MULTILAYER MONOAXIALLY ORIENTED FILM

Abstract

The present invention is directed to a monoaxially oriented multilayer film suitable for shrink lidding applications.

Claims

1. A monoaxially oriented, crosslinked film comprising at least one oxygen barrier layer, the oxygen barrier layer comprising at least one oxygen barrier polymer, wherein the film has a shrinkage in the MD direction in a range from 1 to 30% measured according to ASTM D2732 by immersion in water at a temperature of 90° C. and an immersion time of 5 seconds.

2. The film according to claim 1, wherein the oxygen barrier polymer comprises at least polyamide and/or EVOH.

3. The film according to claim 1, wherein the film has a shrinkage in the MD direction in a range from 5 to 20 measured according to ASTM D2732 by immersion in water at a temperature of 90° C. and an immersion time of 5 seconds.

4. The film according to claim 1, wherein the film comprises a first outer layer comprising like ethylene alpha olefin copolymers, low density polyethylene, high density polyethylenes, ionomers, thermoplastic adhesives, cyclic olefin copolymers, ethylene vinyl acetates, polyamides, polyesters and the like, preferably ethylene alpha olefin copolymer.

5. The film according to claim 1, wherein the film comprises a second outer layer comprising et least one of the following components ethylene alpha olefin copolymers, low density polyethylene, high density polyethylene, ionomers, thermoplastic adhesives, cyclic olefin copolymers, ethylene vinyl acetates, polyamides, polyesters and the like.

6. The film according to claim 1, wherein the film comprises in the barrier layer a blend of an amorphous polyamide with other polyamides, preferably the amorphous polyamide is used in an amount of 10-40% per mass of the polyamide blend, more preferable the amorphous polyamide is 6I/6T.

7. The film according to claim 1, wherein the film further comprises one or more adjacent layer between the first outer layer and a barrier layer and/or between the second outer layer and a barrier layer.

8. The film according to claim 1, wherein the film further comprises at least one abuse layer, wherein the abuse layer is located between a barrier layer and an adjacent layer, in direct contact with both of them.

9. The film according to claim 1, wherein the film comprises or consist of the following layers OUTER LAYER 1/ADJACENT LAYER 1/BARRIER LAYER/ABUSE LAYER/ADJACENT LAYER 2/OUTER LAYER 2

10. The film according to claim 1, wherein the film comprises or consist of the following layers OUTER LAYER 1/ADJACENT LAYER 1/ADJACENT LAYER 2/BARRIER LAYER/ABUSE LAYER/ADJACENT LAYER 3/ADJACENT LAYER 4/OUTER LAYER 2

11. The film according to claim 1, wherein the film comprises or consist of the following layers OUTER LAYER 1/ADJACENT LAYER 1/ADJACENT LAYER 2/ADJACENT LAYER 3/BARRIER LAYER/ABUSE LAYER/ADJACENT LAYER 4/ADJACENT LAYER 5/OUTER LAYER 2

12. The film according to claim 1, wherein the film comprises an antifog compound.

13. A method for packaging, the method comprising using the film according to claim 1 for packaging applications, preferably for food packaging.

14. A method for packaging, the method comprising using of the film according to claim 1 as top lidding film in modified atmosphere packaging (MAP) applications.

15. A pack comprising a film according to claim 1 and a tray.

16. A method for producing a monoaxially oriented, crosslinked film, comprising the following steps: a) Producing a film by extrusion molding; b) Quenching the film immediately after extrusion and exit of the film from the extrusion die, by cooling down the film with a high cooling rate; c) Irradiating the film by electron beam or gamma radiation after quenching; and d) Orienting the film monoaxially after the irradiation step.

17. A monoaxially oriented, crosslinked film obtained by the method according to claim 16.

Description

DETAILED DESCRIPTION

[0061] According to a first aspect the present invention provides a monoaxially oriented, crosslinked film comprising at least one oxygen barrier layer, the oxygen barrier layer comprising at least one oxygen barrier polymer, wherein the film has a shrinkage in the MD direction in a range from 1 to 30% measured according to ASTM D2732 by immersion in water at a temperature of 90° C. and an immersion time of 5 seconds.

[0062] In the film according to the first aspect the oxygen barrier polymer preferably comprises at least polyamide and/or EVOH.

[0063] The film according to the first aspect preferably has a shrinkage in the MD direction in a range from 5 to 20 measured according to ASTM D2732 by immersion in water at a temperature of 90° C. and an immersion time of 5 seconds.

[0064] The film according to the first aspect preferably comprises a first outer layer comprising ethylene alpha olefin copolymer.

[0065] The film according to the first aspect preferably comprises a second outer layer comprising at least one of the following components: ethylene alpha olefin copolymers, low density polyethylene, high density polyethylene, ionomers, thermoplastic adhesives, cyclic olefin copolymers, ethylene vinyl acetates, polyamides, polyesters and the like.

[0066] The film according to the first aspect preferably comprises in the barrier layer a blend of an amorphous polyamide with other polyamides, preferably the amorphous polyamide is used in an amount of 10-40% per mass of the polyamide blend, more preferable the amorphous polyamide is 6I/6T.

[0067] The film according to the first aspect preferably further comprises one or more adjacent layer between the first outer layer and a barrier layer and/or between the second outer layer and a barrier layer.

[0068] The film according to the first aspect preferably further comprises at least one abuse layer, wherein the abuse layer is located between a barrier layer and an adjacent layer, in direct contact with both of them.

[0069] The film according to the first aspect preferably comprises or consists of the following layers [0070] OUTER LAYER 1/ADJACENT LAYER 1/BARRIER LAYER/ABUSE LAYER/ADJACENT LAYER 2/OUTER LAYER 2

[0071] The film according to the first aspect preferably comprises or consists of the following layers [0072] OUTER LAYER 1/ADJACENT LAYER 1/ADJACENT LAYER 2/BARRIER LAYER/ABUSE LAYER/ADJACENT LAYER 3/ADJACENT LAYER 4/OUTER LAYER 2

[0073] The film according to the first aspect preferably comprises or consists of the following layers [0074] OUTER LAYER 1/ADJACENT LAYER 1/ADJACENT LAYER 2/ADJACENT LAYER 3/BARRIER LAYER/ABUSE LAYER/ADJACENT LAYER 4/ADJACENT LAYER 5/OUTER LAYER 2

[0075] Each of ADJACENT LAYER 1-5 can comprise the same or different materials.

[0076] The film according to the first aspect preferably comprises an antifog compound. According to a second aspect the present invention relates to the use of a film according to the first aspect of the invention for packaging applications, preferably for food packaging.

[0077] In one embodiment the invention relates to the use of a film according to the first aspect of the invention as top lidding film in modified atmosphere packaging (MAP) applications.

[0078] According to a third aspect the present invention relates to a pack comprising a film according to the first aspect and a tray.

[0079] According to a fourth aspect the present invention relates to a method for producing a monoaxially oriented, crosslinked film, comprising the following steps: a) Producing a film by extrusion molding; b) Quenching the film immediately after extrusion and exit of the film from the extrusion die, by cooling down the film with a high cooling rate; c) Irradiating the film by electron beam or gamma radiation after quenching; d) Orienting the film monoaxially after the irradiation step.

[0080] According to a fifths aspect the present invention relates to a monoaxially oriented, crosslinked film obtained by the method according to the fourth aspect.

DETAILED DESCRIPTION OF LAYERS

[0081] Barrier Layer

[0082] The barrier layer may include polymers such as polyamide, EVOH and/or polyesters, preferably polyamide and/or EVOH.

[0083] The polyamide is preferably polyamide 6, polyamide 6/66, polyamide 6/12 and/or polyamide 6/66/12.

[0084] Amorphous polyamide can also be used in a blend with other polyamides, preferably the amorphous polyamide is used in an amount of 10-40% per mass of the polyamide blend, more preferably in an amount of 15-35%, even more preferably in an amount of 20-30% per mass of the polyamide blend, most preferably in an amount of 23-27% per mass. Preferable the amorphous polyamide is of 6I/6T structure; e.g., sold from EMS under the name of Grivory G21.

[0085] The EVOH used by the invention may preferably have an ethylene content of 24 to 48% per mol.

[0086] Abuse Layer

[0087] The abuse layer may comprise materials like ethylene alpha olefin copolymers, low density polyethylene, high density polyethylenes, ionomers, thermoplastic adhesives, cyclic olefin copolymers, ethylene vinyl acetates, polyamides, polyesters and the like.

[0088] Adjacent Layer

[0089] The Adjacent layer may comprise materials like ethylene alpha olefin copolymers, low density polyethylene, high density polyethylenes, ionomers, thermoplastic adhesives, cyclic olefin copolymers, ethylene vinyl acetates, polyamides, polyesters and the like.

[0090] If adjacent and/or abuse layers are directly bonded to a barrier layer, it is important to contain at least a part of thermoplastic adhesive in order to attain a reasonable bonding to the barrier layer. A preferred type of thermoplastic adhesive is maleic anhydride grafted polyolefins, eg polyethylene and/or polypropylene.

[0091] First Outer Layer

[0092] The first outer layer comprises materials like ethylene alpha olefin copolymers, low density polyethylene, high density polyethylenes, ionomers, thermoplastic adhesives, cyclic olefin copolymers, ethylene vinyl acetates, polyamides, polyesters and the like.

[0093] Second Outer Layer (Sealing Layer)

[0094] The second outer layer 2 (also sealing layer) comprises materials like ethylene alpha olefin copolymers, low density polyethylene, high density polyethylenes, ionomers, thermoplastic adhesives, cyclic olefin copolymers, ethylene vinyl acetates, polyamides, polyesters and the like. Preferably the layer comprises ethylene alpha olefin copolymers, low density polyethylene and.or EVA.

[0095] In a preferred version of the film, the film is produced by a method incorporating high cooling speed immediately after extrusion and exit of the film from the extrusion die. Such methods are [0096] cast film produced from a longitudinal die [0097] highly air-cooled blown film produced from a tubular die [0098] water cooled blown film produced from a tubular die

[0099] In general, it is preferred for the invention the film to be produced by a highly quenching (very efficient and quick cooling) process such as cast film or water-cooled blown film. This decreases the crystallinity of the film prior to orientation, making the film easier to orient as per MDO process.

[0100] The film is preferably irradiated by electron beam.

[0101] The irradiation dose is preferably at least 1 MRAD, more preferably at least 2 MRAD.

[0102] The dose is preferably up to 20 MRAD, more preferably up to 18 MRAD.

[0103] The gel content of the polyolefin version film is 1 to 60%, more preferably 3 to 50%.

[0104] The film may be irradiated prior or after the MDO orientation. Prior to MDO is preferred, as this is believed it improves the MDO orientation process.

EXAMPLES

Example 1

[0105] A 9-layer film is produced in fast quenching line (so that crystallinity is minimized as much as possible). The film structure is as follows:

TABLE-US-00001 Outer layer 1 100% polyamide 6. Adjacent layer 1 LLDPE based tie layer Adjacent layer 2 70% metallocene LLDPE + 30% low density polyethylene Adjacent layer 3 LLDPE based tie layer Barrier Layer EVOH 38% mol ethylene content Abuse layer 100% copolyamide 6/66 Adjacent layer 4 LLDPE based tie layer Adjacent layer 5 70% metallocene LLDPE + 30% low density polyethylene Outer layer 2 (sealing layer) 70% metallocene LLDPE + 20% low density polyethylene + 10% antifog masterbatch

[0106] The thicknesses of the different layers are from outer layer 1 to outer (sealing) layer 2 as follows:

[0107] 20/5/5/5/8/10/10/10/27

Example 2

[0108] A 9-layer film is produced as in Example 1. The film structure is as follows:

TABLE-US-00002 Outer layer 1 70% metallocene LLDPE + 30% low density polyethylene Adjacent layer 1 70% metallocene LLDPE + 30% low density polyethylene Adjacent layer 2 LLDPE based tie layer Adjacent layer 3 100% copolyamide 6/66 Barrier Layer EVOH 38% mol ethylene content Abuse layer 100% copolyamide 6/66 Adjacent layer 4 LLDPE based tie layer Adjacent layer 5 70% metallocene LLDPE + 30% low density polyethylene Outer layer 2 (Sealing layer) 70% metallocene LLDPE + 20% low density polyethylene + 10% antifog masterbatch

[0109] Thickness of different layers are as follows

[0110] 20/5/5/5/8/10/10/10/27

Example 3

[0111] A further example was produced as follows

TABLE-US-00003 Outer layer 1 70% metallocene LLDPE + 30% low density polyethylene Adjacent layer 1 70% metallocene LLDPE + 30% low density polyethylene Adjacent layer 2 70% metallocene LLDPE + 30% low density polyethylene Adjacent layer 3 LLDPE based tie layer Barrier Layer EVOH 44% mol ethylene content Abuse layer LLDPE based tie layer Adjacent layer 4 70% metallocene LLDPE + 30% low density polyethylene Adjacent layer 5 70% metallocene LLDPE + 30% low density polyethylene Outer layer 2 (Sealing layer) 70% metallocene LLDPE + 30% low density polyethylene

[0112] Thickness of different layers are as follows

[0113] 20/5/5/5/8/10/10/10/27

[0114] Crosslinking by Electron Beam

[0115] The three films according to examples 1, 2, and 3 were afterwards crosslinked by electron beam irradiation at a level of 6 Mrads.

[0116] Gel Content

[0117] The gel content of the materials was calculated as follows:

[0118] The non-polyethylene layers were dissolved in keeping the film in formic acid under ambient conditions for 24 hours. Then the film was left to cool and dried at 40° C. for 10 hours.

[0119] Then the gel content of the polyethylene (or more general polyolefin) part of the multilayer film was measured following the method of ASTM D 2765.

[0120] In case the film comprises other polyolefin, non-polyethylene materials like polypropylene or cyclic olefin copolymers, the measurement of the gel content is done according to ASTM D2765 as well.

TABLE-US-00004 TABLE 1 GEL CONTENT % of FILM polyolefin part of the film 1 4 2 6 3 6

[0121] Monoaxial Orientation

[0122] The films were subsequently monoaxially oriented in a commercial MDO line, comprising totally 12 rollers of which 4 consist the stretching until and the rest are preheating, annealing and cooling rollers.

[0123] The temperature of the stretching rollers was set to 95-110° C. while the stretch ratio (ratio of the initial film thickness divided by the total film thickness) was 4. Thus, the thickness of the final films produced was 25 microns, which is a typical thickness for shrinkable lidding films.

[0124] In order to retain an appropriate level of shrinkage, the temperature of the annealing rollers was kept at a temperature of less than the stretching rollers and also less than 90° C. So, the temperature of the annealing rollers was 85° C.

TABLE-US-00005 TABLE 2 HAZE SHRINKAGE AT MD MD ASTM (ASTM D2732, orientation FILM D1003 90° C., 5 seconds) process 1 4.7 15 stable 2 5.5 14 stable 3 5.6 11 stable

[0125] Antifog

[0126] In many MAP applications of wet products, it is necessary to add antifog to the film to allow for visibility of the contents. The antifog can be added as a masterbatch during extrusion, prebaby in the second outer (sealing) layer (see examples 1, 2) or in a separate coating step. This was done with film 3 where the antifog was added at subsequent coating step. The surface coated is the surface of the film to be in contact with the food packed.

[0127] Well known antifog substances are glycerol esters, polyglycerol esters, ethoxylated sorbitan esters, sorbitan esters of fatty acids and other substances as well known in the art.

[0128] The antifog coating can be done by well-known processes in the art such as spray coating, roller coating, gravure coating, flexographic coating or others.

[0129] Suitability as Shrinlable Top Lidding Film

[0130] The three films were tested as per their suitability as top lidding films.

[0131] The test was done at a customer packing in a Multivac T300 tray sealer. As a known film a biaxially oriented film comprising polyethylene, polyamide and EVOH was used.

Comparative Example

[0132] Films 1, 2, 3 were tested against the known film, which was a biaxially oriented film heat shrinkable in both MD and TD directions. The test showed practically no difference in the pack tightness. Surprisingly, it was noticed that the monoaxial films of the invention showed better processability during operation. The known film was more difficult to cut causing a lot of process interruptions.