DE2134668

1361242 Non woven fabrics MINNESOTA MINING & MFG CO 7 July 1971 [8 July 1970] 31988/71 Heading D1R [Also in Division B5] A sheet-like material consists of a non- woven fibrous web impregnated with an electrically-insulating, moisture-insensitive thermoset resin, the web comprising a blend of at least 15% by weight of discontinuous synthetic heat-softenable fibres, at least partially softenable at temperatures below 200‹C and from 10 to 75% by weight of discontinuous synthetic fibres resistant to temperatures in excess of 275‹C. The heat-softenable fibres are preferably monofilament staple polyethylene terephthalate fibres and the heat-resistant fibres are preferably monofilament aromatic polyamide fibres. Rayon fibres may also be used as the heat-resistant fibres. The blend may also comprise fibres which resist softening in the 150 to 250‹C range e.g. drawn polyethylene terephthalate fibres. The non-woven web may be made by air-laying or garnetting a blend of the fibres, needling the product to increase the density and preferably hot-pressing and/or calendering the needled product. The thermoset resin which may be applied by dipping may be a polyurethane, a silicone, an unsaturated polyester, an acrylic resin, an epoxy resin, a urea-aldehyde resin, a melamine-aldehyde resin or a phenol-aldehyde resin, the resin being cured by heating. The aired material may be used as a backing for an electrically conductive layer e.g. in the preparation of printed circuits.