JPH0679869B2 - 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 heat-sensitive recording method using (1) primary color development does not require a developing step, (2) hardware can be simple and compact, maintenance cost is low, (3) the feel is similar to plain paper, and the sheet itself Due to its relatively low cost, 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, lactam, or 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 plastic film, the recorded image is erased, and the solution of this problem has become a major technical problem for 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. For example, the layer is protected from 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, most of them, like the color developing agent 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 the decolorization of the color-developed part and the color development of the ground-colored part in contact with oil or a plasticizer due to the combination of a specific fluorane compound and an antipyrine complex of zinc thiocyanate, and immersion 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) (Wherein R ₁ and R ₂ are each independently an alkyl group having 1 to 8 carbon atoms or a cyclohexyl group, R ₃ is an alkyl group having 1 to 2 carbon atoms, and R ₄ is hydrogen or a methyl group). The present invention is characterized by utilizing a color-forming reaction between at least one fluorane compound selected from the fluorane compounds described above and an antipyrine complex of zinc thiocyanate represented by the following structural formula (II).

Specific examples of the fluoran compound represented by the general formula (I) include the followings.

3-diethylamino-6-methyl-7-anilinofluorane, 3- (N-ethyl-N-isoamylamino) -6-methyl-7-anilinofluorane, 3- (N-methyl-N-normalhexyl) Amino) -6
-Methyl-7-anilinofluorane, 3- (N-methyl-N-cyclohexylamino) -6-
Methyl-7-anilinofluorane, 3-dinormal butylamino-6-ethyl-7-anilinofluorane, 3-diethylamino-6-ethyl-7- (4'-methylanilino) fluorane 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. A water-soluble substance such as polyacrylamide, polyacrylic acid, starch, gelatin, etc., or an aqueous emulsion such as polystyrene, vinyl chloride-vinyl acetate copolymer, polybutyl methacrylate, etc. may be used as the binder. it 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, condensation products of aromatic carboxylic acid and amine, benzoic acid phenyl ester, higher linear glycol, 3,4-epoxy-dialkyl hexahydrophthalate, higher ketone,
Other heat-fusible organic compounds and the like have 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 on a suitable support such as paper, synthetic paper, plastic film, and drying. It is used in various recording fields, especially thermal labels for POS, which have a lot of chances of contact with oil, plasticizer, and water, thermal ticket, thermal paper applied to recorders for medical measuring instruments, and the like.

[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 structural formula (II) is easy to synthesize, and therefore there are no problems in availability, and it is possible to obtain a high yield, high purity and relatively inexpensively.

(2) By combining at least one selected from the fluorane compounds of the general formula (I) with an antipyrine complex of zinc thiocyanate represented by the structural formula (II), there is no background fog and oil, Even when contacted with a plasticizer, there is no phenomenon such as decolorization of the color-developed part or color development of the ground-colored part. Furthermore, even when contacted with water such as immersion in water, there is little decrease in image density and extremely excellent image stability. A thermosensitive recording material 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 a 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 solvent 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 having the following composition 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-cyclohexyl-N-methylamino) -6-
Methyl-7-anilinofluoran 20 parts 10% Hydroxyethylcellulose aqueous solution 20 parts Water 60 parts [B] liquid Zinc thiocyanate antipyrine complex 20 parts 5% Methylcellulose aqueous solution 20 parts Water 60 parts [C] liquid Urea-formalin condensation resin Fine powder of 20 parts 5% aqueous solution of methylcellulose 20 parts Water 60 parts Using the liquids [A] to [C] obtained as described above,
A thermosensitive coloring layer solution having the following composition was prepared, and a wire bar was selected and dried on a commercially available high-quality paper having a standard basis weight of 50 g / m ^{2 so} that the dry coating amount was 4 to 5 g / m ^2, and then the thermosensitive coloring layer. The heat-sensitive recording sheet (a) of the present invention was produced by calendering so that the surface smoothness was 500 to 600 seconds in terms of flat smoothness.

Thermosensitive color developing layer liquid (1) [A] liquid 10 parts (2) [B] liquid 30 parts (3) [C] liquid 30 parts (4) Isobutylene-maleic anhydride 10 parts 20% aqueous alkali solution of copolymer Example 2 A thermosensitive recording sheet (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.

[D] Liquid 3-diethylamino-6-methyl-7-anilinofluorane 20 parts 10% aqueous solution of hydroxyethyl cellulose 20 parts water 60 parts Example 3 The following liquid [E] was used instead of the liquid [A] of Example 1. A thermal recording sheet (c) was prepared in the same manner as in Example 1 except that it was used.

[E] liquid 3- (N-isoamyl-N-ethylamino) -6-methyl-7-anilinofluorane 20 parts 10% hydroxyethylcellulose aqueous solution 20 parts water 60 parts Comparative Example 1 [A] liquid of Example 1 A thermosensitive recording sheet (d) was prepared in the same manner as in Example 1 except that the following liquid [F] was used instead.

[F] Liquid 3- (N-ethyl-N-p-toluidino) -6-methyl-7-anilinofluorane 20 parts 10% hydroxyethylcellulose aqueous solution 20 parts water 60 parts Comparative Example 2 [A] of Example 1. A thermosensitive recording sheet (e) was produced in the same manner as in Example 1 except that the following liquid [G] was used instead of the liquid.

[G] liquid 3-dinormal butylamino-7- (o-chloroanilino) fluorane 20 parts 10% hydroxyethyl cellulose aqueous solution 20 parts water 60 parts Comparative Example 3 The following [H] liquid was used instead of the [B] liquid of Example 1. A thermal recording sheet (f) was prepared in the same manner as in Example 2 except that the above was used.

[H] liquid Imidazole complex of zinc thiocyanate (melting point: 143-145)
C.) 20 parts 5% aqueous solution of methylcellulose 20 parts water 60 parts Comparative Example 4 The same procedure as in Example 1 was carried out except that the following solution [I] was used instead of the solution [B] in Example 1 to prepare a thermosensitive recording sheet (g). ) Was made.

[I] Liquid Bisphenol A 20 parts 10% Hydroxyethylcellulose aqueous solution 20 parts Water 60 parts Thermal recording sheet (a) obtained as above
(G) was printed at 150 ° C. with a thermal inclination tester (manufactured by Toyo Seiki) at a pressure of 2 kg and a contact time of 1 second. Cotton seed oil was thinly applied to the color-developed portion and the ground-colored portion of the heat-sensitive recording sheets (a) to (g) and left for 24 hours in the room, and the state of change was examined. Also, in Comparative Examples 1 and 2 (d, e), neither the decolored portion of the colored portion nor the colored portion of the ground portion was seen,
In Comparative Example 3 (f), although the color-developed portion was not erased, the background-colored portion was colored. In Comparative Example 4 (g), the background color portion did not develop color, but the color development portion was decolored.

Next, the thermosensitive recording sheets (a) to (g) were printed in the same manner, and a 4 cm square was cut out around the printed portion, and a polyvinyl chloride film (manufactured by Shin-Etsu Polymer Co., Ltd., Polyrap V-300) was cut out. 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 sheets (a) to (g) 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, take out and dry. After that, the density of the colored portion was measured, and the density of the colored portion was compared with the density before the test. The results are shown in Table-2.

From the above, the heat-sensitive recording material of the present invention has no decolorization of the color-developed part and no color development of the ground-colored part even in contact with oil and a plasticizer, and further, the concentration of the color-developed part in contact with water such as immersion in water. It can be seen that the heat-sensitive recording material has little deterioration and has extremely high image stability.

Claims (1)

[Claims] 1. A general formula (Wherein R ₁ and R ₂ are each independently an alkyl group having 1 to 8 carbon atoms or a cyclohexyl group, R ₃ is an alkyl group having 1 to 2 carbon atoms, and R ₄ is hydrogen or a methyl group) At least one fluorane compound selected from among the represented fluorane compounds; A heat-sensitive recording material characterized by utilizing a color-forming reaction with an antipyrine complex of zinc thiocyanate represented by: