JPH0221957B2 - - Google Patents

Description

[Detailed description of the invention]

A thermosensitive recording material is a recording material in which a so-called thermosensitive coloring layer that develops color when heated is formed on the surface of a support such as paper, and is heated and printed using a thermal printer with a built-in thermal head. be. The heat-sensitive color forming layer is composed of a composition consisting of a combination of a color-forming substance, a color developer that causes the color-forming substance to develop color when heated, and a binder, and among these components, the one that most affects the physical properties of the heat-sensitive recording material It is no exaggeration to say that the color developer exerts this effect, and its quality determines the practicality of the recording material. Conventionally, the most commonly used color developer is bisphenol A, which is used in combination with an electron-donating colorless dye such as crystal violet lactone to utilize a color reaction. However, in thermal recording paper using bisphenol A, the melting point of bisphenol A is as high as around 160°C, so in order to obtain sufficient color density, it is necessary to heat the coloring surface to a high temperature. There are problems when using it as thermal recording paper for high-speed printers. That is, it lacks the ability to develop color at low temperatures, reach sufficient color density within a narrow temperature range from the color development start temperature, and develop color simultaneously with heating. Furthermore, the surface smoothness of thermal recording paper using bisphenol A is not uniform, and there remains a problem in terms of resolution when printing denser characters, and there is still room for improvement. However, as a result of extensive research in order to solve this problem, the present inventors discovered that (A) a color-forming substance, (B) a color developer that causes the color-forming substance to develop color when heated, and (C) a binder. In the heat-sensitive recording material consisting of the general formula (B) above,

[Formula] [Here, R ₁ and R ₂ represent an alkyl group. The present inventors have discovered that when bis(hydroxyphenyl)acetic acids represented by the following formula are used, a color-forming substance with significantly superior performance can be obtained, and the present invention has been completed. In the present invention, by using bis(hydroxyphenyl) acetic acids represented by the above general formula, color development at lower temperatures is achieved compared to thermal recording paper that uses bisphenol A as a color developer, which has been commonly used in the past. It is possible to achieve sufficient color development density within a narrow temperature range from the color development start temperature, and because the surface of the recording paper is very smooth, it is possible to print with excellent resolution. The color developer of the present invention, bis(hydroxyphenyl)acetic acid, has the general formula

It is shown by [Formula]. R ₁ and R ₂ are alkyl groups. Examples of the alkyl group include methyl, ethyl, propyl, butyl, amyl, etc., and those having 10 or less carbon atoms are used. R ₁
and R ₂ may be the same or different. Specific examples of compounds include methyl bis(4-hydroxyphenyl)acetate, ethyl bis(4-hydroxyphenyl)acetate, n-propyl bis(4-hydroxyphenyl)acetate, and bis(4-hydroxyphenyl)acetate. n-butyl acetate, bis(3-methyl-4-hydroxyphenyl)methyl acetate, bis(3-methyl-4-hydroxyphenyl)ethyl acetate, bis(3-methyl-4-hydroxyphenyl)acetic acid Examples include n-propyl, but are not necessarily limited to these. Among the above, n-butyl bis(4-hydroxyphenyl)acetate is particularly practical. Such bis(hydroxyphenyl)acetic acids are produced by reacting glyoxylic acid and the corresponding phenol in the presence of a mineral acid or a strongly acidic ion exchange resin, and then esterifying it, or by reacting the glyoxylic acid ester with the corresponding phenol. It can be easily prepared by reacting with The color-forming substances used in the present invention have a lactone ring, a lactam ring, a sultone ring, or a spiropyran ring, and react with the above-mentioned color developer when heated to form a color. Representative examples include the following: There is, but
This is not intended to limit the invention. Crystal violet lactone, malachite green lactone, 3,3-bis(p-dimethylaminophenyl)-
6-Aminophthalide, 3,3-bis(p-dimethylaminophenyl)-
6-(p-toluenesulfamide) phthalide, 3-diethylamino-7-(N-methylanilino)fluoran, 3-diethylamino-7-(N-methyl-p-toluidino)fluoran, 3-dimethylamino-6-methoxyfluoran Orane, 3-diethylamino-7-chlorofluorane, 3-diethylamino-6-methyl-7-chlorofluorane, 3-diethylamino-7-phenylfluorane, 3-morpholino-5,6-benzofluorane, 3-diethylamino -5-methyl-7-dibenzylaminofluorane, 3-diethylamino-7-dibenzylaminofluorane, 3-diethylamino-7,8-benzofluorane, 3-cyclohexylamino-6-chlorofluorane, N- Phenylrhodamine B lactam, acidrhodamine B sultone, benzo-β-naphthospiropyran, 2-methyl-spiropinaphthopyran, 1,3,3-trimethyl-6'-chloro-8'-methoxy-indolinobenthospiropyran, etc. Further, in the present invention, other known color developers may be used in combination within a range that does not impair the effects of the present application. Examples of such color developers include 4,4'-isopropylidene diphenol, 4,4'-isopropylidene bis(2-chlorophenol), 4,4'-isopropylidene bis(2-t-butylphenol), and 4,4'-isopropylidene bis(2-chlorophenol). , 4'-sec butylidene diphenol, 4,4'-(1-methyl-n-hexylidene) diphenol, 4,4'-cyclohexylidene diphenol, 4,4'-thiobis(6-t-butyl-3- Methylphenol), etc. As a binder, polyvinyl alcohol, polyvinyl alcohol derivatives, carboxymethyl cellulose, methyl cellulose, hydroxyethyl cellulose, styrene/maleic acid copolymer or its salt, isobutylene/maleic acid copolymer or its salt, sodium alginate, modified starch, SBR latex, Examples include acrylic latex, gum arabic, terpene resin, and cyclized rubber. In preparing the recording material, an aqueous dispersion of a color-forming substance and an aqueous dispersion of a color developer are prepared separately and then mixed. The binder may be added to at least one of the dispersions. Appropriate amounts of color former, color developer, and binder to be used are 3 to 30% by weight of color former, 6 to 60% by weight of color developer, and 4% by weight of binder.
~40% by weight. The solid content concentration of the recording material is set to 10 in consideration of workability, etc.
~40% by weight is suitable. Known additives such as glyoxal, water-resistant agents such as urea resins, antifoaming agents, dispersants, clay, calcium carbonate, satin white, titanium dioxide, etc. are added to the aqueous liquid obtained as described above, as necessary. You can also do that. There are no particular restrictions on the paper to be coated. For coating, any known method such as a roll coater method, an air doctor method, a blade coater method, etc. may be employed. The coating amount of the coating liquid is preferably about 0.1 to 20 g/m ² , particularly about 3 to 15 g/m ² . The recording material of the present invention will be explained in more detail below with reference to Examples. In the following, "parts" or "%" are based on weight unless otherwise specified. Example 1 Liquid A crystal violet lactone 7 parts Polyvinyl alcohol (10% aqueous solution) (Nippon Gosei Kagaku Co., Ltd. Gohsenol GL-os) 10 parts Stearic acid amide 10 parts Calcium carbonate 25 parts Water 60 parts B liquid Bis(4-Hydroxy) phenyl) n-butyl acetate 25 parts Polyvinyl alcohol (10% aqueous solution) (Nippon Gohsenol GL-05) 10 parts Calcium carbonate 25 parts C-liquid polyvinyl alcohol (10% aqueous solution) (Nippon Gohsenol NL) -05) 110 parts Liquids A, B, and C were prepared, and each of A and B was ground in a sand mill until the average particle size of the solid material became 2 to 3 μm, and then A, B, and C were mixed. This was applied to paper with a basis weight of 50 g/m ² in an amount of 10 g/m ² and dried to obtain thermal recording paper. The physical properties of the recording paper are shown in the table. As a control example, the same experiment as in the same example was conducted except that bisphenol A was used instead of n-butyl bis(4-hydroxyphenyl)acetate. The results are also shown in the table. However, the color density is determined by using the above recording paper at a surface temperature of 110
The sample was brought into contact with a metal block at ℃ for 2 seconds to develop color, and 60 minutes after color development, the color density was determined using a Macbeth densitometer. Further, the smoothness was determined using an Oken type smoothness measuring machine after the recording paper was left in an atmosphere of 20° C. and 65% RH for 72 hours. Examples 2 to 3 In addition to using bis(4-hydroxyphenyl)ethyl acetate in place of n-butyl bis(4-hydroxyphenyl)acetate in Example 1 (Example 2), bis(3-methyl-4- The same experiment as in Example 1 was conducted except that methyl hydroxyphenyl acetate was used (Example 3). The results are also shown in the table.

【table】

Claims (1)

[Scope of Claims] 1. In a heat-sensitive recording material comprising (A) a color-forming substance, (B) a color developer that causes the color-forming substance to develop color when heated, and (C) a binder, as the above (B), the general formula A heat-sensitive recording material characterized by using a bis(hydroxyphenyl)acetic acid represented by the formula: [where R ₁ and R ₂ are alkyl groups]. 2. The heat-sensitive recording material according to claim 1, characterized in that n-butyl bis(4-hydroxyphenyl)acetate is used as a color developer.