Terblends and films of LLDPE, LMW-HDPE and HMW-HDPE

DETAILED DESCRIPTION OF THE INVENTION The blends of this invention which exhibit improved extrusion characteristics such as reduced back pressure, lower power consumption and higher melt strength extrudate generally comprise 50-98 weight percent LLDPE, 1-25 weight percent LMW-HDPE and 1-25 weight percent HMW-HDPE.
Preferably, the LLDPE comprises 70-95 weight percent, the LMW-HDPE comprises 5-20 weight percent, and the HMW-HDPE comprises 1-10 weight percent.
The LMW-HDPE is usually present in amounts greater than the HMW-HDPE.
The LLDPE generally contains up to about 10 weight percent of polymerized higher alpha olefin and has a density between about 0.
9 to about 0.
94, preferably less that 0.
930.
The melt index (MI) is usually from about 0.
4 to about 4 or more and preferably from about 0.
6 to about 2.
LLDPE copolymers of ethylene and hexene are particularly preferred.
The HDPE resins used advantageously have a density of 0.
94 or higher, preferably 0.
95 or higher.
They can be homopolymers or copolymers of ethylene and a small amount of a higher olefin.
The MI (melt index) of the low molecular weight component LMW-HDPE is usually greater than 10, preferably greater that 25.
LMW-HDPE resins having an MI of about 50 have been found to be quite suitable.
The high molecular weight high density polyethylene HMW-HDPE generally will have an MI of less than 1 and preferably less than 0.
5.
This HMW-HDPE component is essential to the composition because it is responsible for the good melt strength of the composition during extrusion and contributes to improving the MD tear and other film properties of the binary blend of LLDPE and LMW-HDPE.
The ternary blends of this invention can be prepared in any way known to those skilled in the art.
Thus, a physical mixture of the three polymers in powder or in pellet form can be blended into a uniform composition in a Banbury mixer or by milling the composition on calendar rolls using temperatures above the melting point of the higher melting component.
In a preferred embodiment, a rough mixture of the three polymers is put through a melt extruder containing a mixing extrusion screw or a mixing section on the extrusion screw