Sunny prospects for EVA sheet extrusion system
By Barry Copping
Posted 8 October 2012
KraussMaffei Berstorff sees major possibilities for EVA in solar energy modules
KraussMaffei Berstorff (KMB) has introduced a flat sheet extrusion system for manufacturers and processors of sheets made of ethylene-vinyl acetate (EVA).
For the first time, says KMB, EVA sheets can be produced at high velocity with a width of more than three metres. Advantages in terms of excellent optical properties, small shrinkage and reducing waste from edge trimming are claimed.
Professor Bernd Poltersdorf, head of sheet and board extrusion at Hannover-based KMB, says: "EVA is on the advance as a raw material for technical sheets and foils. Raw material manufacturers are building up capacity developing specific recipes for various applications.”
In the steadily growing photovoltaic industry, EVA sheet is used to encapsulate silicon cells in around 95% of applications.
KMB claims that laminated safety glass panels are easier and more cost-effective to manufacture using EVA sheet than with the polyvinyl butyral (PVB) more commonly used today.
High optical transmission and low shrinkage
In tests carried out in cooperation with the Fraunhofer Center for Silicon Photovoltaics (CSP) in Halle, KMB demonstrated a high transparency for EVA sheet made on the new extrusion system are highly transparent, at 99% for light of between 420 and 1,100nm wavelength.
Shrinkage of up to 45% seen with current materials could be reduced to less than 5% with EVA, says the company, which tested both a virgin commercial formulation for a new product and 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, says KMB.
Twin-screw extruder enables recycling
The key components of the new extrusion line are a specially configured downstream unit and a twin-screw extruder. The line can produce double-sided, pressed sheet if required. The twin-screw extruder allows recycled material to be incorporated without loss of quality, says KMB, thanks to optimal homogenisation. Individual materials can be fed, rather than pre-prepared compounds, which the company says enhances cost-effectiveness.
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