JPH0712745B2 - Thermal recording material - Google Patents

Description

TECHNICAL FIELD The present invention relates to a heat-sensitive recording material, and more particularly to a heat-sensitive recording material excellent in image stability.

[Prior art]

In recent years, along with social demands such as an increase in the amount of information, resource saving, labor saving, and pollution-free, various recording systems have been put to practical use and improved in the information recording field. The thermal recording method using (1) requires primary color development process, (2) simple and compact hardware, low maintenance cost, (3) feel like plain paper, and the sheet itself Due to its relatively low price, it has been put to practical use in computer output, medical measurement recorder fields, facsimile fields, printer fields, POS labels, vending machine tickets, etc. As the thermosensitive recording material used in such a system, a colorless or light-colored leuco dye having a lactone, a lactam, or a spiropyran ring on a support and an acidic substance, for example, a thermosensitive coloring layer containing an organic acid or a phenolic compound. Those provided (Japanese Patent Publication No. 43-4160, 45-14039, etc.) are known. However, the above-mentioned leuco-type heat-sensitive recording material has the drawback that the stability of the recorded image is poor and the color is easily erased. For example, there is a problem that when a contact is made with oil or a plasticizer (such as dioctyl phthalate) in a plastic film, the recorded image is erased, and the solution of this problem has become a major technical problem in this type of recording material. .

In the past, several proposals aimed at solving this problem have been proposed. For example, in the thermosensitive coloring layer, a large amount of a resin having good water resistance and chemical resistance was added to improve the stability of the thermosensitive coloring layer. In some cases, the thermosensitive coloring layer contains a resin that is cured by heat or light to improve the stability of the thermosensitive coloring layer.In addition, a resin protective layer is formed on the surface of the thermosensitive coloring layer to form a thermosensitive coloring layer. Some are protected from the effects of chemicals and water.

On the other hand, in the field of pressure-sensitive paper, one using a developer having a good chemical resistance has been proposed (JP-A-48-51716, JP-B-5).
1-25174), in this case, although the use of a specific developer is effective for pressure-sensitive paper, it is not effective for heat-sensitive recording paper, and the colored portion is stable when contacted with a plasticizer. However, there is a problem that the background color portion (non-coloring portion) is colored. Japanese Patent Laid-Open No. 59-11286 also discloses a specific developer, which may be suitable for pressure-sensitive paper, but most of them are not suitable for heat-sensitive recording materials. .
That is, the initial density of the background color portion is high (background fog), and only a very low-quality thermal recording material can be obtained. Further, many of them, like the color developing agents in the pressure sensitive paper field, cause the ground color portion to develop color upon contact with a plasticizer.

〔Purpose〕

The object of the present invention is not only to eliminate the decolorization of the color-developed portion and the color of the ground-colored portion upon contact with an oil or a plasticizer by the combination of a specific fluorane compound and an antipyrine complex of zinc thiocyanate, but also to dip in water. Another object of the present invention is to provide a heat-sensitive recording material having extremely high image stability with little reduction in image density even when contacted with water.

〔Constitution〕

That is, the heat-sensitive recording material of the present invention has the general formula (I) (In the formula, R ₁ and R ₂ are chain or cyclic aliphatic hydrocarbon groups, and the hydrocarbon group can contain one ether bond, and R ₃ has 1 to 2 carbon atoms. A hydrocarbon group), and at least one fluorane compound selected from the group consisting of fluorane compounds represented by the following formula (II)
It is characterized by utilizing a color reaction between zinc thiocyanate represented by and an antipyrine complex.

In the fluorane compound represented by the general formula (I), in the formula, R ₁ and R _{2 each} represent a chain or cyclic aliphatic hydrocarbon group. Examples of such a hydrocarbon group include an alkyl group, An alkenyl group, a cycloalkyl group, etc. are mentioned, The carbon number is 1-10 normally. Further, such a hydrocarbon group may contain one ether bond, and such a hydrocarbon group includes, for example, an oxaalkyl group, an oxacycloalkyl group and the like.

Specific examples of the fluorane compound represented by the general formula (I) include the following.

3-Dinormal butylamino-6-ethyl-7-parachloroanilinofluorane, 3- (N-ethyl-N-furfurylamino) -6-methyl-7-anilinofluorane, 3- (N- Ethyl-N-tetrahydrofurfurylamino) -6-methyl-7-anilinofluorane, 3- (N-2-ethoxyethyl-N-ethyl) -6-methyl-7-anilinofluorane, 3- ( N-3 ethoxypropyl-N-ethyl) -6-methyl-7-anilinofluorane and the like.

Each of the above-mentioned fluoran compounds is used alone, or two or more kinds thereof are mixed or laminated and used. Here, the weight ratio of the fluorane compound and the antipyrine complex of zinc thiocyanate is appropriately about 1: 1 to 6.

In the thermosensitive color developing layer of the present invention, various conventional binders may be appropriately used for binding and supporting on a support, and examples thereof include polyvinyl alcohol, methoxycellulose, hydroxyethylcellulose, carboxymethylcellulose, and polyvinyl. Use a water-soluble binder such as pyrrolidone, polyacrylamide, polyacrylic acid, starch, gelatin, etc., or an aqueous emulsion such as polystyrene, vinyl chloride-vinyl acetate copolymer, polybutyl methacrylate, etc., as a binder. You can

Further, in the present invention, if necessary, an auxiliary additive component such as a filler, which is commonly used in this type of heat-sensitive recording material, is further added.
A surfactant, a heat-fusible substance, a lubricant and the like can be used in combination. In this case, as the filler, for example, calcium carbonate, silica, zinc oxide, titanium oxide, aluminum hydroxide, zinc hydroxide, barium sulfate, clay, talc, inorganic fine powder such as surface-treated calcium or silica, etc. ,
Examples thereof include organic fine powders of urea-formalin resin, styrene / methacrylic acid copolymer, polystyrene resin and the like. Examples of the heat-fusible substance include higher fatty acids or their esters, amides or metal salts. , Various waxes, condensates of aromatic carboxylic acids and amines, benzoic acid phenyl esters, higher linear glycols, 3,4-epoxy-dialkyl hexahydrophthalates, higher ketones, other heat-fusible organic compounds, etc. One having a melting point of about 50 to 200 ° C.

The heat-sensitive recording material of the present invention is produced, for example, by applying a heat-sensitive layer-forming coating liquid containing each of the above-mentioned components onto a suitable support such as paper, synthetic paper, or plastic film, and drying. It is used in various recording fields, especially in thermal labels for POS, which often come into contact with oil, plasticizer, and alcohol, thermal ticket, and thermal paper applied to recorders for medical measuring instruments.

〔effect〕

The heat-sensitive recording material of the present invention has the following features.

(1) The antipyrine complex of zinc thiocyanate represented by the above formula (II) is easy to synthesize, and therefore has no problems in availability, and can be obtained in high yield, high purity and relatively inexpensively.

(2) By combining at least one selected from the fluoran compounds represented by the general formula (I) with an antipyrine complex of zinc thiocyanate represented by the formula (II), there is no background fog and oil and a plasticizer. Even in contact with, there is no phenomenon such as decolorization of the color development part or color development of the background color part,
Further, a heat-sensitive recording material having extremely excellent image stability with little decrease in image density even when contacted with water such as immersion in water is obtained. In addition, the color image does not fade over time or the white powder phenomenon does not occur, and is very stable.

〔Example〕

Next, the present invention will be described in more detail with reference to Examples. The parts and% shown below are based on weight.

Reference Example Zinc sulfate _{(ZnSO 4 · 7H 2 O)} 14.4g of potassium thiocyanate
Dissolve 29.2 g in 200 ml of water. Antipyrine 18.8g water 200ml
When the solution dissolved in is dropped into the above solution with stirring, a white precipitate is immediately formed. The precipitate is filtered off, washed with water and dried. The dried white powder was recrystallized with a mixed solution of water and ethanol to obtain 24.2 g of white crystals of an antipyrine complex of zinc thiocyanate having a melting point of 118 to 120 ° C.

Example 1 A mixture composed of the following structures was separately pulverized for 2 days using a magnetic ball mill and dispersed to obtain [A] liquid, [B] liquid,
A liquid [C] was prepared.

[A] liquid 3- (N-ethyl-N-tetrahydrofurfurylamino) -6-methyl-7-anilinofluorane 20 parts 10% aqueous solution of hydroxyethyl cellulose 20〃water 60〃 [B] liquid Antipyrine of zinc thiocyanate Complex 20 parts 5% aqueous solution of methyl cellulose 20 parts water 60 parts [C] liquid Fine powder of urea-formalin condensation resin 20 parts 5% aqueous solution of methyl cellulose 20 parts water 60 〃 Solution [A]-[C] obtained as above. ] Using a liquid,
Thermosensitive coloring layer solution having the following composition was prepared, a commercially available standard basis weight of 50 g / m ² woodfree paper dry coating weight 4-5 g / m ² and composed as applied to choose a wire bar, and Kan燥, then thermosensitive coloring The thermosensitive recording material (a) of the present invention was produced by calendering so that the smoothness of the layer surface was 500 to 600 seconds in terms of Beck's smoothness.

Thermosensitive coloring layer liquid (1) [A] liquid 10 parts (2) [B] liquid 30 parts (3) [C] liquid 30 parts (4) Isobutylene-maleic anhydride copolymer 20% alkaline aqueous solution 10 parts Example 2 Thermal recording material (b) was prepared in the same manner as in Example 1 except that the following liquid [D] was used instead of the liquid [A] of Example 1.
made.

[D] Liquid 3- (N-3-ethoxypropyl-N-ethylamino)
-6-Methyl-7-anilinofluorane 20 parts 10% aqueous solution of hydroxyethyl cellulose 20〃water 60〃 Comparative Example 1 All the examples except that the following solution [E] was used instead of the solution [A] of Example 1. Thermal recording material (c) in the same manner as 1
made.

[E] Liquid 3- (N-ethyl-N-p-tolylamino) -6-methyl-7-anilinofluorane 20 parts 10% Hydroxyethylsululose aqueous solution 20〃 Water 60〃 Comparative Example 2 [of Example 1] Thermal recording material (b) was prepared in the same manner as in Example 1 except that the following solution [F] was used instead of solution A].
made.

[F] Liquid 3-dinormal butylamino-7- (o-chloroanilino) fluorane 20 parts 10% aqueous solution of hydroxyethyl cellulose 20〃water 60〃 Comparative Example 3 The following [G] liquid was used instead of the [B] liquid of Example 1. Thermal recording material (e) in the same manner as in Example 1 except that
made.

[G] Liquid Imidazole complex of zinc thiocyanate (melting point: 143-145)
20 parts 5% aqueous solution of methylcellulose 20〃 water 60〃 Comparative Example 4 The thermal recording material was prepared in the same manner as in Example 1 except that the following [H] solution was used instead of the [B] solution of Example 1. f) was made.

[H] liquid Bisphenol A 20 parts 10% hydroxyethyl cellulose aqueous solution 20〃 water 60〃 Thermal recording materials (a) to (f) obtained as described above
With a thermal inclination tester (manufactured by Toyo Seiki), pressure 2 kg, contact time 1
Printing was performed at 150 ° C for 2 seconds. When cotton seed oil was thinly applied to the coloring part and the background part of the heat-sensitive recording material of (a) to (f) and allowed to stand in the room for 24 hours, the state of change was examined and found to be that of Example (a, b). Also, in Comparative Examples 1 and 2 (c, d), neither decoloring in the colored portion nor coloring in the background color portion was observed, but in Comparative Example 3 (e), there was no decoloring in the coloring portion. , The background color was observed. In Comparative Example 4 (f), the background color portion did not develop color, but the color development portion was decolored.

Next, the thermal recording materials (a) to (f) were printed in the same manner, and a 4 cm square was cut out around the printed portion, and a polyvinyl chloride film (Polylap V-300 manufactured by Shin-Etsu Polymer Co., Ltd.) was cut on this. After stacking one sheet and applying a load of 500 g / cm ² at room temperature for 24 hours, take it out, measure the density of the background color part and the density of the color development part with a Macbeth densitometer (RD-514), and determine the density of the color development part, The results are shown in Table 1 in comparison with the concentration before the test.

Next, print the thermosensitive recording materials (a) to (f) in the same manner, cut out a 4 cm square centering on the printed part, immerse in a 100 ml beaker filled with tap water, store at room temperature for 24 hours, then take out. After drying, the density of the colored part was measured and the density of the colored part was compared with the density before the test. The results are shown in Table-2.

As described above, the heat-sensitive recording material of the present invention has no decolorization of the color-developing part and no color-developing of the ground-color part even when contacted with oil or a plasticizer, and further, the color-developed part after contact with water such as immersion in water. It can be seen that the heat-sensitive recording material has extremely high image stability without any decrease in density.

Claims (1)

[Claims] 1. A general formula (I) (In the formula, R ₁ and R ₂ are chain or cyclic aliphatic hydrocarbon groups, and the hydrocarbon group can contain one ether bond, and R ₃ has 1 to 2 carbon atoms. Represents a hydrocarbon group), and at least one fluorane compound selected from the group consisting of fluorane compounds represented by the following formula (II) A heat-sensitive recording material characterized by utilizing a color-forming reaction with an antipyrine complex of zinc thiocyanate represented by: