The invention relates to crosslinked organosilicone systems formed by the reaction of amino-substituted polysiloxanes with epoxy-substituted-polysiloxanes that exhibit excellent adhesion to a variety of substrates. Subject matter cross-linked silicone systems are useful as elastomers, sealants, electronic potting compounds, encapsulants, conformal coatings, foams, shock adsorbing gels, and molds.
It is well known in the art that organosilicone polymers, such as dimethylpolysiloxane, phenyl- and trifluoropropyl-substituted dimethylpolysiloxane copolymers, and the like, can be cross-linked to produce elastomers, adhesives, sealants, foams and gels via a number of methods. Perhaps the oldest method of achieving cross-linking of silicone polymers is the use of a peroxide, such as 2,4-dichlorobenzoyl peroxide, and heat to produce the cross-linked mass. Another method is the use of vinyl-substituted organopolysiloxane and peroxide, such a ditertiary-butyl peroxide to form a more uniform and reproducible cross-linked mass. Crosslinked organosilicone polymers can also be prepared by the platinum catalyzed hydrosilation reaction between silanic hydrogen fluids and polysiloxanes modified with the unsaturated groups. Examples of such systems are given in U.S. Pat. No. 4,970,252.
Another widely used method of cross-linking organosilicone copolymers is the condensation of hydroxy-terminated silicone polymers with multi-functional alkoxy silanes using metal soaps, such as dibutyltindilaurate, or stannous octoate.
Yet another method of cross-linking organosilicone polymers is by reacting hydroxy-functionalized fluids with silanic hydrogen fluids in the presence of a base, such as described in U.S. Pat. No. 4,177,176.
Examples of the reactive systems utilizing the reaction of an amine with an epoxy group can be found in the prior art. Most of this prior art, however, relate to amino- or epoxy-functionalized, trialkoxy silanes, or their hydrolyzates cured by themselves or with the organic resins.
U.S. Pat. No. 4,542,174 teaches combination of oxirane compounds and acylamino- or cyano-silane which are stable at room temperature and can be utilized as one-component additives for inorganic fillers employed in filled condensation polymer systems.
U.S. Pat. No. 5,314,980 discloses a coating composition comprising and epoxy component selected from the group consisting of epoxy silane, or epoxy silane hydrolysis/condensation products, an amine hardener selected from organic amines, aminosilane and hydrolyzed aminosilane and a metal component-containing stabilizer to delay crosslinking for more than 3 days. U.S. Pat. No. 4,378,250 teaches coating compositions comprising an organic solvent and a mixture of at least two components derived by partial hydrolysis of precursor epoxy- and amino-functionalized alkoxy silanes. Similar reactive coating compositions are disclosed in U.S. Pat. No. 3,961,977.
U.S. Pat. No. 3,837,876 relates to organosilicone compositions, comprising an organic solvent, a certain aminoalkylalkoxysilane and a certain epoxyalkoxysilane, useful in the improvement of adhesion of sealants and primers.
U.S. Pat. No. 5,703,178 describes heat ablative coating compositions prepared by combining an epoxysilane, an epoxy resin, a silicone intermediate, a silicon-modified polyether, an aminosilane, an organometallic catalyst and other components.
Existing silicone crosslinking technologies, although useful, present several disadvantages in the applications:
Platinum catalyzed addition cure systems are prone to catalyst poisoning, and, without the use of an adhesion promoter that must be applied separately, exhibit poor adhesion to metal, plastic, and glass substrates. These systems are also prone to produce by-product hydrogen gas during the cross-linking reaction; a phenomena that can result in the unintentional entrapment of gas bubbles within the cross-linked mass.
Condensation cure silicone systems produce by-products, such a methyl alcohol and ethyl alcohol, and once mixed, have short working life. Since water is essential to achieve cross-linking in these types of systems, other additives are typically required to achieve depth of cure. In addition, condensation cure silicone systems adhere poorly to substrates without use of an adhesion promoter or primer, and accordingly, their uses are limited to applications where these limitations are not restrictive.
Peroxide cross-linked systems require elevated temperatures to initiate cross-linking, and result in the formation of by-product acid or alcohol products. Post curing is generally required to remove these by-products from the cross-linked mass after initial cure. As with hydrosilation cure and condensation cure systems, an adhesion promoter or primer is generally required to obtain adhesion to metal, plastic, or glass substrates.
This invention relates to (1) novel reactive compositions comprising an amino-modified organopolysiloxane and an epoxy-modified organopolysiloxane and (2) a method for rapidly curing this composition into elastomers, sealants, electronic potting materials, encapsulants, conformal coatings, foams, shock adsorbing gels, and molds, wherein no by-product is produced during the curing process and the cross-linked material exhibits adhesion to metals, plastics, synthetic fibers, wood, paper, and glass.
The reactive compositions of present invention comprise:
a. an amino-modified organopolysiloxane of the average general formula:
Q2RSiOxe2x80x94(SiR2O)xxe2x80x94(SiRR1O)yxe2x80x94SiRQ2xe2x80x83xe2x80x83(I)
xe2x80x83wherein Q is R or R1; R is selected from the group consisting of monovalent hydrocarbon groups having 1 to 10 carbon atoms; R1 is R2NHR3; each R2 is the same or different and is a divalent C1-C6 alkylene group, optionally substituted with a hydroxyl group; R3 is alkyl of C1-C6, an alkyl amine of C1-C6 (i.e. a C1-C6 alkyl group substituted with xe2x80x94NH2) or an alkanolamine of C1-C6 (i.e. a C1-C6 alkyl group substituted with xe2x80x94OH and with xe2x80x94NH2); x is zero or a positive number; y is a positive number and x+y are less than 1,100; and
b. an epoxy-modified organopolysiloxane of the average general formula:
Qxe2x80x22RSiOxe2x80x94(SiR2O)xxe2x80x94(SiRR4O)yxe2x80x94SiRQxe2x80x22xe2x80x83xe2x80x83(II)
xe2x80x83wherein Qxe2x80x2 is R or R4; R is as previously defined; R4 is R5 xe2x80x94R6; R5 is a divalent hydrocarbon group with at least two carbons, which may be may be interrupted by an oxygen atom; R6 is an epoxide-containing group.
In formulas (I) and (II) above, the monovalent hydrocarbon groups R include alkyl, aryl and aralkyl groups, and may be the same or different from one another. Examples are methyl, ethyl, butyl, hexyl, phenyl, benzyl, and phenethyl. Of these, lower alkyl groups (C1-C4) are preferred. The most preferable R group is methyl in both formulas.
In formula (I) Q is preferably R, most preferably methyl. In formula (II), Qxe2x80x2 is preferably R4. In formula (I) R2 is preferably ethylene or propylene. R3 is most preferably, hydrogen, but other examples of R3 include methyl, ethyl, propyl, aminoethyl, aminopropyl and propanolamino. Specific R1 groups include propylamine, propanolamine, N-methyl-propylamine and N-propanolamino-aminopropyl.
In formula (II) the R5 groups may be aliphatic, cycloaliphatic, aromatic or mixed aliphatic/aromatic groups, or (poly)ether groups, for instance ethylene, propylene, ethylenephenylene, propyleneoxyethylene, phenylethylene, ethylhexylene, and the like. Exemplary R6 groups include glycidoxy, 3-methyl-4,5-cyclohexenyl oxide and 3,4-cyclohexenyl oxide. Exemplary R4 groups include glycidoxypropyl, 2-(3,4-cyclohexene oxide)ethyl or 2-(3-methyl-4,5-cyclohexene oxide)ethyl.
Preferably x ranges from 20 to 1000 and y ranges from 1 to 50; more preferably x ranges from 50 to 800, most preferably 50 to 500, y ranges from 1 to 20 and x/y ranges from 30:1 to 200:1 in formula (I), and from 5:1 to 30:1 in formula (II).
The composition of the present invention may optionally contain one or more organomodified trialkoxy silanes which are reactive with the above mentioned components. Such silanes may be selected from the group epoxy- and amino-modified silanes of the general formula:
R7oR8pSiX4xe2x88x92(o+p)
wherein R7 is a monovalent hydrocarbon groups having 1 to 10 carbon atoms including alkyl, aryl and aralkyl groups. The R7 groups may be the same or different from one another and are illustrated by methyl, ethyl, butyl, hexyl, phenyl, benzyl and phenethyl. Of these, lower alkyl groups (C1-C4) are preferred. Most preferably R is methyl. xe2x80x9coxe2x80x9d can be zero or 1. R8 is an amino or epoxy-functionalized group and may be as previously defined for R1 or R4 described above. xe2x80x9cpxe2x80x9d is an integer from 1 to 4. X is a hydrolyzable or condensable group bonded directly to Si, for instance OH, alkoxy, chloro, acyloxy, ketoximino, etc.
Amino-modified organopolysiloxanes used in the present invention are prepared, for example, by processes analogous to those disclosed in U.S. Pat. Nos. 3,033,815, 3,146,250 and 4,247,592 (which are incorporated by reference) by hydrolyzing the corresponding dialkoxy amino modified silane in excess water or water-solvent such as tetrahydrofuran mixture, at about 10 to about 50xc2x0 C., preferably, room temperature, for about 2 to about 5 hours followed by vacuum stripping and equilibrating the resulting hydrolyzate with di(alkyl, aralkyl or aryl)-cyclo polysiloxane (source of R2SiO groups) and hexamethyldisiloxane, decamethyltetrasiloxane, or other reactants to serve as the source of the terminal RQ2SiO groups as defined by Formula (I) in the presence of a base catalyst, such as KOH, with heating at about 130 to about 150xc2x0 C. for about 5 to about 12 hours.
Preparation of the epoxy-modified organopolysiloxanes of the present invention involves reacting methylhydrogen-containing organopolysiloxanes with the unsaturated epoxides with a terminal olefinic bond, in the presence of a hydrosilation catalyst, such as for example, hexachloroplatinic acid, at elevated temperature, to produce the epoxy organopolysiloxane. Such procedures are known in the art as indicated in U.S. Pat. No. 3,761,444 or British Patent No.1213779. Examples of suitable epoxides with terminal olefinic groups are given below: 
The compositions of the present invention may be prepared by manual or mechanical mixing (sigma mixer, Cowells mixer or roll mill) of the stoichiometric amounts of the components (a) and (b) or using up to two fold excess of the aminopolysiloxane. Stoichiometry of the system is calculated based on the amine content and the epoxy content, determined by titrations of the functional groups. Such titration methods are well known to those skilled in the art.
The compositions may further contain mineral fillers, such as, for example, aluminum oxide, clay, treated or untreated calcium carbonate and silica, and/or pigments such as titanium dioxide and iron oxide, and/or a plasticizer, such as dimethylpolysiloxane, for instance one having a viscosity of between 50-10,000 cSt, an organic ester or a hydrocarbon plasticizer. The level of the additives in the formulation may vary from about 1.0% to about 90% depending on the filler or the end use, most preferably between about 10% to about 80% of the weight of the total composition. The above mentioned fillers can be introduced into the composition of the present invention by manual mixing, with a spatula or paddle, or by mechanical mixing, with a dough mixer, sigma mixer, Cowells mixer or roll mill. The compositions of the present invention, whether filled or unfilled, can be stored at room temperature for several days but, if necessary, cured rapidly at room temperature or in an oven or on a heated surface or in a HAV (hot air vulcanization) chamber, in the presence of Bronstxc3xad or Lewis acids, such as acetic acid, chloroacetic acid, trichloroacetic acid, citric acid, glycolic acid, tetrabutyltitanate or dibutyltinlaurate. The curing time can be modified by changing the level of the acid in the composition, a typical concentration of the acid being from 0.0001% to 5%, preferably 0.001 to 2%.
The compositions of the present invention can be used in encapsulation, as an elastomer, shock adsorbing gel, adhesive, sealant, electrical potting compound, a conformal coating for electronic circuit boards, or as a coating for fibrous materials, such as woven and non-woven fabric. The composition of the present invention can be further used in combination with other silicone and non-silicone systems used in applications listed above. Specific uses include coatings for the fabric used in automotive air bags, a gel filling material for medical prosthesis, a conformal coating for electronic circuit boards, and a potting material for electronic devices.
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