Extrusion: Ironing-Roll Winder For Jumbo Rolls
Targets cast PP and barrier film applications.
A new ironing-roll winder from Davis-Standard, Pawcatuck, Conn., targets larger-diameter master rolls up to 4 ft on cast-film lines up to 20-ft wide. While the technology can be used for many film types, D-S has found it to be most beneficial for cast PP and barrier films, where post-wrap shrinkage occurs as a result of the types of polymers used in the film structures, or where blocking can occur due to a soft sealant layer with a high coefficient of friction (COF).
The winder incorporates programmable tension control, pre-spreading onto the winding roll, and servo-controlled web entry of the film to influence leveling or layflat of the film prior to the lay-on roll. Roll hardness is improved with a more precise loading force of the lay-on roll against the winding roll, controlling the in-wound air at higher production speeds than previously possible. When optimized, these features reportedly can reduce defects such as tin-canning, caused by blocking and entrapped air that result in annular raised bands on the roll face. Other defects such as buckling, telescoping, and starring can also be reduced with the control features and dynamics of the new winding system, the company says.
Larger-diameter master rolls significantly improve subsequent processing efficiency, according to D-S. A relatively small increase in diameter can significantly increase the film length on a roll, the supplier explains. This reduces downtime in slitter rewinding as well as batch processes like vacuum metalizing.
The downside of winding larger roll diameters is the increased risk of in-wound defects. The variable geometry of the ironing roll enables processors to prewrap the film onto the winding roll prior to the lay-on roll, allowing entrapped air to reduce the COF between each wrap. This promotes film flatness prior to engaging roll hardness with the lay-on roll. This results in improved control, preventing in-wound imperfections.
The winder is available with a tapeless static knife or patented stationary-knife automatic-transfer system, and shafted or shaftless operation. Although the winder is designed primarily for large master-roll winding, in-line slitting is also possible in some shafted applications.
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