JPH0433B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a thermosensitive recording sheet. Conventionally, triphenylmethane type, fluoran type,
Coloring agents (hereinafter referred to as coloring agents) consisting of electron-donating color-forming compounds such as phenothiazine, auramine, and spiropyran, clays (activated clay, etc.), phenolic compounds, aromatic carboxylic acids, aromatic polyesters, etc. The so-called dye coloring type thermal recording sheet, which utilizes a coloring reaction with a color developing agent made of a solid acid such as a valent metal salt and brings both coloring substances into contact with each other using heat to obtain a colored image, is well known. Are known. In general, the performance conditions that a heat-sensitive recording sheet should have are that it is colorless or light-colored, has excellent coloring performance that does not change immediately after the sheet is manufactured and after long-term storage, and that the colored image is robust and sufficiently stable against light and humidity. It must also be economically manufacturable. Already proposed color developers for heat-sensitive recording and sheets coated with the same have advantages and disadvantages in terms of performance, but these heat-sensitive recording sheets are coated onto a support using two reactants. However, there are disadvantages such as color development and fogging before heating during copying, poor storage stability of colored images such as light fastness and water resistance, and failure to develop color instantly after heating. Seats are desired. Especially in recent years,
For use in high-speed printers with short heating pulse widths, there has been a demand for a new color developer that has a good rise in color density upon heating and has gradation properties. As a result of intensive studies aimed at providing a heat-sensitive recording sheet with a good rise in color density upon heating, the present inventors succeeded in inventing a heat-sensitive recording sheet using the following novel color developer. This problem was solved. That is, the heat-sensitive recording sheet of the present invention has the general formula () (In the formula, R is hydrogen, _C1 - _C12 alkyl group, _C3
-C10 cycloalkyl group, _C7 - _C10 aralkyl group or phenyl group, which may be the same or different. ) is characterized by containing one or more of the 2,2'-methylene diphenol compounds represented by () as a color developer, and compared to conventional recording sheets using bisphenol A. As a result, the rise in color density is extremely sharp, and the color density is equal to or higher than that of the previous one. In addition, the colored image has excellent light fastness and water resistance, and its density decreases over time is very small, and it has the advantage that a heat-sensitive recording sheet that is extremely advantageous in handling and storage stability can be obtained at a low cost. Examples of the color developer represented by the general formula () in the present invention include the following compounds:
It is not limited to this. 2,2'-dihydroxydiphenylmethane, 2,
2'-dihydroxy-5-methyl-diphenylmethane, 2,2'-dihydroxy-5-iso-propyldiphenylmethane, 2,2'-dihydroxy-5-
tert-butyldiphenylmethane, 2,2'-dihydroxy-5-tert-octyldiphenylmethane,
2,2'-dihydroxy-5-α-methylbenzyl-diphenylmethane, 2,2'-dihydroxy-
5,5'-dimethyldiphenylmethane, 2,2'-dihydroxy-5,5'-diethyldiphenylmethane, 2,2'-dihydroxy-5,5'-di-iso-propyldiphenylmethane, 2, 2'-dihydroxy-5,5'-di-tert-butyldiphenylmethane,
2,2'-dihydroxy-5,5'-di-tert-octyldiphenylmethane, 2,2'-dihydroxy-
5,5'-dicyclohexyldiphenylmethane,
2,2'-dihydroxy-5,5'-di-α,α-dimethylbenzyldiphenylmethane, 2,2'-dihydroxy-5,5'-diphenyldiphenylmethane, 2,2'-dihydroxy-5 -ethyl-5'-methyldiphenylmethane, 2,2'-dihydroxy-
5-sec-butyl-5'-methyldiphenylmethane,
2,2'-dihydroxy-5-tert-butyl-5'-
Methyldiphenylmethane, 2,2'-dihydroxy-5-tert-octyl-5'-methyl-diphenylmethane, 2,2'-dihydroxy-5-cyclohexyl-5'-methyldiphenylmethane, 2,2'-dihydroxy -5-cyclohexyl-5'-sec-butyldiphenylmethane, 2,2'-dihydroxy-
5-α,α-dimethylbenzyl-5′-methyldiphenylmethane, 2,2′-dihydroxy-5-α,
Examples include α-dimethylbenzyl-5'-tert-butyldiphenylmethane and 2,2'-dihydroxy-5-phenyl-5'-ethyldiphenylmethane. A general method for producing the heat-sensitive recording sheet of the present invention will be described below. As the coloring agent, various types of coloring agents that develop color through a melting reaction with the coloring agent represented by the general formula () can be used. For example, 3,3'-bis(4-
dimethylaminophenyl)-6-dimethylaminophthalide (crystal violet lactone),
3-diethylamino-6-methyl-7-chlorofluorane, 3-diethylamino-7-chlorofluorane, 3-cyclohexylamino-6-chlorofluorane, 3-diethylamino-7-dibenzylaminofluorane, 3-diethylamino -6-
Methyl-7-phenylamino-fluorane, 1,
3,3-trimethylindolino-6'-chloro-
8'-Methoxy-spiropyran, 3-methyl-2,
Examples include common electron-donating color-forming compounds such as 2'-spirobis (benzo[f]chromene). A liquid mixture is prepared by thoroughly mixing a colorless or light-colored coloring agent as described above, or a color developer represented by the general formula (), with a solution or dispersion of a binder in water or an organic solvent. Binders used in the preparation of this mixture include styrene-butadiene polymers, polyvinyl alcohol, carboxymethyl cellulose, hydroxyethyl cellulose, polystyrene, vinyl chloride-vinyl acetate copolymers, synthetic polymers such as gum arabic, and natural or naturally modified polymers. can be mentioned. Also, listing the solvents used:
Benzene, toluene, acetone, methylene chloride,
Examples include organic solvents such as ethyl acetate and cyclohexane, and water. The resulting mixed solution is applied to a support such as paper, natural or synthetic resin film, and dried. The liquid mixture may be poured into a support. The above-mentioned mixing method and coating method are not limited to the heat-sensitive recording sheet of the present invention. For example, the color former is mixed with a binder solution, the color developer is separately mixed with a binder solution, and both mixtures are mixed with a binder solution. The mixture may be mixed and applied to the support, or both mixed solutions may be divided into two parts and applied to the support. Further, both mixed solutions can be applied to the same or separate surfaces of the support, or to different supports. The relative amounts of each component constituting the heat-sensitive recording sheet vary, and suitable ranges are 1 to 15 parts by weight of the color former, 1 to 95 parts by weight of the color former (general formula ()), and 1 to 40 parts by weight of the binder. . This weight is in dry condition. The heat-sensitive recording sheet of the present invention does not cause color fog even though the color forming agent and the color developer are in contact with each other during manufacturing, from application drying to before heating, and even if the sheet is exposed to light before copying. It has good stability over time without deterioration in coloring performance, instantly develops color when heated, and the developed image has extremely good light fastness and fastness. The present invention will be explained below using examples. The following methods were used to measure and evaluate various performances of the recording sheet. 1 Color density Heating the recording sheet using Thermotest Rhoday Aceta (SETARAM, Model 7401) Heating time: 5 seconds Heating element/recording sheet pressure during heating: 10 g/cm ² Heating temperature range: 60 to 180℃ Make it color. Reflectance () was measured 10 minutes after heating and color development using a TSS type Hunter colorimeter (manufactured by Toyo Seiki) using an amber filter. The lower the reflectance, the higher the color density. 2 Light resistance of colored image The sheet colored by method 1 was irradiated with light for 30 minutes to 4 hours using a carbon arc lamp, and measured using a Hunter colorimeter in the same manner as in 1. Io: Reflection of uncolored sheet Residual rate = In/Io-In/Is/Io-Is x 100 (%) where Is: reflectance of the coloring sheet before irradiation, In: reflectance of the coloring sheet after n hours of irradiation. . The higher the residual rate, the better. 3 Storage stability Uncolored and colored recording sheets were stored at 25℃ for 6 days.
After being left for a month, the reflectances of the uncolored and colored sheets before being left are Ko and Ko', and the reflectances after being left are K and K', respectively. K−Ko and K′−
The smaller the difference in Ko', the better the storage stability. 4 Water resistance Store the colored recording sheet in water for 2 hours,
Changes in density of the colored image were observed with the naked eye. Example 1 Solution A: Crystal violet lactone 7g 10% by weight polyvinyl alcohol (Kuraray #217) 30g Water 13g Solution B: 2,2'-dihydroxydiphenylmethane
7g 10% by weight polyvinyl alcohol 30g Water 13g Separately prepare a dispersion of liquid A and B using a sand grinding mill.
3 parts to 67 parts of each liquid were mixed, and the mixture was coated on high-quality paper at a dry coating weight of 2.5 to 3.5 g/m ² and dried to obtain a heat-sensitive recording sheet. The performance of the obtained heat-sensitive recording sheet was evaluated. The results are shown in Table-1. Examples 2 to 11 and Comparative Example 1 Heat-sensitive recording sheets were obtained in Example 1 except that only the color developer was replaced with another color developer. The performance of the obtained heat-sensitive recording sheet was evaluated. Table 1 shows the color developer used and the results of performance evaluation.

【table】

[Table] Example 12 Solution A: Crystal violet lactone 7g 10% by weight polyvinyl alcohol (Kuraray #217) 30g Water 13g Total 50g Solution B: 2,2'-dihydroxy-5-cyclohexyl-5'-methyldiphenylmethane 7g 10% by weight polyvinyl alcohol (Kuraray #217) 30g Water 13g Total 50g Separately prepare a dispersion of liquid A and B using a sand grinding mill.
Mix 10 parts to 20 parts of the solution, add 9.3 parts of light calcium carbonate dispersion (60% by weight), apply this to high-quality paper so that the dry coating amount is 4.5 g/ ^m2 , and dry. A heat-sensitive sheet was obtained. The performance of the obtained heat-sensitive sheet was evaluated by the following method. The results are shown in Table-2. (1) Color density The heat-sensitive sheet is brought into contact with a metal block whose surface temperature is 200℃ for 5 seconds to develop color. One hour after color development, the reflectance was measured using an amber filter of a Hunter colorimeter (manufactured by Toyo Seiki). The lower the reflectance, the higher the color density. (2) Light resistance of colored image The heat-sensitive sheet colored in (1) is exposed for 2 hours using a carbon arc fade meter. The change in color density after the test is measured using a Hunter colorimeter. The higher the residual rate, the better. (3) Degree of scumming on heat-sensitive sheet The degree of scumming on the coated heat-sensitive sheet is measured using a Hunter colorimeter. The higher the reflectance, the less scumming occurs. (4) Storage stability of heat-sensitive sheet The coated heat-sensitive sheet was stored in a constant temperature and humidity chamber at 40%/90℃RH for 24 hours, and the degree of self-coloring after the test was measured using a Hunter colorimeter. Measure. The higher the reflectance, the better the storage stability. Comparative Example 2 A thermosensitive recording sheet was obtained in the same manner as in Example 12, except that the developer was replaced with 2,2'-methylenebis(4-chlorophenol). The obtained thermosensitive sheet was evaluated in the same manner as in Example 12, and the results are shown in Table 2. Comparative Example 3 A heat-sensitive recording sheet was obtained in the same manner as in Example 12, except that the developer was replaced with 2,2'-methylenebis(4-methyl-6-tert-butylphenol). The obtained thermosensitive sheet was evaluated in the same manner as in Example 12, and the results are shown in Table 2. From the results in Table 2, 2,2'-methylenebis(4-chlorophenol) causes stains during the production of thermal sheets, and the storage stability of thermal sheets is also poor. 6-
tert-butylphenol) has a low color density;
It can be seen that the light fastness of the colored image is also poor.

【table】

Claims (1)

[Claims] 1 General formula () (In the formula, R is hydrogen, _C1 - _C12 alkyl group, _C3
-C10 cycloalkyl group, _C7 - _C10 aralkyl group or phenyl group, which may be the same or different from each other. ) represented by 2,
One or two 2'-methylene diphenol compounds
A heat-sensitive recording sheet characterized by containing at least one color developer as a color developer.