help on blown film formulation

[tsd staff]

Hi guys! We're currently trying out to produce a blown film with the following formulation

pvc 100
tin stab 4.5
DOP 9
stearic acid 1.2

however, we cant produce a clear film at lower temp. to be able to get a clear film, we process it 190C which leads us to burnt compound along the line later on so we have to stop and clean out the whole line! could you please suggest how we can improve the formulation so we could run at lower temp? thanks a lot in advance!

[Skip]

Some questions arise----

What is the K-value (mol. wgt.) of your resin? A 190C melt temp. should be OK with the VERY HIGH level of tin stabilizer you have, plus the DOP, unless your extrusion die has some areas of hang-up.
I would suggest a couple of ideas----try a lower K-value resin (K-58-60 vs K-65 for example) that will process at around 175-180C, and try adding a little (0.5phr) ester lubricant like Loxiol G-50 &/or PE wax (0.15phr) to increase lube efficiency. Maybe even a little acrylic process aid like K-120N to improve melt flow.

I'm asuming you're running on a single screw extruder----and of course a positive displacement lower shear twin screw extruder would allow a lower processing temperature.

[Len]

Hi guys! We're currently trying out to produce a blown film with the following formulation

pvc 100
tin stab 4.5
DOP 9
stearic acid 1.2

however, we cant produce a clear film at lower temp. to be able to get a clear film, we process it 190C which leads us to burnt compound along the line later on so we have to stop and clean out the whole line! could you please suggest how we can improve the formulation so we could run at lower temp? thanks a lot in advance!

Whoa! Plasticizer level (9 phr) looks a little on the low side. Borderline anti-plastization levels here! No wonder your having extrusion troubles.

My experience is that 20-60 phr is used in film, depending on hardness needed. Higher plasticizer levels, possibly 15-20 phr will greatly improve extrusion performance! A little ESO (3-5 phr) would help thing along, too. I'd ditch the tin stabilizer for a mixed metal (2-3 phr) Ca/Zn liquid, but there is nothing inherently wrong w/ the tin. I'd say, your level of tin is overkill 2 4.5 phr!

Lubs:
Stearic Acid 0.5 -1.0 phr
Ca Stearate 0.25 phr
Wax 165 0.25 phr

You want a clear film, be careful w/ additives and your state of fusion will has a great effect on clarity.

Len

[tsd staff]

Thanks for all your help guys! Do appreciate it.
Yup, we're using single screw. =)

I took your advise and we run the following formulation (in phr):

PVC (K57) 100
DOP 30
Tin Stab 3
ESO 3
Stearic Acid 0.5

We were able to run at a lower temp of 170 175 180 185. However, the problem encountered is that the film produced was so sticky, i cant open the blown film at all!! I would like to decrease my temp a lil bit further...

So I'll reduce the DOP level to 15 phr and add 0.5 phr of PE wax plus 1 phr of LG PA820 as processing aid.
What do you think about these? Would this make a clear and unsticky blown film?

By the way, we're doing this test to check the inflation fish eye (IFE) of the PVC film. After producing the films, we compare them or count the IFE of film per area. just fyi

[Len]

I'd lose the Tin stabilizer and switch to a Ca/Zn stabilizer, then the ESO will aid your heat stability. I believe the ESO is ineffective in a Tin system, but if you change to a mixed metal stabilizer the ESO will act as a co-stabilizer.

DOP @ 30 phr and ESO @ 3 phr = ~33 phr of total plasticizer, this is over kill. Stickiness is going to be a problem at this plasticizer level. Reduce the DOP to 15 phr, ESO to 3 phr, use a Ba/Zn Stabilizer to 2 phr and try your experimental film.


Len

[tsd staff]

Yeah. It really was a sticky film!

My experimental formulation with

PVC (K57) 100
DOP 15
Tin Stab 3
ESO 3
0.5 PE wax
0.5 Processing aid
0.5 stearic acid

was a failure. I started running at a lower temp and ended up running at 200 195 190 185, 20 rpm but the film wasn't still clear. The formulation of

pvc 100
tin stab 4.5
DOP 9
stearic acid 1.2

was even better. But the problem as i have said is the burning.

I don't have any other liquid stab with me right now so I can't ditch the tin stab just yet. Maybe i'll try increasing the DOP level to 20 phr and loose the ESO, PE wax and PA. But i'll try to get a Ba/Zn stab at least just for trial.

Any inputs guys?

[Skip]

I'm a little confused-----exactly what type of film do you want to make? -----a semi rigid, crinkly cellophane type film, or a fully flexible Saran type film? Obviously the plasticizer levels will determine this.

Len is correct ---ESO is best used with Ca/Zn or Ba/Zn stabilizers---and I would add that ESO should NOT be used with tin mercaptides, since I've seen ESO exude in presence of tin. If tin is your only choice for now, I'd suggest taking out the ESO.

[Len]

I'm a little confused-----exactly what type of film do you want to make? -----a semi rigid, crinkly cellophane type film, or a fully flexible Saran type film? Obviously the plasticizer levels will determine this.

Len is correct ---ESO is best used with Ca/Zn or Ba/Zn stabilizers---and I would add that ESO should NOT be used with tin mercaptides, since I've seen ESO exude in presence of tin. If tin is your only choice for now, I'd suggest taking out the ESO.

Skip, I think you're on to something, here. Houston, we have a problem!

He pulled the ESO and had burning problems, probably related to the lower plasticizer levels, and thus higher process viscosity. He put the ESO in at a higher (overall) plasticize level, got a lower process viscosity and thus had less burning, but the film was sticky. Hum, it looks like the ESO and Tin are conspiring to create this problem.

To me it sound like he's trying to make a semi-rigid film. And, if so, he'll need to stay away from the antiplasticization zone for DOP. He needs to be over the 15 phr "threshold for DOP" to get any sort of reliable properties. This could be done by using the ESO and DOP at 15 and 3 phr respectively to achieve this threshold.

If the film is too flexible at that point, then I'd suggest going to a more efficient plasticizer to replace the DOP. Or consider moving to a higher MW resin to gain some stiffness. He could get better low temp properties w/ either one of these strategies.

Len

[tsd staff]

Len you're right. I'm trying to make a semi-rigid film. I can't move to a higher MW as we're only doing this for low MW resin. I'm not actually concerned about the stiffness or flexibility. My main objectives are to have a clear film so I could see the inflation fish eye and no burning on the line. This is all for testing purposes only you see.

Thanks for all your help guys. I'll try to get a Ba/Zn or Ca/Zn stab for testing. But for the mean time, i'll remove first the ESO and stick with the DOP, PVC, St. Acid and Tin Stab but of course with a higher level of DOP. It seems that the processing aid and PE wax are not helping at all.

[tsd staff]

Hi guys! Let me update you on this subject... I've been doing a lot of tests lately.

The formulation I've settled lately is below using the following process temperature and extruder speed: (185 190 190 195) deg C and 17rpm --SETTING 1.

PVC 100
Tin Stab 4.5
Stearic Acid 1.2
DOP 12

I'm already ok with this setting and formulation. But my main goal is to reduce the inflation fish eye on the film without increasing the temperature.


I tried using GMS instead of stearic acid. However, with the GMS, I can't get the same clarity. So I raised the temperature a little higher to (187 192 192 195) deg C and was able to get the results I wanted. But since I want to operate at a lower temperature to be able decrease the probability of burning, I tried experimenting with the addition of processing aid using setting 1 and the formulation I used is

PVC 100
Tin Stab 4.5
GMS 1.2
DOP 12
PA 1

However, the film comes out so rough and hazy! Aaargh. So I tried reducing the GMS to 1 phr and the PA to 0.4 phr. But still the same results. I tried reducing the extruder speed to 14 rpm to increase residence time but to no avail. I increased the temperature up to (190 192 195 200) but still the same! huhuhu My hope level is so low right now. Some help pleeeease.......