MANUFACTURE OF THERMOSETTING RESIN LAMINATED SHEET

PURPOSE: To suppress the silver transfer phenomenon of a laminated sheet by impregnating raw paper with a thermosetting resin so as to fill the specific number of the pores present in the paper fibers of the raw paper. CONSTITUTION: When raw paper for a laminated sheet is impregnated with a thermosetting resin, 50% or more, pref., 80% or more of the pores present in the paper fibers of the raw paper are impregnated with the thermosetting resin. The pore vol. of the raw paper is measured by a solute excluding method. That is, the raw paper or impregnated paper being an object to be tested is immersed in water and water is allowed to penetrate into the pores of the raw paper to saturate the pores and the object to be tested saturated with water is immersed in an aqueous soln. of a solute of which the molecular size is known and, from the concn. of the diluted aq. soln., the vol. of pores of which the size is smaller than the molecular size of the solute present in the object to be tested is calculated according to a predetermined calculation formula. When the resin impregnation ratio of pores is determined by this method, an impregnation degree can be controlled to 10-90%.