Plasma activation

Plasma activation (or Plasma functionalization) is a method of surface modification employing plasma processing, which improves surface adhesion properties of many materials including metals, glass, ceramics, a broad range of polymers and textiles and even natural materials such as wood and seeds. It is widely used in industrial processes to prepare surfaces for bonding, gluing, coating and painting. Plasma processing achieves this effect through a combination of reduction of metal oxides, ultra-fine surface cleaning from organic contaminants, modification of the surface topography and deposition of functional chemical groups. Importantly, the plasma activation can be performed at the atmospheric pressure using air or typical industrial gases including hydrogen, nitrogen and oxygen. Thus, the surface functionalization is achieved without expensive vacuum equipment or wet chemistry, which positively affects its costs, safety and environmental impact. Fast processing speeds further facilitate numerous industrial applications.

Quality of adhesive bonding such as gluing, painting, varnishing and coating depends strongly on the ability of the adhesive to efficiency cover (wet) the substrate area. This happens when the surface energy of the substrate is greater than the surface energy of the adhesive. However, high strength adhesives have high surface energy. Thus, their application is problematic for low surface energy materials such as polymers. To solve this problem, surface treatment is used as a preparation step before adhesive bonding. It cleans the surface from the organic contaminants, removes a weak boundary layer, chemically bonds to the substrate a strong layer with high surface energy and chemical affinity to the adhesive, and modifies the surface topography enabling capillary action by the adhesive. Importantly, surface preparation provides a reproducible surface allowing consistent bonding results.

Many industries employ surface preparation methods including wet chemistry, exposure to UV light, flame treatment and various types of plasma activation. Advantage of the plasma activation lies in its ability to achieve all necessary activation objectives in one-step without the use of chemicals. Thus, plasma activation is simple, versatile and environmentally friendly.

Many types of plasmas can be used for surface activation. However, due to economic reasons, atmospheric pressure plasmas found most applications. They include arc discharge, corona discharge, dielectric barrier discharge and its variation piezoelectric direct discharge.

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