EP3074406A1

EP3074406A1 - Silanized highly hydrophobic silicic acids

Info

Publication number: EP3074406A1
Application number: EP14799490.9A
Authority: EP
Inventors: Achim Schneider
Original assignee: Wacker Chemie AG
Current assignee: Wacker Chemie AG
Priority date: 2013-11-27
Filing date: 2014-11-19
Publication date: 2016-10-05
Also published as: US20160263540A1; KR20160075691A; DE102013224210A1; JP2017503759A; CN105793271A; WO2015078744A1

Abstract

2.1. The problem addressed by the present invention is that of providing silicic acids which are highly hydrophobic and therefore can be used with particular success to control the rheological or triboelectric properties of liquid media or as flow enhancers. 2.2. The problem is solved by providing silicic acids which are surface-modified with a compound from the group (RO)₃SiR', wherein R' = C_nH₂ _(n-m)+1, n = 9 to 14, m = 0 to n and R = C_qH_2q+1, where q = 1 to 4. Also described is a method for the surface modification of silicic acids, which are treated in a thermal reaction with a modification agent selected from one or more organotrialkoxysilanes of general formula (RO)₃SiR', wherein R' = C_nH₂ _(n-m)+1, where n = 9 to 14 and m = 0 to n and R = C_qH_2q+1, where q = 1 to 4. 2.3. The silicic acids surface-modified according to the invention can be used to control the rheological or triboelectric properties of liquid media, such as, for example, as thickeners and antiblocking agents, or as flow enhancers.

Description

Silanization of highly hydrophobic silicas

The invention relates to silicas which are surface-modified with a compound from the group (R0) ₃ SiR ^, where R ^" = C _n H ₂ (nm) + l / _' n = 9 to 14, m = 0 to n and R = C _q H _{2q +} i with q = 1 to 4, as well as a process for the preparation of these silicic acids and their use as thickening agents, anti-blocking agent, flow aid and for controlling the charging properties.

The surface of unmodified silica, e.g. is prepared by a wet chemical precipitation process or by hydrolysis of tetrachlorosilane in the hydrogen flame is covered with silanol groups, whereby the materials have a hydrophilic character. By silylation, for example with hexamethyldisilazane (DE 2043 629), dichlorosilane (DE 1 163 784 B) or polydimethylsiloxane (EP 0 686 676 A1), it is possible to significantly reduce the number of silanol groups present on the surface. Due to the silicon-organic surface modification, the silica receives a more or less pronounced hydrophobic character.

Due to the altered surface properties associated with the modification, surface-modified silicas often behave distinctly differently from the unmodified agents in many applications. For example, surface-modified, hydrophobic silicic acids are often characterized by significantly higher thickening action in comparison to unmodified starting silicic acid, especially in systems such as solvents, polymers or resins which have polar groups, such as, for example, hydroxy, ceto, epoxy, ether -, ester, carboxyl or nitrogen-containing groups such as primary, secondary, or tertiary amino, amido or ammonium groups. Have special technical relevance in In this context, for example, epoxy resins, polyurethanes, unsaturated polyester resins and aqueous dispersions and emulsions, which are used for example as paints, coatings or adhesives application.

For example, DE 44 19 234 A1 describes a process for the silylation of inorganic oxides, wherein the very finely divided inorganic oxides are treated with at least one silylating agent which has low volatility in the temperature range of the process. Among other things, DE 44 19 234 A1 relates to a highly nonpolar silica prepared by this process. The examples given in the publication show that the thickening effect, for example, in a 25% strength aqueous ethanol solution increases with increasing hydrophobic character of the silica. The hydrophobic nature of the silica was then determined by visual assessment of the wetting behavior of the samples to methanol / water mixtures of various Zusammenset ^¬ tongues and (as a methanol number defined as the weight percent of methanol in water-methanol mixture, in which the Hälf ^¬ te of silica wetted and sunken in the liquid).

In EP 0672731 Bl, the preparation of pyrogenic silicas by treatment with compounds of the formula (RO) ₃ S iC _n H _{2n +} i will be described, wherein n = 10 to 18 and R = lower chain alkyl, such as methyl, ethyl radicals or similar. These are particularly suitable for thickening liquids. In the examples, the compounds hexadecyltrimethoxysilane (H ₃ CO) ₃ SiCi ₆ H ₃₃ and octadecyltrimethoxysilane (H ₃ C0) ₃ SiC ₁₈ H _{37 were used} for the treatment of silicas.

The examined samples of increasing document grade (ie increasing amount of silane used for the modification based on the specific surface area corresponding to the data in Table 3) are characterized by a comparison with the non-surface-modified Aerosil® 200 starting silicic acid (Example 9) Significantly higher thickening of a liquid 1: 1 mixture of propanol / water (see table page 9). If one considers the modification with (H ₃ CO) ₃ S1C ₁₆ H ₃₃ (silane I), the increasing degree of occupation manifests itself in an increasing C content (see Table 4). Although the cited document does not explicitly address the hydrophobicity of the samples, Examples 11 to 14 clearly show that a decreasing percentage C content of the silicas of Example 4 over Example 5 and 6 to Example 7, with a significant decrease in the thickening effect - goes. The C content gives direct information about the proportion of non-polar hydrocarbons present on the silica, which are responsible for the hydrophobic character. As a result, an increasing C content is usually associated with a stronger hydrophobic character of the silicas.

The starting materials used hexadecyltrimethoxysilane

(H3CO) 3 SiCi sH33 and octadecyltrimethoxysilane (H ₃ CO) ₃ SiCi ₈ H37, however, have significant disadvantages due to process engineering considerations. For example, the production of octadecyltrimethoxysilane proves to be rather complicated and cost-intensive, for example because of comparatively high melting and boiling points. In addition, the comparatively high viscosities of said compounds in the customary manufacturing processes or product quality are also negatively noticeable (the kinematic viscosity according to DIN 51562-1 of hexadecyltrimethoxysilane (H ₃ CO) ₃ SiCi ₆ H ₃ 3 is 7.2 mm ² / s at 25 ° C).

As set forth in EP 1 302 444 Al, silylating agents are often preferably added in liquid form as finely divided aerosol, for example achieved by nozzle techniques, to the powdered silica. To achieve the finest possible aerosol droplets and the best possible jet quality, ie as even as possible distribution of droplets of the same size as possible in the entire area of the spray cone, in the Atomization is a low viscosity advantageous. Thus, even distribution of the silylating agent into fine aerosol droplets can achieve a uniform distribution of the documenting agent and thus homogeneous modification of the surface of the silica even at shorter residence times.

Surface-modified silicic acids are used in addition to the use as agents for rheology control but also as a flow aid, anti-blocking agent or for controlling the tribo-electric charging. Of particular technical relevance here is the use as an additive in toner formulations.

Thus, for example, EP 1 502 933 A2 and EP 0 713 153 A2 describe such toner formulations which, in addition to the toner particles which essentially consist of a binder resin and the corresponding pigments, also contain hydrophobic inorganic particles, such as e.g. contain fumed silica, which is crucial in the control of the flow behavior and the charging behavior.

EP 1 502 933 A2 describes that in order to achieve a superior flowability, a uniform chargeability and a good stability even under moist conditions, the most pronounced and uniform hydrophobic character of the inorganic particles is desired (see, for example, paragraph [0048] and [0049 ]).

Also EP 1 302 444 AI describes u.a. in paragraph [0010] and

Problems that may occur in the use of less well-hydrophobized silica as antiblocking, Rieselhilfe and / or charge ^¬ regulatively. In addition, the literature suggests that less well hydrophobicized silicas due to problems of miscibility and compatibility in use as an active filler in liquid, polymer or resin systems medium and high polarity technically inferior be Kings ^¬ nen.

From an application point of view, therefore, the strongest possible hydrophobic character of the silicic acids and a uniform distribution of the slip agents over the surface of the silicic acids in the modification reaction are required.

Frequently, the control of the hydrophobic character of silicic acids by varying their occupancy level. In many FAEL ^¬ len can be easily accomplished by changing amounts of slip agent and optionally modified process conditions ver ^¬ tively this. Thus, the use of relatively large amounts of the surface modifier used as described for example in EP 0 686 676 A1 leads to a product which is not water-wettable and has very low residual silanol contents (determined by GW Sears et al., Analytical Chemistry 1956, 28, 1981ff), whereas the products described in EP 1433749 AI wetted by water due to the lower slip degree and high residual silanol contents ^¬ the.

At very high levels of proof, a further increase of the Be ^¬ legmittels does not lead to a further reduction of the residual silanol. Due to steric considerations, it is not possible to silylate all silanol groups on the surface of the silica. If the entire surface of the silicic acid is already uniformly covered, a further increase in the leveling agent does not lead to a decrease in the residual silanol content.

In addition, a significant increase in document resources often involves technical disadvantages. For example, the proportion of organosilicon constituents which are not chemically bound to the surface of the silica increases can lead to massive problems in a variety of applications, since organosilicon compounds are known to tend to phase separation due to their Unver ^¬ compatibility with many other chemical compounds. As a result, silicone oil or silicone resin droplets can form which, for example, become noticeable in the form of impurities, so-called "silicone craters." The formation of a silicone film can also have negative effects on the desired application, eg the adhesion of an epoxy adhesive often desired to use as small amounts of an organosilicon slip agent for surface modification in order to prevent such problems.

Also, often for safety considerations, a further increase in the document level is undesirable. Thus, for ei ^¬ ne silica sample which has a higher slip level at the same chemical nature of the surface modification, in the determination of explosion characteristics of a dust / air mixture to EN14034 critical values are determined, from which can be derived an increased risk potential, which in turn higher security measures required. In many cases, the dust explosion capacity is directly related to the carbon content of the silica samples, since often only the hydrocarbon residues are available for the oxidative decomposition processes underlying an explosion.

The object of the present invention is to overcome the disadvantages of the current state of the art and to provide silicas which are highly hydrophobic and therefore can be used particularly well for controlling the rheological or triboelectric properties of liquid media or as a flow aid. The object is achieved by the provision of silicas (RO) ₃ SiR ^'i are surface-modified with a compound of the formula wherein R ^x = C _n H _{2 (n} _ _{m) +1,} n = 9 to 14, m = 0 to n and R = C _q H _2q + i with q = 1 to 4.

The silicas according to the invention therefore have groups of the general formula R ^, SiO _3/2 on the surface, where R ^{1 *} = C _n H ₂ (nm) + i with n = 9 to 14, m = 0 to n.

According to the invention, the value m is between 0 and n, with n = 9 to 14 as stated above. The value for m is preferably between 0 and 7 and particularly preferably between 0 and 1.

The radicals R are preferably short-chain alkyl groups such as e.g. Methyl, ethyl, propyl or butyl groups, more preferably methyl or ethyl groups. In a particularly preferred embodiment, R is methyl groups.

The general formula (R0) ₃ SiR comprises the formulas (R ¹ 0) ₃ SiR (R ² O) 2 (R ³ O) SiR ^x ), (R ² O) (R ^ EiR ^ and / or (R ⁴ 0 (R ⁵ 0) (R ⁶ O) SiR and it holds that R describes the individual radicals R ¹ to R ⁶ , these are as defined for R defined and may be different or the same Preferably, the groups selected for R are the same ,

R is a monovalent, optionally mono- or polyunsaturated, optionally branched aliphatic or aromatic hydrocarbon radical having 9 to 14 carbon atoms. It is in the radicals R ¹ *, for example, alkyl groups such as nonyl, decyl, undecyl, dodecyl tridecyl and Tetrade- cyl groups. If the radicals R ^x are unsaturated hydrocarbon radicals, they preferably have the unsaturated moiety at the end of the hydrocarbon radical on. Thus, the preferred unsaturated radicals R ^x are η ony-8-enyl, dec-9-enyl, undec-10-enyl, dodec-11-enyl, tridec-12-enyl and tetradec-13 enyl, ηη-8-inyl, dec-9-ynyl, undec-10-ynyl, dodec-ll-inyl, tridec-12-ynyl and tetradec-13-ynyl groups. However, the unsaturated units can also be present at other points of the hydrocarbon chain, for example in the dodec-9-enyl, dodec-7-enyl, dodec-5-enyl or dodec-3-enyl groups. The radicals R " ¹ may also be optionally polyunsaturated, such as in dodeca-7, 9, 11-triene groups.

The radicals R ^{A are,} as in the abovementioned examples, preferably unbranched radicals. However, it is also possible to use mono- or polysubstituted groups, for example 1-methyl-nonyl or 1, 1-dimethyl-decyl radicals.

In addition, it may be in the unsaturated groups R ^"1 nantrenyl- to aromatic groups such as for example, mesityl, naphthyl, biphenyl, Phe or act anthracenyl groups.

In addition, the radicals R can contain heteroaromatics and in this case are for example aryl, alkyl, alkenyl or alkynyl groups which are substituted by primary, secondary or tertiary amino groups.

It is in the radicals R ^"1 preferably linear unbranched alkyl, alkenyl or alkynyl groups. It is particularly preferably the radicals R ¹ to decyl, dodecyl and tetradecyl groups.

The silicas can be modified with only one kind of the groups R Si0 _3/2 on the surface. But it can also contain two or more different groups may be present on the surface of the modified silicas, which differ in the radical R ^1, ie the group R'Si0 _3/2 can be ^1-t include the groups R SI03 _{/ 2,} where the individual R ¹ , R ² , R ³ , etc. to R ^{fc are selected} from the groups defined above for R. For example, two could contact the flat-bound ^R, Si0 differ _3/2 ~ groups in the length of their carbon chains. The surface of the metal oxide is preferably modified exclusively with one type of the abovementioned groups R ^x .

The surface of the silicic acids may have other groups in addition to the above-mentioned groups. Preference is given here tri- (MeSi0 _3/2) are methylsiloxy- (Me ₃ SIOI _{/ 2),} dimethylsiloxy (Me ₂ Si0 _2/2) or mono- methylsiloxy. Me stands for a methyl group. However, the other groups present on the surface are not limited to those mentioned. It sämtli ^¬ che can rather well-known in the prior art, surface pendant groups on the silica be present.

As known to those skilled in the art, increasing the chain length of a homologous series of polar end-capped chemical compounds is accompanied by a decrease in hydrophilicity, ie, increase in hydrophobicity, as the hydrophobic properties of the organic group are increasingly prevalent.

Thus, for example, the short-chain representatives of the monohydric, primary, linear, unbranched alcohols H2 _{n +} iC _n 0H to propane-l-ol (n = 1-3) are infinitely soluble in water. In the range n = 4-8 the solubility decreases with increasing chain length and continuously from n ^ 9 are the corresponding alcohols in water Al ^¬ finally completely insoluble.

Should as much as possible to achieve a pronounced hydrophobicity of the Kieselsäu ^¬ re therefore slip agent may be particularly suitable, C _n H _{2n +} i wear the organic groups, with the chain length is grown ^¬ an increase in the hydrophobicity to be expected.

Surprisingly, however, it has now been found that the hydrophobicity of the silicas with silanes of the general For ^¬ mel (RO) ₃ SiR ^ are treated up to a chain length of n = 14 carbon atoms can be increased, while the surface modification prolonged with alkyltrialkoxysilanes chain length (eg n = 16 or n = 18, as described in EP 0 672 731) does not lead to a further increase, but even to a reduction in the value for the hydrophobicity.

As described in EP 1502933 A2, the hydrophobic Cha ^¬ rakter a pyrogenic silica by examining the loading netzungsverhaltes of the respective samples with a mixture of water and methanol can be determined. In this case, a mixture of methanol and water, on which floats the sample to be examined hydrophobic, continuously mixed with more Me ^¬ ethanol until the powder is wetted by the liquid phase and sinks into it. The sinking of the sample becomes noticeable in an increasing turbidity of the solution and can be monitored photometrically. As less and less light passes through the solution, the transmission drops rapidly as the sample wets. Fig. 1 of EP 1502933 A2 shows exemplary titration curves of two different? ^¬ chen sample and proposes the use of the value "methanol wettability" before. This hereinafter "methanol number" ge ^¬ aforementioned value corresponds to the methanol concentration in percent by volume, in which the Transmission decreases to 80% of the original value and is referred to as MeOH ₈₀ . A higher number of methanol thus reflects a more pronounced hydrophobicity of the sample investigated.

Silica according to the invention means oxygen acids of silicon and, according to the invention, comprises both

Precipitated silicas, which are produced by wet chemical means, as well as pyrogenic silicic acids, which are obtained by means of a flame process. These are essentially Si0 ₂ particles, ie oxide particles of silicon which carry acidic silanol groups on the surface. The silica is preferably pyrogenically prepared silica. The silicas of the invention, specific Oberflä ^¬ chen of 1 to 800 m ² / g _f preferably 40 to 400 m ² / g and particularly preferably 90 to 270 m ² / g (determined by the BET method according to DIN 9277/66131 and DIN 9277 / 66132).

The tamped densities of the silicas according to the invention can be in the range from 10 to 500 g / l, preferably from 20 to 200 g / l, more preferably from 30 to 60 g / l (determined according to DIN EN ISO 787-11).

The silicas of the invention are characterized in that they aufwei ^¬ sen a residual silanol content of less than 70%, preferably less than 40% and particularly preferably less than 25%. The residual silanol content after the modification can be determined, for example, by acid-base titration, as described, for example, in GW Sears et al. Analytical Chemistry 1956, 28, 1981ff.

The silicas of the invention have a carbon content ^¬ determined according to DIN ISO 10694 of 0-20%, preferably 5-15%, on. In a particularly preferred embodiment, the carbon content of the silicas according to the invention is 8-12%.

The radical R of the organotrialkoxysilane of the general formula (R0) ₃ SiR is defined as R = C _q H _{2q +} i with q = 1 to 4.

Preferably q = 1 and the radical R is a methoxy group. In addition, it is preferable that q = 2 and R is an ethoxy group.

The radical R 'of the organotrialkoxysilane of the general formula (RO) ₃ SiR is defined as R ^x = C _n H _{2 (n} - _m ) ₊ i, n = 9 to 14, m = 0 to n and R = C _g H _{2q +} i with q = 1 to 4. n is preferably even and is preferably 10, 12 or 14, since organotrialkoxysilanes and thus also the corresponding upper surface-modified silicas, where n is a ungeradzah ^¬ liger value, are uneconomical to manufacture. Be ^¬ Sonders n is preferably 12 or 14, which means that the chain length of the radical comprising 12 or 14 carbon atoms.

The silicas of the invention are preferably characterized in that the groups introduced by the modification are firmly bound to the surface of the silicic acid. ^' A firm bond stands for a good chemical binding and is inventively by the with solvents

extractable portion of the modified silica

quantified, which is preferably at most 15% by weight.

The extractable fraction is particularly preferably at most 6% by weight, particularly preferably at most 3% by weight, and in a particular embodiment of the invention at most 2% by weight. A suitable method for evaluating the bond strength of a modification is the quantitative determination of

extractable, i. not chemically bonded to the surface of the silica silane. To determine the

extractable portion of the silicas according to the invention, the solvent tetrahydrofuran (THF) was used.

A solvent (also solvent or solvent) is a

Substance that can dissolve or dilute gases, liquids or solids, without taking into chemical reactions Zvi ^¬ rule solute-dissolving substance is. The solvent tetrahydrofuran used for the investigation of the silicas according to the invention does not dissolve any chemical bonds of the modifiers to the surface of the silica. The extractable hereby components are thus connected only by weaker interactions such as Van der Waals forces with the silica.

A low reading for the extractable fraction indicates a better chemical, that is, stronger binding of the

Modifier on the surface of the silica. The silicas according to the invention have the advantage that they are distinguished by a very high hydrophobicity. The silicas of the invention preferably have a methanol number (MeOH ₈₀ ) of more than 65% by volume, in particular more than 70% by volume. % on. In a particularly preferred embodiment be ^¬ transmits the methanol number of the silicas of the invention.% 73 or more by volume.

As described above, methanol number (MeOH ₈ o) in the context of the invention, the methanol content of an aqueous methanol solution in volume percent to understand that causes sinking of the sample under investigation, whereby the transmission decreases to 80% of its original value. This value read from the titration curve is used for identification. WE ^¬ niger good hydrophobic material which wets already at a lower methanol content and therefore sinks. This less well hydrophobized material can be sorted out.

The invention with tetradecyltrimethoxysilane

(H ₂₉ C ₁₄ S1 (OMe) 3) modified silicas of Examples 1 to 3 had greater numbers of methanol than those under comparable conditions using the corresponding hexadecyl (H ₃₃ Ci ₆ Si (OMe) 3) - and octadecyl (H ₃₇ Ci ₈ Si (OMe) ₃₎ -substituted De ^¬ derivatives Comparative Examples 4 to 6 prepared.

Particularly noteworthy that the difference in methanol numbers was particularly pronounced if the surface modification of the silicas was carried out by means of a, for reasons of improved space / time yield particularly preferred continu ^¬ tinuous production process (MeOH here is ₈ o ~ compared values of Examples 2 and 3 according to the invention with those of Comparative Examples 4 and 5), but even in the batch process with significantly higher reaction times was determined (MeOH ₈₀ - Values of Inventive Examples 1 and 7 compared with that of Comparative Example 6). While the silicas of the invention produced in a continuous process reach from Examples 2 and 3 of methanol numbers of well over 70, (MeOHeo values) achieved less than 65 for the Comparative Examples 4 and 5 ^¬ methanol are charged.

The differences in hydrophobicity found can not be explained by different carbon contents, since these were very similar for all examples and varied within the measurement inaccuracy of the corresponding analytical method.

Deviating residual silanol contents can not be used for explanation, since Examples 2 and 3 according to the invention have an identical residual silanol content as Comparative Examples 5 or 4, but the methanol numbers are significantly higher according to the invention.

In order to be able to make a statement about the homogeneity of the hydrophobing, the term methanol half value (MeOH ₅₀ ) should additionally be introduced here. Analogously to the above definition is here meant one methanol content in volume per ^¬-center, which causes a decrease of the transmission to 50% of the original value. If the two values MeOH ₈ o and MeOH ₅₀ this is very close to each other due to a rapid drop of the transmission with increasing methanol content and indicates therefore indicate a homogeneous Modifi ^¬ cation of the surface of the corresponding silicic acid, since the floating material at a certain Methanolge ^¬ stop sinking quickly.

As already stated, a homoge ^¬ ne modification of the silica is desired in many applications. This is given for the silicas according to the invention and has been confirmed in the ^examples . Thus, the half-methanol numbers (MeOH ₅₀₎ according to the invention by less than 2 vol.%, Preferably less than 1 vol.% Smaller than the numbers of methanol (MeOH ₈ o) of ent ^¬ speaking silicas. In contrast, non-inventive silicas, as shown in the comparative examples, often exhibit a more inhomogeneous modification of the surface, which is expressed in a larger difference of the MeOH ₅₀ value compared to the MeOH ₈ value.

Thus, for example, shows the analysis of the modified silica from Ex. 7, that the use of CL8 compound octadecyltrimethoxysilane compared to the homologous C14 compound tetradecyltrimethoxysilane (Ex. 1) leads to a clotting ^¬ Geren hydrophobicity (methanol number of 65.4 compared to 73 , 3). Moreover, the indicated comparatively large sub ^¬ difference between methanol half-speed and methanol number indicate ei ^¬ ne less homogeneous modification of the surface of the respective silica.

Another object of the present invention relates to a process for the surface modification of silicas, which with a modifying agent selected from one or more Organotrialkoxysilanen of the general formula

(R0) ₃ SiR ^' where R = C _n H ₂ ( _n - _m ) ₊ i with n = 9 to 14 and m = 0 to n and R = C _q H _{2q +} i with q = 1 to 4, in one thermal reaction are treated.

For the radicals R and R, the definition given above for R and R ^v applies.

The modifying agents used (also referred to as slip agents) are preferably monoalkyltrialkoxysilanes, such as, for example, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyltrialkoxysilane, particularly preferably the corresponding methoxy or ethoxy derivatives, nonyl, Decyl, undecyl, dodecyl, tridecyl, tetradecyltrimethoxysilane or nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyltriethoxysilane. most preferably it is Documenting agent to the dodecyl- or tetradecyltrialkoxysilanes dodecyltrimethoxysilane, dodecyltriethoxysilane, tetradecyltrimethoxysilane and / or tetracyltriethoxysilane.

The silicas of the invention may be modified with only one of the above-mentioned proofing agents, but it is also possible to use a mixture of two or more of the aforementioned proofing agents.

In addition, one or more other surface modifying slip agents may be used. Preference is given here hexamethyldisilazane, linear or cyclic oligo / polydiorganosiloxanes, particularly preferably oligo / polydimethyldisiloxanes, diorganodichlorosilanes, especially be ^¬ vorzugt dimethyldichlorosilane, diorganodialkoxysilanes, particularly preferably dimethyldimethoxysilane, Monoorganotrihalogen- silanes, particularly preferably monomethyltrichlorosilane mono- or organotrialkoxysilanes, particularly preferably Monomethyltrime- used thoxysilane.

The comparatively higher viscosities of longer-chain silane compounds are negatively noticeable in the production process as well as in product quality. For example, the kinematic viscosity (according to DIN 51562-1) of hexadecyltrimethoxysilane (H ₃ CO) ₃ SiCi ₆ H33 at 25 ° C., as already stated at the outset, is 7.2 mm ² / s. In contrast, the kinematic viscosity of tetradecyltrimethoxysilane (H ₃ CO) ₃ SiCi ₄ H ₂ 9 at 25 ° C only 5.4 mm ² / s. Therefore, the use of the silane compounds according to the invention in the process according to the invention, as well as for the product quality of advantage. For example, an organotri- alkoxysilane with n = 16 or 18 is more difficult to handle because of the higher viscosity than when n ^ 14.

Thus, the modification process is due to the use of the document means according to the invention with n = 9 to 14 under economic In terms of gaseous aspects, it is advantageous over organotrialkoxysilanes with n> 14. For example, an organotrialkoxysilane with n = 16 or 18 is more expensive than when n <14.

The preparation of the surface-modified silica environmentally summarizes the reaction of the silica with the slip agent in egg ^¬ ner thermal treatment. Preferably, the silica is mixed with the slip agent, wherein the mixing is in particular be ^¬ preferably before the reaction. The mixing process is also referred to as occupancy. Preferably, subsequent to the reaction, a purification of the modified silica ^¬ SUC gene, wherein particularly preferred excess Modifizierungsa ^¬ gene and byproducts are removed.

The following are the process steps Coating, reaction and purification with the numbers (1), (2) and (3) be ^■ called, even if it does not have to be separate process steps. Preferably, the manufacturing process is carried out in separate steps comprising (1) mixing the silica with the modifying agents (occupancy), (2) reacting the silica with the proofing agent, and (3) purifying the modified silica.

The surface modification (reaction) is preferably carried out in an atmosphere which does not lead to oxidation of the upper ^¬ surface-modified silica, ie, preferably less than 10 vol.% Oxygen, more preferably less than 2.5 vol.%, Best results are achieved with less as 1 vol.% oxygen.

The pressure during the process steps ranges from a slight underpressure of 0.2 bar to an overpressure of 100 bar, wherein for technical reasons normal pressure, that is to say pressure-free working in relation to outside / atmospheric pressure, is preferred.

Optionally, protic solvents may be added. A protic solvent is when one Molecule has a functional group from which hydrogen atoms in the molecule can be split off as protons (dissociation). Due to the high polarity of the OH bond, it can be cleaved comparatively easily with elimination of a positively charged hydrogen atom, the proton.

The most important protic solvent is water, which (in simplified terms) dissociates into a proton and a hydroxide ion. Other protic solvents provide z. Alcohols and carboxylic acids. According to the invention, protic solvents may preferably be e.g. vaporizable liquids such as isopropanol, ethanol or methanol or water are added. It is also possible to add mixtures of the abovementioned protic solvents. Preferably, 1 to 50% by weight of protic solvent, based on the silica, are added, more preferably 5 to 25%. Particularly preferred is the addition of water as a protic solvent.

The modification reaction of the invention is preferably carried out in a gas phase process, i. The slip agent is added to the pure, largely dry (therefore powdery) silica. In contrast, the silica is presented in a liquid phase process in liquid phase.

The modifying agents (slip agents) are preferably added to the silica in liquid form. The modifying agents can be admixed in pure form or as solutions in known solvents used industrially, for example, alcohols such as methanol, ethanol, or i-propanol, ethers such as diethyl ether, tetrahydrofuran, or dioxane, or hydrocarbons such as hexanes or toluene. The concentration of the modifying agents in the solution is 5 to 95% by weight, preferably 50 to 95% by weight. The addition in pure form is particularly preferred. According to the invention, the amounts of the liquid constituents are preferably chosen so that the reaction mixture is always a dry powder bed. , Dry powder-spillage in this context means that the mixture is substantially as the silica particles in the Gaspha ^¬ se is present. In contrast, the process control is in the liquid phase, ie the reaction of a silicic acid dispersed in the liquid phase.

In order to ensure that the reaction mixture is present as a dry powder bed, it is preferred that the amounts by weight of liquid constituents used do not exceed the amount by weight of the silicic acid used. From 5 to 50, particularly preferably from 20 to 35, parts by weight of liquid constituents based on 100 parts of the silica are particularly preferably used.

To prepare the inventive silicas substances are used which allow to shorten the necessary for the reaction of silica with the modifying agent response times and / or to lower the ^■ necessary process temperatures beyond.

The auxiliaries are optionally preferably in amounts of up to 10 μπιοΐ per m ² surface to be modified

Silica added. Preference is given to up to 5 pmol per m ² surface of the silica to be modified, more preferably 0.5 to 2.5 μιηοΐ adjuvant per m ² surface of the silica to be modified. The absolute

Surface of the unmodified silica may be measured from its mass and that measured by the BET method (see above)

specific surface area.

Preferably, the inventive

Excipients to substances which have acidic or basic reactive functional groups. These include, for example Brönsted acids such as organic acids such as formic or acetic acid or inorganic acids such as hydrochloric acid, hydrochloric acid, phosphoric acid, sulfuric acid. It is also possible Lewis acids such as boron trichloride or aluminum trichloride are used.

Preferably, the adjuvants used include bases such as hydroxides of alkali and alkaline earth metals, e.g. ,

Potassium hydroxide and sodium hydroxide as well as their derived from the corresponding alcohols or carboxylic acids salts, eg sodium, sodium or sodium acetate. Furthermore, the basic, reactive compounds can be selected from nitrogen-containing compounds such as ammonia or organically substituted primary, secondary or tertiary amines. The monovalent organic ^■ substituents of said amines include saturated and unsaturated, branched and unbranched hydrocarbon radicals, which additionally further heteroatoms or fun-ktionelle. Groups may have. The basic reacting

Compounds can be added in bulk but also as a solution in inert or reactive solvents. Preference is given to aqueous sodium hydroxide or potassium hydroxide solution, aqueous ammonia solution, i-propylamine, n-butylamine, i-butylamine, .alpha.-t-butylamine, cyclohexylamine, triethylamine, morpholine, piperidine or

Pyridine used. ·

Preferably, the slip means are added as finely divided aerosol, characterized in that the aerosol has a sink rate of 0.1 to 20 cm / s. An aerosol is a mixture (dispersion) of solid or liquid suspended particles and a gas.

The mixing (coating) of the silica with the said modifying agents is preferably carried out by nozzle techniques or similar techniques. Effective atomization techniques can be, for example, atomization in 1-fluid nozzles under pressure (preferably at 5 to 20 bar), spraying in 2-fluid nozzles under pressure (preferably with gas and liquid at 2-20 bar), ultrafine distribution with atomizers or gas-solid exchange units with movable, rotating or static internals be a homogeneous Allow distribution of the slip agent with the powdered silica.

The aerosol can be applied via nozzles from above onto the agitated pulverulent solid, the nozzles being located above the fluid level and surrounded by the homogeneous gas phase, or into the fluidized solid, the metering openings being below the fluid level and are therefore surrounded by the heterogeneous particle / gas mixture are introduced. Preference is given to spraying from above.-,.

The addition of the silanes, the protic compound and the excipient-acting basic compounds can be carried out simultaneously or sequentially. Preferably, the coverage is such that first a homogeneous mixture of the silica with the excipient and the protic compound is prepared, which is then mixed with the silane.

The reaction (step 2) is a thermal treatment and is preferably carried out at temperatures of 30 ° C to 350 ° C, more preferably at 40 ° C to 250 ° C, more preferably at 50 ° C to 150 ° C and in a specific Embodiment at 100 ° C to 120 ° C. The temperature profile can be kept constant during the reaction or, as described in EP 1 845 136, have an increasing gradient.

The residence time of the reaction (step 2) is preferably 1 minute to 24 hours, particularly preferably 15 minutes to 300 minutes and, for reasons of space-time yield, particularly preferably 15 minutes to 240 minutes. Assignment (1) and reaction (2) are preferably carried out under me ^¬ chanic or gas-borne fluidization. While in the mechanical fluidization, the particulate powder by moving a body (for example, a stirring blade) in the bed or the fluid is placed in the fluid state, this is in the case of gas-borne fluidization only by introducing a gas, preferably from below (eg in a fluidized bed). A gas-borne fluidization can be carried out by any inert gases that do not react with the modifying agents, the silica and the modified silica, so not to side reactions, Abbaure ^¬ actions. Oxidation processes and flame and explosion phenomena lead. Nitrogen, argon and other noble gases as well as carbon dioxide are preferably used here. The supply of the gases for fluidization is preferably carried out in the range of Gasleerrohrgeschwindigkeiten of 0.05 to 5 cm / s, more preferably from 0.5 to 2.5 cm / s. The term gas empty tube velocity is the quotient of the volume flow of the flowing gas which is present in the region in which the steps (1) occupancy, (2) reaction or (3) purification are carried out and the free cross-sectional area of the corresponding area through which it flows to understand. Particularly preferably, the mechanical fluidization which takes place without additional ^¬ union beyond the inerting gas used by Fiügelrührer, anchor stirrer, and other suitable stirring elements is.

The purification step (3) is preferably ge by movement ^¬ features, slow movement and slight mixing is particularly preferred. The stirring elements are preferably adjusted and moved so that mixing and fluidizing, but not complete turbulence, occurs.

During the purification step to separate unreacted starting materials and by-products, the process temperature be raised if necessary. The cleaning is preferably carried out at a temperature of 100 ° C to 350 ° C, preferably ^¬ 105 ° C to 180 ° C, more preferably from 110 ° C to 140 "C.

To avoid oxidation and purification effectively ge ^¬ Stalten, the cleaning step, the supply of larger amounts of an inert gas, preferably nitrogen, argon and other noble gases and carbon dioxide, corresponding to a superficial gas velocity of preferably 0.001 to 10 cm / s, preferably 0.01 to 1 cm / s.

Assignment, reaction and purification may be carried out as a batch process whereby a quantity of material limited by the capacity of the production vessel is supplied as a whole to the work system and removed as a whole upon completion of the production process, or as a continuous process i.e.. without interruptions. For technical reasons, preference is given to a continuous reaction procedure as described, for example, in EP 1 845 136.

In addition, during the. Modification (coating and / or reaction) or continuous or discontinuous methods of mechanical densification of the silica are used following the cleaning, such as presses, press rolls, grinding units, such as edge mills or ball mills, compaction by screws or screw mixers, screw compressors, briquetting, or compaction by aspiration of the air or gas content by suitable vacuum methods.

Particularly preferred is the mechanical compaction by pressing rollers, grinding units such as ball mills, screws, screw mixers, screw compressors or briquetting during the assignment in step (1). Occupancy and mechanical compaction Thus, in an aggregate at the same time, which for reasons of space / time yield and to save a separate pro-. positive step.

In a further particularly preferred procedure, processes for the mechanical densification of the silica are used following the purification, such as compression by suction of the air or gas contents by suitable vacuum methods or pressure rollers or a combination of both methods.

In addition, the silicas may be ground in a particularly preferred procedure following purification. In this case, aggregates such as pin mills, hammer mills, countercurrent mills, impact mills or devices for grinding sifting can be used.

The invention further provides for the use of the surface-modified silicas according to the invention or the surface-modified silicic acids prepared by the process according to the invention for controlling the flow properties of media such as adhesives, sealants and coating materials, for improving the mechanical properties of

Elastomers and for controlling the charge and flow properties of powders such as toners or powder coatings. Preferred is the use for controlling the rheological properties of liquid media and the use in toners.

The use of the organotrialkoxysilane according to the invention of the general formula (R0) ₃ SiR where R "= C _n H ₂ ( _n -m) + i with n = 9 to 14 and m = 0 to n and R = C _q H _{2q +} i with q = 1 to 4, modified silicic acids is advantageous over the prior art, since the inventive example, in particular in polar systems such as aqueous solutions, for example in mixtures of water with alcohol, have a high thickening effect. The silicas of the invention give dispersions of silicas in liquids with strongly basic groups, which are distinguished by an excellent storage stability of the viscosity.

Analysis methods:

1. Determination of carbon content (% C)

The elemental analysis on carbon was carried out according to DIN ISO 10694 using a CS-530 elemental analyzer from Eitra GmbH (D-41469 Neuss).

2. Determination of Res Content of Unmodified Silanol Silanol Groups (% SiOH)

The determination of the residual silanol content was carried out analogously to G.W. Sears et al. Änalytical Chemistry 1956, 28, 1981ff by acid-base titration of the silica suspended in a 1: 1 mixture of water and methanol. The titration took place in the region above the isoelectric point and below the pH range of the dissolution of the silica. The residual silanol content in% (% SiOH) can therefore be calculated according to the following formula:

% SiOH = SiQH (silyl) / SiOH (phil) * 100 with

SiOTJ (phil) titration from the titration of unbehan ^¬ punched silica

SiOH (silyl): titration volume from the titration of silylated silica. Determination of the proportion of extractable silylating agent

2.50 g of the silica to be examined are placed in a PE screw-cap vessel with a spatula in 47.50 g

Stirred tetrahydrofuran and then closed the vessel. After a rest period of 30 minutes in an ice bath, the

Mixture treated for 30 minutes in an ultrasonic bath with ice cooling (Sonorex Digitec DT 156, BANDELIN electronic GmbH & Co. KG, D-12207 Berlin) and then by ^'

Pressure filtration (5 bar nitrogen) over a PTFE membrane filter (pore size: 0.2 μm, diameter: 47 mm, Sartorius AG, Göttingen) received the clear filtrate. Of these, exactly 10.00 ml are used as an analyte to determine the

Silicon content by atomic absorption spectroscopy (Atom Absorption Spectrometer 2100, Perkin Elmer Waltham, MA, USA) and weighed.

The extractables in% can be calculated as follows:

Extractable ingredients

- ΗΓ ₄ - ^{m THF x} ^ (Analyte) ^ c (Analyte) x (RSi0 _3/2 ) m (Silica) x (Si) m (Analyte) with

m (THF): weight of tetrahydrofuran (= 47.50 g)

V (analysis): volume of the analyte (= 10.00 ml)

m (silica): weight of the surface-modified

Silica (= 2.50 g)

M (Si): molar mass silicon (= 28.09 g / mol)

c (Analyte): Silicon content of the analyte in mg / l

m (Analyze): Weigh out the analyte in g

(RSi0 _{_3/2):} molecular weight of the functional group RSiC> 3/2 in g / mol Determination of methanol number (MeOH ₈₀₎ and Methanolhalbwerts- number (MeOHso)

The wetting behavior of the test samples against ^¬ over a mixture of methanol and water was based on those described in EP 1502933, paragraphs [0166] ff extensively described analysis method. This is a titration method, wherein the haze associated with the sinking of un ^¬ tersuchenden to sample in a mixture of methanol and water is monitored photometrically.

In a beaker (borosilicate, tall form) of diam ^¬ sers 54 mm, the height is 95 mm and the wall thickness of about 2 mm to 70 ml of a solution of 60 vol% methanol and 40 vol% water 60 mg of the silica to be tested. Due to the hydrophobic character of silicas with a methanol number of> 60, the powdery sample initially swims on top and the measured transmission remains virtually unchanged. Samples with a less pronounced hydrophobicity or an inhomogeneous surface modification with larger amounts of poorly hydrophobicized material sink already on addition to the methanol / water.

Mixture partially or wholly in the solution and the measured transmission decreases accordingly. The transmission values were therefore measured in all examples at the beginning of the titration and were nearly 100% in all cases investigated.

With stirring at about 800 revolutions per minute (stirring stage 4.5, 728 magnetic stirrer from Metrohm AG, CH-9100 Herisau) by means of a polytetrafluoroethylene sheathed cylindrical magnetic stirring fish of 15 mm in length and 4.5 mm in height is now with a Addition rate of 10 ml / min methanol added.

The transmission can Company Rhesca Company, Ltd be monitored and recorded and from the titration curve, the Me ^¬ thanolzahl (MeOHeo) can be read, for example, with a powder-wetting tester WET-100P. This gives the methanol content in volume percent methanol, wherein said Trans ^¬ mission to 80% of the original value decreased (transmission before addition of the sample to be examined). Similarly, the methanol half-value (MeOH ₅₀ ) is read as the methanol content in volume percent, which causes a decrease in the transmission to 50%. Examples Example 1:

To 120 g of a hydrophilic silica having a specific surface area of 200 m ² / g ₍ determined by the BET method according to DIN 66131 and 66132 (available under the name HDK ^® N20 from Wacker Chemie AG, Munich, Germany) were atomized under a nitrogen atmosphere over a

Two-fluid nozzle (hollow cone nozzle, model 121, the company nozzles Schlick GmbH, D-96253 Untersiemau / Coburg, 30 ° spray angle, 0.1 mm bore, operated with 5 bar nitrogen) 6.2 g of a

25% aqueous ammonia solution added. Subsequently, 26.3 g of tetradecyltrimethoxysilane were added in an analogous manner (hollow cone nozzle, model 121, the company Düsen-Schlick GmbH, D-96253 Üntersiemau / Coburg, 30 ° spray angle, 0.2 mm bore, operated with 5 bar of nitrogen). The

Reaction mixture was for three. Hours under vigorous

Stirring heated to 120 ° C.

After cooling the product to room temperature, this is analyzed. The analytical data of the resulting colorless powdery reaction product are summarized in Table 1.

Example 2:

In a continuous apparatus are in a mixing vessel under a nitrogen atmosphere at a temperature of 41 ° C to a mass flow of 1000 g / h of a hydrophilic silica having a specific surface area of 200 m ² / g, determined by the BET method according to DIN 66131 and 66132 ( receives ^¬ well below the name HDK ^® N20 from Wacker Chemie AG, Munich, Germany) by spraying via two-component nozzles 52.g / sodium h of a 25% ammonia solution (hollow cone nozzle, model 121, the company jet-Schlick GmbH, D-96253 Untersiemau / Coburg, 30 ° Sprühwin ^¬ kel, 0.1 mm bore, operated with nitrogen at 5 bar), and 220 g / h tetradecyltrimethoxysilane (hollow-cone nozzle, model 121, the company Düsen-Schlick GmbH, D-96253 Untersiemau / Coburg, 30 ° spray angle _f 0.2 mm bore, operated with 5 bar nitrogen) was added. The so charged silica is reacted in a stirred reaction vessel by heating to 97 ° C for 1.4 h and then in a heated to 140 ° C dryer for 20 min under mechanical agitation and a nitrogen flow of 0.3 Nm ³ / h cleaned.

After cooling the product to room temperature, this is ana ^¬ lysed. The analytical data of the resulting colorless powdery reaction product are summarized in Table 1.

Example 3:

In a continuous apparatus are in a mixing vessel under a nitrogen atmosphere at a temperature of 41 ° C to a mass flow of 1200 g / h of a hydrophilic silica having a specific surface area of 200 m ² / g, determined by the BET method according to DIN 66131 and 66132 ( receives ^¬ well below the name HDK ^® N20 from Wacker Chemie AG, Munich, Germany) by spraying via two-component nozzles 62 g / h of a 25% ammonia solution (hollow cone nozzle, model 121, the company jet-Schlick GmbH, D-96253 Untersiemau / Coburg , 30 ° spray angle, 0.1 mm bore, operated with 5 bar nitrogen) and 264 g / h tetradecyltrimethoxysilane (Hohlkegeldüse, Model 121, the company Düsen-Schlick GmbH, D-96253 Untersiemau / Coburg, 30 ° spray angle, 0.2 mm bore, operated with 5 bar nitrogen) added. The so charged silica is reacted in a stirred reaction vessel by heating to 103 ° C for 1.2 h and then cleaned in a heated to 140 ° C dryer for 17 min mechanical movement and a nitrogen flow of 0.3 Nm ³ / h ,

After cooling the product to room temperature, this is analyzed. The analytical data of the resulting colorless powdery reaction product are summarized in Table 1. Example 4 (comparative example)

In a continuous apparatus are in a mixing vessel under a nitrogen atmosphere at a temperature of 45 ° C to a mass flow of 1000 g / h of a hydrophilic Kiesel ^¬ acid having a specific surface area of 200 m ² / g, determined by the BET method according to DIN 66131 and 66132 (obtained ^¬ well below the name of HDK ^® N20 from Wacker Chemie AG, Munich, Germany) by spraying through two-fluid nozzles 44 g / h of a 25% ammonia solution (hollow-cone nozzle, model 121, the company nozzle-Schlick GmbH, D-96253 Untersiemau / Coburg, 30 ° Sprühwin ^¬ angle, 0.1 mm bore, operated with 5 bar nitrogen) and 209 g / h hexadecyltrimethoxysilane (hollow cone nozzle, model 121, the company nozzles Schlick GmbH, D-96253 Untersiemau / Coburg, 30 ° spray angle , 0.2 mm bore, operated with 5 bar nitrogen) added. The silica loaded, in a stirred reaction vessel by heating at 120 ° C for 1.4 h to re ^¬ action and then brought in a heated dryer at 140 ° C for 20 min mechanical agitation and a nitrogen flow of 0.2 Nm ³ / h cleaned.

Example 5 {Comparative Example)

In a continuous apparatus are in a mixing vessel under a nitrogen atmosphere at a temperature of 50 ° C to a mass flow of 600 g / h of a hydrophilic silica having a specific surface area of 200 m ² / g, determined by the BET method according to DIN 66131 and 66132 ( available under the name ^HDK® N20 from Wacker Chemie AG, Munich, Germany) by atomizing over two-component nozzles 26 g / h of a 25% ammonia solution (Hohlkegelüse, Model 121, the company Düsen-Schlick GmbH, D-96253 Untersiemau / Coburg, 30 ° Sprühwin ^¬ kel, 0.1 mm bore, operated at 5 bar nitrogen) and 125 g / h hexadecyltrimethoxysilane (hollow cone nozzle, model 121, the company Düsen-Sehlick GmbH, D-96253 Untersiemau / Coburg, 30 ° ^■ spray angle, 0.2 mm bore, operated with 5 bar nitrogen) was added. The silica loaded is brought to re ^¬ action, and then in a heated dryer at 140 ° C for 34 min mechanical agitation and a nitrogen flow of 0.2 Nm ³ / h in a stirred reaction vessel by heating at 240 ° C for 2.4 h cleaned.

Example 6 (Comparative Example)

To 120 g of a hydrophilic silica having a specific surface area of 200 m ² / g, determined by the BET method

in accordance with DIN 66131 and 66132 (available under the name HDR ^® N20 from Wacker Chemie AG, Munich, Germany) under nitrogen atmosphere by spraying over a

Two-fluid nozzle (hollow cone nozzle, model 121, the company nozzles Schlick GmbH, D-96253 Untersiemau / Coburg, 30 ° spray angle, 0.1 mm bore, operated with 5 bar nitrogen) 6.1 g of a 25% aqueous ammonia solution. Subsequently, in a similar manner, a solution of 22.1 g

Octadecyltrimethoxysilane and 14.5 g of toluene added

(Hollow cone nozzle, model 121, the company Düsen-Schlick GmbH, D-96253 Untersiemau / Coburg, 30 ° spray angle, 0.2 mm bore, operated with 5 bar nitrogen). The reaction mixture is heated to 120 ° C with vigorous stirring for three hours. After cooling the product to room temperature, this is analyzed. The analytical data of the resulting colorless powdery reaction product are summarized in Table 1.

Example 7: To 120 g of a hydrophilic silica having a specific surface area of 200 in ² / g, determined by the BET method according to DIN - 66131 and 66132 (available under the name HDK ^® N20 from Wacker Chemie AG, Munich, Germany) under nitrogen atmosphere by spraying over one

Two-fluid nozzle (hollow cone nozzle, model 121, the company nozzles Schlick GmbH, D-96253 Untersiemau / Coburg, 30 ° spray angle, 0.1 mm bore, operated at 5 bar nitrogen) 6.3 g of a

25% aqueous ammonia solution added. 31.8 g of dodecyltriethoxysilane are then added in an analogous manner (hollow cone nozzle / model 121, the company Düsen-Schlick GmbH, D-96253 Untersiemau / Coburg, 30 ° spray angle, 0.2 mm bore, operated with 5 bar of nitrogen). The reaction mixture is heated to 120 ° C with vigorous stirring for three hours. After cooling the product to room temperature, this is analyzed. The analytical data of the resulting colorless powdery reaction product are summarized in Table 1.

Table 1: Experimental and analytical data of Examples 1-8

SiOH [%] indicates the content of unmodified silanol silanol groups (residual silanol content) C [%] indicates the carbon content.

Konti denotes a continuous production process, batch a discontinuous one.

Claims

Claims :

1. silicas (RO) ₃ SiR ^'t are surface-modified with a compound of formula wherein R ¹ * = C _n H ₂ _(n - _m) + i, n = 9 to 14, m = 0 to n and R = C _q H _{2q +} i with q = 1 to 4.

2. silicas according to claim 1, characterized in that it is in the pyrogenically prepared silicas Kie ^¬ selsäuren.

3. silicic acids according to any one of claims 1 or 2, characterized in that it is the radical R is a Methoxygrup- pe.

4. silicic acids according to any one of claims 1 or 2, characterized in that it is the radical R is an ethoxy group.

5. silicic acids according to any one of claims 1 to 4, characterized

characterized in that n = 12.

6. Silicas according to one of claims 1 to 4, characterized

characterized in that n = 14.

7. Silicas according to one of claims 1 to 6, characterized

characterized in that the solvent-extractable proportion of the modified silicas is at most 15% by weight.

8. Silicas according to one of claims 1 to 7, characterized

in that the methanol number of the modified silicas is greater than 65 vol. % is.

9. A process for the preparation of silicas according to claims 1 to 8, characterized in that the silica acids with a modifying agent selected from one or more organotrialkoxysilanes of the general formula (RO) ₃ SiR where R ¹ = C _n H _{2 (} nm) + i with n = 9 to 14 and m = 0 to n and R = C _q H _{2q +} i with q = 1 to 4, to be treated in a thermal reaction.

10. The method according to claim 9, characterized in that the modifying agent contains dodecyltrialkoxysilane.

11. The method according to claim 9, characterized in that the modifying agent contains tetradecyltrialkoxysilane.

12. Use of the silicic acids according to any one of claims 1 to 8 or prepared according to any one of claims 9 to 11 for controlling the rheological or triboelectric properties ^¬ Eigen ^¬ of liquid media or as a flow aid.