HIGHLY DISPERSIBLE PRECIPITATED SILICA HAVING A HIGH SURFACE AREA

o + p = 3) in which R is preferably represented by
methyl.
The optionally granulated, ungranulated, ground and/or unground precipitated silica may be modified with one or more of the specified organosilanes in mixtures of from 0.5 to 50 parts per 100 parts of precipitated silica, in particular from 1 to 15 parts per 100 parts of precipitated silica, it being possible for the reaction between precipitated silica and organosilane to be carried out during the preparation of the mixture (in situ) or outside by spray application and subsequent thermal conditioning of the mixture, by mixing the silane and the silica suspension with subsequent drying and thermal conditioning (in accordance with DE 3437473 and DE 19609619, for example) or in accordance with the process described in DE 19609619 or DE-C 40 04 781.
Suitable organosilicon compounds include in principle all bifunctional silanes which are able to produce, on the one hand, coupling to the silanol-functional filler and, on the other hand, coupling to the polymer. Common amounts of organosilicon compounds that are used are from 1 to 10% by weight based on the total amount of precipitated silica.
Examples of these organosilicon compounds are: bis(3-triethoxysilylpropyl)tetrasulfane, bis(3-tri-ethoxysilylpropyl)disulfane, vinyltrimethoxysilane, vinyltriethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-aminopropyltri-

methoxysilane, and 3-aminopropyltriethoxysilane. Further organosilicon compounds are described in WO 99/09036, EP 1 108 231, DE 101 37 809, DE 101 63 945, and DE 102 23 658.
In one preferred embodiment of the invention the silane used can be bis(triethoxysilylpropyl)tetrasulfane.
The silica of the invention may be incorporated into elastomer blends, tires or vulcanizable rubber mixtures as a reinforcing filler in amounts of from 5 to 200 parts per 100 parts of rubber, in the form of powders, microbeads or granules, both with silane modification and without silane modification.
Besides mixtures containing exclusively the silicas of the invention, with and without organosilanes of formulae I to III, as fillers, the elastomers may additionally be filled with one or more fillers having a greater or lesser reinforcing effect. As further fillers it is possible to use the following materials:
Carbon blacks: the carbon blacks for use here are produced by the lamp black, furnace black or gas black process and possess BET surface areas of from 20 to 200 m2/g, such as, for example, SAF, ISAF, HSAF, HAF, FEF or GPF blacks. The blacks may also where appropriate contain heteroatoms such as silicon, for example.
Highly disperse pyrogenic silicas, produced, for example, by flame hydrolysis of silicon halides. The silicas may also be present where appropriate in the form of mixed oxides with other metal oxides, such as the oxides of Al, Mg, Ca, Ba, Sn, and titanium. Other commercial silicas.
Synthetic silicates, such as aluminum silicate, alkaline earth metal silicates such as magnesium silicate or calcium silicate, having BET surface

areas of from 20 to 400 m2/g and primary particle
diameters of from 10 to 400 nm.
Synthetic or natural aluminas and aluminum
hydroxides.
Natural silicates, such as kaolin and other
naturally occurring silicon dioxide compounds.
Glass fibers and glass-fiber products (mats,
strands) or glass microbeads.
Starch and modified starch grades.
Natural fillers, such as clays and siliceous
chalk, for example.
As is the case for the metered addition of the organosilanes, the blending ratio is guided by the profile of properties which it is desired to obtain in the finished rubber blend. A ratio of 5 - 95% between the silicas of the invention and the other fillers mentioned above (as a mixture as well) is conceivable and is also realized in this context.
In one particularly preferred embodiment it is possible to use from 10 to 150 parts by weight of silicas, composed in whole or in part of the silica of the invention, together where appropriate with from 0 to 100 parts by weight of carbon black and from 1 to 10 parts by weight of an organosilicon compound, based in each case on 100 parts by weight of rubber, to produce the blends.
Besides the silicas of the invention, the organosilanes, and other fillers, the elastomers form a further important constituent of the rubber blend. The silicas of the invention can be used with accelerators and/or sulfur, and also with rubber grades which can be crosslinked by means of peroxide. Mention may be made in this context of elastomers, natural and synthetic, oil-extended or otherwise, as individual polymers or as blends with other rubbers, such as natural rubbers.

butadiene rubbers, isoprene rubbers, butadiene-styrene rubbers, especially SBR, prepared by means of the solution polymerization process, butadiene-acrylonitrile rubbers, butyl rubbers, and terpolymers of ethylene, propylene, and nonconjugated dienes. For mixtures with the aforementioned rubbers, the following additional rubbers are also suitable:
carboxyl rubbers, epoxy rubbers, trans-polypentenamers, halogenated butyl rubbers, 2-chlorobutadiene rubbers, ethylene-vinyl acetate copolymers, ethylene-propylene copolymers, and, where appropriate, chemical derivatives of natural rubber, and also modified natural rubbers.
The silicas of the invention, with and without silane, find application in all uses of rubber, such as tires, conveyor belts, seals, V-belts, hoses, footwear soles, cable sheaths, roll coverings, damping elements, etc.
The invention additionally provides elastomer blends, particularly vulcanizable rubber blends, which contain the silicas of the invention in amounts from 5 to 200 parts per 100 parts of elastomer or rubber. The incorporation of this silica and the preparation of the mixtures comprising this silica take place in the manner customary in the rubber industry, on an internal mixer or roll unit, preferably at 80-200"C. The pi;esentation or use form of the silicas may be that of a powder, of microbeads or of granules. In this respect too, the silicas of the invention do not differ from the known pale-colored fillers.
The invention further provides elastomer or rubber blends which comprise rubber and at least one precipitated silica of the invention in amounts of from 5 to 200% by weight based on the amount of rubber used. Where appropriate, further fillers selected from those specified above, such as carbon blacks, starch.

aluminum hydroxide, alumina, and silicates, where appropriate one of the abovementioned organosilicon compounds, and also further rubber auxiliaries, such as organosilicon compounds, may be present in the mixture. For the purposes of the present invention, rubber blends and elastomer blends are considered synonymous.
Suitable for preparing the rubber blends of the invention are not only natural rubber but also synthetic rubbers. Preferred synthetic rubbers are described, for example, in W. Hofmann, "Kautschuktechnologie" [Rubber technology], Genter Verlag, Stuttgart 1980. They include polybutadiene (BR) polyisopren (IR)
styrene/butadiene copolymers having styrene contents of from 1 to 60%, preferably from 2 to 50%, by weight (SBR)
isobutylene/isoprene copolymers (IIR) butadiene/acrylonitrile copolymers having aery lonit rile contents of from 5 to 60%, preferably from 10 to 50%, by weight (NBR) partially hydrogenated or fully hydrogenated NBR rubber (HNBR)
ethylene/propylene/diene copolymers (EPDM) and also mixtures of these rubbers. For the preparation of the tires of the invention particular interest attaches to anionically polymerized L-SBR (solution SBR) rubbers having a glass transition temperature of more than -50 "C, and also mixtures thereof with diene rubbers.
The rubber vulcanizates of the invention may comprise further rubber auxiliaries in the customary amounts, such as reaction accelerators, aging inhibitors, heat stabilizers, light stabilizers, ozone protectants, processing auxiliaries, plasticizers, tackifiers, blowing agents, dyes, pigments, waxes, extenders.

organic acids, retardants, metal oxides, and activators, such as triethanolamine, polyethylene glycol, and hexanetriol. These compounds are known in the rubber industry.
The rubber auxiliaries may be used in known amounts, which depend among other things on the intended use. Customary amounts are, for example, amounts from 0.1 to 50% by weight, based on rubber. As crosslinkers it is possible to use sulfur or sulfur donor substances. The rubber blends of the invention may further comprise vulcanization accelerators. Examples of suitable principal accelerators are mercaptobenzothiazoles, sulfenamides, thiurams, dithiocarbamates in amounts from 0.5 to 3% by weight. Examples of coaccelerators are guanidines, thioureas, and thiocarbonates in amounts from 0.5 to 5% by weight. Sulfur can be used customarily in amounts from 0.1 to 10% by weight, preferably 1 to 3% by weight, based on rubber.
The vulcanization of the rubber blends of the invention can take place at temperatures from 100 to 200'C, preferably from 130 to ISCC, under pressures from 10 to 200 bar where appropriate. The blending of the rubbers with the filler, rubber auxiliaries where appropriate, and the organosilicon compound may be carried out in known mixing equipment, such as rolls, internal mixers, and mixing extruders.
The highly dispersible high surface area silicas of the invention have the advantage that they give the rubber vulcanizates improved abrasion resistance owing to the relatively high CTAB surface area. Moreover, dry handling is enhanced by the greater dynamic stiffness at OC and 60 °C, and a reduction is achieved in the rolling resistance, as indicated by the reduced tan 5 (60°C) value.

The rubber blends of the invention are suitable for producing shaped articles, such as for producing pneumatic tires, tire treads, cable sheaths, hoses, drive belts, conveyor belts, roll covers, tires, footwear soles, gaskets, and damping elements.
The rubber blend of the invention is particularly suitable for producing tire treads having an improved, lower rolling resistance, improved wet slip resistance, improved dry properties, and good abrasion resistance, as compared with an identical rubber blend incorporating existing silicas. These tread blends are especially suitable for high-speed automobile and motorbike tires, but also for tires for commercial vehicles, combining reduced rolling resistance with good abrasion resistance.
Additionally, without the addition of organosilicon compounds, the silicas of the invention are suitable in the form of a blend with a typical tread-grade carbon black for enhancing the cut S chip characteristics of tires for construction, agriculture machinery, and mine vehicles.
In order to achieve a good set of values in a polymer mixture, the dispersion of the precipitated silica in the matrix, the polymer, is of critical importance. It can be estimated through the wk coefficient.
Fig. 1 is a diagram of the values needed to calculate the wk coefficient.
The plots show a first maximum in particle size distribution around 1.0 - 100 pm and a further maximum in the region
dispersed in the rubber blends. The second peak, with much smaller particle sizes ( The wk coefficient is thus a measure of the "breakdownability" (i.e. dispersibility) of the precipitated silica. The rule is that, the lower the wk coefficient, the easier it is to disperse a precipitated silica; in other words, the greater the number of particles which are broken down during incorporation into rubber.
The silicas of the invention have wk coefficients £3.4, preferably The physicochemical data of the precipitated silicas of the invention are determined by means of the following methods:
BET surface area Areameter from Strohlein, in
accordance with ISO 5794/Annex D

Determination of the Sears number of silicas
Application:
Free OH groups are detectable by titration with 0.1 N KOH in the range from pH 6 to pH 9.
Apparatus:
Memotitrator DL 70, Mettler, equipped with 10 ml and
20 ml buret, 1 pH electrode and 1 pump {e.g., NOUVAG
pump, type SP 40/6)
Titration vessel, 250 ml, Mettler
Ultra-Turrax 8 000-24 000 rpm
Thermostatted water bath
2 dispensers, 10-100 ml, for metering methanol and
deionized water
1 dispenser, 10-50 ml, for metering deionized water
IKA universal mill M 20
Reagents:
Methanol p.a.
Sodium chloride solution (250 g NaCl p.a. in 11 of
deionized water)
0.1 N hydrochloric acid
0.1 N potassium hydroxide solution
procedure:
10.00 g of sample are ground for 60 seconds in the IKA
universal mill M 20.
2.50 g of this powder are weighed into a 250 ml
titration vessel and 60 ml of methanol p.a. are metered
in. After complete wetting of the sample, 40 ml of
deionized water are added and the mixture is dispersed
using the Ultra Turrax for 30 seconds at a speed of
18 000 rpm.
Using 100 ml of deionized water, particles of sample
adhering to the vessel edge and stirrer are rinsed into

the suspension, which is conditioned to 25 "C in a thermostatted water bath.
The sample is titrated in the Memotitrator DL 70 in accordance with method S 911. If the course of titration is indistinct, a duplicate determination is carried out subsequently.
The results printed out are:
pH
Vi in ml/5 g
V2 in ml/5 g
Calculation:
Vi = (Vi' * 5)/E
V2 = (V2' * 5)/E
Vi' = ml of KOH or ml of HCl consumed to pH 6
V2' = ml of KOH consumed to pH 9
E = initial mass in g
Principle:
First of all the initial pH of the suspension is measured, then according to the result the pH is adjusted to 6 using KOH or HCl. Then 20 ml of NaCl solution are metered in. The titration is then continued to a pH of 9 using 0.1 N KOH.
The determination method is based on the following chemical reactions:
"Si"-OH + NaCl => "Si"-ONa + HCl
HCL + KOH => KCl + H2O.
Determination of the CTAB surface area
Application:
The method is based on the adsorption of CTAB {N-cetyl-N,N,N-trimethylammonium bromide) on the "external" surface, which is also referred to as the "rubber-

active surface", in accordance with ASTM 3765 or Janzen and Kraus in Rubber Chemistry and Technology 44 {1971) 1287.
The adsorption of CTAB takes place in aqueous solution with stirring and ultrasound treatment. Excess, unadsorbed CTAB is determined by back-titration with SDSS {dioctylsodium sulfosuccinate solution, "Aerosol OT" solution) using a titroprocessor, the endpoint being indicated by the maximum clouding of the solution and determined using a phototrode.
For the calculation, an occupancy of 0.35 nm2 per CTAB molecule is assumed, corresponding to 578.435 m2/g.
The phototrode is set to 1 000 mV before commencing titration, corresponding to a transparency of 100%.
Reaction equation: {back-titration)

Apparatus:
IKA universal mill M 20
Titroprocessor, e.g. METTLER, type DL 55 or DL 70,
equipped with:
pH electrode, e.g. Mettler, type DG 111
Phototrode, e.g. Mettler, type DP 550
Bulb buret, 20 ml volume, for SDSS solution
Bulb buret, 10 ml volume, for KOH, 0.1 N
Titration beakers, 100 ml, made of polypropylene
Glass titration vessel, 150 ml volume, closable with
snap-on lid
Conical flasks, 100 ml volume, closable with screw lid
or standard ground stopper
Ultrasound bath (Bandelin Sonorex RK 106S, 35 kHz)
Pressure filtration device

Membrane filter of cellulose nitrate, pore size 0.1 pm, 47 mm 0, e.g. Sartorius, type 113 58
Reagents:
Potassium hydroxide solution, 0.1 N
CTAB solution, 0.0151 mol/1:
5.50 g of CTAB are dissolved with stirring in about 800 ml of warm (about 30-40'C) demineralized water in a glass beaker, the solution is transferred to a 1 1 graduated flask and made up to the mark with demineralized water, after cooling to 23-25'C, and this solution is transferred to a stock bottle. The solution must be stored and the measurement conducted at >23*'C, since below this temperature CTAB crystallizes out. The solution should be prepared at least 12 days before use, but not stored longer than 2 months. The concentration of the CTAB solution is assumed to be exact: 0.0151 mol/1.
SDSS solution 0.00426 mol/1:
1.895 g of SDSS (dioctylsodium sulfosuccinate) in a glass beaker are admixed with about 800 ml of demineralized water and the mixture is stirred until all the material has dissolved. The solution is then transferred to a 1 1 graduated flask, made up to the mark with demineralized water, and transferred to a stock bottle. The solution should be prepared at least 12 days before use, but not stored longer than 2 months.
The concentration of the SDSS solution should be determined daily by means of a blank titration.
The solutions can be purchased in ready-to-use form
from, for example, Kraft, Duisburg {telephone
0203-58-3025) {order No. 6056.4 CTAB solution
0.0151 ml/1; order No. 6057.4 SDSS solution
0.00423 mol/1).

Procedure:
Blank titration (determining concentration of the SDSS
solution),
The consumption of SDSS solution for 5 ml of CTAB
solution should be checked 1 x per day before each
series of measurements.
Pipette precisely 5.00 ml of CTAB solution into
titration beakers.
Add 50.00 ml of demineralized water.
Titrate with the titroprocessor until the end of
titration.
Each blank titration should be performed as a duplicate
determination; where values do not agree, further
titrations should be carried out until the results are
reproducible.
Adsorption:
10.00 g of the granulated, coarsely particulate sample
are ground in the mill.
Weigh in precisely 500.0 mg of the ground sample to a
precision of 0.1 mg.
Transfer the sample amount weighed out quantitatively
to a 150 ml titration vessel with magnetic stirrer bar.
Add exactly 100.0 ml of CTAB solution, close titration
vessel with lid, and stir on a magnetic stirrer for
15 minutes.
Screw the titration vessel onto the titroprocessor and
adjust the pH of the suspension to 9+0.05 using KOH
(0.1 mol/1).
4-minute treatment of the suspension in the ultrasound
bath.
Filtration through a pressure filter fitted with a
membrane filter, using a nitrogen pressure of 1.2 bar.
During adsorption, it must be ensured that the
temperature is held within the range from 23°C to SSC.

Titration:
Pipette 5.00 ml of the above-obtained filtrate into a
100 ml titration beaker and make up to about 50.0 ml
with demineralized water.
Screw titration beaker onto the titrator.
Titrate with SDSS solution in accordance with the
method defined above until clouding reaches a maximum.
Each titration should be performed as a duplicate
determination; where values do not agree, further
titrations should be carried out until the results are
reproducible.
Calculation:
CTAB surface area in g/1 = (Vi + V2)*E*115.687/Vi
Vi = blank sample (ml of SDSS when using 5 ml of
CTAB) V2 = consumption (ml of SDSS when using 5 ml of
filtrate) E = initial mass of CTAB, g/1
The measurement is normally to be given corrected for the anhydrous substance:
CTAB surface area (water-corrected) =
CTAB surface area *100/(100 - water content in %)
wk coefficient: aggregate size distribution by laser diffraction (Coulter)
Apparatus:
Laser diffraction instrument LS 230, Coulter
Bandelin ultrasonic finger, type HD 2200, with DH 13 G
horn
Cooling bath 80 ml
Eppendorf pipette, 5 ml
Centrifuge glass, height 7 cm, 0 3 cm
Petri dish, height 4 cm, 0 7 cm
Dewar vessel, height 21 cm, 0 4 cm

Digital thermometer, accuracy ±0.1 K
Chemicals:
Ethanol, p.a., Merck
Triton X-100, Merck
Sodium hexametaphosphate. Baker
Sample preparation:
Granules are introduced into a mortar and the coarse granules are compressed, not mortared.
1 g of unaged silica (produced no earlier than 10 days before) is weighed into a 30 ml rolled-edge glass vessel, and 20 ml of dispersion solution (20 g of sodium hexametaphosphate made up to 1 000 ml with demineralized water) are added. The sample is then placed in a cooling bath, which prevents the suspension from heating up significantly, and treated with ultrasound for 4.5 minutes (100 W output, 80% pulse). Three dispersion solution specimens are prepared in succession for each silica.
Until the sample is added to the liquid module, the suspension is placed in a petri dish with magnetic stirrer in order to prevent any sedimentation.
Procedure:
Before the beginning of the measurement, the instrument and the liquid module are allowed to warm up for at least 30 minutes, and the module is rinsed automatically for 10 minutes (menu bar "Control/Rinse") .
In the control bar of the Coulter software, the menu item "Measurements" is used to select the file window "Calculate op. model", and the refractive indices are defined (liquid refractive index real = 1.332; material refractive index real = 1.46, imaginary = 0.1). In the file window "Measuring cycle" the output of the pump speed is set to 26% and the ultrasound output to 3%. The items of ultrasound "during sample addition".

"before each measurement", and "during measurement" are
to be activated.
Additionally, the following items are selected in this
file window:
Offset measurement (1 x daily)
Adjustment
Background measurement
Adjust measurement concentration
Enter sample info
Enter measuring info
Start 2 measurements
Automatic rinse
With PIDS data
When calibration is complete, the sample is added.
Dispersed silica is added until a light absorption of
about 45% has been reached and the instrument announces
OK.
The measurement is made using the evaluation model
"Si02_i.rfd".
For each sample added, three duplicate determinations
of 60 seconds are conducted.
The software calculates the particle size distribution
from the raw data plot, on the basis of the volume
distribution.
Typically a bimodal distribution curve is found, with
the mode A at about 0.2 pm and the mode B at about
(2-5) lam. From this it is possible to calculate the wk
coefficient in accordance with Figure 1.
DBF absorption
The DBP absorption (DBF number), which is a measure of
the absorbency of the precipitated silica, is
determined as follows in accordance with the standard
DIN 53601:

The dibutyl phthalate number is determined using the Brabender plastograph with the Multi-Dosimat E 415 (50 1) plotter from Metrohm. The absorbency is dependent on the moisture content, the particle size, and the amount of material analyzed.
Procedure:
12.5 g of silica are introduced into the kneader of the Brabender plastograph. With continued mixing (kneader paddle speed 125 rpm), dibutyl phthalate runs into the mixture at a rate of 4 ml/min. The force required for incorporation is low. Toward the end of determination, the mixture becomes poorly free-flowing. This fact is documented in an increase in the required force, which is indicated on a scale. When the scale has moved by 300 units, DBP metering is shut off automatically.
Evaluation:
The density of DBP is 1.047 g/ml. The DBP absorption is based on the anhydrous, dried silica. When using precipitated silicas with relatively high moisture content, the value must be corrected using the correction table unless the silicas are dried prior to the determination of the DBP number.


The correction figure corresponding to the water content is added to the experimentally determined DBF value; for example, a water content of 5.8% would mean an add-on of 33 g/100 g for the DBF absorption.
Moisture determination
Description:
The silica is dried to constant weight in an IR drier. The loss on drying generally consists predominantly of the water moisture of the silica, and only of traces of other volatile constituents.
Apparatus:
IR drying unit, Mettler, type LP 16 Aluminum weighing boats

Measurement procedure:
2.0 g of silica are introduced into the aluminum boat, tared beforehand, and the lid of the drier is closed. Measurement begins when the start button is pressed and is ended automatically when the decrease in weight per unit time falls below a value of 2 mg/120 s. The following values must be checked and/or set on the

Result:
The loss on drying in % is indicated directly and/or printed out by the instrument.
The following examples are intended to illustrate the invention without restricting its scope.
Example 1
A reactor is charged with 1 480 1 of water and also 0.41 kg of waterglass (density 1.348 kg/1, 27.1% SiOz, 8.00% NaaO) .
Then 8.791 kg/min of waterglass and 1.160 kg/min of sulfuric acid (density 1.84 kg/1, 96% H2SO4) are metered in at 63°C for 22 minutes. Following a 60-minute waiting phase, again, 8.791 kg/min of waterglass and 1.160 kg/min of sulfuric acid are metered in for 45 minutes. Thereafter the addition of waterglass is stopped while that of sulfuric acid is continued until a pH of about 3.3 is reached.
The product obtained is filtered in the usual manner, subjected to long drying or flash drying (rotary tube drier, rack drier, spray drier, nozzle tower drier, spin-flash drier), ground where appropriate, and granulated where appropriate.

In the granule form the product obtained has a BET surface area of 235 m2/g and a CTAB surface area of 185 m2/g.
Example 2
The precipitated silicas of the invention from Example 1 are investigated in an S-SBR/BR rubber blend. As state of the art, the silicas Ultrasil 7000 GR and Zeosil 1205 MP were selected.
The formula used for the rubber blends is that indicated in Table 1 below. In the table, the unit "phr" denotes parts by weight per 100 parts of the crude rubber used. The reference silica Ultrasil 7000 GR in mixture Rl was modified with 6.4 phr of Si 69. In order to take account of the higher surface area of the reference silica Zeosil 1205 MP and of the silica of the invention, in mixtures R2 and A the amount of silane was raised to 8 phr and the amount of sulfur was reduced accordingly. The general procedure for producing rubber blends and their vulcanizates is described in "Rubber Technology Handbook", W. Hofmann, Hanser Verlag 1994. The rubber blends are prepared in an internal mixer in accordance with the mixing specification in Table 2, while Table 3 compiles the methods used for rubber testing. The blends are vulcanized at 165"C for 20 minutes. Table 4 shows the results of rubber testing.


The polymer VSL 5025-1 is a solution-polymerized SBR copolymer from Bayer AG having a styrene content of 25% by weight and a butadiene content of 75% by weight. The copolymer contains 37.5 phr of oil and has a Mooney viscosity (ML l+4/100°C) of 50±4.
The polymer Buna CB 24 is a cis-1,4-polybutadiene (neodymium type) from Bayer AG having a cis-1,4 content of at least 97% and a Mooney viscosity of 44±5. As an aromatic oil, Naftolen 2D from Chemetall is used. Vulkanox 4020 is 6PPD from Bayer AG, and Protektor G35P is an ozone protector wax from HB-Fuller GmbH. Vulkacit D/C (DPG) and Vulkazit CZ/EG (CBS) are commercial products from Bayer AG. Perkazit TBZTD is available from Akzo Chemie GmbH.

Si 69 is the coupling reagent bis(3-triethoxysilyl-propyl)tetrasulfane from Degussa AG.





The dispersion coefficient is determined by a light-optical method. The measurement can be carried out by the Deutsche Institut fiir Kautschuktechnologie e.V. [DIK], Hanover, Germany. In addition, the method is described in H. Geisler, "Bestimmung der Mischgiite", presented at the DIK Workshop, November 27-28, 1997, Hanover, Germany.


As is evident from the data in Table 4, as a result of the higher surface area of the silica of the invention, the Mooney viscosity of the mixtures A is slightly increased as compared to Rl, but is still better than the prior art reference mixture R2, which has an increased viscosity and poor processing properties. The vulcanization characteristics (Dmax-Dmin, t90%, tlO%) of the mixtures Rl and A are very similar to one another, which suggests trouble-free vulcanization, while mixture R2 exhibits a significantly shortened scorch time tlO%. The strain values of Rl and A are comparable, whereas R2 possesses a much higher hardness and strain value 100, indicating a markedly higher silica network owing to the poorer dispersion. Advantages of the mixture A over the reference Rl are evident in the increased dynamic moduli E* OC and eO'C. These higher stiffnesses are particularly

important for high-speed automobile and motorbike tires, since they indicate improved dry handling and higher cornering stability. Despite the higher silica surface area in mixture A, the hysteresis loss tan 5, which is inversely proportional to the rolling resistance value, is - advantageously - virtually unchanged, while mixture R2 in accordance with the prior art shows a significantly higher hysteresis loss. The good reinforcement in combination with the high CTAB surface area of the silica of the invention suggests an improved road abrasion of the mixture A. This improvement in road abrasion is also to be expected when using the high surface area silicas of the invention in natural rubber blends, such as are employed in truck tread mixtures. Particularly in combination with a high surface area, highly structured carbon black such as N 121, excellent road abrasion in the case of truck tires can be predicted.


WE CLAIM:
1. A precipitated siliqa characterized by
BET surface area 170 - 350 m2/g
CTAB surface area >170 m2/g
DBF number 305 - 400 g/100 g
Sears number 23-35.
2. The precipitated silica as claimed in claim 1,
wherein the CTAB surface area is not more than 300 m2/g.
3. The precipitated silica as claimed in either of
claims 1 or 2, having a wk coefficient of ' The precipitated silica as claimed in any of claims 1 to 3, whose surfaces have been modified with organosilanes of the formulae I to III:

arylaromatic radicals having 2-30 carbon
atoms which may be substituted or
un.substituted by the following groups:
hydroxy1, amino, alkoxide, cyanide,

thiocyanide, halogen, sulfonic acid, sulfonic ester, thiol, benzoic acid, benzoic ester, carboxylic acid, carboxylic ester, aerylate, meth-acrylate, organosilane radicals, it being possible for R and R1 to have an identical or different definition or substitution,
n is 0, 1 or 2,
Alk is a divalent unbranched or branched hydrocarbon radical having from 1 to 6 carbon atoms,
m is 0 or 1,
Ar is an aryl radical having from 6 to 12 carbon atoms, preferably 6 carbon atoms, which may be substituted by the following groups: hydroxyl, amino, alkoxide, cyanide, thiocyanide, halogen, sulfonic acid, sulfonic ester, thiol, benzoic acid, benzoic ester, carboxylic acid, carboxylic ester, organosilane radicals,
p is 0 or 1 with the proviso that p and n are not simultaneously 0,
X is a number from 2 to 8,
r isl, 2or3, with the proviso that r + n+in + p=4,
Alkyl is a monovalent unbranched or branched saturated hydrocarbon radical having from 1 to 20 carbon atoms, preferably from 2 to 8 carbon atoms, and
Alkenyl is a monovalent unbranched or branched unsaturated hydrocarbon radical having from 2 to 20 carbon atoms, preferably from 2 to 8 carbon atoms.
5. The process for preparing a precipitated silica having a


in which
a) an aqueous solution of an alkali metal silicate or alkaline earth metal silicate and/or of an organic and/or inorganic base with pH > 9 is introduced as initial charge,
b) waterglass and an acidifier are metered simultaneously into this initial charge with stirring at 55 - 95'C for 10 - 120 minutes,
c) stopping of the metered addition for 30-90 minutes, during which the temperature is maintained, and
d) simultaneous metered addition of waterglass and an acidifier at the same temperature with stirring for 20 - 120 minutes,
e} the mixture is acidified with an acidifier to a
pH of approximately 3.5, and f) the acidified mixture is filtered and dried.
6. The process as claimed in claim 5, wherein the acidifier and/or the waterglass in steps b) and d) each have the same concentration or rate of addition.
7. The process as claimed in claim 5, wherein the acidifier and/or the waterglass in steps b) and d) each have a different concentration or rate of addition.
8. The process as clairned in claim 7 wherein, where the acidifier and/or the waterglass have the same concentration in steps b) and d), their rate of addition in step d) is 125 - 140% of the rate of addition in step b).

9. The process as claimed in any of claims 5 to 8,
wherein drying is carried out using a pneumatic
conveying drier, spray drier, rack drier, belt
drier, rotary tube drier, flash drier, spin-flash
drier or nozzle tower.
10. The process as claimed in any of claims 5 to 9,
wherein drying is followed by granulation with a
roll compactor.
11. The process as claimed in any of claims 5 to 10,
wherein during steps b) and/or d) an organic or
inorganic salt is added.
12. The process as claimed in any of claims 5 to 11, wherein the granulated or ungranulated precipitated silicas are modified with organosilanes in mixtures of from 0,5 to 50 parts per 100 parts of precipitated silica, in particular from 1 to 15 parts per 100 parts of precipitated silica, the reaction between precipitated silica and organosilane being carried out during the preparation of the mixture (in situ) or outside by spray application and subsequent thermal conditioning of the mixture or by mixing the organosilane and the silica suspension with subsequent drying and thermal conditioning.
13. Elastomer blends, vulcanizable rubber blends or vulcanizates comprising the precipitated silica of any of claims 1 to 4.