Shredding or fibrillation method

Abstract

 A method and apparatus for shredding or fibrillating sheet material, such as plastics film. The sheet material is drawn past a series of inter digitating fibrillating members and spacers which rotate. Each spacer (1) is generally elongate and has a concave arcuate portion (3) extending rearwardly from its acute angled leading end (2). The apparatus includes means for reducing the tension of the fibrillating members and/or spacers, once fibrillation has commenced to prevent clogging or jamming caused by the sheet material getting between a spacer and fibrillating member.

Description

[0001] The present invention relates to a shredding or fibrillating method and in particular to a shredding or fibrillating method suitable for shredding or fibrillating plastics materials.

[0002] Currently available shredding or fibrillating methods are able to shred or fibrillate sheet-like paper materials without great difficulty but are not readily able to cope with sheet-like plastics materials. For example, when plastics films of a thickness of about less than 30 microns are passed through conventional shredding or fibrillating machines, the machines frequently clog up. One of the reasons for this is that conventional shredding or fibrillating machines comprise discs machined to a tolerance of approximately one thousandth of an inch. However, a 20 micron plastics film (which is a fairly average film thickness) equates to a machine tolerance of 0.079 of a thousandth of an inch, which is clearly below the machine tolerance of conventional shredding or fibrillating machines. This explains why conventional machines are not able to cope with plastics materials.

[0003] Shredding or fibrillating machines generally work by the action of two sets of inter-digitating cutters and spacers, which rotate thereby drawing the material to be shredded or fibrillated towards and through a shredder/fibrillation head which in turn divides the material into filaments. The rotation of the inter-digitating cutters and spacers causes friction which can act upon the film ( particularly when the film finds its way in between the cutters and spacers). This friction can cause the plastics film to heat up (and even melt) causing the shredder/fibrillation head to jam.

[0004] It is therefore an object ofthe present invention to alleviate some ofthe aforementioned problems associated with conventional shredders or fibrillation machines.

[0005] According to the present invention, there is provided an apparatus for shredding or fibrillating sheet material, such as plastics film, comprising a plurality of interdigitating fibrillating members and spacers, each said spacer being generally elongate having a concave arcuate portion extending rearwardly from the leading end thereof. The invention also extends to a spacer for use in such apparatus, and a method of shredding or fibrillating sheet material comprising drawing said sheet material past a plurality of fibrillating members and spacers as defined above.

[0006] Each elongate spacer preferably comprises two longitudinally extending edges with, preferably, an end portion of a first longitudinally extending edge comprising an acute angled leading end. The concave arcuate portion, preferably terminates at a portion of the second longitudinally extending edge which is opposite and (in use) above the acute-angled leading end.

[0007] Preferably, there is a plurality of such spacers disposed in a spaced array (preferably being substantially equispaced).

[0008] The use of spacers of the nature described above helps to ensure that the film can be drawn past the fibrillating members with minimised risk of wrapping around the fibrillating members so as to cause clogging or jamming.

[0009] According to a second aspect of the invention, the material to be shredded or fibrillated is preferably drawn past a series of inter-digitating fibrillating members and spacers which are at a first tension, and when fibrillation has commenced, the series of inter-digitating fibrillating members and/or the series of spacers are adjusted to a second tension less than the first tension. The invention extends to apparatus for carrying out this method.

[0010] It is preferred that the spacers according to the second aspect of the invention are generally elongate and comprise a concave arcuate portion, extending rearwardly from the leading end, as defined above.

[0011] According to a preferred feature of the present invention, the fibrillating members are preferably provided in a head which is locked into position following adjustment to the second tension. The locking is advantageously carried out with the aid of a locking nut.

[0012] According to a preferred feature of the present invention, the plastics film typically comprises a linear, substantially non-cross-linked polymer, such as polyolefin, polyamide, polyethersulphone, polyetherketone (PEEK). Preferred polymers include polypropylene, polyvinyl chloride and polyester.

[0013] At least a part of the plastics film may be metal-coated. It is preferred that at least one surface of the plastics film is metal-coated and further preferably that both surfaces of the film are metal-coated. A preferred metal is aluminium although other suitable metals include, by way of example, copper, nickel, cobalt, zinc, cadmium, gold and platinum. The term "metal-coated" as used herein is taken to encompass alloy-coated, metal oxide coated and pure metal coated films. The metal coating may be applied to plastics films to a thickness of up to 500 Angstroms which generally gives an optical density in excess of 2.5. Conventional techniques, such as vacuum metallising or sputter coating techniques may be used to apply the metal coating.

[0014] The shredding or fibrillating method according to the present invention can advantageously shred or fibrillate sheet-like material having a thickness of less than 30 microns. Further advantageously, the plastics film, may be shredded into fibrillar elements of width typically of the order of 1mm, possibly with widths as low as 0.05 to 0.1mm.

[0015] An embodiment of the present invention will now be described by way of example only and with reference to the accompanying drawing:

[0016] Figure 1 is a diagrammatic representation of a spacer as used in a method of shredding or fibrillating plastics film, in which there is shown an elongate spacer 1 having an acute-angled leading end 2 and, extending rearwardly from the leading end 2, a concave arcuate portion 3, terminating at an elongate edge 4 of the spacer.

[0017] In a shredding or fibrillation machine, a plurality of the spacers as shown in Figure 1 are disposed in an interdigitating manner with intervening fibrillating members (which may be blades needles or the like). The plastics film is drawn towards a shredder/fibrillation head which divides the film into filaments. The width of the filaments can be varied as required by varying spacing between successive fibrillating members.

[0018] Modifications and variations are envisaged and will be apparent to a person skilled in the art, without departing from the scope of the invention as defined in the appended claims.

Claims

1. A spacer (1) for use in apparatus for shredding or fibrillating sheet material, the spacer being generally elongate having a concave arcuate portion (3) extending rearwardly from the leading end (2).

2. A spacer according to claim 1, having an acute angled leading end (2).

3. A spacer according to claim 1 or claim 2, wherein the arcuate portion (3) terminates at an elongate edge (4) of the spacer.

4. Apparatus for shredding or fibrillating sheet material comprising a plurality of interdigitating fibrillating members and at least one spacer (1) according to any one of claims 1 to 3.

5. Apparatus according to claim 4, wherein said plurality of spacers (1) are disposed in a spaced away.

6. Apparatus according to claim 5, wherein said spacers (1) are substantially equally spaced apart.

7. A method of shredding or fibrillating sheet material, comprising drawing sheet material past a plurality of interdigitating fibrillating members and at least one spacer (1) according to any of claims 1 to 3.

8. Apparatus for shredding or fibrillating sheet material, comprising a plurality of interdigitating fibrillating members and spacers (1) which are at a first tension before fibrillation begins, and means for altering the tension of said inter digitating fibrillating members and/or spacers to a second tension after fibrillation has commenced, in use.

9. Apparatus according to claim 8, wherein said second tension is less than said first tension.

10. Apparatus according to claim 8 or claim 9, including at least one spacer (1) according to any one of claims 1 to 3.

11. Apparatus according to any one of claims 8 to 10, wherein the fibrillating members are in a head, which, in use, can be locked into a desired position following alteration of the tension of the fibrillating members and/or spacers.

12. A method of shredding or fibrillating sheet material, comprising drawing sheet material past a series of inter digitating fibrillating members and spacers which are at a first tension before fibrillation begins, and altering the tension of the fibrillating members and/or spacers to a second tension after fibrillation has commenced.

13. A method according to claim 12, wherein the second tension is less than the first tension.

14. Apparatus according to any one of claims 4 to 6 or 8 to 11, wherein the sheet material is plastics film.

15. Apparatus according to claim 13, wherein the plastics film comprises a linear, substantially non-cross-linked polymer.

16. Apparatus according to claim 13 or 14, wherein at least part of the plastics film is coated with metal, metal oxide or alloy.

17. Apparatus according to any one of claims 4 to 6, 8 to 10 or 13 to 16, wherein the sheet material is of a thickness less than 30 microns.

18. Apparatus according to any one of claims 4 to 6, 8 to 10 or 13 to 17, wherein the sheet material can be shredded into fibrillar elements of width less than 1mm.

Drawing