COMPOSITE POLYMERIC FILM

Abstract

A heat-sealable composite film comprising an oriented polyester substrate layer having a first and second surface is provided. Disposed on the first surface of the substrate layer is a heat- sealable polymeric coating layer comprising a styrenic linear block copolymer thermoplastic elastomer, an ethylene vinyl acetate (EVA) copolymer and a tackifying resin. Also described is a sealed container comprising a receptacle containing a food product, and a lid formed from said heat-sealable composite film.

Claims

1. A heat-sealable composite film comprising an oriented polyester substrate layer having a first and second surface and disposed on a first surface of the substrate layer a heat-sealable polymeric coating layer comprising a styrenic linear block copolymer thermoplastic elastomer, an ethylene vinyl acetate (EVA) copolymer and a tackifying resin, wherein the heat-sealable polymeric layer comprises the EVA copolymer in an amount of from 25 to 35 wt% by total weight of the heat-sealable polymeric layer.

2. A heat-sealable composite film according to claim 1 wherein said polyester substrate layer is biaxially oriented.

3. A heat-sealable composite film according to claim 1 or 2 wherein said polyester substrate layer is polyethylene terephthalate.

4. A heat-sealable composite film according to any preceding claim wherein the styrenic linear block copolymer thermoplastic elastomer consists of polystyrene blocks and rubber blocks derived from butadiene and/or isoprene, or their hydrogenated equivalents.

5. A heat-sealable composite film according to any preceding claim wherein the styrene content of said styrenic linear block copolymer thermoplastic elastomer is in the range from 5 to 50%, preferably from 8 to 30%, preferably 10 to about 20%, and preferably 10 to about 15%, by mass of the copolymer.

6. A heat-sealable composite film according to any preceding claim wherein the styrenic linear block copolymer thermoplastic elastomer comprises rubber blocks which consist of polybutadiene or polyisoprene or combinations thereof, wherein said copolymers are triblock copolymers with polystyrene blocks at each end of a triblock and linked together by said rubber block.

7. A heat-sealable composite film according to any preceding claim wherein the styrenic linear block copolymer thermoplastic elastomer comprises rubber blocks which consist of hydrogenated polybutadiene or polyisoprene or combinations thereof, preferably wherein the hydrogenated styrenic copolymers are selected from: (i) triblock copolymers containing styrene blocks and rubber blocks consisting of ethylene and butylene repeating units; and (ii) triblock copolymers containing styrene blocks and rubber blocks consisting of ethylene and propylene repeating units.

8. A heat-sealable composite film according to any preceding claim wherein the styrenic linear block copolymer thermoplastic elastomer exhibits a weight average molecular weight (Mw) from 50,000 to 400,000, preferably from 50,000 to 200,000, and/or wherein the weight average molecular weight (Mw) of the styrene block is from 5,000 to 50,000, preferably from 5,000 to 25,000.

9. A heat-sealable composite film according to any preceding claim wherein the styrenic linear block copolymer thermoplastic elastomer exhibits a tensile strength, measured according to ASTM D412-16 on film cast from toluene solution, of at least 5 MPa, preferably at least 10 MPa, preferably at least 15 MPa, preferably at least 20 MPa, and preferably in the range of 15 to 30 MPa.

10. A heat-sealable composite film according to any preceding claim wherein the styrenic linear block copolymer thermoplastic elastomer exhibits a solution viscosity of no more than 250 cPs, preferably no more than 100 cPs, preferably at least 5 cPs, preferably at least 10 cPs, measured with a Brookfield Viscometer at 25° C. in a toluene solution at 10 wt%.

11. A heat-sealable composite film according to any preceding claim wherein the styrenic linear block copolymer thermoplastic elastomer exhibits a glass transition temperature of in the range of -50 to -80° C., preferably -60 to -70° C., and/or a melting point of greater than 0° C. and preferably less than 50° C.

12. A heat-sealable composite film according to any preceding claim wherein the heat-sealable polymeric layer comprises the styrenic copolymer in an amount of from 10 to 50 wt%, preferably 20 to 40 wt%, preferably 25 to 35 wt%, by total weight of the layer.

13. A heat-sealable composite film according to any preceding claim wherein the EVA copolymer has a vinyl acetate content in the range of 5 to 50 wt%, 15 to 50 wt%, and preferably 18 to 40 wt%, and optionally comprises an additional comonomer, preferably an ethylenically unsaturated comonomer, preferably selected from acrylic acid and methacrylic acid, preferably wherein the total amount of additional comonomer is no more than 5 wt%.

14. A heat-sealable composite film according to any preceding claim wherein the EVA copolymer exhibits a melting point of from 40° C. to 95° C., preferably 45° C. to 75° C. and/or a melt index of from 5 to 1000, preferably 5 to 600, preferably 5 to 200, preferably 5 to 100 g/10 min.

15. (canceled)

16. A heat-sealable composite film according to any preceding claim wherein the heat-sealable polymeric layer comprises a blend of a first EVA copolymer (EVA-1) and a second EVA copolymer (EVA-2), preferably wherein said first EVA copolymer (EVA-1) has a vinyl acetate content in the range of 20 to 50 wt%, preferably 20 to 40 wt%, and preferably a melt index in the range of from 2.5 to 100, preferably 5 to 100 g/10 min, and said second EVA copolymer (EVA-2) has a VA content in the range of 5 to 20 wt%, preferably 10 to 20 wt%, and preferably exhibits a melt index of from 100 to 1000, preferably 150 to 600 g/10 min.

17. A heat-sealable composite film according to claim 16 wherein the weight ratio of EVA-2/EVA-1 is in the range of greater than 0/100 to 100/100, more preferably greater than 0/100 to 65/100, more preferably 15/100 to 50/100, more preferably 15/100 to 30/100.

18. A heat-sealable composite film according to any of claims 1 to 14 wherein a single grade of EVA copolymer is present in the heat-sealable layer and the vinyl acetate (VA) content of said resin is in the range of 5 to 50 wt%, preferably 15 to 50 wt%, and preferably 18 to 40 wt%, preferably 20 to 30 wt%, preferably 23.0 to 30.0 wt%, preferably 25 to 28 wt%, preferably wherein the melt index of the EVA copolymer is in the range of from 5 to 200, preferably 5 to 100 g/10 min.

19. A heat-sealable composite film according to any preceding claim wherein the tackifying resin is selected from polyterpenes, hydrocarbon resins, rosin and rosin ester resins, and combinations thereof.

20. A heat-sealable composite film according to any preceding claim wherein the tackifying resin exhibits ring and ball softening points from 20° C. to 160° C., preferably 90° C. to 125° C., and/or a number average molecular weights of 200 to 5000, preferably 500 to 2000.

21. A heat-sealable composite film according to any preceding claim wherein the tackifying resin(s) are selected from: natural polyterpene resins derived from alpha-pinene, beta-pinene and d-limonene; hydrocarbon resins derived from petroleum-based feedstocks selected from aliphatic (C.sub.5) hydrocarbon resins, aromatic (C.sub.9) hydrocarbon resins, dicyclopentadiene resins and mixtures thereof; and methyl, triethylene glycol, glycerol, and pentaerythritol esters of rosins.

22. A heat-sealable composite film according to any preceding claim wherein the heat-sealable polymeric layer comprises the tackifying resin in an amount of from 15 to 50 wt%, preferably from 15 to 40 wt%, preferably from 30 to 40 wt%, by total weight of the heat-sealable polymeric layer.

23. A heat-sealable composite film according to any preceding claim wherein a primer coating layer is disposed on the first surface of the substrate layer such that the layer order is substrate layer / primer layer / heat-sealable polymeric coating layer, preferably wherein the primer is a polymer selected from polyvinylidene chloride (PVDC), EVA and ethylene acrylic acid (EAA) resins, preferably from PVDC and EVA resins, and preferably from PVDC resins.

24. A heat-sealable composite film according to claim 23 wherein the primer layer exhibits a dry coat-weight of from about 0.05 to about 1.0 g/m.sup.2, preferably from about 0.1 g/m.sup.2 to about 0.5 g/m.sup.2, and/or a thickness of from 0.05 .Math.m to 1 .Math.m, preferably from 0.05 .Math.m to 0.5 .Math.m.

25. A heat-sealable composite film according to any preceding claim wherein the thickness of the substrate is from about 10 to about 100 .Math.m, and the thickness of the heat-sealable layer is from 5 to 45%, preferably from 10 to 40 % and preferably from 12 to 35 %, of the total thickness of the composite film, and/or a thickness of from 2 to 10 .Math.m, preferably from 3 to 6 .Math.m.

26. A heat-sealable composite film according to any preceding claim which exhibits a heat-seal strength to a polypropylene substrate in the range of 600 to 1500 g/25.4 mm, preferably 800 to 1500 g/25.4 mm, preferably 800 to 1200 g/25.4 mm, preferably 800 to 1125 g/25.4 mm.

27. A heat-sealable composite film according to any preceding claim which exhibits a clarity of at least 70%, preferably at least 75%, preferably at least 80%, and preferably at least 85%.

28. A sealed container comprising a receptacle containing a food product, and a lid formed from a heat-sealable composite film according to any of claims 1 to 27 and 30 to 31, wherein said heat-sealable polymeric layer of the composite film is in direct contact with the receptacle and wherein the composite film is adhered to the receptacle via a peelable heat-seal bond, preferably wherein the receptacle is made from polyolefin, preferably polypropylene or polyethylene, and preferably polypropylene.

29. Use of a composite film according to any of claims 1 to 27 and 30 to 31 as a lid in the packaging of a food product, particularly an ovenable meal, said packaging further comprising a receptacle, particularly wherein the receptacle is made from polyolefin, preferably polypropylene or polyethylene, and preferably polypropylene.

30. A heat-sealable composite film comprising an oriented polyester substrate layer having a first and second surface and disposed on a first surface of the substrate layer a heat-sealable polymeric coating layer comprising a styrenic linear block copolymer thermoplastic elastomer, a tackifying resin and a blend of a first ethylene vinyl acetate (EVA) copolymer (EVA-1) and a second ethylene vinyl acetate (EVA) copolymer (EVA-2), wherein said first EVA copolymer (EVA-1) has a vinyl acetate content in the range of 20 to 50wt% and said second EVA copolymer (EVA-2) has a VA content in the range of 5 to 20 wt%, wherein the weight ratio of EVA-2/EVA-1 is in the range of greater than 0/100 to 65/100, and wherein the heat-sealable polymeric layer comprises a total amount of the EVA copolymer from 20 to 40 wt% by total weight of the heat-sealable polymeric layer.

31. A heat-sealable composite film according to claim 30, wherein the heat-sealable composite film is as defined in any of claims 1 to 14 or 16 to 17 or claims 19 to 27 when dependent on any of claims 1 to 14 or 16 to 17.

Description

EXAMPLES

[0090] The materials noted in Table 1 were used to prepare composite films:

TABLE-US-00001 Raw Material Supplier Description Elvax® 3180 DuPont EVA (28 wt% VA) Elvax® 410 DuPont EVA (18 wt% VA) Elvax® 4260 DuPont EVA (28 wt% VA, 1 wt% methacrylic acid) Elvax 3200-2 DuPont EVA (22.5 wt% VA) Elvax 3185 DuPont EVA (32 wt% VA) Elvax 4031 WLG DuPont EVA (40 wt% VA) Queo™7007LA Borealis AG ethylene-octene-1 copolymer Kraton® G1657ms Kraton SEBS; Styrene/rubber ratio: 13/87 Kraton® D1161 Kraton SIS; Styrene/rubber ratio: 15/85 Kraton® D1102 Kraton SBS; Styrene/rubber ratio: 28/72 Piccolyte® M115 Pinova Solutions Polyterpene resin, softening point 111-119° C. Foral® 85 Pinova Solutions Rosin ester, softening point 80-88° C. Pentalyn® H Pinova Solutions Rosin ester, softening point 94-102° C. Carnauba wax Strahl & Pitsch slip aid Kemamide EZ PMC Biogenix slip aid Syloid® 620 W. R. Grace amorphous silica

Comparative Examples 1 to 4; Examples 5 to 10

[0091] A polyethylene terephthalate (PET) composition was melt-extruded, cast onto a water-cooled rotating quench drum to yield an amorphous cast extrudate. The cast extrudate was heated to a temperature in the range of about 50 to 80° C. and then stretched longitudinally at a forward draw ratio of about 3:1. The film was passed into a stenter oven at a temperature of 100° C. where the film was stretched in the sideways direction to approximately 3 times its original dimensions. The biaxially stretched film was heat-set at a temperature of from 210° C. to 230° C. in a 3-stage crystallizer by conventional means. The PET film thickness was 23 .Math.m.

[0092] A PVDC primer coating was coated off-line at a coat weight of 0.5 g/m.sup.2 to one surface of the PET film.

[0093] A range of composite films were prepared by coating a heat-sealable coating formulation having the composition shown in Table 2 onto the primed surface of the PET substrate prepared as described above. The amounts of the components of the coating formulation are the amounts by weight of each component in the finished heat-sealable coating layer (i.e. the dry weight of the heat-sealable coating layer). The coating formulations in Table 2 were prepared at 20 wt% in toluene, except for Examples 1, 2 and 3 which were prepared at 15 wt% in toluene. The coating was conducted off-line by gravure coating at a coat-weight of 6.0 g/m.sup.2.

[0094] The composite films were heat-sealed (350° F.; dwell time 0.1 second; pressure 80 psi) to a polypropylene substrate and the peel strengths of the composite films were tested as described herein. The results are provided in Table 2.

[0095] The films according to the present invention exhibited an easy and clean peel when manually peeled from the tray. In contrast, the films of Comparative Examples 1, 2 and 3 left a coating residue on the polypropylene substrate after peeling.

TABLE-US-00002 1(C) 2(C) 3(C) 4(C) 5 6 7 8 9 10 EVA copolymer: Elvax® 3180 15.5% Elvax® 410 15.5% Elvax® 4260 48.5% 60% 31% 28.5% 31% 31% 31% Styrenic Block Copolymer: Kraton® G1657ms 97% 60% 48.5% 29% 29% 28% Kraton® D1161 29% 29% Tackifier: Piccolyte® M115 37% 37% 37% 37% 37% 37% 37% Foral® 85 18% Pentalyn® H 19% Other Ingredients: Carnauba wax 5.0% Kemamide EZ 1.5% 1.5% 1.5% 1.5% 1.5% 1.5% 1.5% 1.5% 1.5% Syloid® 620 1.5% 1.5% 1.5% 1.5% 1.5% 1.5% 1.5% 1.5% 1.5% 1.5% Peel strength (g/25.4 mm) 433* 721* 843* 594 874 1013 938 872 694 672 * coating residue observed on the PP substrate after peeling

[0096] The peel strength of the composite films of Comparative Example 4 (no styrenic block copolymer) and Example 6 (styrenic block copolymer) were tested over a range of temperatures, and the results are shown in Table 3. The heat-sealing process and the test method was the same as previously described. The inventive example was found to exhibit superior peel strength at each temperature tested.

TABLE-US-00003 Sealing temperature 325° F. 350° F. 375° F. 400° F. Peel strength for Example 4 (C) (g/25.4 mm) 479 594 506 623 Peel strength for Example 6 (g/25.4 mm) 502 1013 1476 1273

Comparative Example 11 and Examples 12 to 16

[0097] A further series of composite films were prepared to investigate the effect of the vinyl acetate content of the EVA copolymer on peel strength and clarity. The films were prepared using the procedure described for Examples 5 to 10. The coating composition was constituted as follows:

TABLE-US-00004 EVA resin: 35.0 wt% Styrenic Block Copolymer: Kraton® G1657ms 28.0 wt% Tackifier: Piccolyte® M115 35.5 wt% Other: Syloid® 620 1.5 wt%

[0098] The EVA resin was varied as shown in Table 4 below. The coating formulations were prepared at 20 wt% in toluene and off-line coated by gravure coating at a coat-weight of 6.0 g/m.sup.2 onto the PVDC-primed surface of the PET substrate described above. The clarity and peel strength of each composite film, measured as described herein, are in Table 4.

TABLE-US-00005 Example 11 (C) 12 13 14 15 16 EVA resin Queo® 7007LA Elvax® 3200-2 Elvax® 3180 Elvax® 4260 Elvax® 3185 Elvax® 4031 wt% VA 0 22.5 28 28 32 40 Clarity (%) 93.8 85.3 80.5 79.4 76.1 70.1 Peel strength (g/25.4 mm) 799.sup.a 1107 1048 1029 1014 951 a: non-clean peel; coating residue observed on the PP substrate after peeling

[0099] The results in Table 4 demonstrate that clarity generally decreases with increasing VA content of the EVA resin. The results also demonstrate that adhesion performance becomes unsatisfactory as the VA content is reduced to zero.

Examples 17 to 22

[0100] A further series of composite films were prepared to investigate the effect on peel strength and clarity of blends of EVA resins having differing vinyl acetate contents. Examples 17 to 22 were based on Example 14, and replaced part of the Elvax®4260 (28 wt% VA) with Elvax®410(18 wt% VA). The composition of the coating layer and base layer, and the method of preparation of the composite film, were otherwise identical to Example 14. The EVA resin was varied as shown in Table 5 below, which also shows the clarity and peel strength performance.

TABLE-US-00006 Example 14 17 18 19 20 21 22 Wt Ratio of Elvax 410/Elvax 4260 0/100 8/100 17/100 28/100 43/100 67/100 100/100 Clarity (%) 79.4 82.9 89.4 88.0 86.1 73.2 76.9 Peel Strength (g/25.4 mm) 1029 1023 1075 1120 982 1053 1057

[0101] The results in Table 5 demonstrate that an EVA resin with a relatively low VA content can serve as a compatibilizer to prevent or reduce phase separation of an EVA resin having a relatively high VA content, with surprising improvement in the clarity of the resulting coating, and with no adverse effect on peel strength.

Comparative Example 12 and Example 6

[0102] A further series of composite films were prepared to investigate the effect of the amount of EVA copolymer in the coating layer on the peel strength. Comparative Example 12 was based on Example 6, except that the amount of Elvax®4260 was varied as shown in Table 6 below, which also shows the peel strength performance. The composition of the coating layer and base layer, and the method of preparation of the composite film, were otherwise identical to Example 6.

TABLE-US-00007 Example 6 12 (C) Elvax® 4260 31% 10% Kraton® G1657ms 29% 50% Piccolyte® M115 37% 37% Kemamide EZ 1.5% 1.5% Syloid® 620 1.5% 1.5% Peel Strength (g/25.4 mm) 1013 1148* * non-clean peel; coating residue observed on the PP substrate after peeling

[0103] The results in Table 6 demonstrate that adhesion performance becomes unsatisfactory as the amount of EVA relative to the total weight of the coating layer becomes relatively low. The film according to the present invention exhibited an easy and clean peel when manually peeled from the tray. In contrast, the film of Comparative Example 12 left large amounts of coating residue on the polypropylene substrate after peeling.