example 1, 250 parts of styrene / butadiene copolymer latex (solid concentration 48%) and acrylic resin latex containing colloidal silica (trade name: Movinyl 8050, solid concentration 44%). Instead of 180 parts of Hoechst Synthetic Co., Ltd., 400 parts of styrene / butadiene copolymer latex (solid concentration 48%) and acrylic resin latex containing colloidal silica (trade name: Movinyl 8050, solid concentration 44%, Hoechst Synthetic Co., Ltd.) A thermosensitive recording medium was obtained in the same manner as in Example 1 except that 30 parts (manufactured by K.K.) were used.

Example 9 In the formation of the undercoat layer of Example 1, styrene / butadiene copolymer latex (solid concentration 48%) 250
Parts and colloidal silica-containing acrylic resin latex (trade name: Movinyl 8050, solid concentration 44%, Hoechst Synthetic Co., Ltd.) 180 parts, instead of styrene-butadiene copolymer latex (solid concentration 48%) 150
And a colloidal silica-containing acrylic resin latex (trade name: Movinyl 8050, solid concentration 44%, Hoechst Synthetic Co., Ltd.) 280 parts were used to obtain a thermosensitive recording medium in the same manner as in Example 1.

Example 10 In the preparation of the coating for the undercoat layer of Example 1, 160 parts of butyl acrylate / styrene copolymer latex (solid concentration 50%) was used in place of 180 parts of the colloidal silica-containing acrylic resin latex. A thermal recording material was obtained in the same manner as in Example 1 except for the above.

Example 11 In the preparation of the coating for the undercoat layer of Example 1, lecithin (trade name: Separ 380, manufactured by Chukyo Yushi Co., Ltd., solid concentration 20) was used.
%) A thermosensitive recording medium was obtained in the same manner as in Example 1 except that 6 parts of a 50% dispersion of light calcium carbonate was used instead of 15 parts.

Comparative Example 1 Heat-sensitive material was prepared in the same manner as in Example 1 except that the undercoat layer coating solution obtained in the preparation of the undercoat layer coating solution of Example 1 was used to form an undercoat layer by the following method. I got a record.

Formation of Undercoat Layer The above undercoat layer coating solution was applied to one surface of a high-quality paper having a basis weight of 50 g / m ² so that the applied amount after drying was 10 g / m ^2, and then hot air at 70 ° C. When dried by hot air at 120 ° C., an undercoat layer having an apparent specific gravity of 0.45 was formed.

Comparative Example 2 A thermosensitive recording medium was obtained in the same manner as in Example 1 except that the undercoat layer was formed by using the following undercoat layer coating liquid in the formation of the undercoat layer in Example 1.

Preparation of Coating Liquid for Undercoat Layer Styrene / butadiene copolymer latex (trade name:
L1571, manufactured by Asahi Kasei, solid concentration 48%) 250 parts,
60 parts of 10% aqueous solution of carboxymethyl cellulose, 10 parts of ammonium stearate, acrylic resin latex containing colloidal silica (trade name: Movinyl 805
0, solid concentration 44%, Hoechst Synthetic Co., Ltd. 180 parts, lecithin (trade name: Separ 380, Chukyo Yushi Co., Ltd., solid concentration 20%) 15 parts, and a composition consisting of 10 parts of water are mixed and stirred to make an appearance. A coating liquid for undercoat layer having a specific gravity of 0.98 was obtained.

Formation of Undercoat Layer The coating liquid for undercoat layer was applied to the drum surface (surface temperature: 70 ° C.) of the mirror-finished metal drum so that the coating amount after drying was 10 g / m ^2, and the basis weight was 50 g / m ² . Stick high-quality paper on it, and after drying, peel off the mirror-finished metal drum surface and the undercoat layer surface.
The apparent specific gravity is 0.95 after drying the undercoat layer with hot air at 0 ° C.
An undercoat layer was formed.

The heat-sensitive recording material thus obtained was subjected to the following evaluation tests, and the results obtained are shown in Table 1.

[Recording Sensitivity] Evaluator for thermal recording (TH-P
MD type, manufactured by Okura Electric Co., Ltd., and applied energy of 0.
20mJ / dot, 0.30mJ / dot, 0.45m
Recording was performed at J / dot, and the recording density of the obtained recorded image was measured with a Macbeth densitometer (RD-914 type, manufactured by Macbeth Co.).

[Recording Image Quality] A thermal recording type bar code label printer machine (4800RV type, manufactured by Sato) was used.
Printing was performed at 10 inches / second, and the reproducibility of fine lines was visually evaluated. Evaluation Criteria ⊚: Excellent. ◯: Excellent Δ: Somewhat inferior X: Inferior

[Releasability] In the formation of the undercoat layer of each Example and Comparative Example, the releasability of the undercoat layer from the metal drum surface was evaluated by visually judging the state of the surface of the formed undercoat layer. did. Evaluation Criteria A: The surface of the undercoat layer is peeled off very uniformly. ◯: The surface of the undercoat layer is peeled off uniformly. X: The surface of the undercoat layer has slight peeling unevenness.

[0063]

[Table 1]

[0064]

As is clear from the above results, the present invention is a method for producing a thermosensitive recording medium having excellent recording sensitivity and recording image quality.

Claims (5)

[Claims] 1. A method for producing a thermosensitive recording medium comprising a base, an undercoat layer, a thermosensitive recording layer containing a leuco dye and a coloring agent, and a protective layer if necessary.
A method for producing a thermosensitive recording medium, which comprises applying a mechanically foamed coating liquid for an undercoat layer, and then drying the coated surface while pressing it against a heated metal drum surface to provide an undercoat layer. 2. A method for producing a thermosensitive recording medium comprising a support, an undercoat layer, a thermosensitive recording layer containing a leuco dye and a coloring agent, and a protective layer if necessary, which are successively provided on a heated metal drum surface. A method for producing a thermosensitive recording medium, which comprises applying a coating liquid for an undercoat layer that is mechanically foamed and then drying the substrate while pressing the support against the coated surface to provide an undercoat layer. 3. The method for producing a thermosensitive recording medium according to claim 1, wherein the apparent specific gravity of the undercoat layer is 0.1 to 0.5. 4. The method for producing a thermosensitive recording medium according to claim 1, wherein the undercoat layer coating liquid further contains lecithin. 5. The method for producing a thermosensitive recording medium according to claim 1, wherein the coating liquid for the undercoat layer contains a colloidal silica-containing acrylic resin latex as an aqueous resin.