They don't - the Display Electronic Slurry (DES) is a competing 'e-paper' tech that E-Ink corp haven't patented. It has slightly different pros and cons (it has a more defined checkerboard pattern which isn't as nicely grainy as E-Ink corp's MED, but it let's them pour the 'ink' straight into the substrate which potentially has higher contrast and resolution as a result), but ultimately that's irrelevant nitpicking if patents are causing the price of E-Ink screens to be crazily high as people keep falsely claiming. If DES could deliver screens at half the price, then Wiwood (?) would eat E-Ink's lunch.