Stretch film plays a critical role in the packaging industry, ensuring that products are securely wrapped and protected during shipping and storage. However, with different types of stretch films available, choosing the right one can be confusing. Two of the most common types are blown vs cast stretch films, both offering distinct characteristics. This article explores the differences between blown vs cast stretch films, helping you understand which one is ideal for your needs.
1. What Is Stretch Film?
Stretch film is a plastic material used for wrapping and securing products on pallets. It is highly stretchable and wraps tightly around items, holding them in place. This not only ensures the items remain secure during transportation but also protects them from dirt, moisture, and other external elements. Stretch films are usually made from polyethylene (PE), a plastic known for its durability and elasticity.
There are several types of stretch films based on their manufacturing process and specific applications, but the most widely used categories are blown and cast stretch films. Understanding how each type of stretch film is made and its unique properties is essential for choosing the right solution for your packaging requirements.
2. What Is Blown Stretch Film?
Blown stretch film is made through a blown film extrusion manufacturing process. It begins similarly with the granular resin as well as any additives being fed by a heated screw barrel. The resin is then forced into a circular die. Afterwards, the hot resin is vertically blown upward and outward, which is typically referred to as a bubble.
Instead of being cooled quickly, the bubble is cooled gradually by air as it goes up the tower. This slow cooling process is one of the reasons the wrap looks hazy and dull. Once it rises to the very top of the tower, the film is nipped together and drawn down to the winding and slitting stations with guide rollers.
3. What Is Cast Stretch Film?
Cast stretch film is created through a cast extrusion process, which starts with a granular resin being fed into a heated screw barrel. Then, the molten resin is continuously fed through a narrow slot die. The thickness and width of the stretch wrap is actually determined by the dimension of the slot in the die.
After passing through the die, the resin is immediately fed over a chilled roller, which quickly solidifies and cools the film. Tension rollers are used to draw the wrap to the winding and slitting stations.
4. Blown Vs Cast Stretch Film: Key Differences
Cast film and blown film are manufactured differently and have a different extrusion process. The differences between the films are slight but significant. To fully understand the distinctions between the two types of stretch film, let’s compare their characteristics side by side. The table below will show you the key differences between blown vs cast stretch films.
Blown Stretch Film | Cast Stretch Film | |
Cooling | Slow | Fast |
Appearance | Hazy & Dull | Very Clear & Glossy |
Puncture/Tear Resistance | Very High | High |
Stretch Resistance | High | Moderate |
Unwind Noise | High | Low |
Resin Molecule Alignment | Random | Linear |
Cling | High Level of Cling | Consistent Cling |
Durability | Very High | Moderate |
Production Speed | Slower production speed due to the complex process | Faster production speed, saving labor and time |
4.1. The Differences Between Blown Vs Cast Stretch Film In Manufacturing Process
Blown film is produced by using a blown extrusion process where plastic is blown into a bubble and air-cooled.
Cast film is produced via cast extrusion, where the plastic is extruded onto chilled rollers and cooled rapidly.
4.2. The Differences Between Blown Vs Cast Stretch Film In Strength and Puncture Resistance
Blown stretch film is produced through a slow cooling process, which creates a highly structured and resilient film. This gives it superior puncture resistance and tensile strength, making it ideal for wrapping irregular or sharp-edged loads. It also offers excellent memory retention, tightening around the load after being stretched to ensure secure transportation and long-lasting load stability.
Cast stretch film provides sufficient durability for less demanding applications. Its faster cooling process results in a more uniform, but less robust, molecular structure. Cast film is suitable for wrapping regular, lighter loads and produces less noise during application. However, it is not well-suited for heavy-duty tasks, especially those involving sharp or irregularly shaped products.
4.3. The Differences Between Blown Vs Cast Stretch Film In Load Retention
Blown stretch film has a higher load and stretch capacity. Blown stretch film is considered a higher-quality film for load retention. The memory of blown stretch film is superior to cast stretch film. This means that once stretched, blown stretch film stays tighter to the load over a longer period of time.
Cast stretch film has lower load retention capabilities. Its elasticity is not as robust, meaning it may not hold loads as securely once stretched. This can lead to potential shifting or instability during transport, making blown film the better option for demanding applications.
4.4. The Differences Between Blown Vs Cast Stretch Film In Appearance
Blown film has less gloss, thus making product identification and scanning difficult. Cast film has higher gloss levels; this is normally a result of the type of resin used and the quick cooling process. In general, high gloss is an advantage in warehouse stretch wrapping operations as it is easy to see or scan through the film while under warehouse lighting.
4.5. The Differences Between Blown Vs Cast Stretch Film In Yield
Tests have shown that cast film has better elongation (stretches further) than blown film although cast requires higher stretch ratio to achieve higher yield. A semi-automatic or fully automatic stretch wrapper with a geared powered pre-stretch unit will provide more yield. This is due to the secondary stretch that occurs when force to load (tension) is present after exiting the pre-stretch unit. Blown film needs to be thicker to achieve the same yield due to its mechanical properties.
4.6. The Differences Between Blown Vs Cast Stretch Film In Noise Level
Unwinding blown film is a noisy process and causes distraction on the production floor. It is not suitable in enclosed working environments, especially in electronic industries. Cast film is easily unwound without noise.
4.7. The Differences Between Blown Vs Cast Stretch Film In Cost
The main cost difference between blown and cast stretch films is in their production processes. Cast stretch film is manufactured more quickly using a cast extrusion method, which allows for higher volume production at a lower cost per roll. This production efficiency makes cast film more affordable, especially for high-volume applications.
On the other hand, blown stretch film is made through a slower, more labor-intensive blown extrusion process, resulting in higher production costs. Despite its higher price, blown stretch film offers superior strength and puncture resistance, making it suitable for heavy-duty applications.
5. When Do I Use Blown Vs Cast Film?
Choosing between blown and cast stretch film depends largely on the specific needs of your application. Below are some guidelines to help you decide which type of film is more suitable for your packaging needs.
5.1. When To Use Blown Stretch Film
Blown stretch film is best suited for heavy-duty applications or when you’re dealing with irregularly shaped items that may have sharp edges. Here are some scenarios where blown stretch film would be the ideal choice:
- Heavy Loads: If you’re wrapping heavy pallets or large industrial items, blown stretch film offers the strength and durability needed to keep the load secure.
- Irregularly Shaped Products: Blown stretch film is more resistant to punctures, making it perfect for securing products with sharp edges or odd shapes.
- Extreme Conditions: For applications that involve long-distance transportation or harsh environments, blown film’s superior load retention will ensure that items stay tightly wrapped throughout the journey.
However, if you’re sensitive to noise or require high transparency, there may be more suitable choices than blown film.
5.2. When To Use Cast Stretch Film
Cast stretch film is perfect for lighter applications because of its clarity, cost-effectiveness, and quiet application. Here are some situations where cast stretch film is the better option:
- High-Volume Wrapping: If you need a film that’s quick to apply for high-volume packaging, cast stretch film is the more efficient choice.
- Product Visibility: Cast film’s high clarity makes it ideal for applications where product identification is important.
- Noise-Sensitive Environments: If you’re wrapping in an environment where noise reduction is necessary, cast film is the way to go, as it is much quieter during application.
6. Conclusion
In conclusion, both blown vs cast stretch films offer unique advantages depending on the specific requirements of your packaging process. Blown stretch film is known for its durability and superior puncture resistance, making it ideal for heavy-duty applications and irregular loads. Cast stretch film, on the other hand, excels in clarity, cost-efficiency, and ease of application, making it a popular choice for high-volume operations and product visibility.
By understanding the key differences and strengths of each film type, you can make an informed decision that enhances your packaging efficiency and ensures the safe delivery of your products.
7. About Eup Egypt
Eup Egypt is a global leader in the production of masterbatch and plastic additives. We proudly bring customers unique plastic raw material solutions to help their factories optimize production costs and improve their competitiveness in the market.
Some products of EuP Egypt include bioplastic compounds, color masterbatch, additives, engineering plastic compounds, filler masterbatch and bio filler. EuP Egypt is committed to delivering customized solutions tailored to meet specific customer needs, ensuring top-tier quality and performance.
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