--- title: About Blown Film Extrusion description: How Blown Film Extrusion co-extrusion is done image: http://www.bpf.co.uk/Data/Image/Blown%20Film%20Diagram.jpg --- [![fully-integrated film release liner manufacturer](https://www.mtipolyexe.com/hs-fs/hub/27477/file-2242097650.jpg)](https://www.mtipolyexe.com/) Blown Film & Silicone release coatings [![fully-integrated film release liner manufacturer](https://www.mtipolyexe.com/hs-fs/hub/27477/file-2247196912.jpg)](https://www.mtipolyexe.com/) Blown Film & Silicone release coatings ### Blog # MTi Polyexe, Blog, blown film, base films, release liner, plastic film, silicone coatings, silicone release liner, custom coating converting, plastics films, Blown Film Extrusion ## [About Blown Film Extrusion](https://www.mtipolyexe.com/blog/bid/79609/About-Blown-Film-Extrusion) Posted by [Thomas Zickell](https://www.mtipolyexe.com/blog/author/thomas-zickell) on Mon, Mar 12, 2012 @ 05:03 AM - [Tweet](https://twitter.com/share) # Blown Film Extrusion [![Click me](https://no-cache.hubspot.com/cta/default/27477/e3527921-09cc-44c9-aec8-203d96168e40.png)](https://cta-redirect.hubspot.com/cta/redirect/27477/e3527921-09cc-44c9-aec8-203d96168e40) | One of the most common methods of film manufacture is Blown Film (also referred to as the Tubular Film) Extrusion. The process involves extrusion of a plastic through a circular die, followed by "bubble-like" expansion. The principal advantages of manufacturing film by this process include the ability to: - Produce tubing (both flat and gussetted) in a single operation - Regulation of film width and thichness by control of the volume of air in the bubble, the output of the extruder and the speed of the haul-off - Eliminate end effects such as edge bead trim and non uniform temperature that can result from flat die film extrusion - Capability of biaxial orientation (allowing uniformity of mechanical properties) - Blown Film Extrusion can be used for the manufacture of co-extruded, multi-layer films for high barrier applications such as food packaging. | ![](http://www.bpf.co.uk/Data/Image/Blown%20Film%20Diagram.jpg) | | --- | --- | ## The Process Plastic melt is extruded through an annular slit die, usually vertically, to form a thin walled tube. Air is introduced via a hole in the centre of the die to blow up the tube like a balloon. Mounted on top of the die, a high-speed air ring blows onto the hot film to cool it. The tube of film then continues upwards, continually cooling, until it passes through nip rolls where the tube is flattened to create what is known as a ' lay-flat' tube of film. This lay-flat or collapsed tube is then taken back down the extrusion ' tower' via more rollers. On higher output lines, the air inside the bubble is also exchanged. This is known as IBS (Internal Bubble Cooling). The lay-flat film is then either kept as such or the edges of the lay-flat are slit off to produce two flat film sheets and wound up onto reels. If kept as lay-flat, the tube of film is made into bags by sealing across the width of film and cutting or perforating to make each bag. This is done either in line with the blown film process or at a later stage. Typically, the expansion ratio between die and blown tube of film would be 1.5 to 4 times the die diameter. The drawdown between the melt wall thickness and the cooled film thickness occurs in both radial and longitudinal directions and is easily controlled by changing the volume of air inside the bubble and by altering the haul off speed. This gives blown film a better balance of properties than traditional cast or extruded film which is drawn down along the extrusion direction only.  | ![](http://www.bpf.co.uk/Data/Image/3%20Layer%20Die%20Head.jpg) | ![](http://www.bpf.co.uk/Data/Image/Film%20Bubble%20Going%20Into%20Collapsing%20Frame.jpg) | | --- | --- | | *3 layer die head with air ring and internal bubble cooling* | *Film bubble going into a collapsing frame* | |  ![](http://www.bpf.co.uk/Data/Image/Control%20Panel%20From%20Blown%20Film%20Line.jpg) |  ![](http://www.bpf.co.uk/Data/Image/Taking%20An%20Edge%20Trim%20From%20Film%20Web.jpg) | | * Control panel graphic from an automated blown film line* | * Taking an edge trim from film web* | |  ![](http://www.bpf.co.uk/Data/Image/Layflat%20Tube.jpg) |  ![](http://www.bpf.co.uk/Data/Image/Blown%20Film%20Line%20In%20Action.jpg) | | * The layflat tube is separated into 2 single sheets* | * Blown Film Line In Action* | ## Materials Polyethylenes (HDPE, LDPE and LLDPE) are the most common resins in use, but a wide variety of other materials can be used as blends with these resins or as single layers in a multi-layer film structure. these include pp, pa, evoh. In some cases, these materials do not gel together, so a multi-layer film would delaminate. To overcome this, small layers of special adhesive resins are used in between. These are known as “tie layers”. ## Applications | Blown film can be used either in tube form (e.g. for plastic bags and sacks) or the tube can be slit to form a sheet. Typical applications include Industry packaging (e.g. shrink film, stretch film, bag film or container liners), Consumer packaging (e.g. packaging film for frozen products, shrink film for transport packaging, food wrap film, packaging bags, or form, fill and seal packaging film), Laminating film (e.g. laminating of aluminium or paper used for packaging for example milk or coffee), Barrier film (e.g. film made of raw materials such as polyamides and EVOH acting as an aroma or oxygen barrier used for packaging food, e. g. cold meats and cheese), films for the packaging of medical products, Agricultural film (e.g. greenhouse film, crop forcing film, silage film, silage stretch film). | ![](http://www.bpf.co.uk/Data/Image/Blown%20Film%20Examples.jpg) *Applications made from Blow Film* | | --- | --- | ## The Extrusion Dies Here are some cross section diagrams of blown film extrusion dies. Each layer in this 5 layer die is shown in a different colour dies are precision made and as such are expensive but their service life is considerable. Each die head will have a working range of die inserts at different diameters to suit the required application. Different die gaps can also be specified depending on the material being extruded. ## Ancillary Equipment Once the film has been blown, it is drawn off from the tower using ancillary equipment. Dependent on the end product (film or lay-flat tube) various specialist machines are used. The blown Film Process is a continuous process, as such the machinery has to be designed to cope with both the high speeds involved and be able to operate on a 24 hour basis. The photographs below show two types of take off winder, single station, and a tandem winder and two examples of dies... | ![](http://www.bpf.co.uk/Data/Image/Blown%20Film%20Extrusion%20Die%201.gif) | ![](http://www.bpf.co.uk/Data/Image/Blown%20Film%20Extrusion%20Die%202.gif) | ![](http://www.bpf.co.uk/Data/Image/Tandem%20Winder.gif) | ![](http://www.bpf.co.uk/Data/Image/Single%20Station%20Winder.gif) | | --- | --- | --- | --- | | Blown Film Extrusion Die | *Tandem Winder* | *Single Station WInder* | | Tags: [RELEASE FILMS](https://www.mtipolyexe.com/blog/topic/release-films), [blown film](https://www.mtipolyexe.com/blog/topic/blown-film), [plastic film](https://www.mtipolyexe.com/blog/topic/plastic-film), [Polyethylene](https://www.mtipolyexe.com/blog/topic/polyethylene), [blown film extrusion](https://www.mtipolyexe.com/blog/topic/blown-film-extrusion), [Polypropylene](https://www.mtipolyexe.com/blog/topic/polypropylene), [converting](https://www.mtipolyexe.com/blog/topic/converting), [multi-layer film](https://www.mtipolyexe.com/blog/topic/multi-layer-film) ### Subscribe by Email ### Most Popular Posts ### Browse by Tag - [anti skid (10)](https://www.mtipolyexe.com/blog/topic/anti-skid) - [base films (10)](https://www.mtipolyexe.com/blog/topic/base-films) - [blown film (11)](https://www.mtipolyexe.com/blog/topic/blown-film) - [blown film extrusion (11)](https://www.mtipolyexe.com/blog/topic/blown-film-extrusion) - [converting (3)](https://www.mtipolyexe.com/blog/topic/converting) - [custom coating converting (10)](https://www.mtipolyexe.com/blog/topic/custom-coating-converting) - [cutting (1)](https://www.mtipolyexe.com/blog/topic/cutting) - [Earth Day (1)](https://www.mtipolyexe.com/blog/topic/earth-day) - [Film slitting (2)](https://www.mtipolyexe.com/blog/topic/film-slitting) - [FILMS - Coextrusion (4)](https://www.mtipolyexe.com/blog/topic/films-coextrusion) - [FILMS - Ethyl Vinyl Acetate (3)](https://www.mtipolyexe.com/blog/topic/films-ethyl-vinyl-acetate) - [FILMS - Polyethylene (3)](https://www.mtipolyexe.com/blog/topic/films-polyethylene) - [FILMS - Polypropylene (3)](https://www.mtipolyexe.com/blog/topic/films-polypropylene) - [HDPE (2)](https://www.mtipolyexe.com/blog/topic/hdpe) - [How plastics work (1)](https://www.mtipolyexe.com/blog/topic/how-plastics-work) - [LDPE (3)](https://www.mtipolyexe.com/blog/topic/ldpe) - [LLDPE (2)](https://www.mtipolyexe.com/blog/topic/lldpe) - [multi-layer film (2)](https://www.mtipolyexe.com/blog/topic/multi-layer-film) - [plastic film (9)](https://www.mtipolyexe.com/blog/topic/plastic-film) - [Polyethylene (8)](https://www.mtipolyexe.com/blog/topic/polyethylene) - [Polyolefins (7)](https://www.mtipolyexe.com/blog/topic/polyolefins) - [Polypropylene (6)](https://www.mtipolyexe.com/blog/topic/polypropylene) - [RELEASE FILMS (5)](https://www.mtipolyexe.com/blog/topic/release-films) - [release liner (9)](https://www.mtipolyexe.com/blog/topic/release-liner) - [RELEASE PAPERS (7)](https://www.mtipolyexe.com/blog/topic/release-papers) - [rewinding services (2)](https://www.mtipolyexe.com/blog/topic/rewinding-services) - [silicone coatings (9)](https://www.mtipolyexe.com/blog/topic/silicone-coatings) - [silicone release liner (9)](https://www.mtipolyexe.com/blog/topic/silicone-release-liner) - [TPO (5)](https://www.mtipolyexe.com/blog/topic/tpo) ### Posts by Month - [August 2011 (3)](https://www.mtipolyexe.com/blog/archive/2011/08) - [May 2011 (2)](https://www.mtipolyexe.com/blog/archive/2011/05) - [July 2011 (2)](https://www.mtipolyexe.com/blog/archive/2011/07) - [September 2011 (2)](https://www.mtipolyexe.com/blog/archive/2011/09) - [June 2011 (1)](https://www.mtipolyexe.com/blog/archive/2011/06) - [November 2011 (1)](https://www.mtipolyexe.com/blog/archive/2011/11) - [December 2011 (1)](https://www.mtipolyexe.com/blog/archive/2011/12) - [March 2012 (1)](https://www.mtipolyexe.com/blog/archive/2012/03) - [April 2012 (1)](https://www.mtipolyexe.com/blog/archive/2012/04) - [June 2014 (1)](https://www.mtipolyexe.com/blog/archive/2014/06) ### Follow Us ### Scan Me! 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