JP2554556B2 - Thermal print head - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal print head having a simple structure capable of dramatically increasing the resolution density in the sub-scanning direction without lowering the printing quality. Regarding

[0002]

2. Description of the Related Art A thermal print head is often used as a print head mounted in a facsimile, a printer or the like. Among such thermal print heads, the structure of the heat generating portion of the thick film type thermal print head for forming heat generating dots by thick film printing is configured as follows.

That is, as shown in FIGS. 6 and 7,
The glass glaze layer 2 is printed and fired on the ceramic substrate 1, and the common electrode 3 and the individual electrode 4 facing each other in a comb shape are formed on the ceramic substrate 1 by etching or the like. The heating resistors 5 are formed in a strip shape with ruthenium oxide or the like so as to overlap. A protective glass layer 6 is formed on the common electrode 3, the individual electrodes 4, and the heating resistor 5.

As can be seen from FIG. 6, the common electrodes 3 ...
The plurality of electrodes are formed in parallel at equal intervals, while the individual electrodes 4 are formed in parallel at equal intervals so that the tip portions thereof protrude into the inter-electrode regions of the common electrodes. The common electrodes 3 ... Are electrically connected to the power source, while the individual electrodes 4 ... Are electrically connected to the output terminal of the driver IC. The driver IC turns on / off one of the individual electrodes 4 ... Which is selected according to image information. A potential difference is applied between the individual electrode 4 which is in the ON state and the pair of common electrodes 3 ... Which extend on both sides of the individual electrode 4, and the heat generation resistance between the common electrodes 3 and 3 which sandwich the individual electrode 4 in the ON state. The body 5 is partially heated.

By the way, recently, it has been required to improve the resolution density of this type of thermal print head, and the resolution in the main scanning direction (the direction in which the heating resistor 5 extends) is determined by the distance between the common electrodes 3. The resolution density in the sub-scanning direction (the width direction of the heating resistor 5) can be increased by narrowing the width of the heating resistor 5 by reducing the width of the heating resistor 5.

However, although the resolution density in the main scanning direction can be increased relatively easily, the resolution density in the sub scanning direction cannot be increased so easily. That is, since the heating resistor 5 is formed by thick film printing, there is a limit to the minimum width that can be printed without inconvenience. At present, this limit is said to be about 100 μm.

Therefore, it has been generally accepted that the resolution in the sub-scanning direction cannot be increased to 10 dots or more per 1 mm so long as the heating resistor 5 is formed by thick film printing.

In order to overcome such a limitation, recently, as shown in FIG. 8, the resolution density in the sub-scanning direction is not regulated by the width of the heating resistor 5, but the resolution between individual common electrodes is increased. It has been considered to try to define by the amount of protrusion of the electrode, that is, the overlapping width of the tips of the comb-shaped common electrode and the comb-shaped individual electrode. In this case, as in the conventional example shown in FIGS. 6 and 7, the common electrode 3 and the individual electrode 4 are
The width of the heat-generating resistor 5 is not smaller than the overlapping width of, and conversely, the width of the heat-generating resistor 5 is
It is larger than the overlapping width of the common electrode 3 and the individual electrode 4.

In this case, the heating resistor 5 generates heat from the central portion in the width direction of the resistor 5 because the current is concentrated in the overlapping portion of the common electrode 3 and the individual electrode 4, but the heating electrodes 5 and the electrodes 3 and 4 respectively. Due to the difference in the heat transfer coefficient between the inside of the resistor and the inside of the resistor, the shape of heat generated on the surface of the resistor is as shown by hatching in FIG. That is, the surface of the portion that overlaps each of the electrodes 3 and 4 has a concave shape in the heat generation shape because heat escapes to the outside through the electrodes. Even if an attempt is made to print a line in the main scanning direction as described above, the printing form does not become a linear shape with a constant width.
It becomes a meandering one as schematically shown in.

As described above, the meandering of the line print of the minimum unit width in the main scanning direction leads to deterioration of print quality, and it is difficult to accurately define the minimum print width in the sub scanning direction. It means that it is not practical as it is.

The present invention was devised under the circumstances described above, and provides a new structure capable of more accurately defining the minimum print width smaller than the width of the heating resistor. Is the task.

[0012]

In order to solve the above problems, the present invention takes the following technical means. That is, in the thermal print head according to claim 1 of the present application, a plurality of common electrodes arranged at equal intervals on the substrate and the tip portion of the common electrodes are projected into the inter-electrode region by a predetermined length. Formed in a strip shape so as to overlap the heat generation region sandwiched by the plurality of individual electrodes arranged on the substrate, the line connecting the tips of the common electrodes, and the line connecting the tips of the individual electrodes. And a heating resistor that is formed separately from the common electrodes in the extension direction of the common electrodes,
And, a plurality of first heat diffusion layers, a part of which is in contact with the heating resistor, is formed separately for each individual electrode in the extension direction of each of the individual electrodes, and a part of the heating resistor is formed. A plurality of second thermal diffusion layers in contact with each other, wherein the first thermal diffusion layer and the second thermal diffusion layer are patterned by the same material when forming the common electrode and the individual electrode. It is characterized by being a thing.

According to a second aspect of the present invention, in the thermal print head according to the first aspect, the length of the first thermal diffusion layer and the second thermal diffusion layer is the width of the heating resistor. It is characterized in that it is set to almost the same size or more.

In the thermal print head of the present invention, the width of the region sandwiched by the line connecting the tips of the common electrodes and the line connecting the tips of the individual electrodes, that is, the comb teeth like the comb teeth like common electrode. The overlapping width with the individual electrode is smaller than the width of the heating resistor. Therefore, current is concentrated in this overlapping width and the heat generating resistor generates heat. In the invention of the present application, a plurality of first heat diffusion layers that are separated from each common electrode in the extension direction of each common electrode and a part of which contacts the heating resistor, and each extension direction of each individual electrode. A plurality of second heat diffusion layers that are formed separately from the individual electrodes and that are in contact with the heating resistor are provided, and the first heat diffusion layer and the second heat diffusion layer are common. The electrodes and the individual electrodes are patterned by the same material.

Therefore, when the heating resistor portion of the thermal print head is viewed in plan, the first heat diffusion layer extends on the opposite side of each common electrode and the second heat diffusion layer extends on the opposite side of each individual electrode. It becomes a form that extends. As described above, the heat generated in the area of the overlapping portion of each common electrode and each individual electrode is therefore averaged on both sides of the heating resistor at the portion corresponding to each common electrode and the portion corresponding to each individual electrode. Diffused. As a result, the heat generation shape on the surface of the heat generating resistor is substantially in the form corresponding to the overlapping width of the common electrode and the individual electrode as described above. When printing is performed, the problem that the printing meanders is solved.

After all, according to the present invention, although the heating resistor is formed by thick film printing, the printing width in the sub-scanning direction is smaller than the minimum width of the heating resistor that can be formed by thick film printing. It is possible to set the print quality to a good one without meandering while setting it small. This means that the resolution density in the sub-scanning direction can be set to a high resolution that cannot be achieved by the conventional thick film type thermal print head.

Moreover, the first thermal diffusion layer and the second thermal diffusion layer in the present invention can be patterned simultaneously when forming the common electrode and the individual electrode on the substrate. Does not increase the number of steps and causes almost no increase in cost. By setting the lengths of the first heat diffusion layer and the second heat diffusion layer to have sufficient heat capacity which is substantially equal to or more than the width of the heating resistor, for example, the horizontal ruled lines are arranged in the sub-scanning direction. Even when printing is performed in a continuous manner, the printed ruled lines are good without meandering.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The preferred embodiments of the present invention will be described below.
A detailed description will be given with reference to FIGS. 1 to 5. In addition,
In these figures, members or portions equivalent to those in FIGS. 6 to 8 are designated by the same reference numerals.

The thermal print head of the present invention is a so-called thick film type thermal print head, and is basically manufactured by the same process as the conventional example shown in FIGS. That is, as shown in FIG. 2, the common electrode 3 and the individual electrode 4 are formed on the glass glaze layer 2 formed on the ceramic substrate 1 by pattern etching or the like. The heating resistor 5 that is electrically connected to the electrode 4 is formed in a strip-shaped thick film by printing. The heat generating portion of the print head including the common electrode 3, the individual electrode 4 and the heat generating resistor 5 is covered with the protective glass layer 6.

As shown in FIG. 1, the common electrodes 3 are formed so as to extend from the common line 3a in parallel with each other by a predetermined length. On the other hand, the individual electrodes 4 ... Are formed in parallel at equal intervals so that the tips of the individual electrodes 4 project into the inter-electrode regions of the common electrode 3 by a predetermined length. The common electrodes 3 ... Are conducted to a power source (not shown), while the individual electrodes 4 ... Are conducted to output terminals of a driver IC (not shown).
The individual ON / OFF control is similar to the conventional example.

In the present invention, the glass glaze layer 2
In addition to the common electrodes 3 and the individual electrodes 4 formed above, a first heat diffusion layer 7 and a second heat diffusion layer 8 described below form the electrodes 3 and 4 described above. At the same time, it is formed by pattern etching or the like. The first heat diffusion layers 7 are formed separately from the common electrodes 3 in the extending direction of the common electrodes 3. Further, the second thermal diffusion layers 8 ... Are formed in the extension direction of the individual electrodes 4 ... While being separated from the individual electrodes 4.

On the other hand, the heating resistor 5 is a strip-shaped region sandwiched by the line connecting the tips of the common electrodes 3 ... And the line connecting the tips of the individual electrodes 4, that is, the comb-teeth-shaped common electrode. Similarly to 3 ..., It is formed in a strip shape with a width H that is larger than the overlapping width h of the tip portions of the comb-shaped individual electrodes 4 ... At this time, the gaps between the first thermal diffusion layers 7 ... And the tips of the common electrodes 3 ... And the second thermal diffusion layers 8 ...
The gap between each of the individual electrodes 4 and the tip of each individual electrode 4 is appropriately determined, and a part of the first heat diffusion layer 7 and the second heat diffusion layer 8 has the width set as described above. It is necessary to dig under the heat generating resistor 5 and to contact the heat generating resistor 5.

In the above structure, when the individual electrodes 4 ... Are turned on, the current flows between the individual electrodes 4 and the common electrode 3 and flows through the first and second heat diffusion layers 7 and 8. Absent. Therefore, the heating resistor 5 does not generate heat uniformly over its entire width, but generates heat from the central width portion indicated by the symbol h in FIG. However, since the heating resistor 5 itself is formed by thick film printing and has a constant thickness, the surface heating shape is different from that of the conventional example due to the balance of the internal heat storage amount and the heat radiation amount from the electrode. As mentioned in the explanation, the width is not constant,
The surface heating shape is narrowed in the portion overlapping the conductor portion having the heat diffusion function, such as the electrodes 3 and 4.

As can be seen from the plan view of FIG. 1, in the thermal print head of the present invention, the heating resistor 5 is used.
Patterns having a heat diffusion function extend from both sides of each part in the longitudinal direction corresponding to the positions of the electrodes 3 and 4 in. That is, the first thermal diffusion layer 7 extends from the opposite side of the common electrode 3 in the portion overlapping the common electrode 3 ..., and the first heat diffusion layer 7 extends from the opposite side of the individual electrode in the portion overlapping the individual electrode 4. The second heat diffusion layer 8 extends.
This is in sharp contrast to the conventional structure shown in FIG. 8 in which the common electrodes 3 and the individual electrodes 4 extend alternately in a zigzag pattern at each longitudinal portion of the heating resistor 5.
In such a thermal print head of the present invention, the following remarkable operational effects can be obtained.

That is, as shown in FIG. 3A, the overlapping width h of the tips of the common electrodes 3 ... And the individual electrodes 4 ...
m, the width of the heating resistor 5 is 220 μm, and the thermal print head configured without the first thermal diffusion layer 7 and the second thermal diffusion layer 8 as in the present invention, and FIG. ), Common electrode 3, ..., Individual electrode 4
The same printing as that in which the first heat diffusion layer 7 and the second heat diffusion layer 8 of the present invention are formed after the form of the heating resistor 5 is exactly the same as that of FIG. The comparison of the print shape by energy was performed. 3 (B), the gap between the common electrode 3 ... And the individual electrode 4 ... With the thermal diffusion layer 7 and the second thermal diffusion layer 8 is 10 .mu.m. The length of the second heat diffusion layer 8 is 220 μm.

The result of printing by the thermal print head of FIG. 3 (A) is shown in FIG. 4 (A), and the result of printing by the thermal print head of FIG. 3 (B) is shown in FIG.
(B) of each shows. As is clear from these figures, first, when the first and second thermal diffusion layers 7 and 8 as in the present invention are not present, on both sides in the width direction of the heating resistor corresponding to each electrode portion, they are mutually separated. Due to the difference in the amount of thermal diffusion, the printed shape becomes a meandering shape.
The result of printing by the thermal print head having the constitution of the present invention shows that there is no meandering as shown in FIG. 4 (A) and there is a slight change in the width in the longitudinal direction of the print, but the line has a substantially constant width. Are formed.

Next, in the print shape in which the thermal diffusion layers 7 and 8 are not present, the width of the printed line is 80 μm, which is 20 with respect to the overlapping width (60 μm) of the electrodes 3 and 4.
While a width as wide as μm is recognized, in the print shape by the thermal print head having the configuration of the present invention, the line width is constant at 70 μm, and the overlapping width (60 μm) of each of the electrodes 3 and 4 is 60 μm. The increase in width for is 1
It remains at 0 μm.

When the heat diffusion layers 7 and 8 are provided as in the present invention, the print shape and print quality are improved.
Since the pattern having the heat diffusion function extends on both sides of each portion corresponding to the electrodes 3 and 4 in the longitudinal direction of the heat generation resistor, the heat diffusion of the heat generation resistor 5 is on both sides of the width. This is because they are equalized at the same time.

Further, the line width of the heating resistor 5 is set to 120.
μm, and the overlapping width of the common electrode and individual electrode is 4
FIG. 5 shows a comparison between the constitution of the present invention and the conventional constitution when the thicknesses are 0 μm, 60 μm, and 100 μm. As can be seen from this figure, according to the present invention, the print width in the sub-scanning direction, which is smaller than the width of the heating resistor 5, can be more effectively regulated.

As described above, according to the thermal print head of the present invention, although it is a thick film type thermal print head which can be manufactured at a relatively low cost, the sub print size is smaller than the minimum limit width by thick film printing. Since the print width in the scanning direction can be achieved without deteriorating the print quality, the resolution in the sub-scanning direction in the thick film type thermal print head can be dramatically increased.

[Brief description of drawings]

FIG. 1 is an enlarged plan view of an essential part of an embodiment of the present invention.

FIG. 2 is an enlarged sectional view taken along line II-II in FIG.

FIG. 3A is a plan view showing a conventional configuration example. (B) is a plan view showing a configuration example of the present invention.

FIG. 4A is a schematic diagram showing a print shape by the thermal print head having the configuration of FIG. (B) It is a schematic diagram which shows the printing shape by the thermal print head of the structure of (B) of FIG.

FIG. 5 is a graph comparing the print widths when the overlapping width of the common electrode and the individual electrode is variously changed for the configuration of FIG. 3 (A) and the configuration of FIG. 3 (B).

FIG. 6 is an enlarged plan view of a main part of a conventional first example.

FIG. 7 is an enlarged sectional view taken along line VII-VII of FIG.

FIG. 8 is an enlarged plan view of a main part of a second conventional example.

[Explanation of symbols]

 1 Ceramic Substrate 2 Glass Glaze Layer 3 Common Electrode 4 Individual Electrode 5 Heating Resistor 6 Protective Glass Layer 7 First Thermal Diffusion Layer 8 Second Thermal Diffusion Layer

Claims (2)

(57) [Claims] 1. A plurality of common electrodes arranged at equal intervals on a substrate, and a plurality of electrodes arranged on the substrate so that a tip portion of the common electrode has a predetermined length protruding into an inter-electrode region. Of the individual electrodes, a line connecting the tips of the common electrodes, and a heating resistor formed in a strip shape so as to overlap the heating region sandwiched by the lines connecting the tips of the individual electrodes, and the common electrodes. A plurality of first heat diffusion layers that are formed separately for each common electrode in the extension direction of, and a part of which is in contact with the heating resistor, and for each individual electrode in the extension direction of each individual electrode. formed separately, and some are equipped with a plurality of second thermal diffusion layer in contact with the heating resistor, said first
One heat diffusion layer and the second heat diffusion layer, the common electrode and
When forming individual electrodes, pattern with the same material
A thermal print head characterized by being molded . 2. The first thermal diffusion layer and the second thermal diffusion layer
The length is almost equal to or more than the width of the above heating resistor.
The thermal print head of claim 1, wherein the thermal print head is set to .