Low compression set, oil and fuel resistant, liquid injection moldable, silicone rubber

Abstract: There is provided an organopolysiloxane composition having low compression set as well as fuel and oil resistance in addition to high strength, good elongation, and tear com­ prising: (A) 100 parts of a first component comprising: (1) a vinyl-containing liquid organopoly­ siloxane or a blend of vinyl-containing liquid polysiloxanes; (2) optionally, filler; and (3) a catalyst; and (B) from 1 to 100 parts, based on 100 parts of (A), of a hydrogen silicone composition selected from the class consisting of hydrogen containing silanes and hydrogen containing polysiloxanes and mixtures of hydrogen containing polysiloxanes with fillers and high viscosity polysiloxanes; (C) optionally, magnesium oxide to impart oil re­ sistance; (D) optionally, an MQ resin to impart fuel resis­ tance; and (E) optionally, a cerium containing compound or, al­ ternatively, tetramethyldivinyldisilazane to im­ part low compression set.

Description: The present invention relates to liquid injection moldable (LIM) silicone elastomers having low compression set and resistance to fuels and oil. This invention further relates to different catalyst systems used to effect final cure. More particularly, the present invention relates to an organopolysiloxane elastomer which is prepared through an SiH olefin addition reaction in the presence of a catalyst to result in an elastomer with high tensile strength, good elongation and high tear as well as the properties noted above. BACKGROUND OF THE INVENTION Silicone elastomers can be made from many different polyorganosiloxanes, cure mechanisms and fillers. These silicone elastomers have been made from stiff gum polymers as well as water thin fluids. The curing mechanisms have ranged from organic peroxides to moisture sensitive means to radiation. A variety of fillers have also been used, such as reinforcing silica fillers and extending fillers. Presently, silicone elastomeric compositions are usually prepared from a vinyl-containing polydiorganosiloxane, an organohydrogensilicone crosslinker, a platinum catalyst, and, optionally, fillers. The compositions of this type are desirable for many reasons. For instance, they cure without by-products; thus, there is no need for stripping or devolitilization. They can cure at room temperature or at elevated temperatures. They can be stabilized for storage at room temperature by utilization of a platinum catalyst inhibitor. And, they can be made from high and low viscosity polymers. These compositions utilize components that are low enough in viscosity that they are easily pumpable or extrudable as well as have a fast cure time. These compositions also provide cured silicone elastomers which are characterized by high strength and high durometer. These platinum catalyzed silicone elastomers are generally two package systems. One package generally contains the base polymer (which itself contains vinyl unsaturation) and the platinum catalyst. The other package generally contains the base polymer and the organohydrogensilicone. When the two packages are mixed together, the platinum catalyzes the addition of the organohydrogensilicone to the vinyl containing base polymer. Heat sensitive inhibitors are generally used to prevent the catalyst from polymerizing the composition at room temperature. Elevated temperatures are then employed to neutralize the inhibitor and allow the reaction to proceed. The problems with these silicone elastomers, however, is their relatively high compression set which has prevented such elastomers from being used in sealing applications where high temperature resiliency is an important factor. An example of this would include automotive gasketing and similar applications. The compression set of LIM silicone elastomers is generally well above that useful for applications such as gasketing. This problem with compression set stems from the LIM process itself. In order to decrease cycle times, molders will remove the elastomer from the mold prior to final cure. Therefore, in order to improve compression set, another step, post bake, is required where the elastomer is further crosslinked by heating. In addition, automotive gasket applications would also require the use of a gasket material that also has fuel and oil resistance as well as low compression set without any sacrifice of durometer or strength. Silicone elastomers, however, are not known for their fuel/oil resistance. Further, although platinum catalyzed addition reactions are possible at room temperature, inhibitors are often employed to stabilize the compositions until needed. These inhibitors are heat sensitive and are designed to be ineffective at elevated temperatures. Molders of these products, however, are requiring lower and lower reaction temperatures in their processes, requiring development of reaction mechanisms which are still stable at room temperature yet will react at only moderately elevated temperatures. Finally, molders also would like to see a one-part composition that requires no mixing of the catalyst and organohydrogensilicone crosslinker. Accordingly, it is highly desirable to have a silicone rubber composition which cures quickly, if desired, at elevated temperatures and would require no post baking as is traditional with heat vulcanizable silicone rubber compositions. It is also desirable to prepare a silicone rubber composition which can be injection molded. Most silicone rubber compositions and particularly heat vulcanizable silicone rubber compositions, because of their high viscosity, are very difficult to injection mold and require excessively high pressure such as, 276 mPa (40,000 psi) and even higher. In addition, such heat vulcanizable silicone rubber compositions are difficult to injection mold so as to form intricate parts. They require special molds that are to be used in the injection molding process as well as long times to cure at elevated temperatures. Heat vulcanisable silicone rubber compositions are known from DE-A-1185814, EP-A-0239961 and US-A4260536. US-A-4025485 discloses organopolysiloxane compositions comprising a dimethylpolysiloxane, an organohydrogenpolysiloxane, a silica filler, zinc carbonate, ceric oxide, and a platinum compound useful for producing electrically insulating materials and fire-resistant materials with excellent heat stability and flame retardancy. US-A-4108825 discloses flame retardant heat-curable silicone compositions containing ceric hydrate, useful for potting, encapsulating, molding and extrusion processes. EP-A-0234271 discloses compositions containing at least one liquid polydiorganosiloxane having an average of two ethylenically unsaturated hydrocarbon radicals per molecule, an organohydrogensiloxane curing agent, a platinum catalyst and a thermally conductive filler consisting, at least in part, of zinc and magnesium oxides are curable to yield elastomers. The high abrasion resistance, low durometer hardness and high heat conductivity of the elastomers make them particularly useful as coatings for the fuser rolls of electrostatic copiers. GB-A-2049717 discloses a silicone composition which is inhibited at room temperature, but which is capable of accelerated curing at elevated temperatures comprising a vinyl-containing polysiloxane, a hydride polysiloxane, a platinum catalyst, an inhibitor compound having at least one hydroperoxy radical and an organic peroxide accelerator compound having at least one --C--O--O--C-- peroxide group. Such compositions are suitable for extrusion and hot air vulcanization or for liquid injection molding. Accordingly, it is one object of the present invention to provide a liquid injection moldable (LIM), elastomeric silicone rubber composition which in the cured state has a combination of low compression set and resistance to fuel and oil as well as high tensile strength, high elongation, and high tear. It is further an object of this invention to provide an elastomeric silicone rubber composition which requires no post bake step. It is further an object of this invention to provide a one part LIM elastomeric composition. It is further an object of this invention to provide an elastomeric silicone rubber composition which cures at a temperature lower than is normally used to cure such compositions. These and other objects of the present invention are accomplished by means set forth hereinbelow. There is provided by the present invention an organopolysiloxane composition having low compression set as well as fuel and oil resistance in addition to high strength good elongation, and tear comprising: (A) 100 parts of a first component comprising: (1) a blend of vinyl-containing liquid polysiloxanes comprising (a) a high viscosity vinyl-containing organopolysiloxane having a viscosity of from 5000 to 1,000,000 mPa.s (centipoise) at 25°C; (b) a low viscosity vinyl-containing organopolysiloxane having a viscosity of from 50 to 5000 mpa.s (centipoise) at 25°C; (2) filler; and (3) a catalyst selected from a platinum catalyst, a peroxide catalyst or dual peroxide catalyst system comprising a high temperature peroxide and a low temperature peroxide, the high temperature peroxide being a peroxide having a ten hour half-life of greater than 110°C and the low temperature peroxide being a peroxide having a ten hour half-life of 100°C or below; (B) from 1 to 100 parts, based on 100 parts of (A), of a hydrogen silicone composition selected from hydrogen containing silanes and hydrogen containing polysiloxanes; (C) magnesium oxide; (E) cerium hydroxide or tetramethyldivinyldisilazane; and (D) (1) from 1 to 50 parts by weight of an organopolysiloxane resinous copolymer comprising R 3 7 SiO 0.5 monofunctional units and SiO 2 tetrafunctional units, the ratio of monofunctional to tetrafunctional units being from 0.5 to 1 to 1 to 1; or (2) from 20 to 50 parts by weight of an organopolysiloxane resinous copolymer comprising R 3 7 SiO 0.5 monofunctional units, SiO 2 tetrafunctional units, and R 2 7 SiO difunctional units, the ratio of monofunctional units to tetrafunctional units being from 0.5 to 1 to 1 to 1 and the difunctional units are present in an amount equal to 1 to 10 mole percent based on the total number of moles of siloxy units in the copolymer; wherein R 7 is selected from vinyl radicals and monovalent hydrocarbon radicals free of aliphatic unsaturation and wherein the resinous copolymer contains from 2.5 to 10 mole percent of vinyl groups. DETAILED DESCRIPTION OF THE INVENTION Component (A)(1), is a mixture of (a) high and (b) low viscosity vinyl-containing polysiloxanes. The high viscosity, vinyl containing polysiloxane, herein component (A)(1)(a), preferably has no more than 25 mole percent phenyl radicals and may be represented by the following formula: wherein Vi stands for vinyl, R 1 is selected from lower alkenyl, alkyl and aryl radicals and R is selected from monovalent hydrocarbon radicals and halogenated monovalent hydrocarbon radicals, R 2 is selected from alkyl, alkenyl, and aryl radicals, "a" varies from 100 to 10,000 and "b" varies from 0 to 300. Such a polymer is taught by Jeram et al. in U.S. Patent No. 3,884,866; Lee et al. in U.S. Patent No. 4,162,243; Jeram et al. in U.S. Patent No. 4,340,709; Tolentino in U.S. Patent No. 4,382,057; and Sweet in U.S. Patent No. 4,427,801. The low viscosity, vinyl containing organopolysiloxane, herein component (A)(1)(b), is an organopolysiloxane preferably having a vinyl content that may vary from 0.01 mole percent vinyl to 60 mole percent vinyl and having no more than 25 mole percent phenyl radicals. This polymer may be represented by the formula: wherein R, R 1 , and R 2 are as previously defined, R 3 is selected from alkyl, aryl and alkenyl radicals, "c" varies from 0 to 500 and "d" varies from 0 to 200. The organopolysiloxane blend preferably comprises 20 to 90 parts by weight of component (A). Such a polymer is taught by Jeram et al. in U.S. Patents No. 3,884,866 and 4,340,709, and in copending U.S. Patent Application No. 07/285,340, filed 12/19/88 and assigned to the same assignee as the present application. The filler, component (A)(2), is any reinforcing or extending filler known in the prior art. In order to get the high tensile strength, for example, a reinforcing filler is incorporated. Illustrative of the many reinforcing fillers which can be employed are titanium dioxide, lithopone, zinc oxide, zirconium silicate, silica aerogel, iron oxide, diatomaceous earth, calcium carbonate, fumed silica, silazane treated silica, precipitated silica, glass fibers, magnesium oxide, chromic oxide, zirconium oxide, aluminum oxide, alpha quartz, calcined clay, asbestos, carbon, graphite, cork, cotton and synthetic fibers. Preferably, the filler is either a fumed or precipitated silica that has been treated. The treating process may be done in accordance with the teachings of Evans et al. in U.S. Patent No. 4,529,774; Smith in U.S. Patent No. 3,635,743; and Beers in U.S. Patent No. 3,847,848. Alternatively, and most preferably, the filler is treated in-situ; that is the untreated silica filler and the treating agents are added to the silicone elastomer composition separately, and the treatment process is accomplished simultaneously with the mixture of the filler into the elastomer. This in-situ process is taught by Evans in U.S. Patent No. 4,529,774. The catalyst, component (A)(3), promotes the hydrosilation reaction between a silicon hydride and an ethylenically unsaturated polyorganosiloxane. Typically, component (A)(3) is a platinum catalyst. Such catalysts are well known in the art. Preferred catalysts are taught by Lamoreaux in U.S. Patents No. 3,917,432; 3,197,433; and 3,220,972; and by Karstedt in U.S. Patents No. 3,715,334 and 3,814,730; and by Ashby et al. in U.S. Patent No. 4,288,345. The use of platinum, however, necessitates a post bake step, because platinum does not decompose and will continue to crosslink as long as residual amounts of vinyl and silicon hydride exist in the elastomer. Alternatively, the catalyst, component (A)(3), may be a peroxide or it may be a combination of peroxides comprising a low temperature peroxide and a high temperature peroxide. In the molding of silicone LIM compositions, typical molding temperatures are usually about 204°C (400°F). Under such conditions a single peroxide catalyst may be used. However, molding cycle times necessary to achieve final cure in the mold are considered to be excessive. To decrease cycle times, therefore, molders will remove the composition from the mold prior to complete cure, necessitating a post bake step to achieve final cure. This post bake step is necessary because residual peroxide catalyst in the material will continue to catalyze the reaction until the peroxide catalyst has decomposed to non-catalytic products, as determined by the temperature "half-life" of the peroxide. Those skilled in the art are aware that different peroxides will decompose at different activation temperatures to catalyze a particular reaction. It is also known that the catalytic life of a peroxide is inversely proportional to the temperature to which the peroxide is exposed. As the temperature increases above its activation temperature, the catalytic lifespan of the peroxide will decrease. In order to decrease cycle times yet still be able to eliminate the post bake step, it has been found preferable to use a combination of peroxide catalysts comprising a high temperature peroxide catalyst and a low temperature peroxide catalyst. The function of the low temperature peroxide catalyst is to quickly catalyze the reaction at the molding temperature and allow the material to achieve a degree of crosslinking such that the material retains its shape after removal from the mold. Thus, the low temperature peroxide achieves partial crosslinking at the mold temperature in a very short period of time. The high temperature peroxide catalyst uses the residual heat of the silicone elastomer after it has been removed from the mold to continue crosslinking to final cure. Thus, since the material continues to crosslink at low temperatures, i.e. lower than molding temperatures, the post bake step becomes unnecessary. By the terms "low temperature peroxide" and "high temperature peroxide", reference is being drawn to the temperature half life of the peroxide. It is preferable that the high temperature peroxide have a ten hour half life at greater than 110°C. It is also preferable that the low temperature peroxide have a ten hour-half life at 110°C or less. It is more preferable that the high temperature peroxide have a ten hour half life at 115°C or greater and the low temperature peroxide have a ten hour half life at 100°C or less. It has been found that using a combination of a low and a high temperature peroxide catalyst imparts unusually low compression set values to the cured silicone elastomer without sacrifice of durometer, tensile, or elongation. It has also been found that molding temperatures may be decreased if the low temperature peroxide catalyst itself activates at lower temperatures. That is molding has been accomplished at a temperature as low as 177°C (350°F) while maintaining a low compression set. There is no reason that molding may not be accomplished at still lower temperatures as long as the proper high and low temperature peroxides are chosen. It is preferable that the peroxides chosen do not decompose into acids. Acid decomposition products have been found to adversely affect compression set. It has been found that 1,1-Bis(t-butyl peroxy)-3,3,3-trimethylcyclohexane works well as the low temperature peroxide catalyst. It has also been found that 2,5-dimethyl-2,5,-di(t-butyl peroxy) hexane works well as the high temperature peroxide catalyst. The determination of whether to use a precious metal catalyst or a peroxide catalyst is dependent upon the LIM process and the specifications of the molder. A precious metal catalyst has an advantage in that there are no by-products from the hydrosilation reaction between the vinyl containing polysiloxane, component (A)(1), and the silicon hydride, component B. The disadvantage to this type of system, though, necessitates the separation of either the vinyl containing polysiloxane or the silicon hydride from the catalyst in order to prevent premature polymerization. Since the components are separated, a molder must accomplish a mixing step immediately prior to use. The advantage of using a peroxide catalyst is that, since peroxides are heat activated, all the ingredients can be mixed together and stored at room temperature without polymerizing. Thus, peroxide catalytic systems may be used as one-part systems and molders need not worry about the mixing step necessary in precious metal catalytic systems. The disadvantage to using peroxides, however, is the fact that they decompose over time to products that may or may not be troublesome to a particular molder. The hydrogen silicone composition, component (B), may be a silane, but it is most advantageous to use a Si-H containing polysiloxane resin or polysiloxane linear polymer. Thus, in one embodiment of the present invention, the Si-H material of component (B) may be a polysiloxane resin containing monofunctional (M) siloxane units of the formula H(R 4 ) 2 Si) 1/2 and tetrafunctional (Q) siloxane units of the formula SiO 4/2 where the ratio of M units to Q units may vary from 10:1, and is preferably about 2:1. Also, R 4 is preferably a lower alkyl of from 1 to 8 carbon atoms such as methyl and ethyl. Another embodiment of the present invention utilizes an Si-H containing linear polysiloxane polymer represented by the formula: wherein R 5 is selected from hydrogen, monovalent hydrocarbon radicals, and halogenated monovalent hydrocarbon radicals; R 6 is selected from monovalent hydrocarbon radicals and halogenated monovalent hydrocarbon radicals; "e" varies from 1 to 1,000; and "f" varies from 5 to 200. More preferably, "e" varies from 10 to 500 and "f" varies from 5 to 200. Such a polymer is taught by Jeram et al. in U.S. Patent No. 3,884,866; Lee et al. in U.S. Patent No. 4,162,243; and Sweet in U.S. Patent No. 4,427,801. The magnesium oxide, component (C), is used to impart oil resistance to the elastomer. The magnesium oxide is preferably finely divided and is added in an amount up to 10 parts by weight per 100 parts components (A) and (B). More preferably, the amount will range from about 1 to about 8 parts by weight of component (A). The magnesium oxide should be added to the composition prior to curing the elastomer. It should be noted that, since magnesium oxide is a known filler, if added in amounts greater than 10 parts it will act more like a filler than an oil resistant additive. The MQ resin, component (D), imparts fuel resistance to the cured elastomer. Accordingly, there may be present in the composition per 100 parts of the base vinyl-containing diorganopolysiloxane gum blend from 1 to 50 parts by weight of an organopolysiloxane resinous copolymer having therein R 7 / 3SiO 0.5 monofunctional units and SiO 2 tetrafunctional units, where R 7 is a member selected from a class of vinyl radicals and monovalent hydrocarbon radicals free of aliphatic unsaturation where the ratio of monofunctional units to tetrafunctional units being from 0.5 to 1 to 1 to 1, and from where about 2.5 to 10 mole percent of the silicon atoms contain silicon bonded vinyl groups. The radical R 7 can also be any of the radicals given for the radical of R 1 in Formula (1). It should be noted further that this resin should not contain any hydride groups in it. There can also be utilized in the resin difunctional siloxy units. Accordingly, per 100 parts of components (A) and (B) there may be incorporated into the composition from 20 to 50 parts by weight of an organopolysiloxane resinous copolymer comprising R 7 / 3SiO 0.5 monofunctional units and SiO 2 tetrafunctional units and R 7 / 2SiO difunctional units, where R 7 is selected from vinyl radicals and monovalent hydrocarbon radicals free of aliphatic unsaturation where the ratio of monofunctional units to the tetrafunctional units is 0.5 to 1 to 1 to 1 and the difunctional units that are preferably present in amount equal to about 1 to 10 mole percent based on the total number of moles of siloxy units in the copolymer and wherein the resinous copolymer contains from about 2.5 to 10 mole percent of vinyl groups. Such a resinous copolymer can be present in the composition in the foregoing quantities indicated above, and more preferably, at the concentration of 5 to 25 parts by weight per 100 parts of the base vinyl-containing diorganopolysiloxane gum blend. It has been found such vinyl-containing resins produce good fuel resistance as well as good strength. Such resins are known and are produced by methods well known in the art and can be utilized within the prescribed above quantities with good results. Further, such resins are usually produced by hydrolysis of the appropriate chlorosilanes which method is well known in the art. For further information as to such resins, one is referred to the disclosure of Modic, U.S. Pat. No. 3,436,366. The cerium containing compound, component (E), imparts low compression set to the silicone LIM elastomer. Even though the use of a dual peroxide catalytic system (component (A)(3)) imparts low compression set, the use of magnesium oxide (component (C)) will adversely affect this and cause an increase in compression set. It has been found, however, that the use of magnesium oxide may be offset by using a cerium containing compound. It is theorized that cerium will complex with the silicone polymer, the filler, or both to improve the compression set of the silicone elastomer. What has been found to be particularly useful in this regard has been cerium hydroxide (Ce(OH) 4 ). In order to work, however, it is necessary for the cerium hydroxide to undergo a heating step in order to drive off water and allow the cerium to complex with the silicone. There is no limit to the amount of cerium hydroxide that may be added to impart low compression set. An excess will not negatively affect compression set values. It should be noted, however, that if added in amounts greater than 10 parts per 100 parts of components (A) and (8) the cerium hydroxide will act more like a filler than a low compression set additive. An alternative to using cerium hydroxide involves the use of tetramethyldivinyldisilazane to impart low compression set. In order to impart low compression set, there should be added from 0.1 to 10 parts by weight tetramethyldivinyldisilazane per 100 parts components (A) and (B). Preferably, there is added from 0.1 to 1 part by weight tetramethyldivinyldisilazane per 100 parts components (A) and (B). In order to demonstrate various features of this invention, the following examples are submitted. They are for illustrative purposes and are not intended to limit in any way the scope of this invention. A vinyl-containing liquid silicone polymer was prepared using the formulation of Table I. Formulation of Uncured Silicone Elastomer Parts Vinyl-containing polymer/resin blend 100 HMDZ treated fumed silica 20 Minusil R (5 µm (micron)) 10 In order to demonstrate the effect of a dual peroxide catalytic system on compression set, three examples were prepared according to the formulations of Table II (all amounts are in parts). The VCS component is the vinyl-containing silicone of Table I. Dual Peroxide Catalytic System EXAMPLES Component 1 2 3 VCS 100.0 100.0 100.0 Ce(OH) 4 0.5 0.5 0.5 Magnesium oxide 0.5 0.5 0.5 Si-H crosslinker 2.35 2.35 2.6 Low temp peroxide 0.5 0.4 0.4 High temp peroxide 0.0 0.1 0.1 The elastomers obtained from Examples 1 through 3 were each molded at 177°C (350°F) for twelve minutes. Table III summarizes the testing of physical properties of the elastomers after molding for each example. Physical Properties of Dual Peroxide Cure EXAMPLE Test 1 2 3 Monsanto Rheometer 3 minute Max 89.2 98.2 105.0 T-90 80.3 88.4 94.5 Time (seconds) 108.0 123.0 111.0 Shore A 60 62 62 Elong % 322 390 396 Tensile (psi) KPa (919) 6341 (1089) 7514 (1095) 7556 Tear (psi) KPa (256) 1766 (261) 1800 (273) 1801 100% Mod. 544 611 630 Compression Set 21 13 15 EXAMPLES 4-7 In order to demonstrate the effect of magnesium oxide on oil resistance, MDQ resin on fuel resistance, and cerium and tetramethyldivinyldisilazane (TMDVDS) on compression set, three silicone LIM formulations were prepared as Examples 4, 5, and 6. The formulations for each example are summarized in Table IV (all amounts are in parts). Formulations of Examples 4 - 6 EXAMPLE Component 4 5 6 Vinyl polymer (low vis) 70.5 57.7 57.7 MDQ resin 0.0 19.2 19.2 Fumed silica (HMDZ) 0.0 15.4 15.4 Fumed silica (D 4 ) 27.0 0.0 0.0 Ce(OH) 4 0.0 0.0 0.5 Magnesium oxide 0.0 0.5 0.5 Si-H crosslinker 2.8 2.3 2.3 TMDVDS 0.0 0.3 0.0 Platinum catalyst 15ppm 15ppm 15ppm Inhibitor 0.4 800ppm 800ppm HMDZ 6.0 1.97 0.0 Water 3.0 0.5 0.0 Vi(EtO) 3 Si 1.0 0.0 0.0 Extending filler 0.0 7.7 7.7 Normally liquid injection compounds are two component materials sold as a 1/1 A/B mix ratio product. The above formulations of Examples 4, 5, and 6 show the total final composition when A + B parts are mixed together. Example 4 represents a standard silicone LIM compound. It was molded at 204°C (400°F) and cured for 12 minutes followed by a 4 hour post bake. Table V summarizes the physical properties for Example 5 after each step. Physical Testin of Standard LIM (Example 4) 12 min. PB - 4 hrs Shore A 47 50 Elong, % 584 522 Tensile, (psi) KPa (1210) 8349 (1184) 8170 Tear, (psi) KPa (247) 1704 (260) 1794 Compression set 75 22 Examples 5 and 6 were likewise molded at 204°C (400°F) for twelve minutes. No post bake was done. The results of the physical property testing is summarized in Table VI. Physical Testing of Examples 5 and 6 EXAMPLE Test 5 6 Shore A 56 54 Elong % 649 625 Tensile (psi) KPa (1128) 7783 (1130) 7797 Tear, (psi) KPa (205) 1415 (223) 1539 Compression Set 22 18 After curing the elastomers of Examples 4, 5 and 6, each was then immersed for 168 hours and 149°C (300°F) in #1 oil, #2 oil, and #3 oil. After removal from the oils, the physical properties were then tested. Tables VII, VIII, and IX summarize the changes in physical properties for each of the examples. Changes in Physical Properties After Immersion in #1 Oil EXAMPLE Test 4 5 6 Shore A (change) -18.0 - 5.0 - 2.0 Elong (% change) -83.0 -39.0 -36.0 Tensile (% change) -84.0 -38.0 -32.0 % volume swell + 5.6 + 7.0 + 5.0 Changes in Physical Properties After Immersion in #2 Oil EXAMPLE Test 4 5 6 Shore A (change) -20.0 - 7.0 - 5.0 Elong (% change) -31.0 -33.0 -15.0 Tensile (% change) -23.0 -34.0 -17.0 % volume swell +54.0 +13.0 + 9.0 Changes in Physical Properties After Immersion in #3 Oil EXAMPLE Test 4 5 6 Shore A (change) material -12.0 -18.0 Elong (% change) too weak -78.0 -84.0 Tensile (% change) to obtain -82.0 -81.0 % volume swell readings +37.0 +37.0 In addition, each of the cured elastomers in Examples 4, 5 and 6 was then immersed for 48 hours at room temperature in gasohol and in fuel C. After removal from the fuels, the physical properties were then tested. Tables X and XI summarize the changes in physical properties for each of the examples in each of the fuels. Changes in Physical Properties After Immersion in Gasohol EXAMPLE Test 4 5 6 Shore A (change) - 16.0 - 18.0 - 14.0 Elong (% change) - 82.0 - 86.0 - 82.0 Tensile (% change) - 68.0 - 73.0 - 66.0 % volume swell +190.0 +167.0 +157.0 Changes in Physical Properties After Immersion in Fuel C EXAMPLE Test 4 5 6 Shore A (change) - 17.0 - 15.0 - 12.0 Elong (% change) - 85.0 - 83.0 - 81.0 Tensile (% change) - 65.0 - 64.0 - 59.0 % volume swell +237.0 +180.0 +172.0 As can be seen from the above data, standard methyl silicone LIMS, represented by Example 4, have poor oil and fuel resistance and require post bake in order to obtain good compression set.

Claims: A liquid, injection moldable silicone composition comprising: (A) 100 parts of a first component comprising: (1) a blend of vinyl-containing liquid polysiloxanes comprising: (a) a high viscosity vinyl-containing organopolysiloxane having a viscosity of from 5000 to 1,000,000 mPa.s (centipoise) at 25°C; (b) a low viscosity vinyl-containing organopolysiloxane having a viscosity of from 50 to 5000 mpa.s (centipoise) at 25°C; (2) filler; and (3) a catalyst selected from a platinum catalyst, a peroxide catalyst or dual peroxide catalyst system comprising a high temperature peroxide and a low temperature peroxide, the high temperature peroxide being a peroxide having a ten hour half-life of greater than 110°C and the low temperature peroxide being a peroxide having a ten hour half-life of 100°C or below; (B) from 1 to 100 parts, based on 100 parts of (A), of a hydrogen silicone composition selected from hydrogen containing silanes and hydrogen containing polysiloxanes; (C) magnesium oxide; (E) cerium hydroxide or tetramethyldivinyldisilazane; and (D) (1) from 1 to 50 parts by weight of an organopolysiloxane resinous copolymer comprising R 3 7 SiO 0.5 monofunctional units and SiO 2 tetrafunctional units, the ratio of monofunctional to tetrafunctional units being from 0.5 to 1 to 1 to 1; or (2) from 20 to 50 parts by weight of an organopolysiloxane resinous copolymer comprising R 3 7 SiO 0.5 monofunctional units, SiO 2 tetrafunctional units, and R 2 7 SiO difunctional units, the ratio of monofunctional units to tetrafunctional units being from 0.5 to 1 to 1 to 1 and the difunctional units are present in an amount equal to 1 to 10 mole percent based on the total number of moles of siloxy units in the copolymer; wherein R 7 is selected from vinyl radicals and monovalent hydrocarbon radicals free of aliphatic unsaturation and wherein the resinous copolymer contains from 2.5 to 10 mole percent of vinyl groups. A composition according to claim 1 wherein the high viscosity vinyl-containing polysiloxane has no more than 25 mole percent phenyl radicals and has the formula wherein Vi stands for vinyl, R 1 is selected from lower alkenyl, alkyl, and aryl radicals and R is selected from monovalent hydrocarbon radicals and halogenated monovalent hydrocarbon radicals, R 2 is selected from alkyl, alkenyl, and aryl radicals, "a" varies from 100 to 10,000 and "b" varies from 0 to 300; and the low viscosity vinyl-containing polysiloxane has no more than 25 mole percent phenyl radicals and has the formula wherein R, R 1 and R 2 are as previously defined, R 3 is selected from alkyl, aryl, and alkenyl radicals, "c" varies from 0 to 500 and "d" varies from 0 to 200. A composition according to claim 1 or claim 2 wherein the magnesium oxide is present at from 1 to 8 parts by weight of component (A). A composition according to any preceding claim wherein the high temperature peroxide is 2,5-dimethyl-2,5-di(t-butyl peroxy)hexane and the low temperature peroxide is 1,1-bis(t-butyl peroxy)-3,3,3-trimethylcyclohexane. A process for making a liquid injection moldable silicone composition oil resistant comprising adding (c) magnesium oxide to the liquid injection moldable silicone composition, wherein the liquid injection moldable silicone composition comprises: (A) 100 parts of a first component comprising: (1) a blend of vinyl-containing liquid polysiloxanes comprising: (a) a high viscosity vinyl-containing organopolysiloxane having a viscosity of from 5000 to 1,000,000 mPa.s (centipoise) at 25°C; (b) a low viscosity vinyl-containing organopolysiloxane having a viscosity of from 50 to 5000 mPa.s (centipoise) at 25°C; (2) filler; and (3) a catalyst selected from a platinum catalyst, a peroxide catalyst or dual peroxide catalyst system comprising a high temperature peroxide and a low temperature peroxide, the high temperature peroxide being a peroxide having a ten hour half-life of greater than 110°C and the low temperature peroxide being a peroxide having a ten hour half-life of 100°C or below; (B) from 1 to 100 parts, based on 100 parts of (A), of a hydrogen silicone composition selected from hydrogen containing silanes and hydrogen containing polysiloxanes; (E) cerium hydroxide or tetramethyldivinyldisilazane; and (D) (1) from 1 to 50 parts by weight of an organopolysiloxane resinous copolymer comprising R 3 7 SiO 0.5 monofunctional units and SiO 2 tetrafunctional units, the ratio of monofunctional to tetrafunctional units being from 0.5 to 1 to 1 to 1; or (2) from 20 to 50 parts by weight of an organopolysiloxane resinous copolymer comprising R 3 7 SiO 0.5 monofunctional units, SiO 2 tetrafunctional units, and R 2 7 SiO difunctional units, the ratio of monofunctional units to tetrafunctional units being from 0.5 to 1 to 1 to 1 and the difunctional units are present in an amount equal to 1 to 10 mole percent based on the total number of moles of siloxy units in the copolymer; wherein R 7 is selected from vinyl radicals and monovalent hydrocarbon radicals free of aliphatic unsaturation and wherein the resinous copolymer contains from 2.5 to 10 mole percent of vinyl groups. A process for making a liquid injection moldable silicone composition fuel resistant comprising adding to the liquid injection moldable silicone composition (D) (1) from 1 to 50 parts by weight of an organopolysiloxane resinous copolymer comprising R 3 7 SiO 0.5 monofunctional units and SiO 2 tetrafunctional units the ratio of monofunctional units to tetrafunctional units being from 0.5 to 1 to 1 to 1; or (2) from 20 to 50 parts by weight of an organopolysiloxane resinous copolymer comprising R 3 7 SiO 0.5 monofunctional units, SiO 2 tetrafunctional units, and R 2 7 SiO difunctional units, the ratio of monofunctional units to tetrafunctional units being from 0.5 to 1 to 1 to 1 and the difunctional units are present in an amount equal to 1 to 10 mole percent based on the total number of moles of siloxy units in the copolymer; wherein R 7 is selected from vinyl radicals and monovalent hydrocarbon radicals free of aliphatic unsaturation and wherein the resinous copolymer contains from 2.5 to 10 mole percent of vinyl groups, wherein the liquid injection moldable silicone composition comprises: (A) 100 parts of a first component comprising: (1) a blend of vinyl-containing liquid polysiloxanes comprising: (a) a high viscosity vinyl-containing organopolysiloxane having a viscosity of from 5000 to 1,000,000 mPa.s (centipoise) at 25°C; (b) a low viscosity vinyl-containing organopolysiloxane having a viscosity of from 50 to 5000 mPa.s (centipoise) at 25°C; (2) filler; and (3) a catalyst selected from a platinum catalyst, a peroxide catalyst or dual peroxide catalyst system comprising a high temperature peroxide and a low temperature peroxide, the high temperature peroxide being a peroxide having a ten hour half-life of greater than 110°C and the low temperature peroxide being a peroxide having a ten hour half-life of 100°C or below; (B) from 1 to 100 parts, based on 100 parts of (A), of a hydrogen silicone composition selected from hydrogen containing silanes and hydrogen containing polysiloxanes; (C) magnesium oxide; and (E) cerium hydroxide or tetramethyldivinyldisilazane. A process for improving the compression set of a liquid injection moldable composition comprising adding (E) either cerium hydroxide or tetramethyldivinyldisilazane to the liquid injection moldable silicone composition, wherein the liquid injection moldable silicone composition comprises: (A) 100 parts of a first component comprising: (1) a blend of vinyl-containing liquid polysiloxanes comprising: (a) a high viscosity vinyl-containing organopolysiloxane having a viscosity of from 5000 to 1,000,000 mPa.s (centipoise) at 25°C; (b) a low viscosity vinyl-containing organopolysiloxane having a viscosity of from 50 to 5000 mPa.s (centipoise) at 25°C; (2) filler; and (3) a catalyst selected from a platinum catalyst, a peroxide catalyst or dual peroxide catalyst system comprising a high temperature peroxide and a low temperature peroxide, the high temperature peroxide being a peroxide having a ten hour half-life of greater than 110°C and the low temperature peroxide being a peroxide having a ten hour half-life of 100°C or below; (B) from 1 to 100 parts, based on 100 parts of (A), of a hydrogen silicone composition selected from hydrogen containing silanes and hydrogen containing polysiloxanes; (C) magnesium oxide; and (D) (1) from 1 to 50 parts by weight of an organopolysiloxane resinous copolymer comprising R 3 7 SiO 0.5 monofunctional units and SiO 2 tetrafunctional units, the ratio of monofunctional to tetrafunctional units being from 0.5 to 1 to 1 to 1; or (2) from 20 to 50 parts by weight of an organopolysiloxane resinous copolymer comprising R 3 7 SiO 0.5 monofunctional units, SiO 2 tetrafunctional units, and R 2 7 SiO difunctional units, the ratio of monofunctional units to tetrafunctional units being from 0.5 to 1 to 1 to 1 and the difunctional units are present in an amount equal to 1 to 10 mole percent based on the total number of moles of siloxy units in the copolymer; wherein R 7 is selected from vinyl radicals and monovalent hydrocarbon radicals free of aliphatic unsaturation and wherein the resinous copolymer contains from 2.5 to 10 mole percent of vinyl groups. A process for improving the compression set of a liquid injection moldable silicone composition comprising curing the composition with a dual peroxide catalytic system comprising a high temperature peroxide and a low temperature peroxide, the high temperature peroxide being a peroxide having a ten hour half-life of greater than 110°C and the low temperature peroxide being a peroxide having a ten hour half-life of 100°C or below, the liquid, injection moldable silicone composition comprising: (A) 100 parts of a first component comprising: (1) a blend of vinyl-containing liquid polysiloxanes comprising: (a) a high viscosity vinyl-containing organopolysiloxane having a viscosity of from 5000 to 1,000,000 mPa.s (centipoise) at 25°C; (b) a low viscosity vinyl-containing organopolysiloxane having a viscosity of from 50 to 5000 mPa.s (centipoise) at 25°C; (2) filler; and (B) from 1 to 100 parts, based on 100 parts of (A), of a hydrogen silicone composition selected from hydrogen containing silanes and hydrogen containing polysiloxanes; (C) magnesium oxide; (E) cerium hydroxide or tetramethyldivinyldisilazane; and (D) (1) from 1 to 50 parts by weight of an organopolysiloxane resinous copolymer comprising R 3 7 SiO 0.5 monofunctional units and SiO 2 tetrafunctional units, the ratio of monofunctional to tetrafunctional units being from 0.5 to 1 to 1 to 1; or (2) from 20 to 50 parts by weight of an organopolysiloxane resinous copolymer comprising R 3 7 SiO 0.5 monofunctional units and SiO 2 tetrafunctional units, the ratio of monofunctional to tetrafunctional units, and R 2 7 SiO difunctional units, the ratio of monofunctional units being from 0.5 to 1 to 1 to 1 and the difunctional units are present in an amount equal to 1 to 10 mole percent based on the total number of moles of siloxy units in the copolymer; wherein R 7 is selected from vinyl radicals and monovalent hydrocarbon radicals free of aliphatic unsaturation and wherein the resinous copolymer contains from 2.5 to 10 mole percent of vinyl groups.

Inventors: JERAM EDWARD MATTHEW, MARTIN DONALD ALSON, WARD BRIAN JOHN, JERAM, EDWARD MATTHEW, MARTIN, DONALD ALSON, WARD, BRIAN JOHN
Applicants: GEN ELECTRIC, GENERAL ELECTRIC COMPANY
Application year: 1990
Main classification: C08L83
IPC codes: C08L83, C08F299, C08K5, C08K3, C08F290, B29C45