JPH0443797B2 - - Google Patents

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 with improved stability of colored images.

Heat-sensitive recording materials using an electron-donating colorless dye and an electron-accepting compound are disclosed in Japanese Patent Publications No. 14039-1982, Japanese Patent Publication No. 4160-43-1972, and the like. The minimum performance that such a heat-sensitive recording material should have is (1) sufficient color density and color development sensitivity, (2) no fogging (color development phenomenon during storage before use), and (3) The color forming body must have sufficient fastness after coloring, but currently no product has been obtained that completely satisfies these requirements.

Among these, there is a strong demand for stability and improvement of colored images, and research is being carried out diligently.

As a method to improve the stability of color images,
Japanese Patent Publication No. 51-43386 describes the addition of phenol derivatives such as 2,2'-methylenebis(4-methyl-6-tert-butylphenol).
No. 53-17347 discloses that it is possible to add a water-insoluble modified phenolic resin such as rosin modified
No. 72996 describes the addition of terephthalic acid esters, and British Patent Publication No. 2074335A describes the addition of hindered phenols. However, all of the heat-sensitive recording materials produced using these methods have insufficient image stability.

Therefore, an object of the present invention is to provide a heat-sensitive recording material which has good stability of a colored image and also satisfies other requirements.

The object of the present invention is to provide a heat-sensitive recording material containing an electron-donating colorless dye and an electron-accepting compound.
As the electron-accepting compound, one or more salicylic acid derivatives or metal salts thereof represented by the following general formula () or (') are mixed with one or more bisphenol derivatives represented by the following general formula (). This was achieved using a heat-sensitive recording material characterized by the following.

In the above formula, X and Y may each be the same or different and represent an aralkyl group, M represents an n-valent metal atom, and n represents an integer.

In the above formula, Z represents an alkylene residue.

X and Y in the above general formulas () and (')
Among the aralkyl groups represented by M, aralkyl groups having 7 to 18 carbon atoms are particularly preferable, and among the metal atoms represented by M, divalent to trivalent metal atoms are preferable, and zinc, aluminum, magnesium, and calcium are particularly preferable. .

Among the groups represented by Z in the above general formula (),
Alkylene residues having 3 to 10 carbon atoms are preferred.

The mixing ratio of the salicylic acid derivative or its metal salt, which is the electron-accepting compound according to the present invention, and the bisphenol derivative is preferably 90% by weight or less of either component.

In particular, salicylic acid derivatives and their metal salts are
Preferably it is 70% by weight.

The heat-sensitive recording material using the electron-accepting compound according to the present invention has sufficient color density, and the various colored images are extremely stable, with almost no discoloration or fading even after long-term light irradiation, heating, and humidification. This is particularly advantageous in terms of long-term preservation of records.

Next, specific examples of the electron-accepting compound according to the present invention will be shown.

Examples of salicylic acid derivatives 3,5-bis(α-methylbenzyl)salicylic acid, 3,5-dicumylsalicylic acid, and zinc salts and aluminum salts thereof.

Examples of bisphenol derivatives 2,2-bis(4-hydroxyphenyl)propane, 2,2-bis(4-hydroxyphenyl)
Butane, 2,2-bis(4-hydroxyphenyl)pentane, 2,2-bis(4-hydroxyphenyl)-3-methylpropane, 2,2-bis(4-hydroxyphenyl)-3-methylbutane ,
2,2-bis(4-hydroxyphenyl)-3-
Ethylpentane, 2,2-bis(4-hydroxyphenyl)-3-methylpentane, 1,1-bis(4-hydroxyphenyl)butane, 1,1-bis(4-hydroxyphenyl)-2- Ethylhexane, etc.

Electron-donating colorless dyes used in the heat-sensitive recording material of the present invention include triarylmethane compounds, diphenylmethane compounds, xanthene compounds,
Thiazine compounds, spiropyran compounds, etc. are used. Among these, xatene-based compounds whose coloring hue ranges from green-black to red-black are often used in black-coloring heat-sensitive recording materials. Some examples of these include 2-anilino-6-diethylaminofluoran, 2-p-chloroanilino-6-diethylaminofluorane, 2-o-chloroanilino-
6-diethylaminofluorane, 2-(2-methyl-4-chloroanilino)-6-diethylaminofluorane, 2-anilino-3-methyl-6-diethylaminofluorane, 2-anilino-3-methyl-6-ethyltri Aminofluorane, 2-anilino-3-methyl-6-cyclohexylmethylaminofluorane, 2-anilino-3-methyl-
5-chloro-6-diethylaminofluorane, 2
-anilino-3-methyl-6-diethylamino-
8-Methylfluorane, 2-m-trichloromethylanilino-6-diethylaminofluorane, 2
-octylamino-3-chloro-6-diethylaminofluorane, 2-ethoxyethylamino-3
-Chloro-6-diethylaminofluorane, 2-
Examples include ethylamino-3-chloro-6-diethylaminofluoran, 2-anilino-3-chloro-6-diethylaminofluoran, and 2-o-chloroanilino-6-dibutylaminofluoran. These may be used alone or in combination, or in combination with other known color formers.

Heat-sensitive recording materials using the electron-accepting compound of the present invention having hues other than black can be produced by combining them with various electron-donating colorless dyes.

Next, a general method for producing the heat-sensitive recording material according to the present invention will be described.

An electron-donating colorless dye, an electron-accepting compound and, if necessary, a thermofusible substance are sufficiently finely ground and mixed with the binder dissolved or dispersed in a solvent or dispersion medium, and kaolin, talc, and calcium carbonate are added to the liquid. Create a coating liquid by adding inorganic pigments such as If necessary, a paraffin wax emulsion, a latex binder, a sensitivity improver, a metal soap, an ultraviolet absorber, etc. can be added thereto.

The coating solution is applied to a support such as paper, plastic sheet, resin-coated paper, etc. and dried. When preparing a coating liquid, all the components may be mixed and pulverized at the same time from the beginning, or they may be combined into appropriate combinations, separately pulverized and dispersed, and then mixed.

Further, the coating liquid may be poured into the support.

The amounts of each component constituting the heat-sensitive recording material are 1 to 2 parts by weight of an electron-donating colorless dye, 1 part by weight of an electron-accepting compound, and 1 part by weight of an electron-donating colorless dye.
~6 parts by weight, 0 to 30 parts by weight of thermofusible substance, 0 pigments
~15 parts by weight, 1 to 15 parts by weight of binder, and 20 to 300 parts by weight of dispersion medium (solvent).

Water is most desirable as the dispersion medium (solvent).

Examples of binders used in the present invention include styrene-butadiene copolymers, alkyd resins, acrylamide copolymers, vinyl chloride-vinyl acetate copolymers, styrene-maleic anhydride copolymers, synthetic rubbers, gum arabic, polyvinyl alcohol, and hydroxyethyl cellulose. etc. can be mentioned.

Especially in relation to the dispersion medium (solvent), gum arabic,
Water-soluble binders such as polyvinyl alcohol, hydroxymethylcellulose, and carboxymethylcellulose are preferred.

As the thermofusible substance, stearic acid anilide, benzoin, α-naphthol benzoate, β-naphthol p-methylbenzoate, para-t-butylphenol phenoxy acetate, para-phenylphenol p-chlorophenoxy Acetate, 4,4'-cyclohexylitene diphenol diacetate, 4,4'-isopropylidene dimethoxybenzene, β-phenylethyl-p-phenyl phenyl ether, 2-p-chlorobenzyloxynaphthalene, 2-benzyloxynaphthalene , 1-benzyloxynaphthalene, 2-phenoxyacetyloxynaphthalene,
N-octadecylurea, N-hexadecylurea, N,N'-didodecylurea, phenylcarbamoyloxydodecane, stearamide,
Behenic acid amide, behenic acid, stearic acid, erucic acid, palmitic acid, para-hydroxybenzoic acid methyl ester, 4-benzyloxybenzoic acid benzyl ester, 1,2-cyclohexanedicarboxylic acid octadecyl ester-4,5-epoxide, P -N-octadecylcarbamoylbenzoic acid methyl ester, phthalic acid di-phenyl ester, triphenyl phosphate, para-hydroxydiphenyl ether, 2,2-bis{4-(β
-hydroxyethoxy)phenyl}propane, para-bis(β-hydroxyethoxy)benzene,
One or more types of hydroquinone diacetate etc. can be used.

These substances are colorless solids at room temperature;
It is a substance that has a sharp melting point at a temperature suitable for the heating temperature for copying, that is, around 70 to 160°C.

Examples will be shown below, but the present invention is not limited only to these examples.

Example 1 2-anilino-3-, an electron-donating colorless dye
5g of chloro-6-diethylaminofluorane
% polyvinyl alcohol (Sapon value 99%, degree of polymerization
1000) Dispersion was carried out overnight in a ball mill with 50 g of an aqueous solution. On the other hand, similarly, the electron-accepting compound 3,5-bis-α-methylbenzylsalicylic acid 3
g and 7 g of 2,2-bis-(4-hydroxyphenyl)propane were dispersed overnight in a ball mill with 100 g of a 5% polyvinyl alcohol aqueous solution,
After mixing these two dispersions, 20g of kaolin (diyodia kaolin) was added and dispersed well.
Further, 5 g of a 50% dispersion of paraffin wax emulsion (Chukyo Yushi Cellosol #428) was added to prepare a coating liquid.

The coating liquid was applied onto a base paper having a basis weight of 50 g/m ² so that the solid content was 6 g/m ² and heated at 60°C.
The coated paper was dried for 1 minute.

The coated paper is heated at 150℃/1 using a thermal head.
When heated for a few seconds, a black color image was obtained. The colored image was stored at 60℃ and 20% relative humidity for 24 hours, and the residual rate of the color image in the colored area {(density after processing/
The concentration before treatment) x 100} was found to be 88. The fog density in the non-image area was 0.10.

Example 2 In place of the electron-accepting compound of Example 1, 3 g of zinc 3,5-bis-α-methylbenzylsalicylate and 2,2-bis(4
A coated paper was obtained in the same manner as in Example 1 using 7 g of -hydroxyphenyl)propane.

After coloring was carried out in the same manner as in Example 1, the residual rate of the colored image was determined to be 90. The fog density in the non-image area was 0.08.

Example 3 Conducted using 7 g of 3,5-bis-α-methylbenzylsalicylic acid and 3 g of 2,2-bis(4-hydroxyphenyl)propane as electron-accepting compounds in place of the electron-accepting compound of Example 1. Example 1
Coated paper was obtained in the same manner as above.

After coloring was carried out in the same manner as in Example 1, the residual rate of the colored image was determined to be 98. The fog density of non-images was 0.13.

Next, a comparative example will be shown.

Comparative Example 1 A coated paper was obtained in the same manner as in Example 1 except that 10 g of 2,2-bis(4-hydroxyphenyl)propane was used as the electron-accepting compound instead of the electron-accepting compound in Example 1. After coloring was carried out in the same manner as in Example 1, the residual rate of the colored image was determined to be 62.
The fog density in the non-image area was 0.08.

Comparative Example 2 A coated paper was obtained in the same manner as in Example 1 except that 10 g of 3,5-bis-α-methylbenzylsalicylic acid was used as an electron-accepting compound in place of the electron-accepting compound in Example 1. After developing color in the same manner as in Example 1,
The residual rate of the colored image was determined to be 88. However, the fog density in the non-image area is 0.25, which is not suitable for practical use.

Comparative Example 3 In place of the electron-accepting compound used in Example 1, 10 g of benzyl 4-hydroxybenzoate and 2 A coated paper was obtained in the same manner as in Example 1 using 3.3 g of ,2'-methylenebis(4-methyl-6-t-butylphenol). After developing color in the same manner as in Example 1, the residual rate of the colored image was determined to be 40, and the fog density in the non-image area was 0.09, which is inferior to the present invention in terms of the residual rate of the colored image. It is something.

As described above, it can be seen that the electron-accepting compound of the present invention provides an excellent heat-sensitive recording material.

Claims (1)

[Scope of Claims] 1. A heat-sensitive recording material containing an electron-donating colorless dye and an electron-accepting compound, wherein the electron-accepting compound is a salicylic acid derivative represented by the following general formula () or (') or a metal salt thereof. A heat-sensitive recording material characterized by using a mixture of one or more kinds of bisphenol derivatives and one or more kinds of bisphenol derivatives represented by the following general formula (). In the above formula, X and Y may each be the same or different and represent an aralkyl group, M represents an n-valent metal atom, and n represents an integer. In the above formula, Z represents an alkylene residue.