Easy-Sealing Plastomers Get Stiffer & Tougher

 

If you're looking for a film resin with the outstanding heat-sealability of metallocene plastomers but with higher stiffness for easier converting, you may want to try the new Mxsten CV family of linear hexene copolymers resins from Eastman Chemical Co., Kingsport, Tenn. Aimed at high-performance food and non-food packaging, Mxsten CV plastomers comprise three grades with 0.5 to 2.0 MI and densities of 0.905 to 0.910 g/cc. They are said to offer a combination of low heat-seal temperature (down to 166 F) and very high hot tack, along with higher stiffness than other plastomers on the market.

Plastomer is a term that was coined several years ago to describe polyethylene resins with a greater degree of elasticity than typical plastics but not so much as elastomers. Until now, the only commercial plastomers have been two families of low-density (typically 0.859 to 0.915 g/cc) linear copolymers made with metallocene catalysts by Dow Plastics and Exxon Chemical Co. Films made of these plastomers typically have better dart impact, tear strength, and puncture resistance than conventional polyolefin films.

Mxsten CV resins are said to offer those benefits and more. They are made with BP's gas-phase process and proprietary Eastman technology. The company won't yet reveal what sort of catalyst is used.

The first three grades include two for blown film (0.5 MI, 0.905 g/cc and 0.85 MI, 0.910 g/cc) and one for cast film (2 MI, 0.910 g/cc). Business manager Ed Smith says these grades perform in some respects like plastomers with less than 0.90 density.

Eastman's plastomers meet FDA regulations for use in food cook-in bags, bag-in-box applications, meat and poultry packaging, stand-up pouches, lamination webs, and high-performance industrial films. They are priced competitively with high-comonomer (20-25%) EVAs, ionomers, other LDPE copolymers, and plastomers.

Good property balance

Eastman sources say there is usually a trade-off in polyolefin film resins between good sealability--a key parameter for food-packaging films--and film machinability. But Mxsten CV's low blocking tendency and increased stiffness reportedly make it easy to machine despite its excellent sealability.

This material also boasts puncture strength superior to that of other plastomers of the same density--a valuable trait for frozen-food packaging. According to Eastman, dart impact at 35 F is double that of other plastomers of the same density, and instrumented impact is about 25% better.

A third attribute of this material is breathability. Controlling moisture vapor transmission rate (MVTR) is essential for fresh-cut produce packaging. These plastomers are said to permit 25% higher MVTR than plastomers of equal density.