GB2060667A

GB2060667A - A Silicone Rubber Composition for Drive Shaft Seals

Info

Publication number: GB2060667A
Application number: GB8029205A
Authority: GB
Original assignee: Toray Silicone Co Ltd
Current assignee: DuPont Toray Specialty Materials KK
Priority date: 1979-09-14
Filing date: 1980-09-10
Publication date: 1981-05-07
Also published as: FR2464976B1; GB2060667B; DE3034232A1; SE8006416L; BR8005897A; JPS5643351A; IT1141044B; AU535241B2; FR2464976A1; BE885210A; CA1162687A; AU6237080A; IT8024633A0; SU978734A3; DE3034232C2; JPS623182B2

Abstract

A drive shaft seal prepared from organopolysiloxane gum, a reinforcing silica filler, diatomaceous earth, organohydrogenpolysiloxane, and organic peroxide has improved oil leakage and noise reduction properties.

Description

SPECIFICATION A Silicone Rubber Composition for Drive Shaft Seals This invention describes a silicon rubber composition to be used for drive shaft seals. More specifically, this invention describes a heat-vulcanizable silicone rubber composition which is optimal for use in the manufacture of drive shaft seals. Further, this invention relates to an improved drive shaft seal.

It is known that silicone rubber can be used for drive shaft seals in cars because it has excellent physical properties, such as oil resistance and durability. However, when the above-mentioned drive shaft seal is repeatedly subjected to friction when it rubs on the surface of the drive shaft, the noise generated by the friction is unpleasant and is a source of anxiety for the driver of the car. The abrasion due to the friction widens the space between the rubbing surface and the sealing material resulting in oil leakage. The traditional silicone rubber compositions cannot eliminate the above-mentioned factors of anxiety.

The use of diatomaceous earth in silicone rubber is known. It is also known to use diatomaceous earth iri silicone rubber compositions which are to be used for oil resistance in manufacturing oil seals, as shown by Loraine et al. In U.S. Patent No. 3,468,838 issued September 1969. Loraine et al.

show that magnesium oxide is required to provide silicone rubber rubber with sufficient oil resistance to be used as oil seals. Christe in U.S. Patent No. 3,865,778 issued February 11, 1975, also shows that magnesium oxide is required to provide sufficient oil resistance to silicone rubber which contains diatomaceous earth.

Silicone rubber compositions for use as shaft seals and shaft seals made from such compositions are described by Honma et al. in U.S. Patent No. 4,116,920 issued September 26, 1 978. Honma et al.

describe these shaft seal compositions as being 100 parts by weight of a heat curable organopolysiloxane rubber, 5 to 100 parts by weight of a reinforcing silica filler, 5 to 100 parts by weight of diatomaceous earth, 2 to 100 parts by weight of an acicular platy mineral powder and 0.1 to 10 parts by weight of an organic peroxide. The drive shaft seals made from the compositions of this invention are an improvement over the shaft seals of Honma et al., especially in noise reduction and oil leakage properties.

Hatanaka et al. in Japanese Kokai Patent No. Sho 53(1978)-141362, published December 9, 1978, describe heat vulcanizable silicone rubber comprising 100 parts by weight of an organopolysiloxane, 10 to 300 parts by weight of an organosilazane treated fine silica powder, 0.01 to 10 parts by weight of an organohydrogenpolysiloxane, and a catalytic amount of an organic peroxide.

In Example 2, Hatanaka et al. describe precipitated silica and diatomaceous earth Hanaka et al. do not describe their materials as having oil resistance or usefulness in the manufacture of drive shaft seals.

The purpose of this invention is to eliminate the above-mentioned drawbacks and to provide an abrasion-resistant, oil-resistant, durable silicone rubber composition to be used for drive shaft seals which constitutes a motor oil seal and does not generate noise by friction with the rubbing surface of the drive shaft. Drive shaft seals manufactured from organopolysiloxane gum, reinforcing silica filler, diatomaceous earth, organohydrogenpolysiloxane, and organic peroxide provide the desired properties.

This invention relates to a silicone rubber composition to be used for drive shaft seals consisting essentially of (i) 100 parts by weight of an organopolysiloxane gum having the average unit formula RaSiO4~a 2 where each R represents a substituted or unsubstituted monovalent hydrocarbon radical and a has a value of 1.98 to 2.02, (ii) 5 to 100 parts by weight of a reinforcing silica filler, (iii) 5 to 100 parts by weight of diatomaceous earth, (iv) 0.1 to 10 parts by weight of an organohydrogenpolysiloxane having the average unit formula RbHcSO4bc 2 where R is defined above, b has a value of 1 to 2, c has a value of 0.1 to 1.2, and the sum of b+c has a value of 1.8 to 2.2, said organohydrogenpolysiloxane having at least three silicon-bonded hydrogen atoms per molecule, and (v) 0.1 to 10 parts by weight of an organic peroxide.

Component (i) is a principal component of the usual silicone rubber and is a high molecular weight straight or slightly branched-chain organopolysiloxane which is gummy at room temperature.

The organic radicals can be methyl, ethyl, vinyl, phenyl or trifluoropropyl radicals, and at least 50% of all the organic radicals in component (i) are preferably methyl. The endblocking groups can be organosiloxy groups having attached radicals selected from hydroxyl, alkoxy, methyl, vinyl and phenyl radicals. However, the organopolysiloxane is not limited to these examples.

A reinforcing silica filler, component (ii), can be fumed silica, precipitated silica, or a dehydrated form of this silica. Component (ii) is indispensable for the mechanical strength of the silicone rubber and the quantity of this component to be added is 5 to 100 parts by weight, preferably 20 to 70 parts by weight relative to 100 parts by weight of component (i).

Diatomaceous earth as component (iii) is indispensable to the hardness and oil resistance of the silicone rubber. When a silica bulking agent other than the above is used, the drive shaft seal undergoes violent friction resulting in the generation of loud noise. The use of diatomaceous earth does not cause such noise. The quantity of component (iii) to be added is 5 to 100 parts by weight, preferably 20 to 90 parts by weight relative to 100 parts by weight of component (i).

Organohydrogenpolysiloxane, component (iv), is an important component which displays the characteristic of this invention. It imparts the property of slipperiness, the property of reducing noise and the abrasion resistance to the silicone rubber and provides sea lability with respect to motor oil.

Component (iv) is an organohydrogenpolysiloxane having at least three silicon-bonded hydrogen atoms per molecule. The organohydrogenpolysiloxanes have an average unit formula RbHC 4 b, 2 where R is the same as defined above, preferably methyl, b has a value of 1 to 2, c has a value of 0.1 to 1.2, preferably 0.1 to 1 and the sum of h+c has a value of 1.8 to 2.2. The quantity of this component to be added for optimum properties depends on the number of silicon-atom-bonded hydrogen atoms, but is in the range of 0.1 to 10 parts by weight relative to 100 parts by weight of component (i). When this quantity is less than 0.1 part by weight, the purpose of this invention cannot be accomplished.On the other hand, when this quantity exceeds 10 parts by weight, the resulting composition exhibits foaming and stickiness at the time of vulcanization molding processes. The R oi the average unit formula of this component is selected from the same organic radicals defined for component (i) and is preferably methyl.

An organic peroxide, component (v), is a traditional catalyst used for heat-setting silicone rubber compositions. Examples of organic peroxide are benzoyl peroxide, t-butyl perbenzoate, 2,4- dichlorobenzoyl peroxide, monochlorobenzoyl peroxide, dicumyl peroxide, 2,5-bis-(t-butylperoxy)-2,5- dimethylhexane. The amount of organic peroxide can be from 0.1 to 10 parts by weight relative to 1 00 parts by weight of component (i), preferably from 0.1 to 2 parts by weight.

Components (i)-(v) can each be a single compound or they can be mixtures of two or more compounds. The silicone rubber composition produced by the method of this invention can be produced by simply blending the components (i)-(v) mentioned above. However, if necessary, additives such as diphenylsilanediole, diphenylmethylsilanol and low molecular weight organosilicon compounds such as hydroxyl endblocked polydimethylsiloxane which have low degrees of polymerization can be used. Other additives which can be used are mica powder, graphite, polytetrafluoroethylene (Teflon T.M.) powder, magnesium oxide, zinc oxide, pigments, heat-stability agents and oil-resistant agents.The order of blending the components (i)-(v) is arbitrary; however, the best procedure is to first blend component (i) with component (ii) using a kneader mixer. The resulting mixture is then mixed with components (iii) and (iv) using a Banbury mixer or a two-roll mixer, and then mixed with component (v) using a two-roll mixer.

Components (i)-(iii), make up a silicone rubber composition prepared by the method mentioned above. This composition is heat-treated at 100--2000C for several minutes to several hours under elevated or ambient pressure, components (iv) and (v) are added, and then it can be vulcanized. The cured silicone rubber product exhibits excellent mechanical properties, oil resistance, abrasion resistance and tight sealability and does not generate noise so that it is advantageously used for the manufacture of drive shaft seals.

This invention will be further explained by using demonstrative examples. "Part" in the examples means "part by weight".

Example 1 A composition was prepared by placing in a Banbury mixer, 100 parts of a dimethylvinylsiloxy endblocked polydiorganosiloxane gum having 99,84 mol % dimethylsiloxane units and 0.16 mol % methylvinylsiloxane units, and having a plasticity at 250C of 160; 35 parts of precipitated silica having a specific surface area of 240 m2/g; 60 parts of diatomaceous earth and 3 parts of diphenylsilanediol.

The resulting mixture was kneaded well at room temperature and then at 1 700C for 2 hours. The mixture was cooled to a temperature of < 600C and then combined with 10 parts of fine mica powder, trimethylsiloxy endblocked methylhydrogenpolysiloxane (in the quantity given in Table I); having dimethylsiloxane units and methylhydrogensiloxane units in a 1:1 molar ratio and a viscosity of 0.00005 m2/g, and 0.5 part of a paste of 50 weight percent silicone oil and 50 weight percent 2,5dimethyl-2,5-bis(t-butylperoxy)hexane. The resulting silicone rubber mixture was homogeneously kneaded using a two-roll mixer. This silicone rubber composition was cured using a hot press at 170do for 10 minutes and then vulcanized in an oven at 2000C for 4 hours. The hardness and tensile elongation at break (No. 3 dumbell was used) of a 2 mm-thick sheet were measured by the methods of JIS K6301 (equivalent to ASTM D 412 for tensile and elongation and equivalent to ASTM 2240 for hardness). A silicone rubber composition identical to that mentioned above was cured in a metal mold for an oil seal at an elevated temperature under the same conditions as given above. The molded product was placed in a rotary tester for oil seal testing. The drive shaft of the tester was rotated at the rate of 3,000 rpm, and 5 observers slowly walked away from the tester in order to determine the distance at which the friction noise was no longer heard.Under the same conditions, the shaft was continuously rotated for 24 hours in order to measure the volume of test lubricant leakage which was used as a measure of the sea lability of the drive shaft seal. The oil resistance was measured by the following method. Motor oil 1 OW-30 and JIS swelling oil No. 3 were each placed separately in reflux tubes. A test specimen which had been vulcanized by the method mentioned above was immersed in the above-mentioned lubricant. The tube was then allowed to stand in a thermostat at 1 500C for about 70 hours. The change in volume of the test specimen was measured. The JIS swelling oil No. 3 had a kinetic viscosity in the range of 31 .96x 10-6 to 34.18x10-6 m2/g, an aniline point of 69.5+1, and a flash point of 1 62.70C.

For comparison, the composition was prepared by the method of Example 1 with the exception that methylhydrogenpolysiloxane was not used. The test piece was prepared and tested by the methods mentioned above. The results are given in Table 1 (below).

Table 1 Comparative This invention Example Sample No. 1 2 3 4 Polydiorganosiloxane gum (parts) 100 100 100 100 Precipitated silica (parts) 35 35 35 35 Diatomaceous earth (parts) 60 60 60 60 Diphenylsilanediol (parts) 3 3 3 3 Fine mica powder (parts) 10 10 10 10 Methylhydrogenpolysiloxane (parts) 0.5 1.0 2.0 0 50% paste of 2,5-dimethyl-2,5-bis- 0.5 0.5 0.5 0.5 (t-butylperoxy)hexane (parts) Hardness (JIS) 75 74 73 76 Tensile strength (MPa) 5.10 4.81 4.61 4.71 Elongation at break (%) 335 340 360 330 Distance at which the frictional noise 3 3 2 7 is no longer heard (m) Oil leakage in 24 hours (cc) 0 0 0 0.5 Change in Motor oil (10W-30) 16.8 16.5 16.0 17.2 volume (%) JIS Swelling Oil &num;;3 29.5 29.2 29.0 30.5 Example 2 A composition was prepared by placing in a kneader and then homogeneously kneading 100 parts of a dimethylvinylsiloxy endblocked polydiorganosiloxane gum having 95 mol % dimethylsiloxane units, 0.2 mol % methylvinylsiloxane units, and 4.8 mol % methylphenylsiloxane units, and having a plasticity at 250C of 130, 50 parts of fumed silica having a specific surface area of 200 m2/g, 10 parts of a hydroxyl endblocked polydimethylsiloxane with a low degree of polymerization, 0.5 part of vinyltriethoxysilane and 0.5 part of polytetrafluoroethylene powder (Teflon T. M.) 6CJ powder from Mitsui Fluorochemical Co., Tokyo, Japan). The resulting mixture was further kneaded at 1 500C for 2 hours.The mixture was cooled to a temperature of < 600C and then combined with 20 parts of diatomaceous earth, 0.5 part red iron oxide, methylhydrogencyclotetrasiloxane (in the quantity given in Table 2) and 0.6 part of 2,4-dichlorobenzoyl peroxide. The resulting mixture was homogeneously kneaded using a two-roll mixer. This composition was cured using a hot press at 1 200C for 10 minutes and then vulcanized in an oven at 2500C for 4 hours. The properties of the vulcanized silicone rubber composition were measured by methods described in Example 1. For a comparative example, the composition was prepared by the same method as mentioned above with the exception that methylhydrogencyclotetrasiloxane was not added. A test specimen was prepared and measured by the same methods as described above. The results are given in Table 2 (below).

Table 2 Comparative This invention Example Sample No. 5 6 7 8 Polydiorganosiloxane gum (parts) 100 100 100 100 Fumed silica (parts) 50 50 50 50 Hydroxyl endblocked Polydimethyl- 10 10 10 10 siloxane (parts) Vinyltriethoxysilane (parts) 0.5 0.5 0.5 0.5 Polytetrafluoroethylene (parts) 0.5 0.5 0.5 0.5 Diatomaceous earth (parts) 20 20 20 20 Red iron oxide (parts) 0.5 0.5 0.5 0.5 Methylhydrogencyclotetrasiloxane (parts) 0.5 1.0 2.0 0 2,4-Dichlorobenzoyl peroxide (parts) 0.6 0.6 0.6 0.6 Hardness (JIS) 73 72 70 73 Tensile strength (MPa) 7.06 6.28 6.37 6.67 Elongation at break (%) 215 230 210 220 Distance at which the friction noise 5 5 3 20 is no longer heard (m) Oil leakage in 24 hours (cc) 0 0 0 1.5 Change in Motor oil 1 OW-30 18.7 18.5 18.0 1 8.9 volume (%) JIS Swelling Oil &num;3 33.0 32.8 31.5 33.4

Claims

1. A silicone rubber composition to be used for drive shaft seals characterized by (i) 100 parts by weight of an organopolysiloxane gum having the average unit formula R SiO a 4-a 2 where each R represents a substituted or unsubstituted monovalent hydrocarbon radical and a has a value of 1.98 to 2.02, (ii) 5 to 100 parts by weight of a reinforcing silica filler, (iii) 5 to 100 parts by weight of diatomaceous earth, (iv) 0.1 to 10 parts by weight of an organohydrogenpolysiloxane having the average unit formula RbHCSiO4bc 2 where R is defined above, b has a value of 1 to 2, c has a value of 0.1 to 1.2, and the sum of b+c has a value of 1.8 to 2.2, said organohydrogenpolysiloxane having at least three silicon-bonded hydrogen atoms per molecule, and (v) 0.1 to 10 parts by weight of an organic peroxide.

2. The composition according to claim 1 in which c has a value of 0.1 to 1.

3. The composition according to claim 2 in which the reinforcing silica filler of (ii) is present in an amount of 20 to 70 parts by weight and the diatomaceous earth of (iii) is present in an amount of 20 to 90 parts by weight.

4. The composition according to claim 3 in which each R in (i) is selected from the methyl and vinyl groups and R in (iv) is methyl.

5. The composition according to claim 3 in which each R in (i) is selected from methyl, phenyl and vinyl and R in (iv) is methyl.

6. The composition according to claim 4 in which the organohydrogenpolysiloxane of (iv) is a polymer consisting of trimethylsiloxy endblocking units, dimethylsiloxane units and methylhydrogensiloxane units.

7. The composition according to claim 5 in which the organohydrogenpolysiloxane of (iv) is methylhydrogencyclotetrasiloxane.

8. The composition according to claim 1 substantially as herein described with reference to either of the specific examples.

9. A drive shaft seal manufactured from a heat vulcanized silicone rubber which had an unvulcanized composition characterized by (i) 100 parts by weight of an organopolysiloxane gum having the average unit formula R SiO 2 where each R represents a substituted or unsubstituted monovalent hydrocarbon radical and a has a value of 1.98 to 2.02, (ii) 5 to 100 parts by weight of a reinforcing silica filler, (iii) 5 to 100 parts by weight of diatomaceous earth, (iv) 0.1 to 10 parts by weight of an organohydrogenpolysiloxane having the average unit formula RbHc8iO4-b-c 2 where R is defined above, b has a value of 1 to 2, c has a value of 0.1 to 1.2, and the sum of b+e has a value of 1.8 to 2.2, said organohydrogenpolysiloxane having at least three silicon-bonded hydrogen atoms per molecule, and (v) 0.1 to 10 parts by weight of an organic peroxide.

1 0. The drive shaft according to claim 9 substantially as herein described with reference to either of the specific examples.