Of course, the pressures used to manufacture most types of plywood are significantly lower than those needed for particle- and fibre-based products. However, the pressures are still high. Consequently, when the press opens, a panel of any type might stick to one of the press platens, causing a hold-up in the production.
The risk of this can be minimised by using release agents. External release agents are those applied either to the platens or to the surface of the panel, whereas internal release agents are mixed with the panel binder.
Oils and fats, when applied to cake tins and baking trays, act as release agents when cooking. They reduce the contact between the uncooked ingredients and the metal, thus reducing the potential for mechanical interlocking. As all cooks know, this does not work 100% of the time and in addition, the release agent must be applied each time the cooking utensil is used.
Applying a release agent for each panel is not a practical or cost-effective method in a factory situation. Modern release agents therefore consist of bi-polar molecules that are molecules which have a positive and a negative end. These molecules will arrange themselves so that their most compatible end will be orientated to the substrate.
For example, a long-chain carboxylic acid has a hydrophobic tail and a hydrophilic head so when applied to a metal surface the molecules will naturally orientate so that their hydrophobic, that is waxy, tails point outwards. The metal will therefore obtain a waxy finish to which hydrophilic substances such as wood and formaldehyde based adhesives do not readily stick.
Release agents applied to new platens will help maintain the smoothness of the platens for longer. This will be apparent on the surface of the pressed panels. For many panels this is of minor importance because the surface is removed in the following sanding/calibration step. However, there are panels where sanding is not used, so the release agent is then very effective.
Release agents also help keep the platens clean and the platens then provide better heat transfer. This will lead to cost savings through reduced energy usage and, possibly, higher production capacity.
I use a release agent on the caul plates of our laboratory press, not because of the high volumes, but because the small panel size we use often results in excess adhesive being exuded on to the plates and the release agent then helps in the cleaning process.