SiO2 containing dispersion with high salt stability

Abstract

Dispersion comprising particles of a surface-modified, hydrophilic silica, where A) the particles of the surface-modified, hydrophilic silica comprise an aluminium atom and a hydrocarbon radical, a) the aluminium atom is bonded via an oxygen atom to a silicon atom of the particle surface, b) the hydrocarbon radical comprises a silicon atom which is bonded to a carbon atom of the hydrocarbon radical, c) possess an average particle diameter d.sub.50 in the dispersion of 40-200 nm, preferably 60-150 nm, and B) the pH of the dispersion is 8 or more.

Claims

1. A process for preparing an aqueous dispersion comprising particles of a surface-modified, hydrophilic silica, wherein: a) the particles of the surface-modified, hydrophilic silica comprise an aluminium atom and a hydrocarbon radical, wherein: i) the aluminium atom is bound to a silicon atom of the particle surface via an oxygen atom; ii) the hydrocarbon radical comprises a silicon atom which is bound to a carbon atom of the hydrocarbon radical; and ii) the average particle diameter d.sub.50 in the dispersion is 40-200 nm; and b) the pH of the aqueous dispersion is 8 or higher, and wherein the process comprises the steps: aa) adding silica particles comprising hydroxyl groups on their surface to an aqueous solution of an alkali metal aluminate and allowing the silica particles to react; bb) subsequently adding an agent for surface modification in which a silicon atom is bound to a hydrocarbon radical by a carbon atom and the silicon atom is also bound to one or more hydroxyl groups, alkoxy groups, halide groups or mixtures thereof; and cc) allowing the mixture to react, during which pH may optionally be adjusted and the hydrolysis product may optionally be removed.

2. The process of claim 1, wherein, in step aa), the silica particles are introduced in the form of an aqueous dispersion.

3. The process of claim 1, wherein a mixture formed in step bb) is reacted at a pH of 11 or higher, and the mixture is treated thermally at a temperature of 50-95 C. over a period of 1-30 minutes.

4. The process of claim 1, wherein, in step aa), a mixed SiAl oxide is used in which an Al atom is part of the particle surface and the weight ratio of Al.sub.2O.sub.3/SiO.sub.2 is 0.1:99.9-5:95.

5. The process of claim 1, wherein, in step aa), a potassium-doped silica having a potassium content, calculated as K.sub.2O, of 0.005-5 wt % and having a BET surface area of 100 to 350 m.sup.2/g is used.

6. The process of claim 1, wherein the agent for surface modification in step bb) has the formula: X.sub.4-aSi[(CH.sub.2).sub.nY.sub.mR].sub.a, wherein: a=1, 2 or 3; n=1, 2 or 3; and 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; 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; (OCR.sup.1R.sup.2CR.sup.3R.sup.4CR.sup.5R.sup.6).sub.p, wherein p=1-30, R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5, and R.sup.6=independently of one another H or CH.sub.3; and R is a radical which does not impart hydrophobic properties, or is a mixture of the aforementioned radicals R and Y.

7. The process of claim 6, wherein, if m=1, R is H, 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 ##STR00005## and, if m=0, the aforementioned radicals R are without H, CH.sub.3, C.sub.2H.sub.5.

8. The process of claim 1, wherein the agent for surface modification in step bb) 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.3O).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.2O).sub.3Si(CH.sub.2).sub.3(OCH.sub.2CH.sub.2).sub.8-120H.

9. The process of claim 1, wherein the agent for surface modification in step bb) 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.

10. The process of claim 1, wherein the agent for surface modification in step bb) is an aqueous composition which carries organopolysiloxanes having glycidyl ether alkyl radicals, acryloyloxyalkyl radicals and/or methacryloyloxyalkyl radicals, with each silicon in the organopolysiloxane carrying a functional group.

11. The process of claim 10, wherein, in step bb), an organopolysiloxane is used which was obtained by mixing water-soluble organosilanes of the formula I:
H.sub.2N(CH.sub.2).sub.f(NH).sub.g(CH.sub.2).sub.iSi(CH.sub.3).sub.h(OR).sub.3-h(I), wherein if 0f6, g=0; if f=0, g=1; if f>1, 0i6 and 0h1; and R is a methyl, ethyl, propyl or isopropyl group; with: i) water-soluble organosilanes of the formula II:
XCH.sub.2O(CH.sub.2).sub.3Si(CH.sub.3).sub.h(OR).sub.3-h(II), where 0h1 and R is a methyl, ethyl, propyl or isopropyl radical; and X= ##STR00006## ii) and/or organosilanes of the formula III:
H.sub.2CRCOO(CH.sub.2).sub.3Si(CH.sub.3).sub.h(OR).sub.3-h(III), where 0h1, R is a methyl, ethyl, propyl or isopropyl radical and R is a methyl or hydrogen radical; iii) and non-water-soluble organosilanes of the formula IV:
RSi(CH.sub.3).sub.h(OR).sub.3-h(IV), where 0h1, R is a methyl, ethyl, propyl or isopropyl radical and R is a linear, branched or cyclic hydrocarbon radical having 1 to 8 C atoms; in a molar ratio M=a/(b+c+d), where a is the sum of the number of moles of the organosilanes of formula I, b is the sum of the number of moles of the organosilanes of formula II, and c is the sum of the number of moles of the organosilanes of formula III, and d is the sum of the number of moles of the organosilanes of formula IV, where 0M3 and at least b>0 or c>0.

Description

EXAMPLES

(1) Salt Stability at 60 C.

(2) In 900 g of fully demineralized water (DI water), 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.22H.sub.2O, 3.162 g of MgCl.sub.26H.sub.2O, 0.024 g of SrCl.sub.26H.sub.2O and 0.721 g of KCl are dissolved and the solution is made up to 1 litre with DI water.

(3) 99.5 g of this solution are introduced in a 125 ml wide-necked flask made of NALGENE FEP (tetrafluoroethylene-hexafluoropropylene copolymer; Thermo Scientific), 0.5 g of the dispersion under test is added, and the system is homogenized by shaking. The mixture is stored in a drying cabinet at 60 C. and the incidence of a precipitate is monitored visually.

(4) Substances Used

(5) 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 pyrogenic silica having a BET surface area of 200 m.sup.2/g.

(6) AERODISP W 7520 N, Evonik Industries, is a low-viscosity, aqueous silica dispersion having a solids content of 20%, 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.

(7) AERODISP W 7330 N, Evonik Industries, is an aqueous silica dispersion having a solids content of 30%, stabilized with aqueous sodium hydroxide solution. The solid on which it is based is AEROSIL 130, Evonik Industries, a fumed silica having a BET surface area of 130 m.sup.2/g.

(8) AERODISP W 7320 N, Evonik Industries, is an aqueous silica dispersion having a solids content of 20%, stabilized with aqueous sodium hydroxide solution. The solid on which it is based is AEROSIL 130, Evonik Industries, a fumed silica having a BET surface area of 130 m.sup.2/g.

(9) Dispersion of Potassium-Doped Silica

(10) A 100 l stainless steel batching vessel was charged with 45.0 kg of water. Subsequently, with the aid of the suction hose of the Ystral Conti-TDS 3 (stator slots: 4 mm ring and 1 mm ring, rotor/stator distance about 1 mm), under shearing conditions, 30 kg of potassium-doped silica are introduced under suction. The potassium-doped silica corresponds to Example P1 from WO2008/071462. It has a BET surface area of 216 m.sup.2/g. The K fraction is 0.12 wt %, calculated as K.sub.2O. After the end of the addition, the suction port is closed and shearing is continued at 3000 rpm for 20 minutes. Using 20 kg of water, the dispersion is diluted and a pH of 10.0 is set using aqueous sodium hydroxide solution. This is followed by dilution with water to reach an SiO.sub.2 content of 25 wt %, followed by renewed shearing for about 5 minutes for homogenization.

(11) AERODISP W 630, Evonik Industries, is an aqueous aluminium 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.

(12) Sodium aluminate solution, 10 wt %, produced from anhydrous technical sodium aluminate, Sigma-Aldrich, and DI water. A few minor residual insolubles are removed by filtration.

(13) 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 %.

(14) 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 %.

(15) LUDOX CL, Grace, is an aqueous dispersion of Al-clad, colloidal silica with 22 nm particle size. The pH is 3.5-4.5, the solids content 39-43 wt %.

(16) Agents for Surface Modification

(17) OM1: 2-[Methoxy(polyethyleneoxy).sub.6-9propyl]trimethoxysilane

(18) OM2: Hydrolysate of 3-glycidyloxypropyltrimethoxysilane as per Example 1, EP-A-832911

(19) OM3: DYNASYLAN GLYMO, Evonik Industries

(20) Water: this is fully demineralized (DI) water; aqueous sodium hydroxide solution: 25 wt % NaOH; hydrochloric acid: 20 wt % HCl

Example 1 (Inventive)

(21) A dilute sodium aluminate solution composed of 10 g of DE water and 2.37 g of the filtered sodium aluminate solution is admixed slowly dropwise and with stirring with 40 g of AERODISP W 7320. Following the addition, stirring is continued for 10 minutes more. Then 5.90 g of OM2 are added. The mixture is subsequently heated at 90 C. for 10 minutes and the pH is adjusted to 9 using hydrochloric acid.

(22) 0.064 mg Al/m.sup.2 BET surface area; d.sub.50=128 nm; stability in reference solution at 60 C.: 4 weeks.

Example 2 (Inventive)

(23) 2.19 g of the sodium aluminate solution are added to 10 g of water. Then, dropwise and with stirring, 40 g of AERODISP W 7512 S are added and, after the addition, stirring is continued for 10 minutes. Then 3.1 g of OM3 are added dropwise and the mixture is heated to 90 C. with stirring. After 10 minutes, it is cooled to room temperature and the pH is adjusted to 9 using hydrochloric acid.

(24) 0.064 mg Al/m.sup.2 BET surface area; d.sub.50=109 nm; stability in reference solution at 60 C.: 9 weeks

Example 3 (Inventive)

(25) 2.19 g of the sodium aluminate solution are added to 10 g of water. Then, dropwise and with stirring, 40 g of AERODISP W 7512 S are added and, after the addition, stirring is continued for 10 minutes. Then 6.8 g of OM1 are added dropwise and the mixture is heated to 90 C. with stirring. After 10 minutes, it is cooled to room temperature and the pH is adjusted to 9 using hydrochloric acid.

(26) 0.064 mg Al/m.sup.2 BET surface area; d.sub.50=111 nm; stability in reference solution at 60 C.: 3 months

Example 4 (Inventive)

(27) 3.64 g of the sodium aluminate solution are added to 10 g of water. Then, dropwise and with stirring, 40 g of AERODISP W7520 N are added and, after the addition, stirring is continued for 10 minutes. Then 6.8 g of OM1 are added dropwise and the mixture is heated to 90 C. with stirring. After 10 minutes, it is cooled to room temperature and the pH is adjusted to 9 using hydrochloric acid.

(28) 0.064 mg Al/m.sup.2 BET surface area; d.sub.50=101 nm; stability in reference solution at 60 C.: 4 weeks

Example 5 (Inventive)

(29) 400 g of water are introduced as an initial charge, and 45.5 g of the sodium aluminate solution and 200 g of the dispersion of potassium-doped silica are incorporated with the aid of a dissolver. This is carried out a total of 4 times, giving a total of 182 g of sodium aluminate solution and 800 g of the dispersion. With the last addition there is a sharp rise in the viscosity. Then OM1 is added with stirring, with the dispersion becoming highly fluid again. The dispersion is then heated to 90 C. and the temperature is maintained for 30 minutes. After the dispersion has cooled to room temperature, a pH of 9 is set using hydrochloric acid.

(30) 0.128 mg Al/m.sup.2 BET surface area; d.sub.50=72 nm; stability in reference solution at 60 C.: 4 weeks

Example 6 (Comparative Example)

(31) 1.185 g of the sodium aluminate solution are added to 10 g of water. Then 10 g of AERODISP W 7320 N are added slowly and with stirring. This is followed again by addition of 1.185 g of the sodium aluminate solution and 10 g of AERODISP W 7320 N. This procedure is repeated twice more, giving in total a use of 4.74 g of the sodium aluminate solution and 40 g of AERODISP W 7320 N. The resulting dispersion is subsequently aged at 85 C. for 30 minutes.

(32) Following addition of 7.36 g of OM1, stirring is continued at 85 C. for 15 minutes more. After the dispersion has cooled to room temperature, a pH of 9 is set using hydrochloric acid.

(33) 0.128 mg Al/m.sup.2 BET surface area; d.sub.50=119 nm; stability in reference solution at 60 C.: 1 week

Example 7 (Comparative Example)

(34) 40 g of water are admixed with stirring with 1 g of the sodium aluminate solution and then with 5 g of a silica sol prepared from 20 g of Ludox HS 40 from Grace and 20 g of water. This gradual addition is repeated until a total of 8 g of the sodium aluminate solution and 40 g of the silica sol have been added. The addition of the sodium aluminate solution produces small flakes, which slowly dissolve again after the dispersion is added. Stirring is then continued at 70 C. for 3 hours.

(35) Subsequently 10 g of OM2 are added and the mixture is heated to 90 C. After 10 minutes at 90 C., cooling takes place to room temperature and the pH is adjusted to 9 using hydrochloric acid.

(36) 0.127 mg Al/m.sup.2 BET surface area; stability in reference solution at 60 C.: 3-4 days

Example 8 (Comparative Example)

(37) 67 g of AERODISP W 7512 S are admixed slowly and with stirring with 11.3 g of OM1. To start with there is a rise in viscosity, which drops off again, however, on further addition. Then aqueous sodium hydroxide solution is used to set a pH of 11, with stirring, and the mixture is heated to 90 C. After 10 minutes at 90 C., it is cooled and a pH of 9 is set using hydrochloric acid.

(38) Stability in reference solution at 60 C.: 1 day

Example 9 (Comparative Example)

(39) 40 g of AERODISP W 7520 N are admixed slowly and with stirring with 11.3 g of OM1. Then aqueous sodium hydroxide solution is used to set a pH of 11, with stirring, and the mixture is heated to 90 C. After 10 minutes at 90 C., it is cooled and a pH of 9 is set using hydrochloric acid. Stability in reference solution at 60 C.: 1 day

Example 10 (Comparative Example)

(40) 100 g of a LUDOX 30 SM dispersion diluted with water to 10 wt % are admixed dropwise with stirring with 4.3 g of OM1 over the course of 3 hours at 80 C. Stirring at 80 C. is continued for 6 hours.

(41) Stability in reference solution at 60 C.: 1 day

Example 11 (Comparative Example)

(42) 249 g of LUDOX HS 40 are admixed with 30 g of OM1. The dispersion is heated at 80 C. and stirred at this temperature for 16 hours.

(43) Stability in reference solution at 60 C.: 1 day

Example 12 (Comparative Example)

(44) 26.7 g of LUDOX CL are diluted with 13.3 g of water to 20 wt %. This sol is admixed slowly and with stirring with 13.0 g of OM1. Then aqueous sodium hydroxide solution is used to set a pH of 11, with stirring, and the mixture is heated to 90 C. After 10 minutes at 90 C., it is cooled and a pH of 9 is set using hydrochloric acid.

(45) After two days at 60 C., a cloudy precipitate occurs.

(46) 0.174 Al/m.sup.2 BET surface area (calculated from manufacturer figures)

(47) Stability in reference solution at 60 C.: 2 days

Example 13 (Comparative Example)

(48) 26.7 g of AERODISP W 630 are diluted to 20% with 13.3 g of water. This dispersion is admixed slowly and with stirring with 5.67 g of OM1. Aqueous sodium hydroxide solution is then used to set a pH of 11, with stirring, and the mixture is heated to 90 C. After 10 minutes at 90 C., it is cooled, and a pH of 9 is set using hydrochloric acid.

(49) Stability in reference solution at 60 C.: 1 day

(50) The aqueous dispersions of the invention from Examples 1-4 exhibit very good stability in the reference solution at elevated temperatures. This stability is not the case for Comparative Examples 5-13.