JPH05338231A - Thermal head and printing method thereof - Google Patents

Abstract

PURPOSE:To provide a thermal head which maintains similar performance to a conventional one, can conduct printing with more gradations than conventional printing. CONSTITUTION:On the surface of a heating resistor 4 of a thermal head which is formed on a substrate and through which the electricity is turned on selectively to generate heat for printing, a projection 6 having the width in the feed direction d which is narrower than the corresponding width D of the heating resistor is fixed in the main scanning direction. In this way, the narrow width in the feed direction of the projection 6 placed on the heating resistor 4 makes it possible to restrict the part contacting a printing roller to the upper surface of the projection, so that the printing area corresponding to one picture element can be divided into many parts in the feed direction, thereby enabling the printing with a high resolution for higher gradation expression.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal head for printing by heating a thermal paper by passing an electric current through a heating resistor, or by melting the ink of an ink donor film and transferring it to a recording paper. The present invention relates to a printing method using a thermal head.

[0002]

2. Description of the Related Art Conventionally, when performing multi-gradation recording with dots printed by a thermal head, gradation recording, that is, light and shade printing, is obtained by area gradation, density gradation, and the like. In the area gradation, one pixel is formed by a plurality of print dots, and the gradation is artificially expressed by increasing or decreasing the printing area in one pixel area.

In this area gradation printing, the resolution of the reproduced image decreases as the number of gradations increases, and it is difficult to obtain high quality pixels. In order to obtain a high-resolution reproduced image by area gradation, one printing area of the thermal head is converted into one conventional printing area (one pixel area), as disclosed in JP-A-60-248074. In comparison, a method is known in which the number of gradations is increased by narrowing the pixel in the sub-scanning direction and configuring one pixel by a large number of print dots in the sub-scanning direction.

FIG. 5 is a partial plan view illustrating an individual facing type thermal head as an example of a conventional thermal head of this type, and FIG. 6 is a partial sectional view taken along the line AA of FIG. In FIGS. 5 and 6, 01 is a substrate made of ceramics or glass, and an underglaze layer 0 is formed on the upper surface.
11 is provided. 02 is a common electrode, 03 is an individual electrode, 04
Is a heating resistor bridging the common electrode 02 and the individual electrode 03,
Reference numeral 05 is an overglaze layer which is a protective layer.

As shown in the figure, the heating resistor 04 is
The width d _{0 in the} sub-scanning direction is formed to a fraction 1 to several tens of 1 of the width D ₀ (for one pixel) in the same direction of the conventional thermal head. FIG. 7 is a schematic explanatory view of a printing example using the thermal head shown in FIGS. 5 and 6, and P _1, P _{2,
P 3, P 4, P 5} , P 6 is a print example in which is sequentially changed in the main scanning direction gradation of each pixel. Here, in order to simplify the explanation, the width d of the heating resistor 04 of the thermal head in the sub-scanning direction is set.
_{0 is set} to 1/6 of the width D ₀ of one pixel in the same direction. Therefore, here, it is possible to print 7 gradations per pixel.

In the same figure, when the gradation of the pixels not to be printed is the first gradation, P ₁ is the second gradation printed on 1/6 of the area of one pixel, and P ₆ is the whole of one pixel. Is printed on the seventh gradation. Thus, the heating resistor 0 in the sub-scanning direction
By forming the width of 4 to be narrower than the conventional one, it is possible to print with multiple gradations within one pixel.

[0007]

However, in the above-mentioned prior art, if the area of the resistor (width d _{0 in the} sub-scanning direction) is reduced in order to realize a higher number of gradations,
The variation in the resistance value of the heating resistor 04 is increased, the reproducibility of one print dot is extremely reduced, and the unevenness of the density due to the waviness and the unevenness of the surface of the thermal head is generated, and the initial high-quality printing cannot be achieved. ..

Conventionally, it has been practiced to reduce the unevenness and waviness of the surface of the thermal head by using two overglaze layers, but even if the overglaze upper layer is polished by a lapping process or the like, the above-mentioned unevenness of lapping is caused. Since it is done along the waviness of the surface, the surface condition cannot be significantly improved. Therefore, in the conventional thermal head, the printing pressure on the recording medium becomes non-uniform, and it is difficult to perform high-quality gradation printing.

The present invention has been made in view of such a situation, and in terms of resistance value variation and reliability of the heating resistor, while maintaining the same performance as the conventional one, it has more gradations than the conventional one. It is an object of the present invention to provide a thermal head capable of performing the above printing and a printing method using the thermal head.

[0010]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a thermal head for printing by causing a heating resistor 4 formed on a substrate 1 to be selectively energized to generate heat. In the above, the upper surface of the heating resistor 4 is provided with a projection 6 having a width d in the sub-scanning direction narrower than the width D in the sub-scanning direction of the heating resistor in the main scanning direction.

The projection 6 may be made of a good heat conductor, and the same material as the heat generating resistor 4 or metal can be used. Further, in the present invention, the width d in the sub-scanning direction on the upper surface of the heating resistor 4 is the width D in the sub-scanning direction of the heating resistor 4.
In a printing method in which a thermal head having a narrower protrusion in the main scanning direction is brought into contact with a print roller via a recording medium to perform printing, the abutting portion between the heating resistor 4 and the print roller is provided with the protrusion 6. The feature is that printing is performed only on the upper surface.

[0012]

According to the present invention having the above-described structure, it is possible to achieve the same printing performance as that of the conventional thermal head having a heating resistor area for one pixel in terms of resistance variation and reliability of the heating resistor 4. At the same time, the printing area corresponding to one pixel is divided into a large number of times in the sub-scanning direction while only the upper surface of the protrusion is in contact with the printing roller, and high resolution printing with high gradation expression is possible. ..

[0013]

Embodiments of the present invention will now be described in detail with reference to the drawings. 1 is a partial plan view for explaining the structure of a heat generating portion in a first embodiment of a thermal head according to the present invention, and FIG. 2 is a view for explaining the structure of a heat generating portion in a first embodiment of the thermal head according to the present invention. 2 is a partial cross-sectional view taken along line AA of FIG. 1, 1 is a substrate made of ceramics or glass, 11 is an underglaze layer formed on the upper surface of the substrate 1, 2 is a common electrode, 3 is an individual electrode, Reference numeral 4 is a heating resistor, 5 is an overglaze layer, and 6 is a protrusion. Further, d is the width in the sub-scanning direction of the protrusion 6 formed on the heating resistor 4, D is the width in the sub-scanning direction of the heating resistor 4, and the dimension D is the width of one pixel of the conventional thermal head. However, it is not particularly limited. And the d dimension is D
It is set to a fraction of 1 and is set according to the required resolution.

In the thermal head of the illustrated embodiment, the heating resistor 4 is formed by the lift-off method using a thick film material. According to this heating resistor forming method, the rectangular heating resistor 4 and the protrusions 6 can be accurately formed with a desired film thickness easily. In this embodiment, the resolution is 8 dots as an example.
The case of / mm will be described. First, an electrode serving as a current path is formed on the ceramic substrate 1 on which glass (underglaze layer 11) is laid as a base. This electrode is divided into a common electrode 2 and an individual electrode 3, which are formed so as to face each other for each dot (one pixel). The width of one dot in the main scanning direction is about 90 μm to 110 μm, and the space where the common electrode 2 and the individual electrode 3 face each other is 100 μm.
To about 150 μm.

On the upper layer of the common electrode 2 and the individual electrode 3 formed on the underglaze layer 11, a resistor (heating resistor) 4 forming a heating portion is formed by a lift-off method. This is because an opening (here, a rectangle) having a shape corresponding to the heating resistor 4 is formed at a position where the resistor is to be formed by a photosensitive resist in advance, and the heating resistor material ( (Resistance vs. paste) is filled so that there is no space between them, the filled heating resistor material is dried, the unnecessary portion of the resistor is removed by lapping, and finally the photosensitive resist and the resistor material are baked at the same time. The heat generating resistor 4 is obtained by burning away the resist and sintering the resistor pair material.

The heating resistor 4 thus formed has a rectangular shape in its upper surface and cross section. As the photosensitive resist material, PMER N-HC600 manufactured by Tokyo Ohka Kogyo Co., Ltd., which is a negative photosensitive resist, was used. This photosensitive resist has a high viscosity of 600 cp, and a thick film can be formed easily and uniformly. However, it goes without saying that other suitable photosensitive resists may be used.

The photosensitive resist is applied by using a spinner or roll coater method and the film thickness is 15 μm to 25 μm.
It is about m. After coating, it is dried at 70 ° C. for about 20 minutes, exposed to a mask, and subjected to a phenomenon to form the opening. RuO ₂ is used for the thick film resistor material that is the heating resistor.
A resistor paste of the system was used. This material is suitable for forming the heating resistor of the thermal head according to the present invention because it is a material that has little change with time electrically and chemically.
As the material of the heating resistor, an appropriate material other than the above may be used.

After the openings are filled with the resistor paste, the heat-generating resistor material is dried at 130 ° C. for about 10 minutes, and the paste that has overflowed except the openings is removed by lapping, and the temperature is changed from 800 ° C. By firing at 900 ° C. for about 10 minutes, the resistor is sintered and the resist is burned and removed. The thickness of the formed heating resistor 4 is 9 μm to 15 μm.
The width in the main scanning direction is 90 μm to 110 μm.
m, and the width in the sub-scanning direction is 120 μm to 170 μm.

Next, a protrusion 6 narrower than the width D of the heating resistor 4 in the sub-scanning direction is formed in the upper layer of the formed heating resistor 4 by using the lift-off method similar to the above. The process of forming the protrusion is similar to the process of forming the heating resistor 4.
That is, first, a photosensitive resist is applied onto the formed heating resistor 4. The film thickness of the photosensitive resist is the heating resistor 4
Above, it is about 10 μm to 25 μm. Then, a band-shaped slit having a desired width in the sub-scanning direction, which corresponds to the protrusion 6 in the sub-scanning direction, is formed on the heating resistor 4 in the main scanning direction.

A material having good thermal conductivity is embedded in the strip-shaped opening. A thick film Au paste is used as a material having good thermal conductivity, and this paste is filled in the openings by screen printing. In addition to the above materials, thick film glass or a thick film resistor similar to the heating resistor 4 may be used as the material with good thermal conductivity to fill the opening. After filling the opening with Au paste, it is dried, and unnecessary Au paste is removed by lapping.
The photosensitive resist is incinerated by burning the paste and the resist at the same time, and the Au paste is sintered to form the strip-shaped projections 6 in the sub-scanning direction.

The thickness of the protrusion 6 is about 6 μm to 15 μm. The smaller the width d of the protrusion 6 in the sub-scanning direction is, the smaller the area of one print dot can be and the gradation reproducibility can be improved.
In the conventional thermal head shown in FIGS. 5 and 6, when the width of the heating resistor 04 in the sub-scanning direction is set to 20 μm or less, the variation in the resistance value increases and the reliability is lowered, which is not suitable for actual use. However, in the illustrated embodiment of the present invention, since the width of the heating resistor 4 in the sub-scanning direction remains wide, the above problem can be avoided, and the width of the protrusion 6 in the sub-scanning direction can be reduced to the manufacturing limit. It is possible to significantly increase the number of gradations.

The restrictions on the production of the projections 6 are limited in the step of forming the openings of the photosensitive resist, and if the opening width is 10 μm or less, undeveloped portions are generated in the openings and rectangular projections cannot be formed. .. Also, the thickness of the thick film material is reduced by about 30% in the process of sintering from the dry state, so the width of the protrusion is at least 7μ.
It will be about m. In the conventional thermal head, when the width of the heating resistor 04 in the sub-scanning direction is 20 μm, the number of reproducible gradations is about 20, but in the thermal head of the above embodiment of the present invention, the width of the protrusion 6 is 7 μm. In such a case, the number of gradations can be reproduced approximately three times, that is, about 60 gradations.

Further, the resistance value of the heating portion including the heating resistor 4 changes depending on the kind of material of the projection 6 formed on the upper layer of the heating resistor 4. As a matter of course, when Au, which is a conductor, is used, the resistance value of the entire heating resistor is the lowest, and the resistance value increases in the order of the resistor and the glass, which is an insulator. Taking this into consideration, the resistance value of the heating resistor 4 formed first is adjusted.

Finally, as a protective layer, a glass layer is coated on the entire surface including the projections 6 by screen printing to form an overglaze layer 5. This overglaze layer may be a single layer or multiple layers. In the present embodiment, the heat generating portion including the heat generating resistor 4 and the protrusion 6 is described as an example of the individual facing type thermal head, but the common electrode and the individual electrode are formed in a comb tooth shape, and a strip shape is formed on the upper layer in the sub scanning direction. It can also be applied to a thermal head having a so-called alternating lead type heat generating part for forming the heat generating resistor.

FIG. 3 shows a second thermal head according to the present invention.
FIG. 4 is a partial plan view for explaining the structure of the heat generating portion in the embodiment, showing a so-called alternating lead type thermal head to which the present invention is applied. In the figure, 110 is an underglaze layer formed on a substrate (not shown), 20 is a common electrode, 30 is an individual electrode, 40 is a heating resistor, 50 is an overglaze layer, and 60 is a protrusion.

In this type of thermal head, the common electrodes 20 and the individual electrodes 30 are alternately arranged in parallel in the main scanning direction on the underglaze layer 110, and are continuously formed in the main scanning direction. The heating resistor 40 is formed, and the projection 60 continuous in the main scanning direction is further formed on the heating resistor 40. The projection 60 is formed by using Au paste or the like having good thermal conductivity as in the above-mentioned embodiment,
The heating resistor 40 is formed by the same method as that of the above embodiment. Various materials can be adopted for the heating resistor and the protrusions as in the above-mentioned embodiment.

FIG. 4 is a schematic diagram for explaining the printing method using the thermal head according to the present invention. The same reference numerals as those in the explanatory views of the above-described embodiments correspond to the same portions, and 7
Is a print roller, and 8 is a recording medium. As shown in the figure, the thermal head according to the present invention contacts the printing roller 7 via the recording medium 8 and applies a printing current between the common electrode 2 (20) and the individual electrode 3 (30) to generate heat. Body 4 (4
0) is heated, and the heat is transferred to the recording medium 8 such as a thermal paper or an ink donor film (not shown) which is superposed on the recording medium 8 through the projections 6 (60) to heat the recording medium 8 for printing.

As shown in the figure, the thermal head and the print roller 7 face each other only on the upper surface of the projection 6 (60) of the thermal head, and the heat from the heating resistor 4 (40) is applied to the projection 6 (60). Is concentrated on the upper surface of the recording medium 8 and applied to the recording medium 8. Therefore, the printing resolution is determined by the area of the upper surface of the protrusion 6 (60) and does not depend on the area of the heating resistor 4 (40).

As a result, the number of gradations can be arbitrarily set according to the area of the upper surface of the protrusion 6 (60), and desired multi-tone printing can be obtained with high resolution. Then, the protrusion 6 (6
0) can be uniformly formed on the entire surface of the thermal head irrespective of the presence or absence of surface irregularities or waviness associated with the formation of the heating resistor, so that the uneven printing as in the prior art does not occur.

[0030]

As described above, according to the present invention,
Since it is possible to form protrusions that are directly involved in printing while maintaining the same size or arbitrary size of the heating resistor as before,
By forming the width of the protrusion in the sub-scanning direction to be narrow, there is no variation in the resistance value of the heating resistor in the thermal head that performs multi-gradation printing, density unevenness, etc., and in terms of gradation reproducibility. Also, it is possible to achieve a gradation number of about 60, which is three times as large as the conventional gradation number of 20, and it is possible to provide a thermal head having excellent functions by eliminating the drawbacks of the conventional technology.

[Brief description of drawings]

FIG. 1 is a partial plan view illustrating the structure of a heat generating portion in a first embodiment of a thermal head according to the present invention.

FIG. 2 is a partial cross-sectional view taken along the line AA of FIG. 1 for explaining the structure of the heat generating portion in the first embodiment of the thermal head according to the present invention.

FIG. 3 is a partial plan view illustrating a structure of a heat generating portion in a second embodiment of the thermal head according to the present invention.

FIG. 4 is a schematic diagram illustrating a printing method using a thermal head according to the present invention.

FIG. 5 is a partial plan view illustrating an individual facing thermal head as an example of a conventional thermal head.

FIG. 6 is a partial cross-sectional view taken along the line AA of FIG. 5 for explaining an individual facing type thermal head as an example of a conventional thermal head.

FIG. 7 is a schematic explanatory diagram of a printing example using the thermal head shown in FIGS. 5 and 6.

[Explanation of symbols]

1 ... ・ Ceramic substrate, 2 (20) ・ ・ ・ ・ Common electrode 3 (30) ・ ・ ・ ・ Individual electrode 4 (40) ・ ・ ・ ・
Heating resistor 5 (50) ... Overglaze layer
6 (60) ・ ・ ・ ・ Protrusion 7 ・ ・ ・ ・ ・ ・ Printing roller 8 ・
... Recording medium 11 (110) ... Underglaze layer.

Claims (2)

[Claims] 1. A thermal head for printing by causing a heating resistor formed on a substrate to generate heat by selectively energizing the heating resistor, wherein a width in the sub-scanning direction of the heating resistor is above the heating resistor. A thermal head having a protrusion in the main scanning direction that is narrower than the width in the sub scanning direction. 2. A thermal head having a protrusion in the sub-scanning direction whose width in the sub-scanning direction is smaller than the width of the heating resistor in the sub-scanning direction on the upper surface of the heating resistor is brought into contact with a printing roller via a recording medium to perform printing. In the printing method performed, printing is performed by limiting the contact portion between the heating resistor and the printing roller only to the upper surface of the protrusion.