JPS6048395A - Thermal recording sheet - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heat-sensitive recording sheet, and particularly to a color developer used in a heat-sensitive recording sheet.

A heat-sensitive recording sheet is usually prepared by coating a colorless or light-colored colorless dye and a color developer in a separated state together with a binder and other additives on the surface of a base paper.

Then, in the recording apparatus, when this recording sheet is brought into contact with a heating element such as a thermal head or a thermal pen, dye #1 reacts with the color developer to develop a color such as black, which is recorded on sheet 1-.

Conventionally, phenolic color developers have been used as color developers. For example, bisphenol A (melting point 156-1
58'c) is currently widely used due to its quality stability, price, and ease of availability; however, this bisphenol A
has the disadvantage of a high thermal coloring temperature. On the other hand, when phenolic substances with low melting points are used, such as monophenols such as 4-kushabutylphenol, α-naphthol, and β-naphthol, the storage stability and stability of the heat-sensitive recording sheet are poor, and However, not only does the background color gradually develop, but it also has a strong phenol odor, making it impractical. In addition, in Special Publication No. 54-12819, II, II
-(1-Methyl-n-hexylidene) diphenol is described as having a low melting point and being able to create a thermosensitive recording sheet with good stability and color development.
This product has the disadvantage of being difficult to obtain.

In order to improve the above-mentioned drawbacks, P-hydroxybenzoic acid ester (Japanese Patent Application Laid-Open No. 144193/1983) has been proposed, and in particular, its Hensyl ester has been put into practical use. However, this method had drawbacks such as high sublimation and color unevenness in the photographic subject.

As a result of intensive research on methods to improve these conventional drawbacks, the present inventors have discovered that a diester of hydroxyphthalic acid is used as a color developer, and a phenol is added thereto to prevent the background color from yellowing or to prevent the recorded image from fading. The present invention was completed by discovering that the above-mentioned drawbacks could be solved by adding it as a stabilizer.

That is, the present invention resides in a heat-sensitive recording sheet characterized by containing a normally colorless to light-colored color-forming colorless dye, a hydroxyphthalic acid diester having a melting point of about 60 to about 120 DEG C., and a phenol.

The hydroxyphthalic acid diesters used in the present invention include 4-hydroxy-orthofucric acid, 2-14-1
Alternatively, diesters of 5-hydroxyisofucric acid or hydroxy-terephthalic acid can be mentioned. Examples include dialkyl esters and diphenyl esters listed in Table 1, but other hensyl esters and the like may also be used depending on the purpose.

Table 1: Hydroxyphthalic acid diester These hydroxyphthalic acid diesters are preferably 4-hydroxyphthalic acid diesters, and particularly preferred are 4-hydroxyphthalic acid diesters.
Hydroxyfucric acid dimethyl ester.

The above-mentioned hydroxyphthalic acid diester used in the present invention needs to have a melting point of about 60 to about 120°C. If the temperature is too high, a high color recording temperature is required, and the small amount of heat makes it impossible to obtain sufficient thermal response, making it impossible to use it for modern high-speed facsimiles.

Hydroxyphthalic acid diesters are generally produced by sulfonating or halogenating ortho-, iso-1 or terephthalic acid by a conventional method, and then the former is obtained by alkali melting, and the former is obtained by hydrolysis in caustic soda water. It can be easily synthesized by a general method of esterifying hydroxyphthalic acid in the presence of an acid catalyst.

It goes without saying that the hydroxyphthalic acid diester of the present invention can be used alone as a color developer for heat-sensitive recording sheets, but depending on the application and required performance, conventionally used hisphenol A, P, It is also possible to use it in combination with phenols or organic acids such as P-(1-methyl-n-hexylidene) diphenol, TI-t-butylphenol, P-phenylphenol, and novolak type phenol resin.

Furthermore, various types of dyes are well known as the electrochromic colorless to light-colored colorless dyes used in the present invention, and are not particularly limited, but include, for example, the following dyes.

(Compounds having 11 lactone rings ■ Fluorane type (a) 3-diethylamino-6-methyl-7-anilinofluoran (black) (b) 3-(N-ethyl-P-toluidino)-6-methyl-7 Anilinofluorane (black) (c) 3-diethylamino-6-methyl-7-(ol I
・, para-dimethylanilino) fluorane (black) (d) 3-pyrrolidino-6-methyl-7-anilinofluorane (black) (e) 3-piperidino-6-methyl-7-anilinofluorane ( (black) (”-) 3- (N-chlorohexyl-N-methylamino)-6-methyl-7-anilinofluorane (black)
(g) 3-diethylamino-7-(orthochloroanilino)fluoran (black) (h) 3-diethylamino-7-(meta-trifluoromethylanilino)fluoran (black) (January 3-diethylamino-6- Methyl-chlorofluorane (red) (nu) 3-diethylamino-6-methyl-fluorane (
(red) (ru) 3-cyclohexylamino-6-chlorofluorane (orange) ■ Triphenylmethane-phthalide series (() CVL (criscle hioresotolactone)
(Blue) (B) MGL (Green) (C) Gray 1 ■ Indolyl phthalide series (A) Indolylette (red) (B) Indolyl blue (blue) ■ Other azaphthalides, lactams, spiropyrans, There are also chromenoindoles.

Among these dyes, fluoran compounds are particularly preferred; other dyes have drawbacks such as fading or deterioration by light before use, and their uses are limited.

The above-mentioned color developer and color-forming colorless dye are atomized to a particle size of several microns or less using a grinder such as a ball mill, attritor, or sand grinder or an appropriate emulsifier, and various additive materials are added depending on the purpose. Add it to make a coating liquid.

This coating solution usually contains binders such as polyvinyl alcohol, hydroxyethyl cellulose, methyl cellulose, starches, styrene-maleic anhydride copolymer, vinyl acetate-maleic anhydride copolymer, styrene-bucdiene copolymer, and kaolin. Inorganic or organic fillers such as calcined kaolin, diatomaceous earth, cruzi, titanium, calcium carbonate, magnesium carbonate, and aluminum hydroxide are added, and in addition, release agents such as fatty acid metal salts, waxes, etc.
h agents, hensifenone-based or triazole-based ultraviolet absorbers, water-resistant agents such as glyoxal, dispersants, antifoaming agents, and the like can be used.

In the present invention, a phenolic stabilizer is added to the coating liquid in order to prevent the background color from yellowing or to prevent the recorded image from fading.

By applying this coating liquid to paper and various films, the desired heat-sensitive recording sheet can be obtained.

The type and amount of hydroxyphthalic acid diester and the amount of other various components used in the present invention are determined according to the required performance and recording suitability, and are not particularly limited. It is appropriate to use 2 to 10 parts of hydroxyphthalic acid diester, 1 to 20 parts of filler, and 10 to 20% of the binder based on the total solid content.

As the above-mentioned stabilizer, antioxidants used in plastic products, rubber products, and petroleum products are mainly used.
- Melting point 90 as described in Publication No. 116689
Examples include phenols such as monophenols, hydroxynes, and bisphenols that have a solubility in water of 0 and 1 g/100 g or less at a temperature of 0.degree.

Such phenols include, for example, 2-hydroxy-
4-henzyloxyhenzophenone, resorcinol monobenzoicone-t-; 2,5-di-t-butylhydroquinone, 2,5-di-E-amylhydroquinone; 2,
2-methylenebis(4-methyl-6-t-butylphenol), 2,2-methylenebis(4-ethyl-6-t
= Nibutylphenol, 4,4-butylidene bis(3
-methyl-6-L-butylphenol), 4.4'-isopropylidenediphenol, 1.1-his(4-hydroxyphenyl)cyclohexane (also referred to as 4°4-cyclohexylidenediphenol), 2.2- methylenebis(4-methyl-6-cyclohexylphenol),
4゜45-methylenebis(2,6-di-t-butylphenol), 2,2'-isobutylidenebis(4,6-di-methylphenol), bis(3-may-4-hydroxy-5- t-butylhensyl) sulfide, 4.4
-thiobis(6-t-butyl-3-methylphenol), 4,4-thiobis(6-t-butyl-0-cresol), 2,6-bis(2-hyperoxy3-t-butyl-5- and bis(3,3'-bis(4'-hydroxy-3'-t-butylphenol)butyric acid) glycol ester.

The amount of these stabilizers used is 0.05 to 2 times by weight, preferably 0.1 times the weight of 4-hydroxyphthalic acid diester.
~1 times the weight.

Next, the present invention will be specifically explained with reference to examples.

Example Solution A (dye dispersion) 3-diethylamino-6-methyl-7-anilinofluorane 2.0 parts 10% polyvinyl alcohol aqueous solution 4.6 parts Water 2.
5 parts Solution B (color developer dispersion) Color developer* (see Table 2) 6.0 parts Zinc stearate 0.5 parts lO% polyvinyl alcohol aqueous solution 30.0 parts *Table 2 shows the color developer Hydroxyphthalic acid diesters and bisphenol 8 are used as shown in the figure.

Solution C (stabilizer dispersion) 2.2-methylenebis(4-methyl-6-t-butylphenol) and other phenol iJ 1.0 parts 10% polyvinyl alcohol aqueous solution 4.0 parts The can liquid of the above composition was milled into particles using a ball mill. Grind to a diameter of 3 microns.

Next, the dispersion liquid is mixed in the proportions shown below to prepare a coating liquid.

Part A (dye dispersion) 9.1 parts Part B (developer dispersion) 36.5 parts Part C (stabilizer dispersion) 5.0 parts Kaolin clay (50% dispersion) 12.0 parts This coating The liquid was applied to one side of a 50 g/m base paper at a coating amount of 6.0 g/rd and dried, and the sheet was treated with a supercalender so that the flatness of the sheet was 4 degrees for 200 to 300 seconds.

Table 2 shows the results of a quality performance test performed on the obtained black-colored heat-sensitive recording sheet.

(Margin below) Table 2 Note to Table 2: (Measured with 11 Maches Densitometer RD-104.

(2) Tokyo Shibaura Electric - Thermal facsimile KB-48
00 was used, the pulse width was 3.2 ms, and the applied voltage was 18.
The image density recorded in OV is Maches density δ1RD-10
Measured at 4.

(3) Yellowing The thermosensitive recording sheet was left indoors for 3 weeks, and its white background was measured using a Macbeth densitometer R-Rho 104 (using a yellow filter).

As is clear from Table 2, thermal recording sheets 1- (Examples 1-1 to 3-1) according to the present invention containing hydroxyphthalic acid diester and phenols as stabilizers do not contain phenols. Compared to Control Examples 4-1 to 4-3, the ground color is good, there is little change over time, and the color density, especially the dynamic color density when recorded by facsimile, is high.
Yellowing can be improved. Conventionally used bisphenol A (Comparative Example 4-4) is inferior in coloring sensitivity and yellowing to those of Comparative Examples 4-1 to 4-3 in which hydroxyphthalic acid diester was used alone. Furthermore, when no stabilizer is used, there is a tendency for the recorded image to fade.

The same procedure was carried out for 4-hydroxybenzoic acid benzyl ester, but compared to its coloring sensitivity, the coloring sensitivity of 4-hydroxyfucuric acid dimedyl ester was approximately lθ
%it was high.

Furthermore, when a hydroxyphthalic acid diester is used as a color developer, some hydroxyphthalic acid diesters having a hydroxyl group adjacent to a carboxyl group have low color development sensitivity.

Claims (1)

[Scope of Claims] ill A heat-sensitive recording sheet characterized by containing a normally colorless to light-colored colorless dye, a hydroxyphthalic acid diester having a melting point of about 60 to about 120°C, and a phenol. (2) The method according to claim 1, wherein the dye is a fluoran dye. (3) The method according to claim 1, wherein the hydroxyphthalic acid diester is hydroxyflusofucric acid, hydroxyisophthalic acid, or each diester of hydroxyisophthalic acid. (4) The method according to claim 3, wherein the hydroxyphthalic acid diester is 4-hydroxyphthalic acid diester. (5) The method according to claim 4, wherein the 4-hydroxyphthalic acid diester is dimedyl ester. (6) The method according to claim (11), wherein the phenol is a phenol having a melting point of 90'c or more and a solubility in water of 0.1 g/100 g or less. and bisphenols. (8) The hydroquinone is 2,5-di-L-butylhydroxyne or 2,5-di-L-amylhydroquinone. The method according to claim 7. (9) The bisphenols are 2,2-methylene-bis(4-methyl-6-t-butylphenol), 2,2-
Methylene-bis(4-ethyl-6-t-butylphenol'), 1,1-bis(4-hydroxyphenyl)cyclohexane, 2,6-bis(2-hydroxy!-3-t-butyl-5-methylbenzyl) )-4-methylphenol, 2,2-isobutylidenebis(4,6-di-methylphenol).