You have heard the terms cast stretch film and blown stretch film, but I am guessing you don’t know the differences between them, especially their advantages. Wish to find out everything about cast and blown stretch wrap film? Read on.
Let’s begin by explaining what Stretch film is.
Stretch film is a plastic film made from Linear Low Density Polyethylene (LLDPE) that is extremely stretchable. The purpose of stretch film is to wrap around products to keep them secure in place.
The main advantages of using stretch film are:
- Minimize product loss
- Reduce the risk of product tampering
- Reduce worker injury
Stretch films come in different types, widths and thickness. There are also two ways of stretch extrusion: Cast Stretch Film and Blown Stretch film. Certainly both processes have their pros and cons.
The main difference between these two types of Stretch Wrap Film is the way they are created and manufactured. These differences affect the usability and the price of the film.
Cast Stretch Wrap Film
Cast stretch wrap film is made through a cast extrusion process. It started with a granular resin being fed into a heated screw barrel. Next, the molten resin is continuously delivered into a narrow slot die barrel. The dimension of the slot in the die determines the thickness and width of the stretch wrap.
After going through the die, the resin is immediately delivered over a chilled roller, which quickly solidifies and cools the film. To draw the wrap to the winding and slitting stations, tension rollers are used.
The cast stretch film method is much faster than the blown extrusion besides costing less, as more can be made per hour. Pallet machine wrap is the most common type of film produced by this method.
Properties
- Clear and Glossy
- No noise to unwind
- Great strength in the machine direction
- Consistent for pallet wrapping machine
Advantages
- Less expensive – lower cost in manufacturing
- High transparency
- Double sided cling
- Uniform thickness
- No limits on the thickness of the film
- Excellent barrier for moisture, gases and aroma
Disadvantages
- Stretches easily and can cause shifting
- Minimal ability to go back to original state after stretching
- Standard tearing can occur when stressed too much
Blown Stretch Wrap Film
The manufacturing process for blown stretch wrap film is through a blown film extrusion. It begins with the granular resin being fed by a heated screw barrel. Next, the resin is forced into a circular die. Afterwards, the hot resin is vertically blown upward and outward, which is also known as a bubble.
The bubble is not cooled immediately. Instead it is cooled gradually by air as it goes up the tower. This slow cooling process is one of the reasons the wrap film looks hazy and dull. The film is nipped together once it rises to the very top of the tower and it is drawn down to the winding and slitting stations with guide rollers.
Blown stretch wrap film generally costs more to make because the output per hour is less than cast films.
Properties
- Cloudy until stretched
- Loud when releasing from the roll
- Manufacturing process allows greater resistance to breaking
- Bi-directional tear resistance
- Excellent for “C” loads
- 1 side cling, great for higher load retention
Advantages
- High quality, stretch and load holding power
- Produces less manufacturing scrap
- Superior puncture resistance
- Provides maximum toughness
- Has a high level of cling
- Lower gloss reducing reflections
- Stretches much farther to cover more pallets with less film
- Won’t re-stretch once applied
Disadvantages
- The advanced manufacturing process increases the cost
- Not crystal clear; it makes reading and scanning harder
- Noisy
As you can see, both stretch wrap films are great for wrapping your products. It all depends on your individual needs and requirements. There are many Stretch film manufacturers in Malaysia that can help you will your specific application.
To know more, feel free to contact our friendly salespersons.
