Corrosion inhibitors in adhesive bonding of vehicle body structures
In an illustrative embodiment, two panels of different materials may be bonded with a structural adhesive composition comprising microcapsules containing corrosion inhibiting materials for protecting the panels from corrosion. For example, a steel vehicle door outer panel may be bonded to an aluminum alloy or magnesium alloy inner panel using an epoxy adhesive. Dispersed within the uncured adhesive are an abundance of microcapsules filled with a fluid or mobile material for reacting with the iron and/or aluminum or magnesium to inhibit corrosion arising from the facing surfaces of the mixed metal panels. The protective material is released from the microcapsules for diffusion through the cured or uncured interfacial adhesive to react with one or both panel surfaces and form a protective coating on the surfaces.
1. A method of forming a corrosion resistant adhesive bond between facing panel surfaces of different compositions where the composition of at least one of the surfaces is susceptible to corrosion; the method comprising:
applying a curable adhesive composition to a bonding region of at least one of the panel surfaces, the adhesive composition comprising microcapsules of a corrosion inhibiting composition for at least one of the surface compositions, the curable adhesive composition further comprising spacer beads for maintaining an interfacial gap between the facing surfaces until the adhesive is cured;
placing the facing surfaces together to form an adhesive interface;
promoting curing of the adhesive and at a predetermined time after the facing surfaces have been placed together
promoting release of the corrosion inhibiting composition from microcapsules for corrosion inhibiting contact over the adhesive bonding region with at least one of the facing panel surfaces, the release of the corrosion inhibiting composition from at least some of the microcapsules being promoted before the adhesive is cured.
2. A method of forming a corrosion resistant adhesive bond as recited in claim 1 in which the panel surfaces are of different metal alloys.
3. A method of forming a corrosion resistant adhesive bond as recited in claim 2 in which the panel surface to be protected is an aluminum alloy surface and the corrosion inhibiting composition comprises a chromate composition.
4. A method of forming a corrosion resistant adhesive bond as recited in claim 2 in which the panel surface to be protected is a magnesium alloy surface and the corrosion inhibiting composition comprises a chromate composition.
5. A method of forming a corrosion resistant adhesive bond as recited in claim 2 in which the panel surface to be protected is a ferrous alloy surface and the corrosion inhibiting composition comprises a molybdate composition.
6. A method of forming a corrosion resistant adhesive bond as recited in claim 1 in which the curable adhesive composition also contains microcapsules of a catalyst for curing the adhesive and the catalyst-containing microcapsules are caused to release the catalyst to promote curing of the adhesive.
7. A method of forming a corrosion resistant adhesive bond as recited in claim 1 further comprising promoting release of the corrosion inhibiting composition from microcapsules for corrosion inhibiting contact with at least one of the surfaces by application of heat to crack the microcapsules.
8. A method of forming a corrosion resistant adhesive bond as recited in claim 1 further comprising promoting release of the corrosion inhibiting composition from microcapsules for corrosion inhibiting contact with at least one of the surfaces by application of ultrasonic energy to crack the microcapsules.
9. A method of forming a corrosion resistant adhesive bond as recited in claim 1 in which release of the corrosion inhibiting composition from some microcapsules continues after the curing of the adhesive.
10. A method of forming a corrosion resistant adhesive bond between facing panel surfaces of different compositions where the composition of one of the facing panel surfaces is a steel alloy and the composition of the other facing panel surface is an aluminum alloy or a magnesium alloy; the method comprising:
applying a curable adhesive composition to a bonding region of at least one of the panel surfaces, the adhesive composition comprising microcapsules of a corrosion inhibiting composition for at least one of the surface compositions, the curable adhesive composition further comprising spacer beads for maintaining an interfacial gap between the facing panel surfaces until the adhesive is cured;
placing the facing panel surfaces together to form an adhesive interface;
promoting curing of the adhesive; and, before the adhesive is cured
promoting release of the corrosion inhibiting composition from microcapsules for corrosion inhibiting contact over the adhesive bonding region with at least one of the facing panel surfaces.