Metal treatment – Process of modifying or maintaining internal physical... – Processes of coating utilizing a reactive composition which...
Reexamination Certificate
2000-11-20
2002-11-26
Green, Anthony J. (Department: 1755)
Metal treatment
Process of modifying or maintaining internal physical...
Processes of coating utilizing a reactive composition which...
C106S014120, C106S014210, C148S275000
Reexamination Certificate
active
06485580
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
The invention relates to a novel water-based liquid composition, often called a “bath” hereinafter for brevity, even though it may be used with other methods than immersion for establishing contact between the composition and the surface to be treated with it, and to processes using such compositions for treating the surfaces of light metals and light metal alloys for the purpose of imparting thereto an excellent corrosion resistance and an excellent adherence to paint films. This invention can be applied in a particularly advantageous manner to the surface treatment of aluminum fin stock for heat exchangers, aluminum alloy coil, aluminum alloy sheet, and magnesium and magnesium alloy automotive and aerospace components and electronic devices and instruments.
The baths used to treat aluminum and aluminum alloy surfaces can be broadly classified into chromate-type baths and non-chromate-type baths. Chromic acid chromate conversion baths and phosphoric acid chromate conversion baths are typical examples of the chromate-type treatment baths.
Chromic acid chromate conversion baths first reached practical application in about 1950 and even now are widely used for the surface treatment of aluminum (the word “aluminum” and all of its grammatical variations being understood hereinafter, unless the context indicates otherwise, to apply to alloys that contain at least, with increasing preference in the order given, 45, 60, 75, 85, 90, 95, or 99% by weight of aluminum) fin stock for heat exchangers and aluminum wheels, building materials, and aerospace materials. The main components in chromic acid chromate conversion baths are chromic acid and a fluoride-type reaction accelerator. This type of bath produces a conversion coating containing moderate amounts of hexavalent chromium on the metal surface.
Phosphoric acid chromate conversion baths originated with the invention disclosed in U.S. Pat. No. 2,438,877. The main components in phosphoric acid chromate conversion baths are chromic acid, phosphoric acid, and hydrofluoric acid. A conversion coating whose main component is hydrated chromium phosphate is formed by this type of bath on the metal surface. Since the resulting conversion coating does not contain hexavalent chromium, this type of bath is in wide used at the present time as an underpaint treatment for the body stock and lid stock of beverage cans.
While the conversion coatings generated by these chromate-type surface treatment baths exhibit an excellent corrosion resistance and an excellent adherence to paint films, these treatment baths also contain toxic hexavalent chromium. The associated environmental problems have made it desirable to use treatment baths that are completely free of hexavalent chromium.
The method disclosed in Japanese Patent Publication (Kokai or Unexamined) Number Sho 52-131937 (131,937/1977) exemplifies chromium-free surface treatment baths. Surface treatment baths of this type are acidic (pH=approximately 1.5 to 4.0) aqueous coating solutions that contain phosphate, fluoride, and zirconium or titanium or a mixture thereof. The treatment of metal surfaces with such a treatment bath results in the formation on the metal surface of a conversion coating whose main component is an oxide of zirconium or titanium. Non-chromate-type surface treatment baths offer the advantage of not containing hexavalent chromium and for this reason are widely used at present for treating aluminum D
1
can surfaces. Unfortunately, the coatings produced by non-chromate-type surface treatment baths are less corrosion resistant than chromate coatings.
The treatment method disclosed in Japanese Laid Open (Kokai or Unexamined) Patent Application Number Sho 57-41376 (41,376/1982) involves treating the surface of aluminum, magnesium, or an alloy thereof with an aqueous solution containing at least one selection from titanium salts and zirconium salts and at least one selection from imidazole derivatives.
The coatings produced in the working examples of Japanese Laid Open Patent Application Number Sho 57-41376 have an anticorrosion performance corresponding to no rusting at 48 hours according to Japanese Industrial Standard (hereinafter usually abbreviated as “JIS”) Z-2371. This performance, while satisfactory 15 years ago, is not unequivocally satisfactory at present. This patent application also describes the supplementary addition, at from 0.01 to 100 g/L as the compound, of an oxidizer such as nitric acid, hydrogen peroxide, or potassium permanganate, but does not provide a working example supporting the use of a potassium permanganate oxidizer.
Japanese Laid Open (Kokai or Unexamined) Patent Application Number Hei 8-144063 (144,063/1996) teaches a surface treatment method for the formation of conversion coatings on the surface of aluminum stock. This method uses an aqueous solution that contains potassium permanganate or potassium manganate or both in addition to a coating-forming accelerator such as a mineral acid (HNO
3
, H
2
SO
4
, HF), an alkali (KOH, NaOH, NH
4
OH), a neutral fluoride (KF, NaF), an acidic fluoride (NH
4
HF
2
, NaHF
2
, KHF
2
), or a fluorosilicate (MnSiF
6
, MgSiF
6
). However, the conversion coating formed by this treatment bath has not been found to have a corrosion resistance in long-term corrosion-resistance testing equal to or greater than that of chromate coatings.
Thus, as described above, the use of the aforementioned prior-art non-chromate-type surface treatment baths remains associated with problems with the corrosion resistance of the produced conversion coatings and pollution abatement of the effluent from the surface treatment bath. It is for these reasons that at present non-chromate-type surface treatment baths are little used on surface treatment lines where a particularly good corrosion resistance is required, for example, for aluminum fin stock for heat exchangers and aluminiferous metal coil and sheet stock.
In summary, then, there has yet to be established a bath, for treating aluminum and aluminum alloy surfaces, that does not contain hexavalent chromium, that requires little or no pollution abatement, and that has the ability to form highly corrosion-resistant, highly paint-adherent conversion coatings.
The surface treatment methods already mentioned above suffer from a number of practical and economic problems, such as (1) the use of high treatment bath concentrations, (2) the use of high treatment temperatures, and (3) the use of long treatment times, and improvements in each of these areas would be desirable.
Chromate treatments as typified by JIS H-8651 and U.S. Military Standard (“MIL”) M-3171 are in use for treating magnesium and magnesium alloy surfaces (the word “magnesium” and all of its grammatical variations being understood hereinafter, unless the context indicates otherwise, to apply to alloys that contain at least, with increasing preference in the order given, 45, 60, 75, 85, 90, 95, or 99% by weight of magnesium). The conversion coatings generated by these chromate-type surface treatment baths exhibit an excellent corrosion resistance and an excellent adherence to paint films, but these treatment baths also contain highly toxic hexavalent chromium. The associated environmental problems have made it desirable to use treatment baths that are entirely free of hexavalent chromium.
The method disclosed in Japanese Laid Open (Kokai or Unexamined) Patent Application Number Hei 3-6994 (6,994/1991) is an invention typical of the chromium-free non-chromate-type surface treatment baths for magnesium and its alloys. This is a phosphate surface treatment method, and while it does not employ hexavalent chromium, it also does not have the ability to generate high-level properties. More specifically, this treatment method requires the execution of a silicate treatment after the phosphate treatment and the execution of a silicone treatment after the silicate treatment. The phosphate treatment coating by itself provides a low level of corrosion resistance and paint adherence when used as an und
Kawaguchi Motoki
Maeda Kazuhiro
Nakada Kazuya
Harper Stephen D.
Henkel Corporation
LandOfFree
Composition and process for treating surfaces or light... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Composition and process for treating surfaces or light..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Composition and process for treating surfaces or light... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2993999