Method for modifying silica in a liquid phase

Abstract

The present invention relates to a method for modifying the surface of hydrophilic silica having a specific surface area of 10 to 1000 m 2 / g (measured by the BET method according to DIN EN ISO9277 / DIN66132), comprising reacting a suspension of silica in an organic solvent with a liquid polyorganosiloxane composed of 2 units of the general formula R 1 R 2 R 3 SiO 1 / 2 (M) and 0 to 20 units of the general formula R 4 R 5 Si(O 1 / 2 )2(D) (wherein R 1 , R 2 , R 3 , R 4 and R 5 are each a hydroxyl group or a monovalent hydrocarbon group containing 1 to 24 carbon atoms, and based on at least one group R 1 , R 2 , R 3 , R 4 , R 5 and all groups R 1 , R 2 , R 3 , R 4 , R 5 , a maximum of 20 mol% is a hydroxyl group).

Description

Technical Field

[0001] The present invention relates to a method for surface modification of hydrophilic silica with a liquid polyorganosiloxane in a suspension of silica in an organic solvent.

Background Art

[0002] Hydrophobic surface-modified silica modified with polydimethylsiloxane (PDMS) or chloromethylsilane is used as a thickening agent and thixotropic agent in composite materials, coatings and adhesives, especially in vinyl ester, epoxy and polyurethane systems.

[0003] To obtain surface-modified silica, as an example according to WO2008077814 or EP2824148A, hydrophilic silica is fluidized in the gas phase and functionalized with a PDMS-containing plasticizer. Subsequent heat treatment at 150 to 350 °C is particularly important to obtain a particularly good bonding of the PDMS chains to the silica surface. This results in a very low volatile content of less than 0.6% (2 hours at 105 °C). However, this material has the disadvantage of a very long incorporation time. Since the incorporation of silica into the polymer matrix is a cycle time-determining step in many commercial applications, the maximum throughput is strongly associated with the incorporation time.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

[0005] The present invention is 10 to 1000 m 2A method for surface modification of hydrophilic silica having a specific surface area of / g (measured by the BET method according to DIN EN ISO9277 / DIN66132), in which a suspension of silica in an organic solvent is reacted with a liquid polyorganosiloxane composed of 2 units of the general formula R 1 R 2 R 3 SiO 1 / 2 (M) and 0 to 20 units of the general formula R 4 R 5 Si(O 1 / 2 )2(D) (wherein R 1 、R 2 、R 3 、R 4 and R 5 are each a hydroxyl group or a monovalent hydrocarbon group having 1 to 24 carbon atoms, and at least one group R 1 、R 2 、R 3 、R 4 、R 5 、and all groups R 1 、R 2 、R 3 、R 4 、R 5 have a maximum of 20 mol% hydroxyl groups based on).

[0006] The silica modified by this method has consistently good shear thinning viscosity in the polymer matrix, and the incorporation time is dramatically reduced compared to conventionally modified silica.

[0007] The silica modification is carried out at a moderate temperature in the liquid phase.

[0008] The surface of the silica modified by this method has a chain-like siloxane structure with a distribution of chain lengths that is as homogeneous as possible. These siloxane chains are preferably fixed as completely and permanently as possible to the surface of the silica. Furthermore, the siloxane chains are preferably chemically bonded to the surface of the silica via individual binding sites.

[0009] The silica used can be, for example, precipitated silica or fumed silica.

[0010] Particularly preferred is fumed silica produced by a flame reaction from an organosilicon compound containing a mixture with a hydrocarbon, such as silicon tetrachloride or methyltrichlorosilane, or hydrotrichlorosilane or hydromethyldichlorosilane, or other methylchlorosilanes or alkylchlorosilanes, or fumed silica produced from any desired volatile or sprayable mixture of an organosilicon compound and a hydrocarbon as described in, for example, a hydrogen-oxygen flame, or a carbon monoxide-oxygen flame. The silica can be produced, for example, in a purification step, with or without the additional addition of water, and it is preferred not to add water.

[0011] The silica used preferably has a specific surface area (measured by the BET method according to DIN EN ISO9277 / DIN66132) of 40 to 400 m 2 / g, particularly preferably 150 to 270 m 2 / g.

[0012] The bulk density (determined according to DIN EN ISO787-11) of the silica used can be in the range of 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 this method 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%, particularly preferably 45 to 85 mol%, particularly preferably 55 to 75 mol%. A suitable method for determining the residual silanol content after modification by acid-base titration is described, for example, by G.W. Sears et al., Analytical Chemistry 1956, 28, 1981ff.

[0014] The carbon content achieved by this method is preferably 1 wt% to 15 wt%, particularly preferably 2 wt% to 10 wt%, particularly preferably 3 wt% to 8 wt%.

[0015] The groups introduced by modification are firmly bonded to the surface of the silica. The strong bond represents a good chemical bond and, according to the invention, is quantified by the proportion of modified silica extractable with a solvent, which is preferably at most 10% by weight. The extractable fraction is particularly preferably 6% by weight or less, in particular 4% by weight or less, and particularly preferably 2% by weight or less. A suitable method for evaluating the bond strength of the modification is the quantitative measurement of extractable polyorganosiloxanes, i.e., polyorganosiloxanes not chemically bonded to the surface of the modified silica.

[0016] Methyl isobutyl ketone MIBK is preferably used for the determination of extractable polyorganosiloxanes.

[0017] Monovalent hydrocarbon group R 1 ~R 5 may be the same or different and is selected from the group of saturated, monounsaturated or polyunsaturated, unbranched or branched hydrocarbon groups which may have heteroatoms and / or functional groups.

[0018] Preferably, the hydrocarbon groups are alkyl, alkenyl and aryl groups 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 naphthyl groups.

[0019] The alkyl or aryl group may further have additional heteroatoms or functional groups. Preferred here is the general formula R=(CH2) nY (where n = 1 to 24, and Y = vinyl, acrylate, methacrylate, glycidoxy, -SH, -OH, primary amine group (-NH2), secondary amine group (-NHR), for example N - monomethyl group, N - monoethyl group, N - monopropyl group, N - monobutyl group, N - cyclohexyl group or anilino group, tertiary amine group (-NR2), for example N,N - dimethyl group, N,N - diethyl group, N,N - dipropyl group, N,N - dibutyl group, N,N - methylethyl group, N,N - methylpropyl group, N,N - ethylpropyl group, N,N - methylphenyl group, morpholino group, pyrrolyl group, indolyl group, pyrazolyl group, imidazolyl group or piperidyl group, quaternary amine group, for example, N,N,N - trimethylammonium group, N,N,N - triethylammonium group or N,N,N - tripropylammonium group, phosphonato, P(O)(OR 6 )2 (R selected from methyl, ethyl or phenyl group 7 ), isocyanato and protected isocyanato group (-N(H)C(O)G, where the protecting group G is removed as H - G under thermal stress, and here H - G = 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 ε - caprolactam) or dihydro - 3 - yl - 2,5 - furandione) is a monovalent organic group.)

[0020] Furthermore, an additional organosilicon group of the general formula R 11 Si(O 1 / 2 )3 may be present, and the substituent R 11 is selected from the hydrocarbon groups specified above for R.)

[0021] The monovalent hydrocarbon groups R 1 ~R 5 are preferably selected from methyl group, ethyl group, propyl group, butyl group, and phenyl group.)

[0022] The polyorganosiloxane used in this method preferably has from 0 to 15 units, particularly preferably from 1 to 10 units, especially from 2 to 10 units of the general formula R 4 R 5 Si(O 1 / 2 )2(D).

[0023] The polyorganosiloxane used in this method is liquid at 0.10 MPa (absolute value) preferably in the range of 0 to 60 °C, particularly preferably 10 to 50 °C, especially preferably 15 to 30 °C.

[0024] The polyorganosiloxane used in this method has an average viscosity of preferably 5 to 200, particularly preferably 10 to 100, especially 20 to 60 mPa·s at 20 °C.

[0025] The polyorganosiloxane can be used in any desired amount. The amount used is in each case preferably 5% to 50% by weight, particularly preferably 20% to 40% by weight, especially 15% to 25% by weight based on the unmodified hydrophilic silica.

[0026] In a specific embodiment of the present invention, the polyorganosiloxane is used with an additive.

[0027] The organic solvent used to produce the suspension of silica is preferably an aprotic solvent having a boiling point of preferably up to 120 °C, particularly up to 100 °C at 0.10 MPa (absolute value) in each case, such as ketones such as acetone, methyl ethyl ketone, ethers such as diethyl ether, dioxane, hydrocarbons such as pentane, hexane, aromatics such as toluene or other solvents such as hexamethyldisiloxane. Mixtures can also be used.

[0028] Optionally, a protic solvent may be further added to this method. A solvent is called protic when one molecule has a functional group capable of detaching (dissociating) a hydrogen atom in the molecule as a proton. Since the OH bond has a high polarity, it is possible to relatively easily split a protic solvent by detaching a proton, which is a positively charged hydrogen atom.

[0029] The most important protic solvent is water, which dissociates (briefly speaking) into protons and hydroxide ions. Further examples of protic solvents include alcohols and carboxylic acids. According to the present invention, a liquid or vaporizable alcohol such as isopropanol, ethanol or methanol, or water can be added as a protic solvent. It is also possible to add a mixture of the above protic solvents. It is preferable to add a protic solvent in an amount of 1% to 50% by weight, particularly preferably 5% to 25% by weight, based on silica. It is particularly preferable to add water as the protic solvent.

[0030] Furthermore, in the surface modification of hydrophilic silica, it is possible to use substances that shorten the required reaction time and / or lower the process temperature. These catalytic or stoichiometrically effective substances are hereinafter referred to as the term "adjuvant". These preferably include substances that react either acidicly or basicly. These can be selected, for example, from the group of Lewis acids including trivalent aluminum and boron compounds. It is also preferable to use Bronsted acids such as hydrogen halides or organic acids. Particularly preferred here are hydrogen chloride or acetic acid. In a further embodiment, compounds that react basicly, such as hydroxides of alkali metals and alkaline earth metals, and their salts derived from the corresponding alcohols or carboxylic acids are used as adjuvants. 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 described alcohols, carboxylic acids and amines include saturated and unsaturated, branched and unbranched hydrocarbon groups, which may further have additional heteroatoms or functional groups. The adjuvant can be added in pure form or as a solution in an inert or reactive solvent. It is preferable to use aqueous sodium hydroxide or potassium hydroxide solutions, aqueous ammonia, i-propylamine, n-butylamine, i-butylamine, t-butylamine, cyclohexylamine, triethylamine, morpholine, piperidine or pyridine.

[0031] In a preferred embodiment, the amount of adjuvant used is 0.1 wt% to 10 wt% based on the unmodified silica. It is preferable to use 0.2 wt% to 5 wt%. Particularly preferred here is to use 0.5 wt% to 1.5 wt% of the adjuvant based on the unmodified silica.

[0032] The temperature in the surface modification of hydrophilic silica is in the range of 0.10 MPa (absolute value), preferably 20 to 140 °C, particularly preferably 30 to 120 °C, and particularly preferably 40 to 100 °C.

[0033] Removal of the solvent, excess polyorganosiloxane and by-products can preferably be carried out by means of a dryer or spray drying.

[0034] Optionally, after the drying step, the next reaction step may follow to complete the reaction.

[0035] The subsequent reaction is preferably carried out at a temperature of 20 to 300 °C, preferably 20 to 200 °C, particularly preferably 40 to 180 °C.

[0036] Furthermore, a process for the deflocculation of the modified silica, such as a pin mill, hammer mill, countercurrent mill, impact mill or apparatus for grinding and classification, can be used after the drying step.

[0037] <Analysis method> <Determination of carbon content (%C)> Elemental analysis of carbon was carried out in accordance with DIN ISO 10694 using a CS-530 elemental analyzer manufactured by Eltra GmbH (D-41469 Neuss).

[0038] <Determination of the residual content of unmodified silica silanol groups> The residual silanol content was determined by acid-base titration of silica suspended in a 1:1 mixture of water and methanol, similar to G.W. Sears et al., Analytical Chemistry 1956, 28, 1981ff. The titration was carried out in a region above the isoelectric point and below the pH range of silica dissolution.

[0039] Thus, the residual silanol content expressed as % can be calculated according to the following formula. SiOH = SiOH (silyl) / SiOH (fill (phil)) * 100% Wherein SiOH (fill): Titration volume from the titration of untreated silica SiOH (silyl): Titration volume from the titration of silylated silica

[0040] <Determination of the extractable fraction, i.e., the extractable polyorganosiloxane fraction> 2.5 g of the silica for investigation is stirred with a spatula into 47.5 g of MIBK in a screw-top PE container and then the container is closed. After a rest period of 30 minutes in an ice bath, the mixture is treated for 30 minutes while ice-cooled in an ultrasonic bath (Sonorex Digitec DT 156, BANDELIN electronic GmbH & Co. KG, D-12207 Berlin), and then the clear filtrate is obtained by pressure filtration (nitrogen at 5 bar) through a PTFE membrane filter (pore size: 0.2 μm, diameter: 47 mm, Sartorius AG, Göttingen). Exactly 10.00 ml of this filtrate is taken out as an analyte for determining the silicon content by atomic absorption spectrometry (Atom Absorption Spectrometer 2100, Perkin Elmer Waltham, Massachusetts, USA) and weighed.

[0041] The extractable components expressed in weight % can be calculated approximately as follows in a first approximation.

[0042]

Equation

[0043] <Determination of the Viscosity of Polyorganosiloxanes> Determination according to DIN 53019 at 20 °C and 0.10 MPa (absolute value)

Example

[0044] In the following examples, unless otherwise stated, all numerical values regarding amounts and percentages are based on weight, all pressures are 0.10 MPa (absolute value), and all temperatures are 20 °C.

[0045] [Example 1: Production of Highly Hydrophobic Silica in a 2-Liter Glass Reactor and Subsequent Grinding] 1140 g of the solvent hexamethyldisiloxane was first charged into a round 2-liter glass reactor equipped with a precision glass stirrer under an argon blanket. The reactor was covered with a glass lid having a total of four grinding glass necks, and a reflux condenser equipped with a bubble counter and a thermometer immersed in the reactor was attached. A total of 150 g of silica HDK N20 (silica having an initial surface area of 200 m 2 / g and commercially available from Wacker Chemie) was added under an argon blanket using a metal spatula through a grounded metal funnel, and a suspension was formed while vigorously stirring with a precision glass stirrer. Finally, 4 g of aqueous ammonia solution (concentration: 5 mol / liter) and 21 g of plasticizer X345 (a mixture of short-chain α-hydroxy-polydimethylsiloxanes having an average viscosity of 35 - 50 mPa·s) were added to the suspension.

[0046] While stirring vigorously, the 2-liter glass reactor was immersed as much 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 a temperature of 93 °C and boiled under reflux for 2 hours. When the mixture was cooled to room temperature, the solvent and unreacted reactants were removed from the mixture at an oil bath temperature of 130 °C in a rotary evaporator (Heidolph Instruments) equipped with a vacuum pump and a cold trap.

[0047] The dried silica thus obtained was subjected to de-structuring using a fine pulverizer (Sugino dry Burst DB-100S CE, countercurrent dry pulverizer).

[0048] The silica according to the present invention had a carbon content of 4.8% by weight. The rheological properties were tested as follows. The modified silica was dispersed in an epoxy resin, and after storage for 1 day, the viscosity of the mixture was measured at shear rates of 0.1 s -1 and 10 s -1 The thixotropy index was obtained by dividing the viscosity at a low shear rate by the viscosity at a high shear rate. The thixotropy index and incorporation time were determined for two epoxy resin systems.

[0049] <Epoxy resin system 1> A mixture of 8% by weight of modified silica and 92% by weight of an epoxy resin (Epikote (trademark) resin 828 manufactured by Hexion, a commercially available epoxy resin based on bisphenol A and epichlorohydrin).

[0050] The silica modified according to the present invention had a thixotropy index of 38. The incorporation time of this silica according to the present invention was 160 seconds.

[0051] For comparison, unmodified conventional silica X according to the present invention, composed of HDK(R)N20 modified with plasticizer X345 in the gas phase having a carbon content of 4.8% by weight, was used.

[0052] Silica X had an equivalent thixotropy index of 34. The incorporation time of this non-invention silica was 360 seconds.

[0053] <Epoxy resin system 2> A mixture of 79 wt% epoxy resin and 21 wt% amine hardener, with 8 wt% of modified silica in the epoxy resin (Epikote (trademark) resin 828 made by Hexion, a commercially available epoxy resin based on bisphenol A and epichlorohydrin) and 4 wt% of HDK(R) N20 in the amine hardener (Epikure (trademark) hardener MGSO RIMH - 137, commercially available from Hexion).

[0054] Both epoxy resin systems are the same, but in the case of the second system, the amine hardener is added immediately before measurement. Thus, in both cases, the same incorporation time occurs for both epoxy resin systems.

[0055] The silica modified according to the present invention had a thixotropy index of 54.

[0056] [Example 2: Production of highly hydrophobic silica in a 2 - liter three - necked flask and subsequent heat treatment] 855 g of the solvent hexamethyldisiloxane was first charged into a 2 - liter three - necked glass flask equipped with a precision glass stirrer under an argon blanket. A reflux condenser equipped with a bubble counter and thermometer was attached to the reactor. A total of 112 g of silica HDK(R) N20 was added under an argon blanket using a metal spatula through a grounded metal funnel, and a suspension was formed while vigorously stirring with a precision glass stirrer. Finally, 3 g of aqueous ammonia solution (concentration 5 mol / liter) and 16 g of plasticizer X345 were added to the suspension.

[0057] While stirring vigorously, a heating mantle (Pilz(R) heating mantle made by Carlroth) was attached to the three - necked flask. The suspension was heated to a temperature of 50 °C and maintained at this temperature for 2 hours while stirring strongly. The mixture was cooled to room temperature, and the solvent and unreacted reactants were removed from the mixture in a rotary evaporator (Heidolph Instruments) equipped with a vacuum pump and a cold trap at an oil bath temperature of 130 °C.

[0058] Next, the silica thus obtained was heat-treated at 200 °C for 1 hour in a drying cabinet while purging with nitrogen. The final silica according to the present invention had a carbon fraction of 4.8% by weight.

[0059] <Epoxy resin system 1> The silica modified according to the present invention had a thixotropy index of 36. The incorporation time of this silica according to the present invention was 9 seconds.

[0060] Silica X had an equivalent thixotropy index of 34. The incorporation time of this non-invention silica was 186 seconds.

[0061] <Epoxy resin system 2> The silica modified according to the present invention had a thixotropy index of 56.

[0062] Silica X had an equivalent thixotropy index of 60.

Claims

1. 10 to 1000 m ２ / g specific surface area (measured by the BET method according to DIN EN ISO 9277 / DIN 66132) for surface modification of hydrophilic silica, wherein an organic solvent suspension of said silica is reacted with 2 units of the general formula R １ R ２ R ３ SiO １／２ (M) and 0 to 20 units of the general formula R ４ R ５ Si(O １／２ ) ２ (D) (wherein R １ , R ２ , R ３ , R ４ and R ５ are each a hydroxyl group or a monovalent hydrocarbon group having 1 to 24 carbon atoms, and at least one group R １ , R ２ , R ３ , R ４ , R ５ and all groups R １ , R ２ , R ３ , R ４ , R ５ are at most 20 mol% hydroxyl groups based thereon).

2. The method according to claim 1, using fumed silica.

3. The method according to one or more of claims 1 and 2, wherein the carbon content achieved by the method is 1 wt% to 15 wt%.

4. Monovalent hydrocarbon group R １ ~R ５ The method according to one or more of claims 1 to 3, wherein is selected from a methyl group, an ethyl group, a propyl group, a butyl group, and a phenyl group.

5. The method according to one or more of claims 1 to 4, wherein the polyorganosiloxane is liquid in the range of 0 to 60 °C at 0.10 MPa (absolute value).

6. The method according to one or more of claims 1 to 5, wherein the organic solvent used to produce the suspension of the silica is an aprotic solvent.

7. The method according to claim 6, further adding a protic solvent.

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