While adhesives have revolutionised the way in which substrates are bonded together, there are applications where the surface area of the substrate makes bonding problematic. With plasma, the surfaces can be treated and adhesion can take place. Previously problematic materials such as Teflon can now be bonded effectively.

Traditional methods of increasing bonding include cleaning, chemically modifying a surface, and increasing the surface area by using a primer or roughening the surface.

What is plasma?

Plasma is state whereby a gas becomes ionised into a plasma when sufficient energy is added. The ions, electrons and radicals can change the surface area of the material without affecting its properties, eradicating the need for using other decontamination processes for adhesion promotion. It can also be used to provide thin coatings on surfaces through a process called plasma-enhanced chemical vapour deposition (PECVD). When using plasma to promote adhesion, the bond strength can be increased by up to 50 times.

Plasma is used to increase the surface free energy of a material, which is the intermolecular forces on the surface of a material that affect the attraction or repulsion exerted when in contact with another material. With a high energy surface area, materials tend to attract, which makes the application of adhesives easier. Where low surface energy exists in materials such as silicone, plasma is used. There are physical and chemical plasmas available depending on the surface of the substrate.

Image Credit

Applications

Plasma can be used in a variety of applications, including metal bonding adhesives such as www.ct1ltd.com. They can be used for inks, coatings, and for silicone in the manufacturing of PCBs where moisture ingress due to poor adhesion is a common complaint.

A well-known application for plasma is in the adhesion of Teflon for items such as non-stick saucepans. Harsh chemicals were traditionally used in the adhesion process, with mixed results. With the use of plasma, adhesion has improved drastically, which has opened up the possibility of the material being used in other applications.

Plasma also negates the need for using toxic or caustic primers when bonding problematic polymers. PECVD can be used to deposit a film on the substrate instead, which is better for the environment and removes any risk to human health.