The Z1 is scratching the discs as it prints them.
The cartridge may be defective. A small percentage of cartridges may have plastic residue left over from the molding process. This plastic could be protruding slightly below the ribbon. When the ribbon is pressed down during the thermal transfer process, the residue could be scratching the discs.
Try a new cartridge or to salvage the current cartridge, file off the plastic residue with an emery board.