Incremental printing of symbolic information – Thermal marking apparatus or processes – Specific resistance recording element type
Reexamination Certificate
2000-06-21
2001-04-17
Tran, Huan (Department: 2861)
Incremental printing of symbolic information
Thermal marking apparatus or processes
Specific resistance recording element type
Reexamination Certificate
active
06219080
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a thick film thermal head for making a heat-sensitive stencil master.
2. Description of the Related Art
Thermal heads for making a heat-sensitive stencil master generally comprise an array of resistance heater elements and imagewise perforate a stencil master material by selectively energizing the heater elements and are broadly classified into thin film thermal heads and thick film thermal heads by the structure.
FIG. 9
shows an example of a conventional thick film thermal head. In
FIG. 9
, the conventional thick film thermal head comprises a ceramic substrate
95
, a heat insulating layer
92
formed on the ceramic substrate
95
, a plurality of comb-tooth electrodes
94
which are formed on the heat insulating layer
92
and arranged in a row in a direction perpendicular to their longitudinal directions, and a resistance heater
91
which extends in the direction of the row of the comb-tooth electrodes
94
. The resistance heater
91
is formed over the comb-tooth electrodes
94
to continuously extend across the electrodes
94
. With this arrangement, when an electric voltage is applied across a pair of adjacent electrodes, the part of the resistance heater
91
between the electrodes
94
generates heat. That is, parts
91
a
of the resistance heater
91
between adjacent electrodes
94
form resistance heater elements. The resistance heater elements
91
a
are arranged in the direction of the row of the comb-tooth electrodes
94
. This direction will be referred to as “the main scanning direction”, hereinbelow.
When making a stencil master by a thermal head, it is generally necessary to form, on a stencil master material
71
, perforations
72
which are separated from each other in both the main scanning direction X and the sub-scanning direction Y (the direction substantially perpendicular to the main scanning direction) as shown in FIG.
7
.
If the perforations
72
are continuous in the main scanning direction X as shown in
FIG. 8
, ink is supplied to the printing paper through the perforations in an excessive amount, which results in offset and/or strike through.
If each of the resistance heater elements
91
a
is thermally insulated from the parts of the resistance heater
91
on opposite sides of the resistance heater element
91
a
in
FIG. 9
, the width W in the main scanning direction of the area which generates heat when the element
91
a
is energized will be substantially equal to the space P between adjacent electrodes
94
.
However, actually each of the resistance heater elements
91
a
is not thermally insulated from the parts of the resistance heater
91
on opposite sides of the resistance heater element
91
a
, and accordingly, heat generated from each resistance heater element
91
a
propagates to the part adjacent thereto, whereby, as shown in
FIG. 10
, an area
101
wider than the resistance heater element
91
a
, or the space P between adjacent electrodes
94
, becomes hot. When adjacent two resistance heater elements
91
a
are simultaneously energized, the actual heat generating areas
101
of the adjacent resistance heater elements
91
a
become closer to each other as shown in
FIG. 10
, which can result in continuous perforations.
Especially in the case of a thick film thermal head, since the resistance heater
91
is large in thickness, heat generated from each resistance heater element
91
a
spreads over a wide area while it propagates to the surface of the element
91
a
and the width W of the heat generating area more tends to become larger than the space P between the electrodes
94
at the surface of the resistance heater
91
. Accordingly, in the case of a thick film thermal head, the aforesaid problem is more serious.
SUMMARY OF THE INVENTION
In view of the foregoing observations and description, the primary object of the present invention is to provide a thick film thermal head which can form perforations which are separated from each other in the main scanning direction without thermally insulating the resistance heater elements from each other.
The thick film thermal head in accordance with the present invention comprises a plurality of first and second electrodes which extend in a sub-scanning direction and are alternately arranged in a main scanning direction intersecting the sub-scanning direction at predetermined spaces, and a resistance heater which continuously extends in the main scanning direction across the first and second electrodes, parts of the resistance heater between adjacent first and second electrodes forming a plurality of resistance heater elements which are arranged in the main scanning direction and generate heat when energized through the first and second electrodes, and is characterized in that the spaces between the first and second electrodes are smaller than the widths of the first and second electrodes in the main scanning direction.
It is preferred that the spaces between the first and second electrodes are smaller than the width of the resistance heater in the sub-scanning direction.
It is preferred that the width of the resistance heater in the sub-scanning direction is smaller than the perforation pitches in the main scanning direction.
The first and second electrodes are preferably formed of metal having a thermal conductivity not lower than 100 W/mK at 100° C. For example, the electrodes may be formed of silver (422 W/mK in thermal conductivity and 2.08 &rgr;/&OHgr;m in resistivity at 100° C.), copper (395 W/mK in thermal conductivity and 2.23 &rgr;/&OHgr;m in resistivity at 100° C.), gold (313 W/mK in thermal conductivity and 2.88 &rgr;/&OHgr;m in resistivity at 100° C.), aluminum (240 W/mK in thermal conductivity and 7.8 &rgr;/&OHgr;m in resistivity at 100° C.), beryllium (168 W/mK in thermal conductivity and 5.3 &rgr;/&OHgr;m in resistivity at 100° C.), tungsten (163 W/mK in thermal conductivity and 7.3 &rgr;/&OHgr;m in resistivity at 100° C.), magnesium (154 W/mK in thermal conductivity and 5.3 &rgr;/&OHgr;m in resistivity at 100° C.), iridium (145 W/mK in thermal conductivity and 6.8 &rgr;/&OHgr;m in resistivity at 100° C.), molybdenum (135 W/mK in thermal conductivity and 7.6 &rgr;/&OHgr;m in resistivity at 100° C.), brass (128 W/mK in thermal conductivity and 6.3 &rgr;/&OHgr;m in resistivity at 100° C.), or zinc (112 W/mK in thermal conductivity and 7.8 &rgr;/&OHgr;m in resistivity at 100° C.).
It is preferred that a radiator for dissipating heat of the electrodes is provided in a close contact with the electrodes.
In the thick film thermal head of the present invention, since the spaces between the first and second electrodes are smaller than the widths of the first and second electrodes in the main scanning direction, that is, since the widths of the resistance heater elements are smaller than the widths of the electrodes, which have a heat dissipation effect, the heat generated by the resistance heater elements is effectively dissipated through the electrodes. Accordingly, the widths in the main scanning direction of the heat generating areas which become hot when the resistance heater elements are energized can be approximated to the spaces between the electrodes, whereby perforations formed in the stencil master material adjacent to each other can be surely separated from each other and offset and/or strike through can be effectively prevented.
When the resistance heater elements are larger in width in the main scanning direction (the spaces between the first and second electrodes) than width in the sub-scanning direction (the width of the resistance heater in the sub-scanning), heat are more apt to spread in the main scanning direction. Accordingly, when the spaces between the first and second electrodes are smaller than the width of the resistance heater in the sub-scanning direction, adjacent perforations can be more surely separated from each other.
Further, when the picture element density in the sub-scanning direction is not lower than that in the main scanning direction, perforations can be preve
Nixon & Peabody LLP
Riso Kagaku Corporation
Studebaker Donald R.
Tran Huan
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