Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D13/00—Electrophoretic coating characterised by the process
  • C25D13/20—Pretreatment
• • 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
  • C23C22/07—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 phosphates
  • C23C22/08—Orthophosphates
  • C23C22/10—Orthophosphates containing oxidants
• • 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
  • C23C22/40—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 molybdates, tungstates or vanadates
  • C23C22/42—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 molybdates, tungstates or vanadates containing also phosphates
• • 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
  • C23C22/73—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 characterised by the process
• • 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
  • C25D11/36—Phosphatising

Definitions

• the invention relates to a method for coating metal surfaces of substrates with an aqueous, acidic, alkali metal ion and phosphate containing phosphating solution, which is particularly suitable the substrates with a pretreatment layer made of this alkali phosphate to deposit a thin layer of electro-dipping paint and a corresponding one aqueous concentrate and the use of the according to the invention Processed products.
• the fresh, not yet used alkali phosphate solutions usually have practically no or very little Content of aluminum, iron and zinc.
• the aqueous acidic alkali phosphate solutions contain in addition to ions of at least one alkali metal or / and ammonium also phosphate ions and due to the pickling effect of these solutions based on the metallic surfaces ion contents metals detached from the metallic surfaces, e.g. Aluminum, Iron or / and zinc as well as traces of alloy components of the pickled metallic materials.
• the alkali phosphating in the Alkali phosphate layer mainly formed phases are the corresponding Phosphates, oxides and / or hydroxides of the metals from the Surfaces of the base substrates to be treated.
• Alkali phosphate solutions or coatings are used on iron materials also referred to as iron phosphate solutions or coatings.
• iron phosphate solutions or coatings The same applies to aluminum or aluminum alloys where is spoken of aluminum phosphate.
• the most varied Base metals coated with the same alkali phosphate solution be, whereby then the ions of the different base metals in the Enrich solution more.
• the alkali phosphate layers applies that - unlike e.g. the so-called zinc phosphating - often largely or are completely amorphous and extremely fine-grained.
• Alkali phosphate coatings are made according to Werner Rausch: The phosphating von Metallen, Saulgau 1988 (see in particular pages 109 - 118), generally also as layers of the so-called “non-layer-forming Phosphating ". This designation is misleading, as well layers are formed here, which, however, are significantly thinner than other phosphate layers such as the different types of Zinc phosphating.
• the alkali phosphate solution always contains an elevated one Content of at least one alkali metal, e.g. Sodium or / and Ammonium.
• the layers of alkali phosphating are often - in contrast to the crystalline layers of the other types of so-called "layer-forming Phosphating "- mostly X-ray amorphous and show under the scanning electron microscope mostly no crystalline grain shapes.
• the layers of alkali phosphating are often poor in, almost free or Completely free of manganese and zinc, unless manganese or zinc is rich metallic surfaces are treated or pretreated. They are typical poor in, almost free or completely free of cobalt, nickel, titanium or / and similar heavy metals.
• Those in the iron phosphating at least one iron material are mainly formed phases Iron phosphates, iron oxides and / or iron hydroxides such as e.g. Vivianit or / and Magnetite.
• the layers of the alkali phosphating have significantly different properties than those of the zinc phosphating: they are usually only of a layer thickness in the range from 0.1 to 0.8 ⁇ m or only of a layer weight in the range of 0.2 to 1.3 g / m 2nd In contrast to the gray zinc phosphate layers, the much thinner alkali phosphate layers are mostly iridescent and / or transparent, often bluish iridescent.
• the alkali phosphate layers mostly show the colors of "higher order" and, with a slightly changed layer thickness, are also, for example, yellowish, greenish or violet iridescent, whereas layers with a higher layer weight (approximately 0.7-1.3 g / m 2 ) and, if appropriate, corresponding accelerator content more likely to show a gray matt appearance in the phosphating solution.
• Alkali phosphate layers on aluminum or aluminum alloys can also have a silvery iridescent appearance.
• the alkali phosphate layers can be applied as treatment layers without, e.g. applied at least one layer of lacquer becomes. They can also be used as pre-treatment layers before at least a subsequent coating such as with a primer, varnish or / and a different organic coating or with an adhesive or adhesive carrier.
• alkali phosphate coatings are used as pretreatment layers made by contact with an acid before painting aqueous monophosphate and / or orthophosphate-containing phosphating solution and then by electrocoating the entire metal surface and often also by powder coating the from surface parts easily accessible from the outside. These procedures are used today always exhausted. The aim is to make these processes more reliable and to make it cheaper. A significant share of costs due to the comparatively thick electrocoat layer that is used today usually with complex undercuts or / and concealed metal parts such as some radiator elements still a thickness as an average over the entire surface of at least 12 ⁇ m, often more than 15 ⁇ m. Because of the Undercuts or because of hidden cavities must often with a electrical voltage of at least 200 V instead of e.g.
• the sulfates to the phosphating solution precipitate in the phosphate bath contributes to the fact that the alkali phosphate layers formed thereafter are denser and more closed than in increased presence of sulfate in the phosphating solution.
• the then on the alkali phosphate layer Eliminated electrodeposition coating could be Apply particularly evenly and thinner than before. Here it may be the electrodeposition paint coagulated more quickly, so that work is carried out at lower electrical voltages can.
• the Lacquer deposition in the process according to the invention is significantly better than compared to a sulfate-rich phosphating bath. This affects in particular if the sulfate content is due to the addition of Precipitant reduced to less than 50 mg sulfate per liter or approximately in this salary level can be maintained.
• a sulfate content can be regarded as a source of interference, which in particular from the low sulfate content of the water used (mostly city water) and the partially increased sulfate content Contamination of the substrate surfaces to be coated originate can.
• the last-mentioned sulfate levels can mainly be found in corrosion protection oils and forming aids, which were previously on the metallic Surface, be detached and remain in the bath solution can.
• the object of the invention is to propose an alkali phosphating process, in which it is possible to apply the subsequently applied electrocoat layer overall thinner than a sulfate ion containing more Phosphating bath and most processes according to the state of the art Apply technology without affecting the corrosion protection. It is also the task to propose a procedure that also applies to the application of the phosphating solution in spraying is well suited. The process should be easy and safe to use in series.
• the task is accomplished by a process for coating metallic Surfaces with an aqueous acidic alkali phosphating solution in particular before the deposition of a thin electrocoat layer, whereby a layer of an aqueous, optionally containing sulfate ions Alkali phosphating solution deposited and essentially on Base of phosphates / oxides / hydroxides mainly in the metallic Metals such as Aluminum, iron or / and Zinc is formed, which is characterized in that the alkali phosphating solution at least one precipitant for the precipitation of sulfate ions added at a pH in the range of more than 3.5 to 7 becomes.
• the phosphating solution according to the invention is preferably a precipitant with an initial salary in the range of at least 0.001 to 2 g / L, particularly preferably in the range of at least 0.01 or up to 1 g / L, in particular in the range of at least 0.02 or at least 0.1 g / L, added and / or in this concentration range in the phosphating solution held.
• it can also have a higher content Precipitating agents are added or contained in the phosphating solution be, but it does not have a correspondingly beneficial effect. Due to the Precipitation can result in a low level of precipitant in the phosphating solution reduce quickly if necessary.
• the precipitant can be in one Content in the range of 0.001 to 2 g / L in the phosphating solution be contained, particularly preferably in the range of at least 0.01 or up to 1 g / L or up to 0.8 g / L, especially in the range of at least 0.02 or at least 0.1 g / L.
• an aqueous one is preferably used acidic solution used for the deposition of the alkali phosphate layer, the for the precipitation of the sulfate contained in the alkali phosphating solution at least a cation, at least one chelate, at least one complex, at least a polyelectrolyte and / or at least one polymer such as e.g. based of polyacrylamide, polyacrylate, polyethyleneimine and / or polyethylene oxide is added and / or is added with sulfate ions in water poorly soluble and / or insoluble compounds leads.
• the phosphating solution is an addition of ions of barium, calcium or / and strontium in the range of 0 to 1 g per liter, in particular of at least 0.005 or up to 0.8 g per liter, preferably of a total of at least 0.01 or up to 0.5 g per liter, particularly preferred a total of at least 0.05 or up to 0.3 g per liter, very special preferably from a total of 0.02 or up to 0.2 g per liter, added.
• this connection is an addition to at least one type of ions and / or compounds selected from the group of barium ions, barium compounds, strontium ions, Strontium compounds, calcium ions, calcium compounds and Polyelectrolyte (s) particularly advantageous.
• the level of addition of precipitant can be adjusted to the sulfate content of the solution.
• the at least one precipitant of the phosphating solution is preferably used in a content of 0.03 to 0.25 g / L added and / or is in contain this concentration range in the phosphating solution.
• the phosphate solution in the phosphate solution can preferably be in the range from 1 to 30 g P 2 O 5 per liter, particularly preferably in the range from 2 to 25 g P 2 O 5 per liter, very particularly preferably in the range from 3.5 to 20 g P 2 O 5 per liter.
• the phosphate, in particular to a concentrate is preferably added by adding orthophosphoric acid or the corresponding hydrogen phosphates, when added as a powder, for example as disodium hydrogen orthophosphate, rarely as a polyphosphate.
• the phosphating solution can contain iron, in particular in the Have a range of 0.01 to 1 g Fe per liter, especially in the range of 0.08 to 0.8 g Fe per liter.
• the iron content is in the iron phosphating solution comparatively low because a large part of the iron content is canceled.
• the phosphating solution can contain manganese, Have nickel, zinc or / and other heavy metals. Are partial these levels of the coated surfaces and of the used ones Plant and raw materials dependent.
• the content of is preferably Manganese, nickel and / or zinc each not more than 0.2 g per liter, especially preferably not more than 0.1 g per liter.
• the phosphating solution preferably has an ion content of at least one alkali metal, especially sodium, in the range of 0.3 to 10 g per liter, particularly preferably in the range from 0.6 to 9 g per liter of individual ions, especially sodium, preferably in the range from 0.001 to 8.5 g per liter.
• the total content of alkali metal ions 1 to 8.8 g / L in the bath, in particular 1.2 to 6.5 g / L, before all at least 1.5 g / L or up to 4 g / L.
• This usually prevails a sodium content which is preferably 1 to 4.5 g / L, especially at least 1.5 g / L or up to 4 g / L.
• the addition of sodium ions helps with that Adjustment of the pH and is preferably bound to the phosphoric acid.
• the sodium ions can be added, for example, by adding sodium hydroxide be introduced.
• other alkaline earth metal ions such as. Magnesium ions occur that are only a comparative weak or no effect as a precipitant for sulfate. Therefore Magnesium ions or compounds are not very suitable as precipitants.
• the phosphating solution preferably has an ammonium ion content in the range from 1 to 200 mg per liter, particularly preferably in Range from 3 to 150 mg per liter, most preferably in the range from 5 to 120 mg per liter.
• the phosphating solution preferably has a free fluoride ion content in the range from 0 to 500 mg per liter, particularly preferably in Range from 1 to 350 mg per liter, most preferably in the range from 50 to 300 mg per liter.
• Fluoride is preferably added by Addition of hydrofluoric acid.
• the phosphating solution preferably has a content of molybdenum ions / molybdate or / and tungsten ions / tungsten in the range from 0 to 1.5 g per liter, in particular at least 5 mg per liter, preferably from 15 to 500 mg per liter, particularly preferably 30 up to 200 mg per liter, calculated as MoO 3 or WO 3 .
• the ammonium ions optionally in combination with molybdate / molybdenum ions or tungsten / tungsten ions or like molybdate / molybdenum ions or tungsten / tungsten ions, can have an accelerating effect.
• the phosphating solution can also have (other) oxidizing agents.
• the phosphating solution preferably has a content of nitrate ions in the range from 0 to 12 g per liter, particularly preferably in the range from 0.001 to 10 g per liter, very particularly preferably in the range from 0.002 to 8 g per liter, in particular at least 0.2 g per liter or at most 6 g per liter.
• the content of nitrate ions enables the pickling attack to be increased and an equalization of the phosphate layer formation and can also have an accelerating effect on layer formation.
• Nitrate can also contribute to the formation of thin closed layers. The addition of nitrate is therefore particularly preferred.
• the phosphating solution preferably has a content of at least an accelerator other than nitrate, in particular an accelerator selected from the group of chlorate, nitrite, nitroguanidine, nitrobenzenesulfonate (NBS, e.g. with sodium as SNBS;) and other nitro groups Accelerators, in the range of 0 to 6 g per liter, preferably in the range of 0.2 to 4.5 g per liter, particularly preferably in Range from 0.3 to 3 g per liter.
• NBS nitrobenzenesulfonate
• Accelerators in the range of 0 to 6 g per liter, preferably in the range of 0.2 to 4.5 g per liter, particularly preferably in Range from 0.3 to 3 g per liter.
• This accelerator works in one wider pH range, so in a wider pH range can be worked.
• the sum of the contents thereof is preferably Accelerators without nitrate, preferably in the range from 0 to 10 g per liter, in particular in the range from 0.5 to 8 g / L, preferably from at least 1 g / L or up to 6 g / L.
• nitrate can also be used in addition to at least one this accelerator does occur, but need not.
• the phosphating solution preferably has a content of at least a nonionic and / or anionic surfactant in the range of each 0.05 to 15 g per liter, preferably from 0.1 to 6 g per liter, particularly preferably from 0.2 to 3 g per liter.
• These surfactants provide for better wetting of the metal surface and thus for the more uniform Removal of organic contaminants on the metal surface, for a more even pickling attack on the metal surface and for the more uniform formation of phosphate layers on the metal surface.
• the phosphating solution preferably has a content of at least an organic solubilizer in the range of 0 to 1 g per liter, preferably from 10 to 800 mg per liter, particularly preferably from 20 to 500 mg per liter.
• Solubilizers can serve as a one-component surfactant to get in the aqueous solution. They are for the stability of Surfactants of importance in the concentrate according to the invention.
• the phosphating solution advantageously has for reasons of environmental protection no or only a low content of nitrite ions, chromium ions, Nickel ions, cobalt ions, manganese ions and cadmium ions. If the bath has a higher content of at least one of these substances should, for the processed solution, may an elaborate Disposal can be arranged. Therefore, it is preferred not to use these ions on purpose add to the bathroom and avoid as much as possible during operation. Further has the phosphating solution preferably for reasons of corrosion protection the metal parts to be coated also no increased content of chloride ions. Certain levels of aluminum in the phosphating solution can possibly for the precipitation of cryolite, that of calcium u.U. lead to the precipitation of calcium fluoride. Therefore, it is beneficial to have salaries of such ions, if possible, to be kept within those limits in which such precipitates that are not required are avoided or minor can be held. Because there is a need later to remove and dispose of the sludge thus formed.
• the phosphating solution preferably has a temperature in the range from 30 to 70 ° C, particularly preferably in the range from 40 to 65 ° C, entirely particularly preferably in the range from 50 to 60 ° C.
• the phosphating solution preferably has a pH in the range from 3.6 to 7, particularly preferably in the range from 3.8 to 6.5, very particularly preferably in the range from 4 to 6.0. Above pH 6.2 can the pickling reaction may become very weak. It is recommended that Adjust the pH value comparatively precisely.
• the total acidity value may With increasing bath service life, e.g. in the On the order of about 5 points until later, for example up to about 20 points; with higher or lower acidity, the total acidity but also fluctuate in other value ranges.
• the phosphating solution preferably has a total acid score in the range from 2 to 30, particularly preferably in the range from 6 to 27, very particularly preferably in the range from 8 to 22.
• the score of the Total acidity is the number of ml that results when 10 ml of phosphating solution, which was diluted to 50 ml with deionized water, with 0.1-normal sodium hydroxide solution up to a pH of 8.9 at the transition point titrated colorless on pink with phenolphthalein.
• the phosphating solution preferably has a free acid content from 0 to 5 points, particularly preferably in the range from 0.01 to 4.5 Points, very particularly preferably in the range from 0.03 to 3 points.
• the free acid score is the number of ml that results when 10 ml of phosphating solution, diluted to 50 ml with deionized water was, with 0.1 normal sodium hydroxide solution up to a pH of 4.2 is titrated, with KCI being added to the sample to be titrated to saturation if the sample contains complex-bound fluoride, to largely prevent its dissociation.
• the metal parts preferably in a bath over a period of 1 to 10 minutes, especially over Be immersed for 1.5 to 6 minutes.
• the times mentioned refer to the sum of the phosphating times during pre-cleaning / phosphating and cleaning / phosphating.
• cleaning and phosphating can also be carried out in two successive steps Baths are carried out: It is recommended to use the in the first bath set a higher total acid score than in the second Bath and make sure that the free acid content in both baths is as zero as possible.
• the rinsing is preferably carried out over 20 to 80 seconds with a spray pressure from 0.3 to 2.5 bar.
• An unheated bath with fresh water supply is sufficient of city water quality.
• City water quality is preferred to a to have a larger buffer effect.
• the rinsing can take over 20 to 80 seconds with a spray pressure of 0.3 to 2.5 bar.
• Deionized water is preferred used.
• the salt load should be taken by suitable measures such as downstream spray ring with deionized water reduced as much as possible become.
• the drained water should unite Value of the electrical conductivity due to the subsequent electrocoating do not exceed 50 ⁇ S / cm.
• the metal parts pretreated in this way are directly in the Electro dip coating system retracted. The drying can then usually omitted.
• the method according to the invention is preferably used for metal parts - in particular for those of complex geometry - used. Be coated in particular metal parts made of iron or steel materials, aluminum or aluminum alloys, magnesium alloys or galvanized metal parts, the galvanizing layer also being rich in Al or / and Zn Alloys can exist.
• the method according to the invention can be especially for simple structural steels such as Use St 370 well.
• the alkali phosphate layer although ions which are removed from the metal surface by pickling action are involved in the layer structure, can be referred to as a conversion layer. It is ideally suited as temporary storage protection and as a primer for paintwork.
• the alkali phosphate layer preferably has a thickness in the range from 0.05 to 1.4 ⁇ m, in particular in the range from 0.15 to 0.8 ⁇ m, and a layer weight in the range from 0.1 to 1.6 g / m 2 , preferably in the range from 0.15 to 1.4 g / m 2 , particularly preferably in the range up to 1.2 g / m 2 . Layer thickness or layer weight are determined in the dried and hardened state.
• the phosphate layer is often amorphous or almost amorphous.
• the alkali phosphate layer has increased contents of phosphates / oxides / hydroxides of the metals mainly located in the metal surface, such as aluminum, iron and / or zinc.
• the thickness of an immersion lacquer layer applied to the alkali phosphate layer is preferably only in the range from 4 to 12 ⁇ m, particularly preferably in the range from 6 to 10 ⁇ m.
• the first dip lacquer layer applied to the alkali phosphate layer often has a layer weight in the range from 18 to 22.5 g / m 2 , which, assuming a density of the baked lacquer layer of 1.5 g / cm 3, means an average layer thickness in Corresponds to the range of 12 to 15 microns, or even higher layer weights, while in the method according to the invention on similar metal parts with hidden areas, a layer weight in the range of 10 to 17.5 g / m 2 can be achieved, which assumes a density the baked paint layer of 1.5 g / cm 3 corresponds to an average layer thickness in the range from 6.7 to 11.7 ⁇ m.
• Such an immersion lacquer layer can additionally have at least one lacquer layer or other organic-containing coating or / and an adhesive layer especially with painted metal parts such as in the form of Plates are applied.
• the additional lacquer layer usually has decorative tasks and slightly improves corrosion protection or sometimes considerably; it is often done by powder painting applied.
• metal or plastic parts can be glued on are advantageously also pretreated and / or painted. These glued on Parts have e.g. in the case of flat radiators, often in the form of plates.
• the aqueous concentrate according to the invention can be characterized be at least one cation, one chelate, one complex, contains a polyelectrolyte and / or a polymer that is combined with sulfate difficult and / or insoluble compounds leads. It can act as a precipitant in each case at least one cation and / or a compound selected from Contain barium, calcium, strontium and their compounds.
• alkaline earth metal ions such as magnesium ions occur, but only a weak, almost no or no effect unfold as a precipitant for sulfate.
• the inventive Bath solution can be set.
• the metallic coated by the inventive method Bodies can be used as radiator elements, radiators, frames, plates, Fairings, angles, components in the interior of vehicles or aircraft, Use components in apparatus and mechanical engineering.
• the method according to the invention has compared to those previously described and practiced pretreatment processes by alkali phosphating
• the advantage that the thickness of the first layer of lacquer can be significantly reduced can without impairing the corrosion protection in any case becomes.
• the phosphating solution or resulting waste water is poor or free of dissolved sulfate because Sulphate levels in water e.g. because of the danger to concrete or because of Waste water regulations should be kept as low as possible.
• Electrocoating can be coated using the pretreated metal parts were painted at room temperature.
• the substrates to be coated were sample sheets and sheets for Radiator and convector body made of normal structural steel St 370 with one Length of 29.0 cm.
• An aqueous composition was used as the concentrate, which was composed as follows: 200 g / LP 2 O 5 10 g / L NO 3 1 g / L molybdate 80 g / L Well 10 g / LK 1 g / L nitrobenzenesulfonate.
• aqueous composition was used as the solution of the phosphating bath, which was composed as follows after diluting the concentrate with water: 20 g / LP 2 O 5 1 g / L NO 3 0.3 g / L SO 4 0.1 g / L molybdate 8th g / L Well 1 g / LK 0,003 g / L Fe 0.1 g / L nitrobenzenesulfonate.
• this bath contained 0.3 g / L sulfate, after the addition of 0.5 g / L precipitant based on BaCl 2 , the sulfate content of the bath decreased to significantly lower values. An overdosing with precipitant was avoided. The precipitation could be adjusted with BaCl 2 so that only 0.05 g / L sulfate was contained in the bath solution after the sulfate precipitation.
• the phosphate layers produced with this bath solution showed a layer thickness in the range from 0.1 to 0.4 ⁇ m and a layer weight in the range from 0.2 to 0.8 g / m 2 . They mostly showed a bluish iridescent color. Thereafter, the thinnest possible electrocoat was applied. The further investigations were carried out on 4 sheets each coated with dip coating, each with 10 layer thickness measuring points.
• the task was to create the surfaces of the convectors of radiators fürzube füren. Place the convectors inside the radiator are Faraday cages that are more electrically shielded. There was also the task of including the paint weight for the radiators of the convectors, including those over the entire surface to keep the average layer of paint as low as possible.
• sample sheets were alkali-phosphated and electro-coated.
• the electroplating of the sample sheets was carried out in a laboratory basin, in which two sample sheets are held parallel to each other at a distance of 5 mm and electrically contacted together on one end face in order to be electrocoated in this state at 280 V for 200 seconds.
• the thickness of the lacquer layer on the outside of the pair of plates and the wrap-around width of the lacquer layer were measured in the longitudinal direction from above in cm on these metal sheets. The larger the areas that were painted and the greater the widening, the better the phosphate layer was suitable as a base for the electrocoat.

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