EP2798098B1

EP2798098B1 - A composition for pre-treatment of an aluminum surface, a method for preparing and applying the composition, use of the composition and a product

Info

Publication number: EP2798098B1
Application number: EP12710647.4A
Authority: EP
Inventors: Adeval Antonioa Meneghesso
Original assignee: Individual
Current assignee: Individual
Priority date: 2011-12-29
Filing date: 2012-02-28
Publication date: 2015-10-14
Anticipated expiration: 2032-02-28
Also published as: WO2013097002A8; AR085405A1; BRPI1105661B1; WO2013097002A1; BRPI1105661A2; EP2798098A1; EP2798098B8

Description

Field of the Invention

The present invention relates to an aqueous solution used in the pre-treatment of aluminum and alloys thereof, in order to make their surface suitable for receiving the application of a selected painting system.
More specifically, the present invention describes a composition free from chrome and toxic derivatives, as well as a method for preparing said composition, and still a method for applying it to an aluminum surface during the chemical treatment step.
Finally, the present invention relates also to the use of said composition and to a product the surface of which is treated with the composition described before.

Description of the prior art

Aluminum and alloys thereof have been used since 1886 and, although aluminum is the third most abundant chemical element on the earth's crust, its present-day production exceeds the sum of all the other nonferrous metals. Additionally, the techniques of manufacturing it enable the manufacture of the finished product at competitive prices, the main and most economical raw material for industrial use being the ore bauxite.
Although aluminum is the latest metal used on an industrial scale, it is unequaled and has excellent performance in most applications, such as low density and strength. In this regard, although it weight only one third of the weight of steal, its mechanical properties are equivalent.
Products that use aluminum and alloys thereof incorporate the advantages inherent in this metal, such as lightness, electrical conductibility and thermal conductivity, impermeability and opacity, high strength/weigh relationship, beauty, durability, moldability and weldability, corrosion resistance and hardness, recyclability and possibility of a number of finishes.
Various segments use aluminum and alloys thereof in a form that is the most suitable for their purposes, taking advantage of the properties of this metal in receiving various types of treatment on its surface. In this context, aluminum and products thereof can be applied in the segments of packages, transport, electricity, civil engineering, consumption goods, machines and equipment, among others.
It is important to point out that aluminum and alloys thereof can be used with or without finishing processes, that is, for some applications the natural finish of aluminum is totally satisfactory, in both appearance and durability. On the other hand, for applications such as metallic sashes (doors, windows, façades, grids, shower boxes, etc.), furniture (kitchen cabinets, closets, bathroom closets, etc), consumption goods (ice-boxes, kitchen ranges, microwave apparatus, washing machines etc.), transport (open and closed bodyworks, van-type bodyworks, accessories, etc.), decoration articles (chandeliers, lamp-holders, mirrors, knobs, etc), among other applications, the aluminum surfaced requires adequate finish for protection and decoration.
In general, the properties of aluminum do not enable adherence of paints directly on its surface. In order to apply paint, an aluminum surface has to undergo a pre-treatment so that a conversion layer can be created, by means of a chemical treatment, in order to prepare the aluminum for paint adherence. If the pre-treatment is adequate, the paint will have good adherence without the risk of peeling upon cutting the aluminum borders. Besides, said conversion layer is capable of providing high corrosion resistance.
Therefore, the durability of the paint on an aluminum surface depends especially on the paint adherence and on the metal resistance to corrosion, and these properties can be imparted by the conversion layer formed during the pre-treatment.
The painting of an aluminum surface is carried out in the step of finishing the pre-treatment and it is very important for coating some products, mainly for the cases in which the metal is used for decoration and protection purposes.
The process of finishing an aluminum surface can be carried out in more than one way. As an example of finish, mechanical abrasion is considered a relevant process. However, a special configuration of the parts to be treated creates difficulty for this technique. More specifically, with these types of parts there are dead angles, "shadows" that do not allow uniform access of the abrasion jet to all the points of the surface of a metallic piece. So, mechanical abrasion fails to achieve satisfactory homogeneity for subsequent application of a paint film onto the aluminum surface.
Another example consists in carrying out the abrasion by hand. However, this technique has disadvantages like the high cost of labor and more time spent to achieve satisfactory abrasion.
Anodization too is among the processes of finishing an aluminum surface, by means of which a natural oxide film is artificially produced on the aluminum, by means of an electrolyte anode. The newly formed anodic film, prior to the final stage of sealing, is porous and can absorb coloring material. This is the base of most anodized colored finishes and enables printing in determined areas, clearly reproducing small details. However, this technique presents a high manufacture cost of the film formed, so that such a disadvantage makes the present application commercially unfeasible.
Anodization of natural coloration too is often employed to impart additional corrosion resistance. The film is uniform and hard, and internal aluminum accessories, such as door knobs, are often anodized in order to enhance its resistance to wear. This property is further exploited in hard anodization, wherein a dense film with thickness of several microns is developed by means of treatment in cooled electrolyte, for use on air-entry parts on aircrafts, which are subject to abrasive effects of dust from landing-strips. Although this technique is one that has higher corrosion resistance, the high manufacture cost of the film formed makes this application commercially unfeasible.
Therefore, a person skilled in the art knows that an aluminum surface needs some type of adequate finish in order to receive a determined paint, since this metal per se does not have favorable conditions for coating with a pain film.
When a chemical treatment is used during the pre-treatment, the conversion layer formed is capable of both transforming an aluminum surface into a poor conductor and isolating the metallic surface of the paint film applied later. In absence of a chemical treatment, the metallic surface remains conductive under the coating layer, so that the electric current flows freely between possible electrodes existing on the surface of the metal and further enables the occurrence of corrosion.
The pre-treatment has the objective of removing all the impurities present in the aluminum (antioxidant oils, lubricants, grease, metal oxides, etc.), so as to make the metallic surface receptive to the coatings that will be applied later. In general, a good cleaning process ensures a total physical contact between the aluminum surface and the pre-treatment solution for the formation of a conversion layer.
At present, the protocol of leaning an aluminum surface consists in a sequence comprising the steps described in the Brazilian Norm - Norma Brasileira ABNT NBR 14125 of: i) degreasing; ii) first washing; iii) deoxidizing; iv) second washing; v) conversion/chromation; vi) third washing, vii) washing with demineralized water, and viii) drying, which are described in greater detail hereinafter.
The degreasing step (i) may be carried out with the aid of an alkaline solution or an acidic solution.
Degreasing via an alkaline solution takes place when the solution used is generally composed of a mixture of alkaline salts and one or more emulsifiers solubilized in water. The chosen components should diminish the surface tension of water, in order to facilitate the removal and subsequent emulsification of oils and greases present, making them easily rinsable.
The application of this alkaline solution is usually carried out by immersion, but the application by means of sprays becomes more efficient because it incorporates the detergent action of the cleaning alkaline solution into the mechanical action of the directed jets.
At the end of this first degreasing step via alkaline solution, one should ensure minimum removal (pickling) of 1 g/m2 of metallic surface. Finally, this degreasing should enable saponification or emulsion of the oils and greases previously present, ensure a perfect moldability of a metallic surface and eliminate the aluminum oxide that may be present.
Degreasing via an acidic solution takes place when the solution used is applied at room temperature, so as to promote the cleaning of the metallic surface from oils and greases present.
Similarly to the application of an alkaline solution, at the end of this first degreasing step via acidic solution, one should ensure minimum removal (pickling) of 1g/m2 of metallic surface.
The steps of first, second and third washings (ii, iv and vi) are intended to remove the excess solutions of the preceding steps that may remain on the aluminum surface, thus preventing contamination of the subsequent steps by dipping the metallic surface into a water bath. These steps have fundamental importance, and the level of contamination of the washings should be controlled by means of continuous removal of water volume.
The deoxidizing step (iii) consists in removing the oxides existing on the aluminum surface, since they are undesirable for subsequent treatment.
After the cleaning steps described before, a method is usually applied in the production line for verifying the level of cleaning of the metallic surface. This method consists in verifying whether the metallic surface is free from "water break", that is, whether the surface, after being wetted, presents a thin and continuous film of water throughout the surface. Although this test does not indicate the presence of hydrophilic impurities, it is still a good indication that the cleaning process was satisfactory.
The steps of conversion/chromation (v) with amorphous chromate comprises applying aqueous solutions of chrome trioxide (CrO3), containing adequate activating agents like fluorides. In this step, the aluminum surface is converted into an adherent and amorphous layer of mixtures of metallic oxides of iridescent-yellow to light brown color. This layer provides corrosion resistance, paint-film adherence and durability of the aluminum surface when painted.
This conversion process can be carried out by immersion or application of spray, at room temperature (21-32°C) in the interval of time from 15 seconds to 5 minutes.
The step of conversion/chromation (v) with chromophosphate (CrPO4) comprises treating the aluminum surface with aqueous solutions of phosphoric acid (H3PO4), fluorides and chrome trioxide (CrO3) adequately balanced. The aluminum surface is converted into an adherent, thin amorphous layer of lightly greenish iridescent to non-iridescent more intense green color, depending on the alloy of the aluminum surface used.
This conversion process can be carried out by immersion or application of spray, at a temperature ranging from 20° to 45°C, in the interval of time from 15 seconds to 5 minutes.
The step of washing with demineralized water (vii) is similar to the steps of first, second and third washings. However, the conductivity of water at this stage should not exceed 30 microsiemens (µS). By demineralized water one understands a volume of water from which all the mineral salts were removed.
The step of drying (viii) the metallic surface is effected with dry and hot air, at a temperature ranging from 65° to 70°C, so as to eliminate all moisture present. At the end of this step, the aluminum surface is ready to receive application of the coating system (paint) selected.
In conventional systems, the paint is usually applied onto a conversion layer of zinc chromate, result of a chemical treatment process for protection purpose. The conversion layer of lightly iridescent yellowish to light brown color makes it easy for the consumer to identify that the metal was treated before.
However, the aluminum chromate conversion is formed by applying a solution containing chrome and toxic derivatives thereof to the aluminum surface. This solution could be considered effective in the past, when the effects of toxic substances like chrome and the irreparable damages caused to the human health and to the environment were unknown. At present, extensive researches have been carried out in this segment in order to try to find an efficient substitute for hexavalent chrome, used to form said conversion layer.
Solutions without chrome, at present available on the market, form a colorless conversion layer, which invisible to the naked eye. This translucent layer makes it significantly difficult for the consumer to control the step of treating the aluminum chemically, since, at first sight, there is no difference between one metal without pre-treatment and one that has been effectively pre-treated, but has formed a colorless conversion.
In the absence of pre-treatment, the aluminum surface undergoes the finish process and only after about twelve hours from application of the pain is it possible to see that the metal piece did not undergo any chemical treatment to prepare for receiving the coating.
In addition, another disadvantage of obtaining aluminum parts without pre-treatment is that, in the absence of a chemical treatment, the metallic surface remains conductive under the coating layer, so that the electric current can flow freely between possible electrodes existing on the metal surface. Besides, the occurrence of corrosion on the metal that did not undergo an effective chemical treatment is markedly facilitated and the coating applied onto the metal fails to be effective in the long run.
In other words, obtaining aluminum parts with a colorless aluminum layer and, therefore, without the guarantee of durability of the paint film applied as a coating, with deficiencies in isolating the electric current and little or none resistance to corrosion generated in time, becomes an exponential damage to the consumer.
On the other hand, it is pointed out that obtaining aluminum parts with a conversion layer formed by applying the solution with chrome and derivatives thereof also has highly harmful disadvantages, not only for the health of the person in charge of handling the material, but also for the enterprise marketing, since the image of the company may be irreducibly devoid of merit and correlated to the commercialization of parts containing toxic components, which do not contribute at all to the sustainability of the planet.
In the face of the frequent problems encountered in the techniques existing in this segment, it is evident that the market lacks a solution free from chrome and derivatives thereof for chemical treatment of an aluminum surface and alloys thereof, and this solution should be capable of generating a colorful conversion layer, visible at first sight, in order to aid the consumer in obtaining parts resistant to corrosion and apt to maintain the desired finish for an effective period of time.
US 6 193 815 B1 discloses Cr-free aqueous compositions for treating the surface of aluminiferous metals containing as components a flourinated inorganice acid, such as HF, H₂ TiF₆, H₂ SiF₆, H₂ ZrF₆ or H₂ HfH₆, a titanium-containing substance and a water-soluble organoperoxide.

Objectives of the invention

The present invention has the main objective of providing a composition for pre-treatment of an aluminum surface.
The present invention also has the objective of providing a method for preparing and applying the composition onto an aluminum surface.
Finally, the present invention has the objective of achieving the use and obtaining a product with surface treated with the composition described before.

Brief description of the invention

The objectives of the present invention are achieved by means of a composition for pre-treatment of an aluminum surface comprising:

a) from 2% to 10% by weight of a fluorinated organic acid;
b) from 2% to 10% by weight of molybdate, titanate or zirconate of an alkaline metal or alkaline earth metal, or ammonia, optionally in the form of a fluoracid derivative;
c) from 0.02% to 0.2% by weight of hydrogen peroxide or organic peroxide oxidizing agent;

Moreover, the objectives of the present invention are achieved by means of a method for preparing the composition described before, comprising the following steps:

a) preparing solution no. 1 which comprises dissolving the molybdate, titanate or zirconate of an alkaline metal or alkaline earth metal or ammonia, optionally in the form of a fluor acid derivative;
b) preparing solution no. 2 which comprises neutralizing the fluorinated inorganic acid until pH 4.5 is achieved;
c) preparing the final solution which comprises mixing solution no. 1 with solution no. 2 and neutralizing the medium until pH ranging from 5.0 to 5.8 is achieved, finally adding the oxidizing agent.

The objectives of the present invention are also achieved by means of a method for applying said composition, comprising the steps of degreasing, washing, deoxidizing, chemically treating, washing and drying.
Finally, the objectives of the present invention can be achieved by using the composition described above for the chemical treatment of an aluminum surface, and further by a product with its surface treated with said composition.
The present invention has the advantage of using a solution in the chemical treatment of aluminum, prepared with a composition totally free from chrome and toxic derivatives thereof, with capability of converting the aluminum surface into a brown-colored conversion layer that is visible to the naked eye, further capable of enhancing the adherence power of the paint on the aluminum surface, and with excellent corrosion resistance, which in turn surpasses easily the present-day levels of demand of the rules that govern the quality of the painted aluminum.

Detailed description of the invention

The present invention describes an innovator and sustainable solution to the chemical treatment of a surface of aluminum and alloys thereof, which, besides having a composition free from chrome and toxic derivatives, is capable of converting the aluminum surface into an adherent, amorphous conversion layer of brown colour, with possible variations in tons from bluish and/or yellowish.
In a preferred embodiment, the pre-treatment of the aluminum surface begins with the step of degreasing in alkaline medium, by using a product capable of dissolving and removing oils, greases and lubricants resulting from the extrusion of the aluminum, like the alkaline degreasing agent LL-CLEAN M12 produced by the company Italtecno do Brasil Ltda®. Said product has surfactant properties capable of dissolving easily the magnesium-oxide film that tend to form on the aluminum surface.
In order for the step of degreasing in an alkaline medium to be prepared, it is necessary to fill a tank with water up to ¾ of its volume and to heat up to a temperature ranging from 55° to 75°C and to add the alkaline degreasing agent LL-CLEAN M12 at a preferred concentration ranging from 20g/L to 60g/L. One should stir it for a few minutes in order to achieve homogenization of the solution. The aluminum should undergo an immersion bath through dipping into the tank with the homogenized mixture for a preferred period from 1 to 3 minutes, in order to remove all residue adhering to the aluminum surface.
The present application further foresees that the initial degreasing step should be optionally carried out in an acidic medium, using, for example, the acidic degreasing agent LL-TEDCNOCLEAN, produced by the company Italtecno do Brasil Ltda^®. Said product is composed of an acidic solution of organic salts, capable of producing a light homogeneous attack on the aluminum surface in order to remove oils, greases and lubricants.
The preparation of the step of degreasing in an acidic medium is similar to that of degreasing in alkaline medium, wherein the water in the tank is heated up to a temperature ranging from 35°C to 55°C, and the LL-TECNOCLEAN solution, dissolved in water, is mixed in the tank until the desired concentration (preferably from 50g/L to 70g/L) is reached. The aluminum should undergo an immersion bath in the tank with the homogenized mixture for the preferred period from 1 to 3 minutes.
It should be pointed out that, in both the degreasing in alkaline medium and the degreasing in acidic medium, the aluminum may also go through a spray bath. In this case, the aluminum is led by means of a conveyor belt as far as a sort of tunnel that sprays onto the aluminum surface jets of the alkaline solution LL-CLEAN M12 or of the acidic solution LL-TECNOCLEAN, previously homogenized, in order to promote the removal of undesired constituents.
It is pointed out that all the steps of pre-treating the aluminum may be carried out by means of immersion bath or spray. The choice of the type of bath for the surface may vary according to the type of industrial facility.
Once the degreasing step is completed, one then carries out the first washing of the aluminum bath, either by immersion or by spray, preferably with industrial running water, in order to remove excess product used in the degreasing step. The volume of water should be constantly renewed in order to control the level of contamination.
Then, the deoxidizing step is preferably carried out in an acidic medium, using, for instance, the product LL-DESMUT A 30, produced by the company Italtecno do Brasil Ltda^®, for the purpose of removing the oxides existing on the aluminum surface, which in turn are undesirable for carrying out the next steps. The tank water is heated up to a temperature of about 20°C to 25°C, and the solution LL-DESMUT A 30, dissolved in water, is mixed in the tank until the desired concentration (preferably from 40g/L to 50g/L) is reached. The aluminum undergoes an immersion bath or spraying in the tank with the homogenized mixture for the preferred period of from 1 to 3 minutes.
It should be pointed out that the deoxidizing step is optional when the pre-treatment of the aluminum is carried out with acidic degreasing agent. In this case, there is no need for neutralization.
Then, a second washing with industrial running water is preferably carried out, either by immersion or by spraying, in order to remove the excess product used in the deoxidizing step.
In order to obtain better result of the pre-treatment of the aluminum surface, the present application foresees that a third washing, preferably with demineralized water, should be carried out right after the second washing. The demineralized water has the purpose and the capability of removing all the ions present on the aluminum surface.
The above-mentioned steps having been carried out, the aluminum is now in a position to receive the aqueous solution of the present patent application, during the next chemical treatment step, in order to form a colorful conversion layer, visible to the naked eye and free from chrome and toxic derivative thereof.
It should be clarified that the composition of said aqueous solution is preferably prepared in three different steps, namely:

First Step: Preparation of Solution no. 01

Hot dissolution of a mobybdate, titanate or zirconate of an alkali metal or alkaline earth metal or ammonia, optionally in the form of a fluor acid derivative, in demineralized water under agitation.
In a preferred embodiment, the source of molybdate, titanate or zirconate of alkali metal or alkaline earth metal or ammonia is chosen from the group consisting of sodium molybdate, potassium molybdate, fluoro ammonia molybdate acid, fluoro sodium molybdate, fluoro potassium polybdate, molybdic acid, hexafluoro titanic acid, hexa fluor potassium titanate acid, hexa fluoro sodium titanate acid, hexa fluoro ammonia titanate acid, hexa fluoro zirconium acid, hexa fluoro potassium zirconate acid, hexa fluoro sodium zirconate acid and hexa fluoro ammonia zirconate acid.
This first solution has the objective of releasing ions, which, in the end of the preparation of the composition, will be responsible for the corrosion resistance of the metallic surface, as well as for the visible coloration expected at the end of the application of the pre-treatment solution onto the aluminum surface.

Second Step: Preparation of Solution no. 02

Preparation of the mixture of a fluorinated inorganic acid in demineralized water and adjustment of the pH with an alkaline solution until pH 4.5 is reached. In a preferred embodiment, the alkaline solution used for adjusting the pH is an ammonium hydroxide solution. At this step, the pH of the solution should be adjusted for a slightly acidic pH, since the presence of acids may generate conversion, because they react directly with the aluminum surface. Then, the volume spent is written down as percentage (%).
In a preferred embodiment, the fluorinated inorganic acid used is a fluoro silicic acid, hexa fluoro zirconic acid or hexa fluoro titanic acid.
In a second preferred embodiment, the fluorinated inorganic acid is fluoro silicic acid 30% or a hexa fluoro zirconium acid 45C%. These are the preferred sources of silicon and zirconium, respectively.
The employ of a source of fluorine has the function of reacting with the aluminum surface, since fluorine creates the conditions necessary to form the zirconium, silicon, molybdenum and aluminum complexes.

Third Step: Preparation of the Final Solution

One mixes solutions no. 01 and no. 02 under continuous agitation. Then, still under agitation, one neutralizes the medium with an alkaline solution until a pH from 5.0 to 5.8 is reached. One writes down the volume spent as percentage (%).
The solution obtained is cooled down to room temperature, and an oxidizing agent is added. The final solution is left at rest for 12 hours, so that an oxidizing medium is formed in order to complete the reactions. During this period of rest, the decantation of possible solid particles in suspension takes place.
In a preferred embodiment, the alkaline solution used to adjust the pH of the solution is an ammonium hydroxide solution.
The source of oxidizing agent is a hydrogen peroxide or organic peroxides. One observes that the employ of an oxidizing agent has the function of making the reaction that takes place on the aluminum surface feasible, imparting stability to the compound. However, the deficiency or excess oxidizing agent may favor an unfavorable condition for the reaction, so that an undesired complex may be formed.
Once the three steps for preparing the solution free from chrome and toxic derivatives thereof disclosed in the present invention, the application thereof onto an aluminum surface should be effected in accordance with the procedure that is widely known by those skilled in the art, so as to meet fully the requirements of the main Brazilian technical rules of the ABNT (Brazilian Association of Technical Rules).
Preferably, the aqueous solution disclosed in the present application should be added in a tank at a percentage of about 45 g/L to 50 g/L and kept at a temperature ranging from 20°C to 30°C. In order to achieve a better result of the chemical reaction, the pH of the solution should be monitored and kept between about 5.0 and 6.0. Then, the aluminum undergoes a bath, either by immersion or by spraying, for 1 to 3 minutes in the final solution previously adjusted in the operational conditions described, immediately promoting the formation of a conversion layer in the brownish colour, visible to the naked eye, totally free from chrome and toxic derivatives thereof.
Finally, the aluminum surface undergoes a new washing, preferably with demineralized water, in order to remove the excess aqueous solution used in the chemical treatment step, and then the pre-treatment of the aluminum is finished with the step of drying the surface with dry air at a temperature ranging from 65°C to 70°C.
The objective of drying is to eliminate the whole moisture present on the aluminum surface, so that the aluminum will be in an appropriate position to receive the application of the coating process (paint) selected.
It should be pointed out that the aqueous solution developed by means of the present invention, as well as the application thereof onto the aluminum surface, fully meets the requirements of the rules relating to the quality of the aluminum and of its painted alloys.
In this context, the Brazilian rules are in conformity with the international rules like QUALICOAT - Quality Label for the Coating of Aluminum and AMMA - American Materials Manufacturing Alliance.
Such Brazilian rules impart quality to the application of an organic paint film onto the conversion layer formed on the aluminum surface, as follows.

ABNT NBR 14125: Treatment of surface - Organic coating for architectural purpose - Requirement

This rule specifies the requirements for organic coating for architectural purposes, by painting, for the treatment of aluminum surface and alloys thereof.
According to the present rule, the pre-treatment of the aluminum should be composed by one of more of the following steps: degreasing; neutralization and conversion film (constituted by chromation/phosphocromation or anodization). The pre-treated parts should not be stored for over 16 hours and, preferably, should be coated immediately after the pre-treatment, because the risk of loss of adherence increases as time passes. The storage area should be kept in good atmospheric conditions, free from dust. The handling of the pieces should be made with clean cloth gloves, in order to prevent contamination of the surface.
Then, the steps of washing, drying and polymerization should be carried out.
The final product should be within the parameters of thickness of the organic coating; brightness; impact resistance; flexibility; adherence; wet adherence; graphite hardness; resistance to artificial wearing causes; natural weathering causes; accelerated corrosion; acetic saline fog; finish and sampling.

ABNT NBR 15144: Aluminum and alloys thereof - Surface treatment - origanic coating of plates for architectonical purposes

For the purposes of this rule, by "base-plate" one understands a plate with specific finish of the lamination rollers. The tests plates should meet the requirements of organic coating; resistance to corrosion by exposure to saline fog; brightness; impact resistance; adherence; graphite hardness; resistance to artificial wearing causes; bending; cure; surface aspect of the coating; sampling and marking.
In order to carry out the tests, one should sample at least three plates of each batch. One should take from each plate a test specimen measuring at least 120 mm X 120 mm from the part of the plate determined by the manufacturer. For acceptance of the batch, one measures the three test specimens. If the measurement does not meet the above-specified value, the batch should be rejected.
Therefore, the solution of the present patent application meets the quality-parameter rules NB R 14125 and NBR 15144, as well as the requirements defined by the qualitative tests described in the following rules.

ABNT NBR 14901: Treatment of aluminum surfaces and aluminum alloys-determination of the accelerated corrosion resistance - Machu test of the organic coating of paints and varnishes

This rule prescribes the method for determining and evaluating accelerated corrosion resistance by the Machu test method, of dried organic films applied to powder and/or liquid of paints and varnishes on laminated plate products and profiles extruded from aluminum and alloys thereof, with surface pre-treatment.
The test parameters should provide the following conditions:

a) NaCl: 50g/L ± g/L;
b) CH₃COOH (glacial): 10m/L ± 1 m/L;
c) H₂O₂(30%): 5m/L ± 1 m/L;
d) Temperature: 37°C ± 1°C;
e) Test time: 48h ± 0.5h.

The pH of the solution should range from 3.0 to 3.3. After 24 hours, one should add a further 5m/L of hydrogen peroxide (H₂O₂ 30%) and correct the pH with glacial acetic acid or caustic soda. For each test, it is necessary to prepare a new solution. In the results achieved, no infiltration may exceed 0.5 mm for either side of the incision.

ABNT NBR 14682: Aluminum and its alloys - surface treatment - determination of the moisture resistance of coating - pressure-cooker method

This rule specifies the pressure-cooker method for determining the wet adherence of electrophoretic coatings and paints to powder on aluminum and alloys thereof.
The test should be carried out with demineralized water at 20°C, used as a reactant, with maximum conductivity of 10µS. Cut the tests specimen in length of 500mm ± 5 mm and width larger than 25mm, as long as it fits into the pan body.
The test should be carried out at least 1 hour after polymerization. Pour water into the pressure cooker until it reaches the height of 25mm ± 3mm of the test specimen to be tested. Place the pan lid on and heat it until water vapor begins to escape. Adjust the pressure-controlling valve so as to guarantee internal pressure at 100 fluorine ± 10 fluorine. Continue to heat for 1 hour from the moment of the first vapor escape. Eliminate totally the inner pressure of the pan, remove the test specimen and allow it to cool down to room temperature. Apply the adhesive tape to the surface of the test specimen, making sure that no air will be trapped. After 1 minute, pull the tape by hand at an angle of about 45 degrees with strong and uniform traction.
The rule specifies methods for determining adherence to any type of paint applied to aluminum surfaces and alloys thereof through the X-cut and the grid-cut, with one or more application layers.
Initially the determination of the thickness should be carried out after 1 hour from polymerization, and then one should select an area for determining the adherence (as flat as possible) free from imperfections, clean and dry. Measure the thickness of the pain of the area where the adherence will be determined, with the dry-film thickness meter, at least at five different places, making three to five individual readings at each place. The arithmetic mean of the individual reading at one measurement point is considered the thickness of the total area. For paints with thickness of up to 80µm (inclusive), use either the X-cut method or the grid-cut method. For paint with over 80µm up to 600 µm (inclusive), use the X-cut method.
The result achieved should be within the graphic parameters defined by the present rule, so that the expression of the results should be analyzed in accordance with the cut made.

ABNT 1490: Treatment of aluminum surface and alloys thereof - determination of the resistance to corrosion by exposure to acetic saline fog of the organic coating of paints and vanishes

This rule prescribes the method for determination and evaluation of the corrosion resistance, by exposure to acetic saline fog of dry organic films applied to powder and/or liquid of paints and varnishes on laminated-place products and profiles extruded from aluminum and alloys thereof, with pre-treatment of surface.
The test should be carried out on three test specimens of plates and profiles extruded from aluminum or alloys thereof, and fixed within the test chamber with a rigid plastic material, for 1000 hours. Make a cross-incision (90 degrees), with width of 1 mm and length of 100mm, on the surface of the test specimen to be evaluated, until the metal is reached. The test-specimen surface to be evaluated should be preferably parallel to the horizontal flow of fog, in order to prevent direct impact of the latter onto the surface. Flat test specimens should be placed at angles of 15 degrees to 30 degrees with the vertical. In the case of pieces with complex shapes, this positioning should be made considering the region to be evaluated.
The result achieved by means of the infiltrations on the test specimens should not exceed 4mm for either of the incision sides and the result of the batch should be classified in accordance with the table of result classification described by the present rule.
It should be pointed out that the solution disclosed in the present patent application further meets other qualitative tests described in the following rules: NBR 12610, NBR 14126, NBR 14127, NBR 14165, NBR 14849, NBR 14850, NBR 14904 and NBR 14947.

Example

The composition discloses by the present invention can be better understood by means of the following non-limiting embodiment, wherein its advantages can be proven by the fact that it meets efficiently the above-cited Brazilian rules.
According to the preferred but not compulsory embodiment, the composition of said aqueous solution for pre-treatment of aluminum surface is prepared in three different steps, as described hereinafter.

First Step: Preparation of Solution no. 01

In a container of 316L stainless steel, 40% of demineralized water was added, and this volume was heated up to 90°C. Then, 5.80% of ammonium molybdate were added under agitation until total solubilization of the salt.

Second Step: Preparation of Solution no. 02

In a container of 316L stainless steel or ion a polypropylene container, 20% of demineralized water was added. Then, 5.20% of hexafluorosilicic acid 30% were added under agitation for 5 minutes. Still under continuous agitation, the mixture obtained was neutralized with an ammonium hydroxide solution 1:1 until pH 4.5 was reached. The volume spent was written down as percentage (%).
Then, 8.45% of hexa fluoro zirconium 45% was added, under agitation for 5 minutes, in the container with homogenized hexafluorosilicic acid 30%. Still under continuous agitation one neutralized the mixture obtained with an ammonium hydroxide solution 1:1 until pH 4.5 was reached. The volume spent was written down as percentage (%).

Third Step: Preparation of the Final Solution

One added solution no. 01 (previously prepared) in the stainless steel container that held solution no. 02 (previously prepared), under continuous agitation, for 10 minutes. Still under continuous agitation, one neutralized the mixture of the two solutions with ammonium hydroxide 1:1 until pH from 5.0 to 5.8 was reached. The agitation continued for 10 minutes, and the volume spent for neutralization was written down as percentage (%).
The final solution was allowed to cool until room temperature ranging from 20°C to 25°C was reached. Then, one added 0.13% of hydrogen peroxide 130 vol. The total amount of ammonium hydroxide volume 1:1 by percentage (%) used to adjust the pH was subtracted from the percentage value (%) of the demineralized water necessary for completing 100% of the final product. The final solution obtained remained at rest for 12 hours.
Hereinafter, one will demonstrate the reactions that take place in a preferred embodiment of the preparation of the composition for pre-treatment of an aluminum surface.

1) Reaction with ammonium molybdate (NH4)6 Mo7O24.4H20 with pH 5.0 to 6.9, adjusted with ammonia and catalyzed with hydrogen peroxide:

(NH4)6 Mo7O24 + 2Al + 6H2O---Al2(Mo7O24) + 3H2 + 6 NH4 OH
2) Reaction with hexa fluoro zirconium acid with pH 5.0 - 6.9 adjusted with ammonia:

2[(NH4) H (F6Zr) + 2 Al + 4H2O + --- AI2[(F6Zr)2(OH)2] +2NH4 OH + 3H2
3) Reaction with hexafluorosilicic acid with pH adjusted with ammonia to pH 5.0 - 6.9

2Al + 2[(NH4) H (SiF6)] + 4H2O --- AI2[(Si F6)2(OH)2] +2NH4 OH + 3H2
4) Joining the reactions, one will form the complex molybdenum, zirconium and silicon with aluminum, adherent and protective, used as a conversion layer for paint, according to the following reaction: 6Al +14H2O +(NH4)6 Mo7O24 + 2[NH4) H (F6Zr) +2[NH4)H(SiF6]---Al6(Mo7O24)(F6Zr)2 (OH)4 (SiF6)2 + 10 NH4OH +9H2.

Once the three steps for preparation of the composition free from chrome and toxic derivative revealed in the present invention have been completed, the application of the aqueous solution onto the aluminum surface was carried out in accordance with the technical procedures described by the ABNT, which are duly known to those skilled in the art.
Before applying the aqueous solution free from chrome to the aluminum surface, one carried out the conventional steps of pre-treating the metal under the operational conditions cited before in the present application.
The previously prepared aqueous solution was added to a tank at a concentration from 45 g/L to 50g/L, and kept under a temperature ranging from 20°C to 30°C with pH controlled between 5.0 and 6.0. Then, the aluminum underwent an immersion bath in said aqueous solution for 3 minutes, so that a conversion layer of brownish color, clearly visible to the naked eye was immediately formed on its surface.
Finally, a new washing with demineralized water was carried out and the pre-treatment of the aluminum was finished with the step of drying the surface, with dry air at a temperature ranging from 65°C to 70°C.
The aluminum surface was then tested as determined by the qualitative tests described in the Brazilian rules relating to the quality of painted aluminum and alloys thereof, and the efficiency of the colored conversion layer formed by using the composition of the present application was proven, totally free from chrome and toxic derivatives thereof, with a high corrosion resistance and completely apt for receiving the coating (paint) selected.
Preferred embodiments having been described, one should understand that the scope of the present application embraces other possible variations, being limited only by the contents of the accompanying claims, which include the possible equivalents.

Claims

A composition for pre-treatment of an aluminum surface, characterized by being an aqueous solution comprising the following components:
a) from 2% to 10% by weight of a fluorinated inorganic acid;

b) from 2% to 10% by weight of molybdate, titanate or zirconate of an alkali metal or alkaline earth metal or ammonia, optionally in the form of a fluoro acid derivative; and

c) from 0.02% to 0.2% by weight of hydrogen peroxide or organic peroxide oxidizing agent;
where the total weight percentage of said components in aqueous solution ranges from 4.02% to 20.2%.
A composition according to claim 1, characterized in that the fluorinated inorganic acid is silicic fluoro acid, hexa fluoro zirconium acid or hexa fluoro titanic acid.
A composition according to claim 1, characterized in that molybdate, titanate or zirconate of an alkali metal or alkaline earth metal or ammonia are chosen from the group consisting of sodium molybdate, potassium molybdate, fluoro ammonia molybdate acid, fluoro sodium molybdate acid, fluoro potassium molybdate acid, molybdic acid, hexa fluoro titanic acid, hexa fluoro potassium titanate, hexa fluoro sodium titanate, hexa fluoro ammonia titanate acid, hexa fluoro zirconium acid, hexa fluoro potassium zirconate acid, hexa fluoro sodium zirconate acid and hexa fluoro ammonia zirconate acid.
A composition according to claim 1, characterized by comprising demineralized water.
A method for preparing the composition as defined in any one of claims 1 to 4, characterized by comprising the steps of:
a) preparing solution no. 1, which comprises dissolving molybdate, titanate or zirconate of an alkali metal or alkaline earth metal or ammonia, optionally in the form of a fluoro acid derivative;

b) preparing solution no. 2, which comprises neutralizing the fluorinated inorganic acid until pH 4.5 is reached;

c) preparing the final solution, which comprises mixing solution no. 1 with solution no. 2 and neutralizing the medium until pH from 5.0 to 5.8 is reached, finally adding the hydrogen peroxide or organic peroxide oxidizing agent.
A method according to claim 5, characterized in that, in step (a) the molybdate, titanate or zirconate of an alkali metal or alkaline earth metal or ammonia is dissolved in demineralized water.
A method according to claim 5, characterized in that, in steps (b) and (c), the neutralization for adjustment of pH is carried out with ammonium hydroxide solution.
A method for applying the composition as defined in any one of claims 1 to 4, characterized by comprising the steps of degreasing, washing, deoxidizing, chemical treatment, washing and drying.
A method according to claim 8, characterized in that the composition is applied during the chemical treatment step.
A method according to claim 8, characterized in that, in all the steps, the bath of the aluminum surface is carried out by immersion or spraying.
Use of a composition as defined in any one of claims 1 to 4, characterized by being intended for chemical treatment of an aluminum surface.
A product characterized in that its surface is treated with the composition as defined in any one of claims 1 to 4.