Removable printing inks for recyclable plastics

An ink composition comprising:

• (a) a mixture comprising:
• i) polyvinyl chloride-polyvinyl acetate copolymer resin, and a resin selected from the group consisting of polymethyl methacrylate or isobutyl methacrylate copolymer;
• or
• ii) semi-aliphatic polyurethane resin and polytetrafluoroethylene;
• (b) 50 wt % to 90 wt % solvent selected from aliphatic hydrocarbons, cyclic hydrocarbons, aromatic hydrocarbons, ketones, aldehydes, alcohols, ethers, esters, and combinations thereof;
• and
• (c) a colorant resistant to dissolving in a hot caustic solution;
• wherein the amount of resin present in the ink composition is 3.0 wt % to 25 wt %;
• wherein the ink composition is resistant to dissolving in a hot caustic solution employed in a plastic material recycling process in which the plastic material being recycled comprises crystallizable PET-G substrate on which the ink composition had been printed and then removed in the hot caustic wash solution, wherein the ink composition breaks down into small particles that precipitate, allowing for removal from the hot caustic wash solution by filtration in a rinse step;
• wherein the hot caustic solution is an aqueous solution containing 1.5% by weight NaOH at a temperature of 85° C., and which further contains 0.3% by weight non-ionic surfactant;
• whereby the plastic material is not stained or contaminated by the ink composition.