METHOD AND APPARATUS FOR OPENING FIBRILLATED FILM NETWORKS

Abstract: A fibrillated film (2) in the form of a tube is passed over a former (6) which is tapered out from an initial circumference which is less than the circumference of the unopened fibril­ lated tube (2) to a larger circumference appropriate to the degree of opening required for the fibrillated film (2). The former (6) is constructed so that every point on the perimeter of a transverse cross section is equidistant from the perimeter of any other transverse cross-section. Thus the film is opened evenly. Also, by the adjustment of the collection speed, com­ pensation is made for the reduction in length of the film (2).

Description: , "METHOD AND APPARATUS FOR OPENING FIBRILLATED FILM NETWORKS" jh± present invention relates to a method and apparatus for opening fibrillated film networks. In Particular the present invention relates to a method and apparatus for opening a iibrillated tubular iilm formed by any suitable process Fibrillated tubular films may be opened by gripping the network at each side edge e. g. stentering, an:i stretching the netliork transversely to its length. over, when a fibrillated film is opened in the transverse direction there is a contraction in the length of the film and this reduction in length is, as ill be appreciated, difficult to compensate fcr in a continuous operation wnereir the side edges of the network are gripped. Also such methods of gripping necessarily limit the width of the film which may be fully and evenly opened. The aim of the present invention is to provide a method and apparatus by means of which a fibrillated tubular network can be evenly and fully opened on a continuous basis, it being a simple matter to continuously compensate for the reduced length output in comparison with the input. According to the present invention there is provided a method of opening fibrillated film networks comprising passing a fibrillated tubular film over a former which is tapered out from an initial circumference of less than or equal to the circumference of the unopened fibrillated tube, to a larder circumference appropriate to the degree of opening recuirea of the fibrillated film0 The tubular film may be produced by the conventional processes of blown film technology when a suitable syntheto plastics it:ateril may be extruded through an. annular r n: : bie, The tubular film my be cooled by a controlled air current0 The tubular film is then collapsed to a double-layer sheet by passing over rollers and further orientation of polymer chains in the film is effected in a stretching operation, Preferably the synthetic plastics material is a polypropylene or a copolymer of propylene :ith another olefin such as ethylene or mixtures of such polymers and/or copolymers or a mixture of polypropylene with another polyolefin such as polyethylene, Fibrillation of the to layer film is achieved by any suitable fibrillating process0 One such process is described in our British Patent Specification No. 1,073,741 wherein fibrillation is achieved by passing the film over a rotating pinned roller. The fibrillation process chosen is controlled so that the tuo layers of film are not broken completely apart at the side edges of the film. Alternatively fibrillation may be limited to the central area of the two layer film leaving an tinfibrillated film at each edge. Fibrillation may also be limited to other specific areas to leave other unfibrillated strips, The fibrillated tubular film may alternatively be manufactured by curling a flat film which has already been fibrillated by any suitable method, into a tube. The fibrillated tubular film is then passed over the tapered former to open the film network, In this new method, the input speed of the unopened film is higher than that of the output speed of the opened film by an amount to allow for the contraction in length of the film. There is no cockling of the film as it opens transversely and contracts longitudinally on the former because of the very low frictional resistance at the film to former contact and because of the relatively lo- opening tensions in the film. Also this method of opening guarantees that the full width of the fibrillated film is opened. Further, the opening is even across the circumference of the former. According to a further aspect of the present invention there is provided arparatus for opening a tubular fibrillated film network, comprising a tapered former over which the tube of fibrillated film is passed, the former being tapered out from an initial circumference of less than or equal to that of the unopened fibrillated tube to a larger circumference appropriate to the degree of opening required ef the fibrillated film0 The former may be a smooth rounded cone, a combination of elliptical rings, a flat elliptical plate a a bowed bar. It is holever essential that the displacement of the network be kept to a minimum in one plane e. g. the horizontal plane. Thus bowed bars, plates and formers with ellipsoidal shave of minimal minor axis are preferred. To ensure this even opening through to the lay flat wound two pls sheets of fibrillated film, it is important that the topography of the former is designed that each element of the opened networ- travels e same distance over the former0 The shape of the ferner after the largest value of minor axis must be developed so that this is possible, all points on the former at a specific transverse section being equidistant from the said initial circumference of the former. The opening properties of the tubular fibrillated films and their handling and bonding properties in the final matrix beins reinforced, may be enhanced by incorporation in the polymer of silanes, such as ethyl polysilicates and methacryloxypropyltrimethoxy silane types, silica (precipitated or acrogel), silicone glycol copolymer and polyvinylalcohol. These additives may be hydrophobed or not. Other additives include chalk, carbon, alumina, magnesia and other naturally occurring oxides and carbonates. Surface treatments may also be applied such as typical surfactants and antistat agents suitable for treating polypropylene and silica gels. To stabilize the opened out fibrillated netw various alternative operations or combinations of operations are possible. These deend on the heat con of the network before opening, its previoLs thermal history with respect to relaxation or annealing process (previously heat cat net;orks are more difficult to stabilise, and the thickness of the film0 To provide this stabilization heat may be applied through or at tr former, or a stentering machine may be used to hold out the opened web. Alternatively the opened web may be heated by passage through a heat chamber or over a heated surface before collection on, for example, a winder. A further alternative is to steam or heat the web when collected by the winder. The opened tubular web may be separated into two separate layers by the provision of a slitting device. This may, ior example, take the form of a hot blade or other mechanical cutting device, Such opened fibrillated networks, singly or multilayered may be used for reinforcing a water-hardenin moss e.g. cement, resins, paper and other media, which are sufficiently low in viscosity in their state before curing or dewatering. These networks also have interest general textile properties which make them attractive for non-woven fabric end-uses which include interlinings, waddings and filtration cloths. The present invention will now be further described, by way of example, with reference to the accompanying drawings, in which Fig. 1 diagrammatically illustrates the position of one embodiment of former according to the present invention, in an apparatus for producing a web network, Fig. 2 is a plan view of the former of Fig. 1 use, Fig. 3 is a diagrammatic side view of the forma 2, showing the splitting of the tubular fi. Fig. 4 illustrates one method of retairing the web in an opened condition, Fig. 5 illustrates in greater detail, the gripping means of Figo 4, Fig. 6 is a detail of the means of Figs. 4 and 5 ashen in use, Figo 7 is a perspective view of the ormer of Figs0 1 to 4; and Fig. 8 diagra:iatically illustrates a further embodiment of former in accordance with the present invention Apparatus for producing an opened web network from a tubular film is diagrammatically illustrated in Fig. lo The tubular film 1 which is fed in the direction indicated by arrow A is formed by any suitable method. It can be produced by extrusion through an annular ring die (not shown) or by curling a flat film into a tube. The tubular film is collapsed to a double-layer sheet 2 by, for example, being passed over rollers (not shown), and is passed over a rotating fibrillating roller 3 which has outwardly projecting pins 4 which create stag gered slits in the sheet 2. his form of fibrillation is described in detail in our British Patent Specification No, 1,073,741. However, alternative fibrillation methods may be used as desired, As a further alternative the fibrillated sheet may be formed from one or more fibrillated sheets which are curled or joined to form the tube which is subsequently flattened0 The fibrillated double-layer sheet 2 is then passed around a number of guide rollers generally designated 5, and is engaged over the tapered former 6. As can be best seen in Figo 2, the generally conical shape of former 6 causes the tubular film to expand resulting in the slits formed by fibrillation, opening to form an opened tubular network. Cutters 7 in the form of heated blades. slit the sides of the opened tube as it leaves former 6, thaws converting tr opened tubular netalor - into two generally planar opened networks which may be collected together as at 8 in Fig, 3, and passed to a winder assembly, as indicated at 9 in Fig. 4. To compensate for the reduction in length of the network by virtue of the later stretching, winder assembly 9 collects the opened network at a slower rate than the rate at which the fibrillated film 2 is fed to former 6 by feeder F. This differential speed arrangement together with the tapered former 6 of the present invention, thus simply overcomes the problems experienced in prior art constructions, wherein lateral stretching is produced by outside gripping means. Do prevent the opined network from retracting towards its originalform after it has left former 6, the opened network can be treated with, for example, heat or the side edges 10 of the film can be gripped by suitable means such as the caterpillar grips 11 shown in Figs, 4, 5 and 6. The caterpillar grips 11 each comprise two endless belts 12 between which the film passes, the belts being guided around rollers 13 and 14o As seen in Fig. 6, the belts 12 have regularly spaced projections 15 on their outer surface and these projections 15 engage in the opened out slits 16 in the film, produced by fibrillation, and thus hold the film in its expanded state a Figs 7 shows a perspective view of the former 6 which is tapered to a smooth point 17 and has a very small depth in comparison it its width. Whilst the illustrated former is solid it may alternatively be hollow and if so, the former car be filled with a heated fluid e. g. oil or water, to assist heating and stabilization of the opened web0 Fig. 8 shows an alternative embodiment of ormer which comprises a combination of different size elliptical hoops 1 8o Whilst the minor ates of the hoops 18 are approximately the same, the major axes of the hoops vary so as to provide an overall configuration similar to that of the former of Figo 7. his has the advantage that it is cheap to manufacture. However, it is difficult to provide uniform heating for the web from the frameÂ over heat can be supplied directly to the web by convective andlor radiative transfer eOgO hot air and/or radiant heaters respectively. An example of a specification for a typical tubular Ilbrillated network process is now provided; SPECIFICATION Polypropylene Polymer (9S) M.F.I. = 1o5 Polyethylene (10ss) H.D.P.2. M.F.I.=1.5 Extruder 22000 Die 23000 First haul-off speed lOm/min Stretch haul-off speed 75m/min Fibrillator 650 rpm for 16 pins/cm Stretch oven temp 15000 Third haul-off speed 68m/min Relaxation oven temp 120 C Final film of 30 micron thickness (2ply) For width of collapsed tube = 20 cm The tube was passed onto a wedge former of circumference 110 cm to produce 5 x opening of the fibrillated network. The handling of fibrillated films of < 30 micron and above 150 micron is envisaged to be practical. The opening properties of the tubular fibrillated film and their handling and bonding properties in the final matrix being reinforced, can be enhanced by the incorporation in the polymer of silanes, such as polysilicates and methacryloxyproplytrimethoxy silane types, silica (precipitated or aerogel), silicone glycol copolymer and polyvinylalcohol. Other possible additiv include chalk, carbon, aluminium, gnesia and other naturally occuring oxides and carbonates. Surface treatments may also be applied such as typical surfactan and antistat agents suitable for treating polypropylene and silica gels, Once opened the network can be stabile by treatment with heat or it may be held open by mechanic means as described rove. The present invention thus provides a simple but effective method and apparatus for opening fibrillated film networks. These networks are especially useful either singly or in multi layer arrangements, as a reinforcement in water hardening masses.

Claims: DESCRIPTION DESCRIPTION "METHOD AND APPARATUS FOR OPENING FIBRILLATED FILM NETWORKS" The present invention relates to a method and apparatus for opening fibrillated film networks. In particular the present invention relates to a method and apparatus for opening a fibrillated tubular film formed by any suitable process, Fibrillated tubular films may be opened by gripping the network at each side edge e. g. stentering, and stretching the network transversely to its length. However, when a fibrillated film is opened in the transverse direction there is a contraction in the length of the film and this reduction in length is, as will be appreciated, difficult to compensate for in a continuous operation wnerein the side edges of the network are gripped Also such methods of gripping neeessa-ily limit the width of the film which may be fully and evenly opener. The aim of the present invention is to provide a method and apparatus by means of which a fibrillated tubular network can be evenly and sully opened on a continuous basis, it being a simple matter to continuously compensate for the reduced length output in comparison with the input. According to the present invention there is provided a method of opening fibrillated film networks comprising passing a fibrillated tubular film over a former which is tapered out from an initial circumference of less than or equal to the circumference of the unopenea fibrillated tube, to a larder circumference appropriate to the degree of opening required of the fibrillated film. The tubular film may be produced by the conventional processes of blown film technology when a suitable synthetic plastics material may be extruded through an. annular ring die, The tubular film may be cooled by a controlled air current, The tubular film is then collapsed to a double-layer sheet by passing the former (6) is a tapered cone which has a major and a minor axis when considered in transverse cross-section. 10. Apparatus as claimed in claim 9, in which the cone ns hollow to enable a heating medium to be passed therethrough. 11. Apparatus as claimed in claim 8, in which the former (6) comprises at least two different sive rings (18) arranged co-axially with respect to each other and parallel to each other, the rings (18) each having a major and a minor axis. .12. Apparatus as claimed in any one of claims 8 to 11, in which the former (6) is designed so that every point on the perimeter of a cross-section of the former (6) transverse to the intended direction of feed of the tubular film, is equidistant from the perimeter of any other transverse cross-section of the former (6). 13. Apparatus as claimed in any one of claims 8 to 12, in which cutters (7) are provided for cutting the tubular opened network as it leaves the former (6), to produce two substantially plantar networks parallel to each other. 14. Apparatus as claimed in any one of claims 8 to 13, in which grippers (11) are provided for gripping the side edges of the opened network after it leaves the former (6), to thus retain the opened configuration. 15. Apparatus as claimed in claim 14, in which the grippers (11) are formed by pairs of contiguous endless belts, 16. Apparatus as claimed in any one of c12irs 8 to 15, in which a winder assembly (9) is provided for collecting the opened network, the winder assembly (9) being arranged to collect the network at a slower speed than the speed at which it is fed to the former (6) by feeding means (F).

Inventors: ELLIS, DAVID GEOFFREY, FIRTH, COLIN, JOHNSON, DEREK RAYMOND, WARD, TREVOR
Applicants: PLASTICISERS LIMITED
Application year: 1979
Main classification: B29D31
IPC codes: B29C45, B29D28, B29C53, B29C71