Incremental printing of symbolic information – Thermal marking apparatus or processes – Specific resistance recording element type
Patent
1996-01-16
1997-10-21
Tran, Huan H.
Incremental printing of symbolic information
Thermal marking apparatus or processes
Specific resistance recording element type
347208, B41J 2335
Patent
active
056801700
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a thermal printhead, particularly to a structure provided for a head substrate of a thermal printhead.
BACKGROUND ART
Thermal printheads have been widely used for a printer of an OA apparatus such as a facsimile machine, a printer of a ticket vending machine and a label printer. As is commonly known, a thermal printhead selectively provides heat to a printing medium such as thermosensitive paper or thermal-transfer ink ribbon to form needed image information.
In general, thermal printheads are divided mainly into thin film-type thermal printheads and thick film-type thermal printheads depending upon methods of forming their heating resistors and electrode conductor layers for example. In a thin film-type thermal printhead, a heating resistor and an electrode conductor layer are made in the form of a thin film on a substrate or a glass glaze layer by sputtering for example. On the other hand, in a thick film-type thermal printhead, at least the heating resistor is made in the form of a thick film through such steps as screen printing and sintering. The present invention is applicable to both the thin film-type and thick film-type thermal printheads.
For convenience of an explanation, a structure of a typical thick film-type thermal printhead by the prior art is shown in FIG. 14. The thermal printhead shown in the figure comprises an insulating head substrate 21 made of e.g. ceramic material. The head substrate 21 has an obverse surface formed with a glass glaze layer 22 as a heat reservoir, whereas the surface of the glaze layer 22 is formed with a linear heating resistor 23 in the form of a thick film. Further, the surface of the glaze layer 22 is formed with a common electrode pattern 22 having comb-like teeth electrically connected to the heating resistor 23 and with a plurality of individual electrodes 25 electrically connected to the same heating resistor 23, wherein the comb-like teeth of the common electrode pattern 25 divide the linear heating resistor 23 into a plurality of heating dots.
Further, the surface of the glaze layer 22 is formed with a plurality of drive ICs 26 to supply an electric current to the heating resistor 23, wherein each drive IC 26 is connected, via bonding wires 27, to a predetermined portion of the individual electrode 25 and to a predetermined portion of a circuit pattern (not shown) which is formed on the glaze layer 22. The drives IC 26 are enclosed together with the bonding wires 27 by a protecting resin body.
In operation, with the common electrode pattern 24 being kept at a predetermined electrical potential, the heating dots of the heating resistor 23 are selectively actuated to generate heat by selectively passing a current from the drive ICs via the individual electrodes 25. As a result, predetermined images are formed on a printing medium (thermosensitive paper for example) 30 which is backed up by a platen 29.
In the case of a thermal printhead having the above-described structure, a heating resistor 23 is preferably formed as close to a longitudinal edge of the head substrate 21 as possible. This is because the arrangement wherein the heating resistor 23 is formed adjacent to the longitudinal edge of the head substrate 21 advantageously serves not only to avoid interference of the printing medium 30 and the protecting resin body 28 with each other, but also to highten degrees of positioning freedom and printing quality, by holding the head substrate 21 relative to the platen 29 at a certain angle.
However, if the heating resistor 23 is provided adjacent to the longitudinal edge of the head substrate 21, spacing for formation of the common electrode pattern 22 is rendered correspondingly small, thereby failing to ensure a sufficient current capacity (current passage) necessary for heat generation. As a result, the resistance of the common electrode pattern 24 may become disadvantageous, causing irregularities of generated heat between the heating dots due to a voltage drop in the longitudinal direction of the he
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Hoki Hideaki
Nakanishi Masatoshi
Takakura Toshihiko
Taniguchi Hideo
Bednarek Michael D.
Rohm & Co., Ltd.
Tran Huan H.
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