Multilayer film for resealable packaging with improved resealing
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.
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 a hot-melt pressure-sensitive adhesive (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 of, on the basis of its total weight:
30% to 90% by weight of at least one diblock copolymer selected from the group consisting of polystyrene-polyisoprene (SI), polystyrene-polybutadiene-polyisoprene (SBI), polystyrene-polyisoprene-polybutadiene (SIB), polystyrene-polybutadiene (SB), polystyrene-poly(ethylenebutylene) (SEB) and polystyrene-poly(ethylenepropylene) (SEP), and
10% to 70% by weight of at least one triblock copolymer selected from the group consisting of polystyrene-polyisoprene-polystyrene (SIS), polystyrene-polyisoprene-polybutadiene-polystyrene (SIBS), polystyrene-polybutadiene-polystyrene (SBS), polystyrene-poly(ethylenebutylene)-polystyrene (SEBS) and polystyrene-poly(ethylenepropylene)-polystyrene (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);
wherein, the adhesive layer A is:
connected to the layer D by a tie layer B, and
connected to the layer E by 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) selected from the group consisting of 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) selected from the group consisting of a copolymer of ethylene and of propylene (EL1) and a styrene block copolymer (EL2) comprising at least one elastomer block, the styrene block copolymer (EL2) being in the form of a diblock and triblock composition as defined for the composition (a1).
2. The multilayer film as claimed in claim 1 , wherein the composition (a1) consists of a polystyrene-polyisoprene-polystyrene (SIS) triblock copolymer and a polystyrene-polyisoprene (SI) diblock copolymer.
3. The multilayer film as claimed in claim 1 , wherein the tackifying resin(s) (a2) have weight-average molar masses M w of generally between 300 and 5000 Da and are:
(i) rosins of natural origin or modified rosins;
(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, which are optionally modified by the action of phenols; and/or
(iv) copolymers based on natural terpenes.
4. The multilayer film as claimed in claim 1 , wherein 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 , wherein the polyolefin (P) included in at least one of the compositions (b) and (c) is a (PE).
6. The multilayer film as claimed in claim 1 , wherein the polyolefin (P) included in at least one of the compositions (b) and (c) is a (PE) grafted with maleic anhydride.
7. The multilayer film as claimed in claim 1 , wherein 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 (EL1).
8. The multilayer film as claimed in claim 1 , wherein 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.
9. The multilayer film as claimed in claim 1 , wherein the styrene block copolymer (EL2) is included in a hot-melt pressure-sensitive adhesive (HMPSA) composition which is as defined for the hot-melt pressure-sensitive adhesive (HMPSA) composition (a).
10. The multilayer film as claimed in claim 1 , wherein the compositions (b) and (c) of the layers B and C are identical.
11. The multilayer film as claimed in claim 1 , which 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.
12. A process for producing the multilayer film as defined in claim 1 , comprising coextruding 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.
13. The process for producing the multilayer film as claimed in claim 12 , wherein the coextrusion is carried out by bubble blowing.
14. A resealable packaging comprising in said resealable packaging a multilayer film according to claim 1 .
15. The multilayer film as claimed in claim 1 , wherein the polyolefin (P) included in at least one of the compositions (b) and (c) is a (LDPE).
16. The multilayer film as claimed in claim 1 , wherein the polyolefin (P) included in at least one of the compositions (b) and (c) is a (LLDPE) grafted with maleic anhydride.
17. The multilayer film as claimed in claim 1 , wherein the at least one elastomer compound (EL) is a copolymer of ethylene and of propylene (EL1).
18. The multilayer film as claimed in claim 1 , wherein the at least one elastomer compound (EL) is a styrene block copolymer (EL2).
19. The multilayer film as claimed in claim 1 , wherein said composition (a1) contains 50% to 60% by weight of the at least one diblock copolymer.