Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2001-09-24
2003-09-16
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S442000, C524S492000, C521S106000
Reexamination Certificate
active
06620879
ABSTRACT:
DESCRIPTION
The present invention relates to pulverulent polymer compositions based on polyether carboxylates, processes for preparing them and their use.
Water-soluble polymers comprising polyoxyalkylene-containing structural units, carboxylic acid and/or carboxylic anhydride monomers and, if desired, further monomers, hereinafter referred to as polyether carboxylates, have recently found uses in a variety of applications.
Apart from their use as dispersion stabilizer in the preparation of water-soluble copolymers (WO 97/30 094), their use as protective colloid in the production of caking-resistant dispersion powders has been described. However, polyether carboxylates are preferably used in building materials such as concrete, mortars, bitumen, knifing fillers, adhesives, pigment-containing paints and coating compositions, in ceramic compositions, in the refractories industry and petroleum processing to exert a targeted influence on the rheological and/or wetting properties of these building materials. Adsorptive interactions which polyether carboxylates can undergo with the hydraulic binder particles of these building materials (cement, lime, calcium sulfate, etc.) result in stabilization of the mineral particles combined with reduced internal friction and thus in improved flow and processing properties. Although these polymers consist of only two significant structural units, namely a polyoxyalkylene-containing unit and a carboxylic acid(anhydride) monomer, a large number of types of linkage are possible. The structural variety of such polyether carboxylates extends from random, alternating or block polymers through to comb polymers having carboxyl groups in the main chain and polyether units in the side chain. Also included are graft copolymers which are formed by functionalization of polyethers by means of monomers containing carboxylic acid groups.
Finally, the group of polyether carboxylates also includes polyesters which are formed by reaction of polyethers, such as polyethylene glycol, with polybasic carboxylic acids or carboxylic anhydrides. It is immaterial whether these polymers are present as the free acid or in their salt form.
The technical advantage of such products as fluidizers in cement-based building materials is, firstly, that long-lasting processability as desired by the concrete transport industry can be achieved with use of extremely small amounts. Secondly, these additives enable the proportion of water to be reduced so greatly that it is possible to produce high-strength concrete which can be removed from the mold or from which the shattering can be removed after only 12 hours, thus meeting a central requirement of the prefabricated parts industry. In addition, the polymers are free of toxicologically problematical constituents such as formaldehyde, which distinguishes them from conventional cement flow improvers, e.g. as disclosed in EP-B 214 412 or DE-C 16 71 017. For a series of applications, it is useful and desirable to provide the water-soluble polyether carboxylates in the form of their aqueous solutions.
However, the use of aqueous preparations can be completely ruled out in other fields of application where the polymers are required as additives in factory-produced dry mixes.
Apart from logistic and economic advantages (transport of water!), powders have a number of technical advantages over aqueous preparations. Stabilization against attack by microorganisms by means of addition of biocides becomes unnecessary as do the sometimes complicated measures for tank hygiene. Since polyether carboxylates can, owing to their surface-active properties, introduce undesirably high proportions of air into the building material, antifoams are generally mixed into the aqueous preparations after they have been prepared.
Owing to the incompatibility of the antifoam in the aqueous medium of the polyether carboxylate, sedimentation and/or flotation phenomena occur, which leads to considerable problems at the end user.
If the polyether units in the polyether carboxylates are incorporated in the main chain or bound as side chain constituents on the main chain via ester groups, undesirable hydrolysis with destruction of the polymer structure can occur already during storage of the aqueous preparations.
This problem can be countered only “symptomatically” by storage at low temperatures, which greatly restricts the use of such aqueous preparations, particularly in hot climatic zones. In addition to the unsatisfactory stability at temperatures above 30° C., there is the sensitivity to frost. Owing to the abovementioned facts, the use of powders has always been found to be preferable to the use of aqueous preparations.
According to the prior art, polymer powders based on polyether carboxylates are obtained by spray drying the aqueous preparations in a stream of hot air, during which antioxidants and spray-drying auxiliaries are advantageously added so as to
a) prevent spontaneous heating or spontaneous ignition of such polymers during and after the drying process and
b) inhibit adhesion of the wax-like polymer particles in the dryer.
Neglect of the safety risks mentioned under a) has in the past led to fires during the spray drying process. Furthermore, despite the use of spray-drying auxiliaries, it is sometimes difficult to isolate a non-sticky and caking-resistant polymer powder, especially when the proportion of polyether in the polymer is high and the proportion of carboxyl groups is low. These disadvantages, the high energy requirement for spray drying and the emission limits to be adhered to during spray drying are particularly serious.
The procedure in which the polyether carboxylate is firstly produced in a solvent-free polymerization, diluted with water and subsequently neutralized is particularly uneconomical. After that, spray drying is carried out with the abovementioned disadvantages in order to remove the water introduced in the dilution process.
It is therefore an object of the present invention to provide pulverulent polymer compositions based on polyether carboxylates which avoid the disadvantages of the prior art, i.e. give products which are storage-stable at high temperatures and are also insensitive to frost, require no preservatives, are stable to spontaneous ignition and thermal oxidative degradation, give sticking- and caking-resistant powders and are obtainable at a low energy consumption and by a rational process.
According to the invention, this object is achieved by pulverulent polymer compositions comprising
a) from 5 to 95% by weight of a water-soluble polymer made up of polyoxyalkylene-containing structural units, carboxylic acid and/or carboxylic anhydride monomers and, if desired, further monomers, and
b) from 5 to 95% by weight of a finely divided mineral support material having a specific surface area of from 0.5 to 500 m
2
/g (determined by the BET method in accordance with DIN 66 131).
It has surprisingly been found that the incorporation of the polyether carboxylates (component a) into the mineral component b) can be made so effectively that up to 90% by weight of active ingredient, i.e. the polyether carboxylate component, in the polymer composition can be achieved.
In addition, it was particularly surprising that the sticking and caking resistance was considerably increased compared to spray-dried products and additional advantages were found in the use of the compositions in cement-containing building material mixtures.
The water-soluble polymers used for preparing the polymer composition of the invention are products which contain polyoxyalkylene groups, preferably polyethylene glycol or polypropylene glycol groups, in the main chain or in the side chain and additionally comprise carboxylic acid and/or carboxylic anhydride monomers, preferably acrylic acid, methacrylic acid, maleic acid, maleic anhydride, fumaric acid, itaconic acid and itaconic anhydride. Further monomers based on vinyl or acrylate groups can additionally contribute to making up the polyether carboxylates. Examples of such further monomers are styrene
Albrecht Gerhard
Kern Alfred
Leitner Hubert
Weichmann Josef
Degussa Construction Chemicals GmbH
Fulbright & Jaworski L.L.P.
Hu Henry S.
Wu David W.
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