Incremental printing of symbolic information – Thermal marking apparatus or processes – Specific resistance recording element type
Patent
1997-03-12
1999-11-30
Le, N.
Incremental printing of symbolic information
Thermal marking apparatus or processes
Specific resistance recording element type
29611, B41J 2335
Patent
active
059951273
DESCRIPTION:
BRIEF SUMMARY
INDUSTRIAL FIELD OF APPLICATION
The present invention relates to a thermal print head for use in thermal printing apparatus such as a plate-making machine, a facsimile apparatus or a video printer, and a manufacturing method thereof.
BACKGROUND ART
Thermal print heads, which have advantages such as low in noise, simple in maintenance or low running costs, have been widely used in various sorts of recording apparatuses including printers for use in facsimile apparatuses and word processors. In particular, thermal print heads providing high definition of more than about 400 dpi (dots per inch) have been used for stencil printing.
Among various thermal print heads, the ones which are for use in facsimile machines and word processor printers have been strongly demanded to have a finer heating resistor and an increased input energy density for the purpose of improving their resolution. Therefore, these thermal print heads are required to meet such a demand.
In order to satisfy the demand, the thermal print head is first required to have a heating resistor of a high resistive value.
As the materials of the heating resistor, cermet system resistors are widely used. Typical cermet systems are Ta--Si--O and Nb--Si--O. These materials are formed, for example, as a sputter film with use of a sputtering target prepared by mixing Ta and SiO.sub.2 powder and sintering thereof. At this time, a film having a resistivity of several m.OMEGA. to several tens m.OMEGA. can be formed while the amount of SiO.sub.2, sputtering pressure, etc. is controlled.
Meanwhile, for the purpose of obtaining a heating resistor having a high resistive value, there is a method of devising the design of the heating resistor. In the case of the thermal print head, however, it is desirable to make the sheet resistance of the sputter film high per se. To this end, it is considered to make the film thin to thereby have a high sheet resistance. However, making the film thickness small leads to a short life problem with the thermal print head. For the above reason, it is desirable that the film has a high resistivity.
Secondly, it is necessary for the resistive value of the heating resistor to fluctuate less when the heating resistor is used as a thermal print head or during the manufacture of the head on an assembly line.
A Ta--Si--O film has an excellent feature as a heating resistor, but tends to be influenced by its film forming conditions. Accordingly, when the film has a small resistivity, the film is made thinner, which leads to its poor life characteristics. When the film has a large resistivity, on the other hand, the film is required to be thicker, thus prolonging its film forming time. This also disadvantageously results in that the number of substrate films capable of being formed per target is decreased. From these reasons, a resistivity range is usually controlled to be usually about 10 to 20 m.OMEGA..multidot.cm for manufacturing of the film.
Even when the resistivity range of the heating resistor is limited as above, however, it has been found that, when the resistors are manufactured in the form of thermal print heads or devices, the devices have varying characteristics. This means that, even when the resistive films have an identical resistance, they may have respectively different structures. The film structure includes, for example, the degree or range of order and various other defect sorts and densities.
It is difficult to grasp such a film structure on a quantitative basis and to strictly control it. For example, with respect to a film deposited as it is and a film deposited and subjected to a vacuum process at a temperature of 900.degree. C., even when these films are subjected to a comparative analysis based on an X-ray diffractometry or a Raman spectroscopy, they fail to show a significant difference between them, exhibiting similarly broad amorphous patterns. For this reason, it has been difficult to realize a heating resistor having a good life characteristic and also to implement a thermal print head having a good life
REFERENCES:
patent: 4705697 (1987-11-01), Nishiguchi et al.
patent: 4772520 (1988-09-01), Takeno et al.
patent: 4777583 (1988-10-01), Minami et al.
patent: 4845339 (1989-07-01), Kato
patent: 5473357 (1995-12-01), Shirkawa et al.
patent: 5756411 (1998-05-01), Nakahata et al.
Form PCT/ISA/210 for PCT/JP95/01818, Sep. 13, 1995.
Kabushiki Kaisha Toshiba
Le N.
Vo Anh T. N.
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