SILICA WITH REDUCED TRIBO-CHARGE FOR TONER APPLICATIONS

Abstract

Surface-treated fumed silica, with a tribo-electro static charge of −500 μC/g to +500 μC/g, a ratio of the tribo-electro static charge to BET surface area of −3.5 μC/m.sup.2 to +3.5 μC/m.sup.2, a methanol wettability of at least 20% by volume methanol in methanol/water mixture, a ratio of carbon content to BET surface area of at most 0.020 wt. %*g/m.sup.2, a process for its preparation and the use thereof.

Claims

1-15. (canceled)

16. Surface treated fumed silica, comprising: a tribo-electrostatic charge of −500 μC/g to +500 μC/g; a ratio of the tribo-electrostatic charge to BET surface area of −3.5 μC/m.sup.2 to +3.5 μC/m.sup.2; a methanol wettability of at least 20% by volume methanol in a methanol/water mixture; and a ratio of carbon content to BET surface area of at most 0.020 wt. %×g/m.sup.2.

17. The surface treated fumed silica of claim 16, wherein the BET surface area of the silica is 30 m.sup.2/g to 500 m.sup.2/g.

18. The surface treated fumed silica of claim 16, obtained using a surface treatment agent selected from the group consisting of: organosilanes; silazanes; acyclic polysiloxanes; cyclic polysiloxanes; and mixtures thereof.

19. The surface treated fumed silica of claim 16, wherein numerical median particle size d.sub.50 of the silica is less than 10 μm, as determined by static light scattering after 120 s of ultrasonic treatment at 25° C. of a 5% by weight dispersion of the silica in methanol.

20. The surface treated fumed silica of claim 16, wherein the carbon content of the silica is from 0.1% to 5% by weight.

21. The surface treated fumed silica of claim 16, having a loss on drying of less than 0.4% by weight, as determined according to method A of ASTM D280-01.

22. The surface treated fumed silica of claim 16, having a tamped density of silica powder of not more than 250 g/L.

23. The surface treated fumed silica of claim 16, wherein the silica is a silica-based mixed oxide, a silica-based doped oxide, or a mixture thereof comprising at least 50% by weight of silicon dioxide.

24. The surface treated fumed silica of claim 16, wherein the span (d.sub.90−d.sub.10)/d.sub.50 of particle size distribution of the silica is less than 3.0.

25. The surface treated fumed silica of claim 16, wherein the methanol wettability of the silica is 30%-70% by volume methanol in methanol/water mixture.

26. The surface treated fumed silica of claim 18, wherein numerical median particle size d.sub.50 of the silica is less than 10 μm, as determined by static light scattering after 120 s of ultrasonic treatment at 25° C. of a 5% by weight dispersion of the silica in methanol.

27. The surface treated fumed silica of claim 26, wherein the carbon content of the silica is from 0.1% to 5% by weight.

28. The surface treated fumed silica of claim 27, having a loss on drying of less than 0.4% by weight, as determined according to the method A of ASTM D280-01.

29. The surface treated fumed silica of claim 18, wherein the silica is a silica-based mixed oxide, a silica-based doped oxide, or a mixture thereof comprising at least 50% by weight of silicon dioxide.

30. The surface treated fumed silica of claim 18, wherein the methanol wettability of the silica is 30%-70% by volume methanol in methanol/water mixture.

31. A process for producing the surface treated fumed silica of claim 16, comprising the following steps: a) subjecting surface untreated hydrophilic fumed silica with a BET surface area s.sup.1 and a silanol density d.sup.1.sub.SiOH to thermal treatment at a temperature of 300° C. to 1400° C. until the silanol group density d.sup.2.sub.SiOH of the obtained thermally treated silica is reduced by at least 5% of the d.sup.1.sub.SiOH value and the BET surface area s.sup.2 of the obtained thermally treated silica is reduced by at most 30% of the s.sup.1 value; b) surface treating the thermally treated silica obtained in step a) with at least one surface treatment agent selected from the group consisting of: organosilanes; silazanes; acyclic polysiloxanes; cyclic polysiloxanes; and mixtures thereof; c) optionally crushing silica obtained in step a) and/or in step b).

32. The process of claim 31, wherein step a) has a duration of from 2 minutes to 8 hours.

33. The process of claim 31, wherein step a) of the process is conducted in a rotary kiln.

34. A composition comprising the silica of claim 16.

35. The composition of claim 34, wherein the composition is selected from the group consisting of: a toner; a paint; a coating; a silicone; a pharmaceutical or cosmetic preparation; an adhesive; or a sealant.

Description

EXAMPLES

[0141] Analytical Methods

[0142] Tribo-Charge [in ρC/g]

[0143] 50 g of a non-coated ferrite carrier and 0.1 g of the fumed silica were put into a 75-mL glass container, covered with a cap, and shaken for five minutes using a TURBULA® mixer. Subsequently, 0.1 g of the thus prepared mixture was taken out and subjected to nitrogen blowing for 1 minute and measuring the tribo-charge by use of a blow-off static electrometer (TB-200 Model from Toshiba Chemical). The measurement was performed at a temperature of 25° C. and a relative humidity of 55%.

[0144] Methanol wettability [in vol % of methanol in methanol/water mixture] was determined according to the method described in detail, in WO2011/076518 A1, pages 5-6.

[0145] Carbon content [in 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.

[0146] The number of silanol groups relative to BET surface area d.sub.SiOH [silanol density, in SiOH/nm.sup.2] was determined by reaction of the pre-dried samples of silicas with lithium aluminium hydride solution as described in detail on page 8, line 17 thru page 9, line 12 of EP 0725037 A1.

[0147] Loss on drying (LOD, in wt. %) was determined according to ASTM D280-01 (method A).

[0148] 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.

[0149] Preparation of Silicas

Examples 1-3

[0150] Thermal Treatment

[0151] Fumed silica powder AEROSIL® 90 (BET=90 m.sup.2/g, manufacturer: Evonik Resource Efficiency GmbH) was compressed in a roller compactor with a press force of 2 kN/cm. The thus obtained compressed rods were crushed in a screen granulator, and the resulting crushed fragments with a tamped density of about 320 g/L were subjected to thermal treatment in a rotary kiln at 400° C. (example 1), 700° C. (example 2), or 1000° C. (example 3). The mean residence time of the silica in the rotary kiln was in the range 30-60 minutes.

[0152] The obtained coarse particles were milled to obtain powders, which were used for subsequent hydrophobization.

[0153] Surface Treatment

[0154] Hydrophilic silica powder after thermal treatment step (100 g) was put in a reactor. Water (1.0 g) was added at continuous stirring at 25° C. followed by spraying hexamethyldisilazane (HMDS) (10 g) on the silica. The stirring was continued for 120 minutes at 200° C. under the nitrogen gas atmosphere. 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 120° C. in an oven for 3 h to evaporate all the volatiles.

[0155] Physico-chemical properties of the hydrophilic silica after thermal treatment are shown in Table 1. Physico-chemical properties of the corresponding surface treated silica powders are summarized in Table 2 and compared with the commercially available products Aerosil® NX 90 G and Aerosil® NX 90 S, both prepared using the hydrophilic Aerosil® 90 as a precursor and surface treated with HMDS (data based on the product brochure “AEROSIL® Fumed Silica and AEROXIDE® Oxides for Toner Technical Information TI 1222” available online on www.aerosil.com).

[0156] From Table 1 it can be seen, that thermal treatment of silica with a BET surface area of 90 m.sup.2/g at 400-1000° C. for 30-60 minutes led to reducing of the silanol group content d.sub.SiOH by as much as ca. 11-42% while reducing of the BET surface area by only ca. 4-6% as compared to the non-thermally treated starting material (Aerosil® 90).

[0157] It can be seen from Table 2, that thermally treated and hydrophobized with HMDS samples (examples 1-3) provided the materials with tribo-charges in the range −20 . . . −70 uC/g compared with a tribo-charge of about −300 uC/g for the corresponding non-thermally treated and hydrophobized samples (Aerosil® NX 90 G and Aerosil® NX 90 S). Consequently, the ratio of the tribo-charge to BET surface area of the obtained silica materials was with 0.25-0.96 much lower than reported for similar material known from the prior art, e.g. Aerosil® NX 90 G and Aerosil® NX 90 S, see Table 2.

TABLE-US-00001 TABLE 1 Physico-chemical properties of the hydrophilic silica after thermal treatment. reducing reducing of of d.sub.SiOH BET Thermal comparing compared treatment, d.sub.SiOH to AE BET, to AE 90, Example [° C.] [SiOH/nm.sup.2] 90, [%] [m.sup.2/g] [%] AEROSIL ® 90 — 2.18 0 90 0 (AE 90) Example 1 400 1.95 10.6 86 4.4 Example 2 700 1.53 29.8 87 3.3 Example 3 1000 1.27 41.7 85 5.6

TABLE-US-00002 TABLE 2 Physico-chemical properties of the surface treated silica powders. Tribo- methanol Tribo- C-content/ charge/ LOD, BET, wettability, C-content, charge, BET, BET, Example [wt. %] m.sup.2g [vol. %] [wt. %] [uC/g] [wt. % × g/m.sup.2] [uC/m.sup.2] Aerosil ® 90G <0.5 50-80 >40 0.7-1.5 −310 −3.9 . . . −6.2 Aerosil ® 90S <0.5 50-80 >40 0.5-1.5 −300 −3.8 . . . −6.0 Example 1 0.29 73 58 0.88 −70 0.012 −0.96 Example 2 0.09 77 51 0.78 −30 0.010 −0.39 Example 3 0.05 80 44 0.61 −20 0.008 −0.25