Wrinkles in ribbon using Datamax H-4212 printer

1. The printhead in your printer might be scratched (evidenced by thin white streaks through your print). This is common, and the most likely cause. Printhead must be replaced.
2. Material might be stuck on your printhead (usually evidenced by wide white streak vertically through print). Printing surface of printhead can be cleaned with rubbing alcohol and cotton ball.
3. The ribbon might be wrinkling due to uneven tension, producing intermittent diagonal streaks in your print. This is somewhat common, but doesn't fit your description as well as 1 & 2 above. Mechanical adjustment and/or proper media loading solves ribbon wrinkles.
4. Poor pressure and/or printhead alignment. Evidenced by grainy, light or no print on one side or the other of the media. This is somewhat common, but doesn't fit your description as well as 1 & 2 above. Mechanical adjustment solves printhead pressure and alignment issues.

When you have this problem you need to determine if the ribbon is wrinkling before or after the head. If it is before the head then you need to adjust the bar prior to the head. There should be a phillips head screw there and directly behind it there is an adjustment. Loosen the screw and then move the bar (it is slightly arc'd) so it smooths out the ribbon. This is the least likely suspect. Most likely the head is not square. If the head is not square with the roller below it will cause the ribbon to "dance" as I call it. It will slowly move over then jump back to its rightful position. Or it could just wrinkle. If this is the case and your print looks good then you can adjust the ribbon bar right where the ribbon comes out of the head. There are two screws at the top. Loosen both of them and this adjustment bar will slide all the way back. Once this goes back. Manually manupulate it until it smooths out the ribbon. Once you manually figure out where it is smooth then tighten the screws back up. Feed a few labels and see if the ribbon is smooth.

If streaks are perfectly vertical and always present, probably your printhead is scratched and needs to be replaced. Unless the streaks are diagonal and intermittent - then you need adjustment for ribbon wrinkle.
Printheads

poor tension on the rollers?

try pulling the ribbon during stamping, if this corrects it then you may need a tech to come and reseat some drive gears.

Could be down to tension on the ribbon roller/spool. Check to see if you have pulled out the end part of the spool (black bit) that should ensure there is back tension on the ribbon.

The thermal print head is damaged. You can try to clean it with a thermal printer head cleaner. That will only help if it is just clogged up with thermal print ink.

Remove the ribbon and try to remove the crease. Check the printhead for obstructions. You may have to open up both halves of the ribbon cartridge to look for jams or obstructions.

I changed the print head, and the issue was solved.

Printer ribbon has a wrinkle and it transfers to the label in the form of a blank line accross the ribbon.

This is usually caused by temperature of the thermal print head. This is found in the printing preferences of the printer.