JPH0482024B2 - - Google Patents

Description

[Detailed description of the invention]

BACKGROUND OF THE INVENTION The present invention relates to thermosetting silicone rubber compositions. More particularly, the present invention relates to thermosetting silicone rubber compositions having improved tear strength, moderate durometer and low compressive set, while containing an effective amount of curing coagent to reduce the use of reinforcing fillers. . (a) polydiorganosiloxane-based polymer, (b)
Thermosetting silicone rubber compositions comprising an effective amount of reinforcing filler and (c) an effective amount of free radical generating catalyst are well known in the art. It is well known to those skilled in the art that the amount of reinforcing filler used is directly related to many of the physical properties of the resulting silicone rubber. For example, as the amount of reinforcing filler in a silicone rubber composition increases, the durometer, tear strength, and compressive set generally increase slightly.
It is also known to those skilled in the art that if the amount of filler is too high, the processing of the rubber becomes very difficult. For most applications, one skilled in the art can simply adjust the amount of filler to obtain suitable properties. However, in some applications, for example when calendering solvent resistant silicone rubber into fabrics, the desired tight, void-free compound/fabric can be achieved if a sufficient amount of filler is added to obtain the required durometer. Since rubber does not form an interface, its raw strength or bulk modulus is disadvantageous for calendering to fabric. Additionally, the amount of filler required to obtain a suitable durometer increases the compressive strain beyond acceptable limits. Here, the addition of certain curing aids to thermosetting silicone rubber compositions improves tear strength and allows the use of reinforcing fillers while not substantially altering the durometer and lowering the compressive strain. It was discovered that it could be reduced. Konkle, U.S. Pat. No. 2,684,957 discloses a low compressive strain thermosetting silicone rubber composition containing (a) an organopolysiloxane, (b) a vulcanizing agent, and (c) a vulcanizing agent.
For 100 parts by weight of organopolysiloxane,
It is disclosed that it is made from 0.75 to 8 parts by weight of a cadmium compound selected from cadmium oxide, cadmium peroxide and cadmium carbonate. US Pat. No. 2,927,908 to Konkle and Talcott is directed to the use of polytetrafluoroethylene to improve the tensile strength and tear resistance of fluorinated organopolysiloxane rubbers. U.S. Pat. No. 2,979,479 to Modic discloses that a thermosetting silicone rubber composition with improved tear strength comprises (a) an organopolysiloxane, (b) a finely divided silica filler, (c) a curing agent and (d) It is disclosed that it is made from a copolymer of trimethylsiloxy groups and _SiO2 groups, with about 1.0 to 1.5 methyl groups present per silicon atom. U.S. Patent No. Grabicki et al.
No. 3027344 contains (a) an organopolysiloxane, (b) a silica filler, (c) 1 to 20 parts of an organic amine, and (d) 1 to 20 parts of an organic amine.
A thermosetting composition comprising 20 parts of a hydroxyorganosilane selected from diphenylsilanediol and triphenylsilanol is provided, characterized by improved tensile and tear strength. No. 3,652,475 to Wada et al.
(a) a polydiorganosiloxane having a degree of polymerization of at least 3000 and containing up to 0.3 mol% vinyl groups;
100 parts by weight, (b) having a degree of polymerization of at least 3000, 5
1 to 10 parts by weight of a polydiorganosiloxane containing ~20 mol% vinyl groups; (c) 0.5 to 5 parts by weight a polydiorganosiloxane having a degree of polymerization of 10 to 1000 and having 5 to 90 mol% vinyl units; , (d) 20 to 200 parts by weight of a silica filler, and (e) a catalytic amount of an organic peroxide, a thermosetting silicone rubber composition having improved tear strength and excellent compressive set is shown. There is. The above documents use less reinforcing filler,
There is no indication that improved tear strength, satisfactory durometer, or lower compressive set can be obtained by including curing aids such as trimethylolpropane trimethacrylate or triallyl trimellitate. SUMMARY OF THE INVENTION It is an object of the present invention to provide a thermosetting silicone rubber composition capable of reducing the use of reinforcing fillers while obtaining improved tear strength, substantially unchanged durometer and lower compressive strain. It is to provide. Another object of the present invention is to provide a thermosetting silicone rubber composition suitable for calendering into fabrics. Another object of the invention is to provide a method of manufacturing the composition of the invention. According to a first invention, there is provided a thermosetting silicone rubber composition comprising (a) a polydiorganosiloxane-based polymer, (b) an effective amount of a catalyst, and (c) an effective amount of a curing aid. DESCRIPTION OF THE INVENTION The present invention comprises: (a) a polydiorganosiloxane-based polymer; (b) an effective amount of a catalyst; (c) an effective amount of a curing aid; and (d) an optional (but preferred) component. A thermosetting silicone rubber composition is provided comprising: a reinforcing filler; Polydiorganosiloxane (a) is any polymer or mixture thereof known to those skilled in the art to be suitable for use in thermosetting silicone rubber compositions. Generally, such polydiorganosiloxanes have the general formula wherein R is selected from monovalent substituted and unsubstituted organic groups, and a is from about 1.95 to about 2.02, and has a viscosity of at least about 100,000 centipoise at 25°C. Examples of suitable R groups include phenyl, chlorophenyl, aryl and halogenated aryl groups such as xylyl and tolyl, aralkyl groups such as benzyl and phenylethyl, aliphatic groups such as alkyl, alkenyl, cycloalkyl and haloalkyl. , halogenated aliphatic and cycloaliphatic groups such as ethyl, propyl, vinyl, allyl, cyclohexyl, chloromethyl, chloroethyl and 3,
3,3-trifluoropropyl), cyanoalkyl groups such as cyanoethyl. Preferably R is selected from methyl, vinyl, phenyl and 3,3,3-trifluoropropyl groups. Also, the viscosity of polydiorganosiloxane (a) is
From about 1,000,000 centipoise at 25°C
Preferably it is 200000000 centipoise. In addition, within the scope of polydiorganosiloxane (a), for example, copolymers of dimethylsiloxane units and methylphenylsiloxane units, copolymers of dimethylsiloxane units, diphenylsiloxane units, and methylphenylsiloxane units, and dimethyl Also included are copolymers containing two or more different diorganosiloxane units, such as copolymers of siloxane units, methylvinylsiloxane units, and diphenylsiloxane units. Also,
Polydiorganosiloxane (a) also includes mixtures or blends of polymers and/or copolymers. When trying to produce solvent-resistant thermosetting silicone rubber, polydiorganosiloxane (a) is
For example, Evans U.S. Patent No. 4355121
No. 4,492,786 to Evans or US Pat. No. 4,529,774 to Evans.
Other suitable fluorosilicone polymers are also well known in the art. Such fluorosilicone compositions have been found to be particularly suitable for carrying out the present invention. Catalyst (b) may be any of those commonly used to accelerate the curing of silicone rubber;
It includes both chemical vulcanizing agents and high energy radiation sources such as gamma rays from cobalt-60 radiation sources.
Preferably catalyst (b) is 2,4-dichlorobenzoyl peroxide, benzoyl peroxide, di-
One of the organic peroxides commonly used in the silicone field, such as t-butyl peroxide, 2,5-bis(t-butylperoxy)2,5-dimethylhexane or dicumyl peroxide It is. Organic peroxides used as catalysts for thermosetting silicone rubbers are commercially available and are usually mixed with an inert carrier to form a powder or paste. The amount of peroxide used in the thermosetting silicone rubber composition is not limited, but is generally about 0.1 to 100 parts by weight of silicone polymer without added catalyst.
It is 5 parts by weight. Peroxide catalysis is initiated by heating the composition to a temperature sufficient to activate (eg, decompose) the organic peroxide used. Curing aid (c) is any silicone soluble (ie, slightly polar) monomer having at least three olefinic functional groups. These monomers do not initiate cure, but quickly form free radicals once cure begins, thereby increasing the efficiency of the catalyst, and because they are polyfunctional, they form a tight cure matrix. To be involved in establishing
It is called a curing aid. In the practice of this invention, it is preferred to contain from about 0.1 to about 3 parts by weight of curing aid per 100 parts of polydiorganosiloxane (a). More preferably, the curing aid (c) is used in an amount of about 0.2 to about 0.8 parts by weight per 100 parts by weight of the catalyst-powdered silicone polymer;
More preferably, about 0.2 to about 0.4 parts by weight are used. Generally, the curing aid used in the present invention has the general formula or (In the formula, R is hydrogen or a lower alkyl group having 1 to 5 carbon atoms, R ¹ is a lower alkylene group having 1 to 5 carbon atoms, each R ² is independently selected from hydrogen and a methyl group, and R ³ is hydrogen or a methyl group, n is 0 or 1, and m is an integer of 3 to 6). Preferably R is ethyl, R ¹ is methylene,
R ² is hydrogen, R ³ is methyl, n is 1, and m is 3.
Thus, the preferred curing aid of the present invention is trimethylolpropane trimethacrylate. and triallyl trimellitate It is. The olefinic functional groups of the curing coagents do not have to be the same, and furthermore, it is not important to which carbon of the benzene ring the olefinic functional group is attached in the formula. It will also be appreciated that the foregoing formulas are merely illustrative of suitable curing aids, and other variations will be apparent to those skilled in the art within the scope of the invention as well as the claims. The use of the above curing coagents in thermosetting silicone rubber compositions requires the use of less reinforcing filler than heretofore required, yet provides improved tear properties, virtually unchanged durometer and low Apply compressive strain. Additionally, the use of the curing aids listed above can completely eliminate the need for reinforcing fillers in some applications. Most preferably, however, the reinforcing filler is included in the thermosetting silicone rubber composition in small amounts. Examples of suitable reinforcing fillers (d) include, for example, fumed silica, treated fumed silica, precipitated silica and treated precipitated silica. Of course, mixtures of these fillers are also within the scope of the invention. Preferably, the reinforcing filler is a treated silica filler, most preferably treated fumed silica. Filler treatments are described, for example, in Lucas US Pat. No. 2938009, Smith US Pat. No. 3635743, Beers US Pat. No. 3837878, Evans US Pat. This can be done by any method known in the art, such as those shown in . For fluorosilicone rubber thermoset silicone rubbers suitable for calendering into fabrics,
It is particularly preferred to use fluorosilicone treated fillers as shown in Evans US Pat. No. 4,529,774. Generally, the amount of reinforcing filler included in the thermosetting silicone rubber composition is from about 5 to about
100 parts by weight, preferably about 30-50 parts by weight. In addition to the components listed above, the thermosetting silicone compositions of the present invention may contain additives known in the art such as antioxidants, pigments, heat stabilizers, and the like. The compositions of the present invention are made by mixing the various ingredients in any manner known in the art, such as, for example, by a dough mixer. To enable those skilled in the art to more easily carry out the invention, the following illustrative but non-limiting examples are presented. Unless otherwise stated,
All parts are by weight. [Example 1] Methylvinyl-terminated polydiorganosiloxane having a viscosity of 100000000 centipoise at 25°C
100 parts by weight, 3 parts by weight of polydimethylsiloxane diol processing aid of the formula HO-(Si(Me) _2O ) ₅ --H, 1 part by weight of methylvinyl-terminated polydimethylsiloxane processing aid, bis-dimethylvinylsilazane 0.25 parts by weight, cerium hydroxide 0.65 parts by weight,
2,5-bis(t-butylperoxy)-2,5
- Prepare the base fluorosilicone composition by mixing 0.8 parts by weight of dimethylhexane. with 429 g of fumed silica treated with fluorosilicone according to U.S. Pat. No. 4,529,774;
Place 4764 grams of this base composition into a 3 1/2 quart dough mixer. The amount of filler is sufficient to provide a loading of 40 parts by weight. After uniform dispersion of filler, red colorant 47.7
0.25 to 2.0 parts by weight of trimethylolpropane trimethacrylate (Sartomer 350 from Sartomer, Pencilbair, West Thiester)
(commercially available as) (see table). Mix the ingredients thoroughly for 30 minutes and then pass through a 100 mesh 316 standard size screen. The passed compound was then milled on a mill with 1.6 parts by weight of 2,4-dichlorobenzoyl peroxide per 100 parts by weight of the compound [SF-96® containing 12.5% by weight dibutyl phthalate] in a 1000 centistoke liquid. % by weight]. See Table, Compositions B, C, E, F and G. [Example 2] The same procedure as in Example 1 is carried out, except that trimethylolpropane trimethacrylate is replaced with 0.25 parts of triallyl trimellitate per 100 parts by weight of the polymer. Comparative Example For comparison, FSE-7140, commercially available from General Electric Company, is tested, which is an example of a composition that is not effective in calendering fabrics. Also for comparison purposes, the same composition as Example 1 is prepared, except that no curing aid is included. See Table, Composition A. Finally, a composition manufactured by Dow Corning Corporation (LS-63) considered for use in calendering fabrics is also tested.

[Table] The data in the table shows that compared to composition A and LS-63,
The superior performance of compositions C to G made with less filler and curing aid of the present invention is clearly demonstrated. In addition, the silicone elastomer produced therefrom maintains good processability, with virtually no change in durometer (compared to A), tear resistance, compressive strain, and fuel B.
Excellent in terms of solvent swelling.

Claims (1)

[Claims] 1(a) General formula (wherein R is selected from monovalent substituted or unsubstituted organic groups and a varies from 1.95 to 2.02) and has a viscosity of at least 100,000 centipoise at 25° C. 100
parts by weight; (b) 0.1 to 5 parts by weight of a catalyst for accelerating curing; (c) 0.2 to 0.4 parts by weight of a curing aid; and (d) 5 to 40 parts by weight of a reinforcing filler. A thermosetting silicone rubber composition characterized in that the agent consists of a silicone soluble monomer having at least three olefinic functional groups to improve tear strength and low compressive strain. 2 The curing aid has the general formula (In the formula, R is hydrogen or a lower alkyl group having 1 to 5 carbon atoms, R ¹ is a lower alkylene group having 1 to 5 carbon atoms, R ² is hydrogen or a methyl group, and R ³ is hydrogen or a methyl group. and n is 0 or 1). 3. The composition according to claim 2, wherein the curing aid is trimethylolpropane trimethacrylate. 4 General formula for curing aid Claim ¹ having ^: Compositions as described in Section. 5. The composition according to claim 4, wherein the curing aid is triallyl trimellitate. 6(a) General formula (wherein R is selected from monovalent substituted or unsubstituted organic groups and a varies from 1.95 to 2.02) and has a viscosity of at least 100,000 centipoise at 25° C. 100
parts by weight; (b) 0.1 to 5 parts by weight of an organic peroxide catalyst; (c) 5 to 40 parts by weight of a reinforcing filler; and (d) 100 parts by weight of a polydiorganosiloxane to improve tear strength and low compressive strain. Contains 0.2 to 0.4 parts by weight of a curing auxiliary, and the curing auxiliary is expressed by the general formula or (In the formula, R is hydrogen or a lower alkyl group having 1 to 5 carbon atoms, R ¹ is a lower alkylene group having 1 to 5 carbon atoms, each R ² is independently selected from hydrogen and a methyl group, and R ³ is hydrogen or a methyl group, n is 0 or 1, and m is an integer from 3 to 6.
Compositions as described in Section. 7 A fluorosilicone-treated fumed silica in which the polydiorganosiloxane (a) is a fluorosilicone polymer and the reinforcing filler (d) is present in an amount ranging from 30 to 50 parts by weight per 100 parts by weight of the polydiorganosiloxane (a). A composition according to certain claim 6.