GB2076841A - Process for regulating the cure of silicone rubber products - Google Patents

Abstract

The cure rate of a platinum catalyzed addition cured silicone rubber composition is regulated in order to facilitate fabrication by the addition of small amounts of silanol containing materials, ie silanols, silanol-containing low viscosity polysiloxanes, and untreated pyrogenic or fumed silica.

Description

SPECIFICATION Process for regulating the cure of silicone rubber products The present invention relates to platinum catalyzed SiH-olefin silicone compositions utilizing an addition cure reaction and more specifically it relates to an improved process for formulating such silicone rubber products whereby it is possible to regulate the cure of a catalyzed silicone compound. The present invention allows a silicone formulator or fabricator to selectively control the rate of cure thereby providing greater control and flexibility during fabrication. Additionally, the present invention provides a silicone rubber product made by a process utilizing cure regulation techniques disclosed herein.

In U.S. Patent 4,061,609, issued December 6, 1977, Bobear demonstrated a silicone rubber composition which has been shown to be useful, commercially successful, and which has met with wide acceptance in the silicone industry. This patent is hereby incorporated by reference.

Bobear recognized that several major disadvantages of prior art silicone rubber compositions could be eliminated entirely with the use of a proper inhibitor for the platinum catalyzed cure reaction. SiH-olefin platinum catalyzed compositions had been well-known in the art. Such compositions generally comprise a vinyl-containing polysiloxane base material having a treated or untreated filler therein and a hydrogencontaining polysiloxane along with a platinum catalyst which could be solid platinum metal deposited on a solid carrier such as gamma alumina or it could be a solubilized plantinum complex. Normal procedure was to package the vinyl polysiloxane, the filler and the platinum catalyst in one package and to provide a second package containing the hydrogen-containing polysiloxane.The fabricator or other user of the material produced a cured silicone elastomer by mixing the two packages according to specified proportions whereupon the composition could be fabricated to a desired shape and allowed to cure either at room temperature over a period of time or at elevated temperatures in relatively very short period of time.

The above-described compositions which are generally sold in the two component or package format are usually referred to as room temperature vulcanizable silicone rubber compositions and more specifically, SiH-olefin platinum catalyzed room temperature vulcanizable silicone rubber compositions. It is to be understood that these types of compositions could be cured at varying rates depending upon the temperature. For example, at room temperature the composition might take 1 hour to 12 hours to cure but at elevated temperatures such as 100 to 200"C the composition might cure in seconds or minutes.

Such compositions start curing as soon as the two components are mixed together and will usually cure or at least set in approximately 1 hour even at room temperature. Therefore, it was desirable to incorporate into the prior art compositions inhibitors which would retard the curing of the composition for at least 12 hours when the two components were mixed together in order to allow the composition to be fabricated to the desired shape before such composition sets. After the two components have been mixed together but prior to their having set such that they cannot be molded further, it is desirable to have as long a work life as possible.The function of the inhibitor is to increase the work-life of the composition prior to curing at an elevated temperature as well as provide a shelf-stable product The inhibitor must provide suitable work-life yet not impede or any way detract from the final cure and properties of the composition of the silicone elastomer.

Among the prominent prior art inhibitors were acetylenic-functional organic polymers and monomers as shown by Kookootsedes in U.S. Patent 3,445,420.

These inhibitors were ultimately undesirable insofar as the acetylenic radical-containing compounds had to be sealed in air tight containers because exposure or leaks to the atmosphere will cause the acetylenic compound to evaporate thereby decreasing its inhibiting properties. This was a further disadvantage insofar as ordinarily SiH-olefin platinum catalyzed compositions did not otherwise have to be packaged in air tight containers.

Accordingly, Bobear recognized a very effective class of inhibitors utilizing hydroperoxy radicals which were quite effective and overcame many of the prior art disadvantages. As mentioned above, Bobear's rubber composition met with success in the market place and served to provide useful silicone rubber fabricated silicone rubber products. Not only did Bobear avoid the use of explosive acetylenic compounds which require careful manufacturing procedures for their preparation and use but he was able to provide inhibitors having a higher effective rate of inhibition.

Prior SiH-olefin platinum catalyzed compositions usually consisted of polysiloxane polymers having a viscosity of approximately 1000 to 500,000 centipoise at 250iso that such polymers could be manipulated or worked at a rate which is more efficient than possible with higher viscosity polymers. In other words, the lower viscosity polymers serve the additional purpose of assisting in providing additional work-life.

Since Bobear utilized extremely effective inhibitors he was able to provide high viscosity SiH-olfein platinum catalyzed compositions wherein viscosity could range anywhere from one million to 200 million centipoise at 25"C. Not only did these compositions remain workable, the final products exhibited very satisfactory higher tensile strengths. These compositions opened up entirely new markets and uses for these SiH-olefin platinum catalyzed silicone rubber compositions.

The difficulty in developing such high viscosity SiH-olefin platinum catalyzed compositions arose because they normally had to be worked on a mill or other apparatus after the two ingredients were mixed together thereby requiring extended work-life of at least 12 hours. In the past when such high viscosity materials were used, portions of the material would cure right on the miil upon contract and mixing of the two components.

This made it exceedingly difficult to fabricate products. Bobear provided compositions which avoided many of these problems.

The present invention provides cure regulating properties through the addition of silanol-containing materials to a platinum catalyzed silicone compounds. Silanol groups can be found in a variety of materials and are represented by hydroxyl groups which are bonded directly to silicon atoms. These silanol groups can be found in certain low molecular weight siloxane fluids which may be chain-stopped with silanol, or they may be found on the surface of pyrogenic or fumed silica particles.

Prior to the present invention it was wholly unexpected that these materials could provide the basis for a cure regulating process, indeed, these materials were heretofore used for entirely different purposes.

Silanol-stopped polysiloxane fluids were sometimes used as processing aids in orderto improve the rheological and viscoelastic properties of the silicone compound during fabrication. On the other hand, fumed silicas such as Cab-O-Sil and Aerosil are colloidal silicas which were often used as thickeners, or thixotropic or reinforcing agents, or extenders for silicone rubber. In fact, prior to the present invention, fabricators of silicone rubber would have expected that the addition of small amounts of these silanol-containing materials would have provided harder final products, with tighter cross-linking, since additional -SiOH groups will react with -SiH in the presence of platinum to form siloxane bonds and evolve hydrogen.

The present process for cure regulation must be distinguished from the prior disclosure of Bobear relating to cure inhibition. Bobear had found that the presence of hydroperoxy radicals will effectively inhibit the addition cure reaction of a platinum catalyzed silicone rubber. By incorporating effective amounts of these hydroperoxy-containing materials he was able to provide a shelf stable product which could be workable for up to a year or more. The inhibitors, therefore, were designed to eliminate catalytic activity until curing was desired at elevated temperatures. Cure regulators serve an entirely different purpose and it is not intended that they act in the manner of an inhibitor to provide shelf stable compounds.These regulators are provided in small amounts which are sufficient to influence the cure of a catalyzed silicone compound, regardless of whether such a compound is also inhibited. Whereas the inhibitor may be effective for a year, the regulator can be made effective for a few minutes or a matter of days. These silanol cure regulators are designed to offer flexibility to the silicone rubberfabricatorwho is working with a catalyzed compound on a molding or extrusion or injection device, where it is necessary that the compound be workable until cure is intended.

Furthermore, the present invention offers flexibility to the fabricator who may now vary the cure rate of his system thereby facilitating various types of fabrication such as extrusion through a hot air tunnel or a steam autoclave as well as molding via compression, transfer or injection devices.

The flexibility afforded by the opportunity of varying the cure rates, as provided by the present invention can be demonstrated by considering various silicone rubber fabricating techniques. When the catalyzed composition is manipulated through an extrusion device and directed to a hot air vulcanization tunnel or zone, it is desirable that there be a relatively quick cure of the material. That is to say, best results are obtained if the composition begins to cure immediately upon exposure to the HAV zone.

However, if a hot mold technique is utilized such as compression or injection molding, a slower cure is necessary in order that the rubber first obtain the configuration of the molding device before the cure reaction is initiated.

The process of the present invention provides a system for formulating an addition cured silicon rubber composition wherein it is possible to regulate the cure rate of the product to be fabricated. A major ingredient is a silicone base polymer compound which is comprised of 100 parts by weight of a vinyl-containing linear polysiloxane having the formula, (I) RaSiO4-a 2 and blends of such polysiloxanes where R is selected from the class consisting of alkyl radicals of 1 to 8 carbon atoms, vinyl radicals, phenyl radicals, fluoroalkyl radicals of 3 to 10 carbon atoms and mixtures thereof and where the vinyl radical unsaturation in said polymer is at least 0.005 mole percent, and varies from 1.98 to 2.01.

Preferably the vinyl-coating base polysiloxane has the formula given by (II),

which has a viscosity that varies from 1,000 to 300,000,000 centipoise at 250C, where Vi is vinyl and R' is selected from the class consisting of vinyl, phenyl, alkyl radicals of 1 to 8 carbon atoms, fluoroalkyl radicals of3 to 10 carbon atoms and mixtures thereof and where varies from 330 to 11,000.Note that the vznyl-containing polysiloxane can be present as a blend of such polysiloxanes wherein up to 50 percent by weight can be a second vinyl-containing polysiloxane of the formula,

where Vi in vinyl and R2 is selected from the class consisting of alkyl radicals of 1 to 8 carbon atoms, phenyl, fluoroalkyl radicals of 3 to 10 carbon atoms and mixtures thereof, y varies from 1 to 4,000 and z varies from 1 to 4,000 and which has a viscosity that varies from 1,000 to 1,000,000 centipoise at 25 C.

Preferably, the first polysiloxane will have a viscosity varying from 1,000,000 to 200,000,000 centipoise at 25"C and the second polysiloxane has the viscosity which varies from 50,000 to 500,000 centipoise at 25"C.

Also, preferably, the vinyl content of such vinyl-containing polysiloxane or blends will vary from 0.01 to 1.0 mole percent.

To the 100 parts of the vinyl-containing polymer will be added from 0.5 to 50.0 and preferably 0.5 to 3.0 parts by weight of hydrogen-containing polysiloxane. The hydrogen-containing compound can be hydride resin composed of

units and SiO2 units where the ratio of R3 to Si varies from 1.1 to 1.9 and R3 is selected from the class consisting of alkyl radicals of 1 to 8 carbon atoms, phenyl radicals and fluoroalkly radicals of 3 to 10 carbon atoms. Additionally, the resin may contain a number of (R3)2SiO units such that the R3 to Si ratio will vary from 1.5 to 2.1. A particular hydride compound could be a polysiloxane of the formula,

where R4 is as R3 but also includes hydrogen, v varies from 1 to 1,000 and w varies from 0 to 200 and the viscosity of the polymer varies from 1 to 10,000 centipoise at 250C.

Since the present invention provides an addition cured silicon rubber, platinum is used to catalyze the cure reation. As is well-known in the art, at least approximately 0.1 parts platinum is necessary per one million parts vinyl polymer.

The combination of components when mixed, can be cured by well-known means such as extrusion, molding or injection, to provide fabricated silicone rubber products. Of course it is possible for one skilled in the art to add various process aids and fillers to the composition to achieve desired effects.

It can also be seen that a skilled silicone rubber fabricator is able to control the rheological properties of his compositions during formulation by selectively adjusting the relative proportions of components.

The hydroperoxy inhibitors disclosed by Bobear may also be incorporated into the compositions made by the present process. At least 0.004 parts by weight of inhibitor per 100 parts vinyl-containing gum will be effective for inhibiting the platinum catalyzed cure reaction. The inhibitor will contain at least one hydroperoxy radical of the formula -C-O-O-H. Particularly suitable inhibitors are tertiary butyl hydroperoxide, methyl ethyl ketone peroxide, cumene hydroperoxide, 1,1,3,3, - tetramethylbutyl hydroperoxide, and 2, 5- dimethyl- 2, 5- dihydroperoxy hexane.

The types of silanol-containing material contemplated as being useful cure regulators are any of the untreated pyrogenic silicas and fumed silicas such as Aerosil and Cab-O-Sil, as well as the low molecular weight silicone fluids which are sometimes used as process aids. Included among the silanol fluids would be silanol chain-stopped polydimethysiloxane oils, diphenyi silane diol, dimethylphenyl silanol and similar silanol-containing materials.

The process of the present invention allows a silicone rubber fabricator to regulate the cure of catalyzed compound by the seiective addition of 0.01 to 50 and preferably 0.5 to 10 parts by weight of a silanol containing cure regulating agent per 100 parts of vinyl-containing gum.

A basic constituent of the composition made by the process of the present invention, is a vinyl-containing polysiloxane of formula (1), wherein the polymer contains at least 0.005 percent vinyl and preferably contains from 0.01 to 1 mole percent vinyl. Preferably, the polymer is linear and preferably the vinyl is at the terminal positions of the linear polymer chain. However, broadly, in accordance with the present invention the vinyl radicals can be on any part of the polymer chain. Irrespective of whether there is some polymer chain vinyl in the polymer, it is preferred that there be at least some terminal vinyl groups in the polymer.It is understood that this polymer can be a single polymer species or it can be a blend of vinyl-containing polymer materials which can have varying viscosities of from 1,000 to 300,000,000 centipoise at 25"C, with the final blend having a viscosity varying from 11,000 to 300,000,000 centipoise at 25"C.

Most preferably, the polymer of formula (1) has a viscosity that varies from 1,000,000 to 200,000,000 centipoise at 25"C. The other substituent groups in addition to the vinyl radical can be any monovalent hydrocarbon radicals or halogenated monovalent hydrocarbon radicals, preferably not exceeding 10 carbon atoms. Most preferably, the R substituent group is selected from lower alkyl radicals of 1 to 8 carbon atoms, vinyl radicals and phenyl radicals and also fluoroalkyl radicals of 3 to 10 carbon atoms such as, trifluoropropyl.

The most preferred polymer species within the scope of the vinyl-containing polymer offormula (1) is the vinyl-containing polymer offormula (2), a strictly linear polymer with vinyl radical terminal units. This polymer or blend of such polymers may have a viscosity of from 1,000 to 200,000,000 centipoise at 25"C, but is preferably a polymer that has a viscosity of 1,000,000 to 200,000,000 centipoise at 25"C. It can be understood that when the polymers of formula (2) are utilized within those polymers of the scope offormula (1), that the polymers of formula (2) need not be a single polymer species but may be a blend of vinyl-containing polymersofformula (2) having differentviscosities.

In that respect, it should be noted that the R' radicals can be vinyl, although in most instances it is preferred that R' not be a vinyl radical within the scope of formula (2). It is possible to produce compositions where none of the R' radicals are vinyl within the vinyl concentrations specified previously.

It should also be noted that for high viscosity systems it is preferred that the vinyl-containing polymers or blends of such polymers of formulas (1) and (2) have a viscosity of 1,000,000 to 200,000,000 centipoise at 25"C.

Within the scope of formula (2), R' may be selected from vinyl and may be on any portion of the polymer chain. However, only a minimal number of R' radicals may be vinyl radicals in accordance with the disclosure set forth above. Preferably, R' is selected from the class consisting of phenyl, lower alkyl radicals of 1 to 8 carbon atoms and fluoroalkyl radicals of 3 to 10 carbon atoms such as, trifluoropropyl. However, the R' radicals may be selected from any monovalent hydrocarbon radicals and halogenated monovalent hydrocarbon radicals of less than 10 carbon atoms. The viscosity of the polymer in formula (2) may vary anywhere from 1,000 to 300,000,000 centipoise at 25"C, and the value of x may vary from 330 to 11,000.

The above-described vinyl-containing polymers are a basic constituent of the silicone rubber compositions of the present invention. In addition cure systems such as herein provided, another basic constituent is the hydrogen-containing polysiloxane cross-linking agent. Any hydride cross-linking agent normally utilized in SiH-olefin platinum catalyzed reactions to form silicone elastomers or silicone polymers may be utilized in the instant case. The preferred hydride cross-linking agents for utilization in silicone elastomers either at room temperature or elevated temperature are disclosed below.For instance, there may be utilized a hydride cross-linking agent composed of,

units and SiO2 units where the ratio of R3 to Si moieties varies from 1.1 to 1.9 and R is selected from the class consisting generally of any monovalent hydrocarbon radicals or halogenated monovalent hydrocarbon radicals of up to 10 carbon atoms. More preferably, R3 is selected from the class consisting of alkyl radicals of 1 to 8 carbon atoms, phenyl radicals and fluoroalkyl radicals of 3 to 10 carbon atoms. A specific desirable fluoroalkyl radical being trifluoropropyl. Generally, for any hydride cross-linking agent utilized in the instant invention, it is preferred that the hydride cross-linking agent have a hydride content broadly of 0.05 to 5% and more preferably of 0.1 to 1% by weight.

Another hydride cross-linking agent is one containing monfunctional units, tetrafunctional units and also difunctional units. For instance, there may be utilized as a hydride cross-linking agent in the instant invention a hydride silicone resin composed of

units, SiO2 units and (R3)2SiO units where the R3 to Si moiety ratio may vary from 1.5 to 2.1. Again, it is necessary that the hydride content of this silicone resin to within the specification set forth above ifthe proper cross-link density is to be obtained in the final cured product.Broadly speaking, the R3 radical may be selected from any monovalent hydrocarbon radical or hologenated monovalent hydrocarbon radical of up to 10 carbon atoms, but more preferably the R3 radical is selected from lower alkyl radicals of 1 to 8 carbon atoms, phenyl radicals and fluoroalkyl radicals of 3 to 10 carbon atoms, the most preferred fluoroalkyl radical being trifluoropropyl.

It should also be noted that such hydride cross-linking agents desirably may not have any vinyl units in them or other unsaturated groups since this may result in accelerated curing of the composition. However, this is not a stringent requirement with the present composition as it would be with prior art compositions because of the inhibitor additive in the instant compositions. Accordingly, a certain amount of unsaturation can be tolerated in the hydride cross-linking agents. The only undesirable aspect of having a certain amount of unsaturation in the hydride cross-linking agent is that the proper cross-linked density may not be obtained.Generally, less than 0.001 mole percent of unsaturated radicals can be tolerated in the instant hydride cross-linking agent when the inhibitor compound additive of the instant case is utilized and the optimum physical properties in the cured composition are desired.

Another preferred hydride cross-linking agent is that of the formula,

It should be noted that even though the above compound of formula (3) is linear, hydride-containing branch-chained polymers can be utilized as hydride cross-linking agents in the instant invention. However, a polymer that is linear such as that of formula (3), is desirable because it results in a cured elastomer of optimum physical properties. Preferably, in formula (3), R4 generally may be selected from any monovalent hydrocarbon radicals or halogenated monovalent hydrocarbon radicals, preferably, of up to 10 carbon atoms. More preferably, R4 is selected from alkyl radicals of 1 to 8 carbon atoms, phenyl, fluoroalkyl radicals of 3 to 10 carbon atoms and hydrogen, the preferred fluoroalkyl radical being trifluoropropyl.Accordingly, 'Lthe hydride polysiloxane polymer cross-linking agents generally may have a viscosity of from 1 to 100,000 centipoise at 25"C, and more preferably have a viscosity of from 1 to 10,000 centipoise at 25"C. In formula (3), preferably v may vary from 1 to 1000 and w may vary from 0 to 200. Although the hydrogen atoms in the hydrogen polysiloxane polymer of formula (3) may be solely located in the terminal position of the polymer chain, there can also be come hydrogen atoms in the internal position of the polymer chain. The terminal location of the hydrogen atom is desired for optimum physical properties in the cured composition.In this respect, it is also true that the particular hydride cross-linking agent will be selected depending on the end use for which the composition is intended. However, the hydride resins disclosed and the hydrogen polysiloxane of formula (3) are the preferred hydride cross-linking agents for the production of silicone elastomers. Preferably, the viscosity of the polymer of formula (3) varies, as stated previously, from 1 to 10,000 centipoise at 250C, and more preferably varies from 1 to 1,000 centipoise at 25"C.

Another necessary ingredient in the instant composition is a platinum catalyst. Generally, there must be utilized at least 0.1 parts per million of a platinum catalyst in terms of parts of platinum metal. This platinum catalyst may be in any form. It may be a solid platinum metal deposited on a solid carrier or it may be a solubilized platinum complex. Any type of plantinum catalyst will work in the instant invention. More preferably, the platinum complex is a solubilized platinum complex. Many types of platinum compounds for this SiH-olefin addition reaction are known and such platinum catalysts may be used for the reaction of the present case. The preferred platinum catalysts, especially when optical clarity is required, are those platinum compound catalysts which are soluble in the present reaction mixture.The platinum compound can be selected from those having the formula (PtCl2/Olefin)2 and H(PtCl3IOlefin) as described in U.S. Patent No.

3,159,601, Ashby. The olefin shown in the previous two formulas can be almost any type of olefin but is preferably an alkenylene having from 2 to 8 carbon atoms, a cycloalkenylene having from 5 to 7 carbon atoms or styrene. Specific olefins utilizable in the above formulas are ethylene, propylene, the various isomers of butylene, octylene, cyclopentene, cyclohexane, cycloheptene, etc.

Afurther platinum containing material usable in the composition of the present invention is the platinum chloride cyclopropane complex (PtC12/C3H6)2 described in U.S. Patent No. 3,159,662, Ashby.

Still further, the platinum containing material can be a complex formed from chloroplatinic acid with up to 2 moles per gram of platinum of a member selected from the class consisting of alcohols, ethers, aldehydes and mixtures of the above as described in U.S. Patent No.3,220,972, Lamoreaux.

All the patents and patent applications mentioned in this present specification ar hereby incorporated by reference.

A preferred platinum compound is also a flame retardant additive disclosed in Karstedt, U.S. Patent 3,814,730. Generally speaking, this type of platinum complex is formed by reacting chloroplatinic acid containing 4 moles of water of hydration with tetravinylcylotetrasiloxane in the presence of sodium bicarbonate in an ethanol solution.

In a general aspect, per 100 parts of the vinyl-containing polymers of formulas (1) or (2) and blends of such polymers there is utilized at least 0.1 parts per million of platinum metal and more preferably 1 to 50 parts per million of platinum metal whether as solid platinum deposited on a solid carrier or a solubilized platinum complex. With these ingredients there is utilized generally from 1 to 50 parts of the hydride cross-linking agent with the specification set forth above for hydride content, and more preferably from 1 to 25 parts of the hydride cross-linking agent.

Another basic ingredient in the instant composition may be the inhibitor. It has been found that the inhibition level in the curing of the instant composition is accomplished by the presence of the hydroperoxy radical. It has been found that there must be at least 0.004 parts of the inhibitor compound to present to effect some inhibitor activity in the present composition. However, the amount inhibitor compound that is added to the composition will vary in accordance with a particular application of the composition as can be apprecited. The higher the level of the inhibitor that is present, the longer the composition will be shelf stable. For most applications, the concentration of the hydroperoxy inhibitor compound may vary anywhere from 0.01 to 10 parts by weight per 100 parts of the base vinyl-containing compound.However, higher levels of inhibitor compound may be utilized, as desired, to further increase the shelf stability of a one-component orto increase the work-life of a two-component system such that there can be obtained a shelf stability of as much as 6 months or more and a work-life of a number of weeks, if necessary. The above preferred range of concentration is given only for most applications of SiH-olefin platinum catalyzed compositions.

The hydroperoxy-containing compound can have any desired structure as long as it contains a hydroperoxy radical in the molecular structure because it is such hydroperoxy radical that accomplishes the inhibiting activity for reasons that are not known.

Hydroperoxy compounds that may be utilized are methylethylketone peroxide, cumene hydroperoxide, t-butyl hydrkoperoxide, 1 -hydroxycyclohexyl hydroperoxide, 1,1 ,3,3-tetramethylbutyl hydroperoxide, 2,5dimethyl-2,5-dihydroperoxy hexane, deca lin hydroperoxide, 1,1,2,2-tetramethylpropyl hydroperoxide, pmethane hydroperoxide and pinane hydroperoxide. The compounds are manufactured and sold by Pennwalt Corp., Hercules, Inc., and Lucidol Chemical Co.

The above compounds are only exemplary and many others can be utilized since compounds containing hydroperoxy radicals are well-known.

The polymers within the scope of formulas (1) and (2), these are well-known compounds. Reference is made to the patent of Jeram and Striker, U.S. Patent No. 3,884,866, whose disclosure is hereby incorporated by reference. Such polymers are usually made by the equilibration of vinyl-containing cyclic polysiloxanes or non-vinyl-containing chainstoppers at elevated temperatures to produce high viscosity vinyl-containing polymers. Such equilibration reactions are carried out with the use of alkali metal catalysts or in the case in the production of low viscosity vinyl-containing polymers by the use of acid catalysts such as, toluene sulfonic acid or acid-activated ciay. When it is desired that the polymer contain some fluroalkyl groups, a slightly different procedure is utilized such as, for instance, that disclosed in the issued patent of John Razzano, U.S.Patent No. 3,937,684. The hydride cross-linking agents are also well-known as disclosed in the above Jeram and Striker 3,884,866 patent. Simply stated, the hydride resins are simply produced by the hydrolysis of the appropriate hydrochlorosilanes in a two-phase hydrolysis system, that is, with a water immiscible solvent and water, and separating the resulting hydrolyzate.

The hydrogen polysiloxane cross-linking agent of formula (3) is also produced by equilibration process or by hydrolysis processes and more generally by the equilibration of tetrasiloxanes with the appropriate hydride chain-stoppers in the presence of an acid activated equilibration catalyst. For instance, the processes disclosed in U.S. Patent No. 3,853,933, Siciliano and U.S. Patent No. 3,853,934, Siciliano and Holdstock, may be utilized. In the case again where the polymer is a fluorosilicone containing polymer the special procedures disclosed in the above Razzano, U.S. Patent No. 3,937,684, have been utilized.

There may be added other ingredients to the basic composition of the instant case. There may be utilized as a reinforcing agent to give the final composition good physical strength, a vinyl-containing polysiloxane which is utilized at a concentration of from generally 1 to 50 parts to preferably 1 to 25 parts per 100 parts of the basic vinyl-containing polymer of formulas (1) and (2) of a compound of the formula,

In formula (4), the vinyl units are only in the internal portion of the polymer chain. Again, the vinyl content of this polymer must be such that the vinyl concentration of the total vinyl-containing polymers must be at least 0.005 mole percent and may vary anywhere from 0.01 to 1 mole percent. Although a higher vinyl content may be utilized, it serves no purpose and decreases the strength of the composition.In formula (4), Vi is vinyl and the R2 radical may be selected from any monovalent hydrocarbon radical or halogenated monovalent hydrocarbon radical of up to 10 carbon atoms. More preferably, the R2 radical of formula (4) is selected from alkyl radicals of 1 to 8 carbon atoms, phenyl radicals, fluoroalkyl radicals of 3 to 10 carbon atoms, preferably, trifluoropropyl, and mixtures thereof, where y varies from 1 to 4,000 and z varies from 1 to 4,000 and which polymer has a viscosity that generally varies anywhere from 1,000 to 1,000,000 centipoise at 25"C, and more preferably varies from 50,000 to 500,000 centipoise at 25"C. Such vinyl-containing polymers may be produced in accordance with the processes set forth in the aforesaid Razzano and Jeram/Striker patents.These polymers of formula (4) are basically used for the purpose of reinforcing the strength of the basic composition in the absence of a filler. Vinyl-containing silicone resins may also be utilized and specifically vinyl-containing silicone resins having fluoroalkyl substituted groups may be utilized as an additional or alternative additive in the present composition. Preferably, the vinyl-containing polymer of formula (4) has a viscosity that varies anywhere from 50,000 to 500,000 centipoise at 25"C even for higher viscosity compositions.

Example I A silicone base compound was prepared by combining 80 parts by weight of a vinyl chain-stopped polydimethylsiloxane gum having a viscosity of 50,000,000 centipoise at 25"C, with 20 parts by weight of a trimethyl chain-stopped polydimethyl-methyl-vinylsiloxane copolymer having a methylvinyl D unit concentration of approximately 0.6 mole percent and a viscosity of 55,000,000 centipoise at 25"C. To this mixture was added 40 parts by weight of Cab-O-Sil MS-70 filler which had been treated with octamethylcyclotetrasiloxane. These ingredients were combined on a conventional doughmixer. The base compound also contains one-part by weight of a methyl-hydrogen fluid cross-linking agent, per 100 parts of the vinyl-containing gums.This cross-linking agent is a dimethyl vinyl siloxy chain-stopped polydimethylmethylhydrogensiloxane having a viscosity of approximately 50 centistokes at 25"C and a hydrogen content of approximately 1.0 weight percent. An inhibited platinum catalyst masterbatch was prepared by taking a portion of the silicone base compound described above, before the addition thereto of the methyl hydride cross-linker. To 141.5 parts by weight of this base compound was added 5 parts by weight of Lupersol DDM inhibitor and 0.5 parts by weight of platinum catalyst solution which is comprised of approximately 90 weight percent octyl alcohol and 10 weight percent chloroplatinic acid. Next, various amounts of a cure regulating agent were added to samples of the silicone base compound.Samples A, B and C each contained, respectively,1.5,2.0, and 2.5 parts by weight of dimethylsilanol chain-stopped polydimethylsiloxane fluid regulating agent having a viscosity of approximately 30 centi-stokes at 25"C and an approximate silanol content of 8.0 weight percent. Final compounds were prepared and tested in a Monsanto Rheometer, Model 100.

TABLE I Samples A B C Silicone Base Compound 100 100 100 Inhibited Catalyst Compound 2 2 2 Parts Silanol Cure Regulating Agent Per 100 Parts Vinyl Gum 1.5 2.0 2.5 ODR Scorch Time, T, (seconds) 25.2 40.5 48 Those skilled in the art will notice that the amounts of silanol-containing cure regulating agent directly affects the cure of the catalyzed rubber compound as measured by the ODR scorch time.

Example 2 Another example of a silanol-containing cure regulating agent is fumed silica which was tested in the following manner: 4 samples of the silicone base compound prepared in Example 1 were prepared in an anlogous manner. This time each sample contained one-part by weight of the methyl hydride cross-linker per 142 parts of the base compound. Thus, each sample represented 143 parts by weight of the base compound and each was catalyzed with 2.86 parts by weight of the inhibited catalyst masterbatch compound. As a cure regulating agent, various amounts of untreated, silanol-containing Cab-O-Sil HS-5 were added to the mixture which was then tested in the same manner as in Example I. Table II demonstrates the cure regulating properties of the untreated fumed silica.

TABLE II Samples (parts by weight) D E F G Silicone Base Compound 143 143 143 143 Inhibited Catalyst Compound 2.86 2.86 2.86 2.86 Silanol Cure Regulating Agent 0.5 1.0 2.5 5 ODR Scorch Time, T, (minutes) 1.15 1.33 1.35 1.80 Thus, it will be noted that the scorch time for these silicon rubber compounds can be adjusted by varying the amount of the silanol-containing cure regulating agent, which in this case is untreated fumed silica and in the former case was a low molecular weight siloxane fluid. Those skilled in the art will appreciate that scorch time is a function of the cure rate of the compound. Heretofore, such silanol materials had merely been used as common process aids, or as additives to improve rheological properties of the silicone compounds, the process of the present invention allows a skilled fabricator to selectively control the cure rate of his catalyzzed compound, thereby providing the desirable advantages of increasedpotlife and improved workability of the compound while at no time detracting from the inhibition properties of a shelf-stable compound.

Claims (11)

1. A process for regulating the cure of addition cure silicon rubber compounds, comprising the steps of: providing a silicon base compound by combining (i) 100 parts by weight of a vinyl-containing base linear polysiloxane gum ofthe formula: RaSiOa 2 and blends of such polysiloxanes, where R is selected from alkyl radicals of 1 to 8 carbon atoms, vinyl radicals, phenyl radicals, fluoroalkyl radicals of 3 to 10 carbon atoms and mixtures thereof, where the vinyl radical unsaturation in said polymer is at least 0.005 mole percent, and a varies from 1.98 to 2.01, (ii) at least 0.1 parts per million of platinum catalyst based upon the weight of said polysiloxane gums, and (iii) from 0.5 to 50 parts by weight of hydrogen-containing polysiloxane;; regulating the cure of said addition cure silicon rubber compound by adding from 0.01 to 50 parts by weight of a silanol containing cure regulating agent selected from low viscosity silanol containing polysiloxane fluids, silanol-containing untreated pyrogenic silica and fumed silica; and curing said silicon rubber compound.

2. A process as claimed in Claim 1 further comprising the step of providing an inhibited catalyst compound by combining a portion of said vinyl-containing silicone base compound with sufficient amounts of an inhibitor compound having at least one hydroperoxy radical of the formula -C-O-O-H to inhibit a platinum catalyzed silicone rubber compound prior to curing and an amount of platinum catalyst effective for curing said silicone rubber.

3. A process as claimed in Claim 2 wherein said hydroperoxy inhibitor is present in an amount of at least 0.004 parts by weight inhibitor compound per 100 parts by weight vinyl-containing polysiloxane gums.

4. A process as claimed in claim 2 or claim 3, wherein said inhibitor compound is selected from tertiary butyl hydroperoxide, methyl ethyl ketone peroxide, cumene hydroperoxide, 1, 1,3,3, -tetramethylbutyl hydroperoxide, and 2, 5-dimethyl- 2, 5-dihydroperoxy hexane.

5. A process as claimed in any one of the preceding claims wherein said silicone base compound further contains from 1 to 100 parts of methyl siloxy treated silica filler.

6. A process as claimed in any one of the preceding claims wherein said low viscosity silanol containing polysiloxane fluid has the following formula:

wherein R is a monovalent hydrocarbon radical or mixture of such radicals and m equals 0 to 40 such that the silanol containing polysiloxane fluid has a viscosity of approximately 1 to 50 centipoise at 25"C.

7. A process as claimed in any one of the preceding claims wherein said cure regulating agent is present in an amount of 0.5 to 10 parts by weight per 100 parts of vinyl-containing gum.

8. A process as claimed in any one of the preceding claims wherein said vinyl-containing base polysiloxane has the formula:

where x caries from 330 to 11,000, Vi is vinyl, R1 is selected from vinyl, phenyl and alkyl radicals of 1 to 8 carbon atoms, fluoroalkyl radicals of 3 to 10 carbon atoms, and mixtures thereof and having a viscosity of, approximately 1,000 to 300,000,000 centipoise at 25"C.

9. A process as claimed in any one of the preceding claims wherein said cure regulating agent is selected from silanol chain-stopped polydimethylsiloxane oils, diphenyl silane diol, dimethylphenyl silanol.

10. A process as claimed in claim 1, substantiaily as hereinbefore described in any one of the examples.

11. A product made by the process of any one of the preceding claims.