1. Field of the Invention
This invention relates to a cylindrical core for receiving windings of a photographic film web and comprising an opening for receiving an end of the film web and means for resisting circumferential slippage of a wound film web over the core.
2. Description of the Prior Art
Spools of photographic film for cinematographic use are wound onto cylindrical cores for ease of handling.
It has been known for very many years to provide means for resisting circumferential slippage of a wound film web over the core. Such proposals include leading an end of the film web through a slot in the core and clamping it, with or without the use of projections which interengage with the perforations provided in the margins of the film web. It has also been proposed to provide such projections around the periphery of the winding core, whether in fixed relation thereto or carried by a flexible strap wound round the core. Examples of some of the many known constructions are set forth in Patent Specifications Nos GB 637,371, U.S. Pat. No. 3,331,564, U.S. Pat. No. 3,315,911, FR 1,044,194, FR 1,467,511, FR 1,488,581, DE 1,201,679 and in German Federal Republic Utility Models Nos Gbm 1,823,629 and Gbm 1,963,688. Known cores having means for resisting slippage of a wound film web tend to be of rather complicated construction and they are therefore rather expensive and thus unsuitable for use when supplying unused film stock to the cinematographer. Also, many such constructions tend to resist release of the end of a film web on complete unwinding from the core.
This perhaps explains why currently used cores simply have a slot for receiving the end of a film web which is then wound onto the core. Using such cores, the film is held in place by friction, and there is no positive interengagement between the film and the core, so that the film can be released easily on complete unwinding. This is satisfactory when the film web is coated with a hard emulsion, but it gives rise to problems when the emulsion is relatively soft because slippage tends to occur when the film web is under tension and there are only a few windings on the core. As a result, an end portion of the film web may be susceptible to damage. It would of course be possible to make use of a film web bearing a harder emulsion, but this is not always compatible with high photographic quality.
Such currently used cores are generally formed as integral mouldings of plastics material, and because of their construction, they require a moulding die of at least three, and usually four or more parts. It would certainly be possible to form such a core with integral means for resisting slippage of a wound film web, but this would require a more complicated mould which would therefore be very expensive to manufacture. Such a complicated mould would also tend to have a relatively short working life.