Room-temperature-curable silicone composition

Abstract: A room-temperature-curable silicone composition is obtained from diorganopolysiloxane that is endblocked by silanol at both molecular chain terminals and diorganopolysiloxane that is endblocked at one molecular chain terminal by silanol and at the other terminal by trialkylsiloxy; an alkoxy functional silane; an organopolysiloxane resin; a curing catalyst; and a diorganopolysiloxane that contains at least 2 carboxyl groups. This silicone composition has an excellent pre-cure workability and cures into a low-modulus, high-elongation silicone elastomer.

Description: This invention relates to silicone compositions that cure at room temperature into silicone elastomers. More particularly a composition of this type is provided whose post-cure physical properties can be varied over a wide range. Silicone compositions that cure at room temperature into silicone elastomer are known and widely used in the commercial and industrial spheres. The roomtemperature-curing mechanisms include hydrosilylation, UV-irradiation, and condensation between silanol and silicon-bonded functional groups. Among these, condensation-curing silicone compositions have wide use as adhesives, coatings, and sealants because they have a number of distinctive features, such as ease of adhesiveness at room temperature, resistance to cure inhibition by contaminants in the curing environment, ability to cure in a short period of time upon mixing the base and curing agent, the long-term storage stability of their two-part formulations, and their ability to cure in the atmosphere. However, compositions of this type are also subject to limitations on their mechanical properties imposed by the necessity for maintaining pre-cure workability, for example, the mixability, pourability, and finishability in manual operations. In specific terms, the molecular weight of the diorganopolysiloxane main ingredient must be below a certain level to support and facilitate the workability. But, this restriction also makes it difficult to hold the stiffness, which is manifested through such properties as the modulus and durometer of the subsequently cured elastomer. A fundamental approach to solving this problem is the combined use of a polyfunctional crosslinker and a difunctional chain extender. This approach results in a reduced post-cure crosslink density because the diorganopolysiloxane chain undergoes extension (chain elongation) at the same time as crosslinking during the curing reaction. The following two methods have been proposed in this regard: (1) the combined use of siloxane having two N,N-dialkylaminoxy groups in each molecule and siloxane having three N,N-dialkylaminoxy groups in each molecule, or (2) the combined use of silane having two N-alkylacetamide groups in each molecule and silane having three N-alkylacetamide groups in each molecule. There are, however, drawbacks to each of these methods. In the first method (use of N,N-dialkylaminoxy-functional siloxane) the curing reaction produces N,N-dialkylhydroxylamine as a byproduct, and this hydroxylamine has an unpleasant odor. Moreover, hydroxylamine is strongly basic and causes diorganopolysiloxane scission. This leads to cure inhibition when the ambient temperature becomes even slightly elevated. Finally, this method is also economically problematic because N,N-dialkylaminoxy-functional siloxanes are expensive. In the second method (use of N-alkylacetamide-functional silanes), curing is again accompanied by an unpleasant odor from N-alkylacetamide. In addition, when an active hydrogen-containing compound such as an alcohol is also present, the N-alkylacetamide group undergoes a substitution reaction to, for example, the alkoxy group, which again results in cure inhibition. This method is also economically problematic because N-alkylacetamide-functional silanes are expensive. To avoid the use of specialized and expensive functional groups as in the preceding methods, there have also been proposals that chain elongation and crosslinking be carried out using functional groups that are already in wide use and that are not accompanied by secondary reactions. Thus, JP-A 63-83167 teaches the use of RNHCH 2 MeSi(OMe) 2 as chain extender. In this formula Me is, and hereinafter represents methyl. However, not only is it quite difficult to synthesize economically, it is also so difficult to strike a stable balance with the crosslinker so that practical applications are not possible. U.S. Patent 5,300,612, and equivalent to JP-A 6-9875, proposes the use of [(CH 3 ) 3 SiO] 2 Si (OMe) 2 as chain extender. However, when the actual use of chain extender is attempted, one finds that practical applications are not possible due to a large increase in the modulus after degradation testing. U.S. Patent 4,687,829, claimed the use of Ph[(CH 3 ) 3 SiO]Si(OCH 3 ) 2 , but this compound does not provide the initial physical properties that are provided by use of the N,N-dialkylaminoxy group. In this formula Ph is, and hereinafter represents phenyl. In addition, silicone building sealants for weather sealing service desirably must have a durability performance that passes the 10030 or 9030 durability test for building sealants that is specified in Japanese Industrial Standard (JIS) A 5758. However, at the present time the only commercial building sealants that pass these tests are the above described sealants that use N,N-dialkylaminoxy-functional silanes or N-alkylacetamide-functional silanes. Sealants based on silanes having other functional groups simply cannot pass these tests. As a result of extensive investigations, we have already introduced a composition whose cure yields a low-modulus, high-elongation silicone elastomer that can pass the 10030 or 9030 durability test of JIS A 5758. This composition consists of the blend of a higher fatty acid, for example, oleic acid, in a composition whose main ingredients are diorganopolysiloxane, organosiloxane resin, and organosilane. However, since ensuing investigations revealed that this composition had an unsatisfactory adherence for substrates, additional research was carried out that resulted in the present invention. In specific terms, the object of the present invention is to provide a room-temperature-curable silicone composition that has an excellent pre-cure workability and cures into a low-modulus, high-elongation silicone elastomer that exhibits a desirable stiffness. Another object of the present invention is to provide a highly adhesive room-temperature-curable silicone composition that can pass the 10030 or 9030 durability test of JIS A 5758. The present invention is achieved by a room-temperature-curable silicone composition comprising (A) 100 weight parts of diorganopolysiloxane composed of (a) diorganopolysiloxane with a viscosity at 25°C of 0.02 to 1,000 Pa.s that is endblocked by silanol at both molecular chain terminals and (b) diorganopolysiloxane with a viscosity at 25°C of 0.1 to 1,000 Pa.s that is endblocked at one molecular chain terminal by silanol and at the other terminal by trialkylsiloxy in a molar ratio in the range from 1.0: 0.3 to 1.0 : 3.0 moles of (a) to moles of (b); (B) 0.1 to 20 weight parts of organosilane with the general formula R 1 (4-a) Si(OR 2 ) a R 1 and R 2 each represent C 1 to C 20 monovalent hydrocarbon groups and a is 3 or 4 or partial hydrolyzate thereof; (C) 5 to 30 weight parts of organopolysiloxane resin that is solid at ambient temperature and that is composed of the R 3 3 SiO 1/2 and SiO 4/2 units in a molar ratio in the range from 0.5 : 1.0 to 1.2 : 1.0 and where R 3 is a C 1 to C 20 monovalent hydrocarbon group or the hydroxyl group (D) 0.01 to 20 weight parts curing catalyst; and (E) 0.5 to 10 weight parts diorganopolysiloxane having at least 2 -R 4 -COOR 5 groups in each molecule and having the following average general formula wherein R 4 is a divalent hydrocarbon group, R 5 is hydrogen atom or a monovalent hydrocarbon group, R 6 is a C 1 to C20 monovalent hydrocarbon group, A is R 6 or -R 4 -COOR 5 , k is a positive integer, l is 0 or an integer with a value of at least 1, k + l is at least 10, and k /( l + 2) = 5/1 to 500/1. The diorganopolysiloxane (A) the present invention is the base ingredient of our composition and is one of the components that characterizes the subject composition. Diorganopolysiloxane (a) is a diorganopolysiloxane endblocked by silanol at both molecular chain terminals. The viscosity of this diorganopolysiloxane at 25°C is from 0.02 to 1,000 Pa.s, and preferably is from 1 to 100 Pa.s. Diorganopolyssiloxane (a) is exemplified by silanol-endblocked dimethylpolysiloxanes, silanol-endblocked dimethylsiloxane-methylvinylsiloxane copolymers, silanol-endblocked dimethylsiloxane-methylphenylsiloxane copolymers, and silanol-endblocked methyl(3,3,3-trifluoropropyl)polysiloxanes. The silanol-endblocked dimethylpolysiloxanes are preferred. Diorganopolysiloxane (b) is a diorganopolysiloxane endblocked at one molecular chain terminal by silanol and endblocked at the other terminal by trialkylsiloxy. The viscosity of this diorganopolysiloxane at 25°C is from 0.1 to 1,000 Pa.s, and preferably is from 1 to 100 Pa.s. Diorganopolysiloxane (b) is exemplified by dimethylpolysiloxanes endblocked by silanol at one molecular chain terminal and by trimethylsiloxy at the other terminal, dimethylsiloxane-methylvinylsiloxane copolymers endblocked by silanol at one molecular chain terminal and by trimethylsiloxy at the other terminal, dimethylsiloxane-methylphenylsiloxane copolymers endblocked by silanol at one molecular chain terminal and by trimethylsiloxy at the other terminal, and methyl(3,3,3-trifluoropropyl)polysiloxanes endblocked at both terminals by silanol. The component (B) of the present invention functions as a crosslinker for component (A), and is organosilane with the general formula R 1 (4-a) Si(OR 2 ) a where R 1 and R 2 each represent C 1 to C 20 monovalent hydrocarbon groups and a is 3 or 4 or the partial hydrolyzate thereof. Component (B) is exemplified by tetramethoxysilane, tetraethoxysilane, tetraisoproxysilane, methyltrimethoxysilane, vinyltrimethoxysilane, decyltrimethoxysilane, methyltriethoxysilane, phenyltrimethoxysilane, and methyltri(ethoxymethoxy)silane. While a single selection from this class of compounds will ordinarily be used as component (B), two or more selections may be used in combination as necessary. The partial hydrolyzates of these compounds can also be used as component (B). Although the quantity of addition for component (B) is conditioned by a consideration of the amount of component (A) silanol (itself conditioned by the required post-cure properties), the starting materials added in addition to components (A) to (D), and impurities, such as water, that may be present in the starting materials, component (B) must be added at from 0.01 to 20 weight parts per 100 weight parts component (A). The use of more than 20 weight parts results in adverse effects as incomplete curing and so forth. The component (C) of the present invention is used to provide a cured product having a highly controllable modulus and a high recovery ratio. Silicone oils, such as trimethylsiloxy-endblocked dimethylpolysiloxane oils, are already known for the use as modulus regulators, but the use of silicone oils for this purpose is accompanied by problems such as post-cure outmigration and a reduction in the adhesiveness. Herein, the modulus can be freely adjusted through the addition of a resin, which is substantially free of the problems associated with the silicone oils. Moreover, this leads to an improved recovery ratio and better results in durability testing. Component (C) is an organopolysiloxane resin composed of the R 3 3 SiO 1/2 unit (M unit), where R 3 represents C 1 to C 20 monovalent hydrocarbon groups as described above for R 1 and R 2 and SiO 4/2 unit (Q unit) with an M unit/Q unit molar ratio in the range from 0.5 : 1.0 to 1.2 : 1.0. The modulus can be adjusted, even when the M unit is present at higher levels, but this condition leads, for example, to a deterioration in the compression set. Component (C) preferably contains no more than 1 weight% of residual silanol: larger values cause a fruitless consumption of component (B). Component (C) is added at from 5 to 30 weight parts per 100 weight parts of component (A). The component (D) of this invention is a catalyst that accelerates the condensation curing reaction between components (A) - (C). Insofar as the object of the present invention is not impaired, any catalyst known in the art for acceleration of the condensation reaction between components (A) and (B) can be used as component (D). Component (D) is exemplified by tin catalysts such as dialkyltin dicarboxylates, dialkyltin bis(acetylacetonate)s, and tin octoate; iron octoate; zirconium octoate; titanate esters such as tetrabutyl titanate, tetra(i-propyl) titanate, and dibutoxytitanium bis(acetylacetonate); and amine catalysts such as tetramethylguanidine. While component (D) will generally consist of a single catalyst, two or more catalysts may also be used in combination. By combination of two or more catalysts, the preferred use of a combination of dibutyltin bisacetylacetonate and tin octoate. Component (D) must be added at from 0.01 to 20 weight parts per 100 weight parts of component (A). Cure acceleration will be inadequate at below 0.01 weight part, while exceeding 20 weight parts causes adverse effects, such as a loss of water resistance and heat resistance, to appear to a substantial degree. The component (E) of our invention is used to increase the curability. R6 in component (E) represents C 1 to C 20 monovalent hydrocarbon groups, for example, methyl, ethyl, propyl, pentyl, stearyl, 3,3,3-trifluoropropyl, betaphenylethyl, alpha-methyl-beta-phenylethyl, vinyl, and phenyl. The groups R 6 within the single molecule need not all be identical. R 6 will most typically be methyl, but combinations of methyl with other groups are also commonly used. R 5 is hydrogen atom or a monovalent hydrocarbon group, wherein the latter is exemplified by methyl, ethyl, and hexyl. A is R 6 or -R 4 COOR 5 , and the subscript 1 may also be 0 when both A groups are -R 4 COOR 5 . R 4 represents divalent hydrocarbon groups, such as alkylene groups like -CH 2 -, -CH 2 CH 2 -,-CH 2 CH 2 CH 2 -, and -CH 2 CH(CH 3 ) CH2- and alkylenearylene groups such as -(CH 2 ) 2 -C 6 H 4 -. The -R 4 COOR 5 groups may be present in terminal or nonterminal position on the molecular chain or at both positions. This component is readily synthesized, for example, by the method provided in Canadian Patent 1,262,736. The composition of this invention comprises the components (A) to (E) described above, but may also contain, insofar as the object of the present invention is not impaired, silanol-free diorganopolysiloxane; inorganic fillers such as fumed silica, precipitated silica, quartz powder, carbon black, and calcium carbonate; the preceding inorganic fillers that have been subjected to a hydrophobing treatment; fluidity adjusters; silane- or siloxane-based adhesion promoters; pigments; heat stabilizers; flame retardants; organic solvents; antimolds; and antimicrobials. Our room-temperature-curable silicone composition is prepared simply by mixing the components (A) to (E) to homogeneity. Desirable mixing sequences for components (A) to (E) are as follows: (i) the addition of components (A), (B), (C), (D), and (E) in the order given, or (ii) the preliminary mixing of components (B) to (E) to yield a mixture to which component (A) is then added. Failure to do this raises the possibility that in some cases the expected properties will not be obtained, particularly in regard to post-cure flexibility. With the exception of this consideration, the mixing sequence is not particularly critical. The claimed composition supports facile control of its post-cure physical properties, particularly the hardness and modulus, and provides a low-hardness, high-elongation silicone elastomer. Unexpectedly, this composition can pass the 10030 or 9030 durability test for building sealants stipulated in JIS A 5758 and is highly resistant to cure inhibition. Furthermore, this composition readily adheres to substrates in contact with the composition during the composition's cure. This property spectrum makes our composition particularly useful as an adhesive, a coating, or a building sealant. The invention is explained in greater detail below through working examples, in which "parts" denotes "weight parts". The physical properties of the room-temperature-curable silicone elastomer compositions were measured by the methods specified in JIS A 5758, "Sealing compounds for sealing and glazing in buildings". A silane-based primer (Primer D-2 from Dow Corning Toray Silicone Company, Limited) was used as the primer. The adherends were sulfuric acid treated and sealed aluminum test panels as specified in JIS H 4100 (6063S) and were obtained from Nippon Test Panel Kabushiki Kaisha. The following diorganopolysiloxanes were used as the carboxyl-modified silicone (E). Example 1 A room-temperature-curable silicone composition was prepared by mixing the following to homogeneity: 100 parts of dimethylpolysiloxane consisting of the mixture, in a 1 1 molar ratio, of dimethylpolysiloxane (viscosity at 25°C = 12 Pa.s) endblocked at both molecular chain terminals by silanol and dimethylpolysiloxane (viscosity at 25°C = 12 Pa.s) endblocked at one molecular chain terminal by silanol and endblocked at the other terminal by trimethylsiloxy; 13 parts of methylpolysiloxane resin composed of the (CH 3 ) 3 SiO 1/2 and SiO 4/2 units in a 0.7 : 1 molar ratio and having a hydroxyl group content not exceeding 1 weight%; 3.0 parts of decyltrimethoxysilane; 0.06 part of dibutyltin dilaurate; 2.0 parts of diorganopolysiloxane A; and 100 parts of a fatty acid-treated calcium carbonate powder (Viscolite™ U, from Shiraishi Kogyo Kabushiki Kaisha). The H-joint specified in JIS A 5758 was fabricated using this composition, and the 50% modulus, elongation, and maximum stress were measured. The 9030 and 10030 durability tests were also carried out. The results are. 50% modulus (kgf/cm 2 ) 1.8 maximum stress (kgf/cm 2 ) 10.2 elongation (%) 750 9030 durability test pass 10030 durability test pass % cohesive failure in the rubber layer 100% Example 2 A room-temperature-curable silicone elastomer composition was prepared by mixing the following to homogeneity: 100 parts of dimethylpolysiloxane consisting of the mixture, in a 1 : 1 molar ratio, of dimethylpolysiloxane (viscosity at 25°C = 12 Pa.s) endblocked at both molecular chain terminals by silanol and dimethylpolysiloxane (viscosity at 25°C = 12 Pa.s) endblocked at one molecular chain terminal by silanol and endblocked at the other terminal by trimethylsiloxy; 13 parts of methylpolysiloxane resin composed of the (CH 3 ) 3 SiO 1/2 and SiO 4/2 units in a 0.7 : 1 molar ratio and having a hydroxyl group content not exceeding 1 weight%; 3.0 parts decyltrimethoxysilane; 0.06 part dibutyltin dilaurate; 2.0 parts diorganopolysiloxane B; and 100 parts of a fatty acid-treated calcium carbonate powder Viscolite™ U, from Shiraishi Kogyo Kabushiki Kaisha). The properties of this composition were measured as in Example 1, and the results are. 50% modulus (kgf/cm 2 ) 1.7 maximum stress (kgf/cm 2 ) 10.6 elongation (%) 780 9030 durability test pass 10030 durability test pass % cohesive failure in the rubber layer 100% Comparative Example 1 A room-temperature-curable silicone elastomer composition was prepared by mixing the following to homogeneity: 100 parts dimethylpolysiloxane consisting of the mixture, in a 1 : 1 molar ratio, of dimethylpolysiloxane (viscosity at 25°C = 12 Pa.s) endblocked at both molecular chain terminals by silanol and dimethylpolysiloxane (viscosity at 25°C = 12 Pa.s) endblocked at one molecular chain terminal by silanol and endblocked at the other terminal by trimethylsiloxy; 13 parts methylpolysiloxane resin composed of the (CH 3 ) 3 SiO 1/2 and SiO 4/2 units in a 0.7 : 1 molar ratio and having a hydroxyl group content not exceeding 1 weight%; 3.0 parts decyltrimethoxysilane; 0.06 part dibutyltin dilaurate; 1.2 parts oleic acid; and 100 parts of a fatty acid-treated calcium carbonate powder Viscolite™ U, from Shiraishi Kogyo Kabushiki Kaisha). The properties of this composition were measured as in Example 1, and the results are. 50% modulus (kgf/cm 2 ) 1.7 maximum stress (kgf/cm 2 ) 10.6 elongation (%) 780 9030 durability test pass 10030 durability test pass % cohesive failure in the rubber layer 0% Because the room-temperature-curable silicone composition of this invention comprises components (A) to (E), and in particular because it contains the special diorganopolysiloxane (A), organopolysiloxane resin (C), and diorganopolysiloxane (E), the said composition characteristically has an excellent pre-cure workability and cures to give a highly durable, low-modulus, and high-elongation silicone elastomer.

Claims: A room-temperature-curable silicone composition comprising (A) 100 weight parts of diorganopolysiloxane composed of (a) diorganopolysiloxane with a viscosity at 25°C of 0.02 to 1,000 Pa.s that is endblocked by silanol at both molecular chain terminals and (b) diorganopolysiloxane with a viscosity at 25°C of 0.1 to 1,000 Pa.s that is endblocked at one molecular chain terminal by silanol and at the other terminal by trialkylsiloxy in a molar ratio in the range from 1.0 : 0.3 to 1.0: 3.0 moles of (a) to moles of (b); (B) 0.1 to 20 weight parts of organosilane with the general formula R 1 (4-a) Si(OR 2 ) a R 1 and R 2 each represent C 1 to C 20 monovalent hydrocarbon groups and a is 3 or 4 or partial hydrolyzate thereof; (C) 5 to 30 weight parts of organopolysiloxane resin that is solid at ambient temperature and that is composed of the R 3 3 SiO 1/2 and SiO 4/2 units in a molar ratio in the range from 0.5 : 1.0 to 1.2 : 1.0 and where R 3 is a C 1 to C20 monovalent hydrocarbon group or the hydroxyl group) (D) 0.01 to 20 weight parts of curing catalyst; and (E) 0.5 to 10 weight parts diorganopolysiloxane having at least 2 -R 4 -COOR 5 groups in each molecule and having the following average general formula wherein R 4 is a divalent hydrocarbon group, R 5 is hydrogen atom or a monovalent hydrocarbon group, R 6 is a C 1 to C 20 monovalent hydrocarbon group, A is R 6 or -R 4 -COOR 5 , k is a positive integer, l is 0 or an integer with a value of at least 1, k + l is at least 10, and k /( l + 2) = 5/1 to 500/1. The room-temperature-curable silicone elastomer composition according to claim 1, in which in component (B), R 1 is C 8 to C 20 alkyl, R 2 is C 1 or C 2 alkyl, and a is 3. The room-temperature-curable silicone elastomer composition according to claim 1, in which R 3 in component (C) is methyl. The room-temperature-curable silicone elastomer composition according to claim 1, in which component (C) has a hydroxyl content no greater than 1 weight%. The room-temperature-curable silicone elastomer composition according to claim 1, in which the curing catalyst (D) is an organotin compound. The room-temperature-curable silicone elastomer composition according to claim 1, in which in component (E), A is -R 4 -COOR 5 , k is 5 to 20, and l is 0.

Inventors: HATANAKA HIDEKATSU, HORI SEIJI, HATANAKA, HIDEKATSU, HORI, SEIJI, HATANAKA, HIDEKATSU, DOW CORNING TORAY, HORI, SEIJI, DOW CORNING TORAY SILICONE COMP. LTD.
Applicants: DOW CORNING TORAY SILICONE, DOW CORNING TORAY SILICONE COMPANY LTD.
Application year: 1997
Main classification: C08L83
IPC codes: C08L83, C09K3, C08K5