Method for extruding a continuous shaped body
AssigneeZimmer, Inc.
InventorsStefan Zikeli, Friedrich Ecker
Life of this patent
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Abstract
The present invention relates to a method of producing a continuous moulding (11) making use of an extrusion solution containing preferably water, cellulose and a tertiary amine oxide. The extrusion solution is extruded through an extrusion-channel opening (10) so as to form a continuous moulding. The continuous moulding is conducted through an air gap (12) in which it is drawn. In order to increase the non-looping property and in order to reduce the fibrillation tendency, the present invention is so conceived that the mean acceleration and/or the mean heat flow density are controlled in accordance with predetermined formulae.
Claims27
A method of extruding a continuous moulding making use of an extrusion solution, in particular an extrusion solution containing cellulose, water and a tertiary amine oxide, said method comprising the following steps:
- conducting the extrusion solution through an extrusion channel having a predetermined length and a predetermined diameter up to an extrusion-channel opening;
- extruding the extrusion solution through the extrusion-channel opening so as to form an extruded continuous moulding;
- conducting the extruded continuous moulding through an air gap having a predetermined air-gap height;
- accelerating the continuous moulding in the air gap;
- characterized by the following method step:
- controlling the acceleration of the continuous moulding (11), which is averaged essentially over the air-gap height (H), to a value of
- 7 a _ = 10 δ [ 1 β ] 0 , 3 ,
- wherein β is the ratio of the length (L) to the diameter (D) of the extrusion channel (8) and wherein the value of the control parameter δ is at least 0.3.
A method according to one of the above-mentioned claims, characterized by the following method step:
- controlling the extrusion velocity VE of the continuous moulding (11) through the extrusion-channel opening (10) in dependence upon the mean acceleration {overscore (a)}.
A method according to one of the above-mentioned claims, characterized by the following method step:
- conveying the extruded continuous moulding (11) in a substantially tensile stress-free manner on a conveying means (25) to a draw-off unit (15), said conveying means (25) being arranged after the air gap (12) or a coagulation bath zone (14).
A method according to one of the preceding claims, characterized by the following method step:
- drawing off the extruded continuous moulding (11), when it has passed the air gap (12), by means of a draw-off unit (15) at a drawing-off velocity VA.
A method according to one of the above-mentioned claims, characterized by the following method step:
- controlling the extrusion velocity VE of the continuous moulding (11) through the extrusion-channel opening (10) and/or the drawing-off velocity VA of the continuous moulding (11) by the draw-off unit (15) according to the following formula:
- ν2A−ν2E=γ·H·{overscore (α)},
- wherein H is the air-gap height and γ is a correction factor having a value between 7 and 7.4.
A method according to one of the above-mentioned claims, characterized by the following method step:
- drawing the extruded continuous moulding when it has left the extrusion-channel opening in the air gap (12) by means of an airflow flowing around the continuous moulding in the direction of extrusion, the flow velocity of the air (13) exceeding the extrusion velocity of the continuous moulding (11).
A method according to one of the preceding claims, characterized by the following method step:
- controlling the heat flow density Q, which is essentially averaged over the air-gap height, to a value of
- 8 Q = 0 , 004 α · [ 1 β ] 0 , 3
- wherein β is the ratio of the length to the diameter of the extrusion channel and wherein the value of the control parameter α is at least 0.1.
A method according to one of the above-mentioned claims, characterized by the following method step:
- controlling a temperature difference ΔT=TE-TL between the temperature TE of the extrusion solution and the temperature TL of the air surrounding the continuous moulding (11) in the air gap (12) to a value of:
- 9 Δ T = H d · 0 , 004 m . · c E · α · [ 1 β ] 0 , 3
- wherein {dot over (m)} is the mass flow of the extrusion solution through the extrusion-channel opening in g/s, CE is the specific heat capacity of the extrusion solution in W/mm3, d is the hole density of the holes provided on the nozzle disk in hole/mm2 and H is the length of the air gap in mm.
A method according to one of the above-mentioned claims, characterized in that the value β is at least 2.
A method according to one of the above-mentioned claims, characterized in that the specific heat capacity cE of the extrusion solution is at least 2.1 J/(g K).
A method according to one of the above-mentioned claims, characterized in that the specific heat capacity cE of the extrusion solution is at least 2.9 J/(g K).
Dependencies are inferred from the claim text.