Removable printing inks for recyclable plastics
Described herein are ink compositions that will not contaminate recycled plastic materials that come in contact with the inks; labels printed with such inks; and plastic articles having labels printed with such inks; and methods for printing with such inks, and recycled plastic material, such as recycled PET, that has little to no contamination from such inks. For example, during recycling, plastic containers that have been labelled with such inks are subjected to hot caustic wash solutions that cause the ink to separate the labels, When the inks described herein are removed from the label, they form a solid or precipitate, as opposed to dissolving in the hot caustic wash solution. The solid or precipitate is easily separated from the recycled plastic and wash solution, such as by filtration. The separated ink does not contaminate or stain the recycled plastic, or does so to a degree that is tolerable.
1 . 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.
2 . The ink composition of claim 1 , wherein the colorant is selected from the group consisting of: Diarylide Yellow AAMX, Diarylide Yellow AAOA, Monoazo: 3-Hydroxy-2-naphthanilide, Copper Phthalocyanine, carbon black, Dianisidine Orange, Polychloro Copper Phthalocyanine, 3-Amino-9-Ethylcarbazole, and combinations thereof.
3 . The ink composition of claim 1 , further comprising alcohol ethoxylate phosphate ester.
4 . The ink composition of claim 1 , wherein the amount of colorant present in the ink composition is 2.0 wt % to 20 wt %.
5 . The ink composition of claim 1 , wherein the amount of solvent present in the ink composition is 60 wt % to 80 wt %.
6 . The ink composition of claim 1 , further comprising a wax.
7 . The ink composition of claim 1 , further comprising a wax selected from the group consisting of amide wax, erucamide wax, polypropylene wax, paraffin wax, polyethylene wax, polytetrafluoroethylene, carnuba wax, and combinations thereof.
8 . The ink composition of claim 1 , further comprising an additive selected from adhesion promoters, silicones, light stabilizers, de-gassing additives, ammonia, flow promoters, defoamers, antioxidants, stabilizers, surfactants, dispersants, plasticizers, rheological additives, and combinations thereof.
9 . The ink composition of claim 1 , further comprising an extender selected from clay, talc, calcium carbonate, magnesium carbonate, silica and combinations thereof.
10 . The ink composition of claim 1 , further comprising a titanium chelate as an adhesion promoter.