Try polysaccharide thickeners. If an anionic polymer is OK, try xanthan. If an uncharged polymer is obligatory try the more exotic Schleroglucan. Even the very economical guar might be OK, if its unrefined character is not a handicap.

You need to look at thixotropy. Specifically, very high viscosity: about 1 million at 0.3 or 0.5 rpm (brookfield viscometer). Then much lower viscosity at 10-30 rpm. This will produce a screen printable yet non-slumping formulation. I would try to get this by adding a very small size filler particle. 

Here are some publications: http://www.rheosense.com/publications