EP1579030B1 - Process for providing a thin corrosion inhibiting coating on a metallic surface - Google Patents
Process for providing a thin corrosion inhibiting coating on a metallic surface Download PDFInfo
- Publication number
- EP1579030B1 EP1579030B1 EP03789349A EP03789349A EP1579030B1 EP 1579030 B1 EP1579030 B1 EP 1579030B1 EP 03789349 A EP03789349 A EP 03789349A EP 03789349 A EP03789349 A EP 03789349A EP 1579030 B1 EP1579030 B1 EP 1579030B1
- Authority
- EP
- European Patent Office
- Prior art keywords
- coating
- phosphating
- solution
- dispersion
- process according
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
- 238000000576 coating method Methods 0.000 title claims abstract description 192
- 239000011248 coating agent Substances 0.000 title claims abstract description 126
- 238000000034 method Methods 0.000 title claims abstract description 72
- 238000005260 corrosion Methods 0.000 title claims description 28
- 230000007797 corrosion Effects 0.000 title claims description 28
- 230000002401 inhibitory effect Effects 0.000 title description 6
- 229910052783 alkali metal Inorganic materials 0.000 claims abstract description 63
- 150000001340 alkali metals Chemical class 0.000 claims abstract description 63
- 150000003839 salts Chemical class 0.000 claims abstract description 55
- 239000006185 dispersion Substances 0.000 claims abstract description 49
- 239000002253 acid Substances 0.000 claims abstract description 41
- 150000002148 esters Chemical class 0.000 claims abstract description 25
- 150000002500 ions Chemical class 0.000 claims abstract description 23
- 229910052698 phosphorus Inorganic materials 0.000 claims abstract description 23
- 239000011574 phosphorus Substances 0.000 claims abstract description 23
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 claims abstract description 22
- NBIIXXVUZAFLBC-UHFFFAOYSA-K phosphate Chemical compound [O-]P([O-])([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-K 0.000 claims abstract description 22
- 150000001875 compounds Chemical class 0.000 claims abstract description 17
- 150000007513 acids Chemical class 0.000 claims abstract description 13
- 239000002585 base Substances 0.000 claims abstract description 11
- 230000002378 acidificating effect Effects 0.000 claims abstract description 9
- QGZKDVFQNNGYKY-UHFFFAOYSA-O Ammonium Chemical compound [NH4+] QGZKDVFQNNGYKY-UHFFFAOYSA-O 0.000 claims abstract description 8
- 230000007935 neutral effect Effects 0.000 claims abstract description 7
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- 238000004949 mass spectrometry Methods 0.000 claims abstract description 6
- 239000008199 coating composition Substances 0.000 claims abstract description 3
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 55
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- 239000003973 paint Substances 0.000 claims description 18
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- -1 NO3 ions Chemical class 0.000 claims description 17
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- 230000005764 inhibitory process Effects 0.000 claims description 15
- 239000010452 phosphate Substances 0.000 claims description 14
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 claims description 11
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- 238000004040 coloring Methods 0.000 claims 1
- 239000000243 solution Substances 0.000 description 97
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- 239000007921 spray Substances 0.000 description 29
- IDCPFAYURAQKDZ-UHFFFAOYSA-N 1-nitroguanidine Chemical compound NC(=N)N[N+]([O-])=O IDCPFAYURAQKDZ-UHFFFAOYSA-N 0.000 description 28
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- 239000010960 cold rolled steel Substances 0.000 description 23
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 description 20
- 239000010410 layer Substances 0.000 description 16
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- 230000000694 effects Effects 0.000 description 13
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- 235000011007 phosphoric acid Nutrition 0.000 description 10
- 238000005554 pickling Methods 0.000 description 10
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- 230000001276 controlling effect Effects 0.000 description 1
- 229910001431 copper ion Inorganic materials 0.000 description 1
- KUNSUQLRTQLHQQ-UHFFFAOYSA-N copper tin Chemical compound [Cu].[Sn] KUNSUQLRTQLHQQ-UHFFFAOYSA-N 0.000 description 1
- 238000012937 correction Methods 0.000 description 1
- 230000002596 correlated effect Effects 0.000 description 1
- 230000000875 corresponding effect Effects 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 239000013530 defoamer Substances 0.000 description 1
- MNNHAPBLZZVQHP-UHFFFAOYSA-N diammonium hydrogen phosphate Chemical compound [NH4+].[NH4+].OP([O-])([O-])=O MNNHAPBLZZVQHP-UHFFFAOYSA-N 0.000 description 1
- 150000005690 diesters Chemical class 0.000 description 1
- NBIIXXVUZAFLBC-UHFFFAOYSA-M dihydrogenphosphate Chemical compound OP(O)([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-M 0.000 description 1
- XPPKVPWEQAFLFU-UHFFFAOYSA-N diphosphoric acid Chemical compound OP(O)(=O)OP(O)(O)=O XPPKVPWEQAFLFU-UHFFFAOYSA-N 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 230000002708 enhancing effect Effects 0.000 description 1
- 239000006260 foam Substances 0.000 description 1
- 235000019253 formic acid Nutrition 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 239000000174 gluconic acid Substances 0.000 description 1
- 235000012208 gluconic acid Nutrition 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 238000007654 immersion Methods 0.000 description 1
- 235000014413 iron hydroxide Nutrition 0.000 description 1
- UQSXHKLRYXJYBZ-UHFFFAOYSA-N iron oxide Inorganic materials [Fe]=O UQSXHKLRYXJYBZ-UHFFFAOYSA-N 0.000 description 1
- 235000013980 iron oxide Nutrition 0.000 description 1
- 229910000358 iron sulfate Inorganic materials 0.000 description 1
- BAUYGSIQEAFULO-UHFFFAOYSA-L iron(2+) sulfate (anhydrous) Chemical compound [Fe+2].[O-]S([O-])(=O)=O BAUYGSIQEAFULO-UHFFFAOYSA-L 0.000 description 1
- MVFCKEFYUDZOCX-UHFFFAOYSA-N iron(2+);dinitrate Chemical compound [Fe+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O MVFCKEFYUDZOCX-UHFFFAOYSA-N 0.000 description 1
- VBMVTYDPPZVILR-UHFFFAOYSA-N iron(2+);oxygen(2-) Chemical class [O-2].[Fe+2] VBMVTYDPPZVILR-UHFFFAOYSA-N 0.000 description 1
- SZVJSHCCFOBDDC-UHFFFAOYSA-N iron(II,III) oxide Inorganic materials O=[Fe]O[Fe]O[Fe]=O SZVJSHCCFOBDDC-UHFFFAOYSA-N 0.000 description 1
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 1
- NCNCGGDMXMBVIA-UHFFFAOYSA-L iron(ii) hydroxide Chemical class [OH-].[OH-].[Fe+2] NCNCGGDMXMBVIA-UHFFFAOYSA-L 0.000 description 1
- 150000004715 keto acids Chemical class 0.000 description 1
- 229910052749 magnesium Inorganic materials 0.000 description 1
- 239000001630 malic acid Substances 0.000 description 1
- 235000011090 malic acid Nutrition 0.000 description 1
- 150000007522 mineralic acids Chemical class 0.000 description 1
- 239000011259 mixed solution Substances 0.000 description 1
- 150000004712 monophosphates Chemical class 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 229910052758 niobium Inorganic materials 0.000 description 1
- 239000010955 niobium Substances 0.000 description 1
- GUCVJGMIXFAOAE-UHFFFAOYSA-N niobium atom Chemical compound [Nb] GUCVJGMIXFAOAE-UHFFFAOYSA-N 0.000 description 1
- 125000000449 nitro group Chemical group [O-][N+](*)=O 0.000 description 1
- VQTGUFBGYOIUFS-UHFFFAOYSA-N nitrosylsulfuric acid Chemical compound OS(=O)(=O)ON=O VQTGUFBGYOIUFS-UHFFFAOYSA-N 0.000 description 1
- 235000005985 organic acids Nutrition 0.000 description 1
- 235000006408 oxalic acid Nutrition 0.000 description 1
- 239000007800 oxidant agent Substances 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 230000001590 oxidative effect Effects 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 239000003002 pH adjusting agent Substances 0.000 description 1
- 150000004965 peroxy acids Chemical class 0.000 description 1
- 150000003009 phosphonic acids Chemical class 0.000 description 1
- XRBCRPZXSCBRTK-UHFFFAOYSA-N phosphonous acid Chemical compound OPO XRBCRPZXSCBRTK-UHFFFAOYSA-N 0.000 description 1
- 229910052827 phosphophyllite Inorganic materials 0.000 description 1
- 150000003014 phosphoric acid esters Chemical class 0.000 description 1
- AVFBYUADVDVJQL-UHFFFAOYSA-N phosphoric acid;trioxotungsten;hydrate Chemical compound O.O=[W](=O)=O.O=[W](=O)=O.O=[W](=O)=O.O=[W](=O)=O.O=[W](=O)=O.O=[W](=O)=O.O=[W](=O)=O.O=[W](=O)=O.O=[W](=O)=O.O=[W](=O)=O.O=[W](=O)=O.O=[W](=O)=O.OP(O)(O)=O AVFBYUADVDVJQL-UHFFFAOYSA-N 0.000 description 1
- 230000000704 physical effect Effects 0.000 description 1
- 231100000614 poison Toxicity 0.000 description 1
- 230000007096 poisonous effect Effects 0.000 description 1
- 229910052700 potassium Inorganic materials 0.000 description 1
- 239000011591 potassium Substances 0.000 description 1
- 238000010433 powder painting Methods 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 239000000047 product Substances 0.000 description 1
- 239000004172 quinoline yellow Substances 0.000 description 1
- 239000002151 riboflavin Substances 0.000 description 1
- 238000013214 routine measurement Methods 0.000 description 1
- 238000001228 spectrum Methods 0.000 description 1
- 238000004544 sputter deposition Methods 0.000 description 1
- 239000010935 stainless steel Substances 0.000 description 1
- 229910001220 stainless steel Inorganic materials 0.000 description 1
- 239000010421 standard material Substances 0.000 description 1
- BDHFUVZGWQCTTF-UHFFFAOYSA-M sulfonate Chemical compound [O-]S(=O)=O BDHFUVZGWQCTTF-UHFFFAOYSA-M 0.000 description 1
- 150000003460 sulfonic acids Chemical class 0.000 description 1
- 229910052717 sulfur Inorganic materials 0.000 description 1
- 239000011593 sulfur Substances 0.000 description 1
- 239000002344 surface layer Substances 0.000 description 1
- 239000000725 suspension Substances 0.000 description 1
- 229910052715 tantalum Inorganic materials 0.000 description 1
- GUVRBAGPIYLISA-UHFFFAOYSA-N tantalum atom Chemical compound [Ta] GUVRBAGPIYLISA-UHFFFAOYSA-N 0.000 description 1
- 239000011975 tartaric acid Substances 0.000 description 1
- 235000002906 tartaric acid Nutrition 0.000 description 1
- 239000004149 tartrazine Substances 0.000 description 1
- ISIJQEHRDSCQIU-UHFFFAOYSA-N tert-butyl 2,7-diazaspiro[4.5]decane-7-carboxylate Chemical compound C1N(C(=O)OC(C)(C)C)CCCC11CNCC1 ISIJQEHRDSCQIU-UHFFFAOYSA-N 0.000 description 1
- 150000005691 triesters Chemical class 0.000 description 1
- SPDJAIKMJHJYAV-UHFFFAOYSA-H trizinc;diphosphate;tetrahydrate Chemical compound O.O.O.O.[Zn+2].[Zn+2].[Zn+2].[O-]P([O-])([O-])=O.[O-]P([O-])([O-])=O SPDJAIKMJHJYAV-UHFFFAOYSA-H 0.000 description 1
- 238000005491 wire drawing Methods 0.000 description 1
- 150000003752 zinc compounds Chemical class 0.000 description 1
Images
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
- C23C22/73—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
- 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
-
- 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
- C23C22/34—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
Definitions
- This invention relates to a process for coating the surface of a metallic coil, part or wire with an aqueous acidic phosphating solution containing predominantly alkali metal ions and/or ammonium ions as well as in many cases phosphate ions. It relates further on to a phosphating solution to be used in this process for generating excellent corrosion inhibiting coatings on metallic surfaces. In some instances such coating may be used for coldforming of the metallic part.
- Such solutions are called alkali metal phosphating solutions or, if used on iron-rich surfaces, iron phosphating solutions.
- the invention is particularly concerned with a coating resp. conversion coating on aluminum, aluminum alloy, iron alloy like steel and stainless steel, magnesium alloy, zinc or zinc alloy as well as with a process, a concentrate and a solution for the formation of a phosphating coating on surfaces of these metallic materials.
- Such coating solution is especially suitable for the generation of pretreatment coatings on substrate surfaces which will be coated in a second step with at least one organic film, especially at least one film like a thin electrocoating lacquer layer, a paint layer, a silane-rich layer and/or an adhesive layer.
- the coating may be used for a treatment like a passivation without being covered with a further coating like a paint layer.
- alkali metal phosphating coatings are described in relatively few cases in comparison to zinc phosphating or manganese phosphating where there is a huge number of publications.
- Fresh solutions for alkali metal phosphating that had not yet been used show typically only a very low or even practically no content of aluminum, iron and zinc.
- the fresh aqueous acid alkali metal phosphating solutions contain ions of at least one type of alkali metal ions and/or ammonium ions as well as phosphate ions.
- the main phases of the alkali metal phosphating coatings are the corresponding phosphates, oxides and/or hydroxides of the metallic constituents of the metallic base material(s).
- Alkali metal phosphating solutions resp. coatings are called iron phosphating solutions resp. coatings if used on iron alloy surfaces like steel. The same corresponds to aluminum and aluminum alloys where such solutions resp. coatings are described as aluminum phosphating solutions resp. coatings.
- Often surfaces of very different metallic materials may be coated in the same alkali metal phosphating bath at the same time or one after the other whereby the ions of the different metals/alloys of the basic materials will be collected in the bath.
- Such coatings are - in contrast to coatings of the so called zinc-, zinc-manganese- or manganese- phosphating, mostly or totally amorphous or extraordinarily fine-grained.
- Non-coating phosphatings are described in Werner Rausch: The Phosphating of Metals, ASM International, Finishing Publications Ltd., Teddington, England 1990 (especially pages 94 - 100, 120 - 130 ) in detail and are called the "non-coating phosphating" or in other publications “amorphous phosphating".
- the term “non-coating phosphating” is misleading, as there will be coatings generated although such coatings will be significantly thinner than created during e.g. zinc phosphating or zinc-manganese phosphating.
- the very thin alkali metal phosphating coatings are not, poorly or - if coloured or grey - well visible; the coatings may be only visible by colours caused by physical effects, by their kind of grey appearance and/or by their matte appearance.
- the alkali metal phosphating solution contains always a certain content of at least one alkali metal like sodium, potassium and/or of ammonium.
- the alkali metal phosphating coatings are typically - in contrary to the well and coursely crystalline coatings of the so-called "coating-forming phosphatings" - more or less amorphous and show under the scanning electron microscope typically no crystalline grain shapes.
- the alkali metal phosphating coatings are mostly poor, nearly free or totally free of manganese and zinc, if there will not be manganese and/or zinc rich surfaces to be pretreated or treated. They are typically poor, nearly free or totally free of chromium, cobalt, copper, nickel, tin and/or other heavy metals.
- the phases mainly generated and/or precipitated during iron phosphating, which is performed by contacting iron-rich metallic surfaces with an alkali metal phosphating solution, are iron phosphates, iron oxides and iron hydroxides like e.g. vivianite and/or magnetite.
- the contents of the ions dissolved from the metallic surface and then carried in the alkali metal phosphating solution, especially of aluminum, chromium, copper, iron, magnesium, tin, titanium, resp. zinc are relatively low as such compounds resp. cations are normally not added to the bath, but are only or nearly only present because of the pickling effect of the aqueous acidic alkali metal phosphating solution to the metallic surfaces of the parts, sheets, strips or wires to be coated.
- Such contents will precipitate and generate the coating primarily containing phosphates, oxides and/or hydroxides of the metals' content in the solution further on, there may be traces or even low contents of such ions caused by impurities by pickling the bath containers and connecting tubes as well as by dragging in from earlier steps of the process succession.
- a significant difference of the alkali metal phosphating process in comparison to phosphating processes of the "coating-forming phosphating" is further that the cation(s) necessary for the coating formation during alkali metal phosphating is/are always present in a small percentage, mostly or totally dissolved from the surfaces of the metallic base substrates, whereby during e.g. zinc-, zinc-manganese-, zinc-nickel- or zinc-manganese-nickel-phosphating there will be a relatively high addition of e.g. zinc so that zinc is contained mostly in a content of more than 0.3 g/L resp. often of more than 1 g/L in the phosphating solution.
- This high zinc content is often caused by addition of zinc compounds of at least 40 %, mostly more than 60 %, often even more than 80 % of the total content to the bath, whereas only the remaining content is mostly generated by the pickling effect to zinciferous surfaces.
- the coatings generated by zinc-, zinc-manganese-, zinc-nickel- or zinc-manganese-nickel-phosphating show typically the predominantly zinc and/or manganese containing phases hranceaulithe, phosphophyllite, scholzite and/or hopeite in significant crystalline shapes.
- alkali metal phosphating show significant other properties as such from zinc-rich phosphatings: They have mostly a coating thickness in the range from 0.1 to 0.8 ⁇ m resp. only a coating weight in the range from 0.2 to 1.3 g/m 2 .
- the much thinner alkali metal phosphatings are mostly transparent or show iridescent colours related to their extremely thin thickness. Then they show the colours of "higher orders" and may be e.g. nearly transparent, yellowish, golden, reddish, a bit violet, greenish or often bluish, partly iridescent.
- the alkali metal phosphating coatings should have a higher coating weight, especially more than 0.7 and perhaps up to about 1.3 g/m 2 , they may show a more matte-grey appearance.
- aluminum-rich alkali metal phosphatings may occur silvery or silvery-iridescent.
- the alkali metal phosphating coatings may be prepared without any later generation of e.g. at least one paint layer and/or another organic paint-like layer. Then this coating process may be called a treatment. If the phosphating coatings should be used for a protection against corrosion for a limited time, then the coatings may be called a passivation. But they can be used under at least one paint layer and/or another organic paint-like layer like a primer, a lacquer, a silane layer, a base coat and/or a topcoat and/or respectively together with an adhesive and may then be called a pretreatment.
- alkali metal phosphating coatings are produced prior to painting by contacting the aqueous acidic phosphating solution which contains typically at least one mono- and/or orthophosphate and afterwards by electrocoating the phosphated metallic surfaces and/or often by powder painting e.g. of the parts of the metallic construction that are well accessable from outside like radiators and car bodies.
- alkali metal phosphating processes are carried out with solutions that contain alkali metal and/or ammonium and at least one type of phosphate, mostly orthophosphate, as well as always at least one accelerator, thereby showing a pH value during operating in the range of 4 to 6.
- aqueous acidic solutions are contacted to the metallic surfaces typically at temperatures in the range from 48 to 72 °C.
- Their typical coating weights are in the range from 0.3 to 1 g/m 2 .
- the coatings of today are rich in at least one phosphorus compound, show mostly bluish or light grey coloured coatings and often a coating weight in the range from 0.5 to 1.5 g/m 2 .
- DE-A1-100 06 338 describes a typical process for iron phosphating where there has been added a small amount of copper ions to solutions of a pH value in the range from 3.5 to 6.5 at a temperature in the range from 30 to 70 °C and especially at a pH value of about 4.8 of about 55 °C.
- DE-A1-1 942 156 teaches an alkali metal phosphating process by using a high pressure spraying method for contacting the metallic surfaces with solutions of a temperature of 60 °C and of a pH value in the range from 3 to 5.5, especially of a pH value of 4.
- DE-A1-1 914 052 concerns an alkali metal phosphating process by using a rollcoating application with a solution containing 5 to 20 g/L of phosphate ions and 3 to 12.5 g/L of chlorate at a temperature of 54.5 to 60 °C with an extraordinarily unconventional pH value in the range of 1 to 3.5 contacting a coil less than 30 seconds and squeegeeing.
- EP-B1-0 968 320 protects a process for an alkali metal phosphating for radiators by using a surfactant rich solution of a pH value in the range from 4 to 6 at a temperature in the range from 35 to 60 °C and especially of at least 50 °C.
- FR-A-1.155.705 refers to an alkali metal phosphating process by using an ammonium silicon hexafluoride and nitroguanidine containing solution of a pH value in the range from 3 to 6 at a temperature in the range from 50 to 76 °C.
- GB-A-1 388 435 reports an alkali metal phosphating process by using a free fluoride and chlorate containing solution of a pH value in the range from 3 to 6 at a temperature in the range from 50 to 80 °C, especially used with a pH value in the range from 3.65 to 4.4.
- US-A-2,665,231 discloses an alkali metal phosphating process by using a fluoride containing solution of a pH value in the range from 3 to 5.8 at a temperature in the range from 60 to 82 °C, especially used with a pH value in the range from 4.25 to 5.5.
- EP 0 411 606 A2 describes methods of surface-treating aluminum or its alloys by applying aqueous compositions containing niobium and/or tantalum together with fluoride and optionally with titanium and/or zirconium as well as with phosphate.
- the phosphate addition of 0.01 to 0.5 g/L shall be used as pH-adjusting agent.
- EP 0 121 155 A1 teaches processes for the preparation of surfaces of iron or steel for painting by applying alkali metal phosphating solutions containing dihydrogen phosphate and nitrobenzolsulfonate that show a pH in the range from 4.2 to 6.
- DE 1942 156 A1 discloses processes for the treatment of metal surfaces, especially of iron and steel surfaces, by applying alkali metal phosphate resp. ammonium phosphate and benzoate containing solutions at a pH in the range from 3 to 5.5 at high pressures and at temperatures of about 60 °C.
- a process for coating metallic surfaces with a phosphating coating by contacting metallic surfaces at a temperature not above 45 °C and at a pH value less than 3.5 with an aqueous acidic alkali metal phosphating solution or dispersion containing:
- a phosphating coating on a metallic surface prepared by contacting metallic surfaces with an aqueous acidic alkali metal phosphating solution or dispersion having a coating thickness of not more than 0.15 ⁇ m and having a good corrosion protection for the protected metallic material.
- the element content of the coatings was analysed by X-ray Photoelectron Spectroscopy (XPS), which may be used successfully as routine measurement method for controlling the different coatings, but which is an insufficient precise measurement method for such coatings to identify the element content dependent from the depth of the coating. Only the upper 8 nm from the surface into the depth could be analysed and therefore there is an influence of surface impurities.
- XPS X-ray Photoelectron Spectroscopy
- the measurement of the content of phosphorus and other elements in the coating was performed by X-ray Photoelectron Spectroscopy with an instrument 5700LSci of Physical Electronics, with an X-ray source of monochromatic aluminum, a power source of 350 Watts, an analysis region of 2 x 0.8 mm, an exit angle of 65 °, a charge correction for C-(C,H) in C 1s spectra at 284.8 eV and a charge neutralization by electron flood gun.
- the element content of the coatings was analysed by Secondary Neutral Mass Spectroscopy (SNMS) with an INA3 electron gas - SNMS apparatus of Leybold, which is a precise measuring method to identify the element content dependent from the depth of the coating of such thin alkali metal phosphating coatings.
- the samples were sputtered with Ar ions of 1040 eV energy and at a current density of about 1.2 mA/cm 2 .
- An area of 5 mm diameter was sputtered and analysed.
- the atoms of the upper surface layer evaporated and the next atom layers of below were analysed, until the total coating was removed in the sputtered area during the analysis.
- FIG. 1 for the cleaned, but not coated sample 1) shows the impurity effect of the surface region and then the composition of the cold rolled steel material.
- Figure 2 for sample 2) covered with a typical conventional iron phosphating coating of today indicates via the Fe content the thickness of the iron phosphating coating.
- the curves of the content of oxygen and phosphorus are - in the logarithmic graph - more or less proportional ("parallel").
- composition of the conventional iron phosphating coatings is significantly different from the composition of the iron phosphating coatings according to the invention.
- the surface roughness of all samples was measured with a white light interferometer NT3300 of Wyko, each coated panel on three areas.
- the average data of R a per panel varied between 0.89 and 1.02 ⁇ m
- the average data of R z per panel varied between 1.11 and 1.22 ⁇ m
- the average data of R t per panel varied between 6.17 and 7.25 ⁇ m.
- the samples 5) and 6) had been coated in the same manner and under nearly the same conditions, but they showed surface roughness data nearly twice as high as the samples 3) and 4):
- the average data of R a per panel varied at about 1.79 ⁇ m
- the average data of R z per panel varied at about 11.7 ⁇ m
- the average data of R t per panel varied in the range from 11.4 to 12.1 ⁇ m.
- Sample 3 ) has to be compared with sample 5) for the difference in surface roughness and element content; similarly, sample 4) has to be compared with sample 6).
- the rougher surfaces enable a higher amount of neutral parts measured than from more even surfaces, the more even surfaces shall be used for the analytical investigation and evaluation.
- the P content is less than 8 atomic% in a depth of 0.05 ⁇ m below the (original) surface of the alkali metal phosphating coating as analysed by Secondary Neutral Mass Spectroscopy (SNMS) or is less than 6 or even less than 4 atomic% in a depth of 0.1 ⁇ m below the surface of the alkali metal phosphating coating or is less than 3 or less than 2 atomic% in a depth of 0.1 ⁇ m below the surface of the alkali metal phosphating coating.
- the phosphating coating according to the invention has a thickness of not more or less than 0.15 ⁇ m, more preferred of not more than 0.12 ⁇ m, much more preferred of not more than 0.10 ⁇ m.
- the process according to the invention may preferably be characterized in that the temperature of the phosphating solution or dispersion may be during the contacting of the metallic surfaces in the range from 10 to 42 °C or less than 40 °C and more preferred at least 15 °C or up to 38 or up to 35 °C.
- the pH value may preferably be selected in the range starting from 1.8 resp. reaching up to 3.3, more preferred of at least 2 or up to 3.1, especially of at least 2.5 or up to 2.9.
- the coating weight may preferably be selected in the range from 0.03 to 0.4 g/m 2 , more preferred of at least 0.05 or up to 0.36 g/m 2 , most preferred of at least 0.1 or up to 0.32 g/m 2 .
- acids for use in the phosphating solution or dispersion most organic and inorganic acids as well as their water-soluble and/or water-dispersible derivatives, especially salts and/or esters, may be taken, but hydrochloric acid and chlorides are not recommended as they may cause significant crevice corrosion.
- hydrochloric acid and chlorides are not recommended as they may cause significant crevice corrosion.
- mixtures a) of acids, b) of at least one acid with at least one of salts and/or with at least one of ethers or c) of at least one of salts and/or of at least one of ethers.
- At least one acid is used like orthophosphoric acid, diphosphoric acid, monophosphoric acid, at least one of phosphonic acids, e.g. especially at least one with at least one aliphatic and/or aromatic group each, especially at least one of diphosphonic acids, phosphonous acid, phosphorous acid, molybdatophosphoric acid, tungstophosphoric acid and/or at least one of its derivatives like ester(s) and/or salt(s), especially at least one of monoester(s), of diester(s) and/or of triester(s) of a phosphorus containing acid like orthophosphoric acid, more preferred mixed with at least one phosphorus containing acid.
- phosphonic acids e.g. especially at least one with at least one aliphatic and/or aromatic group each, especially at least one of diphosphonic acids, phosphonous acid, phosphorous acid, molybdatophosphoric acid, tungstophosphoric acid and/or at least one of its derivatives like ester(s) and/
- At least one sulfur containing acid and/or at least one of its derivatives like ester(s) and/or salt(s) is used like sulfuric acid, sulfamatic acid, at least one of sulfonic acids like nitrosulfonic acid resp. at least one of their derivatives like ester(s) and/or salt(s).
- At least one nitrogen containing acid and/or at least one of its derivatives like ester(s) and/or salt(s) is used like nitric acid, at least one acid having at least one nitro and/or at least one amino group resp. at least one of its derivatives like ester(s) and/or salt(s).
- At least one organic acid and/or at least one of its derivatives like ester(s) and/or salt(s) is used like at least one of aromatic organic acids, hydroxocarboxylic acids, oxo acids, peracids and/or oxocarboxylic acids resp. at least one of its derivatives like ester(s) and/or salt(s) especially like acetic acid, benzoic acid, citric acid, formic acid, gluconic acid, hydroxy acetic acid, lactic acid, malic acid, oxalic acid, succinic acid, tartaric acid and/or its water-soluble and/or water-dispersible derivative(s) like ester(s) and/or salt(s) may be used.
- Any acid, derivative of it, acid mixture and/or mixture with at least one of its derivatives like ester(s) and/or salt(s) may be used, especially at least one or any mixture that is able to show a pH value e.g. of about 2.4, of about 2.9, of about 3.4, of about 3.9 and/or of about 4.4 and that is able to generate - at least together with the cations present - a thin coating, but a high amount of hydrochloric acid and of chloride is not favourable to be used because of its very strong corroding effect.
- these acids and derivatives especially phosphoric acid and dissolved phosphate esters/salts are especially favourable.
- reducing and/or oxidizing accelerators may be added, but must not be applied. Such accelerator(s) may be favourable to enhance the process, the coating quality and/or to influence the oxidation situation.
- an amount of Fe 2+ ions may be added to the phosphating solution or dispersion, preferably in the range from 0.01 to 1 g/L, more preferred in the range from 0.02 to 0.8 g/L, specifically preferred in the range from 0,03 to 0.5 g/L, most preferred of at least 0.05 or up to 0.3 g/L.
- the addition may be a dissolved iron phosphate. This addition helps in some cases, especially for nonferrous metal surfaces like such of hot-dip-galvanized (HDG) or electrogalvanized materials (EG), to generate a better corrosion inhibiting performance.
- HDG hot-dip-galvanized
- EG electrogalvanized materials
- the phosphating solution or dispersion does not contain more than about 0.5, 1 or 1.5 g/L of Fe 2+ ions, depending on the actual phosphating conditions; the iron content may then be lowered by addition of an oxidizing agent - which may be in some cases an accelerator - and/or by using a cation exchange material, e.g. an adequate resin.
- an oxidizing agent - which may be in some cases an accelerator - and/or by using a cation exchange material, e.g. an adequate resin.
- the phosphating solution or dispersion contains free fluoride, preferably in the range from 0.01 to 1 g/L, and/or complex fluoride, especially of aluminum, boron, silicon, titanium and/or zirconium, preferably each in the range from 0.01 to 1 g/L.
- the content of each of free fluoride resp. of each of the complex fluoride(s) lies in the range from 0.02 to 0.8 g/L, specifically preferred in the range from 0.03 to 0.5 g/L, most preferred of at least 0.05 or up to 0.3 g/L.
- the content of free fluoride and/or of the at least one complex fluoride enhances the pickling effect, especially on galvanized metallic surfaces as well as on aluminum-rich surfaces as oxide contents may be easier removed from the metallic surface; further on, it improves the performance and the quality of the corrosion inhibition and paint adhesion of the thereof formed coating for all metallic material bases.
- an amount of PO 4 ions may be added to the phosphating solution or dispersion preferably in the range from 0.1 to 18 g/L, more preferred in the range from 0.5 to 15 g/L, especially preferred of at least 1 and/or up to 12 g/L, most preferred of at least 2 g/L and/or up to 9 g/L of PO 4 ions.
- the phosphate content may provide the necessary acidity for the primary pickling effect. It also may help in some cases to remove the excess heavy metal content like an iron content out of the solution, that may predominantly or totally be a result of the pickling.
- the orthophosphoric acid may be added as acid, as monoacid and/or as poly acid salt of an alkali metal and/or of an ammonium group or in a small amount as an iron phosphate.
- orthophosphoric acid its ester(s) and/or its salt(s)
- a phosphonic acid and/or other phosphorus containing acid and/or at least one of their salts and/or esters may be added to the solution or dispersion, especially at least one water-soluble ester of phosphoric acid.
- the phosphating solution or dispersion may contain an amount of SO 4 ions in the range from 0.1 to 10 or 18 g/L, preferably of at least 0.5 and/or up to 15 g/L, more preferred in the range from 1 to 12 g/L, much more preferred of at least 2 g/L and/or up to 9 g/L of SO 4 ions.
- the sulfate content may provide the necessary acidity for the primary pickling effect.
- the sulfuric acid may be added as acid or as sulfate of an alkali metal and/or of an ammonium group or in a small amount as an iron sulfate.
- a mixture of at least one phosphorus containing acid and/or its salt(s) and/or its ester(s) with at least one sulphur containing acid and/or its salt(s) and/or its ester(s) may be added to the solution or dispersion; preferably, the content of such phosphorus containing compounds should be at least 50 % by weight of all such acids, salts and esters.
- the phosphating solution or dispersion may contain an amount of NO 3 ions in the range from 0.1 to 18 or to 10 g/L, preferably of at least 0.5 and/or up to 15 g/L, more preferred of at least 1 and/or up to 12 g/L, much more preferred of at least 2 g/L and/or up to 9 g/L of NO 3 ions.
- the nitrate content may provide the necessary acidity for the primary pickling effect.
- the nitric acid may be added as acid, as nitrate of at least one alkali metal and/or ammonium or in a small amount as an iron nitrate.
- a mixture of at least one phosphorus containing acid and/or its salt(s) and/or its ester(s) with at least one nitrogen containing acid and/or its salt(s) and/or its ester(s) may be added to the solution or dispersion; preferably, the content of such phosphorus containing compounds should be at least 50 % by weight of all such acids, salts and esters.
- the phosphating solution or dispersion may contain an amount of groups, ions and compounds together of organic acid(s) and/or of its derivative(s) in the range from 0.1 to 10 or 18 g/L, preferably of at least 0.5 and/or up to 15 g/L, more preferred in the range from 1 to 12 g/L, much more preferred of at least 2 g/L and/or up to 9 g/L of such groups, ions and compounds.
- the phosphating solution or dispersion contains an amount of nitroguanidine and/or other accelerators on the base of guanidine like acetatoguanidine, aminoguanidine, carbonatoguanidine, melanilinoguanidine, nitratoguanidine and ureidoguanidine in the total range from 0.01 to 5 g/L, preferably in the range from 0.015 to 3 g/L, more preferred in the range from 0.01 to 1.2 g/L, much more preferred of at least 0.02 g/L and/or up to 0.6 g/L of the guanidine compound(s).
- Nitroguanidine had shown in several instances to give the best results of all accelerators tested. In comparison to the use of aminoguanidine, the addition of nitroguanidine was a small amount more favourable, especially for the corrosion inhibition.
- the phosphating solution or dispersion may contain at least one surfactant, especially when cleaning and phosphating is carried out with the same solution or dispersion, then preferably with an amount of all surfactants together in the range from 0.01 to 10 g/L. If using at least one surfactant in the phosphating solution, it is preferred to take care not to generate foam. In some cases, it may be favourable to add a defoamer.
- This total surfactant content may preferably vary in the range from 0.1 to 7 g/L, more preferred in the range from 0.3 to 5 g/L, much more preferred of at least 0.5 g/L and/or up to 3 g/L of surfactant(s).
- the cleaning and phosphating may be carried out in the same bath container with the same solution or dispersion, so that in the first time of contacting the metallic components with the phosphating solution or dispersion, the cleaning and pickling effect of the solution or dispersion may prevail, whereas in the further time of the contacting, the coating process with the phosphating coating formation may predominate.
- nearly all types of surfactants resp. surfactant mixtures are suitable to be added to the phosphating solution or dispersion, especially surfactants resp. surfactant mixtures with low-foaming or non-foaming properties and with a cloud-point in the range from 25 to 40 °C, whereby the surfactant mixtures may be free of further constituents than surfactants.
- the phosphating solution is preferably free or nearly free of other heavy metals than those being pickled out of the metallic surface, perhaps with the exception of titanium and/or zirconium, especially in the presence of complex fluoride(s). It is preferably free of chromates, molybdates and tungstates.
- the phosphating solution or dispersion may contain at least one solvent like a propylene glycol and/or a glycol ether; further on it may contain at least one biocide, at least one stabilizing agent for a surfactant like a condensed sulfonic salt, at least one stabilizing agent for the accelerator like a fine-particular silicate-, clay- or clay-like material and/or at least one stabilizing agent for the solution or dispersion itself like a biopolymer.
- a solvent may be preferable for enhancing the cleaning effect of the metallic surface, especially in combination with at least one surfactant. It is favourable to use a guanidine compound in the form of a suspension containing a stabilizing agent, especially the nitroguanidine.
- a phosphating coating is generated showing mostly a colourless, faintly coloured, silvery, golden, yellowish, yellowish-brownish, yellowish-reddish and/or bluish colour. If the coating according to the invention is bluish, there seems to be often a phosphorus content of the coating being not as low as typical for such coatings and there are to be found often corrosion inhibition results less than of excellence. This coating may in several cases be less intensively coloured or may show a less brighter and/or even a matter appearance than conventional coatings. This coating may typically have a coating thickness in the range of up to 1 ⁇ m, mostly only up to 0.6 ⁇ m, often only up to 0.3 ⁇ m.
- a clean, a cleaned and/or a pickled metallic surface is contacted with the solution resp. dispersion.
- the metallic surface may be contacted with the solution resp. dispersion by immersing, spraying, steam-phosphating, roll-coating and/or squeegeeing. All application varieties except of steam-phosphating are often used for coil coating.
- the coated metallic surface is dried after contacting it with the solution resp. dispersion or later on after at least one thereon succeeding rinsing step, preferably by air-drying, oven-drying and/or infrared-drying, especially at temperatures in the range from 20 to 250 °C.
- At least two coatings one after the other on the metallic surface whereby at least one of them is applied with an alkali metal phosphating solution resp. dispersion and whereby at least one other coating may optionally be applied with a conversion coating solution like a zinc- and/or manganese-rich phosphating.
- an alkali metal phosphating coating is generated on a metallic surface and then a coating selected from the group consisting of a conversion coating like a zinc- and/or manganese-rich phosphating coating, a stearate coating and an organic polymer coating is applied thereon, especially for coldforming.
- a metallic surface consisting essentially of metallic materials of aluminum, chromium, titanium and/or zinc as well as at least one alloy containing aluminum, chromium, copper like brass or bronze, iron, magnesium, tin, titanium and/or zinc alloys is covered with a coating of a phosphating solution or dispersion.
- the coating prepared with a process according to the invention may be used for the short-term passivation, for the pretreatment prior to at least one succeeding paint layer, layer of any other organic coating and/or adhesive coating, as a lubricant carrier or as one of the lubricating coatings prior to coldforming.
- the lubricant resp. lubricant carrier may be favourably be used for cans, for machining, for wire drawing and/or for lubricating the moving chains.
- the process may be successfully varied by coating the thin phosphating coating according to the invention with a final seal solution resp. dispersion.
- the results of the salt spray testings show that a second, third and/or fourth coating on the metallic surface generated by contacting the panels phosphated in such way with the final seal solution resp. dispersion enhance the corrosion resistance significantly, although such final seal coatings are very thin.
- such final seal coatings may be generated with a final seal solution/ dispersion containing at least one rare earth element compound like a cerium compound, at least one resin component like acrylic acid and/or at least one silane.
- the coating prepared with a process according to the invention may be used for the corrosion inhibition and/or the lubrication of metallic surfaces, especially for use in aerospace industry, automobile industry, rail transportation, shipbuilding, metal forming, metal working like machining and/or grinding, in metallic container and especially can production, coil industry, for metal sheet applications, wire production, appliances, housings, machines and construction of buildings.
- the baths with these solutions were prepared at 3 % by volume for both formulations, this means for the solution A 3.58 % by weight resp. for the solution B 3.30 % by weight of the concentrate.
- 0.2 g/L nitroguanidine stabilized with a small content of clay-like material was further added.
- the pH value of both phosphating baths was adjusted to 4.5 resp. to 2.8 with an addition of sodium hydroxide.
- Panels of cold rolled steel (CRS) were cleaned with Okemclean ® at 3 % by volume and 54.4 °C for 30 seconds by spraying. The panels were then rinsed and afterwards treated in the phosphating bath A or B for 60 seconds by spraying at various temperatures. This was followed by rinsing and drying with compressed air. The panels were finally painted with a Dupont TGIC polyester powder paint and subjected to a salt spray (fog) test strictly according to ASTM B 117 for 336 hours for the evaluation of the corrosion inhibiting properties strictly according to a ASTM D 1654 rating, with 10 to be the best and 0 the worst.
- CRS cold rolled steel
- Table 2 Composition of the coatings of the different groups Contents in g/L Examples/ Comparison Examples PO 4 3- Na + ClO 3 - NBS Nitro-guanidine Amino-guanidine Carbonate 108, 0.12 0.02 - - 0.02 - 61,64,67, 0.58 0.12 - - 0.2 - 70, 73, 76, 0.58 0.12 - - - 0.2 82, 84, 92, 1.16 0.25 - - 0.02 - 62,65,68, 1.16 0.25 - - 0.2 - 71,74,77, 1.16 0.25 - - - 0.2 83, 85, 95, 1.16 0.25 - - 0.6 - 106, 3.01 0.64 - - 0.5 - 88, 91, 94, 97, 3.01 1.38 2.37 0.90 - - 1-3, 11-14, 19-22, 27-30, 35-38, 51-53, 63, 66, 69, 3.48 0.74
- the coatings became more uniform and changed from grey-brown to blue.
- Lower temperature treatments and lower coating weights were correlated with a better salt spray performance.
- the nitroguanidine-accelerated system B showed a better and more homogeneous appearance of the coatings and a better corrosion inhibition than the chlorate-SNBS-accelerated system A.
- the coating for the panels was homogeneous and went from blue to golden as the temperature increased.
- the CRS panels went from grey-brown to blue as temperature increased.
- the HDG and EG panels showed an etched appearance in all cases, but no colour.
- the aluminum panels were shiny with no apparently visible coating.
- the CRS panels went from blue to golden with increasing temperature, the HDG and EG panels had an iridescent appearance and the aluminum panels had a transparent light tan colour.
- the cold rolled steel panels were treated with aqueous acidic phosphating solutions C containing only a very tiny amount much less of 1 g/L of phosphoric acid only to adapt the pH value of the ready mixed solution to 2.5 resp. 4.5, 0.2 g/L nitroguanidine and 0.2 g/L aminoguanidine bicarbonate. If in all the examples aminoguanidine was added, it was added as bicarbonate, although not always indicated.
- the panels were cleaned with Gardoclean ® S 5206 and rinsed before the nitro- and the aminoguanidine were added.
- the panels were contacted with the phosphating solution for the test with a pH value of 2.5 at ambient temperature and for the test with a pH value of 4.5 at 49 °C.
- the comparison examples illustrate the effect of low and very high pH values of the phosphating solution using 0.2 g/L of nitroguanidine and 0.2 g/L of aminoguanidine carbonate as accelerators and using the base bath solution B of Group 1 containing 3 % by volume of the concentrate containing 1.3 % by weight of phosphoric acid, 11.7 % by weight of monosodium phosphate and the rest being deionized water.
- the CRS panels were cleaned as in the previous examples. Starting with a very acidic bath, the addition of NaOH resulted in very high pH values. The panels were sprayed with this conversion coating solution for 60 seconds at 48.9 °C.
- the phosphating baths were prepared with varying amounts of the base bath formulations starting from Group 1 and varying the accelerator concentrations of A and B.
- the conversion coating baths were operated at 26.7 °C and mostly at a pH value 4.5 for 60 second spraying.
- the last comparison example 79 was the standard chlorate-SNBS-accelerated alkali metal phosphating as outlined in Group 1, but only this was operated at a pH value of 4.5 and at a temperature of 48.9 °C for 80 seconds of spraying.
- the salt spray rating was evaluated according to ASTM D 1654 after 500 hours salt spray (fog) test according to ASTM B 117.
- Table 6 Results of the salt spray test and the coating weight dependent from the accelerator amount of the coating solutions of differently accelerated alkali metal phosphating systems and of the pH value at a temperature of 26.7 °C; * bath without accelerator content Ex./ Comp. Accelerator Accelerator (g/L) Bath * Concentration Vol.
- E 72, E 75 and E 78 show significantly better corrosion results than most of the other samples.
- the coatings were even, of a golden colour at a low pH value and of a blue colour at a high pH value for coatings generated with amino- resp. nitroguanidine.
- the bath solution contained fluoride to treat cold rolled steel, hot dipped galvanized, electrogalvanized and aluminum.
- the base solution B of Group 1 was used by with an additional content of free fluoride, whereby the content of all components of this bath were varied at a temperature of 38 °C.
- the panels were painted with a Ferro TGIC polyester powder paint of 38 to 51 ⁇ m thickness and were put into a salt spray (SS) test chamber according to ASTM B 117 for 250 hours, whereby the test results were measured in mm creep from the scribe. Further on, adhesion was tested according to ASTMD 3359, whereby 5B means that no flaking did occur in the cross-cut area which is the best possible test result, whereas e.g. 2B means that there is a certain amount of flaking in the cross-cut area.
- SS salt spray
- Table 8 Results of the salt spray (fog) test on three CRS panels each dependent from the chemical composition of the coating solutions, the pH value, the contacting time and the temperature; * bath without accelerator content Examples /Comp. Bath * Concentration (g/L) Accelerator (g/L) pH Value contacting time (s) temperature (° C) SS rating for 240 h mm creep E 101 7.2 0.5 2.8 30 32 1 E 102 7.2 0.02 2.8 105 32 1.1 E 103 4.3 0.2 3.0 60 37 0.5 E 104 0.14 0.02 2.8 180 37 1.2 E 105 0.14 1.0 2.8 30 44 1.0 CE 106 3.7 0.5 4.9 105 44 1.6 CE 107 5.4 0.8 6.0 68 54 8.1 CE 108 0.14 0.02 4.9 180 60 9.3 CE 109 - - - - - 0.2,0.5 CE 110 4.6 3.9 4.5 52 60 2 CE 111 4.6 3.9 4.5 52 60 5
- the examples according to the invention showed very good corrosion inhibition results compared with the results of the comparison examples.
- the comparison examples vary with respect to the corrosion inhibition quality depending if there is a further seal or not and especially if this final seal is a chromium containing layer.
- CE 109 showing such additional chromium containing layer covering the phosphate layer should show the best corrosion inhibition properties. Nevertheless, it is astonishing that the best panels according to the invention were able to reach the excellent corrosion inhibition properties of CE 109 which is the best industry standard material on the base of iron phosphate known in the art which in this case is even covered by a strongly further corrosion inhibiting final rinse layer.
- the coatings were even in all cases.
- the contact time, bath concentration and accelerator concentration did not have any apparent effect on the appearance.
- the results of the design of experiments showed clearly a broad region of unusually stable working conditions for an alkali metal phosphating solution below a pH value of 3.5 and astonishingly very constant coating properties.
- the phosphating results on aluminum alloy 6061 were best at a F - content of less than 200 ppm and at a Fe 2+ content less than 120 ppm.
- HDG hot dip galvanized steel
- electrogalvanized steel (EG) they were best at a very low PO 4 content and at a F - content of less than 200 ppm.
- the appearance of the coatings was at least as good as for comparable good alkali metal phosphating coatings used in the market. As best accelerator during all these studies, nitroguanidine was identified.
- the alkali metal phosphating process with the slightly modified working conditions for the solutions according to the invention are well suited for industrial application of coils, parts and wires.
- the use of the phosphating solution at a significantly lower temperature than today usual for the contacting of metallic surfaces helps to reduce heating costs considerably.
- the herein proposed phosphating process is easier than the processes used today as it is quite sufficient to control only total and free acid content, but no other parameters of the bath within short time limits, as the bath behaviour is very stable.
- this process is not only superior because less heating is needed and therefor is cheaper in comparison to actually used processes as there is a significant lower consumption of all chemical compounds of the solution than usual.
- the panels showed excellent thin coatings of more or less tan colour and good or even excellent corrosion inhibition.
- the best standard for an iron phosphate coating coated with a chrome final seal reached a salt spray test rating for 240 h of 0.2 mm creep.
- the results are excellent.
Abstract
Description
- This invention relates to a process for coating the surface of a metallic coil, part or wire with an aqueous acidic phosphating solution containing predominantly alkali metal ions and/or ammonium ions as well as in many cases phosphate ions. It relates further on to a phosphating solution to be used in this process for generating excellent corrosion inhibiting coatings on metallic surfaces. In some instances such coating may be used for coldforming of the metallic part. Such solutions are called alkali metal phosphating solutions or, if used on iron-rich surfaces, iron phosphating solutions.
- The invention is particularly concerned with a coating resp. conversion coating on aluminum, aluminum alloy, iron alloy like steel and stainless steel, magnesium alloy, zinc or zinc alloy as well as with a process, a concentrate and a solution for the formation of a phosphating coating on surfaces of these metallic materials.
- Such coating solution is especially suitable for the generation of pretreatment coatings on substrate surfaces which will be coated in a second step with at least one organic film, especially at least one film like a thin electrocoating lacquer layer, a paint layer, a silane-rich layer and/or an adhesive layer. Alternatively, the coating may be used for a treatment like a passivation without being covered with a further coating like a paint layer.
- Processes for the production of alkali metal phosphating coatings, especially prior to a lacquering, are described in relatively few cases in comparison to zinc phosphating or manganese phosphating where there is a huge number of publications. Fresh solutions for alkali metal phosphating that had not yet been used show typically only a very low or even practically no content of aluminum, iron and zinc. The fresh aqueous acid alkali metal phosphating solutions contain ions of at least one type of alkali metal ions and/or ammonium ions as well as phosphate ions. Because of the pickling effect of such acidic solutions on metallic surfaces, the ions of the dissolved metals like aluminum, iron and zinc as well as traces of other alloy constituents of the pickled metallic materials will be enriched during the ongoing phosphating process in the phosphating solution. Typically, the main phases of the alkali metal phosphating coatings are the corresponding phosphates, oxides and/or hydroxides of the metallic constituents of the metallic base material(s).
- Alkali metal phosphating solutions resp. coatings are called iron phosphating solutions resp. coatings if used on iron alloy surfaces like steel. The same corresponds to aluminum and aluminum alloys where such solutions resp. coatings are described as aluminum phosphating solutions resp. coatings. Often surfaces of very different metallic materials may be coated in the same alkali metal phosphating bath at the same time or one after the other whereby the ions of the different metals/alloys of the basic materials will be collected in the bath. Such coatings are - in contrast to coatings of the so called zinc-, zinc-manganese- or manganese- phosphating, mostly or totally amorphous or extraordinarily fine-grained.
- Alkali metal phosphatings are described in Werner Rausch: The Phosphating of Metals, ASM International, Finishing Publications Ltd., Teddington, England 1990 (especially pages 94 - 100, 120 - 130) in detail and are called the "non-coating phosphating" or in other publications "amorphous phosphating". The term "non-coating phosphating" is misleading, as there will be coatings generated although such coatings will be significantly thinner than created during e.g. zinc phosphating or zinc-manganese phosphating. The very thin alkali metal phosphating coatings are not, poorly or - if coloured or grey - well visible; the coatings may be only visible by colours caused by physical effects, by their kind of grey appearance and/or by their matte appearance. The alkali metal phosphating solution contains always a certain content of at least one alkali metal like sodium, potassium and/or of ammonium. The alkali metal phosphating coatings are typically - in contrary to the well and coursely crystalline coatings of the so-called "coating-forming phosphatings" - more or less amorphous and show under the scanning electron microscope typically no crystalline grain shapes.
- The alkali metal phosphating coatings are mostly poor, nearly free or totally free of manganese and zinc, if there will not be manganese and/or zinc rich surfaces to be pretreated or treated. They are typically poor, nearly free or totally free of chromium, cobalt, copper, nickel, tin and/or other heavy metals. The phases mainly generated and/or precipitated during iron phosphating, which is performed by contacting iron-rich metallic surfaces with an alkali metal phosphating solution, are iron phosphates, iron oxides and iron hydroxides like e.g. vivianite and/or magnetite. The contents of the ions dissolved from the metallic surface and then carried in the alkali metal phosphating solution, especially of aluminum, chromium, copper, iron, magnesium, tin, titanium, resp. zinc are relatively low as such compounds resp. cations are normally not added to the bath, but are only or nearly only present because of the pickling effect of the aqueous acidic alkali metal phosphating solution to the metallic surfaces of the parts, sheets, strips or wires to be coated. Such contents will precipitate and generate the coating primarily containing phosphates, oxides and/or hydroxides of the metals' content in the solution further on, there may be traces or even low contents of such ions caused by impurities by pickling the bath containers and connecting tubes as well as by dragging in from earlier steps of the process succession.
- A significant difference of the alkali metal phosphating process in comparison to phosphating processes of the "coating-forming phosphating" is further that the cation(s) necessary for the coating formation during alkali metal phosphating is/are always present in a small percentage, mostly or totally dissolved from the surfaces of the metallic base substrates, whereby during e.g. zinc-, zinc-manganese-, zinc-nickel- or zinc-manganese-nickel-phosphating there will be a relatively high addition of e.g. zinc so that zinc is contained mostly in a content of more than 0.3 g/L resp. often of more than 1 g/L in the phosphating solution. This high zinc content is often caused by addition of zinc compounds of at least 40 %, mostly more than 60 %, often even more than 80 % of the total content to the bath, whereas only the remaining content is mostly generated by the pickling effect to zinciferous surfaces. The coatings generated by zinc-, zinc-manganese-, zinc-nickel- or zinc-manganese-nickel-phosphating show typically the predominantly zinc and/or manganese containing phases huréaulithe, phosphophyllite, scholzite and/or hopeite in significant crystalline shapes.
- The coatings of alkali metal phosphating show significant other properties as such from zinc-rich phosphatings: They have mostly a coating thickness in the range from 0.1 to 0.8 µm resp. only a coating weight in the range from 0.2 to 1.3 g/m2. In contrary to the mostly dull grey appearing zinc-rich phosphating coatings, the much thinner alkali metal phosphatings are mostly transparent or show iridescent colours related to their extremely thin thickness. Then they show the colours of "higher orders" and may be e.g. nearly transparent, yellowish, golden, reddish, a bit violet, greenish or often bluish, partly iridescent. Only in the case that the alkali metal phosphating coatings should have a higher coating weight, especially more than 0.7 and perhaps up to about 1.3 g/m2, they may show a more matte-grey appearance. Especially aluminum-rich alkali metal phosphatings may occur silvery or silvery-iridescent.
- The alkali metal phosphating coatings may be prepared without any later generation of e.g. at least one paint layer and/or another organic paint-like layer. Then this coating process may be called a treatment. If the phosphating coatings should be used for a protection against corrosion for a limited time, then the coatings may be called a passivation. But they can be used under at least one paint layer and/or another organic paint-like layer like a primer, a lacquer, a silane layer, a base coat and/or a topcoat and/or respectively together with an adhesive and may then be called a pretreatment.
- In general, alkali metal phosphating coatings are produced prior to painting by contacting the aqueous acidic phosphating solution which contains typically at least one mono- and/or orthophosphate and afterwards by electrocoating the phosphated metallic surfaces and/or often by powder painting e.g. of the parts of the metallic construction that are well accessable from outside like radiators and car bodies.
- Typically, today alkali metal phosphating processes are carried out with solutions that contain alkali metal and/or ammonium and at least one type of phosphate, mostly orthophosphate, as well as always at least one accelerator, thereby showing a pH value during operating in the range of 4 to 6. These aqueous acidic solutions are contacted to the metallic surfaces typically at temperatures in the range from 48 to 72 °C. Their typical coating weights are in the range from 0.3 to 1 g/m2. The coatings of today are rich in at least one phosphorus compound, show mostly bluish or light grey coloured coatings and often a coating weight in the range from 0.5 to 1.5 g/m2.
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DE-A1-100 06 338 describes a typical process for iron phosphating where there has been added a small amount of copper ions to solutions of a pH value in the range from 3.5 to 6.5 at a temperature in the range from 30 to 70 °C and especially at a pH value of about 4.8 of about 55 °C.DE-A1-1 942 156 teaches an alkali metal phosphating process by using a high pressure spraying method for contacting the metallic surfaces with solutions of a temperature of 60 °C and of a pH value in the range from 3 to 5.5, especially of a pH value of 4.DE-A1-1 914 052 concerns an alkali metal phosphating process by using a rollcoating application with a solution containing 5 to 20 g/L of phosphate ions and 3 to 12.5 g/L of chlorate at a temperature of 54.5 to 60 °C with an extraordinarily unconventional pH value in the range of 1 to 3.5 contacting a coil less than 30 seconds and squeegeeing.EP-B1-0 968 320 protects a process for an alkali metal phosphating for radiators by using a surfactant rich solution of a pH value in the range from 4 to 6 at a temperature in the range from 35 to 60 °C and especially of at least 50 °C.FR-A-1.155.705 GB-A-1 388 435 US-A-2,665,231 discloses an alkali metal phosphating process by using a fluoride containing solution of a pH value in the range from 3 to 5.8 at a temperature in the range from 60 to 82 °C, especially used with a pH value in the range from 4.25 to 5.5. -
EP 0 411 606 A2 -
EP 0 121 155 A1 teaches processes for the preparation of surfaces of iron or steel for painting by applying alkali metal phosphating solutions containing dihydrogen phosphate and nitrobenzolsulfonate that show a pH in the range from 4.2 to 6. -
DE 1942 156 A1 discloses processes for the treatment of metal surfaces, especially of iron and steel surfaces, by applying alkali metal phosphate resp. ammonium phosphate and benzoate containing solutions at a pH in the range from 3 to 5.5 at high pressures and at temperatures of about 60 °C. - It was an object of the invention to propose an alkali metal phosphating process with very stable bath conditions and with excellent coating appearances and coating qualities using at least one accelerator like nitroguanidine. It was further an object to propose a phosphating process with an improved corrosion resistance in comparison to typical alkali metal phosphating processes used today. Further on, it was an object to propose an alkali metal phosphating process that is stable, well suited for industrial application for coils, parts and wires as well as easier and cheaper in comparison to actually used processes.
- Astonishingly, it has been observed that it is possible to "phosphate" a metallic surface with an unusually low or even with a zero phosphate content. Even other acids than phosphorus containing acids could be used without a loss of the quality of the coatings' properties. Nevertheless, the term "phosphating" is used here for all kinds of coating processes and coatings independent if they contain phosphorus or not.
- According to the present invention, there is provided a process for coating metallic surfaces with a phosphating coating by contacting metallic surfaces at a temperature not above 45 °C and at a pH value less than 3.5 with an aqueous acidic alkali metal phosphating solution or dispersion containing:
- At least one compound of at least one phosphorus containing acid and/or at least one of their derivatives selected from esters and salts in a total content of all kinds of acids and all their derivatives selected from esters and salts together of less than 20 g/L calculated on mole base as orthophosphate, whereby the content of such phosphorus containing compounds/ions is at least 50 % by weight in comparison to all such compounds/ions, at least one ion selected from the group consisting of at least one alkali metal ion and ammonium ion and
- at least one accelerator on the base of guanidine in the total range from 0.01 to 5 g/L,
whereby the phosphating coating has a coating composition with a phosphorus content of not more than 8 atomic% as measured by Secondary Neutral Mass Spectroscopy (SNMS) and
whereby the phosphating coating has a coating weight in the range from 0.01 to 0.5 g/m2. - According to the present invention, there is provided a phosphating coating on a metallic surface prepared by contacting metallic surfaces with an aqueous acidic alkali metal phosphating solution or dispersion having a coating thickness of not more than 0.15 µm and having a good corrosion protection for the protected metallic material.
- It has been found that for steel panels treated with an alkali metal phosphating solution based on a conventional composition, dried and later on painted with a polyester paint, show a corrosion inhibiting effect as measured by salt spray (fog) test clearly depending of the pH value of the alkali metal phosphating solution. At a pH value of the solution of about 7, the salt spray (SS) evaluation showed results of about 5, at a pH value of about 5 SS values of about 2.5 and at a pH value of about 2.5 SS (mm creep from scribe) values of about 1.5 or even less. Further details thereto are found in the examples.
- Tests were performed to identify the phases of different alkali metal phosphating coatings, but there was no X-ray diffraction result to be able to identify the phases. Therefore, it is believed that the thin coatings are amorphous or nearly amorphous.
- Then, the element content of the coatings was analysed by X-ray Photoelectron Spectroscopy (XPS), which may be used successfully as routine measurement method for controlling the different coatings, but which is an insufficient precise measurement method for such coatings to identify the element content dependent from the depth of the coating. Only the upper 8 nm from the surface into the depth could be analysed and therefore there is an influence of surface impurities. The measurement of the content of phosphorus and other elements in the coating was performed by X-ray Photoelectron Spectroscopy with an instrument 5700LSci of Physical Electronics, with an X-ray source of monochromatic aluminum, a power source of 350 Watts, an analysis region of 2 x 0.8 mm, an exit angle of 65 °, a charge correction for C-(C,H) in C 1s spectra at 284.8 eV and a charge neutralization by electron flood gun.
- Finally, the element content of the coatings was analysed by Secondary Neutral Mass Spectroscopy (SNMS) with an INA3 electron gas - SNMS apparatus of Leybold, which is a precise measuring method to identify the element content dependent from the depth of the coating of such thin alkali metal phosphating coatings. The samples were sputtered with Ar ions of 1040 eV energy and at a current density of about 1.2 mA/cm2. An area of 5 mm diameter was sputtered and analysed. During the measurement, the atoms of the upper surface layer evaporated and the next atom layers of below were analysed, until the total coating was removed in the sputtered area during the analysis. In 10 seconds of sputtering, about 10 nm of the upper part of the coating were removed. The measurement method could only be calibrated to a certain amount to the composition of the analysed coatings. The results showed a minor dependency of the surface roughness which was considered in the evaluation.
- For both analyses, XPS and SNMS, the same four samples of cold rolled steel panels were analysed:
- 1) an only cleaned, but not coated panel,
- 2) a typical conventional iron phosphating coating according to the state of the art as produced in today practice by first cleaning and then contacting the panel with an iron phosphating solution containing phosphate, sodium and chlorate at a pH value of 4.5 at a temperature of 50 °C generating a coating of about 0.16 to 0.22 µm thickness,
- 3) a very thin yellow iron phosphating coating according to the invention generated after having cleaned the panel by contacting it with an iron phosphating solution containing phosphate, sodium and 0.2 g/L nitroguanidine at a pH value of 3.0 with a value for total acid of 6 points at a temperature of 37 °C with a coating of about 0.02 to 0.1 µm thickness,
- 4) a thin bluish iron phosphating coating according to the invention generated after having cleaned the panel by contacting it with an iron phosphating solution containing phosphate, sodium and 0.2 g/L nitroguanidine at a pH value of 3.0 at a temperature of 37 °C with a coating of about 0.06 to 0.12 µm thickness, but the value for total acid had fallen below 3 points.
- The results of table 1 show that there is a considerable difference in the composition between the uncoated sample 1), the coated sample according to the state of the art 2) and the coated samples 3) and 4) according to the invention.
- The figures present the element distribution in atomic% as analysed by Secondary Neutral Mass Spectroscopy (SNMS) depending from the depth of the coating which was analysed from the surface (left) into the massive steel material (medium to right) in nm.
Figure 1 for the cleaned, but not coated sample 1) shows the impurity effect of the surface region and then the composition of the cold rolled steel material.Figure 2 for sample 2) covered with a typical conventional iron phosphating coating of today indicates via the Fe content the thickness of the iron phosphating coating. As shown in the following figures, the curves of the content of oxygen and phosphorus are - in the logarithmic graph - more or less proportional ("parallel"). There is a level in the upper and middle parts of the coating of about 30 atomic% of Fe, of about 50 atomic% of O and of about 9 atomic% of P.Figures 3 and 4 for the samples 3) and 4) with the coating according to the invention do not show clear content levels. The coating of sample 4) which is some percent thicker than the coating of sample 3), indicates a content of about 50 atomic% of Fe, of about 35 atomic% of O and of about 6 atomic% of P in the upper parts of the coating.Figure 5 represents the results of sample 5) that is comparable with sample 3) but shows higher surface roughness data and therefore higher signal output.Figure 6 represents the results of sample 6) that is comparable with sample 4) but shows higher surface roughness data and therefore higher signal output, too.Figure 7 represents the curves of the P content of the samples 1) to 4) in comparison, but now - as linear graph - showing clearly different phosphorus contents dependent from the depth analysed in the coating. - Therefore, it is clearly demonstrated that the composition of the conventional iron phosphating coatings is significantly different from the composition of the iron phosphating coatings according to the invention.
- The surface roughness of all samples was measured with a white light interferometer NT3300 of Wyko, each coated panel on three areas. For the samples 1) to 4), the average data of Ra per panel varied between 0.89 and 1.02 µm, the average data of Rz per panel varied between 1.11 and 1.22 µm and the average data of Rt per panel varied between 6.17 and 7.25 µm. In comparison to the samples 3) and 4), the samples 5) and 6) had been coated in the same manner and under nearly the same conditions, but they showed surface roughness data nearly twice as high as the samples 3) and 4): The average data of Ra per panel varied at about 1.79 µm, the average data of Rz per panel varied at about 11.7 µm and the average data of Rt per panel varied in the range from 11.4 to 12.1 µm. Sample 3 ) has to be compared with sample 5) for the difference in surface roughness and element content; similarly, sample 4) has to be compared with sample 6). As the rougher surfaces enable a higher amount of neutral parts measured than from more even surfaces, the more even surfaces shall be used for the analytical investigation and evaluation.
- Preferably, the P content is less than 8 atomic% in a depth of 0.05 µm below the (original) surface of the alkali metal phosphating coating as analysed by Secondary Neutral Mass Spectroscopy (SNMS) or is less than 6 or even less than 4 atomic% in a depth of 0.1 µm below the surface of the alkali metal phosphating coating or is less than 3 or less than 2 atomic% in a depth of 0.1 µm below the surface of the alkali metal phosphating coating. Preferably, the phosphating coating according to the invention has a thickness of not more or less than 0.15 µm, more preferred of not more than 0.12 µm, much more preferred of not more than 0.10 µm.
- The process according to the invention may preferably be characterized in that the temperature of the phosphating solution or dispersion may be during the contacting of the metallic surfaces in the range from 10 to 42 °C or less than 40 °C and more preferred at least 15 °C or up to 38 or up to 35 °C. The pH value may preferably be selected in the range starting from 1.8 resp. reaching up to 3.3, more preferred of at least 2 or up to 3.1, especially of at least 2.5 or up to 2.9. The coating weight may preferably be selected in the range from 0.03 to 0.4 g/m2, more preferred of at least 0.05 or up to 0.36 g/m2, most preferred of at least 0.1 or up to 0.32 g/m2.
- As acids for use in the phosphating solution or dispersion, most organic and inorganic acids as well as their water-soluble and/or water-dispersible derivatives, especially salts and/or esters, may be taken, but hydrochloric acid and chlorides are not recommended as they may cause significant crevice corrosion. There may be even used mixtures a) of acids, b) of at least one acid with at least one of salts and/or with at least one of ethers or c) of at least one of salts and/or of at least one of ethers.
- Preferably, at least one acid is used like orthophosphoric acid, diphosphoric acid, monophosphoric acid, at least one of phosphonic acids, e.g. especially at least one with at least one aliphatic and/or aromatic group each, especially at least one of diphosphonic acids, phosphonous acid, phosphorous acid, molybdatophosphoric acid, tungstophosphoric acid and/or at least one of its derivatives like ester(s) and/or salt(s), especially at least one of monoester(s), of diester(s) and/or of triester(s) of a phosphorus containing acid like orthophosphoric acid, more preferred mixed with at least one phosphorus containing acid.
- Preferably, at least one sulfur containing acid and/or at least one of its derivatives like ester(s) and/or salt(s) is used like sulfuric acid, sulfamatic acid, at least one of sulfonic acids like nitrosulfonic acid resp. at least one of their derivatives like ester(s) and/or salt(s).
- Preferably, at least one nitrogen containing acid and/or at least one of its derivatives like ester(s) and/or salt(s) is used like nitric acid, at least one acid having at least one nitro and/or at least one amino group resp. at least one of its derivatives like ester(s) and/or salt(s).
- Preferably, at least one organic acid and/or at least one of its derivatives like ester(s) and/or salt(s) is used like at least one of aromatic organic acids, hydroxocarboxylic acids, oxo acids, peracids and/or oxocarboxylic acids resp. at least one of its derivatives like ester(s) and/or salt(s) especially like acetic acid, benzoic acid, citric acid, formic acid, gluconic acid, hydroxy acetic acid, lactic acid, malic acid, oxalic acid, succinic acid, tartaric acid and/or its water-soluble and/or water-dispersible derivative(s) like ester(s) and/or salt(s) may be used.
- Any acid, derivative of it, acid mixture and/or mixture with at least one of its derivatives like ester(s) and/or salt(s) may be used, especially at least one or any mixture that is able to show a pH value e.g. of about 2.4, of about 2.9, of about 3.4, of about 3.9 and/or of about 4.4 and that is able to generate - at least together with the cations present - a thin coating, but a high amount of hydrochloric acid and of chloride is not favourable to be used because of its very strong corroding effect. Of these acids and derivatives, especially phosphoric acid and dissolved phosphate esters/salts are especially favourable. To accelerate the phosphating process, reducing and/or oxidizing accelerators may be added, but must not be applied. Such accelerator(s) may be favourable to enhance the process, the coating quality and/or to influence the oxidation situation.
- In the process according to the invention, an amount of Fe2+ ions may be added to the phosphating solution or dispersion, preferably in the range from 0.01 to 1 g/L, more preferred in the range from 0.02 to 0.8 g/L, specifically preferred in the range from 0,03 to 0.5 g/L, most preferred of at least 0.05 or up to 0.3 g/L. The addition may be a dissolved iron phosphate. This addition helps in some cases, especially for nonferrous metal surfaces like such of hot-dip-galvanized (HDG) or electrogalvanized materials (EG), to generate a better corrosion inhibiting performance.
- In case of the coating of steel surfaces, it is favourable to take care that the phosphating solution or dispersion does not contain more than about 0.5, 1 or 1.5 g/L of Fe2+ ions, depending on the actual phosphating conditions; the iron content may then be lowered by addition of an oxidizing agent - which may be in some cases an accelerator - and/or by using a cation exchange material, e.g. an adequate resin.
- In favourable embodiments, the phosphating solution or dispersion contains free fluoride, preferably in the range from 0.01 to 1 g/L, and/or complex fluoride, especially of aluminum, boron, silicon, titanium and/or zirconium, preferably each in the range from 0.01 to 1 g/L. In such cases, it is more preferred that the content of each of free fluoride resp. of each of the complex fluoride(s) lies in the range from 0.02 to 0.8 g/L, specifically preferred in the range from 0.03 to 0.5 g/L, most preferred of at least 0.05 or up to 0.3 g/L. The content of free fluoride and/or of the at least one complex fluoride enhances the pickling effect, especially on galvanized metallic surfaces as well as on aluminum-rich surfaces as oxide contents may be easier removed from the metallic surface; further on, it improves the performance and the quality of the corrosion inhibition and paint adhesion of the thereof formed coating for all metallic material bases.
- In the process according to the invention, an amount of PO4 ions may be added to the phosphating solution or dispersion preferably in the range from 0.1 to 18 g/L, more preferred in the range from 0.5 to 15 g/L, especially preferred of at least 1 and/or up to 12 g/L, most preferred of at least 2 g/L and/or up to 9 g/L of PO4 ions. The phosphate content may provide the necessary acidity for the primary pickling effect. It also may help in some cases to remove the excess heavy metal content like an iron content out of the solution, that may predominantly or totally be a result of the pickling. The orthophosphoric acid may be added as acid, as monoacid and/or as poly acid salt of an alkali metal and/or of an ammonium group or in a small amount as an iron phosphate. Instead or partially instead of orthophosphoric acid, its ester(s) and/or its salt(s), a phosphonic acid and/or other phosphorus containing acid and/or at least one of their salts and/or esters may be added to the solution or dispersion, especially at least one water-soluble ester of phosphoric acid.
- In the process according to the invention, the phosphating solution or dispersion may contain an amount of SO4 ions in the range from 0.1 to 10 or 18 g/L, preferably of at least 0.5 and/or up to 15 g/L, more preferred in the range from 1 to 12 g/L, much more preferred of at least 2 g/L and/or up to 9 g/L of SO4 ions. The sulfate content may provide the necessary acidity for the primary pickling effect. The sulfuric acid may be added as acid or as sulfate of an alkali metal and/or of an ammonium group or in a small amount as an iron sulfate. Especially a mixture of at least one phosphorus containing acid and/or its salt(s) and/or its ester(s) with at least one sulphur containing acid and/or its salt(s) and/or its ester(s) may be added to the solution or dispersion; preferably, the content of such phosphorus containing compounds should be at least 50 % by weight of all such acids, salts and esters.
- In the process according to the invention, the phosphating solution or dispersion may contain an amount of NO3 ions in the range from 0.1 to 18 or to 10 g/L, preferably of at least 0.5 and/or up to 15 g/L, more preferred of at least 1 and/or up to 12 g/L, much more preferred of at least 2 g/L and/or up to 9 g/L of NO3 ions. The nitrate content may provide the necessary acidity for the primary pickling effect. The nitric acid may be added as acid, as nitrate of at least one alkali metal and/or ammonium or in a small amount as an iron nitrate. Especially a mixture of at least one phosphorus containing acid and/or its salt(s) and/or its ester(s) with at least one nitrogen containing acid and/or its salt(s) and/or its ester(s) may be added to the solution or dispersion; preferably, the content of such phosphorus containing compounds should be at least 50 % by weight of all such acids, salts and esters.
- In the process according to the invention, the phosphating solution or dispersion may contain an amount of groups, ions and compounds together of organic acid(s) and/or of its derivative(s) in the range from 0.1 to 10 or 18 g/L, preferably of at least 0.5 and/or up to 15 g/L, more preferred in the range from 1 to 12 g/L, much more preferred of at least 2 g/L and/or up to 9 g/L of such groups, ions and compounds.
- Further on, the phosphating solution or dispersion contains an amount of nitroguanidine and/or other accelerators on the base of guanidine like acetatoguanidine, aminoguanidine, carbonatoguanidine, melanilinoguanidine, nitratoguanidine and ureidoguanidine in the total range from 0.01 to 5 g/L, preferably in the range from 0.015 to 3 g/L, more preferred in the range from 0.01 to 1.2 g/L, much more preferred of at least 0.02 g/L and/or up to 0.6 g/L of the guanidine compound(s). Nitroguanidine had shown in several instances to give the best results of all accelerators tested. In comparison to the use of aminoguanidine, the addition of nitroguanidine was a small amount more favourable, especially for the corrosion inhibition.
- In the process according to the invention, the phosphating solution or dispersion may contain at least one surfactant, especially when cleaning and phosphating is carried out with the same solution or dispersion, then preferably with an amount of all surfactants together in the range from 0.01 to 10 g/L. If using at least one surfactant in the phosphating solution, it is preferred to take care not to generate foam. In some cases, it may be favourable to add a defoamer. This total surfactant content may preferably vary in the range from 0.1 to 7 g/L, more preferred in the range from 0.3 to 5 g/L, much more preferred of at least 0.5 g/L and/or up to 3 g/L of surfactant(s). Especially in one-bath-processes, the cleaning and phosphating may be carried out in the same bath container with the same solution or dispersion, so that in the first time of contacting the metallic components with the phosphating solution or dispersion, the cleaning and pickling effect of the solution or dispersion may prevail, whereas in the further time of the contacting, the coating process with the phosphating coating formation may predominate. In general, nearly all types of surfactants resp. surfactant mixtures are suitable to be added to the phosphating solution or dispersion, especially surfactants resp. surfactant mixtures with low-foaming or non-foaming properties and with a cloud-point in the range from 25 to 40 °C, whereby the surfactant mixtures may be free of further constituents than surfactants.
- The phosphating solution is preferably free or nearly free of other heavy metals than those being pickled out of the metallic surface, perhaps with the exception of titanium and/or zirconium, especially in the presence of complex fluoride(s). It is preferably free of chromates, molybdates and tungstates.
- In the process according to the invention, the phosphating solution or dispersion may contain at least one solvent like a propylene glycol and/or a glycol ether; further on it may contain at least one biocide, at least one stabilizing agent for a surfactant like a condensed sulfonic salt, at least one stabilizing agent for the accelerator like a fine-particular silicate-, clay- or clay-like material and/or at least one stabilizing agent for the solution or dispersion itself like a biopolymer. A solvent may be preferable for enhancing the cleaning effect of the metallic surface, especially in combination with at least one surfactant. It is favourable to use a guanidine compound in the form of a suspension containing a stabilizing agent, especially the nitroguanidine.
- In the process according to the invention, a phosphating coating is generated showing mostly a colourless, faintly coloured, silvery, golden, yellowish, yellowish-brownish, yellowish-reddish and/or bluish colour. If the coating according to the invention is bluish, there seems to be often a phosphorus content of the coating being not as low as typical for such coatings and there are to be found often corrosion inhibition results less than of excellence. This coating may in several cases be less intensively coloured or may show a less brighter and/or even a matter appearance than conventional coatings. This coating may typically have a coating thickness in the range of up to 1 µm, mostly only up to 0.6 µm, often only up to 0.3 µm.
- In the process according to the invention, a clean, a cleaned and/or a pickled metallic surface is contacted with the solution resp. dispersion. The metallic surface may be contacted with the solution resp. dispersion by immersing, spraying, steam-phosphating, roll-coating and/or squeegeeing. All application varieties except of steam-phosphating are often used for coil coating. The coated metallic surface is dried after contacting it with the solution resp. dispersion or later on after at least one thereon succeeding rinsing step, preferably by air-drying, oven-drying and/or infrared-drying, especially at temperatures in the range from 20 to 250 °C.
- There may be applied at least two coatings one after the other on the metallic surface whereby at least one of them is applied with an alkali metal phosphating solution resp. dispersion and whereby at least one other coating may optionally be applied with a conversion coating solution like a zinc- and/or manganese-rich phosphating.
- In the process according to the invention, first an alkali metal phosphating coating is generated on a metallic surface and then a coating selected from the group consisting of a conversion coating like a zinc- and/or manganese-rich phosphating coating, a stearate coating and an organic polymer coating is applied thereon, especially for coldforming.
- In the process according to the invention, a metallic surface consisting essentially of metallic materials of aluminum, chromium, titanium and/or zinc as well as at least one alloy containing aluminum, chromium, copper like brass or bronze, iron, magnesium, tin, titanium and/or zinc alloys is covered with a coating of a phosphating solution or dispersion.
- The coating prepared with a process according to the invention may be used for the short-term passivation, for the pretreatment prior to at least one succeeding paint layer, layer of any other organic coating and/or adhesive coating, as a lubricant carrier or as one of the lubricating coatings prior to coldforming. The lubricant resp. lubricant carrier may be favourably be used for cans, for machining, for wire drawing and/or for lubricating the moving chains.
- The process may be successfully varied by coating the thin phosphating coating according to the invention with a final seal solution resp. dispersion. The results of the salt spray testings show that a second, third and/or fourth coating on the metallic surface generated by contacting the panels phosphated in such way with the final seal solution resp. dispersion enhance the corrosion resistance significantly, although such final seal coatings are very thin. Preferably, such final seal coatings may be generated with a final seal solution/ dispersion containing at least one rare earth element compound like a cerium compound, at least one resin component like acrylic acid and/or at least one silane.
- The coating prepared with a process according to the invention may be used for the corrosion inhibition and/or the lubrication of metallic surfaces, especially for use in aerospace industry, automobile industry, rail transportation, shipbuilding, metal forming, metal working like machining and/or grinding, in metallic container and especially can production, coil industry, for metal sheet applications, wire production, appliances, housings, machines and construction of buildings.
- The following examples illustrate, in detail, embodiments of the invention. The following examples and comparison examples shall help to clarify the invention, but they are not intended to restrict its scope:
- First tests were made in which an aqueous acidic solution as standard chlorate and sodium metanitrobenzene sulfonate (SNBS) accelerated alkali metal phosphating concentrate A containing
- 1.3 % by weight of phosphoric acid,
- 11.7 % by weight of monosodium phosphate,
- 1.0 % by weight of SNBS,
- 10.0 % by weight of sodium chlorate and
- 1.3 % by weight of phosphoric acid,
- 11.7 % by weight of monosodium phosphate and
- the rest being deionized water.
- Starting from these concentrates, the baths with these solutions were prepared at 3 % by volume for both formulations, this means for the solution A 3.58 % by weight resp. for the solution B 3.30 % by weight of the concentrate. To the solution B, 0.2 g/L nitroguanidine stabilized with a small content of clay-like material was further added. The pH value of both phosphating baths was adjusted to 4.5 resp. to 2.8 with an addition of sodium hydroxide.
- Panels of cold rolled steel (CRS) were cleaned with Okemclean® at 3 % by volume and 54.4 °C for 30 seconds by spraying. The panels were then rinsed and afterwards treated in the phosphating bath A or B for 60 seconds by spraying at various temperatures. This was followed by rinsing and drying with compressed air. The panels were finally painted with a Dupont TGIC polyester powder paint and subjected to a salt spray (fog) test strictly according to ASTM B 117 for 336 hours for the evaluation of the corrosion inhibiting properties strictly according to a ASTM D 1654 rating, with 10 to be the best and 0 the worst.
Table 2: Composition of the coatings of the different groups Contents in g/L Examples/ Comparison Examples PO4 3- Na+ ClO3 - NBS Nitro-guanidine Amino-guanidine Carbonate 108, 0.12 0.02 - - 0.02 - 61,64,67, 0.58 0.12 - - 0.2 - 70, 73, 76, 0.58 0.12 - - - 0.2 82, 84, 92, 1.16 0.25 - - 0.02 - 62,65,68, 1.16 0.25 - - 0.2 - 71,74,77, 1.16 0.25 - - - 0.2 83, 85, 95, 1.16 0.25 - - 0.6 - 106, 3.01 0.64 - - 0.5 - 88, 91, 94, 97, 3.01 1.38 2.37 0.90 - - 1-3, 11-14, 19-22, 27-30, 35-38, 51-53, 63, 66, 69, 3.48 0.74 - - 0.2 - 54-56, 72, 75, 78, 3.48 0.74 - - - 0.2 4-6, 15-18, 23-26, 31-34, 39-42, 79, 110, 111 3.78 1.61 2.81 0.32 - - 107, 4.41 0.94 - - 0.8 - 86, 93, 96, 102, 5.80 1.23 - - 0.02 - 101, 5.80 1.23 - - 0.5 - 81, 87, 89, 90, 5.80 1.23 - - 0.6 - Table 3: Coating weight and salt spray test ratings on CRS for a high pH value dependent from the temperature of the coating solutions of differently accelerated alkali metal phosphating systems Comp. Accelerator pH Value Temperature Coating Weight ASTM D 1654 Rating for Salt Spray Tests (° C) (g/m2) 550 h 1008 h CE 1 Nitroguanidine 4.5 54.4 0.18 6 6 CE 2" " 65.6 0.24 5 4 C E 3" " 82.2 0.34 --- 3 CE 4 Chlorate-SNBS 4.5 54.4 0.32 3 0 CE 5" " 65.6 0.52 0 1 CE 6" " 82.2 0.46 --- 1 - The higher the values of the rating, especially after longer testing time, the better the corrosion inhibition results. As the temperature increased in the nitroguanidine-accelerated bath B, the coatings became more uniform and changed from grey-brown to blue. Lower temperature treatments and lower coating weights were correlated with a better salt spray performance. The nitroguanidine-accelerated system B showed a better and more homogeneous appearance of the coatings and a better corrosion inhibition than the chlorate-SNBS-accelerated system A. The coating for the panels was homogeneous and went from blue to golden as the temperature increased.
- The same base bath formulations were used for the following tests with the standard chlorate-SNBS-accelerated system A and with the nitroguanidine-accelerated system B as in
Group 1. Panels of cold rolled steel (CRS), hot dipped galvanized steel (HDG), electrogalvanized steel (EG) and aluminum alloy AA 6061 were cleaned with Gardoclean® S 5206, rinsed, treated in the phosphating baths A or B and then rinsed and dried with compressed air. Based onGroup 1, the temperature range covered was changed to lower temperatures used. The panels were finally painted with Morton Corvel Black powder paint and subjected to salt spray (fog) test for 250 hours according to ASTM B 117. The creepage from scribe was measured according to the rating from 0 to 10 according to ASTM D 1654; the higher the SS values, the better are the results.Table 4: Salt spray test results for different metallic surfaces dependent from the temperature of the coating solutions of differently accelerated alkali metal phosphating systems for a pH value of 4.5 Comp. Accelerator Substrate Temperature (° C) Coating Weight (g/m2) Salt Spray Test Rating for 250 h CE 11 Nitroguanidine CRS 26.7 0.02 7 CE 12 " " 43.3 0.14 2 CE 13 " " 54.4 0.26 3 CE 14 " " 65.6 0.33 3 CE 15 Chlorate-SNBS CRS 26.7 0.23 1 CE 16 " " 43.3 0.23 2 CE 17 " " 54.4 0.50 3 CE 18 " " 65.6 0.27 2 CE 19 Nitroguanidine HDG 26.7 - 3 CE 20 " " 43.3 - 2 CE 21 " " 54.4 - 3 CE 22 " " 65.6 - 1 CE 23 Chlorate-SNBS HDG 26.7 - 3 CE 24 " " 43.3 - 3 CE 25 " " 54.4 - 3 CE 26 " " 65.6 - 4 CE 27 Nitroguanidine EG 26.7 - 2 CE 28 " " 43.3 - 3 CE 29 " " 54.4 - 2 CE 30 " " 65.6 - 0 CE 31 Chlorate-SNBS EG 26.7 - 4 CE 32 " " 43.3 - 3 CE 33 " " 54.4 - 2 CE 34 " " 65.6 - 0 CE 35 Nitroguanidine AA 6061 26.7 - 10 CE 36 " " 43.3 - 10 CE 37 " " 54.4 - 10 CE 38 " " 65.6 - 10 CE 39 Chlorate-SNBS AA 6061 26.7 - 10 CE 40 " " 43.3 - 10 CE 41 " " 54.4 - 10 CE 42 " " 65.6 - 10 - The test results of this test series show that the results are partially better at lower temperatures, but the results depend strongly from the metallic material of the surface contacted. Excellent results could be reached with all panels of the aluminum alloy. Nitroguanidine showed good corrosion inhibition results, whereby it was very astonishing that this could be gained with such a thin coating.
- Again, all panels were homogeneous. For the invention, the CRS panels went from grey-brown to blue as temperature increased. The HDG and EG panels showed an etched appearance in all cases, but no colour. The aluminum panels were shiny with no apparently visible coating. For the chlorate samples, the CRS panels went from blue to golden with increasing temperature, the HDG and EG panels had an iridescent appearance and the aluminum panels had a transparent light tan colour.
- The cold rolled steel panels were treated with aqueous acidic phosphating solutions C containing only a very tiny amount much less of 1 g/L of phosphoric acid only to adapt the pH value of the ready mixed solution to 2.5 resp. 4.5, 0.2 g/L nitroguanidine and 0.2 g/L aminoguanidine bicarbonate. If in all the examples aminoguanidine was added, it was added as bicarbonate, although not always indicated. The panels were cleaned with Gardoclean® S 5206 and rinsed before the nitro- and the aminoguanidine were added. The panels were contacted with the phosphating solution for the test with a pH value of 2.5 at ambient temperature and for the test with a pH value of 4.5 at 49 °C. This was followed by rinsing and drying the panels with compressed air. The such coated panels had a golden appearance and showed a homogeneous coating. The panels were then painted with a Ferro TGIC polyester powder paint. Finally, the panels were checked for paint adhesion by cross hatch and direct impact. There was significant paint loss when these tests were performed and were not acceptable. The panels were then also subjected to salt spray (fog) testing for 250 hours according to ASTM B 117. The panels had a rating of 0 per ASTM D 1654 for all cases after 250 hours, which is further on a bad result. As the solutions did not contain any alkali metal ions, nor ammonium ions, they were not buffered and lacked a significant content of acid.
- The comparison examples illustrate the effect of low and very high pH values of the phosphating solution using 0.2 g/L of nitroguanidine and 0.2 g/L of aminoguanidine carbonate as accelerators and using the base bath solution B of
Group 1 containing 3 % by volume of the concentrate containing 1.3 % by weight of phosphoric acid, 11.7 % by weight of monosodium phosphate and the rest being deionized water. The CRS panels were cleaned as in the previous examples. Starting with a very acidic bath, the addition of NaOH resulted in very high pH values. The panels were sprayed with this conversion coating solution for 60 seconds at 48.9 °C. - An unpainted panel from each test was put into a 100 % humidity test chamber for a water fog test according to ASTM D 1735 for 72 hours and thereafter the surface percentage of red rust was rated. The rest of the panels was painted with a Ferro TGIC polyester powder paint and was put into a salt spray test chamber according to ASTM B 117 for 250 hours and for a copper accelerated acetic acid salt spray (fog) test (CASS) test strictly according to General Motors Engineering Standards June 1997 for 72 hours. The salt spray test results and the CASS test results were measured in mm creep from the scribe. The panels from
test Table 5: Results of the humidity, salt spray and CASS tests dependent from the pH value of the coating solutions of differently accelerated alkali metal phosphating systems Comp. Accelerator pH value Humidity in % Salt Spray in mm CASS in mm CE 51 Nitroguanidine 2.8 10 - 25 0.1 0.2 CE 52 " 7.0 10 - 25 0.2 0.4 CE 53 " 9.0 ---- --- --- CE 54 Aminoguanidine Carbonate 2.8 100 0.2 0.3 CE 55 " 4.5 40 0.1 < 0.1 CE 56 " 6.5 --- --- --- - The corrosion inhibition was only for sample CE 51 of a pH value of 2.8 good and otherwise of medium quality. No coating weights were measured for this group. The coatings in all cases were homogeneous. Both coatings generated with the nitro- and aminoguanidine showed a golden colour at a low pH value and were blue at a high pH.
- Cold rolled steel panels were cleaned and rinsed as in the previous examples and comparison examples. The phosphating baths were prepared with varying amounts of the base bath formulations starting from
Group 1 and varying the accelerator concentrations of A and B. The conversion coating baths were operated at 26.7 °C and mostly at a pH value 4.5 for 60 second spraying. The last comparison example 79 was the standard chlorate-SNBS-accelerated alkali metal phosphating as outlined inGroup 1, but only this was operated at a pH value of 4.5 and at a temperature of 48.9 °C for 80 seconds of spraying. The salt spray rating was evaluated according to ASTM D 1654 after 500 hours salt spray (fog) test according to ASTM B 117.Table 6: Results of the salt spray test and the coating weight dependent from the accelerator amount of the coating solutions of differently accelerated alkali metal phosphating systems and of the pH value at a temperature of 26.7 °C; * bath without accelerator content Ex./ Comp. Accelerator Accelerator (g/L) Bath * Concentration Vol. % pH Value Coating Weight (g/m2) Salt Spray Rating for 500 h CE 61 Nitroguanidine 0.02 0.5 4.5 0.06 0 CE 62 " " 1 " 0.14 0 CE 63 " " 3 " 0.07 0 CE 64 " 0.2 0.5 " 0.16 0 CE 65 " " 1 " 0.13 0 CE 66 " " 3 " 0.01 0 CE 67 " 0.4 0.5 " 0.16 0 CE 68 " " 1 " 0.14 0 CE 69 " " 3 " 0.11 0 CE 70 Aminoguanidine Carbonate 0.2 0.5 " 0.11 0 CE 71 " " 1 " 0.30 0 E 72 " " 3 2.8 0.15 3 CE 73 " 0.1 0.5 4.5 0.03 2 CE 74 " " 1 " 0.19 0 E 75 " " 3 2.8 0.16 3 CE 76 " 0.05 0.5 4.5 0.03 2 CE 77 " " 1 " 0.10 1 E 78 " " 3 2.8 0.01 3 CE 79 Chlorate-SNBS " 3 - 4.5 0.45 1 - The examples according to the invention, E 72, E 75 and E 78, show significantly better corrosion results than most of the other samples. The coatings were even, of a golden colour at a low pH value and of a blue colour at a high pH value for coatings generated with amino- resp. nitroguanidine.
- In this group, a so-called multimetal formulation was used. The bath solution contained fluoride to treat cold rolled steel, hot dipped galvanized, electrogalvanized and aluminum. The base solution B of
Group 1 was used by with an additional content of free fluoride, whereby the content of all components of this bath were varied at a temperature of 38 °C. - A high number of solutions and tests was performed to generate data for intensive studies with design of experiment evaluation. For these experiments, the metallic surfaces, the content of fluoride (50 - 200 mg/L), the content of added Fe2+ (0 - 200 mg/L), the content of phosphate and sodium monophosphate together (1.4 - 7.2 g/L), the content of nitroguanidine as the single accelerator (0.02 - 0.6 g/L) as well as the pH value (2.8 - 4.5) were systematically varied within the mentioned limits, whereby only the examples according to the invention are listed in table 7. In comparison hereto, a chlorate-SNBS-accelerated solution of a pH value of 4.5 was tested at 49 °C with CE 88, CE 91, CE 94 and CE 97, whereas the other comparison examples belong strictly to the data set as shown for the rest of the examples according to the invention. The number of examples and comparison examples tested was reduced for this overview, so that typical results are represented here. From these experiments, systematical calculations were performed and the regions of excellent resp. good resp. stable behaviour selected.
- The panels were painted with a Ferro TGIC polyester powder paint of 38 to 51 µm thickness and were put into a salt spray (SS) test chamber according to ASTM B 117 for 250 hours, whereby the test results were measured in mm creep from the scribe. Further on, adhesion was tested according to ASTMD 3359, whereby 5B means that no flaking did occur in the cross-cut area which is the best possible test result, whereas e.g. 2B means that there is a certain amount of flaking in the cross-cut area.
Table 7: Results of the salt spray (fog) test dependent from the chemical composition of the phosphating solutions and from the pH value at a temperature of 32 °C; * bath without accelerator content Ex./ Comp Metallic Surface Bath * Concentration (g/L) Accelerator (g/L) Fluoride (mg /L) Fe2+ (mg /L) pH Value Adhesion ASTM 3359 SS Rating for 240 h SS Rating for 500 h E 81 CRS 7.2 0.6 200 0 2.8 5B 1 2.5 E 82 " 1.4 0.02 50 200 " 5B 0.5 2 E 83 " 1.4 0.6 200 200 " 5B 0.5 1 E 84 " 1.4 0.02 200 0 " 4B 1 1.5 CE 85 " 1.4 0.6 200 0 4.5 5B 2.5 4 E 86 " 7.2 0.02 200 200 2.8 5B 1 1.5 CE 87 " 7.2 0.6 200 200 4.5 4B 4 9 CE 88 " 4.1 4.4 310 0 4.5 2B 4.5 7 E 89 HDG 7.2 0.6 50 200 2.8 3B 3.5 4 E 90 " 7.2 0.6 200 0 " 3B 4 5 CE 91 " 4.1 4.4 310 0 4.5 2B 10 18 E 92 EG 1.4 0.02 50 200 2.8 5B 2 2.5 E 93 " 7.2 0.02 200 200 " 5B 1.5 3 CE 94 " 4.1 4.4 310 0 4.5 2B 3.5 4 E 95 Al 6061 1.4 0.6 50 0 2.8 4B 0.5 0.5 E 96 " 7.2 0.02 50 0 " 4B 0.5 0.5 CE 97 " 4.1 4.4 310 0 4.5 4B 0.5 1 - Nearly all of the examples according to the invention showed very good corrosion inhibition results resp. for the corrosion-sensitive material HDG even excellent results compared with the results of the comparison examples. The higher the values of the adhesion tests, the better are the results. The coatings were even in all cases. CRS panels according to the invention were grey, HDG panels were very faint golden, EG panels were grey and aluminum panels were of no significant colour. For the control, the CRS panels were golden, EG and HDG panels were transparent and iridescent and aluminum panels were light blue.
- In this group, only cold rolled steel panels were used and different influences were checked, even the influence of the bath temperature. The solutions were free of fluoride and added Fe2+. All the other contents and conditions of the coatings were the same as in
Group 6. Further on, the samples CE 109 and CE 110 were coated with Bonderite® 1000 (CE 109) for having an additional thin chromium final seal covering the phosphate coating resp. Cryscoat® 547 for having an additional thin non-chromium final seal covering the phosphate coating (CE 110) and the last having no additional final seal (CE 111) - each being coated in a typical manner. These coatings may be used as typical industry standards to get a comparison of typical conventional iron phosphating coatings of today.Table 8: Results of the salt spray (fog) test on three CRS panels each dependent from the chemical composition of the coating solutions, the pH value, the contacting time and the temperature; * bath without accelerator content Examples /Comp. Bath * Concentration (g/L) Accelerator (g/L) pH Value contacting time (s) temperature (° C) SS rating for 240 h mm creep E 1017.2 0.5 2.8 30 32 1 E 1027.2 0.02 2.8 105 32 1.1 E 103 4.3 0.2 3.0 60 37 0.5 E 104 0.14 0.02 2.8 180 37 1.2 E 105 0.14 1.0 2.8 30 44 1.0 CE 106 3.7 0.5 4.9 105 44 1.6 CE 107 5.4 0.8 6.0 68 54 8.1 CE 108 0.14 0.02 4.9 180 60 9.3 CE 109 - - - - - 0.2,0.5 CE 110 4.6 3.9 4.5 52 60 2 CE 111 4.6 3.9 4.5 52 60 5 - The examples according to the invention showed very good corrosion inhibition results compared with the results of the comparison examples. The comparison examples vary with respect to the corrosion inhibition quality depending if there is a further seal or not and especially if this final seal is a chromium containing layer. CE 109 showing such additional chromium containing layer covering the phosphate layer should show the best corrosion inhibition properties. Nevertheless, it is astonishing that the best panels according to the invention were able to reach the excellent corrosion inhibition properties of CE 109 which is the best industry standard material on the base of iron phosphate known in the art which in this case is even covered by a strongly further corrosion inhibiting final rinse layer.
- The coatings were even in all cases. The colour changed from golden to blue when either the pH or temperature was increased. The contact time, bath concentration and accelerator concentration did not have any apparent effect on the appearance.
- The results of the design of experiments showed clearly a broad region of unusually stable working conditions for an alkali metal phosphating solution below a pH value of 3.5 and astonishingly very constant coating properties. The phosphating results on aluminum alloy 6061 were best at a F- content of less than 200 ppm and at a Fe2+ content less than 120 ppm. On hot dip galvanized steel (HDG), they were best at a F- content of less than 360 ppm and at a Fe2+ content of more than 80 ppm, although the results were - as usual with HDG in such comparisons - worse than for the other metallic materials tested. On electrogalvanized steel (EG), they were best at a very low PO4 content and at a F- content of less than 200 ppm. On coldrolled steel (CRS), they were best at a F- content of less than 250 ppm. During a long throughput study, it was confirmed that these working conditions as well as the coating properties could be maintained nearly without any variation for all the time without changing the bath, but with continuous replenishment.
- The appearance of the coatings was at least as good as for comparable good alkali metal phosphating coatings used in the market. As best accelerator during all these studies, nitroguanidine was identified. Further on, the alkali metal phosphating process with the slightly modified working conditions for the solutions according to the invention are well suited for industrial application of coils, parts and wires. The use of the phosphating solution at a significantly lower temperature than today usual for the contacting of metallic surfaces helps to reduce heating costs considerably. The herein proposed phosphating process is easier than the processes used today as it is quite sufficient to control only total and free acid content, but no other parameters of the bath within short time limits, as the bath behaviour is very stable. Finally, this process is not only superior because less heating is needed and therefor is cheaper in comparison to actually used processes as there is a significant lower consumption of all chemical compounds of the solution than usual.
- For this investigation, cold rolled steel panels supplied by Q Panel were used as the substrates. Table 9 below lists the bath composition for each variation. The examples 117 to 119 were rinsed with a final seal instead of the rinsing with DI water. CrysCoat UltraSeal is a product of Chemetall Oakite based on water, silane and alcohol. The pretreated panels were painted using TGIC polyester powder paint supplied by Rohm & Haas. Single scribe panels were placed in salt spray testing per ASTM B 117 for 240 hours. The panels were scraped with a metal spatula and the amount of paint loss from the scribe was measured in mm. All variations were subjected to cross hatch adhesion per ASTM D 3359 and direct and reverse impact per ASTM D 2794. In all cases, the rating for the cross hatch adhesion testing was 5B (no loss of adhesion) and for the direct and reverse impact, no cracking or other paint loss was seen up to 160 pounds/inch2 (1.84 kilogramm/meter2). The panels were pretreated as written below:
- 1. Gardoclean S 5206, 3 v/v% b.v., 120 -125 °F (49 - 52 °C), 60 second spray
- 2. Tap water rinse, ambient temperature, 30 second spray
- 3. Conversion coating, 86 - 92 °F (30 - 33 °C)
- 4. Tap water rinse, ambient temperature, 30 second spray
- 5. DI water rinse, 10 seconds or final seal, ambient temperature, 30 second immersion
- 6. Oven dry, 225 °F (107 °C), 5 - 10 minutes
- The panels showed excellent thin coatings of more or less tan colour and good or even excellent corrosion inhibition. In comparison hereto, the best standard for an iron phosphate coating coated with a chrome final seal reached a salt spray test rating for 240 h of 0.2 mm creep. Within the scope of avoiding poisonous chromium compounds, the results are excellent.
Sample | Fe | Mn | Zn | Na | K | Mg | O | N | P |
1) control | 10.8 | 1.5 | 1.0 | 2.3 | < 0.1 | 0.4 | 41.8 | 0.9 | 0.5 |
2) conv. | 7.2 | 0.3 | 0.3 | 1.3 | 0.1 | 0.1 | 50.2 | 1.2 | 10.8 |
3) yellow | 13.6 | 0.1 | 0.7 | 0.2 | n.d. | 0.2 | 56.3 | 0.8 | 1.0 |
4) bluish | 16.1 | 0.3 | 0.7 | n.d. | n.d. | 0.2 | 57.2 | 0.5 | 1.8 |
was compared to another aqueous acidic solution of an alkali metal phosphating concentrate B accelerated only on nitroguanidine containing
Ex. | H3 PO4 | Lactic Acid | Glycolic Acid | Nitroguanidine | NaOH | Ce | Acrylic Acid | CCU | pH Value |
E 112 | 2.2 | 2.0 | - | 0.2 | 1.0 | - | - | - | 3.0 |
E 113 | 2.2 | - | 1.7 | 0.2 | 1.8 | - | - | - | 3.0 |
E 114 | 4.6 | - | - | 0.2 | 2.1 | 0.4 | - | - | 2.9 |
E 115 | 4.6 | - | - | 0.2 | 2.1 | 0.4 | 2.0 | - | 3.1 |
E 116 | 4.3 | - | - | 0.2 | 1.7 | - | - | - | 2.8 |
E 117 | 4.3 | - | - | 0.2 | 1.7 | - | - | - | 2.8 |
E 117* | - | - | - | - | - | - | - | 1.6 * | 2.85* |
E 118 | 4.3 | - | - | 0.2 | 1.7 | - | - | - | 2.8 |
E 118* | - | - | - | - | - | 2.0* | - | - | 4.3* |
E 119 | 4.3 | - | - | 0.2 | 1.7 | - | - | - | 2.8 |
E 119* | - | - | - | - | - | 2.0* | 2.0* | - | 2.9* |
Examples | Further additions | SS rating for 240 h mm creep | Visual appearance of panels | Coating weight (g/m2) |
E 112 | Lactic acid | 1.0 | Even grey-tan colour | 0.02 |
E 113 | Glycolic acid | 1.2 | Even grey-tan colour | 0.07 |
E 114 | Ce nitrate | 2.0 | Even tan colour | 0.01 |
E 115 | Ce nitrate and acrylic acid | 1.2 | Mostly even, deep golden colour | 0.14 |
E 116 | - | 1.5 | Even tan colour | 0.06 |
E 117 | - ; additional final seal: CCU | 0.3 | Even tan colour | 0.08 |
E 118 | - ; additional final seal: Ce nitrate | 0.3 | Even light tan-grey colour | 0.01 |
E 119 | - ; additional final seal: Ce nitrate and acrylic acid | 0.3 | Patchy grey to tan colour | 0.07 |
Claims (18)
- Process for coating metallic surfaces with a phosphating coating by contacting metallic surfaces at a temperature not above 45 °C and at a pH value less than 3.5 with an aqueous acidic alkali metal phosphating solution or dispersion containing:At least one compound of at least one phosphorus containing acid and/or at least one of their derivatives selected from esters and salts in a total content of all kinds of acids and all their derivatives selected from esters and salts together of less than 20 g/L calculated on mole base as orthophosphate, whereby the content of such phosphorus containing compounds/ions is at least 50 % by weight in comparison to all such compounds/ions, at least one ion selected from the group consisting of at least one alkali metal ion and ammonium ion andat least one accelerator on the base of guanidine in the total range from 0.01 to 5 g/L,
whereby the phosphating coating has a coating composition with a phosphorus content of not more than 8 atomic% as measured by Secondary Neutral Mass Spectroscopy (SNMS) and
whereby the phosphating coating has a coating weight in the range from 0.01 to 0.5 g/m2. - Process according to claim 1, whereby the phosphating solution or dispersion contains an amount of PO4 ions in the range from 0.1 to 10 g/L.
- Process according to claim 1 or 2, whereby the phosphating solution or dispersion contains an amount of SO4 ions in the range from 0.1 to 10 g/L.
- Process according to any of the preceding claims, whereby the phosphating solution or dispersion contains an amount of NO3 ions in the range from 0.1 to 10 g/L.
- Process according to any of the preceding claims, whereby an amount of Fe2+ ions is added to the phosphating solution or dispersion, preferably in the range from 0.01 to 1 g/L.
- Process according to any of the preceding claims, whereby the phosphating solution or dispersion contains free fluoride, preferably in the range from 0.01 to 1 g/L, and/or complex fluoride, especially of aluminum, boron, silicon, titanium and/or zirconium, preferably in the range from 0.01 to 1 g/L.
- Process according to any of the preceding claims, whereby the phosphating solution or dispersion contains at least one surfactant, especially when cleaning and phosphating is carried out with the same solution or dispersion, preferably with an amount of all surfactants together in the range from 0.01 to 10 g/L.
- Process according to any of the preceding claims, whereby the phosphating solution or dispersion contains at least one solvent like a propylene glycol and/or a glycol ether, at least one biocide, at least one stabilizing agent for a surfactant like a condensed sulfonic salt, at least one stabilizing agent for the accelerator like a fine-particular silicate-, clay- or clay-like material and/or at least one stabilizing agent for the solution or dispersion itself like a biopolymer.
- Process according to any of the preceding claims, whereby a phosphating coating is generated showing a colourless, faint colouring, silvery, yellowish, golden, yellowish-brownish, yellowish-reddish and/or bluish colour.
- Process according to any of the preceding claims, whereby a clean, a cleaned and/or a pickled metallic surface is contacted with the solution resp. dispersion.
- Process according to any of the preceding claims, whereby the metallic surface is contacted with the solution resp. dispersion by immersing, spraying, steam-phosphating, roll-coating and/or squeegeeing.
- Process according to any of the preceding claims, whereby the coated metallic surface is dried after contacting with the solution resp. dispersion or after at least one thereon succeeding rinsing step by air-drying, oven-drying and/or infrared-drying, especially at temperatures in the range from 20 to 250 °C.
- Process according to any of the preceding claims, whereby there are applied at least two coatings one after the other on the metallic surface whereby at least one of them is applied with a phosphating solution resp. dispersion and whereby at least one other coating may optionally be applied with a conversion coating solution like a zinc- and/or manganese-rich phosphating.
- Process according to any of the preceding claims, whereby first a alkali metal phosphating coating is generated on a metallic surface and then a coating selected from the group consisting of a conversion coating like a zinc-and/or manganese-rich phosphate coating, a stearate coating and an organic polymer coating is applied thereon, especially for coldforming.
- Process according to any of the preceding claims, whereby a metallic surface consisting essentially of metallic materials of aluminum, chromium, titanium and/or zinc as well as at least one alloy containing aluminum, chromium, copper, iron, magnesium, tin, titanium and/or zinc alloys is covered with a coating of a phosphating solution or dispersion.
- Process according to any of the preceding claims, whereby the metallic surface - after coating with the solution of claim 1 - is contacted with a final seal solution or dispersion, especially with a final seal solution/ dispersion containing at least one rare earth element compound, at least one resin component and/or at least one silane.
- Method of use of the coating prepared with a process according to one of the claim 1 to 18 for the short-term passivation, for the pretreatment prior to at least one succeeding paint layer, layer of any other organic coating and/or adhesive coating, as a lubricant carrier or as one of the lubricating coatings e.g. prior to coldforming.
- Method of use of the coating prepared with a process according to one of the claims 1 to 16 for the corrosion inhibition and/or the lubrication of metallic surfaces, especially for use in aerospace industry, automobile industry, rail transportation, shipbuilding, metal forming, metal working (machining, grinding), metallic container and especially can production, coil industry, for metal sheet applications, wire production, appliances, housings, machines and construction of buildings.
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CN101629288B (en) * | 2009-08-21 | 2011-06-22 | 攀钢集团钢铁钒钛股份有限公司 | Passivation treating agent for hot dip aluminum zinc plate and preparation method thereof |
CN102061464B (en) * | 2009-11-12 | 2013-05-15 | 佛山市中国地质大学研究院 | Novel environmentally-friendly passivating agent |
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-
2002
- 2002-12-24 US US10/328,924 patent/US20040118483A1/en not_active Abandoned
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2003
- 2003-12-18 CN CN200380109959.9A patent/CN1754009B/en not_active Expired - Fee Related
- 2003-12-18 ZA ZA200505064A patent/ZA200505064B/en unknown
- 2003-12-18 BR BR0316881-6A patent/BR0316881A/en not_active Application Discontinuation
- 2003-12-18 AT AT03789349T patent/ATE464404T1/en not_active IP Right Cessation
- 2003-12-18 MX MXPA05006897A patent/MXPA05006897A/en active IP Right Grant
- 2003-12-18 EP EP03789349A patent/EP1579030B1/en not_active Expired - Lifetime
- 2003-12-18 RU RU2005123323/02A patent/RU2358035C2/en not_active IP Right Cessation
- 2003-12-18 ES ES03789349T patent/ES2344345T3/en not_active Expired - Lifetime
- 2003-12-18 WO PCT/EP2003/014577 patent/WO2004059034A1/en not_active Application Discontinuation
- 2003-12-18 AU AU2003293945A patent/AU2003293945B2/en not_active Ceased
- 2003-12-18 CA CA002511361A patent/CA2511361A1/en not_active Abandoned
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US20040118483A1 (en) | 2004-06-24 |
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RU2005123323A (en) | 2006-02-10 |
AU2003293945B2 (en) | 2009-01-22 |
ZA200505064B (en) | 2008-09-25 |
CA2511361A1 (en) | 2004-07-15 |
AU2003293945A1 (en) | 2004-07-22 |
DE60332161D1 (en) | 2010-05-27 |
RU2358035C2 (en) | 2009-06-10 |
ES2344345T3 (en) | 2010-08-25 |
EP1579030A1 (en) | 2005-09-28 |
CN1754009A (en) | 2006-03-29 |
MXPA05006897A (en) | 2005-08-18 |
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