Patent EA-004417-B1 (EA)
Title: Method for extruding a continuos shaped body
Inventor: ZIKELI STEFAN
IPC: B29C48/08
Filed: 2001-04-12
Abstract: 1. A method for extruding a continuously molded body from an extrusion solution, in particular an extrusion solution containing cellulose, water and a tertiary amine oxide, comprising the following steps: - passing the extrusion solution through an extrusion duct of a predetermined length and a predetermined diameter to an extrusion duct orifice; - extruding the extrusion solution through the extrusion duct orifice to obtain an extruded, continuously molded body; - passing the continuously molded body through an air gap of a predetermined air gap height; - accelerating the continuously molded body in the air gap; characterized by the following steps: - controlling the heat flow density (11) substantially averaged over the air gap height (H) to obtain a value: where beta is the ratio of length (L) to diameter (D) of the extrusion duct and the value of the control parameter delta is at least 0.3. 2. The method according to claim 1, characterized in that the value of the control parameter delta is at least 0.6. 3. The method according to claim 2, characterized in that the value of the control parameter delta is at least 1.5. 4. The method according to claim 3, characterized in that the value of the control parameter delta is at least 2.2. 5. The method according to any one of the aforementioned claims, characterized by the following step: - controlling temperature VE of the extrusion solution in response to the mean value of acceleration a. 6. The method according to any one of the aforementioned claims, characterized by the following step: - conveying the extruded, continuously molded body (11) substantially without any tensile stress on a conveying means (25) arranged after the air gap (12) or a coagulation bath zone (14), to a withdrawal mechanism (15). 7. The method according to claim 6, characterized by the following step: - controlling the conveying speed of the conveying means (25) in response to the average acceleration a. 8. The method according to any one of the aforementioned claims, characterized by the following step: - withdrawing the extruded, continuously molded body (11) after passage through the air gap (12) by a withdrawal mechanism (15) at a withdrawal speed VA. 9. The method according to claim 8, characterized by the following step: - controlling the withdrawal speed VA of the continuously molded body (11) by the withdrawal mechanism (15) in response to acceleration a. 10. A method according to any one of the aforementioned claims, characterized by the following step: - controlling the extrusion speed VE of the continuously molded body (11) through the extrusion duct orifice (10) and/or the withdrawal speed VA of the continuously molded body (11) by the withdrawal mechanism (15) according to the following formula: where H is the air gap height and gamma a correction factor having a value between 7 and 7.4. 11. The method according to claim 10, characterized in that the value of the correction factor gamma is about 7.2. 12. A method according to any one of the aforementioned claims, characterized by the following step: - stretching the extruded, continuously molded body after its exit from the extrusion duct orifice in the air gap (12) by an air flow in the extrusion direction around the extruded, continuously molded body, wherein the flow velocity of air (13) is greater than the extrusion speed of the continuously molded body (11). 13. The method according to claim 12, characterized by the following step: - controlling the velocity of air (13) in response to the mean acceleration a in the air gap (12). 14. A method according to any one of the aforementioned claims, characterized by the following step: - controlling the heat flow density Q substantially averaged over the air gap height to obtain a value where beta is the ratio of length to diameter of the extrusion duct and the value of the control parameter alpha is at least 0.1. 15. The method according to claim 14, characterized in that the value of the control parameter alpha is at least 0.2. 16. The method according to claim 15, characterized in that the value of the control parameter alpha is at least 0.5. 17. The method according to claim 16, characterized in that the value of the control parameter alpha is at least 1.0. 18. The method according to any one of aforementioned claims 14-17, characterized by the following step: - controlling temperature TE of the extrusion solution in response to the heat flow density Q. 19. The method according to any one of aforementioned claims 14-18, characterized by the following step: - controlling temperature TL of the air surrounding the continuously molded body (11) in the air gap (12) in response to the heat flow density Q. 20. The method according to any one of the aforementioned claims, characterized by the following step: - controlling a temperature difference DeltaT=TE-TL between temperature TE of the extrusion solution and temperature TL of the air surrounding the continuously molded body (11) in the air gap (12) to obtain a value: where m is the throughput of the extrusion solution through the extrusion duct orifice in g/s, cE is the specific thermal capacity of the extrusion solution, in W/mm<3>, d the hole density of the bores provided in the die plate, in hole/mm<2>, and H in mm the length of the air gap. 21. The method according to any one of claims 14-20, characterized in that temperature TL is controlled at a temperature TE which is kept substantially constant. 22. The method according to any one of claims 14-20, characterized in that temperature TE is controlled at a temperature TL which is kept substantially constant. 23. The method according to any one of the aforementioned claims, characterized in that value beta is at least 2. 24. The method according to claim 21, characterized in that value beta is not more than 150. 25. The method according to claim 22, characterized in that value beta is not more than 100. 26. The method according to any one of the aforementioned claims, characterized in that the specific thermal capacity cE of the extrusion solution is at least 2.1 J/(g K). 27. The method according to any one of aforementioned claims 1-25, characterized in that the specific thermal capacity cE of the extrusion solution is at least 2.1 J/(g K).