Pre-Press Technique for Plywood Manufacturing by Using Amino Resin (MF, MUF and UF)

Since loading of assembled lot into the press is an important operation. While smooth loading can ensure quality, a little disturbance may lead to a number of defects in the pressed plywood. Displacement of the face or core veneer in the assembled lot during loading may result in the formation of plywood of lower grade or rejected one, Manual hot pressing loading without elevator is laborious and time-consuming. So for simplicity, the loading of assembled material into the hot press by using autoloader for increase production efficiency pre-press technique is only one option along with manufacturing of quality plywood.

The primary purpose for the pre-press is to allow the wet adhesive to “tack” the veneer and easier to shift of veneer when loading. Prior to hot pressing, pressing of assembled veneer lot after discharged from gluing operation at room temperature to bring a temporary bonding in between glue core and panel core and easy to shifting is the basic function of pre-press technology for plywood manufacturing. During this stage the assembled panel is compressed near to its panel thickness and brings a bonding in between glue core and panel. Veneers are bonding together by gelling of adhesive due to loss of solvent without curing. High pre-press tacking should be in glue to make success for pre-press bonding. The prepress patterns the veneers and transforms the adhesive to uncounted sheets. The load is held under pressure to several minutes to develop consolidation of the veneers.

In Indian plywood industries high viscous phenol formaldehyde resin is used as a prepress adhesive for manufacturing of BWP grade plywood. However for manufacturing of MR & BWR Plywood by using amino resin (MF, MUF, UF) is not successful because of unsatisfactory grips in assembling. Hencethe study is
focused on new solution for production of high quality wood based panels by using pre-press technique by using amino resin (MF,MUF,UF) to make a suitable high tack adhesive system.

Studies has been carried out by taking MUF resin, Plymate-555 and powder MUF resin to make a pre press adhesive system. Plymate-555 is an additive based on natural gum and specialty tackfying chemicals available in local market as trade name Plymate-555 and powder resin (100% solid content) BR-201G was from Allied resin chemicals Ltd. Kolkata. From the study and physical observation, it was observed that satisfactory pre-press tackiness was achieved in between glue core and panel core and becoming easier to shift by autoloader or manual to the hot press without disturbance among the core veneer. Brief of Experimental methods and results are as follows:

Adhesive Formulations for Pre-pressing

Pre-pressing Conditions

Hot Pressing Conditions

Glue Adhesion Values of Prepressed Plywood

To increase the production efficiency and to manufacture the quality plywood now-a-days pre-press technology before hot pressing, become a common practice in modern plywood industries. It was observed that powder resin having solid content 100% and plymate-555 doesn’t show any chemical reaction with Liquid resin even after mixing with hardener and buffer rather than forming creamy and is lump-free during mixing. Satisfactory rheological properties of the adhesive and physicomechanical properties of the plywood made with mixing resin technology was achieved. Satisfactory pre-press results have been achieved at higher concentration of powder resin mix. The chances of pre-cure of dry out was reduced because veneers are held in close contact with each other. The adhesive wets the veneer surface since the layers of veneers have an opportunity to come into intimate contact with each other for greater period of time. Hence the quality of the plywood improved by overcoming warping, pre-curing etc.