I am trying to design labels that are unobtrusive, with with text on a largly black background. These are for electronic equipment and cables electrical-compliance test certificates.

When printed these come out with broken incomplete blacks towards the end of the label. Also smallish white text is poor overall, and worse towards the end.

All of this is set on minimum print speed. Is there anything else I can do to improve the quality, or is  this in fact some basic limitation of the pinter ?