COATING COMPOSITION AND PROCESS

Abstract: An aqueous composition, comprising an aluminozirconate complex and a film-forming polymer and having a pH of at least 3, is useful in reducing long term deterioration of metal surfaces, particularly the exposed surfaces of zinc galvanised steel panels or sheets.

Description: Coating composition and process This invention concerns a composition for coating metal surfaces and to a process for the manufacture of such a composition. in the manufacture of zinc-, zinc alloy-, aluminium- or other metal-coated metal articles or sheet, or articles or sheet of aluminium, aluminium alloys, copper, copper alloys, steel or of other metals or alloys, it is desirable to apply one or more protective coatings to the surface with a view to alleviating the problems of deterioration of the surface in storage and/or of the provision of an effective base for later painting, varnishing, priming, enamelling or like operations. It is to these problems that the invention particularly relates. A zinc-coated steel surface, for example, has a tendency, if untreated, to develop a white coloured powdery deposit in storage, so-called "white rust", which detracts from the appearance of the surface and possibly adversely affects the key of paint and the like onto the surface. European Patent Specification No. 356855 relates to the problem outlined above. That specification refers to the established usage of chromium compounds to achieve the inhibition of corrosion of aluminium and zinc, and cites the considerable problems of effluent monitoring and disposal and the need to take precautions to ensure the protection of plant operatives which arises from the extremely toxic nature of the chromium compounds. The specification teaches that certain aluminium-zirconium complexes may be used in place of the chromium compounds. The approach disclosed in European Patent Specification No. 356855 derived from the earlier teachings in United States Patent No. 4650526 which utilised similar aluminium- zirconium complexes to treat metal surfaces which had already been subjected to a phosphating treatment to improve corrosion resistance, a purpose of the aluminium-zirconium treatment being to improve the adhesion of later siccative organic coatings to the phosphate-treated surface. The United States patent teaches the use of aqueous solutions containing 0.005 to 5% by volume of the commercial aluminium-zirconium complex product. In many instances the performance of the phosphated, aluminium-zirconium complex- treated metal surfaces were found to be inferior to that of chromated metal surfaces in respect of corrosion prevention and adhesion of alkyd paint films. In order to improve the performance of aluminium- zirconium complex-treated metal surfaces European Patent Specification No. 356855 teaches the coating of the complex- treated surface, after rinsing and drying, with an aqueous solution, emulsion or dispersion of a film-forming agent, such as polyacrylic acid. The aluminium-zirconium complex is used at concentrations of 0.1% or 1.0% by volume of the commercial form, which contains 20-24% wt of the complex, and the organic film- forming composition in 0.5 to 1 g/1. It has been found, however, that the process described in the European patent specification may not provide adequate, long-term resistance to surface deterioration since the zircoaluminate coating tends to shrink on drying, before the film-forming agent is applied, leaving regions of the metal surface effectively untreated with complex. It an object of the present invention to provide a non- chromate composition which is suitable for coating or treating metal surfaces, particularly galvanised metal surfaces, to prevent or retard corrosion. It is a further object of the present invention to provide a composition for coating zinc- galvanised metal surfaces which does not strip zinc from the metal during coating or treating in a dip bath. It is yet a further object of the present invention to provide a coating composition which does not suffer the shrinkage problems associated with prior art compositions. According to the present invention it has been found that excellent corrosion prevention and adhesion properties may be obtained on the aforesaid metals, for example on phosphated or non-phosphated surfaces of zinc-, zinc alloy- or aluminium-coated metals, using a one-coat non-rinse process, by the use of a treating composition comprising an aqueous solution, emulsion or dispersion of an organic film- forming polymer and one or more aluminium-zirconium complexes characterised in that the composition has a pH of at least 3. The preferred pH of the composition is from 3 to 7, more preferrably from 4 to 6, though it will be understood that the maximum pH is determined by the pH at which the aluminozirconate precipitates out from the solution, usually at about pH 7 to 8. Galvanised steel panels coated with the compositions of the present invention demonstrate a long term resistance to surface deterioration commensurate with known chromium-based coatings. Further, the compositions of the present invention tend not to suffer the "shrinkage" problems associated with known aluminozirconate coatings. Moreover, because the compositions of the present invention are less acidic than any of the known coatings, there is less of a tendency for zinc galvanised to steel to be stripped off the steel in the dip tank containing the composition, thereby reducing the rate at which the dip tank fluid becomes contaminated with zinc ions and so substantially extending the working life time of the dip tank fluid (In comparison with the working life time of known dip tank fluids, either chromium-based compositions or luminozirconate-based compositions, such as the composition disclosed in UK Patent Application No 9024474.0, the working life time of a dip tank fluid based on the composition of the present invention is expected to be at least three times longer). Aluminium-zirconium complexes which may be utilised according to the invention are, for example, the reaction product of a chelated aluminium moiety, a zirconium oxyhalide and an organofuctional ligand. The organofunctional ligand is complexed with and chemically bound to the chelated aluminium moiety and the zirconium moiety. The chelate-stabilised aluminium moiety has the general formula: Al 2 (OR 1 0) a A b B c (I) wherein A and B are halo-, preferably chloro-, or hydroxy-, "a" is a numerical value of from 0.05 to 2, preferably from 0.1 to 1, "b" is a numerical value of from 0.05 to 5.5, preferably from 1 to 5, "c" is a numerical value of from 0.05 to 5.5, preferably from 1 to 5, provided that 2a + b + c = 6, and -OR^O- is either an alpha-beta or alpha-gamma glycol group in which R* is an alkyl, alkenyl, or alkynyl group having from 1 to 6 carbon atoms, preferably an alkyl group and preferably having 2 or 3 carbon atoms; or an lpha-hydroxy carboxylic acid residue of the formula -OCH(R3)-COOH, where R^ is H- or an alkyl- group having from 1 to 4 carbon atoms, preferably from 2 to 3 carbon atoms. The zirconium oxyhalide, preferably an oxychloride, has the general formula: ZrA d B e (II) wherein A and B are as defined for (I) above, preferably one of A and B is chloro- and the other of A and B is hydroxy-, and "d" and "e" independantly have numerical values of from 0.05 to 4, provided that d + e = 4. The organofunctional ligand (LIG) is derived from one or more of the following: 1) an alkyl-, alkenyl-, alkynyl-, aryl- or aralkyl-carboxylic acid having from 2 to 36 carbon atoms, preferably from 2 to 18 carbon atoms, more preferably from 4 to 18 carbon atoms and even more preferably from 2 to 6 carbon atoms; 2) an aminofunctional carboxylic acid having from 2 to 36 carbon atoms, preferably from 2 to 18 carbon atoms, more preferably from 4 to 18 carbon atoms and more preferably from 2 to 6 carbon atoms; 3) a dibasic carboxylic acid having from 2 to 18 carbon atoms, preferably from 2 to 6 carbon atoms, and wherein both carboxy groups are preferably terminal; 4) acid anhydrides of dibasic acids having from 2 to 18 carbon atoms, preferably from 2 to 6 carbon atoms; 5) a ercapto functional carboxylic acid having from 2 to 18 carbon atoms, preferably 2 to 6 carbon atoms; and 6) an epoxy functional carboxylic acid having from 2 to 18 carbon atoms, preferably from 2 to 6 carbon atoms. The aluminium-zirconium complex may be empirically represented by the general formula: [Al 2 (ORlθ) a A b B c ] x [LIG] y [ZrA d B c ] 2 wherein A and B are as above-defined, and a,b,c,d and e are as defined above, except that, in order to form the bonds depicted, the substituents attached to the metal groups are appropriately reduced, i.e. 2a + b + c = 4 (2a + b + c = 5 when the aluminium moiety is a terminal group), and d + e = 2 (d + e = 3 when the zirconium moiety is a terminal group). When the aluminium moiety or the zirconium moiety terminates the above formula, one of the A or B groups may be replaced by a (Cι-C5)alkoxy- group, x, y and z are independantly at least 1 and may vary from 1 to 100 or more. The molar ratio of x to z may vary from 1.5 to 10 with the preferred ratio being from 3 to 6 and the ratio of (y/(2x + z)) may vary from 0.05 to 3, preferably from 0.05 to 2.0, and more preferably from 0.1 to 0.5. Methods for the preparation of the above described complexes are described in United States Patent Specifications No. 4539048 and 4539049, the disclosures of which are incorporated herein by reference. Very suitably the aluminium-zirconium complexes utilised according to this invention may be those available under the Trade Name Manchem as about 20% to 25% vol solutions in polar solvents such as the lower alcohols, glycols, or glycol ethers of which suitable products are, for example,those designated APG-X, in which the carboxylic acid component is NI_2-(CH2)2- c 0 OH / °r CPG or CPM, in which the carboxylic acid components are HOOC-(CH2)4~COOH. The organic film-forming polymer may be any polymer which is available as and curable in an aqueous solution dispersion or emulsion. Preferably, however, the film- forming polymer is selected from suitable vinyl polymers or copolymers, for example vinyl-acrylic copolymers, polyacrylic and polymethacrylic acids, and polyacrylates and polymethacrylates. The most preferred film-forming polymers are emulsions of acrylic coplymers such as those emulsions available under the Trade Name Neocryl (from ICI). Suitably such polymers may themselves contain corrosion inhibitors. A suitable solids content for the organic film-forming polymer is from about 30% to 50%, or even up to 75%, by weight. The aluminium-zirconium complex may be present in the composition of the present invention in an amount of from 0.2% to 20% by weight based on the weight of the total aqueous composition although particularly successful results have been achieved using at least 5% by weight, for example 5 to 20% by weight, on the same basis. The film-forming polymer may be present in greater than 2%, for example from 2% to 20%, by weight of polymer solids on the same basis. A solution of the aluminium-zirconium compound in an organic polar water-miscible solvent may be mixed with the aqueous solution, dispersion, or emulsion of the film- forming polymer, preferably to give the above stated solids concentrations and the resulting product may therefore have a substantial content of said organic, polar solvent . In a preferred embodiment of the present invention, the composition additionally comprises a non-ionic surfactant. The non-ionic surfactant is preferably present in an amount normally considered excessive for the film-forming polymer alone. In commercially available copolymer emulsions the level of addition of a non-ionic surfactant is typically no more than 2 % by weight on the weight of latex solids, whereas in the compositions of the present invention the surfactant is preferably present in an amount of from more than 2% up to 8.5 wt%, more preferably from 3 to 8 wt %, and yet more preferrably from 3.5 to 5 wt%, based on the weight of polymer solids of the film forming polymer. On the weight of the composition as a whole, this is equivalent to about 0.02 to 1.275 wt%, and more preferrably 0.035 to 0.75 wt%. Whilst any suitable non-ionic surfactant may be employed in the compositions of the present invention, the non-ionic surfactants Synperonic PE/F87 (ICI) , a block copolymer based on ethylene oxide/propylene oxide, or Synperonic NP30 (ICI), a nonyl phenol 30 mole ethylene oxide condensate, are preferred. A small quantity of a defoamer is also preferably included. A typical quantity of about 0.01% to 0.5% by weight of the total composition may be used. A typical defoamer is Tego Foamex 1488 (an emulsion of organo-modified polysiloxanes available from Th. Goldschmidt Ltd. ) . When prepared for use in a dip tank, each litre of a preferred composition of the present invention will typically comprise from 20 to 200g, preferably 30 to 150g, of aluminium- zirconium complex, from 1 to lOOg (polymer solids), preferably from 30 to 95g, of film-forming polymer and from 0.25 to lOg, preferably from 0.75 to 5g, nonionic surfactant. In another aspect, the present invention provides a method of preparation of a composition comprising an aqueous solution, emulsion or dispersion of an organic film-forming polymer and an aluminium-zirconium complex , which composition has a pH of from 3 to 8, preferably of from 4 to 7 , characterised in that the method comprises: (1) preparing in a first vessel an aqueous composition consisting of 4 to 40% by weight of polymer solids; (2) preparing in a second vessel an aqueous composition consisting of 0.4 to 40% by weight of said aluminium-zirconium complex; and (3) mixing simultaneously into a third vessel in substantially equal proportions the aqueous composition prepared in (1) above with the aqueous composition prepared in (2) above. Preferrably, the final composition comprises a non-ionic surfactant which is added in appropriate amounts to any one of the first and/or second or third vessels. Most preferrably, the non-ionic surfactant is added in appropriate amounts to both the first and second vessels. The composition according to the present invention may be applied to the metal surfaces to be treated for example to a metal coil after hot dip or electrogalvanising or aluminium coating and after the temperature of the metal has fallen to below about 85°C preferably to below 80°C. The method of application may be by spray or by immersion with surplus liquid being removed, suitably by passing the metal between rollers or by the use of an air-knife. The metal may then be air or oven dried, for example at from 65°C to 85°C.The thickness of the coating is preferably up to about 50 microns, for example 1 to 10 microns which may be controlled by adjusting the solids concentration of the treating composition appropriately. The coatings attained by the use of the present invention adhere strongly to the metal surface to which they are applied, help to retain the metal surface in bright, uncorroded form, and give a good key to subsequent surface coatings. Accordingly, the compositions of the present invention may suitably be used in or as coatings, such as primers or finishes. These properties may be tested by the following tests. a) Humidity test (1) BS.3900:Part F2:1973(1983) . -resistance to humidity-cyclic condensation. (2) BS.3900:Part F9:1982(1985) -resistance to humidity-continuous condensation. b) Stack test (Butler Building Test). Stacking under artificially humid conditions provided by interleaved wetted filter paper for a number of days followed by a determination of the proportion of the area covered by white rust. c) Adhesion test. BS.3900:Part E6:1974. Cross hatch adhesion test. The invention will now be illustrated by reference to the following Examples and the drawings in which: FIG 1 is a photograph of a galvanised steel panel treated in accordance with the process of EP-A-0356855 and illustrates the problems of "shrinkage" where the metal surface has dark and light regions indicating where the metal surface is coated with zircoaluminate composition or uncoated respectively; and FIG 2 is a photograph of a galvanised steel panel treated in accordance with the process of the present invention and illustrating a dark, even coating of zircoaluminate composition over the metal surface . Example I A composition in accordance with the present invention was prepared as follows: An aqueous solution comprising 2.5g Synperonic NP30 commercial surfactant (available from ICI) was prepared by dissolving the surfactant in 846.5g of demineralised (DM) water at 50°C in a scrupulously clean vessel. To the solution was added lg of Tego Foa ex commercial defoamer. The solution was divided equally into two scrupulously clean vessels. To one vessel was added, under stirring, 50g Manchem APG-X commercial a ino zircoaluminate solution (available from Rhone-Poulenc) and to the other vessel, also under stirring, lOOg Neocryl XK-69 commercial film-forming polymer (available from ICI). The compositions in the two vessels were then discharged into another vessel, where the two compositions were blended together, with care being taken never to allow unequal amounts of the two compositions to be present in the blending vessel at the same time, to form a composition of the present invention. Example II Another composition of the present ivention was prepared by following the process described in Example I, but this time 796.5g of DM water and lOOg Manchem APG-X were used. Galvanised steel panels were treated with the compositions formed in Examples I and II. The compositions were applied at 5% v/v concentration at 20°c by roller application to give a film thickness of 5+/-2 microns after drying. The panels were (a) left unpainted or were coated with (b) a polyester or (c) an alkyd paint. The panels were tested with the following results: Untreated Treated I II I II a)(l) Humidity <24 <24 >500 >500 100% RH § 35 C b)Stack <72 <72 >450 >450 test c)Cross Hatch n/a n/a <5% <5% Adhesion Test RH = relative humidity

Claims: Claims 1. An aqueous composition for coating metal, eg zinc, copper, steel or aluminium, surfaces comprising: l)an aluminium-zirconium complex which is the reaction product of a chelated aluminium moiety, a zirconium oxyhalide and an organofuctional ligand, the organofunctional ligand being complexed with and chemically bound to the chelated aluminium moiety and the zirconium moiety, the aluminium moiety having the general formula: Al 2 (0R 1 0) a A b B c (I) wherein A and B are halo-, preferably chloro-, or hydroxy-, "a" is a numerical value of from 0.05 to 2, preferably from 0.1 to 1, "b" is a numerical value of from 0.05 to 5.5, preferably from 1 to 5, "c" is a numerical value of from 0.05 to 5.5, preferably from 1 to 5, provided that 2a + b + c = 6, and -OR 1 ©- is either an alpha-beta or alpha-gamma glycol group in which R 1 is an alkyl, alkenyl, or alkynyl group having from 1 to 6 carbon atoms, preferably an alkyl group and preferably having 2 or 3 carbon atoms; or an alpha-hydroxy carboxylic acid residue of the formula -0CH(R3)-C00H, where R3 is H- or an alkyl- group having from 1 to 4 carbon atoms, preferably from 2 to 3 carbon atoms; the zirconium oxyhalide, preferably an oxychloride, having the general formula: ZrA d B e (II) wherein A and B are as defined for (I) above, preferably one of A and B is chloro- and the other of A and B is hydroxy-, and "d" and "e" independently have numerical values of from 0.05 to 4, provided that d + e = 4; and the organofunctional ligand (LIG) being one or more of the following: (1) an alkyl-, alkenyl-, alkynyl-, aryl- or aralkyl- carboxylic acid having from 2 to 36 carbon atoms, preferably from 2 to 18 carbon atoms, more preferably from 4 to 18 carbon atoms and even more preferably from 2 to 6 carbon atoms; (2) an aminofunctional carboxylic acid having from 2 to 36 carbon atoms, preferably from 2 to 18 carbon atoms, more preferably from 4 to 18 carbon atoms and more preferably from 2 to 6 carbon atoms; (3) a dibasic carboxylic acid having from 2 to 18 carbon atoms, preferably from 2 to 6 carbon atoms, and wherein both carboxy groups are preferably terminal; (4) acid anhydrides of dibasic acids having from 2 to 18 carbon atoms, preferably from 2 to 6 carbon atoms; (5) a mercapto functional carboxylic acid having from 2 to 18 carbon atoms, preferably 2 to 6 carbon atoms; and (6) an epoxy functional carboxylic acid having from 2 to 18 carbon atoms, preferably from 2 to 6 carbon atoms; and 2) a film-forming polymer; characterised in that the composition has a pH of at least 3. 2. A composition as claimed in claim 1 wherein the composition has a pH of from 3 to 7, preferably a pH from 4 to 6. 3. A composition as claimed in Claim 1 or Claim 2, wherein component 1) is present in the composition in an amount of from 0.2 to 20% by weight of the total composition. 4. A composition as claimed in any one of the preceding claims, wherein component 2 ) is present in an amount of from 2 to 20 % by weight polymer solids of the total composition. 5. A composition as claimed in any one of the preceding claims , wherein component 2 ) is selected from the group consisting of vinyl polymers or copolymers , (meth) acrylic polymers or copolymers , (meth) aery late polymers or copolymers , and mixtures thereof . 6. A composition as claimed in any one of the preceding claims , wherein the composition additionally comprises a non-ionic surfactant . 7 . A composition as claimed in claim 6 , wherein the non-ionic surfactant is present in an amount of from 2 to 8.5 % by weight based on the weight of polymer solids of the film-forming polymer. 8. Use of a composition as claimed in any one of claims 1 to 7 in or as a dip tank fluid for preventing corrosion of metal surfaces. 9. Use of a composition as claimed in any one of claims 1 to 7 in or as a metal primer. 10. A dip tank fluid, suitable for preventing corrosion of zinc galvanised steel, comprising an aqueous composition, each litre of composition comprising from 20 to 200g, preferably 30 to 150g, of an aluminium-zirconium complex as defined in claim 1, from 1 to lOOg (polymer solids), preferably from 30 to 95g, of a film- forming polymer and from 0.25 to lOg, preferably from 0.75 to 5g, of a non-ionic surfactant. 11. A zinc galvanised steel article, e.g. panel, wire, tube, or plate, coated with a composition as claimed in any one of claims 1 to 7. 12. An aluminium article, e.g. panel, wire, tube, or plate, coated with a composition as claimed in any one of claims 1 to 7. 13. A method for the preparation of a composition comprising an aqueous solution, emulsion or dispersion of an organic film- forming polymer and an aluminium-zirconium complex as defined in claim 1, which composition has a pH of from 3 to 8, preferably of from 4 to 7, characterised in that the method comprises: (1) preparing in a first vessel an aqueous composition consisting of 4 to 40% by weight of polymer solids of film- forming polymer; (2) preparing in a second vessel an aqueous composition consisting of 0.4 to 40% by weight of said aluminium-zirconium complex; and (3) mixing simultaneously into a third vessel in substantially equal proportions the aqueous composition prepared in (1) above with the aqueous composition prepared in (2) above. 14. A method as claimed in Claim 13, wherein a non-ionic surfactant is added to any one of the first and/or second or third vessels. 15. A method as claimed in Claim 14, wherein the non-ionic surfactant is added to both the first and second vessels. 16. A metal primer comprising a composition as claimed in any one of claims 1 to 7. 17. A composition or method for preparing a composition or use of a composition subsantially as hereinbefore defined with reference to the examples.

Inventors: CLARKE NEIL, GRUNDY STEPHEN GEORGE, CLARKE, NEIL, GRUNDY, STEPHEN, GEORGE
Applicants: LAPORTE INDUSTRIES LTD, LAPORTE INDUSTRIES LIMITED
Application year: 1992
Main classification: C09D5
IPC codes: C09D5, C23C22