JPS58214209A - Thermoconductive insulating sheet - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in thermally conductive insulating sheets.

Conventionally, mica and polyester have been used as electrical insulating and heat dissipating sheets for heat generating electrical and electronic appliances such as power transistors, thyristors, and PTCs (positive temperature coefficient thermistors). These are coated with heat dissipating grease to improve the adhesion between the hard material Nodame heating element and the fins, but recently there has been a trend towards the use of some thermally conductive rubber sheets that do not require the use of heat dissipating grease. It is in.

This thermally conductive rim sheet is usually made of a composition in which silicone rubber is mixed with a filler that increases thermal conductivity, such as alumina, quartz, boron nitride, magnesium oxide, etc. In these processes, the rubber and filler are uniformly kneaded using a Pan Bali mixer or a roll, then formed into a sheet using an extruder or calender roll, and then cross-linked using a hot air oven or press. It is punched and formed.

In this case, in order to improve thermal conductivity, a large amount of filler is added, but this increases the viscosity of the mixture, which has the disadvantage of easily abrading the machine. In particular, alumina is effective in increasing thermal conductivity, but because it has a high Mohs hardness of 9,
Wear and tear of rolls, screws, spears, punching dies, etc. is unavoidable. Boron nitride is hard to wear due to its low hardness, but
In addition to being expensive, it is difficult to fill highly because it has poor compatibility with silicone rubber. Therefore, alumina
- It has been desired to develop a manufacturing method that can fill a large amount of such a highly hard filler. On the other hand, conventional silicone rubber-based compositions have slow curing speeds5 and require secondary crosslinking depending on the application. Therefore, there has been a desire for a thermally conductive sheet that can be crosslinked at a high speed while minimizing machine wear during processing.

The present invention was developed in view of the above circumstances, and provides a thermally conductive insulation that causes less wear on the machine when mixing fillers to form a composition, significantly increases crosslinking speed, and can be cured in a short time. The purpose is to provide sheets.

The thermally conductive insulating sheet of the present invention is formed by molding a composition obtained by mixing a thermally conductive filler with a mixture of polysiloxane having a C-C bond in the molecule and organopolysiloxane having an sH group in the molecule. and crosslinked.

The thermally conductive insulating sheet of the present invention will be explained in detail below. The mixture of polysiloxane having a c=c bond in the molecule and organopolysiloxane having an SH group in the molecule is disclosed, for example, in US Pat. No. 4,066,603.

In USP 4066603, a compound having a carbon-carbon double bond has a viscosity of 0.3 Pa at 25°C.
This applies to polydimethylsiloxanes of S or higher, whose terminals are blocked with siloxy units selected from the group consisting of methylphenylvinylsiloxy units and dimethyl. on the other hand,
It is a mercaptoorganopolysiloxane with S in the molecule.
Refers to those containing two or more H groups. The amount of SH in the molecule is 16
% by weight or less, and the molecular weight is 1000 or more.

Specifically, the constituent elements are, for example, 'H80nH2nSiOo, 5. Here, R is selected from an alkyl group having 1 to 2 carbon atoms and a phenyl group, and n is an integer of 1 to 4.

At room temperature, it is normally liquid, and becomes six-dimensional when exposed to ultraviolet rays, electron beams, or organic peroxides. Photosensitizers are usually required for UV irradiation.

Further, examples of the thermally conductive filler include alumina, quartz, boron nitride, magnesium oxide, and the like. In particular, in the case of the present invention, alumina and quartz having high hardness are suitable, but are not particularly limited. In addition, reactive monomers, colorants, polymerization inhibitors, flame retardants,
There is no problem in adding organic or inorganic fibers, surfactants, etc. as reinforcing materials. Additionally, a small amount of organic solvent may be added for the purpose of adjusting viscosity.

In mixing the above mixture and the thermally conductive filler, a method applicable to any suitable liquid substance is used. For example, mixing using an agitator, a kneader, a static mixer, etc. is used, and the panburi mixer and rolls used in ordinary rubber processing are unnecessary.

As a method for producing the sheet, a method using a knife coater, which is common in the production of paint, is suitable, but the method is not necessarily limited to this. Furthermore, when the shape is determined, it is appropriate to inject it into a mold and mold it by compression molding, transfer molding, injection molding, or the like. It can be cured simultaneously with molding. Curing of the wide sheet can be achieved in a relatively short time using a hot air oven, an infrared heater, an ultraviolet lamp, an electron beam irradiation device, or the like. In particular, ultraviolet curing is most suitable, and continuous curing can be achieved by using a conveyor belt. Since this example is a liquid composition, in a molding method such as a knife coater that does not use a mold, it is desirable to cure the composition before contacting other solid components. For curing, the above-mentioned methods may be used alone, or two or more methods may be used in combination. Further, a reinforcing layer of woven or nonwoven fabric of organic or inorganic fibers may be interposed between the thermally conductive sheets. It was found that the sheet of this example had an even greater effect when such a reinforcing layer was interposed. In this case, a coupling agent, primer, or the like may be applied to the surface of the woven or nonwoven fabric to provide adhesive properties.

Example 1 Methylphenylvinylsiloxy endblocked polydimethylsiloxane 10 with vinyl content 0.5% by weight
0 parts by weight, 729 parts by weight of γ-mercaptopropyldimethoxysiloxy end-blocked polydimethylsiloxane with 2.1% by weight of -8H, photosensitizer benzophenone 5
A composition consisting of parts by weight, 600 parts by weight of alumina, and 20 parts by weight of fumed quartz is mixed using a stirrer until uniform.

This mixture was dropped onto a polyester film and adjusted to a thickness of 0.20 M using a doctor knife, and then passed through an ultraviolet curing device (80 W/m 2 , irradiation distance 100 mm) for 2 seconds. This was punched into the shape of a power transistor heat dissipation spacer TO-3, and then the polyester film was removed. The thermal resistance when mounted on the power transistor 2SD676 was 0.45°C/W.

Example 2 A glass fiber fabric was impregnated with a mixture having the composition of Example 1, adjusted to a thickness of 0.2 On+m, and cured under the same conditions as Example 1. When this was punched out in the shape of a power transistor heat dissipation spacer TO-6 and mounted, the thermal resistance was o, 50° C./W.

Example 6 A glass fiber fabric was impregnated with the benzophenone and removed composition of Example 1, adjusted to a thickness of 20 m, and then cured by irradiation with an electron beam of 10 Mracl. The thermal resistance of a sheet punched out in the shape of a power transistor heat dissipation spacer To-3 was 0.50° C./W.

Thermal resistance test method Insert a thermally conductive insulating sheet between the power transistor 2SD676 and a copper plate with a thickness of 3.2 rMn, drive the power transistor, measure the collector current and the voltage between the collector and emitter to determine the collector loss. (watt) was calculated. The case temperature and fin temperature of the transistor at various collector losses were measured, and the case/fin thermal resistance (° C./W) was determined from these results.

As described above, in the thermally conductive insulating sheet of the present invention, since the mixture of one of the materials constituting the composition is liquid at room temperature, there is less wear on the machine when kneading with the thermally conductive filler. It can be cured in a short time, and sheets with woven or non-woven fabrics can be easily manufactured. Further, since it is solvent-free and only a small amount is used, a drying step is not necessary.

As described above, the thermally conductive insulating sheet of the present invention has low mechanical wear when mixing fillers to form a composition.
It has the effect of greatly increasing the crosslinking speed and curing in a short time.

Claims (1)

[Claims] 1. A composition obtained by mixing a thermally conductive filler with a mixture of a polysiloxane having a C-C bond in the molecule and an organopolysiloxane having an SH group in the molecule, is molded. and a thermally conductive insulating sheet characterized by being crosslinked. 2. The thermally conductive insulating sheet according to claim 1, wherein a reinforcing woven or nonwoven fabric is interposed between the compositions.