JPS643668B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to thermal print heads.

As is well known, the thermal print head is
As shown in the figure, a protruding glaze layer 2 is formed on the surface of a ceramic substrate 1 such as alumina, and a pair of conductive layers 3 are formed over the glaze layer 2 from the substrate 1.
are provided, and both conductive layers 3 are formed on the top surface of the glaze layer 2.
It is constructed by providing a resistance layer 4 for heat generation over the two sides. In some cases, the resistive layer 4 is formed first and then the conductive layer 3 is formed on its surface. In the figure, a protective layer provided on the surface is omitted.

Incidentally, in a thermal print head having such a structure, it is desired that the conductive layer 3 be as thin as possible. The conductive layer 3 is usually formed by screen printing a thick film paste containing noble metal powder and etching it into a desired pattern. Therefore, when the conductive layer 3 is thick, the amount of thick film paste used is large, and therefore the amount of precious metal is also large, which increases the manufacturing cost. In addition, if it is thick, etching will take a long time, and high-precision etching cannot be expected, and when printing other layers on the surface of the conductive layer, there will be large steps due to unevenness, making printing accuracy difficult. may be damaged.

A more fatal flaw than these is that the thicker the conductive layer 3 is, the higher the thermal conductivity, so the heat generated in the resistive layer 4 is more likely to dissipate via the conductive layer 3. It is. The heat of the resistive layer 4 is conducted to the thermal paper to print, but if the heat escapes to other parts as described above, the temperature will drop, so in order to print clearly, it is necessary to In order to increase the amount, it becomes necessary to increase the applied voltage.

As described above, it is desirable that the conductive layer 3 be thin, but if it is too thin, the following problems will occur. That is, as shown in the enlarged view of FIG. 2, when the conductive paste 5 for the conductive layer 3 is printed on the stepped portion of the glaze layer 2, the paste flows and the shape of the pattern collapses as shown by the dotted line. There is. If the paste is thin, the paste film may break due to this deformation. It is clear that if a conductive layer is formed by sintering with interruptions, it cannot be used as a conductive layer.

SUMMARY OF THE INVENTION An object of the present invention is to provide a thermal print head having a thin conductive layer made of thick film paste that is less likely to deform.

In this invention, a filler is added to a thick film paste consisting of 37-59% by weight of noble metal powder, 1-3% by weight of glass frit, and 40-60% by weight of organic vehicle.
It is characterized by printing and sintering a material containing 800 ppm to form a conductive layer for energizing the resistance layer.

As the noble metal powder, gold, silver, platinum, vanadium, etc. are used alone or in combination. For example, lead borosilicate glass powder can be used as the glass frit. The organic vehicle consists of a resin and a solvent. For example, ethyl cellulose can be used as the resin, and terpineol, butyl carbitol acetate, etc. can be used as the solvent.

This thick film paste is significantly different from the conventional one in that the number of organic vehicles is increased several times.
The organic vehicle is effective in improving the thixotropic properties of the paste, and this improvement can prevent deformation during printing and coating. Therefore, problems will not occur even if the film is made thin. Furthermore, since the organic vehicle is scattered during sintering, the larger the amount of organic vehicle contained, the thinner the conductive film will be formed after sintering.
If the amount of organic vehicle added is less than 40% by weight, it will not be sufficient to improve the thixotropic properties, and if it exceeds 60% by weight, the amount of precious metal added will be too small and conductivity will be impaired, which is not convenient. bad.

As the filler, alumina (Al ₂ O ₃ ) ceramic, titanium oxide (TiO ₂ ), etc. can be used. If such a filler is added, gas on the surface of the substrate or in the paste during sintering will easily diffuse to the outside through the interface between the filler and the paste. If the gas is trapped inside without dissipating, bubbles will occur, which can cause blisters and cracks in the membrane. However, if a filler is mixed in, it becomes possible to reliably prevent blistering and cracking of the film. If the amount added is less than 300ppm, it is insufficient for degassing, and if it exceeds 800ppm,
Since the filler itself is an insulator, its conductivity as a conductive layer is impaired, which is inconvenient, and it also becomes a nuisance during etching, making it impossible to expect highly accurate etching. The particle size of the filler is suitably 0.1 to 0.35μ.

The amount of noble metal may be 59 to 37% by weight depending on the amount of other additives added. Conventionally, this addition amount was 80
Since it is ~90% by weight, the amount of precious metals used will continue to be small, and the manufacturing cost will be accordingly low, which is convenient.

Next, embodiments of the invention will be described. 51% gold by weight
A thick film paste was obtained by adding 2% by weight of lead glass and dispersing it in 47% by weight of an organic vehicle (a mixture of ethyl cellulose and terpineol).
This was screen printed with 500 ppm of alumina added and sintered. The sheet resistance of the obtained conductive layer was 22 mΩ/□, and its thickness was 3 μ (3 coats).
And so. During this formation, there was no deformation at the stepped portion as shown in the figure. Also, swelling of the membrane,
No cracks occurred. Note that no deformation occurred even when the thickness of the conductive layer was 2.5 μm. Therefore, it can be understood that the thickness should be 2.5 to 3 μm.

By the way, in the past, a paste was obtained using 85% by weight of gold, 3% by weight of lead glass, and 12% by weight of organic vehicle, which was screen printed and then sintered at 850°C. The sheet resistance of the obtained conductive layer was 8 mΩ/□, and the thickness was 6 μm (coated twice). When formed with such a thickness, it is possible to avoid discontinuities due to deformation at stepped portions. In the conductive layer thus obtained, 3 to 6 blisters and cracks were observed per 180 cm ³ .

As described in detail above, according to the present invention, it is possible to make the conductive layer used for supplying current to the heat generating resistance layer much thinner than before, and even if it is made this thin, the stepped portion of the conductive layer Since there is no discontinuity in the conductive layer, the formation of blisters and cracks in the film can be prevented, and the conductive layer can be made thinner without any problems, printing of another layer on the surface of the conductive layer is smooth, and the printing of another layer from the resistive layer is smooth. It is also possible to reduce the amount of heat dissipated via the conductive layer, thereby preventing heat wastage and enabling clear printing.

[Brief explanation of drawings]

FIG. 1 is a sectional view of the thermal printer head, and FIG. 2 is a partially enlarged sectional view. 1...Substrate, 2...Glaze layer, 3...Conductive layer, 4...Resistance layer.

Claims (1)

[Claims] 1 Precious metal powder 37-59% by weight, glass frit 1
A thermal print made of a thick film paste consisting of ~3% by weight and 40% to 60% by weight of an organic vehicle to which 300 to 800ppm of filler is added, and used as a conductive layer for current conduction of a heat generating resistor with a thickness of 3μ or less. Head.