Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-08-18
2002-08-27
Mullis, Jeffrey (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S201000, C523S202000, C523S205000, C523S335000, C525S070000, C525S071000, C525S360000
Reexamination Certificate
active
06441062
ABSTRACT:
The invention relates to a process for precipitating microsuspension polymers, to the polymers thus precipitated, to their use for modifying molding compounds, and to molding compounds comprising them.
For the preparation of small addition-polymer particles, which are used in particular as a rubber component in polymer blends, a variety of processes are known.
For example, the polymer particles may be prepared by the microsuspension process. In this procedure a liquid monomer or liquid monomer mixture that is to be polymerized to the particulate polymer is mixed with water and a protective colloid. The preferably water-insoluble polymerization initiator is added even at this point or only after the monomers have been dispersed, and if appropriate after the dispersion has been heated. Intensive stirring at high speed and high shear produces, from the heterogeneous mixture, a dispersion of very small monomer droplets in water. Intensive mixers of any desired construction are used for this purpose. The polymerization is started by heating the dispersion and continued, with moderate stirring in which the droplets are not broken up any further, until a desired conversion has been reached. By adding different monomers at specific times it is possible to obtain core-shell polymer particles, known as graft polymers. The protective colloids used to stabilize the dispersion are generally water-soluble polymers which envelop the monomer droplets and the polymer particles formed from them and so protect against coagulation.
The preparation of particulate microsuspension polymers is described, for example, in DE-A-44 43 886.
If the microsuspension polymers obtained are to be used to modify polymer molding compounds, they are frequently incorporated into the polymers with heating in the form of an aqueous dispersion, with the dispersion medium evaporating. Precipitating the polymer dispersion is difficult, since customary precipitants used for emulsion polymers are ineffective.
One process for producing solid microsuspension polymers is that of spray drying. In the case of this costly process, however, all of the auxiliaries present in the dispersion remain in the spray-dried product. This may lead to the formation of gel specks, to discoloration, or to premature aging.
It is an object of the present invention to provide a process for precipitating microsuspension polymers from a suspension comprising them.
We have found that this object is achieved in accordance with the invention by a process for precipitating microsuspension polymers from a suspension comprising them, where a polymer dispersion prepared by emulsion polymerization is added to the suspension.
In addition, a precipitant for the polymer dispersion may also be added to the suspension. In this case it is possible first to mix the suspension with the polymer dispersion and then to add the precipitant, or to mix the suspension with the precipitant and then to add the polymer dispersion.
It has been found in accordance with the invention that when a polymer dispersion prepared by emulsion polymerization is added it is possible to precipitate microsuspension polymers.
Emulsion polymerization is a heterogeneous reaction procedure in which unsaturated monomers or monomer solutions are emulsified in a continuous phase, generally water, with the aid of an emulsifier system and are polymerized using initiators which form free radicals. The free-radical initiators are preferably soluble in water. The product is a colloidal dispersion of the polymer or polymer solution, known as a latex. In the course of the reaction the emulsifier system forms micelles into which the at least partially water-soluble monomers from the emulsified monomer droplets migrate through the aqueous phase. With the aid of initiators present in the aqueous phase, polymerization is initiated in the micelles. The monomers used must have a certain water solubility in order to be able to migrate from the monomer droplets through the aqueous phase into the micelles. Examples of monomers which can be used are styrene, butadiene, acrylic acid, vinyl chloride, acrylonitrile, and others. A process to this effect is described in Encyclopedia of Polymer Science and Engineering, Volume 6, page 1 (1986), John Wiley and Sons, New York.
Emulsifiers which can be used in this case are anionic, cationic, nonionic or amphoteric surface-active compounds, especially soaps. It is preferred to use anionic or cationic soaps such as salts of long-chain carboxylic acids or sulfonic acids. Examples are sodium, potassium and ammonium salts of C
12-30
fatty acids such as stearic and oleic acid and also the salts of C
10-30
sulfonates, for instance, sodium alkylbenzenesulfonates (LAS) and similar compounds derived from fatty acid radicals. One particularly preferred example is sodium lauryl sulfate. Suitable cationic soaps are, in particular, salts of long-chain amines or polyamines and also quaternary ammonium salts or amines of long-chain polyoxyethylenes and quaternized derivatives thereof, and also amine oxides. Suitable emulsifiers are described in “Emulsion Polymerisation and Emulsion Polymers”, Ed. P. A. Lovell, M. S. El-Aasser, John Wiley and Sons, Chichester (1997), pages 224 to 226. Reference may also be made to the Encyclopedia of Polymer Science and Technology, Volume 5, pages 816 to 819 (1966), John Wiley and Sons.
For the preparation of the emulsion polymers, the emulsifiers are used in an amount of from 0.1 to 10% by weight, preferably from 0.15 to 5% by weight, with particular preference from 0.2 to 2.0% by weight, based on the monomers to be emulsified. Examples of suitable water-soluble initiators are hydrogen peroxide and potassium, ammonium and sodium peroxides.
Processes for preparing the emulsion polymers, and emulsion polymers that can be used, are described, for example, in DE-A-24 27 960, EP-A-0 125 483, EP-A-0 716 101, and EP-A-0 576 960. Preferably, the emulsion polymer is composed of the same monomers used to prepare the microsuspension polymers described below.
Emulsion polymers may be precipitated by adding suitable precipitants, which disrupt the dispersion of the polymer particles. For example, electrolytes such as calcium chloride or magnesium sulfate are added to the dispersions. In general, it is possible to use salts which comprise a polyvalent cation. Furthermore, acids may be used. The treatment with the precipitant, preferably in the form of an aqueous solution, leads to coagulation of the polymer particles, which can then be separated from the dispersion medium, generally water. A procedure to this effect is described in DE-A-24 27 960.
In the same way as the nature of the emulsion polymer to be used is not critical and may be chosen freely, the nature of the microsuspension polymer to be used in accordance with the invention is also freely selectable and not restricted. Suitable microsuspension polymers are described, for example, in DE-A-44 43 886.
A suitable polymer is, for example, an elastomeric microsuspension polymer A′ having an average particle diameter of from 0.08 to 100 &mgr;m.
The morphological structure of the particles can be chosen arbitrarily; for example, the particles may have a uniform composition or may consist of a core with one or more graft shells. The particles may be crosslinked or uncrosslinked and may consist of polymers possessing a glass transition temperature (T
g
) of less than 0° C. (rubber-containing) or of more than 0° C. (brittle). It is also possible—in the case, for example, of particles having a core/shell structure—for there to be two or more phases, some phases having a glass transition temperature of more than 0° C. and other phases having a glass transition temperature of less than 0° C.
Suitable monomers for preparing the microsuspension polymers (MSPs) are those monomers which may be polymerized using free radicals. Examples of such monomers are C
1-36
alkyl (meth)acrylates such as butyl acrylate and ethylhexyl acrylate, which lead to soft monomers, and also methyl methacrylate, ethyl acrylate, and me
Czauderna Bernhard
Heinen Harmut
Koch Jürgen
Mc Kee Graham Edmund
BASF - Aktiengesellschaft
Keil & Weinkauf
Mullis Jeffrey
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