Method for producing a shaped body from a polycondensate

Abstract

The invention relates to a method for producing a shaped body, particularly a profiled piece, from a polycondensate, particularly a polyester such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene terephthalate (PBT) or one of the copolymers thereof. According to the invention, the polycondensate is melted over the course of the method and, later, is rendered solid once again. The invention is characterized in that the total time, during which the temperature of the polycondensate over the course of the method is higher than the melting temperature of the polycondensate, is less than approximately 60 seconds. The method is preferably carried out by means of a multiple screw extruder, whereby the degassing and/or drying of the polycondensate ensues in the solid state at a pressure less than the atmospheric pressure and/or while adding an inert gas. The period of time during which the polycondensate dwells in the extruder after having been melted therein is less than approximately 15 seconds.

1 . A method for manufacturing a molded part, in particular a profile, out of a polycondensate, wherein the polycondensate is melted and later solidified again during the process, characterized in that the overall time for which the temperature of the polycondensate exceeds the melting point of the polycondensate during the process measures less than about 60 seconds.  
     
     
         2 . The method according to  claim 1 , characterized in that the overall time for which the temperature of the polycondensate exceeds the melting point of the polycondensate during the process measures less than about 30 seconds.  
     
     
         3 . The method according to  claim 1  or  2 , characterized in that the residual water content in the melt exceeds 200 ppm.  
     
     
         4 . The method according to one of  claims 1  to  3 , characterized in that the polycondensate is a polyester, in particular polyethylene terephthalate, or one of its copolymers.  
     
     
         5 . The method according to one of the preceding claims, characterized in that the initial form of the polycondensate is present as a loose material, e.g., granulate, flocks or chips, and has an apparent density ranging from 200 kg/m 3  to 950 kg/m 3 .  
     
     
         6 . The method according to one of  claims 4  to  5 , characterized in that the polyethylene terephthalate is present as bottle recyclate.  
     
     
         7 . The method according to one of the preceding claims, characterized in that polycondensate starting material is subjected to partial preliminary drying before melting.  
     
     
         8 . The method according to one of the preceding claims, characterized in that it has a degassing step for removing volatile contaminants and/or decomposition products from the polycondensation melt.  
     
     
         9 . The method according to one of the preceding claims, characterized in that an extruder is used to melt the polycondensate.  
     
     
         10 . The method according to  claim 9 , characterized in that a two-screw or multi-screw extruder, in particular a ring extruder, is used to melt the polycondensate.  
     
     
         11 . The method according to one of  claims 9  to  10 , characterized in that the polycondensate is introduced into the extruder in a solid state, the polycondensate is heated to a temperature below the melting point, and the polycondensate is degassed and/or dried, characterized in that the polycondensate is degassed and/or dried in a solid state at a pressure of below atmospheric pressure and/or with the addition of an inert gas.  
     
     
         12 . The method according to one of  claims 9  to  11 , characterized in that the overall time for which the polycondensate is present as a melt during the process consists of a first time segment in which the polycondensate still remains in the extruder after melted in the extruder, and a second time segment for which the still melted polycondensate is processed outside the extruder,  
     
     
         13 . The method according to  claim 12 , characterized in that the first time segment measures less than about 15 seconds.  
     
     
         14 . The method according to  claim 13 , characterized in that the first time segment measures less than about 10 seconds.  
     
     
         15 . The method according to one of  claims 9  to  14 , characterized in that the processing of the melted polycondensate outside the extruder includes a melt filtration step  
     
     
         16 . The method according to one of  claims 9  to  15 , characterized in that the processing of the melted polycondensate outside the extruder involves the use of a melt pump.  
     
     
         17 . The method according to one of  claims 9  to  16 , characterized in that the processing of the melted polycondensate outside the extruder involves the use of a molding die.  
     
     
         18 . The method according to  claim 17 , characterized in that the molding die has an outlet with a size exceeding 10 mm, in particular exceeding 25 mm, in at least one direction (width or height).  
     
     
         19 . The method according to  claim 17  or  18 , characterized in that the polycondensate is cooled at an initial rate exceeding 300° C. per minute after exiting the molding die.  
     
     
         20 . The method according to  claim 19 , characterized in that the polycondensate is cooled at an initial rate exceeding 600° C. per minute, in particular exceeding 1200° C., after exiting the molding die.  
     
     
         21 . The method according to one of the preceding claims, characterized in that an additive is incorporated into the polycondensate.  
     
     
         22 . A molded part, in particular a profile, manufactured out of a polycondensate using a method according to one of the preceding claims.  
     
     
         23 . The molded part according to  claim 22 , characterized in that the average acetaldehyde content of the molded part measures less than 3 ppm, in particular less than 2 ppm.