CA2201186C

CA2201186C - Partially hydrophobic precipitated silicas

Info

Publication number: CA2201186C
Application number: CA002201186A
Authority: CA
Inventors: Karl Meier; Anja Ramb; Heinz-Gunter Lux; Astrid Muller; Rolf Oelmuller
Original assignee: Degussa Huels AG
Current assignee: Evonik Operations GmbH
Priority date: 1996-03-29
Filing date: 1997-03-27
Publication date: 2000-10-10
Anticipated expiration: 2017-03-27
Also published as: BR9701582A; MY116875A; HUP9700681A2; ES2128186T3; IL120548A0; TR199700241A2; JP4440397B2; EP0798348B1; NO971450D0; JP4440493B2; ID18471A; BG101361A; TW374077B; DE19713316A1; IN191468B; AU1658097A; NO971450L; EP0798348A1; JP2002020112A; RU2140871C1

Abstract

Partially hydrophobic precipitated silica with a methanol crosslinking potential of 10-49% is new. When anhydrous, the silica has a DBP absorption > 250 g/100 g. The average particle size is 1-12 µm and the silica has a carbon content of 0.3-1.85 %, and when dried, it loses 2.6-10 % of its weight. It has a pH of 5.5-10. The silica is prepared by mixing a silica suspension (which has been prepared using known methods) with a material that gives the silica hydrophobic properties. The mixing takes place for a very short time at conditions of low pH and high shear. The resulting suspension is filtered and washed in salt-free conditions, and the filter cake is dried, thermally treated and powdered.

Description

Partially Hydrophobic Precipitated Silicas The invention relates to partially hydrophobic silicas, a process for their preparation, their use as carrier for hydrolysis-sensitive active substances and their use in defoaming agents.
The use of hydrophobic silicas in a hydrophobic liquid for the preparation of a defoaming agent is known (DE-C
2829906); US-A 4377 493; DE-C 3411 759; US-A 4344 858;
Kalman Koczo et al., Journal of Colloid and Interface Science 166, 225-238 (1994), WO 95/05880).
Known defoaming agents consist of a mixture of non-polar oils and hydrophobic particles. The solids content is typically 1-20%. These mixtures are more effective defoaming agents than the oil or the hydrophobic particles alone. Defoaming agents are used in the textile, paper, paint, coating and detergent industries.
Known crop protection agents are substantially used in the form of wettable powders, as dust concentrates, dispersible granulates or as emulsifiable concentrates.
Known wettable powders (WP) consist of the following components:
Pesticide active substance, carrier, dispersing and wetting agents as well as optionally additional additives.
Thorough premixing of these constituents is followed by coarse milling succeeded by fine milling. Use is in the form of an aqueous spray.
Known dust concentrates consist solely of active substance and filler. Formulation is by analogy with the formulation of wettable powders. Fine milling is, however, often omitted.
The dust are applied as dust (DP) after blending with mineral fillers such as kaolin, talcum or dolomite.

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DecJussa Aktiengesellschaft, D-60311 Frankfurt Known dispersible granulates (WG) are solid formulations consisting of pesticide active substance, carrier, _ dispersing and wetting agent as well as optionally other additives. This mixture is finely milled and then granulated using known methods. Use takes the form of aqueous sprays.
Known emulsifiable concentrates (EC) are liquid and contain solvent-containing constituents. Attempts are made to replace the emulsifiable concentrates by solid formulations to avoid solvents that can pose a burden to the environment.
The use of hydrophilic precipitated silica as carrier in the preparation of crop protection agents, pest control agents or concentrated cattle feedstuffs is known (DE-B 16 19 865). The silicas conventionally used have a high oil uptake and a high absorption capacity.
The reduced storage stability of the active substances is, however, a disadvantage in the use of the known precipitated hydrophilic silicas in the preparation of agents containing active substances that are sensitive to hydrolysis. This applies in particular to active substances used in crop protection which could hitherto only be further processed as emulsifiable concentrates because of their sensitivity to hydrolysis.
Known hydrophobic precipitated silicas, such as for example the precipitated silicas according to DE 26 28975 C2, DE-C 27 29 244, DE-A 24 35 860, EP-A 492 124, DE-A 25 13 608, are fully hydrophobised and therefore have the disadvantage of needing a large amount of wetting agent in the formulation.
It is therefore an object to provide a carrier for, in particular, hydrolysis-sensitive active substances, such as crop protection agents or feedstuffs as well as active substances from the chemical industry which ensures a longer storage stability of the active substance.
When defoaming agents are used, the known silica has the disadvantage that this silica sediments out when the defoaming agent is stored for longer periods, in particular with the use of low-viscous oils and a low solids content. The defoaming activity deteriorates because of sedimentation of the known silica. Moreover, the sedimented silica also has to be stirred up again in a laborious process before the defoaming agent is used.
To prevent a tendency to sedimentation, it may be necessary to add a dispersing agent to the defoaming mixture, such as for example a pyrogenic silica, as well as the known silica (Degussa Technical Bulletin Pigments No. 42, page 11). This necessitates a change in the defoaming formulation which, in turn, necessitates further testing, makes the product more expensive and means an additional process step to work in the dispersing agent.
It is, for example, known from DE 28 29 906 C3 that the defoaming active substances may be prepared in such a manner as to achieve a high dispersion stability by adding to a mixture of a defoaming oil and an emulsifier first the hydrophobic and then the requisite amount of hydrophilic silica, with further stirring.
The instant invention has the advantage over this in that the silica can be stirred into a defoaming oil in one process step and then dispersed, thereby obtaining a stable defoaming dispersion without an additional process step.
The object of the invention is a partially hydrophobic precipitated silica which is characterised by a methanol wettability of 10 to 49 ~. The precipitated silica of the invention has a DBP-uptake (dried substance) of greater than 250g/100g (DBP number) and a mean particle size of 1-12 dun.

The partially hydrophobic precipitated silica of the invention has a carbon content of 0.3 to 1.85 $, preferably of 0.5 to 1.5 ~ and/or a pH value of 5.5 to 10 and/or a loss on drying of 2.6 to 10 ~, preferably of 3 to In particular, the partially hydrophobic precipitated silica of the invention can have one or several of the following physical chemical characteristic values:
Surface (BET), m2/g 75 - 250 Tamped density, g/1 70 - 150 (DIN ISO 787/11) Loss on drying 2h/105C,~ 2.6 10.0 -(DIN ISO 787/2) Loss at red heat related to 2h/105C 2.5 7.5 -dried substance, ~

(DIN ISO 3262/11) pH value, 5 % (methanol-aqueous soln.) 5.5 10 -(DIN ISO 787/9) Conductivity (methanol-aqueous soln.) <_ 600 (~tS/cm) DBP uptake, dried substance, g/100 g >_ 250 Methanol wettability, titrated, ~ 10 - 49 Mean particle size, Coulter counter, E,tm 1 -Carbon content, ~ 0'.3 1.85 -Si02, ~ (DIN ISO 3262/19) ~ 98 The silica may be a precipitated silica which has been treated with a water-repellent agent after its production and/or also during its production in order to obtain the above-described characteristics.
Precipitated silicas are known from Ullmanns Enzyklopadie der technischen Chemie, 4th edition, volume 21, pages 458 to 473 (1988).

' 5 The production of fully hydrophobic silicas is, for example, known from DE 44 19 234 A1, DE-C 27 29 244, DE 26 28 975 C2 and DE-OS 21 07 082.
DE 26 28 975 C2 and DE-C 27 29 244 relate to fully hydrophobic precipitated silicas. The two other patent specifications or unexamined German publications relate to fully hydrophobic and partially hydrophobic, pyrogenic silicas with different physical chemical characteristics that are not identical with the characteristics of the precipitated silica of the invention.
The use of fully hydrophobic pyrogenic silicas for dusting onto pesticide granulates is described in DE 29 28 585 A1, the use of pyrogenic silicas as additive in active substance formulations is explained in EP 0 111 112 A1.
The partially hydrophobic precipitated silica of the invention can consist of 85 to 98 % by weight of precipitated silica and 15 to 2 % by weight of water-repellent agent (silicon oil that can have a carbon content of 32.4 %). To obtain the desired degree of water-repellence, the hydrophobic precipitated silica can be prepared by mixing the requisite amount of a hydrophobic agent with a precipitated silica suspension with very short residence time and low pH value; filtering off the water-repellent agent-containing precipitated silica suspension and washing this free of salt; drying the precipitated silica filter cake homogeneously mixed with water-repellent agent using a known process; providing thermic post-treatment or tempering; and then carrying out mechanical or jet milling.
It is, in particular, possible to mix silicon oil homogeneously using high shearing energy with precipitated silica suspension produced using known processes, with or without addition of phase transmitters (e. g. wetting agents, emulsifiers).

Degussa Aktiengesellschaft, D-60311 Frankfurt ~2~~i$6 The continuous shearing device that.may be used may be an Ultra-Turrax, a Kothoff-Mischsirene or a Rheinhiitte mixer.
The precipitated silica suspension homogeneously mixed with water-repellent agent is then separated using known filtration apparatuses (e. g. chamber filtration press, rotary filter) and the solid matter containing water-repellent agent is washed free of salt. In so doing, the water-repellent agent is entirely taken up by the precipitated silica filter cake. The filtrates yielded are no longer contaminated with organosilicon compounds, with the result that the measured TOC contents are < 10 mg/1.
The precipitated silica suspensions used in the mixing process and the water-repellent agent are characterised by the following physical chemical material data:

Degussa Aktiengesellschaft, D-60311 Frankfurt .~21~~ I~~

Precipitated silica A (the substance data relate to a filtered, washed and dried precipitated silica sample, without added water-repellent agent):
BET surface according to DIN 66131 150~50 [m2/g]
Mean size of primary particles from 15-25 [nm]
EM photos Loss on drying according to DIN 55921 2.5-4.5 [~]
after 2 h at 105°C
Loss at red heat (related to the substance 310.5 [
dried for 2 h at 105°C according to DIN 55921) pH value (in 5~S aqueous dispersion 3.5-6.5 according to DIN 53200) Conductivity (in 4~ aqueous < 1000 [~tS]
dispersion) S03 content (related to the substance 0.3 {
dried for 2h at 105°C according to DIN 55921) Na20 content (related to the substance dried 0.3 [~]
for 2h at 105°C according to DIN 55921) ' Degussa Aktiengesellschaft, D-60311 Frankfurt ~~~1 I 8~

Precipitated silica B (the substance data relate to a filtered, washed and dried precipitated silica, without added water-repellent agent):
BET surface according to DIN 66131 300150 [m2/g]
Mean size of primary particles from 10-15 [nm]
EM pho tos Loss on drying according to DIN 55921 2.5-4.5[$]
after 2 h at 105°C
Loss at red heat (related to the substance 3~0.5 dried for 2h at 105°C according to DIN 55921) pH value (in 5~ aqueous dispersion 3.5-6.5 according to DIN 53200) Conductivity { in 4~ aqueous < 1000 [ ~.~.S ]
dispersion) S03 content (related to the substance dried < 0.3 for 2h at 105°C according to DIN 55921) Na20.content (related to the substance dried < 0.3[~]
for 2h at 105°C according to DIN 55921) For hydrophobizing it is, in particular, possible to use silicon oil, consisting of dimethylpoly siloxanes with a viscosity of 20 to 1000 mPas, preferably with 50 mPas as water-repellent agents. It is also possible to use:
R2R'Si, where R=CH30-, C2H5o-, C1-, R'=CH3-, C2H5-, HMDS
(hexamethyl disilazane), D4 (octamethyl tetrasiloxane), D6, D8, R3Si-CnH2n+1'. where n=1-18, R=CH30-, C2H50-, C3H~-O-, C1-, in particular Si 108 (trimethoxyoctyl silane), Si 116, polymethyl siloxanes, polymethyl siloxane emulsions, (trimethyloxyhexadecyl silane), aminopropyl silanes, vinyl silanes, methacrylic silanes.

Degussa Aktiengesellschaft, D-60311 Frankfurt The resultant precipitated silica filter cake homogeneously mixed with water-repellent agent is dried in the subsequent process step in known drying aggregates.
The drying aggregate for drying the water-repellent agent-containing filter cake can be a band dryer or spin-flash dryer. To achieve the desired degree of water-repellence, the dry product containing water-repellent agent is subjected to thermic post-treatment at 300°C to 400°C, preferably 350°C for 30 to 60 minutes in a discontinuous, electrically heated stirrer container or in a continuous electrically heated double screw reactor thermicly treated or tempered and then milled mechanically or using jet mills.
Compared with the above-described preparation comparable in principle with known processes, the partially hydrophobic precipitated silica of the invention can in particular be prepared according to the following process of wet water-repellence which cannot be deduced from the state of the art:
A mass stream of 0.424 kg/h polymethyl siloxane is added using a continuous mixer with high shearing energy input to a mass stream of 160 kg/h of an aqueous precipitated silica suspension with a solids content of 85 g/l, that was prepared using known manufacturing processes, while maintaining a pH value of 3, the temperature of the two components to be mixed being 25 ~ 5°C. In so doing, the residence time in the mixer may not exceed 5 seconds. The command reference input for the coating process is taken to be the dimensionless coating index Bi which describes the ratio to one another of the active substance portions of the two mass streams to be mixed. A coating index of 32 is needed to achieve the hydrophobic property of the precipitated silica of the invention.
The precipitated silica coated with silicone oil is then separated using known processes without using a subsequent Degussa Aktiengesellschaft, D-60311 Frankfurt post-reaction time, washed almost free of electrolyte, dried at 105°C, tempered for 1.0 hour at 370°C and then milled.

5 It has been found that the silica of the invention can be prepared in the mixer due in particular to the low pH
value and the short residence time in the mixer.
Methanol wettabilit« v:hich is a measure of the :~:ater~
10 repellence, is determined as follows:
1. Basic principles Silicas, the surfaces of which are modified with non-hydrolysable organic groups, are generally not wettened with water. These hydrophobic silicas can, however, be wetted using a methanol/water mixture. The proportion of methanol in this mixture - expressed in percent by weight - is a measure of the water-repellence of the modified silica. The higher the proportion of methanol, the better the substance is hydrophobised. _ 2. Apparatus and reagents A 20 ml measuring pipette with graduation of scale A 250 ml separating funnel Methanol p.a.
3. Method _ 200 mg of the hydrophobic silica and 50 ml water are added to a 250 ml separating funnel. The silica remains on the surface of the water. The tip of the measuring pipette filled with methanol is then immersed in the liquid phase {to prevent direct contact between the silica and the pure methanol) and the methanol is allowed to run in slowly. In so doing, the separating funnel is shaken with a circular movement of the hand so that a vortex arises in the Degussa Aktiengesellschaft, D-60311 Frankfurt liquid. Methanol is added until the solid substance is wetted. This is the case when a) the silica is no longer distributed over the entire surface of the liquid phase (already containing methanol) and the relatively clear, film-free liquid becomes visible.
blthe silica film forming over the phase limiting surface at the wall of the separating funnel disappears.
c) moist silica agglomerates remain adhering to the wall of the separating filter on shaking.
4. Calculation Methanol wettability is given in ~ by weight methanol of the methanol/water mixture according to the formula:
Methanol wettability = 0.79 x 100 0.79 + 50 x = methanol consumption in ml In this method, methanol consumption can differ by 2 ml with the same person and the same sample.
DBP uptake (DBP-number), which is a measure of the absorbency of the precipitated silica, is determined as follows:
1. Basic principles The dibutylphthalate number is determined using a Brabender plastograph. The DBP number is a measure of the liquid absorbency or absorption capacity of a product in powder form. Absorption capacity depends on moisture content, on granulation and initial weight of the material investigated.

Degussa Aktiengesellschaft, D-60311 Frankfurt 2. Apparatus and rea eg nts Brabender plastograph with plotter Multi-Dosimat E 415 (50 1) manufactured by Metrohm Dibutylphthalate 3. Method 12.5 g silica are added to the kneader of the Brabender plastograph. Dibutylphthalate flows into the mixture at a speed of 4 ml/minute with constant mixing (revolution speed of the kneader paddles 125 rpm). Power consumption is low during mixing. Towards the end of the determination the mixture becomes poorly flowing. This fact is documented by a rise in power consumption which is shown on a scale. Addition of DBP is automatically discontinued at a scale reading of 300.
4. Calculation The density of DBP is 1.047 g/ml.
ml DBP~1.047~100 ~ by weight DBP uptake =
12.5 The DBP uptake is related to the anhydrous, dried substance. When using precipitated silicas with higher moisture contents, the value must be corrected using the correction table if these precipitated silicas are not -dried before determining the DBP number. Use of the correction table can lead to clear deviations compared to a determination of dried precipitated silicas.
Correction table for dibutylphthalate uptake - anhydrous -Degussa Aktiengesellachaft, D-60311 Frankfort i (Add correction values corresponding to the water content to the value obtained) ~ Water ~ ~0 ,2 ,4 ,6 ,8 $ Dibutylphthalate Degussa Aktiengesellsclsaft, D-60311 Frankfurt DBP uptake _ Initial weight 12.5 g F = 8.376 ml DBP consumption ,0 ,1 ,2 ,3 ,4 ,5 ,6 ,7 ,8 ,9 ~
DBP
uptake 22 184 185 186 1$7 188 188 189 190 191 192 Determining the particle size lCoulter counter) Application: The determination of particle size (charac-teristic particle size curve) of silicas using the Coulter counter occurs in an aqueous electrolyte solution (isotone II).
Determination method: ._ Degussa Aktiengesellschaft, D-60311 Frankfurt The beakers (2 per count), the magnet and the pipette tips are blown dust-free in a stream of nitrogen at 5-6 bar.
The beakers are then inverted on dust-free lens paper, the magnet and the pipette tips being placed into a petri dish 5 that has also been blown out.
0.100 g of the substance to be examined are weighed on an analytical balance and transferred to the beaker. The magnet is added, first moistened with a little isotonic 10 solution and then filled up to the 60 mi mark with isotope. The suspension is then stirred with the magnetic stirrer for ~ minute at setting 3 (scale 1-10). The beaker is then suspended in the ultrasonic bath and sonicated for exactly 1 minute. In so doing, care must be taken to 15 ensure that the depth of immersion in the distilled water of the ultrasonic bath reaches exactly to the 60 ml marking of the beaker. After sonication, the beaker is replaced on the magnetic stirrer and a sample of the suspension is removed using the automatic pipette during stirring (setting 3 again). The total amount removed should be used for the count. If a little less suspension is needed, less suspension should be drawn into the tip of the pipette.
The second 100 ml beaker is filled with isotope II
_solution, placed on the beaker platform and the capillary (100 E,im) and the stirrer immersed. The stirrer is set to a moderate speed.
Solutions and apparatus:
100 ml beakers Automatic pipette - Pipetman manufactured by Gilson Plastic pipette tips Magnetic stirrer and magnet (length 3 mm) Ultrasonic bath: Bandelin, Sonorex RK 102 Analytical balance Dust-free lens paper , Nitrogen bottle with drying device and nozzle Petri dish Stopwatch Grain analysis paper Isotone II solution Coulter counter model TA II
The silica of the invention can be used to manufacture crop protection agents with active substances sensitive to hydrolysis. In so doing it is possibly to manufacture wettable powders or water-dispersible granulates which can be used in water soluble foil bags in outer cardboard packagings. This achieves advantages during transport, with hazardous substance classification, with savings in wasted packaging and the cost reductions associated therewith.
The silica of the invention can, in particular, be used when making use of active substances of the group of phosphoric acid esters (malathion, diazinone, etc.).
The form of application of every other active substance may be formulated by analogy.
The active substance formulations prepared using the silica of the invention, such as for example crop protection agents have the additional advantage of long active substance storage stability.
Storage of 50WP malathion and active substance stability Preparation as 50WP malathion:
A premix is first prepared in the ratio 1 . 1 'using Wessalori S and the wetting agent Ampholaka'XIO. 28 g of the partially hydrophobic precipitated silicas as well as Wessalon'°'S as comparison substance are briefly fluidised in a 500 ml Quickfitl"stirring apparatus. 52.1 g malathion (96 $) are then gradually added dropwise before adding 6 g of the premix as well as 3.0 g Empikolx"LZ/P dispersing agent. 10.9 g filler (Rollokalk)~ are subsequently mixed therewith and the mixture is homogenised using a Turbula mixer.
The samples are stabilised by storing them for 4 days at room temperature. The initial values of CIPAC suspension and the malathion contents are then determined according to CIPAC. The initial values of malathion according to WHO
and isomalathion according to WHO are also determined after 4 days and the samples then stored at 54°C and measured after 7 days, 14 days, 28 days and 56 days.
Testing suspension according to CIPAC-12/3/(M) 1 before and after storage at 54°C:
This method is a spectroanalytical process with W as light source. Malathion reacts/hydrolyses with alkali in Na-00-dimethyldithiophosphate and is converted with Cu/Fe solution into a yellow copper complex and measured at 420 E.tm. The influence of wetting agent on malathion release is presumably great in the case of this method.
Testing malathion content according to WHO/SIF/10.R5 using gas chromatoaraphv before and after storage at 54°C:
The method is based on separation of a substance mixture through substance-specific distribution between stationary phase (column) and a stream of carrier gas which lead to different speeds/retention times. In this method, there is an extraction equilibrium between solvent and silica during detachment of the malathion from the silica that may possibly favour the hydrophobic silica types. The wetting agent presumably exerts hardly any influence.
Testing isomalathion content after WHO/SIF/10.R5 using HPLC before and after storage at 54°C:
To determine the isomalathion content, 0.6 g 50WP
malathion are weighed in and mixed with 65 ~ aqueous Degussa Aktiengesells°haft, D-60311 Frankfurt acetonitrile solution for 30 minutes. The sample is measured against a reference solution after centrifugation and filtration. With this method there is also an extraction equilibrium between solvent and silica that may possibly favour the hydrophobic silica. The wetting agent presumably exerts hardly any influence.
Storage of 1:1 malathion concentrates and active substance stability The active substance solution (96~) is applied to the partially hydrophobic carrier in a ratio of 1:1. This mixture is then tested for storage stability. The values obtained in this manner are exclusively attributable to the effect of the carrier.
The tests employed in the examples section are described as:
Malathion 1:1 formulation 28 g malathion (96~) are added dropwise within 30 minutes to 28 g carrier and then post-stirred for 3 minutes and mixed at a medium setting in a Turbula mixer for 5 minutes.
It is striking that the mixtures are markedly drier compared to the previously formulated 50WP malathion (28 g hydrophobic carrier + 52.1 g malathion + residual formulation constituents).
Testinct malathion content according to CIPAC 12/3 ~(M ~ 1 by means of W/VIS before and after storage at 54°C:
Storage by analogy with 50WP malathion.
Testincr malathion content accordinct to WHO/SIF/10.R5 by means of GC before and after storacte at 54°C:
Storage by analogy with 50WP malathion. ;_ , -.

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The possible influences of, for example, wetting agents on the accuracy of measurements should be considered when evaluating the results of the Fischer suspension power and of the malathion contents and the isomalathion contents of the 50WP malathion.
The process error when determining the malathion content according to CIPAC using UV/VIS is given as t 5 malathion. A double determination that shows a standard deviation of 0.7 ~ is carried out on one sample after 14 days.
The malathion contents according to WHO show a standard deviation between 0.1 and 0.7 ~. The standard deviation of the isomalathion contents, with two double determinations in the total series of measurements, is 0 to 0.03 ~.
The results of the active substance stability are shown graphically in Figures 1 to 5.
The trials show that the active substance stability can be increased by using the partially hydrophobic precipitated silicas of the invention and that wetting and dispersing agents can be economised on, for example, in crop protection formulations in comparison to known fully hydrophobic precipitated silicas.
Preparation of the defoaming dispersions To prepare the 5 ~ defoaming dispersions 57 g of the corresponding oil, for example Shell Risella G 118 (now Shell Risella G 18), viscosity 40cSt., are prepared in 250 ml beakers, 3 g of the silica of the invention or of Sipernat D10 are then added and carefully stirred together. Dispersing then occurs using an Ultra TurraX T50 at 10000 rpm for 5 minutes.

950112 FA/A1 ~'~
Degussa Aktiengesellschaft, D-60311 Frankfurt Stability testing of the defoaming dispersions For this purpose the still hot dispersions are filled into 100 mi glass cylinders, stored in a vibration-free location at room temperature and any possible phase separation recorded at regular time intervals {value in ml clear oil phase).
Trial result ( use in defoaminct accent ) Defoamer 1 month t clear oil dispersion phase[ml]~

KS6 M = silica No. 6 in mineral oil KS6 S = silica No. 6 in silicone oil D10 M = Sipernat D10 in mineral oil D10 S = Sipernat D10 in silicone oil _Fiorures 6 and 7 Figures 6 and 7 show that the precipitated silica of the invention, worked into mineral oil and silicone oil, shows no phase separation at all after 3 months. A considerable phase separation is already encountered with the known Sipernat D10 both used oils after just one month.
Defoaming testing using latex Degussa Aktiengesellschaft, D-60311 Frankfort 160 g latex are weighed into a stainless steel beaker and foamed up for 3 minutes using a Hamilton-Beach-Scovill mixer in switch setting L (lowest stirrer speed: approx.
4000 rpm) after adding 0.3 g defoaming agent. The weight 5 of 100 ml of this foam is determined by differential weighing in a stainless steel measuring cylinder. A high latex weight (almost 100 g) indicates a good defoaming capacity of the corresponding sample. The mean values are determined from at least two single determinations.
10 A Hamilton-Beach-Scovill mixer is a milkshake mixer normally put to household use which can be set at three stirrer speeds (L, M and H). The switch setting "L" means approx. 4000 rpm. The substance to be stirred up is stirred up using a paddle stirrer with moveable "paddles".
Experimental result (use in defoaming actentsl Batches: Latexweight g/100 ms Mean value/standard deviation 1 KS6 M 71 0.5 /

2 KS6 S 89 0.3 /

3 D10 M 78 0.2 /

4 D10 S 90 0.3 /

Blank value 53 0.9 /

KS6 M - silica No. 6 in mineral oil KS6 S - silica No. 6 in silicone oil D10 M - Sipernat D10 in mineral oil D10 S - Sipernat D10 in silicone oil s Formula for calculating foam content in % after performincx the latex test:
100 g-weighed latex weight [gJ after adding defoaming agent*1 100 g - weighed blank value*2[g]
*1: differential weighing after adding the corresponding defoaming agent for latex dispersion and subsequent stirring for three minutes *2: differential weighing after stirring the latex dispersion for three minutes without adding defoaming agent Figure 8 Figure 8 shows that while the precipitated silica of the invention displays a marginally lower defoaming effect than Sipernat D10 in mineral oil, this result must not 20- necessarily continue in subsequent technical application tests, but that the stability is far better than with Sipernat D10. In silicone oil, the precipitated silica of the invention displays an identical defoaming effect to Sipernat D10.
The investigations conducted show that the stability of a defoaming dispersion can be substantially improved using the partially hydrophobic precipitated silica of the invention, whereas the defoaming effect is comparable with a known fully hydrophobic precipitated silica.

Claims

1. A partially hydrophobic precipitated silica, having:
a methanol wettability of 10 - 49 %;
a DBP uptake (dried substance) of greater than 250 g/100 g (DBP number):
a mean particle size of 1 to 12 µm;
a carbon content of 0.3 to 1.85 %;
a loss on drying of 2.6 to 10 %: and a pH of 5.5 to 10.

2. The partially hydrophobic precipitated silica according to claim 1 with a carbon content of 0.5 to 1.5 %.

3. The partially hydrophobic precipitated silica according to claim 1 or 2 with a loss on drying of 3 to 6 %.

4. The partially hydrophobic precipitated silica according to claim 1, 2 or 3, comprising 85 to 98 % by weight precipitated silica, and 2 to 15 % by weight of a water-repellent agent.

5. The partially hydrophobic precipitated silica according to claim 4, wherein the water-repellent agent is silicon oil.

6. A process for the production of the partially hydrophobic precipitated silica according to any one of claims 1 to 5, comprising:

mixing a precipitated silica suspension with a hydrophobic agent with a short residence time of 5 seconds or less and a low pH value of about 3;
filtering off the precipitated silica with the hydrophobic agent to form a solid matter filter cake;
washing the filter cake until free of salt;
drying the filter cake;
thermally treating or conditioning the filter cake; and milling the filter cake into granular form.

7. The process according to claim 6, wherein the filter cake is thermally treated at 300°C to 400°C for 30 to 60 minutes.

8. Use of the partially hydrophobic precipitated silica according to any one of claims 1 to 5, as carrier in active substance formulations.

9. The use of the partially hydrophobic precipitated silica according to claim 8, as carrier in formulations of hydrolysis-sensitive active substances.

10. Use of the partially hydrophobic precipitated silica according to any one of claims 1 to 5 in defoaming agents.