HOMOPOLIMEROS AND COPOL IMEROS PREPARED BY EMULSION AND DEVICE FOR SUCH PREPARATION The invention relates to a process and a device for preparing homopolymers and copolymers, including those of styrene, butadiene, and (I) acrylic acid, and derivatives thereof. themselves, by the technique of emulsion polymerization. The way in which the polymerisations are carried out involves the dispersion of one or more polymerizable monomers in dispersed distribution in an ideally inert liquid in the reaction - usually water - in the presence of detergents or soaps as dispersion aids. The polymerization is carried out predominantly by means of initiating radicals in the micelles containing the monomer formed therein. High molecular masses can be obtained in such a polymerization since the monomer can reach the micelles with unusually. The mechanism is usually that of the polymerization of free radicals; the products of the reaction can, in many cases, be further processed directly in the form of dispersion (as, for example, in the case of the production of paints and adhesives). Known products are homopolymers and copsli erss (P) styrene < S > , vinyl chloride (VC), butadiene (Bu) or methyl methacrylate (MMA). The particle size and its distribution can often be controlled by the use of seeds (particles), aggregated at the beginning or produced in situ. Typical conditions in an industrial-scale process (for example a styrene-butadiene copolymer) or a polyacrylate) are reaction periods of 3 to 12 hours at a temperature of 40 to 100 ° C. DE-A 23 32 637 describes an emulsion polymerization in which butadiene reacts with comonomers such as, for example, styrene, acrylonitrile (AN) or esters of acrylic or methacrylic acid in the presence of customary emulsification aids, such as for example higher fatty acids, (ary1) higher alkyl sulfonates, adducts of alkylene oxides with long chain fatty alcohols, and free radical initiators such as alkali metal persulfates, at a temperature higher than 115 ° C. An advantage over the prior art with operation at a temperature lower than 80 ° C is the higher polymerization rate. However, there is often a negative effect on the performance properties of products prepared at such high temperatures, in relation, for example, to the distribution of the molecular mass, the particle size distribution and, in relation to this, the adhesive resistance for example. In addition, safety aspects (such as the pressure developed when butadiene is a
.F 'Hs, Jf "component) play an increasingly important role in relation to the reaction regime, however, any reaction regime at higher temperatures - in other words, more than 80 ° C, in particular more than 85 ° C - is an important parameter for large-scale industrial plants, since the reaction times can be significantly reduced, in other words, a large-scale industrial process is carried out with shorter cycle times which helps saving investment costs for a greater number of production units A major area of problem that requires solution, however, is heat dissipation, for example to help avoid local overheating events in the case of exothermic reactions, since such overheating can, in many cases, cause secondary reactions, irregular distributions of molecular mass or irregular particle sizes. EP-A 0 486 262 presents the preparation of emulsion copolymers where the energy balance is monitored and the result is used to control the supply of the ca-anomers and the temperature. The control of the temperature is achieved through the use, interalia, of an external heat exchanger. No information is given regarding the quality of the products or regarding the design of the pumps or heat exchanger.
A heat treatment of homopolymers or copolymers of VC, for example by means of an external heat exchanger, to reduce the viscosity after the emulsion polymerization itself, is described in Research Disclosure July 1978, reference 1719, page 17 There is no mention of influencing the main reaction itself. EP-A 608 567, for use in VC suspension polyolization to form homopolymers or copolymers, in a vessel with agitator and an external heat exchanger, describes a special pump (hydrostatic dome) by means of which the reaction mixture is guided at an angle of 90 °, the internal part has a conical hub with a rotor blade that moves with a spiral rotation movement. There are no observations regarding the heat exchanger. The energy of agitation and the energy of circulation must be maintained within a certain proportion. A comparable pump is used in EP-B 0 526 741 also dealing with the suspension polymerization of VC; there, the type of heat exchanger is not considered as a critical factor (see page 4, lines 36 to 40). In the emulsion polymer preparation process of DE-A 44 42 577, the energy released in the course of the exothermic reaction is partly dissipated by distilling off a water / onomer mixture under reduced pressure from the vessel of reaction (a stirred reactor). Even when this measure leads to a certain reduction in the polymerization period, that is, essentially in terms of the time required to add the monomer or the monomers, it is still insufficiently suitable for large-scale industrial plants, especially since it exists little or no adequacy for its generalized use, for example in the case of low boiling point and (co) monomers which are in a gaseous state under standard conditions (for example, butadiene type comonomers). It is an object of the present invention to find a preparation process which can be carried out on an industrial scale and which has a wide field of use but which does not have the disadvantages of the prior art. In other words, particularly, short reaction times should be possible, a broad spectrum of different monomers, including those in the gaseous state under standard conditions, should be accepted, and the product should be at least comparable in terms of performance properties. with the current products. We have found that this object is achieved by means of a process for the preparation of homopolymers or copolymers of at least one of the polymerizable monomers of the group consisting of styrene, butadiene, vinyl chloride, vinyl acetate, vinylidene chloride, (meth) ) alkyl acrylate, (meth) acrylic acid, (meth) acrylonitrile and (meth) Jacri lamide in an emulsion polymerization technique at a temperature of 40 ° C in the presence of a dispersion aid and of a polymerization initiator of free radicals The novel process comprises the preparation of the polymer, at least 85% by weight of which is formed from one or more of these monomers, in the following steps, where a) is added in a first stage water as a solvent that is inert in the reaction, and dispersion aids, seeds and a first part of monomer (s) is added if desired, b) in a second stage, initiator is added, and c) in a third stage stage the rest or else the entire monomer (s) is added directly either in the form of an emulsion and in the presence of additional water and, if desired, additional dispersion aid or other auxiliaries, it being also possible to operate steps a) or b) and c) ) in each case as single steps, and, at certain stages or at each stage, moving the reaction mixture in its dispersion form by means of an external circuit leading to the reaction vessel and back and comprising at least one pump of low cut and at least one heat exchanger having an essentially laminar flow profile, and the polymerization is carried out at a temperature of 40 to 120 * C. In preferred embodiments of the novel process at least 90% by weight, particularly at about 93% by weight of the polymer consists of one or more of the monomers mentioned above, and the polymerization is carried out at a temperature comprised between 50 and 100. 'C, particularly from 60 to 95 ° C and, very particularly, from 70 to 95 ° C. Among the monomers mentioned, styrene, butadiene, alkyl (me) acrylate and (meth) acr are preferred? loni trilo. The novel process can be carried out either by the inclusion of a part of monomer (s) in the initial charge in stage a) or in a combination of a) and b), subsequently, in step c) or in a combination of b) and c), adding to the rest, either by supplying the total amount exclusively in stage c) or in a combination of b) and e). If monomer (s) is included in the initial charge in step a) or in a combination of a) and b), then the amount thereof is from 3 to 30% by weight of the total amount of monomer ( s) to be supplied, preferably from 5 to 25% by weight and, especially, from 8 to 20% by weight. Monomers of zero or low solubility in water are preferably supplied in the form of an emulsion, that is, with water and dispersion aid. Other suitable comonomers in addition to the monomers mentioned above include vinyltoluens, N-methyloxy (meth) acrylamide and C2-C3 hydroxyalkyl (meth) acrylate. Unless otherwise specified, alkyl in loi >; first name-;. of the monomers refers to a linear C 1 -C 9 radical or branched C 3 -C °, methyl, ethyl, isopropyl, n-butyl, tert-butyl, isobutyl or 2-ethylhexyl. The dispersion aids can be included in the initial charge before the addition of the monomer or the monomers or can be supplied in addition to the monomers or in the emulsion of mapomers. The aggregate amount, in relation to the overall amount of monomer (s) as 100% by weight, is from 0.01 to 10% by weight, preferably from 0.05 to 8% by weight (it also depends on the type, whether mam? single or anionic). Known compounds are - in addition to natural soaps - alkyl polyol alkyl ethers such as for example ethoxylated lauryl alcohol, alkyl phenol alkyl ethers, for example those of nonyl phenols or salts of alkyl, aryl or alkyl acids! 1 long chain icos such as for example Na-lauryl sulfate. In addition to these it is also possible that protective colloids are present (in amounts of 0.001 to 15% by weight), such as, for example, cellulose ethers or polyvinyl alcohol. In a preferred embodiment of the invention, dispersion aids are present in step a) either together with seeds or with the first part of monomer (s); it is also possible that all three components are already present in step a). Then in the et pa c) dispe si si auxiliaries should be present. The seeds are already produced in situ or are included in the initial load; if desired, it can be repeated at various times to, for example, cause a polydispersed or poly-odal distribution (for example bimodal). The proportions - in relation to the amount of monomer (s) as 100% by weight - are frequently from 0.1 to 5% by weight, preferably from 0.2 to 3.0% by weight. In a preferred embodiment of the invention, the seeds are present in step a > either together with the first part of manomer (s) or not. Suitable initiators of polymerization for the beginning, for the complete implementation and / or for the continuation of the reaction are water-insoluble or, preferably, water-soluble compounds. Examples of known free radical initiators include hydrogen peroxide, peroxodisulfuric acid and its salts, for example, NH 4 peroxodisulfate, dibenzoyl peroxide, lauryl peroxide, tri-tert-butyl peroxide, azodi isobutyropitrile, alone or together with reducing components such as, for example, Na bisulfite, saponic acid or Fe (Il) salts, for example tert-butyl hydroperoxide with Na-for-aldehyde bisulfite adduct or Na-acetone bisulfite adduct. The polymerization initiator can be added in one or several steps, and in the latter case in various amounts and by various methods; for example, in the case of more complex systems such as, for example, reduction-or idarization initiators, it is also possible that some are included in the initial load and the rest added continuously afterwards. In many cases, the polymerization initiator is measured in parallel with the monomer; it can be added for a shorter or longer period than the period corresponding to the monomer addition. In the use of the reaction it is also possible to add up to 5% by weight - based on the proportion of monomer (s) as 100% by weight - of auxiliaries such as, for example, molecular weight regulators, additional surfactants, acids, salts or complex formation agents. In the case in which the polymerization is carried out in the presence of 3 to 10% by weight of a liquid organic blowing agent, expandable (preferably expanded) polymers can be produced, for example polystyrene e? Palpable. For the purpose of the formulation, for example to increase the storage stability, the final product of the emulsion polymerization can have readings added to it such as, for example, aqueous NaOH solution or bases (such as for example NH3 or amines). appropriate) to establish a pH of 4 to 10. Additional known additives are preservatives such as microbicides, film formers or leveling agents, antifoam agents or resin emulsions that increase adhesion (glues). The equipment used in the external circuit is especially suitable for a large-scale industrial regime. The pump (or pumps) of low cut must have a low cutting effect on the emulsion, must withstand pressures of, for example, up to 15 bar, must be insensitive to gases in the emulsion, must allow a good hourly performance of up to 100 m3 / h, preferably. up to 60 m3 / h, particularly up to 45 m-3 / h, and must also be resistant to temperatures above 100 * C and easy to clean. Ordinary rotary piston pumps or gear pumps are unsuitable for the novel process. Particularly suitable pumps are non-clogged pumps that operate in accordance with the vortex principle; displacement pumps, mono-pumps or disc-flow pumps and any pump of a type which ensures minimum cutting forces can be used to provide little or no interruption of the relatively unstable state of the reaction mixture and the emulsion mixture. finished product. The pumps can preferably be sealed with a double seal of floating rings in a back-to-back arrangement. The exchange or heat exchangers have or have a substantially laminar flow profile; in other words, the action of the cutting forces must be minimal and, when possible, dead zones should not occur (ie, areas not crossed by the flow). Known plate type heat exchangers tend to be inadequate since the gaps and narrow deviations mean that the offered mechanical resistances are excessively large; In addition, they are less suitable for a high pressure resistance configuration and are more difficult to clean. The novel process is especially suitable for preparing aqueous polymer dispersions whose films have a low glass transition temperature (DSC method); it is especially suitable in relation to glass transition temperatures below 150 ° C, preferably below 100 ° C, particularly below 50 ° C. In addition, it is also suitable for polymer dispersions having an average particle size of preferably 50 to 2000 nm, particularly 100 to 1500 nm. The polymer dispersion has a viscosity, in particular, from 30 to 1500 mPas; in the course of the polymerization, the viscosity may also be higher or lower.
In the drawing * Figure 1 shows a diagram of the components needed for the process, and Figure 2 shows a cross section through the preferred embodiment of the heat exchanger, said in plant. The monomer or monomers lb / lb ', and the inhibitor lc are fed from material containers or duct lines 1, with or without the supply of steam through the, in the polymerization reactor 2 (designed to operate , for example, at 15 bar) which in turn is equipped with a motorized agitator 4. The reactor has a heating / cooling jacket 3 whose circuit is fed with cooling water 5b or with steam 5b 'and is operated at through a pump 5a. The finished product from the polymerization reactor can be discharged via line of ducts 6 with steam / nitrogen into a container of material 6a. The (s> low-cut pump (s) 7, preferably a vortex pump that is not capped, transports the reaction mixture-through a line of ducts to the heat exchanger or heat exchangers. , controlled through the circuit 9 by a pump 9 with cooling water 9a or steam 9a 'The exchanger or heat exchangers have an essentially laminar flow profile, and the area of the exchanger is within the order of magnitude of 20. m2 for a volume of approximately 0.3 m3, a spiral heat exchanger is provided.The external circuit leads by means of duct lines back to the reactor 2. In the spiral heat exchanger 8 , the reaction mixture flows from the bottom 10 in the spirally arranged section / channel 11 of the heat exchanger and exits again at outlet 12. The medium that causes the heat exchange (for example a refrigerant or an agent of heating) - of pr Eference water or cooling brine, which can be heated by steam if desired - flows through inlet 13 in part 14 also arranged spirally of the heat exchanger and exits again at the upper end (not shown) . Preferably, the reaction mixture flows countercurrent to the heat exchange medium. The wall to wall distance in the channel for the reaction mixture is preferably larger than in the channel for the heat exchange medium, but may also be of equal or smaller size. The temperature difference between the entry point and the exit point is preferably from 3 to 60 K, preferably from 5 to 30 K, and particularly from 10 to 20 K. The heat exchanger can, if desired, be mounted in suspension 15 to be mobile (for example for clock rotation of 90 *).
In a particularly preferred embodiment of the invention, the heat exchanger or exchangers are arranged horizontally in relation to the polymerization reactor, such that the reaction mixture is "stationary" in the heat exchanger; in other words, the heat exchanger can be completely drained after the end of the polymerization, which is usually carried out in a discontinuous manner, with a complete emptying being preferred for reasons of product homogeneity and product purity. At the bottom end the heat exchanger may have additional drain valves (not shown). The production of the reaction mixture through the external circuit is generally from 5 to 100 m 3 / h (measured in the pump 7), preferably from 10 to 60 m 3 / h and, especially, from 15 to 45 m 3 / h. The overall content of the external circuit (not including the cooling circuits) is approximately 0.9 to 0.95 m3. The monitoring and control of the respective heating / cooling circuits of the polymerization reactor and / or of the exchanger or of the heat exchangers is easily carried out by means of cascade control; in other words, a first temperature measurement is normally carried out inside the polymerization reactor, a second measurement is carried out in the heating / cooling circuit of this reactor, in change with that of the reaction mixture in the line of duels after departure from the heat exchanger, and a third Measurement is carried out in the line of ducts after S3l? r of the heat exchanger in combination with that of the heating / cooling circuit of the heat exchanger. Compared with the prior art, the homopolymers and copolymers prepared according to the present invention can be produced with good yields within short reaction periods and do not exhibit deterioration in their performance properties. For example, unimodal or bimodal distributions can be produced; that is, the particle size distributions have one or two narrow frequency distribution maxima. The examples we present • = below illustrate the invention in greater detail. EXAMPLES In Examples 1 to 16 below and in Comparison Examples VI to V16, the procedure adopted was as follows. The heating / cooling circuit of the polymerization reactor is heated. Hot water is passed into the reactor, and using the low-cut pump in the external circuit, this circuit is filled, including the heat sink. Seeds of the desired final product composition and Na mo persulphate or free radical polymerization initiator are inserted into the reactor (eg, for a 20 to 25 m lamino) and the reaction medium ( at this point it is still unmanned) for about 5 minutes The addition of the monomer or, in general, of the monomers, either directly or in aqueous emulsion, then begins in an increasing amount, the amount fed increases quickly after about 10 to 15 minutes The monomers can be added by varying the proportions of the monomers in a feed stream, but also by varying the amounts fed per unit time, for example, in a first feed portion, the ratio between the first monomer and the second monomer can be 70:30 and then 50:50 in the second part, and in the first time interval the proportion of opomer e s 40% and in the second is 60%. The amount of monomer fed can also vary, for example, such that 75 parts are added in a first time interval, 100 parts are added in a second time interval, of equal length, and 150 parts are added in a third time interval. time interval, which is four times longer, in each case, at a constant feeding speed. Within a time interval, the amount fed may also increase or decrease with inuamente. The end of the addition of the components of the reaction and of the auxiliaries does not yet mark the f? Na3 of the reaction; rather the m z that of the reaction has the opportunity to finish the polymerization. During the above steps and also during the cooling phase mentioned below, the reaction mixture is transported continuously at a rate of approximately 20 to 30 m 3 / hr through the external circuit by means of a low-cut pump. In the cooling phase, the product of the reaction is cooled to 65-70 ° C, the low-cut pump of the external circuit is disconnected and the product is discharged into material containers through a line of duct that uses steam and nitrogen. The monomers used in the examples (always with the external circuit) and comparison examples (always without external circuit) their proportions in percentage by weight
(the d ficit of 100 thought with additional comonomers, predominantly water-soluble monomers such as for example (methacrylamide, unmodified or modified (meth) acrylic acid or crosslinking monomers such as butanediol diacrylate or N-met) The amount of seed that is present in the copolymer only in a minor amount), the polymerization temperatures and the times for the addition of the monomer are presented in the following table: The amount of seed used is approximately 0.2 to 1.2 parts by weight. Monomer Weight O. The weight ratio of the monomer \ water is of the order of 1: 1, and the dispersion aid (the synthesis) is added in a proportion of about 1 part by weight. novel, the performance properties are comparable to the properties obtained with the prior art, for example, the reaction products of examples 1 to 16 can be used as paper coating tape, paint material component / reverse side, adhesive, cement modifier or leather aid. Table
Example / composition PT 2) comparison time 4) example of monomer addition time of in% in for additions in comparison weight 1) onomer β) PT a) b) 100 2.5
1 VI BA 60 / S 10 / AN 25 90 3.0 1.2 - - 2 V2 BA 65 / S 15 / AN 15 85 6.0 2.0 95 3.0
3 V3 BA 48 / S 48 90 3.5 1.5 100 3.0
4 V4 BA 50 / S 15 / AN 30 80 7.0 2.0 95 4.0 5 5 V V55 S 55 / Bu 20 / BA 20 75 8.5 2.0 _ - * .0
6 V6 S 65 / Bu 30 95 4.0 2.0 7 V7 S 4 / Bu 30 5 4.0 2.0 8 V8 BA 55 / VAc 42 90 3.0 1.2 9 V9 BA 88 / AN 10 85 3.0 1.5 1 VI EHA 75 / MA 10 / VAc 1 85 4.0 1.5 11 Vil MMA 5 / BA 45 85 3.0 1.5 12 VI2 BA 55 / S 40 60 3.5 1.5 13 V13 BA 55 / S 3 / AN 10 60 4.5 1.5 14 V14 BMA 90 85 3.0 1.5 15 VI5 EHA 8 / AN 10 70 3.0 1.5 16 V16 BA 85 / VAc 5 / AN 5 85 7.0 2.0
1) BA = Butyl Acrylate S = Styrene VAc = Vini Acetate MMA = Methyl Methacrylate AN = Acrylonitri Bu = Butadiene BMA = N-Butyl Methacrylate EHA = 2-EI-L-Hexylacrylate 2) PT = Temperature polymerization in * C 3) time in b, a) comparison, b) according to the invention, PT = for a) and b) 4) comparison to higher temperature and lower addition times (high temperature method), the Product quality frequently presents performance weaknesses,