The present invention concerns polymeric packaging films, and in particular tear tapes to enable easy opening of packages formed from such films.

Flexible polymeric films are widely used as packing materials for a vast range of goods.

A variety of polymers are used for producing such packaging materials. These poiymers can be synthetic polymers, such as polyolefsns {e.g. polyethylene and/or polypropylene), polystyrene and polyesters; natural poiymers, such as cellulosic materials and biopolymers (e.g. polylactic acid); or combinations of both synthetic and natural polymers.

One particular packaging use for such films is as an overwrap for a variety of goods, for example cigarette packets, video tapes, cookies etc. In this packaging use, the films are tightly sealed over the goods. However, the very properties which confer desirable properties on the films as packaging materials, for example high strength and tear resistance, make such packages difficult to open because the films of which they are made are difficult to tear.

In order to facilitate the opening of such packages, so-called 'tear tapes' have been provided which consist of a narrow strip of a polymeric film adhered to the internal surface of the packaging film, a tab of the tear tape being left free on the outside of the package to facilitate its opening. The package can then be opened by pulling the fear tape through the packaging film. Conventionally, the tear tape is adhered to the packaging film using a pressure sensitive adhesive, for example melted wax, A major problem associated with using pressure sensitive adhesives to attach the tear tape to the packaging film is the resultant reduction in the barrier properties of the packaging film.

More recently, it has been found that the tear tape can be directly heat sealed to the packaging film, for example, by disposing a heat sealable layer on the tear tape and/or packaging film. Suitable materials for the heat sealable layer include ethylene vinyl acetate (EVA), ethylene methyl acrylate and ethylene acrylic acid. However, directly heat sealing the tear tape to the packaging film can have drawbacks such as the formation of unsightly wrinkles on the packaging film in the region surrounding the heat sealed tear tape.

As an alternative to tear tapes, it is also known to use ^f tear strips' in a film. Tear strips differ from tear tapes in that a tear strip is integral to the film itself, rather than a separate film located adjacent to the packaging film. A tear strip is typically defined by two parallel lines of weakness in a film, so that when the tear strip is pulled in a direction generally away from the rest of the packaging, the lines of weakness break in a controlled manner and the packaging can be opened.

GB 1 508 309 discloses a wrapper of polyolefin film having a polyolefin tear tape heat sealed directly thereto by a heat seal extending longitudinally along the tear tape, the polyolefin of the tear tape being compatible with the polyolefin of the wrapper and having a melting point at least 12 ^a C higher than that of the polyolefin wrapper.

WO 32/00192 discloses a method of making a packaging material which includes the steps of providing a tear tape having a fusible coating, contacting the fusible tear tape coating with a surface of a wrapping materia! and directing radiant energy towards a portion of the fusible coating.

US 3,892,057 discloses a plastic film wrapper with a tear tape, the tear tape being heat- sealed along each edge to the film by an edge-to-edge seam Le, the plastic film of the wrapper is not continuous beneath the tear tape.

US 3,098,601 discloses a heat-sealable thermoplastic tear tape fused to the surface of a web of heat-sealable thermoplastic packaging material so that the long dimension of the tear tape is substantially at right angles to the long dimension of the packaging material,

US 5,996,784 discloses a cigarette pack consisting essentially of a thermoplastic film. The cigarette pack has an opening device also made from a thermoplastic material which comprises a thermoplastic tape disposed on the side of the pack exposed to the atmosphere and a tab provided at the end of the tape. The thermoplastic tape is fixed in place over a nominal tear point in the film forming the pack,

US 5,366,295 discloses a flexible liquid impermeable package in the form of a tubular bag with a tear strip for opening the bag. The package comprises a monoaxiaily stretched film which gives it an orientation in one direction and a tear strip which is parallel to the orientation of the film so that the film can be torn along a straight line formed by the weld line between the film and the tear strip without any need for a weakening line to be formed in its thickness.

US 6,416,841 and US 6,749,877 disclose a heat resistant and heat seaiable tear tape that can be used with a plastic package. The tear tape comprises a layer of an oriented film and a layer of a polymer sealant material, such as ethylene vinyl acetate, which has a melt temperature of below approximately 22Q°F,

EP 0 779 219 discloses a method for sealing a narrow tape to a heat sealable strip, especially in cigarette packing machines. The method involves feeding the narrow tape and heat sealable strip, overlapped and correctly positioned, to a sealing unit and then joining them with an ultrasound sealer.

EP 1 754 587 discloses a tearing strip capable of heat shrinkage, consisting of a biaxially oriented carrier foil formed of at least one thermoplastic polyo!efin or olefin- copolymerisate. The elasticity modulus of the tearing strip at room temperature is at least 220 M Pa longitudinally and at least 1400 MPa laterally,

US 2004/0087331 discloses a biodegradable tear-off strip made from a backing film, one surface of which has a sealable layer and the other surface of which has a release layer, wherein at least the backing film has monoaxial orientation and is composed of a biodegradable aliphatic polyester and/or copolyester.

It is also known for tear tapes themselves to contain security features.

EP 1 050 484 discloses a tear strip with security markings which consists of a thermoplastic monoaxially oriented carrier film provided with micro-printing on one side a further provided with a sealing layer on one side and optionally a release layer on the other side. There is a need for an easy-open tear tape mechanism for film packaging which does not suffer from the disadvantages of the prior art. From the description that is to follow, si will become apparent how the present invention addresses the deficiencies associated with the prior art, while presenting numerous additional advantages not hitherto contemplated or possible with prior art tear tape mechanisms.

According to the present invention there is provided a polymeric film web for packaging applications, the film web having a machine direction and a transverse direction and comprising: a polymeric substrate having a major surface; and an elongated strip of material overlaid on the major surface and sealed thereto by means of a heat seal, the materia! of the elongated strip being at least predominantly composed of the same material as the polymeric substrate so that the material of the elongated strip and that of the polymeric substrate bsodegrade or compost at substantially the same rate and/or shrink on the exposure of the film to heat at substantially the same rate and/or by substantially the same amount in one or both of the machine and transverse directions of the film web.

What is meant by 'predominantly composed of the same materiar is that the elongated strip comprises at least about 80%, at least about 85%, at least about 90%, at least about 95%, at least about 97% or at least about 99% of the same material as the polymeric substrate. Preferably, the elongated strip is formed of the same material as the polymeric substrate.

The 'machine direction' is the direction in which the film passes through the machine during manufacture. The 'transverse direction' is perpendicular to the machine direction. The elongated strip of material is a tear tape. The purpose of the elongated strip of materia! in the film web of the invention is to provide, in a package formed from such a film, an easy- open tear tape mechanism. The invention also concerns a sheet of film severed from the film web. When a sheet of film in accordance with the invention is severed from the film web, it may be provided with a tear tab which protrudes from the surface of the sheet of film. The tear tab may be provided at one end of the elongated strip and may be integral therewith. Thus, the tear tab may be formed of substantially the same materia! as the elongated strip, in a package formed from such a sheet, the protruding tear tab provides a means of easily opening the package by pulling the tab and consequently tearing the film along the line of the elongated strip.

The invention consequently provides a package formed from a sheet of film in accordance with the above; and also an article wrapped or otherwise packaged with such a sheet of film.

The film of the invention provides significant advantages over prior art films in terms of biodegradability, compostability, shrink and/or barrier properties. By ensuring that the elongated strip is at least predominantly composed of the same material as that of the polymeric substrate, the invention provides a means for forming an easy open package in which desirable properties such as biodegradability, compostability, shrink or barrier exhibited by the substrate of the package are not compromised by the easy-open mechanism itself.

When the film of the invention is a biodegradable or compostable film, the polymeric substrate may itself be formed from a biodegradable material, Preferably, the biodegradable materia! is formed from a biopolymer such as: cellulose, a ce!!ulosic derivative such as cellulose acetate, polylactic acid (PLA), PHA or another starch, or a polysaccharide based material Consequentiy, the elongated strip is at least predominancy composed of the same material.

In this embodiment, the advantage of biodegradability or eompostabsiity is provided for the entire film. A further advantage is that the constituent parts of the film i.e. the polymeric substrate and the elongated strip, biodegrade or compost at the same rate,

When the film of the invention is a shrink film (i.e. a film that shrinks when exposed to heat) the polymeric substrate may itself be formed from an oriented material. Preferably, the oriented material is formed from a polyolefin (e.g. polypropylene, polyethylene and/or polybutylene), a polyurethane, a polyester (e.g. polyethylene terephtha!ate), a polyamide (e.g. a nylon), a polyvinylha!ide (e.g. PVC), a PvdC material and/or combinations thereof. Consequently, the elongated strip is at least predominantly composed of the same material.

In this embodiment, when the film is used in a packaging application and exposed to conditions of elevated temperature to shrink the film around a package, the material of the elongated strip advantageously shrinks at substantially the same rate or by substantially the same amount as the polymeric substrate, thus, largely preventing the appearance of unsightly wrinkles in the region of the package surrounding the opening mechanism.

The film of the invention does not require a pressure sensitive adhesive to adhere the elongated strip to the polymeric substrate. Rather, the elongated strip is heat sealed to the polymeric substrate. This is advantageous as there is no reduction in the barrier properties of the film. Further advantages include a reduction in the cost of production and the ability to manufacture fully biodegradable films. The polymeric substrate and/or elongated strip may have at least one heat sealing surface with a wide heat seal range. Preferably, the polymeric substrate and the elongated strip each have at least one heat sealing surface with a wide heat seal range, which can be effectively heat sealed together. In the case of the polymeric substrate, the at least one heat sealing surface coincides with the major surface of the polymeric substrate. The heat sealing surface may have a sealing temperature range of from about 100°C to about 150°C. Preferably, the heat sealing surface has a sealing temperature range of from about HOT to about 140T. 0 The polymeric substrate and the elongated strip may be heat sealed together to give a seal strength of at least about 100g/25mm, at least about 150g/25mm, at least about 20Qg/25mm, at least about 250g/25mm, at least about 300g/25mm or at least about 350g/25mm. Preferably, the polymeric substrate and the elongated strip are heat sealed together to give a seal strength of between about 150g/25mm and about 35Qg/25mm,5 more preferably, a sea! strength of between about 200g/25mm and about 300g/25mm, even more preferably, a seal strength of between about 220g/25mrn and about 280g/25mm _f and more preferably still, a seal strength of between about 240g/25mm and about 260g/25mm, 0 The heat sealing surface may be provided by a distinct heat sealing layer within the polymeric substrate and/or elongated strip. The distinct heat sealing layer may have a thickness of from about 0.10 μηι to about 1.5 μηι, Preferably the distinct heat sealing layer has a thickness of from about 0.15 μηη to about 1 μηι , The distinct heat sealing layer may be formed from a polyolefin such as polyethylene, polypropylene and/or polybutylene; aS polyurethane; a polyester; a poiyarrside; a polyvinyihaiide such as PVC; a polyvinylidene halide such as PvdC; a po!yacryiate; an acrylic acid; or copolymers, terpolymers or combinations thereof. Alternatively, the material of the polymeric substrate and/or elongated strip may be inherently heat sealable without the need for a distinct heat sealing layer.

The elongated strip may be heat sealed to the major surface of the polymeric substrate by passing the elongated strip and polymeric substrate over a heater bar. The temperature of the heater bar may be greater than about 18CTC, greater than about 17Q°C, greater than about 180ºC, greater than about 190ºC or greater than about 200X. Preferably, the temperature of the heater bar is in the range of from about 19QT to about 210ºC , more preferably, from about 195ºC to about 205ºC. The temperature of the heater bar is crucial to the formation of an effective heat seal between the polymeric substrate and elongated strip. If the temperature is too low, then the heat seal will not form. However, if the temperature is too high then the structure of the polymeric substrate and/or the elongated strip will decompose.

The elongated strip may be heat sealed to the major surface of the polymeric substrate such that it is substantially in-line with the machine direction of the polymeric substrate.

The polymeric substrate and/or the elongated strip may have a thickness of at least about 10 ,um, at least about 15 μπι, at least about 20 μνη, at least about 25 μm, at least about 30 μτη or at least about 35 μπ\. Preferably, the thickness of the polymeric substrate and/or the elongated strip is from about 20 μτη to about 40 μηι, more preferably still, from about 20 μηι to about 35 ₍ um, and most preferably, from about 25 μηι to about 30 μηι.

Both the polymeric substrate and the elongated strip may comprise a filmic material. The filmic material, prior to the deposition of any additional layerfs), may comprise a biopolymer such as cellulose, a cellulosic derivative such as cellulose acetate, poiylactic acid (PLA), PHA or another starch, or a polysaccharide based material; a polyoiefin such as polypropylene, polyethylene and/or polybuty!ene; a po!yurethane; a polyester such as polyethylene terephthalate; a polyamide such as a nylon; a poiyvinylhalide such as PVC; a PvdC material; and/or copolymers, terpoiymers or combinations thereof.

When the film of the invention is a biodegradable or compostable film, preferably the filmic material comprises a bsopolymer such as: cellulose, a cellulosic derivative such as cellulose acetate, poiylactic acid (PLA), PHA or another starch, a polysaccharide based material, or combinations thereof. More preferably, the filmic material comprises cellulose.

When the film of the invention is a shrink film, preferably the filmic material comprises a polyoiefin such as polypropylene, polyethylene and/or polybutyfene; a polyurethane; a polyester such as polyethylene terephthalate; a polyamide such as a nylon; a poiyvinylhalide such as PVC; a PvdC material; and/or copolymers, terpoiymers or combinations thereof, More preferably, the filmic material comprises polypropylene.

The filmic material may be made by any process known in the art, includsng, but not limited to, techniques of casting films as thin sheets through narrow slit dies, and blown-film techniques wherein an extruded tube of molten polymer is inflated to the desired bubble diameter and/or film thickness.

The filmic material may comprise a biaxially orientated film, for example a biaxially oriented polypropylene {BOPP} film. The biaxially oriented film may be prepared as a balanced film using substantially equal machine direction (M D) and transverse direction (TD) stretch ratios, or can be unbalanced, where the film is significantly more orientated in one direction (usually the TD). Sequential stretching can be used, in which heater rollers effect stretching of the film in the machine direction and a stenter over is thereafter used to effect stretching in the transverse direction. Alternatively, simultaneous stretching, for example, using the so- called bubble process, or simultaneous draw stenter stretching may be used. In the bubble process, the film is extruded in the form of a composite tube which is subsequently quenched, reheated, and then expanded by internal gas pressure to orient in the TD. The film is then withdrawn at a rate greater than that at which it is extruded, to stretch and orient it in the M D.

The degree to which the film is stretched depends on the nature of the film and to some extent on the ultimate use for which the film is intended. For a polypropylene film, satisfactory tensile and other properties are generally developed when the film is stretched between 3 and 10, preferably 7 or 8, times its original dimensions in each of the TD and MD,

After stretching, the biaxially oriented film may be heat-set, while being restrained against shrinkage or even maintained at constant dimensions, at a temperature above the glass transition temperature (Tg) of the polymer but below its melting point. The optimum heat- setting temperature can readily be established by simple experimentation, for example a polypropylene film is heat-set at temperatures in the range of from about I0GT to about 160°C. Heat-setting may be effected by conventional techniques, for example, by means of a stenter system, one or more heated rollers (e.g. as described in GB 1124886) and/or a constrained heat treatment (e.g. as described in EP 023776),

In a preferred embodiment, the film of the invention is a shrink film wherein both the polymeric substrate and elongated strip comprise a biaxially oriented film. This has the advantage that when the film shrinks on exposure to heat, the polymeric substrate and the elongated strip shrink at substantially the same rate and/or by substantially the same amount in both the machine direction and transverse direction of the film. Thus, the formation of unsightly wrinkles in the region surrounding the tear tape mechanism are greatly reduced or completely eliminated.

The filmic material may consist of only one layer, or may be multi-layered, for example, a 3- layer, 4-iayer, 5-layer, 6-layer or 7-layer film. The layers can be combined by any technique known to those skilled in the art, such as lamination or co-extrusion. The co-extrusion technique involves the polymeric components of each of the layers being eoextruded into intimate contact while each still molten. Preferably, the co-extrusion is effected from a multi-channel annular die such that the molten polymeric components constituting the respective individual layers of the multi-layer film merge at their boundaries within the die to form a single composite structure which is then extruded from a common die orifice in the form of a tubular extrudate.

Preferably, the filmic material is a 3~layer film, where one layer (i.e. the core layer) is sandwiched between the other two layers (i.e. the outer layers) such that the sandwiched layer does not form either surface of the sheet. The core layer may have a thickness of about 90% to about 98% of the total thickness of the film. The remainder of such a 3-layer film may comprise two outer layers of another material, with each outer layer having substantially identical thickness. More preferably, the filmic material is a 3-layer film comprising a core layer sandwiched between two outer layers which are distinct heat sealable layers as previously described.

If desired, the core layer of the filmic material may be subjected to a chemical or physical surface-modifying treatment to ensure that any coating and/or layer will better adhere to the core layer, thereby reducing the possibility of the coating and/or layer peeling or being stripped from the core layer. Known prior art techniques for surface pre-treatment prior to coating comprise, for example, film chlorination i.e. exposure of the film to gaseous chlorine, treatment with oxidising agents such as chromic acid, hot air or steam treatment, flame treatment and the like, A preferred treatment, because of its simplicity and effectiveness, is the so-called electronic treatment in which polymeric substrate and/or elongated strip is passed between a pair of spaced electrodes to expose the surface to a high voltage electrical stress accompanied by corona discharge.

Optionally, if even adhesion of the coating and/or layer is desired, an intermediate continuous coating of a primer medium arsd/or anchor coating can be applied to a sheet surface treated by any of the methods described herein. Primer materials may comprise titanates and poly (ethylene imine) and may be applied as conventional solution coatings.

The or each coating and/or layer may be applied sequentially, simultaneously and/or subsequently to any or all other coatings and/or layers.

The filmic material may comprise one or more additive materials. Additives may comprise: dyes; pigments; colorants; metallised and/or pseudo metallised coatings (e.g. aluminium); lubricants; anti-oxidants; surface-active agents; stiffening aids; gloss-improvers; prodegradants; UV attenuating materials (e.g. UV light stabilisers); seaiability additives; tackifiers; anti-blocking agents; additives to improve ink adhesion and/or prirstability; and/or cross-linking agents (such as mefamine formaldehyde resin). Further additives comprise those to reduce the coefficient of friction (COF).

Still further additives may comprise slip aids such as hot slip aids or cold slip aids which improve the ability of a film to satisfactorily slide across surfaces at about room temperature, for example, micro-crystalline wax. Yet further additives may comprise conventional inert particulate additives, preferably having an average particle size of from about 0,2 μπ) to about 4,5 μηι, more preferably from about 0.7 μm to about 3.0 μη\. Decreasing the particle size improves the gloss of the film. The amount of additive, preferably spherical, incorporated into the or each layer is desirably in excess of about 0,05%, preferably from about 0, 1% to about 0.5%, for example, about 0.15%. Suitable inert particulate additives may comprise an inorganic or organic additive, or a mixture of two or more such additives,

It may be desirable to include one or more security features in the filmic material of the elongated strip but not in the filmic material of the polymeric substrate. This has the advantage that any aesthetically detrimental effects to the polymeric film web, due to the inclusion of security features, will be limited to the elongated strip.

Security features which may be added to the elongated strip include but are not limited to: standard optical effects such as printing via flexography or UV-flexography; overt optical effects such as holograms, diffractive optical elements, lenticular images, iridescents, daylight fluorescents and light piping materials, liquid crystals or colour shifting inks; semi- overt optical effects, for example, devices that require a decoder such as hidden lens structures, birefringent values and patterns, micro-text, planchettes or other physical tags, fluorescents, phosphorescents, IR/UV absorbent materials and photochromies; and covert effects such as magnetics and up-converters.

The invention will further be described with reference to the following figures and examples:

Figure 1 - A schematic diagram of a section of a GD4350 overwrap machine. Figure 1 shows a section of a GD4350 overwrap machine. In the machine, a film substrate is driven through a drive roller 1 such that the inside surface 2 of the film substrate contacts the drive roller 1. As a tear tape 3 is driven through the drive roller 1, it contacts the inside surface 2 of the film substrate. A crescent shaped heater 4 is placed into contact with the outside surface 5 of the film substrate such that it is directly positioned over the region of overlap between the tear tape 3 and the film substrate. The heat and pressure applied by the crescent shaped heater 4 results in the sealing of the tear tape 3 to the film substrate. The temperature of the crescent shaped heater 4 is controlled by means of a heater element and a thermocouple connected to a heater controller,

EXAM PLE 1

A GD4350 overwrap machine running at 350 packets per minute was used. The heater bar in the overwrap machine was set to 200°C. A 23NE3Q tear tape with a width of 2.5mm, and a 23N E30 film substrate were fed into the GD4350 overwrap machine and heat sealed together. 23NE3Q is a 3-layer biodegradable film comprising a cellulosic core layer and two heat-seal layers, one on either side of the core layer. Two hundred packets were wrapped using the resulting film web.

The two hundred wrapped packets were opened and the functionality of the tear tape assessed. If the tear tape was positioned correctly and opened the film such that the film was completely removed from the packet, it was deemed as a 'pass'. Any packet where the film did not tear correctly, where the tear tape was positioned incorrectly and/or where the tear tape failed to initiate removal of the film from the packet, was deemed as a 'fail'. The results from the test are shown below:

From the results, it can be seers ' hat the tear tape had a 100% pas s rate, For Ϊ ;ach of the wrapped r. sack ets, the te. sr tape w as in the corr ect position and enabi ed easy rerr oval of the film from 1 the i jacket.

EXAMPLE 2

A GD4350 ove rwrap mac nine running at 350 packets per minute was used. The h< sater bar in the overwrap machine was set to 200ºC. Four ί jifferent film webs we re formed b y feeding a

GLT20 film substrate Into the GD4350 overwrap machine and heat sealing it to one of the following:

1} GLT20 tear tape with a thickness of 20 μηι and a width of 2.5mm; 2) GLT25 tear tape with a thickness of 25 gm and a width of 2.5mm; 3} GLT30 tear tape with a thickness of 30 p.m and a width of 2.0mm; or 4) GLT30 tear tape with a thickness of 30 pm and a width of 2.5mm

GLT20, GLT25 and GLT30 are all shrink films comprising a biaxially oriented polypropylene core layer and two heat seal layers, one on either side of the core layer, comprising poiyolefinic copolymers. Packets were wrapped using sheets from each of the four resulting film webs. Different shrink temperatures were used during wrapping, ranging from 0°C to 150 ^e C.

The wrapped packets were opened and the functionality of the tear tape assessed. If the tear tape was positioned correctly and opened the film such that the film was completely removed from the packet, it was deemed as a 'pass'. Any packet where the film did not tear correctly, where the tear tape was positioned incorrectly and/or where the tear tape failed to initiate removal of the film from the packet, was deemed as a 'fai!'. The results from the test are shown below:

From the results, it can be seen that the tear tapes in each sample had an extremely high pass rate i.e. the tear tape was in the correct position and enabled easy removal of the film from the packet.

Visually, all the wrapped packets had an acceptable appearance i.e. there was limited or no distortion/wrinkling in the region of the tear tape/film substrate overlap.