Effect of cold tack on the bond strength of UF resins in plywood production
: 43 - 48
Elfriede M. Hogger
Hendrikus W. G. van Herwijnen
The cold tack of urea-formaldehyde (UF) resins is an important property used in the production of plywood and veneer lumber to ensure that the veneers adhere to each other during the manufacturing process, thus ensuring transport and feeding into a multi-daylight press. Various factors that can affect cold tack, such as lay-up time, resin amount, resin age, veneer moisture content, veneer temperature and pre-press time, were systematically analyzed based on the tensile shear strength of uncured glue joints. Veneer temperature and moisture content showed the highest influence, but also lay-up time and pre-press time had an effect on cold tack. Models were created to calculate the best conditions for cold tack of UF resins. Based on these findings, the influence of cold tack on the behaviour of the cured bond was then investigated. Factors that significantly influence the cold tack did not show any effect on the tensile shear strength in the cured state.