I currently store my 4x5 negatives in archival sheets with 4x5 pockets, like this one: https://www.bhphotovideo.com/c/product/43007-REG/Print_File_PF454B100_Archival_Storage_Page_for.html
I store those sheets in a locking binder.
Today I fired up the darkroom only to find that every negative I might want to print had gotten dirty somehow and needed to be scrubbed with a pec pad and rewashed. So they're all hanging up to dry and my morning is lost. Additionally it looks like some of them have gotten slightly scratched just sitting in the binder.
I'm not sure how they got dirty inside the binder. It is stored in a fairly clean room with minimal human activity.
How should I be storing my sheet negatives to make sure they stay clean? Or is this just a hazard of the trade and I should plan on re-cleaning any negatives I want to print the night before?