7 Layers Stretch Film Properties

 

Since October, the newest maker of stretch films, Quintec Films Corp., has been coextruding seven-layer cast film up to 105 in. wide on a five-extruder line in Shelbyville, Tenn. This is believed to be the first seven-layer coex structure for any stretch film on the market, though another seven-layer line has since been installed at an undisclosed processor. Up to now, five layers have been the most used in stretch film. What do extra layers add? Plant manager David London says they let Quintec make "the strongest films on the market today.

"They also allow us to run less expensive materials in bulk layers that make up to 70-80% of the film and to use more expensive materials in thinner layers down to 2-5% of the film's thickness," he adds. The idea is to run neat resins, not blends, in the thin layers to maximize product consistency. Besides adding more of what stretch film needs--puncture and tear strength, stretchability, and cling--seven layers give Quintec freedom to develop products that never existed before, such as the first "quiet" high-stretch film. President and CEO Terry Jones says this year he plans to buy a second seven-layer line, possibly with seven extruders.

High stretch, low noise

Quintec's initial product slate includes a high-performance seven-layer film, dubbed QF1. It is composed of five resins, including LLDPE, metallocene PE, and HMW-HDPE. Quintec says this is the first stretch film to incorporate layers of pure HMW-HDPE, which gives high tensile strength (8-9 kpsi). Puncture strength comes from multiple thin layers (each 4% of total thickness) of different metallocene PEs. QF1 comes in 40 to 150 gauge. Forty-gauge film has puncture strength of 100 g and stretch ratio of 150:1.

A more conventional seven-layer product is QF2 film, made in 50 to 150 gauge using five less exotic resins with no metallocene grades. Fifty-gauge QF2 has puncture strength of 100 g and stretch ratio of 175:1.

Next for commercialization is QF3 film, one of whose six test formulations is touted as the first "noiseless" stretch wrap. It won't make the usual high-pitched snapping sound as it unrolls, sparing users the need to wear ear protection.

Quintec has applied for a patent on this low-noise film. Its key ingredient is a thin surface layer of PE with very high tensile strength, which shreds as the film stretches, exposing a layer underneath with high cling (over 90 g).

A look at the hardware

Quintec's 18-million-lb/yr line was built by Black Clawson Converting Machinery LLC in Fulton, N.Y. It consists of a 6-in. main extruder and four 2.5-inchers, two with special screws for metallocene PE. The others have all-purpose screws designed for a wide range of speeds, so that the line can make 30-300 gauge films.

The 124-in. coat-hanger die, built by Extrusion Dies Inc., Chippewa Falls, Wis., has a feedblock with two changeable selector plugs. One plug takes melt from the main extruder and splits it in three parallel streams. The other plug, used in making QF1 film, takes melt from the main extruder and splits it in three around the resins from two satellite extruders. Skin layers come from two separate extruders and enter the feedblock below the selector plug, just above the die. The whole line is controlled by Black Clawson's Integrator 2 system, which keeps process temperatures at recipe setpoints.

After the die, a 40-in.-diam. chill roll has a vacuum box and air knife extending from the 9:00 to 12:00 positions. It is followed by a grooved plate-out roll, a second 18-in. cooling roll, four web support rolls, and two randomizing rolls, before ending up on a tension-controlled automatic winding roll. The chill roll has three edge pins on each side instead of just one on each side, in order to allow high speeds of up to 2000 ft/min.