JP3142540B2 - Safety circuit for flat heater - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a flat heater, and more particularly to a heater provided in a thermal printer of OA equipment.

(Prior Art) In recent years, there has been remarkable spread of OA equipment represented by a copier, a facsimile, and the like. The spread has spread widely to ordinary households, and in order to meet the demands of each user, various types of OA equipment have been reduced in size and thickness as well as their functions have been improved.

Most of the various OA devices are equipped with a printer as an output device, and a thermal transfer printer is often used because of a balance between price and function. In this thermal transfer printer, a heating element called a thermal head is used to apply heat to thermal recording paper or a thermal transfer ribbon to form a color, or to melt ink to transfer the ink to a paper. And
Usually, a thin and compact flat heater is used for the heating element.

This type of flat heater is provided with a safety circuit to prevent an accident due to overheating of the heater. An example of this safety circuit is disclosed in Japanese Patent Application Laid-Open No. 63-160128. In this safety circuit, a fuse circuit (not shown) having a fuse portion on the surface of the heater is formed. The structure of the fuse section will be described with reference to FIGS. 3 and 4.

In FIG. 3, reference numeral 10 denotes a heating element.
The heating element 10 includes an insulating substrate 11 and a conductor or heating resistor pattern screen-printed on the surface of the insulating substrate 11.
Consists of 12 parts. A predetermined position of the conductor or the heating resistor pattern 12 is cut so that a gap 13 is formed. A low-melting-point solder 14 is welded so as to form a bridge between the ends of the opposing patterns with the gap 13 interposed therebetween. In this way, the pattern forms the fuse portion 15 short-circuited by the low-melting-point solder 14. Therefore, in the above-described safety circuit, when the heater is overheated, the solder 14 is melted. Then, the solder bridge is attracted to the end of the pattern by the surface tension of the molten solder, so that the fuse circuit is turned off and the safety circuit operates.

According to this heater, the heat of the heating element can be easily transmitted to the fuse, and the fuse can be easily activated when abnormal heat is generated.

(Problems to be Solved by the Invention) However, in the above-described safety circuit, even if the solder in the fuse portion is melted due to overheating of the heater, if the wettability of the insulating substrate 11 is good, the molten solder spreads on the substrate and the pattern is short-circuited. There is a problem that the fuse circuit does not turn off due to the state as it is and the safety circuit malfunctions. For this reason, the temperature of the head body increases due to overheating of the heater, which may cause a failure of other components.

That is, when the heating resistor pattern 12 is formed by using the thick film technology, it is necessary to increase the adhesion strength to the surface of the insulating substrate 11, so that the surface of the insulating substrate 11 needs to have a moderate roughness. is there. On the other hand, when a moderate roughness is formed on the surface of the insulating substrate 11 and the solder is directly applied to the surface of the insulating substrate 11 on which the roughness is formed, the surface of the insulating substrate 11 wets the solder. As described above, even if the solder melts, if the insulating substrate 11 has good wettability, the molten solder spreads over the substrate, the pattern remains short-circuited, and the fuse circuit is turned off. However, there is a problem that the safety circuit may malfunction.

Further, if it is necessary to avoid forming the heating resistor pattern 12 using the thick film technology, there is a problem that the manufacturing cost increases.

Therefore, an object of the present invention is to solve the above-described problems of the conventional technology, to reduce the manufacturing cost by employing the thick film technology, and to surely turn off the fuse circuit when the heater is overheated. Therefore, it is an object of the present invention to provide a heater in which the safety circuit operates reliably.

[Configuration of the invention]

(Means for Solving the Problems) To achieve the above object, a plate-like insulator, a heating element formed on the surface of the insulator, and a surface of the insulator that conducts heat generated by the heating element A conductive pattern formed by thick film technology and partially provided with a gap, and a conductive alloy mainly formed of low-temperature fusible gold and formed on an insulator and electrically connecting the gaps of the conductive pattern And a poorly wettable pattern formed between the gap and interposed between the surface of the insulator and the conductive alloy and having poorer wettability on the surface of the conductive alloy than the insulator. It is characterized by the following.

(Operation) According to the present invention, a gap is provided in a wiring pattern on an insulator surface, a poor wettability pattern is formed at the gap position, and low-temperature fusible gold is welded to the surface of the poor wettability pattern. Since the wiring pattern was connected and the above gap was short-circuited, the heat of the heating element was easily transmitted to the low-temperature fusible alloy. And, as a result, the fuse circuit can be reliably turned off.

(Embodiment) An embodiment of a heater according to the present invention will be described below with reference to FIG. 1 and FIG.

In FIG. 1, reference numeral 1 denotes a heating element.
The heating element 1 includes an insulating substrate 2 and a wiring pattern 3 formed on the surface of the insulating substrate 2. The insulating substrate 2 is made of a flat heat-resistant insulator typified by an alumina substrate, while the wiring pattern 3 is composed of a heating resistor pattern 3A as a heating element and a conductor pattern 3B as a heat transfer wiring pattern. Divided into These two patterns
3A and 3B may be formed separately on both surfaces of the insulating substrate 2, or may be formed on one surface.

In order to form the heating resistor pattern 3A, first, a ruthenium oxide-based paste or a silver-palladium-based paste is printed on the insulating substrate 2 by using a screen printing method which is a thick film printing technique. Then, the paste is sintered at about 850 ° C. in the air to form a pattern. on the other hand,
The conductor pattern 3B is screen-printed with a silver-based or gold-based paste in the same process, and the same
The pattern can be formed by sintering at ℃.

A gap 4 is provided in a part of the conductor pattern 3B. This gap 4 is about 5 mm for the conductor pattern 3B.
, And the insulating substrate 2 is exposed at that portion.

Then, an insulating pattern 5 made of a poorly wettable body is formed on the surface of the insulating substrate 2 so as to fill the gap 4. Borosilicate glass or the like is used for the insulating pattern 5, and paste borosilicate glass can be printed and sintered in the same manner as the pattern of the conductor pattern 3B. Instead of the insulating pattern 5 made of borosilicate glass, ceramics may be sintered, and the surface thereof may be polished to form a smooth surface.

Further, low-melting-point solder 6 is welded so as to form a bridge between the ends of the conductor pattern 3B facing each other with the gap 4 interposed therebetween. Thus, the conductor pattern 3B forms the fuse portion 7 short-circuited by the low melting point solder 6.

When the fuse section 7 configured as described above is overheated and reaches a predetermined temperature, the solder 6 is melted. As a result, the molten solder 6 forming the bridge is drawn to the end of the conductor pattern 3B on the borosilicate glass insulating pattern 5 by surface tension. As a result, the fuse circuit can be turned off.

In addition, since the low-temperature fusible gold solder used for the bridge can set various melting point temperatures depending on its composition,
The temperature at which the fuse circuit is turned off can be set according to the allowable operating temperature of the heating element.

〔The invention's effect〕

As is apparent from the above description, according to the present invention, the wiring pattern on the insulator surface is provided with a gap in which the poorly wettable pattern is formed, and the low-temperature fusible gold is welded to the gap position to form the wiring pattern. Are connected to form a fuse, so that if the heater is overheated, the alloy forming the fuse is melted and can be reliably separated on the poorly wettable pattern by surface tension. As a result, there is an effect that the fuse circuit can be reliably turned off.

In addition, it is possible to reduce the manufacturing cost by forming the wiring pattern by the thick film technique, and to surely turn off the fuse circuit when the heater is overheated and to operate the safety circuit accurately.

[Brief description of the drawings]

FIG. 1 is a plan view showing an embodiment of a safety circuit of a flat heater according to the present invention, FIG. 2 is a transverse sectional view of the same, FIG. 3 is a plan view showing an example of a safety circuit of a conventional flat heater, and FIG. The figure is the same cross-sectional view. 1 ... heating element, 2 ... insulating substrate, 3 ... wiring pattern,
4 ... gap, 5 ... insulating pattern, 6 ... solder.

Claims (1)

(57) [Claims] 1. A plate-like insulator, a heating element formed on a surface of the insulator, and a thick film technique formed on a surface of the insulator that conducts heat generated by the heating element, and a gap is partially formed. And a conductive alloy formed mainly on a low-temperature fusible alloy and formed on an insulator and electrically connecting gaps of the conductive pattern; and a conductive alloy between a surface of the insulator and the conductive alloy. And a poorly wettable body pattern formed between the gaps and having poorer surface wettability with respect to the conductive alloy than with the insulator.