Apparatus and method for controlled pelletization processing

Abstract

An apparatus and process to maintain control of the temperature of low-melting compounds, high melt flow polymers, and thermally sensitive materials for the pelletization of such materials. The addition of a cooling extruder, and a second melt cooler if desired, in advance of the die plate provides for regulation of the thermal, shear, and rheological characteristics of narrow melting-range materials and polymeric mixtures, formulations, dispersions or solutions. The apparatus and process can then be highly regulated to produce consistent, uniform pellets of low moisture content for these otherwise difficult materials to pelletize.

1 - 27 . (canceled) 
     
     
         28 . A method for pelletizing materials which are otherwise difficult to pelletize in a pelletizer processing line comprising the following steps in the recited sequence:
 forming a melt to be pelletized, said melt including at least two materials to be blended;   passing the melt through a melt cooler to reduce the temperature of the melt to allow extrusion of the melt;   passing said cooled melt through a cooling extruder located downstream of the melt cooler, the cooling extruder including at least one screw that increases dispersive homogeneity of the melt to reduce or eliminate phase separation of the at least two blended materials as the melt is further cooled in the cooling extruder to an appropriate temperature for extrusional pelletization;   feeding the melt into a pelletizer having an extrusion die and pelletizing the melt; and   drying said pellets in a drying device.   
     
     
         29 . The method as claimed in  claim 28 , wherein the pelletizing step is carried out in an underwater, hot face, strand or water ring pelletizer. 
     
     
         30 . The method as claimed in  claim 28 , wherein said step of forming a melt to be pelletized includes filtering the melt and pressurizing the melt sufficiently to ensure its passage through the cooling extruder and through said extrusion die of said pelletizer. 
     
     
         31 . The method as claimed in  claim 28 , wherein, after said melt is passed through said cooling extruder, the melt is further pressurized and passed through a screen changer before entering said extrusion die of the pelletizer. 
     
     
         32 . The method as claimed in  claim 28 , wherein said step of forming a melt to be pelletized includes passing the melt through a diverter valve in order to divert said melt from the processing line when desired. 
     
     
         33 . The method as claimed in  claim 28 , wherein the step of passing the melt through the cooling extruder includes the addition of thermally sensitive ingredients through one or more feeders of said cooling extruder, said sensitive ingredients being solid or liquid and selected from the group consisting of rheological additives, miscibilizing agents, surfactants, expanding agents, catalysts, inhibitors, antioxidants, chain extenders, nucleation agents, flavors, fragrances, colorants, devolatilizing agents, chemical scavengers, or additives appropriate to the application for the materials being pelletized. 
     
     
         34 . The method as claimed in  claim 28 , wherein, after passing said melt through said cooling extruder, the melt is passed through a heat exchanger located downstream of said cooling extruder for additional regulation of the temperature and final mixing of the melt before entering said extrusion die of the pelletizer. 
     
     
         35 . The method as claimed in  claim 28 , wherein, before passing said melt through said melt cooler, the melt is passed through a first extruder for shear mixing and melting. 
     
     
         36 . The method as claimed in  claim 28 , wherein a temperature of said melt during the forming step is between about 200° F. and about 600° F., a temperature of the melt after the melt cooler is between about 100° F. and about 550° F., and a temperature of the melt at the die plate, after passing through the cooling extruder, is between about 75° F. and about 400° F. 
     
     
         37 . The method as claimed in  claim 28 , wherein a temperature of said melt during the forming step is between about 300° F. and about 400° F., a temperature of the melt after the melt cooler is between about 100° F. and about 350° F., and a temperature of the melt at the die plate, after passing through the cooling extruder, is between about 150° F. and about 250° F. 
     
     
         38 . The method as claimed in  claim 28 , wherein a temperature of water for the underwater pelletizer is between about 40° F. and about 200° F. 
     
     
         39 . An apparatus for pelletizing materials which are otherwise difficult to pelletize in a pelletizer processing line comprising:
 a primary mixer and/or an extruder for forming a melt to be pelletized, said melt including at least two materials to be blended;   a melt cooler located downstream of said mixer and/or extruder for receiving the formed melt, said melt cooler reducing a temperature of said received melt to a temperature to allow extrusion of the melt;   a cooling extruder located downstream of said melt cooler to receive the melt after the melt cooler, the cooling extruder including at least one screw that increases dispersive homogeneity of the melt to reduce or eliminate phase separation of the at least two blended materials as the melt is further cooled in the cooling extruder to an appropriate temperature for extrusional pelletization;   a pelletizer located downstream of said cooling extruder, said pelletizer having an extrusion die and pelletizing the melt; and   a drying device for drying said pellets.   
     
     
         40 . The apparatus as claimed in  claim 39 , wherein said cooling extruder is a single, twin, multiple screw, or a ring extruder 
     
     
         41 . The apparatus as claimed in  claim 39 , wherein the pelletizer is an underwater, hot face, strand or water ring pelletizer. 
     
     
         42 . The apparatus as claimed in  claim 39 , wherein the melt cooler has a shell housing and at least one tube with static mixing blades within said at least one tube to further mix the blended material and bring more of the blended material into contact with a wall of the at least one tube outside of which is a flow or oil or water coolant circulating within the shell housing. 
     
     
         43 . The apparatus as claimed in  claim 39 , wherein the melt cooler has a shell housing and at least one tube with static mixing blades within said at least one tube to further mix the blended material and bring more of the blended material into contact with a wall of the at least one tube, and an oil coolant circulating within the shell housing in a countercurrent flow pattern to melt flow. 
     
     
         44 . The apparatus as claimed in  claim 39 , wherein said processing line includes one or more pumps sufficient to pressurize the melt to ensure its passage through the cooling extruder and through said extrusion die of said pelletizer. 
     
     
         45 . The apparatus as claimed in  claim 39 , wherein said processing line includes one or more pumps after said cooling extruder to further pressurize said melt before entering said extrusion die of the pelletizer. 
     
     
         46 . The apparatus as claimed in  claim 39 , wherein said processing line includes a diverter valve in advance of said cooling extruder to divert the melt from the processing line when desired. 
     
     
         47 . The apparatus as claimed in  claim 39 , wherein said cooling extruder includes one or more feeders for the addition of one or more thermally sensitive ingredients. 
     
     
         48 . The apparatus as claimed in  claim 39 , wherein said processing line includes a heat exchanger after said cooling extruder for additional regulation of the material temperature and final mixing before entering said extrusion die of the pelletizer. 
     
     
         49 . The apparatus as claimed in  claim 39 , wherein said processing line includes a first extruder positioned upstream of said melt cooler, said melt passing through said first extruder for shear mixing and melting before passing into said melt cooler. 
     
     
         50 . The apparatus as claimed in  claim 39 , wherein the melt cooler is a coil-type, scrape wall, plate and frame, or a shell and tube design with or without static mixers, or a U-style tube design with or without static mixers. 
     
     
         51 . A method for pelletizing materials which are otherwise difficult to pelletize in a pelletizer processing line comprising:
 forming a melt to be pelletized, said melt including at least two materials to be blended and having a temperature between about 200° F. and about 600° F.;   passing the melt through a melt cooler to reduce the temperature of the melt to a temperature, after the melt cooler, of between about 100° F. and about 550° F.;   passing said cooled melt through a cooling extruder located downstream of the melt cooler, the cooling extruder including at least one screw that increases dispersive homogeneity of the melt, said melt being further cooled in the cooling extruder to a temperature between about 75° F. and about 400° F. for extrusional pelletization; and   feeding the melt into a pelletizer having an extrusion die and pelletizing the melt.   
     
     
         52 . The method as claimed in  claim 51 , wherein the temperature of said melt during the forming step is between about 300° F. and about 400° F., the temperature of the melt after the melt cooler is between about 100° F. and about 350° F., and the temperature of the melt at the die plate, after passing through the cooling extruder, is between about 150° F. and about 250° F.