The term"water-based building material mixtures"generally means plastes, mortars, knifing fillers and/or tape joints to which the amount of water required for handling and processing the mixtures is added at the facilities of the producer or at the building site. The building material mixtures contain additives in addition to the main components like binders and fillers. The most common additives are thickeners, dispersing agents, plasticizers, stabilizers and wetting agents. Well-known thickeners are cellulose ethers. The cellulose ethers improve the water retention and workability of water-containing building material mixtures. Other thickeners are polyacrylamides, polyacrylamide- modifie cellulose ethers, guar derivatives or starch derivatives.

European Patent EP 0 530 768 B1 discloses an additive combination which comprises a cellulose ether, a polyacrylamide and an alkali metal salt or ammonium salt of a crosslinked polyacrylate which may be starch-grafted. Crosslinked polyacrylates are well known as "superabsorbers"for water and increase the water retention ability of the additive composition.

German Patent DE 39 20 025 discloses additive mixtures for gypsum based plastes which contain a) a major amount of a cellulose derivative and b) a small amount of b1) a thickener selected from polyacrylamides and/or starch ethers and of b2) a certain plasticizer containing sulfonic acid groups or sulfonate groups. Unfortunately, the plasticizer b2) containing sulfonic acid groups or sulfonate groups does not have a high thermal stability if it is subjected to elevated processing temperatures and tends to release substantial amounts of sulfur and sulfur dioxides.

European patent application EP-A 0 736 553 discloses that building material mixtures which contain cement, gypsum or lime require a high amount of water to provide a mixture which is ready for use. This amount of water is much higher than the amount, which is necessary for the subsequent hydratation and hardening process. Excess water evaporates and leaves voids in the building material. In order to reduce the excessive amount of water at a given viscosity of the water-containing building material mixture or to improve the workability of the building material mixture at a given water/binder ratio, it has been suggested in European patent application EP-A 0 736 553 to use as plastifying additives copolymers based on oxyalkylene glycol alkenyl ethers and unsaturated dicarboxylic acid derivatives.

The properties of the water-based building material mixtures, such as setting rates or viscosities, can be significantly influenced by the additives, which are included in such building material mixtures. In view of the wide application of water-based building material mixtures, these mixtures have to meet different requirements, which can vary from application to application.

In order to increase the variety of water-based building material mixtures, which are available to the industry, it is one object of the present invention to provide new additive compositions for-such building material mixtures.

A proper wetting and hydration of the inorganic binder in the building material mixtures, such as gypsum, is required to avoid the formation of lumps when the building material mixtures are mixed with water. However, it is known that in the case of gypsum this is often difficult to achieve.

Depending on the specific application, such as in the case of gypsum spray plastes, the formation of lumps creates a major problem and reduces the workability of the plaster composition.

It is a preferred object of the present invention to provide new additive compositions, which can favorably influence the wetting of inorganic binders, such as gypsum.

Accordingly, one aspect of the present invention is an additive composition for water-based building material mixtures, which comprises a) a cellulose ether, starch ether, guar gum and/or xanthan gum, b) a methacrylamide or acrylamide homo-or interpolymer, and c) a non-cross-linked homo-or interpolymer comprising an olefinically unsaturated, carboxylic group (s) containing compound in polymerized form.

Another aspect of the present invention is a process for preparing the above- mentioned additive composition, which includes the step of blending the components, a), b) and c).

Yet another aspect of the present invention is process for preparing the above-mentioned additive composition which includes the steps of coating the component a) with an aqueous solution of the homo-or interpolymer c) and blending the coated component a) with the (meth) acryl amide homo-or interpolymer b).

Yet another aspect of the present invention is a building material mixture which comprises an inorganic binder and a) a cellulose ether, starch ether, guar gum and/or xanthan gum, b) a methacrylamide or acrylamide homo-or interpolymer, and c) a non-cross-linked homo-or interpolymer comprising an olefinically unsaturated, carboxylic group (s) containing compound in polymerized form.

Yet another aspect of the present invention is the use of a) a cellulose ether, starch ether, guar gum and/or xanthan gum, b) a methacrylamide or acrylamide homo-or interpolymer, and

c) the above-mentioned non-cross-linked homo-or interpolymer, for water- based building material mixtures.

It has been found that the additive composition of the present invention provides water-containing building material mixtures, such as plastes, with good water- retention properties, with good sagging resistance when applied to walls, and with excellent workability at all stages of the application process, such as during first and second even-out, floating and finishing of plastes. At least in the most preferred embodiments of the present invention, the lump formation in water-containing building material mixtures will be significantly decreased and the workability will be improved, as compared to comparative building material mixtures which contain a known additive composition.

The additive composition for water-based building material mixtures comprises preferably from 30 to 98.5 percent, more preferably from 60 to 97 percent, most preferably from 75 to 95 percent of component a), preferably from 0.5 to 20 percent, more preferably from 1 to 15 percent, most preferably from 2 to 10 percent of the methacrylamide or acrylamide homo-or interpolymer b), and preferably from 1 to 50 percent, more preferably from 2 to 25 percent, most preferably from 3 to 15 percent, of the polymer c), based on the total weight of a), b) and c).

Cellulose ethers, starch ethers, guar gums and/or xanthan gums which are useful in water-based building materials are known in the art and for example described in European Patent EP 0 504 870 B, page 3, lines 25-56 and page 4, lines 1-30. Preferred starch ethers are hydroxypropyl starch or carboxymethyl starch. By the term"guar gums" and"xanthan gums"includes their derivatives, such as carboxymethyl guar, hydroxypropyl guar, carboxymethyl hydroxypropyl guar or cationized guar.

Preferably, cellulose ethers are included as component a) in the additive composition of the present invention. More preferably, the cellulose ethers are C,-C3-alkyl cellulose ethers, such as methyl cellulose ethers; C,-C3-alkyl hydroxy-C, _3-alkyl cellulose ethers, such as methyl hydroxyethyl cellulose ethers, methyl hydroxypropyl cellulose ethers or ethyl hydroxyethyl cellulose ethers; hydroxy-C, 3-alkyl cellulose ethers, such as hydroxyethyl cellulose ethers or hydroxypropyl cellulose ethers; mixed hydroxy-C,-C3-alkyl cellulose ethers, such as hydroxyethyl hydroxypropyl cellulose ethers, carboxy-C,-C3-alkyl cellulose ethers, such as carboxymethyl cellulose ethers; carboxy-C,-C3-alkyl hydroxy-C,-C3-

alkyl cellulose ethers, such as carboxymethyl hydroxyethyl cellulose ethers; or alkoxy hydroxypropyl hydroxyethyl cellulose ethers, the alkoxy group being straight-chain or branched and containing 2 to 8 carbon atoms.

The viscosity of the cellulose ethers preferably is from 10 to 600,000 mPa's, more preferably from 2,000 to 300,000 mPas, measured as a 2 weight percent aqueous solution using an Ubbelohde viscosimeter.

Component b) of the additive composition of the present invention is a methacrylamide or acrylamide homo-or interpolymer that can be anionic, cationic or nonionic. Component b) is preferably water-soluble, that is, substantially the entire amount of component b) dissolves in the building material mixture of the present invention upon addition of water. Such polymers are described in Ullmann's Encyclopedia of Industrial Chemistry, 5"Edition, pages 143-154. The term"interpolymer"is used herein to indicate a polymer wherein at least two different monomers are polymerized to make the interpolymer.

The methacrylamide or acrylamide homo-or interpolymer preferably contains at least 50 mol percent, more preferably at least 60 mol percent of polymerized acrylamide and/or methacrylamide units. Examples of monomers which can be interpolymerized with acrylamide and/or methacrylamide are 2-acrylamido-2-methylpropanesulfonic acid, N, N-dimethylacryl amide, N-isopropylacryl amide, N, N'-methylene-bisacrylamide, acrylic acid or methacrylic acid.

Preferred anionic methacrylamide or acrylamide homo-or interpolymers are partially saponified polyacrylamides, partially saponified polymethacrylamides or copolymers of acrylamide or methacrylamide with alkali acrylates. Preferred cationic methacrylamide or acrylamide homo-or interpolymers are salts or quaternary products of diethylaminoethyl acrylate, dimethylaminoethylmethacrylate, dimethylaminopropylmethacrylamide, dialkylbisallylammonium salts or aminomethylated acryl amide homo-or interpolymers.

Useful nonionic polyacrylamides or polymethacrylamides are for example homopolymers of acrylamide or methacrylamide. Preferably the methacrylamide or acrylamide homo-or interpolymers have a Brookfield (LVI) viscosity of from 50 to 500 mPas, measured as a 0.25 weight percent aqueous solution at 30 rpm at 25°C.

Component b) of the additive composition of the present invention contributes to early stage thickening and sagging resistance upon addition of water to the building material mixture.

Component c) of the additive composition of the present invention is a non- cross-linked homo-or interpolymer which comprises an olefinically unsaturated, carboxylic group (s) containing compound in polymerized form. Component c) is not comparable with and does not have the same properties as the alkali metal salt or ammonium salt of crosslinked polyacrylates which are disclosed in European Patent EP 0 530 768 B1. The cross-linked polyacrylates disclosed in European Patent EP 0 530 768 B1 have the ability to absorb high amounts of water. In contrast thereto the non-cross-linked component c) acts as a liquifier in the water-based building material mixtures of the present invention. Component c) lowers the water demand of the building material mixture. Lowering the water demand is essential because excess water evaporates, leaves voids in the building material, and may lead to mechanical instabilities of the building material.

The term"interpolymer"as used herein refers to polymers prepared by polymerization of two or more different monomers. The term"polymer"as used herein refers to homo-and interpolymers. The term"olefinically unsaturated, carboxylic group (s) containing compound"as used herein refers to olefinically unsaturated compounds which contain one or more carboxylic acid groups, one or more salts of carboxylic acid group (s), one or more esterified carboxylic acid groups, and/or one or more anhydride groups. One, two or more compounds derived from different olefinically unsaturated carboxylic acids may be polymerized. An olefinically unsaturated, carboxylic acid group (s) containing compound can be derived from the same olefinically unsaturated carboxylic acid but can be comprised in the same or in different forms in the polymer. For example, it can partially be comprised in the polymer in the form of the free acid or a salt thereof and partially in the form of an ester and/or anhydride. One or more olefinically unsaturated, carboxylic group (s) containing compounds can be interpolymerized with one or more polymerizable compounds other than an amide, preferably those described further below.

Preferred salts are the alkali metal salts, such as sodium or potassium salts, the alkaline earth metal salts, such as calcium or magnesium salts, ammonium salts or amine salts, which are for example obtained by reaction of the carboxylic group with a trialkyl amine, such as trimethylamine or triethanolamine, or transition metal salts, such as Fe2+, Fe3+, Al3+ or Ni2+. The salt form of the olefinically unsaturated carboxylic acid is preferred over the free acid form. Preferably more than 50 percent, more preferably at least 70 percent of the total number of carboxylic acid groups are present in the salt form in the polymer c).

Most preferably, one or more olefinically unsaturated carboxylic acids are at least partially comprised as the sodium salt in the polymer c).

Preferred olefinically unsaturated carboxylic acids contain 2 to 12, more preferably 2 to 6, carbon atoms in addition to the carboxyl group (s). They are preferably mono-or dicarboxylic acids. Preferred examples thereof are acrylic acid, methacrylic acid, fumaric acid, maleic acid, the salts thereof, or maleic anhydride. Most preferably, maleic acid, maleic anhydride and/or a maleic acid salt is incorporated in the polymer c).

The olefinically unsaturated carboxylic acid, carboxylic acid salt or carboxylic acid anhydride can be esterified with one or more compounds to form one or more olefinically unsaturated carboxylic acid esters. The esterification step can be carried out before or after the polymerization reaction. The polymerization reaction and the esterification step are generally known in the art.

Preferred homopolymers c) are polymethacrylic acid or, more preferably, polyacrylic acid or a salt thereof. Preferred polyacrylic acids are commercially available under the trademark NARLEX LD 36 V or NARLEX LD 31 from National Starch.

Particularly useful interpolymers c) are those of i) acrylic acid or an acrylic acid salt and ii) methacrylic acid, fumaric acid, maleic acid or a salt thereof. The acid (s) can be partially esterified by an esterification agent described further below, preferably with an oxyalkylene-alkyl alcohol of the formula CH3 [ (CH2) wherein n is 1 to 10, preferably 1 to 4, m is 1 to 10, preferably 1 to 4 and o = 1 to 4, preferably 1 or 2, such as 2- (n-butoxy) ethyl alcohol; and/or with a copolymer produced from 10 to 100 ethylene oxide and/or propylene oxide units.

Other useful interpolymers c) comprise at least one olefinically unsaturated carboxylic acid (salt) and at least one alkyl ester or hydroxyalkyl ester of an olefinically unsaturated carboxylic acid in polymerized form. The molar ratio between the total number of acid (salt) groups and ester groups generally is from 1: 10 to 10: 1, preferably from 1: 4 to 4: 1, more preferably from 1: 2 to 2: 1, most preferably about 1: 1. Preferred examples thereof are copolymers of acrylic acid or methacrylic acid and a C,-C, 2-acrylate or C,-C, 2- methacrylate which optionally contains a hydroxyl group, such as hydroxymethyl acrylate, hydroxyethyl acrylate, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate or butyl methacrylate. Interpolymers comprising at least one olefinically unsaturated carboxylic acid and at least one hydroxyalkyl ester of an olefinically unsaturated carboxylic acid in polymerized form are known from U. S Patent No. 4,473,406.

Interpolymers obtained by copolymerizing 5 to 98 weight percent of an (alkoxy) polyalkylene glycol mono (meth) acrylic ester type monomer (A) and 95 to 2 weight percent of a

(meth) acrylic acid type monomer (B) and 0 to 50 weight percent of another copolymerizable monomer as well as their use as a cement dispersant are known from EP-A-0-753 488.

Other useful interpolymers c) are the polymers based on oxyalkylene glycol alkenyl ethers and unsaturated dicarboxylic acid derivatives disclosed in European Patent application EP-A 0 736 553.

Examples of useful interpolymers c) are also described in U. S. Patent No.

5,650,473 which discloses an interpolymer of styrene or substituted styrene and a carboxylated monomer, such as acrylic acid, methacrylic acid, maleic acid or a half ester thereof.

Component c) preferably is a non-cross-linked interpolymer containing at least one olefinically unsaturated, carboxylic group (s) containing compound and at least one olefinically unsaturated hydrocarbon in polymerized form. The molar ratio between the total number of olefinically unsaturated carboxylic group (s) containing compounds and the total number of olefinically unsaturated hydrocarbons generally is from 1: 10 to 10: 1, preferably from 1: 4 to 4: 1, more preferably from 1: 2 to 2: 1, most preferably about 1: 1. These interpolymers are described in more detail below. The olefinically unsaturated carboxylic group (s) containing compounds and the olefinically unsaturated hydrocarbons can be arranged alternatingly or randomly in the interpolymer c). If the monomer is an unsaturated dicarboxylic (salt), such as maleic acid, the dicarboxylic acid (salt) and the olefinically unsaturated hydrocarbon are preferably arranged alternatingly.

More preferably, the interpolymer c) is i) an interpolymer containing at least one olefinically unsaturated carboxylic group (s) containing compound and at least one aliphatic olefinically unsaturated hydrocarbon in polymerized form, or ii) an interpolymer containing at least one olefinically unsaturated carboxylic group (s) containing compound and at least one vinyl or vinylidene aromatic monomer in polymerized form.

Aliphatic olefinically unsaturated hydrocarbons inclue, for example, a-olefin monomers containing from 2 to 28, preferably from 2 to 12, more preferably from 2 to 8 carbon atoms. Preferred such monomers include ethylene, propylene, butene-1, isobutylene, 4-methyl-1-pentene, hexene-1, octene-1 or the diisobutylenes, such as 2,4,4- trimethylpentene-1 or 2,4,4-trimethylpentene-2.

Suitable vinyl or vinylidene aromatic monomers include, for example, those represented by the following formula:

wherein R'is hydrogen or an alkyl group containing 1 to 4 carbon atoms, preferably hydrogen or methyl; each R2 is independently hydrogen or an alkyl group containing 1 to 4 carbon atoms, preferably hydrogen or methyl; Ar is a phenyl group or a phenyl group substituted with 1 to 5 C,-C4-alkyl substituents; and n has a value from zero to 4, preferably from zero to 2, most preferably zero. Preferred monomers include styrene, a-methyl styrene, the C,-C4-alkyl-or phenyl-ring substituted derivatives of styrene, such as ortho-, meta-, and para-methylstyrene, para-vinyl toluene or mixtures thereof. The most preferred monovinyl aromatic monomer is styrene.

The interpolymer c) can comprise one or more aliphatic olefinically unsaturated hydrocarbons and/or one or more vinyl or vinylidene aromatic monomers in combination with an olefinically unsaturated, carboxylic group (s) containing compound in polymerized form. Preferred examples thereof are interpolymers of i) styrene, ii) isobutylene and iii) maleic acid, maleic anhydride and/or maleic acid salt.

Preferred olefinically unsaturated carboxylic acids are listed further above.

More preferably, an olefinically unsaturated dicarboxylic acid, most preferably maleic acid, maleic anhydride and/or a maleic acid salt is incorporated in the interpolymer c). According to one preferred embodiment of the present invention, maleic anhydride is partially or fully hydrolyzed and optionally transformed into its salt form prior to or after interpolymerization with the olefinically unsaturated hydrocarbon. Preferably, hydrolyzation is carried out prior to polymerization and transformation into its salt form is carried out after polymerization.

The carboxylic acid (satt) or the anhydride can be esterified with one or more groups to form an olefinically unsaturated carboxylic acid ester. The esterification step can be carried out before or after the polymerization reaction of the carboxylic acid (salt) or the anhydride with the olefinically unsaturated hydrocarbon (s). The polymerization reaction and the esterification step are generally known in the art. For example, esterification of maleic anhydride with an alcohol and subsequent copolymerization with a vinylidene aromatic monomer is known from U. S. Patent No. 5,237,024. In case of esterification preferably 2 to

75 percent, more preferably 20 to 60 percent, most preferably about 50 percent of the total number of carboxyl carbon atoms in the polymer are esterified.

Suitable esterification agents are for example polyglycols of the formula R"O [ (CH2) X O] YH wherein R"is a C, 4-alkyl group, preferably methyl or ethyl, x is 2 to 5, preferably 2 to 3, and y is 2 to 150, preferably 5 to 30, which have a molecular weight of from 300 to 5,000, preferably from 700 to 1000. Plaster compositions which comprise gypsum plaster and, as a sole additive, an esterified styrene-maleic anhydride copolymer which have an average molecular weight of 500 to 5000, preferably 1500 to 3000, prior to esterification and which have been esterified with the mentioned polyglycol are known from U. S. Patent No. 3,544,344. Such esterified styrene-maleic anhydride copolymers can be included in the additive composition of the present invention as interpolymer c).

Other suitable esterification agents are those of formula R"-O-(R'-O) mH, wherein R"is a C, 20-alkyl group, preferably methyl or ethyl, a C5. 9-cycloalkyl group or an aryl group, such as phenyl, R'is a C26-alkylene group and m is from 1 to 100, preferably 7 to 20.

Styrene-maleic anhydride copolymers which have been esterified with the mentioned esterification agent and wherein the ratio between the maleic acid half ester units to maleic acid anhydride units is from 3: 1 to 100: 1 and their use as cement plasticizers are known from European Patent application EP 0 306 449. They contain 10 to 100 styrene- (esterified) maleic anhydride units and can also be included in the additive composition of the present invention as component c). Copolymers of an aliphatic olefinically unsaturated hydrocarbon and a half ester of maleic acid which has been esterified with similar esterification agents as well as their use as cement plasticizer are known from German Offenlegungsschrift DE 41 35 956 A1. The copolymers disclosed in DE 41 35 956 A1 are also useful as interpolymers c) in the additive composition of the present invention.

Other suitable esterification agents are oxyalkylene-alkyl alcools of the formula CH,- [ (CH-OUCH-OH, wherein n is 1 to 10, preferably 1 to 4, m is 1 to 10, preferably 1 to 4 and o = 1 to 4, preferably 1 or 2, such as 2- (n-butoxy) ethyl alcohol.

Other suitable esterification agents are those which introduce hydrophobic groups into the interpolymer c), such as the radicals of a hydrophobic polyalkylene glycol or a polysiloxane. Exemplary of such esterification agents are copolymers produced from 10 to 100 ethylene oxide and/or propylene oxide units or polysiloxanes containing 10 to 100 di-C,.

4-alkyl siloxane units. Such esterification agents are preferably used in combination with another, less hydrophobic esterification agent, such as those of formulas R"O [ (CH,)),-O], H or R"-O- (R'-O) mH above. Styrene-maleic anhydride copolymers which have been esterified with a combination of a hydrophobic polyalkylene glycol or polysiloxane and an esterification agent of formula R"-O- (R'-O) mH and their use as cement plasticizers are known from German Patent application DE 41 42 388 A1. They can also be included in the additive composition of the present invention as component c).

Other suitable esterification agents are those of formula R3-0- (R'-O) mH, wherein R3 is the acyl moiety of an aliphatic carboxylic acid containing 12 to 18 carbon atoms and R'and m have the above-mentioned meanings, such as those known from German Patent No. 23 12 616.

Further suitable esterification agents are alcools, preferably those containing 1 to 30 carbon atoms, such as ethanol, propanol, octanol, dodecanol or straight or branched C, 0-C22 monohydric alcohols like oleyl alcohol or stearyl alcool.

Further suitable esterification agents are C8-C22 fatty acids or C,-C, 2 alkyl phenols.

Exemplary of useful interpolymers c) containing at least one olefinically unsaturated, carboxylic acid group (s) containing compound and at least one olefinically unsaturated hydrocarbon in polymerized form are disclosed in the International Patent application WO 95/28362 which discloses comb polymers which comprise pendant carboxylic moieties, preferably graft copolymers which have a backbone of styrene and butadiene and side chains which comprise monomer units derived from acrylic acid, methacrylic acid, maleic acid or fumaric acid.

Other examples of useful interpolymers c) containing at least one olefinically unsaturated, carboxylic acid group (s) containing compound and at least one olefinically unsaturated hydrocarbon in polymerized form are disclosed in German Offenlegungsschrift DE 196 08 044 A1 which discloses hydrophobically modified unsaturated copolymers of monoethylenically unsaturated dicarboxylic acids and olefins containing 2 to 8 carbon atoms.

They are produced by a radically initiated copolymerization of a monomer mixture comprising a) from 40 to 80 mol percent of a monoethylenically unsaturated dicarboxylic acid, their anhydrides, alkali metal and/or ammonium salts, b) from 19.99 to 59.99 mol percent of an olefin containing 2 to 8 carbon atoms, c) 0.01 to 4 mol percent of an olefin

containing 10 to 150 carbon atoms and d) optionally up to 40 mol percent of another comonomer.

The more preferred interpolymers c) are interpolymers of i) styrene and ii) maleic acid and/or a maleic acid salt and/or maleic acid anhydride, more preferably of styrene and maleic acid of which more than 50 percent, more preferably at least 70 percent, is in the salt form, most preferably in the sodium salt form. Other preferred interpolymers c) are interpolymers of i) styrene and ii) maleic acid and/or a maleic acid salt and/or maleic acid anhydride which has been esterified as indicated above.

Other preferred interpolymers c) are those comprising A) structural units derived from an ethylenically unsaturated hydrocarbon; B) structural units derived from an ethylenically unsaturated monomer selected from monocarboxylic acids, salts thereof, dicarboxylic acids, salts thereof, cyclic anhydrides and mixtures thereof; and C) structural units derived from a monomer selected from esters of ethylenically unsaturated monocarboxylic acids, half-esters of ethylenically unsaturated dicarboxylic acids, allyl ethers and vinyl ethers and mixtures thereof having a substituent R linked to the oxygen atom of either the ester groups or the ether groups that is selected from: (i) polyalkylenoxide groups corresponding to the formula wherein R'is independently in each occurrence hydrogen or C,-C4 alkyl, R2 is C,-C44<BR> <BR> <BR> <BR> <BR> hydrocarbyl, t is 0 or 1 and m is an integer in the range of 5 to 200, with the proviso that if R2 is Cl-C5alkyl the polyalkylene oxide group does not contain more than 50 weight percent ethylene oxide moieties based on the weight of the polyalkylene oxide group; and (ii) groups corresponding to the formula wherein t is 0 or 1 and Q is a polysiloxane residue, whereby the molar ratio of units B) to units C) in the copolymer is in the range of 1000: 1 to 5: 1.

The structural units A) preferably correspond to the Formula (I) wherein R4 is C,-C8 alkyl or substituted or non-substituted aryl and R5, R3 and R7 are independently hydrogen or C,-C4 alkyl.

More preferably, the structural units A) are derived from styrene or diisobutylene.

The structural units B) of the interpolymers c) preferably correspond to formulae wherein R8 and R9 are independently hydrogen or C,-C4-alkyi; R'° is hydrogen or C (O) X; and X is OA wherein A is hydrogen, ammonium, alkyl ammonium, alkanol ammonium or 1/n Mon+, M being a metal having the valence n and Y is oxygen.

Preferred units for the structural unit B) are derived from acrylic acid, methacrylic acid, maleic acid, and the salts thereof, as well as from maleic anhydride.

Especially preferred are structural units derived from maleic acid and salt thereof as well as

from maleic anhydride whereby neutralized units derived from maleic acid are most preferred.

The preferred structural units C) of the interpolymer c) comprised in the additive composition of the present invention correspond to the formulae

whereby R, R8, R9 and R'° are defined as above, and R'2, R'3 and R'4 are independently hydrogen or C,-C4 alkyl and p is 0 or 1.

Most preferably the structural units C) are derived from monomers selected from wherein R9 is hydrogen or methyl, and A and R are as defined above.

Particularly preferred are units derived from half-esters of maleic acid. The substituents R are desirably selected from (i) ethylene oxide/propylene oxide copolymer residues bearing a terminal C,-C24 alkyl group and containing no more than 50 weight percent ethylene oxide units based on the weight of R, (ii) polyethylene oxide residues bearing a terminal C6-C3s alkyl moiety containing on an average not more than 10 ethylene oxide units, (iii) poly (propylene oxide) residues bearing a terminal C,-C24 alkyl group, (iv) poly (butylene oxide) residues bearing a terminal C,-C24 alkyl group, (v) butylene oxide/propylene oxide copolymer residues bearing a terminal C,-C24 alkyl group, (vi) ethylene oxide/butylene oxide copolymers bearing a terminal C,-C24 alkyl group and containing no more than 50 weight percent ethylene oxide units based on the weight of R, (vii) ethylene oxide/propylene oxide/butylene oxide terpolymer residues bearing a terminal C,-C24 alkyl group and containing no more than 50 weight percent ethylene oxide units based on the weight of R, and (viii) polymer residues corresponding to the formula wherein EO, PO, BO represent randomly arranged ethylene oxide, propylene oxide and butylene oxide units respectively, u, v, and w are integers of 0 to 200, with the proviso, that no more than 50 weight percent ethylene oxide units based on the weight of R are present and r is 0 to 35.

The polysiloxane residue Q in the formula of substituent R (ii) corresponds preferably to the formula wherein R'5 is independently at each occurrence C,-C6 alkyl, preferably methyl, R18 is R'5 or SiR's3 and n is an integer from 10 to 100.

According to a preferred embodiment of the present invention, if the structural units B) are derived from (meth) acrylic esters, t in Formulae (i) and (ii) of substituent R as defined above, is one. These monomers can be prepared by reacting glycidyl (meth) acrylate with an appropriate hydroxyl functional polyalkyleneoxide or hydroxyl-functional polysiloxane.

In the case of structural units B) derived from half-esters of ethylenically unsaturated dicarboxylic esters, allyl ethers and vinyl ethers, t in Formulae (i) and (ii) of substituent R as defined above, is preferably zero.

The substituents R pending on the structural units C) have preferably a weight average molecular weight in the range of 100 to 10,000, preferably in the range of 500 to 5,000. The molar ratio of structural units B) to structural units C) is in the range of 1,000: 1 to 5: 1, preferably in the range of 500: 1 to 10: 1, and more preferably in the range of 150: 1 to 20: 1. The molar ratio of units A) to the sum of units B) and C) is preferably within the range of 1: 10 to 10: 1. The above-described novel interpolymer C) can be prepared by interpolymerization of monomers that provide for the structural units A), B) and C) as defined above utilizing polymerization methods that are well known to the person skilled in the art. Thus, it is preferred to introduce structural units C) as defined above into the interpolymer by interpolymerizing esters of ethylenically unsaturated monocarboxylic acids, half-esters of ethylenically unsaturated dicarboxylic acids, allyl ethers or vinyl ethers already bearing the substituent R as defined above with other monomers providing for the units A) and B) in the appropriate relative amounts. By subsequent neutralization with caustic the carboxylic groups or the anhydride groups in the interpolymer may be converted into the salt form if desired. In case the half-ester of a dicarboxylic acid, for example, maleic acid, is utilized to provide for structural units C), the half-ester formation can be achieved by the reaction of maleic anhydride with an alcohol providing for the substituent R as defined above, for example, a hydrophobic polyalkylene oxide, by dissolving/dispersing maleic anhydride in the polyalkylene oxide. The reaction temperature is generally in the range of 50°C to 200°C, preferably in the range of 70°C to 170°C and most preferably 90°C to 150°C. The reaction time depends on the temperatures and is generally between 0.5 to 8 hours to completion of the reaction. If the maleic acid is selected as an unsaturated carboxylic acid monomer, it can be used and prepared"in situ"by hydrolyzing maleic anhydride. This can occur by adding water in appropriate ratios to the polyalkylene oxide.

However the simultaneous half-ester formulation and hydrolysis of maleic anhydride is less preferred. Preferred is the conversion in two steps by preparing first the half-ester by using maleic anhydride in excess, wherein the molar ratio of maleic anhydride to polyalkylene oxide is from 1: 1 to 100: 1. In a subsequent step addition maleic anhydride is added to provide for the appropriate ratio of structural units B) and units C) in the final interpolymer.

Thereafter maleic anhydride is hydrolyzed to the desired extent by adding the appropriate amount of water. Water may be present in excess and can be used together with isopropanol.

Still another method is to perform half-ester formation and hydrolysis of maleic anhydride separately and to combine both solutions prior to the polymerization with

the olefinic monomer, for example, styrene. Polymerization is carried out according to known procedures, see for instance U. S. Patent No. 5,138,004.

Preferred is however a method wherein styrene and the initiator are continuously added in a concentrated solution of maleic acid containing the half-ester as described above. If acrylic acid or methacrylic acid is used, it is preferably added together or separately with the styrene stream and the initiator stream into the reaction solution containing the lower alcohol/water mixture and the half-ester. The half-ester can however also be added as a fourth, separate component to the reaction mixture or dissolve in the styrene or (meth) acrylic acid stream. The continuous feed of the monomer streams into the reaction mixture provides low monomer concentrations and, accordingly, low molecular weight. Chain transfer agents, such as dodecylmercaptane, can be used to control the molecular weight. Preferred initiators are peroxo-compounds such as peroxodisulfates or hydrogen peroxide which can be employed in combination with a peroxide decomposer such as ferric salts or a sulfite or an amine in order to accelerate its decomposition. But instead of peroxides, also organic initiators such as azodiisobutyronitrile can be used.

If vinyl ethers or allyl ethers bearing a hydrophobic substituent are used, the unsaturated carboxylic acid such as maleic acid is neutralized and polymerized under neutral pH conditions or slightly alkaline conditions in its salt-form with styrene, because the vinyl ethers are unstable under acidic conditions.

Alternatively, but less preferred, the substituents R may be introduced into the copolymer after copolymerization by subsequent esterification of carboxylic acid groups, anhydride groups or carboxylate groups in the copolymer with an appropriate amount of hydroxyl-functional compounds of the substituents R as defined above to provide for the claimed ratio of structural units B) to structural units C).

The interpolymers c) are particularly useful in building material mixtures containing gypsum. Without wanting to be bound to the theory, it is believed that the carboxylic groups promote complexion of the calcium ions in gypsum and reduce or prevent agglomeration among the gypsum particles and/or agglomeration of the gypsum particles with particles of the component a) or with particles of the (meth) acrylamide homo-or interpolymer b).

Depending on the method of preparing the interpolymers c), 0.5 to 2 percent of sulfonic acid or sulfonic ester groups may be present in the interpolymer, based on the

weight of the interpolymer, in addition to the carboxyl function. However, the interpolymers c) preferably do not contain a significant amount of sulfonic acid or sulfonic ester groups.

The weight average molecular weight (Mw) of the homo-or interpolymer c) is preferably from 2,000 to 100,000, more preferably from 3,000 to 60,000, and most preferably from 5,000 to 20,000.

It has been found that the additive composition of the present invention containing the above-described components a), b) and c) can significantly improve the workability of water-containing building material mixtures, particularly of gypsum-based plastes, and can significantly reduce the lumping tendency. It has been found to be important that the additive composition of the present invention contains a combination of the components a), b) and c). The additive composition provides the necessary early stage shear stability when the building material mixture is mixed with water. The plastifying effect through interaction of component c) with the water-containing gypsum mixture and component b) leads to a smooth and creamy consistency of the plaster. Thereby the wetting and hydration of the gypsum with water is improved significantly.

The additive composition of the present invention can be produced by simply blending components a), b) and c), most conveniently in their dry form. For example, a spray-dried component c) can be blended with components a) and b).

However, it has been surprisingly found that lump formation of water- containing building material mixtures, such as gypsum-based spray plastes, can be further reduced if component a) is coated with an aqueous solution of the homo-or interpolymer c) and the coated component a) is blended with the methacrylamide or acrylamide homo-or interpolymer b) to prepare the additive composition of the present invention.

Accordingly, a preferred embodiment of the present invention is an additive composition for water-based building material mixtures which comprises a) a cellulose ether, starch ether, guar gum and/or xanthan gum, b) a methacrylamide or acrylamide homo-or interpolymer, and c) an above-described non-cross-linked homo-or interpolymer, wherein component a) is coated with the non-cross-linked homo-or interpolymer c). It has surprisingly been found that gypsum-based spray plastes which comprise such coating composition have the same sagging resistance when applied to walls, but a significantly reduced tendency to lump formation and a significantly improved workability, as compared to gypsum-based spray plastes which contain the same components a), b) and c), but which components were simply mixed as dry materials. Improved workability can be generally

observed in all stages of the plastering process, such as first and second even-out, floating and finishing. Most preferably, the entire amount of the component a), such as a cellulose ether, which is used in the additive composition and in the building material mixture of the present invention is coated with component c).

The aqueous solution of the homo-or interpolymer c) preferably contains from 1 to 50 weight percent, more preferably from 5 to 40 weight percent and most preferably from 10 to 30 weight percent of the homo-or interpolymer c). Optionally a C, 8-alcohol, such as isopropanol, or a polyalkyleneoxide glycol is mixed with the aqueous solution of the homo-or interpolymer c). A useful amount is for example from 0.1 to 15 percent, preferably from 0.5 to 5 percent, based on the weight of the aqueous solution. Inorganic salts, such as sodium sulfate, may also be added to the aqueous solution of the homo-or interpolymer c), for example in a concentration of from 0.1 to 5 percent, preferably from 0.2 to 3 percent, based on the weight of the aqueous solution. The aqueous solution of the homo-or interpolymer c) is contacted with such an amount of component a) that the weight ratio between the polymer c) and the component a) generally is from 0.01 to 1: 1, preferably from 0.02 to 0.3: 1, more preferably from 0.03 to 0.18: 1.

The aqueous solution which comprises the homo-or interpolymer c) and optional additives can be added to a dry component a), preferably a cellulose ether. In this case preferably a high intensity continuous mixer is used, for example as manufactured by Gebrüder Lödige or Drais Werke (both in Germany), or Hosokawa Schugi BV (The Netherlands). Alternatively, the aqueous solution which comprises the homo-or interpolymer c) and optional additives can be added to the component a), preferably a cellulose ether, after the production of the component a) while it is still wet and prior to the grinding and drying steps which are usually applied as finishing steps to cellulose ethers after production. In this case a standard mixer, for example as manufactured by Gebruder Lödige or Drais Werke was found to be sufficient. The coated component a) is generally dried, for example in a fluidized bed or flash dryer. In the coating process an outer shell of the homo-or interpolymer c) is produced on cellulose ether particles, agglomeration of cellulose ether particles or on other particles of component a), such as starch ether, guar gum and/or xanthan gum particles.

The coated component a) is then blended with the polyacrylamide b) in such amounts that the blend generally comprises from 80 to 99.5 percent, preferably from 80 to 99 percent, more preferably from 85 to 98 percent of the coated component a) and from 0.5

to 20 percent, preferably from 1 to 15 percent, more preferably from 2 to 10 percent of the (meth) acryl amide homo-or interpolymer b), based on the total weight of a) and b).

The additive composition of the present invention provides excellent properties to water-based building material mixtures, such as cement or lime containing mixtures or, more preferably, gypsum containing mixtures. Examples of cement containing mixtures are cement pastes, that is, a mixture of cement and water; mortar, that is, a mixture of cement, sand and water; or concrete, that is, a mixture of cement, sand, gravel and water.

Other examples of water-based building material mixtures are tile adhesives, grouts, spray textures and stucco compositions. However, the additive composition of the present invention is particularly useful in gypsum-based plaster compositions, such as gypsum- based spray plastes or manual plastes.

The building material mixture of the present invention preferably contains from 0.05 to 5 percent, more preferably from 0.1 to 3 percent, and most preferably from 0.15 to 1 percent of the additive composition of the present invention comprising components a), b) and c). Gypsum-containing building material mixtures are the most preferred ones.

The components a), b) and c) can be added individually or as a mixture to the building material mixture. Most preferably, component a) is coated with component c) and then mixed with component b), as described above prior to incorporation in the building material mixture. In addition to the components of the additive composition of the present invention, the building material mixture may contain known additives, for example a filler, such as sand or perlite, a lightweight additive, floating agent, wetting agent, retarding agent, hydrophobing agent, starch ether and/or air-entraining agent in known amounts. Gypsum- containing building materials may for example contain an inorganic salt, such as sodium lauryl sulfonate; a setting retarder, such as tartaric acid; hydroxypropyl starch and/or a filler, such as perlite in known amounts.

100 weight parts of the building material mixture of the present invention are generally mixed with 15 to 150 weight parts, preferably 40 to 90 weight parts, more preferably 40 to 80 weight parts of water to produce a mixture which is ready for use in the building industry.

The invention is illustrated by the following examples which should not be construed to limit the scope of the present invention. Unless stated otherwise all parts and percentages are given by weight.

Examples 1 to 3 and Comparative Examples A and B In all examples a commercially available methyl hydroxypropyl cellulose ether was used as component a) which had a DSof 1. 15, an MShydroxypropoxyl° 0-55 and a viscosity of 15,000 mPas, measured as a 2 weight percent aqueous solution using an Ubbelohde viscosimeter. The cellulose ether which was used without further modification was designated in the following Table I as"non-coated cellulose ether".

In all examples a water-soluble anionic interpolymer of acryl amide and acrylic acid was used as a component b). All copolymer particles had a size of less than 100 micron. The copolymer is commercially available from SNF Floeger under the trademark SEPARAN.

The material which was designated as"coated cellulose ether"in the following Table I was the above-described methylhydroxypropyl cellulose ether which was coated with an interpolymer c). The interpolymer c) contained styrene and maleic acid in a molar ratio of 1: 1 and had a Brookfield viscosity of 85 Pa's. 80 to 90 percent of the carboxyl groups in the polymer are present in the form of the sodium salt. 600 kg/h of the cellulose ether were contacted with 140 kg/h of a 30 percent aqueous solution of the interpolymer c) at 2000 rpm in a continuous intensive mixer CB 30, manufactured by Gebr. Lödige, Paderborn, Germany.

The material was then dried at 100 st C. The additive compositions of Examples 1 to 3 and Comparative Examples A and B are listed in Table I below. The percentages refer to the weight of the additive, based on the dry weight of a gypsum spray plaster composition which does not contain a cellulose ether nor a (meth) acrylamide homo-or interpolymer.

Table I (Comparative) Cellulose Ether Polyacrylamide Example A 0.263% non-coated 0.007% 1 0.263% coated 0.007% 2 0.248% coated 0.022% 3 0. 221 % coated, 0.022% 0.027% non-coated B 0.248% non coated 0.022% The spray plaster compositions containing the additives listed in Table I above were continuously mixed with an amount of water (in liter per hour) listed in Table II below. The plaster was applied to a wall using a spray plaster machine G78 from Putzmeister, Germany, using a 10 m hose.

The properties of the gypsum spray plaster are listed in Table II below.

The properties are rated visually as follows: 1 = very good 2 = good 3 = acceptable 4 = poor

Table II (Comparative) Example A 1 2 3 B water demand 600/h 580 I/h 610 I/h 610 I/h 630 I/h pressure head 16 bar 16 bar 11 bar 11 bar 16 bar Spray behavior/2 ; slight sagging 2; slight sagging 1 1-2 1 sagging resistance distribution on the 2-3; slightly 2-3; slightly sticky, 1 2 4 wall sticky,"orange"orange skin" (heavy) skin" small lumps 3 3 1-2 2-3 2-4

Example 1 and Comparative Example A contain the same amount of polyacryl amide and can be compared with each other. Examples 2 and 3 can be compared with Comparative Example B.

The comparison between Comparative Example A and Example 1 shows that the water demand was reduced by using the additive composition of the present invention.

When the amount of polyacryl amide was increased, the advantages of the present invention become more apparent. While the water demand in the plaster compositions of Examples 2 and 3 was smaller than in the plaster composition of comparative Example B, the necessary pressure head in Examples 2 and 3 was substantially smaller, which was very advantageous. Furthermore, the plaster compositions of Examples 2 and 3 were more easily distributed on the wall and contain less lumps than the plaster composition of Comparative Example B.