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 Extrusion, Single Screw
 Delaimiation of layers in co-extrusion
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mitch Senior Member Posts: 11 |
posted November 29, 2002 07:52 AM
  
I am relatively new to co-extrusion. we are seeing a problem where our outer layer is becoming detached (pealing back) from the inner layer at a follow on process(heated to 123C). Could anybody tell me where i can find some information on how the 2 layers bond in the extrusion process and any ideas for a root cause for the delamination. The materials are (outer layer) Hytrel Inner melinar. Thanks IP: Logged |
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Steve H Moderator Posts: 386 |
posted November 29, 2002 01:15 PM
G'day Mitch Welcome to the extrusion forum- what are you doing, blown film or sheet? Specific grades of material? Has this combination worked ok and has suddenly stopped working for you? General comments: Maybe you need to look at an adhesive layer (tie). Can you lower the process temps of the secondary processs? TAPPI have a couple of good resources you should get copies of: Film Extrusion Manual-Process, Materials, Properties. (a must have for B/F, cast and sheet extrusion) Coextrusion Coating and Film Fabrication Manual. (a bit dated, but still useful) 2001 Film Extrusion & Coextrusion Short Course Notes. These can be obtained from TAPPI's bookstore www.tappi.org You could also get a copy of SPE's guide on Extrusion Technology and Troubleshooting,available from SPE's bookstore www.4spe.org Both SPE and TAPPI have regular technical conferences and papers on co-ex have been presented at these. Steve Hodgson IP: Logged |
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zabielski Senior Member Posts: 386 |
posted November 30, 2002 09:11 AM
mitch: Both are made by DuPONT. The Hytrel is a ionomer polyester (lightly cross-linked), while Melimar is a PET bottle grade. Do a DSC on both to determine the Tm. In general, the Tm for PET is between 245 - 2265 *C. The Hytrel may be the culprit, as there are many different grades available. Hope your Purchasing Agent did'nt buy a "deal". What are your co-ex temperatures for each polymer? Both have to be pre-dried prior to extruding. You can still co-ex both but typically, hydrolyisis set's in and this could be the root cause to it's strange behavior. Both are hydroscopic. IP: Logged |
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mitch Senior Member Posts: 11 |
posted December 02, 2002 11:12 AM
Thanks all for the info. much appreciated. Is there any test method i can use to check the bond strength between both layers after extrusion before i send it into the next process step. Thanks again IP: Logged |
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alpertl Senior Member Posts: 49 |
posted December 02, 2002 05:15 PM
quote: Another thing you can check for is the layer thickness for each the inner and outer. Try to have you die head helicoid gaps set up as so your layers in the head have close to the smame velocity. IP: Logged |
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Bob Cunningham Senior Member Posts: 115 |
posted December 07, 2002 06:04 PM
Mitch- It's a simple test, but if you take two pieces of masking tape and tape them together at the edge of a piece of film (encapsulating the film), you can try to delaminate the film by pulling the two pieces of tape apart and seeing if the film comes with it. -Bob Cunningham IP: Logged |
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