ADHESIVE SOLUTIONS FOR HARD-TO-BOND PLASTICS

Bonding low surface energy (LSE) plastics such as polypropylene or other thermoplastic olefins with conventional tapes and adhesives typically requires the surfaces to be primed, flame treated or corona treated. These processes convert the low surface energy of these materials to a higher surface energy better suited for most bonding.

As design engineers and production engineers increasingly shift to LSE plastics, they need better and more efficient ways of attaching LSE plastics to themselves, to metals or to other materials. New adhesives and tapes can bond low surface energy plastics without pretreatment, ultimately reducing costs and improving manufacturing efficiencies.

According to Barry Kostyk, Ph.D., 3M Bonding Systems Division key account manager, the most recent advance in adhesive technology allows structural bonding (in excess of 1000 psi in overlap shear) of LSE plastics without priming or other pretreatment step. 3M™ Scotch-Weld™ Structural Plastic Adhesive DP-8005 uses a unique two-part solvent-free acrylic adhesive technology that does not require pretreating. "The structural bond that results is often greater than the strength of the substrates joined," Kostyk said. And because Scotch-Weld Adhesive DP-8005 cures at room temperature, it saves cost, time, oven-curing space, UV lamps and heaters. It also resists many chemicals, water, humidity and corrosion.

Why are low surface energy plastics difficult to bond? Surface energy defines the ability of adhesives and pressure sensitive adhesive tapes to "wet out" plastic surfaces and allow adhesion. Kostyk explained that surface wet out refers to how well a liquid or viscoelastic solid flows and intimately covers a surface. "Maximum adhesion develops when the adhesive or viscoelastic pressure sensitive adhesive tape thoroughly wets out the surface to be bonded," Kostyk said. "The greater the wet out, the better the surface contact and the greater the attractive force between the adhesive and the plastic surface." Surfaces with low surface energy are more difficult to bond because conventional adhesives and tapes cannot wet them out resulting in minimal contact with the plastic surface and unsatisfactory bonds. Plastics with high surface energy like ABS and polycarbonate are easier to bond because they are easier to wet with conventional adhesives and tapes than are low surface energy plastics.

For more information, contact, 3M, 800-362-3550 ext. 5160, Web: www.3m.com/bonding.