Method for producing flame retardant polycarbonate resin composition pellet

A method for producing a polycarbonate resin composition pellet with a twin screw extruder, wherein the polycarbonate resin composition pellet comprises:

• 30 to 95 mass % of a resin pellet (A);
• 5 mass % or more, and less than 40 mass % of a phosphate ester flame retardant (B) that is a liquid at room temperature;
• 0 to 50 mass % of polycarbonate resin flake (C);
• 0 to 30 mass % of an ABS resin (D);
• and
• 0 to 15 mass % of an additive (E) other than component (B), based on a total amount of (A), (B), (C), (D) and (E) being 100 mass %, where the resin pellet (A) includes more than 40 mass % of a polycarbonate resin based on an amount of the resin pellet (A), and,
• the method comprises:
• feeding (A), (C), (D) and (E) in a twin screw extruder and kneading (A), (C), (D) and (E) in a first kneading zone to form a first kneaded mixture;
• then feeding (B) outside and downstream of the first kneading zone and kneading (B) and the first kneaded mixture in a second kneading zone to form a second kneaded mixture;
• and
• decompressing a vent that is downstream of the second kneading zone to devolatilize and extrude the second kneaded mixture, wherein:
• the first kneading zone has a configuration in which a length thereof is 2.5 D to 6.0 D, wherein D is a screw diameter, and consists of at least one selected from the group consisting of an R kneading disc having an angle of twist of 10° to 75°, an N kneading disc having an angle of twist of 75° to 105°, an L kneading disc having an angle of twist of −10° to −75°, an L screw, a sealing ring, a mixing screw and a rotor screw, and includes a combination of the R kneading disc, the N kneading disc and the L kneading disc;
• and
• the second kneading zone has a configuration in which the length thereof is 1.3 D to 4.0 D and consists of at least one selected from the group consisting of an R kneading disc having an angle of twist of 10° to 75°, an N kneading disc having an angle of twist of 75° to 105°, an L kneading disc having an angle of twist of −10° to −75°, an L screw, a sealing ring, a mixing screw and a rotor screw, and includes a combination of the R kneading disc, the N kneading disc and the L kneading disc.