Non-Phosphate Conversion Coatings: Simplifying the Process

In the process of metal finishing there are many steps to get to the point of a finished painted piece that is ready for the end-user. No matter who the customer is, anything less than zero defects in the finished product has become unacceptable. Whether it’s an automobile, an appliance, or a travel mug, a painted surface is expected to have excellent paint adhesion for its useful life, a uniformity in the paint coating, superior corrosion, wear and dent resistance, and an enhanced appearance of the paint finish.

A conversion coating is key to a quality paint finish – it actually transforms the surface of the base metal to a non-metallic crystalline surface. In using a chemical conversion coating, the base metal is involved in the chemical reaction and becomes a component of the protective layer. This coating is much less reactive to corrosion than the raw metal surface and it serves as an absorptive base for the subsequent paint layer. The nature of the conversion coating actually allows the paint to physically interlock with the

metal treatmentcoating, which results in the superior paint adhesion. Since the chemical conversion coating is formed from the surface of the metal substrate outward, how well the conversion coating does its job is dependent on having a clean and properly prepared metal surface. A manufactured metal part will have some sort of contaminants – oils, lubricants, metal filings, weld scale, finger prints, dirt, etc. There are several stages in the process of pretreatment and finishing depending on varying factors such as the type of metal, the specifics of the part to be finished and the paint process. However, a primary benefit of non-phosphate conversion coatings over phosphate conversion coatings is that the number of stages is significantly less – 3 to 5 compared to 5 to 7 or more.

Here is a comparison of typical sequences for phosphate and non-phosphate conversion coatings:

Phosphate Process:

1) Degrease

2) Rinse

3) Surface Activation

4) Phosphate Coating

5) Rinse

6) Seal

7) DI Rinse

8) Paint

Phosphate-Free Process:

1) Degrease

2) Rinse

3) Non-Phosphate coating

4) Paint

The non-phosphate pretreatment coats and seals in the same stage and does not require a post-rinse. Less stages means less maintenance costs. We know this example may not reflect your operation exactly, so let Lily Chemicals discuss your metal pretreatment process with you to determine how the use of advanced pretreatments could reduce the number of stages in your finishing sequence. Lily Chemicals has several products to offer in the non-phosphate category. The Paint Lok 700 series is a zirconium oxide coating for use in multi-stage spray washer and immersion systems for processing ferrous, aluminum, and galvanized metals prior to painting. Paint Lok 700-2X is a non-iron phosphated conversion coating for use in a three or five stage spray washer or immersion system to process ferrous, aluminum and galvanized metals. In some applications this product can be used to replace zinc phosphate products.

Our latest product advancement in this area is Lily Phos Seal GZ-50, especially designed for powder, liquid paints and E-coats. It delivers excellent corrosion resistance and can be applied by immersion or spraying on steel, zinc, stainless steel and aluminum surfaces. At Lily, our staff has the working knowledge to answer your questions and concerns about phosphate replacement pre-treatments and can work with you to identify solutions that are unique to your varied system and application needs. If you would like to improve your environmental impact while taking advantage of the application and performance benefits of non-phosphate metal pre-treatment, call us at 417.485.6271 or click here.

Leave a Reply

Your email address will not be published. Required fields are marked *