Claims
- 1. A process for quenching a molten polymeric film, which comprises forming a molten polymeric film and quenching said film on a cooled casting surface which is electrically earthed, the molten film being passed across an electrode located in spaced relation from the film surface and in the proximity of the region of first contact of the molten film and the casting surface, applying an alternating voltage to the electrode, said voltage being an asymmetrical wave form, having positive and negative portions with the positive peak having a greater magnitude than the negative peak, and exceeding 4.0 kilovolts peak to peak, the peak to peak voltage being at least equal to the A.C. corona discharge inception voltage and having a frequency less than that at which positive and negative electrostatic charges alternately emitted by the electrode are unable to cross the space between the electrode and the molten film before the polarity of the voltage on the electrode changes, so as to produce an rms pinning current to the electrode, including leakage current, in the range 0.2 to 20 milliamperes whereby the electrostatic charges emitted by the electrode are deposited by the applied electric field upon the molten film to cause it to adhere to the casting surface.
- 2. A process according to claim 1, in which the voltage applied to the electrode exceeds the inception voltage of the electrode by at least 1 kilovolt.
- 3. A process according to claim 1, in which the applied voltage exceeds the inception voltage of the electrode and is in the range 8.0 to 12.0 kilovolts peak to peak.
- 4. A process according to claim 1, in which the frequency of the applied voltage is at least 500 Hz.
- 5. A process according to claim 4, in which the frequency of the applied voltage is in the range 1 to 3 kHz.
- 6. A process according to claim 1, in which the resultant rms pinning current applied to the electrode, which includes leakage currents, is in the range 0.2 to 20 milliamperes.
- 7. A process according to claim 1, in which the electrostatic charges are emitted by a wire electrode of diameter from 0.005 to 0.01 inch.
- 8. A proces according to claim 1, in which the alternating voltage applied to the electrode is of sine waveform.
- 9. A process according to claim 1, in which the polymeric film quenched is polyethylene terephthalate film.
- 10. A process according to claim 1, in which the voltage applied to the electrode is maintained above the corona discharge inception voltage of the electrode assembly for at least 75% of the duration of each voltage half cycle, and a lapse time of at least 10 microseconds is maintained in each half cycle during which no discharge current is produced.
- 11. A process according to claim 10, in which the operating voltage is maintained for 90 to 95% of the voltage half cycle.
Priority Claims (2)
Number |
Date |
Country |
Kind |
6031/73 |
Feb 1973 |
UK |
|
34337/74 |
Aug 1974 |
UK |
|
Parent Case Info
This application is a continuation-in-part application of Ser. No. 336,047 filed 26 Feb., 1973 and of Ser. No. 440,571 filed 7 Feb. 1974 (both now abandoned).
US Referenced Citations (7)
Non-Patent Literature Citations (1)
Entry |
"Corona Discharge", McGraw-Hill Encyclopedia, 3, pp. 541-542, 1971. |
Continuation in Parts (1)
|
Number |
Date |
Country |
Parent |
440571 |
Feb 1974 |
|