Why does saran wrap erase the print from thermal paper?

So here at work I have a lot stuff on thermal paper (invoices from vendors, certain customer receipts etc). Some of these, just due to the sheer amount of them, I bundle up by the month and wrap saran wrap* around them a few times to hold them together so I can toss them in a bin for storage.
The odd thing I’ve noticed is that after about a week any of the the thermal print that is in contact with the saran wrap disappears. Why? Anyone have any idea about that?
*It’s not saran wrap per se, it’s the type of wrap you’d see in a grocery store on cut produce or a thinner version of what you’d see wrapped around meat or fish.

Plastic wraps are usually loaded with plasticizers. These may react with the thermal phase change dye.