Stock material or miscellaneous articles – Composite – Of epoxy ether
Reexamination Certificate
2002-07-18
2004-08-10
Buttner, David J. (Department: 1712)
Stock material or miscellaneous articles
Composite
Of epoxy ether
C428S421000, C428S416000
Reexamination Certificate
active
06773815
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to metal surfaces coated with fluoropolymers and more particularly to tubes whose outer surface is coated with fluoropolymers. These tubes are useful for the development of offshore hot oil wells, since it is necessary for the tubes which transport hot oil to withstand corrosion by seawater.
THE TECHNICAL PROBLEM
No steel tube coating which can be readily produced industrially and which can withstand high temperature under offshore conditions is known at the present time. For the development of offshore hot wells, one solution consists in cooling the oil with a heat exchanger before raising it to the surface. This technique is very expensive. Furthermore, the cooling may result in the formation of a cold plug. It is also possible to make use of special steels, but they are prohibitively expensive. A coating made of fluoropolymer, for example PVDF (common abbreviation for polyvinylidene fluoride), as disclosed in the invention makes it possible to convey hot fluids (150° C.) under offshore conditions, using ordinary steel tubes.
PRIOR ART
Patent DE 3 422 920 discloses outer coatings for steel tubes, comprising, successively, a layer of epoxy resin, a layer of grafted polypropylene and, finally, an outer layer of a mixture of polypropylene and of a polypropylene/polyethylene block copolymer. The glass transition temperature Tg of the epoxy resin is between 80° C. and 94° C. These coatings are suitable for hot water at 90° C.
U.S. Pat. No. Re 30 006 discloses outer coatings for steel tubes, comprising, successively, an epoxy resin and a polyethylene modifed by grafting or copolymerization with maleic anhydride. Nothing is stated regarding the Tg of the epoxy resin; however, the polyethylene does not make it possible to work above 80° C.
Patent EP-A-0 770 429 discloses a coated metal surface such as the outer surface of a tube, comprising, successively, a layer of epoxy resin placed next to the metal and having a glass transition temperature of greater than 120° C., a layer of binder based on polypropylene modified by grafting and a layer of thermoplastic polymer. The thermoplastic polymer is chosen from polyamides, polyamide alloys and polypropylene. These coatings do not offer any protection against corrosion by seawater to tubes transporting oil at 150° C.
Patent EP-A-404 752 discloses structures consisting, successively, of a substrate, a primer and a layer of PVDF. The primer is a mixture of an epoxy resin with either PMMA (common abbreviation for polymethyl methacrylate) or a copolymer of methyl methacrylate and of ethyl acrylate. Patent EP-A-0 354 822 discloses similar structures. This coating does not withstand corrosion by seawater when the tubes transport oil at 150° C.
Patent WO 97/27260 discloses structures consisting, successively, of a substrate, a primer and a layer of PVDF. The primer is a mixture of at least two of the following three polymers, namely (i) a PVDF homopolymer, (ii) a PVDF copolymer comprising at least 50 mol % of VF2 and (iii) an acrylic polymer containing carboxylic acid functions, such as, for example, copolymers of methyl methacrylate and of acrylic acid. The substrate may be the outer surface of a tube. Patent WO 97/49777 discloses similar structures. This coating does not withstand corrosion by seawater when the tubes transport oil at 150° C.
It has now been found that a coating comprising, respectively, a layer of epoxy resin, a layer of binder based on PVDF and on at least one polymer chosen from acrylic polymers and oxidized fluoropolymers and a layer of PVDF, the epoxy resin being on the side of the metal, protects the metal against corrosion by seawater even if the metal is at 150° C. Variants of this coating, which are detailed later, may also be used.
BRIEF DESCRIPTION OF THE INVENTION
The present invention relates to a coated metal surface comprising, successively:
a layer (1) of epoxy primer placed next to the metal,
a layer (2) of binder comprising 98 to 50 parts by weight of at least one fluoropolymer L3 per 2 to 50 parts, respectively, of at least one polymer chosen from acrylic polymers L1 and polymers L2 which are fluoropolymers chemically modified by a partial dehydrofluorination followed by an oxidation,
a layer (3) of fluoropolymer.
The present invention also relates to a process for manufacturing these coated surfaces. The metal surface is first degreased, sanded and then heated. The epoxy primer of the layer (1) is deposited in liquid form or by spraying or electrostatic spraying if it is a powder onto the metal surface heated to 200-240° C. After about 20 to 30 seconds, i.e. slightly before the end of the gel time and before the resin has crosslinked, in order for there to remain epoxide functions to react with the binder, the binder of the layer (2) is deposited either by spraying if it is in powder form, or by coating or rolling. Next, the fluoropolymer of the layer (3) is deposited in the same way. As regards the outer surface of metal tubes, the process is performed in the same way for the epoxy primer, and the binder is then either deposited by spraying if it is available in powder form, or extruded through a circular die (also known as a crosshead) arranged concentrically around the tube. The binder may also be extruded through a flat die producing a continuous strip which is wound around the tube, for example by means of rotating the tube on itself. The fluoropolymer is deposited in the same way.
The coating of the invention can readily be produced on a conventional coating line, due to the excellent processability of PVDF. The coating can be applied continuously, at a speed of at least 50 cm/minute, at a temperature of less than 250° C., this temperature making it possible to conserve all the initial properties of the steel. The ease of use is an advantage over other known solutions thermostable polymers such as polysulfone, polyphenylene ether or polyether imide which require either high temperatures or a long and intricate implementation with reactive solvents (post-curing).
According to a first variant, the coating does not comprise the layer (3). However, it is recommended that the layer (2) which becomes the outer layer should be thicker than in the structure of the main invention.
According to a second variant, the coating does not comprise the layer of primer (1), the layer of binder necessarily contains the polymer L2 and the surface is necessarily the outer surface of tubes.
That is to say that in this second variant, the invention relates to a coated metal surface which is the outer surface of tubes, comprising, successively:
a layer (2) of binder placed next to the metal and comprising 98 to 50 parts by weight of at least one fluoropolymer L3 per 2 to 50 parts, respectively, of a mixture comprising at least one polymer chosen from polymers L2 which are fluoropolymers chemically modified by a partial dehydrofluorination followed by an oxidation, and optionally at least one polymer chosen from acrylic polymers L1,
a layer (3) of fluoropolymer.
According to a third variant, the coating does not comprise the layer (2) and the layer (1) comprises a mixture of epoxy primer and of polymer L2.
That is to say that in this third variant, the invention relates to a coated metal surface comprising, successively:
a layer (1) of primer placed next to the metal and comprising 1 to 70 parts of a polymer chosen from polymers L2 which are fluoropolymers chemically modified by a partial dehydrofluorination followed by an oxidation, per 30 to 99 parts, respectively, of an epoxy primer,
a layer (3) of fluoropolymer.
The coating obtained has good impact strength, flexibility allowing slight bending of the tube and excellent adhesion to the metal, even at high temperature (up to 150° C.). These good properties are maintained on contact with seawater.
DETAILED DESCRIPTION OF THE INVENTION
The term “epoxy primer” used for the layer (1) advantageously denotes the product of the reaction of a thermosetting epoxy resin and of a hardener. Their principle is disclosed, for example,
Atofina
Buttner David J.
Keehan Christopher
Millen White Zelano & Branigan P.C.
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