JPH0371036B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to thermal recording, and relates to thermal recording paper that produces stable colored images even when hair styling products or oils and fats are attached to the thermal recording paper, and thermal recording paper that has excellent optical readability in the near-infrared region. Two-component thermal recording paper is generally used for thermal recording. In particular, color former two-component thermal recording paper is the most popular. This thermosensitive recording paper is composed of a basic colorless dye as an electron donor and an organic acidic substance such as a phenol compound, aromatic carboxylic acid, or organic sulfonic acid as an electron acceptor. The thermal melt reaction between these basic colorless dyes and the color developer is an acid-base reaction based on electron donation and acceptance, which forms a metastable "charge transfer complex" and produces a colored image. . However, this type of thermal recording paper has the disadvantage that the colored image formed by heating has poor stability, and the color is easily erased over time or by oil, fingerprints, etc. In addition, such thermal recording paper is also used as a thermal label in POS systems, etc., but in this case, the color is in the visible range, so a semiconductor in the near-infrared range, which is convenient for barcode scanners, is used. When using a laser, the color development could not be read. The present inventors have completed the present invention as a result of extensive research in order to overcome the drawbacks of the prior art. First, regarding the stability of colored images, a thermosensitive color forming layer containing a basic colorless dye and a color developer contains a nitrobenzoic acid metal salt derivative represented by the following general formula () or () as the color developer. It was solved by letting (In both formulas, R ₁ , R ₂ , R ₃ and R ₄ are hydrogen atoms, nitro groups, halogen atoms, C ₁ to C ₁₂ alkyl groups, C ₁ to
It represents a _C12 alkoxy group, a _C3 to _C10 cycloalkyl group, a hydroxyl group, a cyano group, or a benzoyl group, M represents a polyvalent metal, and n represents an integer of 2 to 3. ) In the explanation of general formulas () and (), the C ₁ to C ₁₂ alkyl group and the C ₁ to _{C 12} alkoxy group may be linear or branched, and include methyl group, ethyl group, n -propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, hexyl group, octyl group, nonyl group, dodecyl group, methoxy group, ethoxy group, tert-butoxy group and the like. Examples of the _C3 to _C10 cycloalkyl group include a cyclohexyl group, a 2-ethylcyclohexyl group, and a p-tert-butylcyclohexyl group. Color developers based on polyvalent metal salts of aromatic carboxylic acids are widely applied in the field of pressure-sensitive paper, but are not often used in heat-sensitive recording paper. The reason for this is that the aromatic carboxylic acid polyvalent metal salt color developer has an extremely high melting point due to its nature as a metal salt, and therefore its color development ability based on a thermal melting reaction is inferior. As a result of research on the application of aromatic carboxylic acid polyvalent metal salts to thermal paper, the present inventors discovered that nitrobenzoic acid metal salt derivatives have specific color developing ability and oil resistance. The reason why nitrobenzoic acid metal salt derivatives have such color developing ability and oil resistance is explained as follows. First, the reason why it has better color developing ability than other polyvalent metal salts of aromatic carboxylic acids is because it has a nitro group in its molecule. That is, since the nitro group has extremely strong electron-withdrawing properties, it reduces the electron density on the metal through the π electrons on the benzene ring.
As a result, the nitrobenzoic acid metal salt derivative is thought to act as an electron acceptor, that is, a color developer, for the basic colorless dye (electron donor). Moreover, the reason for the excellent oil resistance is thought to be due to the effect of the nitro group mentioned above. That is, a nitrobenzoic acid metal salt derivative undergoes a thermal melting reaction with a basic colorless dye, a metastable charge transfer complex is formed, and a colored image is obtained. The chemical bonding force between the nitrobenzoic acid metal salt derivative and the basic colorless dye in this color development process is significantly stronger than the chemical bonding force between the conventional color developer and the basic colorless dye. It is thought that even if oils and fats adhere to it, the bond will not break, and the colored image will be stable. In the present invention, the nitrobenzoic acid metal salt derivative used as a color developer is represented by the general formula described above, and specific examples thereof include 4-nitrobenzoic acid,
3-Nitrobenzoic acid, 3,4-dinitrobenzoic acid, 3-methyl-4-nitrobenzoic acid, 3,5-
Dinitrobenzoic acid, 2-benzoyl-4-nitrobenzoic acid, 2-benzoyl-3-nitrobenzoic acid, 3-chloro-4-nitrobenzoic acid, 2-chloro-4-nitrobenzoic acid, 3-methoxy-4- Nitrobenzoic acid, 2-chloro-4-nitro-5-propylbenzoic acid, 2,5-dibenzoyl-4-nitrobenzoic acid, 3-nitro-4-tertiarybutylbenzoic acid, 3,5-dinitro-4- Tertiarybutylbenzoic acid, 3-nitro-4-methylbenzoic acid, 3-nitro-5-methylbenzoic acid, 2-methyl-3-nitrobenzoic acid, 3-nitro-4-chlorobenzoic acid, 3-nitro- 5-chlorobenzoic acid,
3-Nitro-5-methoxybenzoic acid, 3-nitro-6-benzoylbenzoic acid, 3-nitro-5-chloro-6-benzoylbenzoic acid, 3-cyclohexyl-4-nitrobenzoic acid, 2-cyclohexyl-5- Metal salt derivatives such as nitrobenzoic acid, 3-hydroxy-4-nitrobenzoic acid, 3-hydroxy-5-nitrobenzoic acid, 3-cyano-4-nitrobenzoic acid, and 3-cyano-5-nitrobenzoic acid are shown. In particular, 4-nitrobenzoic acid metal salts and 3-
Nitrobenzoic acid metal salt has excellent color developing ability and oil resistance. Furthermore, metals include zinc, calcium, magnesium, tin, aluminum, barium, lead, chromium, manganese, iron, cobalt,
Any polyvalent metal such as nickel or steel may be used, but zinc, tin and iron are particularly good. This is thought to be due to the fact that zinc, tin, and iron are transition metal atoms, and the d orbital is involved in the acid-base reaction. Next, for optical readability in the near-infrared region, we used a basic colorless dye whose color pattern absorbs light in the infrared region, such as a fluorene-based leuco dye, and combined this dye with a metal nitrobenzoate. This problem was solved by combining salt derivatives. The color developer nitrobenzoic acid metal salt derivatives represented by the above general formulas () and () can be used as stabilizers when used in combination with other color developers as described in Japanese Patent Application No. 169269/1988 by the applicant. However, the present invention focuses on the fact that nitrobenzoic acid metal salt derivatives themselves have excellent functions as color developers. On the other hand, the basic colorless dye used in the present invention is preferably a triphenylmethane dye, a fluoran dye, an azaphthalide dye, etc., and specific examples thereof are shown below. Triphenylmethane leuco dye 3,3-bis(p-dimethylamitophenyl)
-6-dimethylaminophthalide [also known as crystal violet lactone] Fluoran leuco dye 3-dimethylamino-6-methyl-7-anilinofluorane 3-(N-ethyl-p-toluideino)-6-methyl- 7-anilinofluorane 3-(N-ethyl-N-isoamyl)amino-
6-Methyl-7-anilinofluorane 3-diethylamino-6-methyl-7-(o,
p-dimethylanilino)fluorane 3-pyrrolidino-6-methyl-7-anilinofluorane 3-piperidino-6-methyl-7-anilinofluorane 3-(N-cyclohexyl-N-methylamino)
-6-Methyl-7-anilinofluorane 3-diethylamino-7-(m-trifluoromethylanilino)fluoran 3-dibutylamino-7-(o-chloroanilino)fluorane 3-diethylamino-6-methyl-chlorofluoran Oran 3-diethylamino-6-methyl-fluorane 3-cyclohexylamino-6-chlorofluorane 3-diethylamino-7-(o-chloroanilino)fluorane 3-diethylamino-benzo[a]-fluorane azaphthalide leuco dye 3 -(4-diethylamino-2-ethoxyphenyl)-3-(1-ethyl-2-methylindol-3-yl)-4-azaphthalide 3-(4-diethylamino-2-ethoxyphenyl)-3-( 1-ethyl-2-methylindol-3-yl)-7-azaphthalide 3-(4-diethylamino-2-ethoxyphenyl)-3-(1-octyl-2-methylindol-3-yl)-4- Azaphthalide 3-(4-N-cyclohexyl-N-methylamino-2-methoxyphenyl)-3-(1-ethyl-2-methylindol-3-yl)-4-azaphthalide These dyes may be used alone or in combination. The above can be used in combination. In addition, among basic color dyes in recent years, when a color is produced by a thermal melting reaction with an electron-accepting substance (developer), it is possible to produce color in the infrared region (particularly in the near-infrared region 700 to 1000 nm).
A basic colorless dye has been developed that absorbs light. Among basic colorless dyes with such characteristics, the following formulas () and () are particularly useful.
There is a fluorene compound represented by The properties of these special dyes could not be utilized with conventional color developers for thermal recording paper, but the nitrobenzoic acid metal salt derivatives of the present invention can be used as color developers for these fluorene compounds. It is particularly effective as a color developer, and its absorption of near-infrared light is much stronger than when other color developers are used. Moreover, it has the characteristic that images with extremely excellent oil resistance and storage stability can be obtained. In particular, the effect is greatest when the color developer zinc p-nitrobenzoate is combined with the fluorene compound () or (). Furthermore, by using the fluorene compound represented by () or () above in combination with the other basic colorless dyes described above, a colored image with a coloring range from visible light to near infrared light can be obtained. Furthermore, sensitizers (for example, dibenzyl terephthalate, benzyl p-benzyloxybenzoate, di-p-tolyl carbonate, p-benzylbiphenyl, phenyl α-naphthyl carbonate) can also be added. The above-mentioned basic colorless dye and nitrobenzoic acid metal salt derivative are atomized to a particle size of several microns or less using a grinder such as a ball mill, attritor, or sand grinder, or an appropriate emulsifying device, and then pulverized according to the purpose. A coating liquid is made by adding various additive materials. This coating liquid usually contains polyvinyl alcohol, modified polyvinyl alcohol, hydroxyethyl cellulose, methyl cellulose, starches, styrene-maleic anhydride copolymer, vinyl acetate maleic anhydride copolymer, styrene-butadiene copolymer, etc. binder, as well as kaolin,
Inorganic or organic fillers such as calcined kaolin, diatomaceous earth, talc, titanium oxide, calcium carbonate, magnesium carbonate, and aluminum hydroxide are added, and in addition, mold release agents such as fatty acid metal salts,
Lubricants such as waxes, benzophenone-based or triazole-based ultraviolet absorbers, water-resistant agents such as glyoxal, dispersants, antifoaming agents, and the like can be used. By applying this coating liquid to paper and various films, the desired thermosensitive recording paper can be obtained. The effects of the present invention include the following points. (1) The image is extremely stable against adhesion of hair conditioners and oils, and does not fade even under high temperature and high humidity. (2) Excellent thermal melting reaction with fluorene-based leuco dyes, and can be applied to optical reading in the near-infrared region. The amount of the nitrobenzoic acid metal salt derivative and the types and amounts of other various components used in the present invention are determined according to the required performance and recording suitability, and are not particularly limited. 1 to 1 part of nitrobenzoic acid metal salt derivative to 1 part of dye
8 parts, 1 to 20 parts of filler are used, and the binder is suitably 10 to 25 parts based on the total solid content. Next, the present invention will be specifically explained using examples. Example 1 Liquid A (dye dispersion) 3-diethylamino-6-methyl-7-anilinofluorane 2.0 parts 10% polyvinyl alcohol aqueous solution 4.6 parts Water 2.5 parts Liquid B (developer dispersion) Color developer (Table 1) 6 parts 10% polyvinyl alcohol aqueous solution 18.8 parts Water 11.2 parts Each solution of the above composition was mixed with an attritor to obtain particles with a particle size of 3
Grinded down to microns. Next, the dispersion liquid is mixed in the proportions shown below to form a coating liquid. Liquid A (dye dispersion) 9.1 parts Liquid B (developer dispersion) 36 parts Kaolin clay (50% dispersion) 12 parts Each of the above coating liquids was applied in an amount of 50 g/m ² on one side of the base paper.
The sheet was coated and dried to a concentration of 6.0 g/m ² , and the sheet was treated with a supercalender to achieve a smoothness of 200 to 300 seconds. Table 1 shows the results of a quality performance test performed on the obtained black-colored thermal recording paper. Comparative example 1 Liquid C (color developer dispersion) Color developer (see Table 1) 6 parts 10% polyvinyl alcohol aqueous solution 18.8 parts Water 11.2 parts All procedures were carried out except that liquid C was used in place of liquid B in Example 1. A thermosensitive recording paper was prepared in the same manner as in Example 1. The quality performance test results are shown in Table 1. Example 2 Liquid D (dye dispersion) Crystal violet lactone 2.0 parts 10% polyvinyl alcohol aqueous solution 4.6 parts Water 2.5 parts Same as Example 1 except that Liquid D was used instead of Liquid A in Example 1. A thermosensitive recording paper was created. The quality performance test results are shown in Table 2. Comparative Example 2 Table 2 shows the quality performance test results of a thermal recording paper prepared in the same manner as in Example 2 except that Liquid C was used instead of Liquid B in Example 2. Example 3 Solution A (dye dispersion 1) 3-diethylamino-6-methyl-7-anilinofluorane 1.8 parts 10% polyvinyl alcohol aqueous solution 4.6 parts Water 2.5 parts Solution E (dye dispersion 2) Formula (2) Fluorene compound 0.9 parts 10% polyvinyl alcohol aqueous solution 2.3 parts Water 1.3 parts Solution F (developer dispersion) Zinc 4-nitrobenzoate 6 parts 10% polyvinyl alcohol aqueous solution 18.8 parts Water 11.2 parts Particle size 3 with a lighter
Grinded down to microns. Next, the dispersion liquid is mixed in the proportions shown below to form a coating liquid. Solution A (dye dispersion 1) 8.9 parts Solution E (dye dispersion 2) 4.5 parts Solution F (developer dispersion) 36 parts Kaolin clay (50% dispersion) 12 parts Each of the above coating solutions was added at 50 g/m ² Coating amount on one side of the base paper
The sheet was coated and dried to a concentration of 6.0 g/m ² , and the sheet was treated with a supercalender to achieve a smoothness of 200 to 300 seconds. Table 3 shows the results of a quality performance test performed on the obtained black-colored thermal recording paper. Example 4 In Example 3, without using liquid A,
A thermosensitive recording paper was prepared in the same manner as in Example 3 except that the proportion of the liquid E was increased to obtain a coating liquid of the proportions shown below. The quality performance test results are shown in Table 3. Solution E (dye dispersion 2) 9 parts Solution F (developer dispersion) 36 parts Kaolin clay (50% dispersion) 12 parts Comparative example 3 Solution G (developer dispersion) Developer (see Table 3) ) 6 parts 10% polyvinyl alcohol aqueous solution 18.8 parts Water 11.2 parts A thermosensitive recording paper was prepared in the same manner as in Example 3 except that Liquid G was used instead of Liquid F in Example 3. The quality performance test results are shown in Table 3. Example 5 Heat-sensitive recording paper was prepared in the same manner as in Example 1, except that the developer listed in Table 4 was used instead of the developer listed in Table 1, and the quality performance test results were evaluated. It is shown in Table 4. Example 6 A thermosensitive recording paper was prepared in the same manner as in Example 5, except that crystal viret lactone was used instead of 3-diethylamino-6-methyl-7-anilinofluorane as the dye in Solution A. The quality performance test results are shown in Table 5. Example 7 Heat-sensitive recording paper was prepared in the same manner as in Example 3, except that the color developer listed in Table 6 was used instead of zinc 4-nitrobenzoate, and the quality test results were displayed. 6.

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[Table] Tables 1 to 6 show that when the color developer nitrobenzoic acid metal salt derivative of the present invention is used, a thermal recording paper with excellent oil resistance, record storage stability, and optical readability in the near-infrared region can be obtained. I understand.

Claims (1)

[Scope of Claims] 1. In a thermal recording paper having a thermosensitive coloring layer containing a colorless basic colorless dye that is usually colorless or light-colored and a color developer, the color developer is represented by the following general formula () or (). A heat-sensitive recording paper characterized by containing a nitrobenzoic acid metal salt derivative. (However, in both formulas, R ₁ , R ₂ , R ₃ and R ₄ are hydrogen atoms,
Nitro group, _halogen atom, C1- _C12 alkyl group,
It represents a _C1 to _C12 alkoxy group, a _C3 to _C10 cycloalkyl group, a hydroxyl group, a cyano group, or a benzoyl group, M represents a polyvalent metal, and n represents an integer of 2 to 3. 2. The heat-sensitive recording paper according to claim 1, wherein the nitrobenzoic acid metal salt derivative is a 4-nitrobenzoic acid metal salt or a 3-nitrobenzoic acid metal salt. 3. The heat-sensitive recording paper according to claim 1 or 2, wherein M in the general formula () or () is zinc, tin, or iron. 4. The thermosensitive recording paper according to claim 1, 2 or 3, wherein the basic colorless dye is a fluorene compound represented by the following general formula () or ().