JPH0227801B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Background and Objectives of the Invention] The present invention relates to a heat dissipation structure for a PTC element.

A PTC element is a resistor with a positive temperature coefficient.
It is a heating element with self-regulating properties. Usually, there are ceramic-based materials mainly made of barium titanate, and plastic-based materials with conductivity imparting agents added to plastic. In particular, ceramic materials are widely used because of their excellent reliability. Since the PTC element is a heat generating element, it is often used in combination with a heat sink. in this case,
Epoxy resin, which has excellent thermal conductivity, has been used as an adhesive to integrate the PTC element and the heat sink. However, because the thermal expansion coefficients of the PTC element and the heat sink, which is mainly made of metal, and the epoxy resin are different, there was a drawback that the epoxy resin could be damaged under conditions of cold/heat cycles or thermal shock.

The present invention solves the above-mentioned drawbacks of the conventional technology, and provides a PTC element heat dissipation structure that can prevent damage to the adhesive layer that integrates the PTC element and the heat dissipation body even under conditions involving rapid temperature changes. The purpose is to

[Summary of the invention] The present invention is characterized in that a PTC element and a heat sink are integrated through an adhesive layer made of a thermally conductive composition containing an addition polymerizable silicone rubber and an inorganic filler. That is.

An example of a PTC element is one in which electrodes are embedded in barium titanate with a small amount of an additive such as samarium oxide added and sintered. The composition is not particularly limited as long as the element has such a positive temperature coefficient. Although the present invention is particularly effective for ceramic PTC elements,
It can also be applied to plastic PTC elements that require heat dissipation. However, in the case of plastic PTC elements, some of them are difficult to adhere to, such as those made mainly of polyolefin and conductivity imparting agents, so it is preferable to perform a primer treatment with a silane coupling agent, etc. before adhering. .

Heat sinks are usually copper, copper alloys, aluminum,
Metals such as iron are used in practice, but highly thermally conductive ceramics such as graphite and silicon carbide are used in applications where corrosion is to be avoided.

What is important in the present invention is that the adhesive layer for integrating the PTC element and the heat sink is formed of a thermally conductive composition containing an addition polymerizable silicone rubber and an inorganic filler.

This composition has strong adhesion to both metals and ceramics, and has elasticity even after curing, so it can follow expansion and contraction caused by rapid temperature changes.

In addition, inorganic fillers are added to further improve the thermal conductivity of addition-polymerized silicone rubber, but since inorganic fillers have a smaller coefficient of thermal expansion than silicone rubber, they It is now possible to bring the coefficient of thermal expansion of the adhesive layer closer to that of metal and ceramic, further increasing its ability to respond to thermal shock.

The addition polymerizable silicone rubber in the present invention includes (a) diorganopolysiloxane having at least two silicon-bonded alkenyl groups in one molecule; (b) at least two silicon-bonded hydrogen atoms in one molecule; and (c) an addition reaction catalyst, which are crosslinked under the catalytic action of component (c) to form a rubber elastic body. Such addition-polymerized silicone rubber is liquid before crosslinking and has excellent viscoelasticity after crosslinking, and can maintain its excellent elasticity for a long period of time even when filled with an inorganic filler that increases thermal conductivity. become.

Examples of inorganic fillers include powders of alumina, quartz, zinc oxide, magnesia, boron nitride, aluminum nitride, silicon carbide, graphite, metals, etc., and these can be used alone or in combination of two or more to give 30 to 70%
You can get the hang of adding it within a volume % range.

In the present invention, in addition to the above-mentioned components, reactive diluents, silicone oil, organic solvents, curing inhibitors such as benzotriazole and hydroperoxide to extend the pot life, and fumes are used to adjust the viscosity. Reinforcing fillers such as silica, colorants, flame retardants, etc. may be added as appropriate. Furthermore, the self-adhesiveness can be improved by adding a silane coupling agent, a titanate coupling agent, an epoxy resin, or the like.

A thermally conductive composition made of the above components is inserted between the PTC element and the heat sink, and then cured at room temperature or by heating to integrate the two.

[Embodiments of the Invention] Example 1 A heat dissipation structure as shown in FIG. 1 was used. 1 is a PTC element mainly made of barium titanate, 2 is a heat sink made of aluminum, and 3 is an adhesive layer made of a thermally conductive composition.

The adhesive layer 3 was formed using a composition consisting of the following components (1) to (7).

(1) 100 parts by weight of dimethylpolysiloxane with both ends blocked with dimethylvinylsilyl groups (2) 20 parts by weight of dimethylpolysiloxane (viscosity modifier) with both ends blocked with silanol groups (3) methyl with both ends blocked with trimethylsilyl groups Hydrogen polysiloxane 12 parts by weight(4) Vinyltrimethoxysilane 2 parts by weight(5) Alumina 350 parts by weight(6) 1% by weight solution of chloroplatinic acid in isopropyl alcohol 1 part by weight(7) 30% by weight of benzotriazole in isopropyl alcohol Solution 0.2 parts by weight The above composition was inserted between the PTC element 1 and the heat sink 2, and cured by heating at 150° C. for 15 minutes.

The resulting heat dissipation structure was heated to 150℃ for 30 minutes and -55℃ for 30 minutes.
As a result of repeating the minute cycle test 100 times, no abnormalities were observed. Furthermore, the heat dissipation characteristics during operation of the PTC element were also good.

Example 2 A heat dissipation structure as shown in FIG. 2 was created. 4 is a plastic PTC heating element, 5 is an iron pipe, and a composition obtained by removing the benzotriazole solution from the composition of Example 1 is inserted between them,
The adhesive layer 6 was formed by heating and curing at 150° C. for 15 minutes.

The plastic PTC resistor 4 was manufactured as follows.

(a) Polyethylene (density 0.94, MI: 0.3)
100 parts by weight (b) Conductive furnace carbon (XC-72)
30 parts by weight (c) 2 parts by weight of trimethylolpropane trimethyl methacrylate (d) 1 part by weight of poly-2,2,4-trimethyl-1,2-dihydroquinoline. After extrusion, it was covered with an insulator and cross-linked by irradiation with a 20 Mrad electron beam.

The obtained heat dissipation structure was subjected to the same cycle test as in Example 1 100 times, and no abnormalities were observed. Furthermore, the heat dissipation characteristics when the PTC resistor 4 was activated were also good.

Comparative Example 1 In the heat dissipation structure of Example 1, the adhesive layer 3 was formed using a thermally conductive bisphenol epoxy resin.

As a result of carrying out the same cycle test as in Example 1, the adhesive layer cracked or peeled within 20 cycles.

Comparative Example 2 In the heat dissipation structure of Example 1, the adhesive layer 3 was formed using a composition that did not contain alumina.

As a result of conducting the same cycle test as in Example 1, no cracks occurred after 100 repetitions, but
Some peeling was observed. Furthermore, the heat dissipation characteristics when the PTC element 4 was activated were poor.

[Effects of the Invention] As explained above, the present invention provides a heat dissipation structure for a PTC element that integrates a PTC element and a heat dissipation body using a thermally conductive composition containing an addition polymerized silicone rubber and an inorganic filler. It is intended to provide
This makes it possible to obtain a heat dissipation structure that can sufficiently withstand severe thermal shock. Moreover, according to the present invention, the thermal conductivity from the PTC element to the heat sink is extremely good, making it possible to extend the life of the PTC element. Furthermore, since the adhesive layer of the present invention is formed from addition polymerized silicone rubber, it does not generate corrosive substances and therefore does not corrode metal.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of Example 1 and Comparative Examples 1 and 2, and FIG. 2 is an explanatory diagram of Example 2. 1: PTC element, 2: heat sink, 3: adhesive layer.

Claims (1)

[Claims] 1 A diorganopolysiloxane having at least two silicon-bonded alkenyl groups in one molecule and a liquid organopolymer having at least two silicon-bonded hydrogen atoms in one molecule are used between the PTC element and the heat sink. A PTC element heat dissipation structure characterized by being integrated via an adhesive layer made of a thermally conductive composition made of an addition-polymerized silicone rubber made of siloxane and an addition reaction catalyst mixed with an inorganic filler.