There are basically 2 types of screen printing inks for T-Shirts:
Waterbased inks and discharge inks
Non-PVC and Plastisol
Waterbased inks and discharge inks on t-shirts:
-What are Waterbased inks: The simple answer is that water based ink is any ink which uses water as a solvent base to carry the pigment. Waterbased inks contain a pigment held in a water based solution of varying viscosity which dyes the t-shirt to the desired colour.
-What are discharge inks: Discharge ink is a type of waterbased inks. Discharge inks have a bleaching effect where the removed the dye from the top layer of the t-shirt fabric and optionally replaces it with another colour. The discharge inks, however, require a very high temperature to activate. As it takes a long time and a very high temperature for the discharge inks to activate, these require a minimum run of 100 t-shirts to print.
Plastisol and Non PVC Plastisol ink Printing on T-Shirts:
-What are Plastisol inks: Plastisol inks, or traditional inks, are solid inks which are applied on the surface of the t-shirt. They do not dry on their own and a high temperature has to be applied for them to 'set' on the t-shirt. They are also commonly known as 'rubber' print. It is the only solution for printing on t-shirts where discharge print cannot be used.
-What are Non PVC Plastisol inks: In non PVC inks, plastic is replaced with acrylic, a much safer and environment friendly plastic than PVC. These also meet all european and US norms of print safety.