JPH04310790A - Thermal recording material - Google Patents

Abstract

PURPOSE:To obtain a thermal recording material which is excellent in thermal stability of an image and satisfying characteristics such as surface powdering, a coloring property, coloring of white part. CONSTITUTION:In a thermal recording material containing a dye precursor which is ordinarily colorless or light colored and an electron acceptive compound which colors the dye precursor by reaction in heating, a compound as given by formula I is contained as the electron acceptive compound.

Description

Description: FIELD OF INDUSTRIAL APPLICATION The present invention relates to a heat-sensitive recording material, and more particularly to a heat-sensitive recording material with excellent image thermal stability. [0002] Heat-sensitive recording materials generally consist of an electron-donating, usually colorless or light-colored dye precursor and an electron-accepting compound (usually called a color developer) on a support. By heating with a thermal head, thermal pen, laser beam, etc., the dye precursor and color developer react instantaneously to obtain a recorded image.
No. 60, Japanese Patent Publication No. 45-14039, etc. Such heat-sensitive recording materials have the advantages of being able to record with relatively simple equipment, being easy to maintain, and producing no noise, and are used in various measurement recorders, facsimile machines, printers, and computer terminals. It is used in a wide range of fields, including machines, labels, and ticket vending machines. However, as the demand for heat-sensitive recording materials has increased significantly in recent years, it has become a problem that they are significantly inferior in image stability compared to other recording methods. The above color developer is generally bisphenol A [2,2
-bis(4-hydroxyphenyl)propane] is used because of its stable quality, low cost, and good color development. Images of heat-sensitive recording materials continue to fade over time even when stored under normal environmental conditions. In addition, white powder often precipitates on the image surface in parallel with color fading (usually referred to as powder blowing), but this phenomenon also significantly impairs image quality. For this reason, current heat-sensitive recordings have serious defects as recording materials, as images become difficult to distinguish or, in extreme cases, may disappear altogether if stored for a long period of time. One of the standard evaluation test items for heat-sensitive recording materials is a storage test under 60℃ conditions (
However, since discoloration is significantly accelerated under these conditions, it is thought that the low thermal stability of the color former is the cause. For the reasons mentioned above, in order to establish thermal recording materials in the market and further expand their use, it is necessary to improve the thermal stability of images and increase their reliability as recording materials. This has become an unavoidable technical issue. [0005] Various studies have been carried out to achieve this objective, and among them, a large number of proposals have been made regarding heat-sensitive recording materials using new color developers in place of bisphenol A. For example, JP-A-57-2108
No. 66, No. 58-82788, No. 58-132593
No. 59-118491, No. 59-187889, and No. 60-13852 disclose arylsulfonylphenol derivatives;
Publication No. 59-169884 proposes bis(4-hydroxyphenyl)sulfone derivatives. However, although heat-sensitive recording materials created based on these proposals have shown some improvement in the thermal stability of images, they are not practical enough in terms of powder blowing, color development, or coloration of white areas. The reality is that we have not yet achieved anything satisfactory. In particular, with regard to the coloring of white backgrounds, as the thermal stability of images improves, there is a tendency for the coloring to increase significantly over time or under the above heat resistance test conditions. This has become a major obstacle. SUMMARY OF THE INVENTION An object of the present invention is to use a specific new phenol compound as an electron-accepting compound to provide an image with excellent thermal stability, as well as powder blowing, color development, and The object of the present invention is to obtain a heat-sensitive recording material having a satisfactory level of characteristics such as coloration of white background. [Means for Solving the Problems] A heat-sensitive recording material containing a normally colorless or light-colored dye precursor and an electron-accepting compound that reacts with the dye precursor upon heating to cause the dye precursor to develop a color,
By containing the compound represented by Chemical Formula 1 as the electron-accepting compound, there is provided a heat-sensitive recording material which has excellent thermal stability of images and also has satisfactory levels of properties such as powder blowing, color development, and white background coloring. I was able to get In formula 1, R1 and R2 represent a hydrogen atom, a halogen atom, an alkyl group, an alkenyl group, or an alkoxy group, and R3 represents an aralkyl group or an aryl group which may have a substituent. When R3 has a substituent, the substituent is preferably a halogen atom, an alkyl group, or an alkoxy group. The compounds of the present invention may be used alone or in combination of two or more thereof. Specific examples of the compounds of the present invention are listed below, but the present invention is not limited thereto. (1) 4-hydroxy-4'-(benzyloxycarbonyloxy)diphenylsulfone (2) 2
, 2'-dimethyl-4-hydroxy-4'-(benzyloxycarbonyloxy)diphenylsulfone (3) 4-hydroxy-4'-(phenoxycarbonyloxy)diphenylsulfone (4) 4-hydroxy-4'-(4 -methylphenoxycarbonyloxy)diphenylsulfone (5) 4-hydroxy-4'-(4-chlorophenoxycarbonyloxy)diphenylsulfone (6) 4-hydroxy-4'-
(4-Methoxyphenoxycarbonyloxy)diphenylsulfone (7) 3,3'-dimethyl-4-hydroxy-4'-(phenoxycarbonyloxy)diphenylsulfone (8) 3,3'-diallyl-4-hydroxy-4
'-(phenoxycarbonyloxy)diphenylsulfone (9) 3,3'-dichloro-4-hydroxy-4'-
(benzyloxycarbonyloxy)diphenylsulfone (10) 2,2'-dimethoxy-4-hydroxy-4'
-(benzyloxycarbonyloxy)diphenylsulfone The compound of the present invention can be produced very easily using commercially available materials according to known carbonate synthesis methods. That is, in the presence of a basic substance, the corresponding bis(
The compounds of the present invention are obtained by reacting 4-hydroxyaryl) sulfone with chloroformate. Next, a specific method for producing the heat-sensitive recording material according to the present invention will be described. The heat-sensitive recording material according to the present invention generally has an electron-donating, usually colorless or light-colored dye precursor and an electron-accepting compound as main components on a support, and these are dispersed and coated in a binder to form a heat-sensitive recording layer. By heating with a thermal head, thermal pen, laser beam, etc., a dye precursor and an electron-accepting compound react instantaneously to obtain a recorded image.
It is disclosed in Publication No. 4039 and the like. Further, pigments, sensitizers, antioxidants, anti-sticking agents and the like are added to the heat-sensitive recording layer as necessary. The dye precursor used in the heat-sensitive recording material according to the present invention is not particularly limited as long as it is generally used in pressure-sensitive recording paper or heat-sensitive recording paper. Specific examples include (1) triarylmethane compound: 3,3-bis(p
-dimethylaminophenyl)-6-dimethylaminophthalide (crystal violet lactone), 3,3-bis(p-dimethylaminophenyl)phthalide, 3-(p
-dimethylaminophenyl)-3-(1,2-dimethylindol-3-yl)phthalide, 3-(p-dimethylaminophenyl)-3-(2-methylindole-3-
yl)phthalide, 3-(p-dimethylaminophenyl)
-3-(2-phenylindol-3-yl)phthalide, 3,3-bis(1,2-dimethylindol-3-yl)-5-dimethylaminophthalide, 3,3-bis(1
,2-dimethylindol-3-yl)-6-dimethylaminophthalide, 3,3-bis(9-ethylcarbazol-3-yl)-5-dimethylaminophthalide, 3,3
-bis(2-phenylindol-3-yl)-5-dimethylaminophthalide, 3-p-dimethylaminophenyl-3-(1-methylpyrrol-2-yl)-6-dimethylaminophthalide, etc. (2) Diphenylmethane compound: 4,4
'-bis(dimethylaminophenyl)benzhydrylbenzyl ether, N-chlorophenylleucoauramine, N-2,4,5-trichlorophenylleucoauramine, etc. (3) Xanthene compound: Rhodamine B
Anilinolactam, Rhodamine B-p-chloroanilinolactam, 3-diethylamino-7-dibenzylaminofluorane, 3-diethylamino-7-octylaminofluorane, 3-diethylamino-7-phenylfluorane, 3-diethylamino -7-chlorofluorane, 3
-diethylamino-6-chloro-7-methylfluorane, 3-diethylamino-7-(3,4-dichloroanilino)fluorane, 3-diethylamino-7-(2-chloroanilino)fluorane, 3-diethylamino-6-methyl -7-anilinofluorane, 3-(N-ethyl-N
-tolyl)amino-6-methyl-7-anilinofluorane, 3-piperidino-6-methyl-7-anilinofluorane, 3-(N-ethyl-N-tolyl)amino-6-methyl-7- Phenethylfluorane, 3-diethylamino-7-(4-nitroanilino)fluorane, 3-dibutylamino-6-methyl-7-anilinofluorane, 3-
(N-methyl-N-propyl)amino-6-methyl-7
-anilinofluorane, 3-(N-ethyl-N-isoamyl)amino-6-methyl-7-anilinofluorane,
3-(N-methyl-N-cyclohexyl)amino-6-
Methyl-7-anilinofluorane, 3-(N-ethyl-
N-tetrahydrofuryl)amino-6-methyl-7-anilinofluorane, etc., (4) Thiazine compounds: benzoylleucomethylene blue, p-nitrobenzoylleucomethylene blue, etc., (5) Spiro compounds :3-methylspirodinaphthopyran, 3-ethylspirodinaphthopyran, 3
, 3'-dichlorospirodinaphthopyran, 3-benzylspirodinaphthopyran, 3-methylnaphtho-(3-methoxybenzo)spiropyran, 3-propylspirobenzopyran, etc., which may be used alone or in combination. The above can be used in combination. The compound of the present invention can also be used in combination with other electron-accepting compounds. In this case, the electron-accepting compound may be any acidic substance that is generally used in heat-sensitive recording materials, such as polyvalent metals such as phenol derivatives, aromatic carboxylic acid derivatives, aryl-substituted thiourea derivatives, and zinc salts of organic compounds. Salt can be used. Binders used in heat-sensitive recording materials include starches, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin, casein, polyvinyl alcohol, modified polyvinyl alcohol, sodium polyacrylate, acrylic acid amide/
Water-soluble acrylic ester copolymers, acrylic amide/acrylic ester/methacrylic acid ternary copolymers, alkali salts of styrene/maleic anhydride copolymers, alkali salts of ethylene/maleic anhydride copolymers, etc. glue,
Examples include latex such as polyvinyl acetate, polyurethane, polyacrylic ester, styrene/butadiene copolymer, acrylonitrile/butadiene copolymer, methyl acrylate/butadiene copolymer, and ethylene/vinyl acetate copolymer. In addition, as sensitizers for further improving sensitivity, waxes such as N-hydroxymethylstearamide, stearamide, palmitic acid amide, naphthol derivatives such as 2-benzyloxynaphthalene, p-benzyl Biphenyl, biphenyl derivatives such as 4-allyloxybiphenyl, 1,2-bis(3-methylphenoxy)ethane, 2,2'-bis(4-methoxyphenoxy)diethyl ether, bis(4-methoxyphenyl)ether, etc. Polyether compounds, carbonic acid or oxalic acid diester derivatives such as diphenyl carbonate, dibenzyl oxalate, bis(p-methylbenzyl) oxalate, etc. can be added in combination. Examples of pigments include diatomaceous earth, talc, kaolin, calcined kaolin, calcium carbonate, magnesium carbonate, titanium oxide, zinc oxide, silicon oxide, aluminum hydroxide, urea-formalin resin, and the like. In addition, higher fatty acid metal salts such as zinc stearate and calcium stearate, waxes such as paraffin, oxidized paraffin, polyethylene, polyethylene oxide, stearic acid amide, castor wax, etc. are used for the purpose of preventing head wear and sticking. , dispersants such as sodium dioctyl sulfosuccinate, ultraviolet absorbers such as benzophenone and benzotriazole,
Furthermore, surfactants, fluorescent dyes, etc. are added as necessary. As the support used in the present invention, paper is mainly used, but nonwoven fabric, plastic film, synthetic paper, metal foil, etc., or a composite sheet of a combination of these can also be used as desired. In addition, in the production of heat-sensitive recording materials, an overcoat layer is provided to protect the heat-sensitive recording layer, and an undercoat layer consisting of a single layer or multiple layers of pigment or resin is provided between the heat-sensitive recording layer and the support. Various known techniques can be used. The coating amount of the heat-sensitive recording layer is determined by the amounts of the dye precursor and color developer, which are color-forming components, and is usually 0.50%.
1 to 1.0 g/m2 is suitable. The compound of the present invention is added in an amount of 5 to 400% by weight, but preferably 20 to 300% by weight, based on the dye precursor. [Example] Next, the present invention will be explained in more detail with reference to Examples. Note that all parts and percentages shown below are based on weight. Example 1 (A) Creation of heat-sensitive coating liquid Dye precursor 3-dibutylamino-6-methyl-7
- 35 parts of anilinofluorane and 80 parts of a 2.5% polyvinyl alcohol aqueous solution were ground in a ball mill for 24 hours to obtain a dye dispersion. Then 4-hydroxy-4'-(
50 parts of benzyloxycarbonyloxy) diphenyl sulfone was ground with 120 parts of a 2.5% polyvinyl alcohol aqueous solution in a ball mill for 24 hours to obtain a dispersion of the compound of the present invention. After mixing these two types of dispersions, the following were added and mixed well while stirring to prepare a heat-sensitive coating liquid. Calcium carbonate 40% aqueous dispersion
130 parts 10% polyvinyl alcohol aqueous solution 1
60 parts 40% aqueous dispersion of zinc stearate
50 parts water

350 copies 003
0] (B) Preparation of heat-sensitive coated paper A coating liquid consisting of the following composition was applied to a base paper with a basis weight of 40 g/m2 as a solid content of 9 g.
/m2 and dried to prepare heat-sensitive coated paper. calcined kaolin
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Styrene-butadiene latex 50% aqueous dispersion
Part 24 Water

200 copies (C) Preparation of heat-sensitive recording material The heat-sensitive coating liquid prepared in (A) was applied onto the surface of the heat-sensitive coating paper prepared in (B) so that the solid content was coated at 3.3 g/m2. It was smeared and dried to create a heat-sensitive recording material. Comparative Example 1 A heat-sensitive recording material was prepared in exactly the same manner as in Example 1 except that bisphenol A was used instead of 4-hydroxy-4'-(benzyloxycarbonyloxy)diphenylsulfone in Example 1. . Comparative Example 2 The procedure was carried out in exactly the same manner as in Example 1 except that bis(4-hydroxyphenyl)sulfone was used instead of 4-hydroxy-4'-(benzyloxycarbonyloxy)diphenylsulfone in Example 1. A thermosensitive recording material was created. Comparative Example 3 Same as Example 1 except that 4-hydroxy-4'-isopropyloxydiphenylsulfone was used instead of 4-hydroxy-4'-(benzyloxycarbonyloxy)diphenylsulfone in Example 1. A thermosensitive recording material was prepared in the same manner. "Evaluation" The heat-sensitive recording materials obtained in Example 1 and Comparative Examples 1 to 3 were calendered so that the Bekk smoothness of the heat-sensitive coated surface was 400 to 500 seconds, and then subjected to a facsimile test made by Okura Electric Co., Ltd. A printing test was conducted using the machine TH-PMD. Printing was carried out by using a thermal head with a dot density of 8 dots/mm and a head resistance of 215 Ω, a head voltage of 12 V, and a pulse width of 1.0 milliseconds, and the color density was measured with a Macbeth RD-918 reflection densitometer. [0036] The printed sample thus obtained was heated to 60°C.
The sample was stored in a thermostatic chamber controlled at 100° C., and the change in color density in the image area over time and the color density in the white background area were measured using the densitometer described above. Powder blowing was evaluated by visually observing and determining the degree of whitening of the image area due to the precipitation of white powder (○: no whitening, ×: severe whitening). These results are shown in Table 1. [Table 1] [Effects of the Invention] As is clear from the examples, the heat-sensitive recording material of the present invention has excellent image thermal stability, is less likely to cause powder blowing, and is reliable as a recording material. has improved significantly. On the other hand, the color development and the coloring of the white background area are also within the permissible range, indicating that this is a heat-sensitive recording material with extremely high practical utility value.

Claims (1)

[Claims] Claim 1: A heat-sensitive recording material containing a normally colorless or light-colored dye precursor and an electron-accepting compound that reacts with the dye precursor upon heating to cause the dye precursor to develop a color, wherein the electron-accepting compound is represented by the following formula 1. A heat-sensitive recording material characterized by containing a compound that [Formula 1] (R1 and R2 are hydrogen atoms, halogen atoms, alkyl groups,
It represents either an alkenyl group or an alkoxy group, and R3 represents an alkyl group or an aryl group which may have a substituent. )