JPS6025058B2 - silicone rubber composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a new and improved silicone rubber composition, and particularly to a silicone rubber composition that significantly improves the deterioration of silicone rubber due to heat history when coexisting with synthetic rubber or plastic. .

Silicone rubber is widely applied in various fields because it has excellent heat resistance, cold resistance, weather resistance, electrical insulation, etc. due to its unique siloxane structure.

In particular, in fields where synthetic rubber and plastics have been used, the use of silicone rubber is increasing due to demands for superior heat resistance, cold resistance, and weather resistance, as well as maintenance-free properties.

However, if silicone rubber comes into contact with certain types of synthetic rubber or plastics or coexists in the same atmosphere, they may deteriorate significantly due to the fillers, additives, and thermal decomposition products of these polymers. It has the disadvantage that it cannot take full advantage of the characteristics inherent in silicone rubber, such as the characteristics inherent in silicone rubber, and therefore cannot be used for mounting.

The present invention aims to provide a silicone rubber composition that eliminates the above-mentioned drawbacks without impairing the excellent properties originally possessed by silicone rubber. R is an unsubstituted or substituted monovalent hydrocarbon group, a is a number from 1.95 to 2.04), and the degree of polymerization is 50 or more. 10 parts by weight of diorganopolysiloxane, and the specific surface area. and 5 to 8 parts by weight of a reinforcing silica-based filler having a content of 50%/ta or more.

} The average particle diameter is 0.3 mounds or less, and the specific surface area is 3
．． Substantially surface-untreated ultrafine calcium carbonate of 0.1 to 1 part by weight and 1 part by weight of [
The curing agent comprises an organic peroxide and/or organohydrogenpolysiloxane as a curing agent in an amount sufficient to cure the i' component, and an addition reaction catalyst.

The present invention will be explained in detail below.

Silicone rubber is widely applied in various fields due to the excellent properties mentioned above, but due to the high unit cost of raw materials,
For example, chlorosulfonated polyethylene, chlorinated polyethylene, hydrin rubber, etc., which have inferior physical properties to silicone rubber but are relatively superior in heat resistance, are used, and there are examples of using silicone rubber only in areas where heat resistance is most needed. do not have.

It may also be used in contact with or in the same atmosphere as PVC, chloroprene, fluorine rubber, etc. However, some of these synthetic rubbers and plastics may release compounds that act as acid reagents for polysiloxanes from their fillers and additives or from the polymer due to thermal deterioration.

For example, PVC undergoes dehydrochlorination, oxidation, decomposition, crosslinking, etc. due to heat, radiation, oxygen, ozone, etc., but especially HC1,
CI-releases ions. It is also known that a similar reaction occurs with chlorinated polyethylene and the like. This acts as a cracking catalyst for polysiloxane and promotes cracking deterioration. Therefore, even in an atmosphere at a temperature that would not normally cause any problems for silicone rubber, significant deterioration could occur. As a result of intensive studies, the present inventors have found that ultrafine calcium carbonate with an average particle diameter of 0.3 mounds or less, a specific surface area of 3.0/ta or more, and with substantially no surface treatment is added. The present invention was completed based on the confirmation that by doing so, it is possible to obtain a silicone rubber elastic body that solves the above problems without impairing the excellent properties of silicone rubber.

To explain this, the silicone rubber compound of component 'i' has the L average composition formula RaSi○4a (where R is a substituted or unsubstituted monovalent hydrocarbon group, and a is 1.95 to 2
．． Diorganopolysiloxane having a degree of polymerization of 50 or more and represented by the number 04), such as dimethylpolysiloxane, dimethylvinylpolysiloxane, dimethylvinylphenylpolysiloxane, 3-trichloropropylmethylvinylpolysiloxane, etc. 10 parts by weight of polysiloxane A reinforcing silica filler with a specific surface area of 50/ta or more, for example, fumed silica, silica airgel, silica hydrogel, known fine silica powder used in isokinetic ordinary silicone rubber is added to
-8 parts by weight are added and mixed, and is usually commercially available as RTV rubber or heat-processed rubber.

In addition, this silicone rubber compound may be used as necessary with non-reinforcing fillers such as diatomite, quartz powder, fused quartz powder, clay, pigments, functional fillers (e.g. carbon black, metal powder, etc.). heat conductive agents such as alumina and magnesia, magnetic flux conductive agents such as ferrite, magnetism imparting agents such as barium titanate, etc.), property improvers (e.g. heat resistance improvers such as cerium oxide and titanium oxide, and difficult-to-use materials such as platinum compounds). It is optional to add and mix a flame retardant (flammability imparting agent, etc.). [o
Ultrafine calcium carbonate, which is the component 1, is an essential component that imparts the features of the present invention to the silicone rubber composition. Calcium carbonate has a measured specific surface area of 3.0 mm/h and is considered to be untreated calcium carbonate whose particle surface is not substantially covered with fatty acids, surfactants, etc., but it satisfies these properties. Examples of calcium carbonate include those commercially available under the names of NEOLITE T (trade name, manufactured by Takehara Chemical Industries Ltd.) and Colocalso S (trade name, manufactured by Shiraishi Calcium Ltd.).

Conventionally, calcium carbonate, which is called virgin calcium carbonate or minor calcium carbonate, has been used mainly as a filler in silicone rubber compounds to reduce costs, but these calcium carbonates exhibit the features of the present invention. It is impossible to do so, and excellent effects can only be achieved by using ultrafine calcium carbonate that satisfies the above conditions.

In order to improve the deterioration of silicone rubber due to thermal history when the rubber elastic body obtained from the composition of the present invention coexists with synthetic rubber or plastic, the specific surface area measured by the air permeation method must be 30 w/ta or more. It is necessary that the amount of calcium carbonate is 3.5 〆/ta or more, and more preferably 3.5 〆/ta or more. Furthermore, the surface of this calcium carbonate must be substantially untreated with fatty acids, surfactants, or the like.

Here, "substantially" should be understood not to mean "there must be no fatty acids, surfactants, etc.," but to mean "mostly the surface of calcium carbonate itself." On the other hand, no matter how large the specific surface area of calcium carbonate is, if most of it has been treated with fatty acids, surfactants, etc., it will not have the property of preventing cracking caused by synthetic rubber or plastic, which is a feature of the present invention. I can't be satisfied.

The amount of ultrafine surface-treated calcium carbonate that satisfies the above conditions is 0.1 to 1 part by weight per part by weight of component 10.

If the amount added is less than 0.1 parts by weight, the desired effect cannot be achieved, while if it exceeds 0.1 parts by weight, problems such as a decrease in heat resistance and inhibition of vulcanization may occur. This is because the characteristics of the system cannot be fully utilized. Various curing agents can be used as one component, depending on the type of silicone rubber compound used as the component. Examples include hydrogen siloxane and addition reaction catalysts (Pt, Pd, Rh or their compounds, etc.), which are usually used in RTV.
It is known as a curing catalyst for rubber or heated diluted rubber, and the amount usually added is sufficient.

In addition, in the present invention, there is no problem in that both may be used in combination as necessary.

The silicone rubber composition of the present invention is heat-treated at a temperature of 50 to 400°C for 1 hour at normal pressure, room temperature, or under normal pressure or pressure, and then further heated at 120°C as necessary.
It is cured by secondary vulcanization at ~25 pC for 3 minutes to ~24 hours, and even when it comes into contact with or coexists with certain synthetic rubbers and plastics in the same atmosphere, it does not impair the excellent properties of silicone rubber. An elastic body having particularly excellent heat resistance can be obtained.

Therefore, the composition according to the present invention can be used in fields where synthetic rubber and plastics are often used together, such as transportation equipment such as peripheral parts of automobile engines, machinery fields, nuclear power plants, etc. Suitable for the electric wire field, etc.

Next, the present invention will be explained with reference to examples, in which all parts in each example indicate parts by weight.

Example 1 (CH3) 96.7 mol% of Daii○ units, (C
6 days 2) 3 mol% Si○ units, (CH3) (CQ=CH
) An organopolysiloxane with a degree of polymerization of 8000, consisting of 0.3 mol % of Si0 units, whose molecular chain terminals are blocked with dimethylvinylsiloxy groups, and a specific surface area of 200.
After adding 50 parts of fumed silica, 4 parts of diphenylsilane diol, and 7 parts of Q-dimethylsiloxane diol having a viscosity of 2 s (2 0), and kneading them uniformly in a kneader, Silicone rubber compound KE5601u (trade name, manufactured by Shin-Etsu Chemical Co., Ltd.) prepared by heat treatment for 2 hours. Surface untreated calcium carbonate whose specific surface area measured by Base, molding temperature 120qo
Press vulcanize for 10 minutes at
Next, vulcanization was performed to create a sheet with a thickness of two feet.

A test piece was punched out from this sheet with a JIS No. 4 dumbbell, and this material was placed in a test tube with an inner volume of 45 M and an inner diameter of 21 mm, together with PVC powder for 2 hours, and sealed.
When the PVC resistance was measured after heat treatment at 0oo for 120 hours, the results shown in Table 1 were obtained.

As is clear from Table 1, when PVC coexists, KE56
It can be seen that although 01u has poor sealing heat resistance, the system to which ultrafine surface-untreated calcium carbonate according to the present invention is added exhibits excellent sealing heat resistance even in the presence of PVC. table
1 Appearance change of rice tongue bell piece: × = Discoloration △ = Slight discoloration ○ = Change in Example 2 KE560 used in Example 1
3 parts of calcium carbonate of the type shown in Table 2 and 0.8 parts of 2,4-dichlorobenzoyl peroxide were added to 1 uloo part and mixed in two rolls, and after molding under the same conditions as Example 1, A test piece was prepared by secondary vulcanization.

The PVC resistance of this product was measured in the same manner as in Example 1.

The results are shown in Table 2. Table 2 *a: Surface-untreated calcium carbonate colocalso S (mentioned above) with an average particle diameter of 0.08r and a specific surface area of 4.1/unit as measured by air permeation method b: Average particle diameter of 0.1 The specific surface area measured by the air permeation method on the mountain surface is 4.7 W/W, and the surface has been treated with fatty acid ester.
Product name] c: Surface-untreated calcium carbonate Akadama [Product name manufactured by Shiraishi Calcium] with an average particle diameter of 0.8 mm and a specific surface area measured by air permeation method of 1.8 mm/mm Example 3 10 parts of dimethylpolysiloxane with a degree of polymerization of about 800, with both ends of the molecular chain blocked with dimethylvinylsiloxy groups, and 25 parts of fumed silica with a specific surface area of 200 whose surface has been treated with trimethylsiloxy groups. 1.5 parts of drogensiloxane and chloroplatinic acid 5Q style, 1.3 parts Adding 0.2 part of 5,7-tetramethyl-1,3,507-tetravinyltetracyclosiloxane,
Silicone rubber compound/ground KEI901RTV (trade name, manufactured by Shin-Etsu Chemical Co., Ltd.) made by uniformly kneading 10 sparse parts, to which 0.5 part of ultrafine surface-untreated calcium carbonate used in Example 1 was added. was molded into a plug boot using LIM.

When this plug boot was attached to a chlorinated polyethylene ignition cord and a mounting test was conducted, no abnormalities were observed in the plug boot itself, let alone the interface that was in contact with the chlorinated polyethylene, even after one year. .

On the other hand, in the plug boots molded without adding calcium carbonate, it was observed that the contact interface deteriorated after three months of the mounting test, and that the rubber elasticity was lost along with the occurrence of cracks.

Claims (1)

[Claims] 1 (a) Average composition formula ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ (In the formula, R is an unsubstituted or substituted monovalent hydrocarbon group, and a is 1.95 to 2
．． 04) with a degree of polymerization of 50 or more and a specific surface area of 50 m
100 parts by weight of a silicone rubber compound consisting of 5 to 80 parts by weight of a reinforcing silica filler of ^2/g or more (b) An average particle size of 0.3 μm or less and a specific surface area of 3
．． 0.1 to 10 parts by weight of ultrafine calcium carbonate with a surface density of 0 m^2/g or more, and (c) an organic curing agent in an amount sufficient to harden the component (a) above. A silicone rubber composition comprising a peroxide and/or an organohydrodiene polysiloxane and an addition reaction catalyst.