Polypropylene-based shrink films
View Patent ↗In one aspect is provided a film, a shrink sleeve film in a particular embodiment, comprising at least one core layer, one skin layer, and optionally one tie layer between the two, wherein the core comprises from 0 to 30 wt % polypropylene by weight of the core layer, and from 70 to 100 wt % of a random propylene-α-olefin copolymer having within the range of from 1 to 10 wt % α-olefins, the α-olefin selected from the group consisting of ethylene and C 4 to C 12 α-olefins, and having an MWD within the range of from 1.2 to 4.5 and a melting point within the range of from 110 to 150° C.; wherein the film possesses a TD Tensile Strength of from 100 to 400 MPa and a MD Tensile Strength of from 20 to 60 MPa. In a particular embodiment, the at least one skin layer comprises a solvent sealable material.
1. A film comprising at least one skin layer, at least one core layer, and at least one tie layer between each, wherein, independently,
(a) at least one skin layer comprises a solvent sealable material;
(b) at least one core layer consisting essentially of
(i) from 0 to 30 wt %, by weight of the core layer, of polypropylene, and
(ii) from 70 to 100 wt %, by weight of the core layer, of a random propylene-α-olefin copolymer having within the range of from 1 to 10 wt % α-olefins, by weight of the copolymer, the α-olefin selected from the group consisting of ethylene and C 4 to C 12 α-olefins, and having an MWD within the range of from 1.2 to 4.5;
(iii) and optionally up to 3 wt %, by weight of the core layer, of additives;
wherein the TD shrinkage is greater than 40% at 121° C., while the MD shrinkage is less than 15% at the same temperature; a TD Tensile Strength (ASTM 882) of from 100 MPa to an upper limit of 400 MPa when stretched at a temperature of from 110° C. to 170° C., and a MD Tensile Strength of from 20 MPa to an upper limit of 70 MPa;
wherein the core layer comprises greater than 70 wt % of the total weight of the film (all layers combined); and
wherein when the skin layer(s) comprise a styrenic copolymer, the tie layer(s) consist of a styrenic copolymer; and wherein when the skin layer comprises a polyester copolymer, the tie layer consists of a polar-modified polyolefin.
2. The film of claim 1 , wherein the MWD of the random propylene-α-olefin copolymer is within the range from 1.5 to 4.0.
3. The film of claim 1 , wherein the random propylene-α-olefin copolymer is produced using a metallocene catalyst composition.
4. The film of claim 1 , wherein the melting point of the random propylene-α-olefin copolymer is within the range of from 115 to 130° C.
5. The film of claim 1 , wherein the at least one tie layer comprises a styrenic copolymer, or a polar-modified polyolefin.
6. The film of claim 1 , wherein the core layer consists essentially of the random propylene-α-olefin copolymer.
7. The film of claim 1 , wherein the TD shrinkage is greater than 50% at a given temperature within the range of from 110 to 125° C., while the MD shrinkage is less than 10% at a given temperature within the same temperature range.
8. The film of claim 1 , wherein the film having a thickness within the range of from 40 to 60 μm has a Haze value of less than 10%.
9. The film of claim 1 , wherein the random propylene-α-olefin copolymer has a melt flow index (230° C., 2.16 kg) within the range of from 0.5 to 200 dg/min.
10. The film of claim 1 , wherein the random propylene-α-olefin copolymer has a melt flow index (230° C., 2.16 kg) within the range of from 1 to 50 dg/min.
11. The film of claim 1 , wherein each skin layer is within the range of from 0.5 to 12 μm in average thickness.
12. The film of claim 1 , wherein each styrenic copolymer has within the range of from 50 to 90 wt % styrene-derived units and a melt mass flow rate within the range of from 1 to 20 dg/min (200° C., 5.0 kg).
13. The film of claim 12 , wherein each styrenic copolymer has a Flexural Modulus (0.250 in, ASTM D790) of less than 2500 MPa.
14. The film of claim 12 , wherein the styrenic copolymer of each skin layer comprises a styrenic copolymer having a Flexural Modulus (0.250 in, ASTM D790) of greater than 2500 MPa and a melt mass flow rate within the range of from 1 to 20 dg/min (200° C., 5.0 kg).
15. The film of claim 12 , wherein the styrenic copolymer is styrene-butadiene copolymer.
16. The film of claim 12 , wherein the polyester copolymer is a polyethylene-terephthalate glycol copolymer.
17. The film of claim 1 , wherein each skin layer also comprises an antiblock agent.
18. The film of claim 1 , wherein ethylene-based polymers are substantially absent from the skin layers.
19. The film of claim 1 , wherein propylene-based polymers are substantially absent from the skin layers.
20. The film of claim 1 , wherein, the at least one skin layer comprises a styrenic copolymer or a polyester copolymer.
21. A sleeve label comprising the film of claim 1 .