Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
  • C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
  • C23C22/34—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing fluorides or complex fluorides
  • C23C22/37—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing fluorides or complex fluorides containing also hexavalent chromium compounds

Definitions

• the invention relates to a method for applying organic coatings to metal surfaces, in which a chromate layer is previously generated on the metal surface by means of an aqueous chromating solution.
• metal surfaces e.g. made of steel, aluminum and / or zinc with a conversion layer in order to increase the corrosion resistance and the adhesion of organic coatings.
• conversion layers are phosphate layers, chromate layers, complex oxide layers and the like.
• passively treat the conversion layer with a dilute chromium-containing rinse solution so that the corrosion resistance and the adhesion of the organic coating subsequently applied is further improved.
• chrome-containing rinse solutions have been replaced to a certain extent by chrome-free rinse solutions in order to keep the treatment of the various waste water streams in metal treatment processes as simple as possible.
• a typical example for the treatment of zinc surfaces, which are provided with a conversion layer, with aftertreatment by an aqueous chromium-containing rinse solution in order to increase the corrosion resistance and the paint adhesion is in US Pat. No. 3,501,352 described.
• the conversion layer is generated immediately before the rinse solution is applied.
• the object of the invention is to provide a method for applying organic coatings on metal surfaces, which can do without aftertreatment with chrome-containing rinse solutions, works simply and economically, leads to products with high corrosion resistance and high adhesion of the organic coating and permits subsequent treatments without the organic coating breaks or peels off.
• the object is achieved by designing the method of the type mentioned at the outset in accordance with the invention in such a way that a film of a chromating solution which contains chromium (VI) ions, zinc ions and fluoride ions in amounts sufficient for layer formation is applied to the clean metal surface Film dries and immediately afterwards the organic coating is applied.
• a film of a chromating solution which contains chromium (VI) ions, zinc ions and fluoride ions in amounts sufficient for layer formation is applied to the clean metal surface Film dries and immediately afterwards the organic coating is applied.
• the method according to the invention is intended in particular for the treatment of steel, aluminum and zinc surfaces.
• the zinc surface may have been obtained, for example, by hot dip galvanizing.
• the chromium (VI) ions are introduced into the chromating solution, for example in the form of chromic acid and / or chromates. If desired, the entry of Chromium (III) ions via the halides including chromium fluoride or mixtures thereof. Care must be taken to ensure that individual components of the components of the added compounds are compatible.
• a particularly suitable source of the chromium content of the chromating solution is a chromium chromate compound, the production of which is described in US Pat. No. 3,501,352.
• various reducing agents are added to a solution of chromic acid in water, which reduce chromium (VI) to chromium (III).
• Such reducing agents are compounds with active hydroxyl groups, aldehyde groups or carbonyl groups. These include monohydric alcohols such as methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, butyl alcohol and the like, dihydric alcohols such as glycol, polyethylene glycol and the like, polyhydric alcohols such as glycerin, manitol, sorbitol and the like, aliphatic and aromatic aldehydes such as formaldehyde , Acetaldehyde, benzaldehyde and the like, phenol and carboxylic acids such as citric acid, tartaric acid and the like.
• inorganic reducing agents can also be used. Suitable reducing agents are, for example, lithium, aluminum and zinc and metal compounds thereof. Of the total reducing agents mentioned, methyl alcohol is particularly suitable.
• a preferred embodiment of the invention provides for a film of a chromating solution to be applied to the metal surface, the total chromium ion content of which is in the range from 0.5 g / l to the saturation limit.
• the chromium content in the working chromating solution can be kept constant at approx. 6 g / l.
• the chromium content of the chromating solution consists of at least 50% by weight chromium (VI).
• the possible difference of 100% is usually in the form of chromium (III) ions. It has proven to be most advantageous to measure the contents of the chromating solution with respect to the chromium ions in such a way that 60 to 80% by weight of the total chromium consists of chromium (VI) ions.
• a further advantageous embodiment of the invention consists in applying a film of a chromating solution to the metal surfaces which contains zinc ions in the range from 0.1 to 10 g / l, preferably in the range from 0.3 to 3 g / l.
• the zinc content is kept constant at about 1 g / l.
• All compounds soluble in the chromating solution can be used as the source of zinc, provided that they are compatible with other constituents of the solution and have no adverse effect on the metal surface to be treated.
• Zinc oxide, zinc hydroxide, zinc carbonate and metallic zinc are particularly suitable zinc compounds.
• the chromating solution used in the process according to the invention contains fluoride.
• fluoride a chromating solution containing fluoride ions in the range from 0.1 to 10 g / l, preferably in the range from 0.5 to 5 g / l.
• a typical fluoride concentration is around 2 g / l.
• the fluoride is also to be introduced as a compound that is soluble in the chromating solution and compatible with the other solution components. These are, in particular, alkali fluorides, such as sodium, potassium and ammonium fluoride.
• the fluoride can also be introduced as zinc fluoride, whereby the zinc is added at the same time.
• a particularly suitable fluoride compound is hydrofluoric acid. It has been found that simple fluorides, e.g. of the aforementioned type are more expedient than complex fluorides, such as fluorosilicate or fluoroborate.
• the chromating solution contains hydrogen ions in order to adjust it to a pH value in the acidic range. It is particularly advantageous to apply a film of a chromating solution to the metal surface, the pH of which is in the range from 2 to 4.5. A typical pH value is approx. 3. The most favorable pH value depends to a certain extent on the concentration of the components of the chromating solution, on the temperature at which the chromating solution is used, and on the duration of the contact between the liquid film and zu treating metal. For iron metal surfaces e.g. good results are achieved in the pH range from 2.5 to 3.5.
• the chromating solution is applied to the cleaned metal surfaces by roller application, brushing, spraying, flooding, dipping and the like. After application, excess chromating solution, e.g. by squeezing rollers. It is particularly advantageous to carry out the removal in this way. that a liquid film of 2.54 to 20.3 microns thick remains. It is then dried.
• a chromate layer with a layer weight in the range from 3.23 to 53.8 mg / m2 should be applied.
• the film is dried by evaporating the water, resulting in an adherent, uniform chromium-containing layer.
• a film of a chromating solution is applied to the metal surface, the temperature of which is in the range from 2 l, 1 to 7 l, 1 ° C., preferably in the range from 32.2 to 60 ° C. Because of the heat capacity of the workpiece and the liquid film itself, the water evaporates and dries Chromate layer generally requires no additional external heat. However, the drying process can be accelerated by an additional supply of heat, for example in the form of heated air.
• the dried chromate layer is coated directly with an organic coating, e.g. provided with paint, varnish and the like.
• organic coating e.g. provided with paint, varnish and the like.
• Typical organic, coating-forming substances are based on plastics and contain acrylate, epoxy or alkyd compounds.
• the organic coating can be single layer and e.g. be a polyester type varnish. It can also have a multilayer structure, e.g. with an epoxy-type base layer and a polyester-type cover layer.
• the chromated and painted metal surface obtained by the process according to the invention has excellent corrosion resistance and good adhesion with regard to the organic coating to the substrate.
• the chromate layer is characterized by good ductility, so that it and the organic coating subsequently applied permit subsequent shaping into numerous shapes without the organic layer breaking or peeling off.
• aqueous acidic concentrate was first prepared: 227 parts by weight of chromic acid were dissolved in 300 parts by weight of water with stirring and a reducing agent was added.
• the reducing agent consisted of an aqueous solution of 12.5 parts by weight of methanol in 50 parts by weight of water.
• the mixture was then heated to 77 ° C. and left at this temperature for 2 h to complete the reaction.
• 14 parts by weight of hydrofluoric acid (70% by weight) and 17.4 parts by weight of zinc oxide were added. Finally, 459 parts by weight of water were added.
• the sheets treated in this way were then provided with a single-layer coating based on polyester (product name 408-lW 374 from Specialty Coatings Co.).
• a second set of sheets received a two-layer paint structure with an epoxy primer (product name 3465-B from Lilly Industrial Coatings Inc.) as the base layer and a polyester paint (product name 78l0l-l0l7A from Lilly Industrial Coatings Inc.) as a top layer.
• the sheets were then subjected to tests to determine paint adhesion and corrosion resistance.
• the paint adhesion (deformability) was tested according to standard methods in accordance with a bending test of 180 ° and impact test.
• the tests to determine the corrosion resistance were carried out according to the salt spray test ASTM B ll7, acetic acid test ASTM B 287 (only for aluminum sheets) and moisture test ASTM D 2247. The results achieved exceeded the requirements specified for the paints used.
• a chromating solution was prepared by diluting 0.27 l of the concentrate mentioned in Example 1 to 6 l with water and adding 90 ml of hydrofluoric acid (20% by weight) and 15 g of zinc oxide.
• the chromating of cleaned steel sheets was carried out as described in Example 1, chromate layers with a chromium content of 26.9 to 32.3 mg / m 2 being achieved.
• Example 2 0.3 l of concentrate from Example 1 were used to prepare the chromating solution, which was diluted to 6 l with water and mixed with 52 ml of hydrofluoric acid (20% by weight).
• Freshly cleaned aluminum sheets were used to carry out the tests and were immersed in the chromating solution at a temperature of 32.2 to 35 ° C. for about 3 seconds. Following the removal of excess chromating solution by squeezing, there was a brief drying.
• the chromate layer obtained contained 0.8 mg / m2 of chromium.
• a first set of sheets was provided with a single-layer coating based on polyester (product name Glidden White Polylure 602-W-l66 from Glidden) and a second set of sheets with a single-layer coating based on acrylate (product name DuPont 884-500l Lucite 2l00 Series from DuPont).
• the chromating solution was prepared by diluting 0.26 l of concentrate according to Example 1 with water to 6 l and adding 10 ml of hydrofluoric acid (20% by weight).

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• Chemical & Material Sciences (AREA)
• General Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Chemical Treatment Of Metals (AREA)

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• 1986
  • 1986-11-01 EP EP86115172A patent/EP0222282A3/fr not_active Withdrawn
  • 1986-11-03 DE DE19863637254 patent/DE3637254A1/de not_active Withdrawn
  • 1986-11-04 GB GB08626306A patent/GB2183680A/en not_active Withdrawn

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