JP2995682B2 - Thermal transfer recording medium - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal transfer recording medium, and more particularly, to a thermal transfer recording medium capable of transferring and printing detailed characters and images on a low-smoothness receiving medium (recording paper). About.

(Prior art)

Many recording methods are known, and all of them have advantages and disadvantages. One of them, the transfer type thermal recording method (thermal transfer recording method), uses a relatively simple apparatus and is relatively simple. It is widely used because it can be printed on plain paper. However, in this thermal transfer recording method, the printing quality is easily influenced by the smoothness of the surface of the transfer receiving paper, and it is difficult to perform clear printing on the transfer receiving paper having the poor surface smoothness.

Conventionally, in order to improve such defects, heat treatment is performed after printing (Japanese Patent Application Laid-Open No. 58-76276).
-96549) or using auxiliary means such as electrostatic force (JP-A-55-65590) or adding a large amount of an oily substance to reduce the melt viscosity during transfer (JP-A-60-25762).
In addition, there have been proposed means for adding a substance having a thermal decomposition property (Japanese Patent Application Laid-Open No. 60-82389) and a thermal expansion property (Japanese Patent Application Laid-Open No. 25762/1985) to perform thermal sensitization. Further, a technique for improving the print quality by forming a multi-layer of the heat-fusible ink layer has also been conventionally proposed, and a heat-fusible ink having only a slightly different melting point is laminated, and either one or both layers are laminated. (JP-A-59-224392), and providing a layer made of a heat-fusible substance containing no coloring material on a heat-fusible ink layer (JP-A-60-97888). Has been proposed.

However, in the method of transferring and recording the ink that has been melted into a liquid state as described above, when the smoothness of the surface of the receiving paper is low, the printing quality of the receiving paper having a high surface smoothness is compared with the printing quality. In this case, only inferior printing quality is obtained, and the fundamental problem of transfer-type thermal recording, in which the printing quality depends on the smoothness of the surface of the receiving paper, has not been solved.

On the other hand, an ink containing a resin having a certain degree of mechanical strength as a main component without exhibiting tackiness when applied with heat energy but being melted into a low-viscosity liquid, has a poor surface smoothness. It is considered that high-quality printing can be performed on transfer paper having poor surface smoothness by using ink that is transferred so as to adhere to the convex portions on the surface and cover the concave portions. However, such resin inks require a larger amount of energy for printing than conventional wax inks, so it is necessary to use a support film that is particularly excellent in heat resistance. The problem described above newly arises and is not always good.

Also known is a method of adding a large amount of an oily substance to an ink layer to lower the melt viscosity during transfer (Japanese Patent Application Laid-Open No. 60-25762). Here, machine oil, castor oil, olive oil, rapeseed oil and the like are known. However, there is a problem that background contamination occurs.

[Problems to be solved by the invention]

The present invention solves the above-mentioned drawbacks and problems, and a clear print can be obtained even on a transfer paper having poor surface smoothness,
Moreover, it is an object of the present invention to provide a thermal transfer recording medium that does not cause background contamination.

[Means for solving the problem]

The present invention is characterized in that in a thermal transfer recording medium having at least a heat-meltable or thermosoftening ink layer and an overcoat layer formed on a support, the overcoat layer contains a particulate elastomer.

By the way, the present inventor has conducted various studies to achieve the above object. As a result, if a particulate elastomer is contained in the surface layer, that is, the overcoat layer of the thermal transfer recording medium, which is in contact with the transfer paper, the thermal head during recording can be obtained. The granular elastomer enters the concave portions of the low-smoothness receiving paper at a pressure of, and as a result, the contact area between the receiving paper and the surface layer, that is, the overcoat layer in the thermal transfer recording medium increases, and the transferability of the ink layer also improves. It was confirmed that a good quality printed image could be obtained. The present invention has been made based on the above.

Hereinafter, the thermal transfer recording medium of the present invention will be described in more detail.

The layer structure of the thermal transfer recording medium in the present invention is, as easily deduced from the above description, (1) an ink layer is provided directly on a support or via a release layer, and a granular layer is formed on the ink layer. Examples thereof include those in which an overcoat layer containing an elastomer is formed, and (2) those in which an adhesive layer is formed between the support and the release layer in the above (1).

As the support (base film) in the present invention,
Examples thereof include plastic films having relatively high heat resistance, such as polyester, polycarbonate, polyacetylcellulose, nylon, and polyimide, as well as glassine paper, condenser paper, metal foil, and composites of the above materials. As the composite, for example, aluminum /
Examples thereof include a paper composite, metal-deposited paper, and metal-deposited plastic film.

When considering the thermal head as a heat source at the time of thermal transfer, the thickness of the support is desirably about 2 to 15 microns.For example, when using a heat source that can selectively heat a thermal transfer ink layer such as a laser beam. Is not particularly limited. When using a thermal head, provide 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 thermal head. Thus, the heat resistance of the support can be improved, or a support material that could not be used conventionally can be used.

For the adhesive layer provided as necessary, rubber or a mixture of rubber and wax can be used. Examples of the rubber used include isoprene rubber, butadiene rubber, styrene butadiene rubber, nitrile rubber, ethylene propylene rubber, styrene propylene rubber, butyl rubber, silicone rubber, fluorine rubber, urethane rubber and the like. Particularly preferred are isoprene rubber, butadiene rubber, ethylene propylene rubber, butyl rubber,
Nitrile rubber. The melting point is preferably from 60 to 200 ° C. As waxes, natural substances such as beeswax, whale wax, candelilla wax, carnauba wax,
Rice bran wax, montan wax, ozokerite, etc., and also, as petroleum wax, paraffin wax,
Examples include polyethylene wax, microcrystalline wax, and the like, as well as various modified waxes, hydrogenated waxes, long-chain fatty acids, and the like.

The thickness of the adhesive layer is 0.01-3 μm, preferably 0.1-1 μm
m.

The release layer, which improves the releasability between the base film and the colored layer (ink layer) during printing, is heated by a thermal head and then melted by heat to form a low-viscosity liquid. What is necessary is just to be comprised so that it may be easy to cut. Therefore, as a main component of the release layer, a wax-like substance that is hard at room temperature and melts when heated is preferably used.

Such wax-like substances include, for example, natural waxes such as beeswax, carnauba wax, spermaceti wax, wood wax, cadelilla wax, rice bran wax, montan wax, etc .: paraffin wax, microcrystalline wax, oxidized wax, ozokerite, In addition to synthetic waxes such as ceresin, ester wax, and polyethylene wax, margaric acid, lauric acid, myristic acid, palmitic acid, stearic acid, and furomenic acid are preferably used.
Higher fatty acids such as behenic acid: higher alcohols such as stearyl alcohol and behenyl alcohol: esters such as fatty acid esters of sorbitan: amides such as stearinamide and oleinamide.

The thickness of the release layer is 0.5 to 8 μm, preferably about 1 to 5 μm. The ink layer contains a binder and a colorant as main components, and when the paper to be transferred has low smoothness, the ink easily penetrates into the paper. It is desirable that the composition be prepared such that it does not have a melting point and that the thermal energy at the time of recording causes stickiness to the transfer receiving paper but does not melt to form a low-viscosity liquid.

Preferred examples of the binder include an ethylene-vinyl acetate copolymer, an ethylene-ethyl acrylate copolymer, and a polyester resin, and a polyamide resin, an epoxy resin, a polyurethane resin, an acrylic resin, and a vinyl chloride resin. Elastomers such as cellulose resin, polyvinyl alcohol resin, petroleum resin, phenolic resin, styrene resin, natural rubber, styrene butadiene rubber, isoprene rubber, and chloroprene rubber. Further, as an auxiliary material of these binders, a tackifier such as terpene resin, coumarone resin, rosin and derivatives thereof, wax, oil and the like can be added.

On the other hand, the colorant is appropriately selected from conventionally known dyes and pigments.As the dye, a basic dye, an oil-soluble dye, an acid dye, a direct dye, a disperse dye, and the like are suitably used. As the pigment, carbon black, phthalocyanine-based pigment and the like are preferably used.

The thickness of the ink layer is 0.5-4 μm, preferably 1-3 μm
m is appropriate.

The overcoat layer is a layer for preventing background stains and improving the printing quality on low-smoothness paper. The overcoat layer contains wax as a main component, and contains an adhesive, a viscosity modifier, and the like as necessary. is there.

The thickness of the overcoat layer is 0.1 to 3 μm, preferably
It is about 0.5 to 2 μm.

By the way, in the thermal transfer recording medium of the present invention, as mentioned above, it is necessary that the layer (overcoat layer) in contact with the paper to be transferred contains a viscous elastomer.

The particle size of the particulate elastomer should be in the range 0.5 to 10 μm, preferably 1 to 5 μm, and smaller than the thickness of the layer containing it. Also,
The amount of particulate elastomer in the layer is between 5 and 60% by volume, preferably between 20 and 40% by volume.

The term “elastomer” generally means a polymer substance exhibiting remarkable elasticity, which can be classified into (1) vulcanized rubber,
(2) thermoplastic elastomer, (3) elastic fiber, (4)
Although it is divided into elastic foams and the like, particularly preferred elastomers in the present invention include synthetic rubbers such as natural rubber, butadiene rubber, styrene butadiene rubber, and nitrile butadiene rubber.

Actually, in order to make the thermal transfer recording medium of the present invention, the above-mentioned layers may be sequentially formed on a support film by a hot melt method, a solvent dispersion coating method, an aqueous emulsion coating method, etc. Must select a solvent that does not melt the granulated elastomer.

〔Example〕

Next, examples and comparative examples will be described. All parts here are parts by weight.

Example 1 (Preparation of release layer forming liquid) A mixture consisting of 95 parts of paraffin wax, 5 parts of ethylene-vinyl acetate copolymer, was heated to about 120 ° C, and then heated with a ball mill.
The mixture was dispersed for a time to obtain a release layer forming liquid.

(Preparation of Colored Layer Forming Liquid) A mixture consisting of 5 parts of ethylene-ethyl acrylate copolymer, 3 parts of polyethylene wax, 2 parts of carbon black and 90 parts of toluene was dispersed in a ball mill for 15 hours to obtain a colored layer forming liquid.

(Preparation of Overcoat Layer Forming Solution) Butadiene rubber emulsion (particle size: 1-2 μm, solid content: 57%) 14 parts Ethylene-vinyl acetate copolymer emulsion 30 parts Water 30 parts Methanol 26 parts Thus, an overcoat layer forming liquid was obtained.

On a polyester film of about 4.5 μm thickness, the release layer forming liquid is hot melt coated so as to have a thickness of about 4 μm when dried, and the colored layer forming liquid is then dried with a thickness of about 2 μm and then the overcoat layer forming liquid. A heat transfer recording medium was prepared by wire bar coating to a thickness of about 2 μm.

Comparative Example 1 A thermal transfer recording medium was prepared in the same manner as in Example 1, except that 14 parts of a butadiene rubber emulsion was omitted from the overcoat layer forming liquid.

Using these two types of thermal transfer recording media, bond paper (Beck smoothness 5 to 5) was obtained using a commercially available thermal transfer printer.
At 6 seconds), printing was performed, and each of whether there was no white spot and whether the sharpness was good was visually evaluated. The results were as shown in Table 1.

[Effects of the Invention] As can be seen from the description of the examples, by including a particulate elastomer in the overcoat layer of the thermal transfer recording medium, there is no white drop even on a low-smoothness receiving paper and good sharpness is obtained. A good printed image can be obtained.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B41M 5/38-5/40

Claims (1)

(57) [Claims] 1. A thermal transfer recording medium in which at least a heat-meltable or thermosoftening ink layer and an overcoat layer are formed on a support, wherein the overcoat layer contains a particulate elastomer. Medium.