JPH0141516B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a heat-sensitive recording medium that performs recording by heating and fixing non-recorded areas by irradiation with light, and more particularly relates to a heat-sensitive recording medium that allows thermal recording with high sensitivity and has excellent storage stability. The thermal recording method, which records by converting electrical information into heat using a thermal head, has come to be widely used in facsimile machines and printers due to its advantages such as being able to make the device smaller and lighter and allowing for noiseless recording. I'm getting old. Conventional thermal recording papers have been of the so-called metal chelate type, which utilizes a reaction between an organic acid metal salt and a reducing agent, and of a dye coloring type, which utilizes a reaction between an electron donating substance and an electron accepting substance. However, these materials have the problem that the recording cannot be fixed and the color develops upon reheating, or the color develops or disappears due to adhesives, cellophane tape, vermilion, etc. Furthermore, dye-colored thermal paper has the disadvantage that the recording is easily discolored by light. Therefore, there has been a need for the development of a heat-sensitive recording paper that can be fixed and that overcomes these drawbacks.
In order to achieve this purpose, there has been an attempt to record by reacting a diazonium salt and a coupler by heating to form an azo dye, and then to fix it by photodegrading the diazonium salt in the non-recording area by irradiating it with light. . Such a reaction system applies the so-called thermal phenomenon diazo method. The heat-developable diazo method is a well-known technique in the field of diazo photography, and when this heat-developable diazo paper is used as a heat-sensitive recording paper, writing is first performed using heat, and then fixing is performed using light. In this way, the order of heating and exposure is reversed from that of the conventional heat development diazo method. Here, heating is carried out by a thermal head in an extremely short period of several milliseconds, so a thermal sensitivity superior to that of the conventional thermal development diazo method is required. The following methods have been proposed to realize heat-developable diazo paper. (1) A method of destroying the acid used for stabilization by heat. US Pat. No. 2,653,091 describes an attempt to use trichloroacetic acid as a thermally decomposable acidic substance. (2) A method in which salts are decomposed by heat to produce acids and bases, and only the acids are volatilized. Dutch Patent No. 30636 contains sodium acetate,
Potassium malonate, and US Pat. No. 2,216,137 lists formates and acetates of zinc, cadmium, lead, etc. (3) A method of generating alkali through heat. A large number are mentioned, including inorganic and organic ammonium salts, organic amines, urea and its derivatives. (4) A method of generating a coupler using heat. US Pat. No. 937,160 proposes the use of a tertiary ester of α-pyrrolecarboxylic acid, and Japanese Patent Publication No. 11952/1983 proposes the use of γ-resorcinic acid derivatives. (5) A method of activating the reactivity of a diazo compound and a coupler using heat. US Pat. No. 2,217,189 and US Pat. No. 2,680,062 use diazosulfonate, which is a diazonium salt with no coupling ability at room temperature. However, among these methods (1), (2), and (3), the substances gradually decompose not only during heating but also at room temperature and make the system basic, resulting in precoupling and poor storage stability. It lacks. In addition, in (4) and (5), the diazo coupling reaction requires a large amount of thermal energy, resulting in insufficient color development sensitivity. There are some cases where two or more methods (1) to (5) are combined appropriately,
As mentioned above, there remain problems with storage stability and color development sensitivity. Diazonium salt, coupler and developer 3
Examples include a multilayer construction method in which at least one of the components is separated by a barrier layer of wax or a polymeric material, and an example in which at least one of the three components is isolated in a microcapsule. However, even with this method, when the materials shown in (2) and (3) above are used as the developer, the basic substances gradually generated from the developer at room temperature pass through the isolation layer and the wall material of the microcapsules and are precapsulated. This results in a ring. Although many proposals have been made regarding the thermal development diazo method, it is still not satisfactory in terms of storage stability and color development sensitivity of recording paper. The object of the present invention is to realize a heat-sensitive recording medium with high heat sensitivity and good storage stability using a diazo compound. As a result of repeated research in order to prevent the above-mentioned drawbacks of the heat development diazo method, the present inventors have found that when using a poorly water-soluble or insoluble diazonium salt having an anion component represented by the following general formula as the diazonium salt, excellent thermal sensitivity can be achieved. It was discovered that it has long-term storage stability.

[Formula] However, R ₁ to _{R 4} each represent an alkyl group, an alkenyl group, a cycloalkyl group, an allyl group, an aryl group, a heterocyclic group, or a cyano group. The diazonium salt used in the present invention is a poorly water-soluble or water-insoluble salt whose anion component is composed of an organic boron anion represented by the above general formula. This diazonium salt of the present invention is Li ⁺
Alternatively, it can be extracted as a precipitate by making an aqueous solution of a salt consisting of Na ⁺ and the above-mentioned organic boron anion and a water-soluble diazonium salt, and mixing the two. Specific examples of organic boron salts that can be used at this time are shown below, but the invention is not limited thereto. Furthermore, conventionally known water-soluble diazonium salts can be used. For example, P-diazo-N,N-
Dimethylaniline chloride zinc chloride, P-diazo-N,N-diethylaniline chloride zinc chloride, P-diazo-N-ethyl-N-hydroxyethylaniline chloride salt zinc, 4-benzamide-2,5-diethoxybenzenediazonium Zinc chloride chloride, 2-methoxy-4-morpholinobenzenediazonium chloride zinc chloride,
4-morpholino-2,5-dibutoxybenzenediazonium chloride, zinc chloride, and the like. Note that diazonium salts can be used alone or in combination of two or more. The heat-sensitive recording medium of the present invention is one in which the above-mentioned slightly water-soluble or water-insoluble diazoboron salt, coupler, basic substance, and various additives are provided on a base material in a single layer or multilayer structure using an appropriate binder. be. Here, the diazoboron salt needs to be applied in a dispersed state in water or a saturated hydrocarbon solvent. Also, in a multilayer structure, care must be taken not to dissolve the diazoboronate when another layer is coated on top of the layer containing the diazoboronate. As the base material used in the present invention, high quality paper, coated paper, art paper, laminated paper, synthetic resin film, woven fabric sheet, metal, glass, etc. can be used. The coupler used in the present invention is any that couples with a diazonium salt in a basic atmosphere to form a dye. Such couplers include resorcinol, catechol, phloroglucin, O-hydroxybiphenyl, α-naphthol, 1,5-di-hydroxynaphthalene, 2,3
-di-hydroxynaphthalene, 2,7-di-hydroxynaphthalene, 1-hydroxynaphthalene-
Sodium 4-sulfonate, N,W acid, sodium 2-hydroxynaphthalene-4-sulfonate,
Sodium 2-hydroxynaphthalene-6-sulfonate, Schiefuric acid, Sodium 2-hydroxynaphthalene-3,6-di-sulfonate, R acid,
Potassium 2-hydroxynaphthalene-6,8-di-sulfonate, G acid, sodium 2,3-dihydroxynaphthalene-6-sulfonate, sodium 2,7-dihydroxynaphthalene-3,6-di-sulfonate, 1, Sodium 8-dihydroxynaphthalene-3,6-di-sulfonate (disodium chromotrope), acetoacetonilide,
Dimedone, 3-methyl-5-pyrazolone, 1-phenyl-3-methyl-5-pyrazolone, 2-hydroxy-3-naphthoic acid-O-toluidinoamide, 4-methoxy-1-naphthol, 2-hydroxy-3-naphthoic acid acid-methyl ester, 2-hydroxy-3-naphthoic acid-O-aniside, 2-
hydroxy-3-naphthoic acid-amyanilide,
2-Hydroxy-3-naphthoic acid-α-naphthylamide, 2-hydroxy-3-naphthoic acid-m-
Xylidine, 2-hydroxy-3-naphthoic acid-
m-nitroanilide, 2-hydroxy-3-naphthoic acid-β-naphthylamide, 2-hydroxy-
3-Naphthoic acid-hydroxyethylamide, 2-
Hydroxy-3-naphthoic acid amide, 2-hydroxy-3-naphthoic acid-p-methoxybenzamide, 2-hydroxy-3-naphthoic acid-m-nitrobenzamide, 2-hydroxy-3-naphthoic acid-p-chlorobenzamide, 2-hydroxy-3
-Naphthoic acid-O-ethoxybenzamide, 2-
Hydroxy-3-naphthoic acid-2,5-dimethoxybenzamide, 2-hydroxy-3-naphthoic acid-2-methyl-4-chlorobenzamide, 2-
Hydroxy-3-naphthoic acid-3-chloro-4,
6-dimethoxybenzamide and the like are suitable. Further, by using one type of coupler or a mixture of two or more types, an image of any color tone can be obtained. In order to carry out the diazo coupling reaction between the diazo boron salt of the present invention and the coupler, various basic substances that generate a basic atmosphere upon heating can be used. These basic substances include, for example, inorganic and organic ammonium salts, organic amines, guanidines, amides, urea, thiourea and their derivatives, thiazoles, pyrroles,
Pyrazoles, pyrimidines, piperazines, indoles, imidazoles, triazoles,
Examples include nitrogen-containing heterocyclic compounds such as morpholins, piperidines, amidines, formamidines, and pyridines, and salts such as sodium acetate and potassium malonate. These basic substances can be used alone or in combination of two or more. A suitable acid stabilizer can be added to prevent coupling between the diazonium salt and the coupler at room temperature. Suitable examples of such acid stabilizers include tartaric acid, citric acid, oxalic acid, boric acid, and phosphoric acid. Other additives that can be added include reducing agents such as thiourea, ascorbic acid, and
Allyl isothiocyanate, etc. are added. In addition, as solubilizing agents for Kuplar, alkali metal salts or alkaline earth metal salts of organic acids such as sodium citrate, calcium citrate, magnesium citrate, sodium tartrate, calcium tartrate, calcium gluconate, caffein, thiophyllin, 1,3 , 6-naphthalene trisulfonate, etc. can also be added. Furthermore, guanidine sulfate, pentaerythritol, and the like, which contribute to promoting thermal color development, can also be added. In addition, for the purpose of preventing staking on heat heads and improving writing properties, known pigments such as silica, barium sulfate, zinc oxide, calcium carbonate, styrene beads, urea-melamine resin, styrene-maleic anhydride copolymer, etc. It is also possible to use fine powder. Various waxes can also be used in the present invention to improve color sensitivity or color density. For example, paraffin wax, microcrystalline wax, montan acid wax, montan acid ester wax, amide wax, etc., and amide waxes are particularly effective. Each layer of the recording paper of the present invention can be coated without a binder or with a suitable binder. Commonly known binders include polyvinyl alcohol, methylcellulose, carboxymethylcellulose, hydroxypropylcellulose, polyvinylpyrrolidone, gum arabic, gelatin, casein, starch, isobutylene-maleic anhydride copolymer salt, styrene-maleic anhydride copolymer salts, methyl vinyl ether-maleic anhydride copolymers, water-soluble binders such as polyacrylates, latexes such as styrene-butadiene latexes, acrylonitrile-butadiene latexes, polyvinyl acetate, polyacrylic acid esters, ethylene-vinegar Examples include various emulsions such as bicopolymers, and rubber binders soluble in saturated hydrocarbons. Next, an example will be described. Synthesis Example 1 While stirring 200 g of a 5% aqueous solution of P-diazo-N,N-dimethylaniline chloride zinc chloride,
5 of sodium tetraphenylborate in it.
% aqueous solution was slowly poured into the solution at room temperature.
The resulting yellow precipitate was suction filtered, washed with water, and then sandwiched between filter papers and air-dried. The yield was 16.5g. Synthesis Example 2 5% aqueous solution of 4-benzamido-2,5-diethoxybenzenediazonium chloride zinc chloride
340g and 5 of sodium tetraphenylborate
Synthesis was carried out in the same manner as in Synthesis Example 1 using 280 g of % aqueous solution. The yield was 23g. Example 1 The following paint was prepared. 10 parts by weight of a 20% aqueous dispersion of the diazonium tetraphenyl boron salt of Synthesis Example 1 10 parts by weight of a 10% aqueous dispersion of stearic acid amide 10 parts by weight of a 10% aqueous solution of PVA This paint has a basis weight of 65 g/m ² Apply it on paper,
Dry with warm air at 60°C. The dry coating weight was 4 g/m ² . Furthermore, the following paints were created. Water 100 parts by weight Sodium 2,3-dihydroxynaphthalene-6-sulfonate 3 parts by weight Urea 4 parts by weight 10% aqueous dispersion of stearic acid amide 20 parts by weight 20% aqueous starch solution 20 parts by weight It was coated on tetraphenyl boron salt coated paper and dried with warm air at 55°C.
The dry coverage of the upper layer was 5 g/m ² . This thermosensitive recording medium is placed on a heating plate at a predetermined temperature for 5 seconds.
When pressed under a pressure of 100 g/m ² to develop color, a blue image was formed. The maximum density at this time was 1.2, and the color development temperature was 90°C, which was the temperature that gave half the maximum density. Further, it was left to stand under light at room temperature for about 1 hour, but it was fixed by exposing it to light under an ultraviolet lamp for about 10 seconds, and no color developed even when it was heated again. Meanwhile, 20~25℃, relative humidity 30~
The unrecorded paper was left for half a year under 60% light shielding. The recording paper that was initially exposed and fixed has a density of 0.20,
The recording paper that was exposed and fixed after six months had a density of 0.22. Furthermore, the maximum color density after six months was 1.1 and the color temperature was 90°C, indicating good storage stability. Example 2 The following paint was prepared. 10 parts by weight of a 20% aqueous dispersion of diazonium tetraphenylboron salt of Synthesis Example 2 10 parts by weight of a 10% aqueous dispersion of stearic acid amide 10 parts by weight of a 10% aqueous solution of PVA This paint has a basis weight of 65 g/m ² Apply it on paper,
Dry with warm air at 60°C. The dry coating weight was 4 g/m ² . Furthermore, the following paints were produced. Water 50 parts by weight Urea 3 parts by weight 20% aqueous dispersion of 2-hydroxy-3-naphthoic acid-O-toluidinoamide 20 parts by weight 10% aqueous dispersion of stearic acid amide 15 parts by weight 20% aqueous starch solution 20 parts by weight This paint was applied onto the previously coated paper and dried with warm air at 55°C. The dry coverage of this layer was 5 g/m ² . When this thermosensitive recording medium was used for recording in the same manner as in Example 1, it showed excellent color development characteristics and excellent storage stability. Example 3 The following paint was prepared. 20% aqueous dispersion of diazonium tetraphenyl boron salt of Synthesis Example 1 20 parts by weight 20% aqueous dispersion of 2-hydroxy-3-naphthoic acid-O-toluidinoamide 30 parts by weight 1,3-di-O-tolylguanidine 15 parts by weight of a 20% aqueous dispersion of starch 25 parts by weight of a 20% aqueous solution of starch This paint was applied onto high-quality paper with ^a basis weight of 65 g/m
A heat-sensitive recording medium with a dry coating weight of 7 g/m ² was prepared by drying with warm air at 55°C. When this thermosensitive recording medium was used for recording in the same manner as in Example 1, it showed excellent color development characteristics and excellent storage stability. Comparative Example A thermosensitive recording medium was produced in the same manner as in Example except that each of the dianium tetraphenyl boron salts used in Examples 1 to 3 was replaced with the dianium salt before synthesis. The coloring properties of this thermosensitive recording medium were slightly inferior to those of the examples, but after one week of preparation,
It was found that the product developed a background color within one month and had poor storage stability. As explained above, the thermosensitive recording medium formed using the sparingly water-soluble or water-insoluble diazoboron salt of the present invention has high thermal sensitivity and excellent storage stability.

Claims (1)

[Scope of Claims] 1. A heat-sensitive recording medium containing a diazonium salt, a coupler, and a basic substance, in which recording is obtained by reacting the diazonium salt and the coupler by heating, the diazonium salt being represented by the following general formula: A heat-sensitive recording medium characterized by using a poorly water-soluble or water-insoluble diazonium salt having an anionic component. [Formula] However, R ₁ to _{R 4} each represent an alkyl group, an alkenyl group, a cycloalkyl group, an allyl group, an aryl group, a heterocyclic group, or a cyano group.