DEVELOPMENT OF SOME HIGH-PRESSURE INDUSTRIAL LAMINATES
At General Electric Plastics Division in 1947, I was given the task of putting a new laminate into production. The basis of this laminate had been developed at the Philadelphia switchgear plant of General Electric which built large circuit breakers. The new laminates were designed to withstand the effects of high-wattage arcs. This laminate was based on a melamine-formaldehyde resin and was arc- and fire-resistant as well as having excellent dielectric properties. In production, a web of kraft paper was led through a solution of sodium silicate (commonly called "water glass" otherwise sometimes used to preserve eggs). The web was immediately led through a boiling concentrated solution of boric acid. The result was an even distribution of sodium borosilicate through the web. The web was run through an oven and the dried paper rolled. This roll was then put through a dip tank with a solution of the melamine resin. When cut into suitable sizes, the material was pressed between press plates and the melamine cured using steam at about 135 degrees C. A similar laminate was made using a bleached cotton fabric for better physical properties. The numbers assigned to these products were 12535 and 12536 respectively for the paper and cloth based laminates. Trials were first made in the laboratory "treater" in the Pittsfield, Mass. operation, then moved to the new plant in Coshocton, Ohio. In Coshocton, laminated panels were made in 0.25 inch thickness and 39 x 39 inches. These sheets were molded in a special press which had been designed for 36 x 36 inch laminates. In order to accommodate the larger sizes, the central hydraulic line pressure to this press of 3000 psi was boosted by a small piston pump to 4500 psi. Although these materials were put into production for a short period, they were never successful. The weakness of the system was the effect of the sodium borosilicate on the melamine resin. The low pH of this salt had a tendency to advance the resin cure before it could be processed. It was necessary to proceed with the laminating process immediately following the treatment with melamine resin. This was not always feasible and the result was impregnated material in which the resin was beyond the stage of bonding. At the time, there was no development effort given to eliminate this problem and these products were dropped. In retrospect, it may have been possible to eliminate the problems with these products with the use of chemical buffers. This suggestion could have resulted from a small conference on the matter, but no such meeting was ever called or even proposed.

For more information, contact G. Marshall Naul, American Plastics History Association, 534 Stublyn Rd., Granville, OH 43023-9554, 614-587-3121.