WO2010038079A1

WO2010038079A1 - Packaging film

Info

Publication number: WO2010038079A1
Application number: PCT/GB2009/051297
Authority: WO
Inventors: Barry Frizell; Wolfgang Zimmerer
Original assignee: Innovia Films Limited
Priority date: 2008-10-03
Filing date: 2009-10-02
Publication date: 2010-04-08
Also published as: GB0818124D0

Abstract

The present invention provides a polymeric film for packaging applications. The film has at least one region of weakness formed therein, wherein a film thickness in the at least one region of weakness is thinner than that outside the at least one region of weakness.

Description

PACKAGING FILM

The present invention relates to a packaging film and particularly to a polymeric film for packaging applications

The packaging industry requires large quantities of film which protect a packaged product from the atmosphere, dirt, grease, etc and exhibit flavour barrier properties in order to maintain the freshness of the product Polyolefins are in demand as film-forming materials by virtue of their strength and clarity However, many other substrate films are useful in this connection For convenience this specification will describe mostly polyolefinic films, but other substrate films are within the scope of the invention as will be made clear herein

In the field of packaging articles the use of polyolefin films is advantageous because they offer excellent shrink tightening properties and sealing properties

However, it is because of the very same excellent shrink tightening and sealing properties that stacking such packaged articles in a commercial environment, e g for storage, transport or display, is difficult

Often, upon sealing of the packaging, air within the packaging becomes trapped therein and cannot escape therefrom This can cause the sealed packaged article to bulge and thereby adopt a shape which prevents convenient stacking of a number of the packaged articles

Attempts have been made to address this problem by using films having holes punched therein Thus, when articles are wrapped air cannot become trapped within the packaging as it is free to flow to the extenor of the wrapped article by way of the punched holes

A process for producing such a ^f!im having punched holes theren is however problematic in tnai a large amouni of film material is wasted in trie material removed from the film to form the holes. Additionally, if there is printed matter on the film, material removed to form the holes may contain some of the printed matter and so the printed matter on the end-product film may have information missing. Additionally, such a punching process may require "stop- start" periodic punching steps. In general such processes require more complicated equipment and are slower than a continuous process.

Another problem with sealed packages arises in connection with microwaveable packages. Such packages need to be pierced to allow steam escape during cooking. Pre-piercing by the manufacturer would render the package non-sealed and consequently inoperative.

The present invention relates to a film and a method of producing a film which overcome or substantially eliminate the aforementioned problems

According to an aspect of the present invention, there is provided a polymeric film, characterised in that the film has at least one region of weakness provided therein, the region of weakness being formed by partial perforation of the film, the perforation extending into but not completely through the film, and wherein the film is adapted to burst in the region of the perforation on the application of force to the film.

Preferably the force is a pressure force, more preferably an air pressure force or a vapour pressure force.

The region of weakness may be continuous or may have a discrete pattern.

Whether the region of weakness is continuous or discontinuous, it does in any event preferably comprise a series of repeat patterns, each of which has a first directionaϊ component which is parallel to a straight longitudinal axis running along the length of the region of weakness and through the centre thereof, and a second directional component which is perpendicular to the said longitudinal axis. Preferably the region of weakness has a pattern vv'hich oscillates above and below the said longitudinal axis. Preferably, the region of weakness is a wavy or zigzag line made up from a series of repeat patterns, waves or wave portions, zigzags or zigzag portions as the case may be One preferred pattern is a Sinusoidal wave

Preferably the region of weakness is an oscillating region of weakness More preferably the region of weakness is an oscillating region of weakness with a repeat unit which itself is oscillating

By oscillating is preferably meant that the region of weakness propagates sequentially above and below a longitudinal axis running along the length of the region of weakness through the centre thereof

Preferably, the multi-directional components of the region of weakness cause bursting of the film m that region to produce a burst flap This allows faster egress of air or vapour than would be the case through a straight line region of weakness for example

The amount of film material removed (ie cut away) along the length of the film line can be an important characteristic in controlling the ease with which the film can be burst at the region of weakness Preferably at least about 10%, more preferably at least about 20%, even more preferably at least about 30%, yet more preferably at least about 40% and most preferably at least about 50% - even as high as 60%, 70% or 80% - of the film may be removed in along the region of weakness Clearly there are other factors, such as the nature of the film material itself and the thickness of the film itself which come into play as well or instead in this connection

Tne films used in accordance witn the present invention can be of a variety of thicknesses according to the application requirements For example they can be from about 10 to about 240μm thick and preferably from about 50 tc about 90μm thick The region of weakness in the film is preferably of a narrower gauge than the rest of the film - for example 1 % 2% 5%, 10% 20% or 50% narrower than the bulk of the ^film or the region of weakness may extend aP or substantially all the way through the f^«lm The invention further provides a sealed package comprising a commercial article packaged in an airtight manner by the film of the invention the sealed package being to some extent inflated by the air inside the package, the package bursting in a controlled manner in the region of weakness when compressed

The invention also provides a microwaveable package comprising an edible article packaged in an airtight manner by the film of the invention, the sealed package becoming to some extent inflated by steam pressure in the package during cooking the package bursting in a controlled manner in the region of weakness in response to the steam pressure

The package of the invention allows the rapid online packaging of for example food products such as tomatoes which are generally provided in a carton tray which in turn is sealed inside the film packaging of the invention in an airtight manner When the package is compressed - for example when it is stacked and boxed for transport - the package bursts in a controlled manner allowing the sufficient egress of air for the package to be stacked more controllably and more efficiently

Because the region of weakness does not extent right through the film, however, it is possible to print on the film prior to its packaging application without the risk of ink being transferred through the film to its underside in the process

The repeat pattern perforated region of weakness can be provided in the film in a rapid on-line manner with no stop-start procedure necessary for complete puncturing of the film

There is also no substantial film waste from stamped out portions of film According to another aspect of the present invention, there is provided a method of producing a polymeric film in accordance with the above comprising passing said film between a first roller and a second roller, urging said second roller against said first roller and forming said at least one region of weakness in said film by way of at least one cutting element located about a periphery of said second roller

The films used in the present invention prior to deposition of any coating and/or skin or lamination layer may comprise any suitable polymeric filmic substrate, such as films made from biopolymers such as any of those described herein [preferably polylactic polygalactic and/or cellulosic films (e g microbial and/or regenerated cellulose film)] , thermoplastic films, polymeric films (for example films comprising polyotefins [e g polypropylene and/or polyethylene] polyurethanes, polyvmylhalides [e g PVC] polyesters [e g polyethylene terephthalate-PET], polyamides [e g nylons] and/or non- hydrocarbon polymers) , and/or multilayer and/or composite sheets formed by any suitable combinations and/or mixtures of thereof Suitable filmic substrates therefore include polyotefmic films, but also polyester films, polyurethane films cellulosic and PLA films

The films of the present invention may consist of only one layer or may comprise a plurality of layers Layers when present can be combined by lamination and/or co-extrusion and/or coating and/or melt coat extrusion

Films may be otherwise treated (for example by corona discharge treatment) to improve certain characteristics of the film, portability or coating adhesion for example

The films of the invention may comprise one or more additive materials such as dyes, pigments, colorants metallised and/or pseudc meiailised coatings (e g aluminium) lubricants antioxidants surface-active agents, stiffening aids, gloss-improvers prodegradants UV attenuating materials (e g UV light stabilisers; sealabihty additives tackifiers anti-Dloclong agents, additives to improve ink adhesion and/or portability cross-linking agents anti-slip and/or anti-block additives and the like

The present invention is described further hereinafter, by way of example only, with reference to the accompanying drawings in which

Fig 1 illustrates a side elevation of a portion of a bsaxially oriented propylene polymer film substrate 1

Fig 2 illustrates a side elevation of a similar film portion having on a surface 2 of substrate 1 , a heat-sealable layer 3 formed from an ethylene-butene-1 random copolymer

Fig 3 illustrates a side elevation of a similar film portion having on a second surface 4 of substrate 1 , a heat-sealable layer 5 formed from an ethylene- butene-1 random copolymer

Fig 4 illustrates a perspective view of a sealed package comprising an article wrapped in a film according to the present invention, where the sealed package is in an inflated condition due to air trapped within the package and

Fig 5 illustrates a perspective view of the sealed package of Fig 4, where the package is being compressed and trapped air is escaping from the package by way of regions of weakness formed in the film

Figs 1 to 3 are self-explanatory and no further description is required

Fig 4 iHubtrateb a sealed package 10 compiismy an article 12 for example a container such as a fruit/vegetable punnet wrapped in a packaging film 14 The packaging film 14 is neat sea'ed at ends thereof ¹6 18 to enclose and seal the film around the article 12 The packaging film 14 is provided with at least one region of weakness 20 which is formed during a suitable film cutting process The region of weakness 20 preferably does not extend through the entire depth of the film

In a preferable arrangement, there is a plurality of regions of weakness 20 with each region of weakness 20 comprising a single perforation More preferably, each region of weakness 20 has a substantially crescent shape

As can be seen from Fig 4, air is trapped within the sealed packaging film 14 of the package 10

Fig 5 illustrates how the regions of weakness 20 operate to release trapped air from within the package 10 upon application of pressure to the package

10

In Fig 5 features which correspond to features already described in relation to Fig 4 are denoted by like reference numerals and will not be discussed further

Pressure applied to the package 10 is indicated by arrows A B This application of pressure causes the pressure of the air trapped within the package 10 to increase As the applied pressure increases the pressure of the trapped air likewise increases until such air pressure is sufficient to cause the packaging film 14 to burst at the regions of weakness 20 Air is then expelled from the package 10 vsa the regions of weakness 20 as indicated by reference numerals 22 This expulsion of air from within the package 10 causes the package 10 to adopt a smaller overall configuration without the undesirable υuigmg of tne packaging film 14 when the package 10 is first sealed As will be appreciated this is advantageous as it allows a plurality of packages to be more easily stacked for storage presβntaiion transport etc

Claims

A polymeric film, characterised in that the film has at least one region of weakness provided therein, the region of weakness being formed by partial perforation of the film, the perforation extending into but not completely through the film, and wherein the film is adapted to burst in the region of the perforation on the application of force to the film

A film according to claim 1 wherein the region of weakness is adapted to burst on application of a pressure force thereto

A film according to claim 1 or claim 2 wherein the region of weakness comprises a series of repeat patterns, each of which has a first directional component which is parallel to a straight longitudinal axis running along the length of the region of weakness and through the centre thereof, and a second directional component which is perpendicular to the said longitudinal axis

A film according to claim 3 wherein the region of weakness has a pattern which oscillates above and below the said longitudinal axis

A film according to claim 4 wherein the region of weakness is a wavy or zigzag line made up from a series of repeat patterns, waves or wave portions, zigzags or zigzag portions

A film according to claim 5 wherein the pattern comprises a sinusoidal wave

A film according to any one of claims 3 to 6 wherein the bidirectional components of the region of weakness cause bursting of the film in that region to produce a burst flap in the film

A seated package comprising a commercial article packaged in an airtight manner by the film according to any one o^f claims 1 to 7 the sealed package being to some extent inflated by the air inside the package, the package bursting in a controlled manner in the region of weakness when compressed.

9. A microwaveable package comprising an edible article packaged in an airtight manner by the film according to any one of claims 1 to 7, the sealed package becoming to some extent inflated by steam pressure in the package during cooking, the package bursting in a controlled manner in the region of weakness in response to the steam pressure.

10. A method of producing a polymeric film in accordance with any one of claims 1 to 7 comprising: passing said film between a first roller and a second roller; urging said second roller against said first roller; and forming said at least one region of weakness in said film by way of at least one cutting element located about a periphery of said second roller.