JPS645837B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermal recording medium that performs recording by heating and fixing non-recorded areas by irradiation with light, and more specifically, it is capable of thermal recording with high sensitivity and has excellent storage stability. The present invention relates to a heat-sensitive recording medium.

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 heat development diazo system.

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 time 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 Also, 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, the above-mentioned developer
When the materials shown in (2) and (3) are used, basic substances gradually generated from the developer at room temperature pass through the partition layer and the wall material of the microcapsules, causing precoupling.

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.

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 by using a certain kind of coupler, the diazonium salt and the coupler react with each other during heating, even in the absence of a basic substance, resulting in color development. This discovery led to the present invention. That is, a compound represented by the following general formula is used as a coupler.

However, R ₀ is a C ₁ to C ₁₈ alkyl group R ₁ , R ₂ is a C ₁ to C ₁₈ alkyl group, or R ₁ , R ₂
may form a heterocycle together with the N atom to which they are attached.

In addition, when using the above coupler, a general water-soluble diazonium salt can be used as the diazonium salt, but by using a poorly water-soluble or water-insoluble diazonium salt having an anion component represented by the following general formula. It was discovered that it exhibits even better properties in terms of thermal sensitivity and storage stability.

However, R ₁ to _{R 4} are an alkyl group, an alkenyl group, and an alkenyl group, respectively.
Represents a cycloalkyl group, allyl group, aryl group, heterocyclic group or cyano group.

As a specific example of the coupler used in the present invention etc. These couplers can be used alone or in combination of two or more.

Diazonium salts that can be used in the present invention include conventionally known ones. For example, P-diazo-N-ethyl-N-hydroxyethylaniline chloride zinc chloride, P-diazo-
N,N-dimethylaniline chloride zinc chloride,
P-diazo-N,N-diethylaniline chloride zinc chloride, 4-benzamido-2,5-diethoxybenzenediazonium chloride zinc chloride, 2
-methoxy-4-morpholinobenzenediazonium chloride zinc chloride, 4-morpholino-2,5
-dibutoxybenzenediazonium chloride zinc chloride, etc.

As the diazonium salt, a poorly water-soluble or water-insoluble diazonium salt having an anion component represented by the following general formula can also be used.

However, R ₁ to _{R 4} are an alkyl group, an alkenyl group, and an alkenyl group, respectively.
Represents a cycloalkyl group, allyl group, aryl group, heterocyclic group or cyano group.

This diazonium salt can be taken out as a precipitate by making a salt consisting of Li ⁺ or Na ⁺ and the above-mentioned organic boron anion and a water-soluble diazonium salt into an aqueous solution, and mixing the two.

Organic boron salts that can be used at this time include, but are not limited to, the following.

Further, the water-soluble diazonium salt that can be used at this time can be arbitrarily selected from the above-mentioned conventionally known diazonium salts.

The heat-sensitive recording medium of the present invention includes the coupler described above,
A diazonium salt and various additives are provided on a base material in a single layer or multilayer structure using a suitable binder.

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.

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. Subsalt chloride is also added as a stabilizer for the diazonium salt.

In addition, guanidine sulfate, which contributes to the promotion of thermal color development,
Pentaerythritol etc. can also be added.
In addition, for the purpose of preventing statesking against heat heads and improving writing properties, known pigments such as silica, barium sulfate, titanium oxide, aluminum hydroxide, zinc oxide, calcium carbonate, styrene beads, urea-melamine resin, styrene-melamine resin, etc. Fine powders such as maleic anhydride copolymers can also be used.

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 Various emulsions such as vinyl copolymers, ethyl cellulose, nitrocellulose, polyvinyl acetate, polyvinyl chloride, polystyrene, polymethacrylic acid ester,
Various known resins such as polyester, terpene resin, and cyclized rubber can be used.

Examples are shown below.

Example 1 The following paints were prepared.

Ethyl acetate 30 parts Toluene 45 parts 2-hydroxy-3-naphtho 6 parts Eic acid-morpholinopropylamide Polyvinyl acetate 4 parts Finely powdered silica ² parts This paint was coated on coated paper with a basis weight of 70 g/m2. apply
It was dried with hot air at 75°C. The dry coating amount was 4 g/m ² . The following paints were also prepared.

Water 100 parts by weight p-Diazo-NN-dimethyl 7 parts by weight Aniline chloride Zinc chloride Tartaric acid 0.5 parts by weight 10% of stearamide 30 parts by weight Aqueous dispersion 15% aqueous solution of PVA 20 parts by weight This paint was coated on the Kuplar coated paper. applied to 55
Warm air drying was performed at ℃. The dry coating weight of the diazonium salt layer was 2.5 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/cm ² to develop color, a purple image was formed. The maximum density at this time was 1.1, and the color development temperature was 92°C, which was the temperature that gave half the maximum density. Further, it was fixed by being left under room light for about 1 hour or exposed under an ultraviolet lamp for about 10 seconds, and no color developed even when heated again. Meanwhile 20-25℃, relative humidity 30-60
The unrecorded paper was left for half a year under light shielding. The recording paper that was initially exposed and fixed had a density of 0.15, and the recording paper that was exposed and fixed six months later had a density of 0.18. Furthermore, the maximum color density after six months was 1.0 and the color temperature was 92°C, indicating good storage stability.

Example 2 p-Diazo-N,N-dimethylaniline chloride While stirring 200 g of a 5% aqueous solution of zinc chloride,
5 of sodium tetraphenylborate in it.
% aqueous solution was slowly poured into the mixture at room temperature.
The resulting yellow precipitate was filtered off by suction, washed with water, and then sandwiched between paper and air-dried. The yield was 16.5g.

The following paint was prepared.

10 parts by weight of diazonium tetra synthesized above 20% aqueous dispersion of phenylboron salt 2-hydroxy-3-naphthoic acid moiety
15 parts by weight 20% aqueous dispersion of rufluorinopropylamide 20% aqueous solution of starch 7 parts by weight This paint was applied on high-quality paper with a basis weight of 65 g/m ^2.
A heat-sensitive recording medium with a dry coating weight of 7 g/m ² was prepared by drying with warm air at ℃.

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.

As explained above, the heat-sensitive recording medium formed using the coupler of the present invention does not contain a basic substance and has high heat sensitivity and excellent storage stability.

Claims (1)

[Scope of Claims] 1. A heat-sensitive recording medium containing a diazonium salt and a coupler, in which recording is obtained by reacting the diazonium salt and the coupler by heating without using a base generator, the coupler having the following general formula: A heat-sensitive recording medium characterized by using the represented compound. However, R ₀ is a C ₁ to C ₁₈ alkyl group, R ₁ and R ₂ are
The _C1 - _C18 alkyl group or _R1 , _R2 may form a heterocycle together with the N atom to which they are bonded. 2. The heat-sensitive recording medium according to claim 1, wherein a sparingly water-soluble or water-insoluble diazonium salt having an anion component represented by the following general formula is used as the diazonium salt. 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.