JPH054230B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field] The present invention relates to improvements in heat-sensitive recording materials containing leuco dyes as color formers. [Prior Art] Thermosensitive recording materials generally have a thermosensitive coloring layer containing a thermochromic composition as a main component on a support such as paper, synthetic paper, or plastic film.
Colored images can be obtained by heating with a thermal pen, laser light, strobe lamp, etc. Compared to other recording materials, this type of recording material does not require complicated processing such as development and fixing, can produce records in a short time using relatively simple equipment, and generates less noise and pollutes the environment. Due to its advantages such as low cost, it is used not only for copying books and documents, but also as a recording material in a wide range of applications such as electronic computers, facsimile machines, ticket vending machines, labels, and recorders. The thermochromic composition used in such heat-sensitive recording materials consists of a general coloring agent and a coloring agent that causes the coloring agent to develop color when heated. Examples of the coloring agent include a colorless material having a lactone, lactam, or spiropyran ring. Alternatively, light-colored leuco dyes have been used, and as color developers, organic acids and phenolic substances have conventionally been used. This recording material that combines a color former and a color developer has the advantage that the resulting image has a clear color tone, a high degree of background whiteness, and the image has excellent light resistance, and is widely used. It's being used. Conventionally, bisphenol A and p-hydroxybenzoic acid esters have been used as color developers for leuco dyes, but these phenols have high color density but lack the stability of colored images, so they cannot be used naturally. There is a problem in that the concentration decreases not only when left standing, but also when it comes into contact with oils and fats such as fingerprints. These phenomena occur not only when using phenols but also when general organic acids are used, and there is a strong desire to overcome them. In the field of pressure-sensitive paper, it has been proposed to use a metal compound of aromatic acid carboxylic acid as a color developer that provides a stable image, as seen in Japanese Patent Publication No. 1327-1982. When applied to thermal paper, although the image is stabilized, the non-image area (background area) develops color due to contact with oils and fats, making it difficult to distinguish the image. The current situation is difficult. It has also been proposed to use metal salts of aromatic oxycarboxylic acids (e.g., salicylic acid, 2-oxy-3-naphthoic acid, etc.) as color developers, but in this case too, they do not come into contact with oils and fats. There is a drawback that the image area is strongly colored and the contrast is reduced. [Objective] The purpose of the present invention is to overcome the problems of the prior art, that is, to provide a heat-sensitive recording material with improved image storage stability and oil resistance, with almost no background coloring, and with improved reliability. shall be. [Structure] According to the present invention, in a heat-sensitive recording material in which a heat-sensitive color forming layer containing a leuco dye and a color developer as main components is provided on a support, the color developer may be a color developer represented by the following general formula (). 2-acyloxybenzoic acid-based compound and/or 1-acyloxy-2-naphthoic acid-based compound represented by the general formula (), and the heat-sensitive coloring layer contains a zinc compound. Recording materials will be provided. (In the formula, R ¹ and R ³ are halogen, alkyl group,
It represents a cycloalkyl group, a halogenated alkyl group, an aryl group, an alkylaryl group, or an aralkyl group, and R ² and R ⁴ represent an alkyl group. ) The color developer used in the present invention is 2-acyloxybenzoic acid and its derivatives represented by the above general formula (), and 1-acyloxy-2-naphthoate having an adjacent acyloxyl group represented by the general formula (). One or more types of acids and derivatives thereof. Examples of the alkyl group and cycloalkyl group for R ¹ and R ³ in the above general formula are methyl, ethyl, n-propyl, isopropyl, n-butyl,
Examples include isobutyl, sec-butyl, tert-butyl, cyclohexyl, and those having up to 18 carbon atoms. Examples of halogens include chlorine, fluorine, bromine, etc., and examples of alkyl halides include chloromethyl and fluoromethyl. , trichloromethyl, chloroethyl, chlorobutyl, etc., and examples of the aryl group, aralkyl group, and alkylaryl group include phenyl, benzyl, phenylethyl, cumyl, phenylpropyl, and the like. Further, examples of the alkyl group for R ² and R ⁴ include those having up to 18 carbon atoms, such as methyl, ethyl, propyl, butyl, capryl, and stearyl. As the zinc compound to be contained in the heat-sensitive coloring layer together with the aromatic carboxylic acid compound mentioned above, inorganic salts, oxides, hydroxides, complex compounds with organic ligands, etc. can be applied, and specific examples include zinc chloride and zinc acetate. , zinc propionate, zinc sulfate, zinc phosphate,
Zinc fluoride, zinc bromide, zinc oxide, zinc hydroxide,
Zinc tartrate, zinc citrate, zinc lactate, zinc acetylacetonate, zinc benzoin, zinc salicylaldoxime, zinc benzoate, zinc p-tert-butylbenzoate, zinc p-octylbenzoate, zinc dimethylglyoxime, etc. It will be done. In the present invention, by using the above-described aromatic carboxylic acid compound and zinc compound in combination, unprecedented improvements in storage stability and oil resistance of images and backgrounds can be obtained. In this case, if the aromatic carboxylic acid compound is used alone, the color developing ability is weak and improvement in storage stability and oil resistance cannot be achieved. On the other hand, a zinc compound alone shows almost no color developing ability. Furthermore,
If the above-mentioned aromatic carboxylic acid compound is used by forming a salt with zinc in advance, the coloring caused by contact with fats and oils on the scalp is strong and is not practical. The above-mentioned aromatic carboxylic acid compound and zinc compound are usually used in a total amount of 30 to 80% by weight in the heat-sensitive coloring layer, and in this case, the ratio of both is usually 0.1 to 10 parts by weight of the latter per 1 part by weight of the former. parts, preferably 0.3 to 5 parts by weight. The amount of the leuco dye described below, which is contained in the heat-sensitive coloring layer together with both of them, is 5 to 30% by weight in the heat-sensitive coloring layer. or,
The heat-sensitive coloring layer is usually provided on the support in an amount of about 2 to 10 g/m ² . The leuco dye used in the present invention may be used alone or in combination.
These leuco dyes can be applied in a mixture of more than one species, and any of the leuco dyes that have been applied to this type of heat-sensitive material can be used, such as triphenylmethane, fluoran, phenothiazine, auramine, etc. , leuco compounds of spiropyran dyes and the like are preferably used. Specific examples of such leuco dyes include those shown below. 3,3'-bis(p-dimethylaminophenyl)
-phthalide, 3,3'-bis(p-dimethylaminophenyl)
-6-dimethylaminophthalide (also known as crystal violet lactone), 3,3'-bis(p-dimethylaminophenyl)
-6-diethylaminophthalide, 3,3-bis(p-dimethylaminophenyl)
-6-chlorphthalide, 3,3-bis(p-dibutylaminophenyl)
Phthalide, 3-cyclohexylamino-6-chlorofluorane, 3-diethylamino-5,7-dimethylfluorane, 3-diethylamino-7-chlorofluorane, 3-diethylamino-7-methylfluorane, 3-diethylamino-7 , 8-benzfluorane, 3-diethylamino-6-methyl-7-chlorofluorane, 3-(N-p-tolyl-N-ethylamino)-6
-Methyl-7-anilinofluorane, 3-pyrrolidino-6-methyl-7-anilinofluorane, 2-{N-(3'-trifluoromethylphenyl)
amino}-6-diethylaminofluorane, 2-{3,6-bis(diethylamino)-9-
(o-chloroanilino)xantylbenzoic acid lactam}, 3-diethylamino-6-methyl-7-(m-
trichloromethylanilino)fluoran, 3-diethylamino-7-(o-chloroanilino)fluoran, 3-dibutylamino-7-(o-chloroanilino)fluoran, 3-N-methyl-N-amylamino-6-methyl-7- Anilinofluorane, 3-N-methyl-N-cyclohexylamino-
6-Methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3-(N,N-diethylamino)-5-methyl-
3 -(2'-Hydroxy-4'-dimethylaminophenyl)-3-(2'-methoxy-5'-chlorophenyl)phthalide, 3-(2'-hydroxy-4'-dimethylaminophenyl)-3- (2'-Methoxy-5'-nitrophenyl)phthalide, 3-(2'-hydroxy-4'-diethylaminophenyl)-3-(2'-methoxy-5'-methylphenyl)phthalide, 3-(2'- Methoxy-4'-dimethylaminophenyl)-3-(2'-hydroxy-4'-chloro-5'-
methylphenyl)phthalide, 3-morpholino-7-(N-propyl-trifluoromethylanilino)fluorane, 3-pyrrolidino-7-trifluoromethylanilinofluorane, 3-diethylamino-5-chloro-7-(N-
benzyl-trifluoromethylanilino)fluorane, 3-pyrrolidino-7-(di-p-chlorophenyl)methylaminofluorane, 3-diethylamino-5-chloro-7-(α-
phenylethylamino)fluoran, 3-(N-ethyl-p-toluidino)-7-(α
-phenylethylamino)fluoran, 3-diethylamino-7-(o-methoxycarbonylphenylamino)fluoran, 3-diethylamino-5-methyl-7-(α-
phenylethylamino)fluorane, 3-diethylamino-7-piperidinofluorane, 2-chloro-3-(N-methyltoluidino)-7
-(p-n-butylanilino)fluorane, 3-(N-benzyl-N-cyclohexylamino)-5,6benzo-7-α-naphthylamino-
4'-bromofluorane, 3-diethylamino-6-methyl-7-mesitidino-4',5'-benzofluorane, etc. In the present invention, in order to bind and support the leuco dye, zinc compound and color developer on a support, various commonly used binders can be used as appropriate, such as polyvinyl alcohol, starch and its derivatives, methoxy Cellulose derivatives such as cellulose, hydroxyethylcellulose, carboxymethylcellulose, methylcellulose, and ethylcellulose, sodium polyacrylate, polyvinylpyrrolidone, acrylic amide/acrylic ester copolymer, acrylic amide/acrylic ester/methacrylic acid ternary copolymer , styrene/maleic anhydride copolymer alkali salt, isobutylene/maleic anhydride copolymer alkali salt, polyacrylamide, sodium alginate, gelatin, casein, and other water-soluble polymers, as well as polyvinyl acetate, polyurethane, styrene/butadiene. Latexes such as copolymers, polyacrylic acids, polyacrylic esters, vinyl chloride/vinyl acetate copolymers, polybutyl methacrylate, ethylene/vinyl acetate copolymers, styrene/butadiene/acrylic copolymers can be used. can. In addition, in the present invention, in addition to the leuco dye and color developer, if necessary, auxiliary additive components commonly used in this type of heat-sensitive recording material, such as fillers, surfactants, thermofusible substances ( or lubricant), etc. can be used in combination. In this case, fillers include, for example, inorganic fine powders such as calcium carbonate, silica, titanium oxide, aluminum hydroxide, barium sulfate, clay, talc, and surface-treated calcium and silica, as well as urea-formalin resin,
Organic fine powders such as styrene/methacrylic acid copolymers and polystyrene resins can be mentioned, and examples of thermofusible substances include higher fatty acids or their esters, amides, or metal salts, as well as various waxes, 50 to 50% of condensates of aromatic carboxylic acids and amines, phenyl benzoate, higher linear glycols, dialkyl 3,4-epoxy-hexahydrophthalates, higher ketones, and other thermofusible organic compounds. Examples include those with a melting point of about 200°C. The heat-sensitive recording material of the present invention can be produced, for example, by applying a heat-sensitive layer-forming coating solution containing each of the above-mentioned components onto a suitable support such as paper, synthetic paper, or plastic film, and drying it. It is used in various recording fields, especially as a heat-sensitive recording material for high-speed recording that requires high image stability. The heat-sensitive recording material of the present invention can be used in various fields, but in particular, it can be advantageously used as a heat-sensitive recording label sheet or a heat-sensitive recording magnetic ticket paper by taking advantage of the above-mentioned excellent color image stability. be able to. In the case of a heat-sensitive recording type label sheet, a heat-sensitive coloring layer containing the above-mentioned fluoran compound and phenolic compound is provided on one side of the support, and a release mount is provided on the other side of the support with an adhesive layer interposed therebetween. In the case of magnetic ticket paper, a magnetic recording layer containing a ferromagnetic material and a binder as main components may be provided in place of the release mount. [Effect] By using a benzoic acid or naphthoic acid compound having an acyloxyl group adjacent to a carboxyl group as a color developer and including it in the heat-sensitive coloring layer together with a zinc compound, the storage stability of the colored image and the background area is improved. A heat-sensitive recording material with excellent properties and oil and fat resistance is obtained. [Example] The present invention will now be described in more detail with reference to Examples. Note that all parts and percentages below are based on weight. Example 1 [Liquid A] 3-(N-methyl-N-cyclohexyl)amino-6-methyl-7-anilinofluorane 10 parts 10% of hydroxyethyl cellulose 10 parts Aqueous solution Water 30 parts Dispersed with a ball mill to obtain an average particle The diameter was reduced to 5μ or less. [Liquid B] Stearic acid amide 20 parts Urea-formalin resin fine particles 10 parts Polyvinyl alcohol 10% aqueous solution 30 parts Water 90 parts Dispersed in a ball mill to reduce the average particle size to 5 μm or less. [Liquid C] 3,5-di-tert-butyl-2-acetoxybenzoic acid 20 parts 10% polyvinyl alcohol aqueous solution 20 parts Water 60 parts [Liquid D] Zinc hydroxide 20 parts Polyvinyl alcohol 10% aqueous solution 20 parts Water 60 parts Dispersion was performed using a ball mill to reduce the average particle size to 5μ or less. The above [liquid A], [liquid B], [liquid C], and [liquid D] are mixed and stirred uniformly, and the resulting coating liquid has a basis weight of approximately 50 g/m ²
A heat-sensitive coloring layer was provided by applying the mixture onto high-quality paper using a laboratory coating rod to give a dry weight of 6 g/m ² and drying, to obtain a heat-sensitive recording material of the present invention. Examples 2 to 14 The heat-sensitive recording material of the present invention was obtained in the same manner as in Example 1 except that the carboxylic acid and zinc compounds shown in Table 1 were used in [Liquid C] and [Liquid D]. Comparative Examples 1 to 4 Comparative heat-sensitive recording materials were obtained in the same manner as in Example 1, except that the carboxylic acid and zinc compounds shown in Table 1 were used in [Liquid C] and [Liquid D].

【table】

[Table] The heat-sensitive recording materials of the present invention and comparative heat-sensitive recording materials obtained as described above were tested using a commercially available thermal gradient tester.
Printing was performed at 140° C. for 1 second, and the image density and background density at this time were measured using a Macbeth densitometer.
Further, after pressing a fingerprint onto the image and background of the obtained recording paper, it was stored for one week and changes in density were observed (oil resistance test). In addition, each recording paper was bound into a commercially available file and stored for one month to observe changes in density (storage resistance test). The results are shown in Table-2.

[Table] As is clear from the results in the table, the heat-sensitive recording material of the present invention has significantly better image and background stability than conventional materials.

Claims (1)

[Scope of Claims] 1. A heat-sensitive recording material in which a heat-sensitive color forming layer containing a leuco dye and a color developer as main components is provided on a support, in which the color developer is 2 represented by the following general formula (). - Using an acyloxybenzoic acid compound and/or a 1-acyloxy-2-naphthoic acid compound represented by the general formula (),
A heat-sensitive recording material characterized in that the heat-sensitive coloring layer contains a zinc compound. (In the formula, R ¹ and R ³ are halogen, alkyl group,
It represents a cycloalkyl group, a halogenated alkyl group, an aryl group, an alkylaryl group, or an aralkyl group, and R ² and R ⁴ represent an alkyl group. )