A method and apparatus for incorporating a powder into a continuous fibrous web containing multiple corrugations. In the method, a fibrous web provided with multiple parallel corrugations is continuously passed over a curved surface having an arc with a radius to web thickness ratio of 0.5-3 and the...http://www.google.com.au/patents/US4699808?utm_source=gb-gplus-sharePatent US4699808 - Method and apparatus for providing powder into fibrous web structures
