Incremental printing of symbolic information – Ink jet – Medium and processing means
Patent
1996-10-17
1998-06-02
Fuller, Benjamin R.
Incremental printing of symbolic information
Ink jet
Medium and processing means
3461401, B41J 201, G01D 1516
Patent
active
057608083
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a thermoelectric printing unit for transferring an ink onto a recording medium. Various thermoelectric printing units are known:
In thermal printing, heat-sensitive paper is printed by a heatable printing head as a result of the heating of selected points on the paper, the heated points changing color.
In the thermal transfer printing method, a color-containing wax layer located on a carrier foil is partially melted by means of heatable printing elements and is transferred onto paper.
In a thermal ink printing unit, ink is sprayed out of a nozzle onto a recording medium. The nozzles have a heating device which can be activated individually for each nozzle. The ink contained in the nozzle is heated by the heating device, thereby producing a gas bubble which expels the ink from the nozzle.
In this case, a liquid which contains color pigments serves as ink. Furthermore, it is heat-resistant to approximately 350.degree. C., is nontoxic, being made, for example, on a water base, and causes no deposit in the nozzles.
Conventionally, the nozzles are located in a printing head. The printing head has an ink supply, from which the nozzles are supplied with ink by means of capillary forces. The maximum spray frequency of such ink-jet printing units having a thermoelectric converter (bubble jet) is limited to approximately 4 kHz. Depending on the drop size, the ink needs 250 .mu.s and above before the ink sucked up as a result of the capillary forces is available for the next spray operation. In contrast, the activation time for the heating element in the nozzle of approximately 5 to 10 .mu.s and the time to drop formation of approximately 50 .mu.s are relatively short. As a consequence of the principle used, the spray frequency cannot be appreciably increased.
U.S. Pat. No. 4,785,311 discloses a cylindrical printing roller, the casing of which has a plurality of passage orifices for a high-viscosity ink which are arranged in a matrix-like manner. The ink is stored inside the printing roller. Each passage orifice is assigned a selectively activatable heating element, by means of which a throughflow of the ink through the passage orifice can be released. Due to gravity, the released ink flows directly onto a recording medium which is in touch contact with the corresponding surface of the printing roller, said surface being located in the region of the released passage orifice.
The printing speed can be increased by means of the known printing roller. Since the printing roller is in direct contact with the recording medium as a consequence of the principle used, there is the risk that the passage orifices will become soiled and consequently the quality of the printing image reduced. Furthermore, on account of the direct contact between the printing roller and recording medium, it is absolutely necessary to arrange the passage orifices on the printing roller as an endless matrix according to the resolution of the printing image. The fineness of the resolution of the printing image is thereby limited, since a large number of passage orifices have to be coupled electrically to an activation unit and the coupling paths cannot be reduced as desired. On account of the storage of the ink in the printing roller, it is extremely difficult to carry out a change of the printing ink when the same printing roller is used.
SUMMARY OF THE INVENTION
The object on which the present invention is based is to provide a thermoelectric printing unit for transferring an ink onto a recording medium, said printing unit making it possible to control the printing speed without losses in the resolution of the printing image, in the quality of the printing image and in the serviceability of the thermoelectric printing unit.
In general terms the present invention is a thermoelectric printing unit for transferring an ink onto a recording medium. The printing unit has a printing drum. More than one matrix row of printing elements which are arranged on the printing drum and which are each designe
REFERENCES:
patent: 3655379 (1972-04-01), Gundlach
patent: 4608577 (1986-08-01), Hori
patent: 4627346 (1986-12-01), Dietzell et al.
patent: 4630075 (1986-12-01), Hori
patent: 4785311 (1988-11-01), Kaneko et al.
patent: 4855768 (1989-08-01), Lino
patent: 5081472 (1992-01-01), Fisher
patent: 5481280 (1996-01-01), Lam et al.
Patent Abstracts of Japan, M-787, vol. 13, No. 25, Jan. 20, 1989, JP-A-63-236-656.
Fuller Benjamin R.
Nguyen Thinh
Oce Printing Systems GmbH
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