Compositions: coating or plastic – Coating or plastic compositions – Metal-depositing composition or substrate-sensitizing...
Reexamination Certificate
2002-10-07
2004-09-14
Klemanski, Helene (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Metal-depositing composition or substrate-sensitizing...
C106S287180
Reexamination Certificate
active
06790265
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to aqueous alkaline zincate solutions and to a process for depositing a zincate coating on aluminum or aluminum alloy substrates. The invention also relates to metal plated aluminum or aluminum alloy substrates.
BACKGROUND OF THE INVENTION
One of the fastest growing worldwide markets is the processing and plating of aluminum and its alloys. Aluminum's unique physical and mechanical characteristics make it particularly attractive for industries such as automotive, electronics, telecommunications, avionics, along with a plethora of decorative applications. Among aluminum's most endearing properties include it's low overall density (2.7 g/cc), high mechanical strength achieved through alloying and heat treating, and its relatively high corrosion resistance. Additional properties include; high thermal and electrical conductance, its magnetic neutrality, high scrap value, and its amphoteric chemical nature. Most aluminum components are made from aluminum alloys with alloying elements including: silicon, magnesium, copper, etc. These alloying mixes are formed in order to achieve enhanced properties such as high-strength or ductility.
The plating of aluminum and its alloys require specific surface preparations for successful electrolytic and electroless deposition. The most common practice used in order to achieve successful electrodeposition is applying an immersion zinc coating (better known as zincate) to the substrate just prior to plating. This procedure has long been considered the most economical and practical method of pre-treating aluminum. The major benefits of applying a zincate layer for pretreatment are the relative low cost of equipment and chemistry, wider operating windows for processing, and ease of applying a controlled deposit.
The presence of other metals in the zincate solutions has an affect on the rate and efficacy of the zinc deposition. Small amounts of alloy components (i.e. Fe, Ni, Cu) improve not only the adhesion of the zincate deposit, but also increase the usability of the zincate on a variety of aluminum alloys. Hence, the addition of Fe ions improves the adhesion on magnesium containing alloys. The presence of nickel in the zincate improves the adhesion of nickel plated directly onto the zincate, and similar effects can be found with addition of copper in the zincate and subsequent copper plate. In general, however, the alloying of zincate has shown to provide thinner and more compact deposits which effectively translate into better adhesion of downstream electroless/electrolytic plating. On the other hand, the composition of an alloying zincate becomes more and more complicated with the additional metal ions in the composition. It makes selection of complexing agents more complicated and critical for the overall performance of the zincate. Zinc-iron-nickel compositions are more sensitive than zinc-iron compositions for the selection of complexing agents and ratio of metal ions in the composition. This becomes even more critical with the addition of the cooper ions in the alloy zincate. Due to its noble position in the galvanic series, the deposition rate of copper in the immersion zincate deposition is much higher than the other elements in the zincate. Therefore, control of the deposition rate of copper becomes important. It is possible to control the deposition rate of copper by the selection of the right complexing agent(s) for copper ions and adequate ratio with the other metal ions. There are few strong complexing agents for copper ions which offer good stability and performance of the alloying zincate, and cyanide appears to be the best candidate. Cyanide is a complexer of choice for the copper containing zincate compositions and it has been the industry standard for that application for many years. A negative aspect for the use of cyanide is the extremely toxic nature of cyanide, and therefore, like other metal finishing products, the search for a cyanide replacement in the alloying zincate has been a topic of interest for many years.
SUMMARY OF THE INVENTION
The present invention provides an improved aqueous alkaline zincate solution comprising hydroxide ions, zinc ions, nickel ions and/or cobalt ions, iron ions, copper ions, and at least one inhibitor containing one or more nitrogen atoms, sulfur atoms, or both nitrogen and sulfur atoms provided said nitrogen atoms are not present in an aliphatic amine or hydroxylamine. The present invention also relates to methods for depositing zincate coatings on aluminum and aluminum alloys comprising applying an immersion zincate coating on an aluminum or aluminum alloy substrate, optionally followed by plating the zincate coated aluminum or aluminum alloy substrate using an electroless or electrolytic metal plating solution.
DETAILED DESCRIPTION OF THE INVENTION
The present invention, in one embodiment, relates to aqueous alkaline zincate solutions, and more particularly to aqueous alkaline zincate solutions which are useful for depositing a zincate coating on aluminum and various aluminum based alloy substrates. Thus, in one embodiment, the aqueous alkaline zincate solutions of the invention comprise hydroxide ions, zinc ions, nickel and or cobalt ions, iron ions, copper ions, and at least one inhibitor containing one or more nitrogen atoms, sulfur atoms, or both nitrogen and sulfur atoms provided said nitrogen atoms are not present in an aliphatic amine or hydroxylamine. In another embodiment, the aqueous alkaline zincate solutions of the present invention are free of cyanide ions, and the zincate solutions may contain one or more metal complexing agents and nitrate ions.
The aqueous alkaline zincate solutions of the present invention may be prepared by dissolving water soluble salts of the desired metals in water. Thus, examples of the source of the zinc ions in the zincate solutions may be zinc oxide, zinc nitrate, zinc chloride, zinc sulfate, zinc acetate, etc.
Nickel ions can be introduced into the zincate solutions by dissolving nickel salts such as nickel chloride, nickel nitrate, nickel sulfate, etc. Cobalt ions may be introduced as cobalt chloride, cobalt nitrate, cobalt sulfate, etc. Salts of iron which are useful in introducing the iron ions include ferrous chloride, ferric chloride, ferrous sulfate, ferric sulfate, ferrous nitrate, ferric nitrate, etc. The copper ions may be introduced by dissolving salts such as cuprous chloride, cuprous nitrate, cupric nitrate, cupric chloride, cuprous sulfate, cupric sulfate, etc. in water.
In one embodiment, the zincate solutions contain nickel ions but no cobalt ions. In another embodiment the zincate solutions contain nickel ions and cobalt ions. In yet another embodiment the zincate solutions contain cobalt but no nickel ions. Because of economics, the zincate baths generally contain only nickel ions or a mixture of nickel with a small amount of cobalt.
The zincate solutions of the present invention also contain hydroxide ion introduced generally as an alkali metal hydroxide such as potassium hydroxide or sodium hydroxide.
In one embodiment, the aqueous alkaline zincate solutions of the present invention will comprise
from about 5 to about 300 g/l of hydroxide ions,
from about 1 to about 30 g/l of zinc ions,
from about 0.1 to about 5.0 g/l of iron ions,
from about 0.01 to about 10 g/l of copper ions, and
from about 0.05 to about 20 g/l of nickel and/or cobalt ions.
In another embodiment, the zincate solutions of the present invention may comprise
from about 5 to about 35 g/l or even up to 100 g/l of hydroxide ions,
from about 1 to about 15 g/l of zinc ions,
from about 1 to about 3 g/l of iron ions,
from about 0.01 to about 3 g/l of copper ions, and
from about 0.05 to about 10 g/l of nickel and/or cobalt ions.
In one embodiment, the concentration of zinc ions is greater than the combined concentration of iron ions, copper ions, and nickel and/or cobalt ions. The zincate solutions of the invention also generally contain nitrate ions introduced as soluble nitrate salts. Examples of useful sa
Joshi Nayan H.
Mehta Maulik D.
Atotech Deutschland GmbH
Klemanski Helene
Renner , Otto, Boisselle & Sklar, LLP
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