April 2006

QUESTION

Can you recommend an adhesive for bonding a clear polystyrene part to glass for a consumer product? The adhesive needs some good shear strength (700-1200 psi), and it must be clear, quick to cure, and easily used by relatively non-skilled operators. The final product will be used indoors and might suffer occasional impacts.

ANSWER

Many adhesives will probably do the job, but the easiest to start with might be a clear 5-minute epoxy dispensed from a twin-syringe and fitted with a static mixer. This type of adhesive will require minimum clamping before the parts can be handled, and will cure completely in 24 hours at room temperature. The curing can be accelerated if desired with mild heating in an oven or by using a heat lamp. If you need something that cures even faster, versions are available that fixture in 30 seconds, but you will need to keep dispensing the adhesive quickly to avoid it setting up in the static mixer. This type of system can be easily automated in the future if your production requirements increase considerably. Keeping in mind the fact that you need some impact resistance, you will have to choose a product that has been plasticized or rubber-toughened.

QUESTION

We want to bond sheets of polystyrene foam to steel and to wood. What adhesives would you recommend that will be effective and safe to use?

ANSWER

This is an application that was traditionally done with contact cements or other solvent-based adhesives. However, because of health and flammability concerns, the modern trend is to use 100% reactive systems. I would suggest using a reactive hot-melt urethane. These adhesives are used routinely for this type of application (e.g., in the manufacture of insulated garage doors or in the construction of panels for recreational vehicles), and they can be applied as beads, sprayed or roll-coated. However, application equipment tends to be rather expensive for automatic assembly.