GB2359273A

GB2359273A - Stretch-wrap film

Info

Publication number: GB2359273A
Application number: GB0003559A
Authority: GB
Inventors: John Ivor Williams
Original assignee: British Polythene Ltd
Current assignee: British Polythene Ltd
Priority date: 2000-02-17
Filing date: 2000-02-17
Publication date: 2001-08-22
Also published as: GB0003559D0

Abstract

A stretch-wrap film 10 comprises at least two distinct elements 12(a),(b) and 14, with a second one of the two elements 14 having a lower permeability to fluids than a first one of the two elements 12(a),(b). The external elements (12) may be LLDPE, LDPE, EVA, or copolymers or terpolymers of ethylene and acrylic acids, esters of acrylic acids, vinyl acetate or styrene. The internal element 14 may be nylon, PET, EVOH, or ethylene - carbon - monoxide - copolymer.

Description

1 2359273 1 Stretch-wrap Fil This invention relates to a stretch-wrap

film, and more particularly, but not- exclusively, to a stretch-wrap film for wrapping silage bales.

The use of stretch-wrap film to wrap bales of grass for silage production is widely practised. In this field, conventional stretch-wrap film essentially comprises linear low-density polyethylene (hereinafter referred to as LLDPE), which is used for its advantageous characteristics of being able to withstand high plastic deformation while io maintaining a high puncture/tear resistance over an extended period.

The fundamental disadvantage with this type of film is the low barrier characteristic of LLDPE towards fluids, and in particular oxygen. This is of particular importance, as the transmission of oxygen into a wrapped silage bale adversely effects the fermentation process and increases silage deterioration due to microbial and ftmgicidal propagation, which all leads to a lower level of final feed quality. Some countries, for example Sweden, Germany and France, have implemented national standards for silage stretch-wrap film, which results in it being not uncommon practise to wrap up to eight layers of this type of stretch-wrap film around silage bales to attempt to decrease the transmission of oxygen.

The present invention seeks to overcome this problem.

According to a first aspect of the present invention, there is provided a stretch- wrap film comprising at least two distinct elements, a second one of the two elements 2 having a lower permeability to fluids than a first one of the two elements. Thus, the previously stated advantageous properties may be combined with a high fluid-barrier characteristic into a film.

Preferably, the at least first and second distinct elements are in the form of first and second layers, respectively. In this case, the first layer may essentially comprise linear low-density polyethylene (LLDPE) or other material having similar plastic deformation and punctureltear resistance characteristics, and the second layer may essentially comprise either nylon or other material having relatively low permeability to io fluids. Advantageously, a third layer may essentially comprise either LLDPE or other material having similar plastic deformation and puncture/tear resistance characteristics and a tackifier, the third layer being interposed between the first and second layers.

Preferably, the film further comprises additives for stabilising the film against degradation, such as ultraviolet degradation and weathering. The additives may include either hindered amine light stabilisers (HALS), carbon black, titanium dioxide, colorants, or any combination thereof.

Preferably, the lower permeability is to gas and, in particular, oxygen.

According to a second aspect of the invention, there is provided a silage bale wrapped with a stretch-wrap film in accordance with the first aspect of the present invention.

3 The invention will now be more particularly described, by way of example, with reference to the accompanying drawing, which shows a fragmentary elevational section through one embodiment of a stretch-wrap film, in accordance with the first aspect of the present invention.

Referring to the drawing, a stretch-wrap film 10 shown therein typically comprises five elements, being layers 12(a) and (b), 14, and 16(a) and (b). Layers 12(a) and (b) are compositionally identical, as are layers 16(a) and (b). Layer 14 is compositionally distinct from both pairs of layers 12(a),(b) and 16(a),(b).

The external layers 12a) and (b) of the stretch-wrap film 10 may essentially be formed from linear low-density polyethylene (hereinafter LLDPE), low-density polyethylene (hereinafter LDPE), ethylenevinylacetate copolymer (hereinafter EVA), other co- and ter-polymers of ethylene and acrylic acids, esters of acrylic acids, vinyl acetate, styrene, or any other suitable material, or combinations thereof, having high plastic deformation and high puncture/tear resistance characteristics.

The interposed layer 14 may essentially be formed from nylon, polyethylene terphthalate, ethylene-vinyl alcohol (hereinafter EvOH) copolymers, ethylene-carbon monoxide copolymers, or any other suitable material, or combinations thereof, having a lower permeability to fluids, and in particular gaseous oxygen, than the other layers 12(a),(b) and 16(a),(b).

The interposed layers 16(a) and (b) may essentially be formed from LLDPE, LDPE, EVA, other copolymers of ethylene and acrylic acids, esters of acrylic acids, 4 vinyl acetate, maleic acid and derivatives thereof, styrene, or any other suitable material, or combinations thereof, and a tackifier, such as polyisobutene. Thus, layers 16(a) and (b) have the added characteristic of being produced with a very high level of cling.

The layers 12(a),(b), 14 and 16(a),(b) of the film 10 are typically coextruded using known blown or cast film production techniques. As such, the interposed layers 16(a) and (b) are highly advantageous in maintaining the secure interrelationship between the external layers 12(a),(b) and the high oxygen-barrier layer 14.

The film 10 is enhanced with additives, typically being incorporated in the external layers 12(a) and (b), for stabilising the film against degradation, such as ultraviolet degradation and weathering, thereby prolonging the life of the in use film 10. The additives may include either hindered arnine light stabilisers (HALS), carbon black, titanium dioxide, colorants, or any combination thereof Colouring additives may also be used where necessary.

The film 10 has typical dimensions of 750 millimetres in width, and around 25 microns thick, with the high-oxygen barrier layer 14 being approximately 2 microns thick. In this way, the plastic deformability of the outer layers 12(a), (b) and 16(a),(b) arenot particularly restricted by the high-oxygen barrier layer 14, and can be typically maintained in the range of 70 to 100% during an in use spiral-wrapping application of the film 10 to a silage bale.

Additionally, in comparison to existing stretch-wrap film, by use of the highoxygen barrier layer 14, oxygen transmission rates can be significantly lowered to at least 800 cubic centimetres per 24 hours, resulting in the need for fewer layers of the in use film 10 to be applied to a silage bale.

Although the high-oxygen barrier layer 14 has been described as being an interposed layer, it may be an external layer with suitable enhancement by the aforementioned additives, if necessary, and appropriate rearrangement of the other layers. The external layer 14 may form part of a two layer stretch-wrap film.

Alternatively, the film 10 may essentially comprise only two distinct elements, having the aforementioned desirable characteristics of LLDPE and nylon, blended into a single layer film.

The embodiment described above is given by way of example only, and various modifications will be apparent to persons skilled in the art. For example, the stretchwrap film 10 may comprise more or less than 5 layers, and more than one high barrier characteristic layer; and the layers 16(a) and (b) may be dispensed with if the layers 12(a) and (b) are formed with the aforementioned tackifier.

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Claims

1. A stretch-wrap film comprising at least two distinct elements, a second one of the two elements having a lower permeability to fluids than a first one of the two elements.

2. A film as claimed in claim 1, wherein the at least first and second distinct elements are in the form of first and second layers, respectively.

io 3. A film as claimed in claim 2, wherein the first layer essentially comprises either linear low-density polyethylene (LLDPE) or other material having similar plastic deformation and puncture/tear resistance characteristics, and the second layer essentially comprises either nylon, or other material having relatively low permeability to fluids.

4. A film as claimed in claim 3, wherein a third layer essentially comprises either LLDPE or other material having similar plastic deformation and puncture/tear resistance characteristics and a tackifier, the third layer being interposed between the first and second layers.

A film according to any one of the preceding claims, further comprising additives for stabilising the film against degradation, such as ultraviolet degradation and weathering.

7 6. A film as claimed in claim 5, wherein the additives may include either hindered amine light stabilisers (HALS), carbon black, titanium dioxide, colorants, or any combination thereof.

7. A film according to any one of the preceding claims, wherein the lower permeability is to gas.

8.

A film as claimed in claim 7, wherein the gas is oxygen.

9. A stretch-wrap film as hereinbefore described with reference to the accompanying drawing.

10. A silage bale wrapped with a stretch-wrap film according to any one of the preceding claims.

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