Patent Application
20100273011
The present invention relates to a silicone composition and more particularly to a silicone composition comprising at least one hydrogenpolysiloxane resin having an average of at least two silicon-bonded hydrogen atoms per molecule, a cross-linking agent having an average of at least two aliphatic carbon-carbon double bonds per molecule, and a hydrosilylation catalyst. The present invention also relates to a silicone adhesive comprising a cured product of at least one hydrogenpolysiloxane resin. The present invention further relates to a coated substrate and to a laminated substrate, each comprising the silicone adhesive.
Silicone adhesives are useful in a variety of applications by virtue of their unique combination of properties, including high thermal stability, good moisture resistance, excellent flexibility, high ionic purity, low alpha particle emissions, and good adhesion to various substrates. For example, silicone adhesives are widely used in the automotive, electronic, construction, appliance, and aerospace industries.
However, when conventional silicone adhesives are exposed to high temperatures, for example temperatures encountered by direct contact with an open flame, the adhesives decompose to form a char, typically a nonadherent powder.
In view of the foregoing, there is a need for a silicone composition that cures to form an adhesive having high char yield, and high adhesion during and after exposure to temperatures above the decomposition temperature of the adhesive.
The present invention is directed to a silicone composition, comprising:
(A) at least one hydrogenpolysiloxane resin having the formula [(HSiO(3-w)/2)(OH)w]m(R12R2SiO1/2)n[(R1R2SiO(2-x)/2)(OH)x]p[(R1SiO(3-y)/2)(OH)y]q[(SiO(4-z)/2)(OH)z]r (I), wherein each R1 is independently C1 to C10 hydrocarbyl or C1 to C10 halogen-substituted hydrocarbyl, both free of aliphatic unsaturation, each R2 is independently R1 or —H, m is from 0.2 to 1, n is from 0 to 0.3, p is from 0 to 0.8, q is from 0 to 0.6, r is from 0 to 0.3, w is from 0 to 0.05, x is from 0 to 0.05, y is from 0 to 0.05, z is from 0 to 0.05, and m+n+p+q+r≈1, provided the resin has an average of at least two silicon-bonded hydrogen atoms per molecule;
(B) a cross-linking agent selected from (i) at least one organopolysiloxane having an average of at least two silicon-bonded alkenyl groups per molecule, (ii) at least one organic compound having an average of at least two aliphatic carbon-carbon double bonds per molecule, and (iii) a mixture comprising (i) and (ii), wherein the ratio of the number of moles of aliphatic carbon-carbon double bonds in the cross-linking agent (B) to the number of moles of silicon-bonded hydrogen atoms in the hydrogenpolysiloxane resin (A) is from 0.002 to 0.4; and
(C) a hydrosilylation catalyst.
The present invention is also directed to a silicone adhesive comprising a cured product of at least one hydrogenpolysiloxane resin having the formula (I) above.
The present invention is further directed to a coated substrate, comprising:
a substrate; and
a silicone adhesive coating on at least a portion of a surface of the substrate, wherein the adhesive coating comprises a cured product of at least one hydrogenpolysiloxane resin having the formula (I) above.
The present invention is still further directed to a laminated substrate, comprising:
a first substrate;
at least one additional substrate overlying the first substrate; and
a silicone adhesive coating on at least a portion of at least one surface of each substrate, provided at least a portion of the adhesive coating is between and in direct contact with opposing surfaces of adjacent substrates, wherein the adhesive coating comprises a cured product of at least one hydrogenpolysiloxane resin having the formula (I) above.
The silicone adhesive of the present invention has high transparency and excellent adhesion to various substrates. Moreover, the silicone adhesive has high adhesion during and after exposure to temperatures above the decomposition temperature of the adhesive, low flammability (as evidenced by low heat release rate), and high char yield.
The silicone adhesive of the present invention is useful in applications requiring adhesives having high adhesion at elevated temperatures, low flammability, and high transparency. For example, the adhesive is useful for bonding glass panels in the fabrication of fire rated windows and glass firewalls.
These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description, appended claims, and accompanying drawings.
A silicone composition according to the present invention comprises:
(A) at least one hydrogenpolysiloxane resin having the formula [(HSiO(3-w)/2)(OH)w]m(R12R2SiO1/2)n[(R1R2SiO(2-x)/2)(OH)x]p[(R1SiO(3-y)/2)(OH)y]q[SiO(4-z)/2)(OH)z]r (I), wherein each R1 is independently C1 to C10 hydrocarbyl or C1 to C10 halogen-substituted hydrocarbyl, both free of aliphatic unsaturation, each R2 is independently R1 or —H, m is from 0.2 to 1, n is from 0 to 0.3, p is from 0 to 0.8, q is from 0 to 0.6, r is from 0 to 0.3, w is from 0 to 0.05, x is from 0 to 0.05, y is from 0 to 0.05, z is from 0 to 0.05, and m+n+p+q+r≈1, provided the resin has an average of at least two silicon-bonded hydrogen atoms per molecule;
(B) a cross-linking agent selected from (i) at least one organopolysiloxane having an average of at least two silicon-bonded alkenyl groups per molecule, (ii) at least one organic compound having an average of at least two aliphatic carbon-carbon double bonds per molecule, and (iii) a mixture comprising (i) and (ii), wherein the ratio of the number of moles of aliphatic carbon-carbon double bonds in the cross-linking agent (B) to the number of moles of silicon-bonded hydrogen atoms in the hydrogenpolysiloxane resin (A) is from 0.002 to 0.4; and
(C) a hydrosilylation catalyst.
Component (A) is at least one hydrogenpolysiloxane resin having the formula [(HSiO(3-w)/2)(OH)w]m(R12R2SiO1/2)n[(R1R2SiO(2-x)/2)(OH)x]p[(R1SiO(3-y)/2)(OH)y]q[SiO(4-z)/2)(OH)z]r (I), wherein each R1 is independently C1 to C10 hydrocarbyl or C1 to C10 halogen-substituted hydrocarbyl, both free of aliphatic unsaturation, each R2 is independently R1 or —H, m is from 0.2 to 1, n is from 0 to 0.3, p is from 0 to 0.8, q is from 0 to 0.6, r is from 0 to 0.3, w is from 0 to 0.05, x is from 0 to 0.05, y is from 0 to 0.05, z is from 0 to 0.05, and m+n+p+q+r≈1, provided the resin has an average of at least two silicon-bonded hydrogen atoms per molecule.
The hydrocarbyl and halogen-substituted hydrocarbyl groups represented by R1 are free of aliphatic unsaturation and typically have from 1 to 10 carbon atoms, alternatively from 1 to 6 carbon atoms. Acyclic hydrocarbyl and halogen-substituted hydrocarbyl groups containing at least 3 carbon atoms can have a branched or unbranched structure. Examples of hydrocarbyl groups represented by R1 include, but are not limited to, alkyl, such as methyl, ethyl, propyl, 1-methylethyl, butyl, 1-methylpropyl, 2-methylpropyl, 1,1-dimethylethyl, pentyl, 1-methylbutyl, 1-ethylpropyl, 2-methylbutyl, 3-methylbutyl, 1,2-dimethylpropyl, 2,2-dimethylpropyl, hexyl, heptyl, octyl, nonyl, and decyl; cycloalkyl, such as cyclopentyl, cyclohexyl, and methylcyclohexyl; aryl, such as phenyl and naphthyl; alkaryl, such as tolyl and xylyl; and aralkyl, such as benzyl and phenethyl. Examples of halogen-substituted hydrocarbyl groups represented by R1 include, but are not limited to, 3,3,3-trifluoropropyl, 3-chloropropyl, chlorophenyl, dichlorophenyl, 2,2,2-trifluoroethyl, 2,2,3,3-tetrafluoropropyl, and 2,2,3,3,4,4,5,5-octafluoropentyl.
In the formula (I) of the hydrogenpolysiloxane resin, the subscripts m, n, p, q, and r are mole fractions. The subscript m typically has a value of from 0.2 to 1, alternatively from 0.4 to 1, alternatively from 0.5 to 0.8; the subscript n typically has a value of from 0 to 0.3, alternatively from 0 to 0.1, alternatively from 0.02 to 0.08, alternatively from 0.03 to 0.06; the subscript p typically has a value of from 0 to 0.8, alternatively from 0.1 to 0.6, alternatively from 0.1 to 0.4; the subscript q typically has a value of from 0 to 0.6, alternatively from 0 to 0.3, alternatively from 0.05 to 0.15; and the subscript r typically has a value of from 0 to 0.3, alternatively from 0 to 0.2, alternatively from 0.05 to 0.15.
Also, in the formula (I) of the hydrogenpolysiloxane resin, the subscripts w, x, y, and z are whole numbers or fractions that represent the average number of hydroxy groups associated with the various units in the formula. The subscript w typically has a value of from 0 to 0.05, alternatively from 0.01 to 0.04, alternatively from 0.01 to 0.03; the subscript x typically has a value of from 0 to 0.05, alternatively from 0.01 to 0.03, alternatively from 0.01 to 0.02; the subscript y typically has a value of from 0 to 0.05, alternatively from 0.01 to 0.04, alternatively from 0.01 to 0.03; and the subscript z typically has a value of from 0 to 0.05, alternatively from 0.01 to 0.04, alternatively from 0.01 to 0.03.
Furthermore, in the formula (I) of the hydrogenpolysiloxane resin, the sum m+n+p+q+r≈ (is approximately equal to) 1. This means that in addition to units having the average formulas shown in the formula (I) above, the hydrogenpolysiloxane resin may contain residual amounts, e.g., not greater than 5 mol %, of one or more units having the following average formulas: (HSiO(3-w′)/2)(OR3)w′, (R1R2SiO(2-x′)/2)(OR3)x′, (R1SiO(3-y′)/2)(OR3)y′, and (SiO(4-z′)/2)(OR3)z′, wherein R1 and R2 are as defined and exemplified above, R3 is C1 to C8 alkyl, w′ is from 0 to 0.05; x′ is from 0 to 0.05; y′ is from 0 to 0.05; and z′ is from 0 to 0.05.
The alkyl groups represented by R3 typically have from 1 to 8 carbon atoms, alternatively from 1 to 6 carbon atoms, alternatively from 1 to 4 carbon atoms. Acyclic alkyl groups containing at least 3 carbon atoms can have a branched or unbranched structure. Examples of alkyl groups include, but are not limited to, methyl, ethyl, propyl, 1-methylethyl, butyl, 1-methylpropyl, 2-methylpropyl, 1,1-dimethylethyl, pentyl, 1-methylbutyl, 1-ethylpropyl, 2-methylbutyl, 3-methylbutyl, 1,2-dimethylpropyl, 2,2-dimethylpropyl, hexyl, heptyl, and octyl; and cycloalkyl, such as cyclopentyl, cyclohexyl, and methylcyclohexyl.
Typically at least 50 mol %, alternatively at least 65 mol %, alternatively at least 80 mol % of the groups R2 in the hydrogenpolysiloxane resin are hydrogen. The term “mol % of the groups R2 in the hydrogenpolysiloxane resin are hydrogen” is defined as the ratio of the number of moles of silicon-bonded hydrogen atoms in the hydrogenpolysiloxane resin to the total number of moles of the groups R2 in the resin, multiplied by 100.
The hydrogenpolysiloxane resin typically has a number-average molecular weight (Mn) of from 500 to 50,000, alternatively from 500 to 10,000, alternatively 1,000 to 3,000, where the molecular weight is determined by gel permeation chromatography employing a refractive index detector and silicone resin (MQ) standards.
The hydrogenpolysiloxane resin can be a solid or a liquid at room temperature. Moreover, the resin typically has a viscosity of from 0.1 to 100,000 Pa·s, alternatively from 1 to 10,000 Pa·s, alternatively from 1 to 100 Pa·s, at 25° C.
The hydrogenpolysiloxane resin typically contains less than 5% (w/w), alternatively less than 2% (w/w), of silicon-bonded hydroxy groups, as determined by 29Si NMR.
In one embodiment, the hydrogenpolysiloxane resin is a hydrogen silsesquioxane resin (H-resin) having the formula (I), wherein m=1. The hydrogen silsesquioxane resin may be represented by the general formula [(HSiO(3-w)/2)(OH)w]b, wherein w is as defined and exemplified above and b has a value such that the hydrogen silsesquioxane resin has a viscosity of from 0.1 to 100,000 Pa·s at 25° C.
Examples of hydrogenpolysiloxane resins having the formula (I) include, but are not limited to, resins having the following formulae:
[(HSiO(3-w)/2)(OH)w]b, [(HSiO(3-w)/2)(OH)w]m[Me3SiO1/2]n[(MeHSiO(2-x)/2)(OH)x]p, [(HSiO(3-w)/2)(OH)w]n[(MeSiO(3-y)/2)(OH)y]q, [(HSiO(3-w)/2)(OH)w]m[PhSiO(3-y)/2)(OH)y]q, and [(HSiO(3-w)/2)(OH)w]m[Me2HSiO1/2]n[(SiO(4-z)/2)(OH)z]r, where Me is methyl, Ph is phenyl, the subscript b has a value such that the hydrogen silsesquioxane resin has a viscosity of from 0.1 to 100,000 Pa·s at 25° C., the subscripts m, n, p, q, r, w, x, y, and z are as described above for the hydrogenpolysiloxane resin having the formula (I), and the sum m+n+p+q+r≈1. Also, in the preceding formulae, the sequence of units is unspecified.
Component (A) can be a single hydrogenpolysiloxane resin or a mixture comprising two or more different hydrogenpolysiloxane resins, each as described above.
Methods of preparing hydrogenpolysiloxane resins are well known in the art; many of these resins are commercially available. Hydrogenpolysiloxane resins are typically prepared by cohydrolyzing the appropriate mixture of chlorosilane precursors in an organic solvent, such as toluene. For example, a silicone resin consisting essentially of HSiO3/2 units, MeHSiO2/2 units, and Me3SiO1/2 units can be prepared by cohydrolyzing a compound having the formula HSiCl3, a compound having the formula MeHSiCl2, and a compound having the formula Me3SiCl in toluene. The aqueous hydrochloric acid and silicone hydrolyzate are separated and the hydrolyzate is washed with water to remove residual acid and heated in the presence of a mild non-basic condensation catalyst to “body” the resin to the requisite viscosity. If desired, the resin can be further treated with a non-basic condensation catalyst in an organic solvent to reduce the content of silicon-bonded hydroxy groups. Alternatively, silanes containing hydrolysable groups other than chloro, such —Br, —I, —OCH3, —OC(O)CH3, —N(CH3)2, NHCOCH3, and —SCH3, can be utilized as starting materials in the cohydrolysis reaction. The properties of the resin products depend on the types of silanes, the mole ratio of silanes, the degree of condensation, and the processing conditions.
Furthermore, methods of preparing hydrogen silsesquioxane resins are well known in the art as exemplified in U.S. Pat. No. 3,615,272 to Collins et al.; U.S. Pat. No. 5,010,159 to Bank et al.; U.S. Pat. No. 4,999,397 to Frye et al.; U.S. Pat. No. 5,063,267 to Hanneman et al.; U.S. Pat. No. 4,999,397 to Frye et al.; Kokai Patent No. 59-178749; Kokai Patent No. 60-86017; and Kokai Patent No. 63-107122.
Component (B) is a cross-linking agent selected from (i) at least one organopolysiloxane having an average of at least two silicon-bonded alkenyl groups per molecule, (ii) at least one organic compound having an average of at least two aliphatic carbon-carbon double bonds per molecule, and (iii) a mixture comprising (i) and (ii), wherein the ratio of the number of moles of aliphatic carbon-carbon double bonds in the cross-linking agent (B) to the number of moles of silicon-bonded hydrogen atoms in the hydrogenpolysiloxane resin (A) is from 0.002 to 0.4. It is generally understood that cross-linking occurs when the sum of the average number of silicon-bonded hydrogen atoms per molecule in component (A) and the average number of aliphatic carbon-carbon double bonds per molecule in component (B) is greater than four.
Component (B)(i) is at least one organopolysiloxane having an average of at least two silicon-bonded alkenyl groups per molecule. As used herein, the term “alkenyl group” refers to a monovalent hydrocarbon group containing one aliphatic carbon-carbon double bond. The organopolysiloxane typically contains an average of at least two, alternatively at least three, silicon-bonded alkenyl groups per molecule.
The structure of the organopolysiloxane can be linear, branched, or resinous. Moreover, in acyclic organopolysiloxanes, the silicon-bonded alkenyl groups can be located at terminal, pendant, or at both terminal and pendant positions.
The organopolysiloxane typically has a number-average molecular weight (Mn) of from 500 to 30,000, alternatively from 500 to 12,000, alternatively 500 to 3,000, where the molecular weight is determined by gel permeation chromatography employing a refractive index detector and polydimethylsiloxane standards.
Examples of organopolysiloxanes suitable for use as component (B)(i) include, but are not limited to, polysiloxanes having the following formulae:
ViMe2SiO(Me2SiO)cSiMe2Vi, ViMe2SiO(Me2SiO)0.25c(MePhSiO)0.75cSiMe2Vi, ViMe2SiO(Me2SiO)0.95c(Ph2SiO)0.05cSiMe2Vi, ViMe2SiO(Me2SiO)0.98c(MeViSiO)0.02cSiMe2Vi, Me3SiO(Me2SiO)0.95c(MeViSiO)0.05cSiMe3, and PhMeViSiO(Me2SiO)cSiPhMeVi, where Me, Vi, and Ph denote methyl, vinyl, and phenyl respectively, and the subscript c, which represents the total number of non-terminal siloxane units in the organopolysiloxane, has a value such that the organopolysiloxane has a number-average molecular weight of from 500 to 30,000.
Component (B)(i) can be a single organopolysiloxane or a mixture comprising two or more different organopolysiloxanes, each as described above. Also, methods of preparing organopolysiloxanes containing silicon-bonded alkenyl groups are well known in the art; many of these compounds are commercially available.
Component (B)(ii) is at least one organic compound having an average of at least two aliphatic carbon-carbon double bonds per molecule. The organic compound can be any organic compound containing at least two aliphatic carbon-carbon double bonds per molecule, provided the compound does not prevent the hydrogenpolysiloxane resin of the silicone composition from curing to form a silicone adhesive, described below, having high char yield, and high adhesion during and after exposure to temperatures above the decomposition temperature of the adhesive. The organic compound can be a diene, a triene, or a polyene. Also, the organic compound can have a linear, branched, or cyclic structure. Further, in acyclic organic compounds, the carbon-carbon double bonds can be located at terminal, pendant, or at both terminal and pendant positions.
The organic compound can contain one or more functional groups other than the aliphatic carbon-carbon double bond. Examples of suitable functional groups include, but are not limited to, —O—, >C═O, —CHO, —CO2—, —C≡N, —NO2, >C═C<, —C≡C—, —F, —Cl, —Br, and —I. The suitability of a particular unsaturated organic compound for use in the silicone composition of the present invention can be readily determined by routine experimentation using the methods in the Examples below.
The organic compound typically has a molecular weight less than 500, alternatively less than 400, alternatively less than 300.
The organic compound can have a liquid or solid state at room temperature. Also, the organic compound is typically soluble in the silicone composition. The normal boiling point of the organic compound, which depends on the molecular weight, structure, and number and nature of functional groups in the compound, can vary over a wide range. Preferably, the organic compound has a normal boiling point greater than the cure temperature of the hydrogenpolysiloxane resin. Otherwise, appreciable amounts of the organic compound may be removed by volatilization during cure.
Examples of organic compounds containing aliphatic carbon-carbon double bonds include, but are not limited to, 1,4-divinylbenzene, 1,3-hexadienylbenzene, and 1,2-diethenylcyclobutane.
Component (B)(ii) can be a single organic compound or a mixture comprising two or more different organic compounds, each as described and exemplified above. Moreover, methods of preparing unsaturated organic compounds are well-known in the art; many of these compounds are commercially available.
Component (B)(iii) is a mixture comprising (B)(i) and (B)(ii), each as described and exemplified above.
The concentration of component (B) is sufficient to cure (cross-link) the hydrogenpolysiloxane resin of component (A). The exact amount of component (B) depends on the desired extent of cure, which generally increases as the ratio of the number of moles of aliphatic carbon-carbon double bonds in component (B) to the number of moles of silicon-bonded hydrogen atoms in component (A) increases. The concentration of component (B) is typically sufficient to provide not greater than 0.4 moles of aliphatic carbon-carbon double bonds, alternatively not greater than 0.2 moles of aliphatic carbon-carbon double bonds, per mole of silicon-bonded hydrogen atoms in component (A). For example, the concentration of component (B) is typically sufficient to provide from 0.002 to 0.4 moles of aliphatic carbon-carbon double bonds, alternatively from 0.01 to 0.1 moles of aliphatic carbon-carbon double bonds, alternatively from 0.01 to 0.05 moles of aliphatic carbon-carbon double bonds, per mole of silicon-bonded hydrogen atoms in component (A).
Component (C) of the hydrosilylation-curable silicone composition is at least one hydrosilylation catalyst that promotes the addition reaction of component (A) with component (B). The hydrosilylation catalyst can be any of the well-known hydrosilylation catalysts comprising a platinum group metal, a compound containing a platinum group metal, or a microencapsulated platinum group metal-containing catalyst. Platinum group metals include platinum, rhodium, ruthenium, palladium, osmium and iridium. Preferably, the platinum group metal is platinum, based on its high activity in hydrosilylation reactions.
Preferred hydrosilylation catalysts include the complexes of chloroplatinic acid and certain vinyl-containing organosiloxanes disclosed by Willing in U.S. Pat. No. 3,419,593, which is hereby incorporated by reference. A preferred catalyst of this type is the reaction product of chloroplatinic acid and 1,3-diethenyl-1,1,3,3-tetramethyldisiloxane.
The hydrosilylation catalyst can also be a microencapsulated platinum group metal-containing catalyst comprising a platinum group metal encapsulated in a thermoplastic resin. Compositions containing microencapsulated hydrosilylation catalysts are stable for extended periods of time, typically several months or longer, under ambient conditions, yet cure relatively rapidly at temperatures above the melting or softening point of the thermoplastic resin(s). Microencapsulated hydrosilylation catalysts and methods of preparing them are well known in the art, as exemplified in U.S. Pat. No. 4,766,176 and the references cited therein; and U.S. Pat. No. 5,017,654.
Component (C) can be a single hydrosilylation catalyst or a mixture comprising two or more different catalysts that differ in at least one property, such as structure, form, platinum group metal, complexing ligand, and thermoplastic resin.
The concentration of component (C) is sufficient to catalyze the addition reaction of component (A) with component (B). Typically, the concentration of component (C) is sufficient to provide from 0.1 to 1000 ppm of a platinum group metal, preferably from 1 to 500 ppm of a platinum group metal, and more preferably from 5 to 150 ppm of a platinum group metal, based on the combined weight of components (A) and (B). The rate of cure is very slow below 0.1 ppm of platinum group metal. The use of more than 1000 ppm of platinum group metal results in no appreciable increase in cure rate, and is therefore uneconomical.
The silicone composition can comprise additional ingredients, provided the ingredient does not prevent the hydrogenpolysiloxane resin from curing to form a silicone adhesive, described below, having high char yield, and high adhesion during and after exposure to temperatures above the decomposition temperature of the adhesive. Examples of additional ingredients include, but are not limited to, hydrosilylation catalyst inhibitors, such as 3-methyl-3-penten-1-yne, 3,5-dimethyl-3-hexen-1-yne, 3,5-dimethyl-1-hexyn-3-ol, 1-ethynyl-1-cyclohexanol, 2-phenyl-3-butyn-2-ol, vinylcyclosiloxanes, and triphenylphosphine; adhesion promoters, such as the adhesion promoters taught in U.S. Pat. Nos. 4,087,585 and 5,194,649; dyes; pigments; anti-oxidants; heat stabilizers; UV stabilizers; flame retardants; flow control additives; fillers, such as reinforcing fillers and extending fillers; and diluents, such as organic solvents and reactive diluents.
The silicone composition typically does not contain an organic solvent. However, the composition may further comprise an organic solvent to reduce viscosity of the composition or facilitate application of the composition on a substrate.
In one embodiment, the silicone composition further comprises a reactive diluent. For example, the silicone composition can further comprise a reactive diluent comprising an organosiloxane having an average of at least two silicon-bonded alkenyl groups per molecule and a viscosity of from 0.001 to 2 Pa·s at 25° C., wherein the viscosity of the organosiloxane is not greater than 20% of the viscosity of the hydrogenpolysiloxane resin, component (A) above, of the silicone composition and the organosiloxane has the formula (R1R42SiO1/2)c(R42SiO2/2)d(R1SiO3/2)e(SiO4/2)f, wherein R1 is C1 to C10 hydrocarbyl or C1 to C10 halogen-substituted hydrocarbyl, both free of aliphatic unsaturation, R4 is R1 or alkenyl, c is 0 to 0.8, d=0 to 1, e=0 to 0.25, f=0 to 0.2, c+d+e+f=1, and c+d is not equal to 0, provided when e+f=0, d is not equal to 0 and the alkenyl groups are not all terminal. Further, the organosiloxane can have a linear, branched, or cyclic structure.
The viscosity of the organosiloxane at 25° C. is typically from 0.001 to 2 Pa·s, alternatively from 0.001 to 0.1 Pa·s, alternatively from 0.001 to 0.05 Pa·s. Further, the viscosity of the organosiloxane at 25° C. is typically not greater than 20%, alternatively not greater than 10%, alternatively not greater than 1%, of the viscosity of the hydrogenpolysiloxane resin in the silicone composition.
Examples of organosiloxanes suitable for use as reactive diluents include, but are not limited to, organosiloxanes having the following formulae:
(ViMeSiO)3, (ViMeSiO)4, (ViMeSiO)5, (ViMeSiO)6, (ViPhSiO)3, (ViPhSiO)4, (ViPhMeSi)2O, (ViMe2Si)2O, (ViPhSiO)5, (ViPhSiO)6, ViMe2SiO(ViMeSiO)nSiMe2Vi, Me3SiO(ViMeSiO)nSiMe3, and (ViMe2SiO)4Si, where Me is methyl, Ph is phenyl, Vi is vinyl, and the subscript n has a value such that the organosiloxane has a viscosity of from 0.001 to 2 Pa·s at 25° C.
The reactive diluent can be a single organosiloxane or a mixture comprising two or more different organosiloxanes, each as described above. Methods of making alkenyl-functional organosiloxanes are well known in the art.
The concentration of the reactive diluent in the silicone composition is typically from 1 to 20% (w/w), alternatively from 1 to 10% (w/w), alternatively from 1 to 5% (w/w), based on the combined weight of the hydrogenpolysiloxane resin, component (A), and the cross-linking agent, component (B).
Also, the concentration of the reactive diluent in the silicone composition is such that the ratio of the sum of the number of moles of aliphatic carbon-carbon double bonds in the cross-linking agent, component (B), and the reactive diluent to the number of moles of silicon-bonded hydrogen atoms in the hydrogenpolysiloxane resin, component (A), is typically from 0.002 to 0.4, alternatively from 0.01 to 0.1, alternatively from 0.01 to 0.05.
In one embodiment, the silicone composition further comprises at least one ceramic filler. Examples of ceramic fillers include, but are not limited to, nitrides such as silicon nitride, boron nitride, aluminum nitride, titanium nitride, and zirconium nitride; carbides such as silicon carbide, boron carbide, tungsten carbide, titanium carbide, zirconium carbide, and molybdenum carbide; metal oxides, such as the oxides of aluminum, magnesium, zinc, beryllium, zirconium, titanium and thorium; silicates, such as the silicates of aluminum, magnesium, zirconium, and titanium; and complex silicates, such as magnesium aluminum silicate.
The silicone composition is typically prepared by combining the principal components and any optional ingredients in the stated proportions at ambient temperature, with or without the aid of an organic solvent. Although the order of addition of the various components is not critical if the silicone composition is to be used immediately, the hydrosilylation catalyst is preferably added last at a temperature below about 30° C. to prevent premature curing of the composition.
Mixing can be accomplished by any of the techniques known in the art such as milling, blending, and stifling, either in a batch or continuous process. The particular device is determined by the viscosity of the components and the viscosity of the final silicone composition.
A silicone adhesive according to the present invention comprises a cured product of at least one hydrogenpolysiloxane resin having the formula (I) above, where the hydrogenpolysiloxane resin is as described and exemplified above for the silicone composition.
As used herein, the term “cured product of at least one hydrogenpolysiloxane resin” refers to a cross-linked polysiloxane resin having a three-dimensional network structure.
The silicone adhesive typically has high transparency. The transparency of the adhesive depends on a number of factors, such as the composition and thickness of the adhesive. For example, a silicone adhesive film having a thickness of 50 μm typically has a % transmittance of at least 80%, alternatively at least 90%, for light in the visible region (˜400 to ˜700 nm) of the electromagnetic spectrum.
The silicone adhesive can be prepared by curing the hydrogenpolysiloxane resin of the silicone composition described above. The hydrogenpolysiloxane resin can be cured by exposing the silicone composition to a temperature of from room temperature (˜23±2° C.) to 250° C., alternatively from room temperature to 200° C., alternatively from room temperature to 150° C., at atmospheric pressure. The silicone composition is generally heated for a length of time sufficient to cure (cross-link) the hydrogenpolysiloxane resin. For example, the composition is typically heated at a temperature of from 150 to 200° C. for a time of from 0.1 to 3 h.
The present invention is further directed to a coated substrate, comprising:
a substrate; and
a silicone adhesive coating on at least a portion of a surface of the substrate, wherein the adhesive coating comprises a cured product of at least one hydrogenpolysiloxane resin having the formula (I) above.
The substrate can be any rigid or flexible material having a planar, complex, or irregular contour. The substrate can be transparent or nontransparent to light in the visible region (˜400 to ˜700 nm) of the electromagnetic spectrum. Also, the substrate can be an electrical conductor, semiconductor, or nonconductor. Examples of substrates include, but are not limited to, semiconductors such as silicon, silicon having a surface layer of silicon dioxide, silicon carbide, indium phosphide, and gallium arsenide; quartz; fused quartz; aluminum oxide; ceramics; glass such as soda-lime glass, borosilicate glass, lead-alkali glass, borate glass, silica glass, alumino-silicate glass, lead-borate glass, sodium borosilicate glass, lithium aluminosilicate glass, Chalcogenide glass, phosphate glass, and alkali-barium silicate glass; metal foils; polyolefins such as polyethylene, polypropylene, polystyrene, polyethylene terephthalate (PET), and polyethylene naphthalate; fluorocarbon polymers such as polytetrafluoroethylene and polyvinylfluoride; polyamides such as Nylon; polyimides; polyesters such as poly(methyl methacrylate); epoxy resins; polyethers; polycarbonates; polysulfones; and polyether sulfones.
In addition, the substrate can be a reinforced silicone resin film prepared by impregnating a fiber reinforcement (e.g., woven or nonwoven glass fabric, or loose glass fibers) in a curable silicone composition comprising a silicone resin, and heating the impregnated fiber reinforcement to cure the silicone resin. Reinforced silicone resin films prepared from various types of curable silicone compositions are known in the art, as exemplified in the following International Patent Application Publications: WO2006/088645, WO2006088646, WO2007/092032, and WO2007/018756.
The coated substrate comprises a silicone adhesive coating on at least a portion of a surface of the substrate. The silicone adhesive coating may be on a portion of one or more surfaces of the substrate or on all of one or more surfaces. For example, when the substrate is a flat panel, the silicone adhesive coating may be on one side, on both sides, or on both sides and the edges, of the substrate.
The silicone adhesive coating comprises a cured product of at least one hydrogenpolysiloxane resin having the formula (I), wherein the cured product is as described and exemplified above for the silicone adhesive of the present invention.
The silicone adhesive coating can be a single layer coating comprising one layer of a silicone adhesive, or a multiple layer coating comprising two or more layers of at least two different silicone adhesives, where directly adjacent layers comprise different silicone adhesives (i.e., cured products have a different composition and/or property). The multiple layer coating typically comprises from 2 to 7 layers, alternatively from 2 to 5 layers, alternatively from 2 to 3 layers.
The single layer silicone adhesive coating typically has a thickness of from 0.03 to 300 μm, alternatively from 0.1 to 100 μm, alternatively from 0.1 to 50 μm. The multiple layer coating typically has a thickness of from 0.06 to 300 μm, alternatively from 0.2 to 100 μm, alternatively 0.2 to 50 μm. When the thickness of the silicone adhesive coating is less than 0.03 μm, the coating may become discontinuous. When the thickness of the silicone adhesive coating is greater than 300 μm, the coating may exhibit reduced adhesion and/or cracking.
The coated substrate can be prepared by forming a silicone adhesive coating on a substrate, where the adhesive coating and the substrate are as defined and exemplified above. For example, a coated substrate comprising a single-layer silicone adhesive coating can be prepared by (i) applying a silicone composition, described above, on a substrate to form a film, and (ii) curing the hydrogenpolysiloxane resin of the film. The silicone composition can be applied on the substrate using conventional methods such as spin coating, dip coating, spray coating, flow coating, screen printing, and roll coating. When present, the solvent is typically allowed to evaporate from the coated substrate before the film is heated. Any suitable means for evaporation may be used such as simple air drying, applying a vacuum, or heating (up to 50° C.).
The hydrogenpolysiloxane resin of the film can be cured under the conditions described above in the method of preparing the silicone adhesive of the present invention.
The method of preparing the coated substrate, wherein the coating comprises a single layer adhesive coating can further comprise repeating the steps (i) and (ii) to increase the thickness of the coating, except the silicone composition is applied on the cured adhesive film rather than the substrate, and the same silicone composition is used for each application.
A coated substrate comprising a multiple layer silicone adhesive coating can be prepared in a manner similar to the method used to prepare a single layer coating, only adjacent layers of the coating are prepared using a silicone composition having a different composition and typically each film is at least partially cured before applying the silicone composition of the next layer. For example, a coated substrate comprising a silicone adhesive coating having two layers can be prepared by (i) applying a silicone composition, described above, on a substrate to form a first film, (ii) at least partially curing the hydrogenpolysiloxane resin of the first film, (iii) applying a silicone composition different from the composition in (i), on the partially cured first film to form a second film, and (iv) curing the hydrogenpolysiloxane resin of the second film.
A laminated substrate according to the present invention comprises
a first substrate;
at least one additional substrate overlying the first substrate; and
a silicone adhesive coating on at least a portion of at least one surface of each substrate, provided at least a portion of the adhesive coating is between and in direct contact with opposing surfaces of adjacent substrates, wherein the adhesive coating comprises a cured product of at least one hydrogenpolysiloxane resin having the formula (I) above.
As used herein, the term “overlying” used in reference to the additional substrates means each additional substrate occupies a position over, but not in direct contact with, the first substrate and any intervening substrate(s).
The substrates and the silicone adhesive coating of the laminated substrate are as described and exemplified above for the coated substrate of the present invention. The laminated substrate comprises a first substrate and at least one additional substrate. The laminated substrate typically contains from 1 to 20 additional substrates, alternatively from 1 to 10 additional substrates, alternatively from 1 to 4 additional substrates. When the laminated substrate is a laminated glass substrate, at least one of the substrates is glass and, optionally, at least one of the substrates is a reinforced silicone resin film, described above.
The laminated substrate comprises a silicone adhesive coating on at least a portion of at least one surface of each substrate. The adhesive coating may be on a portion of one or more surfaces of each substrate or on all of one or more surfaces of each substrate. For example, when the laminated substrate is a laminated glass comprising glass panes, the silicone adhesive coating may be on one side, on both sides, or on both sides and the edges, of each pane.
As shown in
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A suitable method of preparing the laminated substrate is illustrated here for the laminated substrate depicted in
The silicone adhesive of the present invention has high transparency and excellent adhesion to various substrates. Moreover, the silicone adhesive has high adhesion during and after exposure to temperatures above the decomposition temperature of the adhesive, low flammability (as evidenced by low heat release rate), and high char yield.
The silicone adhesive of the present invention is useful in applications requiring adhesives having high adhesion at elevated temperatures, low flammability, and high transparency. For example, the adhesive is useful for bonding glass panels in the fabrication of fire rated windows and glass firewalls.
The following examples are presented to better illustrate the silicone composition and laminated substrate of the present invention, but are not to be considered as limiting the invention, which is delineated in the appended claims. Unless otherwise noted, all parts and percentages reported in the examples are by weight. The following materials were employed in the examples:
Hydrogenpolysiloxane A is a hydrogen silsesquioxane resin having the formula (HSiO3/2)n, where n has a value such that the resin has an Mn of about 10,000, and the resin contains less than 2% (w/w) of silicon-bonded hydroxy groups.
Hydrogenpolysiloxane B is a poly(dimethyl/hydrogenmethyl)siloxane having the formula Me3SiO(Me2SiO)3.2(HMeSiO)5.8SiMe3, where Me is methyl and the subscripts outside the parentheses denote the average numbers of the enclosed units.
Hydrogenpolysiloxane C is an MHQ resin having the formula (HMe2SiO1/2)1.84(SiO4/2), where Me is methyl and the subscripts outside the parentheses (subscript 1 not shown) denote the relative numbers of moles of the enclosed units.
Cross-linking Agent A is an organopolysiloxane having the formula ViMe2SiO(Me2SiO)148SiMe2Vi, where Me is methyl, Vi is vinyl, and the subscript outside the parenthesis denotes the average number of the enclosed unit.
Cross-linking Agent B is an organopolysiloxane having the formula ViMe2SiO(Me2SiO)25SiMe2Vi, where Me is methyl, Vi is vinyl, and the subscript outside the parenthesis denotes the average number of the enclosed unit.
Cross-linking Agent C is an organopolysiloxane having the formula ViMe2SiO(Me2SiO)95.6(ViMeSiO)2.4SiMe2Vi, where Me is methyl, Vi is vinyl, and the subscripts outside the parentheses denote the average numbers of the enclosed units.
Cross-linking Agent D is an organopolysiloxane having the formula HO(ViMeSiO)9H, where Me is methyl, Vi is vinyl, and the subscript outside the parenthesis denotes the average number of the enclosed unit.
Cross-linking Agent E is a solution containing 60% (w/w) of an organopolysiloxane having the formula (Me3SiO1/2)0.4(ViMe2SiO1/2)0.05(SiO4/2)0.55 in xylene, where Me is methyl, Vi is vinyl, and the subscripts outside the parentheses denote mole fractions.
Cross-linking Agent F is 1,3,5-7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane.
Isopar™ L, which is sold by ExxonMobil Chemical, Inc., is a hydrocarbon fluid having a specific gravity of 0.767, and distillation range marked by an initial boiling point of 189° C. and a dry point of 207° C.
Platinum Catalyst is a mixture containing a platinum(0) complex of 1,3-divinyl-1,1,3,3,-tetramethyldisiloxane in toluene, and having a platinum concentration of 1000 ppm.
Silicone Base: a mixture containing 82% of a silicone resin having the formula (PhSiO3/2)0.75(ViMe2SiO1/2)0.25, where the resin has a weight-average molecular weight of about 1700, a number-average molecular weight of about 1440, and contains about 1 mol % of silicon-bonded hydroxy groups; and 18% of 1,4-bis(dimethylsilyl)benzene. The mole ratio of silicon-bonded hydrogen atoms in the 1,4-bis(dimethylsilyl)benzene to silicon-bonded vinyl groups in the silicone resin is 1.1:1, as determined by 29SiNMR and 13CNMR.
Melinex® 516, sold by Dupont Teijin Films (Hopewell, Va.), is a polyethyleneterephthalate (PET) film pretreated on one side with a release agent for slip and having a thickness of 125 μm.
Glass Fabric is a heat-treated glass fabric prepared by heating style 106 electrical glass fabric having a plain weave and a thickness of 37.5 μm at 575° C. for 6 h. The untreated glass fabric was obtained from JPS Glass (Slater, S.C.).
Silicone Base was mixed with 0.5% (w/w), based on the weight of the Base, of Platinum Catalyst. The resulting composition was applied on the release agent-treated surface of a Melinex® 516 PET film (8 in.×11 in.) to form a silicone film. Glass Fabric having the same dimensions as the PET film was carefully laid down on the silicone film, allowing sufficient time for the composition to thoroughly wet the fabric. The aforementioned silicone composition was then uniformly applied to the embedded fabric. An identical PET film was placed on top of the coating with the release agent-treated side in contact with the silicone composition. The stack was then passed between two stainless steel bars separated by a distance of 300 μm. The laminate was heated in an oven according at 150° C. for 10 min. The oven was turned off and the laminate was allowed to cool to room temperature inside the oven. The upper PET film was separated (peeled away) from the reinforced silicone resin film, and the silicone resin film was then separated from the lower PET film. The transparent reinforced silicone resin film had a thickness of about 125 μm.
In each of Examples 2-5 a silicone composition was prepared using the components and amounts specified in Table 1 by dissolving Hydrogenpolysiloxane A in 22 parts by weight of Isopar™ L, adding Cross-linking Agent to the solution, removing the Isopar™ L under reduced pressure at 100° C., and then treating the mixture with Platinum Catalyst.
Samples of each silicone composition (˜2 g) were placed in individual stainless steel pans, heated in an oven at 150° C. for 2 h to cure the hydrogenpolysiloxane resin, and then allowed to cool to room temperature. The adhesive samples were heated in air at 800° C. for 30 min. to produce a char and then allowed to cool to room temperature. The char yield of each adhesive was calculated by dividing the mass of the adhesive after char by the mass of the (cured) adhesive before char and multiplying the quotient by 100. The char yield of each adhesive is reported in Table 2.
Laminated glass composites were prepared using each of the silicone compositions according to the following procedure: Two flat float glass plates (6 in.×6 in.×⅛ in.) were washed with a warm solution of detergent in water, thoroughly rinsed with deionized water, and dried in air. Approximately 2 g of the silicone composition was applied on one side of each glass plate. The reinforced silicone resin film of Example 1 having the same dimensions as the glass plates was placed on the coated surface of one of the glass plates, and the coated surface of the other glass plate was then placed on the exposed surface of the reinforced silicone resin film. The laminate was held under vacuum (2500 Pa) at room temperature for 2 h. The composite was heated in an oven at a rate of 3° C./min. to 150° C., at which temperature the laminate was maintained for 2 h. The oven was turned off and the laminated glass was allowed to cool to room temperature inside the oven.
A torch supplied with propylene at a pressure of 10 psi (6.9×104 Pa) and having an orifice diameter of 2.5 in. was positioned perpendicular to one flat surface of the laminated glass at a distance of 11 in. from the surface. The laminated glass was exposed to the torch for 10 min. and then allowed to cool to room temperature. After heat treatment, the glass plates in the laminate remained bonded to the reinforced silicone resin film.
In each of Comparative Examples 1-3, a silicone composition was prepared using the components and amounts specified in Table 1. In Comparative Examples 1 and 2, the Hydrogenpolysiloxane, Cross-linking Agent, and Platinum catalyst were simply combined in order. In Comparative Example 3, Hydrogenpolysiloxane C and Cross-linking Agent E were combined first, and then xylene was removed under reduced pressure at 100° C. This mixture was then combined with Cross-linking Agent F and Platinum Catalyst.
Samples of each composition were heated to produce adhesives using the method described above in Examples 2-5. The char yield of each adhesive is reported in Table 2.
Furthermore, laminated glass composites were prepared using each of the silicone compositions and then heat-treated, both according to the methods of Examples 2-5. During heat treatment, the glass plates in the laminate separated from the reinforced silicone resin film.
This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/033,446, filed on 4 Mar. 2008, under 35 U.S.C. §119(e). U.S. Provisional Patent Application Ser. No. 61/033,446 is hereby incorporated by reference.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US09/34835 | 2/23/2009 | WO | 00 | 6/24/2010 |
| Number | Date | Country | |
|---|---|---|---|
| 60033446 | Dec 1996 | US |
