Converting Blown-Film Lines from HDPE to LLDPE

Firstly, you will need to run at least 10% LDPE with your linear material to achieve bubble stability. It will be very difficult for you to run 100% LLDPE.

We typically run in the 200 degree C range with this blend.

The original air ring sounds correct. You may have a "high stock" bubble with the HDPE, but you don't need this with LLDPE.

There will be a difference in die construction, although you should be able to run one or the other, just not at optimal conditions.

Your die gap should be in the 0.070" to 0.080" range. Going thinner will improve properties, but increase melt fracture.

Once you add the LDPE you should be able to achieve blow up ratios in the 3:1 and even 4:1 range.

Hope this helps. If you need more help, just ask.

Himanshu Jani
Manager - International Sales Gulf, Middle East & CIS Countries
WINDSOR MACHINES LIMITED
Land Line : 0091 9898042145
Mobile : 0091 98250 36730
E-mail : himanshu@wml.co.in

Dear Participant;

Please ensure following perimeters.

• Blending : 20 % LD
• Blow Up Ratio : 1.5 - 2.3
• Die Gap : 1.8/2.2 (Mono Layer) or 2.2 (Multi Layer)
• Type of Air Ring – Dual Lip
• Air Cooling Lip : 21 degree
• Frost Line : Close to Die Exit
• Die Design : Now a days common Die for LL-LD-HD
• Screw Design : As above
• Nip Height : To be adjust to suit
• Air Flow : Close to Die Exit to suit frost line
• Temperature : 190 –197
• Cooling Temperature at Air Ring : 8-10 degree
• Delta T : 14-15

Hope these data is judiciously used can give happy extrusion of LL-Rich Film.

Himanshu Jani
Manager - International Sales Gulf, Middle East & CIS Countries
WINDSOR MACHINES LIMITED
Land Line : 0091 9898042145
Mobile : 0091 98250 36730
E-mail : himanshu@wml.co.in

Thank you for your comments! It really helped alot Mr. Jani.

Just as a follow up, I'd like to note that I've managed to increase the Blow Up Ratio to 2.72 with a 250mm die with the following settings:

Pressure after screen: 1230 psi

Cooling air ratio: 10%

Line Speed: 60 ft/min

Operating Temperature: 206°C

Screw speed: 26.8 rpm

I must point out that the cooling air ratio is actually a device I've mounted approximately 1 meter away from the die in order to make up for the short tower height.

In my trials, I have run the setting without an air ring. I am wondering if this is the correct way to do it, because I've heard that a number of air rings on the market today can either manually or automatically decrease thickness variation and give an even better blow up ratio. Is this really the case or does the air ring make only marginal differences?

At the moment, I've mixed approximately 11% of LDPE into the batch, which is great for bubble stability - however I've noticed the substrate surface is streaky. Might be due to a dirty die, the extruder screen needing to be changed, or perhaps I should be mixing less LDPE into the batch. I'll try all three before I post again.

I'm attaching some pictures, perhaps you could comment.

Dear Heat71, Good Morning.

I have seen photo and really good that u r getting better result keeping Cooling Ring quite away from Die Exit. May b it is due to processing of Thick Film at low line speed. Or your cooling ring is really effective and giving chilling effect in downward direction towards die.

I still suggest to make it close to Die and let periphery of bubble be close to internal periphery of cooling lip. If it is done u can increase line speed and output accordingly. And once your output is increased u will reduce power consumption and shall result in to low cost film.

As such Air ring is playing prime roll for quality output. For more knowledge please visit website of SATURN.

Himanshu Jani
Manager - International Sales

Gulf, Middle East & CIS Countries
WINDSOR MACHINES LIMITED
Land Line : 0091 9898042145
Mobile : 0091 98250 36730
E-mail : himanshu@wml.co.in