Factoids and Tips

Cast vs Blown

Cast stretch films are quieter than blown stretch films...

Market Share

The market is roughly 65% cast stretch film and 35% blown stretch film with the majority of the blown stretch film for hand wrap applications.

Prestretch vs Poststretch

Prestretch is the process that allows stretch film to be stretched before being applied to a load.

Poststretch is the method of stretching the film by pulling (or tensioning) while the film is applied to the pallet.

Protecting the top of pallet loads

Overwrap (or top wraps) is the amount of stretch film applied over the top of the load. Top sheets are often applied to pallets before this operation for extra protection.

Automatic machines pay for themselves

A good manual operator may get 20% stretch from the film. A semi-automatic stretch wrapper with a pre-stretch unit, on the other hand, stretches the film up to 260% before it’s applied to the load.

Stretch Wrappers

Stretch wrappers are machines that are used to wrap plastic stretch film around a loaded pallet. The film provides extra support while the products are being transported so that they do not tip, spill, or otherwise become damaged. Additionally, wrapped loads can easily be separated and identified, increasing their chances of arriving at the proper destination.

Stretch wrappers are available in a number of sizes and levels of automation. The simplest devices are handheld stretch wrappers, which the operator simply attaches to the pallet load. Once attached, the operator walks around the pallet, unspooling the stretch film around the load.

Automated stretch wrappers are divided into two main categories: turntables and rotary towers. Turntables have a rotating platform onto which the pallet load is placed. As the table rotates, plastic film is drawn from a stationary spool. In rotary towers, by contrast, the arm rotates around the load, dispensing the film around the load. These devices may or may not have a platform on which the pallet may be placed, but it does not spin.

Turntables are available as manual, semi-automatic, or automatic stretch wrappers. Manual devices are operator controlled. The operator attaches the plastic stretch film to the load, and controls the winding of the film around the pallet. Semi-automatic stretch wrappers require an operator to attach the film to the pallet load, but the device takes care of the wrapping. Automatic devices require no operator control. Everything from attachment of the stretch film to the load, to the wrapping is automated. However, an operator may be required to transfer loads on and off of the table, as well as to replenish the film.

Turntables are of high profile or low profile design. Low profile refers to the distance between the floor level and the surface of the table the load is placed on. Low profile units sit closer to the ground. These stretch wrappers are usually accessed by a ramp. In high profile stretch wrappers, the turntable is located on an above ground platform. High profile refers to the distance between the floor level and the surface of the table on which the load will be placed. These stretch wrappers are usually accessed with a fork lift.

Stretch Film

Stretch wrap or stretch film is a highly stretchable plastic film that is wrapped around items. The elastic recovery keeps the items tightly bound. In contrast, shrink wrap is applied loosely around an item and shrinks tightly with heat.

It is frequently used to unitize pallet loads but also may be used for bundling smaller items

Materials and manufacturing methods

The most common stretch wrap material is linear low density polyethylene or LLDPE but other types of polyethylene and PVC can also be used. Many films have about 500% stretch at break but are only stretched to about 100 – 300% in use. Once stretched, the elastic recovery is used to keep the load tight. Other properties such as break strength, cling, clarity, tear resistance, puncture resistance, static discharge, etc. are also important.

Blown film

Blown stretch film is created by forcing molten resin through a circular die, creating a tube, which is “blown some 30 feet high”. The bubble is then flattened and cut into strips that when rolled will produce rolls of flat stretch film. Blown film is generally “labeled” as a tough, hazy, and noisy stretch film best suited for “industrial” type applications.

Cast Film

Cast stretch film is manufactured by sending molten resin through a large extruder that forces a thin layer of film over a large cooled drum. The resulting cooled layer of plastic is then cut and rolled into rolls of cast stretch film. Today most stretch films are actually multiple layers (co-extrusions) of film each with a specific purpose or feature associated.

Functions

Application

Stretch wrap can be applied manually with small rolls (3 or 5 inch wide) of film. Dispensers are also available for larger rolls (perhaps 12 – 15 inch wide).

Machinery is available to automate the operation. This controls the amount of material used, controls the stretch, and controls the application pattern.