JP3446703B2 - Manufacturing method of insulating heat dissipation sheet and insulation heat dissipation sheet - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an insulating and heat radiating sheet which provides a highly electrically insulating film in which moisture absorption and conduction are prevented as much as possible.

[0002]

2. Description of the Related Art Insulating heat-dissipating sheets are usually prepared by dispersing inorganic powders such as organopolysiloxane and BN having excellent thermal conductivity and a curing catalyst in an organic solvent to prepare a coating solution. It is manufactured by sheet-molding it on glass fiber cloth, then drying and press heat vulcanizing.
Used for insulating and radiating heat-generating electronic components such as thyristors. However, the conventional insulating and heat-dissipating sheet has a problem that electric insulation is insufficient, and that moisture absorption and conduction occur especially on a high humidity day. The reason is considered to be that B ₂ O ₃ existing as an oxide film on the surface of the BN particles is combined with molecules of water vapor to form boric acid, and further ionized to generate ions.
That is, it is considered that the reason is that the bond between the BN particles and the organopolysiloxane is insufficient and the surface of the BN particles is exposed, and that the compound is poor in hydrophobicity and easily attracts water vapor molecules.

In order to solve the above problems, the present inventors have previously proposed a method for preventing moisture absorption and conduction by subjecting a raw material BN powder to a surface coating with an amino-modified oil.
However, even in that method, the insulating heat dissipation sheet is heated to a temperature of 40
The electrical resistance after absorbing moisture for 4 hours at ℃ and relative humidity of 95% is 1
It was on the order of 0 ¹⁰ Ω, and there were cases where a high electric resistance exceeding it could not be obtained. The reason is that the amino-modified oil coated with BN powder on the surface has only a physical attachment and no binding force, and the amino group present in the siloxane side chain exhibits hydrophilicity, so It is considered that the reason is that the molecules are easily attracted.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for producing an insulating heat-dissipating sheet which provides an insulating film which is excellent in electric insulation and does not generate moisture absorption and conduction even on a high humidity day. To do.

[0005]

Means and Actions for Solving the Problems The present inventors have
As a result of earnest studies for achieving the above object, the average unit formula R _a SiO _{(4-a) / 2} (R: a monovalent hydrocarbon group, a =
100 parts (1.85 to 2.10) of organopolysiloxane (parts by weight, the same applies hereinafter), BN powder 30 to 500
Part, a coating agent for an insulating heat dissipation sheet containing a curing catalyst,-(CH ₂ ) _n- (3 ≦ n ≦
Silane coupling agents having a hydrocarbon chain of 10), preferably _{- (CH 2) n - (} 4 ≦ n ≦ 10) of one or more B hydrocarbon chain silane coupling agent having a
By blending 0.3 to 30 parts with respect to 100 parts of N powder into a glass fiber cloth by sheet forming and vulcanizing,
The conventional insulating heat dissipation sheet has an electric resistance of about 10 ⁸ to 10 ⁹ Ω immediately after being absorbed at a temperature of 40 ° C. and a relative humidity of 95% for 4 hours, but shows a high electric resistance of 10 ¹¹ Ω or more under such a moisture absorption condition. , It is possible to obtain an insulating and heat dissipation sheet that has high electric insulation and does not cause moisture absorption and conduction even on humid days.
The coating liquid containing the organic solvent for dilution was found to have good sheet formability in any of the roll system, the calendar system, and the doctor blade system, and the present invention has been completed.

Therefore, the present invention provides the following method for manufacturing an insulating heat dissipation sheet and an insulating heat dissipation sheet. Claim 1: On a glass fiber cloth, (a) 100 parts by weight of organopolysiloxane having the following average unit formula (1), R _a SiO _{(4-a) / 2} (1) (where R is monovalent Hydrocarbon group, a is 1.85 to 2.1
Indicates a positive number of 0. (B) 30 to 500 parts by weight of BN powder, (C)-(CH ₂ ) _{n-in the} organic functional group (provided that 3 ≦ n ≦
The silane coupling agent having a hydrocarbon chain of 10) is added to B
0.3 to 30 parts by weight with respect to 100 parts by weight of N powder, (d) Preventing moisture absorption and conduction, which is characterized by vulcanizing after forming a coating agent for an insulating heat dissipation sheet containing a curing catalyst. For manufacturing insulated heat dissipation sheet. Claim 2: The silane coupling agent contains-(CH 2) in the organic functional group.
₂ ) A method for producing an insulating heat dissipation sheet according to claim 1, which is a silane coupling agent having a hydrocarbon chain of _n − (where 4 ≦ n ≦ 10). Claim 3: An insulating heat-dissipating sheet obtained by the method for manufacturing an insulating heat-dissipating sheet according to claim 1 or 2, wherein an aluminum plate and T
₀ sandwiching -3P type the insulating heat dissipating sheet between the transistors, tightening torque using M3 screws 5kgf
・ Mounted in cm, temperature 40 ℃, relative humidity 95
%, The electric resistance between the aluminum plate and the collector of the transistor immediately after absorbing moisture for 4 hours is 1.2 × 10 ¹¹
The above is an insulating heat dissipation sheet.

The present invention will be described in detail below. The organopolysiloxane of the component (a) which constitutes the coating agent for an insulating heat dissipation sheet of the present invention has an average unit formula represented by the following formula (1). _Ra SiO _{(4-a) / 2} (1)

R in the formula (1) is an alkyl group such as a methyl group or an ethyl group, an alkenyl group such as a vinyl group or an allyl group,
Aryl group such as phenyl group, tolyl group, cycloalkyl group such as cyclohexyl group, or chloromethyl group in which a part or all of hydrogen atoms bonded to carbon atoms of these groups are substituted with halogen atom, cyano group, etc., chloropropyl Same or different, unsubstituted or substituted, preferably a monovalent hydrocarbon group having 1 to 12 carbon atoms, particularly 1 to 10 carbon atoms, selected from a group, a cyanoethyl group and the like, and a is a positive number of 1.85 to 2.10. Is a number.

The above-mentioned organopolysiloxane preferably has a linear molecular structure, but there is no particular problem even if it partially has a branched structure in the molecule. It is desirable that the end of the molecular chain of this organopolysiloxane is blocked with a triorganosilyl group such as a trimethylsilyl group, a dimethylvinylsilyl group, a methylphenylvinylsilyl group, a methyldiphenylsilyl group or a hydroxyl group. The degree of polymerization of the organopolysiloxane is not particularly limited, but it is preferable that the degree of polymerization is such that the viscosity at 25 ° C. is 25 cst or more, particularly 5000 cst or more.

[0010] The BN powder to be added as the component (b) to the coating composition for an insulating / radiating sheet of the present invention is an agent for imparting thermal conductivity and electrical insulation to the insulating / radiating sheet. The average particle size of the BN powder used here is 2
It is preferably ˜50 μm. If it is less than 2 μm, the number of grain boundaries increases on the heat dissipation path, and there is a concern that the thermal conductivity will decrease. On the other hand, when it exceeds 50 μm, it may be difficult to finish the surface of the insulating heat dissipation sheet flat. Further, the purity of BN powder is 95% by weight or more,
It is particularly preferably 98% by weight or more. Purity is 95
If the content is less than weight%, there is a concern that characteristics such as thermal conductivity and electric insulation may be deteriorated due to the influence of impurities contained.

The amount of the BN powder blended is required to be 30 to 500 parts, especially 100 to 300 parts, relative to 100 parts of the component (a) organopolysiloxane. If it is less than 30 parts, sufficient heat dissipation cannot be obtained, and if it exceeds 500 parts, BN
It is not preferable because it becomes difficult to uniformly disperse the powder in the coating liquid, or the viscosity of the coating agent increases and the sheet moldability deteriorates.

The component (c) to be added to the coating agent for insulating and heat-radiating sheet of the present invention is a component which contributes to finishing the entire composition to be hydrophobic and preventing moisture absorption and conduction on a high humidity day. All of them have the property of forming an organic silicon compound film having high water resistance. Specifically, it is a silane coupling agent having a hydrocarbon chain of — (CH ₂ ) _n — (n ≧ 2) in an organic functional group, and at least one of these is used in an amount of 0 to 100 parts of BN powder. .3 ~
Add 30 parts. When the properties of the component (c) do not satisfy the above conditions, that is,-(CH ₂ ) _n- (n ≧
The silane coupling agent having no hydrocarbon chain of 2) is poor in hydrophobicity, and the sufficient effect of preventing moisture absorption and conductivity on the day of high humidity, which is the object of the present invention, cannot be obtained.

The component (c) will be described in more detail.
Silane coupling agent is - (CH _{2) n} - although other molecular structures as long as the hydrocarbon chain (n ≧ 2) is not particularly limited, strongly hydrophobic as the value of n is larger, hygroscopic conductive Since the effect of prevention is great, it is preferable that n is 3 to 10, and it can be 4 or more and 10 or less. For example, methacryloxypropyltrialkoxysilane, glycidoxypropyltrialkoxysilane, 3,4-epoxycyclohexylethyltrialkoxysilane and the like are preferably used. Examples of the alkoxy group include lower alkoxy groups such as methoxy and ethoxy.

The compounding amount of the component (c) is such that at least one of the silane coupling agents satisfying the above conditions is BN.
It is 0.3 to 30 parts with respect to 100 parts of powder. When the amount is less than 0.3 part, a sufficient effect of preventing moisture absorption and conductivity cannot be obtained. Further, when it exceeds 30 parts, heat dissipation is deteriorated, which is not preferable.

The method of blending the component (c) is not particularly limited, and (i) a method of directly adding it to the coating liquid,
(Ii) A method of forming a coating film of component (c) on the surface of BN particles by subjecting the BN powder to dry treatment or wet treatment can be adopted, but the latter method in which the surface of BN particles is coated is preferable.

Further, the curing catalyst of the component (d) is appropriately selected depending on the type of the organopolysiloxane of the component (b) and the mechanism of the crosslinking reaction. For example, when the crosslinking reaction is a radical reaction, an organic peroxide is used, and specifically, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, 2,4-dicumyl peroxide, 2,5-
Dimethyl-2,5-bis (tert-butylperoxy) hexane, di-tert-butylperoxide,
Tert-butyl perbenzoate and the like are preferably used. In addition, in the case of addition reaction curing type, an addition reaction catalyst such as an organohydrogenpolysiloxane and a platinum compound is used. Further, conventionally known curing catalysts can also be used in the case of ultraviolet curing type. The addition amount of the curing catalyst of the component (d) can be appropriately adjusted depending on the type and blending amount of other components, but is preferably 0.01 to 10 parts of the total composition.

The coating agent of the present invention is
It is preferable to add an organic solvent for dilution as a component and use it as a coating liquid. The type of the organic solvent for dilution is not particularly limited, and alcohols such as methanol, ethanol and IPA, aromatic solvents such as benzene, toluene and xylene, and ketones such as acetone can be used. In addition, the blending amount of the component (e) is not particularly limited, but the viscosity of the coating liquid is 1000 to 30000 cp.
It is preferable to set the blending amount so that the moldability becomes good.

The insulating heat dissipation sheet coating agent of the present invention has the above-mentioned (a), (b), (c),
It is also possible to mix optional components other than the components (d) and (e). As an optional component, a low molecular weight siloxane or a cyclic siloxane having a polymerization degree of 100 or less for improving fluidity,
Platinum compounds or palladium compounds for imparting flame retardancy, pigments for the purpose of coloring, and the like can be added to the coating liquid in a usual amount.

In the present invention, the coating agent containing the above components is diluted with an organic solvent, if necessary, and molded into a sheet on a glass fiber cloth, followed by vulcanization to obtain high electric insulation. It is possible to obtain an insulating and heat-dissipating sheet that does not generate moisture absorption and conduction even on a high-humidity day.

Here, the sheet forming method is not particularly limited, and a general roll method, a calendar method, a doctor blade method or the like can be adopted. Further, as for the vulcanization method, press heat vulcanization, normal pressure heat vulcanization, steam vulcanization, electron beam vulcanization, ultraviolet ray vulcanization, etc. can be carried out under known conditions according to the properties of the composition and the crosslinking reaction system. .

[0021]

EFFECT OF THE INVENTION By using the coating agent for an insulating / radiating sheet of the present invention, it is possible to obtain an insulating / radiating sheet which is excellent in electric insulation and does not generate moisture absorption and conductivity even under high humidity.

[0022]

EXAMPLES The present invention will be specifically described below by showing Examples and Comparative Examples, but the present invention is not limited to the following Examples.

Example 1 Dimethylsiloxane unit 9
9.85 mol%, methyl vinyl siloxane unit 0.15
Mol%, 100 parts of organopolysiloxane having an average degree of polymerization of about 8000, BN powder (manufactured by Shin-Etsu Chemical Co., Ltd., KBN
(H) -10) 175 parts, 2,5-dimethyl-2,5-bis (t-butylperoxy) hexane 1.5 parts as a curing catalyst, diluting toluene 300 parts and γ-glycidoxypropyltrimethoxy. Silane (Shin-Etsu Chemical Co., Ltd.)
Co., Ltd., KBM403) is coated on both sides of a glass fiber cloth having a thickness of 0.05 mm with a doctor blade to a thickness of 0.25 mm.
After drying for 0 minutes, pressure 100 kg / cm ² , temperature 1
Press heat vulcanization was performed at 70 ° C. for 10 minutes to obtain an insulating heat dissipation sheet. Further, the sheet is kept at a normal pressure of 200 ° C. for 4 hours 2
Next vulcanized.

Here, the amount of γ-glycidoxypropyltrimethoxysilane added was changed as shown in Table 1,
The thermal resistance of these sheets was measured with T ₀ -3-type transistors. Further, the above-mentioned insulating heat dissipation sheet is sandwiched between an aluminum plate and a T ₀ -3P type transistor and attached with a tightening torque of 5 kgf · cm using M3 screws at a temperature of 40 ° C. and a relative humidity of 95%. The electrical resistance between the aluminum plate and the collector of the transistor immediately after moisture absorption under the conditions for 4 hours was determined. In addition, for comparison, the same evaluation was performed on an insulating heat-dissipating sheet made of a coating solution containing no γ-glycidoxypropyltrimethoxysilane. The results are shown together in Table 1.

[0025]

[Table 1]

[Comparative Example 1] An insulating heat dissipation sheet was manufactured under the same conditions as in Example 1 except that γ-glycidoxypropyltrimethoxysilane was changed to tetramethoxysilane having no hydrocarbon chain, and the thermal resistance was measured. And the electric resistance after moisture absorption was evaluated. The results are shown in Table 2.

[0027]

[Table 2]

As is clear from the results of Tables 1 and 2, in the case of the embodiment in which the property of the component (c) which contributes to the prevention of moisture absorption and conductivity of the insulating heat dissipation sheet of the present invention satisfies the conditions of the present invention, Compounding amount is 0.3 with respect to 100 parts of BN powder
The case of ~ 30 parts is 4 at a temperature of 40 ° C and a relative humidity of 95%.
It had a high electric resistance of 10 ¹¹ Ωcm or more even after moisture absorption for a long time, and a great effect of preventing moisture absorption and conductivity was obtained. On the other hand, when the addition amount of the component (c) is less than 0.3 part,
Although the electric resistance after moisture absorption is slightly improved as compared with the case where the component (c) is not added, the effect is small. When the amount of the component (c) added exceeds 30 parts, the electric resistance after moisture absorption is greatly improved, but the thermal resistance is increased and the heat dissipation is deteriorated, which is not preferable. On the other hand, in all the cases of Comparative Examples in which the properties of the component (c) did not satisfy the conditions of the present invention, the electric resistance after moisture absorption was less than 10 ¹⁰ Ωcm, and a sufficient effect of preventing moisture absorption and conductivity was obtained. Absent. Therefore, from the above, the effect of the present invention was confirmed.

─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Toshihiko Shindo 2-13-1, Isobe, Annaka-shi, Gunma Shin-Etsu Chemical Co., Ltd. Precision Materials Research Laboratory (56) Reference JP-A-55-80461 (JP , A) JP 56-106956 (JP, A) JP 1-2221454 (JP, A) JP 54-61253 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB) Name) H01B 19/00 321 H01B 3/16-3/56

Claims (3)

(57) [Claims] 1. A glass fiber cloth comprising: (a) 100 parts by weight of an organopolysiloxane having the following average unit formula (1), R _a SiO _{(4-a) / 2} (1) (where R is a monovalent Hydrocarbon group, a is 1.85 to 2.1
Indicates a positive number of 0. (B) 30 to 500 parts by weight of BN powder, (C)-(CH ₂ ) _{n-in the} organic functional group (provided that 3 ≦ n ≦
The silane coupling agent having a hydrocarbon chain of 10) is added to B
0.3 to 30 parts by weight with respect to 100 parts by weight of N powder, (d) Preventing moisture absorption and conduction, which is characterized by vulcanizing after forming a coating agent for an insulating heat dissipation sheet containing a curing catalyst. For manufacturing insulated heat dissipation sheet. 2. The silane coupling agent is a silane coupling agent having a hydrocarbon chain of — (CH ₂ ) _n — (where 4 ≦ n ≦ 10) in an organic functional group. The method for manufacturing an insulating heat dissipation sheet according to claim 1. 3. An insulating heat dissipation sheet obtained by the method for producing an insulating heat dissipation sheet according to claim 1, wherein the insulating heat dissipation sheet is sandwiched between an aluminum plate and a T ₀ -3P type transistor, and M3 is used. Installed with the tightening torque of 5 kgf · cm using the screw of the temperature of 40
An insulating heat dissipation sheet with an electrical resistance value of 1.2 × 10 ¹¹ or more between the aluminum plate and the collector of the transistor immediately after absorbing moisture for 4 hours under the conditions of ℃ and 95% relative humidity.