PURPOSE:To impregnate a substrate with a varnish having high concentration, by passing the substrate through a specially designed vertical zigzag-shaped impregnating bath having a middle chamber kept in vacuum, thereby removing the air, water, etc. from the surface of the substrate. CONSTITUTION:A substrate 1 to be impregnated is passed through an W-shaped impregnation bath 3 containing a solution of varnish 2, and comprising two side arms corresponding to the inlet 4 and the outlet 5, and a middle vacuum chamber 6 kept higher than both openings 4, 5. The chamber 6 is maintained in vacuum by a vacuum pump 7. The air and water adsorbed to the substrate 1 is removed in the vacuum chamber 6, and the substrate is impregnated with the varnish solution in the right-hand chamber. The impregnated substrate 1 is further passed through an impregnation bath 15 via a guide roller 14, and dried.
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