CA1040780A - Vulcanizable silicone rubber compositions having internal mold release properties - Google Patents
Vulcanizable silicone rubber compositions having internal mold release propertiesInfo
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- CA1040780A CA1040780A CA197,962A CA197962A CA1040780A CA 1040780 A CA1040780 A CA 1040780A CA 197962 A CA197962 A CA 197962A CA 1040780 A CA1040780 A CA 1040780A
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Abstract
ABSTRACT OF THE DISCLOSURE
A composition comprising a vulcanizable poly(di-organo-siloxane) gum and a small effective amount of a methyl, aryl silicone fluid to provide internal mold releasing properties without adversely affecting physical properties. Preferred compositions also contain catalysts and fillers.
A composition comprising a vulcanizable poly(di-organo-siloxane) gum and a small effective amount of a methyl, aryl silicone fluid to provide internal mold releasing properties without adversely affecting physical properties. Preferred compositions also contain catalysts and fillers.
Description
~040780 ~ hi~ invontion r-late- to vulcanlzabl- ~ilicone rubb-r compo-ition~ having intornal mold reloaso propertios. Moro p rticularly, it rolatos to vulcanizablo poly(diorgano~
oxan-) gun co~po~ition- ~hich include a- an lntornal mold roloa-e a mall amount of a ~othyl, aryl silicone copol_ ymer ~luid Current practico in the compros~ion or transfer mold-ing of silicon rubbor includos a ~eparato ~top of ~praying the motal mold~ with ,~'.
~SI-1472 ~04~)780 a detergent type material prior to each molding cycle. The detergent prevents adhesion of the rubber to the mold and facilitates removal of the cured molded parts. A disadvantage encountered in this practice lies in the gradual build-up of residues from the detergent after repeated use. This leads to eventual production of defective parts.
It has now been discovered that the addition of a small amount of a methylaryl silicone fluid to the vulcanizable rubber composition provides an internal mold release effect.
This eliminates the need for spraying the mold and the detrimental effects of residue build-up on ultimate properties.
Dimethyl silicone fluids are ineffective as internal mold release agents.
It is surprising also that the specific fluid employed does not have an adverse effect on the physical properties of the cured silicone rubber. Conventional internal processing aids and lubricants, such as stearic acid, derivatives of stearic acid, and various proprietary compositions all are detrimental to the properties of the silicone rubber.
Description of the Invention. - According to the present invention, in its broadest aspects, there are provided compositions comprising:
(a) a vulcanizable poly(diorganosiloxane)gum;
and (b) a small, but effective mold-releasing amount of a silicone fluid comprising from about 45 to about 90 mole %
of dimethylsiloxane units and from about 10 to about 55 mole %
of diarylsiloxane units; a silicone fluid comprising from about 0 to about 80 mole % of dimethylsiloxane units and from about 20 to about 100 mole % of methylarylsiloxane units; or a silicone fluid comprising from about 45 to about sa mole % of 104(~780 dimethylsiloxane units and from about 10 to about 55 mole % of a combination of methylaryl and diarylsiloxane units.
Another preferred features of thiS invention resides in a method for the production of a silicone rubber having internal mold release properties comprising:
(a) providing a vulcanizable poly(diorganosiloxane)gum;
and (b) adding thereto a small, but effective mold-releasing amount of a silicone fluid comprising from about 45 to about 90 mole ~ of dimethylsiloxane units and from about 10 to about 55 mole % of diarylsiloxane units; a silicone fluid comprising from about 0 to about 80 mole % of dimethyl-siloxane units and from about 20 to about 100 mole % of methylarylsiloxane units; or a silicone fluid comprising from about 45 to about 90 mole ~ of dimethylsiloxane units and from about 10 to about 55 mole % of a combination of methylaryl and diarylsiloxane units.
~ he vulcanizable poly(diorganosiloxane)gums used in the present composition are well known to those skilled in
oxan-) gun co~po~ition- ~hich include a- an lntornal mold roloa-e a mall amount of a ~othyl, aryl silicone copol_ ymer ~luid Current practico in the compros~ion or transfer mold-ing of silicon rubbor includos a ~eparato ~top of ~praying the motal mold~ with ,~'.
~SI-1472 ~04~)780 a detergent type material prior to each molding cycle. The detergent prevents adhesion of the rubber to the mold and facilitates removal of the cured molded parts. A disadvantage encountered in this practice lies in the gradual build-up of residues from the detergent after repeated use. This leads to eventual production of defective parts.
It has now been discovered that the addition of a small amount of a methylaryl silicone fluid to the vulcanizable rubber composition provides an internal mold release effect.
This eliminates the need for spraying the mold and the detrimental effects of residue build-up on ultimate properties.
Dimethyl silicone fluids are ineffective as internal mold release agents.
It is surprising also that the specific fluid employed does not have an adverse effect on the physical properties of the cured silicone rubber. Conventional internal processing aids and lubricants, such as stearic acid, derivatives of stearic acid, and various proprietary compositions all are detrimental to the properties of the silicone rubber.
Description of the Invention. - According to the present invention, in its broadest aspects, there are provided compositions comprising:
(a) a vulcanizable poly(diorganosiloxane)gum;
and (b) a small, but effective mold-releasing amount of a silicone fluid comprising from about 45 to about 90 mole %
of dimethylsiloxane units and from about 10 to about 55 mole %
of diarylsiloxane units; a silicone fluid comprising from about 0 to about 80 mole % of dimethylsiloxane units and from about 20 to about 100 mole % of methylarylsiloxane units; or a silicone fluid comprising from about 45 to about sa mole % of 104(~780 dimethylsiloxane units and from about 10 to about 55 mole % of a combination of methylaryl and diarylsiloxane units.
Another preferred features of thiS invention resides in a method for the production of a silicone rubber having internal mold release properties comprising:
(a) providing a vulcanizable poly(diorganosiloxane)gum;
and (b) adding thereto a small, but effective mold-releasing amount of a silicone fluid comprising from about 45 to about 90 mole ~ of dimethylsiloxane units and from about 10 to about 55 mole % of diarylsiloxane units; a silicone fluid comprising from about 0 to about 80 mole % of dimethyl-siloxane units and from about 20 to about 100 mole % of methylarylsiloxane units; or a silicone fluid comprising from about 45 to about 90 mole ~ of dimethylsiloxane units and from about 10 to about 55 mole % of a combination of methylaryl and diarylsiloxane units.
~ he vulcanizable poly(diorganosiloxane)gums used in the present composition are well known to those skilled in
2~ the art. In general, they are high molecular weight linear polymers. More specifically, they will be members of a family represented by the formula R / R \ R
R2 _ Si 0 ~ Si 0 ~ Si ~2 R ~ Rl J n Rl wherein R and Rl are monovalent hydrocarbon radicals, such as aliphatic, haloaliphatic, and cycloaliphatic radicals, e.g., alkyl, alkenyl, cycloalkyl, haloalkyl, including methyl, ethyl, propyl, chlorobutyl, cyclohexyl, trifluoropropyl, aryl radicals and halogenated aryl radicals such as phenyl, 104(~780 chlorophenyl, xylyl, tolyl, and the like; aralkyl radicals such as phenylethyl, benzyl, and the like, cyanoalkyl, such as cyanoethyl; and R and Rl can be the same or different, but preferably are methyl or methyl and vinyl, n is a number high enough to confer gum like properties on the polymer (see, e.g., Kirk, Ind. Eng. Chem. 51, 515 (1959), and wherein R2 can include the same values as R and Rl as well as hydroxyl, alkoxy, aryloxy, and the like.
The poly(diorganosiloxane)gums are highly viscous masses or gummy elastic solids depending on the state of condensation, the condensing agent employed, and the starting organopolysiloxane uæed to make the gummy material. A
typical gum is obtained by the condensation of a liquid poly(organosiloxane) with one of the well known condensing agents, e.g., ferric chIoride hexahydrate, phenyl phosphoryl chloride, alkaline condensing agents, such as potassium hydroxide, sodium hydroxide and the like. A typically useful gum is prepared by mixing together about 95 mole % of octa-methylcyclotetrasiloxane, and about 0.1 mole % decamethyl-tetrasiloxane at a temperature of 150-175C. for about 4 hours with about 0.01~ potassium hydroxide until a highly viscous gum is obtained.
Illustrative poly(diorganosiloxane)gums will comprise poly(dimethylsiloxanes), copolymers of dimethylsiloxane and methylvinylsiloxane, copolymers of dimethylsiloxane and diphenylsiloxane, terpolymers of dimethylsiloxane, phenyl-methylsiloxane, and methylvinylsiloxane, terpolymers of dimethylsiloxane, methylvinylsiloxane and methyltri-fluoropropylsiloxane, copolymers of dimethylsiloxane and ethylvinylsiloxane, and copolymers of dimethylsiloxane and methylcyanoethylsiloxane. The homo- and copolymers can be blocked at the ends, e.g., with triorganosiloxy units, such as 104~780 trimethylsiloxane, dimethylvinylsiloxane, dimethylphenylsiloxane units, and the like. Preferably, the organo substituents in the gum will be selected from methyl, vinyl, phenyl or tri-fluoropropyl. However, other organic radicals may also be included, such as ethyl, propyl, octadecyl, allyl, cyclohexenyl, naphthyl, chloromethyl, bromophenyl, and the like.
The silicone fluid used as the internal mold release component will comprise a diaryl or methylaryl copolymer of the formula R3 [~
R ~ CH3 ~ ~ CH3 ~ R
lo R2 si -- t --~ 5~ ~si --J~ --R
wherein R, Rl, R2 are defined above and R3 is hydrogen or methyl, preferably hydrogen. The ratio of m, r, and p is variable so long as the total number of ~ 3 groups is not less than 10~ nor more than 75~ of the total number of moities attached to silicon. Examples of such m/r/p ratios would be 0/100/0, 50/0/50, 40/40/20. The units can be randomly interspersed or in blocks and the sum of m, r, and p will be such that the polymer is fluid at ambient tem-peratures. Such fluids will have a viscosity of between 25 and 10,000 centistokes at 25C. Preferably, the dimethyl units will be predominate in a dimethyldiarylsiloxane copolymer and will comprise 50 mole % to 80 mole % of the total units.
For a methylaryldimethyl copolymer, the dimethyl units may or may not predominate and preferably the dimethyl units will be ~04(1i780 from 0 to 40 mole %.
These fluids are prepared by methods which are well known and widely used. For example, a mixture of the appropriate ratio of dimethyldichlorosilane and diphenyl-dichlorosilane and/or methylphenyldichIorosilane is hydrolyzed to make a mixture of linear and cyclic prepolymers. These, or mixtures of the individual linear and cyclic prepolymers, are then equilibrated with compounds, such as disiloxanes, to provide the triorganosiloxy terminating groups. The lower the concentration of equilibration compounds, the higher the molecular weight. The fluid is washed with water, neutralized, dried and devolatilized. Detailed directions are set forth in the Encyclopedia of Polymer Science and Technology, John Wiley and Sons, New York, Vol. 12, page 522 et seq. (1970).
The amount of silicone fluid to be added may vary but generally it will range from 0.005 to about 5.0 parts by weight per 100 parts by weight of silicone gum. Preferably, it will be in the range of 0.1 to 2 parts and especially preferably it will comprise from 0.5 to 1.0 parts by weight (same basis).
The compositions can be vulcanized by any methods conventional in silicone rubber technology, e.g., by heat or high energy radiation. Preferably, however, the composition will include a small but effective amount of a heat-reactive vulcanization catalyst. The preferred such catalysts will be organic peroxides and organic per-esters, for example, benzoyl peroxide, tertiary butyl peracetate, dicumyl peroxide, cumyl tert-butyl peroxide, 2,5-di-tert. butyl peroxy-2,5-dimethyl hexane, 2,4-dichlorobenzoyl peroxide,tert. butyl perbenzoate, hexylene glycol perbenzoate, and the like. The preferred catalysts are dicumyl peroxide, 2,4-dichIoro-benzoyl peroxide and benzoyl peroxide.
1~4~780 The amount of heat-reactive catalyst used will vary, but will generally range from 0.5 to 7 parts by weight, and preferably from about 0.5 to 1.5 parts by weight per 100 parts by weight of the poly(diorganosiloxane)gum.
Generally, the composition may also include a filler or a mixture of fillers. The preferred fillers are finely divided reinforcing fillers, e.g., silica, either aerogel or fumed, having a specific surface area of 50 to 350 m2/g. Other fillers, such as semi-reinforcing and extending fillers, such as diatomaceous earth, ground quartz, alkaline earth carbonates and sulfates (e.g., CaC03) or silicates (e.g., zirconium sili-cate), metallic oxides, such as iron oxide, zinc oxide, aluminum oxide, titanum oxide, and the like, and carbon black, can also be present.
The amount of filler can vary and will depend upon the desired characteristics of the final product. It will generally be between 10 and 150 parts by weight of filler per 100 parts by weight of the silicone gum.
In addition to the components enumerated, the com-positions may also contain other conventional ingredients, such as pigments, thermal stability stability additives and materials such as low molecular weight hydroxyl or alkoxy silanes or silazanes, and the like, which are intended to facilitate processing.
Processing can be carried out in conventional mixers, kneaders, Banburys, mills, continuous compounders and the like.
Generally, the gum will be mixed first, then the filler is added, followed by process aids, the copolymer fluid, pigments and the catalyst.
Vulcanization by compression or transfer molding is carried out in known ways. If benzoyl peroxide is used, 15 minutes at 150C. is useful followed by a post cure for a 104~780 few hours at 200-250C. The 2,4-dichlorobenzoyl peroxide is active at much lower temperatures, e.g., 80C and there is a corresponding shortening in cure time when this is used. These matters are well understood by those skilled in this art.
Descri tion of the Preferred Embodiments. - The P
following examples illustrate the compositions and the process of this invention. They are not to be construed as limiting the invention in any manner whatsoever.
One hundred parts by weight of a silicone rubber (comprising 100 parts of silicone gum, 80 parts of silica filler, processing aids and 0.5 parts of dicumyl peroxide catalyst) is kneaded and mixed with the stated amounts of a dimethylsiloxane-diphenylsiloxane fluid (20 mole % of diphenylsiloxane units, viscosity 500 cps. at 25C., General Electric Company SF-115 ~ . The compositions are transfer molded into standard test pieces and cured for 15 minutes at 165C. The properties are measured and the results are summarized in the Table.
Table - Physical Properties of Vulcanized Compositions of Silicone Rubber and Methyl, Phenyl Silicone Fluid Example Composition(parts by weight) 1 2 3 lA*
vulcanizable silicone rubber 100 100 100 100 dimethyldiarylsiloxane copolymer fluid 0.5 1.01.0 Properties as Molded Hardness, Shore A 79 79 80 81 Tensile strength, psi. - -1240 1140 Elongation, % - -160 120 Compression set, 22/350F. - - 18 27 8SI-1472 ~
Table (cont'd) Example 1 2 3 lA*
Properties as Molded 50~ Tensile modules, psi. 600 570 570 590 Specific gravity - - 1.35 1.34 Properties after Immersion in ASTM #3 Oil, 70 hrs./350F.
Hardness, Shore A - - 62 64 Tensile strength, psi. - - 1142 1110 Elongation, % - - 130 160 Volume change, +~ - - 29 29 * Control There was no sticking in the molds with compositions of Examples 1-3, even though an external mold release agent was not sprayed on the molds between each shot. In contrast, unless a sprayed mold release was used with the control sample, lA, the pieces stuck in the mold.
E ~PLE 4 One hundred parts by weight of a silicone rubber (comprising 100 parts by weight of silicone gum, 100 parts of fillers, processing aids and 0.5 parts of peroxide catalyst) is kneaded and into this is mixed 0.5 parts of a silicone copolymer fluid in which 50% of the total groups attached to silicon are aryl. The composition is molded by the procedure of Example 1 and the results are summarized in Table 2:
Table 2: Physical Properties of Vulcanized Compositions of Silicone Rubber and Methyl, Phenyl Silicone Fluid Example 4 4A*
-Composition ( parts by weight) vulcanizable silicone rubber 100 100 dimethyldiarylsiloxane fluid 0.5 0 lQ46)780 Table 2 (cont'd) Example 4 4A*
Properties as Molded Hardness, Shore A 78 79 Tensile Strength, psi. 1000 1080 Elongation, % 135 120 50% Tensile Modulus 558 590 Properties after Immersion in ASTM #3 Oil, 70 hrs./300F.
Hardness 62 62 Tensile Strength 940 975 Elongation 105 110 * Control There is no sticking to the molds with Composition 4 even though an external mold release agent is not sprayed on the molds between each cycle. In contrast, unless a sprayed mold release is used in control, 4A, the pieces stick to the mold.
The data demonstrate that the internal mold release additive according to this invention does not have an adverse effect on the physical properties of the cured rubber.
Obviously, other variations in the composition and method are possible in light of the above teachings. For instance, either a poly(dimethylsiloxane)gum or a dimethyl-siloxane copolymer with about 0.15 mole O of methylvinyl siloxane can be used. The catalyst can be omitted and the composition can be vulcanized (cured) with high energy radiation. The catalyst can comprise benzoyl peroxide or 2,6-dichlorobenzoyl peroxide or tert butyl peracetate. Instead of methylphenylsiloxane units, the copolymer can contain methyl p-tolylsiloxane units. The filler can be wholly fumed 104~780 colloidal silica or a 80-20 mixture by weight of fumed colloidal silica and diamataceous earth.
Products of this invention have many and varied uses.
They are useful, after molding, as gasket materials, shock absorbers and the like, especially under high temperature conditions.
The invention has been broadly described and variations may be made without departing from the spirit and scope thereof.
R2 _ Si 0 ~ Si 0 ~ Si ~2 R ~ Rl J n Rl wherein R and Rl are monovalent hydrocarbon radicals, such as aliphatic, haloaliphatic, and cycloaliphatic radicals, e.g., alkyl, alkenyl, cycloalkyl, haloalkyl, including methyl, ethyl, propyl, chlorobutyl, cyclohexyl, trifluoropropyl, aryl radicals and halogenated aryl radicals such as phenyl, 104(~780 chlorophenyl, xylyl, tolyl, and the like; aralkyl radicals such as phenylethyl, benzyl, and the like, cyanoalkyl, such as cyanoethyl; and R and Rl can be the same or different, but preferably are methyl or methyl and vinyl, n is a number high enough to confer gum like properties on the polymer (see, e.g., Kirk, Ind. Eng. Chem. 51, 515 (1959), and wherein R2 can include the same values as R and Rl as well as hydroxyl, alkoxy, aryloxy, and the like.
The poly(diorganosiloxane)gums are highly viscous masses or gummy elastic solids depending on the state of condensation, the condensing agent employed, and the starting organopolysiloxane uæed to make the gummy material. A
typical gum is obtained by the condensation of a liquid poly(organosiloxane) with one of the well known condensing agents, e.g., ferric chIoride hexahydrate, phenyl phosphoryl chloride, alkaline condensing agents, such as potassium hydroxide, sodium hydroxide and the like. A typically useful gum is prepared by mixing together about 95 mole % of octa-methylcyclotetrasiloxane, and about 0.1 mole % decamethyl-tetrasiloxane at a temperature of 150-175C. for about 4 hours with about 0.01~ potassium hydroxide until a highly viscous gum is obtained.
Illustrative poly(diorganosiloxane)gums will comprise poly(dimethylsiloxanes), copolymers of dimethylsiloxane and methylvinylsiloxane, copolymers of dimethylsiloxane and diphenylsiloxane, terpolymers of dimethylsiloxane, phenyl-methylsiloxane, and methylvinylsiloxane, terpolymers of dimethylsiloxane, methylvinylsiloxane and methyltri-fluoropropylsiloxane, copolymers of dimethylsiloxane and ethylvinylsiloxane, and copolymers of dimethylsiloxane and methylcyanoethylsiloxane. The homo- and copolymers can be blocked at the ends, e.g., with triorganosiloxy units, such as 104~780 trimethylsiloxane, dimethylvinylsiloxane, dimethylphenylsiloxane units, and the like. Preferably, the organo substituents in the gum will be selected from methyl, vinyl, phenyl or tri-fluoropropyl. However, other organic radicals may also be included, such as ethyl, propyl, octadecyl, allyl, cyclohexenyl, naphthyl, chloromethyl, bromophenyl, and the like.
The silicone fluid used as the internal mold release component will comprise a diaryl or methylaryl copolymer of the formula R3 [~
R ~ CH3 ~ ~ CH3 ~ R
lo R2 si -- t --~ 5~ ~si --J~ --R
wherein R, Rl, R2 are defined above and R3 is hydrogen or methyl, preferably hydrogen. The ratio of m, r, and p is variable so long as the total number of ~ 3 groups is not less than 10~ nor more than 75~ of the total number of moities attached to silicon. Examples of such m/r/p ratios would be 0/100/0, 50/0/50, 40/40/20. The units can be randomly interspersed or in blocks and the sum of m, r, and p will be such that the polymer is fluid at ambient tem-peratures. Such fluids will have a viscosity of between 25 and 10,000 centistokes at 25C. Preferably, the dimethyl units will be predominate in a dimethyldiarylsiloxane copolymer and will comprise 50 mole % to 80 mole % of the total units.
For a methylaryldimethyl copolymer, the dimethyl units may or may not predominate and preferably the dimethyl units will be ~04(1i780 from 0 to 40 mole %.
These fluids are prepared by methods which are well known and widely used. For example, a mixture of the appropriate ratio of dimethyldichlorosilane and diphenyl-dichlorosilane and/or methylphenyldichIorosilane is hydrolyzed to make a mixture of linear and cyclic prepolymers. These, or mixtures of the individual linear and cyclic prepolymers, are then equilibrated with compounds, such as disiloxanes, to provide the triorganosiloxy terminating groups. The lower the concentration of equilibration compounds, the higher the molecular weight. The fluid is washed with water, neutralized, dried and devolatilized. Detailed directions are set forth in the Encyclopedia of Polymer Science and Technology, John Wiley and Sons, New York, Vol. 12, page 522 et seq. (1970).
The amount of silicone fluid to be added may vary but generally it will range from 0.005 to about 5.0 parts by weight per 100 parts by weight of silicone gum. Preferably, it will be in the range of 0.1 to 2 parts and especially preferably it will comprise from 0.5 to 1.0 parts by weight (same basis).
The compositions can be vulcanized by any methods conventional in silicone rubber technology, e.g., by heat or high energy radiation. Preferably, however, the composition will include a small but effective amount of a heat-reactive vulcanization catalyst. The preferred such catalysts will be organic peroxides and organic per-esters, for example, benzoyl peroxide, tertiary butyl peracetate, dicumyl peroxide, cumyl tert-butyl peroxide, 2,5-di-tert. butyl peroxy-2,5-dimethyl hexane, 2,4-dichlorobenzoyl peroxide,tert. butyl perbenzoate, hexylene glycol perbenzoate, and the like. The preferred catalysts are dicumyl peroxide, 2,4-dichIoro-benzoyl peroxide and benzoyl peroxide.
1~4~780 The amount of heat-reactive catalyst used will vary, but will generally range from 0.5 to 7 parts by weight, and preferably from about 0.5 to 1.5 parts by weight per 100 parts by weight of the poly(diorganosiloxane)gum.
Generally, the composition may also include a filler or a mixture of fillers. The preferred fillers are finely divided reinforcing fillers, e.g., silica, either aerogel or fumed, having a specific surface area of 50 to 350 m2/g. Other fillers, such as semi-reinforcing and extending fillers, such as diatomaceous earth, ground quartz, alkaline earth carbonates and sulfates (e.g., CaC03) or silicates (e.g., zirconium sili-cate), metallic oxides, such as iron oxide, zinc oxide, aluminum oxide, titanum oxide, and the like, and carbon black, can also be present.
The amount of filler can vary and will depend upon the desired characteristics of the final product. It will generally be between 10 and 150 parts by weight of filler per 100 parts by weight of the silicone gum.
In addition to the components enumerated, the com-positions may also contain other conventional ingredients, such as pigments, thermal stability stability additives and materials such as low molecular weight hydroxyl or alkoxy silanes or silazanes, and the like, which are intended to facilitate processing.
Processing can be carried out in conventional mixers, kneaders, Banburys, mills, continuous compounders and the like.
Generally, the gum will be mixed first, then the filler is added, followed by process aids, the copolymer fluid, pigments and the catalyst.
Vulcanization by compression or transfer molding is carried out in known ways. If benzoyl peroxide is used, 15 minutes at 150C. is useful followed by a post cure for a 104~780 few hours at 200-250C. The 2,4-dichlorobenzoyl peroxide is active at much lower temperatures, e.g., 80C and there is a corresponding shortening in cure time when this is used. These matters are well understood by those skilled in this art.
Descri tion of the Preferred Embodiments. - The P
following examples illustrate the compositions and the process of this invention. They are not to be construed as limiting the invention in any manner whatsoever.
One hundred parts by weight of a silicone rubber (comprising 100 parts of silicone gum, 80 parts of silica filler, processing aids and 0.5 parts of dicumyl peroxide catalyst) is kneaded and mixed with the stated amounts of a dimethylsiloxane-diphenylsiloxane fluid (20 mole % of diphenylsiloxane units, viscosity 500 cps. at 25C., General Electric Company SF-115 ~ . The compositions are transfer molded into standard test pieces and cured for 15 minutes at 165C. The properties are measured and the results are summarized in the Table.
Table - Physical Properties of Vulcanized Compositions of Silicone Rubber and Methyl, Phenyl Silicone Fluid Example Composition(parts by weight) 1 2 3 lA*
vulcanizable silicone rubber 100 100 100 100 dimethyldiarylsiloxane copolymer fluid 0.5 1.01.0 Properties as Molded Hardness, Shore A 79 79 80 81 Tensile strength, psi. - -1240 1140 Elongation, % - -160 120 Compression set, 22/350F. - - 18 27 8SI-1472 ~
Table (cont'd) Example 1 2 3 lA*
Properties as Molded 50~ Tensile modules, psi. 600 570 570 590 Specific gravity - - 1.35 1.34 Properties after Immersion in ASTM #3 Oil, 70 hrs./350F.
Hardness, Shore A - - 62 64 Tensile strength, psi. - - 1142 1110 Elongation, % - - 130 160 Volume change, +~ - - 29 29 * Control There was no sticking in the molds with compositions of Examples 1-3, even though an external mold release agent was not sprayed on the molds between each shot. In contrast, unless a sprayed mold release was used with the control sample, lA, the pieces stuck in the mold.
E ~PLE 4 One hundred parts by weight of a silicone rubber (comprising 100 parts by weight of silicone gum, 100 parts of fillers, processing aids and 0.5 parts of peroxide catalyst) is kneaded and into this is mixed 0.5 parts of a silicone copolymer fluid in which 50% of the total groups attached to silicon are aryl. The composition is molded by the procedure of Example 1 and the results are summarized in Table 2:
Table 2: Physical Properties of Vulcanized Compositions of Silicone Rubber and Methyl, Phenyl Silicone Fluid Example 4 4A*
-Composition ( parts by weight) vulcanizable silicone rubber 100 100 dimethyldiarylsiloxane fluid 0.5 0 lQ46)780 Table 2 (cont'd) Example 4 4A*
Properties as Molded Hardness, Shore A 78 79 Tensile Strength, psi. 1000 1080 Elongation, % 135 120 50% Tensile Modulus 558 590 Properties after Immersion in ASTM #3 Oil, 70 hrs./300F.
Hardness 62 62 Tensile Strength 940 975 Elongation 105 110 * Control There is no sticking to the molds with Composition 4 even though an external mold release agent is not sprayed on the molds between each cycle. In contrast, unless a sprayed mold release is used in control, 4A, the pieces stick to the mold.
The data demonstrate that the internal mold release additive according to this invention does not have an adverse effect on the physical properties of the cured rubber.
Obviously, other variations in the composition and method are possible in light of the above teachings. For instance, either a poly(dimethylsiloxane)gum or a dimethyl-siloxane copolymer with about 0.15 mole O of methylvinyl siloxane can be used. The catalyst can be omitted and the composition can be vulcanized (cured) with high energy radiation. The catalyst can comprise benzoyl peroxide or 2,6-dichlorobenzoyl peroxide or tert butyl peracetate. Instead of methylphenylsiloxane units, the copolymer can contain methyl p-tolylsiloxane units. The filler can be wholly fumed 104~780 colloidal silica or a 80-20 mixture by weight of fumed colloidal silica and diamataceous earth.
Products of this invention have many and varied uses.
They are useful, after molding, as gasket materials, shock absorbers and the like, especially under high temperature conditions.
The invention has been broadly described and variations may be made without departing from the spirit and scope thereof.
Claims (8)
1. A molding composition comprising:
(a) a vulcanizable poly(diorganosiloxane) gum;
(b) an effective mold-releasing amount, in the range of from about 0.005 to about 5.0 parts by weight per 100 parts by weight of said gum, of a dimethylsiloxanediphenyl siloxane copolymer fluid, having a viscosity in the range of from about 25 to about 10,000 centistokes at 25°C, comprising from about 50 to about 85 mole percent of dimethylsiloxane units and from about 15 to about 50 mole percent of diphenyl-siloxane units; and (c) a small, but effective amount of a vulcaniza-tion catalyst for said gum.
(a) a vulcanizable poly(diorganosiloxane) gum;
(b) an effective mold-releasing amount, in the range of from about 0.005 to about 5.0 parts by weight per 100 parts by weight of said gum, of a dimethylsiloxanediphenyl siloxane copolymer fluid, having a viscosity in the range of from about 25 to about 10,000 centistokes at 25°C, comprising from about 50 to about 85 mole percent of dimethylsiloxane units and from about 15 to about 50 mole percent of diphenyl-siloxane units; and (c) a small, but effective amount of a vulcaniza-tion catalyst for said gum.
2. The molding composition of claim 1 wherein said catalyst is an organoperoxy compound.
3. The molding composition of Claim 1 which further includes from about 10 to about 150 parts by weight per 100 parts by weight of said gum of a filler selected from the group consisting of silica aerogel, fumed colloidal silica, diatoma-ceous earth, ground quartz, alkaline earth carbonates, sulfates, silicates, metallic oxides, carbon black and mixtures thereof.
4. The molding composition of Claim 1, 2 or 3 where-in said vulcanization catalyst is selected from the group con-sisting of dicumyl peroxide, benzoyl peroxide and 2,4-di-chlorobenzoyl peroxide.
5. The molding composition of Claim 3 wherein said filler is selected from the group consisting of silica aerogel and fumed colloidal silica.
6. A molding composition comprising:
(a) a vulcanizable poly(diorganosiloxane) gum;
(b) an effective mold-releasing amount, in the range of from about 0.5 to about 1.0 parts by weight per 100 parts by weight of said gum, of a dimethylsiloxane-diphenyl-siloxane copolymer fluid, having a viscosity of about 500 cps.
at 25°C, comprising about 80 mole percent dimethyl siloxane units and about 20 mole percent diphenylsiloxane units;
(c) a small, but effective amount of a heat-reactive vulcanization catalyst selected from the group con-sisting of dicumyl peroxide, benzoyl peroxide and 2,4-di-chlorobenzoyl peroxide; and (d) from about 10 to about 150 parts by weight per 100 parts by weight of said gum of a filler selected from the group consisting of silica aerogel and fumed colloidal silica.
6. A molding composition comprising:
(a) a vulcanizable poly(diorganosiloxane) gum;
(b) an effective mold-releasing amount, in the range of from about 0.5 to about 1.0 parts by weight per 100 parts by weight of said gum, of a dimethylsiloxane-diphenyl-siloxane copolymer fluid, having a viscosity of about 500 cps.
at 25°C, comprising about 80 mole percent dimethyl siloxane units and about 20 mole percent diphenylsiloxane units;
(c) a small, but effective amount of a heat-reactive vulcanization catalyst selected from the group con-sisting of dicumyl peroxide, benzoyl peroxide and 2,4-di-chlorobenzoyl peroxide; and (d) from about 10 to about 150 parts by weight per 100 parts by weight of said gum of a filler selected from the group consisting of silica aerogel and fumed colloidal silica.
6. The molding composition of claim 1, 2 or 3 wherein said siloxane fluid copolymer has a viscosity of about 500 cps at 25°C.
7. The molding composition of claim 1, 2 or 3 wherein said vulcanizable poly(diorganosiloxane) gum is poly(di-methylsiloxane).
8. The molding composition of claim 1, 2 or 3 wherein said vulcanizable poly(diorganosiloxane) gum contains vinyl siloxy linkages.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US36512173A | 1973-05-30 | 1973-05-30 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1040780A true CA1040780A (en) | 1978-10-17 |
Family
ID=23437550
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA197,962A Expired CA1040780A (en) | 1973-05-30 | 1974-04-22 | Vulcanizable silicone rubber compositions having internal mold release properties |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1040780A (en) |
-
1974
- 1974-04-22 CA CA197,962A patent/CA1040780A/en not_active Expired
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