Plasma Cleaning and Surface Treatment to Improve Adhesive Bonding for Metal

Typical applications

• Remove oil, epoxy, and other contaminations on the surface
• Create hydrogen-bonded hydroxyl functional groups on the surface
• Increase surface energy and surface wettability
• Clean and activate aluminum, stainless steel, gold, and other metal surfaces before bonding to other metal or composite using adhesive

Related products

The strength of bonded joints is of great concern to the aerospace, automotive, medical device, and electronics industries. Bonding of metal to metal, composite materials, adhesive or thin coatings can be very challenging due to low surface energy, contamination, or incompatible chemistry. Plasma surface cleaning and treatment has been widely used to remove surface contaminations, mostly hydrocarbon type organic contamination, generate functional hydroxyl groups, and increases surface wettability. Oxygen and argon plasma surface treatment can significantly improve the bonding strength for adhesives on metal and composite materials. Lap shear strength can be increased severalfold over the traditional chemical cleaning or mechanical abrasion method.

Remove the organic surface contamination with oxygen plasma

Lubricant oils are widely used in the manufacturing process of metal components, such as aluminum, stainless steel, and gold. Even after the surface of the metal is cleaned, it only takes a couple of hours before the airborne contaminant such as nonanal to be adsorbed onto the surface again. If oxygen is used to generate plasma, rf energy can ionize the oxygen gas and cause the breakdown of oxygen molecules. Atomic oxygen is highly reactive. Oil and other organic contaminants can be easily removed with oxygen plasma treatment. The following images show the surface of the oil-contaminated metal surface before and after oxygen plasma treatment.

Increase surface energy and wettability, improve bonding strength

After argon, helium, or oxygen plasma treatment, the carbonaceous contamination will be removed, functional groups like carboxylic acids are added to the surface. These functional groups promote strong chemical bonding to the epoxy film adhesive. In the meantime, polar hydroxyl groups render the surface hydrophilic, which helps create intimate contact between the adhesive and the metal surface. If metal is to be bonded to composite materials, oxygen plasma treatment can also increase the surface roughness of the composite materials and further improve the bonding strength.