Method for printing radiation-curable ink onto a polycarbonate substrate, said method comprising the steps of: a) providing a polycarbonate substrate in the form of a sheet or film having a thickness and having a first and a second surface; b) providing a treating fluid being a homogeneous liquid at a temperature between 15 and 35°C, comprising between 1 and 10 wt% of one or more cyclic ketones being liquid at a temperature between 15 and 35°C, based on the weight of the homogeneous liquid phase, wherein the remainder of the treating fluid consists of a diluent chosen from the group consisting of diacetone alcohol, n -hexane, n- heptane and n -octane; c) treating at least part of at least the first surface of the polycarbonate substrate of step (a) with between 0.06 and 5 g/m 2, based on the treated area, of the treating fluid of step (b) for a period of at least 5 seconds, preferably at a temperature between 15 and 35°C, resulting in a treated polycarbonate substrate layer with swollen areas where the at least first surface is treated with the treating fluid, wherein the one or more cyclic ketones being liquid at a temperature between 15 and 35°C are distributed across at least part of the thickness of the polycarbonate substrate; d) optionally rinsing the at least first surface of the treated polycarbonate substrate layer obtained in step (c) with the diluent to remove an excess of the one or more cyclic ketones being liquid at a temperature between 15 and 35°C; e) optionally drying the treated polycarbonate substrate layer obtained in step (c) or (d) to reduce the weight percentage of the combined amounts of the treating fluid on and in the treated polycarbonate substrate to between 1 ppm and 0.4 wt%, based on the weight of the treated polycarbonate substrate; f) providing the treated polycarbonate substrate obtained in any one of steps (c) to (e) wherein the combined amounts of the treating fluid on and in the treated polycarbonate substrate is between 1 ppm and 0.4 wt%, based on the weight of the treated polycarbonate substrate; g) applying radiation-curable ink onto at least part of the swollen areas of the at least first surface of the treated polycarbonate substrate provided in step (f) using inkjet printing; h) curing the ink applied in step (g) such that the ink adheres to the surface of the at least first surface of the polycarbonate substrate; i) optionally thermoforming the polycarbonate substrate with the cured ink thereon obtained in step (h); and j) optionally applying a coating layer onto at least part of at least the first surface of the polycarbonate substrate with the cured ink thereon obtained in step (h) or onto the thermoformed polycarbonate substrate with the cured ink thereon obtained in step (i), followed by drying or curing the coating layer. a) providing a polycarbonate substrate in the form of a sheet or film having a thickness and having a first and a second surface; b) providing a treating fluid being a homogeneous liquid at a temperature between 15 and 35°C, comprising between 1 and 10 wt% of one or more cyclic ketones being liquid at a temperature between 15 and 35°C, based on the weight of the homogeneous liquid phase, wherein the remainder of the treating fluid consists of a diluent chosen from the group consisting of diacetone alcohol, n -hexane, n- heptane and n -octane; c) treating at least part of at least the first surface of the polycarbonate substrate of step (a) with between 0.06 and 5 g/m 2, based on the treated area, of the treating fluid of step (b) for a period of at least 5 seconds, preferably at a temperature between 15 and 35°C, resulting in a treated polycarbonate substrate layer with swollen areas where the at least first surface is treated with the treating fluid, wherein the one or more cyclic ketones being liquid at a temperature between 15 and 35°C are distributed across at least part of the thickness of the polycarbonate substrate; d) optionally rinsing the at least first surface of the treated polycarbonate substrate layer obtained in step (c) with the diluent to remove an excess of the one or more cyclic ketones being liquid at a temperature between 15 and 35°C; e) optionally drying the treated polycarbonate substrate layer obtained in step (c) or (d) to reduce the weight percentage of the combined amounts of the treating fluid on and in the treated polycarbonate substrate to between 1 ppm and 0.4 wt%, based on the weight of the treated polycarbonate substrate; f) providing the treated polycarbonate substrate obtained in any one of steps (c) to (e) wherein the combined amounts of the treating fluid on and in the treated polycarbonate substrate is between 1 ppm and 0.4 wt%, based on the weight of the treated polycarbonate substrate; g) applying radiation-curable ink onto at least part of the swollen areas of the at least first surface of the treated polycarbonate substrate provided in step (f) using inkjet printing; h) curing the ink applied in step (g) such that the ink adheres to the surface of the at least first surface of the polycarbonate substrate; i) optionally thermoforming the polycarbonate substrate with the cured ink thereon obtained in step (h); and j) optionally applying a coating layer onto at least part of at least the first surface of the polycarbonate substrate with the cured ink thereon obtained in step (h) or onto the thermoformed polycarbonate substrate with the cured ink thereon obtained in step (i), followed by drying or curing the coating layer.