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Shrink wrap is one of many great ways to protect and transport items. It's strong, durable, and tamper-resistant.
This article will explain exactly what it is, what it's made of, the science behind it and its many advantages.
Shrink wrap, or shrink film, is a material made of polymer plastic film used to wrap and package pallets and products.
It is a unique form of plastic packaging as when heat is applied, the film shrinks, forming a tight protective layer around the packaged item.
While both shrink wrap and stretch wrap are used to package and secure products and pallets, their methods are quite different.
While shrink wrap tightens around the packaged item when heated, stretch wrap is wrapped tightly around the packaged item manually, often multiple times, with its elasticity providing the tightness.
There are a number of plastic polymers used to make shrink wrap, offering slightly different properties. The main four are:
Polyvinyl chloride used to be the most commonly used material, as it is lightweight, inexpensive and has a multitude of uses. However, due to a number of reasons, some countries have banned its use, and in countries where it isn't banned, some major companies have opted to ban it. One of PVC's issues is that it releases a dangerous odour when heated, with it being advised that this is done in a well-ventilated area. Another issue is the concerns around its sustainability, as in most cases PVC is not recyclable.
Because of these problems, polyolefin (POF) has replaced PVC as the favoured plastic polymer used to make shrink wrap in a number of applications. Polyolefin is extremely durable and versatile and is approved as a food-safe material. Furthermore, Polyolefin is made from 100% recyclable materials.
Polyethylene and polypropylene are types of polyolefin, with polyethylene derived from ethylene. When PE is used to make shrink film, it is often in its low-density form - low-density polyethylene (LDPE). This is because LDPE has high strength, durability, and offers the best quality for printing images and text on the wrap.
Check out our dedicated article to learn more about the differences between PVC, Polyolefin and Polyethylene Shrink films.
To shrink wrap a product, you simply encase and surround it with the plastic film. This can be done manually or by using a shrink wrap machine.
You then need to apply heat to the shrink wrap. This can be done manually using a heat gun, moving the gun around the product until all of the film tightly covers it, or by passing the product through a heat tunnel, which will evenly apply heat around the product, shrinking the film to enclose it.
Now you know the process, how does the 'shrink' in shrink wrap actually work?
The molecule chains of polymers are very long, being made up of many monomers (hence 'poly'). In their natural state, these long chains are randomly intertwined, coiling and twisting around one another with no specific direction or alignment. When these polymers are used to manufacture plastic, the chains are stretched out in lines, becoming untangled.
This plastic is then wrapped around the goods intended to be shrink wrapped, before heat is applied via a heat gun or heat tunnel. When heat is applied to these straight polymer chains, it provides them with energy and increases molecular motion. This motion results in the polymer chains recoiling and shrinking, returning the molecules back to their tangled state as they press around and cover the item being shrink wrapped. When properly cooled, the polymers will remain in this state, maintaining this tight and durable layer, until enough heat is applied to alter it again.
This tangled state is part of what provides the strength and durability of shrink film, as the intertwining and criss-crossing of the chains makes the polymer harder to break apart.
Depending on the item you're wrapping you may have a number of options available to you. For example, if you need to secure goods on a pallet you may initially opt for 'pallet strapping'. However, pallet strapping comes with a number of downsides. It's easy to overtighten the strapping which can cause damage to the very items they're supposed to protect (especially fairly 'soft' items such as cardboard boxes which can easily have edges crushed by over-tightened strapping). It's also possible for items to twist free from the pallet if not secured correctly, and strapping doesn't protect goods from the elements.
Shrink wrap on the other hand offers a number of substantial benefits including:
The tight nature of the shrink wrap ensures increased protection of the encapsulated goods. The item is protected from dirt and debris, as well as having superior moisture protection, and is therefore protected from all the damage these contaminants could potentially cause. Shrink wrap can also include additives such as UV inhibitors, anti-static treatment, and low and non-fusion options for increased protection.
Wrapping goods in shrink wrap gives superior stability to goods when in transit or storage. The tight wrapping ensures the continued rigidity of the pallet or product so there's no risk of it falling over or items falling out, further protecting items from damage.
Shrink film, especially when made from polyolefin or polyethylene, is tough, durable, tear resistant and puncture resistant. Even with obscure-shaped loads, shrink wrap will not loosen once heated and shrunk. Goods will remain tightly protected and upright when in transit or storage.
Not only is shrink film a relatively low cost, affordable material and form of packaging, it is also a space saver. This tight way of packaging items results in more space available in storage or transit, which could potentially save money when transporting or storing multiple items.
Due to shrink wrapping being tight and secure, it is more difficult for someone to tamper with the goods once wrapped. Furthermore, any tampering would be instantly noticeable as shrink film doesn't loosen or sag, and isn't easily tearable. It's a great way to ensure the sealed items haven't been tampered with.
No matter the size or shape of the item that is being wrapped, shrink wrapping can do it all. From small, intricate pieces, to large obscure shaped loads, shrink film is a convenient and all encompassing solution for wrapping goods and pallets.
Shrink wrap is perfect for transport and transit as it offers a secure, durable and tamper proof packaging. It's also great for displaying and protecting consumer items as it can be made see through and printed on.
Some products and industries that utilise shrink wrap are:
Looking for shrink wrap that meets your needs? Industrial Polythene offers bespoke shrink wrap solutions for any requirement! Get in touch with us to discuss your specific needs.
This article is about heat shrink film. For tubing, see Heat-shrink tubing
Grocery vegetables wrapped with a plastic shrink film. Shrink wrapped ball of twineShrink 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.
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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 ' discuss] 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 , 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.
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A machine designed to continuously wrap up to 35 packets per minuteA 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.
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Shrink wrapped helicopters for transport Shrink film wrap being applied on a soft drink packing line Shrink wrapped pack of bottles with ends (bulls eyes) as handlesShrink 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:
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