EP1981824A2

EP1981824A2 - Dispersion comprising titanium dioxide and polycarboxylate ether

Info

Publication number: EP1981824A2
Application number: EP07704013A
Authority: EP
Inventors: Christoph Tontrup; Wolfgang Lortz; Klaus Deller; Christian Hübsch; Philipp Wieland; Harald Grassl; Stefanie Scheul; Eva Jetzlsperger; Kerstin Becher
Original assignee: Evonik Degussa GmbH; Construction Research and Technology GmbH
Current assignee: Construction Research and Technology GmbH
Priority date: 2006-02-04
Filing date: 2007-01-19
Publication date: 2008-10-22
Also published as: CN100532309C; WO2007088110A3; WO2007088110A2; CN101016201A; DE102006005094A1

Abstract

A dispersion which is free of binders and which contains titanium dioxide and at least one water-soluble poly- carboxylate ether, where - the titanium dioxide has a BET surface area of 20 to 400 m2/g, the water-soluble polycarboxylate ether is a copolymer based on at least one oxyalkylene glycol compound and at least one unsaturated monocarboxylic acid derivative or dicarboxylic acid derivative, the dispersion has a content of titanium dioxide of 5 to 50% by weight, based on the total amount of the dispersion.

Description

Dispersion comprising titanium dioxide and polycarboxylate ether

The invention relates to a concrete additive based on titanium dioxide and polycarboxylate ether.

It has been known for a long time, for example from US 3135617, that an acceleration of setting can be achieved by finely divided amorphous silicon dioxide. This did not gain acceptance, however, since the workability of the fresh concrete was greatly restricted thereby.

WO 01/90024 discloses a concrete composition which contains aggregates, a hydraulic binder, silica sol and a polycarboxylate. The BET surface area of the silica sol is preferably 300 to 900 m²/g. Silica sols are individual particles having a diameter of 3 to 50 nm and are only stable in dispersion. In cement or concrete compositions they have a high reactivity, but no filler effect. This is probably to be attributed to the fact that on account of the very low particle diameter of the silica sols these can rapidly dissolve in an alkaline medium. In order to be able to observe a high early strength when using silica sols, high concentrations of silica sols are necessary, which leads to a marked reduction of the workability.

In WO 02/070429, a composite material is disclosed which contains inorganic aggregates, ultrafine particles, a cement-containing binder and a concrete superplasticizer . The composite material allows the production of highly plasticized concrete, in which no bleeding occurs. The ultrafine particles employed are mainly "silica fume" particles, which are obtained in connection with the production of silicon metal or ferrosilicon . "Silica fume" particles, as a rule, are present as spherical individual particles having a diameter of 150 nm or more. In cement or concrete compositions, they show a strong filler effect, but are not very reactive here on account of their low specific surface area of about 20 m²/g. Further particles of this order of magnitude which can be employed are argillaceous earth, fly ash, natural pozzolana, calcium carbonate, aluminum oxide, barium sulfate and titanium dioxide. The particles specified have the disadvantage that they have a small specific surface area, which leads to a low nucleation rate of the strength-forming phases and thus to low early strengths. Early strength is understood within the context of the present text as meaning the strength of a concrete after < 48 h of cement hydration.

The proportion of the ultrafine particles, based on the total amount of the composite material, is 1 to 30% by weight or about 10 to 25% by weight in the working examples, based on the sum of cement and ultrafine particles. Thus the necessary amount of ultrafine particles is very high.

In US 6752866, a process for the improvement of the early strength is disclosed in which an aqueous dispersion which contains a mineral filler and a special dispersant is added to cement. As mineral fillers, it is possible to employ calcium carbonate, barium carbonate, limestone, dolomite, talc, silicon dioxide, titanium dioxides, kieselguhr, iron oxide, manganese oxide, lime, kaolin, clay, mica, gypsum, fly ash, slag, calcium sulfate, zeolites, basalt, barium sulfate or aluminum trihydroxide . Preferably, calcium carbonate is employed. The disclosed, average particle diameters of the mineral fillers employed are in the range from about 2 to about 10 μm. A special dispersant is essential for the invention disclosed in US 6752866. This contains a copolymer which is obtained by free radical copolymerization of an alkoxypolyalkylene glycol urethane with an anionic or nonionic monomer. No actual details are given for the necessary amounts of mineral filler, dispersant and cement. From the working examples, it is to be inferred that the content of mineral filler is 10% by weight (silicon dioxide, Test number 12) or 30% by weight (silicon dioxide, Test number 17) and the content of dispersant 0.5 (Test number 17) or 0.75% by weight (Test number 12), based on silicon dioxide. On account of the large particle diameter, these dispersions show only a low stability to sedimentation.

In EP-A-I 607378 , for cement-containing systems additives based on pyrogenic metal oxides are described which contain at least one sorbent. The pyrogenic metal oxides can be present in the form of aqueous dispersions. Furthermore, a superplasticizer based on polycarboxylate can be employed. EP-A-1607378, however, contains neither details about the type of polycarboxylate, nor in which range of amounts the polycarboxylate must be added, nor about the manner in which process step the polycarboxylate is added.

Furthermore, the technical teaching must be inferred that the disclosed metal oxide powders silicon dioxide, aluminum oxide, titanium dioxide, cerium oxide, zirconium oxide and mixtures thereof show an essentially similar action.

In Wiss. Z. Hochsch. Archit. Bauwesen. - Weimar 40 (1990), p.183, Wagner and Hauck show that the sequence of addition of the various constituents in the production of a concrete has a significant influence on the early strength and the need of superplasticizer if oxides increasing early strength are employed. In the investigation, the oxide was added separately from the superplasticizer. As a result of the combination of superplasticizer and oxide in a concrete additive, the number of possible various sequences of the addition would be reduced and thus also the possibilities of error. A further advantage of the combination in one concrete additive is that only one addition device is needed, which represents a cost advantage for the user.

The prior art shows that there is a lively interest in developing concrete compositions which have a high early strength with, at the same time, good workability. The prior art further shows that the presently available superplasticizers and particles in the cement or concrete composition are a sensitive system. For example, the sequence of the addition and the concentration of the substances used have a crucial influence on the workability processability and the early strength of the concrete.

It is therefore the object of the invention to make available a concrete additive with which the disadvantages of the prior art can be minimized. In particular, the concrete additive should markedly increase the early strength of concretes with, at the same time, good workability.

The invention relates to a dispersion which is free of binders and which contains titanium dioxide and at least one water-soluble polycarboxylate ether, where

— the titanium dioxide has a BET surface area of 20 to 400 m²/g,

— the water-soluble polycarboxylate ether is a copolymer based on at least one oxyalkylene glycol compound and at least one unsaturated monocarboxylic acid derivative or dicarboxylic acid derivative,

— the dispersion has a content of titanium dioxide of 5 to 50% by weight, based on the total amount of the dispersion . In the present invention, the terms titanium dioxide and titanium dioxide particles designate the same substance.

The dispersion according to the invention is preferably an aqueous dispersion, that is the main constituent of the liquid phase is water. The liquid phase moreover contains the water-soluble polycarboxylate ether.

The dispersion according to the invention is free of binders. Here, binders are understood as meaning inorganic substances, such as, for example, cement, or organic substances, which are processable in the plastic state, and harden in the course of a certain time and thereby combine other substances with one another.

Within the meaning of the invention, the term titanium dioxide also comprises metal mixed oxides with titanium dioxide as the first component. As the second and further components, in particular aluminum oxide, potassium oxide, lithium oxide, sodium oxide, magnesium oxide, calcium oxide, silicon dioxide and/or zirconium dioxide can be preferred. Likewise, it is possible that a mixture of titanium dioxide with the aforementioned mixed oxides is present .

Furthermore, the type of titanium dioxide is not restricted. For instance, it can be titanium dioxide which is precipitated or obtained by sol-gel or pyrogenic processes .

Preferably, a pyrogenic titanium dioxide is a constituent of the dispersion according to the invention. Pyrogenic is to be understood as meaning titanium dioxide particles obtained by flame oxidation and/or flame hydrolysis.

Starting substances for pyrogenic processes which can be employed are organic and inorganic substances. Titanium tetrachloride, for example, is particularly suitable. Suitable organic starting compounds can be, for example, Ti(OR)₄ where R=isopropyl or butyl. The titanium dioxide particles thus obtained are to the greatest extent pore- free and have free hydroxyl groups on the surface. The pyrogenic titanium dioxide particles within the meaning of the present invention are at least partially present in the form of aggregated primary particles. As a rule, the pyrogenic titanium dioxide particles are to the greatest extent present in aggregated form.

The pyrogenic titanium dioxide can also be present as a pyrogenic mixed oxide with titanium dioxide as the first component. As the second and further components, in particular aluminum oxide, potassium oxide, lithium oxide, sodium oxide, magnesium oxide, calcium oxide, silicon dioxide and/or zirconium dioxide can be preferred. Likewise, it is possible that a mixture of pyrogenic titanium dioxide is present with the aforementioned mixed oxides .

The pyrogenic titanium dioxide according to the invention can also be present in surface-modified form. Thus, the surface can be surface-modified, for example, with haloorganosilanes, alkoxysilanes, silazanes, siloxanes, polysiloxanes . Preferably, the silanizing agents used can be trimethoxyoctylsilane [(CH₃O)_S-Si-CsHi₇], octamethyl- cyclotetrasiloxane or hexamethyldisilazane . Since the stability of the dispersion according to the invention is lower, as a rule, in the case of surface-modified titanium dioxide than in the case of unmodified titanium dioxide, the latter is given precedence.

The BET surface area of the titanium dioxide present in the dispersion according to the invention is restricted to values of 20 to 400 m²/g. In the case of pyrogenic titanium dioxide, the BET surface area can preferably be 30 to 150 m²/g, values of 40 to 60 m²/g or of 80 to 100 m²/g being particularly advantageous.

Furthermore, the dispersion according to the invention has a mean diameter (number-based) of the titanium dioxide particles in the dispersion of preferably less than 1 μm, particularly preferably of 50 to 500 nm and very particularly preferably of 70 to 300 nm. Values below 50 nm can only be realized technically with difficulty and do not have any more advantages in use. In the presence of non- aggregated particles the mean diameter is the mean diameter of the individual particles, in the case of aggregated particles the diameter of the aggregates. The content of titanium dioxide in the dispersion according to the invention is 5 to 50% by weight, based on the total amount of the dispersion. Dispersions according to the invention which have a titanium dioxide content of 10 to 30% by weight as a rule show a better stability than more highly filled dispersions and are therefore preferred. Dispersions containing less than 5% by weight of titanium dioxide are not economical on account of the high water content .

The weight ratio polycarboxylate ether/titanium dioxide is not limited. As a rule, values in the dispersion according to the invention of 0.01 to 100 are advantageous and values of 0.05 - 5 are particularly advantageous.

The pH of the dispersion according to the invention can vary within wide limits. As a rule, the pH can be between 2 and 12.

Furthermore, bases or acids can be added to the dispersion according to the invention. As bases, it is possible to employ, for example, ammonia, ammonium hydroxide, tetramethylammonium hydroxide, primary, secondary or tertiary organic amines, sodium hydroxide solution or potassium hydroxide solution. As acids, it is possible to employ, for example, phosphoric acid, sulfuric acid, hydrochloric acid, nitric acid or carboxylic acids.

The dispersion according to the invention can contain a copolymer having the structural groups a) , b) , c) , preferably having the structural groups a) , b) , c) , and d) . Here, the proportion of the structural group a) is 25 to 95 mol%, of the structural group b) 1 to 48.9 mol%, of the structural group c) 0 to 5 mol% and of the structural group d) 0 to 47.9 mol%. In particular the proportion of the structural group a) is 51 to 95 mol% and of the structural group c) is 0.1 to 5 mol% .

The first structural group a) is a mono- or dicarboxylic acid derivative having the general formula Ia, Ib or Ic dar .

COX

CH₂ - CR¹ - - CH₂ — C — - CH₂ - - C - CH₂

COX CH₂ O = C C = O \ / COX Y

Ia Ib Ic

In the monocarboxylic acid derivative Ia, R¹ is hydrogen or an aliphatic hydrocarbon radical having 1 to 20 C atoms, preferably a methyl group. X in the structures Ia and Ib is -0M_a and/or -0- (C_mH_2mO) _n-R² or -NH- (C_mH_2mO) _n-R² having the following meaning for M, a, m, n and R²: M is hydrogen, a mono- or divalent metal cation, ammonium, an organic amine radical and a = ^ or 1, depending on whether M is a mono- or divalent cation. As organic amine radicals, substituted ammonium groups are preferably employed which are derived from primary, secondary or tertiary Ci-20-alkylamines, Ci-20-alkanolamines, C5-8- cycloalkylamines and Cs-i-j-arylamines . Examples of the corresponding amines are methylamine, dimethylamine, trimethylamine, ethanolamine, diethanolamine, triethanol- amine, methyldiethanolamine, cyclohexylamine, dicyclohexyl- amine, phenylamine, diphenylamine in the protonated (ammonium) form.

R² is hydrogen, an aliphatic hydrocarbon radical having 1 to 20 C atoms, a cycloaliphatic hydrocarbon radical having 5 to 8 C atoms, an aryl radical having 6 to 14 C atoms, which can optionally also be substituted, m can be = 2 to 4 and n = 0 to 20. The aliphatic hydrocarbons can in this case be linear or branched and saturated or unsaturated. Preferred cycloalkyl radicals are to be regarded as cyclopentyl or cyclohexyl radicals, preferred aryl radicals as phenyl or naphthyl radicals, which in particular can also be substituted by hydroxyl, carboxyl or sulfonic acid groups.

Instead of or in addition to the dicarboxylic acid derivative according to formula Ib, the structural group a) (mono- or dicarboxylic acid derivative) can also be present in cyclic form corresponding to formula Ic, where Y can be = O (acid anhydride) or NR² (acid imide) having the meaning designated above for R².

The second structural group b) corresponds to formula II

— CH₂ — CR³ —

(CH₂)_P- O -(C_mH_2mO)_n-F ,T2

and is derived from oxyalkylene glycol alkenyl ethers, in which m, n and R² have the meaning designated above. R³ is in turn hydrogen or an aliphatic hydrocarbon radical having 1 to 5 C atoms, which can likewise be linear or branched or alternatively unsaturated, p can assume values between 0 and 3.

Formula II also comprises compounds shown in formula II A

-CH₂-CR³-

(CH₂) p-O- (CH₂) ₄-0- (C₂H₄O) _n'-R²

HA where

R³ is hydrogen or an aliphatic hydrocarbon radical having 1 to 5 C atoms, p is 0 to 3, R² is hydrogen, an aliphatic hydrocarbon radical having 1 to 20 C atoms, a cycloaliphatic hydrocarbon radical having 5 to 8 C atoms, an optionally substituted aryl radical having 6 to 14 C atoms n' is a value from 0 to 190.

According to the preferred embodiments, in the formula Ia, Ib and II m is = 2 and/or 3, so that the groups are polyalkylene oxide groups which are derived from polyethylene oxide and/or polypropylene oxide. In a further preferred embodiment, p in formula II is 0 or 1, i.e. they are vinyl and/or alkyl polyalkoxylates .

The third structural group c) corresponds to the formula IHa or IHb

R⁴ R² R²

— CH — C — — CH — CH CH — CH —

S T (CH₂)_Z V (CH₂)_Z

Ilia 1Mb

In formula IHa, R⁴ can be = H or CH₃, depending on whether acrylic or methacrylic acid derivatives are concerned. S can in this case be -H, -COOM_a or -COOR⁵, where a and M have the abovementioned meaning and R⁵ can be an aliphatic hydrocarbon radical having 3 to 20 C atoms, a cycloaliphatic hydrocarbon radical having 5 to 8 C atoms or an aryl radical having 6 to 14 C atoms. The aliphatic hydrocarbon radical can likewise be linear or branched, saturated or unsaturated. The preferred cycloaliphatic hydrocarbon radicals are in turn cyclopentyl or cyclohexyl radicals and the preferred aryl radicals phenyl or naphthyl radicals. If T = -COOR⁵, S is = COOM_a or -COOR⁵. For the case where T and S are = COOR⁵, the corresponding structural groups are derived from the dicarboxylic acid esters.

In addition to these ester structural units, the structural groups c) can also have other hydrophobic structural elements. These include the polypropylene oxide or polypropylene oxide-polyethylene oxide derivative where

T = — U¹ — (CH — CH₂ — O )_x — (CH₂ — CH₂ — O)_y — R⁶ CH₃

x here assumes a value from 1 to 150 and y from 0 to 15. The polypropylene oxide (-polyethylene oxide) derivatives can in this case be linked via a group U¹ containing the ethyl radical of the structural group c) corresponding to formula Ilia, where U¹ can be = -CO-NH-, -0- or -CH₂-O-. These are the corresponding amide, vinyl or allyl ethers of the structural group corresponding to formula Ilia. R⁶ can in this case in turn be R (for meaning of R see above) or

where U can be = -NH-CO-, -0-, or -OCH₂- and S has the meaning described above. These compounds are polypropylene oxide (-polyethylene oxide) derivatives of the bifunctional alkenyl compounds corresponding to formula Ilia.

As a further hydrophobic structural element, the compounds corresponding to formula Ilia can contain polydimethyl- siloxane groups, which in the formula scheme Ilia corresponds to T = -W-R⁷.

W in this case is

(below called a polydimethylsiloxane group) , R⁷ can be = R^z and r can in this case assume values from 2 to 100.

The polydimethylsiloxane group can not only be bonded directly to the ethylene radical as in formula Ilia, but also via the groups

pn ΓMU /pμ ¹I I w P⁷ nr PO fϊ iTH ϊ W Q⁷

where R⁷ is preferably = R² and s can be = 1 or 2 and z = 0 to 4. R⁷ can moreover also be

— [(CH₂)₃ — NH]₅- CO— C=CH or -(CH₂J₁-O-CO-C = CH

R⁴ S R⁴ S

The corresponding difunctional ethylene compounds corresponding to the formula Ilia are concerned here, which are linked to one another via the corresponding amide or ester groups and where only one ethylene group has been copolymerized.

The situation is similar with the compounds as in formula IHa having T = (CH₂)_Z-V-(CH₂)_Z-CH=CH-R², where z = 0 to 4, V can be either a polydimethylsiloxane radical W or an -0- CO-C6H4-CO-O- radical and R² has the meaning indicated above. These compounds are derived from the corresponding dialkenylphenyldicarboxylic acid esters or dialkenyl- polydimethylsiloxane derivatives .

In the context of the present invention, it is also possible that not only one, but both ethylene groups of the difunctional ethylene compounds have been copolymerized. This corresponds essentially to the structural groups corresponding to the formula IHb

R R

— CH — CH CH — CH —

(CH₂)z V (CH₂)_Z IHb

where R , V and z have the meaning already described.

The fourth structural group d) is derived from an unsaturated dicarboxylic acid derivative of the general formula IVa and/or IVb having the meaning indicated above for a, M, X and Y.

_CH CH _CH CH

COOMa COX c^ _/C^

O Y O

IVa _lVb

Preferably, the copolymers contain 55 to 75 mol% of structural groups of the formula Ia and/or Ib, 19.5 to 39.5 mol% of structural groups of the formula II, 0.5 to 2 mol% of structural groups of the formula Ilia and/or IHb and 5 to 20 mol% of structural groups of the formula IVa and/or IVb.

According to a preferred embodiment, the copolymers according to the invention additionally contain up to 50 mol%, in particular up to 20 mol%, based on the sum of the structural groups a to d, of structures which are based, inter alia, on monomers based on vinyl- or (meth) acrylic acid derivatives such as styrene, methylstyrene, vinyl acetate, vinyl propionate, ethylene, propylene, isobutene, hydroxyalkyl (meth) acrylates, acrylamide, methacrylamide, N-vinylpyrrolidone, allylsulfonic acid, methallylsulfonic acid, vinylsulfonic acid, vinylphosphonic acid, AMPS, methyl methacrylate, methyl acrylate, butyl acrylate, allylhexyl acrylate.

The number of repeating structural units in the copolymers is not restricted. It has proven particularly advantageous, however, to set mean molecular weights of 1000 to 100 000 g/mol .

The copolymers can be prepared in various ways. It is essential here that 51 to 95 mol% of an unsaturated mono- or dicarboxylic acid derivative, 1 to 48.9 mol% of an oxyalkylene alkenyl ether, 0.1 to 5 mol% of a vinylic polyalkylene glycol, polysiloxane or ester compound and 0 to 55 mol% of a dicarboxylic acid derivative are polymerized with the aid of a free radical starter.

Unsaturated mono- or dicarboxylic acid derivatives employed which form the structural groups of the formula Ia, Ib or Ic are preferably: acrylic acid, methacrylic acid, itaconic acid, itaconic anhydride, itaconic acid imide and itaconic acid monoamide.

Instead of acrylic acid, methacrylic acid, itaconic acid and itaconic acid monoamide, their mono- or divalent metal salts, preferably sodium, potassium, calcium or ammonium salts, are used.

Acrylic, methacrylic or itaconic acid esters used are especially derivatives whose alcoholic component is a polyalkylene glycol of the general formula HO- (C_mH_2mO) _n~R² where R² = H, an aliphatic hydrocarbon radical having 1 to 20 C atoms, a cycloaliphatic hydrocarbon radical having 5 to 8 C atoms, an optionally substituted aryl radical having 6 to 14 C atoms, and m = 2 to 4 and n = 0 to 200.

The preferred substituents on the aryl radical are -OH, -COO- or -SO3- groups.

The unsaturated monocarboxylic acid derivatives can only be present as monoesters, while in the case of the dicarboxylic acid itaconic acid diester derivatives are also possible.

The derivatives of the formula Ia, Ib and Ic can also be present as a mixture of esterified and free acids and are used in an amount of preferably 55 to 75 mol%.

The second component for the preparation of the copolymers according to the invention is an oxyalkylene glycol alkenyl ether, which is preferably employed in an amount of 19.5 to 39.5 mol%. In the preferred oxyalkylene glycol alkenyl ethers corresponding to the formula V

CH₂ = CR³ - (CH₂)_P - O - (C_mH_2mO)_n - R² V

R³ is = H or an aliphatic hydrocarbon radical having 1 to 5 C atoms and p = 0 to 3. R², m and n have the meaning already mentioned above. The use of polyethylene glycol monovinyl ether (p = 0 and m = 2) has proven particularly advantageous here, n preferably having values between 1 and 50. The third component employed for the introduction of the structural group c) is preferably 0.5 to 2 mol% of a vinylic polyalkylene glycol, polysiloxane or ester compound. Preferred vinylic polyalkylene glycol compounds used are derivatives corresponding to the formula VI,

CH = C — R⁴

S U¹ — (CH — CH₂ — O)_x — (CH₂ — CH₂ — O)_y — R⁶ Vl CH₃

where S can preferably be -H, or COOM_a and U¹ = -CO-NH-, -0- or -CH₂O-, i.e. they are the acid amide, vinyl or allyl ethers of the corresponding polypropylene glycol or polypropylene glycol-polyethylene glycol derivatives. The values for x are 1 to 150 and for y = 0 to 15. R⁶ can either in turn be R¹ or

— CH₂ — CH — U² — C = CH

R⁴ R⁴ s ,

where U² = -NH-CO-, -0- and -OCH₂- and S is = -COOM_a and preferably -H.

If R⁶ = R² and R² is preferably H, the polypropylene glycol (-polyethylene glycol) monoamides or ethers of the corresponding acrylic (S = H, R⁴ = H) , methacrylic (S = H, R⁴ = CH₃) or maleic acid (S = COOM_a, R⁴ = H) derivatives are concerned. Examples of such monomers are maleic acid N- (methylpolypropylene glycol) monoamide, maleic acid N- (methoxypolypropylene glycol-polyethylene glycol) monoamide, polypropylene glycol vinyl ether and polypropylene glycol allyl ether.

If R⁶ ≠ R², bifunctional vinyl compounds are concerned whose polypropylene glycol- (polyethylene glycol) derivatives are bonded to one another via amide or ether groups (-0- or -OCH₂-) . Examples of such compounds are polypropylene glycol bismaleamic acid, polypropylene glycol diacrylamide, polypropylene glycol dimethacrylamide, polypropylene glycol divinyl ether, polypropylene glycol diallyl ether.

As a preferred vinylic polysiloxane compound, derivatives corresponding to the formula VII are used,

R⁴

CH₂ = C VII W-R⁷

where R⁴ = - H and CH₃,

W

and r = 2 to 100 and R⁷ is preferably = R¹. Examples of such monomers are monovinylpolydimethylsiloxanes .

As further vinylic polysiloxane compound, suitable derivatives are those corresponding to the formula VIII,

R"

CH₂ = C VIII

CO — [NH — (CH₂)₃]_S — W — R⁷

where s can be = 1 or 2 , R⁴ and W have the abovementioned meaning and R⁷ can be either = R² or el se

— [(CHz)₃ — NH]₃ — CO — C = CH

R⁴ S and S is preferably hydrogen.

Examples of such monomers having a vinyl function (R⁷ = R²) are polydimethylsiloxanepropylmaleamic acid or polydimethylsiloxanedipropyleneaminomaleamic acid. If R⁷ ≠ R , they are divinyl compounds such as, for example, polydimethylsiloxane-bis (propylmaleamic acid) or polydimethylsiloxane-bis (dipropyleneaminomaleamic acid) .

As a further vinylic polysiloxane compound, a preferred derivative corresponding to the formula IX is suitable:

R⁴

CH₂ = C IX CO — O — (CH₂)_Z — W— R⁷

where z can be 0 to 4 and R⁴ or W have the abovementioned meaning. R⁷ can be either R² or else

— (CH₂)_Z — O — CO — C = CH

R⁴ S r

S preferably being hydrogen. Examples of such monovinylic compounds (R⁷ = R¹) are polydimethylsiloxane- (l-propyl-3- acrylate) or polydimethylsiloxane- (l-propyl-3- methacrylate) .

If R⁷ ≠ R², they are divinyl compounds such as, for example, polydimethylsiloxane-bis (l-propyl-3-acrylate) or polydimethylsiloxane-bis (l-propyl-3-methacrylate) .

As a vinylic ester compound in the context of the present invention, derivatives corresponding to the formula X are preferably employed,

CH = CH

S I CIOOR^{5 χ} where S is = COOM_a or -COOR⁵ and R⁵ can be an aliphatic hydrocarbon radical having 3 to 20 C atoms, a cycloaliphatic hydrocarbon radical having 5 to 8 C atoms and an aryl radical having 6 to 14 C atoms, a and M have the abovementioned meaning. Examples of such ester compounds are di-n-butyl maleate or fumarate or mono-n- butyl maleate or fumarate.

In addition, compounds corresponding to the formula XI can also be employed

xi

where z in turn can be 0 to 4 and R² has the meaning already known. V can in this case be W (that is a polydimethylsiloxane group) , which corresponds to a dialkenylpolydimethylsiloxane compound such as, for example, divinylpolydimethylsiloxane . Alternatively to this, V can also be -O-CO-C6H4-CO-O-. These compounds are dialkenylphthalic acid derivatives. A typical example of such phthalic acid derivatives is diallyl phthalate.

The molecular weights of the compounds which form structural group c) can be varied within wide limits and are preferably between 150 and 10 000.

The fourth component which can be used for the preparation of the copolymers is preferably 5 to 20 mol% of an unsaturated dicarboxylic acid derivative (XII):

MaOOC - CH = CH - COX XII

having the meaning already indicated for a, M and X.

If X = 0M_a, the unsaturated dicarboxylic acid derivative is derived from maleic acid, fumaric acid, mono- or divalent metals salts of these dicarboxylic acids, such as the sodium, potassium, calcium or ammonium salt or salts with an organic amine radical. Moreover, monomers used which form the unit Ia are polyalkylene glycol monoesters of the abovementioned acids having the general formula XIII:

MaOOC — CH = CH — COO — (C_mH_2mO)_n — R²

having the meaning already indicated for a, m, n and R².

The fourth component can also be derived from the unsaturated dicarboxylic acid anhydrides and imides of the general formula XIV (5 to 20 mol%)

CH = CH

Y '

having the meaning indicated above for Y.

According to the invention, according to a preferred embodiment additionally up to 50, preferably up to 20 mol% of further monomers as described above based on the sum of the structural groups a) to d) are employed.

The dispersion according to the invention can furthermore contain a copolymer whose basis is an oxyalkenyl glycol alkenyl ether and the copolymer contains the structural groups a) , b) and c) . Here, the content of structural group a) is 10 to 90 mol%, of structural group b) 1 to 89 mol%, of structural group c) 0 to 5 mol% and of structural group d) 0.1 to 10 mol%.

The first structural group a) is an unsaturated dicarboxylic acid derivative corresponding to the formula IVa or IVb. - CH CH - CH CH

COO₃M COX ^ ^c _\ ^ ^c ^.

O Y O

IVa IVb

In the dicarboxylic acid derivative corresponding to formula Id, M is = hydrogen, a mono- or divalent metal cation, ammonium ion, an organic amine radical, and a = 1, or if M is a divalent cation, 1/2. There then results, together with a group likewise comprising M_a where a = 1/2, a bridge via M, which only exists theoretically as M_a where a = 1/2.

As a mono- or divalent metal cation, sodium, potassium, calcium or magnesium ions are preferably used. Organic amine radicals employed are preferably substituted ammonium groups which are derived from primary, secondary or tertiary Ci- to C2o-alkylamines, C_x- to C2o-alkanolamines, C₅- to Cs-cycloalkylamines and Cβ~ to Ci₄-arylamines . Examples of corresponding amines are methylamine, dimethyl- amine, trimethylamine, ethanolamine, diethanolamine, tri- ethanolamine, cyclohexylamine, dicyclohexylamine, phenyl- amine, diphenylamine in the protonated (ammonium) form. Moreover, X is likewise -0M_a or -0-(Cr₁H_2nO)_n-R¹ where R¹ = H, an aliphatic hydrocarbon radical having 1 to 20 C atoms, a cycloaliphatic hydrocarbon radical having 5 to 8 C atoms, an aryl radical having 6 to 14 C atoms, which can optionally also be substituted, m = 2 to 4 and n = 0 to 200. The aliphatic hydrocarbon radicals can in this case be linear or branched and saturated or alternatively unsaturated.

Preferred cycloalkyl radicals are to be regarded as cyclo- pentyl or cyclohexyl radicals, preferred aryl radicals as phenyl or naphthyl radicals, which can in particular also be substituted by hydroxyl, carboxyl or sulfonic acid groups. Alternatively to this, X can additionally be -NHR and/or -NR² ₂, which corresponds to the mono- or disubstituted monoamides of the corresponding unsaturated dicarboxylic acid, where R² can in turn be identical to R¹ or instead can be -CO-NH₂.

Instead of the dicarboxylic acid derivative corresponding to formula IVa, the structural group a) (dicarboxylic acid derivative) can also be present in cyclic form corresponding to the formula IVb, where Y can be = 0 (= acid anhydride) or NR² (acid imide) and R² has the meaning designated above.

In the second structural group corresponding to the formula II,

— CH₂ — CR' —

I Ii

(CH₂)p — O — (C_mH_2mO)_n— R¹

which is derived from the oxyalkylene glycol alkenyl ethers, R³ is in turn hydrogen or an aliphatic hydrocarbon radical having 1 to 5 C atoms (which can likewise be linear or branched or alternatively unsaturated) . p can assume values between 0 and 3 and R , m and n have the abovementioned meaning. According to a preferred embodiment, in formula H p = O and m is = 2 or 3, so that these are structural groups which are derived from polyethylene oxide or polypropylene oxide vinyl ethers.

Formula II also comprises compounds shown in formula II A

-CH₂-CR³-

(CH₂) p-O- (CH₂)₄-O- (C₂H₄O) n_'-R²

where

R³ is hydrogen or an aliphatic hydrocarbon radical having 1 to 5 C atoms, p i s 0 to 3 ,

R² is hydrogen, an aliphatic hydrocarbon radical having 1 to 20 C atoms, a cycloaliphatic hydrocarbon radical having 5 to 8 C atoms, an optionally substituted aryl radical having 6 to 14 C atoms n' is a value from 0 to 190.

The third structural group c) corresponds to the formula IHa or IHb

R⁴ R² R²

— CH — C — — CH — CH CH — CH —

S T (CH₂)_Z V (CH₂)_Z

Ilia 1Mb

In formula IHa, R⁴ can be = H or CH₃, depending on whether acrylic or methacrylic acid derivatives are concerned. S can in this case be -H, COOM_a or -COOR⁵, where a and M have the abovementioned meaning and R⁵ can be an aliphatic hydrocarbon radical having 3 to 20 C atoms, a cycloaliphatic hydrocarbon radical having 5 to 8 C atoms or an aryl radical having 6 to 14 C atoms. The aliphatic hydrocarbon radical can likewise be linear or branched, saturated or unsaturated. The preferred cycloaliphatic hydrocarbon radicals are in turn cyclopentyl or cyclohexyl radicals and the preferred aryl radicals phenyl or naphthyl radicals. If T = -COOR⁵, S is = COOM_a or -COOR⁵. If T and S are = COOR⁵, the corresponding structural groups are derived from the dicarboxylic acid esters.

In addition to these ester structural units, the structural groups c) can also have other hydrophobic structural elements. These include the polypropylene oxide or polypropylene oxide-polyethylene oxide derivatives where T = — U¹ — (CH — CH₂ — O )_x — (CH₂ — CH₂ — O)_y — R⁶

CH₃ x in this case assumes a value from 1 to 150 and y from 0 to 15. The polypropylene oxide (-polyethylene oxide) derivatives can in this case be linked via a group U¹ to the ethyl radical of the structural group c) corresponding to formula Ilia, where U¹ can be = -CO-NH-, -0- or -CH₂-O-. In this case, these are the corresponding amide, vinyl or allyl ethers of the structural groups corresponding to formula Ilia. R⁶ can in this case in turn be R¹ (for meaning of R¹ see above) or

— CH₂ — CH — U² — C = CH R⁴ R⁴ S

where U² can be = -NH-CO-, -0- or -OCH₂- and S has the meaning described above. These compounds are polypropylene oxide (-polyethylene oxide) derivatives of the bifunctional alkenyl compounds corresponding to formula Ilia.

W in this case is

(called a polydimethylsiloxane group below) , R⁷ can be = R¹ and r can in this case assume values from 2 to 100.

In particular the proportion of structural groups of the formula Ilia or IHb is 0.1 to 10 mol%. The polydimethylsiloxane group W can be bonded not only directly to the ethylene radical as in formula Ilia, but also via the groups

— CO — [NH - (CH₂)₃]_S — W — R⁷ or — CO — O (CH₂), — VV - R⁷,

where R⁷ preferably i s = R¹ and s can be = 1 or 2 and z can be = 0 to 4 .

R⁷ can moreover additional ly be

- [(CH₂J₃ - NH]₃ - CO — C = CH or - (CH₂J₁ -O - CO - C = CH

R⁴ S R⁴ S Here, the corresponding difunctional ethylene compounds corresponding to the formula Ilia are concerned, which are linked to one another via the corresponding amide or ester groups and where only one ethylene group has been copolymerized.

The situation is also similar with the compounds as in formula IHa having T = -(CH₂)_Z-V-(CH₂)_Z-CH=CH-R¹, where z = 0 to 4, V can either be a polydimethylsiloxane radical W or an -O-CO-C6H4-CO-O- radical and R¹ has the meaning indicated above. These compounds are derived from the corresponding dialkenylphenyldicarboxylic acid esters or dialkenyl- polydimethylsiloxane derivatives .

It is also possible within the context of the present invention that not only one, but both ethylene groups of the difunctional ethylene compounds have been copolymerized. This corresponds essentially to the structural groups corresponding to the formula IHb

R¹ R¹

— CH — CH CH — CH —

(CH₂)z V (CH₂)_Z

INb where R¹, V and z have the meaning already described.

Preferably, these copolymers consist of 40 to 55 mol% of structural groups of the formula IVa and/or IVb, 40 to 55 mol% of structural groups of the formula II and 1 to 5 mol% of structural groups of the formula Ilia or IHb. According to a preferred embodiment, the copolymers additionally contain up to 50 mol%, in particular up to 20 mol%, based on the sum of the structural groups a) , b) and c) , of structural groups whose monomer is a vinyl, acrylic acid or methacrylic acid derivative.

The monomeric vinyl derivatives are preferably derived from a compound which is selected from the group styrene, ethylene, propylene, isobutene or vinyl acetate. As a preferred monomeric acrylic acid derivative, the additional structural groups are in particular derived from acrylic acid or methyl acrylate. A preferred monomeric methacrylic acid derivative is to be regarded as methacrylic acid, methyl methacrylate and hydroxyethyl methacrylate .

The number of repeating structural elements of the copolymers is not restricted here, but it has proven particularly advantageous to adjust the number of the structural elements such that the copolymers have an average molecular weight of 1000 to 200 000.

The second component of the copolymers is an oxyalkylene glycol alkenyl ether, which is preferably employed in an amount of 40 to 55 mol%. In the preferred oxyalkylene glycol alkenyl ethers corresponding to the formula V CH₂=CR³-(CH2)p-O-(C_mH_2mO)n-R¹

V

R³ is = H or an aliphatic hydrocarbon radical having 1 to 5 C atoms and p is = 0 to 3. R¹, m and n have the meaning already mentioned above. The use of polyethylene glycol monovinyl ether (p = 0 and m = 2) has proven particularly advantageous here, n preferably having values between 2 and 15.

As the third component essential to the invention for the introduction of the structural groups c) , 1 to 5 mol% of a vinylic polyalkylene glycol, polysiloxane or ester compound is preferably employed. As a preferred vinylic polyalkylene glycol compound, derivatives corresponding to the formula VI are employed,

Vl

where S can preferably be -H or COOM_a and U¹ = -CO-NH-, -0- or -CH₂O-, i.e. the acid amide, vinyl or allyl ethers of the corresponding polypropylene glycol or polypropylene glycol-polyethylene glycol derivatives are concerned.

The values for x are 1 to 150 and for y = 0 to 15. R⁶ can in turn either be R¹ or

C₁H

where

U² is = -NH-CO-, -0- and -OCH₂- and S is = -C00M_a and preferably -H.

If R⁶ = R¹ and R¹ preferably = H, these are the polypropylene glycol (-polyethylene glycol) monoamides or ethers of the corresponding acrylic (S = H, R⁴ = H) , methacrylic (S = H, R⁴ = CH₃) or maleic acid (S = C00M_a, R⁴ = H) derivatives. Examples of such monomers are maleic acid N- (methylpolypropylene glycol) monoamide, maleic acid N- (methoxypolypropylene glycol-polyethylene glycol) monoamide, polypropylene glycol vinyl ether and polypropylene glycol allyl ether.

If R⁶ ≠ R¹, these are bifunctional vinyl compounds, whose polypropylene glycol- (polyethylene glycol) derivatives are bonded to one another via amide or ether groups (-0- or - OCH₂-) . Examples of such compounds are polypropylene glycol-bismaleamic acid, polypropylene glycol diacrylamide, polypropylene glycol dimethacrylamide, polypropylene glycol divinyl ether, polypropylene glycol diallyl ether.

VII

where R = -H and CH₃,

W=

As a further vinylic polysiloxane compound, suitable derivatives are those corresponding to the formula VIII,

where s can be = 1 or 2, R and W have the abovementioned meaning and R⁷ can either be = R¹ or else

and S is preferably hydrogen.

Examples of such monomers having a vinyl function (R⁷ = R¹) are polydimethylsiloxanepropylmaleamic acid or polydimethylsiloxanedipropyleneaminomaleamic acid. If R⁷ ≠ R¹, they are divinyl compounds such as, for example, polydimethylsiloxane-bis (propylmaleamic acid) or polydimethylsiloxane-bis (dipropyleneaminomaleamic acid) .

As a further vinylic polysiloxane compound, a suitable preferred derivative is one corresponding to the formula

R⁴

CH₂ = C

CO-O-(CH₂)_Z -W-R⁷

IX

where z can be 0 to 4 and R⁴ or W have the abovementioned meaning. R⁷ can either be R¹ or else

where S is preferably hydrogen. Examples of such monovinylic compounds (R⁷ = R¹) are polydimethylsiloxane- (l-propyl-3-acrylate) or polydimethylsiloxane- (l-propyl-3- methacrylate) .

If R⁷ ≠ R¹, these are divinyl compounds, such as, for example, polydimethylsiloxane-bis (l-propyl-3-acrylate) or polydimethylsiloxane-bis (l-propyl-3-methacrylate) . As a vinylic ester compound, in the context of the present invention derivatives corresponding to the formula X are preferably employed,

CH = CH S COOR⁵

X

where S is = COOM_a or -COOR⁵ and R⁵ can be an aliphatic hydrocarbon radical having 3 to 20 C atoms, a cycloaliphatic hydrocarbon radical having 5 to 8 C atoms and an aryl radical having 6 to 14 C atoms, a and M have the abovementioned meaning. Examples of such ester compounds are di-n-butyl maleate or fumarate or mono-n- butyl maleate or fumarate.

In addition, compounds corresponding to the formula XI can also be employed,

CH = CH CH = CH R¹ (CH₂)z-V-(CH₂)z - (CH₂)z R¹

Xl

where z can in turn be 0 to 4 and R¹ has the meaning already known. V can in this case be W (that is a polydimethylsiloxane group) , which corresponds to a dialkenylpolydimethylsiloxane compound, such as, for example, divinylpolydimethylsiloxane . Alternatively to this, V can also be-O-CO-C6H₄-CO-O- . These compounds are dialkenylphthalic acid derivatives. A typical example of such phthalic acid derivatives is diallyl phthalate.

The molecular weights of the compounds which form the structural group c) can be varied within wide limits and are preferably between 150 and 10 000.

Furthermore, additionally up to 50 mol%, in particular up to 20 mol%, based on the monomers having the structural groups as in the formulae II, III and IV of a vinyl, acrylic acid or methacrylic acid derivative can be copolymerized. As a monomeric vinyl derivative, styrene, ethylene, propylene, isobutene or vinyl acetate is preferably used, as a monomeric acrylic acid derivative acrylic acid or methyl acrylate is preferably employed, while as a monomeric methacrylic acid derivative finally methacrylic acid, methyl methacrylate and hydroxyethyl methacrylate are preferably used.

The aforementioned copolymers are disclosed in EP-A-736553 The dispersion according to the invention can furthermore contain a copolymer whose basis is an oxyalkenyl glycol (meth) acrylic acid ester and the copolymer contains the following structural groups:

5-98% by weight of a monomer of the type (a) (alkoxy) polyalkylene glycol mono (meth) acrylic ester of the general formula XV

XV

in which

R¹ is a hydrogen atom or the methyl group,

R²O is one type or a mixture of two or more types of an oxyalkylene group having 2-4 carbon atoms, with the proviso that two or more types of the mixture can be added either in the form of a block or in random form,

R³ is a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, and m is a value which is the average number of the added moles of oxyalkylene groups, m being an integer in the range from 1 to 200.

95 to 2% by weight of a monomer of the (meth) acrylic acid type (b) of the general formula XVI

CH₂ == CC₁-R⁴

COOM¹ XVI

in which

R⁴ is a hydrogen atom or the methyl group, and M¹ is a hydrogen atom, a monovalent metal atom, a divalent metal atom, an ammonium group or an organic amine group,

- and 0 to 50% by weight of another monomer (c) , which is copolymerizable with these monomers, with the proviso that the total amount of (a) , (b) and (c) is 100% by weight.

Typical monomers (a) are: hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, polyethylene glycol mono (meth) acrylate, polypropylene glycol mono (meth) acrylate, polybutylene glycol mono (meth) acrylate, polyethylene glycol-polypropylene glycol mono (meth) acrylate, polyethylene glycol-polybutylene glycol mono (meth) acrylate, polypropylene glycol-polybutylene glycol mono (meth) acrylate, polyethylene glycol-polypropylene glycol-polybutylene glycol mono (meth) acrylate, methoxypolyethylene glycol mono (meth) acrylate, methoxypolypropylene glycol mono (meth) acrylate, methoxypolybutylene glycol mono (meth) acrylate, methoxypolyethylene glycol-polypropylene glycol mono (meth) acrylate, methoxypolyethylene glycol-polybutylene glycol mono (meth) acrylate, methoxypolypropylene glycol-polybutylene glycol mono (meth) acrylate, methoxypolyethylene glycol-polypropylene glycol- polybutylene glycol mono (meth) acrylate, ethoxypolyethylene glycol mono (meth) acrylate, ethoxypolypropylene glycol mono (meth) acrylate, ethoxypolybutylene glycol mono (meth) acrylate, ethoxypolyethylene glycol-polypropylene glycol mono (meth) acrylate, ethoxypolyethylene glycol-polybutylene glycol mono (meth) acrylate, ethoxypolypropylene glycol-polybutylene glycol mono (meth) acrylate and/or ethoxypolyethylene glycol-polypropylene glycol-polybutylene glycol mono (meth) acrylate .

Typical monomers (b) are: acrylic acid and methacrylic acid, mono- and divalent metal salts, ammonium salts and/or organic amine salts thereof.

Typical monomers (c) are: esters of aliphatic alcohols having 1 to 20 C atoms with (meth) acrylic acid; unsaturated dicarboxylic acids such as maleic acid, fumaric acid, citraconic acid, mono- and divalent metal salts, ammonium salts and/or organic amine salts thereof; mono- or diesters of unsaturated dicarboxylic acids such as maleic acid, fumaric acid, citraconic acid with aliphatic alcohols of 1 to 20 C atoms, with glycols having 2 to 4 C atoms, with (alkoxy) polyalkylene glycols of 2 to 100 added moles of the aforementioned glycols; unsaturated amides such as (meth) acrylamide and (meth) acrylalkylamide; vinyl esters such as vinyl acetate and vinyl propionate; aromatic vinyl compounds such as styrene; unsaturated sulfonic acids, such as (meth) allylsulfonic acid, sulfoethyl (meth) acrylate, 2-methylpropanesulfonic acid (meth) acrylamide, styrenesulfonic acid, mono- and divalent metal salts, ammonium salts and/or organic amine salts thereof.

A further subject of the invention is a process for the preparation of the dispersion according to the invention, in which a) a polycarboxylate ether in the form of a powder or as an aqueous solution of the polycarboxylate ether is added with stirring to an aqueous starting dispersion of titanium dioxide and the mixture is optionally diluted further with water or b) a titanium dioxide powder is dispersed in an aqueous solution of a polycarboxylate ether by means of a suitable dispersing unit and is subsequently optionally diluted further with water or c) the titanium dioxide powder is dispersed in an aqueous phase, preferably in water, and subsequently the resulting dispersion is added to an aqueous solution of the polycarboxylate ether. The mixing in of the dispersion can in this case be carried out under very low shear energy, for example by means of a propeller stirrer.

The dispersion of the titanium dioxide powder can be carried out at low degrees of filling in equipment which introduces a comparatively low shear energy into the system (e.g. dissolvers, rotor-stator systems). In order to achieve high degrees of filling, shear energies of > 1000 kJ/m³ must be applied in order to obtain a stable dispersion of low viscosity. High shear energies can be achieved, for example, using stirred ball mills, high- pressure homogenizers or planetary kneaders . Optionally, using dispersing units which make available a lower energy input, for example a dissolver, a predispersion can initially be produced.

Suitable dispersing units are understood as meaning those whose energy input suffices to disperse the titanium dioxide powder so that the aggregates have a mean diameter of less than 1 μm.

The dispersion of the titanium dioxide powder can be carried out at low degrees of filling in equipment which introduces a comparatively low shear energy into the system (e.g. dissolvers, rotor-stator systems).

In order to achieve high degrees of filling, shear energies of > 1000 kJ/m³ must be applied in order to obtain a stable dispersion of low viscosity. High shear energies can be achieved, for example, using stirred ball mills, high- pressure homogenizers or planetary kneaders .

In particular, the process disclosed in DE-A-10317066 can be employed.

Furthermore, a process disclosed in WO 2005/063369 can advantageously be employed, in which at least two streams of a predispersion are sprayed to a collision point by means of pumps, preferably high-pressure pumps, through in each case one nozzle into a milling space surrounded by a reactor housing, the milling space being flooded with the predispersion and it being removed from the milling space by means of overpressure of the predispersion flowing back into the milling space. A process which is disclosed in German patent specification DE 10204470 is carried out in a similar manner. Here, at least two streams of a pre- dispersion are sprayed to a collision point by means of pumps, preferably high-pressure pumps, through in each case one nozzle in a reactor space surrounded by a reactor housing and water vapor is introduced into the reactor space through an opening such that in the reactor space a vapor atmosphere prevails which consists predominantly of water vapor, and the finely divided dispersion and vapor and/or partially condensed vapor, which consists mainly of water, are removed from the reactor space by means of overpressure of the entering water vapor on the gas inlet side .

Optionally, using dispersing units which make available a lower energy input, for example a dissolver, a predispersion can initially be produced.

An advantageously employable starting dispersion is obtained by introducing into water an aggregated titanium dioxide powder having a specific surface area of 20 to 150 m /g, at least one amino alcohol having 1 to 6 carbon atoms and at least one carboxylic acid from the group comprising dibasic carboxylic acids and/or hydroxycarboxylic acids having 2 to 6 carbon atoms, producing a predispersion therefrom by energy input of less than 200 kJ/m³ and subsequently by milling the predispersion by means of a high energy mill at a pressure of at least 500 bar producing a dispersion in which the aggregated titanium dioxide powder has a mean, volume-related aggregated diameter of less than 150 nm.

The content of titanium dioxide is at least 20% by weight. The titanium dioxide employed can preferably be a pyrogenically prepared titanium dioxide.

The amino alcohol is preferably present in the dispersion to 2.5 to 7.0 μmol/m² of specific surface area of Tiθ2 and the carboxylic acid to 1.0 to 3.5 μmol/m² of specific surface area of Tiθ2. Values for the amino alcohol of 3.3 to 5.0 μmol/m² of specific surface area of Tiθ2 and 1.5 to 2.5 μmol/m² of specific surface area of Tiθ2 for the carboxylic acid are particularly preferred. Suitable amino alcohols are: monethanolamine, diethanolamine, triethanolamine, monoisopropanolamine, diisopropanolamine, triisopropanolamine, N, N- dimethylisopropanolamine, 3-amino-l-propanol, l-amino-2- propanol and/or 2-amino-2-methyl-l-propanol .

Suitable carboxylic acids are: oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, maleic acid, fumaric acid, lactic acid, malic acid, tartaric acid and/or citric acid.

This starting dispersion is distinguished, in addition to the low aggregate size of the titanium dioxide particles, by its stability and low viscosity. Further dispersions are contained in the still unpublished German patent application having the application number 102004037118.0 of July 30, 2004.

A further subject of the invention is the use of the dispersion according to the invention as a concrete additive .

A further subject of the invention is a cement-containing preparation which contains the dispersion according to the invention .

Preferably, the content of titanium dioxide in the cement- containing preparation is 0.01 to < 2% by weight, based on the cement .

Examples

Analysis: The particle diameter in the dispersion is determined by means of dynamic light scattering, measuring apparatus: Horiba LB-500. The relatively coarsely divided powders P5 and P6 are measured by means of laser diffraction according to ISO 13320-1.

The BET surface area is determined according to DIN 66131. Standard mortar was prepared according to DIN EN 196. The strength was tested according to DIN 1164 on prisms of size 4 x 4 x 16 cm.

Materials employed Pl: Aeroxide^® P25 TiO₂: BET surface area 50 m²/g, content of titanium dioxide > 99.50% by weight.

P2 : titanium dioxide powder according to WO2005/054136, Example A7 : BET surface area 91 m²/g.

P3 : titanium-silicon mixed oxide powder according to DE-A- 102004001520, Example 12: BET surface area 43 m²/g, content of titanium dioxide 49% by weight, content of silicon dioxide 51% by weight.

P4: Aerosil^® 200: BET surface area 200±25 m²/g, content of silicon dioxide > 99.8% by weight P5: TiPure^® R 706, Dupont : BET surface area < 10 m²/g, content of titanium dioxide 93% by weight.

P6: TiOxide^® TR 92, Huntsman: BET surface area < 10 m²/g, content of titanium dioxide 94% by weight.

Polycarboxylate ether (PCE) is prepared according to EP-A- 1189955, Example 2, the amounts being modified such that a 45 percent solution is obtained.

Dispersions

DIa: 299 g of Pl are added to 1 kg of a solution of PCEl in water (concentration 102 g/1 of water) and dispersed using a ball mill.

DIb, Die, Did, D2, D3, D4, D5 and D6 are prepared analogously to DIa using Pl, P2, P3, P4, P5 and P6, but using different amounts of PCEl solution and different powders. D7 contains no titanium dioxide, but only PCE and is not a dispersion. The composition of the dispersions is shown in Table 1. Table 1 : Dispersions

a) for D3: total of TiO₂ and SiO₂ for D4 : Only SiO₂

Preparation of standard mortars Cement: CEM I 52.5 Mergelstetten, temperature 20⁰C. The dispersions according to Table 1 are added to the mortar mixtures. The oxide content and the PCEl content in % by weight, based on the cement weight, are listed in Table 2. Sufficient of the various dispersions was always added such that the initial flow measurement was 24 +/- 1 cm. The amounts necessary for this are likewise listed in Table 2. The water/cement ratio was 0.4 in all experiments.

The results of the strengths measured after 8h are compiled in Table 2.

Starting from the dispersions Dla-d, D2 and D3 according to the invention, marked increases in the early strength are observed compared to the pure superplasticizer D7.

A comparison of DIa and D2 with D5 and D6 clearly shows that a high specific surface area is advantageous if high early strengths are to be achieved. It is surprising, however, that the dispersions containing titanium dioxide DIa and titanium-silicon mixed oxide D3 at the same concentration of the solid based on the binder have comparatively good or even a markedly higher early strength in comparison to D4 (Aerosil^@200) , although the specific surface area of the titanium dioxide-containing particles is markedly lower. Previously, it has been assumed that reactive oxides having the larger specific surface area must show the higher early strength. From this, it can be concluded that in addition to a high specific surface area the titanium dioxide content makes a significant contribution to the increase in the early strength.

A comparison of D3 and D4 in Table 2 also shows a further positive effect of the titanium dioxide content of the particles: at the same high concentration of the reactive solid of 0.5% of the binder, although approximately the same high early strengths are achieved, the superplasticizer requirement is about 30% higher with D4. This means that the workability of the fresh concrete is significantly less affected by reactive particles which contain titanium dioxide than by reactive silicic acids of the same specific surface area. This means a cost saving for the user, since he has to use less superplasticizer

Figure 1 shows the heat development in the cement paste sample article in mW/g of cement in the period of time 0.5- 24 h after addition of the mixing water to the cement. The cement used was CEM I 42.5 Bernburg. DIa is added such that the amount of titanium dioxide is 0.5% by weight, based on the cement employed (curve 1) . The water/cement ratio was constant at 0.5. Comparison was carried out against a sample which contains no titanium dioxide (curve 2) . The heat development is to be attributed to the exothermic reaction of the silicate phases in the cement with water. The maximum in the curve obtained by calorimetry can be correlated with the development of strength in the cement, that is a maximum occurring at an earlier point in time means a development of early strength commencing earlier in the component .

From the results, it can unequivocally be concluded that the use of DIa causes a marked acceleration of cement hydration. The beginning of silicate hydration, and the maximum of the heat development are markedly earlier than in the case of the blank value.

Table 2 : Dispersions^*' and development of early strength of mortar prisms produced therewith

*)D1-D3: according to invention; D4-D7 comparative examples; &) D4 : silicon dioxide; #) mean aggregate diameter (number-related); $) g of dispersion/kg of cement; §) based on binder; a) FTS = flexural tensile strength after 8 h; b) CS = compressive strength after 8 h

Claims

Patent claims :

1. A dispersion which is free of binders and which contains titanium dioxide and at least one water-soluble polycarboxylate ether, wherein — the titanium dioxide has a BET surface area of 20 to 400 m²/g,

- the water-soluble polycarboxylate ether is a copolymer based on at least one oxyalkylene glycol compound and at least one unsaturated monocarboxylic acid derivative or dicarboxylic acid derivative,

- the dispersion has a content of titanium dioxide of 5 to 50% by weight, based on the total amount of the dispersion .

2. The dispersion as claimed in claim 1, wherein the titanium dioxide is a mixed oxide having titanium dioxide as the first component and aluminum oxide, potassium oxide, lithium oxide, sodium oxide, magnesium oxide, calcium oxide, silicon dioxide and/or zirconium dioxide as the second component.

3. The dispersion as claimed in claims 1 or 2, wherein the titanium dioxide is a pyrogenic titanium dioxide.

4. The dispersion as claimed in claim 3, wherein the pyrogenic titanium dioxide has a BET surface area of 30 to 150 m²/g.

5. The dispersion as claimed in claims 1 to 4, wherein the titanium dioxide particles in the dispersion have a mean, number-related diameter of less than 1 μm.

6. The dispersion as claimed in claims 1 to 5, wherein the proportion of titanium dioxide in the dispersion is in total 5 - 50% by weight, based on the total amount of the dispersion.

7. The dispersion as claimed in claims 1 to 6, wherein the weight ratio polycarboxylate ether/titanium dioxide is 0.01 to 100.

8. The dispersion as claimed in claims 1 to 7, wherein the basis of the copolymer is an oxyalkenyl glycol alkenyl ether and the copolymer contains the following structural groups:

a) 25 to 95 mol% of the structural groups of the formula Ia and/or Ib and/or Ic

where

R¹ = hydrogen or an aliphatic hydrocarbon radical having 1 to 20 C atoms

X = - 0M_a, -0- (C_mH_2mO)_n-R², -NH- (C_mH_2mO)_n-R²

M = hydrogen, a mono- or divalent metal cation, ammonium ion, an organic amine radical, a = ^ or 1

R² = hydrogen, an aliphatic hydrocarbon radical having

1 to 20 C atoms, a cycloaliphatic hydrocarbon radical having 5 to 8 C atoms, an optionally substituted aryl radical having 6 to 14 C atoms

Y = O, NR² m = 2 to 4 and n = 0 to 200,

b) 1 to 48.9 mol% of structural groups of the general formula II — CH₂ — CR —

(CH₂)_p-O-(C_mH_2mO)_n-Fr

where

R³ is hydrogen or an aliphatic hydrocarbon radical having 1 to 5 C atoms p is 0 to 3 and

R , m and n have the abovementioned meaning,

0 to 5 mol% of structural groups of the formula Ilia

where S = -H, - COOM_a, - COOR⁵

T = -U¹- (CH (CH3) -CH₂-O)_x- (CH₂-CH₂-COy-R⁶ -W-R⁷

-CO- [NH- (CH₂) ₃] _s-W-R⁷ -CO-O- (CH₂) _Z-W-R⁷ - (CH₂) _Z-V- (CH₂) _Z-CH=CH-R² -COOR⁵ if S = -COOR⁵ or COOM_a

U¹ = -CO-NH-, -0-, -CH₂O- U² = -NH-CO-, -0-, -OCH₂- V = -0-CO-C₆H₄-CO-O - or -W-

R⁴ = H , CH₃

R⁵ = an aliphatic hydrocarbon radical having 3 to 20 carbon atoms, a cycloaliphatic hydrocarbon radical having 5 to 8 C atoms, an aryl radical having 6 to 14 C atoms

r = 2 to 100 s = 1 , 2 z = 0 to 4

X = 1 to 150 y = 0 to 15

and

d) 0 to 47.9 mol of structural groups of the general formula IVa and/or IVb

having the meaning indicated above for a, M, X and Y.

9. The dispersion as claimed in claim 8, wherein the copolymer contains 51 to 95 mol% of the structural groups of the formula Ia and/or Ib and/or Ic and 0.1 to 5 mol% of structural groups of the formula Ilia or IHb.

10. A dispersion as claimed in claims 1 to 7, wherein the basis of the copolymer is an oxyalkenyl glycol alkenyl ether and the copolymer contains the following structural groups:

a) 10 to 90 mol% of structural groups of the formula IVa and/or IVb

-CH CH -CH CH

COO₃M COX ^ ^c _{\ s}" ^c ^.

O Y O

IVa IVb

where

M = hydrogen, a mono- or divalent metal cation, ammonium ion, organic amine radical, a = 1, or for the case where M is a divalent metal cation, is 1/2,

X = likewise -0M_a or

-0-(C_1nH₂TOO)_n-R¹ where R¹ = H, an aliphatic hydrocarbon radical having 1 to 20 C atoms, a cycloaliphatic hydrocarbon radical having 5 to 8 C atoms, an optionally substituted aryl radical having 6 to 14 C atoms, m = 2 to 4, n = 0 to 200,

-NHR² and/or -NR² ₂ where R² = R¹ or -CO-NH₂ and Y = O, NR²

b) 1 to 89 mol% of structural groups of the formula II — CH₂ — CR' —

I Ii

(CH₂)p — O — (C_mH_2mO)_n— R¹ VI in which R = H, an aliphatic hydrocarbon radical having 1 to 5 C atoms p = 0 to 3 and R¹, m, n have the abovementioned meaning and

c) 0 to 10 mol% of structural groups of the formula IHa or IHb

FT R'

-CH- C — — CH — CH CH — CH —

S T (CH₂)_Z V (CH₂)_Z

Ilia 1Mb

where

S = -H, -COOM_a, -COOR⁵

T = — U¹ — (CH — CH₂ — O )_x — (CH₂ — CH₂ — O)_y — R⁶

CH₃

-W-R⁷

-CO- [NH- (CH₂) 3] _s-W-R⁷

-CO-O- (CH₂) _z-W-R⁷

- (CH₂) _Z-V- (CH₂) _Z-CH=CH-R¹

-COOR⁵ if S = -COOR⁵ or C00M_a

U¹ = -CO-NH-, -0-, -CH₂O-

U² = -NH-CO-, -0-, -OCH₂

V = -0-CO-C₆H₄-CO-O- or -W-

W =

R⁴ = H, CH₃ R⁵ = an aliphatic hydrocarbon radical having 3 to 20 C atoms, a cycloaliphatic hydrocarbon radical having 5 to 8 C atoms, an aryl radical having 6 to 14 C atoms

R⁷ = R¹, -(CH₂)_z-O-CO-C = CH

R⁴ S

r = 2 to 100; s = l, 2; z = 0 to 4 x = 1 to 150; y = 0 to 15.

11. The dispersion as claimed in claim 10, wherein the copolymer contains 0.1 to 10 mol% of structural groups of the formula IHa or IHb.

12. A dispersion as claimed in claims 1 to 7, wherein the basis of the copolymer is an oxyalkenyl glycol

(meth) acrylic acid ester and the copolymer contains the following structural groups:

5-98% by weight of a monomer of the type (a)

(alkoxy) polyalkylene glycol mono (meth) acrylic ester of the general formula XV

CH₂ =C - R¹ COO(R²O)_mR³ XV in which R¹ is a hydrogen atom or the methyl group,

R³ is a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, and

m is a number which is the average number of the added moles of oxyalkylene groups, m being an integer in the range from 1 to 200.

CH₂ = C - R⁴ XVI

COOM¹ in which

and 0 to 50% by weight of another monomer (c) which is copolymerizable with these monomers, with the proviso that the total amount of (a) , (b) and (c) is 100% by weight .

13. A process for the preparation of the dispersion as claimed in claims 1 to 12, which comprises

a) adding a polycarboxylate ether in the form of a powder or as an aqueous solution of the polycarboxylate ether with stirring to an aqueous starting dispersion of titanium dioxide and optionally diluting further with water or

b) dispersing a titanium dioxide powder in an aqueous solution of a polycarboxylate ether by means of a suitable dispersing unit and subsequently optionally diluting further with water

or

c) dispersing the titanium dioxide powder in an aqueous phase, preferably in water, and subsequently adding the resulting dispersion to an aqueous solution of the polycarboxylate ether.

14. The use of the dispersion as claimed in claims 1 to 13 as a concrete additive.

15. A cement-containing preparation comprising the dispersion as claimed in claims 1 to 13.

16. The cement-containing preparation as claimed in claim 15, which contains 0.01 to <2 % by weight of titanium dioxide, based on cement.