Oven Skin Packaging Film

Abstract

A vacuum skin packaging film produced by the hot blown film method and comprising a polyester having a melting point of more than 200 C.

Claims

1. A crosslinked plastic film comprising a layer comprising polyester having melting point more than 200 C and glass transition temperature of at least 60 C.

2. The film according to claim 1, wherein the film is produced by the hot blown film process.

3. The film according to claim 1, wherein the film is not oriented.

4. The film according to claim 1, wherein the film comprises a further layer comprising an oxygen barrier material.

5. The film according to claim 1, wherein the film comprises ethylene alpha olefin copolymer.

6. The film according to claim 1, wherein the film comprises ethylene vinyl acetate.

7. The film according to claim 1, wherein the film further comprises an outer layer of EVA and/or EMA.

8. The film according to claim 1, wherein the layer comprising the polyester is the inner layer of the film.

9. Use of the film according to claim 1, as vacuum skin packaging film.

10. Use of the film according to claim 1, in ovenable applications.

11. A vacuum skin package comprising the film of claim 1.

12. Use of the vacuum skin package according to claim 11 in ovenable applications.

13. The film according to claim 2, wherein the film is not oriented.

Description

DETAILED DESCRIPTION

[0059] The present invention describes a crosslinked film comprising a sealing layer comprising polyester.

[0060] In a preferable embodiment, the polyester has a melting point of higher than 200 C, more preferably higher than 220 C.

[0061] In a preferable embodiment, the polyester has a glass transition temperature of at least 60 C.

[0062] In a further preferable embodiment, the polyester has an intrinsic viscosity (IV) at least 0.65, as measured by ASTM D5225.

[0063] In a further preferable embodiment, the film is electron beam radiated with a dose of more than 4 megarads.

[0064] In a further preferable embodiment, the film comprises an outer layer comprising EVA and or EMA.

[0065] In a further preferable embodiment, the film is produced by the hot blown film process and is not stretched.

[0066] In a further preferred embodiment, the film is thermally laminated to paper and the polyester sealing later is sealed to a top lidding film that can also withstand ovenable conditions.

Film Construction

[0067] Preferably the film comprises 5 to 15 layers, more preferably 7 to 12 layers.

[0068] A typical example of the film construction in 7 layer mode is

[0069] Outer layer/intermediate layer/tie layer/barrier layer/tie layer/intermediate layer/inner layer

[0070] The film is preferably produced by the hot blown film method and is not heat shrinkable.

Barrier Layer(s)

[0071] The film in a preferable embodiment contains high oxygen barrier materials 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. The EVOH preferably comprises 24% mol to 50% mol ethylene, more preferably 27% mol to 48% mol.

Intermediate Layer(s)

[0072] Preferably, the intermediate 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.

[0073] The vinyl acetate content of the EVA used in the intermediate layers is 3% to 90% by weight, preferably 5% to 80% by weight. Preferred melt flow indexes are 0.3 to 5 measured at 190 C, 2.16 kilos.

[0074] In a further preferred version, the film comprises at least 30% by weight ethylene alpha olefin copolymers with density less than 0.920 g/cm3.

Tie Layer(s)

[0075] 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.

[0076] 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.

Outer Layer

[0077] The outer layer of the film comprises preferably EVA and/or EMA.

[0078] Preferably the melting point of the EVA and/or EMA is less than 100 C.

[0079] If the melting point is more than 100 C the bonding to the paper sheet may be compromised.

Sealing Layer

[0080] The sealing layer of the film comprises polyester which preferably has a melting point of higher than 200 C, more preferably higher than 220 C. In a preferable embodiment, the glass transition temperature of the polyester is at least 60 C.

[0081] The sealing layer may comprise other polymers that are blendable to the polyester.

[0082] In general, the above layers may comprise further well known in the art additives such as antiblock, slip, antifog, polymer processing enhancers and others. Additives that would enhance the crosslinking are also inside the scope of the invention as long as they are approved for food contact.

[0083] In a preferred embodiment, the polyester containing sealing layer may comprise antifog additive.

[0084] As another preferred option, an antifog coating may be applied on the sealing layer

Crosslinking

[0085] The crosslinking may be done by various methods but the preferred are e-beam, gamma radiation and peroxides. The dose of the crosslinking is preferably more than 4 mrads, even more preferably more than 6 mrads, even more preferably more than 10 mrads.

Container

[0086] The film of the invention can be used both as vacuum skin packaging film for ovenable applications or as film bondable to paper and sealable to lidding film comprising polyester sealing layer.

[0087] In the case of vacuum skin packaging film:

[0088] The container can be a film or sheet thermoformed in line with the vacuum skin packaging process or a ready made tray.

[0089] In one preferable embodiment of the invention, the container is a tray or sheet with thickness at least 300 microns.

[0090] In a further preferable embodiment, this tray or sheet comprises polyester, preferably CPET.

[0091] In the case of a film bondable to paper, the film has a layer that can be thermally bonded to pare (such as EVA or EMA).

Mode of Production

[0092] The film is preferably produced by the hot blown film method as well known in the art.

[0093] The film is preferably not biaxially or monoaxially oriented (stretched).

EXAMPLE 1

[0094] From a commercial hot blown film line we produced the following film

[0095] *External layer, thickness 20 microns

[0096] *Intermediate layer 1, thickness 10 microns

[0097] *Tie layer 1, thickness 8 microns

[0098] *EVOH, thickness 8 microns

[0099] *Tie layer 2, thickness 8 microns

[0100] *Intermediate layer 2, thickness 15 microns

[0101] *Internal layer, thickness 21 microns.

[0102] The layers are as follows

[0103] External layer is 100% PET terephthalate-isophthalate copolymer with a melting point of 228 C and glass transition temperature of 75 C.

[0104] Intermediate layer 1 is anhydride modified ethylene alpha olefin copolymer, grade Admer™ 1955 from Mitsui.

[0105] Tie layer 1 and 2 are of a blend of 70% Attane™ SL4100 VLDPE from Dow Chemical and 30% Bynel® 41E710 (modified anhydride LLDPE) from Dow Chemical.

[0106] Intermediate layer 2 is an ethylene vinyl acetate copolymer having 18% by weight vinyl acetate and melt flow index 0.5 measured at 190 C and 2.16 kilos as per ASTM 1238.

[0107] Internal layer comprises a medium density polyethylene, having a density of 0.934 and a melt flow index of 1 measured under 190 C and 2.16 kilos according to ASTM D1238.

[0108] The EVOH layer comprised the grade Eval™ H171B which is a 38% mol ethylene grade.

[0109] The film was electron beam radiated with a dose of 12 Mrads.

[0110] Example 1 was a film to be used in a conventional vacuum skin packaging process, sealing to an APET or CPET tray.

[0111] The terms “external” and “internal” layer as used show the position of the layers in the hot blown film bubble. They are not to be confused to the terms “inner” and “outer ” layer as defined.

EXAMPLE 2

[0112] From a commercial hot blown film line we produced the following film

[0113] *External layer, thickness 20 microns

[0114] *Intermediate layer 1, thickness 10 microns

[0115] *Tie layer 1, thickness 8 microns

[0116] *EVOH, thickness 8 microns

[0117] *Tie layer 2, thickness 8 microns

[0118] *Intermediate layer 2, thickness 15 microns

[0119] *Internal layer, thickness 21 microns.

[0120] The layers are as follows

[0121] External layer is 100% PET terephthalate-isophthalate copolymer with a melting point of 228 C and glass transition temperature of 75 C.

[0122] Intermediate layer 1 is an hydride modified ethylene alpha olefin copolymer, grade Admer 1955 from Mitsui.

[0123] Tie layer 1 and 2 are of a blend of 70% Attane™ SL4100 VLDPE from Dow Chemical and 30% Bynel® 41E710 (modified anhydride LLDPE) from Dow Chemical.

[0124] The EVOH layer comprised the grade Eval™ H171B which is a 38% mol ethylene grade.

[0125] Intermediate layer 2 is an ethylene vinyl acetate copolymer having 18% by weight vinyl acetate and melt flow index 0.5 measured at 190 C and 2.16 kilos as per ASTM 1238.

[0126] Internal layer is an ethylene vinyl acetate copolymer having 14% by weight vinyl acetate melt flow index 0.35 measured at 190 C and 2.16 kilos as per ASTM D1238.

[0127] The film was electron beam radiated with a dose of 12 Mrads.

[0128] The film of example 2 was a film able to bond to a paper substrate and sealable to a polyester based lidding film as part of an ovenable application.

COMPARATIVE EXAMPLE

[0129] The comparative example involved a film used in vacuum skin packaging applications.

[0130] The comparative film did not comprise polyester in the structure and had a thickness of 90 microns, same as the two films of Examples 1 and 2.

[0131] The comparative example is a well proven film in vacuum skin packaging applications and has excellent formability. However, it cannot withstand high temperatures as the ones developed during the oven cooking of the film.

[0132] Comparatively to this, it is generally known in the art that the use of polyester in vacuum skin packaging films creates problems related to formability and/or sealing. For this we refer to WO2019/002105 page 4, lines 9 to 20 which gives an idea of the formability issues presented by the current films used in the art.

Formability Test 1

[0133] The films of examples 1, 2 and the comparative example were tested as per formability during vacuum skin packaging process using an in house vacuum skin packaging tray sealer. The trays used were mono APET.

[0134] As a part of this test, 30 packs with fresh beef were made out of each of the films.

[0135] The number of blowouts (breakage of the packs due to inadequate melt strength of the material) was noted. This is a test often used to evaluate the suitability of the films as per the demanding vacuum skin packaging process.

[0136] The dome temperature (machine setting) was 200 C.

[0137] The film of the example 1 had the polyester layer at the inside of the pack (sealing layer to the APET tray).

[0138] The film of the example 2 had the polyester layer at the outside of the pack (in contact to the machine dome).

[0139] Out of the 30 packs the film 1 of the invention had 3 blowouts.

[0140] Out of the 30 packs the film 2 had 4 blowouts.

[0141] Out of the 30 packs the comparative film had 4 blowouts.

[0142] Therefore, it seems that the films of the present invention have unexpectedly at least same formability compared to the commercial films already used in the vacuum skin packaging field

Peel Test

[0143] The packs were evaluated by their opening.

[0144] The packs made from the film of example 1 and the APET trays were found to be easily peelable at to the satisfaction of the panel.

[0145] The packs made from the film of example 2 and the APET trays were found to be too easily peelably to the APET. However, film 2 is targeted to adhere peelably to paper, seal to ovenable top lidding film and offer an ovenable environmentally friendly solution.

Adhere to Paper

[0146] Seal tests were arranged between the internal layer of example 2 (EVA layer) and coated paper.

[0147] The tests were done in the temperature range 110-130 C, seal time 1-2 seconds using a lab Brugger heat sealing machine. This process simulates the bonding of paper to plastic film during inline thermal adhesion as made in commercial machines.

[0148] It was found that the film of the example 2 has a nice peel effect from the paper, thus allowing the easy separation between paper and plastic after the pack is thrown as waste.

Oven Evaluation

[0149] A coated paper piece 20×20 cm was fully covered by sealed stripes of film of example 2 as described above. Then a piece of meat was placed on the plastic layer and the pack was sealed at the edges using a top lidding film comprising polyester. In the state of the art, the oven resistant top lidding films are generally polyester based and the sealing layer comprises polyester.

[0150] The pack was put in an oven at 200 C. After 30 minutes the seal between the film of example 2 and the top lidding film opened due to the hot air from the inside of the pack. This is a desirable effect to improve cooking quality.

[0151] 10 minutes later the cooking process stopped and the meat cooking was evaluated.

[0152] There was not tearing or melting of the plastic, so the film can be used in ovenable applications.

[0153] The comparative example film having a polyolefin based sealing layer, is not able to heat seal to a top lidding film comprising polyester. The film of the present invention can be used in the oven application as it seals to polyester top lidding film.