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
  • C23C22/36—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 phosphates
  • C23C22/364—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 phosphates containing also manganese cations
• • 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
  • C23C22/18—Orthophosphates containing manganese cations
  • C23C22/186—Orthophosphates containing manganese cations containing also copper cations
• • 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
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
  • Y02T50/00—Aeronautics or air transport
  • Y02T50/60—Efficient propulsion technologies, e.g. for aircraft

Definitions

• the present invention relates to a process for coating metallic surfaces as well as the use of the substrates with metallic surfaces coated by the process according to the invention.
• This process is intended to serve as a pretreatment before a further coating, in particular paint application, or as a treatment without subsequent coating.
• zinc-manganese-nickel phosphating generally zinc contents were chosen in the range from 0.6 to 2 g/l and manganese contents were chosen in the range from 0.4 to 1 g/l, the zinc content normally being higher than the manganese content.
• Prephosphating has hitherto been used for galvanised steel strip material.
• post-phosphating the second phosphating
• DE-A1-40 13 483 describes a process for the phosphating of metal surfaces with aqueous, acidic phosphating solutions that contain zinc, manganese, copper, phosphate and oxidising agents as well as only traces of nickel, in which the concentration of Fe 2+ ions should be kept below 0.1 g/l. Copper contents in the range from 3 to 5 mg/l are mentioned in the examples. Serious problems may however arise with the phosphating solutions mentioned there on galvanised surfaces, while the quality of the tri-cation processes based on high nickel content Zn—Mn—Ni phosphating is achieved.
• DE-A1-42 10 513 relates to a process for producing copper-containing, nickel-free phosphate layers by spraying and/or dipping with a phosphating solution that contains 0.2 to 2 g/l of zinc, 5 to 30 g/l of P 2 O 5 , 0.005 to 0.025 g/l of copper and 0.5 to 5 g/l of a compound based on hydroxylamine, calculated as HA, by means of which phosphate crystals are produced having an edge length in the range from 0.5 to 10 ⁇ m.
• All copper-containing embodiments either have a Zn:Mn ratio of >1 or a high nickel content.
• EP-A-0 675 972 describes a process for the production of copper-containing, largely nickel-free zinc phosphate layers with an aqueous composition, as well as the aqueous composition itself, which contains 0.026 to 0.074 g/l of copper, 0.45 to 2 g/l of zinc, 0.1 to 10 g/l of compounds based on hydroxylamine, calculated as HA, total acid values in the range from 5 to 40 points as well as free acid in the range from ⁇ 0.5 to +0.8 point, and which may preferably contain total contents of up to 2 g/l of manganese and cobalt.
• All copper-containing embodiments either have a Zn:Mn ratio of >1 or even no manganese at all.
• DE-A1-196 06 017 describes a process for the phosphating of metal surfaces with aqueous, acid phosphating solutions that contain specific contents of zinc but only traces of manganese and copper in addition to phosphate and at least one accelerator and also, as far as possible, only traces of nickel. No aqueous compositions with a Zn:Mn ratio of ⁇ 1 can be employed in this process.
• DE-A1-196 34 685 discloses an aqueous solution for producing phosphate layers as well as the associated phosphating process, in which the phosphating solution is adjusted with zinc, phosphate, nitroguanidine as accelerator and with further additives so that phosphate crystals with a maximum edge length of ⁇ 15 ⁇ m are produced at comparatively low temperatures, and a low layer weight and a good paint adhesion are achieved.
• All copper-containing embodiments have a Zn:Mn ratio of >1, or with a Zn:Mn ratio of ⁇ 1 have copper contents of only up to 0.005 g/l.
• nitroguanidine as accelerator is however often disadvantageous, since with prolonged use of the phosphating bath—in some cases even after a day—in the presence of copper a bath poison is formed that seriously affects the layer formation on steel surfaces. If necessary the bath then has to be discarded and reconstituted.
• the object of the invention is therefore to obviate the disadvantages of the prior art in a phosphating system free of added nickel and also to eliminate the serious paint adhesion problems, in particular on galvanised or zinc surfaces.
• a process should be provided for coating galvanised surfaces that is as far as possible industrially suitable for coating individual parts as well as for coating strip material at high speeds.
• the phosphating process should be at least equivalent as regards corrosion resistance to the phosphating systems that are currently used for pretreatment or treatment, but should also be inexpensive and should be able to be used in an environmentally friendly manner, in particular largely free of nickel.
• the object consisted in particular of providing an industrially usable, largely nickel-free phosphating process for prephosphating.
• This object is achieved by a process for the coating of metallic surfaces by manganese-zinc phosphating with an aqueous phosphating solution, in which no nickel is intentionally added to the phosphating solution, which process is characterised in that
• the zinc:manganese weight ratio of the phosphating solution is maintained in the range from 0.05:1 to 0.99:1,
• zinc in the range from 0.05 to 5 g/l
• manganese in the range from 0.075 to 5.2 g/l
• copper in the range from 0.008 to 0.050 g/l
• the zinc:manganese weight ratio of the phosphating solution is preferably in the range from 0.5:1 to 0.9:1, in particular in the range from 0.65:1 to 0.8:1.
• the coating is of high quality over a very wide range of the zinc:manganese weight ratios of the phosphating solution. If however in very acidic solutions the zinc content drops below 0.2 g/l, the coating quality on high iron content surfaces may also fall.
• the phosphating solution preferably has zinc contents in the range from 0.5 to 3.8 g/l, for strip material especially in the range from 1.6 to 3.5 g/l and for parts especially in the range from 0.6 to 2 g/l and particularly preferably in the range from 0.8 to 1.1 g/l.
• a zinc content in the range from 0.3 to 1.3 g/l is often sufficient, whereas with dipping, zinc contents in the range from 0.7 to 1.9 g/l are necessary.
• the zinc content is preferably in the range from 1.1 to 3.5 g/l. If the zinc content of the phosphating solution is too low, then the layer formation is incomplete, in particular on high iron content surfaces.
• zinc surfaces within the context of the present invention includes not only the surfaces of zinc alloys, but also galvanised surfaces, in particular those of iron alloys and steel.
• aluminium surfaces include surfaces of aluminium and aluminium alloys
• iron surfaces include surfaces of high iron content alloys.
• the manganese content of the phosphating solution is preferably in the range from 0.2 to 4 g/l, for strip material especially in the range from 1.7 to 3.0 g/l, and for parts in particular in the range from 0.5 to 3.8 g/l and particularly preferably in the range from 1 to 3 g/l.
• a significant improvement in the paint adhesion on the phosphated surfaces is achieved by an increased manganese content.
• the manganese content is preferably in the range from 1.9 to 2.4 g/l.
• the copper content is preferably in the range from 0.009 to 0.045 g/l, particularly preferably in the range from 0.010 to 0.040 g/l, and for strip material especially in the range from 0.012 to 0.25 g/l and for parts especially in the range from 0.012 to 0.030 g/l.
• the copper content is preferably in the range from 0.008 to 0.048 g/l, particularly preferably in the range from 0.017 to 0.043 g/l.
• the copper content was generally found to be in the range from 5 to 35 mg/m 2 .
• the corrosion resistance of an iron surface is improved by adding copper.
• Copper contents in the range from 0.020 to 0.050 g/l do not lead to poorer quality layers; however, higher copper contents in combination with too long a residence time of the substrates in the baths can result in a non-uniform deposition of copper on the surfaces to be phosphated.
• the paint adhesion can be significantly improved by the addition of small amounts of titanium, hafnium and/or zirconium hexafluoride. These amounts are preferably in the range from 0.003 to 0.3 g/l, particularly preferably in the range from 0.004 to 0.1 g/l. However, in the case of aluminium surfaces these hexafluorides should generally be limited to values of up to 0.05 g/l—calculated as F 6 —since otherwise there may be a marked interference in the layer formation.
• a content of silicon hexafluoride in particular in the range from 0.5 to 4 g/l SiF 6 and preferably in the range from 1 to 3 g/l, may be advantageous in order to improve the homogeneity of the phosphate layer, in particular with zinc surfaces, and to stabilise the bath as regards zinc precipitation in the presence of free fluoride and thereby to ensure that the zinc contents remain dissolved in the bath.
• the phosphating solution is free of additions of oxo anions of halogens, in particular of nickel, and of aluminium contents greater than 0.05 g/l.
• the bath may have a nickel content of up to 0.1 g/l and in extreme cases, on account of very high nickel content metallic surfaces, even up to 0.25 g/l.
• the coating process according to the invention may be distinguished by the fact that the phosphating solution has a content of silver in the range from 0.0001 to 0.05 g/l, preferably in the range from 0.001 to 0.03 g/l.
• the phosphating solution may also contain contents of Fe 2+ ions in the range of up to about 1 g/l, especially in the case of iron surfaces. Neither minor nor larger Fe 2+ contents in the phosphating bath normally interfere in widely different metal surfaces.
• the phosphating solution may have a content of sodium in the range from 0.01 to 10 g/l and/or a content of potassium in the range from 0.01 to 10 g/l, preferably a content of sodium in the range from 1 to 5 g/l, most particularly preferably in the range from 3 to 4 g/l.
• the addition of sodium is usually advantageous in order to reduce the levels of free acid.
• the addition of sodium may help to precipitate, for example as cryolite, a part of the aluminium content in the phosphating solution, which depending on the circumstances can adversely affect the layer formation on steel and in some cases also the paint adhesion. Potassium is less recommended than sodium, not only on account of the somewhat higher costs but also, in certain circumstances, on account of the poorer coat properties.
• the zinc:phosphate weight ratio of the phosphating solution may be maintained in the range from 0.016:1 to 1.33:1, phosphate being calculated as PO 4 .
• this ratio is maintained in the range from 0.02:1 to 0.8:1, particularly preferably in the range from 0.025:1 to 0.25:1.
• the phosphating solution may have a content of phosphate in the range from 3 to 75 g/l, phosphate being calculated as PO 4 , preferably in the range from 7.5 to 37 g/l, particularly preferably in the range from 10 to 30 g/l, most particularly preferably in the range from 12 to 26 g/l, and in the case of strip material especially in the range from 17 to 21 g/l.
• the phosphate content is preferably in the range from 12 to 18 g/l.
• the bath may tend to become unstable unless the content of free acid is increased, failing which there may be a fairly marked precipitation of phosphate. If this weight ratio is too low, then the corrosion resistance and the paint adhesion may be impaired.
• the phosphating solution may have a chloride content in the range from 0.01 to 10 g/l and/or a chlorate content in the range from 0.01 to 5 g/l, preferably a chloride content in the range from 0.1 to 6 g/l and preferably a chlorate content in the range from 0.1 to 3 g/l.
• An addition of chloride and possibly also chlorate or chlorate alone in specific amounts should be avoided in the phosphating of zinc surfaces on account of the danger of the formation of white spots (specks), if nitrate and/or nitrite are present.
• aluminium contents from aluminium or aluminium-zinc surfaces may be a problem without the presence of fluoride
• free fluoride for example as HF or as sodium bifluoride
• silicon hexafluoride can stabilise the phosphating solution, i.e. reduce the precipitation of phosphates, and can also reduce the formation of specks in zinc surfaces.
• the phosphating solution may have a content of free fluoride in the range from 0.001 to 0.8 g/l, preferably in the range from 0.01 to 0.5 g/l, particularly preferably in the range from 0.03 to 0.2 g/l, calculated as F.
• a content of free fluoride may be beneficial for the phosphating of aluminium surfaces and for the precipitation of aluminium.
• about 1 to 60% of the total fluorine content is present in the form of free fluoride and the remainder is present as complex fluoride and as unassociated hydrofluoric acid.
• the phosphating solution may have a content of total fluoride in the range from 0.01 to 5 g/l, preferably in the range from 0.1 to 1 g/l, calculated as F.
• the phosphating solution may have a content of at least one accelerator in the range from 0 to 40 g/l, preferably in the range from 0.02 to 30 g/l, particularly preferably in the range from 0.1 to 20 g/l.
• the accelerator may help to suppress the formation of hydrogen bubbles on the surfaces. Due to the better contact with the surface to be coated—since this is not partially covered by hydrogen bubbles—more crystal nuclei can be formed there.
• the presence of an accelerator is not absolutely essential, especially in the case of zinc surfaces.
• An accelerator is however of considerable advantage, generally in the case of aluminium, iron and steel surfaces, since in this way the phosphate layer can be produced in a finely crystalline form because the phosphate layer can thereby be sealed more quickly and easily and because the corrosion protection and the paint adhesion can be improved in this way.
• the phosphating solution may have a nitrite content in the range from 0.01 to 0.3 g/l, a nitrate content in the range from 1 to 30 g/l, a content of compounds based on peroxide in the range from 0.001 to 3 g/l, preferably in the range from 0.01 to 0.15 g/l, calculated as H 2 O 2 , a content of nitrobenzenesulfonate (NBS), nitropropane, nitroethane and/or other nitro-organic compounds with oxidising properties—with the exception of compounds based on nitroguanidine—with a total content in the range from 0.1 to 3 g/l calculated as NO 2 , a content of compounds based on nitroguanidine in the range from 0.1 to 5 g/l, a chlorate content preferably in the range from 0.05 to 4 g/l, a content of reducing sugar compounds in the range from 0.1 to 10 g/
• Chlorate additions are normally used in nitrite-free and nitrate-free baths if zinc surfaces are to be coated.
• the nitrate content is preferably in the range from 12 to 19 g/l. If low nitrate contents or even nitrate-free solutions are used in the prephosphating, then an addition of 0.5 to 3 g/l of peroxide, calculated as H 2 O 2 , is preferred.
• the phosphating solution has a content of nitrite in the range from 0.05 to 0.2 g/l.
• nitrite like the nitrogen-containing gases that may possibly be formed therefrom, has the disadvantage that it is extremely toxic, nitrite has the advantage that it is inexpensive and its action is very well known and can be effectively controlled.
• the phosphating solution has a content of nitrate in the range from 5 to 25 g/l. On account of the weak action of this accelerator higher contents of nitrate are often employed.
• the phosphating solution has a content of compounds based on peroxide in the range from 0.01 to 0.1 g/l.
• the phosphating solution has a total content of nitrobenzenesulfonate and/or other nitro-organic compounds with oxidising properties in the range from 0.5 to 2 g/l.
• the phosphating solution has a content of compounds based on hydroxylamine in the range from 0.5 to 2 g/l.
• the ratio of the contents of compounds based on hydroxylamine, calculated as HA, to the sum total of zinc and manganese in the phosphating solution is in the range from 1:2 to 1:4.
• hydroxylamine may be catalytically decomposed in the presence of a specific copper content.
• At least one compound based on perboric acid, lactic acid, tartaric acid, citric acid and/or a chemically related hydroxycarboxylic acid may advantageously be added in order to stabilise the bath, the concentrate or the replenishment solution, in particular to prevent or reduce precipitations from one of these solutions, as well as to increase the crystallinity of the phosphate layer, whereby the water resistance of the phosphate layer is substantially improved.
• an addition of a polymeric alcohol may also be advantageous in order to form phosphoric acid esters with this alcohol, especially during the drying, which have a beneficial effect as lubricants in forming.
• the addition of a polymeric alcohol may affect the reaction with the excess free phosphoric acid that is possibly present in the phosphating solution, by improving the crystallinity and the water resistance of the phosphate coating.
• the prephosphating is particularly suitable for the implementation of a rinse phosphating by spraying and/or dipping with spraying/dipping times approximately in the range from 3 to 15 seconds and at a temperature in the range from 45° to 65° C., particularly with galvanised surfaces.
• the prephosphating is particularly suitable for the production of strip material by rinse processes, in which rinsing is performed after the application of the phosphate layer. This process is suitable in particular for automobile production.
• the phosphating solution for the prephosphating may contain the following amounts:
• copper in the range from 0.008 to 0.050 g/l.
• post-phosphating according to the invention may also be carried out in the following way, in which first of all prephosphated, optionally at least partially formed/shaped and optionally at least partially welded metallic substrates are phosphated by manganese/zinc phosphating with an aqueous phosphating solution in which no nickel is intentionally added to the phosphating solution or the phosphating solution only has a nickel content of up to 0.3 g/l, which is characterised in that
• the phosphating solution contains the following amounts:
• zinc in the range from 0.05 to 5 g/l and manganese in the range from 0.075 to 5.2 g/l.
• the phosphating solution may have the following contents, in particular for parts:
• zinc:phosphate weight ratio in the range from 0.02 to 0.12
• nitrate in the range from 0 up to 22 g/l and/or at least one other accelerator selected from the group comprising nitrite or compounds based on hydroxylamine, nitroguanidine and/or peroxide, in each case in the range from 0.01 to 2 g/l.
• the phosphating solution may have the following contents, in particular for strip material, particularly preferably for galvanised strip surfaces:
• the complex fluoride SiF 6 is contained in an amount in the range from 0 to 4.5 g/l, calculated as SiF 6 , and
• nitrate in the range from 0 up to 22 g/l and/or at least one further accelerator selected from the group comprising nitrite or compounds based on hydroxylamine, nitroguanidine and/or peroxide, in each case in the range from 0.01 to 2 g/l.
• the phosphating solution for the prephosphating may preferably have the following contents:
• zinc:phosphate weight ratio in the range from 0.06 to 0.23
• the nitrate content if nitrate is added as accelerator, is preferably in the range from 3 to 22 g/l, and the content of at least one compound based on peroxide is in the range from 0.5 to 2.5 g/l, especially if a nitrate-free process is used.
• the phosphating solution may also preferably have the following contents:
• zinc:phosphate weight ratio in the range from 0.02 to 0.12
• nitrate in the range from 0 up to 22 g/l and/or at least one further accelerator selected from the group comprising nitrite or compounds based on hydroxylamine, nitroguanidine and/or peroxide, in each case in the range from 0.01 to 2 g/l.
• the metallic substrates may be coated for a time of up to 20 minutes, strip material preferably being coated for a time ranging from 0.1 to 120 seconds and particularly preferably for a time ranging from 0.3 to 60 seconds, and parts preferably being coated for a time ranging from 1 to 12 minutes and particularly preferably for a time ranging from 2 to 8 minutes.
• the temperature of the phosphating solution for the coating may be in the range from 10° to 72° C., for strip material preferably in the range from 40° to 70° C. and for parts preferably in the range from 20° to 60° C. and particularly preferably in the range from 32° to 58° C.
• the free acid level may be from 0.1 to 10 points
• the total acid may be from 5 to 50 points
• the total acid according to Fischer may be from 3 to 25 points
• the ratio of the free acid to total acid according to Fischer (S value) may in particular be in the range from 0.01 to 0.7, wherein the concentration of free acid is preferably 0.15 to 4 points, the concentration of total acid according to Fischer is preferably 12 to 35 points and the ratio of the free acid to total acid according to Fischer (S value) is preferably in the range from 0.03 to 0.3.
• the prephosphating it is particularly preferred to have values of the free acid in the range from 3 to 4.4 points and values of the total acid according to Fischer in the range from 18.5 to 21 points and thus an S value in the range from 0.14 to 0.24.
• the total content of phosphate ions is determined following the measurement of the free acid, by titrating the titration solution after addition of 20 ml of 30% neutral potassium oxalate solution, with 0.1 M NaOH using phenolphthalein as indicator until the colour turns from colourless to red.
• the consumption of 0.1 M NaOH in ml between the colour change with dimethyl yellow and the colour change with phenolphthalein corresponds to the total acid according to Fischer (TAF). If this value is multiplied by 0.71, the total content of phosphate ions is obtained (see W. Rausch: “Die Phosphatierung von Metallen”, Eugen G. Leuze-Verlag 1988, pp. 300 ff).
• the so-called S value is obtained by dividing the value of the free acid by the value of the total acid according to Fischer.
• the total acid (TA) is the sum total of the contained divalent cations as well as free and bound phosphoric acids (the latter being phosphates).
• the total acid is determined from the consumption of 0.1 M sodium hydroxide using phenolphthalein as indicator. This consumption in ml corresponds to the point value of the total acid.
• the pH of the phosphating solution may be in the range from 1 to 4, preferably in the range from 2.2 to 3.6.
• the phosphating solution may be applied to the surface of the substrates by knife coating, flow coating, spraying, sprinkling, brushing, dipping, nebulising or rolling, individual process steps being able to be combined with one another—in particular spraying and dipping, spraying and squeezing off as well as dipping and squeezing off, and optionally subsequent squeezing off.
• substrates with a metallic surface predominantly containing aluminium, iron, copper, magnesium, tin or zinc in particular surfaces of at least one of the materials based on aluminium, iron, steel, zinc and/or alloys with a content of aluminium, iron, copper, magnesium, tin or zinc, can be coated with the phosphating solution.
• a phosphate coat can be precipitated from the phosphating solution that has a layer weight in the range from 0.2 to 6 g/m 2 , preferably in the range from 1 to 4 g/m 2 .
• a layer weight in the range from 0.2 to 6 g/m 2 , preferably in the range from 1 to 4 g/m 2 .
• a layer weight of the phosphate layer in the range from 0.2 g/m 2 to 1 g/m 2 is sufficient.
• a layer weight of up to 6 g/m 2 and thus a complete covering is however not disadvantageous, apart from an increased consumption of chemicals.
• a layer weight in the range from 1 g/m 2 to 6 g/m 2 is particularly preferred, especially 1 to 2 g/m 2 , in particular if the substrates with the prephosphate coating are to be used for welding.
• metallic surfaces may be cleaned, pickled, rinsed and/or activated before the phosphating.
• the cleaning is preferably carried out with an alkaline agent and takes place in particular over a time ranging from 10 seconds to 15 minutes.
• a weak alkaline cleaning agent may be employed for metallic surfaces, in most cases over 2 to 4 minutes. The treatment times are correspondingly shorter for strong alkaline cleaning agents. It may be advantageous to add a titanium-containing activator to the cleaning agent.
• An acidic cleaning may also be chosen in particular for aluminium and aluminium alloys.
• any water of sufficiently pure quality is suitable for the subsequent rinsing. Tap water is recommended. If the activation can take place in a separate bath or rinsing step, which is most advantageous, then fully deionised water should be used as solvent after prior rinsing.
• An activation is often very advantageous in order to form crystal seeds.
• the activation may in particular be based on titanium. An activation over 10 to 30 seconds is often sufficient, although in principle the activation time may range from 0.1 second up to at least 5 minutes. The activation may also be longer than 5 minutes, though this does not have any beneficial effect. It may be advantageous to add copper and/or one of the additives known in principle to the activation.
• the phosphated substrates may be rinsed at least once and optionally treated after a rinse procedure or between two rinse procedures, with a post-rinse solution to confer additional passivation.
• a post-rinse solution to confer additional passivation.
• any water of sufficiently pure quality is suitable for the rinsing after the phosphating.
• Tap water or fully deionised water is recommended—for example dipping in cold tap water for 10 seconds—followed in the next rinse step by fully deionised water—for example spraying with cold, fully deionised water for 10 seconds.
• an addition of for example zirconium hexafluoride or of one of the organic substances known in principle may be employed, whereby a further improvement in the corrosion resistance and paint adhesion of the coating may be achieved.
• the metallic surfaces can be prephosphated before the phosphating.
• the prephosphating of substrates is advantageous if for example the prephosphated strip is subsequently formed/shaped or if parts are intermediately stored, bonded and/or welded in the corrosion-protected state.
• the substrates pretreated in this way can thereby be much more easily formed/shaped and are protected against corrosion.
• the metallic surfaces are welded, bonded and/or formed/shaped after the phosphating (prephosphating) and are then optionally rephosphated.
• the phosphating plants in the automobile industry use weakly alkaline cleaning agents, but in some cases also strongly alkaline cleaning agents. It was surprising that the first crystalline prephosphating layer according to the invention is substantially more resistant to the influence of strongly alkaline cleaning agents. With the short treatment times that are normally employed, the first phosphate layer according to the invention was not or was only slightly affected by a strong alkaline cleaning agent.
• the first and/or second phosphate layer applied to the metal part may be wetted with an oil, a dispersion or a suspension, in particular with a forming oil or anti-corrosion oil and/or with a lubricant such as a dry lubricant, for example with a wax-containing mixture.
• the oil or the lubricant serves as additional temporary corrosion protection and may in addition also facilitate a forming procedure, the unformed metal part also having an increased corrosion resistance.
• a coating with an oil may also be of benefit for the second phosphate layer if the parts to be painted have to be transported to a distant paint shop.
• Any oil layer or lubricant layer that is present can be removed from the first or second phosphate layer in order to prepare the coating for painting, forming, assembly, bonding or welding.
• the oil must be removed before a subsequent paint coat, though it does not necessarily have to be removed for other process procedures.
• the metal parts provided with a first and/or second phosphate layer may be painted, coated with another type of organic coating and/or with an adhesive layer, and then optionally formed/shaped, wherein the metal parts coated in this way may in addition be bonded and/or welded to other parts.
• a very wide range of organic coatings are known that can be used on a phosphate layer. In this connection not all organic coatings are covered by the definition of paints.
• the metal parts provided with a first and/or second phosphate layer may be provided with a coating either before or only after the forming and/or assembly.
• the phosphate-coated metal parts according to the invention may if necessary be oiled in a so-called strip plant or may if necessary be degreased and/or cleaned, before they are subsequently coated in a paint shop.
• the phosphate-coated metal parts according to the invention may if necessary be oiled for the production of for example equipment linings, may if necessary be formed/shaped and may if necessary may be degreased and/or cleaned, before they are subsequently—if desired—coated in a paint shop. For economic reasons the deoiling is preferably omitted before the bonding or welding.
• the phosphate-coated metal parts according to the invention may be oiled and formed/shaped for the production of for example automobiles, in which connection several metal parts are then welded together, bonded together or joined together in some other way, following which the assembled parts can be degreased and/or cleaned before they can subsequently be coated in a paint shop.
• the metal parts coated by the process according to the invention may, as prephosphated metal parts, for a renewed conversion treatment or for a renewed conversion pretreatment, in particular before being painted, or, as pretreated metal parts—in particular for the automobile industry—especially before being painted or as end-phosphated metal parts that are optionally also subsequently painted, organically coated in some other way and/or coated with a film, be coated with an adhesive layer, formed/shaped, assembled and/or welded together.
• a normal precondition for welding is that the phosphate layer is not too thick and that any organic coating that optionally is applied is electrically conducting.
• the metal parts provided with a first and/or second phosphate layer may be coated with a paint, with another type of organic coating, with a film and/or with an adhesive layer and if necessary formed/shaped, wherein the metal parts coated in this way may in addition be bonded or welded to other parts and/or may be joined to one another in a some other way.
• a passivating solution directly to the first and/or second phosphate layer, in particular by spraying, dipping or rolling.
• a post-rinse solution is preferably used to further enhance the corrosion resistance and the paint adhesion, which solution may contain at least one substance based on Cr, Ti, Zr, Ce and/or other rare earth elements including lanthanum or yttrium, tannin, silane/siloxane, phosphorus-containing self-assembling molecules, phosphonates or polymers.
• the coating according to the invention is equivalent as regards corrosion resistance and paint adhesion to a comparable high nickel content coating, but is significantly cheaper and significantly more environmentally friendly than the high nickel content coating.
• the high-grade coating quality is largely independent of the chosen accelerator or accelerator mixture.
• the coating process according to the invention is also unexpectedly robust.
• the same high-grade properties could be achieved by a Zn:Mn ratio in the very wide range from 0.9:1 to 0.3:1.
• the same high-grade properties could be obtained also outside this range provided the composition of the bath was suitably adapted.
• the process according to the invention has the advantage compared to the aforedescribed and implemented processes that it provides excellent coatings with low consumptions of chemicals and comparatively low costs, in particular of HDG, and is in this connection particularly environmentally friendly.
• no nickel is added in this process, fewer heavy metals are discharged into the waste water, phosphate slurry and in the grinding dust.
• the paint adhesion can be improved still further.
• a concentrate for making up the phosphating solution or a replenishment solution for replenishing the phosphating solution may contain in particular zinc, manganese, copper and phosphoric acid, but only in certain cases alkalis and/or accelerators.
• the substrates coated by the process according to the invention may be used for strip production, for the production of components or car body parts or preassembled elements in the automobile or aerospace industry, in the building and construction industry, in the furniture industry, for the production of instruments and units, in particular domestic appliances, measuring instruments, control devices, testing devices, structural components, claddings/linings as well as small parts; as wire, wire coiling, wire mesh, metal sheeting, cladding/lining, screening, car bodies or parts of car bodies, parts of vehicles, trailers, mobile homes or missiles, as electronic or microelectronic components, as coverings, housings, lamps, lights, hanging light units, items of furniture or furniture parts, components of domestic appliances, frames, profiled sections, moulded parts of complicated geometry, beam-barrier, radiator or sauna parts, automobile bumpers, parts of or with at least one pipe and/or a profiled section, window, door or bicycle frames, or as small parts such as for example screws, nuts, flanges, springs or spectacle frames.
• instruments and units in particular domestic appliances,
• test sheets consisted of an aluminium alloy AlMgSi of thickness 1.2 mm or of uncoated, continuously annealed car body steel (CRS) or of steel galvanised on both sides with a coating of a hot-dip galvanising (HDG) or of an electrolytic galvanising (EG) with a total thickness of 0.7 mm.
• the surface area of the substrates was 400 cm 2 (measured over both surfaces).
• composition of the relevant phosphating solution as well as the results of the tests are shown in Tables 1 to 3.
• TABLE 1 Composition of the phosphating solutions in g/l or points of free acid (FA) or total acid (TA) HA Zn Mn Ni Cu TiF6 + ZrF6** PO 4 NO 2 NO 3 etc.
• the baths contained aminor amount to a certain amount of sodium as well as, for the pretreatment of aluminium surfaces, an amount of free fluoride in the range from 80 to 250 mg/l by addition of ammonium bifluoride.
• the total acid is given approximately.
• the layer weight of the HDG sheets coated according to the invention was almost constant, in the range from 2.0 to 2.1 g/cm 2 with a manganese content in the range from 1 to 2.5 g/l, and was almost exactly 1.0 g/cm 2 with a copper content in the range from 5 to 20 mg/l.
• compositions with a nitrate acceleration (B 21-B 23) and on the other hand with a nitrate-free peroxide acceleration (B 24-B 26) were successfully tested and compared to a nickel-free prephosphating and to a very low copper content or high nickel content phosphating (VB 26 and VB 27).
• copper-free and relatively high copper content phosphating solutions (VB 21-VB 24) were used compared to the phosphating solutions according to the invention with a certain copper content.
• Hydrofluoric acid was added in five tests. The sample sheets were treated, as in the experiments involving Examples B 1 to B20, according to the steps a) to c), though the titanium-containing activator was sprayed on.
• a nickel-containing prephosphating was applied in a layer weight of about 1.5 g/m 2
• phosphate layers were applied in a layer weight of about 3 g/m 2
• the comparison examples like the prephosphatings according to the invention of the examples B 21 to B 26 according to the invention (without post-phosphating), were painted with a automobile paint structure according to BMW and tested.
• the baths contained a very small to a specific amount of sodium. Due to the high nitrate levels a comparatively minor amount of nitrite was formed, which had a strongly accelerating effect.

Landscapes

• 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)
• Chemically Coating (AREA)
• Application Of Or Painting With Fluid Materials (AREA)

Applications Claiming Priority (3)

Publications (1)

Family

ID=7676531

Family Applications (1)

Country Status (8)

Cited By (20)

Families Citing this family (9)

Citations (4)

Family Cites Families (6)

• 2001
  • 2001-03-06 DE DE10110834A patent/DE10110834B4/de not_active Expired - Fee Related
• 2002
  • 2002-03-01 DE DE50213269T patent/DE50213269D1/de not_active Expired - Lifetime
  • 2002-03-01 JP JP2002569484A patent/JP4201600B2/ja not_active Expired - Fee Related
  • 2002-03-01 EP EP02702390A patent/EP1390564B1/de not_active Revoked
  • 2002-03-01 US US10/467,850 patent/US20040129346A1/en not_active Abandoned
  • 2002-03-01 CA CA002440151A patent/CA2440151A1/en not_active Abandoned
  • 2002-03-01 AU AU2002235928A patent/AU2002235928A1/en not_active Abandoned
  • 2002-03-01 WO PCT/EP2002/002290 patent/WO2002070782A2/de not_active Ceased
  • 2002-03-01 AT AT02702390T patent/ATE422564T1/de not_active IP Right Cessation

Patent Citations (4)

Also Published As

Similar Documents

Legal Events