Oriented film producing facility with thickness and orientation control means

An oriented film producing facility comprising:

• a facility for melting a molding material;
• an extruder having a die for shaping the molding material to a not-oriented film;
• a base film molding apparatus for producing a base film by cooling the not-oriented film shaped through the die;
• a longitudinal drawing machine for drawing the cooled base film in a longitudinal direction with a low speed roll and a high speed roll;
• a lateral drawing machine for drawing the longitudinally drawn film in a lateral direction by holding both edges of the longitudinally drawn film;
• a thickness measuring apparatus for measuring a thickness of the longitudinally drawn film in real time after the cooled base film is drawn in the longitudinal direction and for generating a signal corresponding to the thickness measured;
• a retardation measuring apparatus for measuring a retardation of the longitudinally drawn film caused by birefringence in real time after the cooled base film is drawn in the longitudinal direction,
• a computing apparatus for computing a degree of orientation of the longitudinally drawn film from the measured retardation by dividing the measured retardation by the measured thickness and for generating a signal corresponding to the computed degree of orientation;
• and
• a computer for processing the signals corresponding to the measured thickness and to the computed degree of orientation and for outputting a control signal to a control means for changing a longitudinal draw ratio in longitudinal drawing by the longitudinal drawing machine based on results of thickness and orientation comparison operations so that the measured thickness and the computed degree of orientation coincide with preset target values of thickness and degree of orientation to thereby control a drawing condition of the longitudinal drawing machine in accordance with the control signal wherein the computer comprises a thickness comparison means for performing the thickness comparison operation to compare a preset thickness with the measured thickness and an orientation comparison means for performing the orientation comparison operation to compare a preset degree of orientation with the computed degree of orientation.