High performance plastics, polymers, and composite materials are widely used in the production of high-tech or high-reliability products. These materials have properties that lend themselves well to the manufacture of products due to several factors; they are relatively inexpensive and easily molded or formed into complex shapes, and bulk physical properties may be selected from a wide range of parameters such as rigidity and temperature stability. Unfortunately, fabrication procedures that require bonding are difficult to achieve.
Bonding processes by any method and for any purpose permit the utilization of these engineered materials in combination with transformative design concepts. Appropriate surface preparation is the essential first step to provide consistent and reliable adhesive or cohesive bond strength.
Appropriate surface preparation is the essential first step to provide consistent and reliable adhesive or cohesive bond strength. Major bonding elements comprise substrate, adhesive, bondline surface area and (for adhesive joining) joint design. These factors must be optimized as needed for a particular bonding application to obtain maximum adhesion (or cohesion) between the bonding elements. Bonding factors relate to several functional aspects of the bonding interface or bond line and include the following:
- Maximizing mechanical interlocking: Increasing the surface roughness increases “lock and key” physical anchoring between the adhesive and surface. A microscopically rough surface increases the area of physical contact and enhances wettability through capillary flow.
- Matching cohesion energy: The degree of cohesion energy match of the adhesive with the surface should be optimized to create a highly wettable bonding interface. Establishment of such an interface decreases stress in the bondline because continuity exists between the various surfaces – substrate and adhesive.
- Increasing surface absorption and reactivity: Surfaces should have sites that are polar or contain reactive chemistries with which the adhesive reacts to form, for example, acid-base pairs. Examples of reactive sites include surfaces containing hydroxyl, carbonyl, carboxylic acid and other functional groups which serve as chemical anchors.
Conventional surface treatment options for joining substrates pose different constraints in terms cost of ownership, environmental compliance, and performance. CO2 Composite Spray™ and Centrifugal CO2™ processing technologies provide an effective, eco-friendly and robust platform for preparing many types of substrate surfaces for numerous medical, aerospace, automobile, ophthalmic and microelectronic bonding applications.