Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1998-09-11
2001-01-16
Mayes, Curtis (Department: 1734)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S230000, C156S307100
Reexamination Certificate
active
06174405
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to compositions and methods for forming coatings upon substrates, and more particularly, liquid crystal polymers for in situ coating of co-cured composite structures and methods of applying the same.
BACKGROUND OF THE INVENTION
As is well known, metallic and composite structures mounted upon the exterior of ships and aircraft can experience significant degradation and damage due to their exposure to erosion-corrosion attack. In this regard, such structures are constantly subjected to oxidation, moisture, fouling, salt-spray, UV radiation, chemicals, and high and low temperatures, among other things, that can cause such structures to experience significant degradation and damage over time. As a consequence, such structural components must be constantly repaired or replaced to thus prevent the possibility that a given vessel or aircraft will be damaged permanently, if not destroyed.
To attempt to prevent the damage caused by fatigue and environmental exposure on such composite and metallic components, a variety of coating agents and methods of applying the same to such components have been developed to improve their durability. Among such processes well-known to those skilled in the art is thermal spraying, which comprises insertion of feed stock particles, typically of a polymer-like material, into a high-energy heat source that propels the particles, while in a semi-liquid state, onto the surface of the component sought to be protected. Once propelled onto the surface sought to be protected, the particles cool, and through repeated deposition of many such particles, a deposit builds up. Among such substances used for forming protective coatings via thermal spraying include polyurethane, polyethylene, polyacrylonitrile, polyvinylchloride and ethylene vinylalcohol.
While each of the aforementioned compounds are suited for application via thermal spraying, such compounds typically fail to provide an adequate degree of protection to the surface upon which they are applied. In this regard, each of the aforementioned compounds fails to provide a sufficiently proficient barrier against either oxygen or water vapor permeation. For example, while ethylene vinylalcohol provides a high degree of resistance to oxygen permeation, such compound generally fails to provide a high enough degree of resistance to water vapor permeation. Polyvinyldychloride, on the other hand, provides a high degree of resistance to water vapor permeation, but a substantially lesser degree of resistance to oxygen permeation. As is well-known, however, the ability of either water or oxygen to permeate through a given coating and directly contact the surface of a metallic or composite structure can substantially damage such structure over time.
In addition to failing to provide a sufficient barrier to either oxygen permeation and/or water vapor permeation, such protective coatings further typically fail to provide a sufficient degree of resistance to fouling and chemical exposure. Likewise, such coatings further often fail to posses sufficient dimensional stability and hardness for use in high fatigue and environmental exposure application.
Accordingly, there is thus a need in the art for a composition and method of applying the same that can be utilized to form a protective coating upon a metallic or composite structure that can provide a higher degree of protection to the surface thereof from chemicals and environmental exposure than prior art coating compositions. There is further a need for improved coating compositions that, in addition to providing a greater degree of protection than prior art coating compositions, may be quickly and easily applied as per convention coating techniques. A still further need exists in the art for such coating compounds that may be formulated from nontoxic, readily available and relatively inexpensive chemical compositions.
SUMMARY OF THE INVENTION
The present invention addresses and alleviates the above-identified deficiencies in the art. Specifically, the present invention is directed to novel liquid crystal polymers for use in forming protective coatings upon composite and metallic structures that are subjected to fatigue and environmental exposure, as well as methods of applying the same. The Liquid Crystal Polymers (LCPs) comprise high-melting point thermal plastics selected from the group consisting of co-polyesters, co-polyesteramides, and multiple monomer wholly aromatic polyesters that are utilized in an isotropic film form. In more refined embodiments, such polymers may be modified to include rigid elements, such as rod-like monomers, incorporated into the backbones thereof to thus impart an impervious microstructure and increased hardness and impact strength. Advantageously, the LCPs of the present invention contain neither volatile organic compounds (VOC's) nor heavy metals, such as lead and the like.
The method of the present invention is directed to applying the aforementioned novel coating materials onto a given substrate. According to a preferred embodiment, the method comprises the initial step of applying a layer of a release agent, such as TEFLON® or FREKOTE®, to the tooling surface to be used for curing the composite structure. Thereafter, the LCP is thermally sprayed upon the surface via conventional spraying techniques or placed on the tool as a thin film. Preferably, the LCP is applied to a thickness from 0.002 to 0.010 inches. Thereafter, the composite laminating material for forming the structural component is applied to the coated tooling surface and cured therewithin. In an optional step, an adhesive may be applied between the uncured composite and coated tooling surface prior to curing. After curing, the structure with the LCP coating formed thereon is removed from the tooling for use in final assembly.
It is therefore an object of the present invention to provide novel coating compositions and methods for applying the same that are capable of forming a more durable and protective coating when applied to a given metallic or composite structure than prior art coating compositions and techniques.
Another object of the present invention is to provide novel coating compositions and methods of applying the same that can provide a higher degree of protection to substrates coated therewith when subjected to erosion and/or corrosion attack.
Another object of the present invention is provide novel coating compositions and methods of applying the same that can be easily and readily utilized and applied using existing coating technology.
Another object of the present invention is to provide novel coating compositions and methods of applying the same that are non-toxic and pose no threat to the environment.
Still further objects of the present invention include providing novel coating compositions and methods of applying the same that are relatively inexpensive, impart greater protection from oxygen and moisture permeation, have greater dimensional stability and hardness, and provide greater protection from chemical exposure than prior art compositions and methods.
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Anderson Terry J.
Hoch, Jr. Karl J.
Mayes Curtis
Northrop Grumman Corporation
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