posted September 10, 2004 07:15 AM               

I'm having some problem with a blend of 70%LLDPE octene / 30%HDPE.

I would like to know a temperature profile for blown film extrusion of this blend.

And if it's possible I would like to know the die diameter and die gap best suited for this blend to make a 1 mil film.

posted September 10, 2004 10:05 AM               

The MI of the resins.
The temperatures that have not worked.
The screw design type.
Screw RPM
Screw diameter
Expected output rate
A description of the problems you have had.

This will help in suggesting better process conditions.

posted September 10, 2004 05:21 PM               

I will get all the info you asked for but I will only be able to provide the info for monday.

posted September 13, 2004 09:06 AM               

Description of the problem : We were producing a blend of LLDPE and HDPE on a rulli standard extruder.

Extruder :
Screw dia : 2.95 inch (75 mm)
L/D : 32:1
Die dia : 13.78 inch
Di gap : 70 mill

There was a lot of gels and the film was not strong at all. The resin blend was

Resin (70%) : FY-120-D LLDPE octene (Nova chemicals)
MI : 0.98
Density : 0.92
Slip : 1000 ppm
Anti-block : 2800 ppm

Resin(30%) : Formolene E924 HDPE
MI : 0.04
Density : 0.949

Temperatures

Zone 1 : 165 Zone 2 : 165 Zone 3 : 170 Zone 4 : 170 Zone 5 : 170 Zone 6 : 170
Adaptor : 175 Screens : 170 Adaptor 2 : 180
Die 1 : 185 Die 2 : 185 Die 3 : 185 Die : 185

Melt temperature : 180

Tests :

1-I changed the temperature to go at a 185 melt temp. The problem got worse.

2- We have an other Rulli standard extruder and we tried the same blend on it and it worked. Here is the description of the other extruder.

Screw dia : 2.76 inch (70 mm)
L/D : 30:1
Die dia : 11.81 inch
Die gap : 63 mill

The temperatures were similar with a 181 melt temp.

3- We then changed the FY-120-D LLDPE octene for a LLDPE Hexene and everything was working fine.

I hope taht you can give me an answer about what could be wrong.

posted September 13, 2004 11:52 AM               

One LLDPE melts much differently than the other, and when interacting with a specific screw design more unmelted resin is discharged from the screw. Not only are there unmleted particles, but also pellets which melted late in the screw are poorly blended with the HDPE, resulting in poor product physical characterisitcs.

For this condition there are several potential solutions;

Increase the screen pack density to increase the back pressure. This helps melting and mixing.

Slow down the screw RPMs. This will move the completion of melting towards the feed throat.

If you want good performance on a variety of resin blends I would suggest a barrier style screw followed by a mixing section. This will assure that the resin is melted, well mixed, and the discharge temperature is even.