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A Method for Providing Low Oligomer Content Polyethylene Terephthalate

IP.com Disclosure Number: IPCOM000129139D
Publication Date: 2005-Sep-28
Document File: 1 page(s) / 22K

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Abstract

A two step polymerization process to produce a Polyethylene terephthalate (PET) homopolymer with reduced oligomer content. This process consists of a melt phase process followed by a solid state polymerization process. This two step process can produce a PET with an inherent viscosity of 0.60 dl/g having approximately 30% of the oligomer content of a similar viscosity material made solely by a melt process. This lower oligomer content PET will run cleaner in extrusion and sheet stretching processes.

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A Method for Providing Low Oligomer Content Polyethylene Terephthalate

Polyethylene terephthalate (PET) for sheet and film making processes is typically made in a continuous or a batch polymerization process to an inherent viscosity (IV) typically in the range of 0.55 to 0.65 dl/g.  This polymer is then extruded through strand dies, quenched and chopped into pellets.  The resulting PET will have an equilibrium concentration of oligomers between 1.8 to 2.2 weight percent having a molecular weight of less than 1000.  Low molecular weight species will off-gas during the casting and/or stretching of sheet.  These low molecular weight species will then migrate through the process equipment condensing to solid form on equipment surfaces.  The solids, sometimes referred to as sublimate, will drop off on to the sheet causing cleanliness issues.

A two step polymerization process has been found to significantly reduce these oligomers.  This process combines the typical melt process with a solid state polymerization (SSP) process.  Polymers made by this process have been found to have oligomer contents as low as a 0.7 weight percent of molecular species having a molecular weight of less than 1000. When this material is melted the oligomers begin to reform as the polymer begins to move back towards an equilibrium state.  With short enough melt residence times the oligomeric content will still remain lower than the 1.8 to 2.2 weight percent level.  This lower content of oligomer...