JPH0236989A - Heat-sensitive recording sheet - Google Patents

Abstract

PURPOSE:To obtain a heat-sensitive recording sheet with exceedingly high coloring sensitivity and also excellent stability of a color development section and a non-color development section by using nuclear halogen-substitution aromatic ester phosphate and/or nuclear halogen-substitution aromatic ester phosphite. CONSTITUTION:Nuclear halogen-substitution aromatic ester phosphate and/or nuclear halogen-substitution aromatic ester sulphite with a melting point of 65 deg.C or more can be used as a coloration improver. Especially those with a melting point of 65-120 deg.C having superior stability at normal temperature and coloration sensitivity during heating are favorable. The reasons are as follows: The hydrolysis by acidic materials such as bisphenol A is accelerated due to the electron absorption by halogen atoms during thermal melting, and the rings of color-developing lactone compounds are easily opened with resultant concentrated phosphorous acid. Consequently, coloration sensitivity is increased and thermal resistance at temperature lower than the melting temperature is increased by the barrier effects of halogen atoms thus contributing to color stability.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a heat-sensitive recording sheet that has extremely high color development sensitivity and excellent stability in color development areas and non-color development areas.

(Prior art) Thermosensitive recording sheets are devices that use thermal energy to express images such as characters and figures on recording sheets, and have recently been used in fields such as various printer recorders, facsimiles, POS labels, and automatic ticket gates. It started to be done. There are various thermal recording methods, but from the viewpoint of image clarity, resolution, image tone, etc., we use a color-forming compound such as crystal violet lactone (CVL), which is a dye precursor, and an acidic substance that develops the color. The main method is to use

In this method, a phenol compound such as hisphenol A, which is solid at room temperature but melts and liquefies when heated and acts as an acid component, is conventionally used as an acidic substance.

At this time, the heat-sensitive material is required to have a high degree of whiteness, and that its whiteness does not easily decrease even when stored. Usually, in order to obtain clear color development, 140~
It is necessary to maintain the temperature at about 150°C for a certain period of time. Therefore, various approaches have been widely researched and reported in order to develop colors faster and more easily and vividly.

For example, there is a method of adding stearin, acid amide, etc. as a coloring performance improver (Japanese Patent Application Laid-Open No. 54139740), a method of using benzyl p-hydroxybenzoate, etc. as an acidic substance (Japanese Patent Application Laid-open No. 74762/1987), etc. However, although the methods described in these publications improve the color development sensitivity, they are still insufficient, and the stability of the color development area and non-color development area is also not satisfactory.

Previously, the present inventors conducted extensive studies and found that aromatic phosphate esters and/or aromatic phosphite esters are superior as coloring performance improvers compared to conventional ones (Japanese Unexamined Patent Publication No. 6
2-267186).

(Problems to be Solved by the Invention) However, even if the aromatic phosphate ester and/or aromatic phosphite are used as a coloring performance improver, the stability of the non-coloring area, especially at high temperatures (60°C) The stability was insufficient.

(Means for Solving the Problems) In view of this situation, the inventors of the present invention conducted further intensive studies and found that a nuclear halogen-substituted aromatic phosphoric acid ester and/or a nuclear halogen-substituted aromatic phosphorus having a melting point of 65°C or higher When an acid ester is used as a performance improver, the effect of improving color development sensitivity is significantly higher than that of conventional color development performance improvers, and the stability of color development areas and non-color development areas is also excellent.Thermal recording/-1
・We have discovered that it can be obtained, and have completed the present invention.

That is, the present invention provides a heat-sensitive recording sheet having a coating film containing a color-forming compound, an acidic substance, and a color-forming performance improver, in which the color-forming performance improver or a nuclear halogen-substituted aromatic phosphate ester having a melting point of 65° C. or higher is used. and/or a nuclear halogen-substituted aromatic phosphite ester.

The reason why the heat-sensitive recording sheet of the present invention has high color development sensitivity and particularly excellent stability of color development and non-color development areas is as follows:
1) Due to the electron-withdrawing property of halogen atoms, hydrolysis by acidic substances such as bisphenol A is promoted during thermal melting.
(2) The ring-opening of the color-forming lactone compound by the more acidic (phosphorous acid) produced is facilitated, improving color development sensitivity, and (2) heat resistance below the melting temperature is increased due to the barrier effect of the halogen atom. There are two possible reasons why this method improves stability.

As the nuclear halogen-substituted aromatic phosphoric acid ester and/or the nuclear halogen-substituted aromatic phosphite used as the coloring performance improver in the present invention, any one with a melting point of 65°C or higher can be used, but especially those with a melting point of 65°C or higher can be used. Those having a melting point of 65 to 120°C are preferred because they are particularly excellent in stability and color development sensitivity upon heating.

As a specific example, at least one compound represented by the following structural formulas (1) to (8) is preferred.

, CHl (CH3)2CH Although those with a melting point of less than 65°C, such as phosphoric acid tri(0-chlorophenyl) ester with a melting point of 37°C and phosphoric acid triethyl ester that is liquid at room temperature, have the effect of improving coloring performance, It works at room temperature or slightly higher temperature and lacks the ability to maintain white color during storage.

Examples of the color-forming compound used in the present invention include, but are not limited to, the following compounds.

3.3-bis(p-dimethylaminophenyl)phthalide, 3,3-bis(p-dimethylaminophenyl)-6-
Dimethylaminophthalide (also known as crystal violet lactone = CVL), 3.3-bis(p-dimethylaminophenyl) 6-aminophthalide, 3.3-bis(p-
dimethylaminophenyl)-6-nitrophthalide, 3.
3-His(p-dimethylaminophenyl)phthalide, 3
, 3-bis3-dimethylamino-7methylfluorane,
3-diethylamino-7-chlorofuran, 3-diethylamino-6-chloro7-methylfluorane, 3-diethylamino-7anilinofluorane, 3-diethylamino-6methyl-7-anilinofluorane, 3-diethylamino-6-chloro7-anilinofluorane piperidino-6-methyl-7-anilinofluorane, 3(N-
Ethyl-p=toluidino)-7-(N-methylanilino)
Fluoran, 3-(N-ethyl p-1-luidino)-6
-Fluorane phthalides such as methyl-7-anilinofluorane, lactams such as rhodamine B lactam, 3-
Examples include spiropyrans such as methylspirodinaphthopyran, 3-ethylspirodinaphthopyran, and 3-benzylspironaphthopyran. Of course, these compounds must be colorless or light-colored and develop color when reacting with acidic substances.

In addition, acidic substances are solid at room temperature and have a molecular weight of 65 to 180
Any compound that melts and liquefies when heated to about 0.degree. C., opens the ring of the color-forming compound, and develops color may be used, and any of them will function well in the presence of a color-forming performance improver. Examples include, but are not limited to, the following.

4-phenylphenol, 4-hydroxyacetophenone, 2.2'-dihydroxydiphenyl, 2.2'-methylenehis (4-chlorophenol), 2.2'-methylenehis (4-medy-6-t-butylphenol), 4
．． 4'-isopropylidene diphenol (also known as hisphenol A), 4,4'-impropylidene bis (2-chlorophenol), 4,4'-impropylidene bis (
2-methylphenol), 4,4'-ethylene his (2
-methylphenol), 4,4'-thiohis (6-t-
butyl-3-methylphenol), 1,1-his(4-
hydroxyphenyl)-cyclohexane, 2.2'-bis(4-hydroxyphenyl)-〇-heftane, 4.4
Examples thereof include '-cyclohequinyldenhis (2-inpropylphenol), 4147-sulfonylhisphunino L=, salicylic acid anilide, novolak type phenol resin, benzyl p-hydroxybenzoate, and the like.

These acidic substances contain 100 parts by weight of a color-forming compound (hereinafter referred to as
It is usually used in an amount of 10 to 1.000 parts, preferably L<l;tloO-500 parts.

The coloring performance improver is usually used in an amount of 1-1 to 100 parts of the acidic substance.
1,000 parts, preferably L<li30-100 parts.

The color-forming compound, acidic substance, and color-forming performance improver are all used in the form of fine particles, preferably fine particles having a particle diameter of several microns or less.

In order to produce a heat-sensitive recording sheet, there are various generally known methods available. Usually, a coating film is prepared by dispersing a color-forming compound, an acidic substance, and a color-forming performance improver in water, and then Sea I・Method of applying to the base material, ■Color development・Prepare a coating solution in which the metal and the acidic substance are separately dispersed in water, and at least one of them contains a color development performance improver. It is possible to adopt a method of applying a coating liquid to a sealant substrate in a layered manner. Of course, an aqueous binder such as polyvinyl alcohol, methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, starch, or styrene-maleic acid copolymer is added to the above coating liquid. In addition, in order to improve performance, the coating liquid may contain ultraviolet absorbers such as benzophenone and triazole, fillers such as nylonium carbonate, lubricants such as polyethylene wax and paraffin wax, waterproofing agents, etc. Various other agents can also be added. Furthermore, various dispersants for dispersing various drugs in water can be added to the coating liquid.

The coating liquid generally has a dry weight of 2 ml per 1 m 2 of sheet substrate.
The heat-sensitive recording sheet 1 of the present invention is obtained by coating it on a sheet base material so that it has a molecular weight of 122 to 122, and then drying it at room temperature to about 50°C.

Paper is generally used as a notebook material, but synthetic resin sheets, non-woven fabric sheets, etc. can also be used as appropriate.

(Examples) Next, the present invention will be explained in more detail with reference to Examples, Comparative Examples, and Test Examples, but the present invention is not equally limited by these. In addition, parts and percentages in the examples are based on weight.

Example I Solution A (dye liquid) 3-(N-methyl-p-toluidino)-6methyl-7-
Anilinofluorane 1.0 parts Compound of structural formula (1) (melting point 117°O) 2.0 parts 10% polyhinyl alcohol aqueous solution 30 parts Water
50 copies total
11.0 parts Solution B (acidic substance liquid) Hisphenol A 3.0 parts Calcium carbonate 30 parts Zinc stearate 0.5 parts 10% borihinyl alcohol aqueous solution 7.0 parts Water
100 copies total
23.5 parts The above solution and Solution B were separately blended, and each was pulverized and dispersed using a bait condenser to obtain a coating solution stock solution.

Next, 11.0 parts of liquid A and 23.5 parts of liquid B were mixed to make a heat-sensitive coating liquid, and it was coated on 64.57'/m2 of 1-quality paper so that the coating amount after drying was 87 parts m2. The heat-sensitive recording sheet of the present invention was obtained by coating and drying.

This sheet was excellent in color development sensitivity and stability of color development areas and non-color development areas.

Examples 2 to 8 Structural formulas (2) to (8) in place of the compound of structural formula (1)
Compounds [melting point is 9 in order from the compound of structural formula (2)]
5°C 1109°C 190°C 190°C 194°C 187°C and 75°C. A heat-sensitive recording sheet of the present invention was obtained in the same manner as in Example 1, except that the following was used.

All of these sheets were excellent in color development sensitivity and stability of color development areas and non-color development areas.

Example 9 The amount of the compound of structural formula (1) added was changed to 1.0 part, and A
A thermosensitive recording sheet of the present invention was obtained in the same manner as in Example 1 except that the amount of liquid used was 10 parts.

This /-t was excellent in color development sensitivity and stability of color development areas and non-color development areas.

Example 10 The amount of the compound of structural formula (1) added was changed to 4.0 parts, and A
A thermosensitive recording sheet of the present invention was obtained in the same manner as in Example 1 except that the amount of liquid used was 13 parts.

This sheet was excellent in color development sensitivity and stability of color development areas and non-color development areas.

Comparative Example 1 A heat-sensitive recording sheet for comparison was obtained in the same manner as in Example 1, except that the addition of the compound of structural formula (1) was omitted and the amount of liquid A used was reduced to 9.0 parts.

This sheet was extremely poor in color development sensitivity and stability of color development areas.

Comparative Example 2 Stearic acid amide (
A heat-sensitive recording sheet for comparison was obtained in the same manner as in Example 1 except that a material with a melting point of 10,000 was used.

This sheet was extremely poor in color development sensitivity and stability of color development areas and non-color development areas.

Comparative Example 3 Same as Example 1 except that the addition of the compound of structural formula (1) was omitted, the amount of liquid A used was 9 parts, and benzyl p-hydroxybenzoate was used instead of hisphenol A. A thermosensitive record of /-1 was obtained for comparison.

This sheet had significantly poor color development sensitivity and stability of the color development area.

Comparative Example 4 A heat-sensitive recording sheet for comparison was obtained in the same manner as in Example 1, except that tos-naphthyl phosphate (melting point: 98° C.) was used instead of the compound of structural formula (1).

This sorting was poor in the stability of colored areas and non-colored areas.

Comparative Example 5 A thermal recording sheet for comparison was obtained in the same manner as in Example 1, except that tripp-methylphenyl phosphate (melting point: 76°C) was used instead of the compound of structural formula (1).

In this case, the stability of the non-color developing area is poor.

Test Examples Tests regarding the coloring sensitivity and stability of coloring areas and non-coloring areas of the thermosensitive recording sheets obtained in Examples 1-10 and Comparative Examples 1-5 were conducted as follows.

The results are shown in Table-1.

[Evaluation of color development sensitivity] Using an MSI type super-head printing device manufactured by Matsushita Electronic Components Co., Ltd., printing was performed on a sheet under the conditions of a pulse width of 0.1 to 10 milliseconds to develop color, and the degree of color development was determined as Macbeth. The pulse width at which the color density value reached l O was determined from the color density/pulse width curve, and the color sensitivity was evaluated based on the magnitude of this pulse width value ( The smaller the pulse width value, the higher the color development sensitivity.)

[Evaluation of stability of colored areas and non-colored areas] Using a sheet that was colored under the above conditions, the stability of colored areas and non-colored areas was evaluated under the following two conditions (Condition A and Condition B). Ta.

(Condition A) The above sheet was left in an atmosphere with a temperature of 60° C. and humidity of 25%, and after 24 hours, the degree of whitening and decolorization of the colored area and background fogging of the non-colored area was visually evaluated according to the following criteria. .

1) Evaluation of colored areas ■ Evaluation criteria for whitening @1 No whitening ○: Two whites are not noticeable △: Two whites ×: Significant whitening ■ Evaluation criteria for discoloration ◎ No bleaching ○, no discoloration △ : Discoloration ×: Significant discoloration 2) Evaluation of non-colored areas ■Evaluation criteria for background fog @, No background fog ○, Background fog is moderate △, Background fog ×: Significant background fog (Condition B) The sheet was left in an atmosphere with a temperature of 40° C. and a humidity of 90%, and the degree of decolorization of the colored portion after 24 hours was visually evaluated using the same criteria as in Condition A.

(Effect of the invention) Thermal recording system of the present invention To is, Extremely sensitive color development high, Furthermore, the stability of the colored and non-colored areas is also excellent.

Claims (1)

[Scope of Claims] 1. In a heat-sensitive recording sheet having a coating film containing a color-forming compound, an acidic substance, and a color-forming performance improver, the color-forming performance improver is a nuclear halogen-substituted aromatic phosphoric acid having a melting point of 65° C. or higher. A heat-sensitive recording sheet characterized by being an ester and/or a nuclear halogen-substituted aromatic phosphite. 2. The heat-sensitive writing sheet according to claim 1, wherein the coloring performance improver is at least one compound represented by the following structural formulas (1) to (8). (1) ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ (2) ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ (3) ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ (4) ▲ Numerical formulas, chemical formulas, tables, etc. Yes ▼ (5) ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ (6) ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ (7) ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ (8) ▲ Mathematical formulas, chemical formulas, tables, etc. There are etc.▼