JPS62140882A - Transfer-type thermal recording medium - Google Patents

Abstract

PURPOSE:To contrive formation of high-quality printed images having excellent clearness and fixability irrespective of the smoothness of a transfer recording material, by a construction wherein a heat-sticking main constituent of a thermally transferrable ink layer is constituted of an ethylene-vinyl acetate copolymer, which comprises at least 15wt% of vinyl acetate, and a resin difficultly compatible with the copolymer, the amount of the resin being 5-50wt% based on the amount of the copolymer. CONSTITUTION:A transfer-type thermal recording medium comprises, for example, a heat-resistant base 1, a releasable layer 2 and a thermally transferrable ink layer 3. An ethylene-vinyl acetate copolymer incorporated in the ink layer comprises at least 15wt% of vinyl acetate. A resin difficultly compatible with the copolymer resin, which separates out when being left to stand after being mixed with the copolymer resin in a thermally melted state, is a highly polar resin which is soluble in a solvent used for the copolymer resin, and is, for example, ethyl cellulose or a vinyl chloride- vinyl acetate copolymer. Such a resin is added in an amount of 5-50wt% based on the amount of the ethylene-vinyl acetate copolymer, whereby preservability and anti-blocking properties can be enhanced while maintaining sensitivity and image quality and without increasing the number of manufacturing steps.

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to a recording medium used for transfer-type thermal recording, and more specifically, it relates to a recording medium used for transfer-type thermal recording, and more specifically, a recording medium that is capable of clear and strong recording regardless of the shape or properties of the surface of the transfer medium. The present invention relates to a transfer type thermosensitive recording medium.

[Prior art] The transfer type thermal recording method is popular as a plain paper recording method with a simple device, but the print quality is easily affected by the smoothness of the surface of the transfer paper, and the transfer paper has a poor surface smoothness. It was difficult and rare to print clearly on the paper. Various attempts have been made to improve these drawbacks.

For example, heat treatment after printing (Japanese Patent Laid-Open No. 58-76276)
, magnetic force during transfer (JP-A-52-96549) and electrostatic force (
The melt viscosity during transfer is lowered by using auxiliary means such as JP-A-55-65590), or by adding a large amount of oily substance (JP-A-60-25762), or by adding a thermally decomposable substance ( Measures have been proposed such as adding a heat-expandable substance (JP-A-60-82389) or a thermally expandable substance (JP-A-60-25762) to increase sensitization.Also, multi-layered heat-melting ink layers have been proposed. Techniques for improving print quality are also known, such as forming a heat-melting ink layer into two layers with slightly different melting points, and adding a pigment to either one layer or both layers ( Japanese Patent Publication No. 59-224
392), a layer made of a heat-melting substance containing no colorant is provided on the melting ink layer (Japanese Patent Laid-Open No. 60-9788)
8) and other technologies have been proposed. However, all of these conventional methods record by transferring ink that has melted into a liquid state, and with these methods, if the surface of the transfer medium is low, the smoothness of the surface may be affected. In comparison with high-quality transfer paper, only inferior print quality can be obtained, and the conventional drawback that print quality depends on the smoothness of the surface of the transfer medium cannot be fundamentally solved.

On the other hand, by providing an ink layer mainly composed of a resin that exhibits tackiness due to the thermal energy applied during printing but does not melt into a low-viscosity liquid and has a certain degree of mechanical strength, the surface It is known that high-quality printing can be obtained even on transfer media with poor surface smoothness by applying ink to the convex portions of the surface of the transfer paper and transferring the ink to cover the concave portions. ing. An ink layer containing such a resin can firmly fix a printed image not only on paper but also on a transfer medium such as a plastic film. However, if an ink layer whose main component is such a resin has a thermal sensitivity that enables transfer using the thermal energy of a thermal head, an ink layer whose main component is a wax that has the same level of thermal sensitivity It has the disadvantage that it has stronger adhesiveness at low temperatures than that of 100%, and is more likely to cause blocking during storage before use. In order to eliminate these drawbacks, measures such as increasing the amount of pigment added, using a resin with a higher melting point, adding wax, or providing an anti-blocking layer on the side opposite to the ink layer are available. However, all of these methods are undesirable because they lead to new drawbacks such as poor sensitivity, reduced strength during heat softening, and increased cost due to increased number of steps.

[Purpose] The present invention is capable of producing high-quality printed images with excellent clarity and fixation properties, regardless of whether paper with a low surface smoothness or plastic film with a high surface smoothness is used as a transfer medium. The object of the present invention is to obtain a transfer-type heat-sensitive recording medium with high thermal sensitivity, which is easy to form, has excellent blocking resistance, and is easy to manufacture.

[Structure] That is, the present invention provides a transfer-type thermal recording medium in which a heat-transferable ink layer consisting of one or more layers is provided on a heat-resistant support, in which the layer closest to the transfer medium of the ink layer is used for printing. Ethylene-vinyl acetate, which exhibits tackiness due to thermal energy at the time of heating, does not melt into a low-viscosity liquid, and whose main thermo-adhesive component contains 15% by weight or more of vinyl acetate as a copolymer component. a polymer;
This ethylene vinyl acetate copolymer and a resin that is difficult to mix with the ethylene vinyl acetate copolymer, and the content of the resin that is difficult to mix with the ethylene vinyl acetate copolymer is 5 to 50% by weight based on the ethylene vinyl acetate copolymer. The gist of the present invention is a transfer type thermosensitive recording medium characterized by the following.

To explain the present invention in detail below, as the heat-resistant support used in the transfer type heat-sensitive recording medium of the present invention, known ones such as polyester film and polyimide film can be used. Films that generate heat are preferred.

The heat transferable ink layer formed on the heat-resistant support is
It may be a single layer or a laminate of multiple layers; in the case of a single layer, the only layer is the layer farthest from the support, i.e., the top layer or surface layer, or When a layer called the overcoat layer is applied with natural energy, it exhibits stickiness, but it does not melt into a low viscosity liquid and is adjusted to have a certain degree of mechanical strength. Such adjustment cannot be achieved by using wax as the main component, but is made possible by using an appropriate resin.

Polyamide resins, polyester resins, polyvinyl acetate resins, and ethylene-vinyl acetate copolymers are examples of resins that exhibit stickiness when heat energy is applied, but have enough mechanical strength to melt without becoming a low-viscosity liquid. As a result of intensive research by the present inventors, we found that ethylene vinyl acetate is the main component of the layer closest to the transfer medium due to its sensitivity, fixing power, flexibility, pigment dispersibility, etc. Copolymers were found to be most suitable.

The properties of the ethylene vinyl acetate copolymer vary greatly depending on the ratio of ethylene and vinyl acetate, but for the purpose of the present invention, it is desirable that the vinyl acetate content be 15% by weight or more.

In the present invention, the resin that is difficult to miscible with the ethylene vinyl acetate copolymer resin refers to a resin that has a relationship such that even if it is mixed in a heated molten state, it will separate when left to stand, and it has a large polarity. Resins such as polyamide resins, cellulose resin derivatives such as ethyl cellulose, resins having large substituents that sterically hinder side chains such as polystyrene, polyvinyl chloride, vinyl chloride vinyl acetate copolymers, etc. However, resins that are soluble in solvents that dissolve ethylene vinyl acetate copolymer resins, such as ethyl cellulose and vinyl chloride vinyl acetate copolymers, are particularly desirable. The content of such resin is 5 to 50% by weight based on the ethylene vinyl acetate copolymer,
By adding in this amount, storage stability and blocking resistance can be improved without impairing sensitivity or image quality or increasing the number of manufacturing steps.

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

Example 1 30 parts by weight of a 20% toluene solution of EVAFLEX 21α (manufactured by Mitsui Polychemicals), an ethylene-vinyl acetate copolymer with a vinyl acetate content of 28% by weight, 30 parts by weight of ethyl cellulose (ethyl cellulose K type, manufactured by Percules) 20% toluene solution 1265 parts by weight Carbon black 1.5 parts Toluene 20 parts by weight The above composition was kneaded and dispersed in a ball mill for 20 hours to prepare an ink layer liquid. This ink layer liquid was applied onto a polyimide film having a thickness of 7 μm using a wire bar so that the thickness after drying would be 5 μm, and was dried to obtain a transfer type thermosensitive recording medium 1 of the present invention.

FIG. 1 is a sectional view showing the layer structure of the transfer type thermosensitive recording medium thus obtained, in which 1 is a heat-resistant support and 3 is an ink layer.

Example 2 Ink layer liquid composition 2 2 of ethylene vinyl acetate copolymer (Sumitate KA-10 manufactured by Sumitomo Chemical) with a vinyl acetate content of 28% by weight
0% toluene solution 35 parts by weight Vinyl chloride vinyl acetate copolymer (densa vinyl
20% methyl ethyl ketone (MEK>28 liquid 9 parts by weight carbon black 1.2 parts by weight toluene/
M E K = 80/20 mixed solvent 20 parts by weight The above composition was treated in the same manner as in Example 1 to prepare an ink layer liquid. A release layer was formed on a 6 μm thick polyester film by hot melt coating microcrystalline wax (manufactured by Nippon Oil Co., Ltd.) heated to 155° F. to a thickness of 2 μm. Next, the ink layer liquid was applied onto the release layer using a wire bar so that the thickness after drying would be 5 μm, and dried to obtain the transfer type thermosensitive recording medium 2 of the present invention.
I got it.

FIG. 2 is a cross-sectional view of the transfer type thermosensitive recording medium thus obtained, in which 1 is a heat-resistant support, 2 is a release layer, and 3 is an ink layer.

As a comparative example, an ink layer was prepared in the same manner as in Example 1 except that ethyl cellulose was removed from Ink Layer Liquid Composition 1 of Example 1 and carbon black was increased by that amount.
A transfer type thermosensitive recording medium 3 having the structure shown in the figure was prepared. Furthermore, as a comparative example, an ink layer was prepared in the same manner as in Example 2, except that the vinyl chloride vinyl acetate copolymer was removed from the ink layer liquid composition 2 of Example 2, and the amount of ethylene vinyl acetate copolymer was increased by that amount. A transfer type thermosensitive recording medium 4 having the structure shown in FIG. 2 was prepared.

The products of the present invention and comparative products obtained as described above were tested for print quality and storage stability as described below, and the results are shown in Table 1.

Print quality test Transfer type thermal recording media 1 and 3 were printed on bond paper by applying thermal energy of 2.5 mJ/dat using an 8 dot/city line head type printing tester.

For transfer type thermal recording media 2 and 4, printing was performed on bond paper using a serial type thermal printer TP2220 manufactured by Ricoh.

Preservability Test Transfer type thermal recording media were stacked so that the ink side and back side were in contact with each other, a load of 1 kg was applied, and the medium was left at 50'C for 72 hours to check for occurrence of blocking.

Table 1 As is clear from the above results, the products of the present invention had clear prints, did not cause blocking during storage, and were highly satisfactory. It was also confirmed that the print fixation was also good.

On the other hand, in the case of the comparative product, all properties were inferior to the product of the present invention, and especially in the storage test, blocking was severe and the ink layer was partially or completely peeled off. Further, regarding the transfer thermosensitive recording medium 4, when the ink surfaces were brought into contact with each other, they tended to stick and were difficult to handle.

Although the above results were obtained using bond paper with a relatively rough surface as the transfer medium, the product of the present invention also produced clear prints with good fixing properties when printed on a polyester sheet with a smooth surface.

[Effects] As described above, according to the transfer type thermal recording medium of the present invention, good print quality can always be obtained regardless of the surface condition and quality of the transfer medium, and there is no blocking or ink during storage. The ink layer is not damaged due to adhesion between layers. Moreover, as is clear from the examples, it can be easily manufactured industrially.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the structure of an embodiment of a transfer type thermosensitive recording medium of the present invention, and FIG. 2 is a sectional view showing the structure of another embodiment. 1...Heat-resistant support, 2...Peeling layer 3...Ink layer

Claims (1)

[Claims] In a transfer-type thermosensitive recording medium in which a heat-transferable ink layer consisting of one or more layers is provided on a heat-resistant support, the layer closest to the transfer medium of the ink layer exhibits tackiness due to thermal energy during printing. , an ethylene vinyl acetate copolymer that does not melt into a low viscosity liquid and whose heat-adhesive main component contains 15% by weight or more of vinyl acetate as a copolymer component, and this ethylene vinyl acetate copolymer. The content of the resin that is difficult to miscible with the ethylene vinyl acetate copolymer is 5 to 50% of the ethylene vinyl acetate copolymer.
A transfer type heat-sensitive recording medium characterized in that it is a weight percent.