Melt fi ltration | process feature The requirements for melt fi lters have
changed over time, and so has the variety of designs available to end-users, says Raj Shah of Pall Corporation
Choosing the
best melt fi lter technology
Melt fi ltration of polymers plays a key role in setting quality criteria for virgin resins and various extruded end products. Depending on the process and application, melt fi lters are designed to remove both soft and hard contamination. Over the years, the requirements for melt fi lters have changed – and with them, the choices and designs available to end-users. The product of a typical resin or fi lm plant passes
through a melt fi lter before being packaged and shipped for end-use processing. Thus the melt fi lter is often responsible for setting end-product specifi cations on all resins, and many fi lm products. For many resins and fi lms, the quality achieved through melt fi ltration is the primary – and many times the only – differentiator between two producers. Selecting a melt fi ltration system requires more than just the normal ‘cost vs. quality’ considerations: it requires an understanding of the design principles, methodology, and abilities of the melt fi lter supplier with respect to your requirement. This article intends to show end-users the various
choices they will encounter in media and melt fi ltration technology, and detail the considerations involved in choosing the right melt fi lter for any application. It includes a broad comparison between high-fi lter-area systems and limited-area screenchangers. Before attempting to select melt fi lter technology,
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some key questions must be considered, including: What is the nature of the contamination to be removed? Is it soft particles such as gels? Hard particles? Or both?
What is the particle size distribution of the contami- nation?
Is the polymer gelatinous? Is the virgin resin melt fi ltered? If it is, to what level – and with what type of fi lter medium and fi lter technology?
If the end-product is fi lm, will it be stretched in one
DESPITE A VARIETY OF STYLE AND SIZES, SCREEN
CHANGERS OFFER LIMITED FILTER AREA CAN USE ONLY WIRE MESH AS THE FILTER MEDIUM
December 2012/January 2013 | FILM & SHEET EXTRUSION 39
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