US3518169A - Alkali solution treatment of cathodically chromated metal surface - Google Patents
Alkali solution treatment of cathodically chromated metal surface Download PDFInfo
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- US3518169A US3518169A US471703A US3518169DA US3518169A US 3518169 A US3518169 A US 3518169A US 471703 A US471703 A US 471703A US 3518169D A US3518169D A US 3518169DA US 3518169 A US3518169 A US 3518169A
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- 229910052751 metal Inorganic materials 0.000 title description 18
- 239000002184 metal Substances 0.000 title description 18
- 239000003513 alkali Substances 0.000 title description 6
- 238000004532 chromating Methods 0.000 description 27
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 26
- 239000000243 solution Substances 0.000 description 17
- 229910000831 Steel Inorganic materials 0.000 description 15
- 239000010959 steel Substances 0.000 description 15
- 238000000034 method Methods 0.000 description 13
- 230000008569 process Effects 0.000 description 13
- 150000001450 anions Chemical class 0.000 description 12
- 239000003792 electrolyte Substances 0.000 description 11
- 238000007654 immersion Methods 0.000 description 10
- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical compound [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 description 9
- 159000000011 group IA salts Chemical group 0.000 description 9
- 150000003839 salts Chemical class 0.000 description 9
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 8
- 239000011651 chromium Substances 0.000 description 8
- 229910052804 chromium Inorganic materials 0.000 description 8
- 239000004922 lacquer Substances 0.000 description 8
- 229910001209 Low-carbon steel Inorganic materials 0.000 description 7
- 239000011248 coating agent Substances 0.000 description 7
- 238000000576 coating method Methods 0.000 description 7
- 238000005260 corrosion Methods 0.000 description 7
- 230000007797 corrosion Effects 0.000 description 7
- 238000007598 dipping method Methods 0.000 description 7
- 239000000203 mixture Substances 0.000 description 7
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 6
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 6
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 6
- WGLPBDUCMAPZCE-UHFFFAOYSA-N Trioxochromium Chemical compound O=[Cr](=O)=O WGLPBDUCMAPZCE-UHFFFAOYSA-N 0.000 description 6
- ZCDOYSPFYFSLEW-UHFFFAOYSA-N chromate(2-) Chemical class [O-][Cr]([O-])(=O)=O ZCDOYSPFYFSLEW-UHFFFAOYSA-N 0.000 description 6
- 229910000423 chromium oxide Inorganic materials 0.000 description 6
- 239000007921 spray Substances 0.000 description 6
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 description 5
- 229910001245 Sb alloy Inorganic materials 0.000 description 5
- 235000011114 ammonium hydroxide Nutrition 0.000 description 5
- 239000002140 antimony alloy Substances 0.000 description 5
- 210000003298 dental enamel Anatomy 0.000 description 5
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 4
- 239000002253 acid Substances 0.000 description 4
- 230000009471 action Effects 0.000 description 4
- 239000012670 alkaline solution Substances 0.000 description 4
- 229920000180 alkyd Polymers 0.000 description 4
- 229910052782 aluminium Inorganic materials 0.000 description 4
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 4
- 239000007864 aqueous solution Substances 0.000 description 4
- 239000003795 chemical substances by application Substances 0.000 description 4
- QTBSBXVTEAMEQO-UHFFFAOYSA-N Acetic acid Chemical compound CC(O)=O QTBSBXVTEAMEQO-UHFFFAOYSA-N 0.000 description 3
- QGZKDVFQNNGYKY-UHFFFAOYSA-O Ammonium Chemical compound [NH4+] QGZKDVFQNNGYKY-UHFFFAOYSA-O 0.000 description 3
- KWYUFKZDYYNOTN-UHFFFAOYSA-M Potassium hydroxide Chemical compound [OH-].[K+] KWYUFKZDYYNOTN-UHFFFAOYSA-M 0.000 description 3
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 3
- 239000002390 adhesive tape Substances 0.000 description 3
- 150000008044 alkali metal hydroxides Chemical class 0.000 description 3
- 239000000908 ammonium hydroxide Substances 0.000 description 3
- JOPOVCBBYLSVDA-UHFFFAOYSA-N chromium(6+) Chemical compound [Cr+6] JOPOVCBBYLSVDA-UHFFFAOYSA-N 0.000 description 3
- 238000001035 drying Methods 0.000 description 3
- 125000001495 ethyl group Chemical group [H]C([H])([H])C([H])([H])* 0.000 description 3
- -1 halogen anions Chemical class 0.000 description 3
- 229910052742 iron Inorganic materials 0.000 description 3
- 150000002739 metals Chemical class 0.000 description 3
- 239000011780 sodium chloride Substances 0.000 description 3
- BVKZGUZCCUSVTD-UHFFFAOYSA-M Bicarbonate Chemical class OC([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-M 0.000 description 2
- XTEGARKTQYYJKE-UHFFFAOYSA-M Chlorate Chemical compound [O-]Cl(=O)=O XTEGARKTQYYJKE-UHFFFAOYSA-M 0.000 description 2
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 description 2
- WMFOQBRAJBCJND-UHFFFAOYSA-M Lithium hydroxide Chemical compound [Li+].[OH-] WMFOQBRAJBCJND-UHFFFAOYSA-M 0.000 description 2
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 description 2
- ZLMJMSJWJFRBEC-UHFFFAOYSA-N Potassium Chemical compound [K] ZLMJMSJWJFRBEC-UHFFFAOYSA-N 0.000 description 2
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 2
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 description 2
- 150000007513 acids Chemical class 0.000 description 2
- 150000005325 alkali earth metal hydroxides Chemical class 0.000 description 2
- 229910045601 alloy Inorganic materials 0.000 description 2
- 239000000956 alloy Substances 0.000 description 2
- 238000009835 boiling Methods 0.000 description 2
- 150000001642 boronic acid derivatives Chemical class 0.000 description 2
- HUCVOHYBFXVBRW-UHFFFAOYSA-M caesium hydroxide Chemical compound [OH-].[Cs+] HUCVOHYBFXVBRW-UHFFFAOYSA-M 0.000 description 2
- 150000004649 carbonic acid derivatives Chemical class 0.000 description 2
- KRVSOGSZCMJSLX-UHFFFAOYSA-L chromic acid Substances O[Cr](O)(=O)=O KRVSOGSZCMJSLX-UHFFFAOYSA-L 0.000 description 2
- 238000002845 discoloration Methods 0.000 description 2
- 238000004090 dissolution Methods 0.000 description 2
- AWJWCTOOIBYHON-UHFFFAOYSA-N furo[3,4-b]pyrazine-5,7-dione Chemical compound C1=CN=C2C(=O)OC(=O)C2=N1 AWJWCTOOIBYHON-UHFFFAOYSA-N 0.000 description 2
- 238000010438 heat treatment Methods 0.000 description 2
- 229910052759 nickel Inorganic materials 0.000 description 2
- 238000007747 plating Methods 0.000 description 2
- 229910052700 potassium Inorganic materials 0.000 description 2
- 239000011591 potassium Substances 0.000 description 2
- CPRMKOQKXYSDML-UHFFFAOYSA-M rubidium hydroxide Chemical compound [OH-].[Rb+] CPRMKOQKXYSDML-UHFFFAOYSA-M 0.000 description 2
- 229910052708 sodium Inorganic materials 0.000 description 2
- 239000011734 sodium Substances 0.000 description 2
- 239000011135 tin Substances 0.000 description 2
- 229910052718 tin Inorganic materials 0.000 description 2
- 229910052725 zinc Inorganic materials 0.000 description 2
- 239000011701 zinc Substances 0.000 description 2
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 1
- USFZMSVCRYTOJT-UHFFFAOYSA-N Ammonium acetate Chemical class N.CC(O)=O USFZMSVCRYTOJT-UHFFFAOYSA-N 0.000 description 1
- 229910000975 Carbon steel Inorganic materials 0.000 description 1
- 239000004593 Epoxy Substances 0.000 description 1
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 1
- 229920000877 Melamine resin Polymers 0.000 description 1
- 229910002651 NO3 Inorganic materials 0.000 description 1
- NHNBFGGVMKEFGY-UHFFFAOYSA-N Nitrate Chemical compound [O-][N+]([O-])=O NHNBFGGVMKEFGY-UHFFFAOYSA-N 0.000 description 1
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 1
- 229910019142 PO4 Inorganic materials 0.000 description 1
- 150000001242 acetic acid derivatives Chemical class 0.000 description 1
- 230000002378 acidificating effect Effects 0.000 description 1
- 229910001860 alkaline earth metal hydroxide Inorganic materials 0.000 description 1
- 229910000147 aluminium phosphate Inorganic materials 0.000 description 1
- 235000019257 ammonium acetate Nutrition 0.000 description 1
- PRKQVKDSMLBJBJ-UHFFFAOYSA-N ammonium carbonate Chemical compound N.N.OC(O)=O PRKQVKDSMLBJBJ-UHFFFAOYSA-N 0.000 description 1
- 235000012501 ammonium carbonate Nutrition 0.000 description 1
- 229910052788 barium Inorganic materials 0.000 description 1
- DSAJWYNOEDNPEQ-UHFFFAOYSA-N barium atom Chemical compound [Ba] DSAJWYNOEDNPEQ-UHFFFAOYSA-N 0.000 description 1
- 230000004888 barrier function Effects 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- KGBXLFKZBHKPEV-UHFFFAOYSA-N boric acid Chemical compound OB(O)O KGBXLFKZBHKPEV-UHFFFAOYSA-N 0.000 description 1
- 239000004327 boric acid Substances 0.000 description 1
- 239000010962 carbon steel Substances 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 229910001430 chromium ion Inorganic materials 0.000 description 1
- ABXXWVKOBZHNNF-UHFFFAOYSA-N chromium(3+);dioxido(dioxo)chromium Chemical compound [Cr+3].[Cr+3].[O-][Cr]([O-])(=O)=O.[O-][Cr]([O-])(=O)=O.[O-][Cr]([O-])(=O)=O ABXXWVKOBZHNNF-UHFFFAOYSA-N 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 230000003111 delayed effect Effects 0.000 description 1
- 230000001627 detrimental effect Effects 0.000 description 1
- 235000011180 diphosphates Nutrition 0.000 description 1
- CEALXSHFPPCRNM-UHFFFAOYSA-L disodium;carboxylato carbonate Chemical compound [Na+].[Na+].[O-]C(=O)OC([O-])=O CEALXSHFPPCRNM-UHFFFAOYSA-L 0.000 description 1
- 238000001704 evaporation Methods 0.000 description 1
- 230000008020 evaporation Effects 0.000 description 1
- 150000004675 formic acid derivatives Chemical class 0.000 description 1
- 229910052736 halogen Inorganic materials 0.000 description 1
- 150000002366 halogen compounds Chemical class 0.000 description 1
- TVZISJTYELEYPI-UHFFFAOYSA-N hypodiphosphoric acid Chemical class OP(O)(=O)P(O)(O)=O TVZISJTYELEYPI-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
- 229910052744 lithium Inorganic materials 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- JDSHMPZPIAZGSV-UHFFFAOYSA-N melamine Chemical compound NC1=NC(N)=NC(N)=N1 JDSHMPZPIAZGSV-UHFFFAOYSA-N 0.000 description 1
- 229910017604 nitric acid Inorganic materials 0.000 description 1
- 150000003891 oxalate salts Chemical class 0.000 description 1
- VLTRZXGMWDSKGL-UHFFFAOYSA-M perchlorate Inorganic materials [O-]Cl(=O)(=O)=O VLTRZXGMWDSKGL-UHFFFAOYSA-M 0.000 description 1
- VLTRZXGMWDSKGL-UHFFFAOYSA-N perchloric acid Chemical compound OCl(=O)(=O)=O VLTRZXGMWDSKGL-UHFFFAOYSA-N 0.000 description 1
- 235000021317 phosphate Nutrition 0.000 description 1
- ACVYVLVWPXVTIT-UHFFFAOYSA-N phosphinic acid Chemical class O[PH2]=O ACVYVLVWPXVTIT-UHFFFAOYSA-N 0.000 description 1
- AQSJGOWTSHOLKH-UHFFFAOYSA-N phosphite(3-) Chemical class [O-]P([O-])[O-] AQSJGOWTSHOLKH-UHFFFAOYSA-N 0.000 description 1
- 150000003013 phosphoric acid derivatives Chemical class 0.000 description 1
- 239000011253 protective coating Substances 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 150000004760 silicates Chemical class 0.000 description 1
- LJRGBERXYNQPJI-UHFFFAOYSA-M sodium;3-nitrobenzenesulfonate Chemical compound [Na+].[O-][N+](=O)C1=CC=CC(S([O-])(=O)=O)=C1 LJRGBERXYNQPJI-UHFFFAOYSA-M 0.000 description 1
- 229910052712 strontium Inorganic materials 0.000 description 1
- SOBHUZYZLFQYFK-UHFFFAOYSA-K trisodium;hydroxy-[[phosphonatomethyl(phosphonomethyl)amino]methyl]phosphinate Chemical compound [Na+].[Na+].[Na+].OP(O)(=O)CN(CP(O)([O-])=O)CP([O-])([O-])=O SOBHUZYZLFQYFK-UHFFFAOYSA-K 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
- C25D11/38—Chromatising
Definitions
- Cathodic chromating is a process in which hexavalent chromium ionderived from chromic acid, chromates or dichromates in a treating solution is electrolytically reduced, mainly to the trivalent state, to form a protective coating of a hydrated chromium oxide complex on a suitable for the formation of a uniform hydrated chromium oxide coating, of blue or bluish purple color, which provides superior corrosion resistance and lacquer adhesion property.
- sulfate anion is'involved in the electrolytic reduction of hexavalent chromium. In that condition, however, it is physically adsorbed in the hydrated chromium oxide film on metal surfaces.
- the sulfate anion adsorbed in the film is water soluble and accelerates I the corrosion of treated metal surfaces under highly humid conditions. By heating the metals, this soluble sulfate anion changes to insoluble form in the film, but a number of cracks show in the film, so that corsion resistance is not improved by simple heating.
- the addition agent which gives sulfate anion is necessary to form a superior film but it gives a detrimental effect on the corrosion resistance of the formed film.
- Such a behavior as sulfate anion may be cathode metal.
- the expression hydrated chromium oxide coating is employed, for the film formed by chromating. An analysis of the formed film shows that it contains no other metals than chromium and does not consist: of simple metallic chromium. The analysis also shows the film contains a very little amount of an anion which originallypresents in the chromating solution as an addition agent. Y
- the anion in the coating is fixed as a member of a co-ordinated complex structure of the coating. In a wetted stage, however, the anion is not firmly fixeid in the structure and behaves as if it absorbs physical y.
- a coating formed in chromium plating is a simple metallic chromium and the one formed in dip chromating is mainly a chromium chromate and in some cases is a mixture of a chromate and an oxide of metal to be coated, while the one formed in anodic chromating is a mixture of a chromate and an oxide of metal to be coated.
- disulfonic acid, sulfuric acid or their respective salts which gives sulfate anion is most observed in strongly acidic anions :such as nitrate, chlorate, perchlorate, and halogen anions in cathodic chromating
- strongly acidic anions such as nitrate, chlorate, perchlorate, and halogen anions in cathodic chromating
- an immersion or a cathodic treatment immediately after the previous cathodic treatment and before the surface of the metal is allowed to dry, in an aqueous solu tion containing at least one alkaline salt selected from the group consisting of ammonium hydroxide, alkali metal hydroxides, alkali earth metal hydroxides and alkaline salts of weak acids before drying the film formed in cathodic chromating is most efiective.
- An alkaline salt used in the present invention is selected from the following salts.
- (l) Ammonium hydroxide (l) Ammonium hydroxide.
- Alkali metal hydroxides LiOH, NaOl-I, KOH, RbOH, CsOH.
- Alkali earth metal hydroxides Ba(0H) -8-H O, Sr( OH 2 8'H O.
- Alkaline salts of weak acids Acetates, CH COOLi-2H O, CH C0ONa-3H O,
- NaKCO -6H O, NaI-ICO KHCO NH HCO Chromates and dichromates, Li CrOl -2H O,
- Treating time in the case of immersion
- Treating time in the case of cathodic treatment
- Treating current density (only in the case of cathodic treatment)-0-10 a./sq. dm.
- the optimum concentration of alkaline salts is within the range from 1 g./liter to 100 g./liter. Within this range, one or more than one alkaline salts can be added. Generally an increase in concentration results in a higher removal efficiency of adsorbed anion. However, when the concentration of alkaline salts exceeds 100 g./liter, dissolution of the film formed in cathodic chromating begins to occur. When the concentration is less than 1 g./liter, the process needs a longer-period to remove adsorbed anion, which is impractical in high speed commercial operation.
- an increase in immersion time results in a higher removal efiiciency of adsorbed anion, but with a concentration of l-100 g./liter of salt and at a temperature of 30-70 C., the immersion time of 1-30 seconds is sufficient. When the period exceeds 30 seconds, dissolution of the formed film is initiated.
- the period of, e.g., seconds is often not practical.
- a cathodic treatment is necessary in the alkaline solution mentioned above because the immersion treatment is less effective.
- the current density should be controlled to within 10 a./ sq. dm. If the current density exceeds 10 a./ sq. dm., the formed film will be partially dissolved and the corrosion resistance of the film will not be improved.
- An immersion treatment in hot water of 80-90 C. is also effective to remove adsorbed anion but this takes as long as 2 minutes which is not practical in high speed commercial operation.
- an immersion treatment in an alkaline solution is less effective for the removal of adsorbed anion, but in such case, the dried film behaves as a hard barrier against the action of an alkaline solution.
- the action of the alkaline solution is delayed. Therefore in such a very short-period operation as in the commercial production, a cathodic treatment in a concentration of more than 100 g./liter of alkaline salts and at a temperature of more than 70 C. is necessary to obtain the effective action of alkali.
- the action of alkali is always effective in lower concentrations at lower temperatures even in high speed operation as described above. Therefore, the alkali treatment must be immediately performed before allowing the film formed in cathodic chromating to be dried.
- iron and steel treated according to the present invention can withstand outdoor exposure tests for 2 months in winter and for 15 days in summer and resist salt spray tests for 48 hours without any sign of rust. They further resist humidity chamber tests under the condition of relative humidity of 90%, at 40 C., for one week without any sign of discoloration of the film.
- the lacquered sheet was deeply drawn to the cup with a drawing ratio of 2.2 and stretch formed in the cup wall.
- the lacquer adhesion on the stretched part of the cup side quite withstood even the adhesive tape test.
- no adhesion loss of the lacquer was found on the cup wall, even when tested with adhesive tape after the cup was immersed in a boiling 3% sodium chloride solution for one hour.
- Metals having the following surface are suitable for treatment according to the present invention; iron, steel, aluminum, zinc, tin, nickel, chromium, their respective alloys.
- EXAMPLE 1 A 0.25 mm. cold rolled low carbon steel sheet, socalled black plate, is cathodically cleaned for 20 seconds at a current density of 4 a./sq. dm. at C. in a 7% sodium hydroxide solution, then rinsed with water, pickled for 10 seconds at room temperature in a 7% sulfuric acid, again rinsed with water, and immediately treated cathodically using a lead antimony alloy anode under the following condition in an electrolyte of the following composition, again immediately rinsed with water, then immediately dipped in the treating solution of the present invention indicated below, and again immediately rinsed with water, and dried.
- EXAMPLE 2 A 0.5 mm. cold rolled low carbon steel sheet was subjected to the same pretreatment and the same cathodic chromating as described in Example 1, immediately rinsed with Water, then immediately dipped in the treating solution of the present invention under the following condition and again immediately rinsed with Water, and dried.
- EXAMPLE 5 The same kind of cold rolled low carbon steel sheet was subjected to the same pretreatment as described in Example 1, and then immediately treated cathodically using a lead antimony alloy anode under the following condition in an electrolyte of the following composition, again immediately rinsed with water, then immediately dipped in the treating solution of the present invention under the following condition and again immediately rinsed with water, and dried.
- EXAMPLE 6 The same kind of cold rolled low carbon steel sheet was subjected to the same pretreatment as described in Example 1, immediately treated in the same cathodic chromating as described in Example 5, immediately rinsed with water then immediately dipped in the treating solution of the present invention under the following condition and again immediately rinsed with water, and dried.
- EXAMPLE 7 The same kind of cold rolled low carbon steel sheet was subjected to the same pretreatment and the same cathodic chromating as described in Example 1-, then immediatelyrinsed, with water, immediately dipped. in the treating solution of the present invention under the following condition and again immediately rinsed with water, and dried.
- EXAMPLE 8 The same kind of cold rolled low carbon steel sheet was subjected to the same pretreatment as described in Example 1, immediately treated cathodically using a lead antimony alloy anode under the following condition in an electrolyte of the following composition, again immediately rinsed with water, then immediately dipped in the treatment solution of the present invention under the following condition and immediately rinsed with water, and dried.
- EXAMPLE 9 A 0.5 mm. aluminum sheet (99.0%) was cleaned for 10 seconds at room temperature in 4% sodium dicarbonate solution, rinsed with water, immediately treated cathodically using a lead antimony alloy anode under the following condition in an alectrolyte of the following composition, again immediately rinsed with water, then immediately dipped in the treating solution of the present invention and again immediately rinsed with water, and dried.
- a process for treating metal which comprises cathodically chromating said metal in the presence of sulfate ions, rinsing the chromated metal with water before being allowed to dry, removing entrapped sulfate ions by immersion in a aqueous solution containing a total of from 1 to 100 grams per liter of at least one water-soluble alkaline compound selected from the group consisting of ammonium hydroxide, alkali metal hydroxides, alkaline earth metal hydroxides, and alkali metaland ammonium acetates, borates, carbonates, bicarbonates, chromates, dichromates, formates, oxalates, phosphates, pyrophosphates, hypophosphates, phosphites, hypophosphites and silicates applying a cathodic current to the catholically chromated surface wh le immersed in said aqueous solution, removing from bath, rinsing with water, and thereafter drying.
- a process according to claim 1 wherein the cathodic treatment is conducted for not more than 2 seconds.
- a process according to claim 1 wherein the temperature of the aqueous solution is from 30 to C. 5. A process according to claim 1 wherein the current density for cathodically treating the metal is not more than 10 amperes per square decimeter.
- a process according to claim 1 wherein the metal to be treated has a surface selected from the group consisting of iron, steel, aluminum, zinc, tin, nickel, chromium and alloys thereof.
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Chemical Kinetics & Catalysis (AREA)
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- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Chemical Treatment Of Metals (AREA)
Description
United States Patent Oflice 3,518,169 Patented June 30, 1970 7 3,518,169 l ALKALI SOLUTION TREATMENT OF CATHOD- ICALLY CHROMATED METAL SURFACE v Taro Oyama and Tsuneo Inui,,Kudamatsu-shi, Japan, assignors to Toyo Kahan Co., Ltd., Tokyo, Japan, a corporation of Japan v No Drawing. Filed July 13, 1965, Ser. No. 471,703
Int. Cl. C23f 13/00; C2311 11/00 US. Cl. 204-35 6 Claims ABSTRACT on THE DISCLOSURE The present invention relatesto a process for improving the properties of the coating formedin the cathodic chromating of metal surfaces. Cathodic chromating is a process in which hexavalent chromium ionderived from chromic acid, chromates or dichromates in a treating solution is electrolytically reduced, mainly to the trivalent state, to form a protective coating of a hydrated chromium oxide complex on a suitable for the formation of a uniform hydrated chromium oxide coating, of blue or bluish purple color, which provides superior corrosion resistance and lacquer adhesion property.
If no sulfate anion is present in the chromating electrolyte, the film formed shows yellowish stains and has poor corrosion resistance and lacquer adhesion property. Thus, sulfate anion is'involved in the electrolytic reduction of hexavalent chromium. In that condition, however, it is physically adsorbed in the hydrated chromium oxide film on metal surfaces. The sulfate anion adsorbed in the film is water soluble and accelerates I the corrosion of treated metal surfaces under highly humid conditions. By heating the metals, this soluble sulfate anion changes to insoluble form in the film, but a number of cracks show in the film, so that corsion resistance is not improved by simple heating.
As described above, the addition agent which gives sulfate anion is necessary to form a superior film but it gives a detrimental effect on the corrosion resistance of the formed film. Such a behavior as sulfate anion may be cathode metal. In the present specification the expression hydrated chromium oxide coating is employed, for the film formed by chromating. An analysis of the formed film shows that it contains no other metals than chromium and does not consist: of simple metallic chromium. The analysis also shows the film contains a very little amount of an anion which originallypresents in the chromating solution as an addition agent. Y
When the wetted hydrated chromium oxide coating formed immediately after the chromating is dried at an appropriate temperature, the anion in the coating is fixed as a member of a co-ordinated complex structure of the coating. In a wetted stage, however, the anion is not firmly fixeid in the structure and behaves as if it absorbs physical y.
As shown in the specific examples in the present specification, the conditions for a cathodic chromating process are quite different from those for chromium plating, dip chromating and anodic chromating. A coating formed in chromium plating is a simple metallic chromium and the one formed in dip chromating is mainly a chromium chromate and in some cases is a mixture of a chromate and an oxide of metal to be coated, while the one formed in anodic chromating is a mixture of a chromate and an oxide of metal to be coated.
In the cathodic chromating process various addition agents such as boric acid, phosphoric acid, sulfuric acid, disulfonic acid, nitric acid, acetic acid, or their respective salts and halogen compounds are added to the electrolyte which mainly contains hexavalent chromium ion derived from chromic acid, chromates or dichromates as described in US. Pats. Nos. 2,733,199, 2,780,592, 2,769,774, 2,998,- 361, 3,032,487, 3,257,295, 3,288,691 and 3,296,100.
Of these addition agents, disulfonic acid, sulfuric acid or their respective salts which gives sulfate anion is most observed in strongly acidic anions :such as nitrate, chlorate, perchlorate, and halogen anions in cathodic chromating In order to remove the anion adsorbed in the hydrated chromium oxide film and to improve the properties of the film, an immersion or a cathodic treatment, immediately after the previous cathodic treatment and before the surface of the metal is allowed to dry, in an aqueous solu tion containing at least one alkaline salt selected from the group consisting of ammonium hydroxide, alkali metal hydroxides, alkali earth metal hydroxides and alkaline salts of weak acids before drying the film formed in cathodic chromating is most efiective.
- An alkaline salt used in the present invention is selected from the following salts.
(l) Ammonium hydroxide. (2) Alkali metal hydroxides: LiOH, NaOl-I, KOH, RbOH, CsOH.
(3) Alkali earth metal hydroxides: Ba(0H) -8-H O, Sr( OH 2 8'H O. (4) Alkaline salts of weak acids: Acetates, CH COOLi-2H O, CH C0ONa-3H O,
CH COOK, CH3CO0NH4 Borates, Li B O7'5H2O, -Na2B407 101 120, K B O -5H 0,
NH4'HB407 Carbonates and bicarbonates, Li CO Na CO l0H O, I K CO -3/2'H O, Rbzcog, CS2CO3, (NH4)2CO3'H20,
. NaKCO -6H O, NaI-ICO KHCO NH HCO Chromates and dichromates, Li CrOl -2H O,
HCOONH;
The conditions required for performing the process described in the present invention will be summarized as follows:
(1) Concentration of alkaline salts-l-lOO g./ liter (2) Treating temperature3070 C.
(3) Treating time (in the case of immersion)130 secends (4) Treating time (in the case of cathodic treatment)- not more than 2 seconds (5) Treating current density (only in the case of cathodic treatment)-0-10 a./sq. dm.
The optimum concentration of alkaline salts is within the range from 1 g./liter to 100 g./liter. Within this range, one or more than one alkaline salts can be added. Generally an increase in concentration results in a higher removal efficiency of adsorbed anion. However, when the concentration of alkaline salts exceeds 100 g./liter, dissolution of the film formed in cathodic chromating begins to occur. When the concentration is less than 1 g./liter, the process needs a longer-period to remove adsorbed anion, which is impractical in high speed commercial operation.
Of the conditions, an increase in temperature results in a higher removal efficiency of adsorbed anion. At higher temperatures, however, the evaporation loss of water increases rapidly. Accordingly, operation should preferably be controlled at a temperature below 70 C. On the other hand, a decrease in temperature results in a lower removal efficiency of adsorbed anion. When the temperature is below 30 C., the process requires a longer period. Therefore, it is preferable to conduct the operation within the temperature range between 30 C. and 70 C.
In an immersion treatment, an increase in immersion time results in a higher removal efiiciency of adsorbed anion, but with a concentration of l-100 g./liter of salt and at a temperature of 30-70 C., the immersion time of 1-30 seconds is sufficient. When the period exceeds 30 seconds, dissolution of the formed film is initiated.
In the high speed operation which requires continuous and short-time treatment, the period of, e.g., seconds, is often not practical. When the treating period of not more than 2 seconds are required, a cathodic treatment is necessary in the alkaline solution mentioned above because the immersion treatment is less effective. In this case, the current density should be controlled to within 10 a./ sq. dm. If the current density exceeds 10 a./ sq. dm., the formed film will be partially dissolved and the corrosion resistance of the film will not be improved.
An immersion treatment in hot water of 80-90 C. is also effective to remove adsorbed anion but this takes as long as 2 minutes which is not practical in high speed commercial operation.
When the film formed in cathodic chromating is dry, an immersion treatment in an alkaline solution is less effective for the removal of adsorbed anion, but in such case, the dried film behaves as a hard barrier against the action of an alkaline solution. Under ordinary conditions, i.e., in concentrations of alkaline salt, in the period of immersion, in current density, temperature, etc., as heretofore disclosed, the action of the alkaline solution is delayed. Therefore in such a very short-period operation as in the commercial production, a cathodic treatment in a concentration of more than 100 g./liter of alkaline salts and at a temperature of more than 70 C. is necessary to obtain the effective action of alkali.
On the other hand in the wetted film before drying, the action of alkali is always effective in lower concentrations at lower temperatures even in high speed operation as described above. Therefore, the alkali treatment must be immediately performed before allowing the film formed in cathodic chromating to be dried.
After cathodic chromating, iron and steel treated according to the present invention can withstand outdoor exposure tests for 2 months in winter and for 15 days in summer and resist salt spray tests for 48 hours without any sign of rust. They further resist humidity chamber tests under the condition of relative humidity of 90%, at 40 C., for one week without any sign of discoloration of the film.
After applying a film of about 10 microns of modified alkyd or modified epoxy lacquer on steel sheet treated according to the present invention, the lacquered sheet was deeply drawn to the cup with a drawing ratio of 2.2 and stretch formed in the cup wall. The lacquer adhesion on the stretched part of the cup side quite withstood even the adhesive tape test. Furthermore, no adhesion loss of the lacquer was found on the cup wall, even when tested with adhesive tape after the cup was immersed in a boiling 3% sodium chloride solution for one hour.
Metals having the following surface are suitable for treatment according to the present invention; iron, steel, aluminum, zinc, tin, nickel, chromium, their respective alloys.
The examples of the present invention are as follows:
EXAMPLE 1 A 0.25 mm. cold rolled low carbon steel sheet, socalled black plate, is cathodically cleaned for 20 seconds at a current density of 4 a./sq. dm. at C. in a 7% sodium hydroxide solution, then rinsed with water, pickled for 10 seconds at room temperature in a 7% sulfuric acid, again rinsed with water, and immediately treated cathodically using a lead antimony alloy anode under the following condition in an electrolyte of the following composition, again immediately rinsed with water, then immediately dipped in the treating solution of the present invention indicated below, and again immediately rinsed with water, and dried.
1) The electrolyte and the condition of cathodic chromating:
Chromic acid-50 g./ liter Ethyl alcohol--0.2 g./liter Sulfuric acid-0.2 g./1iter Hydrofiuosilicic acid0.3 g./liter Temperature-50 C.
Current density-20 a./ sq. dm. Time-10 seconds (2) The treating condition of the present invention:
Sodium carbonate-100 g./liter Temperature55 C. Dipping time-2 seconds A transparent, bluish purple film was formed. Steel sheet thus treated showed very little rusty spots when subjected to a salt spray test with a 5% sodium chloride solution for 48 hours at 35 C. It also showed no rusty spot and no discoloration when subjected to a humidity chamber test with a relative humidity of for one week at 40 C.
EXAMPLE 2 A 0.5 mm. cold rolled low carbon steel sheet was subjected to the same pretreatment and the same cathodic chromating as described in Example 1, immediately rinsed with Water, then immediately dipped in the treating solution of the present invention under the following condition and again immediately rinsed with Water, and dried.
Ammonia water (28% )30 g./liter Temperature40 C. Dipping time10 seconds A transparent, bluish purple film Was formed. Steel sheet thus treated showed no rusty spot when subjected to the same salt spray test as in Example 1 for 24 hours. Furthermore, when the steel sheet thus treated was coated with about 10 microns of modified alkyd' white enamel and EXAMPLE 3 r The same kindjpf cold rolled low carbon steel sheet Was subjected to the same pretreatment as described in Example 1, immediately treated cathodically using a lead antimony alloy anode under the following condition in an electrolyte of the following composition, immediately rinsed with water, then' immediately dipped in the treating solution of ,the present inventionunder the following condition and again immediately rinsed water, and 'dried."
1) The electrolyte and the condition of cathodic cromating:
Chromic-aeid-SO g./ liter Ethyl alcohol-+0.25 g./ liter Sulfuricaeid- -QSO. g./ liter 1 1 Temperature-50 C. Current density-20 a./ sq. dm. Time-20 seconds .i:
(2) The treating condition bf the present invention: Ammonium carbonate--'-1' g'.7liter Temperature'-50;C M Dip ingtime -ZJOsecondsi' I, H U A transparent, bluish yellowfi-lm was formed. Steel sheet thus-treated had-the similar corrosion resistance to those in Example 1 and-the similar lacquer adhesion property to thosein Example. 2. i 1 i "EX A M PIIE 4 The same kind of cold rolled carbon steel sheet was subjected to the same pretreatmentas described in Example 1, treated inthe same cathodic chromating as described in Example3,- immediately rinsed with water, then immediately treated cathodically in the treating solution of the present invention under the following condition and again immediately rinsed with water, and dried.
Trisodium phosphate70 g./ liter Temperature60 C.
Current density-40 a./ sq. dm. Treating time-1 second A bluish yellow, transparent film was formed. Steel sheet thus treated was found to have almost no rusty spots when subjected to the same salt spray test as in Example 1 for 48 hours and had the similar lacquer adhesion property to those in Example 2, and when the deeply drawn cup of the lacquered sheet was immersed in a boiling 3% sodium chloride solution for one hour, the adhesive tape test failed to peel oif the lacquer film.
EXAMPLE 5 The same kind of cold rolled low carbon steel sheet was subjected to the same pretreatment as described in Example 1, and then immediately treated cathodically using a lead antimony alloy anode under the following condition in an electrolyte of the following composition, again immediately rinsed with water, then immediately dipped in the treating solution of the present invention under the following condition and again immediately rinsed with water, and dried.
1) The electrolyte and the condition of cathodic chromating:
Chromic acid-60 g./liter Phenol-2.4-disulfonic acid-0.6 g./ liter Temperature-50" C.
Current density20 a./ sq. dm. Time-30 seconds 6 (2) The treating condition of the present invention:
Potassium carbonate-50 g./ liter Potassium dichromate--10 g./liter Temperature-70 C.
Dipping time-2 seconds A blue, transparent film was formed. Steel sheet thus treated showed a few rusty spotswhen subjected to the outdoor exposure test during 2 months. Furthermore, when the steel sheet treated was coated with about 10 microns of melamine modified alkyd enamel and subjected to the same salt spray test as in Example 1 for hours, no blister of the enamel was found.
EXAMPLE 6 The same kind of cold rolled low carbon steel sheet was subjected to the same pretreatment as described in Example 1, immediately treated in the same cathodic chromating as described in Example 5, immediately rinsed with water then immediately dipped in the treating solution of the present invention under the following condition and again immediately rinsed with water, and dried.
Lithium carbonate-30 g./ liter Temperature-60" C. Dipping time-5 seconds A blue, transparent film was formed. Steel sheet thus treated showed no rusty spot after being subjected to a humidity chamber test as in Example 1. This steel sheet was coated with about 10 microns of modified alkyd white enamel and deeply drawn to the cup with drawing ratio of 2.2, no adhesion loss of the enamel was foun on the cup side. v
EXAMPLE 7 The same kind of cold rolled low carbon steel sheet was subjected to the same pretreatment and the same cathodic chromating as described in Example 1-, then immediatelyrinsed, with water, immediately dipped. in the treating solution of the present invention under the following condition and again immediately rinsed with water, and dried.
Barium hydroxide-20 g./liter Temperature70 C. Dipping time5 seconds A bluish purple film was formed. Steel sheet thus treated had the similar properties to those in Example 1.
EXAMPLE 8 The same kind of cold rolled low carbon steel sheet was subjected to the same pretreatment as described in Example 1, immediately treated cathodically using a lead antimony alloy anode under the following condition in an electrolyte of the following composition, again immediately rinsed with water, then immediately dipped in the treatment solution of the present invention under the following condition and immediately rinsed with water, and dried.
1) The electrolyte and the condition of cathodic chromating:
Sodium dichromate-SOO g./ liter Chromium sulfate-10 g./liter Ammonium sulfate-20 g./ liter Temperature50 C.
Current density-25 a./sq. dm. Time8 seconds (2) The treating condition of the present invention:
Ammonia water (28% )--40 g./ liter Temperature-601 C. Dipping time-10 seconds A blue, transparent films was formed. Steel sheet thus 7 treated had the similar corrosion resistance to' those in Example 1.
EXAMPLE 9 A 0.5 mm. aluminum sheet (99.0%) was cleaned for 10 seconds at room temperature in 4% sodium dicarbonate solution, rinsed with water, immediately treated cathodically using a lead antimony alloy anode under the following condition in an alectrolyte of the following composition, again immediately rinsed with water, then immediately dipped in the treating solution of the present invention and again immediately rinsed with water, and dried.
(1) The electrolyte and the condition of cathodic chromating:
Chromic acid50 g./1iter Ethyl alcohol0.15 g./ liter Sulfuric acid0.20 g./liter Ammonium fiuosi1icate1.0 g./liter Temperature-40 C.
Current density-12.5 a./sq. dm. Time20 seconds (2) The treating condition of the present invention:
Ammonium carbonate-30 g./liter Temperature55 C. Dipping time-10 seconds A grayish white film was formed. Aluminum sheet thus treated did not change when subjected to a salt spray test as in Example 1 for 120 hours.
What we claim is:
' 1. A process for treating metal which comprises cathodically chromating said metal in the presence of sulfate ions, rinsing the chromated metal with water before being allowed to dry, removing entrapped sulfate ions by immersion in a aqueous solution containing a total of from 1 to 100 grams per liter of at least one water-soluble alkaline compound selected from the group consisting of ammonium hydroxide, alkali metal hydroxides, alkaline earth metal hydroxides, and alkali metaland ammonium acetates, borates, carbonates, bicarbonates, chromates, dichromates, formates, oxalates, phosphates, pyrophosphates, hypophosphates, phosphites, hypophosphites and silicates applying a cathodic current to the catholically chromated surface wh le immersed in said aqueous solution, removing from bath, rinsing with water, and thereafter drying.
. 2. A process according to claim 1 wherein the chromated metal is immersed for from 1 to 30 seconds.
3. A process according to claim 1 wherein the cathodic treatment is conducted for not more than 2 seconds.
4. A process according to claim 1 wherein the temperature of the aqueous solution is from 30 to C. 5. A process according to claim 1 wherein the current density for cathodically treating the metal is not more than 10 amperes per square decimeter.
6. A process according to claim 1 wherein the metal to be treated has a surface selected from the group consisting of iron, steel, aluminum, zinc, tin, nickel, chromium and alloys thereof.
References Cited UNITED STATES PATENTS W. B. VANSISE, Assistant Examiner U.S. Cl. X.R. 2014-5 6
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US3904491A (en) * | 1973-10-12 | 1975-09-09 | Nat Steel Corp | Controlling electrolyte concentration in electrolytic and rinsing treatment of chrome plated steel strip |
US4082620A (en) * | 1977-04-29 | 1978-04-04 | Bell Telephone Laboratories, Incorporated | Process for chromating metallic surfaces |
EP0052056A1 (en) * | 1980-11-06 | 1982-05-19 | Nippon Steel Corporation | Method for producing a selective absorption sheet of solar radiation and the product |
US4522892A (en) * | 1982-04-17 | 1985-06-11 | Nippon Steel Corporation | Method for producing a steel strip having an excellent phosphate-coating property |
US5275891A (en) * | 1990-10-04 | 1994-01-04 | Hitachi Metals, Ltd. | R-TM-B permanent magnet member having improved corrosion resistance and method of producing same |
US20040175582A1 (en) * | 2002-12-05 | 2004-09-09 | Olin Corporation, A Corporation Of The Commonwealth Of Virginia | Laser ablation resistant copper foil |
US20040180225A1 (en) * | 2002-12-05 | 2004-09-16 | Brenneman William L. | Peel strength enhancement of copper laminates |
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US20040175582A1 (en) * | 2002-12-05 | 2004-09-09 | Olin Corporation, A Corporation Of The Commonwealth Of Virginia | Laser ablation resistant copper foil |
US20040180225A1 (en) * | 2002-12-05 | 2004-09-16 | Brenneman William L. | Peel strength enhancement of copper laminates |
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