JPH044713B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION An object of the present invention is to provide a positive temperature coefficient thermistor heating element that can stably generate a large amount of heat at a low cost.

Figures 1, 2, 4, and 5 are cross-sectional views of conventional PTC thermistor heating elements, respectively.
The figure is a perspective view of a positive temperature coefficient thermistor used therein. The examples shown in FIGS. 1 and 2 are examples in which a metal heat sink and a positive temperature coefficient thermistor are bonded together by pressure bonding, and FIGS. 4 and 5 are examples in which they are bonded with a conductive adhesive. In Fig. 1, 1 is a positive characteristic thermistor;
2 and 3 are electrodes attached to it, which are made of thermal sprayed aluminum, Ni plating, etc. Reference numerals 4 and 5 denote metal heat sinks, which have an uneven shape to increase the surface area, and are made of aluminum from the viewpoint of cost and thermal conductivity. 6 is a stainless steel spring plate, 7 is an insulator frame, and 8 is a metal plate spacer. In FIG. 2, the shape of the positive temperature coefficient thermistor is the same as that in FIG. Holes are made on both sides of the metal heat sinks 9 and 10, and bolts 13 and 14 are passed through the holes through insulating bushes 11 and 12 made of heat-resistant Teflon, etc., and tightened with nuts 17 and 18. 15 and 16 are spring washers. And each metal heat sink 4, 5, 9,
When a voltage is applied to 10, PTC thermistor 1 generates heat, and the heat is radiated by metal heat radiators 4, 5, 9, and 10, making it possible to obtain a large amount of heat. In addition, since a positive temperature coefficient thermistor is used as the heat source, it has a self-temperature control effect, and
It is a safe and useful heater that does not overheat. When using a positive temperature coefficient thermistor, in order to increase the heat generation amount, the positive temperature coefficient thermistor 1 and metal heat sinks 4, 5,
The lower the thermal resistance between the positive temperature coefficient thermistor 1 and the metal heat sinks 4, 5, the better.
If there are warps in 9 and 10, the contact area will be reduced, which is most detrimental to reducing thermal resistance. Therefore, in the examples shown in FIGS. 1 and 2, the surface of the positive temperature coefficient thermistor and the metal heat radiator were flat-polished and brought into close contact with each other, and then crimped with a spring or the like.

In this way, in the examples shown in Figures 1 and 2,
In order to fully utilize the effect of the metal heat radiator and obtain a large amount of heat, it is necessary to polish the surface of the element and the metal heat radiator, which requires a large number of steps and is very expensive. In addition, since it is pressed with a spring,
The pressure welding force changed and the amount of heat generated was unstable due to heat-induced fatigue of the spring or heat-induced creep of the insulating frame 7 shown in FIG.

In order to overcome these drawbacks, an example using a conductive adhesive is shown in FIGS. 4 and 5.

In Fig. 4, 19 is a positive characteristic thermistor;
Electrodes 20 formed on both sides by aluminum spraying, etc.
20' is given. Reference numerals 21 and 21' are conductive adhesives made of epoxy adhesive mixed with silver powder, etc., which bond the electrodes and the metal heat sinks 22 and 22'. In this way, the positive temperature coefficient thermistor 19 and the metal heat sink 2
2, 22' are bonded with conductive adhesive 21, 21', even if the bonding surfaces between the metal heat radiators 22, 22' and the positive temperature coefficient thermistor 19 are not smooth, there is conductivity between the irregularities. Filled with adhesive 21, 21',
Thermal resistance is reduced. Therefore, the metal heat sink 22,
22' and the PTC thermistor 19 are sufficiently thermally bonded without polishing, and the metal heat sink 22,
The effect of 22' is exerted and the amount of heat generated increases. In addition, spring washers, springs, frames, etc. that were necessary when the metal heat radiating elements 22, 22' and the PTC thermistor 19 were bonded together by crimping are no longer required, and the PTC thermistor heating element can be manufactured at low cost with a small number of parts. Can be provided.

Furthermore, since the thermal coupling does not use springs or the like, there is little variation and a constant amount of heat can be maintained at all times. Furthermore, since the metal heat sinks 22, 22' also serve as electrodes, there is no need for a new configuration for taking out the electrodes, but in the conventional example shown in FIG. 4, the conductive adhesives 21, 21' Metal heat sink 22, 2
2' and the electrodes 20, 20' of the positive temperature coefficient thermistor 19 are bonded together, so a reliable electrical connection between the two can be obtained.

Yet another conventional example is shown in FIG. Figure 5a
is a perspective view of a positive temperature coefficient thermistor used in this conventional example, and FIG. 5b is a sectional front view of a positive temperature coefficient thermistor heating element. In FIG. 5, 23 is a positive temperature coefficient thermistor, and 24 and 24' are electrodes made of aluminum or the like formed on both sides thereof. Conductive adhesives 25 and 25' are located at the center of the electrode surface, and insulating adhesives 26 and 26' are applied around them. After each adhesive is applied in this state, the metal heat sinks 27 and 27' are brought into contact and bonded.

In the conventional example shown in FIG. 5, an expensive conductive adhesive containing a large amount of silver or the like is used only on a part of the adhesive surface, and the amount used is small. Therefore, compared to the conventional example shown in FIG. 4, a positive temperature coefficient thermistor heating element can be provided at a lower cost. In the conventional example shown in FIG. 4, since the conductive adhesive 21, 21' is applied to the entire surface, when the metal heat sinks 22, 22' are bonded,
The conductive adhesive 21, 21' protrudes from the edge, and the electrodes 20, 20' and metal heat sinks 22, 2 on the opposite side are exposed.
There was a risk of a shot due to contact with 2', but the 5th
In the example shown in the figure, conductive adhesive 2 is applied almost only in the center.
5 and 25', only the insulating adhesives 26 and 26' protrude from the ends, and there is no fear of shoots, making it possible to provide a safe PTC thermistor heating element. However, since conductive adhesives contain a large amount of silver powder mixed into the resin, they are expensive, have extremely weak adhesive strength, and have limited heat resistance and lack reliability.

As mentioned above, although it has been known that a heat radiating element with a large input power can be obtained by fixing a metal heat radiator to a positive temperature coefficient thermistor, there has been no sophisticated method for realizing this. That is, if the conventional structure was mechanically crimped, it would be necessary to polish both surfaces, and a spring and a frame would be required, resulting in an increase in the number of parts and an increase in cost. In addition, the compression force was reduced due to deformation of the spring and frame due to high temperatures, resulting in poor reliability. In addition, even with the method using conductive adhesive, although expensive silver is used, the conductive adhesive contains a large amount of metal powder, so its hardness is hard, resulting in positive characteristics of the metal heat sink. The adhesion strength to the thermistor was weak, it was susceptible to vibration and shock, and the conductive adhesive also suffered from thermal deterioration, resulting in poor reliability. In addition, there are also positive temperature coefficient thermistors in which a metal heat sink is fixed to the electrode surface using a screw or the like via a heat conductive agent mixed with a metal oxide such as silicone oil. It was due to parts. This is because in order to establish electrical contact between the two through an insulating heat conductive agent, it is necessary to apply an external force to the two. In other words, there is a large difference in coefficient of thermal expansion between a ceramic positive temperature coefficient thermistor and a metal heat sink, and when used as a heat sink, the temperature of both rises and the dimensions of both change. A shift will occur at the interface. Therefore, in order to ensure reliable conduction even if the two move out of alignment, the insulating heat conductive agent interposed between the positive temperature coefficient thermistor and the metal heat sink is a paste-like material such as silicone oil or silicone grease. Rather than using a material to adhere them together, the structure was such that the two could be easily shifted, and a separate member was used to secure them together by pressing from the outside.

The present invention has been made in an attempt to overcome the above-mentioned drawbacks, and focuses on eliminating the discrepancy between a metal heat sink and a positive temperature coefficient thermistor due to the difference in thermal expansion coefficients in actual use. The object of the present invention is to reduce the size of the heating element and fix it to a compact positive temperature coefficient thermistor in an inexpensive and reliable manner, thereby providing a reliable positive temperature coefficient thermistor heating element that can be used with large inputs at a low cost.

FIG. 6 shows an embodiment of the present invention. In Fig. 6, 28 is a positive temperature coefficient thermistor, 29 and 29' are electrodes provided by thermal spraying, and 30 and 30' are insulating adhesives such as silicone and epoxy that harden near the Curie temperature of the positive coefficient thermistor 28. It has elasticity that absorbs the difference in elongation length due to the difference in thermal expansion between the positive temperature coefficient thermistor 28 and the metal heat sinks 31, 31', and presses the metal heat sinks 31, 31' against the electrode surface. It is glued together. Figure 6b is
An enlarged view of a portion of the contact surface between the metal heat radiator 31 and the positive temperature coefficient thermistor 28 is shown. Here, the surface of the electrode 29 is provided by thermal spraying as described above, and when viewed microscopically, it has small irregularities, and when pressed, the insulating adhesive 30 is pushed into the concave part, and the metal The surfaces of the heat sink 31 and the electrode 29 are in direct contact and can be bonded together while remaining electrically connected. The situation is shown in Figures 6c and d. Here, FIG. 6c shows the surface of the electrode 29 and the metal heat sink 31.
This figure shows how the contact resistance with the insulating adhesive 30 changes depending on the pressure applied when the insulating adhesive 30 is inserted between them. Moreover, FIG. 6d shows the state of the experiment at that time. At this time, the positive temperature coefficient thermistor 28 is provided with electrodes 29, 29' made of sprayed aluminum with a thickness of 30μ to 50μ, and insulating adhesives 30, 3
A silicone adhesive with a viscosity of 200 poise was used as 0'. The size of the positive temperature coefficient thermistor 28 is 10 mm x 30 mm x 2.8 mm, and the metal heat sink 31, 3
1' is made of aluminum. In this way, 0.5Kg
If a force of more than w/cm ² is applied, the positive temperature coefficient thermistor 2
Even if the insulating adhesive 30, 30' is interposed between the electrode 29, 8 and the metal heat sink 31, 31',
It can be seen that electrical connection between 29' and the metal heat sinks 31, 31' is possible.

In this way, since the electrodes 29 and 29' are applied by metal spraying, the surfaces are moderately rough compared to electrodes made of silver paste or Ni plating, and the unevenness can be removed from the metal heat sinks 31 and 31. Even if the surface of the electrodes 29 and 29' is not specially formed, the electrodes 29 and 29' have irregularities, and therefore are suitable as electrodes for use in the present invention. In addition, it can be easily formed thicker than electrodes made of silver paste or Ni plating, and since it is in a porous state, when the metal heat radiators 31, 31' are applied and pressed, the metal heat radiators 31, 31' The convex portions of the electrodes 29, 29' that are in contact with the electrodes 29, 29' are crushed, and the contact area becomes large. Furthermore, even if there is variation in the height of the convex parts, the high parts are crushed and the electrodes 29, 29' themselves absorb the variation and the number of contact points increases, so the contact state is stable. becomes. Furthermore, since the metal heat radiator and the PTC thermistor are in direct contact with each other at many points distributed over the entire surface of the PTC thermistor as described above, the thermal coupling between the two is good, and the effectiveness of the metal heat radiator is improved. It is possible to provide a heating element with a large amount of heat and a sufficient amount of heat.

In addition, an insulating adhesive is interposed between the metal heat sink and the PTC thermistor, and unlike conductive adhesives, this adhesive does not contain a large amount of metal powder inside, so it has a large resin content. The adhesive strength is stronger than conductive adhesives, and since it does not contain metal powder, it is not as hard as conductive adhesives, but has elasticity, and the recesses distributed on the electrode surface. is filled with the insulating adhesive and distributed uniformly between the metal heat sink and the positive temperature coefficient thermistor,
It is firmly attached on both sides. Therefore, there is no need for a member that presses the metal heat radiator from the outside, and a compact heat generator can be provided. At this time, since the adhesive used is an adhesive that hardens near the Curie temperature of the positive temperature coefficient thermistor, the adhesive can be cured at the Curie temperature, that is, the temperature of the actual operating state when used as a heating element. Here, the positive temperature coefficient thermistor is made of ceramic and has a coefficient of thermal expansion that is very small compared to that of metal, and there is a large difference between the two. Therefore,
When the two are placed in a state where there is a temperature difference, there will be a difference in length, so it is important to take these into consideration when joining and using the two as a heating element. In the present invention, only an insulating adhesive is used for fixing the metal heat sink and the positive temperature coefficient thermistor. As mentioned above, this adhesive has higher adhesive strength than a conductive adhesive, and also has higher elasticity than a conductive adhesive.

In the present invention, only such an insulating adhesive is used, and since the insulating adhesive is filled in the recesses distributed on the electrode surface, the convex portions on the electrode surface are directly connected to the metal heat sink. Even though they are in contact, the thickness of the adhesive is maintained at an appropriate level due to the presence of the recess, and it is possible to absorb the deviation of the bonded surfaces due to the difference in coefficient of thermal expansion between the metal heat sink and the PTC thermistor.

Furthermore, because we use an insulating adhesive that hardens near the Curie temperature of the PTC thermistor, the metal heat sink and the PTC thermistor will stick and harden at the temperature at which the heating element is actually used, that is, in high-temperature conditions. can. Generally, the creep phenomenon occurs more easily in adhesives at high temperatures than at low temperatures, and the adhesive strength decreases. In this way, the present invention can reduce the temperature during actual use.
In other words, by using an adhesive that hardens near the Curie temperature, it is possible to eliminate dimensional deviations between the metal heat sink and the positive temperature coefficient thermistor during actual use, that is, at high temperatures, and to prevent stress on the adhesive at high temperatures, where the adhesive deteriorates quickly. This was done so that it would not be applied. In addition, when not in use, misalignment occurs due to the difference in thermal expansion coefficient between the two, but at that time, the adhesive strength is less likely to deteriorate due to the low temperature, and as mentioned above, due to the elasticity of the insulating adhesive, It is something that can be absorbed. As described above, according to the present invention, the metal heat sink and the positive temperature coefficient thermistor can be reliably fixed,
There is no peeling during actual use, and a heating element that is highly reliable and suitable for practical use can be provided even without a member that presses both of them from the outside. And since there is no need for a member to press the metal heat radiator from the outside, a compact heat generator can be provided.

In the examples, only the shape of the metal heat radiator is shown as a comb-shaped block heat radiator, but other shapes may be used.
Various heat radiators are possible, such as a die-cast heat radiator with holes, a heat radiator formed by processing a flat plate into a corrugated shape, or a simply flat plate-shaped heat radiator, but the present invention
This is not limited to this in any way. Similarly, the shape of the PTC thermistor may be any shape such as a square, a disk, or a donut.

As described above, according to the present invention, the thermal bonding between the electrode surface and the metal heat sink is sufficient by interposing the insulating adhesive, even without polishing the electrode surface and the metal heat sink to be particularly flat, and furthermore, the positive temperature coefficient thermistor Since the metal heat sink and the PTC thermistor are in direct contact with each other at many points distributed over the entire surface, the thermal coupling between the two is improved, allowing the metal heat sink to fully demonstrate its effectiveness and reducing the amount of heat generated. A large positive temperature coefficient thermistor heating element can be easily provided. In addition, since the electrodes are applied by thermal spraying, unevenness can be easily formed on the electrode surface, and by simply pressing and bonding, there is no need to use expensive conductive adhesives, and insulating adhesives can be used. The metal heat radiating element can also serve as an electrode, and a compact heating element can be provided at low cost with a simple configuration. Insulating adhesives are electrically insulating even if they stick to other parts or protrude slightly, so there is no danger of shoots, etc., and they are easy to handle, simplifying assembly jigs and reducing man-hours. It is also effective in reducing
Furthermore, the insulating adhesive has sufficient strength and heat resistance, and is highly reliable.

In addition, since the adhesive used is one that hardens near the Curie temperature of the PTC thermistor, misalignment of the bonded surface due to the difference in thermal expansion coefficient between the metal heat sink and the PTC thermistor will occur under actual use, i.e. It is possible to provide a heating element that can be removed at high temperatures when the adhesive deteriorates significantly, that allows the two to be firmly fixed even after long-term use, that is highly reliable, and that is excellent for practical use.

[Brief explanation of drawings]

Figures 1, 2, and 4 are sectional front views of a conventional positive temperature coefficient thermistor heating element, Figure 3 is a perspective view of a positive temperature coefficient thermistor of the same heating element, and Figures 5 a and b are another conventional example. A perspective view of an example positive temperature coefficient thermistor and a sectional front view of a positive coefficient thermistor heating element, FIG. 6a,
b, c, and d are diagrams showing a sectional front view, a partially enlarged sectional view, a characteristic diagram, and a characteristic measurement diagram of an embodiment of the present invention. 28...Positive characteristic thermistor, 29, 29'...
Electrode, 30, 30'... Insulating adhesive, 31, 3
1'...Metal heat sink.

Claims (1)

[Claims] 1 A positive temperature coefficient thermistor is provided with electrodes by metal spraying, and a metal heat sink is fixed to the electrode surface using only an insulating adhesive that hardens near the Curie temperature of the positive temperature coefficient thermistor, and the convexity of the electrode surface is fixed to the positive temperature coefficient thermistor. A positive temperature coefficient thermistor heating element, wherein the part is in direct contact with the metal heat radiating element, and the concave part of the electrode surface is filled with an insulating adhesive.