Hydrophobic Silica Fine Powder and Its Manufacture

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Hydrophobic Silica Fine Powder and Its Manufacture Europäisches Patentamt *EP001316589A2* (19) European Patent Office Office européen des brevets (11) EP 1 316 589 A2 (12) EUROPEAN PATENT APPLICATION (43) Date of publication: (51) Int Cl.7: C09C 1/30, C01B 33/18 04.06.2003 Bulletin 2003/23 (21) Application number: 02258304.1 (22) Date of filing: 02.12.2002 (84) Designated Contracting States: • Watanabe, K. c/o Shin-Etsu Chemical Co., Ltd. AT BE BG CH CY CZ DE DK EE ES FI FR GB GR Annaka-shi, Gunma-ken (JP) IE IT LI LU MC NL PT SE SI SK TR • Ueno, S. c/o Shin-Etsu Chemical Co., Ltd. Designated Extension States: Fukui-ken (JP) AL LT LV MK RO (74) Representative: Stoner, Gerard Patrick et al (30) Priority: 30.11.2001 JP 2001365554 MEWBURN ELLIS York House (71) Applicant: SHIN-ETSU CHEMICAL CO., LTD. 23 Kingsway Chiyoda-ku Tokyo (JP) London WC2B 6HP (GB) (72) Inventors: • Konya, Y., c/o Shin-Etsu Chemical Co., Ltd. Annaka-shi, Gunma-ken (JP) (54) Hydrophobic silica fine powder and its manufacture (57) A hydrophobic silica fine powder is prepared by has an aerated bulk density of 100-300 g/l, a specific premixing a hydrophilic silica fine powder with a dimer surface area of 40-300 m2/g, a primary particle diameter diol siloxane or cyclic siloxane as a hydrophobizing of 10-120 nm, and a degree of hydrophobization of agent, mixing them in a ball mill for achieving dispersion 40-80 as measured by methanol titration and is less and for achieving cleavage or disintegration and consol- bulky, easy to handle and disperse and stable in a idation, and thereafter heating at 100-300°Cinanam- kneaded mixture. monia or amine-containing atmosphere. The powder EP 1 316 589 A2 Printed by Jouve, 75001 PARIS (FR) 1 EP 1 316 589 A2 2 Description [0005] The inventors have found that by premixing a hydrophilic silica fine powder obtained by hydrolysis or [0001] This invention relates to hydrophobic silica fine oxidative firing in flame of an (organo)halosilane or (or- powders, useful e.g. as dispersant for dispersing ingre- gano)alkoxysilane with a hydrophobizing agent in the dients in cyclic or linear siloxane (i.e., organo(poly)si- 5 form of a dimer diol siloxane and/or cyclic siloxane, mix- loxane) and/or hydrophobic organic solvent to form a ing the hydrophobizing agent with the powder in a mill, wax, paint and ink or as a filler for RTV silicone compo- e.g. a ball mill, for achieving dispersion of the hydropho- sitions; and a method for preparing the same. bizing agent and for effecting cleavage or disintegration and consolidation, and heating, e.g. at 100°C to 300°C, BACKGROUND 10 in an ammonia or amine-containing atmosphere, there is obtained a good hydrophobic silica fine powder. It may [0002] Hydrophobic silica fine powder is generally have an aerated bulk density of 100 to 300 g/l, a specific produced by first forming a hydrophilic silica fine powder surface area of 40 to 300 m2/g, a primary particle diam- and treating the powder with silicon compounds having eter of 10 to 120 nm, and a degree of hydrophobization hydrophobic groups. In the most common known proce- 15 of 40 to 80 as measured by methanol titration. This new dure, tetrachlorosilane in a vapor phase is subjected to hydrophobic silica fine powder has advantages includ- high-temperature hydrolysis by an oxyhydrogen flame ing ease of handling, effective dispersion and kneaded to form a hydrophilic silica fine powder commonly known mixture stability. as fumed silica. Then, hexamethyldisilazane (HMDS) or [0006] In one aspect, we provide hydrophobic silica dimethyldichlorosilane and water are added to the 20 fine powder prepared or preparable by premixing a hy- fumed silica. Condensation reaction of silanol-bearing drophilic silica fine powder, obtained or obtainable by hydrophobic groups resulting from hydrolysis with sila- hydrolysis or oxidative firing in flame of an (organo)ha- nol on the silica surface is effected at 100 to 300°Cto losilane or (organo)alkoxysilane, with a hydrophobizing form siloxane bonds, whereby the silica surface is cov- agent in the form of a dimer diol siloxane and/or cyclic ered with hydrophobic groups. In this way, silica fine 25 siloxane, milling the hydrophobizing agent with the pow- powder exhibiting hydrophobic properties is obtained. der (e.g. in a ball-mediated mill) to effect dispersion and [0003] Silica fine powder having a large specific sur- cleavage or disintegration and consolidation, and there- face area indicative of fine particles tends to partially after heating, e.g. at 100°Cto300°C, in an ammonia or bind through siloxane bonds to take network and dumb- amine-containing atmosphere. bell structures even when synthesized at temperatures 30 [0007] The hydrophobic silica fine powder has an aer- below the melting point of silica: 1,423°C. Additionally, ated bulk density of 100 to 300 g/l, a specific surface water which is added for hydrolysis of the treating agent area of 40 to 300 m2/g, a primary particle diameter of used for hydrophobization of silica fine powder causes 10 to 120 nm, and a degree of hydrophobization of 40 the silica fine powder to agglomerate, interfering with to 80 as measured by methanol titration. the dispersion of the hydrophibizing agent such as tri- 35 [0008] In another aspect , the present invention pro- methylsilanol or dimethyldisilanol. In subsequent heat vides a method for preparing a hydrophobic silica pow- treatment for hydrophobization in the presence of by- der, preferably with the above-described properties, products including ammonia, acid (such as hydrogen comprising the steps of premixing a hydrophilic silica chloride) and alkali, agglomerated portions mediated powder obtained by hydrolysis or oxidative firing in with water give rise to binding of silica. This results in a 40 flame of an (organo)halosilane or (organo)alkoxysilane bulky powder in which network and dumbbell portions with a hydrophobizing agent in the form of a dimer diol are complexly entangled to define voids that remain siloxane and/or cyclic siloxane; mixing the hydrophobiz- empty and which powder is difficult to handle during ing agent with the powder in a ball-mediated mill for storage and transportation. When the powder is dis- achieving dispersion and for effecting cleavage or dis- persed in a liquid, the particles behave like coarse par- 45 integration and consolidation; and thereafter heating at ticles and settle down due to insufficient hydrophobiza- 100°Cto300°C in an ammonia or amine-containing at- tion and a complex partially bound structure, resulting mosphere. in poor dispersion. When such silica fine powder is add- [0009] Typically, the dimer diol siloxane is 1,3-dime- ed to a silicone composition and kneaded therewith, thyl-1,3-bis(trimethylsiloxy)-1,3-dihydroxydisiloxane, strong shear forces cause the silica bonds to be cleaved 50 and the cyclic siloxane is hexamethylcyclotrisiloxane or to create ionic active sites which can absorb moisture octamethylcyclotetrasiloxane. In the premixing step, to become silanol. This undesirably brings about a vis- 1.7310-6 to 10310-6 mol of the hydrophobizing agent cosity rise and cure of the silicone product, detracting is preferably added per square meter of silica surface from shelf stability. area. The ammonia or amine-containing atmosphere is [0004] Therefore, an object of the invention is to pro- 55 preferably established by flowing an ammonia-contain- vide a hydrophobic silica fine powder which is easy to ing gas, adding ammonia water or adding a water-solu- handle and disperse and remains stable in a kneaded ble amine. mixture, and a method for preparing the same. 2 3 EP 1 316 589 A2 4 FURTHER EXPLANATIONS; OPTIONS AND mixed/kneaded mixture remains unstable during stor- PREFERRED FEATURES age, giving rise to such troubles as viscosity increase and cure. [0010] A hydrophobic silica fine powder is prepared [0013] To overcome the above-mentioned problems, by premixing a hydrophilic silica fine powder obtained 5 the present invention accomplishes hydrophobization by oxidative firing in flame of an (organo)halosilane or by uniformly dispersing the hydrophobizing agent over (organo)alkoxysilane with a hydrophobizing agent in the silica surfaces at the same time as cleaving the binding form of a dimer diol siloxane or cyclic siloxane or a mix- structure between silica fine particles, then heat treating ture thereof, mixing the hydrophobizing agent with the in an ammonia or amine-containing atmosphere. powder in a ball-mediated mill for achieving dispersion 10 [0014] The hydrophobizing agent used herein is a and for effecting cleavage or disintegration and consol- dimer diol siloxane having two silanol groups, which idation, and thereafter heating in an ammonia or amine- eliminates a need for hydrolysis or a cyclic siloxane hav- containing atmosphere. The dimer diol siloxane used ing easily cleavable siloxane bonds and easily convert- herein is preferably 1,3-dihydroxy-1,1,3,3-tetraorgano- ible to a silanol group-terminated linear siloxane, which disiloxane of the formula: 15 eliminates a need for hydrolysis as well. Since the dimer diol siloxane or cyclic siloxane has or can have hy- drophilic silanol groups and can directly cover silica sur- faces, it does not cause agglomeration which in turn, causes increased binding and poor dispersion of the 20 treating agent which would occur when water is com- bined. The treating agent is uniformly dispersed and highly compatible with silanol on the silica surface. The dimer diol siloxane has a bond distance close to that of wherein groups R are selected independently from me- -O-Si-O-Si-O- on the silica surface, bonds in pair with thyl, ethyl, vinyl, trifluoropropyl, and trimethylsiloxy 25 two Si atoms, assumes a stable hydrophobic structure, groups, and the number of silicon atoms per molecule and provides hydrophobic groups which are free of ster- is 2 to 6, preferably 2 to 4.
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