FUMED SILICA WITH MODIFIED SURFACE ACTIVITY

Abstract

Fumed silica powder, surface treated with a surface treatment agent selected from the group consisting of organosilanes, silazanes, acyclic polysiloxanes, cyclic polysiloxanes, and mixtures thereof, wherein the powder has: a) a number of silanol groups relative to BET surface area d.sub.SiOH of at least 0.85 SiOH/nm.sup.2, as determined by reaction with lithium aluminium hydride; b) a methanol wettability of more than 40% by volume of methanol in methanol-water mixture; c) a tamped density of not more than 200 g/L.

Claims

1-15. (canceled)

16. A fumed silica powder that has been surface treated with an agent selected from the group consisting of: organosilanes, silazanes, acyclic polysiloxanes, cyclic polysiloxanes, and mixtures thereof; wherein the fumed silica powder comprises: a) a number of silanol groups relative to BET surface area d.sub.SiOH of at least 0.85 SiOH/nm.sup.2, as determined by reaction with lithium aluminium hydride; b) a methanol wettability of more than 40% by volume of methanol in a methanol-water mixture; c) a tamped density of not more than 200 g/L.

17. The fumed silica powder of claim 16, wherein the fumed silica powder comprises a BET surface area of 30-500 m.sup.2/g.

18. The fumed silica powder of claim 16, wherein the surface treatment agent is selected from the group consisting of: octyltrimethoxysilane, octyltriethoxysilane, hexadecyltrimethoxysilane, hexadecyltriethoxysilane, dimethyldichlorosilane, chloro trimethylsilane, octamethylcyclotetrasiloxane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane, glycidyloxypropyltrimethoxysilane, glycidyloxypropyltriethoxysilane, aminopropyltriethoxysilane, hexamethyldisilazane, polydimethylsiloxanes, and mixtures thereof.

19. The fumed silica powder of claim 16, wherein the fumed silica powder comprises a numerical median particle size d.sub.50 of less than 100 μm.

20. The fumed silica powder of claim 16, wherein the fumed silica powder comprises a carbon content of from 0.5% to 10% by weight.

21. The fumed silica powder of claim 16, wherein the fumed silica powder comprises a number of silicon atoms in the surface treatment agent relative to BET surface area d.sub.[Si] of at least 1.0 [Si atoms]/nm.sup.2.

22. The fumed silica powder of claim 16, wherein the silica has a cumulative pore volume of pores >4 nm determined by a mercury intrusion method according to DIN ISO 15901-1 of at least 8.0 cm.sup.3/g.

23. The fumed silica powder of claim 16, wherein the fumed silica powder comprises a bulk density d.sub.bulk of less than 0.20 g/mL as determined by a mercury intrusion method according to DIN ISO 15901-1 at 0.0031 MPa.

24. The fumed silica powder of claim 16, wherein the fumed silica powder comprises a skeletal density of d.sub.sk of at least 0.50 g/mL, as determined by a mercury intrusion method of DIN ISO 15901-1 at 417 MPa.

25. The fumed silica powder of claim 16, wherein the fumed silica powder comprises a porosity of at least 60% as determined by a mercury intrusion method according to DIN ISO 15901-1 P=(1−d.sub.bulk/d.sub.sk).

26. The fumed silica powder of claim 16, wherein the ratio d.sub.[Si]/d.sub.SiOH is 0.5 to 10.

27. The fumed silica powder of claim 17, wherein the surface treatment agent is selected from the group consisting of: octyltrimethoxysilane, octyltriethoxysilane, hexadecyltrimethoxysilane, hexadecyltriethoxysilane, dimethyldichlorosilane, chloro trimethylsilane, octamethylcyclotetrasiloxane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane, glycidyloxypropyltrimethoxysilane, glycidyloxypropyltriethoxysilane, aminopropyltriethoxysilane, hexamethyldisilazane, polydimethylsiloxanes, and mixtures thereof.

28. The fumed silica powder of claim 27, wherein the fumed silica powder comprises a numerical median particle size d.sub.50 of less than 100 μm.

29. The fumed silica powder of claim 27, wherein the fumed silica powder comprises a carbon content of 0.5% to 10% by weight.

30. The fumed silica powder of claim 29, wherein the fumed silica powder comprises a number of silicon atoms in the surface treatment agent relative to BET surface area d.sub.[Si] of at least 1.0 [Si atoms]/nm.sup.2.

31. The fumed silica powder of claim 29, wherein the silica has a cumulative pore volume of pores >4 nm determined by mercury intrusion method according to DIN ISO 15901-1 of at least 8.0 cm.sup.3/g.

32. The fumed silica powder of claim 29, wherein the fumed silica powder comprises a bulk density d.sub.bulk of less than 0.20 g/mL as determined by the mercury intrusion method according to DIN ISO 15901-1 at 0.0031 MPa.

33. A process for producing the fumed silica powder of claim 16, comprising the following steps: a) subjecting a hydrophilic silica powder with a tamped density of not more than 200 g/L to thermal treatment at a temperature of 300° C. to 1400° C.; b) surface treating the hydrophilic silica powder subjected to thermal treatment in step a) in the presence of a surface treatment agent selected from the group consisting of: organosilanes, silazanes, acyclic polysiloxanes, cyclic polysiloxanes, and mixtures thereof and water; c) optionally crushing or milling the silica after step a) and/or b).

34. A composition comprising the fumed silica powder according of claim 16.

35. The composition of claim 34, wherein the composition is used as a paint, a coating, a silicone, a pharmaceutical, a cosmetic, an adhesive, a sealant, or a toner.

Description

EXAMPLES

[0136] Analytical Methods. Determination/Calculation of Parameters.

[0137] Methanol wettability [vol % of methanol in methanol/water mixture] was determined according to the method described in detail, in WO2011/076518 A1, pages 5-6.

[0138] Carbon content [wt. %] was determined by elemental analysis according to EN ISO3262-20:2000 (Chapter 8). The analysed sample was weighed into a ceramic crucible, provided with combustion additives and heated in an induction furnace under an oxygen flow. The carbon present is oxidized to CO.sub.2. The amount of CO.sub.2 gas is quantified by infrared detectors. SiC is not burned and therefore does not affect the value of the carbon content.

[0139] The number of silanol groups relative to BET surface area d.sub.SiOH [in SiOH/nm.sup.2] was determined by reaction of the pre-dried samples of silica powders with lithium aluminium hydride solution as described in detail on page 8, line 17 thru page 9, line 12 of EP 0725037 A1.

[0140] The number of silicon atoms in the surface treatment agent relative to BET surface area of the silica powder of the present invention d.sub.[Si] [in Si atoms/nm.sup.2] was calculated from the carbon content related to the presence of the surface treatment, and considering the chemical structure of the surface treatment, e.g. the number of carbon atoms per silicon atom of the surface treatment agent (N.sub.C/Si):

d.sub.[Si][Si atoms/nm.sup.2]=(C*[wt. %]×N.sub.A)/(Mr.sub.C [g/mol]×N.sub.C/Si×BET [m.sup.2/g]×10.sup.20)  (3),

wherein Mr.sub.C=12,011 g/mol is an atomic weight of carbon,

[0141] N.sub.A is Avogadro number (˜6.022*10.sup.23).

[0142] N.sub.C/Si is the ratio of carbon to silicon atoms in the surface treatment agent.

[0143] The d.sub.[Si]/d.sub.SiOH ratio was calculated by dividing the number of silicon atoms in the surface treatment agent relative to BET surface area (d.sub.[Si]) by the number of silanol groups relative to BET surface area (d.sub.SiOH).

[0144] Loss on drying (LOD, in wt. %) was determined according to ASTM D280-01 (method A).

[0145] Specific BET surface area [m.sup.2/g] was determined according to DIN 9277:2014 by nitrogen adsorption in accordance with the Brunauer-Emmett-Teller method.

[0146] Preparation of Silica Powders

[0147] Process parameters for preparation of silica powders can be found in Table 1.

[0148] Physicochemical properties of the corresponding silica powders can be found in Table 2.

Comparative Example 1

[0149] A silica powder AEROSIL® R812 hydrophobized with HMDS (BET=172 m.sup.2/g, manufacturer: EVONIK Resource Efficiency GmbH) was used as a reference material.

Comparative Example 2

[0150] A silica powder was prepared according to the (inventive) example of WO 2009/015970 A1 by hydrophobization of a hydrophilic silica with BET=302 m.sup.2/g with HMDS in the presence of water and was used as a reference material.

Comparative Example 3

[0151] Thermal Treatment

[0152] AEROSIL® 300 hydrophilic silica powder (BET=300 m.sup.2/g, manufacturer: EVONIK Resource Efficiency GmbH) was subjected to thermal treatment in an XR 310 chamber kiln from Schröder Industrieöfen GmbH. For this purpose, multiple layers with a bed of height up to 1 cm were subjected to a temperature programme. The temperature ramp was 300 K/h up to the target temperature of 1025° C.; the hold time was 3 hours; then the samples were cooled (without active cooling) until removal.

[0153] Hydrophobization

[0154] Hydrophobization of the thermally treated powder was effected at elevated temperature over the gas phase. For this purpose, hexamethyldisilazane (HMDS, 8.6 wt % relative to the weight of the thermally treated hydrophilic silica powder) as hydrophobizing agent was evaporated. Silica powder was heated in a thin layer to 100° C. in a desiccator and then evacuated. Subsequently, vaporized HMDS was admitted into the desiccator until the pressure had risen to 300 mbar. After the sample had been purged with air, it was removed from the desiccator.

Example 1

[0155] Silica powder of example 1 was prepared similarly to comparative example 3, but for the hydrophobization part, which was conducted as follows:

[0156] Hydrophilic silica powder after sintering step (100 g) was put in a grounded metal bucket and mixed by a propeller mixer at 500 rpm, and water (2.8 g) was sprayed at continuous stirring at 25° C. onto their surface followed by spraying of hexamethyldisilazane (HMDS) (11 g). The mixing was continued for 15 minutes. After this time, the bucket was sealed with a lid containing several holes of 0.5-1 mm diameter for pressure compensation and stored for 6 hours at 145° C. in an oven. After this time, the silica powder was put into a drying pan and dried in a thin layer of up to 1 cm thickness in the nitrogen atmosphere at 145° C. in an oven for 3 h to evaporate the volatiles.

Example 2

[0157] Silica powder of example 2 was prepared similarly to comparative example 3, but for the hydrophobization part, which was conducted as follows:

[0158] Hydrophilic silica powder after sintering step (100 g) was put in a grounded metal bucket and mixed by a propeller mixer at 500 rpm, and water (5.0 g) was sprayed at continuous stirring at 25° C. onto their surface followed by spraying of hexamethyldisilazane (HMDS) (10 g). The mixing was continued for 15 minutes. After this time, the bucket was sealed with a lid containing several holes of 0.5-1 mm diameter for pressure compensation and stored for 6 hours at 145° C. in an oven. After this time, the silica powder was put into a drying pan and dried in a thin layer of up to 1 cm thickness in the nitrogen atmosphere at 145° C. in an oven for 3 h to evaporate the volatiles.

Example 3

[0159] Silica powder of example 3 was prepared similarly to comparative example 3, but for the hydrophobization part, which was conducted as follows:

[0160] Hydrophilic silica powder after sintering step (100 g) was put in a grounded metal bucket and mixed by a propeller mixer at 500 rpm, and water (10 g) was sprayed at continuous stirring at 25° C. onto their surface followed by spraying of hexamethyldisilazane (HMDS) (15 g). The mixing was continued for 15 minutes. After this time, the bucket was sealed with a lid containing several holes of 0.5-1 mm diameter for pressure compensation and stored for 6 hours at 145° C. in an oven. After this time, the silica powder was put into a drying pan and dried in a thin layer of up to 1 cm thickness in the nitrogen atmosphere at 145° C. in an oven for 3 h to evaporate the volatiles.

Example 4

[0161] Silica powder of example 4 was prepared similarly to comparative example 3, but for the hydrophobization part, which was conducted as follows:

[0162] Hydrophilic silica powder after sintering step (100 g) was put in a grounded metal bucket and mixed by a propeller mixer at 500 rpm, and water (10 g) was sprayed at continuous stirring at 25° C. onto their surface followed by spraying of hexamethyldisilazane (HMDS) (9.4 g). The mixing was continued for 15 minutes. After this time, the bucket was sealed with a lid containing several holes of 0.5-1 mm diameter for pressure compensation and stored for 6 hours at 145° C. in an oven. After this time, the silica powder was put into a drying pan and dried in a thin layer of up to 1 cm thickness in the nitrogen atmosphere at 145° C. in an oven for 3 h to evaporate the volatiles.

[0163] The silica powders of comparative examples 1-3 and example 1 were all prepared using the same amount of the surface treatment agent (HMDS) related to the BET surface area of the hydrophilic silica powder (Table 1). In comparative examples 1 and 3, no water was used during the hydrophobization, in comparative example 2 no thermal treatment was performed (Table 1). Examples 1-4 according to the invention differ only in the quantity of HMDS and water applied (Table 1).

[0164] Table 2 summarizes the physicochemical properties of the thus obtained silica powders. The silica powder prepared in comparative example 2 shows a higher d.sub.SiOH number (0.82 SIOH/nm.sup.2) than the silicas in the both comparative examples 1 (0.46 SIOH/nm.sup.2) and 3 (0.16 SIOH/nm.sup.2). However, the d.sub.SiOH number of the silica powders from the inventive examples 1-4 are still substantially higher (0.91-1.23 SIOH/nm.sup.2). The hydrophobicity of silica materials from examples 1-4 are comparable to that of the silica from comparative example 2. Thus, examples 1-4 show silica powders having an increased polarity at similar hydrophobicity when compared to the silica from comparative example 2.

TABLE-US-00001 TABLE 1 Process parameters for preparing silica powders. Si atoms BET before surface in surface Water, Water/Si atoms surface Thermal treatment agent, treatment [wt % in surface treatment, treatment, (wt % related agent/BET related water/BET treatment agent Example [m.sup.2/g] [° C.] to silica)* [μmol/m.sup.2] to silica] [μmol/m.sup.2] [mol/mol] Comparative 300 No HMDS (18) 7.4 0 0 0 example 1 Comparative 300 No HMDS (18) 7.4 4.5 8.33 1.12 example 2 Comparative 185 1025 HMDS (11, in 7.4 0 0 0 example 3 vapour form) Example 1 185 1025 HMDS (11) 7.4 2.8 8.41 1.14 Example 2 185 1025 HMDS (10) 6.7 5.0 15.0 2.24 Example 3 185 1025 HMDS (15) 12.6 10 37.5 2.99 Example 4 185 1025 HMDS (9.4) 9.4 10 37.5 4.78

TABLE-US-00002 TABLE 2 Physico-chemical properties of the silica powders methanol Material LOD, BET, wettability, d.sub.SiOH, C-content, .sub.d[Si], (Example) % m.sup.2/g % [SIOH/nm.sup.2] [%] [Si/nm.sup.2] d.sub.[Si]/d.sub.SiOH Comparative <0.5 260 55 0.46 2.5 1.61 3.5 example 1 Comparative <0.4 220 65 0.82 3.5 2.66 3.1 example 2 Comparative <0.1 190 45 0.16 1.13 0.99 6.2 example 3 Example 1 0.1 148 60 0.90 1.8 1.98 2.2 Example 2 0.1 148 60 0.91 2.0 2.27 2.5 Example 3 0.1 146 65 0.96 2.4 2.72 2.8 Example 4 0.1 150 65 1.23 2.6 2.93 2.4