DE102010011935A1 - Preparing inorganic-oxide particles, useful e.g. as a filler, comprises partially functionalizing particles on its surface with chlorine, converting the chloro-functionalized particles into gas phase and pyrolyzing the reaction product - Google Patents

Abstract

Preparing inorganic-oxide particles, which are least partially coated with carbon, comprises at least partially functionalizing particles comprising metal or metalloid oxides, metal or metalloid hydroxides and/or acids of the metal or metalloid or their polymer mixtures at least on its surface with chlorine, converting the chloro-functionalized particles into the gas phase or in solution with an organic chemical nucleophile with at least 3 carbon atoms per molecule and pyrolyzing the reaction product in a non-oxidizing atmosphere. Independent claims are also included for: (1) the inorganic oxide particles, which are least partially coated with carbon on its surface, obtained by the above mentioned method; and (2) a rubber mixture or a rubber product with a filler comprising the particles.

Description

The invention relates to a process for the preparation of inorganic-oxide particles which at least partially occupied by carbon, d. H. "Carbonized", the carbonized particles thus obtained, their use as fillers and products with these fillers.

Fillers are used in various materials and composites, also called composites, to modify properties and increase mechanical strength. Among other things, fillers are used in technical elastomers and rubber articles. Today one tries to tailor the fillers for the product purpose of measure. In addition to the selection of the base filler, a functionalization of the fillers is considered for the change of the filler characteristics. The fillers present as particles are selectively changed, for example, on their surface by physisorption, chemisorption or chemical reaction. Covalent bonds between filler particle and reagent can be produced by chemical reactions on the surface; the filler particles are thus provided with functional groups on their surface, i. H. "Functionalized". The functional groups are then able, with the matrix to be reinforced, with reinforcing elements z. B. metal or react with other fillers or associate. The composite materials get so different, new properties.

An essential class of fillers includes a wide variety of oxides and hydroxides as well as acids and acid anhydrides of metals and non-metals. There are amorphous and crystalline representatives of this inorganic-oxide filler group. Of particular importance within this group are the silicic acid derivatives. These include (ortho) silicic acid, silica gel and silica gel, silica, silica and diatomaceous earth, as well as various forms of water glass. In general, this group includes all variants, derivatives and products of and with silicon dioxide (SiO ₂ ).

Even technical carbon black is an attractive filler. Soot consists of the smallest, often spherical, particles that may be agglomerated. Particle size and surface structure vary greatly depending on the preparation. As a rule, carbon black consists of at least 90% by weight of carbon, besides there are pyrolysis products of the starting materials. Carbon black appears as an undesirable product in combustion processes, but is used as a filler in the form of well-defined carbon black. To a great extent, in addition to silica or silica products, carbon black is used as a filler in the rubber industry for tires and other engineering rubber products. It also has significance as a lightweight conductive filler for protection against electrostatic charge in composites. The classification of standard carbon blacks is usually based on the American ASTM standard. The specific surface area of soot particles may be between 10 and more than 1000 m ² / g.

Especially in elastomer products and especially in technical rubber products such as vehicle tires, gaskets, hoses and the like, inorganic-oxide fillers (white fillers, silica) and carbon black (black filler, black carbon) are used together. It is therefore natural to try to combine the properties of both fillers and couple these fillers together.

It is already known to deposit carbon on silica and silica based fillers by means of vapor deposition (PVD and CVD) processes. For example, it is from the DE 27 03 181 A1 a siliceous filler having an adhesive carbonaceous coating, the silicic acid particles of which are contacted with an organic compound at a catalytic cracking temperature of between 250 and 1000 ° C in a non-oxidizing atmosphere. For this purpose, the vapor of the organic compound, in the example propane, in a fluidized bed reactor can be brought into contact with the particles. The disadvantage is that the thus applied, pyrolytically obtained carbon shell causes a smoothing of the particles. In addition, the method does not lead to a true chemical, ie covalent attachment of the produced carbon black layer to the particles. The produced layer is therefore more susceptible to abrasion. However, it is desirable that the carbon should be in fixed association with the white filler in order to achieve particular effects caused by this fixed spatial association and to maintain the absolutely uniform degree of mixing within composites.

There is therefore still a need for a hybrid filler of a white filler, in particular a metal or Halbmetalloxidfüllstoff on the one hand and a carbon black or graphite carbon on the other. The object of the invention is to develop a novel filler of this type for various applications.

• – als Ausgangsstoff Partikel aus der Gruppe der Metall- oder Halbmetalloxide, der Metall- oder Halbmetallhydroxide oder der Säuren eines Metalls- oder Halbmetalls einschließlich von Gemischen und polymeren Gemischen der Stoffe dieser Gruppe ausgewählt werden, wobei die Partikel wenigstens an ihrer Oberfläche und dort wenigstens teilweise mit Chlor funktionalisiert sind,
• – die chlorfunktionalisierten Partikel der zuvor genannten Gruppe in der Gasphase oder in Lösung mit einem organisch-chemischen Nucleophil mit wenigstens 3 Kohlenstoffatomen je Molekül umgesetzt werden
• – und das Umsetzungsprodukt in nicht-oxidierender Atmosphäre pyrolysiert wird.

The object is achieved by a method for producing inorganic-oxide particles which are at least partially coated with carbon, in which

• - As starting material particles are selected from the group of metal or semimetal oxides, the metal or semimetal or the acids of a metal or semimetal including mixtures and polymeric mixtures of the substances of this group, wherein the particles at least on their surface and there at least partially are functionalized with chlorine,
• - The chlorofunctionalized particles of the aforementioned group are reacted in the gas phase or in solution with an organic-chemical nucleophile having at least 3 carbon atoms per molecule
• - And the reaction product is pyrolyzed in a non-oxidizing atmosphere.

Preferably, the pyrolysis is carried out at a temperature of at least 600 ° C, more preferably at least 750 ° C. In general, pyrolysis temperatures between about 400 and 1400 ° C are possible. However, low pyrolysis temperatures favor reactions that disrupt the binding of the nucleophile to the starting particles and thereby reduce the carbon occupancy level in the final product. A pyrolysis temperature of at least 600 ° C is therefore recommended. Good results are generally obtained at temperatures between 650 ° C and 1000 ° C or 900 ° C or preferably between 750 ° C and 1000 ° C, more preferably between 750 and 900 ° C.

To avoid side reactions, the pyrolysis temperature should be reached quickly. Heating rates between 100 and 1200 ° C / h are currently considered suitable. It is particularly preferred when heating in the process according to the invention with heating rates of at least 5 ° C / min.

Good results can be achieved if the pyrolysis is carried out for at least 8 hours. Very good carbonizations were obtained at pyrolysis times of between 12 and 48 hours. However, the required pyrolysis is also dependent on the maximum pyrolysis, at very high pyrolysis temperatures from 800 ° C pyrolysis of about 4 hours may be sufficient.

The pyrolysis product can be further thermally treated - annealed - be. Such a thermal aftertreatment is also carried out at temperatures of at least 400.degree.

The starting material for the process form particles from the group of metal or semimetal oxides, metal or semimetal hydroxides or acids of the metal or semimetal including mixtures and polymeric mixtures of the substances of this group. The oxides include the acid anhydrides. Accordingly, all silica type fillers including fumed or precipitated silica, silica gel and other silica forms, titania, zirconia, zinc oxide, alumina, and other oxidic materials known to those skilled in the art are suitable as starting particles.

Before they can be used for the process according to the invention, the particles must be at least partially functionalized with chlorine on their surface. For this example, the methods are suitable, as in the WO 05/061631 A1 are described.

Alternatively, the particles can also be prepared directly as chlorofunctionalized particles, as in US Pat EP 1 526 115 A1 described. In any case, covalent Cl-Si bonds and / or O-Si bonds are to be generated.

The disclosure of the WO 2005/061631 A1 and the EP 1 526 115 A1 are expressly incorporated into the description of this invention by reference, as those skilled in the art can readily refer to the manufacturing specifications of these references for the purposes of the invention, so that they need not be described again here.

The de novo synthesis of chlorosiloxane particles (also called CSN particles below) after the EP 1 526 115 A1 is carried out by a gas phase reaction between silicon (IV) chloride and oxygen at temperatures above 960 ° C. Are obtained spherical, X-ray amorphous particles which have a primary particle diameter of about 10 to 1500 nm, depending on the reaction conditions. CSN particles are characterized by an exceptionally high content of chlorine, with the chlorine atoms being almost exclusively on the particle surface. The high degree of chlorine coverage offers particularly good initial conditions for a dense subsequent occupancy with the chlorine-substituted pyrolysis precursor. CSN particles are therefore particularly preferred as starting particles.

Alternatively, the chloroform-functionalized particles can be purified by the methods of WO 05/061631 A2 be obtained by particles of oxidic compounds of metals and / or metalloids with Silicon tetrachloride be implemented. Also in this way surface Si-Cl bonds form in good coverage and a large specific surface area is obtained.

Preferably, the starting particles for the process according to the invention are selected such that they have more than 3 chlorine atoms per nm ² , more preferably more than 6.5 chlorine atoms per nm ² . This creates the best prerequisites for achieving a high occupation density with the nucleophile, which is covalently bound to the particles by substitution of the chlorine atoms and from which the carbon coating is formed by pyrolysis.

The chlorine-functionalized starting particles provide a particularly suitable basis for the connection of carbon-rich pyrolysis precursors by means of nucleophilic substitution, because the silicon-chlorine bonds on the particle surface show a high reactivity towards nucleophiles of all kinds.

As has been found in the context of the invention, the pyrolysis precursors can be specifically covalently bound by nucleophilic substitution of the chlorine atoms on the particle surface in such a way that the degree of coverage is maintained during the subsequent handling of the particles. The abrasion that these particles suffer when mixed with a surrounding matrix material, is particularly low. Due to this, even within elastomers, i. H. with relatively high internal friction, the conductivity values stable over the service life. Furthermore, it is possible to achieve a relative to the starting material large or little reduced specific surface area.

The reaction of the chlorofunctionalized particles with the nucleophile, which forms the pyrolysis precursor, ie is converted by pyrolysis to a carbon-rich coating, can also according to the rules EP 1 526 115 A1 and WO 05/016131 A2 respectively.

Furthermore, it has been found that covalently bound material remains under pyrolysis conditions to significantly larger proportions on the surface, while physisorbed reagent first passes into the gas phase and is deposited from here only in smaller quantities on the surface. Accordingly, it is advantageous to attach the largest possible amount of nucleophile on the surface.

The covalently bound nucleophile forms the later binding site between silica and carbon black. In addition to the covalently bonded nucleophile, additional non-covalently bound organic material may be used to assist in the formation of the soot layer. The bound nucleophile should expand for the most part in the radial direction of the particles, and the steric bulk of the nucleophile should not be too large along the particle surface.

Preferably, therefore, the organic nucleophile selected is one having a primary aliphatic radical, preferably having from 3 to 30 carbon atoms.

Secondary aliphatic radicals, araliphatic or aromatic radicals are also possible, provided that they can satisfy the steric requirements.

It is furthermore preferred if the organochemical nucleophile is an alcohol, a thiol, an amine, an alkali metal organyl, more preferably a lithium organyl, or a Grignard compound. It is, as stated above, currently considered to be particularly advantageous if said nucleophiles have primary or secondary aliphatic or araliphatic radicals. However, cycloaliphatic and aromatic radicals are not excluded since they can form layered structures on the surface.

In a particularly preferred embodiment of the invention, the organochemical nucleophile is an alcohol having at least 6 carbon atoms, preferably a primary alcohol having at least 6 carbon atoms, more preferably at least 12 or at least 16 carbon atoms.

For the first time, the invention provides inorganic-oxide particles which are at least partially coated with carbon on their surface and, as shown by scanning electron micrographs, have a voluminous, specific surface which is well suited for anchoring the particles in a matrix material is. In contrast to the particles obtained by physisorption on the surface, the carbonization is mechanically very stable. These new particles are obtainable by the method according to the invention with the features characterizing this method.

The particles obtained by the method are characterized by a particle size between about 10 nm and 20 microns, a low, but present conductivity and a partially graphite-like surface structure. When incorporated into a matrix material, the conductivity remains largely constant due to mixing irrespective of the mixing time, which, according to current knowledge, is due to the stable, covalent attachment of the carbon to the particle surface.

The carbon: metal or carbon: metal ratio can preferably be set to values greater than 2 at%. It is also desirable to have a BET surface area generally not more than 20% less than the starting particles. The latter can reach the skilled person by process optimization in the field of work-up (drying, washing, tempering, etc.) or pyrolysis (temperature, time, heating rate), which is within the skill of the art.

The novel particles can generally be used in a conventional manner as fillers. They are particularly suitable as fillers in inorganic / organic composite materials, in particular as electrically conductive reinforcing fillers in inorganic / organic composite materials. Their low conductivity provides protection against electrostatic charge in these materials, which is desirable for many applications. Furthermore, they are particularly suitable as fillers in elastomers, in particular in rubber mixtures and vulcanized rubbers or rubbers. They offer a high-performance filler that combines the properties of conventional fillers made of soot and silica. Finally, they are also suitable for use as a toner, as an electrode material, as a catalyst material or as a chromatographic column material.

The invention also includes rubber blends and rubber products containing the carbonated particles of the present invention as a filler.

Advantages of the invention

Particulate particles made from CSN particles (chlorosiloxane particles) consist of a core of amorphous silica firmly enclosed by a shell of graphitic carbon. The shell does not have to be completely formed. A relatively low carbon occupancy rate can bring particular benefits through better exposure of the white filler.

The particle size is arbitrary and can be varied at least in the range of about 10 nm to 20 microns. The carbon content and the associated layer thickness can be adjusted as needed using the nucleophile chain length as well as the pyrolysis conditions and is in the percentage range based on the total weight of the particles. The particles have a low, but always present, electrical conductivity. Composites containing the particles of the invention are protected by the particles from electrostatic charges. The core of the particles in the case of silica and silica is usually disordered and X-ray amorphous, while the degree of order of the carbon shell can be influenced by the manufacturing process. Crystalline oxide particles are also suitable as starting particles. If already existing particles are functionalized with chlorine-as described in the cited patents by reaction with silicon tetrachloride-it may be advantageous to increase the hydroxyl group number or oxygen density at the surface of the particles prior to chlorine functionalization by acid treatment, base treatment or oxidation.

The same applies to particles of silica, which are treated first with silicon tetrachloride and then with the method according to the invention. The process according to the invention furthermore permits the design of special fillers based on further inorganic-oxide fillers whose profile of properties can be changed in the abovementioned sense. Suitable starting particles include titanium oxides, zirconium oxides, zinc oxide or aluminum oxides, which are first functionalized with chlorine and then carbonized in accordance with the invention.

Presentation method in general

For the preparation of the particles are first so-called CSN particles according to the provisions of the European patent application EP 1 526 115 A1 manufactured with the desired diameter. Various starting particles are also commercially available. This applies not only to the purely inorganic-oxide base fillers but also to the superficially chloroform-functionalized forms. The chloroform-functionalized starting particles are then purified according to the regulations of WO 2005/061631 D1 reacted with an alcohol of specific chain length and then at temperatures between about 600 and 900 ° C, preferably between about 750 and 850 ° C and pyrolyzed here in most examples at about 800 ° C in an inert gas atmosphere. This forms the carbon coverage, the thickness of the chain length of the alcohol used and their completeness depends heavily on the pyrolysis. The benefits of the invention are illustrated below by way of example with the aid of the nucleophile alcohol, but other nucleophiles could be used accordingly.

In the following, the invention will be described in more detail by means of concrete examples and with the aid of test results for specific parameters and properties. This is to illustrate the invention without limiting it. The person skilled in the art can easily transfer the findings of the experimental part to other alcohols and nucleophiles.

EXAMPLES

Due to the pronounced sensitivity to hydrolysis of some reactants, intermediates and products, all work is carried out under anhydrous conditions as far as possible. Equipment may be evacuated and baked out. The inert gas used is argon. All work is carried out under inert gas atmosphere, the gas is also used for aeration and rinsing.

silica example

For the surface modifications described below with chlorine, the precipitated silica Ultrasil ^® VN3 and Ultrasil ^® 360 (Degussa, Germany) were used, which differ primarily in their average particle size.

The silicic acid to be functionalized is first dried for 11 h at a reduced pressure of 10 ^-2 mbar and room temperature. Subsequently, 10 g of the dried silica are introduced and mixed in an argon countercurrent with 80 ml of silicon tetrachloride. The suspension is refluxed for 18 h with vigorous stirring at a temperature of 80 ° C. To maintain the protective gas atmosphere, a weak stream of argon is constantly passed through the apparatus during the reaction. After completion of the reaction, the reaction mixture is cooled to room temperature and the excess silicon tetrachloride is removed by condensation. To remove residual silicon tetrachloride is dried for one hour at a reduced pressure of 10 ^-2 mbar. The chlorine content on the reacted silica is determined by means of titration of the hydrogen chloride liberated during the hydrolysis with NaOH. It lies with these precipitated silicas up to a maximum of w (Cl) = 10%.

The chlorofunctionalized silica is suspended in 80 mL of anhydrous tetrahydrofuran. For this purpose, 9 eq of triethylamine and then 3 eq of alcohol (for example 1-octanol, 1-hexadecanol or benzyl alcohol) are added in the argon countercurrent, based on the determined chlorine content. The reaction mixture is heated at 80 ° C for 16 h with vigorous stirring at reflux. After cooling, the suspension is filtered off under an argon atmosphere, the filter cake washed several times in anhydrous dichloromethane and anhydrous tetrahydrofuran and dried under reduced pressure.

The subsequent pyrolysis of the particles coated with alcohol as a nucleophile was carried out under substantially water- and oxygen-free reaction conditions in an argon protective gas atmosphere. The educt is weighed on a porcelain combustion boat and then placed in the argon countercurrent in the middle of a quartz glass tube. The tube reactor was initially baked and then purged with argon. The quartz tube is placed in a tube furnace. The pyrolyses were carried out in a temperature range from 450 ° C to 950 ° C and for a duration of 24 h, 36 h and 48 h, calculated from reaching the selected pyrolysis temperature. The heating rate was 250 ° C / h. After completion of the pyrolysis is cooled to room temperature and the product obtained is removed in the argon countercurrent

Chlorosiloxane (CSN) Example

The preparation of the CSN particles is carried out according to the working instructions from the EP 1 526 115 A1 , In a vertically constructed tube furnace, silicon tetrachloride and oxygen are introduced from above with the aid of argon as the carrier gas, where they are reacted at high temperatures. The gas flows are controlled by float flow meters. The formed CSN particles are collected at the lower end of the tube furnace in a round bottom flask. The chlorine formed in the reaction is removed in a gas washing bottle filled with sodium hydroxide solution. Volume flow argon 88 l / h Flow rate O ₂ 88 l / h top temperature 1180 ° C Precursortemperatur 20 ° C duration of test 80 min

The main differences between CSN particles and chlorofunctionalized silicas are their different morphology and the significantly higher chlorine content of the CSN particles. The chlorine content w (Cl) is up to about 30% for the CSN particles and about 10% for the functionalized silicas.

test results

Reference is made to the following figures:

Carbon content (w (C)) as a function of pyrolysis temperature and duration;

SEM image of Perkasil KS 300-PD with chemisorbed cetyl alcohol (EHT = 10.00 kV, WD 7.5 mm Mag 20.00 KX);

SEM image of Perkasil KS 300-PD with physisorbed cetyl alcohol (EHT = 20.00 kV, WD 8 mm Mag 20.00 KX);

SEM image of the sample pyrolyzed at 900 ° C. with chemisorbed cetyl alcohol (EHT 10.00 kV, WD 7.5 mm, Mag 20.00 KX);

SEM image of the sample pyrolyzed at 900 ° C. with physisorbed cetyl alcohol (EHT 10.00 kV, WD 8.0 mm, Mag 5.00 KX);

The dependence of the carbon content on 1-hexadecanol-coated CSN particles was determined by the pyrolysis temperature and time. The results are in shown

The absolute values w (C) do not necessarily indicate the properties of the particles and are therefore not a quality standard per se. Since complete masking of the starting particles is not desired, too thick or complete carbon coating may also be detrimental. The w (C) values are therefore aligned and targeted according to the intended purpose. In addition to the absolute values for the carbon content w (C), however, the morphology of the product particles and the obtaining of a large specific surface area (measured as BET values), but above all a uniformly finely structured, pore-rich and morphologically similar surface to the starting particles, are considerable Importance. The new particles obtained via the chloro-functionalized intermediate suggest that they can be successfully used for a variety of purposes.

Scanning electron micrographs (SEM) of a sample of 1-hexadecanol chemically bound on chlorofunctionalized silica were taken on the one hand ( ) and a sample having only physisorbed 1-hexadecanol on the same base silica ( ). The finer and more uniform distribution of the alcohol is easily recognizable and provides a better starting basis for the structure of the pyrolytically obtained carbon occupancy.

Both samples were then pyrolyzed at 900 ° C under the same conditions. The scanning electron micrograph of the pyrolyzed sample with previously chemically bound alcohol is in shown the inclusion of the pyrolyzed sample with only physisorbed alcohol in , The structure of the new hybrid material, which is more similar to the starting filler, can be clearly seen.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 2703181 A1 [0006]
• WO 05/061631 A1 [0014]
• EP 1526115 A1 [0015, 0016, 0017, 0022, 0037, 0044]
• WO 2005/061631 A1 [0016]
• WO 05/061631 A2 [0018]
• WO 05/016131 A2 [0022]
• WO 2005/061631 [0037]

Claims (14)

Process for the preparation of inorganic-oxide particles, which are at least partially coated with carbon, characterized in that the starting material particles from the group of metal or semimetal oxides, metal or semimetal hydroxides or acids of the metal or semimetal including mixtures and polymers Mixtures of the substances of this group are selected, wherein the particles are functionalized at least on their surface and there at least partially with chlorine, that the chlorofunctionalized particles are reacted in the gas phase or in solution with an organic chemical nucleophile having at least 3 carbon atoms per molecule and that the reaction product is pyrolyzed in a non-oxidizing atmosphere. A method according to claim 1, characterized in that the pyrolysis is carried out at a temperature of at least 600 ° C, preferably at least 750 ° C. A method according to claim 1 or 2, characterized in that is heated to the pyrolysis with heating rates of at least 5 ° C / min. Method according to one of claims 1 to 3, characterized in that the pyrolysis is carried out for at least 4 hours. Method according to one of claims 1 to 4, characterized in that a thermal aftertreatment is carried out at at least 400 ° C. Method according to one of claims 1 to 5, characterized in that as starting particles are selected those in which the surface functionalization is more than 3 chlorine atoms per nm ² , preferably more than 6.5 chlorine atoms per nm ² . Process according to any one of Claims 1 to 6, characterized in that the organochemical nucleophile is an alcohol, a thiol, an amine, an alkali metal organyl or a Grignard compound. Process according to any one of Claims 1 to 7, characterized in that the organochemical nucleophile is one having a primary aliphatic radical and preferably having from 3 to 30 carbon atoms. A method according to claim 7 or 8, characterized in that the organochemical nucleophile is an alcohol having at least 6 carbon atoms, preferably a primary alcohol having at least 6 carbon atoms. Inorganic-oxide particles which are at least partially coated with carbon on their surface, obtainable by a process according to one of Claims 1 to 9. Particles according to claim 10, characterized by a particle size between about 10 nm and 20 microns, a low conductivity and a partially graphite-like surface structure. Use of the particles according to Claim 10 or 11 as filler in inorganic / organic composite materials, in particular as electrically conductive reinforcing filler in inorganic / organic composite materials, and as filler in elastomers, in particular in rubber mixtures and vulcanized rubbers or rubbers, as toner, as catalyst support material or as chromatographic column material. A rubber composition with a filler containing the particles according to claim 10 or 11. A rubber product with a filler containing the particles of claim 10 or 11

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