Incremental printing of symbolic information – Thermal marking apparatus or processes
Reexamination Certificate
2003-02-17
2004-07-20
Feggins, K. (Department: 2861)
Incremental printing of symbolic information
Thermal marking apparatus or processes
C347S208000
Reexamination Certificate
active
06765601
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention generally relates to a thermal printhead that is used to print images onto recording paper by means of thermo-sensitive printing or thermal ink-transfer printing.
2. Background Information
FIG. 16
shows an example of a conventional thermal printhead. This thermal printhead includes a common electrode
163
, individual electrodes
164
, and a belt shaped heating resistor
165
, all of which are disposed on top of an insulating substrate
161
. The common electrode
163
includes a belt shaped common line
163
b
, and a plurality of projections
163
c
that project out from the common line
163
b
like the teeth of a comb. Each first end
164
a
of each individual electrode
164
is interposed between two adjacent-projections
163
c
. Each individual electrode
164
and each projection
163
c
intersect with the heating resistor
165
and are in electrical contact therewith. Note that, although not shown in the figures, a terminal is formed on one end of the common line
163
b
of the common electrode
163
, and the common electrode
163
is connected to a voltage application means via this terminal. In addition, terminals are formed on second ends of each individual electrode
164
(not shown in the figures). These terminals are each connected to drive IC chips that serve to independently apply a voltage to each individual electrode
164
.
In a thermal printhead constructed in this manner, for example, a positive voltage is applied to the common electrode
163
while one individual electrode
164
is connected to ground. An electric potential difference is produced in a region H on the heating resistor
165
that is disposed between two adjacent projections
163
c
and which has a grounded individual electrode
164
that intersects therewith. Electricity flows through the region H and generates heat therein, thereby allowing a one dot (one pixel) image to be printed on a thermo-sensitive type of recording paper.
However, in the thermal printhead noted above, it is well known that the temperature distribution on each region H will not be uniform when heated up. In other words, it is well known that the central portions between the individual electrode
164
and the adjacent projections
163
c
will be the hottest, and that the temperature will drop as one moves away from the central portions. The temperature difference between the ends of each region H and the central portions thereof will be more pronounced as the size of each region H increases. This creates a problem in that when using a two-color thermo-sensitive paper as a recording medium for thermal printheads, it is easy to produce colors other than those intended.
For example, when one uses a black/red two-color thermo-sensitive paper and attempts to print a one dot image that is entirely black thereon, the temperature differentials on each region H on the heating resistor
165
causes a large red image to be printed around the periphery of the black image. Note that a two-color thermo-sensitive paper used with thermal printheads is paper which turns a first color (e.g., black) when at or above a predetermined temperature, and turns a second color (e.g., red) at a temperature lower than the predetermined temperature.
Furthermore, increasing the temperature of not only the central portions of each region H but the end portions and their vicinity to a predetermined temperature suitable for printing tends to require a great deal of electrical energy, and thus a great deal of electrical power will be consumed by the thermal printhead. Reducing the size of each region H is thought to be one means for controlling the amount of electrical power consumed. This is because the amount of energy needed can be reduced if the size of the regions H are reduced, even though the regions H are heated up to the predetermined temperature.
However, in the thermal printhead shown in
FIG. 16
, all of the regions along the length of the heating resistor
165
are capable of generating heat except for both ends thereof. Because of this, when one attempts to reduce the width of the regions H by reducing the array pitch W of the projections
163
c
of the common electrode
163
, it will be necessary to increase the total number of projections
163
c
and individual electrodes
164
. Thus, although the print image resolution will increase, the task of forming the patterns for the common electrode
163
and the individual electrodes
164
will be more difficult. Furthermore, the number of drive IC chips for applying a voltage to the individual electrodes
164
must be increased, and thus the cost of manufacturing the thermal printhead will increase. In addition, if the size of one dot is reduced, the heat capacity of each region H will be reduced, and thus there is a concern that the temperature of each region H will increase higher than necessary when that region is heated up, due to the effect of the temperature of other regions H adjacent thereto, and that thermal degradation will occur.
SUMMARY OF INVENTION
An object of the present invention is to provide technology for preventing undesirable colors from being generated around the periphery of a desired color even when a two-color thermo-sensitive paper is used as a recording medium.
Another object of the present invention is to make uniform the temperature distribution of a region corresponding to one dot of a heating resistor employed in a thermal printhead.
Another object of the present invention is to reduce the amount of electrical power consumed by a thermal printhead while preventing the manufacturing costs thereof to increase.
In order to solve the aforementioned problems, a thermal printhead according to the present invention is employed to print images on a thermo-sensitive paper. According to a first aspect of the present invention, a thermal printhead is comprised of:
a substrate;
a belt shaped heat resistor disposed on top of the substrate;
a common electrode having a common line disposed along a longitudinal direction of the heat resistor, and a plurality of projections that each project from the common line and which intersect with and electrically connect to the heat resistor; and
a plurality of individual electrodes that are each disposed between mutually adjacent projections which intersect with and electrically connect to the heat resistor.
In this thermal printhead, when an electric potential difference is produced between the individual electrodes and projections of the common electrode, a plurality of regions that have a substantially fixed electric potential (fixed electric potential regions) are formed on the heating resistor in positions in which at least one variable electrical potential region is disposed therebetween. Here, the variable electric potential regions are regions on the heating resistor that are disposed between adjacent pairs of projections and which have an individual electrode that intersects therewith.
The common electrode may be any shape that allows a fixed electric potential regions to be produced on the heating resistor when a voltage is applied between the common electrode and an individual electrode. For example, a fixed electric potential region can be formed between two projections on the heating resistor. In another example, wide projections can be formed, and the portions thereof that are in contact with the heating resistor can form the fixed electric potential regions.
According to another aspect of the present invention, the temperatures of the variable electric potential regions are higher than the fixed electric potential regions when an electric potential difference is produced between the common electrode and the individual electrodes.
An electric potential difference is produced on both ends of each variable electric potential region when an electric potential difference is produced between the common electrode and the individual electrodes. Due to this electric potential difference, electricity flows to the variable electric potential regions and heats these reg
Nagahata Takaya
Nishi Kouji
Feggins K.
Rohm & Co., Ltd.
Shinjyu Global IP
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