Heat Sealing

Quick Start

This is really just a pointer to two apps elsewhere on my site that concern the ability to get good adhesion via heat sealing. But there's a neat trick described at the bottom of the page that you might find helpful.

One area of adhesion where entanglement is very much seen as important is heat sealing. For strong seals it is vital that the polymer (typically PE) melts sufficiently across the interface to be able to allow entanglement to take place.

The problem arises for those who want a controlled low peel. If they over-heat then they get full entanglement. If they under-heat nothing happens. So they need a polymer system where there is a broad temperature response and where the critical entanglement length is sufficiently large that the intermingling across the interface is never in danger of reaching entanglement. If intermingling increases by 10% then from de Gennes, the bond strength increases by 10%, which may be OK for low peel seals. But if that extra 10% takes the polymer into the entanglement zone, peel can increase by more than a factor of 2.

Heat sealing can be performed with heated jaws, induction heating, ultrasonics and various pulse heating techniques. For my full-scale models of two of these techniques the links will take you to the relevant AbbottApps pages. I am told that it is unlikely that I could write a good-enough app to be able to model the ultrasonic method. The apps let you choose various polymers, such as "narrow" and "wide" PE, where the former is relatively linear PE with a sharp melting point and the latter is a relatively branched PE with a broad melting point.

Treatments to help heat sealing

Any treatment such as corona that functionalises the surface is unlikely to help with heat sealing because there will be a solubility mismatch (see the HSP page) that will reduce intermingling within the unfunctionalised bulk. To be successful, treatment under argon would seem to be required.

However, tricks like flash treatments, discussed in the Corona page, that melt/freeze the surface in super-fast time gives an amorphous surface that heat seals at much lower temperatures. This fact seems to be generally unknown, so feel free to take commercial advantage of it over your competitors.