Silicon dioxide dispersion

Abstract

Providing a SiO2 dispersion in which the SiO2-containing phase is such that the average particle size (dmax) of the SiO2 as measured by Small Angle Neutron Scattering (SANS) at a maximum half width intensity of the distribution curve has a specific value at 1.5dmax. A SiO2 dispersion containing: (A) an external flowable phase containing polymerizable monomers, oligomers and/or polymers; and (B) a disperse SiO2-containing phase is such that the average particle size (dmax) of the SiO2 as measured by Small Angle Neutron Scattering (SANS) at a maximum half width intensity of the distribution curve of 1.5dmax is 3-50 nm. An Independent claim is also included for production of the dispersion by: (i) polycondensing an aqueous silicate solution to 3-50 nm particle size; (ii) adjusting to an alkaline pH; (iii) optionally concentrating the sol; (iv) mixing with the external phase ingredients; and (v) optionally removing the water or other solvents.

1 . A silicon dioxide dispersion comprising 
 a) an external fluid phase comprising 
 a1) polymerizable monomers, oligomers and/or prepolymers convertible to polymers by nonradical reactions; and/or  
 a2) polymers,  
   b) a disperse phase comprising amorphous silicon dioxide,    characterized in that the average particle size d max  of the silicon dioxide as measured by means of small-angle neutron scattering (SANS) is between 3 and 50 nm at a maximum half-width of the distribution curve of 1.5 d max .    
     
     
         2 . The dispersion of  claim 1 , characterized in that the average particle size is between 6 and 40 nm, preferably 8 and 30 nm, more preferably 10 and 25 nm.  
     
     
         3 . The dispersion of  claim 1  or  2 , characterized in that the half-width of the distribution curve is not more than 1.2 d max , preferably not more than d max , more preferably not more than 0.75 d max .  
     
     
         4 . The dispersion of one of  claims 1  to  3 , characterized in that the fraction of the external phase as a proportion of the dispersion is 20-90% by weight, preferably 30-80% by weight, more preferably 40-70% by weight.  
     
     
         5 . The dispersion of one of  claims 1  to  4 , characterized in that the fraction of the disperse phase as a proportion of the dispersion is 10-80% by weight, preferably 20-70% by weight, more preferably 30-60% by weight.  
     
     
         6 . The dispersion of one of  claims 1  to  5 , characterized in that the silicon dioxide particles are substantially spherical.  
     
     
         7 . The dispersion of one of  claims 1  to  6 , characterized in that it further comprises auxiliaries selected from the group consisting of solvents, plasticizers, crosslinkers, catalysts, stabilizers, dispersants, curing agents, reaction mediators and agents for influencing the fluidity of the dispersion.  
     
     
         8 . The dispersion of one of  claims 1  to  7 , characterized in that it is water-free.  
     
     
         9 . The dispersion of one of  claims 1  to  8 , characterized in that the external phase comprises at least one substance selected from the group consisting of polyols, polyamines, linear or branched polyglycol ethers, polyesters and polylactones.  
     
     
         10 . The dispersion of one of  claims 1  to  8 , characterized in that the external phase comprises at least one reactive resin.  
     
     
         11 . The dispersion of one of  claims 1  to  10 , characterized in that the polymerizable monomers, oligomers and/or prepolymers contain C, 0, N and/or S atoms in the main chain.  
     
     
         12 . The dispersion of one of  claims 1  to  11 , characterized in that the external fluid phase comprises polymerizable monomers without radically polymerizable double bonds and/or reactive resins.  
     
     
         13 . The dispersion of one of  claims 1  to  12 , characterized in that the external fluid phase further comprises silanes.  
     
     
         14 . The dispersion of  claim 13 , characterized in that the silanes are present in an amount of 60-150 mol % based on the molar amount of the silanol groups on the surface of the silicon dioxide particles of the amorphous phase.  
     
     
         15 . A process for preparing a dispersion of one of  claims 1  to  14 , characterized by the following steps: 
 a) introducing an aqueous silicate solution,  
 b) polycondensing the silicate to a particle size of 3-50 nm,  
 c) adjusting the resulting silica sol to an alkaline pH,  
 d) optionally concentrating the sol,  
 e) mixing the sol with constituents of the external fluid phase of the dispersion,  
 f) optionally removing water and/or other solvent constituents from the dispersion.  
 
     
     
         16 . The process of  claim 15 , characterized in that the aqueous silicate solution is an alkali metal silicate solution, in particular a sodium silicate and/or potassium silicate solution.  
     
     
         17 . The process of  claim 16 , characterized in that the concentration of the aqueous silicate solution is 20-50% by weight.  
     
     
         18 . The process of one of  claims 15  to  17 , characterized in that the silica sol in step c) is adjusted to a pH of between 10 and 12.  
     
     
         19 . The process of one of  claims 15  to  18 , characterized in that the silica sol in step d) is concentrated to a concentration of 30-40% by weight.  
     
     
         20 . The process of one of  claims 15  to  19 , characterized in that in step f) water is removed by means of a process selected from the group consisting of distillation, membrane separation, extraction and use of a molecular sieve.  
     
     
         21 . The use of a dispersion of one of  claims 1  to  14  for producing a polymeric material.  
     
     
         22 . The use of  claim 21 , characterized in that the material is selected from the group consisting of polyurethanes, polyureas, epoxy resins, polyester resins and polysiloxanes.  
     
     
         23 . The use of  claim 21  or  22 , characterized in that the material is a thermoset.  
     
     
         24 . The use of  claim 21  or  22 , characterized in that the material is a thermoplastic.  
     
     
         25 . The use of  claim 21  or  22 , characterized in that the material is a polymeric coating, a paint, an ink or a foam.  
     
     
         26 . A polymeric material, characterized in that it has been produced from a dispersion of one of  claims 1  to  14 .