JPH082698B2 - Thermal recording - Google Patents

Description

The present invention relates to a heat-sensitive recording material, and more particularly to a heat-sensitive recording material having excellent high-speed recording characteristics and high stability of raw paper and recorded images.

<Prior Art> Generally, a heat-sensitive recording material obtained by coating a colorless or pale-colored leuco dye and a developer that develops the color of the leuco dye on heat is disclosed in JP-B-45-14035. Has been put to practical use. To record on this thermosensitive recording medium,
A thermal printer with a built-in thermal head is used, but such a thermal recording method does not generate noise during recording, does not require developing and fixing, is maintenance-free, and has a relatively small equipment, compared to other recording methods. Due to its low cost, it is widely used as a computer output, a printer for facsimiles, calculators, etc., a measuring recorder and a paper wrapper for vending machines.

In recent years, these recording devices are becoming compact and energy-saving, and as a required characteristic of the heat-sensitive recording paper used therefor, there is a demand for high-density color development with low applied energy, that is, a demand for sophistication. It is rising. On the other hand, downsizing of the equipment makes it more likely that the temperature of the space for loading the recording paper will rise due to the effect of heat accumulation in the recording head and the effect of heat generation from the electric circuit. There is a growing demand for thermal stability that is easy to increase the concentration and contrary to high sensitivity.

As a method of increasing the sensitivity, generally, a method of lowering the melting point of a leuco dye or a developer or a method of improving the compatibility of both is taken, and a method of adding a sensitizer as a third component is examined. Has been done. For example, as a leuco dye,
56-52759, JP-A-59-120653, JP-A-60-208360
No. 1 discloses materials having a melting point of 180 ° C. or less and excellent recording sensitivity. As the color developer, p-hydroxybenzoic acid ester (JP-A-54-74762), diphenol or monophenol sulfone compound (JP-A-57-210886, JP-A-59-96991, diphenol sulfide compound (JP-A-59-96991) 57-33187), diphenol disulfide compound (JP-A-59-52694), and various other studies have been conducted.
Examples of sensitizers include waxes (JP-A-48-129231), naphthol derivatives (JP-A-7-64593), naphthoic acid derivatives (JP-A-5-64592), and ether compounds (JP-A-60-7).
8780) and various other materials are being studied.

However, the thermal recording material produced by using these methods is relatively excellent in terms of high sensitivity, but the sublimation of the color developer and the sensitizer is strong, so that the color fading of the image is severe, and At present, the properties are still insufficient, because the compatibility with the dye is too good to cause background fog, or excessive melting point drop causes thermal instability.

Furthermore, as the market size of thermal recording media expands worldwide, in addition to the problems of thermal stability and image stability described above, the background fog of recording paper and the deterioration of printing performance over time under transportation processes and various storage environmental conditions may occur. It is becoming an important issue. This is caused by the effects of heat and humidity over a long period of time,
It is considered that the developer dissolves due to water and causes fog on the background, or the developer and sensitizer dissipate by heat and the color density decreases. The current situation is that a high-sensitivity thermosensitive recording medium has not yet been developed, which maintains long-term storage stability (hereinafter referred to as raw paper storage stability) of paper) and has good image storability.

<Problems to be Solved by the Invention> The present invention has been made in view of the above problems.
Specifically, the present invention relates to a thermosensitive recording medium which has not only good high-speed recording property and excellent stability in the image area, but also improved long-term storage stability of raw paper.

<Means for Solving Problems> The present invention provides a thermosensitive recording medium comprising a support and a thermosensitive coloring layer containing, as a main component, a leuco dye and a developer capable of coloring the leuco dye under heat. 2,2-bis (4
-Hydroxyphenyl) propane is used, and the leuco dye has a melting point of 19 with the compound represented by the following general formula (1).
A thermosensitive recording containing a compound represented by the following general formula (2) at 0 ° C. or higher, which is mixed, and further containing a sensitizer represented by the following general formula (3) and an antioxidant represented by the following general formula (4). It is the body.

General formula (1) General formula (2) (In the formula, R ₁ and R ₂ are each an alkyl group having 1 to 8 carbon atoms,
Shows a cycloalkyl group. R ₁ and R ₂ are-(CH ₂ ) _n-
It may be formed by bonding with a group. Where n is 4 or 5
Indicates. ) General formula (3) (In the formula, each R represents a hydrogen atom, a halogen atom or a lower alkyl group.) General formula (4) (In the formula, R ₁ represents a t-butyl or cyclohexyl group, and R ₂ represents an alkyl group having 1 to 3 carbon atoms.) The leuco dye of the general formula (1) used in the present invention has a melting point of 180 to 184. C., and when used alone has a serious drawback in image stability. Melting point used in the present invention
Specific examples of the leuco dye of the general formula (2) at 190 ° C. or higher include 3-diethylamino-6-methyl-7.
-Anilylfluorane, 3-pyrrolidino-6-methyl-
7-anilinofluorane, 3-piperidino-6-methyl-7-anilinofluorane, 3-cyclohexylmethylamino-6-methyl-7-anilinofluorane and the like are mentioned, and the leuco of the general formula (1) is mentioned. The weight ratio of the mixture of the dye and the leuco dye of the general formula (2) is preferably 98/2 to 91/9. Outside of this range, that is, when the amount of the leuco dye of the general formula (2) is large, the background fog is severe under high temperature and high humidity environment, and the long-term storage stability of raw paper is lacking. The problem that the stability of the recorded image is lacking is likely to occur.

The sensitizer of the general formula (3) used in the present invention is not only excellent in recording sensitivity, but also characterized in that it does not impair image stability or storage stability of raw paper. Specific examples include oxalic acid dibenzyl ester, oxalic acid di (p-methylbenzyl) ester, and oxalic acid di (p-chlorobenzyl) ester.

Specific examples of the antioxidant of the general formula (4) used in the present invention include 1,1,3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane, 1,1, Examples thereof include 3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane, and it is preferable to add 0.2 parts by weight or more to 1 part by weight of the leuco dye. If the amount is out of this range, that is, if the amount added is small, the problem of poor image stability in a high humidity environment tends to occur.

The thermosensitive coloring layer in the thermosensitive recording medium of the present invention comprises inorganic and organic pigments as a conventional filler such as heavy and light calcium carbonate, aluminum hydroxide, titanium oxide, zinc oxide, barium sulfate, talc, clay and satin. White, kaolinite, polyolefin particles, urea-formalin resin particles and the like can be added to improve the sharpness of the color image.

In addition, lubricants such as zinc stearate and calcium stearate are used for the purpose of improving matching with the thermal recording head, and paraffin wax, microcrystalline wax, etc. for the purpose of preventing pressure fog when smoothing the recording paper surface. Is added as needed.

The thermosensitive coloring layer is provided on a support, and in that case, paper, synthetic paper, resin film, or a composite of these is used, but paper is preferable in terms of cost. Further, for the purpose of improving the sharpness of the recorded image, it is possible to provide an undercoat layer on the surface of the support and to provide a thermosensitive coloring layer thereon.

In the heat-sensitive recording material of the present invention, a coating material containing these substances is generally prepared by preparing a dispersion liquid using water containing a water-soluble polymer as a dispersant and a well-known conventional stirring / grinding technique. It is prepared by mixing with a binder, various surfactants and antifoaming agents as necessary. As this binder, a water-soluble or water-insoluble resin binder can be used, for example, gelatin, casein, polyvinylpyrrolidone, polyvinyl alcohol, modified polyvinyl alcohol, starch, modified starch, isobutylene-maleic anhydride copolymer. Resin, diisobutylene-maleic anhydride copolymer resin, styrene-maleic anhydride copolymer resin, polyacrylamide, modified polyacrylamide, carboxymethyl cellulose, methyl cellulose, hydroxyethyl cellulose, further vinyl acetate, acrylic ester, vinyl chloride- Vinyl acetate copolymer, SBR, NBR
These emulsions, latexes, etc. are used alone or as a mixture. In addition, it is possible to add a waterproofing agent, if necessary.

These prepared paints are formed as a thermosensitive coloring layer by applying and drying the paint on a support by a conventionally known and commonly used coating technique such as air knife coating, blade coating, roll coating and the like.

<Examples> Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples. In addition, all the components are shown in parts by weight.

Example 1 A mixture having the following composition was subjected to dispersion treatment with a sand grinder to prepare dispersions [A] to [E].

[A] liquid 3-dibutylamino-6-methyl-7-anilinofluorane [compound of general formula (1)] 40 parts 5% aqueous methylcellulose solution 40 parts water 20 parts [B] liquid 3-methylcyclohexylamino-6 -Methyl-7-anilinofluorane [Compound of the general formula (2), melting point 202
[C] 40 parts 5% aqueous solution of methyl cellulose 40 parts water 20 parts [C] liquid 2,2-bis (4-hydroxyphenyl) propane 50 parts calcium carbonate 100 parts 10% polyvinyl alcohol aqueous solution 10 parts water 140 parts [D] liquid Shu Acid dibenzyl ester [compound of general formula (3)]
40 parts 10% polyvinyl alcohol aqueous solution 10 parts water 50 parts [E] liquid 1,1,3-tris (2-methyl-4hydroxy-5-cyclohexylphenyl) butane [compound of general formula (4)]
40 parts 10% aqueous polyvinyl alcohol solution 10 parts water 50 parts Using the liquids [A] to [E] obtained as described above,
Prepare a thermosensitive coloring layer paint with the following composition, coat it on a high-quality paper with a basis weight of 55 g / m ² to a dry coating amount of 6 g / m ^2, and then dry it with a super calender so that the Beck smoothness will be 500 seconds. Surface treatment was performed to obtain the thermosensitive recording medium of the present invention.

[A] liquid 47.5 parts [B] liquid 2.5 parts [C] liquid 240 parts [D] liquid 75 parts [E] liquid 25 parts 10% polyvinyl alcohol aqueous solution 200 parts Example 2 3 of [B] liquid of Example 1 -Methylcyclohexylamino-6-methyl-7-anilinofluorane instead of 3
A thermosensitive recording medium of the present invention was obtained in the same manner as in Example 1 except that -diethylamino-6-methyl-7-anilinofluorane (melting point 195 ° C) was used.

Example 3 The present invention was carried out in the same manner as in Example 1 except that oxalic acid di (p-methylbenzyl) ester was used instead of the oxalic acid dibenzyl ester of the sensitizer [D] solution. A thermosensitive recording medium was obtained.

Example 4 Instead of 1,1,3-tris (2-methyl-4hydroxy-5-cyclohexylphenyl) butane of the solution [E] which is the antioxidant of Example 1, 1,1,3-tris (2 A thermosensitive recording medium of the present invention was obtained in the same manner as in Example 1 except that -methyl-4hydroxy-5-t-butylphenyl) butane was used.

Comparative Example 1 A thermosensitive recording medium for comparison was obtained in the same manner as in Example 1 except that the liquid [A] was used instead of the liquid [B] in Example 1 and no leuco dye was mixed.

Comparative Example 2 Except that 3-ethylisoamylamino-6-methyl-7-anilinofluorane was used instead of 3-dibutylamino-6-methyl-7-anilinofluorane in the liquid [A] of Example 1. A thermal recording medium for comparison was obtained in the same manner as in Example 1.

Comparative Example 3 Instead of 3-methylcyclohexylamino-6-methyl-7-anilinofluorane in the liquid [B] of Example 1, 3-methylpropylamino- which is a leuco dye other than the present invention.
A thermal recording medium for comparison was obtained in the same manner as in Example 1 except that 6-methyl-7-anilinofluorane (melting point 178 ° C.) was used.

Comparative Example 4 Instead of the 2,2-bis (4-hydroxyphenylpropane) of the liquid [C] of Example 1, p- which is a developer other than the present invention is used.
A comparative heat-sensitive recording material was obtained in the same manner as in Example 1 except that benzyl hydroxybenzoate was used.

Comparative Example 5 A thermosensitive recording medium for comparison was prepared in the same manner as in Example 1 except that parabenzyl biphenyl as a sensitizer other than the present invention was used in place of the oxalic acid dibenzyl ester in the liquid [D] of Example 1. Got

Comparative Example 6 1,1,3-Tris (2-methyl-) of the solution [E] of Example 1
In the same manner as in Example 1 except that 2,2'-methylenebis (4-methyl-6-t-butylphenol), which is an antioxidant other than the present invention, was used in place of 4-hydroxy-5-cyclohexylphenyl) butane. A thermal recording medium for comparison was obtained.

Comparative Example 7 A thermosensitive recording medium for comparison was obtained in the same manner as in Example 1 except that the liquid [E] was not added.

The thermal recording materials of Examples and Comparative Examples obtained as described above were tested for recording density, image storage stability and raw paper storage stability. The results are shown in Table 1.
The test method is shown below.

(1) Recording density Power consumption with a thermal printer manufactured by Matsushita Electronic Components Co., Ltd.
0.5W / dot, scanning line density 8 x 7.7dot / mm, pulse width
Printed at 1.0 msec and print density is Macbeth reflection densitometer RD-9
Measured at 14.

(2) Image storage stability Moisture resistance A sample printed under the above conditions was left in an environment of 30 ° C and 90% RH for 1 week, and the residual rate was calculated according to the following formula.

Heat resistance The sample printed under the above conditions was left in a constant temperature bath at 60 ° C. for 24 hours, and the residual rate was determined in the same manner as in the previous section.

(3) Storage stability of raw paper The samples of Examples and Comparative Examples were left in an environment of 50 ° C and 90% RH for 1 month, and the background density was measured to evaluate the background fogging. Further, the sample after the test was printed under the recording condition of the item (1), the recording density was measured, and the coloring performance with respect to the density of the untested sample was determined by the following formula.

As is clear from Table 1, the thermosensitive recording medium of the present invention has not only excellent recording density but also good image storage stability, and further has remarkable advantages in raw paper storage stability. Recognize.

<Effects of the Invention> The thermosensitive recording medium of the present invention has excellent image storage stability while maintaining good recording density, and also has excellent raw paper storage stability in a harsh environment for a long period of time. Is a very sensitive thermal recording medium.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-58-208092 (JP, A) JP-A-60-19584 (JP, A) JP-A-60-96488 (JP, A) JP-A-55- 41277 (JP, A) JP 64-15583 (JP, A) JP 63-151481 (JP, A)

Claims (3)

[Claims] 1. A thermosensitive recording medium comprising a support and a thermosensitive coloring layer comprising, as a main component, a leuco dye and a developer capable of coloring the leuco dye under heat, the developer is 2,2-bis ( 4-hydroxyphenyl) propane, wherein the leuco dye is a mixture of a compound represented by the following general formula (1) and a compound represented by the following general formula (2) having a melting point of 190 ° C. or higher, and further the following general formula: A thermal recording material comprising a sensitizer represented by (3) and an antioxidant represented by the following general formula (4). General formula (1) General formula (2) (In the formula, R ₁ and R ₂ are each an alkyl group having 1 to 8 carbon atoms,
Shows a cycloalkyl group. R ₁ and R ₂ are-(CH ₂ ) _n-
It may be formed by bonding with a group. Where n is 4 or 5
Indicates. ) General formula (3) (In the formula, each R represents a hydrogen atom, a halogen atom or a lower alkyl group.) General formula (4) (In the formula, R ₁ represents a t-butyl or cyclohexyl group, and R ₂ represents an alkyl group having 1 to 3 carbon atoms.) 2. The weight mixing ratio of the leuco dye represented by the general formula (1) to the leuco dye represented by the general formula (2) having a melting point of 190 ° C. or higher is from 98/2 to 91/9. The heat-sensitive recording material according to claim 1, wherein 3. The heat-sensitive recording material according to claim 1, wherein the antioxidant represented by the general formula (4) is added in an amount of 0.2 parts by weight or more per 1 part by weight of the leuco dye.