JPH0367517B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a new heat-sensitive recording material containing a normally colorless or slightly pale color-forming dye in a heat-sensitive coloring layer, an organic acid or phenolic substance that causes the color-forming dye to develop color when heated, and a binder. More specifically, the heat-sensitive recording material has storage stability, especially the water resistance of the coating film, the water resistance of the colored part, the fading that occurs when it comes into close contact with a plastic film containing a large amount of plasticizer (hereinafter referred to as plasticizer resistance), and the resistance to meat and food. This invention relates to a heat-sensitive recording material with improved discoloration (hereinafter referred to as oil resistance) that occurs when oil such as edible oil is attached. Hitherto, various types of heat-sensitive recording sheets have been known in the art (e.g., Japanese Patent Publication No. 1983-1973), in which a coating material obtained by dispersing a lactone compound such as crystal violet lactone and a phenol compound such as bisphenol A in a binder such as polyvinyl alcohol solution is coated on a support.
14039). However, when this type of heat-sensitive recording sheet is heated, the color-forming lactone compound and the organic acid or phenol compound in the area chemically react to develop color, but in this case, the basic requirements for a heat-sensitive recording sheet are The characteristics of this paper are that it has good color development, has an appearance as white as possible and has the appearance of natural paper, and has a long shelf life.The most important properties are (a) high sensitivity, and (b) states king ( It is required to have good compatibility with the thermal head, including (c) no adhesion of residue to the thermal head. In this way, heat-sensitive recording materials are desired to have the above-mentioned characteristics depending on their use, but these types of dye-type color-forming materials are unstable to light, water, temperature, plasticizers, oil, etc. Therefore, changes over time during storage are always a problem. Therefore, when desired printing is performed on such a recording sheet, the recorded color appears extremely clearly, but if a plastic film containing a large amount of plasticizer (for example, a soft vinyl chloride film) is used in the coloring area, If they are kept in close contact with each other or if they are stored with oil or fat attached, the adhesive part will fade in color, which is a drawback. Also, when the colored part is in contact with water for a long period of time, significant discoloration usually occurs. These discolorations are particularly noticeable in color-forming type heat-sensitive recording materials that use dyes mainly composed of colorless or light-colored lactone compounds, and this discoloration depends on the chemical structure of the color-forming lactone compound used. It is presumed that the above-mentioned disadvantages arise because plasticizers and oils, especially organic acids and phenolic compounds, dissolve in plasticizers and oils without any heat-sensitive recording material coming into contact with oils or plasticizers. There has been a strong demand for a solution to this problem. The object of the present invention is to solve the above-mentioned problems and provide a heat-sensitive recording material having improved water resistance, plasticizer resistance and oil resistance, and long-term storage stability. By providing a protective layer containing a water-soluble polymer and a fluorine-based acrylic polymer on the surface of the thermosensitive coloring layer provided on the support, the present inventors have realized that plasticizers, oils, etc. can penetrate into the thermosensitive coloring layer. We have discovered that it is effective in preventing color fading when it comes into close contact with a soft polyvinyl chloride film or when it is exposed to oil, and is also effective in desensitizing color development and reducing whiteness. has been reached. In other words, when coating the surface of a heat-sensitive recording material with cottonseed oil, for example, it is possible to coat the surface of a heat-sensitive recording material with conventional heat-sensitive recording materials without a protective layer or water-soluble polymers with barrier properties (e.g.
In the case of heat-sensitive recording materials provided with a protective layer containing PVA, casein, etc.) and a curing agent, the colored part disappears in 0.5 to 5 hours when left at 40°C, whereas the fluorinated acrylic of the present invention disappears in 0.5 to 5 hours. In heat-sensitive recording materials containing polymers, it hardly disappears even after 24 hours or more. The protective layer of the heat-sensitive recording material of the present invention contains a curing agent, a lubricant, and/or a pigment in addition to the water-soluble polymer and the curing agent.
Adds water resistance to the coating film and prevents discoloration when immersed in water. Furthermore, when recording on the coating surface, it prevents staking of the thermal head to the film surface and prevents scum from adhering to the thermal head. can do. Therefore, this product can be used, for example, as a thermal recording type ticket for automatic ticket vending machines, as well as for coupon tickets and commuter passes that require long shelf life, as well as for POS.
Not only is it suitable for use as label paper that adheres to the packaging surface of fresh foods and oily meats packaged with vinyl chloride film, but also facsimile paper for long-term shelf life. It also has the practical benefit of being able to be used as printer paper. The materials used in the present invention will be explained in detail below. (1) 3-diethylamino-
6-Methyl-7-anilinofluorane, 3-pyrrolidino-6-methyl-7-anilinofluorane, 3-piperidino-6-methyl-7-anilinofluorane, 3-(N-methyl-N- cyclohexylamino)-6-methyl-7-anilinofluorane, 3-diethylamino-7-chloroanilinofluorane, 3-[N-ethyl-(pmethylphenyl)amino]-6-methyl-7-anilinofluoran Oran, 3-diethylamino-7-
(metatrifluoromethyl)anilinofluorane, 3,3-bis-(P-
dimethylaminophenyl)-6-dimethylaminophthalide (crystal violet lactone), 3,3-bis-(P-dibutylaminophenyl) phthalide, 3,3-bis-(P-dimethylaminophenyl) phthalide , triphenylmethane series such as 4-hydroxy-4'-dimethylaminotriphenylmethane lactone, 3-methyl-di-β-naphthospirolane, 1,3,3-trimethyl-6'-chloro-8'-methoxyindolino Spirolane dyes such as benzospirolane, and leuco dyes such as auramine, rhodamine lactam, and fethiazine are also used.
However, the present invention is not limited to these representative examples. (2) Color-developing substances that cause color-forming dyes to develop color when heated include inorganic solid acidic substances such as acid clay, zeolite, and silicon oxide, and organic acids such as oxalic acid, maleic acid, gallic acid, and benzoic acid, and their derivatives. Although phenolic compounds and metal salts are also used, it is preferable to use phenolic compounds with low water solubility, and among them, phenolic compounds having two or more hydroxyl groups in the molecule are preferred. For example, 4,4'-isopropylidene diphenol, 4,4'-isopropylidene bis(2-chlorophenol), 4,4'-
Isopropylidene (2-methylphenol),
4,4'-isopropylidene bis(2,1-tert
-butylphenol), 4-4'-sec-butylidene diphenol, 4,4'-cyclohexylidene diphenol, 4-tert-butylphenol,
4,4'-cyclohexylidene diphenol, 4
-tert-butylphenol, 4-phenylphenol, 4-hydroxydiphenooxide, naphthol, β-naphthol, methyl-4-hydroxybenzoate, dimethyl 4-hydroxyphthalate, 4-hydroxyacetophenone, P-
Examples include oxybenzoic acid esters, novolak type phenolic resins, halogenated novolak type phenolic resins, and one or more of them can be used arbitrarily. However, the present invention is not limited to the above examples. (3) The binder for the thermosensitive coloring layer is not particularly limited, and all known binders can be used. It is preferable that the liquid does not develop color, aggregate, or become highly viscous when mixed with the liquid. In addition, characteristics such as not inhibiting color development and strong film formation are required, but there are particular requirements regarding compatibility with summerheads such as staking, scum adhesion, and abrasion in order to provide a protective layer. For example, polyvinyl alcohol, starches, hydroxyethyl cellulose,
Highly water-soluble materials such as gum arabic, polyvinylpyrrolidone, alkali salts of acrylic acid (or methacrylic acid) ester copolymers, alkali salts of styrene/maleic anhydride copolymers, and alkali salts of isobutylene/maleic anhydride copolymers. Examples include molecular compounds, polymer latexes such as styrene/butadiene copolymers, polyvinyl acetate, and acrylic acid ester copolymers, and emulsions. Furthermore, in addition to the above-mentioned color-forming dye, color-developing substance, and binder, various substances shown below can be added to the heat-sensitive color-forming layer according to the present invention, if necessary. For example, inorganic pigments and other fillers are added to further improve coating suitability and whiteness, and various waxes such as higher fatty acid amides, higher fatty acid metal salts, and dibenzyl terephthalate are added to improve color development sensitivity. Compatible antifoaming agents, dispersants, wetting agents, etc. can be used to further improve the dispersibility and coating suitability of the thermofusible substances and sub-melting point substances. (4) As the material for the protective layer to be formed on the surface of the heat-sensitive coloring layer, the above-mentioned water-soluble polymer and fluorine acrylic polymer are used as protective layer forming agents, and a curing agent, pigment, lubricant, etc. are used in combination. Polymers include polyvinyl alcohol, modified polyvinyl alcohol, casein, starches, hydroxyethylcellulose, gum arabic, polyvinylpyridone,
Alkali salts of acrylic acid (or methacrylic acid) ester copolymers, alkali salts of styrene/maleic anhydride copolymers, alkali salts of isobutylene/maleic anhydride copolymers, diisobutylene/maleic anhydride copolymers Selected from alkali salts, water-soluble polymer compounds such as acrylamide copolymers, etc. The requirements for a protective layer forming agent are that it has excellent film-forming performance and that the resulting film does not dissolve in plasticizers, oils, organic solvents, etc., and at the same time, it must be able to form a heat-sensitive coloring layer during coating. In order to prevent color development, the water-soluble polymer compound must have sufficient film-forming performance even under relatively low-temperature drying conditions of 100° C. or lower. Examples of the fluorinated acrylic polymer include various conventionally known or well-known polymers without particular limitation, such as acrylates or methacrylates containing perfluoroalkyl groups having 3 to 20 carbon atoms Examples include homopolymers of unsaturated esters, and copolymers of these and other comonomers. Also Polymers or copolymers of polyfluoroalkyl group-containing polymerizable compounds such as H(CF ₂ ) ₁₀ CH ₂ OCOCH=CH ₂ , CF ₂ Cl(CF ₂ ) ₁₀ CH ₂ OCOC(CH ₃ )=CH ₂ Although other examples may be mentioned, those containing a perfluoroalkyl group as mentioned above are preferred. In the present invention, if the ease of obtaining the above substance and other considerations are taken into account, the general formula RfROCOCR′=CH ₂
(However, in the formula, Rf is a linear or branched perfluoroalkyl group having 3 to 20 carbon atoms, R is a linear or branched alkylene group having 1 to 10 carbon atoms, R Polymers of acrylates or methacrylates containing a terminal perfluoroalkyl group represented by (' represents a hydrogen atom or a methyl group) or copolymers with other comonomers are particularly advantageous as polyfluoroalkyl group-containing polymers. It can be said. Furthermore, it is particularly desirable that Rf be a perfluoroalkyl group having 6 to 12 carbon atoms, and that R be an alkylene group having 2 to 4 carbon atoms. However, in addition to the above-mentioned polyfluoroalkyl group-containing polymerizable compounds, ethylene, vinyl acetate, vinyl chloride, vinyl fluoride, vinylidene halides, acrylonitrile, methacrylonitrile, styrene, α-methylstyrene, p- Methylstyrene, acrylic acid and its alkyl esters, methacrylic acid and its alkyl esters, acrylamide, methacrylamide, diacetone acrylamide, methylolated diacetone acrylamide, methylolated diacetone acrylamide,
N-methylol acrylamide, vinyl alkyl ether, halogenated alkyl vinyl ether,
Can be used as a copolymer of one or more polymerizable compounds that do not contain a fluoroalkyl group, such as vinyl alkyl ketone, butadiene, isobrene, chlorobrene, glycidyl acrylate, and maleic anhydride, as a constituent unit of the polymer. It is. Examples of emulsions of these fluorine acrylic polymers include Asahi Guard, AG-550 (both trade names, manufactured by Asahi Glass Co., Ltd.), Scotchiban, and FC-
808 (all product names, manufactured by 3M Company in the United States) and F-
Commercially available products such as 60 (trade name, manufactured by Dainippon Ink Co., Ltd.) can be used as desired. Further, as the curing agent, a curing agent such as a dialdehyde type such as glyoxal or polyaldehyde, a polyamine type such as polyethyleneimine, an epoxy type polyamide resin, a diglycidyl type such as glycerin diglycidyl ether, or a dimethylol urea type is used. Furthermore, pigments include kaolin, clay, talc, calcium carbonate, calcined clay, titanium oxide,
Examples include diatomaceous earth, anhydrous silica, synthetic aluminum silicate, synthetic magnesium silicate, aluminum oxide, etc., but in order to make the coating film dense and maintain oil barrier properties, the above-mentioned water-soluble polymer as a film forming agent is used. Fine particles with good affinity and a large apparent specific gravity are more preferably used. Further, as the lubricant, higher fatty acids, higher fatty acid amides, higher fatty acid metal salts, paraffin wax, microcrystalline wax, etc. can be used. Therefore, the amount of water-soluble polymer, fluorine acrylic polymer, and curing agent must be at least 50% by weight of the total components of the protective layer.If it is less than this, the plasticity and oil resistance properties will deteriorate. Degrading and unsuitable. The amount of curing agent is 5 to 100% by weight, preferably 20 to 80% by weight, based on 100% by weight of the water-soluble polymer.
In this case, if the amount of curing agent is less than 5% by weight, crosslinking will not be able to proceed sufficiently, and therefore, not only will sufficient water resistance and compatibility with summerhead not be obtained, but the molecular structure due to crosslinking will become too dense. Therefore, the desired effect cannot be obtained due to a decrease in plasticizer resistance and oil resistance. The amount of fluorine acrylic polymer blended is preferably 1 to 50% by weight, preferably 2 to 10% by weight of the total components of the protective layer.If the amount is less than 1% by weight, the barrier properties of the water-soluble polymer may be affected. A specific oil resistance based on a synergistic effect cannot be expressed, and if it exceeds 50% by weight, the oil resistance decreases, making it unsuitable. The coating amount of the protective layer is adjusted as appropriate to the extent that heat conduction from the summer head to the coloring layer is not inhibited, but it is usually 1 to 10 g/m2, preferably ² to 7 g/m2.
It is preferable to set it to g/m ² . In this way, desired effects can be obtained without reducing thermal sensitivity. Supports used in the present invention include high quality paper,
Papers such as medium-quality paper, art paper, coated paper, cast coated paper, paperboard, and thin paper are generally used, but plastic film, synthetic paper, laminated paper, aluminum foil, etc. can also be used. The present invention will be explained in more detail below using Examples. However, the present invention is not limited to this example. Example 1 (1) Preparation of liquid A 3-(N-methyl-N-cyclohexylamino)
-6-Methyl-7-anilinofluorane 6 parts 5% hydroxyethyl cellulose aqueous solution 24 parts (2) Solution B preparation 4,4'-isopropylidene diphenol 25 parts Stearamide 16 parts 5% hydroxyethyl cellulose aqueous solution 140 parts Above Part A and Part B are separately ground and dispersed in a sand mill to an average particle size of 3 μm or less. (3) Preparation of liquid C 10% polyvinyl alcohol 100 parts 30% fluorine acrylic polymer emulsion
2 parts (Asahi Glass Co., Ltd., AG-550) 60% kaolin dispersion 5 parts 30% calcium stearate 5 parts 30% polyaldehyde solution 30 parts (4) Formation of coloring layer 40 parts of 30% kaolin aqueous dispersion, 30 parts of A liquid Part, B liquid
200 parts and 100 parts of a 10% polyvinyl alcohol aqueous solution as a binder are mixed to prepare a coating liquid. This coating liquid was applied to a base paper of 50 g/m ² with a dry weight of 7 g/m2.
After coating to a thickness of m ² , a calendering treatment was performed to provide a heat-sensitive coloring layer with a solid smoothness of 250 seconds. (5) Formation of protective layer A protective layer was formed by coating liquid C on the coloring layer to a dry weight of 3 g/m ² to obtain a heat-sensitive recording material having a two-layer structure. Example 2 Example 1 except that a 10% acrylamide-acrylonitrile copolymer aqueous solution (manufactured by Showa Denko) was used instead of polyvinyl alcohol, which is a water-soluble polymer in liquid C (protective layer paint) used in Example 1. A heat-sensitive recording material having a two-layer structure was obtained in the same manner as above. Example 3 Example 2 was carried out in the same manner as in Example 1, except that an ammonium solution of casein (10% aqueous solution) was used instead of polyvinyl alcohol, which is a water-soluble polymer, in liquid C (protective layer paint) used in Example 1. A heat-sensitive recording material having a layered structure was obtained. Example 4 FC-808 (trade name, manufactured by 3M Company, USA) was used instead of AG-550 (trade name, manufactured by Asahi Glass Co., Ltd.), which is a fluorine acrylic polymer, in liquid C (protective layer paint) used in Example 1. ) was used in the same amount as in Example 1 to obtain a heat-sensitive recording material having a two-layer structure. Example 5 F-60 (trade name, manufactured by Dainippon Ink Co., Ltd.) was used in the same amount in place of AG-550, which is a fluorine acrylic polymer, in liquid C (protective layer paint) used in Example 1. A heat-sensitive recording material having a two-layer structure was obtained in the same manner as in Example 1 except that the material was used. Comparative Examples 1 to 3 The same procedures as in Examples 1, 2, and 3 were used, except that a paint obtained by removing the fluorine acrylic polymer from Liquid C (protective layer paint) used in Examples 1, 2, and 3 was used. A heat-sensitive recording material having a two-layer structure was obtained. After each heat-sensitive recording material of the above Examples and Comparative Examples was left at room temperature for 3 days, it was colored with a solid black record using Copix 7100 (trade name, manufactured by Toshiba Electric Corporation). A clear black color image was obtained at a high density of 1.2 or higher. Next, a specified test piece was prepared from this material by a conventional method, and the water resistance, PVC film resistance, and oil resistance of the colored part were measured by the following tests, and satisfactory results were obtained for all of them (see attached table). ). (1) Water resistance test: After immersing the test piece in water for 24 hours (at room temperature), take it out, dry it, measure the color density using a Macbeth reflection densitometer, and calculate the ratio (%) to the density before immersion in water. (2) PVC film resistance test: Layer a soft polyvinyl chloride film on the specimen and measure the concentration when the two are in contact for 24 hours at 20°C under a load of 300g/m ² . (3) Oil resistance test: Apply cottonseed oil to the test piece using the usual method, and measure the residual concentration after leaving it at 20°C and 40°C for 24 hours.

[Table] ○ = No discoloration at all, △ = Discoloration observed, × = Significant discoloration.
As is clear from the above table, it is known that Examples 1 to 5 are improved in vinyl chloride film resistance and oil resistance compared to Comparative Examples 1 to 3.

Claims (1)

[Claims] 1. A protective layer containing a water-soluble polymer and a fluorine-based acrylic polymer is formed on the surface of a heat-sensitive coloring layer formed on a support, and the heat-sensitive coloring layer is coated with water-resistant, oil-resistant, and anti-corrosive coatings. A heat-sensitive recording material characterized by being imparted with plasticizer properties. 2. The heat-sensitive recording material according to claim 1, wherein the protective layer contains a curing agent, a lubricant, and/or a pigment in addition to a water-soluble polymer and a fluorine-acrylic polymer.