JPH0514634B2 - - Google Patents

Description

Detailed Description of the Invention Technical Field The present invention provides a method for producing an aqueous dispersion coating solution for forming a thermal transfer material, which is safe and easy to handle and can form a homogeneous thermal transfer ink layer by coating on a support. Regarding.

BACKGROUND ART In recent years, with the rapid development of the information industry, various information processing systems have been developed, and recording methods and devices suitable for each information processing system have also been developed and adopted. As one such recording method, the thermal recording method has recently been widely used because the apparatus used is lightweight, compact, noiseless, and has excellent operability and maintainability.

However, among the recording papers used in thermal recording methods, ordinary thermal recording paper is a color-forming processed paper containing a color former and a color developer, so it is expensive, and records can be tampered with. The paper has disadvantages in that it has poor storage stability, such as the paper easily developing color due to heat or organic solvents, and the recorded image fading in a relatively short period of time.

In recent years, a thermal transfer recording method has been attracting particular attention as a method that maintains the advantages of the above-mentioned thermal recording method and compensates for the drawbacks associated with the use of thermal recording paper.

This thermal transfer recording method generally uses a thermal transfer material in which a thermal transferable ink layer made of a heat-melting binder and a colorant dispersed is formed on a sheet-like support. The thermally transferable ink layer is superimposed on the recording medium so as to be in contact with the recording medium, and heat is supplied from the support side of the thermal transfer material by a thermal head to transfer the melted ink layer onto the recording medium. A transfer ink image is formed according to the shape of heat supply. According to this method, it is possible to maintain the above-mentioned advantages of the thermal recording method, use plain paper as a recording medium, and eliminate the above-described disadvantages associated with the use of thermal recording paper.

In order to form a heat-transferable ink layer on a support, a method is generally adopted in which a heat-melt ink prepared by dispersing a colorant in a heat-melt binder is melt-coated onto the support. However, in hot-melt coating, the viscosity of the coating liquid due to melting of the hot-melt ink generally has a high temperature dependence, and strict temperature control is required at high temperatures. There is a problem in that it is difficult to control the thickness, especially when the layer thickness is thin, and it is difficult to form a uniform thin layer of the thermally transferable ink layer. In contrast, attempts have been made to eliminate the disadvantages of hot-melt coating by dissolving or dispersing hot-melt ink in an organic solvent to reduce the viscosity of the coating solution, and then evaporating the solvent. has also been done. However, in this case, there are problems such as the danger of fire due to the organic solvent used, interference with the occupational safety of workers, and environmental pollution.

Purpose of the Invention In view of the above circumstances, an object of the present invention is to provide a method for producing an aqueous dispersion coating liquid for forming a thermal transfer material, which is safe and easy to handle, and can easily form a homogeneous thermal transferable ink layer. be.

Summary of the Invention According to the research conducted by the present inventors, it is extremely effective to form a coating liquid in which a hot-melt ink composition is dispersed in an aqueous solution of a water-soluble polymer in order to achieve the above-mentioned object. This was confirmed. In other words, such a coating liquid dispersed in an aqueous polymer solution has a low viscosity and can be applied at substantially room temperature, eliminating the need for temperature control at high temperatures as required for hot melt coating. Not only that, but by removing moisture after coating, a thin layer of the thermally transferable ink layer can also be formed with high precision. In particular, since the dispersion medium contains a water-soluble polymer compound, the film-forming temperature of the coating liquid can be lowered compared to when the heat-melt ink is dispersed in water that does not contain such a water-soluble polymer compound. This makes it possible to form a thermal transfer layer at room temperature. Furthermore, since the water-soluble polymer compound added has an adhesion effect with the support, it is also possible to improve the adhesion between the thermal transferable ink layer and the support. Furthermore, since no organic solvent is used in the coating liquid, problems such as fire danger, deterioration of the working environment, and exhaust pollution caused by organic solvents do not occur.

The method for producing a coating liquid for forming a thermal transfer material according to the present invention is based on the above-mentioned findings, and more specifically, it is an aqueous dispersion for forming a homogeneous thermal transfer ink layer by coating on a support and drying. A method for producing a coating liquid, which includes a step of kneading a hot-melt binder and a colorant and then mixing with water in the presence of a surfactant to form a dispersion, and an aqueous solution of the dispersion and a water-soluble polymer compound. It is characterized by having a step of mixing.

The present invention will be explained in more detail below. In the following description, "%" and "parts" indicating quantitative ratios are as follows:
Unless otherwise specified, measurements are based on weight.

DETAILED DESCRIPTION OF THE INVENTION The heat-melting ink that provides the coating solution for forming a thermal transfer material according to the present invention is basically the same as that constituting the thermal transfer ink layer in a conventional thermal transfer material. The main components are a hot-melt binder and a colorant.

As the heat-melting binder, carnauba wax, paraffin wax, Sasol wax,
Waxes such as microcrystalline wax and castor wax; stearic acid, palmitic acid, lauric acid, aluminum stearate, lead stearate, barium stearate, zinc stearate, zinc palmitate, methyl hydroxystearate, glycerol monohydroxy Higher fatty acids such as stearate or derivatives such as their metal salts and esters; polyethylene, polypropylene, polyisobutylene, polyethylene wax,
Thermal products made of olefin alone or copolymers such as polyethylene oxide, polytetrafluoroethylene, ethylene-acrylic acid copolymer, ethylene-ethyl acrylate copolymer, ethylene-vinyl acetate copolymer, or derivatives thereof. Plastic resin, etc. are used. These heat-melting binders may be used alone or in a mixture of two or more.

Coloring agents include carbon black, nigrosine dye, lamp black, sudan black SM, alkali blue, first yellow G, benzidine.
Yellow, Pigment Yellow, India First Orange, Irgazine Red, Paranitroaniline Red, Toluidine Red, Carmine FB, Permanent Bordeaux FRR, Pigment Orange R, Lysol Red 20, Lake
Red C, Rhodamine FB, Rhodamine B Lake,
Methyl Violet B Lake, Phthalocyanine Blue, Pigment Blue, Brilliant Green B, Phthalocyanine Green, Oil Yellow GG, Zapon First Yellow CGG, Kayasetsu Y963, Kayasetsu YG, Sumiplast Yellow GG, Zapon First Orange RR, Oil Scarlet, Sumiplast Orange G, Orazole Brown B, Zapon First Scarlet CG, Eisenspiron Red BEH,
All known dyes and pigments such as Oil Pink OP, Victoria Blue F4R, First Gen Blue 5007, Sudan Blue, and Oil Peacock Blue can be used.

On the other hand, water-soluble polymer compounds include water-soluble synthetic polymer compounds such as vinyl acetate resins such as polyvinyl alcohol and polyvinyl butyral, acrylic ester resins or their derivatives, polyethylene glycol, polyurethane resins, and polyester resins. , cellulose derivatives such as methylcellulose, ethylcellulose, and hydroxyethylcellulose, and natural water-soluble polymer compounds such as starch, gum arabic, and casein.

The following method is used to obtain the coating liquid of the present invention from the heat-melt ink comprising the heat-melt binder and colorant as described above and the water-soluble polymer compound. That is, the hot-melt binder and colorant are melt-kneaded and then dispersed in water in the presence of a surfactant. Then, the obtained dispersion and
The coating liquid of the present invention can be obtained by mixing the water-soluble polymer compound which has been made into an aqueous solution in advance.

During dispersion, it is preferable to heat the water to 70°C or higher to facilitate the dispersion of the hot-melt ink.
It is preferable that about 20 parts of surfactant be used and the particle size of the dispersed heat-melting ink be 10 μm or less. As the surfactant, any of anionic, cationic, amphoteric, and nonionic surfactants can be used. Further, for dispersion, a conventional dispersing machine such as a stirring blade such as a propeller or a turbine blade, a homogenizer, a colloid mill, an attritor, or an ultrasonic mixer is used.

The ratio of heat-melt ink to water in the coating solution of the present invention is usually heat-melt ink/water =
A range of 5/95 to 80/20, preferably 15/85 to 60/40 is used. Also, the ratio of heat-melt ink to water-soluble polymer compound is heat-melt ink/water-soluble polymer compound.
The range of the water-soluble polymer compound used is 95/2 to 60/40, preferably 95/5 to 70/30. If the ratio of the water-soluble polymer compound is below the above range, the effect of lowering the minimum film forming temperature after coating and the effect of improving the adhesion between the thermal transferable ink layer and the support will be insufficient. This causes disadvantages such as the thermally transferable ink layer becoming sticky even after drying and insufficient thermal transferability.

In addition to the above-mentioned components, the coating solution of the present invention may also contain an antifoaming agent, an agent for improving wetting with the support, and the like.

The coating liquid of the present invention thus obtained is applied onto a support and dried to form a thermally transferable ink layer having a thickness of 0.5 to 30 μm, preferably 1 to 20 μm. wood is obtained.

As the support, conventionally known films and papers can be used as they are, such as relatively heat-resistant plastic films such as polyester, polycarbonate, triacetyl cellulose, nylon, and polyimide, cellophane, or parchment paper. It can be used suitably. The thickness of the support is
When considering a thermal head as a heat source during thermal transfer, it is desirable to have a thickness of about 2 to 15 microns, but there are no particular restrictions when using a heat source such as a laser beam that can selectively heat the thermal transfer ink layer. do not have. Also, when using a thermal head,
The heat resistance of the support is improved by providing a heat-resistant protective layer made of silicone resin, fluorine resin, polyimide resin, epoxy resin, phenol resin, melamine resin, nitrocellulose, etc. on the surface of the support that comes into contact with the heat head. Alternatively, support materials not previously available may be used.

Methods for applying the coating solution of the present invention onto a support include blade coating, spray coating, roll coating, rod coating,
A method such as gravure coating is employed as appropriate.

Effects of the Invention As described above in detail, according to the present invention, a hot-melt ink consisting of a hot-melt binder and a colorant is dispersed in water in the presence of a surfactant, and then a water-soluble A thermal transfer method that is safe and easy to handle and can form a homogeneous thin thermal transfer ink layer at a relatively low temperature and with good adhesion to the support by dispersing and mixing it with an aqueous solution of a molecular compound. A method for producing an aqueous dispersion coating solution for material formation is provided.

Hereinafter, the present invention will be explained in more detail with reference to Examples and Comparative Examples.

Example 1 [Kneading of heat-melting binder and colorant] Carbon black 15 parts by weight Paraffin (mp60-65°C) 50 Carnauba wax 20 Ethylene-vinyl acetate copolymer (ethylene/vinyl acetate = 90/10 ) 15〃 The above composition was heated and dispersed using an attritor to obtain a kneaded product.

[Production of coating liquid] 90 parts by weight of the kneaded product obtained above, 10 parts by weight of polyoxyethylene (7 mol) stearyl ether,
After melting and mixing at 90℃, while stirring with a homomixer.
300 parts by weight of hot water at 90°C was gradually added. After the addition was completed, the mixture was kept at 90°C, stirred for an additional 15 minutes using a homomixer, and then cooled to room temperature to obtain an aqueous dispersion.

50 parts by weight of a 10% aqueous solution of polyvinyl alcohol was added and mixed with 100 parts by weight of the above aqueous dispersion to obtain a coating liquid for forming a thermally transferable ink layer.

[Manufacture and evaluation of thermal transfer material] The above coating solution was applied onto polyethylene terephthalate with a thickness of 6μ using a wire bar, until the dry coating film was 6μ.
Apply it so that it looks like this, leave it to dry at 25℃ for 3 hours,
A thermal transfer material was obtained.

The adhesion between the base material of the thermal transfer material obtained here and the thermal transfer ink layer was good, and when a printing test was performed using a thermal head, clear printing was obtained.

Comparative Example 1 The aqueous dispersion obtained in Example 1 was used as it was in Example 1.
Using a wire bar on polyethylene terephthalate with a thickness of 6μ in the same manner as above, the dry coating thickness was
It was applied to a thickness of 6 μm and left to dry at 25°C. The coating film did not form a completely continuous film, and the adhesion between the substrate and the thermal transferable ink layer was poor.

Example 2 10% of the polyvinyl alcohol used in Example 1
70 ethyl acrylate instead of 50% parts by weight of the aqueous solution
A heat-sensitive transfer material was obtained in the same manner using 30 parts by weight of a 15% aqueous solution of potassium hydroxide neutralized copolymer consisting of 30 parts by weight and 30 parts by weight of methacrylic acid. The ink layer formed a uniform and smooth coating, and the adhesion between the base material and the thermal transferable ink layer was good, and when a printing test was performed using a thermal head, clear printing was obtained.

Claims (1)

[Claims] 1 After kneading the hot-melt binder and colorant,
Coating on a support, characterized by comprising a step of mixing with water in the presence of a surfactant to form a dispersion, and a step of mixing the dispersion with an aqueous solution of a water-soluble polymer compound. A method for producing an aqueous dispersion coating liquid for drying to form a homogeneous thermal transferable ink layer.