Challenges of adhesive bonding to advanced engineering materials
Advanced engineering plastics and elastomers have many benefits: they can be strong, tough and effective over a wide range of temperatures. While they may have excellent bulk properties and low cost they are often difficult to join. Mechanical bolting, clamping and welding can be expensive and create stress concentrations. And the materials tend to have extremely poor surface properties with low surface energies that lack reactive polar groups so adhesive bonding is ineffective. Moreover, although technically clean, their surfaces are contaminated with recycled materials, flow agents, plasticizers and release agents. Adhesive bonding is better than mechanical bolting and welding - but it is tricky.

For effective bonding, the surfaces need to be cleaned using solvents, and the adhesives themselves are often formulated with volatile organic compounds (VOC), chemicals that are toxic and environmentally hostile. Some adhesive manufacturers have developed "do it all" adhesives that provide a one step process for structural bonding and can be used without surface preparation. But they can be cumbersome to use, with a short work life, and costly.

There is an alternative. The surfaces can be treated with Openair^® plasma and then a solvent-free adhesive or coating employed.

As an example, many next generation automotive vehicle components are made of polypropylene (PP) or other polyolefins with added glass fibers or talc, giving lightweight components that can be produced on fully automated lines. Several world leading automotive manufacturers and suppliers are using Openair^® plasma systems to achieve strong, reliable bonding so these components can be easily integrated into vehicle assemblies. The use of Openair^® plasma is helping them increase their market share and profitability.

Leading automotive manufacturers and suppliers are using Openair® plasma to gain a significant competitive edge.

The combination of substrate, plasma and adhesive
provide the solution
Polymer surfaces can be activated by Openair^® Plasma, where even hard to bond plastics like polypropylene (PP) or partially fluorinated compounds show clear improvements in adhesion, in some cases by 30 to 50 fold. This occurs because the molecular chains on the surface are oxidized, typically increasing oxygen content to between 20 and 35%. Because the activation occurs on the surface, the adhesive needs to be formulated without aggressive solvents so the oxygen groups are not etched away.

An example is the bonding of liquid crystal polymer (LCP) and poly ether ether ketone (PEEK). In one case involving PEEK, the customer could achieve a bond strength of 3MPa in a lap shear test with unmodified surfaces. When the same adhesive was used, pre-treatment with Openair^® plasma resulted in only a 20% increase in shear strength. But with an adhesive reformulated to leverage the functionalization of plasma, the strength increased by a factor of 12, and more than 3 times better than had ever been achieved before using mechanical surface preparation.

Headlight manufacturing is demanding: they have to be light, strong, relatively inexpensive and resist moisture penetration, and they use a combination of materials (lens and reflector) that accentuate defects, plus they need to last many years.

Epoxy paint and coatings with 2K-PUR are bonded to Transport superstructures quickly, efficiently and with long term strength by activating the surfaces with Openair® plasma. The treatment is achieved using four rotating jets in a fully automated process with 100% plasma monitoring for in-line quality control.

Airbag coverings of polyurethane (PUR) are glued into the polypropylene (PP) coverings using Openair® plasma to remove internal and external mold release agents.