SPECIFICATIONPeroxide acelerators for inhibited silicone compositionsThe present invention reiates to an SiH-olefin platinum catalyzed composition and more particuiarly the present invention relates to a one component SiH-olefin platinum catalyzedcompositions having an inhibitor compound therein as well as a cure accelerator for curing the composition at accelerated rates.
Compositions comprising an SiH-olefin platinum catalyzed composition are weil-known. Such compositions generally comprise a vinyl-containing polysiloxane, a hydride polysiloxane as a crosslinking agent, and a platinum catalyst. Various other ingredients can be added to the basic composition to modify or change its properties. Normally such a composition is taken and the vinylsiloxane is packaged separately from the hydride siloxane, the platinum being packaged in one or the other of the ingredients. When it is desired to cure the composition, the two packages are mixed and allowed to cure at room temperature to a silicone elastomer or the mixture can be heated at elevated temperatures and will cure to a silicone elastomer in a matter of seconds. Inhibitors for such compositions were well-known.Thus, as is disclosed in Kookootsedes et al USP 3, 445, 420 acetylenic compounds are disclosed to be effective inhibitors for SiH-olefin platinum catalyzed composition.
However, the trouble with such acetylenic compounds is that the compounds evaporated from the silicone mixture and accordingly have to be packaged in air leak-proof packages and in addition do not have as much inhibitive activity as could be desired.
Accordingly, as will be noted later, it is desirable to have extended inhibited activity of the SiHolefin platinum catalyzed compositions at room temperature for hot air vulcanization processes and forliquid injection molding applications. Such extended inhibited activity of SiH-olefin platinum compositions was not provided by the Prior Art. It was highly desirable to be able to develop an inhibitor forSiH-olefin platinum catalyzed composition that would inhibit the curing of the composition at room temperature for as much as six months a year of up to one year or more, such that the composition would not cure at room temperature, but would cure at elevated temperatures in a matter of seconds upon being heated to temperatures above 1 000C or more.
In the past inhibitors such as those of the Kookootsedes Patent were of sufficient utility to allow the two packages of a SiH-olefin platinum catalyzed composition to be mixed, molded and then cured at elevated temperatures to produce a silicone rubber part.
However, such inhibitors were ineffective to produce the same result in a one component SiHolefin platinum catalyzed composition, that is a composition where the two packages were mixed by the silicone producer and were shipped as a single package to the fabricator. Then, the fabricator, over a period of six months or more, could take the one component material and form the desired part and heat the silicone composition at elevated temperatures to produce the elastromeric silicone part. Recently, such an inhibitor has been found so that inhibited SiH-olefin platinum catalyzed composition could be produced, which had in the one component form extended shelf-life and would cure at elevated temperatures to a silicone elastomer in a relatively rapid time. This inhibitor compound is any compound containing the hydroperoxy radical as disclosed in Bobear USP 4, 061 609.
Such a one component composition was especially preferred for hot air vulcanization in the formation of silicone parts. Briefly, to give some background of the matter, thermoplastics are normally heated to melt them. They are formed to the desired part in the heated state and then they are cooled so as to set the thermoplastic to the desired form. To distinguish heat vulcanizable silicone rubber compositions and even SiH-olefin platinum catalyzed compositions that are cured at elevated temperature such compositions are set in the cool form and then they are heated so as to cure the silicone ingredients to form a silicone elastomer. Accordingly, in the hot air vulcanization process, normally, the heat cured rubber is extruded whole or shaped whole in the part desired and then it is heated by hot air so as to vulcanize the silicone ingredients to form a silicone elastomer.There are two methods for hot air vulcanization: (1) an oven which is heated at a temperature of anywhere from 6000 to 1 000F through which the formed part passes and is heated so as to form a silicone elastomer; (2) a steam system which passes superheated steam over the formed part so as to vulcanize it.
It can be appreciated that the steam system is more expensive in terms of equipment and also is not as versatile in terms of moving it from location to location. Accordingly, the hot air oven is more flexible for hot air vulcanization and is desired to be utilized. In the case of traditional heat vulcanizable silicone rubber compositions used in such hot air vulcanization procedures and usually comprised of a vinylcontaining polysiloxane gum, having a viscosity from 1 ,000,000 to 300,000,000 centipoise, to which there is added a silica filler and as a curing catalyst a peroxide catalyst; the composition upon being heated at elevated temperatures above 1 000C and more preferably above 2000C cures to a silicone elastomer.
It was found that when 2,4-dichlorobenzoyal peroxide was used as a catalyst in such compositions, such compositions could be hot air vulcanized at temperatures as low as 7000F at a period of anywhere from 20 to 60 seconds. The only other catalyst that would work in hot air vulcanization was dicumyl peroxide. However, this would only work with steam vulcanization. The disadvantages of steam vulcanization having been discussed previously. However, 2,4-dichlorobenzoyl peroxide catalyst has a disadvantage in that it is somewhat toxic, and accordingly, cannot be utilized in medical applications as much as would be desired.
Another difficulty of such systems was that the cured rubber would be somewhat sticky and would not have as high a flex life as would be desired. It should be noted that such heat curable systems using 2,4-dichlorobenzoyl peroxide as the catalyst where one component systems are fabricated would simply be molded to the desired part and then be hot air volcanized to the cured elastomeric part.
Accordingly, it was highly unexpected that an SiH-olefin platinum catalyzed composition could be fabricated to a one component system as disclosed in the foregoing Bobear patent. These compositions were found to be more desirable for hot air vuilcanization in the formation of extruded tubing than even the systems utilizing the dichlorobenzoyl peroxide catalyst or the dicumyl peroxide. For one thing, theSiH-olefin compositions of USP 4,061,609 were completely non-toxic and do not form any undesirable ash on the cured product.
In another aspect such SiH-olefin platinum catalyzed compositions have the advantage that they produce a slick non-sticky surface which upon curing is highly desirable in medical tubing and in addition, result in improved flex-life over the heat curable compositions that were cured with peroxides.
Thus, the flex-life of silicone rubber is related to its modulus, usually the lower the modulus of the silicone rubber the better the flex-life. It has been found that the Bobear compositions with high modulus give better flex-life than peroxides cured compositions having low modulus.
Such improved flex-life is desirable in any application where the silicone rubber is going to have a high amount of bending of the part, such as, for instance, where it is utilized to form for instance aPeristaltic Pump. There are other applications where such flex-life is important for silicone elastomeric parts.
Accordingly, the SiH-olefin platinum catalyzed compositions of Bobear are highly desirable for hot air vulcanization, however, some difficulty has been experienced in their use, in that hydroperoxy inhibitor in the compositions is so effective that the compositions will not cure unless they are heated to temperatures at 1 0000 F for a longer period of time than is desirable for hot air vulcanization.
Accordingly, it has become highly desirable to be able to utilize a cure accellerator in such SiHolefin platinum catalyzed compositions which would accelerate the cure of the compositions and allow them to cure properly at temperatures of 7000F as distinguished from temperatures of 10000 F. Liquid injection molding machines are a new innovation in the molding art. Briefly, such liquid injection molding machines operate by having a heated mold. The liquid plastic material is force injected into the mold, and cured at a very rapid rate in the mold. Such liquid injection molding machines are finding wider and wider application in the plastics industry due to the fact that they are very efficient and allow the preparation of many plastic parts over a short period of time.The composition of Bobear USP 4,061,609, at the low viscosity of anywhere from 1000 to 100,000 centipoise at 250C may be suitable for liquid injection molding machines, however, it does not have a sufficient rapid cure rate at elevated temperatures. Accordingly, it would be highly desirable to be able to produce an SiH-olefin platinum catalyzed composition with an extended shelf-life in the one component form which will cure rapidly at elevated temperatures. If such composition could be devised, they may be suitable for liquid injection molding machines.
In accordance with the above there is provided by the present invention a platinum catalyzed silicone rubber composition with an improved work-life and shelf-life at room temperature in a onecomponent form and an accelerated curing rate at elevated temperatures comprising (a) 100 parts by weight of a vinyl-containing base linear polysiloxane of the formula, RaSi04e12 (1) 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 where the vinyl radical of saturation on said polymer is at least .005 mole percent, a varies from1.98 to 2.01; (b) at least .1 parts per million of platinum; (c) from 1 to 50 parts by weight of a hydrogen containing polysiloxane and (d) at least .007 parts by weight of an inhibitor compound having at least one radical of the formula --CC--OO-O-H per 100 parts of said vinyl-containing polymer and (e) from .01 to 10 parts by weight of an organic peroxide accelerated compound having at least one radical of the formula --CC--OO--O-C-. This composition is packaged as a one-component system.
There may be other ingredients in the composition such as vinyl terminated fluids and fluids terminated with the vinyl group at one end of the polymer and a methyl group at the other end of the polymer having a viscosity varying from 1,000 to 1,000,000 centipoise at 250C and more preferably varying from 1 ,000 to 50,000 centipoise at 250C. The hydride polysiloxane crosslinking agent may be a hydride resin composed of monofunctional siloxy units and tetrafunctional siloxy units or may be a hydride containing low viscosity polymer. Platinum catalysts may be a platinum in any form such as platinum deposited on carbon black or platinum deposited in gamma alumina but is more preferably a platinum complex and desirably a platinum solubilized complex such as platinum complexed with a vinylsiloxane in which a substance is free of chlorine content. There may also be present in the composition extending and reinforcing fillers, examples of reinforcing fillers being fumed silica and precipitated silica. Any of the well-known ingredients for SiH-olefin platinum catalyzed compositions which do not effect the hydroperoxide inhibitor or the organic peroxide accelerator may be utilized in the instant compositions and processes.
The preferred form of the vinyl-containing polysiloxane base polymer is of the formula,
where such a polymer has a viscosity that varies from 1 ,000 to 300,000,000 centipoise and more preferably varies from 1,000,000 to 200,000,000 centipoise wherein in the formula Vi is vinyl and R1 is selected from vinyl, phenyl or alkyl radicals of 1 to 8 carbon atoms and fluoroalkyl radicals of 3 to 8 carbon atoms and mixtures thereof and where x varies such that the polymer has a viscosity varying from 1,000 to 300,000,000 centipoise at 250C.
It should be noted that in the preferred polymer form of the polymer of Formula (2) that there can be only vinyl groups on the terminal silicone atoms in the polymer chain and that there be no alphatic unsaturation in the internal portion of the polymer chain. If this is the case, the most desirable composition results in terms of physical properties. However, it should be noted that compositions can be made within the instant invention in which there is a vinyl unsaturation in the internal position of the polymer chain.
As a basic constituent there is present in the present composition the 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 different viscosities of anywhere from 1 ,000 to 300,000,000 centipoise at 250C, with the final blend having a viscosity varying from 11,000 to 30,000,000 centipoise at 250 C.
Most preferably, the polymer of formula (1) has a viscosity that varies from 1,000 to 200,000,000 centipoise at 250C. The other substituent groups in addition to the vinyl radical can be any monovalent hydrocarbon radicals or halogenated monovalent hydrocarbon radicals, preferably not exceding 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 of formula (1) is the vinyl-containing polymer of formula (2), that is, where the polymer or formula (1) is strictly linear polymer with vinyl radical terminal units. This polymer or blend of such polymers may have a viscosity of anywhere from 1,000 to 200,000,000 centipoise at 250C, but is preferably a polymer that has a viscosity of 1,000,000 to 200,000,000 centipoise at 250C. It can be understood that when the polymers of formula (2) are utilized within those polymers of the scope of formula (1), that the polymers of formula (2) need not be a single polymer species but may be a blend of vinyl-containing polymers of the formula of formula (2) of different viscosities.In that respect, it should be noted that some of 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 within the instant invention 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 250C. However, for one-component systems and with the present inhibitor additive of the present invention it is preferred that the vinyl-containing polymers within the scope of formulas (1) and (2) have a viscosity of anywhere from 1,000 to 500,000 centipoise at 250C, and generally have a viscosity of anywhere from 1,000 to 100,000 centipoise at 250C.
In the formula within the scope of formula (2), R' may be selected from vinyl and may be on any portion of the polymer chain within the scope of formula (2). However, only a minimal part of R' radicals may be vinyl radicals in accordance with the disclosure set forth herein above. Preferably, R' is selected from 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.
In accordance with the disclosure set forth hereinabove, the viscosity of the polymer in formula (2) may vary anywhere from 1 ,000 to 300,000,000 centipoise at 250C, and the value of x may vary from 330 to 1,000. With this basic constituent of the present invention there is needed a hydride crosslinking agent Any hydride crosslinking 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 crosslinking agents for utilization in the formation of silicone elastomers either at room temperature or elevated temperatures are disclosed below.For instance, there may be utilized a hydride crosslinking agent composed of,
units and SiO2 units where the ratio of R3 to Si moietites varies from 1.1 to 1.9 and R3 is selected from generally of any monovalent hydrocarbon radicals of up to 10 carbon atoms. More preferably, R3 is selected from of alkyl radicals of 1 to 8 carbon atoms, phenyl radicals and fluoralkyl radicals of 3 to 10 carbon atoms. A specific desirable fluoroalkyl radical being trifluoropropyl. Generally, for any hydride crosslinking agent utilized in the instant invention, it is preferred that the hydride crosslinking agent have a hydride content broadly of 0.05 to 50% and more preferably of 0.1 to 1% by weight.
Another hydride crosslinking agent may be utilized is not only one containing monofunctional units and tetrafunctional units but also one composed of monofunctional units, tetrafunctional units and difunctional units. For instance, there may be utilized as a hydride crosslinking agent in the instant invention of 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 be within the specification set forth above if the proper crosslink density is to be obtained in the final cured product.Broadly speaking, the R3 radical may be selected from any monovalent hydrocarbon radical or halogenated 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 crosslinking 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 in the present composition as 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 crosslinking agents in the compositions of the instant case. The only undesirable aspect of having a certain amount of unsaturation in the hydride crosslinking agent is that the proper crosslinked density may not be obtained. Generally, less than 0.001 mole percent of unsaturated radicals can be tolerated in the instant hydride crosslinking 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 crosslinking agent is that of the formula,
It should be noted that even though the above compound of formula (3) is linear that hydridecontaining branch-chained polymers can be utilized as hydride crosslinking 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, the hydride polysiloxane polymer crosslinking agents generally may have a viscosity of anywhere from 1 to 100,000 centipoise at 250C. and more preferably have a viscosity of anywhere from 1 to 10,000 centipoise at 250C. In formula (3), preferably v may vary anywhere from 1 to 1,000 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 positions of the polymer chain, there can also be some 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 crosslinking 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 crosslinking 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 at250C.
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 maybe a solid platinum metal deposited on a solid carrier or it may be a solubilized platinum complex.
Any type of platinum 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 (PtCI2-Olefin)2 and H(PtCI3-Olefin) as described in USP #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, cyclohexene, cycloheptene, etc.
A further platinum containing material usable in the composition of the present invention is the platinum chloride cyclopropane complex (PtCI2-C3H6)2 described in USP #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 alcohois, ethers, aldehydes and mixtures of the'above as described in USP #3,220,972, Lamoreaux.
All the patents and patent applications mentioned in this present specification are incorporated into the present application by reference.
The preferred platinum compound to be used not only as a platinum catalyst but also as a flameretardant additive is that disclosed in Karstedt, USP #3,814,730. Generally speaking, this type of platinum complex is formed by reacting chloroplatinic acid containing 4 moles of water of hydration with tetravinylcyclotetrasiloxane 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 utilized as solid platinum deposited on a solid carrier or a solubilized 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 crosslinking agent within the specification set forth above for hydride content, and more preferably from 1 to 25 parts of the hydride crosslinking agent.
The other basic ingredient in the instant composition is the inhibitor. Accordingly, in the present mixture there must be at least 0.007 parts per 100 parts of the vinyl-containing polymer of an inhibitor compound which can be any organic or silicone compound containing at least one hydroperoxy radical.
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 0.007 parts of the inhibitor compound present to effect some inhibitor activity on the present composition. However, the amount of inhibitor compound that is added to the composition will vary in accordance with a particular application of the composition as can be appreciated. The higher the level of the inhibitor that is present, the longer the composition will be shelf stable for a one-component system and the longer the composition will have a work-life if it is a two-component system. 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 or to 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.
As far as the structure of the hydroperoxy containing compound it 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.
Other hydroperoxy inhibitor compounds that may be utilized in the instant invention are, for instance, cumene hydroperoxide, 1, 1,3, 3-tetramethylbutylhydroperqxide and 2, 5-dimethyl-2, 5-dihydroperoxy hexane.
Other compounds that may be utilized are t-butyl hydroperoxide, 1 -hydroxycyclohexyl hydroperoxide, 1, 1, 3, 3-tetramethylbutyl hydroperoxide, 2, 5-dimethyl-2, 5-dihyroperoxy hexane, decalin hydroperoxide, 1, 1,2, 2-tetramethylpropyl hydroperoxide, p-methane hydroperoxide and pinane hydroperoxide. These 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.
In terms of the packaging of the instant basic composition, the inhibitor compound may be packaged either with the vinyl-containing compound or it may be packaged with the hydride crosslinking agent. In a two-component system, the vinyl-containing polymer of formulas (1) and (2) above is packaged separately from the hydride crosslinking agent. The platinum catalyst is normally compounded or mixed in with the vinyl-containing polymers of formulas (1) and (2). The inhibitor compound may then be inserted or mixed with the hydride crosslinking agent especially so if the hydride crosslinking agent contains any unsaturation.
In most cases it would be preferred to mix the inhibitor compound along with the platinum catalyst in the vinyl-containing polymers of formulas (1) and (2). Accordingly, when it is necessary to cure the composition the two components are mixed together and by the passage of time at room temperature or by the utilization of elevated temperatures to decompose the inhibitor compound, the composition can be cured to a silicone elastomer.
The other basic ingredients in the composition of the instant case from .1 to 10 parts by weight based on 100 parts of the base vinyl-containing polymer of an organic peroxide compound having a --CC--OO--O-C- radical in the compound. The compound must have at least one such radical. It should be noted that all peroxide compounds that were tested were found to act as accelerators in the compositions of the instant case, that is, all organic peroxide compounds, that is compounds having a --CC--OO--O-C- radical were found to function effectively as accelerators when added to SiH-olefin platinum catalyzed compositions in which there was a hydroperoxy compound as an inhibitor.
It should be noted that the instant invention is limited to the use of such organic peroxide accelerators in hydroperoxy inhibited SiH-olefin platinum catalyzed compositions. It is not known whether an organic peroxide would have functioned as an accelerator in the curing of SiH-olefin platinum catalyzed compositions when inhibitors other than hydroperoxy compounds are used in such compositions. It should be noted that there may be more than one peroxide radical in the organic peroxide compound and as such the compound will function more effectively as an accelerator.
It should also be noted that the inhibitor is a hydroperoxy compound that is a compound having at least one radical of the formula, C--OO--O-H and is to be distinguished from accelerator compound which has at least one radical of the formula C-0-C. It has been determined that when organic peroxide compounds having such radicals are added to SiH-olefin platinum catalyzed compositions which are inhibited with hydroperoxy compounds, that the combination of the two peroxides results in a composition which has extended shelf-life at room temperature, but which can cure rapidly at elevated temperatures, that is temperatures of above 100 or 2000C or temperatures as high as 7000 F.
It should also be noted that with respect to the lower limit of the accelerator, that is the .1 part by weight level, it has been determined that it is at this level at which the organic peroxide compound has any effectiveness as an accelerator. If concentration of the accelerator is 10 parts by weight or more, the accelerator is very effective. It should be noted that there is nothing critical about this upper 10 parts limit, that additional amounts of the organic peroxide accelerator can be utilized to further accelerate the curing of the composition at elevated temperatures; the only prohibition with respect to the additional amounts being the cost and the fact that above 10 parts does not markly increase the rate of curing of the composition at elevated temperatures.Preferably, there is utilized anywhere from .5 parts by weight to 5 parts by weight of the organic accelerator peroxide compound per hundred parts of the vinyl base polymer formula (1).
As noted previously, all organic peroxide compounds having at least one --CC--OO-OO--C- radical in a molecule of the compound function effectively as an accelerator in the compositions of the instant case. Accordingly, the invention is not limited to only the peroxide compounds disclosed below as accelerators, but is intended to encompass all organic peroxide compounds having at least one --CC--OO--O-C- radical in the molecule of the compound.
Examples of such compounds as for instance 2, 5 dimethyl, 2, 5 (tertiarybutyl peroxy) hexane, 2, 5 dimethyl, 2, 5 (tertiarybutyl peroxy) hexyene-3, dicumyl peroxide, tertiarybutyl perbenzoate, 2, 5 dichloro benzoyl peroxide, tertiary butyl peroxy isopropyl carbonate, etc. The above peroxide compounds will function as curing accelerators for the compositions of the instant invention. The instant invention is not limited solely to these compounds. All organic peroxide compounds having at least one radical of the formula -C-O-0-C- can be utilized as accelerators in the compositions of the instant case, that is they can be utilized as accelerators in SiH-olefin platinum compositions in which there is present a hydroperoxy compound as an inhibitor.It should be noted that if the compound has a hydroperoxy radical and a peroxide radical that is "--CC--OO-O-H" radical a "-C-O-O-C" radical that it will function both as an inhibitor and as an accelerator. Tests should be made with such a compound before it is used to see the extent of the inhibitor activity versus the accelerator activityin the compositions in question. Broadly, there is meant to be disclosed and claimed as the invention of the instant case, the use of organic peroxide compounds in SiH-olefin platinum catalyzed composition in which there is present a hydroperoxy compound as an inhibitor compound. On utilizing such a combination of compounds if is possible to increase the cure rate by at least twice.Thus, by the use of such compositions it is possible to decrease the time it takes for the composition to cure at elevated temperatures by a factor of 1/2 or more or to decrease the cure time by a factor of 5 or 6 times in some cases.
These are the basic ingredients of the instant composition. As far as the production of 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, USP # 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 chain stoppers 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 clay. In the case when the polymer is desired to contain some fluoroalkyl groups when a slightly different procedure is utilized such as, for instance, that disclosed in the issued patent of John Razzano, USP # 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.
In the case of fluorosiiicone-containing hydride crosslinking agents, special procedures have to be utilized, for instance, those disclosed in the following Jeram Patent applications: Jeram, US S. N.
619,592, filed October 6, 1975, entitled "Solvent Resistant Room Temperature Vulcanizable SiliconeRubber Compositions", and Jeram US S. N. 619,691, filed October 6, 1975, entitled "Solvent ResistantRoom Temperature Vulcanizable Silicone Rubber Compositions", whose disclosures are hereby incorporated into the present case by reference.
The hydrogen polysiloxane crosslinking agent of formula (3) is also produced by equilibration processes or by hydrolysis processes and more generally by the equilibration of tetrasiloxanes and the appropriate hydride chainstoppers in the presence of an acid activated equilibration catalyst. For instance, the processes disclosed in USP #3,853,933 - Siciliano and USP #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, USP # 3,937,684 have been utilized.
It should be noted, as stated above, that the above composition by utilizing enough inhibitor compound in the basic or modified composition of the instant case can be made into a one-component system, that is, where all the ingredients are mixed together and the composition is utilized to prepare a fabricated part and simply heated at elevated temperatures to create the cured silicone elastomer in a matter of minutes by decomposing the hydroperoxy inhibitor.
By the utilization of the present inhibitor compounds and sometimes in quantities in excess of 1 5 parts per 100 parts of the vinyl-containing polymers of formulas (1) and (2), the present composition can be packaged into a single component which at room temperature will have a shelf-life of 3 months to a year, but which when heated at elevated temperature would cure into a silicone elastomer in a matter of minutes. By reference to elevated temperatures, it is meant temperatures above 100 C. As can be appreciated, the higher temperature such as, 1 500 to 2000C can be utilized.
As stated previously, when such a one-component system is prepared it is preferred that the vinylcontaining polymer or blends of polymers have a viscosity of anywhere from 1 ,000 to 1 ,000,000' centipoise at 250C, such that the total mixture will not have a viscosity exceeding 1,000,000 centipoise at 250C. However, in accordance with the present invention, one-component compositions having a viscosity above 1,000,000 centipoise can also be prepared.In accordance with the present invention, such a one-component system is simply prepared by mixing all the basic ingredients together which is composed of the vinyl-containing polysiloxanes, the hydride crosslinking agent which also may be composed of a single type of hydride crosslinking agent of the ones disclosed above, or a mixture of such hydride containing crosslinking agents, the platinum catalyst and the inhibitor additive.
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 polysiíoxanevvhich is utilized at a concentration of anywhere 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 this formula, 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 vinylcontaining 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 250C, and more preferably varies from 50,000 to 500,000 centipoise at 250C. Such vinyl-containing polymers may be produced in accordance with the processes set forth in the aforesaid Razzano and Jeram/Striker Patents mentioned above. These polymers of formula (4) are basically 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. Such resins are disclosed in the aboveJeram Patent Applications which are hereby incorporated by reference, as well as the processes for producing them. Preferably, the vinyl-containing polymer of formula (4) has a viscosity that varies anywhere from 50,000 to 100,000 centipoise at 250C even for higher viscosity compositions.
The other additive that may be utilized in the instant invention is a filler and accordingly per 100 parts of the basic vinyl-containing polymer there may be utilized anywhere from 5 to 1 50 parts of a filler selected from the class of well-known reinforcing fillers such as, fumed silica and precipitated silica and extending fillers such as, titanium oxide.For instance, there may be utilized a filler in the broad range set forth above or more preferably in the range of 10 to 75 parts which filler is selected from the class consisting of titanium oxide, lithopone, zinc oxide, zirconium silicate, silica aerogel, iron oxide, diatomaceous earth, calcium carbonate, fumed silica, cyclic polysiloxane treated silica, siloxane treated silica, precipitated silica, glass fibers, magnesium oxide, chromic oxide, zirconium oxide, alpha quartz, calcined clay, asbestos, carbon, graphite, cork, cotton and synthetic fibers. The reinforcing fillers of fumed silica and precipitated silica are preferred when a high strength in the resulting silicone elastomer is desired, especially fumed and precipitated silica which have been treated with silicone compounds as is well-known in the art.However, in the case when it is desirable not to increase the uncured viscosity of the composition to too high a level which is sometimes caused by the reinforcing fillers, then the other fillers may be utilized. Also, it is well-known in the art that extending fillers may be used in combination with reinforcing fillers, treated or untreated, to get the proper balance in final physical properties in the silicone elastomer. Other additives may be utilized in the instant composition as is well-known in SiH-olefin platinum catalyzed composition. Accordingly, the additional additives that may be added to the basic composition of the instant case to produce desired end properties in the cured silicone elastomer are many.For instance, there may be utilized additional flame-retardant additives; there may be utilized heat aging additives as well as pigments and process aids such as that disclosed in Konkle, USP #2,890,188. It is only necessary that the additive does not interract with the hydroperoxy radical such that the hydroperoxy inhibitor compound loses its effectiveness.
It should be noted that the present hydroperoxy inhibitor and an organic peroxide accelerated compound combination is not disclosed solely for one-compound SiH-olefin platinum catalyzed compositions. Such a combination can be utilized with a two-component SiH-olefin platinum catalyzed composition. However, it is only in one-compound systems where the hydroperoxy inhibitor compound has been found to be very effective in producing such inhibited compositions that the accelerator and hydroperoxy inhibitor compound combination is particularly desired so as to have a one-component composition with an extended shelf-life at room temperature which will cure rapidly at elevated temperatures. Thus, such compositions are suitable for hot air vulcanization in one instance or for liquid injection molding in another instance. As can be appreciated for hot air vulcanization, the onecomponent system will have a viscosity of above 1,000,000 centipoise at 250C and for liquid injection molding or for other low viscosity applications the SiH-olefin platinum catlayzed composition with all of the ingredients mixed therein will have a viscosity below 1,000,000 centipoise at 250C and preferably below 500,000 centipoise at 250C. More preferably the composition will have a viscosity below 100,000 centipoise at 250C. The examples below are given for the purpose of illustrating the present invention. They are not given for any purpose of setting limits and boundaries to the disclosure of the instant invention but are merely intended as illustrations. All parts in the examples are by weight.
EXAMPLE 1There was prepared a Composition A, comprising 80 parts by weight of a dimethylpolysiloxane polymer having a viscosity varying from 30--80,000,000 centipoise at 250C and having .6 mole percent concentration of methyl vinyl siloxy units. To 20 parts of this polymer there was added to 80 parts by weight of a vinyl terminated dimethylpolysiloxane polymer having a viscosity in the range of 14 to 50,000,000 centipoise at 250C; and to these two gums there was added 3 parts by weight of a dimethyl silanol containing process aid having a viscosity varying in the range of 25 to 40 centipoise at 250C. To this mixture there was added 67 parts by weight of an octamethylcyclotetrasiloxane treated fumed silica filler.This mixture which is referred to as Composition A in Table 1 below was then utilized as such and to it there was added various amounts of hydride crosslinking agent, platinum catalyst and the hydroperoxy inhibitor as well as various amounts of peroxide accelerators as shown in Table 1 below.
In Table 1, Lupersol DDm is a tradename for methylethyl ketone peroxides in dimethyl phthalate; BPIC is tertiary butyl peroxy isopropyl carbonate, Lupersol 130 is 2, 5-dimethyl-2, 5-bis (T-butyl peroxy) hexyene - 3. The resulting compositions were press cured in a large mold and pressed sheets were obtained on which the Physical Properties were measured. This data was obtained in a MonsantoOscillating Disc Reometer, Model MPV was used to obtain T-90 data. The Rotor oscillated over 30 arc at 900 cpm (cycles per minute). During this test, the instrument measures torque versus time. From the plot there was possible to determine how long it took to obtain a 90% cure. The results are set forth inTable 1 below.
TABLE I Compound #1 #2 #3 #4 #5Composition A 170 170 170 170 170Lupersol DDM 0.2 0.2 0.2BPIC 1 1Lupersot 130 1 1Lamoreaux's Catalyst Pt complexed with octyl alcohol 0.02 0.02 0.02Linear hydridemethylpolysiloxane of 5-40 centipoise, viscosity at 25 C and having 0.7-0.9 weight percent hydrogen 3 3 3ODR - Model MPV - Large Mold - 12/100/x1/340 F/900 cpmT90 13.5' 3.3' 16.5' 3.05' 21.5Press CureShore A 60 74 56 73 69Tensile Strength (psi) 1167 1264 1157 1192 1074Elongation (%) 670 620 780 660 730Die B Tear (pi) 160 210 172 235 261 The time to 90% cure t-90 is 13.5 minutes with Lupersol 130 alone and 21.5 minutes with a hydroperoxide Lupersol DDM, inhibited addition cure alone. However, the t-90 is 3.3 minutes with a combined system. Again in the case of BPIC alone the t-90 is 16.5 minutes. When BPIC is then combined with the inhibited cure system the t-90 is reduced to 3.05 minutes. The above data shows that the cure rate of the hydroperoxy inhibited system is markedly reduced at elevated temperatures by the incorporation in the system of an organic peroxide compound.
EXAMPLE 2Inhibitor level is cut in half as compared to Table 1.
#1 #2 #3Comp. A 170 170 170DDM 0.1 0.1 0.1Pt Catalyst 0.02 0.02 0.02Linear hydridemethyl-polysiloxane of 5-40 centipoise,viscosity at 250C and having 0.7-0.9 weight percenthydrogen 3 3 3Lupersol 101 1BPIC 1 Tgg 11.2' 7.3' 2.8'Press CureShore A 72 70 71Tensile 1178 1193 1243Elong. 740 590 720 DieBTear 289 288 264