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(Photo credit: SML)

APET sheet

SML - Crystal clear big-size cups: What to be aware of when calendering extra-thick APET sheet

1:38 min Sheets & Films
Redlham, Austria

Calendering is a common method to produce extra-thick APET sheet for the thermoforming of big cups containing up to one liter in Europe or 32 ounces in the US. To obtain a crystal-clear product, a couple of fundamental factors must be taken into consideration. The intrinsic viscosity (IV) of the melt is a key to any successful production.

“If a glass-like quality is required for thermoforming APET sheet in the range from 1,200 to 2,000 microns, manufacturing becomes relatively demanding. Process knowledge is a basic prerequisite for a successful production,” Rupert Becker, Product Manager at SML, comments.

Choosing the right raw materials: IV value over 0.78 g/dl 

'A highly viscous melt is essential for the production of crystal-clear, extra-thick APET sheet. Using raw materials with an IV value higher than 0.78 g/dl, in combination with pre-drying and single screw extrusion, guarantees minimum IV loss for the melt throughout the production process as a whole.

Calendering on slanted roll stacks 

A slanted roll stack allows the highly viscous melt to stabilise before entering the nip, where the sheet thickness is determined. Disturbances or interruptions with regard to the melt bead can be largely excluded. This contributes enormously towards the formation of highly transparent APET sheet, the optical quality of which is comparable with  PC or PMMA sheet, that are usually also manufactured on slanted roll stacks. 

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