Method for impregnating a fibrous base material with a substantially air-free varnish

A method for impregnating a fibrous base material with a varnish liquid, wherein the so-impregnated base material is substantially air free, comprising:

• (a) passing the base material under the surface of and through a supply of low-viscosity liquid contained in a reservoir therefor such as to impregnate the base material with the low-viscosity liquid and displace air from the base material so as to provide a substantially air-free base material, said low viscosity liquid having a viscosity of about 100 cP or less;
• (b) passing the air-free base material through an entrance for and into a syphon and pinching the base material at a first position near the syphon entrance but above the low-viscosity liquid surface, so as to remove from the base material a portion of the low-viscosity liquid therein and return the removed low-viscosity liquid portion to the supply thereof;
• (c) supplying an inert gas which is soluble in the low-viscosity liquid into he syphon so as to maintain an inert gas atmosphere therein sufficient to maintain the air-free condition of the base material;
• and
• (d) passing the air-free base material through an exit of the syphon and under the surface of and through a supply of varnish liquid contained in a reservoir therefor sufficiently to displace the low-viscosity liquid from the air-free base material and impregnate the air-free base material with the varnish, and pinching the base material at a second position near the syphon exit but above the varnish liquid surface, so as to prevent inert gas in the syphon from flowing into the varnish liquid, and pinching the base material between said first and second positions.