MULTILAYER MONOAXIALLY ORIENTED CROSSLINKED FILM AND PROCESS

Abstract

The present invention is directed to a monoaxially oriented, cross-linked multilayer film.

The invention is further directed to a method of producing and preserving a food product using such a film, bag or pouch and to a packaged food product obtained therefrom.

Claims

1. A monoaxially oriented, cross-linked multilayer film comprising an outer layer, a sealing layer, and a core layer arranged between the outer layer and the sealing layer.

2. The multilayer film according to claim 1, wherein the core layer comprises an oxygen barrier material, preferably EVOH, polyamide, or PVDC.

3. The multilayer film according to claim 2, wherein the EVOH comprises preferably 24 to 50% ethylene per mol, more preferably 27 to 48% ethylene per mol, more, even more preferably, the EVOH has an ethylene content of 29 to 48% per mol.

4. The multilayer film according to claim 2, wherein the polyamide used is homo or copolymer of polyamide 6 (polycaprolactam), preferably polyamide 6, polyamide 6/66, polyamide 6/66/12, or an inherently amorphous polyamide.

5. The multilayer film according to claim 1, wherein the core layer comprises a polyolefin, EVA, or a polyamide, preferably the polyolefin is LLDPE.

6. The multilayer film according to claim 1, wherein the film further comprises a first abuse layer between the outer layer and the core layer and/or a second abuse layer between the core layer and the sealing layer, preferably the first and/or second abuse layer comprise EVA, preferably the EVA can be used a single polymer in the first and/or second abuse layer or in a form of blend with EMA, ethylene alpha olefin copolymers, styrene polymers, or LDPE.

7. The multilayer film according to claim 1, wherein the film further comprises a first tie layer between the first abuse layer and the core layer and/or a second tie layer between the core layer and the second abuse layer.

8. The multilayer film according to claim 7, wherein the first and/or second tie layer comprise a polyolefin, preferably LLDPE, maleic anhydride modified EVA, maleic anhydride modified polyethylene, maleic anhydride modified EMA, maleic anhydride modified elastomer, partially saponified EVA copolymer or polyurethane elastomer.

9. The multilayer film according to claim 1, wherein the sealing layer comprises a polyolefin, preferably an ethylene copolymer, more preferably ethylene alpha olefin copolymer or ethylene ester copolymer, preferably EVA and/or EMA.

10. The multilayer film according to claim 1, wherein the outer layer comprises a polyethylene, preferably a low-density polyethylene, a linear low-density polyethylene, a medium-density polyethylene or a high-density polyethylene.

11. A method for producing an oriented multilayer film according to claim 1, comprising the following steps: a) a film extrusion step b) a crosslinking step c) a monoaxial orientation step.

12. The method for producing a multilayer film according to claim 11, wherein the crosslinking is performed before the monoaxial orientation step c) or after the monoaxial orientation step c).

13. A monoaxially oriented, crosslinked multilayer film obtained by a method according to claim 11.

14. A method for packaging, the method comprising using the multilayer film according to claim 1 in a vacuum skin packaging process.

15. The method according to claim 14, wherein the film is used as top lidding film.

16. A monoaxially oriented, crosslinked multilayer film obtained by a method according to claim 12.

Description

DETAILED DESCRIPTION

[0067] The present invention relates to a monoaxially oriented, cross-linked multilayer film comprising an outer layer, a sealing layer, and a core layer arranged between the outer layer and the sealing layer.

[0068] In one embodiment, the core layer comprises an oxygen barrier material, preferably EVOH, polyamide, or PVDC.

[0069] If the core layer comprises as oxygen barrier material EVOH, then preferably the EVOH comprises 24 to 50% ethylene per mol, more preferably 27 to 48% ethylene per mol, more, even more preferably, the EVOH has an ethylene content of 29 to 48% per mol.

[0070] If the core layer comprises as oxygen barrier material polyamide, then preferably the polyamide used is homo or copolymer of polyamide 6 (polycaprolactam). The polyamide used is preferably polyamide 6, polyamide 6/66, polyamide 6/66/12, or an inherently amorphous polyamide.

[0071] In alternative embodiment, the multilayer film comprises a core layer comprising a polyolefin, EVA, or a polyamide, preferably the polyolefin is LLDPE.

[0072] The multilayer film can further comprises a first abuse layer between the outer layer and the core layer and/or a second abuse layer between the core layer and the sealing layer. Preferably, the first and/or second abuse layer comprise EVA. Preferably the EVA can be used a single polymer in the first and/or second abuse layer or in a form of blend with EMA, ethylene alpha olefin copolymers, styrene polymers, or LDPE.

[0073] The multilayer film can further comprises a first tie layer between the first abuse layer and the core layer and/or a second tie layer between the core layer and the second abuse layer. Preferably, the first and/or second tie layer comprise a polyolefin, preferably LLDPE, maleic anhydride modified EVA, maleic anhydride modified polyethylene, maleic anhydride modified EMA, maleic anhydride modified elastomer, partially saponified EVA copolymer or polyurethane elastomer.

[0074] Preferably, the sealing layer comprises a polyolefin, preferably an ethylene copolymer, more preferably ethylene alpha olefin copolymer or ethylene ester copolymer, preferably EVA and/or EMA.

[0075] Preferably, the outer layer comprises a polyethylene, preferably a low-density polyethylene, a linear low-density polyethylene, a medium-density polyethylene or a high-density polyethylene.

[0076] The present invention further relates to a method for producing an oriented multilayer film according to one of the preceding claims comprising the following steps: [0077] a) a film extrusion step [0078] b) a crosslinking step [0079] c) a monoaxial orientation step.

[0080] The crosslinking can be performed before the monoaxial orientation step c) or after the monoaxial orientation step c). The film is preferably irradiated by electron beam. The irradiation dose is preferably at least 1 MRAD, more preferably at least 2 MRAD. The dose is preferably up to 20 MRAD, more preferably up to 18 MRAD.

[0081] In a preferred embodiment, the film is produced by a method incorporating high cooling speed immediately after extrusion and exit of the film from the extrusion die.

[0082] Such methods include [0083] cast film produced from a longitudinal die [0084] highly air cooled blown film produced from a tubular die [0085] water cooled blown film produced from a tubular die

[0086] In another preferred method the film is produced by conventional air cooled hot blown film process.

[0087] Film Structure

[0088] The film is generally a film comprising from 3 to more than 9 layers.

[0089] Such layers can be a sealing layer (in direct contact with the food), core layer (comprising optionally an oxygen barrier material), abuse layers, adhesive tie layers (allowing bonding between layers that have no physical adhesion), and an outer layer.

[0090] In one embodiment, the film may comprise an outer layer, a sealing layer and a core layer located between the outer and the sealing layer.

[0091] Outer layer/core layer/sealing layer

[0092] In another embodiment the multilayer film can further comprises a first abuse layer between the outer layer and the core layer and/or a second abuse layer between the core layer and the sealing layer.

[0093] Outer layer/first abuse layer/core layer/sealing layer, or

[0094] Outer layer/core layer/second abuse layer/sealing layer, or

[0095] Outer layer/first abuse layer/core layer/second abuse layer/sealing layer

[0096] In a further embodiment the multilayer film can further comprises a first tie layer between the first abuse layer and the core layer and/or a second tie layer between the core layer and the second abuse layer.

[0097] Outer layer/first abuse layer/first tie layer/core layer/second abuse layer/sealing layer, or

[0098] Outer layer/first abuse layer/core layer/second tie layer/second abuse layer/sealing layer, or

[0099] Outer layer/first abuse layer/first tie layer/core layer/second tie layer/second abuse layer/sealing layer

[0100] Sealing Layer

[0101] The sealing layer of the film is preferably polyolefin based, more preferably ethylene copolymer based, more preferably ethylene alpha olefin copolymer based or ethylene ester based (such as EVA and/or EMA). For being able to seal to more unconventional bottom sheets or trays like aluminum the sealing layer may comprise tackifiers or other compounds.

[0102] The thickness of the sealing layer is from 5 to 100 microns, more preferably from 10 to 80 microns.

[0103] Core Layer

[0104] The film in one embodiment comprises in the core layer a high oxygen barrier material so that it protects the components of the pack from the detrimental effect of oxygen ingress. EVOH is a preferred option but also polyamide and PVDC are viable alternatives.

[0105] If the core layer comprises as oxygen barrier material EVOH, then preferably the EVOH comprises 24 to 50% ethylene per mol, more preferably 27 to 48% ethylene per mol, more, even more preferably, the EVOH has an ethylene content of 29 to 48% per mol.

[0106] If the core layer comprises as oxygen barrier material polyamide, then preferably the polyamide used is homo or copolymer of polyamide 6 (polycaprolactam). The polyamide used is preferably polyamide 6, polyamide 6/66, polyamide 6/66/12, or an inherently amorphous polyamide.

[0107] In an alternative embodiment, in cases where the food does not need a protection from oxygen, the film may comprise in the core layer a polyolefin, EVA, or a polyamide, preferably the polyolefin is LLDPE.

[0108] The thickness of the core layer can be from 3 to 20 microns, with a preferable thickness being 5 to 16 microns.

[0109] Abuse Layer(s)

[0110] Preferably, the abuse layers comprise EVA. The EVA can be alone in this layer or in a form of blend or compound. Suitable blending partners for the EVA include EMA, ethylene alpha olefin copolymers, styrene polymers, LDPE and others.

[0111] The vinyl acetate content of the EVA used in the intermediate layers is 3 to 90%, preferably 5 to 80 to 80%. Preferred melt flow indexes are 0.3 to 5 measured at 190C, 2.16 kilos.

[0112] In a further preferred version, the film comprises at least 30% per weight ethylene alpha olefin copolymers with density less than 0.920 g/cm3.

[0113] Tie Layer(s)

[0114] As well known in the art, there is no natural adhesion between polyolefins such as EVA and high barrier polymers such as EVOH. Therefore, suitable adhesive resins must be used so that the film does not collapse under the oven heating.

[0115] Suitable materials for the tie layer process include maleic anhydride modified EVA, maleic anhydride modified polyethylene, maleic anhydride modified EMA, maleic anhydride modified elastomer, partially saponified EVA copolymer and polyurethane elastomer.

[0116] Outer Layer

[0117] The outer layer of the film comprises preferably, low density polyethylene, linear low density polyethylene medium density polyethylene or high density polyethylene.

EXAMPLES

Example 1

[0118] Extrusion Process

[0119] A 7 layer film is produced in an air cooled how blown film line. The film structure is as follows

[0120] Outer layer 100% of linear low-density polyethylene material Dowlex NG5056E from Dow Chemical company.

[0121] First abuse layer EVA having 12% per mass vinyl acetate content

[0122] First tie layer LLDPE based tie layer

[0123] Barrier Layer EVOH 44% mol having a melt flow index of about 2 measured at 190C, 2.16 kilos

[0124] Second tie layer LLDPE based tie layer

[0125] Second abuse layer EVA having 12% per mass vinyl acetate content

[0126] Sealing layer 70% metallocene LLDPE +30% low density polyethylene

[0127] Thickness of different layers are as follows

[0128] 30/30/20/20/20/30/30 with total thickness 180 microns

[0129] MDO Process

[0130] Then the film was monoaxially oriented using a well-known in the art monoaxial orientation process. The film produced by the process had a total thickness of 55 microns.

[0131] Crosslinking

[0132] The film was crosslinked at a dose of 12 Mrads.

Example 2

[0133] A film similar to sample 1 was produced with the difference that the crosslinking process was done prior to the MDO orientation process,

Example 3

[0134] Same film as example 1 was produced but the EVOH was replaced by amorphous polyamide Grivoty G21 supplied by company EMS.

[0135] The MDO and crosslinking process followed the example 1 with the difference that the final film thickness was 65 microns.

Example 4

[0136] Same as example 1 but instead of EVOH the material used in the two abuse layers was used. This example is a film without any presence of oxygen barrier material.

[0137] The MDO and crosslinking process followed the example 1 with the difference that the final film thickness was 65 microns.

Comparative Example

[0138] As a comparative example a commercial vacuum skin packaging film was used (FLEXION CER 100N1 from Flexopack).

[0139] Measurement of Vacuum Skin Packaging Performance

[0140] The five films were tested as per their vacuum skin packaging performance in a Sealpac machine. 20 meat pieces were used for evaluation of each one having as reference the forming capabilities of each one and the presentation of the packs.

TABLE-US-00001 NUMBER OF FILM TOTAL NUMBER ACCEPTABLE REFERENCE OF PACKS PACKS Example 1 20 17 Example 2 20 18 Example 3 20 15 Example 4 20 16 Comparative 20 17 Example