JPH0626909B2 - Thermal head - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal head of a thermal printer for forming thermal transfer recording on a recording paper surface, and more particularly to reduction of pinholes in its protective film.

[Conventional technology]

FIG. 2 is a plan view showing a conventional thermal head disclosed in, for example, Japanese Patent Laid-Open No. 58-131077, and FIG.
It is a sectional view taken along the line III-III of the drawings, and in these drawings,
(2) is an insulating substrate on which a thin film circuit is formed. This thin film circuit includes a plurality of heating elements (4 ₁ ) to (4 _n ) linearly arranged on the substrate (2) and a heating element.
A common terminal (6) for commonly connecting one end of each of (4 ₁ ) to (4 _n ).
Consisting When the heating element (4 ₁₎ to the driving signal input terminal of the other ends connected to separate (4 _n) (8 ₁₎ to (8 _n), a wiring conductor made of Al film or the like (10) . As shown in FIG. 3, this thin film circuit is covered with a protective film (12).

The conventional thermal head is configured as described above, and when performing print recording on the recording paper surface, this thermal head is
Via the transfer master material coated with heat-meltable ink,
In a state of being in close contact with the recording paper surface, selectively passing a drive signal current corresponding to the print information between the common terminal (6) and the driving signal input terminal (8 ₁₎ ~ (8 _n), the heating element (4 ₁ ) to (4 _n ) are selectively heated and the thermal head is used as a heating element.
It is moved in the direction of arrow A which is orthogonal to the arrangement direction of (4 ₁ ) to (4 _n ). The heat-meltable ink applied to the transfer master material is partially melted by the heating elements (4 ₁ ) to (4 _n ) according to the print information, and the melted heat-meltable ink is transferred to the recording paper surface, A print record is serially formed on the recording paper surface.

[Problems to be solved by the invention]

In the conventional thermal head as described above, the pinhole in the protective film (12) covering the substrate (2) has a lower wiring conductor.
(10) has been reached, and the protective film (12) is touched by mistake, or the protective film of the ink ribbon is
If it gets in contact with (12), the protective film (1
2) Sweat, ink, etc. infiltrate into the pinhole inside, corroding and deteriorating the wiring conductor (10) of this sweat, ink, etc., causing disconnection of the wiring conductor (10) during driving, and the print quality is significantly deteriorated. There was a problem in that it might end up.

In addition, such a thermal head or a thermal printer having the thermal head mounted therein has a problem that the same phenomenon as described above occurs when a moisture resistance test or the like is performed. In particular, in the suburbs near the coast, since the environment atmosphere is rich in chlorine, the above-mentioned phenomenon is remarkable and the reliability of the equipment is deteriorated.

Further, there is a problem that a short circuit occurs when the surface of the thermal head comes into contact with a metal foil or the like during handling of the thermal head. Alternatively, when the head contacts with an ink ribbon whose inside is coated with a metal for printing, a short circuit occurs and the drive circuit of the thermal head does not work.

This is due to the external connection terminals (6) and (8) of the thermal head.
When plating ₁ ) to (8 _n ), a plating metal also deposits inside the pinhole, and this metal rises up at the opening of the pinhole to form a convex portion. It seems to do.

Many thermal heads used to have the structure shown in FIG. 4, and in the wiring conductor (10), a glaze layer (14) made of glass or the like is provided on the substrate (2) for about 40 to 50 μm. It was In such a thermal head, no matter how rough the surface is, if the glaze layer (14) is formed, the surface of the glaze layer (14) is extremely smooth, so that no problem such as pinholes occurs. However, in recent years, a thermal head having a structure in which a glaze layer (14) is partially provided on a part of the substrate (2) as shown in FIG. 5 is mainly used.
In this case, since the glaze layer (14) is hardly formed on the substrate (2) in the portion of the wiring conductor (10), the above-mentioned problems occur.

The present invention has been made in order to solve the above problems, and even if contact with a human body or metal occurs during installation or replacement of a thermal head in a thermal printer,
Even if it is used for a long time in a humid or salt-containing atmosphere, or even if a metal-coated ink ribbon or thermal paper with a metallic part is used, drive circuit failure due to wire breakage or short circuit due to corrosion It is an object of the present invention to provide a highly reliable thermal head that does not generate heat.

[Means for solving problems]

An insulating substrate having a surface roughness of 0.3 μRa or less in terms of center line average roughness, a thin film circuit having a plurality of heating elements formed on the substrate and selectively generating heat, and covering the thin film circuit And a protective film.

[Action]

In the present invention, the surface roughness of the substrate is 0.3 μRa or less in terms of the center line average roughness, so that the generation of pinholes in the protective film is suppressed.

〔Example〕

The basic structure of the thermal head according to the present invention is substantially the same as that described in the prior art. Further, according to the present invention, the surface roughness of the substrate (2) is 0.3 μRa as the center line average roughness.
It is characterized by the following.

The thermal head is, for example, heating element on the substrate (2) having a partial glaze layer (14) (4 ₁₎ ~ (4 _n), the wiring conductors (1
0) and the protective film 12 are sequentially formed by a method such as vacuum deposition or sputtering. Heating element (4 ₁ )
In most cases, a glaze layer (14) is partially formed on (4 _n ) to store heat. In some cases, the heating elements (4 ₁ ) to (4 _n ) are not formed between the substrate (2) and the wiring conductor (10). The material of the substrate (2) is alumina, AlN, Be
O, SiC, Si ₃ N ₄ , ZrO ₂ or the like is used.

The film thickness of the wiring conductor (10) on the substrate (2) is usually about 0.5 to 2 μ, and the thickness of the protective film (12) thereon is 5 to 10 μ.
Is. In such a structure, the surface roughness of the substrate (2) has a great influence on the generation of pinholes in the protective film (12). If the thickness of the protective film (12) is increased, the number of pinholes is reduced, but the cost is increased and the thermal conductivity is deteriorated, which is not preferable in terms of the function of the thermal head. Therefore, the surface roughness of the substrate (2) is set to 0.3 μRa or less in terms of center line average roughness.

In the thermal head configured as described above, the roughness of the surface of the substrate (2) is set to 0.3 μRa or less in terms of the center line average roughness, thereby exhibiting a remarkable effect of reducing corrosion, contact with the human body or metal, It is possible to improve the driving reliability in the use of a metal coated ink ribbon or thermal paper, in a humid environment, in an atmosphere containing chlorine.

Experimental Example 1 Alumina, AlN, and SiC were used as the substrate material, and several types of surface roughness were set and adjusted by changing the volume filling rate or polishing, and after forming a glass glaze layer on a part, Ta ₂
N, Ta-Si, a heating element Cr-Si, Al and Cu of the wiring conductor, a protective film having a two-layer structure by a wear-resistant film of the anti-oxidation film and of Ta ₂ O _{5 which} has a SiO _2, vacuum deposition or Supatsutaringu methods Several thermal heads prepared by sequentially laminating with the above are soaked in artificial sweat having the component composition shown in Table 1 and pulled up, and allowed to stand in an atmosphere of 40 ° C. and 90% relative humidity for 48 hours, and then broken. The defect occurrence rate was investigated. Further, artificial seawater having the composition of components shown in Table 2 was prepared, the sample was immersed and pulled up, and the same test as above was conducted. The results of these tests are shown in Table 3. In addition, in this sample, the film thickness of the heating element is about 1000 to 2000Å, and the wiring conductor is about 1
˜2 μm, and the protective film was about 6 to 10 μm.

Experimental Example 2 A head with Ni or Sn electrolytic plating applied to the external connection terminal was connected to a drive circuit, and power was turned on to drive heat, and an aluminum foil was adhered to the surface of the protective film on the head wiring portion.
No short circuit occurred.

Experimental Example 3 Regarding the thermal heads of Condition 2 and Condition 4 in Table 3, it is necessary to generate the minimum peak heat generation temperature required for printing.
When the printing power per dot was examined, it was 1.2 W for condition 4 and 0.7 W for condition 2. Thus, by suppressing the surface roughness, the resistance of the wiring conductor decreased, It is possible to save power consumption, and therefore
It is possible to extend the driving life of a portable printer using a battery or the like.

Experimental Example 4 When the thermal responsiveness of the thermal heads of Condition 2 and Condition 4 in Table 3 was examined, the results are shown in the thermal response curve of FIG. The thermal head was as shown by the broken line B. That is, as shown by the solid line portion in FIG. 1, the thermal response of the thermal head is such that the smaller the surface roughness is, the more quickly the temperature rises when the voltage is applied to the heating element, and when the voltage application is stopped. It can be seen that the temperature drops rapidly.

Therefore, according to the invention, the roughness of the substrate surface or the volume density of the substrate material interacts with each other, the thermal response of the thermal head is improved, and the printing speed can be increased.
In addition, high print quality without tailing due to residual heat is provided.

〔The invention's effect〕

As described above, according to the present invention, since the pinholes are not generated in the protective layer, even if contact with a human body or metal occurs during installation or replacement of the thermal head to the thermal printer, it is also necessary to keep them wet. Even if it is used for a long time in an atmosphere or an atmosphere containing salt, or even if a metal-coated ink ribbon or thermal paper with a metallic part is used, the drive circuit malfunctions due to a broken wire or a short circuit due to corrosion. There is an effect that the reliability of the thermal printer can be made extremely high without causing the problem.

[Brief description of drawings]

FIG. 1 is a graph showing the thermal response of the thermal head according to the present invention, FIG. 2 is a plan view showing a conventional thermal head, FIG. 3 is a sectional view taken along the line III-III of FIG. 2, and FIG. And FIG. 5 is a sectional view of another conventional thermal head. In the figure, (2) is a substrate, (4 ₁ ) to (4 _n ) are heating elements,
(6) a common terminal, (8 ₁₎ ~ (8 _n) of the drive signal input terminal,
(10) is a wiring conductor, (12) is a protective film, and (14) is a glaze layer. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. Surface roughness is 0.3 μRa in terms of centerline average roughness.
The following insulating substrate and formed on this substrate,
A thermal head comprising: a thin film circuit including a plurality of heating elements that selectively generate heat; and a protective film that covers the thin film circuit.