Introduction to Surface Treatment of Metal

In order for the ink or coat to bond with the surface in an effective manner, an adhesive should be able to fully wet the surface of every substrate that’s about to be joined together. This would mean that strong striking interactions should be formed connecting together the substrates and the adhesives. And for meeting these conditions, the substrate surface has to be chemically receptive, clean, and convincingly smooth to the preferred adhesive.

Surface treatment helps greatly in determining the life of a bond or how long should it last. If you’ve selected an adhesive that can easily endure active duty conditions that the bond will be introduced to, then the service and life outlook of that bond will directly depend on the level of applied surface treatment. The steps of bonding are further increased, along with additional costs, with the introduction of this treatment.

surface treatment prior to coating
surface treatment prior to coating

By ensuring that the adhesive can completely wet the substrate’s actual surface, surface treatment upholds adhesion instead of wetting the apparent surface. There are many cases where a surface is in actual a layer of dirt, grease, oil or several other contaminants. Consequently, the method applied for treating such surfaces will rely upon the kind of impurity and the outlook of the material to be adhered.

Following surface treatment, the adhesive is applied without any delay. But, if this is not achievable, then the surface should remain protected after treatment with the help of Kraft paper or something alike. Also, do refrain from placing any fingerprints on the surface that’s freshly prepared. There may be a need to redo the entire surface treatment process if a substrate is not applied with an adhesive and stored for more than a day. Shelf life of the surface treatment depends on the material. Materials like teflon will have short shelf lives – minutes/hours whereas Polystyrene will be measured in years.

What is Plasma Treatment and Corona Surface Treatment?

It is often necessary to bond plastic materials to metals or other plastic materials, or simply to print on a plastic surface. To do this successfully, the liquid adhesive, or ink, should be able to wet the surface of the material. Wettability depends on one specific property of the surface: surface energy, also often referred to as surface tension. The poor wettability of polymers presents the designer with the problem of bonding or decorating these materials. Surface treatment
can improve the wettability of the material by raising its surface energy, positively affecting adhesive characteristics by creating bonding sites. The most advanced and successful surface treatment methods are based on the principle of high-voltage discharge in air – Plasma or Corona treatment.

Further readings:

Wikipedia article on Plasma Discharge

Thorough technical article about how Corona Treatment and Surface Treatment works – by leading industry company

If you speak German, you can read the following articles on surface treatment:

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