WO2010137001A2

WO2010137001A2 - Composition, process and plant for the surface treatment of rolled metal

Info

Publication number: WO2010137001A2
Application number: PCT/IB2010/052395
Authority: WO
Inventors: Luciano Scarpellini
Original assignee: Luciano Scarpellini
Priority date: 2009-05-28
Filing date: 2010-05-28
Publication date: 2010-12-02
Also published as: WO2010137001A3; ITBO20090348A1

Abstract

A treatment composition for the surface treatment of rolled metal for use in particular in a coil coating or pre-coating process and plant, comprising water as the solvent means and at least one resin binder in the solvent means designed to provide when in use a surface film structure covering a surface of the rolled metal. The treatment composition further comprises means passivating the surface of the rolled metal in the solvent medium. A plant comprises a first station for application of the composition to one or both sides of a strip of rolled metal, followed by a stove to dry the composition and another station for the application of a finishing layer to one side of a strip. The invention makes it possible to eliminate the various stages of surface conversion and passivation of the metal which in known processes precede application of the primer to the surface of the rolled metal. The composition is also useful as a single product for use in providing surface finishes similar to back coating.

Description

Composition, process and plant for the surface treatment of rolled metal

This invention relates to a composition for the surface treatment of rolled metal.

The invention also relates to a process and plant for the surface treatment of rolled metal using the aforesaid composition.

The process known as coil coating, or pre-coating for the painting of rolled metal, is known. This is based on the simple concept that it is easier, more effective and more economic to degrease, chemically pre-treat and paint a continuous flat surface rather than carry out these operations on irregular shapes. Pre-coated products are presented in the form of rolls or sheets which receive their protective and/or decorative coating before they pass through subsequent stages of production, for example for exterior and interior fittings for the construction market, for the domestic electrical articles manufacturing sector, and the like. Specific reference will be made below to the coil coating or pre-coating process of products supplied in the form of rolls of metal strip, even though the invention should not be understood to be restricted to that scope, and may also find immediate and natural application in processes in which the metal products are in the form of sheets.

In a typical coil coating process a metal strip is caused to pass through a continuous treatment plant and is subjected to the various stages of processing in succession. Typically unwinding or unrolling of the roll of metal strip takes place first, and the strip is then subjected to suitable cleaning, for example acid or alkaline degreasing with possible brushing in between, depending on the substrate, in order to remove any oxides present, followed by chemical conversion of the surface of the metal strip, for example cobalt nitrate plating. The strip is then rinsed, and is then passivated. After drying the strip passes through a painting head which applies a first coat of primer or base paint on one or more sides of the strip. The strip then passes through a first stove which polymerises the primer, and is then cooled, first with air and then with water. The strip then passes through a second painting head which applies a finishing or top coat on one or both sides of the strip, which is then again passed through the stove to polymerise the paint film, and then cooled again as before, before being rewound into a coil. In some applications one of the two sides of the strip does not need a high quality finish, as a result of which a coat of so-called back coating is applied to it after passivation, that is a paint product having poorer characteristics and a lower price than the top paint of higher quality applied to the other side of the strip.

Chemical conversion of the surface of the metal strip is designed to avoid corrosion of the metal, against which painting alone is generally insufficient, in that the paint film is normally permeable to air and moisture, and therefore oxygen, which is responsible for oxidation and therefore corrosion of the metal. Chemical conversion or pre-treatment of the surface of the rolled metal prevents corrosion by depositing particular chemical compounds on the surface of the metal . These chemical compounds which form part of the conversion layer are generally based on heavy metal oxides or phosphates and are therefore inert and not very reactive to air and oxygen, thus avoiding oxidation and the formation of rust on the metal surface.

One example of surface conversion which is particularly suitable and frequently used for zinc-coated steel surfaces is cobalt nitrate plating; salts based on cobalt are deposited on the surface of the metal strip. These salts are soluble in the starting formulation, but under particular temperature, pH and concentration conditions become insoluble and precipitate out on the zinc-coated steel strip, anchoring themselves to its surface.

Between the chemical conversion stage and the passivation stage the metal strip is subjected to washing, typically carried out with clean water, better if demineralised. The purpose of this washing is to eliminate chemical residues present on the surface of the strip in order to prevent contamination of the subsequent treatment solutions.

The subsequent stage of passivation is designed to seal the conversion layer mentioned above, and to appreciably increase corrosion resistance. During this stage acid products containing chromium or based on zirconium, which are typically applied by spraying onto the surface of the metal strip, are typically used in this stage.

The painting heads mentioned above comprise a set of rollers of various kinds and number, arranged in various ways, which typically include at least one backing roller on which the strip being painted runs, at least one application roller which transfers the paint product to the surface of the strip, and at least one dipping roller which collects the paint product from a tank of paint to transfer it to the application roller. In some cases, provision is made for at least one gauging roller to control the thickness of the paint product film. It will however be obvious from this brief description that a painting head comprises a particularly important and costly component of the entire coil coating or rolled metal pre-coating plant. The liquid paint products used as primer or as finishing coat in coil coating processes for rolled metals, whether as a top finish or a back coating, have the function of protecting and/or decorating the substrates to which they are applied and have the ability to form a surface covering film or skin, which is generally continuous and adheres to the substrate to which they are applied. Various paint product compositions for metals are known, and these typically comprise at least one resin binder, typically a mixture of polymers with the ability to cross-link, dispersed in a solvent medium of the organic type which allows easy application of the paint to the surface of the rolled metal, and which is then designed to evaporate during the stage in which the painted product passes through the stove. Paint compositions of the known type also often include pigments which are used to provide covering power and/or colour to the film adhering to the surface of the rolled metal. These known compositions often also comprise so-called fillers, that is generally inorganic powders which have no direct influence on the colour but are used to impart particular properties to the paint film, for example passifying properties, to impart structural, anti- corrosion properties and similar characteristics. In addition to this, known paint compositions almost always comprise small quantities of additives having various functions such as improved spreading, scratch resistance, prevention of sedimentation, dispersibility of fillers and pigments, adhesion, etc.

Methods to increase the efficiency and productivity and reduce the cost of coil coating processes of the known type described above have been proposed. One example is provided by the so-called no-rinse cycle, that is one in which there is no rinsing, which makes no provision for rinsing or final passivation of the metal strip after a particular composition has been applied or the surface of the rolled metal has been converted. This composition is applied to the surface of the metal strip and dried in a stove at a temperature of approximately 50-80⁰C, after which the metal strip can be painted directly without the need to proceed with passivating its surface. Despite the fact that this particular no-rinse cycle makes it possible to eliminate the stages of rinsing and passivation which follow surface conversion of the metal strip, it is nevertheless necessary to provide a particular roller application head similar to the painting heads already mentioned for application of the composition to convert the surface of the rolled metal, with a consequent considerable increase in plant costs. Furthermore, the system provides for the use of perfectly flat strips and continuous control of the thickness of the chemical solution applied, so as to keep the quantity of deposit provided by pre-treatment constant at all times. In addition to this it is frequently necessary or in any event desirable that an operator should always be present continuously to check that pre-treatment is proceeding satisfactorily, depending upon the wear on the application rollers, and replacing them when necessary. Finally, the no-rinse cycle requires at least three stages of rinsing after initial degreasing of the metal strip, of which the last is with lightly acidified demineralised water, as well as the drying stove.

The object of this invention is to resolve and overcome the problems in the known art, providing a process for the surface treatment of rolled metal of the coil coating or pre- coating type which is economical, ecological and reliable, as well as being simple and practical to apply, and which provides final results of a quality similar to, if not better than, that of processes of the known type.

US-2009/0101512-A describes a method for providing a multilayer coating film comprising a chemical conversion coating film and an electrodeposition coating film applied to the chemical conversion coating film without the need for intermediate washing. The chemical conversion coating film comprises any one of a long series of metal compounds, and any one of a long list of resin compositions. The various examples of compositions described in this document are however all centred on the use of an epoxy resin, which has particular disadvantages in terms of cross-linking when its use in the coil coating sector is considered. Furthermore, the process illustrated in US-2009/0101512-A cannot be adapted to coil coating because transport of the compounds in passing from the first tank to the second tank would irremediably contaminate the finished product. The electro- deposition process is very slow and its application in the coil coating sector, where the speeds of treating the rolled metal are very high in order to ensure good productivity, would rule out any savings which might be made with the method indicated in the prior document.

WO-2008/022819-A describes a chromium-free anti-corrosion protection composition. The document indicates a very large number of variants which can be obtained by a combination of the components indicated. The composition comprises an organic polymer which can be selected from an extensive group, and may be hardened by any known techniques. Obviously the huge variety of compositions described theoretically will have properties which are very different from each other, and it is effectively impossible that all can have been tested in order to obtain a stable product with repeatable properties and effects. It does however appear that most of the compositions which can be obtained through the teaching of this prior document need further surface treatments, and in particular need to be coated with a back coating product, as is known in the specific coil coating sector. The object of this invention is therefore also that of providing an innovative treatment composition, making a specific selection in comparison with the generic nature of the known formulations, for specific use in a process for the surface treatment of rolled metal of the type mentioned above which can easily be applied using known methods and in particular, but not restricted thereto, using simple spray application techniques, and which allow high productivity.

Another object of the invention is to provide a plant for implementing the abovementioned process, in particular a plant which is very much more economical than known plants, and has no stations for surface conversion and passivation of the rolled metal.

In order to accomplish the abovementioned objects the invention relates to a process of the type mentioned above in which a composition comprising at least one alkyd resin binder in a solvent medium is used, in which such composition also comprises means to passivate the surface of the rolled metal in the solvent means, in particular but not exclusively water. The invention also relates to such a composition in itself, as well as plant for implementing the aforesaid process and application of the composition in a coil coating process. In particular the plant is characterised by the presence of two single working stations applying two respective treatment products, with heating means, in particular a stove, between the only two operating application stations.

This invention has many advantages. To begin with the coil coating process is appreciably simplified, because the composition according to this invention is functionally similar to a primer, although ensuring the anti-corrosive capacity specific to surface conversion treatments. The composition according to this invention may be applied to the rolled metal strip in the same way as a primer and using the same painting heads, so that the stages of surface conversion, in particular cobalt nitrate plating and passivation, as well as all the accessory stages intermediate between these, are completely eliminated from the coil coating process according to this invention. The result is a much simpler, less harmful and faster and economical process. The need to dispose of waste waters and sludges from the cobalt nitrate plating and passivation tanks, as in plant of the known type, is also eliminated, with a consequent improvement in environmental impact.

In a specific variant of this invention the solvent in the surface treatment composition is water, instead of being an organic solvent as in the known art. This being the case, the great advantage for both the environment and for the health of operators deriving from elimination of the need to treat and dispose of the organic solvent and the fumes deriving from its evaporation during the paint drying stage will be immediately obvious. A further advantage of using water as the primary solvent is a reduction in insurance charges because of the non-flammability of the composition.

According to another specific variant of this invention, the resin binding the surface treatment composition is an alkyd resin, preferably of the medium oil or short oil type. These resins are relatively cheap and provide high performance, and make it possible to obtain a stable composition with good surface performance.

According to a further variant of the invention, the passivating medium in the surface treatment composition comprises zirconium fluoride, and in particular, although not exclusively, a fluorine complex or zirconium in a mixture with hydrofluoric acid, especially when the composition comprises water as solvent. Optimum anti-corrosion treatment of the surfaces of the rolled metal strip is obtained with such a composition.

According to a preferred variant of the invention the treatment product also comprises at least one colouring pigment, and more preferably this colouring pigment comprises titanium dioxide TiO₂ in order to impart a white colour to at least one side of the metal strip. Like paint products of the known type, but unlike the products normally used in the pre- treatment of rolled metal in coil coating processes, the composition according to this invention may then comprise one or more additives and/or fillers, such as for example, without this being considered restrictive, a surface tension regulator or anti-foaming additives.

In a specific variant, after the stage of degreasing at least one side of the strip and before the stage of applying a treatment product, the process according to the invention comprises a stage of brushing at least one surface of the strip, and comprises a stage of passing the rolled metal strip through a stove, with subsequent cooling, after the stage of applying a treatment product and before the stage of rewinding the strip.

In the plant according to this invention there is no provision for the costly and complex stages for chemical conversion and passivation of the strip as in plants of the known art. In addition to this it has been surprisingly found that the composition according to this invention may also effectively act as a finishing for one side of the strip where in processes of the known art a back coating product is instead applied. This result makes it possible to further reduce the costs of coating or coil coating metal strips with a single high finish surface. In addition to this it has been surprisingly found that the composition according to this invention comprises a base providing a better grip than known back coating products as regards for example the application of a layer of foam, which is often used for example in industrial and construction industry applications.

Other advantages and characteristics of the present invention will become clear from the following detailed description which is given with reference to the appended drawing which is provided purely by way of non-limiting example, and in which a plant for implementing a coil coating process according to the invention is illustrated.

With reference now to the single appended figure, reference number 1 indicates as a whole a plant for the coil coating or pre-coating of a strip 2 of rolled metal originating in a known way from a roll (not illustrated) which is unwound in a known way. Strip 2 first passes through an entry accumulator 3 which in a known way acts as an accumulation buffer to take up any discontinuities in speed of processing which may occur in the various subsequent stations in plant 1. A typical speed with which strip 2 passes through plant 1 is between approximately 45 and approximately 220 m/minute. Entry accumulator 3 comprises two sets of rollers 30, 31 facing each other, which can move with respect to each other in order to increase or reduce the length of travel of strip 2 within entry accumulator 3. Strip 2 then passes through a cleaning station, for example a degreasing station and possibly a brushing station, and then preferably passes through a second degreasing station 5 and a rinsing station 6.

The purpose of degreasing is to remove all traces of oil, grease, soiling, dirt or residues caused by the previous processing which the rolled metal has undergone. Alkaline solutions of preferably between 10 and 30 g/1 containing surface tension regulators are used at degreasing stations 4 and 5. The degreasing operations are preferably performed by spraying at temperatures of the order of approximately 50- 60⁰C. Any brushing at degreasing and brushing station 4 is carried out mechanically in a known way in order to remove oxides and any metal dust which degreasing alone will not succeed in perfectly removing. At rinsing station 6, which preferably uses clean water, and better demineralised water, residues from the previous degreasing are removed.

Strip 2 which has been degreased and rinsed in this way is caused to pass through a first painting head 7 for application of the treatment composition according to this invention, comprising a solution, preferably in water, of a resin binder, and in particular an alkyd resin, and a passivating agent, preferably a fluorine complex of zirconium in a mixture with hydrofluoric acid, on one or both sides of strip 2. First painting head 7 comprises a backing roller 32, preferably of chrome-plated steel, on which strip 2 runs, and an application roller 33, preferably coated with rubber or similar materials, which transfers the treatment composition to the surface of strip 2. A dipping roller (which cannot be seen in the figure) picks up the treatment composition from a product tank 34 to transfer it to application roller 34. Preferably at least one gauging roller (which cannot be seen in the figure) is provided to control the thickness of the treatment composition film.

After the treatment composition has been applied by first painting head 7, strip 2 passes through a first stove 8 and subsequently through the first cooling stations, which use air 9 and water 10. First stove 8 is of the generally known type and in particular may be preferably of the catenary or flotation type. Evaporation of the solvent in the treatment composition takes place in stove 8. Because this solvent is water in a preferred embodiment of this invention there is no need to provide special means for treatment of the fumes leaving first stove 8. The operating temperature of first stove 8 makes it possible to achieve the polymerisation temperature of the resin binding the treatment composition according to this invention applied by first painting head 7, which is between approximately 140⁰C and approximately 240⁰C. In order to achieve this temperature, the temperature of first stove 8 may be between approximately 150⁰C and approximately 36O⁰C, more preferably between approximately 250⁰C and 350⁰C, depending upon the thickness of strip 2 and its speed within the stove, and therefore the desired productivity of the plant.

After leaving first stove 8 strip 2 is preferably first cooled with forced air for a few seconds in first air cooling station 9 in order to lower its temperature to approximately 100-180⁰C. Strip 2 is then preferably cooled with water for a few seconds at first water cooling station 10 in order to reduce its temperature to approximately 20-30⁰C.

Strip 2 which has been cooled in this way is led through a second painting head 11 for the application of a painting product of a generally known type on one or both sides of strip 2 to provide a surface finish for the rolled metal. The characteristics of second painting head 11 are similar to those of first painting head 7, and in any event are generally known in the sector of coil coating or pre-coating processes for rolled metal. In the frequent situation in which strip 2 does not require a high quality finish on both sides in the final applications for which it is intended, but can have one side of lesser quality, similar to the side on which the paint product known as back coating is applied in known processes, there is then no need to apply any further paint product, the composition according to this invention applied by first painting head 7 mentioned above being sufficient for the purpose.

Strip 2 then passes through a second paint stove 12, similar to first stove 8, and subsequently through second air 13 and water 14 cooling stations similar to first air and water cooling stations, 9, 10. Strip 2 is finally delivered to an exit accumulator 15, which is similar to entry accumulator 3, before being gathered on a winding reel (not shown in the figure) in order to be wound again into a roll for storage, transport and delivery to the plants where the rolled metal which has been pre-coated in this way will subsequently be used.

The treatment composition according to this invention which is to be used in implementing the coil coating process carried out in plant 1 described above comprises a resin binder. Preferably this resin binder is a polymer which is not saponifiable in dispersion, which cross-links through oxidation. The polymer is preferably an alkyd resin in an aqueous dispersion. The composition also comprises a passivating agent in the form of a fluorine complex of zirconium in a mixture with hydrofluoric acid.

Alkyd resins are known in general terms for the production of paints and varnishes. So-called long-oil alkyds, that is containing from 60 to 70% of a drying oil (for example, but not restricted to, linseed oil, wood oil, oiticica oil, fish oil, etc.), medium-oil, that is containing from 40 to 60% of a semi-drying oil (for example, but not restricted to, soya oil, dewatered castor oil, tall oil, etc.), or short oil, that is containing from 30 to 40% of a non-drying and therefore saturated oil (for example, but not restricted to, coconut oil, castor oil, palm oil, etc.) may be used. One advantage of the use of alkyd resins is that these can be produced from recycled materials, for example PET, using techniques which are generally known in the sector. Medium oil and short oil alkyd resins are preferred for preparation of the treatment composition according to this invention.

The treatment composition according to this invention, in a non-restrictive example, preferably comprises from approximately 10 to approximately 45%, more preferably from approximately 20 to approximately 40%, and even more preferably from approximately 25 to approximately 35% of a resin binder, preferably a medium oil (soya) resin binder. The same composition preferably comprises from approximately 10 to approximately 40%, more preferably from approximately 15 to approximately 35%, and even more preferably from approximately 20 to approximately 30% of a pigment (TiO₂) . This composition preferably comprises from approximately 0.1 to approximately 3%, more preferably from approximately 0.2 to approximately 2%, and even more preferably from approximately 0.5 to approximately 1% of a surface tension regulator. This composition preferably comprises from approximately 0.1 to 5%, more preferably from approximately 1 to approximately 3%, and even more preferably from approximately 1.5 to approximately 2.5% of a surfactant. The composition preferably comprises from approximately 0.05 to approximately 5%, more preferably from approximately 0.1 to approximately 1%, and even more preferably from approximately 0.2 to approximately 0.4% of a fluorine complex of zirconium. The composition preferably comprises from approximately 0.1 to approximately 10%, more preferably from approximately 1 to approximately 5%, and even more preferably from approximately 2.5 to approximately 3.5% of butyl glycol. The composition preferably comprises from approximately 0.001 to approximately 0.1%, more preferably from approximately 0.01 to approximately 0.05%, and even more preferably from approximately 0.02 to approximately 0.04% of hydrofluoric acid. The composition preferably comprises from approximately 0.01 to approximately 1%, more preferably from approximately 0.5 to approximately 0.8%, and even more preferably from approximately 0.1 to approximately 0.4% of dimethylethanolamine . The composition also comprises as much water as is necessary.

Colouring pigments may be added to the treatment composition to provide the composition with the ability to colour strip 2, which is useful for reducing the thickness of the film of paint product subsequently applied if the latter does not have good covering power. Colouring pigments are of the generally known type and are compatible with the solvent used. In a preferred variant of the treatment composition, titanium dioxide, as indicated above in the example indicated, which provides a white colour, is used as a colouring pigment .

Additives and/or fillers may be added to the composition in various proportions according to need in order to obtain particular performance from the treatment composition according to this invention. These additives and/or fillers are of the generally known type and may for example comprise, but without restriction, surfactants and anti-foaming additives, amines, anti-oxidants , anti-sedimentation additives, or other additives generally known in the sector or the like. However, the composition according to this invention is selected in such a way as to have a low impact on the environment, and this in particular is ensured both by the fact that it comprises water as a solvent and by the fact that the particular resin used has no need of catalysts or activators or accelerators, usually substances having a high environmental impact, for cross-linking. In the description above, reference has been made to a plant with two painting heads, or more generally two stations for application of the treatment products. Of course a plant constructed according to this invention may also have a larger number of painting heads or application stations for example to ensure a rapid change of finishing painting product. The specific feature of the plant according to this invention is nevertheless that it has only two application stations which are operational at any given time and play an active part in the process of the surface treatment of the rolled metal strip, applying first the composition according to this invention on the two sides of the strip, and then - preferably on only one of the two sides of the strip - the finishing product.

Naturally, the principle of the invention remaining the same, the forms of embodiment and details of construction may be varied widely without thereby departing from the scope of this invention as specifically defined in the following claims .

Claims

1. A plant for the surface treatment, "coil coating", of rolled metal, comprising stations for the application of treatment products on a strip (2) of rolled metal passing through them, characterised in that the plant comprises only- two operating application stations (7, 11) which work actively to apply layers of two corresponding treatment products to at least one of the sides of the strip of rolled metal, with means (8) for heating the strip of rolled metal being placed between the two operating application stations.

2. A plant according to Claim 1, characterised in that the only two operating application stations comprise a first station (7) for application of a layer of a first treatment composition to both sides of the strip (2) of rolled metal, and a second application station (11) subsequent to the first station in the direction in which the strip (2) of rolled metal is fed for application of a layer of a second finishing treatment composition on at least one of the sides of the rolled metal strip, on top of the layer of first treatment composition.

3. A plant according to Claim 2, characterised in that the first treatment composition operatively applied by the first application station (7) comprises:

- water as the solvent means,

- at least one alkyd resin binder in the solvent means, designed to form when in use a surface film structure covering the surfaces of the rolled metal strip, and in the solvent medium, at least one means for passivating the surface of the rolled metal.

4. A plant according to Claim 3, characterised in that the heating means (8) placed between the only two operating application stations are stove means which head the strip on the surfaces of which the layer of first treatment product has been applied, to a temperature of between approximately 140⁰C and approximately 240⁰C.

5. A plant according to any one of Claims 1 to 4, characterised in that the first application station of the only two application stations applies the first treatment product to both sides of the rolled metal strip, while the second successive application station applies the second treatment product as a finishing to only one side of the rolled metal strip.

6. A treatment composition for the surface treatment of rolled metal in a plant according to any one of Claims 1 to 5, comprising:

- water as the solvent means,

- at least one alkyd resin binder in the solvent means designed to form when in use a surface film structure covering a surface of a rolled metal, and in the solvent means, means for passivating the surface of the rolled metal.

7. A composition treatment according to Claim 6, characterised in that the alkyd resin is a resin of the medium oil or short oil type.

8. A treatment composition according to Claim 6 or 7, characterised in that the passivating means comprises a fluorine complex of zirconium.

9. A treatment composition according to any one of Claims 6 to 8, characterised in that it comprises: a) preferably from approximately 10 to approximately 45%, more preferably from approximately 20 to approximately 40%, and even more preferably from approximately 25 to approximately 35% of a resin binder, preferably a medium oil alkyd resin, b) preferably from approximately 0.05 to approximately 5%, more preferably from approximately 0.1 to approximately 1%, and even more preferably from approximately 0.2 to approximately 0.4% of a fluorine complex of zirconium, c) preferably from approximately 0.1 to approximately 10%, more preferably from approximately 1 to approximately 5%, and even more preferably from approximately 2.5 to approximately 3.5% of butyl glycol, d) preferably from approximately 0.001 to approximately 0.1%, more preferably from approximately 0.01 to approximately 0.05%, and even more preferably from approximately 0.02 to approximately 0.04% of hydrofluoric acid, e) preferably from approximately 0.01 to approximately 1%, more preferably from approximately 0.5 to approximately 0.8%, and even more preferably from approximately 0.1 to approximately 0.4% of dimethylethanolamine, and f) as much water as is required.

10. A treatment composition according to Claim 9, characterised in that it further comprises preferably from approximately 10 to approximately 40%, more preferably from approximately 15 to approximately 35%, and even more preferably from approximately 20 to approximately 30% of at least one colouring pigment.

11. A treatment composition according to Claim 10, characterised in that the at least one colouring pigment comprises titanium dioxide TiO₂.

12. A treatment composition according to any one of Claims 6 to 11, characterised in that it further comprises preferably from approximately 0.1 to approximately 3%, more preferably from approximately 0.2 to approximately 2%, and even more preferably from approximately 0.5 to approximately 1% of a surface tension modifying agent, and further preferably from approximately 0.1 to approximately 5%, more preferably from approximately 1 to approximately 3%, and even more preferably from approximately 1.5 to approximately 2.5% of a surfactant.

13. A process for the surface treatment of rolled metal, comprising at least one stage of application of a treatment product to at least one side of a rolled metal strip, characterised in that the treatment product is a treatment composition according to any one of Claims 6 to 12, the metal strip passing through heating means before a subsequent stage of application of finishing treatment product to at least one side of the rolled metal strip.

14. A process according to Claim 13, characterised in that it comprises a plurality of stages of application of a treatment product to at least one side of the strip, the treatment composition according to any one of Claims 6 to 12 being applied during the first stage of the said plurality of stages of application of a treatment product.