Composition of Pelletized and Powdery LLDPE and Liquid Polyolefin for the Production of Film

This invention relates to compositions suitable for forming a film by a bubble extrusion process comprising a blend of a pelletized linear low density polyethylene containing from 0 to about 15 mol percent of a comonomer of a mono-olefin having 3 to 12 carbon atoms, 0 to about 20 mol percent of a pelletized low density polyethylene, sufficient and preferably about 20 to 25 mol percent of a powdery linear low density polyethylene containing from 0 to about 15 mol percent of a comonomer of a mono-olefin having from 3 to about 12 carbon atoms and 1 to 10 mol percent of a liquid polyolefin, with the preferred polyolefin being polybutene.

Recently linear low density polyethylenes have become available in pelletized form and they have properties which render them desirable for use in making film by the bubble extrusion process. Unfortunately high clarity, high tack film which is essential to food packaging and pallet wrap films can only be accomplished with such LLDPE resins by chill roll casting or similar techniques which employ chilled rolls or mandrels for rapid cooling of the molten extrudate.

I have discovered how to compound the linear low density polyethylenes containing from 0 to about 15 mol percent of a comonomer of a mono-olefin having 3 to about 12 carbon atoms whereby it can be used on blow extrusion film equipment to produce film suitable for such uses as a stretch pallet wrap or as a food contact wrap where high clarity and tack are essential. Also the films produced from my composition have the desired clarity and tack without the need to use special chill rolls.

This compounding can be done in the conventional manner such as by stirring the ingredients together, viz during extrusion or in a tumbler, but a preferred practice is to premix certain of the ingredients before making the final blend. In the preferred method a Blend A and a Blend B are made and these are blended to give a Blend C that is the feed from the hopper to the screw of said extruder that forces the composition as a tubular film from the die where the air blows the film in the normal manner before it is wrapped, preferably after being slit on a mandrel to give a roll of film. Generally Blend A comprises a mixture of a liquid polyolefin, preferably of the polybutenes, with a powdery linear low density polyethylene containing from 0 to about 15 mol percent of a comonomer of a mono-olefin having from 3 to 12 carbon atoms such as propylene, butene, amylenes, hexenes, etc. with insufficient liquid polyolefin to render the mass a fluid at atmospheric pressure and a temperature of about 40.degree. C., viz about 1 to 15 mol percent, and preferably 3 to 10 mol percent.

The second component of the blend is pelletized linear low density polyethylene and preferably it is blended with as much low density polyethylene as possible to give a lower cost extruding composition consistent with obtaining satisfactory clarity and other physical properties.

The linear low density polyethylenes are available commercially as pellets in several grades, viz containing varying amounts of the comonomer such as propylene, butene, pentene or hexenes as specifically represented by Dowlex.TM. 2045 having a melt index (gram/10 minutes) of 1 and a density (gram/cubic centimeter) of 0.920 or Unipel.TM. linear low density polyethylene of about 0.918 to 0.920 density.

The low density polyethylenes are produced by conventional high pressure process, are well known and available from a number of commercial sources. Likewise the liquid polyolefins are available as oils in many grades, as resins under various trade designations such as Wing-Tack.TM. and Piccolite.TM. resins.

While certain representative embodiments and details have been shown for the purpose of illustrating the invention it will be apparent to those skilled in this art that various changes and modifications may be made therein without departing from the spirit or scope of the invention.