JPS6297881A - Thermal recording sheet - Google Patents

Abstract

PURPOSE:To obtain thermal recording sheet enhanced in light resistance of a colored dye and having a sensitivity comparable to that of a conventional thermal recording sheet, by dispersing a colorless dye included by cyclodextrin and an acidic substance for converting the colorless dye into a colored dye when being heated, in a binder. CONSTITUTION:A color forming layer 4 comprises a colorless dye 1 included by cylclodextrin and an acidic substance 2 which are dispersed in a binder. When being heated by a thermal head 6, the colorless dye 1 is converted into a colored dye in the included state under the function of the acidic substance 2. Since the colored dye thus formed remains in the state of being included by cyclodextrin and the yield of fluorescence of the dye is increased, the probability of the transition from the excited singlet to the triplet state of the dye is decreased, resulting in that the quantity of excited triplets is reduced. The colorless dye may be leuco methylene blue, leuco malachite green or the like, while the acidic substance may be bisphenol A, boric acid, nickel nitrate or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a heat-sensitive recording sheet used in various printers, facsimile machines, and the like.

[Conventional technology]

A thermosensitive recording sheet is a recording material in which a so-called thermosensitive coloring layer that develops color by heating is formed on the surface of a support, such as paper, and a thermal printer equipped with a thermal spatula is used for heating.

The heat-sensitive recording method using the above-mentioned recording materials is used not only for copying books and documents, but also for recording the output of computers, facsimiles, measuring instruments, and the like. Conventionally, as a heat-sensitive recording sheet, for example, Japanese Patent Application Laid-Open No. 5'7-679
As seen in Publication No. 3, there was something like Figure 2. In the figure, [2) is an acidic substance, C3) is a colorless dye,
C4) is a coloring layer, (5) is a support, (6) is a thermal head, and (7) is a coloring portion. The coloring layer (4) is made by dispersing an acidic substance (2) and a colorless dye (3) in a binder.

Next, the operation will be explained. The acidic substance (2) heated by the thermal head (6) melts and reacts with the colorless dye (3), converting the colorless dye into a colored dye and producing color.0 [Problems to be solved by the invention] Conventional The heat-sensitive recording sheet is constructed as described above, but colored dyes obtained by converting colorless dyes with acidic substances, which are usually called basic dyes, generally have the problem of poor light resistance. Ta.

Note that this is probably due to the strong sensitivity to singlet oxygen.

This invention was made to solve the above-mentioned problems, and aims to improve the light resistance of colored dyes converted from colorless dyes and to obtain heat-sensitive recording sheets with sensitivity comparable to conventional ones. The purpose is

[Means for solving problems]

The heat-sensitive recording sheet according to the present invention includes a colorless dye encapsulated in cyclodextrin and an acidic substance that converts the colorless dye into a colored dye by heating, dispersed in a binder.

[Effect]

The colorless dye in this invention reacts with an acidic substance and is converted into a colored dye while still being clathrated in cyclodextrin, so as the fluorescence yield increases, an excited doublet becomes an excited triplet. The probability of transition is reduced and light resistance is improved.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
In the figure, (1) is a colorless dye included in cyclodextrin, and the coloring layer (4) is a colorless dye (1) in a binder.
and acidic substance (2) are dispersed therein.

Next, the operation will be explained. When heated by the thermal head (6), the colorless dye clathrated in the cyclodextrin is converted into a colored dye by the action of the acidic substance (2) while remaining clathrated. At this time, the rate of conversion to colored dye is not affected by the presence of cyclodextrin. The formed colored dye remains clathrated in the cyclodextrin, and the fluorescence yield of the dye increases, which reduces the probability of the dye's transition from the excited doublet state to the triplet state. The number of excited triplet pupils decreases. The color fading of the dye is carried out via excited triplet molecules, and as the number of triplet atoms decreases, the photobleaching rate of the dye decreases. Therefore, it is thought that the light resistance of the colored portion (7) of the heat-sensitive recording sheet is improved.

The colorless dyes used in this invention include leucomethylene blue and leucomethylene blue.

Crystal violet lactone, p-damine B lactam, etc. are mentioned.

Examples of the cyclodextrin include α-β-γ-cyclodextrin, 2,3.5-0-)rifthyl-β-cyclodextrin, and the like.

In addition, as a binder, polyvinyl alcohol, polyvinylpyrrolidone, starch, polymethyl methacrylate,
Examples include polystyrene and methylcellulose.

Another acidic substance is bisphenol A.

Examples include boric acid, oxalic acid, maleic acid, citric acid, salicylic acid, stearic acid, urea nitrate, and nickel nitrate.

Example 1 Benzoyl leucomethylene blue 05 parts, β-cyclodextrin 2 parts dimethyl sulfoxide 100 parts
After dissolving in a heavy volume, the solvent is removed using a rotary evaporator. 2.5 parts by weight of this and 100 parts by weight μ
10% polyvinyl alcohol aqueous solution was kneaded in a ball mill overnight. Add 1 part of nickel nitrate to this material, apply it to high-quality paper with a wire coater to a final thickness of 0 μm, and dry and clean at room temperature. To the completed thermal recording paper 1
If you hold the weight warmed to 50°C for 5 seconds, the OD (absorbance)
1.1 blue print is obtained. Even when half of this print was covered with aluminum foil and irradiated with ultra-high pressure mercury lamp light with a light intensity of 150 mW/asl for 30 minutes, the irradiated area and the non-irradiated area could not be distinguished.

Example 2 0 ifmalachite green o, s heavy kn part, γ-cyclodextrin double hawk part dimethyl sulfoxide 100
After dissolving in the electric resistance stitch, remove the solvent using a rotary evaporator. This one has 2.5 mold part and 10 of 100 heavy M part
% polyvinylpyrrolidone aqueous solution was kneaded in a ball mill all day and night. Add 1 part by weight of pisphenol A to this,
It is applied to high-quality paper with a wire bar to a final thickness of 15 μm and dried at room temperature.

When a weight heated to 100'C was placed on the resulting thermal recording paper for 5 seconds, a green print of ODo 9 was obtained. Even when half of the print was covered with aluminum foil and irradiated with ultra-high-pressure mercury lamp light with a light intensity of 150 mW/a- for 30 minutes, the irradiated area and the non-irradiated area could not be distinguished.

Comparative Example Penzoylloifmethylenep Al-0.5 parts by weight 10
A 10% polyvinyl alcohol aqueous solution of 0 li was kneaded with a ball miller all day and night. 1 part by weight of nickel nitrate is added to this mixture, and the mixture is applied onto high-quality paper using a wire coater to a final thickness of 10 μm, and dried at room temperature. When a weight loosened to 150℃ is placed on the thermal recording paper for 5 seconds, the result is 0D12.
A blue print was obtained, and it was found that the sensitivity was almost the same as in Example 1. Half of this print was covered with aluminum foil and exposed to ultra-high pressure mercury lamp light with a light intensity of 150 mWlad for 10 minutes.
After irradiation for a minute, discoloration of the irradiated area was observed. From a comparison of the above two examples and the comparative example, it was found that the photosensitivity of both examples was almost the same as before, and the light resistance after printing was excellent. is clear.

〔Effect of the invention〕

As described above, according to the present invention, a colorless dye clathrated in cyclodextrin and an acidic substance that converts this colorless dye into a colored dye by heating are dispersed in a binder, so that light resistance after printing is improved. This method has the effect of providing a heat-sensitive recording sheet with excellent light sensitivity and comparable photosensitivity to conventional sheets.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a heat-sensitive recording sheet according to an embodiment of the present invention, and FIG. 2 is a sectional view showing a conventional heat-sensitive recording sheet. In the figure, (1) is a colorless dye included in cyclodextrin, f2) is an acidic substance, (4) is a coloring layer, and (5)
is a support, (6) is a thermal head, and (7) is a coloring part. In addition, in the figures, the same symbols indicate the same or equivalent parts〇

Claims (5)

[Claims] (1) A heat-sensitive recording sheet in which a colorless dye encapsulated in cyclodextrin and an acidic substance that converts the colorless dye into a colored dye by heating are dispersed in a binder. (2) Claim 1 in which the colorless dye is a leuco dye
Heat-sensitive recording sheet as described in section. (3) The heat-sensitive recording sheet according to claim 1 or 2, wherein the colorless dye is benzoylleucomethylene blue. (4) The thermosensitive recording sheet according to any one of claims 1 to 3, wherein the cyclodextrin is β-cyclodextrin. (5) The heat-sensitive recording sheet according to any one of claims 1 to 4, wherein the acidic substance is nickel nitrate.