International projectionist (Jan-Dec 1955)

* ■■ ;' : ::ss: : FIG. 1. Broadside view of the DuPONT splicer. (This is a laboratory not a production model, although the latter type is now in work by several prominent manufacturers.) At "A" is a plunger which actuates a knife blade for cutting the adhesive strips into lengths of the proper size. "B" indicates two plungers which lock the mechanism top to its base after the film has been positioned properly on the latter, film in precise registration. knife-blade can cut a two-frame length of tape to be dispensed. The Splicing Procedure To make a splice with this device, the two lengths of film to be joined are positioned onto the registering pins of the base unit, shown in Fig. 4. Actuating the plunger at the forward end of the dispenser unit causes the knife-blade to cut a two-frame length of tape on the sprocket wheel. Now the dispenser unit is positioned into channels in the base unit and moved from right to left. This rolls the precut length of tape off the sprocket wheel and applies it, in register, to the films to be spliced. The film is then turned over and the operation repeated to complete the splice. The dispenser cannot be positioned into the channels of the base unit unless the knife-blade plunger has been actuated to cut off a twoframe length of tape. Rolling the tape off a sprocket wheel is one way to apply it smoothly, in register with the film, and without occluding air bubbles. There are other ways to apply perforated adhesive tape to film, some of which may be more attractive than the method shown here. Good Light Transmission Mylar tape and its adhesive layer are essentially transparent and colorless, and when applied to both sides of a motion picture film reduce the optical transmission of the two frames 'C" and "D" indicate clamps for holding the involved by only about 7%, an amount which allows the splice to go completely unnoticed on the screen. Stress-strain measurements on both butt and lap splices show that, for load values far in excess of those which perforations can withstand, the elongation or stretching of any of the tape splices is indistinguishable from that of the unspliced film. A tensile pull of more than 50 lbs. is required before the tape splices begin to yield. This load is more than five times that at which the perforations would be torn from the film. A dynamic stress-strain test of both lap and butt tape splices was also carried out. In this test a five-pound stress was applied and relieved 120 times, and a twenty-pound stress was applied and relieved 40 times, each over a ten-minute period at room temperature. 74 degrees F. Yet, as a result of this test, the tape splices showed no measurable deviation from the behavior of unspliced cellulose triacetate film. It is well known that even a fivepound load, applied at these low frequencies of application to triacetate film running over a sprocket, is more than enough to completely strip the perforations. Tests at High Humidity Tests of tensile strengths of tape splices made at a range of relative humidities confirm the general impression that there should be little change with humidity. At high humidities, 95% to 100%, there is some reduction in ultimate strength, though the splices showed satisfactory behavior for stresses much in excess of the strength of perforations as they run on sprockets. It is interesting to note that unspliced cellulose triacetate film also shows reduced strength at high relative humidity. At low humidity, where conventional solvent cement splices tend to become weak, no similar tendency is shown by the tape splices. Tensile Strength High An effect of temperature on splice tensile strength was investigated, and no significant difference was found in the stress range of normal operations. Even at temperatures as high as 140 degrees F. the tape splices were stronger than the perforations. And at temperatures as low as26 degrees F. the tape splices showed FIG. 3 (top). Stripped-down view of splicer tape-dispensing unit (refer to Fig. 2). "A" is the plunger which is connected to the knife "B". At "C" is the sprocket which engages the film and from which the adhesive tape is literally rolled onto the film. The supply reel for the tape is shown at "D". At "E" is shown a rubber roller which prevents metal parts from contacting the film while a splice is being made and while the sprocket "C" is rolling the tape along the splice area. INTERNATIONAL PROJECTIONIST • MARCH 1955