Before introducing stretch wrapping, shrink wrapping was the more common method of unit load packaging. The fact that both systems, with their various application methods, are now in everyday commercial use indicates that each has specific characteristics that optimally meet the needs of a particular application. Comparing both techniques helps understand the market development and limitations of stretch wrapping.
Shrink wrap vs Stretch wrap – Load Tension Wrap
Both systems are designed to provide a tensioned wrap of the load, ensuring that the individual components, i.e., sacks, cartons, trays, etc., are held as an integral load. Where there is a risk of load settlement or change, the stretch wrap can have a greater degree of accommodation in that its recoverable strain is higher.
Shrinkwrap and stretch wrap words confuse the user, but there is a vast difference when they perform. Shrinkwrap performs with a loosened wrap of PE to a unit or multiple items and shrinks it when heat is applied, creating tight and tamperproof protection.
When the PE is used for the stretch application, it needs to wrap around the packaging item. The PE has elastic memory of the plastic film and maintains its ability to cling to itself, keeping a tighter wrap around the packaging item.
However, stretch wrap only applies tension in the hoop direction, whereas shrink wrapping applies tension in all directions.
Advantages and Disadvantages
#1. Because the wrapping systems act as an additional package, it has been found that the inner package can be reduced in substance and hence cost. However, the high tensile forces generated during the stretch wrap operation can limit such savings too high. Particularly with cartons which may crush if made too thin or if the applied tensions are Spiral stretch wrapping provides little or no weather protection unless a top sheet is used. There is still the risk of moisture access between the plies. Shrinkwrapping gives a total top cover, and if used with a fuse sheet on the base of the pallet, a complete hermetic closure can be obtained.
#2. Spiral stretch-wrap systems generally offer maximum flexibility in varying unit load sizes. It is essential that a system has to accommodate a heterogeneous product mix.
#3. Stretch wrapping is more sensitive to road irregularities. Projecting corners of cartons, pallets, etc., can punctuate stretch wrap during its application under high tension. On the other hand, shrink wrapping is very tolerant of such projections. As the hot film starts to shrink, it first comes in contact with such projections. As these have not been significantly raised in temperature, the film will ‘freeze’ immediately on communication, and the shrinkage will continue in the remaining film. Thus, the film thickness is not drawn away from such projection points due to its earlier freezing.
#4. The protection offered by shrink wrapping and stretch wrapping with a top cover opens up opportunities for outdoor storage. When exposed to sunlight, there may be a need to protect the wrapping/or the product from ultra-violet light. The thicker films used for shrink wrap provide the opportunity to tailor the recipe to extend the life of the wrapping material and also include an u.v. absorber/barrier to prevent the UV light from attacking the product inside. While the films for spiral systems can be modified, their reduced thickness leads to an earlier physical deterioration.
#5. The early stretch-wrapping machines were almost as expensive as shrinkwrapping pallet systems. However, the larger user was attracted by the substantial energy savings and lower unit film costs. A change from shrink to stretch wrapping gave a 10- 20% saving in film costs. With the introduction of the thinner linear low-density polyethylene blends, this saving has increased to over 30% in some cases.
#6. A better opportunity for printing is shrink wrapping film, and it can be used as a tamperproof solution.