JPH0354077B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a heat-sensitive recording sheet, and particularly to a heat-sensitive recording sheet that has excellent color development and image stability during high-speed recording. In general, a heat-sensitive recording sheet consists of a heat-sensitive color-forming layer whose main components are a color-forming colorless dye and a color developer such as a phenolic substance, provided on a support such as paper or film. Color recording is obtained through a chemical reaction. Compared to other recording materials, this heat-sensitive recording sheet can produce records in a relatively short time without undergoing complicated processes such as phenomenon and fixing, does not generate noise, and is relatively inexpensive. Due to the advantages of books,
It is widely used not only for copying documents, but also as a recording material for various information and measuring instruments such as electronic computers, facsimile machines, telex machines, and medical measuring instruments. However, in recent years, with the development of society, there has been a growing demand for faster recording, so there is a strong desire for faster recording devices themselves and for the development of recording materials that can meet this demand. Conventionally, such heat-sensitive recording sheets for high-speed recording are disclosed in Japanese Patent Application Laid-open No. 53-39139 and Japanese Patent Application Laid-open No. 53-26139.
Publication No. 53-5636, Japanese Patent Publication No. 53-5636
As disclosed in Publication No. 11036 etc., various waxes, fatty acid amides, alkylated biphenyl, substituted biphenyl alkali, coumarin compounds,
It has been proposed to add a heat-melting substance with a low melting point, such as diphenylamines, to the heat-sensitive coloring layer as a sensitizer or melting point depressant. In this method of adding a sensitizer, it is necessary to melt the sensitizer before the color reaction occurs, so in high-speed recording, not only is it not possible to obtain sufficient thermal responsiveness to minute amounts of heat with short pulses. , since the fusible substance in the coloring layer melts, it has the disadvantage of easily causing problems such as adhesion of residue on the thermal head, bleeding, trailing, and ghosting.
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 sheet for high-speed recording without the addition of such an increaser or melting point depressant. Since the melting point is usually as high as 160 to 240°C, in order to obtain a heat-sensitive recording sheet suitable for high-speed recording without adding a sensitizer or melting point depressant, we need a color developer with a low melting point and the ability to develop color from a colorless dye. Large phenolic substances have been used. Regarding color developers for phenols,
Many substances have been described in various documents including Publication No. 14039, but among these, 2,2-bis(4'-bidroxyphenyl)propane (bisphenol A melting point 156-158℃) has a high quality. It is widely used due to its stability, price, and ease of acquisition.
However, this bisphenol A has the drawback of a high thermal coloring temperature. In contrast, phenolic substances with low melting points, such as 4-tert-butylphenol (melting point 94
~99℃), α-naphthol (melting point 95-96℃), β-
When monophenols such as naphthol (melting point 119-122°C) are used, the shelf life and stability of the heat-sensitive recording sheet are poor, and the background color gradually develops even at room temperature, as well as a so-called phenol odor. Strong and impractical. In addition, 2,2-bis(4'-hydroxyphenyl) normal hexane (melting point 99-103°C) is used in Japanese Patent Publication No. 54-12819, and 1,1-bis(4'-hydroxyphenyl) in JP-A No. 55-27253. '-Hydroxyphenyl) alkanes (alkanes have 3 to 13 carbon atoms) each have a low melting point and can be used to produce thermal recording sheets with good stability and color development, but these substances cannot be synthesized. It is difficult and there are problems with availability. Further, in JP-A-56-144193, lower alkyl esters or benzyl esters of p-hydroxybenzoic acid are easily synthesized,
Although it is described that a high-sensitivity heat-sensitive recording sheet can be produced, this sheet has the disadvantage that the coloring part undergoes rapid natural discoloration, and crystals of the phenolic substance precipitate in the coloring part (so-called white powder phenomenon). . As mentioned above, at present, there are almost no color developers that have been found that can produce clear, high-density, and stable color images during high-speed recording using color developers that can be practically used industrially. It is. The inventors of the present invention have conducted various studies to improve these many drawbacks, and as a result, they have developed an extremely excellent practical product by using a phenolic substance represented by the following formula () as a color developer. It was discovered that a heat-sensitive recording sheet for high-speed recording having the following characteristics could be obtained, leading to the completion of the present invention. That is, the present invention is a heat-sensitive recording sheet characterized in that a heat-sensitive coloring layer containing at least one leuco dye and a phenolic substance represented by the following general formula () is provided on a support. (In the formula, X represents a lower alkyl group and/or a halogen atom, n is 0 to 3, and when multiple substituents X are bonded to the benzene nucleus, the substituents X may be the same or different. (The lower alkyl group is usually preferably one having 1 to 4 carbon atoms, and the halogen atom includes chlorine, fluorine, etc.) According to the present invention, that is, the above general formula () By using the above phenolic substance, a heat-sensitive recording sheet can be obtained which exhibits the excellent properties listed below. (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) It is easy to synthesize, can be obtained in high yield and purity, and can be manufactured at relatively low cost. Next, the leuco dyes used in the present invention are:
Commonly colorless to light-colored colorless dyes include triphenylmethane-based, fluoran-based, phenothiazine-based, auramine-based, spiropyran-based dyes, etc., and examples thereof include, but are not limited to, crystal violet. Lactone 3-diethylamino-6-methyl-7-anilinofluorane 3-(N-ethyl-p-toluidino)-6-methyl-7-anilinofluorane 3-diethylamino-6-methyl-7-(ortho, para-dimethylanilino)fluorane 3-pyrrolidino-6-methyl-7-anilinofluorane 3-piperidino-6-methyl-7-anilinofluorane 3-(N-cyclohexyl-N-methylamino)
-6-Methyl-7-anilinofluorane 3-diethylamino-7-(orthochloroanilino)fluoran 3-diethylamino-7-(meta-trifluoromethylanilino)fluorane 3-diethylamino-6-methyl-7- Chlorofluoran, 3-diethylamino-6-methylfluoran, 3-cyclohexylamino-6-chlorofluoran, and the like. Moreover, it is preferable to use the compound of formula () used in the present invention in an amount of 1 to 6 times the amount of the leuco dye. Specific examples of the phenolic substance represented by the general formula () include those shown below. In addition, in the heat-sensitive coloring layer of the present invention, it is possible to appropriately use various conventional binders for bonding and supporting on the support, such as polyvinyl alcohol, methoxycellulose, hydroxyethylcellulose, carboxymethylcellulose, and polyvinylpyrrolidone. , polyacrylamide, polyacrylic acid, starch, gelatin, etc., or water-based emulsions such as polystyrene, vinyl chloride-vinyl acetate copolymer, polybutyl methacrylate, etc. can be used as the binder. can. 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 applying a coating liquid for forming a heat-sensitive layer containing the above-mentioned components onto a suitable support such as paper, synthetic paper, or plastic film, and drying it. It is used in the recording field, 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. Example 1 A mixture having the following composition was separately ground and dispersed for two days using a magnetic ball mill [A]
Liquid [B] and liquid [C] were prepared. [A] Liquid 3-(N-cyclohexyl-N-methylamino)-
6-Methyl-7-anilinofluorane 20 parts by weight 10% hydroxyethyl cellulose aqueous solution 20 〃 Water 60 〃 [B] Liquid 4-benzylmercaptophenol 20 parts by weight 10% hydroxyethyl cellulose aqueous solution 20 〃 Water 60 〃 [C] Liquid carbonate Calcium 20 parts by weight 5% methyl cellulose aqueous solution 20 Using solutions [A] to [C] obtained as above, a heat-sensitive coloring layer solution having the following composition was prepared, and a commercially available high-grade liquid with a standard basis weight of 50 g/m ² was prepared. Dry coating amount on paper: 4-5g/
The heat-sensitive recording sheet ^of the present invention (a ) was created. Thermosensitive coloring layer liquid [A] 10 parts by weight [B] solution 30 [C] solution 30 20% alkaline aqueous solution of isobutylene-maleic anhydride copolymer 10 Example 2 Substitute for [B] solution in Example A thermosensitive recording sheet (b) was prepared in the same manner as in Example 1 except that the following liquid [D] was used. [D] Liquid 4-p-chlorobenzylmercaptophenol
20 parts by weight 10% hydroxyethyl cellulose aqueous solution 20 〃 Water 60 〃 Comparative example A thermosensitive recording sheet (c) was prepared in the same manner as in Example 1 except that the following liquid [E] was used instead of liquid [B] in Example 1. I made it. [E] Liquid bisphenol A 20 parts by weight 10% hydroxyethyl cellulose aqueous solution 20 parts by weight Water 60 Thermal recording sheet (a) obtained as above
(c) was printed at high speed using a G-fax machine (manufactured by Ricoh Co., Ltd.) (printing speed: 0.94 msec, applied voltage: 16 V,
Macbeth RD-
Measured with 514. The results are shown in Table-1.

[Table] As is clear from Table 1, it can be seen that the heat-sensitive recording sheet of the present invention has extremely excellent color development during high-speed recording.

Claims (1)

[Claims] 1. At least one leuco dye on a support,
A heat-sensitive recording sheet comprising a heat-sensitive coloring layer containing a phenolic substance represented by the following general formula (). (In the formula, X represents a lower alkyl group and/or a halogen atom, n is 0 to 3, and when multiple substituents X are bonded to the benzene nucleus, those substituents X may be the same or different. good)