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Table IV. Sound Recording Properties
Sample
Saturation output
2% dist. output
Zero signal
S/N
2% dist.
S/N
Freq. of 10-db loss
Amplitude modulation
Commercial tape Experimental coating
24.7db 21.3db
16.4db 10.8db
66.7db 67.8db
57.7db 52.3db
7300 cps 7200 cps
1.5% 6.0%
base. The magnetic oxide coating comDosition proposed in this paper has been bund to be satisfactory for both of these film base materials.
Curl of the Film Due to the Coating
The film curl due to the coating is :losely associated with adhesion. Each s controlled by the amount of solvent attack on the surface. An increase in solvent attack improves adhesion and tends to increase curl. Thus, the formula must be adjusted so that the solvent attack ^ives the necessary adhesion of the track without causing undesirable curl of the film. The formula proposed here gives no curl problem for high-acetyloracetatepropionate bases, provided the coating is :ured by circulating air at 110 F for at 'east 2.8 min.
However, unacceptable curl does result when tracks 0.100 in. wide are coated :>n cellulose acetate-butyrate base. Alhough this base is not being used for any current Eastman 16mm films, some 16mm film perforated along one |;dge has been produced in the past on ;:his base. Tracks 0.050 in. wide or less |io not cause objectionable curl when :oated on films using this base.
Surface Irregularities
Surface tension causes the wet coating :o form a convex surface. If the solvent has high attack for the surface to Artiich the coating is made, it is characterstic for the coating to dry with a crack n the middle. In general, flatter crackTee surfaces are obtained if the solvents lave low attack for the surface and if the brmula contains a small amount of very
high-boiling solvent such as butyl cellosolve or butyl lactate. Usually, formulas having very low attack on film base will give coatings having irregular edges, which must be avoided.
Sound Quality
The sound quality of magnetic tracks 0.100-in. wide and 0.4-mil thick has been determined by coating tracks on 16mm film which was later slit to ^--in. width. The track was positioned in the middle of the -J-in. strip. Sound measurements and comparisons with commercial magnetic tapes were made in the Kodak Research Laboratories on a high-quality ^-in. tape recorder.
There are two basic difficulties in comparing 0.100-in. magnetic tracks with commercial ^-in. tape. A narrow track will never have width and surface uniformity that is possible with -J-in. tape. Since the magnetic heads used in testing tapes were 0.125-in. wide, this means that all edge variation on narrow tracks was picked up by the heads. Also, the narrow tracks were tested on base material 5.5-mil thick. Commercial tape base is about 1.5-mil thick. This thickness difference and the associated difference in flexibility greatly affects head contact with the tracks. Both of these factors act to the detriment of the narrow track.
Table IV lists various sound measurements for a track 0.100-in. wide and 0.4mil thick, and also lists comparison figures typical of the best commercial tapes.
All data reported here were determined using a nominal bias current,
Thomas R. Dedell: Magnetic Tracks for Processed 16mm Film
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