Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2000-06-13
2002-07-09
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C524S458000, C526S079000, C526S080000, C526S087000, C526S340000
Reexamination Certificate
active
06417297
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for reducing the odor emission of aqueous vinylaromatic/1,3-diene copolymer dispersions and of redispersion powders which are obtainable by drying such polymer dispersions.
2. The Prior Art
Aqueous polymer dispersions based on vinylaromatic/1,3-diene copolymer dispersion and redispersion powders prepared therefrom, as a rule by spray-drying, are used in particular in the building sector as bodifiers in cement-containing and non-cement-containing, pulverulent ready-mixed formulations. One problem of such dispersions and redispersion powders is that they still contain, as a rule, volatile components having an intense odor. Examples of these volatile components include mercaptans, which serve as molecular weight regulators during polymerization, ammonia, which is used for neutralization, residual monomers, unpolymerizable impurities in the monomers, volatile reaction products of the monomers, which are formed under the reaction conditions, and volatile degradation products of the polymers. The resulting odor is found to be unpleasant both by the manufacturers and by the consumers, which is why there is a need for deodorized aqueous polymer dispersions and deodorized redispersion powders.
It is known that polymer dispersions can be deodorized by physical or chemical aftertreatment. For example, distillation processes, in particular steam distillation, and stripping with inert gases, may be mentioned as physical processes, as stated, for example, in EP-A-327006 (U.S. Pat. No. 5,708,077). The disadvantage of this process is that many dispersions are not sufficiently stable for this type of deodorization, so that coagulum formation occurs. This will necessitate expensive filtration prior to further use. A further disadvantage of the process is that, although it is capable of reducing the amount of volatile substances in the aqueous polymer dispersion, the question of disposal of the substances remains open.
It is also known that polymer dispersions can be freed from monomers having an intense odor by chemical aftertreatment. For example, DE-A 4419518 states that the level of residual monomers can be reduced chemically by free radical post polymerization with the action of redox initiator systems. U.S. Pat. No. 4,529,753 describes a process by means of which the content of residual monomers of aqueous polymer dispersions can be reduced by means of free radical post polymerization after the end of the main polymerization reaction, by the action of special free radical redox initiator systems. Such redox initiator systems comprise at least one oxidizing agent, at least one reducing agent and one or more transition metal ions occurring in different valency states.
However, the disadvantage of the processes described above is that, when used in polymer dispersions having an intense odor, such as, for example, styrene/butadiene dispersions, they can partially reduce the residual monomer content. However they cannot effectively reduce the unpleasant odor caused by styrene and byproducts having an intense odor, for example mercaptans, unpolymerizable impurities in the monomers, volatile reaction products of the monomers, and volatile degradation products of the polymers.
DE-A 19728997 describes deodorized aqueous polymer dispersions which are obtainable by adding the zinc salt of ricinoleic acid and/or the zinc salt of abietic acid or analogous resin acids and/or further zinc salts of other saturated or unsaturated hydroxylated fatty acids having 16 or more C atoms. However, the disadvantage of this procedure is that, owing to an additional electrolyte load, it adversely affects the stability of the aqueous polymer dispersion.
The adsorbent effect of adsorbents with respect to volatile organic substances is known. WO-A 98/11156 describes a process in which the addition of even small amounts (from 0.1 to 20% by weight, based on polymeric components of the dispersion) of active carbon to polymer dispersions is capable of binding the odor-forming, volatile impurities so strongly that they are virtually no longer perceptible both in the polymer dispersions and in the products produced using the polymer dispersions. The disadvantage of this process is that, for effective odor reduction, the residence time of the active carbon is up to several hours and then as a rule (in particular for pigmented systems, for example emulsion paints) the dispersion has to be filtered for further use. This is disadvantageous both from the economic point of view and from the ecological point of view, especially since the question of the disposal of the contaminated active carbon filtered off remains open.
Aqueous styrene/butadiene polymer dispersions are two-phase systems which consist of an aqueous phase and a polymer phase. Both the dispersed polymer particles and the aqueous dispersing medium are available as possible locations for the presence of the components having an intense odor. A partition equilibrium is established between these two phases. The disadvantage of the known methods of reducing the amount of volatile components in aqueous polymer dispersions is that they include essentially either only the aqueous dispersing medium or only the polymer particles. This means that a significant total reduction of the amount of volatile components in the aqueous polymer dispersion takes place essentially under diffusion control (repeated adjustment of the partition equilibrium). Presumably the unsatisfactory rate of reduction of the amount of volatile odor substances in aqueous polymer dispersions for use in the known processes can be attributed.
DE-A 19853421 discloses a process for reducing the odor emission of aqueous vinylaromatic/1,3-diene copolymer dispersions, in which acrylate monomers are preferably added toward the end of the copolymerization. However, this procedure is not capable of eliminating all odor substances; in particular, evidently thermal decomposition products of the vinylaromatics and dienes are not eliminated.
SUMMARY OF THE INVENTION
Surprisingly, it was found that deodorization of both the odor substances present in the aqueous phase and those present in the polymer phase takes place if alkyl esters of unsaturated carboxylic acids and vinyl esters of aliphatic carboxylic acids are added to the reaction mixture in one step or in two successive steps toward the end of the main polymerization.
The present invention relates to a process for reducing the odor emission of aqueous vinylaromatic/1,3-diene copolymer dispersions and of redispersion powders obtainable therefrom by drying, by emulsion polymerization of a mixture containing at least one vinylaromatic and at least one 1,3-diene in the presence of one or more surfactant substances and optionally drying of the polymer dispersion obtained thereby, wherein 0.01% to 15.0% by weight of one or more monomers selected from the group consisting of the branched or straight-chain alkyl esters having 1 to 8 C atoms in the alkyl radical of monounsaturated monocarboxylic acids or dicarboxylic acids and 0.01% to 15.0% by weight of one or more monomers selected from the group consisting of the vinyl esters of branched or straight-chain aliphatic carboxylic acids having 1 to 10 C atoms are added in one step or in two successive steps toward the end of the polymerization, when the total content of free monomers in the aqueous polymer dispersion is in the range from ≧0 to ≦20% by weight, it also being possible optionally to add the vinyl ester fraction as early as the beginning of or during the polymerization, and the data in % by weight being based in each case on the polymer content of the dispersion.
Suitable vinylaromatics are styrene and methylstyrene, styrene preferably being copolymerized. Examples of 1,3-dienes are 1,3-butadiene and isoprene, 1,3-butadiene being preferred. In general, 20% to 80% by weight of vinylaromatic and 20% to 80% by weight of 1,3-diene are copolymerized, it being possible optionally also to copolymerize further monomers,
Ball Peter
Mayer Theo
Wacker Polymer Systems GmbH & Co. KG
Wu David W.
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