Enviromentally-Friendly Plasma-Enhanced Chemical Vapor Deposition (PECVD) Processes for Industrial Applications

Industrial emissions of hazardous air pollutants have attracted the attention of environmental protection agencies in most countries around the world. Efforts focus on the enforcement of tight regulations related to the operation of wet chemical stations, paint and coating applications, gaseous manufacturing, photolithography, and electronics packaging processes.<br/>Plasma-Enhanced Chemical Vapor Deposition (PECVD) has been the preferred method for the deposition of thin coatings of well-controlled properties for several decades. It is considered a dry chemistry method as the coatings produced by this technology do not require drying or curing. Also, as nanoscale materials are being produced, they require minimal volumes of precursor chemicals. The low energy requirements and minimal consumption of chemicals classify PECVD processes as environmental-friendly. Additionally, plasma-based processes are used as surface preparation methods for several different types of materials and can replace solvent cleaning which is typically used to improve the wettability and bonding to adhesives, paints, and various coatings.<br/> Depending on the treated material and the type of adhesives used, plasma surface activation or cleaning are not always sufficient to provide stable long-time adhesion, especially under various environmental conditions, where the variation of temperature and humidity can be detrimental. To overcome this challenge, recent research work has focused on the combination of specialized precursor chemistries and plasma reactive species to generate nanocoatings of tunable properties and functionality.<br/> In this work, the results from a study focusing on adhesion-promoting PECVD coatings on metal surfaces will be presented. Stainless steel and 6061 aluminum alloy substrates were treated with atmospheric-pressure plasma processes utilizing siloxane-based precursor chemistries for the development of nanocoatings. Following the plasma treatment, a polyurethane-based adhesive (Sikaforce-840) was applied on the metal coupons for lap shear testing. Results from the mechanical testing showed an increase of the adhesive strength of steel from 3 MPa to 12MPa, while the aluminum coupons exhibited a 10x increase compared to the untreated materials. Examples from the testing of various organosilicon coating chemistries on on a 2-part epoxy adhesive will also be presented. An overview of the fundamental plasma-surface interactions will be discussed to provide a better understanding of the adhesion mechanism.