Process for preparing a masterbatch comprising 20-90 wt % of a polymer additive dispersed in 10-80 wt % of a thermoplastic polymer, said process comprising the steps of: —providing the additive in liquid form, —optionally heating the additive, —adding solid particles of the thermoplastic polymer to the liquid additive, —heating the resulting mixture to a temperature in or above the melting temperature of the polymer, —treating the mixture with shaping equipment to form solid particles.