Problems sealing a cap on Flouronated HDPE bottle

[eetm]

We currently package 16 and 32 oz HDPE bottles that are either flourinated treated or not. The bottles are made by one manufacturer using the same molds. We send out about 1/3 of these to get treated. We have no problems with sealing the caps on the non treated bottle but have problems with the treated bottles. The caps have a sheet of aluminum embedded and after the cap is torqued to the bottle it passes through an induction sealer. The induction sealer has to be run at full power output for the treated bottles and runs at a much lower setting for non-treated bottles.
I'm looking for a solution to this problem or reasons why this is happening. Thx in advance.

 

[Demon3]

I assume you fluiorinate the HDPE to improve the barrier properties. However, if I tell you that fully fluorinating polyethylene creates PTFE (Teflon) you might see why you are having adhesion problems. Yes, you are effectively creating a non-stick Teflon surface on your polyethylene. No surprise that the adhesion is not good then. To exemplify PE has the structure -(CH2-CH2)- whereas PTFE is -(CF2-CF2)-.

It is therefore hard to suggest a solution. One thing to look at is to minimise the amount of fluorination, just enough to give good barrier but not enough to give bad adhesion. Perhaps this is possible. Another option would be to somehow mask off the tops of the bottles so they don't get fluorinated and the rest of the bottle still does.

The aluminium foil you mentioned. Make sure that is free of any oils, often lubricant oils are used to make Al foil. Also, can you roughen the foil to improve adhesion?

 

[patprimmer]

You have basically turned the surface layer of HDPE into PTFE or "Teflon".

You need to Trim the surface you with to seal, after the treatment so as to give an untreated surface to act against.

Regards

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[eetm]

Thanks for the quick replies. When we run these treated bottles under the induction sealer at a slow speed we get a good seal but a reduced production efficiency. Any ideas why this happens?

 

[Demon3]

Yes, that would work too. Just trim off the surface. I had another idea that could work. That is if you flame treated the top of the bottle before the fluorination it would be oxidised and may give better adhesion later.