Extrusion die and extrusion method of sheet using the same

An extrusion die comprising:

• a storage part configured to hold a raw material, the storage part defining a first width in a lateral direction perpendicular to a flow direction of the raw material;
• a pressure part configured to move the raw material through the storage part in the flow direction at a predetermined pressure;
• a first die defining a second width in the lateral direction that is less than the first width, such that a flow width of the raw material passing through the storage part becomes narrower as the raw material passes into the first die;
• a second die in fluid communication with the first die, the second die defining a width in the lateral direction that increases from the second width to a third width that is greater than the second width, such that the flow width of the raw material passing through the first die becomes wider and a flow thickness in a depth direction perpendicular to the lateral direction and the flow direction becomes smaller as the raw material passes through the second die;
• and
• a heating part configured to heat the raw material passing through the second die, an entirety of the heating part being located closer to an outlet side of the second die than an inlet side,
• wherein a start portion and an end portion of a heating zone of the heating part each define a curved line shape transverse to the flow direction of the raw material, both the start portion and the end portion have a fan arc shape, and the fan arc shape of the end portion defines a first arc length that is greater than a second arc length of the fan arc shape of the start portion.