JPH03280317A - Safety circuit of flat heater - Google Patents

Abstract

PURPOSE:To ensure 'OFF' state of a fuse circuit by providing a gap on which a threaded defective pattern is formed, on a wiring pattern on the surface of an insulator, and by welding a low temperature fusible alloy to the gap position, so as to connect a wiring pattern and to obtain a fuse thereby. CONSTITUTION:A heating element 1 is composed of a base material 2 and a wiring pattern 3 formed on the surface of the base material 2, and the wiring pattern 3 is formed out of a heating resistor pattern 3A and a conductor pattern 3B. A gap 4 is provided on a part of the conductor pattern 3B. The part of the conductor pattern 3B is notched in a certain size, and the base material 2 in the part is exposed thereby, and the gap 4 is thus formed, while an insulating pattern 5 composed of a wetting defect is formed on the surface of the base material 2 in such a way that the gap 4 is filled, and a fuse part 7 is formed by welding a solder 6 of low melting point in such a way that a bridge is formed on the edge of the conductor pattern 3B that is opposed over the gap 4. When the fuse part 7 is overheated to a preset temperature, the solder 6 is melted and is attracted to the end part of the conductor pattern 3B, and the circuit is turned 'OFF' thereby.

Description

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

(Prior Art) In recent years, office automation equipment such as copy machines and facsimile machines have become widespread. OA equipment has become widespread, even in general households, and in order to meet the demands of each user, various types of OA equipment have not only improved their functionality but also become smaller and thinner.

Furthermore, most of each FJiOAaZj is equipped with a printer as an output device, and thermal transfer printers are often used due to the balance between price and functionality. This thermal transfer printer uses a heating element called a thermal head to apply heat to thermal recording paper or a thermal transfer ribbon to develop color, or to melt ink and transfer it to paper. A thin and compact planar heater is usually used as this heating element.

This type of flat heater is equipped with a safety circuit to prevent accidents due to overheating of the heater.

An example of this safety circuit is JP-A-63-160128.
There is one shown in the publication. This safety circuit includes a fuse circuit (not shown) with a fuse section on the surface of the heater.
is formed. The structure of this fuse portion will be explained with reference to FIGS. 3 and 4.

In FIG. 183, reference numeral 10 indicates a heating element, and this heating element 10 has an insulating substrate 11 and an insulating substrate 11.
It consists of a conductor or heat generating resistor pattern 12 screen printed on the surface of the conductor or heating resistor pattern 12. This conductor or heating resistor pattern 12 is cut at a predetermined position to form a gap 13. And this gap 13
A low melting point solder 14 is welded to form a bridge between the opposite ends of the pattern.

In this way, the pattern forms a fuse portion 15 short-circuited by the low melting point solder 14. Therefore, in the safety circuit described above, when the heater overheats, the solder 14 melts. The solder bridge is then drawn to the edge of the pattern by the surface tension of the molten solder, turning off the fuse circuit and activating the safety circuit.

(Problem to be Solved by the Invention) However, in the above-mentioned safety circuit, even if the solder at the fuse part melts due to overheating of the heater, if the insulating substrate 11 has good wettability, the molten solder spreads on the substrate and the pattern is short-circuited. If this happens, the fuse circuit will not turn off and the safety circuit will malfunction. As a result, the heater overheats, raising the temperature of the head body, which may cause other parts to malfunction.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a safety circuit for a flat heater in which the fuse circuit is reliably turned off and the safety circuit operates accurately when the heater overheats, thereby solving the problems of the conventional techniques described above. It is about providing.

[Structure of the invention]

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a gap in the wiring pattern on the surface of the insulator, forms a pattern of poor wettability at the position of the gap, and forms a pattern of poor wettability in the wiring pattern on the surface of the insulator. connect the wiring pattern by melting the low temperature fusible alloy on the surface of the
It is characterized in that the gap is short-circuited.

(Function) According to the present invention, a gap is provided in the wiring pattern on the surface of the insulator, a pattern of poor wettability is formed at the position of the gap, and a low temperature fusible alloy is welded to the surface of the pattern of poor wettability. By connecting the wiring patterns and shorting the gap, the heater overheats and melts the alloy, which is reliably separated on the poor wettability pattern due to surface tension, and as a result, the fuse circuit is reliably turned off. can do.

(Embodiment) An embodiment of the safety circuit for a flat heater according to the present invention will be described below with reference to FIGS. 1 and 2.

In FIG. 1, reference numeral 1 indicates a heating element, and the heating element 1 is composed of an insulating substrate 2 and a wiring pattern 3 formed on the surface of the insulating substrate 2. In FIG. The insulating substrate 2 is made of a flat heat-resistant insulator such as an alumina substrate, while the wiring pattern 3 is divided into a heating resistor pattern 3A and a conductor pattern 3B. Both patterns 3A and 3B may be formed separately on both sides of the insulating substrate 2, or may be formed on one side.

To form the heating resistor pattern 3A, first, a ruthenium oxide paste or a silver palladium paste is printed on the insulating substrate 2 using a screen printing method, which is a thick film printing technique. Then, this paste is sintered in air at about 850° C. to form a pattern. On the other hand, the conductive pattern 3B can be formed by screen printing a silver-based or gold thread paste in a similar manner and sintering it in air at about 850°C.

Further, a gap 4 is provided in a part of this conductor pattern 3B. This gap 4 covers the conductor pattern 3B by approximately 5
A notch is cut out over a length of mm, and the insulating substrate 2 is exposed in that part.

Then, an insulating pattern 5 made of a material with poor wettability is formed on the surface of the insulating substrate 2 so as to fill this gap 4. Borosilicate glass or the like is used for this insulating pattern 5, and paste-like borosilicate glass can be printed and sintered similarly to the pattern of the conductor pattern 3B. Instead of the insulating pattern 5 made of borosilicate glass, it is also possible to sinter ceramics and polish its surface to form a smooth surface.

Furthermore, low melting point solder 6 is welded to form a bridge between the ends of the conductor patterns 3B facing each other across the gap 4. In this way, the conductor pattern 3B has a fuse part 7 short-circuited with a low melting point half [116].
It is designed to form a

When the fuse portion 7 configured as described above becomes overheated and reaches a predetermined temperature, the solder 6 melts. 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 due to surface tension. As a result, the fuse circuit can be turned off.

Note that the low-temperature fusible alloy solder used in the bridge can have various melting point temperatures depending on its composition, so the temperature at which the fuse circuit turns off can be set depending on the allowable operating temperature of the heating element. .

〔Effect of the invention〕

As is clear from the above description, according to the present invention, a gap in which a pattern of poor wettability is formed is provided in the wiring pattern on the surface of an insulator, and a low-temperature fusible alloy is welded to the gap position to form the wiring pattern. were connected to form a fuse, so when the heater overheats, the alloy forming the fuse melts and can be reliably separated on the poor wettability pattern due to surface tension. As a result, effects such as being able to reliably turn off the fuse circuit are achieved.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing an embodiment of a safety circuit for a flat heater according to the present invention, FIG. 2 is a cross-sectional view of the same, FIG. 3 is a plan view showing an example of a conventional safety circuit for a flat heater, and FIG. The figure is a cross-sectional view of the same. DESCRIPTION OF SYMBOLS 1... Heating element, 2... Insulating substrate, 3... Wiring pattern, 4... Gap, 5... Insulating pattern, 6...
··solder.

Claims (1)

[Claims] A gap is provided in the wiring pattern on the surface of the insulator, a pattern of poor wettability is formed at the position of this gap, a low temperature fusible alloy is welded to the surface of the pattern of poor wettability, the wiring pattern is connected, and the gap is closed. A safety circuit for a flat heater characterized by a short circuit.