WO2006063575A1 - Method and device for the separation of polymer mixtures - Google Patents

Abstract

The invention relates to a method for the separation of polymer mixtures and a device for carrying out said method, of application to the separation of polymer mixtures on processing thermoplastic plastics. According to the invention, a polymer mixture for separation is fused or plastified in a shear gap of a shear element with annular flow channels of varying diameter, whereby fractions of the polymer mixture are led off from the screw gap in at least two locations, which have annular flow paths of varying diameter. The device comprises a separating chamber (1) with conical inner walls, in the middle of which a rotating mixing rotor (2) with an outer conical form is mounted to form a shear gap (3), whereby the device is provided with one introduction channel (4) and at least two outlet channels (5).

Description

Method and device for separating polymer mixtures

The invention relates to a method for separating polymer mixtures and to an apparatus for carrying out the method.

The method of separating polymer blends, as well as the device, finds application in the processing of thermoplastics.

The polymer mixtures to be separated are mixtures of material-like components which differ in the structure of the polymer chains, such as, for example, polyolefins.

In addition, with the inventive method from the polymer mixtures and foreign components z. B. from air bubbles, sand admixtures u.a. result, be separated.

As a separation method of plastics, a number of different mechanical methods are known. For example, DE 43 29 270 A1 teaches that comminuted plastic mixtures, suspended in a carrier liquid, are separated in the flow-differential process into floating and sinking fractions in order to separate fractions each having the same density. With this method, the separation of a plastic mixture is possible only with different density of the components.

Furthermore, DE 36 01 175 A1 introduces a separation process in which a polymer mixture is heated in a high-speed mixer until plasticization and agglomeration of the polymer particles having the lowest melting point and then fed to a cooling mixer. Cooled dissolved polymer parts are subsequently separated in a separator in agglomerates and non-deformable particles. With this method, the separation of a plastic mixture is possible only at different melting points of the components. It However, it has been found that by means of the known processes separate polymer mixtures are not sufficiently homogeneous for a number of applications.

According to EP 0 714 918 A2 DE 695 07 868 T2 or its German translation DE 695 07 868 T2, a process for the separation of polymers from polymer blends is proposed in which a separation process by shearing within a capillary takes place. This method is based on different melt viscosities of the respective different proportions of the polymer mixture.

However, the described solution suffers from the disadvantage that, according to the description, it can only be applied to mutually incompatible polymer mixture fractions. Apparently similar components obviously do not have the property differences sufficient for the separation according to the method of EP 0 714 918 and can not be separated with sufficient accuracy, as a result of which further processing problems such as insufficient phase binding capacity or poor spinnability continue to exist for the components to be separated.

In addition, a separation due to purely viscous effects requires high shear rates in the capillary wall area, which can be realized only by high flow velocities.

On the other hand, the relatively small flows perpendicular to the main flow, which make up the actual separation effect, require long residence times of the polymer mixture to be separated in the flow tube. As a serious disadvantage results from the fact that very large pipe or Kapillarlength must be technically realized, in turn, in addition to high equipment costs also cause large energy costs due to the large pressure losses to be overcome. The invention is therefore based on the object to develop a method for separating polymer mixtures from materially similar components with approximately the same density and approximately the same melting points.

Furthermore, the object is to provide a device suitable for carrying out the method.

This object is achieved by a method and a device according to the claims.

The method according to the invention is specified in claim 1. Advantageous embodiments are listed in the subclaims 2 to 7.

The device according to the invention for carrying out the method according to claim 1 is specified in claim 8. Advantageous embodiments of the device are listed in the subclaims 9 to 19.

The essence of the invention is to use viscoelastic properties of the components of the polymer mixtures for the desired separation and removal:

In the process according to the invention, a polymer mixture to be separated in the molten or plasticized state is exposed in a shear gap to shear with annular flow paths of different diameters. Different viscoelastic tensile stresses build up in the various components of the polymer mixture, which can lead to different local accumulations of the components in the shear gap.

The inventive method can be carried out in an advantageous manner so that the annular current paths through a arranged in a separation chamber above rotationally symmetric Knetrotor example in a Ke- gel form or in a round plate shape in conjunction with one of the respective shape for the shear gap adapted inner wall of the separation chamber can be generated. In a Knirtotor in conical shape different designs are possible. For example, it is possible to provide an inwardly curved or an outwardly curved conical shape. In the same way, there is a possibility of the design with a stepped or paragraphed conical shape of a Knetrotors.

The different viscoelastic tensile stresses of the respective components generated in the shear gap lead to the following conditions in the separation chamber: Polymer components with higher viscoelastic stresses displace polymers with lower viscoelastic stresses from the region of smaller diameter of the current paths and accumulate there - conversely, this results for displaced ones Polymer components of lower viscoelastic tensile stress in the range of larger flow path diameter. The different current path diameters result from the contour design of the rotor.

This results in a separation of the polymer mixture into two different polymer fractions, which differ in the structure of the polymer chains and thus in their viscoelasticity or in the melt index and can be derived as separate melt strands at different locations of the separation chamber.

In a particular embodiment of the method, the throughput or the metering rate for the polymer mixture can be regulated.

The device according to the invention consists of a separation chamber, preferably with a hollow cone-shaped inner wall, which is controllably heated. The kneading rotor has the outer shape of a cone and thus forms a shear gap with the hollow cone shape of the inner wall of the separation chamber. A polymer mixture to be separated is previously melted or plasticized in a plasticizer, for example an extruder, in order to then feed it to the shearing gap. The rotation of the Knetrotors causes in the adhering polymers ring formations. These rings generate viscoelastic tensile stresses. In the process, polymers with higher viscoelastic stresses on the rotating kneading rotor pull toward the kneading rotor tip, whereby polymers with lower viscoelastic stresses are displaced from the kneading rotor tip and collect both at the furthest circumference of the kneader rotor and at its cone base. The kneading rotor is designed so that its conical shape is mounted on a machine element rotatably mounted on the cone tip and below the cone base preferably in rolling bearings. The Knetrotor is designed below the cone base so that a torque can be transmitted to him by a drive. The separation chamber housing consists of two outer shapes and a central shape. In the middle mold channels are arranged, which are designed outside the separation chamber for the flow of polymer masses controllable. There is a feed channel for introducing the polymer mixture into the shear gap and at least two bleed channels, which divert the polymer fractions from the separation chamber present. A first discharge channel is preferably at the level of the conical rotor tip and a second discharge channel is preferably arranged at the level of the conical base surface of the kneading rotor. In the two outer shapes of the separation chamber housing, the bearings for the bearing of the rotor are fitted centrally.

The quality of the separation process is influenced by the throughput of the polymer mass per unit time and by the temperature. A decisive influencing factor is the residence time of the polymer mass in the separation chamber. A longer residence time ensures a better separation, but enhances the structural destruction in the shear gap. Dwell times can be influenced with the throughput and can be adjusted by its control. Realizable solutions have been found with the inventions with surprisingly simple technology in order to separate polymer mixtures from material-like components into polymer fractions having different properties, such as polyethylenes, polypropylenes, etc., in continuous operation.

If appropriate, the process can be run several times to increase the purity.

A use of the separation process for separating substances without viscoelastic properties such as air inclusions, color pigments, etc. from polymer mixtures having at least one viscoelastic component proceeds in an analogous manner.

In the following two embodiments, the device according to the invention and the method carried out with it will be explained in more detail.

In the accompanying drawings show

1: the sectional view of the separation device according to the invention, Fig. 2: the overall view of a separation plant with inventive

Separating device and Fig. 3: the side view of a separation plant.

The device according to the invention is gem. Fig. 1 of a separation chamber 1 with a hollow cone-shaped inner wall and can be heated to a temperature of about 190 ⁰ C (the existing heating is not shown). In the middle of the separation chamber 1 a rotatably mounted Knetrotor 2 is arranged, which is designed with its outer cone shape so that it forms a Scherspait 3 with a gap width of 2.5 mm with the hollow cone shape of the inner wall of the separation chamber. For both embodiments, a separation chamber 1 according to the invention was used with a Knetrotor 2 with the following dimensions:

Diameter of the cone base 7 of Knetrotors 2 100 mm

Diameter of the tip of Knetrotors 2 20 mm

Height of the cone from the cone base to the cone top 120 mm

In the first embodiment, separations were carried out on the following polymer mixture:

Polymer mixture

HDPE (type "Lacqtene", manufacturer: Atofina) and LDPE (type "Montell", manufacturer: Atofina) in the mass ratio 50: 50.

To characterize the polymer mixture to be separated, rheological investigations were carried out on the basis of determinations of the melt index (MFI value according to DIN / ISO 1133) with the following results:

polymer components

LDPE "Montell" MFI 5/190 = 2.935 g / 10 min

HDPE "Lacqtene" MFI 5/190 = 0.374 g / 10 min

MFI 2.16 / 230 = 0.13 g / 10 min

polymer blend

HDPE / LDPE MFI 5/190 = 1.255 g / 10 min.

The polymer mixture was prepared by the following technology:

Dosing and mixing of the corresponding granules of the two polymer components in a mixer,

Melting the polymer mixture in an extruder,

^• Production of a polymer mixture granulate. In the practice of the method according to the invention, the polymer mixture HDPE / LDPE with the MFI value = 1.255 g / 10 min is melted or plasticized supplied to a shear gap 3 and exposed to annular flows, in which different viscoelastic tensile stresses of the different components are generated. By a Knetrotor 2 in the form of cones, in conjunction with an inner wall of the separation chamber 1 adapted to the shear gap 3 of this shape, the annular flow paths of different diameters are ensured. As a result of the process carried out separated polymer fractions are derived at two locally offset points from the shear gap 3, ie in the range of minimum flow path diameter, a polymer fraction with higher viscoelastic stresses with the MFI = 1, 2-2,1 g / 10 min and in the range the maximum flow path diameter a polymer fraction with lower viscoelastic stresses with the MFI value = 4.5-10 g / 10 min.

In a separation plant according to Figures 2 and 3, the polymer mixture to be separated is HDPE / LDPE having the MFI value of 1.255 g / 10 min. Before in a plasticizer, e.g. an extruder 9 with geared motor 10, molten or plasticized to supply it to the shear gap 3. The rotation of the Knetrotors 2 causes ring formations in the adhering polymers. These rings create viscoelastic tensile stresses. In this case, polymers with higher viscoelastic stresses on the rotating kneading rotor 2 pull toward the kneading rotor tip 6, as a result of which polymers with lower viscoelastic stresses are displaced by the kneading rotor tip 6 and accumulate both at the furthest circumference of the kneading rotor 2 and at its cone base surface 7.

The kneading rotor 2 is designed so that its conical shape is mounted on a machine element rotatably mounted on the Knetrotorspitze 6 and below the cone base 7, preferably in rolling bearings 8. The machine element is designed extended below the cone base 7 in order to transmit a torque by a drive 10. The separation chamber 1 consists of two ßenformen and a central shape, which form a common housing. In the middle form channels are arranged, which are designed outside the separation chamber 1 for the flow of polymer masses controllable.

There are a feed channel 4 for introducing the polymer mixture HDPE / LDPE with the MFI value = 1, 255 g / 10 min in the shear gap 3 and at least two discharge channels 5, which derive the polymer fractions from the separation chamber 1, is present. A first discharge channel 5 is approximately at the level of the conical knector rotor tip 6, and a second discharge channel 5 is arranged approximately at the level of the conical base surface 7 of the kneading rotor 2.

From the discharge channel 5 in the vicinity of the kneading rotor tip 6, the polymer fraction with the MFI value = 1, 2- 2.1 g / 10 min and from the discharge channel 5 in the vicinity of the cone base 7, the polymer fraction with the MFI = 4.5 -10 g / 10 min. The throughput is about 4 to 8 g / min. The segregation ratio is 1: 1. In the two outer forms of the separation chamber 1, the rolling bearings 8 are fitted centrally for the storage of Knetrotors 2.

The realized process parameters are shown in the following overview:

Separation of the polymer mixture HDPE / LDPE

• Temperature of the separation chamber 1 190 ⁰ C

• Speed of kneading rotor 2 100 - 200 1 / min • Throughput or dosing speed 4 - 8 g / min

• Degassing ratio 1: 1

For the evaluation of the separation effect, the melt index values MFI according to DIN / ISO 1133 of the two polymer fractions from the different melt strands were determined. This led to the following results: Separation result for the polymer mixture HDPE / LDPE

Polymer fraction as a melt strand from the discharge channel 5 near the kneading rotor tip 6 MFI 5/190 = 1.2-2.1 g / 10 min,

• Polymer fraction as a melt strand from the discharge channel 5 near the cone base 7 MFI 5/190 = 4.5 - 10 g / 10 min.

It can be seen from the result that with the method according to the invention a very good separation effect of a polymer mixture in two polymer fractions was achieved. The MFI values of the melt index measured as a measure of the structuring differ depending on the experimental parameters at least three times in the case of the polymer fractions from the polymer mixture HDPE / LDPE.

The general increase in MFI values observed in addition can be attributed to the structure destruction in shearing gap 3, which can be influenced by the throughput.

In the second exemplary embodiment, investigations were likewise carried out on the following polymer mixture using the process according to the invention and using the separation chamber 1 according to the invention:

Polymer mixture of HDPE (type "Lacqtene", manufacturer: Atofina) and PP (type "Daplen", manufacturer: Borealis) in a mass ratio of 50: 50 To characterize the polymer mixture to be separated, rheological investigations were carried out on the basis of determinations of the melt index MFI according to DIN / ISO 1133 with the following results:

components

HDPE "Lacqtene" MFI 2.16 / 230 = 0.13 g / 10 min

PP "Daplen" MFI 2.16 / 230 = 4.58 g / 10 min

polymer blend

HDPE / PP MFI 2,16 / 230 = 1, 03 g / 10 min.

The polymer mixture was prepared by the following procedure:

Dosing and mixing the corresponding granules of the polymer components in a mixer,

Melting the polymer mixture in an extruder,

Extruding polymer mixture strands,

• Production of a polymer mixture granulate.

The inventive method was again carried out using the separation chamber 1 according to the invention for the separation of the polymer mixture. The realized process parameters are shown in the following overview:

Separation of the polymer mixture HDPE / PP

• Temperature of the separation chamber 230 ⁰ C

• Speed of kneading motor 150 1 / min

• Throughput / dosing rate 3 to 9 g / min

• Degassing ratio 1: 1 For the evaluation of the separating effect, the melt index values MFI according to DIN / ISO 1133 of the polymer fractions from the different melt strands were determined. The following results were obtained:

Separation result for the polymer mixture HDPE / PP

Polymer fraction as a melt strand from the discharge channel 5 near the kneading rotor tip 6 MFI 2,16 / 230 = 1, 9-2,1 g / 10 min, polymer fraction as melt strand from the discharge channel 5 in the vicinity of the cone surface 7 MFI 2, 16/230 = 8.1 - 9.5 g / 10 min.

It can also be seen from this result that a very good separation effect was achieved with the method according to the invention.

The MFI values measured as a measure of the structuring differ, depending on the process parameters realized, at least fourfold in the case of the polymer fractions from the polymer mixture HDPE / PP. The general increase in MFI values observed in addition can be attributed to the structure destruction in shearing gap 3, which can be influenced by the throughput.

Reference to the patent application

Method and device for separating polymer mixtures

Separation chamber 1

Knet rotor 2

Shear gap 3

Feed channel 4

Discharge channel 5

Knetrotorspitzspitze 6

Cone base 7

Rolling bearings 8

Extruder 9

Geared motor 10

Claims

claims 1. A method for separating polymer mixtures from materially similar components, in which a polymer mixture to be separated is melted or plasticized in a shear gap (3) subjected to shearing with annular current paths, wherein the annular current paths have different diameters and that fractions of the polymer mixture at least two places from the Shearing gap (3) are derived, which are touched by annular current paths of different diameters. 2. The method of claim 1, are removed in the fractions of the polymer mixture in the region of the minimum flow path diameter and in the region of the maximum flow path diameter. 3. The method of claim 1 or 2, wherein the annular current paths by a rotationally symmetric Knetrotor (2) in conjunction with a shape of the shear gap (3) adapted to the inner wall of the separation chamber (1) are generated. 4. The method of claim 3, wherein the annular current paths by a Knetrotor (2) in a rectilinear or inwardly curved conical shape in conjunction with one of these shape for the shear gap (3) adapted inner wall of the separation chamber (1) are produced. 5. The method of claim 3, wherein the annular current paths are generated by a kneading rotor (2) in an outwardly curved conical shape in conjunction with an inner wall of the separation chamber (1) adapted to this shape for the shear gap. 6. The method of claim 3, wherein the annular current paths by a Knetrotor (2) in a conical shape, which is stepped in or paragraphs, in conjunction with one of these form for the shear gap (3) adapted inner wall of the separation chamber (1 ) are produced, wherein in places that are close to the gradations or paragraphs of the Knetrotors (2), fractions of the polymer mixture from the shear gap (3) are additionally derived. 7. The method according to any one of claims 1 to 6, wherein the throughput or the metering rate for the polymer mixture can be controlled. 8. Apparatus for carrying out the method according to claims 1 to 7, consisting of a separation chamber (1) with a hollow cone-shaped inner wall, in the middle of a rotatably mounted Knetrotor (2) is arranged with an outer cone shape so that it with the hollow cone shape of the inner wall the separation chamber (1) forms a shear gap (3), wherein the device is equipped with a supply channel (4) and at least two discharge channels (5). 9. Apparatus according to claim 8, wherein the rotationally symmetrical Knetrotor (2) has an inwardly curved conical shape with one of this shape for the shear gap (3) adapted inner wall of the separation chamber (1). 10. Apparatus according to claim 8, wherein the rotationally symmetrical kneading rotor (2) has an outwardly curved conical shape with one of these shape for the shear gap (3) adapted inner wall of the separation chamber (1). 11. Device according to claims 8 to 10, wherein a first discharge channel (5) in the vicinity of the conical Knetrotorspitze (6) and a second discharge channel (5) in the vicinity of the conical base surface (7) is arranged. 12. The apparatus of claim 8, wherein the conical shape of the Knetrotors (2) is stepped in or paragraphs with one of these shape for the shear gap (3) adapted inner wall of the separation chamber (1), said stages or paragraphs each with Discharge channels (5) are equipped. 13. Device according to claims 8 to 12, having a controllable heating. 14. Device according to claims 8 to 13, wherein the shearing gap (3) has a transversely to the annular current paths changing gap width. 15. Device according to one of claims 8 to 13, wherein the separation chamber (1) consists of two outer molds and a central mold. 16. Device according to one of claims 8 to 15, wherein the kneading rotor (2) is designed so that the conical shape is rotatably mounted on a machine element at the Knetrotorspitzspitze (6) and below the Ke- geig round surface (7). 17. The apparatus of claim 16, wherein the kneading rotor (2) is mounted in rolling bearings (8). 18. The apparatus of claim 17, wherein the rolling bearing (8) in the two outer shapes of the separation chamber (1) are fitted centrally. 19. Device according to one of claims 8 to 18, wherein the machine element of Knetrotors (2) below the conical base surface (7) is designed to be extended. For this 2 pages drawings.