WO1998037020A1 - Gels de silice hydrophobes presentant une zone superficielle limitee - Google Patents

Gels de silice hydrophobes presentant une zone superficielle limitee Download PDF

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Publication number
WO1998037020A1
WO1998037020A1 PCT/US1998/003273 US9803273W WO9837020A1 WO 1998037020 A1 WO1998037020 A1 WO 1998037020A1 US 9803273 W US9803273 W US 9803273W WO 9837020 A1 WO9837020 A1 WO 9837020A1
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Prior art keywords
silica
silica hydrogel
hydrogel
hydrophobic silica
mixture
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PCT/US1998/003273
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English (en)
Inventor
Gary T. Burns
James R. Hahn
Charles W. Lentz
Clifford C. Reese
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Dow Corning Corporation
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Application filed by Dow Corning Corporation filed Critical Dow Corning Corporation
Priority to BR9810408-0A priority Critical patent/BR9810408A/pt
Priority to EP98908610A priority patent/EP0963345A1/fr
Priority to JP53688398A priority patent/JP2001513066A/ja
Priority to CA002280795A priority patent/CA2280795A1/fr
Priority to AU66605/98A priority patent/AU6660598A/en
Publication of WO1998037020A1 publication Critical patent/WO1998037020A1/fr

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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B33/00—Silicon; Compounds thereof
    • C01B33/113—Silicon oxides; Hydrates thereof
    • C01B33/12—Silica; Hydrates thereof, e.g. lepidoic silicic acid
    • C01B33/16—Preparation of silica xerogels
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK  ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
    • C09C1/00—Treatment of specific inorganic materials other than fibrous fillers; Preparation of carbon black
    • C09C1/28—Compounds of silicon
    • C09C1/30—Silicic acid
    • C09C1/3081—Treatment with organo-silicon compounds
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/12—Surface area
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/90—Other properties not specified above

Definitions

  • the present invention is hydrophobic silica gels having reduced surface area and a method for their preparation.
  • the method comprises three steps, where in the first step a mixture comprising a silica hydrosol and a colloidal silica is formed.
  • the mixture is heat treated in the presence of a strong mineral acid at a pH less than about 1 to form a silica hydrogel having incorporated therein colloidal silica.
  • the silica hydrogel is contacted with an organosilicon compound in the presence of a catalytic amount of a strong acid to effect hydrophobing of the silica hydrogel thereby forming a hydrophobic silica gel having a surface area within a range of about 100 m 2 /g to 450 m 2 /g as measured in the dry state.
  • the hydrophobic silica gel is contacted with a sufficient quantity of a water-immiscible organic solvent to convert the hydrophobic silica hydrogel into a hydrophobic silica organogel.
  • the organic solvent can then be removed from the organogel to form a hydrophobic silica gel having a surface area within a range of about 100 m /g to 450 m /g as measured in the dry state.
  • a water soluble compound of cerium or iron may be added in the second step to improve the heat stability of the hydrophobic silica gel.
  • hydrophobic silica gels prepared by the present method are useful in many applications such as thermal insulating, reinforcing and extending filler in natural rubbers, and as filler in floatation devices, they are particularly useful as reinforcing fillers in silicone rubber compositions. It is well known that silicone rubber formed from the vulcanization of polydiorganosiloxane fluids or gums alone generally have low elongation and tensile strength values. One means for improving the physical properties of such silicone rubber involves the incorporation of a reinforcing silica filler into the fluid or gum prior to curing.
  • silica reinforcing fillers have a tendency to interact with the polydiorganosiloxane fluid or gum causing a phenomenon typically referred to as "crepe hardening."
  • a great deal of effort has been made in the past to treat the surface of reinforcing silica fillers with organosilanes or organosiloxanes to make the surface of the silica hydrophobic. This surface treatment reduces or diminishes the tendency of the compositions to crepe harden and improves the physical properties of the cured silicone rubber.
  • Lentz U. S. Pat. No. 3,122,520, teaches a procedure where an acidic silica hydrosol is first heated to develop a reinforcing silica structure and then mixed with an organosilicon compound, an acid catalyst, and a water-immiscible organic solvent to produce a hydrophobic silica filler.
  • the organosilicon compounds taught by Lentz are limited to those compounds in which the organic radicals bonded to silicon atoms have less than 6 carbon atoms, organosilicon compounds having no organofunctional substituents bonded to silicon atoms, and to organosilicon compounds having no hydrogen bonded to silicon atoms.
  • Alexander et al. U. S. Pat. No. 2,892,797, describe silica sols modified by treatment with a solution of a metalate so that the silica particles are coated with no more than a molecular layer of a combined metal which forms an insoluble silicate at a pH between 5 and 12.
  • Aluminum, tin, zinc, and lead are taught as the preferred metals.
  • Alexander et al. teach that silica sols which carry a metal upon the surface of the particles according to their invention have increased stability at pH extremes. Termin et al., U. S. Pat. No. 3,850,971, and Termin et al. U. S. Pat. No.
  • porous silicic acid having a specific surface area of about 50 m 2 /g to 1000 m 2 /g can be made by hydrolyzing methyl or ethyl silicate or polymethyl or polyethyl silicate with about 70 to 120% of the stoichiometric amount of water with moderate stirring.
  • Termin et al. teach that transition metals such as iron oxides and chromium oxides may be used as hydrolysis activators and that such metals may appear in the end product.
  • Nauroth et al., U. S. Pat. No. 4,360,388, teach cerium containing precipitated silica.
  • Nauroth et al. teach that silicone rubber compositions reinforced with the cerium containing precipitated silica exhibit excellent heat stability and that the cerium containing precipitated silica acts as a fire retardant agent.
  • hydrophobic silica gels prepared by the present method have improved compatibility with polydiorganosiloxane polymers, when compared to silica gels prepared in the absence of the colloidal silica. Therefore, the present hydrophobic silica gels incorporating the colloidal silica are especially suited for use as reinforcing fillers in compositions curable to form silicone rubber. Such cured compositions can have improved physical properties such as tear and tensile strength, when compared to compositions using hydrophobic silica gels as reinforcing filler without the incorporation of colloidal silica.
  • the present invention is hydrophobic silica gels having reduced surface area and a method for their preparation.
  • the method comprises three steps, where in the first step a mixture comprising a silica hydrosol and colloidal silica is formed.
  • the mixture is heat treated in the presence of a strong mineral acid at a pH less than about 1 to form a silica hydrogel having incorporated therein colloidal silica.
  • the silica hydrogel is contacted with an organosilicon compound in the presence of a catalytic amount of a strong acid to effect hydrophobing of the silica hydrogel thereby forming a hydrophobic silica gel having a surface area within a range of about 100 m 2 /g to 450 m 2 /g as measured in the dry state.
  • the hydrophobic silica gel is contacted with a sufficient quantity of an organic solvent immiscible with water to convert the hydrophobic silica hydrogel into a hydrophobic silica organogel.
  • the organic solvent can be removed from the hydrophobic silica organogel to form a hydrophobic silica gel having a surface area within a range of about 100 m 2 /g to 450 m 2 /g as measured in the dry state.
  • the present invention is hydrophobic silica gels having reduced surface area and a method for their preparation.
  • the method for preparing the hydrophobic silica gels comprises:
  • each R 1 is independently selected from a group consisting of hydrocarbon radicals comprising about 1 to 12 carbon atoms and organofunctional hydrocarbon radicals comprising about 1 to 12 carbon atoms
  • the method of the present invention is a three-step procedure, comprising steps (A), (B), and (C) for making hydrophobic silica gels having colloidal silica incorporated therein.
  • Step (A) of the method comprises forming a mixture comprising a preformed silica hydrosol having an average particle size less than 4 nanometers (nm) and a preformed silica hydrosol having an average particle size of at least 4 nm, referred to herein as "colloidal silica".
  • Step (B) of the method comprises heating the mixture comprising the silica hydrosol and colloidal silica under strong acid conditions to form a silica hydrogel having the colloidal silica incorporated therein.
  • Step (C) comprises contacting the silica hydrogel prepared in step (B) with an organosilicon compound which reacts with the silica hydrogel to give a hydrophobic silica hydrogel.
  • an organosilicon compound which reacts with the silica hydrogel to give a hydrophobic silica hydrogel.
  • sufficient water-immiscible organic solvent is added in step (C) to convert the silica hydrogel or hydrophobic silica hydrogel to the corresponding organogel.
  • the solvent can then be removed from the hydrophobic silica organogel to form a hydrophobic silica gel.
  • Hydrophobic silica gels prepared by the present method have reduced surface area which improves their ease of incorporation into silicone rubber compositions and make them suitable as reinforcing fillers in such compositions
  • silica hydrosols means those hydrosols of silica having an average particle size less than 4 nanometers (nm).
  • Silica hydrosols useful in the present method can be prepared by, for example, deionizing sodium silicate by a method such as the use of an ion exchange resin.
  • the silica hydrosol may be prepared by hydrolyzing a silane at a low temperature.
  • the silica hydrosol may be prepared by acidifying a sodium silicate mixture.
  • the silica hydrosol provides about 0.02 g to 0.5 g of SiO 2 per ml of the mixture.
  • the silica hydrosol provides about 0.05 g to 0.2 g of SiO 2 per ml of the mixture.
  • the mixture of the present method requires the presence of about 0.1 to 50 weight percent of colloidal silica, based on the total weight of the mixture.
  • colloidal silica based on the total weight of the mixture.
  • colloidal silica refers to hydrosols of silica having an average particle size of at least 4 nm. Preferred is when the mixture comprises about 10 to 30 weight percent of colloidal silica, based on the total weight of the mixture.
  • colloidal silica useful in the present method and compositions can be described as a colloidal amorphous silica that has not at any point existed as a gel during its preparation.
  • the method of preparation of the colloidal silica is not critical to the present method and compositions and can be any of those known in the art.
  • the colloidal silica can be prepared by, for example, combining an aqueous solution of a soluble metal silicate, such as sodium silicate, and an acid so that the colloidal particles grow in a weakly alkaline solution until the desired particle size is achieved.
  • a colloidal silica having an average particle size within a range of 4 to about 300 nm. Even more preferred is a colloidal silica having an average particle size within a range of about 6 to 100 nm.
  • the mixture comprising the silica hydrosol and the colloidal silica must comprise a sufficient concentration of a strong mineral acid such that the pH of the mixture is less than about pH 1.
  • a strong mineral acid such that the pH of the mixture is less than about pH 1.
  • the strong mineral acid there should be a sufficient amount of the strong mineral acid present so that the pH is essentially 0, that is so that the pH cannot be measured.
  • any strong mineral acid can be used.
  • the term "strong mineral acid” refers to those acids which ionize to the extent of at least 25 percent in 0.1 N aqueous solution at 18°C.
  • the strong mineral acid may be, for example, hydrochloric, hydroiodic, sulfuric, nitric, and phosphoric acid.
  • step (B) the mixture comprising the silica hydrosol and the colloidal silica is heated at a temperature within a range of about 20°C to 250°C. Preferred is when the mixture is heated at a temperature within a range of about 75°C to 150°C. Even more preferred is when, in step (A), the mixture is heated at a temperature within a range of about 90°C to l lO°C.
  • step (B) the heating time required varies with the temperature and acid concentration. Generally, the higher the temperature and the greater the acid concentration the shorter the heating time needed.
  • step (B) The heating of step (B) must be continued until the silica hydrogel having the colloidal silica incorporated therein acquires a structure such that the final product after hydrophobing has a surface area as measured in the dry state within a range of about 100 m 2 /g to 450 m 2 /g as determined by the Brunauer Emmett and Teller
  • the surface area of the silica hydrogel at the conclusion of step (B) is immaterial provided it is such that the surface area of the dried product after the hydrophobing of step
  • step (C) is within the above described range.
  • the surface area of the silica hydrogel is reduced by the hydrophobing reaction, since the organosilyl groups which become attached to the surface of the silica hydrogel increase the average particle size.
  • the surface of the silica hydrogel can be above 450 m /g provided that the hydrophobing treatment brings it within a range of about 100 m /g to 450 m /g.
  • To determine the proper heating conditions during conduct of step (B) it is necessary to proceed with the hydrophobing of step (C) and then measure the surface area of the resulting product in the dry state. If the surface area of the resulting product in the dry state is above 450 m 2 /g, then the acid heating conditions of step (B) were too mild.
  • step (B) If the surface area of the resulting product in the dry state is below 100 m 2 /g, then the acid heating conditions of step (B) were too severe. Examples of suitable acid concentrations, temperatures, and times for conduct of step (B) are provided in the Examples herein. If the surface area of the hydrophobic silica gel in the dry state is above or below the described range, the hydrophobic silica gels have diminished reinforcing properties in silicone elastomers.
  • the silica organogel of step (B) may be subjected to a shearing force to reduce aggregate particle size and to improve the uniformity of the particle size distribution prior to the conduct of the hydrophobing reaction of step (C).
  • the shearing force may be applied to the silica organogel by any of those methods known in the art.
  • the shearing force may be applied, for example, by a mechanical means such as a high-speed mixer or by ultrasound.
  • This reduction in aggregate particle size and improved uniformity of the particle size can provide for hydrophobic silica gels which when compounded into silicone elastomer compositions provide for lower viscosity compositions, more stable compositions, and for cured silicone elastomers having improved clarity and physical properties.
  • step (C) of the present method the silica hydrogel of step (B) is contacted with one or more of the defined organosilicon compounds described by formulas (1) and (2) in the presence of a catalytic amount of a strong acid to effect hydrophobing of the silica gel.
  • the strong acid can be the same acid which was used in step (B).
  • the silica hydrogel can be washed free of acid and a catalytic amount of strong acid added either prior to, simultaneously with, or subsequent to the addition of the organosilicon compound.
  • the catalytic amount of the strong acid can be generated in situ by hydrolysis of the chlorosilane or the reaction of the chlorosilane directly with hydroxyls of the silica hydrogel.
  • the limitations on pH as described for step (B) do not apply. It is only necessary that a catalytic amount of a strong acid be present in an amount sufficient to effect reaction of the organosilicon compound with the silica hydrogel. Examples of useful acids include hydrochloric, sulfuric, and benzene sulfonic acids. It is preferred that in step (C) the strong acid catalyst provide a pH less than about 2.5.
  • the temperature at which the hydrophobing of step (C) is conducted is not critical and can be from about 20°C to 250°C. Generally it is preferred that the hydrophobing of step (C) be conducted at a temperature within a range of about 30°C to 150°C.
  • the hydrophobing of Step (C) can be conducted at the reflux temperature of the water- immiscible organic solvent when it is present.
  • each R 1 can be independently selected from a group consisting of hydrocarbon radicals comprising about 1 to 12 carbon atoms and organofunctional hydrocarbon radicals comprising about 1 to 12 carbon atoms.
  • R 1 can be a saturated or unsaturated hydrocarbon radical.
  • R 1 can be a substituted or non-substituted hydrocarbon radical.
  • R 1 can be, for example, alkyl radicals such as methyl, ethyl, propyl, t-butyl, hexyl, heptyl, octyl, decyl, and dodecyl; alkenyl radicals such as vinyl, allyl, and hexenyl; substituted alkyl radicals such as chloromethyl, 3,3,3-trifluoropropyl, and 6-chlorohexyl; and aryl radicals such as phenyl, naphthyl, and tolyl.
  • alkyl radicals such as methyl, ethyl, propyl, t-butyl, hexyl, heptyl, octyl, decyl, and dodecyl
  • alkenyl radicals such as vinyl, allyl, and hexenyl
  • substituted alkyl radicals such as chloromethyl, 3,3,3-trifluoropropy
  • Rl can be an organofunctional hydrocarbon radical comprising 1 to about 12 carbon atoms where the the organic portion of the radical is substituted with reactive atoms or groups such as mercapto, disulfide, polysulfide, amino, carboxylic acid, carbinol, ester, or amido.
  • a preferred organofunctional hydrocarbon radical is one having disulfide or polysulfide functionality.
  • each X is independently selected from a group consisting of halogen and alkoxy radicals comprising about 1 to 12 carbon atoms.
  • halogen it is preferred that the halogen be chlorine.
  • X is an alkoxy radical, X may be, for example, methoxy, ethoxy, and propoxy.
  • each X is selected from a group consisting of chlorine atoms and methoxy.
  • the viscosity of the organosiloxanes described by formula (2) is not limiting and can range from that of a fluid to a gum.
  • organosilicon compound may be provided to the present method as a single compound as described by formulas (1) or (2) or as a mixture of two or more organosilicon compounds described by formulas (1) and (2).
  • organosilicon compounds include diethyldichlorosilane, allylmethyldichlorosilane, methylphenyldichlorosilane, phenylethyldiethoxysilane, 3,3,3- trifluoropropylmethyldichlorosilane, trimethylbutoxysilane, sym- diphenyltetramethyldisiloxane, trivinyltrimethylcyclotrisiloxane, hexaethyldisiloxane, pentylmethyldichlorosilane, divinyldipropoxysilane, vinyldimethylchlorosilane, vinylmethyldichlorosilane, vinyldimethylmethoxysilane, trimethylchlorosilane, hexamethyldisiloxane, hexenylmethyldichlorosilane, hexenyldimethylchlorosilane, dimethylchlorosilane,
  • the amount of organosilicon compound added to the method is that sufficient to adequately hydrophobe the silica hydrogel to provide a hydrophobic silica gel suitable for its intended use.
  • the organosilicon compound should be added to the method in an amount such that there is at least 0.04 organosilyl unit per SiO 2 unit in the silica hydrogel, the SiO 2 units including both those provided by the silica hydrosol and the colloidal silica.
  • the upper limit of the amount of organosilicon compound added to the process is not critical since any amount in excess of the amount required to saturate the silica gel will act as a solvent for the method.
  • the hydrophobic silica hydrogel of step (C) may be used as is or may be recovered for use by such methods as centrifugation or filtration.
  • the hydrophobic silica hydrogel may be dried by the use of such methods as heating or reducing pressure or a combination of both heating and reducing pressure.
  • a water-immiscible organic solvent in sufficient amount to convert the silica hydrogel or hydrophobic silica hydrogel to the corresponding organogel is added.
  • the organic solvent can be added prior to, simultaneously with, or subsequent to the addition of the organosilicon compound. That is the silica hydrogel can be first converted into an organogel by replacement of the water with the organic solvent and then hydrophobed.
  • the organosilicon compound and the organic solvent can be added simultaneously to the silica hydrogel. Under these conditions the reaction of the silica hydrogel with the organosilicon compound and the replacement of the water in the hydrophobic silica hydrogel with the organic solvent may occur simultaneously.
  • the organosilicon compound can be added prior to the organic solvent, in which case the silica hydrogel reacts with the organosilicon compound and the resulting product is then converted into an organogel by an addition of an organic solvent. In the latter two cases the conversion to a silica organogel is accomplished by a phase separation, in which the hydrophobic silica organogel passes into the organic solvent phase.
  • a preferred method is where a water-immiscible organic solvent is added after formation of the hydrophobic silica hydrogel thereby effecting formation of a hydrophobic silica organogel.
  • any organic solvent immiscible with water can be employed.
  • suitable water-immiscible solvents include low molecular weight siloxanes such as hexamethyldisiloxane, octamethylcyclotetrasiloxane, diphenyltetramethyldisiloxane and trimethylsilyl endblocked polydimethylsiloxane fluids.
  • siloxane When a siloxane is employed as a solvent it may serve both as a solvent and as a reactant with the silica hydrogel.
  • suitable solvents include aromatic hydrocarbons such as toluene and xylene; heptane and other aliphatic hydrocarbon solvents; cycloalkanes such as cyclohexane; ethers such as diethylether and dibutylether; halohydrocarbon solvents such as methylene chloride, chloroform, ethylene chloride, and chlorobenzene; and ketones such as methylisobutylketone.
  • aromatic hydrocarbons such as toluene and xylene
  • heptane and other aliphatic hydrocarbon solvents such as cyclohexane
  • ethers such as diethylether and dibutylether
  • halohydrocarbon solvents such as methylene chloride, chloroform, ethylene chloride, and chlorobenzene
  • ketones such as methylisobutylketone.
  • the amount of water-immiscible organic solvent is not critical so long as there is sufficient solvent to convert the hydrophobic silica hydrogel into a silica organogel.
  • the solvent should have a boiling point below about 250°C to facilitate its removal from the hydrophobic silica organogel, however the boiling point is not critical since the solvent may be removed from the hydrophobic silica organogel by centrifuging or other suitable means.
  • the resulting product may be employed per se. That is the hydrophobic silica organogel may be used directly as a reinforcing agent in silicone rubber or in any other uses for which this type of product can be used. Alternatively, the solvent may be removed from the hydrophobic silica organogel and the resulting dry hydrophobic silica gel used.
  • a surfactant or a water- miscible solvent may be added in the presence or absence of any water-immiscible organic solvent added to the method.
  • Suitable surfactants can include, for example, anionic surfactants such as dodecylbenzene sulfonic acid, nonionic surfactants such as polyoxyethylene(23)lauryl ether and
  • Suitable water-miscible solvents can include, for example, alcohols such as ethanol, propanol, isopropanol, n-butanol, and tetrahydrofuran.
  • step (C) of the present method an effective amount of a heat stabilizing agent selected from a group consisting of water soluble compounds of cerium and iron may be added.
  • a heat stabilizing agent selected from a group consisting of water soluble compounds of cerium and iron
  • an effective amount it is meant that the water soluble compound of cerium or iron is present in the hydrophobic silica gel at a concentration sufficient to provide improved heat stability to those compositions in which the hydrophobic silica gel is incorporated.
  • Such compositions can include, for example, silicone rubber, natural rubber, and synthetic organic rubber.
  • (C) excluding solvents, is considered useful in the present process.
  • the water soluble compound of cerium or iron comprises about 0.1 %Wt./Vol. to 1 %Wt./Vol. on the same basis.
  • water soluble compounds which may be useful in the present method include FeCl 3 , FeBr 2 , FeBr 3 .6H 2 O, FeCl 2 .4H 2 O, FeI 2 .4H 2 O, Fe(NO 3 ) 3 .6H 2 O, FePO 4 .2H 2 O,
  • a preferred water soluble compound of cerium or iron for use in the present method is selected from the group consisting of FeCl 3 and CeCl 3 .9H 2 O.
  • Example 1 A silica gel having incorporated therein colloidal silica was hydrophobed with hexamethyldisiloxane. 750 ml of PQ N Clear Sodium Silicate (PQ Corporation, Valley Forge, PA) was diluted with 1350 ml of deionized water. This solution was added at a rate of 420 ml per minute to a rapidly stirred solution comprising 280 ml of concentrated hydrochloric acid (HCl) (Fisher Certified, Fisher Scientific, Fair Lawn, NJ) diluted with 620 ml of deionized water. The resulting mixture was stirred for 2 minutes and then the pH adjusted to 2.5 using a sodium silicate solution. The resulting 3100 ml of silica hydrosol contained 0.1 g of SiO 2 per milliliter.
  • HCl concentrated hydrochloric acid
  • silica hydrosol prepared as described above was deionized by pumping through a 1.5 m x 5 cm column packed with 1500 ml of Dowex 50WX8-100 ion exchange resin in the acid form (The Dow Chemical Company, Midland, MI) at a rate of 60 ml per minute.
  • the pH of the column effluent was monitored until the pH dropped below 0.5, at which point the next 2000-2400 ml of deionized silica hydrosol effluent was collected.
  • the deionized silica hydrosol was agglomerated by placing 1 L of the deionized silica hydrosol in a 5 L flask and, while stirring, adding 273 ml of colloidal silica (Ludox® SM, DuPont Chemicals, Wilmington, DE, average particle size of 10 nm) and 392 ml of concentrated HCl (Fisher Certified).
  • the silica hydrogel which formed within a few minutes of addition of the HCl was broken-up by additional stirring to form a suspension comprising an agglomerated silica hydrogel having incorporated therein the colloidal silica.
  • the silica hydrogel suspension was heat treated at 100°C for 3 hours and then cooled to room temperature.
  • the heat-treated silica hydrogel suspension was hydrophobed as follows. To the heat-treated silica hydrogel suspension, with stirring, was added 555 ml of isopropanol followed by 288 ml of hexamethyldisiloxane. The resulting mixture was stirred for 1 hour at room temperature. Then, 1 L of toluene was added to the mixture. This mixture was mildly stirred for an additional 5 minutes, stirring stopped, and the aqueous phase drained from the bottom of the flask. The toluene phase was washed with 500 ml of deionized water. The flask was then fitted with a Dean-Stark trap and the toluene phase refluxed to remove residual water.
  • Example 2 A silica gel having incorporated therein colloidal silica was hydrophobed with hexamethyldisiloxane. A deionized silica hydrosol was prepared as described in Example 1.
  • the deionized silica hydrosol was agglomerated by placing 1 L of the deionized silica hydrosol in a 5 L flask and, while stirring, adding 216 ml of colloidal silica (Nalco® 1050, Nalco Chemical Co., Chicago, IL) and 375 ml of concentrated HCl (Fisher Certified).
  • the silica hydrogel which formed within a few minutes of addition of the HCl was broken-up by additional stirring to form a suspension comprising an agglomerated silica hydrogel having incorporated therein the precipitated silica.
  • the silica hydrogel suspension was heat treated by refluxing for 3 hours and then cooled to room temperature.
  • the heat-treated silica hydrogel suspension was hydrophobed as follows.
  • the toluene phase was transferred to an open container in an exhaust hood and the toluene allowed to evaporate leaving as product a hydrophobic silica gel.
  • the hydrophobic silica gel was dried for 4 hours at 150°C to remove residual toluene.
  • the yield of dried hydrophobic silica gel was 267 g.
  • the BET surface area of the dried hydrophobic silica gel was determined by the method described supra, and the result is reported in Table 1.
  • Example 3 A silica gel having incorporated therein colloidal silica was hydrophobed with hexamethyldisiloxane.
  • a deionized silica hydrosol was prepared as described in Example 1. The deionized silica hydrosol was agglomerated by placing 1 L of the deionized silica hydrosol in a 5 L flask and, while stirring, adding about 130 ml of colloidal silica (Nalco® 1140, Nalco Chemical Co.) and 375 ml of concentrated HCl (Fisher Certified).
  • the silica hydrogel which formed within a few minutes of addition of the HCl was broken-up by additional stirring to form a suspension comprising an agglomerated silica hydrogel having incorporated therein the colloidal silica.
  • the silica hydrogel suspension was heat treated by refluxing for 3 hours and then cooled to room temperature.
  • the heat-treated silica hydrogel suspension was hydrophobed as follows. To the heat-treated silica hydrogel suspension, with stirring was added 530 ml of isopropanol followed by 100 ml of hexamethyldisiloxane. The resulting mixture was stirred for 1 hour at room temperature. Then, 1750 ml of toluene were added to the mixture. This mixture was stirred for an additional 5 minutes, stirring stopped, and the aqueous phase drained from the bottom of the flask. The toluene phase was washed with 500 ml of deionized water. The flask was fitted with a Dean-Stark trap and the toluene phase refluxed to remove residual water.
  • the toluene phase was transferred to an open container in an exhaust hood and the toluene allowed to evaporated leaving as product a hydrophobic silica gel.
  • the hydrophobic silica gel was dried for 4 hours at 150°C to remove residual toluene.
  • the yield of dried hydrophobic silica gel was 186 g.
  • the BET surface area of the dried hydrophobic silica gel was determined by the method described in Example 2 and the result is reported in Table 1.
  • Example 4 A silica gel having incorporated therein colloidal silica, hydrophobed with hexamethyldisiloxane, and heat stabilized by the addition of FeCl 3 was prepared.
  • the resulting silica hydrogel was cut into approximately 1 cm squares and washed with deionized water until the pH of the effluent was about pH 2.1.
  • the washed silica hydrogel was placed in a 5 L flask, 839 ml of concentrated HCl (Fisher Certified) added, and the resulting mixture heated to reflux for 5 hours. The refluxed silica hydrogel was cooled to room temperature.
  • the heat-treated silica hydrogel suspension was hydrophobed as follows. To the silica hydrogel, with stirring, was added 1049 ml of isopropanol, 543 ml of hexamethyldisiloxane and 8.3 g of FeCl 3 . After stirring the flask content 1 hour at room temperature, 2 L of toluene were added. After mild stirring the flask content for an additional 5 minutes, stirring was stopped and the aqueous bottom phase drained from the flask. The toluene phase was washed with 500 ml of deionized water. The flask was fitted with a Dean-Stark trap and the toluene phase refluxed to remove residual water.
  • Example 5 A silica gel having incorporated therein colloidal silica, hydrophobed with hexamethyldisiloxane, and heat stabilized by the addition of FeCl 3 was prepared.
  • One liter of the deionized silica hydrosol was placed in a 5 L flask and while stirring 273 ml of Ludox® SM (DuPont Chemicals) were added, followed by 392 ml of concentrated HCl.
  • the silica hydrogel which formed within a few minutes of addition of the HCl was broken-up by additional stirring to form a silica hydrogel suspension.
  • the silica hydrogel suspension was heat-treated at 100°C for 3 hours and then cooled to room temperature.
  • the heat-treated silica hydrogel was hydrophobed as follows. To the heat-treated silica hydrogel, with stirring, was added 555 ml of isopropanol, 288 ml of hexamethyldisiloxane, and 2.7 g of FeCl 3 . The resulting mixture was stirred for 1 hour at room temperature and then 1 L of toluene was added to the mixture. This mixture was mildly stirred for an additional 5 minutes, then stirring stopped and the aqueous phase drained from the bottom of the flask. The toluene phase was washed with 500 ml of deionized water. The flask was fitted with a Dean-Stark trap and the toluene phase refluxed to remove residual water.
  • Example 6 A silica gel having incorporated therein colloidal silica, hydrophobed with hexamethyldisiloxane and vinyldimethylchlorosilane, and heat stabilized by the addition of FeCl 3 was prepared. A deionized silica hydrosol was prepared as described in Example 1.
  • the deionized silica hydrosol was agglomerated by placing 1 L of the deionized silica hydrosol in a 5 L flask and while stirring adding 273 ml of colloidal silica (Ludox® SM, DuPont Chemicals) and 392 ml of concentrated HCl (Fisher Certified). The mixture was heat-treated by refluxing for 3 hours with stirring to form a suspension comprising a silica hydrogel having incorporated therein the colloidal silica. The resulting heat-treated silica hydrogel was cooled to room temperature.
  • the heat-treated silica hydrogel was hydrophobed as follows. To the heat-treated silica hydrogel, with stirring, was added 555 ml of isopropanol, 78 ml of hexamethyldisiloxane, and 2.7 g of FeCl 3 . The resulting mixture was stirred for 1 hour at room temperature. Then, 2 L of toluene were added to the mixture. This mixture was stirred for several minutes, stirring stopped, and the aqueous phase drained from the bottom of the flask. The toluene phase was washed with 1 L of deionized water. The treatment flask was then fitted with a Dean-Stark trap and the toluene phase refluxed to remove residual water.
  • the toluene phase was heated at 110°C to remove residual hexamethyldisiloxane and then 5 ml of vinyldimethylchlorosilane were added. This mixture was refluxed for 1 hour and cooled to room temperature. About 50 ml of deionized water were added to the flask to washout residual HCl and the toluene phase refluxed to remove residual water. The toluene phase was transferred to an open container in an exhaust hood and the toluene allowed to evaporate leaving as product a hydrophobic silica gel. The hydrophobic silica gel was dried overnight at 85°C. The yield of dried hydrophobic silica gel was 214 g.
  • Example 7 A silica gel having incorporated therein colloidal silica, hydrophobed with hexamethyldisiloxane arid vinyldimethylchlorosilane, and heat stabilized by the addition of FeCl 3 was prepared. The silica hydrogel was sheared prior to hydrophobing to reduce aggregate particle size and to improve the uniformity of the particle size distribution. A deionized silica hydrosol was prepared by a method similar to that described in Example 1.
  • the deionized silica hydrosol was agglomerated by placing 1 L of the deionized silica hydrosol in a 5 L flask and while stirring adding 273 ml of colloidal silica (Ludox® SM, DuPont Chemicals) and 392 ml of concentrated HCl (Fisher Certified). The mixture was heat treated by refluxing for 3 hours with stirring to form a suspension comprising an silica hydrogel having incorporated therein the colloidal silica. After cooling to room temperature the silica hydrogel was sheared in a Waring Blender
  • the heat-treated and sheared silica hydrogel was hydrophobed as follows. To the silica hydrogel, with stirring, was added 555 ml of isopropanol, 117 ml of hexamethyldisiloxane, and 2.7 g of FeCl 3 . The resulting mixture was stirred for 1 hour at room temperature. Then, 2 L of toluene were added to the mixture. This mixture was mildly stirred for several minutes, stirring stopped, and the aqueous phase drained from the bottom of the flask. The toluene phase was washed with 1 L of deionized water. The flask was then fitted with a Dean-Stark trap and the toluene phase refluxed to remove residual water.
  • the toluene phase was heated at 110°C to remove residual hexamethyldisiloxane and then 5 ml of vinyldimethylchlorosilane were added to the flask. This mixture was refluxed for 1 hour and cooled to room temperature. About 50 ml of deionized water were added to the flask to washout residual HCl and the toluene phase refluxed to remove residual water.
  • the toluene phase was transferred to an open container in an exhaust hood and the toluene allowed to evaporate leaving as product a hydrophobic silica gel.
  • the hydrophobic silica gel was dried overnight at 85°C. The yield of dried hydrophobic silica gel was 209 g. Selected physical parameters of the dried hydrophobic silica gel were characterized by standard methods and the results are reported in Table 2.
  • Example 8 A silica gel having incorporated therein colloidal silica, hydrophobed with hexamethyldisiloxane and vinyldimethylchlorosilane, and heat stabilized by the addition of FeCl 3 was prepared. The silica hydrogel was sheared prior to hydrophobing to reduce aggregate particle size and to improve the uniformity of the particle size distribution. A deionized silica hydrosol was prepared by a method similar to that described in Example 1.
  • the deionized silica hydrosol was agglomerated by placing 1.5 L of the deionized silica hydrosol in a 5 L flask and while stirring adding 409.5 ml of colloidal silica (Ludox® SM, DuPont Chemicals) and 588 ml of concentrated HCl (Fisher Certified). The mixture was heat treated by refluxing for 3 hours with stirring to form a suspension comprising a silica hydrogel having incorporated therein the colloidal silica.
  • colloidal silica Lidox® SM, DuPont Chemicals
  • silica hydrogel was sheared in a Waring Blender (Model 7011) for 2 minutes and then returned to the 5 L flask.
  • the heat-treated and sheared silica hydrogel suspension was hydrophobed as follows. To the silica hydrogel suspension, with stirring, was added 832.5 ml of isopropanol, 175 ml of hexamethyldisiloxane, and 4 g of FeCl 3 . The resulting mixture was stirred for 1 hour at room temperature. Then, 3.2 L of toluene were added to the mixture. This mixture was mildly stirred for several minutes, stirring stopped, and the aqueous phase drained from the bottom of the flask.
  • the toluene phase was washed with 1 L of deionized water. The flask was then fitted with a Dean-Stark trap and the toluene phase refluxed to remove residual water. The toluene phase was heated at 110°C to remove residual hexamethyldisiloxane and then 3.75 ml of vinyldimethylchlorosilane were added to the flask. This mixture was refluxed for 1 hour and then cooled to room temperature. About 50 ml of deionized water were added to the flask to washout residual HCl and the toluene phase refluxed to remove residual water.
  • Example 9 Each of the dried hydrophobic silica gels prepared in Examples 1 through 5 were compounded into a liquid silicone rubber composition, the composition cured, and the physical properties determined.
  • Each of the dried hydrophobic silica gels was compounded at 38 parts per hundred (pph) by weight into a polydimethylsiloxane gum containing about 0.15 mole percent vinyl radicals substituted on silicon atoms and having a plasticity of about 55 to 65.
  • a base composition was blended 0.7 pph by weight of 2,5-bis(tert-butylperoxy)-2,5-dimethylhexane, based on the weight of the polydimethylsiloxane gum.
  • the catalyzed base composition was cured in appropriate configurations for physical property testing by hot pressing at 34.5 MPa for 15 minutes at 175°C.
  • Example 10 Each of the dried hydrophobic silica gels prepared in Examples 6 through 8 were compounded into a silicone rubber composition, the composition cured, and the physical properties determined. Each of the dried hydrophobic silica gels was compounded at the parts per hundred (pph) by weight described in Table 2 into a siloxane mixture. The temperature at which this compounding was effected is also provided in Table 2.
  • the siloxane mixture comprised 83.8 weight percent vinyldimethylsiloxy endblocked polydimethylsiloxane having a viscosity of 55 Paxs at 25°C and 16.2 weight percent of a vinyldimethylsiloxy end-blocked poly(vinylmethyl)dimethylsiloxane copolymer having 2 mole percent vinyl substitution on silicon and a viscosity of 0.35 Paxs at 25°C.
  • a cure system comprising a low-molecular weight polydimethyl(methylhydrogen)siloxane fluid, neutralized complex of platinum dichloride with sym-divinyltetramethyldisiloxane, and 1-ethynyl-cyclohexanol.
  • the catalyzed base composition was cured in appropriate configurations for physical property testing by hot pressing at 34.5 MPa for 10 minutes at 150°C.
  • the cured compositions where post-cured for 1 hour at 177°C. Physical properties of the cured compositions were determined by test methods described in Example 9 and the results are reported in Table 2.

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Dispersion Chemistry (AREA)
  • Inorganic Chemistry (AREA)
  • Silicon Compounds (AREA)
  • Compositions Of Macromolecular Compounds (AREA)

Abstract

L'invention concerne des gels de silice hydrophobes présentant une zone superficielle limitée, ainsi qu'un procédé servant à les préparer. Ce procédé comprend trois étapes, la première étape consistant à préparer un mélange composé d'un hydrosol de silice et de silice colloïdale. La deuxième étape consiste à effectuer le traitement thermique du mélange en présence d'un acide minéral fort à un pH inférieur à 1 afin d'obtenir un hydrogel de silice dans lequel est incorporée de la silice colloïdale. La troisième étape consiste à mettre en contact l'hydrogel de silice avec un composé d'organosilicium en présence d'une quantité catalytique d'un acide fort afin de rendre hydrophobe l'hydrogel de silice, ce qui permet d'obtenir un gel de silice hydrophobe dont la zone superficielle est située dans une plage de 100 m2/g à 450 m2/g, mesurée à l'état sec. Dans un procédé préféré, on met en contact le gel de silice hydrophobe avec une quantité suffisante d'un solvant organique non miscible avec l'eau, dans le but de convertir l'hydrogel de silice hydrophobe en organogel de silice hydrophobe.
PCT/US1998/003273 1997-02-24 1998-02-18 Gels de silice hydrophobes presentant une zone superficielle limitee WO1998037020A1 (fr)

Priority Applications (5)

Application Number Priority Date Filing Date Title
BR9810408-0A BR9810408A (pt) 1997-02-24 1998-02-18 Sìlica géis hidrofóbicas com área de superfìcie reduzida
EP98908610A EP0963345A1 (fr) 1997-02-24 1998-02-18 Gels de silice hydrophobes presentant une zone superficielle limitee
JP53688398A JP2001513066A (ja) 1997-02-24 1998-02-18 縮小した表面積を有する疎水性シリカゲル
CA002280795A CA2280795A1 (fr) 1997-02-24 1998-02-18 Gels de silice hydrophobes presentant une zone superficielle limitee
AU66605/98A AU6660598A (en) 1997-02-24 1998-02-18 Hydrophobic silica gels with reduced surface area

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US80600597A 1997-02-24 1997-02-24
US08/806,005 1997-02-24

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CN104745145A (zh) * 2013-12-26 2015-07-01 安集微电子（上海）有限公司 一种二氧化硅颗粒改性的制备方法及应用
WO2016075906A1 (fr) * 2014-11-11 2016-05-19 パナソニックＩｐマネジメント株式会社 Aérogel et son procédé de fabrication
CN109019612B (zh) * 2016-05-28 2020-05-05 天津朗华科技发展有限公司 一种稀土增韧硅固态硅气凝胶
CN110589839B (zh) * 2019-09-23 2021-02-23 东莞创利科技发展有限公司 一种二氧化硅增强剂及其制备方法和应用

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GB783868A (en) * 1954-10-06 1957-10-02 Midland Silicones Ltd A process of preparing hydrophobic organo-silicon powders
US3122520A (en) * 1959-10-05 1964-02-25 Dow Corning Method of making silicone rubber fillers
FR2085772A1 (fr) * 1970-04-01 1971-12-31 Bayer Ag
SU369131A1 (fr) * 1969-11-12 1973-02-08
US4360388A (en) * 1980-02-12 1982-11-23 Degussa Aktiengesellschaft Cerium containing precipitated silica, process for its production
EP0653378A1 (fr) * 1993-11-04 1995-05-17 ENIRICERCHE S.p.A. Procédé de préparation de xérogels de silice sphériques poreux
US5708069A (en) * 1997-02-24 1998-01-13 Dow Corning Corporation Method for making hydrophobic silica gels under neutral conditions

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FR1092407A (fr) * 1953-10-19 1955-04-21 Du Pont Solides siliceux estérifiés superficiellement et leurs utilisations
GB783868A (en) * 1954-10-06 1957-10-02 Midland Silicones Ltd A process of preparing hydrophobic organo-silicon powders
US3122520A (en) * 1959-10-05 1964-02-25 Dow Corning Method of making silicone rubber fillers
SU369131A1 (fr) * 1969-11-12 1973-02-08
FR2085772A1 (fr) * 1970-04-01 1971-12-31 Bayer Ag
US4360388A (en) * 1980-02-12 1982-11-23 Degussa Aktiengesellschaft Cerium containing precipitated silica, process for its production
EP0653378A1 (fr) * 1993-11-04 1995-05-17 ENIRICERCHE S.p.A. Procédé de préparation de xérogels de silice sphériques poreux
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AU6660598A (en) 1998-09-09
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CN1248226A (zh) 2000-03-22
KR20000075594A (ko) 2000-12-26
EP0963345A1 (fr) 1999-12-15

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