CA2020449A1

CA2020449A1 - Polymer powders which are redispersible in water and can be prepared by atomizing aqueous polymer dispersions, and their use as additives in hydraulic binders

Info

Publication number: CA2020449A1
Application number: CA 2020449
Authority: CA
Inventors: Wilhelm F. Beckerle; Rolf Dersch; Gernot Franzmann; Ludger Leber; Brigitte Gareiss
Original assignee: Individual
Current assignee: BASF SE
Priority date: 1989-07-14
Filing date: 1990-07-04
Publication date: 1991-01-15
Also published as: JPH0356536A; FI903427A0; EP0407889A1; DE3923229A1

Abstract

O.Z. 0050/40946 Abstract of the Disclosure: Polymer powders which are redispersible in water and are obtainable by atomizing aqueous polymer dispersions to which from 3 to 50% by weight, based on the polymer, of a water-soluble alkali metal salt or alkaline earth metal salt of a phenol-sulfonic acid/formaldehyde condensate has been added are used as additives in hydraulic binders.

Description

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O.Z. 0050/40946 Polymer powders which are L-edispersible in water and can be prepared by atomizinq aqueous ~olymer dispersions, and their use as additives in hydraulic binders The present invention relates to polymer powders which are redispersible in water and are obtainable by atomizing aqueous polymer dispersions to which from 3 to 50% by weight, based on the polymer, of a water-soluble alkali metal salt or alkaline earth metal sal~ of a phenolsulfonic acid/formaldehyde condensate has been added, and their use as additives in hydraulic binders.
It is known that redispersible dispersion powders can be prepared by atomizing aqueous polymer dispersions in a stream of hot air. In the case of dispersions whose polymers have glass transition temperatures below about 50C, it is necessary to add assi~tants to prevent the polymer particles from forming a film in the drier with formation of wall deposits and lumps, and to achieve adequate blocking resistance of the powders.
In addition to water-insoluble inert additives, such as finely divided silica, other possible additives are dispersions of polymers having a high s~yrene content ~c~: ~7/O~ (DE-A 2 238 903~ or aqueous copolymer solutions based on vinylpyrrolidone and vinyl acetate tDE-A 3 143 071) and water-soluble sulfonat~-containing condensates of mela-mine and formaldehyde tDE-A 2 049 114). ~
For the preparation of polymer powders which are redispersible in water and have particularly high block-ing re~istance, DE-A 3 143 070 recommends the addition of a water-soluble naphthalene ulfonic acid/formaldehyde con-densate in the form of the alkali metal salt or alkaline earth metal salt. In this proce g, free-flowing powders which are readily redispersible in water can be obtained, even from contact adhesive copolymer disper-sions. Such redisper~ible polymer powders are suitahle, for example, a~ additive~ in hydraulic binder3 which have a viscosity-reducing effect and impart ela~tic properties 2 ~
- 2 - O.Z. 0050/40946 to the et mortar.
~ he advantages of the concrete or mortar which are achievable by this process are, however, offset by the fact that the flow is restricted, which is disadvan~
tageous, for example in self-leveling filling compounds.
It is an object of the present invention to pro-vide redispPrsible polymer powders which guar~n~ee good flow when used as additives in hydraulic binders.
We have found that this object is achieved by the polymer powders mentioned at the ou~set and their use as additives in hydraulic binders.
Preferred embodiments of the invention are des-cribed in the subclaims.
The polymer dispersions for the preparation of redispersible polymer powders can be obtained in a con-ventional manner by emulsion polymerization of olefinic-ally unsaturated monomer~ in the presence of the usual polymerization initiators, emulsifiers and diYpersant~ at elevated temperatures, for example up to about 95C. The mean particle size can be adjusted by conventional measures, for example via the type and amount of the emulsifiers: for the preparation of coarse-particled polymer dispersions, a small amount of emulsifier and nonionic or highly ethoxylated ionic emulsifiers are generally advantageou Protective colloids, for example polyvinyl alcohol, frequently have an advantageous effect. Polymerization in the presence of a seed latex can al~o be advantageous, particularly if the formation of new particles is suppressed. Finally, coarse particled dispersions can also be produced by controlled agglomeration of finely divided latic~s.
Preferred polymer di~persions have a mean par-ticle diameter (weight average) of from 400 to 5,000 nm, in particular from 650 to 5,000 nm. ~he measurement of the mean particle sizes of polymer dispersions, for example with the aid of an ultracentrifuge, i~ ~amiliar to the skilled worker. The LT value, ie. the light 2''J.~ i c"~l - 3 - O.Z. 0050/40946 transmittance of the aqueous dispersion diluted to 0.01%
by weight, a standard parameter which is readily obtain-able experimentally, can also be used as a measure of the mean particle size of a polymer dispersion of similar 5 monomer composition.
In the preparation of the polymer powders, the polymer content of the dispersion may vary from 30 to 65, in particular from 45 to 60, % by weight. The polymers generally have glass transition temperatures of from +50 to -60C, polymers having a glass transition temperature of less than +25C preferably being used. Examples of olefinically unsaturated monomers from which the polymers may be derived are vinylaromatic monomers, such as styrene, monoolefinically unsatura~ed carboxylates of, in general, 4 to 14 carbon atoms, in particular acryla~es and me~hacrylates of alkanols of l to 8 car~on atoms, and vinyl esters, in particular of acetic and propionic acid, as well a~ vinyl laurate and vinyl esters of versatic acids. Other suitable polymers are those which are derived from vinyl chloride and/or vinylidene chloride or from diolefins, in particular butadiene. In addition, the polymers may contain, as polymerized units, acrylo-nitrile and/or mono- and/or dicarboxylic acids of, in general, 3 to 5 carbon atoms and/or their amides which may be substituted at the nitrogen atom, in particular acrylic acid, methacrylic acid, itaconic acid, acryl-amide, methacrylamide, N-methylolacrylamide and -meth-acrylamide and N-metho~ymethylacrylamide and -methacryl-amide. The amount of such monomers can be varied within wide ranges. It i~ from 0 to 40, frequently from 10 to 30, % by weight in the case of acrylonitrile, and fre-quently from 0.5 to 5, in particular from 1 to 4, % by weight in the case of monoolefinically unsaturated mono-mers having polar groups, such as acrylic acid or N-methylolmethacrylamids. The polymers may also contain, as polymerized units, small amounts of olefinically un-saturated e~ters of alkanediol~, such as ethylene glycol - 4 - o.Z~ 0050/40946 monoacrylate and diacrylate and the corresponding meth-acrylates and butane-1,4-diol monoacrylate and diacrylate and the corresponding methacrylates. Finally, polymer dispersions which contain, as polymerized units, ethylene and vinyl acetate in a molar ratio of, in general, from 15 : 85 to 85 : 15 are also suitable.
Preferably used copolymers are those of acrylates and methacrylates of alkenols of 1 to 8 carbon atoms, which may contain, as polymerized unit~, not more than 65, in particular from 15 to 60, % by weight of styrene or a mixture of styrene and not more than 40~ by weight, based on the styrene/acrylonitrile mixture, of acrylo-nitrile. For such acrylate/styrenecopolymer dispersions the LT value is in general less thatn 20~, frequently less than 10%.
In the preparation of the polymer powders, water-soluble alkali metal and/or alkaline earth metal salts of phenolsulfonic acid/formaldehyde condensates are added to the polymer dispersions prior to atomization, in an amount of from 3 to 50, preferably from 3 to 15, in par-ticular from S to 10, % by weight, based on the polymer content of the aqueous polymer dispersion~. The conden-sates contain in general 1 or 2 formaldehyde radicals, in particular 1 formaldehyde radical, per phenol radical and in particular 1 sulfo group per molecule. They are preferably used in the form of the Na salt~. The alka-line earth metal salts and in particular the Ca salt~ are particularly preferred since they give a nonhygroscopic powder. Such salts of phenol~ulfonic acid/formaldehyde conden3ates are commercially available.
In addition to the condensates, water-insoluble finely divided solids, for example finely divided ~ilica or water-soluble proteckive colloids, for example poly-vinyl alcohols or vinylpyrrolidone (co)polymers, may also have been added to the polymer dispersions in the prep-aration of the polymer powder~.
Atomization of the aqueous polymer disper~ion~

1~ .J f,J iJ 1. ,: c3 - 5 - O.Z. 0050/40946 which contain the salts of the phenolsulfonic acid/form-aldehyde condensates can be carried out in a conventional manner, in particular using one-material or multi-material nozzles or atomizer disks. The dispersions are generally atomized in a warm air stream, in which the water evaporates. Atomization can be carried out under atmospheric or reduced pressure. In general, the temp-erature of the warm air stream used for spray d~ying is from 100 to 200C, in particular from 120 to 170C. The dry redispersible polymer powders can be separated off in a conventional manner, in particular using cyclones or filter separators.
Polymer powders having high blocking resistance are obtained in a high yield even using comparatively small amounts of phenolsulfonic acid/formaldehyde conden-sates and can be readily stored at room temperature, without caking. The polymer powders are readily redi~-persible in water. After stirring in water, they can be cast into films which are ~imilar in their tensile strength and elongation at break to films obtained from the primary dispersions.
~ hen used for modifying hy~raulic binders, the polymer powders are mixed with, for example, cement, from 5 to 30% by weight, based on cement, of polymer powder preferably being used, and further proce~sing by mixing with water and if necessary mineral additives gives mortars having good flow and high flexibility.
Furthermore, the flexural strength and adhesive strength o~ such mortars are generally higher than in the ca~e o~ plastic-free comparative samples. In addition to the mechanical properties, processing is also advantage-ously effec~ed by the novel polymer powders: the polymer powders impart to the mortar a more fluid consistency, which changes only slightly during processing. Because they also harden rapidly, the polymer powders are there-fore particularly suitable for flow mortars, for example self-leveling flooring plasters or filling compounds.

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- 6 - O.Z. 0050/409~6 In the Examples which follow, parts and percent-ages are by weight. The mean particle size (weigh~
average) of the polymer dispersions was determined with the aid of an analytical ultracentrifuge. The glass 5 transition temperatures of the polymers were determined by the method of differential thermal analysis.
Preparation of the polymer powder The amount, stated in Table 2, of the calcium salt of a phenolsulfonic acid/~ormaldehyde condensate or of the calcium salt of a naphthalenesulfonic acid/formal-dehyde condensate was added to the aqueous dispersions of the polymers stated in Table 1 below. The mixture was atomized via a two-material nozzle of an IWK drier at 25C at a rate of 80 kg~hour. Precipitated hydrophobic silica was metered in an amount of 3~ by weight, based on the dispersion, by means of a screw and via a further nozzle. The IWK drier was simultaneously fed with 2300 m3 (S.T.P.)/hour of warm air at 120C, and the product obtained was separated off in a cyclone.
The compositions and characteri~tics of the poly-mer dispersions used are listed in Table 1.

Dis- Polymer Poly- Glass LT Mean per- composition mer transi- value particle sion con- tion weight tent ~ Temp. C ~ average nm A 46 parts of styrene 50 16 7 832 54 parts of butyl acrylate 0.8 part of acryl-amide 0.8 part of meth-acrylamide B 29 parts of styrene 55 -7 36 234 69 parts of butyl acrylate 2 parts of acryl-amide ~ ~ S~ C) _ 7 _ o.z. 0050/40946 ~he polymer powders obtained using the various amounts, stated in Table 2, of the phanolsulfonic acid/
formaldehyde condensate showed little or no tendency to block (testing of blocking resis~ance under a pressure of 5 0.785 N/cm2 at 23C for 24 hours) and could if necessary readily be milled and easily redispersed in water.
Properties of mortar modified with the polymer powders The solidification time was characterized using mortars having a plastic/cement ratio of 0.1, on the 1~ basis of the Vicat solidification time (DIN 1164, Part S) .
The flow was determined using a mortar of the following composition:
137.0 g of cement PZ 55 71.4 g of quartz powder W 4 141.6 g of quartz sand 0.15-0.6 13.7 g of polymer powder 75.35 g of water Some of the mortar was placed in a ring of 7 cm diameter and 4 cm height, and the ring was pulled upward.
The diameter of the spread-out mortar cake in cm indi-cates the flow of the mortar.
The value~ obtained in the mea~urements using the novel polymer powders are listed in Table 2. For com-parison, the flow of the mortar without the addition of polymer powder (Example N) or with only 1.37 g of the calcium salt of the phenolsulfonic acid/formaldehyde con-densate (Example NI) is also mentioned.

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- 9 - O.Z. 0050/40946 For comparison, Table 3 states the corresponding values obtained when the calcium salt of the naphthalene-sulfonic acid/formaldehyde condensate is used instead of the calcium salt of the phenolsulfonic acidJformaldehyde S condensate.
For Example NII, 1.37 g of this product were accordingly used instead of the polymer powder.

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Claims

1. A polymer powder which is redispersible in water and is obtainable by atomizing an aqueous polymer disper-sion to which from 3 to 50% by weight, based on the poly-mer, of a water-soluble alkali metal salt or alkaline earth metal salt of a phenolsulfonic acid/formaldehyde condensate has been added.

2. A polymer powder as claimed in claim 1, wherein the polymer particles of the aqueous polymer dispersion have a weight average particle size of from 400 to 5,000 nm.

3. A polymer powder as claimed in claim 1, to which from 3 to 15% by weight of the salt have been added.

4. A polymer powder as claimed in claim 1, wherein the salt is an alkaline earth metal salt.

5. A method of using a polymer powder, which is redispersible in water and is obtainable by atomizing an aqueous polymer dispersion to which from 3 to 50% by weight, based on the polymer, of a water-soluble alkali metal salt or alkaline earth metal salt of a phenolsul-fonic acid/formaldehyde condensate has been added, as an additive in hydraulic binders.