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Method of bonding perfluoroelastomeric materials to a surface

Method of bonding perfluoroelastomeric materials to a surface description/claims

This application claims priority to U.S. Provisional Patent Application Nos. 60/897,660, filed Jan. 26, 2007 and 60/897,651, filed Jan. 26, 2007, the contents of each of which are incorporated herein by reference.

Perfluoroelastomers have readily been used to form various types of O-rings or seals. Such seals are commonly manufactured by first producing a complete mold for the seal in the desired seal configuration and then compression molding a compound that includes perfluoropolymers along with curing agents to form a completely cured perfluoroelastomer seal or other part. However, with the ever-increasing need for larger and larger seals or unusual configurations, molding complete parts becomes more and more expensive and less of an economical practicality. This is because to form such parts requires not only the molds but also an infrastructure sufficient to handle the large or unusually sized molds, including presses and pumps related to molding operations.

One approach developed to address this need has been to produce seals from rod stock and splice the two rod stock ends together to form the required size seal. Traditional splicing techniques have not proven very successful with perfluoroelastomers. Splicing with an adhesive provides a weak point in the seal that is prone to attack because adhesives developed in the past generally do not match the chemical resistance of perfluoroelastomers.

Methods of bonding a cured perfluoroelastomer to itself using a thermoplastic perfluoropolymer bonding agent have been disclosed. However, such processes result in fusing of the perfluoroelastomer ends leading to an intermediate fusing layer i.e., a layer of fused perfluoropolymer. This provides a non-homogenous section within the perfluoroelastomer part i.e., the fused perfluoropolymer layer. Thus, the fused perfluoropolymer could result in a “weak” point due to increased susceptibility to chemical or physical attack, increased compression set and reduced low temperature compliance than the rest of the perfluoroelastomer seal material. There is, therefore, a need in the art for an improved method of bonding and/or welding perfluoroelastomers and parts formed from them that is simple and economical and provides for a homogenous finished part that substantially retains the strength of a solid finished piece.

In addition to the challenges associated with joining perfluoroelastomer surfaces, it is noted that perfluoroelastomers, by virtue of the manner in which they are typically cured and formed as noted above, and their unique vulcanization properties (included physical and solubility properties) have not, however, been successfully adopted for certain uses and applications in which their chemical resistance and elastomeric properties would otherwise be advantageous, such as in surface passivation or other coating use.

Whereas attempts have been made to dissolve curable perfluoropolymers in fluorinated solvents, such as, Fluorinert® FC-40, FC-75 and FC-77 to try to prepare coatings, the resulting coatings are typically not resistant to flow or to certain solvents, because the coatings were not cross-linked. Attempts to incorporate curatives, such as, organic peroxides with associated co-curatives; such as, triallyl isocyanurate (TAIC), were unsuccessful due to the poor solubility of such hydrocarbon-containing curatives in the highly fluorinated solvents needed to dissolve the uncured perfluoropolymer. Likewise, bisphenyl-based curatives, such as bisaminophenol (BOAP) typically also exhibit poor solubility in such highly fluorinated solvents needed to dissolve perfluoropolymers curable with BOAP such as those with cyano-group containing curesite monomers.

This lack of the ability to cure high molecular weight curable perfluoropolymers in solution has restricted the use of perfluoroelastomer coatings to non-critical applications where “flow” of the uncured material is acceptable.

Attempts have been made to form perfluoroelastomer coatings in the past, however, the uses and particular perfluoropolymer systems formed into coatings are limited. U.S. Pat. No. 6,523,650 provides one example of use of a perfluoroelastomer coating on an electrostatic printing component as an outer coating. The patent describes dissolving an elastomeric DuPont Kalrez® perfluoroelastomer, derived from 3-phenoxypropylvinyl ether and at least one fluorine-containing ethylenically unsaturated monomer, in solvent and applying it as a coating. However, the patent does not describe whether the perfluoroelastomer is in a cured state upon dissolution and/or how the cure system is affected by dissolution.

U.S. Pat. No. 5,268,002 teaches coating of pellicles for photomask applications with a coating formed of a low molecular perfluoroelastomer polymer that acts as an antireflective coat for the pellicles. Such pellicles have a core layer of a polymer, such as nitrocellulose, among others. The perfluoroelastomer polymers include tetrafluoroethylene (TFE), perfluoroalkylvinyl ether (PAVE) and a curesite monomer such as perfluoro-(8-cyano-5-methyl-3.6-dioxa-1-octene) (8-CNVE). The patent uses such polymers to form low molecular weight perfluoroelastomers having these components by pyrolyzing the elastomer noted above and then dissolving the low molecular weight polymer in a fluorocarbon solvent such as Fluorinert® FC-40, Fluorinert® FC-75 or Fluorinert® FC-77. The pyrolysis enhances the solubility to enable the resulting materials to be used in coating form. See also, U.S. Pat. No. 5,256,747.

Moreover, there is a need in the art for an easy-to-form surface coating that can incorporate the advantages of a standard perfluoroelastomeric coating (as opposed to a low molecular weight coating), including allowing for use of a standard cure system and final cured perfluoroelastomer compound without complex process steps, while maintaining desired coating properties suitable for use on process equipment and the like and a process for preparing the same. The invention disclosed herein addresses this need and the need for a method of perfluoroelastomer joining or splicing disclosed above.

Included within the several embodiments of the invention is a method of bonding a perfluoroelastomer material to first surface that includes: (a) contacting a first surface with a bonding agent comprising a curable perfluoropolymer and a curing agent; and (b) curing the bonding agent to form a perfluoroelastomer material that is bonded to the first surface. In the practice of such method, the bonding agent may be a solution prepared by dissolving the curable perfluoroelastomer and the curing agent in a solvent. In an embodiment of the invention, the perfluoroelastomer material formed in step (b) is a coating layer or, alternatively, the first surface is a surface of a perfluoroelastomer member and the perfluoroelastomer material formed is a perfluoroelastomer weld.

In one embodiment of the method, the first surface is a surface of a perfluoroelastomer member, the bonding agent is also contacted to a second surface and step (c) further includes curing the bonding agent to form a perfluoroelastomer weld between the first surface and the second surface. Upon curing, the perfluoroelastomer weld includes essentially the same perfluoroelastomer as the perfluoroelastomer member.

An embodiment of the invention also includes method of forming a perfluoroelastomer coating that includes: (a) dissolving a curable perfluoropolymer and a curing agent in a solvent to form a solution, (b) applying the solution to a surface; and (c) curing the perfluoropolymer to form a cured perfluoroelastomeric coating on the surface. Additionally, coated substrates including a cured perfluoroelastomer coating applied on at least one surface of the substrate are also within the scope of the invention.

In another embodiment of the invention a method of bonding a perfluoroelastomer member to a surface is disclosed. The method includes (a) contacting a first surface of a perfluoroelastomer member with a bonding agent comprising: a curable perfluoropolymer, and a curing agent; (b) placing the bonding agent also in contact with a second surface; and (c) curing the bonding agent to form a perfluoroelastomer weld between the first and second surface, wherein upon curing the perfluoroelastomer weld comprises essentially the same perfluoroelastomer as the perfluoroelastomer member.

In another embodiment, a method of bonding a perfluoroelastomer seal to a gland is disclosed and includes placing a bonding agent comprising a curable perfluoropolymer and curing agent within gaps formed between a perfluoroelastomer seal and a gland; and curing the bonding agent; wherein upon curing, the perfluoropolymer forms essentially the same perfluoroelastomer as the perfluoroelastomer seal.

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