Process for priming aluminum materials and primers

Details Process for priming aluminum materials and primers Process for priming aluminum materials and primers

2000-02-24

2003-11-25

Reddick, Judy M. (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

At least one aryl ring which is part of a fused or bridged...

C524S429000, C524S437000, C524S492000, C524S493000

Reexamination Certificate

active

06653384

ABSTRACT:

FIELD OF THE INVENTION AND RELATED ART OF STATEMENT
This invention relates to priming to be performed as pretreatment before the application of coatings to the surface of articles made from aluminum or its alloys (hereinafter referred to as aluminum materials) and, more particularly, to a process for priming aluminum materials with excellent corrosion resistance and primers therefor.
Aluminum materials are generally characterized by lightweight, good processability, and excellent thermal conductivity and are consumed in a wide variety of applications, for example, in fins to be installed in the heat-exchanging unit of an air conditioner and in sashes and other construction materials. Depending upon where or for what purpose aluminum materials are used, various coatings are applied to the surface of the aluminum materials to provide such properties as hydrophilic, antibacterial, corrosion-resistant, scratch-resistant, antistatic, and lubricative or to improve the external appearance.
In application of the aforementioned coatings, priming is generally performed to protect the aluminum materials themselves against corrosion or promote the adhesion of the coating films to the surface of aluminum materials and, in particular, priming assumes importance in the cases where the application of coatings is intended for providing the aforementioned properties or improving the external appearance.
OBJECT AND SUMMARY OF THE INVENTION
The present inventors have conducted extensive studies on how to perform priming with excellent corrosion resistance, found that such priming can be performed by applying a primer containing the nitrate or related compound of a specific metal to the surface of an aluminum material so that the amount; of adhering metal becomes 1.0 mM/m
2
or more and then baking the primer, and completed this invention.
Accordingly, an object of this invention is to provide a process for priming the surface of an aluminum material with excellent corrosion resistance.
Another object of this invention is to provide primers suitable for priming the surface of an aluminum material with excellent corrosion resistance.
Thus, this invention relates to a process for priming an aluminum material which comprises applying a primer containing the nitrate or related compound of a metal selected from aluminum, zirconium, cerium, chromium, and iron to the surface of an aluminum material so that the amount of adhering metal becomes 1.0 mM/m
2
or more and then baking the primer.
Primers useful for the process of this invention for priming contain water-soluble acrylic acid-based polymers in the range of 3.5 to 22.5 g/l as solids concentration, the nitrate or related compound of a metal selected from aluminum, zirconium, cerium, chromium, and iron in the range of 30 to 500 g/l, a hydrofluoric acid-based compound in the range of 1.0 to 5.0 g/l as elemental fluorine, and an organic reducing agent in the range of 5 to 30 g/l.
Water-soluble acrylic acid-based polymers useful for the primers of this invention are water-soluble polymers to be obtained by polymerization or copolymerization of compounds such as acrylic acid, methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, methacrylic acid, methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, maleic acid, and itaconic acid and they may be used singly or as a mixture of two kinds or more. As these water-soluble acrylic acid-based polymers need to undergo chelation with the co-existing metal ions to become insoluble in water when baked at a relatively low temperature for a short time, their average molecular weight is preferably 10,000 to 300,000. Such water-soluble acrylic acid-based polymers are available as commercial products, for example, Acumer 2100 and Acumer 1510 (tradename of Rohm and Haas).
The nitrate or related compound of a metal useful for the primers of this invention is the nitrate or related compound of a metal selected from aluminum, zirconium, cerium, chromium, and iron, either of a single metal or of a mixture of two kinds or more of metals. Concrete examples of such metal nitrates and related compounds are aluminum nitrate [Al(NO
3
)
3
·9H
2
O, molecular weight 375], zirconium nitrate [Zr(NO
3
)
4
·5H
2
O, molecular weight 492], zirconium oxynitrate [ZrO(NO
3
)
2
·2H
2
O, molecular weight 267], cerium nitrate [Ce(NO
3
)
3
·6H
2
O, molecular weight 434], chromium nitrate [Cr(NO
3
)
3
·9H
2
O, molecular weight 400], and iron nitrate [Fe(NO
3
)
3
·9H
2
O, molecular weight 404].
Primers of this invention contain organic reducing agents and form films in which the organic-reducing agents coexist. In consequence, where chromium nitrate is used as metal nitrate, any hexavalent chromium ions that form and try to be set free are reduced to trivalent chromium ions and no environmental problem would arise as the release of hexavalent chromium ions is completely prevented. However, on account of a favorable impression created by chromium-free corrosion-resistant priming, it is desirable to use the nitrate or related compound of a metal selected from aluminum, zirconium, cerium, and iron. In particular, the nitrate or related compound of a metal selected from aluminum and zirconium forms primer films which are corrosion-resistant to varying degrees depending upon the amount of adhering metal and, in addition, colorless and transparent and its usage in the primers intended for clear coatings is preferable from the standpoint of accentuating the metallic appearance of aluminum.
Hydrofluoric acid-based compounds to be used in the primers of this invention include, for examples hydrofluoric acid and soluble hydrofluoric acid salts such as silicon fluoride, boron fluoride, titanium fluoride, zirconium fluoride, and zinc fluoride and they may be used singly or as a mixture of two kinds or more.
As for organic reducing agents, those which are soluble in water, do not decompose or evaporate during baking, and remain in the primer films to perform a reducing action are satisfactory; concrete examples are polyhydric alcohols and saccharides such as ethylene glycol, glycerol, erythritol, arabitol, mannitol, glucose, and fructose and they may be used singly or as a mixture of two kinds or more.
From the standpoint of improving the resistance to pitting corrosion of the material to be treated. it is allowable to add, if necessary, phosphoric acid-based compounds to the primers of this invention; for example, phosphoric acids such as orthophosphoric acid, pyrophosphoric acid, metaphosphoric acid, and phosphorous acid and, to the extent of 5 g/l or less, alkali phosphates such as sodium phosphate, sodium pyrophosphate, sodium polyphosphates, and sodium hexametaphosphate. Moreover, in order to promote the adhesion of primer film to coating for quality improvement or to raise the viscosity of the priming bath for ease of application and improvement of workability, it is allowable to add silica, preferably pulverized to particles with an average diameter of 1 &mgr;m or less, particularly to primary particles 50% or more of which is 1 &mgr;m or less in diameter.
The primers of this invention normally contain the aforementioned components at the following concentrations: water-soluble acrylic acid-based polymers in the range of 3.5 to 22.5 g/l, preferably 7 to 15 g/l, as solids concentration; nitrate or related compound of metal in the range of 30 to 500 g/l, preferably 50 to 150 g/l; hydrofluoric acid-based compound in the range of 1.0 to 5.0 g/l, preferably 2.0 to 3.0 g/l, as elemental fluorine; organic reducing agent in the range of 5 to 30 g/l, preferably 8 to 15 g/l; phosphoric acid-based compound to be added as needed in the range of 2.5 to 14.5 g/l, preferably 4 to 8 g/l, as PO
4
; and silica 0.1 or less, preferably 0.05 or less, in terms of the solid ratio [silica/(total solids)].
There is the possibility that water-soluble acrylic acid-based polymers with a solids concentration of less than

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