Laminates are made by coating sheets of paper with melamine-aldehyde resin and other sheets with phenol-aldehyde resin and drying and partially curing the sheets in ovens. Stacks are formed with a melamine-aldehyde treated overlay sheet on top, a melamine-aldehyde treated print sheet next, then typically about seven phenol-aldehyde treated sheets. The stacks are then cured under heat and pressure in a press at about 800 to 1200 psi to produce the laminate.
The speed at which laminates can be made is largely determined by the amount of time required to cure the slowest-curing resin. Until now, the slowest-curing resin was the phenol-aldehyde resin.
However, it has recently been discovered that water soluble carbonates and bicarbonates will accelerate the curing of phenol-aldehyde resins without adverse effects. A full description of the accelerated phenol-aldehyde resins is given in my copending application, Ser. No. 363,774, filed of even date, now U.S. Pat. No. 3,897,589, titled "Laminate Made With Accelerated Melamine-Aldehyde Resin And Accelerated Phenol-Aldehyde Resin And Method Of Making It," and incorporated herein by reference.
Since the discovery of those accelerated phenol-aldehyde resins the melamine-aldehyde resin is now the slowest-curing resin.
Efforts have been made to accelerate the curing of melamine-aldehyde resins, but many of the compounds which have accelerated the curing have also produced adverse side effects which render them unacceptable. These adverse side effects include sticking to the pressing plates, failure to pass a hot water-hot wax test, delamination during a 2 hour water boil test, lack of resin stability during storage, and various other effects.