Opportunity is missed by most people because it is dressed in overalls and looks like work. - Thomas Edison
Danny - you can always add a little nylobond for adhesion promoter. Or potentially use an air dry solvent ink. Croft: I would not go with silicone -- pvc gassing under heat can poison the Si bond -- basically meaning the catalyst may not kick off and cross link.
Frog- you are correct. It improves tensile strength (adhesion) but decreases elongation. Maybe I read wrong, but I thought Danny said he had adhesion issues with standard plastisols. Rereading - yes if it cracked due to not enough elasticity and then loss of adhesion - nylon additive would not be advised.Most yoga mats are not terribly stretchy though -- just foamy! The thing is with plastisol ink - when printing on a cured plastisol (yoga mat in this case), you are literally printing on a sheet of vinyl and adhesion is difficult. This is the same phenomena on inter-coat adhesion issues (delaminating) when printed a color on an OVER flashed white ink. However in this case, the blown foam of the mat gives a bit of a rougher surface to adhere to. An air dry vinyl ink would probably be the best solution overall.
my yoga matt appears to be screened looking under a loop, semi pliable ink, feels and looks like it will stick forever... although a very small imprint