JPS6225160A - Curable silicone composition - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION BACKGROUND OF THE INVENTION The present invention relates to composite materials made from cork and silicone rubber. More particularly, the present invention relates to a composite material particularly useful as a gasket or sealing means comprising a relatively large amount of cork and a silicone elastomer binder.

Gasket materials, such as those used in equipment such as automobile engines and dishwashers, that can be exposed to high temperatures and/or organic materials for extended periods of time are known in the art. Nevertheless, it would be desirable to have a material suitable for use as a gasket or sealing means that is more suitable and less expensive for certain applications than currently available gasket materials.

Accordingly, it is an object of the present invention to provide a composite material useful as a gasket or sealing means in automobile engines, appliances, etc., comprising cork particles and a silicone elastomer effective to bond the cork particles.

Another object of the present invention is to provide a method of making silicone polymer/cork composites useful as gaskets or sealing means.

These and other objects are accomplished by a composite material comprising (a) cork particles and (b) an amount of silicone elastomer effective to bond the cork particles.

DESCRIPTION OF THE INVENTION According to a first invention, there is provided a curable composition comprising (a) cork particles and (b) two curable silicone compositions effective to bond the cork particles.

The cork particles used in the present invention are commercially available, such as No. 5 U.

S, U number 10 that passes through the sieve, S, particle called coarse particles that remains on the sieve, U number 10,
S, the sieve passes through, but No. 20 U, S.

Particles called medium particles, number 20 U and S, remain on the sieve, and particles number 40 pass through the sieve.

S, as long as it falls within a broad tolerable range, such as particles called fine particles that remain on the sieve.

Preferably, the cork particles used in the practice of the present invention are fine or medium-sized, as this results in a smoother textured composition that is more easily processed.

The curable silicone composition used in the practice of this invention is
Any material known in the silicone field may be used. Preferably, silicone elastomers are prepared from thermosetting silicone compositions in which the polydiorganosiloxane-based polymer has a viscosity of less than about 1° ooo, ooo centipoise at 25°C. The viscosity of polydiorganosiloxane at 25°C is about 1. 000.
If it is larger than 000 centipoise, a sufficient amount of cork particles cannot be dispersed therein to obtain a suitable silicone/cork composite.

The preferred thermosetting silicone rubber composition of the present invention is (
a) a polydiorganosiloxane-based polymer having a viscosity of less than about 1,000,000 centipoise at 25° C., preferably having some aliphatic unsaturation;
(b) optionally an effective amount of reinforcing filler; and (c)
Consisting of an effective amount of catalyst.

Any reinforcing filler known in the art may be used in the practice of this invention, including fumed silica, treated fumed silica, precipitated silica, or treated precipitated silica. If treated silica is used, e.g., Lucas U.S. Pat. No. 2,938,009 or Smith (So+lth) U.S. Pat. No. 3,635.
, 743, known in the art.

The most commonly used catalysts for thermosetting silicone rubbers are organic peroxides, which are usually used in amounts of about 0.10 to about 5 weight percent of the total composition. Those skilled in the art will be able to select suitable catalysts without undue experimentation; however, 2,5-bis(t-butylperoxy)-2
, 5-dimethyl Δ, xane and digmyl peroxide have been found to be particularly effective. If desired, a high energy radiation source such as cobalt-60 can be used in place of a peroxide catalyst to effect curing of the silicone composition.

Other types of thermosetting silicone compositions that can be used in the practice of this invention include (a) about 1,000 at 25°C;
(b) an organohydrodiene polysiloxane crosslinker; (c) optionally a-mobility reinforcement; a filler and (d) a noble metal or noble metal-containing hydrolylation catalyst.

If a solvent resistant thermosetting silicone rubber composition is desired, it is preferred to include at least 5 mole percent perfluoroalkylsiloxane at position 44 in the base polymer. When the latter addition-curable silicone compositions are used, it is preferred that the crosslinker also contain two available perfluoroalkylsiloxy units.

The addition-curable silicone rubber composition may also contain extender fillers, heat stabilizers, reinforcing resins, and the like.

Although the thermosetting compositions described above are preferred for practicing the invention, condensation curable compositions can also be used.

It is only necessary that the silicone composition be present in an amount effective to bind the cork particles, so the ratio of cork to curable silicone composition will vary over a wide range. Although the amount of silicone composition required depends mostly on the particle size of the cork, it has been found that a suitable gasket material can be made from 100 parts of cork and 500 parts of silicone composition. Preferably from about 250 to about 450 parts by weight of silicone composition per 100 parts by weight of cork are used.

Although the cork and silicone compositions can be mixed by any conventional rubber compounding equipment, such as a dough mixer or a Banbury mixer, a 20-mill mixing mill is particularly effective for mixing the cork and thermoset silicone compositions. It was found that The use of this 20-liter mixing mill also
A hardened, strong and elastic gasket that can be compressed to a large extent!・Provides a continuous hardened sheet that is easy to handle and serves as a material. The gasket material is preferably cut to size before curing, so that excess material can be returned to the mixing device.

It will be appreciated by those skilled in the art that in addition to use in automotive and appliance gas traps, the compositions of the present invention may also be used as high temperature surface abrasions, kungjon materials, vibration damping materials, and insulation materials.

To enable those skilled in the art to more easily carry out the invention, the following examples are given by way of illustration and not as a limitation. Figures are based on vehicle volume unless otherwise specified.

EXAMPLES Example 1 100 parts by weight of vinyl-terminated polydimethylsiloxane having a viscosity of 80,000 centipoise at 25°C are mixed with 50 parts by weight of octamethylcyclotetrasiloxane-treated fumed silica in a laboratory dough mixer. 5 parts by weight of the compounding yeast thus obtained was added to 20 parts by weight.
/40 mesh cork particles 15, 20, 25 and 3
0 parts by weight and 2.5-bis(t-butylperoxy)-
Blend at 20-lumyl with 0.6711a percent 2,5-dimethylhexane. A sheet of this material is press cured at 350'l'' for 15 minutes. The physical properties of the cured sheet are shown in Table 1.

Table 1 Part by weight of cork relative to 75 parts of silicone base Hardness 56 5G 53 45 Tensile strength psi 416 398 339 27
5 Elongation % 150 130 90 90 Tear B
ppi 106 9B 7 [f 5
g specific gravity 1.0370.9440.8100.745
The appearance of the cured sheet is good, with a uniform distribution of cork in the silicone elastomer binder.

Additionally, uncured materials exhibit good physical integrity which facilitates the sheeting and preforming operations required for many gasketing operations.

Example 2 In a laboratory dough mixer, 50o, oo at 25°C
99 parts by weight of a vinyl-terminated polydimethylsiloxane having a viscosity of 0 centipoise to a methyl-terminated polydimethylsiloxane lrf having 13.5 mole % vinyl groups on the chain and having a viscosity of go, ooo centipoise at 25°C. ! , 'Blend with W part. The resulting polymer blend is mixed with 42 parts of octamethylcyclotetrasiloxane treated fumed silica. 75 parts by weight of the obtained blending base was mixed with 25 parts by weight of 20/40 mesh cork fine particles and 2,5-bis(t-butylperoxy).
Blend with 2,5-dimethylhexane at 0.67 deuterium and 20 lumyl. 15 sheets made of silicone rubber/cork laminated material under 350
Press harden for minutes.

The physical properties of the cured sheets are shown in Table H.

Table ■ Shore A Hardness 47 Tensile Strength psi 320 Elongation % 100 Specific Gravity 0.77 In addition to having all the desirable properties illustrated in Example 1, this material has improved kneadability and reduced kneadability in the uncured state. It exhibits tackiness.

Claims (1)

Claims: 1. A curable composition comprising (a) cork particles and (b) an effective amount of a curable silicone composition to bond the cork particles. 2. The composition according to claim 1, wherein the curable silicone composition is a thermosetting silicone composition. 3. The particle size of the cork particles is about 0.005 inches in diameter to about 0.000 inches in diameter.
．． The composition according to claim 1 or 2, which is 5 inches. 4. The particle size of the cork particles is about 0.02 inch to about 0.02 inch in diameter.
2. The composition of claim 1 or 2, which is 2 inches. 5. The thermosetting silicone composition comprises: (a) a polydiorganosiloxane-based polymer having a viscosity at 25°C of less than about 1,000,000 centipoise; (b) optionally, as a component, an effective amount of a reinforcing filler; A composition according to claim 2 comprising c) an effective amount of catalyst. 6. The composition of claim 5, wherein the polydiorganosiloxane-based polymer contains at least about 5 mole percent perfluoroalkylsiloxane units. 7. The composition according to claim 5, wherein the catalyst is an organic peroxide. 8. The catalyst is 2,5-bis(t-butylperoxy)-2
, 5-dimethylhexane, digmyl peroxide or a mixture thereof. 9. The thermosetting composition comprises: (a) a polydiorganosiloxane-based polymer having a viscosity at 25° C. of less than about 1,000,000 centipoise and having at least two olefinic groups per molecule; 3. The composition of claim 2, comprising a hydrogen polysiloxane crosslinker; (c) optionally an effective amount of reinforcing filler; and (d) a noble metal or noble metal-containing hydrosilylation catalyst. 10. The composition of claim 9, wherein the polydiorganosiloxane-based polymer contains at least about 5 mole percent perfluoroalkylsiloxane units. 11. The composition of claim 10, wherein the organohydrogenpolysiloxane crosslinking agent contains an effective amount of perfluoroalkylsiloxane units. 12. The composition of any of claims 1, 2, 3, 5, or 9, wherein up to about 500 parts by weight of the curable silicone rubber composition is present per 100 parts by weight of cork. 13. A method for making a curable composition comprising mixing (a) cork particles and (b) an effective amount of a curable silicone composition to bond the cork particles. 14. The method of claim 13, wherein up to about 500 parts by weight of the curable silicone composition are used per 100 parts by weight of cork. 15. About 250 to about 450 per 100 parts by weight of cork
14. The method of claim 13, wherein parts by weight of the curable silicone composition are used. 16. The method according to claim 13 or 14, wherein the curable silicone composition is a thermosetting silicone composition. 17. The method according to claim 16, wherein the mixing is carried out in a two-roll mill mixer, a dough mixer or a Banbury mixer. 18. An article comprising (a) cork particles and (b) an amount of cured silicone elastomer effective to bond the cork particles. 19. The article of claim 18, wherein the cured silicone elastomer is a reaction product of a thermosetting silicone composition. 20. The article of claim 18 or 19, wherein the cork particle size ranges from about 0.005 inches to about 0.5 inches in diameter. 21. The cork particle size ranges from about 0.02 inches in diameter to about 0.02 inches in diameter.
．． The product according to claim 18 or 19, which is 2 inches. 22. The article of claim 20, wherein up to about 500 parts by weight of silicone elastomer are present per 100 parts by weight of cork particles. 23, about 250 to about 4 per 100 parts by weight of cork particles
21. The article of claim 20, wherein 50 parts by weight of silicone elastomer are present. 24. The silicone elastomer comprises: (a) a polydiorganosiloxane-based polymer having a viscosity at 25°C of less than 1,000,000 centipoise; (b) an optionally effective amount of a reinforcing filler; and (c) an effective amount of a catalyst. 20. The article of claim 19 made from a thermosetting silicone composition. 25. The silicone elastomer comprises: (a) a polydiorganosiloxane having a viscosity at 25° C. of less than 1,000,000 centipoise and having at least two olefin groups per molecule; (b) an organohydrogenpolysiloxane crosslinking agent (c) 20. The article of claim 19 made from a thermosetting silicone rubber composition comprising:) optionally an effective amount of a reinforcing filler; and (d) a noble metal or noble metal-containing hydrosilylation catalyst. 26. (1) mixing (a) cork particles and (b) an amount of a curable silicone composition effective to bond the cork particles; (2) curing the composition of step (1); The manufacturing method of the product. 27. The method according to claim 26, wherein the curable silicone composition is a thermosetting silicone composition. 28. The method of claim 27, wherein curing is effected by exposing the composition of step (1) to an elevated temperature for a period sufficient to effect curing. 29. The method of claim 28, including the step of forming the product into the desired shape before curing. 30. The method of claim 29, wherein the cork particle size ranges from about 0.005 inches to about 0.5 inches in diameter and includes up to about 500 parts by weight silicone elastomer per 100 parts by weight of cork particles.