Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1997-06-04
2003-11-25
Buttner, David J. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S003000, C524S005000, C525S057000, C525S058000, C523S342000
Reexamination Certificate
active
06653372
ABSTRACT:
The present invention relates to a novel process for preparing an addition-polymer powder by drying an aqueous addition-polymer dispersion whose film has a glass transition temperature Tg≦30° C. and to which a drying assistant has been added. (Film in the sense of the film formed by the aqueous addition-polymer dispersion when dried at 10° C. above the minimum filming temperature (DIN 53 787, 1974) but not below 20° C.)
The present invention furthermore relates to the addition-polymer powder obtained from the novel process and to its use for modifying binding mineral building materials.
Binding mineral building materials are generally known. The term applies to formulations comprising, as essential constituents, pulverulent inorganic binders such as lime, cement and/or gypsum, typically together with aggregates comprising sands, gravels, crushed rocks or other fillers such as, for example, natural or synthetic fibers and which, by mixing with water, are converted into their ready-to-use form (mortar or concrete), which, left alone, will harden to a rocklike state over time in air or in some cases even under water.
It is further generally known that, to control their mechanical property profile in the hardened rocklike state, binding mineral building materials are frequently used modified with finely divided addition polymers (as used herein, addition polymer shall encompass such high molecular weight compounds as are obtainable by free-radical polymerization of starting monomers containing at least one ethylenically unsaturated group).
The modifying effect of the finely divided addition polymer is frequently determined less by its chemical nature in many cases than by its physical properties, especially its glass transition temperature.
Addition polymers suitable for use as modifiers therefore can have very different monomer compositions and a glass transition temperature Tg (herein to be understood as the quasi-static glass transition temperature of DIN 53 765 (differential scanning calorimetry, 20° C./min, midpoint)) which can vary within a wide range, for example from −60 to +180° C. Examples of the modification of binding mineral building materials with addition polymers include for example U.S. Pat. No. 4,340,510, GB-B 1 505 558, U.S. Pat. Nos. 3,196,122, 3,043,790, 3,239,479, DE-A 4 317 035, DE-A 43 17 036, DE-A 43 20 220, EP-A 537 411, DE-B 16 69 903, BE-A 84 54 499, JP-A 54/43285, U.S. Pat. No. 4,225,496, DE-A 32 20 384, DE-A 28 37 898, U.S. Pat. No. 3,232,899 and JP-A 91/131 533.
These finely divided modifying addition polymers are usually incorporated in the form of their aqueous dispersions. These are systems of essentially spherical coils of intertwined polymer chains dispersed in an aqueous medium. The diameter of the polymer coil particles is generally mainly within the range from 10 0.01 to 5 &mgr;m, for example mainly within the range from 0.01 to 1 &mgr;m. The advantages of the aforementioned procedure therefore include the fact, on the one hand, that the addition polymer is present in the aqueous dispersion in a particularly finely divided form and that, on the other, the mixing water required is already present as dispersing medium.
However, the disadvantage of an aqueous addition-polymer dispersion as a use form is that it is not fully satisfactory as a shipment form. For instance, its transportation to the site of use will always include the transportation of the universally readily available (mixing) water as well as the transportation of the modifying polymer; secondly, it can only be added to the binding mineral building material at the site of use, since the binding mineral building material would otherwise harden before use.
The most convenient form of using an aqueous addition-polymer dispersion under the aforementioned aspects is therefore that of an addition polymer which is redispersible on addition of water (cf. for example DE-A 42 06 429). Together with the other mortar, concrete or render constituents, the redispersible polymer can be used to manufacture storable dry mixtures which are convenient to ship and which merely need to be mixed with water to convert them into the ready-to-use form.
In principle, addition polymers which redisperse on addition of water are obtainable by drying their aqueous dispersions, and they are normally obtained in powder form. Examples of such drying processes are freeze drying and spray drying. The latter method, which involves spraying the addition-polymer dispersion into a hot air stream to dewater it, is especially convenient for producing large quantities of powder. The drying air and the spray-dispensed dispersion are preferably passed cocurrently through the dryer (cf. for example EP-A 262 326 or EP-A 407 889).
Whereas the drying of addition-polymer solutions is normally fully reversible, one disadvantage of addition-polymer powders created by drying aqueous addition-polymer dispersions is that the redispersibility of the addition-polymer powders in water is generally not fully satisfactory in that the polymer particles resulting from the redispersing usually do not achieve the state of subdivision of the aqueous starting dispersion (primary particle diameter distribution), which reduces their modifying effect on addition to binding mineral building materials.
This is because, unlike solutions, the aqueous dispersions of addition polymers do not form thermodynamically stable systems. On the contrary, the system is trying all the time to reduce the area of interface between addition polymer and dispersing medium by combining small primary particles into larger secondary particles (eg. globules, coagulum), which can be prohibited for a prolonged period for the disperse state in the aqueous medium by adding dispersants.
In general, dispersants are substances capable of stabilizing the interface between the dispersed polymer and the aqueous dispersing medium. The stabilizing effect is primarily due to a steric and/or electrostatic screening of the dispersed polymer particles, the envelope around which is formed by the dispersant.
However, if aqueous addition-polymer dispersions are to be dried, then, the separating effect of the dispersants is frequently no longer adequate and irreversible secondary particle formation will occur to a certain extent; that is, the secondary particles remain as such on redispersion and reduce the modifying effect of the aqueous addition polymer obtainable by redispersion. This applies all the more the lower the glass transition temperature of the dispersed addition polymer is.
It is well known, then, that there are substances whose addition to aqueous addition-polymer dispersions reduces the appearance of irreversible secondary particle formation in the drying process.
These substances are generically known as drying assistants, In many cases they are known in particular for use as spraying assistants, since spray drying promotes the formation of irreversible secondary particles to a particular degree. At the same time, they generally reduce the formation of polymer deposits on the spray dryer wall and thus raise the yield of powder. Based on dispersed polymer, the drying assistants are normally added in amounts of from 1 to 30% by weight, frequently from 1 to 20% by weight.
Low addition quantities are frequently desirable.
According to TIZ-Fachberichte, 109 (1985), No. 9, 698, the drying assistants used hitherto are generally water-soluble substances which, in the course of the drying operation, form a matrix in which the water-insoluble, dispersant-enveloped primary addition-polymer particles are embedded. The surrounding matrix protects the primary addition-polymer particles from irreversible secondary particle formation. The usual outcome is a reversible formation of secondary particles (agglomerates typically from 1 to 250 &mgr;m in size), comprising numerous primary addition-polymer particles separated from one another by the drying assistant matrix. On redispersion in water, the matrix redissolves and the original, dispersant-enveloped primary polymer particl
Angel Maximilian
Dragon Andree
Pakusch Joachim
Roser Joachim
BASF - Aktiengesellschaft
Buttner David J.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
LandOfFree
Preparation of addition-polymer powder does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Preparation of addition-polymer powder, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Preparation of addition-polymer powder will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3174794