JPH089264B2 - Thermal recording sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a heat-sensitive recording sheet which is extremely excellent in color developing sensitivity.

(Prior Art and Problems) A thermal recording sheet is used to develop images such as characters and figures on the recording sheet by heat energy, and is used in various fields such as printer recorders and facsimiles in recent years. became. There are various thermal recording systems, but from the viewpoints of image sharpness, resolution, image color tone, etc., a dye forming precursor, for example, a color forming lactone compound such as crystal violet lactone (CVL), and an acidic substance for forming the color. The main method is to use and. In this system, a phenolic compound such as bisphenol A, which has been solid at room temperature conventionally but is melted and liquefied by heating to act as an acid component, is used as the acidic substance. At this time, it is required that the heat-sensitive material has high whiteness and that the whiteness does not easily decrease even when stored. In order to obtain a clear color, it is usually necessary to keep the temperature at about 140 to 150 ° C. for a certain period of time or longer. Therefore, various approaches have been extensively studied and reported in order to develop a clear color more quickly and easily. For example, there is a method of adding stearic acid amide or the like as a sensitizer (JP-A-54-139740) or a method of using benzyl p-hydroxybenzoate or the like as an acidic substance (JP-A-54-74762). However, although the methods described in these publications improve the coloring sensitivity, they are still unsatisfactory.

(Means for Solving Problems) In view of such a situation, the inventors of the present invention, as a result of various studies,
As a result, they have found a compound having a markedly improved effect as compared with conventional sensitizers, and completed the present invention.

That is, the present invention, in a heat-sensitive recording sheet for heat-sensitive color development with a color-forming lactone compound and an acidic substance, as a sensitizer, a melting point of 60 ℃ or more, aromatic phosphate ester and / or aromatic phosphite ester The present invention aims to provide a heat-sensitive recording sheet, which comprises
In particular, aromatic phosphates and / or which do not have a hydroxyl group directly linked to a benzene ring or a condensed benzene ring.
Or containing an aromatic phosphite,
It aims to provide a novel form of thermal recording sheet.

The thermosensitive recording sheet of the present invention is excellent in the stability of the color-developed portion and the non-color-developed portion and, in addition, is remarkably excellent in the color-developing sensitivity. The reason for this is not clear, but it can be inferred as follows. The specific aromatic phosphoric acid ester and / or aromatic phosphite ester used as a sensitizer in the present invention does not act at room temperature at all, but when it is heated and melted and liquefied, the same melt-liquefied acidic acid is used. material,
For example, it is rapidly hydrolyzed by bisphenol A,
Since it produces more acidic phosphoric acid and / or phosphorous acid, it is believed that this accelerates the ring opening of the chromophoric lactone compound and accelerates the color development remarkably.

The aromatic phosphoric acid ester and / or aromatic phosphorous acid ester used as the sensitizer in the present invention has a melting point of 60.
Any of those above ℃ can be used, but among them, 60-120 is particularly excellent in stability at room temperature and color development sensitivity when heated.
Those at ℃ are preferred. As a specific example, the following structural formula (1)
The compounds represented by formulas (7) to (7) are preferable, and the compounds of structural formulas (1) and (7) are particularly preferable.

Incidentally, those having a melting point of less than 60 ° C., for example, a phosphoric acid triphenyl ester having a melting point of 50 ° C. or a phosphoric acid triethyl ester which is liquid at ordinary temperature, has a sensitizing action, acts at ordinary temperature or slightly higher temperature, It lacks the ability to retain white color during storage.

Examples of the chromophoric lactone compound used in the present invention include, but are not limited to, the followings.

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 -Bis (p-dimethylaminophenyl) phthalide, 3,3-bis-3-dimethylamino-7-methylfluorane, 3-diethylamino-7-chlorofuran, 3-diethylamino-
6-chloro-7-methylfluorane, 3-diethylamino-7-anilinofluorane, 3-diethylamino-6
-Methyl-7-anilinofluorane, 3-piperidino-
6-Methyl-7-anilinofluorane, 3- (N-ethyl-p-toluidino) -7- (N-methylanilino) fluorane, 3- (N-ethyl-p-toluidino) -6-
Fluoranphthalides such as methyl-7-anilinofluorane, lactams such as rhodamine B lactam, spiropyrans such as 3-methylspirodinaphthopyran, 3-ethylspirodinaphthopyran and 3-benzylspironaphthopyran And so on. Of course, these compounds must be colorless or light-colored and develop a color by reacting with an acidic substance.

In addition, the acidic substance is a solid at room temperature, 60 ~ 180 ℃
It is sufficient that it is melted and liquefied when it is heated to the position to open the lactone ring of the color forming lactone compound to develop a color, and all of them function well in the presence of a sensitizer. For example, the following may be mentioned, but the invention is not limited thereto.

4-phenylphenol, 4-hydroxyacetophenone, 2,2'-dihydroxydiphenyl, 2,2'-methylenebis (4-chlorophenol), 2,2'-methylenebis (4-methyl-6-t-butylphenol), 4 ,Four'
-Isopropylidene diphenol (also known as bisphenol A), 4,4'-isopropylidene bis (2-chlorophenol), 4,4'-isopropylidene bis (2-methylphenol), 4,4'-ethylene bis (2 -Methylphenol), 4,4'-thiobis (6-t-butyl-3-methylphenol), 1,1-bis (4-hydroxyphenyl) -cyclohexane, 2,2'-bis (4-hydroxyphenyl) -N-heptane, 4,4'-cyclohexylidenebis (2-isopropylphenol), 4,4'-sulfonylbisphenol, anilide salicylate, novolac type phenol resin, benzyl p-hydroxybenzoate and the like can be mentioned.

These acidic substances are usually used in an amount of 10 to 1,000 parts, preferably 100 to 500 parts, based on 100 parts by weight of the chromophoric lactone compound (hereinafter simply referred to as "parts").

The sensitizer is usually 1 to 1,000 parts for 100 parts of the acidic substance,
Preferably 30 to 100 parts are used.

The color forming lactone compound, the acidic substance and the sensitizer 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, various generally known methods can be used. Usually, a color-forming lactone compound, an acidic substance and a sensitizer are dispersed in water to prepare a coating solution, which is used as a sheet. Method of applying to a substrate, preparing a coating liquid in which a color-forming lactone compound and an acidic substance are separately dispersed in water, and a sensitizer is contained in at least one of them, and the coating liquid is applied to a sheet substrate. It is possible to employ a method of applying a laminated coating to the above. Of course, as the binder, an aqueous binder such as polyvinyl alcohol, methyl cellulose, hydroxyethyl cellulose, kirvoxymethyl cellulose, starches, and styrene-maleic acid copolymer is added to the above coating liquid. In addition, if necessary, a benzophenone-based compound may be added to the above coating solution to improve performance.
An ultraviolet absorber such as a triazole type, a filler such as calcium carbonate, a lubricant such as polyethylene wax and paraffin wax, a water resistant agent, and various other agents can be added. Furthermore, various dispersants for dispersing various chemicals in water can be added to the coating liquid.

The dry weight of the coating liquid is generally 2 to 1 per 1 m ^{2 of the} sheet base material.
Apply 2g to the base material of the sheet, then
The thermal recording sheet of the present invention can be obtained by drying at about 50 ° C.

Paper is generally used as the sheet base material, but synthetic resin sheets, non-woven fabric sheets and the like can also be used as appropriate.

(Effect of the Invention) The thermosensitive recording sheet of the present invention has extremely high color development sensitivity,
Moreover, there is an advantage that the stability of the colored portion and the non-colored portion is excellent.

(Examples) Next, the present invention will be described more specifically with reference to Examples, Comparative Examples, and Test Examples, but the present invention is not limited thereto. All parts and% in the examples are based on weight.

Example 1 Solution A (dye solution) 3- (N-methyl-p-toluidino) -6-methyl-7
-Anilinofluoran 1.0 part Compound of structural formula (1) (melting point 98 ° C) 2.0 parts 10% polyvinyl alcohol aqueous solution 3.0 parts water 5.0 parts total 11.0 parts B liquid (acidic substance liquid) bisphenol A 3.0 parts calcium carbonate 3.0 parts stearin Zinc acid 0.5 parts 10% aqueous solution of polyvinyl alcohol 7.0 parts Water 10.0 parts Total 23.5 parts The above-mentioned solutions A and B were separately blended and pulverized and dispersed by a paint conditioner to obtain a coating solution stock solution.

Next, 11.0 parts of solution A and 23.5 parts of solution B were mixed to form a heat-sensitive coating solution, which was applied to a high quality paper of 64.5 g / m ² so that the coating amount after drying was 8 g.
It was coated so as to be / m ² and dried to obtain a heat-sensitive recording sheet of the present invention.

This sheet was excellent in color forming sensitivity and stability in the color forming part and the non-color forming part.

Examples 2 to 7 Instead of the compound of structural formula (1), structural formula (2) to
The same procedure as in Example 1 was repeated except that the compound of (7) [melting point was 95 ° C, 113 ° C, 115 ° C, 76 ° C, 66.5 ° C, 98.5 ° C in order from the compound of structural formula (2)]. To obtain a thermosensitive recording sheet of the present invention.

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

Example 8 The amount of the compound of structural formula (1) added was changed to 1.0 part, and
A thermosensitive recording sheet of the present invention was obtained in the same manner as in Example 1 except that the amount of the liquid used was 10 parts.

This sheet was excellent in color forming sensitivity and stability in the color forming part and the non-color forming part.

Example 9 The addition amount of the compound of structural formula (1) 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 the liquid used was 13 parts.

This sheet was excellent in color forming sensitivity and stability in the color forming part and the non-color forming part.

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 the solution A used was 9.0 parts.

 This sheet was inferior in color development sensitivity.

Comparative Example 2 A thermosensitive recording sheet for comparison was obtained in the same manner as in Example 1 except that stearic acid amide (melting point: 100 ° C.) was used instead of the compound of structural formula (1).

This sheet was inferior in color forming sensitivity and stability of color forming part and non-color forming part.

Comparative Example 3 The addition of the compound of structural formula (1) was omitted, the amount of liquid A used was 9 parts, and p- was used instead of bisphenol A.
A heat-sensitive recording sheet for comparison was obtained in the same manner as in Example 1 except that benzyl hydroxybenzoate was used.

This sheet was inferior in color development sensitivity and stability of the color development part.

Comparative Example 4 A thermosensitive recording sheet for comparison was obtained in the same manner as in Example 1 except that triphenyl phosphate (melting point: 50 ° C.) was used instead of the compound of structural formula (1).

This sheet was inferior in stability of the colored portion and the non-colored portion.

Comparative Example 5 A thermosensitive recording sheet for comparison was obtained in the same manner as in Example 1 except that phosphoric acid triethyl ester which was liquid at room temperature was used instead of the compound of structural formula (1).

This sheet was inferior in stability of the colored portion and the non-colored portion.

Test Example 1 The tests on the dynamic color density of the thermosensitive recording sheets obtained in Examples 1 to 9 and Comparative Examples 1 to 5, and the stability of the colored portion and the non-colored portion were carried out as follows. The results are shown in Table 1.

・ Measurement of dynamic color density The density of the image printed on the sheet with the pulse width of 0.5 ms was measured by using the MSI type thermal head printer manufactured by Matsushita Electronic Components Co., Ltd. Macbeth RD-91 manufactured by Macbeth Co.
It was measured using 8.

・ Evaluation of the stability of the coloring part and non-coloring part The part which was colored by pressing the hot plate of 140 ℃ at 2.0kg / cm ² for 1 second and the other non-coloring part were 40 ℃ and 90%.
After left standing for 24 hours under RH conditions, the degree of whitening or background fog in the colored and non-colored areas was visually evaluated according to the following criteria.

1) Evaluation criteria for color development area ◎: No whitening ○: Almost no whitening △: Whitening exists ×: Significant whitening 2) Evaluation criteria for non-coloring area ◎: No background fog ○: Almost no background fog △: Background fog × : There is significant background fog

Claims (1)

[Claims] 1. A heat-sensitive recording sheet for heat-sensitive color development with a color-forming lactone compound and an acidic substance, which has, as a sensitizer, a fragrance having a melting point of 60 ° C. or higher and having no hydroxyl group directly linked to a benzene ring or a condensed benzene ring. A heat-sensitive recording sheet containing a group-group phosphoric acid ester and / or an aromatic phosphorous acid ester.