Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
1995-03-07
2001-01-09
Davis, Jenna (Department: 1771)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C423S335000, C423S339000
Reexamination Certificate
active
06171699
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to novel silica-based granular particulates, to various processes for the preparation thereof, and to the use of such novel silica particulates as reinforcing fillers for elastomeric matrices.
2. Description of the Prior Art
It has long been known to this art to use precipitated silica as a white reinforcing filler material for elastomers.
However, like any reinforcing filler, it must be suitable for processing and easily formulated into mixtures.
Its powder form is unsatisfactory to the extent that it gives rise to an appreciable amount of dust and is slow to be formulated into mixtures (low apparent density).
A granular form has heretofore been proposed which provides an appropriate solution for the aforesaid two problems, but which often results in inadequate dispersion of the filler in elastomeric matrices.
Various solutions too have been proposed to avoid this particular disadvantage.
Thus, European Patent No. 18,866, assigned to the assignee hereof, describes granular silica materials in the form of homogeneous spheres having a mean particle size greater than 80 &mgr;m, in particular from 200 to 300 &mgr;m.
The spherical particulates are made by atomizing a precipitated silica suspension.
Because of its properties, this type of product was found to be especially attractive for reinforcing elastomers.
However, need still exists for an improved product in respect of one or possibly several aspects at the same time. Thus, the need remains in this art for silica particulates having a potentially higher and more homogeneous granulometry, which are denser, have an even lower proportion of fines, and which are less fragile.
Moreover, the preparative processes for granules and especially those described above, conventionally entail the use of atomizers. These devices impose certain requirements on the suspensions to be atomized, especially with regard to the dry solids content thereof, which cannot exceed a certain maximum value. They also entail considerable maintenance.
These processes also suffer from the disadvantage of limiting the products obtained to a certain granulometry range, especially because of the low dry solids content mentioned above.
Thus, another problem exists in this art, namely, simplifying the processes for the preparation of silica particulates and enhancing the number of options provided thereby.
SUMMARY OF THE INVENTION
Accordingly, a major object of the present invention is the provision of improved silica-based granular particulates having enhanced properties and characteristics vis-a-vis those of the prior art.
Another object of this invention is the provision of simplified processing for the production of such improved silica particulates, which processing provides a broad spectrum of available options.
Briefly, the present invention features improved silica-based granular particulates, in the form of substantially spherical particles having a mean size of at least 300 &mgr;m, and an apparent density ranging from 0.15 to 0.32.
In a second embodiment of the invention, the silica-based granular material is a densified granulate comprising substantially spherical particulates having a mean size of at least 80 &mgr;m and a relative density greater than 0.32.
This invention also features a process, in particular for the preparation of granular particulates according to the first embodiment noted hereinabove.
This process according to the invention comprises the following stages:
(i) contacting and intimately admixing a suspension of silica, at least one hydrophobizing agent and at least one slightly or non-water-miscible organic solvent, thereby producing a liquid phase substantially free of silica and a plurality of silica-based granules;
(ii) separating said liquid phase from the granules; and
(iii) optionally washing and then drying said granules.
This invention also features a second process especially adapted for the preparation of granular particulates according to the aforesaid second embodiment.
This second preparative process according to the invention is characterized in that it comprises the following steps:
(i) contacting and intimately admixing a suspension of silica, at least one hydrophobizing agent and at least one slightly or non-water-miscible organic solvent, thereby producing a liquid phase substantially free of silica and a plurality of silica-based granules;
(ii) separating the liquid phase from the granules; and
(iii) densifying said granules thus separated.
The aforenoted processes are reliable and flexible. Indeed, they require only simple and inexpensive equipment. They make it possible to obtain products over an entire range of sizes and densities.
Finally, in a general manner, this invention features any silica-based granular material made using the two processes described above.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
More particularly according to the present invention, as aforesaid, two types of products are produced, and each will be described in greater detail below.
Both cases involve silica-based granular particulates. According to this invention, the term “silica-based” is intended broadly to mean granules composed essentially of elements or a mixture of elements selected from among the silicic acids, silica, silicates and silico-aluminates.
The granular materials according to the invention are typically based on precipitated silica. They are in the form of substantially spherical particulates.
For the first type of granules, i.e., according to the first embodiment, the mean particle size is at least 300 &mgr;m. In a preferred embodiment, the mean particle size of the granules ranges from 300 to 2500 &mgr;m, more preferably from 350 to 1000 &mgr;m.
Their apparent density ranges from 0.15 to 0.32 g/ml. This is the density of filling in the compacted state according to AFNOR standard No. T 30-42. More preferably, such density ranges from 0.20 to 0.30 g/ml.
These particular granules are comprised of a silica having a BET surface area typically of at least 50 m
2
/g. Advantageously, it ranges from 50 to 350 m
2
/g, and preferably from 100 to 300 m
2
/g.
BET specific surface area is determined according to the BRUNAUER-EMMET-TELLER method described in the
Journal of the American Chemical Society,
60, p. 309 (February, 1938).
The CTAB surface area of the silica constituting the subject granules is advantageously at least 40 m
2
/g. More preferably it ranges from 40 to 320 m
2
/g, and even more preferably from 80 to 270 m
2
/g.
The CTAB surface area is the external surface area determined by absorption of cetyl trimethyl ammonium bromide at pH 9 according to the method described by JAY, JANSEN and G. KRAUS in
Rubber Chemistry and Technology,
44, p. 1287-1296 (1971).
Moreover, another characteristic of the granular particulates of this first type is their porosity.
As utilized herein, all pore volumes are determined using mercury porosity measurements, and the pore diameters are calculated using the WASHBURN equation, with an angle of contact theta=130° and a surface tension gamma=484 Dynes/cm.
The porosity measurements were carried out on products dried at 150° C. under a pressure of 1 Pa. The porosities specified reflect the intra-granular porosities and thus involve pores having diameters from 10&mgr; to 0.001&mgr;.
The granular materials of the first type have a maximum total pore volume (VPT) of 3.6 cm
3
/g, and more specifically between 3.6 cm
3
/g for particulates having a density of 0.15 and 1.40 cm
3
/g for particulates having a density of 0.32, the latter correlation being in relation to products of substantially monodispersed sizes.
In addition to this global pore volume, the same granules are characterized by pore distribution. Thus, these materials essentially meet the following conditions: a maximum of approximately 80% of the total pore volume is constituted by pores having a diameter at most substantially equal to the value provided below, as a function of the BET specific surface ar
Deleuil Michel
Parmentier Francois
Burns Doane Swecker & Mathis L.L.P.
Davis Jenna
Rhone-Poulenc Chimie
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