FILM LAYERS MADE FROM POLYMER BLENDS
Publication Date: 2003-Nov-14
The IP.com Prior Art Database
AbstractFilm layers made from formulated polymer compositions are disclosed. Film layers made from such formulated compositions have surprisingly good heat seal properties, and an especially good reduction in heat seal initiation temperature. The polymer compositions preferably have at least one homogeneously branched ethylene/alpha-olefin interpolymer and at least one heterogeneously branched ethylene polymer. The homogeneously branched ethylene/alpha-olefin interpolymer has a density lower than that of the formulated composition and of the heterogeneously branched ethylene polymer.
FILM LAYERS MADE FROM POLYMER BLENDS
FIELD OF THE INVENTION
This invention relates to compositions comprising specific polymer blends. The polymer blends preferably comprise:
(A) at least one homogeneously branched ethylene/alpha-olefin interpolymer having specific characteristics, blended together with
(B) a heterogeneously branched ethylene polymer.
Such compositions are particularly useful in film applications (e. g., heat sealable packaging film).
For many years, the heat shrinkable films industry has endeavored to reduce film gauge while maintaining performance in response to initiatives associated with source reduction. Lower gauges allow for increased footage on rolls, which benefits the customer by reducing downtime (changeover time).
However, prior strategies involving films having single resin layers or conventional melt blends of resins, especially linear low density polyethylene (LLDPE), typically resulted in performance concessions. For instance, some improvement in optical quality and percent free shrink, may have been seen, but with an undesirable degradation in impact strength. In the case of other blend compositions, good impact resistance and abrasion resistance could be obtained, but with an accompanying degradation in free shrink and clarity.
Thus, the technical challenge remained to design display films with higher impact resistance than LLDPE but with optical and shrink properties comparable to LLDPE. The inventors have found that the use of a multicomponent polymer compositions permits property tailoring without compromising clarity, impact resistance, free shrink, or resistance to tear propagation. The result is a stronger, more abuse resistant film having the shrink and optical properties presently provided by LLDPE. These inventive films result in lower failures at a processor’s packaging machine, or during distribution of contents. The tensile strength of this film is superior to many conventional films, thereby permitting downgauging. A down-gauged film with performance properties comparable to prior LLDPE formulations at their previous gauge can account for less downtime and changeovers at the customer’s plant owing to the above mentioned greater roll footage. The ability to deliver higher value heat shrinkable film without a significant cost premium is a distinct advantage of the films of this invention. Other resins recognized for providing certain performance features (i.e. clarity, seal initiation temperature, low temperature shrink) such as metallocene resins, or other blends, cannot provide abrasion resistance, nor deliver low temperature and low haze performance without a substantial cost penalty.
The use of select polymer compositions thus provides superior mechanical strength properties while preserving excellent optical and shrink values comparable to e.g. D955ä film (trademark of Sealed Air Corporation). These performance attributes can lead to higher performance films a...