JP2936560B2 - 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 having excellent light-fast ground color and good heat-resistant ground color.

[0002]

2. Description of the Related Art In general, a heat-sensitive recording medium having a heat-sensitive recording layer mainly composed of a colorless or light-colored leuco dye and a color developer which reacts with the leuco dye upon heating to produce a color is disclosed in Japanese Patent Publication No. 45-1.
Published in No. 4035 and widely used. In order to perform recording on this thermosensitive recording medium, a thermal printer or the like having a built-in thermal head is used, but such a thermosensitive recording method is different from other recording methods conventionally used in practice.
Facsimile machines have been developed with the development of the information industry because of the features such as no noise during recording, no need for development and fixing, maintenance-free, relatively inexpensive and compact equipment, and very clear color development. Widely used for computer and computer fields, various measuring instruments, labels, etc. However, heat-sensitive recording materials using this type of heat-sensitive recording material are inferior in the preservability of the ground color portion against light and heat, so that discoloration occurs when exposed to sunlight for a long time or exposed to high temperatures. The appearance of the recording paper deteriorates, and the image of the thermal recording paper is damaged.

Therefore, Japanese Patent Application Laid-Open No. 4-189179,
JP-A-4-189180 describes the use of a dye having a specific substituent for the purpose of improving light resistance. However, when these dyes were used, the color-forming ability was low, and sufficient preservability of the ground color portion could not be obtained. On the other hand, JP-A-62-18626 and JP-A-6-64324 describe a method in which an inorganic filler having an ultraviolet shielding effect is contained in a heat-sensitive recording layer or a protective layer. 193883 discloses a method of including a benzotriazole-based hydrophobic ultraviolet absorber in a protective layer. However, when an inorganic filler or a hydrophobic ultraviolet absorber having an ultraviolet shielding effect is contained in the protective layer, there are disadvantages in that the barrier properties of the protective layer are reduced, and that scum sticking and sticking occur. Japanese Patent Application Laid-Open No. 62-184880 describes a method of including a fluorescent whitening agent in a protective layer, but the improvement effect of the fluorescent whitening agent alone is mainly based on the appearance of white paper. ,
It did not reach the point where the light resistance was improved.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a thermosensitive recording medium having high color sensitivity and excellent light resistance and heat resistance of a ground color portion.

[0005]

Means for Solving the Problems As a result of intensive studies, the present invention has achieved the above-mentioned object by providing a protective layer containing a specific dye precursor and a specific component in a thermal recording layer. It was found that a recording medium was obtained, and the present invention was completed. That is, the present invention, on a support,
In a heat-sensitive recording medium comprising at least a colorless or light-colored dye precursor and a developer capable of causing the dye precursor to develop color when heated, and a heat-sensitive recording medium having a protective layer provided on the heat-sensitive recording layer, The layer contains 2,4-dimethyl-6-[(4-dimethylamino) anilino] -fluoran as a dye precursor, and the protective layer contains a binder, a water-soluble ultraviolet absorber, a fluorescent dye, and The present invention relates to a heat-sensitive recording material containing aluminum.

In the heat-sensitive recording material of the present invention, a water-soluble ultraviolet absorber is preferably used as the ultraviolet absorber contained in the protective layer, since it is excellent in preventing adhesion of dregs and sticking. Various known water-soluble ultraviolet absorbers can be used. For example, 2-hydroxy-
4-methoxybenzophenone-5-sulfonic acid, sodium 2-hydroxy-4-methoxybenzophenone-5-sulfonate, potassium 2-hydroxy-4-methoxybenzophenone-5-sulfonate, 2,2′-dihydroxy-4,4 '-Dimethoxybenzophenone-5-sulfonic acid sodium, 2,4-dihydroxybenzophenone-5-sulfonic acid sodium, 2,2'-dihydroxy-4,4'-dimethoxybenzophenone-5,5'-
Sodium disulfonate, sodium 2,4-dihydroxybenzophenone-5'-sulfonate, 2,2'4
Benzophenone-based ultraviolet absorbers such as sodium 4'-tetrahydroxybenzophenone-5,5'-disulfonate, 2- (2'-hydroxy-4'-methoxy-5 '
-Sulfophenyl) benzotriazole sodium salt,
Benzotriazole-based ultraviolet absorbers such as 2- (2′-hydroxy-4′-butoxy-5′-sulfophenyl) benzotriazole sodium salt and the like can be mentioned. In the present invention, the benzophenone-based ultraviolet absorber having a sulfone group is preferred among them because it has a high effect of preventing adhesion of dregs and sticking, and in particular, 2-hydroxy-4-amine having a sulfonic acid group is preferred.
Methoxybenzophenone-5-sulfonic acid is most preferred because of its good head abrasion resistance. Also, two or more kinds can be used in combination as needed.

It is also possible to use a hydrophobic ultraviolet absorber in combination as long as the effects of the present invention are not impaired. Examples of the hydrophobic ultraviolet absorber include 2,4-dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-octyloxybenzophenone, 2-hydroxy-4-dodecyloxybenzophenone, and 2,2 ′. -Dihydroxy-4-methoxybenzophenone, 2,2'-dihydroxy-4,4'-dimethoxybenzophenone, 2-hydroxy-4-methoxy-
Benzophenone ultraviolet absorbers such as 5-sulfobenzophenone, 2- (2′-hydroxyphenyl) benzotriazole, 2- (2′-hydroxy-5′-methylphenyl) benzotriazole, 2- (2′-hydroxy-5) '-Tert-butylphenyl) benzotriazole,
2- (2'-hydroxy-3 ', 5'-di-tert-butylphenyl) benzotriazole, 2- (2'-hydroxy-3'-tert-butyl-5'-methylphenyl)-
5-chlorobenzotriazole, 2- (2'-hydroxy-3 ', 5'-di-tert-butylphenyl) -5-chlorobenzotriazole, 2- (2'-hydroxy-
3 ', 5'-di-tert-aminophenyl) benzotriazole, 2- (2'-hydroxy-3', 5'-di-te
rt-butylphenyl) -5-tert-butylbenzotriazole, 2- (2'-hydroxy-3'-dodecyl-
5′-methylphenyl) benzotriazole, 2-
[2′-hydroxy-4 ′-(2 ″ -ethylhexyl) oxyphenyl] benzotriazole, methyl-3
Condensation product with-[3-tert-butyl-5- (2H-benzotriazol-2-yl) -4-hydroxyphenyl] propionate-polyethylene glycol (molecular weight: about 300), 5-tert-butyl-3- (5-chloro-2H-
Benzotriazol-2-yl) -4-hydroxybenzene-octyl propionate, 2,2-methylenebis [4- (1,1,3,3-tetramethylbutyl) -6
-(2H-benzotriazol-2-yl) phenol, 2- (2'-hydroxy-3'-sec-butyl-
Benzotriazole UV absorbers such as 5'-tert-butylphenyl) -5-tert-butylbenzotriazole, and salicylic acid UV absorbers such as phenyl salicylate, p-tert-butylphenyl salicylate and p-octylphenyl salicylate Agent, 2-ethylhexyl-2
A cyanoacrylate-based ultraviolet absorber such as -cyano-3,3'-diphenylacrylate, ethyl-2-cyano-3,3'-diphenylacrylate;
6,6, -tetramethyl-4-piperidyl) sebacate, bis (2,2,6,6-tetramethyl-4-piperidyl) succinate, 2- (3,5-di-tert-ester)
Hindered amine-based ultraviolet absorbers such as -butyl) malonic acid-bis (1,2,2,6,6-pentamethyl-4-piperidyl) ester and the like.

[0008] Regarding the amount of the water-soluble ultraviolet absorber used,
It is preferred to be present in 2 to 30% by weight based on the total solid content of the protective layer. More preferably, it is in the range of 8 to 20% by weight. When the amount of the ultraviolet absorber in the protective layer is 2% by weight or less, the effect on light resistance is reduced. When the amount is 30% by weight or more, the coating of the protective layer becomes thicker with time, resulting in poor coating suitability.

As the fluorescent dye in the protective layer of the present invention, various known dyes can be used, and examples thereof include a stilbene derivative, a coumarin derivative, a pyrazoline derivative, and a bisstyryl biphenyl derivative. In particular, a diaminostilbene disulfonic acid derivative has a high effect on light resistance, and is therefore preferable.
The amount of the fluorescent dye used is preferably 0.01 to 3% by weight based on the total solid content of the protective layer. More preferably, it is in the range of 0.1 to 2% by weight. When the amount of the ultraviolet absorber in the protective layer is 0.01% by weight or less, the effect on light resistance is reduced. Leads to.

In the present invention, the ratio of the water-soluble ultraviolet absorber and the fluorescent dye contained in the protective layer is from 4: 1 to 1: 1.
Desirably, it is in the range of 200: 1. If the amount of the fluorescent dye is too large, the coating of the protective layer is colored. If the amount is too small, the effect on light resistance is reduced.

[0011] The protective layer of the present invention contains aluminum hydroxide as a filler. In the present invention, a water-soluble ultraviolet absorber is contained in the protective layer, but the water-soluble ultraviolet absorber forms ions such as sodium salts upon solubilization in water. It adversely affects the head electrochemically and causes head wear. It is considered that the aluminum hydroxide used in the present invention is excellent in adsorbing these ions, and therefore reduces head wear. The average particle size of the aluminum hydroxide particles is preferably about 15 μm or less, more preferably 0.5 μm or less, from the viewpoints of good recorded images, smoothness of the protective layer, and barrier properties (hiding properties). ~
10 μm. The amount of aluminum hydroxide used is not particularly limited, but it is generally desirable to adjust the amount in the range of about 5 to 500 parts by weight per 100 parts by weight of the binder component.

The binder in the protective layer of the present invention includes:
It is possible to use a binder composed of a polymer compound usually used in the field of thermal recording. Specific examples of such a binder include, for example, starches, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin, casein, gum arabic, polyvinyl alcohol, carboxy-modified polyvinyl alcohol, acetoacetyl group-modified polyvinyl alcohol, silicon-modified polyvinyl alcohol, polyvinyl acetate , Vinyl chloride-vinyl acetate copolymer, ethylene-vinyl acetate copolymer, acrylonitrile-butadiene-styrene copolymer, vinyl acetate-acrylic acid copolymer, ethylene-acrylic acid copolymer, styrene-acrylic acid copolymer Copolymer, acrylic ester resin, acrylic emulsion, diisobutylene / maleic anhydride copolymer, styrene / maleic anhydride copolymer, styrene / butadiene copolymer emulsion , Methyl methacrylate - butadiene copolymer, methyl methacrylate - styrene - butadiene copolymer, styrene polymer, isoprene polymer, butadiene polymer,
Vinyl chloride polymer, vinylidene chloride polymer, urea resin,
Melamine resin, amide resin, polyurethane resin and the like can be exemplified, and are not particularly limited. Among them, when a hydrophobic polymer such as a styrene-acrylic acid copolymer, an ethylene-acrylic acid copolymer, and an acrylic emulsion is used as a main component, a barrier is used. It is more preferable because a thermosensitive recording medium having excellent printability and high print density can be obtained.

Further, in the protective layer, if necessary, a lubricant such as zinc stearate, calcium stearate, polyethylene wax, carnauba wax, paraffin wax, ester wax and the like, and 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. Further, 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.

In the heat-sensitive recording material of the present invention, the colorless or light-colored dye precursor contained in the heat-sensitive recording layer includes:
2,4-Dimethyl-6-[(4-dimethylamino) anilino] fluoran is used. This compound is most suitable for obtaining a heat-sensitive recording material having a good light-fast ground color and heat-resistant ground color.

[0015] In addition, within a range that does not impair the effects of the present invention,
If necessary, it can be used in combination with a conventionally known colorless or pale color dye precursor. Specifically, for example, 3,
3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide, 3- (4-diethylamino-2-methylphenyl) -3- (4-dimethylaminophenyl)
-6-dimethylaminophthalide, 3-diethylamino-
Blue-coloring dyes such as 7-dibenzylamino-benzo [a] fluoran, 3- (N-ethyl-Np-tolyl) amino-7-N-methylanilinofluoran, 3-diethylamino-7-aniline Green chromogenic dyes such as linofluoran and 3-diethylamino-7-dibenzylaminofluoran;
3,6-bis (diethylamino) fluoran-γ-anilinolactam, 3-cyclohexylamino-6-chlorofluorane, 3-diethylamino-6-methyl-7-chlorofluorane, 3-diethylamino-7-chlorofluoran , Rhodamine (o-chloroanilino) lactam,
Rhodamine (p-chloroanilino) lactam, 3-diethylamino-7,8-benzofluoran, 3- (N-ethyl-p-toluidino) -7-methylfluoran, 3-
Red-coloring dyes such as diethylamino-6,8-dimethylfluoran, 3- (N-ethyl-N-isoamyl) amino-6-methyl-7-anilinofluoran, 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-di (n
-Pentyl) amino-6-methyl-7-anilinofluoran, 3-diethylamino-7- (o-chlorophenylamino) fluoran, 3-di (n-butyl) amino-7
-(O-chlorophenylamino) fluoran, 3-diethylamino-7- (o-fluorophenylamino) fluoran, 3-di (n-butyl) amino-7- (o-fluorophenylamino) fluoran, 3- (N- Ethyl-
p-Toluidino) -6-methyl-7-anilinofluoran, 3- (N-ethyl-p-toluidino) -6-methyl-7- (p-toluidino) fluoran, 3-diethylamino-6-chloro-7 -Anilinofluoran, 3- (N
-Methyl-N-n-propylamino) -6-methyl-7
-Anilinofluoran, 3-dimethylamino-6-methyl-7-anilinofluoran, 3-dibutylamino-6
-Methyl-7-m-toluidinofluoran, 3- (N-
n-hexyl-N-ethyl) amino-6-methyl-7-
Anilinofluoran, 3- (N-ethyl-N-isobutyl) amino-6-methyl-7-anilinofluoran, 3
-Diethylamino-6-methyl-7-p-ethoxyanilinofluoran, 3-pyrrolidino-6-methyl-7-anilinofluoran, 3-piperidino-6-methyl-7-
Anilinofluoran, 2,2-bis {4- [6 '-(N
-Cyclohexyl-N-methylamino) -3'-methylspiro [phthalide-3,9'-xanthen-2'-ylamino] phenyl} propane, 3-diethylamino-7
Black-color-forming dyes such as-(3'-trifluoromethylphenyl) aminofluorane; 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,
3-bis [1,1-bis (4-pyrrolidinophenyl) ethylene-2-yl] -4,5,6,7-tetrabromophthalide, 3-p- (p-dimethylaminoanilino) anilino- 6-methyl-7-chlorofluoran, 3-p-
(P-chloroanilino) anilino-6-methyl-7-chlorofluorane, 3,6-bis (dimethylamino) fluorene-9-spiro-3 ′-(6′-dimethylamino)
Dyes having an absorption wavelength in the near infrared region such as phthalide are exemplified.

Examples of the color developer used for coloring the specific dye precursor contained in the heat-sensitive recording layer of the present invention include the following known color developers. Activated clay, attapulgite, colloidal silica, inorganic acid substances such as aluminum silicate, 4,4'-isopropylidene diphenol, 1,1-bis (4-hydroxyphenyl) cyclohexane, 2,2-bis (4-hydroxyphenyl) -4-methylpentane, 4,4'-dihydroxydiphenyl sulfide, hydroquinone monobenzyl ether, benzyl 4-hydroxybenzoate, 4,4'-
Dihydroxydiphenylsulfone, 2,4′-dihydroxydiphenylsulfone, 4-hydroxy-4′-isopropoxydiphenylsulfone, bis (3-allyl-4
-Hydroxyphenyl) sulfone, 4-hydroxy-
4'-methyldiphenylsulfone, 4-hydroxyphenyl-4'-benzyloxyphenylsulfone, 3,4
-Dihydroxyphenyl-4'-methylphenylsulfone, bis (4-hydroxyphenylthioethoxy) methane, 1,5-di (4-hydroxyphenylthio) -3-
Oxapentane, butyl bis (p-hydroxyphenyl) acetate, methyl bis (p-hydroxyphenyl) acetate,
1,1-bis (4-hydroxyphenyl) -1-phenylethane, 1,4-bis [α-methyl-α- (4′-hydroxyphenyl) ethyl] benzene, 1,3-bis [α-methyl- α- (4′-hydroxyphenyl) ethyl] benzene, di (4-hydroxy-3-methylphenyl) sulfide, 2,2′-thiobis (3-tert-octylphenol), 2,2′-thiobis (4-tert Octylphenol), phenolic compounds such as N, N ′
Thiourea compounds such as -di-m-chlorophenylthiourea, p-chlorobenzoic acid, 4- [2- (p-methoxyphenoxy) ethyloxy] salicylic acid, 4- [3- (p
-Tolylsulfonyl) propyloxy] salicylic acid, 5
-[P- (2-p-methoxyphenoxyethoxy) cumyl] aromatic carboxylic acids such as salicylic acid, and zinc, magnesium, aluminum,
Examples thereof include salts with polyvalent metals such as calcium, titanium, manganese, tin, and nickel, and organic acid substances such as an antipyrine complex of zinc thiocyanate and a composite zinc salt of terephthalaldehyde acid and another aromatic carboxylic acid. Is done. Among them, 4-hydroxy-4′-isopropoxydiphenylsulfone and bis (3-allyl-4-hydroxyphenyl) sulfone are preferably used because of excellent storage stability of recorded images.

The use ratio of the dye precursor and the developer is appropriately selected depending on the type of the dye precursor and the developer used, and is not particularly limited. In general, the ratio is 1 part by weight of the dye precursor. The developer is used in an amount of 1 to 50 parts by weight, preferably about 2 to 10 parts by weight.

In the heat-sensitive recording medium of the present invention, a sensitizer can be added to the heat-sensitive recording layer according to the purpose. Specific examples of the sensitizer include stearamide, methoxycarbonyl-N-stearic acid. Benzamide, N-benzoylstearic acid amide, N-eicosanoic acid amide, ethylene bistearic acid amide, behenic acid amide, methylenebisstearic acid amide, methylolamide, N-methylolstearic acid amide, dibenzyl terephthalate, dimethyl terephthalate, terephthalic acid Dioctyl acid, benzyl p-benzyloxybenzoate, 1-hydroxy-2-
Phenyl naphthoate, dibenzyl oxalate, oxalic acid
Di-p-methylbenzyl, di-p-chlorobenzyl oxalate, 2-naphthylbenzyl ether, m-terphenyl, p-benzylbiphenyl, 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- (2-methylphenoxy) ethane, p-methylthiophenylbenzyl ether, 1,4-di (phenylthio) butane, p-acetotoluidide, p-acetophenethidide, N-acetoacetyl -P-toluidine, di (β-biphenylethoxy)
Benzene, p-di (vinyloxyethoxy) benzene,
Examples thereof include 1-isopropylphenyl-2-phenylethane and the like.

Various pigments can be used in the heat-sensitive recording layer. For example, kaolin, clay, calcium carbonate, calcined clay, calcined kaolin, aluminum hydroxide, titanium oxide, diatomaceous earth, particulate anhydrous silica, Examples include inorganic pigments such as activated clay, organic pigments such as styrene microballs, nylon powder, polyethylene powder, urea / formalin resin filler, and raw starch particles.

Various auxiliaries can be added to the heat-sensitive recording layer, if necessary, such as sodium dioctylsulfosuccinate, sodium dodecylbenzenesulfonate, sodium lauryl alcohol sulfate,
Dispersants such as fatty acid metal salts and the like, zinc stearate, calcium stearate, polyethylene wax, carnauba wax, paraffin wax, ester wax and other waxes, defoamers, coloring dyes and the like are appropriately added.

In the present invention, it is possible to add a storability 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′-tetramethyldiphenyl sulfone,
2,2-bis (4-hydroxy-3,5-dibromophenyl) propane, 2,2-bis (4-hydroxy-3,
5-dichlorophenyl) propane, 2,2-bis (4-
Hindered phenol compounds such as hydroxy-3,5-dimethylphenyl) propane, 1,4-diglycidyloxybenzene, 4,4′-diglycidyloxydiphenylsulfone, 4-benzyloxy-4 ′-(2-methylglycidyl) Oxy) diphenyl sulfone, diglycidyl terephthalate, cresol novolak type epoxy resin,
Epoxy compounds such as phenol novolak type epoxy resin and bisphenol A type epoxy resin, N, N'-di-
2-naphthyl-p-phenylenediamine, sodium or polyvalent metal salts of 2,2′-methylenebis (4,6-di-tert-butylphenyl) phosphate, bis (4-ethyleneiminocarbonylaminophenyl) methane, and the like. Can be

The method of forming the heat-sensitive recording layer and the protective layer is not particularly limited. For example, an appropriate method such as air knife coating, variver blade coating, pure blade coating, rod blade coating, short dwell coating, curtain coating, die coating and the like can be used. After the coating liquid for the recording layer is applied and dried on the support by a coating method, the coating liquid for the protective layer is further applied and dried on the recording layer. The support is appropriately selected from paper, plastic film, synthetic paper, nonwoven fabric, metal deposit, and the like.
The coating amount of the recording layer coating liquid is 2 to 12 g / dry weight.
m ^2, is preferably adjusted 3 to 10 g / m ² approximately, the coating amount of the protective layer coating composition is 0.1 to 20 g / m ² by dry weight, preferably 0.5 to 10 g / m ² range of about You.

[0023]

The discoloration of the ground color portion due to the light of the heat-sensitive recording medium is one of the causes of the yellowing reaction caused by the exposure of the dye precursor in the heat-sensitive recording layer to ultraviolet rays.
In the present invention, the protective layer provided on the heat-sensitive recording layer contains a water-soluble ultraviolet absorber having a different absorption wavelength region and a fluorescent dye, thereby absorbing light in a wider range than the single case. Therefore, it is considered that the yellowing reaction of the dye precursor in the heat-sensitive recording layer is efficiently prevented. Further, in the present invention, by using 2,4-dimethyl-6-[(4-dimethylamino) anilino] -fluoran as a dye precursor, an excellent light-fast ground color can be obtained. Although the reason is not clear, it is considered that the discoloration of the fluoran-based dye and the discoloration phenomenon also involve the bonding position of the anilino group.In the case of the dye precursor, the structure has an anilino group on the left side. It is presumed that some change occurs in the mechanism of action due to light and the yellowing reaction is suppressed. Further, the dye precursor has a high melting point, and is considered to contribute to the improvement of the heat resistance of the ground color portion.

[0024]

EXAMPLES The present invention will be described below with reference to examples.
Unless otherwise stated, the middle part indicates parts by weight. [Example 1] Formation of heat-sensitive recording layer Liquid A (developer dispersion liquid) 4-hydroxy-4'-isopropoxydiphenylsulfone 6.0 parts 10% aqueous polyvinyl alcohol solution 18.8 parts Water 11.2 parts Each liquid of the composition was ground with a sand grinder to an average particle size of 1 micron. Liquid B (dye dispersion liquid) 2,4-dimethyl-6-[(4-dimethylamino) anilino] fluoran 2.0 parts 10% aqueous polyvinyl alcohol solution 4.6 parts Water 2.6 parts Each liquid of the above composition Was ground to an average particle size of 1 micron with a sand grinder. Subsequently, the dispersion liquid was mixed at the following ratio to obtain a coating liquid. Liquid A 36.0 parts Liquid B 9.2 parts Kaolin clay (50% dispersion) 12.0 parts Each of the above coating liquids is coated on one surface of a 50 g / m ² support.
The coating was dried at 0 g / m ² to form a heat-sensitive recording layer. Formation of Protective Layer Liquid C (Water-soluble UV absorber) 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid 5.0 parts Water 21.0 parts Prepare the above aqueous solution, and then mix the dispersion at the following ratio. To obtain a coating solution. 10% aqueous solution of polyvinyl alcohol 60.0 parts Aluminum hydroxide (50% dispersion) 50.0 parts Zinc stearate 10.0 parts C solution 26.0 parts Water 50.0 parts Fluorescent dye (diaminoaminobenzenesulfonic acid derivative; chirpy key) 0.5 part of each coating solution was coated on the recording layer so as to have a coating amount of 4.0 g / m ² and dried and then subjected to a super calender treatment to obtain a heat-sensitive recording material.

[Example 2] In the formation of the protective layer in Example 1, solution C (water-soluble ultraviolet absorber) 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid 7.0 parts Water 29.4 parts An aqueous solution was prepared, and then a dispersion was mixed at the following ratio to obtain a coating liquid. 10% aqueous solution of polyvinyl alcohol 60.0 parts Aluminum hydroxide (50% dispersion) 50.0 parts Zinc stearate 10.0 parts C solution 36.4 parts Water 50.0 parts Fluorescent dye (diaminoaminophensulfonic acid sulfonic acid derivative; chirpy key) A thermosensitive recording medium was obtained in the same manner as in Example 1 except that 0.7 part of Chinoval ABPliq.

[Example 3] In the formation of the protective layer of Example 1, solution C (a water-soluble ultraviolet absorber) 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid 17.3 parts Water 72.7 parts An aqueous solution was prepared, and then a dispersion was mixed at the following ratio to obtain a coating liquid. 10% aqueous solution of polyvinyl alcohol 60.0 parts Aluminum hydroxide (50% dispersion) 50.0 parts Zinc stearate 10.0 parts C solution 90.0 parts Water 50.0 parts Fluorescent dye (diaminoaminobenzene sulfonate derivative; chidicakey) A thermosensitive recording medium was obtained in the same manner as in Example 1 except that 1.5 parts of Chinoval ABPliq.

Example 4 In the preparation of solution C of Example 1, 2-hydroxy-4-methoxybenzophenone-5 was used.
-A thermosensitive recording medium was obtained in the same manner as in Example 1, except that sodium sulfonic acid was changed to sodium 2,2'-dihydroxy-4,4'-dimethoxybenzophenone-5,5'-disulfonic acid. Example 5 Example 1 was repeated except that 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid was changed to sodium 2-hydroxy-4-methoxybenzophenone-5-sulfonate in the preparation of solution C of Example 1. In the same manner as in the above, a thermosensitive recording medium was obtained. [Example 6] In the preparation of solution A of Example 1, 4-hydroxy-4'-isopropoxydiphenyl sulfone was added to 4-
A heat-sensitive recording material was obtained in the same manner as in Example 1 except that hydroxy-4'-n-propoxydiphenylsulfone was used. [Example 7] In the preparation of solution A of Example 1, 4-hydroxy-4'-isopropoxydiphenyl sulfone was added to 2,
A heat-sensitive recording material was obtained in the same manner as in Example 1 except that 4'-dihydroxydiphenyl sulfone was used. Example 8 In the formation of the protective layer of Example 1, 10%
A thermosensitive recording medium was obtained in the same manner as in Example 1, except that the aqueous polyvinyl alcohol solution was changed to a 20% acrylic emulsion.

Comparative Example 1 In the preparation of Solution B of Example 1, 2,4-dimethyl-6-[(4-dimethylamino)
Anilino] 3- (N-ethyl-N-)
A heat-sensitive recording material was obtained in the same manner as in Example 1 except that (isoamylamino) -6-methyl-7-anilinofluoran was used. [Comparative Example 2] In the preparation of solution B of Example 1, 3-Nn-dibutylamino-7- (o) was used instead of 2,4-dimethyl-6-[(4-dimethylamino) anilino] fluoran.
Example 1 except that -chloroanilino) fluorane was used.
In the same manner as in the above, a thermosensitive recording medium was obtained. Comparative Example 3 A thermosensitive recording medium was obtained in the same manner as in Example 1 except that Liquid D was prepared and blended in place of Liquid C in the formation of the protective layer of Example 1. Liquid D (hydrophobic ultraviolet absorber) 2- (2'-hydroxy-5'-methylphenyl) benzotriazole 5.0 parts 3% PVA aqueous solution 1.0 part Water 20.0 parts The above composition is subjected to sand grinder. Milled to an average particle size of 1 micron. Comparative Example 4 A thermosensitive recording medium was obtained in the same manner as in Example 1, except that the liquid C was not used in the formation of the protective layer in Example 1 and the number of the fluorescent dye was changed to 1.0 part.

Table 1 shows the results of quality performance tests performed on the heat-sensitive recording materials obtained in the above Examples and Comparative Examples. Note (1) Color development: manufactured by Tokyo Shibaura Electric-Thermal facsimile K
Using B-4800, applied energy 18.03V,
The image density recorded with a pulse width of 3 or 2 milliseconds was measured with a Macbeth densitometer (RD-914, using an amber filter). Note (2) Light fastness: The heat-sensitive recording medium printed under the above conditions was treated with a fade meter (BH, manufactured by Toyo Seiki Co., Ltd.) for 12 hours, and the density of the background was measured with a Macbeth densitometer. (Use a blue filter.) Note (3) Heat resistance;
After standing for a while, the density of the blank paper was measured with a Macbeth densitometer. Note (4) Scrap adhesion; Panasonic Panafax UF
Visual evaluation after printing 20 B4 vertical stripe originals in the copy mode using -60. ○: very small △: small ×: large Note (5) Sticking: Using a Panasonic Panafax UF-22, printing in transmission mode and visual evaluation. ○: The sound is quiet △: The sound is loud ×: A stick pattern appears in the image

[0030]

[Table 1]

As is clear from Table 1, in Examples 1 to 8 satisfying the requirements of the present invention, a heat-sensitive recording material having a very excellent light-fast ground color and a good heat-resistant ground color was obtained. On the other hand, 2,4-dimethyl-6-[(4
In Comparative Examples 1 and 2 in which no [-dimethylamino) anilino] fluorane was used, the quality balance was poor in terms of color sensitivity and light fastness. In Comparative Examples 3 and 4 in which the protective layer did not contain a water-soluble ultraviolet absorber, dregs adhered. And sticking occurred, and sufficient light resistance was not obtained.

[0032]

As described above, the protective layer contains a water-soluble ultraviolet absorber, a fluorescent dye and aluminum hydroxide, and 2,4-dimethyl-6- as a dye precursor.
By using [(4-dimethylamino) anilino] fluoran, high light resistance and heat resistance of a ground color portion can be obtained, so that the appearance is impaired without discoloration even when stored for a long time in sunlight or under high temperature. An excellent heat-sensitive recording medium without any problem is obtained.

Continued on the front page (72) Inventor Sumio Miyake 1-30-6 Kamiochiai, Shinjuku-ku, Tokyo Nihon Paper Industries Co., Ltd. Product Development Laboratory (72) Yoshimi Midorikawa 1-30-6 Kamiochiai, Shinjuku-ku, Tokyo Date (72) Inventor Yutaka Wakita 1-30-6 Kamiochiai, Shinjuku-ku, Tokyo Nihon Paper Co., Ltd. Product Development Laboratory (56) References JP-A-8-295082 (JP, A JP-A-8-311358 (JP, A) JP-A-60-125694 (JP, A) JP-A-8-282117 (JP, A) JP-A-8-267922 (JP, A) 267933 (JP, A) JP-A-8-267932 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B41M 5/26-5/34

Claims (5)

(57) [Claims] 1. A heat-sensitive recording layer comprising, as main components, at least a colorless or light-colored leuco dye and a developer capable of causing the leuco dye to develop color when heated, and a protective layer provided on the heat-sensitive recording layer. The heat-sensitive recording material contains 2,4-dimethyl-6-[(4-dimethylamino) anilino] -fluorane as a dye precursor in the heat-sensitive recording layer, and a binder and a water-soluble ultraviolet absorbing agent in the protective layer. A thermosensitive recording medium characterized by containing an agent, a fluorescent dye and aluminum hydroxide. 2. The heat-sensitive recording material according to claim 1, wherein the water-soluble ultraviolet absorber is a benzophenone derivative having a sulfone group. 3. The heat-sensitive recording material according to claim 1, wherein the water-soluble ultraviolet absorber is a benzophenone derivative having a sulfonic acid group. 4. The content of the water-soluble ultraviolet absorber is 2 to 30% by weight based on the total solids of the protective layer, and the content of the fluorescent dye is 0.01 to 3% by weight based on the total solids of the protective layer. %. The thermosensitive recording medium according to claim 1, 2 or 3. 5. The heat-sensitive recording material according to claim 1, wherein the binder in the protective layer contains a hydrophobic polymer as a main component.