JPS6311998B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a thermal recording paper with excellent mechanical suitability and high whiteness. 2. Description of the Related Art Heat-sensitive recording paper that utilizes a color-forming reaction between a colorless dye and a phenol compound is well known. When such thermal recording paper is used in thermal facsimile, the phenomenon of adhesion or stickiness between the thermal head and the surface of the thermal recording paper (``state-king'') occurs.
). This phenomenon prevents smooth feeding of the recording medium, resulting in short line spacing during recording, blurring of recorded images, and peeling noise. Furthermore, there is the problem that substances that are in a molten state when heated transfer, adhere, and accumulate on the thermal head, impairing the stabilization of image density (referred to as "piling").
It cannot be said that it is sufficient for practical use. In order to improve the above-mentioned difficulties, the present inventors first incorporated an inorganic pigment with an oil absorption of 80 ml/100 g or more into the recording layer, such as amorphous silicon oxide, calcined clay, or calcined alumina. I filed an application to do so. However, when such inorganic pigments are included in the recording layer, the mechanical suitability is improved, but on the other hand, there is a drawback that the whiteness of the recording paper decreases over time.
The cause of this decrease in whiteness is not clear, but it is presumed that the pigment acts as a solid acid and causes a color reaction with colorless dyes under the influence of temperature, moisture, etc., resulting in a decrease in whiteness. Ru. This reduction in whiteness leads to a reduction in commercial value, and this improvement was necessary. The present inventors attempted to neutralize the acidic points on the surface of the pigment with ammonia, amine, caustic soda, etc., but this did not have any effect on improving the whiteness. Therefore, the present inventors conducted further intensive studies based on the progress of such experiments, and as a result, they were able to arrive at the present invention. Therefore, the main object of the present invention is to provide a heat-sensitive recording paper which has excellent mechanical aptitude for stacking and piling, and has a high degree of whiteness. In a heat-sensitive recording material provided on a support, a heat-sensitive recording layer containing an organic acid or phenol compound that causes a coloring reaction upon contact with heat and an inorganic pigment with an oil absorption of 80 ml/100 g or more; This is achieved by containing at least one of wollastonite and calcium silicate. The reason why wollastonite and calcium silicate are effective in maintaining the whiteness of thermal recording paper is probably because these pigments are water-insoluble and have strong alkaline properties, so the combination of oil-absorbing pigments and colorless dyes is difficult. It is presumed that it acts to inhibit the color reaction between the two. Similar properties can also be seen in other carbonates such as calcium carbonate and magnesium carbonate, but their ability to inhibit color reactions is inferior to that of wollastonite and calcium silicate, and moreover, they cannot be added to paints. It is difficult to use because it has the disadvantage that sometimes the shock is large and the viscosity increases, impairing the suitability of paints. Examples of colorless dyes used in the constitution of the present invention include 3.3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide and 3.3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide.
bis(p-dimethylaminophenyl) phthalide,
3-(p-dimethylaminophenyl)-3-(1.2-
Triallylmethane dyes such as dimethylindol-3-yl) phthalide, 4.4'-bis-dimethylaminobenzhydrylbenzyl ether, N-halophenyl-leucoauramine, N-2.4.5-trichlorophenylleucoauramine, etc. diphenylmethane dye, 7-diethylamino-3-chlorofluoran, 7-diethylamino-3-chloro-
2-methylfluorane, 2-phenylamino-3
-Methyl-6-(N-ethyl-N-p-tolyl)
Fluoran dyes such as aminofluorane, thiazine dyes such as benzoyl leucomethylene blue, p-nylobenzyl leucomethylene blue, 3-
Methyl spirodinite pyran, 3-ethyl-
Examples include spiro dyes such as spiro-dinaphthopyran and 3-propyl-spiro-dibenzopyran. Examples of organic acids or phenol compounds that produce a coloring reaction when heated with colorless dyes include 4-tertiarybutylphenol, 4-hydroxydiphenoxide, α-naphthol, β-naphthol, 4-tertiarybutylphenol, 4-hydroxydiphenol,
-Hydroxyacetophenol, 4-tert-octylcatechol, 2.2'-dihydroxydiphenol, 2.2'-methylenebis(4-methyl-6
-tertiary-isobutylphenol), 4.4'-
Isopropylidene bis(2-tertiary-butylphenol), 4.4′-secondary-butylidenephenol, 4-phenylphenol, 4.4′-isopropylidene diphenol, 2.2′-methylenebis(4-chlorophenol), hydroquinone,
4.4'-Cyclohexylidine diphenol, novolac type phenolic resin, phenolic compounds such as phenolic polymers, paratertiary butyl benzoic acid, trichlorobenzoic acid, terephthalic acid, 3-sec-butyl-4-hydroxybenzoic acid, 3 -cyclohexyl-4-hydroxybenzoic acid, 3.5-dimethyl-4-hydroxybenzoic acid,
Salicylic acid, 3-isopropylsalicylic acid, 3-
tertiarybutylsalicylic acid, 3-benzylsalicylic acid, 3-(α-methylbenzyl)salicylic acid,
3-chloro-5-(α-methylbenzyl)salicylic acid, 3.5-ditasiybutylsalicylic acid, 3
-phenyl-5-(α,α-dimethylbenzyl)
Aromatic carboxylic acids such as salicylic acid, 3.5-di-α-methylbenzyl salicylic acid, and these phenolic compounds, aromatic carboxylic acids such as zinc, magnesium, aluminum, calcium,
Examples include organic acidic substances such as salts with polyvalent metals such as titanium, manganese, tin, and nickel. In the heat-sensitive recording material of the present invention, the usage ratio of the colorless dye and the organic acid or phenol compound in the recording layer is appropriately selected depending on the types of the colorless dye and the organic acid or phenol compound used, and is not particularly limited. For example, 1 to 50 parts by weight, preferably 4 to 10 parts by weight of the organic acid or phenolic substance may be used, although it is not necessary to do so, per 1 part by weight of the colorless dye. Further, the amount of the oil-absorbing pigment used in the present invention added to the recording layer is generally about 5 to 80
It can be incorporated in an amount of about 10 to 60% by weight (dry weight). Therefore, wollastonite is introduced into the recording layer, which is a feature of the present invention.
The amount of calcium silicate added varies depending on the acid strength of the oil-absorbing pigment used, but is generally 0.1 to 300% by weight of the oil-absorbing pigment. Preferably, the amount is about 30 to 150% by weight. In addition, the coating liquid for forming the recording layer contains starches, hydroxyethyl cellulose, methyl cellulose, polyvinyl alcohol, styrene/acrylic acid copolymer, acrylamide resin, styrene/butadiene, as is well known in the conventional art. Binders such as latex, surfactants such as sodium dioctyl sulfosuccinate and sodium dodecylbenzenesulfonate, ultraviolet absorbers such as benzophenones and triazoles, stearamide, palmitic acid amide, 2.6-
Various auxiliary agents such as sensitivity regulators such as diisopropylnaphthalene, mold release agents such as zinc stearate and aluminum stearate, fluorescent dyes, methyl violet, coloring dyes, and preservatives can be added as appropriate and necessary. . The method of forming the recording layer of the heat-sensitive recording medium of the present invention is not particularly limited. Generally, specific adhesives and other auxiliary agents are dissolved and added to a coating liquid in which a colorless coloring agent and organic acid or phenolic compound are dispersed using a ball mill, attritor, sand grinder, etc., or a pulverizer. It can be obtained by applying the coating liquid prepared in this manner onto base paper using a conventional coating machine. If necessary, the smoothness of the recording medium can be increased by calendering or the like. The amount of the coating liquid forming the recording layer applied to the support is not particularly limited, but is usually in the range of 2 to 15 g/m ² , preferably 3 to 12 g/m ² in terms of dry weight. The thus obtained heat-sensitive recording material of the present invention has excellent mechanical suitability due to the presence of the oil-absorbing pigment, and at the same time has high whiteness due to the presence of wollastonite or calcium silicate, and can record clear images. be. The present invention will be described in more detail with reference to Examples below, but it is of course not limited thereto. Further, unless otherwise specified, parts and percentages in the examples indicate parts by weight and percentages by weight, respectively. Example 1 Preparation of liquid A 2-phenylamino-3-methyl-6-(N-
Ethyl-p-tolyl) aminofluorane 20 parts Stearamide 40 parts Polyvinyl alcohol (10% aqueous solution) 100 parts Water 140 parts This composition was ground with a sand grinder to an average particle size of 3 μm. Preparation of Solution B 4.4'-Isopropylidene diphenol (bisphenol A) 100 parts Stearamide 60 parts Polyvinyl alcohol (10% aqueous solution) 160 parts Water 270 parts This composition was ground with a sand grinder to an average particle size of 3 μm. Formation of coloring layer: 100 parts of liquid A, 200 parts of liquid B, oil absorption 180ml/100
g silicon oxide (20% dispersion) 100 parts, wollastonite 5
Part and polyvinyl alcohol (10% aqueous solution)
Mix 300 parts to make a coating liquid. This coating liquid was applied to a base paper of 50 g/m ² with a coating amount of 8 g/m2 after drying.
It was coated in an amount of m ² to obtain heat-sensitive recording paper. Example 2 100 parts of liquid A and 200 parts of liquid B used in Example 1, 100 parts of calcined clay (30% dispersion) with an oil absorption of 110 ml/100 g, 10 parts of calcium silicate, and polyvinyl alcohol (10% aqueous solution) ) mixed in the proportion of 350 parts,
Use as a coating liquid. This coating liquid was applied onto a 50 g/m ² base paper so that the coating amount after drying was 8 g/m ² to obtain a heat-sensitive recording paper. Comparative Example 1 In Example 1, a coating solution containing no wollastonite was prepared, and heat-sensitive recording paper was obtained in the same manner. Comparative Example 2 A thermal recording paper was obtained in the same manner as in Example 1, except that kaolin (oil absorption: 55 ml/100 g) was used instead of silicon oxide. The mechanical suitability of the thermal recording papers obtained in the above Examples and Control Examples was examined using a thermal facsimile (Model Toshiba KB-500). When the whiteness and recording density of these recording papers were measured using a Macbeth RD-100R densitometer, the data were as shown in the attached table.

[Table] (Note) ○ mark is good, × mark is defective

Claims (1)

[Claims] 1. A heat-sensitive recording layer provided on a support with a heat-sensitive recording layer containing a colorless dye, an organic acid or phenol compound that produces a color reaction upon contact with the colorless dye during heat, and an inorganic pigment with an oil absorption of 80 ml/100 g or more. 1. A heat-sensitive recording paper, characterized in that the recording layer contains at least one of wollastonite and calcium silicate.