JPH0562597B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a novel thermosensitive recording sheet that has extremely high color development sensitivity and excellent stability in color development areas and non-color development areas. (Conventional technology and problems) Thermal recording sheets print characters and characters using thermal energy.
It is a device that displays images such as figures on a recording sheet, and has recently come to be used in fields such as various printers, recorders, facsimile machines, POS labels, and automatic ticket gates. 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 acid that develops the color. The main method is to use substances. 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. On this occasion,
A heat-sensitive recording sheet is also required to have high whiteness and excellent stability in colored and non-colored areas. Usually, in order to obtain vivid color development, it is necessary to maintain the temperature at around 140 to 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, a method of adding stearic acid amide etc. as a sensitizer (Japanese Patent Application Laid-open No.
139740) and a method using benzyl p-hydroxybenzoate as an acidic substance (Japanese Unexamined Patent Application Publication No. 1983-1989).
74762), but although the methods described in these publications improve color sensitivity,
This was still insufficient, and the safety of the colored and non-colored areas was not satisfactory. (Means for Solving the Problems) In view of this situation, the present inventors have conducted various studies and found that the use of a specific oxalic acid ester as a sensitizer results in lower color development sensitivity than conventional sensitizers. The present inventors have discovered that a new heat-sensitive recording sheet can be obtained which has a significantly high improvement effect 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 with a color-forming lactone compound and an acidic substance, in which the general formula () COOR ¹ | COOR ² ... () [where R ¹ and R ² ] is used as a sensitizer. may be the same or different, and each represents an alkyl group having 1 to 20 carbon atoms, a cycloalkyl group, an aryl group, -C _o H _2o -Ar (in the formula, an integer of n1 to 8, and Ar represents an aryl group). ) or -C _o H _2o -CO-Ar.However, an alkyl group having 1 to 20 carbon atoms may be substituted with a halogen atom, and a cycloalkyl group, an aryl group , −C _o H _2o −Ar and −C _o
Ar in H _2o -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 It may be substituted with a sulfonic acid group or a halogen atom. ] A novel heat-sensitive recording sheet characterized by containing an oxalic acid ester represented by: ”. 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. The reason why the coloring sensitivity is so excellent is not clear, but it can be inferred as follows. The oxalic acid ester of the general formula () used as a sensitizer in the present invention has no effect at room temperature, but when heated to melt and liquefy, acidic substances similarly melted and liquefied, such as bisphenol A
Since it is hydrolyzed more quickly to produce a more acidic dibasic acid, it is thought that this further promotes the ring opening of the color-forming lactone compound and significantly accelerates color development. Examples of the sensitizer used in the present invention include oxalic acid esters represented by the above general formula ().Among them, the following structural formula (1 ) to (8) are preferred, particularly oxalic acid dibenzyl esters which may have a lower alkyl group, a lower alkoxy group, or a halogen atom as a nuclear substituent as shown in structural formulas (4) to (8). is 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-bis-3-dimethylamino-7-methylfluoran, 3-diethylamino-7-chlorofluoran, 3-diethylamino-6-chloro-7
-Methylfluorane, 3-diethylamino-7-
Anilinofluorane, 3-diethylamino-6-
Methyl-7-anilinofluorane, 3-dibutylamino-6-methyl-7-anilinofluorane,
3-piperidino-6-methyl-7-anilinofluorane, 3-(N-ethyl-p-triidino)-7
-(N-methylanilino)fluorane, 3-(N-
Ethyl-p-toluidino)-6-methyl-7-anilinofluorane, 3-N-ethyl-N-isoamylamino-6-methyl-7-anilinofluorane, 3-N-methyl-N-cyclohexylamino Fluorane phthalides such as -6-methyl-7-anilinofluorane, 3-diethylamino-7-O-chloroanilinofluorane, 3-dibutylamino-7-O-chloroanilinofluorane, Rhodamine B Examples include lactams such as lactam, spiropyrans such as 3-methylspirodinaphthopyran, 3-ethylspirodinaphthopyran, and 3-benzylspironaphthopyran. Of course, these compounds must be colorless or light-colored and develop color when reacting with acidic physical properties. In addition, acidic substances are solid at room temperature and are
Any compound may be used as long as it melts and liquefies when heated to about 180° C., opens the lactone ring of the color-forming actone compound, and develops color, and all of them function well in the presence of a sensitizer. 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'-isopropylidenebis(2-methylphenol), 4,4'-ethylenebis(2-methylphenol), 4,4'-thiobis(6-t-butyl-3-methylphenol), 1, 1-bis(4-
hydroxyphenyl)-cyclohexane, 2,2
-bis(4-hydroxyphenyl)-n-heptane, 2,2-bis(4-hydroxyphenyl)-
4-methylpentane, 4,4'-cyclohexylidene bis(2-isopropylphenol), 4,
Examples thereof include 4'-sulfonyldiphenol, salicylic acid anilide, novolac type phenolic resin, and benzyl p-hydroxybenzoate. These acidic substances are chromogenic lactone compounds100
Usually 10 to parts by weight (hereinafter simply referred to as parts)
1000 parts are used, preferably 100-500 parts. The sensitizer is usually used in an amount of 1 to 100 parts of the acidic substance.
1000 parts are used, preferably 30-100 parts. The color-forming lactone compound, acidic substance, and sensitizer are all used in the form of fine particles, preferably fine particles with a particle diameter of several microns or less. Various generally known methods can be used to produce heat-sensitive recording sheets, but usually a coating liquid is prepared by dispersing a color-forming lactone compound, an acidic substance, and a sensitizer in water, and this is applied to the sheet. Method of applying to the substrate: Prepare a coating liquid in which a color-forming lactone compound and an acidic substance are separately dispersed in water, and at least one of them contains a sensitizer, and then apply these coating liquids to the sheet substrate. A method such as layered coating can be adopted. Of course, the above coating liquid may contain binders such as polyvinyl alcohol, methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, starches, styrene, etc.
Add an aqueous binder such as a maleic acid copolymer. In addition, in order to improve performance, the coating liquid may contain ultraviolet absorbers such as benzophenone and triazole, fillers such as calcium carbonate, etc.
A lubricant such as polyethylene wax or paraffin wax, a waterproofing agent, and various other chemicals 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 obtained by applying the coating liquid to the sheet substrate so that its dry weight is generally 2 to 12 g per 1 m ² of the sheet substrate, and then drying it 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 novel thermosensitive 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) 3-(N-ethyl-p-toluidino)-6-methyl-7-anilinofluorane 1.0 parts Oxalic acid ester of structural formula (1) 2.0 parts 10% polyvinyl alcohol aqueous solution 3.0 Part water 5.0 parts Total 11.0 parts Solution B (acidic substance liquid) Bisphenol A 3.0 parts Calcium carbonate 3.0 parts Zinc stearate 0.5 parts 10% polyvinyl alcohol aqueous solution 7.0 parts Water 10.0 parts Total 23.5 parts Separate the above A and B solutions. They were blended and ground and dispersed using a paint conditioner to obtain a coating liquid 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/m ² of high-quality paper so that the coating weight after drying was 8 g/m ² 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 8 Structural formula (1) in place of oxalate ester
A thermosensitive recording sheet of the present invention was obtained in the same manner as in Example 1 except that dibasic acid esters (2) to (8) were used. All of these sheets were excellent in color development sensitivity and stability of color development areas and non-color development areas. Example 9 A thermosensitive recording sheet of the present invention was obtained in the same manner as in Example 4, except that the amount of the oxalic acid ester of structural formula (4) was changed to 1.0 parts, and the amount of liquid A was changed to 10 parts. . This sheet was excellent in color development sensitivity and stability of color development areas and non-color development areas. Example 10 A heat-sensitive recording sheet of the present invention was obtained in the same manner as in Example 4, except that the amount of oxalic acid ester of structural formula (4) was changed to 4.0 parts and the amount of liquid A was changed to 13 parts. . This sheet was excellent in color development sensitivity and stability of color development areas and non-color development areas. Comparative Example 1 Omitting the addition of the oxalate ester of structural formula (1),
A heat-sensitive recording sheet for comparison was obtained in the same manner as in Example 1 except that the amount of liquid A used was 9.0 parts. This sheet had poor color development sensitivity. Comparative Example 2 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 oxalic acid ester of structural formula (1). This sheet was inferior in color development sensitivity and stability of color development areas and non-color development areas. Comparative Example 3 Omitting the addition of the oxalate ester of structural formula (1),
A heat-sensitive recording sheet for comparison was obtained in the same manner as in Example 1, except that the amount of liquid A used was 9 parts and benzyl p-hydroxybenzoate was used instead of bisphenol A. This sheet was inferior in color development sensitivity and stability of color development areas. Test Example 1 Tests regarding the dynamic coloring density and the stability of colored areas and non-colored areas of the thermosensitive recording sheets obtained in Examples 1 to 10 and Comparative Examples 1 to 3 were conducted as follows. The results are shown in Table-1. ●Measurement of dynamic color density Using an MSI type thermal head printing device manufactured by Matsushita Electrical Parts Co., Ltd., the density of an image printed on a sheet with a pulse width of 0.5 milliseconds was measured using a Macbeth density meter RD-918 manufactured by Macbeth Co., Ltd. (USA). Measured using ●Evaluation of stability of colored and non-colored parts (A) The colored parts were pressed against a hot plate at 140°C for 1 second at a pressure of 2.0 kg/cm ² and the other non-colored parts were heated at 40°C. The samples were left under conditions of 90% RH for 24 hours, and the degree of whitening or background fog in colored areas and non-colored areas was visually evaluated using the following criteria. (1) Evaluation criteria for colored areas ◎: No whitening ○: Almost no whitening △: Whitening ×: Significant whitening (2) Evaluation criteria for non-colored areas ◎: No background fog ○: Almost no background fog △: Background fog Yes ×: Significant background fog ●Evaluation of stability of colored and non-colored areas (B) The leaving conditions for colored and non-colored areas were 50℃ and 55℃.
Evaluation was carried out in the same manner as in the above stability evaluation (A) except that the conditions were changed to 3 months at %RH.

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Claims (1)

[Scope of Claims] 1. In a heat-sensitive recording sheet that heat-sensitively develops color using a color-forming lactone compound and an acidic substance, the general formula () is used as a sensitizer. [During the ceremony. R ¹ and R ² may be the same or different, and each of R 1 and R 2 may be the same or different, and may be an alkyl group having 1 to 20 carbon atoms, a cycloalkyl group, an aryl group, -C _o H _2o -Ar (in the formula, n is 1 to 8) integer, Ar represents an aryl group,
The same applies below. ) or -C _o H _2o -CO-Ar. However, the alkyl group having 1 to 20 carbon atoms may be substituted with a halogen atom, and the cycloalkyl group, aryl group, -CnH _2o -Ar and -C _o
Ar in H _2o -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 It may be substituted with a sulfonic acid group or a halogen atom. ] A novel heat-sensitive recording sheet characterized by containing an oxalic acid ester represented by: 2. The heat-sensitive recording sheet according to claim 1, wherein the oxalate ester is a dibenzyl oxalate ester which may have a lower alkyl group, a lower alkyloxy group, or a halogen atom as a nuclear substituent. 3. The thermal recording according to claim 1, wherein the oxalic acid ester is one or more oxalic acid esters selected from the group consisting of oxalic acid dibenzyl esters represented by the following structural formulas (4) to (8). Sheet for use.