Ultra-thin stretch-oriented blown shrink film now can be processed using the Layer Sequence Repeater (LSR) technology developed by BBS Corp., Spartanburg, S.C. In a paper to be delivered later this month at the SPE Polyolefins 2013 Conference in Houston, BBS reports producing films containing 25 to 77 nano-layers of nylon 6/66, EVOH, and PE and then biaxially orienting them. “We found that the more layers there are in the film structure, the easier it is to stretch-orient at astounding stretch ratios of up to 7x7 compared with 5x5 normally,” says Henry Schirmer, inventor of the LSR and president of BBS. “Having 77 nano-layers within an ultra-thin 26 gauge film means that each nano-layer is truly in the nanometer measuring range. The average thickness in this example is 8.6 nm.” The LSR is an independent unit inside the die (see image). It forms the nano-layer stack and inserts it between other layers in the film.
The paper, coauthored by shrink-film processor Bollore of France (U.S. office in Dayville, Conn.) and EVOH supplier Soarus LLC, Arlington Heights, Ill., was eye opening to Schirmer for several other reasons. First, it led to a theory that nano-layers create a new order of crystal structure in EVOH that is consistent with forming a copolymer with nylon 6/66, as observed using differential scanning calorimetry (DSC) analysis.
Another new theory of Schirmer’s explains polymer flow within the LSR. “While the LSR has very narrow slots for alternating layer flow, there are very many slots, meaning that the overall flow is very relaxed because it is all slow and in parallel against many metal surfaces,” he states. “The melt therefore has more alignment, like a carding machine combing cotton, but with less melt orientation than normal. This means more polymer is available for stretch orientation, as we have seen with the high stretch ratios. BBS technology is available through Alpha Marathon, Woodbridge, Ont.