Oven skin packaging process

Abstract

The invention relates to a vacuum skin food package for use in a conventional oven and more particularly to a food package able to withstand conditions up to 200° C. comprising a thermoplastic lid film which is free of polyester and contains crosslinked EVA.

Claims

1. An ovenable vacuum skin pack comprising a top lidding film and a bottom container, wherein the top lidding film comprises at least 30% by volume of crosslinked ethylene vinyl acetate copolymer (EVA) and is free of polyester, further wherein the top lidding film comprises at least four layers, wherein the at least four layers comprise a sealing layer configured to seal to the bottom container, a barrier layer, a tie layer adjacent to the barrier layer, and an intermediate layer adjacent to the tie layer; wherein said sealing layer comprises EVA, ethylene methacrylate copolymer (EMA), ethylene acid copolymer or ionomer; wherein the tie layer comprises maleic anhydride modified polyethylene, maleic anhydride modified EMA, maleic anhydride modified elastomer or polyurethane elastomer; wherein said intermediate layer comprises EVA: wherein the bottom container comprises polyester or aluminum; and wherein the pack is free of visible thermal degradation after one hour at 200 degrees Celsius (°C) in a conventional oven.

2. The pack of claim 1, wherein the top lidding film comprises at least 50% by volume of crosslinked ethylene vinyl acetate copolymer.

3. The pack of claim 1, wherein the top lidding film comprises at least 70% by volume of crosslinked ethylene vinyl acetate copolymer.

4. The pack of claim 1, wherein the top lidding film contains less than 10% per volume of ionomer.

5. The pack of claim 2, wherein the top lidding film contains less than 10% per volume of ionomer.

6. The pack of claim 3, wherein the top lidding film contains less than 10% per volume of ionomer.

7. A cook-in process comprising the following steps: (a) putting the food in a container comprising polyester or aluminum; (b) making a vacuum skin pack comprising a top lidding film, which comprises at least 30% per volume of crosslinked ethylene vinyl acetate copolymer (EVA), is free of polyester, conforms to the product, and seals to the container of step (a) thus creating an intact package, further wherein the top lidding film comprises at least four layers, wherein the at least four layers comprise a sealing layer configured to seal to the container, a barrier layer, a tie layer adjacent to the barrier layer, and an intermediate layer adjacent to the tie layer, wherein the sealing layer comprises EVA, ethylene methacrylate copolymer (EMA), ethylene acid copolymer or ionomer and wherein the tie layer comprises maleic anhydride modified polyethylene, maleic anhydride modified EMA, maleic anhydride modified elastomer or polyurethane elastomer; and wherein said intermediate layer comprises EVA; (c) putting the pack in a conventional oven; and (d) cooking the pack for up to 200° C. for up to 2 hours.

Description

DETAILED DESCRIPTION

(1) The present invention describes an ovenable vacuum skin pack wherein the top lidding film comprises at least 30% by volume of crosslinked ethylene vinyl acetate copolymer, is free of polyester and wherein the bottom container comprises polyester or aluminum.

(2) Preferably the top lidding film comprises at least 50% by volume of crosslinked ethylene vinyl acetate copolymer, more preferably at least 70% by volume of crosslinked ethylene vinyl acetate copolymer.

(3) In one of the preferred versions, the top lidding film further comprises an ionomer. The neutralization ratio of the ionomer is preferably more than 55%, preferably more than 70%. Preferably the top lidding film comprises less than 80% ionomer per volume, more preferably less than 50%, even more preferably less than 20%, most preferably less than 10%. In another preferred version the film is ionomer free.

(4) In a further preferable version the top lidding film comprises at least two layers, and the inner layer comprises EVA, EMA, ethylene acid copolymer or ionomer.

(5) In a further preferable version the top lidding film comprises an intermediate layer.

(6) According to the invention, the top lidding film comprises at least 30% by volume crosslinked EVA. The crosslinked EVA may preferably be a component of the intermediate layers or the inner layer.

(7) The present invention describes a cook-in process comprising the following steps: a) Putting the food in a container comprising polyester or aluminum b) Making a vacuum skin pack while a top lid film which comprises at least 30% per volume of crosslinked ethylene vinyl acetate copolymer conforms to the product and seals to the container of step 1 thus creating an intact package c) Putting the pack in a conventional oven d) Cooking the pack for up to 200° C. for up to 2 hours

(8) Preferably the top lid film of the present invention as described above is used in the cook-in process of the present invention, including all the above disclosed options for the top lidding film.

Top Lidding Film Construction

(9) Preferably the film comprises 5 to 15 layers, more preferably 7 to 12 layers. A typical example of the film construction comprises 7 layers in the following arrangement:

(10) Outer layer/intermediate layer/tie layer/barrier layer/tie layer/intermediate layer/inner layer

(11) The film is preferably produced by the hot blown film method. Preferably the film is not heat shrinkable.

Barrier Layer(s)

(12) Preferably the film comprises high oxygen barrier materials so that it protects the components of the pack from the detrimental effect of oxygen ingress. Preferably the high oxygen barrier material is selected from EVOH, polyamide, and PVDC. More preferably the high oxygen barrier material is EVOH. The EVOH comprises preferably 24 to 50% ethylene per mol, more preferably 27 to 48% ethylene per mol.

Intermediate Layer(s)

(13) 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.

(14) The vinyl acetate content of the EVA used in the intermediate layers is preferably 3 to 90% per weight, more preferably 5 to 80%. Preferred melt flow indexes are 0.3 to 5 measured at 190° C., 2.16 kilos. As per ASTM D1238.

(15) In one preferred version, the intermediate layers of the film are free from ionomer.

Tie Layer(s)

(16) 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.

(17) 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

(18) The outer layer of the film preferably comprises LLDPE, LDPE or HDPE produced by Ziegler Natta or metallocene catalyst.

Inner Layer

(19) The inner layer of the film would be able to seal the film to the container (bottom film or tray).

(20) Preferable options for this layer include EVA copolymer, EMA copolymer, ethylene acid copolymer and ionomer.

(21) 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.

Crosslinking

(22) The crosslinking may be done by various methods but the preferred are e-beam, gamma radiation and peroxides.

Container

(23) The container can be a film or sheet thermoformed in line with the vacuum skin packaging process or a ready-made tray.

(24) In one preferable version of the invention, the container is a tray or sheet with a thickness of at least 300 microns.

(25) In a further preferable version, the tray or sheet comprises polyester, preferably CPET.

(26) There are different options for manufacturing the CPET comprising sheet or tray. One possibility is a 3 layer construction A/B/C wherein the A and C layers consist of virgin polymer while B comprises recycled polymer.

(27) In another preferable version the container is a tray comprising aluminum. Aluminum can be supplied in two options, as plain aluminum with no coating, or as aluminum with a coating, preferably the coating is polyester.

(28) In general, making a vacuum skin pack with uncoated aluminum tray is a challenge for the art. However, this option has certain advantages over the use of polyester, e.g. easier to manufacture and more convenient. The inventors of the present invention could show that an uncoated aluminum tray can be easily used applying the top lidding film according to the present invention.

EXAMPLE 1

(29) From a commercial hot blown film line we produced the following film Outer layer, thickness 10 microns Intermediate layer 1, thickness 35 microns Tie layer 1, thickness 8 microns EVOH, thickness 8 microns Tie layer 2, thickness 8 microns Intermediate layer 2, thickness 15 microns Inner layer, thickness 16 microns.
Wherein the

(30) Outer layer is 100% per weight LLDPE with density 0.918 and MFI 1 at 190° C., 2.16 kilos

(31) Intermediate layer 1 and 2 are EVA 12% per weight VA

(32) Tie layer 1 and 2 are anhydride modified LLDPE with MFI 2.5 at 190° C., 2.16 kilos.

(33) Inner layer comprises an EVA based compound.

(34) None of the layers comprise polyester.

(35) The film was irradiated at a level to achieve a gel content of 65%. Gel content is measured according to ASTM D2765.

(36) Then the film was put on a vacuum skin packaging machine as top lidding film.

(37) As container, CPET trays were used.

(38) The product packed was 500 gr beef portions.

(39) The vacuum skin packs produced were judged as appealing in appearance. There were no breaks of the top lidding film as is often the problem in vacuum skin packaging production.

Cook-In Test

(40) The vacuum skin pack was tested in a house oven setting the temperature to 200° C. in normal convection mode (no forced air).

(41) After 1 hour cooking the packs were opened and tested as per film degradation, cooking quality and food palatability.

(42) There was no visible thermal degradation of the top lidding film.

(43) The cooking quality was very good.

(44) Palatability was very good.

EXAMPLE 2

(45) From a commercial hot blown film line we produced the following film Outer layer, thickness 10 microns Intermediate layer 1, thickness 35 microns Tie layer 1, thickness 8 microns EVOH, thickness 8 microns Tie layer 2, thickness 8 microns Intermediate layer 2, thickness 15 microns Inner layer, thickness 16 microns.
Wherein the

(46) Outer layer is 100% LLDPE with density 0.918 and MFI 1 at 190° C., 2.16 kilos

(47) Intermediate layer 1 and 2 are EVA 12% VA per weight

(48) Tie layer 1 and 2 are anhydride modified LLDPE with MFI 2.5 at 190 C and 2.16 kilos.

(49) Inner layer comprises an ethylene acrylic acid copolymer

(50) None of the layers comprise polyester.

(51) The film was irradiated at a level to achieve a gel content of 70%.

(52) Then the film was put on a vacuum skin packaging machine as top lidding film.

(53) As container, plain and coated aluminum trays were used.

(54) The product packed was 500 gr beef portions.

(55) The vacuum skin packs produced were judges as appealing in appearance. There were no breaks of the top lidding film as is often the problem in vacuum skin packaging options.

(56) The sealing was very good in the case of coated aluminum trays and acceptable (easy open but still no leaker areas) in the case of plain aluminum.

Cook-In Test

(57) The vacuum skin pack was tested in a house oven putting the set temperature at 200° C. in normal convection mode (no forced air).

(58) After 1 hour cooking the packs were opened and tested as per film degradation, cooking quality and food palatability.

(59) There was no visible thermal degradation of the top lidding film.

(60) The cooking quality was very good.

(61) Palatability was very good.

COMPARATIVE EXAMPLES

(62) Two comparative combinations were used.

Comparative Example 1

(63) Comparative Example 1 is based on example 1 and a polyester material was used instead of EVA in the intermediate layers. The film was tested both crosslinked and un-crosslinked.

(64) Both films have severe problems running at the vacuum skin packaging machine.

(65) The un-crosslinked film did not have enough memory and broke during the operation.

(66) The crosslinked film was better but did not have enough memory to follow the meat irregularities and cavities. Therefor it was also judged not suitable for the operation.

Comparative Example 2

(67) Comparative Example 2 is based on example 2 wherein the EVA used in the intermediate layers of example 2 was replaced by a zinc ionomer. The film was crosslinked with same dose as in example 2.

(68) The film could withstand with success the vacuum skin packaging process, even following the packed products irregularities and cavities.

Cook In Test

(69) At this stage under the already tested conditions of the examples above the film was torn.

(70) It will be understood that various details of the presently disclosed subject matter may be changed without departing from the scope of the presently disclosed subject matter. Furthermore, the foregoing description is for the purpose of illustration only, and not for the purpose of limitation.