RU2816976C1 - Precipitated silicon dioxide, method for its production and use thereof - Google Patents

Abstract

FIELD: various technological processes.

SUBSTANCE: invention relates to precipitated silicon dioxide, a method for production thereof and use thereof. Precipitated silicon dioxide is characterized by the following physical and chemical parameters: CTAB-surface: not more than 115 m²/g, absorption of DOA: not less than 130 ml/(100 g), Ro-Tap>300 mcm: not less than 86%, V(d₅-d₅₀)/V(d₅-d₁₀₀): less than 0.66. Precipitated silicon dioxide is obtained by a method in which an aqueous solution of an organic and/or inorganic salt and/or silicate of an alkali or alkali-earth metal and/or an organic and/or inorganic base with pH not less than 9 is prepared. Into the initial solution while stirring and at temperature of 80–98 °C liquid glass and acidifying agent are simultaneously dosed for 60–120 minutes. Then addition of liquid glass is stopped and only acid is dosed in amount smaller than before to achieve pH value of mixture of 8.5–8.6. After that, the mixture is stirred for 45–200 minutes at a temperature higher than 85 °C. Acidified with sulfuric acid to pH 3.5–4.5, filtered, dried to loss during drying less than 8% and granulated.

EFFECT: improved dispersibility of silicon dioxide in rubber mixtures.

10 cl, 5 tbl, 3 ex

Description

The present invention relates to precipitated silica, a method for its production and its use.

From WO 2012/059234, elastomeric compositions are known which contain at least one isoprene elastomer and silica as a reinforcing mineral filler, wherein the silica has a CTAB surface area of 40 to 525 m ² /g, a BET surface area of 45 to 550 m ² /g, a width Ld ((d ₈₄ -d ₁₆ )/d ₅₀ ), measured by particle size analysis on an XDC analyzer after ultrasonic deagglomeration, of at least 0.91 and a pore volume distribution with the ratio V(d ₅ -d ₅₀ )/V(d ₅ -d ₁₀₀ ) of at least 0.66, and which uses 3-acryloxypropyltriethoxysilane as an adhesion promoter (or coupling agent).

From EP 2102104 there is further known a method for producing silicon dioxide with a CTAB surface from 40 to 525 m ² /g, a BET surface from 45 to 550 m ² /g, a width Ld ((d ₈₄ -d ₁₆ )/d ₅₀ ), measured by granulometric analysis on an XDC analyzer after disaggregation by ultrasound of at least 0.91 and a pore volume distribution V(d ₅ -d ₅₀ )/V(d ₅ -d ₁₀₀ ) of at least 0.66.

From EP 1831297 and WO 2006/072704 it is known to use silica with a BET surface area of at least 60 m ² /g as a mineral filler in a thermoplastic polymer material to increase its rigidity while maintaining or improving its toughness.

In addition, from US 2005/032965 and WO 2008/077948, silicon dioxide is known with a CTAB surface from 40 to 525 m ² /g, a BET surface from 45 to 550 m ² /g, a grain size distribution width Ld ((d ₈₄ - d ₁₆ )/d ₅₀ ), measured by analyzing the particle size on an XDC analyzer after crushing with ultrasound, at least 0.91 and the pore volume distribution V(d ₀ -d ₅₀ )/V(d ₅ -d ₁₀₀ ) at least 0.66.

The disadvantage of known types of silica in the target specific surface area range is that they are poorly dispersed in rubber compounds and thus have poor wear resistance properties, especially when used as tread compounds.

The present invention was based on the object of providing a silica which, in comparison with silica of known types, would have better dispersibility in rubber compounds. At the same time, such silicon dioxide should, if possible, be presented in the form of granules so that it can be incorporated into the rubber matrix (base) as well as possible and be easily introduced into it.

The object of the invention is precipitated silicon dioxide, characterized by the following physicochemical parameters:

CTAB surface: not more than 115 m ² /g, preferably not more than 105 m ² /g, preferably not more than 90 m ² /g, especially preferably from 45 to 90 m ² /g, most preferably from 65 to 90 m ² / g, especially from 70 to 90 m ² /g,

DOA absorption: not less than 130 ml/(100 g), preferably not less than 140 ml/(100 g), especially preferably from 145 to 190 ml/(100 g),

Ro-Tap>300 µm (proportion of particles larger than 300 µm in sieve analysis on a Ro-Tap screening machine): at least 86%, preferably 86 to 98%, particularly preferably 86 to 95%, especially 90 to 95 %,

V(d ₅ -d ₅₀ )/V(d ₅ -d ₁₀₀ ): less than 0.66, preferably from 0.30 to 0.65, especially from 0.30 to 0.64.

The silica according to the invention may have a BET surface area of not more than 125 m ² /g, preferably not more than 115 m ² /g, particularly preferably from 70 to 105 m ² /g.

The silicon dioxide proposed in the invention may have a Sears number _ex (ml KOH in terms of 1.5 g of silicon dioxide) from 7.0 to 20.0 ml/(1.5 g), preferably from 9.0 to 15.0 ml /(1.5 g), particularly preferably from 11.0 to 14.0 ml/(1.5 g).

The silicon dioxide proposed in the invention can be characterized by a density of silanol groups of at least 5.4 OH/nm ² , preferably not less than 5.5 OH/nm ² .

The silicon dioxide proposed in the invention can be characterized by losses on drying from 2 to 10%, preferably from 4 to 8%.

The silica according to the invention may have a pH value from 4.0 to 7.0, preferably from 5.5 to 7.0.

The silicon dioxide proposed in the invention can have an electrical conductivity of no more than 1200 μS/cm, preferably from 200 to 800 μS/cm.

The silicon dioxide proposed in the invention can have a residue after calcination of 3 to 5%, preferably 4 to 5%.

The silica proposed in the invention can be characterized by a Ro-Tap value <75 μm (the proportion of particles with a size of less than 75 μm in sieve analysis on a Ro-Tap screening machine) of no more than 10%, preferably no more than 8%.

The silica according to the invention may have a bulk density of at least 180 g/l, preferably 200 to 350 g/l, particularly preferably 250 to 330 g/l, most preferably 250 to 320 g/l.

The silicon dioxide proposed in the invention can be characterized by a TAR value (grain fraction 3.14-5.00 mm) from 15 to 60%, preferably from 20 to 50%.

The silica according to the invention can have a PV value in the pressure range from 0.0042 to 414 MPa at a contact angle of 140°, measured by mercury porosimetry, in the range from 1.00 to 3.00 ml/g, preferably from 1.35 to 2.40 ml/g, particularly preferably 1.35 to 2.00 ml/g.

The silica according to the invention can have a maximum pore size (Hg, -dV/dlogD, contact angle 140°, surface tension 480 mN/m) of 35 to 100 nm, preferably 45 to 80 nm, particularly preferably 50 to 70 nm .

The silicon dioxide proposed in the invention can be used in compacted (compressed) form, especially preferably in the form of granules. In this case, at least 50% of the granules in the resulting Ro-Tap fraction >300 μm have a maximum extent of one granule (defined as “granule length”) in height, width or length that can be at least 1.0 mm, preferably greater than 1.5 mm , particularly preferably more than 2.5 mm, most preferably more than 3.0 mm.

Another object of the invention is a method for producing the precipitated silicon dioxide proposed in the invention, characterized in that

a) prepare an aqueous solution of organic and/or inorganic salt and/or silicate of an alkali or alkaline earth metal and/or organic and/or inorganic base with a pH of at least 9,

b) into this initial solution with stirring and at a temperature ranging from 80 to 98°C for 60-120 minutes, preferably at a temperature ranging from 85 to 98°C for 80-110 minutes, liquid glass and acidifying agent are simultaneously dosed means,

c) then the addition of liquid glass is stopped and only the acid is dosed in a smaller amount than before to achieve a pH value of the mixture (measured at 60°C) ranging from 8.3 to 10.0,

d) after which the mixture is further stirred for 45-200 minutes, preferably 60-150 minutes, at a high temperature of at least 85°C, preferably above 90°C, but without further addition of starting materials,

e) acidify with sulfuric acid to a pH value of approximately 3.5-4.5 (measured at 60°C) and

e) filtered, dried, preferably using spray dryers or flash vortex dryers, to a loss on drying of less than 8% and then granulated.

The method proposed in the invention can be carried out at temperatures not lower than 80°C throughout the entire precipitation process, and maturation can be carried out at temperatures not lower than 85°C. As a result, in addition to a specific surface area in the range of not more than 115 m ² /g, an internal structure that is extremely high for this range of specific surface values is also obtained, which is very advantageous for incorporation into a matrix, such as, for example, rubber. This is manifested in high DOA absorption values. These structures are largely retained even after the actual structure-destroying granulation because the resulting high density of silanol groups results in a stabilized silica structure.

The amount of the initial solution can be from 20 to 90%, preferably from 30 to 90%, especially preferably from 40 to 90%, of the final volume of the precipitated product. The initial solution can be used without or with only a small amount of electrolyte (salt), and electrolytes can be added continuously or in batches (preferably at the beginning of precipitation).

Optionally, it is possible to further add organic or inorganic salts also at stage a), b), c), e) or f). They can be added in solution or as a solid, in each case continuously or in portions. It is also possible that the salts are dissolved in one or more components and then added simultaneously with them. Salts may contain the following anions and cations: Li ⁺ , Na ⁺ , K ⁺ , Rb ⁺ , Be ²⁺ , Mg ²⁺ , Ca ²⁺ , Sr ²⁺ , Ba ²⁺ , H ⁺ , F ^- , Cl ^- , Br ^- , I ^- , SO ₃ ^2- , SO ₄ ^2- , HSO ₄ ^- , PO ₃ ^3- , PO ₄ ^3- , NO ₃ ^- , NO ₂ ^- , CO ₃ ^2- , HCO3 ^- , OH ^- , TiO ₃ ^2- , ZrO ₃ ^2- , ZrO ₄ ^4- , ^AlO _2- , Al ₂ O ₄ ^2- , BO ₄ ^3- .

Suitable organic salts are salts of formic, acetic and propionic acids. The specified ions of alkali or alkaline earth metals should be mentioned as the cation. The concentration of these salts in the initial solution can range from 0.01 to 5.00 mol/l. Preferably, Na ₂ SO ₄ is used as the inorganic salt. The acidifying agent can be supplied to steps b), c) and e) in the same or different ways, i.e. with the same or different concentrations and/or supply rates. Likewise, liquid glass can be supplied to steps a) and b) to carry out the reaction in the same or different ways.

Along with liquid glass (sodium silicate solution), it is also possible to use other silicates, such as potassium or calcium silicate. In addition to sulfuric acid, other acidifying agents such as HCl, HNO ₃ , H ₃ PO ₄ or CO ₂ can also be used as acidifying agent. Methods for filtering and drying silica are known to those skilled in the art, such as those described in publication EP 1762544 B1 and the patents cited therein. Preferably, the silica is dried in an air dryer, spray dryer, stack dryer, belt dryer, rotary tube dryer, vacuum spray dryer, spin flash dryer or spray tower dryer. These drying methods also include spray, one- or two-component nozzle or integrated fluidized bed options. Preferably, the precipitated silica has, after the drying step, the form of particles with an average diameter of more than 15 µm, in particular more than £ µm, particularly preferably more than 200 µm. After drying, granulation can also be carried out in a roller press followed by a crusher, through which the final length of the granules is adjusted.

Another object of the invention is a rubber mixture containing

(A) rubber or a mixture of rubbers and

(B) at least one precipitated silica according to the invention.

The rubber can be natural rubber and/or synthetic rubbers. Preferred synthetic rubbers are described, for example, by W. Hofmann in the reference book Kautschuktechnologie, Genter Verlag, Stuttgart, 1980. Such synthetic rubbers can be, in particular, polybutadiene (SKD), polyisoprene (SKI), styrene-butadiene copolymers (SBC ), for example emulsion polymerized styrene-butadiene rubber (E-SBR) or solution polymerized styrene-butadiene rubber (R-SBR) with a styrene content preferably from 1 to 60 wt. %, especially preferably from 5 to 50 wt. %, chloroprene (CH), copolymers of isobutylene and isoprene (SCII), copolymers of butadiene and acrylonitrile (SKN) with an acrylonitrile content of 5 to 60 wt. %, preferably from 10 to 50 wt. %, partially or fully hydrogenated nitrile butadiene rubber (SNBR), copolymers of ethylene, propylene and diene monomer (EPDM), the above rubbers additionally containing functional groups, such as carboxy groups, silanol groups or epoxy groups, for example epoxidized natural rubber, functionalized carboxylic acid groups and SKN or functionalized with silanol groups (-SiOH), respectively siloxy groups (-Si-OR) SKS, as well as mixtures of such rubbers and their masterbatches. It is also possible to use latexes of the above rubbers, especially in combination with liquid phase mixing or continuous liquid phase mixing.

In one preferred embodiment, the rubbers may be sulfur vulcanizable rubbers. For the manufacture of tire treads for passenger cars, primarily SKS (R-SKS) obtained by anionic polymerization in solution with a glass transition temperature above -50°C, as well as their mixtures with diene rubbers, can be used. In a particularly preferred embodiment, it is possible to use R-SKS with a vinyl content in their butadiene part of more than 20 wt. %. In the most preferred embodiment, it is possible to use R-SKS with a vinyl content in their butadiene part of over 50 wt. %.

In a preferred embodiment, mixtures of the above rubbers can be used, in which mixtures the R-SKS accounts for more than 50 wt. %, especially preferably more than 60 wt. %.

In tread mixtures, it is primarily possible to use combinations of dissimilar polymers in the form of R-SKS/SKD and R-SKS/SKD/NC of non-functionalized and/or functionalized types, often also with the addition of resins. Such resins may be of natural or synthetic origin and may be chemically modified or present as mixtures of different resins.

The rubber mixture proposed in the invention may contain additional fillers. The following fillers can be used in the rubber compounds proposed in the invention:

- carbon black: the grades of carbon black used for these purposes can be obtained using methods for producing flame, furnace, gas or thermal carbon black and have a BET surface area from 20 to 200 m ² /g. These grades of carbon black may also optionally contain heteroatoms such as silicon (Si);

- amorphous silicon dioxide, obtained, for example, by precipitation of silicate solutions or by flame hydrolysis of silicon halides, with a specific surface area (BET surface) from 5 to 1000 m ² /g, preferably from 20 to 400 m ² /g and with a primary size particles from 10 to 400 nm. Such silica may optionally also be present as a mixed oxide with other metal oxides such as Al oxides, Ga oxides, B oxides, Mg oxides, Ca oxides, Ba oxides, Zn oxides and titanium oxides. Silicon dioxide may also be doped with one or more of these metal ions;

- synthetic silicates such as aluminum silicate, alkaline earth metal silicates such as magnesium silicate or calcium silicate, with a BET surface area of 20 to 400 m ² /g and a primary particle diameter of 10 to 400 nm;

- synthetic or natural aluminum oxides and hydroxides;

- natural silicates such as kaolin and silicas of other naturally occurring types;

- natural fibers, in particular cellulose, micro- and/or nanocellulose and products thereof;

- glass fiber and glass fiber products (fiberglass mats, glass strands) or glass microbeads.

Preferably, amorphous silica obtained by precipitation of silicate solutions can be used, with a BET surface area of 20 to 400 m ² /g, particularly preferably 100 to 250 m ² /g, in amounts of 5 to 150 wt. parts, in each case based on 100 parts of rubber.

These fillers can be used individually or in a mixture with each other.

The rubber mixture may contain the precipitated silicon dioxide proposed in the invention in an amount from 5 to 150 wt. parts and organosilane in an amount from 0.1 to 20 wt. parts, preferably from 1 to 18 wt. parts, especially preferably from 5 to 15 mass. parts, while the content of the corresponding component in mass. parts are indicated in terms of 100 mass. parts of rubber.

The rubber mixture may additionally contain silicone oil and/or alkylsilane.

The rubber composition according to the invention may additionally contain further known ingredients, such as, for example, cross-linking agents, vulcanization accelerators, reaction accelerators, reaction retardants, antioxidants, stabilizers, processing aids, plasticizers, waxes or metal oxides, as appropriate. activators such as triethanolamine, polyethylene glycol or hexanetriol.

The above additional ingredients of rubber compounds can be used in usual quantities, depending, among other things, on the purpose of the rubber compound. Such usual amounts may be, for example, from 0.1 to 50 mass. % based on the mass of rubber.

Sulfur or organic sulfur donor compounds can be used as crosslinking agents.

The rubber mixture according to the invention may contain further vulcanization accelerators. Examples of suitable vulcanization accelerators include mercaptobenzothiazoles, sulfenamides, guanidines, dithiocarbamates, thioureas, thiocarbonates, as well as their zinc salts, such as zinc dibutyl dithiocarbamate.

The rubber mixture proposed in the invention may additionally contain thiuram sulfide and/or carbamate as an accelerator and/or corresponding zinc salts, a nitrogen-containing coactivator, optionally further ingredients, optionally further accelerators. The mass ratio between the accelerator and the nitrogen-containing coactivator can be at least 1.

The rubber mixture proposed in the invention may contain tetrabenzylthiuram disulfide or tetramethylthiuram disulfide in an amount of at least 0.25 wt. parts in terms of 100 mass. parts of rubber, diphenylguanidine in an amount of at least 0.25 wt. parts in terms of 100 mass. parts of rubber and cyclohexyl- or dicyclohexylsulfenamide.

Preferably, sulfenamides can be used together with guanidines and thiurams, especially preferably cyclohexylsulfenamide or dicyclohexylsulfenamide together with diphenylguanidine and tetrabenzylthiuram disulfide or tetramethylthiuram disulfide.

Vulcanization accelerators and sulfur can be used in quantities from 0.1 to 10 wt. parts, preferably from 0.1 to 5.0 wt. parts, based on the weight of the rubber used. In a particularly preferred embodiment, sulfur and sulfenamides can be used in amounts of from 1.0 to 4.0 wt. parts, thiurams in quantities from 0.2 to 1.0 wt. parts and guanidines in quantities from 0.0 to 3.0 wt. parts.

Another object of the invention is a method for preparing a rubber mixture according to the invention, characterized in that rubber or a mixture of rubbers, the precipitated silica according to the invention and, if necessary, further ingredients of the rubber mixture are mixed together in a mixer.

The process of mixing rubbers with filler and with optionally used further ingredients of rubber compounds can be carried out in conventional mixing devices such as rollers, closed rubber mixers and screw mixers. Typically, such rubber mixtures can be prepared in closed rubber mixers, wherein first, in one or more successive thermomechanical mixing stages, the rubbers, filler, precipitated silica according to the invention and the ingredients of the rubber mixtures are mixed at a temperature ranging from 100 to 170°C. In this case, the sequence and moment of adding individual components can have a decisive influence on the properties of the resulting rubber mixture. Typically, the rubber mixture obtained in this way can be mixed in a closed mixer or on rollers with crosslinking agents at a temperature ranging from 40 to 110 ° C to obtain an unvulcanized rubber mixture, the so-called green mixture, which is subjected to further processing in subsequent technological stages, such as such as molding and vulcanization.

The vulcanization of the rubber mixture according to the invention can be carried out at a temperature in the range from 80 to 200°C, preferably from 130 to 180°C, optionally under a pressure in the range from 10 to 200 bar.

From the rubber mixtures proposed in the invention, molded products can be produced by vulcanization.

The rubber mixture proposed in the invention can be used for the manufacture of molded products, for example for the manufacture of pneumatic tires, especially their treads, in the carcass or in the sidewall, cable sheaths, hoses, drive belts, conveyor belts, covers for various rolls, shoe soles, sealing elements , such as, for example, sealing rings, and shock-absorbing or vibration-damping elements.

The advantage of the precipitated silica according to the invention is that the corresponding rubber compounds are characterized by improved dispersion of silica therein. In addition, the rubber compounds proposed in the invention are characterized by improved hardening and better tear resistance. In addition, the achieved increased dynamic stiffness values, determined at 60°C, should lead to higher driving stability, i.e. to improved handling characteristics on dry road surfaces.

Measurement and analysis methods

Determination of base number

The alkaline number (AL) means the amount of hydrochloric acid in ml (with a sample volume of 50 ml, a volume of distilled water of 50 ml and a concentration of hydrochloric acid used of 0.5 mol/l) consumed during direct potentiometric titration of alkaline solutions or suspensions until the value is reached pH equal to 8.30. In this way, the content of free alkalis in a solution or suspension is determined.

The pH measuring device (Knick, type 766 pH-Meter Calimatic with temperature sensing element) and the pH electrode (Schott single-rod measuring chain, type N7680) are calibrated using two buffer solutions (pH = 7.00 and pH = 10, 00) at room temperature. The single-rod measuring circuit is immersed in the test solution, or test suspension, which is maintained at a temperature of 40° C. and consists of 50.0 ml of precipitation suspension and 50.0 ml of deionized water. After this, a solution of hydrochloric acid with a concentration of 0.5 mol/l is added dropwise until a constant pH value of 8.30 is achieved. Due to the only slow equilibrium between the silica and the free alkalis present, a waiting time of 15 minutes is required before the acid consumption is finally read. At the selected quantities of substances and concentrations, the read value of the hydrochloric acid consumption in ml directly corresponds to the alkaline number, which is a dimensionless quantity.

pH value: Determination of the pH value (warm) of silica according to DIN EN ISO 787-9

Measurements of the pH value during the production of silica are carried out on “warm” silica, namely at 60°C.

The measurement is carried out in accordance with DIN EN ISO 787-9 with the details described below.

Prepare a 5% (by weight) aqueous suspension of the test sample. To do this, use completely demineralized water.

The sample suspension is shaken for at least 5 minutes on a shaker before pH measurement.

The pH measurement is carried out using a previously calibrated pH meter from Metrohm, type: 780 with pH electrode type 6.0228.000 (Metrohm).

CTAB surface: Definition according to ISO 5794-1. Appendix G

This method is based on the adsorption of buffered CTAB (N-cetyl-N,N,N-trimethylammonium bromide) in an aqueous solution on the “outer” surface of silica, also called the “rubber mixing surface”. Unadsorbed CTAB is determined by back titration with dioctyl sodium sulfosuccinate (NDSS) solution. The end point of the titration is determined by the maximum increase in the turbidity of the solution.

The measurement is carried out in accordance with ISO 5794-1, Annex G, with the details, additions and derogations described below.

During sample preparation, coarse silica and silicate samples are preferably finely ground using a suitable mill or mortared and sifted through a 90 µm sieve, rather than subjected to mortar grinding and sieve fractionation as is the case herein. with hole size 150 microns.

Suspensions of test samples and a CTAB solution with an expected CTAB surface area of less than 200 m ² /g are stirred for 10 minutes. Suspensions of test samples and a CTAB solution with an expected CTAB surface area of at least 200 m ² /g are mixed in accordance with the standard for 35 minutes.

After adsorption, the silica is filtered through a polyamide filter with a hole size of 0.2 μm.

Titration of the filtrate is carried out on a titration processor from Metrohm with an automatic sampler and titrator Titrando 809. Spectrosense 523 nm from Metrohm is used as a photometric sensor (photorode).

BET surface (N ₂ , ₀ multi-point method): Determination according to DIN ISO 9277

This procedure is intended to determine the specific surface area of silica using the Brunauer-Emmett-Teller (BET) method for nitrogen adsorption in accordance with DIN ISO 9277. In this method, the measured value is determined by low-temperature nitrogen adsorption at certain partial pressures. This analysis is carried out as a multipoint analysis and is approximately linear in the partial pressure (p/po) range from 0.05 to 0.2 when measuring a total of 5 points.

The measurement is carried out in accordance with the DIN ISO 9277 standard with the details described below.

Before weighing (taking samples), granular samples are carefully crushed with a spatula and then kept for 60 minutes at 160±2°C in vacuum in a vacuum heating thermostat (degasser) VacPrep™ 061 from Micromeritics.

To determine the BET surface, the following 5 relative pressure points (p/p ₀ ) are recorded in the adsorption phase ^: 0.0500; 0.0875; 0.1250; 0.1625 and 0.2000.

For measurements, a TriStar 3000 series device (3000/3020/3030) from Micromeritics with a static volumetric measurement method and a Dewar vessel is used.

Ro-Tap>300 µm; Ro-Tap<75 µm: Sieve analysis according to ISO 5794-1 Annex F

Sieve analysis is carried out on a rotary sieve machine (Ro-Tap RX-29 analytical sieve machine with timer, Tyler). The method is carried out in accordance with ISO 5794-1, Annex F. For sieve analysis, laboratory sieves with different opening sizes are placed on top of each other (analytical sieve with metal sieve cloth, according to ISO 3310-1 standard, nominal opening size 75 µm, sieve diameter 200 mm; analytical sieve with metal sieve cloth, according to ISO 3310-1, nominal opening size 150 µm, sieve diameter 200 mm; analytical sieve with metal sieve cloth, according to ISO 3310-1, nominal opening size 300 µm, sieve diameter 200 mm). A column of sieves in the specified sequence is mounted in an analytical sieving machine. The residues on the sieves are determined in the following way. The sample is carefully homogenized before analysis. On a precision balance, 100 g of sample is weighed into a beaker with an accuracy of 0.01 g and the sample is quantitatively transferred to the upper sieve (with a hole size of 300 μm). Using a Ro-Tap machine, sift with a hammer for 5 minutes. Upon completion of sieving, remove the column from the sieves and hang the fractions on a tray, on a 75-μm sieve, on a 150-μm sieve, and on a 300-μm sieve.

Calculation of residues on sieves

Ro-Tap<75 µm in %=(A _P ⋅ 100%)/E, as well as

Ro-Tap>300 µm in %=(A ₃₀₀ ⋅ 100%)/E

And

Ro-Tap>150 µm in %=(A ₁₅₀ ⋅ 100%)/E, where

A300 means the residue on a sieve with a hole size of 300 microns in grams, A _P means the residue on the pallet in grams, E means the sample in grams.

pH value: Determination on silica according to DIN EN ISO 787-9

The measurement is carried out in accordance with DIN EN ISO 787-9 with the details described below.

Before taking a sample, the granulated sample material is crushed to a powder state by grinding in a mortar.

Next, prepare a 5% (by weight) aqueous suspension of the test sample. To do this, use completely demineralized water.

The sample suspension is shaken for at least 5 minutes on a shaker before pH measurement.

pH measurement is carried out at 23±2°C on a previously calibrated pH meter from Metrohm, type: 780 with pH electrode type 6.0228.000 (Metrohm).

Drying loss: Determination according to DIN EN ISO 787-2

In this case, the weight loss of the sample is determined when it is kept in a drying cabinet for 2 hours at 105°C.

The measurement is carried out in accordance with DIN EN ISO 787-2 with the details described below.

The bottle (with a polished lid, diameter approximately 80 mm, height approximately 30 mm) is heated without a stopper for approximately 1 hour at 105°C. After cooling, the lid is inserted into the desiccator. On a precision scale, the mass is determined with an accuracy of 0.01 g. Next, 5-10 g of the sample are accurately weighed (the weight depends on the bulk density) and distributed in an even layer at the bottom of the bottle. The bottle is carefully opened and kept in a drying oven for 2 hours at 105 + 2°C (the lid is heated together with the bottle, which, however, is not yet closed with it).

Then the bottle is carefully closed with a lid, placed in a desiccator to cool and re-weighed to the nearest 0.01 g.

Calculation

where E denotes the initial mass in grams, A denotes the final mass in grams.

Sears number _ref (SN): Determination on hydrophilic silica

Titration of silicon dioxide with a titrated solution of potassium hydroxide with a concentration of 0.1 mol/l in the pH range from 4 to 9 allows one to determine the Sears number _ref as a measure reflecting the amount of free silanol groups.

This method for determining the Sears number is based on the following chemical reactions, where ≡SiOH conventionally denotes the silanol group of silicon dioxide:

Analysis methodology

Approximately 10.00 g of silica in powder, spherical or granular form is uniformly ground for 60 seconds in a Fritsch mill (model Pulverisette 14 with 80 µm sieve) at 10,000 rpm. Approximately 1.50 g of thus treated silica is weighed to the nearest 0.1 mg into a 250 ml beaker and mixed with 150 ml of NaCl solution (p(NaCl) = 200 g/l with pH set to 3 using hydrochloric acid with (HCl) = 1 mol/l). After complete wetting of the sample, the suspension is dispersed for 30 s using an Ultra Turrax PT-1300D dispersant (Polytron) at a rotation speed of 20,000 rpm.

Before titration processes, the pH meter (methrom LL Unitrode pH electrode, type PT1000) is calibrated using buffer solutions (pH 4.00, pH 7.00 and pH 9.00) at room temperature. First, the initial pH value of the suspension is measured with a pH meter, after which, depending on the result obtained, the pH value is set to 4.00 using a solution of potassium hydroxide (0.1 mol/l), respectively, a solution of hydrochloric acid (0.1 mol/l) . After this, titration is carried out with a titrated KOH solution with a concentration of 0.1 mol/l until a pH value of 9.00 is achieved. The consumption of KOH solution in ml to change the pH value from 4.00 to 9.00 corresponds to the volume V _pH4-9 . Blank titration is carried out in the same way (without adding silicon dioxide). The value obtained as a result of a blank titration of the solution corresponds to the volume of potassium hydroxide solution V _BL that is necessary to titrate a NaCl solution without silicon dioxide from a pH value of 4 to a pH value of 9.

The Sears number _ex in terms of the original substance with the unit of measurement ml/(1.5 g) is calculated as follows:

where T means the titer of the titrated KOH solution used, and E means the sample weight in grams.

Silanol group density (SD): Calculation using Sears number SN per CTAB surface

Based on the Sears number, the flow rate is known to be 0.1N. KOH in ml/(1.5 g):

Using the CTAB surface and Avogadro's number (N _A ), the following expression is obtained:

This implies the density of silanol groups (SD) in OH/nm ² :

Moreover, in the formulas for the density of silanol groups SD, the value SN and the CTAB surface are used dimensionless, since they are already taken into account in the calculation.

Residue after ignition: Determination according to ISO 3262-1, respectively ASTM D 6740

By calcining the precipitated silica for 2 hours at 1000°C in a calcination furnace, the total water content (physically and chemically bound) and thus the content of all volatile components (loss on ignition) are determined, from which the calcination residue can be calculated.

Taking measurements

On an analytical balance, approximately 500 mg of silicon dioxide are weighed out into two porcelain or melting crucibles using a spatula with an accuracy of ±0.1 mg. Then the crucibles with silicon dioxide in them are calcined for 120±5 minutes in a calcination oven at 1000±50°C.

After calcination, the crucibles are placed in a desiccator with a suitable drying agent for approximately 1.5-2.0 hours to cool and reweighed on an analytical balance. Measurements are carried out in duplicate.

Definition of numerical value

First, the loss on ignition is determined based on the dried substance:

where GV means the loss on ignition based on the substance dried for 2 hours at 105°C in %, m _E means the mass of suspended silicon dioxide in grams, m _A means the mass of calcined silicon dioxide in grams, TV means the loss on drying for 2 h at 105°C in %.

The residue after calcination based on the starting material is calculated as follows:

and from here it follows

For this purpose, drying losses are determined using the method described in the section "Determination of drying losses in accordance with DIN EN ISO 787-2" (see above).

TAR: Granulate abrasion by friability test

To determine the degree of abrasion by testing the granulate for fragility, the fine and coarse fractions of silicon dioxide are removed and a fraction of 3.15-5.00 mm is used. This granulate fraction is subjected to repeated mechanical stress for 30 minutes in a rotating test chamber (eg ERWEKA TAR 220 with test drums on the left and right). Then the resulting fine fraction is separated by sifting through a sieve with a hole size of 500 microns. The difference in weight in % corresponds to the degree of abrasion of the granulate.

The degree of abrasion is determined in duplicate.

A representative 50 g sample of the silica being analyzed is taken for testing. By careful manual sieving (analytical sieves with metal sieve cloth, according to ISO 3310-1 standard, sieves diameter 200 mm, nominal opening size 500 µm, 3.15 mm, 5.00 mm, sieve tray), a particle size fraction of 3.15 is screened out -5.00 mm. This eliminates the fine fraction and very large particles. On an analytical or precision balance, exactly 5.00 ± 0.1 g of the 3.15-5.00 mm fraction is weighed. If the amount of the specified fraction screened is insufficient, the measurement cannot be performed. A representative portion of the sample quantity should be taken for testing. The sample is loaded into a test drum, which is then mounted on the abrasion tester. The device is operated for 30 minutes at a test drum speed of 65 rpm. The material is then poured quantitatively onto a 500 µm sieve and the adhering fines are removed by moderate shaking/motion. The granulate particles are then reweighed on a precision or analytical balance with an accuracy of 0.01 g.

Definition of numerical value

where “Abrasion” means the degree of abrasion when testing the granulate for fragility in%, E means a sample of the sifted fraction of 3.15-5.00 mm in grams, A means the remainder after applying the load and separating the fine fraction in grams.

The measurement result is the average of two separate measurements and is expressed as a percentage accurate to one decimal place.

DOA Absorption: Determination according to ISO 19246

To carry out the measurements, 12.50 ± 0.02 g of the sample is loaded into the kneading chamber of an absorbtometer type "Absorptometer E with extended functionality/processing unit" from Brabender. Dioctyl adipate (DOA) (e.g. Plastomoll DOA) is then dosed at a rate of 4 ml/min with constant mixing. The rotation speed of the kneader is 125 rpm. Based on the curve constructed from the raw data, the program calculates a polynomial. The value of this polynomial, equal to 70% of the maximum torque, serves to establish the absorption of DOA in terms of starting material in ml/(100 g). Measurements are carried out in accordance with ISO 19246 standard.

In the case of silica granulates, measurements are carried out on a particle size fraction of 1.00-3.15 mm, which must be prepared at the preparatory stage by sifting through appropriate sieves.

The following settings must be made in the meter software.

Measurement conditions

Dosing speed (burette): 4.0 ml/min

Kneader rotation speed: 125 min ^-1

Temperature: 23.0°C

Processing of measurement results

Torque threshold: 100 mN⋅m

End: 60s after reaching maximum torque

Torque limit: 10000 mN⋅m

Polynomial

Start: 50% of maximum torque

End: 20s after reaching maximum.

Using suitable reference materials with different DOA absorptions, the measuring kneader can be normalized individually using the Brabender® software. Based on the established normalization function (direct equation of the form y=a⋅x+b), according to the protocol of measurement results, it is possible to draw a conclusion about the absorption of DOA (normalized) in terms of the starting substance in ml/(100 g), expressed as a value equal to 70% of maximum torque.

Electrical conductivity: Determination according to DIN EN ISO 787-14

The electrical conductivity of silicon dioxide is determined in accordance with DIN EN ISO 787-14. However, in contrast to the recommendations of this standard, the following changes were made during measurements.

To carry out measurements, prepare a 4% aqueous suspension (4.00 g of silicon dioxide per 100 ml of deionized water).

Measurements are carried out directly on the suspension and not on the filtrate.

Measurements are carried out at 20.0±0.5°C and conductivity is indicated for a standard temperature of 20°C.

Determination of pore radius and volume based on mercury porosimetry (Hg indentation) in accordance with DIN 66133

The pore radius of silica samples, their corresponding volume and their size distribution are determined in the pressure range from 0.003 to 420 MPa. Measurements are carried out using an AutoPore IV 9520 porosimeter from Micromeritics in accordance with DIN 66133.

The sample is dried in an oven at 105±2°C for 2 hours.

To carry out measurements, a sample of the prepared sample is taken into a type 16 penetrometer from Micromeritics. A sample of approximately 330 mg is taken from the sample with an accuracy of 0.001 g. After this, the penetrometer in the low pressure port on the measuring device is slowly evacuated to a pressure of 50 μm Hg. and leave at this pressure for 5 minutes. After this, the penetrometer is filled with mercury, first in the low-pressure port, and then in the high-pressure port to a pressure of 420 MPa, and the experimentally recorded curve (pressure-volume curve) is recorded. Work with the AutoPore porosimeter is carried out in accordance with the operating instructions from Micromeritics and is controlled by software. The result of each measurement is corrected to the result of a blank measurement on the penetrometer. The full measurement range is from 0.003 to 420 MPa.

The following values are calculated as the measurement results from the experimentally recorded curve.

Maximum Pore Size:

Hg, -dV/dlogD; contact angle 140°, surface tension 480 mN/m in nm PV value:

Hg, 0.0042-414 MPa; contact angle 140°, surface tension 480 mN/m in ml/g

determined according to WO 2008/077948 based on mercury porosimetry

Bulk Density: Determination according to ASTM D1513

On a precision scale (accuracy 0.1 g), a 1000 ml measuring cylinder (with a scale division of 20 ml) with a filling funnel inserted into it (with a capacity of at least 1 liter) is tared. The test sample is thoroughly mixed by carefully turning the container with it. When analyzing granulates, special care must be taken to ensure that no additional fines are formed. After mixing, silica in an amount of 500-700 ml is carefully transferred into a 1-liter beaker (with rough graduation) using a scoop. A sample of silica is poured at once through a funnel into a graduated cylinder. After settling (without mechanical compaction), the bulk volume is read with an accuracy of 5 ml. In this case, you should ensure that the filling volume is from 500 to 700 ml. At the same time, to calculate the bulk density, the mass of the sample is determined with an accuracy of ±0.1 g.

Bulk density is calculated using the following formula:

where D means the bulk density in g/l, V means the volume of the sample after filling in ml, m means the mass of the sample in g.

Measurements are carried out in duplicate. In the case where the results of both measurements differ from each other by more than 3%, the value of the third measurement is used to calculate the average value. The result is indicated as a whole number without decimal places.

Examples

Example 1

1140 liters of water and 150 kg of liquid glass are loaded into a reactor equipped with a propeller stirrer and heated to 88.8°C. Then, over 100 minutes, 727.9 kg of liquid glass (density 1.345 kg/l, 27% SiO ₂ , 8% Na ₂ O) and 77.6 kg of sulfuric acid (density 1.84 kg/l, 96%) are simultaneously added nal H ₂ SO ₄ ), as a result of which the BN in the reaction mixture ranges from 24 to 27.

Sulfuric acid (density 1.84 kg/l, 96% H ₂ SO ₄ ) is then added, resulting in a pH of 8.6 (measured at 60° C.) in the reaction mixture.

The temperature in the precipitation tank is increased over 5 minutes to 94°C and the suspension is maintained for 55 minutes at 94°C with stirring to allow it to mature.

After this, sulfuric acid (density 1.84 kg/l, 96% H ₂ SO ₄ ) is fed further at a dosing rate of 0.70 kg/min until a pH value of 7 (measured at 60° C.) is achieved. Sulfuric acid is then continued to be added at a dosing rate of 0.35 kg/min until a pH value of 4.0 (measured at 60° C.) is reached.

The resulting suspension is filtered in the usual way, the filter cake is washed with water and dried in a vortex dryer with flash evaporation. The powder obtained in this way is granulated, i.e. compacted in a roller press and then crushed with a crusher.

Example 2

1164 liters of water and 150 kg of liquid glass (SC 25-26) are loaded into a reactor equipped with a propeller stirrer and heated to 89.0°C. Next, over 100 minutes, liquid glass (density 1.345 kg/l, 27% SiO ₂ , 8% Na ₂ O) is simultaneously added at an average dosing rate of 7.3 kg/min and sulfuric acid (density 1.84 kg/l, 96 % H ₂ SO ₄ ) with an average dosing speed of 0.82 kg/min.

Sulfuric acid (density 1.84 kg/l, 96% H ₂ SO ₄ ) is then added further, resulting in a pH value of 8.5 in the reaction mixture (measured at 60° C.).

The temperature in the precipitation tank is increased over 5 minutes to 94°C and the suspension is maintained for 55 minutes at 94°C with stirring to allow it to mature.

After this, sulfuric acid (density 1.84 kg/l, 96% H ₂ SO ₄ ) is first fed further at a dosing rate of 0.70 kg/min until a pH value of 7 (measured at 60 ° C) is reached, and acidification is then continued at a dosing rate of 0.35 kg/min until a pH value of 4.0 (measured at 60° C.) is reached.

The resulting suspension is filtered in the usual way, the filter cake is washed with water and dried in a vortex dryer with flash evaporation. The powder obtained in this way is granulated, i.e. compacted in a roller press and then crushed with a crusher.

Silicon dioxide has the analytical parameters indicated in Table 1.

The reference silica I is ZEOSIL ^® 1085 GR from Solvay SA

Example 3

Study of rubber properties

The recipe for rubber compounds (raw tire compound) is given below in Table 2. In this case, the value “part/100 parts rubber” represents the mass fraction of the corresponding component in terms of 100 parts of raw rubber used.

The rubber mixture is prepared in three stages in a closed mixer in accordance with the following list of working operations presented in tabular form (Table 3).

The general method for preparing rubber compounds and obtaining their vulcanizates is described in the reference book "Rubber Technology Handbook", W. Hofmann, Hanser Verlag, 1994.

The duration of vulcanization of each test sample is 15 minutes at 165°C. Rubber properties were studied using the methods presented in Table 4.

The data from the study of the rubber properties of the 5 rubber compounds proposed in the invention, given in Table 5, indicate that the quality of dispersion, respectively, the dispersibility of the silicon dioxide proposed in the invention, exceeds the state of the art, i.e. rubber mixture 1 (comparative). In the rubber mixtures 2 and 3 proposed in the invention, according to the results of direct analysis for the presence of defects on the vulcanizate section, clearly less undispersed silicon dioxide is detected during tactile examination of the surface topography and during its optical examination with the DisperTester device. As a result, the results of all hardening-related measurements are also clearly improved. In a tensile test, it is possible to clearly improve the tensile moduli at a constant elongation at break. This is also consistent with the improved Tear C and Graves test results obtained under different measurement conditions. The rubber compounds proposed in the invention also have improved wear resistance when tested for abrasion according to DIN compared to the comparative mixture. These advantages indicate that a tire treaded with a rubber compound containing and reinforced with silica according to the invention will have markedly improved wear resistance. The ball rebound elasticity at 23°C and the dielectric loss coefficient tan δ at 0°C also show clearly improved performance in relation to the behavior of similar treads on wet roads. High stiffness at high temperatures (E* at 60°C and modulus (max) in APRS) under these measurement conditions additionally indicate improved handling characteristics on dry road surfaces compared to the state of the art. In general, therefore, such rubber compounds and the silica according to the invention are able in a very special way to optimize and improve the overall performance of, for example, tires for winter conditions or even more specialized tires for northern winters (so-called " Scandinavian tires).

Claims (20)

1. Precipitated silicon dioxide, characterized by the following physicochemical parameters: surface of N-cetyl-N,N,N-trimethylammonium bromide-(CTAB): no more than 115 m ² /g, absorption of dioctyl adipate (DOA): not less than 130 ml/(100 g), rotary screening machine (Ro-Tap) >300 microns: no less than 86%, pore volume distribution V(d ₅ -d ₅₀ )/V(d ₅ -d ₁₀₀ ): less than 0.66. 2. Precipitated silicon dioxide according to claim 1, characterized in that the CTAB surface is no more than 90 m ² /g. 3. Precipitated silicon dioxide according to claim 1, characterized in that the pore volume (PV) in the pressure range from 0.0042 to 414 MPa at a contact angle of 140° is from 1.00 to 3.00 ml/g. 4. Precipitated silicon dioxide according to claim 1, characterized in that the density of silanol groups is at least 5.4 OH/nm ² . 5. Precipitated silica according to claim 1, characterized in that the bulk density is at least 180 g/l. 6. Precipitated silicon dioxide according to claim 1, characterized in that the length of one granule is at least 1 mm. 7. A method for producing precipitated silicon dioxide according to claim 1, characterized in that a) prepare an aqueous solution of organic and/or inorganic salt and/or silicate of an alkali or alkaline earth metal and/or organic and/or inorganic base with a pH of at least 9, b) liquid glass and an acidifying agent are simultaneously dosed into this initial solution with stirring and at a temperature ranging from 80 to 98°C for 60-120 minutes, c) then the addition of liquid glass is stopped and only the acid is dosed in a smaller amount than before to achieve the pH value of the mixture (measured at 60°C) in the range from 8.5 to 8.6, d) after which the mixture is stirred for 45-200 minutes at a high temperature above 85°C, but without further addition of starting materials, e) acidified with sulfuric acid to a pH value of 3.5-4.5 (measured at 60°C) and e) filtered, dried to a drying loss of less than 8% and then granulated. 8. A rubber mixture containing (A) rubber or a mixture of rubbers and (B) at least one precipitated silica according to claim 1. 9. A method for preparing a rubber mixture according to claim 8, characterized in that rubber or a mixture of rubbers, precipitated silicon dioxide according to claim 1 and, if necessary, further ingredients of the rubber mixture are mixed together in a mixer. 10. The use of rubber compounds according to claim 8 for the manufacture of tires, cable sheaths, hoses, drive belts, conveyor belts, coatings for various rolls, shoe soles, sealing elements and shock-absorbing vibration-damping elements.