Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2001-05-11
2003-05-06
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C524S458000, C524S457000, C524S460000, C524S564000
Reexamination Certificate
active
06559236
ABSTRACT:
FIELD OF THE INVENTION
BACKGROUND OF THE INVENTION
The present invention relates to processes for the preparation of aqueous dispersions of (co)polymerizates using a polymer with cationic functionality and optionally using conventional additives. The invention also relates to the aqueous dispersions preparable with the processes according to the invention, dispersible powders obtainable from the dispersions, as well as the use thereof.
The stabilization of aqueous polymer dispersions (latices) is known from the prior art. Unlike polymer solutions, aqueous polymer dispersions are not thermodynamically stable systems. For this reason to the dispersions are generally added dispersing agents, which have an interfacial stabilizing action. In general, they are water-soluble compounds, present either in the form of protective colloids or emulsifiers. Due to their amphiphilic structure emulsifiers, which usually have a molecular weight below 1500, have a stabilizing action by reducing the interfacial tension between the polymerizate and the aqueous dispersing medium. The stabilizing action of protective colloids is mainly based on a steric shielding of the dispersed particles. They are generally substances with a molecular weight above 1500 and they can be both chemically and physically bound to the dispersed particles. In the widest sense, said protective colloids are themselves polymeric materials, which can therefore impair the action of the modifying polymerizate.
Such stabilizers, which can also be used in emulsion polymerization, are e.g. conventional surfactants, water-soluble polymers, such as polyvinyl alcohol or polyvinyl pyrrolidone, as well as polymerizable monomers. Such polymerizable, functional monomers, which can be used in polymerized form as a substitute for conventional surfactants, are e.g. carboxyl monomers, acrylamides or polymerizable surfactants with sulphonate groups.
A problem when using stabilizing agents is the coalescence, i.e. the undesired flowing together of the latex particles in the emulsion, so that it is no longer possible to obtain a redispersible powder. This agglomeration to larger polymerizate secondary particles (coagulate), for a given polymerizate content of the aqueous dispersion, becomes all the more critical the more finely divided the particles in the disperse distribution, because the interface grows superproportionally with decreasing particle diameter.
Apart from stabilized, aqueous polymerizate dispersions, great significance is in particular attacked to powders rendered available by drying from these dispersions. Redispersible powders are advantageous due to their easy handling, the easier, space-saving transportation, the easier dosability and the less expensive storage. As a result of the readily available dispersing medium (water) the powder form is also desirable in this respect.
The polymer powders produced by drying processes, such as e.g. freeze or spray drying, where in particular in the case of spray drying larger powder quantities can be produced, should be completely reversibly dispersible. However, when adding water, generally not completely satisfactory results are obtained. This is due to the fact that on drying, the highly disperse particles in the dispersion necessarily approach one another until in the case of contact of the surfaces of the particles irreversible changes occur, such as the aforementioned coalescence or also an aggregation of the particles. As a result the surface characteristics of the disperse phase are modified in such a way that on adding water, the affinity of the particles for one another is greater than that to water, so that there is no real redispersion.
In addition, the aforementioned emulsifiers or protective colloids, such as e.g. polyvinyl alcohol, can lead to a reduction of the reactivity of the redispersed polymer particles. In other words, the redispersible powder, following dispersion again, can partly or entirely lose its reactivity, together with the characteristics associated therewith.
One possibility of preventing an irreversible change to the external form of the aqueous polymer dispersion after drying consists of the addition of so-called drying aids, which are also known as spraying aids. These drying aids are water-soluble substances, which on drying form a matrix and in this way embed the polymer particles. On redispersing with water the matrix dissolves again and the polymer particles are reobtained in a virtually unchanged form. EP 770 640 A2 makes use of such a procedure. It describes the preparation of polymerizate powders by drying aqueous polymerizate dispersions, the dispersed polymerizates, which have a positive or negative surface charge, being maintained in solution, accompanied by the addition of a drying aid. This drying aid is a polyelectrolyte, which dissociates into a polyion and a counterion, in which the counterion must have the opposite charge to the polymerizate surface charge. Therefore the polyelectrolyte fulfils the function of an additional stabilizer, which keeps the polymerizate in solution. The polymerizate is not polymerized in the presence of the stabilizer, but is instead present as a finished polymer. The stabilizing effect is here achieved by a further molecule virtually acting as an emulsifier.
Another possibility for obtaining stabilized dispersions from a water-insoluble latex is known from EP 441 037 A1. The latter describes anionically stabilized dispersions from latex and a quaternary, cationic polymer, both components being separately preparable and storable as soluble polymers. Both components are then sprayed together onto the application surface, in order to form a dry coating which cannot be washed out, the cationic polymer serving as a coagulant. Therefore the cationic polymers do not contribute to the stabilization of the dispersion and instead destroy the same, accompanied by the precipitation of the latex polymers (so-called demulsification) and formation of a coating.
EP 286 008 B1 describes the use of aqueous, cationic plastic dispersions for impregnating and priming absorbent substrates. The cationic dispersion polymerizates contain 80 to 99 wt. % ethylenically unsaturated monomers from the group vinyl esters, methacrylic esters, acrylic esters, vinyl aromatics, vinyl chloride, ethylene, acrylonitrile, diesters of maleic acid and/or fumaric acid and vinyl pyrrolidone, 1 to 20 wt. % ethylenically unsaturated, cationic, water-soluble monomers, 0 to 19 wt. % ethylenically unsaturated, hydrophilic monomers with one or more functional groups from the series COOH, —NR
1
R
2
, —CONR
1
R
2
, in which R
1
and R
2
stand for H or —CH
2
OR with R═H or (C
1
-C
8
)-alkyl, and up to 19 wt. % ethylenically unsaturated monomers with one or more OH groups. The monomers are chosen in such a way that the minimum cationic activity of the dispersions is 20 to 200 &mgr;mole/g solids, 15- measured at pH 7 and 60 to 99% of the cationic charge is on the surface of the particles, and the dispersions have a minimum film formation temperature (MFT) between 0 and 40° C. The polymerizate particles of the dispersions have an average particle diameter of 0.02 to 0.2 &mgr;m. The cationic dispersions are used for impregnating and priming brickwork, concrete, plaster surfaces, ground plaster, gypsum surfaces or bricks. However, dispersible powders are not described.
SUMMARY OF THE INVENTION
According to JP 55-104 955 A, an aqueous dispersion of a cationic-ethylenically unsaturated polymer is described, which has a glass transition temperature Tg<50° C. and contains a cationic, water-soluble or water-dispersible, ethylenically unsaturated oligomer and/or polymer and/or cationizable, ethylenically unsaturated monomers in aqueous phase. The polymers serve as additives for improving the characteristics of cement products. As a result there is an improvement to the water resistance, water tightness, strength, adhesion, chemical stability and durability of a cement product, such as mortar. The emulsion polymerization of these polymers is either brought abou
Koelliker Robert
Willimann Hongli
Asinovsky Olga
National Starch and Chemical Investment Holding Corporation
Roland, Esq. Thomas F.
Seidleck James J.
LandOfFree
Method for producing aqueous dispersions of (co)polymers,... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for producing aqueous dispersions of (co)polymers,..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for producing aqueous dispersions of (co)polymers,... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3092397