METHOD FOR PRODUCING FILAMENTS OF POLYACRYLONITRILE AND EXTRUSION HEAD FOR CARRYING OUT SAID METHOD

Abstract

A method for producing filaments of polyacrylonitrile and an extrusion head for carrying out said method are provided, wherein the method comprises preparing a polyacrylonitrile polymer solution and passing said solution through an extruder plate that determines the formation of filaments, a central chamber being defined between the extruder plate and a floating plate connected to a vibrating system, said chamber being surrounded by a peripheral chamber into which the polymer solution is introduced under pressure. The polymer solution then passes through to the central chamber via small radial conduits that accelerate the material, and is subjected to vibration in the central chamber before passing through the extruder plate.

Claims

1. A method for producing filaments of polyacrylonitrile, comprising preparing a polyacrylonitrile polymer solution and passing said solution through an extruder plate that determines the formation of filaments, which are introduced in a coagulating medium, before the extrusion step in the extruder plate, the material of the polymer solution to be extruded is subjected to a vibration which is applied by a floating plate connected to a vibrating system, said material of the polymer solution passing into the pre-extrusion vibrating area via radial conduits that accelerate the material.

2. The method for producing filaments of polyacrylonitrile according to claim 1, wherein the vibration that is applied to the material of the polymer solution is generated by ultrasound by a piezoelectric device formed by a high-frequency sonotrode.

3. The method for producing filaments of polyacrylonitrile according to claim 1, wherein back pressure offsetting the pressure of the fluid material of the polymer solution is applied on the floating plate.

4. An extrusion head for carrying out the method of claim 1, comprising an inlet for introducing a polyacrylonitrile polymer solution under pressure and an extruder plate provided with calibrated holes for forming filaments of the polymer solution by making said solution pass through said extruder plate, wherein a central chamber is defined between the extruder plate and a floating plate, there being arranged around said central chamber a peripheral chamber into which the inlet opens, said peripheral chamber being communicated with the central chamber via small radial conduits, whereas a vibrating system is arranged connected to the floating plate.

5. The extrusion head according to claim 4, wherein the floating plate is held by means of elastic membranes.

6. The extrusion head according to claim 4, wherein a back pressure chamber provided with an inlet for introducing air under pressure therein is defined above the floating plate.

7. The extrusion head according to claim 4, wherein the vibrating system is connected to the floating plate in the middle area, where said floating plate forms a cavity communicated with the exterior through holes, a filter being arranged between said cavity and the central chamber.

8. The extrusion head according to claim 4, wherein the holes of the extruder plate have a diameter between 100 and 120 microns.

Description

DESCRIPTION OF THE DRAWINGS

[0025] FIG. 1 shows a production line for producing filaments of polyacrylonitrile, with the system for producing filaments object of the invention.

[0026] FIG. 2 shows an enlarged cross-section view of the phase for producing filaments of polyacrylonitrile according to the invention.

[0027] FIG. 3 is an enlarged cross-section view of the head for producing filaments of polyacrylonitrile according to the invention.

[0028] FIG. 4 is a view according to section IV-IV indicated in FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

[0029] The object of the invention relates to a system for forming filaments (1) of polyacrylonitrile (PAN), in order to produce tows (2) with the filaments (1) of polyacrylonitrile, in an installation, such as the one shown in FIG. 1, comprising a formation and coagulation phase (3) for the formation and coagulation of the filaments (1), one or more drawing phases (4) for drawing the tows (2) formed from the filaments (1), one or more washing phases (5), a drying phase (6), and a take-up reel (7) for taking up the obtained tows (2).

[0030] Before forming the filaments (1), PAN polymer solution is prepared and introduced under pressure in a head (8) wherein the filaments (1) are formed by passing the polymer solution through an extruder plate (9), said filaments (1) then passing into a coagulating medium (10) where a group of filaments (1) are brought together in order to form a tow (2), as seen in FIG. 2.

[0031] The head (8) has an inlet (11) through which the PAN polymer solution is introduced under pressure, said solution reaching a peripheral chamber (12) from where it enters, via small radial conduits (13), a central chamber (14) defined between the extruder plate (9) and a floating plate (15) which is held by means of elastic membranes (16) and connected to a vibrating system (17), preferably an ultrasound vibrating system, by means of a piezoelectric device formed by a high-frequency sonotrode, without this embodiment being limiting.

[0032] A back pressure chamber (18) is furthermore defined above the floating plate (15), into which chamber (18) air is introduced under pressure through an inlet (19); the vibrating system (17) is connected to the floating plate (15) in the middle area, wherein said floating plate (15) forms a cavity (20) communicated with the exterior through holes (21), a filter (22) being arranged between said cavity (20) and the central chamber (14).

[0033] This being the case, the PAN polymer solution that is introduced under pressure through the inlet (11) reaches the peripheral chamber (12) through which it is distributed, passing through the radial conduits (13) into the central chamber (14), from where it exits through the extruder plate (9) which is provided with a distribution of calibrated holes (23) measuring between 100 and 120 microns in diameter and determining the formation of the filaments (1).

[0034] The vibrating system (17) produces a vibrating operation of the floating plate (15), which exerts an action on the material of the polymer solution in the central chamber (14), which causes the micro-air bubbles to separate towards the source of the vibration, being eliminated, together with part of the solvent of the solution, through the filter (22) which allows the passage of the air bubbles and solvent, but not the material of the polymer.

[0035] Furthermore, the vibration allows reducing the pressure required for extruding the polymer solution through the holes (23) of the extruder plate (9), and it favors alignment of the molecules of the material in the axial direction of the filaments (1) that are formed, while the pressure of the back pressure chamber (18) offsets the pressure of the fluid material of the solution, reducing the load of the vibrating system (17).

[0036] In addition, the extruder plate (9) has a plane configuration, which favors pressure being the same on the entire extrusion surface, which is an important requirement for the flow rate of the material being extruded to be homogenous and for the resulting filaments (1) to have identical features.

[0037] Furthermore, the vibrating system allows increasing concentration homogeneity in the polymer solution, which leads to greater homogeneity in the material extruded through each of the holes (23), meaning that each of the filaments (1) contains the same amount of polymer and that the sections of the generated filaments (1) are more homogenous once they have been treated.

[0038] The radial conduits (13) furthermore accelerate the material in the passage from the peripheral chamber (12) to the central chamber (14), thereby determining a laminar flow of the material towards the middle area of said central chamber (14) under conditions which in turn favor the elimination of micro-air bubbles and the alignment of the molecules of the material in the formation direction of the filaments (1) through the extruder plate (9).

[0039] Use of vertical dry-jet wet spinning method is preferably envisaged, whereby the filaments (1) that are formed are cooled in the passage through an air gap (24) before the coagulating medium (10), wherein the high tensions that are generated in the passage through the extrusion holes (23) are reduced. In addition, the material passing through the extrusion holes (23) is made to have a higher polymer concentration, filaments (1) having better properties being obtained.

[0040] The final shape of the section of the filaments (1) is determined in the coagulating medium (10), depending on process speed, such that to obtain a suitable circular section, the speed must be slow, while the extruded material is subjected to tensions in the coagulating medium (10) that favor alignment of the molecules.