CA1326098C - Curable organosiloxane compositions - Google Patents
Curable organosiloxane compositionsInfo
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- CA1326098C CA1326098C CA000573690A CA573690A CA1326098C CA 1326098 C CA1326098 C CA 1326098C CA 000573690 A CA000573690 A CA 000573690A CA 573690 A CA573690 A CA 573690A CA 1326098 C CA1326098 C CA 1326098C
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
- C08L83/00—Compositions of macromolecular compounds obtained by reactions forming in the main chain of the macromolecule a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon only; Compositions of derivatives of such polymers
- C08L83/04—Polysiloxanes
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G77/00—Macromolecular compounds obtained by reactions forming a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon in the main chain of the macromolecule
- C08G77/04—Polysiloxanes
- C08G77/12—Polysiloxanes containing silicon bound to hydrogen
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G77/00—Macromolecular compounds obtained by reactions forming a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon in the main chain of the macromolecule
- C08G77/04—Polysiloxanes
- C08G77/20—Polysiloxanes containing silicon bound to unsaturated aliphatic groups
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G77/00—Macromolecular compounds obtained by reactions forming a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon in the main chain of the macromolecule
- C08G77/04—Polysiloxanes
- C08G77/22—Polysiloxanes containing silicon bound to organic groups containing atoms other than carbon, hydrogen and oxygen
- C08G77/24—Polysiloxanes containing silicon bound to organic groups containing atoms other than carbon, hydrogen and oxygen halogen-containing groups
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G77/00—Macromolecular compounds obtained by reactions forming a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon in the main chain of the macromolecule
- C08G77/70—Siloxanes defined by use of the MDTQ nomenclature
Abstract
CURABLE ORGANOSILOXANE COMPOSITIONS
ABSTRACT
The tear strength of cured organosiloxane elastomers can be increased without adversely affecting other physical properties if the composition used to prepare the elastomer is curable by a platinum-catalyzed hydrosilation reaction and contains a mixture of two liquid diorganovinyl-siloxy terminated polydiorganosiloxanes, one of which constitutes from 70 to 95 percent by weight of said mixture and contains vinyl or other ethylenically unsaturated hydrocarbon radicals only at the terminal positions. The second polydiorganosiloxane contains both terminal vinyl radicals and from 1 to 5 mole percent of vinyl radicals on non-terminal repeating units.
ABSTRACT
The tear strength of cured organosiloxane elastomers can be increased without adversely affecting other physical properties if the composition used to prepare the elastomer is curable by a platinum-catalyzed hydrosilation reaction and contains a mixture of two liquid diorganovinyl-siloxy terminated polydiorganosiloxanes, one of which constitutes from 70 to 95 percent by weight of said mixture and contains vinyl or other ethylenically unsaturated hydrocarbon radicals only at the terminal positions. The second polydiorganosiloxane contains both terminal vinyl radicals and from 1 to 5 mole percent of vinyl radicals on non-terminal repeating units.
Description
~ 326~98 CURABLE ORGANOSILOXANE COMPOSITIONS
This invention relates to curable organosiloxane compositions. More particularly, this invention relates to organosiloxane compositions that can be transported by pumping and cured by a platinum-catalyzed hydrosilation reaction to form elastomers exhibiting superior physical properties, particularly tensile strength and tear strength, without sacrificing other desirable properties, such as hardness of the cured elastomer or processability of the curable composition.
Curable organosiloxane compositions containing at least one polydiorganosiloxane with at least two silicon-bonded vinyl radicals, an organohydrogensiloxane or organic peroxide curing agent and a silica filler are well known in the art pertaining to silicone elastomers. It is also known to improve the physical properties, particularly tensile and tear strengths, of cured elastomers prepared from these curable compositions by using two or more vinyl-containing polydiorganosiloxanes of different molecular weights or a single vinyl-containing polydiorganosiloxane having a bimodal molecular weight distribution.
An ob~ective of this invention is to define a class of organosiloxane compositions that can be cured to yield ela~tomers exhibiting the combination of high tear and tensile strengths in addition to a durometer hardness value, measuret on the shore A scale, of at least 45. A preferred class of the present compositions are "extrudable" as defined in the aforementioned Lee et al. patent. Specifically, the compositions can be extruded at a rate of at least 20 grams per minute through a 3.175 millimeter-diameter orifice under a pressure of 620 kilopascals (kPa) at 25C.
This invention relates to curable organosiloxane compositions. More particularly, this invention relates to organosiloxane compositions that can be transported by pumping and cured by a platinum-catalyzed hydrosilation reaction to form elastomers exhibiting superior physical properties, particularly tensile strength and tear strength, without sacrificing other desirable properties, such as hardness of the cured elastomer or processability of the curable composition.
Curable organosiloxane compositions containing at least one polydiorganosiloxane with at least two silicon-bonded vinyl radicals, an organohydrogensiloxane or organic peroxide curing agent and a silica filler are well known in the art pertaining to silicone elastomers. It is also known to improve the physical properties, particularly tensile and tear strengths, of cured elastomers prepared from these curable compositions by using two or more vinyl-containing polydiorganosiloxanes of different molecular weights or a single vinyl-containing polydiorganosiloxane having a bimodal molecular weight distribution.
An ob~ective of this invention is to define a class of organosiloxane compositions that can be cured to yield ela~tomers exhibiting the combination of high tear and tensile strengths in addition to a durometer hardness value, measuret on the shore A scale, of at least 45. A preferred class of the present compositions are "extrudable" as defined in the aforementioned Lee et al. patent. Specifically, the compositions can be extruded at a rate of at least 20 grams per minute through a 3.175 millimeter-diameter orifice under a pressure of 620 kilopascals (kPa) at 25C.
2- 1326~8 The present inventor has discovered that the aforementioned ob~ective can be achieved using a curable composition comprising a mixture of two liquid polydiorgano-siloxanes, both of which have diorganovinylsiloxy terminal units. One of these is substantially free of non-terminal vinyl-substituted diorganosiloxane units and the second contains from 1 to 5 mole percent of these units. These compositions are cured using a platinum-catalyzed hydrosilation reaction.
This invention provides a curable organosiloxane composition comprising the product obtained by mixing to homogeneity A. from 70 to 95 weight percent, based on the total weight of (A) and (B), of a first diorganovinylsiloxy terminated polydiorganosiloxane exhibiting a viscosity of from 20 to 200 Pa-s at 25C. and containing essentially no ethylenically unsaturated hydrocarbon radicals bonded to non-terminal silicon atoms, B. from 5 to 30 weight percent, based on the total weight of (A) and (B), of a second diorganovinylsiloxy terminated polydiorganosiloxane that is miscible with said first polytiorganosiloxane and exhibits a viscosity of from 0.1 to 200 Pa-s at 25C., where from 1 to 5 mole percent of the non-terminal repeating units of said second diorganovinylsiloxy-terminated polydiorganosiloxane contain a vinyl radical, C. an amount sufficient to cure said composition of an organohydrogensiloxane that is miscible with (A) ant (B), ant contains an average of more than two silicon-bonded hydrogen atoms per molecule, D. a platinum hydrosilation catalyst in an amount sufficient to promote curing of said composition at a temperature of from ambient to 2S0C., and ~3~ 1 ~ 9 ~
E. from 10 to 60 weight percent, based on the weight of said composition, of a reinforcing silica filler.
1. The Vinyl-Containing Polydiorganosiloxanes The in~entive features considered responsible for the unique combination of physical propertie~ exhibited by elastomers prepared from the present curable composition are 1) the presence in the composition of two miscible diorganovinylsiloxy-terminated polydiorganosiloxanes the first of which, referred to hereinafter as ingredient A, contains vinyl or other ethylenically unsaturated radicsls only at the terminal positions of the molecule and i9 present at a higher concentration than the second of the two diorganovinylsiloxy-terminated polydiorgano~iloxanes, referred to hereinafter as ingredient B, and 2) the pre~ence in ingredient B of vinyl radicals on from 1 to 5 mole percent of the non-terminal repeating units.
Experimental data contained in the accompanying examples demonstrate that the physical properties of the cured elastomer are adversely affected when vinyl radical~
sre present in the non-terminal units of ingredient A or the concentration of non-terminal vinyl radicals in ingretient B
is out~ite the present limits of from 1 to 5 mole percent of the non-terminal repeating units.
The term "essential absence of non-terminal ethylenically unsaturated radicals" used to tescribe ingredient A mean~ that the only ethylenically unsaturated hytrocarbon radicalY present on the non-terminal ~ilicon atom~ of thi~ ingretient result from impurities present in the reactants used to prepare ingredient A or from untesired rearrangements occurring during preparation of this ingredient.
_4 1326~9~
Ingredient A i8 a liquid diorganovinylsiloxy-terminated polydiorganosiloxane, and can be represented by the average general formula V 2 iO(R 2SiO)XSiR2Vi where Vi represents a vinyl radical, R and R' are individually monovalent hydrocarbon radical~ or haloqen ~ubstituted monovalent hydrocarbon radicals, R and R' are substantially free of ethylenic unsaturatlon, and x represents a de~ree of polymerization equi~alent to a viscosity of from 20 to 200 Pa-s at 2SC. In preferred embodiments, the viscosity of ingredient A is from 40 to 70 Pa-s.
The R and R' radicals bonded to the silicon atoms of ingredient A contain from 1 to 20 carbon atoms and can be identical or different. Because ingredient A is a liquid at 25C., at least one of the R' radicals on each of the non-terminal silicon atoms is lower alkyl, most preferably methyl. The remaining R' radical can be alkyl such as methyl or ethyl; substitutet alkyl such as chloromethyl, 3-chloropropyl or 3,3,3-trifluoropropyl; cycloalkyl such as cyclohexyl; or aryl such as phenyl. Most preferably, any R
and R' radical3 other than methyl are phenyl or 3,3,3-tri-j fluoropropyl, this preference being based on the availability of the intermediate~ used to prepare these polydiorgano-silo~ane~ and the properties of curet elastomers prepared by curing compositions containing these polymers.
Methods for preparing the liquid polydiorgano-silo~anes used as ingredients A and B of the present compositions by hydrolysis and condensation of the corrcsponding halosilane~ or cyclic polydiorganosilo~anes are sufficiently disclo~et in the patent and other literature that a detailed description of preparative methods in this specification is not necessary.
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.: .
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~5~ 1326~98 Ingredient B is a liquid diorganovinylsiloxy-terminated polydiorganosiloxane and can be represented by the average general formula Vi~''2SiO~R'''2SiO)y(ViR'''SiO)zSiR''zVi In this formula, Vi repre~ents a vinyl sadical and R'' and R''' are selected from the same group of monovalent ~ydrocarbon radicals and halogen ~ubstituted monovalent hydrocarbon radicals as R and R'. Because ingredient~ A and B should be miscible with one another, the silicon-bonded hydrocarbon radicals present in these ingredients ~hould be aelected from the same class, e.g. lower alkyl. These hydrocarbon radicals are preferably identical.
The deBree of polymerization represented by the ~um of y and z is equivalent to a visco~ity of from 0.1 to 200 Pa~s, preferably from 0.1 to 20 Pa ~, and the ratio z/(y~z) is from 0.01 to 0.05, which specifies the requirement for this ingredient that from 1 to 5 mole percent of the non-terminal repeating units contain a vinyl radical. The degree of polymerization of Ingredient B is preferably less than the degree of polymerization of Ingredient A.
Preferred embodiment~ of lngredient A and B include but are not limited to dimethylvinylsiloxy-terminated polydimethylsilo~anes, dimethylvinylsiloxy-termtnated-polymethyl-3,3,3-trifluoropropylsiloxanes, dimethylvinylsiloxy-terminated-dimethylsiloxane/3,3,3-trifluoropropylmethylsilo~ane copolymers and dimethylvinylsiloxy-terminated-dimethylsiloxane/methyl-phenylsiloxane copolymers.
To achieve high tear strength without adversely affecting other physical properties of the cured elastomer ingretient B constitutes from ~ to 30 percent, preferably from 5 to 15 percent, of the combinet weight of ingretients A
ant B. Compositions containing more than about 30 percent by '~ .
-6- ~ 8 weight of ingredient B yield elastomers with too high a degree of crosslinking, resultin~ in reduced values of elongation, tear stren~th and tensile strength. Less than about 5 percent by weight of ingredient B will not provide the desired high level of tear strength.
2. The Organohydrogensiloxane Curing Agent The organosiloxane compositions of this invention are cured by a platinum catalyzed hydrosilation reaction.
The curing agent is an organohydrogensiloxane containing an average of more than two silicon-bonded hydrogen atoms per molecule. The organohydrogensiloxane contains from as few as four silicon atoms per molecule up to an average of 20 or more, and can have a viscosity of up to 10 Pa-s or higher at 25C. The repeating units of this ingredient include but are not limited to HSiOl 5, R*HSiO and/or R*2HSiOo 5 in addition to one or more of monoorganosiloxy, diorganosiloxane, triorganosiloxy and SiO4/2 units. In these formulae, R*
repre~ents a monovalent hydrocarbon or halocarbon radical as defined hereinabove for the R radical of ingredient A.
Alternatively, the organohydrogensiloxane can be a cyclic compound containing diorganosiloxane and organo-hydrogensiloxane units or a compound of the formula Si(OSiR*2H)4-For those embodiments of the present composition wherein the hydrocarbon radical~ of ingredients A and ~, represented by R', R'' and R''', are methyl, R* is methyl and the curing agent is preferably a linear trimethylsiloxy terminated dimethylsiloxane/methylhydrogensiloxane copolymer containing an average of from 10 to about 50 repeating ~nits per molecule, of which from 3 to 5 are methylhydrogensiloxane.
The molar ratio of silicon-bonded hydrogen atoms to vinyl or other ethylenically unsaturated hydrocarbon radicals -7- ~ ~32 ~
in compositions curable by a hydrosilation reaction is critical with respect to the properties of the cured elastomer. The optimum ratio for the present curable compositions will be determined at least in part by the molecular weights of ingredients A and B, the type of curing agent and the concentration of any resinous organosiloxane copolymer described hereinafter. This optimum value can readily be determined by those skilled in the art with a minimum of experimentation, and is not part of this invention.
For preferred compositions of this invention, the molar ratio of silicon-bonded hydrogen atoms to vinyl and other ethylenically unsaturated hydrocarbon radicals is between 1 and 2.
3. The Platinum Hydrosilation Catalyst and Optional Inhibitor Hydrosilation reactions are typically conducted in the presence of a catalyst that is a platinum group metal or a compound of such a metal. Platinum compounds such as hexachloroplatinic acid, and particularly complexes of these compounds with relatively low molecular welght vinyl-containing organosiloxane compounds are preferred catalysts because of their high activity and compatibility with the organosiloxane reactants. These complexes are described in U.S. Patent No. 3,419,593 that issued to David N. Willing on December 31, 1968. Complexes with low molecular weight organosiloxanes wherein the silicon-bonded hydrocarbon radical8 are vinyl and either methyl or 3,3,3-trifluoropropyl are particularly preferred because of their ability to catalyze a rapid curing of the elastomer at temperatures of at least about 70C.
The platinum-containing catalyst can be pre~ent in an amount equivslent to as little as one part by weight of -8- 132~98 platinum per one million parts of curable composition.
Catalyst concentrations equivalent to from 5 to 50 parts of platinum per million of curable composition are preferred to achieve a practical curing rate. Higher concentrations of platinum provide only marginal improvements in curing rate, and are therefore economically unattractive, particularly when the preferred catalysts are used.
Mixtures of the aforementioned vinyl-containing reactant~, curing agents and platinum-containing catalysts may begin to cure at ambient temperature. To obtain a longer working time or "pot life", the activity of the catalyst under ambient conditions can be retarded or suppressed by addition of a suitable inhibitor.
Known platinum catalyst inhibitors include the acetylenic compounds disclosed in U.S. Patent No. 3,445,420, which issued on May 20, 1969 to Kookootsedes et al.
Acetylenic alcohols such as 2-methyl-3-butyn-2-ol constitute a preferred class of inhibitors that will suppre~s the activity of a platinum-containing catalyst at 25C.
Compositions containing these catalysts typically require heating at temperatures of 70C. or above to cure at a practical rate.
If it desired to increase the pot life of a curable composition under ambient conditions, this can be accomplished using an olefinically substituted siloxane of the type described in U.S. Patent No. 3,989,667, which issued on November 2, 1976 to Lee and Marko. Cyclic methylvinyl-siloxanes are preferred.
Inhibitor concentrations as low as one mole of inhibitor per mole of platinum will in some instances impart satisfactory storage stability and cure rate. In other instances, inhibitor concentrations of up to 500 or more moles of inhibitor per mole of platinum are required. The optimum concentration for a given inhibitor in a given ~ 3 ~ 8 compos}tion can readily be determined by routine experimentation and does not con~titute part of this invention.
This invention provides a curable organosiloxane composition comprising the product obtained by mixing to homogeneity A. from 70 to 95 weight percent, based on the total weight of (A) and (B), of a first diorganovinylsiloxy terminated polydiorganosiloxane exhibiting a viscosity of from 20 to 200 Pa-s at 25C. and containing essentially no ethylenically unsaturated hydrocarbon radicals bonded to non-terminal silicon atoms, B. from 5 to 30 weight percent, based on the total weight of (A) and (B), of a second diorganovinylsiloxy terminated polydiorganosiloxane that is miscible with said first polytiorganosiloxane and exhibits a viscosity of from 0.1 to 200 Pa-s at 25C., where from 1 to 5 mole percent of the non-terminal repeating units of said second diorganovinylsiloxy-terminated polydiorganosiloxane contain a vinyl radical, C. an amount sufficient to cure said composition of an organohydrogensiloxane that is miscible with (A) ant (B), ant contains an average of more than two silicon-bonded hydrogen atoms per molecule, D. a platinum hydrosilation catalyst in an amount sufficient to promote curing of said composition at a temperature of from ambient to 2S0C., and ~3~ 1 ~ 9 ~
E. from 10 to 60 weight percent, based on the weight of said composition, of a reinforcing silica filler.
1. The Vinyl-Containing Polydiorganosiloxanes The in~entive features considered responsible for the unique combination of physical propertie~ exhibited by elastomers prepared from the present curable composition are 1) the presence in the composition of two miscible diorganovinylsiloxy-terminated polydiorganosiloxanes the first of which, referred to hereinafter as ingredient A, contains vinyl or other ethylenically unsaturated radicsls only at the terminal positions of the molecule and i9 present at a higher concentration than the second of the two diorganovinylsiloxy-terminated polydiorgano~iloxanes, referred to hereinafter as ingredient B, and 2) the pre~ence in ingredient B of vinyl radicals on from 1 to 5 mole percent of the non-terminal repeating units.
Experimental data contained in the accompanying examples demonstrate that the physical properties of the cured elastomer are adversely affected when vinyl radical~
sre present in the non-terminal units of ingredient A or the concentration of non-terminal vinyl radicals in ingretient B
is out~ite the present limits of from 1 to 5 mole percent of the non-terminal repeating units.
The term "essential absence of non-terminal ethylenically unsaturated radicals" used to tescribe ingredient A mean~ that the only ethylenically unsaturated hytrocarbon radicalY present on the non-terminal ~ilicon atom~ of thi~ ingretient result from impurities present in the reactants used to prepare ingredient A or from untesired rearrangements occurring during preparation of this ingredient.
_4 1326~9~
Ingredient A i8 a liquid diorganovinylsiloxy-terminated polydiorganosiloxane, and can be represented by the average general formula V 2 iO(R 2SiO)XSiR2Vi where Vi represents a vinyl radical, R and R' are individually monovalent hydrocarbon radical~ or haloqen ~ubstituted monovalent hydrocarbon radicals, R and R' are substantially free of ethylenic unsaturatlon, and x represents a de~ree of polymerization equi~alent to a viscosity of from 20 to 200 Pa-s at 2SC. In preferred embodiments, the viscosity of ingredient A is from 40 to 70 Pa-s.
The R and R' radicals bonded to the silicon atoms of ingredient A contain from 1 to 20 carbon atoms and can be identical or different. Because ingredient A is a liquid at 25C., at least one of the R' radicals on each of the non-terminal silicon atoms is lower alkyl, most preferably methyl. The remaining R' radical can be alkyl such as methyl or ethyl; substitutet alkyl such as chloromethyl, 3-chloropropyl or 3,3,3-trifluoropropyl; cycloalkyl such as cyclohexyl; or aryl such as phenyl. Most preferably, any R
and R' radical3 other than methyl are phenyl or 3,3,3-tri-j fluoropropyl, this preference being based on the availability of the intermediate~ used to prepare these polydiorgano-silo~ane~ and the properties of curet elastomers prepared by curing compositions containing these polymers.
Methods for preparing the liquid polydiorgano-silo~anes used as ingredients A and B of the present compositions by hydrolysis and condensation of the corrcsponding halosilane~ or cyclic polydiorganosilo~anes are sufficiently disclo~et in the patent and other literature that a detailed description of preparative methods in this specification is not necessary.
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~5~ 1326~98 Ingredient B is a liquid diorganovinylsiloxy-terminated polydiorganosiloxane and can be represented by the average general formula Vi~''2SiO~R'''2SiO)y(ViR'''SiO)zSiR''zVi In this formula, Vi repre~ents a vinyl sadical and R'' and R''' are selected from the same group of monovalent ~ydrocarbon radicals and halogen ~ubstituted monovalent hydrocarbon radicals as R and R'. Because ingredient~ A and B should be miscible with one another, the silicon-bonded hydrocarbon radicals present in these ingredients ~hould be aelected from the same class, e.g. lower alkyl. These hydrocarbon radicals are preferably identical.
The deBree of polymerization represented by the ~um of y and z is equivalent to a visco~ity of from 0.1 to 200 Pa~s, preferably from 0.1 to 20 Pa ~, and the ratio z/(y~z) is from 0.01 to 0.05, which specifies the requirement for this ingredient that from 1 to 5 mole percent of the non-terminal repeating units contain a vinyl radical. The degree of polymerization of Ingredient B is preferably less than the degree of polymerization of Ingredient A.
Preferred embodiment~ of lngredient A and B include but are not limited to dimethylvinylsiloxy-terminated polydimethylsilo~anes, dimethylvinylsiloxy-termtnated-polymethyl-3,3,3-trifluoropropylsiloxanes, dimethylvinylsiloxy-terminated-dimethylsiloxane/3,3,3-trifluoropropylmethylsilo~ane copolymers and dimethylvinylsiloxy-terminated-dimethylsiloxane/methyl-phenylsiloxane copolymers.
To achieve high tear strength without adversely affecting other physical properties of the cured elastomer ingretient B constitutes from ~ to 30 percent, preferably from 5 to 15 percent, of the combinet weight of ingretients A
ant B. Compositions containing more than about 30 percent by '~ .
-6- ~ 8 weight of ingredient B yield elastomers with too high a degree of crosslinking, resultin~ in reduced values of elongation, tear stren~th and tensile strength. Less than about 5 percent by weight of ingredient B will not provide the desired high level of tear strength.
2. The Organohydrogensiloxane Curing Agent The organosiloxane compositions of this invention are cured by a platinum catalyzed hydrosilation reaction.
The curing agent is an organohydrogensiloxane containing an average of more than two silicon-bonded hydrogen atoms per molecule. The organohydrogensiloxane contains from as few as four silicon atoms per molecule up to an average of 20 or more, and can have a viscosity of up to 10 Pa-s or higher at 25C. The repeating units of this ingredient include but are not limited to HSiOl 5, R*HSiO and/or R*2HSiOo 5 in addition to one or more of monoorganosiloxy, diorganosiloxane, triorganosiloxy and SiO4/2 units. In these formulae, R*
repre~ents a monovalent hydrocarbon or halocarbon radical as defined hereinabove for the R radical of ingredient A.
Alternatively, the organohydrogensiloxane can be a cyclic compound containing diorganosiloxane and organo-hydrogensiloxane units or a compound of the formula Si(OSiR*2H)4-For those embodiments of the present composition wherein the hydrocarbon radical~ of ingredients A and ~, represented by R', R'' and R''', are methyl, R* is methyl and the curing agent is preferably a linear trimethylsiloxy terminated dimethylsiloxane/methylhydrogensiloxane copolymer containing an average of from 10 to about 50 repeating ~nits per molecule, of which from 3 to 5 are methylhydrogensiloxane.
The molar ratio of silicon-bonded hydrogen atoms to vinyl or other ethylenically unsaturated hydrocarbon radicals -7- ~ ~32 ~
in compositions curable by a hydrosilation reaction is critical with respect to the properties of the cured elastomer. The optimum ratio for the present curable compositions will be determined at least in part by the molecular weights of ingredients A and B, the type of curing agent and the concentration of any resinous organosiloxane copolymer described hereinafter. This optimum value can readily be determined by those skilled in the art with a minimum of experimentation, and is not part of this invention.
For preferred compositions of this invention, the molar ratio of silicon-bonded hydrogen atoms to vinyl and other ethylenically unsaturated hydrocarbon radicals is between 1 and 2.
3. The Platinum Hydrosilation Catalyst and Optional Inhibitor Hydrosilation reactions are typically conducted in the presence of a catalyst that is a platinum group metal or a compound of such a metal. Platinum compounds such as hexachloroplatinic acid, and particularly complexes of these compounds with relatively low molecular welght vinyl-containing organosiloxane compounds are preferred catalysts because of their high activity and compatibility with the organosiloxane reactants. These complexes are described in U.S. Patent No. 3,419,593 that issued to David N. Willing on December 31, 1968. Complexes with low molecular weight organosiloxanes wherein the silicon-bonded hydrocarbon radical8 are vinyl and either methyl or 3,3,3-trifluoropropyl are particularly preferred because of their ability to catalyze a rapid curing of the elastomer at temperatures of at least about 70C.
The platinum-containing catalyst can be pre~ent in an amount equivslent to as little as one part by weight of -8- 132~98 platinum per one million parts of curable composition.
Catalyst concentrations equivalent to from 5 to 50 parts of platinum per million of curable composition are preferred to achieve a practical curing rate. Higher concentrations of platinum provide only marginal improvements in curing rate, and are therefore economically unattractive, particularly when the preferred catalysts are used.
Mixtures of the aforementioned vinyl-containing reactant~, curing agents and platinum-containing catalysts may begin to cure at ambient temperature. To obtain a longer working time or "pot life", the activity of the catalyst under ambient conditions can be retarded or suppressed by addition of a suitable inhibitor.
Known platinum catalyst inhibitors include the acetylenic compounds disclosed in U.S. Patent No. 3,445,420, which issued on May 20, 1969 to Kookootsedes et al.
Acetylenic alcohols such as 2-methyl-3-butyn-2-ol constitute a preferred class of inhibitors that will suppre~s the activity of a platinum-containing catalyst at 25C.
Compositions containing these catalysts typically require heating at temperatures of 70C. or above to cure at a practical rate.
If it desired to increase the pot life of a curable composition under ambient conditions, this can be accomplished using an olefinically substituted siloxane of the type described in U.S. Patent No. 3,989,667, which issued on November 2, 1976 to Lee and Marko. Cyclic methylvinyl-siloxanes are preferred.
Inhibitor concentrations as low as one mole of inhibitor per mole of platinum will in some instances impart satisfactory storage stability and cure rate. In other instances, inhibitor concentrations of up to 500 or more moles of inhibitor per mole of platinum are required. The optimum concentration for a given inhibitor in a given ~ 3 ~ 8 compos}tion can readily be determined by routine experimentation and does not con~titute part of this invention.
4. The Silica Filler To achieve the high levels of tear strength and other physical propertie~ that characterize cured elastomers prepared using the compositions of this invention, the compositions must contain a reinforcing silica filler. The filler is typically treated with any of the known silica treating agents to prevent a phenomenon referred to as "creping" or "crepe hardening" during processing of the curable composition.
Any finely divided form of silica can be used as the reinforcing filler. Colloidal silicas are preferred because of their relatively high ~urface area, which is typically at least 50 square meters per gram. Fillers having surface areas of at least 300 square meters per gram are preferred for use in the present compositions. Colloidal silicas can be prepared by precipitation or a fume process.
Both of these preferred types of silica are commercially available.
The amount of finely divided silica used in the present compositions is at least in part determined by the physical properties desired in the cured elastomer. Liquid or pumpable polyorganosiloxane compositions typically contain from about 10 to about 60 percent by weight of silica, based on the weight of polydiorganosiloxane. This value is preferably from about 30 to about 50 percent.
The ~ilica treating agent can be any of the low molecular weight organosilicon compounds disclosed in the art as being suitable for preventing creping of organosiloxane compositions during processing. The treating agents are typically liquid hydroxyl terminated polydiorganosiloxanes , .
- lo- ~ 9 8 containing an average of from 2 to about 20 repeatin~ units per molecule, and organosilicon compounds such as hexaorgano-disiloxanes and hexaorganodisilazanes that hydrolyze under the conditions used to treat the silica to form compounds with silicon-bonded hydroxyl groups. Preferably, at least a portion of the silicon-bonded hydrocarbon radicals present on the treating agent are identical to a majority of the hydrocarbon radicals present in ingredients A and B. A small amount of water can be added together with the silica treating agent(s) as a processing aid.
It is believed that the treating agents function by reacting with silicon-bonded hydroxyl groups present on the surface of the silica particles to reduce interaction between these particles.
Any finely divided form of silica can be used as the reinforcing filler. Colloidal silicas are preferred because of their relatively high ~urface area, which is typically at least 50 square meters per gram. Fillers having surface areas of at least 300 square meters per gram are preferred for use in the present compositions. Colloidal silicas can be prepared by precipitation or a fume process.
Both of these preferred types of silica are commercially available.
The amount of finely divided silica used in the present compositions is at least in part determined by the physical properties desired in the cured elastomer. Liquid or pumpable polyorganosiloxane compositions typically contain from about 10 to about 60 percent by weight of silica, based on the weight of polydiorganosiloxane. This value is preferably from about 30 to about 50 percent.
The ~ilica treating agent can be any of the low molecular weight organosilicon compounds disclosed in the art as being suitable for preventing creping of organosiloxane compositions during processing. The treating agents are typically liquid hydroxyl terminated polydiorganosiloxanes , .
- lo- ~ 9 8 containing an average of from 2 to about 20 repeatin~ units per molecule, and organosilicon compounds such as hexaorgano-disiloxanes and hexaorganodisilazanes that hydrolyze under the conditions used to treat the silica to form compounds with silicon-bonded hydroxyl groups. Preferably, at least a portion of the silicon-bonded hydrocarbon radicals present on the treating agent are identical to a majority of the hydrocarbon radicals present in ingredients A and B. A small amount of water can be added together with the silica treating agent(s) as a processing aid.
It is believed that the treating agents function by reacting with silicon-bonded hydroxyl groups present on the surface of the silica particles to reduce interaction between these particles.
5. Optional Ingredients In addition to the vinyl-containing polydiorgano-siloxanes, curing agent, catalyst and silica filler, the organosiloxane compositions of this invention can contain one or more additives that are conventionally present in curable compositions of this type. These materials are added to impart or enhance certain properties of the cured elastomer or facilitate processing of the curable composition.
Typical additives include but are not limited to pigments, dyes, adhesion promoters, flame retardants, heat and/or ultraviolet light ~tabilizers and resinous organosiloxane copolymers to enhance the physical properties of the curet elastomer.
A preferred type of resinous copolymer contains repeating unit~ of the general formula SiO 4/2 in addition to triorganosiloxy units of the general formulae R 3SiOl/2 and diorganovinylsiloxy units of the general formula CH2=CH(R2)2SiO1~2. In these formulae, Rl and R2 are individually monovslent hydrocar~on or substituted monovalent -11- ' ~ 326i~8 hydrocarbon radicals as previously defined for the R' and R'' radicals of the ingredients A and B.
The molar ratio of the combination of triorgano-siloxy units and diorganovinylsiloxy units to SiO4/2 units in the resinous copolymer is from 0.7 to 1.2, inclusive. The vinyl-containing units constitute from 2 to 8 percent by weight of the copolymer, which preferably contains at least two vinyl radicals per molecule. In preferred embodiments of the copolymer, the ranges for the molar ratio of diorgano-vinylsiloxy:triorganosiloxy:SiO4/2 units i9 0.08-0.1:0.06-1:1.
The resinous copolymers can be prepared as described in U.S. Patent No. 2,676,182, which issued to Daudt and Tyler on April 20, 1954. The copolymers described in this patent contain from 2 to 23 percent by weight of hydroxyl groups, which is considerably above the maximum level of about 0.8 weight percent preferred for precursors of the present copolymers. The hydroxyl content of the precursor can be conveniently reduced to the desired level by employing a higher concentration of triorganosiloxane capping agent than the concentration range taught by Daudt et al.
Briefly, the method of Daudt et al. comprises reacting a silica hydrosol under acidic conditions with the appropriate amount of hexamethyldisiloxane or trimethyl-chlorosilane. The resinous copolymers used to prepare the present elastomers can be obtained by reacting Daudt et al's.
product with the required amount of a hexaorganodisilazane or a hexaorganodisiloxane wherein each silicon atom contains a vinyl radical and two methyl or other hydrocarbon radicals represented by Rl and R2 in the foregoing formula.
Typical additives include but are not limited to pigments, dyes, adhesion promoters, flame retardants, heat and/or ultraviolet light ~tabilizers and resinous organosiloxane copolymers to enhance the physical properties of the curet elastomer.
A preferred type of resinous copolymer contains repeating unit~ of the general formula SiO 4/2 in addition to triorganosiloxy units of the general formulae R 3SiOl/2 and diorganovinylsiloxy units of the general formula CH2=CH(R2)2SiO1~2. In these formulae, Rl and R2 are individually monovslent hydrocar~on or substituted monovalent -11- ' ~ 326i~8 hydrocarbon radicals as previously defined for the R' and R'' radicals of the ingredients A and B.
The molar ratio of the combination of triorgano-siloxy units and diorganovinylsiloxy units to SiO4/2 units in the resinous copolymer is from 0.7 to 1.2, inclusive. The vinyl-containing units constitute from 2 to 8 percent by weight of the copolymer, which preferably contains at least two vinyl radicals per molecule. In preferred embodiments of the copolymer, the ranges for the molar ratio of diorgano-vinylsiloxy:triorganosiloxy:SiO4/2 units i9 0.08-0.1:0.06-1:1.
The resinous copolymers can be prepared as described in U.S. Patent No. 2,676,182, which issued to Daudt and Tyler on April 20, 1954. The copolymers described in this patent contain from 2 to 23 percent by weight of hydroxyl groups, which is considerably above the maximum level of about 0.8 weight percent preferred for precursors of the present copolymers. The hydroxyl content of the precursor can be conveniently reduced to the desired level by employing a higher concentration of triorganosiloxane capping agent than the concentration range taught by Daudt et al.
Briefly, the method of Daudt et al. comprises reacting a silica hydrosol under acidic conditions with the appropriate amount of hexamethyldisiloxane or trimethyl-chlorosilane. The resinous copolymers used to prepare the present elastomers can be obtained by reacting Daudt et al's.
product with the required amount of a hexaorganodisilazane or a hexaorganodisiloxane wherein each silicon atom contains a vinyl radical and two methyl or other hydrocarbon radicals represented by Rl and R2 in the foregoing formula.
6. Preparation of Curable Compo~itions The silica filler can be treated in the presence of at least a portion of the other ingredients of the present -12- ~3~ 8 compositions by blending these ingredients together until the filler is completely treated and uniformly dispersed throughout the composition to form a homogeneous material.
The ingredients that are present during treatment of the silica typically include the treating agents and at least a portion of the polydiorganosiloxanes referred to herein as ingredient3 A and B. Because silica treatment is typically carried out at temperatures above ambient, the organo-hydrogensiloxane and platinum-containing catalyst are typically added after treatment of the silica has been completed.
Irrespective of the type of mixer used, blending of the silica, filler treating agent(s), ingredients A and optionally, ingredient B is continued while the composition i9 heated at temperatures from about 100 to 250C. under reduced pressure to remove volatile materials. The resultant product is then cooled prior to being blended with the organohydrogensiloxane (Ingredient C) and/or the platinum catalyst (Ingredient D), depending upon whether it is desired to prepare a one-part or two-part curable composition of this invention. The optional additives referred to hereinbefore can be added at this time or during blending of the silica with inBredient A.
In-situ treatment of the silica can require anywhere from 15 minutes to 2 hours, depending upon the amount of material being processed, the viscosity of the material and the ~hear rate to which the material is sub~ected during processing.
Alternatively, treatment of the silica can occur before the silica is blended with other ingredients of the pre9ent compo9itions. Methods for treating finely divided silica fillers prior to incorporating the silica into a polyorganosiloxane composition are known in the art.
-13- 1326~98 To ensure adequate blending of all ingredients the mixing equipment in which the present compositions are prepared should be capable of sub~ecting the composition to a high rate of shear. The advantage of using this type of a "high intensity" mixer to prepare silica filled polyorgano-siloxane compo~itions is taught in U.S. Patent No. 3,690,804, which issued to Minuto on June 1, 1976. In accordance with the disclosure of this patent, the tip of the stirring tevice in the mixer i8 rotated at a speed of from 25 to about 250 feet per second, which would generate considerable shearing forces. The exemplified compositions are blended in a ~Henschel~* high inten~ity DiYe~r wherein the rotor ~as operated at a speed of 3800 revolutions per minute, equivalent to a rotor tip speed of 157 feet per second.
Dough type mixers equipped with "sigma" shape blades, are not as efficient as mixers wherein the mixing surfaces are of a relatively flat "paddle" configuration.
Examples of the padtle type mixers include the ~Hen~chel~* ~ixer ti8closed in the aforementioned Minuto patent and certain mixers manufacturet by Neulinger A.G. The blade i8 preferably rotated at a speed of at least 100 revolutions per minute.
Curable compo3itions prepared using the present methot typically exhibit viscosities of about 0.5 up to about 1000 Pa s at 25C. To facilitate blending and transfer of the compositions ant minimize entrapment of air during mi~ing, a visco~ity of less than about 10 Pa-s at 25C. i~
preferred, particulsrly for extrudable compositions.
The ingredients that are present during treatment of the silica typically include the treating agents and at least a portion of the polydiorganosiloxanes referred to herein as ingredient3 A and B. Because silica treatment is typically carried out at temperatures above ambient, the organo-hydrogensiloxane and platinum-containing catalyst are typically added after treatment of the silica has been completed.
Irrespective of the type of mixer used, blending of the silica, filler treating agent(s), ingredients A and optionally, ingredient B is continued while the composition i9 heated at temperatures from about 100 to 250C. under reduced pressure to remove volatile materials. The resultant product is then cooled prior to being blended with the organohydrogensiloxane (Ingredient C) and/or the platinum catalyst (Ingredient D), depending upon whether it is desired to prepare a one-part or two-part curable composition of this invention. The optional additives referred to hereinbefore can be added at this time or during blending of the silica with inBredient A.
In-situ treatment of the silica can require anywhere from 15 minutes to 2 hours, depending upon the amount of material being processed, the viscosity of the material and the ~hear rate to which the material is sub~ected during processing.
Alternatively, treatment of the silica can occur before the silica is blended with other ingredients of the pre9ent compo9itions. Methods for treating finely divided silica fillers prior to incorporating the silica into a polyorganosiloxane composition are known in the art.
-13- 1326~98 To ensure adequate blending of all ingredients the mixing equipment in which the present compositions are prepared should be capable of sub~ecting the composition to a high rate of shear. The advantage of using this type of a "high intensity" mixer to prepare silica filled polyorgano-siloxane compo~itions is taught in U.S. Patent No. 3,690,804, which issued to Minuto on June 1, 1976. In accordance with the disclosure of this patent, the tip of the stirring tevice in the mixer i8 rotated at a speed of from 25 to about 250 feet per second, which would generate considerable shearing forces. The exemplified compositions are blended in a ~Henschel~* high inten~ity DiYe~r wherein the rotor ~as operated at a speed of 3800 revolutions per minute, equivalent to a rotor tip speed of 157 feet per second.
Dough type mixers equipped with "sigma" shape blades, are not as efficient as mixers wherein the mixing surfaces are of a relatively flat "paddle" configuration.
Examples of the padtle type mixers include the ~Hen~chel~* ~ixer ti8closed in the aforementioned Minuto patent and certain mixers manufacturet by Neulinger A.G. The blade i8 preferably rotated at a speed of at least 100 revolutions per minute.
Curable compo3itions prepared using the present methot typically exhibit viscosities of about 0.5 up to about 1000 Pa s at 25C. To facilitate blending and transfer of the compositions ant minimize entrapment of air during mi~ing, a visco~ity of less than about 10 Pa-s at 25C. i~
preferred, particulsrly for extrudable compositions.
7. Fabrication ant Curing of Shaped Articles The present curable composition~ can be formed into 8haped article8 by pres8 molding, in~ection molding, extrusion, or any of the other methods used to fabricate organosilo~ane composition8.
~Tra~eDark ~,, ;
-14- 1326~98 In the absence of one of the aforementioned catalyst inhibitors, the compositions will cure at ambient temperature over a period of several hours or days, or within in several minutes when heated at temperatures of up to 250~C. Compositions containing one of these catalyst inhibitors are typically cured by heating them for several minutes at temperatures of from 50 to about 250C. A
preferred range is from 100 to 200C.
As discussed hereinbefore, cured elastomeric articles prepared using the curable compo9itions of this invention exhibit tear strengths above about 240 pounts per inch (42 kN/m) and tensile strengths above 9300 kPa without any adverse effect on the other desirable properties of the cured elastomer or the extrutability of the composition from which it i9 formet. This unique combination of properties ma~e the elastomers desirable for a number of end use applications, including gaskets and other fabricated articles wherein at least a portion of the article is relatively thin and sub~ected to large amounts of stress. Articles of this type include diaphragms and blatters.
The following example describes preferred curable compositions of this invention ant the properties of elastomers prepared by curing these compositions. The example is intentet to illustrate the present invention ant shoult not be interpretet as limiting the invention as tefinet in the accompanying claim~. Unless indicated to the contrary, all parts and percentages are by weight and all viscosities were measuret at 25C.
EXAMPLE
Curable organosiloxane composltions were prepared by blenting to homogeneity in a dough type ~ix~r the entire quantity of a fume sillca having a no~inal surface area of 250 m per gram (ingredient E), two filler treating agents ;
1~ .
~ ` --15- ~ ~2~98 described hereinafter, water and an amount of a dimethyl-vinylsiloxy endblocked polydimethylsiloxane having a viscosity of about 5~ Pa-s at 25C. (ingredient A) equal to 1.3 times the weight of the filler. This mixture was heated for one hour by circulating steam through the jacket of the mixer while volatile materials were removed under red~ced pressure. Following completion of the heating cycle, the remaining portion of ingredient A was added together with the entire amount of one of 4 different embodiments of ingredient B that are within the scope of this invention and 2 that are not. These embotiments are tescribed hereinafter. These resultant compositions were then blended to homogeneity under ambient conditions. Two-part curable compositions were prepared by diviting this product into 2 equal parts.
One of these parts was combined with 1) a trimethylsiloxy terminated polydiorganosiloxane having an average of five methylhydrogensiloxane units, three dimethylsiloxane units per molecule and containing from 0.7 to 0.8 weight percent of silicon-bonded hydrogen atoms as the curlng agent (ingredient C) and 2) 0.05 parts of methyl-butynol as a platinum catalyst inhibitor (ingredient F). The amount of ingrodient C was equivalent to a molar ratio of silicon-bonded hydrogen atoms to vinyl radicals in the total curable composition of 1.8.
The second part of the product from the silica treatment operation was combined with a reaction protuct of hexachloroplatinic acid and sym-tetramethyldivinyldisiloxane that ha~ been diluted with a liquid dimethylsiloxy terminated polydimethylsiloxane in an amount sufficient to achieve a platinum content of 0.7 weight percent (ingredient D), based on the weight of both parts of the curable composition.
Four embodiments of ingredient B corresponding to the present invention were used in the compositions.
~'.~,.
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Ingredient Bl was a dimethylvinylsiloxy terminated dimethylsiloxane/methylvinylsiloxane copolymer exhibiting a viscosity of 10 Pa ~ and containing 1 mole percent of methylvinylsiloxane units.
Ingredient B2 was a dimethylvinylsiloxy terminated dimethylsiloxane/methylvinylsiloxane copolymer exhibiting a viscosity of 10 Pa- 9 and containing 3 mole percent of methylvinylsiloxane units.
Ingredient B3 was a dimethylvinyl~iloxy terminated dimethylsiloxane/methylvinylsiloxane copolymer containing 5 mole percent of methylvinylsiloxy units and exhibiting a viscosity of 10 Pa 9.
Ingredient B4 was a is a dimethylvinylsiloxy terminated dimethylsiloxane/methylvinylsiloxane copolymer exhibiting a vi~cosity of 0.3 Pa-s and containing 2 mole percent of methylvinylsiloxane units.
For comparative purposes, a dimethylvinylsiloxy terminated polydimethylsiloxane containing no methylvinyl-siloxane units and exhibiting a visc09ity of 0.45 Pa-s (ingredient B5) and a liquid dimethylvinylsiloxy terminated dimethylsiloxane/methylvinylsiloxane copolymer exhibiting a viscosity of about 16 Pa-~ containing 22 mole percent of methylvinyl8iloxane units (ingredient B6) were used in place of an ingredient B of this invention containing from 1 to 5 mole percent of methylvinylsiloxane units. The combination of ingredient B5 with ingredient A provided a molecular weight distribution for vinyl-containing polydimethyl-siloxane8 that i8 within the range taught and claimed in U.S.
Patent No. 4,162,243, i88ued to Lee et al. on July 24, 1979.
The silica treating agents were (1) 1.0 part of a hydroxyl terminated diorganosiloxane copolymer wherein the repeating units consist essentially of dimethylsiloxane and methylvinyl8iloxane units and the copolymer contains about 10 -17- 132~9~
weight-percent of vinyl radical and about 16 weight percent of hydroxyl radicals; and (2) hexamethyldisilazane, used at a level of 8.9 parts in all but one of the formulations as specified in the following Table 1.
The amount of water added to each of the compositions during treatment of the silica was 1.9 parts.
Curable compositions were prepared by combining and mixing t O homogeneity t~e two parts of each formulation.
These compositions were cured in the form of sheets having a thickness of 1.9 mm. by placing the compositions in a hydraulic press and heating them for 5 minutes at a temperature of 150~. Test samples were then cut from each of the sheets to determine the physical properties of the cured materials.
The American Society of Testing and Materials (ASTM) test methods used to measure the various properties evaluated included ASTM-412 for tensile strength and elongation, ASTM-D625, Die B for tear strength and ASTM-D2240, Shore A scale for durometer hardness values.
Table 1 summarizes the amounts of ingredients A, B, C and E present in each of the compositions evaluated. The physical properties of the cured compositions are summarized in Table 2.
The data in Table 2 demonstrate that by using the curable compositions of this invention one is able to substantially improve the tear strength of cured elastomer~
relative to prior art elastomers prepared using extrudable organosiloxane compositions without adver3ely affecting other desirable properties of the cured elastomer such as tensile strength, hardness and elongation.
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-14- 1326~98 In the absence of one of the aforementioned catalyst inhibitors, the compositions will cure at ambient temperature over a period of several hours or days, or within in several minutes when heated at temperatures of up to 250~C. Compositions containing one of these catalyst inhibitors are typically cured by heating them for several minutes at temperatures of from 50 to about 250C. A
preferred range is from 100 to 200C.
As discussed hereinbefore, cured elastomeric articles prepared using the curable compo9itions of this invention exhibit tear strengths above about 240 pounts per inch (42 kN/m) and tensile strengths above 9300 kPa without any adverse effect on the other desirable properties of the cured elastomer or the extrutability of the composition from which it i9 formet. This unique combination of properties ma~e the elastomers desirable for a number of end use applications, including gaskets and other fabricated articles wherein at least a portion of the article is relatively thin and sub~ected to large amounts of stress. Articles of this type include diaphragms and blatters.
The following example describes preferred curable compositions of this invention ant the properties of elastomers prepared by curing these compositions. The example is intentet to illustrate the present invention ant shoult not be interpretet as limiting the invention as tefinet in the accompanying claim~. Unless indicated to the contrary, all parts and percentages are by weight and all viscosities were measuret at 25C.
EXAMPLE
Curable organosiloxane composltions were prepared by blenting to homogeneity in a dough type ~ix~r the entire quantity of a fume sillca having a no~inal surface area of 250 m per gram (ingredient E), two filler treating agents ;
1~ .
~ ` --15- ~ ~2~98 described hereinafter, water and an amount of a dimethyl-vinylsiloxy endblocked polydimethylsiloxane having a viscosity of about 5~ Pa-s at 25C. (ingredient A) equal to 1.3 times the weight of the filler. This mixture was heated for one hour by circulating steam through the jacket of the mixer while volatile materials were removed under red~ced pressure. Following completion of the heating cycle, the remaining portion of ingredient A was added together with the entire amount of one of 4 different embodiments of ingredient B that are within the scope of this invention and 2 that are not. These embotiments are tescribed hereinafter. These resultant compositions were then blended to homogeneity under ambient conditions. Two-part curable compositions were prepared by diviting this product into 2 equal parts.
One of these parts was combined with 1) a trimethylsiloxy terminated polydiorganosiloxane having an average of five methylhydrogensiloxane units, three dimethylsiloxane units per molecule and containing from 0.7 to 0.8 weight percent of silicon-bonded hydrogen atoms as the curlng agent (ingredient C) and 2) 0.05 parts of methyl-butynol as a platinum catalyst inhibitor (ingredient F). The amount of ingrodient C was equivalent to a molar ratio of silicon-bonded hydrogen atoms to vinyl radicals in the total curable composition of 1.8.
The second part of the product from the silica treatment operation was combined with a reaction protuct of hexachloroplatinic acid and sym-tetramethyldivinyldisiloxane that ha~ been diluted with a liquid dimethylsiloxy terminated polydimethylsiloxane in an amount sufficient to achieve a platinum content of 0.7 weight percent (ingredient D), based on the weight of both parts of the curable composition.
Four embodiments of ingredient B corresponding to the present invention were used in the compositions.
~'.~,.
~t -16- ~32~
Ingredient Bl was a dimethylvinylsiloxy terminated dimethylsiloxane/methylvinylsiloxane copolymer exhibiting a viscosity of 10 Pa ~ and containing 1 mole percent of methylvinylsiloxane units.
Ingredient B2 was a dimethylvinylsiloxy terminated dimethylsiloxane/methylvinylsiloxane copolymer exhibiting a viscosity of 10 Pa- 9 and containing 3 mole percent of methylvinylsiloxane units.
Ingredient B3 was a dimethylvinyl~iloxy terminated dimethylsiloxane/methylvinylsiloxane copolymer containing 5 mole percent of methylvinylsiloxy units and exhibiting a viscosity of 10 Pa 9.
Ingredient B4 was a is a dimethylvinylsiloxy terminated dimethylsiloxane/methylvinylsiloxane copolymer exhibiting a vi~cosity of 0.3 Pa-s and containing 2 mole percent of methylvinylsiloxane units.
For comparative purposes, a dimethylvinylsiloxy terminated polydimethylsiloxane containing no methylvinyl-siloxane units and exhibiting a visc09ity of 0.45 Pa-s (ingredient B5) and a liquid dimethylvinylsiloxy terminated dimethylsiloxane/methylvinylsiloxane copolymer exhibiting a viscosity of about 16 Pa-~ containing 22 mole percent of methylvinyl8iloxane units (ingredient B6) were used in place of an ingredient B of this invention containing from 1 to 5 mole percent of methylvinylsiloxane units. The combination of ingredient B5 with ingredient A provided a molecular weight distribution for vinyl-containing polydimethyl-siloxane8 that i8 within the range taught and claimed in U.S.
Patent No. 4,162,243, i88ued to Lee et al. on July 24, 1979.
The silica treating agents were (1) 1.0 part of a hydroxyl terminated diorganosiloxane copolymer wherein the repeating units consist essentially of dimethylsiloxane and methylvinyl8iloxane units and the copolymer contains about 10 -17- 132~9~
weight-percent of vinyl radical and about 16 weight percent of hydroxyl radicals; and (2) hexamethyldisilazane, used at a level of 8.9 parts in all but one of the formulations as specified in the following Table 1.
The amount of water added to each of the compositions during treatment of the silica was 1.9 parts.
Curable compositions were prepared by combining and mixing t O homogeneity t~e two parts of each formulation.
These compositions were cured in the form of sheets having a thickness of 1.9 mm. by placing the compositions in a hydraulic press and heating them for 5 minutes at a temperature of 150~. Test samples were then cut from each of the sheets to determine the physical properties of the cured materials.
The American Society of Testing and Materials (ASTM) test methods used to measure the various properties evaluated included ASTM-412 for tensile strength and elongation, ASTM-D625, Die B for tear strength and ASTM-D2240, Shore A scale for durometer hardness values.
Table 1 summarizes the amounts of ingredients A, B, C and E present in each of the compositions evaluated. The physical properties of the cured compositions are summarized in Table 2.
The data in Table 2 demonstrate that by using the curable compositions of this invention one is able to substantially improve the tear strength of cured elastomer~
relative to prior art elastomers prepared using extrudable organosiloxane compositions without adver3ely affecting other desirable properties of the cured elastomer such as tensile strength, hardness and elongation.
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Claims (2)
1. A curable organosiloxane composition comprising the product obtained by mixing to homogeneity A. from 70 to 95 weight percent, based on the total weight of (A) and (B), of a first diorganovinylsiloxy terminated polydiorganosiloxane exhibiting a viscosity of from 20 to 200 Pa?s at 25°C. and containing essentially no ethylenically unsaturated hydrocarbon radicals bonded to non-terminal silicon atoms, B. from 5 to 30 weight percent, based on the total weight of (A) and (B), of a second diorganovinylsiloxy terminated polydiorganosiloxane that is miscible with said first polydiorganosiloxane and exhibits a viscosity of from 0.1 to 200 Pa s at 25°C., where from 1 to 5 percent of the non-terminal repeating units of said second diorganovinyl-siloxy-terminated polydiorganosiloxane contain a vinyl radical, C. an amount sufficient to cure said composition of an organohydrogensiloxane that is miscible with (A) and (B), and contains an average of more than two silicon-bonded hydrogen atoms per molecule, D. a platinum hydrosilation catalyst in an amount sufficient to promote curing of said composition at a temperature of from ambient to 250°C., and E. from 10 to 60 weight percent, based on the weight of said composition, of a treated reinforcing silica filler.
2. A composition according to claim 1 where said first diorganovinylsiloxy terminated polydiorganosiloxane (A) is represented by the average general formula ViR2SiO(R'2SiO)xSiR2Vi where Vi represents a vinyl radical, R and R' are individually monovalent hydrocarbon radicals or halogen substituted monovalent hydrocarbon radicals, and contain from 1 to 20 carbon atoms, R and R' are substantially free of ethylenic unsaturation, and x represents a degree of polymerization equivalent to a viscosity of from 20 to 200 Pa?s at 25°C., and said second diorganovinylsiloxy terminated polydiorgano-siloxane is represented by the average general formula ViR''2SiO(R'''2SiO)y(R'''ViSiO)zSiR''2Vi where Vi represents a vinyl radical and R'' and R''' are selected from the same group of monovalent hydrocarbon radicals and halogen substituted monovalent hydrocarbon radicals as R and R', the degree of polymerization represented by the sum of y and z is equivalent to a viscosity of from 0.1 to 200 Pa?s, and the ratio z/(y+z) is from 0.01 to 0.05.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US07/089,107 US4753978A (en) | 1987-08-25 | 1987-08-25 | Curable organosiloxane compositions |
| US89,107 | 1987-08-25 |
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| Publication Number | Publication Date |
|---|---|
| CA1326098C true CA1326098C (en) | 1994-01-11 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000573690A Expired - Fee Related CA1326098C (en) | 1987-08-25 | 1988-08-03 | Curable organosiloxane compositions |
Country Status (6)
| Country | Link |
|---|---|
| US (1) | US4753978A (en) |
| EP (1) | EP0305073B1 (en) |
| JP (1) | JPH0710952B2 (en) |
| AU (1) | AU597511B2 (en) |
| CA (1) | CA1326098C (en) |
| DE (1) | DE3851395T2 (en) |
Families Citing this family (56)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5876792A (en) * | 1988-03-14 | 1999-03-02 | Nextec Applications, Inc. | Methods and apparatus for controlled placement of a polymer composition into a web |
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-
1987
- 1987-08-25 US US07/089,107 patent/US4753978A/en not_active Expired - Lifetime
-
1988
- 1988-08-03 CA CA000573690A patent/CA1326098C/en not_active Expired - Fee Related
- 1988-08-08 DE DE3851395T patent/DE3851395T2/en not_active Expired - Lifetime
- 1988-08-08 EP EP88307310A patent/EP0305073B1/en not_active Expired - Lifetime
- 1988-08-24 JP JP63208470A patent/JPH0710952B2/en not_active Expired - Fee Related
- 1988-08-24 AU AU21446/88A patent/AU597511B2/en not_active Ceased
Also Published As
| Publication number | Publication date |
|---|---|
| EP0305073B1 (en) | 1994-09-07 |
| JPS6469660A (en) | 1989-03-15 |
| AU597511B2 (en) | 1990-05-31 |
| EP0305073A2 (en) | 1989-03-01 |
| DE3851395D1 (en) | 1994-10-13 |
| EP0305073A3 (en) | 1990-07-04 |
| US4753978A (en) | 1988-06-28 |
| DE3851395T2 (en) | 1995-04-27 |
| AU2144688A (en) | 1989-03-02 |
| JPH0710952B2 (en) | 1995-02-08 |
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Legal Events
| Date | Code | Title | Description |
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| MKLA | Lapsed |