JPS5953672B2 - Heating element and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention efficiently heats air, liquid, etc. without using a heating element having positive resistance-temperature characteristics (hereinafter abbreviated as P-TC characteristics) made of ceramics such as barium titanate. Relatively high-power, highly reliable resin/carbon-based P-T- that heats up well.
The present invention provides a heating element having C characteristics and a method for manufacturing the same.

Conventionally, techniques for manufacturing a resin/carbon heating element having PTC characteristics and a structure thereof have been reported. In general, the electrode configuration of a heating element is as shown in Fig. 1, in which electrodes 2 are formed opposite to each other in the thickness direction of a heating part 1, and a metal terminal is directly embedded in a part of the electrode 2, or a metal plate is press-bonded or A terminal 3 is provided by being attached to the electrode 2 by a method such as soldering.

On the other hand, a resin/carbon-based heating element with P-TC characteristics is composed of crystalline resin and conductive particles as its main components, and the thermal expansion of the heating element in the P-TC region is inevitable. The shrinkage coefficient shows a much larger value than that of the non-PTC region. In this way, when a metal terminal is pressed into a heat-generating part, there is of course a very large difference between the thermal expansion and contraction of the heat-generating part and that of the metal terminal. This may cause poor contact and lead to a burnout accident.

Furthermore, since the terminals are attached to the heat generating part itself, there are problems in that the heat dissipated from the terminals is large and causes temperature unevenness with other parts, as well as poor thermal efficiency. The present invention has been made to eliminate the above-mentioned drawbacks of the conventional technology, and the following is a second example of an embodiment of the present invention.
This will be explained with figures.

As shown in FIG. 2, the present invention provides a terminal mounting portion at the end position (or any intermediate position) of a resin/carbon-based heat generating portion 4 whose main components are crystalline resin and conductive particles. An insulating part 5 is provided, and the insulating part 5 is integrally connected to the heat generating part 4 by an appropriate means. The purpose is to eliminate poor contact at the terminal joint part, suppress heat radiation from the terminal 6 attached to the non-heat generating insulating part 5, eliminate local temperature unevenness, and obtain a heating element with uniform heat. It is.

Further, reference numeral 7 denotes an electrode provided to face the surfaces of the heat generating part 4 and the insulating part 5 in the thickness direction so as to conduct them. In this case, a particularly serious problem was the electrode crack that occurred when the portion of the electrode 7 at the joint 8 between the heat generating portion 4 and the insulating portion 5 repeatedly generated heat.

This is an important issue that must be resolved, as a concentrated current flows through the electrode crack and generates heat that exceeds the heat resistance temperature of the resin that makes up the heat generating part, resulting in a fatal burnout accident for the heat generating element. It was a great challenge. As mentioned above,
The coefficient of thermal expansion of the heat generating part 4 increases rapidly in the P-T-C region, and a large difference in thermal expansion occurs between the heat generating part 4 and the insulating part 5 made of ordinary thermosetting resin or thermoplastic resin, which is the cause. Therefore, cracks occur.

Therefore, in the present invention, a resin that makes the thermal expansion of the insulating part 5 approach that of the heat generating part 4 is selected to eliminate the crack in the joint part 8 shown in FIG. 2.

In reality, the temperature of the insulating part 5 during heat generation is lower than that of the heat generating part 4, and in order to match the thermal expansion of the two, a crystalline resin that is the same as the crystalline resin of the heat generating part 4 or has a lower melting point is used. and a thermosetting resin as a reinforcing agent as needed in the insulation part 5.
It can be obtained by blending with. In addition, the method for joining the heat generating part 4 and the insulating part 5 is that they are both mechanically strong and easy to form into any desired shape, so they are cold-formed separately and then heated in the same mold. Intermittent pressure molding is most suitable for mass production and can provide a resin/carbon heating element having PTC characteristics at low cost. Furthermore, it is necessary to establish electrical continuity between the heat generating part 4 and the insulating part 5 by some method, but since the heat generating element of the present invention is made of a mixture of crystalline resin and cannibal as described above, thermal expansion during heat generation, An electrode configuration that absorbs shrinkage, has good conductivity, and has adhesive strength is required.

A method proposed as a method that meets this condition is to apply a resin-based conductive paste such as silver paste or copper paste as a base treatment film to the surfaces of the heat generating part 4 and the insulating part 5, and then apply a good conductive layer on top of it as a base treatment film. This is a method of obtaining the electrode 7 by forming a single layer or multiple layers of metal plating such as titanium, copper, or nickel that undergoes thermal expansion and contraction. Next, specific examples will be described in detail.

First, crystalline resin (melting point 185°C by differential thermal analysis)
500 g of carbon black was melted on a hot roll, and 500 g of carbon black was added thereto and dispersed and kneaded. This kneaded material is pulverized to obtain a resin/carbon mixed powder. This powder 4
00g glass fiber blended thermosetting polyester resin 60
Blend 0g and mix uniformly with a V-type mixer. This mixed powder is placed in a mold, and an intermediate molded product of the heat generating part is made by cold pressing. Separately, 600 g of the glass fiber-containing thermosetting polyester resin and 400 g of crystalline resin (melting point 120°C) were mixed and cold-press molded to obtain an intermediate molded product for the insulation part. .

Then, the intermediate molded parts of the heating part and the insulation part, which were each intermediately molded by cold pressing, and the metal terminal 6 were combined in the same mold, and the temperature was 150°C, 150kg/Cnl.
Simultaneous hot pressing was carried out for 90 seconds at a ram pressure of .

As a result, the heat generating part 4 and the insulating part 5 are integrally connected, and the terminal 6 is attached to the insulating part 5. Next, masking is performed to prevent short circuits between different electrodes, silver paste is applied and baked on the surfaces of the heat generating part 4 and the insulating part, and a 0.2 to 0.3 μm copper film is formed on it by electroless plating. Then, a 2μ electrolytic copper film is applied on top of it for the purpose of lowering the electrode resistance, and a 5μ nickel plating is electrolytically or electrolessly applied to the top layer to serve as an electrode for the heat generating part 4 and to insulate it from the heat generating part 4. An electrode 7 having a structure that ensured conduction of the portion 5 was formed. The initial resistance of the heating element manufactured as described above at room temperature is 0.5Ω, and the resistance temperature characteristic shows a so-called PTC characteristic in which the resistance value increases rapidly from 150℃ as shown in Figure 3. It's showing.

FIG. 4 shows the measurement of the thermal expansion of the above-mentioned heating element with respect to the ambient temperature, where A is the heat generating part 4 in FIG. Insulating part 5 and C, which are made of a mixture with a crystalline resin having a melting point lower than that of the resin, respectively show the thermal expansion curves of an insulating part made of glass fiber-containing thermosetting polyester resin alone as a comparison of B above. . Now, when D-Cl2V was applied between the different electrodes of the heating element shown in Fig. 2 manufactured as described above, the internal center temperatures of the heating part 4 and the insulating part 5 were 160°C and 105°C, respectively. .

As can be seen from FIG. 4, the thermal expansion of 1.1% at 160° C. of the heat generating portion 4 and the 1.0% thermal expansion of the insulating portion 5 at 105° C. almost matched, and no electrode cracking occurred during actual energization. Furthermore, in order to check the joint strength between the heat generating part 4 and the insulating part 5, the bending strength [breaking load/unit cross-sectional area] of the joint part 8 was measured to be 5 to 8.
kg/MI, which was smaller than 8 to 9 kg/MiL of the heat generating part 4 and 10 to 12 kg/MIL of the insulating part 5, but it did not break down in practice. As described above, the heating element of the present invention has a self-temperature control function and has improved reliability due to thermal deformation, which has been considered a drawback of resin/carbon heating elements, and is suitable for practical use in industries. It is of great value.

[Brief explanation of drawings]

Fig. 1 is a perspective view of a conventional molded heating element, Fig. 2 is a perspective view showing an embodiment of the heating element according to the present invention, Fig. 3 is a diagram showing an example of the resistance temperature characteristics of the heating element, FIG. 4 is a diagram showing an example of thermal expansion with respect to ambient temperature in each part of the heating element of the present invention. 4...Heating part, 5...Insulating part, 6...
...terminal, 7...electrode.

Claims (1)

[Scope of Claims] 1. A heat generating part having a positive temperature coefficient of resistance made of crystalline resin and conductive particles, and a heat generating part having the same degree of thermal expansion in a temperature range where the positive temperature coefficient of resistance of this heat generating part increases greatly. an insulating part that expands and is integrally connected to the heat generating part by appropriate means, an electrode provided on opposing surfaces of the heat generating part and the insulating part, and an electrically connected to the electrode. A heating element characterized by comprising a terminal attached to an insulating part. 2. The heating element according to claim 1, wherein the insulating part contains at least a crystalline resin having a melting point that is the same as or lower than that of the crystalline resin constituting the heating part. 3. The heating element according to claim 1 or 2, comprising an electrode having a resin-based conductive paste as a base treatment film on the surfaces of the heating part and the insulating part, and a metal film applied thereon. . 4. A heat generating part made of crystalline resin and conductive particles having a positive temperature coefficient of resistance, and an insulating part having a thermal expansion comparable to the thermal expansion in the temperature range where the positive temperature coefficient of resistance of this heat generating part increases greatly. , each is cold-pressed separately and then hot-pressed in the same mold to be integrally bonded, and electrodes are provided on the opposing surfaces of the heat generating part and the insulating part, and electrically connected to the electrodes. A method of manufacturing a heating element, comprising: attaching a terminal to the insulating part so as to be connected.