Stock material or miscellaneous articles – Composite – Of wax or waxy material
Patent
1995-04-26
1997-03-18
Hess, Bruce H.
Stock material or miscellaneous articles
Composite
Of wax or waxy material
428195, 4284881, 428500, 428913, 428914, B41M 526
Patent
active
056121407
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a thermal transfer recording medium which is devised to form print images of high quality even on a paper sheet having poor surface smoothness (hereinafter referred to as "rough paper"). Hereinafter this thermal transfer recording medium is referred to as "rough paper-adaptable thermal transfer recording medium".
BACKGROUND ART
A conventional rough paper-adaptable thermal transfer recording medium uses the so-called bridgingly transferable heat-meltable ink layer which is transferred as bridging over depressed portions of a rough paper while adhering to only protruded portions thereof. In order to impart such bridging transferability to an ink layer, a heat-meltable material having a high melt viscosity such as a high melt viscosity resin, for example, ethylene-vinyl acetate copolymer, is used as a main component of the vehicle thereof.
However, such an ink layer having a high melt viscosity is poor in fixing property and, hence, involves drawbacks such as falling-off of print images obtained therefrom due to abrasion or the like. In order to improve the fixing property of such an ink layer, a large amount of energy must be applied during thermal transfer.
A heat-meltable material having a high melt viscosity shows a small viscosity change over the temperature range of temperatures in the vicinity of ordinary temperature to transferring temperature due to the characteristics of the material.
FIG. 1 is a graph schematically showing relationships between temperature and melt viscosity with respect to various heat-meltable materials. Curve B shows a viscosity curve of an ethylene-vinyl acetate copolymer having a high melt viscosity.
As described above, a heat-meltable material having a high melt viscosity shows a small viscosity change and, hence, when it is attempted to lower the viscosity of the material at a temperature for transferring in order to improve fixing property of print images, the material shows a low viscosity even at temperatures in the vicinity of ordinary temperature, as shown in Curve C of FIG. 1.
Accordingly, when an ink layer is adapted to be transferred with a small amount of energy, the ink layer exhibits poor bridging transferability and also has a decreased softening point, resulting in the following drawback. When printing is performed continuously, heat is accumulated in a thermal head to heat the overall head. Since the softening point of the ink layer is low, portions of the ink layer which correspond to non-activated heat generating dots are also softened, resulting in scumming of a receptor paper.
In view of the foregoing, an object of the present invention is to provide a thermal transfer recording medium which exhibits good bridging transferability and fixing property and has a high softening temperature, thereby forming clear print images even on a rough paper with a small amount of energy and causing no scumming of a receptor paper even in continuous printing.
DISCLOSURE OF THE INVENTION
The present invention provides a thermal transfer recording medium comprising a foundation and a heat-meltable ink layer provided on the foundation, the ink layer containing 50 to 80% by weight of an ethylene-vinyl acetate copolymer having a vinyl acetate content of not more than 19% by weight, 0 to 20% by weight of a wax having a melting point of 70.degree. to 90.degree. C., 0 to 20% by weight of a resin having a glass transition point of 50.degree. to 140.degree. C., and 20 to 50% by weight of a coloring agent, provided that at least one of the wax having a melting point of 70.degree. to 90.degree. C. and the resin having a glass transition point of 50.degree. to 140.degree. C. is necessarily contained, the vehicle in the ink layer having a softening point of 60.degree. to 85.degree. C., a melt viscosity at 100.degree. C. of not lower than 1,000 poises and a melt viscosity at 160.degree. C. of not higher than 400 poises.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a graph showing melt viscosity curves of a heat-meltable ink layer used
REFERENCES:
patent: 4983445 (1991-01-01), Ueyama
Fujicopian Co. Ltd.
Hess Bruce H.
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