Film or sheet materials are provided currently in roll form within a dispensing pack or dispensing apparatus, and means for cutting the film or sheet by use of a cutter bar may be provided in association with the package or apparatus.

The invention includes such dispensing packs and apparatus when they incorporate the cutter bar of this invention.

As will be appreciated by those skilled in the art, it is not feasible to provide a smooth sharp cutting edge on a package of rolled film used for domestic and household purposes, or even use sharply pointed or very thin teeth on a cutter bar, because of the safety risks in having such a cutting edge unprotected on a dispensing package.

Toothed cutting edges are the preferred cutter bar constructions currently being used in conjunction with dispensing packs.

The construction of cutter bars currently in existence takes a number of forms, the present invention is concerned with cutter bars having a plurality of teeth to form the cutting edge of the bar.

With cutter bars currently in use, the applicant has found that they suffer from the disadvantage that they can tend to tear or stretch the film or sheet material as the cut is being attempted to be initiated.

This is more evident when dispensing and cutting thicker or multi-layer plastic films, but is evident across the range of films and sheets in use today.

This presents a problem with existing cutter bars which needs to be addressed.

The present invention may be employed where the film is of a thin plastics material and the dispenser is a box containing a roll of the film, the box being provided with a cutter bar adjacent an opening in the box through which the film is drawn as is unrolled, and then cut using the cutter bar.

The invention may also be employed where the film is of a paper or paper-like material, or of a thin aluminium material, similarly dispensed from a roll within a box.

In such cases the cutting is usually conducted with the user holding the film with one hand, and the box containing the roll of film in the other hand and pulling the film over the cutter bar. Alternatively, in the case where the box containing the roll of film is secured to a wall or other surface, the film may be held with two hands and pulled down against the cutter bar.

According to the invention there is provided a cutter bar for film or sheet material having two elongated edges and two ends. The cutter bar being

provided on at least the elongated edge with a plurality of teeth along the effective length of said edge; characterised in that at least one tooth at one end of the cutter bar is angled away from the centre of the cutter bar.

In one embodiment of the invention a plurality of teeth at one end of the cutter bar are angled away from the centre of the cutter bar.

In a second embodiment of the invention, the plurality of teeth are grouped together. In this embodiment of the invention the other end of the cutter bar is also provided with a group of teeth, and each tooth of each group is angled away from the centre of the cutter bar.

In a third embodiment of the invention, where angled teeth are provided at both ends of the cutter bar, one group of angled teeth consists of half of the teeth of the bar with each tooth being angled away from the centre of the bar towards one end, and, the other group of angled teeth consists of the other half of the teeth of the bar, which are angled away from the centre of the bar towards the second end.

In a fourth embodiment of the invention the group of angled teeth at one or both ends of the cutter bar will each extend over a length which represents between 15 and 30 percent of the length of the cutter bar.

The cutter bars in accordance with the invention have been found to reduce the stretching and tearing of film or sheet as the cut is being initiated, and to make the remainder of the cutting operation easier to perform. The applicant believes that this may be due to the fact that the angling of the tooth or group of teeth at the end of the cutter bar, outwardly from the centre of the bar, exert a greater holding and/or penetrating force on the film or sheet, whereby to more effectively perforate the film or sheet at its edge, and thus commence the cut in an easier manner and without stretching or tearing. The applicant, however, does not wish to be bound by such a theory.

In order that the invention may be more fully described, a particularly preferred example will now be described with reference to a cutting bar useful for cutting of a plastic film used for wrapping and sealing of household items and with reference to the drawings, in which : Fig 1 is an enlarged view of one end of a cutter bar in accordance with the invention; Fig 2 is an enlarged view of a conventional tooth of the cutter bar, at the one end shown in Fig 1 ; and Fig 3 is an enlarged view of angled tooth of the cutter bar, at the one end shown in Fig 1.

Referring firstly to Fig 1 there is shown one end of a cutter bar 10, which is in the form of a thin elongated strip of metal having a first end 2 and a second end (not shown), together with two edges 6 and 8. Cutter bar 10 is provided on edge 6 with the plurality of teeth 12 which extend for the length of edge 6.

As will be seen clearly in Fig 1, teeth 12 are of two different types, shown at 16 and 14. The majority of cutter bar 10 carries teeth 16, each of which are symmetrical and are directed perpendicularly from elongated cutter bar 10. They have a longitudinal axis 18, perpendicular to the longitudinal axis of cutter bar 10. Teeth 14 appear at end 2 of cutter bar 10 and are angled away from the centre of cutter bar 10. Teeth 14 thus have a longitudinal axis 20, angled away from the centre of the bar and towards end 2.

The amount of angulation of teeth 14 is defined for the purposes of this specification as the"angulation ratio", which can be determined from reference to Fig 1.

The angulation ratio is the ratio of the angles Y and Z which are formed between the perpendicular to the longitudinal axis of the cutter bar and the angle made by edge 22 of teeth 14 for angle Y, and, the edge 26 of teeth 14 for angle Z.

As it is possible for edge 26 to be formed at an angle which is past the perpendicular, to give a tooth in which edges 26 and 22 are not opposed but are angled in the same direction, in determining the angulation ratio it is the numerical size of angle X which is used, irrespective of whether edge 26 is opposed to edge 22 in a particular tooth, or not.

The angulation ratio for the cutter bar of this particular embodiment is determined by the ratio of angle Y to angle Z which in this case is 9: 1.

The angulation ratio for teeth 16 is, because of the symmetrical nature of teeth 16, a ratio of 1: 1. That is angle W is the same as angle X so that W: X = 1 : 1.

Referring now to Figs 2 and 3 and in relation to the shape of the teeth 12, is convenient to define the teeth by reference to the tooth angle A and tooth radius R. The teeth of the cutter bar described in this particular example have a tooth angle A of 60° and a tooth radius of 0.135mm. Tooth radius R is the same for the peak 27 of the tooth as for the curvature 28 between adjacent teeth 12.

The spacing between teeth 12 is 0. 8mm.

The invention is not limited in any way to the foregoing preferred embodiment.

While it is recognised in the art that the ability to cut film relates to the amount of teeth area available for contact with the film, the spacing between teeth can vary from O. 5mm to l. Omm.

The tooth radius R need not be the same either for all teeth on the cutting bars of the invention, or for the peak of each tooth and the curvature between adjacent teeth. Where the radius R is greater for the curvature between teeth than for the peak of each tooth then the angle X shown in Fig 1 will be reduced.

The quantity of teeth 14 that are formed at one end of a cutter bar of the invention can vary between 1 percent and 50 percent of the cutter bar length. The preferred range is a value between 2 percent to 30 percent and the most preferred range is a value between 10 percent to 25 percent.

The thickness of cutter bar 10 may also vary but the comments provided above regarding the safety aspect of cutter bars generally, for use with household packages, apply in relation to the thickness suitable for the cutter bars of the invention, from a safety point of view.

It has been found that an acceptable level of safety can be achieved with a thickness of the cutter bar ranging between 0. 18mm and 0.3mm. The most preferred range for the thickness of the cutter bar is 0. 19mm to 0.22mm.