Pigments are commonly added to tetrafluoroethylene (TFE) polymer resins to create color in articles made of the resins. Heretofore, pigments have been added by dry mixing the pigment directly into the resin; however, due to tendency of the pigment particles to adhere to one another, it is difficult to obtain uniformly dispersed particles. It has also been known heretofore to add pigment directly to aqueous dispersions of non-melt-processible TFE polymer especially when the polymer has been produced by the aqueous dispersion polymerization process. Upon coagulation of the polymer and the pigment particles, the pigment becomes mixed with the coagulated polymer. Unfortunately, pigments are generally hydrophobic and tend to clump during the agitation that is needed to coagulate the polymer, thus resulting in poorly dispersed pigment.
The precipitated polymer produced by the aqueous dispersion polymerization process is referred to in the TFE polymer field as "fine powder" resin and will be so referred to herein.
USPTO Backgrounds
USPTO Backgrounds