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(11) | EP 0 781 633 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | A cutting device for thin, flexible materials |
| (57) The present invention is a cutting device (10) for films. The cutting device according
to the present invention further comprises bristles (20) which prevent the film to
elongate and wrap around the knife. Consequently, the cutting device ensures always
a complete cut through the thickness of the film, even when the film is thin and flexible. |
Field of the invention
Background of the invention
[0002] A wide variety of single-use type packaging materials are known. Many of said packaging materials are in the form of thin, flexible films. The thin, flexible films may comprise a single layer of one material or of different layers of different materials. The various layers in a film allow to obtain a composite, multi-layer material in a desired combination of properties otherwise not available from a single layer of a single composition. It is hereinafter understood that a "thin" film means a film having a thickness of less than 200 µm.
[0003] The material or materials of the film can be variably chosen in function of the protection needed for the contained material. For example, in the field of detergent packaging containing detergent there are severe demands upon the properties of the film. Such properties are, for example, moisture impermeability, gas impermeability, ultraviolet rays-intercepting property, water-proof property, mechanical strengths, cost, flexibility, and the like. In particular, for dry laundry compounds, which sometimes are compositions sensitive to moisture and/or oxygen, the film can comprise a moisture and/or oxygen barrier layer.
[0004] Thin, flexible films are considered by the packaging industry to very interesting from the environmental viewpoint. Indeed, the amount of packaging material can be reduced by using thin films to make packaging, like bags or pouches. The films can be re-formed into flexible bags. These may be manufactured according to the methods well known to the man skilled in the art, and described for example in the U.S. Patent No. 3 380 646 or in the document EP-A-626 319. The process may be a continuous, a semi-continuous or a multi-step batch process. The process of re-forming the film into a packaging comprises several steps, inter alia cutting or severing of parts of the film with a cutting device, for example to divide formed bags one from another. We found that thin, flexible films have the tendency to elongate and to wrap around the cutting device. This may result in an uncompleted cut through the thickness of the film.
[0005] It is therefore an object of the present invention to provide a cutting device which cuts efficiently through the thickness of a thin flexible film.
Summary of the invention
[0006] The present invention is a cutting device for films comprising a knife. The cutting device further comprises bristles. The bristles are fixed at one end and are free at the opposite end of the bristles. These bristles are placed in such a manner that when cutting the film is placed between the knife and the bristles. The bristles are disposed substantially parallel to each other and substantially perpendicular to the film when cutting the film whereby the open ends of the bristles point towards the knife.
Brief description of the drawings
[0007] Figure 1a is a cross sectional view of a cutting device of the prior art. Figure 1b is the cutting device of Figure 1a during the cutting procedure of a film.
[0008] Figure 2a is a cross sectional view of a cutting device according to the present invention. Figure 2b is the cutting device of Figure 2a during the cutting procedure of a film.
Detailed description of the invention
[0009] The material of the film for the present invention may be selected from the group consisting of: tissue, metal, paper, cardboard, plastic materials and a combination thereof. As plastic materials polyolefines, like polyethylene (=PE), or (oriented) polyethylene terephthalate, or (oriented) polypropylene or a combination thereof, may be used. When the film is a multi-layer material, the intermediate layers may comprise, for example, a perfume barrier layer, a gas barrier layer, an oxygen barrier layer, a moisture barrier layer, or a combination thereof. Preferably, the intermediate layer is made of a material selected from the following group consisting of: aluminium (metal) foil, ethyl vinyl alcohol co-polymer (=EVOH), lacquer coating and a combination thereof. Possible lacquer coatings are, for example, Flexplastol ® 2KB-Lacquer 9A 918 920 or Flexoplastol ® 2KB-Lacquer 9A 919 920 commercially available from BASF Lacke + Farben AG, Stuttgart.
[0010] The film comprising multi-layers may be achieved by laminating the layers together. The lamination of layers means that the different layers are attached to each other in a solid state, i.e. the different layer are not melted together as in the extrusion process. In the lamination process lower temperatures with respect to the extrusion. As a preferred option, a tie layer may be used at least on one side of the intermediate layers to strengthen the bonding between the intermediate layers and the other layers. Said tie layer is preferably made of glue. A preferred glue is a polyurethane-based adhesive. By polyurethane-based adhesives we intend all the adhesives based on polyurethane known to the person skilled in the art. In particular, solvent based (including water) and solvent-free adhesive systems comprising polyurethane are usable for the purpose of the present invention. This tie layer can be also applied on both sides of said intermediate layer and/or of the other layers.
[0011] Figure 1a illustrates an example of a cutting device of the prior art. This cutting device is usually used in a packaging machine, specifically in packaging machines suitable to form films into a packaging, like a bag or a pouch. These packaging machines include inter alia at least one cutting device (10). The cutting device comprises a knife (12). As hereinafter referred to, "knife" means any device which is able to cut through the thickness of a film. The cutting device may be used to severe parts of the film to form a bag or a pouch in a certain geometrical configuration, or to cut the formed bags or pouches to separate the single bags or pouches from each other. The function of the cutting device is described, for example, in the U.S. Patent No. 3 380 646 or in the document EP-A-626 319.
[0012] To allow a neat cut by the cutting device, the film is usually fixed before the cutting. The film is fixed in such a manner that the film is unable to move in any direction. Figure 1a actually shows a film (1) which is fixed, for example, with a clamp. The film is fixed between the two halves (14, 14') of a clamp. One half of the clamp (14) allows the knife (12) to reach the film fixed between the clamp and to cut through the thickness of the film in a perpendicular direction with respect to the film. The opposite half (14') of the clamp comprises a sufficient space (15) to enable the cutting movement of the knife. As schematically illustrated in Figure 1b, we found that especially thin and flexible film have the tendency to elongate and to wrap around the knife. Consequently, it is possible that the film does not succeed in cutting through the entire thickness of the film, resulting in an uncompleted cut.
[0013] To solve this problem, the cutting device according to the present invention further comprises bristles (20), as shown in Figure 2a. These bristles are located opposite to the knife such that the film is between the bristles and the knife. In our example above, where the film is clamped, the bristles are located in the space (15) of the half (14') of the clamp opposite the knife. The bristles are disposed substantially parallel to each other and substantially perpendicular to the film when cutting the film. This means that when the knife makes its cutting movement, the knife pushes the film against the bristles, as shown in Figure 2b. The bristles reduce the space for elongation of the film, since the movement of the film is blocked by the bristles. Consequently, the film is prevented by the bristles to further elongate and wrap around the knife, as in the example shown in Figure 1b. Nevertheless, the bristles do not impede the knife to perform its cutting movement. Indeed, the open ended bristles allow the passage of the knife in between the bristles. Therefore, the knife achieves a clean, complete cut through the thickness of the film.
[0014] The bristles are made of a material which resistant enough to prevent any further elongation of the film which may result into an uncompleted cut through the thickness of the film. In particular, we found that the thickness of the film and the thickness of the bristles and the density of the bristles are important parameters to determine if the bristles oppose a sufficient resistance to a further elongation of the film. The "density of the bristles" is given by the number of bristles interacting per unit area of the surface of the film. Preferably, the bristles are made of metal filaments, more preferably filaments of made of steel.
[0015] The upgrade of the cutting device further comprising the bristles is cheap and simple. Indeed, the bristles may be grouped in a kind of brush which is then fixed on the cutting device opposite the knife with the open ends of the bristles pointing towards the knife. The position of the bristles with respect to the position of the knife does not require a high precision, since the thickness of the bristles is usually much smaller than the dimensions of the knife. Consequently, a high tolerance between the dimension of the bristles and the dimension of the knife is given. We further found that the bristles clean the knife at least partially from the plastic residues after each cutting movement, especially when the bristles are made of metal. Therefore, also a reduced maintenance of the cutting device can be achieved.
1. A cutting device (10) for films comprising a knife, characterised in that the cutting device further comprises bristles (20), the bristles being fixed at one
end and being free at the opposite end of the bristles, the bristles being placed
in the cutting device in such a manner that when cutting the film is placed between
the knife and the bristles, the bristles being disposed substantially parallel to
each other and substantially perpendicular to the film when cutting the film whereby
the free ends of the bristles point towards the knife.
2. A cutting device according to claim 1 characterised in that the bristles (20) are
made of metal filaments.
3. A cutting device according to claim 2 characterised in that the bristles (20) are
made of filaments made of steel.
4. A cutting device according to any of the preceding claims characterised in that the
bristles (20) are grouped together to form a brush.