WO1993006179A1

WO1993006179A1 - Aqueous composition and uses thereof

Info

Publication number: WO1993006179A1
Application number: PCT/EP1992/002186
Authority: WO
Inventors: Neil Clarke; Stephen George Grundy
Original assignee: Laporte Industries Limited
Priority date: 1991-09-25
Filing date: 1992-09-21
Publication date: 1993-04-01
Also published as: GB9120441D0; AU2598792A; ZA927310B

Abstract

An aqueous composition, comprising a film-forming polymer and a non-ionic surfactant in an excessive amount, is useful in reducing long term deterioration of metal surfaces, particularly the exposed surfaces of zinc galvanised steel panels or sheets.

Description

Aqueous composition and uses thereof

This invention concerns a composition for coating metal surfaces and to the use 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 poiyacrylic 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 is 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 invention to provide a composition for coating or treating zinc- galvanised metal surfaces which does not strip zinc from the metal during coating or treating in a dip bath.

According to the present invention it has been found that satisfactory 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 a stabilised aqueous solution, emulsion or dispersion of an organic film-forming polymer and an excessive amount of one or more non- ionic surfactants. The preferred pH of the composition is at least 3, preferably from 3 to 7, yet more preferrably from 4 to 6, though it will be understood that the maximum pH is determined by the pH at which the film-forming polymer and/or surfactant become unstable in 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 preferred 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. Furthermore, because the compositions of the present invention comprise no aluminium-zirconate complexes, the cost of the coating composition is greatly reduced in comparison to compositions containing such complexes.

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, poiyacrylic 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 film-forming polymer may be present in greater than 2%, for example from 2% to 20%, by weight of polymer solids based on the weight of the total aqueous composition.

The non-ionic surfactant is present in an excessive amount, by which is meant an amount of more than that amount normally considered appropriate for the film-forming polymer. 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 the 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 preferred surfactants are selected from the group consisting of ethylene oxide/propylene oxide block copolymers and phenol/ethylene oxide condensates. For example, 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, which are most 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 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. 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.

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.

The invention will now be illustrated by reference to the following Examples and the drawing 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. It has been surprisingly found that metal surfaces coated with the composition of the present invention give as much protection to the surface against white rust as surfaces coated inaccordance with the teachings of EP-A-0356855.

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 Ig of Tego Foamex 1488 commercial defoamer. Under stirring, lOOg Neocryl XK-69 commercial film-forming polymer (available from ICI)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 was 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 tested with the following results:

Test Untreated Treated

I II I II

(l)Humidity <24 <24 >450 >450 100% RH § 35C = relative humidity

Claims

1. An aqueous composition for coating metal, eg zinc, copper,

5 steel or aluminium, surfaces comprising a film-forming polymer and a nonionic surfactant characterised in that the amount of non-ionic surfactant in the composition is excessive for the amount of polymer solids of the film-forming polymer in the composition.

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2. A composition as claimed in claim 1 wherein the composition has a pH of at least 3, preferably a pH from 3 to 7, and more preferably a pH from 4 to 6.

153. A composition as claimed in any one of the preceding claims, wherein the film-forming polymer is present in an amount of from 2 to 20 % by weight polymer solids of the total composition.

4. A composition as claimed in any one of the preceding claims , 20 wherein the film-forming polymer is selected from the group consisting of vinyl polymers or copolymers, (meth)acrylic polymers or copolymers, (meth)aerylate polymers or copolymers, and mixtures thereof.

255. A composition as claimed in any one of the preceding claims, wherein the non-ionic surfactant is present in an amount of from more than 2% to 8.5 % by weight, more preferably 2.5% to 6%, based on the weight of polymer solids of the film-forming polymer.

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6. Use of a composition as claimed in any one of claims 1 to 5 in or as a dip tank fluid for preventing corrosion of metal surf ces.

357. Use of a composition as claimed in any one of claims 1 to 5 in or as a metal primer.

6. A dip tank fluid, suitable for preventing corrosion of zinc galvanised steel, comprising an aqueous composition, each litre of composition comprising 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.

7. 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 5.

8. An aluminium article, e.g. panel, wire, tube, or plate, coated with a composition as claimed in any one of claims 1 to 5.

9. A metal primer comprising a composition as claimed in any one of claims 1 to 5.

10. A composition or use of a composition subεantially as hereinbefore defined with reference to the examples.