JPH025595B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a heat-sensitive recording material, and more particularly, to a heat-sensitive recording material that has excellent color development during high-speed recording and excellent stability of colored images. Heat-sensitive recording materials that utilize a heated color-forming reaction between colorless dyes, which are usually colorless or light-colored, and color developers (phenols, organic acids, etc.)
It has been published in publications such as Japanese Patent Publication No. 45-14039 and Japanese Patent Application Laid-Open No. 48-27736, and has been widely put into practical use. In general, heat-sensitive recording materials are produced by pulverizing and dispersing a color-forming colorless dye and a color developer such as a phenolic substance into fine particles, and then mixing the two to form a binder, filler, sensitivity enhancer, lubricant, and other auxiliaries. A coating liquid obtained by adding an agent is applied to a support such as paper or film, and a color recording is obtained by an instantaneous chemical reaction caused by heating. A thermal printer, facsimile, or the like having a built-in thermal head is used to heat such a heat-sensitive recording material to develop color. In addition, compared to other recording materials, such recording materials can produce records in a relatively short time without complicated processing such as development and fixing, and do not generate noise.
Because it has the advantage of being relatively inexpensive, it is widely used not only for copying books and documents, but also as a recording material for various information and measuring instruments such as electronic computers, facsimiles, telex, and medical measuring instruments. ing. However, in recent years, with the development of society, there has been a growing demand for faster recording, so there is a strong desire not only to increase the speed of the recording apparatus itself, but also to develop recording materials that can meet this demand. Conventionally, such heat-sensitive recording materials for high-speed recording were disclosed in Japanese Patent Application Laid-Open No.
No. 39139, JP-A-53-26139, JP-A-53-5636
As stated in publications such as JP-A-53-11036,
It has been proposed that heat-melting substances with low melting points, such as various waxes, fatty acid amides, alkylated biphenyls, substituted biphenyl alkanes, coumarin compounds, and diphenylamines, are added to the heat-sensitive coloring layer as sensitizers or melting point depressants. ing. However, in the method of adding a sensitizer, it is necessary to melt the sensitizer before the color reaction occurs, so in high-speed recording, it is difficult to obtain sufficient thermal responsiveness to minute amounts of heat in short pulses. However, since the fusible substance in the color forming layer melts, problems such as adhesion of residue on the thermal head, smearing, trailing, and ghosting are likely to occur. Furthermore, even under storage conditions of high temperature or high humidity, background coloring (fogging) occurs over time, and the contrast of recorded images often deteriorates. Therefore, it is desirable to have a heat-sensitive recording material for high-speed recording without the addition of such a sensitizer or melting point depressant. For this purpose, it is necessary to use a color developer with a low melting point, and
It is essential to use phenolic substances that have a great ability to color colorless dyes. However, conventionally known phenolic substances with low melting points as color developers for heat-sensitive recording materials, such as 4-t-butylphenol (melting point 94-99°C), α-naphthol (melting point 95-96°C), β- Naphthol (melting point 119~
When monophenols such as 122℃) are used, the storage stability and stability of the heat-sensitive recording material are poor, and the background color gradually develops even at room temperature, as well as a strong so-called phenol odor, making it impractical. . Also,
In Japanese Patent Publication No. 54-12819, 2,2-bis(4'-hydroxyphenyl) normal hexane (melting point 99-103°C) is used;
The publication discloses that by using 1,1-bis(4'-hydroxyphenyl)alkane (the number of carbon atoms in the alkane is 3 to 13), a heat-sensitive recording material with a low melting point, stability, and good color development can be made. However, these substances are difficult to synthesize and have problems in terms of economy and availability. Furthermore, JP-A-56-144193 discloses that lower alkyl esters or benzyl esters of p-hydroxybenzoic acid are effective as high-sensitivity color developers; It fades naturally, and
It has the disadvantage that white powder precipitates in the coloring area. However, among the above-mentioned low-melting point color developers, p-hydroxybenzoic acid esters are the best in terms of color development during high-speed recording, whiteness of the background, economical efficiency, and availability. If the defects such as decolorization and precipitation of white powder are improved, it will become ideal as a heat-sensitive recording material for high-speed recording. Therefore, the present inventors have conducted intensive research to develop a heat-sensitive recording material that has excellent color development during high-speed recording, has excellent storage stability, and has excellent stability of colored images. Hydroxybenzoic acid esters [general formula ()

[Formula] (wherein R represents an alkyl group having 1 to 4 carbon atoms or a benzyl group or phenyl group which may have a substituent)] and a colorless dye that is usually colorless or light colored. ,
It has been found that the objective can be achieved by further adding a specific compound. The present invention was completed based on this knowledge. That is, the present invention provides a heat-sensitive recording material in which a heat-sensitive coloring layer is provided on a support, wherein the heat-sensitive recording material contains at least one color-forming colorless dye that is usually colorless or light-colored and is represented by the general formula () above. At least one of the compounds and the following general formula () (In the formula, R ₁ , R ₂ , R ₃ are hydrogen or have 1 to 4 carbon atoms.
represents an alkyl group. However, R ₁ , R ₂ , and R ₃ do not become hydrogen at the same time. ) It is characterized by containing at least one kind of compound represented by. Using the compound of the general formula () in combination,
The reason why p-hydroxybenzoic acid esters prevent natural decolorization and precipitation of white powder, which are disadvantages of p-hydroxybenzoic acid esters, is not clear, but it is probably because they melt when heated and cause a coloring reaction. Recrystallization of p-hydroxybenzoic acid esters due to a decrease in temperature is thought to be the cause of natural decolorization of the image area and precipitation of white powder, and this is caused by the combined use of the compound of general formula () above. This is thought to be because crystallization is inhibited as a result of maintaining the supercooled state. According to the present invention, a heat-sensitive recording material having the following excellent properties can be obtained. (1) Highly sensitive heat-sensitive recording sheets can be produced without the need for sensitizers or melting point depressants. In particular, because it has excellent thermal responsiveness, high-density, clear images can be obtained even in high-speed, high-density recording. (2) There are no problems such as adhesion of residue or states king to the thermal head, and the recording suitability is excellent. (3) By coating thin base paper or film, excellent copying paper for infrared and strobe flash type thermal copying machines can be obtained. (4) It is possible to reduce the amount of coating and improve production efficiency. (5) Stable colored images, natural decolorization, and no white powder precipitation. (6) There is almost no discoloration of the background over time, and an extremely high quality heat-sensitive recording material can be obtained. Examples of normally colorless to light-colored color-forming colorless dyes used in the present invention are shown below, but the invention is not limited thereto. That is, 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide, 3,
3-bis(p-dimethylaminophenyl) phthalide, 3-(p-dimethylaminophenyl)-3-
Triallylmethane dyes such as (1,2-dimethylindol-3-yl)phthalide; 4,4'-bis-dimethylaminobenzhydrylbenzyl ether, N-halophenyl-leukoolamine, N-
Diphenylmethane dyes such as 2,4,5-trichlorophenyl leuco auramine; Thiazine dyes such as benzoyl leucomethylene blue and p-nitrobenzyl leucomethylene blue; 3-methyl-
Spiro-dinaphthopyran, 3-ethyl-spiro-
Spiro dyes such as dinaphthopyran and 3-propyl-spiro-dibenzopyran; 2-anilino-3-
Methyl-6-(N-ethyl-p-toluidino)fluoran, 2-p-toluidino-3-methyl-6
-(N-ethyl-p-toluidino)fluorane,
3-diethylamino-6-methyl-7-anilinofluorane, 3-diethylamino-7-(2-carbomethoxyanilino)fluorane, 3-(N-
Cyclohexyl-N-methylamino)-6-methyl-7-anilinofluorane, 3-pyrrolidino-
6-methyl-7-anilinofluorane, 3-piperidino-6-methyl-7-anilinofluorane,
3-diethylamino-6-methyl-7-chlorofluorane, 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide, 3-
Diethylamino-6-methyl-7-xylidinofluorane, 3-diethylamino-7-chloroanilinofluorane, 7-diethylamino-3-chlorofluoran, 7-diethylamino-3-chloro-2-methylfluorane, 3 -Methyl-6-(N
-p-tolyl-N-ethylamino)fluorane,
Examples include fluoran dyes such as 3-pyrodino-6-methyl-7-p-butylanilinofluorane and 2-phenylamino-3-methyl-6-(N-ethyl-N-p-tolyl)aminofluorane. . Next, p-hydroxybenzoic acid esters represented by the general formula () will be illustrated. Next, compounds represented by the general formula () are illustrated. The compound represented by the general formula () used in the present invention may be used in an amount of 100 to 700 parts by weight per 100 parts by weight of the colorless dye.
It is preferable to use parts by weight. Further, the compound represented by the general formula () is preferably used in an amount of 10 to 200 parts by weight per 100 parts by weight of the compound represented by the general formula (). In addition, in the heat-sensitive color forming layer of the present invention, various commonly used binders may be used as appropriate in order to bond and support the heat-sensitive color forming layer on the support, such as polyvinyl alcohol, methoxy cellulose, hydroxyethyl cellulose, Binds water-soluble materials such as carboxymethylcellulose, polyvinylpyrrolidone, polyacrylamide, polyacrylic acid, starch, gelatin, etc., or water-based emulsions such as polystyrene, vinyl chloride-vinyl acetate copolymer, polybutyl methacrylate, etc. It can be used as an agent. In addition, if necessary, conventional auxiliary additives such as fine powders such as calcium carbonate, silica, alumina, magnesia, talc, titania, barium sulfate, and aluminum stearate may be added to the heat-sensitive coloring layer to develop color. Image clarity can be improved. The heat-sensitive recording material of the present invention is produced by coating a heat-sensitive coloring layer forming coating solution containing the above-mentioned components on a suitable support such as paper, synthetic paper, or plastic film.
It is produced by drying and is used in various recording fields, especially as a heat-sensitive recording material for high-speed recording. Next, the present invention will be explained in more detail with reference to Examples. Note that all parts here are parts by weight. Example 1 A mixture having the following composition was separately ground and dispersed for two days using a magnetic ball mill to obtain liquid [A],
[B] solution, [C] solution, and [D] solution were prepared. [A] Liquid 3-(N-cyclohexyl-N-methylamino)-6-methyl-7-anilinofluorane
20 parts 10% hydroxyethyl cellulose aqueous solution 20 parts Water 60 parts [B] Liquid p-hydroxybenzoic acid benzyl ester 20 parts 10% hydroxyethyl cellulose aqueous solution 20 parts Water 60 parts [C] Liquid bis(3-tert-butyl-4-hydroxy- 6-
Methylphenyl) sulfide 20 parts 10% hydroxyethylcellulose aqueous solution 20 parts Water 60 parts [D] Liquid calcium carbonate 20 parts 5% methylcellulose aqueous solution 20 parts Water 60 parts Using [A] to [D] solutions obtained as above , prepare a coating liquid for forming a heat-sensitive coloring layer with the following composition, apply it to commercially available high-quality paper with a standard basis weight of 50 g/m ² using a selected wire bar so that the dry coating amount is 4 to 5 g/m ² , and dry. The heat-sensitive recording sheet (a) of the present invention was then calendered so that the surface smoothness of the heat-sensitive coloring layer was 500 to 600 seconds in terms of Beck smoothness. Coating liquid composition for forming a thermosensitive coloring layer [A] 10 parts of liquid [B] 30 parts of liquid [C] 10 parts of liquid [D] 30 parts of liquid 20% of isobutylene-maleic anhydride copolymer
Alkaline aqueous solution 10 parts Example 2 Thermal sensitivity was carried out in the same manner as in Example 1 except that the following liquid [E] was used instead of liquid [B] in Example 1, and the following liquid [F] was used instead of liquid [C]. I made a record sheet (b). [E] Liquid p-hydroxybenzoic acid isobutyl ester
20 parts 10% hydroxyethyl cellulose aqueous solution 20 parts water 60 parts [F] Liquid bis(3-methyl-4-hydroxyphenyl)
Sulfide 20 parts 10% hydroxyethyl cellulose aqueous solution 20 parts Water 60 parts Example 3 A thermosensitive recording sheet (c) was prepared in the same manner as in Example 1 except that the following liquid [G] was used instead of liquid [C] in Example 1. I made it. [G] Liquid bis(3,5-dimethyl-4-hydroxyphenyl) sulfide 20 10% hydroxyethyl cellulose aqueous solution 20 parts water 60 parts Example 4 Use the following solution [H] instead of solution [B] in Example 1. A thermosensitive recording sheet (d) was prepared in the same manner as in Example 1 except that the following was used. [H] Liquid p-hydroxybenzoic acid o-chlorobenzyl ester 20 parts 10% hydroxyethyl cellulose aqueous solution 20 parts Water 60 parts Example 5 The same procedure was carried out except that the following solution [] was used instead of solution [B] in Example 1. A thermosensitive recording sheet (e) was prepared in the same manner as in Example 1. [I] Liquid p-hydroxybenzoic acid m-methylbenzyl ester 20 parts 10% hydroxyethyl cellulose aqueous solution 20 Liquid water 60 parts Example 6 Except for using the following [J] solution instead of [B] solution in Example 1. A thermosensitive recording sheet (f) was prepared in the same manner as in Example 1. [J] Liquid p-hydroxybenzoic acid p-isopropylbenzyl ester 20 parts 10% hydroxyethyl cellulose aqueous solution 20 parts Water 60 parts Example 7 Except that the following [K] solution was used instead of [B] solution in Example 1. A thermosensitive recording sheet (g) was prepared in the same manner as in Example 1. [K] Liquid p-hydroxybenzoic acid phenyl ester 20 parts 10% hydroxyethyl cellulose aqueous solution 20 parts Water 60 parts Comparative example Example 1 [A] solution, [B] solution, [C] solution, [D]
Example 1 except that the composition of the liquid was changed as follows.
A thermosensitive recording sheet (h) was made in the same manner as above. Thermosensitive coloring layer solution [A] Solution 10 parts [B] Solution 40 parts [C] Solution 0 parts [D] Solution 30 parts 20% of isobutylene-maleic anhydride copolymer
Alkaline aqueous solution 10 parts The heat-sensitive recording materials (a) to (h) obtained as above are printed at high speed using a G-prototype facsimile machine (manufactured by Ricoh Co., Ltd.) (printing speed: 0.94 msec, applied voltage:
20V), and the color density and background density were measured using Macbeth Densitometer RD-514 (manufactured by Macbeth, USA). Further, after this printed sample was left indoors for one week, the density of the colored area and the density of the background area were measured, and the state of precipitation of white powder was also observed. The results are shown in Table-1. As is clear from Table 1, the heat-sensitive recording material (heat-sensitive recording sheet) of the present invention has excellent color development during high-speed recording, and the stability of colored images is also extremely high. In addition, there is almost no coloration of the background over time, which is common when different color developers are mixed, and in practical use,
It can be seen that this is an extremely useful heat-sensitive recording material.

【table】

Claims (1)

[Scope of Claims] 1. At least one type of normally colorless or light-colored color-forming colorless dye, at least one type of compound represented by the following general formula (), and at least one type of compound represented by the following general formula (). 1. A heat-sensitive recording material, characterized in that a heat-sensitive coloring layer containing: is formed on a support. (In the formula, R represents an alkyl group having 1 to 4 carbon atoms, or a benzyl group or phenyl group that may have a substituent.) (In the formula, R ₁ , R ₂ , R ₃ are hydrogen or have 1 to 4 carbon atoms.
represents an alkyl group. However, R ₁ , R ₂ , and R ₃ do not become hydrogen at the same time. )