JPH0331159B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a light-fixing type thermosensitive recording medium that performs recording by heating and fixing non-recorded areas by light irradiation, and more specifically, it is capable of thermal recording with high sensitivity,
The present invention also relates to a light-fixing type heat-sensitive recording medium which has excellent storage stability, has a black color tone, and has a low background density after fixing. [Prior art] The thermal recording method, which records by converting electrical information into heat using a thermal head, is often used in facsimile machines and printers because the device can be made smaller and lighter, and it can record without noise. It has come to be used. Conventional heat-sensitive 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, so that the color develops when reheated, or the color develops or disappears due to adhesives, cellophane tape, vermilion, etc. Therefore, there is a need for the development of a fixable heat-sensitive recording paper that overcomes these drawbacks. In order to achieve these objectives, attempts have recently been made to apply diazo coloring systems to thermosensitive recording paper. Recording is carried out by reacting a diazonium salt and a coupler by heating to form an azo dye, and after recording, further light irradiation is performed to photodecompose the diazonium salt in the unrecorded area to effect fixation. Although the order of exposure and heating is reversed in such a photofixable thermosensitive recording medium, it can be regarded as an extension of the so-called heat development diazo photography technique. However, in heat-sensitive recording, heating is carried out by a thermal head in an extremely short time of several milliseconds, so thermal sensitivity is required to be far superior to that of conventional heat-developable diazo media. It is also necessary to solve the problems peculiar to recording with a thermal head, such as stagnation and debris adhesion to the head. Furthermore, the development of heat-developable diazo paper over the past 30 years is as follows.
Despite the various attempts summarized in (1) to (5), the current situation is that nothing with sufficient characteristics has yet been obtained. (1) A method in which a developer such as urea that creates a basic atmosphere through thermal decomposition is included in the system. (2) A method of incorporating a thermally decomposable acidic substance such as trichloroacetic acid into the system. (3) A method in which a compound that is activated by heating and has coupling properties, such as γ-resorcinic acid, is incorporated into the system. (4) A method in which a diazonium salt such as diazosulfonate, which is activated by heating and has coupling properties, is incorporated into the system. (5) A method of microcapsulating a heat-melting basic substance or using a polymeric binder to separate it from the photosensitive layer consisting of a diazonium salt, coupler, acidic substance, etc. and make it exist in the system. Therefore, it is not possible to obtain a photofixable thermosensitive recording medium simply by applying conventional heat development diazo photographic technology. From this point of view, the present inventors have already discovered that excellent storage stability can be obtained by using a poorly water-soluble material as the main component, diazonium salt, and coupler. It was also revealed that high thermal sensitivity can be achieved by using an appropriate thermofusible material. Therefore, thermal sensitivity and storage stability have reached a level where a compatible photofixable thermosensitive recording medium can be obtained. On the other hand, the color tone developed depends on the combination of diazonium salt and coupler used. Most conventional media have a blue color, but recently there is a demand for a black color tone. In order to obtain a black color tone, attempts have been made to use phloroglucin, especially in heat-developable diazo paper. However, recording paper containing phloroglucin as a coupler tends to cause pre-coupling under high humidity, and has the disadvantage that even after fixing, the background tends to discolor in bright places. A method has also been used in which a β-naphthol-based blue coupler and a phenol-based or active methylene-based yellow to red coupler are mixed. However, in this case, since the rate of coupling with the diazonium salt differs depending on each coupler, it is extremely difficult to always show black color under any coloring conditions. [Object of the Invention] The present invention has been made to solve the above-mentioned drawbacks, and its object is to provide a black color-forming light-fixing type thermal recording medium that always exhibits good pure black tone under any heating conditions. Our goal is to provide the following. [Structure of the Invention] To summarize the present invention, the present invention relates to a black color-forming photo-fixable heat-sensitive recording medium, which contains a diazonium salt and a coupler as main components. A diazonium salt represented by the formula [], a blue coloring coupler represented by the following general formula [], a yellow coloring coupler represented by the following formula [], a water-insoluble or poorly water-soluble basic guanidine derivative, and the following: It is characterized by containing an organic boron salt represented by the general formula []. (However, in the formula, R ₁ is an alkyl group or alkoxy group having 1 to 4 carbon atoms, R ₂ and R ₃ are alkyl groups having 1 to 4 carbon atoms, and X represents a counter anion component.) (However, in the formula, n is an integer of 1 to 18, R ₄ and R ₅ are alkyl groups having 1 to 18 carbon atoms, or R ₄ and R ₅ are groups that form a heterocycle with the N atom to which they are bonded. ) (However, in the formula, R ₆ to _{R 9} are each an unsubstituted aryl group or an aryl group having a substituent, and M is Li
or Na) Specific examples of the diazonium salts used in the present invention include the following. In order to improve the storage stability under high humidity of the photofixable heat-sensitive recording medium of the present invention, it is desirable to select a water-insoluble or slightly water-soluble diazonium salt. For this purpose, preferable counter-anion components of the diazonium salt include BF ₄ ^- , PF ₆ ^- , and organic boron ions represented by the following general formula. However, each R represents an alkyl group, an alkenyl group, a cycloalkyl group, an aryl group, a heterocyclic group, or a cyano group. A specific example is shown below.

【formula】

【formula】

【formula】

【formula】

【formula】

[Formula] These diazonium salts have appropriate coupling properties, so even when two types of couplers with different reactivities are reacted, they can react in a well-balanced manner. Specific examples of the blue coloring coupler represented by the general formula [] used in the present invention are shown below. According to the composition of the present invention, black coloring is achieved, but it also has better heat sensitivity than when a normal naphthol-based coupler (naphthol AS, etc.) is used as a blue-coloring coupler, and also It has the advantage of lower density, and in naphthol AS systems, yellowing occurs when the background portion is heated after fixing, but the present invention can significantly reduce such yellowing. The mixing ratio of the above blue color coupler and yellow color coupler is usually 10:1 to 1:10 in molar ratio,
Preferably it is 5:1 to 1:3. The molar ratio of the diazonium salt to the coupler mixture is suitably 1:1 to 1:5. In the medium of the present invention, it is preferable to use a basic substance in order to create a basic atmosphere suitable for the coupling reaction between the diazonium salt and the coupler during heating. Conventional basic substances include urea and its derivatives,
Water-soluble ones such as inorganic and organic ammonium salts and organic amines have been used. However, in order to improve shelf life under high humidity conditions, it is preferable to use water-insoluble or poorly water-soluble basic guanidine derivatives. An example of this is the following general formula [] or []: [However, R ₁₀ to _{R 14} represent hydrogen, alkyl having 18 or fewer carbon atoms, cyclic alkyl, aryl, acyl, acylamino, or amino group, and at least one of R ₁₀ to _{R 13} is an aryl group; is lower alkyl, alkoxy, nitro, acylamino,
It may have a substituent selected from an alkylamino group and halogen, _R15 is lower alkylene, phenylene, naphthylene or

It is preferable to use a sparingly water-soluble guanidine base represented by the formula: (wherein X represents lower alkylene, SO ₂ , S ₂ , S, O, -NH-, or a single bond). Specific examples include 1,3-di-o-tolylguanidine,
1,2,3-triphenylguanidine, 1,3-
diphenyl-2-o-tolylguanidine, 1,3
-diphenyl-2-m-tolylguanidine, 1,
3-diphenyl-2-p-tolylguanidine,
1,3-diphenyl-2-cyclohexylguanidine, 1,2,3-tricyclohexylguanidine, 1,3-dicyclohexyl-2-phenylguanidine, 4,4'-bis-(1,3-dicyclohexylguanidino)-diphenylmethane ,4,
4'-bis-(1,3-dicyclohexylguanidino)-diphenyl ether, 1,3-di-p-methoxyphenylguanidine, 1-benzoyl-3
-phenylguanidine, o-tolylbiguanide,
Examples include p-di(1,3-diphenylguanidino)diphenyl and di-(triphenylguanidino)methane. In the present invention, in order to further improve storage stability at high humidity, an organic boron salt of the general formula [] is used, which is an agent for rendering diazonium salts insoluble in water or hardly soluble in water. A specific example of this is shown below.

【formula】

【formula】

〔Example〕

Next, the specific production of the photofixable thermosensitive recording medium of the present invention will be described with reference to Examples, but the present invention is not limited thereto. Example 1 A paint having the following formulation was prepared, applied onto high-quality paper with a basis weight of 64 g/m ² using a wire bar, and then dried at 55°C. The dry coating amount was 5.0 g/m ² .

[Formula] of 20 % water dispersion 3g

20% aqueous dispersion of [formula] 4.5g 20% aqueous dispersion of naphthol AS-G 4.5g 20% aqueous dispersion of 1,3-di-o-tolylguanidine 2.5g 40% aqueous dispersion of calcium carbonate 10g 5 g of a 20% aqueous dispersion of benzoin 2 g of a 20% aqueous solution of sodium tetraphenylboronate 14 g of a 10% aqueous solution of PVA The photofixable thermosensitive recording medium thus obtained was placed on a heating plate at a predetermined temperature under a pressure of 10 g/cm ² for 5 seconds. In addition, when it was pressed to develop color, a black image was formed.
The maximum density at this time was 1.35 (amber filter), and the color development temperature was 76°C, which was the temperature that gave half the maximum density. In addition, using a thermal recording paper printing test device (manufactured by Matsushita Electronic Components Co., Ltd.), the applied voltage was 16 V and the pulse width was 3.7 ms.
When printing was performed under these conditions, a black image with a density of 1.15 was obtained. When the fixing sensitivity was investigated using an exposure device using an ultra-high pressure mercury lamp as the light source and a step tablet, it was found that fixing could be achieved with an energy of 250 mJ/cm ² . The background density after fixing was as low as 0.18 with blue filter, giving it excellent naturalness as a recording paper. Furthermore, even if the skin part was heated after fixing (120°C, 10 seconds), the density in Blue Fita only increased to 0.21, and almost no change was observed. On the other hand, regarding storage stability, store unrecorded media at 20℃ and 60% relative humidity (RH) for 6 months or
When the soil concentrations were measured after being left for 24 hours under light-shielded conditions at 40°C and 90% RH, they were 0.18 and 0.23, respectively. After establishment, the ground color was only slightly gray. Example 2 A paint having the following formulation was applied onto a high-quality paper with a basis weight of 64 g/m ² using a wire bar and dried at 120° C. to prepare a pre-coated paper. The dry coating weight was 3.5 g/m ² . 30 g of 10% aqueous solution of PVA 5 g of 20% aqueous solution of glyoxal 15 g of 40% aqueous dispersion of calcium carbonate A diazo paint having the following formulation was applied onto the precoated paper using a wire bar and dried at 60°C. The dry coating weight was 28 g/m ² .

[Formula] 0.6g Stearic acid amide 3g Finely powdered silica 2g Sodium tetraphenylboronate 0.4g Vinyl chloride-vinyl acetate copolymer 2.5g (PVC/vinyl acetate = 86/14) Methyl ketone 50g Further, the following formulation was applied on this diazo layer. Coupler paint was applied with a wire bar and dried at 55°C. The dry coating weight was 3.5 g/m ² .

〔Effect of the invention〕

As explained above, the black color-forming light-fixing heat-sensitive recording medium of the present invention is obtained by combining a specific diazonium salt, a specific blue color-forming coupler, a specific yellow color-forming coupler, and a specific organic boron salt. This has the advantage that a black image with high contrast can be obtained and there is little discoloration of the background density when heated after fixing.

Claims (1)

[Scope of Claims] 1. A photofixable heat-sensitive recording medium containing a diazonium salt and a coupler as main components, a diazonium salt represented by the following general formula [], a blue-coloring coupler represented by the following general formula [] , a yellow color-forming coupler represented by the following formula [], a water-insoluble or poorly water-soluble basic guanidine derivative,
and a black color-forming photofixable heat-sensitive recording medium, which contains an organic boron salt represented by the following general formula []. (However, in the formula, R ₁ is an alkyl group or alkoxy group having 1 to 4 carbon atoms, R ₂ and R ₃ are alkyl groups having 1 to 4 carbon atoms, and X represents a counter anion component.) (However, in the formula, n is an integer of 1 to 18, R ₄ and R ₅ are alkyl groups having 1 to 18 carbon atoms, or R ₄ and R ₅ are groups that form a heterocycle with the N atom to which they are bonded. ) (However, in the formula, R ₆ to _{R 9} are each an unsubstituted aryl group or a substituted aryl group, and M is Li
or Na)