Polylactic acid shrink films and methods of casting same
A heat-shrinkable polylactic acid (PLA) film and a method of its manufacture are provided. In an exemplary embodiment, the PLA films exhibit heat-induced shrinkage in the transverse direction with little to no concomitant shrinkage in the machine direction. The films may comprise any grade of PLA polymer, optionally including additives, such as antiblock, slip, plasticizers, viscosity enhancers and combinations thereof. A method of cast and tenner manufacture is disclosed, which includes a temperature conditioning step.
1. A shrink film comprising polylactic acid (PLA) polymer blend which, upon exposure to 60° C. heat for 10 seconds, exhibits shrinkage in the transverse direction of 10% to 50% of the original dimension and shrinkage in the machine direction that does not exceed 10% of the original dimension, wherein the PLA polymer blend comprises:
(a) 65 weight percent to 75 weight percent of PLA polymer having 11 to 13 percent by weight D-lactide; and
(b) 10 weight percent to 20 weight percent of a PLA polymer having 1 to 2 percent by weight D-lactide.
2. The shrink film of claim 1 , in which the shrinkage in the machine direction does not exceed 5% of the original dimension.
3. The shrink film of claim 1 , further comprising 5 weight percent to 25 weight percent of one or more additives.
4. The shrink film of claim 3 , in which the one or more additives is a antiblock additive, a slip additive, a plasticizer, a viscosity enhancer, or combinations thereof.
5. The shrink film of claim 4 , in which the antiblock additive is selected from the group consisting of natural silica, synthetic silica, talc, talc filled magnesium, calcium carbonate, and N,N′-Ethylene Bis(Stearamide) (EBS).
6. The shrink film of claim 4 , in which the slip additive is selected from the group consisting of oleamide, erucamide, stearamide, behenamide, oleyl palmitamide, stearyl erucamide, ethylene bis-oleamide, EBS, and combinations thereof.
7. The shrink film of claim 6 , in which the viscosity enhancer comprises a stabilizer or a coupling agent.
8. A method of casting a PLA shrink film which, upon exposure to 60° C. heat for 10 seconds, exhibits shrinkage in the transverse direction of 10% to 50% of the original dimension and shrinkage in the machine direction that does not exceed 10% of the original dimension, the method comprising (a) melting PLA polymer at a temperature between 170° C. to 200° C. to form a molten mass, (b) extruding the resulting molten mass, (c) casting the extrusion to form a film, (d) equilibrating the film at a temperature between 60° C. and 90° C., and (e) stretching the film in the transverse direction.
9. The method of claim 8 , further comprising (f) annealing the film.
10. The method of claim 9 , in which the annealing is carried out at a temperature between 50° C. and 90° C.