Drug – bio-affecting and body treating compositions – Dentifrices
Reexamination Certificate
2002-03-18
2003-09-02
Rose, Shep K. (Department: 1614)
Drug, bio-affecting and body treating compositions
Dentifrices
C423S335000, C423S339000
Reexamination Certificate
active
06613309
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to silicas having an inhomogeneous structure or composition, to processes for preparing them, and to their use in dental care compositions.
2. Description of the Background
Readily dispersible silicas are prepared, for example, in accordance with EP 0 901 986 or EP 0 647 591 by precipitating waterglass with sulfuric acid, followed by drying. The dried products are subsequently ground and/or granulated.
In another process, silicas are prepared, likewise by acid precipitation, but are dried by being sprayed in hot air and at the same time shaped into beads, which are easily destroyed. Thus EP 0 18 866 describes the preparation of spray-dried silica having an average particle diameter of more than 80 &mgr;m, the particles being solid and possessing a homogeneous structure.
For use in dental care compositions, important parameters for silicas include not only their thickening action and abrasiveness, but also their specific surface areas (BET, CTAB) and their oil absorption capacity (DBP).
Since only specialty silicas, i.e., silicas that are complicated to prepare, combine sufficient thickening action and abrasiveness, dental care compositions normally utilize two different types of silica.
A need therefore continues to exist for a method of preparing a silica which at one and the same time covers broad ranges of physicochemical data such as BET or CTAB surface area, and has good abrasiveness in conjunction with a good thickening action.
SUMMARY OF THE INVENTION
Accordingly, one object of the present invention is to provide a silica material which is not only characterized by broad ranges of physicochemical data such as BET or CTAB surface area, but also has good abrasiveness in conjunction with a good thickening action.
Briefly, this object and other objects of the present invention as hereinafter will become more readily apparent can be attained by a silica material comprising at least two silica fractions, wherein the at least two silica fractions differ by at least 10% in at least one of their BET surface area values, their CTAB surface area values or their DBP absorption values.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
It has surprisingly been found that silica that has an inhomogeneous composition is readily adjustable to meet the requirements needed for silicas used in dental care compositions. Moreover, the silica of the invention produces little dust when handled, thereby facilitating handling of the material and prevents dust contamination of customer's plants.
The silicas of the invention are particularly suitable as fillers in dental care compositions. The abrasive figures of the silicas of the invention according to the RDA method are within the range of 45% to 70% that is typical for modem toothpaste silicas, but may also lie above or below this range, depending on the chosen mixture of the precipitating suspensions and on their technical preparation. Likewise within the typical flow range are the toothpastes prepared from these silicas. In the shear stress tests, in fact, they have a shear rate of from 100 s
−1
to 500 s
−1
up to a shear stress of 600 Pa, depending on the silica mixture of the invention that is used and on the concentration that is used in the paste. Higher or lower shear rates within the specified shear stress range may occur depending on the chosen mixture of the precipitating suspensions and on their technical preparation.
The structure of the silica material of the invention, comprising at least two silica fractions, results in an inhomogeneity of the product silica, which is reflected at the same time in good abrasiveness and thickening action and also in a low fines content.
Silicas of the invention possess a fines content of not more than 10% with a particle diameter of less than or equal to 63 &mgr;m (Alpine sieve residue).
A similar concept, i.e. inhomogeneous silicas, is disclosed in EP 0 942 029. In this publication rubber compositions are described which comprise a precipitated silica in two different aggregate sizes. The different aggregate sizes are employed for the ready dispersibility of the silica in the rubber blend.
The different silica fractions of the present invention are not described in the publication. Moreover, in the present case a different aggregate size of the silica fractions is of secondary importance. What is important, however, is that the silica fractions differ in their physicochemical data.
For the purpose of the present invention, silica fractions refer to different grades of silicas which result from different processes of preparation or process variants, and thereby have a difference of 10% in their values of at least one of the above-mentioned physicochemical properties. Such a difference exists preferably for two, with particular preference three, of these parameters.
The differences in the abovementioned parameters may be obtained by means of different processes of preparing the silica fractions. Accordingly, all, one or more of the silica fractions may be precipitated silicas and/or pyrogenic silicas. In the case of precipitated silicas, in particular, it is possible to obtain different silica fractions by means of different precipitation processes. Silicas of the invention may also be prepared from fractions of precipitated and pyrogenic silicas.
For precipitated silicas, a variety of precipitation methods are known and are described, for example, in EP 0 901 986, EP 0 937 755, EP 0 643 015 and EP 0 647 591. In the publications, illustratively, two precipitated silicas from different preparation processes can be processed to give the inhomogeneous silica of the invention.
The silica fractions may be precipitated silicas or pyrogenic silicas, and the fractions may be mixed at different steps in the process that are normally carried out in the preparation of silicas.
When using fractions of precipitated silicas, mixing may take place following the precipitation of silicate with an acid (generally waterglass, i.e., sodium silicate, with sulfuric acid) by mixing together the precipitation suspensions or the filtercakes obtained following filtration of the suspensions, and also liquefied (resuspended) filtercakes. It is also possible to add ready-prepared and dried silica fractions, as solids, to the suspensions or to the filtercakes.
The mixtures obtained in this manner may have to be filtered and dried by a customary technique. Examples of drying processes are spray drying, nozzle spray drier, rack drier, rotary tube drier, and spin flash drier processes.
Drying may be followed by a final grinding and/or granulation step.
It is also possible to mix the silica fractions in the dry state. This may be followed by resuspension, with the above drying steps, and/or by grinding/granulation.
The silica of the invention may have the following physicochemical data:
BET surface area
30-300 m
2
/g, especially 30-200 m
2
/g
CTAB surface area
30-300 m
2
/g, especially 30-200 m
2
/g
DBP absorption
80-300 g/100 g
The above physicochemical data ranges pertain to the silica of the invention per se, and not to the silica fractions which make-up the silica.
In the manner described, the physicochemical data of the silica fractions must differ by at least 10%, preferably by at least 15%, with particular preference by at least 20%.
The physicochemical data are determined by the following methods:
BET surface area
Areameter, from Strohlein, to ISO 5794/Annex D
CTAB surface area
at pH 9 by the method of Jay, Janzen and Kraus in
Rubber Chemistry and Technology 44 (1971) 1287
DBP number
ASTM D 2414-88
The present invention also provides a process for preparing silicas comprising at least two silica fractions, in which at least two silica fractions which differ by at least 10% in the values of at one least one property of the properties of the BET surface area, the CTAB surface area and the DBP absorption. The silicas having these different values are mixed with one another.
The proportion of the respective fractions in the s
Schmoll Ralf
Storeck Arnold
Uhrlandt Stefan
Degussa - AG
Rose Shep K.
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