Q. We have a problem achieving good pre-press tack with our urea-formaldehyde adhesive for plywood manufacturing. Are there any special techniques or additives you might suggest to overcome this problem?
A. There are several areas that should be considered when attempting to maximize pre-press tack in hardwood plywood operations. Stand time, pre-press time, spread levels, water content in mix, additives, and resin choice are all areas which should be examined.
Allow a minimum stand time of 15 to 20 minutes prior to pre-pressing. This will allow time for the moisture to dissipate. Be sure to avoid dryout of the gluline during this process. By minimizing the water in the adhesive mix you can also help to develop tack. Spread should be minimized but be careful not to reduce it to the point that dry-out is risked. Pre-press should be about 15 to 30 minutes.
There are tackifiers available that can aid in the process. Adding wheat gluten at a level of about 5% to start will lend tack to the mix as will the addition of PVA at approximately 10%. (Percentages are based on the weight of the resin). If using a wheat flour it's a good idea to use a high grade flour such as Robertson's Glu X. They can be reached at firstname.lastname@example.org or 812-358-2758.
Finally, if the above suggestions don't work, it might be a good idea to investigate the availability of a tackier pre-press resin. There are a number of Urea Resins available.
Jeff Pitcher is Marketing Director for Custom-Pak Adhesives in Newark, Ohio.