Method for the production of a polymer dispersion by radical aqueous emulsion polymerization with a continuously produced aqueous monomer emulsion

p0001The present invention relates to a process for the preparation of a polymer dispersion by free-radical polymerization of an aqueous monomer emulsion.

p0002Generally, in the preparation of polymer dispersions by emulsion polymerization, batch, semi-batch and continuous processes are differentiated by various methods of the addition of the monomers into the reaction vessel.

p0003In <nplcit id="ncit0001" npl-type="b"><text>Kirk-Othmer, Encyclopedia of Chemical Technology, 3rd ed., Vol. 1, p. 397 ff</text></nplcit>. A semibatch process for emulsion polymerization using the example of the large-scale polymerization of acrylates is described. A monomer emulsion prepared in a separate batch vessel is continuously fed into the polymerization reactor, where an aqueous initiator solution is added and polymerized.

p0004In <nplcit id="ncit0002" npl-type="b"><text>Kirk-Othmer, Encyclopedia of Chemical Technology, 3rd ed., Vol. 14, p. 92 ff</text></nplcit>. There is a comparative overview of batch, semibatch and continuous processes in emulsion polymerization. According to a general procedure for a semibatch process, the emulsion feed can comprise all the ingredients used for the emulsion polymerization, for example monomers, surface-active substances, water and regulators, the monomer emulsion being produced in a separate feed tank, the so-called feed tank. The initiator, however, must not be mixed into the monomer emulsion, since polymerization in the feed tank could then occur.

p0005In the <nplcit id="ncit0003" npl-type="b"><text>Encyclopedia of Polymer Science and Engineering, Vol. 6, pp. 10 ff. (1986)</text></nplcit>), Batch, semi-batch and continuous reactors for emulsion polymerization are also described. As before, as a possible variant of the batch and semibatch process, the preparation of a monomer emulsion is described in a separate batch vessel, which can contain all the emulsion components, with the exception of the initiator. This is fed directly into the polymerization reactor in a separate feed. In the continuous processes described, the monomers are fed continuously to the reactor (s), either without prior emulsification together with the aqueous phase, or in the form of a monomer emulsion, which is prepared separately in the stock.

p0006Semibatch processes in which a continuous feed is fed to a stirred reactor but no product is withdrawn during the reaction are preferred over the batch process. Thus, the composition of the feed and the initial filling can be easily varied and thus a multiplicity of different dispersions can be produced in one and the same reactor. In addition to these advantages, further advantages of the semibatch process lie in their increased safety on account of the low monomer quantities in the reactor in each case compared to the batch process and a better removal of the heat of reaction, in particular in the case of dispersions in which, during polymerization, Strong viscosity increase. Furthermore, the possible regulation of the feed rates of the monomers or of the monomer emulsion and thus an improved reaction control is advantageous.

p0007The introduction of the monomers into the polymerization reactor can be carried out in the semibatch process, for example, separately from the feed of the initiator in the pure form as the only feed, for example in the reactor <patcit id="pcit0001" dnum="EP0575625A"><text>EP-A-0 575 625</text></patcit> Described. Further methods for adding the monomers into the polymerization reactor are, as also described above, the joint addition with the aqueous phase without prior emulsification and the addition of a monomer emulsion prepared in a separate batch vessel.

p0008Processes of the prior art with the addition of the monomers in a non-emulsified or pure form have the following disadvantages:<ol><li>A) The energy required for emulsifying the monomers must be applied by the stirrer of the polymerization reactor. This requires either the use of special, more expensive, partially complicated and difficult to clean stirrers or an increase in the power input into the reaction mass by increasing the stirrer speed or using larger stirrers. The latter measures lead to an increased shear stress on the dispersions and thus to an increased coagulate formation.</li><li>B) Insufficient emulsification in the reactor can lead to the formation of a pure monomer phase in the reactor, ie the specifically lighter, non-reacted monomer forms a coherent layer which floats on the other reaction mass. After the emulsion feed has ceased, the cooling effect of the cold feeds is omitted and a strong rise in temperature in the boiler interior can occur by reacting this concentrated monomer phase. In addition, the reaction of such a concentrated monomer phase leads to increased coagulation and to severe reactor contamination.</li></ol>

p0009The <patcit id="pcit0002" dnum="EP0037923A"><text>EP-A-0037923</text></patcit> Describes a process for the preparation of aqueous polymer dispersions having a solids content of up to 75% by weight. In this process, a monomer emulsion is prepared from two monomers which are not copolymerizable alone and another monomer which is copolymerizable with both monomers, with the addition of a high proportion of polymerization inhibitor. The resulting monomer emulsion is used as the feed for polymerization by the feed process.

p0010The <patcit id="pcit0003" dnum="US3637563A"><text>US-A-3,637,563</text></patcit> Describes a process for the preparation of polymer dispersions with a high solids content by converting monomers and emulsifier into a stable water-in-oil emulsion with a water content of about 10% by weight, and the monomer emulsion thus prepared by the addition process into aqueous initiator solution Polymerized.

p0011The previously described semibatch processes, in which a monomer emulsion is fed continuously to the polymerization reactor, all require the preparation and preparation of this emulsion in a separate vessel before the beginning of the reaction. However, this method variant has the following disadvantages:<ol><li>A) The initiator can not be mixed with the monomer emulsion, since a polymerization in the feed vessel can then be expected. However, a separate introduction of initiators into the reactor results in a locally increased electrolyte concentration at the inlet site, which leads to increased undesirable coagulate formation.</li><li>B) The emulsions used for aqueous free-radical emulsion polymerization are not thermodynamically stable, ie, the monomer emulsion can be separated by coalescence of the monomer droplets and to form a monomer phase in the feed vessel. At the same time, emulsifier is released which forms micelles in the reactor and can thus initiate the growth of another undesired particle generation. In addition, the introduction of a pure monomer phase at the end of the feed causes the above-described problems due to high temperature rise, increased coagulation and reactor contamination.</li><li>C) In the preparation of more highly concentrated dispersions, the monomer emulsion added to the polymerization reactor must have a high monomer content. This generally leads to emulsions with a high viscosity and thus to problems in the promotion of these emulsions. Furthermore, highly concentrated aqueous monomer emulsions tend to separate.</li></ol>

p0012In none of the abovementioned publications, there is a reference to the use of a continuously prepared aqueous monomer emulsion in the free-radical aqueous emulsion polymerization for the preparation of polymer dispersions.

p0013The <patcit id="pcit0004" dnum="US5250576A"><text>US-A-5,250,576</text></patcit> Describes a continuous process for the preparation of a special high-internal phase emulsion (HIPE) with a high proportion of disperse aqueous phase and its subsequent polymerization and dewatering to produce absorber foams. The method comprises:<ol><li>A) preparing an oil phase from monomers such as, for example, styrene and p-methylstyrene, comonomers, for example alkyl acrylates and methacrylates, butadiene, etc., crosslinkers, and emulsifiers;</li><li>B) preparing an aqueous phase from a water-soluble electrolyte and a water-soluble initiator;</li><li>C) simultaneous introduction of oil and water phase into a dynamic mixing zone;</li><li>D) preemulsifying;</li><li>E) HIPE formation in the dynamic mixing zone by increasing the flow rate of the water phase and / or lowering the flow rate of the oil phase;</li><li>F) continuously conveying the mixture from the dynamic to a static mixing zone, through which the mixture flows, producing a stable water-in-oil emulsion;</li><li>G) Polymerization and dewatering.</li></ol>

p0014In contrast to free-radical aqueous emulsion polymerization, in which polymerization takes place in the micelles and not in the monomer droplets (oil phase), the polymerization takes place in the oil phase in this process, so that it is to be regarded as a special case of bulk polymerization. The process also does not aim at the preparation of a stable aqueous polymer dispersion, but serves to produce a polymer foam which can be dewatered to an absorber. Accordingly, the above-described problems specific to the preparation of aqueous polymer dispersions, such as, for example, the formation of coagulum, in the process of the<patcit id="pcit0005" dnum="US5250576A"><text>US-A-5,250,576</text></patcit> not matter.

p0015It is an object of the present invention to provide a process for the preparation of preferably highly concentrated polymer dispersions by free-radical polymerization of an aqueous monomer emulsion, the above-described disadvantages, in particular the increased coagulation, the contamination of the polymerization vessel and a temperature rise shortly before or after the polymerization End of the monomer addition.

p0016Surprisingly, it has now been found that the object is achieved by a process for the preparation of an aqueous polymer dispersion, an aqueous monomer emulsion continuously produced in accordance with its consumption being fed to the reaction vessel.

p0017The invention thus provides a process for the preparation of a polymer dispersion by free-radical polymerization of an aqueous monomer emulsion which is characterized in that the monomer emulsion is continuously prepared as a function of consumption and the emulsion polymerization of the continuously produced monomer emulsion is carried out in a semi-batch process. According to the invention, the components of the monomer emulsion are thereby mixed in at least one mixing device for the emulsion, the mixing device used being at least one inline mixer which is arranged directly in front of the reaction vessel.

p0018The process according to the invention is suitable for the preparation of homo- and copolymers, so that for the continuous preparation of the monomer emulsion, at least one monomer-containing feed is fed into the mixing device. The addition of several monomers can be carried out separately or in mixtures, which can be produced, for example, by combining the individual feeds in a common pipeline.

p0019The monomers can be fed in pure form (oil phase) or together with water to the mixing device. A surface-active substance (emulsifier) ​​is preferably added to water-containing monomer feeds even before entering the mixing device for the preparation of the monomer emulsion.

p0020The initiator is added via a separate feed, generally in aqueous phase, but monomer feed and initiator feed can be combined before entering the mixing apparatus. If desired, the initiator can also be introduced directly into the reactor independently of the monomer emulsion.

p0021The addition of the other components of the monomer emulsion, which are defined in more detail below, is carried out jointly with one of the above-mentioned feeds or separately in pure form, as a solution in water or a suitable solvent.

p0022When the semibatch process according to the invention is carried out, some of the aqueous phase and optionally one or more of the monomers and / or the other components of the monomer emulsion are initially charged in the reactor.

p0023The components can be fed into the mixing device by conventional methods. These include, for example, the direct addition of all components or the formation of suitable premixes.

p0024According to a suitable embodiment of the process according to the invention for the preparation of copolymers, for example, a mixture of one or more water-soluble monomers, an emulsifier and optionally further additives as the first feed can be combined with an aqueous solution of an initiator as the second feed, for example in a common pipeline. To this mixture, for example, at least one water-insoluble monomer can be added in pure form (oil phase) as a third feed, optionally via a metering device. The mixture of the three feeds is continuously emulsified in a mixing device, as described in detail below, according to the consumption, and is fed directly to the reaction vessel.

p0025As a mixing device for the continuous preparation of the aqueous monomer emulsion, one or more mixers can be used in the process according to the invention, which can be mixers of the same or different types, which are used in any sequence, arrangement and combination, Combination of parallel and row arrangement or parallel arrangement of all mixers. If several mixers are used, the row arrangement is preferred.

p0026Suitable mixers are, in particular, dynamic mixers, the mixing elements of which contain moving parts and static mixers, ie mixing elements without moving parts inside, which operate according to the inline principle.

p0027Preferably, the mixers are chosen from among rotor-stator systems, preferably colloid mills or toothed-wheel dispersing machines, ultrasonic homogenizers, high-pressure homogenizers, tube-flow mixers, jet dispersants, shear-gap mixers, heat exchangers and curved tubular flow reactors having a substantially circular or ellipsoidal cross-section.

p0028Suitable dynamic inline mixers are, for example, the scraping-type heat exchangers described in the ZFL Journal of Food Technology and Process Engineering (1982) 33 (3), p. 139 et seq., Such as, for example, tooth-ring dispersing machines, colloid and corundum disk mills As well as high-pressure and ultrasonic homogenizers.

p0029Suitable dynamic inline mixers are also tube flow mixers.

p0030Suitable static inline mixers are, for example, those described in ZFL Journal of Food Technology and Process Engineering (1982) 33 (3), p. 139 ff., Such as Ross-ISG mixers, Which divide it into partial streams which are subsequently laterally displaced and recombined in a different order, or static mixers, which comprise several homogeneous, fixed mixing elements, each of which is offset by 90 ° one behind the other into a pipe or a channel (for example, Kenics) -, Sulzer SMV and Sulzer SMX mixers).

p0031Further suitable static inline mixers are scaler mixers such as those described in the <patcit id="pcit0006" dnum="EP101007B"><text>EP-B-101 007</text></patcit> Described.

p0032Further suitable mixers are also devices for inline emulsification, such as membranes, jet mixers and curved, tubular devices with a substantially circular or ellipsoidal cross-section.

p0033The mixing device used is at least one inline mixer, which is mounted directly in front of the reaction vessel.

p0034Particularly preferably, the mixing device comprises a dynamic mixer and / or a static mixer. If two mixers are used, they are connected in series. As a dynamic mixer, a tube flow-through mixer or a tooth-rim dispersing machine, eg of the Megatron type from Kinematica, is preferably used.

p0035It is preferred to use, as a mixing device, a tube flow mixer or a tooth-ring dispersing machine, in combination with a static mixer.

p0036Advantageously, a tubular device with several successive bends with alternating curvature directions is used as the mixing device. Such devices are described in the<patcit id="pcit0007" dnum="DE19634450"><text>German patent application DE 196 34 450</text></patcit> Described.

p0037The device with a substantially circular or ellipsoidal cross section has several, preferably directly successive, curvatures with alternating directions of curvature, wherein a reversal of the direction of curvature takes place no later than when the distance of the center of gravity of the pipe cross-section that is traversed at the beginning of a curvature is 200 times the pipe diameter, The curvature can comprise up to three revolutions around the axis of curvature.

p0038When the ellipsoidal cross-section of the device is the pipe diameter, the mean value between the large and the small axis is to be understood.

p0039Preferably, in the case of an ellipsoidal cross-section, the ratio of large semiaxes to small semiaxes is in the range from 5: 1 to 1: 1.

p0040Curvatures with alternating directions of curvature are understood here to be a sequence of curved tube segments, the next tube segment (section of the tube between two successive curvature reversals) leading into another, preferably the opposite direction of the preceding one, ie a change occurs with each curved tube segment , Preferably a reversal of the direction of curvature. This embodiment of the device permits the manufacture of windings with a spatially particularly favorable, ie compact, arrangement which is particularly suitable for industrial practice.

p0041Preferably, the curvature is such that the center of gravity of the pipe cross-sectional area describes a semicircle per curvature.

p0042The radius of curvature of the curved tube segments is preferably 0.5 to 100 times, preferably 1 to 80, 2 to 50 or 2 to 20 times the diameter of the tube cross-sectional area.

p0043The dimensions of the device are generally such that the ratio of length to diameter is in the range of 100: 1 to 1,000,000: 1, preferably 1,000: 1 to 100,000: 1 and 50,000: 1, respectively.

p0044According to a preferred embodiment, the device is constructed as a winding, which is single-layered, as viewed from the incoming flow, about at least two axes. The axes can form an angle to one another, but are preferably substantially parallel. In the case of non-self-supporting winding, these axes can preferably be realized by tubes or rods, which may be round or angular. The term "winding around at least two axes" is used here for illustrative purposes only. It is not necessary for the axes to be realized during the application, for example in the form of pipes or rods.

p0045If a winding is arranged around a plurality of axes, preferably arranged in a plane, a band-like or wall-like configuration results.

p0046The windings mentioned are a spatially particularly favorable arrangement and allow a compact embodiment of the device according to the invention. They are easily transportable, which is an advantage especially during maintenance work. The number of windings arranged one above the other is arbitrary; it depends on the respective requirements.

p0047Aqueous monomer emulsions suitable for the process according to the invention<ol><li>A) at least one ethylenically unsaturated monomer,</li><li>B) optionally at least one initiator suitable for initiating aqueous emulsion polymerizations,</li><li>C) one or more surface-active substances, </li><li>D) optionally further additives.</li></ol>

Component a)

p0048Monomers or diesters of ethylenically unsaturated C.sub.1 -C.sub.4-diols which are useful for the process according to the invention are₃-C₆Mono- or dicarboxylic acids with C₁-C₂₀Alkanols or C₂-C₂₀Diols, vinyl-C₁-C₂₀Vinylaromatic compounds, ethylenically unsaturated nitriles, vinyl halides, vinyl-C₁-C₂₀Alkyl ether, C₂-C_8thMono- and diolefins, C₃-C₆Monoethylenically unsaturated mono- or dicarboxylic acids, their salts or their amides, and N-mono- or N, N-di-C₁-C₂₀Alkylamines or hydroxyalkylamides, N-vinyllactams, ethylenically unsaturated alkyl- or arylsulfonic acids and / or salts thereof, and mixtures of different monomers of one type and / or of different types.

p0049Examples of suitable monomers are C₁-C₁₂Alkyl acrylates and C₁-C₁₂Such as the esters of acrylic acid or methacrylic acid with methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, tert-butanol, pentanol, hexanol, 2-ethylhexanol, octanol, decanol, dodecanol Vinyl acetate, vinyl chloride, vinyl stearate, vinyl acetate, vinyl acetate, vinyl acetate, vinyl acetate, vinyl acetate, vinyl acetate, Acrylamidopropane sulfonic acid and its alkali salts, sulfonated styrene and its alkali salts, acrylic acid, methacrylic acid, maleic acid, fumaric acid and itaconic acid

p0050Examples of further monomers a) which are generally present in minor amounts include N-alkyl- and N-hydroxyalkylamides of the abovementioned ethylenically unsaturated carboxylic acids, the diesters of dihydric alcohols with the abovementioned ethylenically unsaturated monocarboxylic acids, the vinyl or allyl esters of the Ethylenically unsaturated carboxylic acids, N, N'-divinyl or N, N'-diallyl urea derivatives or divinyl aromatics.

p0051Particularly suitable monomer combinations for the process according to the invention are, for example, n-butylacrylate with vinyl acetate; N-butylacrylate with styrene; N-butyl acrylate with ethylhexyl acrylate; Butadiene with styrene; Butadiene with acrylonitrile and / or methacrylonitrile; Butadiene and isoprene with acrylonitrile and / or methacrylonitrile; Butadiene with acrylates; Butadiene with methacrylic acid esters. All of the abovementioned monomer combinations can also contain small amounts of further monomers, preferably acrylic acid, methacrylic acid, acrylamide and / or methacrylamide.

Component b)

p0052Suitable free-radical polymerization initiators are all those which are capable of initiating free-radical aqueous emulsion polymerization. These may be both peroxides, for example alkali metal peroxodisulfates, and also azo compounds. Combined systems which are composed of at least one organic reducing agent and at least one peroxide and / or hydroperoxide, for example tert-butyl hydroperoxide with the sodium salt of hydroxymethanesulfinic acid or hydrogen peroxide with ascorbic acid, are also used. Combined systems are also used which contain a small amount of a metal compound which is soluble in the polymerization medium and whose metallic component can occur in several valence states, for example ascorbic acid / ferrous sulfate / hydrogen peroxide, the sodium salt of hydroxymethanesulfinic acid, sodium sulfite, Sodium hydrogen sulfite or sodium bisulfite and tert-butyl hydroperoxide or alkali peroxodisulfates and / or ammonium peroxodisulfate instead of hydrogen peroxide. Preferred initiators are the ammonium or alkali metal salts of peroxosulfates or peroxodisulfates, in particular sodium or potassium peroxodisulfate. The amount of free-radical initiator systems used is preferably from 0.1 to 2% by weight, based on the total amount of the monomers to be polymerized.

Component c)

p0053The emulsion polymerization is carried out in the presence of suitable emulsifiers and protective colloids. These substances are customarily used in amounts of up to 10% by weight, preferably 0.5 to 5% by weight and in particular 0.5 to 3% by weight, based on the monomers to be polymerized.

p0054Suitable protective colloids are, for example, polyvinyl alcohols, cellulose derivatives or copolymers based on vinylpyrrolidone. Suitable emulsifiers are, in particular, anionic and nonionic emulsifiers, such as ethoxylated mono-, di- and trialkylphenols, ethoxylates of long-chain alkanols, alkali and ammonium salts of alkyl sulfates, sulfuric acid semiesters of ethoxylated alkanols and ethoxylated alkylphenols, alkylsulfonic acids and alkylarylsulfonic acids. A detailed description of protective colloids and emulsifiers can be found in<nplcit id="ncit0004" npl-type="b"><text>Houben-Weyl, Methoden der Organischen Chemie, Vol. XIV / 1, Macromolecular Substances, Georg-Thieme-Verlag, Stuttgart, 1961, pp. 192-208 and 411-420</text></nplcit>.

p0055Useful non-ionic emulsifiers are araliphatic or aliphatic, non-ionic emulsifiers, for example ethoxylated mono-, di- and trialkylphenols (EO grade: 3 to 50, alkyl radical: C₄-C₁₀), Ethoxylates of long-chain alcohols (EO grade: 3 to 50, alkyl radical: C_8th-C₃₆) And polyethylene oxide / polypropylene oxide block copolymers. Preference is given to ethoxylates of long-chain alkanols (alkyl radicals: C₁₀-C₂₂, Average degree of ethoxylation 10 to 50), and more preferably those having a linear C₁₂-C₁₈And an average degree of ethoxylation of 10 to 50 and ethoxylated monoalkylphenols.

p0056Suitable anionic emulsifiers are, for example, alkali metal salts and ammonium salts of alkyl sulfates (alkyl radical: C_8th-C₁₂), Of sulfuric acid half-esters of ethoxylated alkanols (EO grade: 2 to 50, alkyl radical: C₁₂-C₁₈) And ethoxylated alkylphenols (EO grade: 3 to 50, alkyl residue: C₄-C₉), Of alkylsulfonic acids (alkyl radical: C₁₂-C₁₈) And alkylarylsulfonic acids (alkyl radical: C₉-C₁₈). Further suitable emulsifiers are found in<nplcit id="ncit0005" npl-type="b"><text>Houben-Weyl, Methoden der organischen Chemie, Vol. XIV / 1, Macromolecular Substances, Georg-Thieme-Verlag, Stuttgart, 1961, pp. 192-208</text></nplcit>). Suitable anionic emulsifiers are also bis (phenylsulfonic acid) ethers or their alkali metal or ammonium salts, which have one or two aromatic rings with one or two aromatic rings₄-C₂₄Alkyl group. These compounds are generally known, for example from the<patcit id="pcit0008" dnum="US4269749A"><text>U.S. Patent No. 4,269,749</text></patcit> And commercially available, for example, as Dowfax® 2A1 (trademark of the Dow Chemical Company).

p0057Suitable cationic emulsifiers are preferably quaternary ammonium halides, for example trimethylcetylammonium chloride, methyltrioctylammonium chloride, benzyltriethylammonium chloride or quaternary compounds of NC₆-C₂₀Alkylpyridines, NC₆-C₂₀Alkylmorpholines or NC₆-C₂₀-alkylimidazoles, for example N-laurylpyridinium chloride.

Component d)

p0058Conventional regulators can be used for controlling the molecular weight, for example mercapto compounds, such as mercaptoethanol, mercaptopropanol, mercaptobutanol, mercaptoacetic acid, mercaptopropionic acid, mercaptotrimethoxysilane, butylmercaptan and t-dodecyl mercaptan. Also suitable are organic halogen compounds, such as tetrachlorocarbon or bromotrichomethane. Further suitable additives are, for example, the pH-adjusting agents, antioxidants, deodorants, biocides, crosslinking agents, dyes and pigments.

p0059The emulsion prepared according to the invention is polymerized in a reactor suitable for this purpose. These include, for example, stirred reactors, boiler cascades. The emulsion polymerization of the continuously prepared monomer emulsions is carried out in a semibatch process.

p0060In the semibatch process according to the invention, the continuous phase can be partially charged, ie, the reactor is filled proportionately with water and optionally a surface-active substance and / or a monomer.

p0061The polymerization can also be carried out using a seed latex which can be prepared in the reactor vessel at the beginning of the reaction or can be added as a component to the remaining components of the monomer emulsion before entry into the mixing apparatus.

p0062The process according to the invention is particularly suitable for the preparation of polymer dispersions having a high solids content. This is preferably in the range from 25 to 75% by weight, particularly preferably at least 50% by weight and particularly preferably at least 60% by weight. The disadvantages known from the prior art, in particular as a result of partial or complete demixing of separately prepared (preemulsified) monomer emulsions, are avoided.

p0063The invention is illustrated by the following non-limiting examples.

Examples

p0064To satisfy the advantages of a polymerization with continuous emulsion production according to the consumption in comparison with the feed of pure monomer or in comparison with the feed of an emulsion prepared separately in a batch vessel, the following four dispersions were prepared in each case with the following three dosing processes:

Dosing Method 1 (Comparison)

p0065The separately premixed feeds 1A and 1B were metered into a stirred tank (polymerization vessel) via a common feed line, but without prior emulsification.

Dosing Method 2 (Comparison)

p0066The feeds 1A and 1B were emulsified in a batch vessel, and from there into the stirred tank. The feed 2 was metered into the stirred tank via a separate feed line.

Dosing method 3 (according to the invention)

p0067Feed 1A and 2 were combined in a pipeline. The feed 1B was now metered into this mixture of feeds 1A and 2. The mixture of feed 1A, 1B and 2 was then emulsified by means of an inline mixing element (a or b), which was mounted directly in front of the stirred tank in the feed line, and subsequently passed into the stirred tank.

p0068As inline mixing elements were:<ol><li>A) a static mixer of type SMX-S, DN 3.2 consisting of 10 blending elements from Sulzer Chemtech,</li><li>(B) a Megatron MT 5000 tooth-ring dispersing machine from Kinematica is used.</li></ol>

p0069Dispersion 1:

p007013 kg of water were placed in a stirred tank and heated to 90 ° C. Subsequently, 5% of the feed 1 and 9% of the feed 2 were added and the mixture was polymerized for 5 minutes. Subsequently, the remaining amounts of feed stream 1A and B and feed stream 2 were metered in within the course of 3 hours, while maintaining the polymerization temperature, in each case according to one of the above-described metering processes. Subsequently, polymerization was carried out for 1 h to complete the conversion.

Feed 1:

p0071<dl id="dl0001" compact="compact"><dt>A:</dt><dd>24.94 kg of water 4.33 kg Emulsifier I 1.25 kg of acrylic acid 1.50 kg of 50% strength by weight aqueous solution of acrylamide</dd><dt>B:</dt><dd>25.00 kg of n-butylacrylate 23.00 kg vinyl acetate</dd></dl>

Feed 2:

p0072Solution from:<ul><li>0.375 kg sodium peroxodisulfate</li><li>4.98 kg of water</li></ul>

p0073Solids content: 52.0%

Dispersion 2:

p007415 kg of water were introduced into a stirred tank and heated to 85 ° C. 6% of the feed 1 and 10% of the feed 2 were then added and the mixture was polymerized for 10 minutes. The remaining amounts of feed stream 1A and B and feed stream 2 were then metered in at a rate of 3.5 hours after the addition of one of the above-described metering processes, while maintaining the polymerization temperature. Subsequently, polymerization was carried out for 1 h to complete the conversion.

Feed 1:

p0075<dl id="dl0002" compact="compact"><dt>A:</dt><dd>19.01 kg of water 2.00 kg of emulsifier II</dd><dt>B:</dt><dd>30.00 kg n-Butyl acrylate 20.00 kg styrene</dd></dl>

Feed 2:

p0076Solution from:<ul><li>0.30 kg sodium peroxodisulfate</li><li>4.70 kg of water</li></ul>

p0077Solids content: 55.6%

Dispersion 3:

p00784.33 kg of water were introduced into a stirred tank and heated to 85 ° C. Subsequently, 5% of the feed 1 and 8% of the feed 2 were added and the mixture was polymerized for 5 minutes. The remaining amounts of feed stream 1A and B and feed stream 2 were then metered in within the course of 3.5 h after maintaining the polymerization temperature after each of the above-described dosing processes. Subsequently, polymerization was carried out for 1 h to complete the conversion.

Feed 1:

p0079<dl id="dl0003" compact="compact"><dt>A:</dt><dd>10.25 kg of water 1.33 kg Emulsifier II 1.50 kg Emulsifier III 1.00 kg acrylic acid 1, 40 kg of 25% strength by weight aqueous solution of sodium hydroxide</dd><dt>B:</dt><dd>15.00 kg of ethylhexyl acrylate 34.00 kg of n-butylacrylate</dd></dl>

Feed 2:

p0080Solution from:<ul><li>0.35 kg of sodium peroxodisulfate</li><li>5.48 kg of water</li></ul>

p0081Solids content: 68.6%

Dispersion 4:

p0082A mixture of 16.7 kg of water and 0.3 kg of itaconic acid was introduced into a pressure-resistant stirred tank and heated to 85 ° C. Subsequently, 4.8% of the feed 1 and 9% of the feed 2 were added and the mixture was polymerized for 10 minutes. The remaining amounts of feed 1A and B and feed 2 were then metered in at a rate of 4.5 hours after each of the above-described metering processes, while maintaining the polymerization temperature. Subsequently, polymerization was carried out for 1.5 h to complete the conversion.

Feed 1:

p0083<dl id="dl0004" compact="compact"><dt>A:</dt><dd>19.21 kg of water 3.00 kg of emulsifier II 0.69 kg of acrylic acid 0.40 kg 25% strength by weight aqueous solution of sodium hydroxide</dd><dt>B:</dt><dd>31.00 kg of styrene 18.00 kg of butadiene 0.44 kg of tert-dodecyl mercaptan</dd></dl>

Feed 2:

p0084Solution from:<ul><li>0.35 kg of sodium peroxodisulfate</li><li>5.50 kg water</li></ul>

p0085Solids content: 53.7%

p0086Emulsifiers used were:<dl id="dl0005" compact="compact"><dt>Emulsifier I:</dt><dd>30% strength by weight aqueous solution of the sulfuric acid half-ester of ethoxylated isononylphenol, EO degree: 25</dd><dt>Emulsifier II:</dt><dd>15% strength by weight aqueous solution of sodium lauryl sulfate</dd><dt>Emulsifier III:</dt><dd>20% strength by weight aqueous solution of ethoxylated isooctylphenol, EO grade: 25</dd></dl>

p0087Following the preparation of the dispersions,<ul><li>The content of coagulum> 50 μm</li><li>The contamination of the polymerization vessel</li><li>The increase of the boiler internal temperature after addition is investigated according to the following methods:</li></ul>

coagulum

p00881 kg of the corresponding dispersion was filtered through a piece of nylons of known weight and a mesh width of 50 μm. The collected coagulate was thoroughly rinsed with distilled water and dried together with the nylone network at room temperature. By weighing back, the weight of the collected coagulate was determined. The amounts of coagulum are given in percent (based on the mass of the dispersion).

Contamination of the polymerisation vessel

p0089After the dispersion had been drained from the stirred tank, this was rinsed with water, the contamination of the vessel wall and stirrer was visually observed and evaluated according to the following criteria:<ol><li>1 very little soiling of stirrer and / or boiler wall</li><li>2 slight contamination of stirrer and / or boiler wall</li><li>3 moderate contamination of stirrer and / or boiler wall</li><li>4 Strong contamination of stirrer and / or boiler wall</li></ol>

Temperature rise after inflow

p0090For this purpose, the temperature which directly prevails at the inlet in the stirred tank was compared with the maximum temperature reached according to the inlet temperature. The differences ΔT determined in this case are indicated in ° C.

p0091The results of the experiments are summarized in Tables 1 to 4 below.<tables id="tabl0001" num="0001"><table frame="all"><title>Table 1:</title><tgroup cols="5"><colspec colnum="1" colname="col1" colwidth="36mm" /><colspec colnum="2" colname="col2" colwidth="30mm" /><colspec colnum="3" colname="col3" colwidth="30mm" /><colspec colnum="4" colname="col4" colwidth="33mm" /><colspec colnum="5" colname="col5" colwidth="33mm" /><thead valign="top"><row><entry namest="col1" nameend="col5" align="left">Results of the Experiments for Dispersion 1</entry></row><row><entry>Dispersion 1</entry><entry>Dosing method 1</entry><entry>Dosing method 2</entry><entry>Dosing method 3a)</entry><entry>Dosing method 3b)</entry></row></thead><tbody><row><entry>coagulum</entry><entry align="center">0.14%</entry><entry align="center">0.09%</entry><entry align="center">&lt;0.01%</entry><entry align="center">&lt;0.01%</entry></row><row><entry>ΔT after inflow</entry><entry align="center">8 ° C</entry><entry align="center">4 ° C</entry><entry align="center">-</entry><entry align="center">-</entry></row><row><entry>Boiler contamination</entry><entry align="center">4</entry><entry align="center">2</entry><entry align="center">1</entry><entry align="center">1</entry></row></tbody></tgroup></table></tables><tables id="tabl0002" num="0002"><table frame="all"><title>Table 2:</title><tgroup cols="5"><colspec colnum="1" colname="col1" colwidth="36mm" /><colspec colnum="2" colname="col2" colwidth="30mm" /><colspec colnum="3" colname="col3" colwidth="30mm" /><colspec colnum="4" colname="col4" colwidth="33mm" /><colspec colnum="5" colname="col5" colwidth="33mm" /><thead valign="top"><row><entry namest="col1" nameend="col5" align="left">Results of the Experiments for Dispersion 2</entry></row><row><entry>Dispersion 2</entry><entry>Dosing method 1</entry><entry>Dosing method 2</entry><entry>Dosing method 3a)</entry><entry>Dosing method 3b)</entry></row></thead><tbody><row><entry>coagulum</entry><entry align="center">0.2%</entry><entry align="center">0.11%</entry><entry align="center">0.02%</entry><entry align="center">&lt;0.01%</entry></row><row><entry>ΔT after inflow</entry><entry align="center">8 ° C</entry><entry align="center">7 ° C</entry><entry align="center">Approx. 1 ° C</entry><entry align="center">-</entry></row><row><entry>Boiler contamination</entry><entry align="center">3</entry><entry align="center">2</entry><entry align="center">1</entry><entry align="center">1</entry></row></tbody></tgroup></table></tables><tables id="tabl0003" num="0003"><table frame="all"><title>Table 3:</title><tgroup cols="5"><colspec colnum="1" colname="col1" colwidth="36mm" /><colspec colnum="2" colname="col2" colwidth="30mm" /><colspec colnum="3" colname="col3" colwidth="30mm" /><colspec colnum="4" colname="col4" colwidth="33mm" /><colspec colnum="5" colname="col5" colwidth="33mm" /><thead valign="top"><row><entry namest="col1" nameend="col5" align="left">Results of the Experiments for Dispersion 3</entry></row><row><entry>Dispersion 3</entry><entry>Dosing method 1</entry><entry>Dosing method 2</entry><entry>Dosing method 3a)</entry><entry>Dosing method 3b)</entry></row></thead><tbody><row><entry>coagulum</entry><entry align="center">0.15%</entry><entry align="center">0.1%</entry><entry align="center">0.02%</entry><entry align="center">0.01%</entry></row><row><entry>ΔT after inflow</entry><entry align="center">10 ° C</entry><entry align="center">7 ° C</entry><entry align="center">2 ° C</entry><entry align="center">-</entry></row><row><entry>Boiler contamination</entry><entry align="center">4</entry><entry align="center">3</entry><entry align="center">2</entry><entry align="center">1</entry></row></tbody></tgroup></table></tables><tables id="tabl0004" num="0004"><table frame="all"><title>TABLE 4</title><tgroup cols="5"><colspec colnum="1" colname="col1" colwidth="36mm" /><colspec colnum="2" colname="col2" colwidth="30mm" /><colspec colnum="3" colname="col3" colwidth="30mm" /><colspec colnum="4" colname="col4" colwidth="33mm" /><colspec colnum="5" colname="col5" colwidth="33mm" /><thead valign="top"><row><entry namest="col1" nameend="col5" align="left">Results of the Experiments for Dispersion 4</entry></row><row><entry>Dispersion 4</entry><entry>Dosing method 1</entry><entry>Dosing method 2</entry><entry>Dosing method 3a)</entry><entry>Dosing method 3b)</entry></row></thead><tbody><row><entry>coagulum</entry><entry align="center">0.12%</entry><entry align="center">0.08%</entry><entry align="center">&lt;0.01%</entry><entry align="center">&lt;0.01%</entry></row><row><entry>ΔT after inflow</entry><entry align="center">8 ° C</entry><entry align="center">6 ° C</entry><entry align="center">-</entry><entry align="center">-</entry></row><row><entry>Boiler contamination</entry><entry align="center">3</entry><entry align="center">2</entry><entry align="center">1</entry><entry align="center">1</entry></row></tbody></tgroup></table></tables>

p0092As the results of Tables 1 to 4 show, by continuous production and addition of the monomer emulsion in the production of polymer dispersions the coagulate formation is reduced, the temperature increase after inflow is avoided and the boiler pollution is reduced. Thus, the method according to the invention is superior to the hitherto known one.