DE19809220A1 - Process for the continuous production of polymer dispersions by aqueous emulsion polymerization - Google Patents

Abstract

The invention relates to a method for the continuous production of a polymer dispersion by means of an aqueous radical emulsion polymerization of at least one ethylenically unsaturated monomer in a reactor. According to the invention, an emulsion of the monomer or of the monomers in an aqueous phase is fed into the reactor, and the average droplet size of the monomer drops which are emulsified in an aqueous phase ranges from 1 to 20 mu m according to the polymerization conditions. The method results in a polymer dispersion having a low coagulate content.

Description

The present invention relates to a method for continuous Lichen production of polymer dispersions by aqueous emuls ion polymerization of at least one ethylenically unsaturated ten monomer in a reactor, wherein an emulsion of the Mono mers or the monomers in an aqueous phase in the reactor feeds.

Methods for continuous emulsion polymerization are knows. The first patents date back to 1937 and 1938 (GB 517.951 and FR 847.151). The most common is the application of a continuously operated stirred tank reactor described for for an overview see, for example, Encylopedia of Polymer Science and Engineering 1986, Volume 6, pages 11 to 18. Due the action of shear force by the stirrer is increased Tendency to coagulate the polymer, which then becomes very easily settles on the stirrer or on the reactor inserts. A special Design of the stirred reactors mentioned is in DE-A-10 71st 341. The reactor consists of a cylindrical one Tube equipped with washers attached to a shaft, which lead to the formation of the so-called Taylor rings when the Stirrer is rotated. Even with such reactors polymer caking and deposits form due to existing or formed gas bubbles in the system, which ver strengthens on the shaft and accumulate in low-flow zones and trigger coagulation of the polymer there. Occur too due to the rotating discs shear forces that also increase cause the polymer to coagulate.

Another improvement are reactors consisting of two concentric cylinders exist, the inner and / or outer Outer cylinder is rotated. Such reactors and their application for emulsion polymerization are described in Polymer International 30 (1993) 203-206; Chemical engineering Science, Vol. 50, 1409-1416 (1995); as well as in EP-A-498 583. Similar disadvantages occur in reactors of this type as in the reactors described in DE-A-10 71 341.

Another alternative to the stirred reactors is the use pulsed, packed columns, as in Chem. Eng. Sci. Vol. 47, 2603-2608 (1992) and EP-A-336 469. Columns of these Kind contaminate and clog very easily with coagulate.  

After all, tubular reactors often come without additional installation such as a static mixer or stirrer dung. There are numerous studies that deal with the Emul sion polymerization in a tubular reactor with both laminar and also deal with turbulent flow. An overview of this ar is found in Reactors, Kinectics and Catalysis, AIChE Journal, 1994, Vol. 40, 73-87. Patent publications in which Tube reactors for emulsion polymerization are described DE-A-26 17 570, DD-A-238 163, DD-A-234 163, DD-A-233 573, DD-A-233 572, DE-A-33 02 251, CZ-A-151 220 and EP-A-633 061.

All reactors to carry out emulsion polymerization common is the problem of coagulum formation, for example what in a tube reactor very easily leads to clogging of the tubes. There is also easy formation of wall coverings, which ensures safe warmth delivery or delivery obstructed. One has therefore tried to Additional measures and special reaction management the Koagu to avoid latification, see AIChE Journal, 1994, Vol. 40, 73-87, or by optimizing the reactor dimensions and the Ma terials for the pipes, see ACS Symp. Ser. 104, 113 (1979) and EP-A-96794.

The present invention is therefore based on the object Process for the continuous production of polymer dispersion to be provided by aqueous emulsion polymerization len, in which the formation of coagulum is reduced.

Surprisingly, it has now been found that this problem has been solved is when the average droplet size for the polymer used monomer emulsion so controlled that it under the polymerization conditions is µm 20 µm.

The present invention therefore relates to a method for continuous production of a polymer dispersion by aq Emulsion polymerization of at least one ethylenically un saturated monomer M in a reactor, making an emulsion of the monomer or monomers in an aqueous phase in the Re feeds actuator and wherein the method is characterized is that the average droplet size in the aqueous phase emulsified monomer droplets under the polymerization conditions ≦ 20 µm.

The stability of the emulsion in terms of droplet size of the emulsified monomer droplets, under the polymerization conditions has proved to be essential for the method according to the invention proven. This droplet size is said to be under the conditions of the bottom Lymerisation lie in the range mentioned, d. H. she may  do not change under the polymerization conditions so that the average droplet size is significantly above 20 µm. Under polymerization conditions, the temperature, Pressure and flow conditions as well as the dwell time and the Exposure to additives such as B. addition of initiator to understand which the monomer emulsion is exposed to during the polymerization becomes.

Preferably the average droplet size of the monomer emulsion is ≦ 10 µm, in particular ≦ 8 µm and particularly preferably ≦ 5 µm.

Furthermore, it has proven to be preferred that the droplet size distribution of the monomer emulsion, expressed as

and determined by means of Fraunhofer diffraction, in the range from 0.2 to 0.8, in particular 0.25 to 0.5 or 0.6.

Virtually all monomers are for the process according to the invention M can be used by the process of aqueous, radical Emulsion polymerization can be polymerized.

Suitable monomers M generally comprise at least one monomer M1 which is selected from vinylaromatic monomers such as styrene, α-methylstyrene, ortho-chlorostyrene or vinyltoluenes, the vinyl esters of aliphatic monocarboxylic acids having 1 to 12 carbon atoms such as vinyl acetate, vinyl propionate, vinyl butyrate, Vinyl valerate, vinyl nano hexanoate, vinyl 2-ethyl hexanoate, vinyl decanoate, vinyl laurate and vinyl versatate® (vinyl esters of branched, aliphatic carboxylic acids with 6 to 11 carbon atoms, which are commercially available as Versatic® X acids from SHELL AG). Furthermore, esters of α, β-ethylenically unsaturated C ₃ -C ₈ mono- or C ₄ -C ₈ dicarboxylic acids come with C ₁ -C ₁₂ and in particular C ₁ -C ₈ alkanols or C ₅ -C ₈ cycloalkanols as Monomere M1 in question. Suitable C ₁ -C ₁₂ -alkanols are, for example, methanol, ethanol, n-propanol, i-propanol, 1-butanol, 2-butanol, isobutanol, tert-butanol, n-hexanol and 2-ethylhexanol. Appropriate cycloalkanols are, for example, cyclopentanol or cyclohexanol. Esters of acrylic acid, methacrylic acid, crotonic acid, maleic acid, itaconic acid, citraconic acid or fumaric acid are particularly suitable. Specifically, these are (meth) acrylic acid methyl ester, (meth) acrylic acid ethyl ester, (meth) acrylic acid n-butyl ester, (meth) acrylic acid isobutyl ester, (meth) acrylic acid tert-butyl ester, (meth) acrylic acid 1-he xyl ester, (meth) acrylic acid-2-ethylhexyl ester, maleic acid dimethyl ester or maleic acid di-n-butyl ester. The monomers M1 also include monomers such as butadiene, C ₂ -C ₆ olefins such as ethylene, 1-propene, 1-butene, isobutene and 1-hexene, and vinyl and vinylidene chloride.

As a rule, the monomers M1 make up at least 50% by weight preferably at least 80% by weight, in particular 90 to 99.9% by weight and very particularly preferably 95 to 99.5% by weight of the polymer based monomers M.

In a preferred embodiment of the present invention, the monomers M1 comprise:
up to 100% by weight, in particular 30 to 99% by weight and very particularly preferably 40 to 95% by weight of at least one monomer M1a, selected from the C ₁ -C ₁₂ -alkyl esters, in particular from the C ₂ - C ₈ alkyl esters of acrylic acid and
0 to 75 wt .-%, in particular 1 to 70 wt .-% and very particularly preferably 5 to 60 wt .-% of at least one monomer M1b, selected from the C ₁ -C ₄ alkyl esters of methacrylic acid, for. As methyl methacrylate, ethyl methacrylate, n-butyl methacrylate and tert-butyl methacrylate, and vinyl aromatic monomers, e.g. B. styrene and α-methylstyrene,
the weight of the monomers M1a and M1b being added to 100% by weight.

The polymers often also contain copolymerized monomers which have an acidic functional group. This applies in particular to those polymers which contain vinyl-aromatic compounds and / or one or more of the abovementioned alkyl esters in copolymerized form with ethylenically unsaturated carboxylic acids. Examples of monomers M2 with acidic functional groups are ethylenically unsaturated mono- and dicarboxylic acids, e.g. As acrylic acid, methacrylic acid, acrylamidoglycolic acid, crotonic acid, itaconic acid, fumaric acid, maleic acid, and also the half esters of ethylenically unsaturated ter dicarboxylic acids with C ₁ -C ₁₂ alkanols, for. B. monomethyl maleate and mono-n-butyl maleate. The monomers M2 also include monomers with sulfonic acid groups and / or phosphonic acid groups or their salts, in particular their alkali metal salts. Examples include vinyl and allyl sulfonic acid, (meth) acrylamidoethane sulfonic acid, acrylamidopropane sulfonic acid, (meth) acrylamido-2-methylpropane sulfonic acid, vinyl and allyl phosphonic acid, (meth) acrylicoxyethylphosphonic acid, (meth) acrylamidoethanephosphonic acid and (meth) acrylamido-2-methylpropanophosphonic acid as well as the salts of such as sodium vinyl sulfonate. If desired, the monomers M2 are used in amounts of 0.1 to 10% by weight and in particular in amounts of 0.2 to 5% by weight, based on the total weight of the monomers M.

Furthermore, the dispersed polymers can also be monomers M3 polymerized contain an increased water solubility, d. H. greater than 60 g / l at 25 ° C, and in contrast to the monomers M2 contain no neutralizable, acidic group. These include the amides of the aforementioned ethylenically unsaturated ten carboxylic acids, e.g. B. acrylamide and methacrylamide, N-vinyllac tame, e.g. B. N-vinyl pyrrolidone and N-vinyl caprolactam, further Acrylonitrile and methacrylonitrile. The monomers M3, if desirable in amounts of 0.1 to 10 wt .-%, based on the Ge total weight of the monomers M to be polymerized, where with the monomers acrylonitrile and methacrylonitrile also in quantities up to 50% by weight, and preferably up to 30% by weight can.

Furthermore, the dispersed polymers can also contain, in copolymerized form, those monomers M4 which increase the crosslinking density of the polymers. These are copolymerized in a minor amount, generally up to 10% by weight, preferably up to 5% by weight and in particular up to 1% by weight, based on the total amount of the monomers to be polymerized. The monomers M4 comprise compounds which, in addition to a polymerizable double bond, contain at least one epoxy, hydroxy, N-alkylol or carbonyl group. Examples of these are the N-hydroxyalkyl and N-alkylolamides of α, β-monoethylenically unsaturated carboxylic acids with 3 to 10 carbon atoms, such as 2-hydroxyethyl (meth) acrylamide and N-methylol (meth) acrylamide, the hydroxyalkyl esters of said ethylenically unsaturated Carboxylic acids, e.g. B. hydroxyethyl, hydroxypropyl and hydroxybutyl (meth) acrylate, furthermore the ethylenically unsaturated glycidyl ether and ester, e.g. B. vinyl, allyl and Methal lylglycidylether, glycidyl acrylate and methacrylate, the Diaceto nylamide of the above ethylenically unsaturated Carbonsäu ren, for. B. diacetonyl (meth) acrylamide, and the esters of acetylacetic acid with the above hydroxyalkyl esters of ethylenically un saturated carboxylic acids, for. B. Acetylacetoxyethyl (meth) acrylate. Furthermore, the monomers M4 comprise compounds which have two non-conjugated, ethylenically unsaturated bonds, e.g. B. the diesters of dihydric alcohols with α, β-monoethylenically unsaturated C ₃ -C ₁₀ monocarboxylic acids. Examples of such compounds are alkylene glycol diacrylate and dimethacrylates, such as ethylene glycol diacrylate, 1,3-butylene glycol diacrylate, 1,4-butylene glycol diacrylate, propylene glycol diacrylate, divinylbenzene, vinyl methacrylate, vinyl acrylate, allyl methacrylate, allyl methacrylate, allyl methacrylate lat, tricyclodecenyl (meth) acrylate, N, N'-divinylimidazolin-2-one or triallyl cyanurate.

Depending on the application, the dispersed polymers can also contain copolymerized modifying monomers. Which includes hydrophobically modifying monomers, monomers which wet the tion of coatings based on aqueous polymer dispersion and those monomers that increase pigment binding power improve aqueous polymer dispersions, provided that the polymer risk dispersions used as binders for emulsion paints be set.

Monomers that improve wet grip include in particular their polymerizable derivatives of imidazolidin-2-one (see e.g. B. EP-A 184 091, US 4,219,454). Monomers that make up the pigment Improve binding strength of aqueous polymer dispersions, be known monomers containing siloxane groups (see e.g. EP-A 327 006, EP-A 327 376).

Furthermore, the polymers dispersed in the aqueous polymer dispersions to be stabilized according to the invention may also contain copolymerized hydrophobically and / or hydrophilically modifying monomers. Hydrophobic modifying monomers are in particular those monomers with a low water solubility (ie less than 0.01 g / l at 25 ° C). These include, for example, the C ₁₃ -C ₂₂ alkyl esters of ethylenically unsaturated carboxylic acids, e.g. B. stearyl acrylate and stearyl methacrylate, the vinyl and allyl esters of saturated fatty acids, e.g. B. vinyl stearate, also olefins with more than 6 carbon atoms, and C ₂ -C ₄ alkyl-substituted, vinyl aromatic compounds, z. B. tert-butyl styrene.

The monomer emulsion is prepared by emulsification of the monomers in the aqueous phase. For this purpose the Monomers in the usual way, for example by ultrasonic Ho mogenization by means of an ultrasonic sonotrode and / or Use a static and / or dynamic mixer emul yaws. This is preferably done by installing the mixer in-line. Suitable mixers are known to the person skilled in the art, for example can static mixers, e.g. B. of the type Sulzer SMX or around high-speed dynami working according to the rotor-stator principle cal mixers, high pressure homogenizers, gas injectors, high pressure perforated membranes etc.

The monomers can be used individually or as a mixture in the aqueous Phase can be emulsified. It is preferred to start the monomers first pre-emulsify, for example with the help of a static Mi  and then homogenize, for example under Use a dynamic mixer.

The individual components of the monomer emulsion can be fully continuous finely, partly continuously or in a mixture of full and are supplied partially continuously. With fully continuous All individual components, i.e. H. Water, Emul gator, various monomers and auxiliary substances, each separately, for example via a pipeline or from a storage tank, con continuously via a mixture control in the desired ratio dosed into the device used for emulsification. The The emulsion emerging from the device then has the correct one Composition and can be continuously fed into the reactor become.

In the semi-continuous procedure, at least two Batch container used. In one of the batch containers Emulsion prepared, which is then continuously in the reactor can be fed. During the infeed, the second Batch container made another batch of the emulsion. After The consumption of the emulsion in the first batch container is reduced to second batch container changed and in this way the reactor continuously charged with the emulsion.

In a mixed mode approach, the two combined previous approaches. Part of the components is provided in one or more batch containers and continuously dosed into an emulsifying device. Opp an intermediate is also sufficient for individual components barrel, the period of time until the intermediate vessel runs empty sufficient, a new batch in the upstream batch tank to provide. In this emulsifying device further com components directly, for example from a pipeline or a La tank, dosed. The one emerging from the emulsifying device The emulsion then has the correct composition and is used in the Reactor driven.

In all cases, aids or apparatus can also be used Control of temperature and / or pressure or other property the respective metering flows.

The polymerization initiator can be used in the preparation of the Emulsion or afterwards. For safety reasons it will be admitted as late as possible. It turned out to be special proved to be preferred to prepare the emulsion first and then to mix in the polymerization initiator. Preferably done  the mixing of the initiator among those below for the emul alloy specified temperature conditions.

It has also proven to be particularly preferred, at least to carry out the homogenization process at a temperature, which are not more than 50 ° C, in particular not more than 30 ° C and particularly preferably not more than 20 ° C or 10 ° C, of the polymerization temperature differs. Preferably done however both pre-emulsification and homogenization and the mixing of the polymerization initiator at this tempera door. It is preferred, particularly in the case of a polymer on temperature above 60 ° C to work at a temperature which is lower than the polymerization temperature. But it is also possible at temperatures above the polymerization temperature rature to emulsify and then z. B. by metering one cold feed, such as the initiator solution, the polymerization set temperature.

The emulsion polymerization can be used to set a defin polymer particle size also takes place in the presence of seed latex gen. Preferably 0.01 to 3 wt .-% and in particular 0.05 to 1.5% by weight of a seed latex (solids content of the Seed latex, based on total monomer amount). The latex has usually a weight-average particle size of 10 to 100 nm and in particular 20 to 50 nm. Its constituent mono Examples are styrene, methyl methacrylate, n-butyl acrylate lat and mixtures thereof, the seed latex in subordinate Also measure monomers M2 or M3, preferably less than 10 % By weight, based on the total weight of the polymer particles in the Seed latex, copolymerized. The seed latex will preferably used in the preparation of the monomer emulsion mixes.

In addition to water, the aqueous phase of the emulsion can contain up to 30 % By weight of a water-miscible organic solvent, such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobu Contain tanol, t-butanol, acetone, methyl ethyl ketone and the like.

The polymer dispersions are produced by radicals lische aqueous emulsion polymerization of said monomers in Presence of at least one radical polymerization initia tors and optionally at least one surfactant sub punch.

All those come as radical polymerization initiators conditions that are capable of a radical aqueous Trigger emulsion polymerization. It can be both  Peroxides (preferred), e.g. B. alkali metal peroxodisulfates or Al potassium metal peroxides, as well as azo compounds. As a butt Polymerization initiators often also become so-called redox initiators used, consisting of at least one organic reducing agent and at least one peroxide and / or hydroperoxide sets are, e.g. B. tert-butyl hydroperoxide with sulfur compounds gene, e.g. B. the sodium salt of hydroxymethanesulfinic acid, sodium sulfite, sodium disulfite, sodium thiosulfate or acetone bisulfite or hydrogen peroxide with ascorbic acid. Also be combi systems used that contain a small amount of one in the polymer contain a soluble metal compound, the me metallic component occur in several valence levels can, e.g. B. ascorbic acid / iron (II) sulfate / hydrogen peroxide, where, instead of ascorbic acid, the sodium salt of Hydroxymethanesulfinic acid, acetone bisulfite, sodium sulfite, natri umhydrogen sulfite or sodium bisulfite and instead of water peroxide organic peroxides such as tert-butyl hydroperoxide or Alkali peroxodisulfates and / or ammonium peroxodisulfate are used become. The amount of the radicals used is preferably rule initiator systems, based on the total amount of poly merizing monomers, 0.1 to 2 wt .-%.

Limit suitable for carrying out the emulsion polymerization Surfactants are the most common for these purposes protective colloids and emulsifiers used. The interfacial Tive substances are usually used in amounts of up to 5% by weight. preferably 0.1 to 5% by weight and in particular 0.2 to 3% by weight, based on the monomers to be polymerized. It larger quantities can also be used.

Suitable protective colloids are, for example, polyvinyl alcohols, Starch and cellulose derivatives or containing vinyl pyrrolidone Copolymers. A detailed description of other suitable The protective colloid can be found in Houben-Weyl, Methods of Orga African Chemistry, Volume XIV / 1, Macromolecular Substances, Georg-Thieme-Ver lag, Stuttgart 1961, pp. 411-420. Mixtures of emulsifiers and / or protective colloids can be used. Preferably are used exclusively as emulsifiers ren used, their relative molecular weights differ to the protective colloids are usually below 2000. they are preferably anionic or nonionic in nature.

The anionic emulsifiers include alkali and ammonium salts of alkyl sulfates (alkyl radical: C ₈ -C ₁₂ ), of sulfuric acid semiesters of ethoxylated alkanols (EO degree: 2 to 50, alkyl radical: C ₁₂ to C ₁₈ ) and ethoxylated alkylphenols (EO degree: 3 to 50, alkyl radical: C ₄ -C ₉ ), of alkyl sulfonic acids (alkyl radical: C ₁₂ -C ₁₈ ) and of alkyl rylsulfonic acids (alkyl radical: C ₉ to C ₁₈ ). Further suitable emulsifiers can be found in Houben-Weyl, Methods of Organic Chemistry, Volume XIV / 1, Macromolecular Substances, Georg-Thieme-Verlag, Stuttgart, 1961, pp. 192-208). Suitable anionic emulsifiers are also the abovementioned salts S, in particular the salts of sulfonated succinic acid di-C ₄ -C ₁₈ -alkyl esters, and among these particularly preferably the sodium salts.

Preferred anionic emulsifiers are also mono- and di-C ₄ -C ₂₄ -alkyl derivatives of the doubly sulfonated diphenyl ether or its salts. The mono- and di-C ₆ -C ₁₈ alkyl derivatives are particularly preferred. Technical mixtures are frequently used which have a proportion of 50 to 90% by weight of the monoalkylated product, for example Dowfax® 2A1 (trademark of the Dow Chemical Company). The connections are e.g. B. from US-A-4,269,749 be known and commercially available.

In addition to the anionic emulsifiers mentioned, nonionic emulsifiers can also be used. Suitable nonionic emulsifiers are araliphatic or aliphatic nonionic emulsifiers, for example ethoxylated mono-, di- and trialkyl phenols (EO grade: 3 to 50, alkyl radical: C ₄ -C ₉ ), ethoxylates of long-chain alcohols (EO grade: 3 to 50 , Alkyl radical: C ₈ -C ₃₆ ), and poly ethylene oxide / polypropylene oxide block copolymers. Preferred are ethoxylates of long-chain alkanols (alkyl radical: C ₁₀ -C ₂₂ , average degree of ethoxylation: 3 to 50) and among them particularly preferably those based on native alcohols or oxo alcohols with a linear or branched C ₁₂ -C ₁₈ alkyl radical and a degree of ethoxylation from 8 to 50.

The molecular weight of the polymers can be reduced by adding Amounts, usually up to 2 wt .-%, based on the polyme rising monomers, one or more, the molecular weight regulating substances, e.g. B. organic thio compounds, silanes, Allyl alcohols or aldehydes can be adjusted.

The monomer emulsion thus prepared is then optionally brought to polymerization temperature and continuously one Reactor fed and polymerized continuously. For that he Processes according to the invention can all be used for continuous Emulsion polymerization useful reactors who the. For example, it can be a continuous flowing stirred kettle, a stirred kettle cascade, a tubular reactor (including loop reactor), a Taylor reactor, or egg NEN, continuously operated known to those skilled in the art Act reactor or a combination thereof. Particularly preferred however, one uses a curved tubular flow freak  Tor with a substantially circular or ellipsoidal cross cut, the flow reactor several curvatures with old has direction of curvature and with a change the direction of curvature occurs at the latest when the from the beginning a curvature of the pipe's center of gravity cross-sectional area is 200 times the diameter, wherein a curvature can comprise up to three revolutions around the axis of curvature can. This flow reactor is described in PCT / EP97 / 04654 ben, the contents of which are hereby fully referred to becomes.

Curves with an alternating direction of curvature are to be understood here as a sequence of curved pipe segments, the next pipe segment in each case (section of the pipe between two successive reversals of curvature, e.g. the sections between two axis intersections in FIG. 1) into another, preferably that opposite direction of the previous leads, ie there is a change with each curved pipe segment, preferably a reversal of the direction of curvature. This configuration of the reactor achieves as uniform a flow as possible and thus narrows the residence time distribution of the volume units. In addition, the design of the reactor allows the production of windings with a spatially special, ie compact, arrangement, so that they are particularly suitable for in industrial practice (more detailed information on the resulting structures follow below). With the re-actuator, a high Bodenstein number can be realized, which is generally ≧ 10 and preferably ≧ 100 and can be up to 1000 and more. It is a measure of the width of the residence time distribution, the higher it is, the narrower and more symmetrical the residence time distribution.

The direction of curvature is preferably reversed at the latest then when the distance of the Center of gravity of the pipe cross-sectional area 150 times, in particular 100 times, preferably 80 times, particularly preferably that 50 times, 30 times or 25 times the pipe diameter.

This distance is generally at least 5 times the Pipe diameter and in particular it is in the range of 10 to 150 times, in particular 10 to 100 times, preferably 10 to 80 times and particularly preferably 10 to 50 times, 10 to 40 times chen or 10 to 30 times the pipe diameter.

A curvature can include not only a partial revolution, but also one and up to two or three revolutions around the axis of curvature (axis through the intersection of R ₁ and R ₂ , see FIG. 1). The angle that the normal vector of the main flow direction of a curvature sweeps up to the change in the curvature direction is therefore generally ≦ 1080 °, preferably ≦ 720 ° and particularly preferably ≦ 360 °.

It is preferably essentially sinusoidal curvatures. Sinusoidal curvatures in the present case are understood to mean all types of, preferably periodically recurring, curvatures essentially in one plane. An example of this is the curvature shown in FIG. 1. It is clear that the ratio of R ₁ / R ₂ , ie the ratio of amplitude to period length / 4, can be in a wide range. However, it is preferably in the range from 5: 1 to 1:50, in particular 3: 1 to 1: 5 and particularly preferably 1: 1. It can also be seen that not only curvatures are to be recorded in which the tangent in the Turning point forms an angle other than 90 ° with the axis, but also those in which the angle mentioned is 90 °, that is to say semi-circular tubular segments lined up, which are particularly preferred.

The radius of curvature of the curved pipe segments is preferred be 0.5 to 100 times, preferably 1 to 80, 2 to 50 or 2 to 20 times the diameter of the pipe cross cutting surface.

The dimensions of the reactor are generally such that the ver Ratio from length to diameter in the range from 100: 1 to 1000000: 1, preferably 1000: 1 to 100000: 1 or 50000: 1 lies.

If necessary, one or more of the curved pipe segments elements are connected by straight pipe segments. The relationship from straight to curved pipe section is then ≦ 5, preferably ≦ 2, in particular ≦ 1 and particularly preferably ≦ 0.5 or ≦ 0.25.

The device can also be constructed from several reactor units be, with the reactor in each unit different geomes trie and / or dimensions and / or radii of curvature can. For example, the pipe diameter can be in one unit can be increased to react at a lower flow rate lize or the radius of curvature can be varied to to set special product properties.

The cross section of the reactor is preferably circular or ellipsoid. This also includes modified circular or ellipses solid cross sections, e.g. B. cross-sections that are made by rounding the Result in corners of a square or a rectangle. In case of  Swirl tubes (see below) is the basic shape of the reactor tube in the essentially circular or ellipsoid.

In the case of an ellipsoidal cross section, the ratio is large half axis too small semiaxis in general in the range from 5: 1 to 1: 1, especially in the range from 2: 1 to 1: 1.

According to a preferred embodiment, the device is designed, as seen from the incoming flow, ascending and a ply winding around at least two axes. The axes can form an angle to one another, but they are preferably each essentially parallel. In the case of a non-self-supporting winding, these axes can preferably be realized by tubes or rods, which can be round or angular. The term "winding around at least two axes" is used here for illustration only. It is not necessary that the axes are also implemented in the application, e.g. B. in the form of tubes or rods. With a winding around 2 parallel axes, z. B. the arrangement shown in Figs. 2, 3 and 6.

If one winds around several, preferably in one plane on ordered axes, a band-like or wall-like configuration results, as shown in FIGS. 4 and 5.

Finally, it is also possible to make a winding around a plurality of substantially parallel axes running through the corners of a polygon, in particular an equilateral polygon, and perpendicular to its surface. The polygon can have an even and preferably an odd number of corners, at least 3 or 5. A heptagon has proven to be particularly useful (see FIGS. 7 and 8). A polygonal winding can be understood by curvatures along angled axes merged to form a polygon (perpendicular to the aforementioned preferred parallel axes).

The outside distance of the axes around which the winding is guided can be varied in a wide range. Generally be it bears 1 to 10 times, preferably 1 to 5 times and in particular 1 to 3 times the diameter of the reactor tube, the single to double distance is particularly preferred.

The winding is also determined by the pitch. she is generally 1 to 10 times, especially that 1 to 3 times the reactor diameter (with circular cross section) or in the case of an ellipsoidal reactor cross section of the axis, the points in the direction of the aisle.  

The windings mentioned are particularly favorable in terms of space Arrangement and allow a compact design of the fiction moderate device. They are easily portable, which is special which proves to be an advantage in maintenance work. The number of over each winding is arbitrary, it is aligned according to the respective requirements.

The curved reactor can, depending on the requirements of the feeding reaction, of metal, a metal alloy, glass or be made of a plastic. There are no be here restrictions, the pipe must only be resistant to the Re action participants and stable under the reaction conditions be. If the reactor is made of metal, it can, for example made of copper or copper alloys, steel or stainless steel any Be made.

If the reactor is made of a plastic, are fluorine containing plastics, e.g. B. tetrafluoroethylene and polyethylene, Polypropylene or polyvinyl chloride preferred.

The reactor can consist of profile tubes, in particular swirl tubes or corrugated pipes, be made or an inner coating point. This will, depending on the needs of the perform the reaction, acid-proof, alkali-proof or solvent-proof etc. chosen. Examples of interior coatings are especially flu containing plastics, such as tetrafluoroethylene, polyethylene or Polypropylene. In addition, the inside of the pipe can be chemically action be inerted, e.g. B. passivated by treatment with Nitric acid, electropolished or mechanically polished.

If desired, the reactor according to the invention can be additional have or can be combined with other equipment. Appropriately, along the curved reactor at a or several places means for feeding chemicals, at for example catalysts, reagents, solvents etc. and / or for cleaning, e.g. B. by using pig systems be seen.

In addition, the reactor pulsation means, for. B. pumps to accomplish a pulsed reaction. Further can start at or anywhere along the curved Pipe facilities can be provided with which, for. B. for the purpose separation, gas bubbles of an inert gas such as nitrogen and / or pigs can be fed. Furthermore, on Sub-segments of the curved reactor, which is usually 10% of the Do not exceed reactor distance, usual mixing elements provided  hen, for example, packing, static or dynamic Mixer.

In general there are also measuring points along the curved reactor len and facilities for sampling provided.

The reactor generally also includes heating or heating means Cooling of the medium flowing through. A heating or coolable container, which may be divided into zones, be usable, the tube reactor in whole or in part closes to control the temperature as desired lieren. It is also possible to use the heating or cooling medium To let pipes flow around which the tubular reactor is wound. The reactor can also be equipped with jacket heating or cooling be allowed.

Finally, the reactor can be combined with other Ap fittings upstream and / or parallel and / or downstream can be combined.

In principle, the spatial orientation of the reactor is not one limited. However, an alignment with essentially is preferred Lichen horizontal and / or continuously increasing Rohrver run. The direction of flow is preferably from the bottom to the bottom above.

For polymerization, it has proven to be particularly useful in a flow, characterized by an average Reynolds number from 1-10000, preferably 10-1000, often 20-100 to work. The reaction temperature is generally in the range from 40 to 150 ° C, especially 60 to 120 ° C.

The reactor is further explained by the following figures tert. Show it:

Fig. 1 is a schematic representation of a sinusoidal Krüm mung,

Fig. 2 is a side view of a reactor in the form of a winding around two rods,

Fig. 3 is a plan view of the reactor according to Fig. 2,

Fig. 4 shows a reactor in the form of a winding about six arranged in a plane rods,

Fig. 5 is a plan view of the reactor according to Fig. 4,

Fig. 6 is a side view of a reactor in the form of a comparison with FIG. 2 modified winding around two rods,

Fig. 7 is a partial schematic view of a reactor in the form ei ner winding 7 at the corners of an equilateral poly gons arranged rods,

Fig. 8 is a schematic plan view of a winding loop ge Mäss Fig. 7.

Fig. 2 shows a reactor in the simplest form as a winding. The reactor comprises two parallel rods 1 . A tube is wound around these rods in such a way that a curved reactor 2 with an alternating direction of curvature results. This can be clearly seen in FIG. 3, ie FIG. 3 shows a winding in the form of a figure eight. The distance between the two rods 1 corresponds to approximately 1.5 times the diameter of the reactor 2 . The reactor has an inlet 3 and an outlet 4 , ie the medium in the reactor 2 flows in an ascending direction.

Fig. 4 shows a further embodiment of a reactor according to the Invention. It comprises 6 rods 1 , around which a tube 2 with egg nem inlet 3 and an outlet 4 is wound so that a Ge braid is formed around the rods 1 , so that a reactor in the form of a palisade wall results. FIG. 5 shows that the winding corresponds to ei nem sinusoidal curvature.

Fig. 6 shows an alternative embodiment of a winding around two rods 1. The winding is guided so that the radius of curvature of a curvature sweeps approximately 600 °.

Another embodiment of the reactor according to the invention can be seen in the form of a partial side view of FIG. 7. Fig. 8 shows a single winding loop around seven bars 1 , which are arranged at the corners of an equilateral heptagon. The rods 1 are continuously wrapped with a tube 2 , so that a basket-like winding with an inlet 3 and an outlet 4 ( FIG. 7) is formed. This device is characterized by a compact arrangement and is therefore particularly suitable for industrial use.

The polymerization can be at normal pressure, negative pressure or above pressure. An Un ter pressure can be set.

Because of the slowing reaction with decreasing The polymerization is generally not until Full sales carried out. If desired, an Absen can then Reduction of the residual monomer content and the content of non-polymer volatile constituents in a manner known per se be performed. One way to do this is in a Post-polymerization in one or more, in parallel or behind interconnected other reactors. Preferably used a continuous reactor, particularly preferably one Tube reactor, in particular a curved tubular through flow reactor of the type described above, one continuously flowed through stirred tank or a stirred tank cascade. It can but also one or more other downstream reactors, e.g. B. two alternating batch operated stirred tanks, who used the. The operating conditions, such as temperature, Pressure, flow rate, stirrer speed, dwell time etc., can be varied compared to the main reactor.

Another way to lower the residual monomer content consists of chemical deodorization by adding one to additional initiator system, which at the transitions between the individual reactors or at certain points along or along the reactors can be added. Likewise, on these Other fabrics also score points for adjusting certain properties th of the dispersion, for example acids or bases for adjustment tion of the pH value can be added.

Removal of non-polymerizable volatiles is generally done by physical deodorization in the An close to the main reactor or to the post-polymerization or chemical deodorization. The removal of the volatile constituents entering the gas phase reduced on these components in the dispersion. The physi Kalische Deodorierung can continuously, for example in egg thin film evaporator or a stripping column (see DE-A-196 21 027 and DE-A-197 16 373) or discontinuously, at for example in a stirrer through which a stripping agent flows boiler, done. As a stripping agent for the stripping column and Stirred kettles are generally used in steam, see e.g. B. DE-A-12 48 943.  

The inventive method is useful for the production of Polymer dispersions with a wide proportion of polymer mass. Before the polymer mass fraction is preferably in the range from 25 to 75, in particular 50 to 70 wt .-%. Especially when using the Curved tubular flow reactor described above can also be dispersions of polymers with a glass over transition temperature <50 ° C, especially <30 ° C, without coagulation problems produce. The viscosity of the polymer dispersions can also be in vary over a wide range. In general, it is less less than 800 mPa.s and preferably less than 500 mPa.s (be agrees with DIN 53 019). It is preferably an im essential monomodal polymer dispersion.

The polymer dispersions obtainable according to the invention have a coagulum content of less than 0.5 g / kg of polymer, in particular less than 0.3 g / kg of polymer. The weight average particle size of the dispersed polymer particles is generally in the range from 50 to 400 nm, preferably 60 to 200 nm. The particle size distribution, expressed as

is generally in the range of 0.1 to 0.4, especially 0.150 to 0.350. Particle size and particle size distribution was determined using an analytical ultracentrifuge.

Examples

The experiments described in the following examples were carried out in a reactor made of steel tube (material number 1.4571) with a length of 100 m, an inner diameter of 10 mm and an outer diameter of 14 mm. The reactor was steadily rising in the form of an equilateral bend according to FIG. 8. The bending radius was 42 mm. The outer diameter of the overall construction was 312 mm.

A. Was used to measure the droplet size spectrum of the emulsion Dilute sample of the emulsion to 1% and ver with Fraunhofer diffraction measure up. For this purpose, an identical experimental approach was used emulsified and stored overnight. The separated water phase was used to dilute the emulsion sample Modification of the monomer droplets by the dilution as far as possible to avoid. The measurement was made after about 10 to 30 minutes Sampling. Further measurements were taken 30 and 60 minutes after the first measurement.  

In the case of hot samples, these were introduced into a Water-ice bath shock-cooled and after reaching room temperature, such as described above, measured.

example 1

2887 parts of a mixture of 1444 parts of n-butyl acrylate (nBA), 1386 parts of styrene (S) and 58 parts of acrylic acid (As) (feed 1) and 4382 parts of a mixture of 39 parts of sodium lauryl sulfate, 212 parts of polystyrene seed (34% in water) and 4131 parts of water (Feed 2) were placed in separate vessels. The two zu Runs were converted into a static Mi. Sulzer SMX shear, 3 mm, guided and pre-emulsified. On finally was heated to 80 ° C. The emulsion obtained was in a dynamic mixer (Kinematika Megatron Inlinemischer type MT 36-48 Dex-DW) homogenized at 15000 rpm. In the preserved Emulsion then became 231 parts of a 15% sodium persulfate solution solution (inlet 3) at the same time as inlet 1 and 2 do and with a static mixer of the type mentioned above mixed in. The emulsion was then added to a total throughput of 15 kg / h in the tubular steel reactor with a residence time of 30 min polymerized time and 95 ° C polymerization temperature 5 h. Which he Results are summarized in Table 1 below posed.

Example 2

The procedure was analogous to Example 1, but the Zu Runs 1 and 2 in the static mixer before pre-emulsification heated to approx. 80 ° C. A ge ringer wall covering that does not interfere with the further course of the experiment takes care. The results are shown in Table 1 below compiled.

Example 3

2927 parts of a mixture of 1464 parts of n-butyl acrylate, 1346 Parts of methyl methacrylate and 117 parts of acrylic acid (feed 1) and 4382 parts of a mixture of 118 parts of sodium lauryl sulfate, 97 Parts of polystyrene seed (33% in water), 47 parts of 10% sodium hydroxide alkali and 4450 parts of water (feed 2) were in separate vessels presented. The two inlets were in the specified ratio nis into a static mixer of the type Sulzer SMX, 3 mm and pre-emulsified. The emulsion obtained was then broken down Heated to 75 ° C and in a dynamic mixer (Kinematika Megatron Inlinemic type MT 36-48 Dex-DW) homogenized at 15000 rpm. In this emulsion 123 parts of a 15% sodium persul  Fat solution (inlet 3) at the same time as inlet 1 and 2 dosed and added with the static mixer of the above type mixes. Subsequently, with a total throughput of 15 kg / h in the steel reactor with a residence time of 30 min and polymer at 75 ° C. polymerized temperature 5 h. The results obtained are compiled in Table 1 below.

Example 4

The procedure was analogous to Example 3, but the Zu Runs 1 and 2 in a static mixer to 75 ° C before pre-emulsification heated up. The results obtained are as follows Table 1 compiled.

Example 5

The procedure was analogous to Example 3, but became a homogeneous nization instead of the dynamic mixer 30 mm diameter notrode in a 50 ml flow cell Volume at 100% power and 100% amplitude (approx.2.3 kW) homogeneous nized. The results obtained are shown in the following Ta belle 1 compiled.

Table 1

Test results

Claims (22)

1. A process for the continuous preparation of a polymer dispersion by aqueous radical emulsion polymerization of at least one ethylenically unsaturated monomer in a reactor, wherein an emulsion of the monomer or monomers in an aqueous phase is fed into the reactor, characterized in that the mean droplet size monomer droplets emulsified in the aqueous phase under the polymerization conditions ≦ 20 microns. 2. The method according to claim 1, characterized in that the Droplet size of the mono emulsified in the aqueous phase mer droplets ≦ 10 µm, in particular ≦ 8 µm. 3. The method according to claim 1 or 2, characterized in that the droplet size distribution of the monomer droplets emulsified in the aqueous phase, expressed as (d ₉₀ -d ₁₀ / d ₅₀ ) is in the range from 0.2 to 0.8. 4. The method according to any one of the preceding claims, characterized characterized in that using the monomer emulsion tion of 0.1 to 3 wt .-% of an emulsifier, based on the Total weight of the monomers. 5. The method according to any one of the preceding claims, characterized characterized in that using the monomer emulsion ultrasonic sonotrode, static or dynamic mix mixer, a high pressure homogenizer or one Combination of them. 6. The method according to any one of the preceding claims, characterized characterized in that the emulsification of the monomers in egg temperature that does not exceed 50 ° C, especially by no more than 30 ° C from the polymerization temperature differs. 7. The method according to claim 6, characterized in that also the initiator at a temperature in the monomer emulsion is mixed, which is not more than 50 ° C from the poly temperature differs. 8. The method according to any one of the preceding claims, characterized characterized in that the polymerization temperature in the range from 40 to 120 ° C.   9. The method according to any one of the preceding claims, characterized characterized in that one as a polymerization initiator water-soluble per compound used. 10. The method according to any one of the preceding claims, characterized in that the monomers M comprise at least one monomer M1 which is selected from vinyl aromatic monomers, vinyl esters of aliphatic monocarboxylic acids having 1 to 12 carbon atoms, esters, α, β-ethylenically unsaturated C ₃ - C ₈ mono- or C ₄ -C ₈ dicarboxylic acids with C ₁ -C ₁₂ alkanols, butadiene and C ₂ -C ₆ olefins. 11. The method according to claim 10, characterized in that the monomers M1 25 to 100 wt .-% of at least one monomer M1a, selected from C ₁ -C ₁₂ alkyl esters of acrylic acid and 0 to 75 wt .-% of at least one monomer M1b, which is selected from the C ₁ -C ₄ alkyl esters of methacrylic acid and vinyl aromatic monomers. 12. The method according to claim 10 or 11, characterized in that the monomers M also comprise monomers M2 with acidic functional groups, which are selected from acrylic acid, methacrylic acid, crotonic acid, itaconic acid, fumaric acid, maleic acid, the half-esters of ethylenically unsaturated dicarboxylic acids C ₁ -C ₁₂ alkanols and acrylamidoglycolic acid. 13. The method according to any one of the preceding claims, characterized characterized in that the polymerization is carried out in a curved tubular flow reactor with in essence union circular or ellipsoidal cross-section, the Flow reactor several bends with alternating bends direction and wherein a change in curvature direction takes place at the latest if the from the beginning of a Curvature of the center of gravity of the pipe cross cutting area is 200 times the pipe diameter, with a curvature up to three revolutions around the axis of curvature may include. 14. The method according to claim 13, characterized in that a Reversal of the direction of curvature occurs when the from the beginning of the Curvature from the center of gravity of the pipe cross-sectional area is blue Open distance in the range of 10 to 200 times the pipe diameter knife lies.   15. The method according to claim 13 or 14, characterized in that the curvature is designed so that the focus of the Pipe cross-sectional area per semicircle be writes. 16. The method according to any one of claims 13 to 15, characterized shows that the radius of curvature is 0.5 to 100 times the Diameter of the pipe cross-sectional area. 17. The method according to any one of claims 13 to 16, characterized records that the ratio of length to diameter of Re actuator ranges from 100: 1 to 1000000: 1. 18. The method according to any one of claims 13 to 17, characterized records that the flow reactor as a winding by at least two, essentially parallel axes, is formed. 19. The method according to claim 18, characterized in that the Flow reactor as a winding around several in one plane ordered, substantially parallel axes is formed. 20. The method according to claim 10, characterized in that the Flow reactor as winding around n essentially parallel, perpendicular through the corners of a substantially equilateral polygons extending axes is formed if n a odd number ≧ 3. 21. The method according to any one of claims 13 to 20, characterized records that ar in the flow reactor at a flow processed by an average Reynolds number in the range of 1 to 10,000 is characterized. 22. Polymer dispersion, obtainable by a process according to ei nem of claims 1 to 21.