Process of attaching reinforcing ply to ply containing mica-rich and mica-poor faces
View Patent ↗The present invention relates to a sheet structure for electrical insulation or flame resistance comprising a barrier ply having a mica-rich face and a mica-poor face and a reinforcing ply containing a saturable backing layer attached to the mica-poor face of the barrier ply.
1. A process for making a sheet structure comprising the steps of:
a.) forming a ply containing a mica-rich face and a mica-poor face; and
b.) attaching a reinforcing ply to the mica-poor face of the ply of step a), said reinforcing ply comprising a saturable backing layer,
wherein the reinforcing ply is attached to the ply of step a) by laminating;
with the provisos:
(i) mica is present in both the mica-rich face and mica-poor face,
(ii) mica in the mica-rich face is present in an amount of at least 60 weight percent based on the total weight of components in the mica-rich face and,
(iii) mica in the mica-poor face is present in an amount less than 40 weight percent based on the total amount of components in the mica-poor face.
2. The process of claim 1 wherein the ply of step a) is formed on a paper machine.
3. The process of claim 2 wherein the mica-rich and mica-poor faces of the ply of step a) are formed by supplying separate mica-rich and mica-poor slurries to the paper machine.
4. The process of claim 1 wherein the saturable backing layer of the reinforcing ply is a spunlaced material.