Shrink wrap, also shrink film, is a material made up of polymer plastic film. When heat is applied, it shrinks tightly over whatever it is covering. [1] [2] [3] Heat can be applied with a handheld heat gun (electric or gas), or the product and film can pass through a heat tunnel on a conveyor.
The most commonly used shrink wrap is polyolefin.[ citation needed ] 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. [1]
PVC is the most used shrink wrap, due to its light weight, and inexpensive capabilities. PVC is durable, and can be used for many different purposes.[ dubious ] However, it should be used in a well-ventilated area, as it can give off a strong, harmful odor. PVC has been banned in many countries, due to the harmful products created by its decomposition. PVC has some negative qualities including, it is not good for bundling, leaves carbon deposits, and has a low shrink force.[ citation needed ]
Polyolefin or POF shrink wrap is a premium shrink wrap, as it is extremely durable and versatile. POF is puncture resistant, and has a strong seal strength, which allows it to be used for irregularly shaped items. POF is available in 35, 45, 60, 75, and 100, 1 mil gauges. POF shrink wrap is made from 100% recyclable materials, and is FDA approved. It has great clarity, and a glossy self-appearance, as appearance is critical. POF is great for bundling multiple items together, and has the ability to shrink completely and quickly.
PE, a polyolefin, is used in several forms of flexible protective packaging. There are 3 different forms PE can take place in. These include Low-Density Polyethylene (LDPE), Linear Low-Density Polyethylene (LLDPE), and High-Density Polyethylene (HDPE). For shrink wrapping LDPE would be the best choice, as it has a higher strength, and more durability for heavier items. These wraps can also have graphic images printed on them, and LDPE provides the greatest quality. PE gauges can go all the way up to 1200, allowing for a great range of gauges. The disadvantage for PE is that it does not have a great shrink rate, and has lower clarity than other wraps.
A shrink 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 multi-layer 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 or oven 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 pre-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. Pre-formed plastic shrink bags have one end open, the product is placed in the bag, sealed, and sent for heat shrinking.
Shrink wrap 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 premium comics and manga, mainly to preserve their mint condition, as casual previewing prior to purchase wears or damages stock, rendering it unsaleable.
Vegetables such as cucumbers can be individually shrink wrapped to extend the shelf life. [4]
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. Foam cushioning can be held securely in shrink film, eliminating use of a traditional corrugated box. [5] 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 be used as a Tamper-evident band.
It can also combine two packages or parts into a Multi-pack.
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:
Polyethylene or polythene (abbreviated PE; IUPAC name polyethene or poly(methylene)) is the most commonly produced plastic. It is a polymer, primarily used for packaging (plastic bags, plastic films, geomembranes and containers including bottles, etc.). As of 2017, over 100 million tonnes of polyethylene resins are being produced annually, accounting for 34% of the total plastics market.
A thermoplastic, or thermosoftening plastic, is any plastic polymer material that becomes pliable or moldable at a certain elevated temperature and solidifies upon cooling.
Packaging is the science, art and technology of enclosing or protecting products for distribution, storage, sale, and use. Packaging also refers to the process of designing, evaluating, and producing packages. Packaging can be described as a coordinated system of preparing goods for transport, warehousing, logistics, sale, and end use. Packaging contains, protects, preserves, transports, informs, and sells. In many countries it is fully integrated into government, business, institutional, industrial, and for personal use.
Plastic wrap, cling film, Saran wrap, cling wrap, Glad wrap or food wrap is a thin plastic film typically used for sealing food items in containers to keep them fresh over a longer period of time. Plastic wrap, typically sold on rolls in boxes with a cutting edge, clings to many smooth surfaces and can thus remain tight over the opening of a container without adhesive. Common plastic wrap is roughly 0.0005 inches thick. The trend has been to produce thinner plastic wrap, particularly for household use, so now the majority of brands on shelves around the world are 8, 9 or 10 μm thick.
A heat sealer is a machine used to seal products, packaging, and other thermoplastic materials using heat. This can be with uniform thermoplastic monolayers or with materials having several layers, at least one being thermoplastic. Heat sealing can join two similar materials together or can join dissimilar materials, one of which has a thermoplastic layer.
High-density polyethylene (HDPE) or polyethylene high-density (PEHD) is a thermoplastic polymer produced from the monomer ethylene. It is sometimes called "alkathene" or "polythene" when used for HDPE pipes. With a high strength-to-density ratio, HDPE is used in the production of plastic bottles, corrosion-resistant piping, geomembranes and plastic lumber. HDPE is commonly recycled, and has the number "2" as its resin identification code.
Low-density polyethylene (LDPE) is a thermoplastic made from the monomer ethylene. It was the first grade of polyethylene, produced in 1933 by Dr John C. Swallow and M.W Perrin who were working for Imperial Chemical Industries (ICI) using a high pressure process via free radical polymerization. Its manufacture employs the same method today. The EPA estimates 5.7% of LDPE is recycled in the United States. Despite competition from more modern polymers, LDPE continues to be an important plastic grade. In 2013 the worldwide LDPE market reached a volume of about US$33 billion.
Linear low-density polyethylene (LLDPE) is a substantially linear polymer (polyethylene), with significant numbers of short branches, commonly made by copolymerization of ethylene with longer-chain olefins. Linear low-density polyethylene differs structurally from conventional low-density polyethylene (LDPE) because of the absence of long chain branching. The linearity of LLDPE results from the different manufacturing processes of LLDPE and LDPE. In general, LLDPE is produced at lower temperatures and pressures by copolymerization of ethylene and such higher alpha-olefins as butene, hexene, or octene. The copolymerization process produces an LLDPE polymer that has a narrower molecular weight distribution than conventional LDPE and in combination with the linear structure, significantly different rheological properties.
Heat-shrink tubing is a shrinkable plastic tube used to insulate wires, providing abrasion resistance and environmental protection for stranded and solid wire conductors, connections, joints and terminals in electrical wiring. It can also be used to repair the insulation on wires or to bundle them together, to protect wires or small parts from minor abrasion, and to create cable entry seals, offering environmental sealing protection. Heat-shrink tubing is ordinarily made of polyolefin, which shrinks radially when heated, to between one-half and one-sixth of its diameter.
A blister pack is any of several types of pre-formed plastic packaging used for small consumer goods, foods, and for pharmaceuticals.
In-mould labelling is the use of paper or plastic labels during the manufacturing of containers by blow molding, injection molding, or thermoforming processes. The label serves as the integral part of the final product, which is then delivered as pre-decorated item. Combining the decoration process with the moulding process cuts the total cost, but can increase the manufacturing time. The technology was first developed by Owens-Illinois in cooperation with Procter & Gamble to supply pre-labelled bottles that could be filled on the product filling line. This was first applied to Head & Shoulders shampoo bottles.
Skin pack, or skin packaging, is a type of carded packaging where a product is placed on a piece of paperboard or in trays, and a thin sheet of transparent plastic is placed over the product and paperboard or trays. The printed paperboard/tray usually has a heat-seal coating. The plastic film is softened by heat and draped over the product on the card/tray. Vacuum is used to assist a firm fit. The film bonds to the heat-seal coating on the paperboard.
An overwrap or wrap is a method of sealing a contained product, typically as part of retail packaging. It is often made of plastic film or paper. The wrap is applied over the bare product or can be applied over another form of packaging. It is typically used to protect products, but can be used decoratively.
Heat-shrinkable sleeve is a corrosion protective coating for pipelines in the form of a wraparound or tubular sleeve that is field-applied.
Stretch wrap or stretch film, sometimes known as pallet wrap, 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. While it is similar to plastic food wrap, it is not usually made of material rated as safe for food contact.
The term unit load refers to the size of an assemblage into which a number of individual items are combined for ease of storage and handling, for example a pallet load represents a unit load which can be moved easily with a pallet jack or forklift truck, or a container load represents a unit for shipping purposes. A unit load can be packed tightly into a warehouse rack, intermodal container, truck or boxcars, yet can be easily broken apart at a distribution point, usually a distribution center, wholesaler, or retail store for sale to consumers or for use.
Plastic film is a thin continuous polymeric material. Thicker plastic material is often called a "sheet". These thin plastic membranes are used to separate areas or volumes, to hold items, to act as barriers, or as printable surfaces.
A shrink tunnel or heat tunnel is a heated tunnel mounted over or around a conveyor system. Items have shrink film loosely applied; with heat, the film shrinks to fit snugly around the wrapped object.
Packaging machinery is used throughout all packaging operations, involving primary packages to distribution packs. This includes many packaging processes: fabrication, cleaning, filling, sealing, combining, labeling, overwrapping, palletizing.
Plastic-coated paper is a coated or laminated composite material made of paper or paperboard with a plastic layer or treatment on a surface. This type of coated paper is most used in the food and drink packaging industry.
