Twin-screw extruder and kneading method using twin-screw extruder

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 shaft distance C, 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 Dl of the first screw portion to the shaft 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 decreases gradually from the first screw portion toward the third screw portion,
• the insertion hole of the screws in the second barrel portion is structured so as to decrease gradually from the first barrel portion toward 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 shaft 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.