CORE FOR FILM SPOOL

Abstract: A cylindrical core (1) for receiving windings of a photographic film web comprises a hub (3) having an axial re-entrant channel and an insert (4) fitting into and engaging shoulders (13), (16) of that channel to define with the channel a slot (26) for receiving an end of a film web (2). Interengaging elements (19), (25) are provided for resisting relative axial movement between the hub (3) and the insert (4) when the latter is inserted into the channel (11), and the insert (4) incorporates projections (24) for engaging at least one marginal perforation of a film web to prevent circumferential slippage of the film web.

Description: BACKGROUND OF THE INVENTION 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 preventing circumferential slippage of a wound film web over the core. 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 preventing 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, US 3,331,564, US 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 preventing 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 of course 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. Finally, there is disclosed in CH-A-293 148 a cylindrical core for receiving windings of a photographic film web comprising an opening for receiving an end of the film web. The core comprises a hub having an axial channel communicating with the core opening, and an insert fitting into said channel, said insert incorporating engaging means for engaging at least one marginal perforation of said film web to prevent circumferential slippage of the film web wound over the core. The described core does not allow easy disengagement of the trailing end of a film from the core and furthermore it has no means for securing the axial position of the insert in the channel of the hub. SUMMARY OF THE INVENTION Objects of the invention It is an object of this invention to provide a cylindrical core for receiving windings of a photographic film web comprising an opening for receiving an end of the film web and means for preventing circumferential slippage of a wound film web over the core which is of inexpensive, reliable construction and which allows easy disengagement of a wound film from the core. Statement of the invention According to this invention a cylindrical core for receiving windings of a photographic film web, comprising an opening for receiving an end of the film web, a hub having an axial channel communicating with said opening, an insert fitting into said channel, said insert incorporating engaging means for engaging at least one marginal perforation of said film web to prevent circumferential slippage of the film web wound over the core, is characterised in that said axial channel extends in a chordal direction, that the insert engages shoulder means of said channel, said shoulder means been arranged to prevent movement of the insert in said chordal direction, that means are provided in the axial channel and in the insert for resisting relative axial movement between the hub and the insert, and in that the engaging means are disposed so as to disengage from the film web when the film web is unwound. Such a core can be of simple construction and therefore quite inexpensive to produce. It provides a positive anchorage of the end of the film web while ensuring that the film end is automatically released from the core at the end of the unwinding of the film. The hub of a said core may be, and preferably is produced as an integral plastics moulding, this being the easiest and least expensive way of producing it. The moulding operation is simplified when, as is preferred, said hub is free from undercuts in opposed axial mould-release directions. The hub can be moulded using a two-piece moulding die which opens and closes according to the axial direction of the hub and which can accordingly be of simple and rugged construction and therefore relatively inexpensive and long-lasting. An axially opening two-piece moulding die may show the disadvantage that a very tiny circular bead may be produced on the outer cylindrical periphery of the hub, usually halfway of its length. This bead is caused by an insufficient closure of both moulding dies. In the case of very good finished dies, the bead may become almost inexistent, except for some places where yet a breakthrough of the moulded plastic occurs in the form of minuscule dots spaced along an imaginary circle on the outer surface of the hub. These dots, or a complete peripheral bead as the case may be, may damage the first windings of a wound film along a central line, as a consequence of so-called pressure-sensitization, which means that the places of the film which exhibited too high a pressure show these pressure marks after development of the film in the form of spots or streak(s) of increased optical density. According to a particular embodiment of the invention, the described defect is overcome by giving the hub a shape that comprises an outer cylindrical portion which is connected via a central radial web to an inner cylindrical portion. Shrinkage of the web after the cooling down of the moulded hub causes the central portion of the outer cylindrical periphery of the hub to slightly reduce in diameter, whereby occasional protruberances at said locus are withdrawn within the general periphery of the hub. For similar reasons of simplified moulding, it is preferred that the insert is an integral plastics moulding, and that the insert is free from undercuts in opposed mould-release directions. Advantageously, the insert is provided with means for snap-fit engagement within said channel for resisting relative axial movement between the hub and the insert. This makes it very easy to ensure easy insertion and retention of the insert. Preferably, the insert is provided with two projections for engaging marginal perforations of a film web. This promotes a secure retention of the film web against circumferential slippage. It is preferred that the film receiving slot defined by the insert and the channel has a width which increases towards the mouth of the slot. This facilitates insertion of the film end into the slot for retention, and also release on completion of its unwinding. BRIEF DESCRIPTION OF THE DRAWINGS A preferred embodiment of the invention will now be described in greater detail with reference to the accompanying diagrammatic drawings in which: Figure 1 is an axial view of a photographic film winding core in accordance with the invention comprising a hub and a separate insert, the latter being shown in cross-section along the line I-I of Figure 3, Figure 2 is a cross-section of the hub of Figure 1 along the lines II-II, Figures 3 and 4 are respectively elevation and plan views of the insert of Figure 1, and Figure 5 is a detail cross-sectional view to an enlarged scale of the core of Figure 1 assembled and carrying a film web. In the drawings, a cylindrical core 1 for receiving windings of a photographic film web 2 (Figure 5) comprises an integrally moulded hub 3 and an integrally moulded insert 4. The hub comprises an outer cylindrical portion 5 (Fig. 1) which is connected via a central radial web 6 and reinforcing ribs 7 to an inner portion 8. In the embodiment illustrated, the inner portion 8 of the hub 3 defines a circular hole 9 with an optional rectangular keyway 10 for locating the hub 3 on an axle (not shown). In a variant, the inner hub portion 8 defines a square hole for receiving an axle. The hub 3 has an axial channel 11 formed in its outer cylindrical portion 5 and radial web 6, that channel being formed to open outwardly in a chordal direction. In Figures 1 and 5, the channel 11 has an upper wall 12 which is undercut to provide a shoulder 13, and a lower wall 14 which is undercut to provide two shoulders respectively 15 and 16. The lower channel wall 14 is shown in elevation in Figure 2, from which it will be seen that a first shoulder 15 is shaped symmetrically about its centre to provide outer downwardly inclined portions 17, medial horizontal portions 18 and a central downwardly projecting portion 19 bounded by shoulders 20. The integrally moulded insert 4 is shaped to fit into the channel 11. The insert 4 has a base plate defining flanges 21, 22 which respectively engage the shoulders 13, 16 of the re-entrant of the channel 11 to prevent outward movement of the insert when it has been assembled to the hub 3. Upstanding from the base plate of the insert 4 is a yoke 23 which carries at its corners barbs 24 projecting to one side of the yoke, which barbs are spaced, shaped and arranged to engage in performations to be found along the margins of a photographic film web. Upstanding from the base plate of the insert 4 on the opposite side of the yoke 23 to the barbs 24 are two inwardly inclined resilient arms 25. On insertion of the insert 4 into the channel 11 of the hub 3, these arms 25 are first pressed down towards the insert base plate as they bear against one of the inclined portions 17 of the shoulder 15 undercut in the channel 11. As an end of one of those arms 25 passes beneath the projecting portion 19 of that shoulder 15, it will snap up next to the shoulder 20 further from the side of insertion. The length of the downwardly projecting portion 19 is arranged to be substantially equal to the separation of the ends of the arms 25 in this condition, with the result that an end of each arm 25 bears against one of the shoulders 20 and the insert is held against movement relative to the hub in its axial direction. When the insert 4 is inserted into the hub channel 11, the upper wall 12 of that channel and the insert yoke 23 together define a slot 26 for receiving an end of a film web 2 as shown in Figure 5, when marginal perforations which are provided on a film web can engage the barbs 24 to prevent circumferential slippage of the web 2 as it is wound onto the core 1. Slippage is also prevented during unwinding. When the final turn of the film web peels away from the core, the web lifts from the barbs 24 and may bear briefly against the upper wall 12 bounding the slot 26 before the end of the film web is released from the core. The slot 26 widens towards its mouth, so as to provide sufficient clearance between the wall 12 and the barbs 24 to facilitate this release. The hub 3 and insert 4 are each constituted as an integral moulding of plastics material. Due to the design of the hub, it is free from undercuts in opposed axial mould-release directions, and it can thus be moulded easily in a two-part moulding die. The insert 4 is also free from undercuts in opposed mould-release directions, and it too can be moulded easily in a two-part moulding die. This affords considerable benefits in tooling costs, and is also beneficial for the life of the moulding die. According to a particular feature of the present invention, the web 6 operates to cause radial shrinking of a limited central zone of the outer cylindrical periphery of the hub. The lateral limits of such zone 27, see Fig. 2, are indicated by the broken lines 28, and the width of such zone will generally be slightly wider than the thickness of the web 6. The radial shrinking of the peripheral zone 27 causes a tiny peripheral bead which may result from an imperfect closure of both moulding dies, and which is illustrated by dash-and-dot line 29, to become located just under the general outer periphery of the hub whereby an increased local pressure on a wound film is avoided. The magnitude of the radial shrinking described hereinbefore depends on the type of plastic used for the moulding, the thickness of the web 6 as compared with the wall thickness of the cylindrical outer and inner hub portions, etc., and it should be determined on an empirical basis. The mentioned control may entail other deformations of the hub which are not desired and therefore the described feature should be applied with care. Good results have been obtained for a standard 35-mm filmcore, with web thicknesses situated between 2.5 and 4.5 mm for cylindrical hub portions 5 and 8 having a thickness of 2.5 mm. The core in accordance with the present invention may be made in a size suitable for receiving a film web of any required nominal width, for example the core may be made to any of the sizes specified in American National Standard ANSI PH 1.13-1979 or Draft American National Standard PH 22.37. The core may be made in any suitable plastics material, such as polystyrene, polyamide, high density polyethylene, etc., reinforced as the case may be with carbon or glass fibers.

Claims: A cylindrical core (1), for receiving windings of a photographic film web (2), comprising an opening for receiving an end of the film web, a hub (3) having an axial channel (11) communicating with said opening, an insert (4) fitting into said channel, said insert (4) incorporating engaging means (24) for engaging at least one marginal perforation of said film web (2) to prevent circumferential slippage of the film web wound over the core, characterised in that said axial channel extends in a chordal direction, in that the insert (4) engages shoulder means (13,16) of said channel, said shoulder means been arranged to prevent movement of the insert in said chordal direction, in that means (19,25) are provided in the axial channel and in the insert for resisting relative axial movement between the hub (3) and the insert (4), and in that the engaging means (24) are disposed so as to disengage from the film web (2) when the film web is unwound. A film core according to claim 1, wherein said hub (3) is an integral plastics moulding. A film core according to claim 2, wherein said hub (3) is free from undercuts in opposed axial mould-release directions. A film core according to claim 1, 2 or 3, wherein the hub (3) comprises an outer cylindrical portion (5) which is connected via a central radial web (6) to an inner portion (8), the thickness of the radial web controlling the radial shrinkage of the central portion of the outer cylindrical periphery of the hub. A cylindrical core according to claim 4, wherein the wall thickness of the central radial web (6) is larger than the wall thickness of the outer cylindrical portion (5). A film core according to any preceding claim, wherein said insert (4) is an integral plastics moulding. A film core according to claim 4, wherein said insert (4) is free from undercuts in opposed mould-release directions. A film core according to any preceding claim, wherein the insert (4) is provided with means (25) for snap-fit engagement within said channel (11) for resisting relative axial movement between the hub and the insert. A film core according to any preceding claim, wherein the insert (4) is provided with two projections (24) for engaging marginal perforations of a film web (2). A film core according to any preceding claim, wherein the film receving slot (26) defined by the insert (4) and the channel (11) has a width which increases towards the mouth of the slot.

Inventors: BUELENS, EDWARD, DE SMEDT, ROGER FRANS, MUYLLE, WILFRIED EDGARD
Applicants: AGFA-GEVAERT NAAMLOZE VENNOOTSCHAP
Application year: 1988
Main classification: G03B21
IPC codes: G03B21, G03C3