JP2000151160A - Heat radiation sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat radiation sheet which excels both in heat conductivity and flame retardant property by including, in the sheet, at least the specified number of fillers which have good heat conductivity and are different in average grain diameter and a viscous layer which is plastically deformed under pressure. SOLUTION: This sheet includes at least two or more types of fillers which also serve for a flame retardant and have a good heat conductivity and are different in average grain diameter. It also includes at least a viscous layer 1 which is plastically deformed under pressure. Since the viscous layer 1 is blended with two or more types of fillers which are different in average grain diameter and have a good heat conductivity, a high blending quantity is achieved by a close-packed filling method, etc., thereby obtaining a radiation sheet having good heat conductivity. Even when a radiator has a large deformation such as a large unevenness, the sheet can be attached airtightly in a large area to both the heating element and a heatsink, since the viscous layer 1 is also plastically deformed and therefore has good heat radiation efficiency. For the fillers, such materials as to serve as a flame retardant are used. So, the sheet can be easily provided with a flame retardant property, resulting in obtaining a heat radiation sheet which excells both in heat conductivity and a flame retardant property.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat radiating sheet which is excellent in heat conductivity and can be imparted with flame retardancy as required, and is suitable for radiating heat from a heating element such as electric equipment and electronic equipment.

[0002]

2. Description of the Related Art Conventionally, as a heat radiation sheet used for heat radiation treatment of a heating element such as an electric device or an electronic device, a thin film is formed on a surface of a silicone rubber sheet containing a powder of aluminum oxide or boron nitride or a polyimide (amide) film. (Japanese Patent Application Laid-Open No. 56-161699, Japanese Patent Publication No. 2-24)
383).

The heat radiating sheet is generally used in such a manner that it is interposed between a heat generating element and a heat sink such as a heat radiating fin. Therefore, good heat radiation treatment by heat transfer requires good contact with both the heating element and the heat sink. However, the conventional heat dissipation sheet has a problem that poor adhesion occurs even when a thin adhesive layer is provided on a substrate. In particular, in the case of a heating element such as a transistor having large deformation such as unevenness, poor adhesion is likely to occur. Poor adhesion due to gaps or the like greatly reduces the heat transfer efficiency, and the heat dissipation sheet is not sufficiently used, so that the heat dissipation efficiency is poor.

[0004] On the other hand, it is desired that the heat radiating sheet has the above-mentioned heat conductivity due to being in contact with the heating element, and also has flame retardancy that can withstand a temperature rise due to heat storage from the viewpoint of safety and the like. V-0 level flame retardancy in tests is often required. However, the above-mentioned conventional heat dissipation sheet is inferior in flame retardancy, and it is necessary to balance heat conductivity and flame retardancy by adding a flame retardant together with a heat conductive powder such as boron nitride. Therefore, there is a problem that it is difficult to achieve the V-0 level flame retardancy in the UL-94 combustion test.

[0005]

SUMMARY OF THE INVENTION The present invention has excellent adhesion to both a heating element and a heat sink, and is unlikely to cause poor adhesion even when the heating element has large irregularities such as a transistor. An object of the present invention is to provide a heat-dissipating sheet that has excellent heat transfer capability and can easily impart flame retardancy as required, and is excellent in both heat transfer and flame retardancy.

[0006]

According to the present invention, there is provided a viscous layer which contains at least two kinds of fillers having good thermal conductivity and different average particle diameters which may also serve as a flame retardant, and which is plastically deformed by pressing. A heat radiation sheet characterized by the following.

[0007]

According to the present invention, the viscosity of the viscous layer can be reduced by using the filler in a combination of different average particle diameters with the same compounding amount as compared with a system using a single average particle diameter. Its thermal conductivity can be improved, and it is also excellent in processability and adhesiveness. As a result, it is possible to further increase the compounding amount of the filler while achieving good workability and adhesiveness, and to obtain a heat radiation sheet having more excellent thermal conductivity.

As a result, even in the case of a heating element such as a transistor having a large deformation such as unevenness due to plastic deformation of the viscous layer, it adheres well to both the heating element and the heat sink over a wide area, resulting in poor adhesion. The heat dissipation sheet is excellent in exhibiting the original heat transfer ability of the heat dissipation sheet, exhibits high heat transfer efficiency, and has a high heat dissipation efficiency.
In addition, by using a substance also used as a flame retardant as a filler, a heat radiation sheet which can easily impart flame retardancy and is excellent in both heat conductivity and flame retardancy can be obtained. This is based on the combination of the use of a heat transfer and flame retardant filler having excellent heat transfer properties and flame retardancy, and the above-mentioned plastically deformable viscous layer.

That is, the filler for both heat transfer and flame retardancy is inferior in heat conductivity to a thermally conductive powder such as aluminum oxide and boron nitride, which has a poor flame retarding action. When used, the thermal resistance increases, but in the present invention, the wide area good adhesion through the plastically deformable viscous layer compensates for the increase in thermal resistance due to the decrease in thermal conductivity. In addition, the heat-transfer- and flame-retardant filler exhibits a good flame-retardant action and exhibits excellent properties in both heat transfer and flame retardancy. As a result, V-0 level flame retardancy in the UL-94 combustion test can be easily achieved.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The heat radiating sheet according to the present invention has good thermal conductivity, which may also serve as a flame retardant, and has a different average particle size.
It contains at least one or more fillers and has at least a viscous layer that is plastically deformed by pressing. An example is shown in FIG. Reference numeral 1 denotes a heat dissipation sheet composed of the viscous layer itself.

[0011] The purpose of plastic deformation due to the pressure of the viscous layer is to achieve excellent thermal resistance even when the adherend has a large change in shape such as irregularities due to plastic deformation. And Therefore, the viscous layer can be formed of an appropriate material that flows by pressing and exhibits plastic deformability. Generally, a rubber-based or resin-based polymer or the like having a composition that exhibits plastic deformation by adjusting the molecular weight or the like is used.

The viscous layer is preferably excellent in insulation, flame retardancy, heat resistance, corrosion resistance and the like. From this point, for example, natural rubber and silicone rubber, polyisobutylene and polybutene, styrene butadiene rubber and nitrile rubber, chloroprene rubber and butyl rubber, EPM, rubber polymers such as ethylene propylene rubber and acrylic rubber such as EPDM, polyolefin and Elastomeric polymers such as polyester, polystyrene and polyurethane, and synthetic resins having excellent elasticity such as ethylene-vinyl acetate copolymer and soft polyvinyl chloride are preferably used.

[0013] Even if the polymer is essentially a hard polymer such as the polyvinyl chloride described above, the present invention provides a viscous or pressurized fluid in a state where it is provided with an appropriate compounding agent such as a plasticizer or a softener. Can be used to form a viscous layer. In the case of a rubber-based polymer, it is preferable to set it in an unvulcanized state without vulcanization from the viewpoint of plastic deformability and the like.

From the viewpoint of the performance and the like, materials that can be particularly preferably used for forming the viscous layer include, for example, synthetic rubbers such as butyl-based, fluorine-based, isobutylene-based, butene-based, silicone-based, and ethylene-propylene-based rubbers, and natural rubbers. And polybutadiene. One or more of the above materials such as rubber-based or resin-based polymers can be used.

The viscous layer contains at least a filler having good thermal conductivity, and two or more fillers having different average particle diameters are used as the filler. This makes it possible to achieve a heat dissipation sheet having a high blending amount by a close-packing method or the like and excellent heat conductivity.

The form of the filler used is not particularly limited, but generally a spherical filler is used. In that case, the larger the particle size, the easier it is to mix a large amount, but there is also a disadvantage that the surface is likely to be uneven, which causes a decrease in the adhesion. It is preferable to use spherical particles having an average particle diameter of 0.1 to 100 μm, especially 0.3 to 50 μm, and particularly 0.5 to 20 μm, from the viewpoint of considering such a large amount of compounding and prevention of a decrease in adhesion.

The ratio of the average particle diameters to be changed is from 1: 1.5 to 20, preferably from 1: 2 to 12, from the point of approaching the closest packed arrangement as much as possible, that is, the point of increasing the blending amount. In particular, 1: 4 to 10 is preferable. Even when three or more fillers having different average particle diameters are used, it is preferable that the above-mentioned average particle diameter ratio is achieved in two relations with those having the next largest average particle diameter.

The proportion of the filler having a different average particle size can be appropriately determined based on the layout design of the different particle size material. In general, it is advantageous to use as many average particle sizes as possible, such as to increase the thermal conductivity, so as to approach the closest packed arrangement as much as possible. The proportion of the large average particle size is 100 parts by weight or less, preferably 5 to 80 parts by weight, particularly 10 to 60 parts by weight.

It should be noted that it is not restricted to use a large number of particles having a smaller average particle size, for example, 95 parts by weight or less for 100 parts by weight of a small average particle size.
In particular, the next largest average particle size can be used at a usage ratio of 5 to 80 parts by weight, particularly 10 to 60 parts by weight.

In the above, an appropriate filler can be used as the filler having good thermal conductivity, and there is no particular limitation.
Therefore, any of known thermal conductive powders such as, for example, boron nitride, aluminum nitride, and aluminum oxide can be used.
A good heat conductive filler that can be preferably used also serves as a flame retardant.

By using the above-mentioned filler for heat transfer and flame retardant, it is necessary to balance the heat transfer and flame retardancy by adjusting the compounding amount of the heat transfer agent and the flame retardant since they are separate bodies. By adjusting the compounding amount of the filler that can also be used for heat transfer and flame retardancy, a heat radiation sheet excellent in both heat transfer and flame retardancy can be easily formed.

As the filler for both heat transfer and flame retardancy, an appropriate filler having excellent heat conductivity and flame retardancy imparting properties can be used. Above all,
A metal hydroxide such as aluminum hydroxide or magnesium hydroxide can be preferably used from the viewpoint of compatibility between heat conductivity and flame retardancy imparting property and noncorrosiveness. The metal hydroxide also has an advantage of being excellent in insulation.

The plastic deformability of the viscous layer is such that it maintains its shape without flowing when it is not pressed, and is plastically deformed when pressed when it is not pressed, in view of good adhesion due to small force and handleability of the heat radiating sheet. Is preferable, and a viscous state of a degree similar to the viscosity of a conventional pressure-sensitive adhesive layer made of a pressure-sensitive adhesive is preferable.

Incidentally, based on measurement at 60 ° C. by a flow tester (nozzle diameter 1.0 mm, nozzle length 1.0 m
m, load 40 kg), 1 × 10 ⁴ to 1 × 10 ⁷ poise, especially 5 × 10 ^{5 to} 5 × 10 ⁶ poise, especially 1 × 10 ⁵ to 1 ×
It is preferable to use a state showing a viscosity of 10 ⁶ poise.

Therefore, the amount of the filler having good heat conductivity, including the filler for heat transfer and flame retardancy, depends on the combination of the shape and the average particle size of the filler, the presence or absence of surface treatment, or the viscosity of the base viscous substance. The viscosity can be appropriately determined based on the above-mentioned target viscosity from the viewpoints of viscosity, thermal conductivity, compatibility with the flame-retardant action, plastic deformability by a small force, and good adhesion. In the present invention, it is also possible to form a viscous layer in which a filler is arranged in a close-packed manner.

In addition to maintaining good heat handling and heat transfer properties of the heat radiating sheet and achieving a flame retardancy of V-0 level in a UL-94 combustion test, the filler is also used as a heat transfer and flame retardant filler. Based on the total amount including (flame retardant) or other flame retardants, a viscous layer having a composition containing a flame retardant of 45% by volume or more, preferably 50 to 85% by volume, particularly 55 to 75% by volume. Is preferred. When only the filler for heat transfer and flame retardancy, and therefore only the filler having good thermal conductivity according to the present invention, is used,
As described above, the close-packed arrangement may be employed.

In the present invention, one type or two types having the same average particle size or a combination of different average particle sizes may be used.
It is possible to use more than one kind of filler having good thermal conductivity or a filler also used for heat transfer and flame retardancy. Further, an appropriate known flame retardant such as, for example, a phosphorus compound, an organic halide, antimony trioxide, platinum or a platinum compound can be used in combination in the viscous layer if necessary. In that case, the average particle size of the combined use can be in accordance with the above.

Further, in forming the viscous layer, the material for forming the viscous layer may be, for example, a processing aid such as low molecular weight polyethylene or zinc oxide, process oil or stearic acid, carbon black or an antioxidant, or a property improving agent. Various additives can be added as necessary.

The viscous layer can be formed by an appropriate method such as a method of applying a viscous layer forming material on a separator or a method of forming the viscous layer forming material into a sheet by an extrusion molding method. The viscous layer can be formed as a superposed layer of two or more viscous layers of the same type or different types by, for example, a recoating method or a multilayer extrusion molding method.

The thickness of the viscous layer can be appropriately determined according to the purpose of use. 0.1 to 10 from the point of wide area good adhesion to the adherend and thinness due to plastic deformation
mm, preferably 0.3-5 mm, especially 0.5-3 mm.

The heat radiation sheet according to the present invention may be composed of the above-mentioned viscous layer 1 itself as shown in FIG. 1 or may be made of the viscous layers 1 and 3 of the elastic base material 2 as shown in FIGS. It may be provided on one side or both sides.
A heat-dissipating sheet with only a viscous layer that is less susceptible to deformation restraint is advantageous from the viewpoint of improving heat-dissipation efficiency due to wide-area good adhesion to both the heating element and the heat sink due to the plastic deformation of the viscous layer.

On the other hand, the elastic substrate is intended to hold the viscous layer. By using the elastic substrate, based on the elastic deformation of the elastic substrate, it is possible to obtain a large area on the adherend by the plastic deformation of the viscous layer. It is possible to prevent the adhesion from being greatly reduced, and to ensure good adhesion over a wide area. Therefore, by combining the viscous layer and the elastic base material, while sufficiently maintaining the plastic deformability of the viscous layer, achieving the recycling of the heating element or the heat sink by, for example, providing easy removability based on the elastic base material, It is possible to provide a new advantage that can improve the shape stability or the self-supporting property of the heat radiation sheet.

The elastic substrate can be formed of an appropriate material exhibiting elasticity. Incidentally, examples thereof include rubber-based polymers and synthetic resins exemplified in the above-mentioned viscous layer. An elastic substrate excellent in flexibility, flame retardancy, heat resistance, corrosion resistance, insulation properties, stain resistance, and the like is preferable.

For the formation of the elastic substrate, one or more rubber-based polymers, synthetic resins and the like can be used. In this case, when a rubber-based polymer is used, it is preferable to use a vulcanized rubber from the viewpoints of elasticity and shape retention. When a synthetic resin, particularly a thermoplastic resin, is used, it is preferable to partially crosslink by an appropriate method such as electron beam irradiation in order to improve heat resistance.

In the vulcanization treatment of the rubber-based polymer described above,
Although an appropriate vulcanizing agent such as a sulfur-based or resin-based vulcanizing agent can be used, a peroxide-based vulcanizing agent can be preferably used from the viewpoint of corrosion resistance and the like. Incidentally, as the peroxide vulcanizing agent, di-t-butyl peroxide, dicumyl peroxide, α, α′-bis (t-butylperoxy) -p-diisopropylbenzene and the like can be mentioned as typical examples. However, the present invention is not limited to this, and any known peroxide-based vulcanizing agent can be used.

In the vulcanization treatment, an appropriate vulcanization aid such as triallyl isocyanurate, ethylene glycol acrylate, trimethylolpropane trimethacrylate or N, N'-m-phenylenebismaleimide is used in combination. Can also.

In the case of using an elastic base material, in order to make the viscous layer sufficiently exhibit heat conductivity and the like to obtain a sheet and the like having excellent heat dissipation efficiency, in the present invention, the elastic base material also has at least good heat conductivity. In the case of imparting flame retardancy, a filler for both heat transfer and flame retardancy is blended together with another flame retardant as required.

The above-mentioned filler having good thermal conductivity, filler for heat transfer and flame retardancy, and other flame retardants can be the same as those of the above-mentioned viscous layer. As the filler, aluminum hydroxide can be preferably used. Further, the average particle size of the filler and the like to be used can be in accordance with the above, if necessary. Also in the case of an elastic base material, the heat transfer and flame retardant filler exhibits a particularly advantageous effect when it is made of a non-silicone-based material containing no silicone component.

The amount of the filler and the like can be the same as in the case of the viscous layer. However, while maintaining good handling properties and heat transfer properties of the heat radiating sheet, the V-weight in the UL-94 combustion test is maintained.
Rather than achieving a flame retardancy of −0 level, based on the total amount including the filler (flame retardant) for heat transfer and flame retardant or other flame retardants, 50% by weight or more, especially 60 to 60% It is preferable to use an elastic substrate having a composition containing 80% by weight, particularly 65 to 75% by weight of a flame retardant.

The formation of the elastic substrate can be performed by obtaining a sheet-like material by an appropriate method such as a calendering method or an extrusion molding method. In that case, the vulcanized rubber sheet can be obtained by subjecting an unvulcanized rubber sheet formed by a calendering method or the like to a suitable vulcanization treatment according to the vulcanizing agent in the composition, such as a method of heating. . When forming the elastic substrate, appropriate additives such as a processing aid and a property improving agent can be blended according to the case of the above-mentioned viscous layer.

The thickness of the elastic substrate can be appropriately determined according to the purpose of use and the like, and may be thinner or thicker than the viscous layer. From the point of wide area and good adhesion to the adherend due to plastic deformation of the viscous layer, the thickness is equal to or less than the thickness of the viscous layer.
It is preferable to use an elastic substrate having a thickness of /1.1 to 1/5 times, particularly 1/2 to 1/3 times.

In view of the above point and the point of thinning, the general thickness of the elastic substrate is 0.1 to 3 mm, preferably 0.2 to 2 mm,
In particular, it is set to 0.3 to 1 mm. From the viewpoint of reducing the thickness, the thickness of the entire heat dissipation sheet is preferably 10 mm or less, more preferably 5 mm or less, and particularly preferably 1 to 3 mm.

The viscous layer may be provided on the elastic substrate, for example, by coating a viscous layer forming material on the elastic substrate, or by transferring the viscous layer coated on the separator to the elastic substrate. method,
It can be carried out by an appropriate method such as a method of simultaneously forming a laminate having an elastic substrate and a viscous layer by a two-layer or three-layer multilayer extrusion molding method.

The heat radiating sheet according to the present invention is a method in which various heat generating elements and a heat sink are pressed through a heat radiating sheet, such as a method in which a heat generating element such as an electric component or an electronic component is interposed between a heat sink such as a heat radiating fin. It can be used in an appropriate method such as. In this case, there is no particular limitation on the application surface of the heat radiating sheet, but in the case where the viscous layer is provided only on one surface of the elastic base material, the viscous layer may be bonded to the surface of the heating element and the heat sink having large irregularities. preferable.

[0045]

Example 1 75 parts of high molecular weight polyisobutylene (parts by weight, the same applies hereinafter), 40 parts of low molecular weight polyisobutylene, polybutene 5
0 parts, process oil 15 parts, carbon black 2 parts,
0.5 parts of stearic acid and 50 aluminum hydroxide powder
The composition obtained by kneading 0 parts was formed into a sheet having a thickness of 1.0 mm through a vent-type extruder to obtain a heat radiation sheet comprising the viscous layer. The aluminum hydroxide powder was used in a ratio of 3 parts having an average particle diameter of 1 μm to 3 parts having an average particle diameter of 8 μm.

Example 2 A heat dissipation sheet was obtained in the same manner as in Example 1, except that 1 part of the aluminum hydroxide powder having an average particle diameter of 1 μm and 1 part of 8 μm were used.

Example 3 A heat radiation sheet was obtained in the same manner as in Example 1 except that aluminum hydroxide powder was used at a ratio of 1 part of 8 μm to 3 parts of an average particle diameter of 1 μm.

Example 4 A heat radiation sheet was obtained in the same manner as in Example 1, except that the amount of the aluminum hydroxide powder was changed to 600 parts.

Comparative Example 1 A heat radiation sheet was obtained in the same manner as in Example 1 except that 500 parts of aluminum hydroxide powder having an average particle size of 1 μm was used alone.

Comparative Example 2 A heat dissipation sheet was obtained in the same manner as in Example 1, except that 500 parts of aluminum hydroxide powder having an average particle size of 8 μm was used alone.

Comparative Example 3 A heat radiation sheet was obtained in the same manner as in Example 1 except that 550 parts of aluminum hydroxide powder having an average particle size of 1 μm was used alone.

Evaluation Test The following characteristics were examined for the heat radiation sheets obtained in the examples and comparative examples. Viscosity The viscosity at 60 ° C. was measured with a flow tester (CFT-500, manufactured by Shimadzu Corporation) (nozzle diameter 1.0 mm, nozzle length 1.0 mm, load 40 kg).

Adhesive force The adhesive force by 90-degree peeling was examined in accordance with JIS Z 0237.

Thermal conductivity In the thickness direction of the sheet, a laser flash method (manufactured by Rigaku Denki Co., Ltd., thermal constant measuring device LF / TCM-FA8510) was used.
It was examined at 30 ° C. according to B).

Flame retardancy (V level) The V level as flame retardancy was examined in accordance with the UL-94 combustion test method.

The above results are shown in the following table.

From the comparison between Examples 1 to 3 and Comparative Examples 1 and 2 in the table, the viscosity can be reduced by combining the same amount of fillers with different particle diameters, and a good adhesive strength is maintained. It can be seen that the conductivity can be improved. Further, as compared with Examples 1 and 4, it is possible to achieve a good adhesive strength and a lower viscosity than the comparative example while achieving a 20% increase of the filler compounding amount in a configuration using many large average particle diameter materials. It can be seen that the thermal conductivity can be greatly improved.

On the other hand, from Comparative Example 3, it can be seen that in the system having the same particle size, although the amount of the filler is smaller than that in Example 4, the increase in viscosity is large and the degree of improvement in thermal conductivity is small. Note that the viscosity is related to the workability of a sheet or the like,
In Comparative Example 3, when the amount of the filler was set to 600 parts according to Example 4, it was difficult to form a sheet.

From the above, it can be seen that a heat dissipation sheet excellent in processability, adhesive strength or adhesion, and heat conductivity can be obtained by using a combination of different diameter fillers. In addition, it can be seen that the close-packing method in which small particles are arranged in the gaps between large particles greatly contributes to improvement in workability, adhesive strength, and heat conductivity. In terms of flame retardancy, it can be seen that the use of a filler for both heat transfer and flame retardation makes it possible to easily achieve a high level of flame retardancy of V-0 level in UL-94 at the compounding ratio of the examples and the like. .

[Brief description of the drawings]

FIG. 1 is an explanatory view of an embodiment.

FIG. 2 is an explanatory view of another embodiment.

FIG. 3 is an explanatory view of still another embodiment.

[Explanation of symbols]

 1,3: viscous layer 2: elastic substrate

Claims (3)

[Claims] 1. A heat dissipation sheet comprising at least two or more fillers having good thermal conductivity and different average particle diameters, and at least having a viscous layer which is plastically deformed by pressing. 2. The heat-dissipating sheet according to claim 1, wherein fillers having different average particle diameter ratios of 1: 2 to 12 are contained in a close-packing method. 3. The heat radiation sheet according to claim 1, wherein the filler also serves as a flame retardant.