Stock material or miscellaneous articles – Hollow or container type article – Polymer or resin containing
Reexamination Certificate
1996-10-28
2001-05-22
Reddick, Judy M. (Department: 1713)
Stock material or miscellaneous articles
Hollow or container type article
Polymer or resin containing
C428S035700, C428S036910, C428S418000
Reexamination Certificate
active
06235361
ABSTRACT:
TECHNICAL FIELD
The present invention relates to polymer-coated metal surfaces and more particularly to pipes the external surface of which is coated with a thermoplastic polymer. The Applicants have discovered thermoplastic polymer coatings which exhibit a peel strength at 130° C. which is higher than 400 N/5 cm. A means of obtaining this peel strength is, for example, to place between the metal and the thermoplastic a layer of epoxy resin which has a glass transition temperature higher than 120° C. and a layer of polypropylene-based binder, the layer of epoxy resin being against the metal.
BACKGROUND OF THE INVENTION
U.S. Pat. No. 4,606,953 to Suzuki et al. (and DE 3422920) describes coatings for steel pipes, including successively a layer of epoxy resin, a layer of grafted polypropylene and finally an external layer of a mixture of polypropylene and of a polypropylene/polyethylene block copolymer. The glass transition temperature (T
g
) of the epoxy resin is between 80 and 94° C. These coatings are suitable for hot water at 90° C.
U.S. Pat. Re. No. 30,006 to Sakayori et al. describes coatings for steel pipes including successively an epoxy resin and a polyethylene modified by grafting or copolymerization with maleic anhydride. Nothing is written concerning the T
g
of the epoxy resin; however, the polyethylene does not make it possible to work above 80° C. Thus, the prior art has not described any coating which has a high peel strength at 130° C. like that of the invention.
SUMMARY OF THE INVENTION
The present invention is therefore a metal surface coated with a thermoplastic polymer, the coating exhibiting a peel strength at 130° C. (measured according to DIN standard 30 670) which is higher than 400 N/5 cm.
DETAILED DESCRIPTION OF THE INVENTION
The metal surface may be of any kind; however, the invention is particularly useful for the external surface of pipes, it being possible for these pipes to have an external diameter, for example, of up to 0.8 m or up to 1.5 m and a thickness of 2 to 25 mm.
The thermoplastic polymer may be of any kind, provided that its working temperature is higher than or equal to 130° C. and preferably between 130 and 150° C.
To give an example, polypropylene, polyamides and polyamide blends may be mentioned, it being possible for these polymers to be filled with glass fibers. Polypropylene is intended to mean propylene homopolymers and the copolymers of propylene with at least one alpha-olefin and with propylene predominating by weight. This alpha-olefin is, for example, ethylene.
Polyamide is intended to mean the products of condensation:
of one or more amino acids such as aminocaproic, 7-aminoheptanoic, 11-aminoundecanoic and 12-aminododecanoic acids or of one or more lactams such as caprolactam, oenantholactam and lauryllactam;
of one or more salts or mixtures of diamines such as hexamethylenediamine, dodecamethylenediamine, metaxylylenediamine, bis-p-aminocyclohexylmethane and trimethylhexamethylenediamine with diacids such as isophthalic, terephthalic, adipic, azelaic, suberic, sebacic and dodecanedicarboxylic acids; or
of mixtures of certain monomers, which results in copolyamides.
Polyamide mixtures may be employed. PA-6 and PA-6,6 are advantageously employed.
A polyamide blend within the meaning of the invention is intended to mean the mixtures of polyamide which are in the form of polyamide matrix in which nodules of a polymer (A) or of a rubber are dispersed, the blend having to exhibit a working temperature as indicated above.
By way of example of polymer (A) there may be mentioned the above polypropylene, crosslinked polyethylenes or crosslinked mixtures of (i) ethylene copolymers including maleic anhydride and of (ii) ethylene copolymers including glycidyl methacrylate.
As example of rubbers it is possible to mention: styrene-butadiene (SBR), nitrile-butadiene (NBR), natural rubber, polyisoprene, polybutadiene, butyl rubber, styrene-butadiene-styrene (SBS) block copolymers, styrene-isoprene-styrene (SIS) copolymers and styrene-ethylene/butene-styrene (SEBS) copolymers.
The polymer (A) and the rubber may optionally carry functional groups to facilitate compatibilizing with the polyamide. These functional groups can be obtained by grafting at least one unsaturated carboxylic acid, an anhydride and the derivatives of these acids and anhydrides. By way of example of carboxylic acids it is possible to mention: acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, crotonic acid, itaconic anhydride, nadic anhydride, maleic anhydride and substituted maleic anhydrides such as, for example, dimethylmaleic anhydride.
By way of examples of derivatives it is possible to mention: salts, amides, imides and esters, such as sodium mono- and dimaleate, acrylamide, maleimide and dimethyl fumarate. The grafting processes are known to a person skilled in the art.
The formation of the polyamide matrix can also be facilitated by adding a compatibilizing agent to the mixture of polyamide and of polymer (A) or of rubber. This product is known per se. To give an example it is possible to mention: polypropylene grafted with an unsaturated carboxylic acid, a carboxylic acid anhydride or their derivatives. These products can be chosen from the products of grafting which are described above.
The compatibilizing agent may also be a mixture of grafted polypropylene and of an elastomer such as an EPR or EPDM rubber.
Where polypropylene is concerned, the compatibilizing agent is advantageously an ethylene/propylene copolymer with propylene predominating and grafted with a product which has a site that is reactive with amines and then condensed with polyamides or polyamide oligomers which have a single amine end. These compatibilizing agents and the corresponding polyamide blends are described in U.S. Pat. No. 5,342,886 to Glotin et al., the content of which is incorporated into the present application.
The quantity of polyamide forming the matrix of these polyamide blends may be between 55 and 95% by weight of the combination of the polyamide and of the polymer (A) or of the rubber. These polyamide blends can be manufactured by the usual melt-blending techniques (twin screw, Buss or single screw).
The peel strength at 130° C. is at least 400 N/5 cm; it can reach 650 N/5 cm if the thermoplastic is filled with glass fibers. At 150° C. the peel strength is higher than 180 N/5 cm; it can reach 200 N/5 cm in the case of polyamides or polyamide blends and 350 N/5 cm in the case of thermoplastics filled with glass fibers
The Applicants have discovered that a means for obtaining these peel strengths is, for example, to place between the metal and the thermoplastic a layer of epoxy resin which has a glass transition temperature higher than 120° C. and a layer of binder based on functionalized polypropylene, the layer of epoxy resin being against the metal.
The present invention also relates to this metal surface thus coated.
The basis of the epoxy resins is described, for example, in the Kirk-Othmer Encyclopedia of Chemical Technology, Vol. 9—pages 267-289, 3rd edition. It suffices to choose a resin which has the required T
g
. These resins are in most cases polyglycidyl ethers of a polyphenol.
The following are advantageously employed:
products of condensation of bisphenol A and of epichlorohydrin;
epoxy-cresol novolak (ECN) resins;
epoxy phenol novolaks;
resins derived from bisphenol F;
derivatives of polynuclear phenols and of glycidyl ethers;
cycloaliphatic resins;
resins derived from aromatic amines such as:
derivatives of tetraglycidylmethylenedianiline,
derivatives of triglycidyl-p-amino-phenol,
derivatives of triazines such as triglycidyl isocyanurate;
resins derived from hydantoin.
The resins employed in the present invention are crosslinkable between 180 and 250° C. Crosslinking can be carried out, for example, with amines such as dimethylethanolamine and methylenedianiline or amides such as dicyandiamide, or else phenolic resins.
These resins may include additives such as silicones, pigments such as titanium dioxide, iron oxides, carbon black,
Jacquemet Regis
Perret Patrice
Atofina
Pennie & Edmonds LLP
Reddick Judy M.
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