JPH0117874B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to heat-sensitive recording materials. A heat-sensitive recording material is a recording material in which a heat-sensitive coloring layer that can form a colored image by heating is provided on a support such as paper, and the heating is performed using a thermal printer equipped with a thermal head. Widely used. Because such heat-sensitive recording materials can easily produce colored images simply by heating, their uses have rapidly expanded with the development of the information industry, and today they are used only for copying books, documents, etc. It is also widely used for recording the output of various information and measuring instruments such as electronic computers, facsimiles, and telex. The heat-sensitive coloring layer of the heat-sensitive recording material contains a colorless or light-colored leuco dye having a lactone ring, lactam ring, or spiropyran ring, and an acidic substance or phenol that reacts with the leuco dye to develop color when heated. However, it has been widely used because the color tone is clear and there is little fogging phenomenon (coloring phenomenon around the heated part). However, when a thermosensitive recording material using a thermosensitive coloring layer having the above composition is brought into contact with a thermal element such as a thermal head or a thermal pen to obtain a colored image, the components in the thermosensitive coloring layer are dissolved. Ingredients stick to the thermal head or pen, causing so-called scum adhesion and staking phenomena. In addition, such heat-sensitive recording materials are sensitive to rubbing, and therefore have the disadvantage of being accompanied by a pressure coloring phenomenon in which coloring occurs due to rubbing. For this reason, the density of the obtained colored image is low and the image lacks sharpness, and furthermore, when recording for a long time, the running performance of the thermal head is hindered, which is a drawback. In addition, in recent years there has been an increasing demand for higher speed and higher density image information recording, and with this, it is possible to cope with higher speeds and higher densities, and even when recording for long periods of time, there is no problem of dust adhesion to the thermal head, etc. There is a need for a heat-sensitive recording material that does not cause this phenomenon. The present invention aims to solve the above-mentioned drawbacks, and is capable of increasing the speed and density of image information without causing deposits on thermal elements such as thermal heads and the staking phenomenon. It is an object of the present invention to provide a heat-sensitive recording material that has excellent heat-sensitive properties capable of coping with the above problems and is less likely to be accompanied by pressure coloring phenomena. The present invention provides a heat-sensitive recording material provided on a support with a heat-sensitive coloring layer containing as a main component a colorless or light-colored leuco dye and an acidic substance or a phenolic compound that reacts with the leuco dye to develop color when heated. In the heat-sensitive coloring layer, an alkaline earth metal salt or an alkali metal salt of stearic acid and a general formula

[Formula] (wherein R ¹ is an alkyl group having 1 to 30 carbon atoms). As the leuco dye used in the heat-sensitive coloring layer in the present invention, conventionally known colorless or light-colored leuco dyes are used, and specific examples include the following compounds. (a) Triphenylmethane-based leuco dye represented by the general formula below (wherein R ₁ , R ₂ and R ₃ are selected from hydrogen, hydroxyl, halogen, alkyl, nitro, amino, dialkylamino, monoalkylamino or allyl). The following compounds are listed as representative examples of such leuco dyes. (1) 3,3-bis(p-dimethylaminophenyl)-phthalide (2) 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide (commonly known as crystal violet lactone) (3 ) 3,3-bis(p-dimethylaminophenyl)-6-diethylaminophthalide (4) 3,3-bis(p-dimethylaminophenyl)-6-chlorophthalide (5) 3,3-bis(p-dimethylaminophenyl)-6-chlorophthalide -dimethylaminophenyl)-phthalide (b) Fluoran leuco dye represented by the following general formula (wherein R ₁ , R ₂ and R ₃ are as defined above). The following are listed as typical compounds of such leuco dyes. (1) 3-cyclohexylamino-6-chlorofluorane (2) 3-(N,N-diethylamino)-5-methyl-7-(N,N-dibenzylamino)fluoran (3) 3-dimethylamino- 5,7-dimethylfluorane, (4) 3-diethylamino-7-methylfluorane (5) 3-diethylamino-7,8-dibenzfluorane, (6) 3-diethylamino-6-methyl-7-chlorofluoran Oran (7) 3-pyrrolidino-6-methyl-7-anilinofluorane (c) Lactone compound represented by the following general formula (In the formula, R ₁ and R ₂ represent hydrogen, a lower alkyl group, a substituted or unsubstituted aralkyl group, a phenyl group, a cyanoethyl group, or a β-halogenated ethyl group, or R ₁ and R ₂
is combined with −(CH ₂ −) ₄ , −(CH ₂ −) ₅ or −(
_CH2- )0-( _CH2- ) ₂ , _R3 and _R4 are
It represents hydrogen, a lower alkyl group, an amino group, or a phenyl group, and either one of R ₃ and R ₄ is hydrogen, and X ₁ , X ₂ and X ₃ represent hydrogen, a lower alkyl group, a lower alkoxyl group, or a halogen. , represents a halogenated methyl group, nitro group, amino group or substituted amino group, and X ₄ is hydrogen, halogen,
represents a lower alkyl group or a lower alkoxyl group, n is an integer from 0 to 4). The following are listed as representative lactone compounds. (1) 3-(2'-hydroxy-4'-dimethylaminophenyl)-3-(2'methoxy-5-chlorophenyl) phthalide (2) 3-(2'-hydroxy-4'-dimethylaminophenyl) )-3-(2'-methoxy-5-nitrol phenyl) phthalide (3) 3-(2'-hydroxy-4'-dimethylaminophenyl)-3-(2-methoxy-5'-methylphenyl) phthalide (4) 3-(2'-Methoxy-4'-dimethylaminophenyl)-3-(2'-hydroxy-4'-chloro-5'-methylphenyl)phthalide The acidic substance or phenolic compound used in the present invention can be heated It sometimes develops color by reacting with the leuco dye, and specific examples include the following compounds. (1) Boric acid (2) Oxalic acid (3) Maleic acid (4) Tartaric acid (5) Citric acid (6) Succinic acid (7) Benzoic acid (8) Stearic acid (9) Gallic acid (10) Salicylic acid (11) ) 1-hydroxy-2-naphthoic acid (12) o-hydroxybenzoic acid (13) m-hydroxybenzoic acid (14) 2-hydroxy-p-toluic acid (15) 3,5-xylenol (16) Thymol (17 ) p-tert-butylphenol (18) 4-hydroxyphenoxide (19) Methyl-4-hydroxybenzoate (20) 4-hydroxyacetophenone (21) α-naphthol (22) β-naphthol (23) Catechol (24) Resorcin (25) Hydroquinone (26) 4-tert-octylcatechol (27) 4,4'-sec-butylidenephenol (28) 2,2'-dihydroxydiphenyl (29) 2,2'-methylenebis (4-methyl-6-
tert-butylphenol) (30) 2,2-bis(4-hydroxyphenyl)
Propane (commonly known as bisphenol A) (31) 4,4'-isopropylidene-bis(2-
tert-butylphenol) (32) 4,4'-sec-butylidene diphenol (33) Pyrogallol (34) Phloroglucin (35) Phloroglycin carboxylic acid Alkaline earth metal stearate contained in the heat-sensitive coloring layer in the present invention Salts or alkali metals include sodium stearate, potassium stearate, magnesium stearate and calcium stearate, with calcium stearate being particularly preferred. Further, in the present invention, the compound contained in the heat-sensitive coloring layer is represented by the following general formula (). (In the formula, R ₁ is an alkyl group having 1 to 30 carbon atoms). Among these, those in which R ₁ has 16 to 22 carbon atoms are particularly preferred. In the present invention, the amount of stearate added to the heat-sensitive coloring layer is 1 to 20% of the total weight of the leuco dye and the acidic substance or phenolic compound.
Preferably, the amount is double the amount (weight). Further, the amount of the compound represented by the general formula () to be added is preferably 1 to 10 times (by weight) the total weight of the leuco dye and the acidic substance or phenolic compound. It is preferable to use a binder when disposing each component contained in the heat-sensitive coloring layer on a support such as paper. Specific examples of the binder include the following compounds. (1) Polyvinyl alcohol (2) Methoxycellulose (3) Hydroxyethyl cellulose (4) Carboxymethyl cellulose (5) Polyvinylpyrrolidone (6) Polyacrylamide (7) Polyacrylic acid (8) Starch (9) Gelatin (10) Polystyrene ( 11) Vinyl chloride-vinyl acetate copolymer (12) Polybutyl methacrylate Fine powder of calcium carbonate, silica, alumina magnesia, talc, barium sulfate, aluminum stearate, etc. may be further added to the heat-sensitive coloring layer of the present invention. Accordingly, the clarity of the colored image can be improved. EXAMPLES The present invention will be further explained below with reference to Examples and Comparative Examples, but the present invention is not limited thereto. Example A mixture having the following composition was ground and dispersed for 24 hours using a ball mill to prepare liquids [A] and [B]. [A] Liquid crystal violet lactone 60 parts by weight 5% polyvinyl alcohol solution 60 parts by weight Water 180 parts by weight [B] Liquid bisphenol A 60 parts by weight 5% polyvinyl alcohol solution 60 parts by weight Water 180 parts by weight Next, from the following composition The mixture was pulverized and dispersed in an attritor for 6 hours to form liquid [C] and liquid [D].
A liquid was prepared. [C] Liquid

[Formula] 60 parts by weight 5% methylcellulose aqueous solution 60 parts by weight Water 180 parts by weight [D] Liquid Calcium stearate 100 parts by weight 5% methylcellulose aqueous solution 100 parts by weight Water 120 parts by weight Next [A] 1.0 part by weight, [B] liquid 4.0 parts by weight,
[C] 2.0 parts by weight of liquid, [D] 2.0 parts by weight of liquid and 20%
A thermosensitive coloring layer forming liquid was prepared by mixing 2.0 parts by weight of an aqueous polyvinyl alcohol solution. This thermosensitive color forming layer forming liquid was coated on a commercially available high quality paper with a standard basis weight of 60 g/m ² so that the dry coating amount was 7 g/m ² to produce a thermosensitive recording material. A facsimile machine [OKIFAX-7100 manufactured by Oki Electric Industry Co., Ltd.] was applied to the heat-sensitive recording material produced in this way.
When printing at high speed using the printer, there was hardly any residue adhesion to the thermal head, stagnation phenomenon, or pressure coloring, and there was no obstruction to the high-speed running of the thermal head, and clear blue images were obtained. Ta. Comparative example A mixture consisting of the following composition was prepared using an attritor.
A liquid [E] was prepared by grinding for a time. [E] Liquid stearic acid amide 60 parts by weight 5% methyl cellulose aqueous solution 60 parts by weight Water 180 parts by weight A thermosensitive coloring layer was prepared in the same manner as in the example except that liquid [E] was used instead of liquid [C] in the example. A forming liquid was prepared, and then a heat-sensitive recording material was produced. When printing was carried out on the heat-sensitive recording material for comparison produced in this manner in the same manner as in the examples, it was found that the running properties of the thermal head were poor, and some scum adhesion, staking phenomenon, and pressure coloring phenomenon were observed, and the printing was not very clear. No blue image was obtained.

Claims (1)

[Scope of Claims] 1. A heat-sensitive recording material comprising a heat-sensitive color-forming layer on a support, which contains a colorless or light-colored leuco dye and an acidic substance or phenolic compound that reacts with the leuco dye to develop color when heated. A heat-sensitive recording material, characterized in that the heat-sensitive coloring layer contains an alkaline earth metal salt or an alkali metal salt of stearic acid and a compound represented by the following general formula. (In the formula, R ₁ is an alkyl group having 1 to 30 carbon atoms).