Organopolysiloxane compositions

Abstract: The invention provides an RTV organopolysiloxane composition comprising (A) a terminally di- or trifunctional organopolysiloxane, (B) an alkoxysilane, (C) calcium carbonate surface treated with a carboxylic acid having a melting point of at least 100°C, and (D) a condensation catalyst. The composition cures into a cured product capable of forming a durably thermoresistant and water immersion-resistant bond to substrates such as surface treated aluminum members, fluoro-resin coated steel strips and acrylic resin electrodeposited steel strips.

Description: This invention relates to vulcanizable organopolysiloxane compositions, their preparation and use. In particular it relates to compositions of the type commonly known as room-temperature vulcanizable (RTV) compositions, readily vulcanizable with moisture in the air to form rubbery elastomers. Of prior art room temperature vulcanizable (RTV) organopolysiloxane compositions, one-part RTV silicone compositions are well known. These compositions are stored in the absence of moisture. When it is desired to cure the composition, the package is opened and the composition is applied to any desired site whereupon it reacts with moisture in the air and cures into a rubbery elastomer. Early RTV organopolysiloxane compositions were comprised of a silanol-terminated polymer, an acyloxy crosslinking agent and a tin catalyst. Alkoxy functional type compositions were then developed. More illustratively, Nitzsche and Wick USP 3,065,194 discloses a silicone rubber composition comprising a diorganopolysiloxane having a silanol end-blocking group, an alkoxy functional crosslinking agent, and a metal salt of a chelate organometallic compound serving as a crosslinking catalyst. Other one-part alkoxy functional RTV compositions include a composition of a silanol end-blocked diorganopolysiloxane premixed with a crosslinking catalyst as disclosed in Brown et al. USP 3,161,614 and a composition comprising an alkoxy end-blocked linear siloxane polymer and a solid catalyst as disclosed in Cooper et al. USP 3,383,355. Furthermore, USP 3,499,859 discloses a hydrocarboxy end-blocked diorganopolysiloxane polymer and a metal-containing curing catalyst used in combination with boron nitride. Cooper et al., USP 3,542,901 discloses a composition comprising a mixture of a linear siloxane having di- or tri-functional end-blocking units and a linear siloxane having a chemically non-functional inert end-blocking unit at one end and a di- or tri-functional end-blocking unit at another end, a catalyst, and a crosslinking agent. Brown et al. USP 3,122,522 discloses an organopolysiloxane intermediate containing cellosolvoxyl blendable with a catalyst. Weyenberg USP 3,175,993 discloses an organopolysiloxane intermediate end blocked with an alkoxylated silcarbane group together with a catalyst. However, the aforementioned catalysts are disadvantageous in these alkoxy systems, and the titanium salts disclosed are likely to gel and give rise to an undesirable viscosity increase during mixing and long-term storage prior to use. As solutions to these problems, Smith and Hamilton USP 3,689,454 and 3,779,986, Weyenberg USP 3,294,739 and 3,334,067, and Clark et al. USP 3,719,635 disclose alkoxy-curable compositions utilizing titanium ester chelate catalysts instead of the metal salts of the aforementioned patents. The titanium chelate catalysts serve to control gelation and control an undesirable viscosity increase during mixing and storage for a long term of 1 or 2 years. More specifically, in conjunction with the one-part type alkoxy RTV composition, Weyenberg USP 3,294,739 and 3,334,067 disclose titanium chelate catalysts which are advantageously used to prepare appropriate curable compositions. These prior art RTV organopolysiloxane compositions, however, have problems in adhesion to aluminum stocks which have been surface treated for good weatherability. When the RTV compositions are applied to such aluminum stocks, long-term heating and water immersion can result in peeling. Without primers, these compositions do not bond well to difficult-to-bond substrates which have recently enjoyed a widespread use, for example, fluoro-resin coated steel strips and acrylic resin electrodeposited steel strips. Additionally thermoresistant and water immersion-resistant adhesion is unsatisfactory. An improvement in these problems is thus desired. US-A-5, 302, 648 discloses a silicone rubber composition comprising hydrosiloxane, alkoxysilane, curing catalyst and a calcium carbonate filler treated with resin acid. EP-A-438221 discloses a sealant composition comprising alkoxysiloxane, alkoxysilane titanium catalyst and a calcium carbonate filler treated with an acid having a melting point below 100°C. The general aim herein is to provide new and useful organopolysiloxane compositions (as well as manufacture methods, uses and cured products thereof), particularly of the kind curable by moisture, e.g. ambient moisture e.g. at or around room temperature (RTV). Preferred aims include, independently; good bonding to bonding-resistant substrates e.g as mentioned; bond resistance to heat and/or water immersion. We have found that by blending organopolysiloxane of the following general formula (1), silane of the following general formula (2), surface treated calcium carbonate, and condensation catalyst, we can obtain useful RTV organopolysiloxane compositions of a dealcoholysis one-part type. We have obtained cured products capable of forming a satisfactory bond to difficult-to-bond substrates such as surface treated aluminum members, fluoro-resin coated steel strips and acrylic resin electrodeposited steel strips without a need for a primer. We also noted highly heat-resistant and water immersion-resistant bonding, and good shelf stability. Therefore, the present invention provides a room temperature vulcanizable (RTV) organopolysiloxane composition comprising (A) organopolysiloxane of the following general formula (1), (B) silane of the following general formula (2), (C) 10-200 parts by weight calcium carbonate having a mean particle size of 0.01 to 2µm and be surface treated with 1 to 25% by weight based on the calcium carbonate of a carboxylic acid having a melting point of at least 100°C, and (D) condensation catalyst. R 1 and R 2 are independently selected from substituted or unsubstituted monovalent hydrocarbon groups, R 3 is a methyl, ethyl, propyl, butyl or vinyl group, letter m is a positive integer, d is an integer of 0 to 10, and n is equal to 0 or 1. R 4 is a methyl, ethyl, propyl, butyl or vinyl group, R 5 is a substituted or unsubstituted monovalent hydrocarbon group, and letter a is equal to 0 or 1. A first component (A) of the RTV organopolysiloxane composition of the invention is organopolysiloxane selected from those of the following general formula (1) : wherein R 1 and R 2 , which may be identical or different, are selected from substituted or unsubstituted monovalent hydrocarbon groups, R 3 is a methyl, ethyl, propyl, butyl or vinyl group, letter m is a positive integer, d is an integer of 0 to 10, and n is equal to 0 or 1. In formula (1), each of R 1 and R 2 is a substituted or unsubstituted monovalent hydrocarbon group, preferably having 1 to 10 carbon atoms, more preferably 1 to 8 carbon atoms, for example, alkyl groups such as methyl, ethyl, propyl, butyl, and hexyl, aryl groups such as phenyl and tolyl, aralkyl groups such as vinyl, allyl, butenyl, benzyl and 2-phenylethyl, and substituted ones of these groups wherein one or more or all of the hydrogen atoms each attached to a carbon atom are replaced by halogen atom or cyano groups, such as chloromethyl, trifluoropropyl, and cyanoethyl. Of these, methyl, phenyl, vinyl, and trifluoropropyl are preferred. Methyl is most preferred because of the ease of synthesis of the organopolysiloxane. R 3 is a substituent selected from the group consisting of methyl, ethyl, propyl, butyl and vinyl. Letter d is an integer of 0 to 10, preferably equal to 0 or 2 because of the ease of synthesis and the cost of the organopolysiloxane. Letter n is equal to 0 or 1. Then the organopolysiloxane of formula (1) is an organopolysiloxane having a di- or trifunctional terminal. The organopolysiloxane having a difunctional terminal is preferred from the standpoint of storage. Letter m representative of a degree of polymerization is a positive integer, preferably in the range of 50 to 2,000, more preferably 300 to 1,000 from the standpoints of viscosity and ease of working. The organopolysiloxane of formula (1) preferably has a viscosity of 0.00005 to 1m 2 s -1 (50 to 1,000,000 cs), more preferably 0.005 to 0.1 m 2 s -1 (5,000 to 100,000 cs) at 25°C. Examples of the organopolysiloxane of formula (1) are given below by chemical formulae. Note that Me is methyl, Ph is phenyl, letters p and q are positive integers, and p (in case of the formulae which do not show "q") or the sum of p + q (in case of the formulae which show "q") is an integer corresponding to m. A second component (B) is silane selected from those of the following general formula (2) : wherein R 4 is a methyl, ethyl, propyl, butyl or vinyl group, R 5 is a substituted or unsubstituted monovalent hydrocarbon group, and letter a is equal to 0 or 1. In formula (2), R 4 is a methyl, ethyl, propyl, butyl or vinyl group, and R 4 O is a hydrolyzable group. R 5 is a substituted or unsubstituted monovalent hydrocarbon group, options as for R 1 in formula (1). For the ease of synthesis, R 5 is preferably selected from alkyl groups of 1 to 8 carbon atoms and alkenyl groups of 2 to 10 carbon atoms, typically methyl, ethyl, vinyl, and phenyl. Letter a is equal to 0 or 1. Illustrative examples of the silane of formula (2) include alkoxysilanes such as methyltrimethoxysilane, vinyltrimethoxysilane, phenyltrimethoxysilane, methyltriethoxysilane, tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, and 3-chloropropyltrimethoxysilane, and partial hydrolysates of these organic silicon compounds. The silane (B) is preferably used in an amount of 0.1 to 20 parts, more preferably 0.5 to 5 parts by weight per 100 parts by weight of the organopolysiloxane (A). A composition containing less than 0.1 part of the silane (B) on this basis would become short of curing whereas a composition containing more than 20 part of the silane (B) would cure into a hard product which loses the sealant function. A third component (C) is calcium carbonate which has been surface treated with carboxylic acid having a melting point of at least 100°C, preferably at least 150°C. Better adhesion is achieved by using calcium carbonate with a mean particle size of 0.01 to 0.2 µm and surface treating the calcium carbonate with 1 to 2.5% by weight the carboxylic acid. The calcium carbonate has a mean particle size of 0.01 to 0.2 µm, preferably 0.02 to 0.1 µm. Calcium carbonate particles with a size of less than 0.01 µm tend to agglomerate whereas particles with a size of more than 0.2 µm would detract from the mechanical properties of rubber. The type of the surface treating agent is not critical insofar as it is or includes the acid having a melting point of at least 100°C. Typical treating agents are rhodinic acid, abietic acid, dehydroabietic acid, and saturated fatty acids, represented by C n H 2n+1 COOH, having a melting point of at least 100°C. These treating agents may be used alone or in admixture of two or more. Abietic acid and dehydroabietic acid are preferred. The amount of the treating agent is 1 to 2.5%, more preferably 1.8 to 2.3% by weight based on the calcium carbonate. Less than 1% of the treating agent may sometimes be less effective for adhesion improvement. Over 2.5%, increases the possibility that part of the treating agent may separate from the calcium carbonate, exacerbating adhesion. Any conventional surface treating method may be employed for the treatment of calcium carbonate with the carboxylic acid. The amount of the carboxylic acid-treated calcium carbonate blended is 10 to 200 parts, preferably 50 to 100 parts by weight per 100 parts by weight of the organopolysiloxane (A). A composition containing less than 10 parts of the calcium carbonate on this basis may flow too readily, leading to working difficulties. A composition containing more than 200 parts of the calcium carbonate may be rather hard, also leading to working difficulties in some cases In the composition of the invention, a condensation catalyst (D) is blended for promoting the curing thereof. The condensation catalyst used herein may be selected from those commonly used in this type of composition as a curing promoter. Exemplary catalysts include metal Lewis acids, for example, organic tin compounds such as dibutyltin dimethoxide, dibutyltin diacetate, dibutyltin dioctate, dibutyltin dilaurate, dimethyltin dimethoxide, and dimethyltin diacetate, and organic titanium compounds such as tetrapropyl titanate, tetrabutyl titanate, tetra-2-ethylhexyl titanate, and dimetoxytitanium diacetonate; amine compounds such as 3-aminopropyltrimethoxysilane, and salts thereof, alone or in admixture of two or more. Usually the condensation catalyst is used in an amount of less than 10 parts, preferably 0.01 to 5 parts by weight per 100 parts by weight of the organopolysiloxane (A). More than 10 parts of the condensation catalyst may induce cracks and rupture after a durability test. Too less amounts of the condensation catalyst are undesirable for practical use because the curing time becomes long. This is routine. In addition to the condensation catalyst, the composition of the invention may contain various other additives if desired, for example, fillers, pigments, silica, dyestuffs, tackifiers, thixotropic agents, antiseptic agents, flame retardants, and antibacterial agents. These optional components can be added using conventional practice regarding selection of this nature and quantity. The organopolysiloxane composition can be stored in the absence of water. On typical use, the package is opened to expose the composition to air whereupon the composition reacts with water in air at room temperature and thus cures into a rubbery elastomer. Thus, the present teachings enable an RTV organopolysiloxane composition which is shelf stable and cures into a cured product capable of forming a satisfactory bond to difficult-to-bond substrates such as surface treated aluminum members, fluoro-resin coated steel strips and acrylic resin electrodeposited steel strips without a need for primer. The cured product maintains improved thermoresistant and water immersion-resistant adhesion. The composition is applicable to a wide variety of substrates, finding a wide variety of applications. EXAMPLE Examples of the invention are given below by way of illustration and not by way of limitation. All parts are by weight and the viscosity is a measurement at 25°C. Example 1 A universal mixer was charged with 60 parts of a trimethoxy-terminated dimethylpolysiloxane having a viscosity of 0.02 m 2 s -1 (20,000 centistokes), 50 parts of calcium carbonate with a particle size of 0.10 µm treated with 2.3% of dehydroabietic acid (melting point 172°C), 3 parts of methyltrimethoxysilane, 0.02 part of polypropylene glycol, 0.1 part of dibutyltin dimethoxide, and 1 part of γ-aminopropyltriethoxysilane. The mixture was deaerated and mixed. An H shaped test specimen was prepared from this sample. Example 2 A universal mixer was charged with 60 parts of a trimethoxy-terminated dimethylpolysiloxane having a viscosity of 0.05 m 2 s -1 (50,000 centistokes), 50 parts of calcium carbonate with a particle size of 0.10 µm treated with 2.3% of abietic acid (melting point 175°C), 2 parts of methyltrimethoxysilane, 0.02 part of polypropylene glycol, 0.1 part of dibutyltin dimethoxide, and 1 part of γ-aminopropyltriethoxysilane. The mixture was deaerated and mixed. An H shaped test specimen was prepared from this sample. Example 3 A universal mixer was charged with 60 parts of a methyldimethoxy-terminated dimethylpolysiloxane having a viscosity of 0.02 m 2 s -1 (20,000 centistokes), 50 parts of calcium carbonate with a particle size of 0.10 µm treated with 2.3% of abietic acid, 3 parts of methyltrimethoxysilane, 0.02 part of polypropylene glycol, 0.1 part of dibutyltin dimethoxide, and 1 part of γ-aminopropyltriethoxysilane. The mixture was deaerated and mixed. An H shaped test specimen was prepared from this sample. Example 4 A universal mixer was charged with 60 parts of a trimethoxy-terminated dimethylpolysiloxane having a viscosity of 0.02 m 2 s -1 (20,000 centistokes), 25 parts of calcium carbonate with a particle size of 0.10 µm treated with 2.3% of rhodinic acid, 25 parts of calcium carbonate with a particle size of 0.10 µm treated with 2.3% of abietic acid, 3 parts of methyltrimethoxysilane, 0.02 part of polypropylene glycol, 0.5 part of tetrabutoxytitanate, and 1 part of γ-aminopropyltriethoxysilane. The mixture was deaerated and mixed. An H shaped test specimen was prepared from this sample. Example 5 A universal mixer was charged with 60 parts of a ethylene trimethoxysilyl-terminated dimethylpolysiloxane having a viscosity of 0.02 m 2 s -1 (20,000 centistokes) shown below, 43 parts of calcium carbonate with a particle size of 0.06 µm treated with 2.3% of abietic acid, 3 parts of tetramethoxysilane, 0.02 part of polypropylene glycol, 0.1 part of dibutyltin dimethoxide, and 1 part of γ-aminopropyltriethoxysilane. The mixture was deaerated and mixed. An H shaped test specimen was prepared from this sample. (m is a number such that the viscosity of the compound is 20,000 centistokes at 25°C.) Comparative Example 1 A universal mixer was charged with 60 parts of a trimethoxy-terminated dimethylpolysiloxane having a viscosity of 0.02 m 2 s -1 (20,000 centistokes), 50 parts of calcium carbonate with a particle size of 0.10 µm treated with 2.3% of stearic acid (melting point 72°C), 3 parts of methyltrimethoxysilane, 0.02 part of polypropylene glycol, 0.1 part of dibutyltin dimethoxide, and 1 part of γ-aminopropyltriethoxysilane. The mixture was deaerated and mixed. An H shaped test specimen was prepared from this sample. Comparative Example 2 A universal mixer was charged with 60 parts of a methyldimethoxy-terminated dimethylpolysiloxane having a viscosity of 0.02 m 2 s -1 (20,000 centistokes), 50 parts of calcium carbonate with a particle size of 0.10 µm treated with 2.3% of a treating agent in the form of a 6/4 (weight ratio) mixture of stearic acid and oleic acid (melting point 16°C), 3 parts of methyltrimethoxysilane, 0.02 part of polypropylene glycol, 0.1 part of dibutyltin dimethoxide, and 1 part of γ-aminopropyltriethoxysilane. The mixture was deaerated and mixed. An H shaped test specimen was prepared from this sample. Comparative Example 3 A universal mixer was charged with 60 parts of a trimethoxy-terminated dimethylpolysiloxane having a viscosity of 0.05 m 2 s -1 (50,000 centistokes), 50 parts of calcium carbonate with a particle size of 0.10 µm treated with 2.3% of stearic acid, 3 parts of methyltrimethoxysilane, 0.02 part of polypropylene glycol, 0.1 part of dibutyltin dimethoxide, and 1 part of γ-aminopropyltriethoxysilane. The mixture was deaerated and mixed. An H shaped test specimen was prepared from this sample. Comparative Example 4 A universal mixer was charged with 60 parts of α,ω-dihydroxydimethylpolysiloxane having a viscosity of 0.02 m 2 s -1 (20,000 centistokes), 50 parts of calcium carbonate with a particle size of 0.10 µm treated with 2.3% of rhodinic acid, 7 parts of methyltrimethoxysilane, 0.02 part of polypropylene glycol, 0.1 part of dibutyltin dimethoxide, and 1 part of γ-aminopropyltriethoxysilane. The mixture was deaerated and mixed. An H shaped test specimen was prepared from this sample. The RTV organopolysiloxane compositions of Examples 1-5 and Comparative Examples 1-4 were subject to a bond strength test after aging and after water immersion. The aging test included aging at 20°C for 14 days and subsequent aging at 30°C for 14 days. The water immersion test included the aging test and immersion in water at 50°C for 28 days or immersion in water at 100°C for 28 days. The bond strength test was a tensile bond strength test as prescribed in JIS A 5758 and used substrates of float glass, JIS aluminum, fluoro-resin coated steel strips, and acrylic resin electrodeposited steel strips. Examination of the tensile bond test was made by visually observing the failure and determining a proportion of cohesive failure of the sealing material. As to the durability, the situation after the test was visually observed. The results are shown in Tables 1 to 3. Initial test results (aging 20°C/14 days → 30°C/14 days) Test item tensile bond strength (proportion of cohesive failure of sealing material, %) Substrate Float glass JIS aluminum Fluororesin Acryl electrodeposit Example 1 100 100 100 100 2 100 100 100 100 3 100 100 100 100 4 100 100 100 100 5 100 100 100 100 Comparative Example 1 100 100 100 100 2 100 100 100 100 3 100 100 100 100 4 100 100 100 100 Test results after water immersion (aging 20°C/14 days → 30°C/14 days → water immersion 50°C/28 days) Test item tensile bond strength (proportion of cohesive failure of sealing material, %) Substrate Float glass JIS aluminum Fluororesin Acryl electrodeposit Example 1 100 100 100 100 2 100 100 100 100 3 100 100 100 100 4 100 100 100 100 5 100 100 100 100 Comparative Example 1 100 80 40 0 2 100 50 0 0 3 100 60 0 0 4 100 100 100 100 Test results after water immersion (aging 20°C/14 days → 30°C/14 days → water immersion 100°C/28 days) Test item tensile bond strength (proportion of cohesive failure of sealing material, %) Substrate Float glass JIS aluminum Fluororesin Acryl electrodeposit Example 1 100 100 100 100 2 100 100 100 100 3 100 100 100 100 4 100 100 100 100 5 100 100 100 100 Comparative Example 1 100 80 60 80 2 100 50 40 30 3 100 70 50 50 4 80 80 50 50 It is evident from Tables 1 to 3 that the RTV compositions embodying the invention (Examples 1 to 5) cure into products which establish a firm bond to difficult-to-bond substrates which bond is durably resistant to heat and water immersion. While the invention has been described with reference to what are presently considered to be some preferred embodiments, other variations and modifications will become apparent to those skilled in the art within the scope of the general teachings herein.

Claims: A vulcanizable organopolysiloxane composition comprising (A) organopolysiloxane of the following general formula (1) : wherein groups R 1 are independently selected, and groups R 2 are independently selected, from substituted and unsubstituted monovalent hydrocarbon groups, groups R 3 are selected from methyl, ethyl, propyl, butyl and vinyl, m is a positive integer, d is an integer from 0 to 10 and n is 0 or 1; (B) silane of the following general formula (2): wherein groups R 4 are selected from methyl, ethyl, propyl, butyl and vinyl, R 5 is substituted or unsubstituted monovalent hydrocarbon group, and a is 0 or 1; (C) 10-200 parts by weight calcium carbonate having a mean particle size of 0.01 to 0.2 µm and being surface treated with 1 to 2.5% by weight based on the calcium carbonate of carboxylic acid having a melting point of at least 100°C, and (D) condensation catalyst. A composition according to any one of the preceding claims wherein the carboxylic acid is abietic acid and/or dehydroabietic acid. A composition according to any one of the preceding claims wherein the condensation catalyst is a metal Lewis acid. A method comprising curing a composition according to any one of the preceding claims by exposing it to ambient air containing moisture.

Inventors: FUJIKI HIRONAO, MIYAKE MASATOSHI, NAGAI KAZUKIYO, SAKAMOTO TAKAFUMI, FUJIKI, HIRONAO, MIYAKE, MASATOSHI, NAGAI, KAZUKIYO, SAKAMOTO, TAKAFUMI, Fujiki, Hironao, c/o Shin-Etsu Chem. Co.,Ltd, Miyake, Masatoshi, c/o Shin-Etsu Chem. Co.,Ltd, Nagai, Kazukiyo, c/o Shin-Etsu Chem. Co.,Ltd, Sakamoto, Takafumi, c/o Shin-Etsu Chem. Co.,Ltd
Applicants: SHINETSU CHEMICAL CO, SHIN-ETSU CHEMICAL CO., LTD.
Application year: 1997
Main classification: C08L83
IPC codes: C08K3, C08K5, C08L83, C08K7, C08K9