Method and apparatus for making crystalline PET pellets

Abstract

A method and apparatus for underwater pelletizing and subsequent drying of polyethylene terephthalate (PET) polymers and other high temperature crystallizing polymeric materials to crystallize the polymer pellets without subsequent heating. High velocity air or other inert gas is injected into the water and pellet slurry line to the dryer near the pelletizer exit. Air is injected into the slurry line at a velocity of from about 100 to about 175 m³/hour, or more. Such high-speed air movement forms a vapor mist with the water and significantly increases the speed of the pellets into and out of the dryer such that the PET polymer pellets leave the dryer at a temperature sufficient to self-initiate crystallization within the pellets. A valve mechanism in the slurry line after the gas injection further regulates the pellet residence time and a vibrating conveyor after the dryer helps the pellets to achieve the desired level of crystallinity and to avoid agglomeration.

Description

RELATED APPLICATIONS [0001] This is a continuation-in-part application of copending application, Ser. No. 10 / 717,630, filed Nov. 21, 2003.BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present invention generally relates to a method and apparatus for underwater pelletizing and subsequent drying of polyethylene terephthalate (PET) polymers. More specifically, the present invention relates to a method and apparatus for underwater pelletizing PET polymers and subsequent drying of the PET polymer pellets in a manner to self-initiate the crystallization process of the PET particles and produce pellets having a desired level of crystalline structure rather than an amorphous structure. [0004] 2. Description of the Prior Art [0005] Underwater pelletizing systems for producing pellets of polymeric or other plastic materials has been known for many years. The starting materials such as plastic polymers, coloring agents, additives, fillers and reinforcing agents, and m...

AI Technical Summary

Benefits of technology

[0013] The present invention is directed to an underwater pelletizing system that produces PET pellets in a hot enough condition to self-initiate the crystallization process therein and ultimately provide a sufficiently crystalline character such that the PET pellets do not require a separate heating step in order to undergo end user processing. It has been discovered that this elevated heat condition can be accomplished by reducing the residence time of the pellets in the water slurry in order to leave enough heat in the PET pellets during the drying stage so that the crystallization process is initiated from inside the pellets. To do this, it is necessary to separat

Problems solved by technology

A major drawback of using underwater pelletizing, as well as other pelletizing systems, for processing PET into pellet shapes is the typically amorphous condition of these pellets when they leave the dryer of the underwater pelletizing system.

Typically, increasing the water flow through the water box of the underwater pelletizer and increasing the water temperature, along with pipe dimensional changes and reducing the distance between the pelle

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