Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
  • C25D11/02—Anodisation
  • C25D11/04—Anodisation of aluminium or alloys based thereon
  • C25D11/16—Pretreatment, e.g. desmutting
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
  • C25D11/02—Anodisation
  • C25D11/04—Anodisation of aluminium or alloys based thereon
  • C25D11/18—After-treatment, e.g. pore-sealing
  • C25D11/24—Chemical after-treatment
  • C25D11/246—Chemical after-treatment for sealing layers
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
  • C25D11/02—Anodisation
  • C25D11/04—Anodisation of aluminium or alloys based thereon
  • C25D11/06—Anodisation of aluminium or alloys based thereon characterised by the electrolytes used
  • C25D11/08—Anodisation of aluminium or alloys based thereon characterised by the electrolytes used containing inorganic acids
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
  • C25D11/02—Anodisation
  • C25D11/04—Anodisation of aluminium or alloys based thereon
  • C25D11/18—After-treatment, e.g. pore-sealing
  • C25D11/24—Chemical after-treatment
  • C25D11/243—Chemical after-treatment using organic dyestuffs

Definitions

• Anodized aluminum has low resistance to alkalis and to acids.
• domains such as automotive and building there is a pressing need for anodized articles the surface of which, while preserving their characteristic appearance, can withstand contact with strong alkaline solutions, and possibly also with strong acid solutions.
• Treatments to improve this resistance are notably the subject of standards, such as those of the European Aluminum Anodisers Association, these are referred as "Qualanod" standards.
• standards such as those of the European Aluminum Anodisers Association
• products treated in accordance to these standards mainly directed to buildings material, prove not to pass the tests of the automotive industry.
• the present invention aims at solving this problem. If in the first place the products for automotive industry are concerned, the invention also applies to any type of anodized product including those intended for building or domestic appliances.
• the anodized aluminum product treated first is one obtained that presents no prior defects, to that effect the anodization must follow the best known practices.
• usage anodization is carried out in electrolytic solution that includes an inorganic acid.
• acids most common is sulfuric acid.
• Other acids are also of interest notably those that are less susceptible to dissolve the anodic oxide film created.
• the anodization conditions such as voltage, temperature are well known from prior art that gives products free of any defects but need a precise control especially when using sulfuric acid solution. For example to low temperature corresponds a slow rate forming of the oxide layer, but if the temperature is too high the dissolution rate is increased. The temperature is usually not above 24°C.
• the anodic solution is immediately removed and the product washed to prevent further dissolution of the oxide film.
• the usual thickness selected must be sufficient to allow for the necessary resistance, chemical and mechanical. This is normally above 5 ⁇ m, and preferably above 10 ⁇ m. The thickness is preferably not above 50 ⁇ m to prevent possible defect formation such as cracks.
• Anodization leads to an oxide layer the structure resulting in a porous system that has poor resistance notably to acids or alkaline solutions. It is common to prevent these corrosive chemicals to penetrate the porous structure by sealing the pores.
• the usual sealing is made by hydration of the aluminum oxide that swells and obstructs the pores. Hydration may be made by way of hot water or steam. ("hot sealing"). This is done at temperature above 95°C.
• hot sealing Another possibility called “cold sealing” is starting with an impregnation step that includes contact with a first solution e.g. of nickel fluoride used for its properties to form insoluble complexes with aluminium and plug the pores, producing a good sealing.
• Other metallic salts notably of chromium may substitute to those of nickel. In this cold impregnation the temperature is not above 30°C. The impregnation is followed by ageing in a hot water treatment. Impregnation needs also careful control notably of nickel and fluoride respective concentrations.
• a first post treatment is using a solution of silicates in which the products are immersed under conditions that result in a further sealing or coating with "silicates polymers".
• a second treatment is following that includes using specific silanes solutions that adds another coating.
• this type of treatment using silicate is still to be improved.
• the invention provides for conditions to carry out this step, that makes both more efficient control and prevent possible defects.
• the treated products must be free of any powder deposit at the surface of the material that could alter the final aesthetic appearance.
• the products are thus immersed in the silicates solution.
• the silicate solution used is preferably one of alkaline metal, sodium, potassium or lithium or mixture thereof. These, notably sodium and potassium, are readily available in commerce and extensively used in many industrial sectors, notably as thickening agents.
• the solutions are containing an amount of silicate that depends on the stability. When increasing the concentration there is a limit above which the solution turns a gel. The concentration that allows remaining stable for long period of time are also depending on the nature of the silicate including the molar ratio SiO 2 /M 2 O (M standing for Na, K or Li). The higher this ratio, the lower the possible amount of silicate when trying to prevent the gel formation.
• the ratio is at least of 2.5, and preferably at least of 3.
• the silicate solution is preferably at pH above 5 and preferably above 6.
• This concentration for sodium silicate is preferably higher than lg/l and preferably from 10 to 30g/l.
• the coating also depends on temperature of the solution. Faster deposition of silicates is obtained with the highest temperature. For easiness of control over the process, the temperature is preferably higher than 40°C and does not exceed 95°C. The best temperature range according to the invention is from 60 to 80°C.
• the processing time depends on the previous parameters and is most usually between 5 and 50 minutes.
• the next step according to the invention is a treatment with a solution of one or more silanes or silanols that result from hydrolysis of these silanes.
• silanes used according to the invention are alkoxy-silanes that may be hydrolyzed to give in silanols that may react with hydroxyl groups leading to covalent bonds according to the known general mechanism: Al-OH+R-SiOH ⁇ Al-O-Si-R +H 2 O
• silanols are seldom available as such for reason that, to be stable, they need to be in greatly diluted solutions. For this reason it is most often necessary to have the silanols prepared when needed.
• the silanes used according to the invention are preferably of the general formula: R'(CH 2 )nSi(OR) 3 with n at most equal to 4 where -OR is one of: -OCH 3 , -OC 2 H 5 , -OCOCH 3 and R' is a radical from: vinyl, epoxy, methacrylate, primary amine, di-amine, mercapto.
• -OR is one of: -OCH 3 , -OC 2 H 5 , -OCOCH 3 and R' is a radical from: vinyl, epoxy, methacrylate, primary amine, di-amine, mercapto.
• the silanes that are used may also be bis-silanes of the general formula: (RO) 3 -Si(CH 2 )nR' (CH 2 )n-Si(OR) 3 with R, R' and n , having the same significance as indicated above.
• bis-silanes preferred ones are: (C 2 H 5 O) 3 Si(CH 2 )Si(OC 2 H 5 ) 3 (C 2 H 5 O) 3 Si(CH 2 ) 3 -S 4 -(CH 2 ) 3 Si(OC 2 H 5 ) 3 (C 2 H 5 O) 3 Si(CH 2 ) 3 -NH-(CH 2 ) 3 Si(OC 2 H 5 ) 3 .
• the concentration in silanes is less than 8% by weight of the solution, and most preferably less than 5% by weight. At these concentrations the hydrolysis tends to get to completion. To limit the processing time the concentration is preferably no less than 0.1% by weight.
• organo-silanes that are useful have a limited solubility as such in water.
• Using a water alcohol mixture enhance the solubility to the necessary concentration.
• the presence of alcohol may also regulate the hydrolysis of the silanes, and possibly makes the final drying easier.
• the content of alcohol may be up to 15% by weight of the mixture.
• hydrolysis of silanes needs time and depends on various factors notably the type of organo-silanes, the medium of the reaction and the pH. Hydrolysis in water proceeds more quickly than in mixture of water and organic solvent such as ethanol, and tends to completion. Playing with pH may catalyze the hydrolysis and enhance its speed.
• hydrolysis is faster with the smallest alkoxy group of the silanes, e.g. hydrolysis of methoxy-silanes is 6 to 10 times faster than ethoxy-silanes of the same structure.
• the treatment may be started when the concentration of silanols is sufficient, this corresponding to the solution becoming clear showing a true solution where before it was mostly a suspension.
• Application on the surface may be e.g. by dipping or by spraying.
• the necessary contact time depends notably on the temperature. For example, at a temperature of 15 to 35°C, this contact may be from 0.5 to 5 minutes.
• Silanols reacts with hydroxyl groups linked to the metal, but may also give rise to condensation reactions of the silanols themselves to forms silanes films.
• the former are increasing the adhesion to the substrate when the silanols condensates are promoting formation of a film the thickness of which depends on the concentration of the silanes solutions. Typical thickness may be up to 400nm.
• the structure of the film is possibly cross-linked depending on the specific silanes used (or mixture of silanes). The cross-linking is normally high with bis-silanes and better protection is obtained.
• the aluminum article is dried at temperature that may be from ambient to as high as 120°C, preferably from 40 to 120°C.
• temperature may be from ambient to as high as 120°C, preferably from 40 to 120°C.
• the above mentioned reactions are going n during the drying step.
• Anodized aluminum and aluminum alloys according to the invention exhibit specific resistance to the corrosive action that are the subject of the tests specified by the automotive industry. They notably have a weight loss at most of 10mg/dm 2 surface and preferably at most 5 mg/dm 2 , and most preferably at most 1mg/dm 2 when submitted to acid followed by alkaline test according to the specifications of the corrosion test 9.57448 from Fiat group. This weight loss is notably obtained for corrosion tests in which the acid is at a pH 1 and the alkali solution is at pH 13.5.
• Samples of aluminum profile are prepared prior to anodic oxidation by cleaning the pieces and polishing up to a surface roughness R a of 0.6 ⁇ .
• Chemical pickling or electrochemical treatment of surface may be preferred to confer another appearance, notably etched appearance to other samples.
• the anodization bath is containing 200 ⁇ 10g/l sulfuric acid. This solution is maintained at about 15°C. The current density is about 1.8 A/dm 2 .
• the anodization is carried out till the oxide layer is 20 ⁇ . At the indicated current density this needs about 45 minutes.
• the anodized article is thoroughly washed in deionized water to remove any adhering solution.
• a sealing process is then made to close the pore of the oxide layer.
• the sealing is of the "cold sealing" type including an impregnation with nickel ions.
• the example is made with Ni2+ at 1.2g/l and fluoride ions at 0.250g/l.
• the temperature selected is 28°C and treatment is maintained for 20 minutes.
• the solution is continuously filtered to remove any precipitate.
• the anodized samples are immersed in an aqueous solution of sodium silicate.
• the solution is prepared by diluting to 11, 10ml of a sodium silicate solution containing by weight:
• the pH is 8.0.
• Treatment of the samples is by immersion at a temperature of 70°C.
• the immersion time is 10 minutes.
• the various parameters are selected so that no precipitation occurs during the treatment.
• continuous filtration of the solution is carried out.
• the samples are washed in tap water then in demineralized water and dried.
• Careful examination of the product is done to control that no defects such as spots or powdery appearance of the surface may be detected.
• Table 1 The conditions recited in table 1 for anodization and sealing and silicate treatment are other possible examples substitutes to the ones indicated above. Table 1. It includes various conditions relating to the steps: anodization, sealing and treatment with silicates.
• Preliminary treatment Anodizing parameters Coloring Sealing Additional treatment Application A Chemical polishing H 2 SO 4 200g/l A1 dissolved 7g/l 20 ⁇ 1°C 1.5 A/dm 2 45 minutes Organic dying "Black MLW" 1 10g/l 45°C 10 minutes Impregnation Sealing Ni 2+ 1.2 g/l F - 0.250g/l 28°C 20 minutes Sodium silicate sol.
• Temperature sealing chemical specialties available on the market are based on a solution of about 10 g/nickel acetate and 0.2-05 g/l of a surfactant acting as a "bloom preventer" (i.e. it avoid the formation of powder on the anodic layer surface). Temperature 85-90 °C, dipping time 1 minute / micron (i.e. 20 min) 3 - Hot sealing chemical specialties available on the market contains essentially a mixture of surfactant used at a concentration of 1-2 ml/l acting as a "bloom preventer" (i.e.
• silanes composition is the one sold by the company CHEMETAL under the name "OXILAN MM 0706".
• the solution contains 3% by weight of this composition of silanes in water with addition of ethanol (5% by weight).
• the samples are immersed in the solution at room temperature during 2 minutes. After this the samples are removed from the tank and without washing directly dried in a hot air flow at 60°C for 20 minutes.
• the product made according to the invention was analyzed at each stage of the preparation. This allows to confirm that the product in itself may be the subject of identification without having recourse to the process for making it.
• a possible investigation includes an X-ray photoelectron spectrometry (XPS).
• XPS X-ray photoelectron spectrometry
• This method allows for identification of the elements entering in the surface layer of the product.
• the method permit analysis of very thin layers (around 20-30 ⁇ ) preventing a possible confusion with elements from under-layers. Nevertheless when the layers considered exhibit average thicknesses that are less than these figures, and/or the roughness of the surface is noticeable, part of the measurements may indicate a limited amount of elements from under-layers.
• each analysis is distinct according to the stage of the preparation. This confirm that the method definitely permits analysis of each top layer whatever the layers located underneath. This is notably the case of the silane top layer (4) including nitrogen (the starting silane is an amino-silane). It also contains an amount of carbon that clearly exceeds the amount of the previous layers, as the silane contains organic parts.
• the anodized part (1) includes carbon and nitrogen corresponding to the black coating part. Sealing in (2) appears notably through the presence of Ni and F. These elements are also appearing but definitely at a lower concentration in the product at the silicate treatment step (3) making clear that the layer of silicate is a thin one and possibly intervening to further sealing the pores. This layer also indicates that Al content is less than in sub-layers (2).
• Silanes of 4-7 above are sold pre-hydrolyzed and thus directly water soluble.

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• 2014
  • 2014-11-21 EP EP14194333.2A patent/EP3023522A1/de not_active Withdrawn
• 2015
  • 2015-10-08 ES ES15778287T patent/ES2741525T5/es active Active
  • 2015-10-08 WO PCT/EP2015/073271 patent/WO2016078826A1/en active Application Filing
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