JP3477938B2 - Thermal recording medium - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-sensitive recording material utilizing a color-forming reaction between a leuco dye and a coloring agent, and more particularly to a heat-sensitive recording material having excellent recording running properties. It is. [0002] Hitherto, a thermosensitive recording medium which utilizes a reaction between a leuco dye and a color former to contact both coloring materials by heat to obtain a recorded image is well known. Such a thermosensitive recording medium is relatively inexpensive, and since the recording apparatus is compact and its maintenance is relatively easy, it is widely used as a recording medium in a facsimile, a medical measuring instrument, an automatic ticket vending machine, and the like. Along with this, the quality required has been varied over a wide range such as oil resistance and plasticizer resistance, and various improvements have been made mainly on leuco dyes and coloring agents. [0003] However, many thermal recording media having excellent quality have a problem in recording running performance due to adhesion of debris to the thermal head (head debris) and wear of the head. Therefore, in order to improve such head scum, various methods have been proposed for adding a pigment or the like having excellent oil absorbency to the heat-sensitive recording layer. However, high oil-absorbing pigments such as fine-particle silicon oxide pigments have a remarkable effect in preventing head scum, but have a drawback that head wear occurs when recording for a long time. Further, a heat-sensitive recording medium containing aluminum hydroxide in a heat-sensitive recording layer is described in JP-B-63-7957 and JP-A-4-128087. There is such a problem. SUMMARY OF THE INVENTION An object of the present invention is to provide a heat-sensitive recording medium which is excellent in recording sensitivity, in particular, in which a thermal head has little wear and head scum. SUMMARY OF THE INVENTION The present inventors have developed a thermosensitive recording medium having a thermosensitive recording layer containing a leuco dye, a coloring agent and an adhesive on a support. A graft copolymer of polyvinyl alcohol and (acrylamide / acrylonitrile / vinylpyrrolidone) copolymer is used, and aluminum hydroxide is contained in the heat-sensitive recording layer in an amount of 5 to 25% by weight based on the total solid content of the heat-sensitive recording layer. By doing so, the inventors have found that the above-mentioned object is achieved, and have completed the present invention. DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heat-sensitive recording material having a heat-sensitive recording layer containing a leuco dye, a coloring agent and an adhesive on a support, comprising polyvinyl alcohol and (acrylamide / acrylonitrile). (Vinylpyrrolidone) A specific adhesive composed of a graft copolymer with a copolymer is used, and aluminum hydroxide is contained in the heat-sensitive recording layer in an amount of 5 to 25% by weight based on the total solid content of the heat-sensitive recording layer. When aluminum hydroxide is less than 5% by weight with respect to the total solid content of the heat-sensitive recording layer, head scum is liable to occur, and when it exceeds 25% by weight, head abrasion is liable to occur. The range of weight% is more preferred. Although the reason why such an effect is obtained is not always clear, it is suitable for absorbing the melt which causes the adhesion of dregs in the heat-sensitive recording layer due to the interaction between aluminum hydroxide and a specific adhesive. This is probably because voids are formed and the affinity between aluminum hydroxide and the specific adhesive is strong. The use amount of the specific adhesive is not particularly limited, but is 10 to 30 with respect to the total solid content of the heat-sensitive recording layer.
It is desirable to use it in the range of weight%. The polyvinyl alcohol and (acrylamide / acrylonitrile / vinylpyrrolidone) copolymer used as an adhesive in the heat-sensitive recording layer is not particularly limited as long as it is water-soluble, but the polyvinyl alcohol may be (acrylamide / acrylonitrile / vinylpyrrolidone). The range of 20 to 100% by weight of the copolymer is preferred. (Acrylamide, acrylonitrile, vinylpyrrolidone)
60 to 90% by weight of acrylamide based on the copolymer,
The preferred range is 1 to 20% by weight of acrylonitrile and 3 to 25% by weight of vinylpyrrolidone. Further, in the copolymer (acrylamide / acrylonitrile / vinylpyrrolidone), acrylic acid, methacrylic acid, itaconic acid,
It is also possible to copolymerize ethylenically unsaturated carboxylic acids such as maleic acid and fumaric acid and acrylic esters such as methyl (meth) acrylate and butyl acrylate. The polyvinyl alcohol to be graft-copolymerized is not particularly limited.
0 to 2000 completely saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, acetoacetyl group-modified polyvinyl alcohol and the like are used. In the present invention, as the leuco dye constituting the heat-sensitive recording layer, various known leuco dyes can be used, and specific examples thereof are as follows. 3,3-bis (p-dimethylaminophenyl) -6-methylaminophthalide, 3,3-bis (2-phenylindole-3-
Triarylmethane dyes such as yl) -6-dimethylaminophthalide and 3-p-dimethylaminophenyl-3- (1-methylpyrrole-3-yl) -6-dimethylaminophthalide; Diphenylmethane dyes such as bis-dimethylaminobenzhydryl benzyl ether, N-halophenyl-leuco auramine and N-2,4,5-trichlorophenyl leuco auramine; thiazines such as benzoyl leucomethylene blue and p-nitrobenzoyl leucomethylene blue Dye, 3-methyl-spiro-
Spiro dyes such as dinaphthopyran, 3-ethyl-spiro-dinaphthopyran, 3-methyl-naphtho (6'-methoxybenzo) spiropyran, 3-propyl-spiro-dibenzopyran, rhodamine-B-anilinolalactam, rhodamine (p- Lactam dyes such as nitroanilino) lactam and rhodamine (o-chloroanilino) lactam; 3-dimethylamino-7-methoxyfluoran, 3-diethylamino-6-methoxyfluoran,
3-diethylamino-7-chlorofluorane, 3-diethylamino-6-methyl-7-chlorofluorane, 3-
(N-ethyl-p-toluidino) -7-methylfluoran, 3-diethylamino-7-N-methylaminofluoran, 3-diethylamino-7-N-methyl-N-benzylaminofluoran, 3-diethylamino- 7-N-
Diethylaminofluoran, 3- (N-ethyl-p-toluidino) -6-methyl-7-anilinofluoran, 3
-(N-ethyl-p-toluidino) -6-methyl-7-
(P-toluidino) fluoran, 3-dimethylamino-
6-methyl-7-anilinofluoran, 3-diethylamino-6-methyl-7-anilinofluoran, 3-di (n-butyl) amino-6-methyl-7-anilinofluoran, 3- ( N-cyclohexyl-N-methylamino) -6-methyl-7-anilinofluoran, 3-diethylamino-6-methyl-7-xylidinofluoran,
3-diethylamino-7- (o-chloroanilino) fluoran, 3-di (n-butyl) amino-7- (o-chloroanilino) fluoran, 3- (N-ethyl-Nn-
Amyl) amino-6-methyl-7-anilinofluoran, 3- (N-ethyl-N-isoamyl) amino-6
Methyl-7-anilinofluoran, 3- (N-ethyl-
Fluoran dyes such as (N-cyclopentyl) amino-6-methyl-7-anilinofluoran; Of course, the present invention is not limited to these leuco dyes, and two or more leuco dyes can be used in combination. Various known colorants can be used in combination with the leuco dye, and examples thereof include the following. 4,4′-dihydroxy-diphenylmethane, 4,4′-isopropylidene diphenol, 4,
4'-cyclohexylidenediphenol, 4,4'-
(1,3-dimethylbutylidene) bisphenol, 2,
2-bis (4-hydroxyphenyl) -4-methylpentane, 4,4'-dihydroxydiphenyl sulfide, 4,4'-thiobis (6-tert-butyl-3-methylphenol), 4,4'-dihydroxydiphenyl Sulfone, 2,4′-dihydroxydiphenyl sulfone,
4-hydroxy-4'-methyldiphenyl sulfone, 4
-Hydroxy-4'-methoxydiphenyl sulfone, 4
-Hydroxy-4'-isopropoxydiphenylsulfone, 4-hydroxy-3 ', 4', 5'-trimethyldiphenylsulfone, 3,4-dihydroxy-4'-methyldiphenylsulfone, bis (3-allyl-4-hydroxy Phenyl) sulfone, 1,3-di [2- (4-hydroxyphenyl) -2-propyl] benzene, hydroquinone monobenzyl ether, bis (4-hydroxyphenyl) acetic acid butyl ester, 4-hydroxybenzophenone, 2,4- Dihydroxybenzophenone, 2,4
4'-trihydroxybenzophenone, 2,2 ', 4
4′-tetrahydroxybenzophenone, dimethyl 4-hydroxyphthalate, methyl 4-hydroxybenzoate,
Phenyl 4-hydroxybenzoate, benzyl 4-hydroxybenzoate, tolyl 4-hydroxybenzoate, phenethyl 4-hydroxybenzoate, p-chlorobenzyl 4-hydroxybenzoate, 4-hydroxybenzoic acid-p-
Phenolic compounds such as methoxybenzyl, novolak type phenolic resins, and phenolic polymers. Zinc p-tert-butylbenzoate, zinc 3-cyclohexyl-4-hydroxybenzoate, 4- [2-
Aromatics such as (p-methoxyphenoxy) ethyloxy] zinc salicylate, 4- [2- (p-tolylsulfonyl) propyloxy] zinc salicylate, 5- [p- (2-p-methoxyphenoxyethoxy) cumyl] zinc salicylate Zinc salts of carboxylic acids and the like. Of course, two or more color formers can be used in combination as needed. The ratio of the leuco dye to the color former should be appropriately selected according to the type of the leuco dye and the color former used, and is not particularly limited.
The coloring agent is used in an amount of 100 to 700 parts by weight, preferably about 150 to 400 parts by weight based on 00 parts by weight. Preparation of the coating solution for the heat-sensitive recording layer containing these is generally performed by dispersing the leuco dye and the color former together or separately using a stirring / pulverizing machine such as a ball mill, an attritor, or a sand mill using water as a dispersion medium. It is prepared by In such a coating solution, in addition to the above-mentioned specific adhesive, starch, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin,
Casein, gum arabic, polyvinyl alcohol, styrene / maleic anhydride copolymer salt, styrene / acrylic acid copolymer salt, styrene / butadiene copolymer emulsion and the like can be used in combination. Various assistants can be further added to the coating solution, for example, sodium salt of dioctylsulfosuccinate, sodium salt of dodecylbenzenesulfonate,
Dispersants such as lauryl alcohol sulfate / sodium salt; lubricating agents such as stearic acid, polyethylene, carnauba wax, paraffin wax, zinc stearate, calcium stearate; and other antifoaming agents, fluorescent dyes, coloring dyes, and the like. Further, in the heat-sensitive recording layer, sensitizers such as fatty acid amides such as stearic acid amide and methylene bisamide stearate;
2′-methylenebis (4-methyl-6-tert-butylphenol), 4,4′-butylidenebis (6-tert-butyl-3-methylphenol), 1,1,3-tris (2-methyl-4-hydroxy) -5-tert-butylphenyl) butane, 1,1,3-tris (2-methyl-4-
Hindered phenols such as hydroxy-5-cyclohexylphenyl) butane, p-benzylbiphenyl,
1,2-bis (phenoxy) ethane, 1,2-bis (4
-Methylphenoxy) ethane, 1,2-bis (3-methylphenoxy) ethane, 1- (2-methylphenoxy)
Ethers such as -2- (4-methoxyphenoxy) ethane and 2-naphthylbenzyl ether; dibenzyl terephthalate; 1-hydroxy-2-naphthoic acid phenyl ester; oxalic acid dibenzyl ester;
Compounds such as esters such as -methylbenzyl) ester and di (4-chlorobenzyl) oxalate;
UV absorbers such as (2'-hydroxy-5'-methylphenyl) benzotriazole and 2-hydroxy-4-benzyloxybenzophenone; and 1,1,3-lithos (2- Methyl-4-hydroxy-5-cyclohexylphenyl) butane, 1,
1,3-lithos (2-methyl-4-hydroxy-5-te
rt-butylphenyl) butane, 4-benzyloxy-
Compounds such as 4 '-(2,3-glycidyloxy) diphenylsulfone and 2,2'-methylenebis (4,6-di-tert-butylphenyl) phosphate are added as appropriate. In the present invention, the method of forming the heat-sensitive recording layer is not particularly limited, and the heat-sensitive recording layer can be formed by a conventionally known technique. For example, a coating solution for a heat-sensitive recording layer is coated on a support with an air knife. Coating, drying, and the like by a suitable coating device such as a coater, a blade coater, a bar coater, a gravure coater, and a curtain coater. As the support, paper, plastic film, synthetic paper and the like are used, but paper is preferably used in terms of cost and applicability. Also, there are no particular limitation on the coating amount of the heat-sensitive recording layer coating liquid, generally drying weight 2~12g / m ^2, preferably from 2 to 8 g / m ²
It is adjusted to be within the range. In the present invention, it is possible to provide an overcoat layer on the heat-sensitive recording layer for the purpose of enhancing the preservability of the recorded image against chemicals and the like. It is of course possible to provide an undercoat layer between the body and the heat-sensitive recording layer, and various known techniques in the field of manufacturing a heat-sensitive recording medium, such as applying an adhesive, can be added. The present invention will be described in more detail with reference to the following examples, but it should be understood that the present invention is by no means restricted thereto. Parts and% in Examples are parts by weight and% by weight, respectively, unless otherwise specified. Example 1 Formation of undercoat layer Fired clay [trade name: Ansilex, manufactured by EMC] 8
5 parts, light calcium carbonate (trade name: Shiratoku Ginka PZ, manufactured by Shiraishi Industry Co., Ltd.) 15 parts, SBR latex [trade name: L
−1571, solid concentration 48%, manufactured by Asahi Kasei Corporation) 17
Parts, a coating liquid consisting of 20 parts of a 25% aqueous solution of polyvinyl alcohol (trade name: PVA205, manufactured by Kuraray Co., Ltd.) and 120 parts of water was coated on high-quality paper having a basis weight of 45 g / m ² after drying with a bevel plate coater. An undercoat layer was formed by coating and drying to 7 g / m ² . Solution A Preparation 3-Di (n-butyl) amino-6-methyl-7-anilinofluoran 10 parts, 1,2-di (3-methylphenoxy) ethane 20 parts, methylcellulose 5% aqueous solution 20 parts And a composition consisting of 50 parts of water and water were pulverized with a sand mill until the average particle diameter became 0.8 μm to obtain a liquid A. Solution B Preparation 4, A composition comprising 30 parts of 4'-isopropylidene diphenol, 5 parts of a 10% aqueous solution of ammonium salt of styrene / maleic copolymer, and 60 parts of water was subjected to sand milling to give an average particle size of 1. The mixture was pulverized until the particle size became 0 μm to obtain a liquid B. Formation of heat-sensitive recording layer 80 parts of solution A, 50 parts of solution B, 20 parts of a 60% slurry of aluminum hydroxide (trade name: Heidilite H42, manufactured by Showa Denko KK), 30% dispersion of zinc stearate 10 Department,
A coating liquid consisting of 60 parts of a 15% aqueous solution of polyvinyl alcohol and (acrylamide / acrylonitrile / vinylpyrrolidone) copolymer [trade name: Polymalon 2000, manufactured by Arakawa Chemical Industry Co., Ltd.], and 125 parts of water, 5 g / m ² on the undercoat layer after drying
After coating and drying with a rod blade coater to form a heat-sensitive recording layer, a super calender treatment was performed to obtain a heat-sensitive recording material. Example 2 In forming the heat-sensitive recording layer of Example 1, aluminum hydroxide [trade name: Hydrite H42, manufactured by Showa Denko KK] was replaced with 20 parts of a 60% slurry. Heidilight H42, manufactured by Showa Denko KK]
% Heat-sensitive recording medium was obtained in the same manner as in Example 1 except that 10 parts of a 10% slurry and 12 parts of a 50% light calcium carbonate slurry were used. Comparative Example 1 In forming the heat-sensitive recording layer of Example 1, instead of 20 parts of a 60% slurry of aluminum hydroxide (trade name: Heidilite H42, manufactured by Showa Denko KK), fine silicon oxide particles (trade name: Mizuka Seal P630, manufactured by Mizusawa Chemical Co., Ltd.]
A thermosensitive recording medium was obtained in the same manner as in Example 1, except that 60 parts of 0% slurry was used. Comparative Example 2 In the formation of the heat-sensitive recording layer of Example 1, a graft copolymer of polyvinyl alcohol and (acrylamide / acrylonitrile / vinylpyrrolidone) copolymer [trade name:
Instead of 60 parts of a 15% aqueous solution of Polymalon 2000, Arakawa Chemical Co., Ltd., polyvinyl alcohol [trade name:
A thermosensitive recording medium was obtained in the same manner as in Example 1 except that 60 parts of a 15% aqueous solution of PVA110 (manufactured by Kuraray Co., Ltd.) was used. Comparative Example 3 In forming the heat-sensitive recording layer of Example 1, 2 parts of this 60% slurry of aluminum hydroxide (trade name: Heidilite H42, manufactured by Showa Denko KK) was used instead of 20 parts of this slurry. Except for the above, a thermosensitive recording medium was obtained in the same manner as in Example 1. Comparative Example 4 In forming the heat-sensitive recording layer of Example 1, 40 parts of this 60% slurry of aluminum hydroxide (trade name: Heidilite H42, manufactured by Showa Denko KK) was used instead of 20 parts of this slurry. Except for the above, a thermosensitive recording medium was obtained in the same manner as in Example 1. The following evaluation tests were performed on the thus obtained heat-sensitive recording medium, and the results are shown in Table 1. [Recording density] Thermal recording simulator (manufactured by Okura Electric Co., Ltd., TH-PDM, applied energy 0.20 mJ / do)
The density of the recorded image obtained using t) was measured with a Macbeth densitometer (RD914, manufactured by Macbeth). [Head Casing] Toshiba Word Processor JW95K
After continuously recording one million characters of ASCII code using V, head residue adhering to the thermal head was visually determined as follows. A: Almost no adhesion of head residue. ：: There is little adhesion of head scum. X: There is much adhesion of head scum. [Head wear] Toshiba word processor JW95K
After continuously recording 1 million ASCII code characters using V, the wear state of the thermal head was observed with an optical microscope. Evaluation criteria ：: No wear was observed on the surface of the head. ×: Wear is observed on the surface of the head. [Table 1] As can be seen from the results shown in Table 1, the heat-sensitive recording medium of the present invention has very little head scum adhesion and head abrasion and has excellent recording sensitivity.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-7-76172 (JP, A) JP-A-7-61129 (JP, A) JP-A 7-179055 (JP, A) JP-A-6-172 155909 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) B41M 5/28-5/34

Claims (1)

(57) [Claims 1] In a heat-sensitive recording medium provided with a heat-sensitive recording layer containing a leuco dye, a coloring agent and an adhesive on a support, the adhesive comprises polyvinyl alcohol and ( (Acrylamide / acrylonitrile / vinylpyrrolidone) copolymer and aluminum hydroxide in the heat-sensitive recording layer in an amount of 5 to 2 with respect to the total solid content of the heat-sensitive recording layer.
A heat-sensitive recording material containing 5% by weight.