WO1999003598A1 - Coating and anti-corrosive coating based on epoxy paints - Google Patents

Abstract

The subject of the invention is a coating for the anticorrosion protection of a metal structure, comprising a primary layer of powdered epoxy paint applied to the metal structure and a secondary layer of powdered modified epoxy paint applied to said primary layer, the paint powdered epoxy resin comprising an epoxy resin and a functionalized thermosplastic polyolefin polymer capable of reacting with the epoxy resin.

Description

 Anticorrosive coating and coating method based on epoxy paints

The subject of the invention is a coating for the anticorrosion protection of a metallic structure, comprising a primary layer of epoxy paint and a so-called secondary layer of modified epoxy paint.

It also relates to a method for anticorrosive coating of a metal structure, as well as the use of a modified epoxy paint to constitute an anticorrosion coating of a metal structure.

Finally, it relates to, as a new industrial product, a modified epoxy paint comprising an epoxy resin and a functionalized thermoplastic polyolefin polymer comprising reaction groups containing labile hydrogens capable of reacting with the glycidyl ether groups of said epoxy resin. For the purposes of the present invention, the term “metallic structure” is intended to mean, in particular steel or cast iron tubes and pipes, their accessories (fittings, tees, elbows, valves, etc.), tanks (of gas, of fuel, etc. .) in particular those intended to be buried or immersed. Such metallic structures are used worldwide for the transport or storage of petroleum, petroleum products, gas or water.

The metal structures must be protected against corrosion on the one hand and mechanical stress on the other, in order to guarantee the management of safety in use over a long period.

The external coating of these metal structures must therefore offer resistance to wear and tear, cathodic detachment, when cathodic protection is applied, and it must prevent damage related to transport and installation.

For the exterior coating of metal structures, monolayer systems are known based on reactive epoxy powder paint applied to a thickness of approximately 400 μm. However, these coatings have drawbacks because they offer poor mechanical resistance during unexpected shocks, which are inevitable during the transport or the laying of these metal structures. When applied in greater thickness (from 500 μm to 1000 μm), these monolayer systems remain fragile mechanically due to the extreme rigidity of the coatings thus obtained. A three-layer process is also known, consisting in applying a base layer, or primary layer, based on epoxy resin on the metal substrate, then a hard thermoplastic adhesive, and finally a polyethylene or polypropylene film of several millimeters. This system is clearly superior to the monolayer epoxy powder painting process, since it combines the properties of the latter (excellent adhesion to metal) with that of a thick polyolefinic thermoplastic film (good mechanical resistance). The drawbacks of using the last polyolefin layer by extrusion, however, limit the use of this process to coating metallic structures of simple geometric shapes such as tubes. This system is therefore unusable on more complicated forms such as those of accessories or tanks.

Finally, at the present time, a two-layer system is known, comprising a base layer, or primary layer, in powder form based on epoxy resin, applied directly to the metal substrate, and a polyolefinic powder composed a mixture of thermoplastic adhesive and a polyolefin to harden it. If the use of powdered adhesive alone would allow good bonding between layers, its composition, which must take into account film-forming by fusion, however, makes it too soft for good resistance to penetration under load. Cutting is then necessary with a hard thermoplastic polymer based on e - itv-e. Other polyethylene or polypropylene. However, this addition of a nonpolar polymer alters the adhesion, which results in a very low resistance to cathodic delamination and a peeling between the epoxy primer layer and the second finishing layer in polyolefin powder.

The object of the present invention is to provide a coating comprising at least one primary layer and one secondary layer capable of effectively protecting against corrosion of metallic structures, in particular buried or submerged, whatever their shapes.

According to the invention, the coating is obtained by applying to the metal structure a first base layer of epoxy powder, - which will be referred to as a primary layer, and an overcoat of modified epoxy powder, called a secondary layer, or layer mechanical protection.

The secondary layer comprises an epoxy resin and its hardener, a functionalized polyolefin polymer, crosslinking agents, catalysts, pigments and fillers, as well as additives.

The coating system according to the invention is therefore entirely applied by dusting, so that it can be used on all forms of metal structures. The primary layer of epoxy powder keeps all the properties of thermosetting epoxy polymers (excellent adhesion to metal), which results in very good resistance to cathodic delamination. As for the secondary layer in epoxy powder object of the invention, it is modified with a thermoplastic resin of the functional polyolefin type, which makes it possible to combine the excellent impact resistance provided by the flexibility of these linear macromoiecules and the great resistance to penetration under load of polymers epoxy thermosets. This polyolefin type resin does not behave. as an organic "extender", because these two polymers, epoxy resin and polyolefin resin, are made compatible by the presence in the polyolefin macromolecule of functional groups capable of reacting with the oxyran group of the epoxy resin. These functional groups are in particular groups comprising labile hydrogens capable therefore of reacting with the glycidyl group of the epoxy resin. The fact that the two layers, primary and secondary, are of epoxy nature allows excellent compatibility between the layers.

The anticorrosion protection system according to the invention most generally comprises only the two primary and secondary layers, the performance obtained meeting all the requirements of the technique. It is however possible, without departing from the scope of the invention, to deposit other layers on the bilayer system, primary-secondary, according to the invention.

The epoxy powder paint used to form the primer, or base coat, can be of the type known for this kind of application. The suitable epoxy resins have an equivalent epoxy weight of between 300 and 4000, preferably between 600 and 2000. They are, for example, epoxy resins of the diglycidyl ether type of bisphenol A (DGEBA) which have a functionality of approximately 2. Epoxidized novolak resins can also be used, with their functionality greater than 2. These epoxy resins are also used for cutting. Such epoxy resins are commercially available under the designation DER 664 U or DER 642 U or DER 672 U (manufacturer: DOW CHEMIC7ΛL) or EPIKOTE 3003, 3004 and 2014 (manufacturer: SHELL CHIMIE).

For the hardening of the primer, cross-linking agents of the multifunctional polymeric type containing groups with labile hydrogens are suitable. For example, we will use phenolic resins, resins based on Bisphenol A or Bisphenol F and their derivatives, dicyandiamides, imidazole and imidazoline derivatives, carboxylic acids and acid anhydrides, aromatic amines, their adducts, alone or in combination. Their concentration will generally vary depending on the case from 5 to 35 parts per hundred parts of epoxy resin.

Reaction catalysts can also be used to accelerate curing. They are generally already contained in commercially available hardeners such as DEH 82 or EPIKURE DX 171 or XB 3082 (manufacturer: DOW CHEMICAL, SHELL CHIMIE, CIBA) or even CASAMID 710 or EPIKURE 108 FF (manufacturers: SWAN and SHELL CHIMIE) .

The paint intended to constitute the primer may also contain well-known ingredients such as inert mineral fillers of the barium sulfate type, and fillers based on silica, on silicates, such as, for example, talc, kaolin, magnesium, aluminum silicate, mica and the like, inorganic or organic pigments, spreading agents such as liquid polyacrylates, anticorrosion and degassing pigments, such as, for example, benzoin.

The primary layer thus obtained, the formulation and method of application of which are perfectly known to man art, is particularly suitable for receiving the secondary layer which characterizes the invention.

The secondary layer is obtained using a powder paint based on the same ingredients as those mentioned for the paint intended for the constitution of the primary layer, but it is modified with a functionalized thermoplastic polyolefin polymer, this functionalization being in particular obtained thanks to reaction groups containing labile hydrogens which can react with the glycidyl ether groups of the epoxy resin. These reaction groups can be added to the polyolefin chain by copolymerization or by grafting. These are, for example, carboxylic acids, their anhydrides or their esters. Preferably, the ethylene terpoly esters / acrylic ester / maleic anhydride, or the ethylene copolymers / esters of acrylic or methacrylic acids are used. Products of this type are commercially available, in particular under the name LOTADER 3200 P3 or 3300, or OREVAC PPC or PPT (manufacturer: ATOCHEM) or LUCALEN A 2910 or

A 2910 M (manufacturer / BASF AG).

In order to catalyze the polyaddition reaction between the reactive hydrogen groupings of the functionalized polyolefin polymer and the glycidylether groups of the epoxy resin, specific catalysts can be used, such as for example tertiary amines or derivatives of imidazole or of imidazoline, or organometallic salts.

The modified epoxy paint used for constituting the secondary layer of the coating according to the invention comprises from 40 to 90%, preferably from 50 to 85%, and even more preferably from 70 to 80% by weight of epoxy resin with its hardener, and from 10 to 60%, preferably from 15 to 45%, and even more preferably from 20 to 30% by weight of functionalized thermoplastic polyolefin polymer.

The anticorrosion coating in accordance with the invention therefore comprises a primary layer of epoxy paint applied to the metal structure and a secondary layer of modified epoxy paint applied to said primary layer, the modified epoxy paint comprising an epoxy resin and a functionalized thermoplastic polyolefin polymer capable of reacting with the epoxy resin, the functionalized thermoplastic polyolefin polymer more generally comprising reaction groups containing labile hydrogens capable of reacting with the glycidyl ether groups of the epoxy resin. The invention also relates to a method for anticorrosive coating of a metal structure, this method being characterized by the fact:

- that a primary layer of powdered epoxy paint is applied to the previously prepared metal structure,

- That a secondary layer of powdered modified epoxy paint is applied to the primary layer, said modified epoxy paint comprising an epoxy resin and a functionalized thermoplastic polyolefin polymer capable of reacting with the epoxy resin.

In accordance with the invention, the primary layer and the secondary powder layer are applied with a "powder lance" gun, or electrostatic, or triboelectrostatic, on the metal surface to be protected. Previously, the surface of the metal structure is prepared by removing it in the usual way from rust, grease, oils, dust, then pickled by blasting with abrasive to obtain a minimum surface cleanliness equivalent to the Sa 2 standard. , 5 according to ISO 8501-1, and a surface roughness between 40 microns and 100 microns, preferably between 60 and 80 microns. If necessary, a chemical pretreatment is also carried out, such as for example chromating and / or phosphating. The metal surface thus prepared is then preheated to a temperature between 160 ° C and 250 ° C, preferably between 210 ° C and 230 ° C.

The primer, or base layer, is then applied to this hot surface according to conventional powder coating spraying methods, in order to obtain a thickness which can vary from 200 microns to 700 microns, preferably from 400 to 500 microns. In a time between 10 seconds and 60 seconds, preferably between 15 and 30 seconds, the secondary layer is then applied to the primary layer according to the usual methods of spraying powder coating, to obtain a thickness of between 300 and 1500 microns , preferably between 500 and 600 microns. Post-cooking can then be carried out by any means capable of providing calories, such as for example radiant panels, baking at a temperature between 180 ° C and 250 ° C, preferably between 210 ° C and 230 ° C, for a time between 1 and 15 minutes, preferably 3 and 5 minutes.

To achieve the best performance, it is necessary that the base layer is not fully crosslinked when it is overcoated with the secondary layer, but it is necessary to reach a complete level of crosslinking of the primary layer once the two layers applied. The invention can be better understood using the following embodiment, which is given purely by way of illustration and without limitation. EXAMPLE:

Formulation of paints for the primary layer and for the secondary layer:

- primary layer:

Epoxy resin of molecular weight 1400 67 Dicyandiamide 3 Tin dibutyldilaurate 1 Triethylene Diamine 1 Ethyl 2 Imidazole 1 Acrylic spreading agent 1 Baryte sulfate 16 Aluminum potassium silicate hydrate 6% Chromium oxide 3% Titanium oxide 1 %

secondary layer

80 parts by weight of the powder paint used as the primary layer described above mixed dry with 20 parts by weight of LOTADER 3200 P3, sold by the company ATOCHEM.

After application of the two layers thus formulated on a metallic structure, a thickness of 400 microns is noted for the primary layer and 600 microns for the secondary layer. The application conditions were 220 ° C. with a time between layers of 15 seconds, the post curing was carried out in an oven for 5 minutes at 220 ° C.

The performances of the coating thus obtained are as follows: a) cathodic detachment according to NFA 49712 28 days at 20 ° C; result: 3 millimeters. b) resistance to penetration under load by punching according to NFA 49712; result: 0 micron (not measurable) c) impact resistance according to NFA 49712; result:> 20 J (10 mm thick steel plate). d) resistance to salt spray according to NFX 41002; result: 3000 hours without rusting or hulling. e) adhesion according to ISO 4624; result: more than 20 MPa.

Thanks to the invention, there is therefore an extremely effective and efficient anticorrosion coating for metallic structures.

Claims

1. Coating for the anticorrosion protection of a metal structure, characterized in that it comprises a primary layer of epoxy paint applied to the metal structure and a secondary layer of modified epoxy paint applied to said primary layer, the modified epoxy paint comprising an epoxy resin and a functionalized thermoplastic polyolefin polymer capable of reacting with the epoxy resin. 2. Coating according to claim 1, characterized in that the functionalized thermoplastic polyolefin polymer comprises reaction groups containing labile hydrogens capable of reacting with the glycidyl ether groups of the epoxy resin. 3. Coating according to claim 2, characterized in that the reaction groups are out on the polyolefin chain by copolymerization or by grafting. 4. Coating according to any one of claims 1 to 3, characterized in that the functionalized thermoplastic polyolefin polymer is chosen from copolymers of olefins and organic acids and / or αe their anhydrides and / or their esters. 5. Coating according to any one of claims 1 to 4, characterized in that the modified epoxy paint comprises from 40% to 90 °, preferably from 50% to 85 o, and more preferably still from 70% to 80% by weight of epoxy resin with its hardener, and from 10% to 60%, preferably from 15% to 45%, and more preferably still from 20% to 30% by weight of functionalized thermoplastic polyolefin polymer. 6. Coating according to any one of claims 1 to 5, characterized in that the modified epoxy paint comprises catalysts for the reaction between the reaction groups of the functionalized thermoplastic polyolefin polymer and the glycidyl ether groups of the epoxy resin, these catalysts preferably being chosen from tertiary amines, imidazole derivatives, imidazoline derivatives, and organometallic salts. 7. Method for anticorrosive coating of a metal structure, characterized by the fact: - that a primary layer of powdered epoxy paint is applied to the prepared metal structure, - That a secondary layer of powdered modified epoxy paint is applied to the primary layer, said modified epoxy paint comprising an epoxy resin and a functionalized thermoplastic polyolefin polymer capable of reacting with the epoxy resin. 8. Coating method according to claim 7, characterized in that the functionalized thermoplastic polyolefin polymer comprises reaction groups containing labile hydrogens capable of reacting with the glycidyl ether groups of the epoxy resin. 9. Coating method according to either of claims 7 and 8, characterized in that the functionalized thermoplastic polyolefin polymer is chosen from copolymers of olefins and / or organic acids and / or their anhydrides and / or their esters. 10. Coating method according to any one of claims 7 to 9, characterized in that the modified epoxy paint comprises from 40 to 90%, preferably from 50 to 85%, and even more preferably from 70 to 80% by weight of epoxy resin with its hardener, and from 10 to 60%, preferably from 15 to 45%, and even more preferably from 20 to 30% by weight of functionalized thermoplastic polyolefin polymer, and which it comprises optionally catalysts for the reaction between the reaction groups of the functionalized thermoplastic polyolefin polymer and the glycidyl ether groups of the epoxy resin, these catalysts preferably being chosen from tertiary amines, imidazole or imidazoline derivatives, and the salts organometallic. 11. Method according to any one of claims 7 to 10, characterized in that the epoxy paint and the modified epoxy paint are applied with a powder gun or electrostatically or triboelectrostatically on the surface of the heated metal structure. 12. Method according to any one of claims 7 to 11, characterized in that the primer is applied to the hot metal surface so as to obtain a thickness of 200 to 700 μm, preferably 400 to 500 μm, then that in a time of between 10 and 60 seconds, preferably between 15 and 30 seconds, the secondary layer is applied to said primary layer to obtain a thickness between 300 and 1500 μm, preferably between 500 and 600 μm, and that the metal structure is subjected to post-baking. 13. Method according to any one of claims 1 to 12, characterized in that the secondary layer is applied to the primary layer while the latter is not completely crosslinked. 14. Modified powdered epoxy paint comprising a powdered epoxy resin and a functionalized thermoplastic polyolefin polymer comprising reaction groups containing labile hydrogens capable of reacting with the glycidylether groups of the epoxy resin. 15. Use of an epoxy paint modified in powder comprising an epoxy resin and a functionalized thermoplastic polymer capable of reacting with the epoxy resin to form an anticorrosion coating of a metallic structure, in particular a buried or immersed metallic structure.