Soft Multi-Layer Shrink Films
Disclosed is a multi-layer heat shrink film and a method of making the film comprising a core layer comprising at least one α-olefin copolymer selected from propylene-based elastomers, ethylene plastomers, metallocene catalyzed linear low density polyethylenes, and blends thereof, and an equal or lesser amount of a polypropylene having a melting point higher than α-olefin copolymer; at least one skin layer comprising a cyclic olefin copolymer (COC); and at least one tie layer between at least one skin layer and the core layer, the tie layer comprising a material or blend of soft materials having a Hardness (ISO 7619, Type A) of from 45 to 100; and a Tensile Strength (ISO 37) of from 10 MPa to 30 MPa.
1 . A multi-layer heat shrinkable film comprising:
a) a core layer comprising:
(i) from 5 wt % to 50 wt % of a polypropylene, and
(ii) an α-olefin copolymer selected from at least one of propylene-based elastomers, ethylene plastomers, metallocene catalyzed linear low density polyethylenes, and blends thereof, the α-olefin copolymer having a melting point lower than the polypropylene;
b) at least one skin layer comprising a cyclic olefin copolymer (COC); and
c) at least one tie layer between at least one skin layer and the core layer, the tie layer comprising a material or blend of materials having a Hardness (ISO 7619, Type A) of from 45 to 100; and a Tensile Strength (ISO 37) of from 10 MPa to 30 MPa.
2 . The film of claim 1 , wherein the tie layer comprises a styrenic block copolymer.
3 . The film of claim 2 , wherein the styrenic block copolymer comprises from 15 wt % to 50 wt % styrenic derived units, by weight of the copolymer.
4 . The film of claim 2 , wherein the styrenic block copolymer is a styrene-ethylene/butylene-styrene terpolymer having a melt flow rate (MFR, ASTM D 1238, 230° C. at 2.16 kg) of from 0.5 g/10 min to 12 g/10 min.
5 . The film of claim 1 , comprising two skin layers, each of the skin layers comprising a cyclic olefin copolymer.
6 . The film of claim 1 , wherein the α-olefin copolymer has a peak melting point in the range of from 60° C. to less than 125° C.
7 . The film of claim 1 , wherein the polypropylene in the core layer comprises from 60 wt % to 100 wt % propylene-derived units and from 0 wt % or 1 wt % to 40 wt % C 2 or C 4 to C 10 α-olefin derived units, and possessing a melting point (ASTM D3418) of at least 125° C.
8 . The film of claim 1 , wherein the polypropylene in the core layer comprises from 70 wt % to 95 wt % propylene-derived units and has a melting point of at least 130° C.
9 . The film of claim 1 , wherein the COC is selected from random copolymers of ethylene or propylene and a cyclic olefin comprising at least one of norbornene, norbornene derivatives, tetracyclododecene, and tetracyclododecene derivatives.
10 . The film of claim 1 , wherein the α-olefin copolymer is one or more propylene-based elastomers having a melting point from less than 105° C.
11 . The film of claim 10 , wherein the propylene-based elastomer comprises propylene and within the range of from 6 wt % to 25 wt % C 2 or C 4 to C 10 α-olefin derived units.
12 . The film of claim 11 , wherein the COC has a glass transition temperature of from 70° C. to 80° C.
13 . The film of claim 1 , wherein each skin layer comprises at least 50 wt % of COC.
14 . The film of claim 1 , comprising a three-layer film monoaxially oriented in the transverse direction.
15 . The film of claim 5 , wherein the two skin layers comprise at least 90 wt % of a COC having a glass transition temperature of from 70° C. to 80° C.; and further comprising a tie layer in between each skin layer and each side of the core layer, the tie layers comprising styrenic block copolymers.
16 . The film of claim 1 , wherein the peel force of the inventive films was at least 400 g/inch.
17 . The film of claim 1 , wherein the TD shrinkage of the film is at least 10%.
18 . A label comprising a film according to claim 1 .
19 . The label of claim 18 , wherein the shrink label is a sleeve label.
20 . A method of forming a TD shrinkable film comprising coextruding at least three layers of material comprising:
a) a core layer including at least:
(i) from 5 wt % to 50 wt % of a polypropylene, and
(ii) an α-olefin copolymer selected from at least one of propylene-based elastomers, ethylene plastomers, metallocene catalyzed linear low density polyethylenes, and blends thereof, the α-olefin copolymer having a melting point lower than the polypropylene;
b) at least one skin layer comprising a cyclic olefin copolymer (COC); and
c) at least one tie layer between at least one skin layer and the core layer, the tie layer comprising a material or blend of materials having a Hardness (ISO 7619, Type A) of from 45 to 100; a Tensile Strength (ISO 37) of from 10 MPa to 30 MPa;
forming an at least a three-layer film therefrom;
stretching the film in the machine direction (MD) at a temperature that is within a range of from 4° C. below the T g of the COC in the skin layer(s) to a temperature greater than or equal to the T g of the COC in the skin layer(s) at a stretching ratio within the range of from 1.05 to 2.8, at a stretching time within the range of from 1 to 10 seconds; and
stretching in the transverse direction (TD) at a temperature within the range of from 70° C. to 120° C. at a stretching ratio within the range of from 4 to 10.
21 . The method of claim 20 , wherein the peel force of the film is at least 400 g/inch.
22 . The method of claim 20 , wherein the TD shrinkage of the films is at least 10% after exposure to boiling water.
23 . The method of claim 20 , wherein the upper range of the MDO temperature is no more than 15° C. above the T g temperature.
24 . The method of claim 20 , wherein the MDO temperature, at a line speed of from 90 fps to 600 fps, is set at a temperature within the range of from 70° C. to 90° C.
25 . The method of claim 20 , wherein the tie layer comprises (or consists essentially of) a styrenic block copolymer.
26 . The method of claim 20 , further comprising forming a label from the film.