JPH0463792B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for producing a heat-sensitive recording material, and in particular, a method for producing a heat-sensitive recording material, in which a heat-sensitive recording layer containing an electron-donating dye and an electron-accepting compound is provided on a support. The present invention relates to a method for producing a heat-sensitive recording material. (Prior Art) Heat-sensitive recording materials using colorless electron-donating dyes and electron-accepting compounds are disclosed in Japanese Patent Publications No. 45-14039, Japanese Patent Publication No. 4160-43, and the like. The minimum performance that such a heat-sensitive recording material should have is (1) sufficient color density and color development sensitivity, (2) no fogging (color development phenomenon during storage before use), etc. . In particular, in recent years facsimile has been required to be faster in order to reduce transmission costs, and in response to this demand there has been a demand for thermosensitive recording sheets with excellent thermal responsiveness. Here, a thermal recording sheet with excellent thermal responsiveness refers to thermal paper that produces a sufficient color reaction when heated for a short period of time (generally 1 ms or less), and conventional technology has not yet reached a sufficient level. is the current situation. (Object of the invention) The object of the present invention is to have high color density and color development sensitivity;
An object of the present invention is to provide a method for producing a heat-sensitive recording material that causes less fog. (Structure of the Invention) An object of the present invention is to provide a method for producing a heat-sensitive recording material in which an aqueous dispersion of an electron-donating colorless dye and an electron-accepting compound is coated on a support. The solubility in water is 0.5 or less, and the alkylnaphthalene which is liquid at 60°C is dispersed in water to form an emulsion with a volume average particle size of 10 μm or less, which is 1 to 500% by weight based on the electron-donating colorless dye. This was achieved by a method for producing a heat-sensitive recording material, which is characterized by the addition of heat-sensitive recording materials. The heat-sensitive recording material produced according to the present invention requires 20% or more of the heating time required for recording when the current applied to the thermal head is constant compared to the material without the addition of the aqueous alkylnaphthalene emulsion as described above.
It will be reduced by 50%. The alkylnaphthalene used in the present invention, which has a solubility in water at 20°C of 0.5 or less and is liquid at 60°C, is preferably one that dissolves the color former and color developer when heated. in particular
It is preferable that the solubility in at least one of the color forming agent or the color developer at 150°C is 5 or more, preferably 10 or more, but even if the solubility is less than 5, the effect is significant compared to the emulsion that is not added at all. Shows. Further, the alkylnaphthalene used in the present invention is liquid at 60°C, and even if it is solid at room temperature, it can be used as long as it liquefies at 60°C or higher when heated. Generally, the color development start temperature required for thermosensitive recording paper is 60°C or higher, so it is sufficient if it is liquid at 60°C. On the other hand, an essential physical property required of the alkylnaphthalene used in the present invention is water solubility, which needs to be 0.5 or more at 20°C. If the solubility is higher than this, fogging will occur when preparing the coating solution. The preferred solubility range is 0.1 or less. Particularly preferred examples of the alkylnaphthalene used in the present invention include monoisopropylnaphthalene, diisopropylnaphthalene, and the like. Further, the alkylnaphthalene used in the present invention is added to the heat-sensitive coating liquid as an aqueous emulsion due to restrictions in liquid preparation. In this case, the volume average particle diameter of the alkylnaphthalene emulsion is 10 μm or less, preferably 5 μm or less. By using an emulsion having such a volume average particle size, the distribution of alkylnaphthalene in the heat-sensitive recording layer can be made extremely uniform, and the coloring density and coloring sensitivity can be increased. Generally, oil emulsification is performed by applying high shear force to an oil/water mixture in the presence of a surfactant to emulsify it, but known emulsification techniques such as self-emulsification can also be applied. On the other hand, there is also a method of emulsification using a water-soluble polymer as a protective colloid, which is more preferable for use in the present invention. This seems to be because the method of using an emulsifier apparently increases the water solubility of the alkylnaphthalene. The surfactant used in emulsion formation by the emulsification method may be nonionic, anionic, or cationic, but anionic surfactants are preferred. Specific examples of emulsifiers include alkyl sulfonates, alkylbenzene sulfonates, long chain carboxylates, higher alcohol sulfate ester salts, long chain amine salts, ethanol amyl ester salts, tetraalkylammonium salts, alkylphenol ethylene oxide adducts, Examples include fatty acid amide ethylene oxide adducts and higher alcohol ethylene oxide adducts. Generally, an alkyl group has 10 carbon atoms.
You can use up to 20 items. Protective colloids include natural polymer derivatives such as gelatin, casein, gum arabic, starch and its derivatives, alginate, hydroxyethylcellulose, methylcellulose, and carboxymethylcellulose, as well as polyacrylates, polyvinylpyrrolidone, styrene maleic anhydride, Polyvinyl alcohol etc. are used. The amount of alkylnaphthalene added in the present invention is usually 1 to 500% by weight based on the color former.
Preferably it is 10 to 200% by weight. The main coloring agents used in the present invention include (1) triarylmethane-based, (2) diphenylmethane-based, (3) xanthene-based, (4) thiazine-based, (5) spiropyran-based compounds, etc. As a specific example,
Examples include those described in JP-A No. 55-27253. Among them, (1) triarylmethane type,
(3) Xanthene-based coloring agents are preferably those that cause less fog and provide high coloring density, such as crystal violet lactone, 2-anilino-3-
Methyl-6-diethylaminofluorane, 2-anilino-3-methyl-6-triethylaminofluorane, 2-anilino-3-methyl-6-cyclohexylmethylaminofluorane, 2-β-ethoxyethylamino-3-chloro -6-diethylaminofluorane, 2-o-chloroanilino-6-
Examples include diethylaminofluorane. As a color developer, it is solid at room temperature, especially at 80℃.
A compound having a melting point higher than that is desirable. Preferred compounds include phenols and aromatic carboxylic acid derivatives. Specific examples of particularly preferred compounds include p-octylphenol, p-
tert-butylphenol, p-phenylphenol, 1,1-bis(p-hydroxyphenyl)-
2-Ethyl-butane, 2,2-bis(p-hydroxyphenyl)propane, 2,2-bis(p-hydroxyphenyl)pentane, 2,2-bis(p-hydroxyphenyl)propane, 2,2-bis(p-hydroxyphenyl)pentane,
-hydroxyphenyl)hexane, 2,2-bis(4-hydroxy-3,5-dichlorophenyl)
Examples include propane, 1,1-bis(p-hydroxyphenyl)cyclohexane, and the like. Among these, bisphenols are particularly preferred because they have high color density and relatively good storage stability. Preferred examples of aromatic carboxylic acid derivatives include p-hydroxybenzoic acid, ethyl p-hydroxybenzoate, butyl p-hydroxybenzoate,
Benzyl p-hydroxybenzoate, 3,5-di-
Examples of tert-butylsalicylic acid, 3,5-di-α-methylbenzylsalicylic acid and carboxylic acid include polyvalent metal salts thereof. In addition, a thermofusible substance is added for the purpose of improving thermal responsiveness in combination with these color forming agents and color developing agents. These thermofusible substances are added at the time of dispersing the color former and/or color developer, and are more effective if dispersed at the same time. Specifically, higher fatty acid amides (thearic acid amide, palmitic acid amide, erucic acid amide, oleic acid amide, etc.), ethylene bisstearamide, acetanilide, acetoacetamide, and their derivatives are well known. Furthermore, naphthol derivatives (α-naphthol benzyl ether, etc.), benzotriazoles, etc. are used. Dispersion of color formers and color developers is generally carried out using an aqueous solution of a water-soluble polymer as a dispersion medium. Specific examples of water-soluble polymers include polyacrylamide, polyvinylpyrrolidone, polyvinyl alcohol, and styrene-maleic anhydride. Synthetic water-soluble polymers such as acid copolymers, ethylene-maleic anhydride copolymers, and isobutylene-maleic anhydride copolymers, natural water-soluble polymers such as hydroxyethyl cellulose, starch derivatives, gelatin, casein, and their modified products. can be mentioned. The dispersion liquid of the color former and the color developer is mixed in a ratio of the color former to the color developer in the range of 1:1 to 1:10, preferably 1:2 to 1:4, and inorganic or organic Oil-absorbing pigments, wax, mold release agents, etc. are added. For inorganic or organic oil-absorbing pigments, JIS
-K5101 preferably has an oil absorption of 50 ml/100 g or more, specifically, kaolin, calcined kaolin, talc, waxite, diatomaceous earth, calcium carbonate, magnesium hydroxide, magnesium carbonate,
Examples include titanium oxide, barium carbonate, urea-formalin filler, and cellulose filler. As the wax, paraffin wax, polyethylene wax, cownabar wax, etc., higher fatty acid amide, etc. are added in the form of an emulsion. Mold release agents are generally polyvalent metal salts of higher fatty acids.
Zinc salts are especially desirable. The heat-sensitive coating liquid thus obtained is applied onto a support such as paper or plastic and dried. The coating amount is 0.2g/ ^m2 to 1.0 in terms of coloring agent.
g/m ² , preferably 0.3 g/m ² to 0.7 g/m ² . (Examples of the Invention) Examples are shown below, but the present invention is not limited to these examples. Examples 1 to 3 As a coloring agent, 5 g of crystal violet lactone was mixed with 5% polyvinyl alcohol (saponification degree 99
%, degree of polymerization 10,000) and was dispersed in a ball mill overnight with 50 g of an aqueous solution. At the same time, 20 g of bisphenol A as a color developer was dispersed overnight with 200 g of a 5% polyvinyl alcohol aqueous solution. After mixing these two types of dispersions, 20g of calcium carbonate was added to disperse well, and the alkylnaphthalenes shown in Table 1 were added to the alkylnaphthalenes.
Stir and emulsify at a ratio of 63% water, 7% funnel oil,
The emulsion was added so as to have the alkylnaphthalene solid content weight % (based on the color former) shown in Table 1 to prepare a coating liquid. The coating solution was coated onto a base paper having a basis weight of 50 g/m ² so that the solid content coating amount was 7 g/m ² and subjected to calendering treatment to obtain a coated paper. The resulting heat-sensitive recording sheet was colored and printed, and its sensitivity and fog were measured. Sensitivity was determined by developing color using a commercially available facsimile machine at a printing energy (calculated from power and application time) of 40 mJ/mm.
The values are the densities measured by the Macbeth densitometer in the printed and non-printed areas (using a visual filter). From the purpose of the present invention, the higher the print density, the more preferable the fog is. Comparative Example 1 In the above example, a coated paper was prepared without adding oil, and the same evaluation as in the example was performed. Comparative Example 2 Coated paper was prepared in Example 1 with the amount of oil added greater than that of the present invention as shown in Table 1. From the results in Table 1, it can be seen that the heat-sensitive recording material produced according to the present invention has extremely excellent thermal responsiveness and has little fog. 【table】

Claims (1)

[Claims] 1. In a method for producing a heat-sensitive recording material in which an aqueous dispersion of an electron-donating colorless dye and an electron-accepting compound is coated on a support, the solubility of the aqueous dispersion in water at 20°C is 0.5 or less, Liquid alkylnaphthalene is dispersed in water at 60°C to form an emulsion with a volume average particle size of 10 μm or less, and the amount is 1 to 500% relative to the electron-donating colorless dye.
1. A method for producing a heat-sensitive recording material, which comprises adding % by weight.