Mineral Technologies Mineral TechnologiesMinteqSpecialty Minerals
CareersContact UsProduct Data SheetsMSDSSitemapSearch
About SMIOur MineralsPaperSpecialty ApplicationsExhibitionsPublicationsUseful Links
 
Polymere Blown Film Basics

Blown Film Process and Blown Film Line
The blown film process involves extruding a continuous thin-walled tube of plastic and inflating it immediately after it leaves the die. (See the schematic diagram below.) The inner/outer pressure differential causes the tube to stretch, increasing its diameter and reducing its wall thickness to the desired gauge. 

Air is trapped within the blow tube (bubble) between the die and collapsing rolls. The collapsing rolls squeeze the films walls together to convert the bubble to a layflat film. This facilitates the winding of film onto a take-up roll.


Blown Film Types
Blown film is less than 10 mils (250 microns) and typically between 0.5 to 4 mils (12–100 microns). Films are generally of the clarity type (clear) or opaque type (pigmented). 


Blown Film Composition
Blown film is generally composed of polyethylene, LDPE, or LLDPE. Recently, PP blown film resin grades have appeared on the market. Additives are incorporated into the resin to meet specific end-use requirements, including reducing polymer degradation (antioxidants), film blocking (antiblocks), coefficient of friction (COF, slip agents) and melt fracture (polymer process aids PPA). Additive addition levels vary between 500 and 10,000 ppm. 


Multilayer Blown Films
Films are seldom blown as single-layer structures. Films with 5, 7, and 9 layers are quite common, using both multiple extruders and so-called splitter dies, which divert melt streams into different layers of the film. These composite film structures allow end-product designers to specify films with unique property mixtures. The high throughput of large film lines allow this sophistication and the total customer value it implies to be achieved in remarkably cost-effective ways.

 

Learn more: