Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Physical dimension specified
Reexamination Certificate
1998-08-11
2001-06-05
Chen, Vivian (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Physical dimension specified
C428S324000, C428S332000, C428S339000, C428S421000, C428S422000, C428S450000, C428S454000, C428S458000, C428S473500, C428S474400, C524S049000, C427S458000, C427S470000, C427S475000, C427S485000, C427S486000, C427S180000, C427S189000, C427S195000, C427S202000, C427S203000
Reexamination Certificate
active
06242089
ABSTRACT:
FIELD OF THE INVENTION
The instant invention relates to a composition of ethylene-tetrafluoroethylene copolymer (ETFE) which can be used as a coating or a surface-protecting laminate on a substrate to retard permeation by water to the substrate.
BACKGROUND OF THE INVENTION
ETFE copolymers are known in the art. U.S. Pat. No. 4,123,602—Ukihashi et al. (1978) discloses such polymers with about 40 to 60 mole % of each comonomer, using modifiers such as 1% perfluoro butylethylene. Such modifiers and other adjuvants are common in the art and are considered to be part of the copolymer.
Films of various fluoropolymers including ETFE, which can have various fillers including mica, are used for cladding metal substrates in Japanese Kokai 4-229246—Sahara et al. (1992). There is no focus in this kokai on minimizing permeation or on using mica in ETFE, or on what proportions would be needed.
Mica coated with oxides to produce sparkling optical effects is the subject of U.S. Pat. No. 3,087,829—Linton (1963).
Mica is used in fluoropolymer coatings for cookware to minimize stain formation, as in U.S. Pat. No. 4,353,950—Vassiliou (1982).
The disclosure of the previously identified patents and patent publications is hereby incorporated, by reference.
SUMMARY OF THE INVENTION
The instant invention solves permeation and corrosion problems associated with conventional ETFE containing coatings by providing an additive such as mica. A mixture comprising or consisting essentially of ETFE and mica can be used effectively as a powder. The powder of ETFE and mica and be applied upon a substrate in order to provide a permeation and corrosion resistant coating.
The instant invention provides a permeation-resistant composition of matter comprising or consisting essentially of at least one fluoropolymer such as a copolymer of ethylene and tetrafluoroethylene (ETFE) and at least one additive such as mica which is either uncoated or coated with oxide, wherein the ETFE is a copolymer of about 40 to about 60 mole % of ethylene and about 60 to about 40 mole % tetrafluoroethylene, based on the copolymer, and wherein the additive is present in amounts of about 3 to about 25% by weight based on the ETFE plus mica, e.g., normally about 7.5 to about 15% by weight mica.
In one aspect, the instant invention provides coating compositions, processes and coatings that can be laminated onto a suitable substrate.
In another aspect, the instant invention relates to a dry powder coating that can be adhered to a substrate by one or more primer coatings or layers. The dry powder can be heated in order to form a substantially continuous coating or layer upon the substrate, e.g, a substrate coated with a primer.
DETAILED DESCRIPTION
While any suitable fluoropolymer can be employed in connection with the instant invention, it has been found that an ETFE based fluoropolymer and typically about 10% by weight mica in a coating gives maximum resistance to water permeation. Any suitable process can be employed for applying the fluoropolymer containing composition onto a substrate, e.g., an electrostatic-spray process for applying a powder mixture comprising ETFE and mica. Depending upon the conditions of the spraying process, some of the mica of the composition can be lost; but, under normal process conditions the resultant coating contains at least about 4 to 5% by weight mica in the coating on the coated substrate.
The coating of the instant invention can be employed in a virtually unlimited array of environments for improving the corrosion and permeation resistance of the underlying substrate, e.g., water vapor permeation resistance. Examples of such substrates include molds, tubes, chemical containers and reactors, among others. For example, for coating the inside of chemical containers or equipment vessels by rotolining, or for coating by film lamination a minimum of about 5% mica is satisfactory. More mica is generally better than less, but over a certain level such as over 25%, excess mica can degrade the mechanical integrity and properties of the coating. Normally, a mica having a platelet thickness of about 1-2 microns and an average diameter of about 10 to 130 microns is employed. If desired, one or more water or corrosion resistant additives can be employed along with mica. Additionally other additives may be used such as those that alter the properties of the coating composition or the coated substrate. For instance, various flow agents such as silica may be added to the ETFE /mica blend to improve ease of application.
The use of a coating consisting essentially of mica in ETFE in accordance with the invention retarded water penetration drastically in standard Atlas Cell tests using ASTM method C868, from 2 days with no mica, to over 2 weeks with about 10% mica.
While the previous description has focused upon a coating consisting essentially of ETFE and mica, a skilled person in this art understands that one or more fluoropolymers can be employed instead of and in conjunction with ETFE. For best results, however, the composition will contain ETFE as the predominant fluoropolymer. Suitable ETFE is available commercially and typically has an average particle size of less than about 50 microns.
The instant invention can be employed as a coating on a variety of substrates which may include a plurality of films, coatings or layers in order to obtain a composite or laminate structure. For example, one or more primer coatings or layers can be located between the substrate and ETFE/mica composition. While any suitable primer can be employed, examples of particularly useful primers include a mixture of ETFE with adhesion promoting polymers such as amide-imide polymers, polyphenylene sulfide (PPS), mixtures thereof, among others. One or more primer coatings can be prepared and applied by using any suitable conventional method. When a primer is employed, the ETFE/mica composition becomes a so-called topcoat. That is, the ETFE/mica composition is exposed to the environment containing the corrosive or permeating species thereby protecting the underlying substrate.
The topcoat composition can be obtained by using any suitable method. One such method comprises dry blending ETFE and mica powders by using about 90% by weight TEFZEL*R* ETFE sold commercially by DuPont Company (as product code 532-6018) and about 10% platelet shaped Iriodine*R* oxide coated mica additive from Merck, Germany.
While any suitable substrate can be coated, examples of suitable substrates include steel, high carbon steel, aluminum, among others. Depending upon the characteristics desired in the coated substrate, at least one member from the group of pigments, flow agents, stablizers, among others, can be added to the ETFE/mica or primer coatings. An example of a suitable stabilizer comprises copper iodide, e.g., cuprous iodide (CuI).
The surface characteristics or substrate profile are not critical parameters for the final performance of the coating; but, surface roughening by any conventional means such grit blasting, etching, among others, can aid adhesion of the coating to the substrate. If desired, a primer coating or layer can be located between the instant coating and the substrate. While the primer does not play a critical role for the permeation resistance of the coating, the primer can enhance adhesion of the coating to the substrate thereby improving the useful life of the coating. One suitable primer is sold by the DuPont Company as product code 699-123. An example of a suitable primer composition, which was obtained from commercially available materials, is given in Table I (in weight percent).
TABLE I
Primer Composition
Carbon black
0.990
Acrylic emulsion copolymer
0.283
Colloidal silica, Ludox*R* AM from DuPont
0.876
Amide imide polymer
3.015
Polyphenylene sulfide
3.003
50:50 Ethylene-tetrafluoroethylene
19.340
copolymer
4,4′-Methyene dianiline
0.033
Hydroxypropyl cellulose
0.091
Cuprous iodide
0.014
Sodium polynaphthalene sulphonate
0.073
Octyl phenol polyether alcohol
1.382
Deionized water
64.721
Triethanol amine
0.039
N,N-Dimethylethanolamin
Chen Vivian
E. I. Du Pont de Nemours and Company
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