JPH07215705A - Boron nitride powder for adding to silicone rubber and silicone rubber product - Google Patents

Abstract

PURPOSE:To provide a boron nitride powder for adding to silicone rubber and a silicone rubber product using the same free from the generation of crack at the time of vulcanizing even in adding into the silicone rubber in large quantities and capable of suppressing the deterioration of the mechanical properties of the silicone rubber at minimum. CONSTITUTION:The boron nitride for adding to silicone rubber is obtained by treating the surface of the boron nitride powder with a silane coupling agent having unsaturated double bond group bonding with silicon atom through a bivalent organic group in an organic functional group. The silicone rubber product is obtained by adding the boron nitride powder treated by this way into the silicone rubber and after that, vulcanizing with the radical reaction using an organic peroxide by heating.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to boron nitride powder for addition of silicone rubber, and in particular, even if a large amount of this is added to silicone rubber, cracks do not occur in the silicone rubber. TECHNICAL FIELD The present invention relates to a boron nitride powder for silicone rubber addition, in which deterioration of mechanical properties is minimized, and a silicone rubber product to which the boron nitride powder is added.

[0002]

2. Description of the Related Art Since hexagonal boron nitride (abbreviated as BN hereinafter) has excellent thermal conductivity and electrical insulation properties, materials such as resin and rubber are provided with the thermal conductivity and / or electrical insulation properties. It has been added as an enhancer,
It is also used to add to silicone rubber to improve its physical properties. Regarding the blending with this silicone rubber, if BN powder is added to the silicone rubber composition used for wire coating, anode cap, etc., BN
The breakdown voltage was 29 kv / mm when powder was not added.
It is said that the amount of BN powder added can be increased to v / mm or more (see Japanese Patent Publication No. 53182/1993), but the amount of BN powder added is limited to 50 parts by weight per 100 parts by weight of raw rubber. If it is added more than that, roll workability is deteriorated, and cracks are generated during molding or vulcanization.

Further, the addition of this BN powder has a disadvantage that even if the amount is less than 50 parts by weight, the elasticity of the rubber is lost and the properties such as tensile strength and compression set are deteriorated. As described above, the addition of this improves the dielectric breakdown voltage, but without BN powder, the tensile strength was 98 kg / cm ² and the elongation was 255%.
When BN powder of μm is added, the mechanical properties are lowered to a tensile strength of 66 kg / cm ² and an elongation of 185%. When the amount of BN powder added is 60 parts by weight, roll workability deteriorates and It turns out that there is a disadvantage that molding becomes impossible.

[0004]

Therefore, in order to solve these problems, the present inventors have found that if the BN powder is added to the silicone rubber by simultaneously mixing the silica-based filler and the BN powder, Since it is possible to manufacture a dense compound containing no rubber, these problems can be solved to some extent, and the amount of BN powder added can be adjusted to
It was found that cracks do not occur during molding and vulcanization even when the amount is 50 parts by weight or more relative to 100 parts by weight (see Japanese Patent Application No. 5-207323). Is only in contact at the interface, and because there is no binding force between them, the tensile strength was 93 kg / cm ² and the compression set was 10% when BN powder was not added, but 100 parts by weight of BN powder was added. In the case, the tensile strength is 67kg / cm ² ,
It was found that the mechanical properties deteriorated to a compression set of 25%.

[0005]

The present invention relates to a BN powder for addition of silicone rubber and a silicone rubber product using the same, which solves the above disadvantages and problems, and the BN powder for addition of silicone rubber is BN. Characterized in that the surface of the powder is treated with a silane coupling agent having an unsaturated double bond group which is bonded to a silicon atom through a divalent organic group in the organic functional group, This silicone rubber product is characterized in that the BN powder thus treated is added to silicone rubber and then heated and vulcanized by a radical reaction using an organic peroxide.

That is, the inventors of the present invention have conducted various studies on methods for preventing the mechanical properties of silicone rubber from being deteriorated due to the addition of BN powder. As a result, the surface of this BN powder is preliminarily divalent in an organic functional group. When treated with a silane coupling agent having an unsaturated double bond group bonded to a silicon atom through the organic group of 1), a siloxane film having a side chain having an unsaturated double bond group is formed on the surface of the BN particles. Therefore, when this BN powder is blended with silicone rubber, a crosslinking reaction occurs between the BN powder and the molecules of the silicone rubber, a bond is given between the BN particles and the silicone rubber, and the silane coupling agent is added. Since the contained hydrocarbon chain of the divalent organic group acts as a cushion for absorbing external force, the silicone rubber added with this should be added in a large amount. 11. The crack is not generated, the rubber elasticity is not lost, and completed the present invention found that is minimized even decrease in mechanical properties due to the BN powder addition. This will be described in more detail below.

[0007]

The present invention relates to a BN powder for silicone rubber addition and a silicone rubber product using the same.
This BN powder for silicone rubber addition is obtained by treating the surface of the BN powder with a silane coupling agent having an unsaturated double bond group in the organic functional group, which is bonded to a silicon atom through a divalent organic group. The BN powder treated in this way is
Since a bond is provided between the N particles and the silicone rubber, the silicone rubber product obtained by adding this to the silicone rubber and vulcanizing it with an organic peroxide does not cause cracks, and the addition of BN powder An advantage is given that deterioration of mechanical properties due to is suppressed to a minimum.

The BN powder used in the present invention may be made by a known method. It is to be blended with silicone rubber, and in the case of fine powder of less than 0.3 μm, agglomerated particles are In some cases, it may be difficult to uniformly disperse in the silicone rubber compound, and if it exceeds 30 μm, the distance between BN particles after addition becomes large, which may not sufficiently contribute to the improvement of thermal and electrical properties. Therefore, the average particle size is preferably 0.3 to 30 μm. Further, if the purity of this BN is less than 95%, the improvement of thermal conductivity, electrical insulation, etc. may be insufficient due to the influence of impurities contained, so this is 95% or more, particularly 98% or more. It is preferable. In the present invention, the surface of the BN powder is treated with a silane coupling agent having an unsaturated double bond group which is bonded to a silicon atom through a divalent organic group in the organic functional group. Examples of the saturated double bond group include a vinyl group, a vinyloxy group, an acryloxy group, and a methacryloxy group.

[Chemical 1] (Where X is a hydrolyzable group such as a methoxy group or an ethoxy group, R ¹ is an alkyl group such as a methyl group, R ² is a divalent organic group such as-(CH ₂ )-, R ³ is hydrogen or methyl. An alkyl group such as a group, m may be represented by 2 or 3, and n ≧ 2), and various types of commercially available products under the following product names [Shin-Etsu Chemical Co., Ltd. product name] The thing is illustrated.

[0009]

[Table 1]

The surface treatment of the BN powder with the silane coupling agent is a dry method in which the BN powder is charged into a machine capable of high-speed stirring such as a Henschel mixer, and the silane coupling agent is slowly added dropwise to the machine, followed by heat treatment. Either a treatment method or a wet treatment method in which BN powder is added to the silane coupling liquid, the mixture is stirred, and then dried. Therefore, for example, 1) a silane coupling agent is dissolved in alcohols such as methanol and ethanol, 2) water is added, and then a hydrolysis catalyst such as acetic acid or a tin compound is added and stirred to prepare a silane solution. 3) Add BN powder to this silane solution,
4) Drying may be performed.

B by the silane coupling agent
The amount of the silane coupling agent used for treating the N powder may be appropriately adjusted according to the specific surface area of the BN particles.
This is usually 0.1 to 5.0 parts by weight with respect to 100 parts by weight of BN powder, according to which BN having a siloxane coating formed on the surface thereof by treatment with a silane coupling agent.
A powder can be obtained, the chemical structure of which is shown below.

[Chemical 2]

As described above, this silane coupling agent has a hydrolyzable group and an unsaturated double bond group in the functional group, which is a divalent organic group such as-(CH ₂ ) _n.
Since it is assumed that they are bonded to the silicon atom through the hydrocarbon chain represented by-(n ≧ 2), the surface of the BN powder is treated with this, and the hydrolyzable group undergoes hydrolytic polycondensation. This B
A siloxane coating is formed on the surface of the N powder, and the divalent organic group serves to buffer the external force applied to the silicone rubber product. Therefore, when the BN powder is added to the silicone rubber base compound, the siloxane coating is added. The unsaturated double bond group present therein causes a cross-linking reaction with the molecules of the silicone rubber to chemically bond the BN powder and the silicone rubber, so that the silicone rubber product does not crack and the BN This provides the advantage that the reduction in mechanical properties of the silicone rubber due to the addition of powder is reduced.

The silicone rubber product of the present invention can be obtained by adding the BN powder thus treated to a silicone rubber base compound and then thermally vulcanizing it by a radical reaction with an organic peroxide. The silicone raw rubber used here is represented by the general formula R _a SiO _{(4-a) / 2,} where R is an alkyl group such as a methyl group, an ethyl group, a propyl group or a butyl group, a vinyl group, an allyl group or butenyl. Groups, such as alkenyl groups, phenyl groups, tolyl groups, and other aryl groups, some of the hydrogen atoms bonded to the carbon atoms of these groups are replaced with halogen atoms, cyano groups, etc., chloromethyl groups, trifluoropropyl groups The same or different unsubstituted or substituted monovalent hydrocarbon group selected from cyanoethyl groups and the like, and is composed of an organopolysiloxane in which a is a positive number from 1.95 to 2.05, which is linear. However, it may have a partially branched structure in the molecule, and the degree of polymerization of this compound is not particularly limited, but it is generally about 3,000 to 13,000.

Further, the silicone rubber base compound is said to be obtained by adding a silica filler to the organopolysiloxane for the purpose of reinforcing, thickening, improving processability and increasing the amount. The silica filler is fumed silica, wet type. Silica, quartz fine powder, diatomaceous earth, etc. are used, but if the amount of this compound is less than 5 parts by weight relative to 100 parts by weight of organopolysiloxane, the desired reinforcing property cannot be obtained. Since the extrusion property of the product is extremely deteriorated, it may be 5 to 500 parts by weight, preferably 10 to 300 parts by weight.

The method of mixing the silicone rubber base compound with the above-mentioned BN powder is not particularly limited, and it may be mixed with a general kneader, two rolls, etc. This is an organopolysiloxane and a silica filler. The BN powder may be mixed with the silica filler at the same time when is mixed to form a base compound.

The silicone rubber compound thus prepared is blended with an organic peroxide, and is heat-vulcanized by heating to obtain a silicone rubber product.
This organic peroxide converts it into benzoyl peroxide,
When an acyl-based organic peroxide such as 2,4-dichlorobenzoyl peroxide is used, the dimethylene bridge between methyl groups is given priority, and the bridge by the unsaturated double bond group on the surface of BN particles may not work sufficiently. Therefore, it is preferable to use an alkyl organic peroxide such as 2,5-dimethyl-2,5-bis (t-butylperoxy) hexane or di-t-butylperoxide for this. For example, the crosslinking reaction between the methyl group and the unsaturated double bond group is preferentially promoted, so that the unsaturated double bond group on the surface of the BN particles acts for crosslinking, and as a result, the BN powder and the silicone rubber are bonded. become.

The amount of the organic peroxide added may be appropriately adjusted according to the types of other components and the compounding ratio thereof, but it may be 0.1 to 10% by weight based on the whole composition. Although the vulcanization conditions are not particularly limited, the vulcanization conditions may be a heat treatment under ordinary pressure or under pressure at about 80 to 200 ° C. It should be noted that this crosslinking method may be based on an addition reaction or an ultraviolet curing reaction, but in this case, the unsaturated double bond group on the surface of the BN particles does not work for crosslinking and the object of the present invention is not achieved. Therefore, it is necessary to use an organic peroxide method, particularly an alkyl organic peroxide method, because the vinyl group on the surface of the BN particles crosslinks and bonds with the molecule of the silicone rubber. In addition, the elasticity of the rubber is not deteriorated even by the addition of the BN powder, and the advantage that the deterioration of the mechanical properties by the addition of the BN powder is minimized is given.

[0018]

EXAMPLES Examples and comparative examples of the present invention will be given below.
Parts in the examples are parts by weight. Was dissolved Example 1 formula _{(CH 3 O) 3 Si (} CH 2) 3 OCH = CH silane coupling agent · KBM1203 represented by ₂ [Shin-Etsu Chemical Co., Ltd. trade name 3 parts in 50 parts of methanol Then, 100 parts of water and 20 parts of 60% acetic acid water were added and mixed to prepare a silane solution. Then BN powder / KBN
(K) -10 [trade name of Shin-Etsu Chemical Co., Ltd.] 100 parts of 173 parts of this silane solution was added and mixed, and then dried at 120 ° C. under a reduced pressure of 30 mmHg and treated with a silane coupling agent BN powder Was produced.

Next, 99.62 mol% of methylfluoropropyl siloxane unit, 0.33 mol% of dimethyl siloxane unit, and 0.05 mol% of methyl vinyl siloxane unit,
Organopolysiloxane with an average degree of polymerization of 6,000 100
25 parts of silica filler / Aerosil 200 [trade name of Nippon Aerosil Co., Ltd.] was kneaded to make silicone rubber compound, and 100 parts of BN powder treated as above and 2,5-dimethyl as a curing catalyst were kneaded. -2,5-bis (t
-Butyl peroxy) hexane 1.5 parts were mixed by two rolls in sequence, and then put into two vulcanization molds of 150mm x 120mm x 2mm sheet and 29.20mmφ x 12.70mmh cylinder, 165 ℃, 100kg / First press thermal vulcanization at 15 cm ² for 15 minutes and atmospheric pressure thermal vulcanization at 200 ° C for 4 hours to make a silicone rubber sheet and cylinder, and using this sheet, its thermal conductivity and tensile strength JIS also using a cylinder
When the compression set was measured by the method of -K6301, the results shown in Table 2 below were obtained.

Example 2 The curing catalyst used in Example 1 was an acyl-based 2,4
When the silicone rubber sheet and the cylinder were prepared by treating in the same manner as in Example 1 except that the dichlorobenzoyl peroxide was used, and the physical properties thereof were examined, the results shown in Table 2 below were obtained.

Comparative Example 1 BN powder treated with the silane coupling agent used in Example 1 was treated with B not treated with the silane coupling agent.
A silicone rubber sheet and a cylinder were prepared in the same manner as in Example 1 except that N powder was used, and the physical properties thereof were examined. The results shown in Table 2 below were obtained.

Comparative Example 2 The silane coupling agent used in Example 1 was represented by the chemical formula (CH ₃ O).
KBM1003 represented by _3- SiCH = CH ₂ [Shin-Etsu Chemical Co., Ltd.
[Product name] except that the silicone rubber sheet and the cylinder were processed in the same manner as in Example 1 and the physical properties thereof were examined. The results shown in Table 2 below were obtained.

[0023]

[Table 2]

[0024]

The present invention relates to a BN powder for silicone rubber addition and a silicone rubber product. As described above, this BN powder for silicone rubber addition has a divalent organic group in the organic functional group on the surface of the BN powder. It is characterized in that it is treated with a silane coupling agent having an unsaturated double bond group bonded to a silicon atom via a BN powder obtained by treating a silicone rubber in this way. The BN powder for addition of silicone rubber has a siloxane coating on its surface, which is characterized by being thermally vulcanized by a radical reaction using an organic peroxide. When added to the silicone rubber, the BN powder and the silicone rubber are chemically bonded to each other, so that the silicone rubber has cracks during vulcanization. Without the which upon heating vulcanization with an organic peroxide silicone rubber product advantage that also reduction of mechanical properties without reducing the rubber elasticity becomes minimum ones by the addition of BN powder is given.

Claims (2)

[Claims] 1. The surface of a boron nitride powder is treated with a silane coupling agent having an unsaturated double bond group which is bonded to a silicon atom through a divalent organic group in an organic functional group. Boron nitride powder for adding silicone rubber, characterized by: 2. A silicone rubber product obtained by adding the boron nitride powder for silicone rubber addition according to claim 1 to silicone rubber and then thermally vulcanizing it by a radical reaction using an organic peroxide. .