JPH0497893A - Thermal recording material - Google Patents

Abstract

PURPOSE:To obtain a thermal recording material imparting an image having good preservability and having high sensitivity by containing an electron donating leuco dye, a specific electron acceptive compound and a specific oxalic ester compound. CONSTITUTION:A thermal recording material contains an electron donating leuco dye, an electron acceptive compound represented by general formula [I] (wherein R is an alkyl group, an alkoxy group, an alkylthio group, an aryl group or a halogen atom, M is a polyvalent metal and n is the valence of M) and an oxalic ester compound represented by general formula [II] (wherein X1 and X2 may be same or different and are a hydrogen atom, a halogen atom, a lower alkyl group or a lower alkoxy group, Z is a direct bond or an oxygen atom and m is an integer of 1-4). As R of the general formula [I], a 1-20C alkyl group, a 1-20C alkoxy group, a 1-20C alkylthio group, a 6-20C aryl group or a halogen atom is pref. and, among them, a 7-20C substituted or non-substituted alkoxy group, an aryl substituted alkoxy group, an aryloxy substituted alkoxy group and an alkoxy substituted alkoxy group are especially pref. As a polyvalent metal represented by M, zinc, nickel, aluminum or cobalt are designated and zinc is especially pref. This recording material is excellent in color forming properties and also excellent in stability and chemical resistance with the elapse of time.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of the Invention) The present invention relates to a heat-sensitive recording material, and more particularly to a recording material with high sensitivity and improved image preservation.

(Prior art) Recording materials using electron-donating colorless dyes and electron-accepting compounds include pressure-sensitive paper, thermal paper, and photosensitive pressure-sensitive paper.

It is already well known as electrically conductive thermal recording paper, thermal transfer paper, etc. For example, UK patent 2140449, US patent 44
80052, 44369'! 0, Special public service Sho 60-239
92, JP 57-179836, JP 60-12355
6, 60-123557 etc. for details.

In recent years, research has been intensively conducted to improve the properties of recording materials, such as (1) color density and color sensitivity, and (2) fastness of color bodies, but there is a strong demand for improving the storage stability of non-image areas and image areas in particular. .

The present inventors investigated the oil solubility, water solubility, partition coefficient, pKa, substituent habitability, substituent position, and crystallinity when mixed with each of the electron-donating colorless dye and electron-accepting compound. We have pursued the development of good recording material materials and recording materials, focusing on characteristics such as changes in solubility.

(Purpose of the invention) Therefore, an object of the present invention is to improve the storage stability of images.

An object of the present invention is to provide a highly sensitive heat-sensitive recording material.

(Structure of the Invention) The object of the present invention is to provide an electron-donating colorless dye, an electron-accepting compound represented by the following general formula [1], and a compound represented by the general formula (11).
This was achieved by a heat-sensitive recording material characterized by containing an oxalic acid ester compound shown in the following.

(1) In the formula, R represents an alkyl group, an alkoxy group, a furkylthio group, an aryl group, or a halogen atom.

M represents a polyvalent metal, and n represents the valence of M.

[11] In the formula, × and ×2 may be the same or different,
Hydrogen atom, halogen atom, lower alkyl group, lower flukoxy group, 2 represents a direct bond or an oxygen atom, m is 1
Represents an integer of ~4.

Among the groups represented by R in general formula (1), the number of carbon atoms is 1 to
20 furkyl groups, carbon atoms 1-20 flukoxy groups, carbon atoms 1-20 furkylthio groups, carbon atoms! ! 6
~20 7-aryl groups or halogen atoms are preferred,
Among these, mono- or unsubstituted flukoxy groups having 7 to 20 carbon atoms, aryl-substituted flukoxy groups, 7-aryloxy-substituted alkoxy groups, and flukoxy-substituted flukoxy groups are particularly preferred.

Examples of the polyvalent metal represented by M include zinc, nickel, aluminum, cobalt, etc., and zinc is particularly preferred.

Specific examples of the group represented by R in the general formula (+) include methyl group, ethyl group, propyl group, isopropyl group,
Butyl group, t-butyl group, pentyl group, hexyl group, t
-octyl group, n-octyl group, t-nonyl group, n-decyl group, 5ec-decyl group, t-dodecyl group, 5ec-
dodecyl group.

5ec-tetradecyl group, methoxy group, ethoxy group, propoxy group, isopropoxy group, butoxy group, t-butoxy group, pentyloxy group, hexyloxy group, benzyloxy group, p-methylbenzyloxy group, p-ethylbenzyloxy group group, p-chlorobenzyloxy group, p-
Methoxybenzyloxy group, β-phenylethoxy group,
α-phenylethoxy group, γ-phenylpropyloxy group.

Octyloxy group, decyloxy group, tetradecyloxy group, hexadecyloxy group, octadecyloxy group,
β-phenoxyethoxy group, β-p-methylphenoxyethoxy group, β-p-chlorophenoxyethoxy group, β
-p-methoxyphenoxyethoxy group, β-4-t-butylphenoxyethoxy group, β-4-t-octylphenoxyethoxy group, β-p-benzyloxyphenoxyethoxy group, β-p-cumylphenoxyethoxy group.

3-phenoxypropyloxy group, 4-phenoxybutoxy group, β-2-naphthyloxyethoxy group, phenyl group, 4-butoxyphenyl group, 4-octyloxyphenyl group, β-octyloxyethoxy group, butylthio group, (2 -(2-phenoxyethoxy)ethoxy group, chlorine, bromine, fluorine.

Examples include, but are not limited to, iodine.

Specific examples of the compound represented by the general formula [II] according to the present invention include oxalic acid dibenzyl ester, oxalic acid di(p-methylbenzyl) ester, oxalic acid di(p-chlorobenzyl) ester, and oxalic acid dibenzyl ester. (m-methylbenzyl) ester, oxalate di(p-ethylbenzyl) ester, oxalate di(p-methoxybenzyl) ester, oxalate bis(β-phenoxyethyl) ester, oxalate bis(β-O-chloro phenoxyethyl) ester, bis(β-p-chlorophenoxyethyl) oxalate
ester, oxalate bis(β-p-ethylphenoxyethyl) ester, oxalate bis(β-m-methoxyphenoxyethyl) ester, oxalate bis(β-ρ-methoxyphenoxyethyl) ester, oxalate bis(4-
(phenoxybutyl) ester, etc. especially,
Oxalic acid dibenzyl ester, which is a compound represented by compound (II+), and di(p-methylbenzyl oxalate)
ester, oxalic acid di(p-chlorobenzyl) ester, oxalic acid di(m-methylbenzyl) ester, oxalic acid di(p-ethylhensyl) ester, oxalic acid di(p-ethylhensyl) ester,
-methoxyhensyl) ester is preferred.

In the present invention, a sensitizer can be used in combination with compound (11). Examples of sensitizers that can be used in combination are:
Examples include compounds disclosed in JP-A-58-57989, JP-A-58-87094, and JP-A-63-39375, and amide compounds and/or urea compounds are particularly preferred.

Examples of the electron-donating colorless dye of the present invention include triphenylmethane phthalide compounds, fluoran compounds, phenothiazine compounds, indolyl phthalide compounds, and leuco auramine compounds.

Rhodamine lactam compounds, triphenylmethane compounds, triazene compounds, spiropyran compounds 1
There are various compounds such as fluorene compounds.

Specific examples of phthalides are listed in U.S. Reissued Patent Specification Column 23.0
No. 24, U.S. Pat. No. 3,491.111, U.S. Pat. No. 3,491,112, U.S. Pat.

Specific examples of fluorans can be found in US Pat. No. 3,624.
No. 107, No. 3.627.787, No. 3,641
, No. 011, No. 3.462.828, No. 3.68
No. 1,390, No. 3.920.510, No. 3.9
No. 59,571, specific examples of spyrodibilanes are given in U.S. Patent No. 3,971.808, and pyridine and pyrazine compounds are given in U.S. Patent No. 3,775,424.
issue.

No. 3,853,869, No. 4,246,318, and specific examples of fluorene compounds are given in Japanese Patent Application No. 61-2409.
It is described in No. 89 etc.

Among these, fluoran compounds are particularly preferred.

The electron-accepting compound according to the present invention may be used in combination with other phenol derivatives, metal salts of aromatic layer carboxylic acids, acid clay, bentonite, novolac resins, metal-treated novolac resins, metal complexes, etc. An example is Special Publication No. 40-9309.

Japanese Patent Publication No. 45-14039, Japanese Patent Publication No. 52-140483
No., JP-A-48-51510, JP-A-57-2108
No. 86, JP-A No. 58-87089.

JP-A-59-11286, JP-A-60-176795
No. 61-95988, etc. At this time, it is preferable that the electron-accepting compound according to the present invention is used in an amount of 20% by weight or more.

In particular, it is preferably used in an amount of 30% by weight or more.

In the recording material according to the present invention, the electron-accepting compound is preferably used in an amount of 50 to 1000% by weight, more preferably 100 to 500% by weight of the electron-donating colorless dye.

The compound of general formula (11) according to the present invention is preferably used in an amount of 50 to 500% by weight of the electron-donating colorless dye,
More preferably, it is 100 to 300%.

When these are applied to recording materials, they are used in the form of fine dispersions, minute droplets, or films.

When used for thermal paper, JP-A-62-144゜989
No. 62-244.883, etc. Specifically, the electron-donating colorless dye, the electron-accepting compound, and the aromatic ether compound are crushed and dispersed in a dispersion medium to a particle size of 3 μm or less, preferably 1.5 μm or less. Generally, an aqueous polymer solution with a concentration of about 0.5 to 10% is used as a dispersion medium, and dispersion is carried out using a ball mill, sand mill, or
This is done using a horizontal sand mill, attritor, colloid mill, etc.

Additives may be added to the coating liquid thus obtained as necessary to meet various requirements. An example of an additive is an inorganic pigment in the binder to prevent staining of the recording head during recording.

Oil-absorbing substances such as polyurea fillers are dispersed, and fatty acids and metal soaps are added to improve mold releasability from the head, and thermofusible substances are added to improve thermal response sensitivity. .

Therefore, in general, in addition to electron-donating colorless dyes that directly contribute to color development, one-electron-accepting compounds, and aromatic ether compounds, thermofusible substances, pigments, and waxes are used.

Additives such as antistatic agents, ultraviolet absorbers, antifoaming agents, conductive agents, fluorescent dyes, and surfactants are coated on the support to form a recording material.

Furthermore, if necessary, a protective layer may be provided on the surface of the heat-sensitive recording layer. A coating liquid similar to the protective layer may be applied to the back side in order to correct the curl balance of the support or to improve chemical resistance from the back side.Adhesive on the back side It may be applied and further combined with release paper to form a label.

Typically, electron-donating colorless dyes and electron-accepting compounds are.

It is dispersed and applied in a binder. Water-soluble binders are generally used, such as polyvinyl alcohol, hydroxyethyl cellulose, hydroxypropyl cellulose, and epichlorohydrin-modified polyamide. Ethylene-maleic anhydride copolymer, styrene-maleic anhydride copolymer, isobutylene-maleic anhydride copolymer.

Polyacrylic acid, polyacrylic acid amide, methylol-modified polyacrylamide, starch derivatives.

Examples include casein and gelatin. In addition, water-resistant agents are added to these binders for the purpose of imparting water resistance.
Emulsions of hydrophobic polymers, specifically styrene-butadiene rubber latex.

Acrylic resin emulsion etc. can also be added. The coating liquid is applied onto base paper, high quality paper 2 synthetic paper, plastic sheet, resin coated paper or neutral paper.

(Examples of the invention) Examples are shown below, but the present invention is not limited thereto.1% by weight unless otherwise specified in the examples.
represents.

Example-1 2-anilino-3-methyl-6-N-ethyl-N-isoamylaminofluorane, 4-benzyloxythiobenzoic acid zinc salt, and oxalic acid dibenzyl ester, 2 each
09 to 1009 5% polyvinyl alcohol (Clari P
VA 105) It was dispersed with an aqueous solution using a sand grinder, and the volume average particle diameter was set to 1 μ by microtrack.

On the other hand, calcium carbonate (manufactured by Shiraishi Kogyo; Unibar 70) 80
9 was dispersed with a 0.5% solution of sodium hexametaphosphate 1609 using a homogenizer.

Disperse each dispersion as described above into an electron-donating colorless dye dispersion 59. Electron-accepting compound dispersion 109, thermofusible substance dispersion 109. A calcined kaolin dispersion liquid was mixed in a ratio of 259 parts, and an emulsion of zinc stearate 49 parts, an aqueous solution of 2% sodium (2-ethylhexyl) sulfosuccinate 59 parts, and a paraffin wax dispersion (manufactured by Chukyo Yushi Co., Ltd.; Hydrin D-337, solid content). 59 (concentration 30%) was added to obtain a coating liquid. 1 tsubo weight of this coating liquid is 509/m2
The mixture was applied onto high-quality paper using a wire bar so that the dry coating amount was 69/m2, and calendering was performed to obtain a coated paper.

Example-2 4-benzyloxythiobenzoic acid zinc salt of Example-1,
A coated paper was obtained in the same manner as in Example 1 using 4-β-phenoxyethoxythiobenzoic acid zinc salt instead.

Example-3 Thermal recording paper was prepared in the same manner as in Example-1 except that the thermal coating liquid was prepared using oxalic acid di(p-methylbenzyl) ester instead of using oxalic acid dibenzyl ester. I got it.

Example-4 Thermal recording paper was prepared in the same manner as in Example-1, except that the thermal coating liquid was prepared using oxalic acid di(p-O lobenzyl) ester instead of using oxalic acid dibenzyl ester. I got it.

Example-5 A coated paper was obtained in the same manner as in Example-3 except that methylolstearylamide 59 was added to oxalic acid di(p-methylbenzyl) ester 259 of Example-3.

Comparative Example-1 A coated paper was obtained in the same manner as in Example-1 except that zinc thiobenzoate was used in place of the zinc salt of 4-benzyloxythiobenzoate in Example-1.

Comparative Example-2 A coated paper was obtained in the same manner as in Example-1 except that parabenzylbiphenyl was used instead of dibenzyl oxalate in Example-1.

Comparative Example-3 Example-1 except that bisphenol-A was used instead of 4-benzyloxythiobenzoic acid zinc salt in Example-1.
Coated paper was obtained in the same manner as above.

Comparative Example-4 A coated paper was obtained in the same manner as in Example-1 except that the oxalic acid dibenzyl ester dispersion of Example-1 was not added.

Performance comparison (color development) The color density was printed using a thermal printing tester (KLT head) manufactured by Kyocera Corporation at +20 mJ/mm2, and the color density was measured using a Macbeth RD-918 type densitometer. .

[Image storage stability] Printing was performed on a heat-sensitive recording material in the same manner as in the color development evaluation, and the resulting sample was left at 40°C and 90% RH for 24 hours, and the density of the printed area was measured using Macbeth RD-918. The remaining concentration was measured.

[Chemical Resistance] Marks were made on the printed and non-printed areas with a yellow marker pen (PEN-2, manufactured by Zebra Co., Ltd.), and 24 hours later, the following evaluations were made.

(1) Background fogging ○: No fogging on the background is observed.

Δ: Some fogging occurs, but the printed portion is readable.

×: Fogging is severe and the printed area cannot be read. C) Discoloration of the image area O: No discoloration is observed and the printed area can be clearly read.

Δ: There is some low density 1, but the print is readable. × ;The color disappears completely.

No. table As shown in Table 1, The recording material of the present invention is Excellent color development.

and stability over time Excellent chemical resistance It can be seen that

Claims (1)

[Claims] (1) Electron-donating colorless dye and the following general formula [I]
A heat-sensitive recording material comprising an electron-accepting compound represented by the following formula and an oxalic acid ester compound represented by the following general formula [II]. ▲There are mathematical formulas, chemical formulas, tables, etc.▼[I] ▲There are mathematical formulas, chemical formulas, tables, etc.▼[II] [I] In the formula, R is an alkyl group, an alkoxy group, an alkylthio group, an aryl group, a halogen atom, M represents a polyvalent metal, and n represents the valence of M. [II] In the formula, X_1 and X_2 may be the same or different, a hydrogen atom, a halogen atom, a lower alkyl group, a lower alkoxy group, Z represents a direct bond or an oxygen atom, and m is an integer of 1 to 4. represent. (2) Claim 1, wherein the group represented by R in the electron-accepting compound represented by the general formula [I] is an aryloxyalkoxy group having 8 to 20 carbon atoms. Claim No. 1, characterized in that the group represented by R in the electron-accepting compound represented by the general formula [I] of the heat-sensitive recording material (3) is an aralkyloxy group having 7 to 20 carbon atoms. The heat-sensitive recording material according to item 1. (4) The heat-sensitive recording material according to claim 1, wherein the polyvalent metal represented by M in the electron-accepting compound represented by the general formula [I] is zinc. (5) The heat-sensitive recording material according to claim 1, wherein the oxalic acid ester compound represented by the general formula [II] is a compound represented by the general formula [III]. ▲There are mathematical formulas, chemical formulas, tables, etc.▼ [III] (X^3 and X^4 may be the same or different and represent a hydrogen atom, a halogen atom, a lower alkyl group, or a lower alkoxy group.) (6) The heat-sensitive recording material according to claim 1, characterized in that the compound represented by the general formula [II] or [III] is used in combination with an amide compound or a urea compound as a thermofusible compound.