JPS5914991A - Heat sensitive recording material - Google Patents

Abstract

PURPOSE:To provide a heat sensitive material excellent in color formability at the time of high speed recording, preservability and the stability of a color image, obtained by forming a heat sensitive color forming layer containing a color formable colorless dye, P-hydroxybenzoic esters and a specific compound. CONSTITUTION:A colorless or light colored color formable dye (A), 100-700 pts.wt. (per 100pts.wt. component A) P-hydroxybenzoic esters shown by formula I (wherein R is 1-4C alkyl, benzyl or phenyl) (B) and 10-200pts.wt. (per 100 pts.wt. component B) compound shown by formula II (wherein R1-R3 are H or 1-4C alkyl but simultaneously take no H) [e.g., bis(3-butyl-4-hydroxy-6- methylphenyl)sulfide] are respectively dispersed in a binder to form a dispersion which is, in turn, mixed to obtain a coating liquid. This coating liquid is applied to a support and dried to obtain an objective recording material.

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 that are usually colorless or light-colored and color developers (phenols, organic acids, etc.)
It has been published in publications such as No.-14039 and Japanese Patent 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 color recording is obtained by an instantaneous chemical reaction caused by heating.

A thermal solinter, a facsimile machine, etc. having a built-in thermal head is used to heat the heat-sensitive recording material to develop color. Compared to other recording materials, such recording materials can produce records in a relatively short time without complex processes such as development and fixing, and do not generate noise. Due to its advantages such as being 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 Kameko calculators, facsimiles, telex machines, 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 are disclosed in Japanese Patent Application Laid-Open No. 53-39139 and Japanese Patent Application Laid-open No. 53-2613.
No. 9, JP-A-53-5636, JP-A-53-1103
As stated in publications such as No. 6, heat-sensitive heat-melting substances such as various waxes, fatty acid amides, alkylated biphenyls, substituted biphenyl alkanes, coumarin compounds, and diphenylamines with low melting points are used as sensitizers or melting point depressants. It has been proposed to add it to the coloring layer. However, in the method of adding a sensitizer, it is necessary to first melt the sensitizer prior to the color reaction, so in high-speed recording, it is difficult to obtain sufficient thermal responsiveness to minute amounts of heat with short pulses. Instead, the fusible substance in the coloring layer melts, so □
Problems such as adhesion of debris, bleeding, trailing, and ghosting on the thermal head are likely to occur. Furthermore, even under storage conditions of high temperature or high humidity, background coloring (fading) 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 essential to use a phenolic substance as a color developer that has a low melting point and has a high ability to develop color from colorless dyes. However, conventionally known phenolic substances with a low melting point as color developers for heat-sensitive recording materials, such as 4-t-butylphenol (melting point 94 to 99°C),
When monophenols such as , α-naphthol (melting point 95-96°C), and β-naphthol (melting point 119-122°C) are used, the storage stability and stability of the heat-sensitive recording material are poor, and it gradually becomes dark even at room temperature. Not only does the color develop, but it also has a strong so-called phenol odor, making it impractical. Furthermore, in Japanese Patent Publication No. 54-12819, z, 2-bis (4'-
hydroxyphenyl) normal hexane (melting point 99-1
03°C), and in JP-A-55-27253, by using 1°l-bis(4'-hydroxyphenyl)alkane (alkane has 3 to 13 carbon atoms),
Although it is stated that heat-sensitive recording materials with low melting points, stability, and good color development can be made, these substances are difficult to synthesize and have problems in economic efficiency and availability. 56
Publication No. 144193 discloses that a lower alkyl ester or benzyl ester of p-hydroxybenzoic acid is effective as a high-sensitivity color developer, but the color of this product naturally fades in the image area over time. = 5 = Also, it has the disadvantage that white powder is deposited 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 drawbacks 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. p-hydroxybenzoic acid esters [general formula (1) HO()COOR (where R is an alkyl group having 1 to 4 carbon atoms or a benzyl group which may have a substituent,
Represents a phenyl group. )] and a normally colorless or light-colored color-forming colorless dye, and by further adding a specific compound to the combination, it has been found that the objective can be achieved. The present invention was completed based on this knowledge.

6- That is, in the present invention, a heat-sensitive coloring layer is provided on a support, and at least one compound represented by Sagi's general formula (1) and the following general formula (II) (wherein, RI p R1s R
, represents hydrogen or an alkyl group having 1 to 4 carbon atoms. However, R, , R, , R, are considered to be the same characteristics.

The reason why the combined use of the compound of general formula (II) prevents the natural decolorization of the image area and the precipitation of white powder, which are disadvantages of p-hydroxybenzoic acid esters, is not clear, but it is probably because It is thought that p-hydroxybenzoic acid esters, which are melted by heating and undergoes a coloring reaction, are recrystallized by lowering the temperature, which is the cause of the natural decolorization of the image area and the precipitation of white powder. This is considered to be because the combination of compound (n) maintains a supercooled state, thereby inhibiting crystallization.

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 sticking 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 number of coating lids and improve production efficiency.

(5) Colored images are stable, natural decolorization, and no white powder precipitation.

(6) There is almost no coloration at the peaks of the background, 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-dimethylamino7thallide, 3,3-bis(p-
Triallylmethane dyes such as dimethylaminophenyl) phthalide, 3-(p-dimethylaminophenyl)-3-(1,2-dimethylindol-3-I/I/) phthalide; 4°4'-his-dimethyl Diphenylmethane dyes such as aminobenzhydryl benzyl ether, N-halophenyl-leuco-o')mi7,N-2,4,5-)lichlorophenylleucoauramine; benzoyl leucomethylene blue, p-nitrobenzyl leucomethylene blue, etc. Thiazine dye; 3-methyl-spiro-dinaphthopyran, 9-3-ethyl-spiro-dinaphthopyran, 3-propyl-
20-series dyes such as spiro-dipenzobilane; 2-anilino-3-methyl-6-(N-ethyl-p-)luidino)
Fluoran, 2-p-toluidino-3-methyl-6-(
N-ethyl-p-)luidino)fluorane, 3-diethylamine-6-methyl-7-anilinofluorane, 3-
Diethylamino-7-(2-calzemethoxyanilino)
Fluoran, 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-diethylamine-6-
Methyl-7-xylidinofluorane, 3-diethylamine-7-chloroanilinofluorane, 7-diethylamino-3-chlorofluorane, 7-diethylamino-1
〇- -3-chloro-2-methylfluorane, 3-methyl-6
-(N-p-)dyl-N-ethylamino)fluoran,
3-Pyrosino6-methyl-7-p-butylanilinofluorane, 2-phenylamino-3-methyl-6-(N
Examples include fluoran dyes such as -ethyl-Np-tolyl)aminofluorane.

Next, p-hydroxybenzoic acid esters represented by the general formula (1) will be illustrated.

Next, compounds represented by general formula (II) will be illustrated.

131 The compound represented by the general formula (1) used in the present invention is preferably used in an amount of 100 to 700 parts by weight per 100 parts by weight of the colorless dye. Further, it is preferable to use 10 to 200 parts by weight of the compound represented by the general formula (n) per 100 parts by weight of the compound represented by the general formula (13).

Note that 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 a support, such as polyvinyl alcohol, methoxy cellulose, hydroxy Water-soluble materials such as ethyl cellulose, cal-14-xymethylcenolose, polyvinyl 20 lydone, polyacrylamide, polyacrylic acid, starch, gelatin, etc., or polystyrene, vinyl chloride-vinyl acetate copolymer, polybutyl methacrylate, etc. Aqueous emulsions such as those described above can be used as binders.

In addition, if necessary, conventional auxiliary additives, such as fine powders of calcium carbonate, silica, alumina, magnesia, Merck, titania, barium sulfate, aluminum stearate, etc., 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 coloring 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. Note that all the parts here are heavy lid parts.

Example Work A mixture consisting of the following compositions was separately pulverized and dispersed for 2 days using a magnetic i-luminescent machine to obtain liquid [A], liquid [B], and liquid [C].
] solution and llD] solution were prepared.

(A) Liquid 3-(N-cyclohexyl-N-methylamino)-6-
Methyl-7-anirithufluorane 20 parts 10-hydroxyethyl cellulose water soluble i 2 (
1 water
60 parts CB) Liquid p-hydroxyammon Ktia benzyl ester
20 parts 10% hydroxyethyl cellulose aqueous solution 20
Department water
60 parts [C] Liquid bis(3-tertbutyl-4-hydroxy-6-methylphenyl) sulfide 20 parts 1
0% hydroxyethylcellulose aqueous solution 2
0 parts water
60 parts CD) Liquid calcium carbonate 20 parts 5% methylcellulose soluble i 20 parts water
Using 60 parts or more of the solutions (A) to (D) obtained in the above manner, a coating solution for forming a heat-sensitive coloring layer having the following composition was prepared.
A wire bar was selected and applied to a commercially available high-quality paper of g/g to give a dry coating weight of 4 to 51/m', and then dried, and then the smoothness of the surface of the heat-sensitive coloring layer was 500 to 600 in Bekk smoothness.
The sheet was calendered in such a manner that it would last for a second, thereby producing a heat-sensitive recording sheet (a) of the present invention.

Coating liquid composition for forming thermosensitive coloring layer [A″l i 10 parts [
B) Liquid
30 parts [C] liquid
10 parts CDE liquid
30 parts inzotylene-maleic anhydride copolymer 20 thialkali aqueous solution 10
Part 17 - Example 2 Instead of the CB) solution of Example 1, use the following [E] solution, EC)
A thermosensitive recording sheet) (b) was prepared in the same manner as in Example 1, except that the following CF solution was used instead of the solution.

(E) Liquid p-hydroxybenzoic acid isodithyl ester
20 parts 10% human xyethylcellulose aqueous solution
ZOS 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 CG) was used instead of liquid [C] in Example 1.

CG) Liquid bis(3,S-dimethyl-4-hydroxyphenyl) sulfide 20 parts 10-hydroxyethyl cellulose water f
tm 20 Part IB-Wed 6
0 parts Comparative Example Example 1 [A) solution, [B] solution, [C] solution, [D] solution,
A thermal recording sheet) (d) was prepared in the same manner as in Example 1, except that the composition was changed as shown below.

Thermosensitive coloring layer liquid (A) liquid
10 parts [B) Liquid
40 parts (C) liquid
0 parts CD) liquid
20 parts aqueous solution of inzotylene-maleic anhydride copolymer
10 or more copies of the heat-sensitive recording materials (,) to (d) obtained in the above manner were transferred to a G-IV prototype facsimile machine.
(Made by Ricoh) at high speed (Printing speed: 0.941
sec, applied voltage = 20 cm), and the color density and background density were measured using a Macbeth densitometer RD-514 (manufactured by Macbeth, USA). In addition, after leaving this printed sample indoors for a week, we measured the density of the colored part and the density of the background part, and also observed the state of precipitation of white powder (-.
Shown in 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 the colored image is also extremely high. In addition, there was almost no coloration of the background over time, which is common when different color developers are mixed, and it can be seen that this is a practically extremely useful heat-sensitive recording material.

(Margin below)

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 (I), and a compound represented by the following general formula (...). 1. A heat-sensitive recording material, characterized in that a heat-sensitive coloring layer containing at least one compound is formed on a support. General formula (1) (In the formula, R represents an alkyl group having 1 to 4 carbon atoms or a benzyl group or phenyl group which may have a substituent.) General formula (II) (In the formula, RI s R,j R, is hydrogen or carbon number 1-
4 represents an alkyl group. However, RI + R, l n
. cannot become hydrogen at the same time. )