Method for producing thermoplastic moulding compounds

Abstract

The invention relates to a method for producing a thermoplastic molding compound (73), said method comprising: (a) feeding a dispersion (1) containing rubber and a precipitation solution (3) into a precipitation tank (5), producing an aqueous suspension (9) containing rubber particles; (b) optionally sintering the rubber particles contained in the aqueous suspension (9) containing rubber particles to form larger particles; (c) mechanically dewatering the aqueous suspension containing rubber particles to obtain rubber particles (33) containing residual moisture and a liquid phase (35) containing fine particle rubber; (d) feeding the rubber pellets (33) containing residual moisture into an extruder (57) comprising a suction zone (55), a dewatering section (59), at least one feed section (65) for at least one other polymer (67) and / or additive, a mixing section (69) and a discharge zone (71), the liquid phase containing residual rubber separated in the dewatering section (59) being collected in a buffer tank (63) comprising at least one stirrer (75); and returning the liquid phase (77) containing the residual rubber collected in the buffer tank (63) to the deposition tank (5).

Description

manual

[0001] The present invention relates to a method for producing a thermoplastic molding compound, comprising: (a) feeding a dispersion containing rubber and a precipitation solution into a precipitation vessel to produce an aqueous suspension containing rubber particles, (b) optionally sintering the rubber particles present in the aqueous suspension containing the rubber particles to obtain larger particles, (c) mechanically dewatering the aqueous suspension containing rubber particles to obtain rubber particles containing residual water and a liquid phase containing finely divided rubber, (d) feeding the rubber particles containing residual moisture into an extruder, the extruder comprising a suction zone into which the rubber particles containing residual moisture are fed; a dewatering section in which a liquid phase containing residual rubber is removed from the rubber particles containing residual moisture; at least one feed section for at least one other polymer and / or additives; a mixing section in which the rubber particles, at least one other polymer and the additives are mixed together to obtain a melt of a thermoplastic molding compound; and a discharge section through which a molten strand is extruded from the extruder.

[0002] Thermoplastic molding compounds that can be produced by this method are in particular molding compounds containing at least one rubber component, for example acrylonitrile-styrene-acrylate copolymers (ASA) or acrylonitrile-butadiene-styrene copolymers (ABS) molding compounds. The production of such thermoplastic molding compounds is described, for example, in EP-A 0 734825, WO-A 2020 / 043690, WO-A 2015 / 000873 or WO-A 2015 / 004112.

[0003] For production, generally firstly granular rubbers, more particularly graft rubbers based on butyl acrylate or graft rubbers based on butadiene, are prepared by emulsion polymerization in an aqueous system and then by precipitation from a precipitation solution.

[0004] The resulting granules are then typically dewatered, for example by filtering, sieving, decanting, pressing out water or centrifuging, optionally washed with water during or after dewatering, and then optionally dried thermally to remove more water. The granulated rubber is then fed to an extruder and further dewatered before being mixed with the other components in the extruder and processed into a thermoplastic molding compound.

[0005] A disadvantage of all known processes is that, when dewatering the aqueous suspension containing the rubber particles and when dewatering the rubber particles in the extruder, a liquid phase is produced which still contains up to 15% by weight of rubber (based on the total amount of water and rubber), which liquid phase is usually disposed of together with the removed water. Although it is generally known from WO 2015 / 000873 that the removed water can be returned to the operation, its direct recovery may result in the following: the rubber obtained from the removed liquid phase leads to deposits or blockages in downstream equipment components. In addition, due to the high rubber content in the water produced during the dewatering process in the extruder, deposits or blockages may even occur at the drain of the extruder.

[0006] It is therefore an object of the present invention to provide a process for producing thermoplastic molding compounds which provides better yields and which minimizes the amount of precipitated salts and products removed with the water from the operation while minimizing the risk of pipe blockages.

[0007] This object is achieved by a method for producing a thermoplastic molding compound, the method comprising: (a) feeding a dispersion containing rubber and a precipitation solution into a precipitation vessel to produce an aqueous suspension containing rubber particles, (b) optionally sintering the rubber particles present in the aqueous suspension containing the rubber particles to obtain larger particles, (c) mechanically dewatering the aqueous suspension containing rubber particles to obtain rubber particles containing residual water and a liquid phase containing finely divided rubber, (d) feeding the rubber particles containing residual moisture into an extruder, the extruder comprising a suction zone into which the rubber particles containing residual moisture are fed; a dewatering section in which a liquid phase containing residual rubber is removed from the rubber particles containing residual moisture; at least one feed section for at least one other polymer and / or additives; a mixing section in which the rubber particles, at least one other polymer and the additives are mixed together to obtain a melt of a thermoplastic molding compound; and a discharge section through which a molten strand is extruded from the extruder. The liquid phase containing the residual rubber removed in the dehydration section is collected in a buffer container, which includes at least one agitator, which is used to agitate the liquid phase containing the residual rubber to prevent the accumulation of rubber particles contained in the liquid, and the liquid phase containing the residual rubber collected in the buffer container is returned to the sedimentation container.

[0008] Surprisingly, stirring the liquid phase containing residual rubber in the buffer vessel is sufficient to reduce or even prevent clogging of the pipe through which the liquid phase containing residual rubber passes.

[0009] It has also been found that, since precipitation and sintering are usually repeated at elevated temperatures, repeated thermal loading of the rubber particles returned to the precipitation vessel containing the liquid phase of the residual rubber does not adversely affect the mechanical properties of the thermoplastic molding compound produced by the process. This means that recycling can increase rubber yields while minimizing the amount of rubber removed from the wastewater operation while maintaining the same product quality. The amount of wastewater and therefore the amount of precipitation salts required is likewise minimized, while precipitation and / or sintering can be carried out simultaneously with a reduced solids content, thereby reducing the risk of blockages in this process step.

[0010] The liquid phase containing the residual rubber obtained in the dewatering section of the extruder generally contains more than 1% by weight of rubber, more preferably from 3% to 20% by weight of rubber, more particularly from 5% to 15% by weight of rubber.

[0011] Due to the rubber portion in the liquid phase containing residual rubber, there is a risk of forming deposits and / or blockages in the pipeline between the dewatering section of the extruder and the buffer container. In order to prevent these deposits and / or blockages, the liquid phase containing residual rubber is preferably mixed with water after being removed from the extruder. The amount of water mixed with the liquid phase containing residual rubber is preferably adjusted so that the rubber portion of the liquid phase containing residual rubber after adding water does not exceed 15 weight %, more preferably the rubber portion is in the range of 2 weight % to 12 weight %, more particularly the rubber portion is in the range of 4 weight % to 10 weight %.

[0012] In order to further increase the yield and to minimize the amount of rubber removed from the wastewater operation, it is additionally preferred to return the liquid phase containing the finely divided rubber to the precipitation vessel.

[0013] Since the rubber in the liquid phase containing the finely divided rubber obtained by mechanical dehydration in step (c) is the same as the rubber in the liquid phase containing the residual rubber produced in the dehydration section of the extruder in step (d), it is also preferred that the liquid phase containing the finely divided rubber is introduced into a buffer vessel and mixed with the liquid phase containing the residual rubber removed in the dehydration section before returning to the sedimentation vessel. In this way, only one return pipe is required to enter the sedimentation vessel, and the rubber-containing liquid can be returned from the buffer vessel to the sedimentation vessel in a targeted manner, depending on the production conditions. When the liquid phase containing the finely divided rubber and the liquid phase containing the residual rubber are introduced into the sedimentation vessel, it is not necessary to match them.

[0014] The rubber used in the method of the present invention can be a grafted rubber. Preferably, the rubber comprises a grafted shell of one or more other (usually non-elastic) polymers. For this reason, a single-stage or multi-stage elastic base stage (elastomeric base stage) can be obtained by polymerization of one or more of the monomers butadiene, isoprene, chloroprene, styrene, alkylstyrene, C1 to C10 alkyl esters of acrylic acid or methacrylic acid and a small amount of other monomers (including crosslinking monomers), wherein the hard graft layer is polymerized by one or more of the following monomers: styrene, alkylstyrene, acrylonitrile, methyl methacrylate. It is also possible to use seeds obtained based on the monomers butadiene, isoprene, chloroprene, styrene, alkylstyrene, C1 to C10 alkyl esters of acrylic acid or methacrylic acid and a small amount of other monomers (also including crosslinkable monomers) to produce the starting stage.

[0015] Preferred rubbers are those based on butadiene / styrene / acrylonitrile, n-butyl acrylate / styrene / acrylonitrile, butadiene / n-butyl acrylate / styrene / acrylonitrile, n-butyl acrylate / styrene / methyl methacrylate, butadiene / styrene / acrylonitrile / methyl methacrylate and butadiene / n-butyl acrylate / methyl methacrylate / styrene / acrylonitrile. Up to 10% by weight of polar monomers or crosslinking monomers carrying functional groups can be incorporated into the seed and / or core and / or shell by polymerization.

[0016] Examples of rubbers used in the process of the invention include polymers of conjugated dienes, such as butadiene with an outer graft shell, in particular based on vinyl aromatic compounds, such as SAN copolymers. The rubber may also be a rubber based on a crosslinked polymer of C1- to C10-alkyl acrylates, such as n-butyl acrylate or ethylhexyl acrylate, grafted with a polymer based on vinyl aromatic compounds, such as SAN copolymers. In addition, the process is also suitable for grafted rubbers that predominantly comprise copolymers of conjugated dienes and C1 to C12 alkyl acrylates, such as butadiene-n-butyl acrylate copolymers, and one or more graft layers consisting of SAN copolymers, polystyrene or PMMA. Butadiene grafted rubbers and butyl acrylate grafted rubbers are particularly preferred.

[0017] Rubbers are usually produced in water-soluble systems, for example by emulsion polymerization, such as described in WO-A 2020 / 043690. Emulsion polymerization forms a water-soluble dispersion in which water is the continuous phase and the rubber particles produced in the polymerization are the dispersed phase.

[0018] For processing, the dispersion is introduced into a sedimentation vessel. For delivery of dispersions from emulsion polymerization, a peristaltic pump is preferably used if the dispersion storage tank does not provide sufficient gradient for pumpless gravity addition.

[0019] The solids content of the dispersion supplied to the precipitation vessel is preferably 10% to 50% by weight, more preferably 20% to 45% by weight, particularly preferably 30% to 40% by weight. The solids present in the dispersion are rubber in the form of particles.

[0020] In the precipitation vessel, the dispersion is converted into an aqueous suspension containing the rubber particles by adding a precipitation salt solution (preferably containing at least one salt and / or one acid).

[0021] In the present invention, a dispersion is understood to be a mixture of particles in a liquid phase having a volume-average particle size Dv in the range of 20 to 999 nm, preferably in the range of 50 to 800 nm. The volume-average particle size Dv (or the average particle size according to De Broucker) is an average parameter based on a unit volume of the particles. The volume-average particle size of the particles in the dispersion can be determined by light scattering (laser diffraction), for example using a Beckman Coulter instrument.

[0022] A suspension is understood to be a mixture of particles in a liquid phase, the particles of which are larger than the particles of a dispersion. To determine the particle size of a suspension, for example, the D10 value, the D50 value or the D90 value can be used, depending on the type of determination of the particle size and particle size distribution, wherein the D10 value refers to the particle size of less than 10% by weight of the particles, the D50 value refers to the particle size of less than 50% by weight of the particles, and the D90 value refers to the particle size of less than 90% by weight of the particles. The particles in the suspension generally have a D10 value in the range of 50 to 400 μm, a D50 value in the range of 200 to 2000 μm, and / or a D90 value in the range of 500 to 4000 μm. The particles in the suspension particularly preferably have a D10 value in the range of 50 to 400 μm, a D50 value in the range of 200 to 2000 μm, and a D90 value in the range of 500 to 4000 μm. The particle size of the suspension particles is preferably determined by wet sieving using a sieve tower containing sieves of different mesh sizes. After sieving, the weight of the particles on each sieve is measured, so that the D10 value, D50 value and D90 value can be obtained.

[0023] The precipitation solution preferably comprises a divalent or trivalent salt, and in particular the precipitation solution comprises at least one alkaline earth metal salt, preferably a magnesium salt and / or a calcium salt, particularly preferably at least one magnesium salt.

[0024] The at least one alkaline earth metal salt is more particularly chosen from alkaline earth metal halides (such as chlorides), alkaline earth metal sulfates, alkaline earth metal phosphates (such as orthophosphates or pyrophosphates), alkaline earth metal acetates and alkaline earth metal formates. The at least one alkaline earth metal salt is preferably chosen from chlorides and sulfates.

[0025] Preferred alkaline earth metal salts are magnesium sulfate (e.g. magnesium sulfate monohydrate (Mg[SO4]·H2O), magnesium sulfate pentahydrate (Mg[SO4]·5H2O), magnesium sulfate hexahydrate (Mg[SO4]·6H2O) and Epsom salt (Mg[SO4]·7H2O)), magnesium chloride, calcium chloride, calcium formate, magnesium formate or mixtures thereof. Particular preference is given to using magnesium sulfate.

[0026] If the precipitation solution contains a trivalent salt, anhydrous aluminum sulfate or aluminum sulfate containing water of crystallization is particularly preferred.

[0027] The amount of salt added depends on the water content in the dispersion and is preferably in the range from 0.1 to 3% by weight, preferably in the range from 0.5 to 3% by weight, in particular in the range from 0.5 to 2% by weight, based in each case on the amount of water in the dispersion.

[0028] The pH of the mixture of the dispersion obtained in step (a) and the precipitation solution is preferably in the range of 3 to 10. The precipitation can be carried out in the acidic range or in the alkaline range; in the case of precipitation in the acidic range, the pH of the mixture is preferably in the range of 3 to 7, in particular in the range of 4 to 6, and in the case of precipitation in the alkaline range, the pH of the mixture is preferably in the range of 7 to 9, in particular in the range of 8 to 9.

[0029] The pH value can be adjusted, for example, by adding buffer salts, acids and / or bases, for example using sulfuric acid, phosphoric acid, sodium hydroxide solution, potassium hydroxide solution, sodium and potassium carbonate salts (e.g. sodium carbonate Na2CO3 and / or sodium bicarbonate NaHCO3 or mixtures thereof), sulfates or phosphates (e.g. tetrasodium pyrophosphate). Preferably, for example, at least one buffer salt from the group of sodium salts, in particular a buffer salt selected from the group consisting of sodium carbonate, sodium sulfate and sodium phosphate, preferably a buffer salt selected from the group consisting of sodium carbonate Na2CO3 and sodium bicarbonate NaHCO3 is added.

[0030] The buffer salt, acid and / or base can be added as early as possible during the emulsion polymerization to produce the rubber, or mixed in the precipitation vessel in step (a). Preferably, the buffer salt or base is added during the emulsion polymerization to produce the rubber. The acid is added in the precipitation vessel or immediately before introduction into the precipitation vessel.

[0031] In order to precipitate the rubber from the dispersion and obtain an aqueous suspension containing rubber particles, the precipitation solution and the dispersion are generally mixed for a period of 5 to 50 minutes, preferably 5 to 40 minutes.

[0032] The precipitation in step (a) can be carried out in a temperature range of 20 to 150° C., preferably 40 to 100° C., particularly preferably 45 to 99° C., likewise preferably 60 to 95° C. The dispersion is preferably mixed with the at least one precipitation solution at a temperature of 30 to 95° C., preferably 40 to 95° C., particularly preferably 40 to 90° C.

[0033] In order to obtain larger particles, the rubber particles in the aqueous suspension containing rubber particles obtained in step (a) may be aggregated so as to obtain larger particles in the subsequent sintering step (b). For this purpose, the aqueous suspension containing rubber particles obtained in step (a) is preferably transferred to a sintering container, and the temperature of the aqueous suspension containing rubber particles in the sintering container is maintained in the range of 70 to 150° C., preferably in the range of 75 to 140° C., and particularly preferably in the range of 85 to 140° C. In particular, the aqueous suspension containing rubber particles is maintained at this temperature for 10 to 90 minutes, preferably 15 to 90 minutes, and particularly preferably 15 to 80 minutes.

[0034] Particularly preferably, the mixing of the dispersion and the precipitation solution in step (a) is carried out at a temperature range of 30 to 95° C., preferably at a temperature range of 40 to 90° C., and if step (b) is carried out, the sintering in step (b) is carried out at a temperature range of 70 to 150° C., preferably at 80 to 140° C., for at least 5 minutes.

[0035] The precipitation of the rubber particles in step (a) and the sintering in step (b) can be carried out in different containers or in the same container, wherein carrying out the precipitation and sintering in the same container is possible, in particular when the process is a batch operation, because in this case, the initial mixing of the dispersion with the precipitation solution at a relatively low temperature is followed by sintering of the rubber particles at a relatively high temperature. Therefore, it is preferred to use a precipitation container in step (a) and a sintering container in step (b), wherein the sintering container and the precipitation container are two different containers. For conveying the aqueous suspension containing the rubber particles, the sintering container and the precipitation container are connected by a connecting pipe, which can accommodate a pump.

[0036] In order to obtain the most uniform particle size distribution of the resulting aggregated particles, it is advantageous that the precipitation and sintering of the rubber particles in the precipitation container are both carried out continuously. In order to keep the suspension containing the rubber particles in motion and prevent the rubber particles from settling, especially even when the suspension cannot be fed to subsequent equipment components due to, for example, downtime, the connecting pipeline between the precipitation container and the sintering container is provided with a pumping circulation loop, in which the aqueous suspension containing the rubber particles is pumped and circulated.

[0037] For continuous operation, it is more advantageous to make the sintering vessel larger than the precipitation vessel if the desired residence time in the sintering vessel is greater than the residence time in the precipitation vessel.

[0038] After precipitation or, if step (b) is carried out, after sintering, the aqueous suspension containing the rubber particles is dewatered to obtain rubber particles containing residual water and a liquid phase containing finely divided rubber.

[0039] The water content of the rubber particles containing residual moisture is preferably not more than 60% by weight, more preferably not more than 50% by weight, and in particular not more than 40% by weight, in each case based on the total mass of the rubber particles containing residual moisture. The water content can be determined in particular using suitable analytical instruments (e.g. drying and weighing devices), wherein the sample is dried until a constant weight is reached within a certain time. For example, the water content of the rubber particles containing residual moisture can be determined at 180° C. in a halogen moisture analyzer HR73 from Mettler Toledo until a constant weight is reached within 30 seconds.

[0040] The water content of the rubber granules containing residual moisture obtained in step (c) is in particular in the range from 10% to 50% by weight, preferably in the range from 20% to 45% by weight and in particular in the range from 20% to 40% by weight, in each case based on the total mass of the rubber granules containing residual moisture.

[0041] Mechanical dehydration is usually carried out by continuous or batch centrifugation and / or filtration. Mechanical dehydration is preferably achieved by continuous centrifugation. For this purpose, the aqueous suspension containing the rubber particles is centrifuged, for example, at a centripetal acceleration of 200·g to 2000·g, wherein the gravitational acceleration g=9.81 m / s 2 , preferably centrifuging at a centripetal acceleration of 500·g to 1300·g for a time of 1 second to 5 minutes, preferably 1 to 120 seconds.

[0042] In order to prevent the rubber particles from settling, in particular in the event of a malfunction of the continuously operating mechanical dewatering device, it is also advantageous if the connection between the sintering container and the continuously operating mechanical dewatering device, in particular at least one centrifuge or at least one filtering device, is provided with a pumped circulation circuit, in which the suspension containing the sintered rubber particles is pumped in a circulation circuit before being fed to the centrifuge and / or filtering device.

[0043] If a batch centrifuge with discontinuous emptying is used, a buffer vessel equipped with an agitator is required to collect the suspension containing the rubber particles.

[0044] The rubber particles containing residual moisture can then be washed with water and / or a mixture of water and a polar, water-soluble solvent and then dried, for example as described in WO-A 2020 / 043690.

[0045] Since the liquid phase separated in step (c) of mechanically dehydrating the aqueous suspension containing rubber particles from the rubber particles containing residual moisture still contains finely divided rubber, the liquid phase containing the finely divided rubber is preferably returned to the precipitation vessel.

[0046] The rubber granules containing residual moisture are then fed into an extruder for producing a thermoplastic molding compound, the extruder comprising a suction zone into which the rubber granules containing residual moisture are fed; a dewatering section in which a liquid phase containing residual rubber is at least partially removed from the rubber granules containing residual moisture; at least one feed section for at least one other polymer and / or additives; a mixing section in which the rubber granules, at least one other polymer and the additives are mixed together to obtain a melt of the thermoplastic molding compound; and a discharge section through which a molten strand is extruded from the extruder.

[0047] For example, the extruder is constructed as described in WO 2015 / 004112 or WO 2015 / 000873.

[0048] The rubber granules containing residual moisture are fed into the suction zone of the extruder through a metering device.

[0049] The dewatering section is located after the suction zone and preferably comprises at least one retention element and at least one associated drain, wherein at least one drain and the drain of the suction zone are preferably equipped with a wire mesh composite plate, a fine-mesh plate or a slotted screen. As an alternative or in addition, the at least one drain can also be equipped with a packing screw. Preferably, all drains are equipped with a packing screw.

[0050] In a feed section adjacent to the dewatering section, the further components of the thermoplastic molding compound are preferably fed into the extruder as a melt.

[0051] The mixing section is provided with mixing, kneading and / or other plasticizing elements as they are usually used in extruders.

[0052] A degassing section with at least one degassing opening can be located after the mixing section; in the degassing section, moisture or other components still contained in the thermoplastic molding compound are further removed as impurities in the form of steam from the thermoplastic molding compound. The degassing opening can be open or, for example, can be provided with a filling screw.

[0053] The end of the extruder is formed by a discharge zone, to which a tool is connected, through which the thermoplastic molding compound is discharged from the extruder.

[0054] The extruder used has at least one drain, but may also have a plurality of drains, for example two or three drains. However, the extruder may also have a very large number of drains, for example up to 30 drains.

[0055] The drain openings can be located anywhere on the circumference of the extruder housing, for example on the top side, at the side or facing downwards. The drain openings can also be arranged in pairs, facing each other. Any other arrangement of the drain openings is also conceivable. The filling screw can be mounted on the drain openings.

[0056] Dewatering usually takes place downstream of the suction zone in the conveying direction. In the simplest case, there is only one drain, which is arranged downstream of the suction zone.

[0057] The drain openings can be configured in a manner known per se and their geometry corresponds to known openings, as they are also usually used for removing gaseous substances from the extruder. This allows the use of drain openings that are grooves and / or holes in the extruder housing. For example, circular holes or figure eight-shaped holes (i.e. two directly adjacent circular holes) are suitable as drain openings, wherein the longitudinal axis of the figure eight can be arranged, for example, at right angles (transverse) or parallel (longitudinal) to the conveying direction of the extruder.

[0058] Alternatively, the drain opening can also be rectangular, square or oval. A square or rectangular drain opening can have rounded corners. If the extruder comprises a plurality of drain openings, the individual drain openings can also each have a different shape and / or size. Alternatively, a drain opening of any shape, such as a rectangle, can be cut out of the extruder housing, and an insert having the desired drain opening shape can then be used in this cut-out; for example, in the case of a double screw fixing of the packing screw, the drain opening is preferably in the shape of a figure eight.

[0059] The extruder is preferably operated in such a way that the average pressure in the area of ​​the drain is in the range of 10 to 55 bar, in particular in the range of 15 to 35 bar. Short-term pressure peaks of more than 55 bar may also occur. The pressure can be monitored with a standard pressure gauge. The monitoring here can be based on a direct measurement of the mechanical pressure or on the measurement of the pressure of membranes, piezoelectric elements, sensors or other common components, such as those used by technicians in pressure technology monitoring.

[0060] The drains can be operated under normal pressure, vacuum or overpressure, and all drains can have the same or different pressures. In this case, the moisture content of the extruded material can be adjusted within certain limits by a corresponding overpressure or underpressure. At underpressure, the absolute pressure is generally 2 to 900 mbar (abs), preferably 10 to 800 mbar (abs), in particular 30 to 500 mbar (abs), while at overpressure, the pressure is generally between 1.1 and 20 bar (abs). However, dehydration is preferably carried out under normal pressure or vacuum. In vacuum operation, water is extracted in gaseous and non-liquid form. Therefore, the gas extraction ports operated under vacuum are also called degassing ports. In contrast, drains are those openings from which water is extracted in liquid form.

[0061] Closing the drain with a wire mesh composite plate, fine-mesh plate or slotted screen, or attaching a filler screw, largely prevents the rubber from exiting the extruder through the drain along with the water.

[0062] However, it is not possible to prevent part of the rubber from leaving the extruder through the drain together with the water. Typically, the liquid phase containing residual rubber drawn off from the extruder through the drain still contains more than 1% by weight of rubber, more preferably 3% to 20% by weight of rubber, more particularly 5% to 15% by weight of rubber, each based on the total mass of the liquid phase containing residual rubber.

[0063] In order to minimize the amount of rubber removed from the operation, according to the invention, the liquid phase separated off in the dewatering section and containing residual rubber is collected in a buffer vessel.

[0064] In order to prevent the rubber particles still present in the liquid phase from accumulating - i.e., in the case where the density of the rubber is greater than the density of the liquid phase, the rubber particles will settle, while in the case where the density of the rubber is lower than the density of the liquid phase, the rubber particles will float - the buffer container includes at least one agitator with which the liquid phase containing the residual rubber is stirred.

[0065] The liquid phase collected in the buffer vessel and containing the residual rubber is returned to the precipitation vessel for reuse.

[0066] The buffer container can be any container equipped with an agitator, as long as the agitator can be operated to prevent the accumulation of rubber particles. For example, a suitable agitator that can be used in the buffer container is a propeller agitator.

[0067] Since the rubber content of the residual rubber phase extracted from the extruder through the drain is relatively high, the residual rubber liquid phase is preferably mixed with water after removal from the extruder in order to prevent deposits and / or blockages in the pipeline between the extruder and the buffer container into which the residual rubber liquid phase is introduced. The water here is preferably introduced directly after the drain, continuously or discontinuously, into the residual rubber liquid phase. However, the addition can also be carried out at any other point in the pipeline between the extruder and the buffer container, particularly preferably directly after the drain.

[0068] The amount of water added to the liquid phase containing residual rubber is preferably selected so that after the addition of water the liquid phase containing residual rubber still contains not more than 15% by weight of rubber, more preferably from 2% to 12% by weight of rubber and more particularly from 4% to 10% by weight of rubber, each based on the total mass of the liquid phase containing residual rubber.

[0069] It has been found that the addition of water after the drain combined with agitation of the liquid phase containing residual rubber in the buffer vessel is sufficient to reduce or even prevent clogging of the pipe through which the liquid phase containing residual rubber passes.

[0070] The water added to the liquid phase containing the residual rubber may be, for example, fresh water, in particular completely deionized water (demineralized water).

[0071] Since it cannot be excluded that a greater amount of liquid phase containing residual rubber is fed into the buffer vessel than is withdrawn from it (for example, if the production and processing of rubber has to be interrupted, but the extrusion operation is continued), the buffer vessel preferably has an overflow so that the liquid phase containing residual rubber can be discharged from the operation as wastewater. Since the wastewater contains rubber, it must be treated in suitable equipment before it can be discharged into the environment or fed into another operation as process water.

[0072] In the other polymer feed section near the dewatering zone, the other polymer or polymers are fed to the extruder depending on the thermoplastic molding compound to be produced.

[0073] Preferably, the thermoplastic molding compound produced by the process of the invention is a butyl acrylate-styrene-acrylonitrile copolymer, an acrylonitrile-butadiene-styrene copolymer or an acrylonitrile-styrene-acrylate copolymer.

[0074] Therefore, the thermoplastic polymer fed in the further polymer feed section is preferably a polymer selected from styrene-acrylonitrile copolymer (SAN), polystyrene (PS), polymethyl methacrylate (PMMA) or a mixture thereof.

[0075] SAN polymers, PMMA or mixtures of these polymers are preferred. In addition, the thermoplastic polymers fed to the feed section adjacent to the dewatering zone can also be polyalkylene terephthalates such as polycarbonate (PC), polybutylene terephthalate (PBT) and polyethylene terephthalate (PET), polyoxymethylene (POM), polyphenylene sulfide (PPS), polysulfone (PSU), polyether sulfone (PES), polyamide (PA) or mixtures of these thermoplastic polymers. In addition, thermoplastic elastomers, such as thermoplastic polyurethane (E-TPU), can also be used.

[0076] In addition, the thermoplastic polymer fed to the feed section adjacent to the dehydration section can also use copolymers based on styrene / maleic anhydride, styrene / imidized maleic anhydride, styrene / maleic anhydride / imidized maleic anhydride, styrene / methyl methacrylate / imidized maleic anhydride, styrene / methyl methacrylate, styrene / methyl methacrylate / maleic anhydride, methyl methacrylate / imidized maleic anhydride, styrene / imidized methyl methacrylate, imidized PMMA or mixtures of these polymers.

[0077] In all the styrene-containing thermoplastic polymers mentioned, part or all of the styrene may be replaced by α-methylstyrene or ring-alkylated styrene or acrylonitrile. Among the latter thermoplastic polymers, polymers based on α-methylstyrene / acrylonitrile, styrene / maleic anhydride, styrene / methyl methacrylate and copolymers with imidized maleic anhydride are preferred.

[0078] In the other section of the extruder adjacent to the feed section of at least one other polymer, the supplied components are usually melted, mixed, homogenized, degassed if necessary, and extruded from the extruder in the form of a melt strand. The melt strand can then be cut into granules, for example.

[0079] In order to buffer the production fluctuations in the various process steps, it is preferred to first feed the liquid phase containing the finely divided rubber to a return water container and then to the precipitation container. This also makes it possible to control the amount of the liquid phase containing the finely divided rubber mixed with the dispersion in the precipitation container, for example, to obtain a desired solid content in the mixture of the emulsion-polymerized dispersion and the liquid phase containing the finely divided rubber supplied to the precipitation container.

[0080] Since the amount of finely divided rubber in the liquid phase containing finely divided rubber is very low, usually not exceeding 2% by weight, especially in the range of 0.01% by weight to 1% by weight (based on the total mass of the liquid phase containing finely divided rubber), it is more preferred that the recovery water container is a sedimentation container in which the rubber-rich phase and the rubber-poor phase are formed. The rubber-rich phase may be the upper phase or the lower phase, depending on the density of the rubber.

[0081] In order to prevent the liquid phase existing in the return water container from being agitated and mixed by the introduction of other liquid phase containing finely divided rubber, and also to prevent foaming in the return water container, it is preferred to introduce the liquid phase containing finely divided rubber into the return water container through a dip tube. This can prevent the initial rubber-rich phase and the initial low-rubber phase from mixing again, especially if the return water container is a sedimentation container.

[0082] The rubber-rich phase can be returned directly from the return vessel to the sedimentation vessel. The rubber content in the low-rubber phase is preferably not more than 0.5% by weight, more preferably in the range of 0.001% by weight to 0.1% by weight, particularly preferably in the range of 0.001% by weight to 0.07% by weight, in each case based on the total mass of the low-rubber phase.

[0083] Since the water of the recycled rubber-rich phase contains not only finely divided rubber but also dissolved salts and / or acids from the precipitation solution fed to the precipitation vessel, it is further preferred that the rubber-rich phase returned directly to the precipitation vessel is mixed with the precipitation solution likewise introduced into the precipitation vessel before introduction into the precipitation vessel. Mixing the precipitation solution with the returned rubber-rich phase before introduction into the precipitation vessel has the further advantage that the formation of undesirably large rubber particles due to locally high concentrations of the precipitation solution in the precipitation vessel and very rapid precipitation can be prevented.

[0084] The salt content can be determined, for example, by conductivity measurement or titration, the acid content can be determined by pH determination, and the flow rate can be determined by providing a suitable flow meter known to the person skilled in the art in the pipeline upstream of the mixing point. In order to adjust the desired concentration of salt and / or acid for precipitation, the mass flows of the supplied precipitation solution and the returned rubber-rich phase are determined respectively, and the desired amount of precipitation solution is added using a ratio control device.

[0085] In order to recover the rubber from the low-rubber phase and not send it to disposal with the wastewater, the low-rubber phase is preferably concentrated and then sent to a sedimentation vessel.

[0086] The waste water formed during the concentration is sent for disposal, wherein the amount of waste water preferably corresponds to the amount of water supplied with the dispersion and precipitation solution minus the amount of water removed from other points of the operation, in particular the water still present in the rubber particles containing residual moisture. This makes it possible to achieve continuous operation without constantly increasing the amount of water in the operation due to recycled water.

[0087] Any process known to those skilled in the art for separating solids from solid-containing liquids may be used to concentrate the rubber particles present in the low rubber phase. It is particularly preferred that the rubber particles are concentrated from the low rubber phase by filtration. Filtration of the low rubber phase produces a rubber-rich retentate and a filtrate that is substantially free of rubber, and the rubber-rich retentate is recovered to a precipitation vessel.

[0088] The filtration of the low rubber phase can be operated continuously. In this case, the low rubber phase is concentrated by pressing the fluid through the filter when the fluid flows through the filter. This causes the rubber-rich retentate to return to the sedimentation container, and the filtrate that is substantially free of rubber can be disposed of as waste water. In order to adjust the rubber content in the retentate, for example, the volume flow through the filter, the pressure difference at both ends of the filter and / or the filter surface area can be adjusted. Only one filter or two or more filters can be used here, in which case the filters can be connected in parallel and / or in series.

[0089] However, as an alternative and preferred, the filtration operation is such that the rubber contained in the low rubber phase accumulates as a filter cake on the filter of the filtration device, and the liquid is removed from the filter as a substantially rubber-free filtrate. In this case, the resulting filter cake is discontinuously rinsed into a precipitation container with deionized water or filtered return water.

[0090] Filters that can be used to concentrate rubber from a low-rubber phase are, for example, edge gap filters. For example, edge gaps are suitable as filter materials, wherein the gap size of the filter is preferably in the range of 10 to 500 μm, more preferably in the range of 50 to 250 μm, in particular in the range of 75 to 200 μm.

[0091] During the filtration process, solids are usually deposited on the filter to form a filter cake. Depending on the volume flow rate of the low rubber phase through the filtration device, at least a portion of the filter cake can be flushed from the filter with the low rubber phase, where the rubber accumulates during the filtration process and is returned to the sedimentation vessel together with the retentate.

[0092] If the filter cake formed cannot be washed away with the retentate, the filter is preferably cleaned regularly. The time for cleaning the filter can be determined, for example, by the increase in the necessary pressure difference required to force the filtrate through the filter. Even if the filtration is carried out so that the rubber separates from the low-rubber phase to form a filter cake, the filter cake thus produced is cleaned regularly from the filter as described above, and the cleaning liquid in which the rubber is present is returned to the precipitation container.

[0093] If the filters used do not require a positive pressure on the retentate side and / or a negative pressure on the filtrate side, the time required for cleaning the filter can also be determined by the filtrate volume flow or the solids content in the retentate.

[0094] The cleaning of the filter can be achieved by passing a cleaning liquid through the filter from the filtrate side to the retentate side, thereby cleaning the filter cake from the filter. Alternatively, the cleaning liquid can also be supplied to the filter instead of the low rubber phase. Since the filter cake mainly contains rubber, it is preferred to introduce the cleaning liquid containing the rubber from the filter cake into the sedimentation vessel. In order to enable the cleaning liquid containing the rubber present therein to be introduced into the sedimentation vessel, it is preferred to use such a cleaning liquid: it only contains components that are also present in the liquid in the sedimentation vessel. Therefore, it is particularly preferred to use water as the cleaning liquid.

[0095] The filtrate which is substantially free of rubber is removed from the operation and preferably provided to wastewater treatment before the wastewater is discharged into the environment. Alternatively, the filtrate which is substantially free of rubber may be substituted for the above-mentioned fresh water (particularly deionized water) or added to the residual rubber-containing liquid phase together with the fresh water downstream of the drain.

[0096] If the amount of liquid phase comprising finely divided rubber supplied to the return water container from the mechanical dewatering is greater than the amounts of rubber-rich phase and rubber-poor phase withdrawn from the return water container, resulting in the filling level in the return water container possibly exceeding the maximum filling level, the return water container preferably comprises an overflow through which the wastewater flow can be discharged from the return water container.

[0097] If the rubber has a lower density than the liquid, it will float in the return container, so that the rubber-rich phase is located in the upper region of the return container. In this case, the overflow is preferably arranged in the lower region of the return container, so that in the event that the filling level in the return container exceeds the maximum filling level, ideally only the low-rubber phase can be withdrawn. In order to allow the liquid to be discharged without providing an additional valve, it is therefore preferred that the pipe forming the overflow initially extends upwards to the height of the maximum filling level and comprises a bend of at least 90° there, so that the low-rubber phase can be discharged through the overflow as soon as it has reached the maximum filling level due to the hydrostatic pressure.

[0098] If the density of the rubber is higher than the density of the liquid, the rubber will sink accordingly. In this case, the rubber-rich phase is located at the bottom of the return container and the low-rubber phase is located at the top, so that when the overflow is arranged in the upper region of the return container, preferably at the highest filling level, the low-rubber phase flows into the overflow when the filling level in the return container is too high.

[0099] In particular, when the return water container is used in a dual-purpose device for producing both rubber with a lower density than the liquid and rubber with a higher density than the liquid, it is preferred to arrange an overflow at the top of the return water container (preferably at the position of the maximum filling level) and an overflow at the bottom of the return water container, wherein the overflow at the top of the return water container is closed when the density of the rubber is lower than the density of the liquid, and the overflow at the bottom of the return water container is closed when the density of the rubber is higher than the density of the liquid. It is more preferred if the overflow at the bottom is connected to the overflow at the top of the return water container by a conduit, wherein the conduit opens to the overflow downstream of the closing member, and the height of the opening of the conduit to the overflow is preferably the same as the connection of the overflow to the return water container.

[0100] As soon as the filling level in the return water container exceeds the maximum filling level, the rubber-rich phase flows into the overflow. In order to prevent the rubber-rich phase which subsequently flows into the overflow from entering the wastewater disposal and thus causing a loss of the rubber contained in the rubber-rich phase, in this case it is preferred to provide a circulation conduit which branches off from the overflow and opens into the conduit through which the low-rubber phase flows for concentration, in particular filtration. This prevents the liquid drawn from the overflow which still contains rubber from being sent to disposal and thus prevents the rubber present therein from being removed from the operation as waste.

[0101] The liquid phase containing residual rubber collected in the buffer vessel can be directly returned to the sedimentation vessel or introduced into the return vessel. In the second case, the liquid phase containing residual rubber is mixed with the phase containing finely divided rubber, which is produced during the mechanical dehydration of the aqueous suspension containing rubber particles. In order to prevent the liquid phase in the return vessel from being agitated and mixed by the introduction of the liquid phase containing residual rubber, and further to prevent foaming in the return vessel, the phase containing residual rubber is preferably fed into the pipe that introduces the liquid phase containing finely divided rubber into the return vessel.

[0102] As an alternative to using a return vessel, it is also possible to introduce the liquid phase containing finely divided rubber which is produced during the mechanical dewatering of the aqueous suspension containing rubber particles into a buffer vessel and then return it to the sedimentation vessel and mix it with the liquid phase containing residual rubber removed in the dewatering stage. This has the advantage, inter alia, that by introducing the liquid phase containing finely divided rubber into the buffer vessel, the solids content in the buffer vessel is reduced, thereby further reducing the tendency to form deposits or blockages, in particular in the connecting line from the buffer vessel to the sedimentation vessel.

[0103] Regardless of whether the liquid phase containing finely crushed rubber is introduced into the buffer container and mixed therewith with the liquid phase containing residual rubber, the liquid phase containing residual rubber collected in the buffer container is first introduced into the return water container, or the liquid phase containing finely crushed rubber from the return water container and the liquid phase containing residual rubber from the buffer container are separately introduced into the precipitation container, it is preferred that the liquid phase containing residual rubber and / or the liquid phase containing finely crushed rubber or the mixture of the liquid phase containing finely crushed rubber and the liquid phase containing residual rubber returned from the buffer container to the precipitation container is mixed with the precipitation solution before being introduced into the precipitation container.

[0104] As a pump for conveying the liquid phase containing sintered rubber particles or (if no separate sintering step is carried out) the suspension containing rubber particles obtained in step (a) to the mechanical dewatering, a centrifugal pump configured as a vortex pump is preferably used. As a pump for conveying the low-rubber phase to the filtration, an eccentric screw pump is preferably used.

[0105] Since the solid fraction of the liquid phase containing the residual rubber is introduced into a buffer container and then returned from the buffer container to a return container or directly into a sedimentation container, it is likewise preferred to use a centrifugal pump configured as a vortex pump.

[0106] If the buffer container is arranged below the extruder, the water discharged through the drain can flow directly into the buffer container. In this case, it is not necessary to use a pump to transfer the liquid phase from the extruder to the buffer container. If the pressure of the liquid phase containing residual rubber when leaving the extruder is greater than the pressure in the buffer container, it is also not necessary to have a separate pump to transfer the liquid phase containing residual rubber to the buffer container.

[0107] For conveying aqueous suspensions containing rubber particles and / or conveying a rubber-rich phase and / or conveying a liquid phase containing residual rubber, a centrifugal pump configured as a vortex pump is preferably used. Preferred centrifugal pumps have an open or semi-open impeller, wherein the impeller is a radial wheel with a relatively large channel for conveying solids contained in the medium. In addition, such an open or semi-open impeller is least prone to failure when used to convey liquids containing particles.

[0108] Therefore, the use of an eccentric screw pump or a centrifugal pump configured as a vortex pump can convey a liquid phase containing rubber particles without the pump being blocked by the rubber particles contained in the liquid phase because a sufficiently large flow channel is included through which the liquid can pass without contacting the impeller of the pump.

[0109] In order to prevent the eccentric screw pump from wearing or clogging due to the expansion of the plastic caused by the residual monomers that may still be contained, so as to be able to uniformly deliver the liquid phase containing the rubber particles, it is further preferred that the stator and / or the rotor of the eccentric screw pump is made of chlorosulfonated polyethylene rubber (CMS), such as DuPont Performance Elastomers. Or with its coating. Alternatively, the stator and / or rotor of the eccentric screw pump can also be made of metal (such as steel or aluminum). It is particularly preferred that the stator or rotor is made of CMS and the other part is made of metal.

[0110] Since the rubber particles continue to aggregate and thus become larger with increasing residence time, it is further preferred that the particle size of the rubber particles precipitated in step (a) and / or of the rubber particles of the liquid phase sintered or containing residual rubber in step (b) can be controlled. For this purpose, for example, a pump can be used which includes cutting tools for particle comminution and / or a particle comminution machine is connected upstream of the pump.

[0111] Suitable particle crushers are, for example, wet mills, which are passed through a liquid phase containing the rubber particles and usually contain cutting tools, wherein the cutting tools can be rigidly contained in the particle crusher or can be configured as a rotor and a stator. Suitable particle crushers are, for example, Siefer machine.

[0112] For example, pumps comprising rotor-stator toothed mixing elements for comminuting particles are commercially available from BWS Technologie GmbH under the name Online homogenizer.

[0113] An exemplary embodiment of the invention is shown in the drawings and is explained in more detail in the following description.

[0114] The individual figures show a flow chart of the method of the invention.

[0115] For processing rubber from a rubber-containing dispersion, a rubber-containing dispersion 1 (e.g. obtained by emulsion polymerization) is introduced into a precipitation vessel 5 together with a precipitation solution 3. Here, the dispersion 1 is preferably conveyed only by gravity into the precipitation vessel 5. If conveying by gravity is not possible, in particular if the dispersion tank for intermediate storage of the dispersion is too low, the dispersion 1 is preferably conveyed into the precipitation vessel 5 using a peristaltic pump.

[0116] In the precipitation vessel, the rubber-containing dispersion 1 and the precipitation solution 3 are mixed with a mixing unit 7 (e.g., a stirrer) to form an aqueous suspension containing rubber particles. The aqueous suspension 9 containing rubber particles is removed from the precipitation vessel and supplied to an optional sintering vessel 11, where the rubber particles aggregate to provide larger particles. In order to prevent the rubber particles from settling, the suspension containing rubber particles in the sintering vessel 11 is also mixed using a mixing unit 13 (e.g., a stirrer).

[0117] In order to convey the aqueous suspension 9 containing rubber particles from the precipitation container 5 into the sintering container 11, a first pump 15 is installed in the pipeline connecting the precipitation container 5 and the sintering container 11. Preferably, the first pump 15 is part of a pumping circulation loop 17, wherein, in particular in the event of a failure to remove from the sintering container 11, for example in the event of a malfunction of a plant component downstream of the sintering container, the suspension 9 containing rubber particles is kept in motion, thereby preventing the particles from settling. In this case, the first pump 15 is preferably a centrifugal pump configured as a vortex pump.

[0118] The suspension 18 now containing larger rubber particles is supplied from the sintering container 11 to a mechanical dewatering 19. The mechanical dewatering 19 here can be carried out, for example, by centrifugation or filtration, with centrifugation being preferred. In order to empty the sintering container 11, a discharge pipe 20 is preferably provided at the bottom of the sintering container.

[0119] In normal operation, the discharge pipe 20 is closed and the aqueous suspension 18 containing the larger rubber particles produced in the sintering vessel is removed through the extraction pipe at the top of the sintering vessel 11.

[0120] In particular in the case of batch mechanical dewatering 19, the aqueous suspension containing rubber particles supplied to the mechanical dewatering 19 must be temporarily stored. For this purpose, a buffer container 21, for example, can be provided in which the aqueous suspension containing rubber particles 18 is temporarily stored. In order to prevent the rubber particles from settling out of the suspension, it is preferred that the buffer container 21 comprises a mixing unit, for example a stirrer, with which the suspension can be stirred.

[0121] Alternatively, or in addition, it is further preferred to provide a second pumping circulation loop 23 as shown in the figure, in which the aqueous suspension containing rubber particles can be pumped and circulated. The aqueous suspension containing rubber particles is mixed in the second pumping circulation loop 23 to prevent the rubber particles from settling. The second pumping circulation loop 23 is particularly advantageous when mechanical dewatering is continuously performed.

[0122] If the mechanical dewatering device 19 is operated continuously, it is sufficient to provide a second pumping circulation loop 23 , although a buffer container 21 may alternatively or additionally be connected upstream of the mechanical dewatering device 19 .

[0123] If the mechanical dewatering device 19 is operated batchwise, a buffer container 21 is required to temporarily store the suspension before it is supplied to the mechanical dewatering device 19. However, here it is also possible to connect a pumping circulation loop 23 upstream of the buffer container 21, as shown.

[0124] In order to convey the aqueous suspension containing rubber particles from the sintering container 11 to the mechanical dewatering device 19 and to circulate in the pumping circulation loop 23, a second pump 25 is installed in the pumping circulation loop 23. Further preferably, a bypass 27 is provided so that the second pump 25 can be bypassed, and a third pump 29 is installed in the bypass 27.

[0125] As an alternative to the embodiment shown here, the second pump 25 and the third pump 29 can also be connected in series. This is particularly advantageous when the third pump 29 cannot build up a sufficiently high pressure relative to the second pump 25, because in this case a circulation flow from the pressure side to the suction side will be established.

[0126] Preferably, the second pump 25 and the third pump 29 are centrifugal pumps configured as vortex pumps, similar to the first pump 15 .

[0127] Since the particles may further aggregate in the pumping circulation loop 23, it is more preferred if the second pump 25 and / or the third pump 29 are equipped with a cutting device for particle crushing. Using the cutting device, the particle size of the rubber particles can be adjusted to the desired size, and particles that have reached an undesirable size due to aggregation will be crushed. In particular, when the suspension 18 containing rubber particles is conveyed directly to the mechanical dewatering 19, it is preferred that the second pump 25 and the third pump 29 are connected in series, in which case the second pump 25 preferably does not contain a cutting device and builds up the necessary pressure, and the third pump 29 with a cutting device is connected downstream of the second pump. If a buffer container 21 is present, no significant pressurization is required, and the second pump 25 and the third pump 20 can be operated in parallel.

[0128] As an alternative or in addition to the pump with cutting device, the pumping circulation loop 23 can also contain a particle crusher to prevent the formation of oversized rubber particles. The particle crusher is preferably a wet grinding device.

[0129] The sintering of the rubber particles in the sintering vessel 11 is usually carried out at a temperature higher than that at which the mechanical dewatering 19 is carried out. Therefore, it is preferred that a heat exchanger 31 is provided in the connecting pipe from the sintering vessel 11 to the mechanical dewatering 19 to cool the aqueous suspension containing the rubber particles. If a pumping circulation loop 23 is provided between the sintering vessel 11 and the mechanical dewatering 19, the heat exchanger 31 is preferably located at a position in the pumping circulation loop through which the aqueous suspension containing the rubber particles flows, even if the suspension is introduced directly from the sintering vessel 11 into the mechanical dewatering 19 and does not flow in a loop in the pumping circulation loop. When a buffer vessel 21 is used, it is also possible to choose to use cooling to adjust the temperature of the buffer vessel 21, for example by means of a double jacket or cooling pipes running in the buffer vessel.

[0130] In the mechanical dewatering 19 , the rubber particles are separated from the aqueous suspension containing the rubber particles, and rubber particles 33 containing residual moisture and a liquid phase 35 containing finely divided rubber are obtained.

[0131] The liquid phase 35 containing the finely chopped rubber is introduced into a return water container 37. The return water container 37 is preferably a sedimentation container in which the finely chopped rubber in the liquid phase containing the finely chopped rubber is accumulated, thereby forming a rubber-rich phase and a rubber-low phase.

[0132] Preferably, the rubber portion in the rubber-rich phase 39 is large enough so that the rubber-rich phase can be directly withdrawn from the return water container 37 and recycled into the sedimentation container 5 .

[0133] In order to transfer the rubber-rich phase 39 from the return water container 37 to the settling container 5, a pump 41 may be installed in the connecting pipe from the return water container 39 to the settling container 5. However, it is preferred that the return water container 37 is located higher than the settling container 5 so that the rubber-rich phase 39 can flow into the settling container 5 purely under the action of gravity, thereby eliminating the need for the pump 41.

[0134] It is further preferred if the recovered rubber-rich phase 39 is mixed with the precipitation solution 3 before introduction into the precipitation vessel 5 .

[0135] In order to obtain the rubber contained in the low rubber phase 43 as a product and not dispose of it with the wastewater generated by the operation, the low rubber phase 43 is sent from the return water container 37 to the filter 45. The filter 45 concentrates the rubber in the low rubber phase to form a rubber-rich retentate 47, which is introduced into the sedimentation container 5.

[0136] If the filtration 45 is carried out so that a filter cake is formed on the filter in the filtration device, the filter cake is preferably rinsed off regularly and the washing liquid in which the rubber is present is introduced as rubber-rich retentate 47 into the precipitation container 5. In order not to introduce any unwanted components into the precipitation container 5, backwashing is preferably carried out with water, in particular completely deionized water 49. Alternatively, the filtrate 51 can be used for backwashing.

[0137] The pore size of the filter used for filtration 45 is preferably selected so that substantially all of the finely divided rubber present in the low-rubber phase is separated out, thereby forming a substantially rubber-free filtrate 51 which can be discharged as wastewater and supplied to wastewater treatment and then to disposal.

[0138] The low rubber phase 43 is preferably conveyed to the filtration 45 using a fourth pump 53. Any pump capable of conveying a liquid phase containing only a low solid fraction can be used here. Suitable pumps are, for example, centrifugal pumps or eccentric screw pumps. When an eccentric screw pump is used, it is particularly preferred that the stator and / or rotor of the eccentric screw pump is made of chlorosulfonated polyethylene rubber (CMS).

[0139] The rubber granules 33 containing residual moisture extracted from the mechanical dewatering 19 are fed to the suction zone 55 of the extruder 57 for the production of thermoplastic molding compounds, in particular ABS or ASA. The rubber granules containing residual moisture pass through the suction zone and enter the dewatering section 59 of the extruder 57 under increased pressure. In the dewatering section 59, water is further squeezed out of the rubber granules containing residual moisture and introduced into a buffer container 63 through at least one drain port 61.

[0140] In order to prevent the pipeline from the drain 61 to the buffer container 63 from being blocked, water is preferably introduced into the pipeline continuously or discontinuously. Preferably, water is introduced directly after the drain 61. The water can be fresh water, in particular fully deionized water, or can be fed into the filtrate 51 produced in the filter 45.

[0141] The dewatered rubber particles are fed to a feed section 65 for at least one further polymer and / or additive, wherein in particular a thermoplastic polymer 67 , for example a SAN copolymer, is fed to the feed section 65 for producing a thermoplastic molding compound.

[0142] In a mixing section 69 adjacent to the feed section 65, the thermoplastic polymer is mixed with the rubber and homogenized to obtain a thermoplastic molding compound.

[0143] The mixing section 69 may be provided with degassing ports at the beginning and end, followed by a discharge zone 71 from which the thermoplastic molding compound 73 is preferably discharged in the form of molten strands which can subsequently be cut into pellets. The thermoplastic molding compound is particularly preferably an ABS copolymer or an ASA copolymer.

[0144] Since the liquid phase supplied to the buffer container 63 still contains residual rubber, the buffer container 63 has an agitator 75 by which the residual rubber is kept in the liquid phase and the residual rubber is prevented from accumulating. Depending on whether the density of the rubber used is lower than or higher than the density of the liquid, if the liquid phase containing the residual rubber in the buffer container 63 is not agitated, the rubber may float or settle.

[0145] The liquid phase 77 containing the residual rubber is returned from the buffer container 63 to the precipitation container 5. In this case, it is particularly preferred to mix the liquid phase 77 containing the residual rubber with the precipitation solution 3 before introducing it into the precipitation container 5. To this end, as shown in the figure, the rubber-rich phase 39 and the liquid phase 77 containing the residual rubber can be introduced into the feed line of the precipitation solution 3 from different positions, or two separate feed lines for the precipitation solution 3 can be provided, in which case the rubber-rich phase 39 is introduced into one feed line and the phase 77 containing the residual rubber is introduced into the other feed line.

[0146] Furthermore, the rubber-rich phase 39 may be mixed with the phase 77 containing residual rubber before being mixed with the precipitation solution 3 .

[0147] In addition to the above-described variants, it is also possible to introduce the phase 77 containing residual rubber into the return water container 37 instead of into the sedimentation container 5. In this case, the phase 77 containing residual rubber and the liquid phase 35 containing finely divided rubber are combined directly in the return water container 37. If the phase 77 containing residual rubber is to be introduced into the return water container 37, it is particularly preferred to introduce the phase 77 containing residual rubber into the liquid phase 35 containing finely divided rubber before introducing the phase 77 containing residual rubber into the return water container 37. In particular, this can avoid unnecessary turbulence of the liquid surface in the return water container 37. If the phase 77 containing residual rubber is to be introduced directly into the return water container 37, it is preferably introduced into the return water container 37 via a dip tube in the same way as the liquid phase 35 containing finely divided rubber.

[0148] In order to convey the phase 77 containing residual rubber, a pump 79 is preferably provided, which is realized by a centrifugal pump configured as a free-flow pump. In particular, a centrifugal pump with an open or semi-open impeller is used here to prevent the pump 79 from being blocked.

[0149] In order to prevent the buffer container 63 from being unable to absorb more liquid phase containing residual rubber from the dewatering section 59 (for example, if extrusion is still in progress but sedimentation must be interrupted, so that no liquid phase 77 containing residual rubber can enter the sedimentation container 5), the buffer container 63 preferably has an overflow port 81.

[0150] When the maximum filling level is reached, the liquid phase containing the residual rubber can flow out of the buffer container 63 through the overflow.

[0151] In this case, the liquid phase containing the residual rubber flowing out through the overflow port 81 is usually disposed as waste water after being properly treated.

Claims

1. A method for producing a thermoplastic molding compound (73), comprising: (a) feeding a dispersion (1) containing rubber and a precipitation solution (3) into a precipitation vessel (5) to produce an aqueous suspension (9) containing rubber particles, (b) optionally sintering the rubber particles contained in the aqueous suspension containing rubber particles (9) to obtain larger particles, (c) mechanically dehydrating the aqueous suspension containing rubber particles to obtain rubber particles (33) containing residual water and a liquid phase (35) containing finely divided rubber, (d) feeding the rubber particles (33) containing residual moisture into an extruder (57), the extruder (57) comprising a suction zone (55) into which the rubber particles (33) containing residual moisture are fed; a dewatering section (59) in which a liquid phase containing residual rubber is removed from the rubber particles containing residual moisture; at least one feed section (65) for at least one other polymer (67) and / or additives; a mixing section (69) in which the rubber particles, at least one other polymer and the additives are mixed together to obtain a melt of a thermoplastic molding compound (73); and a discharge section (71) through which a molten strand is extruded from the extruder (57), The liquid phase containing the residual rubber removed in the dehydration section (59) is collected in a buffer container (63), the buffer container (63) includes at least one agitator (75), the liquid phase containing the residual rubber is stirred by the agitator to prevent the accumulation of rubber particles still contained in the liquid, and the liquid phase containing the residual rubber (77) collected in the buffer container (63) is returned to the sedimentation container (5).

2. The method according to claim 1, characterized in that The liquid phase containing the finely divided rubber is returned to the precipitation vessel (5).

3. The method according to claim 1 or 2, characterized in that: The liquid phase containing the residual rubber is removed from the extruder (57) and mixed with water.

4. The method according to claim 2 or 3, characterized in that: The liquid phase containing the finely divided rubber is introduced into a buffer vessel (63) before being returned to the sedimentation vessel (5) and mixed with the liquid phase containing the residual rubber removed in the dewatering section (59).

5. The method according to any one of claims 1 to 4, characterized in that The liquid phase (77) containing residual rubber and / or the liquid phase containing finely divided rubber which is returned from the buffer container (63) to the precipitation container (5) is mixed with the precipitation solution (3) before being introduced into the precipitation container (5).

6. The method according to any one of claims 1 to 5, characterized in that The buffer container (63) has an overflow (81) through which the liquid phase containing the residual rubber can be discharged from the process as waste water.

7. The method according to claim 2, characterized in that The liquid phase containing the finely divided rubber is collected in a return water container (37).

8. The method according to claim 7, characterized in that The return water vessel (37) is a sedimentation vessel in which a rubber-rich phase (39) and a low-rubber phase (43) are formed.

9. The method according to claim 8, characterized in that The rubber-rich phase (39) is mixed with the precipitation solution (3) and introduced into the precipitation vessel (5).

10. The method according to claim 8 or 9, characterized in that: The low rubber phase (43) is concentrated and then returned to the precipitation vessel (5).

11. The method according to any one of claims 7 to 10, characterized in that The liquid phase containing the residual rubber collected in the buffer container (63) is introduced into the return water container (37).

12. The method according to any one of claims 1 to 11, characterized in that A centrifugal pump or an eccentric screw pump configured as a vortex pump is used to recover the liquid phase (77) containing residual rubber and / or the liquid phase containing finely divided rubber and / or the rubber-rich phase (39) and / or the concentrated low-rubber phase (47) from the buffer container (63).

13. The method according to claim 12, characterized in that The vortex pump includes a stator and / or a rotor made of chlorosulfonated polyethylene rubber.

14. The method according to any one of claims 1 to 13, characterized in that The rubber is grafted butyl acrylate rubber or grafted butadiene rubber.

15. The method according to any one of claims 1 to 14, characterized in that The thermoplastic molding compound is a butyl acrylate-styrene-acrylonitrile copolymer, an acrylonitrile-butadiene-styrene copolymer, or an acrylonitrile-styrene-acrylate copolymer.

Images