Heat Shrinkable Film

Abstract

A heat shrinkable film comprising an outer layer comprising ethylene vinyl acetate, a sealing layer comprising ethylene alpha olefin copolymer and a layer comprising ethylene vinyl alcohol.

Claims

1. A biaxially oriented heat shrinkable film comprising an outer layer comprising ethylene vinyl acetate, a sealing layer comprising an ethylene alpha olefin copolymer with density less than 0.915 g/cm.sup.3 and an oxygen barrier layer comprising ethylene vinyl alcohol.

2. The biaxially oriented heat shrinkable film according to claim 1, wherein the film does not comprise polyamide, polyester and PVDC.

3. The biaxially oriented heat shrinkable film according to claim 1, wherein the film is of the construction outer layer-intermediate layer-barrier layer-intermediate layer-inner layer.

4. The biaxially oriented heat shrinkable film according to claim 1, wherein the film is of the construction outer layer-intermediate layer 1-intermediate layer 2-barrier layer-intermediate layer 3-intermediate layer 4-inner layer.

5. The biaxially oriented heat shrinkable film according to claim 1, wherein the ethylene content of the ethylene vinyl alcohol is from 27% to 44% by mol.

6. The biaxially oriented heat shrinkable film according to claim 1, wherein the outer layer further comprises a second polymer.

7. The biaxially oriented heat shrinkable film according to claim 6, wherein the second polymer of the outer layer is ethylene alpha olefin copolymer having a density from 0.880 g/cm.sup.3 to 0.920 g/cm.sup.3.

8. The biaxially oriented film according to claim 1, wherein at least one layer of the film is crosslinked.

9. The biaxially oriented heat shrinkable film according to claim 8, wherein crosslinking is performed by irradiation.

10. The biaxially oriented heat shrinkable film according to claim 9, wherein the irradiation is done prior to orientation.

11. The biaxially oriented heat shrinkable film according to claim 1, wherein the film exhibits a shrinkage of at least 25% in at least one of machine direction and transverse direction, measured in water at 90° C. according to ASTM D2732.

12. The biaxially oriented heat shrinkable film according to claim 1, wherein the outer layer further comprises from 0.1-10% w/w of a slip and/or antiblock compound.

13. The biaxially oriented heat shrinkable film according to claim 1, wherein the sealing layer comprises at least one polyolefin.

14. Use of the film according to claim 1 for packaging.

15. The biaxially oriented heat shrinkable film according to claim 1, wherein the sealing layer comprises at least one polyolefin.

16. The biaxially oriented heat shrinkable film according to claim 15, wherein the at least one polyolefin is a blend of polyolefins.

17. Use of the file according to claim 14 as food packaging.

Description

DETAILED DESCRIPTION

[0051] According to a first aspect the present invention is directed to a biaxially oriented heat shrinkable film, comprising an outer layer which comprises an EVA copolymer, a sealing layer comprising an ethylene alpha olefin copolymer with density less than 0.915 g/cm.sup.3 and an oxygen barrier layer comprising EVOH.

[0052] The film of the invention exhibits a shrinkage of at least 25% measured according to ASTM D2732 in water at 900 C in at least one of the MD, TD directions.

[0053] Outer Layer

[0054] According to a preferred embodiment of the invention, the EVA copolymer comprises from 6% to 28% by weight VA (vinyl acetate), more preferably from 9% to 25%, even more preferably from 12% to 18%.

[0055] According to a further preferred embodiment of the invention, the EVA copolymer has a melt flow index of 0.2 to 5 measured at 1900 C and 2.16 kilogram weight, as described by ASTM D1238.

[0056] According to a another preferred embodiment, the outer layer comprises a further polymer selected from low density polyethylene, high density polyethylene, cyclic olefin copolymer, ethylene butene copolymer, ethylene hexene copolymer, ethylene octene copolymer and polypropylene. Preferably the further polymer is a plastomer ethylene alpha olefin copolymer with density from 0.880 g/cm.sup.3 to 0.920 g/cm.sup.3.

[0057] As the EVA of the outer layer of the invention are quite sticky, it is preferred to comprise from 0.1-10% by weight slip and or antiblock compound. The coefficient of friction of the outer layer is preferably less than 0.5 measured according to ASTM D1894 (kinetic coefficient of friction-film to film configuration).

[0058] Inner Layer

[0059] In the film according to the present invention, the inner sealing layer comprises a ethylene alpha olefin copolymer with density of less than 0.915 g/cm.sup.3.

[0060] In a preferred embodiment the sealing layer comprises a homogeneous alpha olefin copolymer with a density less than 0.915 g/cm.sup.3.

[0061] In another embodiment of the invention the inner layer comprises a blend of two homogeneous ethylene alpha olefin copolymers which have both densities less than 0.915 g/cm.sup.3.

[0062] The inner layer may further comprise a polyolefin or a blend of different polyolefins. In a preferred embodiment of the structure, the sealing layer comprises at least one homogeneous polyolefin.

[0063] In a preferable embodiment of the invention, the inner layer comprises ethylene norbornene copolymer (cyclic olefin copolymer), such as Topas from Polyplatics or Apel from Mitsui.

[0064] Oxygen Barrier Layer

[0065] The multilayer film of the invention comprises an oxygen barrier layer comprising EVOH.

[0066] Preferably the oxygen barrier material is located in an intermediate layer of the film.

[0067] In general, EVOH with an ethylene content from 48% to 24% by mol is preferred, more preferably from 27% to 44% by mol.

[0068] Other Intermediate Layers

[0069] Between the sealing layer and the oxygen barrier layer, a tie layer could be used. Preferred materials for this tie layer may be ethylene ester copolymers, such as ethylene vinyl acetate copolymers, ethylene methyl acrylate copolymers and other materials well known in the art. A preferred embodiment might include maleic anhydride modified ethylene ester copolymers or maleic anhydride modified LLDPE. Commercial products are for example BYNEL from Dupont and ADMER from Mitsui.

[0070] Between the outer and the barrier layer there may be another layer incorporating a tie layer. Preferred materials for this tie layer may be ethylene ester copolymers, such as ethylene vinyl acetate copolymers, ethylene methyl acrylate copolymers and other materials well known in the art. A preferred embodiment might include maleic anhydride modified ethylene ester copolymers or maleic anhydride modified LLDPE. Commercial trademarks are for example BYNEL from Dupont and ADMER from Mitsui.

[0071] A preferred construction of the multilayer film is as follows [0072] Outer layer-intermediate layer-barrier layer-intermediate layer-inner layer

[0073] Other preferred construction are as follows. [0074] Outer layer-intermediate layer 1-intermediate layer 2-barrier layer-intermediate layer 3-intermediate layer 4-inner layer

[0075] Any of the layers described above may also include additives well known in the art, such as slip agents, antiblock, polymer processing aids, antistatic, antifog, acid scavengers, odour scavengers and the like. A person skilled in the art may select the right additives according to any particular needs.

[0076] The thickness of the film is preferably from 10 to 150 microns, more preferably from 20 to 120 microns. The thickness of the outer layer is preferably from 1 to 50 microns, more preferably from 3 to 25 microns. The thickness of the inner layer is preferably 5 to 100 microns, more preferably from 10 to 60 microns.

[0077] In order the material to have a high shrinkability at 90° C., it is needed to be biaxially oriented for example by using the double bubble process or the tenter frame process.

[0078] Both processes are well known in the art. The double bubble process is especially preferred.

[0079] Preferably, the film or some layers of the film are crosslinked.

[0080] A preferable crosslinking method is irradiation by electron beam or UV radiation or gamma ray. Other methods are also known in the art. Irradiation with use of electron beam is preferred.

[0081] According to a further aspect, the present invention discloses a bag or pouch comprising a film according to the present invention.

[0082] In a further aspect, the invention is directed to the use of the films or the bag or pouch of the invention for packaging, such as for packaging food. For example, the food item is put inside the bag and the air is removed (vacuumizing) with the help of a vacuum device. Subsequently, the open end of the bag is sealed and the vacuum pack is placed in a heat shrinking media such as hot water under a temperature that ensures the shrink of the pack (e.g. 85-90° C.). The pack then is ready and is characterized by appealing appearance and long shelf life because of the absence of oxygen.

[0083] The Examples disclose embodiments of the present invention:

EXAMPLES

Example 1

[0084] A 5 layer film is produced in a double bubble (the double bubble method is described in U.S. Pat. No. 3,456,044) commercial line with the following recipe

TABLE-US-00001 Inner (sealing layer), 56% P1 + 40% P2 + 4% additives Adjacent layer 100% T1 Barrier layer 100% EVOH 1 Adjacent layer 100% T1 Outer layer  95% E1 + 5% slip antiblock masterbatch

[0085] The meanings of EVOH1, T1, P1, P2, E1 are shown in Table 1.

[0086] The thickness of the structure is 23/9/5/9/8 starting from the inner and going to the outer layer.

Example 2

[0087] A 5 layer film is produced in a double bubble (the double bubble method is described in U.S. Pat. No. 3,456,044) commercial line with the following recipe

[0088] The film of the example 2 was produced by crosslinking prior to the film orientation the outer and the adjacent layer.

TABLE-US-00002 Inner (sealing layer), 56% P1 + 40% P2 + 4% additives Adjacent layer 100% T1 Barrier layer EVOH1 Adjacent layer 100% T1 Outer layer  95% E1 + 5% slip antiblock masterbatch

Example 3

[0089] A 5 layer film is produced in a double bubble (the double bubble method is described in U.S. Pat. No. 3,456,044) commercial line with the following recipe

TABLE-US-00003 Inner (sealing layer), 56% P1 + 40% P2 + 4% additives Adjacent layer 100% T1 Barrier layer EVOH1 Adjacent layer 100% T1 Outer layer  60% E1 + 35% P1 + 5% slip antiblock masterbatch

TABLE-US-00004 TABLE 1 Melt Melting Manufac- Index Density point Type Description turer g/10 min g/cm.sup.3 ° C. E1 EVA Versalis 0.3 0.935  93 GREENFLEX FC45 EVOH 1 H171B EVAL 1 1.17 172C P1 AFFINITY DOW 1.6 0.896  94C PF1140 P2 TAFMER MITSUI 3.5 0.885 Less 4085 than 70C T1 ADMER1955 MITSUI 0.89

[0090] Comparative Test

[0091] The above examples are compared to the commercial product BRE. This film has barrier layer comprising PVDC and is well established in the market. It is the comparative film shown below, e.g. in table 2.

[0092] Further Processing of the Samples

[0093] The samples were further processed as follows; [0094] Example 1 was irradiated only after orientation [0095] Example 2 was irradiated only before orientation [0096] Example 3 was irradiated before orientation similar to example 2

[0097] The level of irradiation of all the films was 6 mrads.

[0098] Tests [0099] 1. Haze measurement. The haze measurement was done according to ASTM D 1003. [0100] 2. Gloss measurement. This was done according to BS 2782. [0101] 3. Shrinkage measurement done according to ASTM 2732 at 90° C. [0102] 4. Puncture resistant test.

[0103] Puncture resistance is measured using a MECMESIN instrument comprising a vertical stand VERSA TEST, a load cell AFG 100N, which is mounted on the stand, and a digital height gauge MITUTOYO SDV 60B. A cylindrical shaft ending to a conical indenter is attached to the load cell. The indenter has an angle of 60° and a tip of 0.5 mm in diameter.

[0104] The film is conditioned at 23° C. and about 50% RH for at least 24 hours prior to the measurement. Square samples of 8.5 cm×8.5 cm are prepared and clamped on a 5 cm diameter circular base. The indenter moves perpendicular to the film and force is measured as the indenter comes into contact with and ruptures the film. The speed of the indenter is set to 25 mm/min. Maximum force needed to puncture the film is recorded. The puncture force of a material is determined by averaging the values obtained for at least 5 samples of the material tested.

TABLE-US-00005 TABLE 2 PUNCTURE SHRINKAGE RESISTANCE IN (MD/TD) UNSHRUNK HAZE GLOSS 90° C. FILM Example 1 6 120 48/48 14 Newtons Example 2 7.5 112 51/51 15 Newtons Example 3 7.7 110 45/44 14 Newtons Comparative 6 120 50/47 11 Newtons example

[0105] Burn Through Test

[0106] The test was done on a vacuum heat seal VC999 machine.

[0107] Different sealing times were used and the heat abuse of the seal area was evaluated as per the following rate [0108] 5 no abuse [0109] 4 slight abuse [0110] 3 medium [0111] 2 a lot of abuse [0112] 1 totally burned

[0113] In sealing time 1 and 2 seconds the results were

TABLE-US-00006 SEAL TIME 1 SEC SEAL TIME 2 SEC EXAMPLE 1 4.4 3.5 EXAMPLE 2 4.5 3.7 EXAMPLE 3 4.3 3.4 COMPAR. EXAMPLE 3.1 2.5

[0114] It is a surprising effect that a low heat resistant polymer like EVA can withstand such conditions that simulate the real application conditions.