JPS63183878A - Thermal recording sheet - Google Patents

Abstract

PURPOSE:To obtain a thermal recording sheet with a remarkably high color- forming sensitivity and a superior stability in color-forming portions and non- color-forming portions, by containing a specific dibasic ester as a sensitizer. CONSTITUTION:In a thermal recording sheet to be thermally colored by a color- forming lactone dompound and an acid substance, a dibasic ester shown by Formula I is contained as a sensitizer. In the Formula, (n) represents an integer 1-8, and R<1> and R<2> may be either ther same or different and represent 1-20 C alkyl, cycloalkyl,-CmH2m-Ar (wherein m represents an integer 1-8, and Ar represents aryl), or-CmH2m-CO-Ar. Here, halogen atom may be substituted for the 1-20 C alkyl, and alkyl, cycloalkyl, aryl, aralkyl, phenacyl, alkyloxy, aryloxy, aralkyloxy, arylcarbonyl, arylsulfonyl, nitro, ammonium sulfonic group, or halogen atom may be substituted for the cycloalkyl and the Ar in the-CmH2m- Ar and the-CmH2m-CO-Ar.

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 and problems) A thermal recording sheet is a device that uses thermal energy to express images such as characters and figures on the recording sheet, and has recently been used in various printer recording needles, facsimiles, PO3s, bells, and automatic ticket gates. It has come to be used in fields such as There are various thermal recording methods, but from the viewpoint of image clarity, resolution, image tone, etc., we use a color-forming lactone 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 bisphenol 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 recording sheet is also required to have high whiteness and excellent stability in the colored and non-colored areas.

Usually, in order to obtain vivid color, it is necessary to use 140 to 15
It is necessary to maintain the temperature at about 0°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, a method of adding stearic acid amide etc. as a sensitizer (Japanese Unexamined Patent Publication No. 139740/1989), and a method of adding p-
Method using benzyl hydroxybenzoate etc.
4-74762), but although the methods described in these publications improve color development sensitivity, they are still not satisfactory. Furthermore, a method of adding aryl ester derivatives of aliphatic basic acids and dibasic acids having melting points of 40°C to 150°C as sensitizers (JP-A-5
No. 8-71191), but although the method described therein sufficiently improves color development sensitivity, it is not satisfactory in terms of stability of color development areas and non-color development areas.

(Means for Solving the Problems) In view of this situation, the present inventors have conducted various studies and found that when a specific dibasic acid ester is used as a sensitizer, the color development sensitivity is lower than that of conventional sensitizers. The present inventors have discovered that it is possible to obtain a heat-sensitive recording sheet that has a significantly high effect of improving color and also has excellent stability in coloring areas and non-coloring areas, and has completed the present invention.

That is, the present invention provides a heat-sensitive recording sheet that is heat-sensitively colored by a color-forming lactone compound and an acidic substance, in which the general formula (1) is used as a sensitizer.
) [In the formula, n represents an integer of 1 to 8. Also R1 and R2
may be the same or different, and each has 1 to
20 alkyl group, cycloalkyl group, -C,R2,-
Ar (in the formula, m is an integer of 1 to 8, Ar represents an atomyl group, and the same applies below) or -C,1lzs-Co-
Indicates Ar. However, the alkyl group having 1 to 20 carbon atoms may be substituted with a halogen atom, and the cycloalkyl group, C+JIz+m Ar and -C@l(,.

Ar in -CO-Ar is an alkyl group, cycloalkyl group, aryl group, aralkyl group, phenacyl group, alkyloxy group, aryloxy group, aralkyloxy group, arylcarbonyl group, arylsulfonyl group, nitro group, ammonium sulfonic acid It may be substituted with a group or a halogen atom. ] A heat-sensitive recording sheet characterized by containing a dibasic acid ester represented by the following. ”.

The heat-sensitive recording sheet of the present invention has extremely high color development sensitivity and is also excellent in stability of color development areas and non-color development areas. In particular, as a result of examining stability during long-term storage, it was found that the dibasic acid ester of the present invention represented by the general formula (1) is superior to other dibasic acid esters. Among these, dibasic acid esters of the following structural formulas (1) to Q5) are preferable because they are excellent in color development sensitivity during heating and stability of color development and non-color development regions, and in particular, structural formulas (4), (6),
(71, (8), (9) and dibasic acid esters of Oa are preferred.

Examples of the color-forming lactone 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-bis(p-dimethylaminophenyl)phthalide,
3,3-bis3-dimethylamino-7-methylfluoran, 3-diethylamino-7-chlorofuran, 3-diethylamino-6-chloro-7-methylfluoran, 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-)luidino)-6-methyl-7-anilinofluorane, 3-N
-ethyl-N-isoamylamino-6-methyl-7-anilinofluorane, 3-N-methyl-N-cyclohexylamino-6-methyl-7-anilinofluorane, 3-
Fluorane phthalides such as N,N-diethylamino-7-0-chloroanilinofluorane, lactams such as rhodamine B lactam, 3-methylspirodinaphthopyran, 3-ethylspirodinaphthopyran, 3-benzyl Examples include spiropyrans such as spironaphthopyran.

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 60 to 180
Any compound may be used as long as it melts and liquefies when heated to about °C, opens the lactone ring of the color-forming lactone compound, and develops color. Examples include, but are not limited to, the following.

4-phenylphenol, 4-hydroxyacetophenone, 2.2'-dihydroxydiphenyl, 2.2'-methylenebis(4-chlorophenol), 2.2'-methylenebis(4-methyl-6-t-butylphenol),
4.4'-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-hebutane, 4.
Examples thereof include 4'-cyclohexylidene bis(2-isopropylphenol), 4,4'-sulfonyldiphenol, salicylic acid anilide, novolak type phenol resin, and benzyl p-hydroxybenzoate.

These acidic substances are usually used in an amount of 10 to 1.000 parts by weight per 100 parts by weight (hereinafter simply referred to as parts) of the color-forming lactone compound.
parts, preferably 100 to 500 parts.

The sensitizer is usually used in an amount of 1 to 1000 parts per 100 parts of the acidic substance.
parts, preferably 30 to 100 parts.

The color-forming lactone compound, acidic substance, and sensitizer 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 a color-forming lactone compound,
A method of preparing a coating liquid in which an acidic substance and a sensitizer are dispersed in water and applying this to a sheet substrate; ■Preparing a coating liquid in which a color-forming lactone compound and an acidic substance are separately dispersed in water; A method can be adopted in which at least one of the coating liquids contains a sensitizer and the coating liquids are laminated and coated on the sheet base material. 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 UV absorbers such as benzophenone and triazole, fillers such as calcium carbonate, lubricants such as polyethylene wax and paraffin wax, waterproofing agents, and other various substances. drugs can be added. Furthermore, various dispersants for dispersing various drugs in water can be added to the coating liquid.

The dry weight of the coating liquid is 1. (Generally 2~
The heat-sensitive recording sheet of the present invention can be obtained by coating a sheet base material in an amount of 12 g and then drying at room temperature to about 50°C.

Paper is generally used as the sheet base material, but synthetic resin sheets, nonwoven fabric sheets, etc. can also be used as appropriate.

(Effects of the Invention) The heat-sensitive recording sheet of the present invention has the advantage of extremely high color development sensitivity and excellent stability in color development areas and non-color development areas.

(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 any way. In addition, all parts and percentages in the examples are based on weight.

Example 1 Solution A (dye liquid) Dibasic acid ester of structural formula (1) 2.0 parts 1
0% polyvinyl alcohol aqueous solution 3.0 parts water
5.0 part B
Liquid (acidic substance liquid) Bisphenol A 3.0 parts Calcium carbonate 3.0 parts Zinc stearate 0.5 parts lO% polyvinyl alcohol aqueous solution 7.0 parts Total
23.5 parts The above solution and Solution B were separately blended and each was pulverized and dispersed with a paint conditioner 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, which was applied onto 64.5 g/+rr high-quality paper so that the coating amount after drying was 8 g 10 f, and dried. A heat-sensitive recording sheet of the present invention was obtained.

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

Examples 2 to 15 Structural formula (2) instead of dibasic acid ester of structural formula (1)
) ~ A thermosensitive recording sheet of the present invention was obtained in the same manner as in Example 1, except that the dibasic acid ester of α-Tsu was used.

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

Example 16 The heat-sensitive recording sheet of the present invention was prepared in the same manner as in Example 7, except that the amount of the dibasic acid ester of structural formula (7) was changed to 1.0 parts, and the amount of liquid A was changed to 10 parts. I got it.

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

Example 17 The heat-sensitive recording sheet of the present invention was produced in the same manner as in Example 7, except that the amount of the dibasic acid ester of structural formula (7) was changed to 4.0 parts, and the amount of liquid A was changed to 13 parts. I got it.

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

Comparative Example 1 1 Omitting the addition of the dibasic acid ester of structural formula (1), A
A thermosensitive recording sheet for comparison was obtained in the same manner as in Example 1 except that the amount of liquid used was 9.0 parts.

This sheet had poor color development sensitivity.

Comparative Example 2 fjl A thermosensitive recording sheet for comparison was obtained in the same manner as in Example 1 except that stearic acid amide was used instead of the dibasic acid ester of formula (1).

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

Comparative Example 3 Example 1 except that the addition of the dibasic acid ester 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 heat-sensitive recording sheet for comparison was obtained in the same manner as above.

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

Comparative Example 4 Example 1 except that bis(p-benzylphenyl) malonate was used instead of the dibasic acid ester of structural formula (1).
A heat-sensitive recording sheet for comparison was obtained in the same manner as above.

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

Comparative Example 5 A heat-sensitive recording sheet for comparison was obtained in the same manner as in Example 1 except that dim-tolyl adipate was used instead of the dibasic acid ester of structural formula (1).

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

Comparative Example 6 A heat-sensitive recording sheet for comparison was obtained in the same manner as in Example 1 except that stearic acid amide was used instead of the dibasic acid ester of structural formula (11).

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

Test Example 1 Tests regarding the dynamic color density and the stability of colored areas and non-colored areas of the thermosensitive recording sheets obtained in Examples 1 to 17 and Comparative Examples 1 to 6 were conducted as follows. The results are shown in Table-1 and Table-2.

・Measurement of dynamic color density Using an MSI type thermal head printing device manufactured by Electronic Components ■, the density of the image printed on a sheet with a pulse width of 0.5 milliseconds was measured using a Macbeth density meter RD-9 manufactured by Macbeth Co., Ltd. (USA).
18 was used for measurement.

・Evaluation of stability of colored and non-colored areas (A) 140°C
The colored part was pressed against a hot plate for 1 second at a pressure of 2.0 kg/cnl, and the other non-colored part was heated at 40°C.
The sample was left for 24 hours under the condition of 90% RH, and the degree of whitening or background fog in the colored and non-colored areas was visually evaluated using the following criteria.

l) Evaluation criteria for colored areas ◎: No whitening O: Almost no whitening △: Whitening ×: Significant whitening 2) Evaluation criteria for non-colored areas ◎: No background fogging ○: Almost no background capri △: There is background fogging. Except for the above stability evaluation (A)
It was evaluated in the same way.

Table-1 Table-2

Claims (1)

[Claims] In a heat-sensitive recording sheet that heat-sensitively develops color using a color-forming lactone compound and an acidic substance, the sensitizer is a compound of the general formula (I
) ▲There are mathematical formulas, chemical formulas, tables, etc.▼...(I) [In the formula, n represents an integer from 1 to 8. Also R^1 and R
^2 may be the same or different, and each represents an alkyl group having 1 to 20 carbon atoms, a cycloalkyl group, -C_mH
_2_m-Ar (in the formula, m is an integer of 1 to 8, Ar represents an aryl group, and the same applies below) or -C_mH_
2_mCO-Ar is shown. However, the alkyl group having 1 to 20 carbon atoms may be substituted with a halogen atom, and the cycloalkyl group, -C_mH_2_m-Ar and -
Ar in C_mH_2_m-Co-Ar includes an alkyl group, cycloalkyl group, aryl group, aralkyl group, phenacyl group, alkyloxy group, aryloxy group, aralkyloxy group, arylcarbonyl group, arylsulfonyl group, nitro group, ammonium It may be substituted with a sulfonic acid group or a halogen atom. ] A heat-sensitive recording sheet characterized by containing a dibasic acid ester represented by the following.