JPH07117358A - Thermal recording material - Google Patents

Abstract

PURPOSE:To improve storage stability and head matching properties by adding a specific salicylic acid derivative or a metal salt thereof as an electron acceptive compd. and interposing an undercoat layer containing org. intermediate pigment between a support and a thermal recording layer. CONSTITUTION:A thermal recording material is obtained by providing a thermal recording layer containing a usually colorless or light-colored dye precursor and an electron acceptive compd. reacting with the dye precursor at the time of heating to develop a color on the upper surface of a support. In this case, as the electron acceptive compd., a salicylic acid derivative represented by general formula (X1 and X2 are each a hydrogen atom, an alkyl group, an aralkyl group, an aryl group or a halogen atom and R is an alkyl group, an alkenyl group, an aralkyl group or an aryl group) or a metal salt thereof is added. An undercoat layer containing org. intermediate pigment is interposed between the support and the thermal recording layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-sensitive recording material, and more particularly to a heat-sensitive recording material having good recording sensitivity, storage stability of a background portion and an image portion, and head matching property.

[0002]

[Prior art]

In general, a heat-sensitive recording material comprises a support and a heat-sensitive recording layer mainly composed of an electron-donating, usually colorless or light-colored dye precursor and an electron-accepting developer. By heating with a thermal head, a heating pen, a laser beam or the like, a dye precursor and a developer react instantaneously to obtain a recorded image. JP-B-43-4160, 45-45
No. 14039 is disclosed. Such a heat-sensitive recording material has the advantages that recording can be obtained with a relatively simple device, that maintenance is easy, and that noise is not generated, and measurement recorders, facsimiles, printers, computer terminals, It is used in a wide range of fields such as labels and ticket vending machines. Conventional thermal recording materials using an electron-donating colorless dye precursor and an electron-accepting compound have characteristics such as high color density, but on the other hand, the recorded image area is different from plastic such as polyvinyl chloride. It has the disadvantage that the storage characteristics of the recorded image are poor, such as the contact image is erased by permeation of plasticizers and additives contained in the plastic, and the product is erased by contact with chemicals contained in foods and cosmetics. Or
Alternatively, it has a drawback that the writing traces become discolored when writing with a writing instrument on the background part, and it is the current situation that the application is subject to certain restrictions, and its improvement has been strongly desired. .

As means for improving the storage characteristics of the recorded image area and the background area, a salicylic acid derivative having a substituent such as an alkyl group, an aralkyl group, an alkyloxy group and an acyl group or a metal salt thereof is used as an electron accepting compound. Thermal recording materials to be used have been proposed. (JP-A-62-16968
1 gazette, the same 63-22683 gazette, the same 63-959.
(Gazette No. 77)

However, the salicylic acid derivative described in this publication has insufficient storage characteristics of a color image, insufficient storage stability of the background portion, and low color development sensitivity. It was hard to say that it was a heat-sensitive recording material compatible with high-speed recording.

As a method for improving the sensitivity, many methods have been proposed in which an intermediate layer having a high heat insulating property is provided between the thermosensitive recording layer and the support to enhance the thermal efficiency acting on the thermosensitive recording layer. For example, in JP-A-63-227374, the heat conductivity of the support member is set to 0.04 kcal / mh ° C. or less by using a foamed plastic material or the like, and in JP-A-1-113282, it is specified. There has been proposed a method of enhancing the heat insulating property of the intermediate layer by using the above organic hollow pigment. However, when an intermediate layer using these known organic hollow pigments is applied to a heat-sensitive recording material containing a salicylic acid derivative described in this publication, there is a problem that running defects such as printing dust and sticking occur. It was Further, when a foamed plastic material or particles having a particle size of 10 μm or more is used, sufficient heat insulation of the undercoat layer can be obtained, but the smoothness of the coated surface cannot be obtained, resulting in uneven color density during printing. As a result, there arises a problem that sensitivity cannot be obtained.

[0007]

The present invention relates to a heat-sensitive recording material, and more specifically, to obtain a heat-sensitive recording material having good recording sensitivity, storage stability of the background portion and image area, and head matching property. Is.

[0008]

As a result of earnest research, the inventors of the present invention have invented the heat-sensitive recording material of the present invention. That is, the heat-sensitive recording material of the present invention is a heat-sensitive recording material containing, on a support, an electron-accepting compound that reacts with a normally colorless to light-colored dye precursor upon heating to develop the dye precursor, An undercoat layer containing, as an electron-accepting compound, at least one salicylic acid derivative represented by the following chemical formula 2 (general formula 1) or a metal salt thereof, and an organic hollow pigment between the heat-sensitive recording layer and the support. It is characterized by being provided.

[Chemical 2] (In the formula, X ₁ and X ₂ represent a hydrogen atom, an alkyl group, an aralkyl group, an aryl group, or a halogen atom, and R represents
It represents an alkyl group, an alkenyl group, an aralkyl group, or an aryl group. )

In the present invention, the use of the organic hollow pigment enhances the heat insulating property of the undercoat layer, thereby improving the coloring efficiency of the heat-sensitive recording layer and achieving high sensitivity. Such a mechanism for increasing the sensitivity itself has been disclosed in many documents and is already known, but in the heat-sensitive recording material of the present invention, the following specific organic hollow pigment is used as the electron-accepting compound. It was found that in a heat-sensitive recording material coated with a heat-sensitive recording layer containing at least one salicylic acid derivative represented by the general formula 1 or a metal salt thereof, the sensitivity was specifically improved and the head matching property was good. Of. Further, an overcoat layer may be provided on the heat-sensitive recording material, if necessary.

Specific examples of the salicylic acid derivative represented by the general formula 1 or a metal salt thereof according to the present invention include, for example,
Although the following are listed, the present invention is not limited thereto.

(1) 3-Methyloxycarbonylaminosalicylic acid (2) 3-Ethyloxycarbonylaminosalicylic acid (3) 3-n-Propyloxycarbonylaminosalicylic acid (4) 3-Isopropyloxycarbonylaminosalicylic acid (5) 3- n-Butyloxycarbonylaminosalicylic acid (6) 3-isobutyloxycarbonylaminosalicylic acid (7) 3-sec-butyloxycarbonylaminosalicylic acid (8) 3-n-pentyloxycarbonylaminosalicylic acid (9) 3-isopentyloxycarbonyl Aminosalicylic acid (10) 3-n-hexyloxycarbonylaminosalicylic acid (11) 3-n-heptyloxycarbonylaminosalicylic acid (12) 3-n-octyloxycarbonylaminosalicylic acid (13) 3 (2'-Ethylhexyl) oxycarbonylaminosalicylic acid (14) 3-n-nonyloxycarbonylaminosalicylic acid (15) 3-n-decyloxycarbonylaminosalicylic acid (16) 3-n-undecyloxycarbonylaminosalicylic acid (17) 3-n-dodecyloxycarbonylaminosalicylic acid (18) 3-n-tridecyloxycarbonylaminosalicylic acid (19) 3-n-tetradecyloxycarbonylaminosalicylic acid (20) 3-n-pentadecyloxycarbonylaminosalicylic acid (21) ) 3-n-hexadecyloxycarbonylaminosalicylic acid (22) 3-n-heptadecyloxycarbonylaminosalicylic acid (23) 3-n-octadecyloxycarbonylaminosalicylic acid (24) 3-cyclopen (25) 3-Cyclohexyloxycarbonylaminosalicylic acid (26) 3-Allyloxycarbonylaminosalicylic acid (27) 3-Benzyloxycarbonylaminosalicylic acid (28) 3-Phenyloxycarbonylaminosalicylic acid (29) 3- (4'-Methylphenyl) oxycarbonylaminosalicylic acid (30) 3- (4'-methoxyphenyl) oxycarbonylaminosalicylic acid

(31) 3- (4'-chlorophenyl) oxycarbonylaminosalicylic acid (32) 3- [2 '-(4-methoxyphenyl) oxyethyl] oxycarbonylaminosalicylic acid (33) 4-methyloxycarbonylaminosalicylic acid ( 34) 4-Ethyloxycarbonylaminosalicylic acid (35) 4-n-propyloxycarbonylaminosalicylic acid (36) 4-Isopropyloxycarbonylaminosalicylic acid (37) 4-n-butyloxycarbonylaminosalicylic acid (38) 4-isobutyloxy Carbonylaminosalicylic acid (39) 4-sec-butyloxycarbonylaminosalicylic acid (40) 4-n-pentyloxycarbonylaminosalicylic acid (41) 4-isopentyloxycarbonylaminosalicylic acid (42) ) 4-n-hexyloxycarbonylaminosalicylic acid (43) 4-n-heptyloxycarbonylaminosalicylic acid (44) 4-n-octyloxycarbonylaminosalicylic acid (45) 4- (2′-ethylhexyl) oxycarbonylaminosalicylic acid 46) 4-n-nonyloxycarbonylaminosalicylic acid (47) 4-n-decyloxycarbonylaminosalicylic acid (48) 4-n-undecyloxycarbonylaminosalicylic acid (49) 4-n-dodecyloxycarbonylaminosalicylic acid (50) ) 4-n-Tridecyloxycarbonylaminosalicylic acid (51) 4-n-tetradecyloxycarbonylaminosalicylic acid (52) 4-n-pentadecyloxycarbonylaminosalicylic acid (53) 4-n-hexadecylo Cycarbonylaminosalicylic acid (54) 4-n-heptadecyloxycarbonylaminosalicylic acid (55) 4-n-octadecyloxycarbonylaminosalicylic acid (56) 4-cyclopentyloxycarbonylaminosalicylic acid (57) 4-cyclohexyloxycarbonylaminosalicylic acid ( 58) 4-allyloxycarbonylaminosalicylic acid (59) 4-benzyloxycarbonylaminosalicylic acid (60) 4-phenyloxycarbonylaminosalicylic acid

(61) 4- (4'-methylphenyl) oxycarbonylaminosalicylic acid (62) 4- (4'-methoxyphenyl) oxycarbonylaminosalicylic acid (63) 4- (4'-chlorophenyl) oxycarbonylaminosalicylic acid (64) 4- [2 '-(4-methoxyphenyl) oxyethyl] oxycarbonylaminosalicylic acid (65) 5-methyloxycarbonylaminosalicylic acid (66) 5-ethyloxycarbonylaminosalicylic acid (67) 5-n-propyloxy Carbonylaminosalicylic acid (68) 5-isopropyloxycarbonylaminosalicylic acid (69) 5-n-butyloxycarbonylaminosalicylic acid (70) 5-isobutyloxycarbonylaminosalicylic acid (71) 5-sec-butyloxycarbonic acid Aminosalicylic acid (72) 5-n-pentyloxycarbonylaminosalicylic acid (73) 5-Isopentyloxycarbonylaminosalicylic acid (74) 5-n-hexyloxycarbonylaminosalicylic acid (75) 5-n-heptyloxycarbonylaminosalicylic acid ( 76) 5-n-octyloxycarbonylaminosalicylic acid (77) 5- (2′-ethylhexyl) oxycarbonylaminosalicylic acid (78) 5-n-nonyloxycarbonylaminosalicylic acid (79) 5-n-decyloxycarbonylaminosalicylic acid (80) 5-n-undecyloxycarbonylaminosalicylic acid (81) 5-n-dodecyloxycarbonylaminosalicylic acid (82) 5-n-tridecyloxycarbonylaminosalicylic acid (83) 5-n Tetradecyloxycarbonylaminosalicylic acid (84) 5-n-pentadecyloxycarbonylaminosalicylic acid (85) 5-n-hexadecyloxycarbonylaminosalicylic acid (86) 5-n-heptadecyloxycarbonylaminosalicylic acid (87) 5- n-octadecyloxycarbonylaminosalicylic acid (88) 5-cyclopentyloxycarbonylaminosalicylic acid (89) 5-cyclohexyloxycarbonylaminosalicylic acid (90) 5-allyloxycarbonylaminosalicylic acid

(91) 5-benzyloxycarbonylaminosalicylic acid (92) 5-phenyloxycarbonylaminosalicylic acid (93) 5- (4'-methylphenyl) oxycarbonylaminosalicylic acid (94) 5- (4'-methoxyphenyl) ) Oxycarbonylaminosalicylic acid (95) 5- (4'-chlorophenyl) oxycarbonylaminosalicylic acid (96) 5- [2 '-(4-methoxyphenyl) oxyethyl] oxycarbonylaminosalicylic acid (97) 6-methyloxycarbonylamino Salicylic acid (98) 6-ethyloxycarbonylaminosalicylic acid (99) 6-n-propyloxycarbonylaminosalicylic acid (100) 6-isopropyloxycarbonylaminosalicylic acid (101) 6-n-butyloxycarboni Aminosalicylic acid (102) 6-isobutyloxycarbonylaminosalicylic acid (103) 6-sec-Butyloxycarbonylaminosalicylic acid (104) 6-n-pentyloxycarbonylaminosalicylic acid (105) 6-isopentyloxycarbonylaminosalicylic acid (106) 6-n-hexyloxycarbonylaminosalicylic acid (107) 6-n-heptyloxycarbonylaminosalicylic acid (108) 6-n-octyloxycarbonylaminosalicylic acid (109) 6- (2'-ethylhexyl) oxycarbonylaminosalicylic acid (110) ) 6-n-nonyloxycarbonylaminosalicylic acid (111) 6-n-decyloxycarbonylaminosalicylic acid (112) 6-n-undecyloxycarbonylaminosalicylic acid (113) 6-n-dodecyloxycarbonylaminosalicylic acid (114) 6-n-tridecyloxycarbonylaminosalicylic acid (115) 6-n-tetradecyloxycarbonylaminosalicylic acid (116) 6-n-pentadecyloxycarbonylamino Salicylic acid (117) 6-n-hexadecyloxycarbonylaminosalicylic acid (118) 6-n-heptadecyloxycarbonylaminosalicylic acid (119) 6-n-octadecyloxycarbonylaminosalicylic acid (120) 6-cyclopentyloxycarbonylaminosalicylic acid

(121) 6-Cyclohexyloxycarbonylaminosalicylic acid (122) 6-allyloxycarbonylaminosalicylic acid (123) 6-benzyloxycarbonylaminosalicylic acid (124) 6-phenyloxycarbonylaminosalicylic acid (125) 6- (4 '-Methylphenyl) oxycarbonylaminosalicylic acid (126) 6- (4'-methoxyphenyl) oxycarbonylaminosalicylic acid (127) 6- (4'-chlorophenyl) oxycarbonylaminosalicylic acid (128) 6- [2'-( 4-Methoxyphenyl) oxyethyl] oxycarbonylaminosalicylic acid

In the metal salt of the salicylic acid derivative represented by the general formula 1 according to the present invention, the metal salt contains a monovalent metal salt such as sodium, potassium or lithium, but is preferably sparingly soluble in water. Alternatively, it is a water-insoluble divalent, trivalent or tetravalent metal salt, more preferably a divalent or trivalent metal salt.

Specific examples of the divalent, trivalent or tetravalent metal salt are zinc, cadmium, mercury, magnesium, calcium, barium, nickel, tin, gallium, chromium, copper, molybdenum, tungsten, zirconium, strontium and manganese. , Cobalt, titanium, aluminum and iron salts can be mentioned, but zinc, calcium, barium, nickel, manganese, cobalt and aluminum salts are preferable. A zinc salt is particularly preferable. The metal salt of salicylic acid represented by the general formula 1 may form a solvate such as a hydrate depending on the production conditions, and the solvate is also suitable as the electron-accepting compound of the present invention.

The salicylic acid derivative represented by the general formula 1 or its metal salt according to the present invention can be prepared by a known method {for example,
J. Pharm. Sci. , 52, 927 (196
3), Bull. de. Socie. Chim. Fra
nce, 1189 (1955)}. That is, for example, the aminosalicylic acid derivative can be suitably synthesized by reacting a chloroformate compound in an approximately equivalent amount.

If necessary within the scope of the object of the present invention,
It is also possible to use the following electron-accepting compounds in combination.
The electron-accepting compound is not particularly limited as long as it is an acidic substance. For example, activated clay, acid clay, inorganic acid substances such as bentonite,

P-Phenylphenol, p-hydroxyacetophenone, 4-hydroxy-4'-methyldiphenylsulfone, 4-hydroxy-4'-isopropoxydiphenylsulfone, 4-hydroxy-4'-benzenesulfonyloxydiphenylsulfone, 1 , 1-bis (p-hydroxyphenyl) propane, 1,1-bis (p-hydroxyphenyl) pentane, 1,1-bis (p-hydroxyphenyl) hexane, 1,1-bis (p-hydroxyphenyl) cyclohexane , 2,2-
Bis (p-hydroxyphenyl) propane, 2,2-bis (p-hydroxyphenyl) hexane, 1,1-bis (p-hydroxyphenyl) -2-ethylhexane,
2,2-bis (3-chloro-4-hydroxyphenyl)
Propane, 1,1-bis (p-hydroxyphenyl)-
1-phenylethane, 1,3-di- [2- (p-hydroxyphenyl) -2-propyl] benzene, 1,3-di- [2- (3,4-dihydroxyphenyl) -2-propyl] benzene , 1,4-di- [2- (p-hydroxyphenyl) -2-propyl] benzene, 4,4'-dihydroxydiphenyl ether, 4,4'-dihydroxydiphenyl sulfone, 3,3'-dichloro-4,4 ′-
Dihydroxydiphenyl sulfone, 3,3'-diallyl-4,4'-dihydroxydiphenyl sulfone, 3,
3'-dichloro-4,4'-dihydroxydiphenyl sulfide, methyl 2,2-bis (4-hydroxyphenyl) acetate, butyl 2,2-bis (4-hydroxyphenyl) acetate, 4,4'-thiobis (2 -T-butyl-5-
Methylphenol), benzyl p-hydroxybenzoate, chlorobenzyl p-hydroxybenzoate, dimethyl 4-hydroxyphthalate, benzyl gallate, stearyl gallate, phenol derivatives such as novolac type phenolic resin, and the like.

If the undercoat layer can contain a larger amount of air (= heat insulating material) with the same coating layer thickness, the heat insulating property can be improved and the sensitivity can be increased. In the heat-sensitive recording material of the present invention, the void ratio of the organic hollow pigment is 30.
~ 90%, preferably in the range of 40-60%,
It was found that the heat insulating effect was further developed. here,
If the porosity is less than 30%, the heat insulating property tends to decrease. If the porosity exceeds 90% and increases, the particle strength tends to decrease, which is not preferable. Further, the surface strength may be reduced, or particles may be broken during the coating process.

The average particle size of the organic hollow pigment contained in the undercoat layer is 0.1 to 10.0 μm, preferably 0.5 to 3.0 μm, more preferably 0.8 to 1.2 μm.
m. Here, when the average particle size is less than 0.1 μm, the density of the particles and the particle purity of the porosity tend to be lowered during drying due to the manufacturing method. Further, if it exceeds 10.0 μm, the smoothness tends to be deteriorated, and uneven coating amount may occur.

The organic hollow pigments usable in the present invention include styrene-acrylic resin, polystyrene resin, acrylic resin, polyethylene resin, polypropylene resin, polyacetal resin, chlorinated polyether resin, polyvinyl chloride resin and the like. A thermoplastic resin may be used. Further, as the thermoplastic material, phenol-formaldehyde resins, urea-formaldehyde resins, melamine-formaldehyde resins, furan resins, etc., unsaturated polyester resins produced by addition polymerization, and crosslinked M
MA resin etc. are mentioned. Among these, styrene-acrylic resin, polystyrene resin, acrylic resin, cross-linked MMA resin and the like are preferable, but when a thermosensitive recording layer containing the salicylic acid derivative represented by the general formula 1 and its metal salt is used, A styrene-acrylic resin is particularly desirable in consideration of the absorbability of printing dust made of a colored product and the liquidity of the coating liquid. Further, the shape is preferably spherical in appearance. More specifically, the shape determined by an electron micrograph is considered to be an ellipse, and an eccentricity of 0.9 or less is considered to be almost spherical.

The thickness of the undercoat layer provided in the present invention is 1 to 35 μm, preferably 10 to 28 μm, more preferably 18 to 23 μm. Here, if the thickness of the undercoat layer is less than 1 μm, the heat insulating property tends to decrease. Further, if the film thickness exceeds 35 μm, the smoothness tends to decrease, and uneven coating amount may occur.

Paper is mainly used as a support for the heat-sensitive recording material according to the present invention. In addition to paper, various non-woven fabrics, synthetic resin films, laminates, synthetic papers,
A metal foil or the like, or a composite sheet in which these are combined can be arbitrarily used according to the purpose.

The layer structure of the heat-sensitive recording material of the present invention is basically two layers of heat-sensitive recording layer / undercoat layer or three layers of overcoat layer / heat-sensitive recording layer / undercoat layer, but it is necessary. Accordingly, the undercoat layer may be composed of a plurality of layers of 2 layers or 3 layers or more. Further, a back coat layer may be provided on the surface of the support opposite to the surface on which the heat-sensitive recording layer is provided for the purpose of preventing curling, preventing electrification and the like. The back coat layer is also composed of a single layer or a plurality of layers. The heat-sensitive recording layer can be obtained by mixing the respective aqueous dispersions obtained by finely pulverizing the respective color-forming components, the binder, etc., and coating and drying the mixture on the support. In this case, for example, each color-forming component may be contained in one layer to form a multilayer structure.

The heat-sensitive recording material according to the present invention may contain a heat-fusible substance in order to improve its thermal response. As the heat-fusible substance, a substance having a melting point of 60 to 180 ° C. is preferable, and a substance having a melting point of 80 to 140 ° C. is particularly preferable. For example, benzyl p-benzyloxybenzoate, stearic acid amide, palmitic acid amide, N-methylol stearic acid amide, β-naphthylbenzyl ether, N-stearyl urea, N, N ′.
-Distearyl urea, β-naphthoic acid phenyl ester, 1-hydroxy-2-naphthoic acid phenyl ester, β-naphthol (p-methylbenzyl) ether,
1,4-dimethoxynaphthalene, 1-methoxy-4-benzyloxynaphthalene, N-stearoylurea, 4
-Benzylbiphenyl, 1,2-di (m-methylphenoxy) ethane, 1-phenoxy-2- (4-chlorophenoxy) ethane, 1,4-butanediol phenyl ether, dimethyl terephthalate and the like can be mentioned.

The above-mentioned heat-fusible substances may be used alone or as a mixture, and in order to obtain a sufficient heat response, it is preferably used in an amount of 10 to 300% by weight based on the dye precursor. It is more preferable to use 20 to 250% by weight.

The material of the overcoat layer used in the present invention may be any material that has been conventionally used generally, and will be specifically mentioned below, but the material is not limited thereto. For example, as the water-soluble polymer compound, alginate, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, carboxy modified polyvinyl alcohol, acetoacetylated polyvinyl alcohol, sulfonated modified polyvinyl alcohol, gelatin, casein, sodium polyacrylate. , Polyacrylamide, acrylamide / acrylic acid ester copolymer, acrylamide / acrylic acid ester / methacrylic acid terpolymer, and the like, and these can be used alone or in combination of two or more kinds. In addition, film-forming polymers such as acrylic latex, vinyl acrylic resin, vinyl acetate / ethylene copolymer, silicon / acrylate compound, styrene butadiene latex, and casein,
Gum arabic, oxidized starch, etherified starch, cationized starch and the like are also included.

In the overcoat layer, pigments such as calcium carbonate, zinc oxide, titanium dioxide, aluminum hydroxide, barium sulfate and zinc sulfate are used.
Inorganic pigments such as talc, kaolin, clay, styrene acrylic resin, polystyrene resin, acrylic resin, polyethylene resin, polypropylene resin, polyacetal resin,
Examples include thermoplastic resins such as chlorinated polyether resins and polyvinyl chloride resins. Further, as thermosetting resins having three-dimensional cross-linking, phenol-formaldehyde resins, urea-formaldehyde resins, melamine-formaldehyde resins, xylene-formed by addition condensation reaction.
Formaldehyde resins, toluene-formaldehyde resins, guanamine-formaldehyde resins, aniline-formaldehyde resins, furan resins, etc., unsaturated polyester resins produced by addition polymerization, and crosslinked MMA
It is also possible to add organic pigments such as resins, and lubricants such as zinc stearate, calcium stearate, polyethylene wax, carnauba wax, paraffin wax and ester wax.

Further, in the overcoat layer, if necessary, a surfactant (dispersing agent, wetting agent) such as sodium dioctylsulfosuccinate, sodium dodecylbenzenesulfonate, sodium lauryl alcohol sulfate / sodium salt, and fatty acid metal salt is used. As agents) Glyoxal, methylolmelamine, dimethylolurea, potassium persulfate, sodium persulfate, crosslinking agents such as ammonium persulfate, benzophenone-based and triazole-based UV absorbers, fluorescent dyes, colored dyes or colored pigments in each wavelength range Various auxiliaries and the like can be added.

The coating liquid for the overcoat layer is generally prepared by dispersing water in a dispersion medium and dispersing the specific pigments, binders, auxiliary agents, etc. as described above, and if necessary, a mixer, attritor, ball mill, roll mill. Mixing etc.
After being sufficiently mixed and stirred by a stirrer, the heat-sensitive recording layer is coated by a known coating device. Although the coating amount of this coating liquid is not particularly limited, it is generally applied in a range of 0.1 to 10 g / m ² , preferably 1 to 4 g / m ² as a dry weight.

Further, in the heat-sensitive recording layer, pigments such as diatomaceous earth, talc, kaolin, calcined kaolin, calcium carbonate, magnesium carbonate, titanium oxide, zinc oxide, silicon oxide, aluminum hydroxide, urea-formalin resin, and others. For the purpose of preventing head abrasion, sticking, etc., higher fatty acid metal salts such as zinc stearate and calcium stearate, waxes such as paraffin, oxidized paraffin, polyethylene, oxidized polyethylene, stearamide, castor wax, etc., and dioctylsulfosuccinic acid. A dispersant such as sodium acid salt, a benzophenone-based or benzotriazole-based ultraviolet absorber, a surfactant, a fluorescent dye, or the like may be contained.

In addition, for the purpose of preventing head wear and sticking, higher fatty acid metal salts such as zinc stearate and calcium stearate, waxes such as paraffin, oxidized paraffin, polyethylene, oxidized polyethylene, stearic acid amide and caster wax. , A dispersant such as sodium dioctylsulfosuccinate, an ultraviolet absorber such as a benzophenone-based or benzotriazole-based,
Further, a surfactant, a fluorescent dye, etc. are added as needed.

The coating solution for the heat-sensitive recording layer is generally prepared by dispersing water in a dispersion medium and dispersing the specific pigments, binders, auxiliaries and the like as described above, and if necessary, a mixer, attritor, ball mill, Mixing of roll mill etc.
After being sufficiently mixed and stirred by a stirrer, the undercoat layer or the base paper is coated by a known coating device. Although the coating amount of this coating liquid is not particularly limited, it is generally applied in a range of 0.1 to 10 g / m ² , preferably 3 to 7 g / m ² as a dry weight.

As the adhesive used for the undercoat layer and the heat-sensitive recording layer according to the present invention, various kinds of commonly used adhesives can be optionally used. For example, starches, hydroxyethyl cellulose, methyl cellulose,
Carboxymethyl cellulose, gelatin, casein, polyvinyl alcohol, modified polyvinyl alcohol, sodium polyacrylate, acrylic acid amide / acrylic acid ester copolymer acrylic acid amide / acrylic acid ester /
Water-soluble adhesive such as methacrylic acid terpolymer, alkali salt of styrene / maleic anhydride copolymer, alkali salt of ethylene / maleic anhydride copolymer, polyvinyl acetate, polyurethane, polyacrylic ester, Examples thereof include styrene / butadiene copolymer, acrylonitrile / butadiene copolymer, methyl acrylate / butadiene copolymer, and latex such as ethylene / vinyl acetate copolymer.

Various additives can be further added to the undercoat layer. For example, pigments, surfactants, thermoplastic substances and the like used in ordinary coated paper may be added.

The undercoat layer coating liquid generally contains water as a dispersion medium and contains the specific pigment, binder, and
Further, it is adjusted by dispersing auxiliary agents and the like, and if necessary, sufficiently mixed and stirred by a mixer / attritor, ball mill, roll mill or other mixing / stirring machine, and then coated on the undercoat layer by a known coating device. To be done. The coating amount of this coating liquid is not particularly limited, but is generally 0.1 to 20 g / m ² in dry weight, preferably 5 to
It is applied in the range of 10 g / m ² .

Examples of the method for applying the coating liquid to these coating layers on the base paper include blade coating, air knife coating, gate roll coating, spray coating, squeeze coating, reverse roll coating, gravure roll and transfer roll. A method such as coating, E-bar coating, curtain coating or die coating is used. In particular, free-fall vertical curtain coating type, extrusion coating vertical type, curtain coating system slide type and non-slide type, extrusion coating system non-slide type, which are widely used as emulsion coating methods in the photographic industry. Heads can be used.

The heat-sensitive recording material of the present invention can be directly subjected to various processes, for example, for facsimiles, printers, business cards, cards such as postcards, confidential documents such as confidential postcards, tags, and food labels. Or barcode label,
Label application such as Carla code label, logistics label, AT
For M-CD, Handy terminal, Thermal magnetic recording,
It can be used for tickets, video printers, etc. Among these, the applications that require preservability are for cards, confidential documents, tags, labels, ATM-CDs.
It is especially used for applications, handy terminals, heat-sensitive magnetic recording, tickets, etc.

[0041]

EXAMPLES Next, the present invention will be described in more detail by way of examples. All parts and% shown below are based on weight. Further, the value indicating the coating amount is the coating amount after drying unless otherwise specified.

Hereinafter, the present invention will be described in more detail with reference to Examples.

Example 1 <Undercoat layer> The void ratio of the organic hollow pigment is 51%,
Moreover, to 400 g of 25% styrene-acrylic resin particle aqueous dispersion having an average particle size of 1.0 μm, 40 g of 50% styrene-butadiene latex and 10 g of water are added and sufficiently stirred,
An undercoat layer coating liquid was obtained. 50 g / m ^{2 of} this coating liquid
It was coated on a base paper having a basis weight of 10 μm so as to obtain a film thickness of 20 μm in solid content, and dried.

<Thermosensitive recording layer> 3-dibutylamino-6-methyl-7-anilinofluorane 30 which is a dye precursor
Parts were pulverized with 70 parts of a 2.5% aqueous solution of polyvinyl alcohol in a ball mill for 24 hours to obtain a dye dispersion liquid. Next, 25 parts of zinc 4-n-octyloxycarbonylaminosalicylate was added to a 2.5% polyvinyl alcohol aqueous solution 7
It was pulverized together with 5 parts by a dyno mill (sand mill manufactured by WEB) to obtain an electron accepting compound dispersion liquid having a volume average particle diameter of 2 μm or less. After mixing the above two kinds of dispersion liquids, the following components were added with stirring and mixed well to prepare a heat-sensitive coating liquid. 30% dye dispersion 100 parts 25% electron-accepting compound dispersion 150 parts 30% 2-benzyloxynaphthalene dispersion 150 parts 50% calcium carbonate aqueous dispersion 100 parts 40% zinc stearate aqueous dispersion 25 parts 10% polyvinyl Aqueous alcohol solution 200 parts Water 280 parts The above coating solution is coated on the above-mentioned undercoat layer coated paper in a solid content of 5 parts.
The coating was performed so that a coating amount of g / m ² was obtained, and the coating was dried.

Example 2 A thermosensitive recording material was prepared in the same manner as in Example 1 except that the zinc 4-n-octyloxycarbonylaminosalicylate of Example 1 was changed to zinc 4-n-decyloxycarbonylaminosalicylate. did.

Example 3 A thermosensitive recording material was prepared in the same manner as in Example 1 except that the zinc 4-n-octyloxycarbonylaminosalicylate of Example 1 was changed to zinc 4-n-phenyloxycarbonylaminosalicylate. did.

Example 4 The organic hollow pigment constituting the undercoat layer was mixed with a porosity of 3
A heat-sensitive recording material was obtained in the same manner as in Example 1 except that styrene-acrylic resin particles having a 5% average particle diameter of 1.0 μm were used.

Example 5 An organic hollow pigment constituting the undercoat layer was added with a porosity of 6
A heat-sensitive recording material was obtained in the same manner as in Example 1 except that styrene-acrylic resin particles having a 5% average particle diameter of 1.0 μm were used.

Example 6 A thermosensitive recording material was prepared in the same manner as in Example 1 except that the organic hollow pigment constituting the undercoat layer was changed to styrene-acrylic resin particles having an average particle size of 0.7 μm and a porosity of 52%. Got

Example 7 A thermosensitive recording material was prepared in the same manner as in Example 1 except that the organic hollow pigment constituting the undercoat layer was changed to styrene-acrylic resin particles having an average particle size of 1.5 μm and a porosity of 50%. Got

Example 8 An organic hollow pigment constituting the undercoat layer was added with a porosity of 5
A heat-sensitive recording material was obtained in the same manner as in Example 1 except that the cross-linked MMA resin particles having an average particle diameter of 1.0 μm and 1% were used.

Example 9 The void ratio of the organic hollow pigment constituting the undercoat layer was 5
A heat-sensitive recording material was obtained in the same manner as in Example 1 except that 1% benzoguanamine-formaldehyde resin particles having an average particle size of 1.0 μm were used.

Example 10 A thermosensitive recording material was obtained in the same manner as in Example 1 except that an overcoat layer shown below was provided on the thermosensitive recording layer.

<Overcoat layer> 40 parts of 25% polyvinyl alcohol aqueous solution, 10 parts of 10% sodium alginate aqueous solution, 4 parts of 40% zinc stearate aqueous dispersion and 85 parts of water are mixed to prepare a coating solution for the overcoat layer. Then, a thermosensitive recording material was obtained by coating on the thermosensitive recording layer so as to obtain a coating amount of 3 g / m ² in terms of solid content, drying and processing with a super calendar.

Comparative Example 1 The organic hollow pigment constituting the undercoat layer had a particle size of 1.
A thermosensitive recording material was obtained in the same manner as in Example 1 except that the calcined kaolin of 2 μm was used.

Comparative Example 2 The organic hollow pigment constituting the undercoat layer had a particle size of 1.
A heat-sensitive recording material was obtained in the same manner as in Example 1 except that the non-hollow styrene-acrylic resin particles of 0 μm were used.

Comparative Example 3 A thermosensitive recording material was prepared in the same manner as in Example 1 except that the zinc 4-n-octyloxycarbonylaminosalicylate in Example 1 was changed to 2,2-bis (4-hydroxyphenyl) propane. Was produced.

Comparative Example 4 Thermal recording was carried out in the same manner as in Example 1 except that the zinc 4-n-octyloxycarbonylaminosalicylate of Example 2 was changed to zinc 3,5-di (α-methylbenzyl) salicylate. The material was made.

The thermosensitive recording materials prepared in Examples 1 to 10 and Comparative Examples 1 to 4 were calendered so that the Bekk smoothness of the thermosensitive recording surface was 400 to 500 seconds, and then subjected to the following evaluation tests. I served.

[Coloring property] Examples 1 to 10 and Comparative Examples 1 to 1
The heat-sensitive recording material prepared in No. 4 was printed using a heat-sensitive facsimile printing tester under the condition of applied energy of 0.45 mJ, and the optical density of the color-developed image obtained was Macbeth R.
The measurement was performed using D918 (visual filter), and the results are shown in Table 1. This characteristic is at a sufficient level if the optical density is 1.30 or more.

[Humidity and heat resistance] The printed thermal recording material obtained in the above color development test was allowed to stand in an environment of a temperature of 40 ° C. and a humidity of 80% RH for 24 hours, and then the optical density of the color image portion was Macbeth RD918 ( It was measured using a visual filter) and the results are shown in Table 1. This characteristic is at a sufficient level if the optical density is 90% of the color density.

[Test for Writing implement on the background part] In the writing implement test, after writing the non-image area with a highlighter pen, the stain on the non-image area after standing for 72 hours at room temperature was visually evaluated on a 10-point scale. The results are shown in Table 1. Here, the larger the number, the better the printability, and a value of 8 or more is a sufficient level.

[Print residue] Examples 1 to 10 and Comparative Example 1
When each of the thermal recording materials prepared in 4 to 4 was printed under the condition of an applied energy of 0.45 mJ using a thermal facsimile printing tester, the printing residue attached to the thermal head of the facsimile was visually evaluated in 10 steps, The results are shown in Table 1. Here, the larger the number, the better the printability, and a value of 8 or more is a sufficient level.

[Dot Reproducibility] The thermal recording materials prepared in Examples 1 to 10 and Comparative Examples 1 to 4 were each applied with a thermal facsimile printing tester to give an applied energy of 0.45 m.
Printing was performed under the conditions of J, and the printability of the image was represented by the dot reproducibility (%) represented by the black ratio of the dots, and the results are shown in Table 1. Here, the larger the number, the better the printability.
A level of 5% or more is a sufficient level.

[0065]

[Table 1]

From the results shown in Table 1 above, Examples 1 to 3 obtained good results in terms of color developability, resistance to heat and humidity, resistance to writing implements, printing residue, and dot reproducibility. Example 4 is Examples 1 to 3.
Since the void ratio of the hollow particles constituting the undercoat layer is lower than that of (1), the color developability is slightly low but at a sufficient level. Since Example 5 has a higher porosity of hollow particles than Examples 1 to 3,
Excellent color development and slightly low dot reproducibility, but at a sufficient level. In Example 6, since the particle size of the hollow particles is smaller than that in Examples 1 to 3, the color developability is slightly low but at a sufficient level.
In Example 7, the particle size of the hollow particles is larger than those in Examples 1 to 3, so that the color development is excellent and the dot reproducibility is slightly low, but at a sufficient level. Since the hollow particle material of Example 8 is different from that of Examples 1 to 3, the coloring property and the printing residue property are slightly low, but they are at a sufficient level. Since the hollow particle material of Example 9 is different from that of Examples 1 to 3, the coloring property and the printing residue property are slightly low, but they are at a sufficient level. In Example 10, by coating the overcoat layer, the printing dust characteristics were excellent and the color development was low, but the level was sufficient. Comparative Example 1 is inferior in color developability and dot reproducibility due to the difference in heat insulating property of the pigment material forming the undercoat layer, and is not at a sufficient level. In Comparative Example 2, since the pigment forming the undercoat layer is non-spherical, the heat insulating property is low and the color developability is low.
The dot reproducibility is inferior and not at a sufficient level. Comparative Example 3 is inferior in level because it is inferior in wet heat storage resistance and writing instrument resistance due to the difference in electron accepting compound. Comparative Example 4 is inferior in level due to the difference in the electron-accepting compound, which is inferior in color developability, resistance to humidity and heat storage, resistance to writing instruments, printing residue characteristics, and dot reproducibility.

[0067]

The heat-sensitive recording material of the present invention is an undercoat containing a specific salicylic acid derivative or a metal salt thereof as an electron-accepting compound and containing a specific organic hollow pigment between the heat-sensitive recording layer and the support. By providing the layer, good recording sensitivity, storage stability of the background portion and image portion, and head matching property can be obtained, which is of high practical value.

Claims (5)

[Claims] 1. A heat-sensitive recording material comprising, on a support, an usually colorless to light-colored dye precursor and an electron-accepting compound which reacts when heated to form a color on the dye precursor. An undercoat layer containing at least one salicylic acid derivative represented by the following chemical formula 1 (general formula 1) or a metal salt thereof and containing an organic hollow pigment between the heat-sensitive recording layer and the support. A heat-sensitive recording material characterized by: [Chemical 1] (In the formula, X ₁ and X ₂ represent a hydrogen atom, an alkyl group, an aralkyl group, an aryl group, or a halogen atom, and R represents
It represents an alkyl group, an alkenyl group, an aralkyl group, or an aryl group. ) 2. The heat-sensitive recording material according to claim 1, wherein the organic hollow pigment has a porosity of 40 to 60%. 3. The heat-sensitive recording material according to claim 1, wherein the organic hollow pigment has an average particle diameter of 0.8 to 1.2 μm. 4. The heat-sensitive recording material according to claim 1, wherein the organic hollow pigment is styrene-acrylic resin. 5. The heat-sensitive recording material according to claim 1, wherein an overcoat layer is provided on the heat-sensitive recording layer.