Precipitated silica and method for producing the same

Abstract

A chemically modified precipitated silica characterized by the presence of methyl moieties chemically bonded to the silica, and a method for its manufacture are disclosed.

Description

[0001] This application claims the benefit of European Patent Application No. 19305861.7 filed on June 27, 2019, the entire contents of which are incorporated herein by reference for all purposes. Technical Field

[0002] The present invention relates to chemically modified precipitated silica and a process for its preparation. Background Art

[0003] It is known to use precipitated silica as a reinforcing filler in polymer compositions. It is also known to chemically modify the surface of precipitated silica with organosilicon compounds to improve the compatibility of the precipitated silica with the polymer matrix. The chemical modification of the precipitated silica is usually performed at the end of the silica precipitation process and is often performed as an additional step after drying.

[0004] It has now been found that chemically modified precipitated silicas capable of providing compositions having good heat dissipation properties can be obtained by modification during the silica precipitation reaction using an alkali metal alkyl siliconate. During a specific phase of the silica precipitation process, the presence of an alkali metal alkyl siliconate in the reaction medium allows the formation of silica chemically modified with an alkyl group. The chemical modification of the silica occurs during the precipitation process without requiring any subsequent modification step.

[0005] The use of alkali metal alkyl siliconates in the preparation of modified precipitated silica has been disclosed, for example, in WO 2018 / 019373, which discloses a process comprising an acid, a precipitated silica and / or [SiO 4 / 2 ] precursor material and an organosilicon alkoxide, wherein the modification reaction takes place during or directly after the reaction to produce the precipitated silica. The precipitated silica obtained by this process has a low content of salts and is useful as a reinforcing filler in silicone elastomer compositions (in toners or developers).

[0006] It has now been found that if the precipitation process comprises a step carried out at low pH, followed by a step carried out at higher pH during which an alkali metal methylsiliconate is added to the reaction medium, the precipitated silica obtained is able to improve the heat dissipation characteristics of the elastomeric composition and / or its curing behavior. The tire comprising said elastomeric composition is characterized in particular by a reduced rolling resistance. Summary of the invention

[0007] A first object of the present invention is to provide a novel chemically modified precipitated silica which can be used as a reinforcing filler, for example, in polymer compositions. A second object of the present invention is to provide a method for producing the chemically modified precipitated silica.

[0008] The precipitated silica of the invention is characterized in particular by the presence of methyl groups covalently attached to the silica.The silica of the invention is defined in detail in the description that follows and in the claims and examples. DETAILED DESCRIPTION

[0009] The precipitated silica of the present invention comprises a 4 / 2 ] and units having the formula [(CH3)SiO 3 / 2 ] and is characterized in that the precipitated silica 13 There are two resonance peaks attributed to the methyl group in the C NMR spectrum: the first resonance peak is in the region between -2.0 ppm and -5.0 ppm, and the second resonance peak is in the region between -5.5 ppm and -9.0 ppm, and the ratio (intensity of the second peak) / (intensity of the first peak) is greater than 0.40.

[0010] The expression "resonance peak between -X and -Y ppm" is used herein to indicate that when the chemical shift scale is calibrated with the resonances of adamantane (at 38.5 ppm and 29.4 ppm), the maximum of the resonance peak exists at 13 The region between -X ppm and -Y ppm of a C NMR spectrum.

[0011] It is observed that the resonances of the methyl groups in the silica of the present invention are shifted relative to the resonances of the same methyl groups of the alkali metal methyl siliconate used to prepare the precipitated silica. For example, when the alkali metal methyl siliconate is potassium methyl siliconate, the single methyl resonance at -1.1 ppm is split into a first peak between -2.0 ppm and -5.5 ppm and a second peak between -5.5 ppm and -9.0 ppm. The first peak may be between -3.0 ppm and -5.0 ppm. The second peak may be between -6.5 ppm and -8.5 ppm.

[0012] The ratio (intensity of the second peak) / (intensity of the first peak) is greater than 0.40. The ratio (intensity of the second peak) / (intensity of the first peak) is preferably equal to or greater than 0.45, even equal to or greater than 0.50, and further equal to or greater than 0.52.

[0013] The ratio (intensity of the second peak) / (intensity of the first peak) can be as high as 5.00.

[0014] The ratio (intensity of the second peak) / (intensity of the first peak) may be between 0.40 and 5.00, even between 0.45 and 3.00, between 0.45 and 2.00, still further between 0.45 and 1.60, between 0.50 and 1.60.

[0015] The silicon dioxide of the present invention comprises methyl groups chemically bonded to at least a portion of the Si atoms in the silicon dioxide structure.

[0016] In this specification, the terms "silicon dioxide" and "precipitated silica" are used as synonyms. The expression "precipitated silica" defines an amorphous silica produced by acidifying a sodium silicate solution, followed by filtering the precipitate and drying in the absence of any step in which water is extracted from the precipitate using an organic solvent (e.g., alcohol or supercritical fluid).

[0017] The precipitated silica of the present invention has a carbon content of at least 0.2 wt%, typically from 0.2 wt% to 10.0 wt%. Throughout this article, the carbon content is defined as the amount of carbon by weight relative to the total weight of the silica. The carbon content represents the amount of methyl moieties chemically bonded to the precipitated silica. The carbon content is typically less than 10.0 wt%, and it may even be less than 5.0 wt%. Advantageously, the carbon content is from 0.2 wt% to 5.0 wt%, even from 0.3 to 4.0 wt%. The carbon content may be from 0.2 wt% to 3.5 wt%, even from 0.3 to 3.0 wt%, preferably from 0.3 to 2.0 wt%.

[0018] The expressions wt% and % by weight are used as synonyms.

[0019] In general, the precipitated silica according to the present invention has a particle size between 40 and 600 m 2 The CTAB surface area can be at least 50 m 2 / g, at least 60m 2 / g, at least 80m 2 / g, or even at least 120m 2 / g, at least 160m 2 / g, at least 205m 2 / g, at least 210m 2 / g. The CTAB surface area can be up to 450m 2 / g, up to 380m 2 / g, even up to 300m 2 / g. The CTAB surface area can be particularly between 50 and 450 m 2 / g, especially between 60 and 380m 2 / g, for example, between 80 and 300 m 2 / g.

[0020] In an embodiment, the precipitated silica of the present invention is characterized by:

[0021] -CTAB surface area is 40m 2 / g and 600m 2 / g, preferably 50m 2 / g and 380m 2 / g, more preferably 60m 2 / g and 300m 2 / g; and

[0022] - Carbon content from 0.2 wt% to 3.5 wt%, preferably from 0.3 wt% to 3.0 wt%.

[0023] The silica of the present invention is further characterized by a large median particle size (particle diameter) d50 for a given CTAB surface area value. In particular, it has been found that, at a given CTAB surface area, the median particle size of the silica of the present invention is higher than that measured on known organically modified precipitated silicas.

[0024] It has been found that the median particle size d50 and the CTAB surface area of ​​the silica of the invention are such that:

[0025] |d50|>164.5-0.3*|CTAB| (I).

[0026] In formula (I), |CTAB| represents the 2 / g represents the numerical value of the surface area of ​​CTAB. |CTAB| is a dimensionless number. As an example, if the measured value of CTAB is 200m 2 / g, then |CTAB| is 200.

[0027] In formula (I), |d50| represents the numerical value of the median particle size d50 measured by centrifugal sedimentation and expressed in nm. For example, if the value of d50 measured by centrifugal sedimentation is 100 nm, |d50| is 100. d50 represents the diameter below (and above) which 50% of the total mass of aggregate is found. Thus, d50 represents the median particle size of a given distribution, wherein the term "size" in this context is intended to be "diameter". |d50| is a dimensionless number.

[0028] The precipitated silica according to the invention typically has a 2 / g and 650m 2 / g, especially at 70m 2 / g and 500m 2 / g, even between 90 and 400m 2 / g, for example, between 90 and 370 m 2 The BET surface area can be determined according to the Brunauer-Emmett-Teller method as detailed in standard NF ISO 5794-1, annex E (June 2010).

[0029] The precipitated silica according to the invention has a carbon dioxide content of at most 0.50 g / cm 3 , preferably 0.15 to 0.50 g / cm 3 , especially at 0.15 and 0.40 g / cm 3 The packing density between.

[0030] The precipitated silica of the invention can advantageously be obtained by a process comprising the reaction of a silicate with an acid to produce a suspension of precipitated silica, said reaction comprising at least one step in which at least one alkali metal methylsiliconate is provided to the reaction medium after 50% of the precipitation reaction has occurred.

[0031] A second object of the present invention is therefore a process for preparing the precipitated silica according to the invention.

[0032] The term "silicate" is used herein to refer to one or more than one silicate that may be added during the process of the method of the invention. The term "silicate" is used herein to refer to a compound selected from the group consisting of alkali metal silicates. Advantageously, it is selected from the group consisting of sodium silicate and potassium silicate. The silicate may be in any known form, such as a metasilicate or a disilicate.

[0033] In cases where sodium silicate is used, the sodium silicate generally has a SiO2 / Na2O weight ratio of between 2.0 and 4.0, in particular between 2.4 and 3.9, for example between 3.1 and 3.8.

[0034] The silicate is usually provided in solution, typically having a concentration between 3.9 wt% and 25.0 wt%, for example between 5.6 wt% and 23.0 wt%, in particular between 5.6 wt% and 20.7 wt%. Throughout this document, the silicate concentration in solution is expressed as the amount by weight of SiO2.

[0035] The term "acid" is used herein to refer to one or more than one acid that may be added during the course of the method of the invention. Any acid may be used in the method. Typically, inorganic acids such as sulfuric acid, nitric acid or hydrochloric acid, or organic acids such as acetic acid, formic acid or carbonic acid are used. Sulfuric acid is preferred.

[0036] The acid can be metered into the reaction medium in dilute or concentrated form. The same acid can be used in different concentrations at different stages of the process.

[0037] In a preferred embodiment of the process, sulfuric acid and sodium silicate are used in all stages of the process.

[0038] The process according to the invention is characterized in that at least one alkali metal methylsiliconate is added to the reaction medium after 50% of the precipitation reaction has taken place.

[0039] The expression "after 50% of the precipitation reaction has taken place" is used herein to indicate any stage of the process in which the amount of SiO2 produced up to said given stage is greater than 50 wt% of the final amount of SiO2 produced in the process.

[0040] Depending on the process, the percentage of silica precipitation can be monitored in different ways. In one variant of the process, 50 wt % of the total amount of silicate formed corresponds to 50 % of the total amount of silicate to be added to the reaction medium during the process.

[0041] In an alternative variation, 50 wt% of the total amount of silica formed is achieved when the neutralization ratio of the reaction medium reaches 50%. The term "neutralization ratio" is defined as the H generated by the acid added to the reaction medium. + The ratio between the number of moles of silicate and the number of moles of alkali metal derived from the silicate in the reaction medium.

[0042] Notable examples of suitable alkali metal methylsiliconates are those having the general formula, general formula (II):

[0043] HO-[Si(CH3)(OM)-O-] n H (II)

[0044] Or general formula (III):

[0045] (CH3)2Si(OM)2

[0046] wherein n is an integer from 1 to 6, especially from 1 to 3, preferably 1; and M is an alkali metal, preferably sodium or potassium.

[0047] Preferably, the alkali metal methylsiliconate is selected from sodium methylsiliconate or potassium methylsiliconate.

[0048] The method of the present invention comprises the following steps:

[0049] (i) providing a starting solution having a pH between 2.0 and 5.0, preferably between 2.5 and 5.0;

[0050] (ii) adding a silicate and an acid simultaneously to the starting solution so that the pH of the resulting reaction medium is maintained between 2.0 and 5.0;

[0051] (iii) stopping the addition of acid while continuing to add silicate to the reaction medium until a pH of the reaction medium between 7.0 and 10.0 is obtained;

[0052] (iv) adding a silicate and an acid simultaneously to the reaction medium obtained in (iii) so that the pH is maintained between 7.0 and 10.0; and

[0053] (v) stopping the addition of the silicate while continuing to add the acid to the reaction medium until a pH value of the reaction medium of less than 6.0 is reached and a silica suspension is obtained, the process being characterized in that, in step (iv) or (v), at least one alkali metal methylsiliconate is metered into the reaction medium.

[0054] The addition of the alkali metal methylsiliconate takes place after 50% of the total amount of silicate has been added to the reaction medium.The total amount of silicate used to obtain a given final amount of silica can be determined at the beginning of the process by a person skilled in the art according to common general knowledge.

[0055] In a first embodiment of the process, all of the addition of the alkali metal methylsiliconate occurs during step (iv).

[0056] In a second embodiment of the process, all of the addition of the alkali metal methylsiliconate occurs during step (v).

[0057] In a first aspect of the embodiment, step (v) comprises two stages, a first stage in which the acid and the alkali metal methyl siliconate are metered simultaneously into the reaction medium at a pH between 7.0 and 10.0, followed by a second stage in which the addition of the alkali metal methyl siliconate is stopped, while the addition of the acid is continued and the pH of the reaction medium is reduced to below 6.0.

[0058] The process may comprise additional steps, notably steps wherein the pH is further altered by adding silicate and / or acid to the reaction medium.

[0059] Without wishing to be bound by theory, it is believed that the combination of conducting the first precipitation stage between pH 2.5 and 5.0 and adding the alkali metal methyl siliconate after 50% of the precipitation reaction has occurred allows the methyl moieties of the alkali metal alkyl siliconate to be incorporated into different parts of the structure of the precipitated silica, as shown by the presence of different methyl groups in the NMR spectrum of the product.

[0060] In all the process embodiments outlined above, and regardless of the stage of addition of the at least one alkali metal methylsiliconate, the cumulative amount of said compound metered into the reaction medium is at least 0.5 wt %, typically at least 1.0 wt %, even at least 5.0 wt %. The total amount of at least one alkali metal methylsiliconate is typically not more than 10.0 wt %. Suitable ranges are generally from 1.0 to 10.0 wt %, from 2.0 to 10.0 wt %, even from 2.0 to 8.0 wt %. The amount of alkali metal methylsiliconate is calculated relative to the silica concentration in the starting solution (calculated as the sum of the initial amount of silicate and the initial amount of alkali metal methylsiliconate).

[0061] The cumulative amount of said compound metered into the reaction medium is such that the carbon content in the precipitated silica is at least 0.2 wt %, typically from 0.2 to 10.0 wt %. The addition rate of the alkali metal methylsiliconate can be adjusted by means known to those skilled in the art to obtain the desired content of methyl moieties in the precipitated silica.

[0062] The reaction vessel in which the entire reaction of the silicate with the acid takes place is usually equipped with appropriate stirring and heating equipment.

[0063] The entire reaction of silicate with acid is generally carried out at a temperature between 40° C. and 96° C., in particular between 80° C. and 95° C. According to one variant of the invention, the entire reaction of silicate with acid is carried out at a constant temperature, generally between 40° C. and 96° C., in particular between 80° C. and 95° C.

[0064] According to another variant of the invention, the temperature at the end of the reaction is higher than the temperature at the beginning of the reaction: thus, it is preferred to maintain the temperature at the beginning of the reaction between 40°C and 80°C and then increase the temperature, preferably up to a value between 80°C and 96°C, maintaining the temperature at this value until the end of the reaction.

[0065] At the end of the steps just described for each of the process embodiments, a suspension of precipitated silica is obtained which is subsequently subjected to a separation (liquid / solid separation) step. Thus, the process in all its embodiments typically comprises a further step of filtering the suspension of precipitated silica and drying the precipitated silica. The process does not comprise any step in which water is extracted from the precipitate using an organic solvent (e.g. an alcohol or a supercritical fluid).

[0066] Separation generally comprises filtration followed by washing if necessary. Filtration is performed according to any suitable method, for example by means of a belt filter, a rotary filter, such as a vacuum filter, or, preferably, a filter press.

[0067] The filter cake is then subjected to a liquefaction operation. The term "liquefaction" is intended here to indicate a process in which a solid, ie the filter cake, is transformed into a fluid-like substance. After the liquefaction step, the filter cake is in a flowable, fluid-like form and the precipitated silica is in the form of a suspension.

[0068] The liquefaction step may include a mechanical treatment that results in a reduction in the particle size (granulometry) of the silicon dioxide in the suspension. The mechanical treatment may be performed by passing the filter cake through a high shear mixer, a colloid-type grinder or a ball mill. Optionally, the liquefaction step may be performed by subjecting the filter cake to a chemical action, such as by adding water or an acid. Both mechanical and chemical treatments may be performed. The suspension of precipitated silicon dioxide obtained after the liquefaction step is subsequently dried.

[0069] Drying can be carried out according to means known in the art. Preferably, drying is carried out by atomization. For this purpose, any type of suitable atomizer can be used, in particular a turbine, nozzle, hydraulic or two-fluid spray dryer.

[0070] When a nozzle spray dryer is used for the drying operation, the precipitated silica that can then be obtained is generally in the form of substantially spherical beads. After this drying operation, the recovered product can optionally be subjected to a grinding or micronizing step; the precipitated silica that can then be obtained is generally in the form of a powder.

[0071] Finally, the dried, ground or micronized product as indicated previously can optionally be subjected to an agglomeration step, which comprises, for example, direct compression, wet granulation (i.e. using a binder such as water, a silica suspension, etc.), extrusion or, preferably, dry pressing. The precipitated silica that can then be obtained by this agglomeration step is generally in the form of granules.

[0072] The precipitated silica of the present invention can be used in many applications, such as making thermal insulation materials. The precipitated silica of the present invention can also be used to prepare resorcinol-formaldehyde / silica composites, as absorbents or as additives in concrete or paper.

[0073] The precipitated silica of the invention can be used particularly advantageously as filler in polymer compositions.

[0074] Therefore, another object of the present invention is a composition comprising the precipitated silica of the present invention. The composition advantageously comprises the precipitated silica of the present invention and at least one polymer. The at least one polymer can be selected from thermosetting polymers and thermoplastic polymers. Notable non-limiting examples of thermosetting polymers include thermosetting resins such as epoxy resins, unsaturated polyester resins, vinyl ester resins, phenolic resins, epoxy acrylate resins, urethane acrylate resins, phenoxy resins, alkyd resins, carbamate resins, maleimide resins, and cyanate resins.

[0075] Notable non-limiting examples of suitable thermoplastic polymers include styrene-based polymers such as polystyrene, (meth)acrylate / styrene copolymers, acrylonitrile / styrene copolymers, styrene / maleic anhydride copolymers, ABS, ASA, and AES; acrylic polymers such as polymethyl methacrylate; polycarbonates; polyamides; polyesters such as polyethylene terephthalate and polybutylene terephthalate; polyphenylene ether; polysulfones; polyaryletherketones; polyphenylene sulfide; thermoplastic polyurethanes; polyolefins such as polyethylene, polypropylene, polybutylene, poly-4-methylpentene, ethylene / propylene copolymers, ethylene / α-olefin copolymers; copolymers of α-olefins and various monomers such as ethylene / vinyl acetate copolymers, ethylene / (meth)acrylate copolymers, ethylene / maleic anhydride copolymers, ethylene / acrylic acid copolymers; aliphatic polyesters such as polylactic acid, polycaprolactone, and aliphatic diol / aliphatic dicarboxylic acid copolymers.

[0076] The silica of the invention can advantageously be used as a reinforcing filler in an elastomeric composition. Thus, a preferred object of the invention is a composition comprising the silica of the invention and one or more elastomers. The elastomer preferably exhibits at least one glass transition temperature between -150°C and +300°C, for example between -150°C and +20°C.

[0077] For example, elastomers derived from aliphatic or aromatic monomers containing at least one unsaturation may be used, such as, in particular, ethylene, propylene, butadiene, isoprene, styrene, acrylonitrile, isobutylene or vinyl acetate, polybutyl acrylate or mixtures thereof. Mention may also be made of functionalized elastomers, elastomers functionalized by chemical groups positioned along the macromolecular chain and / or at one or more of its ends (e.g., by functional groups capable of reacting with the silica surface), and halogenated polymers.

[0078] Notable non-limiting examples of suitable elastomers are diene elastomers. Mention may be made, among the diene elastomers, for example, of polybutadiene (BR), polyisoprene (IR), butadiene copolymers, isoprene copolymers, or mixtures thereof, and in particular styrene / butadiene copolymers (SBR, in particular ESBR (emulsion) or SSBR (solution)), isoprene / butadiene copolymers (BIR), isoprene / styrene copolymers (SIR), isoprene / butadiene / styrene copolymers (SBIR), ethylene / propylene / diene terpolymers (EPDM), and also related functionalized polymers (for example, with pendant polar groups or polar groups at the chain ends, these polar groups being able to interact with silica).

[0079] Mention may also be made of natural rubber (NR) and epoxidized natural rubber (ENR).

[0080] The polymer composition may be vulcanized with sulfur, or crosslinked, in particular with peroxides or other crosslinking systems (eg diamines or phenolic resins).

[0081] Generally, these polymer compositions additionally comprise at least one (silica / polymer) coupling agent and / or at least one covering agent; they may also comprise, in particular, antioxidants.

[0082] Notable non-limiting examples of coupling agents are, for example, "symmetrical" or "asymmetrical" silane polysulfides; mention may be made more particularly of: bis((C1-C4)alkoxy(C1-C4)alkylsilyl(C1-C4)alkyl)polysulfides (in particular, disulfides, trisulfides or tetrasulfides), such as, for example, bis(3-(trimethoxysilyl)propyl)polysulfide or bis(3-(triethoxysilyl)propyl)polysulfide, such as triethoxysilylpropyltetrasulfide. Mention may also be made of monoethoxydimethylsilylpropyltetrasulfide. Mention may also be made of silanes containing masked or free thiol functions or thioester groups, such as 3-octanoylthio-1-propyltriethoxysilane.

[0083] The weight ratio of the silica of the present invention in the polymer composition can vary within a fairly wide range. It generally accounts for from 10% to 200%, in particular from 20% to 160%, of the amount by weight of the one or more polymers. In one embodiment, the precipitated silica of the present invention can account for from 20% to 80%, for example from 30% to 70%, of the amount by weight of the one or more polymers. In an alternative embodiment, it can account for from 80% to 140%, for example from 90% to 120%, of the amount by weight of the one or more polymers.

[0084] A particular object of the present invention is a composition comprising the precipitated silica of the invention and at least one polymer chosen from the group consisting of diene elastomers, natural rubber and epoxidized natural rubber as described above in detail, the amount of precipitated silica typically being from 20% to 160% by weight of the amount of polymer or polymers.

[0085] The silica according to the invention may advantageously constitute the entirety of the reinforcing inorganic filler and even the entirety of the reinforcing filler of the polymer composition.

[0086] Compositions comprising the precipitated silica of the present invention can be used to manufacture a variety of articles. Non-limiting examples of finished products comprising the precipitated silica of the present invention and the composition described above are, for example, soles, floor coverings, gas barriers, flame retardant materials and also engineering parts (such as cableway rollers), seals for household appliances, seals for liquid or gas pipelines, brake system seals, pipes (flexible), sheaths (especially cable sheaths), cables, engine mounts, battery separators, conveyor belts, or transmission belts. The composition of the present invention can be advantageously used to manufacture tires and tire components.

[0087] Another object of the invention is a tire or a tire component comprising the precipitated silica according to the invention.

[0088] Should the disclosure of any patents, patent applications, and publications incorporated herein by reference conflict with the description of the present application to the extent that it renders a term unclear, the present description shall take precedence.

[0089] The present invention will now be described with reference to the following examples, which are for illustrative purposes only and are not intended to limit the scope of the present invention.

[0090] Examples

[0091] Analytical methods

[0092] The physicochemical properties of the precipitated silicas of the present invention were determined using the methods described below.

[0093] CTAB surface area

[0094] The CTAB surface area was determined according to standard NF ISO 5794-1, Annex G (June 2010).

[0095] Determination of total carbon content

[0096] Use carbon / sulfur analyzer such as Horiba EMIA 320 V2 to measure total carbon content.The principle of this carbon / sulfur analyzer is based on the combustion of solid sample in the oxygen stream in induction furnace (being adjusted to about 170mA) and in the presence of combustion promoter (about 2g of tungsten (particularly Lecocel 763-266), about 1g of iron and about 0.25g of tin).The carbon (weight is about 0.2g) present in the sample to be analyzed is combined with oxygen to form CO , CO.These gases are analyzed by infrared detectors subsequently.The water produced during these oxidation reactions from the moisture of this sample and is removed by passing through the sleeve (cartridge) comprising a dehydrating agent (magnesium perchlorate) so as not to interfere with infrared measurement.

[0097] The results are expressed as weight percent of elemental carbon relative to the total weight of the silica sample.

[0098] 13 C NMR spectrum

[0099] The 1D spectrometer was used on a Bruker Avance Solids 300 spectrometer operating at 7.04 T. 13 The products were characterized by C MAS NMR spectroscopy. A commercial 4 mm high speed probe (DVT4) with a rotation frequency of 10 KHz was used with cross polarization of 90° pulses, 3 ms contact time and 5 s cycle time and 10,000-20,000 transients. The region of the spectrum analyzed for identification of methyl resonances was from -15 ppm to 10 ppm.

[0100] Calibration was performed relative to adamantane, which is characterized by two chemical shifts at 38.5 ppm and 29.4 ppm.

[0101] Data analysis was performed using built-in TOPSPIN 4.0.6 software. The strongest signals between -2.0 ppm and -5.0 ppm and between -5.5 ppm and -9.0 ppm in the spectrum were manually selected, and the intensity of each peak was determined.

[0102] Determination of BET surface area

[0103] The BET surface area was determined according to the Brunauer-Emmett-Teller method as detailed in standard NF ISO 5794-1, Annex E (June 2010), with the following modifications: the sample was predried at 200° C.±10° C.; the partial pressure p / p used for the measurement was 0 Between 0.05 and 0.3.

[0104] Determination of particle size distribution and particle size by centrifugal sedimentation in a disc centrifuge (CPS)

[0105] The d50 values ​​are determined by centrifugal sedimentation in a disc centrifuge using a centrifugal light transmission particle sizer model "CPS DC 24000UHR" sold by CPS Instruments. This instrument is equipped with the operating software supplied with the device (operating software version 11g).

[0106] The same method and the same tools described in WO 2018 / 202752 A1 (paragraphs

[00155] -

[00178] ) were applied for determining the d50 of the silica of the present invention.

[0107] Examples

[0108] Example 1

[0109] In a 25 L stainless steel reactor are introduced: 16.7 L purified water, 260.2 g Na2SO4 (solid). The solution is stirred and heated to 92° C. The entire reaction is carried out at this temperature. A 7.7 wt % sulfuric acid solution is metered into the reactor until the pH of the medium reaches a value of 3.8.

[0110] Then, a sodium silicate solution (SiO2 / Na2O ratio = 3.46; SiO2 concentration = 19.5 wt%, used during the entire process) was introduced at a flow rate of 112 g / min over a period of 15 min simultaneously with a 7.7% wt sulfuric acid solution. The flow rate of the sulfuric acid solution was adjusted so that the pH of the reaction medium was maintained at a value of 4.1. After this step, the silicate solution was introduced for another 10 minutes at the same flow rate, the pH being kept constant at 4.1 using 95% wt sulfuric acid.

[0111] The introduction of acid was stopped while the addition of silicate was maintained at a flow rate of 123 g / min until the reaction medium reached a pH of 8.0.

[0112] Sodium silicate was metered into the reactor simultaneously at a flow rate of 178 g / min and 95 wt % sulfuric acid solution over a period of 8 min. The flow rate of the sulfuric acid solution was adjusted so that the pH of the reaction medium was maintained at a value of 8.0. Then, 331 g of potassium methylsiliconate solution ( BS 16, Wacker Chemie AG (50 wt %) was metered into the reaction medium, while keeping the sodium silicate flow rate constant. The pH was maintained at pH 8.0 using 95 wt % sulfuric acid.

[0113] At the end of the simultaneous additions, the pH of the reaction medium was brought to 4.8 with 95 wt % sulfuric acid. The reaction mixture was allowed to stand for 5 minutes.

[0114] The silica suspension thus obtained was filtered on a filter press and washed. The filter cake thus obtained was mechanically broken up while adding water to a solid content of 15.4 wt %. The pH of the silica suspension obtained was brought to 6.2 by adding 7.7 wt % sulfuric acid solution. The suspension obtained was dried by a nozzle spray dryer to obtain precipitated silica S1. The properties of the precipitated silica S1 are reported in Table 1.

[0115] Example 2

[0116] In a 25 L stainless steel reactor are introduced: 15.7 L purified water and 244.4 g Na2SO4 (solid). The solution is stirred and heated to 92° C. The entire reaction is carried out at this temperature. A 7.7 wt % sulfuric acid solution is metered into the reactor until the pH of the medium reaches a value of 3.8.

[0117] Then, a sodium silicate solution (SiO2 / Na2O ratio = 3.46; SiO2 concentration = 19.5 wt%, used during the entire process) was introduced at a flow rate of 105 g / min over a period of 15 min simultaneously with a 7.7% wt sulfuric acid solution. The flow rate of the sulfuric acid solution was adjusted so that the pH of the reaction medium was maintained at a value of 4.1. After this step, the silicate solution was introduced for another 10 minutes at the same flow rate, the pH being kept constant at 4.1 using 95% wt sulfuric acid.

[0118] The introduction of acid was stopped while the addition of silicate was maintained at a flow rate of 123 g / min until the reaction medium reached a pH of 8.0.

[0119] Sodium silicate and 95 wt % sulfuric acid solution were metered in simultaneously at a flow rate of 167 g / min over a period of 18 min. The flow rate of the sulfuric acid solution was adjusted so that the pH of the reaction medium was maintained at a value of 8.0. Then, 368 g of potassium methylsiliconate solution ( BS 16, Wacker Chemie; 50 wt %) was metered into the reaction medium. The pH was maintained at a pH value of 8.0 using 95 wt % sulfuric acid.

[0120] At the end of the simultaneous additions, the pH of the reaction medium was brought to 4.8 with 95 wt % sulfuric acid. The reaction mixture was allowed to stand for 5 minutes.

[0121] The silica suspension thus obtained was filtered on a filter press and washed. The filter cake thus obtained was mechanically crushed while adding sodium aluminate solution (Al2O3 concentration: 12 wt%) to obtain an Al / SiO2 concentration of 3000 ppm. The pH of the silica suspension obtained was brought to 6.2 by adding 7.7 wt% sulfuric acid solution. The suspension obtained was dried by a nozzle spray dryer to obtain precipitated silica S2. The properties of the precipitated silica S2 are reported in Table 1.

[0122] Example 3

[0123] In a 25 L stainless steel reactor are introduced: 16.7 L purified water and 260.2 g Na2SO4 (solid). The solution is stirred and heated to 92° C. The entire reaction is carried out at this temperature. A 7.7 wt % sulfuric acid solution is metered into the reactor until the pH of the medium reaches a value of 3.8.

[0124] Then, a sodium silicate solution (SiO2 / Na2O ratio = 3.46; SiO2 concentration = 19.5 wt%, used during the entire process) was introduced at a flow rate of 112 g / min over a period of 15 min simultaneously with a 7.7% wt sulfuric acid solution. The flow rate of the sulfuric acid solution was adjusted so that the pH of the reaction medium was maintained at a value of 4.1. After this step, the silicate solution was introduced for another 10 minutes at the same flow rate, the pH being kept constant at 4.1 using 95% wt sulfuric acid.

[0125] The introduction of acid was stopped while the addition of silicate was maintained at a flow rate of 123 g / min until the reaction medium reached a pH of 8.0.

[0126] Sodium silicate and 95 wt % sulfuric acid solution were metered in simultaneously at a flow rate of 178 g / min over a period of 8 min. The flow rate of the sulfuric acid solution was adjusted so that the pH of the reaction medium was maintained at a value of 8.0. Then, 993 g of potassium methylsiliconate solution ( BS 16, Wacker Chemie; 50 wt %) was metered into the reaction medium, while keeping the sodium silicate flow rate constant. The pH was maintained at a value of 8.0 using 95 wt % sulfuric acid.

[0127] At the end of the simultaneous additions, the pH of the reaction medium was brought to 4.8 with 95 wt % sulfuric acid. The reaction mixture was allowed to stand for 5 minutes.

[0128] The silica suspension thus obtained was filtered on a filter press and washed. The filter cake thus obtained was mechanically broken up while adding water to a solid content of 15.4 wt %. The pH of the silica suspension obtained was adjusted to 6.2 by adding 7.7 wt % sulfuric acid solution. The suspension obtained was dried by means of a nozzle spray dryer to obtain precipitated silica S3. The properties of the precipitated silica S3 are reported in Table 1.

[0129] Table 1

[0130]

[0131] Comparison with Silica CS1: A sample of Premium 200MP (available from Solvay SA).

[0132] Example 4-Comparative Example 1

[0133] Silica S1 was evaluated in a SBR / BR matrix. These compositions, expressed as parts by weight per 100 parts of elastomer (phr), are described in Table 2 below.

[0134] Table 2

[0135]

[0136] The process for preparing these rubber compositions is carried out in two consecutive preparation stages: a first stage of thermomechanical processing at high temperature, followed by a second stage of mechanical processing at a temperature less than 110° C., in order to introduce the vulcanization system.

[0137] The first stage is carried out using a mixing device of the Brabender brand internal mixer type (capacity 380 mL). In the first process of this first stage, the elastomer and reinforcing filler (introduced in batches) are mixed with the coupling agent, the resin, the DPG and the stearic acid. The duration is about 3 to 4 min30, the dripping temperature is about 140°C to 150°C. After cooling the mixture (temperature below 100°C), the second process enables the incorporation of zinc oxide and protective agent / antioxidant and silanization. The duration of this process is 4 minutes, and the dripping temperature is about 150°C to 160°C.

[0138] After the mixture has been cooled (temperature less than 100° C.), the vulcanization system (sulphur and accelerators such as CBS) is added during the second process step. It is carried out on an open rubber mixer preheated to 50° C. The duration of this phase is between 2 and 6 minutes.

[0139] Each final mixture was subsequently calendered in the form of sheets having a thickness of 2-3 mm.

[0140] Mechanical properties of vulcanized products

[0141] The measurements were carried out on the vulcanized compositions cured at 160°C for 1 hour.

[0142] The Shore A hardness measurements on these vulcanized products were carried out in accordance with standard ASTM D 2240. The values ​​given are measured in 3 seconds.

[0143] The uniaxial tensile tests were carried out on an Instron 5564 device at a speed of 500 mm / min with test specimens of type H2 according to the specifications of standard NF ISO 37. The x% modulus and tensile strength corresponding to the stress measured at x% tensile strain are expressed in MPa; the elongation at break is expressed in MPa.

[0144] The values ​​of loss factor (tan δ) and amplitude of elastic modulus in dynamic shear (ΔG') were recorded on vulcanized samples (with 8 mm 2 The sample was subjected to double alternating sinusoidal shear strain at a temperature of 40°C and a frequency of 10 Hz. The strain amplitude sweep process was carried out according to an outward-return cycle, going outward from 0.1% to 50% and then returning from 50% to 0.1%. The values ​​reported in Table 3 were obtained from the return strain amplitude sweep and relate to the maximum value of the loss factor (tan δmax).

[0145] Table 3

[0146] Comparative Example 1 Example 4 Shaw A pts 61 60 Modulus 100 MPa 2.7 2.6 Modulus 300 MPa 13.3 12.7 Tensile Strength MPa 20.3 20.6 Elongation at break ％ 405 426 ΔG' MPa 1.8 1.4 tanδmax NU 0.266 0.234

[0147] The composition comprising the silica of the invention exhibits significantly reduced energy dissipation values ​​(ΔG′ and tan δ max ) and similar mechanical properties relative to compositions comprising precipitated silica according to the prior art.

Claims

1. A precipitated silica comprising a 4 / 2 ] and units having the formula [(CH3)SiO 3 / 2 ] and characterized in that: In the precipitated silica 13 The precipitated silica is prepared by a method comprising the following steps: (i) providing a starting solution having a pH between 2.0 and 5.0; (ii) adding a silicate and an acid simultaneously to the starting solution so that the pH of the resulting reaction medium is maintained between 2.0 and 5.0; (iii) stopping the addition of the acid while continuing to add the silicate to the reaction medium until a pH of the reaction medium between 7.0 and 10.0 is obtained; (iv) adding a silicate and an acid simultaneously to the reaction medium obtained in (iii) so that the pH is maintained between 7.0 and 10.0; and (v) stopping the addition of the silicate while continuing to add the acid to the reaction medium until a pH of the reaction medium of less than 6.0 is reached and a silica suspension is obtained; wherein in step (iv) or (v) at least one alkali metal methylsiliconate is metered into the reaction medium, wherein step (v) comprises a first stage in which the acid and the alkali metal methylsiliconate are metered simultaneously into the reaction medium at a pH between 7.0 and 10.0, followed by a second stage in which the addition of the alkali metal methylsiliconate is stopped, while the addition of the acid is continued and the pH of the reaction medium is lowered to below 6.

0.

2. The precipitated silica according to claim 1, wherein The ratio (intensity of the second peak) / (intensity of the first peak) is between 0.50 and 1.

60.

3. Precipitated silica according to claim 1 or 2, having a carbon content of from 0.2 wt% to 10.0 wt% relative to the total weight of the silica.

4. The precipitated silica according to claim 1 or 2, characterized in that CTAB surface areas range from 40 to 600 m 2 / g range.

5. The precipitated silica according to claim 1 or 2, characterized in that CTAB surface areas range from 50 to 450 m 2 / g range.

6. The precipitated silica according to claim 1 or 2, characterized in that CTAB surface area is 50 m 2 / g and 380 m 2 / g, and the carbon content is from 0.2 wt% to 3.5 wt%.

7. The precipitated silica according to claim 1 or 2, characterized in that CTAB surface area is 50 m 2 / g and 380 m 2 / g, and the carbon content is from 0.3 wt% to 3.0 wt%.

8. The precipitated silica according to claim 1 or 2, characterized in that The median particle size d50 of the silica and the CTAB surface area are such that: |d50| > 164.5 - 0.3*|CTAB| Where |CTAB| represents m 2 |d50| represents the numerical value of the CTAB surface area expressed in nm and |d50| represents the numerical value of the median particle size d50 measured by centrifugal sedimentation.

9. A method for preparing the precipitated silica according to any one of claims 1 to 8, the method comprising the following steps: (i) providing a starting solution having a pH between 2.0 and 5.0; (ii) adding a silicate and an acid simultaneously to the starting solution so that the pH of the resulting reaction medium is maintained between 2.0 and 5.0; (iii) stopping the addition of the acid while continuing to add the silicate to the reaction medium until a pH of the reaction medium between 7.0 and 10.0 is obtained; (iv) adding a silicate and an acid simultaneously to the reaction medium obtained in (iii) so that the pH is maintained between 7.0 and 10.0; and (v) stopping the addition of the silicate while continuing to add the acid to the reaction medium until a pH of the reaction medium of less than 6.0 is reached and a silica suspension is obtained; wherein in step (iv) or (v) at least one alkali metal methylsiliconate is metered into the reaction medium, wherein step (v) comprises a first stage in which the acid and the alkali metal methylsiliconate are metered simultaneously into the reaction medium at a pH between 7.0 and 10.0, followed by a second stage in which the addition of the alkali metal methylsiliconate is stopped, while the addition of the acid is continued and the pH of the reaction medium is lowered to below 6.

0.

10. The method of claim 9, wherein the pH of the starting solution in step (i) is between 2.5 and 5.

0.

11. The method according to any one of claims 9 to 10, wherein: The at least one alkali metal methylsiliconate is sodium methylsiliconate or potassium methylsiliconate.

12. A composition comprising the precipitated silica of any one of claims 1 to 8 and at least one polymer.

13. The composition of claim 12, wherein the polymer is selected from the group of elastomers.

14. An article comprising the precipitated silica of any one of claims 1 to 8 or the composition of claim 12.

15. The article of claim 14 in the form of a shoe sole, a floor covering, a gas barrier, a cableway roller, a seal for household appliances, a seal for a liquid or gas pipeline, a brake system seal, a pipe, a jacket, a cable, an engine mount, a battery separator, a conveyor belt, a transmission belt, a tire.

16. The article of claim 14 in the form of a cable jacket.

17. The article of claim 14, which is a thermal insulation material, a resorcinol-formaldehyde / silica composite, concrete, or paper.

18. A tire or a tire element comprising the precipitated silica of any one of claims 1 to 8 or the composition of claim 12.

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