The transparent support on which the light sensitive emulsion is coated.
Audio & Video
Also known as a ‘Backing’ for tapes. There are three different types of bases in use: Cellulose Acetate (CA), Polyvinylchloride (PVC) and [legacy-smartlink:Polyester (PET)].
Many bases have been used over the years to support motion picture film. These range from Cellulose Nitrate through Cellulose Diacetate, Cellulose Triacetate to Polyester (PET).
CA (Cellulose Acetate)
Tensile strength approx 9 kg/sq. mm, heat resistant up to approx. + 160°C. Storage in air conditioned rooms recommended (°C and %RH) as drying out causes shrinkage (risk of deformation and brittleness). CA was used for magnetic recording film (16mm 17.5 and 35mm) and for domestic tapes as well and is no longer used.
Tensile strength approximately twice as high as that of CA. Unaffected by moisture. Dissolves relatively easily, only limited resistance to heat when new and therefore a risk of deformation if overheated. Used for studio and domestic tapes.
Chemically correct expression, Polyethylene terephthalate; tensile strength approx three times as high as that of CA. Heat resistant when new. Resistant to low temperatures and relatively unaffected by moisture. Polyethylene terephthalate in a pre-stretched (tensing) state is used exclusively for the polyester backings of recording tapes.
Case, Dominic. 1996 Motion picture film processing, Focal Press, Eastwood, N.S.W.