IMPROVED ELECTROSTATIC PINNING USING A BIASED, CONDUCTIVE SHIELD

Electrostatic pinning is a technology used to improve the intimacy of contact of an extruded resin onto a casting wheel in the process of pr oducing plastic films such as polyethylene terephthalate (PET). This i mprovement is achieved by spraying electrical charge onto the resin ju st prior to contact with the casting wheel, creating an electrostatic force of attraction between the resin and wheel. This work focuses on altering the electrostatic pinning hardware, rather than resin formula tion, for improved performance. A biased, semicircular, conductive shi eld is placed around the pinning wire to increase its resin-charging e fficiency. This results in a pinning system having increased latitude with respect to resin formulation. It is shown that a spectral analysi s of the profilometry of pinned resin samples provides a method for qu antifying pinning quality. This method is used to demonstrate a direct correlation between pinning quality and net current deposited on the extruded resin by the pinning hardware. Another important result is th e existence of an optimal shield bias voltage that depends upon the pi nning wire voltage. This apparatus is shown to perform well for a vari ety of PET resin formulations incorporating various levels of metal ad ditives.