Dispersions of spherical inorganic particles

Details Dispersions of spherical inorganic particles Dispersions of spherical inorganic particles

1991-12-16

1994-01-11

Kunemund, Robert

Chemistry of inorganic compounds

Silicon or compound thereof

Oxygen containing

423 69, 106491, 2523152, 2523156, C09D 1700, C01B 3318

Patent

active

052778886

DESCRIPTION:

BRIEF SUMMARY
SUMMARY OF THE INVENTION

The invention relates to dispersions of spherical inorganic particles which are stable and agglomerate-free.
Fine, spherical inorganic particles, such as, for example, TiO.sub.2 or ZrO.sub.2 particles, and in particular spherical SiO.sub.2 particles, are of particular interest, being valuable auxiliaries in the industrial and scientific area and interesting, scientific study objects, as well as carrier material in chromatography.
Some fields of use of such nonporous, spherical SiO.sub.2 particles are described in, for example, German Offenlegungsschrift 3,616,133. The preparation of such monodisperse, spherical SiO.sub.2 particles is described in German Offenlegungsschrift 3,616,133. The corresponding TiO.sub.2 or ZrO.sub.2 particles can likewise be prepared by methods known to the person skilled in the art and are also commercially available.
For all applications, the particles are required to be present in a highly monodisperse form and without agglomerates. However, it has been found that the dispersions of such spherical particles in the usual dispersing media, such as alcohols, especially, for example, ethylene glycol, are not sufficiently stable.
Especially in the case of particles having a diameter >500 nm, the dispersions known to date with ethylene glycol or other alcohols are not stable. The settling rate is dependent on the particle diameter and even particles having sphere diameters of, for example, 0.5 .mu.m, 1.0 .mu.m, 1.2 .mu.m or 1.5 .mu.m settle out very rapidly and form agglomerates. However, such dispersions are unsuitable for most applications.
It was therefore the object of the present invention to find dispersions of spherical inorganic particles which contain the fine particles in an ideally distributed and agglomerate-free form, and which are also stable where relatively large diameters of the particles are present.
It has now been found, surprisingly, that organic dispersing media which are viscous or solid at room temperature are outstandingly suitable as dispersants for such spherical particles.
The invention therefore relates to dispersions of spherical inorganic particles, characterized in that organic dispersing media having solidification points in the range of 200.degree.-120.degree. C. are used as dispersants. Dispersions of spherical SiO.sub.2, TiO.sub.2 or ZrO.sub.2 particles are particularly preferred. The particle size is preferably between 0.05 and 10 .mu.m.
Polyethers, polyalkylene glycols, paraffins, resins, waxes, vinyl polymers, polysiloxanes, polyolefins, polyamides or the like, as well as copolymers, such as, for example, a copolymer of polyethylene waxes and vinyl acetate, can preferably be used as organic dispersing media.
Critical parameters for the suitability of a dispersing medium are the polarity and solidification points, and, associated therewith, also the molecular weight. The polarity can be influenced by the chemical composition of the organic dispersing medium.
For the preparation of stable dispersions, it is of course advantageous to choose a dispersant which has a polarity similar to that of the particles to be dispersed. Thus, for example, dispersants of relatively high polarity are preferably chosen for the more hydrophilic SiO.sub.2 particles. On the other hand, corresponding nonpolar dispersants are more suitable for modified SiO.sub.2 particles (the preparation and description of such modified SiO.sub.2 particles are to be found in German Offenlegungsschrift 3,616,133), which may have a hydrophobic character. This also applies to the ZrO.sub.2 and TiO.sub.2 particles. This means that the dispersing medium must be chosen so that good compatibility with the particles is ensured.
The most important parameter is the solidification point of the dispersing medium. In order to obtain a dispersion according to the invention, the solidification point must be between 20.degree. and 120.degree. C., preferably between 30.degree. and 70.degree. C. This means that the dispersion is viscous or solid at room temperature. The ideal

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