Edge pinning system
This system gives electrostatic to edges of molten resin to have it adhere electrostatically to the cooling roll. It consists of a power supply that generates high DC voltage, electrostatic electrodes that apply electrostatic by generating ions, and high-voltage cables. The electrodes come in a pair and are mounted on the left and right sides of the roll.
1) Prevention of neck-in
When molten resin extruded from a T-die contacts a cooling roll, neck-in occurs due to factors such as the resin’s own weight or the tensional force of the cooling roll. In this edge pinning system, the left and right electrodes, which are mounted at contact points on both edges of the cooling roll, have molten resin adhere to the roll in a uniform width, fixing it in position. Molten resin that adheres electrostatically to the roll has Coulomb force. This allows it to minimize the neck-in caused by fluctuations of tensional force, unlike being held by an air nozzle, etc. Because the position of the molten resin is fixed at both edges of the cooling roll, a uniform tensional force is also applied in the direction of extrusion, resulting in reduction of uneven thickness.
2) Prevention of slack in center
Molten resin film shrinks when it is cooled. This causes misalignment of the edges, which results in slack in the film’s center*1. The edge pinning system prevents this problem because the position of the molten resin is fixed at both edges of the cooling roll.
*1 Contraction stress is generated when molten resin is solidified, which creates tensional force in the horizontal direction. Combined with insufficient cooling, etc., the tensional force causes slack in the film’s center. In our tests of the edge pinning system, the film had no slack even when speed was increased by 10%-20% under the same cooling conditions.