JPH0231678B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a heat-sensitive recording material, and more specifically, a heat-sensitive recording material having a structure in which a heat-sensitive coloring layer containing a usually colorless or light-colored leuco dye and an acidic substance capable of causing the leuco dye to develop color when heated is formed on a support. Concerning improvement of heat-sensitive recording materials. A thermosensitive recording material is a recording material with a structure in which a so-called thermosensitive coloring layer that develops color when heated is formed on a support such as paper, synthetic paper, or resin film. A thermal pen or the like is used. Such recording materials are used not only for copying books, documents, etc., but also for recording the output of electronic computers, facsimiles, calculators, etc., and are widely used in fields such as labels and ticket paper. The thermosensitive coloring layer that records an image by developing color when heated contains a combination of a coloring substance and a color developing substance that reacts with the coloring substance and develops color when heated. In this case, as the color-developing substance, for example, a colorless or light-colored leuco dye having a lactone, lactam or spiropyran ring is used, and as the color-developing substance, various acidic substances such as bisphenol A are used. Such a combination of a color-forming substance and a color-developing substance produces a clear color tone, and has thus far been applied to many heat-sensitive recording materials. However, the current situation is that there are various problems that need to be solved in practice with this combination. In particular, the problem of background coloring is the biggest cause of colored images with poor contrast, and it is strongly desired to prevent this problem. In addition to background color development over time, background color development is caused by liquid fog during the production of heat-sensitive recording materials, especially when forming the heat-sensitive color layer and preparing the coating solution, and pressure during the calendering process performed to improve the surface smoothness of the heat-sensitive color layer. This is often caused by fogging. Such background coloring is caused by one of the components forming the heat-sensitive coloring layer.
The cause is often the acidic substance itself. Conventionally, bisphenol A has been widely used as an acidic substance, but it has the disadvantage that it tends to cause liquid fog. As a result of extensive research in view of the above-mentioned problems, the present inventors have found that by using a special phenolic substance as a color-developing acidic substance that causes the leuco dye in the thermosensitive coloring layer to develop color when heated, it is possible to develop a background color. The present inventors have discovered that a heat-sensitive recording material with a very small amount of heat can be obtained, and have completed the present invention. That is, the present invention relates to a heat-sensitive recording material having a structure in which a heat-sensitive coloring layer containing a leuco dye and an acidic substance that causes the leuco dye to develop color when heated is formed on a support, as a main component. (In the formula, R ¹ is an alkylene group having 1 to 4 carbon atoms, R ²
The present invention provides a heat-sensitive recording material characterized by using a phenolic substance represented by an alkyl or alkoxy group having 1 to 18 carbon atoms, hydrogen or a halogen. The phenolic substances of the above general formula () include hydroquinone monobenzyl ether, hydroquinone monophenyl ethyl ether, hydroquinone-p-methoxymonobenzyl ether, hydroquinone-m-chloromonobenzyl ether, hydroquinone-p-ethyl monobenzyl ether, Examples include hydroquinone monophenyl butyl ether. When the phenolic substance of the general formula () is used, it has the advantage of not only low background color development but also excellent storage stability (no increase in background density over time). The amount of the phenolic substance of general formula () used in the present invention is leuco dye 1 in the heat-sensitive coloring layer.
The amount is usually 0.2 to 10 parts by weight, preferably 1 to 4 parts by weight. Next, specific examples of the leuco dye and binder used in the present invention will be shown. (A) Leuco dye As the leuco dye, the leuco forms of the various dyes shown below, which are usually colorless or light-colored, are used. (a) Leuco compound of triphenylmethane dye represented by the following general formula: (In the formula, R _X , R _Y and R _Z are hydrogen, hydroxyl group,
Halogen, alkyl group, nitro group, amino group, dialkylamino group, monoalkyl group,
It is an allyl group. ) Specific examples of the above leuco compounds are as follows. 3,3-bis(p-dimethylaminophenyl)-phthalide 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide (also known as crystal violet lactone) 3,3-bis(p- dimethylaminophenyl)-6-diethylaminophthalide 3,3-bis(p-dimethylaminophenyl)-6-chlorophthalide 3,3,-bis(p-dibutylaminophenyl)phthalide (b) In the following general formula Leuco compounds of fluoran dyes represented: In the formula, R _X , R _Y and R _Z are the same as in (a) above. Specific examples of the above compounds are as follows. 3-Cyclohexylamino-6-chlorofluoran 3-(N,N-diethylamino)-5-methyl-7-(N,N-dibenzylamino)fluoran 3-dimethylamino-5,7-dimethylfluoran 3- Diethylamino-7-methylfluoran 3-diethylamino-7,8-benzfluoran (c) Leuco compound of fluoran dye: 3-diethylamino-6-methyl-7-chlorofluoran 3-pyrrolidino-6-methyl-7 -anilinofluorane 2-{N-3'-trifluoromethylphenyl)
amino}-6-diethylaminofluorane 2-{3,6-bis(diethylamino)-9-
(o-chloroanilino)xantylbenzoic acid lactam} (d) Lactone compound represented by the following general formula: In the formula, R ₁ and R ₂ represent hydrogen, a lower alkyl group, a substituted or unsubstituted aralkyl group, a substituted or unsubstituted phenyl group, a cyanoethyl group, or a β-halogenated ethyl group, or R ₁ and R ₂ combine to form (-CH ₂ )- ₄ , (-
CH ₂ ) − ₅ also represents (−CH ₂ ) − ₂ O(−CH ₂ ) − ₂ ,
R ₃ and R ₄ represent hydrogen, a lower alkyl group, an alkyl group, an amino group or a phenyl group, and either one of R ₃ and R ₄ is hydrogen,
X ₁ , X ₂ and X ₃ are hydrogen, lower alkyl group,
Represents a lower alkoxyl group, a halogen atom, a halogenated methyl group, a nitro group, an amino group, or a substituted amino group, and X ₄ is hydrogen,
It represents a halogen, a lower alkyl group or a lower alkoxyl group, and n represents 0 or an integer of 1-4. Specific examples of the above compounds are as follows. 3-(2'-hydroxy-4'-dimethylaminophenyl)-3-(2'-methoxy-5'-chlorophenyl)phthalide 3-(2'-hydroxy-4'-dimethylaminophenyl)-3- (2'-methoxy-5'-nitrophenyl)phthalide 3-(2'-hydroxy-4'-diethylaminophenyl)-3-(2'-methoxy-5'-methylphenyl)phthalide 3-(2'-methoxy- 4'-dimethylaminophenyl)-3-(2'-hydroxy-4'-chloro-5'-methylphenyl)phthalide. (B) Binder The following various binders can be used to bind and support the thermosensitive coloring layer on the support. polyvinyl alcohol, methylcellulose,
Water-soluble materials such as hydroxyethyl cellulose, carboxymethyl cellulose, polyvinylpyrrolidone, polyacrylamide, polyacrylic acid derivatives, starch, oxidized starch, gelatin, casein, gum arabic, etc., or polystyrene, vinyl chloride-vinyl acetate copolymer, polyester, etc. Aqueous emulsions such as butyl methacrylate can be used as binders. The heat-sensitive recording material of the present invention further includes calcium carbonate, silica, alumina, magnesia, talc, barium sulfate, zinc oxide, etc. in the heat-sensitive coloring layer.
Fine powders such as titanium oxide and aluminum stearate are added to improve the clarity of colored images, and linseed oil, tung oil, wax, paraffin, polyethylene wax, chlorinated paraffin,
The running properties of the thermal head can be further improved by adding a lubricant such as a higher fatty acid metal salt. Examples of the present invention are shown below. Example 1 Dispersions A and B having the following component compositions were obtained by dispersing for 10 hours using a ball mill. [Dispersion A] 3-pyrrolidino-6-methyl-7-anilinofluorane 1 part by weight Hydroxyethylcellulose (10% aqueous solution)
1 Water 3 [Dispersion B] Hydroquinone monobenzyl ether 3 parts by weight Methyl cellulose (5% aqueous solution) 3 Polyvinyl alcohol (PVA-117, manufactured by Kuraray, 10% aqueous solution) 1.5 Water 7.5 Dispersions A and B Equal parts by weight were mixed, coated on a commercially available high-quality paper (50 g/m ² ) to give a dry weight of 0.5 g/m ² , and dried. The smoothness of the obtained thermal paper
A thermal recording material was obtained by calendering for 300 to 500 seconds. Example 2 A heat-sensitive recording material was obtained in the same manner as in Example 1 except that hydroquinone-p-methoxybenzyl ether was used in place of hydroquinone monobenzyl ether. Comparative Example 1 A comparative heat-sensitive recording material was obtained in the same manner as in Example 1 except that bisphenol A was used instead of hydroquinone monobenzyl ether. The five types of heat-sensitive recording materials described above were developed at 150° C. using a thermal gradient tester, and the background density and image density at that time were measured using a Macbeth densitometer.
Further, the heat-sensitive recording material after color development was left at a temperature of 60° C. for 24 hours, and changes in background density and image density were measured.
The results are shown in Table-1.

[Table] As is clear from the results in Table 1, the heat-sensitive recording material according to the present invention has a lower background density than the conventional product using bisphenol A. In terms of storage stability, there is less decrease in image density and increase in background density over time than with conventional products.

Claims (1)

[Scope of Claims] 1. A heat-sensitive recording material having a structure in which a heat-sensitive coloring layer containing a leuco dye and an acidic substance that causes the leuco dye to develop color when heated is formed on a support, wherein the acidic substance is generally formula (In the formula, R ¹ is an alkylene group having 1 to 4 carbon atoms, R ²
is an alkyl or alkoxy group having 1 to 18 carbon atoms, hydrogen, or a halogen.