NOVEL MULTILAYER FILM FOR RESEALABLE PACKAGING WITH IMPROVED RESEALING

Abstract

1) Multilayer film comprising 2 thin layers D and E of a thermoplastic material bonded together by a continuous layer A consisting of a hot-melt pressure-sensitive adhesive composition comprising: from 40% to 70% by weight of a composition of styrene block copolymers consisting of a mixture of diblock and triblock copolymers; and from 30% to 60% by weight of one or more tackifying resins;

said multilayer film being such that the adhesive layer A is: connected to the layer D by means of a tie layer B, and connected to the layer E by means of a tie layer C,

each of the 2 layers B and C respectively consisting of a composition (b) and (c) each comprising: a polyolefin (P) chosen from a polyethylene (PE) and a polypropylene (PP), optionally modified with an unsaturated carboxylic anhydride; and at least one elastomer compound (EL) chosen from a copolymer of ethylene and of propylene (EL1) and a styrene block copolymer (EL2) comprising at least one elastomer block.

2) Process for producing said film by coextrusion.

3) Use of said film for producing resealable packagings.

Claims

1. A multilayer film comprising 2 thin layers D and E of a thermoplastic material bonded together by a continuous layer A which has a thickness ranging from 7 to 50 μm, and consists of an HMPSA composition (a) comprising, 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 30% to 90% by weight of at least one diblock copolymer chosen from the group comprising SI, SBI, SIB, SB, SEB and SEP, and of 10% to 70% by weight of at least one triblock copolymer chosen from the group comprising SIS, SIBS, SBS, SEBS and SEPS; the total content of styrene units of said composition (a1) ranging 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); said multilayer film being further characterized in that the adhesive layer A is: connected to the layer D by means of a tie layer B, and connected to the layer E by means of a tie layer C; each of the 2 layers B and C respectively consisting of a composition (b) and (c) each comprising: a polyolefin (P) chosen from a polyethylene (PE) and a polypropylene (PP), optionally modified with an unsaturated carboxylic anhydride which is either a ring comprising 4 or 5 carbon atoms or a linear chain comprising 6 or 8 carbon atoms; and at least one elastomer compound (EL) chosen from a copolymer of ethylene and of propylene (EL1) and a styrene block copolymer (EL2) comprising at least one elastomer block.

2. The multilayer film as claimed in claim 1, characterized in that the composition (a1) consists of an SIS triblock copolymer and an SI diblock copolymer.

3. The multilayer film as claimed in claim 1, characterized in that the tackifying resin(s) (a2) that can be used have weight-average molar masses M.sub.w of generally between 300 and 5000 Da and are chosen in particular from: (i) rosins of natural origin or modified rosins, such as, for example, the rosin extracted from pine gum, wood rosin extracted from tree roots and derivatives thereof which are hydrogenated, dehydrogenated, dimerized, polymerized or esterified with monoalcohols or polyols, such as glycerol; (ii) resins obtained by hydrogenation, polymerization or copolymerization (with an aromatic hydrocarbon) of mixtures of unsaturated aliphatic hydrocarbons having approximately 5, 9 or 10 carbon atoms resulting from petroleum fractions; (iii) terpene resins generally resulting from the polymerization of terpene hydrocarbons, such as, for example, monoterpene (or pinene), in the presence of Friedel-Crafts catalysts, which are optionally modified by the action of phenols; (iv) copolymers based on natural terpenes, for example styrene/terpene, α-methylstyrene/terpene and vinyltoluene/terpene.

4. The multilayer film as claimed claim 1, characterized in that each of the constituent compositions (b) and (c) of the tie layers B and C comprises: from 50% to 98% by weight of the polyolefin (P); and from 2% to 50% by weight of the elastomer compound (EL); based on the total weight of said composition.

5. The multilayer film as claimed in claim 1, characterized in that the polyolefin (P) included in at least one of the compositions (b) and (c) is a (PE), preferably an (LDPE).

6. The multilayer film as claimed in claim 1, characterized in that the polyolefin (P) included in at least one of the compositions (b) and (c) is a (PE) grafted with maleic anhydride, preferably an (LLDPE) grafted with maleic anhydride.

7. The multilayer film as claimed in claim 1, characterized in that at least one of the constituent compositions (b) and (c) of the tie layers B and C comprises: from 50% to 85% by weight of (PE) grafted with maleic anhydride; and from 15% to 50% by weight of copolymer of ethylene and of propylene (EU).

8. The multilayer film as claimed in claim 1, characterized in that the styrene block copolymer (EL2) is in the form of a diblock and triblock composition as defined for the composition (a1).

9. The multilayer film as claimed in claim 1, characterized in that at least one of the constituent compositions (b) and (c) of the tie layers B and C comprises: from 70% to 98% by weight of (PE); and from 2% to 30% by weight of styrene block copolymer (EL2) comprising at least one elastomer block.

10. The multilayer film as claimed in claim 1, characterized in that the styrene block copolymer (EL2) is included in an HMPSA composition which is as defined for the HMPSA composition (a).

11. The multilayer film as claimed in claim 1, characterized in that the compositions (b) and (c) of the layers B and C are identical.

12. The multilayer film as claimed in claim 1, characterized in that it is a film comprising 5 layers consisting of the adhesive layer A, the 2 intermediate layers B and C and the 2 external layers D and E, according to the sequence D/B/A/C/E wherein the “/” sign signifies that the faces of the layers in question are in contact.

13. A process for producing the multilayer film as defined in claim 1, characterized in that it comprises the coextrusion of the hot-melt pressure-sensitive adhesive composition (a), of the compositions (b) and (c), and of the constituent materials of the layers D and E.

14. The process for producing the multilayer film as claimed in claim 13, characterized in that the coextrusion is carried out by bubble blowing.

15. A resealable packaging comprising in said resealable packaging a multilayer film according to claim 1.

Description

EXAMPLE A (REFERENCE): COMPOSITION (A) OF THE LAYER A

[0195] A composition consisting, on the basis of % weight/weight, of 59.5% of Kraton® D1113BT, 25% of Escorez® 1310 LC, 15% of Dercolyte® S115 and 0.5% of Irganox® 1010 is prepared, in the form of granules with a diameter of approximately 4 mm, by simply mixing the ingredients at 160° C. by means of a twin-screw extruder.

[0196] An MFI of 57 g/10 minutes is measured.

EXAMPLE B (REFERENCE): THREE-LAYER FILM D/A/E CONSISTING OF A LAYER A OF THE COMPOSITION OF EXAMPLE A

[0197] This three-layer film is produced by means of a continuously operating bubble-blowing coextrusion pilot-scale device, in which device 3 extruders are fed in the following way: [0198] one is fed with the composition (a) of example A, and [0199] the other two are fed with LDPE;
the 3 compositions being in the form of granules having a size of approximately 4 mm.

[0200] The process parameters are adjusted so as to produce a three-layer film consisting: [0201] as layer A, of a layer with a thickness of 15 μm consisting of the composition of example A, [0202] as complexable thin layer D, of a layer with a thickness of 25 μm consisting of LDPE; [0203] as a sealable and splittable thin layer E, a layer with a thickness of 10 μm also consisting of LDPE.

[0204] Among the parameters usually set, mention may made of a degree of radial expansion of the bubble equal to 3, a drawing speed of 7 m/minute and an overall throughput of 11 kg/hour.

[0205] The three-layer film thus obtained has a total thickness of 50 μm and a length of 50 m and is packaged in the form of a reel with a machine width of 250 mm.

[0206] Measurement of the First-Opening Force by Peeling in T at 23° C.:

[0207] A sample in the form of a rectangular sheet with A4 format (21×29.7 cm) is cut out from the three-layer film thus obtained.

[0208] The external face of the complexable layer D of this sample is: [0209] in a first step, subjected to a corona surface treatment (by means of a plasma), then [0210] in a second step, complexed (in other words laminated) on a PET film having a thickness of 23 μm by means of a polyurethane-based solvent-based adhesive and using a coating device of the Mayer bar type.

[0211] The rectangular sheet is then placed under pressure for 24 h.

[0212] Said rectangular sheet is then folded along a line located in its middle and parallel to the small side of the rectangle, which results in the sealable and splittable layer E being brought into contact with itself.

[0213] Partial sealing is then carried out using two heating clamping jaws at 130° C. applied under a pressure of 6 bar for 1 second, so as to obtain sealed regions of rectangular shape (8 cm in length and 1 cm in width) arranged perpendicularly to the line of folding. Each sealed zone is cut to obtain a tensile test specimen in which the sealed zone 8 cm in length is extended (to that of its ends which is opposite the line of folding) by 2 bands approximately 2 cm in length, left free and non-sealed.

[0214] These two free bands are attached to two holding devices (known as jaws) respectively connected to a stationary part and a movable part of a tensile testing device, which are located on a vertical axis. This tensile testing device is a dynamometer.

[0215] While a drive mechanism imparts a uniform rate of 300 mm/minute to the movable part, resulting in the peeling of the 2 sealed layers, 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 carried out in a climate-controlled room maintained at a temperature of 23° C.

[0216] The force obtained is shown in table 1.

[0217] Measurement of the Second-Opening Force by Peeling in T at 23° C.:

[0218] The 2 parts of the preceding test specimen are, after peeling, repositioned facing one another and brought into contact manually. They are then subjected to a pressure exerted by means of a roller with a weight of 2 kg, with which a to-and-fro movement is carried out in a direction parallel to the length of the test specimen.

[0219] A tensile test specimen is thus obtained which is identical in shape to that prepared for the preceding peeling test, which is then repeated.

[0220] The force obtained is shown in table 1.

EXAMPLE 1: FILM COMPRISING 5 LAYERS D/B/A/C/E WITH LAYER A CONSISTING OF THE COMPOSITION OF EXAMPLE A AND LAYERS B AND C CONSISTING OF ADMER™ AT1955E

[0221] Example B is repeated by modifying the coextrusion process so as to add to the three-layer film 2 layers B and C having the same thickness of 5 μm and the same composition, namely the product Admer™ AT1955E as shown in table 1.

[0222] A 5-layer film with a total thickness equal to 60 μm is obtained.

[0223] The 1.sup.st-opening and 2.sup.nd-opening forces are shown in table 1.

EXAMPLE 2: FILM COMPRISING 5 LAYERS D/B/A/C/E WITH LAYER A CONSISTING OF THE COMPOSITION OF EXAMPLE A AND LAYERS B AND C CONSISTING OF 95% OF LDPE AND 5% OF THE COMPOSITION OF EXAMPLE A

[0224] Example 1 is repeated by modifying the coextrusion process so as to add to the three-layer film 2 layers B and C having the same thickness of 5 μm and the same composition. Said composition consists (by weight) of 95% of LDPE and of 5% of the composition of example A. The composition of the 2 layers B and C is obtained by feeding the corresponding extruders with the appropriate amount of LDPE granules and granules of the composition of example A.

[0225] The 1.sup.st-opening and 2.sup.nd-opening forces are shown in table 1.

EXAMPLES 3-5: FILM COMPRISING 5 LAYERS D/B/A/C/E WITH LAYER A CONSISTING OF THE COMPOSITION OF EXAMPLE A AND LAYERS B AND C CONSISTING OF LDPE AND OF THE COMPOSITION OF EXAMPLE A

[0226] Example 2 is repeated using as constituent material of the 2 tie layers B and C that indicated in table 1.

[0227] The 1.sup.st-opening and 2.sup.nd-opening forces are also shown in table 1.

[0228] The results for 1.sup.st-opening forces obtained for examples 1-5 are of the same order of magnitude as that obtained for example B, and correspond to an entirely acceptable resealable packaging opening quality.

[0229] The results obtained for the 2.sup.nd-opening force reveal a clear increase compared to example B, thereby significantly indicating an improvement in the quality of the resealing of the resealable packaging, following the 1.sup.st opening thereof.

TABLE-US-00001 TABLE 1 Example B Example 1 Example 2 Example 3 Example 4 Example 5 Constituent Not involved Admer ™ 95% LDPE 90% LDPE 80% LDPE 70% LDPE material of the 2 tie AT1955E and 5% and 10% and 20% and 30% layers B and C composition composition composition composition example A example A example A example A 1.sup.st-opening force 4.93 6.80 4.73 4.65 5.32 5.88 (N/cm) 2.sup.nd-opening force 0.96 2.98 1.26 1.33 1.32 1.27 (N/cm)