GB2348162A

GB2348162A - A method of providing a line of weakness in packaging film

Info

Publication number: GB2348162A
Application number: GB0003646A
Authority: GB
Inventors: Philip Ferris
Original assignee: MUNDET U K Ltd
Current assignee: MUNDET U K Ltd
Priority date: 1999-02-17
Filing date: 2000-02-17
Publication date: 2000-09-27
Also published as: GB0003646D0; GB9903570D0

Abstract

A method of providing a line of weakness in packaging film used to package articles such as cigarettes or toiletries. The film is subjected to treatment with a laser beam so as to form an elongate groove in the film. The line of weakness formed by the groove is torn to facilitate removal of the article from the packaging.

Description

PACKAGING FILM The present invention relates to a method of producing a line of weakness in packaging film.

Various products are packaged in plastic film, such as polypropylene film, which may be difficult to tear in a controlled manner and to alleviate this problem the film may incorporate an integral tear strip appropriately located so that its removal by tearing facilitates release of the product from the film packaging.

One known type of tear strip comprises an elongate strip of the packaging film bounded on each side by perforations providing lines of weakness which tear easily and in a controlled manner when pulled, typically by an indicator tab incorporated at a free end portion of the strip.

However, perforations compromise the integrity of the film and this type of integral tear strip is therefore unsuitable for products such as medical products, food etc, for which sealed airtight packaging is desirable or necessary.

The problem may be obviated by providing a separate tear strip attached externally to the packaging film to encourage controlled tearing but this is not as cost effective as an integral tear strip in so far as extra material and processing are required for the separate tear strip.

It is an object of the present invention to provide a simple, efficient and cost effective method of providing a line of weakness in film packaging which maintains the integrity of the packaging film.

According to a first aspect of the invention therefore there is provided a method of providing a line of weakness in packaging film wherein the film is subjected to treatment with a laser beam so as to form an elongate groove therein.

With this arrangement, a line of weakness is formed by the groove along which the film can be torn so as to facilitate removal of the packaging, but the integrity of packaging is not thereby compromised.

This method is therefore suitable for packaging film which is to be used to package products for which an airtight seal is considered necessary or desirable. Examples of such products are food e. g. confectionery products, tobacco products e. g. cigarettes, perfumes and toiletries, medical products, videos, cassettes and compact discs etc.

Furthermore, this method affords accurate control of the characteristics of the groove in so far as the laser beam may be precisely controlled.

Preferably the film is moved relative to the laser beam so that the beam traces a path along the film thereby forming the elongate groove.

Preferably, the speed of the film relative to the beam is adjusted, together with the power of the laser beam, to control the depth of the groove relative to the thickness of the film. These parameters are preferably controlled so that the groove is formed by melting the upper part of the film.

Preferably at the same time, the width of the laser beam is adjusted by focusing the beam using, for example, a mirror or a lens, so that as the groove is formed, ridges are formed from the melted film material which is moved in a lateral direction and deposited longitudinally along respective sides of the groove.

These ridges or"wells"provide regions of strength on respective sides of the groove and these act as a guide for controlled tearing along the groove.

By controlling the width and depth of the groove, the tearing characteristics, e. g tear resistance can be controlled.

The groove may be arranged in any suitable manner, for instance it may follow a straight line, a curve etc. There may be a pair of spaced apart grooves which form the boundary of an elongate tear-strip of the packaging film. Alternatively, the boundary of the tear-strip may be formed by a single continuous groove.

With this arrangement, the tear strip may be torn from the packaging to facilitate convenient removal of a product packaged therein in so far as the strip is located in an appropriate position on the packaging. Where an elongate strip is provided, this may include any suitable means of indicator e. g. at a free end of the strip such as a tab or flap, or colouring/texturing of the groove, ridges etc.

The laser beam may be produced by any suitable device, which may be for example a gas laser device. Preferably the laser device is operable to deliver a low power laser beam, and to this end a slow flow gas laser device may be used.

Where more than one groove is required a plurality of laser beams may be used at the same time. However, the heat generated in the film by the laser treatment may cause distortion (crinkling) in the surrounding film.

Thus, when the relative positions of the grooves are such that this would mean that the laser beams are applied close together on the film (for example, in order to provide a pair of spaced apart grooves as referred to above) the distortion generated by treatment with one laser beam may interfere with the accurate formation of a groove by an adjacent beam.

Therefore, where multiple laser beams are used, these may be applied at locations spaced apart longitudinally of the groove.

With this arrangement, the film distorted by treatment with one laser beam may be allowed to cool and'relax' (i. e. flatten) before that part of the film is effected by another/the other laser beam.

The method described above is suitable for any type of packaging film, such as plastic and is particularly suitable for use with polypropylene film.

According to a second aspect of the invention, there is provided packaging film for packaging an article, the film incorporating a line of weakness provided by an elongate groove or grooves which are formed by subjecting the film to treatment with a laser beam or beams.

The invention will now be described further by way of example and with reference to the accompanying drawings in which: Figure 1 is a perspective view of a section of packaging film showing a groove formed according to the invention; and Figure 2 is a section view taken along line AA of Figure 1.

Referring to the drawings, a section of polypropylene packaging film 1 is shown. The film 1 incorporates an elongate tear strip 2 bounded on each side by a respective continuous parallel elongate groove 4. The grooves 4 provide lines of weakness on respective sides of the strip 2.

Each groove 4 is formed by subjecting the film 1 to treatment with a respective one of a pair of laser beams (indicated by arrows X and Y respectively). The film is stored in reel form and is unwound and drawn under the laser beams so that each beam X and Y traces an elongate path on the film defining the perimeter of the strip.

In this embodiment, the grooves 4 are formed simultaneously by a pair of laser beams X, Y which, in use, are positioned spaced apart both laterally of the elongate tear strip 2 (to be formed) and longitudinally (providing a leading beam X and a trailing beam Y).

The lateral spacing determines the width of the tear strip 2.

Heat is generated in that part of the film material under treatment by a laser beam and this heat causes the surrounding film to curl and wrinkle which would interfere with accurate formation of a groove by the other laser beam. The longitudinal spacing of the beams X and Y means that the film distorted by treatment with the leading laser beam X is allowed to cool (thereby relaxing and flattening) before it is treated by the trailing laser beam Y and accurate formation of the grooves is not effected. It will be appreciated that a single laser beam could also be used.

The laser beams are produced by a slow flow (as opposed to a fast flow) gas (carbon dioxide) laser device which incorporates a convex micro lens housed in a nozzle (not shown) with a beam focus window set to 15-20 microns in diameter.

The focal length is micrometer adjusted to 25.4mm.

Focusing of the laser beam is highly critical due to the fact that the film material is very fine, approximately 20 microns thick. The power of the laser beams and the speed at which the film is passed under each beam is adjusted so as to precisely control the depth 8 of the grooves 4. It is essential that the grooves do not extend beyond the thickness of the film, as this would compromise the integrity of the packaging.

The depth 8 of the grooves 4 relative to the film thickness 10 determines the strength of the groove 4 and therefore the tear resistance of the strip 2. The tear resistance should be low enough to facilitate easy tearing but the packaging film must also be able to withstand normal handling.

It has been found that precise control of the beam power and focus to produce a very fine, low power beam allows distortion of the profile of the film in such a way that as the groove is formed, a continuous elongate ridge 12 of material is formed on each side of the groove. The beam from a slow flow laser device produces a laser beam which is powerful enough only to melt and deform the upper part of the packaging film as it is drawn under the beam. The movement of the fine beam along the film shifts the melted material laterally to form the elongate groove and the melted material is deposited as upstanding ridges which extend longitudinally along respective sides of the groove. The ridges or"wells"provide strength along the periphery of the groove and act as a guide for controlled tearing of the strip 2 (as shown in figure 1).

With this method, the grooves formed provide lines of weakness bounded by ridges which enable the film to be torn along the grooves in a controlled manner, but do not compromise the integrity of the packaging. Where a film substrate other than polypropylene is used, the laser beam (s) parameters can be adjusted accordingly.

It is of course to be understood that the invention is not intended to be restricted to the details of the above embodiment which are described way of example only.

Claims

CLAIMS 1. A method of providing a line of weakness in packaging film wherein the film is subjected to treatment with a laser beam so as to form an elongate groove therein.
2. A method according to claim 1 in which the film is moved relative to the laser beam so that the beam traces a path along the film thereby forming the elongate groove.
3. A method according to claim 2 in which the speed of the film relative to the beam is adjusted, together with the power of the laser beam, to control the depth of the groove relative to the thickness of the film.
4. A method according to claim 2 in which the speed of the film relative to the beam and the power of the laser beam are controlled so that the groove is formed by melting the upper part of the film.
5. A method according to claim 2 or claim 3 in which the width of the laser beam is adjusted by focusing the beam so that as the groove is formed, ridges are formed from the melted film material which is moved in a lateral direction and deposited longitudinally along respective sides of the groove.
6. A method according to any preceding claim in which a pair of spaced apart grooves are formed, the said grooves which form the boundary of an elongate tear-strip of the packaging.
7. A method according to any preceding claim in which a single continuous groove is formed, said groove forming the boundary of a tear strip of the packaging film.
8. A method according to any preceding claim in which multiple laser beams are used to form multiple elongate grooves and the said beams are applied at locations spaced apart longitudinally of the groove.
9. Packaging film for packaging an article, the film incorporating a line of weakness provided by an elongate groove or grooves, which are formed by subjecting the film to treatment with a laser beam or beams.
10. A method of forming a line of weakness in packaging film substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.
11. Packaging film substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.