JPS59192594A - Thermal recording material - Google Patents

Abstract

PURPOSE:To obtain a thermal recording material excellent in heat responsibility and adaptability to recording and excellent also in stability in preservation under hot and/or humid conditions and image contrast, by using a specified phenolic substance as a color developer for a leuco dye. CONSTITUTION:A phenolic compound of the formula, wherein R is an alkylene group having at least one hydroxyl group, is used as a color developer in a thermal recording material utilizing a color forming reaction between a leuco dye and a color developer. Since the thermal recording material can be produced without using any sensitizer or any melting point lowering agent, the material is excellent in heat responsivity, and a clear image can be obtained with high sensitivity.

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, and contain a colorless or light-colored dye such as a leuco dye as a color former, and a phenolic compound (particularly bisphenol A) as a color developer to make the color develop when heated. A coloring system consisting of an acidic substance such as an organic acid is further provided with a heat-sensitive coloring layer in which a binder, a filler, a sensitivity improver, a lubricant, and other auxiliary agents are dispersed. 45-140
No. 39, Japanese Unexamined Patent Publication No. 48-27736, etc., and has been widely put into practical use. This type of thermal recording sheet produces a colored image 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, facsimiles, 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. 53-391.39 and Japanese Patent Application Laid-open No. 53-261
No. 39, JP-A-53-5636, JP-A-53-110
In No. 36, etc., heat-melting substances with low melting points such as various waxes, fatty acid amides, alkylated biphenyls, substituted biphenylalkanes, coumarins, and diphenylamines are added to the heat-sensitive coloring layer as described above as sensitizers (or melting point depressant)
It has been proposed that it be added as 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 with 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 they require a low melting point to form a heat-sensitive coloring layer suitable for high-speed recording without adding a sensitizer. Moreover, it is essential to use a color developer that has a large ability to develop color from the color former. By the way, regarding color developers to be used in combination with colorless or light-colored dyes, especially phenolic compounds, Japanese Patent Publication No. 45-1/10
39 and other publications, but among these, bisphenol A is known for its stable quality, low price, and
It is widely used due to its ease of acquisition. However, since bisphenol A has a high melting point of 156 to 158° C., it has the drawback of low thermal sensitivity (and therefore high thermal coloring temperature). In contrast, phenolic compounds with low melting points,
For example, 4-t,-butylphenol (melting point 94-99
When monophenols such as α-naphthol (melting point 95-96°C), β-naphthol (melting point 119-122°C) are used, the storage stability of the heat-sensitive recording sheet is poor, and it gradually fogs up even at room temperature. Not only does this produce a strong phenol odor, it is not practical. In addition, 2,23-monobis(4'-hydroxyphenyl) normal hexane (melting point 99-103°C) is disclosed in Japanese Patent Publication No. 54-1.2819, and 1,1 It is described that a thermosensitive recording sheet with high heat sensitivity, storage stability, and good color development can be made by using -bis(4'-hydroxyphenyl) alkanes (the number of carbon atoms in the alkane is 3 to 13). However, all of these substances 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 described above, conventional heat-sensitive recording sheets for high-speed recording have advantages and disadvantages, whether they use a sensitizer or melting point depressant or not, and none of them can be said to be practical.

14= [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 storage stability even under high temperature and/or high humidity. and to provide a heat-sensitive recording material with excellent image contrast.

The second object of the present invention is to have excellent storage stability at room temperature despite using a phenolic compound with high heat sensitivity.
To provide an extremely practical heat-sensitive recording material that has no phenol odor and no problem of availability.

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.

〔composition〕

That is, the heat-sensitive recording material of the present invention is characterized in that a phenolic substance represented by the general formula (wherein R represents an alkylene group having at least one hydroxyl group) is used as a color developer for the leuco dye. .

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
It may be bonded to the main chain of the alkylene group or to a branch chain bonded to the main chain.

In addition, the number of hydroxyl groups bonded to the alkylene group is usually 1 to 1.
There are 3 pieces.

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)fluoran, 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-anilinofluoran, 3-diethylamino-7-(o-chloroanilino)fluoran, 3-diethylamino-7-(m-trifluoromethylanilino)fluoran.

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.

7-H 8- Note that in the present invention, in order to bind and support the leuco dye and color developer on the support, various conventional binders may be used as appropriate, such as polyvinyl alcohol. , methoxycellulose, hydroxyethylcellulose, carboxymethylcellulose, polyvinylpyrrolidone, polyacrylamide, polyacrylic acid, starch, gelatin, etc., or water-based emulsion types such as polystyrene, vinyl chloride-vinyl acetate copolymer, polybutyl methacrylate. can be used as a binder.

In addition, in the present invention, if necessary, conventional auxiliary additives such as fine powders such as calcium carbonate, silica, barium sulfate, and aluminum stearate may be added,
The clarity of colored images can be improved.

The heat-sensitive recording material of the present invention can have various structures, including all conventionally known structures that utilize a color-forming reaction between a leuco dye and a color developer. For example, the heat-sensitive recording material of the present invention has a structure in which a leuco dye and a color developer are supported on a support as the same coating layer or separate coating layers, or a heat-sensitive recording material in which a leuco dye is supported as a transfer layer. It can be used as a thermal transfer type heat-sensitive recording material consisting of a transfer sheet supported on a body and a receptor sheet supported on a support using a color developer as a receptor layer.

In the case of thermal transfer type thermal recording materials, the transfer sheet is
A desired colored image can be formed on the receptor layer surface of the receptor sheet by stacking the receptor sheets so that the receptor layer is in contact with the transfer layer of the transfer sheet and thermally printing from the front or back surface of the polymerized sheet. .

The heat-sensitive recording material of the present invention can be produced, for example, 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.

〔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 a sensitizer or a melting point depressant, it has particularly excellent thermal responsiveness, and therefore high sensitivity and clear images can be obtained.

(2) For the same reason as in (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 in (1) above, there are no problems such as adhesion of residue to the thermal head, bleeding, trailing, ghosting, etc., and the recording suitability is excellent.

(4) By using the phenolic compound of the above formula, fogging does not occur at room temperature and phenol odor does not occur, making it extremely practical.

(5) The phenolic compound of the above formula is easy to synthesize, so 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 white powder phenomenon occurs.
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 a 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 ray 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 12
- Dissolve and add 20.2 g of p-hydroxybenzenethiol. Then, 2-hydroxy-1°3-
9.42 g of dichloropropane was added dropwise at room temperature, and after the 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 mfl of water was added to the residue, and the precipitated crystals were taken out and thoroughly washed with water. After drying, it was recrystallized with a mixed solvent of toluene and ethyl acetate to obtain 1,3-di(4-hydroxyphenylthio)-2-hydroxypropane (the above compound No.
(3) 15.5 g of white crystals of ) were obtained. Melting point 108~
109°c0 Theoretical value 58.42% 5.23%
20.79% Synthetic product 58.51% 5.18%
'20.68% Example 1 The mixtures of the non-execution method were each pulverized and dispersed in a magnetic ball mill for 2 days to prepare liquids A, B and C.

-υ[Formulation- 5-(N-cyclohexyl-N-methylamino)-6-
Methyl-7-anilite fluorane 20 parts 10% hydroxyethyl cellulose 20 parts aqueous solution
60 parts B liquid formulation 1.3-di(4'-hydroxyphenylthio)-2-
20 parts of hydroxypropane (compound N
o, (3)) 10% 20 parts aqueous solution of hydroxyethyl cellulose
60 parts C-solution formula calcium carbonate 20 parts 5% aqueous solution of methylcellulose 20 parts water
Using 60 parts or more of the solutions [A] to [C] obtained as described above, a heat-sensitive coloring layer solution having the following composition was prepared, and the standard basis weight was 1.5.
0g/rrF commercially available high-quality paper @ dry coating amount 4-5 g/
rr? Select a wire bar, apply and dry, and then the surface smoothness of the heat-sensitive coloring layer is 5 on the Bekk smoothness scale.
The heat-sensitive recording sheet (a) of the present invention was prepared by calendering for a time of 00 to 600 seconds.

Thermosensitive coloring layer liquid (A) 10 parts (B)
Liquid 30 parts [C] Liquid
20% alkaline aqueous solution of 30 parts isobutylene-maleic anhydride co-10 parts polymer Example 2 A thermosensitive recording sheet was prepared in the same manner as in Example 1 except that the following liquid (D) was used in place of CB in Example 1. I made (b).

[D] Solution 1.6-di(4'-hydroxyphenylthio)-2゜4-dihydroxyhexane 20 parts (compound No. (9)) 10% of hydroxyethyl cellulose 20 parts aqueous solution 6
0 copies Example 3 A thermosensitive recording sheet 15-1 (c) was prepared in the same manner as in Example 1 except that the following ICE solution was used instead of the solution (B) in Example 1.

[Liquid E], 4-di(4)-hydroxyphenylthio)-2゜3-dihydroxybutane 20 parts (compound No. (7)) 10% of hydroxyethyl cellulose 20 parts aqueous solution
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 the CBl liquid in Example 1.

[F] Liquid bisphenol A 20 parts 10% hydroxyethyl cellulose 20 parts aqueous solution
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 the liquid CB) in Example 1.

16- [E] Liquid P-hydroxybenzoic acid benzyl 20 parts 10% of stellate hydroxyethyl cellulose 20 parts aqueous solution water
60 copies or more of heat-sensitive recording sheets (a) to (
e) was performed using a thermal printing experimental device with a thin film head manufactured by Matsushita Electronic Components Co., Ltd., with a head power of 0.45 W/dot, 1 line recording time of 20 m5 ec/fl, and a scanning line density of 8 x 3.
．． Pulse width is 1.6, 2.0 under the condition of 85 dots/mm.
, 2.4 (msec), and the print density was measured using a Macbeth densitometer RD-514 (filter W-106). The results are shown in Table-1.

Table-1 Also, after leaving the above printed matter (with a pulse width of 2.4 m5ec) for one week, check the color density again using a Macbeth densitometer (Rr).
-514. In addition, white powder phenomenon in the colored area was also observed at that time. The results are shown in Table-2.

Table 2 In addition, heat-sensitive recording sheets (a) to (e) were tested using an inclination tester (manufactured by Toyo Seiki) at a pressure of J2 kV and a contact time of 150
Printed at °C. 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.

From Table 3 below, it can be seen that the heat-sensitive recording material 1 of the present invention has excellent color development during high-speed recording, has no white powder phenomenon in the colored image area, no discoloration due to oil, and has extremely stable colored images and is highly practical. It can be seen that it is a heat-sensitive recording material.

Patent Applicant Ricoh Co., Ltd. - Representative Patent Attorney Toshiaki Ikeura 19 - Procedural Amendment 1, Indication of Case Patent Application No. 67520 of 1982 2, Name of Invention Thermal Recording Material 3, Person Making Amendment Case and Relationship Patent applicant address 1-3-6 Nakamagome, Ota-ku, Tokyo Name
(674) Rico Co., Ltd. - Representative Hama 1
) Hiro 4, Agent 151 Address 1-58-10 Yoyogi, Shibuya-ku, Tokyo -
Nishiwaki Building 113 Name (7450) Patent attorney Ikeura Sanka Telephone number (370) 2533 5, Date of amendment order Voluntary 6, Number of inventions increased by amendment 0 7, Subject of amendment Detailed explanation of the invention in the specification Column 2
0-8. Contents of amendment The following amendments will be made to the specification of this application.

(1) Page 16, lines 13 to 15, 11,6-di (4
'-hydroxyphenylthio)-2,4-dihydroxyhexane (compound No. (9)) 3 was replaced with "1,4-di(4'-hydroxyphenylthio)-2-hydroxybutane (compound No. Correct to J.

(2) Table 1 on page 18 is corrected as follows.

(3) Table 2 on page 19 is corrected as follows.

Claims (1)

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