With the new flat sheet extrusion system, KraussMaffei Berstorff offers a particularly advantageous solution for manufacturers and processors of sheets made of ethylene-vinyl acetate (EVA).For the first time, EVA sheets can be produced at high velocity with a width of over 3 m. These have optimal visual properties, return for the edge trimming and low shrinkage.
"EVA is on the advance as a raw material for technical sheets and foils," explained Prof. Bernd Poltersdorf, Head of Sheet and Board Extrusion at KraussMaffei Berstorff, Hanover. "Globally, therefore, raw material manufacturers are building up capacity for EVA and developing specific recipes for various applications," Poltersdorf explained further.
In the steadily growing photovoltaic industry, EVA sheets already today are used as encapsulating sheets for silicon cells in solar modules in 95 percent of their applications. The use of EVA sheets in laminated safety glass panels is also of interest, because these are more cost-effective and easier to manufacture than the sheets made of polyvinyl butyral (PVB) used today. "With the new flat-sheet extrusion line, KraussMaffei Berstorff now offers an exciting solution for both growth markets," said Poltersdorf.
In extensive tests carried out in cooperation with the Fraunhofer Center for Silicon Photovoltaics (CSP) in Halle, it was proven that EVA sheets that are manufactured on the new extrusion system are highly transparent. They exhibit a transmission in a glass EVA glass test body in the spectral range between 420 and 1,100 nm of 99 percent.
Simultaneously, the shrinkage of up to 45 percent seen today could be reduced to below 5 percent. And the highlight of these results is that they were determined for both a commercial formula for a new product and for a sample that had been recycled three times. The recyclability of EVA sheets makes the manufacturing process significantly more economical and ecologically sound, and thus more lucrative for foil manufacturers.
A special downstream unit and the twin-screw extruder are core components of the new extrusion line. The downstream unit is now being developed by the KraussMaffei Berstorff engineers specially for manufacturing EVA sheets and has been registered for a patent. It is mainly responsible for the sheet's low shrinkage and high visual properties.
Aside from that, a double-sided, pressed sheet can be manufactured with it, which is an attractive alternative for many applications. The twin-screw extruder used allows the incorporation of the recycled goods without loss of quality thanks to its optimal homogenization. It also provides the sheet manufacturer the additional option of working with individual components instead of precompounds, which in turn is more cost-effective.
