JPS638147B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to room temperature vulcanizable silicone rubber compositions, and more particularly to low modulus room temperature vulcanizable silicone rubber compositions that have good shelf life as a result of the use of certain catalyst systems. Sealants are well known. Sealants, particularly those used in high-rise buildings, must adhere to the substrate to which they are applied and preferably have elastomeric properties. The use of such sealants in high-rise buildings is well known and is applied where the window glass meets the building to seal the glass to the metal frame and provide a weather-resistant seal. Furthermore, once a window glass is sealed to a metal frame using a sealant, especially in high-rise buildings, it is used to hermetically protect the material against weather elements to prevent moisture and dust from entering the building. There are many areas where sealants are desirable. Many sealants are used in these applications, particularly polysulfides. Furthermore, it is particularly desirable that the sealant be an elastomer in its cured form, ie, capable of being compressed or expanded, and thus having a modulus of elasticity and elastic memory. Preferably, the sealant is in the form of a true elastomer, which expands and contracts at the joint in which it is placed and remains sealed against the elements. It should be noted that in certain such sealant applications, sealants with high tensile strength and good adhesion to the substrate are preferred. In this application, the toughness of the sealant is of primary importance.
The lack of elastic modulus of the sealant is of minor importance. Small such sealant applications are necessarily applied to sealing joints with small joint movements. It is preferred to use a low modulus sealant so that the sealant can accommodate significant relative expansion and contraction in the joint opening. Here, low modulus sealant means a sealant with medium tensile strength but high elongation. Such sealants can be made tougher by incorporating treated fillers. However, the important property for sealants is elongation rate, and therefore,
Preferably, it can be compressed and expanded by at least 25% of the distance of the joint thickness, and more preferably, it can be expanded and compressed by 50% of the joint thickness. The more the sealant expands and compresses with respect to the joint thickness or its own thickness, the more the sealant will have some adhesion to the substrate, i.e., will not pull away or be released from the substrate when expanded or contracted. The more you do, the more desirable it becomes. One such sealant useful in high-rise construction is a one-component room temperature vulcanizable silicone rubber sealant. One of these sealants
Examples can be found, for example, in US Pat. No. 3,296,161. This patent discloses the use of dialkoxydiasiloxysilane additives to improve the bond strength of one-component room temperature vulcanizable silicone rubber acyloxy systems. Other patents disclosing such sealants are for example U.S. Pat. No. 3,382,205 to Beers, in which R ₂ SiO units,
Room temperature vulcanizable silicone rubber compositions are disclosed that include a fluid consisting of RSiO _3/2 units and R ₃ SiO _1/2 units, where R is a monovalent hydrocarbon group. The above additives are for one-component room temperature vulcanizable silicone rubber compositions. These one-component RTV compositions (hereinafter RTV refers to room temperature vulcanizable silicone rubber compositions) are composed of silanol-terminated diorganopolysiloxane polymers (organo groups are monovalent hydrocarbon groups), reinforcing or bulking a filler selected from the group consisting of silica fillers (such fillers may be treated or untreated; an example of a reinforcing filler is fumed silica); and a crosslinking agent (which may be any alkyltriacyloxysilane but is preferred). is methyltriacetoxysilane). It is preferable to use catalysts in these systems to accelerate curing, and such catalysts are preferably metal salts of monocarboxylic acids (metals range from lead to manganese in the periodic table). The basic components of silanol polymer, filler, acyloxy crosslinker and metal salt of carboxylic acid are simply mixed under anhydrous conditions. When it is desired to cure the system, the mixture is simply applied and exposed to atmospheric moisture, releasing acetic acid and curing into a silicone elastomer. When the crosslinking agent is methyltriacetoxy, many additives can be added to such compositions to modify the properties. Beers U.S. patent no. disclosed above
No. 3,382,205 and Kulpa, U.S. Pat. No. 3,296,161, disclose two additives that can be added to such systems to improve properties, and in Kulpa's case, adhesion promoters. used,
In the case of Beers' additive, the modulus of the system is also reduced as well as the improvement in adhesion promotion. Such a sealant composition without significantly modified ingredients results in a silicone sealant that expands +25% and compresses -25% at a joint 1/6 to 1 inch wide when placed in the joint. Therefore,
Traditional sealants such as the compositions described above, particularly silicone sealants of the compositions described above, have been modified to provide +50% expansion and -50% expansion at 1/16 to 1 inch wide joints.
to have a compression of There are many methods for reducing the modulus of acyloxy-functional silicone sealants or other silicone sealants. One modification that can be made to silicone sealants is to increase the viscosity, molecular weight, or polymer chain length of the basic silanol-terminated diorganopolysiloxane polymer. Increasing the viscosity, increasing the molecular weight, and increasing the chain length of the polymer all mean the same thing, i.e., by increasing the viscosity, the molecular weight of the polymer increases and this makes the final silicone elastomer more elastic and therefore has a lower modulus. Long chain polymers are not as highly crosslinked as short chain polymers, and therefore silicone elastomers formed from long chain polymers are more elastic and have a lower modulus. Another method of reducing modulus is to use in the composition a diorganopolysiloxane polymer extender oil that is non-reactive to the system and acts simply as a plasticizer. This also makes the composition more elastic and reduces the modulus of the cured system. Another way to reduce the modulus of the system is to add the fluids of Beers, US Pat. No. 3,382,205; these fluids act as chain-terminating fluids and reduce the amount of crosslinking done by the acyloxy-functional silane crosslinker. do. Lower crosslinking makes the cured composition more elastic and therefore lower modulus. Finally, reinforcing fillers, fumed or precipitated silica, may be added to the composition and are preferably treated to increase the tensile strength or toughness of the composition. Therefore, all of the above modifications can be made to a one-component acyloxy-functional RTV system, resulting in +50% swelling and -50% swelling of the joint.
compression is given as desired. It is therefore highly desirable to prepare such low modulus acyloloki functional silicone sealants to meet the specific compression and expansion requirements set forth above. However, such preparation compromises the shelf life of the compositions, which can last for 6 to 9 months, after which they cure very slowly or not at all. After a period of 6 or 9 months, the time until the composition becomes tack-free (non-tack time) becomes undesirably long. In accordance with the foregoing, the low modulus room temperature vulcanizable silicone rubber composition with good shelf life provided by the present invention has (A)(1) a viscosity of 25°C.
a first mixture of 100 parts by weight of a 50,000 to 350,000 centipoise silanol-terminated diorganopolysiloxane polymer in which the organo groups are monovalent hydrocarbon groups and (2) 5 to 100 parts by weight of a filler, and (B) ( 3) Acyloxy functional silane of formula RSi(OCOR') ₃ , where R and
(R' is a monovalent hydrocarbon group) 60 to 100 parts by weight; and (4) a catalyst selected from the group consisting of zinc salts of carboxylic acids, zirconium salts of carboxylic acids, and mixtures thereof.
0.1 to 5 parts by weight, and 1 to 20 parts by weight of the second mixture per 100 parts of the first mixture. While having good cure and shelf life over long periods of time, e.g. 18-27 months after preparation, such compositions nevertheless have long non-stick times, e.g. 40-60 minutes. After a period of 18 to 27 months, if a low modulus composition with good shelf life and cure is desired, a cocatalyst system is added in addition to the acyloxy-functional silane in mixture (B) in the above composition. used. Such a cocatalyst system includes 0.5 to 5 parts by weight of a tin salt of a carboxylic acid and 0.001 to 0.4 parts by weight of a cocatalyst selected from the group consisting of a zinc salt of a carboxylic acid and a zirconium salt of a carboxylic acid. As already pointed out, these cocatalyst systems are the first
The shelf life is good, unlike the first catalyst system, the composition remains cured even after 18-27 months of preparation, and the non-stick time is short at 20 minutes, unlike the long non-stick time of the first catalyst system composition. or within that range. One type of tin salt used in the cocatalyst system is sibutyltin dilaurate. A preferred tin salt that provides an advantageous non-stick time to the compositions of this invention is dimethyltin neodecanoate. A preferred zirconium salt is zirconium octoate and a preferred zinc salt is zinc octoate. Other zinc and zirconium salts work just as effectively in the present invention. The above compositions may include any of the many well-known additives described below. The base polymer of the one-component room temperature vulcanizable silicone rubber composition of the present invention is a silanol-terminated diorganopolysiloxane polymer having a viscosity of 50,000 to 350,000, more preferably 100,000 to 250,000 centipoise at 25°C. The higher the viscosity of the base polymer, the lower the modulus of the resulting composition. The organo group of the diorganopolysiloxane polymer can be selected from any monovalent hydrocarbon group and halogenated monovalent hydrocarbon group. Examples of substituents represented by organo groups include alkyl groups having 1 to 8 carbon atoms, such as methyl, ethyl, and propyl, and cycloalkyl groups having 4 carbon atoms, such as cyclohexyl and cyclohebutyl.
-8, mononuclear aryl groups such as phenyl, methylphenyl, etc., and alkenyl groups such as vinyl, allyl, etc. Furthermore, the organo groups in such diorganopolysiloxane polymers represent halogenated monovalent hydrocarbon groups such as fluoroalkyl groups such as 3,3,3-trifluoropropyl. Such diorganopolysiloxane polymers are preferably 100% linear diorganopolysiloxane polymers. but,
A combined amount of monofunctional siloxy units and trifunctional siloxy units up to 0.1% by weight is permitted in the polymer. That is, the total amount of monofunctional siloxy units and trifunctional siloxy units cannot exceed 0.1% by weight. Preferably, the linear diorganopolysiloxane polymer has the formula (In the formula, R ² is selected from a monovalent hydrocarbon group and a monovalent halogenated hydrocarbon group, and these are the same groups mentioned as examples for the organo group above, and t is a heavy The viscosity of the coalescence is 50,000 to 350,000 at 25℃
The value is preferably 100,000 to 250,000 centipoise. The preparation of such silanol-terminated diorganopolysiloxane polymers is well known in the art. Briefly, a diorganodichlorosilane containing up to 10% by weight of mono- or trifunctionality is taken and this chlorosilane is hydrolyzed in water. The hydrolyzate thus obtained is taken out, water is separated from it, and 1 to 5% by weight of potassium hydroxide is added thereto. The hydrolyzate is heated to a temperature of 100°C or higher, preferably 150°C, for 1 to 8 hours to selectively form cyclopolysiloxane. The hydrolyzate mixture contains a low molecular weight cyclopolysiloxane as well as a low molecular weight silanol-terminated diorganopolysiloxane polymer as obtained from hydrolysis with water. If this hydrolyzate is subjected to cracking with potassium hydroxide at high temperature,
Most of the silicone hydrolyzate content is primarily converted to cyclotetrasiloxane. Take the above cyclotetrasiloxanes, mix them together, and add 50-500 ppm potassium hydroxide and desired amount of water as a chain stopper to these cyclotetrasiloxanes.
The resulting mixture is then heated at an elevated temperature to selectively form the desired silanol-terminated diorganopolysiloxane polymer in an equilibrium reaction above 100°C, preferably above 150°C. The final viscosity of the polymer formed depends on the amount of water added as a chain terminator. The more water present as a chain terminator, the lower the molecular weight of the silanol-terminated diorganopolysiloxane polymer formed. Conversely, the less water added, the higher the molecular weight of the silanol-terminated diorganopolysiloxane polymer formed. In addition to water, low molecular weight silanol-terminated diorganopolysiloxane polymers can be used as chain terminators, i.e. the polymers obtained when diorganodichlorosilane is hydrolyzed in water can also be used as chain terminators. . Once the desired amount of silanol-terminated diorganopolysiloxane polymer has been formed in the equilibrium reaction, the alkali metal hydroxide catalyst, i.e., calcium hydroxide, is neutralized and unreacted cyclics are stripped away to form the desired base. Produces polymers. The process for forming silanol-terminated diorganopolysiloxane polymers with fluoroalkyl substituents differs from the process for making diorganopolysiloxane polymers with non-halogenated substituents.
Fluoroalkyl substituted polymers can be made from both cyclotrisiloxane and cyclotetrasiloxane. However, a process for preparing polymers from cyclotrisiloxane is preferred, which provides the highest conversion of cyclic trisiloxane to the desired polymer. According to the invention, 5 to 100 parts by weight, more preferably 10 to 30 parts by weight of filler are used per 100 parts by weight of the basic silanol-terminated polymer. Such fillers are selected from reinforcing fillers and extending fillers. Reinforcing fillers are well known fumed silicas and precipitated silicas. Reinforcing fillers are preferred in the compositions of this invention if it is desired to increase the tensile strength of the cured silicone elastomer. However, a disadvantage of reinforcing fillers is that they unduly increase the viscosity of the composition before curing and reduce elongation properties. These effects can be alleviated by treating the filler as described below. If it is desired to increase the tensile strength of the composition to some extent without unduly increasing the viscosity or unduly reducing the elongation of the composition before curing, extender fillers are incorporated into the composition at the above concentrations. be able to. Examples of extender fillers are titanium dioxide,
Zirconium silicate, silica aerogel, iron oxide, diatomaceous earth, glass fiber, polyvinyl chloride,
It is crushed quartz. Other examples of extender fillers that can be used are litovone, zinc oxide, calcium carbonate, magnesium oxide, chromium oxide, zirconium oxide,
These include aluminum oxide, α-quartz, baked clay, carbon, graphite, quartz, cotton, and synthetic fibers. According to the invention, the filler used is preferably reinforcing, especially fumed silica, which improves the tensile strength and toughness of the final elastomeric sealant, even in small amounts, for example. Furthermore, if such fumed silica is used in small amounts and in sufficient amounts, it will not unduly reduce cured elastomer elongation. It is preferred to treat the filler to prevent it from reducing the elongation of the cured composition and increasing the viscosity of the uncured composition to undesirable levels. Thus, silica fillers can be treated with cyclic polysiloxanes, such as those disclosed in Lucas, US Pat. No. 2,938,009. Another method of treating fillers that can be used in the present invention is disclosed in Brown, US Pat. No. 3,024,126. Furthermore,
Smith, U.S. Pat. No. 3,635,734 and Beers, 1972
Fillers treated with silazane according to the disclosure of U.S. Pat. However, the most preferred treated fillers in this invention are fumed silicas treated with cyclopolysiloxanes, more particularly cyclotetrapolysiloxanes such as octamethylcyclotetrasiloxane. The above mixture of filler and silanol-terminated diorganopolysiloxane polymer forms the base mixture of the composition of the invention. According to the invention, 1 to 20 parts by weight of the catalyst mixture are added to 100 parts of this basic mixture. This catalyst mixture generally consists of a crosslinking agent, an adhesion promoter and the actual catalyst that promotes the reaction. Thus, 1 to 20 parts by weight of catalyst mixture are used per 100 parts of base mixture. The mixture of silanol-terminated diorganopolysiloxane polymer and filler can be considered a first mixture or base mixture, with preferably 1 to 10 parts by weight of catalyst mixture or second mixture for every 100 parts by weight of this first mixture. Parts by weight can be used in such catalyst mixtures, with the formula RSi(OCOR') ₃ (wherein R and R' are monovalent hydrocarbon groups, preferably a C1-C8 alkyl group or a phenyl group). and most preferably a methyl group). The acyloxy-functional silane is a crosslinking agent in the compositions of this invention. The most preferred and most common of these crosslinking agents is, of course, methyltriacetoshisilane. The functions of such crosslinking agents and the means for obtaining them are well known to those skilled in the art, so there is no need to explain them. Catalysts that can be used with such acyloxy-functional silane crosslinkers are tin salts of carboxylic acids, such as dibutyltin dilaurate or tin neodecanoate.
However, as mentioned above, when a low modulus composition is desired and the above-mentioned tin catalyst is used, the shelf life of the composition is an unacceptable 6-9 months, after which time the composition will not cure. Therefore, in the second mixture, in place of the tin salt, a catalyst selected from the group consisting of zinc salts of carboxylic acids, zirconium salts of carboxylic acids, and mixtures thereof is used.
It was highly unexpected to find a composition with an acceptable shelf life by combining 5 parts by weight with an acyloxy functional silane.
Preferably, 0.5 to 3 parts by weight of such salts are used.
Preferred, of course, are zinc octoate or zirconium octoate catalysts. The only drawback of such compositions is that although the shelf life is good and extends from 18 to 27 months, the non-stick time is nevertheless long. Thus, when a zirconium salt or a zinc salt is used in place of the tin salt in the composition as described above, the non-stick time of the composition is from 30 minutes to 60 minutes. If this is accepted, and instead of traditional tin salts, zirconium salts, zinc salts or mixtures thereof can be used as catalysts in the compositions of the invention, the non-stick time of the compositions will usually be longer. But the shelf life will be good. It should be pointed out that in conventional compositions, i.e., prior art low modulus compositions containing tin salts, after storage for 6 to 9 months, a permanent surface tack remains after several days of curing. That is, the non-stick time was extended to the point where the composition was no longer tacky except after a very long period of time. This is not the case with the compositions of the present invention using zirconium or zinc salts. After 30 minutes, 60 minutes or up to 2 hours, the composition becomes non-tacky and hardens.
It has a shelf life ranging from 18 to 27 months. Conventional compositions using low modulus compositions, i.e., low modulus conventional compositions using tin salts as catalysts, exhibited reduced overall cure even after storage for more than 9 months, resulting in a decrease in overall cure after 24 hours of curing. Even they have a putty-like consistency and permanent deformation occurs under applied pressure. Initially, this effect is seen as a loss in shore A hardness. Even into the later stages of aging, even after one month at ambient conditions, there was still a putty-like consistency and the composition cured very slowly and never seemed to cure. The low modulus compositions of the present invention containing zirconium or zinc salts at the above concentrations cure within 24 hours, despite the fact that the tack-free time is as long as 1 hour even after 9 months. In the second catalyst mixture, preferably from 60 to more preferably 100 parts by weight of a crosslinking agent together with generally 0.1 to 5 more preferably 0.5 to 3 parts by weight of a catalyst selected from zinc salts and zirconium salts of carboxylic acids. is used in an amount of 80 to 100 parts by weight. Additionally, in a more preferred embodiment of the invention, a cocatalyst system is used with the crosslinking agent, the cocatalyst system containing from 0.1 to 5 parts by weight of an alkyltin salt of a carboxylic acid and a zinc salt of a carboxylic acid and a carboxylic acid. 0.001 to 0.4 parts by weight of a cocatalyst selected from the group consisting of zirconium salts. More preferably, 0.01 to 0.2 parts by weight of a zinc salt or zirconium salt of a carboxylic acid is used as a cocatalyst in the system together with 0.1 to 1 part by weight of a dialkyltin salt of a carboxylic acid (the number of carbon atoms in the alkyl group is 1 to 2). be exposed. A cocatalyst system of a tin salt and a zirconium or zinc salt is preferred over a single catalyst system of either a zirconium salt or a zinc salt, and the compositions produced by this cocatalyst system remain cured even after 18 to 27 months of storage. Good non-stick time is 15-20 minutes. Combinations using zinc or zirconium salts in combination with dialkyltin salts, i.e., compositions without cocatalyst systems, have a good shelf life and provide good cure after storage for 18 to 27 months, but the non-stick time is is longer, from 30 minutes to 60 minutes
minutes or more. Compositions containing cocatalyst systems using tin salts in combination with zirconium or zinc salts have a good shelf life of 18 months or 27 months.
It cures well even after storage for several months, and the non-stick time is short, 15 to 30 minutes. A less preferred tin salt which can be used in combination with the zinc or zirconium salts is, for example, dibutyltin dilaurate. However, one preferred tin salt for the compositions of the present invention is one containing a dialkyl group, which is a dialkyltin soap of a carboxylic acid, where the dialkyl group is dimethyl and the carboxylic acid moiety has from 2 to 2 carbon atoms. 22, most preferably neodecanoate. Therefore, the most preferred tin salt is dimethyltin neodecanoate, which is combined with either a zinc salt or a zirconium salt to form the cocatalyst system of the present invention. Accordingly, to prepare the compositions of the present invention, a cocatalyst system or a catalyst system is mixed with an acyloxy-functional silane, and this second mixture is mixed at a concentration of 1 to 20 parts by weight per 100 parts by weight of the first mixture. The entire mixture is then packed into moisture-resistant containers. Such compositions are maintained in an anhydrous state until curing is desired. The composition is then applied as a sealant by any desired method and cured on exposure to atmospheric moisture to form an elastomeric silicone sealant. Although the composition is disclosed and claimed in the form of a mixture of the two, the claims in this disclosure are directed to a one-component RTV system. All components are mixed together into a single mixture and stored as is. When it is desired to use the composition or convert it into a silicone elastomer, it is simply removed by squeezing it from a tube or extruding it from a caulking tube and exposed to atmospheric moisture, thus exposing the acyloxy functionality to atmospheric moisture. The silane is hydrolyzed and crosslinked to form a silicone elastomer. The language of the claims in the specification discloses the formation of two mixtures that are mixed together to form a single component system of the composition of the invention;
This is to show how the composition is actually prepared, and to facilitate the description of the various ingredients and the restatement of the key points of the description. There are additional ingredients in the compositions of the invention, particularly those that are present in the compositions of the invention to render the compositions low modulus. As previously indicated, it is desirable to use a high viscosity silanol-terminated diorganopolysiloxane base polymer in the compositions of the present invention in order to lower the modulus and increase the elongation of the composition. In the above compositions, in particular in order to reduce the modulus of the composition, a plasticizer is added per 100 parts of silanol-terminated diorganopolysiloxane polymer in the first mixture of the one-component composition of the invention. The plasticizer is a diorganopolysiloxane polymer whose organo group is a monovalent hydrocarbon group and whose viscosity at 25°C is 10 to 5000 centipoise. The organo groups of such diorganopolysiloxane polymers are the same as the organo groups of silanol-based polymers. These diorganopolysiloxane polymers are triorganosilyl end-terminated. Diorganopolysiloxane polymers are strictly linear.
However, up to 1% combined tri- and mono-functionality is allowed. The plasticizer diorganopolysiloxane polymer is used in an amount of 1 to 50 parts by weight, preferably 20 to 30 parts by weight, per 100 parts of the silanol-terminated diorganopolysiloxane polymer. Additionally, the viscosity of the polymer is preferably between 10 and 5000 centipoise at 25°C.
It is 10 to 500 centipoise. The most preferred diorganopolysiloxane polymers for use in the present invention are substantially linear polymers terminated with trimethylsiloxy and having a viscosity of 10 to 500 at 25°C.
centipoise dimethylpolysiloxane polymers, such polymers can be made by methods well known in the art. Thus, a polymer is produced by simply hydrolyzing the diorganodichlorosilane together with the triorganochlorosilane and separating the fluid formed. It is recognized that such fluids are not completely linear and may contain up to 1% of mono- and tri-functional siloxy units. However, such units do not impair the plasticizing effect of the diorganopolysiloxane polymer. Thus, the use of a plasticizer or diorganopolysiloxane fluid containing triorganosiloxy end-capping units, at the amounts used, reduces the modulus of the composition. To further reduce the modulus of the composition, monofunctional siloxy units, difunctional siloxy units, and trifunctional siloxy units may be added per 100 parts by weight of the silanol-terminated diorganopolysiloxane polymer in the base or first mixture. From 1 to 25 parts by weight, preferably from 5 to 15 parts by weight of chain-terminating fluid having siloxy units may be used. Thus, preferably the fluid has R ³ ₂ SiO units, R ³ ₃ SiO _0.5
units and R ³ SiO _1.5 units, where the ratio of organosiloxy units to diorganosiloxy units is
from 0.11 to 1.4, and the ratio of triorganosiloxy units to single diorganosiloxy is from 0.02 to about 1.0;
R ³ is a monovalent hydrocarbon group. Here, the term R ³
is a monovalent hydrocarbon group, but it includes both a monovalent hydrocarbon group and a monovalent halogenated hydrocarbon group such as 3,3,3-trifluoropropyl. The groups represented by the R ³ group are exactly the same as those already shown in the definitions of the organo group and the R ² group for the silanol-terminated diorganopolysiloxane polymer which is the base polymer in the composition of the present invention. It is. Such polymers of monofunctional, difunctional and trifunctional siloxy units contain from 0.1 to 8% by weight of hydroxyl groups. These silicone or chain-stopping fluids have two advantages. In another aspect, the fluid acts as an adhesion promoter, allowing the cured composition to adhere to various substrates, resulting in better adhesion than would otherwise be the case. The production of such fluids is also well known in the art and generally involves hydrolyzing a suitable amount of diorganodichlorosilane with monoorganotrichlorosilane and triorganochlorosilane in water and separating and purifying the product fluid formed. Examples of such fluids consisting of mono-, di- and tri-functional siloxy units are disclosed in Beers, US Pat. No. 3,382,205, and are used in one-component RTV compositions. This patent uses such fluids to improve the shelf life of one-component acyloxy-functional silane RTV compositions. However, the use of such fluids in combination with other fluids to modify the present invention to jointly reduce the modulus of the composition and increase shelf life is not disclosed in the Beers patent. However, this increase in tensile strength and decrease in modulus is more than offset by the other components and modifications disclosed above, resulting in a low modulus, one-component RTV composition with desirable modulus and shelf life. You can get things. Finally, the compositions of the present invention employ adhesion promoters or components that act primarily as adhesion promoters. Therefore,
In the second mixture, the catalyst mixture, there is present from 5 to 40 parts by weight of an adhesion promoter, preferably a di-tert-alkoxydiacyloxy functional silane. More preferably, from 10 to 30 parts by weight of di-t-alkoxydiacyloxy functional silane is used. More broadly, dialkoxydiacyloxy functional silanes may be used as adhesion promoters. However, in the compositions of the present invention, di-t-alkoxydiacyloxy functional silanes are more effective as adhesion promoters than conventional dialkoxysilane components or additives. Preferably, di-tert-butoxydiacyloxysilane is used as the adhesion promoter in the compositions of the invention, the concentration used being between 60 and 100% by weight of the acyloxy-functional silane crosslinker of the formula given above. 10 to 30 parts by weight based on parts. This adhesion promoter is disclosed in Kulpa US Pat. No. 3,296,161. Although the disclosure herein specifically illustrates the use of such adhesion promoters in one-component acyloxy-functional RTV compositions, the invention is not limited to such adhesion promoters. Other adhesion promoters can be used in the compositions of this invention. It will also be appreciated that other plasticizers than the triorganosilyl-terminated diorganopolysiloxane polymers used as plasticizers in the present invention can be used. Furthermore, monofunctional siloxy units as already disclosed,
Other chain-terminating fluids than fluids consisting of difunctional siloxy units and trifunctional siloxy units can be used. The above ingredients and additives are detailed because they result in a composition with competitive low modulus properties and a good shelf life with long shelf life of 18 or 27 months. The curing was good even after a long time, and here the catalyst was the above-mentioned zinc salt or zirconium salt catalyst alone.
More preferably, a tin catalyst is used with a zirconium or zinc salt as the cocatalyst system, which is the preferred system of the present invention. Although variations may be made to the above compositions, a one-component RTV low modulus composition is disclosed that has an acceptable shelf life after a storage period of 18 to 27 months.
The above-mentioned composition has the above-defined components in both the broader and more narrow sense. Therefore, although the prior art has disclosed very few of the additives of the present invention for use in one-component RTV compositions, compositions that combine low modulus and good tensile strength properties are not available. The optimal combination of components of the present invention to produce a composition with good shelf life and subsequent curing after a storage period of 18 to 27 months after manufacture has not been disclosed by the prior art. The following examples are given to illustrate the present invention, and are not included for the purpose or reason of setting limitations or definitions on the scope of the present invention or the scope of the claims. Parts in the examples are by weight unless otherwise stated. Example 1 To prepare base compounds X, 2X and 3X, a silanol-stopped dimethylpolysiloxane polymer having the viscosities shown in Table 1 was taken and added with the stated amount of octamethylcyclotetrasiloxane-treated fumed silica and at 25°C. A trimethylsiloxy-terminated dimethylpolysiloxane oil with a viscosity of 100 centipoise was mixed. In addition to the indicated amounts of these oils, the mixture also contains a silicone oil consisting of trimethylsiloxy monofunctional siloxy units, difunctional siloxy units, and monomethyltrifunctional siloxy units and having a hydroxyl group content of 0.5% by weight as indicated. was added. Ingredients of the above type were combined in the amounts indicated. To the base compound was added a catalytic amount and concentration of a second mixture consisting of a crosslinker, an adhesion promoter, and a catalyst component as indicated. The composition had the properties as described.

【table】

Table 1 The values in Table 1 above indicate compositions with the lowest modulus, good shelf life and good cure rate after accelerated aging only when using the catalyst system of the present invention. Only when the components and catalyst system of the present invention were used in the compositions were systems with low modulus, good tensile properties, and good hardening after aging obtained. A performance comparison was made between Composition 3X and prior art sealants. The results were as follows.

TABLE The above results demonstrate that Composition 3X, the composition of the present invention, has superior low modulus and curing properties compared to prior art sealants. Example 2 Base composition 4X, as shown in Table 3 below:
5X, 6X, 7X and 8X were prepared. The formation of this base compound requires a final viscosity of 80000 at 25°C.
silanol-terminated dimethylpolysiloxane formulations having a final viscosity of 95,000 centipoises at 25°C for Composition 8X.
Take 100 parts by weight of this silanol polymer, add 15.5 parts by weight of fumed silica treated with octamethylcyclotetrasiloxane, and add 15.5 parts by weight of fumed silica, which has a viscosity of 100% at 25°C.
22.0 parts by weight of centipoise trimethylsiloxy-terminated dimethylpolysiloxane oil, and 6.5 parts of a silicone oil fluid containing 0.5% by weight of hydroxyl groups, consisting of trimethyl monofunctional siloxy units, dimethyl difunctional siloxy units, and monomethyl trifunctional siloxy units. was added. A catalyst mixture was added to the above base compound in the amounts and components shown in Table 3 below. Results are presented for initial cure and cure after accelerated aging to determine the shelf life of the composition.

[Table] The results in Table 3 show that the composition catalyzed only with tin soap had a good initial cure and good initial non-tack time, but very poor cure after accelerated aging; The composition cured only with octoate, i.e. 7X, or the composition cured only with zinc octoate, i.e. 8X, has a long initial non-stick time, but the initial curing is good and the non-stick time after accelerated aging is as long as 40 minutes. Good hardening after aging. As demonstrated by the results in Table 3, zinc octoate and zirconium octoate,
That is, zinc and zirconium salts of carboxylic acids were good catalysts for the low modulus compositions of the present invention and gave the compositions good shelf life. Example 3 To prepare the base compound, the viscosity at 25°C
100 parts by weight of 112,000 centipoise silanol-terminated dimethylpolysiloxane oil fluid, 18.5 parts by weight of fumed silica treated with octamethylcyclotetrasiloxane, 25 parts by weight of trimethylsiloxy-terminated dimethylpolysiloxane oil with a viscosity of 100 centipoise at 25°C, monotrimethyl Consists of functional siloxy units, dimethyl difunctional siloxy units, and monomethyl trifunctional siloxy units with 0.5 hydroxyl groups
It was formed from 8 parts by weight of silicone oil containing % by weight. A catalyst mixture was added to the resulting mixture. The amount of the catalyst mixture and the types and amounts of its components are shown in Table 4. The tack-free time, cure rate, and post-cure after initial cure and after accelerated aging, as shown in Table 4, for slightly different compositions and for comparison with the 3X composition of Example 1. Given about the condition.

[Table] Corn oil

【table】

[Table] As shown by the above results in Table 4,
The tack-free time of the compositions provided by the low modulus compositions of the present invention cured with a combination of zinc octoate and dimethyltin neodecanoate or a combination of zirconium octoate and dimethyltin neodecanoate is 15 -20 minutes, with good cure after either initial cure after preparation or cure after accelerated aging, indicating good shelf life for both of these compositions. As shown by the above results, a composition with good tensile properties and low modulus, as well as a composition with good non-tack time, acceptable and long shelf life is obtained.

Claims (1)

[Claims] 1 (A) (1) The organo group is a monovalent hydrocarbon group at 25°C.
Silanol-terminated diorganopolysiloxane polymer 100 with a viscosity of 50,000 to 350,000 centipoise
parts by weight and (2) a first mixture of 5 to 100 parts by weight of filler and (B) (3) represented by the formula RSi(OCOR') ₃ (wherein R and R' are monovalent hydrocarbon groups); and (4) 0.1 to 5 parts by weight of an alkyltin salt of a carboxylic acid and 0.001 to 0.4 parts by weight of a zinc salt of a carboxylic acid or a zirconium salt of a carboxylic acid. 1 to 100 parts by weight of the first mixture
A low modulus room temperature vulcanizable silicone rubber composition with good shelf life comprising 20 parts by weight of a second mixture. 2. The composition of claim 1, wherein the filler is selected from the group consisting of fumed silica and precipitated silica. 3. The composition of claim 1, wherein the filler is treated with cyclotetrapolysiloxane. 4. Claim 1, in which 1 to 50 parts by weight of a plasticizer of diorganopolysiloxane whose organo group is a monovalent hydrocarbon group and whose viscosity at 25°C is 10 to 5000 centipoise is used in (A). Compositions as described. 5. The composition according to claim 4, wherein the diorganopolysiloxane polymer is dimethylpolysiloxane. 6 (R ³ ) ₂ SiO units, R ³ ₃ SiO _0.5 units and R ³ SiO _1.5
The ratio of organosiloxy units to diorganosiloxy units is 0.11 to 1.4, and the ratio of triorganosiloxy units to diorganosiloxy units is
0.02 to 1.0 and R ³ is a monovalent hydrocarbon group.
A composition according to claim 1, wherein parts by weight are present. 7. The composition of claim 1, wherein from 5 to 40 parts by weight of a di-t-alkoxydiacyloxy functional silane adhesion promoter is present in the second mixture. 8. The composition of claim 7, wherein the di-t-alkoxydiacyloxy functional silane is di-t-butoxydiacetoxysilane. 9. The composition of claim 1, wherein the zinc salt is used in the second mixture at a concentration of 0.01 to 0.2 parts by weight of zinc octoate. 10. The composition of claim 1, wherein the zirconium salt is used in the second mixture at a concentration of 0.01 to 0.2 parts by weight of zirconium octoate. 11. The composition of claim 1, wherein the tin salt in the second mixture is dibutyltin dilaurate and is used at a concentration of 0.1 to 1.0 parts by weight. 12. The composition of claim 1, wherein the tin salt in the second mixture is dimethyltin neodecanoate at a concentration of 0.1 to 1.0 parts by weight.