Patent ID: 7175675

Claim:
A method of dyeing a thermoplastic article selected from the group consisting of pellets and strands comprising: (a) providing said thermoplastic article that includes at least one thermoplastic polymer; (b) immersing at least a portion of said thermoplastic article in a dye bath comprising, (i) at least one dye, (ii) water, (iii) at least one carrier represented by the following general formula I, R—O—(CH 2 ) n —OH I wherein R is a radical selected from linear or branched C 1 –C 18 alkyl, benzyl, benzoyl and phenyl, and n is 2 or 3, and (iv) a diol selected from at least one of linear or branched C 2 –C 20 aliphatic diols, poly(C 2 –C 4 alkylene glycol), cycloaliphatic diols having from 5 to 8 carbon atoms in the cyclic ring, monocyclic aromatic diols, bisphenols and hydrogenated bisphenols; (c) retaining said portion of said thermoplastic article in said bath for a period of time at least sufficient to form a dyed thermoplastic plastic article; (d) removing said dyed thermoplastic article from said bath; and (e) (i) contacting said dye bath with particulate activated carbon to form a mixture of said dye bath and particulate activated carbon; (ii) isolating from said mixture a dye-free liquid comprising water, said carrier and said diol; and (iii) optionally adding at least one dye to said dye-free liquid, thereby forming a further dye bath.