AU2008264082B2

AU2008264082B2 - Dry construction material mixtures based on calcium sulfate

Info

Publication number: AU2008264082B2
Application number: AU2008264082A
Authority: AU
Inventors: Stefan Friedrich; Peter Gaeberlein; Gregor Herth; Michael Schinabeck
Original assignee: Construction Research and Technology GmbH
Current assignee: Construction Research and Technology GmbH
Priority date: 2007-06-14
Filing date: 2008-04-28
Publication date: 2013-03-28
Anticipated expiration: 2028-04-28
Also published as: AU2008264082A1; EP2167444A1; CN101679119B; CN101679119A; JP2010529270A; EP2167444B1; JP5553748B2; DE102007027477A1; WO2008151879A1

Abstract

The invention relates to dry construction material mixtures based on calcium sulfate as a binder, comprising a redispersable polymer powder, water-retaining agents based on polysaccharide structures, setting retarders, and a super-absorbent copolymer.

Description

Construction Research [20070483] PF [59305] & Technology GmbH Dry construction material mixtures based on calcium sulfate The present invention relates to building material dry mixes based on calcium sulphate and 5 their use. "R. Bayer, H. Lutz, Dry Mortars, Ullmann's Encyclopedia of Industrial Chemistry, 6th ed., vol. 11, Wiley-VCH, Weinheim, (2003), 83-108" gives an overview of the uses and composition of dry mortars, e.g. binders, aggregates and various additives. In addition to 0 cement-containing dry mixes, dry mixes based on calcium sulphate as binder are customarily used. As described, for example, in relation to joint fillers for gypsum plasterboards in DE-A-4331141, additives such as redispersible polymer powders and/or cellulose ethers are used in these gypsum plaster systems for improving the process in properties, in particular the stiffness. However, these additives, in particular the redispersible polymer powders, are very 5 costly. The use of superabsorbents in building material mixes is likewise known. For example, US-A-2003144386 describes the use of superabsorbents in cement-containing systems for increasing the strength development and also mentions a possible use in gypsum based building material mixes. US-B-6187887 describes water-soluble or water-swellable copolymers containing sulpho groups which are used for increasing the water retention in 0 building material systems. These copolymers differ from the essentially insoluble superabsorbents in that they are soluble in water and have very little if any water uptake capacity. The technologies disclosed in the abovementioned documents are in need of improvement in respect of their economics. The desired economically advantageous, high-yield dry mixes 5 should display good product properties both in the fresh state and in the cured state. It was therefore an object of the present invention to provide economical and high-quality dry mixes for producing aqueous building material systems. 0 This object is achieved by a dry mix, preferably a joint filler for gypsum plasterboards, characterized in that it comprises a) from 10 to 98 percent by weight of a binder based on calcium sulphate, Construction Research [20070483] PF [59305] & Technology GmbH 2 b) from 0.5 to 7 percent by weight of a redispersible polymer powder, 5 c) from 0.1 to 1.5 percent by weight of a water retention agent which is based on polysaccharide structures and is preferably soluble in water and is preferably selected from the group consisting of cellulose ethers, starch ethers and microbially produced or naturally occurring polysaccharides, 0 d) from 0.01 to 2.0 percent by weight of a setting retarder and either ea) from 0.02 to 2.0 percent by weight of anionic, pulverulent copolymer which is preferably swellable by means of water or salt solutions and is particularly preferably insoluble in water and can preferably be prepared by free-radical 5 polymerization of ethylenically unsaturated vinyl compounds and whose particle size distribution determined in accordance with the standard edana 420.2-02 is such that more than 98 percent by weight pass a sieve having a mesh size of 200 jim, with the copolymer comprising 0 ea-i) from 10 to 70 molpercent of structural units containing a sulphonic acid group and having the general formula (1)

-CH

2 -CR1 C=0 N H

R

2 -C-R3 H-C-R4

SO

3 Ma where 5 the radicals R 1 are identical or different and are each hydrogen or a methyl radical, the radicals R 2 , R , R 4 Construction Research [20070483] PF [593051 & Technology GmbH 3 are each case identical or different and are each, independently of one another, hydrogen, an aliphatic, branched or unbranched hydrocarbon radical having from I to 6 carbon atoms or an aromatic hydrocarbon radical having from 6 to 14 carbon atoms, 5 the ions M are identical or different and are each hydrogen, a monovalent or divalent metal cation or an ammonium ion, the indices a are identical or different and are each either 1/2 or 1, 0 ea-ii) from 30 to 90 molpercent of structural units containing a (meth)acrylamido group and having the general formula (II)

-CH

2 -CR1 C=0 NR5R6 5 where R' is as defined above, the radicals R 5 and R 6 0 are in each case identical or different and are each, independently of one another, hydrogen, a branched or unbranched aliphatic hydrocarbon radical having from 1 to 20 carbon atoms, a cycloaliphatic hydrocarbon radical having from 5 to 8 carbon atoms or an aryl radical having from 6 to 14 carbon atoms, 5 ea-iii) from 0.3 to 1 molpercent of structural units derived from water-soluble monomer compounds which have more than one free-radically polymerizable, ethylenically unsaturated vinyl group, 0 or, as an alternative to ea), Construction Research [20070483] PF [593051 & Technology GmbH 4 eb) from 0.02 to 2.0 percent by weight of a cationic pulverulent copolymer which is preferably swellable by means of water or salt solutions and is particularly preferably insoluble in water and can preferably be prepared by free-radical polymerization of ethylenically unsaturated 5 vinyl compounds and whose particle size distribution determined in accordance with the standard edana 420.2-02 is preferably such that more than 98 percent by weight pass a sieve having a mesh size of 200 gm, with the copolymer comprising 0 eb-i) from 10 to 70 molpercent of cationic units containing a quaternized nitrogen atom and having the general formula (III)

-CH

2 -CR1 C=0 X

Y

I a

(CH

2 )m R7-N!R8 R9 where 5 Ri is as defined above, the radicals R 7 , R 8 , R 9 , R1 0 are in each case identical or different and are each, independently of one another, hydrogen, a branched or unbranched aliphatic hydrocarbon radical having from 1 to 20 carbon atoms, a 0 cycloaliphatic hydrocarbon radical having from 5 to 8 carbon atoms or an aryl radical having from 6 to 14 carbon atoms, the indices m are identical or different and are each an integer from I to 6, the radicals X 5 are identical or different and are each oxygen or N-R10, the ions Y-a are identical or different and are each a halide, Ci-C 4 -alkylsulphate,

C-C

4 -alkylsulphonate or sulphate, Construction Research [200704831 PF [593051 & Technology GmbH 5 the indices a are identical or different and are each either 1/2 or 1, e%-ii) from 30 to 90 molpercent of structural units containing a 5 (meth)acrylamido group and having the general formula (II)

-CH

2 -CR1 C=0 N R5R6 where 0 R' is as defined above, R' and R 6 are each as defined above, eb-iii) from 0.03 to 1 molpercent of structural units derived from preferably 5 water-soluble monomer compounds which have more than one free radically polymerizable, ethylenically unsaturated vinyl groups. The requirements which modem gypsum-based building material dry mixes have to meet, especially in the field of joint fillers for gypsum plasterboards but also knifing fillers and 0 gypsum plasters, are very high in respect of their properties both in the as yet uncured state (rheological process and properties such as thixotropic behaviour and water retention) and in the cured state (abrasion resistance, scratch resistance, joint strength and deflection underload). DE-A-4331141 describes the improvement in processing properties such as stiffness of joint fillers achieved by means of additives such as cellulose ethers and 5 redispersible polymer powders. However, the additives mentioned, particularly the dispersion powders, are very expensive compared to the other components of dry mixes. A further improvement in the joint strength and deflection underload of joint fillers is likewise desirable. It is also necessary to reduce the setting rates by means of setting retarders since binders such 0 as, in particular, a-calcium sulphate hemihydrate and p-calcium sulphate hemihydrate generally set within minutes and the processing time is too short.

Construction Research [200704831 PF [59305] & Technology GmbH 6 This leads to the technical problem of improving the yield and economics of the dry mortars by means of suitable measures without a reduction in quality of the building material products having to be accepted. Properties such as joint strength and deflection underload of joint fillers should likewise be improved. 5 This object is achieved by the use of the dry mixes of the invention which contain a superabsorbent, pulverulent copolymer (superabsorbent) which is suitable for increasing the tolerance to high water/binder ratios. The polymer chemistry of the superabsorbent has, according to the invention, been adapted so that a high water uptake capacity is ensured even 0 in aqueous systems containing calcium ions. It has surprisingly been found that it is not only possible to maintain or improve the abovementioned desired product properties but also to achieve a considerable reduction in the amounts of expensive constituents of the formulation, e.g. the redispersible dispersion powders. To clarify the terminology, it should also be added that dry mixes are frequently also referred 5 to as dry mortars in the literature. Detailed description of the invention a) The binder based on calcium sulphate can be present in various degrees of hydration. o Preferred binders for the purposes of the invention are a-calcium sulphate hemihydrate, p calcium sulphate hemihydrate and anhydrite which is free of water of crystallization, or mixtures of the binders mentioned. Particularly preference is given to a-calcium sulphate hemihydrate and B-calcium sulphate hemihydrate. It is also possible to use anhydrite dust (finely milled anhydrite) which is relatively unreactive and sets only partially. 5 To prepare the hemihydrate forms, gypsum (CaSO4 - 2 H 2 0) is calcined with elimination of water. Depending on the calcination method, the c-hemihydrate or the p-hemihydrate is obtained. Rapid heating in open plants forms the p--hemihydrate as a result of the water being given off very quickly and leaving voids behind. The a-hemihydrate is formed during dehydration in closed autoclaves; the crystal form is relatively dense and the water 0 requirement for the binder a-hemihydrate is significantly lower. Calcium sulphate can also be obtained as by-product of particular industrial processes such as flue gas desulphuration. The abovementioned binders based on calcium sulphate are hydrated on addition of water, Construction Research [20070483] PF [59305] & Technology GmbH 7 resulting in formation of calcium sulphate dehydrate (gypsum). Calcium sulphate dehydrate forms acicular crystals which grow into one another and adhere to one another. Gypsum plaster products having excellent hardness and compressive strength can be obtained in this way. The proportion by weight of the hydraulic binder based on calcium 5 sulphate in the dry mix is, depending on the application, from 10 to 98 percent by weight, preferably from 20 to 90 percent by weight, and preferably from 50 to 80 percent by weight. b) The term redispersible polymer powders refers to (co)polymers which can be obtained as 0 a water-based dispersion by appropriate polymerization processes such as emulsion polymerization processes and are converted into a polymer powder in a further step by suitable drying measures such as spray drying. When mixed into water or aqueous systems, the redispersible polymer powder once again forms a water-based dispersion, hence the term redispersible polymer powder. The use of redispersible dispersion powders 5 in aqueous building material mixtures allows important product properties, in particular properties which are important in the cured state, for example abrasion resistance, scratch resistance, tensile strength in bending and surface adhesion to various substrates, to be improved. Redispersible polymer powders are known to act essentially as organic binders in the building material mixture which has been made up with water, with this effect being 0 based mainly on formation of a polymer film from the primary particles as a result of evaporation of water. Suitable (co)polymers include those based on one or more ethylenically unsaturated monomers which can be selected from among one or more of the following monomer 5 groups: vinylaromatics, vinyl esters of branched or unbranched alkylcarboxylic acids having from 1 to 15 carbon atoms, dienes, (meth)acrylic esters of branched or unbranched alcohols having from 1 to 10 carbon atoms, vinyl halides and olefins. The monomers should preferably have a hydrophobic character. Examples of preferred monomers which come within the group of vinylaromatics are 0 styrene, vinyltoluene and c-methylstyrene. As preferred vinyl esters of branched or unbranched alkylcarboxylic acids having from 1 to 15 carbon atoms, mention may be made of vinyl acetate, vinyl propionate, vinyl butyrate, vinyl 2-ethylhexanoate, I methylvinyl acetate, vinyl laurate and vinyl esters of monocarboxylic acids which have a Construction Research [200704831 PF [593051 & Technology GmbH 8 tertiary carbon atom in the x position relative to the acid group and have from 5 to 11 carbon atoms (vinyl versatates), for example VeoVa5* (vinyl pivalate), VeoVa9*, VeoVal0* and VeoVall* (trade names of Shell), with vinyl acetate and the abovementioned vinyl versatates being particularly preferred. Preferred dienes are 1,3 5 butadiene and isoprene, and preferred (meth)acrylic esters of branched or unbranched alcohols having from I to 10 carbon atoms are methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, and 2-ethyl acrylate. Preferred olefins are ethylene, propylene, 1-butene and 2-methylpropene, particularly preferably ethylene. Preferred vinyl halide monomers are vinyl chloride and vinylidene 0 chloride. As (co)polymers suitable as redispersible polymer powders, preference is given to the following types, with the figures for the respective monomers being % by weight based on the (co)polymer and, if appropriate together with further monomer units, adding up to 100% by weight: 5 From the group of polymers of vinyl alkylcarboxylates, preference is given to vinyl acetate polymers which may be partially hydrolysed; vinyl acetate-ethylene copolymers having an ethylene content of from I to 60% by weight; vinyl acetate copolymers with from I to 50% by weight of one or more, further vinyl ester monomers such as vinyl laurate, vinyl pivalate and in particular VeoVa9*, VeoVa10* and VeoVall* (trade 0 names of Shell), with these copolymers being able to contain from 1 to 40% by weight of ethylene as further monomer; vinyl ester-ethylene-vinyl chloride copolymers having an ethylene content of from I to 40% by weight and a vinyl chloride content of from 20 to 90% by weight (possible vinyl esters are, for example, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl 2-ethylhexanoate, I-methylvinyl acetate, vinyl laurate and vinyl 5 esters of monocarboxylic acids which have a tertiary carbon atom in the alpha position relative to the acid group and have from 5 to 11 carbon atoms (vinyl versatates), for example VeoVa5* (vinyl pivalate), VeoVa9*, VeoVal0* and VeoVal 11 (trade names of Shell)); vinyl acetate-acrylic ester copolymers which contain from I to 60% by weight of acrylic ester, preferably n-butyl acrylate, and may additionally contain from 1 to 40% by 0 weight of ethylene. Among the group of (meth)acrylic ester polymers, preference is given to copolymers composed of the monomer units n-butyl acrylate and/or 2-ethylhexyl acrylate; copolymers of methyl methacrylate with n-butyl acrylate and/or 2-ethylhexyl acrylate and copolymers Construction Research 1200704831 PF [59305] & Technology GmbH 9 of methyl methacrylate with 1,3- butadiene. Among the group of vinyl halide copolymers, preference is given to the abovementioned vinyl ester-ethylene-vinyl chloride copolymers and also vinyl chloride-ethylene copolymers and vinyl chloride-acrylate copolymers. 5 Among the group of vinylaromatic copolymers, preference is given to styrene-butadiene copolymers and styrene-acrylic ester copolymers such as styrene-n-butyl acrylate or styrene-2-ethylhexyl acrylate having a styrene content of in each case from 10 to 70% by weight. In a further embodiment, particular preference is given to vinyl acetate polymers, vinyl 0 acetate-ethylene copolymers having an ethylene content of from 1 to 60% by weight, vinyl acetate copolymers with from 1 to 50% by weight of one or more, further vinyl ester monomers such as vinyl laurate, vinyl pivalate and in particular vinyl versatates such as VeoVa9*, VeoVal0* and VeoVall* (trade names of Shell), with these copolymers additionally being able to contain from 1 to 40% by weight of ethylene as further 5 monomer. Particular preference is also given to vinyl acetate-acrylic ester copolymers which contain from I to 60% by weight of acrylic ester, preferably n-butyl acrylate, and may additionally contain from 1 to 40% by weight of ethylene. Particular preference is also given to styrene-butadiene copolymers and styrene-acrylic ester copolymers such as styrene-n-butyl acrylate or styrene-2-ethylhexyl acrylate having a styrene content of in 0 each case from 10 to 70% by weight. The redispersible polymer powder b) is very particularly preferably present as vinyl acetate polymer, vinyl acetate-ethylene copolymer, vinyl acetate-vinyl ester copolymer and/or vinyl acetate-vinyl ester-ethylene copolymer, with the vinyl ester monomers being 5 selected in each case from the group consisting of vinyl laurate, vinyl pivalate and vinyl versatates, also as vinyl acetate-acrylic ester copolymer, vinyl acetate-acrylic ester ethylene copolymer, styrene-butadiene copolymer and styrene-acrylic ester copolymer, with the acrylic esters in each case being esters of branched or unbranched alcohols having from I to 10 carbon atoms. D If appropriate, the (co)polymers can additionally contain functional comonomer units in an amount of from 0.1 to 10% by weight, based on the total weight of the polymer. These functional copolymer units can be selected from the group consisting of monocarboxylic Construction Research [200704831 PF [59305] & Technology GmbH 10 or dicarboxylic acids, for example (meth)acrylic acid and/or maleic acid; the group consisting of ethylenically unsaturated carboxamides such as (meth)acrylamide; from the group consisting of ethylenically unsaturated sulphonic acids and salts thereof, preferably vinylsulphonic acid and/or styrenesulphonic acid; from the group consisting of multiply 5 ethylenically unsaturated comonomers, for example divinyl adipate, triallyl isocyanurate, diallyl maleate and/or allyl methacrylate. The proportion of structural units containing a (meth)acrylamido group in the redispersible polymer powders of the general formula (II) is preferably less than 25 mol%. The (co)polymerization is carried out by processes well known in the industry, e.g. the emulsion polymerization process. The dispersions obtained 0 can be stabilized either by means of an emulsifier or by means of a protective colloid such as polyvinyl alcohol. To obtain the redispersible polymer powders, drying is carried out, usually by conventional processes such as spray drying, freeze drying, coagulation of the dispersion and subsequent fluidized-bed drying. The preferred process is spray drying. The redispersible polymer powders are present in the dry mix based on calcium sulphate 5 in an amount of from 0.5 to 7% by weight, preferably from 0.8 to 5% by weight, particularly preferably from 1.0 to 3% by weight. c) The preferably water-soluble water retention agents based on polysaccharide structures serve not only to retain water but also to set rheological properties of the corresponding 0 building material mixes, for example the viscosity and/or the thixotropy. In systems based on calcium sulphate as binder, not only the water retention but also, in particular, the stiffness in joint filler applications is improved. A good stiffness is particularly important in order to prevent sagging of the joint filler in the joint. Preference is given to cellulose ethers, for example alkylcelluloses such as 5 methylcellulose, ethylcellulose, propylcellulose and methylethylcellulose, hydroxy alkylcelluloses such as hydroxyethylcellulose (HEC), hydroxypropylcellulose (HPC) and hydroxyethylhydroxypropylcellulose, alkylhydroxyalkylcelluloses such as methylhydroxyethylcelluose (MHEC), methylhydroxypropylcelluose (MHPC) and propylhydroxypropylcellulose. Preference is given to the cellulose ether derivatives 0 methylcellulose (MC), hydroxypropylcellulose (HPC), hydroxyethylcellulose (HEC) and ethylhydroxyethylcellulose (EHEC), and particular preference is given to methylhydroxyethylcelluose (MHEC) and methylhydroxypropylcelluose (MHPC). The abovementioned cellulose ether derivatives, which can in each case be obtained by Construction Research [200704831 PF [59305] & Technology GmbH 11 appropriate alkylation or alkoxylation of cellulose, are preferably present as nonionic structures. On the other hand, carboxymethylcellulose (CMC), for example, is less suitable since the carboxylic acid groups interact with calcium ions and thus reduce the solubility of the carboxymethylcellulose and consequently its effectiveness. This effect is 5 reinforced by calcium-containing setting accelerators. In addition, preference is also given to using nonionic starch ether derivatives such as hydroxypropylstarch, hydroxyethylstarch and methylhydroxypropylstarch. Preference is given to hydroxypropylstarch. The starch ether derivatives are present in the dry mix either alone or, preferably, in combination with one or more of the abovementioned cellulose ether 0 derivatives; they are particularly preferably present together with methylhydroxyethylcellulose (MHEC) and/or methylhydroxypropylcelluose (MHPC). Preference is likewise given to microbially produced polysaccharides such as welan gum and/or xanthans and naturally occurring polysaccharides such as alginates, carregeenans and galactomannans. These can be obtained from appropriate natural products by 5 extractive processes, for example in the case of alginates and carregeenans from algae, in the case of galactomannans from carob seeds. The choice of the water retention agents and the amount(s) used is made according to requirement and is established by appropriate routine tests. It is possible for one or more of the abovementioned water retention agents to be present in the dry mix of the invention. o The water retention agents based on polysaccharide structures are present in the hydraulically setting dry mix in an amount, based on the dry mix, of from 0.1 to 1.5% by weight, preferably from 0.2 to 1.2% by weight, particularly preferably from 0.3 to 1.0% by weight. 5 d) In contrast to, for example, cement-containing, hydraulically setting systems, the hydration of x- and p-calcium sulphate any hemihydrate, in particular, occurs very quickly. For this reason, the use of setting retarders is necessary when binders based on calcium sulphate are used. Suitable setting retarders for binders based on calcium sulphate are, as described in 0 "R. Bayer, H. Lutz, Dry Mortars, Ullmann's Encyclopedia of Industrial Chemistry, 6th ed., vol. 11, Wiley-VCH, Weinheim, (2003), 83-108" and "Franz Wirsching, Calcium sulfate, Ullmann's Encyclopedia of Industrial Chemistry, vol. 6, Wiley-VCH, Weinheim, (2003), 89-121", preferably fruit acids or their salts, for example citric acid, citrates, Construction Research [20070483] PF [59305] & Technology GmbH 12 tartaric acid, tartates, malic acid and/or malates. Gluconic acid or gluconates and calcium phosphate are likewise suitable as setting retarders. Also suitable are synthetic amino acid derivatives, for example the product Retardan@ P from Tricosal, Illertissen Germany. This is the calcium salt of a polyoxymethylene amino acid. As preferred setting retarders, 5 mention may also be made of degradation and hydrolysis products of proteins, e.g. amino acids. Particular preference is given to tartaric acid or tartrates and citric acid or citrates. The setting retarders are present in the dry mix in an amount of from 0.01 to 2.0% by weight, preferably from 0.1 to 1.5% by weight and particularly preferably from 0.2 to 1.0% by weight. 0 The abovementioned setting retarders can have an adverse effect on the strengths of the gypsum plaster products if they are used in very large amounts relative to the binder, since the development of the gypsum crystal structure is influenced. This can be the case, for example, when citric acid is used in amounts of greater than 0.2% by weight based on the binder. 5 ea) and eb) The pulverulent copolymers which are swellable by means of water or aqueous salt solutions are crosslinked, high molecular weight, either anionic or cationic poly electrolytes which can be obtained by free-radical polymerization of suitable, 0 ethylenically unsaturated vinyl compounds and subsequent drying of the copolymers obtained. In industry, they are usually referred to as superabsorbent polymers (SAP) or simple superabsorbents. On contact with water or aqueous systems, they take up water and swell to form a hydrogel. It is possible for them to take up a weight of water which is a multiple of the weight of the pulverulent copolymer. For the present purposes, hydrogels 5 are water-containing gels based on hydrophilic but crosslinked water-insoluble polymers which are present as three-dimensional networks. The hydrogel formed from the pulverulent, superabsorbent copolymer by uptake of water should contain very little material which is soluble in water so as not to have an adverse effect on the rheological properties of the building material mixes. In the present invention, it is advantageous to 0 use superabsorbents which have a high water absorption capacity even at high salt concentrations, in particular at high calcium ion concentrations. The pulverulent copolymers (superabsorbents) used according to the invention are Construction Research [200704831 PF [59305] & Technology GmbH 13 preferably present as either anionic or cationic polyelectrolytes and essentially not as polyampholytes. For the purposes of the present invention, polyampholytes are polyelectrolytes which bear both cationic and anionic charges on the polymer chain. The greatest preference is thus given to copolymers which are purely anionic or cationic in 5 nature. However, it is possible for up to 10%, preferably less than 5%, of the total charge of a polyelectrolyte to be replaced by opposite charges. This applies both to the case of predominantly anionic copolymers having a relatively low cationic content and conversely to the case of predominantly cationic copolymers having a relatively low anionic content. 0 The anionic superabsorbent copolymers ea) will firstly be described in detail below. Structural units containing a sulphonic acid group and having the general formula I are present as anionic structural units. Monomers containing sulphonic acid groups are preferred over monomers containing carboxylic acid groups since they form more stable hydrogels which can take up more water in aqueous salt solutions, particularly in the 5 presence of calcium ions. In particular, the superabsorbents containing sulphonic acid groups are superior in terms of this property to the superabsorbents containing mainly carboxylic acid groups, e.g. those based on crosslinked high molecular weight polyacrylic acid. The structural unit containing a sulphonic acid group and corresponding to the general formula I is preferably derived from the copolymerization of one or more of the 0 monomer species 2-acrylamido-2-methylpropanesulphonic acid, 2-methacrylamido-2 methylpropanesulphonic acid, 2-acrylamidobutanesulphonic acid, and/or 2-acrylamido 2,4,4-trimethylpentanesulphonic acid or the salts of the acids mentioned. Particular preference is given to 2-acrylamido-2-methylpropanesulphonic acid and its salt compounds. The cations in the salt compounds of the acids can in each case be 5 monovalent or divalent metal cations, e.g. preferably sodium, potassium, calcium or magnesium ions, or ammonium ions derived from ammonia, primary, secondary or tertiary, C 1

-C

2 0-alkylamines, C 1

-C

20 -alkanolamines, Cs-C 8 -cycloalkylamines and C 6 -C arylamines. The alkyl radicals can in each case be branched or unbranched. Examples of appropriate amines are methylamine, dimethylamine, trimethylamine, ethanolamine, 0 diethanolamine, triethanolamine, cyclohexylamine, dicyclohexylamine, phenylamine and diphenylamine. Preferred cations are alkali metal ions and/or ammonium ions, particularly preferably the sodium ion. In the anionic superabsorbent copolymers, the structural units containing a sulphonic acid Construction Research 1200704831 PF [59305] & Technology GmbH 14 group are present in an amount of from 10 to 70 molpercent, preferably from 15 to 60 molpercent and very particularly preferably from 20 to 50 molpercent. Furthermore, structural units containing a (meth)acrylamido group and corresponding to 5 the general formula II are also present in the anionic superabsorbent copolymers ea). The structural units containing a (meth)acrylamido group are present in a manner analogous to the cationic superabsorbent copolymers. The following description applies to both the anionic superabsorbent copolymers and the cationic superabsorbent copolymers. For example, these structural units are derived from the copolymerization of one or more of 0 the monomer species acrylamide, methacrylamide, N-methylacrylamide, N-methylmethacrylamide, N,N-dimethylacrylamide, N-ethylacrylamide, N,N--diethyl acrylamide, N-cyclohexylacrylamide, N-benzylacrylamide, N,N-dimethyl aminopropylacrylamide, N,N-dimethylaminoethylacrylamide and/or N-tert butylacrylamide. Preference is given to methylacrylamide, N,N-dimethylacrylamide and 5 methacrylamide, and particular preference is given to acrylamide. In both the anionic and cationic superabsorbent copolymers, the structural units containing a (meth)acrylamido group are present in an amount of from 30 to 90 molpercent, preferably from 40 to 85 molpercent and very particularly preferably from 50 to 80 molpercent. o The structural units of the anionic superabsorbent copolymer which are derived from preferably water-soluble monomer compounds having more than one free-radically polymerizable, ethylenically unsaturated vinyl group will be referred to as crosslinker monomers in the further description. They are also present in an analogous way in the cationic superabsorbent copolymers. The following description of the crosslinker 5 monomers applies both to the anionic superabsorbent copolymers and the cationic superabsorbent copolymers. The structural unit corresponding to the crosslinker monomers is preferably derived from the polymerization of one or more of the following monomer species: multiply (meth)acrylic-functional monomers such as 1,4-butanediol diacrylate, 0 1,4-butanediol dimethacrylate, 1,3-butylene glycol diacrylate, 1,3-butylene glycol dimethacrylate, diethylene glycol diacrylate, diethylene glycol dimethacrylate, ethylene glycol dimethacrylate, ethoxylated bisphenol A diacrylate, ethoxylated bisphenol A dimethacrylate, ethylene glycol dimethacrylate, 1,6-hexanediol diacrylate, 1,6-hexanediol Construction Research [20070483] PF [59305] & Technology GmbH 15 dimethacrylate, neopentyl glycol dimethacrylate, polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, triethylene glycol diacrylate, triethylene glycol di methacrylate, tripropylene glycol diacrylate, tetraethylene glycol diacrylate, tetraethylene glycol diacrylate, tetraethylene glycol dimethacrylate, dipentaerythritol pentaacrylate, 5 pentaerythritol tetraacrylate, pentaerythritol triacrylate, trimethylolpropane triacrylate, trimethylol trimethacrylate, cyclopentadiene diacrylate, tris(2-hydroxyethyl) isocyanurate triacrylate and/or tris(2-hydroxy) isocyanurate trimethacrylate; monomers having more than one vinyl ester or allyl ester group with a corresponding carboxylic acid, for example divinyl esters of polycarboxylic acids, diallyl esters of polycarboxylic acids, triallyl 0 terephthalate, diallyl maleate, diallyl fumarate, trivinyl trimellitate, divinyl adipate and/or diallyl succinate; monomers having more than one (meth)acrylamido group e.g. N,N' methylenebisacrylamide and/or N,N'-methylenebismethacrylamide, and monomers having more than one maleimide group, e.g. hexamethylenebismaleimide; monomers having more than one vinyl ether group, e.g. ethylene glycol divinyl ether, triethylene glycol 5 divinyl ether and/or cyclohexanediol divinyl ether. It is also possible to use allylamino or allylammonium compounds having more than one allyl group, e.g. triallylamine and/or tetraallylammonium salts. Among the group of monomers having more than one vinylaromatic group, mention may be made of divinylbenzene. In selecting the appropriate monomers having more than one ethylenically unsaturated 0 vinyl group, care should preferably be taken to ensure that these have a good hydrolysis resistance in aqueous systems. For this reason, methacrylic-functional crosslinker monomers are preferred over the corresponding acrylic-functional crosslinker monomers; the (meth)acrylamido-ffunctional monomers and the allylamino-functional monomers are particularly preferred. Examples of particularly preferred crosslinker monomers are N,N' 5 methylenebisacrylamide, N,N'-methylenebismethacrylamide, triallyl isocyanurate, triallylamine and/or tetraallylammonium salts, and very particularly preferred crosslinker monomers are N,N'-methylenebisacrylamide, N,N'-methylenebismethacrylamide, triallyl isocyanurate and/or triallylamine. It is in each case possible for one or more of the crosslinker monomers to be represented in the copolymers. The crosslinker monomers are o present in an amount of from 0.03 to 1 molpercent, preferably from 0.05 to 0.7 molpercent, in the anionic and cationic superabsorbent copolymers. The amount of crosslinker monomers should be at least so high that very water-insoluble copolymers or copolymers having a low content of soluble material or a low content of extractable Construction Research [20070483] PF [59305] & Technology GmbH 16 material are obtained. A person skilled in the art will be able to determine the amount of crosslinker monomers in a simple manner by carrying out routine tests. Crosslinking occurs during the course of the copolymerization reaction; in addition, after-crosslinking can also be carried out subsequent to the copolymerization reaction, as described for 5 superabsorbents in "F. Buchholz, A. Graham, Modern Superabsorber Technology, John Wiley & Sons Inc., 1989, 55-67". Apart from the abovementioned three types of structural units which are necessary in the anionic copolymers according to the main claim, from 1 to 20 molpercent of further, 0 preferably hydrophilic structural units can optionally be present. These are preferably derived from uncharged or anionic, ethylenically unsaturated monomers. In the case of cationic monomers, the abovementioned restrictions in respect of the proportions in the anionic copolymer apply, i.e. up to 10 percent, preferably less than 5 percent, of the anionic charges can be replaced by cationic charges. Examples of possible uncharged 5 monomers are acrylonitrile, methacrylonitrile, vinylpyridine, vinylpyridine, vinyl acetate and/or hydroxyl-containing (meth)acrylic esters such as hydroxyethyl acrylate, hydroxypropyl acrylate and/or hydroxypropyl methacrylate. The optional structural units are preferably derived from monomers selected from the group consisting of ethylenically unsaturated carboxylic acids and dicarboxylic acids and 0 their anhydrides, e.g. methacrylic acid, ethacrylic acid, ca-chloroacrylic acid, a cyanoacrylic acid, p-methylacrylic acid (crotonic acid), ac-phenylacrylic acid, p acryloxypropionic acid, sorbic acid, a-chlorosorbic acid, 2'-methylisocrotonic acid, cinnamic acid, maleic acid and maleic anhydride, p-chlorocinnamic acid, p-stearic acid, itaconic acid, citraconic acid, mesacronic acid, glutaconic acid, aconitic acid, fumaric acid 5 and/or tricarboxylethylene. The further structural units are preferably derived from acrylic acid and its salts and/or ethylenically unsaturated sulphonic acid monomers and in each case their corresponding salts, e.g. vinylsulphonic acid, allylsulphonic acid, styrenesulphonic acid, sulphoethyl acrylate, sulphoethyl methacrylate, sulphopropyl acrylate, sulphopropyl methacrylate and/or 2-hydroxy-3-methacryloxypropylsulphonic 0 acid. The cationic superabsorbent copolymers eb) will be described below. In the cationic copolymers, the structural unit containing a quaternized nitrogen atom and corresponding to the general formula III is preferably derived from the polymerization of one or more Construction Research [200704831 PF 1593051 & Technology GmbH 17 monomer species selected from the group consisting of [2 (acryloyloxy)ethyl] trimethylammonium salts, [2-(methacryloyloxy)ethyl]trimethyl ammonium salts, [3-(acryloylamino)propyl]trimethylammonium salts and [3-(methacryloylamino)propyl]trimethylammonium salts. The salts mentioned are 5 preferably present as halides or methosulphates. Particular preference is given to [3-(acryloylamino)propyl]trimethylammonium salts and/or [3-(methacryloylamino) propyl]trimethylammonium salts. Very particular preference is given to [3-(acryloylamino)propyl]trimethylammonium chloride (DIMAPA-Quat) and/or [3-(methacryloylamino)propyl]trimethylammonium chloride (MAPTAC). 0 The structural unit containing a quaternary nitrogen atom and having the general formula III is present in an amount of from 10 to 70 molpercent, preferably from 15 to 60 molpercent and particularly preferably from 20 to 50 molpercent, in the cationic superabsorbent copolymers. 5 Like the anionic superabsorbent copolymers ea), the cationic superabsorbent copolymers eb) contain the same structural units containing (meth)acrylamido groups and having the general formula II. The structural units of the general formula II have been described in detail above for the anionic copolymers and this description is hereby incorporated by 0 reference at the present point. The structural units derived from preferably water-soluble monomer compounds which have more than one free-radically polymerizable, ethylenically unsaturated vinyl group (crosslinker monomers) are likewise present both in the cationic superabsorbent copolymer and in the anionic superabsorbent copolymer. This structural unit has likewise 5 been described in detail above for the anionic superabsorbent copolymers. This description is hereby likewise incorporated by reference at this point. Apart from the abovementioned three types of structural units which are necessary in the cationic copolymers according to the main claim, from 1 to 20 molpercent of further, preferably hydrophilic structural units can optionally be present. These are preferably 0 derived from uncharged or cationic, ethylenically unsaturated monomers. In the case of anionic monomers, the abovementioned restrictions in respect of the proportions in the cationic copolymer apply, i.e. up to 10 percent, preferably less than 5 percent, of the cationic charges can be replaced by anionic charges. Examples of possible uncharged Construction Research [20070483] PF [59305] & Technology GmbH 18 monomers are acrylonitrile, methacrylonitrile, vinylpyridine, vinyl acetate and/or hydroxyl-containing (meth)acrylic esters such as hydroxyethyl acrylate, hydroxypropyl acrylate and/or hydroxypropyl methacrylate. Examples of suitable cationic monomers are N,N-dimethyldiallylammonium chloride and N,N-diethyldiallylammonium chloride. 5 In a particularly preferred embodiment of the anionic superabsorbent copolymer ea), the copolymer ea) contains structural units of which from 20 to 50 molpercent are derived from 2-acrylamido-2-methylpropanesulphonic acid (corresponding to structural unit I), and from 50 to 80 molpercent are derived from acrylamide (corresponding to structural 0 unit II) and the crosslinker monomer is triallylamine and/or N,N'-methylenebisacrylamide. In a likewise particularly preferred embodiment of the cationic superabsorbent copolymer eb), the copolymer e 1 ) contains structural units of which from 20 to 50 molpercent are derived from [3-(acryloylamino)propyl]trimethylammonium chloride (corresponding to structural unit III) and from 50 to 80 molpercent are derived from acrylamide 5 (corresponding to structural unit ID and the crosslinker monomer is triallylamine and/or N,N'-methylenebisacrylamide. The anionic or cationic superabsorbent copolymers used according to the invention can be prepared in a manner known per se by linking of the monomers forming the respective 0 structural units by means of free-radical polymerization (anionic copolymers: structural units of the general formulae I, II and the above-described crosslinker monomers; optionally further anionic or uncharged monomers; cationic copolymers: structural units of the general formulae III, II and the above-described crosslinker monomers, optionally further cationic or uncharged monomers). 5 All monomers present as acid can be polymerized as free acids or in their salt form. Furthermore, neutralization of the acids can also be effected after the copolymerization by addition of appropriate bases, and partial neutralization before or after the polymerization is likewise possible. The neutralization of the monomers or the copolymers can, for example, be effected by means of the bases sodium hydroxide, potassium hydroxide, 0 calcium hydroxide, magnesium hydroxide and/or ammonia. Further suitable bases are primary, secondary or tertiary Ci-C 2 0-alkylamines having branched or unbranched alkyl groups, C-C 20 -alkanolamines, C 5 -Cs-cycloalkylamines, and/or C 6

-C

14 -arylamines. It is possible to use one or more bases. Preference is given to neutralization by means of alkali Construction Research [200704831 PF [593051 & Technology GmbH 19 metal hydroxides and/or ammonia, particularly preferably sodium hydroxide. The inorganic or organic bases should be selected so that they form salts which are relatively readily soluble in water with the respective acid. 5 The monomers are preferably copolymerized by free-radical bulk, solution, gel, emulsion, dispersion or suspension polymerization. Since the products according to the invention are hydrophilic copolymers which are swellable in water, polymerization in an aqueous phase, polymerization in an inverted emulsion or polymerization in inverse suspension. In particularly preferred embodiments, the reaction is carried out as a gel polymerization or 0 as an inverse suspension polymerization in organic solvents. The copolymerization of the superabsorbent polymer can, in a particularly preferred embodiment, be carried out as an adiabatic polymerization and be initiated either by means of a redox initiator system or by means of a photoinitiator. In addition, a 5 combination of the two initiation variants is possible. The redox initiator system consists of at least two components, viz. an organic or inorganic oxidizing agent and an organic or inorganic reducing agent. Use is frequently made of compounds having peroxide units, e.g. inorganic peroxides such as alkali metal and ammonium persulphate, alkali metal and ammonium perphosphates, hydrogen peroxide and its salts (sodium peroxide, barium 0 peroxide) or organic peroxides such as benzoyl peroxide, butyl hydroperoxide or peracids such as peracetic acid. However, it is also possible to use other oxidizing agents, for example potassium permanganate, sodium and potassium chlorate, potassium dichromate, etc. As reducing agent, it is possible to use sulphur-containing compounds such as sulphites, thiosulphates, sulphinic acid, organic thiols (for example ethyl mercaptan, 5 2-hydroxyethanethiol, 2-mercaptoethylammonium chloride, thioglycolic acid) and others. Furthermore, ascorbic acid and low-valency metal salts are possible [copper(I); manganese(II); iron(II)]. It is also possible to use phosphorus compounds, for example sodium hypophosphite. 0 In the case of photopolymerization, this is initiated by means of UV light which brings about the disintegration of a photoinitiator. As photoinitiator, it is possible to use, for example, benzoin and benzoin derivatives such as benzoin ethers, benzil and its derivatives, e.g. benzil ketals, acryldiazonium salt, azo initiators such as 2,2'-azobis- Construction Research [20070483] PF [59305] & Technology GmbH 20 (isobutyronitrile), 2,2'-azobis(2-amidinopropane) hydrochloride, and/or acetophenone derivatives. The proportion by weight of the oxidizing component and the reducing component in the 5 case of the redox initiator systems is in each case preferably in the range from 0.00005 to 0.5% by weight, particularly preferably in each case from 0.001 to 0.1% by weight. In the case of photoinitiators, this range is preferably from 0.001 to 0.1% by weight, particularly preferably from 0.002 to 0.05% by weight. The percentages by weight given for oxidizing and reducing component and photoinitiators are in each case based on the mass of the 0 monomers used for the copolymerization. The choice of polymerization conditions, in particular the amounts of initiator, is made with the objective of producing very long chain polymers. However, owing to the insolubility of the crosslinked copolymers, the molecular weights can be measured only with great difficulty. 5 The copolymerization is preferably carried out in aqueous solution, preferably in concentrated aqueous solution, either batchwise in a polymerization vessel (batch process) or continuously by the "continuous conveyor belt" method described in US-A-4857610. A further possibility is polymerization in a continuously or discontinuously operated kneading reactor. The process is usually initiated at a temperature in the range from -20 to 0 20*C, preferably from -10 to 10'C, and carried out at atmospheric pressure without external heating, with a maximum final temperature, which is dependent on the monomer content, of from 50 to 150*C being obtained as a result of the heat of polymerization. After the copolymerization is complete, comminution of the polymer, which is present as a gel, is generally carried out. If the copolymerization is carried out on a laboratory scale, 5 the comminuted gel is dried in a convection drying oven at from 70 to 180*C, preferably from 80 to 150*C. On an industrial scale, drying can also be carried out continuously in the same temperature ranges, for example on a belt dryer or in a fluidized-bed dryer. In a further preferred embodiment, the copolymerization is carried out as an inverse 0 suspension polymerization of the aqueous monomer phase in an organic solvent. Here, the monomer mixture which has been dissolved in water and neutralized if appropriate is polymerized in the presence of an organic solvent in which the aqueous monomer phase is insoluble or sparingly soluble. The copolymerization is preferably carried out in the Construction Research [20070483] PF [593051 & Technology GmbH 21 presence of "water-in-oil" emulsifiers (W/O emulsifiers) and/or protective colloids based on low molecular weight or high molecular weight compounds which are used in proportions of from 0.05 to 5% by weight, preferably from 0.1 to 3% by weight, based on the monomers. The W/O emulsifiers and protective colloids are also referred to as 5 stabilizers. It is possible to use customary compounds known as stabilizers in inverse suspension polymerization technology, e.g. hydroxypropylcellulose, ethylcellulose, methylcellulose, mixed cellulose acetate butyrate ethers, copolymers of ethylene and vinyl acetate, of styrene and butyl acrylate, polyoxyethylenesorbitan monooleate, monolaurate or monostearate and block copolymers of propylene oxide and/or ethylene oxide. 0 Organic solvents used are, for example, linear aliphatic hydrocarbons such as n-pentane, n-hexane, n-heptane, branched aliphatic hydrocarbons (isoparaffins), cycloaliphatic hydrocarbons such as cyclohexane and decalin, and aromatic hydrocarbons such as benzine, toluene and xylene. Further suitable solvents are alcohols, ketones, carboxylic 5 esters, nitro compounds, halogen-containing hydrocarbons, ethers and many other organic solvents. Preference is given to organic solvents which form azeotropic mixtures with water, particularly preferably those which have a very high proportion of water in the azeotrope. o The water-swellable copolymers are initially obtained in swollen form as finely divided aqueous droplets in the organic suspension medium and are preferably isolated as solid spherical particles in the organic suspension medium by removal of the water. Removal of the suspension medium and drying leaves a pulverulent solid. It is known that inverse suspension polymerization has the advantage that the particle size distribution of the 5 powders can be controlled by variation of the polymerization conditions and it is therefore usually possible to avoid an additional process step (milling step) for adjusting the particle size distribution. Preference is given to anionic and cationic superabsorbent copolymers whose particle size 0 distribution determined in accordance with the standard edana 420.2-02 is such that more than 98 percent by weight pass a sieve having a mesh size of 200 pm and particularly preferably more than 98 percent by weight pass a sieve having a mesh size of 100 gm. Very particular preference is given to more than 98 percent by weight passing a sieve Construction Research 1200704831 PF [593051 & Technology GmbH 22 having a mesh size of 63 pm. The particle size distribution can be set by milling of the products obtained after drying of the copolymers. Large particles would result in visually recognizable inhomogeneous regions in which only the hydrogel formed by swelling of the superabsorbent is present in 5 the aqueous building material mixes. The risk of demixing of the hydrogels would also be increased and further important properties such as the strength development could be adversely affected. Advantageous superabsorbent copolymers quickly develop their full water uptake capacity in the aqueous systems. A slow water uptake would likewise lead to undesirable 0 after-thickening due to slow withdrawal of water from the building material mix. To test whether after-thickening is present, water is added to the building material mix, e.g. a joint filler, and the mixture is stirred. The slump should preferably change by less than 0.5 cm between the third and tenth minute after the addition of water. 5 A preferred property of both the anionic and cationic superabsorbent copolymers is their insolubility in aqueous solutions or the property of having only a low proportion of extractable material. The proportion of extractable material is the proportion which can diffuse from the superabsorbent polymer into a surrounding aqueous medium. The method of determining the proportion of extractable material is described in more detail in the o section on test methods. The proportion of extractable material is, in each case based on the mass of the superabsorbent, preferably less than 10% by weight, particularly preferably less than 9% by weight and very particularly preferably less than 8% by weight. 5 Last but not least, the uptake capacity of the anionic and cationic superabsorbents in aqueous salt solutions and in particular in solutions containing calcium ions is preferably very high for economic reasons. The uptake capacity is defined as the ratio of the mass of liquid taken up and the mass of the dry superabsorbent (reported in g/g) and is determined in accordance with the standard edana 440.2-02 with modification of the method, i.e. 0 replacement of the 0.9 percent strength sodium chloride solution specified there as test liquid by a one percent strength calcium formate solution. The method is described in more detail in the section on test methods. In the case of products which are produced by the gel polymerization process, the uptake capacity is preferably more than 10 g/g, Construction Research [20070483] PF [59305] & Technology GmbH 23 particularly preferably more than 15 g/g and very particularly preferably greater than 20 g/g. In the case of products which have been produced by the inverse suspension polymerization process, the uptake capacity determined by the same method is preferably greater than 5 g/g, particularly preferably greater than 10 g/g and in particular greater than 5 15 g/g. The superabsorbent polymers preferably have such an uptake capacity and are present in the dry mix in such an amount that they can take up from 10 to 40% by weight, preferably from 15 to 35% by weight, particularly preferably from 20 to 30% by weight, of the amount of water added to the dry mix. Both the anionic superabsorbent copolymers and the cationic superabsorbent copolymers are present in the dry mix in an amount of 0 from 0.02 to 2.0% by weight, preferably from 0.1 to 1.5% by weight, particularly preferably from 0.2 to 1.0% by weight. The anionic superabsorbent copolymers are preferred over the cationic superabsorbent copolymers. The superabsorbent copolymers hold water or salt solutions containing calcium ions as are 5 present in the building material mixes as hydrogel in microregions. The dry mixes containing superabsorbent copolymers according to the invention or the building material mixes formed by addition of water are particularly economically advantageous since the amounts of redispersible polymer powder used can be reduced considerably. 0 Further customary additives such as air pore formers, antifoams, acrylate-based thickeners, functional sheet silicates, plasticizers customary for cement-containing systems, for example polycarboxylate ethers (PCE), melamine-formaldehydesulphonates (MFS), p-naphthalene formaldehydesulphonates (BNS) and fibres such as cellulose fibres or synthetic fibres (e.g. aramid fibres) can also be present in the dry mixes of the invention. In a particular 5 embodiment of the invention, fillers are present in the dry mixes. These are only slightly soluble or swellable in the aqueous systems. In particular, they do not act as a binder. Preferred fillers are, for example, ground limestone, chalk, marble, mica and/or talc, with chalk being particularly preferred and ground limestone being very particularly preferred. The 0 fillers can also be present as lightweight fillers such as hollow glass microspheres such as foamed glass and as aluminosilicates such as pearlites and expanded clay. Natural lightweight fillers such as mineral foam, palmice, foamed lather and/or expanded vermiculite can likewise be used. Preference is given to fillers having a particle size Construction Research [200704831 PF [593051 & Technology GmbH 24 distribution such that in a sieving test in accordance with DIN EN 933-1 more than 95% by weight pass a sieve having a mesh opening of 0.25 mm, with particular preference being given to more than 95% by weight passing a sieve having a mesh opening of 0.125 mm. The fillers are present in the dry mix in an amount of from 2 to 85% by weight, preferably 5 from 10 to 70% by weight and particularly preferably from 15 to 50% by weight. In a preferred embodiment of the invention, the dry mix contains f) from 0.0005 to 0.05 percent by weight of a copolymer which contains (meth)acrylamido 0 groups and does not have contain any structural units derived from monomer compounds which contain more than one free-radically polymerizable, ethylenically unsaturated vinyl group and comprise f-i) from 60 to 100 molpercent of structural units of the general formula (II) 5

-CH

2 -CR1 0=O NR5R6 where R I is as defined above, 0 R' and R 6 are in each case identical or different and are each, independently of one another, hydrogen, a branched or unbranched aliphatic hydrocarbon radical having from I to 20 carbon atoms, a cycloaliphatic hydrocarbon radical having from 5 to 8 carbon atoms or an aryl radical having from 6 5 to 14 carbon atoms. The copolymers f) containing (meth) acrylamido groups will be described in more detail below. The copolymers f) which contain (meth)acrylamido groups and comprise structural units of the general formula (II) are used as additive for improving the processability, in 0 particular the stiffness. For example, the structural units are formed by copolymerization of one or more of the monomer species acrylamide, methacrylamide, N-methylacrylamide, Construction Research [20070483] PF [59305] & Technology GmbH 25 N-methylmethacrylamide, N,N-dimethylacrylamide, N-ethylacrylamide, N,N-diethyl acrylamide, N-cyclohexylacrylamide, N-benzylacrylamide, N,N-dimethylamino propylacrylamide, N,N-dimethylaminoethylacrylamide and/or N-tert-butylacrylamide. Preference is given to methylacrylamide, N,N-dimethylacrylamide and methacrylamide, 5 particularly preferably acrylamide. The copolymers f) containing (meth)acrylamido end groups can preferably contain from 3 to 40 molpercent of further structural units which are derived in a known way from anionic or cationic structural units. Preferred anionic structural units are (meth)acrylic acid and in each case its salts. The structural units derived from (meth)acrylic acid can also be obtained by 0 partial saponification of the amido groups. Preferred cationic structural units are derived, for example, from the cationic structural units of the general formula (III). The structural unit which contains a quaternary nitrogen atom and corresponds to the general formula (III) is preferably formed by polymerization of one or more monomer species selected from the group consisting of [2-(acryloyloxy)ethyl]trimethylammonium salts, [2-(methacryloyl 5 oxy)ethyl]trimethylammonium salts, [3-(acryloylamino)propyl]trimethylammonium salts and [3-(methacryloylamino)propyl]trimethylanmmonium salts. The salts mentioned are preferably present as halides or methosulphates. Particular preference is given to [3-(acryloylamino)propyl]trimethylammonium salts and/or [3-(methacryloyl amino)propyl]trimethylammonium salts. Very particular preference is given to o [3-(acryloylamino)propyl]trimethylammonium chloride (DIMAPA-Quat) and/or [3-(methacryloylamino)propyl]trimethylammonium chloride (MAPTAC). Further examples of preferred cationic monomers are N,N-dimethyldiallylammonium chloride and N,N-diethyldiallylammonium chloride. The copolymers f) containing (meth)acrylamido groups preferably have a molecular weight 5 (weight average) of from 1.106 to 1.107. They are preferably present in powder form in the dry mix, preferably in an amount of from 0.0005 to 0.1% by weight, particularly preferably from 0.001 to 0.05% by weight and very particularly preferably from 0.003 to 0.03% by weight. 0 In a specific embodiment of the invention, the dry mixes contain g) from 0.1 to 1.5 percent by weight of a water-soluble copolymer which contains sulpho groups and comprises Construction Research [200704831 PF [59305] & Technology GmbH 26 g-i) from 3 to 96 molpercent of structural units of the general formula (I)

-CH

2 -CR1 CO NH

R

2 --C-R3 CH-R4

SO

3 Ma (I) where 5 R1 is as defined above, R 2, R , R4 are each as defined above, M and a are as defined above, g-ii) from 3 to 59 molpercent of structural units of the general formula (II)

-CH

2

-CRI

CO (II)

NR

5

R

6 0 where R1 is as defined above,

R

5 and R 6 are each as defined above, 5 and at least one further structural unit selected from among g-iii) from 0.001 to 10 molpercent of structural units of the general formula (IV)

-CH

2 -CR1 (IV) G where Construction Research [200704831 PF [59305] & Technology GmbH 27 RI is as defined above, the radicals G are identical or different and are each -COO(CnH 2 nO)p-R" or

-(CH

2 )q-O(CnH 2 nO)p-R", 5 the radicals (R12)r R" are identical or different and are each (2 or an unsaturated or saturated, linear or branched aliphatic alkyl radical having from 10 to 40 carbon atoms, 0 the radicals R 12 are identical or different and are each hydrogen, a Ci-C-alkyl group, an arylalkyl group having a CI-C 12 -alkyl radical and a

C

6

-C

1 4 -aryl radical, the indices 5 n are identical or different and are each an integer from 2 to 4, the indices p are identical or different and are each an integer from 0 to 200, the indices q are identical or different and are each an integer from 0 to 20, 0 the indices r are identical or different and are each an integer from 0 to 3, and 5 g-iv) from 0.1 to 30 molpercent of structural units of the general formula (V)

-CH

2 -CR1 z (V) where R' is as defined above, Z is -(CH2)q-O(CH 2 nO)p-R, 0 n, p and q are as defined above, Construction Research [20070483] PF [59305] & Technology GmbH 28 the radicals

R

13 are identical or different and are each hydrogen or a C 1

-C

4 -alkyl radical. 5 The water-soluble copolymers containing sulpho groups g) will be described in more detail below. The water-soluble copolymers containing sulpho groups g) represent further water retention agents and differ from the above-described polysaccharide-based water retention agents and the preferably water-insoluble anionic, superabsorbent copolymers ea) which have likewise been described above. The water-soluble copolymers containing sulpho groups are 10 preferably used in powder form in the dry mix. They contain structural units of the general formulae I and II, with at least one further structural unit selected from among the structural units IV and V being present. Specifically, this means that the copolymers may comprise structural units of the general formulae I, II, IV or structural units of the general formulae I, II, V or structural units of the general formulae I, II, IV, V. The proportion of structural units 5 of the general formula I in the water-soluble copolymer containing sulpho groups is in the range from 3 to 96 molpercent, that of the structural units of the general formula II is in the range from 3 to 59 molpercent, that of the structural units of the general formula IV is in the range from 0.001 to 10 molpercent and that of the structural units of the general formula V is in the range from 0.1 to 30 molpercent. Preferred copolymers contain from 30 to 80 0 molpercent of structural units of the general formula I and from 5 to 50 molpercent of structural units of the general formula II, also from 0.1 to 5 molpercent of structural units of the general formula IV or from 0.2 to 15 molpercent of structural units of the general formula V, or else both structural units IV and V in the corresponding, abovementioned amounts. 5 The structural unit of the general formula I is preferably derived from monomers such as 2-acrylamido-2-methylpropanesulphonic acid, 2-methacrylamido-2-methylpropanesulphonic acid, 2-acrylamidobutanesulphonic acid, 2-acrylamido-2,4,4-trimethylpentanesulphonic acid and their respective salt compounds. Particular preference is given to 2-acrylamido-2 methylpropanesulphonic acid and its salt compounds. 0 The structural unit of the general formula II is preferably derived from monomers such as acrylamide, methacrylamide, N-methylacrylamide, N,N-dimethylacrylamide, N-ethyl acrylamide, N-cyclohexylacrylamide, N-benzylacrylamide, N-methylolacrylamide, N-tert butylacrylamide.

Construction Research [200704831 PF 1593051 & Technology GmbH 29 The structural unit of the general formula IV is preferably derived from monomers such as tristyrylphenolpolyethylene glycol 1100 methacrylate, behenylpolyethylene glycol 1100 methacrylate, stearylpolyethylene glycol 1100 methacrylate, tristyrylphenolpolyethylene glycol 1100 acrylate, tristyrylphenolpolyethene glycol 1100 monovinyl ether, 5 behenylpolyethene glycol 1100 monovinyl ether, stearylpolyethene glycol 1100 monovinyl ether, tristyrylphenolpolyethylene glycol 1100 vinyloxybutyl ether, behenylpolyethylene glycol 1100 vinyloxybutyl ether, tristyrylphenolpolyethylene glycol-block-propylene glycol allyl ether, behenylpolyethylene glycol-block-propylene glycol allyl ether, stearylpolyethylene glycol-block-propylene glycol allyl ether. 0 The structural unit of the general formula V is preferably derived from monomers such as allylpolyethylene glycol (350 to 2000), methylpolyethylene glycol (350 to 2000) monovinyl ether, polyethylene glycol (500 to 5000) vinyloxybutyl ether, polyethylene glycol-block propylene glycol (500 to 5000) vinyloxybutyl ether and methylpolyethylene glycol-block propylene glycol allyl ether. 5 The copolymers g) used according to the invention are prepared in a manner known per se by linking of the monomers derived from the corresponding structural units I, II, IV and V by means of free-radical, bulk, solution, gel, emulsion, dispersion or suspension polymerization. It has been found to be advantageous to set the number of structural units so that the water 0 soluble copolymers containing sulpho groups have a number average molecular weight of from 50 000 to 20 000 000. The water-soluble copolymers containing sulpho groups g) are preferably present in the dry mix in an amount of from 0.1 to 1.5% by weight, particularly preferably from 0.3 to 1.2% by weight and very particularly preferably from 0.5 to 1.0% by weight. 5 In a further specific embodiment of the invention, the dry mix contains h) from 0.1 to 1.5 percent by weight of a water-soluble cationic copolymer comprising 0 h-i) from 5 to 60 molpercent of structural units of the general formula (VI), Construction Research [200704831 PF [593051 & Technology GmbH 30

-CH

2

-CR'

Co T V R 14-N*-R 1 (W R' 6 (VI) where

R

1 is as defined above,

R'

4 and R" 5 are in each case identical or different and are each, independently of one 5 another, hydrogen, an aliphatic hydrocarbon radical having from 1 to 20 carbon atoms, a cycloaliphatic hydrocarbon radical having from 5 to 8 carbon atoms and/or an aryl radical having from 6 to 14 carbon atoms, the radicals 16 14 15 R are identical or different and are each a substituent identical to R or R 0 -(CH 2 )x-SO 3 La, SO 3 La or S0 3 La, the ions L are identical or different and are each a monovalent or divalent metal cation, ammonium cation or quaternary ammonium cation (NRR 14 Ri 5

R

1 6 ) , the indices 5 a are identical or different and are each 2 or 1, the radicals T are identical or different and are each oxygen, -NH and/or -NR 4 , the radicals 0 V are identical or different and are each -(CH 2 )m-, -a or the indices m are identical or different and are each an integer from 1 to 6, the ions W~ are identical or different and are each a halogen atom, C 1

-C

4 -alkylsulphate or Construction Research [200704831 PF [593051 & Technology GmbH 31 C I-C 4 -alkylsulphonate, h-ii) from 20 to 59 molpercent of a structural unit having the general formulae (VIIa) and/or (VI~b):

-CH

2 -CR- -CH 2

-CR

1 CO N-CO-R"

NR

14

R

1 5 0 (VIla) (VIlb) 5 where the radicals Q are identical or different and are each hydrogen or -CHR 14 R', R', R 14 , R" are each as defined above, with the proviso that when Q is not hydrogen 0 then R1 4 and R" in the general formula (VIIb) can together form a -CH 2 (CH 2 )y- methylene group so that the general formula (VIIb) represents the following structure: -CH2-CR RIZ CH C=O

H

2 C - (CH 2 )y 5 where the radicals R 17 are identical or different and are each a hydrogen atom, a Ci-C 4 -alkyl radical, a carboxylic acid group or a carboxylate group -COOLa, where the indices y are 0 identical or different and are each an integer from I to 4, and L and a are each as defined above, Construction Research [200704831 PF [59305] & Technology GmbH 32 h-iii) from 0.01 to 3 molpercent of structural units of the general formula (VIII)

-CH

2

-CR

(Vill) U 5 where the radicals U are identical or different and are each -COO(CH 2 nO),-R1' or

-(CH

2 )q-O(CnH 2 nO),-R the indices 0 n are identical or different and are each an integer from 2 to 4, the indices s are identical or different and are each an integer from 1 to 200, the indices q are identical or different and are each an integer from 0 to 20, 5 the radicals R are identical or different and are each (R )z the radicals R19 are identical or different and are each hydrogen, a Ci-C-alkyl group or an arylalkyl group having a Ci-C 1 2 -alkyl radical and a C 6

-C

14 -aryl radical, 0 the indices z are identical or different and are each an integer from 1 to 3 and R1 is as defined above. The cationic copolymers h) will be described in more detail below. The copolymers h) 5 represent further water retention agents and differ from the above-described polysaccharide based water retention agents c) and the preferably water-insoluble cationic, superabsorbent copolymers eb) which have likewise been described above. The water-soluble cationic copolymers h) are preferably used in powder form in the dry mix. In addition, the rheological modification, the water retention capacity, the stickiness and the processing properties can be 0 optimally set for the respective application via the composition of the copolymers.

Construction Research [200704831 PF [593051 & Technology GmbH 33 The good solubility in water which is necessary for use of the copolymers h) in aqueous building material applications is ensured, in particular, by the cationic structural unit of the general formula VI. The uncharged structural unit of the general formulae VIla and/or VIIb is required mainly for construction of the main chain and achievement of suitable chain lengths, 5 while the hydrophobic structural units of the general formula VIII make associative thickening, which is advantageous for the desired product properties, possible. In the cationic copolymers h), the structural unit of the general formula VI preferably results from polymerization of one or more monomer species selected from the group consisting of 0 [2-(acryloyloxy)ethyl]trimethylammonium salts, [2-(methacryloyloxy)ethyl] trimethylammonium salts, [3-(acryloylamino)propyl]trimethyl ammonium salts, [3-(methacryloylamino)propyl]trimethylammonium salts, N-(3-sulphopropyl)-N-methyacryl oxyethyl-N,N-dimethylammonium betaine, N-(3-sulphopropyl)-N-methyacrylamidopropyl N,N-dimethylammonium betaine and/or 1-(3-sulphopropyl)-2-vinylpyridinium betaine. The 5 salts mentioned are preferably present as halides or methosulphates. Particular preference is given to [3-(acryloylamino)propyl]trimethylammonium salts and/or [3-(methacryloylamino)propyl]trimethylammonium salts. Very particular preference is given to [3-(acryloylanino)propyl]trimethylammonium chloride (DIMAPA-Quat) and/or [3-(methacryloylamino)propyl]trimethylammonium chloride (MAPTAC). 0 It is in principle practicable to replace up to about 15 molpercent of the structural units of the general formula VI by further cationic structural units which are derived from N,N dimethyldiallylanmonium chloride and N,N-diethyldiallylammonium chloride. The structural unit of the general formula VIIa preferably results from polymerization of one 5 or more of the monomer species acrylamide, methacrylamide, N-methylacrylamide, N,N dimethylacrylamide, N-ethylacrylamide, N-cyclohexylacrylamide, N-benzylacrylamide, N-methylolacrylamide, N-tert- butylacrylamide, etc. Examples of monomers as basis of the structure VIIb are N-methyl-N-vinylformamide, N-methyl-N-vinylacetamide, N-vinylpyrrolidone, N-vinylcaprolactam and/or N-vinylpyrrolidone-5-carboxylic acid. 0 The structural unit of the general formula VIII preferably results from polymerization of one or more of the monomer species tristyrylphenolpolyethylene glycol 1100 methacrylate, tristyrylphenolpolyethylene glycol 1100 acrylate, tristyrylphenolpolyethene glycol 1100 monovinyl ether, tristyrylphenolpolyethylene glycol 1100 vinyloxybutyl ether and/or Construction Research [20070483] PF [593051 & Technology GmbH 34 tristyrylphenolpolyethylene glycol-block-propylene glycol allyl ether. In a preferred embodiment of the invention, the structural units of the general formula VI are present in the copolymer in a proportion of from 15 to 50 molpercent, those of the general 5 formula VIIa and/or VIIb are present in a proportion of from 30 to 55 molpercent and those of the general formula VIII are present in a proportion of from 0.03 to 1 molpercent. In addition to the abovementioned structural elements of the general formulae VI, VIla and/or VIIb and VIII, it is also possible for up to 40 molpercent of further structural elements which 0 are preferably derived from [2-(methacryloyloxy)ethyl]diethylamine, [3 (acryloylamino)propyl]dimethylamine and/or [3-(methacryloylamino)propyl]dimethylamine to be present in the copolymers. The copolymers h) according to the invention are preferably prepared in a manner known per se by linking of the monomers forming the structural units of the general formulae VI, VIIa and/or VIIb and VIII and if appropriate further monomers by 5 means of free-radical polymerization. Since the products used according to the invention are water-soluble copolymers, polymerization in the aqueous phase, polymerization in an inverted emulsion or polymerization in inverse suspension is preferred. The copolymers are advantageously prepared by gel polymerization in the aqueous phase. 0 It has been found to be advantageous to set the number of structural units so that the water soluble cationic copolymers h) have a number average molecular weight of from 50 000 to 20 000 000. The water-soluble cationic copolymers h) are preferably present in the dry mix in an amount of from 0.1 to 1.5% by weight, particularly preferably from 0.3 to 1.2% by weight and very 5 particularly preferably from 0.5 to 1.0% by weight. Mixing of the dry mixes of the invention with water gives the building material mixes of the invention. The building material mix of the invention is preferably used as joint filler for gypsum plasterboards in accordance with DIN 1168, knifing filler in accordance with DIN 1168 and 0 as plaster in accordance with DIN 18550. Knifing fillers serve, for example, for final working of a substrate to obtain flat surfaces (walls or ceilings).

Construction Research [200704831 PF [593051 & Technology GmbH 35 Examples I Test methods 5 Determination of the uptake capacity of the superabsorbent copolymers The determination of the uptake capacity of the superabsorbents according to the invention is carried out in accordance with the standard edana 440.2-02 developed for the hygiene industry with modification of the method, i.e. replacement of the 0.9 percent strength sodium 0 chloride solution specified there as test liquid by a one percent strength calcium formate solution. This method, also referred to as "tea bag test", is carried out by welding a defined amount (about 200 mg) of superabsorbent polymer into a tea bag and dipping it into a one percent strength calcium formate solution for 30 minutes. The tea bag is subsequently allowed to drip for five minutes and is weighed. A tea bag without superabsorbent polymer is 5 concomitantly tested as blank. To calculate the uptake capacity, the following formula is used: Uptake capacity = (final weight - blank - initial weight)/initial weight (g/g) 0 Determination of the proportion of extractable material in the superabsorbent copolymers The proportion of extractable material is determined by extraction of the superabsorbent copolymer in 0.9 percent strength sodium chloride solution with subsequent determination of total organic carbon (TOC determination). For this purpose, 1.0 g of the superabsorbent 5 polymer is left to stand for sixteen hours in one litre of 0.9 percent strength by weight sodium chloride solution and subsequently filtered off. After determination of the TOC content of the filtrate, the proportion of extractable material is calculated via the known carbon content of the superabsorbent polymer.

Construction Research [20070483] PF [593051 & Technology GmbH 36 II Synthesis of superabsorbent copolymers Copolymer 1 (anionic superabsorbent copolymer) 5 160 g of water were placed in a 2 1 three-neck flask provided with stirrer and thermometer and 352.50 g (0.74 mol, 28 mol%) of 2-acrylamido-2-methylpropanesulphonic acid sodium salt (50% strength by weight solution in water), 286.40 g (2.0 mol, 72 mol%) of acrylamide (50% strength by weight solution in water) and 0.3 g (0.0021 mol, 0.08 mol%) of methylenebisacrylamide were subsequently added in succession. After setting the pH to 7 by 0 means of 20% strength sodium hydroxide solution and flushing with nitrogen for thirty minutes, the mixture was cooled to about 5 0 C. The solution was transferred to a plastic container having dimensions (w - d - h) of 15 cm - 10 cm - 20 cm and 16 g of one percent strength 2,2'-azobis(2-amidinopropane) dihydrochloride solution, 20 g of one percent strength sodium peroxodisulphate solution, 0.7 g of one percent strength Rongalit C solution, 16.2 g of 5 0.1 percent strength tert-butyl hydroperoxide solution and 2.5 g of 0.1 percent strength Fe(II) sulphate heptahydrate solution were subsequently added in succession. The copolymerization was initiated by radiation with UV light (two Philips tubes; Cleo Performance 40 W). After about two hours, the now hard gel is taken from the plastic container and cut into cubes having an edge length of about 5 cm by means of scissors. Before the gel cubes were 0 comminuted by means of a conventional mincer, they were painted with the release agent Sitren 595 (polydimethylsiloxane emulsion; from Goldschmidt). The release agent is a polydimethylsiloxane emulsion which was diluted with water in a ratio of one to twenty. The resulting gel granules of copolymer 1 were uniformly distributed over a drying mesh and dried to constant weight at about 120-140*C in a convection drying oven. This gave about 5 375 g of white, hard granules which were converted into a pulverulent state by means of a centrifugal mill. The average particle diameter of the polymer powder was from 30 to 50 pim and the proportion of particles which do not pass a sieve having a mesh size of 63 ptm was less than 2% by weight. 0 The uptake capacity of the copolymer 1 in a one percent strength calcium formate solution is 32 g/g and the proportion of extractable material is 7.0 percent. The product has been found to be shear staple and, in particular, displays no after-thickening, e.g. in the tile adhesive. The copolymer 1 reaches its maximum water uptake capacity within four minutes, which Construction Research [200704831 PF [59305] & Technology GmbH 37 corresponds approximately to the customary times over which cement-containing building material mixes are mixed with water. Copolymer 2 (cationic superabsorbent copolymer) 5 276.5 g of water were placed in a 2 1 three-neck flask provided with stirrer and thermometer. 246.90 g (0.72 mol, 27 mol%) of DIMAPA-Quat (60% strength by weight solution in water) 262.60 g (1.84 mol, 73 mol%) of acrylamide (50% strength by weight solution in water) and 0.3 g (0.0021 mol, 0.08 mol%) of methylenebisacrylamide were subsequently added in 0 succession. After setting the pH to 7 by means of 20% strength sodium hydroxide solution and flushing with nitrogen for thirty minutes, the mixture was cooled to about 5*C. The solution was transferred to a plastic container having dimensions (w - d -h) of 15 cm - 10 cm 20 cm and 16 g of one percent strength 2,2'-azobis(2-amidinopropane) dihydrochloride solution, 20 g of one percent strength sodium peroxodisulphate solution, 0.7 g of one percent 5 strength Rongalit C solution, 16.2 g of 0.1 percent strength tert-butyl hydroperoxide solution and 2.5 g of 0.1 percent strength Fe(II) sulphate heptahydrate solution were subsequently added in succession. The polymerization was initiated by radiation with UV light (two Philips tubes; Cleo Performance 40 W). After about two hours, the hard gel was taken from the plastic container and processed further in the same way as described above for copolymer 1. 0 This gave about 375 g of white, hard granules which were converted into a pulverulent state by means of a centrifugal mill. The average particle diameter of the polymer powder was from 30 to 50 pm and the proportion of particles which do not pass a sieve having a mesh size of 63 pm was less than 2% by weight. The uptake capacity of the copolymer 2 in a one percent strength calcium formate solution is 29 g/g and the proportion of extractable material 5 is 9.0 percent. Comparative polymer 1 The comparative polymer 1, viz. Luquasorb* 3746 SX from BASF AG, is a crosslinked 0 partially neutralized sodium polyacrylate. In a one percent strength calcium formate solution, the gel collapses, i.e. virtually complete loss of the absorption capacity occurs. Comparative polymer 2 Construction Research 120070483] PF [593051 & Technology GmbH 38 The comparative polymer 2, viz. Luquasorb@ AF 2 from BASF AG, is a crosslinked copolymer of acrylamide and acrylic acid, with the acrylic acid having been neutralized by means of sodium hydroxide. The commercial product Luquasorb@ AF 2 (1000-3000 jim) was milled by means of a centrifugal mill so that the proportion of particles which do not pass a 5 sieve having a mesh size of 63 gm was less than 2% by weight. The product was prepared by the gel polymerization process. In a one percent calcium formate solution, the uptake capacity is 10 g/g. III Use tests 0 Joint filler for gypsum plasterboards The ready-to-use formulated dry mixes are, after appropriate homogenization (mixing), sprinkled into a defined amount of water with stirring. The system is subsequently allowed to age for one minute. The mixture is then stirred vigorously by means of a trowel until a 5 composition having a uniform consistency has been formed (about one minute). A first visual examination of this system is then carried out immediately. Determination of the slump The determination of the slump was carried out after the ageing time in accordance with 0 DIN 18555, part 2. Determination of the processing quality (processability) and stickiness The processing quality and the stickiness on the trowel were assessed qualitatively by the processor. For this purpose, gypsum plasterboards were screwed in an abutting fashion on a 5 wooden frame and the appropriate test system was applied over the joints by means of a spatula or trowel. Determination of the joint strengths To assess the joint strengths, the deflection of fracture strengths in N/cm of joint length were 0 determined. They were determined on 30-30 cm test specimens having a central towelled-over Construction Research [20070483] PF [593051 & Technology GmbH 39 joint (without joint strip), with the distance between the points of support being 20 cm, i.e. 10 cm on each side of the joint. The deflection (mm) to fracture serves as a measure of the elasticity. 5 The test results for the joint filler are shown in Table 1.

0.0: 00 C4 ' ) )CAV 60 C0 - - 00 W a)~CO 00 0.0 Nli~ C) U mo C C 0 C> o~~~~oC N 0o00 0 ~0 -0'C N tn > t0 0 Nl tn -n k0 'n C> 0 C> CN~ -) 00C 0 C 0' 0 O 6 \C C 0 q -i C) 0O 0 60 0 0 0 N C>~ W 0~ __ C tn en N ~00 0 C)zt 0 N(~CCD 060 00 . 0 00 N 0 o-)W D C: 0 6 0 0 W.C> N 0 00~ kn. > W) aN Q - 00 N o c >C ~ 0~ ~0 On > ~ * .~~~W o c O - N ) ~ ~ a- 06 N2 cU .2 2 ~ Q 0000 __ >_ co & Technology GmbH 41 0 From Wacker Chemie AG, Burghausen 2) From. Aqualon, Disseldorf 3) From Tricosal GmbH, Illertissen 4) Luquasorb" 3746 SX (from BASF AG, Ludwigshafen) 5 9 Luquasorb" AF 2 (from BASF AG, Ludwigshafen) 6) Praestol0 2640 (from Ashland, Deutschland, Krefeld) 7) Arbocel ZZC 500 (from J. Rettenmaier & Sbhne GmbH + Co., Rosenberg) ) Mowiol* 10-98 (from Kuraray Europe GmbH, DUsseldorf) 10 9) Omyacarb* AL 130 (from Omya, Oftringen) Examples 1, 2 and 4 which are according to the invention display significantly higher joint strengths and deflections compared to the comparative examples. A joint strength and deflection similar to that for the reference (see Comparative 15 Example 1) is also achieved when the amount of redispersible polymer powder is reduced (Examples 3 and 5). In contrast, both the processability/stickiness and the joint strength and deflection are much worse in Comparative Example 4. The reduction in the amount of the costly redispersible polymer powder without a reduction in the quality of the building material products represents a considerable economic benefit for the user. 20 Owing to the superabsorbent used according to the invention, the redispersible polymer powder displays better film formation, which has a positive effect on the flexibility of the building materials. The slump of the test mixtures in Table 1 was set to 16 ± 0.3 cm. The use of the 25 superabsorbents according to the invention leads to a reduction in the amount of free water available in the test mix, since part of the water is bound to the superabsorbent. Since this would result in unwanted stiffening of the test mixes without further corrective measures, the amount of an additive having a thickening action (component of type c) and/or f)) was accordingly reduced in order to achieve the desired slump. In 30 Comparative Examples 2 and 3, the superabsorbents which are not according to the invention in the joint filler absorbed barely any water, so that the amounts of the thickening components of type c) and/or f) could not be reduced or be reduced very little. The use of superabsorbents which are not according to the invention (Comparative Examples 2 and 3) also do not result in higher deflections or result in only slightly & Technology GmbH 42 higher joint strengths compared to Comparative Example I which serves as reference.

Claims

1. Dry mix, characterized in that it comprises 5 a) from 10 to 98 percent by weight of a binder based on calcium sulphate, b) from 0.5 to 7 percent by weight of a redispersible polymer powder, c) from 0.1 to 1.5 percent by weight of a water retention agent which is based 10 on polysaccharide structures, d) from 0.01 to 2.0 percent by weight of a setting retarder and either ea) from 0.02 to 2.0 percent by weight of anionic pulverulent copolymer, with 15 the copolymer comprising ea-i) from 10 to 70 molpercent of structural units containing a sulphonic acid group and having the general formula (I) -CH 2 -CR1 C=0 NH R 2 -C-R3 H-C-R4 SO 3 Ma 20 where the radicals R' are identical or different and are each hydrogen or a methyl 25 radical, the radicals R 2 , R 3 , R 4 & Technology GmbH 44 are each case identical or different and are each, independently of one another, hydrogen, an aliphatic, branched or unbranched hydrocarbon radical having from 1 to 6 carbon atoms or an aromatic hydrocarbon radical having from 6 to 14 carbon atoms, 5 the ions M are identical or different and are each hydrogen, a monovalent or divalent metal cation or an ammonium ion, the indices a are identical or different and are each either 1/2 or 1, 10 ea-ii) from 30 to 90 molpercent of structural units containing a (meth)acrylamido group and having the general formula (II) -CH 2 -CR1 C=o NR5R6 15 where R' is as defined above, the radicals R 5 and R 6 20 are in each case identical or different and are each, independently of one another, hydrogen, a branched or unbranched aliphatic hydrocarbon radical having from I to 20 carbon atoms, a cycloaliphatic hydrocarbon radical having from 5 to 8 carbon atoms or an aryl radical having from 6 to 14 carbon atoms, 25 ea-iii) from 0.03 to 1 molpercent of structural units derived from monomer compounds which have more than one free-radically polymerizable, ethylenically unsaturated vinyl group, 30 or, as an alternative to ea), & Technology GmbH 45 eb) from 0.02 to 2.0 percent by weight of a cationic pulverulant copolymer, with the copolymer comprising eb-i) from 10 to 70 molpercent of cationic units containing a 5 quaternized nitrogen atom and having the general formula (III) -CH 2 -CR1 C=0 X Y | a (CH 2)m R7-N!R8 R9 where R1 is as defined above, 10 the radicals R7, R , R9, R10 are in each case identical or different and are each, independently of one another, hydrogen, a branched or unbranched aliphatic hydrocarbon radical having from 1 to 20 carbon atoms, a cycloaliphatic hydrocarbon radical having 15 from 5 to 8 carbon atoms or an aryl radical having from 6 to 14 carbon atoms, the indices m are identical or different and are each an integer from 1 to 6, the radicals X 20 are identical or different and are each oxygen or N-R10, the ions Ya are identical or different and are each a halide, C 1 -C 4 -alkyl sulphate, C 1 -C 4 -alkylsulphonate or sulphate, the indices a 25 are identical or different and are each either 1/2 or 1, eb-ii) from 30 to 90 molpercent of structural units containing a (meth)acrylamido group and having the general formula (I) & Technology GmbH 46 -CH 2 -CR 1 C=0 NR5R 6 where 5 RI is as defined above, R 5 and R 6 are each as defined above, eb-iii) from 0.03 to 1 molpercent of structural units derived from 10 monomer compounds which have more than one free-radically polymerizable, ethylenically unsaturated vinyl group.

2. Dry mix according to Claim 1, characterized in that the binder is present as c-calcium sulphate hemihydrate and/or p-calcium sulphate hemihydrate. 15

3. Dry mix according to Claim 1, or 2, characterized in that from 2 to 85% by weight of fillers are present.

4. Dry mix according to any of Claims 1 to 3, characterized in that the setting 20 retarder is selected from the group consisting of citric acid, citrate, tartaric acid, tartrate, maleic acid, malate, gluconic acid, gluconate, calcium phosphate, synthetic amino acid derivatives and degradation and hydrolysis products of proteins. 25

5. Dry mix according to any of Claims I to 4, characterized in that the redispersible polymer powder is present as vinyl acetate polymer, vinyl acetate-ethylene copolymer, vinyl acetate-vinyl ester copolymer and/or vinyl acetate-vinyl ester ethylene copolymer, with the vinyl ester monomers in each case being selected from the group consisting of vinyl laurate, vinyl pivalate and vinyl versatates, 30 also as vinyl acetate-acrylic ester copolymer, vinyl acetate-acrylic ester-ethylene copolymer, styrene-butadiene copolymer and styrene-acrylic ester copolymer, & Technology GmbH 47 with the acrylic esters in each case being esters with branched or unbranched alcohols having from 1 to 10 carbon atoms.

6. Dry mix according to any of Claims I to 5, characterized in that the water 5 retention agent based on polysaccharide structures is present as methylhydroxyethylcellulose and/or methylhydroxypropylcellulose.

7. Dry mix according to any of Claims 1 to 6, characterized in that the structural units containing a sulphonic acid group and having the general formula (I) in the 10 anionic copolymer are derived from 2-acrylamido-2-methylpropanesulphonic acid and/or its salts.

8. Dry mix according to any of Claims 1 to 6, characterized in that the cationic structural units containing a quaternary nitrogen atom and having the general 15 formula (III) in the cationic copolymer are derived from [3-(methacryloyl amino)propyl]trimethylammonium salts and/or [3-(acryloyl amino)propyl]trimethylammonium salts.

9. Dry mix according to any of Claims 1 to 8, characterized in that the structural 20 units containing (meth)acrylamido groups and having the general formula (II) are derived from acrylamide, methacrylamide, methacrylamide, and/or N,N dimethylacrylarmide.

10. Dry mix according to any of Claims 1 to 9, characterized in that the structural 25 units derived from monomer compounds having more than one ethylenically unsaturated vinyl group are derived from triallyl isocyanurate, triallylamine, N,N'-methylenebisacrylamide and/or N,N'-methylenebismethacrylamide.

11. Dry mix according to any of Claims 1 to 7, 9 and 10, characterized in that the 30 anionic pulverulant copolymer contains from 20 to 50 molpercent of structural units derived from 2-acrylamido-2-methylpropanesulphonic acid and from 50 to 80 molpercent of structural units derived from acrylamide and the crosslinker monomer is triallylamine and/or N,N'-methylenebisacrylamide. & Technology GmbH 48

12. Dry mix according to any of Claims 1 to 6, 8 and 9, characterized in that the cationic pulverulant copolymer contains from 20 to 50 molpercent of structural units derived from [3-(acryloylamino)propyl]trimethylammonium chloride and from 50 to 80 molpercent of structural units derived from acrylamide and the 5 crosslinker monomer is triallylamine and/or N,N'-methylenebisacrylamide.

13. Dry mix according to any of Claims I to 12 containing f) from 0.0005 to 0.05 percent by weight of a copolymer which contains 10 (meth)acrylamido groups and does not have contain any structural units derived from monomer compounds which contain more than one free radically polymerizable, ethylenically unsaturated vinyl group and comprises 15 f-i) from 60 to 100 molpercent of structural units of the general formula (II) -CH 2 -CR1 C=0 NR5R6 where 20 RI is as defined above, R5 and R6 are in each case identical or different and are each, independently of one another, hydrogen, a branched or unbranched aliphatic hydrocarbon 25 radical having from I to 20 carbon atoms, a cycloaliphatic hydrocarbon radical having from 5 to 8 carbon atoms or an aryl radical having from 6 to 14 carbon atoms.

14. Dry mix according to any of Claims I to 13 containing 30 & Technology GmbH 49 g) from 0.1 to 1.5 percent by weight of a water-soluble copolymer which contains sulpho groups and comprises g-i) from 3 to 96 molpercent of structural units of the general formula (I) -CH 2 -CR1 CO NH R 2 -C-R3 CH--R 4 SO 3 Ma (I) 5 where R1 is as defined above, R 2 , R 3 , R 4 are each as defined above, M and a are as defined above, 10 g-ii) from 3 to 59 molpercent of structural units of the general formula (ID -- C H 2 -C R' C O (II) NR 5 R 6 where RI is as defined above, 15 R5 and R6 are each as defined above, and at least one further structural unit selected from among g-iii) from 0.001 to 10 molpercent of structural units of the general formula (IV) -CH 2 -CR1 (IV) G where & Technology GmbH 50 RI is as defined above, the radicals G are identical or different and are each -COO(CnH 2 nO),-R" or (CH 2 )q-O(CnH 2 nO)p-R 1 , 5 the radicals (R12)r R are identical or different and are each -(R2) or an unsaturated or saturated, linear or branched aliphatic alkyl radical having from 10 to 40 carbon atoms, 10 the radicals R are identical or different and are each hydrogen, a Ci-C 6 -alkyl group, an arylalkyl group having a Ci-C 12 -alkyl radical and a C 6 -C 14 -aryl radical, the indices 15 n are identical or different and are each an integer from 2 to 4, the indices p are identical or different and are each an integer from 0 to 200, the indices q are identical or different and are each an integer from 0 to 20, 20 the indices r are identical or different and are each an integer from 0 to 3, and 25 g-iv) from 0.1 to 30 molpercent of structural units of the general formula (V) -CH2-CRI z (V) where R' is as defined above, Z is -(CH 2 )q-O(CnH 2 nO)p-RD, 30 n, p and q are as defined above, & Technology GmbH 51 the radicals R 13 are identical or different and are each hydrogen or a CI-C 4 -alkyl radical.

15. Dry mix according to any of Claims I to 14 containing 5 h) from 0.1 to 1.5 percent by weight of a water-soluble cationic copolymer comprising h-i) from 5 to 60 molpercent of structural units of the general formula (VI), -CH 2 -CR Co T V -N*-R5 (W ) (VI) 10 where RI is as defined above, R 1 4 and R 15 are in each case identical or different and are each, independently of one another, hydrogen, an aliphatic hydrocarbon radical having from I to 15 20 carbon atoms, a cycloaliphatic hydrocarbon radical having from 5 to 8 carbon atoms and/or an aryl radical having from 6 to 14 carbon atoms, the radicals R 16 are identical or different and are each a substituent identical to R14 or R", -(CH 2 )x-SO 3 La, /0 _SO 3 La or _C SO 3 La, 20 the ions L are identical or different and are each a monovalent or divalent metal cation, ammonium cation or quaternary ammonium cation (NRiR14RIsR16)', the indices 25 a are identical or different and are each V 2 or 1, & Technology GmbH 52 the radicals T are identical or different and are each oxygen, -NH and/or -NR 4 , the radicals 5 V are identical or different and are each -(CH 2 )m-, -0 - or , the indices m are identical or different and are each an integer from 1 to 6, the ions W- are identical or different and are each a halogen atom, C 1 -C 4 10 alkylsulphate or Ci-C 4 -alkylsulphonate, h-ii) from 20 to 59 molpercent of a structural unit having the general formulae (VIIa) and/or (VIlb): -CH2-CR'- -CH 2 -CR I I| Co N-CO-R" NR 14 R 15 Q (Vila) (VIlb) 15 where the radicals Q are identical or different and are each hydrogen or -CHR 4 R", R1, R14, R" are each as defined above, with the proviso that when Q is not hydrogen then R1 4 and R 1 5 in the general formula (VIIb) can together 20 form a -CH 2 -(CH 2 )y- methylene group so that the general formula (VIIb) represents the following structure: & Technology GmbH 53 -CH 2 -CR' R-7 CH C=O I I H 2 C - (CH 2 )Y where the radicals 5 R are identical or different and are each a hydrogen atom, a CI-C 4 -alkyl radical, a carboxylic acid group or a carboxylate group -COOLa, where the indices y are identical or different and are each an integer from 1 to 4, and L and a are each as defined above, 10 h-iii) from 0.01 to 3 molpercent of structural units of the general formula (VIII) -CH 2 -CR' (Vill) U where 15 the radicals U are identical or different and are each -COO(CnH 2 nO),-R' 8 or -(CH 2 )q-O(CnH 2 nO),-R' the indices n are identical or different and are each an integer from 2 to 4, 20 the indices s are identical or different and are each an integer from 1 to 200, the indices q are identical or different and are each an integer from 0 to 20, the radicals 25 R are identical or different and are each - (R 19 )z the radicals 54 R19 are identical or different and are each hydrogen, a C 1 -C 6 -alkyl group or an arylalkyl group having a C 1 -C 12 -alkyl radical and a C 6 -C 14 -aryl radical, the indices z are identical or different and are each an integer from 1 to 3 and R1 is as defined above.

16. Building material mix containing a dry mix according to any of Claims 1 to 15 and water.

17. Use of the building material mix according to Claim 16 as joint filler for gypsum plasterboards in accordance with DIN 1168, as knifing filler in accordance with DIN 1168 and as plaster in accordance with DIN 18550.

18. Dry mix substantially as hereinbefore described with reference to the examples. WATERMARK PATENT & TRADE MARK ATTORNEYS