What is blown film?

Blown films extrusion is one of many polymer manufacturing processes. It is a manufacturing process that produce films of plastic sheeting and tubes. These sheets or tubes can either be fully cylindrical, or have other object inserted into them so they form useful objects like commodity and specialized polymer films that are typically used in packaging such as shrink, stretch, barrier films (used to protect deli meat), frozen food packaging, and shopping bags.

The blown film process is used to produce a wide variety of products, ranging from simple monolayer films for bags to very complex multilayer structures used in food packaging. Multilayer film structures may be made by blown film coextrusion and combines two or more molten polymer layers.

Simple schematic of a blown film process
                                                                                   Simple schematic of a blown film process
Two common blown film line machines
                                                                             Two common blown film line machines

How is the Blown Film Process?

Blown film extrusion includes many complex stages:

The first step is to melt the polymer and some additives (if have) in an extruder. Polymer resin, often in the form of beads, is loaded into a hopper and fed into a heated barrel with a screw. The screw is used to transport the polymer down the barrel. The beads are gradually heated to melt the polymer. The heat profile is an important part of extrusion as the polymer may thermally degrade if overheated. When the molten material reaches the end of the barrel, it is extruded through a die. It is at this point that blown film extrusion differs from other extrusion processes.

There are a few different types of dies used in blown film extrusion with the most common being annular, which is a simple circle die. The molten polymer enters the die head and air is injected via a hole in the die center to radially inflate the polymer into a thin tube that is many times its original, extruded diameter. It is this step of the process that can be adjusted to achieve the desired film thickness and width.

The hot tube film is then cooled, typically with high speed air, and pulled upward by equipment called nip rollers. On most medium to large size film lines, this vertical tube may extend several stories into the air. As the film cools it crystallizes at what is called the frost line. As the tube reaches the nip rollers, at the top of the line, the film is now cool enough to flatten and is then referred to as lay-flat or collapsed tubing. The film is then transported downstream by rollers for further processing (e.g. slit, printed, vented, converted into bags) and is eventually wound into rolls.

There are several advantages of manufacturing film using the blown film extrusion process including the ability to manipulate the mechanical properties of the final plastic based on the process conditions and base polymer(s) used. For example, blown film extrusion inflates the polymer radially while at the same time drawing the polymer upward with rollers. These forces stretch the polymer in both the transverse and draw directions, providing strength in the film. The extent of inflating and drawing can be adjusted to achieve the desired strength in the transverse and draw directions of the final product. Blown film extrusion is also versatile and able to manufacture a variety of single or multi-layer films with a range of film thickness and width.

What is ending product of blown film process?

Markets that blown film extrusion serves are as follows:

– industrial films and bags such shopping bags, T-shirt bags, etc

– agricultural and construction films

– barrier films

– stretch films

– PVC cling films

– laminating films

– can liners

– high barrier small tube systems.

What is the main input materials of blown film process?

There are many types of polymers that can be used in blown film extrusion with the most common being polypropylene and polyethylene (LDPE, HDPE and LLDPE). This method can manufacture monolayer films as well as more complex multi-layer films that involve co-extrusion to combine more than one plastic into a single film.

Besides, for industrial and agricultural field, filler masterbatch is used popularly to improve the performance of ending film, improve the financial problem particular to increasing plastic resin period, etc. Plus, color masterbatch with plenty of colors like red, green, blue, black, white, brown, etc could make resulting bags look colorful, avoid some environmental conditions and have good looking. Addition, desiccant masterbatch plays a really important role to solve some moisture problem due to wet condition in store room

Dai A Industry have provided excellent and suitable quality of masterbatch for any blown film line and help improve any problem in blown film process. With insurance and good service, you will have a great experience with us.

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