Polyolefin based peelable seals
View Patent ↗The invention relates to a polyolefin-based heat sealable and peelable seal. The peelable seals comprise from 5 to 98 percent by weight of a propylene based plastomer or elastomer and from 2 to 95 percent by weight of a second polymer selected from the group consisting of polyethylene, polybutylene, and styrenic polymer and mixtures thereof. The invention also relates to tamper evident peelable seals. The invention also relates to methods of making and using the heat sealable, peelable seal.
1. A peelable seal layer comprising:
a. from about 5 to about 98 percent by weight of a reactor grade propylene based plastomer or elastomer having a molecular weight distribution of less than 3.5 and a density of less than about 0.89 g/cc;
b. from about 2 to about 95 percent by weight of a second polymer selected from the group consisting of polyethylene, polybutylene, and styrenic polymer and mixtures thereof;
wherein the peelable seal has a heat seal initiation temperature less than 120° C. when sealed at a bar pressure of 40 psi with a dwell time of 0.5 seconds.
2. The peelable seal of claim 1 wherein the second polymer is a polyethylene selected from the group consisting of low density polyethylene, linear low density polyethylene, ultra or very low density polyethylene, medium density polyethylene, high density polyethylene, ethylene vinyl acetate copolymers and mixtures thereof.
3. The peelable seal of claim 1 wherein the second polymer is a styrenic polymer selected from the group consisting of general purpose polystyrene (“GPPS”) and high impact polystyrene (“HIPS”), ethylene-styrene interpolymers (ESI), styrenic block polymer, and mixtures thereof.
4. The peelable seal of claim 1 wherein the propylene based elastomer or plastomer contains from about 5% to about 15% by weight of the propylene based elastomer or plastomer of units derived from ethylene.
5. The peelable seal of claim 1 wherein the propylene based elastomer or plastomer has a heat of fusion less than 90 J/gm.
6. The peelable seal of claim 1 wherein the propylene based elastomer or plastomer has a heat of fusion less than 70 J/gm.
7. The peelable seal of claim 1 wherein the second polymer is a low density polyethylene.
8. The peelable seal of claim 1 wherein the second polymer is an ethylene vinyl acetate copolymer.
9. The peelable seal of claim 1 further comprising one or more additives from a group comprising antioxidants, ultraviolet light stabilizers, thermal stabilizers, slip agents, antiblock, pigments or colorants, processing aids, crosslinking catalysts, flame retardants, fillers and foaming agents.
10. The peelable seal of claim 9 characterized in that the seal exhibits stress whitening upon un sealing.
11. The peelable seal of claim 1 wherein the seal has a seal strength in the range of 0.5 to 5 lb/in.
12. The peelable seal of claim 1 wherein the seal has a seal strength in the range of 1.5 to 3 lb/in.
13. The peelable seal of claim 7 wherein the LDPE comprises 20 to 40 percent by weight of the overall composition.
14. The peelable seal of claim 3 wherein the styrenic polymer comprises 2 to 20 percent by weight of the overall composition.
15. The peelable seal of claim 14 which is characterized by exhibiting some amount of stress whitening upon peeling of the seal.
16. The peelable of seal of claim 14 wherein the styrenic polymer comprises from 2 to 5 percent by weight of the composition and the peelable seal is characterized as having a haze less than 15% for 60 micron films as determined by ASTM 1003.
17. The peelable seal of claim 2 further comprising polybutylene.
18. The peelable seal of claim 1 wherein the seal has a seal strength in the range of 0.5 to 7 lb/in.
19. The peelable seal of claim 7 wherein the LDPE comprises 10 to 40 percent by weight of the overall composition.
20. The peelable seal of claim 1 wherein the peelable seal has a heat seal initiation temperature less than 100° C.