Using a 120T frame, I used Serimat screen printing inks to print on white adhesive vinyl. Unfortunately, I was unable to achieve a clean print.Why is this?

The most likely reason is that the ink was too dense and needed to be diluted using a normal thinner 290.15, or slow thinner 290.23.

The second possible reason is that the ink remained on the frame for too long and clogged part of the mesh, in which case the ink will only partially pass through the frame.

Here’s a useful rule of thumb: to get a complete, uniform print, the fluidity of the ink should be comparable to that of chocolate spread.
If it isn’t, a sufficient quantity of thinner needs to be added.

It’s important to bear in mind that, most of the time, solvent-based inks need to be thinned using an appropriate thinner.