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1950 MEASURING ELECTRIFICATION OF FILM 41
test roller. This process corresponds to the passage of the film over a number of rollers of this same material.
Examination of the Lucite roller curve shows that for the film used in this case, a high positive potential, Vj, is always reduced by passage over the roller until the incoming potential, VI} becomes about +2.5 kv. In the next passage over this roller or a duplicate roller, negative charges are added and the film leaves with a potential of —1.5 kv. Continuing the step-by-step process, the film reaches a stable potential level of approximately —4.5 kv, again the point of intersection with the 45-deg line. In the case of the printer's gelatin roller, if film, charged either positively or negatively, contacts this roller, it will be brought to a level of about — 1 kv. This occurs in a very few roller passages because of the steepness of the curve. Numerous types of curves are found with different roller-film combinations and, in many cases, quite different data are found on the support side from those on the emulsion side.
CLEANING PADS AND SOLUTIONS
In order to test the effect of rubbing film with a cleaning pad, a 2in.-diameter roller was covered with the test material, and the film passed over the material on the roller with a 60-deg wrap, the roller being held stationary. The same technique of measurement as described above was used.
It is found that ordinary velvet produces very little electrical charging when rubbed against either the emulsion or the support side of Eastman Plus-X Panchromatic Negative (processed) Film. The curves lie very close to the 45-deg line (Fig. 4), showing that this film may pass across the velvet at any potential and its potential level will not be altered. This may, therefore, be termed a "neutral" combination.
Mouton fur, on the other hand, alters considerably the potential level of processed motion picture negative film (see Fig. 5). In contact with the emulsion side, mouton fur discharges the film when it is charged to either positive or negative values, with the exception of positive potentials under 2 kv. With this exception, the film will always leave the fur at a lower potential than it possessed upon reaching the fur. Low positive potentials will be increased but will not exceed a 2-kv level. This corresponds to the point of intersection with the 45-deg line. The mouton fur will discharge the support side very rapidly when charged positively. Between +4.5 kv and zero, the polarity is reversed by the fur, and for all approaching negative potentials, still higher negative values result. Successive passages