| Shrink wrapping is a particularly well-established form | | | | The HCL may be dealt with through ventilation. It is |
| of packaging that has developed over the past four | | | | to be stressed that all materials should be used with |
| to five decades. | | | | regard to good manufacturing practice and as a |
| Essentially, material is produced such that molecules | | | | consequence, polyolefin films will also require |
| are stretched as part of the manufacturing process. | | | | ventilation in the same way. The by-products of |
| When this material is subjected to heat, the elastic | | | | combustion should always be considered in relation to |
| memory of the plastic is activated, causing the | | | | the use of any specific machine operator. |
| material to shrink around the product. | | | | Carbon deposits require regular cleaning whilst the |
| This is a traditional division between packaging for | | | | presence of HCL will give rise to a need for regular |
| transit and packaging for display, whilst the latter has | | | | maintenance of the sealer. As polyolefin’s |
| a further division into food and non-food applications. | | | | have no chlorine, this does not arise with their use. |
| The key to the application of shrink wrap for transit | | | | The plasticiser in PVC will harden in cold conditions |
| is cost so that the material and its application provide | | | | and soften in hot conditions and this may well cause |
| the lowest cost solution in delivering the product | | | | strength problems in cold weather and equally |
| from the manufacturer to the end user. | | | | machineability problems in hot. Again, as polyolefin |
| The conventional definition of a transit wrap involves | | | | material has no plasticiser, these are not issues where |
| the use of a sleeve sealer and polyethylene film. An | | | | this film is concerned. |
| individual or bundled wrap provides the necessary | | | | PVC requires storage at normal room temperature |
| solution of achieving the shipment at the lowest cost. | | | | failing which it is likely to start to shrink. Polyolefin will |
| A typical wrap offers two open sides as a | | | | tolerate higher storage temperatures. |
| consequence of the use of a sleeve although in | | | | The overall machineability of PVC still gives this |
| certain applications the sleeve may be effectively | | | | material some market share but, increasingly, |
| eliminated by the use of appropriate machinery. | | | | polyolefin has dealt with its lower overall |
| Generally, the latter is not a particular requirement. | | | | machineability whilst offering the benefits noted |
| Polyethylene has the attributes of strength at a | | | | above so that it is now by some considerable margin, |
| certain thickness together with shrink ratios and slip. | | | | the principal display material. |
| Accordingly, a user will be able to specify a thickness | | | | Display wrapping involves the creation of a two |
| to provide the necessary pack integrity to the end | | | | dimensional bag around the product. |
| user and shrink ratios to ensure that the wrap is | | | | This is conventionally performed using an L Sealer |
| tight. Slip can be altered to ensure that packs stack | | | | with centre folded film. The sealer allows continuous |
| appropriately. | | | | production of wrapped packs that are then |
| There are further benefits of shrink wrap since | | | | processed through a shrink tunnel. |
| waste disposal after delivery is relatively insignificant | | | | L sealers are found in a variety of forms â€" |
| whilst the material has clarity to allow product to be | | | | manual, semi and fully automatic. A large part of the |
| identified. In addition, there are tamper-evidence and | | | | manual and semi automatic market has been taken |
| moisture-prevention benefits depending on the exact | | | | by combined seal and shrink machinery. These |
| application. | | | | machines are commonly referred to as chamber |
| Normal applications involve the collation of products | | | | machines. |
| although individual packs are readily benefited from | | | | Fully automatic L sealers have found increasing use as |
| transit wrapping. | | | | their cost and versatility have improved. |
| The market also offers developments in this area | | | | The highest output speeds are offered by flow |
| such as coloured and printed films. Polyethylene is not | | | | wrappers using side seal or overlap mechanisms. |
| a particularly good medium for product enhancement | | | | Nevertheless the common feature of a two |
| through printing or pigmentation as it has a naturally | | | | dimensional bag remains the principal similarity |
| soft surface which allows scuffing and dust retention | | | | between all these sealers. |
| whilst it is also relatively cloudy. | | | | Polyolefin films offer a variety of attributes so that a |
| However, polyethylene may frequently offer | | | | very large range of applications can be made. |
| sufficient optics so that it is acceptable in these | | | | In general, these are not found in food applications |
| applications. | | | | although once more, definitions continue to be |
| As technology has advanced in this market so have | | | | stretched. Polyolefin is quite well used in certain |
| applications crossed over traditional definitions in | | | | applications notably pizza and egg wrapping as well as |
| certain areas. | | | | produce packaging. However, a more precise |
| Consequently, certain transit packs are found using | | | | definition might be that polyolefin is not used to |
| normal display films where the pack and its marketing | | | | extend the shelf life of a food product. This applies |
| benefit from the increased investment in a material | | | | generally except where shrink barrier film is used |
| that offers better optics and machineability. | | | | although this latter product is particularly specialised. |
| There are highly specialised display films that are | | | | Normally, other materials than shrink are used to |
| designed to offer the same strength as polyethylene | | | | extend shelf life and as a consequence, shrink is |
| but with far better optics and the marketing benefit | | | | found only in certain food applications although |
| is such, in these very specific areas, that the greater | | | | volumes can be significant. |
| film cost can be justified. | | | | Display applications for polyolefin have almost no limits |
| Display shrink wrap is traditionally oriented towards | | | | as materials have been engineered to deal with any |
| non-food point of sale packaging where the principal | | | | given requirement. |
| goal is product enhancement with some limited pack | | | | Soft shrink as well as perforation and printing are |
| protection through an overall wrap. | | | | standard offers. At a more specialised level, slip and |
| The latter is the main distinguishing feature of display | | | | anti-fog treatments are also available. |
| packaging, the partial wrap with a sleeve generally | | | | There are a few notable ranges of polyolefin shrink |
| found is replaced with a total wrap involving the | | | | film that offer better machineability and performance |
| creation of a two dimensional bag around the | | | | than the majority of the market and these are |
| product. | | | | particularly distinguished by technical differentiation in |
| Some years ago, the conventional film used for this | | | | manufacturing. These lead to irradiated grades which |
| purpose was PVC â€" polyvinylchloride with | | | | offer enhanced strength and multi-layer complexes |
| plasticiser; an amorphous crystalline structure. | | | | that may be tailored to a particular requirement. |
| PVC has largely been replaced by polyolefin shrink | | | | Polyolefin manufacture typically uses three or five |
| film although PVC continues to be offered. | | | | layer extrusion and this confers performance benefits |
| PVC has particular benefits in that it is the easiest of | | | | as a consequence. |
| any films to seal and shrink but it suffers from | | | | It will be noted that the key to market movement is |
| problems on sealing, whilst it also has strength and | | | | the development of material to address specific |
| storage issues. | | | | requirements, since its application is relatively |
| PVC’s sealing temperature is very close to | | | | uncomplicated. |
| its degradation temperature at which a number of | | | | There is no doubt that polyolefin shrink film will |
| by-products are created. These include very small | | | | continue to develop so that it addresses even more |
| quantities of hydrogen chloride gas and carbon | | | | uses than at present. |
| deposits on the sealer. | | | | |