JPH0332473B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermochromic recording material with improved storage stability.

More specifically, the constituent materials of the recording layer formed on the support include a coupler compound contained via a binder, and a base sufficient to cause the compound to sufficiently react with a p-phenylenediamine compound to form a dye. A recording material containing four components, a generating substance and a reaction accelerator, which has a multilayer structure in which one or two of the components are separated from the remaining components by a separation layer made of an oil-based or water-based polymer compound. This is a thermochromic recording material with improved storage stability.

As is well known, heat-sensitive recording materials include (a) so-called heat-sensitive coloring materials that utilize the reaction between leuco dyes and acidic substances; When formed as a single layer on a support, there is a drawback that long-term fixation of the image applied to the surface of the layer cannot be expected. For this reason, there has been a demand for ways to improve these points.

On the other hand, apart from this, there are (b) fixable recording materials that utilize a reaction between a diazo compound and a coupler compound. However, this method uses a base-generating substance and generates a base by heating, thereby starting the reaction system.
Since it is a diazo-type heat-sensitive recording material that increases the pH and causes the diazo compound and coupler compound to react to develop color, the color reaction between the diazo compound and the coupler compound, which are the main components, tends to proceed under normal conditions. Therefore, any one of those two components
It is necessary to separate the component from other components to prevent the color reaction from proceeding under normal conditions. As an isolation means for this purpose, (1) The heat-sensitive recording layer provided on the support is multilayered to physically isolate both components.

(2) Both components in a single-layer heat-sensitive recording material are isolated by being covered with microcapsules (hereinafter referred to as microcapsules).

(3) Separating both components or one of them in the same recording material as discontinuous particles.

Various methods have already been proposed and are known, but these methods have various practical difficulties and have not yet been put into practical use. In particular, since the coating liquid for this type of recording material uses a solvent, it is likely to cause various problems in terms of process control.

Furthermore, apart from the above method (B), in order to improve the storage stability of the heat-sensitive recording material, as related to the above method (B), the color-forming components in the material are microencapsulated in advance, and if necessary, In addition, the triallylmethane compound can be used to create an electron-donating organic coloring agent such as a diphenylmethane compound, and an electron-accepting coloring agent made of an organic or inorganic acidic substance. There are products that are microencapsulated and then subjected to the same coloring reaction as described above, if necessary, but all of them have practical advantages and disadvantages.
It is said that this is not always satisfactory.

As a result of various studies to solve the above-mentioned problems, the inventors of the present invention have developed a method of utilizing thermal energy for the so-called coupling reaction in which a coupler compound and a P-phenylenediamine compound react, and a record containing both of the above. By forming a multilayer structure in which any one or two of the materials (four components) are separated from the remaining components via a separation layer made of an oil-based or water-based polymer compound, the reaction can be effectively progressed. The present invention was completed by experimentally confirming that the above-mentioned drawbacks can be solved.

That is, the present invention provides for a coupler compound contained in the constituent materials of a recording layer formed on a support via a binder, and a base sufficient to cause the compound to sufficiently react with a p-phenylenediamine compound to form a dye. In a recording material consisting of four components: a base generating substance capable of supplying It consists of a multilayer structure separated by layers.

In the above-mentioned recording material (four components), one or two of the components are separated from the remaining components by a separation layer made of oil-based and water-based polymer compounds. This is done in order to impart long-term storage stability to the present invention, based on the experimental results of the present inventors that when one or two components are missing, no color develops even when heated. . Needless to say, this separation layer softens or melts when heated during use and develops color when the four components come into contact with each other.

The above-mentioned coupling reaction is generally carried out in an alkaline aqueous solution during the development of color photographs, but as this reaction is known to be difficult to occur in low pH ranges, it is usually not carried out in the reaction system of a single recording layer. Normally, storage stability at room temperature is achieved by making the system itself have a low pH, for example, 1 to 3. For this reason, in order to achieve satisfactory color development in practical use, not only a large amount of base generating substance is required, but also the color development sensitivity is poor, which is impractical.

On the other hand, according to the present invention, the desired pH can be set arbitrarily by having the system configuration as described above, so by setting a high pH, the amount of base generating substance used can be reduced. At the same time, an improvement in color development sensitivity can be expected at the same time.

Therefore, if the pH of this reaction system is kept at a weakly acidic to weakly alkaline level (approximately 4 to 9) to facilitate the coupling reaction of the system, one or more of the above-mentioned materials (four components) may be added during heating. Since the separation layer that separates the two components from the remaining components is easily softened or melted, the reaction proceeds in a short period of time and color is developed, and the color appears as a high concentration on the surface of the recording layer. This coloring, once developed, does not fade and has the effect of being stable and durable for long-term fixation. On the other hand, in the non-heated part, the coupling reaction does not occur and one or two of the above four components still exist in a state of isolation from the remaining components by the separation layer, so the part does not develop color. It remains in a state with long-term storage stability. As described above, the present invention has a great advantage in that it can provide a thermochromic recording material with improved storage stability.

The following are examples of materials that can be used in the present invention.

(1) Binders: - Starch and its derivatives, gelatin, casein, polyvinyl alcohol, carboxymethyl cellulose, hydroxyethyl cellulose,
One or two types of oil-based and water-based polymer compounds such as acrylamide (2) Coupler compounds: - As cyan color-forming couplers, α-naphthol and its derivatives, phenol and its derivatives, etc., as yellow color-forming couplers, acetate, etc. There are acylamide-type compounds represented by acetic anilide, diacylmethane-type compounds represented by dibenzoylmethane, aldehyde compounds represented by benzaldehyde and glutaraldehyde, and magenta coloring couplers.
Examples include pyrazolone type compounds represented by 1-phenyl-3-methyl-5-pyrazolone, acylacetonitrile type compounds represented by α-cyanoacetophenone, benzyl cyanide and derivatives thereof.

(3) P-phenylenediamine compound: -N,N-dimethyl-p-phenylenediamine, N,N-diethyl-p-phenylenediamine, 4-amino-N-ethyl-N-(β-hydroxyethyl )-aniline, 4-amino-3-
Methyl-N-diethylaniline, 4-amino-
Sulfates and hydrochlorides of 3-methyl-N-ethyl-N-(β-hydroxyethyl)-aniline, 4-amino-3-methyl-N-ethyl-N-(β-methanesulfonamidoethyl)-aniline, etc. There is.

(4) Base generating substances: - imidazole and its derivatives, amide compounds represented by urea or benzamide, guanidine compounds represented by guanidine, aniline compounds represented by aniline, etc., as well as sodium and potassium salts of organic acids. It can also be used as an agent to raise the pH of the system by heating.

(5) Reaction accelerator: − Ca, Mg, Al, Zn, Fe, Ni, Sn, pb, Cu,
Metal oxides, sulfides, halides, sulfates, nitrates, carbonates, such as Ag, Pt, Au, Co, Ti, etc.
There are organic acid salts, etc., and peroxides of organic compounds can also be used as reaction accelerators.

(6) Separation layer materials: - polyvinyl chloride, polyvinyl acetate, vinyl chloride/vinyl acetate copolymer, polyester, polystyrene, nylon, acrylic, acrylonitrile, polyamide, polyurethane, polyvinyl butyral, ethyl cellulose, cellulose acetate butyrate, polyvinyl alcohol,
A thermofusible polymer compound that loses separation performance by softening or melting upon heating, such as hydroxyethyl cellulose, can be used. Further, these may be solvent-based or water-based.

(7) Supports: - General papers such as high-quality paper and coated paper, laminated paper coated with synthetic polymer resin, synthetic paper, and films made of synthetic polymer compounds.

Furthermore, in the present invention, in addition to the above-mentioned materials, surfactants, thermofusible substances, organic and inorganic pigments, etc. can be used in combination in the system as required.

The amounts (weight ratio) of the binder, coupler compound, p-phenylenediamine compound, base generator and reaction accelerator used in the present invention are as follows. For 10 parts of binder, the coupler compound is usually 0.1 to 10 parts, preferably 2 to 4 parts, the p-phenylenediamine compound is usually 0.1 to 10 parts, preferably 2 to 4 parts, and the base generator is usually 40 parts. 10 to 20 parts, the reaction accelerator is usually water-soluble
0.1 to 10 parts, preferably 0.5 to 1.5 parts, and insoluble ones dispersed in fine particles, usually 5 to 50 parts, preferably 10 to 1.5 parts.
20 copies will be used.

Further, the coating amount of the recording layer of the present invention is usually 1 to 10 g/m 2 and preferably 1 to 10 g/m ² as a layer containing a recording material.
3 g/m ² , and the separation layer usually has a weight of 1 to 10 g/m ² , preferably 1 to 3 g/m ² .

The present invention will be specifically explained below using Examples. In the examples, parts refer to parts by weight, and % refers to % by weight.

Example 1 [Liquid A] 1.5 parts of N,N-diethyl-p-phenylenediamine sulfate 100 parts of polyvinyl alcohol (5% aqueous solution) The above composition was mixed with N,N-diethyl-p-phenylene via a stirrer. Solution A was prepared by stirring until the diamine was completely dissolved.

[Liquid B] Polyester 20 parts Toluene 80 parts The above composition was stirred using a stirrer until the polyester was completely dissolved to prepare Solution B.

[Liquid C]

α-Naphthol 1.4 parts Guanidine 5 parts Ferrous sulfate 0.5 parts Polyvinyl alcohol (5% aqueous solution) 100 parts The above composition was stirred with a stirrer until completely mixed and dissolved to prepare Solution C.

Next, the liquids A to C prepared as described above were sequentially applied to a polyethylene laminate paper (support) whose surface had been subjected to corona treatment to prepare a recording paper. To do this, first apply liquid A on the support so that the coating amount after drying is 3 g/m ² , dry it with air at 60°C (constant temperature), and then apply liquid B on the top surface as described above to 3 g/m 2 . After drying with ^air at 60° C., 3 g/m ² of liquid C was applied on the top surface as described above and drying with air at 60° C. to obtain recording paper. Next, this recording paper is 110
By heating for 1 second on a hot plate at .degree. C., a clear cyan colored layer was obtained. Separately, uncolored paper of the recording paper was stored for one month at 60° C. and 80% PH, but it was stable and satisfactory, with no background coloring at all.

Example 2 In Solution C of Example 1, 1-phenyl-3-methyl-5-pyrazolone was used instead of α-naphthol.
A recording paper was obtained in exactly the same manner as in Example 1, except that 1.7 parts were mixed. Next, this was heated on a hot plate at 110° C. for 1 second to obtain a clear magenta colored layer. Separately, uncolored paper of the recording paper was stored for a long period of one month at 60° C. and 80% PH, but it remained stable with no background coloration.

Example 3 A recording paper was obtained in exactly the same manner as in Example 1, except that 1.8 parts of acetoacetanilide was mixed in place of α-naphthol. Next, this was heated for 1 second on a hot plate at 110°C to obtain a clear yellow colored layer. Separately, uncolored paper of the recording paper was stored for a long period of one month under conditions of 60° C. and 80% PH, but it remained stable with no background coloring at all.

Example 4 [Liquid D] N,N-diethyl-p-phenylenediamine sulfate 1.5 parts Guanidine 5 parts Polyvinyl alcohol (5% aqueous solution) 100 parts The above composition was mixed with a stirrer until completely dissolved. The mixture was stirred to prepare Solution D.

[Liquid E]

Vinyl chloride/vinyl acetate copolymer 20 parts Toluene 80 parts The above composition was stirred using a stirrer until the vinyl chloride/vinyl acetate copolymer was completely dissolved.
A liquid was prepared.

[F liquid]

α-Naphthol 1.4 parts Ferrous sulfate 0.5 parts Polyvinyl alcohol (5% aqueous solution) 100 parts The above composition was completely mixed using a stirrer and stirred until dissolved to prepare Solution F.

The thus obtained liquids D to F were sequentially applied to polyethylene laminate paper whose surface had been subjected to corona treatment in the same manner as in Example 1 to prepare recording paper. Next, this recording paper was heated for 1 second on a hot plate at 110°C to obtain a clear cyan colored layer. Also, apart from this, uncolored paper of the recording paper
Although it was stored for a long period of one month under conditions of 60°C and 80% PH, it remained stable with no background coloration at all.

As explained above, in the present invention, a coupler compound contained in a recording layer formed on a support via a binder reacts with a p-phenylenediamine compound when the compound undergoes a coupling reaction with a p-phenylenediamine compound by heating. In a recording material containing four components, a base generating substance and a reaction accelerator capable of supplying sufficient base necessary for promotion, one or two of the components are made from the remaining components and an oil-based or water-based polymer compound. Since it has a multilayer structure separated by a separation layer, when the recording layer containing the four components comes into contact with thermal energy, any one or two of the recording materials (four components) are separated from the remaining components. As the separating layer softens or melts, the coupler compound and the p-phenylenediamine compound undergo a coupling reaction due to heating, and at the same time, the PH of the recording layer decreases. This, together with the presence of the reaction accelerator used in the mixture, has the effect of making the coupling reaction faster and in a shorter time, and also making the color development more concentrated.

The colored portion (for example, an image) once colored in this manner can withstand long-term fixation without fading, and has the effect of being stable.

Furthermore, in the present recording layer, in the non-contact portion that does not come into contact with thermal energy, any one or two of the four components still exist in a state of isolation from the remaining components via the separation layer. This part does not develop color and has the effect of remaining in a state of long-term storage stability (see Examples).

Therefore, thermochromic recording materials that can exhibit these effects simultaneously are highly valued as having improved the storage stability of conventionally known recording materials of this type, and have great practical benefits.

Claims (1)

[Claims] 1. A coupler compound contained in the constituent material of the recording layer formed on the support via a binder;
a P-phenylenediamine compound that reacts with a coupler compound to form a dye; a base generating substance for providing a pH range necessary for the coupler compound to initiate a reaction with the P-phenylenediamine compound; A recording material containing four components of a reaction accelerator that accelerates a reaction, in which one or two of the components are separated from the remaining component by a separation layer made of an oil-based or water-based polymer compound. A thermochromic recording material with improved storage stability characterized by: