Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Reexamination Certificate
2002-01-18
2004-03-09
Koslow, C. Melissa (Department: 1755)
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
C106S481000
Reexamination Certificate
active
06702887
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a silica with an inhomogeneous structure and a manufacturing process thereof.
2. Discussion of the Background
Easily dispersible silicas are manufactured by precipitating water glass with sulfuric acid and subsequent drying as described in EP 0 901 986 and EP 0647 591. The dried products are then ground and/or granulated.
Any silica can be manufactured dust-free by mechanical granulation. However, generally this additional process stage reduces the level of dispersibility.
In another process, silicas are also manufactured by acidic precipitation. However, these are dried by means of atomization in hot air and, at the same time, formed into easily destructible spheres. For instance, EP 018 866 describes the manufacture of spray-dried silica with an average particle diameter of more than 80 &mgr;m, where the particles have a homogeneous structure and are solid.
Spray-dried silicas are particularly suitable as fillers, as they are very easily dispersible. The dispersibility is a very important criterion for the processing of the silica, as a homogeneous and rapid intermingling in the respective matrix has a high economic significance. In addition to dispersibility, the specific surface areas (BET, CTAB) and the oil absorption capacity (DBP) are important characteristics.
However, not all silicas can be manufactured dust-free by spray drying. Generally, no one type of silica is able to fulfill all the required criteria. A mixture of several types of silica can only be manufactured with a high degree of dust due to the above-mentioned high degree of dispersibility (i.e. low mechanical stability).
It is therefore desirable to manufacture a silica that covers a wide range of properties such as BET and CTAB surface area with a high degree of dispersibility but with a low dust concentration. As explained above, this cannot be achieved for all silicas through spray drying or granulation.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a silica having large BET and CTAB surface areas and a high degree of dispersibility combined with a low dust concentration.
It is another object of the present invention to provide a process for the manufacture of such silica.
These and other objects have been achieved by the present invention, the first embodiment of which includes a silica, comprising:
at least two silica fractions;
wherein at least two silica fractions differ by at least 10% in at least one measured value for a BET surface area, a CTAB surface area and a DBP absorption.
Another embodiment includes a process for manufacturing a silica containing at least two silica fractions, comprising:
mixing at least two silica fractions which differ by at least 10% in at least one measured value for a BET surface area, a CTAB surface area and a DBP absorption.
DETAILED DESCRIPTION OF THE INVENTION
It was surprisingly discovered that silica with an inhomogeneous structure can be easily adapted to suit the specific requirements of large BET and CTAB surface areas and still demonstrate a good degree of dispersibility.
Subject of the present invention is therefore a silica containing at least two silica fractions which differ in at least one measured value for a BET surface area, a CTAB surface 25 area and a DBP absorption by at least 10%.
The silica that is the subject of the present invention is therefore particularly suitable as a filler in an article made of an elastomer compound, such as a tire.
The structure of the silica consisting of at least two silica fractions causes the silica to become inhomogeneous, which is reflected in a particularly good degree of dispersibility and a low concentration of fine particles.
The silica according to the present invention has a fine particle concentration of no more than 10%, preferably no more than 5% and most preferably no more than 2.5%, with an average particle diameter of 63 &mgr;m or less, preferably 60 &mgr;m or less and most preferably 55 &mgr;m or less (Alpine screen residue).
A similar concept is described in EP 0 942 029. In this case, rubber compositions are described that contain precipitated silicas with two different aggregate sizes. The different aggregate sizes are used to facilitate easy dispersibility of the silicas in the rubber compound.
However, the different silica fractions in the present invention are not described. Besides, a different aggregate size of the silica fractions in this case is of subordinate importance. What is important are the differences in properties, such as BET and CTAB surface areas and DBP absorption.
“Silica fractions” within the meaning of the present invention are used to describe various types of silica, which, due to different manufacturing processes or variants, exhibit a difference of at least 10% in at least one of the above-mentioned properties. Preferably two, particularly preferably three of these parameters exhibit such a difference.
The differences in the above parameters can be obtained through different manufacturing processes for the silica fractions. For instance, all, one, or several of the silica fractions can be precipitated silica and/or fumed silica. In the case of precipitated silica, it is particularly possible to obtain different silica fractions through different precipitation processes. Silica according to the present invention can also be manufactured from fractions of precipitated silica and fumed silica.
Various precipitation methods are known for precipitated silica and are described, for example, in EP 0 901 986, EP 0 937 755, EP 0 643 015, or EP 0 647 591. In these examples, two precipitated silicas from different manufacturing processes are processed into inhomogeneous silica according to the present invention. It is also possible to combine hydrophobized silica fractions with untreated silica fractions to create a silica according to the present invention.
The silica fractions can be precipitated silica or fumed silica. The fractions can also be mixed during the different process stages that are usually carried out during the manufacture of silica.
When fractions of precipitated silica are used, after the silicate has been precipitated with an acid (as a rule, water glass, i.e. sodium silicate with sulfuric acid), the mixture can be produced by mixing the precipitation suspensions or the filter cakes obtained after the suspensions have been filtered or by mixing the re-suspended filter cakes. It is also possible to add previously manufactured, dried or hydrophobized silica fractions as a solid substance to the suspension.
The thus obtained compounds must be filtered off and dried in the usual manner.
Drying can occur, for example, in a spray drier, a jet drier, a rack drier, a rotary drier, or a spin-flash drier.
After the drying process it is possible to grind and/or granulate the mixture.
It is also possible to mix the silica fractions in a dry state. In this case they can be re-suspended with the above-mentioned subsequent drying stages and/or grinding/granulation.
Silica according to the present invention can exhibit the following properties:
a BET surface area of 80-300 m
2
/g, preferably 80-230 m
2
/g;
a CTAB surface area of 80-300 m
2
/g, preferably 80-230 m
2
/g; and
a DBP absorption of 150-350 g/100 g, preferably 200-300 g/100 g.
These data refer to the silica according to the present invention as such and not to the silica fractions.
As described, the above properties of the silica fractions must differ by at least 10%, preferably at least 15%, particularly preferably at least 20%.
The above properties are determined by the following methods:
BET surface area:
Areameter from Stöhlein, according to ISO 5794/
Annex D,
CTAB surface area:
at pH 9, according to Jay, Janzen and Kraus in
“Rubber Chemistry and Technology” 44
(1971) 1287, and
DBP factor:
ASTM D 2414-88.
A further subject of the present invention is a process for the manufacture of a silica containing at least two silica fractions that differ by at least 10% in at least one measured valu
Blume Anke
Luginsland Detlef
Schmoll Ralf
Uhrlandt Stefan
Deguss AG
Koslow C. Melissa
Manlove Shalie
LandOfFree
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