Hi, I was wondering with the danger of pvc or pcv ( I forget which it is

) in some plastic flips, if the graded coins I have are safe.
The flips are sealed but they are somewhat flexible and I recall hearing flips that are more rigid and less flexible are safer from having the ugly oils oozing onto coins as they are what make the flips more flexible.
Short version: Has anyone ever found any damage on their coins from the soft flips ICCS uses to certify coins?
Thanks w-dog