A 1K UV-ink jet printing ink composition comprising effect pigments, wherein the composition comprises: a) at least one difunctional (meth)acrylate monomer, b) at least one photoinitiator, c) effect pigments having a volume averaged particle size distribution with a D98<10 μm, d) optionally trifunctional and/or polyfunctional (meth)acrylate monomers, and wherein the viscosity of the ink jet printing ink composition is at maximum 30 mPas, measured at 25° C. for 10 minutes with a Brookfield R/S rheometer using a double gap cylinder according to DIN 53453 (German Industrial Standards) at 150 rpm and wherein the total concentration of the at least one difunctional (meth)acrylate monomer of a) and the trifunctional and/or polyfunctional (meth)acrylate monomers of d) is in a range of 75 to 100 wt.-%, based on the total amount of (meth)acrylate monomers.
