Ask Dr. Dave
Question: Many of the adhesives I see in the construction industry are still solvent-based. I'm surprised that these haven't been replaced by water-based or 100%-solids systems. Why is this?
Answer: Although VOC regulations and flammability concerns have prompted a general trend toward using safer adhesives systems, there are many reasons why solvent adhesives are still important. There have been tremendous strides in the development of water-based latex adhesives over the last few years, but in many instances the solvent systems work better, particularly in bonding non-porous materials where it is difficult for the water to evaporate; in this case, solvent systems have a real advantage over water-based systems. Expect to see further improvements in the performance and speed of latex systems over the next few years as acrylic latex adhesives become more important, although there may be a cost penalty associated with this. 100%-solid reactive systems will also gain momentum and will include one and two-component polyurethanes. Unfortunately, higher costs and the need to package two components have inhibited the penetration of these adhesives, but the increase in productivity gained by using a fast two-component adhesive should be a real benefit, particularly with the introduction of some of the new two-component cartridges that can be used in a conventional caulking gun.
Question: We use a high-performance, two-component epoxy on small parts in a metal assembly operation, but it doesn't cure fast enough to let us handle the parts in a minute or two. What can you suggest to help us? We cannot change the adhesive because it meets customers' specifications.
Answer: Many two-component epoxies can be fixtured very rapidly by exposing them to high heat for a short time, either with a heat gun or through induction curing. Another technique that is used frequently is to tack the parts in place using a small fillet of UV adhesive or a hot melt, and then allowing the epoxy to cure at room temperature. This technique allows you to handle the parts within a few seconds.