JPH0398282A - Ptc heating element - Google Patents

Abstract

PURPOSE:To obtain a highly reliable heating element without generating any peeling caused by thermal expansion difference by directly bonding a PTC heating element with a metal radiator using a corrugated fin with adhesives. CONSTITUTION:Adhesives 24, 25 are applied onto the electrode surfaces on the both surfaces of a PTC heating element body 20, respectively, and respective bent protruding parts of the fins 222, 232 of metal radiators 22, 23 are pressed onto the surfaces of electrode layers 212, 213, then dried and baked. In this case, by the press contact of the radiating fins 222, 232 to the electrode layers 212, 213, the respective protruding parts of the radiating fins 222, 232 are passed through the adhesive layers and directly touched by the electrode layers 212, 218. Consequently, the electric continued state and also thermal continued state between the electrode layers 221, 212 of the PTC element 21 and the fins 222, 232 are ensured.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a barium titanate semiconductor or a barium titanate semiconductor, which is used as an auxiliary heater for an indoor heater or an air conditioner, or a heat source for a dryer for clothes and bedding. The present invention relates to PTC heating elements such as polymer PTC.

[Prior Art] This type of heating element is known as a positive temperature coefficient thermistor heating element, and is made of PTFE with electrode layers formed on both sides.
The C semiconductor substrate constitutes a PTC heating element. A metal heat radiator is attached to this heat generating element so that heat exchange is performed at this heat radiator portion. In this case, the bonding surface between the PTC heating element and the metal heat sink requires not only mechanical adhesive strength but also electrical and thermal bonding.

Conventionally, such a PTC heating element is configured as shown in FIG. 4, for example. In this figure, PTC heating element 11
For example, paris titanate. On both the front and back sides of the element body l2, which is formed of a semiconductor and is formed into a rectangular plate shape,
It is constructed by forming thin electrode layers 131 and 132.

Metal heat radiators 141 and 142 are set on the front and back surfaces of the heating element 1l, respectively. The metal heat sink 141 is composed of metal plates 151 and 152 set in parallel, and a metal corrugate fin 16 formed by folding back a thin metal plate, which is interposed between the metal plates 151 and 152. 141 and 1
42 and the corrugated fin 16 are joined together by brazing or the like and are integrated. Although not shown in its entirety in the figure, the heat sink 142 is similarly configured.

Then, the electrode layers 131 and 13 of the PTC heating element 11
2, integrally formed metal heat sinks 141 and 142 are placed on the respective surfaces of the metal heat sinks 141 and 142 with an insulating adhesive 171.
and 172 were adhesively fixed.

These metal heat sinks 141 and 142 and PTC heating element 1l
When bonding with adhesives 171 and 172,
In some cases, the metal plate constituting the heat dissipation body and the electrode surface of the heating element 11 each utilize slight irregularities, and the irregularities are filled with an insulating adhesive to create a gap between the metal plate and the electrode layer. It is made to be glued.

Therefore, the heating elements 11 of the heat sinks 141 and 142
The filling amount of the adhesive varies depending on the flatness of the adhesive surface of the metal plate 151 facing the surface of the metal plate 151 and the surfaces of the electrode layers 131 and 132 of the heating element 11. For example, if an excessive amount of adhesive is applied, poor electrical continuity will occur between the metal plate of the heat radiator and the electrode layer of the heat generating element l1, and the heat generating element will no longer function as a heat generating element. Therefore, when manufacturing this heating element, there was an improvement in yield and productivity.

In addition, because the structure is such that the metal bending plate of the heat sink and the heating element are directly bonded, heat cycles (thermal stress)
This also caused problems such as deterioration of heat dissipation characteristics. Specifically, due to the difference in thermal expansion characteristics at the bonded part,
The metal plate may peel off from the surface of the heating element 11,
Heat dissipation characteristics deteriorate.

Furthermore, attempts have been made to bond the heat radiator and the heat generating element together by using a conductive adhesive and an insulating adhesive in combination. However, if the adhesive protrudes from the periphery of the adhesive surface or drips down, problems arise in electrical insulation, resulting in poor reliability.

[Problems to be solved by the invention This invention was made in view of the above points, and
C A heating element and a metal heat sink can be easily joined to improve workability, and the adhesive strength is excellent in electrical and thermal contact, and has excellent durability. The present invention aims to provide a PTC heating element that can be used as a PTC heating element.

[Means for Solving the Problems] In the PTC heating element according to the present invention, each electrode surface of the PTC heating element having electrode layers formed on both sides is formed by bending a thin metal plate into a wave shape. The folded portion of the radiation fin is brought into direct contact with the electrode surface of the heat generating element, and the fins are bonded to each other with an adhesive.

5 [Function] In the PTC heating element configured in this way, the PTC
For example, after applying an insulating adhesive to the electrode surface of the heating element,
The heat dissipating fin folded convex portion formed in the shape of a corrugated fin is brought into pressure contact with the adhesive applied surface, and can be constructed by pressurizing and drying and baking. Direct contact between the electrode surface of the heat generating element and the convex portion of the fin provides electrical and thermal bonding, and in particular, the bond formed between the convex portion of the fin and the electrode surface. The adhesive effectively ensures adhesive strength. In this case, even if the amount of adhesive applied is excessive, for example, the excess adhesive will be retained between the convex parts of the fins and will not affect the electrical and thermal contact, and the fins will not be subject to thermal stress. As a result, problems such as peeling caused by the difference in thermal expansion do not occur, and a highly reliable heating element can be obtained.

[Embodiments of the Invention] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Figure 1 shows its overall configuration.
The C heating element 21 has a rectangular plate shape, and one PTC heating element main body 20 is constructed by arranging a plurality of PTC elements 2I (five in the illustrated example) in series.

The PTC element 21, as shown partially in cross section in FIG.
For example, the main body 211 is made of barium titanate semiconductor or polymer PTC, and both sides are plated with Ni electroless plating.
Electrode layer 2 {2 and 213 made of ``Ag paste'' or ``ohmic Ag paste + cover Ag paste'' etc.
The structure has been formed.

Heat sinks 2 are provided on both sides of the heating element main body 20, respectively.
2 and 23 are set oppositely. The heat radiating bodies 22 and 23 are constituted by metal plates 221 and 231 and heat radiating fins 222 and 232, respectively.

The radiation fins 222 and 232 are corrugated fins each having a structure in which a thin metal plate with good thermal conductivity is folded back into a wave shape.
The folded convex portions on one side of each are brought into contact with the surfaces of the metal plates 221 and 231, respectively, and the contact portions are fixed, for example, by brazing, so that the integrated heat radiators 22 and 23, respectively, are assembled. be configured.

Adhesives 24 and 25 are applied to the electrode surfaces on both sides of the heating element main body 20, respectively, and the metal plates 221 and 231 of the metal heat sinks 22 and 23 are bent, respectively, and the fins 222 and 232 on the opposite side are bent. the electrode layers 212 and 213 where the adhesives 24 and 25 are present.
Press it against the surface, dry and bake.

In this case, the radiation fins 222 and 232 are connected to the electrode layer 21.
2 and 213, the radiation fin 2
The protrusions 22 and 232, respectively, penetrate the adhesive layer and directly contact the electrode layers 212 and 213. Then, the adhesive is collected on both sides of each of the convex portions of the fins 222 and 232 in a triangular cross-section, and hardens to firmly adhere and fix each of the convex portions of the fins to the electrode surface. become.

In the PTC heating element, not only the fixation of the metal heat radiating elements 22 and 23 and the electrode layer of the PTC element 21, but also electrical and thermal bonding between them is required.

In response to this requirement, in the heating element shown in FIG.
and 232 and the electrode layers 211 and 212 of the PTC element 2l are ensured, and the fin 22
The convex portions of electrode layers 211 and 232, respectively,
By being pressed into contact with 12, not only electrical continuity but also thermal continuity is ensured.

Here, the adhesives 24 and 25 on the peaks of the fins 222 and 232, respectively, have the effect of supplementing heat conduction (radiation) from the PTC element 2L to the radiation fins 222 and 232.

For this purpose, the insulating adhesive used here has to have not only adhesive strength but also heat resistance against the heat generated by the PTC heating element 2l.
It is necessary to have high durability against heat cycles and high thermal conductivity in order to improve the heat dissipation performance of the heating element 21. As such an adhesive, for example, a silicone adhesive containing fine powder of red iron oxide (iron oxide), silica, alumina, etc. as a filler is suitable.

As shown in Table 1, Cu SAg
When conductive powder such as % carbon is added, the heating element 21
The heat dissipation performance is improved.

Furthermore, as is clear from this table, the conductive powder was
By adding up to 1% of the conductive powder, the heat dissipation characteristics of the heating element 21 are improved.
If it exceeds vol%, the adhesive strength will decrease and durability problems will occur.

Here, even if about 20 vol% of conductive powder is added,
The insulation properties of this adhesive do not pose any problems due to percolation effects.

In the PTC heating element configured in this manner, the metal heat radiation fins 222 and 232 and the PTC heating element 21 are directly joined, so that occurrence of conduction failure is reliably prevented. At the same time, the heat dissipation fins 222 and 232 each relieve the thermal stress caused by 10 cycles of heat, thereby achieving excellent durability.

In other words, in the past, the structure was such that an insulating adhesive was filled between the flat metal plate and the PTC heating element, so if there were irregularities on the joint surface, this would not be a problem.
If the flatness of both surfaces to be joined is good, an insulating adhesive film is interposed between the heating element and the metal flat plate, and the electrical continuity between the heating element and the metal flat plate is poor. becomes.

In this regard, in the heating element shown in the example, for example, PT
C Even if there is a change in the amount of adhesive applied to the electrode surface of the heating element, excess adhesive will be removed from both sides of the ridges of the heat dissipation fins.
It only adheres between the heat generating element and the heat dissipating fin and P.
It is possible to ensure electrical continuity with the TC heating element.

Next, the PTC heating element shown in the example will be explained according to its manufacturing process. First, a copper corrugated fin with louvers and a brass plate with a thickness of 0.31 are bonded together using high-temperature solder (Su-5). %) to form the heat sinks 22 and 23. Here, if the material used is A1l, the corrugated fin provided with louvers is composed of a single plate with a thickness of 100 μm, and this corrugated fin and a plate with a thickness of 0.5 μm are used.
By vacuum brazing the 1 m long A plate, a heat dissipating body with a metal plate drilled on only one side is formed.

That is, the heat sinks 22 and 2 configured in this way
3, one surface is constituted by a mountain part of a metal heat radiation fin, and the shape of each of these heat radiation bodies 22 and 23 is width 16 mm x length 125 nun x height 10+++
m, and the fin pitch (distance between the peaks of the fins) 2
．． 5mm 〇 Also, 2 5mm x 1 6mm x 2. A PTC heating element with a diameter of 5 mm and a Tc of 220°C is dip-pinned into a silicone adhesive, the adhesive is applied to the surface of the PTC heating element, and then the peaks of the fins of the heat sink are placed on the surface of the PTC heating element. Set the pressure and dry under pressure at 50°C for 15 minutes. Then, while maintaining this pressurized state, this PT
ACIOOV was applied to the C heating element for 312 minutes, and the silicone adhesive was cured by the heat generated by the PTC heating element at about 220°C. Then, silicone adhesive is further applied to the outer periphery of the PTC heating element for reinforcement, and is cured.

The PTC heating element constructed in this manner has a temperature of 0.25°C at a temperature of 25°C. 650W for air volume of 5/l1in
The amount of heat generated (output) is obtained. On the other hand, as shown in Table 1, when conductive powder is added to the silicone adhesive, the heat dissipation performance becomes even better.

In the PTC heating element configured in this way, the shape of the radiation fins can be set arbitrarily, for example, as shown in (A) in Figure 3.
The shapes shown in ~(C) can be selected. In particular, the shape of the fins shown in FIG. 3 (B) and (C) is
The contact point (area) with the PTC heating element 21 increases, which is effective for improving the heat dissipation performance of the heating element.

In addition, in the description of the embodiments so far, an insulating adhesive was used to connect the metal heat radiation fin and the PTC heating element. However, if there are no problems with workability during assembly and rework to prevent adhesive from extruding or getting in, conductive adhesive (silicon-based Ag adhesive) or high-temperature solder (Sn 5%) can be used instead of insulating adhesive. Alternatively, 2.5% Sn-2.5% Ag) may be used.

[Effect of the invention] As described above, according to the PTC heating element according to the present invention, P
By directly bonding the TC heating element and the metal heat sink using corrugated fins using, for example, an insulating adhesive, mutual adhesive strength and electrical and thermal contact can be maintained in good condition. Moreover, problems such as peeling do not occur in high-temperature conditions, and it can be made to have excellent durability. In addition, since the PTC heating element does not have a metal plate in contact with it, it can be easily reduced in weight compared to conventional products, and can be effectively applied as an auxiliary heater for various heaters and air conditioners. It can also be used effectively as a heat source for dryers, etc.

1 4 Table 1 However, the judgment criteria are: Heat radiation performance = 600W or more Durability change - within ±10% Also, heat radiation performance is 25℃ and air flow 0. 5m3/min
Regarding durability, the operating durability was set at 1000lIjj.

Here, sample no. 2 to 6 contain copper (Cu) as conductive powder.
) using sample No. 7 is silver (Ag) powder, sample No. No. 8 used carbon powder.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional configuration diagram illustrating a PTC heating element according to an embodiment of the present invention, Fig. 2 is a sectional view showing a part of the heating element taken out and enlarged, and Fig. 3 (A) to (C) shows an example of a radiation fin used in the heating element according to the present invention, and FIG. 4 is a sectional view illustrating the structure of a conventional PTC heating element. 20... PTC heating element body, 21... PTC heating element, 211... Main body, 212, 213... Electrode layer, 221, 231... Metal plate, 222 23
2...Radiation fin, 24, 25...Insulating adhesive.

Claims (1)

[Claims] A PTC heating element having electrode layers formed on each of its front and back surfaces, and a thin metal plate bent into a wave shape, which is placed opposite each of the front and back surfaces on which the electrode layers of the PTC heating element are set. and a heat dissipation fin formed by the heat dissipation fin, the wavy folded part of the heat dissipation fin is brought into contact with the electrode surface of the PTC heating element, and the two are bonded to each other by an adhesive. Features PTC heating element.