초록 ▼

An improved process for pelletizing thermoplastic material, particularly ultra low melt viscosity thermoplastic polymer, using an underwater pelletizer adapted to prevent extruded material from agglomerating in the pelletizer, which pelletizer comprising a cutting assembly having (1) a shroud fixedl

An improved process for pelletizing thermoplastic material, particularly ultra low melt viscosity thermoplastic polymer, using an underwater pelletizer adapted to prevent extruded material from agglomerating in the pelletizer, which pelletizer comprising a cutting assembly having (1) a shroud fixedly mounted on the outer periphery of the cutting assembly thereby preventing pellets from being trapped between the die face and the cutting assembly; and (2) novel knives contoured to conform in their angular positions to the curvature of the shroud to avoid pellet agglomeration.

대표청구항 ▼

A process for pelletizing a molten ultra low melt viscosity thermoplastic material having a melt viscosity of 300,000 cps or lower in a liquid medium, said process comprising the steps of: (a) extruding said molten ultra low melt viscosity thermoplastic material through an extrusion die plate said d

A process for pelletizing a molten ultra low melt viscosity thermoplastic material having a melt viscosity of 300,000 cps or lower in a liquid medium, said process comprising the steps of: (a) extruding said molten ultra low melt viscosity thermoplastic material through an extrusion die plate said die plate comprising: a die face at a downstream side of the die plate; a die ring formed on a downstream side of the die face, said die ring having a wear surface projecting outwardly from the die face and having a recessed cavity in the center of said projecting surface of said die ring, said recessed cavity having a bottom surface facing an inner surface of a hub; and a channel means extending from an upstream side of the die plate and the die ring to the die face, and said channel means forming an orifice in the die ring for said extruded material to exit the die plate; wherein said molten ultra low melt viscosity thermoplastic material is delivered from the upstream side of the die plate to the die face through said channel means and exits said die plate through said orifice in the die ring to form an extruded strand of said ultra low melt thermoplastic material; and (b) cutting said extruded strand of ultra low melt viscosity thermoplastic material into pellets using a cutting assembly, said cutting assembly comprising: said hub connected to a driving shaft; cutting blades mounted on the hub, said cutting blades having cutting edges; and a shroud element fixedly mounted on an outer periphery of the hub, said shroud element having a slots for inserting and affixing the cutting blades to the inner surface of the hub, wherein said shroud element substantially covers said recessed cavity of said die ring, said shroud element having an outer diameter substantially equal to an inner diameter of said recessed cavity thereby allowing said cutting edges of the cutting blades to move adjacent the downstream surface of the die ring, wherein substantially all the cut pellets are prevented from entering the recessed cavity by causing a portion of the shroud element to protrude into the recessed cavity of the die ring, the outer periphery of said shroud element being in close proximity to the inner diameter of the recessed cavity to provide a barrier against migration of said pellets into said recessed cavity, wherein said process further comprises advancing said shroud element and said cutting assembly toward the die ring to compensate for wearing of the cutting blades; wherein said shroud portion protruding into the recessed cavity reduces in size through grinding of said shroud portion against the bottom surface of said recessed cavity as said shroud element and said cutting assembly advances.