I have a Canon Pixma ix6820 printer that we use with all black ink cartridges to print transparency films for screen printing. We use Illustrator to design our art and send to PrintFab for printing dialogue. The printer always produces banding at the very beginning of the print job. Then it is fine. The top of the image is banded or faint but it resolves itself within a quarter of an inch or so. We have tried soaking the print head and running cleaning jobs from the printer itself, as well as adjusting settings to push out extra ink. Any idea why this happens or any way to prevent it?