Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
1997-09-30
2003-12-09
Zalukaeva, Tatyana (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S067000, C526S080000, C526S082000, C526S920000, C526S922000, C524S543000, C524S459000
Reexamination Certificate
active
06660814
ABSTRACT:
The inventions relates to a process and a device for preparing homopolymers and copolymers, including those of styrene, butadiene and (meth)acrylic acid and derivatives thereof, by the emulsion polymerization technique.
The manner in which polymerizations are carried out involves bringing one or more polymnerizable monomers into disperse distribution in a liquid which is ideally inert in the reaction—usually water—in presence of detergents or soaps as dispersing auxiliaries. Polymerization takes place predominantly by means of initiator radicals in the monomer-containing micelles that are formed. High molecule masses can be obtained in such a polymerization, since monomer is able to make its way continually into the micelles. The mechanism is normally that of a free-radical polymerization; the reaction products can in many cases be processed further directly in dispersion form (as, for example, in the case of the production of paints and adhesives. Known products are homo- and copolymers (P) of styrere (S), vinyl chloride (VC) butadiene (Bu) or methyl methacrylate (MMA). The particle size and its distribution can often be controlled by the use of see (particles), added to start with or produced in situ. Typical conditions in an industrial-scale process (taking the example of a styrene-butadiene copolymer or a polyacrylate) are reaction periods of from 3 to 12 h at from 40 to 100° C.
DE-A 23 32 637describes an emulsion polymerization in which butadiene is reacted with comonomers such as styrene, acrylonitrile (AN) or esters of acrylic or methacrylic acid in the presence of customary emulsifying auxiliaries, such as higher fatty acids, higher alkyl (aryl)sulfonates, adducts of alkylene oxides with long-chain fatty alcohols, and free-radical initiators such as alkali metal persulfates, at more than 115° C. An advantage over the prior art with operation at less than 80° C. is said to be the higher polymerization rate. However, there is often an adverse effect on the performance properties of products prepared at such high temperatures, in respect for example of the molecular mass distribution, the particle size distribution and, in association therewith, the adhesive strength, for example. In addition, safety aspects (such as the pressure developed when butadiene is a component) are increasingly playing an important role in connection with the reaction regime.
Nevertheless, 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 plant, since the reaction times can be significantly reduced; in other words, a large-scale industrial process is carried out with lower cycle times, which helps save on investment costs for a greater number of plant units. A major problem area which then requires solution, however, is the dissipation of heat, for example in order to help avoid instances of local overheating in the case of exothermic reactions, since such overheating can in many cases lead to secondary reactions, irregular molecular mass distributions or irregular particle sizes. EP-A 0 486 262discloses the preparation of emulsion copolymers where the energy balance is monitored and the result is used to control the supply of the comonomers and the temperature. Temperature control is effected by the use, inter alia, of an external heat exchanger. No information is given about the quality of the products or the design of the pumps or heat exchanger.
A heat treatment of homo- or copolymers of VC, by means for example of an external heat exchanger, for reducing viscosity after the actual emulsion polymerization is described in Research Disclosure July 1978, reference 17149, p. 17. No mention is made of influencing the actual main reaction.
EP-A 0 608 567, for use in the suspension polymerization of VC to form homo- or copolymers, in a vessel with stirrer and an external heat exchanger, describes a special pump (Hydrostal pump) by means of which the reaction mixture is guided at an angle of 90°C., the interior having a conical hub with a rotor blade which movies with a spirally rotating motion. No remarks are made about the heat exchanger. Stirring energy and circulation energy must he kept within a certain proportion. A comparable pump is used in EP-B 0 526 741 as well, which also deals with the suspension polymerization of VC; there, the type of heat exchanger is regarded as not being critical (see p. 4, lines 36 to 40).
In the process for preparing emulsion polymers of DE-A 44 42 577, the energy liberated in the course of the exothermic reaction is dissipated in part by distilling off a water/monomer mixture under reduced pressure from the reaction vessel (a stirred reactor). Although this measure does lead to a certain reduction in the polymerization period, i.e. essentially in the time required for adding the monomer or monomers, it is still not sufficiently suitable for large-scale industrial plant, especially since there is little or no provision for it to be used widely, for example for low-boiling comonomers and (co)monomers which are gaseous under standard conditions (for example, comonomers of the butadiene type).
It is an object of the present invention to find a preparation process which can be carried out on an industrial scale and has a broad field of use but which does not have the disadvantages of the prior art. In other words, in particular, short reaction times should be possible, a broad spectrum of different monomers, including those which are gaseous under standard conditions should be accepted, and the products should be at least comparable in terms of the performance properties with current products.
We have found that this object is achieved by a process for preparing homo- or copolymers of at least one of the polymerizable monomers of is the group consisting of styrene, butadiene, vinyl chloride, vinyl acetate, vinylidene chloride, alkyl (meth)acrylate (meth)acrylic acid, (meth)acrylonitrile and (meth)acrylamide in an emulsion polymerization technique at at lease 40° C. in the presence of a dispersing auxiliary and of a free-radical polymerization initiator. The novel process comprises preparing the polymer, at least 85% by weight of which is formed from one or more of these monomers, in the following stages, where
a) in a first stage water is added as a solvent which is inert in the reaction, and dispersing auxiliaries, seed and a first portion of monomer(s) arc added if desired,
b) in a second stage initiator is added, and
c) in a third stage the remainder or all of the monomer(s) is added directly or in emulsion form and in the presence of further water and, if desired, further dispersing auxiliary or other auxiliaries, it also being possible to operate the stage a) and b) or b) and c) in each case as single stages, and in certain stages or every stage moving the reaction mixture in its dispersion form by means of an external circuit which leads from and back to the reaction vessel and comprises at at least one low-shear pump and at least one heat exchanger having an essentially laminar flow profile, and carrying out polymerization at from 40 to 120° C.
In preferred embodiments of the novel process at least 90% by weight, in particular at least 93% by weight, of the polymer consists of one or more of the abovementioned monomers, and the polymerization is carried out at from 50 to 100°C., in particular from 60 to 95° C. and, very particularly, from 70 to 95°C. Of the monomers mentioned, preference is given to styrene, butadiene, alkyl (meth)acrylate and (meth)acrylonitrile.
The novel process can be carried out either by including a portion of monomer(s) in the initial charge in stage a) or in a combination of a) and b) and subsequently, in stage c) or in a combination of b) and c), adding the remainder, or by supplying the total amount exclusively in stage c) or in a combination of b) and c). If monomer(s) is (are) included in the initial charge in stage a) or in a combination of a) and b), then the amount thereof is judiciously from 3 to 30% by weight of the to
Kastenhuber Walter
Klanig Wolfgang
Klostermann Rainer
Kröner Huberrus
Morrison Bradley Ronald
BASF - Aktiengesellschaft
Keil & Weinkauf
Zalukaeva Tatyana
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