Silica particles surface-treated with silane, process for producing the same and uses thereof

An organic resin composition comprising;

• (a) 100 parts by weight of an organic resin;
• and (b) from 0.01 to 10 parts by weight of silane-surface-treated fine silica particles wherein said silane-surface-treated fine silica particles comprise primary particles having a particle diameter of from 0.1 to 5 μm,
• and the fine silane-surface-treated silica particles are obtained by:
• (A) introducing an R2SiO3/2 unit to the surface of a hydrophilic fine silica particle comprising an SiO2 unit to form a hydrophobic fine silica particle
• by adding to an aqueous dispersion medium or mixed-solvent dispersion medium comprising the hydrophilic fine silica particle, a trifunctional silane compound represented by formula (II):
• R2Si(OR4)3 (II)
• wherein R2 represents a substituted or unsubstituted monovalent hydrocarbon group having 1 to 20 carbon atoms, and the R4 groups may be the same or different and may each represent a monovalent hydrocarbon group having 1 to 6 carbon atoms, or a partial hydrolysis-condensation product thereof or a mixture thereof, to treat the surfaces of the hydrophilic fine silica particles and form an aqueous hydrophobic fine silica particle dispersion;
• and
• (B) introducing an R13 SiO1/2 unit to the surface of the hydrophobic fine silica particle
• by converting the dispersion medium of the aqueous hydrophobic fine silica particle dispersion into a ketone solvent to obtain a hydrophobic fine silica particle ketone solvent dispersion, and adding to the hydrophobic fine silica particle ketone solvent dispersion a monofunctional silazane compound represented by formula (III):
• R13SiNHSiR13 (III)
• wherein the R1 groups may be the same or different and each may represent a substituted or unsubstituted monovalent hydrocarbon group having 1 to 6 carbon atoms, a monofunctional silane compound represented by formula (IV):
• R13SiX (IV)
• wherein the R1 groups are as defined in formula (III), and X represents hydroxyl group or a hydrolyzable group, or a mixture thereof to triorganosilylate the reactive groups remaining on the surface of the hydrophobic fine silica particles
• wherein the fine silica particles fulfill the following conditions (i) and (ii),
• (i) when an organic compound which is liquid at room temperature and has a dielectric constant of from 1 to 40 F/m and fine silane-surface-treated silica particles are mixed in a weight ratio of 5:1 and shaken, the fine silane-surface-treated silica particles disperse uniformly in the organic compound;
• and
• (ii) the quantity of primary particles remaining as primary particles when methanol is evaporated under heating from a dispersion prepared by dispersing the fine silane-surface-treated silica particles in methanol and thereafter holding the fine silane-surface-treated silica particles at a temperature of 100° C. for 2 hours, is at least 20% based on the quantity of primary particles originally present.