METHOD FOR PRODUCING POLYMERS IN WHICH FILLERS ARE INCORPORATED AND HOMOGENEOUSLY DISTRIBUTED

Abstract

For the production of polymers in which there are fillers with particle sizes below 10 μm incorporated and homogeneously distributed, a polymer starting material is input into a twin-screw extruder and is melted there to give a melt. In a conveying and mixing section, a suspension, which is formed of the fillers and of a carrier liquid, is injected into the melt. The melt viscosity is reduced by injection of the carrier liquid in the conveying and mixing section in that a cleavable polycondensate is used as polymer and low-molecular-weight cleavage product arising during the polycondensation is used as carrier liquid, and therefore the molten polymer is at least to some extent depolymerized within the conveying and mixing section. That the mixture, which is formed of the melt whose viscosity is reduced by cleavage, of the remainder of the carrier liquid and of the fillers, is homogenized.

Claims

1. A method for the production of polymers in which there are fillers incorporated and homogeneously distributed, the method comprising: providing fillers with particle sizes below 10 μm; inputting a polymer starting material into a twin-screw extruder and is melted there to provide a melt; and injecting, in a conveying and mixing section, a suspension comprised of the fillers and of a carrier liquid, into the melt; reducing the melt viscosity by injection of the carrier liquid in the conveying and mixing section such that a cleavable polycondensate is used as a polymer and low-molecular-weight cleavage product arising during the polycondensation is used as carrier liquid, and therefore the molten polymer is at least partially depolymerized within the conveying and mixing section; homogenizing the mixture, which is formed of the melt whose viscosity is reduced by cleavage, of the remainder of the carrier liquid and of the fillers; and increasing, after the homogenization, the viscosity of the melt by use of a devolatilizing extruder in which, for the viscosity increase, a polycondensation is carried out, in that a vacuum is applied and the cleavage product is removed from the devolatilizing extruder via the vacuum.

2. The method as claimed in claim 1, wherein, before the suspension is injected, carrier liquid is injected into the melt in order to induce the cleavage.

3. The method as claimed in claim 1, wherein a hydrolysable polycondensate is used as polymer and water is used as carrier liquid, and therefore the melt is hydrolyzed within the conveying and mixing section, wherein the mixture of the melt whose viscosity is reduced by hydrolysis, of the remainder of the water and of the fillers is homogenized, and wherein, after the homogenization, the viscosity of the melt is finally in turn increased by use of a devolatilizing extruder in which, for the viscosity increase, a polycondensation is carried out, in that a vacuum is applied and the water is removed from the devolatilizing extruder via the vacuum.

4. The method as claimed in claim 3, wherein the polymer is polyester.

5. The method as claimed in claim 1, wherein a polycondensate produced with elimination of a monohydric or polyhydric alcohol is used as polymer, and a monohydric or polyhydric alcohol is used as carrier liquid.

6. The method as claimed in claim 1, wherein a control device controls the individual process steps and initiates a start-up procedure in which initially only carrier liquid is injected into the conveying and mixing section to reduce the viscosity of the polymer starting material, and wherein, after subsequent switchover by the control device from carrier-liquid injection to suspension injection the suspension is incorporated into the low-viscosity melt.

7. The method as claimed in claim 1, wherein the pressure in an injection chamber of the twin-screw extruder is between 25 bar and 50 bar.

8. The method as claimed in claim 7, wherein the pressure in the injection chamber is adjusted or controlled to 5 bar above to below the phase-transition boundary of the carrier liquid.

9. The method as claimed in claim 7, wherein the pressure in the injection chamber is controlled to between 20 bar and 200 bar, wherein a pressure sensor in the injection chamber provides the actual pressure values to the control device, which sets the required pressure by influencing an adjustable melt-flow restrictor arranged between the twin-screw extruder and the devolatilizing extruder, and/or by influencing a suspension pump.

10. The method as claimed in claim 7, wherein an inert gas is added in the region of the injection chamber in order to maintain or improve control of the pressure.

11. The method as claimed in claim 1, wherein the control device controls the evacuation rate in the devolatilizing extruder by adjusting the reduced pressure for a specified flow rate and flow velocity, thus permitting adjustment of the viscosity of the discharged melt.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0038] The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawing which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein the sole FIGURE shows an extruder and a devolatilizing extruder according to an exemplary embodiment.

DETAILED DESCRIPTION

[0039] The FIGURE shows a twin-screw extruder 1 and a devolatilizing extruder 2, both these two devices being arranged in succession in the form of a cascade. The twin-screw extruder has a feed hopper 3, by way of which polymer starting material can be introduced gravimetrically into the twin-screw extruder. In the twin-screw extruder 1, the polymer starting material is plastified and transported by way of a conveying and mixing section 4 to the outgoing end 5′ of the twin-screw extruder 1. The outgoing end 5′ of the twin-screw extruder 1 leads, by way of a flow restrictor 5, directly into the ingoing end 6 of the devolatilizing extruder 2.

[0040] In the region of the conveying and mixing section 4, the twin-screw extruder 1 has an injection chamber 7 with injection nozzle 7′, which can be fed from a water-supply line 8 or from a suspension pump 9, where the suspension pump 9 can withdraw the suspension from a suspension silo 10. The suspension silo 10 has mixing units 11, by way of which the filler particles remain distributed as uniformly possible in the suspension, with no agglomeration of the filler particles in the suspension.

[0041] The devolatilizing extruder 2 has a vacuum connection 12, i.e. in this case merely a devolatilizing duct by way of which, in the region of an evacuation drum 13, the melt conveyed from the twin-screw extruder 1 into the devolatilizing extruder 2 can be devolatilized.

[0042] The melt is introduced by way of a discharge unit 14, e.g. a screw or pump, into a discharge die 15.

[0043] Coupled to the drive 17 of the twin-screw extruder 1 and the drive 18 of the devolatilizing extruder 2 there is a control device 16. It is thus possible to achieve ideal control of the plastifying and mixing procedure, and of the devolatilizing procedure, separately from one another and respectively per se. Also controlled by way of the control device 16, although this is not depicted in detail, are the intake of the feed hopper 3, the suspension pump 9, the mixing unit 11, the water-supply line 8, adjustable conveying and shearing elements 19 of the devolatilizing extruder 2, the vacuum connection 12, or the discharge unit 14. However, other sensors not depicted, e.g. the pressure gauge 20 or pressure sensor on the vacuum connection, temperature sensor, RPM counter, etc. transmit signals to the control device 16, which controls not only start-up but also production by way of the cascade arrangement.

[0044] In the twin-screw extruder 1, the polymer starting material is first plastified, and is transported by way of the conveying and mixing section 4 to the outgoing end 5. The control device 16 here controls the drive 17 in relation to rotation rate and power consumption and, as determined by the signals from a pressure sensor 21, the flow restrictor 5 in relation to the pressure generated in the conveying and mixing section 4.

[0045] By way of a gas connection 22 likewise controllable by the control device 16 it is possible to feed inert gas into the injection chamber 7 under appropriately controllable pressure, in order that the viscosity of the melt can be even more effectively influenced.

[0046] For the start-up procedure, the water-supply line 8 is first activated by way of the control device 16, while no drive is yet applied to the suspension pump 9. Once an appropriate pressure, which can be determined by the pressure sensor 21, has been generated in the conveying section, and the introduction of water has resulted in a desirably low viscosity of the polymer melt, the control device 16 is used to discontinue the water supply 8 and activate the suspension pump 9 so that the suspension can then be conveyed by the suspension pump 9 from the suspension silo 10 into the twin-screw extruder 1. Here, the suspension is incorporated in the most ideal manner into the polymer melt, with control of the rotation rate and the power consumption of the drive 17. Once the polymer melt, thus mixed, has been discharged from the twin-screw extruder 1, the melt is passed by way of conveying and shearing elements 19 into the evacuation drum 13 of the devolatilizing extruder 2. The conveying and shearing elements 19 and the signals from the pressure gauge 20 serve here to meter the melt prior to entry into the evacuation drum 13 in a manner that gives an ideal quantity of melt present in the evacuation drum, where it is circulated and transported by way of screws; the surface that the melt offers to the vacuum here is maximized and continuously self-renewing, and the devolatilization of the melt can therefore take place very rapidly and effectively. This results in a further increase of the chain length of the polymer molecules, despite the shear forces that are also introduced into the melt by way of the evacuation drum. The viscosity of the polymer melt increases. For a preset flow rate and flow velocity, the desired viscosity of the polymer melt can be set by using the control device 16 to adjust the vacuum.

[0047] At the outgoing end of the evacuation drum the melt is introduced by way of the discharge unit 14 into the discharge die 15.

[0048] The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.