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PPG launches green Zircobond pre-treatment
Friday, 26 June 2009 00:00

PPG’s new automotive pre-treatment technology has been tested by GM in Germany. Finishing has found out that the testing has gone so well it is now being used full time

PPG Industries has launched a new environmentally responsible automotive pretreatment technology in Europe at the General Motors production facility in Gliwice, Poland.  GM-Poland began processing vehicles with Zircobond pretreatment at the end of 2008 and moved to full-scale production in January 2009.  The commercial launch of Zircobond pretreatment is a significant step for PPG and global OEMs in support of environmentally responsible technologies.  Pittsburgh-based PPG is a global supplier of paints coatings, chemicals, optical products, specialty materials, glass and fibreglass.

Metal pretreatment cleans and provides corrosion protection to automotive body surfaces.  However, traditional zinc-phosphate pretreatment processes generate sludge containing heavy metals such as nickel, zinc and manganese, which are subject to environmental regulations.  As an alternative pretreatment based on zirconium chemistry and a proprietary blend of additives, Zircobond pretreatment shows a ‘green’ way into the future by keeping the process costs low.

For years, tri-cationic zinc phosphating has provided reliable corrosion protection and paint adhesion.  However, despite the constant improvements made to the process, some problems remain.  These include the use of heavy metals like nickel, an undesirable build-up of sludge in the bath during the zinc phosphate deposition process, zinc phosphate staining in pipes, stringent bath parameter control and the forming of toxic process reactants (nitrous gases).

New process and its benefits
The newly developed Zircobond process addresses environmental concerns and offers economic advantages while delivering the high performance that automotive manufacturers expect from their coatings providers.

Zircobond benefits
• Environmentally responsible technology
• Low energy demand
• Low capital investments and low operating costs

Zircobond pretreatment produces minimal toxic, regulated heavy metals and generates at least 80 percent less sludge byproduct compared to the standard zinc phosphate pretreatment process.  Zircobond pretreatment offers a “greener” alternative, replacing heavy metals used in tri-cationic phosphate, especially the nickel metal and its compounds.

The new Zircobond process can be used in existing pretreatment lines and, following a simple pH adjustment, is safe for the conventional waste treatment systems used in most automotive production facilities.  Zircobond pretreatment lines also require fewer boil-outs and stage cleanings.  Therefore, in addition to addressing the growing regulatory and environmental concerns surrounding pretreatment technologies, Zircobond pretreatment by PPG offers potential cost savings in maintenance, energy reduction, water usage and waste disposal.

 Zircobond pretreatment can also increase production efficiency and generate additional cost savings.  Specifically, the Zircobond chemistry allows for the use of reduced temperature baths (15-32°C), resulting in minimal agitation and fewer rinse cycles than the current processes.  As a result, using Zircobond pretreatment could generate substantial energy savings on the production line.  Estimates show that, depending on the manufacturing footprint, there is potential for annual savings of up to several hundred thousand dollars with the use of Zircobond pretreatment due to reductions in associated costs, such as energy, maintenance, and labor.

Potential savings are even greater in greenfield applications, where fewer process stages could generate up to several million dollars in savings on new facility capital investments.  With Zircobond pretreatment, PPG has created an environmentally responsible, ‘green’ solution that addresses regulatory concerns and is designed to deliver economic incentives.

Process sequence
The Zircobond process can easily be incorporated into existing pretreatment plants and requires less bath agitation and fewer rinse stages relative to the existing process.  Experience has shown that two or three rinse stages can be eliminated following the Zircobond pretreatment stage, depending on the design of the plant.  Bath agitation before the formation of the coating is not required.

One specific advantage of the Zircobond process, resulting from the special chemistry and the selection of proprietary additives, is that the process can be operated at a lower temperature or even at room temperature.  This leads to a reduction in heating costs, which is of particular benefit on production lines with large volume process tanks.  Reduced maintenance requirements also bring additional savings.  Zinc phosphating stages must be cleaned at regular intervals in order to prevent the pipes and the heating unit from becoming blocked.  With the Zircobond process, the stages need to be cleaned less frequently.

Performance testing
Today, vehicle bodies are made of a number of different substrates, such as soft deep drawing steels and ultra-high-strength steels.  In addition to steel, car bodies contain zinc, aluminum, magnesium, zinc-magnesium and other light metals.  This typical metal mix increases the need for an alternative pretreatment process.  The Zircobond pretreatment is based on inorganic zirconium salts, which protect any metallic surface by forming a nanoscale layer of zirconium oxide.  The high alkaline or acidic resistivity of the Zircobond coating provides excellent undercreep resistance in accelerated weathering tests.  The Zircobond process deposits comparably on aluminum, magnesium, steel and zinc substrates, making it an ideal treatment for modern multi metal processes.

The newly developed Zircobond pretreatment system meets OEM performance requirements for corrosion protection and adhesion, when combined with the electrodeposition coating.

Figure 6 shows the adhesion test results of Zircobond pretreatment on different substrates in comparison with zinc phosphate.  The adhesion of electrodeposition coatings on zinc phosphate decreases in the following order: ZE>St>Z>Al.  The adhesion on sheet metal coated using Zircobond pretreatment is significantly greater.  A number of tests using different electrodeposition coatings confirmed this high level of adhesion.