{"id":74171,"date":"2016-06-20T00:00:00","date_gmt":"2016-06-20T04:00:00","guid":{"rendered":"https:\/\/www.lantech.com\/blog\/blown-vs-cast-how-is-stretch-film-made\/"},"modified":"2020-10-08T12:32:55","modified_gmt":"2020-10-08T16:32:55","slug":"blown-vs-cast-how-is-stretch-film-made","status":"publish","type":"post","link":"https:\/\/www.lantech.com\/blown-vs-cast-how-is-stretch-film-made\/","title":{"rendered":"Blown vs. Cast – How is stretch film made?"},"content":{"rendered":"

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There’s no single “best” film<\/h2>\n

Every application and company is different. Sure, there are commonalities, but there’s a lot of detail that film experts and local reps consider when suggesting the optimal stretch film for an application. The “best stretch film” is relative – based on your goals, circumstances and expectations.<\/p>\n

Film gauge, pre-stretch capability, puncture resistance, tear propagation and other performance characteristics are examples of the specs which the film experts will consider with you as they help to select a film.<\/p>\n

There’s a basic difference in how films are manufactured though that’s interesting to understand as someone who relies on the “system” of stretch wrapping equipment<\/a> and film to safely deliver your loads to their destination.<\/p>\n

Films are either blown or cast.<\/p>\n

Let’s look at the difference in the manufacturing process. Please note – this is intended to be informative and not to specify one method or material or another.<\/p>\n

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Film extrusion<\/h2>\n\"how-stretch-film-is-made-polymeric-feed-stock.jpg\"All stretch film starts with some polymeric feed stock. Often referred to as resin, the small pellets of plastic material look like BB’s and are delivered by rail car or in gaylords.<\/p>\n

The chemical engineering of film is a very complex topic and often films include multiple layers – each of which may include different resins and additives.<\/p>\n

An example of additives used in stretch film include pigment (for tinted or opaque\u00a0films used for security), tackifier (to provide ‘cling’ so the film can stick to itself) and UV resistance (to prevent deterioration of film when products such as mulch and fertilizer are stored outside.)<\/p>\n

The extrusion process involves the heating and compression of resin – once melted and at the right temperature for the needed viscosity it is pushed through a die which creates a continuous layer of plastic.<\/p>\n

Blown stretch film<\/h2>\n

\"extrusionBlown film is created as the thick layer of extruded\u00a0film emerges from a circular die and a large bubble of air is blown inside. The volume of the bubble, and the original diameter and thickness of the extruded tube determine the ultimate gauge (thickness) of the material.<\/p>\n

The vertical bubble, which may be many feet tall, allows the film to cool gradually as it is pulled up by rollers which collapse the bubble and control the thin, flat tube of film as it is wound.<\/p>\n

Often in the rewind process the edges are slit off and rolls are slit to width and wound in line as the film is extruded.<\/p>\n

This is a vertical process as shown in the schematic.<\/p>\n

It’s estimated that approximately 20-30% of stretch film manufactured today is blown.<\/p>\n

 <\/p>\n

\"someCast stretch film<\/h2>\n

Cast film production involves\u00a0a different process. In this case the resin is extruded through a linear die and oozes\u00a0out onto large diameter chilling rollers. (Note that they may not actually be cold, but rather are much cooler than the semi-molten plastic.) Depending on the original thickness of extrusion, sometimes film is thinned to the target gauge by winding the resulting film faster than it is extruded.<\/p>\n

This is a horizontal process as shown in the schematic.<\/p>\n

Cast film represents the other 70-80% of stretch film manufacturing according to general industry estimates.<\/p>\n

Similarities between blown and cast stretch film<\/h2>\n

When you wonder\u00a0“How is stretch film made?”\u00a0often you’re really asking “What’s the difference between films?” or “Is cast or blown stretch film better for my application?” Those are all reasonable questions, and ones that your local film experts can answer best in the context of your requirements.<\/p>\n

The reality is that there are a lot of similarities between cast and blown stretch film. Both types can offer money saving pre-stretch performance and effective load containment.<\/p>\n

Generally both types can handle a range of applications. Looking at the differences between them, though, some application suitability starts to emerge.<\/p>\n

Differences between stretch\u00a0film that is cast vs. blown<\/h2>\n

For all the commonalities, there are some differences. Every formulation and manufacturers is a bit different, but some general rules of thumb apply.<\/p>\n

Blown stretch film tends to:<\/p>\n