CA1223098A - One component acid-scavenged rtv bonding silicone rubber compositions - Google Patents

Abstract

ONE COMPONENT ACID-SCAVENGED RTV
BONDING SILICONE RUBBER COMPOSITIONS
Abstract of the Disclosure An acid scavenger additive for a one-component, acyloxy-functional RTV composition. The acid scavenger is selected from magnesium materials, zinc materials, and aluminum materials. The acid scavenger prevents a discoloration of the metallic substrate and a decrease in bonding properties of the RTV composition to the substrate on which it is applied.

Description

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ONE COMPONENT ACID-SCAVENGED REV
BONDING SILICONE RUBBER COMPOSITIONS
Background of the Invention The present invention relates to one-component REV silicone rubber compositions and more particularly the present invention relates -to one-component silicone rubber compositions with good bond:iIlcJ proprieties even at hi.cJh humidity conditions.
One-component REV silicone rubber compositions (REV stands for room temperature vulcanizable) are well known. Examples of such coy positions are for instance disclosed in US. Patent 3',38 , issued May 7, 1968 to Beers, and US. Patent 3,296,195, issued January 3, 1967 to Gauziness. Those compositions comprise as the basic ingredient a sullenly terminated diorganopolysi].oxane polymer having a viscosity varying from 100 to 1,000,000 centipoise at 25C., an acyloxy functional Eros slinking agent and a metal salt of a carboxylic acid as a curing promoter.
The composition may contain fillers, self-bondlng additives, f1.ame-retardant additives and other ingredients that are necessary. The most common acyloxy functional cross-linking agent is methyl, triacetoxysilane. The most common and the most desirable curing promoter is a tin soap. The most common types of fillers are fumed silica or precipitated silica treated or untreated with various types of -- 1 ., . ~,.~

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extending fillers such as crushed quartz, diatomaceous earth etc. A preferred self-bonding additive for such a composition is disclosed in Kulpa, US. Patent 3,296,151 issued January 3, 1967.
Irrespective of what ingredients are utilized, such compositions are packaged in a single package in the substantial absence of moisture and stored as such. When it is- desired to cure the composition seal on the package is broken and the composition is applied to cross-link and cure by exposure to atoms-phonic moisture to a silicone elastomers with final cure taking place in a period of time varying anywhere frown 24 to 72 hours. Other types of one-co~lponent REV compositions are also known with various types of cross-linking agents such as alkoxy functional cross-linking agents such as are disclosed in Beers US. Patent 4,100,129, issued July 11, 1978.
The Aztecs functional REV systems are desirable ; in that they are relatively simple and inexpensive to produce. However, such compositions had one major drawback and that is that they gave off acetic acid ; upon curing which was corrosive in some applications and had a pungent odor. Nevertheless, such Aztecs functional REV systems were utilized as sealants and gasket

2; forming materials in the automotive industry as early as 1971 for various purposes. It was found that these Aztecs functional REV systems Audi acceptable bonding I

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proper en to thy substrates eve: at high humidity conditions that is, at a Relative Humidity of 80% or more. However, as stated, such Aztecs systems were corrosive and the acid that was released tended to 5 discolor the metal to which it was applied. Since that time, the use of REV in the automotive industry has increased and it has been desirable to find a gasket sealant for automotive applications which would have good bonding properties to the steel or metal substrate. Accordingly, it was highly desirable to find a one component REV system which was relatively non-corrosive and which could be utilized as a casketing material in the automotive industry, and which further did not have a pungent odor. It should he noted that the alkoxy functional REV of Beers US. Patent 4,100,129 did have these properties, that is it was not corrosive and did not give off a pungent odor, but unfortunately such systems cured too slowly for automotive applications in most cases.
Z0 Accordingly, it was highly desirable to develop a one-component REV system that was relatively non-corrosive and did not give off a pungent odor and which ha high . temperature thermal properties and could he utilized . satisfactorily as a casketing sealant in automotive . 25 applications.
An example of such a sealant is disclosed in Beers, US. Patent 4,257,g32. Such sealant which was acyloxy ~23~<~8 SUE

functional differed from the traditional Aztecs functional REV systems in that the acyloxy group in the cross-linking agent had from 5 to 30 carbon atoms and was most preferably methyl iris (2-ethyl hexanoxy) Solon. There was incorporated into such a composition a plasticizer and an adhesion promoter which generally comprised a fluid polysiloxane having a high degree of tri-functionality or twitter-functionality as disclosed in the foregoing patent, fumed silica as the filler, a tin soap and preferably iron oxide as a thermal stabilizer for the composition.
It was disclosed in this pa-tent -there may be preferably incorporated ion -the composition as -the self-bonding agent a sill isocyanurate. Thor modifications of this system are for instance, disclosed in Smith et at, United States Patent Number 4,247,445, issued January 27, 1981. Another modification of this system was the utilization as disclosed in Mitchell, et at, United States Patent Number 4,273,698, issued June 16, 1981, the incorporation therein of sill Maltese, sill numerates and sill succinates as self-bonding additives. The foregoing sill Maltese, sill numerates and sill succinates of the foregoing Mitchell et at US. patent was preferable to the isocyanurates as adhesion promoters since they gave better bonding properties -to the foregoing RUT systems of United States Patent Number 4,257,932, issued March 24, 1981.
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the pre-reacting of the cross-linking agent with the acyloxy functional Solon cross-linking agent and preferably also the tin soap so as to yield more shelf stable compositions, as disclosed in US. Patent No.
4,308,372, issued December 29, 1981 to Dziark et at.
All of these patents disclose improvements over the basic composition of US. Patent No. 4,257,932, issued March 24, 1981 to Beers, which result in an improved composition. Elowever, the improvements disclosed in the foregoing Mitchell, et at. patent and the Dziark et alp patent were especially desirable in the application of the 2-ethyl hexanoxy functional REV
system in the automotive industry.
However, it was found that such compositions had a problem when applied as a casketing material. At environments of up to 50g Relative Humidity, most of the time the composition had acceptable bonding properties. However, it was noted that such systems did create a brown film on the steel substrate. However, what was more noticeable was that in the area of 70, 80 and more percent Relative Humidity the liberated acid upon the cure of the 2-ethyl hexanoxy system would react with the iron in the steel to form iron octet which would cause a brown ~Z~3~
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oil deposit on the steel and which acted as a release agent destroying the self-bonding properties of the composition. Although there was some loss of adhesion with the Aztecs systems, it was much more noticeable with 2-ethyl hexanoxy REV systems.
Accordingly, it was highly desirable to find a scavenger which wound lock up the acid as it was no-leased in the REV system such that the self-bonding pro-parties of the system would be maintained. It should be noted that self-bonding properties are highly desirable in REV systems, otherwise a primer has to he utilized which requires additional material and labor; thus in-creasing the cost of producing the silicone gasket, Accordingly, it was highly desirable to solve this problem 50 that the 2-ethyl hexanoxy REV system would have good self-bonding properties to metal substrates, and other substrates even at hick percent Relative Humidity of 70, 80 or more.
It is one object of the present invention to provide for a hexanoxy functional REV system with good self-bonding properties even at high percent Relative Humidity.
It is yet another object of the present invention to provide for a hexanoxy functional REV system that does not discolor the underlying metal to which it is Apple en' - which has good self-bonding properties to the underlying, .................................... ...................... .

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It lo yet an additional object of the present invention to provide fur an acid scavenger for Alex functional REV systems so as to maintain the self-S bonding properties of the composition even at high percent relative humidity.
It is yet also an additional object of the preset invention to provide a process for forming a silicone gasket in the automotive industry from an ac~loxy lung-tonal REV system in wish the system contains an acid scavenger.
It is yet still an additional object of the present invention to provide a process for forming a . silicone gasket against a metal substrate for auto-motive applications in which the silicone gasket has good self-bonding properties even at elevated percent Relative Humidity, is relatively non-corrosive, does not discolor toll metallic substrate and does not have a pungent odor.
It is still an additional object of the present invention to provide for an improved silicone gasket . for top automotive industry which has good self-bonding properties to metallic substrates.
. These and other objects of the present invention are 25 accomplished by means of the disclosures set forth here . below .
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Summary o-f the -Invention In accordance with the above objects, there is provided by the present invention a one-component REV silicone rubber composition with good bonding properties even at high humidity conditions comprising (A) 100 parts by weight of a sullenly end-stopped diorganopolysiloxane polymer having a viscosity varying from 100 to 1,000,000 centipoise at 25C. where the organ groups are monovalent hydrocarbon radicals and (B) from .1 to 10 parts by weight of an acyloxy cross-linking agent owe the formula r RmSi (OR em where R is a monovalent hydrocarbon radical of 1 to 8 carbon atoms and Al is an acyloxy radical of 2 to 30 carbon atoms, m is 0 or 1; (C) from .01 to 10 parts by weight of a curing promoter which is a metal salt of carboxylic acid; and (D) an effective amount of acid scavenger selected from the class consisting of zinc materials, magnesium materials, aluminum materials and mixtures thereof The most preferred materials within the above group are the metals, the oxides and the carboxylic acid salts. It should be noted further that the oxides must be utilized at a smaller concentration than the salts. If the oxides are utilized at somewhat above their ranges disclosed below, then what happens is that they inhibit the cure of the composition and the composition will cure slowly if at all, depending on how much of the materials has been placed in the composition.

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Accordingly while zinc oxide and possibly even aluminum oxide are- disclosed as fillers for acyloxy functional one-component REV systems, nevertheless if they are utilized in the 2-ethylhexanoxy system at above the concentration S limits disclosed in the ranges below, then they will in-habit the cure of the composition. Accordingly, we will now proceed to a more detailed description of the invent Shea.
Description of Preferred Embodiment it must be noted that preferably there is utilized the foregoing materials of zinc, aluminum end magnesium as acid scavengers in the instant composition The car-boxlike acid salts of zinc and magnesium, operate in the present invention and the oxides of these metals should 15 also operate within the scope of the present invention as acid scavengers.
Accordingly, only slightly basic or amphoteric metals would be desirable as acid scavengers in the instant composition. If the material it slightly ask 20 or amphoteric it will absorb the acid that is riven off during the hydrolysis to form an innocuous salt without detracting from the final cured properties of the compost-lion. Accordingly, zinc, magnesium and aluminum compounds will function effectively in the instant case even as - 25 zinc and magnesium metals.
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Aluminum metal might also function effect lively as an acid scavenger. There does not appear any reason why this metal powder cannot function effectively as acid scavengers in acyloxy-functional Al systems.
on addition, it is not known whether this lack or decrease in the self-bonding properties of a composition takes place with compositions other than acyloxy-. functional REV systems at high humidity conditions. How-ever, if the REV system gives off an acid during cure, and the composition is applied to metallic substrate, then conceivably the same type of phenomenon would be encountered and the same scavengers as utilized in the instant invention would be suitable to prevent loss of self-bonding properties.
It should be noted that the functions of the acid scavengers of the instant case are twofold one, to prevent or tie up the acids that are given off so as to decrease or eliminate the formation of an oily residue at the interface of the silicone rubber composition and the metallic substrate which would cause a decrease in self-bonding properties of the composition and the other is to prevent the acid given off from attacking the ; metallic substrate and resulting in discoloration of the substrate. It would also appear that other types ox compounds of zinc, aluminum and magnesium can be utilized '.

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as acid scavengers other thy the carbolic acid salts or the oxides or the eta powder. However, these other expounds would have to be neutral, or slightly basic. Further, although surety salts are preferred, any carbcxylic acid salts can be utilized in the instant invention as acid scavengers, other than aluminum carboxylic acid salts, and particularly carboxylic acid salts that average from 6 to 30 carbon atoms. There may ye utilized individual salts, Oxides, and metal powers or there may be utilized mixtures thereof depend-in on the type of ingredients that are used.

Further, zinc oxide is a scavenger in the instant case although not as effective as My and My. The most effective scavengers are the magnesium materials.
Aluminum car~oxylic acid salts such as an aluminum Stewart are not effective scavengers. Hkhever, other aluminum compounds and toe metal, although not as effective as the zinc and magnesium materials, should function to some extent as scavengers.
In this respect, there is a broad range in which the foregoing materials may be utilized in the system.
That is, the amount of material that will be used in the system will depend on the type of material it is.
Thus, broadly, there may be utilized an effective amount - of zinc, aluminum or magnesium material or mixtures thereof up to generally 6 part by weight of the material ~2~3~
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per 100 parts of the sullenly terminated diorganopoly-selection base polymer. If more than 6 parts are utilized, then the material would inhibit the cure of the dcyloxy-functional REV system in which it is incorvoratec.
Preferably the oxides and the metal powders are utilize in a concentration of anywhere from 0.05 - 2.0 parts by weight while the carboxylic acid salts are utilized in a concentration of anywhere from 3.0 to 6.0 parts by weigh-per 100 parts of the sullenly base polymer. As stated, it more than the specified amount of material is utilize in the composition, the cure of the composition will be inhibited, that is, it may not cure for weeks, for months, or not at all, or it may remain tickles to the touch for a long period of time or if too much of the oxides are use-, they may cause gellation of the composition before it cures completely and obtains its optimum physical roper-ties. In this respect, it should be noted that income cure results in poor physical properties of the compost on as well as making it very tacky to the touch This is highly undesirable in a silicone elastomers As indicate above and as shown in the examples below, the amount of concentration of the ingredient that is utilized will depend upon the ingredient that is used. Its optimum concentration will have to be determined by experimental an.

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The acid scavenger material is not utilized as a filler in the instant composition. That is, fillers are normally used in the composition to Pitter cheapen the cost of the composition - for instance extending fillers -or to increase the physical properties of the composition or give preferred select properties to the composition.
Most fillers such as fumed silica are utilized in the composition to increase its physical properties such as Tear, Hardness, and Tensile Strength. This is to be distinguished in the present composition in which oxides such as aluminum oxide, magnesium oxide and zinc oxide are utilized to absorb the acid that is formed from the cross-linkin~ agent when it hydrolyzes upon cure of the system. It should be noted that zinc oxide, and magnesium oxide have been disclosed as extending fillers for acyloxy-functional REV systems.
However, these ingredients when utilized as a filler are used not only at higher concentrations than the acid scavengers of the instant case, but they are also utilized in the traditional sense of fillers and not for absorption of acids formed by the hydrolysis of a cross-linking agent so as to preserve the self-bonding properties of the composition as is the case with the instant case.

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It must also be appreciated that the present phenomenon is noted to some extent with Aztecs functional Revs that is, with a cross-linking agent such as methyltriacetoxysilane. However, in those cases, while the acid does attack and discolor the metal substrate, the liberation and forming of a non-oily roused at the surface does not affect the self-bondin~
properties ox the acetoxy-functional composition anywhere near as great as is the case for the 2-ethylhe~anoxy functional REV system. Accordingly, the acid scavengers of the instant case can he utilized wit those systems not depending on how desirable it is to improve the self-bonding properties. However, the acid scavengers of to instant case are effective in preventing the discoloration of the metallic substrate by the acetic acid that it given off when the Aztecs system cures. Accordingly, the acid scavengers of the present invention are especially effective in preventions discoloration of metallic substrates of all types of acyloxy functional REV systems, and are most effective in preventing the decrease in self-bonding properties of one-component acyloxy functional REV systems where the acyloxy group has from 5 to 30 carbon atoms. It should also be noted that the discoloration of the ; 25 metallic surface, that is the discoloration of the substrate as well as the loss of sel,-bonding properties, is most noticeable with metallic substrates such as ., i . .. I...... ................... ... .. ..........

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zinc and iron substrates. It is not noticeable and it is not the case with plastic, glass, and ceramic sub-striates. Accordingly, the acid scavengers of the present case find most use in acyloxy-~unctional REV systems where the acyloxy group has from 5 to 30 carbon atoms, where the REV system is to be applied to metallic substrates, such as steel.
It is postulated that this phenomenon also occurs to some extent with a masonry or concrete substrate, that is the discoloration of the substrate around the sealant, and the possible loss of self-bonding properties. Accord-tingly, the acid scavengers of the present case would wind utility as ingredients to stop the loss of sel-bonding properties o. acvloxy functional REV systems where the REV system is to be applied to masonry substrates such as concrete as well as when it is applied to metallic sub-striates such as steel, but not stainless steel. An oily residue is not formed on stainless steel. As noted above, the acid scavengers absorb the acid and turn it into an innocuous salt without detracting from the physical properties of the cured composition.
This is especially important where the cured sift-cone elastomers is to be applied as a gasket in combo-session for automotive applications. Thus the composition is applied by machines or other means such as in . a layer between metallic substrates on which there . is applied another metallic layer there over to form a gasket between two metallic substrates in which --it-- , -. . .

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the cured silicone elastomeric gasket acts as a seal.

Such silicone elastomeric gaskets must have quick curing I- properties, be fairly non-corrosive, not have an objection Al odor, and have good oil resistance as 5 well as good thermal and weathering properties at high temperatures. Especially important is that such silicone elastomers gaskets have good self-bonding adhesion to the metallic substrate. Primers can be utilized to enhance adhesion. However, the use of primers increases the lo cost of applying or forming the silicone gasket.
Accordingly it is desirable to have a silicone elastom~ric composition with good self-bonding properties which the present invention accomplishes.
It must also be noted that within the above broad 15 definitions of concentrations of oxides and salts that there can be utilized a combination of a salt and oxide at a concentration within the preferred ranges disclosed above. However, the optimum levels whether ..... .
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oxides or natal polymers are used my themselves or in combination with metal salts, must be determined by experimentation and depend to some extent on the other ingredients of the composition. Accordingly, it is left to a worker skilled in the art to determine the best Go optimum concentration of metal salts or oxides in the composition to achieve the optimum acid scavenger function in an acyloxy-functional one-component REV
. system.
It should be noted that generally iris are utilized at a concentration of 10 parts or more by weight per 100 parts by weight of sullenly terminated diorgano-polysiloxane base polymer, and that the present acid ~czvengers are utilized in concentrations considerably below those levels.
With respect to the instant invention, it is now necessary to proceed to a brief description of toe archways components that may be present in the composition. us has been noted above, the basic polymer of the composition comprises a sullenly terminated diorganopolysiloxane .. . .. .. ..... . .. ... . .
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polymer hazing a viscosity varying from 100 - 1,000,000 centipoise at Corey the organ group is a monovalent hydrocarbon radical. The monovalent hydrocarbon radical can be any monovalent hydrocarbon radical such as alkyd radicals of 1 - 8 carbon atoms as methyl,ethyl,propyl, etc., cycloalkyl radicals such as cyclohexyl, cycloheptyl, etc.; mononuclear aureole radicals such as phenol, methylphenyl, ethylphenyl, etc.; alkenyl radicals such as vowel, alveoli, etc.;
and fluoroalkyl radicals of 3 - 8 carbon atoms such as 3, 3, 3, trifluoropropyl, to Preferably, the sullenly based polymer has the formula, HESS i o 1 I s where R3 and R4 are independently selected monovalent hydrocarbon radicals and the value of s is such that the viscosity of the polymer varies from 100 to 1,000,000 centipoise at SKYE. and more preferably varies from 100 to 100,000 centipoise at 25C. Tile radicals R3 and R4 - can be any of the monovalent hydrocarbon radicals pro-piously identified for the organ group for the term - "organ" in the sullenly terminated diorganopolysiloxane polymer. Per 100 pats of such polymer that may be I; present from .1 to 10 parts by weight of an acyloxy - functional cross-linXing agent of the formula, R S, (OR ) m 4-m -, -18-. . .
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where R is a monovalent hydrocarbon radical of 1 - 8 carbon atoms and R is an acyloxy radical of 2 - 30 carbon atoms, m is 0 or 1. Preferably R is methyl and Al is benzoxy or 2-ethylhexanoxy. The symbol Al can also 5 be Aztecs Accordingly, the three most preferred acyloxy functional cross-linking agents is methyl-triace~oxysilane, methyl-tris benzoxysilane, and methyl-tris 2-ethylhexanoxy Solon.
Although the improvement of the present invention will apply in any acid-functional one-component REV system, it is most preferably applied to acyloxy functional REV systems, specifically those in which the acyloxy group varies prom 5 - 30 carbon atoms. Finally, there may be present from 0.01 - 10 parts by weight of a curing promoter which is a metal salt of a carboxylic acid. Preferably the metal salt of a carboxylic acid that is a curing promoter is a tin salt. The most preferred tin salts are, for instance, dibutyl tin dilaurate, dibutyltindiacetate, dibutyl tin oxide, and dim ethyl tin bis-neodecanoate. In a case where the cross-linking agent is 2-ethylhexanoxy, then preferably the tin salts are dibutyl tin diacetate, dibutyl tin oxide and dim ethyl tin bis-neodecanoate disclosed in the fore-- going Beers Us Patent 4,257,9~2. There may also be used as disclosed in the foregoing patent from 1 - 10 parts by weight per 10~ parts of the sullenly polymer of an iron oxide thermal stabilizer.

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There may also be used anywhere from 10 Jo 200 parts by weight of a filler. The filler, if it is a rein-forcing filler, it is preferably present at a concern-triune of lo to lo parts by weight. Examples of reinforcing fillers are for instance fumed silica and precipitated silica. These fillers may be present, treated, or untreated, but preferably are treated with cyclopolysiloxane such as disclosed in Lucas US.
Patent 2,938,009, Lichtenwalner, US. Patent 3,004,859 lo and or soullessness as disclosed in Smith, US. Patent 3,635,743. Such patents are exemplary of such treatment technology. Preferably the reinforcing type of fillers are treated so that the filler will not unduly increase the viscosity of the composition in the uncured state. The rest of the filler may be a reinforcing or extending filler. All of the filler or some of the filler can be an extending filler. Examples of extending fillers, are for instance, titanium dioxide lithopone, ~e-exidc zirconium silicate, silica argyle, irk diatomaceous earth, fibers, calcium carbonate, chronic oxide, zirconium oxide, alpha quartz, calcined clay, carbon black graphite, cotton, synthetic fibers, etc.
It should be noted that these extending fillers are utilized preferably in addition to the reinforcing fillers for various purposes. Most notably, they may I
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make the composition paintable, or they may increase or reinforce the properties of the composition without unduly increasing the uncured viscosity of the composition. However they are not anywhere near as effective as the fumed silica and precipitated silica in increasing the cured physical properties of the silicone rubber composition.
Per 100 parts of the sullenly terminated polymer on the base polymer of the instant composition, there may also be present from 1 to 10 parts of iron oxide as a terminal stabilizer as disclosed in -the ~oregoincJ US. Patent 4,257,932, issued March 24, :L981 to Beers.
There is also disclosed in the foregoing patent, that there may also be present from 2 to 20 parts by weight of a fluid polysiloxane containing a high degree of tri-functionality, ~étra-functionality or a mixture of in- and tetra-functionality, comprising (i) from 25 to 60 mole percent of moo-alkylsiloxy units; sulks units or a mixture of such units;
(ii) from 1 to 6 mole percent of in-alkylsiloxy units;
(iii) from 34 to 74 mole percent of dialkylsiloxy units, said polysiloxane containing from about .1 to 2% by weight of a silicone bonded hydroxyl groups.
For more information in-to such fluids, one is referred Jo the foregoing USE Patent 4,257,932 and US. Patent 3,382,205, issued May 7, 1968 to Beers.

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It is generally advantageous in such compositions to decrease the amount of fumed silica in the composition so that the composition has the desirable properties of the cured state but does not have an undesirably 5 high viscosity in the uncured state. Accordingly, when the concentration of fumed silica is reduced below a certain point, the uncured silicone rubber composition does not have a sag control. That is, it is not thixotropic. Accordingly, a sag control agent may be incorporated into the composition which is a small amount ox a polyether as disclosed iII Wright et alp United States Patent ~,261,758, issued April 14, 1981.
Accordingly, per 100 parts of the sullenly terminated diorganopolysiloxane polymer, there may be incorporated into the composition from .03 to 2.0 parts by weight Ox a l~olyether selected from a class consisting of A -- O -- CXH 2 x ) B
and (A - O - ~CXH2xO) I
wherein A and B represent radicals selected from the 20 class consisting of hydrogen, alkyd radicals containing from 1 Jo 12 carbon atoms, cycloalkyl radicals containing 5 Jo 7 carbons in the ring, mononuclear and binocular aureole radicals and mononuclear aureole lower alkyd groups attached to the aromatic nucleus contain a total of no more than 5 carbon atoms;
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where R is alkyd containing from 1 Jo 11 carbon atoms, Q is a residue of a polyhydric initiator radical containing at least two hydroxyl radicals selected from the class consisting of ethylene, glycol, glycerol, trim ethyl-polypropane~ and other polyhydric alcohols having from to 6 hydroxyl groups, a is a number having a value of from 4 to 2000; x is a number having a value of 2 to 4;
y has a value of from 2 to 10 and z has a value of prom 1 to 5; the polyether having a molecular weight of from about 300 to about 200,000. There may also be present in the composition from .1 Jo 3 parts by weight of a self-bonding agent. The self-bonding agent may be a isocyanurate as disclosed in the foregoing Biers US.
Patent No. 4,257,932. If the self-bonding agent is an isocyanurate, it is preferably 1, 3, Tracy trimethoxy-silylpropyl isocyanurate. Most preferably, such additive is preferably selected from sill Maltese, sill numerates and sill succinates as well as selection Maltese and mixtures thereof. Examples of such self-bonding additives which are preferred for the composition of the instant invention are for instance disclosed in the foregoing Mitchell et Allis, Patent A ,273,698 issued June 16, 1981.
Preferably the cross-linking agent is reacted with a self-bonding additive prior to being incorporated into the composition. The cross-linking agent, that is the ~23(~9~
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awry functional cross-linking agent and the self-bonding additive are prereacted prior to being incorporated into the composition. This is especially true if the 2-ethylhexanoxy junctional Solon cross-linking agent is utilized and also a self bonding additive selected from sill Maltese, sill fumarates, and sill succinates. This prereacted self-bonding additive and cross linking agent is disclosed in the US. Patent of Dziark et at, Patent No. 4,308,372, issued December 29, lg81. The most preexred Scholl-bonding additive is for instance bis-trimethoxypropyl fumarate or alternatively bis-trimethoxypropyl Malta. There may be other additives in the composition as desired, such as flame-retardant additives, further heat agent additives, plasticizers, etc. These additional additives will not affect the efficiency and suitability of the acid scavengers in carrying out their function.
The foregoing acid scavengers will not affect the uncured properties of the composition as far as is known. These acid scavengers may be incorporated in the composition in any manner which may be desired.
That is, generally they may be added to the catalyst component and mixed with the other ingredients as desired.
The entire mixture is made substantially an hydrous and packaged as such. To cure the composition, the seal ............................................... .... , .. , . ..... ...... .. ., .. , . . . - - .. . , .. ..... ,, ., ., ., ., ., .. ., .. - ..
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on the package is broken, and the composition applied whereupon on exposure to atmospheric moisture the come position cures to a silicone elastomers with final cure taking place in 24 - 72 hours. It must be appreciated that it is necessary to have a curing promoter in the composition if the composition is to cure to a full cure in the 24 - 72 hour period. Without a curing promoter, the cure may take a longer period of time and may not be as complete.
In the instant composition, the magnesium materials the aluminum materials, and zinc materials junction as acid scavengers. That is, they absorb and react with the acid that is given up during the cure of the composition and the hydrolysis of the cross-linking agent so as to prevent such acids and salts detracting from the physical properties of the composition and will not affect deleteriously the self-bonding properties of the compost-lion. One function of the acid scavengers is to improve the self-bonding properties of the composition or rather to prevent the acid that is liberated at a high percent relative humidity from detracting from the sel-bonding properties of the composition and the other is to prevent the acid that is liberated from attacking and discoloring the metal substrate on which the silicone rubber composition is applied. As can be seen from the examples below the acid scavengers of the instant case perform their function very well. It should also be issue 605I-499 noted that the various constituents of the compositions of the instant case which haze bee described and which are well known have not been described in great detail since workers skilled in the art may be referred to the foregoing patents and patent applications referred to herein for further information on the subject.
The examples below are given for the purpose of illustrating the present invention. They are not given for the purpose of illustrating limits and boundaries to the instant invention. All parts are by weight.

okay no In the -ego examples there was utilized a Sealant A. Sealant A comprised 66.423 by weight ox a blend of sullenly terminated dimethylpolysiloxane polymers having a blend viscosity of 4500 centipoise at 25C., 3.98% of iron oxide, 6.64% by weight of a tri-functional fluid containing 3 mole percent trim ethyl-sulks mono-functional units, 40 mole percent of monomethylsiloxy tri-functional units, 57 mole percent ox dimethylsiloxy, di-functional sulks units and .5 percent hydroxy groups. The composition also contains I weight of U KIWI which is a polyether sold by the Union Carbide Corporation, Connecticut. To this mixture was added 15.94% by weight of octamethyl-cyclotetrapolysiloxane treated fumed silica, 4.70% by weight of methyl iris ~-ethylhexanoxy Solon 2.03%
by weight of bis-trimetnoxypropyl fumarate, and .1% by weight of dimethyltin bis-neodecanoate.

,.. ,......... ..... : .. ......... _.. ... :.. -.. -.. :.. I. --I
SUE

Such a sealant which was tested with various types of acid scavengers in it was compared with the following Aztecs Sealant B. Sealant B comprised 71.63% by weight of a sullenly terminated dimethylpolysiloxane having 6000 centipoise viscosity at 25C., 2.16% of iron oxide, 7.88% of tri-func~ional fluid containing 3 mole percent of trimethylsiloxy monofunctional units, 20 mole percent methyl trifunctional sulks units, 77 mole percent of dimethylsiloxy di-functional units and lo approximately .5 weight percent of sullenly to this mixture of Sealant B there was added 14.32~ ox' octame-thyl~
cyclotetrapolysiloxane treated fumed silica, 3.19~ of methyltriacetoxysilane, .79% by weight of di-tertiary-butoxydiacetoxysilane and .03% of dibutyltindilaurate.
Example l There was prepared and tested in Sealant A and a Sealant B containing no acid scavengers in them. This data was compared with a composition containing 3.66 weight percent zinc Stewart and .46% by weight of magnesium oxide.
All of the compositions were tested after cure for five days at 77% and 80% relative humidity.
There were samples of Sealant with the acid scavenger, which were further exposed to 4 hours at 250F. to simulate the temperature increase encountered ~ZZ3~
SUE
in d starting automobile engine. results are set forth in Table I below. The shear adhesion in psi and percent cohesive failure was measured as follows:
The substrate and screen were both cleaned by first immersing in Tulane and then scrubbing and drying with laboratory tissue.
The typical shear adhesion test specimen was prepared using previously cleaned 1 inch by 4 inch by a 0.040 inch cold-rolled steel substrate. This substrate was clamped into place by means of a steel bar bolted over one end to a 1/2 inch thick rigid machined steel jig.
The jig was so designed as to leave one square inch of exposed surface area. The sealant was applied to the exposed surface. A 1 by 4 inch 20 mesh piece of stainless steel screen was then embedded into the sealant at a bond line thickness of 0.010 to 0.015 inches. The excess sealant was removed from the top and sides of the specimen by means of a spatula. The resulting specimen -was then allowed to cure in the environments described in the examples.
; After completion of cure the specimens were pulled apart at the rate of 0.5 inches per minute using a Monsanto Extensiometer.

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.

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.

isle SUE
TABLE I

Shear Adhesion Performance after Five Days at 77F. and go Relative Humidity Sex t B Sealant A lank A with on S rate and Moo

4 his 4 hut 4 his Into 250~F.~ vial 250~F.Initial 250F.

Shapiro adhesion psi 142 12943 27 135 198 cohesive Failure 7 3 0 0 80 lo As the results indicate, the adhesion performance of the zinc Stewart, magnesium oxide in Sealant A was superior to the other two specimens. In addition, this specimen exhibited no discoloration of the steel sub-tryout whereas the Aztecs specimen had a bright brown discoloration at the sealant, metal interface and the other Sealant A specimen had a dark brown oily deposit`
in the sealant steel interface.
Example 2 Sealant A and Sealant B were tested for shear adhesion with various levels of magnesium oxide. These runs were made with a direct comparison with Sealant B
which contained no scavenger. Again the samples were prepared as set forth in Example 1 and exposed to 80%
relative humidity for five days at 77F. At the end of that period they were tested for shear adhesion both in psi and percent. cohesive failure and also after four . .. , .. .. , ...... ..................................... _ .... _ ... .............. ..... ... .; ... . ..... .

lL~Z3~913 SUE

hours at 25UF. The results are set forth in Table II
below: Sealant A and Sealant B are the same sealant as defined previously TABLE II

The Effect of Magnesium Oxide on the Adhesion Performance of Sealant A at 80% Relative Humidity and 77F.

Sealant A Sealant B
MgOShear Adhesion no Scavenger) : 10 Level(psi/% OF (psiJ%C.F.) ~wt.%)Initial 4 hrs.!250~FInitial 4 hrs.l250F.

0.35263/90 217/70 95/0 1~7/0 O 35 (1) 202/75 180/85 71/0 6~0 0 15182/55 215/65 71/n 6~/0 . 15 (1) This was a repeat of the preceding experiment using another newly prepared formulation.

As the results of Table II indicate, there is obtained a superior self-bonding composition with Sealant A with an acid scavenger as compared with Sealant B. It should be noted that the optimum level of acid scavenger, that is, of magnesium oxide alone appeared to be .35% by weight. Again similar tests were run utilizing zinc Stewart as the acid scavenger in Sealant A as compared to Sealant B utilizing no acid scavenger in the composition - 25 Gwen, after the shear adhesion specimens were prepared, the - samples were exposed to 80% Relative Humidity for five . . .
.
.
-.

. .
... .

I.

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days at 77 F. At the end of that period, samples were tested for shear adhesion and percent cohesive failure.
Other samples were further exposed for four hours at 250F. before being tested for shear adhesion and percent cohesive failure. The results for the zinc Stewart and zinc oxide at various levels are indicated in Table III below. As noted previously, Sealant B
was the formulation as identified previously and wherein the Sealant B samples had no acid scavenger in I them.

TALE III
The Effect of Zinc Stewart on the Adhesion Performance of Sealant A
at 80% Relative Humidity and '77 F.
Sealant A Sealant B
Zinc Stewart Shear Adhesion (No Scavenger) Level (White) (psi./% OF (psi./% OF
Initial 4 hrs./250 Initial 4 hrs./250 F.

3.8125/75 210/100 157/3 153/100 Z~0 Level (wt.%) _ 0.35128/10 191/95 71/0 64/0 0.70189/40 291/100 71/0 64/~

It should be noted that in the above experiment the zinc oxide containing sealant samples exhibited some sun-face tack after curing for five days at 50% RHO but not after the 80% RHO cure or exposure to 250F. for four hours.
As the results in Table III show, both zinc Stewart and zinc oxide are effective acid scavengers for the Sealant A

.. ..... . ... ................ ...... ........... ......................... ............................................. ............

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system, Although, the levels at which each on was effective differed markedly as explained above Example 3 There was prepared a Sealant C similar to Sealant A comprising the following composition: 66.42% by weight of a sullenly terminated dimethylpolysiloxane polymer blend having a viscosity of 4500 centipoise plus or minus 500 centipoise at 25C., 3.98~ of iron oxide; various levels of acid scavengers; 6.64 lo by weight ox a tri-functional fluid of Sealant A;
.13% by weight of a polyether which sold under the name of Pluracol-7, a polyether sold under the above trade name by the Wyandotte Chemicals Corporation;
15.94% of octamethacyclotetrasiloxane treated fumed silica filler; 4.70% of methyl iris 2-ethylhexanoxy Solon; 2.09~ by weight of bis-tri-methoxy propel numerate (or Malta) and .10% of dim ethyl tin bus-neodecanoate. These samples were prepared as in Example 1 which were exposed to 80% Relative tumidity, 80 F. for five days. The samples were also part baked for four hours at 250F. to simulate engine heat up. The shear adhesion and % cohesion failure results of Sealant C mixed with various levels of zinc Stewart and magnesium oxide under the foregoing conditions are listed in Table IV.

, ...... , _, _ _ . .......... _ _ . .... . . _ . _ _ . _ .. _ _ . .............................................. _ .. _ 122309~3 swig TABLE IVY

Effect of Zinc Stewart - Magnesium Oxide Combinations on the Adhesion Performance of Sealant C at: 80F/
. 80% RHO

Zinc Stewart level, White % 10.8 3.6 2.6 O
Magnesium Oxide. Wt. % 103 0.5 0.3 Shear Adhesion, PsV% OF 35/90~2) Lowe ~.12/100 30-65/0 (11 Samples were also post-baked for 4 hours.J250F
to simulate engine heat-up. For quality control purposes, this is for 8 hrs./150F.
(2) Inhibition of Cure Noted at 10.8 Wit Zinc Stewart.
Example 4.
Into Sealant C which was prepared as in Example 3 there were incorporated various amounts of zinc Stewart by itself as an excellent scavenger was compared to Sealant C without any acid scavenger as a control. The composition was the save in each case except there was utilized tune various levels of zinc Stewart as indicated in Table V below. The results are set forth in Table V.

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TABLE V

Effect of Zinc Stewart on Sealant C Adhesion Performance at 8QF~aO% RHO
cure Times 5 Days) zinc Stewart Level, ~t.%10.8* 3.8 2.6 1.3 0 shear Asian psi/% C~F.35190 210/lt)0 45/0 6~.5 30~65/0 (Steel Substrate *Cure butted lo Moo included The results of Tale V were samples which were aged for five days at 803 Relative Humidity and 80F. Each sample was then post-baked for four hours at 250F. to simulate engine heat-up. As the results in Table V indicate, zinc 15 Stewart was a very effective acid scavenger and self-bonding improver at a level of 3.8% by weight. Similar tests on the same Sealant C composition but with various levels of magnesium oxide showed similar improvements in self-bonding properties of the Sealant C composition after 20 the sample was aged at 80% Relative Humidity and 80F.
` for five days and then post-baked for four hours at 250F.
- Each sample was subjected to this procedure. The result-in shear adhesion tests which were curried out in the same manner as set forth in Example 1 are set forth in Table 25 VI below.
Jo --I' .

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BLUE VI

The Effect of Magnesium Oxide on Sealant C Adhesion Performance at 80~F/80% RHO * (Cure Time 5 Days) Magnesium 1.4 a .5 Owe 0~23 0.16 Owe Owe Oxide Level (Maglite D) Adhesion, 45/0 130/30 165/85 215/~ 291/100 215/70 248/100 3~-6~/0 s~xked hours.J250F.
As the results of Table VI show magnesium oxide appeared to be very effective as an acid scavenger to improve the sel~-bondLng properties of the sealant C composition at levels of ~16% by weight or somewhat less. The results of both Tables V and VI show that zinc Stewart and magnesium oxide were effective self-bonding improvements for the 2-ethylhexanoxy functional REV systems. It should be noted that the magnesium oxide utilized in these tests was sold unsex the name Magllte-D, a trade-name of Merck Chemical Corporation, of New Jersey.
As the results above indicate, there is obtained advantageous improvement in self-bonding properties of acyloxy-functional REV systems and especially those in which the cross-linking agent is 2-ethylhexanoxy functional at 80~ Relative Humidity even when the cured composition is exposed to 80% Relative Humidity for extended periods of time. The most effective acid scavensersfor accomplishing this purpose have been found Jo be zinc Stewart, zinc oxide, magnesium oxide and museum metal However, other materials, that is other metal salts of ~Z~3~ SUE

carboxylic acids other than the foregoing metals of zinc and magnesium should be just as effective as the zinc Stewart. Preferably the carboxylic acid group carbon content varies from 6 to 30 carbon atoms. In addition, all the oxides should also function effectively although at lower levels as the foregoing magnesium oxide and zinc oxide, as well as the metal powders. No format lion of gas was noted with the magnesium and zinc powders.
Further, although the present system was devised when the acyloxy REV system is to be applied to a metallic sub-striate, it can be appreciated that similar advantages will also be found in the utilization of such acid scavengers when the acyloxy-functional REV system is applied to other types of substrates.

Example 5 In Examples - 9, the shear adhesion specimens were first cured for five days under the conditions desk cried and then post-baked for four hours at 250~F. In each experiment the conditions for the control were 77F~
and 50% Relative Humidity. The elevated humidity environ-mint was maintained at 80F. and 80 percent Relative tumidity. In each case, in Examples 5 - 9, the composition was the same as Sealant A on page 26 except for the type and amount of the scavenger defined below. The Control .;,~.
composition was the same as Sealant With the same amount of scavenger and cured under normal conditions.

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A composition the same as Sealant A was prepared into which aluminum Stewart was incorporated at a concentra-lion of 2.78 weight percent. The control sealant con-twined the same amount of scavenger.
Shear Adhesion Results:
1 Control: the sample was cured 5 days at phoned 50% Relative Humidity followed by a post-bake of four hours at 250F.
Shear Adhesion = 247 psi at 100%
cohesive failure.
2. Elevated Humidity: The sample was cured five days at 80F. and 80% Relative Humidity followed by a post bake of four hours at 250F. Shear Adhesion = 3 psi at 0%
cohesive failure.

Conclusion Aluminum Stewart does not function as a scavenger.

Example 6 Alumina (aluminum oxide was incorporated in the Sealant A composition at a concentration of 0.5 weight percent. The control sealant contained the same amount of scavenger.
1. Control Shear Adhesion = 292 psi at 100%
cohesive failure.

... ,.. ,......... ,....... . _ . _ ., .. . ... = , _ _ , .,, ,,, ,, =, ,_ I, ~Z~3~9~3 swig 2. Elevated Humidity Shear Adhesion - 39 psi at I
- cohesive failure.
Thy test conditions were the same as in Example 5.

Conclusion Aluminum oxide has a low degree of scavenger activity in comparison with the control shown in Example 9.

Exile 7 Powdered magnesium metal ox a particle size of 70 -80 mesh was incorporated into Sealant A composition at a concentration of 0.71 weight percent. Top control sealant contained the same amount of scavenger.
lo 1. Control Shear Adhesion = 190 psi at 90%
cohesive failure.
2. Elevated Humidity Shear Adhesion - 212 psi at 96~
cohesive failure.
The test conditions were the same as in Example 5.

. . .
.
Magnesium metal is an excellent scavenger.
I. , ~223Q~3 SUE

.

Example 8 Powdered zinc metal of a particle size of about 20 mesh was incorporated in the Sealant A composition at a concentration of 0.71 weight percent. The Control con-twined the same amount of scavenger.
1, Control Shear Adhesion = 18~ psi at 100%
cohesive failure.
2. Elevated Humidity Shear Adhesion - 105 psi at 0%
cohesive failure.
The test conditions were the same as in Example 5.

Conclusion zinc metal is a mildly active scavenger.

Example No test scavenger was used in this example. The composition was the same as Sealant A. This is the experimental control.
1. standard Conditions Shear Adhesion = 288 psi at 97%
cohesive failure.
2. Elevated Humidity Shear Adhesion = 11 psi at I
cohesive failure.

Alumina, magnesium metal and zinc have varying degrees of activity as scavengers as indicated above.

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Claims (26)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for forming a one-component RTV
silicone rubber composition with good bonding properties even at high humidity conditions, comprising:
(1) mixing (A) 100 parts by weight of a silanol end-stopped diorganopolysiloxane polymer having a viscosity from 100 to 1,000,000 centipoise at 25°C where the organo groups are monovalent hydrocarbon radicals;
(B) from .1 to 10 parts by weight of an acyloxy functional cross-linking agent of the formula, Rm Si (OR1)4-m where R is a monovalent hydrocarbon radical of 1 to 8 carbon atoms and R1 is an acyl radical of 2 to 30 carbon atoms, m is 0 or 1;
(C) from .01 to 10 parts by weight of a curing promoter which is a metal salt of a carboxylic acid; and (D) an amount of acid scavenger selected from:
(i) 0.01-2 parts by weight of magnesium oxide, zinc oxide or aluminum oxide, (ii) 0.01-2 parts by weight of magnesium metal, zinc metal or aluminum metal, (iii) about 4 parts by weight of a magnesium salt of a carboxylic acid, or (iv) mixtures thereof.

2. The process of claim 1 wherein the acid scavenger is selected from magnesium stearate.

3. A process for forming a one component RTV
silicone rubber composition with good bonding properties at high humidity conditions, comprising:
(1) mixing (A) 100 parts by weight of a silanol end-stopped diorganopolysiloxane polymer having a viscosity from 100 to 1,000,000 centipoise at 25°C where the organo groups are monovalent hydrocarbon radicals;
(B) from .1 to 10 parts by weight of an acyloxy functional cross-linking agent of the formula Rm Si (OR1)4-m where R is a monovalent hydrocarbon radical of 1 to 8 carbon atoms, R1 is an acyl radical of 2 to 30 carbon atoms, and m is 0 or 1;
(C) from .01 to 10 parts by weight of a curing promoter which is a metal salt of a carboxylic acid; and (D) from .01 to 2 parts of an acid scavenger selected from the group consisting of magnesium oxide, zinc oxide and aluminum oxide or mixtures thereof.

4. A process for forming a one component RTV
silicone rubber composition with good bonding properties at high humidity conditions, comprising:
(1) mixing (A) 100 parts by weight of a silanol end-stopped diorganopolysiloxane polymer having a viscosity from 100 to 1,000,000 centipoise at 25°C where the organo groups are monovalent hydrocarbon radicals;
(B) from .1 to 10 parts by weight of an acyloxy functional cross-linking agent of the formula Rm Si (OR1)4-m where R is a monovalent hydrocarbon radical of 1 to 8 carbon atoms, R1 is an acyl radical of 2 to 30 carbon atoms and m is 0 or 1;
(C) from .01 to 10 parts by weight of a curing promoter which is a salt of a carboxylic acid; and (D) from .01 to 2 parts of an acid scavenger selected from the group consisting of magnesium metal, zinc metal and aluminum metal or mixtures thereof.

5. A process of forming a one component RTV
silicone rubber composition with good bonding properties at high humidity conditions, comprising:
(1) mixing (A) 100 parts by weight of a silanol end-stopped diorganopolysiloxane polymer having a viscosity from 1.00 to 1,000,000 centipoise at 25°C where the organo groups are monovalent hydrocarbon radicals;
(B) from .1 to 10 parts by weight of an acyloxy functional cross-linking agent of the formula Rm Si (OR1)4-m where R is a monovalent hydrocarbon radical of 1 to 8 carbon atoms, R1 is an acyl radical or 2 to 30 carbon atoms, and m is 0 or 1;
(C) from .01 to 10 parts by weight of a curing promoter which is a salt of a carboxylic acid; and (D) about 4 parts by weight of a magnesium salt of a carboxylic acid as an acid scavenger.

6. An article of manufacture comprising a laminated article having a plurality of metal pieces wherein between the metal pieces there is a layer of a one-component RTV silicone rubber composition with good bonding properties even at high humidity conditions comprising:
(A) 100 parts by weight of a silanol end-stopped diorganopolysiloxane polymer having a viscosity varying from 100 to 1,000,000 centipoise at 25°C where the organo groups are monovalent hydrocarbon radicals;
(B) from .1 to 10 parts by weight of an acyloxy functional cross-linking agent of the formula, RmSi (OR1)4-m where R is a monovalent hydrocarbon radical of 1 to 8 carbon atoms and R1 is an acyloxy radical of 2 to 30 carbon atoms, m is 0 or 1;
(C) from .01 to 10 parts by weight of a curing promoter which is a metal salt of a carboxylic acid; and (D) from 0.1 to 4 parts by weight of acid scavenger selected from the class consisting of zinc materials, magnesium materials, aluminum materials and mixtures thereof.

7. The article of manufacture of claim 6 where the acid scavenger comprises from .01 to 2 parts by weight of a material selected from the class consisting of zinc oxide, magnesium oxide, aluminum oxide, and mixtures thereof.

8. The article of manufacture of claim 6 where there is present from 3 to 4 parts by weight of an acid scavenger selected from the class consisting of zinc and magnesium salts of carboxylic acids.

9. The article of manufacture of claim 8 where the acid scavenger is selected from the class consisting of zinc stearate and magnesium stearate.

10. The article of manufacture of claim 9 where the cross-linking agent is methyl triacetoxysilane.

11. The article of manufacture of claim 9 where the cross-linking agent is methyl, tris(2-ethylhexanoxy)silane.

12. The article of manufacture of claim 11 where the curing promoter is dimethyl tin bis-neodecanoate.

13. The article of manufacture of claim 12 further including from 1 to 10 parts by weight of an iron oxide thermal stabilizer.

14. The article of manufacture of claim 13 further comprising having therein from 10 to 100 parts by weight of a filler.

15. The article of manufacture of claim 14 wherein the filler is present from 10 to 100 parts by weight and is selected from the class consisting of fumed silica and precipitated silica.

16. The article of manufacture of claim 15 where the filler is treated with cyclopolysiloxanes prior to being incorporated into the composition.

17. The article of manufacture of claim 16 where the filler is treated with silazanes prior to being incorporated in the composition.

18. The article of manufacture of claim 16 where there is further present from 2 to 20 parts by weight of a fluid polysiloxane containing a high degree of trifunctionality, tetra functionality or a mixture of tri and tetra functionality comprising:
(i) from 25 to 60 mole percent of mono-alkylsiloxy units, siloxy units or a mixture of such units;
(ii) from 1 to 6 mole percent of trialkyl-siloxy units;
(iii) from 34 to 74 mole percent of dialkylsiloxy units, said polysiloxane containing from about .1 to 2% by weight of a silicone bonded hydroxyl groups.

19. The article of manufacture of claim 18 further including a sag control agent comprising from .03 to 2 parts by weight of a polyether selected from the class consisting A - O - (CxH2xO)n - B
and (A-O-(CxH2xO)???(Q)z wherein A and B represent radicals selected from the class consisting of hydrogen, alkyl radicals containing from 1 to 12 carbon atoms, cycloalkyl radicals containing 5 to 7 carbons in the ring, mononuclear and binuclear aryl radicals and mononuclear aryl lower alkyl radicals wherein alkyl groups attached to the aromatic nucleus contain a total of no more than 5 carbon atoms;
where R2 is alkyl containing from 1 to 11 carbon atoms, Q is a residue of a polyhydric initiator radical containing at least two hydroxyl radicals selected from the class consisting of ethylene, glycol, glycerol, trimethylol-propane, and the polyhydric alcohols having from 2 to 6 hydroxyl groups, a is a number having a value of from 4 to 2000; x is a number having a value of 2 to 4;
y has a value of from 2 to 10, and z has a value of from 1 to 5; the polyether having a molecular weight of from about 300 to about 200,000.

20. The article of manufacture of claim 19 further including from .1 to 3 parts by weight of a self-bonding agent.

21. The article of manufacture of claim 20 wherein the self-bonding agent is 1,3,5-tristri-methoxysilylpropyl isocyanurate.

22. The article of manufacture of claim 20 wherein the self-bonding additive is selected from a class consisting of silyl maleates, silyl fumarates, silyl succinates, and mixtures thereof.

23. The article of claim 22 wherein the self-bonding additive is bis-trimethoxy propyl fumarate.

24. The article of manufacture of claim 22 wherein the self-bonding additive is bis-trimethoxy-propyl maleate.

25. The article of manufacture of claim 22 wherein the silanol end-stopped diorganopolysiloxane polymer has the formula, where R3 and R4 are independently selected from mono-valent hydrocarbon radicals and the value of s is such that the viscosity of the polymer varies from 100 to 1,000,000 centipoise at 25°C.

26. The article of manufacture of claim 6 where the layer of one-component RTV silicone rubber composition is a gasketing layer between the plurality of metal surfaces.