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
  • C25D11/06—Anodisation of aluminium or alloys based thereon characterised by the electrolytes used
  • C25D11/10—Anodisation of aluminium or alloys based thereon characterised by the electrolytes used containing organic 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
  • C25D11/20—Electrolytic after-treatment
  • C25D11/22—Electrolytic after-treatment for colouring layers

Definitions

• the invention relates to a method for the surface treatment of aluminum or Aluminum alloys according to the features of claim 1.
• the corrosion resistance can be improved by reinforcing the natural oxide skin after chemical or electrochemical processes still increased become.
• the reinforced oxide layer is absorbent so that it is soluble in water Dyeing dye or dye precursome.
• the surface oxidation of the alumimium surface or the surface of Aluminum alloys can be obtained chemically by dipping the workpieces in Solutions of weakly acting agents or by chromating and phosphating respectively.
• anodic oxidation is electrochemical (Anodization, Eloxal method) more advantageous, since so thicker oxide coatings obtained Be as by chemical treatment.
• hard anodization At low temperatures (up to about + 10 ° C, preferably 2 to 3 ° C), high current densities (up to 2.5 A / dm 2 ) and generally low sulfuric acid concentrations (up to about 10 wt .-% ig) , optionally mixed with phosphoric acid, very hard, abrasion-resistant oxide layers are obtained (hard anodization). In this case, a layer thickness of the oxide layer of> 50 microns can be achieved. These workpieces obtained by hard anodization are used in particular for die-cast aluminum parts, eg for engine construction. There is a maximum achievable layer thickness, which is about 45 microns in the GS process, for example. At this maximum layer thickness, dissolution rate of the alumina is equal to its rate of formation.
• anodic oxidation methods e.g. the coating of aluminum coils (can-making), generally by performing an aluminum strip is made by a sulfuric acid electrolyte. There are Layer thicknesses of 2 to 3 microns desired.
• the object of the present invention is to provide an over the classic prior art method of faster anodizing process for Aluminum or aluminum alloys, which also has a better current efficiency, that is, to cause even lower energy losses by cooling.
• This Process should be suitable both for anodization by means of diving and for a continuous anodization, e.g. of tapes or wires by means of a electrolytic pulling process.
• the method should be at a Hard anodization allow the achievement of greater maximum layer thicknesses than this with the methods of the prior art, e.g. with the GS method, is possible.
• This object is achieved on the basis of a method for surface treatment of aluminum or aluminum alloys by anodic oxidation of the Aluminum or aluminum alloys (anodization) in an electrolyte.
• the inventive method is then characterized in that the concentration of the alkanesulfonic acid and the further acid. 3 to 30 wt .-% of the electrolyte.
• the electrolyte contains 10 to 30 wt .-%, particularly preferably 10 to 25 wt .-% of an alkanesulfonic acid.
• the electrolyte may contain further acids, in particular selected from sulfuric acid, Phosphoric acid and oxalic acid.
• alkanesulfonic acids in the surface treatment of aluminum or aluminum alloys is already known from the prior art. These However, known processes essentially relate to the use of alkanesulfonic acids in the electrolytic metal salt coloration of aluminum, wherein a Alkanesulfonic acid used as an additive or as the basis of an acidic electrolyte solution and not the use of alkanesulfonic acids in anodic oxidation (Anodization) of aluminum or an aluminum alloy.
• US 4,128,460 relates to a process for dyeing aluminum or aluminum alloys by electrolysis, comprising the anodization of the aluminum or the Aluminum alloys by conventional methods and subsequent electrolysis in a bath containing an aliphatic sulphonic acid and a metal salt, in particular a tin, Copper, lead or silver salt containing sulfonic acid.
• a metal salt in particular a tin, Copper, lead or silver salt containing sulfonic acid.
• US 4,128,460 is a Increasing the stability of the electrolysis bath by increasing the oxidation stability of the used metal salts and a uniform coloring of the surface of the Achieved aluminum or aluminum alloys.
• the Brazilian applications BR 91001174, BR 9501255-9 and BR9501280-0 refer to methods for electrocoating anodized aluminum when used of electrolytes and metal salts, which are mainly pure Methanesulfonic acid, methanesulfonates of tin or copper or methanesulfonates of nickel, lead or other salts. According to these applications become so an increase of the specific electrical conductivity of the solution, Reduce the time for coloring in a simple way and with more reliable Control, reproducibility of the same color tones and low operating costs.
• BR 9501255-9 Only in BR 9501255-9 are special reaction conditions for anodization disclosed the surface of aluminum, wherein the use of methanesulfonic acid as Additive is mentioned in a sulfuric acid-based electrolyte. Methanesulfonic acid is present therein in an amount of 10 parts by weight relative to Sulfuric acid, i. less than 2 wt .-% of the electrolyte used. Another Reference to the use of alkanesulfonic in the anodizing or advantages of a Such use is not disclosed in BR 9501255-9.
• the alkanesulfonic acid-containing electrolyte used in the dyeing step According to JP 57 126 993, the alkanesulfonic acid-containing electrolyte used in the dyeing step.
• the present invention it has been found that when using Alkanesulfonic acids as the basis of the electrolyte used in the anodizing one faster anodization occurs than with the prior art methods.
• This is also with regard to a subsequent electrolytic dyeing of the anodized Surface crucial because in such a two-stage process, comprising a Anodization and subsequent staining of the anodized surface, the Anodization is the rate-limiting step. It is, depending on the color of the Surface, 5-50 times slower than the subsequent staining.
• the electrolysis time to reach a subsequent dyeing step optimal alumina layer thickness of generally 10 to 30 microns, preferably from 15 to 25 microns is generally 5 to 40 minutes, preferably 10 to 30 Minutes, whereby the exact time depends among other things on the current density.
• alkanesulfonic acids have a much less corrosive effect on the Anodization formed alumina layer as e.g. the commonly used Sulfuric acid.
• the method according to the invention especially in hard anodization, larger layer thicknesses in a shorter time achieve than with the methods of the prior art.
• Another great advantage of the method according to the invention is the clear lower energy consumption during anodizing, since at the same amperage a significantly lower voltage compared to the pure sulfuric acid electrolyte established. This also has the consequence that the necessary energy for cooling the Anodising bath is significantly lower.
• the inventive method is for both anodization of aluminum or aluminum alloys with the electro-dip method suitable as well as for a continuous anodization, for example of tapes, pipes or wires, by an electrolytic pulling-through method, e.g. for production of Aluminum sheet for can production.
• the inventive method can both DC and with AC operation are preferred, the method is preferred with DC operated.
• the electrolyte may contain other acids, For example, sulfuric acid, phosphoric acid or oxalic acid.
• the electrolyte contains either the only acid is an alkanesulfonic acid or a mixture of sulfuric acid and Alkane sulfonic acid.
• the electrolyte must be 20 to 100 parts by weight of a Alkanesulfonic acid and 80 to 0 parts by weight of a further acid selected from Sulfuric acid, phosphoric acid or oxalic acid, the sum of alkanesulfonic acid and sulfuric acid, phosphoric acid or oxalic acid is 100 parts by weight and a Concentration of 3 to 30 wt .-% of the electrolyte makes up.
• the electrolyte contains 20 to 90 parts by weight of an alkanesulfonic acid and 80 to 10 parts by weight Sulfuric acid.
• alkanesulfonic acids are to be understood as meaning aliphatic sulfonic acids. These may optionally be substituted on their aliphatic radical with functional groups or heteroatoms, for example hydroxy groups. Preference is given to alkanesulfonic acids of the general formulas R-SO 3 H or HO-R'-SO 3 H used.
• R is a hydrocarbon radical which may be branched or unbranched, with 1 to 12 carbon atoms, preferably having 1 to 6 carbon atoms, especially preferably an unbranched hydrocarbon radical having 1 to 3 carbon atoms, most preferably having 1 carbon atom, that is methanesulfonic acid.
• R ' is a hydrocarbon radical which may be branched or unbranched, having 2 to 12 Carbon atoms, preferably having 2 to 6 carbon atoms, more preferably one unbranched hydrocarbon radical having 2 to 4 carbon atoms, wherein the Hydroxy group and the sulfonic acid group bonded to any carbon atoms with the restriction that they do not share the same carbon atom are bound.
• methanesulfonic acid according to the invention as Alkanesulfonic acid used.
• aluminum and aluminum alloys be oxidized anodically.
• Particularly suitable aluminum alloys are alloys of aluminum with silicon, manganese, zinc, copper and / or Magnesium. It can be silicon, manganese, zinc, copper and / or magnesium too a content of 15% by weight of (Si), 4% by weight of (Mn), 5% by weight (Zn), 5% by weight (Cu) or 5 wt .-% (Mg) may be contained in the alloy, including cast alloys are included.
• the process conditions of the pre-anodization preferably correspond to the Conditions of the classic GS (direct current sulfuric acid) known from the prior art or GSX (D.C. sulfuric acid-oxalic acid) electrolysis.
• the anodization is preferred at temperatures from 0 to 30 ° C performed. If too high temperatures are applied, one occurs irregular deposition of the oxide layer, which is undesirable.
• the hard anodization, the thick oxide layers with less Porosity and thus high hardness and great protection of the aluminum surface are desired, at low temperatures of generally 0 to 5 ° C, preferably 0 to 3 ° C performed. Due to less compared to pure sulfuric acid Corrosive property of alkanesulfonic acids over alumina are large Layer thicknesses of the oxide layer using the inventive method of> 30 ⁇ m, preferably from 40 to 100 ⁇ m, more preferably from 50 to 80 ⁇ m in shorter Times possible than when using pure sulfuric acid as the basis of the electrolyte. These aluminum oxide surfaces obtained by hard anodization are used in the generally not used for a subsequent dyeing step of the surface.
• the anodization according to the invention for obtaining a porous alumina surface which is particularly suitable for subsequent coloring of the surface is, is generally at temperatures of 17 to 30 ° C, preferably at 18 to 28 ° C. carried out.
• the method according to the invention is distinguished from the methods of the prior art characterized in that it is carried out at a higher temperature can be considered as the methods of the prior art.
• energy costs are saved.
• in the general is a cooling of the electrolyte solution during the anodization necessary because the anodization is exothermic.
• this embodiment of the inventive method at temperatures of generally 17 to 30 ° C. be, depending on the current density and the electrolysis time, layer thicknesses of from 5 to 40 ⁇ m, preferably from 10 to 30 ⁇ m.
• the process according to the invention is generally carried out at a current density of 0.5 to 5 A / dm 2 , preferably 0.5 to 3 A / dm 2 , particularly preferably 1 to 2.5 A / dm 2 .
• the voltage is generally 1 to 30 V, preferably 2 to 20 V.
• the electrolyte In addition to the alkanesulfonic acid used in the invention or a mixture of Alkanesulfonic acid and sulfuric acid, the electrolyte generally contains water and, if necessary, other additives such as aluminum sulfate.
• devices for carrying out the method according to the invention are in In general, all known devices suitable for electro-diving or for continuous anodic oxidation of aluminum or aluminum alloys, e.g. by means of an electrolytic passage method are suitable. Especially Preference is given to devices made of metals which are resistant to alkanesulfonic acids or devices which are plasticized, e.g. Polyethylene or polypropylene, lined are used.
• the pretreatment of the aluminum or aluminum alloys is a decisive step, since it determines the optical quality of the final product. Because the The oxide layer generated during anodization is transparent and this transparency also in the Dyeing process in step c) is maintained, any surface defects of the metallic remains Workpiece visible until the finished part.
• the pretreatment is carried out by conventional methods such as mechanical and / or electropolishing, dewaxing with neutral surfactants or organic Solvents, glazes or stains. It is then generally mixed with water rinsed.
• step a) also alkanesulfonic acid-containing solutions (for example, in the case of glazing and electropolishing) used.
• alkanesulfonic acids have already been mentioned above mentioned an insert in the anodizing step (step b)).
• Step b) relates to the anodizing process according to the invention, which relates to the Pre-treatment of aluminum or aluminum alloy connects. This The inventive method has already been explained in detail above.
• the coloring of the aluminum oxide layer is done by the absorption of organic or inorganic dyes in the capillary formed by the pores Anodization in step b) obtained oxide layer
• step c in step c), generally all of them may be after Known prior art method for coloring anodized aluminum be used. It usually distinguishes the chemical and the electrolytic coloring.
• Organic dyes Alizarin series dyes or indigo dyes
• Inorganic dyes can in a chemical coloring by precipitation reactions or by hydrolysis of Heavy metal salts are deposited in the pores. The running processes However, they are difficult to control and therefore often cause problems with the Reproducibility, ie with the same color nuances. Therefore, have yourself For a long time more and more the electrolytic process for coloring of Alumina layers enforced.
• Step c) of the process according to the invention is therefore preferably carried out by electrolytic process in a metal salt-containing electrolyte.
• the aluminum oxide layers obtained after step b) of the process according to the invention be, by means of direct or alternating current, preferably by means of alternating current, dyed in a metal salt-containing electrolyte. This is from the metal salt solution Metal deposited on the pore bottom of the oxide layer.
• Suitable metal salts are generally salts selected from tin, copper, silver, Cobalt, nickel, bismuth, chromium, palladium and lead or mixtures of two or more several of these metal salts. Preference is given in the process according to the invention Tin, copper or silver salts or mixtures thereof used.
• the sulfates of said metals are used, and there are Electrolyte solutions based on sulfuric acid used.
• the electrolyte In addition, additives can be added to improve the dispersion and Reducing the oxidation of the metal ions used, e.g. the oxidation of Tin (II) to insoluble tin (IV).
• the electrolyte contains 20 to 100 parts by weight of an alkanesulfonic acid and 80 to 0 parts by weight Sulfuric acid, the sum of alkanesulfonic acid and sulfuric acid 100 Parts by weight is and a concentration of 0.1 to 20 wt .-%, preferably 0.1 to 15 Wt .-% of the electrolyte. Most preferably, the electrolyte contains 100 parts by weight of an alkanesulfonic acid.
• Suitable alkanesulfonic acids have already been used for the process according to step c) above for use in anodization (step b)). Especially preferred is methanesulfonic acid.
• Tin (IV) salts are prevented from a tin (II) salt-containing electrolyte and the addition of additives such as the environmentally harmful phenol or toluene sulfonic acid is not required.
• the metal salts are generally in a concentration of 0.1 to 50 g / l, preferably from 0.5 to 20 g / l, more preferably from 0.2 to 10 g / l, based on the used metal, used in the electrolyte.
• the electrolyte In addition to the corresponding acid, preferably sulfuric acid or an alkanesulfonic acid or a mixture of the two acids, and the metal salt used or a Mixture of several metal salts, the electrolyte generally contains water and, if required, other additives such as litter improver. Especially when using alkanesulfonic acid-containing electrolytes, however, is the addition of additives in the general not required.
• the electrolysis time in step c) is 0.1 to 10 minutes, preferably 0.5 to 8 minutes, more preferably 0.5 to 5 minutes, the electrolysis time depends on the metal salts used and the desired color depth.
• the electrolytic coloring in step c) is carried out at alternating current.
• the current density is generally 0.1 to 2 A / dm 2 , preferably 0.2 to 1 A / dm 2 .
• the voltage is generally 3 to 30 V, preferably 5 to 20 V.
• Electrodes are usually used in a process for electrolytic Coloring of alumina layers suitable electrodes such as stainless steel, or Graphite electrodes suitable. It can also be an electrode from the deposited Metal, e.g. Tin, silver or copper.
• the method according to the invention becomes a gold coloration of the oxidized surface of aluminum or aluminum alloys in an electrolyte containing silver salts, optionally in a mixture achieved with tin and / or copper salts.
• gold-colored aluminum pieces are of particular interest for the production of decorative objects, as demand after gold-colored aluminum objects is large.
• these gold-colored alumina surfaces are obtained by staining in step c) at a concentration of an alkyl sulfonate of silver, calculated as Ag + , of 2 to 50 g / l, preferably 3 to 20 g / l and a product of current density and stress of 0.5 to 10 AV / dm 2 , preferably 1 to 5 AV / dm 2, over a period of generally 0.05 to 4 minutes, preferably 0.3 to 3 minutes.
• a detailed description of the production of gold-colored aluminum oxide layers can be found in the simultaneously filed application DE-A .... entitled "Process for producing gold-colored surfaces of aluminum or aluminum alloys by means of silver-containing formulations".
• the workpieces are in the generally rinsed with water, especially with running water.
• This Purge step follows both step b) and step c), if this is performed on.
• the pores of the oxide layer produced are generally following step b), if step c) is not performed, or following step c), if this is performed, sealed (Sealing), to obtain a good corrosion protection.
• This proofing can be done by about 30- to 60-minute immersion of the workpieces in boiling, distilled water can be achieved. The oxide layer swells, thereby the pores are closed.
• the water can also contain additives.
• the workpieces instead of boiling water in Tensioned water vapor of 4 to 6 bar aftertreated.
• the post-sealing is preferably carried out by means of water or water vapor
• Alkanesulfonic acid and / or their salts can be recovered.
• This recovery can be attached to any step in which an alkanesulfonic acid can be used connect or parallel to these steps.
• a Recovery is, for example, together with the at step b) and, if this is performed, step c) subsequent rinsing step (d1)) possible.
• a such recovery can e.g. by means of electrolytic membrane cells, by Cascade rinsing, or by simple concentration e.g. the rinsing solutions respectively.
• Another embodiment of the present invention is the use of a Alkanesulfonic acid in a process for the anodic oxidation of aluminum or Aluminum alloys (anodizing) to increase the speed of anodic oxidation.
• This makes it possible to have faster alumina deposition to achieve than with the methods of the prior art.
• alkanesulfonic acids as Base of the electrolyte can be obtained in a shorter time thicker layers than in the Use of pure sulfuric acid as the electrolyte base.
• the Energy consumption significantly lower, as sets a lower voltage and less to be cooled.
• inventively produced workpieces based on aluminum or Aluminum alloys for example, in construction, in particular for Production of window profiles or facade components, in car or aircraft construction, both for the production of body parts and for the production of aluminum die-cast parts, e.g. in engine construction, and in packaging, in particular for Production of cans, for example by a continuous electrolytic Pull-through method, e.g. continuous band anodization.
• Anodizing electrolytes were used, each containing 18% by weight of an acid or an acid mixture and 8 g / l of aluminum.
• the electrolytes were used for the anodization of pure aluminum sheets, which were each precodized for 2 minutes in the classical GS process, wherein anodization was carried out in each case at a current intensity of 1.2 A / dm 2 for 30 minutes.
• the anodizing bath was in each case thermostated at 20 ° C.
• the alumina layer thickness, the porosity or microstructure of the surface and the microhardness were determined. Table 1 below shows the layer thicknesses of the oxide layer obtained as a function of the electrolyte used and the anodization voltage and any necessary cooling:
• Example 2 Analogously to Example 1, but it was at 2 ° C and an electrolysis time of 40 min electrolyzed.
• the layers consistently showed a significantly lower porosity and an increased hardness in comparison to example 1.
• the sheets anodized in MSA methanesulfonic acid
• the porosity of the sheets 3 and 4 (according to the invention, the acid im Electrolyte corresponds to those specified in Table 1 under No. 3 or 4 Compositions) is lower than the other.
• MSA methanesulfonic acid
• the plates anodized according to Nos. 3 and 4 in Table 1 were dyed for different periods of time.
• the colorations listed in Table 2 below were obtained:

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• 2000
  • 2000-07-10 DE DE10033435A patent/DE10033435A1/de not_active Withdrawn
• 2001
  • 2001-07-10 BR BR0112434-0A patent/BR0112434A/pt not_active IP Right Cessation
  • 2001-07-10 PL PL36081701A patent/PL360817A1/xx not_active Application Discontinuation
  • 2001-07-10 AU AU2001281971A patent/AU2001281971A1/en not_active Abandoned
  • 2001-07-10 ES ES01960487T patent/ES2234870T3/es not_active Expired - Lifetime
  • 2001-07-10 CA CA002415556A patent/CA2415556A1/en not_active Abandoned
  • 2001-07-10 WO PCT/EP2001/007932 patent/WO2002004716A1/de active IP Right Grant
  • 2001-07-10 US US10/332,586 patent/US20040004003A1/en not_active Abandoned
  • 2001-07-10 AT AT01960487T patent/ATE287977T1/de not_active IP Right Cessation
  • 2001-07-10 DE DE50105209T patent/DE50105209D1/de not_active Expired - Fee Related
  • 2001-07-10 EP EP01960487A patent/EP1301656B1/de not_active Expired - Lifetime
  • 2001-07-10 TW TW090116875A patent/TWI243864B/zh active
  • 2001-07-10 CN CNB018139329A patent/CN1192128C/zh not_active Expired - Fee Related
  • 2001-07-10 JP JP2002509566A patent/JP2004502877A/ja not_active Withdrawn
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