JPH0326675B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a thermal recording paper, and more particularly to a thermal recording paper that has excellent heat resistance and water resistance and has improved heat-sensitive characteristics, and particularly relates to a thermal recording paper that has improved color development sensitivity. . The minimum performance required for a recording layer of thermal recording paper is excellent self-coloring resistance, pressure coloring resistance, heat sensitivity, light resistance, heat decoloring resistance, moisture decoloring resistance, and water resistance. However, we have not yet obtained anything that completely satisfies these requirements. First, as a method for improving self-coloring resistance, a water-soluble alkanolamine compound is added to JP-A-48-101943 (Japanese Patent Publication No. 51-29830).
JP-A-49-11141 (Japanese Patent Publication No. 51-2823) describes the addition of a basic organic compound. As a method to improve water resistance, there is
No. 3643, JP-A-49-32646, JP-A-50-30539
No., JP-A-52-145228 and JP-A-53-13929
The use of a water-soluble binder and a water-resistant agent in combination is described in No. As a method to improve colorfastness, there is
- Adding a phenol resin which is a condensation product of a phenol compound and an aliphatic aldehyde or an alkyl vinyl ether to No. 52245, JP-A-49
−45747 (Special Publication No. 51-43386), 4,4′−
adding a phenol derivative such as thiobis(6-t-butyl-3-methyl-phenol);
JP-A-53-17347 describes the addition of a water-insoluble modified phenol resin such as rosin-modified or terpene-modified resin. In addition, as a method to improve heat-sensitive characteristics,
No. 49-17748 and Japanese Patent Publication No. 51-39567 describe the combined use of an organic acid and a phenolic compound as an acidic substance, or the use of a polyvalent metal salt of a compound having an alcoholic hydroxyl group. JP-A No. 49-11140 (Japanese Patent Publication No. 51-29945) describes the use of a copolymer of hydroxyethyl cellulose and maleic anhydride. Furthermore, JP-A-49-34842, JP-A-49-115554, JP-A-Sho
No. 50-149353, JP-A-52-106746, JP-A-53-
No. 5636, JP-A-53-11036, and JP-A-53-
48751 etc., nitrogen-containing organic compounds such as thioacetanilide, phthalonitrile, acetamide, di-β-naphthyl-p-phenylenediamine, fatty acid amide, acetoacetanilide, diphenylamine, benzamide, carbazole, etc. It has been described that thermofusible substances such as -m-tolylbutane, 4,4'-dimethylbiphenyl, etc., or carboxylic acid esters such as dimethyl isophthalate, diphenyl phthalate, etc. are added as sensitizers. There is. The present inventors manufactured thermal recording paper using a known fluoran compound as a coloring agent and according to the methods described in the above-mentioned patent publications and the methods described in the above-mentioned patent publications. When the surface was tested, it was found that the heat-sensitive characteristics were poor, such as a high initial color development temperature (Ts) by heating, a small rising temperature coefficient (r) of the color density curve, and a small maximum color density (Dmax). Ta. Therefore, it is not practical as a thermal recording paper for facsimile, especially high-speed facsimile. Furthermore, when the thermally colored recording paper was left in an atmosphere of 50 to 60 DEG C. and 20% relative humidity for 3 to 5 days, the concentration of the coloring agent decreased compared to that immediately after coloring. That is, heat decolorization resistance is low. Further in an atmosphere of 50-60℃ and relative humidity 80-90% 12
When left for ~24 hours, the concentration of the coloring agent that developed the color decreases compared to the coloring density immediately after coloring, and in some cases, the color disappears completely, and even traces of the coloring agent that created the color can no longer be seen. . In other words, the moisture decoloring resistance is low. When thermal recording paper that uses a water-soluble binder as a binder or thermal recording paper that has been colored by heating is immersed in water for a long time, both the uncolored thermal recording layer and the colored thermal recording layer will flow. , or faded. In other words, water resistance is poor. In addition, conventionally known compounds have a whitening phenomenon, that is, when colored areas are left for a short period of time, colored crystals are liberated on the surface, which causes loss of commercial value as thermal paper. The present inventors have completed the present invention as a result of intensive research in order to improve the above-mentioned drawbacks of heat-sensitive recording paper using known fluoran compounds. That is, the present invention provides a heat-sensitive recording paper comprising, on a support, a recording layer basically comprising a colorless or slightly pale fluoran compound, an acidic substance that causes the fluoran compound to develop color when heated, and a binder. The following general formula is contained in the recording layer: (In the formula, R ₁ is a hydrogen atom, a lower alkyl group, or a halogen atom, R ₂ is a hydrogen atom, a C ₁ to C ₈ alkyl group, a cyclohexyl group, or a substitutable phenyl group, and R ₃ is an alkoxy group. (R ₂ and R ₃ may form a saturated ring together with N.) Regarding recording paper. This benzenesulfonamide compound is a white crystal synthesized from benzenesulfonyl chloride and an amine and is difficult to dissolve in water. The normally colorless or light-colored fluoran compound used in the thermal recording paper of the present invention can be selected from a large number of conventionally known fluoran compounds. formula (In the formula, R ₄ is a lower alkyl group, R ₅ is a lower alkyl group, a cyclohexyl group, or an optionally substituted phenyl group, and R ₄ and R ₅ together with the nitrogen atom to which they are bonded form a heterocycle. can,
R ₆ is a hydrogen atom, a halogen atom, a lower alkoxy group or a lower alkyl group, R ₇ is a hydrogen atom,
It is a lower alkyl group, a halogen atom or a trifluoromethyl group, and R ₈ is a hydrogen atom or a lower alkyl group. ) is a conventionally known compound represented by The representative compounds are listed as follows: 2-(2-chlorophenylamino)-6-diethylaminofluoran, 2-(2-chlorophenylamino)-6-di-n-butylaminofluoran,
Examples include 2-anilino-3-methyl-6-diethylaminofluoran, but the fluoran compound is not limited to these fluoran compounds. The acidic substance used in the present invention is a substance that is solid at room temperature and can react with a color forming agent when heated. Typical examples include phenolic compounds or stearic acid described in Japanese Patent Publication No. 14039/1983. , benzoic acid, gallic acid, salicylic acid, etc., which have the property of liquefying or vaporizing at temperatures above 50°C, or their metal salts such as aluminum and zinc. Acidic substances that can be suitably used are the above-mentioned phenolic compounds, a typical example of which is 4,4'-isopropylidene diphenol (bisphenol A). Next, representative examples of the benzenesulfonamide compound represented by the general formula [] (hereinafter referred to as an additive compound) according to the present invention are shown in the table, but these representative examples are not intended to limit the present invention.

[Table] A water-soluble or water-insoluble binder is used as a binder to bind a mixture of a color former, an acidic substance, and an additive compound onto a support sheet. Typical examples include polyvinyl alcohol, methylcellulose, hydroxyethylcellulose, carboxymethylcellulose, gum arabic, starch,
There are gelatin, casein, polyvinylpyrrolidone, styrene-maleic anhydride copolymer, polyacrylic acid amide, polyacrylate, terpene resin, petroleum resin, etc., but binders that can be particularly preferably used in the present invention are water-soluble binders. A typical example is polyvinyl alcohol. In order to produce the thermal recording paper of the present invention, a fluoran compound as a coloring agent, an acidic substance and a general formula []
From the viewpoint of the performance of thermal recording paper, it is preferable to provide a layer in which each component consisting of one or more of the additive compounds represented by is present as fine particles in a uniform state in one thermal recording paper. Each component consisting of a coloring agent and an additive compound exists in a uniform state as fine particles in one layer, and a layer in which fine particles of an acidic substance exist in a uniform state is provided by adhering to this layer. A method in which each component consisting of an acidic substance and an additive compound is present as fine particles in a uniform state in one layer, and fine particles of a coloring agent are present in a uniform state by being brought into close contact with this layer. There is a method of providing a layer, and a method of adhering layers in which color formers, additive compounds, and acidic substances exist in the form of fine particles in separate layers in a uniform state. When manufacturing the heat-sensitive recording paper of the present invention, the weight ratio of each of the above-mentioned components and binder in the recording layer is 0.1 to 10 times that of the additive compound selected from the general formula [] to the color former. , preferably 0.3-3
and acidic substances are 2 to 10 times, preferably 4 to 10 times.
6 times, and the binder is 0.3 to 3 times, preferably 0.5
~1 times. The color former, acidic substance, and additive compound are preferably each separately dispersed using a dispersing machine such as a ball mill, a sand mill, or a paint conditioner.
A suspension that is dispersed in water or an organic medium containing a binder, preferably water in which the binder is dissolved, and ground to a particle size of 1 to 6 μm, preferably 3 to 5 μm. Create. If necessary, an antifoaming agent, dispersant, or brightener may be added for dispersion and pulverization. Next, a suspension of each of the separately dispersed and pulverized components described above is mixed so that the weight ratio of each component in the recording layer is as described above to prepare a paint for forming a heat-sensitive recording layer. This paint is applied to the surface of the paper using a wire bar #6 to #10 so that the solid weight after drying is 3 to 7 g/ ^m2, and then dried in a blow dryer at room temperature to 70°C. Manufactures thermal recording paper. If necessary, inorganic or organic fillers may be added to the paint to improve the fusing resistance, writability, etc. of the thermal head. The thermal recording paper of the present invention obtained in this way has extremely excellent thermal properties, heat decolorization resistance, moisture decolorization resistance, and water resistance, and is free from the whitening phenomenon that impairs its commercial value as a thermal paper. This successfully overcomes the drawbacks of conventionally known thermal recording paper. The performance of the recording layer of the thermosensitive recording paper was tested using the following test method. In other words, self-coloring density,
Macbeth RD
Measurements were made using a -514 reflection densitometer. Color development by heating was carried out using a Rodiaceta type thermotest tester (manufactured by the French National Textile Research Institute) under conditions of a heating temperature of 70 to 160°C, a heating time of 5 seconds, and a load of 100 g/cm ² .
Further, decoloring of the coloring agent after coloring by heating was carried out using a constant temperature and humidity tester. The present invention will be specifically explained below using Examples, but the present invention is not limited to these Examples. Example 1 Solution A (dye dispersion) 2-(-chlorophenylamino)-6-dibutylamino-fluorane 4.0 parts 10% polyvinyl alcohol aqueous solution 40.0 parts Solution B (developer dispersion) 4,4'-isopropylidene Diphenol (bisphenol A) 7.0 parts 10% polyvinyl alcohol aqueous solution 40.0 parts Water 10.0 parts Solution C (additive compound dispersion) Additive compound (listed) 7.0 parts 10% polyvinyl alcohol aqueous solution 40.0 parts Water 10.0 parts Above composition Each liquid of the product is ball milled to a particle size of 2 to 3.
Grind down to microns. Next, each dispersion liquid is mixed in the following proportions to form a paint. Solution A (dye dispersion) 3 parts Solution B (developer dispersion) 10 parts Solution C (additional compound dispersion) 3 parts Furthermore, as a control, solutions A and B were mixed in the following proportions to prepare a paint. Part A (dye dispersion) 3 parts Part B (developer dispersion) 10 parts Water 3 parts These paints were applied to the surface of high-quality paper using a #10 wire bar coater until the solid content weight after drying was 5.
g/m ² and placed in a blow dryer to dry. Regarding the obtained thermal recording paper, the one of the present invention was
(A) to (D), the control is shown as (E), and the results of the performance tests of each thermal recording paper are shown in the column of Example 1 in the table.

[Table] As is clear from the table, compared to the thermal recording paper (A) to (D) obtained in Example 1 of the present invention and the control thermal recording paper (E), the color density is higher, especially the color development. Sensitivity has been improved.

Claims (1)

[Scope of Claims] 1. A heat-sensitive recording paper provided on a support with a recording layer basically comprising a colorless or slightly pale fluoran compound, an acidic substance that causes the fluoran compound to develop color when heated, and a binder. In the recording layer, the following general formula (In the formula, R ₁ is a hydrogen atom, a lower alkyl group, or a halogen atom, R ₂ is a hydrogen atom, a C ₁ to C ₈ alkyl group, a cyclohexyl group, or a substitutable phenyl group, and R ₃ is an alkoxy group. (R ₂ and R ₃ may form a saturated ring together with N.) Thermal recording paper.