JPH0612643B2 - Thermally conductive insulation sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention is useful for allowing a heat conductive insulating sheet, particularly a heat generating electronic device such as a transistor or a heat dissipation fan to be in close contact with the heat to be released to the outside. The present invention relates to a heat conductive insulating sheet having excellent rubber elasticity with excellent heat conductivity and insulation.

(Prior Art) Conventionally, mica plates and polyester films coated with grease have been used as insulating heat dissipation sheets, but since these lack thermal conductivity, synthetic rubbers such as silica, alumina, and nitrides have been used. A heat-dissipating sheet to which boron or various inorganic substances having high thermal conductivity and electrical insulation are added has been used.

However, in order to improve the heat conductivity of this kind of heat conductive heat dissipation sheet, it is necessary to add a large amount of these compounds, and this large amount of compound loses the properties of rubber, and the desired heat generating electric It also has the disadvantage of weakening the adhesion to the components and the radiation fins.

(Structure of the Invention) The present invention relates to a heat conductive insulating sheet that solves such disadvantages, which is composed of organopolysiloxane and boron nitride and is irradiated with X-rays in the thickness direction of the sheet. <00 in the obtained X-ray diffraction diagram
The peak ratio between the 2> plane and the <100> plane is 30 or less.

That is, as a result of various investigations by the present inventors on the production of an insulating rubber-like heat dissipation sheet having excellent thermal conductivity, a mixture of organopolysiloxane and boron nitride has a rubber component as a main material whose organopolysiloxane is Therefore, it is said that boron nitride has excellent electrical insulation properties, and since boron nitride is an excellent heat conductive substance, it also has good heat conductivity. The ride is easily oriented so as to be parallel to the heat radiating surface of the sheet in the a-axis direction, and as the degree of orientation advances, the heat radiating property of the sheet decreases significantly. If the ratio α of the peak of the 002> face to the peak of the <100> face is small, the orientation degree of this boron nitride increases as α increases, It was found that the boron nitride particles are randomly distributed on the sheet surface, the number of particles perpendicular to the a-axis direction of the sheet surface is increased, and the thermal conductivity is improved. Three
The present invention has been completed by confirming that it is preferable to set it to 0 or less.

The organopolysiloxane as a main material forming the heat conductive insulating sheet of the present invention has an average composition formula R is an alkyl group such as a methyl group, an ethyl group, a propyl group or a butyl group, an alkenyl group such as a vinyl group or an allyl group, an aryl group such as a phenyl group or a tolyl group, a cycloalkyl group such as a cyclohexyl group, Or, selected from a chloromethyl group, a trifluoropropyl group, a cyanoethyl group, etc., in which a part or all of hydrogen atoms bonded to carbon atoms of these groups are substituted with a halogen atom, a cyano group, etc., preferably 50 mol% thereof The above may be an identical or different unsubstituted or substituted monovalent hydrocarbon group having a methyl group, and a may be a substantially linear diorganopolysiloxane having a molecular weight of 1.85 to 2.10. , This one has a viscosity of 25 cS or more at 25 ° C, especially 5,0
It is preferable to use a silicone rubber having a polymerization degree of 00 cS or more.

Further, the boron nitride present in this sheet in order to improve the thermal conductivity of this sheet has the <002> plane and the <1> plane of the X-ray diffraction diagram when irradiated with X-rays in the thickness direction.
When the peak ratio with respect to the (00) plane is large, in the sheet made of the above-mentioned blend with the organopolysiloxane, the sheet is likely to be oriented parallel to the a-axis direction of the sheet, which causes poor heat dissipation of the sheet. , The peak ratio α between the <002> plane and <100> in this X-ray diffraction diagram
Is required to be 30 or less. The boron nitride used here may have a commercially available hexagonal structure, but it is particularly preferable to react boron oxide with nitrogen gas in the presence of a suitable reducing agent such as carbon. If the amount of the boron nitride compounded is 50 parts by weight or less with respect to 100 parts by weight of the above-mentioned organopolysiloxane, the thermal conductivity is not sufficiently improved.
When the amount is 500 parts by weight or more, the rubber elasticity is significantly deteriorated and the thermal conductivity is rather deteriorated. Therefore, it is necessary to set the range of 50 to 500 parts by weight, and the preferable range is 100 to 400 parts by weight. It

The heat conductive insulating sheet of the present invention is obtained by vulcanizing and curing a mixture of the above-mentioned predetermined amount of organopolysiloxane and boron nitride into a sheet, which is a pressure molding method, an extrusion molding method, a calendar. The composition may be molded into a desired shape by a molding method, a casting molding method, or the like, or the composition may be dissolved in a solvent or the like and applied to glass cloth or the like, and then dried and molded. Also,
This molded product is cured by mixing an organopolysiloxane with an organic peroxide in advance, and molding this molded product, for example, at 100 kg / cm ²
It may be heated under pressure at 170 ° C.

The sheet thus obtained has excellent electrical insulation and thermal conductivity, but this sheet has a <0 value in the X-ray diffraction diagram obtained by irradiating X-rays in its thickness direction.
It is necessary that the peak ratio α between the 02> plane and the <100> plane be 30 or less. In order to make the peak ratio of this sheet 30 or less, for example, a method of using boron nitride obtained by mixing boric acid and carbon black and nitriding in a nitriding furnace, dissolving the composition in a solvent or the like before curing. And a method of using boron nitride having a low crystallinity can be mentioned.

The heat conductive insulating sheet of the present invention thus obtained has excellent electric insulation and heat conductivity, and has an insulating property such as a volume resistivity of 1 × 10 ¹⁵ Ω · cm. 1
Since it exhibits a thermal conductivity of 0 × 10 ⁻³ Cal / sec · cm · C, it is useful for heat insulation of heat-generating elements such as transistors and thyristors.

Next, examples of the present invention will be described. In the examples, parts indicate parts by weight, and each measured value in the examples indicates a measurement result by the following method.

〔Thermal resistance〕

A transistor TO-3 type punched sample is a transistor 2SD113 [Toshiba brand name] and a fin.
FBA-150-PS [Product name of OS Co., Ltd.] is sandwiched between and attached to a torque inverter, and a transistor transient thermal resistance measuring device TH-156 [Kuwano Electric Co., Ltd.]
Manufactured goods] by applying power of DC10V, 3A, 1
It was calculated from the ΔV _EB (mV) after a minute by the following formula.

ΔV _EBS ... with sample sandwiched ΔV _EB ΔV _EBG ... Δ when heat-dissipating grease G746 [trade name of Shin-Etsu Chemical Co., Ltd.] is applied to transistors
V _EB C ………… Temperature coefficient of ΔV _EB of transistor (ΔV
_{EB /} ΔT ≈ 2.2 mV / ° C) α ………… Correction term by base current (α = 0.9W) [Thermal conductivity] Shows Thermo QTM-D with 6 × 15 cm sample sheet
II Measured using a rapid thermal conductivity meter [trade name of Showa Denko KK].

[Orientation]

Cut out the heat dissipation sheet into 2 x 2 cm and attach it to the jig for X-ray diffraction with cellophane tape.
3 with CuKα ray using [Rigaku Denki Co., Ltd. product name]
Scanning 2θ, 20 ° to 60 ° under conditions of 0 KV and 15 mA, and 26.9 ° <002> plane and 41.6 ° <1
The orientation ratio α was obtained by obtaining the peak ratio of the <00> plane.

Examples 1 and 2, Comparative Examples 1 and 2 2% of 1% toluene solution containing 0.2 mol% of vinyl groups whose both ends are blocked with vinyldimethylsilyl groups
Commercially available hexagonal boron nitride, UHP-EX (trade name, manufactured by Showa Denko KK), was added to 100 parts of dimethylpolysiloxane raw rubber having a relative viscosity of 2.0 at 0 ° C.
00 parts, octamethylcyclotetrasiloxane 50 parts,
1.5 parts of 2,5-dimethyl-2,5-di (t-butylperoxy) hexane and 800 of perchlorethylene
Part was added and dissolved and mixed uniformly using a homogenizer to make a coating liquid. Then, this coating liquid was cast on a mold in which a mold was dug to a depth of 0.45 mm, and then placed on an ultrasonic shaker. Shake for 10 minutes at room temperature, dry and press to obtain sheet I, thickness 0.0
This was coated on both sides of a 5 mm glass cloth with a wire bar coat, shaken on an ultrasonic shaker for 10 minutes, dried and pressed to make Sheet II, and ultrasonically shaken above for comparison. Sheets III and IV were prepared in the same manner except that no mechanical shaking was performed, and the thermal resistance and X-ray diffraction patterns of the sheets I to IV thus obtained were compared with the <002> plane and the <100> plane. Peak ratio α
Was measured, and the results as shown in Table 1 were obtained. The X-ray diffraction patterns of these sheets are as shown in FIGS. 1a, 1b and 2a, b, respectively.

Examples 3 to 6 and Comparative Examples 3 to 5 4.47 kg of boric acid (first-grade reagent) and 1.0 kg of acetylene black (manufactured by Denki Kagaku Co., Ltd.) were mixed with a ribbon braider and then 10 kg of nitrogen gas was added in a reducing nitriding furnace. After nitriding reaction at 1,800 ° C for 4 hours while flowing, the reaction product obtained is crushed with a crusher, pickled with hydrochloric acid, washed with water, dried and sized with a sieving machine. The average particle size is 11.1
1 kg of boron nitride powder having a size of μm was obtained.

Then, 100 parts of the organopolysiloxane raw rubber used in Example 1 was added to the boron nitride 2 obtained above.
00 parts, octamethylcyclotetrasiloxane 50 parts,
1.5 parts of 2,5-dimethyl-2,5-di (t-butylperoxy) hexane and 800 of perchlorethylene
Parts are mixed and dissolved and mixed with a homomixer to form a coating solution, which is applied to both sides of a glass cloth having a thickness of 0.05 mm by wire bar coating, dried and then vulcanized and molded by a press generator. And thermally conductive insulating sheets V to VIII having a thickness of 0.2 to 0.8 mm were prepared.

Next, the thermal conductive insulating sheets V to VIII and the commercially available heat radiating sheets BFG30, 45 and 80 (trade name of Denki Kagaku Co., Ltd.) were used as samples IX to XI, and their thermal resistance, thermal conductivity and X-ray diffraction pattern < When the peak ratio α between the 002> plane and the <100> plane was measured, the results shown in Table 2 were obtained, and the X-ray diffraction patterns of these sheets are shown in FIG.
~ D, as shown in Figures 4a-4c.

Examples 7 to 8 The thermal conductivity of 0.2 mm and 0.8 mm in thickness was the same as in Examples 3 to 6 except that the amount of boron nitride added in Examples 3 to 6 was 300 parts. Insulation sheet XI
I, XIII are made, thermal resistance, thermal conductivity about these,
When the peak ratio α was measured, the results shown in Table 3 below were obtained.

BRIEF DESCRIPTION OF THE DRAWINGS Both figures show the peaks of <002> plane and <100> plane in an X-ray diffraction diagram of a heat conductive insulating sheet, and FIGS. 1, 2 and 2 a and b are comparative examples 1 and 2, and 3 a, b, c and d are examples 3 and 4,
5, 6 and 4 a, b and c are Comparative Examples 3 and 4, 5 and FIGS. 5 a and b are <002> faces and <1> of Examples 7 and 8, respectively.
The peak of the <00> plane is illustrated.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshihiro Kubota 2-13-1, Isobe, Annaka City, Gunma Prefecture Shin-Etsu Chemical Co., Ltd. Silicone Electronic Materials Research Laboratory (72) Inventor Toshimi Kobayashi Gunma Prefecture Nakaichi Isobe 2-13-1 Shin-Etsu Chemical Co., Ltd. Silicon Silicon Electronic Materials Research Laboratory (72) Inventor Tokio Sekiya 2-13-1, Isobe, Annaka-gun, Gunma Shin-Etsu Chemical Co., Ltd. Silicone Electronic Materials Technical Research Institute (56) References Japanese Patent Publication No. S57-42921 (JP, B2)

Claims (1)

[Claims] 1. A <002> plane and an <10> plane in an X-ray diffraction diagram obtained by irradiating an X-ray in the thickness direction of the sheet, which is composed of organopolysiloxane and boron nitride.
0> surface has a peak ratio of 30 or less.