SEALABLE PEELABLE POLYESTER FILMS

Abstract

A polymeric film comprising a polyester substrate layer and a heat-scalable polymeric layer disposed on one surface of said polyester substrate layer, wherein the heat-scalable polymeric layer comprises copolyester A having a glass transition temperature Tg(A) in an amount WA and copolyester B having a glass transition temperature Tg(B) in an amount WB, wherein: (i) WA>WB; (ii) WA is at least 50 wt % by total weight of the heat-scalable polymeric layer; (iii) WB is at least 10 wt % by total weight of the heat-scalable polymeric layer; (iv) Tg(A)>Tg(B); (v) Tg(B) is in the range of ?35? C. to ?10? C.; and (vi) Tg(A) is preferably in the range of ?15? C. to 5? C.

Claims

1. A polymeric film comprising a polyester substrate layer and a heat-sealable polymeric layer disposed on one surface of said polyester substrate layer, wherein the heat-sealable polymeric layer comprises copolyester A having a glass transition temperature Tg(A) in an amount W.sub.A and copolyester B having a glass transition temperature Tg(B) in an amount W.sub.B, wherein: (i) W.sub.A>W.sub.B; (ii) W.sub.A is at least 50 wt % by total weight of the heat-sealable polymeric layer; (iii) W.sub.B is at least 10 wt % by total weight of the heat-sealable polymeric layer; (iv) Tg(A)>Tg(B); (v) Tg(B) is in the range of ?35? C. to ?10? C.; and (vi) Tg(A) is preferably in the range of ?15? C. to 5? C.

2. A polymeric film according to claim 1 wherein said polyester substrate layer is oriented, preferably biaxially oriented.

3. A polymeric film according to claim 1 wherein said substrate layer polyester is polyethylene terephthalate (PET) or a PET-based copolyester.

4. A polymeric film according to claim 1, wherein Tg(B) is at least 5? C., preferably from 10 to 15? C., lower than Tg(A).

5. A polymeric film according to claim 1, wherein Tg(A) is in the range of ?10? C. to 0? C.

6. A polymeric film according to claim 1, wherein Tg(B) is in the range of ?30? C. to ?15? C.

7. A polymeric film according to claim 1, wherein copolyester A and copolyester B are independently selected from copolyesters derived from at least 3 different monomeric repeating units, and preferably 3 different monomeric repeating units, and preferably derived from an aromatic dicarboxylic acid, an aliphatic dicarboxylic acid and a glycol, preferably wherein the aromatic dicarboxylic acid is terephthalic acid, and preferably wherein the aliphatic dicarboxylic acid has the general formula C.sub.nH.sub.2n(COOH).sub.2 wherein n is 2 to 8, and preferably wherein the glycol is ethylene glycol.

8. A polymeric film according to claim 7, wherein the aromatic dicarboxylic acid in copolyester A is the same as the aromatic dicarboxylic acid in copolyester B, preferably wherein the glycol in copolyester A is the same as the glycol in copolyester B, and preferably wherein the aliphatic dicarboxylic acid in copolyester A is different from the aliphatic dicarboxylic acid in copolyester B.

9. A polymeric film according to claim 1, wherein copolyester A and copolyester B are independently selected from copolyesters in which the acid fraction contains an aromatic dicarboxylic acid and an aliphatic dicarboxylic acid, wherein the aliphatic dicarboxylic acid makes up from 10 to 90 mol %, preferably from 20 to 80 mol %, preferably from 30 to 70 mol %, preferably from 40 to 60 mol % of the total acid fraction of the copolyester, with the balance being made up of the aromatic dicarboxylic acid.

10. A polymeric film according to claim 7, wherein the aliphatic dicarboxylic acid content of copolyester A is lower than the aliphatic dicarboxylic acid content of copolyester B.

11. A polymeric film according to claim 7, wherein the aliphatic dicarboxylic acid content of copolyester A is no more than 50 mol %, preferably from 10 to 50 mol %, preferably from 20 to 50 mol %, preferably from 30 to 50 mol %, for instance from 40 to 50 mol % of the total acid fraction of the copolyester.

12. A polymeric film according to claim 7, wherein the aliphatic dicarboxylic acid content of copolyester B is greater than 40 mol %, preferably greater than 45 mol %, preferably greater than 50 mol %, preferably greater than 55 mol %, preferably from 50 to 90 mol %, preferably from 50 to 80 mol %, preferably from 50 to 70 mol %, for instance from 50 to 60 mol % of the total acid fraction of the copolyester.

13. A polymeric film according to claim 1, wherein copolyester A is the major copolyester in the heat-sealable layer and is present in an amount W.sub.A which is from 50 to 90 wt %, preferably from 50 to 89 wt %, by total weight of the heat-sealable polymeric layer.

14. A polymeric film according to claim 1, wherein copolyester B is the minor copolyester in the heat-sealable layer and is present in an amount W.sub.B which is from 10 to 50 wt %, preferably from 10 to 45 wt %, by total weight of the heat-sealable polymeric layer.

15. A polymeric film according to claim 1, wherein the heat-sealable layer further comprises one or more anti-blocking agent(s) to improve the handling properties of the film, preferably wherein the total amount of anti-blocking agent(s) is no more than about 5 wt %, and preferably from about 1 to about 5 wt %, by total weight of the heat-sealable polymeric layer, and preferably wherein said anti-blocking agents are selected from silica, fatty amides and waxes, and combinations thereof.

16. A polymeric film according to claim 1, wherein the softening point of copolyester A is from 120 to 160? C., preferably from 130 to 150? C., determined according to ASTM E28-18.

17. A polymeric film according to claim 1, wherein the softening point of copolyester B is from 60 to 120? C., preferably from 80 to 110? C., determined according to ASTM E28-18.

18. A polymeric film according to claim 1, wherein the tensile strength at break of copolyester A is at least 1000 psi, preferably from 1500 to 5000 psi, determined according to ASTM D638-14.

19. A polymeric film according to claim 1, wherein the tensile strength at break of copolyester B is at least 200 psi, preferably from 250 to 1500 psi, preferably less than 1500, determined according to ASTM D638-14.

20. A polymeric film according to claim 1, wherein the elongation at break of copolyester A is at least 250%, preferably from 500 to 2000%, determined according to ASTM D638-14.

21. A polymeric film according to claim 1, wherein the elongation at break of copolyester B is at least 500%, preferably from 1000 to 2500%, determined according to ASTM D638-14.

22. A polymeric film according to claim 1, wherein said heat-sealable polymeric layer is a coated heat-sealable polymeric layer, preferably having a dry coat-weight of from 1 to 5 g/m.sup.2.

23. A polymeric film according to claim 1, wherein the total thickness of the film is from 5 to 250 ?m, preferably from 8 to 125 ?m, preferably from 8 to 50 ?m, and preferably from 12 to 26 ?m.

24. A polymeric film according to claim 1, wherein the heat-seal peel strength of the film is in the range of 500 to 1400 g/inch, preferably 500 to 1200 g/inch, measured as defined herein, when heat-sealed to the APET layer of an APET-CPET coextruded substrate with a dwell time of 1 second, a pressure of 40 psi (275.79 kPa) and at a temperature (and preferably any temperature) in the range of from 121 to 204? C.

25. A lidding film comprising the polymeric film according to any of claim 1 further comprising a metallic foil layer such that the layer sequence is: metallic foil layer/polyester substrate layer/polymeric heat-sealable layer.

26. A lidding film according to claim 25 wherein the metallic foil layer is an aluminium foil layer and/or the thickness of the metallic foil layer is in the range of about 25 to about 50 ?m.

27. A lidding film according to claim 25 wherein the longest dimension of the lidding film is no more than 70 mm, and preferably wherein the lidding film is circular, preferably having a diameter of no more than 70 mm.

28. A lidding film according to claim 25 further comprising a paper or foam layer disposed on the side of the metallic foil layer which is remote from the polymeric substrate layer, such that the layer sequence is: paper or foam layer/metallic foil layer/polyester substrate layer/heat-sealable layer, preferably wherein an adhesive layer is disposed between the metallic foil layer and the paper or foam layer.

29. A lidding film according to claim 25 further comprising a pulpboard layer and a wax layer, such that the layer sequence is pulpboard layer/wax layer/metallic foil layer/polymeric substrate layer/polymeric heat-sealable layer.

30. A lidding film according to claim 29 wherein the paper, foam of pulpboard layer is 50-1000 ?m in thickness.

31. A lidding film according to claim 25 which is a cap-liner.

32. A method of sealing a container comprising an opening, wherein said method comprises the steps of: (i) providing or preparing the film according to claim 1; (ii) laminating the film from step (i) with a metallic foil, and either a paper or foam layer or pulpboard and wax layers, to form a cap-liner comprising the layer sequence: (a) paper or foam layer/metallic foil layer/polyester substrate layer/polymeric heat-sealable layer, or (b) pulpboard layer/wax layer/metallic foil layer/polymeric substrate layer/polymeric heat-sealable layer; (iii) providing a container; (iv) providing a cap for the container; (v) inserting the cap-liner from step (ii) inside the cap; (vi) disposing the cap over the opening of the container such that the heat-sealable layer of the cap-liner contacts the container; and (vii) subjecting the cap to electromagnetic induction heating, thereby sealing the cap-liner to the container.

33. A method of sealing a container comprising an opening, wherein said method comprises the steps of: (i) providing or preparing the film according to claim 1; (ii) laminating the film from step (i) with a metallic foil to provide a lidding film comprising the layer sequence: metallic foil layer/polyester substrate layer/polymeric heat-sealable layer; (iii) providing a container; (iv) disposing said lidding film from step (ii) over the opening of the container such that the heat-sealable layer of said lidding film contacts the container; and (v) subjecting the lidding film to electromagnetic induction heating, thereby sealing the lidding film to the container.

34. A method of sealing a container comprising an opening, wherein said method comprises the steps of: (i) providing or preparing the film according to claim 1; (ii) providing a container; (iii) disposing said film according to step (i) over the opening of the container such that the heat-sealable layer of said film contacts the container; (iv) subjecting the film to conductive heat and optionally pressure, thereby sealing the film to the container.

35. A sealed container comprising a container with an opening and further comprising a film according to claim 1, wherein said film is sealed around the edges of said opening, preferably wherein the sealed container further comprises a cap which is disposed over said sealed opening, and preferably wherein the sealed container is an induction-sealed container.

Description

EXAMPLES

[0135] A series of coated films were prepared by coating a coating composition on a biaxially oriented PET film of thickness 12.5 ?m and then dried. The dry coat-weight of the coating composition was 2.3 g/m.sup.2. The coating compositions were as follows.

Comparative Example 1

[0136] A coating solution was prepared by dissolving copolyester 1 (532 g) and copolyester 2 (133 g) in THF (2,800 g) at 55? C., followed by the addition of slip/anti-blocking ingredients (fatty amide 10.5 g; silica 24.5 g). Copolyester 1 was a PET-based copolyester in which the dicarboxylic acid fraction comprised 45 mol % azelaic acid, and which exhibited a tensile strength of 2700 psi and an elongation of 1000%, measured as defined herein. Copolyester 2 was a PET-based copolyester in which the dicarboxylic acid fraction comprised 33 mol % isophthalic acid, and which exhibited a tensile strength of 11000 psi and an elongation of 5%, measured as defined herein.

Example 1

[0137] A coating solution was prepared by dissolving copolyester 1 (476 g) and copolyester 2 (203 g) in THF (2,800 g) at 55? C., followed by the addition of slip/anti-blocking ingredients (fatty amide 10.5 g; silica 10.5 g). Copolyester 1 was a PET-based copolyester in which the dicarboxylic acid fraction comprised 45 mol % azelaic acid, and which exhibited a tensile strength of 2700 psi and an elongation of 1000%, measured as defined herein. Copolyester 2 was a PET-based copolyester in which the dicarboxylic acid fraction comprised 58 mol % sebacic acid, and which exhibited a tensile strength of 1000 psi and an elongation of 1600%, measured as defined herein.

Example 2

[0138] A coating solution was prepared by dissolving copolyester 1 (476 g) and copolyester 2 (203 g) in THF (2,800 g) at 55? C., followed by the addition of slip/anti-blocking ingredients (fatty amide 10.5 g; silica 10.5 g). Copolyester 1 was a PET-based copolyester in which the dicarboxylic acid fraction comprised 45 mol % azelaic acid, and which exhibited a tensile strength of 2500 psi and an elongation of 1200%, measured as defined herein. Copolyester 2 was a PET-based copolyester in which the dicarboxylic acid fraction comprised 58 mol % sebacic acid, and which exhibited a tensile strength of 1000 psi and an elongation of 1600%, measured as defined herein.

Cap-Liners

[0139] Each of the films was made into a one-piece cap-liner by laminating the film with an aluminium foil layer (of thickness 25.4 ?m) followed by laminating with a layer of paper foam (of thickness 127 ?m). The cap-liner was inserted into a white 38/400 cap (SKS Bottle & Pkg, Inc.) and induction-sealed to a white PET bottle (Packaging Options Direct, US) having a neck diameter of 38 mm in which the wall thickness of the bottle neck was 2.2 mm. Induction-sealing was performed on an Ifoiler Induction Sealer (Pillar Tech. LLC) using a cap torque of 20 lbf*in (pound-force-inch), an air gap (induction sealer head to bottle cap) of ? (3.175 mm) and a conveyor line speed 60 feet/min (18.288 m/min).

[0140] Table 1 shows the properties of the copolyesters, the films containing them and the cap-liners made therefrom, characterised according to the test methods described hereinabove.

[0141] The data in Table 1 show that the variation in heat-seal peel strength over the temperature range of 121 to 204? C. is much larger for Comparative Example 1 and advantageously smaller for Examples 1 and 2. Thus, the inventive examples advantageously exhibit a much lower variation in heat-seal strength with changes in temperature. It will be appreciated that temperatures can be controlled more precisely in a heat-sealing system than in an induction system and that the heat-seal testing was conducted at different temperatures in order to recreate the varying temperature conditions in a conventional induction-sealing system.

[0142] The data in Table 1 also show that the variation in heat-seal peel strength after ageing is much larger for Comparative Example 1 and advantageously smaller for Examples 1 and 2. Thus, the inventive examples advantageously exhibit a much smaller increase in heat-seal strength over time.

[0143] A similar trend was observed for the induction-seal peel strength data in Table 1. The variation in peel strength after ageing is advantageously much smaller for Example 2 (Example 1 was not tested), compared to Comparative Example 1, which was observed at all power settings tested for each film. The power setting was adjusted to optimise the seal strength of the heat-seal bond. For Comparative Example 1 the optimal setting was 48% of the potential power output of the induction sealing system, whereas for Example 2 the optimal setting was 32% of the potential power output of the induction sealing system in order to provide comparable aged peel strengths to Comparative Example 1. It will be appreciated that the inventive Example also surprisingly allows a reduction in the energy used to make an appropriate heat-seal bond, thereby improving the economy and sustainability of the process.

TABLE-US-00001 TABLE 1 Induction-seal peel strength Copolyester 1 Copolyester 2 Heat-seal peel strength (PS) of cap-liner (g) Co- Co- (PS) of film (g/inch) ?-PS on diacid Amount Tg Ts diacid Amount Tg Ts Aged ?-PS on Power Aged ageing (mol %) (wt %) (? C.) (? C.) (mol %) (wt %) (? C.) (? C.) T .sup.e Unaged (24 h) ageing output Unaged (24 h) (%) C. Azelaic 76 wt % ?8 150 isophthalic 19 wt % 70 150 T.sub.1 711 1142 431 44% 496 753 52% Ex. 1 acid (45 acid (33 T.sub.2 >1078 .sup.a >1556 .sup.c .sup.478 .sup.c 46% 463 839 81% mol %) mol %) T.sub.3 >1326 .sup.b.sup. >1600 .sup.d.sup. n/a .sup.d 48% 679 1020 50% Ex. 1 Azelaic 68 wt % ?8 150 sebacic 29 wt % ?22 100 T.sub.1 929 1123 194 acid (45 acid (58 T.sub.2 914 1092 178 mol %) mol %) T.sub.3 1165 1308 143 Ex. 2 Azelaic 68 wt % ?7 145 sebacic 29 wt % ?22 100 T.sub.1 777 941 164 28% 503 669 33% acid (45 acid (58 T.sub.2 841 990 149 30% 914 910 ?4% mol %) mol %) T.sub.3 897 1022 125 32% 970 1106 14% Key .sup.a 1 of 6 samples shredded; .sup.b 3 of 6 samples shredded; .sup.c 5 of 6 samples shredded; .sup.d 6 of 6 samples shredded .sup.e heat-seal temperatures were: T.sub.1 = 121? C.; T.sub.2 = 177? C.; T.sub.3 = 204? C.