ES2865428T3 - Method for treating metal surfaces with an aqueous composition and aqueous composition - Google Patents

Abstract

A method of treating an iron or iron alloy metal surface to provide corrosion protection, adhesiveness of the coating and / or the adhesive, and said method comprises applying an aqueous composition to the iron or iron alloy metal surface; said composition comprises: trivalent chromium (Cr3 +): 1.16-7.0 g / l total fluoride (F-): 1.3-7.7 g / l organic corrosion inhibitor up to 2.0 g / l water-soluble polymers: 0-4.0 g / l surfactant soluble in water 0-1.0 g / l organo-functional silane and / or oligomer 0-4.0 g / l pH regulating agent 0-1.0 g / l fluoride regulating people 0-1.0 g / l where the molar ratio from Cr3 + to F- varies is in the range of 0.25-0.4, and where the pH varies in the range of 2.0-4.4, where the weight of the coating, measured by XRF after drying is in the range of 20- 200 mg chromium / m2.

Description

DESCRIPTION

Method for treating metal surfaces with an aqueous composition and an aqueous composition.

The invention relates to a method for treating metal surfaces with an aqueous composition and to an aqueous composition for treating metal surfaces.

The mechanical and chemical treatment of metal surfaces to improve corrosion resistance and / or to improve adhesion to a subsequently applied coating, such as an adhesive layer, a paint layer, a layer of paint, is well known in the art. lacquer or other finishing coat. For example, mechanical shot blasting has been used to remove scale and / or oxides from metal surfaces, as well as to improve adhesiveness, when chemical treatment steps were impractical. Water-based cleaning of metal parts made especially from iron and iron alloys, without proper chemical treatment, will result in rapid rust (also known as "flash rust") if parts are not painted within a few hours. Degreasing oiled surfaces with a suitable solvent, such as thinner or heptane, does not produce rapid oxidation. However, solvent degreasing poses significant risks to the health and safety of personnel and the environment. Chemical treatment of metal surfaces with zinc-coated steel (alloy), mild steel or aluminum and their alloys with aqueous solutions of chromate (chromium VI) produces what is known as a "chromate conversion layer", which provides resistance. corrosion resistant and has better adhesion, as well as preventing immediate oxidation prior to painting.

It is also recognized that these aqueous chromate-based solutions suffer from the toxicity of their Cr6 + component. Cr6 + is classified as a carcinogenic substance and will be banned in almost all industrial applications where there are high exposure risks for workers. Disposal of toxic treatment compositions also poses a problem, albeit to a lesser extent, if it is converted to trivalent chromium, which is comparatively harmless. However, this conversion carries additional costs and expenses.

Phosphate coatings have also been used to improve the adhesion of coatings such as paint, and the corrosion resistance of steel. Some major disadvantages of phosphate coatings are the need for multiple rinsing steps, sludge removal, and energy consumption. Also, these coatings are often sealed with a hexavalent chromium solution, to achieve optimum adhesiveness and corrosion resistance. Therefore, these phosphate coatings suffer from several environmental, health and safety disadvantages.

Today, the use of chromate-free (paint) primers has become more common. It appears that mechanical and chemical pretreatments of metals are more important to ensure corrosion protection of metal paint systems.

The current legislation has also advanced and is gradually being applied, with a view to reducing and finally abandoning hexavalent chromium-based metal treatment compositions.

Therefore, in the art, there is a need for treatments that are substantially free of hexavalent chromium compounds, which offer corrosion resistance and bond to treated metal surfaces in a manner similar to what is obtained by treating these metal surfaces with conventional solutions. comprising hexavalent chromium.

Various proposals to meet this need have been described in the patent literature. For example, WO 2006/088518 has described a process for preparing zirconiochrome conversion coatings on iron and iron alloys, to improve corrosion resistance and adhesive strength. This known method comprises treating iron and iron alloys with an acidic aqueous solution having a pH between about 2.5 and 5.5, preferably 3.7-4.0 for steel surfaces. The acidic aqueous solution comprises, per liter of solution, from about 0.01 to 22 grams of a trivalent chromium compound, about 0.01 to 12 grams of a hexafluorozirconate, about 0.0 to 12 grams of at least one fluorocompound selected from the group comprising : tetrafluoroborate, hexafluorosilicate and mixtures thereof, from about 0.0 to 10 grams of at least one divalent zinc compound, from 0.0 to about 10 grams of at least one water-soluble thickener, and from 0.0 to about 10 grams of at least one water soluble surfactant. The aforementioned known treatment contains at least zirconium and the preferred soluble trivalent chromium species contains a sulfate anion. These foreign cations and anions will negatively affect the formation of insoluble species. Therefore, the remaining unreacted solution must be rinsed with tap or demineralized water to be removed from the substrate, resulting in additional waste that requires disposal processes, or other processing.

Document WO 2006/088519 A1 describes a similar treatment, in which the solution also comprises a stabilizer compound selected from polyhydroxy and carboxylic compounds. In practice, these Preparations are used in low concentrations of the species effective to prevent excessive attack and instant oxidation during drying. However, low concentrations result in less dense protective layers on the metal surface and therefore can affect the performance of shielding and / or adhesive bonding.

From EP 111897 A1 a leave-in process is known for treating metal surfaces, in particular for the subsequent application of organic coating compositions, in which the metal surface is moistened with a solution of an aqueous bath having a pH in the range 2-3 and contains 0.5-10 g / L of chromium (III) ions, 0.55-11 g / L of fluoride ions, 0.6-12.5 g / L of phosphate and 0.15-5.0 g / L of a forming agent of an organic film that is soluble or homogeneously dispersed in water, such as a water soluble acrylic polymer.

An object of the invention is to provide a method of protecting an organic iron or iron alloy coating surface against corrosion and / or improving the durable adhesion properties of said organic coating or an adhesive using a metal surface treatment solution. .

Another object of the invention is to provide a method for the treatment of the alternative metal and a solution based on trivalent chromium for the protection of an organic iron or iron alloy coated surface against corrosion and / or to improve the properties of adhesion of said organic coating or an adhesive that uses a solution for treating a metallic surface.

Still another object is to provide a method and solution for metal treatment that dries in place and does not require a rinse step after application.

Still another object is to provide a solution for treating dry-in-place metals for use at room temperature on iron and iron alloys without rapid oxidation.

Another object is to provide a method for the treatment of metals and a solution for its application to an already phosphated iron and iron alloy surface that replaces a conventional chrome plated seal on said surface.

Therefore, in a first aspect the invention provides a method for treating an iron or iron alloy metal surface to provide protection against corrosion, adhesiveness of the coating and / or of the adhesive, and said method comprises the application of an aqueous composition to the iron or iron alloy metal surface; said composition comprises:

trivalent chromium (Cr3 +): 1.16-7.0 g / l total fluoride (F-): 1.3-7.7 g / l organic corrosion inhibitor up to 2.0 g / l water-soluble polymers: 0-4.0 g / l water-soluble surfactant 0 -1.0 g / l organo-functional silane and / or oligomer 0-4.0 g / l pH regulating agent 0-1.0 g / l fluoride regulating people 0-1.0 g / l

where the molar ratio of Cr3 + to F- varies from 0.25-0.4, and where the pH varies from 2.0-4.4, where the weight of the coating, measured by XRF after drying, is in the range of 20-200 mg chromium / m2.

In a second aspect, the invention provides an aqueous composition as defined above for treating an iron or iron alloy metal surface.

In the following, the invention is described first with respect to the composition and the components thereof. The aqueous composition according to the invention does not have hexavalent chromium and contains, as its main constituent elements, trivalent chromium ions and fluoride ions in a molar ratio of Cr3 + to: F- varying from 0.25-0.4. Surprisingly, it was found that a solution having a relatively simple composition with respect to its components without the need for more complex specific compounds (fluoromethalate) as a source of fluoride ions offers good results with regard to corrosion resistance and adhesiveness. These fluoromethalate compounds as used in the prior art will introduce foreign polyvalent metal ions and it is believed that they do not play an important role in corrosion resistance or adhesiveness and could complicate the preparation of the composition in terms of the desired ratios of the components. On the contrary, the composition according to the invention can be easily prepared. Inorganic anions outside of fluorides, such as phosphates, are conveniently absent from the composition. of the invention. These other inorganic anions increase the solubility of the conversion layer that is produced and impact its performance. Also, the stability and maintenance of the treatment bath could become more complicated. Metal surfaces that can be suitably treated with the composition according to the invention include iron and iron alloys such as cold rolled steel, mild steel and carbon steels. A conventional phosphate conversion coating may be applied to the metal surface, prior to exposure to the composition according to the invention. The composition can be easily applied, even in repair and maintenance conditions, such as outdoor pipeline applications in the field, ship building, highway work, maritime industrial equipment, and other (non-mobile) steel structures. Typically, the composition can be applied directly to the metal surface, after conventional mechanical and / or chemical pre-treatment, such as abrasive stripping, sanding and scraping, and degreasing / stripping, respectively. It is not necessary to rinse after the application of the composition. The treatment solution can be air dried under the prevailing conditions and does not require special measures or apparatus. In any case, the metal substrate subjected to treatment must be dry before carrying out the subsequent painting or adhesive bonding processes. To reduce process time, force drying methods can be used, for example oven drying, infrared drying and forced air drying. Once the composition has been applied and has dried sufficiently, the iron or iron alloy surface thus treated can be coated with organic paint, optionally including the pre-application of a paint primer and / or an adhesion system. .

The layer that has been formed from the composition improves the adhesiveness of the coating to be applied later, for example, a paint coat system or an adhesive bonding system. The best adhesion shows good corrosion resistance when the metallic surface thus coated is exposed to corrosive conditions. In addition, it appears that the layer that is formed allows the thickness of the layer of a conventional paint primer to be reduced, or even to obviate the primer altogether. Trivalent chromium is present in an amount of 1.16-7.0 g / l. A preferred range is 3.0-6.0 g / l. Total fluoride is present in a range of 1.3-7.7 g / l. The molar ratio of Cr3 + to F is 0.25-4.0, preferably 0.30-0.36, more preferably 0.32-0.34, such as 1: 3. The stoichiometric ratio of CrF3 or slightly higher was found to give good results in terms of corrosion resistance and / or bonding characteristics.

Trivalent chromium can be obtained by reducing chromic acid (H2CrO4) with chemical agents that can be oxidized with chromic acid, such as methanol or hydrogen peroxide, without leaving residual products in the starting solution after heating. Another attractive source is to use CrF3.4H2O as the starting material. This compound is poorly soluble in water, but it is accompanied by acid components such as HF and acid homopolymers and copolymers. HF is preferably used as it does not introduce foreign anions.

The pH ranges from 2.0-4.4, preferably 2.7-3.8, in particular 2.7-3.4. To fix the acidity at the required level, the composition can contain pH regulating agents, such as alkali metal hydroxides, such as sodium hydroxide, potassium hydroxide and ammonia, in an amount of 0-1.0 g / l. It is believed that the alkali metal ions do not contribute, or contribute to a much lesser extent, to the formation of the protective layer and thus the protection and / or bonding characteristics thereof.

As said, the molar ratio of fluoride to trivalent chromium is preferably equal to or slightly higher than the stoichiometric ratio of CrF3. This can be regulated by incorporating fluoride regulating agents that offer an additional source of fluoride anions. If present, these fluoride regulating agents are present in an amount of up to 1.0 g / l. Preferred examples include hydrofluoric acid, alkali metal fluorides, and ammonium, in particular sodium fluoride and ammonium bifluoride.

The composition according to the invention contains an organic corrosion inhibitor in an amount of up to 2.0 g / l, preferably 0.0001-2.0, more preferably 0.1-1.0 g / l. Therefore, the organic corrosion inhibitor is a necessary component of the composition according to the invention. The organic corrosion inhibitor can act as a rapid oxidation inhibitor, preventing so-called "flash rust" during drying of the treatment composition applied to the iron or iron alloy surfaces. In addition, the organic corrosion inhibitor is believed to contribute to ultimate strength after application of a coating such as paint. The organic corrosion inhibitor must be slightly water soluble or mixable in water. Examples include: N, N-dimethyl propylene urea, tolitriazole, zinc phthalate, imidazoline maleate, caprylic acid, phthalic acid, alkyl esters of phosphonic acid, n-butyric acid, benzotriazole, tolitriazole, divalent salts of phthalate , nitrobenzoate, 1-octanol, tannic acid, divalent nitro maleate salts, 2-mercaptobenzimidazole, propargyl alcohol, propargyl alcohol ethoxylates, iso-nitrophthalate zinc salt, 2-butyn 1,4 diol, 2-butyn 1,4 diol alkoxylates, alkanolamine salt of nitrogenous organic acids, quaternary amines and combinations thereof.

The concentration and nature of the organic corrosion inhibitor or corrosion inhibitor mixture should be selected such that they do not block the deposition of trivalent chromium on the metal during treatment.

In addition to the above components, the composition may contain additional components from a selected group of optional compounds. These optional compounds include water-soluble homopolymers and copolymers preferably based on the following monomers: acrylic acid, methacrylic acid, vinyl alcohol, vinyl ether, maleic acid, vinyl phosphonic acid, vinyl sulfonic acid, methyl vinyl ether, and combinations thereof, up to 4.0 g / l, preferably 0.01-4.0 g / l, more preferably 0.1-1 g / l. These polymers improve the wetting performance of the treatment composition, as well as the adhesion of subsequently applied organic coatings. Too high concentrations will reduce the wet adhesion of an organic coating. Another optional compound is a water soluble surfactant, which can be present in an amount up to 1.0 g / l. A preferred concentration range is 0.001-0.5 g / L, while a more preferred concentration ranges from 0.01-0.1 g / L. Surfactants which can be used in the composition according to the invention include acid stable low foaming anionic and nonionic surfactants such as alkaryl sulfonates and polyethylene glycol fatty amines. The surfactant provides uniform wetting of the substrate and effective removal of oil and dirt. If the amount of surfactant is too high, it can cause excessive foaming in the process.

Another component that may also be present is an organofunctional silane and / or a hydrolyzed oligomer thereof. If present, the concentration goes up to 4.0 g / l. The reactive functional group is at least one selected from a mercapto group, an amino group, a vinyl group, an epoxy group and a methacryloxy group, advantageously in an amount of 1 to 40 mg / l based on Si.

The method of treating an iron or iron alloy metal surface to provide corrosion resistance and adhesion of a coating or adhesive comprises a step of applying the aqueous composition according to the invention described above, to the metal surface. Normally, the metal surface to be treated with the composition according to the invention is pretreated using known mechanical or chemical pretreatment processes or a combination thereof to obtain a more wettable surface, which normally requires the surface to be rough. and substantially free of rust, scale, oxides, grease, oil, and the like. Mechanical pretreatment processes include dry blasting, sanding, scraping and abrasion. Chemical pretreatment includes degreasing and pickling (acid / alkaline / solvent). Typically, a chemical pretreatment is followed by a rinsing step with tap water or demineralized water. Combinations of mechanical pretreatment and chemical pretreatment are also possible in any order.

Surprisingly it has been found that the composition according to the invention can also replace solvent degreasing of oiled iron or iron alloy surfaces without scale or rust. After the application of the composition according to the invention, in particular a composition such as the present one that contains a surfactant, on this type of surface, the removal of oil, grease and dirt occurs simultaneously, with the formation of the conversion layer. , whereby the solvent degreasing step as in the prior art is now superfluous. Thus, in one embodiment of the method according to the invention, an oiled iron or iron alloy surface, but free of scale and rust, is brought into contact with the present composition.

The composition according to the invention also makes it possible to replace a conventional chromate seal on an already phosphated iron and iron alloy surface.

The way of applying the composition according to the invention to the metal surface is not limited. However, the homogeneity and uniformity of the wet film applied to the substrate before drying will be advantageous. Suitable application methods include spraying, dipping, cleaning, brushing, rolling, and the like. Excess treatment liquid on parts with intricate geometries can be removed with compressed air prior to drying. After application, it is no longer necessary to perform a rinsing step to remove non-reactive and / or unreacted species from the formed layer. On the contrary, the metal surface to which the composition according to the invention is applied can be allowed to dry immediately, for example, with air optionally at an elevated temperature, such as an oven with air conditioning.

The coating weight (after drying measured by XRF (X-ray fluorescence) ranges from 20 to 200 mg chromium / m2. Higher coating weights will reduce the adhesion properties of the organic coating layers that are subsequently applied. No no beneficial effect on corrosion protection has been recorded at lower coating weights.

A post-applied paint system and / or an adhesive bonding system can be applied using conventional methods and equipment, such as spraying, brushing, and roller coating.

The various characteristics of the treatment composition discussed above are equally applicable to the method according to the invention.

The invention is illustrated by the following examples according to the invention and comparative examples.

The trivalent chromium compound "Cr (III) Fluoride" as indicated in the following Tables was obtained by reducing a solution of chromic acid in a stoichiometric ratio of chromium to fluoride of 1 to 3. The source of fluoride was an aqueous solution of fluoride of hydrogen. Methanol in water was used as the reducing agent. After 4 hours of reduction at 80 ° C, hexavalent chromium could not be detected using a sdiphenylcarbazide test method (the detection limit for Cr (VI) is less than 0.03 ppm). Methanol and methanol oxidation products such as formalin and formic acid could not be detected by TOC (total organic carbon) measurements.

Aqueous metal surface treatment liquids having the composition indicated in Table 1 were prepared and applied to the metal surfaces as indicated in Tables 2-4.

The surfaces thus exposed to pretreatment, treatment and organic coating were subjected to adhesion and corrosion tests in accordance with the quality standards prescribed by GSB and Qualitysteelcoat: Cross cut adhesion polished adhesion (Protection of steel structures against corrosion by means of systems protective paint) EN ISO 16276-2; ASTM D3359; Adhesion Resversed impact (Rapid deformation tests (impact resistance) ASTM D2794 or EN ISO 6272-1 and Corrosion tests: Accelerated corrosion tests according to ASTM B117 Neutral Salt Spray for iron, iron alloys and steels Zinc Coated Tables 2-4 summarize the test results.

Table 4: Test result

From the above examples and the test results, it appears that the compositions according to the invention exhibit better performance with respect to coating adhesion, wettability, flash oxidation inhibition and corrosion resistance than comparative examples, which fail in one or more of these respects or are worse.

Claims (15)

1. A method of treating an iron or iron alloy metal surface to provide corrosion protection, adhesiveness of the coating and / or the adhesive, and said method comprises applying an aqueous composition to the iron or iron alloy metal surface. iron; said composition comprises: trivalent chromium (Cr3 +): 1.16-7.0 g / l total fluoride (F '): 1.3-7.7 g / l organic corrosion inhibitor up to 2.0 g / l water-soluble polymers: 0-4.0 g / l water-soluble surfactant 0 -1.0 g / l organo-functional silane and / or oligomer 0-4.0 g / l pH regulating agent 0-1.0 g / l fluoride regulating people 0-1.0 g / l where the molar ratio of Cr3 + to F- varies is in the range of 0.25-0.4, and where the pH varies in the range of 2.0-4.4, where the weight of the coating, measured by XRF after drying is in the range range of 20 200 mg chromium / m2. 2. Method according to claim 1, wherein the concentration of trivalent chromium (Cr3) in the aqueous composition is in the range of 3.0 to 6.0 g / L. 3. Method according to claim 1 or 2, wherein the Cr3 + .F molar ratio in the aqueous composition is in the range of 0.30-0.36, preferably 0.32-0.34 and more preferably 1: 3. 4. Method according to any of the preceding claims, wherein the composition comprises dissociated CrF3.4H2O. Method according to any of the preceding claims, wherein the concentration of organic corrosion inhibitor in the aqueous composition is in the range of 0.0001-2.0, preferably 0.1-1.0 g / L. 6. Method according to any of the preceding claims, wherein the concentration of the water-soluble polymers in the aqueous composition is in the range of 0.01 to 4.0, preferably 0.1 to 1.0 g / L. 7. Method according to any of the preceding claims, wherein the concentration of the water-soluble surfactant in the aqueous composition is in the range 0.001-0.5, preferably 0.01-0.1 g / L. Method according to any one of the preceding claims, in which the pH is in the range of 2.7 to 3.8, preferably 2.7 to 3.4. 9. Method according to any one of the preceding claims, wherein the organic corrosion inhibitor is selected from the group including: N, N-dimethyl propylene urea, tolythriazole, zinc phthalate, imidazoline maleate, caprylic acid, acid phthalic, alkyl esters of phosphonic acid, n-butyric acid, benzotriazole, tolitriazole, divalent salts of phthalate, nitrobenzoate, 1-octanol, tannic acid, divalent salts of nitro maleate, 2-mercaptobenzimidazole, propargyl alcohol, propargyl alcohol ethoxylates, iso-nitrophthalate zinc salt, 2-butyn 1,4 diol, 2-butyn 1,4 diol alkoxylates, alkanolamine salt of nitrogenous organic acids, quaternary amines and combinations thereof. A method according to any preceding claim, wherein the metal surface is selected from a solvent degreased metal surface of iron or iron alloy, a metal surface of iron or iron alloy from which scale has been mechanically removed, and oxides, an iron or iron alloy metallic surface that has already been provided with a phosphate conversion coating, and an oiled iron and iron alloy metallic surface that is free of scale and oxides. 11. Aqueous composition for treating an iron or iron alloy metal surface, in particular for use in the method according to any of the preceding claims, the composition of which consists of: trivalent chromium (Ce3 +): 1.16-7.0 g / l total fluoride (F '): 1.3-7.7 g / l organic corrosion inhibitor up to 2.0 g / l water-soluble polymers: 0-4.0 g / l water-soluble surfactant 0-1.0 g / l organo-functional silane and / u oligomer 0-4.0 g / l pH regulating agent 0-1.0 g / l fluoride regulating people 0-1.0 g / l where the molar ratio of Cr3 + to F- is in the range of 0.25-0.4, and where the pH varies in the range of 2.0 4.4. 12. Composition according to claim 11, in which the concentration of trivalent chromium (Cr3) is in the range of 3.0-6.0 g / L Composition according to claim 11 or 12, in which the Cr3: F- molar ratio is in the range of 0.30-0.36, preferably 0.32-0.34 and more preferably 1: 3. Composition according to any of the preceding claims from 11 to 13, in which the concentration of organic corrosion inhibitor is in the range of 0.0001 to 2.0, preferably 0.1 to 1.0 g / L. Composition according to any of the preceding claims from 11 to 14, in which the concentration of the water-soluble polymers in the aqueous composition ranges from 0.01 to 4.0, preferably from 0.1 to 1 , 0 g / L; and / or the concentration of the water-soluble surfactant in the aqueous composition is in the range of 0.001-0.5, preferably 0.01-0.1 g / L; and / or the pH is in the range 2.7-3.8, preferably 2.7-3.4.