Metal working – Method of mechanical manufacture – Electrical device making
Patent
1997-02-10
1999-11-09
Echols, P. W.
Metal working
Method of mechanical manufacture
Electrical device making
29874, 347 59, H01R 4316, H05B 300
Patent
active
059790407
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method of making an auxiliary electrode layer for a common electrode pattern in a thermal printhead.
BACKGROUND ART
Thermal printheads have been widely used for a printer of an office automation 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.
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 (heating dots) 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.
In general, for thermal printheads, a series of linear heating dots are formed preferably adjacent to a longitudinal edge of the head substrate. This is because the arrangement of disposing the series of heating dots adjacent to a longitudinal edge of the head substrate advantageously makes it possible to avoid interference with the printing medium as well as to increase degrees of positioning freedom and improve printing quality by holding the head substrate relative to the platen at a certain angle.
However, when the series of heating dots are adjacent to a longitudinal edge of the head substrate, space for formation of the common electrode pattern is correspondingly reduced, thereby failing to provide a sufficient current capacity (current passage) necessary for heat generation. As a result, the resistance of the common electrode pattern will cause a problem of irregular heat generation at the heating dots due to a voltage drop along the series of heating dots, which results in deterioration of printing quality. Particularly for color printing, which has been coming into wider use recently, it is highly required to ensure a large current capacity since all of the heating dots are frequently heated simultaneously to perform so-called "solid printing."
To meet such a requirement, International Publication WO 95/32867 discloses a thermal printhead with the arrangement shown in FIGS. 5 and 6 of the attached drawings of the present application. (Note that the above international publication was published on Dec. 7, 1995, which is later than the priority date of the present application, Jun. 13, 1995, so that the international publication is not to be regarded as prior art against the present application.) The above-mentioned thermal printhead will be described below.
The thermal printhead illustrated in FIGS. 5 and 6 includes a head substrate 11 of an insulating material such as alumina-ceramic for example. The head substrate 11, which is rectangular in cross section, includes an obverse surface 11a, a reverse surface 11b opposite to the obverse surface 11a, a first longitudinal edge surface 11c and a second longitudinal edge surface 11d opposite to the first longitudinal edge surface 11c. The obverse surface 11a of the head substrate 11 is formed with a glass glaze layer 12 as a heat reservoir. The glass glaze layer 12 includes a convex portion 12a, adjacent to the first longitudinal edge surface 11c of the head substrate 11, which has a curved cross section.
The surface of the glaze layer 12 is formed with a thin film of a resistor layer 13. The resistor layer 13 is divided by slits S (see FIG. 6) at a predetermined pitch to extend transversely of the head substrate 11 (that is, perpendicularly of the longitudinal edge surfaces 11c, 11d of the head substrate 11).
The surface of the resistor layer 13 is formed with a common electrode pattern 14 adjacent to the first longitudinal edge surface 1
REFERENCES:
patent: 4630073 (1986-12-01), Hashimoto
patent: 5317341 (1994-05-01), Tatsumi
Patent Abstracts of Japan--vol. 012, No. 087 (M-678), Mar. 19, 1988 & JP 62 227764 A (Seiko Epson Corp), Oct. 6, 1987, *abstract* rel. to claims 1-4,Narita Toshio; Thermal Printing Head; Jun. 10, 1987.
Patent Abstracts of Japan--vol. 014, No. 450 (M-1030), Sep. 27, 1990 & JP 02 179765 A (NEC Corp), Jul. 12, 1990, *abstract* rel. to claim 1, Tachiki Shigemi; Thermal Head Substrate; Dec. 7, 1990.
Bednarek Michael D.
Echols P. W.
Rohm & Co., Ltd.
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