Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2001-05-17
2004-06-29
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S079000, C526S080000, C526S087000, C526S340000, C524S458000
Reexamination Certificate
active
06756454
ABSTRACT:
The invention relates to a process for reducing the odor emission of aqueous protective-colloid-stabilized vinylaromatic-1,3-diene copolymer dispersions, and also of redispersion powders which are obtainable by drying polymer dispersions of this type.
Aqueous polymer dispersions based on vinylaromatic-1,3-diene copolymer dispersions and redispersion powders obtainable therefrom, generally by spray drying, are used chiefly in the construction sector as agents for increasing the quality of finished pulverulent mixtures of cement or non-cement type. A problem with dispersions and redispersion powders of this type is that they generally still comprise volatile high-odor constituents, e.g. mercaptans which serve as molecular weight regulators during the polymerization, ammonia, which is used for neutralization, residual monomers, non-polymerizable contaminants of the monomers, volatile reaction products formed from the monomers under the conditions of the reaction, or also volatile degradation products of the polymers. The resultant odor is perceived as unpleasant both by the producers and by the users, and there is therefore a need for deodorized aqueous polymer dispersions.
It is known that polymer dispersions can be deodorized by physical chemical post-treatment. An example of a physical process is a distillative process, in particular steam distillation, or stripping using inert gases, as mentioned, for example, in EP-A 327006. A disadvantage of this process is that many dispersions do not have sufficient stability for this type of deodorization, and coagulation therefore occurs, requiring complicated filtration before subsequent use. Another disadvantage of the process is that although it is capable of reducing the proportion of volatile substances in the aqueous polymer dispersion it does not resolve the issue of disposal of these substances.
It is also known that polymer dispersions can be freed from high-odor monomers by chemical post-treatment. For example, DE-A 4419518 describes a chemical process for lowering the amount of residual monomers by free-radical post-polymerization with exposure to redox initiator systems. U.S. Pat. No. 4,529,753 describes a process in which the residual monomer content of aqueous polymer dispersions can be reduced by free-radical post-polymerization brought about by particular free-radical redox initiator systems after the main polymerization reaction is complete. Redox initiator systems of this type include at least one oxidant, at least one reducing agent, and one or more transition metal ions which occur in different valence states.
However, a disadvantage of the processes recommended above is that although they can bring about some reduction of residual monomer content when used in high-odor polymer dispersions, such as styrene-butadiene dispersions, they are not able effectively to reduce the unpleasant odor brought about by styrene and high-odor byproducts, for example mercaptans, non-polymerizable contaminants of the monomers, volatile reaction products of the monomers or volatile degradation products of the polymers.
DE-A 19728997 describes deodorized aqueous polymer dispersions obtainable by adding the zinc salt of ricinoleic acid and/or the zinc salt of abietic acid or, respectively, analogous resin acids and/or other zinc salts of other saturated or unsaturated hydroxylated fatty acids having 16 or more carbon atoms. A disadvantage of this method, however, is that, due to additional electrolyte loading, it impairs the stability this method, however, is that, due to additional electrolyte loading, it impairs the stability of the aqueous polymer dispersion.
The adsorbing action of adsorbents with respect to volatile organic substances is known. WO-A 98/11156 describes a process in which adding even small amounts (from 0.1 to 20% by weight, based on polymeric constituents of the dispersion) of active carbon in polymer dispersions binds the odor-forming volatile contaminants so strongly that these are practically no longer detectable either in the polymer dispersions or in the products produced using the polymer dispersions. A disadvantage of this process is that the residence time of the active carbon is up to two more hours for effective odor reduction, and the dispersion generally then has to be filtered (in particular for pigmented systems, e.g. emulsion paints) before further use. This is a disadvantage both from an economic point of view and also ecologically, especially since the disposal of the contaminated active carbon filtered off is an issue which remains open.
EP-A 283348 relates to a process for removing residual monomer, i.e. unreacted acrylonitrile, from acrylonitrile polymer dispersions by post-polymerization via addition of any desired monomers copolymerizable with acrylonitrile. In contrast, the object of the present application also includes minimizing the nuisance caused by non-polymerizable odoriferous substances.
Aqueous protective-colloid-stabilized styrene-butadiene polymer dispersions are two-phase systems which are composed of an aqueous phase and a polymer phase. Both the dispersed polymer particles and the aqueous dispersion medium are locations where high-odor constituents may be present. Between these two phases a distribution equilibrium becomes established. The disadvantage of the known methods for reducing the proportion of volatile constituents in aqueous polymer dispersions is, specifically, that they essentially affect either solely the aqueous dispersion or solely the polymer particles. This means that any significant total reduction in the proportion of volatile constituents in the aqueous polymer dispersion will essentially be diffusion-controlled (reestablishment of the distribution equilibrium) and this is probably the reason for the unsatisfactory rate of reduction in the proportion of volatile odoriferous materials in aqueous polymer dispersions when the known methods are used.
Surprisingly, it has been found that deodorization of the odoriferous materials located both in the aqueous phase and the polymer phase takes place if, toward the end of the main polymerization, esters of unsaturated carboxylic acids are added to the reaction mixture.
The invention provides a process for reducing the odor emission of aqueous protective-colloid-stabilized vinylaromatic-1,3-diene copolymer dispersions and of redispersion powders obtainable therefrom by drying, by emulsion polymerization of a mixture comprising at least one vinylaromatic and at least one 1,3-diene in the presence of one or more protective colloids and, if desired, drying the resultant polymer dispersion, which comprises, toward the end of the polymerization, when the total free monomer content of the aqueous polymer dispersion is from 0 to 20% by weight, adding from 0.01 to 15.0% by weight of one or more monomers selected from the class consisting of branched or unbranched alkyl esters, having from 1 to 8 carbon atoms in the alkyl radical, of monounsaturated mono- or dicarboxylic acids, where the data in % by weight are in each case based on the polymer content of the dispersion.
Preference is given to adding the alkyl esters of acrylic acid, methacrylic acid, fumaric acid, maleic acid or itaconic acid, such as methyl methacrylate, methyl acrylate, n-butyl methacrylate, n-butyl acrylate, ethyl methacrylate, ethyl acrylate, 2-ethylhexyl methacrylate, 2-ethylhexyl acrylate, diisopropyl fumarate, diethyl fumarate or mixtures of these. n-Butyl acrylate is particularly preferred.
The alkyl esters mentioned may be added as such or in aqueous emulsion. The amount added is preferably from 0.1 to 5% by weight, based on the polymer content of the aqueous polymer dispersion. The addition takes place toward the end of the polymerization, when the total free monomer content of the aqueous polymer dispersion is from 0 to 20% by weight, in other words the conversion of the entire amount of monomer used is from 80 to <100%. The addition preferably takes place when the total free monomer content of the aqueous dispersion, based on the polymer content
Ball Peter
Mayer Theo
Brooks & Kushman P.C.
Rajguru U. K.
Seidleck James J.
Wacker-Chemie GmbH
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