Reinforced plastics carrier for printed circuits

Abstract

Non-woven glass-fiber webs for reinforcing plastics material carrying printed circuits are produced by the wet process from E-glass fibers bonded with polyvinyl alcohol. The polyvinyl alcohol used is a powder or suspension, has a degree of hydrolization of 98-100%, and a viscosity, as a 4% solution in water of 20° C., of 20-100 cP. Preferably the polyvinyl alcohol has a degree of swelling at 20° C. of between 3 and 8, and in the dry form a particle size of between 50 and 180μ. A plurality of these glass fiber webs are impregnated with a solution of an epoxy resin, arranged as a laminate, then compressed at elevated pressure and temperature to form the final laminate.

We claim: 
     
       1. A process for making an insulating sheet for printed circuits, which comprises the steps of forming a 0.005-0.05% suspension of fibers and particulate binder in water, said fibers being fibers of E glass 5-30 mm long and 5-15μ thick and said binder being a particulate polyvinyl alcohol having a degree of hydrolization of 98-100%, being present in the amount of 5-25% based upon weight of the glass fibers, said binder having a particle size of .[.50-180 mμ.]. .Iadd.50-180μ .Iaddend.and a degree of swelling .[.of .]. .Iadd.at .Iaddend.20° C. of 3-8, and having a viscosity measured as a 4% solution in water at 20° C. of 20-100 cP; processing this suspension on a fiber web making machine by dewatering to form a non-woven glass fiber web; drying said glass fiber web by heating to a temperature of 85°-100° C. to dissolve the polyvinylalcohol granules in their own swelling water and subsequently further heating to an increased temperature to evaporate the water and dehydrate and harden the polyvinyl alcohol; impregnating a plurality of said glass fiber webs with a solution of an epoxy resin and hardener in acetone, evaporating the acetone; arranging said plurality of webs as a laminate; and compressing said webs into an insulating sheet laminate at elevated pressure and temperature. 
     
     
       2. The process as defined in claim 1 wherein the binder has a degree of hydrolization of 99.5% and a viscosity of 30 cP and is present in an amount of 15% by weight of glass fiber. 
     
     
       3. A laminate for printed circuit boards, made by the process of claim 1, the electrical characteristics of which fully satisfy the DIN standard for a G-10 laminate. 
     
     
       4. A laminate for printed circuit boards, made by the process of claim 2, the electrical characteristics of which fully satisfy the DIN standard for a G-10 laminate. .Iadd. 5. A non-woven glass fiber web characterized in that water in which the web has been kept for 24 hours at 20° C. has a conductivity of not more than 20 μS/cm which consists essentially of E-glass fibers having a thickness of 5-15μ and a length of 5-30 mm, and a binder; said web being made by the steps of: (a) forming a 0.005-0.05% suspension in water of said fibers and from 5-25%, based upon weight of the fibers, of said binder in swollen particulate form, said particulate binder being polyvinyl alcohol having a degree of hydrolization of 98-100%, a dry particle size of 50-180μ, a degree of swelling in water at 20° C. of 3-8, and having a viscosity, measured as a 4% solution in water at 20° C., of 20-100 cP;   (b) dewatering said suspension on a fiber web making machine to form a wet, non-woven glass fiber web;   (c) heating the wet web obtained in step (b) to a temperature sufficient to dissolve said swollen binder particles in their own swelling water; and then   (d) further heating the web of step (c) at a temperature sufficient to dry the web and to dehydrate and harden the polyvinyl alcohol binder. .Iaddend. .Iadd. 6. A process for making a non-woven glass fiber web characterized in that water in which the web has been kept for 24 hours at 20° C. has a conductivity of not more than 20 μS/cm, which comprises the steps of:   (a) forming a 0.005-0.05% suspension in water of E-glass fibers of 5-15μ thickness and 5-30 mm length together with from 5-25%, based upon weight of the glass fibers, of particulate polyvinyl alcohol having a degree of hydrolization of 98-100%, a dry particle size of 50-180μ, a degree of swelling in water at 20° C. of 3-8, and having a viscosity measured as a 4% solution in water at 20° C., of 20-100 cP;   (b) dewatering said suspension on a fiber web making machine to form a wet, non-woven glass fiber web having swollen particulate binder retained therein;   (c) heating the wet web of step (b) to a temperature sufficient to dissolve said swollen binder particles in their own swelling water; and then   (d) further heating the web of step (c) at a temperature sufficient to dry the web and to dehydrate and harden the polyvinyl alcohol binder..Iaddend.