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topic 6703

Environmentally friendly (non-chromate) surface treatment of aluminum for polyamide co-extrusion


This topic has properly been discussed before, but we are interested in non-chromating processes as surface treatment of aluminum before polyamide co-extrusion. The production is based on coil coating and the important parameters are (of course) to obtain a more environmental friendly process with the same or better adhesion and corrosion resistance. The combination of coil coating and co-extrusion of polyamide on aluminium is a little special and cannot be directly compared with painting.

A) We would like to know about companies, who have made a successful change to non-chromating process for a similar production situation.

B) We would like to know about today's best known alternative for a similar production situation.

C) We would like to know about relevant projects.

D) We would like to know about regulations, laws or other official directives on the field of hexavalent chromium in US and Europa.

Best regards,

Jean Bruland
- Denmark


Brass plating is employed on steel for the adhesion of rubber; it is necessary for good adhesion. So I would like to know, first, if the hexavalent chrome is needed for the adhesion of the polyamide. Your scientists may have already established the answer.

If it is not needed for adhesion, then the corrosion protection must established for the replacement technology.

But then you need the interaction component of corrosion and adhesion under field conditions.

tom pullizi signature
Tom Pullizzi
Falls Township, Pennsylvania


Yes you can anodize the aluminum as a pretreatment for polyester coating; but for other coatings, though untested, I believe it should also work.

Khalil Sawalha
aluminum - Amman Jordan


The hexavalent chromium improves both the adhesion and the corrosion resistance - so the alternative should have both properties. About the brass plating, can that be used in coil coating?

We have made some trials with both phosphoric and sulphuric anodization, but we did not obtain any good adhesion.

I have found two relevant on-going projects:

1)Joint Group on Pollution Prevention (JG-PP) project no.: J-00-OC-016 "Nonchromate Aluminium Pretreatments"

2)National Center for Manufacturing Sciences (NCMS) Project no.: 170604 "Recent Alternatives for Chromate Conversion Coatings"

Jean Bruland
- Denmark


Jean, Although the coating requirements for a metal substrate prior to a final polymer coating is a little out of my area of expertise, I can provide you with regulatory info regarding "hex Cr" in waste discharges.

Our waste water discharges are controlled at this facility by local and Federal regulation. As for local control the governing body is the, " Metropolitan Water Reclamation District of Greater Chicago, MWRD". This organization has control of all discharges to the sanitary sewer and controls the limits on the following items:

1. Cn, 5.0 mg/l
2. FOG, 250 mg/l
3. pH, 5-10
4. Cd, 2.0 mg/l
3. Tot. Cr, 25.0 mg/l
4. Hex. Cr, 10.0 mg/l
5. Cu, 3.0 mg/l
6. Fe, 250 mg/l
7. Ni, 10.0 mg/l
8. Pb, 0.5 mg/l
9. Zn, 15.0 mg/l
10. Hg, 0.001 mg/l

These are maximums, never to be exceeded. These are known as the toxic heavy metals group.

As for Federal requirements, these are covered under the Code of Federal Regulations, " 40CFR,467,SS .36 .37. Under these regulations for the Aluminum Forming Industry Category, discharges are mass based on pounds of production. Current max. discharge allowed for pollutants is as follows:

1. Cr, 0.0979 lb/day
2. Cn, 0.0528 lb/day
3. Zn, 0.2673 lb/day
4. FOG, 2.6147 lb/day

I hope this gives you some idea of how things are controlled here in the States. As for Denmark, I'm more than sure they have regulations in effect as well, and if not Denmark, then surely the E.U..


Neil E. Hatfield
- Franklin Park, Illinois USA


Neil, Thank you for the information about waste water regulations. It is very useful.

We are also interested in regulations concerning the amount of hexavalent chromium on the product. E.g. I think there are some regulations in the automotive industry like: 2 mg/car in year 2003, but I have not found the official papers.

Jean Bruland
- Denmark

Ed. note: the European Directive is on-line right here at


Thanks Ed.

Jean Bruland
- Denmark

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