Ionomer compositions with low haze and high moisture resistance and articles comprising the same
A sodium/zinc mixed ionomer comprises carboxylate groups and a combination of counterions that consists essentially of sodium cations and zinc cations. The sodium/zinc mixed ionomer is the neutralization product of a precursor acid copolymer. The precursor acid copolymer comprises copolymerized units of an α-olefin and an α,β-ethylenically unsaturated carboxylic acid, and it has a melt flow rate of about 10 to about 4000 g/10 min. In addition, the precursor acid copolymer, when neutralized to a level of about 40% to about 90%, and when comprising counterions that consist essentially of sodium ions, produces a sodium ionomer that has a freeze enthalpy that is not detectable or that is less than about 3.0 j/g, when determined by differential scanning calorimetry. Further provided are articles comprising or prepared from the sodium/zinc mixed ionomer.
1. A composition comprising a sodium/zinc mixed ionomer, wherein said sodium/zinc mixed ionomer is the neutralization product of a precursor acid copolymer; and wherein
(a) the precursor acid copolymer comprises copolymerized units of ethylene and about 20 to about 30 wt % of copolymerized units of an α,β-ethylenically unsaturated carboxylic acid selected from the group consisting of acrylic acid and methacrylic acid, based on the total weight of the precursor acid copolymer; wherein the precursor acid copolymer has a melt flow rate of about 10 to about 4000 g/10 min, as determined in accordance with ASTM D1238 at 190° C. and 2.16 kg; wherein the precursor acid copolymer, being neutralized to a level of about 40% to about 90% based on the total number of the carboxylic acid groups present in the precursor acid copolymer, produces a sodium ionomer, said sodium ionomer comprising carboxylate groups and counterions, and said counterions consisting essentially of sodium ions; and wherein the sodium ionomer has a melt flow rate of about 0.7 to about 25 g/10 min and a freeze enthalpy that is not detectable or that is less than about 3.0 j/g, when determined by differential scanning calorimetry in accordance with ASTM D3418; and
(b) said sodium/zinc mixed ionomer comprises carboxylate groups and a combination of counterions; said combination of counterions consisting essentially of about 1 to about 99 equivalent % of sodium cations and about 99 to about 1 equivalent % of zinc cations, based on the total number of equivalents of carboxylate groups in the sodium/zinc mixed ionomer.
2. The composition of claim 1 , wherein about 30% to about 90% of the acid moieties of the precursor acid copolymer are neutralized to form the sodium/zinc mixed ionomer.
3. The composition of claim 1 , wherein about 40% to about 70% of the acid moieties of the precursor acid copolymer are neutralized to form the sodium/zinc mixed ionomer.
4. The composition of claim 1 , wherein the sodium/zinc mixed ionomer has a melt flow rate (MFR) of about 0.7 to about 35 g/10 min at 190° C. and 2.16 kg.
5. The composition of claim 1 , wherein the precursor acid copolymer comprises about 20 to about 25 wt % of copolymerized units of the a,β-ethylenically unsaturated carboxylic acid.
6. The composition of claim 1 , wherein the combination of counterions consists essentially of about 50 to about 95 equiv % of the sodium cations and about 5 to about 50 equiv % of the zinc cations.
7. An article comprising or produced from the composition of claim 1 .
8. The article of claim 7 that is in the form of a film or a sheet or a molded article.
9. The article of claim 8 that is a film or sheet prepared by a process selected from the group consisting of dipcoating, solution casting, lamination, melt extrusion, blown film, extrusion coating, and tandem extrusion coating.
10. The article of claim 8 that is a molded article prepared by a process selected from the group consisting of compression molding, injection molding, extrusion molding, and blow molding.
11. The article of claim 10 that is an injection molded article.
12. The article of claim 11 that has a minimum thickness of at least about 3 mm.
13. The article of claim 11 that has a multi-layer structure having at least one layer that consists essentially of the composition, said at least one layer having a minimum thickness of at least about 1 mm.
14. The article of claim 13 that is a container.
15. The article of claim 11 that is a sheet, a container, a cap or stopper, a tray, a medical device or instrument, a handle, a knob, a push button, a decorative article, a panel, a console box, or a footwear component.
16. The article of claim 15 that is a container.
17. The article of claim 11 that is produced by a process selected from the group consisting of co-injection molding; over-molding; injection blow molding; injection stretch blow molding and extrusion blow molding.
18. An article prepared by injection molding, said article consisting essentially of the composition of claim 1 and having a thickness of about 1 to about 100 mm.