SILICE SILANISEE

SILANIZED SILICA

Abrégé français

La présente invention fournit une silice produite par pyrogénation silanisée avec les propriétés physico-chimiques suivantes : une surface spécifique de 80 à 400 m/g, des particules primaires d'une taille de 7 à 40 nm, une densité tassée de 50 à 300 g/L, une valeur de pH de 3 à 10, une teneur en carbone de 0,1 à 15 %, un indice DBP d'un pourcentage inférieur à 200. L'invention fournit également une méthode de production de cette silice produite par pyrogénation silanisée, comprenant la pulvérisation de la silice produite par pyrogénation dans un récipient à mélange sous agitation intense, d'abord avec de l'eau ou de l'acide dilué, puis avec de l'hexaméthyldisilazane, en mélangeant pendant 15 à 30 minutes et en mettant à une température de 100 à 400.degrés.C pour une période de 1 à 6 h.

Abrégé anglais

The present invention provides a silanized pyrogenically- produced silica with the following physico-chemical properties: Specific surface area m2/g 80 - 400 Primary particle size nm 7 - 40 Tamped density g/l 50 - 300 pH value 3 - 10 Carbon content % 0.1 - 15 DBP number % < 200. The invention also provides a method of producing the above silanized pyrogenically-produced silica, comprising spraying pyrogenically-produced silica in a mixing container under intensive mixing, first with water or dilute acid and then with hexamethyldisilazane, mixing for 15 to 30 minutes, and tempering at a temperature of 100 to 400°C for a period of 1 to 6 h.

Revendications

The embodiments of the invention in which an exclusive
property or privilege is claimed are defined as follows:
1. Silanized pyrogenically-produced silica with the
following physico-chemical properties:
Specific surface area m2/g 80 - 400
Primary particle size nm 7 - 40
Tamped density g/l 50 - 300
pH value 3 - 10
Carbon content % 0.1 - 15
DBP number % < 200.
2. A method of producing the silanized
pyrogenically-produced silica according to claim 1,
comprising spraying pyrogenically-produced silica in a
mixing container under intensive mixing, first with water
or dilute acid and then with hexamethyldisilazane, mixing
for 15 to 30 minutes, and tempering at a temperature of 100
to 400°C for a period of 1 to 6 h.
3. The method according to claim 2, further
comprising subsequently destructuring or compressing said
silica by mechanical action.
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4. The method according to claim 2 or 3, further
comprising grinding said silica.
5. A polymer composition comprising a polymer and
the silanized pyrogenically-produced silica according to
claim 1.
6. The polymer composition according to claim 5
which has a low viscosity and low flow point.
7. A method of producing a low-viscosity polymer
system with a low flow point, the method comprising adding
to a polymer composition the silanized pyrogenically-
produced silica of claim 1.
8. A method of modifying the properties of a paint
or a film, the method comprising adding thereto the
silanized pyrogenically-produced silica of claim 1.
9. A coating composition comprising a liquid polymer
system and the silanized pyrogenically-produced silica of
claim 1.

Description

CA 02203726 2000-10-26
..
SILANIZED SILICA
Introduction
The present invention relates to a low-thickening,
silanized silica, a method of its production and its use.
Summary of the Invention
The present invention provides a silanized
pyrogenically-produced silica with the following physico-
chemical properties:
Specific surface area m2/g 80 400
-


Primary particle size nm 7 - 40


Tamped density g/1 50 300
-


pH value 3 - 10


Carbon content ~ 0.1 -
15


DBP number ~ < 200.



The invention also provides a method of producing the
above silanized pyrogenically-produced silica, comprising
spraying pyrogenically-produced silica in a.mixing
container under intensive mixing, first with water or
dilute acid and then with hexamethyldisilazane, mixing for
15 to 30 minutes, and tempering at a temperature of 100 to
400°C for a period of 1 to 6 h.
Preferably, the hydrophobic, silanized silica obtained
thereby is subsequently destructured/compressed by
mechanical action (e.g. in a ball mill) and then ground in
a mill (e. g. an air-jet mill or pinned disk mill).
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CA 02203726 2000-10-26
Detailed Description of Invention
In carrying out the present invention, a silica
pyrogenically produced by the flame hydrolysis of SiCl4 can
be preferably used as the starting material silica.
Hexamethyldisilazane is preferably used as the
surface-modifying reagent.
In a further aspect of the present invention, the low-
thickening, silanized silica produced in accordance with
the method disclosed herein is used for producing low-
viscosity polymer systems with a low flow point such as
e.g. 1- and 2-component peroxide condensation- and
addition-cross-linking silicon rubber systems, adhesives,
molding compounds, jointing compounds, etc. In addition,
the silica of the invention can be used as a flatting
agent, e.g. in paints, foils, as free-flow agent (e. g.
S.A.P., fire-extinguishing powder), for the production of
cable gels, as an anti-sedimentation agent in liquid
plastic systems and reaction resins (e. g. synthetic marble,
polymer concrete, dentures), and as a polishing agent
and/or scouring bodies.
Good mechanical strength is obtained in a polymer
system reinforced with synthetic silicas only with a very
high degree of filling. Good mechanical strength can be
provided in known silicas only by an in-situ hydrophobing
of the reinforcing silica during the production/compounding
of corresponding jointing compounds, molding compounds and
doubling compounds, etc. This method consumes a
significant amount of time and energy.
The silica in accordance with the invention makes
possible a high degree of filling, and therewith good
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CA 02203726 2000-10-26
' mechanical strength, by means of its low thickening action
and low flow point. Hence, the above-mentioned, expensive
compounding process using known silicas can be eliminated.
The method in accordance with the invention has the
advantage that, as a result of the continuous nature of the
method, reduced variations occur in the~quality of the
product.
EXAMPLE
Aerosil'?' 200, a pyrogenically-produced silica by
Degussa AG, is mixed with 4.3 parts water and 18.5 parts
HMDS (hexamethyldisilazane) and tempered at 140°C. The
hydrophobic, silanized silica is then compressed on a
continuously operating vertical ball mill to approximately
250 g/1. The silica is then ground by an air-jet mill.
The silica obtained has the following properties:
ExampleBET Tamped pH C-contentDrying AnnealingDBP


m2/g density loss loss number



VT 145 188 7.3 2.7 2.4 0.3 90


1128/I


Application technology test
2K-RTV silicone rubber (degree of filling 20~)
Rheology: Flow point 1.9 Pa
Viscosity 30.9 s-1
Mechanical properties: Tensile strength 1.7 N/mm2
Breaking elongation 230
Tear strength 14.0 N/mm
Shore A hardness 34
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