MULTILAYER FILM FOR RESEALABLE PACKAGING

Abstract

The invention relates to: 1) a multilayer film for resealable packaging, wherein said multilayer film includes a layer having a thickness of between 7 and 300 m and consisting of a hot-melt pressure-sensitive adhesive composition having an MFI of 0.01 and 100 g/10 minutes, including 40 to 70% of an SIS styrene block copolymer mixture having a styrene content of 10 to 16% and a diblock copolymer content of 60% to 90%; and 30 to 60% of one or more tackifying resins having a softening temperature of between 5 and 140 C.; 2) a method for manufacturing said film by means of coextrusion; and 3) the use of said film for manufacturing resealable cartons.

Claims

1. A multilayer film comprising 2 thin layers of thermoplastic material bonded to one another by a continuous layer, characterized in that said layer has a thickness of between 7 and 300 m and is composed of a hot-melt pressure-sensitive adhesive composition having a melt flow index (or MFI) ranging from 0.01 to 100 g/10 minutes comprising: from 40 to 70% of a mixture of styrene block copolymers, said mixture having a total content of styrene units ranging from 10 to 16% and consisting of: from 60 to 90% of one or more diblock copolymers of Styrene/Isoprene (SI) type, and of from 10 to 40% of one or more linear Styrene/Isoprene/Styrene (SIS) triblock copolymers, and from 30 to 60% of one or more tackifying resins having a softening temperature of between 5 and 140 C.

2. The multilayer film as claimed in claim 1, characterized in that the pressure-sensitive adhesive composition has an MFI ranging from 2 to 70 g/10 minutes.

3. The multilayer film as claimed in claim 1, characterized in that the content of SI diblocks of the mixture of styrene block copolymers varies from 60 to 80%.

4. The multilayer film as claimed in claim 1, characterized in that the content of SI diblocks of the mixture of styrene block copolymers varies from 70 to 80%.

5. The multilayer film as claimed in claim 1, characterized in that the content of mixture of styrene block copolymers of the composition is less than or equal to 60%.

6. The multilayer film as claimed in claim 1, characterized in that the tackifying resin has a weight-average molar mass M.sub.w of between 300 and 5000 Da and is chosen from: (i) rosins of natural or modified origin, such as, for example, the rosin extracted from pine gum, wood rosin extracted from tree roots and their derivatives which are hydrogenated, dehydrogenated, dimerized, polymerized or esterified by 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 fraction of phenols; (iv) copolymers based on natural terpenes, for example styrene/terpene, -methylstyrene/terpene and vinyltoluene/terpene.

7. The multilayer film as claimed in claim 1, characterized in that the tackifying resin is aliphatic.

8. The multilayer film as claimed in claim 7, characterized in that the resin belongs to the categories (ii) or (iii).

9. The multilayer film as claimed in claim 1, characterized in that the pressure-sensitive adhesive composition comprises a plasticizer in an amount not exceeding 5%.

10. The multilayer film as claimed in claim 1, characterized in that the thickness of the bonding adhesive layer is between 10 and 300 m.

11. The multilayer film as claimed in claim 1, characterized in that the thickness of the bonding adhesive layer is between 10 and 50 m.

12. A three-layer film as defined in claim 1.

13. A process for the manufacture of the multilayer film as defined in claim 1, characterized in that it comprises the coextrusion of the hot-melt pressure-sensitive adhesive composition with the materials of the 2 adjacent thin layers.

14. The process for the manufacture of the multilayer film as claimed in claim 13, characterized in that the hot-melt pressure-sensitive adhesive composition and the constituent materials of the 2 thin layers are fed into the coextrusion device in the form of granules with a size of between 1 and 10 mm.

15. The process for the manufacture of the multilayer film as claimed in claim 13, characterized in that the coextrusion is carried out by blown film coextrusion.

16. In a process for the manufacture of resealable cartons, said process comprising employing a multilayer film, the improvement comprising using as said film a multilayer film according to claim 1.

17. A resealable carton to which carton has been applied a multilayer film according to claim 1.

Description

EXAMPLE 1

[0080] The adhesive composition shown in the following table, to which 0.5% of Irganox 1010 is added, is prepared in the form of a viscous liquid at 160 C. by simple mixing of the ingredients at this temperature using a twin-screw extruder.

[0081] The MFI is shown in the table.

[0082] Measurement of the Force of First Opening by Peeling at 5 C.:

[0083] A multilayer film including an adhesive layer formed on said composition is prepared in the following way.

[0084] Approximately 8 g of the adhesive composition are placed on a square PET sheet with a side length of 15 cm and a thickness of 50 m. A second PET sheet identical to the first is then applied and a pressure of 100 kg/cm.sup.2 is exerted on the assembly for 2 minutes, at a temperature of 120 C., using a hydraulic press. The thickness of the adhesive layer in the multilayer film, monitored using a sliding caliper, is approximately 250 m.

[0085] The rectangular test specimen of 1 cm by 10 cm is cutout from the multilayer film thus obtained, a 180 peel test being carried out on this test specimen. For this, the 2 layers of PET film included in this band are detached from one of the 2 ends of this test specimen and over approximately 2 cm, and the 2 free ends obtained are attached to 2 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.

[0086] While a drive mechanism imparts a uniform rate of 100 mm/minute to the movable part, resulting in the detachment of the 2 PET layers, the detached ends of which are gradually displaced 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 assembly consisting of the test specimen, the stationary jaws and the movable jaws to which said test specimen is attached is placed in a thermostatically controlled chamber maintained at a temperature of 5 C., so that the detachment is carried out after stabilization at this temperature.

[0087] The result is expressed in N/cm.

[0088] Measurement of the Force of Second Opening by Peeling at 5 C.:

[0089] The 2 PET layers of the preceding test specimen are, after they have been detached, 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 along a direction parallel to the length of the test specimen.

[0090] The preceding peel test is then repeated on the multilayer thus obtained, after stabilizing for 15 minutes at 5 C.

[0091] The result is expressed in N/cm.

EXAMPLE 2-4

[0092] Example 1 is repeated using, for the ingredients of the compositions, the contents shown in the table.

[0093] The forces of 1st and 2nd openings obtained are also shown in the table.

Example A (Comparative)

[0094] Example 1 is repeated using a mixture of Kraton D1111 and Kraton D1113BT in the proportions shown, so as to obtain the composition exemplified by the application WO 02/064694.

[0095] It is observed that the force of 1st opening of examples 1 to 4 is lowered with respect to that of example A, indicating an easier opening of the resealable packaging. Furthermore, examples 2 to 4 exhibit a significant increase in the force of 2nd opening with respect to that of example A, which reflects an improvement in the quality of the resealing of the packaging once opened.

TABLE-US-00001 TABLE Content in % Ingredient Example 1 Example 2 Example 3 Example 4 Example A Quintac 3520 65 60 60 55 Kraton D1111 18 Kraton D1113BT 47 Escorez 1310 LC 17.5 20 25 22.5 17.5 Dercolyte S115 17.5 20 15 22.5 17.5 MFI 20 23 27 35 21 Content of styrene units of the 15 15 15 15 18 mixture of styrene block copolymers Content of diblocks of the 78 78 78 78 45 mixture of styrene block copolymers Force of 1st opening at 5 C. 25 30 33 35 43 (N/cm) Force of 2nd opening at 5 C. 18 22 24 24 21 (N/cm)