Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Physical dimension specified
Patent
1988-03-21
1989-07-18
Robinson, Ellis P.
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Physical dimension specified
428323, 428409, 4284744, 428913, 428914, B41M 526
Patent
active
048492876
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to an image transfer material (such as ink ribbon and ink sheet) for thermal recording of the electric current-conducting type.
BACKGROUND ART
Recently, the thermal image transfer recording system is used in addition to the electrophotographic, ink jet and electrostatic recording system. As one of the thermal image transfer recording systems, the electric current-conducting system has been proposed. In this system, instead of giving thermal energy to the ink layer with a thermal head, electric current is conducted through an electroconductive film having a certain electric resistance, and the ink layer is melted or sublimated by the generated Joule's heat. For example, U.S. Pat. No. 4,103,066 discloses the use of a polycarbonate film containing carbon black as a base film of the material. Also, U.S. Pat No. 4,269,892 discloses the use of a polyester resin containing carbon black as the base film of the material. However, since the above-mentioned resins have poor affinity (wettability and the like) for the carbon black, the obtained films have poor mechanical characteristics. For example, as stated in U.S. Pat. No. 4,269,892, polycarbonate has small tensile elongation and the polyester has a tensile strength of as low as 4 kg/mm.sup.2. Further, if a large current is conducted for the purpose of high speed printing, since the heat resistance of the film is not sufficient, the film may be thermally deformed or pinholes may be formed in the film. Thus, it is difficult to conduct high speed printing which generates much heat. Further, to compensate for this disadvantage, the film should have a thickness as great as 15 .mu.m or more.
DISCLOSURE OF THE INVENTION
The present invention solves the above-mentioned problems and provides an image transfer material for thermal recording, which has a small thickness, by which high speed printing can be conducted and good printing quality can be obtained, and which is free from film breakage, wrinkles and pinholes.
That is, the present invention provides an image transfer material for thermal recording comprising an aromatic polyamide film with a thickness t (.mu.m) of 1-10 .mu.m, which film contains 10-40% by weight of carbon black and has a tensile strength in at least one direction of not less than 8 kg/mm.sup.2, the specific surface resistivity Rs (K.OMEGA./.quadrature.) of the film satisfying the relationship of 2.ltoreq.Rs x t.ltoreq.100, the dimensional change of the film in at least one direction at 200.degree. C. under the load of 1 kg/mm.sup.2 being not more than 5%; and an ink layer formed on the film.
Since an aromatic polyamide having a good affinity for the carbon black (wettability) is used as the polymer constituting the base film, adding a large amount of carbon black does not degrade the mechanical characteristics of the film and the small thickness of 1-10 .mu.m of the film does not bring about wrinkles and film breakage during a run. Since the thinness of the film reduces the thermal diffusion, topical heating of the ink can be accomplished, so that the printing quality may greatly be improved. Further, since the heat capacity of the film, and in turn, the recording energy is reduced, the size of the power supply, cassette and the like may be reduced, so that the printer can be made compact.
On the other hand, in cases where high speed printing is desired, a large amount of energy can be given and the high speed printing can be accomplished without causing heat damage and pinholes. Although the reason why the pinholes are scarecely formed is not clear, it is assumed that since the base film is not deformed in printing due to high dimensional stability at high temperature, defects such as voids are unlikely to be formed; or even if the dimension is slightly changed, defects such as voids are unlikely to be formed because the affinity of the polymer for the carbon black is good. By employing a film having, in addition to the heat resistance, excellent affinity for carbon black, i.e., by employing a film havi
REFERENCES:
patent: 4103066 (1978-07-01), Brooks et al.
patent: 4269892 (1981-05-01), Shattuck et al.
Itoh Nobuaki
Kobayashi Hiroaki
Mizouchi Masanori
Miller Austin R.
Robinson Ellis P.
Schwartz P. R.
Toray Industries
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