Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1995-01-05
2002-10-29
Gallagher, John J. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S329000, C524S492000, C524S588000
Reexamination Certificate
active
06471820
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to moisture-curable silicone compositions, and methods for preparing such compositions.
2. Description of the Related Art
Moisture-curable silicone sealants in the form of thixotropic pastes are known. The user generally applies the paste by extruding it from a tube, aerosol can, caulking cartridge, or automatic pumping equipment onto a surface to be sealed and/or mated. One problem with such pastes is that they are messy and difficult to apply reliably and accurately. In addition, once applied the paste can be readily dislodged. The paste must also be allowed to “skin over” or “set up” once applied, necessitating a waiting period between the time the sealant is applied and the time the object to which the paste is applied can be used.
Solid sealant strips made of Gore-Tex® microporous polytetrafluoroethylene are also known. Such strips create a seal by conforming to surface imperfections and filling gaps between mating surfaces, rather than adhering to the surface. The inability of such strips to adhere to the surface, coupled with a relatively low compression set resistance, creates a tendency for the seal to fail when the mated surfaces move relative to each other. In addition, these strips do not have sufficient adhesive strength to seal over a hole or gap in a surface.
SUMMARY OF THE INVENTION
In a first aspect, the invention features a moisture-curable silicone sealing composition having a storage shear modulus of at least 9.0 KPa and a loss shear modulus of at least 4.0 KPa prior to curing when measured at 25°±1° C. at a frequency of 0.1 rad/sec. Unlike thixotropic pastes and solid sealant strips, the composition is tacky and self-supporting at room temperature prior to curing. Preferably, the composition further exhibits a storage shear modulus of at least 80 KPa and a loss shear modulus of at least 50 KPa prior to curing when measured at 25°±1° C. at a frequency of 100 rad/sec.
In a second aspect, the invention features a moisture-curable silicone sealing composition having a viscosity of at least 98.5 KPa Sec prior to curing when measured at 25°±1° C. at a frequency of 0.1 rad/sec. Unlike thixotropic pastes and solid sealant strips, the composition is tacky and self-supporting at room temperature prior to curing. Preferably, the composition further exhibits a viscosity of at least 940 Pa Sec prior to curing when measured at 25°±1° C. at a frequency of 100 rad/sec prior to curing.
In preferred embodiments of both aspects, the sealing composition is in the form of a ribbon, rope, or sheet. The sealing composition preferably has an elongation value of about 200 to about 1200% (preferably about 350 to about 600%) after curing.
Preferred compositions include a hydroxy-terminated polydialkylsiloxane, fumed silica, and a silane crosslinking agent. The polydialkylsiloxane preferably is present in an amount ranging from about 35 to about 85% by wt. (more preferably from about 65 to about 75% by wt.). The fumed silica preferably is present in an amount ranging from about 5 to about 30% by wt. (more preferably from about 20 to about 25% by wt.), and has a surface area of at least 50 m
2
/g (preferably ranging from about 130 m
2
/g to about 400 m
2
/g). The silane is preferably present in an amount ranging from about 1 to about 15% by wt. (more preferably from about 2.5 to about 6% by wt.). The sealing composition is preferably essentially free of curing catalysts.
The invention further features methods of sealing two surfaces together by applying the above-described sealing compositions to the first surface, and then contacting the first surface with the second surface in the presence of moisture to bond the two surfaces together.
Throughout this application the following definitions apply:
A “tacky” composition is a composition which passes the Tack Test described infra under Test Procedure D.
A “self-supporting” composition is a composition which passes the Stretch Test described infra under Test Procedure C.
The invention provides tacky, self-supporting sealing compositions which (unlike thixotropic pastes) can be readily and accurately applied by hand because they do not transfer to any substantial extent to the user's hands. Because the sealing compositions are self-supporting, they can be provided, e.g., in the form of ropes, ribbons, or sheets stored in laminated packages and conveniently dispensed simply by lifting the rope, ribbon, or sheet out of the package. The compositions can then be formed by hand into a variety of shapes to seal a number of mating surfaces. In addition, the sealing compositions are functional upon application; there is no substantial set-up time following application. The invention thus combines the ease of handling associated with solid sealant strips with the sealing behavior of curable thixotropic pastes.
Other features and advantages of the invention will be apparent from the following description of the preferred embodiments thereof, and from the claims.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Preferred silicone sealant compositions according to the invention contain (a) 35-85% by wt. of a hydroxy-terminated polydialkylsiloxane; (b) 5-30% by wt. fumed silica; and (c) 1-15% by wt. of a silane crosslinking agent. The particular amounts of ingredients, and the conditions under which they are processed, are selected such that the uncured composition is tacky and self-supporting (and thus readily handled, particularly when provided in the form of a ribbon, rope, or sheet). In general, it is desired that the composition be tacky enough to adhere to a clean metal substrate, yet not be so tacky that it transfers to the user's hands. Similarly, the composition must have sufficient integrity to retain its shape, but must not be so stiff that it cannot be easily formed by hand into the shape needed for a-particular application.
The viscosity and storage and loss shear moduli of the sealing composition measured at low (0.1 rad/sec) frequency according to Test Procedure A provide a quantitative measure of the “handlability” of the sealing composition. It is generally preferred that the composition exhibit a viscosity of at least 98.5 KPa Sec at 0.1 rad/sec, and a storage shear modulus of at least 9.0 KPa and a loss shear modulus of at least 4.0 KPa at 0.1 rad/sec.
The viscosity and complex shear modulus of the sealing composition measured at high (100 rad/sec) frequency according to Test Procedure A provide a quantitative measure of the “processability” of the sealing composition. It is generally preferred that the composition exhibit a viscosity of at least 940 Pa Sec at 100 rad/sec, and a storage shear modulus of at least 80 KPa and a loss shear modulus of at least 50 KPa at 100 rad/sec.
Any of the hydroxy-terminated polydialkylsiloxanes typically used in known sealing compositions may be used in the sealing compositions according to the invention. One class of preferred materials includes polydialkylsiloxanes having viscosities at 25° C. ranging from about 0.08 m
2
/s to about 0.3 m
2
/s. Examples of commercially available polydialkylsiloxanes failing within this class include those available from PPG Industries, Inc. under the designations Masil SFR 80,000, SFR 150,000, and SFR 300,000, and those available from Huls America of Piscataway, N.J. under the designation PS348.7. Hydroxy-terminated polydialkylsiloxanes having lower viscosities may also be used if the viscosity of the polymer is increased in situ during processing.
Fumed silicas having relatively high surface areas (e.g., in the range 50-400 m
2
/g) are generally preferred. Such silicas are commercially available from Cabot Corp. of Tuscola, Ill. under the trade designations L-90, LM-130, LM-150, MD-7, MS-55, MS-75D, H5, M5, HS-5, EH-5, TS720, TS530, and TS610, and from Degussa Corp. of Dublin, Ohio under the trade designations Aerosil 90, 130, 150, 200, 300, 380, R202, R810, R811, R812, R975, R976, R972, and R974.
Particularly preferred are hydrophobic fumed silicas (i.e.,
3M Innovative Properties
Gallagher John J.
Pribnow Scott R.
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