A cooperative research programme has been launched in the frame of a European project aiming at optimising the removal of stickies in deinking lines, especially by slot screening. Soft PSA particles being the most difficult stickies to remove as they can be extruded through slots, basic research work was focused on understanding the extrusion mechanisms. A single slot screening device was used at CTP to visualise the extrusion of cylindrical PSA particles. Numerical simulation of the extrusion of viscoelastic particles was performed at LEGI and special test equipment was developed at LEMTA to determine the dynamic behaviour of the adhesive material. Water-based acrylic adhesives revealed to be much weaker than hot-melt rubber adhesives, especially at high temperature after alkaline soaking, and required lower pressure and less time to be extruded through the slot. Gentle screening conditions with low pressure during the positive pressure pulse as well as reduced temperature and pH should thus minimise stickies extrusion as expected. Both experimental and numerical simulation results led to the same conclusions about the effects of key screening parameters. Linear relations were observed between the normalised particle diameter and the extrusion pressure and time. Particles 2 or 3 times larger than the slot width were effectively extruded at typical extrusion pressures observed in screens, but the time required to pass the slot was up to two orders of magnitude higher than the duration of the positive pressure pulse, which suggests that particle extrusion should take place step by step over several revolutions of the rotor. The tests performed to compare milled slots with sharp inlet edges to wedge wire slots with higher inlet radius, showed less particle extrusion with the milled slots, as expected. Further investigations are however required to conclude, as the behaviour of adhesive particles during the reverse pulse should also be taken into account in multistep extrusion mechanisms. Future research should include the analysis of the reverse extrusion of adhesive particles through slots with complete characterisation of the rheological properties of the adhesive material at the high strain rates observed in the extrusion process.