JPH03108581A - Sheet for thermal recording - Google Patents

Abstract

PURPOSE:To improve color development sensitivity, and to enhance the stability of a color developing section and a non-color developing section by adding at least one kind of the aromatic thiophosphoric ester of nucleus substitution or non-nucleus substitution having the melting point of 65 deg.C or higher as a color-development performance improver. CONSTITUTION:In a sheet for thermal recording having a film including a color developing compound, an acidic substance and a color-development performance improver, at least one kind of the aromatic thiophosphoric ester of nucleus substitution or non-nucleus substitution having the melting point of 65 deg.C or higher is contained as the color-development performance improver. That is, a barrier effect works by introducing sulfur ions, heat resistance at the time of melting is increased, and ionicity contributes to the improvement of stability. Accordingly, the sheet for thermal recording having high color development sensitivity and the particularly excellent stability of a color developing section and a non-color-developing section is acquired.

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) A heat-sensitive recording sheet is a sheet that uses thermal energy to express images such as characters and figures on the heat-sensitive recording sheet.
In recent years, due to its simplicity, it has come to be widely used in fields such as facsimile paper, POS labels, various printer recorders, and automatic ticket gates. There are various methods for thermal recording, but from the viewpoint of image clarity, resolution, image tone, etc., it is preferable to use a dye precursor, such as a color-forming compound such as crystal violet lactone (CVL), and a color-forming method using it. The mainstream method is to use acidic substances. In this method, a phenol compound such as bisphenol A, which is solid at room temperature and melts and liquefies when heated and acts as an acid component, has been used as an acidic substance.

Here, the heat-sensitive recording sheet is required to have high sensitivity, no background fogging (high degree of whiteness), and excellent stability in colored and non-colored areas. Among these, there is a strong demand for high sensitivity in response to increased speed and energy saving of facsimiles, and various improvement methods have been reported.

For example, a method of adding stearic acid amide etc. as a coloring performance improver (Japanese Unexamined Patent Publication No. 54-139740) and a method of using benzyl p-hydroxybenzoate etc. as an acidic substance (Japanese Unexamined Patent Publication No. 54-74762) are available. However, although the methods described in these publications improve the coloring sensitivity, they are still insufficient, and the stability of the colored and non-colored areas is 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 Patent Application Laid-Open No. 62-1992-1). 267186).

(Problem to be Solved by the Invention) However, even if the above-mentioned 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 ), and performance I (lance) was unsatisfactory.

(Means for Solving the Problems) In view of this situation, the inventors of the present invention have conducted further intensive studies and found that a nuclear-substituted or non-nuclear-substituted aromatic thiophosphoric acid ester having a melting point of 65° C. or higher is used as a coloring performance improver. The inventors have now discovered that a heat-sensitive recording sheet can be obtained which has superior color development sensitivity and even better stability of color developing areas and non-color developing areas compared to conventional color development performance improvers, and has 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 improving agent, in which a nuclear-substituted or non-nuclear-substituted aroma with a melting point of 65° C. or higher is used as a color-forming performance-improving agent. At least one of the group thiophosphoric acid esters
The present invention provides a heat-sensitive recording sheet characterized by grains containing seeds.

The reason why the heat-sensitive recording sheet of the present invention has high color development sensitivity and particularly excellent stability in color development areas and non-color development areas is as follows.
It is thought that the introduction of sulfur atoms has a barrier effect, increasing heat resistance during melting, and at the same time, ionicity contributes to improving stability.

In the present invention, the nuclear-substituted or non-nuclear-substituted aromatic thiophosphoric acid ester used as the coloring performance improver has a melting point of 65°
C or higher can be used, but among them, those with a melting point of 75 to 140° are particularly excellent in stability under heat and color development sensitivity.
C is preferred. As a specific example, the following structural formula (1
) to (10) are mentioned.

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-
Dimethylamino 7thalide (also known as crystal violet lactone-CVL), 3゜3-bis(p-dimethylaminophenyl)-6aminophthalide, 3,3-bis(p-
dimethylaminophenyl)-6-nitro7thalyl',3
．． 3-bis(p-dimethylaminophenyl)phthalide,
3-dimethylamino-7-methylfluorane, 3-diethylamino-7-chlorofluorane, 3-diethylamino-6-chloro-7-methylfluorane, 3''ethylamino-7-anilinofluorane, 3-diethylamino -6-Methyl-7-anilinofluorane, 3-dibutylamino-7-.

Chloroanilinofluorane, 3-dibutylamino-7-
o-fluorofluorane, 3-piperidino-6-methyl-7-anilinofluorane, 3-(N-ethyl-p-toluidino)-7-(N-methylanilino)fluorane,
3-(N-ethyl p-toluidino)-6-methyl-7-
Anilinofluorane, 3-N-ethyl-N-ynamylamino-6-methyl-7-anilinofluorane, 3-N
-Methyl-N-cyclohexylamino-6-methyl-7
- Examples include fluoranphthalides such as anilinofluorane, lactams such as rhodamine B lactam, and spiropyrans such as 3-methylspirodinaphthopyran, 3-ethylspironaphthopyran, 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 are 65 to 180°
Any compound may be used as long as it melts and liquefies when heated to the C position, opens the lactone ring of the color-forming compound, and develops color. Examples include, but are not limited to, those listed below.

4-phenylphenol, 4-hydroxyacetophenone, 2.2'-dihydroxydiphenyl, 2.2'-methylenebis(4-chlorophenol), 2.2'-methylenebis(4-methyl-5-t-butylphenol),
4.4'-isoglopylidene diphenol (also known as bisphenol A), 4.4'-isoglopylidene bis(2-chlorophenol), 4.4'-isopropylidene bis(
2-methylphenol), 4,4'-ethylenebis(2
-methylphenol), 4,4'-thiobis(6-t-
butyl-3-methylphenol), ■, 1'-bis(4
-hydroxyphenyl)-cyclohexane, 2.2'bis(4-hydroxyphenyl)-〇-hebutane, 4.4
Examples include '-cyclohexylidene bis(2-isopropylphenol), 4,4'-sulfonyldiphenol, 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 100 to 500 parts.

The coloring performance improver is usually used in an amount of 1 to 100 parts of the acidic substance.
1,00 parts, preferably 30 to 100 parts are used.

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.

Various generally known methods can be used to produce a heat-sensitive recording sheet, but usually: 1. Prepare a coating liquid in which a color-forming compound, an acidic substance, and a color-forming performance improver are dispersed in water; The method for applying this to the sheet base material is to prepare a coating liquid in which a color-forming compound and an acidic substance are separately dispersed in water, and at least one of them contains a color-forming performance improver. A method such as lamination coating on a sheet base material can be adopted. Of course, an aqueous binder such as polyvinyl alcohol, methyl cellulose, hydroxyethyl cellulose, carboxyethyl cellulose, starch, or styrene-maleic acid copolymer may be 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 calcium carbonate, lubricants such as polyethylene wax and paraffin wax, waterproofing agents, etc. Various other drugs can be added. Furthermore, various dispersants for dispersing various drugs in water can be added to the coating liquid.

The heat-sensitive recording sheet of the present invention can be prepared, for example, by applying a coating liquid whose dry weight is 2 to 12. ? It is obtained by coating the sheet base material so as to give the following properties, and then drying it at room temperature to 50°C to form a coating film.

As the sheet base material, paper is generally used, but other synthetic resin sheets, nonwoven 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 limited thereto. In addition, all parts and percentages in the examples are based on weight.

Example 1 Solution A (dye liquid) Compound of structural formula (1) (melting point 91°C) 2.0 parts B
Liquid (acidic substance liquid) Bisphenol A Calcium carbonate Zinc stearate 3.0 parts 3.0 parts 0.5 parts Total 23.5 parts The above liquid and liquid B were separately blended and each was pulverized and dispersed with a paint conditioner. A coating liquid stock solution was obtained.

Next, 11.0 parts of liquid A and 23.5 parts of liquid B were mixed to form a heat-sensitive coating liquid, which was coated on 64.5.9 parts m2 of high-quality paper with a coating weight of 8.5 parts after drying. ? /m'' and dried to obtain the heat-sensitive recording sheet of the present invention.

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

Examples 2 to 10 A total of 11.0 parts to (10) of Structural Formula (2) in place of the compound of Structural Formula (1) (melting points are 130°C, 102°C in order from the compound of Structural Formula (2)) C192℃, 87'0,1
03°C199°c, 119°0, 105°0. 13
It is 6°C. A heat-sensitive recording sheet of the present invention was obtained in the same manner as in Example 1, except that ) was used.

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

Example 11 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 sheet was excellent in color development sensitivity and stability of color development areas and non-color development areas.

Example 12 The amount of the compound of structural formula (1) was changed to 4.0 parts, and A
A heat-sensitive 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 thermosensitive 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 9.0 parts.

This sheet has extremely poor color development sensitivity and is
.

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 100°C 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 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 bisphenol A. A heat-sensitive recording sheet for comparison was obtained.

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 tri-β-naphthyl phosphate (melting point: 113°C) was used in place of structural formula (1).

This sheet had poor stability in colored areas and non-colored areas.

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

This sheet has poor stability in the non-color developing area.

Test Example 1 Tests regarding the color development sensitivity and stability of color development areas and non-color development areas of the thermosensitive recording sheets obtained in Examples 1-12 and Comparative Examples 1 to 5 were conducted as follows.

The results are shown in Table-■.

[Evaluation of color sensitivity 1 Using an MSI type thermal head printing device manufactured by Matsushita Electronic Components Co., Ltd., print and color on a sheet under the conditions of a pulse width of 0.1-1.0 milliseconds, and measure the color density using Macbeth. The pulse width at which the color density value reached 1.0 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 coloring area and non-coloring area] Under the above conditions,
Using the colored printed sheets, the stability of colored areas and non-colored areas was evaluated under the following two conditions (Condition A and Condition B).

(Condition A) The above sheet was left in an atmosphere with a temperature of 60°C and a 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 ◎: No whitening ○: Almost no whitening △: Whitening ×: Significant whitening ■ Evaluation criteria for decoloring @: No decoloring ○: No decoloring Almost none △: Discolored Fog (Condition B) The sheet was left in an atmosphere at a temperature of 40° C. and a humidity of 90%, and the degree of discoloration of the colored portion after 24 hours was visually evaluated using the same criteria as Condition A.

Table 1 (Effects of the invention) The heat-sensitive recording sheet of the present invention has extremely high color development sensitivity.
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, a nuclear-substituted or non-nuclear-substituted material having a melting point of 65° C. or higher is used as the color-forming performance improver. A heat-sensitive recording sheet containing at least one aromatic thiophosphoric acid ester. 2. The heat-sensitive recording sheet according to claim 1, wherein the nuclear-substituted or non-nuclear-substituted aromatic thiophosphoric acid ester has a melting point of 75 to 140°C. 3. The heat-sensitive recording sheet according to claim 1, wherein the nuclear-substituted or non-nuclear-substituted aromatic thiophosphoric acid ester is a compound represented by the following structural formulas (1) to (10). (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. ▼ (9) ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ (10) ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼