We have a lab extruder with a 3" die on it. Our air ring works good with HDPE but when we run LDPE we have gloss and haze problems. We heard that LDPE needs different air ring angle from HDPE. Can anybody advise what the correct angle ranges are for LDPE and HDPE? Thank you. Eric
Normally you would run HDPE with a long neck, expanding into the frost line maybe twenty inches or more above a 3 in air ring. You would normally have a blowup ratio of 4 or 5 to 1, so you would be making 12 to 15 in layflat. Air rings for this generally shoot straight up. LDPE for a 3 in die would use something like a 3:1 blowup for 9 or 10 in layflat. The bubble would normally sit down on the air ring, angling up at I guess 60deg. A HD airring can work OK, but for good optics etc, you need to get the frost line up a bit but not a high neck like HD. Temperature affects optics - you need lower temps for LD, depends on grade but say 160-170C versus 190-220C for HD.
On a lab extruder with low output and a clean adequate screen pack you should be able to get nice film. Of course, the right air ring does help. Another matter is the die. If an HD die with a big gap and not enough screen pack restriction, you can get bad optics.
Hope it helps
All the best
Ian Macmillan
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