Metal oxide-containing dispersion with high salt stability

1. An aqueous dispersion containing a hydrophilic metal oxide powder comprising a metal oxide and a surface modification of the metal oxide, wherein:

a) the metal oxide is a mixed aluminum-silicon oxide; and

b) the surface modification comprises:

b1) silicon and Al atoms;

b2) wherein the silicon atoms are at least partly bound to a hydrocarbon radical by a C atom; and

b3) wherein the Al/Si molar ratio of the surface modification is 1:2-1:20;

wherein the surface modification has the formula Si—(CH 2 ) n —Y m —R, wherein Si is the Si atom bonded to a hydrocarbon radical via a C atom, n=1, 2 or 3 and m=0 or 1;

wherein the Al 2 O 3 /SiO 2 weight ratio in the surface-modified metal oxide powder is 0.1:99.9-5:95;

and wherein:

when m=1: R=—H, —CH 3 , —C 2 H 5 , —OH, —OCH 3 , —OC 2 H 5 , —C(═O)OCH 3 , —C(═O)OC 2 H 5 , —O—C(═O)CH 3 , —O—C(═O)CH═CH 2 , —O—C(═O)CH═CH(CH 3 ), —C(═O)CH 3 , —C(═O)H, NH 2 ; or

when m=0: R=—OH, —OCH 3 , —OC 2 H 5 , —C(═O)OCH 3 , —C(═O)OC 2 H 5 , —O—C(═O)CH 3 , —O—C(═O)CH═CH 2 , —O—C(═O)CH═CH(CH 3 ), —C(═O)CH 3 , —C(═O)H, or NH 2 ; and

Y=—(OCR 1 R 2 —CR 3 R 4 ) o —, where o=1-30, and R 1 , R 2 , R 3 , R 4 =independently of one another H or CH 3 , or —(OCR 1 R 2 —CR 3 R 4 —CR 5 R 6 ) p —, where p=1-30, R 1 , R 2 , R 3 , R 4 , R 5 , R 6 =independently of one another H or CH 3 , —NHCH 2 CH 2 O—, —NH(CH 2 ) 2 NH(CH 2 ) 2 —, or —NH(CH 2 ) 2 NH(CH 2 ) 2 —.

2. The aqueous dispersion of claim 1 , wherein the proportion of water is 50-90 wt % and the proportion of surface-modified metal oxide powder is 10-50 wt %.

3. The aqueous dispersion of claim 1 , wherein

Y=—(OCR 1 R 2 —CR 3 R 4 )O—, o=5-15 and R 1 , R 2 , R 3 , R 4 =H.

4. The aqueous dispersion of claim 3 , wherein the proportion of water is 50-90 wt % and the proportion of surface-modified metal oxide powder is 10-50 wt %.

5. The aqueous dispersion of claim 1 , wherein no more than 100 ppm of dispersants are present.

6. The aqueous dispersion of claim 1 , wherein the Al 2 O 3 /SiO 2 weight ratio in the surface-modified metal oxide powder is in the range 0.2:99.8-3:97.

7. The aqueous dispersion of claim 1 , wherein the dispersion has a median particle diameter d 50 of 40-200 nm.

8. A surface-modified mixed aluminum-silicon oxide powder,

wherein:

a) the Al 2 O 3 /SiO 2 weight ratio is 0.1:99.9-5:95;

b) the surface modification:

b1) comprises silicon atoms and aluminum atoms;

b2) comprises the formula Si—(CH 2 ) n —Y m —R, wherein Si is the Si atom bonded to a hydrocarbon radical via a C atom, n=1, 2 or 3 and m=0 or 1; and

b3) comprises an Al/Si molar ratio of 1:2-1:20; and wherein:

when m=1: R=—H, —CH 3 , —C 2 H 5 , —OH, —OCH 3 , —OC 2 H 5 , —C(═O)OCH 3 , —C(═O)OC 2 H 5 , —O—C(═O)CH 3 , —O—C(═O)CH═CH 2 , —O—C(═O)CH═CH(CH 3 ), —C(═O)CH 3 , —C(═O)H, NH 2 , or

when m=0: R=—OH, —OCH 3 , —OC 2 H 5 , —C(═O)OCH 3 , —C(═O)OC 2 H 5 , —O—C(═O)CH 3 , —O—C(═O)CH═CH 2 , —O—C(═O)CH═CH(CH 3 ), —C(═O)CH 3 , —C(═O)H, or NH 2 ; and

Y=—(OCR 1 R 2 —CR 3 R 4 )O—, where o=1-30, and R 1 , R 2 , R 3 , R 4 =independently of one another H or CH 3 , or —(OCR 1 R 2 —CR 3 R 4 —CR 5 R 6 ) p —, where p=1-30, R 1 , R 2 , R 3 , R 4 , R 5 , R 6 =independently of one another H or CH 3 , —NHCH 2 CH 2 O—, —NH(CH 2 ) 2 NH(CH 2 ) 2 —, or —NH(CH 2 ) 2 NH(CH 2 ) 2 —.

9. The surface-modified mixed aluminum-silicon oxide powder of claim 8 , wherein Y=—(OCR 1 R 2 —CR 3 R 4 ) o —, o=5-15 and R 1 , R 2 , R 3 , R 4 =H.

10. The surface-modified mixed aluminum-silicon oxide powder of claim 8 , wherein the Al 2 O 3 /SiO 2 weight ratio in the surface-modified metal oxide powder is 0.2:99.8-3:97.

11. A process for producing the aqueous dispersion of claim 1 , comprising: dispersing in an aqueous solvent a powder comprising mixed aluminum-silicon oxides and having hydroxyl groups at the surface of particles in the powder; subsequently adding a surface modifying agent; reacting the mixture; and optionally removing the hydrolysis product, wherein the surface modifying agent is obtained by mixing:

a) a compound with the structure of X 4-a [Si—(CH 2 ) n —Y m —R] a with

b) at least one metal compound selected from the group consisting of aluminum alkoxides, aluminum acetylacetonates, and sodium aluminate;

wherein

a=1, 2 or 3;

n=1, 2 or 3;

m=0 or 1, wherein:

when m=1: R=—H, —CH, —C 2 H 5 , —OH, —OCH, —OC 2 H 5 , —C(═O)OCH 3 , —C(═O)OC 2 H 5 , —O—C(═O)CH 3 , —O—C(═O)CH═CH 2 , —O—C(═O)CH═CH(CH 3 ), —C(═O)CH 3 , —C(═O)H, NH 2 ; or

and

when m=0: R=—OH, —OCH, —OC 2 H 5 , —C(═O)OCH 3 , —C(═O)OC 2 H 5 , —O—C(═O)CH 3 , —O—C(═O)CH═CH 2 , —O—C(═O)CH═CH(CH 3 ), —C(═O)CH 3 , —C(═O)H, or NH 2 ; and

Y=—(OCR 1 R 2 —CR 3 R 4 ) o —, where o=1-30, and R 1 , R 2 , R 3 , R 4 =independently of one another H or CH, or —(OCR 1 R 2 —CR 3 R 4 —CR 5 R 6 ) p —, where p=1-30, R 1 , R 2 , R 3 , R 4 , R 5 , R 6 =independently of one another H or CH 3 , —NHCH 2 CH 2 O—, —NH(CH 2 ) 2 NH(CH 2 ) 2 —, or —NH(CH 2 ) 2 NH(CH 2 ) 2 —.

12. The process of claim 11 , wherein Y=—(OCR 1 R 2 —CR 3 R 4 ) o —, o=5-15 and R 1 , R 2 , R 3 , R 4 =H.

13. The process of claim 11 , wherein the metal oxide powder is introduced in the form of an aqueous dispersion.

14. The process of claim 11 , wherein the process comprises reacting the mixture by adjusting the pH to 11 or higher, subjecting the mixture to thermal treatment at a temperature of 50-95° C. over a period of 1-30 minutes and then optionally adjusting the pH to 8-10.

15. The process of claim 11 , wherein a metal oxide powder produced by pyrogenic means is employed.

16. The process of claim 11 , wherein X is selected from the group consisting of H, OH, OCH 3 , OC 2 H 5 , OCH 2 CH 2 H 3 , OCH(CH 3 ) 2 , and Cl.