Defoaming of aqueous polymer dispersions

Abstract

The invention relates to methods for producing polymers based on ethylenically unsaturated monomers in the form of aqueous dispersions (polymer dispersions) by means of radically initiated emulsion polymerization, characterized in that the aqueous dispersions of the polymers based on ethylenically unsaturated monomers are defoamed by being applied to a rotating disk (4).

Description

[0001] Defoaming of aqueous polymer dispersions

[0002] The invention relates to methods for defoaming aqueous dispersions of polymers based on ethylene unsaturated monomers (polymer dispersions) produced by means of radically initiated emulsion polymerization, and to a device for defoaming polymer dispersions.

[0003] Polymers based on ethylene unsaturated monomers are used in a wide variety of applications, for example in aqueous dispersions or water-redispersible polymer powders, such as coatings or adhesives for diverse substrates. These polymers are generally stabilized by protective colloids, such as polyvinyl alcohols, or low-molecular-weight surfactants.

[0004] During the production of polymer dispersions via emulsion polymerization, or during the handling of such polymer dispersions, for example, when transferring them from the polymerization reactor to another container, foam regularly forms, which complicates further processing. One reason for this is that the conversion of the monomers during polymerization is usually incomplete. The polymerization rate is generally high up to monomer conversion levels of 80% to 85%, but then slows down considerably with increasing conversion levels. Therefore, in industrial practice, emulsion polymerization is often terminated at monomer conversions of 90% to 97%. Residual monomers remaining in the polymer dispersion regularly cause foaming problems during further handling.Foaming problems are particularly pronounced when emulsion polymerization takes place at elevated pressure, for example at 5 to 120 bar abs., as is common in the copolymerization of gaseous monomers such as ethylene, and the resulting polymer dispersion is transferred from the polymerization reactor to a low-pressure vessel, also called an expansion reactor, where it is depressurized to, for example, atmospheric pressure. During this process, residual monomers, such as ethylene or vinyl acetate, and water are transferred into the gas phase, forming foam. Foam formed in this way has, for example, a density of 0.1 to 0.6 kg / L.

[0005] To further process polymer dispersions, the foam must be eliminated, or rather, the gas and dispersion phases must be separated as completely as possible. In industrial practice, various methods for defoaming polymer dispersions are currently common: Firstly, the addition of chemical defoamers – however, this approach is limited, for example, by requirements regarding the composition and properties of the polymer dispersions. Secondly, mechanical foam destruction or foam compaction, for example by stirring, is used, but this involves time and equipment costs and is also limited by the limited shear stability of the polymer dispersions. Finally, the separation of the gas and dispersion phases can also be achieved simply by allowing the dispersions to settle, but this requires a corresponding investment of time and storage containers with a correspondingly large volume.Often, several or all of these options are used in combination.

[0006] In batch or semi-batch polymerization processes, defoaming is currently often carried out in a vessel two to three times the size of the polymerization reactor. In this vessel, the foam is broken down under stirring over an extended period, separating the gas and dispersion phases. The dispersion is then typically processed further in the same vessel. However, in the case of producing polymer dispersions using continuous processes, such as emulsion polymerization in a tubular reactor, existing defoaming approaches reach additional limits. This is because several correspondingly large vessels would need to be cycled, and the defoaming process following the continuous emulsion polymerization would have to be operated discontinuously.However, combining continuous and discontinuous process steps represents a problematic break in the process design, making such processes inefficient, inflexible, and difficult to handle. Against this background, the task was to provide continuous processes for defoaming aqueous dispersions of polymers based on ethylene-unsaturated monomers produced by radical-initiated emulsion polymerization, particularly also in the case of gaseous monomers such as ethylene, as well as suitable defoaming devices that enable defoaming to be carried out as efficiently as possible, for example, with only one defoaming vessel and / or in smaller defoaming vessels, preferably also without the need for defoamers and / or within a shorter time and thus more economically advantageous, preferably with increased monomer recovery.

[0007] Surprisingly, the problem was solved by defoaming polymers of ethylene unsaturated monomers produced by radically initiated emulsion polymerization in the form of aqueous dispersions by applying them to a rotating disk ( 4 ).

[0008] Degassing liquids using centrifugal force with rotating discs is a well-known technique, particularly in the food and pharmaceutical industries, for removing small amounts of residual gas, as described, for example, by M. Goldberg et al. in I&EC Process Design and Development, Vol. 6, No. 2, pages 196 to 200. However, in such applications with small amounts of residual gas, foaming generally does not occur, or at least not a significant one. The focus here is solely on the release of the residual gas components, which is why such methods are unsuitable for defoaming polymer dispersions. This is even more true for polymer dispersions with larger amounts of residual monomers or residual gas and the associated massive amounts and problems of foaming.In some cases, for example when transferring polymer dispersions from pressure polymerization reactors to expansion reactors, the polymer dispersions can consist entirely of foam. Furthermore, polymer dispersions naturally tend to coagulate and are also regularly shear-thinning, and therefore behave completely differently from food and pharmaceutical products, especially with regard to the type, behavior, and quantity of foam.

[0009] The invention relates to processes for the production of polymers based on ethylene unsaturated monomers in the form of aqueous dispersions (polymer dispersions) by means of radically initiated emulsion polymerization, characterized in that the aqueous dispersions of the polymers based on ethylene unsaturated monomers are defoamed by application to a rotating disk (4).

[0010] For the sake of clarity, it should be noted that Figures 1, 2A and 2B represent particular, preferred embodiments of the present invention and that the present invention is by no means limited to the combination of features shown in the figures.

[0011] The terms rotating disk and rotatable disk are in the following also abbreviated as disk according to the invention ( 4 ).

[0012] The term defoaming generally means complete or at least partial removal of foam from the polymer dispersion and generally also includes degassing, i.e., the release of gas from the polymer dispersion, or generally a separation of gaseous and liquid phases of the polymer dispersion.

[0013] The rotating or rotatable disk (4) is preferably a circular disk. According to the invention, the disk (4) generally rotates about its center point. The disk (4) according to the invention particularly preferably has the shape of a cylinder, more preferably a rotary cylinder, in particular a flat cylinder or rotary cylinder. According to the invention, the cylinder generally rotates about its axis. The radius of the cylinder is generally a multiple, preferably at least 10 times, and in particular 20 to 60 times larger than its thickness (13). The disk (4) according to the invention has a radius of preferably 10 to 200 cm, particularly preferably 20 to 125 cm, and most preferably 30 to 75 cm. The disk (4) according to the invention has a thickness (13) of preferably 0.5 to 10 cm, particularly preferably 1 to 5 cm, and most preferably 1.5 to 3 cm.The disk (4) according to the invention can have different thicknesses (13) at different locations, but preferably has essentially the same thickness (13) everywhere.

[0014] Both or preferably one flat side of the disk (4) according to the invention has several or preferably one recess. Preferably, at least one, in particular one, recess of a flat side of the disk (4) according to the invention is oriented in the direction in which one or more supply lines (11) for the polymer dispersion and optionally one or more supply lines for additives are located.

[0015] A further object of the present invention is a defoaming device for aqueous polymer dispersions, characterized in that the defoaming device comprises a container (6) which contains a rotating or rotatable disk (4) and one or more supply lines (11) for the polymer dispersion and optionally one or more supply lines for additives, wherein the rotating or rotatable disk (4) is horizontally oriented in the container (6) and both or preferably one flat side of the rotating or rotatable disk (4) has several or preferably one recess, wherein at least one, in particular one, recess of a flat side of the rotating or rotatable disk (4) is oriented in the direction in which one or more supply lines for the polymer dispersion (11) and optionally one or more supply lines for additives are located.

[0016] The polymer dispersion applied to the disk (4) according to the invention generally experiences a centrifugal force as a result of the rotation of the disk (4) and is accelerated outwards on the disk (4). The polymer dispersion preferably deposits itself on the disk (4) according to the invention in the form of a thin layer or film, with a layer thickness of preferably 0.05 to 5 mm, particularly preferably 0.1 to 2 mm, and most preferably 0.2 to 1 mm, especially at the outermost edge of the disk (4) according to the invention, preferably in the segment S3 (21) mentioned below. The layer or film thickness can be determined, for example, via the mass flow rate of the polymer dispersion and its density or via formula 2 described below for determining the film thickness θ. Alternatively, the layer or film thickness can also be determined by means of laser interference measurement, i.e., laser interferometry.

[0017] The polymer dispersion applied to the disk (4) according to the invention is preferably flung against the inner wall of the defoaming device by the rotation of the disk (4). At the edge of the disk (4) according to the invention, particularly as it exits the disk (4), the polymer dispersion is preferably transformed into droplet or thread form as a result of the rotation of the disk (4). On the inner wall of the defoaming device, the polymer dispersion preferably runs downwards, particularly in the form of a film.

[0018] The polymer dispersion is preferably defoamed directly on the disk (4) according to the invention, and is particularly preferably completely defoamed as it leaves the disk (4). Preferably, further defoaming occurs upon impact, especially upon contact, of the polymer dispersion with the inner wall of the defoaming device. Further defoaming also preferably occurs as the polymer dispersion runs downwards along the inner wall of the defoaming device.

[0019] A flat side of the disk (4) according to the invention preferably has a depression in and around the center of rotation (14) of the disk (4) according to the invention. The center of rotation (14) is generally the point, in particular the center of a circle, or the axis, in particular the axis of a cylinder, about which the disk (4) according to the invention rotates. The disk (4) according to the invention is preferably rotationally symmetrical with an axis of symmetry through its center of rotation (14). The flat side of the disk (4) according to the invention, which has a depression, is preferably arranged spatially facing upwards and in particular in the direction in which one or more supply lines (11) for the polymer dispersion are located. The disk (4) according to the invention preferably has an overall rising profile in a cross-section, in particular in every cross-section, through its center of rotation (14) starting from its center of rotation (14) towards its edge.The profile extending from the center of rotation (14) of the disk (4) according to the invention towards its edge can be linear, continuous, or, in particular, discontinuously rising, more preferably having segments with different slopes, and especially preferably having rising and flat segments. Preferably, the disk (4) according to the invention is planar, flat, or planar about its center of rotation (14). Preferably, the profile extending from the center of rotation (14) of the disk (4) according to the invention towards its edge is not completely planar, flat, or flat. Preferably, the profile extending from the center of rotation (14) of the disk (4) according to the invention towards its edge is not descending, in particular not descending at any point or in any segment. The profile of the disk (4) according to the invention preferably has no edges or corners, in particular no sharp edges.The profile of the disc (4) according to the invention preferably has exclusively flat, curved, rounded and rounded segments or areas.

[0020] Starting from the deepest point of the depression (bottom of the depression), particularly from the center of rotation (14), the profile towards the edge of the disk (4) according to the invention has a slope of preferably 2% to 350%, more preferably 5% to 100%, and most preferably 10% to 20%. The slope is defined here in the usual mathematical sense, i.e., height divided by distance in the radial direction of the disk (4). The profile of the disk (4) according to the invention can be divided into several segments with different slopes, as illustrated by way of example in Figure 2B. A first segment S1 (19) is located at the bottom of the depression. The segment S1 (19) is preferably horizontal, planar, or flat.A second segment S2 (20) adjoins the bottom of the recess or segment S1 (19) and preferably has the steepest slope, in particular the steepest average or the steepest absolute slope, of the entire profile of the disc (4) according to the invention. The average slope of a segment is the total slope in % from the beginning to the end of that segment. The absolute slope of a segment is the total slope in centimeters from the beginning to the end of that segment. Segment S2 (20) is generally not horizontal, planar, or flat. A third segment S3 (21) follows the second segment S2 (20) and preferably extends from there to the edge of the disc (4) according to the invention. The transition from segment S2 (20) to S3 (21) is preferably the point where the profile flattens out, in particular at the inflection point of the profile slope between S2 (20) and S3 (21).The transitions from the second segment S2 (20) to the third segment S3 (21) and to the first segment S1 (19) are indicated in Figure 2B by reference numerals (18) and (17), respectively. The third segment S3 (21) has a slope towards the edge of the disk (4) according to the invention, which is preferably less than the slope in the second segment S2 (20). The third segment S3 (21) has an average or absolute slope towards the edge of the disk (4) according to the invention, which is preferably less than the average or absolute slope in the second segment S2 (20). The slope of the third segment S3 (21) preferably decreases towards the edge of the disk (4) according to the invention. The different segments S1 (19), S2 (20) and S3 (21) are therefore generally characterized by different slopes. Further segments may exist between segments S1 (19), S2 (20) and S3 (21).Preferably, the disk (4) according to the invention consists of the three segments S1 (19), S2 (20) and S3 (21). The transition between the segments S1 (19), S2 (20) and S3 (21) is particularly preferred to be continuous.

[0021] The slope, in particular the average slope, in segment S1 (19) is preferably 0%, more preferably 0% to 2%. The slope, in particular the average slope, in segment S2 (20) is preferably 35% to 350%, more preferably 50% to 200%, and most preferably 75% to 150%. The slope, in particular the average slope, in segment S3 (21) is preferably 1% to 30%, more preferably 2% to 20%, and most preferably 5% to 15%. The slopes in the second segment S2 (20) and in the third segment S3 (21) are identified in Figure 2B by reference numerals (15) and (16), respectively.

[0022] The polymer dispersion can be applied to any point on a flat side of the disk (4) according to the invention or distributed over the entire surface of a flat side of the disk (4) according to the invention. Preferably, the polymer dispersion is applied to the center of a flat side, particularly in the region of the center of rotation (14) of the disk (4) according to the invention. It is especially preferred that the polymer dispersion is applied to the recess, particularly in the region of the center of rotation (14) of the disk (4) according to the invention, and most preferably in the region of the first segment S1 (19).

[0023] The supply line (11) for the polymer dispersion is preferably a pipe with a diameter (10) of preferably 2 to 50 cm, particularly preferably 5 to 30 cm and most preferably 8 to 20 cm.

[0024] The polymer dispersion is preferably applied to the disk (4) according to the invention via several or, in particular, one supply line (11), especially a supply tube. The supply line (11) for the polymer dispersion is preferably inserted in the head of the container (6) of the defoaming device. The supply line (11) for the polymer dispersion is preferably guided vertically downwards in the container (6) of the defoaming device. The end of the supply line (11) that points towards the disk (4) according to the invention preferably projects into the recess of the disk (4) according to the invention or is preferably located below the upper edge of the recess. The end of the supply line (11) that points towards the disk (4) according to the invention is generally open.

[0025] The recess of the disk (4) according to the invention is preferably at least 0.25 to 4 times as deep, particularly preferably at least half to twice as deep, and most preferably 0.8 to 1.2 times as deep as the clear diameter of the supply line (11) (pipe diameter) for the polymer dispersion. The supply line (11) for the polymer dispersion preferably terminates at least half and / or at most two pipe diameters above the bottom of the recess, particularly preferably at least half and / or at most one pipe diameter above the bottom of the recess. At the bottom of the recess, a circular surface with a diameter preferably corresponding to at least the outer diameter (10) of the supply pipe (11) of the polymer dispersion, in particular 1.1 to 2, more preferably 1.2 to 1.5 times the outer diameter (10) of the supply pipe (11) of the polymer dispersion, is designed horizontally, flat, or planar.

[0026] The disk (4) according to the invention can, for example, be dimensioned based on the shear acting on the polymer dispersion. For this purpose, the mean radial shear rate y in the layer or film of the polymer dispersion at the edge, in particular in segment S3 (21) , of the disk (4) according to the invention is preferably considered. The mean radial shear rate y [1 / s] is obtained, for example, from the following formula 1:

[0027] The film thickness ö [m] is preferably designed using the following formula 2: The variables in formulas 1 and 2 represent the following physical quantities: o [rad / s] : angular velocity, r [m] : radial distance from the center of rotation (14) of the

[0028] disk ( 4 ) , p [kg / m3] : density of the degassed polymer dispersion, rj [Pa s] : viscosity of the degassed polymer dispersion, m [kg / s] : mass flow rate (total mass flow rate across the disk)

[0029] (4) ) ,

[0030] 0 [rad] : Inclination angle at the disc edge, in particular average inclination angle in segment S3 (21) .

[0031] The mean radial shear rate y increases with increasing disk radius r and increasing angular velocity o. For the conservative design of the disk (4) according to the invention and its rotational speed, the residual gas factor s is preferably used. The residual gas factor s [ (kg°' 7 2 s 1 '^) / (m 1 ' 2 5 wheels 2 ) ] is preferably determined using the following formula 3: m 0,72 £ = - d 1 - 25 ■ CO 2

[0032] The variables in formula 3 represent the following physical

[0033] Sizes: s [ (kg°' 7 2 s 1 ' 28 ) / (m 1 ' 25 wheel 2) ] : residual gas factor, m [kg / s] : mass flow rate (total mass flow rate over the disk (4) ) , d [m] : diameter of the disk (4) , o [rad / s] : angular velocity.

[0034] The disk (4) according to the invention and its rotational speed are preferably designed such that the residual gas factor s is preferably less than 0.0004, most preferably less than 0.0002, particularly at pressures in the defoaming device of 0.9 to 2 bar abs., preferably 1 to 1.5 bar abs.

[0035] The rotating disk (4) has an angular velocity a of preferably 50 to 5000 rpm, particularly preferably 500 to 4000 rpm and most preferably 1500 to 3000 rpm.

[0036] The defoaming device, as exemplified in Figure 1, is generally a container (6) containing a disk (4) according to the invention. The disk (4) according to the invention is preferably horizontally oriented in the defoaming device. The distance between the disk according to the invention

[0037] (4) and the inner wall of the defoaming device is not essential. Advantageously, the dimensions of the defoaming device and the rotating disk (4) are designed such that the polymer dispersion comes into contact with the inner wall of the defoaming device when the process is carried out.

[0038] The disk (4) according to the invention is typically connected to a drive (5). The drive (5) sets the disk (4) according to the invention into rotation. Motors commonly used for such purposes are suitable as the drive (5). The drive (5) of the disk (4) according to the invention is preferably located in an area outside the container (6) of the defoaming device. The drive (5) can, for example, be connected to the disk (4) according to the invention via a drive shaft (12), in a conventional manner.

[0039] (5), in particular the drive shaft (12), is preferably connected to the side of the disk (4) according to the invention that is opposite the or more supply lines (11) of the polymer dispersion or the recess of the disk (4) according to the invention. The drive (5) of the disk (4) is preferably from below.

[0040] The polymer dispersion can be transferred, for example, from any container, preferably from a polymerization reactor, into the defoaming device or onto the rotating disk (4). The pressures in the polymerization reactor or other container are preferably 1 to 200 bar abs., more preferably 5 to 170 bar abs., particularly preferably 30 to 150 bar abs., and most preferably 50 to 90 bar abs. The pressures in the defoaming device are preferably 0.3 to 6 bar abs., particularly preferably 0.6 to 3 bar abs., and most preferably 0.9 to 1.5 bar abs. The pressures in the respective polymerization reactor are preferably higher than in the respective defoaming device. During the transfer of the polymer dispersion from a polymerization reactor or other container into the defoaming device or onto the rotating disk (4), the polymer dispersion is preferably depressurized.The polymer dispersion is preferably depressurized at specific points, for example via a valve (depressurization valve) (2) which is preferably located between the polymerization reactor or other container and the defoaming device and is usually connected to the polymerization reactor or other container and the defoaming device by pipes (1) and (3).

[0041] The polymer dispersion is transferred from the polymerization reactor, in particular via a piping system, preferably directly into the defoaming device. After leaving the polymerization reactor, the polymer dispersion preferably flows continuously through a piping system, which may optionally contain internal components such as a pressure relief valve (2), until it enters the defoaming device. The polymer dispersion is preferably introduced into the defoaming device immediately after pressure relief at the pressure relief valve (2). After leaving the polymerization reactor and before passing the pressure relief valve (2) and / or after passing the pressure relief valve (2), the polymer dispersion is preferably not stored, in particular not in a collection or intermediate tank.The polymer dispersion is preferably introduced into the defoaming device within 0.01 to 100 s, particularly preferably within 0.01 to 10 s, and most preferably within 0.01 to 1 s after decompression at the defoaming valve (2). After introduction into the defoaming device, particularly after exiting the supply line (11), the polymer dispersion is preferably applied directly or within < 100 s, particularly preferably within 0.01 to 100 s, even more preferably within 0.01 to 10 s, and most preferably within 0.01 to 1 s, to the disk (4) according to the invention. In the process according to the invention, the foam contained in the polymer dispersion is generally separated into a gas phase and a defoamed polymer dispersion.The gas released during the defoaming of the polymer dispersion is preferably discharged at the head of the defoaming device, for example via a nozzle, preferably above the disc (4) according to the invention, for example via a pipe (8) in which a valve (7), in particular a pressure regulating valve, may preferably be installed. The polymer dispersion defoamed according to the invention is discharged, for example via a nozzle at the bottom of the container (6) of the defoaming device, preferably below the disc (4) according to the invention, for example via a pipe (9).

[0042] Furthermore, unless otherwise specified, the defoaming devices can be designed like conventional degassing devices and are not bound to any particular embodiments. The defoaming devices can be based on commonly used materials, such as stainless steel. Conventional degassing devices are also commercially available, for example from KA-Process Maschinenbau Kaltenbach GmbH or FrymaKoruna; however, such commercial degassing devices generally have planar rotating disks (4), i.e., without the inventive recess and profile, and generally need to be modified according to the invention, as described above.

[0043] The polymer dispersion applied to the disk (4) according to the invention has a temperature of preferably 40 to 150°C, particularly preferably 50 to 130°C and most preferably 60 to 110°C.

[0044] The polymer dispersion applied to the disk (4) according to the invention has a shear-thinning viscosity of preferably 0.01 to 100 Pa s, particularly preferably 0.1 to 10 Pa s and most preferably 0.5 to 3 Pa s (determined by a shear rheometer at 25°C with a solids content of the polymer dispersion of 50%).

[0045] The polymer dispersion applied to the disk (4) according to the invention has a density of preferably 0.05 to < 0.8 kg / L, particularly preferably 0.1 to 0.5 kg / L and most preferably 0.1 to 0.3 kg / L (determination: gravimetric).

[0046] The polymer dispersion applied to the disk (4) according to the invention has a residual gas content of preferably 25 to 95 vol.%, particularly preferably 50 to 90 vol.%, and most preferably 70 to 90 vol.%. The residual gas content can be determined, for example, via the actual density of the polymer dispersion and the density of the corresponding fully defoamed polymer dispersion. The components of the residual gas have boiling points at 1 bar of preferably < 200°C.

[0047] The polymer dispersion taken from the defoaming device has a density of preferably > 0.8 to 1.5 kg / L, particularly preferably 0.85 to 1.3 kg / L and most preferably 0.9 to 1.2 kg / L (determination: gravimetric).

[0048] The polymer dispersion taken from the defoaming device has a residual gas content of preferably 0 to 23 vol.%, particularly preferably 0 to 8 vol.%, and most preferably 0 to 4 vol.%. The residual gas content can be determined, for example, via the actual density of the polymer dispersion and the density of the corresponding fully defoamed polymer dispersion. The respective polymer dispersion taken from the defoaming device generally has a lower residual gas content than the polymer dispersion applied to the disk (4) according to the invention.

[0049] The polymer dispersion taken from the defoaming device has a Brookfield viscosity of preferably 20 to 5000 mPas, particularly preferably 100 to 3500 mPas (determined with a Brookfield viscometer at 23°C at 20 rpm with a solids content of 50%). The polymers are produced by radical-initiated polymerization of the ethylene unsaturated monomers in aqueous medium according to the emulsion polymerization process, preferably in the presence of protective colloids and / or emulsifiers. Such processes are known per se.

[0050] The polymerization can be carried out by batch or semi-batch processes, and preferably by continuous processes. Continuous processes are preferably carried out in a tubular reactor and particularly preferably in a stirred tubular reactor, as described, for example, in US 2023-0406978.

[0051] The polymerization temperature is generally 40°C to 150°C, preferably 60°C to 110°C. The polymerization is preferably carried out at a pressure of 5 to 120 bar abs., particularly in the case of the copolymerization of gaseous comonomers such as ethylene, 1,3-butadiene, or vinyl chloride.

[0052] The ethylene unsaturated monomers are preferably selected from the group comprising vinyl esters, (meth)acrylic acid esters, vinyl aromatics, olefins, 1,3-dienes and vinyl halides and optionally further monomers copolymerizable with them.

[0053] Suitable vinyl esters are those of carboxylic acids with 1 to 18 carbon atoms. Vinyl acetate, vinyl propionate, vinyl butyrate, vinyl-2-ethylhexanoate, vinyl laurate, 1-methylvinyl acetate, vinyl pivalate, and vinyl esters of alpha-branched monocarboxylic acids with 9 to 11 carbon atoms, for example VeoVa9® or VeoVal O® (trade names of Hexion), are preferred. Vinyl acetate is particularly favored.

[0054] Suitable monomers from the group of acrylic acid esters or methacrylic acid esters are, for example, esters of unbranched or branched alcohols with 1 to 15 carbon atoms. Preferred methacrylic acid esters or acrylic acid esters are methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl methacrylate, n-butyl acrylate, n-butyl methacrylate, t-butyl acrylate, t-butyl methacrylate, and 2-ethylhexyl acrylate. Methyl acrylate, methyl methacrylate, n-butyl acrylate, t-butyl acrylate, and 2-ethylhexyl acrylate are particularly preferred.

[0055] Preferred vinyl aromatics are styrene, methylstyrene, and vinyltoluene. Vinyl chloride is the preferred vinyl halide. Preferred olefins are ethylene and propylene, and preferred dienes are 1,3-butadiene and isoprene.

[0056] Optionally, 0 to 10 wt.%, based on the total weight of the monomer mixture, auxiliary monomers can be copolymerized. Preferably, 0.1 to 5 wt.% auxiliary monomers are used. Examples of auxiliary monomers are ethylene-unsaturated mono- and dicarboxylic acids, preferably acrylic acid, methacrylic acid, fumaric acid, and maleic acid; ethylene-unsaturated carboxylic acid amides and nitriles, preferably acrylamide and acrylonitrile; mono- and diesters of fumaric acid and maleic acid, such as the diethyl and diisopropyl esters, as well as maleic anhydride; ethylene-unsaturated sulfonic acids or their salts, preferably vinylsulfonic acid and 2-acrylamido-2-methylpropanesulfonic acid.Other examples include pre-crosslinking comonomers such as polyethylene unsaturated comonomers, for example diallyl phthalate, divinyl adipate, diallyl maleate, allyl methacrylate, or triallyl cyanurate, or post-crosslinking comonomers, for example acrylamidoglycolic acid (AGA), methyl acrylamidoglycolic acid methyl ester (MAGME), N-methylolacrylamide (NMA), N-methylol methacrylamide, N-methylolallyl carbamate, alkyl ethers such as the isobutoxy ether or esters of N-methylol acrylamide, N-methylol methacrylamide, and N-methylolallyl carbamate. Epoxy-functional comonomers such as glycidyl methacrylate and glycidyl acrylate are also suitable. Other examples are silicon-functional comonomers, such as acryloxypropyltri(alkoxy)- and methacryloxypropyltri(alkoxy)-silanes, vinyltrialkoxysilanes and vinylmethyldialkoxysilanes, where, for example, ethoxy and ethoxypropylene glycol ether residues may be present as alkoxy groups.Also mentioned are monomers with hydroxy or CO groups, for example methacrylic acid and acrylic acid hydroxyalkyl esters such as hydroxyethyl, hydroxypropyl or hydroxybutyl acrylate or methacrylate, as well as compounds such as diacetone acrylamide and acetylacetoxyethyl acrylate.

[0057] Preferably, one or more monomers are selected from the group comprising vinyl esters; vinyl ester mixtures containing several monomers from the group comprising vinyl esters, olefins, vinyl aromatics, vinyl halides, acrylic acid esters, methacrylic acid esters, fumaric and / or maleic acid mono- or diesters;

[0058] (Meth)acrylic esters; (Meth)acrylic ester mixtures containing one or more monomers from the group comprising methacrylic esters, acrylic esters, olefins, vinyl aromatics, vinyl halides, fumaric and / or maleic mono- or diesters; monomers or monomer mixtures of dienes such as butadiene or isoprene, as well as of olefins such as ethene or propene, wherein the dienes may be copolymerized, for example, with styrene, (meth)acrylic esters or the esters of fumaric or maleic acid; monomers or monomer mixtures of vinyl aromatics, such as styrene, methylstyrene, vinyltoluene; monomers or monomer mixtures of vinyl halides such as vinyl chloride, wherein the monomer mixtures may further comprise auxiliary monomers.

[0059] Monomer mixtures of vinyl acetate with

[0060] 1 to 50 wt.% ethylene; monomer mixtures of vinyl acetate with 1 to 50 wt.% ethylene and 1 to 50 wt.% of one or more further comonomers from the group of vinyl esters with 3 to 12 carbon atoms in the carboxylic acid residue such as vinyl propionate, vinyl laurate, vinyl esters of alpha-branched carboxylic acids with 9 to

[0061] II C atoms such as VeoVa9®, VeoVal O®; monomer mixtures of one or more vinyl esters, 1 to 50 wt.% ethylene and preferably 1 to 60 wt.% (meth) acrylic acid esters of unbranched or branched alcohols with 1 to 15 C atoms, especially n-butyl acrylate or 2 ethylhexyl acrylate; monomer mixtures with 30 to 75 wt.% vinyl acetate, 1 to 30 wt.% vinyl laurate or vinyl ester of an alpha-branched carboxylic acid with 9 to 11 C atoms, as well as 1 to 30 wt.% -% (Meth) Acrylic acid esters of unbranched or branched alcohols with 1 to 15 carbon atoms, especially n-butyl acrylate or 2-ethylhexyl acrylate, which also contain 1 to 40 wt% ethylene; monomer mixtures with one or more vinyl esters, 1 to 50 wt% ethylene and 1 to 60 wt% vinyl chloride; wherein the aforementioned monomer mixtures may each also contain the aforementioned auxiliary monomers in the aforementioned amounts, and the values ​​in wt% add up to 100 wt%.

[0062] Particularly preferred are (meth)acrylic ester monomer mixtures, such as monomer mixtures of n-butyl acrylate or 2-ethylhexyl acrylate or copolymers of methyl methacrylate with n-butyl acrylate and / or 2-ethylhexyl acrylate; styrene-acrylic ester monomer mixtures with one or more monomers from the group consisting of methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, and 2-ethylhexyl acrylate; vinyl acetate-acrylic ester monomer mixtures with one or more monomers from the group consisting of methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, and 2-ethylhexyl acrylate, and optionally ethylene; and styrene-1,3-butadiene monomer mixtures. where the aforementioned monomer mixtures may also contain auxiliary monomers in the stated quantities, and the values ​​given in wt.% add up to 100 wt.% each.

[0063] Examples of particularly preferred comonomers for vinyl chloride monomer mixtures are α-olefins such as ethylene and propylene, vinyl esters such as vinyl acetate, acrylic acid esters and methacrylic acid esters of alcohols with 1 to 15 carbon atoms such as methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, n-butyl acrylate, t-butyl acrylate, n-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl acrylate, fumaric and maleic acid mono- or diesters such as the dimethyl and diethyl esters of maleic acid and fumaric acid.

[0064] Most preferred are monomer mixtures with vinyl acetate and 5 to 50 wt% ethylene; monomer mixtures with vinyl acetate and 1 to 50 wt% ethylene and 1 to 50 wt% of a vinyl ester of µ-branched monocarboxylic acids with 9 to 11 carbon atoms; monomeric mixtures with 30 to 75 wt% vinyl acetate, 1 to 30 wt% vinyl laurate or a vinyl ester of a µ-branched carboxylic acid with 9 to 11 carbon atoms, and 1 to 30 wt% (meth) acrylic acid esters of unbranched or branched alcohols with 1 to 15 carbon atoms, which optionally also contain 1 to 40 wt% ethylene; monomer mixtures with vinyl acetate, 5 to 50 wt% ethylene and 1 to 60 wt% vinyl chloride; as well as monomer mixtures containing 60 to 98 wt% vinyl chloride and 1 to 40 wt% ethylene, wherein the monomer mixtures may each contain auxiliary monomers in the aforementioned amounts, and the values ​​in wt% add up to 100 wt% each.

[0065] The monomer selection and the selection of the comonomer weight fractions are carried out such that a glass transition temperature Tg of -50°C to +50°C, preferably from -20°C to +30°C, generally results. The glass transition temperature Tg of the polymers can be determined in a known manner using differential scanning colorimetry (DSC). Tg can also be approximately predicted using the Fox equation. According to Fox TG, Bull. Am. Physics Soc. 1, 3, page 123 (1956): 1 / Tg = xl / Tgl + x2 / Tg2 + ... + xn / Tgn, where xn represents the mass fraction (wt% / 100) of monomer n and Tgn is the glass transition temperature in Kelvin of the homopolymer of monomer n. Tg values ​​for homopolymers are listed in Polymer Handbook 2nd Edition, J.U. Wiley & Sons, New York (1975).

[0066] The initiation of polymerization can be carried out in a manner conventional for emulsion polymerization, as described, for example, in US20230406978. Regulating substances can be used during polymerization to control the molecular weight, if necessary.

[0067] Suitable protective colloids include, for example, partially saponified polyvinyl alcohols; polyvinylpyrrolidones; polyvinyl acetals; water-soluble polysaccharides such as starches (amylose and amylopectin), celluloses and their carboxymethyl, methyl, hydroxyethyl, and hydroxypropyl derivatives; proteins such as casein or caseinate, soy protein, and gelatin; lignin sulfonates; synthetic polymers such as poly(meth)acrylic acid, copolymers of (meth)acrylates with carboxyl-functional comonomer units, poly(meth)acrylamide, polyvinylsulfonic acids and their water-soluble copolymers; melamine formaldehyde sulfonates, naphthalene formaldehyde sulfonates, and styrene maleic acid and vinyl ether maleic acid copolymers. Partially or fully saponified polyvinyl alcohols are preferred.

[0068] Protective colloids are generally added during polymerization in a total amount of 1 to 20 wt%, based on the total weight of the monomers. The protective colloid component can, for example, be added entirely beforehand or partially and partially added later.

[0069] Anionic, cationic, or nonionic emulsifiers are suitable for polymerization. Examples of anionic surfactants include alkyl sulfates with a chain length of 8 to 18 carbon atoms, alkyl or alkylaryl ether sulfates with 8 to 18 carbon atoms in the hydrophobic residue and up to 40 ethylene or propylene oxide units, alkyl or alkylaryl sulfonates with 8 to 18 carbon atoms, and esters and semi-esters of sulfosuccinic acid with monohydric alcohols or alkylphenols. Examples of nonionic surfactants include alkyl polyglycol ethers or alkylaryl polyglycol ethers with 8 to 40 ethylene oxide units. Generally, emulsifiers are used in amounts of 0.1 to 5% by weight, based on the amount of monomer.

[0070] The aqueous polymer dispersions obtained thereby have a solids content of preferably 30 to 75 wt.%, particularly preferably 50 to 60 wt.%.

[0071] To produce water-dispersible polymer powders, the aqueous polymer dispersions, optionally after the addition of protective colloids as drying aids, are dried in a conventional manner, for example by fluidized bed drying, freeze-drying or spray drying, as described, for example, in US20080098933.

[0072] The process according to the invention advantageously enables the continuous defoaming of polymer dispersions and is highly compatible with continuous polymerization processes. With the continuous foam destruction and phase separation enabled by the invention, i.e., the separation of the polymer dispersion phase and the gas phase of the foam, downstream processes such as post-polymerization, packaging, filtration, or filling operations can also be carried out efficiently in a continuous manner.All of this contributes to the fact that, for example, the investment costs in the downstream section can be reduced by 40% with the inventive method compared to conventional discontinuous or semi-continuous defoaming processes, for example because conventional expansion or defoaming tanks can be completely eliminated or reduced in volume or number, or because the cycle time is reduced. Due to the smaller dimensions and / or the fewer number of defoaming devices, the inventive approach is also more resource-efficient and therefore also suitable for significantly reducing the ecological footprint of the plant.

[0073] Furthermore, the defoaming process according to the invention allows for more efficient monomer recovery, particularly ethylene recovery, thereby reducing operating costs. This is because, after discontinuous defoaming, the polymer dispersion is completely removed from the defoaming vessel, which is then filled with nitrogen. Consequently, the ethylene released in the next defoaming cycle is contaminated with nitrogen and thus produced with a lower degree of purity, which is not the case with the process according to the invention.

[0074] The process according to the invention advantageously provides access to polymer dispersions with low residual monomer contents. This is particularly important when the polymer dispersions are subsequently dried to a powder in a spray dryer, since residual monomers must be laboriously removed from the dryer exhaust air to comply with emission limits. The process according to the invention allows polymer dispersions to be defoamed almost instantly, so that the cycle time of defoaming according to the invention is dramatically reduced compared to conventional, batch-wise defoaming. Batch-wise defoaming using residence time can be dispensed with according to the invention. Furthermore, the use of defoamers can be dispensed with according to the invention, which is also desirable for environmental and cost reasons.

[0075] The design of the rotating or rotatable disk (4) according to the invention, in particular also with the preferred embodiments of the profile according to the invention, as well as by the application of the polymer dispersion to the disk (4) according to the invention, can further improve the defoaming of the polymer dispersions.

[0076] What was also surprising was that all these effects could be achieved according to the invention with shear-thinning polymer dispersions and / or polymer dispersions with high residual monomer content.

[0077] The following examples serve to explain the invention in detail and are in no way to be understood as a limitation.

[0078] Example 1:

[0079] Reference polymer dispersion ion:

[0080] An aqueous vinyl acetate-ethylene copolymer dispersion (solids content 54%; copolymer based on 90.7 wt.% vinyl acetate and 9.3 wt.% ethylene) produced by aqueous emulsion polymerization and with a residual vinyl acetate content of 3.1% was placed in an autoclave and heated to 90°C. Ethylene was added while stirring until a saturation pressure of 15 bar was reached. The stirrer in the autoclave was then switched off, and the pressure was maintained at 15 bar by means of pressure control and further ethylene addition. The resulting reference polymer dispersion was used in the defoaming processes of the following (comparative) examples 1a to 1c.

[0081] The reference polymer dispersion simulates a polymer dispersion as is typically obtained during emulsion polymerization.

[0082] Comparative example la:

[0083] 3 kg of the reference polymer dispersion were blown through a valve at a rate of 40 kg / h into a defoamer open to the atmosphere.

[0084] This resulted in a foam with a density of 0.2 kg / L (determined by weighing with a measuring cup).

[0085] After letting the foam stand in the defoamer container for 5 minutes, the density of the foam was 0.4 kg / L.

[0086] Comparison example lb:

[0087] An inclined blade agitator with a diameter of 8 cm was inserted 3 cm above the bottom of a defoamer tank and operated at a constant speed of 1000 rpm. The diameter of the inclined blade agitator corresponded to one-third of the diameter of the defoamer tank.

[0088] In the defoamers equipped in this manner and open to the atmosphere, 3 kg of the reference polymer dispersion were blown off at a rate of 40 kg / h via a valve. After the blow-off process was complete, the agitator continued to run for 5 minutes. The agitator was then switched off.

[0089] The density of the polymer dispersion thus obtained was 1.0 kg / L (determined by weighing with a measuring cup).

[0090] The density of the completely gas-free dispersion was 1.08 kg / L.

[0091] The polymer dispersion of the comparison example lb was therefore only 92.6% defoamed.

[0092] Example lc :

[0093] A rotatable disk (4) with a diameter of 150 mm was mounted horizontally above the bottom of a defoaming vessel (6) and rotated at a constant speed of 2000 rpm by means of a drive (5). The rotatable disk (4) had a profile as shown in Figures 2A and 2B and was designed with the details as specified in the general description with the preferred embodiments.

[0094] Via a valve (2), 3 kg of the reference polymer dispersion was applied at a rate of 40 kg / h over the top of the defoamer container (6) through a pipe (11) onto the bottom of the depression of the rotating disc (4) and pulled by centrifugal force over the rotating disc (4) and flung against the inner wall of the defoamer container (6), from where the dispersion ran off onto the bottom of the defoamer container (6) and was immediately and continuously removed from the defoamer container (6) via a pipe (9).

[0095] The density of the defoamed polymer dispersion thus obtained was 1.08 kg / l (determined by weighing with a measuring beaker).

[0096] The defoaming process according to the invention thus resulted in a completely defoamed polymer dispersion.

Claims

1. Patent claims:

1. A process for producing polymers based on ethylenically unsaturated monomers in the form of an aqueous dispersion by means of radically initiated emulsion polymerization, characterized in that the aqueous dispersion of the polymers based on ethylenically unsaturated monomers is defoamed by application to a rotating disk (4).

2. Method according to claim 1, characterized in that a flat side of the rotating disk (4) has a depression and the aqueous dispersion of the polymers based on ethylene unsaturated monomers is applied into the depression of the rotating disk (4).

3. Method according to claim 1 or 2, characterized in that the aqueous dispersion of the polymers based on ethyl-enically unsaturated monomers forms a layer with a layer thickness of 0.05 to 5 mm on the rotating disk (4).

4. Method according to claims 1 to 3, characterized in that the rotating disk (4) has an angular velocity o of 50 to 5000 rpm.

5. Method according to claims 1 to 4, characterized in that the aqueous dispersion of the polymers based on ethylenically unsaturated monomers is transferred from a polymerization reactor to the rotating disk (4), wherein a pressure of 1 to 200 bar abs. prevails in the polymerization reactor and a pressure of 0.3 to 6 bar abs. prevails in the defoaming device in which the rotating disk (4) is located, with the proviso that the pressure in the polymerization reactor is greater than in the defoaming device.

6. Method according to claims 1 to 5, characterized in that the aqueous dispersion of the polymers based on ethyl-enically unsaturated monomers, which is applied to the rotating disk (4), has a density of 0.05 to < 0.8 kg / L and the aqueous dispersion of the polymers based on ethylene unsaturated monomers, which is taken from the defoaming device in which the rotating disk (4) is located, has a density of > 0.8 to 1.5 kg / L.

7. Defoaming device for aqueous dispersions of polymers based on ethylene unsaturated monomers, characterized in that the defoaming device comprises a container (6) containing a rotating or rotatable disk (4) and one or more feed lines (11) for the aqueous dispersion of the polymers based on ethylene unsaturated monomers and optionally one or more feed lines for additives, wherein the rotating or rotatable disk (4) is horizontally oriented in the container (6) and both or preferably one flat side of the rotating or rotatable disk (4) has several or preferably one recess, wherein at least one, in particular one, recess of a flat side of the rotating or rotatable disk (4) is oriented in the directionin which one or more supply lines (11) for the aqueous dispersion of the polymers based on ethylene unsaturated monomers and, if applicable, one or more supply lines for additives are located.

8. Method according to claims 1 to 6 or defoaming device according to claim 7, characterized in that the disk (4) is circular and rotates or is rotatable about its center of the circle, wherein the disk (4) has a radius of 10 to 200 cm and has a thickness (13) of 0.5 to 10 cm.

9. Method according to claim 1 to 6 or 8 or defoaming device according to claim 7 or 8, characterized in that the disk (4) has an overall rising profile in a cross-section through its center of rotation (14) starting from its center of rotation (14) towards its edge.

10. Method according to claim 9 or defoaming device according to claim 9, characterized in that the profile of the disk (4) is not descending at any point from the center of rotation (14) of the disk (4) towards the edge of the disk (4).

11. Method according to claim 9 or 10 or defoaming device according to claim 9 or 10, characterized in that the profile of the disk (4) has a gradient of 2% to 350% from the center of rotation (14) of the disk (4) to the edge of the disk (4).

12. Method according to claims 9 to 11 or defoaming device according to claims 9 to 11, characterized in that the profile of the disk (4) has several segments, wherein a first segment S1 (19) is located at the deepest point of the depression of the disk (4) and is flat, and a second segment S2 (20) adjoins the first segment S1 (19) and has the greatest rising slope of the entire profile of the disk (4), and a third segment S3 (21) follows the second segment S2 (20) and extends to the edge of the disk (4) and rises in the direction of the edge of the disk (4) and has a slope that is smaller than the slope in the second segment S2 (20).

13. Method according to claim 12 or defoaming device according to claim 12, characterized in that the The gradient in the second segment S2 (20) is 35% to 350% and in the third segment S3 (21) is 1% to 30%.

14. Method according to claims 2 to 6 or 8 to 13 or defoaming device according to claims 7 to 13, characterized in that the end of a supply line (11) with which an aqueous dispersion of the polymers based on ethylenically unsaturated monomers is applied to the disc (4) projects into the recess of the disc (4). 15.A method according to claim 14 or a defoaming device according to claim 14, characterized in that the depression of the disk (4) is 0.25 to 4 times as deep as the clear diameter of a supply line (11) with which an aqueous dispersion of the polymers based on ethylenically unsaturated monomers is applied to the disk (4), and / or a supply line (11) with which an aqueous dispersion of the polymers based on ethylenically unsaturated monomers is applied to the disk (4) terminates at least half and at most two clear diameters of this supply line (11) above the deepest point of the depression of the disk (4), and / or at the deepest point of the depression of the disk (4) a circular area with a diameter that is 1 to 2 times the outer diameter (10) of the supply line (11) with which an aqueous dispersion of the polymers based on ethylenically unsaturated monomers is applied to the disk (4) Monomers are applied to the disk (4), which is designed to be flat.

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