|Chemical company Eastman announced on its website they won a court case (link). against competitor Wellman over patents related to high clarity and high purity PET resins that can be used for the production of PET bottles. The embattled Wellman patents are numbered 7094863 and 7129317 ,date from May and November 2004 (filed) to 2006 (granted) and are now now made obsolete. They deal with a variety of PET that crystallises at a lower temperature and regular PET. In the final stage of PET bottle production a so-called preform (a small test tube shaped container) is reheated to a temperature just above the glass-transition and blow molded to its final dimensions. Slower crystallizing PET means lower processing temperatures without loosing clarity (= crystallisation). The patents also specify how this was done: replacing expensive antimony or germanium catalysts by catalysts based on titanium such as tetrabutyltitanate, titanium being a poor nucleator in crystallisation .Titanium can cause yellowing of the resin but the patents also specify the addition of cobalt which in addition to being a catalyst itself has a native blue color cancelling out the titanium-yellow. |
A similar Eastman patent number 7300967 (filed November 12, 2004 granted November 27, 2007) also deals with titanium for improved reheat & clarity but for an entirely different reason: the preforms are reheated with infrared lamps and metallic titanium particles (not titanium catalysts) increases heat absorption in the infrared without affecting color.
Eastman in turn is suing Indorama (Link Link) and DAK LCC (Link Link) for unauthorized use of its IntegRex PET (introduced 2007). Just one of the patents covering this technology is number 5597891 (filed in 1995) and one key aspect is the elimination of so-called solid-stating (Link). In this process PET of intermediate melt viscosity is post-polymerized in the solid state (high vacuum, high temperature, batch or continuous, for many hours and therefore expensive!) to a high viscosity quality that can be used in bottle manufacture. Incidentally the process also removes any acetaldehyde in the resin that can negatively affect the flavor of any liquid in PET bottles produced from it. The trick as described in the patent is to remove volatiles during the extrusion phase. The Indorama and DAK cases are interesting because Eastman sold some of its (outdated?) PET business to each party in 2007.