Twin-screw extruder including variable diameter of screws and barrel and kneading method using the twin-screw extruder including variable diameter of screws and barrel

A kneading method using a twin-screw extruder comprising:

• a barrel comprising a material feed opening at an end, and a discharge opening at the other end;
• and
• two screws provided in the barrel parallel to each other, maintaining a certain center distance C between a center of a shaft of one screw and a center of a shaft of the other screw, the two screws rotating in the same direction while the screws engage with each other, wherein
• each of the screws comprises a first screw portion, a second screw portion and a third screw portion from the end of the barrel toward the other end of the barrel,
• the barrel comprises a first barrel portion, a second barrel portion and a third barrel portion corresponding to the first screw portion, the second screw portion and the third screw portion,
• the two screws transfer a material fed through the material feed opening to the discharge opening while the material is kneaded,
• the kneaded material is discharged through the discharge opening,
• the first screw portions comprise double thread screws engaging with each other,
• a ratio D1/C of an external diameter D1 of the first screw portion to the center distance C ranges from 1.25 to 1.40,
• an insertion hole of the screws in the first barrel portion comprises a predetermined gap relative to the external diameter D1 of the first screw portion,
• the first screw portion transfers the material fed through the material feed opening such that the material passes through a first portion including the first screw portion and the first barrel portion,
• the second screw portion is structured such that an external diameter D2 is decreased from the external diameter D1 of the first screw portion to the external diameter D3 of the third screw portion such that the first screw portion is connected to the third screw portion,
• a hole diameter F2 of the insertion hole in the second barrel portion is decreased from an hole diameter F1 of the insertion hole in the first barrel portion such that the first barrel portion is connected to the third barrel portion,
• the second screw portion transfers the material transferred from the first portion such that the material passes through a second portion including the second screw portion and the second barrel portion,
• the third screw portions comprise triple thread screws engaging with each other,
• a ratio D3/C of an external diameter D3 of the third screw portion to the center distance C ranges from 1.05 to 1.10,
• the insertion hole of the screws in the third barrel portion comprises a predetermined gap relative to the external diameter D3 of the third screw portion, and
• the third screw portion transfers the material transferred from the second portion such that the material passes through a third portion including the third screw portion and the third barrel portion.