CA2087777A1 - Heat cured elastomer compositions based on a vinyl functional resin, a single vinyl chain-stopped polymer, and vinyl-on-chain polymers - Google Patents
Heat cured elastomer compositions based on a vinyl functional resin, a single vinyl chain-stopped polymer, and vinyl-on-chain polymersInfo
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- CA2087777A1 CA2087777A1 CA 2087777 CA2087777A CA2087777A1 CA 2087777 A1 CA2087777 A1 CA 2087777A1 CA 2087777 CA2087777 CA 2087777 CA 2087777 A CA2087777 A CA 2087777A CA 2087777 A1 CA2087777 A1 CA 2087777A1
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Abstract
PATENTS
ABSTRACT OF THE DISCLOSURE
Heat curable elastomeric silicone rubber compositions are produced which, upon heat-curing, exhibit a tear strength of greater than 200, a compression set of less than 20%, good tensile strength, and good heat-age and oil resistance properties. A vinyl-on-chain siloxane gum is added to a blend comprising 1) a vinyl-stopped organo-polysiloxane gum, 2) a silica filler, 3) an MQ or M-D
vinyl-Q resin, or blends thereof, and 4) a cross-linking agent to produce a silicone elastomer which is heat curable in the presence of a peroxide catalyst.
ABSTRACT OF THE DISCLOSURE
Heat curable elastomeric silicone rubber compositions are produced which, upon heat-curing, exhibit a tear strength of greater than 200, a compression set of less than 20%, good tensile strength, and good heat-age and oil resistance properties. A vinyl-on-chain siloxane gum is added to a blend comprising 1) a vinyl-stopped organo-polysiloxane gum, 2) a silica filler, 3) an MQ or M-D
vinyl-Q resin, or blends thereof, and 4) a cross-linking agent to produce a silicone elastomer which is heat curable in the presence of a peroxide catalyst.
Description
2~87r~77 P~TENTS
60SI~14 IMPROVED HEAT CURBD ~LASTOMER COMPOSITIONS BASED ON A
VINYL FUNCTIONAL RESIN, A SINGLE VINYL CHAIN-STOPPED
POLY~ER, AND VINYL-ON-CHAIN POLYNERS
FIELD OF_THE INV~NTION
The present invention relates to heat cured ~ilicone elastomer compositions. ~ore particularly, the invention relates to heat cured silicone elastomer compositions haring the proper~ies of high tear strength, good tensile ~trength, low compra~sion set, good oil resistance, and good heat age resistance.
~he invention further relates to gaskets comprising the heat cured silicone elastomer compositions.
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6Qg~I-1489 ~ACRGROVND OF THE INVENT~ON
Heat curable silicone rubber compo~ition~ are known in the art. Such ~ompo~ition8 are known for their ability to resi~t change at elevated temperature and exposur~ to adver~e conditions over ext~nded period~ of time. As a result, thesQ composition~ have become attractivo for gasketing appl~cations. Efforts in the past have been made to produce he~t cured silicone elastomer compositions having good tear and tensile strength and reduced compres~ion set properti~s. A problem with such efforts, however, has bsen the sacrifice of satisfactory tear strength and - elongation characteristics while attemp~ing to improve compression set, oil and heat age rQsistance charac-teri~tics, and vice versa. A balance of these propsrties i8 necessary to provide a composition for gasketing applications in internal combustion engines.
U.S. Patent No. 3,671,480 to Wada et al. (Wada) discloses a heat curable ela~tomeric silicone composition having improved tear strQngth comprising a mixture of two vinyl-unsaturated polydiorgano-polysiloxanes, one of which appears to have a high molecular weight and the other o~ which appears ~o have ~:
60SI~14 IMPROVED HEAT CURBD ~LASTOMER COMPOSITIONS BASED ON A
VINYL FUNCTIONAL RESIN, A SINGLE VINYL CHAIN-STOPPED
POLY~ER, AND VINYL-ON-CHAIN POLYNERS
FIELD OF_THE INV~NTION
The present invention relates to heat cured ~ilicone elastomer compositions. ~ore particularly, the invention relates to heat cured silicone elastomer compositions haring the proper~ies of high tear strength, good tensile ~trength, low compra~sion set, good oil resistance, and good heat age resistance.
~he invention further relates to gaskets comprising the heat cured silicone elastomer compositions.
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- 2 - PATENq~S
6Qg~I-1489 ~ACRGROVND OF THE INVENT~ON
Heat curable silicone rubber compo~ition~ are known in the art. Such ~ompo~ition8 are known for their ability to resi~t change at elevated temperature and exposur~ to adver~e conditions over ext~nded period~ of time. As a result, thesQ composition~ have become attractivo for gasketing appl~cations. Efforts in the past have been made to produce he~t cured silicone elastomer compositions having good tear and tensile strength and reduced compres~ion set properti~s. A problem with such efforts, however, has bsen the sacrifice of satisfactory tear strength and - elongation characteristics while attemp~ing to improve compression set, oil and heat age rQsistance charac-teri~tics, and vice versa. A balance of these propsrties i8 necessary to provide a composition for gasketing applications in internal combustion engines.
U.S. Patent No. 3,671,480 to Wada et al. (Wada) discloses a heat curable ela~tomeric silicone composition having improved tear strQngth comprising a mixture of two vinyl-unsaturated polydiorgano-polysiloxanes, one of which appears to have a high molecular weight and the other o~ which appears ~o have ~:
3 2~7 7 7 7 60SI-I489 a low molecular weight. The -composition further comprises a polyorganohydrogensiloxane, a silica filler and a platinum compound. The examples in Wada report te~r strength values of about 50 kg~cm, i.e., about 2~0 pi. Compre~sion set values are not given.
U.S. Patent No. 3,652,475 to Wada et al. (Wada) disclose~ heat curable elastomeric silicone compo-sitions reportedly having high tear strength, good compre~sion set and resiliency. The compo~itions compri~e two vinyl-unsaturated polydiorgano-polysiloxane~ each having a degree of polymerization of at least 3000, a vinyl-unsaturated polydiorgano-~ polysiloxane having a degree o polymerization of from 10 to 1000, a silica filler, and an organic p~roxide catalyst. The samples prepared in the Wada exampleshad tear strength ~alues of about 40 kg/cm, i.e., about 225 pi.
U.S. Patent No. 4,539,357 ~obear '3573 discloses a heat-curable silicone composition comprising a vinyl-terminated linear diorganopolysiloxane gum having aviacosity in the range of ls106 to 20xlO' centipoise at 25C, a vinyl-containing diorganopolysiloxane gum having a viscosity of lxlOs to 20xlO' centipoise at 25C, a filler, a hydride-containing polysiloxane, and an organic peroxide or organic hydroperoxide curing agent. The composition ~ay further compri~e a ~inyl-containing organopolysiloxane resin copolymer. It i~
stated in Bobear '357 at column 6, l~ne~ 22-29 that there should be no vinyl-containing fluid in the compo~ition since it has been found that composition~
containing vinyl-containing fluid3 of a vi3cosi~y of 500,000 centipoi~Q or 1Q~8 r~ult in elastomers with good taar strength initially, but after the com~position _ 4 _ ~ PATENTS
~a~ i . 60sI l489 ha~ been sub~ected to po~t-cure, its tear ~trength propertie~ degrade dramatically. After post-cure, the Bobear '357 compo~ition ha~ a tear ~trength of above 200 pi.
~.S. Patent No. 4,061,609 to ~obear disclo~es a platinum catalyzed silicone rubber composition com-pri~ing a vinyl-containing polysiloxane or a blend of ~uch poly~iloxanes, platinum, and a hydrogen-containing polysiloxane. Preferably, the ~inyl-containing poly-siloxane has a visco~ity in the range of 1,000 to 300,000,000. A low vi~cosity vinyl-containing poly~iloxane may be added to the basic composition as _ a reinforcing agent to give the inal composition good~
phy~ical ~trength. Claim 4 in ~obear recite~ a first polysiloxane having a viscosity of l,000,000 to 200,000,000 centipoi~e at 25C and a second poly-~iloxane having a viscosity of S0,000 to 500,000 centipoi~e at 25C. The Bobear patent i~ directed to improving the work life of ~ one rubber compo-~itions. In the example~, tear strength value~ of greater than 200 pi were obtained, but the compo3itions having these values contained two high viscosity vinyl-cont~ining polysiloxa~ss ~ather than one high visco~ity vinyl-containing polysiloxane and one low visco~ity ~inyl-containing polysiloxane.
l~.S. Patent No. 3,660,345 to Bo~ear disclose~
organopolysiloxane compositions which are convertib}e to elastomers ha~ing high tear 3trength and resiliency.
The compo~ition~ comprise a two component bland of vinyl-containing organopoly~iloxane~, ~ilica filler, and a proceq~ aid which can be a methoxy-~erminated polysiloxane, a ~ilanol-terminated polydimethyl-siloxane, or h~xamethyldi~ilazane, for example. A
2 a 87 7 7 6PATE~TS
peroxide is used as the catalyst. The vi3c08ity of one of the two vinyl-containing organopoly~iloxane~ can be in the range of 1 to 1 billion centipoise at 25C, while the viscosity of the other can bo between 100,000 to 2,000,000,000 centipoise at 25C. The ~xamples in Bobear report tear ~trength values of greater than 200 pi .
~ .5. Patent No. 3,~96,068 to Creamer discloses heat-curable silicone gumstock composition~ having hi`qh die "B" tear strength as well a~ low compres~ion ~et values. The compositions comprisQ a vinyl-containing diorganopolysiloxane gum and a linear ~inyl-containing 1uid having a vi8cosity of from 10 to 150,000-centistokes at 25C. The cros~-linkable vinyl siloxane gum has a viscosity in Qxcess of 200,000 cQntistokes at ~5C. The Creamer composition is cured by a peroxide catalyst. Some of the ~amples prepared in Crezmer had tear strength valuRs in excess of 150 pi. Tear strength after post cure was not measured in any of the e~amples, which i8 significant since, as pointed out previously herein, it ha~ ~een found that tear ~trength drops dramatically after post cure in compositions containiny low viscosity vinyl-containing fluids.
U.S. Patent No. 3,884,866 to Jeram et al. (Jeram) discloses a high strength organopolysiloxane compo-sition ~uited for low pressure in~ection molding, comprising: (A) a component containing (i3 a vinyl-containing high viscos~ty organopolysiloxane having a viscosity of 5000 to 1,000,000 centipoise at 25C, (ii) a vinyl-containing }ow viscosity organopolysiloxane having a viscosity of S0 to 5000 centipoi~e at 25C, (iii) a filler, and (iv3 a pla~inum catalyst; and (~) - 6 - PArEN~S
æ~ g~ ~7 ~ 60S~ 9 a hydrogen siloxane co~position. Th~ highQst tear strength reported in the examples was 250 pi.
Although heat curable silicone rubber compositions having tear strength of greater than 250, reasonably good tensllQ strQngth and low compression ~e~
propQrties are known in the art, compositions ~or use in gasketing applications in combustion engines must also exhibit excellent heat age rQsistance and oil resistance over time. Compositions are also desired which are more easily processed, have more repe~table and consist~nt resultR, and have ~table propQrties.
These properties are also desirable in compositions uned for sQaling and vibration dampening. Thus, it i8 desirable to provide heat cured silicone Qlastomer compositions having the properties and durability that ~nable their use in gasketing, sealing and vibration dampening appl}cations.
SUMMARY OF THE INVENTION
The present invention is bas~d upon the discovery that a balance of propertie~ necessary for a compo-sition used in gasketing, sealing and vibration dampening applications can be achieved by adding a vinyl-stopped, vinyl-on-chain siloxane gum to a heat-curable gum/resin silicone ela~tomer.
According to the present invention, compositions can be produced which, upon heat-curing, exhibit a tear 3trength of between about 200 and about 300, a compres-~ion set of les~ than 20, good tensile strength, and good hsat-age and oil resistance propertiQs. The compositions are also easily proce~ed and produce repeatable and consistent results. A vinyl-on-chain siloxane gum, componen~ (D~, i8 added to a blend ~t~
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2 ~ 87 7 7 7 6pSI-1489 comp~ising (A) a vinyl-stopped organopolysiloxane gum, (B) an MQ or M D-vinyl Q resin or blends thereof, (C) a silica filler, and (G) an organohydrogensiloxane cross-linking agent. The mixture produces a silicone elastomer which is heat curable in the presQnce o~ a catalyst.
In one group of compositions, blends are formulated which comprise, by weight:
(A) 100 parts by weight of ~inyl-stopped diorganopolysiloxanQ having a viscosity of about 3 million to about 100 million CQntipoi8e (Cp8) at 25~C;
(B) up to 30 parts by weight based on Component (A) of (1) an organopolysiloxanQ resin copolymer. Tho rQsin copolymQr may contain R3SiO1~l monofunctiona~
llnit~ (M units) and SiO2 quadri-~unctional units ~Q
units), where each R is indepQndently selected ~rom the group consisting of vinyl radicals and mono~alent hydrocarbon radicals free of aliphatic unsaturation.
The ratio of M units to Q units ranges from about 0.5:1 to about 1.5:1, wherein the resin copolymer contains about 0.5 to 10.0 weight ~ vinyl groups. Alternatively, Component (B) may comprise (2) an organopolysiloxane re~in copolymer contain~ng ~ and Q units as a~oresaid and R2SiO2,2 difunctional (D units) where each R is independently ~elected from the group consisting of vinyl radicals and monovalent hydrocarbon radicals free of aiiphatic unsaturation. Each M unit may represent ~ or M' e.g. M-vinyl units, and each D
unit may represent D or D' e.g. D-~inyl units. The ratio of ~ units to Q units is from 0.5:1 to about 1.5:1 and the D unit are present in an amount of from about 1 to 70 mol percent based upon the total number of mols of siloxy units in the copolymer. The resinous ~ ~ ~ 7 7 7 7 PllTEl TS
copolymer contains from about 0.5 to about 10.0 weight p2rcent vinyl groups. The organopolysiloxane resin copolymer of Component (B) may contain mixture~ o~ the MQ and the M D-vinyl Q, resins.
(CJ up to about 200 parts based upon Component (A) of a finely divided silica filler;
(D) up to about 100 parts based upon Component (A) of a vinyl-~topped, vinyl-on-chain polymer having ~rom about 5xl o-5 to about 5 weight percent vinyl; and (G) a random copolymer ~ormed of a polydimethyl siloxanQ (PDMS) and a polymethyl hydrogan siloxanQ
(PMHS) having the form:
R3SiO(SiORHSiOR2)XSiR3 wherein each R is independently chosen from a hydrogen or monovalent hydrocarbon radical free of aliphatic unsaturation containing 1 to about 8 carbon atoms, and x ranges from about 2 to about 100. In the present invention, the hydride is present in an amount ranging from about 0.1 to 10 weigh~ percent of Component ~A), preferably 0.5 to 8, and more preferably 0.8 to 2.5 parts by weight. When a hydride agent is employed, a platinum catalyst may be substituted ~or the peroxide catalyst to cura the composition. In Component (G~ x may vary 80 that (G) has a viscosity ranging from about 5 to 500 cps, preferably from about 10 to about 100 cps and more preferably from about 10 to 50 cps at 25C.
In order to improve propertie3 or processing, the composition may also contain:
(E) up to about 2 parts by waight of a tetramethyl-divinyl silazane based upon 100 parts by weight of Component (A); and 2 9 8 7 ~ ~ 7 6 os I I 4 8 9 (F) up to abou~ 10 parts of a processing aid comprising low viscosity silanol stopped siloxane fluid of a about 3 to 500 centipoise at 2SC, or a dim~thyl trimethoxy siloxane polymer, or similar COmpQ~itions such as silanol or methoxy ~luids of other vi8co8itie8.
From 15 to 20 parcent of a cyclic methyl tetramer may be used to treat the filler prior to compounding.
A Rmall amount of water may also be added to incrQase the processibility of the blend. I~ used, only up to about 0.1 partR by weight water based on Component ~A) is usually employed.
In addition to the foregoing, a heat aging component such a~ fumed TiO2, iron octoate, Ce(OH)4, or-mixtures thQreof, may be presQnt in relatively small amounts, e.g., up to 2 part~ by weight based upon Component (A). In the examples below the heat aging component consists of 33 weight percent TiO2, 5 weight percent iron octoate solution (which comprises about 12 weight percent iron in mineral spirits), 1~ weight percent treated fumed silica (160 m2/gm), and 50 weight percent of an 800 penetration vinyl-stopped, vinyl-on-chain gum.
An acid acceptor, Component (I), may also be added to soak up acid. This acid could otherwise cause cleavage of th~ product matrix. In one embodLment, (I) comprises a masterbatch of about 25% MgO in a vinyl siloxane polymer.
The heat-curable compositions of the present invention provide heat cured silicone elastomers having high tear strength, good tensilQ strength, low compression set, and good heat-age and oil resistance.
This exc~llent balance of properties is exhibited - 10 - P~TENTS
2 0 ~ ~ 7 ~ 7 60SI-1489 throughout extended periods of use at high temperatures making these compositions extremely attractive for ga~keting, sealing and vibration dampening applications DES~RIPTION 5~rHE INVENTION
5The compositions of the present invention contain (A) a vinyl-stopped diorganosiloxane gum or gums having a viscosity of about 3 million to 100 million cps at 25C; (B) an oryanopolysiloxane resin of the MQ or N D-vinyl Q types: (C) a finely divided silica filler; (D) a vinyl-on-chain siloxane gum; and (G) an organohydrogensiloxane cross-linking agent.
Combinations of various other COmpOnQnts as dQscribad-horQin may also be added.
The vinyl-on-chain siloxane gum i8 add~d in an amount of up to about 100 parts by weight based on Component (A). The actual amount of Component (D) to be added varies depending upon the vinyl content in Component (D) and the amount of cross-linking dasired.
The amount of cros6-linking can closely control the properties exhibited by the cured product.
According to an embodLment of the present invention, the vinyl-on-chain polym~r is a diorganosiloxane gum h~ving a vinyl content of about 3 weight percent vinyl, or higher. Herein, thi~ typP of gum is referred to as a "very high vinyl-on-chain~' gum.
When using a very high vinyl-on-chain gum, about 0.1 to about 10 parts, preferably up to 4 parts by weight i8 added ba~ed on Component (A). One Example of a Yery high vinyl-on-chain gum is a siloxane g~m having 4.08 weight percent vinyl and being about 2500-3500 D units in length, herein designated Component (Dl).
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20 8~ 7 7 ~ 60SI-148g In another embodiment, a vinyl-on-chain gum is added which has a vinyl content of between about 0.1 and about 3 weight percent vinyl, herein ~eferred to as a "high vinyl-on-chain" gum. When using a high vinyl-on-chain gum, about 0.1 to about 10 parts by weight are added ba~ed upon Component (A). In the Examples below, Component (D2) i8 a high vinyl-on-chain gum having a vinyl content of about 0.6 weight percent.
In yet another embodLment, a "moderate vinyl-on-chain", vinyl-stopped gum is used, defined herein as containing from about 5x10-5 up to about l.0 weight percent vinyl. Nhen using a moderate vinyl-on-chain, -. vinyl chain-stoppQd gum, about 0.1 to about 100 parts~
by weight are added based on Component (A). In the Examples below, Component (D3) has a vinyl content of approximately 0.0~ weight percent.
The vinyl polymer or polymers of Component (D) contain vinyl-on-chain groups and vinyl and-groups. In preferred embodiments, Component (D) has the formula:
ViSiOR12 (SiORlRVl)~(SiOR22)y SiR12Vi Wherein Vi is vinyl, RVl i~ a vinyl radical having from 2 to about 10 carbon atoms, each R1 is indepen-dently chosen ~rom a vinyl radical having from 2 to about 10 carbon atoms, and a monovalent hydrocarbon free radical free of aliphatic unsaturation and containing 1 to about 8 carbon atoms, each R2 i8 independently chosen from a vinyl radical having from 2 to about lO carbon atoms, and a monovalent hydro-carbon free radical free of aliphatic unsaturation and containing 1 to about 8 carbon atoms, and x and y are integers, wherein x, y, RV~, R1 and R2 are chosen such - 12 - r PATEN~S
2~87 ~7 60SI-1489 that Component (D) has a weight percent vinyl concen-tration in the range from about 5x10-5 to about 5 weight percent, preferably from about 0.01 to about 4, and more preferably from about 0.05 to about 4. The S amount of Component (D) added to the blend may be increased whon the vinyl concentration of Component (D) i8 low, and a les~er amount of Component (D) may be added when its vinyl concentration i8 high. For example, when u~ing a vinyl-on-chain gum having a vinyl content of about 4 weight percent, only about 0.5 parts by weight based on Component (A) is added. When using a gum having a vinyl content of only about 0.6 weight percent, however, 5 part~ by weight are added based on Component (A).
The vinyl-on-chain units of Component (D) provide increasod cross-linking of the cured rubber and enhance those properties necessary for u3e in gasketing, sealing and vibration dampening applications.
The vinyl containing polymers of Component (D) can be made by a process well known in the art, for example, by reacting cyclotetrasiloxanes in the presence of low molecular weight, linear vinyl chain stopper3 at high temperatures in the presence of basic cataly~ts so as to yield a polymer of the de~ired molecular weight. When the reaction i~ over, the catalyst is neutralized and the excess cyclics are vented off to result in the desired polymer. By controll-ing the amount of chain stopper and the temperature of the reaction, the molecular weight of the desired vinyl-containing polymer end product can be controlled. For more d~tail~ of the process by which such vinyl containing polymers are produced, reference i8 made, for example, to U.S. Patent No. 3,660,345, - 13 ~ 2 PATENTS
which is incorRorated herein by reference. Component (D) i~ preferably a vinyl-on-chain diorganopolysiloxane or vinyl-on-chain diorganosiloxane blend.
Component (A) is a vinyl containing diorgano siloxanQ gum or blend of such gum5 having a viscosity from about 3,000,000 to about 100,000,000 cps at 25Co Preferably, the gum has a ~i8c08ity of betweQn about 7,000,000 and 84,000,000 cps, more preferably, about 13,000,000 cps at 25C. The gum i~ preferably vinyl-stopped and has substantially no vinyl-on-chain. The organo groups in the gum should all be monovalent hydrocarbon radicals. The gum may have a weight percent vinyl cQncQntration of from about sx10-5 to-about 1. The gum preferably has a weight percent vinyi concentration in the range from about 6.5x10-5 to about 0.03, more preferably from about 8x10-5 to about 1.5x10-~and more preferably yet from about 8x10-5 to about 1.2x10-'. The organo groups in the viny~ polymer or polymers of the gum should all be monovalent hydrocarbon radicals.
In a preferred embodiment, Component (A) has the structure:
ViSiORl2 ~ SiORl2 ) X ( SiOR22 ) y SiRl2Vi;
wherein Vi is vinyl and each Rl i8 independently chosen from monovalent hydrocarbon free radicals free of aliphatic unsaturation and containing 1 to about 8 carbon atom~; each R2 is independently chosen from monov~lent hydrocarbon radicals containing 1 to about 8 carbon atoms; and x and y are integers chG~en ~uch that the viscosity is about 3,000,000 to about 100,000,000 cps at 25. In other preferred ~ ' 2 ~ ~7 ~ ~ ~ 60SI-1489 embodiments, x and y are integers chosen such that Component (A) ha~ a vi~cosity which ranges from about 3,000,000 to about 85,000,000 cps at 25C and a weight percent vinyl concentration in the range from about 5x10-5 to about 2xlO-~, preferably from about 8x10-5 to about l.5xlO-~ and more preferably from about 8.0xlO-s to about 1.2xlO-'.
In accordance with tha invention, the amount of Component (A~ present in the ~inal product may vary.
However, for purposes of explanation herQin, it i8 a~sumed that 100 part3 by weight of the gum is combined with varying amounts of the other component~, and the amount of gum in the final product may thereby be inferred. In the Examples b~low, Component ~A) is a vinyl-stoppQd gum of about 6000 D units in length and has substantially no vinyl-on-chain.
Component (B) may be (1) an organopolysiloxane resin copoly~er in an appropriate ~olvent (e.g.
xylene). The resin copolymer may contain R3SiO1~2 monofunctional units (M units) and SiO2 quadri-functional units (Q units), where each R is indepen-dently selected from the group consisting of vinyl radicals and monovalent hydroc~rbon radicals free of aliphatic unsaturation. The ratio of M units to Q
units ranges from about 0.5:1 to about 1.5:1, wherein about 0.5 to 10.0 weight percent are vinyl groups.
Alternatively, Component (B) may co~p~ise (~) an organopolysiloxane resin copolymer containing M and Q
units as aforesaid and R2SiO2/2 difunctional (D or D
vinyl units), in an appropriate solvent, where each R
is independQntly selectQd from the group consisting of vinyl radicals and monovalent hydrocarbon radicals free of aliphatic un~aturation. The ratio of ~ units to Q
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units is from 0.5:1 to about 1.5:1 and the D or D vinyl units are present in an amount of from about 1 to 70 mol percent based upon the total number of mols of siloxy units in the copolymer. The resinous copolymer contains from about 0.5 to about 10.0 weight percent ~inyl groups. The organopolysiloxanQ resin copolymer of Component (B) may contain mixtures of the MQ and the M-D vinyl-Q, resins.
The organopolysiloxane rQsin copolymers of Component (~) in the present composition and their manufacture are well known in the art. Such rQsin~ are usually produced by hydrolysi~ o chlorosilanes in a - process dQscribQd in U.S. Patent No. 3,436,366 which is~
incorporated herQin by rQferQncQ.
Component (B) is presQnt in the composition of the present invention in an amount ranging from about 1.0 to about 30, preferably from 1.0 to 20 and more prefer-~bly from 4 to about 12 par~s by weight basQd on Component (A). Component (B) in the Examples below comprises (B2) dispersed in xylene. Much of the ~ylene has been vacuum stripped 80 as to result in a co~po-sition comprising 60% by waight solids and 40% by weight xylene.
The process for manufacturing the compositio~
includes a cook and strip step to facilitate the removal of the residual xylene from the finished compound.
Component (C) comprise~ from about 5 to about 200, preferably from about 10 to about 100 and more preferably from about 20 to about 50 parts by weight of reinforcing fillers such as SiO2 based on Component (A~. Examples of reinforcing fillers that may be used include fumed silica and precipitated silica, with - 16 - ~ PATENTS
~ 7 ~ ~ ~ 60SI-1489 fumed silica being preferred. The filler may be pre-treated or treated in-situ with various agents, for example cyclopolysiloxanes as disclosed in U.S. Patent No. 2,938,009 to Lucas and silazanes as disclosed in U.S. Patent No. 3,635,743 to Smith. The cyclopoly-siloxanes may be, for example, a cyclotetramethyl s~loxane present in the amount of about 15 to 20 weight percent of the filler. Preferred fumed silica fillers may have a ~urface area of ab~ut 100 m2/gm to about 300 m2/gm and pre~erably about 160 m2Jgm to about 240 m2/gm~
The higher surfacQ area ~iller~ tend to result in better properties, however, they are more expensiva than the lower surface area fillQrs and require surface`
trea~ments ox more processing aid to incorporate them into the gum. In the Examples below, the filler Component (C) comprises a fumed silica filler having a surface area of about 160 m2/gm and which has been pretreated with octamethyl cyclotetrasiloxane. Where Component (Cl) is used, the filler has a surface area of about 240 mZ/gm and has been pretreated with octamathyl cyclotetrasilo~ane.
Component (~) is a vinyl terminated silazane coupling agent and surface treatment for the filler which may take the form:
ViSiR2NHSiR2~i wherein R i8 an organic such as CH3. The coupling agent promotes bonding between Component~ tA) and (C) and between components (B~ and (C)~ and may be applied to the filler, Component (C), prior to mixing with the other components.
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Component (E) may be ~inyl stopped linear silazane such as tetramethyl-divinyl silazane. The material is added for enhancing the bonding of filler to polymer.
In the present inventionr the silazane also acts as a filler treatment in-situ.
Component (E) i~ preferably prQsent in an amount of up to about 2 percent, more preferably up to about 0.3 percent by weight based on the weight of Component (A). Component (E3 may be present in an amount of only 10 about 0.03 parts by weight based on 100 part~ of Component (A), however, ~lightly higher amounts are preferred.
- In addition to, in con~unction with, or in place of Component (E), small amounts o~ hexamethyl disilazane may be used to treat fumed silica filler prior to mixing the filler with the other components, or in-situ. If used, up to about 20 parts by weight of hexamethyl disilazane i8 added based on 100 parts filler.
Other components may also ba employed as di~cussed hereinafter. For example, in order to allow for easier incorporation of the filler in the gum, Component (F), a processing aid or plasticizer is employed. In the preferred embodiment, Component (F) is a low vi3c08ity silanol stopped siloxane fluid ha~ing a viscosity ranging from about 3-500 cps and preferably 3 to 50 Cp8 at 25C. The siloxane fluid i8 an equilibri~m mix of low molecular weight oligomers of about 4 to about 10 D units, preferably between 4 and 6 repeating units in length with a minimum amount of cyclics in equilibrium with the oligomer6. The procQssing aid ~F) may have the ~orm o~ ~R~SiOl,2)XOH where each R i~ CH3 and x i8 between 4 and 10, preferably between 4 and 6, with .. . . -~ 87 177 60 I-1482 resulting cyclics of the same number of ~nits in eguilibrium. Alkoxy terminated siloxanes such as trimethyoxy siloxane may also be used as process aids.
In the present invention, the proces~ing aid i8 present in amountQ between 2 and 10 weigh~ percent of Component (A) preferably between 2.5 and 5.0 parts by waight and most preferably about 3.5 parts by weight based on Component (A). It should be understood that typically the more filler that i8 used the greater amount of processing aid is employed. In the Examples below, Component (F) has a silanol content of about 7.5 ~ by weight although a silanol content of about 5 to about 10 weight percent i8 expected to provide good re~ult~.
In addition to the foregoing, Component (G) in the form of a hydride cross-linking agent may be employed.
In a preferred embodiment, Component (G3 may be a random copolymer formed of a polydimethyl siloxane (PDMS) and a polymethyl hydrogen siloxane (PMHS) having the form:
R3SiO(SiORHSiOR2)XSiR3 wherein Pach R is independently chosen from a hydrogen or monovalent hydrocarbon radical free of aliphatic unsaturation containing 1 to about B carbon atoms, and ~ ranges from about 2 to about 100. In the present invention, component (G) i8 pre~ent in an amount ranging from about 0.1 to 10 weight percent of Component (A), preferably 0.5 to 8, and more preferably 0.8 to 2.5 parts by weight. When a hydride agent is employed, a platinum catalyst may be substituted for the peroxide catalyst to cure the composition. In Component ~G~ x may vary so that (G) has a viscosity 9 ~ 7 PATENTS
ranging from about 5 to 500 Cp8, preferabl~ from about 10 to about 100 Cp8 and more preferably ~rom about 10 to 50 cps at 25C.
~he linear hydride described above can be made by many procedures which are known in the art and particu-larly by the hydrolysis of appropriate chlorosilanes.
See ~or example, U.S. Patent No. 4,041,101 which is incorporated herein by reference. In the Examples below, Component (G) has a viscosity of about 30 centistokes, a hydride content of about 0.8 percent by weight, and a chain length of about 100 units.
A small amount of water may also be added to - increase tha processibility of the blend. If used, only up to about 0.1 parts by weight water based on Component (A) is usually employed.
To improve the heat-age resistance of the cured compositions of the present invention, Component (H~, a heat-age additive, may be employed. The heat aging component such as fumed TiO2, iron octoate, Ce(OH)4, or mixtures thereof, may be present in relatively small amounts, e.g., up to 2 parts by weight based upon Component (A). In the examples below the heat aging component consists of 33 weight percent TiO2, 5 weight percent iron octoate (12% iron in mineral spirits~, 10 weight percent treated fumed silica (160 m2/gm), and 50 weight percent of an 800 penetration vinyl-stopped, vinyl-on-chain gum.
Only up to about two parts by weight Component (H) i~ needed based on Component (~) to Lmprove the heat-age characteristics of the compo~ition. In theExamples below, 0.8 parts by weight of Component (H) is used based on Component (A).
~.~
- 20 - 7 ~ ~ PATENTS
2 ~
Penetration i8 measured using Vniversal Penetrometer by Precision Scientific Model No. 73510 with a Yub~tantially air free sample. The sample penetration i8 measured at 25C~1C using a 100 gr weight and a 1/4" diameter by 3/16" needle foot with rounded edges. The needle is lowered until it ~ust touches the surface of the polymer. Then, the tLme to achieve up to 300 mm penetration is determined or the amount of penetration after 60 sec. Penetration gum i8 defined as:
D ~ trati~ X 60 sec. at 25C
Time Penetration may be controlled by controlling the molecular weight and th~ viscosity of the gum.
An acid acceptor, such as MgO or ZnO, Component (I), may also be added in amounts from 0.5 to about 10 parts by weight based on ~omponent A. This acid could otherwise causQ cleava~e of the product matrix. In the Examples below, 1.0 parts by weight of MgO masterbatch which comprises about 25% MgO in a methyl vinyl poly-siloxane is used for Component (I) based on Component (A).
Other components which may be added to the blends of the present invention include, but are not limited tos (~) a heat age additive comprising cexium hydroxide, preferably about 75% by weight~ master-batched in polydimethylsiloxane fluid having a viscosity of about 30,000 Cp8 at 25C.
In order to form a heat curable rubber, an organic peroxide, free radical initiator or curing catalyst is provided. The preferred peroxide curing agents are ~ ~
2 ~ 8 7 7 ~ ~ PATE~TS
thermal decomposition organic peroxides conveniently used to cure silicone elastomers. Examples of suitable organic peroxide free radical initiator8 for usa in the pre~ent invention are disclosed, for example, in U.S.
Patent No. 4,539,357 to ~obear which i~ incorporated herein by refQrence. Suitable peroxide catalysts include dialkyl peroxide such as di-tertiary-butyl peroxide, tertiary-butyl-triethylmethyl peroxide, di-tertiary-butyl-tertiary-triphenyl peroxide, k-butyl perbenzoate and a di-tertiary alkyl peroxide such a-q dicumyl peroxide. Under cQrtain conditions hereinaftQr dc~cribed, such a~ when a hydride is used, a platinum catalyst may be Qmployed in~tead as an initiator. In the examplQA below, tha preferred catalyst is a vinyl sp~cific catalyst such as 2,5 dimethyl-2,5-di(t-butyl peroxy) hexane Q.g., (Luper801 ~lOl).
Frequently used thermal decomposition catalysts activate within a temperature range of about 330F to about 390F.
Copending U.S. patent application serial no.
07/587,876, filed September 25, l990, attorney docket no. 60SI-1336, incorporated herein by reference, discloses heat curable silicone rubber compositions containing blends o~ vinyl containing organopoly-siloxane gums and oils, MQ and M-D vinyl-Q resins, filler and a proce~s aid axe cured with a peroxide initiator. The compositions are formulated for increased tear strength and reduced compressîon sat properties.
~ ' - ' .
- 22 - ~ 7 ~ PATENTS
EXAMPLES
The ~ollowing Exa~.ples ~hown below u~ed components mixed in variou~ proportion~ to produce heat curable siliconQ rubber compositions:
EXAMPLES I - Iy The Components (A) - (I) were mixed in various proportions to produce the compositions of Examples I-IV li~ted below in Table I. In each Example, Component~ A-G were mixed prior to adding Component~ H
and I. The component~ are expressed in parts by weight .
T~BLE I
Example Component I II III IV
A 88 88 85 89.5 Dl - - - 0.5 E 0.14 0.14 d.l4 0.14 F 3.5 3.5 3.5 3.5 G 1.4 1.4 1.4 1.4 Nater 0.1 0.1 0.1 0.1 H 0.8 0.8 0.8 0.8 I 1.0 1.0 1.0 1.0 - 2~7`~
Table~ IIa IIc bQ7 ow show thQ propertiE~EI of the cQmposit~on~ of Examples I-I~ aftQr f~r~t (Ila~, s~cond ~IIb) and third (IIc) cure~. All c~ condltion~ e with a peroxide catalyst . q~he camposi~t Qns of th~
5 E~mple~ were molded at 350 for 15 m~nu~e~ after a compound w~3t-in or aqing period of 3 days, 7 days and 23 days. The propertiQs of the composition~ a~ter 3 d~y8 are 3ho~m in Tabla IIa. T~e proper~3s aftE~r 7 dayu and 23 days are ~hown in Table~ IIb and IIC, 10 respectiYe7 y.
Test data were obtaine~ from the following ASTM methods and procedures: Shore A - 0-2240; Tensile, Elongation and modulus -D-412 (Die C); Tear - D-624 (D~e 3); and Compression Set - 0-3gS
(method B ) .
~ ~L
E~ample p~:~perty Shore A 50 49 51 50 Tensile, p~i 1953 2046 1285 ~545 2G Elon~ation, % 733 749 7g?
B, ppi 170 150 2S0 271~
Comp. Set, ~ 20 . 7 18 . 8 17 . 9 1~.6 ~antple 25 P~P~rty I r~ T~
Shore Sl 49 50 51 Tensile, p~i 1460 131U 1440 14~5 Elongation, ~ 796 789 8 01 B17 Te~r-B, ppi 276 276 249 270 30 Comp. Se~ % _ 17.7 17.9 17.4 ~-`
2 0 ~ ~ ~ 7 ~ P~TENT~
TABLE IIc Example ProPerty I II III IV
Shore - 48 49 51 Tensile, psi - 1401 1501 1~5 Elongation, % - 806 810 792 Tear-B, ppi - 255 257 297 Comp. Set, ~
Table IId below shows the change in the values of the properties of the compositions of Examples I-IV
after heat-aging for 168 hours at 350F per ASTM D573.
Repeated tQst re~ults appear in parenthesis ( ).
TABLE IId Example 15 Property I II III IV
Shore A ~5 +4 ~6 +6 (+5) (l6) (~6) Tensiler % -23.2 -10.7 -18.9 -26.9 (-4.2) (-20.9) ( 7.5) Elongation,% -15.1 -10.6 -16.4 -19.5 (-12.5~ ~-14.3) ~-10.7) ~ able IIe below shows the change in the ~alues of the properties of the compositions of Example I-IV
after immersion in AS~M #1 oil for 168 hour~ at 300F
per A3TM D471. Repeated test results appear in parQnthesis ~ ).
~77~
TABLE IIe Exam~le Property I II III IV
Shore A -3 -4 _3 _3 (-5) (-4) (-4) Tensile, ~ -28.3 -12.9 -23 -38 (-26.8) (-35.8) (-20j Elongation,% -14. 4 -6. 3 -14.2 -22 (-lg.l) (-28.5) (-14.8) Volume, ~ 4.5 4.8 4.9 ~.9 (4.9) (4.5) (5.4) Tablo IIf below shows the change in the value o~
properties of the composition of ExamplQs I-IV after immer~ion in ASTM #2 oil for 168 hours at 300F per 15 ASTM D471.
~A~LE I.If Exam~le Property I II III IV
Shore A -7 -8 -7 -6 Tensile, % -34.6 -22.1 -26.7 -17.0 Elongation,% -20.7 -16. 6 -20.5 -9.3 Volume, ~ 10.4 10.2 10.3 10.6 Table IIg below show~ the data obtained from individual test specimens for tear strength property, ~5 of the compo~itions of Examples I-IV, when tested per ASTM D624 B.
2~87777 - 26 - PATE~TS
TABLE IIq Property Example Tear B (ppi) I II III IV
Specimen 1 167 139 262 314 Specimen 2 170 147 240 ~76 Specimen 3 254 256 260 264 Specimen 4 2B7 274 249 254 Specimen 5 276 282 270 270 Specimen 6 252 276 242 281 Specimen 7 -- 298 257 297 Specimen 8 -- 253 212 296 Specimen 9 -- 256 265 307 The compositions of Examples II-IV exhibit enhanced properties which make them useful for many ga~keting and sealing applications. Although it may not be immediately apparent, due to the wide variation in data a~sociated with elastomer testing (particularly where ~ change in property tested i8 involved), the observed trend is an Lmprovement in compression 8et, tear strength consistency, heat age and oil im~ersion resi~tance when cross link density is increased by inclusion of Component ~D).
EXAMPLE~ V-XII
The Components ~A) - (I) were mixed in various proportions to produce the compositions of Examples V-XII listed below in Table III. The component~ are expressed in parts by weight. Componsnt (Cl) i8 a 2~7 7 ~ ~
tetramer treated fumed 6ilica filler similar to Component (C~ but has a surface area of 240 m2/gm.
co~Ronont ~aoDlo v VI vsI v~Ir IX X XI XII
A 85 BS 85 35 35 35 35 as c 29 - 29 - 29 - 29 Cl -29 - 29 - 29 - 29 ~tor .1 .1 .1 .1 .1 .1 .1 .1 15 ~ .8 .n .B .8 .8 .3 .8 .8 I 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 Examples V-VIII were mixed in a tangential blade doughmixer whereas Examples IX-XII were mixed in an overlapping, sigma blade doughmixer. ExEmples V, VI, IX and X were cooked for a period of one hour at 360F.
Examples VII, VIII, XI and XII were cooked for a period of four hours at 360F. Tables IVa and IVb below Qhow the median values of the properties of the compositions of Examples V-XII.
;2 5 DU~ IVa ProPorty ~x~Dlo V VI VII Vlll Ag~ in days 7 ~ 3 2 9boro A 51 51 52 53 Tsn~llo, p-i 1360 1~7 lU8 1~05 Uong~tlon, t 721 785 721 698 To~r-~3, ppi 23- 239 262 210 1000 ~oduluD, p~i 219 19~ 22~ 237 200- ~odulu, p~i 35~ 321 37~ 392 3001~ duluD, pDi 509 4~1 51~3 5~5 - 28 ~ 7 7 7 7 P~TENTS
60SI-1~489 TA~g IVb ProDortY ~xa~Pln IX X X~ XrI
Ago ln day- 7 ~ 3 2 9~ore A 51 52 52 52 T D - 11e~ P-1 1155 1603 1407 1552 Rlo~gntlon, t 803 010 725 792 T ~r-a, PP1 202 209 20~ 219 100~ ~OdU1U-, P-1 201 20a 22~ 216 1 0 200- ~cdUlu-~ p-l 333 3-0 372 352 300~ ~odulu-, p-l 459 ~65 50a ~a1 Tables Va and Vb below ~how the average ~alu~s of the properties o the compositions of Examples V-XII.
.. ~
15 PrO~rtY l~xanpl~
V V1 Vl~ y~I~
Ag- ln day- 7 ~ 3 2 abor~ A 51 51 52 53 S-n-llo, p-l 1359 1~3~ 1377 1396 2 0 Rlong-tlon, ~ 721 707 71- 631 T Ur-a, ppl 220 241 25~ 213 lOOt dulu-, p-l 219 193 219 237 200t dulu-, p-l 366 320 376 393 300~ Iodulu-, p~l 50a ~ 521 5~7 _~g.~
PropsrtY ~a~le IX X Xl XlY
Ag~ in d~y 7 3 2 8bOre A 51 52 52 52 Tenollo, p-l 14~3 1594 1419 1502 ~longatlon, ~ 793 815 7~D 795 Tbar-13, ppl 194 210 203 220 100~ ~odulue, p~l tOl 209 223 217 200~ ~odulu~, p~l 333 341 370 353 300~ loodulu-, pDl ~59 ~65 507 ~03 ~087~7 Tables VIa and YIb below show the change in the ~alues of the properties of the compositions of Example~ V-XII after heat aging for 168 hour~ at 350F
per ASTM D573.
~ABLE VIa Property Example V VI VII VIII
Shore A +5 ~5 +4 ~5 TQnsile -11.4 -10.0 -11.8 -4.2 % change Elongation -13.0 -13.4 -9.6 -9.5 % change TABLE VI~
ProPerty Example IX X XI XII
Shore A +5 +5 +4 +5 Tensile -17.2 -17.2 -17.4 -13.7 % change 210ngation -16.7 -15.0 -13.9 -13.6 % change Tables VIIa and VIIb below show the change in the values of the properties of the compositions of Examples V-XII after exposure to ASTM reference oil #l for 168 hour~ at 300~F per ASTM D47~.
3 o ~ 7 PATENTS
TABLE VIIa Property Example V VI VII VIII
Shore A -4 -4 -5 -3 Tensile -24.7 -16.4 -18.2 -19.2 ~ change Elongation -24.2 -19.2 -16.5 -24.3 ~ change Volume 4.8 5.1 4.9 5.2 % change TABLE VIIb Property Example IX X ~I XII
Shore A -5 4 -4 -4 Tensile -23.0 -20.2 -23.3 -21.0 % change Elongation -19.4 -15.8 -16.4 -16.7 ~ change Volume 4.6 4.8 5.0 4.9 ~ change rables VIIIa and VIIIb balow show the change in the values of the properties of the compositions of Ex~mples V-XII after expo~ure to ASTM reference oil #2 for 168 hours at 300nF per AST~ D471.
31 2~777 PATENTS
TABLE VIIIa Pro~erty Example V VI VII VIII
5hore A -7 -7 -7 -6 TensilQ -10.6 -8.8 -17.2 -11.4 ~ change Elongation -12.1 -I4.4 -13.6 -14.6 % change Volume 10.4 10.3 10.7 10.4 % change . .
TA~LE VIIIb Pro~erty Example IX X XI XII
Shore A -7 -7 -8 -7 15 Tensile -16~5 -17.2 -31.3 -11.3 % change Elongation -17.2 -14.5 -24.3 -12.2 % change ~olume 10.4 10.5 10.7 10.4 % change EXAMPLES XIII - XIV
The Components lA) ~ were mixed in ~arious proportions to produce the compositions of Examples XIII and XIV lis~ed below in Table IX~ In each :
2~8~
Example, Components A-G were mixed prior to adding Components H, I and ~. The components ar~ expressed in parts by weight.
TA~L~ IX
Example Component XIII XIV
A 87.0 89.5 B 10.0 10 10 Dl -- 0.5 D3 3.0 --E 0.14 0.14 F 3.5 3.5 G 1.4 1.4 15 ~ater C.l 0.1 O.S 0.5 I 1.0 1.0 0.5 0.5 Table X below shows the properties of the compo~ition3 of Example~ XIII and XIV.
, ' - 2~7~
3 3 _ PATENTS
TABLE X
Ex~mpl~
Property XIII XIV
Shore A 47 50 Tensile, psi 1677 1512 ~longation, % 892 787 Tear-B, ppi 183 145 Comp. Set t % 24.5 20.2 100~ modulu~, p8i 153 179 Specific Gravity 1.116 1.116 After 168 hour heat-aqe at 350~F
Shore A 53 56 Tensile, p8i 1417 1413 Elongation, ~ 816 748 Although the present invention has been described in connection with preferred embodiment~ J it will be appreciated by those skilled in the art that additions, modifications, ~ubstituents and deletion~ not specifically dQscribed may be made without departing from the spirit and scope of the invention defined in the appended claims.
U.S. Patent No. 3,652,475 to Wada et al. (Wada) disclose~ heat curable elastomeric silicone compo-sitions reportedly having high tear strength, good compre~sion set and resiliency. The compo~itions compri~e two vinyl-unsaturated polydiorgano-polysiloxane~ each having a degree of polymerization of at least 3000, a vinyl-unsaturated polydiorgano-~ polysiloxane having a degree o polymerization of from 10 to 1000, a silica filler, and an organic p~roxide catalyst. The samples prepared in the Wada exampleshad tear strength ~alues of about 40 kg/cm, i.e., about 225 pi.
U.S. Patent No. 4,539,357 ~obear '3573 discloses a heat-curable silicone composition comprising a vinyl-terminated linear diorganopolysiloxane gum having aviacosity in the range of ls106 to 20xlO' centipoise at 25C, a vinyl-containing diorganopolysiloxane gum having a viscosity of lxlOs to 20xlO' centipoise at 25C, a filler, a hydride-containing polysiloxane, and an organic peroxide or organic hydroperoxide curing agent. The composition ~ay further compri~e a ~inyl-containing organopolysiloxane resin copolymer. It i~
stated in Bobear '357 at column 6, l~ne~ 22-29 that there should be no vinyl-containing fluid in the compo~ition since it has been found that composition~
containing vinyl-containing fluid3 of a vi3cosi~y of 500,000 centipoi~Q or 1Q~8 r~ult in elastomers with good taar strength initially, but after the com~position _ 4 _ ~ PATENTS
~a~ i . 60sI l489 ha~ been sub~ected to po~t-cure, its tear ~trength propertie~ degrade dramatically. After post-cure, the Bobear '357 compo~ition ha~ a tear ~trength of above 200 pi.
~.S. Patent No. 4,061,609 to ~obear disclo~es a platinum catalyzed silicone rubber composition com-pri~ing a vinyl-containing polysiloxane or a blend of ~uch poly~iloxanes, platinum, and a hydrogen-containing polysiloxane. Preferably, the ~inyl-containing poly-siloxane has a visco~ity in the range of 1,000 to 300,000,000. A low vi~cosity vinyl-containing poly~iloxane may be added to the basic composition as _ a reinforcing agent to give the inal composition good~
phy~ical ~trength. Claim 4 in ~obear recite~ a first polysiloxane having a viscosity of l,000,000 to 200,000,000 centipoi~e at 25C and a second poly-~iloxane having a viscosity of S0,000 to 500,000 centipoi~e at 25C. The Bobear patent i~ directed to improving the work life of ~ one rubber compo-~itions. In the example~, tear strength value~ of greater than 200 pi were obtained, but the compo3itions having these values contained two high viscosity vinyl-cont~ining polysiloxa~ss ~ather than one high visco~ity vinyl-containing polysiloxane and one low visco~ity ~inyl-containing polysiloxane.
l~.S. Patent No. 3,660,345 to Bo~ear disclose~
organopolysiloxane compositions which are convertib}e to elastomers ha~ing high tear 3trength and resiliency.
The compo~ition~ comprise a two component bland of vinyl-containing organopoly~iloxane~, ~ilica filler, and a proceq~ aid which can be a methoxy-~erminated polysiloxane, a ~ilanol-terminated polydimethyl-siloxane, or h~xamethyldi~ilazane, for example. A
2 a 87 7 7 6PATE~TS
peroxide is used as the catalyst. The vi3c08ity of one of the two vinyl-containing organopoly~iloxane~ can be in the range of 1 to 1 billion centipoise at 25C, while the viscosity of the other can bo between 100,000 to 2,000,000,000 centipoise at 25C. The ~xamples in Bobear report tear ~trength values of greater than 200 pi .
~ .5. Patent No. 3,~96,068 to Creamer discloses heat-curable silicone gumstock composition~ having hi`qh die "B" tear strength as well a~ low compres~ion ~et values. The compositions comprisQ a vinyl-containing diorganopolysiloxane gum and a linear ~inyl-containing 1uid having a vi8cosity of from 10 to 150,000-centistokes at 25C. The cros~-linkable vinyl siloxane gum has a viscosity in Qxcess of 200,000 cQntistokes at ~5C. The Creamer composition is cured by a peroxide catalyst. Some of the ~amples prepared in Crezmer had tear strength valuRs in excess of 150 pi. Tear strength after post cure was not measured in any of the e~amples, which i8 significant since, as pointed out previously herein, it ha~ ~een found that tear ~trength drops dramatically after post cure in compositions containiny low viscosity vinyl-containing fluids.
U.S. Patent No. 3,884,866 to Jeram et al. (Jeram) discloses a high strength organopolysiloxane compo-sition ~uited for low pressure in~ection molding, comprising: (A) a component containing (i3 a vinyl-containing high viscos~ty organopolysiloxane having a viscosity of 5000 to 1,000,000 centipoise at 25C, (ii) a vinyl-containing }ow viscosity organopolysiloxane having a viscosity of S0 to 5000 centipoi~e at 25C, (iii) a filler, and (iv3 a pla~inum catalyst; and (~) - 6 - PArEN~S
æ~ g~ ~7 ~ 60S~ 9 a hydrogen siloxane co~position. Th~ highQst tear strength reported in the examples was 250 pi.
Although heat curable silicone rubber compositions having tear strength of greater than 250, reasonably good tensllQ strQngth and low compression ~e~
propQrties are known in the art, compositions ~or use in gasketing applications in combustion engines must also exhibit excellent heat age rQsistance and oil resistance over time. Compositions are also desired which are more easily processed, have more repe~table and consist~nt resultR, and have ~table propQrties.
These properties are also desirable in compositions uned for sQaling and vibration dampening. Thus, it i8 desirable to provide heat cured silicone Qlastomer compositions having the properties and durability that ~nable their use in gasketing, sealing and vibration dampening appl}cations.
SUMMARY OF THE INVENTION
The present invention is bas~d upon the discovery that a balance of propertie~ necessary for a compo-sition used in gasketing, sealing and vibration dampening applications can be achieved by adding a vinyl-stopped, vinyl-on-chain siloxane gum to a heat-curable gum/resin silicone ela~tomer.
According to the present invention, compositions can be produced which, upon heat-curing, exhibit a tear 3trength of between about 200 and about 300, a compres-~ion set of les~ than 20, good tensile strength, and good hsat-age and oil resistance propertiQs. The compositions are also easily proce~ed and produce repeatable and consistent results. A vinyl-on-chain siloxane gum, componen~ (D~, i8 added to a blend ~t~
'':
.
- 7 - P~TENTS
2 ~ 87 7 7 7 6pSI-1489 comp~ising (A) a vinyl-stopped organopolysiloxane gum, (B) an MQ or M D-vinyl Q resin or blends thereof, (C) a silica filler, and (G) an organohydrogensiloxane cross-linking agent. The mixture produces a silicone elastomer which is heat curable in the presQnce o~ a catalyst.
In one group of compositions, blends are formulated which comprise, by weight:
(A) 100 parts by weight of ~inyl-stopped diorganopolysiloxanQ having a viscosity of about 3 million to about 100 million CQntipoi8e (Cp8) at 25~C;
(B) up to 30 parts by weight based on Component (A) of (1) an organopolysiloxanQ resin copolymer. Tho rQsin copolymQr may contain R3SiO1~l monofunctiona~
llnit~ (M units) and SiO2 quadri-~unctional units ~Q
units), where each R is indepQndently selected ~rom the group consisting of vinyl radicals and mono~alent hydrocarbon radicals free of aliphatic unsaturation.
The ratio of M units to Q units ranges from about 0.5:1 to about 1.5:1, wherein the resin copolymer contains about 0.5 to 10.0 weight ~ vinyl groups. Alternatively, Component (B) may comprise (2) an organopolysiloxane re~in copolymer contain~ng ~ and Q units as a~oresaid and R2SiO2,2 difunctional (D units) where each R is independently ~elected from the group consisting of vinyl radicals and monovalent hydrocarbon radicals free of aiiphatic unsaturation. Each M unit may represent ~ or M' e.g. M-vinyl units, and each D
unit may represent D or D' e.g. D-~inyl units. The ratio of ~ units to Q units is from 0.5:1 to about 1.5:1 and the D unit are present in an amount of from about 1 to 70 mol percent based upon the total number of mols of siloxy units in the copolymer. The resinous ~ ~ ~ 7 7 7 7 PllTEl TS
copolymer contains from about 0.5 to about 10.0 weight p2rcent vinyl groups. The organopolysiloxane resin copolymer of Component (B) may contain mixture~ o~ the MQ and the M D-vinyl Q, resins.
(CJ up to about 200 parts based upon Component (A) of a finely divided silica filler;
(D) up to about 100 parts based upon Component (A) of a vinyl-~topped, vinyl-on-chain polymer having ~rom about 5xl o-5 to about 5 weight percent vinyl; and (G) a random copolymer ~ormed of a polydimethyl siloxanQ (PDMS) and a polymethyl hydrogan siloxanQ
(PMHS) having the form:
R3SiO(SiORHSiOR2)XSiR3 wherein each R is independently chosen from a hydrogen or monovalent hydrocarbon radical free of aliphatic unsaturation containing 1 to about 8 carbon atoms, and x ranges from about 2 to about 100. In the present invention, the hydride is present in an amount ranging from about 0.1 to 10 weigh~ percent of Component ~A), preferably 0.5 to 8, and more preferably 0.8 to 2.5 parts by weight. When a hydride agent is employed, a platinum catalyst may be substituted ~or the peroxide catalyst to cura the composition. In Component (G~ x may vary 80 that (G) has a viscosity ranging from about 5 to 500 cps, preferably from about 10 to about 100 cps and more preferably from about 10 to 50 cps at 25C.
In order to improve propertie3 or processing, the composition may also contain:
(E) up to about 2 parts by waight of a tetramethyl-divinyl silazane based upon 100 parts by weight of Component (A); and 2 9 8 7 ~ ~ 7 6 os I I 4 8 9 (F) up to abou~ 10 parts of a processing aid comprising low viscosity silanol stopped siloxane fluid of a about 3 to 500 centipoise at 2SC, or a dim~thyl trimethoxy siloxane polymer, or similar COmpQ~itions such as silanol or methoxy ~luids of other vi8co8itie8.
From 15 to 20 parcent of a cyclic methyl tetramer may be used to treat the filler prior to compounding.
A Rmall amount of water may also be added to incrQase the processibility of the blend. I~ used, only up to about 0.1 partR by weight water based on Component ~A) is usually employed.
In addition to the foregoing, a heat aging component such a~ fumed TiO2, iron octoate, Ce(OH)4, or-mixtures thQreof, may be presQnt in relatively small amounts, e.g., up to 2 part~ by weight based upon Component (A). In the examples below the heat aging component consists of 33 weight percent TiO2, 5 weight percent iron octoate solution (which comprises about 12 weight percent iron in mineral spirits), 1~ weight percent treated fumed silica (160 m2/gm), and 50 weight percent of an 800 penetration vinyl-stopped, vinyl-on-chain gum.
An acid acceptor, Component (I), may also be added to soak up acid. This acid could otherwise cause cleavage of th~ product matrix. In one embodLment, (I) comprises a masterbatch of about 25% MgO in a vinyl siloxane polymer.
The heat-curable compositions of the present invention provide heat cured silicone elastomers having high tear strength, good tensilQ strength, low compression set, and good heat-age and oil resistance.
This exc~llent balance of properties is exhibited - 10 - P~TENTS
2 0 ~ ~ 7 ~ 7 60SI-1489 throughout extended periods of use at high temperatures making these compositions extremely attractive for ga~keting, sealing and vibration dampening applications DES~RIPTION 5~rHE INVENTION
5The compositions of the present invention contain (A) a vinyl-stopped diorganosiloxane gum or gums having a viscosity of about 3 million to 100 million cps at 25C; (B) an oryanopolysiloxane resin of the MQ or N D-vinyl Q types: (C) a finely divided silica filler; (D) a vinyl-on-chain siloxane gum; and (G) an organohydrogensiloxane cross-linking agent.
Combinations of various other COmpOnQnts as dQscribad-horQin may also be added.
The vinyl-on-chain siloxane gum i8 add~d in an amount of up to about 100 parts by weight based on Component (A). The actual amount of Component (D) to be added varies depending upon the vinyl content in Component (D) and the amount of cross-linking dasired.
The amount of cros6-linking can closely control the properties exhibited by the cured product.
According to an embodLment of the present invention, the vinyl-on-chain polym~r is a diorganosiloxane gum h~ving a vinyl content of about 3 weight percent vinyl, or higher. Herein, thi~ typP of gum is referred to as a "very high vinyl-on-chain~' gum.
When using a very high vinyl-on-chain gum, about 0.1 to about 10 parts, preferably up to 4 parts by weight i8 added ba~ed on Component (A). One Example of a Yery high vinyl-on-chain gum is a siloxane g~m having 4.08 weight percent vinyl and being about 2500-3500 D units in length, herein designated Component (Dl).
- ll - PATENTS
20 8~ 7 7 ~ 60SI-148g In another embodiment, a vinyl-on-chain gum is added which has a vinyl content of between about 0.1 and about 3 weight percent vinyl, herein ~eferred to as a "high vinyl-on-chain" gum. When using a high vinyl-on-chain gum, about 0.1 to about 10 parts by weight are added ba~ed upon Component (A). In the Examples below, Component (D2) i8 a high vinyl-on-chain gum having a vinyl content of about 0.6 weight percent.
In yet another embodLment, a "moderate vinyl-on-chain", vinyl-stopped gum is used, defined herein as containing from about 5x10-5 up to about l.0 weight percent vinyl. Nhen using a moderate vinyl-on-chain, -. vinyl chain-stoppQd gum, about 0.1 to about 100 parts~
by weight are added based on Component (A). In the Examples below, Component (D3) has a vinyl content of approximately 0.0~ weight percent.
The vinyl polymer or polymers of Component (D) contain vinyl-on-chain groups and vinyl and-groups. In preferred embodiments, Component (D) has the formula:
ViSiOR12 (SiORlRVl)~(SiOR22)y SiR12Vi Wherein Vi is vinyl, RVl i~ a vinyl radical having from 2 to about 10 carbon atoms, each R1 is indepen-dently chosen ~rom a vinyl radical having from 2 to about 10 carbon atoms, and a monovalent hydrocarbon free radical free of aliphatic unsaturation and containing 1 to about 8 carbon atoms, each R2 i8 independently chosen from a vinyl radical having from 2 to about lO carbon atoms, and a monovalent hydro-carbon free radical free of aliphatic unsaturation and containing 1 to about 8 carbon atoms, and x and y are integers, wherein x, y, RV~, R1 and R2 are chosen such - 12 - r PATEN~S
2~87 ~7 60SI-1489 that Component (D) has a weight percent vinyl concen-tration in the range from about 5x10-5 to about 5 weight percent, preferably from about 0.01 to about 4, and more preferably from about 0.05 to about 4. The S amount of Component (D) added to the blend may be increased whon the vinyl concentration of Component (D) i8 low, and a les~er amount of Component (D) may be added when its vinyl concentration i8 high. For example, when u~ing a vinyl-on-chain gum having a vinyl content of about 4 weight percent, only about 0.5 parts by weight based on Component (A) is added. When using a gum having a vinyl content of only about 0.6 weight percent, however, 5 part~ by weight are added based on Component (A).
The vinyl-on-chain units of Component (D) provide increasod cross-linking of the cured rubber and enhance those properties necessary for u3e in gasketing, sealing and vibration dampening applications.
The vinyl containing polymers of Component (D) can be made by a process well known in the art, for example, by reacting cyclotetrasiloxanes in the presence of low molecular weight, linear vinyl chain stopper3 at high temperatures in the presence of basic cataly~ts so as to yield a polymer of the de~ired molecular weight. When the reaction i~ over, the catalyst is neutralized and the excess cyclics are vented off to result in the desired polymer. By controll-ing the amount of chain stopper and the temperature of the reaction, the molecular weight of the desired vinyl-containing polymer end product can be controlled. For more d~tail~ of the process by which such vinyl containing polymers are produced, reference i8 made, for example, to U.S. Patent No. 3,660,345, - 13 ~ 2 PATENTS
which is incorRorated herein by reference. Component (D) i~ preferably a vinyl-on-chain diorganopolysiloxane or vinyl-on-chain diorganosiloxane blend.
Component (A) is a vinyl containing diorgano siloxanQ gum or blend of such gum5 having a viscosity from about 3,000,000 to about 100,000,000 cps at 25Co Preferably, the gum has a ~i8c08ity of betweQn about 7,000,000 and 84,000,000 cps, more preferably, about 13,000,000 cps at 25C. The gum i~ preferably vinyl-stopped and has substantially no vinyl-on-chain. The organo groups in the gum should all be monovalent hydrocarbon radicals. The gum may have a weight percent vinyl cQncQntration of from about sx10-5 to-about 1. The gum preferably has a weight percent vinyi concentration in the range from about 6.5x10-5 to about 0.03, more preferably from about 8x10-5 to about 1.5x10-~and more preferably yet from about 8x10-5 to about 1.2x10-'. The organo groups in the viny~ polymer or polymers of the gum should all be monovalent hydrocarbon radicals.
In a preferred embodiment, Component (A) has the structure:
ViSiORl2 ~ SiORl2 ) X ( SiOR22 ) y SiRl2Vi;
wherein Vi is vinyl and each Rl i8 independently chosen from monovalent hydrocarbon free radicals free of aliphatic unsaturation and containing 1 to about 8 carbon atom~; each R2 is independently chosen from monov~lent hydrocarbon radicals containing 1 to about 8 carbon atoms; and x and y are integers chG~en ~uch that the viscosity is about 3,000,000 to about 100,000,000 cps at 25. In other preferred ~ ' 2 ~ ~7 ~ ~ ~ 60SI-1489 embodiments, x and y are integers chosen such that Component (A) ha~ a vi~cosity which ranges from about 3,000,000 to about 85,000,000 cps at 25C and a weight percent vinyl concentration in the range from about 5x10-5 to about 2xlO-~, preferably from about 8x10-5 to about l.5xlO-~ and more preferably from about 8.0xlO-s to about 1.2xlO-'.
In accordance with tha invention, the amount of Component (A~ present in the ~inal product may vary.
However, for purposes of explanation herQin, it i8 a~sumed that 100 part3 by weight of the gum is combined with varying amounts of the other component~, and the amount of gum in the final product may thereby be inferred. In the Examples b~low, Component ~A) is a vinyl-stoppQd gum of about 6000 D units in length and has substantially no vinyl-on-chain.
Component (B) may be (1) an organopolysiloxane resin copoly~er in an appropriate ~olvent (e.g.
xylene). The resin copolymer may contain R3SiO1~2 monofunctional units (M units) and SiO2 quadri-functional units (Q units), where each R is indepen-dently selected from the group consisting of vinyl radicals and monovalent hydroc~rbon radicals free of aliphatic unsaturation. The ratio of M units to Q
units ranges from about 0.5:1 to about 1.5:1, wherein about 0.5 to 10.0 weight percent are vinyl groups.
Alternatively, Component (B) may co~p~ise (~) an organopolysiloxane resin copolymer containing M and Q
units as aforesaid and R2SiO2/2 difunctional (D or D
vinyl units), in an appropriate solvent, where each R
is independQntly selectQd from the group consisting of vinyl radicals and monovalent hydrocarbon radicals free of aliphatic un~aturation. The ratio of ~ units to Q
`. .
`:
~ , ,.
units is from 0.5:1 to about 1.5:1 and the D or D vinyl units are present in an amount of from about 1 to 70 mol percent based upon the total number of mols of siloxy units in the copolymer. The resinous copolymer contains from about 0.5 to about 10.0 weight percent ~inyl groups. The organopolysiloxanQ resin copolymer of Component (B) may contain mixtures of the MQ and the M-D vinyl-Q, resins.
The organopolysiloxane rQsin copolymers of Component (~) in the present composition and their manufacture are well known in the art. Such rQsin~ are usually produced by hydrolysi~ o chlorosilanes in a - process dQscribQd in U.S. Patent No. 3,436,366 which is~
incorporated herQin by rQferQncQ.
Component (B) is presQnt in the composition of the present invention in an amount ranging from about 1.0 to about 30, preferably from 1.0 to 20 and more prefer-~bly from 4 to about 12 par~s by weight basQd on Component (A). Component (B) in the Examples below comprises (B2) dispersed in xylene. Much of the ~ylene has been vacuum stripped 80 as to result in a co~po-sition comprising 60% by waight solids and 40% by weight xylene.
The process for manufacturing the compositio~
includes a cook and strip step to facilitate the removal of the residual xylene from the finished compound.
Component (C) comprise~ from about 5 to about 200, preferably from about 10 to about 100 and more preferably from about 20 to about 50 parts by weight of reinforcing fillers such as SiO2 based on Component (A~. Examples of reinforcing fillers that may be used include fumed silica and precipitated silica, with - 16 - ~ PATENTS
~ 7 ~ ~ ~ 60SI-1489 fumed silica being preferred. The filler may be pre-treated or treated in-situ with various agents, for example cyclopolysiloxanes as disclosed in U.S. Patent No. 2,938,009 to Lucas and silazanes as disclosed in U.S. Patent No. 3,635,743 to Smith. The cyclopoly-siloxanes may be, for example, a cyclotetramethyl s~loxane present in the amount of about 15 to 20 weight percent of the filler. Preferred fumed silica fillers may have a ~urface area of ab~ut 100 m2/gm to about 300 m2/gm and pre~erably about 160 m2Jgm to about 240 m2/gm~
The higher surfacQ area ~iller~ tend to result in better properties, however, they are more expensiva than the lower surface area fillQrs and require surface`
trea~ments ox more processing aid to incorporate them into the gum. In the Examples below, the filler Component (C) comprises a fumed silica filler having a surface area of about 160 m2/gm and which has been pretreated with octamethyl cyclotetrasiloxane. Where Component (Cl) is used, the filler has a surface area of about 240 mZ/gm and has been pretreated with octamathyl cyclotetrasilo~ane.
Component (~) is a vinyl terminated silazane coupling agent and surface treatment for the filler which may take the form:
ViSiR2NHSiR2~i wherein R i8 an organic such as CH3. The coupling agent promotes bonding between Component~ tA) and (C) and between components (B~ and (C)~ and may be applied to the filler, Component (C), prior to mixing with the other components.
- 17 ~ 2 ~ 3 7 7 7 7 PATENTS
Component (E) may be ~inyl stopped linear silazane such as tetramethyl-divinyl silazane. The material is added for enhancing the bonding of filler to polymer.
In the present inventionr the silazane also acts as a filler treatment in-situ.
Component (E) i~ preferably prQsent in an amount of up to about 2 percent, more preferably up to about 0.3 percent by weight based on the weight of Component (A). Component (E3 may be present in an amount of only 10 about 0.03 parts by weight based on 100 part~ of Component (A), however, ~lightly higher amounts are preferred.
- In addition to, in con~unction with, or in place of Component (E), small amounts o~ hexamethyl disilazane may be used to treat fumed silica filler prior to mixing the filler with the other components, or in-situ. If used, up to about 20 parts by weight of hexamethyl disilazane i8 added based on 100 parts filler.
Other components may also ba employed as di~cussed hereinafter. For example, in order to allow for easier incorporation of the filler in the gum, Component (F), a processing aid or plasticizer is employed. In the preferred embodiment, Component (F) is a low vi3c08ity silanol stopped siloxane fluid ha~ing a viscosity ranging from about 3-500 cps and preferably 3 to 50 Cp8 at 25C. The siloxane fluid i8 an equilibri~m mix of low molecular weight oligomers of about 4 to about 10 D units, preferably between 4 and 6 repeating units in length with a minimum amount of cyclics in equilibrium with the oligomer6. The procQssing aid ~F) may have the ~orm o~ ~R~SiOl,2)XOH where each R i~ CH3 and x i8 between 4 and 10, preferably between 4 and 6, with .. . . -~ 87 177 60 I-1482 resulting cyclics of the same number of ~nits in eguilibrium. Alkoxy terminated siloxanes such as trimethyoxy siloxane may also be used as process aids.
In the present invention, the proces~ing aid i8 present in amountQ between 2 and 10 weigh~ percent of Component (A) preferably between 2.5 and 5.0 parts by waight and most preferably about 3.5 parts by weight based on Component (A). It should be understood that typically the more filler that i8 used the greater amount of processing aid is employed. In the Examples below, Component (F) has a silanol content of about 7.5 ~ by weight although a silanol content of about 5 to about 10 weight percent i8 expected to provide good re~ult~.
In addition to the foregoing, Component (G) in the form of a hydride cross-linking agent may be employed.
In a preferred embodiment, Component (G3 may be a random copolymer formed of a polydimethyl siloxane (PDMS) and a polymethyl hydrogen siloxane (PMHS) having the form:
R3SiO(SiORHSiOR2)XSiR3 wherein Pach R is independently chosen from a hydrogen or monovalent hydrocarbon radical free of aliphatic unsaturation containing 1 to about B carbon atoms, and ~ ranges from about 2 to about 100. In the present invention, component (G) i8 pre~ent in an amount ranging from about 0.1 to 10 weight percent of Component (A), preferably 0.5 to 8, and more preferably 0.8 to 2.5 parts by weight. When a hydride agent is employed, a platinum catalyst may be substituted for the peroxide catalyst to cure the composition. In Component ~G~ x may vary so that (G) has a viscosity 9 ~ 7 PATENTS
ranging from about 5 to 500 Cp8, preferabl~ from about 10 to about 100 Cp8 and more preferably ~rom about 10 to 50 cps at 25C.
~he linear hydride described above can be made by many procedures which are known in the art and particu-larly by the hydrolysis of appropriate chlorosilanes.
See ~or example, U.S. Patent No. 4,041,101 which is incorporated herein by reference. In the Examples below, Component (G) has a viscosity of about 30 centistokes, a hydride content of about 0.8 percent by weight, and a chain length of about 100 units.
A small amount of water may also be added to - increase tha processibility of the blend. If used, only up to about 0.1 parts by weight water based on Component (A) is usually employed.
To improve the heat-age resistance of the cured compositions of the present invention, Component (H~, a heat-age additive, may be employed. The heat aging component such as fumed TiO2, iron octoate, Ce(OH)4, or mixtures thereof, may be present in relatively small amounts, e.g., up to 2 parts by weight based upon Component (A). In the examples below the heat aging component consists of 33 weight percent TiO2, 5 weight percent iron octoate (12% iron in mineral spirits~, 10 weight percent treated fumed silica (160 m2/gm), and 50 weight percent of an 800 penetration vinyl-stopped, vinyl-on-chain gum.
Only up to about two parts by weight Component (H) i~ needed based on Component (~) to Lmprove the heat-age characteristics of the compo~ition. In theExamples below, 0.8 parts by weight of Component (H) is used based on Component (A).
~.~
- 20 - 7 ~ ~ PATENTS
2 ~
Penetration i8 measured using Vniversal Penetrometer by Precision Scientific Model No. 73510 with a Yub~tantially air free sample. The sample penetration i8 measured at 25C~1C using a 100 gr weight and a 1/4" diameter by 3/16" needle foot with rounded edges. The needle is lowered until it ~ust touches the surface of the polymer. Then, the tLme to achieve up to 300 mm penetration is determined or the amount of penetration after 60 sec. Penetration gum i8 defined as:
D ~ trati~ X 60 sec. at 25C
Time Penetration may be controlled by controlling the molecular weight and th~ viscosity of the gum.
An acid acceptor, such as MgO or ZnO, Component (I), may also be added in amounts from 0.5 to about 10 parts by weight based on ~omponent A. This acid could otherwise causQ cleava~e of the product matrix. In the Examples below, 1.0 parts by weight of MgO masterbatch which comprises about 25% MgO in a methyl vinyl poly-siloxane is used for Component (I) based on Component (A).
Other components which may be added to the blends of the present invention include, but are not limited tos (~) a heat age additive comprising cexium hydroxide, preferably about 75% by weight~ master-batched in polydimethylsiloxane fluid having a viscosity of about 30,000 Cp8 at 25C.
In order to form a heat curable rubber, an organic peroxide, free radical initiator or curing catalyst is provided. The preferred peroxide curing agents are ~ ~
2 ~ 8 7 7 ~ ~ PATE~TS
thermal decomposition organic peroxides conveniently used to cure silicone elastomers. Examples of suitable organic peroxide free radical initiator8 for usa in the pre~ent invention are disclosed, for example, in U.S.
Patent No. 4,539,357 to ~obear which i~ incorporated herein by refQrence. Suitable peroxide catalysts include dialkyl peroxide such as di-tertiary-butyl peroxide, tertiary-butyl-triethylmethyl peroxide, di-tertiary-butyl-tertiary-triphenyl peroxide, k-butyl perbenzoate and a di-tertiary alkyl peroxide such a-q dicumyl peroxide. Under cQrtain conditions hereinaftQr dc~cribed, such a~ when a hydride is used, a platinum catalyst may be Qmployed in~tead as an initiator. In the examplQA below, tha preferred catalyst is a vinyl sp~cific catalyst such as 2,5 dimethyl-2,5-di(t-butyl peroxy) hexane Q.g., (Luper801 ~lOl).
Frequently used thermal decomposition catalysts activate within a temperature range of about 330F to about 390F.
Copending U.S. patent application serial no.
07/587,876, filed September 25, l990, attorney docket no. 60SI-1336, incorporated herein by reference, discloses heat curable silicone rubber compositions containing blends o~ vinyl containing organopoly-siloxane gums and oils, MQ and M-D vinyl-Q resins, filler and a proce~s aid axe cured with a peroxide initiator. The compositions are formulated for increased tear strength and reduced compressîon sat properties.
~ ' - ' .
- 22 - ~ 7 ~ PATENTS
EXAMPLES
The ~ollowing Exa~.ples ~hown below u~ed components mixed in variou~ proportion~ to produce heat curable siliconQ rubber compositions:
EXAMPLES I - Iy The Components (A) - (I) were mixed in various proportions to produce the compositions of Examples I-IV li~ted below in Table I. In each Example, Component~ A-G were mixed prior to adding Component~ H
and I. The component~ are expressed in parts by weight .
T~BLE I
Example Component I II III IV
A 88 88 85 89.5 Dl - - - 0.5 E 0.14 0.14 d.l4 0.14 F 3.5 3.5 3.5 3.5 G 1.4 1.4 1.4 1.4 Nater 0.1 0.1 0.1 0.1 H 0.8 0.8 0.8 0.8 I 1.0 1.0 1.0 1.0 - 2~7`~
Table~ IIa IIc bQ7 ow show thQ propertiE~EI of the cQmposit~on~ of Examples I-I~ aftQr f~r~t (Ila~, s~cond ~IIb) and third (IIc) cure~. All c~ condltion~ e with a peroxide catalyst . q~he camposi~t Qns of th~
5 E~mple~ were molded at 350 for 15 m~nu~e~ after a compound w~3t-in or aqing period of 3 days, 7 days and 23 days. The propertiQs of the composition~ a~ter 3 d~y8 are 3ho~m in Tabla IIa. T~e proper~3s aftE~r 7 dayu and 23 days are ~hown in Table~ IIb and IIC, 10 respectiYe7 y.
Test data were obtaine~ from the following ASTM methods and procedures: Shore A - 0-2240; Tensile, Elongation and modulus -D-412 (Die C); Tear - D-624 (D~e 3); and Compression Set - 0-3gS
(method B ) .
~ ~L
E~ample p~:~perty Shore A 50 49 51 50 Tensile, p~i 1953 2046 1285 ~545 2G Elon~ation, % 733 749 7g?
B, ppi 170 150 2S0 271~
Comp. Set, ~ 20 . 7 18 . 8 17 . 9 1~.6 ~antple 25 P~P~rty I r~ T~
Shore Sl 49 50 51 Tensile, p~i 1460 131U 1440 14~5 Elongation, ~ 796 789 8 01 B17 Te~r-B, ppi 276 276 249 270 30 Comp. Se~ % _ 17.7 17.9 17.4 ~-`
2 0 ~ ~ ~ 7 ~ P~TENT~
TABLE IIc Example ProPerty I II III IV
Shore - 48 49 51 Tensile, psi - 1401 1501 1~5 Elongation, % - 806 810 792 Tear-B, ppi - 255 257 297 Comp. Set, ~
Table IId below shows the change in the values of the properties of the compositions of Examples I-IV
after heat-aging for 168 hours at 350F per ASTM D573.
Repeated tQst re~ults appear in parenthesis ( ).
TABLE IId Example 15 Property I II III IV
Shore A ~5 +4 ~6 +6 (+5) (l6) (~6) Tensiler % -23.2 -10.7 -18.9 -26.9 (-4.2) (-20.9) ( 7.5) Elongation,% -15.1 -10.6 -16.4 -19.5 (-12.5~ ~-14.3) ~-10.7) ~ able IIe below shows the change in the ~alues of the properties of the compositions of Example I-IV
after immersion in AS~M #1 oil for 168 hour~ at 300F
per A3TM D471. Repeated test results appear in parQnthesis ~ ).
~77~
TABLE IIe Exam~le Property I II III IV
Shore A -3 -4 _3 _3 (-5) (-4) (-4) Tensile, ~ -28.3 -12.9 -23 -38 (-26.8) (-35.8) (-20j Elongation,% -14. 4 -6. 3 -14.2 -22 (-lg.l) (-28.5) (-14.8) Volume, ~ 4.5 4.8 4.9 ~.9 (4.9) (4.5) (5.4) Tablo IIf below shows the change in the value o~
properties of the composition of ExamplQs I-IV after immer~ion in ASTM #2 oil for 168 hours at 300F per 15 ASTM D471.
~A~LE I.If Exam~le Property I II III IV
Shore A -7 -8 -7 -6 Tensile, % -34.6 -22.1 -26.7 -17.0 Elongation,% -20.7 -16. 6 -20.5 -9.3 Volume, ~ 10.4 10.2 10.3 10.6 Table IIg below show~ the data obtained from individual test specimens for tear strength property, ~5 of the compo~itions of Examples I-IV, when tested per ASTM D624 B.
2~87777 - 26 - PATE~TS
TABLE IIq Property Example Tear B (ppi) I II III IV
Specimen 1 167 139 262 314 Specimen 2 170 147 240 ~76 Specimen 3 254 256 260 264 Specimen 4 2B7 274 249 254 Specimen 5 276 282 270 270 Specimen 6 252 276 242 281 Specimen 7 -- 298 257 297 Specimen 8 -- 253 212 296 Specimen 9 -- 256 265 307 The compositions of Examples II-IV exhibit enhanced properties which make them useful for many ga~keting and sealing applications. Although it may not be immediately apparent, due to the wide variation in data a~sociated with elastomer testing (particularly where ~ change in property tested i8 involved), the observed trend is an Lmprovement in compression 8et, tear strength consistency, heat age and oil im~ersion resi~tance when cross link density is increased by inclusion of Component ~D).
EXAMPLE~ V-XII
The Components ~A) - (I) were mixed in various proportions to produce the compositions of Examples V-XII listed below in Table III. The component~ are expressed in parts by weight. Componsnt (Cl) i8 a 2~7 7 ~ ~
tetramer treated fumed 6ilica filler similar to Component (C~ but has a surface area of 240 m2/gm.
co~Ronont ~aoDlo v VI vsI v~Ir IX X XI XII
A 85 BS 85 35 35 35 35 as c 29 - 29 - 29 - 29 Cl -29 - 29 - 29 - 29 ~tor .1 .1 .1 .1 .1 .1 .1 .1 15 ~ .8 .n .B .8 .8 .3 .8 .8 I 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 Examples V-VIII were mixed in a tangential blade doughmixer whereas Examples IX-XII were mixed in an overlapping, sigma blade doughmixer. ExEmples V, VI, IX and X were cooked for a period of one hour at 360F.
Examples VII, VIII, XI and XII were cooked for a period of four hours at 360F. Tables IVa and IVb below Qhow the median values of the properties of the compositions of Examples V-XII.
;2 5 DU~ IVa ProPorty ~x~Dlo V VI VII Vlll Ag~ in days 7 ~ 3 2 9boro A 51 51 52 53 Tsn~llo, p-i 1360 1~7 lU8 1~05 Uong~tlon, t 721 785 721 698 To~r-~3, ppi 23- 239 262 210 1000 ~oduluD, p~i 219 19~ 22~ 237 200- ~odulu, p~i 35~ 321 37~ 392 3001~ duluD, pDi 509 4~1 51~3 5~5 - 28 ~ 7 7 7 7 P~TENTS
60SI-1~489 TA~g IVb ProDortY ~xa~Pln IX X X~ XrI
Ago ln day- 7 ~ 3 2 9~ore A 51 52 52 52 T D - 11e~ P-1 1155 1603 1407 1552 Rlo~gntlon, t 803 010 725 792 T ~r-a, PP1 202 209 20~ 219 100~ ~OdU1U-, P-1 201 20a 22~ 216 1 0 200- ~cdUlu-~ p-l 333 3-0 372 352 300~ ~odulu-, p-l 459 ~65 50a ~a1 Tables Va and Vb below ~how the average ~alu~s of the properties o the compositions of Examples V-XII.
.. ~
15 PrO~rtY l~xanpl~
V V1 Vl~ y~I~
Ag- ln day- 7 ~ 3 2 abor~ A 51 51 52 53 S-n-llo, p-l 1359 1~3~ 1377 1396 2 0 Rlong-tlon, ~ 721 707 71- 631 T Ur-a, ppl 220 241 25~ 213 lOOt dulu-, p-l 219 193 219 237 200t dulu-, p-l 366 320 376 393 300~ Iodulu-, p~l 50a ~ 521 5~7 _~g.~
PropsrtY ~a~le IX X Xl XlY
Ag~ in d~y 7 3 2 8bOre A 51 52 52 52 Tenollo, p-l 14~3 1594 1419 1502 ~longatlon, ~ 793 815 7~D 795 Tbar-13, ppl 194 210 203 220 100~ ~odulue, p~l tOl 209 223 217 200~ ~odulu~, p~l 333 341 370 353 300~ loodulu-, pDl ~59 ~65 507 ~03 ~087~7 Tables VIa and YIb below show the change in the ~alues of the properties of the compositions of Example~ V-XII after heat aging for 168 hour~ at 350F
per ASTM D573.
~ABLE VIa Property Example V VI VII VIII
Shore A +5 ~5 +4 ~5 TQnsile -11.4 -10.0 -11.8 -4.2 % change Elongation -13.0 -13.4 -9.6 -9.5 % change TABLE VI~
ProPerty Example IX X XI XII
Shore A +5 +5 +4 +5 Tensile -17.2 -17.2 -17.4 -13.7 % change 210ngation -16.7 -15.0 -13.9 -13.6 % change Tables VIIa and VIIb below show the change in the values of the properties of the compositions of Examples V-XII after exposure to ASTM reference oil #l for 168 hour~ at 300~F per ASTM D47~.
3 o ~ 7 PATENTS
TABLE VIIa Property Example V VI VII VIII
Shore A -4 -4 -5 -3 Tensile -24.7 -16.4 -18.2 -19.2 ~ change Elongation -24.2 -19.2 -16.5 -24.3 ~ change Volume 4.8 5.1 4.9 5.2 % change TABLE VIIb Property Example IX X ~I XII
Shore A -5 4 -4 -4 Tensile -23.0 -20.2 -23.3 -21.0 % change Elongation -19.4 -15.8 -16.4 -16.7 ~ change Volume 4.6 4.8 5.0 4.9 ~ change rables VIIIa and VIIIb balow show the change in the values of the properties of the compositions of Ex~mples V-XII after expo~ure to ASTM reference oil #2 for 168 hours at 300nF per AST~ D471.
31 2~777 PATENTS
TABLE VIIIa Pro~erty Example V VI VII VIII
5hore A -7 -7 -7 -6 TensilQ -10.6 -8.8 -17.2 -11.4 ~ change Elongation -12.1 -I4.4 -13.6 -14.6 % change Volume 10.4 10.3 10.7 10.4 % change . .
TA~LE VIIIb Pro~erty Example IX X XI XII
Shore A -7 -7 -8 -7 15 Tensile -16~5 -17.2 -31.3 -11.3 % change Elongation -17.2 -14.5 -24.3 -12.2 % change ~olume 10.4 10.5 10.7 10.4 % change EXAMPLES XIII - XIV
The Components lA) ~ were mixed in ~arious proportions to produce the compositions of Examples XIII and XIV lis~ed below in Table IX~ In each :
2~8~
Example, Components A-G were mixed prior to adding Components H, I and ~. The components ar~ expressed in parts by weight.
TA~L~ IX
Example Component XIII XIV
A 87.0 89.5 B 10.0 10 10 Dl -- 0.5 D3 3.0 --E 0.14 0.14 F 3.5 3.5 G 1.4 1.4 15 ~ater C.l 0.1 O.S 0.5 I 1.0 1.0 0.5 0.5 Table X below shows the properties of the compo~ition3 of Example~ XIII and XIV.
, ' - 2~7~
3 3 _ PATENTS
TABLE X
Ex~mpl~
Property XIII XIV
Shore A 47 50 Tensile, psi 1677 1512 ~longation, % 892 787 Tear-B, ppi 183 145 Comp. Set t % 24.5 20.2 100~ modulu~, p8i 153 179 Specific Gravity 1.116 1.116 After 168 hour heat-aqe at 350~F
Shore A 53 56 Tensile, p8i 1417 1413 Elongation, ~ 816 748 Although the present invention has been described in connection with preferred embodiment~ J it will be appreciated by those skilled in the art that additions, modifications, ~ubstituents and deletion~ not specifically dQscribed may be made without departing from the spirit and scope of the invention defined in the appended claims.
Claims (32)
1. A heat cured silicone rubber composition comprising in parts by weight:
(A) 100 parts by weight of a vinyl-stopped organopolysiloxane having a viscosity of about 3 million to about 100 million cps at 25°C;
(B) about 1 to about 30 parts by weight based upon Component (A) of an organopolysiloxane resin copolymer comprising:
1) R3SiO1/2 units (M units) and SiO2 units (Q
units) where each R is independently selected from the group consisting of vinyl radicals and monovalent hydrocarbon radicals free of aliphatic unsaturation with a ratio of M units to Q units ranging from 0.5:1 to about 1.5:1, where the copolymer contains from about 0.5 to 10 weight percent vinyl groups, or
(A) 100 parts by weight of a vinyl-stopped organopolysiloxane having a viscosity of about 3 million to about 100 million cps at 25°C;
(B) about 1 to about 30 parts by weight based upon Component (A) of an organopolysiloxane resin copolymer comprising:
1) R3SiO1/2 units (M units) and SiO2 units (Q
units) where each R is independently selected from the group consisting of vinyl radicals and monovalent hydrocarbon radicals free of aliphatic unsaturation with a ratio of M units to Q units ranging from 0.5:1 to about 1.5:1, where the copolymer contains from about 0.5 to 10 weight percent vinyl groups, or
2) R2SiO1/2 units (M units) and SiO2 units (Q
units) and RVi2SiO1/2 units (D vinyl units) where each R
is as defined above and each RVi is a vinyl containing radical having from 2 to about 10 carbon atoms, and where the ratio of M units to Q units is from 0.5:1 to about 1.5:1, and the D vinyl units are present up to about 70 mol percent based upon the total number of mols of siloxy units in the copolymer, and where the resinous copolymer contains from about 0.5 to about 10.0 weight percent vinyl groups, or
units) and RVi2SiO1/2 units (D vinyl units) where each R
is as defined above and each RVi is a vinyl containing radical having from 2 to about 10 carbon atoms, and where the ratio of M units to Q units is from 0.5:1 to about 1.5:1, and the D vinyl units are present up to about 70 mol percent based upon the total number of mols of siloxy units in the copolymer, and where the resinous copolymer contains from about 0.5 to about 10.0 weight percent vinyl groups, or
3) mixtures of 1 and 2;
(C) up to about 200 parts by weight based upon Component (A) of a finely divided filler;
(D) up to about 10 parts based upon Component (A) of a vinyl-on-chain polymer having a vinyl content of about 5 x 10-3 to about 5 weight percent, Component (D) increasing the amount of cross-linking within the heat cured silicone rubber composition; and (G) from about 0.1 to about 10 weight percent based on Component (A) of a hydride cross-linking agent.
2. The heat cured silicone rubber composition of claim 1, wherein Component (A) has the structure:
ViSiOR12 (SiOR12)x(SiOR22)y SiR12Vi;
wherein Vi is vinyl and each R1 is independently chosen from monovalent hydrocarbon free radicals free of aliphatic unsaturation and containing 1 to about 8 carbon atoms;
each R2 is independently chosen from monovalent hydrocarbon radicals containing 1 to about 8 carbon atoms, and x and y are integers chosen such that the viscosity is about 3,000,000 to about 100,000,000 cps at 25°.
3. The heat cured silicone rubber composition of claim 1, wherein Component (D) has the formula:
ViSiOR12 (SiOR1RVi)x(SiOR22)y SiR12Vi wherein Vi is vinyl, RVi is a vinyl radical having from 2 to about 10 carbon atoms,, each R1 is independently chosen from a vinyl radical having from 2 to about 10 carbon atoms, and a monovalent hydrocarbon free radicals free of aliphatic unsaturation and containing 1 to about 8 carbon atoms, each R2 is independently chosen from a vinyl radical having from 2 to about 10 carbon atoms, and a monovalent hydrocarbon free radicals free of aliphatic unsaturation and containing 1 to about 8 carbon atoms, and x and y are integers, wherein x, y, RVi, R1 and R2 are chosen such that Component (D) has a weight percent vinyl concentration in the range from about 0.001 to about 5 weight percent.
(C) up to about 200 parts by weight based upon Component (A) of a finely divided filler;
(D) up to about 10 parts based upon Component (A) of a vinyl-on-chain polymer having a vinyl content of about 5 x 10-3 to about 5 weight percent, Component (D) increasing the amount of cross-linking within the heat cured silicone rubber composition; and (G) from about 0.1 to about 10 weight percent based on Component (A) of a hydride cross-linking agent.
2. The heat cured silicone rubber composition of claim 1, wherein Component (A) has the structure:
ViSiOR12 (SiOR12)x(SiOR22)y SiR12Vi;
wherein Vi is vinyl and each R1 is independently chosen from monovalent hydrocarbon free radicals free of aliphatic unsaturation and containing 1 to about 8 carbon atoms;
each R2 is independently chosen from monovalent hydrocarbon radicals containing 1 to about 8 carbon atoms, and x and y are integers chosen such that the viscosity is about 3,000,000 to about 100,000,000 cps at 25°.
3. The heat cured silicone rubber composition of claim 1, wherein Component (D) has the formula:
ViSiOR12 (SiOR1RVi)x(SiOR22)y SiR12Vi wherein Vi is vinyl, RVi is a vinyl radical having from 2 to about 10 carbon atoms,, each R1 is independently chosen from a vinyl radical having from 2 to about 10 carbon atoms, and a monovalent hydrocarbon free radicals free of aliphatic unsaturation and containing 1 to about 8 carbon atoms, each R2 is independently chosen from a vinyl radical having from 2 to about 10 carbon atoms, and a monovalent hydrocarbon free radicals free of aliphatic unsaturation and containing 1 to about 8 carbon atoms, and x and y are integers, wherein x, y, RVi, R1 and R2 are chosen such that Component (D) has a weight percent vinyl concentration in the range from about 0.001 to about 5 weight percent.
4. The heat cured silicone rubber composition of claim 1, further comprising:
(E) up to about 2 parts by weight of a tatramethyl-divinyl silazane based on 100 parts by weight of Component (A).
(E) up to about 2 parts by weight of a tatramethyl-divinyl silazane based on 100 parts by weight of Component (A).
5. The heat cured silicone rubber composition of claim 1, further comprising:
(F) up to about 10 parts by weight based upon Component (A) of a silanol stopped siloxane fluid having a viscosity of about 3 to about 500 cps at 25°C.
(F) up to about 10 parts by weight based upon Component (A) of a silanol stopped siloxane fluid having a viscosity of about 3 to about 500 cps at 25°C.
6. The heat cured silicone rubber composition of claim 1, wherein said filler, Component (C), is treated with up to about 20 parts by weight, based on 100 parts by weight of Component (C), of cyclic ethyl tetramer.
7. The heat cured silicone rubber composition of claim 3, wherein Component (D) has a vinyl content of about 3 weight percent or higher and is present in an amount of between about 0.1 and about 10 parts by weight based on Component (A).
8. The heat cured silicone rubber composition of claim 3, wherein Component (D) has a vinyl content of between about 0.1 and about 3 weight percent and is present in an amount of between about 0.1 and about 10 parts by weight based on Component (A).
9. The heat cured silicone rubber composition of claim 3, wherein Component (D) has a vinyl content of about 0.001 and about 0.1 weight percent and is present in an amount of between about 0.1 and about 100 parts by weight based on Component (A).
10. The heat cured silicone rubber composition of claim 1, wherein Component (G), is an organohydrogensiloxane cross-linking agent having a hydride content of about 0.8 percent by weight.
11. The heat cured silicone rubber composition of claim 1, wherein Component (G) has the formula R3SiO(SiORHSiOR2)xSiR3 wherein each R is independently chosen from a hydrogen or monovalent hydrocarbon radical free of aliphatic unsaturation containing 1 to about 8 carbon atoms, and x varys 80 that (G) has a viscosity ranging from about 5 to 500 cps at 25°C.
12. The heat cured silicone rubber composition of claim 1, further comprising Component (H) up to about 2 parts by weight based upon Component (A) of a heat-age additive.
13. The heat cured silicone rubber composition of claim l, further comprising Component (I), up to about 10 parts based on Component (A) of an acid acceptor.
14. The heat cured silicone rubber composition of claim 1, wherein said rubber has a compression set of less than about 20.
15. The heat cured silicone rubber composition of claim l, wherein said rubber has a tear strength of at least 150 pi.
16. The heat cured silicone rubber composition of claim l, wherein said rubber has a tear strength of between about 150 and about 300 pi.
17. The heat cured silicone rubber composition of claim l, wherein the filler has a surface area of at least 100 m2/gm.
18. The heat cured silicone rubber composition of claim l, wherein the filler has a surface area of between about 160 and about 240 m2/gm.
19. The heat cured silicone rubber composition of claim 1, comprising 20 to 50 parts by weight based on Component (A) of Component (C).
20. The heat cured silicone rubber composition of claim 3, wherein Component (A) has the structure:
ViSiOR12 (SiOR12)x(SiOR22)y SiR12Vi;
wherein Vi is vinyl and each R1 is independently chosen from monovalent hydrocarbon free radicals free of aliphatic unsaturation and containing 1 to about 8 carbon atoms;
each R2 is independently chosen from monovalent hydrocarbon radicals containing 1 to about 8 carbon atoms, and x and y are integers chosen such that the viscosity is about 3,000,000 to about 100,000, 000 cps at 25°.
ViSiOR12 (SiOR12)x(SiOR22)y SiR12Vi;
wherein Vi is vinyl and each R1 is independently chosen from monovalent hydrocarbon free radicals free of aliphatic unsaturation and containing 1 to about 8 carbon atoms;
each R2 is independently chosen from monovalent hydrocarbon radicals containing 1 to about 8 carbon atoms, and x and y are integers chosen such that the viscosity is about 3,000,000 to about 100,000, 000 cps at 25°.
21. The heat cured silicone rubber composition of claim 20, wherein Component (D) has a vinyl content of about 3 weight percent or higher and is present in an amount of between about 0.1 and about 10 parts by weight based on Component (A).
22. The heat cured silicone rubber composition of claim 20, wherein Component (D) has a vinyl content of between about 0.1 and about 3 weight percent and is present in an amount of between about 0.1 and about 10 parts by weight based on Component (A).
23. The heat cured silicone rubber composition of claim 20, wherein Component (D) has a vinyl content of about 0.001 and about 0.1 weight percent and is present in an amount of between about 0.1 and about 100 parts by weight based on Component (A).
24. A heat cured silicone rubber gasket comprising in parts by weight:
(A) 100 parts by weight of a vinyl-stopped organopolysiloxane having a viscosity of about 3 million to about 100 million cps at 25°C;
(B) about 1 to about 30 parts by weight based upon Component (A) of an organopolysiloxane resin copolymer comprising 1) R3SiO1/2 units (M units) and SiO2 units (Q
units) where each R is independently selected from the group consisting of vinyl radicals and monovalent hydrocarbon radicals free of aliphatic unsaturation with a ratio of M units to Q units ranging from 0.5:1 to about 1.5:1, where the copolymer contains from about 0.5 to 10 weight percent vinyl groups, or 2) R3SiO1/2 units (M units) and SiO2 units (Q
units) and RVi2SiO2/2 units (D vinyl units) where each R
is as defined above and each RVi is a vinyl containing radical having from 2 to about 10 carbon atoms, and where the ratio of M units to Q units is from 0.5:1 to about 1.5:1, and the D vinyl units are present up to about 70 mol percent based upon the total number of mols of siloxy units in the copolymer, and where the resinous copolymer contains from about 0.5 to about 10.0 weight percent vinyl groups, or 3) mixtures of 1 and 2;
(C) up to about 200 parts by weight based upon Component (A) of a finely divided filler;
(D) up to about 10 parts based upon Component (A) of a vinyl-on-chain polymer having a vinyl content of about 0.001 to about 5 weight percent, Component (D) increasing the amount of cross-linking within the heat cured silicone rubber composition; and (G) from about 0.1 to about 10 weight percent based on Component (A) of a hydride cross-linking agent.
(A) 100 parts by weight of a vinyl-stopped organopolysiloxane having a viscosity of about 3 million to about 100 million cps at 25°C;
(B) about 1 to about 30 parts by weight based upon Component (A) of an organopolysiloxane resin copolymer comprising 1) R3SiO1/2 units (M units) and SiO2 units (Q
units) where each R is independently selected from the group consisting of vinyl radicals and monovalent hydrocarbon radicals free of aliphatic unsaturation with a ratio of M units to Q units ranging from 0.5:1 to about 1.5:1, where the copolymer contains from about 0.5 to 10 weight percent vinyl groups, or 2) R3SiO1/2 units (M units) and SiO2 units (Q
units) and RVi2SiO2/2 units (D vinyl units) where each R
is as defined above and each RVi is a vinyl containing radical having from 2 to about 10 carbon atoms, and where the ratio of M units to Q units is from 0.5:1 to about 1.5:1, and the D vinyl units are present up to about 70 mol percent based upon the total number of mols of siloxy units in the copolymer, and where the resinous copolymer contains from about 0.5 to about 10.0 weight percent vinyl groups, or 3) mixtures of 1 and 2;
(C) up to about 200 parts by weight based upon Component (A) of a finely divided filler;
(D) up to about 10 parts based upon Component (A) of a vinyl-on-chain polymer having a vinyl content of about 0.001 to about 5 weight percent, Component (D) increasing the amount of cross-linking within the heat cured silicone rubber composition; and (G) from about 0.1 to about 10 weight percent based on Component (A) of a hydride cross-linking agent.
25. The heat cured silicone rubber gasket of claim 24, wherein Component (A) has the structure:
ViSiOR12 (SiOR12)x(SiOR22)y SiR12Vi;
wherein Vi is vinyl and each R1 is independently chosen from monovalent hydrocarbon free radicals free of aliphatic unsaturation and containing 1 to about 8 carbon atoms;
each R2 is independently chosen from monovalent hydrocarbon radicals containing 1 to about 8 carbon atoms, and x and y are integers chosen such that the viscosity is about 3,000,000 to about 100,000,000 cps at 25°.
ViSiOR12 (SiOR12)x(SiOR22)y SiR12Vi;
wherein Vi is vinyl and each R1 is independently chosen from monovalent hydrocarbon free radicals free of aliphatic unsaturation and containing 1 to about 8 carbon atoms;
each R2 is independently chosen from monovalent hydrocarbon radicals containing 1 to about 8 carbon atoms, and x and y are integers chosen such that the viscosity is about 3,000,000 to about 100,000,000 cps at 25°.
26. The heat cured silicone rubber gasket of claim 24, wherein Component (D) has the formula:
ViSiOR12 (SiOR1RVi)x(SiOR22)y SiR12Vi wherein Vi is vinyl, RVi is a vinyl radical having from 2 to about 10 carbon atoms, each R1 is independently chosen from a vinyl radical having from 2 to about 10 carbon atoms, and a monovalent hydrocarbon free radicals free of aliphatic unsaturation and containing 1 to about 8 carbon atoms, each R2 is independently chosen from a vinyl radical having from 2 to about 10 carbon atoms, and a monovalent hydrocarbon free radicals free of aliphatic unsaturation and containing 1 to about 8 carbon atoms, and x and y are integers, wherein x, y, RVi, R1 and R2 are chosen such that Component (D) has a weight percent vinyl concentration in the range from about 0.001 to about 5 weight percent.
ViSiOR12 (SiOR1RVi)x(SiOR22)y SiR12Vi wherein Vi is vinyl, RVi is a vinyl radical having from 2 to about 10 carbon atoms, each R1 is independently chosen from a vinyl radical having from 2 to about 10 carbon atoms, and a monovalent hydrocarbon free radicals free of aliphatic unsaturation and containing 1 to about 8 carbon atoms, each R2 is independently chosen from a vinyl radical having from 2 to about 10 carbon atoms, and a monovalent hydrocarbon free radicals free of aliphatic unsaturation and containing 1 to about 8 carbon atoms, and x and y are integers, wherein x, y, RVi, R1 and R2 are chosen such that Component (D) has a weight percent vinyl concentration in the range from about 0.001 to about 5 weight percent.
27. The heat cured silicone rubber gasket of claim 24, further comprising:
(E) up to about 2 parts by weight of a tetramethyl-divinyl silazane based on 100 parts by weight of Component (A).
(E) up to about 2 parts by weight of a tetramethyl-divinyl silazane based on 100 parts by weight of Component (A).
28. The heat cured silicone rubber gasket of claim 24, further comprising:
(F) up to about 10 parts by weight based upon Component (A) of a silanol stopped siloxane fluid having a viscosity of about 3 to about 500 cps at 25°C.
(F) up to about 10 parts by weight based upon Component (A) of a silanol stopped siloxane fluid having a viscosity of about 3 to about 500 cps at 25°C.
29. The heat cured silicone rubber gasket of claim 26, wherein Component (D) has a vinyl content of about 3 weight percent or higher and is present in an amount of between about 0.1 and about one part by weight based on Component (A).
30. The heat cured silicone rubber gasket of claim 26, wherein Component (D) has a vinyl content of between about 0.1 and about 3 weight percent and is present in an amount of between about 0.1 and about 10 parts by weight based on Component (A).
31. The heat cured silicone rubber gasket of claim 26, wherein Component (D) has a vinyl content of about 0.001 and about 0.1 weight percent and is present in an amount of between about 0.1 and about 100 parts by weight based on Component (A).
32. The invention as defined in any of the preceding claims including any further features of novelty disclosed.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US84230992A | 1992-02-26 | 1992-02-26 | |
| US842,309 | 1992-02-26 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2087777A1 true CA2087777A1 (en) | 1993-08-27 |
Family
ID=25287028
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2087777 Abandoned CA2087777A1 (en) | 1992-02-26 | 1993-01-21 | Heat cured elastomer compositions based on a vinyl functional resin, a single vinyl chain-stopped polymer, and vinyl-on-chain polymers |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2087777A1 (en) |
-
1993
- 1993-01-21 CA CA 2087777 patent/CA2087777A1/en not_active Abandoned
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