JPH0550399B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a heat-sensitive recording material. More specifically, the present invention relates to a liquid composition containing a colorless to light-colored color-forming compound for preparing a heat-sensitive recording sheet that exhibits little background coloration and has excellent preservability of colored images, particularly resistance to anti-soaking agents. Conventional technology Conventionally, heat-sensitive recording sheets, such as heat-sensitive recording paper, have been produced by coating paper with an aqueous coating solution containing a colorless or light-colored color-forming compound, a phenolic compound, a binder, etc., and other additives in the form of fine particles. It is manufactured by coating it on plastic sheets, etc. The heat-sensitive recording sheet obtained in this way tends to have a phenomenon in which the coated surface becomes naturally colored during storage, and this phenomenon is known as "ground coloring" or "background staining." As a method to prevent this phenomenon, in JP-A-55-164191, a dispersion of a color-forming compound (leuco dye) is heat-treated at 50 to 100°C, and after cooling, it is mixed with a phenolic compound dispersion to form a coating solution. A method has been proposed to obtain the .
Furthermore, Japanese Patent Application Laid-Open No. 57-195692 proposes a method using a coating liquid obtained by mixing a heat-treated liquid of a specific fluoran compound with a color developer liquid. Problems to be Solved by the Invention The above-mentioned methods do not sufficiently improve background color development and background stains, and in particular, it is difficult to improve color development with high sensitivity in line with recent demands for higher sensitivity of heat-sensitive recording materials. In particular, when compounds are used, their effects are not sufficient. On the other hand, thermosensitive recording sheets tend to cause a phenomenon in which the colored recorded images are erased by the softening agent contained in the plastic sheet or the like. Under the above circumstances, in order to obtain more stable thermally recorded images, it is desired to develop a thermal recording sheet that has improved background color development and background staining, and has high anti-soak properties. Means for Solving the Problems The present inventors have completed the present invention as a result of various studies aimed at improving the above-mentioned drawbacks. That is, the present invention consists of a colorless to light-colored color-forming compound that develops color by reacting with a phenolic compound, water, and a water-soluble polymer compound, which is heat-treated at a temperature of 40 to 100°C at a pH of 8 to 11 in the presence of an alkaline compound. A liquid composition for a heat-sensitive recording sheet is provided. The present invention will be explained in detail. In the present invention, for example, an unpulverized mixture consisting of a color-forming compound, a water-soluble polymer, and water is prepared, and a ball mill, a sound grinder, an attritor, etc.
The particle size of the color-forming compound after pulverization using a paint conditioner, kneader, etc. is the average particle size.
Grind to 2μ or less. The above mixture contains 5 to 70 parts by weight of the color-forming compound, preferably 10 to 50 parts by weight.
parts by weight, 0.1 to 20 parts by weight of water-soluble polymer compound,
Preferably, the proportion is adjusted to be 0.5 to 10 parts by weight, with the remainder being water (100 parts by weight in total). Add an alkaline compound as described below to the finely ground aqueous mixture until the pH of the treatment liquid reaches 8 to 11 (usually 0.01 to 10 parts by weight based on the above mixture).
The treatment is carried out at 40-100°C, preferably 50-80°C, with stirring. Processing time is 10 minutes to 3 hours, usually 30 minutes to 3 hours.
60 minutes is enough. As mentioned above, heat treatment in the presence of an alkaline compound is conveniently carried out after pulverizing a mixture consisting of a color-forming compound, a water-soluble polymer compound, and water. It is also possible to add an alkaline compound to a mixture of a polymer and water and perform a hot pulverization treatment, or a method of pulverizing the mixture under heating and adding an alkaline compound during the pulverization can be adopted as necessary. Specific examples of (A) color-forming compound, (B) water-soluble polymer compound, and (C) alkaline compound that can be used in the present invention are given below. (A) Color-forming compound Rhodamine-β as a xanthene compound
-anilinolactam, rhodamine (p-nitroanilino)lactam, 2-dibenzylamino-
6-Diethylaminofluorane, 2-anilino-3-methyl-6-diethylamino-fluorane, 2-anilino-3-methyl-6-cyclohexylmethylaminofluorane, 2-anilino-3-methyl-6-isopentylethylamino Fluoran, 2-anilino-3-methyl-6-
Dibutylaminofluorane, 2-p-chloroanilino-3-methyl-6-diethylaminofluorane, 2-p-fluoroanilino-3-methyl-6-diethylaminofluorane, 2-p-
Fluoroanilino-3-methyl-6-dibutylaminofluorane, 2-anilino-3-methyl-6-(p-toluidinoethyl)aminofluorane, 2-p-toluidino-3-methyl-6-
Diethylaminofluorane, 2-0-chloroanilino-6-diethylaminofluorane, 2-
0-chloroanilino-6-dibutylaminofluorane, 2-0-fluoroanilino-6-diethylaminofluorane, 2-0-fluoroanilino-6-dibutylaminofluorane, 2-m
-chloroanilino-6-diethylaminofluorane, 2-anilino-3-methyl-6-piperidinofluorane, 2-anilino-3-methyl-
6-pyrrolidinofluorane, 2-m-trifluoromethylanilino-6-diethylaminofluorane, 2-dihexylamino-6-diethylaminofluorane, 2-butylamino-3-chloro-6-diethylaminofluorane, 2 -Ethoxyethylamino-3-chloro-6-diethylaminofluorane, 2-anilino-3-chloro-6-diethylaminofluorane, 2-diphenylamino-6-diethylaminofluorane, 2-anilino-3-methyl-6-diph enylaminofluorane, 2-phenyl-6-diethylaminofluorane, 2-chloro-3-methyl-6-diethylaminofluorane, 2-chloro-6-diethylaminofluorane, 2-methyl-6-diethylaminofluorane, 6 -diethylamino-1,2-benzfluorane, etc., 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide (also known as crystal violet lactone) as a triarylmethane compound, 3, 3-bis(p-dimethylaminophenyl)phthalide, 3-(p-dimethylaminophenyl)-3-(1,2-dimethylaminoindol-3-yl)phthalide, 3-
(p-dimethylaminophenyl)-3-(2-methylindol-3-yl)phthalide, chromenes, etc., 3-methyl-3-spiro-dinaphthopyran, 3-benzylspiro-dinaphthopyran, 3 as a spiropyran compound, -methyl-naphtho-(3-methoxy-benzo)spiropyran,
3-propyl-spiro-dibenzopyran, 1,
3,3-trimethyl-6'-nitro-8'-methoxyspiro (indoline-2,2'-benzopyran), 1,3,3-trimethyl-6'-nitrospiro (indoline-2,2'-benzopyran)
etc., 4 as a diphenylmethane compound,
4'-bis-dimethylaminobenzhydrin benzyl ether, N-halophenyl-leucoauramine, N-2,4,5-trichlorophenylleucoauramine, etc., benzoylleucomethylene blue as a thiazine compound, p-nitrobenzyl Examples include leucomethylene blue. These leuco dyes may be used alone or in combination. (B) Water-soluble polymer compounds methylcellulose, methoxycellulose, hydroxyethylcellulose, carboxymethyl, sodium carboxymethylcellulose,
Cellulose, polyvinyl alcohol, carboxy group-modified polyvinyl alcohol, sulfonic acid group-modified polyvinyl alcohol, polyvinylpyrrolidone, polyacrylamide, polyacrylic acid,
Starch and its derivatives, casein, gelatin, alkali salts of styrene-maleic anhydride copolymers, water-soluble ones such as alkali salts of iso(or diiso)butylene-maleic anhydride copolymers, polyvinyl acetate, vinyl chloride/ Water-soluble emulsions such as vinyl acetate copolymers, polystyrene, polyacrylic acid esters, polyurethanes, and styrene/butadiene/acrylic acid copolymers are used. (C) Alkaline compound Sodium carbonate, potassium carbonate, ammonium carbonate, sodium hydrogen carbonate, ammonium hydrogen carbonate, aqueous ammonia, sodium hydroxide, potassium hydroxide, calcium hydroxide, etc. are used. The liquid composition of the present invention obtained as described above is mixed with a finely divided phenolic compound as a color developer and a binder according to a conventional method to form a coating solution, which is then used for paper, plastic sheets, and synthetic materials. A heat-sensitive recording sheet is prepared by coating paper or the like, and the usual method for preparing a coating liquid is as follows. First, the color developer is pulverized together with a water-soluble polymer, and then the ratio of the color-forming compound to the color developer is 1:1 by weight.
A coating solution is prepared by mixing the components at a ratio of 1 to 1:10 (color forming compound: color developer) and then adding a binder. In addition, waxes (e.g. paraffin wax, polyethylene wax),
Sensitizers such as biphenyls (e.g. parabenzyl biphenyl), fatty acid amides (e.g. stearic acid amide), fillers (e.g. clay, talc, calcium carbonate,
Kaolin), antifoaming agents, etc. can also be added. Apply 5 to 40 g of the coating liquid obtained in this way onto a sheet such as paper, plastic sheet, synthetic paper, etc.
Coat with a bar coater etc. to a thickness of m ² and dry to obtain a heat-sensitive recording sheet. Examples The present invention will be explained in more detail by examples. In the examples, "parts" indicate parts by weight. Example 1 The following composition was prepared using a sound grinder.
The color-forming compound was ground until the average particle size was 0.4μ (liquid [A]). [A] Liquid 2-anilino-3-methyl-6-isopentylethylaminofluorane (coloring compound) 25% PVA aqueous solution water 25 parts 20〃 55〃 Add 10% sodium carbonate aqueous solution to 100 parts of the above pulverized liquid
0.5 part was added (PH9), and after stirring at 80 to 85°C for 30 minutes, the mixture was allowed to cool to room temperature to obtain a composition of the present invention ([A-1] liquid). 30% of the composition below using a sound grinder
The mixture was pulverized for a minute (liquid [B]). [B] Liquid p-hydroxybenzoic acid benzyl ester 4,4'-thio-bis(3-methyl-6-tert-butylphenol) Heavy calcium carbonate 15% casein aqueous solution 10.2 parts 10.2〃 20〃 20〃 79.6〃 Next, 8 parts of liquid [A-1], 70 parts of liquid [B], 5 parts of carboxyl-modified SB latex emulsion (solid content 48%), and 17 parts of water were mixed to prepare a coating solution, weighing 50 g. The composition of the present invention was coated on a high-quality paper of 30 g/m ² at a liquid amount of 30 g/m ² and dried to obtain a heat-sensitive recording sheet using the composition of the present invention. Example 2 The following composition was ground using a sound grinder until the average particle size of the color-forming compound was 0.7 μm (solution [C]). [C] Solution 2-0-Fluoroanilino-6-dibutylaminofluorane (color-forming compound) 25% PVA aqueous solution water 25 parts 10〃 65〃 10% potassium carbonate aqueous solution 0.5 to 100 parts of the above pulverized liquid
(PH9), stirred at 70 to 75°C for 30 minutes, and then allowed to cool to room temperature to obtain a composition of the present invention ([C-1]
liquid). The following composition was ground using a sound grinder. [D] Liquid bis-(3-allyl-4-hydroxy phenyl) sulfone parabenzyl biphenyl heavy calcium carbonate 15% casein aqueous solution 13.8 parts 13.8 27.6 27.6 60.8 Next [C-1] 8 parts of liquid A coating solution was prepared by mixing 72 parts of liquid [D], 5 parts of carboxyl-modified SB latex emulsion (solid content 48%), and ¹⁵ parts of water. is 30g/ ^m2
A heat-sensitive recording sheet using the composition of the present invention was obtained by coating and drying the composition. Example 3 Add 2 parts of 28% ammonia water to 100 parts of the pulverized liquid [C] of Example 2 (PH 10 to 11), stir at 60 to 65°C for 1 hour, and then cool to room temperature to prepare the composition of the present invention. was obtained ([C-2] liquid). This [C-1] solution was used instead of the [C-1] solution in the example.
2] A heat-sensitive recording sheet using the composition of the present invention was obtained in the same manner as in Example 2 except that the liquid was used. Example 4 A mixture of the following compositions was ground using a sound grinder at a temperature of 50° C. for 30 minutes to obtain a composition of the present invention (liquid [E]). [E] Liquid 2-anilino-3-methyl-6-dibutylaminofluorane (color-forming compound) 25% PVA aqueous solution 10% sodium carbonate aqueous solution 25 parts 10〃 64.5〃 0.5〃 Then 8 parts of [E] liquid, carried out Example 1 [B] solution 70
A coating solution was prepared by mixing 5 parts of carboxyl-modified SB latex emulsion (solid content 48%) and ¹⁷ parts of water ^. A heat-sensitive recording sheet using the composition of the present invention was obtained by coating and drying the composition. Example 2 A mixture consisting of the following composition was ground using a sound grinder at a temperature of 60 to 70°C for 4 hours to obtain a composition of the present invention (liquid [F]). [F] Solution 2-anilino-3-methyl-6-cyclohexylaminofluorane (coloring compound) 25% PVA aqueous solution Water 10% sodium carbonate aqueous solution 25 parts 20〃 54.5〃 0.5〃 Of [E] solution of Example 4 A heat-sensitive recording sheet using the composition of the present invention was obtained in the same manner as in Example 4, except that liquid [F] was used instead. Comparative Example 1 A comparative heat-sensitive recording sheet was obtained in the same manner as in Example 1, except that liquid [A] was used instead of liquid [A-1] in Example 1. Comparative example 2 [A] liquid was used instead of [A-1] liquid in Example 1.
A comparative heat-sensitive recording sheet was obtained in the same manner as in Example 1, except that a liquid obtained by stirring at 80 to 85° C. for 30 minutes and cooling was used. Comparative Example 3 A comparative heat-sensitive recording sheet was obtained in the same manner as in Example, except that liquid [C] was used instead of liquid [C-1] in Example 2. Comparative Example 4 A comparative heat-sensitive recording sheet was obtained in the same manner as in Example 4, except that the mixture in which 10% sodium carbonate was not added to the composition of Example 4 [E] was heat-treated. Comparative Example 5 A comparative heat-sensitive recording sheet was obtained in the same manner as in Example 5, except that the mixture in which 10% sodium carbonate was not added to the composition of Example 5 [F] was heat-treated. The following quality performance test was conducted using a heat-sensitive recording sheet using the composition of the present invention obtained as described above and a comparative heat-sensitive recording sheet.

【table】

[Table] As is clear from the table, the heat-sensitive recording sheets prepared using the compositions of the present invention are superior in ground coloring properties and anti-sodifying agent resistance of colored images compared to the comparative heat-sensitive recording sheets. Effects of the Invention A liquid composition containing a color-forming compound for preparing a heat-sensitive recording sheet with less background color development and background smearing and excellent anti-soaking agent resistance of the colored image was obtained.

Claims (1)

[Claims] 1 Consists of a colorless to light-colored color-forming compound that develops color by reacting with a phenolic compound, a water-soluble polymer compound, and water, and has a pH of 8 in the presence of an alkaline compound.
11. A liquid composition for a heat-sensitive recording sheet, which is heat-treated at a temperature of 40°C to 100°C.