SO2 Containing Dispersion With High Salt Stability

Abstract

An aqueous dispersion comprising a surface-modified hydrophilic mixed oxide powder comprising silicon and aluminum and water, characterized in that

a) the surface of the particles has Si and Al atoms and
b) the surface modification has an Si atom bonded to a hydrocarbon radical via a C atom, and
c) the carbon content of the surface-modified mixed oxide powder is 3-25% by weight.

Claims

1-28. (canceled)

29. An aqueous dispersion comprising a surface-modified hydrophilic mixed oxide powder comprising silicon and aluminum, wherein: a) the surface of particles in the powder has Si and Al atoms; b) the surface modification comprises an Si atom bound to a hydrocarbon radical by a C atom; and c) the carbon content of the surface-modified mixed oxide powder is 3-25% by weight.

30. The aqueous dispersion of claim 29, wherein the Si atom which is bound to the hydrocarbon radical by a C atom forms SiOAl bonds, the Al atom being a constituent of the particle surface.

31. The aqueous dispersion of claim 29, wherein the Al.sub.2O.sub.3/SiO.sub.2 weight ratio in the surface-modified mixed oxide powder is 0.1:99.9-5:95.

32. The aqueous dispersion of claim 29, wherein the (Al.sub.2O.sub.3/SiO.sub.2).sub.surface/(Al.sub.2O.sub.3/SiO.sub.2).sub.ttl is 0.1-10.

33. The aqueous dispersion of claim 29, wherein the surface-modified mixed oxide powder is present predominantly or completely in the form of aggregated particles.

34. The aqueous dispersion of claim 29, wherein the surface-modified mixed oxide powder has a median particle diameter d.sub.50 in the aqueous dispersion of 40-200 nm.

35. The aqueous dispersion of claim 29, wherein the hydrocarbon radical bonded to an Si atom by a C atom is interrupted by one or more heteroatoms.

36. The aqueous dispersion of claim 29, wherein the surface modification has the formula Si(CH.sub.2).sub.nY.sub.mR, wherein Si is the Si atom bound to a hydrocarbon radical by a C atom and: n=1, 2 or 3 and m=0 or 1; Y(OCR.sup.1R.sup.2CR.sup.3R.sup.4).sub.o, wherein o=1-30 and R.sup.1, R.sup.2, R.sup.3, R.sup.4=independently of one another H or CH.sub.3; or (OCR.sup.1R.sup.2CR.sup.3R.sup.4CR.sup.5R.sup.6).sub.p, wherein p=1-30 and R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5, R.sup.6=independently of one another H or CH.sub.3, NHCH.sub.2CH.sub.2O, NH(CH.sub.2).sub.2NH(CH.sub.2).sub.2, NH(CH.sub.2).sub.2NH(CH.sub.2).sub.2; R is a radical which does not impart hydrophobic properties or is a mixture of the above mentioned radicals R and Y.

37. The aqueous dispersion of claim 29, wherein the proportion of water is 50-90% by weight and the proportion of surface-modified mixed oxide powder is 10-50% by weight.

38. The aqueous dispersion of claim 29, wherein the pH of the liquid phase of the aqueous dispersion is 8 to 12.

39. A process for producing the aqueous dispersion of claim 29, comprising: a) dispersing in an aqueous solvent a mixed oxide powder comprising silicon and aluminum, which comprises Si atoms and Al atoms each bearing hydroxyl groups on the surface of particles in the powder; and b) subsequently adding an agent for surface modification in which an Si atom is bound to a hydrocarbon radical by a C atom and the Si atom is further bound to one or more hydroxyl groups, alkoxy groups, halide groups or mixtures thereof; c) allowing the mixture to react and optionally separating the hydrolysis product and adjusting pH; wherein the agent for surface modification is added in such an amount as to obtain a carbon content of 3-25% by weight, taking account of the hydroxyl groups, alkoxy groups or halide groups eliminated in the hydrolysis.

40. The process of claim 39, wherein the mixed oxide powder comprising silicon and aluminum is introduced in the form of an aqueous dispersion.

41. The process of claim 39 wherein the mixture is reacted by adjusting the pH to 11 or higher, thermally treating the mixture at a temperature of 50-95 C. over a period of 1-30 minutes, and then optionally adjusting the pH to 8-10.

42. The process of claim 39, wherein a mixed silicon-aluminum oxide powder produced by pyrogenic means is employed.

43. The process of claim 39, wherein the agent for surface modification has the formula X.sub.4-a[Si(CH.sub.2).sub.nY.sub.mR].sub.a, where a=1, 2 or 3; n=1, 2 or 3; m=0 or 1; XH, OH, OCH.sub.3, OC.sub.2H.sub.5, OCH.sub.2CH.sub.2H.sub.3, OCH(CH.sub.3).sub.2; Cl, and R is a radical which does not impart hydrophobic properties or is a mixture of the above mentioned radicals R and Y.

44. The process of claim 43, wherein, in the case where m=1, RH, CH.sub.3, C.sub.2H.sub.5, OH, OCH.sub.3, OC.sub.2H.sub.5, C(O)OCH.sub.3, C(O)OC.sub.2H.sub.5, OC(O)CH.sub.3, OC(O)CH.sub.3, OC(O)CHCH.sub.2, OC(O)CHCH(CH.sub.3), C(O)CH.sub.3, C(O)H, NH.sub.2; or ##STR00004## and in the case where m=0, the aforementioned radicals R are without H, CH.sub.3, C.sub.2H.sub.5.

45. The process of claim 39, wherein the agent for surface modification is selected from the group consisting of: (CH.sub.3O).sub.3Si(CH.sub.2).sub.3OCH.sub.3; (CH.sub.3O).sub.3Si(CH.sub.2).sub.3(OCH.sub.2CH.sub.2).sub.3OCH.sub.3; (CH.sub.3O).sub.3Si(CH.sub.2).sub.3(OCH.sub.2CH.sub.2).sub.6-9OCH.sub.3; (CH.sub.3 O).sub.3Si(CH.sub.2).sub.3(OCH.sub.2CH.sub.2).sub.9-12OCH.sub.3; (CH.sub.3O).sub.3Si(CH.sub.2).sub.3(OCH.sub.2CH.sub.2).sub.21-24OCH.sub.3; and (CH.sub.3CH.sub.2 O).sub.3Si(CH.sub.2).sub.3(OCH.sub.2CH.sub.2).sub.8-12OH.

46. The process of claim 39, wherein the agent for surface modification is selected from the group consisting of: (RO).sub.3Si(CH.sub.2).sub.3NH.sub.2; (RO).sub.3Si(CH.sub.2).sub.3CHCH.sub.2NH.sub.2; (RO).sub.3Si(CH.sub.2).sub.3NH(CH.sub.2).sub.2NH.sub.2; (RO).sub.3Si(CH.sub.2).sub.3NH(CH.sub.2).sub.2NH(CH.sub.2)NH.sub.2; (RO).sub.3Si(CH.sub.2).sub.3N[(CH.sub.2).sub.2NH(CH.sub.2)NH.sub.2].sub.2; and RCH.sub.3, C.sub.2H.sub.5.

47. The process of claim 39, wherein the agent for surface modification is an aqueous composition which bears organopolysiloxanes having glycidyl ether alkyl radicals, acryloyloxyalkyl radicals and/or methacryloyloxyalkyl radicals, with each silicon in the organopolysiloxane bearing a functional group.

48. A surface-modified mixed oxide powder comprising silicon and aluminum obtainable by: a) dispersing in an aqueous solvent a mixed oxide powder comprising silicon and aluminum, which comprises Si atoms and Al atoms each bearing hydroxyl groups on the surface of particles in the powder; and b) subsequently adding an agent for surface modification in which an Si atom is bound to a hydrocarbon radical by a C atom and the Si atom is further bound to one or more hydroxyl groups, alkoxy groups, halide groups or mixtures thereof; c) allowing the mixture to react and optionally separating the hydrolysis product and adjusting pH.

Description

EXAMPLES

[0062] Salt Stability at Elevated Temperature

28.500 g of NaCl, 0.220 g of NaHCO.sub.3, 4.066 g of Na.sub.2SO.sub.4, 1.625 g of CaCl.sub.22 H.sub.2O, 3.162 g of MgCl.sub.26 H.sub.2O, 0.024 g of SrCl.sub.26 H.sub.2O and 0.721 g of KCl are dissolved in 900 g of deionized water (DI water) and the solution made up to 1 liter with DI water.

[0063] 99.5 g of this solution are initially charged into a 125 ml wide-necked bottle made of NALGENE FEP (tetrafluoroethylene-hexafluoropropylene copolymer; Thermo Scientific), 0.5 g of the dispersion under test is added and the mixture is homogenized by shaking. The mixture is stored in a drying cabinet at 60 C. and the occurrence of a precipitate is visually monitored.

Input Materials

[0064] Mixed silicon-aluminum oxide

A: AEROSIL MOX 170, Evonik Industries

[0065] The powder has the following properties:

99% by weight silicon dioxide, 1% by weight aluminum oxide. The BET surface area is 173 m.sup.2/g.
(Al.sub.2O.sub.3/SiO.sub.2).sub.ttl/(Al.sub.2O.sub.3/SiO.sub.2).sub.surface=0.9.
B: In accordance with EP-A-995718, example 1. The powder has the following properties:
99.7% by weight SiO.sub.2, 0.27% by weight Al.sub.2O.sub.3 content. The aluminum oxide content is distributed homogeneously. The BET surface area is 55 m.sup.2/g.

[0066] AERODISP W 7512 S, Evonik Industries, is an acidic, low-viscosity, aqueous silica dispersion having a solids content of 12%. The solid on which it is based is AEROSIL 200, Evonik Industries, a fumed silica having a BET surface area of 200 m.sup.2/g.

[0067] AERODISP W 7520 N, Evonik Industries, is a low-viscosity, aqueous silica dispersion having a solids content of 20% which is stabilized with aqueous sodium hydroxide solution. The solid on which it is based is AEROSIL 200, Evonik Industries, a fumed silica having a BET surface area of 200 m.sup.2/g.

[0068] AERODISP W 630, Evonik Industries, is an aqueous aluminum oxide dispersion having a pH of 3-5 and a solids content of 30%. The solid on which it is based is AEROXIDE Alu C, Evonik Industries, a fumed aluminium oxide having a BET surface area of 100 m.sup.2/g.

[0069] LUDOX SM 30, Grace, is an aqueous, NaOH-stabilized, colloidal silica dispersion having a particle size of 8 nm and an SiO.sub.2 content of 30 wt %.

[0070] LUDOX HS 40, Grace, is an aqueous, NaOH-stabilized, colloidal silica dispersion having a particle size of 12 nm and an SiO.sub.2 content of 40 wt %.

[0071] LUDOX CL, Grace, is an aqueous dispersion of Al-coated, colloidal silica having a particle size of 22 nm. The pH is 3.5-4.5, the solids content 39-43 wt %.

[0072] Agents for Surface Modification

SM1: 2-[methoxy(polyethyleneoxy).sub.6-9propyl]trimethoxysilane
SM2: hydrolysate of 3-glycidyloxypropyltrimethoxysilane according to example 1, EP-A-832911

[0073] Water: deionized water is used; aqueous sodium hydroxide solution: 25% by weight NaOH; hydrochloric acid: 20% by weight HCl

Example 1 (Inventive): Mixed Silicon-Aluminium Oxide A and SM1

Production of a 20 Percent Dispersion of Mixed Silicon-Aluminum Oxide A

[0074] A 100 I stainless steel mixing vessel was initially charged with 37 kg of water. Subsequently, under shear conditions (Ystral Conti-TDS 3 (stator slots: 4 mm ring and 1 mm ring, rotor-stator gap about 1 mm), an initial 10 kg of AEROSIL MOX 170 are aspirated. The remaining 5 kg were aspirated stepwise in amounts of about 1 kg each time. After addition was complete, the mixture was sheared at 3000 rpm for 30 min. To grind any residual proportions of coarse particles this predispersion was passed in two runs through a Sugino Ultimaizer HJP-25050 high-energy mill at a pressure of 2500 bar with diamond nozzles of 0.25 mm in diameter, thus subjecting it to further intensive grinding.

[0075] The median particle diameter d.sub.50 determined by static light scattering (LA-950, Horiba Ltd., Japan) is 112 nm.

[0076] 9.63 g of SM1 are added gradually to 40 g of this dispersion while stirring. There is an initial viscosity increase though this falls again upon further addition. The mixture is then adjusted to pH 11 with aqueous sodium hydroxide solution with stirring and the mixture is heated to 90 C. After 10 minutes at 90 C. the mixture is left to cool to room temperature and the mixture is adjusted to pH 9 with hydrochloric acid.

d.sub.50=121 nm; stability in reference solution at 60 C.: 9 months.

Example 2 (Inventive): Mixed Silicon-Aluminum Oxide B and SM2

[0077] A 20 percent dispersion of mixed silicon-aluminum oxide B is produced according to example 1. The median particle diameter d.sub.50 determined by static light scattering (LA-950, Horiba Ltd., Japan) is 82 nm.

[0078] 6.82 g of DYNALYSAN HYDROSIL 2926 are added slowly to 40 g of this dispersion while stirring. The mixture now has a pH of 2.84. The pH is then adjusted to 11 with sodium hydroxide solution and the mixture heated to 90 C. for 10 min. After cooling, the pH is adjusted to 9 with hydrochloric acid.

d.sub.50=93 nm; stability in reference solution at 60 C.: 1 month

Example 3 (Comparative)

[0079] 11.3 g of SM1 are added slowly with stirring to 67 g of AERODISP W 7512 S. There is an initial viscosity increase though this falls again upon further addition. The mixture is then adjusted to pH 11 with aqueous sodium hydroxide solution with stirring and the mixture is heated to 90 C. After 10 minutes at 90 C. the mixture is cooled and adjusted to pH 9 with hydrochloric acid.

d.sub.50=109 nm; stability in reference solution at 60 C.: 1 day

Example 4 (Comparative)

[0080] 11.3 g of SM1 are added slowly with stirring to 40 g of AERODISP W 7520 N. The mixture is then adjusted to pH 11 with aqueous sodium hydroxide solution with stirring and the mixture is heated to 90 C. After 10 minutes at 90 C. the mixture is cooled and adjusted to pH 9 with hydrochloric acid.

d.sub.50=99 nm; stability in reference solution at 60 C.: 1 day

Example 5 (Comparative)

[0081] 4.3 g of SM1 are added dropwise over 3 hours at 80 C. with stirring to 100 g of a LUDOX 30 SM dispersion diluted with water to 10% by weight. The mixture is stirred at 80 C. for a further 6 hours. Stability in reference solution at 60 C.: 1 day

Example 6 (Comparative)

[0082] 30 g of SM1 are added to 249 g of LUDOX HS 40. The dispersion is heated to 80 C. and stirred at this temperature for 16 hours.

[0083] Stability in reference solution at 60 C.: 1 day

Example 7 (Comparative)

[0084] 26.7 g of LUDOX CL are diluted to 20% with 13.3 g of water. 13.0 g of SM1 are added to this sol slowly and with stirring. The mixture is then adjusted to pH 11 with aqueous sodium hydroxide solution with stirring and the mixture is heated to 90 C. After 10 minutes at 90 C. the mixture is cooled and adjusted to pH 9 with hydrochloric acid.

[0085] Stability in reference solution at 60 C.: 2 days

Example 8 (Comparative)

[0086] 26.7 g of AERODISP W 630 are diluted to 20% with 13.3 g of water. 5.67 g of SM1 are added to this dispersion slowly and with stirring. The pH is then adjusted to 11 with aqueous sodium hydroxide solution with stirring and the mixture heated to 90 C. After 10 minutes at 90 C. the mixture is cooled and adjusted to pH 9 with hydrochloric acid.

[0087] Stability in reference solution at 60 C.: 1 day

[0088] The dispersions according to the invention of examples 1 and 2 exhibit very good salt stability at elevated temperatures. This stability is not present for comparative examples 3-8. Fumed silicas are used in examples 3 and 4, colloidal silica sols in examples 5 and 6, an Al-coated silica sol in example 7 and fumed aluminum oxide in place of the mixed silicon-aluminum oxide powder in example 8.

Example 9 (Inventive): Redispersible Powder

[0089] A dispersion produced according to example 1 is used to generate an easily redispersible powder with the aid of a Mini Spray Dryer B-290 from BCHI Labortechnik GmbH using nitrogen as the hot gas medium: Stirring-in using a magnetic stirrer affords a d.sub.50 of 155 nm, with a dissolver after 5 minutes at 2000 rpm a d.sub.50 of 136 nm and with an ULTRA-TURRAX T 25, IKA-Werke GmbH & CO. KG after a minute at 9000 rpm a d.sub.50 of 130 nm.