Stereo lithography three-dimensional printing apparatus and method of forming colored three-dimensional object

A three-dimensional printing apparatus, comprising:

• a tank filled with a liquid material;
• a platform movably disposed above the tank;
• a lighting module used for projecting light towards the liquid material;
• a control unit coupled to the platform and the lighting module and configured to control the platform to move along a direction, such that at least one layer object of a three-dimensional object is cured on the platform by the lighting module;
• wherein the at least one layer object is a structural layer used to define the shape of the three-dimensional object
• a photosensitizer coating unit coupled to the control unit and configured to form at least one_photosensitizer films on the layer object, wherein the photosensitizer film comprises a resin material and a photosensitizer;
• an exposure unit coupled to the control unit and configured to expose the photosensitizer for a color change so as to enhance the color diversity of the three-dimensional object;
• and
• a drying unit electrically connected to the control unit and configured to dry the photosensitizer film top down for keeping the photosensitizer film formed on the layer object from leaving the layer object as the photosensitizer film is immersed in the liquid material;
• wherein the photosensitizer coating unit is configured to form a second photosensitizer film after the photosensitizer of a first photosensitizer film has been exposed and executed a drying program by the drying unit, so as to stack multiple layers of the photosensitizer film on the at least one layer objects to enhance color diversity;
• wherein after the first photosensitizer film and second photosensitizer film are formed on the at least one layer object, the second photosensitizer film is exposed and dried, then the three dimensional object is lowered into the tank with the platform, a second layer object is formed on top of at least a portion of multiple layers of the photosensitizer film, and then a second forming of the first and second photosensitizer film is formed on the second layer object.