First thing that needs to be understood is a photochemical process called Polymerisation or Curing. It is a process by which a specialised UV Ink is dried instantly on interaction with very intense ultraviolet light. UV inks produce more detailed images.
On application, the UV ink stays on the surface of the media of application (Different types of metals, plastics and even human skin). They are different from normal inks in this respect and do not penetrate into the surface. As an end result, the pigment in the ink sticks to the surface and is hardened by UV. This gives a slightly plastic textured feel to the print.