JPH0454599B2 - - 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 processes such as development and fixing, can obtain 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 many ways such as electronic computers, facsimile machines, ticket vending machines, labels, and recorders. The thermochromic composition used in such heat-sensitive recording materials generally consists of a coloring agent and a coloring agent that causes the coloring agent to develop color when heated.The coloring agent may be a colorless or color-forming composition containing, for example, lactone, lactam, or spiropyran. Light-colored leuco dyes and organic acids and phenolic substances have conventionally been used as color developers. This recording material that combines a color former and a color developer has the advantage that the resulting image has a bright color tone, has a high background whiteness, and has excellent light resistance, so it is widely used. has been done. However, on the other hand, the reliability of the image is insufficient because the image may develop color or fade due to contact with fingerprints or oils and fats, resulting in a loss of contrast. is also true. In particular, bisphenol A and p-hydroxybenzoic acid esters are easily discolored by fingerprints and oils, and their reliability as recording paper has become a major problem. In order to stabilize images, methods using salicylic acid or metal salts of hydroxynaphthoic acids as color developers have been proposed (Japanese Patent Publication No. 1983-
No. 25174), but in this case, there is a drawback that the scalp color develops when it comes into contact with fingerprints and oils and fats. [Objective] The object of the present invention is to overcome the problems of the prior art, that is, to improve reliability, the image area is stable even when it comes into contact with fingerprints, oils, etc., and there is almost no coloring in the background area. The purpose of the present invention is to provide heat-sensitive recording materials. [Configuration] According to the present invention, a salicylic acid compound, a 2-hydroxy-1-naphthoic acid compound, a 1-hydroxy-2-naphthoic acid compound, and a 3-hydroxy-2-naphthoic acid compound are provided on the support. A first layer containing at least one color developer selected from the above and a second layer containing a zinc compound are laminated adjacently or via an intermediate layer, and the first and second layers Provided is a heat-sensitive recording material characterized in that at least one of the above contains a leuco dye. The color developer used in the present invention includes salicylic acid and its derivatives, and naphthoic acid and its derivatives having a hydroxyl group adjacent to the carboxyl group.
The compound may be one or more types, but usually a compound represented by the following general formula is used. (In the above formula, R ₁ , R ₂ , R ₃ and R ₄ represent hydrogen, halogen, alkyl group, cycloalkyl group, aryl group, alkylaryl group or aralkyl group, and n ₁ is an integer of 0 to 4. and n ₂ to n ₄ are integers from 0 to 6, and when n ₁ to n ₄ are 2 or more,
(R ₁ to _{R 4} may be different from each other) Specific examples of the color developer of the present invention include 3,5-dimethylsalicylic acid, 3-phenylsalicylic acid, 3,
5-dichlorosalicylic acid, 3,5-di-tert-butylsalicylic acid, 5-cumylsalicylic acid, 3,5
-Dicumylsalicylic acid, 3-hydroxy-2-naphthoic acid, 2-hydroxy-1-naphthoic acid, 1
-Hydroxy-2-naphthoic acid, 4-bromo-3
-Hydroxy-2-naphthoic acid, 4-fluoro-3
-Hydroxy-2-naphthoic acid, 3,5-dicyclohexylsalicylic acid, (N-isopropylcarbonyl)-5-aminosalicylic acid, and the like. Examples of zinc compounds include inorganic zinc salts and organic zinc compounds, such as zinc oxide, zinc hydroxide, zinc sulfate, zinc carbonate, zinc oxalate, zinc chloride, zinc bromide, zinc borosulfate, and zinc phosphate. , zinc acetate, zinc stearate, zinc salicylaldoxime, zinc benzoate, zinc dimethylglyoxime, zinc acetylacetonate, and the like. The above-described salicylic acid-based or naphthoic acid-based compound (color developer) and zinc compound are contained in separate first and second layers, respectively. in this case,
The order in which the first layer containing the color developer and the zinc compound are laminated on the support of the second layer is arbitrary, and the first layer is placed on top,
The second layer may be the lower layer, or the first layer may be the lower layer and the second layer may be the upper layer. In this case, the first and second layers may be provided adjacent to each other, or may be laminated with an intermediate layer interposed therebetween. The intermediate layer is formed of a water-soluble resin, a curable water-soluble resin, latex, or the like. Specific examples include polyvinyl alcohol, isobutylene maleic anhydride copolymer, modified polyamide styrene-butadiene latex, polystyrene latex, urethane latex, ethylene vinyl acetate copolymer latex, and acrylic copolymer latex. In the present invention, a first dye containing the above-mentioned color developer is used.
Either or both of the layer and the second layer containing the zinc compound contain a leuco dye. The leuco dyes used in the present invention may be applied alone or in a mixture of two or more types. As such leuco dyes, those applied to this type of heat-sensitive material can be arbitrarily applied. For example, triphenylmethane-based leuco dyes can be used. , fluoran series, phenothiazine series, auramine series,
Leuco compounds of spiropyran-based dyes 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-diptylaminophenyl)
Phthalide, 3-cyclohexylamino-6-chlorofluoran, 3-dimethylamino-5,7-dimethylfluoran, 3-diethylamino-7-chlorofluoran, 3-diethylamino-7-methylfluoran, 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-tripleomethylanilino)fluorane, 3-pyrrolidino-7-(di-p-chlorophenyl)methylaminofluorane, 3-diethylamino-5-chloro-7-(α-
henylethylamino)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-betylanilino)fluorane, 3-(N-benzyl-cyclohexylamino)-
5,6-benzo-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, color developer, and zinc compound on a support, various conventional 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. The above-described first layer and second layer, as well as the intermediate layer provided as necessary, may contain fillers commonly used in heat-sensitive recording materials, if necessary. In this case, fillers that do not contain zinc are used, such as calcium carbonate, silica, titanium oxide, aluminum hydroxide, barium sulfate, clay, talc, and inorganic microorganisms such as surface-treated calcium carbonate and silica. In addition to powder, organic fine powders such as urea-formalin resin, styrene/methacrylic acid copolymer, and polystyrene resin can be used. Further, the first layer and the second layer may contain a surfactant, a thermofusible substance (or lubricant), etc., if necessary. Examples of thermofusible substances include:
In addition to higher fatty acids or their esters, amides or metal salts, various waxes, condensates of aromatic carboxylic acids and amines, benzoic acid phenyl esters,
Examples include higher linear glycols, dialkyl 3,4-epoxy-hexahydrophthalates, higher ketones, and other heat-fusible organic compounds having a melting point of about 50 to 200°C. In the heat-sensitive recording material of the present invention, for example, a coating solution for forming a first layer, a second layer, and an intermediate layer containing each of the above-mentioned components is placed on a suitable support such as paper, synthetic paper, or plastic film in a predetermined order. It is manufactured by coating, drying, and laminating, and is used in various recording fields, especially as a heat-sensitive recording material for high-speed recording that requires high reliability. In this case, the amounts of the leuco dye, salicylic acid or hydroxynaphthoic acid compound, and zinc compound used are usually 5 to 30% by weight, 30 to 70% by weight, and 30 to 80% by weight, respectively.
It is. Further, the amount of gold deposited in the heat-sensitive coloring layer formed on the support is usually 2 to 10 g/m ² . [Effects] By containing the salicylic acid or hydroxynaphthoic acid compound and the zinc compound in separate layers, a heat-sensitive recording material that is excellent in fingerprint resistance and oil resistance and provides highly reliable images is produced. [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-cyclohexylamino)-
6-Methyl-7-anilinofluorane 10 parts 10% aqueous solution of hydroxyethylcellulose 10〃 Water 30〃 [Liquid B] 3-hydroxy-2-naphthoic acid 20 parts Polyvinyl alcohol 10% aqueous solution 15〃 Water 65 parts [Liquid C] ] Zinc oxide 20 parts Polyvinyl alcohol 10% aqueous solution 15〃 Water 65〃 [Liquid D] Octadecyl carbamoyl (p-methoxycarbonyl) benzene 20 parts Polyvinyl alcohol 10% aqueous solution 15〃 Water 65〃 [Liquid E] Urea formalin resin powder 10 parts 10% polyvinyl alcohol aqueous solution 10 Water 70 The mixtures having the above compositions were each dispersed in a ball mill to prepare Solutions A to E. Mix liquids A, C, and D obtained as above and apply on a commercially available high-quality paper with a basis weight of 50 g/m ² using a labo coating rod so that the dye adhesion amount is 0.5 g/m ² . Dry to form the lower layer. Then, B
The liquid and E liquid were mixed, and the mixture was coated on the lower layer to a dry solid content of 3 g/m ² and dried to form an upper layer. Example 2 A lower layer was formed in the same manner as in Example 1 using Liquids A, C, and D of Example 1, and then Liquid F consisting of Liquid E and 25 parts of styrene-butadiene latex (20%) was formed. The mixture was coated on the lower layer and dried to form an intermediate layer so that the dry adhesion amount was 2.5 g/m ² . Further, liquid B and liquid E were mixed and coated on the intermediate layer so that the dry solid content was 3 g/m ² , and dried.
The upper layer was formed. Example 3 A lower layer was formed using liquids B and E, and liquids A, C, and
A heat-sensitive recording material was prepared in the same manner as in Example 2, except that the upper layer was formed using Liquid D. Comparative Example 1 Liquids A, B, C, D, and E of Example 1 were mixed, and the dye adhesion amount was 0.5 g/ ^m2 .
A heat-sensitive recording material for comparison was obtained by coating and drying on similar high-quality paper. Comparative Example 2 A heat-sensitive recording material for comparison was obtained in the same manner as in Comparative Example 1, except that bisphenol A was used in place of 3-hydroxy-2-naphthoic acid in liquid B of Comparative Example 1. 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 carried out under the conditions of 120° C., 2 kg, and 5 seconds, and the image density and background density at this time were measured using a Macbeth densitometer. In addition, after pressing the fingerprints of five people on the image and skin of the obtained recording paper, it was placed in a constant temperature bath at 40℃.
It was stored for one day and the change in concentration was observed (fingerprint resistance test). In addition, a thin layer of cottonseed oil was applied to the image and background of each recording paper, and the paper was stored in a constant temperature bath at 40° C. for one day and changes in concentration were observed (oil resistance test). Table 1 shows the results.
Shown below.

[Table] From the results in Table 1, it can be seen that the heat-sensitive recording material of the present invention has significantly improved fingerprint resistance and oil resistance, and provides highly reliable images.

Claims (1)

[Claims] 1 At least one selected from salicylic acid compounds, 2-hydroxy-1-naphthoic acid compounds, 1-hydroxy-2-naphthoic acid compounds, and 3-hydroxy-2-naphthoic acid compounds on the support. A first layer containing a color developer and a second layer containing a zinc compound are laminated adjacently or via an intermediate layer, and at least one of the first and second layers is coated with a leuco dye. A heat-sensitive recording material characterized by containing.