Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1999-02-08
2001-01-23
Ball, Michael W. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S281000, C219S121690
Reexamination Certificate
active
06176959
ABSTRACT:
FIELD OF THE INVENTION
This invention relates in general to adhesive bonding, and in particular to a method for adhesively bonding two adherends to each other by first microtexturing subsequently mating surfaces with a laser beam having ultraviolet and infrared wavelength capability and pico-second pulse duration substantially equivalent to a free electron laser. Such microtexturizing provides a tailored surface topography and stable oxide morphology on one or both surfaces to be bonded prior to application thereto of an adhesive and the positioning of the respective surfaces against each other.
BACKGROUND OF THE INVENTION
The formation of effective adhesive bonds is critical in many applications, including the formation of a joint between two adherends. Fundamental to the formation of an effective bond is acceptance of the bonding material or adhesive by the articles to be joined, compatibility of the surface geometries, and environmental stability of the two sites where adhesion is to occur. In particular, the surface geometry must be such as to provide maximum wetted surface per unit area and interlocking features that result in a high strength bond-line.
While surface preparation or texturizing to achieve the foregoing characteristics is desired, prior art approaches for preparing adherends have not met this goal. For example, chemical cleansing and texturizing treatments preceding adhesive applications can easily result in surface and sub-surface contamination at the sites to be joined to thereby interfere with bonding. Further, with chemical as well as conventional laser beam treatments, surface textures are inadequately refined to efficiently interact with surface tension characteristics, wetability of adhesives, or to provide an optimum surface topography. Further, typical metal oxides formed on bonding surfaces generally are unstable and result in poor bond-line durability or fatigue life when used in a hostile environment as exemplified by hot-wet.
In view of the above considerations, it is apparent that a need is present for methodology that enhances adhesive bonding of two parts. Accordingly, it is a primary object of the present invention to provide a process for adhesively bonding two adherends to each other wherein a laser beam having free-electron laser characteristics aimed at surfaces to be adhered ablates organic and halogenated residues present on the surfaces.
Another object of the present invention is to provide a bonding process wherein such a laser beam aimed at surfaces to be adhered microtexturizes the surfaces by glazing the surfaces and forming a controlled stable oxide layer.
Yet another object of the present invention is to provide a process for adhesively bonding two adherends wherein such a laser beam aimed at surfaces to be adhered microtexturizes the surfaces to a controlled topography by forming depressions and whisker projections on the surfaces to enhance mechanical interlocking of the two adherends with the adhesive and substantially match surface tensions of the surfaces and the adhesive being used.
These and other objects of the invention will become apparent throughout the description thereof which now follows.
SUMMARY OF THE INVENTION
The present invention is a process for adhesively bonding two adherends to each other. The process comprises directing a laser beam having characteristics of a free electron laser to a respective surface of each of a first and/or second adherend to effectuate a microtexturizing of the surface. As used throughout herein, the term “laser beam” is defined to mean a laser beam having characteristics equivalent to those of a free-electron laser with respect to energy, ultraviolet and infrared capability, and pico-second pulse duration. Resultant microtexturizing causes ablation of any organic and halogenated residues present on the surface, glazes the surface, forms a stable metal oxide layer, and tailors the topography to optimum geometry for maximum shear strength and surface wetting with the adhesive by forming depressions and whisker projections on the surfaces to thereby substantially increase wetted area, match surface tensions of the surfaces with the adhesive being used and maximize bond strength. The laser beam is particularly capable of creating this morphology and producing an oxide that is stable in a hostile environment, thereby providing a tailored oxide that, in many instances, is stable enough to eliminate the need for priming a surface prior to applying an adhesive. After such microtexturizing, an adhesive is applied to at least one roughened surface and the two textured surfaces are placed against each other such that the adhesive, with associated curing process, bonds the adherends to each other along these respective roughened surfaces. The laser beam microtexturizes the surfaces.
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patent: 4673409 (1987-06-01), Van Kampen
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patent: 5338915 (1994-08-01), Hildebrand et al.
patent: 5473138 (1995-12-01), Singh et al.
Ball Michael W.
Stetina Brunda Garred & Brucker
Tolin Michael A
Vought Aircraft Industries, Inc.
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