MULTILAYER FILM FOR RECLOSABLE PACKAGING WITH POLYPROPYLENE LAYER OBTAINED BY FLAT SHEET CO-EXTRUSION

Abstract

A multilayer film comprises an adhesive layer A comprising an HMPSA composition (a); a complexable thin layer B comprising a PolyPropylene (PP) composition (b); and a heat-sealable and breakable layer C comprising a PolyPropylene (PP) composition (c). Layers B and C are bonded together by layer A and the film is characterized in that the melt flow indices of compositions (a), (b) and (c), denoted MFI(a), MFI(b) and MFI(c), respectively, are such that the ratios MFI(a)/MFI(b) and MFI(a)/MFI(c) are each between 0.3 and 3.5. A process for manufacturing the film comprises flat sheet coextrusion of composition (a) and of compositions (b) and (c) at a temperature of between 150° C. and 250° C. Resealable packaging can comprise the multilayer film.

Claims

1-14. (canceled)

15. A multilayer film comprising: an adhesive layer A consisting of an extrudable HMPSA composition (a); a complexable thin layer B consisting of a PolyPropylene (PP) composition (b) denoted PP(b); and a heat-sealable and breakable layer C consisting of a PolyPropylene (PP) composition (c) denoted PP(c); wherein layers B and C are bonded together by layer A and said film is characterized in that the melt flow indices: of the HMPSA composition (a), measured in g/10 minutes at a temperature of 190° C. and a total weight of 2.16 kg, and denoted MFI(a), and of compositions (b) and (c), measured in g/10 minutes at a temperature of 230° C. and a total weight of 2.16 kg, and denoted MFI(b) and MFI(c), respectively, are such that the ratios MFI(a)/MFI(b) and MFI(a)/MFI(c) are each between 0.3 and 3.5.

16. The multilayer film as claimed in claim 15, characterized in that the melt flow indices MFI(b) and MFI(c) are each between 2.5 and 30 g/10 minutes.

17. The multilayer film as claimed in claim 15, characterized in that the MFI(a) is in a range from 4 to 100 g/10 minutes.

18. The multilayer film as claimed in claim 15, characterized in that the extrudable HMPSA composition (a) comprises, on the basis of the total weight of said composition: from 40% to 70% by weight of a composition (a1) of styrene block copolymers comprising at least one elastomer block, said composition (a1) consisting, on the basis of its total weight: of 10% to 90% by weight of at least one diblock copolymer selected from the group consisting of SI, SBI, SIB, SB, SEB and SEP, and of 10% to 90% by weight of at least one triblock copolymer selected from the group consisting of SIS, SIBS, SBS, SEBS and SEPS; wherein the total content of styrene units of said composition (a1) ranges from 10% to 40% by weight on the basis of the total weight of (a1); and from 30% to 60% by weight of one or more tackifying resins (a2).

19. The multilayer film as claimed in claim 15, characterized in that compositions (b) and (c) are compositions of the same PolyPropylene PP.

20. The multilayer film as claimed in claim 15, characterized in that compositions (b) and (c) consists of a PP.

21. The multilayer film as claimed in claim 15, characterized in that compositions (b) and (c) are PP-based compositions which comprise, in addition to said PP, an additive comprising an anti-fogging agent, a processing aid, a slip agent and/or an antiblocking agent.

22. The multilayer film as claimed in claim 15, characterized in that it consists of three layers A, B and C.

23. The multilayer film as claimed in claim 15, characterized in that it comprises, in addition to the three layers A, B and C, additional thin layers comprising: a rigid layer, a printable layer, and/or a layer with a barrier effect against oxygen, water vapor or carbon monoxide.

24. The multilayer film as claimed in claim 15, characterized in that its total thickness varies in a range from 20 to 300 μm.

25. The multilayer film as claimed in claim 15, characterized in that the thickness of the adhesive layer A varies in a range from 5 to 50 μm and the thickness of the heat-sealable and breakable layer C varies in a range from 5 to 25 μm.

26. A process for manufacturing the multilayer film as defined in claim 15, comprising flat sheet coextrusion of the HMPSA composition (a) and of compositions (b) and (c) at a temperature of between 150° C. and 250° C.

27. Resealable packaging comprising the multilayer film as defined in claim 15.

28. The resealable packaging of claim 15, wherein the multiplayer film is a cover film of a resealable tray.

Description

Examples A1, A2 and A3 (References): Compositions (a) of Layer A

[0171] Each of the compositions A1, A2 and A3 is prepared beforehand in the form of granules about 4 mm in diameter, by simply mixing the ingredients listed in Table 1, using a twin screw extruder.

[0172] The MFI measured is also given in Table 1.

Example 1 (According to the Invention): B/A/C Three-Layer Film with Layer A having Composition A2 and Layers B and C made of PP with an MFI Equal to 8 g/10 min

[0173] This three-layer film is manufactured by means of a continuously operating flat sheet coextrusion pilot-scale device, in which device three extruders are fed: [0174] one is fed with composition A2 of Example A2, and [0175] the other two are fed with PP RD204CF from the company Borealis; the three compositions being in the form of granules having a size of approximately 4 mm

[0176] This pilot device consists of a one-piece extrusion head with a rectangular die 250 mm wide and 300 μm high, and a chrome-plated chill roll cooled by an internal water circulation system.

[0177] The process parameters are adjusted so as to produce a three-layer film consisting: [0178] as layer A, of a layer with a thickness of 15 μm consisting of composition A2, [0179] as complexable thin layer B, of a layer with a thickness of 30 μm consisting of said PP; [0180] as heat-sealable and breakable thin layer C, of a layer with a thickness of 15 μm also consisting of said PP.

[0181] Among the parameters usually set, mention may be made of a temperature of 200° C. for the one-piece extrusion head and the rectangular die, and a line speed of 10 m per minute.

[0182] The three-layer film thus obtained has a total thickness of 60 μm and a length of 50 m and is packaged in the form of a reel with a machine width of 250 μm The composition of layer A is shown in Table 2, as is the grade of PP used for layers B and C.

[0183] A check is made on the appearance of the resulting three-layer film, including the homogeneity of its thickness. The absence of sticky edges and the absence of “coextrusion waves” is noted, indicating the conformity of the film obtained. Such conformity is reported in Table 2 by the mention “OK”.

[0184] The term “coextrusion waves” refers to the possible presence on a three-layer film obtained by flat sheet coextrusion of lines (or waves) that correspond to an excess thickness and indicate an unacceptable non-uniformity of thickness of said film.

[0185] Once the conformity has been established, the three-layer film is subjected to the tests B.1. and B.2. described below.

Test B.1. Measurement of the First-Opening Force by T-Peeling, at 23° C., of the Three-Layer Film Previously Heat-Welded on a PET/PP Complex

[0186] Rectangular test specimens E1 that are 25 cm long and 3 cm wide are cut from the three-layer film B/A/C obtained previously.

[0187] In addition, a PET/PP complex film is used, consisting of a 23 μm thick PET layer which is laminated with polyurethane (2 μm layer) on a 50 μm thick PP layer. Rectangular test specimens E2 that are 25 cm long and 3 cm wide are cut from this complex film.

[0188] A test specimen E1 is then placed opposite between two test specimens E2, the three specimens being superimposed, so that layers B and C of E1 are in contact with the PP layer of E2.

[0189] Partial sealing is then performed using two heating clamping jaws at 150° C. applied under a pressure of 4.6 bar for 1 second, so as to obtain a sealed area of rectangular shape (15 cm in length and 1 cm in width). Said sealed area is arranged lengthwise and is located in the center of the assembly of the three superimposed test specimens, so that 5 cm of unsealed films protrude on both sides in the lengthwise direction, and 1 cm of unsealed films protrude on both sides in the width direction.

[0190] The loose film strips on one side of the three-test-specimen assembly, relative to the sealed area, are attached: [0191] to a first attachment device (called a jaw) that is connected to the fixed part of a tensile testing apparatus, as regards the one of the two strips E2 that is facing layer C of E1, and [0192] to a second jaw connected to the movable part of said tensile testing apparatus, as regards the other strip E2 and the strip E1.

[0193] The fixed and mobile parts of the tensile testing apparatus, which is a dynamometer, are located on the same vertical axis.

[0194] The three strips thus fixed make it possible, by displacement of the jaws of the dynamometer, to solicit (or peel) the interface between layer C of the film B/A/C constituting E1 and the PP of E2 which faces it.

[0195] While a drive mechanism imparts a uniform rate of 300 mm/minute to the movable part, resulting in the peeling of the three sealed test specimens E1and E2, the ends gradually move along a vertical axis with the formation of an angle of 180°. A force sensor connected to said movable part measures the force withstood by the test specimen thus held. The measurement is performed in a climate-controlled room maintained at a temperature of 23° C.

[0196] The force obtained is shown in table 2.

Test B.2. Measurement of the Second-Opening Force by T-Peeling, at 23° C., of the Three-Layer Film Heat-Welded on a PET/PP Complex

[0197] The two parts of the preceding test specimen are, after peeling, repositioned facing each other and brought into contact manually. They are then subjected to a pressure exerted by means of a roller with a mass of 2 kg, with which a to-and-fro movement is performed in a direction parallel to the length of the test specimen.

[0198] A tensile test specimen is thus obtained which is identical in shape to that prepared for the preceding peeling test, which is then repeated.

[0199] The force obtained is shown in table 2.

Examples 2 to 5 (According to the Invention): B/A/C Three-Layer Films

[0200] For each of these examples, Example 1 is repeated: [0201] optionally replacing composition A2 of layer A with composition A1, A2 or A3 (detailed in Table 1), as shown in Table 2; and [0202] optionally replacing the grade of PP RD204CF in layers B and C with the grade of PP shown in Table 2.

[0203] The appearance of the resulting three-layer film is identical to that of the three-layer film in Example 1 and is noted as OK in Table 2.

Example 6 (Comparative): B/A/C Three-Layer Film with Layer A of Composition A1 and Layers B and C made of PP with an MFI Equal to 8 g/10 min

[0204] Example 1 is repeated, replacing composition A2 of layer A with composition A1, as shown in Table 3.

[0205] Coextrusion waves are observed on the resulting three-layer film, which have the effect of rendering said film non-compliant.

Examples 7 to 9 (Comparative): B/A/C Three-Layer Films with PP Layers B and C of MFI Equal to 1.8 g/10 min

[0206] Example 1 is repeated: [0207] optionally replacing composition A2 in layer A with composition A1, A2 or A3, as shown in Table 3; and [0208] replacing the grade of PP RD204CF in layers B and C with the grade of PP PPR 3260, also as shown in Table 3.

[0209] Sticky edges and/or coextrusion waves are observed on the resulting three-layer film, which have the effect of rendering said film non-compliant.

TABLE-US-00001 TABLE 1 Composition (a) of layer A Amount in weight/weight % Ex. A1 Ex. A2 Ex. A3 Ingredient (reference) (reference) (reference) Quintac ® 3433 N 59.7 — — Quintac ® 3520 — 59.7 — Kraton ® D1111 — — 59.7 Escorez ® 1310 LC 39.8 — — Regalite ® R1125 — 39.8 39.8 Antioxidant 0.5 0.5 0.5 MFI (in g/10 minutes) 30 25 10

TABLE-US-00002 TABLE 2 B/A/C three-layer films according to the invention Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Layer A Composition (a) A2 A3 A1 A2 A3 MFI.sub.(a) 25 10 30 25 10 (in g/10 minutes) Layers Grade of PP RD204CF RD204CF PP511A PP511A PP511A B and C MFI.sub.(PP) 8 8 25 25 25 (in g/10 minutes) B/A/C MFI.sub.(a)/MFI.sub.(PP) 3.1 1.2 1.2 1.0 0.4 three- Appearance of OK OK OK OK OK layer the film film First-opening 3.9 7.14 3.85 NA 5.5 force (N/cm) Second-opening 0.64 0.78 0.61 NA 0.66 force (N/cm) NA = result Not Available

TABLE-US-00003 TABLE 3 comparative B/A/C three-layer films Ex. 6 Ex. 7 Ex. 8 Ex. 9 (comp) (comp) (comp) (comp) Layer A Composition (a) A1 A1 A2 A3 MFI.sub.(a) (in 30 30   25   10   g/10 minutes) Layers Grade of PP RD204CF PPR 3260 PPR 3260 PPR 3260 B and C MFI.sub.(PP) (in  8  1.8  1.8 1.8 g/10 minutes) MFI.sub.(a)/MFI.sub.(PP)   3.7 16.7 13.9 5.5 B/A/C Appearance of coextrusion coextrusion coextrusion coextrusion three-layer the film waves waves waves waves film sticky edges sticky edges