JP3358287B2 - Thermal recording medium - Google Patents

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 leuco dye, a color former and a color-forming reaction, and relates to a heat-sensitive recording material which is excellent in storage stability of recorded images, recording running property and printability. It is about.

[0002]

2. Description of the Related Art Heat-sensitive recording materials are known which utilize a color reaction between a colorless or light-colored leuco dye and an organic or inorganic colorant and contact the two color-forming substances by heat to obtain a recorded image. Have been. Such a thermosensitive recording medium is relatively inexpensive, and its recording equipment is compact and easy to maintain, so that it is used not only as a recording medium for facsimile machines and various computers but also in a wide range of fields.

For example, as one of the fields of use, with the expansion of POS (point of sales) systems at retail stores and the like, the use of thermosensitive recording materials as labels for displaying products and the like is increasing. However, in a heat-sensitive recording material using a combination of a colorless or pale-colored leuco dye and an acidic substance in a color-forming system, there is a difficulty in solvent resistance and the like, and when a solvent is brought into contact with the recording layer, the recording density is reduced, There is a disadvantage that unnecessary color development called background fog occurs. Also, when a thermal label composed of such a coloring system is applied to a POS system in a supermarket or the like, the label often comes into contact with water, wraps, oil, and the like, and as a result, recording of the thermal label due to the influence thereof. Defects in which the image (printing) fades are observed. Therefore, the thermal recording medium is required to have storage properties such as water resistance, plasticizer resistance, and oil resistance.

In recent years, printing on a thermosensitive recording medium by a method such as letterpress, gravure, or offset has become popular, and performance excellent in printability is required. Conventionally, in order to improve the storage stability of a recorded image, a method of applying a water-soluble polymer compound such as an aqueous emulsion of a resin having chemical resistance and a water-soluble polymer compound such as polyvinyl alcohol on the heat-sensitive recording layer, Japanese Patent Application No. 5-379 discloses the use of a graft copolymer of a polymer containing an ethylenically unsaturated carboxylic acid and silicone for the protective layer.
Japanese Patent Publication No. 4-22153 proposes to use a polyurethane ionomer in Japanese Patent Publication No. 63-63. However, the methods proposed in the past are accompanied by new disadvantages such as a decrease in recording runnability with the improvement, and the effect of improving the storage stability is not always sufficient, and the printability is also insufficient. Met.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a thermosensitive recording medium which solves the above-mentioned disadvantages, has excellent storage stability of recorded images and excellent recording running properties, and has good printability. It is in.

[0006]

Means for Solving the Problems The present inventors have provided a heat-sensitive recording layer containing a colorless or pale-colored leuco dye and a coloring agent, and a protective layer mainly containing polyvinyl alcohol and a pigment on a support. In the heat-sensitive recording medium provided sequentially, a graft copolymer of a polymer containing an ethylenically unsaturated carboxylic acid and silicone, and a polyurethane ionomer are contained in a protective layer , and the polyurethane ionomer is
Is 5 to 40% by weight based on the total solids of the protective layer.
And the graft copolymer is a polyurethane iono
By containing 10 to 50% by weight based on the mer ,
The inventors have found that the above-mentioned objects are achieved, and have completed the present invention.

[0007]

According to the present invention, there is provided a heat-sensitive recording medium having a colorless or light-colored leuco dye and a colorant, and a protective layer comprising polyvinyl alcohol and a pigment as main components. in the layer, one which contains a specific graft copolymer polyurethane ionomer, coercive
In the protective layer, 5 to 40% by weight, more preferably 10 to 30% by weight of the polyurethane ionomer is used based on the total solid content of the protective layer.
It is desirable that the graft copolymer be contained in an amount of 10 to 50% by weight, more preferably 15 to 30% by weight, based on the polyurethane ionomer. When the amount of the polyurethane ionomer is 5 relative to the total solid content of the protective layer,
To be printed aptitude is not improved less than wt%, also storability is lowered relative such as a plasticizer of the recording image and more than 40 wt%. If the specific graft polymer is less than 10% by weight based on the polyurethane ionomer, sticking occurs during recording and a uniform recorded image cannot be obtained, and if it exceeds 50% by weight, printing unevenness occurs.

The polyurethane ionomer used in the present invention is obtained by polymerizing a polyisocyanate with a polyol having an anionic hydroxyl group such as a carboxyl group, a carboxyl group, a sulfone group or a sulfone group without using an emulsifier. Influence on the body (background fog, reduction in recording density) can be avoided. As a salt of a carboxyl base or a sulfone base, a salt of sodium, potassium, ammonium or the like is preferable. Particularly, an ammonium salt is preferable.

In the graft copolymer of a polymer containing an ethylenically unsaturated carboxylic acid and silicone, specific examples of a polymer containing an ethylenically unsaturated carboxylic acid include polyacrylic acid, polymethacrylic acid, and the like. Examples thereof include polyitaconic acid, polycrotonic acid, polyfumaric acid, and polymaleic acid, and a copolymer having the above-mentioned monomer components, a copolymer of acrylic acid and methyl methacrylate, and a copolymer of maleic acid and styrene. Further, as the silicone, dialkylpolysiloxane such as dimethylpolysiloxane and diethylpolysiloxane,
Diphenyl polysiloxane compounds and the like can be mentioned. The carboxylic acid in the graft polymer is sodium, potassium,
It is preferably used as a salt such as ammonium.

The preferred ratio of silicone to polymer containing ethylenically unsaturated carboxylic acid is 5 to 5
0% by weight, more preferably in the range of 10 to 30% by weight. If the proportion of silicone is less than 5% by weight, the water resistance of the protective layer may decrease, and if it exceeds 50% by weight, the adhesive strength may decrease.

As the colorless or monochromatic leuco dye used in the heat-sensitive recording layer, various known dyes can be used, and specifically, for example, 3,3-bis (p-dimethylaminophenyl) -6-dimethyl A blue-coloring dye such as aminophthalide, 3- (N-ethyl-Np-tolyl) amino-7-
N-methylanilinofluoran, 3-diethylamino-
Green chromogenic dyes such as 7-anilinofluoran, 3-diethylamino-7-dibenzylaminofluoran, 3-cyclohexylamino-6-chlorofluoran, 3-diethylamino-6-methyl-7-chlorofluoran, 3-diethylamino-7-chlorofluoran, rhodamine (o
-Chloroanilino) lactam, rhodamine (p-chloroanilino) lactam, 3-diethylamino-6,8-dimethylfluoran, 3,3'-bis (1-n-butyl-
Red-coloring dyes such as 2-methylindol-3-yl) phthalide, 3- (N-methyl-N-cyclohexyl) amino-6-methyl-7-anilinofluoran, 3-diethylamino-6-methyl-7 -Anilinofluoran, 3-
Di (n-butyl) amino-6-methyl-7-anilinofluoran, 3-diethylamino-7- (o-chlorophenylamino) fluoran, 3-diethylamino-7-
(O-fluorophenylamino) fluoran, 3- (N
-Ethyl-p-toluidino) -6-methyl-7-anilinofluoran, 3- (N-ethyl-N-tetrahydrofurfurylamino) -6-methyl-7-anilinofluoran, 3-diethylamino-6 -Chloro-7-anilinofluoran, 3-dimethylamino-6-methyl-7-anilinofluoran, 3-dibutylamino-6-methyl-7
-M-toluidinofluoran, 3- (Nn-hexyl-N-ethyl) amino-6-methyl-7-anilinofluoran, 3-diethylamino-6-methyl-7-p-ethoxyanilino Fluoran, 3-pyrrolidino-6-methyl-7-anilinofluoran, 3-piperidino-6-methyl-7-anilinofluoran, 3-diethylamino-
Black-color-forming dyes such as 7- (m-trifluoromethylphenyl) aminofluoran and the like, 3,3-bis [1- (4-methoxyphenyl) -1- (4-dimethylaminophenyl)
Ethylene-2-yl] -4,5,6,7-tetrachlorophthalide, 3,3-bis [1- (4-methoxyphenyl) -1- (4-pyrrolidinophenyl) ethylene-2-
Yl] -4,5,6,7-tetrachlorophthalide, 3-
p- (p-chloroanilino) anilino-6-methyl-7
-Chlorofluorane, 3,6-bis (dimethylamino)
Dyes having an absorption wavelength in the near infrared region, such as fluorene-9-spiro-3 '-(6'-dimethylamino) phthalide; Of course, the present invention is not limited to these, and two or more of them can be used in combination as needed.

Various materials are known for the coloring agent used in combination with the leuco dye as described above, for example, 4,4'-isopropylidenediphenol, 1,1-
Bis (4-hydroxyphenyl) cyclohexane, 4,
4'-cyclohexylidenediphenylol, benzyl 4-hydroxybenzoate, 4,4'-dihydroxydiphenylsulfone, 2,4'-dihydroxydiphenylsulfone, 4-hydroxy-4'-isopropoxydiphenylsulfone, bis (3- Allyl-4-hydroxyphenyl) sulfone, 4-hydroxy-4'-methyldiphenyl sulfone, 4-hydroxyphenyl-4'-benzyloxyphenyl sulfone, 2,2'-thiobis (3-te
rt-octylphenol), 2,2'-thiobis (4-
phenolic compounds such as tert-octylphenol),
Thiourea compounds such as N, N'-di-m-chlorophenylthiourea, N- (p-toluenesulfonyl) carbamoyl acid p-cumylphenyl ester, N- (p-toluenesulfonyl) carbamoyl acid p-benzyloxyphenyl ester , N- (o-toluoyl) -p-toluenesulfonamide, N- (p-toluenesulfonyl) -N '
- compounds having -SO ₂ NH- bond in the (p- tolyl) in molecule such as urea, p- chlorobenzoic acid, 4- [2-(p
-Methoxyphenoxy) ethyloxy] salicylic acid, 4
Aromatic carboxylic acids such as-[3- (p-tolylsulfonyl) propyloxy] salicylic acid, 5- [p- (2-p-methoxyphenoxyethoxy) cumyl] salicylic acid, and zinc and magnesium of these aromatic carboxylic acids; Salts with polyvalent metals such as aluminum, calcium, titanium, manganese, tin, nickel, etc., and organic acid substances such as antipyrine complex of zinc thiocyanate, complex zinc salt of terephthalaldehyde acid and other aromatic carboxylic acids, etc. Is exemplified. Among them, 4-hydroxy-4'-isopropoxydiphenylsulfone and bis (3-allyl-4-hydroxyphenyl) sulfone are preferably used because of their excellent general preservability of recorded images.

The ratio of the leuco dye to the colorant is appropriately selected according to the type of the leuco dye and the colorant used, and is not particularly limited. 1 to 50 parts by weight, preferably 2 to
About 10 parts by weight of a color former is used.

Further, a sensitizer can be used in combination depending on the purpose. Specific examples of the sensitizer include, for example, stearic acid amide, methoxycarbonyl-N-stearic acid benzamide, N-benzoylstearic acid amide, N-eicosanoic acid amide, ethylenebisstearic acid amide, behenic acid amide, methylenebisstearic acid amide , N-
Methylol stearamide, dibenzyl terephthalate, dimethyl terephthalate, dioctyl terephthalate,
Benzyl p-benzyloxybenzoate, phenyl 1-hydroxy-2-naphthoate, 2-naphthyl benzyl ether, m-terphenyl, dibenzyl oxalate, di-p-methylbenzyl oxalate, di-p-oxalate Chlorobenzyl, p-benzylbiphenyl, p-tolylbiphenyl ether, di (p-methoxyphenoxyethyl)
Ether, 1,2-di (3-methylphenoxy) ethane, 1,2-di (4-methylphenoxy) ethane, 1,
2-di (4-methoxyphenoxy) ethane, 1,2-di (4-chlorophenoxy) ethane, 1,2-diphenoxyethane, 1- (4-methoxyphenoxy) -2- (3
-Methylphenoxy) ethane, p-methylthiophenylbenzyl ether, 1,4-di (phenylthio) butane, p-acetotoluizide, p-acetophenethidide,
Examples thereof include N-acetoacetyl-p-toluidine, di (β-biphenylethoxy) benzene, p-di (vinyloxyethoxy) benzene, 1-isopropylphenyl-2-phenylethane and the like. The use amount of these sensitizers is not particularly limited, but it is generally desirable to adjust the sensitizer within a range of about 4 parts by weight or less based on 1 part by weight of the color former.

A method for preparing a coating solution for a heat-sensitive recording layer containing these substances is generally a method in which water is used as a dispersion medium and wet pulverization is carried out using an attritor, a ball mill, a sand mill or the like. For example, after dissolving with heat or solvent,
A method of emulsifying by dispersing in water is exemplified. Various dispersants can be used for wet grinding, for example, polyvinyl alcohol, methylcellulose, carboxymethylcellulose, hydroxyethylcellulose, vinyl acetate resins containing sulfonic acid groups, starches, sodium polyacrylate, sodium polysulfonate, dioctyl sulfo. Dispersants such as sodium succinate, sodium dodecylbenzenesulfonate, sodium salt of lauryl alcohol sulfate, and fatty acid metal salt are exemplified.

In the thermosensitive recording layer, binders are usually compounded. Specific examples of such binders include starches, hydroxyethylcellulose, and the like.
Methylcellulose, carboxymethylcellulose, gelatin, casein, gum arabic, polyvinyl alcohol, carboxy-modified polyvinyl alcohol, acetoacetyl group-modified polyvinyl alcohol, silicon-modified polyvinyl alcohol, diisobutylene / maleic anhydride copolymer salt, styrene / maleic anhydride copolymer Combined salt, ethylene
Acrylic acid copolymer salts, styrene / acrylic acid copolymer salts, styrene / butadiene copolymer emulsions, urea resins, melamine resins, amide resins, polyurethane resins and the like can be mentioned. The binder is preferably 5 to 40% by weight, more preferably 10 to 30% by weight based on the total solid content of the recording layer.
It is blended in about weight%.

Various known pigments can be added to the heat-sensitive recording layer, for example, magnesium carbonate, calcite-based light calcium carbonate, aragonite-based light calcium carbonate,
Heavy calcium carbonate, calcium sulfoaluminate,
Aluminum hydroxide, alkali-modified silica, kaolin,
Inorganic pigments such as clay, calcined kaolin, titanium oxide, diatomaceous earth, colloidal silica, activated clay, and the like, and organic pigments such as styrene microballs, nylon powder, polyethylene powder, urea / formalin resin filler, raw starch particles, and the like.

If necessary, lubricants such as zinc stearate, calcium stearate, polyethylene wax, carnauba wax, paraffin wax, ester wax, etc., sodium salt of dioctyl sulfosuccinate, sodium salt of dodecylbenzene sulfonate, sodium salt of lauryl alcohol sulfate, Dispersants such as fatty acid metal salts, ultraviolet absorbers such as benzophenone, etc., other antifoaming agents, fluorescent dyes, coloring dyes and the like can also be added.

Further, in the present invention, it is possible to add a storage stability improving agent to the heat-sensitive recording layer. Examples of such a preservability improver include the following. 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 (2-methyl-6-tert-butylphenol), 4,4'-butylidenebis (6-tert-butyl-
m-cresol), 1- [α-methyl-α- (4′-hydroxyphenyl) ethyl] -4- [α ′, α′-bis (4 ″ -hydroxyphenyl) ethyl] benzene, 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 -Bis (4-hydroxy-3,5-dichlorophenyl) propane, 2,2-
Hindered phenol compounds such as bis (4-hydroxy-3,5-dimethylphenyl) propane, 1,4-diglycidyloxybenzene, 4,4'-diglycidyloxydiphenylsulfone, 4-benzyloxy-4'-
(2-methylglycidyloxy) diphenyl sulfone,
Epoxy compounds such as diglycidyl terephthalate, cresol novolak type epoxy resin, phenol novolak type epoxy resin, bisphenol A type epoxy resin,
N, N'-di-2-naphthyl-p-phenylenediamine, sodium or polyvalent metal salt of 2,2'-methylenebis (4,6-di-tert-butylphenyl) phosphate, bis (4-ethyleneiminocarbonyl Aminophenyl) methane and the like. Among them, 1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane is preferably used because it has an excellent effect on water resistance and hardly causes background fog.

In the present invention, the method for forming the heat-sensitive recording layer is not particularly limited, and it can be formed according to a conventionally well-known and commonly used technique, for example, air knife coating, variver blade coating, pure blade coating, rod blade. Coating, short dwell coating, curtain coating,
The recording layer is formed by applying a coating solution for a recording layer on a support by a suitable coating method such as die coating and drying. The support is appropriately selected from paper, plastic film, synthetic paper, nonwoven fabric, metal deposit, and the like. The coating amount of the coating liquid for the recording layer is 2 to 2% by dry weight.
12 g / m ^2, is preferably adjusted in the range of about 3 to 10 g / m ^2.

The heat-sensitive recording material of the present invention has an important feature in that a protective layer in which a polyurethane ionomer and a silicone-based graft copolymer are selectively combined as a resin component is provided on the heat-sensitive recording layer thus obtained. Have

The polyurethane ionomer used in the present invention is different from an emulsion type in which a polyurethane resin is dispersed in water with a conventional emulsifier or the like, and is different from an ionic urethane resin, that is, an ionic group of the polyurethane ionomer. This is a so-called colloid-dispersed aqueous urethane resin that is dissolved in water or dispersed in extremely fine particles without using a solvent.

In the protective layer, starches, hydroxyethylcellulose, methylcellulose, carboxymethylcellulose, gelatin,
Casein, gum arabic, polyvinyl alcohol, carboxy-modified polyvinyl alcohol, acetoacetyl group-modified polyvinyl alcohol, silicon-modified polyvinyl alcohol, diisobutylene / maleic anhydride copolymer salt, styrene / maleic anhydride copolymer salt, ethylene / acrylic acid At least one of a copolymer salt, a styrene / acrylic acid copolymer salt, a styrene / butadiene copolymer emulsion, a urea resin, a melamine resin, an amide resin, and a polyurethane resin is 5 to 5% of the total solid content of the recording layer. 30% by weight
It is blended in the range of the degree. Among them, acetoacetyl group-modified polyvinyl alcohol and carboxy-modified polyvinyl alcohol are particularly preferably used because they can form a strong film.

In order to further improve printability and sticking, a pigment may be added to the protective layer as needed. Specific examples thereof include calcium carbonate, zinc oxide, aluminum oxide, and the like. Titanium dioxide, silicon dioxide, aluminum hydroxide, barium sulfate, zinc sulfate, talc, kaolin, clay, calcined kaolin, inorganic pigments such as colloidal silica, styrene microballs, nylon powder, polyethylene powder, urea / formalin resin filler, raw starch Organic pigments such as particles are exemplified. Generally, it is desirable to adjust the amount of use in the range of about 5 to 300 parts by weight with respect to 100 parts by weight of the binder component.

Further, in the protective layer, if necessary, a lubricant such as zinc stearate, calcium stearate, polyethylene wax, carnauba wax, paraffin wax, ester wax or the like, or a surfactant such as sodium dioctyl sulfosuccinate (dispersant, wetting agent) Agents), an antifoaming agent, and various auxiliaries such as water-soluble polyvalent metal salts such as potassium alum and aluminum acetate. In order to further improve the water resistance, a curing agent such as glyoxal, boric acid, dialdehyde starch, or an epoxy compound can be used in combination.

The method for preparing the coating liquid for forming the protective layer is not particularly limited. In general, water is used as a dispersion medium, and a polyurethane ionomer, a silicone-based graft copolymer, a binder, a pigment to be added as necessary, It is prepared by mixing agents and the like.

In the present invention, the method of forming the protective layer is not particularly limited, and it can be formed according to a conventionally well-known and conventional technique. For example, air knife coating, variver blade coating, pure blade coating, rod blade coating, The protective layer is formed on the recording layer by applying an appropriate coating method such as short dwell coating, curtain coating, or die coating on the recording layer, followed by drying. The coating amount of the coating liquid for the protective layer is 0.1 to 20 g by dry weight.
/ M ² , preferably in the range of about 0.5 to 10 g / m ² .

If necessary, a protective layer may be provided on the back side of the thermosensitive recording medium to further improve the storage stability. Furthermore, an undercoat layer is provided on the support, or a smoothing treatment such as super calendaring is performed after each layer is coated,
Alternatively, various known techniques in the field of heat-sensitive recording material production can be added as necessary, such as applying a pressure-sensitive adhesive treatment to the back surface of the recording material to process it 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 to such specific Examples. Parts and% in Examples are parts by weight and% by weight, respectively, unless otherwise specified.

Example 1 Preparation of Solution A 10 parts of 3-di (n-butyl) amino-6-methyl-7-anilinofluoran, 25 parts of 1,2-di (3-methylphenoxy) ethane, methyl cellulose Of 5% aqueous solution and 50 parts of water were pulverized with a sand mill until the average particle diameter became 1 μm.

Solution B Preparation A composition comprising 30 parts of 4-hydroxy-4'-isopropoxydiphenylsulfone, 5 parts of a 5% aqueous solution of methylcellulose, and 25 parts of water has a mean particle size of 1 using a sand mill.
Milled to a μm.

Preparation of Solution C Aluminum hydroxide (trade name: Heidilite H-42,
A composition comprising 60 parts of Showa Denko KK, 0.1 part of sodium polyacrylate, and 40 parts of water was dispersed with a stirrer.

Formation of heat-sensitive recording layer 100 parts of solution A, 120 parts of solution B, 30 parts of solution C, 80 parts of a 10% aqueous solution of polyvinyl alcohol, and 20 parts of water were mixed and stirred, and the obtained coating solution was 60 g / vol. coating amount after drying on one surface of woodfree paper having m ² was formed a heat-sensitive recording layer by coating and drying so that 5 g / m ^2.

Formation of protective layer Polyurethane ionomer (trade name: Hydran AP-
30, 80 parts by Dainippon Ink and Chemicals, 20 parts by weight, 20 parts by weight of silicone-based graft copolymer (trade name: Cymac, concentration: 30%), polyvinyl alcohol modified by acetoacetyl group (trade name: Gosefimer Z-) 200, manufactured by Nippon Synthetic Chemical Co., Ltd.), 200 parts of a 10% aqueous solution, 60 parts of kaolin (trade name: UW-90, manufactured by EMC), 10 parts of a 30% dispersion of zinc stearate, and 200 parts of water. The coating liquid for the protective layer obtained by mixing and stirring was applied and dried on the recording layer so that the coated amount after drying was 3 g / m ^2, and then subjected to a super calender treatment to obtain a heat-sensitive recording material.

Example 2 As a protective layer, 80 parts of a polyurethane ionomer (trade name: Hydran AP-40, manufactured by Dainippon Ink and Chemicals, Inc., concentration: 20%), a silicone-based graft copolymer (trade name: Cymac, concentration: 30) %) 20
Part, acetoacetyl group-modified polyvinyl alcohol (trade name: Gosefimer Z-200, manufactured by Nippon Synthetic Chemical Co., Ltd.)
200% of a 10% aqueous solution of kaolin [trade name: UW-9]
0, manufactured by EMC Co., Ltd.], except that a coating solution for a protective layer obtained by mixing and stirring a composition comprising 60 parts, 10 parts of a 30% dispersion of zinc stearate, and 200 parts of water was used. A thermosensitive recording medium was obtained in the same manner.

Example 3 80 parts of a polyurethane ionomer (trade name: Hydran AP-30, manufactured by Dainippon Ink and Chemicals, Inc., concentration: 20%) as a protective layer, a silicone-based graft copolymer (trade name: Cymac, concentration: 30) %) 20
Parts, 200 parts of a 10% aqueous solution of polyvinyl alcohol (trade name: PVR117, manufactured by Kuraray), 60 parts of kaolin (trade name: UW-90, manufactured by EMC), 10 parts of a 30% dispersion of zinc stearate, and 200 parts of water In the same manner as in Example 1, except that a coating liquid for a protective layer obtained by mixing and stirring the composition consisting of parts was used.

Comparative Example 1 As a protective layer, 100 parts of a polyurethane ionomer (trade name: Hydran AP-30, manufactured by Dainippon Ink and Chemicals, 20% concentration), acetoacetyl group-modified polyvinyl alcohol (trade name: Gosefimer Z) -200, manufactured by Nippon Synthetic Chemical Co., Ltd.)
0 parts, kaolin (trade name: UW-90, manufactured by EMC) 6
Thermosensitive recording medium in the same manner as in Example 1 except that a coating solution for a protective layer obtained by mixing and stirring a composition comprising 0 parts, 10 parts of a 30% dispersion of zinc stearate, and 200 parts of water was used. I got

[Comparative Example 2] Silicone graft copolymer (trade name: Cymac, concentration 30%) 1 as a protective layer
00 parts, 200 parts of a 10% aqueous solution of acetoacetyl group-modified polyvinyl alcohol (trade name: Gosefimer Z-200, manufactured by Nippon Synthetic Chemical Company), kaolin [trade name: U
W-90, manufactured by EMC] 60 parts, zinc stearate 3
A heat-sensitive recording material was obtained in the same manner as in Example 1, except that a coating liquid for a protective layer obtained by mixing and stirring a composition comprising 10 parts of a 0% dispersion and 200 parts of water was used.

Comparative Example 3 A 30% dispersion of a soap-free self-crosslinking acrylic ester resin as a protective layer 10
0 parts, 200 parts of a 10% aqueous solution of acetoacetyl group-modified polyvinyl alcohol (trade name: Gosefimer Z-200, manufactured by Nippon Synthetic Chemical Company), kaolin [trade name: UW
-90, manufactured by EMC] 60 parts, zinc stearate 30
% Was obtained in the same manner as in Example 1 except that a coating liquid for a protective layer obtained by mixing and stirring a composition consisting of 10 parts of a 10% dispersion and 200 parts of water was used.

The six types of heat-sensitive recording media thus obtained were subjected to the following quality evaluation tests, and the results are shown in Table 1. [Evaluation] [Coloring density] Using a thermal evaluation device (trade name: TH-PMD, manufactured by Okura Electric Co., Ltd.), each thermosensitive recording medium was colored at an applied energy of 0.45 mJ / dot, and the coloring density of the obtained recorded image was obtained. Was measured in visual mode using a Macbeth densitometer (RD-914, manufactured by Macbeth).

[Running Ability] In the above method, running performance was evaluated based on the loudness of sound (sticking sound) generated during recording. ◎ ─Excellent running performance. ○ ─ Good runnability. × ─ Poor runnability.

[Solvent Resistance] The surface of the recording paper was wiped with a gauze impregnated with ethanol, and the state of fog was visually evaluated. ○ ─ There is no fog and the recorded image is clear. Δ─ Although some fogging occurs, the recorded image is legible. × ─ Fog occurs, and the recorded image is distorted and unreadable.

[Oil Resistance] After the salad oil was dropped on the recorded image and allowed to stand in the room for one day, the state of the recorded image was visually evaluated. ○ ─ The recorded image is clear. △ ─ The recorded image is slightly distorted, but is legible. × ─ The recorded image is distorted and unreadable.

[Printing Suitability] Using 0.4 cc of the ink for Offline (tack value: 13), printing was performed on a roll with the ink after passing through a water roll in an RI type printing tester, and the fixability of the ink was evaluated. did. ◎ ─ Very good ink fixation. ○ ─ Ink fixation is good. × ─ Ink does not fix.

[0045]

[Table 1]

[0046]

As is clear from the results shown in Table 1, the heat-sensitive recording material of the present invention has excellent storage stability of recorded images, excellent running property during recording, and excellent printability. Met.

Claims (1)

(57) [Claims] 1. A thermosensitive recording medium comprising a support and a thermosensitive recording layer containing a colorless or pale-colored leuco dye and a colorant, and a protective layer containing polyvinyl alcohol and a pigment as main components in that order. during the graft copolymer of the polymer and silicone-containing ethylenically unsaturated carboxylic acids, and is contained polyurethane ionomer,該Po
The content of urethane ionomer increases the total solid content of the protective layer
5 to 40% by weight based on the weight of the graft copolymer
10 to 50% by weight based on the polyurethane ionomer
A heat-sensitive recording material characterized by being contained.