Shrink wrap is a particularly well-established form of packaging that has been developed over the last four or five decades.
Essentially, the material is produced in such a way that the molecules are stretched as part of the manufacturing process. When this material is subjected to heat, the elastic memory of the plastic is activated, causing the material to shrink around the product.
This is a traditional division between transit packaging and display packaging, while the latter has an additional division into food and non-food applications.
The key to the transit shrink wrap application is cost, so that the material and its application provide the lowest cost solution for delivering the product from manufacturer to end user.
The conventional definition of a transit wrap involves the use of a sleeve sealer and polyethylene film. Individual or bundled wrapping provides the solution needed to achieve lowest cost shipping.
A typical wrap offers two open sides as a result of the use of a sleeve, although in certain applications the sleeve can be effectively removed through the use of appropriate machinery. Generally, the latter is not a particular requirement.
Polyethylene has the attributes of strength at a certain thickness along with shrink and slip rates. Consequently, a user will be able to specify a thickness to provide the necessary package integrity to the end user and shrinkage ratios to ensure the wrapper is airtight. The slip can be modified to ensure that the packages are stacked correctly.
There are other benefits of shrink wrapping, as waste disposal after delivery is relatively negligible, while the material is clear to allow product identification. In addition, there are moisture prevention and tamper evident benefits depending on the exact application.
Normal applications involve product bundling, although individual packages easily benefit from transit wrapping.
The market also offers developments in this area, such as colored and printed films. Polyethylene is not a particularly good medium for product enhancement through printing or pigmentation, as it has a naturally smooth surface that allows for scratching and dust retention, while also being relatively cloudy.
However, polyethylene can often offer enough optics to be acceptable in these applications.
As technology has advanced in this market, applications have crossed traditional definitions in certain areas.
Consequently, certain transit packages are found using normal display films where the package and its merchandising benefit from increased investment in a material that offers better optics and machinability.
There are highly specialized display films that are designed to offer the same strength as polyethylene but with much better optics and the marketing benefit is such, in these very specific areas, that the higher cost of the film can be justified.
Display shrink wrap is traditionally geared toward non-food point-of-purchase packaging, where the primary goal is to enhance the product with some limited package protection through blanket wrapping.
The latter is the main distinguishing feature of display packaging, the partial wrapping with a sleeve that is usually found is replaced by a full wrap that involves the creation of a two-dimensional bag around the product.
Some years ago, the conventional film used for this purpose was PVC – polyvinyl chloride with plasticizer; an amorphous crystalline structure.
PVC has been largely replaced by polyolefin shrink films, although PVC is still offered.
PVC has particular benefits in that it is the easiest film to seal and shrink, but it has sealing problems, while it also has strength and storage problems.
The sealing temperature of PVC is very close to its degradation temperature at which a number of by-products are created. These include very small amounts of hydrogen chloride gas and carbon deposits on the sealant.
HCL can be treated through ventilation. It must be emphasized that all materials must be used with respect to good manufacturing practices and as a consequence polyolefin films will also require ventilation in the same way. Combustion by-products should always be considered in relation to the use of any specific machine operator.
Carbon deposits require regular cleaning, while the presence of HCL will result in the need for regular sealant maintenance. As polyolefins do not have chlorine, this does not happen with their use.
The plasticizer in PVC will harden in cold conditions and soften in hot conditions and this can cause strength problems in cold weather and machinability problems in hot weather as well. Again, as the polyolefin material is plasticizer free, these are not problems as far as this film is concerned.
PVC requires storage at normal room temperature, otherwise it is likely to start shrinking. Polyolefin will tolerate higher storage temperatures.
The overall machinability of PVC still gives this material some market share but, increasingly, polyolefin has addressed its lower overall machinability while offering the aforementioned benefits, so it is now, by a considerable margin. , the main display material.
Display wrapping involves creating a two-dimensional bag around the product.
This is conventionally done using an L Sealer with center folded film. The sealer enables the continuous production of wrapped packages which are then processed through a shrink tunnel.
L Sealers come in a variety of forms: manual, semi-automatic, and fully automatic. A large part of the manual and semi-automatic market has been occupied by combined sealing and shrink-wrapping machinery. These machines are commonly known as bell machines.
Fully automatic L-sealers have found increasing use as their cost and versatility have improved.
The highest output speeds are offered by flow wrappers that use side seal or overlap mechanisms. However, the common feature of a two-dimensional bag remains the main similarity between all these sealers.
Polyolefin films offer a variety of attributes so that a wide range of applications can be realized.
These are generally not found in food applications although, once again, the definitions continue to be stretched. Polyolefin is used quite well in certain applications, notably pizza and egg wrapping, as well as produce packaging. However, a more precise definition might be that the polyolefin is not used to extend the shelf life of a food product. This generally applies, except when using shrink barrier film, although the latter product is particularly specialized.
Materials other than shrinkage are typically used to extend shelf life, and as a consequence shrinkage is found only in certain food applications, although the volumes can be significant.
Display applications for polyolefin are almost limitless as the materials have been designed to meet any given requirement.
Soft shrink as well as perforation and printing are standard offerings. On a more specialized level, anti-slip and anti-fog treatments are also available.
There are some notable ranges of polyolefin shrink films that offer better machinability and performance than most on the market and are particularly distinguished by technical differentiation in manufacturing. This leads to irradiated grades that offer higher strength and multi-layer complexes that can be tailored to a particular requirement.
Polyolefin manufacturing typically uses three or five layer extrusion and as a consequence this confers performance benefits.
It will be noted that the key to market movement is the development of material to address specific requirements as it is relatively straightforward to apply.
There is no doubt that polyolefin shrink film will continue to develop to address even more uses than it does today.