Shrink wrap film Composition
The most commonly used shrink wrap is polyolefin. It is available in a variety of thicknesses, clarities, strengths and shrink ratios. The two primary films can be either crosslinked, or non crosslinked. Other shrink films include PVC, Polyethylene, Polypropylene, and several other compositions.
Coextrusions and laminations are available for specific mechanical and barrier properties for shrink wrapping food. For example, five layers might be configuration as EP/EVA/copolyester/EVA/EP, where EP is ethylene-propylene and EVA is ethylene-vinyl acetate copolymer.
Shrink wrap film Manufacture
A "shrink wrap film" can be made to shrink in one direction (unidirectional or mono-directional) or in both directions (bidirectional).
Films are stretched when they are warm to orient the molecules from their initial random pattern. Cooling the film sets the film's characteristics until it is reheated: this causes it to shrink back toward its initial dimensions.
Prior to orientation, the molecules of a sheet or tube are randomly intertwined like a bowl of spaghetti. The molecules are coiled and twisted and have no particular alignment. However when a draw force is imposed, the amorphous regions of the chains are straightened and aligned to the direction of orientation. By applying proper cooling, the molecules will be frozen in this state until sufficient heat energy is applied to allow the chains to shrink back. One can visualize this phenomenon by stretching a rubber band and dipping it into liquid nitrogen so as to freeze in the stretched state. The band will remain in this state as long as it is kept at sufficiently cold temperatures. However, when enough heat energy is applied, the rubber band will shrink back to its original relaxed state.
Orientation on a commercial scale can be achieved using either of two processes: a tenterframe or a bubble process. Tenterframe technology is used to produce a variety of “heat-set” products, with biaxially oriented polypropylene (BOPP) being the most common (heat-setting is a process whereby a film is reheated in a constrained state such that the shrink properties are destroyed).
The second commercial process is the bubble process, sometimes referred to as the tubular process. In this process, a primary tube is produced by either blowing or casting the tube onto an external or internal mandrel, respectively. It is common to use water to help cool the primary tube at this point. After the primary tube has been cooled, it is then reheated and inflated into a second bubble using air much like a balloon is blown. Upon inflation, the tube is oriented in both directions simultaneously.
The family of shrink films has broadened over the years with many multilayer constructions being sold today. Shrink film attributes include shrink, sealability, optics, toughness, and slip. With regard to shrink properties, there are onset temperature, free shrink, shrink force, shrink temperature range, memory, and overall package appearance.
Shrink wrap is applied over or around the intended item, often by automated equipment. It is then heated by a heat gun or sent through a shrink tunnel oroven for shrinking.
Shrink wrap can be supplied in several forms. Flat rollstock can be wrapped around a product, often with heat sealing to tack the film together. Centerfolded film is supplied on a roll with the plastic is folded in half: product is placed in the center portion, the remaining three edges are sealed to form a bag, and the package then heated which causes the bag to shrink and conform to the product placed in the bag. Pre-formed shrink bags plastic bags are used with one end open: the product is placed in the bag, sealed, and sent for heat shrinking.
"Shrink wrap films" can be used to wrap buildings. It can wrap roofs after hurricanes, earthquakes, tornadoes and other disasters. Shrink wrap can be used for environmental containments to facilitate safe removal of asbestos, lead and other hazards.
Shrink wrap is sometimes used to wrap up books, especially adult-oriented ones and certain comics and manga, mainly to prevent them from being read by minors.
Software on carriers such as CDs or DVDs are often sold in boxes that are packaged in shrink wrap. The licenses of such software are typically put inside the boxes, making it impossible to read them before purchasing. This has raised questions about the validity of such shrink wrap licenses.
Shrink wrap is commonly used as an overwrap on many types of packaging, including cartons, boxes, beverage cans and pallet loads. A variety of products may be enclosed in shrink wrap to stabilize the products, unitize them, keep them clean or add tamper resistance. It can be the primary covering for some foods such as cheese, meats,vegetables and plants. Heat-shrink tubing is used to seal electric wiring.
Shrink bands are applied over parts of packages for tamper resistance or labels. It can also combine two packages or parts.
Shrink wrap is also commonly used within more industrial applications using a heavier weight shrink film. The principles remain the same with a heat shrinking process using a hand held heat gun. The following shrink wrap applications are becoming more widely used and accepted:
1.PolyVinylChloride (PVC) FILMS
For making PVC films for packaging purpose, polyvinylidene chloride is applied as a water-based coating to other plastic films such as biaxially-oriented polypropylene ( BOPP Films) and polyester (PET Films). PVC packaging is mostly used in food packaging industry but is not limited to it only. This PVC coating increases the barrier properties of the film and thus reduces the permeability of the film to oxygen and flavours. Therefore, PVC packaging extends shelf life of the food inside the package.
PVC Film Properties and Features
PVC films provide controlled oxygen and water vapor transmission. They operate satisfactorily on high speed packing machines. These plastic films offer exceptionally good stretch and are easily heat-sealed. They limit excessive moisture build-up while preventing the food from dehydrating.
PVC films are temperature sensitive, developing a tendency to shatter and split at cold temperatures and shrink back or block when exposed to high temperatures. The color may also change to yellow when exposed to heat.
Types of PVC Films
Rigid PVC Films - have excellent printing capabilities and are used for various applications including door panels, stationary, lampshades, ceiling foil, and cooling tower. They are also used for blister packaging.
Semi-Rigid PVC Films - have excellent printing capabilities and are used for a variety of applications including bookbinding and PVC packaging.
Flexible PVC Films - are unplasticized PVC with plasticizers blended into them. They offer excellent lay-flat, a large selection of opaque colors and prints. They are used for bookbinding, pool liner, graphics, and water bed. Some of the sub-types of flexible PVC films include :-
Applications: PVC Films and Packaging
PVC films have excellent thermo-formability, good chemical resistance and optimized protection. As such, they are not only used for food packaging but also for pharmaceutical packaging worldwide. They have been a major contributor to food safety, both protecting and preserving food. PVC films are used for a wide range of pharma and medical packaging. In fact, they are ideal for blister packing of tablets, capsules, needles, syringes, vials, ampoules, ointment tubes, suppository packs, medical kits, surgical dressings etc.
PVC films are also used in supermarket and case-ready processor industries because of their uniform gauge control. Precision gauge control results in exceptional clarity, elasticity and recovery, and welded package seals. This supports increased outputs on automatic packaging machinery. PVC packaging films are also used for packaging of stationery such as sketch pens, pens, etc.
Some technical applications of PVC films include print-carrying substrates, credit cards, adhesive tapes, office equipment, furniture frontage, pipe insulation and recycling films.
2. Biaxially-Oriented Polypropylene (BOPP) film
Bopp Films Features
The main feature of Bopp films are improved stiffness, high tensile strength, excellent optics and good water barrier properties. They range from 15 to 50 microns and are most commonly 15 to 30 microns. These bopp packaging films can be monolayer or coextuded structures, and transparent, opaque, or metallized. They also have the advantage of being non-toxic and fully recyclable.
Bopp films are printed out of new printing technology, Indigo Omnius. They provide excellent UV light protection, humidity, aroma and light barriers. Bopp films have superior strength at low gauges, flatness, clarity and excellent printability. They can be treated with acrylic and PVDC PVDC coatings for better sealability and barrier properties. The Bopp films use mainly homopolymer PP and random copolymer PP.
Applications: BOPP Films and Packaging
3. (Low Density Polyethylene) LDPE film
Low Density Polyethylene (LDPE) currently dominates the collation films market segment with its good shrink behavior, especially in trans-direction (TD). However LDPE exhibits significant benefits . When our LDPE is blended with other Linear Low Density Polyethylene and High Density Polyethylene, it offers the highest performance on all key shrink parameters for collation shrink films.
This optimized performance is characterized by:
We are a well known manufacturer of LDPE Shrink wrap Films. LDPE (Low Density Polyethylene) Shrink Film is used for wrapping products like pharmaceuticals, cosmetics, glass bottles, cans, tins, beverages, tetra packs, cartons, consumer durables, stationery and all sorts of industrial products. LDPE Shrink Film is mainly used for unitizing and bundling multiple units of products for better handling and ease of distribution. Our LDPE Shrink Film provides extra protection, and makes the pack pilfer proof and reduces theft in transit. Our LDPE Shrink Film is also used on automatic shrink wrapping machines. We offer customized shrink films to cater variety of customer varying on their requirements.
“Special purpose shrink wrap films made from high strength material for extra holding force mainly used for packing of packaged drinking water and beverages /cold drinks packed in pet bottles. This high strength shrink film can be used for packing bottles without the use of bottom card board tray thus resulting in savings in packing material cost. The tight wrapping of the pack enables high stacking of packs over each other thus saving space and reduce damage in transit.”
Shrink Wrap Films