In his March 2009 column, Dr. Dave discusses moisture-cured polyurethane adhesives and the best way to apply adhesive to a polypropylene or polyester scrim without plugging pores.

Question:I’m looking for moisture-cured polyurethane adhesives for the bonding of polystyrene sheet to galvanized iron sheet in the manufacture of industrial panels for use in construction. I need good adhesion with a cure time of no more than three hours. Can you recommend some products that will serve this purpose?

Answer:I don’t think that a moisture-cured polyurethane is the best way to achieve your desired cure times. You need to look at a two-component structural polyurethane of the type used to assemble structural insulated panels. A modern alternative is to use a reactive urethane hot-melt adhesive that will give you virtually instant handling strength followed by a full cure over a period of 24 hours or so. These adhesives are used widely in applications such as assembling insulated garage doors or panel bonding in recreational vehicle assembly. The only negative to these hot melts is that application equipment is quite expensive.

Question:I’d like to be able to apply an adhesive to a polypropylene or polyester scrim without plugging the pores.  Do you have any suggestions on how to do that?

Answer:I suggest two possible methods of bonding this material. First, you could apply the adhesive while maintaining positive air pressure through the material. Another method would be to consider thermal bonding of the material by running it through a heated roller system where one roller is embossed to create pinpoint bonding, which is similar to the method used for the thermal bonding of non-woven fabrics.