Stretch wrapping is one of the most common tools for unitizing products for transport. However, just because a pallet is wrapped and looks good to the naked eye does not mean it is wrapped well, efficiently, or most importantly... SAFELY.
When the proper stretch wrapping is negated, problems can arise during shipping. Depending on the severity of the problem, your business may end up with a bruised reputation and potential safety failures.
Below, we will explore the various types of stretch film so that you can decide which is best for your particular applications and needs.
What Is Stretch Film?
Stretch wrap or stretch film is an extremely elastic plastic wrap that is stretched around various products (such as pallets of boxes) for shipping and transportation. The elastic recovery or stretchability of the film secures the products and ensures they are tightly bound.
Stretch wrap sticks tightly to itself and is used in millions of companies across the globe. It is often implemented in the unitizing of various products. Still, it can also be leveraged for packaging bundles of small objects.
Types Of Stretch Film
There are many different types of stretch film. Below you will find a list of each type. Beneath the list, we will investigate each film's capabilities, common uses, and varied dynamic qualities. You should take notes here as there is a lot of information to digest.
- Machine Stretch
- Cast Stretch
- Blown Stretch
- Pre-Stretch
- Hay Baling Stretch
- Hand Stretch
- Color Stretch
- UVI Stretch
- VCI Stretch
- Vented Stretch
- Reinforced Stretch
- No Cling Stretch
Machine Stretch Films
Machine stretch film was created to be used by a stretch wrap machine. It has the upper hand over hand film in various ways, including but not limited to quicker and greater efficiency in packaging, lower material spending, greater safety, and superior load containment. There are several kinds of machine stretch films: cast machine stretch film, blown machine film, and pre-stretched films.
Cast Stretch Film
Cast stretch film is made by applying a comprehensive manufacturing operation called cast extrusion. This action mandates the continual thrusting of a thermoplastic substrate into a flat die and onto a cooled roll.
The film gauge is resolved by how quickly the casting roll drags the plastic away from the die. This treatment causes cast films to boast superior clarity, allowing end users to observe the wrapped objects. This film stretches easier due to the molecules being aligned as they're extruded.
Cast stretch film is exceedingly quiet when removed from the roll and relatively simple to stretch. Cast stretch film also provides two-sided cling that grants wrapped products the ability to remain firmly wrapped during transportation.
While cast stretch film has multiple fantastic attributes, such as a more affordable cost than blown film, it does not hold a candle to blown film in sustaining strength or protection against tearing. Cast stretch film can generally stretch easily but has less robust stretch memory than other films.
Blown Stretch Film
Blown stretch film is created through a function called blown extrusion. This operation involves plastic melt being pushed into a circular slit die, resulting in a refined tube.
Next, the air is pushed into the tube, granting the volume of air enclosed to expand the tube to the optimal width. The tube is topped with an air ring which is then blown onto the substrate to chill. Chilling the material provides the blown film with greater strength and flexibility than other wraps.
As blown film is generally more robust than most other stretch wraps, it also boasts excellent resistance to tearing.
This is advantageous when containing loads with pointy edges vulnerable to collapsing thinner films. Blown films provide a high degree of memory when stretched. This means that packages remain secured.
Unfortunately, blown film is more expensive and has poorer transparency than other films. It also produces what some consider an annoying level of noise when compared to other similar substrates.
Want to learn more about stretch film?
Pre-Stretch Film
Pre-stretched film is expanded near its breaking point before it is wrapped onto rolls. This film does not necessitate as much energy as other stretch films to achieve the same wrapping force.
Pre-stretched film consumption often uses around 50% less than other stretch films, making for potentially extreme cost reductions.
Hay Baling Stretch Film
Hay baling stretch film is a multi-layer specialty stretch wrapping substrate made for wrapping baled rolls of hay. It is used primarily in the agricultural and farming industries.
Also known as silage stretch wrap, many types of these wraps feature LDPE (low-density polyethylene) formulations with oxygen barriers to keep your hay bales dry.
Non-Machine Stretch Films
Hand Stretch Film
Hand stretch film is made exclusively to be wrapped by human labor manually. It is also known as hand film, hand stretch wrap, hand wrap, or manual pallet wrap.
It is commonly used by companies that wrap small volumes of products. Generally speaking, that would be companies that wrap less than 50 pallets per day.
The capabilities of manual stretch film must be continually checked against the various potential improvements that come with switching to a stretch wrapping machine.
Selecting the proper stretch application for your packaging line will improve efficiency and result in a more cost-effective production.
Color Stretch Film
Color stretch films were created to serve a very specialized niche area of packaging needs that other stretch film types cannot adequately service.
Color stretch film is perfect for warehouse color coding, international transportation, or dating inventory. Color stretch wrap is designed to be resistant to puncture.
UVI Stretch Film
Ultraviolet film is a stretch film with special light-discouraging additives that defend it from photographic degeneration in applications where wrapped products are kept outside and exposed to the elements.
VCI Stretch Film
VCI, or Vapor Corrosion Inhibitor stretch film, is made specifically for wrapping metal components, so they don't rust. This formulation prevents the oxidation of metals and is commonly used for packaging tools, metal pipes, and other metal products or materials.
Reinforced Stretch Film
Reinforced stretch films are thick films with especially strong formulations used to package and protect hefty loads for transportation and shipping. For example, this type of film is commonly used for palletizing and unitizing bricks and cinder blocks.
Vented Stretch Film
Vented stretch film is commonly utilized in applications where airflow and oxygen need to be available for packaged products. IE: wrapping pallets of wood, hot bakery items, etc.
NO Cling Stretch Film
No cling stretch film is used for packaging products such as carpeting so that the products being packaged can slide on and over each other without getting caught and tearing. There is also a variant of no-cling stretch film that has only one side that clings called one-sided cling stretch film.
Specialty Stretch Films
In some cases, specialized wrapping projects require the implementation of performance films with multiple layers with very high stretch capabilities. In addition, gauge reductions can be used, resulting in uncommon thicknesses of stretch films for similar applications.
More Information About Stretch Film
After familiarizing yourself with the different types of stretch film listed above, you will be able to start formulating your ideas on which is the best fit for your company and the products you are packaging with the packaging machinery or labor force that you have.
Depending on your budget, packaging line, and machinery, you may still not be sure which stretch film suits you. It would help if you considered reaching out to at least three vendors and asking for recommendations on a film that best suits your unique needs.
Getting a professional analysis of your packaging line, machinery, labor force, and current materials is also a good idea. With the information provided by said analysis, you can choose the best stretch wrapping solution for your business.
Finally, a quality preventative maintenance program will ensure that you always run the best stretch wrap for your particular applications.
As time passes, this program will allow for expert advice on making changes as new advancements in stretch wrap develop through technological innovation, product considerations, and the types of equipment you are utilizing.
Finally, if you are looking for more information about stretch film, you should review the complete guide to stretch film linked below.
Vertical form fill seal (VFFS) packaging machines are used in almost every industry today, for good reason: They are fast, economical packaging solutions that conserve valuable plant floor space.
Whether you're new to packaging machinery or already have multiple systems, chances are you're curious as to how they work. In this article, we are walking through how a vertical form fill seal machine turns a roll of packaging film into a shelf-ready finished bag.
Simplified, vertical packing machines start with a large roll of film, form it into a bag shape, fill the bag with product, and seal it, all in a vertical fashion, at speeds of up to 300 bags per minute. But there's a lot more to it than that.
1. Film Transport & Unwind
Vertical packaging machines use a single sheet of film material rolled around a core, usually referred to as rollstock. The continuous length of packaging material is referred to as the film web. This material can vary from polyethylene, cellophane laminates, foil laminates and paper laminates. The roll of film is placed on a spindle assembly at the rear of the machine.
When the VFFS packaging machine is operating, the film is usually pulled off the roll by film transport belts, which are positioned to the side of the forming tube which is located at the front of the machine. This method of transport is the most widely used. On some models, the sealing jaws themselves grip the film and draw it downward, transporting it through the packaging machine without the use of belts.
An optional motor-driven surface unwind wheel (power unwind) may be installed to drive the film roll as an assist to the driving of the two film transport belts. This option improves the unwinding process, especially when the film rolls are heavy.
2. Film Tension
During unwinding, the film is unwound from the roll and passes over a dancer arm which is a weighted pivot arm located at the rear of the VFFS packaging machine. The arm incorporates a series of rollers. As the film transports, the arm moves up and down to keep the film under tension. This ensures that the film will not wander from side to side as it is moving.
3. Optional Printing
After the dancer, the film then travels through the printing unit, if one is installed. Printers may be thermal or ink-jet type. The printer places desired dates/codes on the film, or may be used to place registration marks, graphics, or logos on the film.
4. Film Tracking and Positioning
Once the film has passed under the printer, it travels past the registration photo-eye. The registration photo eye detects the registration mark on printed film and in turn, controls the pull-down belts in contact with the film at the forming tube. The registration photo-eye keeps the film positioned correctly so the film will be cut in the appropriate spot.
Next, the film travels past film tracking sensors that detect the position of the film as it's traveling through the packaging machine. If the sensors detect that the edge of the film shifts out of normal position, a signal is generated to move an actuator. This causes the entire film carriage to shift to one side or the other as needed to bring the edge of the film back to the correct position.
5. Bag Forming
From here, the film enters a forming tube assembly. As it crests the shoulder (collar) on the forming tube, it is folded around the tube so that the end result is a length of film with the two outer edges of the film overlapping each other. This is the beginning of the bag forming process.
The forming tube can be set up to make a lap seal or fin seal. A lap seal overlaps the two outer edges of the film to create a flat seal, while a fin seal marries the insides of the two outer edge of film to create a seal that sticks out, like a fin. A lap seal is generally considered more aesthetically pleasing and uses less material than a fin seal.
A rotary encoder is placed near the shoulder (collar) of the forming tube. The moving film in contact with the encoder wheel drives it. A pulse is generated for every length of movement, and this is transferred to the PLC (programmable logic controller). The bag length setting is set on the HMI (human machine interface) screen as a number and once this setting is reached the film transport stops (On intermittent motion machines only. Continuous motion machines do not stop.)
The film is drawn down by two gear motors which drive the friction pull-down belts located on either side of the forming tube. Pull down belts that utilize vacuum suction to grip the packaging film can be substituted for friction belts if desired. Friction belts are often recommended for dusty products as they experience less wear.
6. Bag Filling and Sealing
Now the film will briefly pause (on intermittent motion packaging machines) so the formed bag can receive its vertical seal. The vertical seal bar, which is hot, moves forward and makes contact with the vertical overlap on the film, bonding the layers of film together.
On continuous motion VFFS packaging equipment, the vertical sealing mechanism remains in contact with the film continuously so the film does not need to stop to receive its vertical seam.
Next, a set of heated horizontal sealing jaws come together to make the top seal of one bag and the bottom seal of the next bag. For intermittent VFFS packaging machines, the film comes to a stop to receive its horizontal seal from jaws that move in an open-close motion. For continuous motion packaging machines, the jaws themselves move in up-down and open-close motions to seal the film as it is moving. Some continuous motion machines even have two sets of sealing jaws for added speed.
An option for a 'cold sealing' system is ultrasonics, often used in industries with heat-sensitive or messy products. Ultrasonic sealing uses vibrations to induce friction at a molecular level that generates heat only in the area between film layers.
While the sealing jaws are closed, the product that is being packaged is dropped down the middle of the hollow forming tube and filled into the bag. A filling apparatus like a multi-head scale or auger filler is responsible for the correct measurement and release of discrete quantities of product to be dropped into each bag. These fillers are not a standard part of a VFFS packaging machine and must be purchased in addition to the machine itself. Most businesses integrate a filler with their packaging machine.
7. Bag Discharge
After the product has been released into the bag, a sharp knife within the heat seal jaws moves forward and cuts the bag. The jaw opens and the packaged bag drops. This is the end of one cycle on a vertical packing machine. Depending upon the machine and bag type, VFFS equipment can complete between 30 and 300 of these cycles per minute.
The finished bag can be discharged into a receptacle or onto a conveyor and transported to downline equipment like check weighers, x-ray machines, case packing, or carton packing equipment.
Considering a VFFS packaging machine purchase?
Shopping for a new vertical form fill seal packaging machine doesn't have to be stressful. Download our free guide for 5 questions to ask packing machine manufacturers.
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Originally published 5/4/17, updated 4/13/18, 5/15/20