Extrudable hot-melt pressure-sensitive adhesives for resealable packaging having improved organoleptic properties
1) Hot-melt pressure-sensitive adhesive composition with MFI of 0.01 to 200 g/10 minutes and comprising: from 45 to 70% by weight of a composition of styrene block copolymers of SIS type with an SI diblock content of 30 to 90% and a content of styrene units of 10 to 40%; and from 30 to 55% by weight of at least one tackifying resin having a softening temperature of between 5 and 150° C., and obtained by a process comprising: a first stage of polymerization of: a composition (i) essentially composed of unsaturated hydrocarbons having 9 carbon atoms, or a composition (ii) essentially composed of dicyclopentadiene and of its derivatives having 10 carbon atoms; then a second stage of hydrogenation of the polymer thus obtained.
1. A hot-melt pressure-sensitive adhesive composition a having a melt flow index ranging from 0.01 to 200 g/10 minutes and comprising, on the basis of the total weight of the said composition, a:
from 45 to 70% by weight of a composition a1 of styrene block copolymers comprising at least one elastomer block, the said composition a1 comprising, on the basis of its total weight:
of 30 to 90% by weight of at least one Styrene-Isoprene (SI) diblock copolymer, and
of 10 to 70% by weight of at least one Styrene-Isoprene-Styrene (SIS) linear triblock copolymer;
the total content of styrene units of the said composition a1 varying from 10 to 40% by weight on the basis of the total weight of a1; and
from 30 to 55% by weight of at least one tackifying resin a2 having a softening temperature of between 5 and 150° C. and obtained by a process comprising:
a first stage of polymerization of a composition:
a composition (i) comprising unsaturated hydrocarbons having 9 carbon atoms, or
a composition (ii) comprising dicyclopentadiene or its derivatives having 10 carbon atoms; then
a second stage of hydrogenation of the polymer thus obtained, the polymer being completely hydrogenated.
2. The hot-melt pressure-sensitive adhesive composition according to claim 1 , having a content of SI diblocks in the composition a1 of 50 to 80%.
3. The hot-melt pressure-sensitive adhesive composition according to claim 1 , wherein the softening temperature of the tackifying resin a2 is between 80 and 150° C.
4. The hot-melt pressure-sensitive adhesive composition according to claim 1 , consisting of the composition a1 and of a tackifying resin a2.
5. The hot-melt pressure-sensitive adhesive composition according to claim 1 , having a melt flow index ranges from 2 to 70 g/10 minutes.
6. The hot-melt pressure-sensitive adhesive composition according to claim 1 , provided in the form of granules with a size of between 1 and 10 mm.
7. A multilayer film comprising two layers B and C of thermoplastic material bonded together by an adhesive layer A, wherein layer A has a thickness of between 7 and 50 μm and comprises the hot-melt pressure-sensitive adhesive composition a as defined in claim 1 .
8. The multilayer film according to claim 7 , having a thickness of the adhesive layer A of 7 to 35 μm.
9. The multilayer film according to claim 7 , comprising, in addition to the layers A, B and C, two tie layers D and E such that the adhesive layer A is:
connected to the layer B via the layer D, and
connected to the layer C via the layer E.
10. The multilayer film according to claim 9 , wherein the tie layers D and E are compositions d and e, which are identical or different, which have a melting point from approximately 80 to 120° C. and comprise:
ethylene homopolymers or copolymers,
propylene homopolymers or copolymers,
copolymers of ethylene with a polar comonomer, or
grafted olefin homopolymers or copolymers.
11. A three-layer film according to claim 7 , consisting of the adhesive layer A and the two layers B and C, according to the sequence B/A/C in which the “/” sign means that the faces of the layers concerned are in direct contact.
12. A film comprising five layers according to claim 9 , consisting of the adhesive layer A, the two intermediate layers D and E and the two external layers B and C, according to the sequence B/D/A/E/C in which the “/” sign means that the faces of the layers concerned are in direct contact.
13. A process for the manufacture of the multilayer film as defined in claim 7 , comprising coextruding the hot-melt pressure-sensitive adhesive composition a and constituent materials of the layers B and C and, optionally, of the layers D and E.
14. The manufacturing process according to claim 13 , wherein the constituent compositions and materials of the layers A, B, C and optionally D and E, are fed into the coextrusion device in the form of granules with a size of 1 to 10 mm.
15. The process for the manufacture of the multilayer film according to claim 13 , wherein a coextrusion device that is a bubble blowing coextrusion device is employed.
16. A resealable packaging, comprising the multilayer film as defined in claim 7 .
17. A multilayer film comprising two layers B and C of thermoplastic material bonded together by an adhesive layer A, wherein layer A has a thickness of between 7 and 25 μm and comprises the hot-melt pressure-sensitive adhesive composition a as defined in claim 1 .
18. A resealable packaging, comprising the multilayer film as defined in claim 17 .
19. The hot-melt pressure-sensitive adhesive composition according to claim 1 , wherein the second stage of hydrogenation of the polymer achieves the reduction of the amount of residual monomers and/or oligomers which were employed in the reactions for the polymerization, and thereby achieves the lowering of risk of detrimental change in taste and/or odor of a foodstuff in contact with a multilayer film comprising two layers B and C of thermoplastic material bonded together by an adhesive layer A, wherein layer A has a thickness of between 7 and 50 μm and comprises said hot-melt pressure-sensitive adhesive composition.