JPS6213385A - Production of thermal transfer sheet - Google Patents

Abstract

PURPOSE:To obtain a thermal transfer sheet free of safety problems or hygienic problems, being inexpensive and having a uniform coated film enabling printing with high image quality, by using a dispersed coating liquid obtained by dispersing an ink in a dispersant comprising water as a main constituent. CONSTITUTION:A mixed liquid obtained by mixing a wax, a pigment, a surfactant and water is agitated while heating the liquid to a temperature not lower than the melting point of the wax to emulsify the liquid, followed by cooling to obtain a suspended liquid in which fine particles of the wax are uniformly dispersed in water. The suspended liquid is applied to a base such as a polyester film by a gravure roll, offset gravure, a bar coater or the like in the same manner as in an ordinary case of applying a solution. In a drying step, in which water is sufficiently evaporated off, the coated material is preferably heated to a temperature not lower than the melting point of the wax, whereby a high coated film strength is obtained after drying, and the coated surface is provided with a sufficient smoothness. At least one of various ester waxes ordinarily used as a binder for a thermal transfer ink can be used either singly or in combination as the wax, and it may be mixed with a polymer for imparting flexibility.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing a thermal transfer recording sheet.

[Conventional technology]

Thermal transfer method, especially the thermal transfer method in which solid ink is applied at room temperature onto a base material such as capacitor paper or polyester film, and the ink is melted and liquefied by heating with a thermal head, etc., and then transferred to plain paper to create a recorded image. Natural or synthetic waxes with specific melting points, such as paraffin, microcrystalline, carnauba, and montan, are usually used as binders for inks, and various dyes and pigments are used as coloring agents, as well as various types of waxes for the purpose of imparting flexibility. resin,
A recording sheet is used in which an ink prepared by dispersing various additives such as mineral oil and metal salts is coated on the above-mentioned base material.

The method of applying ink onto a substrate is usually to use a gravure roll or the like to apply the heated and molten ink directly onto the substrate, but in this case, the viscosity of the coating liquid may vary due to uneven heating temperature, etc. 2. Easy to cause irritation, uneven coating thickness, and traces of coating fluid flow. This tends to lead to deterioration in the image quality of the transferred image, and is particularly unsuitable for color hard copies that require high image quality. For this reason, a solvent coating method using wax that is relatively easily soluble in solvents has been proposed in recent years (Japanese Patent Laid-Open Nos. 58-128897 and 59-57).
No. 791).

Xylene, toluene, ethanol, acetone, etc. are used as solvents.

However, in such a manufacturing process using solvent coating, a large amount of solvent evaporates during drying, which may pose a risk of fire or damage the health of process workers, resulting in safety problems. In order to deal with these problems, solvent coating equipment requires the use of large volumes of books, and if the solvent used is not sufficiently evaporated, it may cause bad odors during use or storage. tends to lead to an increase in manufacturing costs.

[Problem that the invention seeks to solve]

An object of the present invention is to provide a method for producing a heat-sensitive transfer sheet that is free from safety problems such as fire.

Another object of the present invention is to provide a manufacturing method that poses no health problems to workers.

Another object of the present invention is to provide a manufacturing method that allows use of inexpensive manufacturing equipment.

Still another object of the present invention is to provide a method for manufacturing a heat-sensitive transfer sheet that is inexpensive and capable of producing high-quality recorded images.

[Means and effects for solving the problem] As a result of intensive studies, the present inventors have found that when applying heat-melting ink onto a heat-sensitive transfer substrate, a dispersion medium containing water as a main component is used as a coating liquid. It was found that the use of a dispersion coating liquid in which ink was dispersed was found to be most effective, and the present invention was completed.

This method of producing a heat-sensitive transfer sheet is characterized by heating and mixing the materials to a temperature above the melting point of the low-melting point material, cooling the mixture to form a suspension, applying the suspension onto a substrate, and drying it.

In solvent coating methods, organic solvents have conventionally been used as solvents to dissolve wax substances and colorants. Using a solvent whose main component is water as a solvent for normal coating solutions is clearly disadvantageous in terms of the solubility of wax substances. A stable water-wax emulsion is synthesized by adding a coloring agent and an emulsifier (dispersing agent) and heating this liquid above the melting point of the wax, and this emulsion is applied to the base material with the ink material. By doing so, it is possible to obtain a uniform ink material coating film that is equivalent to or better than that obtained by ordinary solvent coating methods.

That is, in the method of the present invention, a liquid mixture of wax, pigment, surfactant, and water is heated above the melting point of the wax, stirred, emulsified, and then cooled, so that wax fine particles are uniformly dispersed in water. A suspension is obtained.

This is applied onto a base material such as polyester using a gravure roll, offset gravure, bar coater, etc. in the same manner as normal solution coating.

In the drying process, if enough water is evaporated, a heat-sensitive transfer sheet can be obtained.

In the drying step, if the wax is preferably heated to a temperature higher than its melting point, the coating strength after drying will not be high and the coated surface will have sufficient surface smoothness.

The types of wax used in the method for manufacturing such a thermal transfer sheet include carnauba wax, montan wax, and montan wax, which are used as binders for ordinary thermal transfer inks.
Paraffin wax, beeswax, microcrystalline wax, ceresin, and various other ester waxes can be used alone or in a blend, and in order to impart flexibility, they can be used in a JIJ mom-blend.

In addition, as a colorant, ordinary carbon black and various other dyes and pigments can be used, but when creating a dispersion coating liquid, if there is a high probability that the colorant will be included in the aqueous phase, it will not be possible to coat it on the substrate. When a film is formed, the colorant does not easily separate from the binder, which tends to cause scumming and uneven printing during recording, and the desired hue cannot be obtained due to reaggregation of the colorant. Therefore, it is better to use an oil-based colorant as the nitrogenous coloring material so that the probability that the coloring material is included in the oily layer (0 layer) in the dispersion coating liquid (% phase) is increased. Dyes and pigments can easily be made oily due to their chemical structure and post-processing during synthesis; even reed and carbon black can be made sufficiently oily by surface treatment using mineral oil or other oil. Obtainable.

Dispersants used to create a dispersion coating liquid with sufficient stability for coating include stearic acid, triethanolamine, sorbitan monostearate, polyoxyethylene sorbitan monostearate, and other glycol fatty acid esters. Various surfactants including fatty acid esters of polyhydric alcohols such as sorbitan fatty acid esters can be used alone or in combination.

Various types of coaters can be used during application, including kiss coaters (including those with Meyer rods), gravure coaters, offset syllabi, and reverse roll coaters; Therefore, it is necessary to be very careful to prevent rust from forming inside the drying room.

〔Example〕

Example l Carbon black M2400B 200I manufactured by Mitsubishi Chemical Corporation
A mixture of 150 cc of oleic acid and 150 cc of oleic acid is prepared by thoroughly mixing it using a ball mill, and this is designated as colorant A.

Next, 300 g of Colorant A was premixed with 1,401,700 g of Nippon Seiro Co., Ltd./1 Rough-in Wax Na 140 in a mixing kettle under heating at 75°C. This was further thoroughly kneaded using three rolls to prepare a raw material ink.

Materials having the following composition were thoroughly stirred with a mixer under heating at 80°C, and then cooled to obtain a dispersion coating liquid.

This coating liquid was applied onto a 13 μm thick capacitor paper using a bar coater, and then dried in a dryer at 90° C. for 1 hour to obtain a heat-sensitive transfer sheet with a uniform coating film.

When this thermal transfer sheet was subjected to a printing test using a P6 printer manufactured by Fuji Xerox, a clear different color recorded image was obtained.

Example 2 Dye Diaresin RED E5B manufactured by Mitsubishi Chemical Corporation
150# in the same way as in Example 1, in a pre-mixing oven with 1,401,850 g of paraffin wax
After mixing under heating, the mixture was sufficiently kneaded using three rolls to obtain a raw material ink.

A material having the following composition was rapidly stirred under heating at 80°C and cooled to obtain a dispersion coating liquid.

This coating liquid was applied onto a 6 μm thick polyester base material using a gravure coater, and dried while the temperature and air volume of the drying chamber were sufficiently high. A uniform and strong ink layer was formed ( At this time, there was no need to recover the generated steam, so it was released indoors and into the atmosphere.)

When this thermal transfer sheet was subjected to a printing test using a printer in the same manner as in Example 1, a clear, bluish-red recorded image was obtained.

〔Effect of the invention〕

Claims (1)

[Claims] A coloring agent, a low melting point material, and a dispersant are dispersed and mixed in a solvent mainly composed of water, and this mixture is heated to a temperature higher than the melting point of the low melting point material, and then cooled to form a suspension. A method for producing a heat-sensitive transfer sheet, which comprises coating it on a base material and drying it.