Regarding your request for information for the screen printer.
First, is the printer producing banners made of nylon or jackets. There is a
difference. If he/she is doing banners, then he/she is stuck with their
current ink due to the thinness of the substrate.
However, if they are printing on jackets, there is an ink produced by
International Coatings Co., 13929 Easte 166th Street, Cerritos, CA,
90702-7666, Ph: 310-926-0747, Fax 310-926-9486, their 1900 Series. This is
a plastisol formulated specifically for nylon jackets.
Regarding your question on waste inks -- yes they can be mixed as long as
there are no white or yellow pigments in the inks.
Screen printing ink containers fall under the empty container rule, and to
the best of my knowledge can be recycled.