bad old plastic coin flips?

I just bought some (primarily copper) coins online. They are from the 1700 through the 1800s, packaged in plastic 2x2 pouches. In the pocket next to the coin are old-looking typed labels. I suspect these are from a previous collection being sold by someone who is not interested in coins.
The coins feel a little greasy/sticky. When removed from the soft , flexible plastic, I noticed a faint green imprint of the coin remaining. I'm guessing that these are not coin-safe pouches.

How do I clean any contaminants off the coins? Gentle rinse with a mild soap and warm water, or acetone, or both?

Are the coin pouches likely to be the problem? I was thinking about warning the seller that he may need to take steps to protect any other coins if he still has any.

The green is copper sickness, it can't come off!
Probably due to PVC in the flips.

Like my one of my old plastic books. I once had a 1941 British Indian coin in one flip (opened for many days) and after 1 month there were filthy green dust about the pattern of my coin. I don't know they were verdigris or not but they maybe something rubbish. Soap and acetone may have reactants.

Yes, it's likely to be the coin flips. Older types include a plasticizing agent which reacts with the metal. I'd be very hesitant to put anything of value in even brand new ones from China for any length of time.

Dish soap first to remove the waxy grease from the surface. Then acetone to remove the residue.

I got this problem once, when I got two albums full of coins with this problem. Coins stayed for about 25 years in PVC holders some of them were very damaged because of this.
I think the issue is with copper and PVC together, since the coins without copper in their alloy (mainly aluminium coins) were ok. Strangely, brass coins get away with that sticky feeling.

I used lemon juice on a paper towel then cold water to remove the lemon juice (its acidity can lead to other problems if you don't correctly remove it I guess). Don't push too hard or you will damage the coin.

I did that with silver coins from various eras and content in silver, Roman antonianii, bronze coins, copper and copper-nickel coins, and they are safe and well right now.
Here are pics from the antoninianii that were very sticky and green (moreover, they smelled bad...) :

Before and after

Thank you all. I advised the seller that if he has more coins, he should look at his flips. He said he had inherited the coins and now that he knows to watch for PVCs, he'll use something safer from now on.
Who knows what valuable coin(s) you all might have saved...
Thanks