WO2004024443A1

WO2004024443A1 - Secondary sealing barrier films

Info

Publication number: WO2004024443A1
Application number: PCT/NZ2003/000203
Authority: WO
Inventors: Stephen Meyer; Annant Narayan
Original assignee: Danaflex Packaging Corporation Limited
Priority date: 2002-09-12
Filing date: 2003-09-12
Publication date: 2004-03-25
Also published as: AU2003265021A1; AR041232A1

Abstract

The invention relates generally to a shrink-wrap film (1) or tubing that includes secondary sealing properties at temperatures less than 100°C, to a process for preparing a shrink wrap film and products therefrom. In particular the shrink wrap film (1) includes at least one outer layer (6) including a polyolefin resin; at least one oxygen barrier layer (4) and an inner non-ionomer sealant layer (2).

Description

Secondary Sealing Barrier Films

This invention relates generally to a shrink-wrap film or tubing that includes secondary sealing properties, a process for preparing a shrink wrap film and products therefrom. In particular, the invention is directed to a shrink-wrap film or tubing having secondary sealing properties at temperatures less than 100°C, to a process for preparing such films and to products therefrom.

Background of the Invention

By way of background information, when fresh produce such as meat or poultry is vacuum packed in a film and the film is heat shrunk in a hot water or hot air process, there are parts of the inner layers of the bag, which remain in contact. This occurs at the flaps/edges/sides of the bag where there is no meat product. The meat contains juices that can flow into the flap area. The presence of liquid in the flap areas is undesirable from a presentation perspective for customers where presentation of packs plays an important part of the selling process.

A secondary sealing effect is achieved where the two inner layers of the material adhere to each other when they come into contact during the heat shrink process. It is known from Du

Pont publication XP 002157257 H-56747 that ionomer based films comprising Surlyn can be used to achieve a secondary sealing effect after heat shrinking in a hot air tunnel. However, non-ionomer based oxygen barrier heat shrink film products are not known to have a secondary sealing property at temperatures less than 100°C.

Additionally, conventional non ionomer sealant layers typically comprise polyethylenes such as linear low density polyethylene (LLDPE) and low density polyethylene (LDPE), however, a secondary sealing effect is not achieved with such sealant layers at temperatures less than 100°C. This is because the sealant layer of current barrier products has a DSC melt point of greater than 100°C meaning that the film must be subjected to temperatures of greater than 100°C to make the sealant layers adhere together. Typical hot water shrink temperatures are 85-95°C and so this desired secondary sealing effect cannot be achieved in conventional commercial environments. It is an object of the invention to provide non-ionomer based oxygen barrier heat shrink film products having a secondary sealing property at temperatures less than 100°C or to at least provide the public with a useful alternative.

Summary of the Invention

In a first aspect of the present invention there is provided a heat shrink barrier film including at least one outer layer including a polyolefin resin; at least one oxygen barrier layer; and - an inner non-ionomer sealant layer; wherein in use, the sealant layer is adapted to provide a secondary sealing effect when the heat shrink barrier film is exposed to temperatures of between 80-100°C.

Preferably, the outer layer includes a resin or blend of resins selected from EVA, LLDPE, m-LLDPE, plastomers and metallocene catalysed plastomers.

Preferably an outer tie layer is intermediate the oxygen barrier layer and outer layer, and more preferably the outer tie layer includes a resin or blend of resins selected from EVA m-LLDPE, plastomers, and metallocene catalysed plastomers.

Preferably an inner tie layer is intermediate the oxygen barrier layer and sealant layer, and more preferably the inner tie layer includes a resin or blend of resins selected from EVA m-LLDPE, plastomers, and metallocene catalysed plastomers.

Preferably, the oxygen barrier layer includes a resin or blend of resins selected from PVDC, nylon or EVOH.

Preferably the sealant layer is adapted to provide a secondary sealing effect when the heat shrink barrier film is exposed to temperatures of between 85-95°C.

Preferably, the inner non-ionomer layer is adapted to be co-extruded with the barrier layer.

In a second aspect of the present invention there is provided a heat shrink barrier film including at least one outer layer including EVA resin as a component at least one oxygen barrier layer including PVDC resin; at least one inner layer including EVA resin as a component; at least one inner tie layer comprising a polyolefin; and - an inner non-ionomer sealant layer; wherein in use, the sealant layer is adapted to provide a secondary sealing effect when the heat shrink barrier film is exposed to temperatures of between 80-100°C.

Preferably, the sealant layer is adapted to provide a secondary sealing effect when the heat shrink barrier film is exposed to temperatures of between 85-95°C.

Preferably the sealant layer is between 5 - 12 micrometres in thickness.

More preferably the sealant layer is between 7 - 10 micrometres in thickness.

Preferably, the outer layer comprises a first outer layer including EVA and a second outer tie layer including EVA.

Preferably the inner tie layer includes a resin or blend of resins selected from EVA m-LLDPE, plastomers, and metallocene catalysed plastomers.

Preferably, the inner non-ionomer layer is adapted to be co-extruded with the PVDC barrier layer.

Preferably the sealant layer is between 5 - 12 micrometres in thickness.

More preferably the sealant layer is between 7 - 10 micrometres in thickness.

Preferably the gauge of the heat shrink barrier film is between 40 - 90 micrometres.

More preferably the gauge of the heat shrink barrier film is between 45 - 85 micrometres.

Preferably the sealant layer comprises a blend of (a) LLDPE, and (b) a polyolefin plastomer or blend of plastomers having a DSC melt point less than 100°C. More preferably, the sealant layer comprises a blend of

(a) a maximum of 50% LLDPE, and

(b) a minimum of 50% of a polyolefin plastomer.

Most preferably, the sealant layer comprises a blend of

(a) 50% LLDPE polythethylene resin, Dow Dowlex 2247 G, and

(b) 50% of a polyolefin plastomer Dow Affinity EG 8100.

In a further embodiment preferably the sealant layer comprises a blend of

(a) a first polyolefin plastomer, and

(b) a second polyolefin plastomer.

More preferably, the sealant layer comprises a blend of

(a) 90% of the first polyolefin plastomer, and

(b) 10% of the second polyolefin plastomer.

Most preferably, the sealant layer comprises a blend of (a) 90% of the first polyolefin plastomer Dow Affinity PF1 140, and

(b) 10% of the second polyolefin plastomer Dow Affinity PT 1450.

In a third aspect the present invention provides a heat shrink barrier film including at least one outer layer including a plastomer as a component - at least one oxygen barrier layer including PVDC resin; and an inner non-ionomer sealant layer including a metallocene plastomer as a component; wherein in use, the sealant layer is adapted to provide a secondary sealing effect when the heat shrink barrier film is exposed to temperatures of between 80-100°C.

More preferably the sealant layer is between 7 - 10 micrometres in thickness. Preferably, the inner non-ionomer sealant layer is adapted to be co-extruded with the PVDC barrier layer.

Preferably the sealant layer is between 5 - 12 micrometres in thickness.

More preferably the sealant layer is between 7 - 10 micrometres in thickness.

Preferably the outer layer includes a blend of ExxonMobil Exact 0203 plastomer and Eurcamide slip.

Preferably, the sealant layer includes a blend of

(a) 50% Exact 0203 (metallocene plastomer) and

(b) 50% EG8100 (metallocene plastomer).

In a fourth aspect the present invention provides a method of heat shrink wrapping a consumable product including the steps of

(i) wrapping and vacuum packaging the consumable product with a heat shrink film defined above; (ii) exposing the wrapped product to a temperature of between 80 - 100°C thereby facilitating the heat shrinkage of the film about the product and thereby effecting secondary sealing between any first portion of the inner layer of the film in contact with any second portion of the inner layer of the film.

Preferably the wrapped product is exposed to temperatures of between 85-95°C.

Preferably the heat shrinkage is achieved in a hot air tunnel or hot water bath.

Preferably the method includes the step of vacuum packing the consumable product prior to the step of exposing the wrapped product to the heat shrinkage temperature. In a further aspect, the invention provides wrapped consumable products obtained by a method defined above.

Preferably such products include fresh meat, poultry, cheeses and the like. Further aspects of the present invention will become apparent with reference to the following detailed description given by way of example only and with reference to the accompanying Figures in which:

Figure 1 Shows schematically the cross sectional structure of a film of one embodiment of the invention.

Figure 2 Shows schematically in cross sectional views the process of wrapping a product with a heat shrink film of the invention and the secondary sealing effect that is achieved between the inner layers of film that are brought into contact and then exposed to a heat shrink step.

Figure 3 Shows schematically a cross sectional view of how a secondary seal may be formed between two sealant layers of the heat shrink film of the present invention.

Various abbreviations are used throughout the specification. These abbreviations are to be understood as meaning the following:

LLDPE - Linear Low Density Polyethylene resin

LDPE - Low Density Polyethylene resin m-LLDPE - Metallocene Linear Low Density Polyethylene Resin

EVA - Ethylene Vinyl Acetate resin

PVDC - Polyvinylidene chloride resin

EVOH - Ethylene Vinyl Alcohol resin

DSC - Differential Scanning Calorimetry

Detailed Description of the Invention

With reference to the accompanying figures the invention will be described in detail.

Figure 1 shows schematically a cross sectional structure of a film (1) of one embodiment envisaged by the invention. The film (1 ) is made up of a sealant layer (2), an inner tie layer (3), an oxygen barrier layer (4), an outer tie layer (5) and an outer layer (6). It is preferred that the inner tie layer (3), the outer tie layer (5) and the outer layer (6) are made predominantly from EVA resin. The outer layer (6) can optionally include about 5% of a product that comprises a slip additive (approximately 4% by weight) and an antiblock additive (approximately 10% by weight) in combination in a carrier resin (approximately

86% by weight). The preferred actual combined amount of the slip and anitblock additive is up to about 1 % by weight of the outer layer. This is preferred so as to prevent the outer layer becoming too sticky. The slip additive is typically an erucamide fatty acid and the antiblock additive is typically a synthetic silica. However, it is to be appreciated that other known antiblock and slip additives and related products can also be used. It is also preferred that the oxygen barrier layer (4) comprises PVDC. The overall gauge of the film (1 ) is preferably 45 to 85 micrometres. It is preferred that the sealant layer (2) has a gauge of approximately 7 to 10 micrometres.

The sealant layer can comprise a blend of linear low density polyethylene along with a polyolefin plastomer. In a further embodiment the sealant layer can comprise a blend of polyolefin plastomers. The sealant layer must at least be able to provide the properties of providing a secondary sealing effect when the film (1) is exposed to temperatures of between 80 to 100°C. It is preferred however that the sealant layer (1) is able to exhibit the secondary sealing effect when the film (1) is exposed to temperatures of between 85 to

95°C, in particular those temperatures that can be readily achieved in a hot water bath.

The films of the invention can be produced by a conventional tubular co-extrusion or sequential co-extrusion tubular techniques. In the conventional tubular co-extrusion technique a hot melt of resins is extruded through an annular circular die. The tube that is formed is cooled and flattened and the resulting tape is then fed through a hot water bath at a temperature of from about 80 to 98°C. This heating step is done just prior to orientating the film. The orientation temperature range is well known for many polymeric materials and are generally below the melting point of the film. On leaving the bath the tube is then inflated to give the desired wall thickness of the tube and sets the cross direction stretch.

This "trapped bubble" technique is known in the art. The tube is then drawn away from the nip rollers that trap the air bubble. The rate of draw is controlled to provide the longitudinal stretch. The film is then rapidly cooled to set the orientation, cross linked using an electron beam, and rolled up to give the desired biaxially orientated film. The cross linking step is carried out to provide some additional strength to the film and to minimise any delamination of the layers making up the film during any subsequent heat shrinking step. By this technique, shrinkability is imparted to the properties of the film by the orientation of the film during its manufacture. This allows the film to shrink, or, if restrained, to create shrink tension within the packaging film on exposure to heat, for example, in a hot water bath or by exposure to hot air. In a typical process, the degree of stretch in both the longitudinal and transverse directions can be varied to impart the desired degree of shrinkability to the film upon subsequent heating.

The tubes that are created by this technique can either be split to create a single layer of film or the tubes can be employed to wrap products therein meaning that the ends of the tube simply need to be closed as part of a bag making and vacuum packaging process.

In the conventional tubular co-extrusion technique one die is used. The resin for each product layer enters the die separately. At the die exit, the resins of each layer emerge in contact thus forming the continuous tube with the layers in contact with one another according to the product structure.

In the sequential coextrusion process, two or more dies can be involved. The resins of two or more layers can enter the first die separately and be brought together in contact at the die exit. The combined tube may then enter a second die where additional layers are extruded onto the existing layers, and the resulting multilayer product emerges from the second die. The tubes that are created by this technique can also either be split to create a single layer of film or the tubes can be employed to wrap products therein meaning that the ends of the tube simply need to be closed as part of a bag making and vacuum packaging process.

Figure 2 shows schematically the process involved in wrapping a consumable product (7) in a film (8). In an alternative embodiment a tube of film can be used and this is illustrated as tube end (9). The consumable product that is encompassed by the film is then vacuum packed so that the film collapses around the consumable product. The film is then heat shrunk at temperatures less than 100°C and the inner layer of each layer of film (8) that overlap undergo secondary sealing (10). The secondary sealing (10) closes off the microchannels between the inner layers of film (8) or the inner layers of tube (9) and prevents juices flowing from the consumable product between the layers of film. An expanded cross sectional view of the secondary sealing achieved between a first layer (1 1) and a second layer (12) of film is illustrated in figure 3. Secondary sealing (13) is achieved between the sealant layer of the first layer (11 ) and the sealant layer of the second layer (12). The secondary sealing (13) that is achieved is essentially a weld between the layers. This welding effect closes off the microchannels that would otherwise exist between these layers after vacuum packaging and heat shrinking. The weld thereby prevents the flow of juices from the consumable product between the layers thereby improving the appearance of the overall wrapped consumable product.

The inventors have also found that the actual composition of the sealant layer formulation can also be determined provided the overall differential scanning calorimetry melt point of the resultant sealant layer formulation is approximately 85 to 95°C. The differential scanning calorimetry measure is simply one measure of the melt point of a resin that can be used to identify suitable secondary sealing temperatures. A differential scanning calorimeter enables one to measure thermal transitions and is widely used in the art for the characterisation of polymers and materials.

Further specific details of the formulation of the sealant layer is provided in the following examples 1 and 2.

Example 1

In a first embodiment the trial product used the following formulation as the sealant layer:

Dow Dowlex 2247G resin (formerly known as Dow Dowlex 2247A) (50%) and Dow Affinity resin EG 8100 (50%). In the resulting film, the secondary sealing effect was well formed at 85°C. The DSC melt point of 2247A is 123°C. The DSC melt point of EG 8100 is 55°C. The thickness of the sealant layer was 7-10 microns.

This embodiment has been field tested with a meat packaging line using a hot water shrink tunnel. Favourable results were obtained and good secondary sealing effects were observed thereby preventing the meat juices flowing into the flap area of the wrapped product and improving the overall presentation of the final meat product. Example 2

In a second embodiment the trial product used the following formulation as the sealant layer:

Dow Affinity PF1 140 resin (90%) and Dow Affinity resin PT1450 (10%). In the resulting film the secondary sealing effect started at 93°C and was well formed at 95°C. The DSC melt point of PF1140 is 94C. The DSC melt point of PT1450 is 98C. The thickness of the sealant layer was 7-10 microns.

Comparative Example

The films of the examples were further compared with that of a film using a conventional sealant layer.

The conventional sealant layer comprised solely a LLDPE/LDPE blend, in particular a blend of Dowlex 2247A 90% (LLDPE) and Equistar NA204000 10% (LDPE).

The results are tabulated in Table 1.

Table 1

The secondary sealing effect was observed in the first instance by vacuum packaging blocks of wood, heat shrinking the wrapped blocks of wood in hot water at 85°C and testing the ability of the flap areas to seal together. Example 3

An alternative embodiment of the present invention is provided in this example.

The film of this example comprises an inner sealant layer, an oxygen barrier layer, and an outer layer. The outer layer comprises ExxonMobil Exact 0203 plastomer and Eurcamide slip (2%). It is to be appreciated that the Eurcamide slip could be present in percentages from 0-6% of the total weight of the outer layer. The oxygen barrier layer comprises PVDC (Dow Saran) and the inner layer/sealant layer comprises 50% Exact 0203 (metallocene plastomer) and 50% EG8100 (metallocene plastomer). In this particular embodiment an inner and outer tie layer comprising EVA resins are included in the film. The outer tie layer is positioned between the outer layer and the oxygen barrier layer. The inner tie layer is positioned between the oxygen barrier layer and the inner/sealant layer. The overall gauge of the film is preferably 40 to 85 micrometres. It is preferred that the sealant layer has a gauge of approximately 5 to 10 micrometres. This embodiment, while providing the desired secondary sealing effect at temperatures of above 80°C when the film is heat shrunk, also provides a film having visually improved properties of increased gloss and clarity.

This invention means that an existing current hot water shrink process can be used to adhere the inner layers of the sealant layer formulation, thus, for example stopping the meat juices flowing into the pack flaps and improving presentation.

The shrink achieved in both the machine direction and cross directions of the film is favourable and in fact is improved over that observed for the comparative example which illustrates a conventional shrink wrap film.

An added benefit provided by the present invention include the fact that an ionomer or acid copolymer based resin, which are traditionally expensive is not required.

Where in the foregoing description reference has been made to integers known to have equivalents in the art, then those equivalents are hereby incorporated as if individually set forth. While the invention has been described with reference to preferred embodiments and examples thereof it is to be appreciated that variations and modifications may be made thereto without departing from the spirit or scope of the invention.

Claims

What we claim is

1. A heat shrink barrier film including at least one outer layer including a polyolefin resin; - at least one oxygen barrier layer; and an inner non-ionomer sealant layer; wherein in use, the non-ionomer sealant layer provides a secondary sealing effect when the heat shrink barrier film is exposed to temperatures of between 80-100°C.

2. The heat shrink barrier film according to claim 1 wherein the outer layer includes a resin or blend of resins selected from one or more of EVA, LLDPE, m-LLDPE, plastomers and metallocene catalysed plastomers.

3. The heat shrink barrier film according to claim 1 or claim 2 wherein an outer tie layer is intermediate the oxygen barrier layer and outer layer.

4. The heat shrink barrier film according to claim 3 wherein the outer tie layer includes a resin or blend of resins selected from one or more of EVA m-LLDPE, plastomers, and metallocene catalysed plastomers.

5. The heat shrink barrier film according to any one of claims 1 to 4 wherein an inner tie layer is intermediate the oxygen barrier layer and sealant layer.

6. The heat shrink barrier film according to claim 5 wherein the inner tie layer includes a resin or blend of resins selected from one or more of EVA m-LLDPE, plastomers, and metallocene catalysed plastomers.

7. The heat shrink barrier film according to any one of claims 1 to 6 wherein the oxygen barrier layer includes a resin or blend of resins selected from PVDC, nylon or EVOH.

8. The heat shrink barrier film according to any one of claims 1 to 7 wherein the non-ionomer sealant layer provides the secondary sealing effect when the heat shrink barrier film is exposed to temperatures of between 85-95°C.

9. The heat shrink barrier film according to any one of claims 1 to 8 wherein the inner non-ionomer layer is adapted to be co-extruded with the barrier layer.

10. A heat shrink barrier film including - at least one outer layer including EVA resin as a component at least one oxygen barrier layer including PVDC resin; at least one inner layer including EVA resin as a component; at least one inner tie layer comprising a polyolefin; and an inner non-ionomer sealant layer; wherein in use, the non-ionomer sealant layer provides a secondary sealing effect when the heat shrink barrier film is exposed to temperatures of between 80-100°C.

1 1. The heat shrink barrier film according to claim 10 wherein the sealant layer provides the secondary sealing effect when the heat shrink barrier film is exposed to temperatures of between 85-95°C.

12. The heat shrink barrier film according to claim 10 or claim 1 1 wherein the sealant layer is between 5 - 12 micrometres in thickness.

13. The heat shrink barrier film according to claim 1 1 wherein the sealant layer is between 7 - 10 micrometres in thickness.

14. The heat shrink barrier film according to any one of claims 10 to 13 wherein the outer layer comprises a first outer layer including EVA and a second outer tie layer including EVA.

15. The heat shrink barrier film according to any one of claims 10 to 14 wherein the inner tie layer includes a resin or blend of resins selected from one or more of EVA m-LLDPE, plastomers, and metallocene catalysed plastomers.

16. The heat shrink barrier film according to any one of claims 10 to 15 wherein the inner non-ionomer layer is adapted to be co-extruded with the PVDC barrier layer.

17. The heat shrink barrier film according to any one of claims 10 to 16 wherein the sealant layer is between 5 - 12 micrometres in thickness.

18. The heat shrink barrier film according to any one of claims 10 to 17 wherein the sealant layer is between 7 - 10 micrometres in thickness.

19. The heat shrink barrier film according to any one of claims 10 to 18 wherein the heat shrink barrier film is between 40 - 90 micrometres in thickness.

20. The heat shrink barrier film according to any one of claims 10 to 19 wherein the heat shrink barrier film is between 45 - 85 micrometres in thickness.

21. The heat shrink barrier film according to any one of claims 10 to 20 wherein the sealant layer comprises a blend of LLDPE, and a polyolefin plastomer or blend of plastomers having a DSC melt point less than 100°C.

22. The heat shrink barrier film according to claim 21 wherein the sealant layer comprises a blend of a maximum of 50% LLDPE, and a minimum of 50% of a polyolefin plastomer.

23. The heat shrink barrier film according to claim 21 or claim 22 wherein the sealant layer comprises a blend of

50% LLDPE polythethylene resin, and 50% of a polyolefin plastomer.

24. The heat shrink barrier film according to any one of claims 10 to 20 wherein the sealant layer comprises a blend of a first polyolefin plastomer, and a second polyolefin plastomer.

25. The heat shrink barrier film according to claim 24 wherein the sealant layer comprises a blend of

90% of the first polyolefin plastomer, and 10% of the second polyolefin plastomer.

26. A heat shrink barrier film including at least one outer layer including a plastomer as a component at least one oxygen barrier layer including PVDC resin; and an inner non-ionomer sealant layer including a metallocene plastomer as a component; wherein in use, the inner non-ionomer sealant layer provides a secondary sealing effect when the heat shrink barrier film is exposed to temperatures of between 80-100°C.

27. The heat shrink barrier film according to claim 26 wherein the non-ionomer sealant layer is adapted to provide the secondary sealing effect when the heat shrink barrier film is exposed to temperatures of between 85-95°C.

28. The heat shrink barrier film according to claim 26 or claim 27 wherein the sealant layer is between 7 - 10 micrometres in thickness.

29. The heat shrink barrier film according to any one of claims 26 to 28 wherein the inner non-ionomer sealant layer is adapted to be co-extruded with the PVDC barrier layer.

30. The heat shrink barrier film according to any one of claims 26 to 29 wherein the sealant layer is between 5 - 12 micrometres in thickness.

31. The heat shrink barrier film according to any one of claims 26 to 30 wherein the sealant layer is between 7 - 10 micrometres in thickness.

32. The heat shrink barrier film according to any one of claims 26 to 31 wherein the heat shrink barrier film is between 40 - 90 micrometres in thickness.

33. The heat shrink barrier film according to any one of claims 26 to 32 wherein the heat shrink barrier film is between 45 - 85 micrometres in thickness.

34. The heat shrink barrier film according to any one of claims 26 to 33 wherein the outer layer includes a blend of ExxonMobil Exact 0203 plastomer and Eurcamide slip.

35. The heat shrink barrier film according to claim 34 wherein the sealant layer includes a blend of

50% Exact 0203 (metallocene plastomer) and 50% EG8100 (metallocene plastomer).

36. A method of heat shrink wrapping a consumable product including the steps of wrapping and vacuum packaging the consumable product with a heat shrink barrier film as defined in any one of claims 1 to 9, 10 to 25 or 26 to 33; exposing the resulting wrapped product to a temperature of between 80 - 100°C thereby facilitating heat shrinkage of the film about the product and thereby facilitating a secondary sealing effect between any first portion of the inner non-ionomer sealant layer of the film in contact with any second portion of the inner non-ionomer sealant layer of the film.

37. The method according to claim 36 wherein the wrapped product is exposed to temperatures of between 85-95°C.

38. The method according to claim 36 or claim 37 wherein the heat shrinkage step is achieved in a hot air tunnel or hot water bath.

39. The method according to any one of claims 36 to 38 which further includes a vacuum packing step, whereby the consumable product is vacuum packed prior to the step of exposing the wrapped product to the heat shrinkage temperature.

40. A wrapped consumable product obtained by the method defined in any one of claims 36 to 39.