Electrolysis: processes – compositions used therein – and methods – Electrolytic material treatment – Organic
Reexamination Certificate
2001-02-22
2003-09-16
Phasge, Arun S. (Department: 1753)
Electrolysis: processes, compositions used therein, and methods
Electrolytic material treatment
Organic
C205S705000, C252S500000, C156S345420
Reexamination Certificate
active
06620308
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to materials for use as coatings and adhesives that may be disbanded from a surface to which they are applied without harm to that surface. The invention further relates to methods of disbonding adhesives and coatings from substrate surfaces.
Adhesive bonds and polymeric coatings are commonly used in the assembly and finishing of manufactured goods. Adhesive bonds are used in place of mechanical fasteners, such as screws, bolts and rivets, to provide bonds with reduced machining costs and greater adaptability in the manufacturing process. Adhesive bonds distribute stresses evenly, reduce the possibility of fatigue, and seal the joints from corrosive species. Similarly, polymer-based coatings are commonly applied to the exterior surface of manufactured products. These coatings provide protective layers that seal the surface from corrosive reactants, as well as provide a painted surface that can be aesthetically pleasing.
Among the best adhesives and coatings in terms of strength and durability are those based on thermosetting polymers. Typically applied as a liquid mixture of low molecular weight monomers, these adhesives wet and penetrate pores on the substrate surface. On cure, insoluble and infusible crosslinked polymers are formed that are mechanically interlocked and often covalently bound to the substrate to which they are applied. Common amine-cured epoxies are a typical example of adhesives and coatings that employ thermosetting mixtures.
Although adhesive bonds offer many advantages over mechanical fasteners, adhesive bonds are essentially permanent. There are no methods available for ready disassembly of adhesively bonded objects. The separation strategies that do exist typically involve time-consuming chemical procedures requiring high temperatures and aggressive chemicals. Examples of such techniques are described in U.S. Pat. No. 4,171,240 by Wong and U.S. Pat. No. 4,729,797 by Linde et al. These techniques, although generally effective, are quite harsh and can damage the objects being separated, making them unsuitable for many applications.
Similarly, conventional coating materials, such as polyurethanes, epoxies, phenolics, melamines, and the like, are essentially permanent. Such coatings are often removed with an aggressive chemical agent that is applied to the coating surface to degrade the coating material. Mechanical abrasion, such as sand blasting or wire brushing, is also employed. Although these techniques are effective in removing the polymer coating, they are time and labor intensive, as well as being quite harsh and likely to cause damage to the underlying surface.
To provide materials that are more easily removed from a substrate, the prior art describes adhesives formed from reactive monomers containing linkages susceptible to chemical degradation. Such materials are described in U.S. Pat. Nos. 5,512,613 and 5,560,934 to Afzali-Ardakani et al. and in U.S. Pat. No. 4,882,399 to Tesoro et al. Additionally, S. Yang et al in “Reworkable Epoxies: Thermosets with Thermally Cleavable Groups for Controlled Network Breakdown”,
Chem. Mater.
10:1475 (1998) and Ogino et al. in “Synthesis and Characterization of Thermally Degradable Polymer Networks”,
Chem. Mater.
10(12):3833 (1998) describe curable resins containing thermally labile linkages. Other polymers containing thermally labile or thermally reversible crosslinks are described in U.S. Pat. No. 3,909,497 to Hendry et al. and U.S. Pat. No. 5,760,337 to Iyer et al. An alternative approach to bond cleavage is described in U.S. Pat. No. 5,100,494 to Schmidt which discloses embedding a nichrome heating element within a thermoplastic so that the adhesive softens or melts upon resistive heating. Although these specially prepared materials are more readily cleaved from the substrate, they still require conditions that are harsh to delicate substrates or adjacent adhesive bonds.
Thus, there remains a need in the art for a material capable of being disbanded selectively and precisely under mild conditions. Such a material would provide adhesive bonds and coatings that could be employed in a variety of applications where facile removal of the material from the surface is desired.
SUMMARY OF THE INVENTION
The present invention provides a composition capable of strong, yet temporary, substrate bonding or coating that is removable without damage to the underlying substrate. It may be used in both temporary and permanent bonding and coating applications.
An electrochemically disbondable composition of the invention includes a matrix functionality and an electrolyte functionality. The matrix functionality provides an adhesive bond to a substrate, and the electrolyte functionality provides sufficient ionic conductivity to the composition to support a faradaic reaction at an interface with an electrically conductive surface in contact with the composition. The adhesive bond is weakened at the interface on application of an electrical potential across the interface. In preferred embodiments, the disbondable composition is a phase separated material having first regions of substantially matrix functionality and second regions of substantially electrolyte functionality.
The “matrix functionality” of a material is the ability of a material or a mixture of materials to join by mechanical or chemical bonding to a substrate and to adhere to the substrate by virtue of this bond. Matrix functionality also provides mechanical strength to the material, such that the material is capable of transferring load between substrates or, as a coating, is self-supporting.
The “electrolyte functionality” of a material is the ability of the material to conduct ions, either anions, cations or both. The ions are provided by a salt added to the material or are chemically incorporated into the material as an ionomer, that is, a polymer containing ionized groups. The electrolyte functionality is understood to derive from the ability of the composition to solvate ions of at least one polarity.
The term “faradaic reaction” means an electrochemical reaction in which a material is oxidized or reduced.
The term “adhesive” refers to polymer-based materials which are capable of holding materials together by surface attachment. An adhesive typically forms a bond to a substrate by mechanical interlocking and often covalent bonding to the substrate. The adhesive is chemically distinct from the bonded substrate and the bonded materials may be dissimilar from one another.
In one embodiment of the invention, the matrix functionality is provided by a polymer selected from the group consisting of epoxies, phenolics, acrylics, melamines, maleimides, and polyurethanes.
In another embodiment of the invention, the polymer has a variable crosslink density to form regions of low crosslink density having a relatively high ionic conductivity and regions of high crosslink density having a relatively high mechanical strength.
In another embodiment of the invention, the polymer includes coordination sites that are capable of solvating ions and that support the electrolyte functionality of the composition.
In other embodiments, the electrolyte functionality is provided by an electrolyte additive selected from the group consisting of ionically conductive monomers, oligomers and polymers, and ionomers and may be localized in regions within the polymer to form a secondary phase of high ionic conductivity and mobility.
In one preferred embodiment, the disbondable composition is an adhesive, and may have a lap shear strength in the range of 2000-4000 psi. In another preferred embodiment, the composition is a coating, and may be resistant to delamination from a substrate to which it is applied.
In another aspect of the invention, an electrochemically disbondable composition is provided having an uncured polymeric material having an electrolyte located therein. The uncured polymeric material, when cured, provides in combination with the electrolyte, sufficient solubility and mobility to the electrolyte to support a faradaic reaction
EIC Laboratories Inc.
Phasge Arun S,.
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