MXPA97006897A - Coating for metali surface - Google Patents

Abstract

The invention relates to a metal surface coated with a thermoplastic polymer and comprising at least one adhesive placed between the metal surface and the thermoplastic polymer, the adhesive having a Vicat point less than or at most substantially equal to the possible heating temperature of the metallic surface. According to a variant, an epoxy resin is added between the metal and the adhesive. The invention is particularly useful for the outer surfaces of tubes that can not be heated beyond 55 to 70 ° C. The adhesive is preferably a copolymer of atylene / alkyl (meth) acrylate / maleic anhydride

Description

METAL SURFACE COVERING FIELD OF THE INVENTION The present invention relates to a coating for metal surfaces and, more particularly, to tubes whose outer surface is coated with a thermoplastic polymer. This technique is used, for example to protect buried or submerged pipes against corrosion.

BACKGROUND OF THE INVENTION According to the prior art, the tubes are heated to between 130 and 200 ° C and then polyethylene powder is sprayed on it and a continuous polyethylene coating is obtained by melting. The surface heated in this way can also be coated with a first layer of an inserted polyolefin and, subsequently, with an outer layer of polyethylene. WO 92/03234 describes a process in which the tube is heated to at least 200 ° C, then, 200 μm of epoxy resin is deposited on it, before the end of the crosslinking, a layer of 500 is deposited μm of an ethylene copolymer grafted with maleic anhydride and, finally, a layer of at least 300 μm of polyethylene is deposited. fl 437 / 97MX BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention relates to the coating of metal surfaces that do not need to be heated, either because they already have a coating on the other side, for example, a polyethylene, or because the metal surface can not be heated, such as for example cast iron, or because the metal and the coating on the other side do not tolerate heating. These are, for example, steel tubes whose interior is painted or coated with polyethylene or cast iron or cast iron tubes or alternatively steel tubes with an internal cement coating. These surfaces can barely be heated beyond 60 ° C. The Applicant has discovered that by using an adhesive having a Vicat point less than or at most substantially equal to the possible heating temperature of the metal surface, coatings with a peel or peel strength of up to 300 or 400 N / can be obtained. 5 cm at 23 ° C. If the Vicat point is above this temperature, the peel strength is then quite insufficient and the coating is unacceptable. The present invention relates to a metal surface coated with a thermoplastic polymer J1 / T / MX comprising at least one adhesive placed between the metal surface and the thermoplastic polymer, the adhesive having a smaller Vicat point or as maximum substantially equal to the possible heating temperature of the metal surface. The invention also relates to a process for coating these surfaces. The invention relates to surfaces that can not be heated up to the temperatures normally used for these steel surfaces of the prior art, ie, beyond 100 ° C and up to 200 ° C. This refers, for example, to cast iron or cast iron coated on one of its faces with a product that does not tolerate high temperatures, such as for example polyethylene or cement. In this way, the invention can be related to the coating on one or both sides of the metal surface, depending on whether the other side is already coated or if only one of the faces is to be coated. The invention is particularly useful for the outer surface of the tubes, it is possible that these tubes have, for example, an outer diameter of up to 0.8 or 1.5 m and a thickness of from 2 to 25 mm. For the purposes of the invention, the possible heating temperature refers to the E'1437 / 97MX temperatures from approximately 50 to 100 ° C and, normally, from 55 to 70 ° C. Examples of thermoplastic polymers that may be mentioned are polyolefins, polyamides and blends of polyamide and polyolefins, it is possible that these polymers have a glass fiber filler. Because the metal surface can not be heated, the operating temperature of the coated surfaces of the invention is relatively low and, thus, ranges from about 50 to 100 ° C. Therefore, it is not necessary to use polyamides. The polyolefins are advantageously used. Examples of polyolefins which may be mentioned are: polyethylene, polypropylene, copolymers of ethylene or propylene with at least one alpha-olefin.

LDPE, LLDPE, VLDPE and can be mentioned among others. - copolymers of ethylene with at least one monomer selected from unsaturated carboxylic acid esters, carboxylic acids totally or partially neutralized by metals or alkaline agents, such as for example zinc or lithium or, vinyl esters of saturated carboxylic acids. Polyethylene or polypropylene are used advantageously. [1437 / / MX The thermoplastic polymer can be loaded with glass fibers, talc, clays, aluminas or silica. It can also contain antioxidants, etc. The adhesive is any product that allows the union of the thermoplastic to the metal surface and that has a Vicat point less than or at most, substantially equal to the possible heating temperature of the metal surface. The Vicat point is therefore at most 50 or 100 ° C and, normally, from 55 to 70 ° C maximum. For example, for a cast iron pipe that can not be heated beyond 60 ° C, the adhesive has a Vicat point not higher than 60 or 65 ° C, advantageously below 55 ° C and, preferably , between 20 and 50 ° C. According to one form of the invention, the adhesive can be a polymer to which a functional group was provided by grafting or copolymerization with a monomer selected from: (i) unsaturated carboxylic acids, (ii) unsaturated carboxylic anhydrides, ( iii) derivatives of these acids or anhydrides such as, for example, salts, amides, imides or esters or (iv) unsaturated epoxides. In accordance with another form of the invention, the adhesive can be a polymer in a fusion-type formulation by heating.The melting adhesives by iii, ir, heating or hot melt are mixtures of a base polymer (constituting the core or core of the melting adhesive by heating) with a tackifying or tackifying resin, waxes, stabilizers and, optionally, fillers It is sufficient to select from these products those having a suitable Vicat point.These adhesives may have a flow index of melt or flow index (MFI) of between 0.5 and 1,000 (g / 10 min at 190 ° C under load of 2.16 kg) The applicant has also discovered that if the FI is greater than 10 and preferably, it is between 15 and 100, then it is easier to apply the adhesive, the layer is homogeneous and a good resistance to peeling is definitely obtained.On the other hand, if the MFI is very low, for example, between 0.5 and 10, it is necessary Take care to ensure the distribution of adhesive on the surface. The adhesive in advantageous form is a copolymer: ethylene - optionally one or more onomers selected from: unsaturated carboxylic acid esters, such as for example alkyl (meth) acrylates; E'1437 / 7MX • vinyl esters of saturated carboxylic acids, such as for example vinyl acetate or propionate; . alpha-olefins such as for example 1-butene, - of the grafted or copolymerized functional monomer described above. The functional monomer can be an unsaturated carboxylic acid, an anhydride or derivatives of these acids or anhydrides. Examples of the carboxylic acids are methacrylic acid, maleic acid, fumaric acid, itaconic acid, crotonic acid, itaconic anhydride, nadic anhydride, maleic anhydride and substituted maleic anhydrides, such as, for example, dimethylmalic anhydride. Examples of the derivatives that may be mentioned are salts, amides, imides and esters, such as, for example, mono- and sodium dimaleate, acrylamide, maleimide and dimethyl fumarate. Among the salts of (meth) acrylic acid which may be mentioned are the zinc or lithium salts (ionomers). The functional monomer can also be an unsaturated epoxide, such as, for example, glycidyl (meth) acrylate, glycidyl ether of ally, glycidyl ether of glycidyl itaconate, or glycidyl maleate. Examples of adhesives that may be mentioned are: ['11 7 / 97MX - polyethylene, polypropylene, ethylene / propylene copolymers, ethylene / butene copolymers, all these products are grafted with maleic anhydride or with glycidyl methacrylate, - ethylene / (meth) acrylate / anhydride copolymers maleic, maleic anhydride is grafted or copolymerized, - ethylene / vinyl acetate / maleic anhydride copolymers, maleic anhydride is grafted or copolymerized, - the two previous copolymers in which the maleic anhydride is replaced by glycidyl methacrylate, - copolymers of ethylene / (meth) acrylic acid and, optionally, salts thereof. The alkyl (meth) acrylates can be, for example, methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, methyl or ethyl methacrylate. The adhesive is preferably a copolymer of ethylene / alkyl (meth) acrylate / maleic anhydride. According to a specific form of the invention, the amount of alkyl (meth) acrylate can be up to 45% by weight of the copolymer and, typically, from 5 to 40%. Maleic anhydride is present in E'14 / 7 / 97MX amounts that can be up to 10% by weight and usually from 0.2 to 5%. The alkyl (meth) acrylate is preferably methyl, ethyl or n-butyl acrylate. The adhesive may comprise inorganic fillers, such as talc, CaCO3, etc. The amount of inorganic fillers may be up to 10% of the amount of the adhesive. According to another form of the invention, the metal surface coated according to the method of the invention also comprises at least one epoxy resin between the metal surface and the adhesive. Thus, in accordance with this specific form, the coated surface successively comprises the metal surface, at least one epoxy resin cap, at least one layer of adhesive and at least one layer of thermoplastic polymer. The principle of epoxy resins is described, for example, in Encyclopedia of Chemical Technology Vol. 9, Kirk-Othmer pages 267-289 of the 3rd edition. These resins are usually polyglycidyl ethers of a polyphenol. The following are used, for example: - the condensation products of bisphenol A and epichlorohydrin; EU437 / 97MX - epoxy-cresol novolac resins (ECN); - epoxy-phenol novolaks; - resins derived from bisphenol F; - derivatives of polynuclear phenols and glycidyl ether; - cycloaliphatic resins - resins derived from aromatic amines, for example:. tetraglycidylmethylenedianiline derivatives • triglycidyl-p-aminophenol derivatives • triazine derivatives such as for example triglycidyl isocyanurate. - Resins derived from hydantoin. The resins used in the present invention are preferably two-component systems that can be cross-linked at room temperature. The crosslinking can be carried out, for example, with amines, for example dimethylethanolamine and methylenedianiline, or amides, for example dicyandiamide or alternatively phenolic resins. These resins may comprise additives such as silicones, pigments such as titanium dioxide, iron oxides, carbon black, fillers such as calcium carbonate, talc or mica. The gelling time advantageously is between 20 and 30 minutes. P14 Í7 / 97MX The gel time is defined by the AFNOR NFA 49-706 standard. It refers to the time required to effect a rapid increase in viscosity at a certain temperature. It is advantageous to use an epoxy resin in liquid form. The catalyst (for crosslinking) is added thereto. The thickness of the optional epoxy resin layer can be between 20 and 400 μm and, preferably, between 50 and 150 μm. The thickness of the adhesive layer can be between 100 and 500 μm, preferably between 200 and 350 μm. The thickness of the thermoplastic polymer layer can be between 0.5 and 5 mm and, preferably, between 1.5 and 3 mm. The present invention also relates to a process for the manufacture of these coated surfaces. The metal surface must first be degreased and / or blast cleaned with grit or sand. The optional epoxy resin is deposited in liquid form on the metal surface. After approximately 20 to 30 minutes, ie at the end of the gel time, the tube is heated and the adhesive is then deposited by stratification or lamination. E'1 37 / 97HX The thermoplastic polymer is then deposited in the same way. As regards the outer surface of metal tubes, the process is carried out in the same way for the epoxy resin and the adhesive and, subsequently, it is extruded through an annular die arranged or arranged concentrically around the tube. The adhesive can also be extruded through a flat die that produces a continuous strip that is wound around the tube, for example, by rotating the tube on itself. The thermoplastic polymer is deposited in the same way.

Examples 1 to 3 These examples relate to the coating of cast iron pipes with an outer diameter of 118 mm and a thickness of 8 mm, of the following type: cast iron / adhesive / LDPE l 250 to 300 μm thickness 2.5 mm LDPE 1 denotes a low density polyethylene with a flow index (MFI) of 0.2 with a charge of carbon black (1 002 CJ black by Elf Atochem) The adhesives have the following properties: P1437 / 97MX Orevac 1 denotes an E / VA / GMA copolymer containing 6% GA (VA denotes vinyl acetate and GMA denotes glycidyl methacrylate) Lotader 1 denotes an ethylene / ethyl acrylate / maleic anhydride copolymer containing 17% by weight of acrylate and 3% by weight of MAH. Lotader 2 denotes an ethylene / ethyl acrylate / maleic anhydride copolymer containing 9% by weight of acrylate and 3% by weight of MAH. The tube that was not cleaned with shot blast is heated up to 60 ° C. The adhesive is deposited on the tube by extrusion at 230 ° C (melting temperature) and then covered with LDPE 1 by extrusion at 220 ° C (melting temperature) The tube is then cooled with water for 3 minutes. 1'1 Í // 9 / MX The results are given below in Table 1: Example 4 A cast iron tube is coated as follows cast iron / epoxy / Lotader l / LDPE adhesive l e = 70 μm, 250 to 300 μm / 2.5 mm Application conditions Cleaning the tube with shot blast (granularity Rz = 70 μm) Liquid Epoxy Resin Liquid Epoxy Resin from Raychem S1301 (component A) Catalyst (component B) Mixture: component A / component B A is a mixture of 4-glycidyloxy-N, N-diglycidylaniline and bisphenol A. B is a cycloaliphatic amine.

L 14? // '«f! I; The application of the mixture to the tube is with a brush.

Crosslinking: for 30 min. at 23 ° C The process is then carried out according to the previous examples. - tube heating at 60 ° C. - extrusion of the adhesive and after the LDPE: adhesive: melting temperature = 230 ° C LDPE: melting temperature = 220 ° C Cooling of the tube coated with water for 3 min. Adhesion measurement: 400 N / 5 cm at 23 ° C 75 N / 5 cm at 50 ° C (the measurement was made on a 50 mm wide strip) 97MX

Claims (8)

1. NOVELTY OF THE INVENTION Having described the present invention, it is considered as a novelty and, therefore, the content of the following CLAIMS is claimed as property: 1. A metallic surface covered with a thermoplastic polymer and comprising at least one adhesive placed between the metal surface and the thermoplastic polymer, the adhesive has a Vicat point less than or at most substantially equal to the possible heating temperature of the metal surface. The object according to claim 1, wherein the thermoplastic polymer in advantageous form is polyethylene or polypropylene. 3. The object according to claim 1 or 2, wherein the adhesive is a hot melt adhesive. The object according to claim 1 or 2, wherein the adhesive is a polymer to which a functional group was provided by grafting or copolymerization with a monomer selected from: (i) unsaturated carboxylic acids, (ii) carboxylic acid anhydrides unsaturated, (iii) derivatives of these acids or anhydrides or (iv) unsaturated epoxides. 5. The object according to claim 4, in ['1437 / 97MX where the adhesive is a copolymer: - of ethylene - optionally of one or more monomers selected from: • esters of unsaturated carboxylic acid; • vinyl esters of saturated carboxylic acids; • alpha-olefins - of the copolymerized functional or grafted monomer. The object according to any of the preceding claims, comprising at least one epoxy resin between the metal surface and the adhesive. The object according to claim 6, wherein the epoxy resin has a gel time at room temperature of about 20 to 30 minutes. The object according to any of the preceding claims, wherein the metal surface is the outer surface of a tube. F'l 437 / 97MX