Patent ID: 8557154

Claim:
A method for preparing polyolefin pellets in a spherical shape by cutting a raw material containing a molten polyolefin resin which is extruded from an extrusion orifice formed on a die surface of a die into a predetermined length with an underwater cutter which is set in close vicinity to said die surface of said die and rotates in water, thereby obtaining polyolefin pellets, wherein the method satisfies the following conditions (A) to (C) simultaneously: (A) an average linear velocity u of said raw material passing through said extrusion orifice as defined by the equation (Eq-1) is equal to or more than 50 mm/sec and equal to or less than 650 mm/sec, (B) a virtual aspect ratio r as defined by the equation (Eq-2) is equal to or less than 1.6, and (C) r/u as obtained by dividing the virtual aspect ratio r by the average linear velocity u is equal to or more than 0.002, u = Q π × R 2 ( Eq ⁢ - ⁢ 1 ) r = Q × t 2 × π × R 3 ( Eq ⁢ - ⁢ 2 ) in said equations (Eq-1) and (Eq-2), Q is an extrusion flow rate (mm 3 /sec) of said raw material per orifice of the extrusion orifices. R is a radius (mm) of the extrusion orifice, and more than 1.0 mm and equal to or less than 3.0 mm, and t is a cutting time (sec) defined as an inverse number of the number which is obtained by multiplying the number of revolutions of the underwater cutter by the number of blades of the underwater cutter, and more than 0.005 sec and equal to or less than 0.05 sec.