A method of producing a floor panel (1), including providing a carrier (3) including a thermoplastic material, applying a primer comprising at least one salt, preferably a metal salt, on a first surface of the carrier (3), printing by means of digital printing a first print (10) on said first surface of the carrier (3) with an aqueous pigment ink composition, and applying a protective layer (4) on said first surface of the carrier (3) and applying the carrier (3) on a core (2) and pressing by applying heat and pressure the protective layer (4), the carrier (3) and the core (2) together to form a floor panel (1). Also, a method for forming a decorative substrate.