Are there any negative effects with heat disapation from install'in a plastic film screen protector?

A screen protector will not negatively affect heat dissipation on any of Apples Products. The Aluminum housing is part of cooling it down. However, during high ambient temps, it's normal for the iPads & iPhones to feel warmer than normal. Yes, there were some cases of batteries overheating, but if there is not an active recall then you should be just fine.

Also, if you are having some heavy apps running while it is charging, then that can also be a source of the higher than normal heat you are referring to. If your iPad/iPhone is within the "Overheating" range, they will automatically shutdown, and display a heat warning message.

Hope i answered your question.

Not that matters.

I'm saying that it has an effect, but not much.

Since you don't think i solved your problem, at least did I Help?