Nanjing GIANT Machinery Co.,Ltd.

In a process for extruding a thermoplastic resin in a single screw extruder, a barrel of a twin screw extruder has a channel, a feed section and a first melt seal located after the feed section. The process is improved by supplying solid polymer into the feed section and venting moisture extracted from the polymer during the conversion of the polymer from a solid to a melt into a vent area and through a rear vent positioned in the feed section.

This sheet production extruder can be further illustrated by the following examples of preferred embodiments thereof, although it will be understood that these examples are included merely for purposes of illustration and are not intended to limit the scope of the invention unless otherwise specifically indicated.

Example 1

Poly(ethylene terephthalate) pellets are loaded directly from a Gaylord container to a feed hopper of a 1.5-inch Killion single screw extruder without pre-drying. The hopper, which is open to the atmosphere, is filled with pellets. Pellet moisture level is measured on a Mark IV moisture analyzer to be 0.09 weight percent, which is higher than the 0.005 weight percent moisture level recommended for processing. The extruder is equipped with a vent port behind the feed hopper. The feed hopper is connected to a coarse vacuum pump pulling approximately 25 cubic feet per minute of air through the pellet bed. Barrel temperatures in the extruder are set from 500° to 550° F. Screw speeds are varied from 25 to 100 RPM.

Example 2

Pellets of poly(ethylene terephthalate) modified with 1,4-cyclohexanedimethanol are extruded using an identical process as in Example 1. Initial pellet moisture is 0.14 weight percent, which is higher than the 0.08 weight percent moisture level recommended for processing. Barrel zone temperatures are between 450° and 500° F. After extruding about 50 lbs. of pellets, the dry ice trap is found to contain approximately 22 ml of water in addition to polyester fines. Extrudate appearance also is improved.

The method of the present invention utilizing a rear vented single screw extruder for removal of moisture, other volatiles, and fines has significant advantages over the prior art. Applying vacuum to the pellets entering the extruder extracts surface moisture before the moisture has a chance to cause any hydrolysis. In a standard vented extruder, the surface moisture is already blended into the polymer before reaching the vent causing some hydrolysis degradation.

This invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the single screw extruder.