Apparatus for the edges of thermoplastic webs

Claim 1

Apparatus for edge knurling a moving length of thermoplastic web having two opposite side margins, comprising a backing wheel for supportive engagement with one side of the web margin adjacent each such edge; a freely rotatable knurling wheel for engaging the opposite side of each said web edge margin, said knurling wheel comprising a solid outer cylindrical rim having an exterior knurling pattern thereon composed of a plurality of raised minute surface projections separated by depressions, an inner hub, and means interconnecting said rim and said hub which limit the heat transfer from said rim to said hub; heating means spaced from said rim for heating a peripheral portion of said rim without contacting the same, which portion is remote from the point of engagement with said web to a uniform elevated temperature during knurling to thereby directly conductively heat the contacting web margins as said wheels rotate; and means for biasing said wheels during operation against the corresponding web margin passing through the nip thereof with sufficient force to cause the regions of the web surface engaged and heated by said projections to be depressed and the intervening regions of said surface to become slightly raised relative to the overall original surface of the web without deformation of the reverse surface as a consequence of said engagement by said projections.