JPH0456755B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field] The present invention relates to a heat-sensitive recording material, and particularly to a heat-sensitive recording material that has excellent color development and other recording suitability, and has good image stability. [Prior Art] General heat-sensitive recording materials are coated on a support such as paper or film with a colorless or light-colored color-forming dye such as a leuco dye as a color-forming agent and a phenolic compound (especially A coloring system consisting of an acidic substance such as bisphenol A) or an organic acid is further provided with a heat-sensitive coloring layer in which binders, fillers, sensitivity improvers, lubricants, and other auxiliary agents are dispersed. It was introduced in Japanese Patent Publication No. 4160, Japanese Patent Publication No. 45-14039, Japanese Patent Application Laid-open No. 48-27736, etc., and has been widely put into practical use. This type of thermal recording sheet produces colored images through an instantaneous chemical reaction between a coloring agent and a color developer during heating (a thermal printer or facsimile machine with a built-in thermal head is used for heating). Therefore, compared to other recording materials, recording can be obtained in a short time using relatively simple equipment without complicated processing such as development and fixing, there is less noise generation and environmental pollution, and the cost is low. Due to these advantages, it is useful not only for copying books, documents, etc., but also as a recording material for various information and measuring instruments such as electronic computers, facsimile machines, telex machines, and medical measuring instruments. On the other hand, in recent years, along with the development of society, there has been an increasing demand for higher speed and higher density recording. For this reason, there is a strong desire not only to increase the speed of the recording apparatus itself, but also to develop recording materials that can support this speed. Therefore, from this point of view, Japanese Patent Application Laid-open No.
No. 39139, JP-A-53-26139, JP-A-53-5636
No. 53-11036, etc., in addition to the above-mentioned heat-sensitive coloring layer, various waxes, fatty acid amides, alkylated biphenyl, substituted biphenyl alkanes,
It has been proposed that heat-melting substances with low melting points such as coumarins and diphenylamines are added as sensitizers (or melting point depressants). However, in the method of adding a sensitizer, it is necessary to melt the sensitizer before the color reaction occurs, so it is difficult to obtain sufficient thermal response in high-speed recording where only a small amount of heat is supplied in a short pulse. However, since the sensitizer in the coloring layer melts, there are problems in recording suitability, such as adhesion of residue to the thermal head, smearing, trailing, ghosting, and other problems. Furthermore, when stored at high temperatures and/or high humidity, fogging occurs over time and often reduces the contrast of recorded images. Therefore, it is desirable that a heat-sensitive recording sheet for high-speed recording has a structure in which no sensitizer is added. However, colorless or light-colored color-forming dyes used in heat-sensitive recording sheets usually have a high temperature of 160 to 240°C, so in order to construct a heat-sensitive color-forming layer suitable for high-speed recording without adding a sensitizer, it is necessary to have a low melting point. Moreover, it is essential to use a color developer that has a large ability to develop color from the color former. By the way, there are many descriptions of color developers, especially phenolic compounds, in combination with colorless or light-colored dyes in various documents, including Japanese Patent Publication No. 45-14039, but among these, bisphenol A has stable quality. It is widely used due to its flexibility, low price, and easy availability. but,
This bisphenol A has a high melting point of 156-158℃, so it has low thermal sensitivity (therefore, the thermal coloring temperature is high).
There is a drawback. In contrast, phenolic compounds with low melting points, such as 4-t-butylphenol (melting point 94-99°C), α-naphthol (melting point 95°C),
-96℃), β-naphthol (melting point 119-122℃), etc., the storage stability of the heat-sensitive recording sheet is poor, and not only fogging gradually occurs even at room temperature, but also a so-called phenol odor. Strong and impractical. In addition, special public service 1977-
No. 12819 contains 2,2-bis(4'-hydroxyphenyl) normal hexane (melting point 99-103℃),
In JP-A No. 55-27253, 1,1-bis(4'-hydroxyphenyl)alkane (alkane has 3 to 13 carbon atoms) is used to improve heat sensitivity, storage stability, and color development. It has been described that heat-sensitive recording sheets with good quality can be made, but all of these materials are difficult to synthesize and have problems in availability. Furthermore, JP-A-56-144193 describes that lower alkyl esters or benzyl esters of p-hydroxybenzoic acid are easy to synthesize, and that high-sensitivity heat-sensitive recording sheets can be made using them. However, this product has storage disadvantages in that the colored part tends to fade over time and crystals of the phenolic compound precipitate (so-called white powder phenomenon). Furthermore, conventional heat-sensitive recording materials have the disadvantage that their colored images are erased by fingerprints, oil, and the like. As mentioned above, conventional heat-sensitive recording sheets for high-speed recording, those using sensitizers or melting point depressants, and those without, each have their own advantages and disadvantages, and none of them can be said to be practical. [Objective] The first object of the present invention is that there is no need to use a sensitizer or a melting point depressant, and therefore it has excellent thermal response and recording suitability, and also has good storage stability and image contrast even under high temperature and/or high humidity. The purpose of the present invention is to provide an excellent heat-sensitive recording material. The second object of the present invention is to provide an extremely practical thermosensitive record that has excellent storage stability at room temperature, no phenol odor, and no problems in availability despite the use of a highly heat-sensitive phenolic compound. The goal is to provide materials. A third object of the present invention is to provide a heat-sensitive recording material with extremely excellent image stability in which a colored image does not fade due to fingerprints, oil, etc. [Structure] That is, the heat-sensitive recording material of the present invention uses the general formula (In the formula, R represents an alkylene group having at least one hydroxyl group.) It is characterized by using a phenolic substance represented by the following formula. In the phenolic substance represented by the above general formula, the alkylene group R usually has 1 to 8 carbon atoms, and the hydroxyl group is bonded to the main chain of the alkylene group or to a branched chain bonded to the main chain. It's okay. Further, the number of hydroxyl groups bonded to the alkylene group is usually 1 to 3. The leuco dye (colorless or light-colored dye) used in combination with such a phenolic compound may be any conventionally known leuco dye, including the following. Crystal violet lactone, 3-diethylamino-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7-(o,
p-dimethylanilino)fluorane, 3-(N-ethyl-p-toluidino)-6-methyl-7-anilinofluorane, 3-pyrrolidino-6-methyl-7-anilinofluorane, 3-piperidino- 6-Methyl-7-anilinofluorane, 3-(N-cyclohexyl-N-methylamino)
-6-Methyl-7-anilinofluorane, 3-diethylamino-7-(o-chloroanilino)fluoran, 3-diethylamino-7-(m-trifluoromethylanilino)fluorane, 3-diethylamino-6-methyl- 7-chlorofluoran, 3-diethylamino-6-methylfluoran, 3-cyclohexylamino-6-chlorofluoran, etc. Here, the ratio of the leuco dye to the phenolic compound of the above formula is suitably about 1:1 to 6 (by weight). Specific examples of the phenolic compound represented by the above general formula include those shown below. Furthermore, in the present invention, a conventional color developer may be used in combination, if necessary.

【table】

〔effect〕

The heat-sensitive recording material of the present invention thus obtained has the following features. (1) Since it can be made into a product without using sensitizers or melting point depressants, it has particularly excellent thermal responsiveness.
Therefore, high sensitivity and clear images can be obtained. (2) For the same reason as (1) above, fogging does not occur even under high temperature or high humidity, and image contrast does not deteriorate. (3) For the same reason as (1) above, there are no problems such as adhesion of residue to the thermal head, smearing, trailing, ghosting, etc., and excellent recording suitability is achieved. (4) By using the phenolic compound of the above formula, fogging does not occur at room temperature and no phenolic odor is generated, making it extremely practical. (5) The phenolic compound of the above formula is easy to synthesize;
Therefore, there are no problems in obtaining it, and it can be obtained in high yield, high purity, and at a relatively low cost. (6) For the same reason as mentioned in (4) above, the colored image does not fade over time or cause white powder phenomenon, and is very stable. (7) By using the phenolic compound of the above formula, it is possible to obtain a heat-sensitive recording material with extremely excellent image stability in which the colored image is not erased by fingerprints, oil, etc. For similar reasons, it also has the following features: (8) Those using thin base paper or film as a support are particularly excellent as thermal recording materials for infrared and strobe flash type thermal copying machines. (9) It is possible to reduce the amount of coating and improve production efficiency. [Example] Next, the present invention will be explained in more detail with reference to Synthesis Examples and Examples. Note that the parts and percentages shown below are based on weight. Synthesis Example Dissolve 6.4 g of sodium hydroxide in 22 g of methanol and add 20.2 g of p-hydroxybenzenethiol. This mixture was then added with 2-hydroxy-
Add 9.42 g of 1,3-dichloropropane dropwise at room temperature,
After the dropwise addition was completed, the mixture was heated and reacted under methanol reflux conditions for 2 hours. After heating, the mixture was cooled and methanol was distilled off under reduced pressure. 500 ml of water was added to the residue, and the precipitated crystals were taken out and thoroughly washed with water. After drying, it is recrystallized from a mixed solvent of toluene and ethyl acetate to obtain 1,3-di(4-hydroxyphenylthio).
15.5 g of white crystals of -2-hydroxypropane (the above compound No. (3)) were obtained. Melting point 108-109℃. Elemental analysis results Carbon hydrogen sulfur theoretical value 58.42% 5.23% 20.79% Synthetic product 58.51% 5.18% 20.68% Example 1 The following mixtures were pulverized and dispersed in a magnetic ball mill for 2 days to obtain liquids A, B and C. Prepared. A liquid formulation 3-(N-cyclohexyl-N-methylamino)-6-methyl-7-anilinofluorane
20 parts 10% aqueous solution of hydroxyethyl cellulose
20 parts water 60 parts B liquid formulation 1,3-di(4-hydroxyphenylthio)
-2-hydroxypropane (compound No. (3))
20 parts 10% aqueous solution of hydroxyethyl cellulose
20 parts Water 60 parts Liquid C formulation Calcium carbonate 20 parts 5% aqueous solution of methylcellulose 20 parts Water 60 parts Using liquids [A] to [C] obtained as above, prepare a heat-sensitive coloring layer liquid with the following composition. The dry coating amount is 4 to 5 g/m ² on commercially available high-quality paper with a standard basis weight of 50 g/m ^2.
Select a wire bar to apply and dry, then calender so that the surface smoothness of the heat-sensitive coloring layer is 500 to 600 seconds in Beck smoothness.
A thermosensitive recording sheet (a) of the present invention was produced. Thermosensitive coloring layer solution [A] 10 parts [B] solution 30 parts [C] solution 30 parts Isobutylene-maleic anhydride copolymer 20 parts
% alkaline aqueous solution 10 parts Example 2 A thermosensitive recording sheet (b) was prepared in the same manner as in Example 1 except that the following liquid [D] was used in place of [B] in Example 1. [D] Liquid 1,4-di(4'-hydroxyphenylthio)
-2-Hydroxybutane (Compound No. (5)) 20 parts 10% aqueous solution of hydroxyethylcellulose
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 [E] was used instead of liquid [B] in Example 1. [E] Liquid 1,4-di(4'-hydroxyphenylthio)
-2,3-hydroxybutane (compound No. (7))
20 parts 10% aqueous solution of hydroxyethyl cellulose
20 parts Water 60 parts Comparative Example 1 A thermosensitive recording sheet (d) was prepared in the same manner as in Example 1 except that the following liquid [F] was used instead of liquid [B] in Example 1. [F] Liquid Bisphenol A 20 parts 10% aqueous solution of hydroxyethylcellulose
20 parts Water 60 parts Comparative Example 2 A thermosensitive recording sheet (e) was prepared in the same manner as in Example 1 except that the following liquid [G] was used instead of liquid [B] in Example 1. [E] Liquid p-hydroxybenzoic acid benzyl ester
20 parts 10% aqueous solution of hydroxyethylcellulose
20 parts Water 60 parts The thermal recording sheets (a) to (e) obtained in the above manner were recorded for one line using a thermal printing experimental device equipped with a thin film head manufactured by Matsushita Electronic Components Co., Ltd. at a head power of 0.45 W/dot. Time 20msec/, scanning line density 8 x 3.85
Pulse width is 1.6, 2.0, 2.4, under dot/mm condition.
(msec), and the print density was measured using a Macbeth densitometer RD-514 (filter W-106).
The results are shown in Table-1.

[Table] Also, the above printed matter (pulse width 2.4msec)
After leaving it for a week, check the color density again with a Macbeth densitometer.
Measured with RD-514. In addition, white powder phenomenon in the colored area was also observed at that time. The results are shown in Table-2.

[Table] In addition, heat-sensitive recording sheets (a) to (e) were heated to 150°C using a tilt tester (manufactured by Toyo Seiki) at a pressure of 2 kg and a contact time of 1 second.
It was printed with. Next, a thin layer of cottonseed oil was applied to the colored image area, and after leaving it at room temperature for 24 hours, it was confirmed whether the color had disappeared. The results are shown in Table-3.

[Table] From the above, the heat-sensitive recording material of the present invention has excellent color development during high-speed recording, has no white powder phenomenon in the colored image area, no decolorization due to oil, etc., and is a highly practical heat-sensitive recording material with extremely stable colored images. It can be seen that it is.

Claims (1)

[Scope of Claims] 1. In a heat-sensitive recording material that utilizes a color-forming reaction between a leuco dye and its color developer, as the color developer, the general formula (In the formula, R represents an alkylene group having at least one hydroxyl group.) A heat-sensitive recording material characterized by using a phenolic compound represented by the following formula.