JPH068069B2 - Thermal recording - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to a heat-sensitive recording material having improved light resistance, and more specifically, an image of the heat-sensitive recording material even when exposed to sunlight or fluorescent lamp for a long time. The present invention relates to a heat-sensitive recording material in which fading and background coloring are extremely small.

<Prior Art> Generally, a heat-sensitive recording material obtained by coating a colorless or light-colored leuco dye and a developer that develops the color of the leuco dye on heat is disclosed in JP-B-45-14035. , Has been widely put into practical use. A thermal printer or the like having a built-in thermal head is used for recording on this heat-sensitive recording material, but such a heat-sensitive recording method is (1)
No noise during recording, (2) No need for developing and fixing, (3) Maintenance-free, (4) Equipment is relatively inexpensive and compact, so computer output, facsimile, calculator Printer, etc.
It is widely used in the fields of measurement recorders, automatic ticket vending machines, and thermal recording label printers.

However, the heat-sensitive recording material using this kind of heat-sensitive recording material has a defect in light resistance of the image portion and the background portion. That is, when exposed to sunlight or fluorescent light for a long time, the density of the image area is reduced and the background area is discolored. Particularly in applications such as heat-sensitive tickets, heat-sensitive coupons, and heat-sensitive recording labels for automatic ticket vending machines, the possibility of exposure to the above-mentioned sunlight and fluorescent lamps is a serious problem. Conventionally, benzophenone, benzotriazole,
It is known to add an ultraviolet absorber such as salicylate, but the heat-sensitive recording still has satisfactory light resistance due to background fogging, insufficient stability of the image area and insufficient effect of preventing background discoloration. The current situation is that the body has not been obtained.

<Means for Solving Problems> The inventors of the present invention have conducted extensive studies in view of the above problems, and as a result, the deterioration of the light resistance of the thermosensitive recording medium was caused not only by the influence of ultraviolet rays but also by the visible portion having a wavelength of 600 nm or less. It has been found that the above phenomenon is caused by a light ray containing the compound, and the effect that the effect has been weakened only by the addition of the ultraviolet absorber which has been conventionally proposed is represented by the leuco dye represented by the following formula [1] and the following formula [2]. A color developer and a benzotriazole-based UV absorber represented by the following formula [3] are mixed in the thermosensitive coloring layer, and the mixing ratio of these three components is 1 part by weight of the color developer per 1 part by weight of the leuco dye. .
It was achieved by using 5 to 5 parts by weight and 0.5 to 5 parts by weight of the ultraviolet absorber.

[1] formula (Wherein R ₁ and R ₂ are alkyl groups or cycloalkyl groups) [2] Formula [3] Expression (Wherein R ₁ , R ₂ and R ₃ are hydrogen atoms, halogen atoms or alkyl groups) Examples of the leuco dye of the above formula [1] in the present invention include, for example, 3-diethylamino-7- (o- Chloroanilino) fluorane, 3-ethylisoamylamino-7
Examples thereof include-(o-chloroanilino) anilinofluorane and 3-dibutylamino-7- (o-chloroanilino) fluorane, which may be used alone or in combination of two or more kinds. In the present invention, it is desirable to use only the leuco dye of the above formula [1], but it can be used in combination with other colorless or light-colored leuco dye as long as the light resistance is not impaired. Specific examples of other leuco dyes that can be used in combination include crystal violet lactone and 3-diethylamino-
7-chlorofluorane, 3-diethylamino-6-methyl-7-chlorofluorane, 3-dichlorohexylamino-6-chlorofluorane, 3-diethylamino-7-dibenzylaminofluorane, 3-pyrrolidino-6- Methyl-7-anilinofluorane, 3-piperidino-6-methyl-7-anilinofluorane, 3-cyclohexylmethylamino-6-methyl-7-anilinofluorane, 3
-Ethylisoamylamino-6-methyl-7-anilinofluorane and the like can be mentioned.

The color developer of the formula [2] in the present invention is preferably used alone, but may be used in combination with one or more kinds of the color developers described below as long as the light resistance is not impaired. Examples of the developers used in combination include α-naphthol and β-naphthol.
Naphthol, 4-t-butylphenol, 4-t-octylphenol, 4-phenylphenol, 2,2-bis (p-hydroxyphenyl) propane, 2,2-bis (p
-Hydroxyphenyl) butane, 4,4'-cyclohexylidenediphenol, 2,2-bis (2,5-dibromo-4-)
Hydroxyphenyl) propane, 4,4'-isopropylidenebis (2-t-butylphenol), 2,2'-methylbis (4-chlorophenol), 4,4'-sulfonyldiphenol, 4,4'- Examples include derivatives of thiobisphenol, benzoic acid, salicylic acid, tartaric acid, gallic acid and the like.

As the benzotriazole-based UV absorber of the formula [3] in the present invention, conventionally known ones are used, for example, 2- (2'-hydroxy-5'-methylphenyl) benzotriazole and 2- (2'- Hydroxy-3'-t
-Butyl-5'-methylphenyl) benzotriazole, 2- (2'-hydroxy-5'-t-octylphenyl) benzotriazole, 2- (2'-hydroxy-
3'5'-di-t-amylphenyl) benzotriazole, 2- (2'-hydroxy-3 ', 5'-di-t-butylphenyl) benzotriazole, 2- (2'-hydroxy-3'-t- Butyl-5'-methylphenyl)-
Examples thereof include 5-chlorobenzotriazole and 2- (2'-hydroxy-3 ', 5'-di-t-butylphenyl) -5-chlorobenzotriazole, but the invention is not limited thereto.

In the present invention, the compounding ratio of the developer of the formula [2] is 1.5 to 5 parts by weight per 1 part by weight of the leuco dye of the formula [1]. The compounding ratio is specified as 0.5 to 5 parts by weight. this is,
When the compounding ratio of the color developer of the formula [2] is less than a predetermined amount, the photobleaching of the image area is severe, and when it is large, the discoloration of the background becomes severe, and conversely, the ultraviolet absorber of the benzotriazole type of the formula [3] is used. This is because the background discoloration is severe when the blending ratio is less than the predetermined amount, and the image fading is severe when the blending ratio is large.

In the present invention, a leuco dye of the formula [1], a developer of the formula [2] and a UV absorber of the formula [3] in a predetermined amount are applied to a support such as paper, synthetic paper, It is characterized in that a thermosensitive coloring layer is formed by coating on a resin film or a composite thereof. A water-soluble or water-insoluble resin binder can be used as the material for binding to these supports, that is, the binder of the heat-sensitive color forming layer, but water-soluble resins are preferable, for example, casein, gelatin, polyvinyl. Alcohol, polyvinylpyrrolidone, starch, modified starch, isobutylene-maleic anhydride resin, diisobutylene-maleic anhydride resin, styrene-maleic anhydride resin, polyacrylamide, modified polyacrylamide, carboxymethyl cellulose, methyl cellulose, hydroxyethyl cellulose, and acetic acid. Vinyl, acrylic ester, vinyl chloride-vinyl acetate copolymer, SBR, N
The emulsions such as BR and the latex are used alone or in combination. Further, it is possible to add a waterproofing agent, if necessary.

Further, the thermosensitive coloring layer in the present invention, inorganic and organic pigments as a conventional filler, for example, heavy and light calcium carbonate, aluminum hydroxide, talc, clay, satin white, kaolinite, polyolefin particles, polystyrene. Particles, urea-formalin resin particles and the like can be added to improve the sharpness of the color image.

Furthermore, in the present invention, in order to improve the recording sensitivity, various conventional thermoplastic substances can be added to the thermosensitive coloring layer, if necessary. Examples of the heat-fusible substance include organic compounds having an appropriate melting point. Examples thereof include higher fatty acid amides such as stearic acid amide, beeswax, animal waxes such as Sierra kurowa, vegetable waxes such as carnauba wax, and montan wax. Mineral wax such as, paraffin wax, wax such as microcrystalline wax, higher fatty acid, higher fatty acid ester, dimethyl terephthalate, aromatic carboxylic acid ester such as diphenylphthalate, alkylnaphthalene derivative, alkyldiphenyl derivative, alkyl A terfenyl derivative or the like is used.

In addition, lubricants such as zinc stearate and calcium stearate, various surfactants, defoaming agents and the like are added as necessary.

On the heat-sensitive color forming layer constituting the heat-sensitive recording material of the present invention, it is possible to further provide a conventionally known protective layer in order to improve chemical resistance. As a result, not only the light resistance but also the chemical resistance is improved, and the storage characteristics are remarkably improved.

The protective layer is mainly formed of resins having excellent chemical resistance and good film-forming properties. The resin for the protective layer is preferably a water-soluble polymer, for example, polyvinyl alcohol, modified polyvinyl alcohol, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, starch and its derivatives, casein, sodium alginate, polyvinyl pyrrolidone, polyacrylamide, modified polyacrylamide, etc. Resin is used. In addition, in order to increase the water resistance of the protective layer, glyoxal as a water resistance agent,
Chromium alum, melamine resin, melamine formaldehyde resin, polyamide resin, polyamide-epichlorohydrin resin, etc. are added. Further, if necessary, pigments, waxes and the like are added for matching with the heat-sensitive recording head.

<Examples> The present invention will be described in detail below with reference to Examples. All parts are parts by weight.

Example 1 A mixture having the following composition was ground by a ball mill for 1 day.
Dispersion was performed to prepare liquids [A] to [D].

[A] Liquid 3-dibutylamino-7- (o-30 parts chloroanilino) fluorane 5% Hydroxyethyl cellulose 50 parts Aqueous solution water 20 parts [B] Liquid bis- (3-allyl-4-hydro 30 parts xyphenyl) sulfone 5% Hydroxyethyl cellulose 50 parts Aqueous water 20 parts [C] liquid 2- (2'-hydroxy-5'-30 parts Methylphenyl) benzotriazol 5% Hydroxyethyl cellulose 50 parts Aqueous water 20 parts [D] liquid Light calcium carbonate 40 parts 10 % Polyvinyl Alcose Aqueous solution 20 parts Liquid water 40 parts Using the liquids [A] to [D] obtained as described above, a thermosensitive coloring layer paint having the following composition was prepared and weighed to 45 g / m ² of high-quality paper. It was applied and dried so that the dry coating amount was 5 to 6 g / m ² . Further, it was processed with a calendar so that the smoothness of the thermosensitive coloring layer was 400 to 600 seconds to prepare a thermosensitive recording material of the present invention.

Thermosensitive coloring layer coating [A] liquid 30 parts [B] liquid 60 parts [C] liquid 30 parts [D] liquid 135 parts 10% polyvinyl alcohol 100 parts aqueous solution Example 2 In Example 1, the leuco dye of the liquid [A] was used. Was replaced with 3-diethylamino-7- (o-chloroanilino) fluorane to prepare a thermosensitive recording medium of the present invention in the same manner.

Example 3 In Example 1, the UV absorber of the liquid [C] was added to
A thermosensitive recording medium of the present invention was prepared in the same manner except that (2'hydroxy-3'-t-butyl-5'-methylphenyl) benzotriazole was used.

Comparative Example 1 A sample of Comparative Example 1 was prepared in the same manner as in Example 1 except that 3-cyclohexylmethylamino-6-methyl-7-anilinofluorane was used as the leuco dye of the solution [A].

Comparative Example 2 In Example 1, the developer of the liquid [B] was changed to 2,2-bis (p
A sample of Comparative Example 2 was prepared in the same manner except that -hydroxyphenyl) butane was used.

Comparative Example 3 A sample of Comparative Example 3 was prepared in the same manner as in Example 1, except that the ultraviolet absorber of the liquid [C] was 2-hydroxy-4-methoxybenzophenone.

Comparative Examples 4 to 7 Samples of Comparative Examples 4 to 7 were prepared in the same manner as in Example 1 by using the liquids [A] to [D] of Example 1 and adjusting the thermosensitive color developing layer coating composition in the following compounding parts. It was adjusted.

Next, with respect to the samples of Examples 1 to 3 and Comparative Examples 1 to 7, by using a thermal gradient tester (manufactured by Toyo Seiki Co., Ltd.), a hot plate at 130 ° C. is brought into contact with the plate at a pressure of 1000 g / cm ² for 3 seconds to form a color image. Created. The reflection densities of the colored image portion and the background portion were measured with a Macbeth reflection densitometer and used as values before the test.

As a light resistance test, exposed to sunlight for 20 hours and 5000 Lu
The sample was exposed to a fluorescent light beam of x for 500 hours, and the reflection densities of the color image portion and the background portion were measured with a Macbeth reflection densitometer and used as the values after the test. The test results of Examples and Comparative Examples are shown in Table-1.

As can be seen from the above results, the heat-sensitive recording material of the present invention has extremely excellent light resistance, and can be advantageously applied to applications such as heat-sensitive tickets, heat-sensitive tickets, and heat-sensitive recording labels that require light resistance. Was confirmed.

<Effects of the Invention> Since the present invention has the above-mentioned constitution, it is possible to impart extremely excellent light resistance to the thermosensitive recording medium. Further, by providing a known protective layer on the thermosensitive color developing layer, not only light resistance but also chemical resistance can be improved. Utilizing such characteristics, it is highly likely to be exposed to sunlight or fluorescent light, and can be advantageously applied to applications such as heat-sensitive tickets, heat-sensitive tickets, and heat-sensitive recording labels that require light resistance. it can.

Claims (1)

[Claims] 1. A thermosensitive coloring layer containing a leuco dye represented by the following formula [1], a developer represented by the following formula [2] and a compound represented by the following formula [3] on a support. In the thermosensitive color developing layer, 1 part by weight of the leuco dye represented by the formula [1] contains 1 part by weight of the developer represented by the formula [2].
A thermosensitive recording medium comprising 5 to 5 parts by weight, and 0.5 to 5 parts by weight of the compound represented by the formula [3]. [1] formula (Wherein R ₁ and R ₂ are alkyl groups or cycloalkyl groups) [2] Formula [3] Expression (In the formula, R ₁ , R ₂ and R ₃ are hydrogen atom, halogen atom or alkyl group)