Incremental printing of symbolic information – Thermal marking apparatus or processes – Specific resistance recording element type
Reexamination Certificate
2002-03-21
2004-06-22
Feggins, K. (Department: 2861)
Incremental printing of symbolic information
Thermal marking apparatus or processes
Specific resistance recording element type
Reexamination Certificate
active
06753893
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method of producing a thermal head. Particularly, this invention relates to the structure of a thermal head and a method of producing the thermal head, which offer high recording quality with improvement in the structure of a recording section for recording on a recording medium inserted between a platen and the recording section, for prevention of shifting of the recording section from a correct position to be recorded.
BACKGROUND ART
Thermal heads have an important place in the fields of OA (Office Automation)-devices and fax machines. A thermal head is made up of heating resistors arranged on a substrate. The heating resistors generate heat for recording on heat-sensitive papers or films of type-setting developing paper. Several developments have been in progress for their low noise level and low running cost. Thermal heads have recently attracted attention as being used for video printers, for example.
FIG. 1
is a plan view of an overall structure of a conventional thermal head, partially cut away in several stages for easy understanding.
FIG. 2
is an enlarged cross sectional view taken on arrows X—X of the thermal head shown in FIG.
1
. In these drawings, the thermal head is provided with an aluminum substrate
1
formed with long narrow flat surface and having thickness for certain rigidity, a ceramic substrate
2
formed on a main surface of the aluminum substrate
1
and having a thickness of 0.5 to 1.0 mm, thermal resistance and relatively large coefficient of heat transfer, and several integrated circuits
8
(abbreviated to IC hereinafter) aligned in row at the side of the ceramic substrate
2
. Formed on the center portion of the ceramic substrate
2
in the width direction in this structure is a glaze layer
3
as a heat-retention layer having a semi-gabled transversal surface formed in the longitudinal direction. A heating-resistor layer
4
is formed on the surface of the ceramic substrate
2
including the glaze layer
3
.
The glaze layer
3
is mainly made of glass. The heating-resistor layer
4
includes an alloy, such as, Ta-SiO and made by a thin-film forming method, such as, sputtering. A conductive layer of aluminum, for example, is formed on the surface of the heating-resistor layer
4
, and further, a common electrode
5
and separated electrodes
6
are formed thereon by photo-engraving. The common electrode
5
is formed like teeth of a comb on the one side of the glaze layer
3
from the center thereof. Several electrodes
6
are formed at the IC
8
side like strips aligned like teeth of a comb. The tips of the common electrode
5
and those of the separated electrodes
6
face each other at the summit of the semi-gabled glaze layer
3
with a predetermined gap. Connected to the other edge of each separated electrode
6
is a lead wire
9
extended from the IC
8
. A heat- and abrasion-resistant protective-film layer
7
is formed by, for example, sputtering, over the surfaces of the common electrode
5
and the electrodes
6
.
In this structure, a recording section
10
covers the summit of the protective-film layer
7
formed over the glaze layer
3
and the surrounding, as a thermal head having resolution of 220 to 400 d/i (the number of dots per inch).
The thermal head described above is provided with the recording section
10
at the portion corresponding to the summit of the glaze layer
3
, thus having the common electrode
5
and the separated electrodes
6
with the tips of comb-like teeth facing each other over the center summit. The positions of the tips facing each other are sometimes shifted from the correct positions due to incomplete production process. This problem is discussed with respect to
FIGS. 3
to
5
.
The glaze layer
3
is usually formed with a semi-gabled transversal surface as illustrated in FIG.
3
(
a
) by screen printing, for example. As shown in FIG.
3
(
b
), the heating-resistor layer
4
and the conductive layer are stacked thereon. The photo-engraving is applied to the conductive layer to form the common electrode
5
and separated electrodes
6
with a gap
10
A between the tips thereof. In the process of forming the glaze layer
3
on the ceramic substrate
2
, as illustrated in
FIG. 4
, several glaze layers, for example, glaze layers
31
and
32
are simultaneously formed on a main surface of one ceramic substrate
2
followed by cutting on a dashed line Y to form a substrate (glazed ceramic substrate) having two glaze layers.
As described, since the conventional thermal head has a semi-gabled cross section, shifting of portions (recording section) at which electrodes facing each other if occur during patterning causes variation in height of the recording section from the substrate surface. Moreover, in formation of several glazed layers, wrinkles formed on a plate during screen printing could lower accuracy in straightness, thus causing undulation Z on a part of the glaze layer
2
. Due to these problems, even photoengraving, a highly accurate electrode forming step, is applied to the conductive layer, as illustrated in
FIG. 5
, the recording section
10
, which has to be located on the summit of the semi-gabled structure, is shifted from the summit, thus lowering printing quality.
DISCLOSURE OF THE INVENTION
A purpose of the present invention is, for solving the problems discussed above, to provide a thermal head and a method of producing the thermal head, by protecting a recording section from being shifted in height from a substrate, for attaining a higher printing quality and reliability and also a simplified production process.
Another purpose of the present invention is to provide a thermal head and a method of producing the thermal head, by protecting a recording section from being shifted which may otherwise occur due to shifting of a heating-resistor layer and separated electrodes caused by undulation of a glaze layer.
In order to attain the purposes, the thermal head according to the first aspect of the present invention includes a longitudinal substrate; a heat-retention layer made of a heat-retaining material, having at least a sticking-out section lying on one main surface of the substrate in a longitudinal direction at a constant width; a heating-resistor member made of a resistive material, formed at least on the sticking-out section of the heat-retention layer at a predetermined thickness; a common electrode provided as touching the heating-resistor member; a plurality of separated electrodes provided as facing a tip of the common electrode with a gap, at least an edge of each separated electrode touching the heating-resistor member, another edge of each separated electrode being connected to a driver circuit; and a protective layer formed on the heating-resistor member, a heating-resistor member portion provided on the gap between the common electrode and the separated electrodes functioning as a recording section, wherein the sticking-out section is formed in straight in the longitudinal direction of the substrate and has a almost flat summit surface, the recording section being formed on the flat summit surface.
In the thermal head according to the first aspect, the common electrode and the separated electrodes may be formed as rising from a side edge of the substrate in the longitudinal direction to a side face of the sticking-out section of the heat-retention layer and covering a side edge, in the longitudinal direction, of the heating-resistor member formed on the summit surface.
In the thermal head according to the first aspect, the heat-retention layer may have a skirt section formed on the main surface of the substrate at a almost constant thickness, the sticking-out section being formed on the skirt section as sticking out therefrom.
In the thermal head according to the first aspect, the heating-resistor member may be formed within a summit surface of the sticking-out section.
In the thermal head according to the first aspect, the separated electrodes and the common electrode may be formed as touching the heating-resistor mem
Feggins K.
Kabushiki Kaisha Toshiba
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