Some bubbles get popped in the forming roller after extrusion of the bubble-wrap 4

[mah1975]

thread712-461270

Hi Mykolaj/(or anyone experienced),

I was using 50% LDPE and 50% LDPE and optimized the air vacuum but still some bubbles get popped (or sucked in) on the forming roller in every meter of the film.

1) Is it because of the 50% and 50% ratio? As per your suggestion, if I use 70% LDPE and 30% LLDPE will this solve the problem? Do you have any explanation and experience of bubbles being popped while manufacturing? And how to solve this?
2) I found some of the bubble wrap films are very thin but very strong. It takes a lot of force to pop them. My resin supplier told me to use more LLDPE to make it stronger. Any idea or experience?
3) You said more LLDPE is not good because of shrinkage properties. But I found that LLDPE has a shrinkage range from 2.0 ~ 2.5 and LDPE has a more wider range of 2.0 ~ 4.5 Could you explain more about the shrinkage properties of LLDPE and how does it affect in the bubble wrap film?

Regards,
marifca

 

[Mykolaj]

Hello!
1. Two main things for forming perfect bubbles - clean bubble roller and good raw material. If your defective bubbles are repeated on the film every few seconds in the same place - that means you have to clean up your bubble roller. If defective bubbles every time are situated in different spots - that means your raw material could be better. I've tried 40%, 50%, and 70% LDPE and if the polymer is good you will make great bubble wrap. From my experience, I can say that Sabic and Lotren are better than the others and Polymir, Socar, Sibur are not the best for bubble wrap production.
2. You can add different kinds of metallocene LLDPE (DOW, Exxon, etc) to make it stronger but usually price of the bubble wrap with high content of mLLDPE becomes uncompetitive.
3. You are talking about the shrinkage range of LDPE and LLDPE heat shrink films. And I was talking about shrinkage of melted material. For example, the width of your t-die is 1.8 m but you can't make a film with a width of 1.8 m because on the way from the t-die to the bubble roller width of the film lowers to 1.4-1.7 m. Depends on what material you use. Higher content of LLDPE - lower width of the bubble wrap you can achieve. Sometimes it is completely impossible to make 1,5 m films with high LLDPE content. And you have to change edge knives more often if you use a lot of LLDPE.