Method for modifying silica in the liquid phase

Abstract

The invention relates to a method for modifying the surface of hydrophilic silica having a specific surface area of 10 to 1000 m2 / g (measured according to the BET method as per DIN EN ISO 9277 / DIN 66132), in which method a suspension of the silica in an organic solvent is reacted with liquid polyorganosiloxane composed of 2 units of the general formula R1R2R3SiO1 / 2 (M) and 0 to 20 units of the general formula R4R5Si(O1 / 2)2 (D), where R1, R2, R3, R4 and R5 each are a hydroxyl group or a monovalent hydrocarbyl group comprising 1 to 24 C atoms, and at least one group R1, R2, R3, R4, R5 and at most 20 mol.%, based on all groups R1, R2, R3, R4, R5, are hydroxyl groups.

Description

[0001] Process for modifying silica in the liquid phase

[0002] The invention relates to a process for the surface modification of hydrophilic silica with liquid polyorganosiloxane in a suspension of the silica in an organic solvent.

[0003] Hydrophobic, surface-modified silicas modified with polydimethylsiloxanes (PDMS) or with chloromethylsilanes are used as thickening and thixotropic agents in composites, coatings and adhesives, especially in vinyl ester, epoxy and polyurethane systems.

[0004] To obtain a surface-modified silica, a hydrophilic silica is fluidized in the gas phase and functionalized with a PDMS-containing plasticizer, for example according to W02008077814 or EP2824148. Subsequent annealing at 150 to 350 °C is particularly important to ensure particularly good bonding of the PDMS chains to the silica surface. This results in very low volatile contents of less than 0.6% (2 h at 105 °C). However, the material has the disadvantage of very long incorporation times. Since the incorporation of silica into polymer matrices is the cycle time-determining step in numerous commercial applications, the maximum throughput is strongly linked to the incorporation time.

[0005] The invention relates to a process for the surface modification of hydrophilic silica with a specific surface area of ​​10 to 1000 m 2 / g (measured according to the BET method according to DIN EN ISO 9277 / DIN 66132) , in which a suspension of the silica in an organic solvent with liquid polyorganosiloxane consisting of 2 units of the general formula R 1 R 2 R 3 SiOi / 2 (M) and 0 to 20 units of the general formula R 4 R 5 Si ( O1 / 2 ) 2 ( D) is reacted, where R 1 , R 2 , R 3 , R 4 and R 5 each represents a hydroxyl radical or a monovalent hydrocarbon radical having 1 to 24 C atoms, where at least one radical R 1 , R 2 , R 3 , R 4 , R 5 and at most 20 mol-%, based on all radicals R 1 , R 2 , R 3 , R 4 , R 5 Hydroxy residues are .

[0006] The silica modified by the process exhibits consistently good shear thinning in polymer matrices with drastically reduced incorporation times compared to conventionally modified silica.

[0007] Silica modification is carried out at moderate temperatures in the liquid phase.

[0008] The silica modified by this process exhibits chain siloxane structures on its surface, which exhibit a chain length distribution that is as homogeneous as possible. These siloxane chains are preferably permanently fixed to the surface of the silica as completely as possible. Furthermore, the chemical bonding of the siloxane chain to the surface of the silica preferably occurs via a single bonding point.

[0009] Precipitated silica or pyrogenic silica can be used as silica.

[0010] Particularly preferred is fumed silica which is produced in a flame reaction from organosilicon compounds, e.g. from silicon tetrachloride or methyltrichlorosilane, or hydrogentrichlorosilane or hydrogenmethyldichlorosilane, or other methylchlorosilanes or alkylchlorosilanes, also in a mixture with hydrocarbons, or any volatilizable or sprayable mixtures of organosilicon compounds, as mentioned, and hydrocarbons, e.g. in a hydrogen-oxygen flame, or also a carbon monoxide-oxygen flame. The production of the silica can take place optionally with or without the additional addition of water, for example in the purification step; preferably no addition of water.

[0011] The silica used preferably has specific surfaces of 40 to 400 m 2 / g and particularly preferably 150 to 270 m 2 / g (measured according to the BET method according to DIN EN ISO 9277 / DIN 66132).

[0012] The bulk densities of the silica used (determined according to DIN EN ISO 787-11) can be in the range from 10 to 200 g / l, preferably 20 to 100 g / l, particularly preferably 20 to 60 g / l.

[0013] The degree of modification achieved by the process can be analyzed by determining the residual silanol content. The modified silica preferably has a residual silanol content in the range of 30 to 90 mol%, more preferably 45 to 85 mol%, and especially preferably 55 to 75 mol%. A suitable method for determining the residual silanol content after modification by acid-base titration is described, for example, in GW Sears et al. Analytical Chemistry 1956, 28, 1981ff.

[0014] The carbon content achieved by the process is preferably 1 wt. % to 15 wt. %, more preferably 2 wt. % to 10 wt. %, especially preferably 3 wt. % to 8 wt. %. The groups introduced by the modification are firmly bound to the surface of the silica. A strong bond represents good chemical bonding and is quantified according to the invention by the solvent-extractable fraction of the modified silica, which is preferably at most 10 wt. %. More preferably, the extractable fraction is at most 6 wt. %, in particular at most 4 wt. % and especially preferably at most 2 wt. % A suitable method for assessing the bond strength of a modification is the quantitative determination of extractable polyorganosiloxane, i.e. polyorganosiloxane not chemically bound to the surface of the modified silica.

[0015] Methyl isobutyl ketone MIBK is preferably used for the determination of extractable polyorganosiloxane.

[0016] The monovalent hydrocarbon residues R 1 to R 5 may be the same or different and are selected from the group of saturated, mono- or polyunsaturated, unbranched or branched hydrocarbon radicals, which may contain heteroatoms and / or functional groups.

[0017] Hydrocarbon radicals are preferably alkyl, alkenyl and aryl radicals such as methyl, ethyl, propyl, such as n-propyl or i-propyl, butyl, such as n-butyl, i-butyl or t-butyl, hexyl, such as n-hexyl or i-hexyl, octyl, such as n-octyl or i-octyl, dodecyl, tetradecyl, hexadecyl, octadecyl, vinyl, allyl, phenyl, o-tolyl, m-tolyl, p-tolyl, xylyl, mesityl or naphtyl radicals.

[0018] The alkyl or aryl radicals may also contain other heteroatoms or functional groups. Monovalent organic groups of the general formula R=(CH2) are preferred. n Y with n = 1 to 24 and Y = vinyl, acrylate, methacrylate, glycidoxy, -SH, -OH, primary amine residue (-NH2), secondary amine residue (-NHR) such as N-monomethyl, N-monoethyl, N-monopropyl, N-monobutyl, N-cyclohexyl or anilino residue, tertiary amine residue (-NR2) such as N, N-dimethyl, N, N-diethyl, N, N-dipropyl, N, N-dibutyl, N, N-methylethyl, N, N-methylpropyl, N, N-ethylpropyl, N, N-methylphenyl, morpholino, pyrrolyl, indolyl, pyrazoyl, imidazoyl or piperidyl residue, quaternary amine residue such as N, N, N-trimethylammonium, N, N, N-triethylammonium or N, N, N-tripropylammonium residue, phosphonato-, -P(O) (OR 6 ) 2 (R 7selected from a methyl, ethyl or phenyl group), isocyanato and protected isocyanato group (-N(H)C(O)G, where the protective group G is split off under thermal stress as HG, with HG = methyl 2-hydroxybenzoate, 2-hydroxypyridine, 1-hydroxymethyl-1,2,4-triazole, N,N-diethylhydroxylamine, 2-butanone oxime, dimethyl malonate, ethyl acetoacetate, diisopropylamine, benzyl-tert.-butylamine, tert.-butylmethylamine, tert.-butylisopropylamine, 2-isopropylimidazole, 3,5-dimethylpyrazole or s-caprolactam) or dihydro-3-yl-2,5-furandione.

[0019] In addition, other organosilicon groups of the general formula R 1] -Si (01 / 2)3 may be present, where the substituent R 11 is selected from the hydrocarbon radicals mentioned above for R.

[0020] Preferably, the monovalent hydrocarbon residues R 1 to R 5selected from methyl, ethyl, propyl, butyl and phenyl radicals.

[0021] The polyorganosiloxane used in the process preferably has 0 to 15 units, particularly preferably 1 to 10 units, in particular 2 to 10 units of the general formula R 4 R 5 Si (O1 / 2) 2 (D).

[0022] The polyorganosiloxane used in the process is preferably liquid in the range from 0 to 60°C, particularly preferably from 10 to 50°C, especially preferably from 15 to 30°C at 0.10 MPa (abs.).

[0023] The polyorganosiloxane used in the process preferably has an average viscosity of 5 to 200, particularly preferably 10 to 100, in particular 20 to 60 mPa s at 20°C.

[0024] The polyorganosiloxane can be used in any desired amount. The amount used is preferably 5 to 50 wt.%, particularly preferably 20 to 40 wt.%, and especially 15 to 25 wt.%, based in each case on the unmodified hydrophilic silica.

[0025] In a special embodiment of the invention, the polyorganosiloxane is used with the addition of an auxiliary substance.

[0026] The organic solvent used to prepare the silica suspension is preferably an aprotic solvent, preferably with a boiling point of at most 120°C, in particular at most 100°C, in each case at 0.10 MPa (abs.), for example a ketone such as acetone, methyl ethyl ketone, ether such as diethyl ether, dioxane, hydrocarbon such as pentane, hexane, aromatic such as toluene, or another solvent such as hexamethyldisiloxane. Mixtures can also be used.

[0027] If necessary, the process can be supplemented with protic

[0028] Solvents are added. From a protic

[0029] A molecule is said to be a solvent if it has a functional group from which hydrogen atoms can be split off as protons (dissociation). Due to the high polarity of the OH bond, it can be split relatively easily, releasing a positively charged hydrogen atom, the proton.

[0030] The most important protic solvent is water, which (simplified) dissociates into a proton and a hydroxide ion.

[0031] Other protic solvents include, for example, alcohols and carboxylic acids. According to the invention, protic solvents that can be added include, for example, liquid or vaporizable alcohols such as isopropanol, ethanol, or methanol, or water. Mixtures of the abovementioned protic solvents can also be added. Preferably, 1 to 50 wt.% of protic solvent, based on the metal oxide, is added, particularly preferably 5 to 25 wt.%. The addition of water as the protic solvent is particularly preferred.

[0032] During the surface modification of the hydrophilic silica, substances can also be used which reduce the necessary reaction times and / or enable the process temperatures to be reduced. These catalytically or stoichiometrically active substances are referred to below as auxiliaries. They preferably comprise acidic or basic substances. They can be selected, for example, from the group of Lewis acids, which include, for example, trivalent aluminum and boron compounds. Bronsted acids, such as hydrogen halides or organic acids, are also preferably used. Hydrogen chloride or acetic acid are particularly preferred here. In a further embodiment, basic compounds are used as auxiliaries, for example hydroxides of alkali and alkaline earth metals and also their salts derived from the corresponding alcohols or carboxylic acids.Furthermore, they can be selected from nitrogen-containing compounds such as ammonia or organically substituted primary, secondary, or tertiary amines. The monovalent organic substituents of the above-mentioned alcohols, carboxylic acids, and amines include saturated and unsaturated, branched and unbranched hydrocarbon radicals, which may also contain other heteroatoms or functional groups. The auxiliaries can be added in bulk or as a solution in inert or reactive solvents. Preference is given to using aqueous sodium hydroxide or potassium hydroxide solution, aqueous ammonia solution, i-propylamine, n-butylamine, i-butylamine, t-butylamine, cyclohexylamine, triethylamine, morpholine, piperidine, or pyridine.

[0033] In a preferred embodiment, the amounts of auxiliary agent used are 0.1 to 10 wt.%, based on the unmodified silica. Preferably, 0.2 to 5 wt.% are used. Particularly preferred is the use of 0.5 to 1.5 wt.% of auxiliary agent, based on the unmodified silica.

[0034] The temperature during the surface modification of the hydrophilic silica is preferably 20 to 140°C, particularly preferably 30 to 120°C, especially preferably 40 to 100°C at 0.10 MPa (abs.).

[0035] The removal of solvents, excess polyorganosiloxane, and by-products can preferably be carried out using dryers or spray drying. If necessary, the drying step can be followed by a post-reaction step to complete the reaction.

[0036] The post-reaction preferably takes place at temperatures of 20 - 300 °C, preferably 20 - 200 °C and particularly preferably at 40 - 180 °C.

[0037] In addition, following the drying step, processes for deagglomeration of the modified silica can be used, such as pin mills, hammer mills, countercurrent mills, impact mills or devices for grinding and classifying.

[0038] Analysis methods:

[0039] Determination of carbon content (%C)

[0040] The elemental analysis for carbon was carried out according to DIN ISO 10694 using a CS-530 elemental analyzer from Eitra GmbH (D-41469 Neuss).

[0041] Determination of the residual content of unmodified silicic acid silanol groups

[0042] The residual silanol content was determined analogously to GW Sears et al. (Analytical Chemistry 1956, 28, 1981ff.) by acid-base titration of silica suspended in a 1:1 mixture of water and methanol. The titration was carried out above the isoelectric point and below the pH range of dissolution of the silica.

[0043] The residual silanol content in % can therefore be calculated using the following formula:

[0044] SiOH = SiOH (silyl) / SiOH (phil) *100% with SiOH(phil) : Titration volume from the titration of the untreated silica

[0045] SiOH (silyl) : Titration volume from the titration of silylated silica

[0046] Determination of the extractable fraction, i.e. the fraction of extractable polyorganosiloxane

[0047] 2.5 g of the silica to be analyzed are stirred into 47.5 g of MIBK in a PE screw-capped vial using a spatula, and the vial is then sealed. After a 30-minute resting period in an ice bath, the mixture is treated for 30 minutes in an ultrasonic bath with ice cooling (Sonorex Digitec DT 156, BANDELIN electronic GmbH & Co. KG, D-12207 Berlin). The clear filtrate is then obtained by pressure filtration (5 bar nitrogen) through a PTFE membrane filter (pore size: 0.2 pm, diameter: 47 mm, Sartorius AG, Göttingen). Exactly 10.00 ml of this sample is taken and weighed as the analyte for determining the silicon content using atomic absorption spectroscopy (Atom Absorption Spectrometer 2100, Perkin Elmer Waltham, MA, USA).

[0048] The extractable components in wt.% can be calculated as follows in a first approximation:

[0049] Extractable components m(MIBK) XV(Analyzate) c(Analyzate) XM(R 4 R 5 SiO2 / 2) m(metal oxide) XM(Si) m(analyze) with m(MIBK) : weight of MIBK (= 47.50 g)

[0050] V(analyze) : Volume of the analyzer (= 10.00 ml) m (metal oxide) : Weight of the surface-modified metal oxide (= 2.50 g)

[0051] M(Si) : Molar mass of silicon (=28.09 g / mol) c(Analyze) : Silicon content of the analyzer in mg / 1 m(Analyze) : Weight of the analyzer in g M (R4R5S1O2 / 2 ) : Molecular mass of the D-groups R4R5S1O2 / 2 in g / mol

[0052] Determination of the viscosity of the polyorganosiloxane

[0053] Determination according to DIN 53019 at 20 ° C and 0 , 10 MPa ( abs . )

[0054] Examples

[0055] In the following examples, unless otherwise stated, all quantities and percentages are based on weight, all pressures are 0.10 MPa (abs.) and all temperatures are 20 ° C.

[0056] Example 1 : Preparation of a highly hydrophobic silica in a 2L glass reactor followed by grinding

[0057] In a round 2L glass reactor equipped with a KPG stirrer, 1140 g of hexamethyldisiloxane solvent were placed under an argon blanket. The reactor was covered with a glass lid with a total of four ground necks and equipped with a reflux condenser with a bubble counter and a thermometer immersed in the reactor. A total of 150 g of silica HDK N20 (silica with an initial surface area of ​​200 m) were added via a grounded metal funnel using a metal scoop. 2 / g, commercially available from Wacker Chemie AG) was added under argon blanket and a suspension was created by vigorous stirring with the KPG stirrer. Finally, 4 g of aqueous ammonia solution (concentration: 5 mol per liter) were added to the suspension, as well as 21 g of the

[0058] Plasticizer X345 (mixture of short-chain a-hydroxy polydimethylsiloxane with an average viscosity of 35 to 50 mPa s).

[0059] With vigorous stirring, the 2 L glass reactor was immersed as far as possible in an oil bath heated to 120 °C using a magnetic stirrer (Heidolph Instruments MR Hei-Tec Magnetic Stirrer). The suspension was heated to 93 °C and refluxed for two hours. After the mixture cooled to room temperature, it was freed from solvent and any unreacted reactants in a rotary evaporator (Heidolph Instruments) equipped with a vacuum pump and cold trap at an oil bath temperature of 130 °C.

[0060] The dry silica thus obtained was structured in a fine grinding device (Sugino Dry Burst DB-100S CE, a countercurrent dry mill).

[0061] The inventive silica had a carbon content of 4.8 wt.%. The rheological properties were tested as follows: the modified silica was dispersed in epoxy resin, and after one day of storage, the viscosity of the mixture was measured at a shear rate of 0.1 s -1 and 10 s -1 The thixotropy index was determined by dividing the low shear rate viscosity by the high shear rate viscosity. The thixotropy index and the incorporation time were determined for two epoxy resin systems:

[0062] Epoxy resin system 1 :

[0063] Mixture of 8 wt.% modified silica and 92 wt.% epoxy resin (EpikoteTM Resin 828 from Hexion, a commercially available epoxy resin based on bisphenol A and epichlorohydrin).

[0064] The silica modified according to the invention had a thixotropy index of 38. The incorporation time of this silica according to the invention was 160 s.

[0065] For comparison, a conventional silica X made from HDK® N20 modified with plasticizer X345 in the gas phase with a carbon content of 4.8 wt.% was used.

[0066] Silica X had a comparable thixotropy index of 34. The incorporation time of this non-inventive silica was 360 s.

[0067] Epoxy resin system 2 :

[0068] Mixture of 8 wt.% modified silica in epoxy resin (EpikoteTM Resin 828 from Hexion, a commercially available epoxy resin based on bisphenol A and epichlorohydrin) and 4 wt.% HDK® N20 in amine hardener (EpikureTM Curing Agent MGSO RIMH-137, commercially available from Hexion), in a mixing ratio of 79 wt.% epoxy resin and 21 wt.% amine hardener.

[0069] Both epoxy resin systems are identical, except that an amine hardener is added to the second system shortly before measurement. Therefore, the same processing times are required for both epoxy resin systems.

[0070] The silica modified according to the invention had a thixotrophy index of 54.

[0071] Example 2: Preparation of a highly hydrophobic silica in a 2L 3-neck flask with subsequent annealing

[0072] In a 2L, three-neck glass flask equipped with a precision glass stirrer, 855 g of hexamethyldisiloxane solvent were placed under an argon blanket. The reactor was equipped with a reflux condenser with a bubble counter and a thermometer. A total of 112 g of HDK® N20 silica were added via a grounded metal funnel using a metal scoop under an argon blanket, and a suspension was created with vigorous stirring using the precision glass stirrer. Finally, 3 g of aqueous ammonia solution (concentration: 5 mol per liter) and 16 g of the plasticizer X345 were added to the suspension. While stirring vigorously, the three-neck flask was fitted with a heating mantle (Pilz® heating mantle from Carlroth). The suspension was heated to 50 °C and maintained at this temperature for two hours with vigorous stirring.After the mixture had cooled to room temperature, it was freed from the solvent and any unreacted reactants in a rotary evaporator (Heidolph Instruments) equipped with a vacuum pump and a cold trap with an oil bath temperature of 130 °C.

[0073] The resulting silica was then annealed in a drying cabinet under nitrogen purge for one hour at 200 °C. The final silica according to the invention had a carbon content of 4.8 wt.%.

[0074] Epoxy resin system 1 :

[0075] The silica modified according to the invention had a thixotropy index of 36. The incorporation time of this silica according to the invention was 9 s.

[0076] Silica X had a comparable thixotropy index of 34. The incorporation time of this non-inventive silica was 186 s.

[0077] Epoxy resin system 2 :

[0078] The silica modified according to the invention had a thixotropy index of 56.

[0079] Silica X had a comparable thixotropy index of 60.

Claims

Patent claims 1. Process for the surface modification of hydrophilic silica with a specific surface area of ​​10 to 1000 m 2 / g (measured according to the BET method according to DIN EN ISO 9277 / DIN 66132) , in which a suspension of the silica in an organic solvent with liquid polyorganosiloxane consisting of 2 units of the general formula R 1 R 2 R 3 SiOi / 2 (M) and 0 to 20 units of the general formula R 4 R 5 Si (O1 / 2) 2 (D), where R 1 , R 2 , R 3 , R 4 and R 5 each represents a hydroxyl radical or a monovalent hydrocarbon radical having 1 to 24 C atoms, where at least one radical R 1 , R 2 , R 3 , R 4 , R 5 and at most 20 mol-%, based on all radicals R 1 , R 2 , R 3 , R 4 , R 5 Hydroxy residues are .

2. A process according to claim 1, wherein pyrogenic silica is used.

3. Process according to one or more of the preceding claims, wherein the carbon content achieved by the process is 1 wt.% to 15 wt.%.

4. Process according to one or more of the preceding claims, in which the monovalent hydrocarbon radicals R 1 to R 5 selected from methyl, ethyl, propyl, butyl, and phenyl radicals.

5. Process according to one or more of the preceding claims, wherein the polyorganosiloxane is liquid in the range from 0 to 60°C at 0.10 MPa (abs.). Process according to one or more of the preceding claims, in which the organic solvent used to prepare the silica suspension is an aprotic solvent. Process according to claim 6, in which a protic solvent is additionally added.

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