JPH0117875B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a thermal recording paper consisting of a color-forming substance and a phenolic color developer that causes the color-forming substance to develop color when heated. The present invention provides a heat-sensitive recording paper that is significantly prevented from deterioration. Conventionally known color developers used in so-called dye-coloring thermosensitive recording papers in which the leuco base of triphenylmethane dyes or fluoran dyes are color-forming substances are disclosed in Japanese Patent Publications No. 3680-1983 and Japanese Patent Publication No. 3680-1973.
As seen in No. 14039, the melting point is usually 200.
It is below ℃. The reason for this is that when the melting point of the color developer is high, the thermal energy given to the recording paper is insufficient, resulting in the disadvantage that the density of the thermally developed color is low and cannot be used practically. Therefore, the color developers used in this type of thermal recording paper are mostly limited to those with a melting point of 200°C or less, and the one currently in practical use is 4,4'-isopropylidene diphenol (bis). Phenol A, melting point 156
°C) is well known. Furthermore, with this type of heat-sensitive thermal recording paper, the color-forming substance and the color-developing substance dissolve due to contact with or penetration of various organic solvents, or the color-developing substance dissolves and a color-forming reaction progresses, so the white paper area becomes colored. This has disadvantages in that it stains the recording paper, and that once heated, the color fades, making it difficult to read. Currently, thermal recording paper is used, for example, for facsimiles, thermal printers, thermal pen recording, and vending tickets, but due to the above-mentioned drawbacks, there are various restrictions on the use and storage of thermal recording paper. occurs. For example, vinyl chloride resin is blended with large amounts of plasticizers such as dibutyl phthalate and dioctyl phthalate during the molding process, so if a film made of this resin is stored with heat-sensitive recording paper in contact, the plasticizer will migrate. It is known that white paper parts become colored over time, and areas that were once colored by heat fade and become difficult to read. When a phenolic resin is used to overcome these drawbacks, the plasticizer resistance of the colored part is good, but the blank part develops color and cannot be used. In addition, generally known phenolic color developers and color-forming substances have drawbacks such as insufficient plasticity resistance in the color-forming part and insufficient color density during thermal color development. There is. As a result of various studies regarding the above-mentioned drawbacks, the present inventors determined that 4,4'-dihydroxydiphenyl sulfone (bisphenol S, melting point 235-250°C) is used as a color developer in the heat-sensitive layer, which is basically composed of a color-forming substance and a color developer. )
It has been found that by using a thermosensitive layer and further mixing a heat-soluble substance into the heat-sensitive layer, it has a coloring density sufficient for practical use, and deterioration of the white paper area and the coloring area due to plasticizers is significantly prevented. . It has also been found that by providing a layer consisting of bisphenol S and a water-soluble binder between the heat-sensitive layer and the support, deterioration of the white paper area and the colored area due to the plasticizer can be further prevented. That is, the present invention provides a heat-sensitive recording paper with improved plasticizer resistance, which is characterized by forming a heat-sensitive layer basically consisting of a color-forming substance, bisphenol S, and a heat-soluble substance on a support. be. Even when the thermal recording paper of the present invention is stored in a film made of vinyl chloride resin, the white part of the thermal recording paper does not develop color, and even the areas that are once colored by heat are preserved well. Among thermal recording paper,
It has also become possible to use it in cases such as coupon tickets and commuter passes, which are generally inserted into a vinyl chloride resin film or the like for a long period of time. Embodiments of the present invention will be described in detail. The chromogenic substance and bisphenol S used in the invention are dispersed in powder form in the aqueous solution of the binder. In this case, the dispersed particles are made into particles as small as possible using a grinder such as a ball mill, specifically 5 μm.
It is desirable to grind the particles to the following particle size. In addition, if necessary, the heat-soluble substance and bisphenol S are dispersed together in powder form in an aqueous binder solution, and either pulverized to a particle size of 5μ or less using the method described above, or directly applied to the heat-sensitive layer. Mix inside. Furthermore, fillers such as talc and clay or lubricants can be added to prevent the coated material from sticking to the heating head during thermal coloring. Examples of the thermosoluble substances used in the present invention include waxes such as animal and vegetable waxes, polyethylene waxes, and synthetic waxes, higher fatty acids, and higher fatty acid amides, and further include calcium stearate, zinc stearate, and the like. These thermosoluble substances must be solid at room temperature, and preferably have a melting point of 65°C or higher. The optimum amount of thermofusible material used in the present invention is between about 1 weight percent and 50 weight percent of total solids. Particularly good results are obtained between 5 and 20 weight percent. If the amount of this heat-soluble substance added is small, the density during thermal coloring will be low, and if it is too large, the density during thermal coloring will be effective, but it may cause phenomena such as blurring of the recorded image and adhesion of sticky substances to the heat-generating head. It appears and I don't like it. Examples of color-forming substances used in the present invention include crystal violet lactone, malachite green lactone, 3,3'-bis(paradimethylaminophenyl)-6-aminophthalide, and 3,3'-bis(paradimethylaminophthalide). enyl)-6-(paratoluenesulfonamido)phthalide, 3-diethylamino-7-(N-methylanilino)fluoran, 3
-diethylamino-7-(N-methyl-para-toluidine)fluoran, 3-dimethylamino-6
-methoxyfluorane, 3-diethylamino-7
-Chlorfluorane, 3-diethylamino-6-
Methyl-7-chlorofluorane, 3-diethylamino-7-phenylfluorane, 3-morpholino-5,6-benzofluorane, 3-diethylamino-5-methyl-7-dibenzylaminofluorane, 3-diethylamino -7-benzylaminofluorane, 3-diethylamino-7,8-benzofluorane, 3-cyclohexylamino-6-
Chlorfluorane, N-phenylrhodamine B lactam, acidrhodamine B sultone, benzo-
Examples include β-naphthospiropyran, 2-methyl-spiropinaphthopyran, 1,3,3-trimethyl-6'-chloro-8'-methoxy-indolinobenzospiropyran. In the present invention, since the above-mentioned three components, namely bisphenol S, color-forming substance, and heat-soluble substance, are dispersed and coated on a support such as paper, a binder is required to bind each component. Generally known water-soluble binders are suitable for this binder, specifically hydroxyethyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, starch, polyacrylic acid, polyacrylamide, styrene-maleic acid copolymer, styrene- Examples include butadiene latex. Next, examples will be described to further specifically explain the present invention. In this specification, all "parts" are "parts by weight."
shall represent. Example 1 Part A 3-diethylamino-7-chlorofluorane 1 part 5% polyvinyl alcohol aqueous solution 1 part Water 2.2 parts Part B 4,4'-dihydroxydiphenyl sulfone 5 parts Calcium stearate 0.5 part Fatty acid amide S (manufactured by Nitto Chemical Co., Ltd.) Stearamide) 5 parts 5% polyvinyl alcohol aqueous solution 10.5 parts Water 21.3 parts After grinding both A and B separately in a ball mill for 2 days, both A and B and 15% oxidized starch aqueous solution 66
and 26 parts of a 40% calcium carbonate dispersion were thoroughly mixed to make a heat-sensitive coating liquid, and the coating liquid was coated on high-quality paper with a basis weight of 160 g/m ² so that the coating amount after drying was approximately 7 g/m ² . It was coated and dried to produce heat-sensitive recording paper. Further, as a control example, the following solution was used instead of Solution B in Example 1. Solution C 4,4'-isopropylidene diphenol 5 parts Calcium stearate 0.5 parts Fatty acid amide S (Nitto Chemical stearamide) 5 parts 5% polyvinyl alcohol aqueous solution 10.5 parts Water 21.3 parts Both solutions A and C were prepared in Example 1. A similar process was carried out to obtain thermal recording paper. After thermally printing each of the two types of thermal recording paper obtained by the above method using a thermal facsimile machine, Oki FAX 7000 (trade name, manufactured by Oki Electric Co., Ltd.), a commercially available soft chloride was applied to the thermal coloring surface. A vinyl resin film was brought into contact and treated in a dryer at 45°C for 48 hours, after which the density of the thermally printed area and the blank area was measured. Note that this vinyl chloride resin film contains 30% by weight of dioctyl phthalate as a plasticizer. The results are shown in Table-1.

[Table] As can be seen from Table 1, the thermal paper of the present invention has a markedly improved density retention rate in the thermally printed area due to the PVC film treatment, and is also superior to the control example in terms of whiteness reduction in the white paper area. As a result, the storage stability as a thermal paper has been improved. Example 2 Fatty acid amide S5 in liquid B in Example 1
The same treatment as in Example 1 was carried out except that 2.5 parts of fatty acid amide S and 2.5 parts of methylolamide (methylolated stearic acid amide, manufactured by Nippon Kasei Co., Ltd.) were used. When we conducted a plasticizer test, we found that the density of the thermal printing area after PVC film treatment was 1.20 before treatment.
It showed a good result of 0.97 (concentration residual rate 81%).

Claims (1)

[Claims] 1. In a heat-sensitive layer consisting of a basically colorless or light-colored color-forming substance provided on a support and a phenolic color developer that causes the color-forming substance to develop color when heated,
A heat-sensitive recording paper which uses 4,4'-dihydroxydiphenyl sulfone as a color developer and further mixes a heat-soluble substance into the heat-sensitive layer to prevent deterioration of the white paper area and the colored area due to plasticizers.