Chemistry of inorganic compounds – Silicon or compound thereof – Oxygen containing
Reexamination Certificate
2000-04-17
2001-09-18
Griffin, Steven P. (Department: 1754)
Chemistry of inorganic compounds
Silicon or compound thereof
Oxygen containing
C423S339000
Reexamination Certificate
active
06290924
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to novel precipitated silica particulates, to a process for the preparation thereof, and to the use of such novel silica particulates as a reinforcing material for elastomeric matrices.
2. Description of the Prior Art
It is known to this art that precipitated silica is a useful reinforcing filler for elastomeric matrices.
However, as with any reinforcing filler, it must be easily manipulated and readily incorporated into the material to be reinforced.
Silica typically exists in the form of a powder. However, such powder form is not completely satisfactory in that it generates large amounts of dust and is incorporated into the matrix only slowly (low apparent density).
For this reason, silica in granulated form has been proposed to the art, which conveniently resolves the aforementioned problems, but which frequently results in an insufficient dispersion of the filler in the elastomers and provides a lesser degree of reinforcement relative to a filler in the powder form.
To obviate this disadvantage, EP 18,866, assigned to the assignee hereof, proposed certain homogeneous silica spheres having a mean particle size greater than 80 &mgr;m, a BET surface area of 100 to 300 m
2
/g and a density of approximately 0.29.
This type of silica material has been found to be particularly advantageous in light of its elastomer reinforcing properties.
However, there is an existing need in this art to still further improve these materials relative to one or more of their characteristics/properties. For example, need continues to exist for silica particulates which are well dispersed in elastomers and, in particular, have a higher density.
SUMMARY OF THE INVENTION
Accordingly, a major object of the present invention is the provision of novel silica particulates having a highly specific morphology, i.e., in the form of beads, which novel silica beads are not only well dispersed in elastomers but also enhance the properties of such elastomers.
Briefly, in a first embodiment, the present invention features novel silica particulates in the form of essentially spherical beads having a mean particle size of at least 80 &mgr;m, a maximum BET specific surface area of 130 m
2
/g, a fill density in the packed state (DRT) greater than 0.32, and a total pore volume of at least 1.6 cm
3
/g.
In a second embodiment of the invention, the novel silica particulates are in the form of essentially spherical beads having a mean particle size of at least 80 &mgr;m, a BET surface ranging from 100 to 130 m
2
/g, a density ranging from 0.28 to 0.32, and a total pore volume ranging from 1.6 to 3.3 cm
3
/g.
In a third embodiment of the invention, the silica particulates are in the form of essentially spherical beads having a mean particle size of at least 80 &mgr;m, a BET surface of less than 100 m
2
/g and a density ranging from 0.28 and 0.32.
This invention also features a process for the production of such novel silica beads, comprising providing a silica suspension by reacting a silicate with an acidifying agent and then precipitating same, followed by the drying by atomization of such suspension, and wherein the precipitation is carried out according to the following sequence:
(i) a base mixture is first prepared, containing at least a portion of the total amount of the silicate required for the reaction and an electrolyte;
(ii) adding the acidifying agent to such base mixture until a pH of about 7 is obtained;
(iii) optionally, adding any additional acidifying agent and the remaining amount of the silicate to the reaction medium; and
(iv) drying the resulting suspension which has a dry solids content of at least 18% by weight and a pH of at least 4.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
More particularly according to the present invention, it will be appreciated that the subject silica particulates are in the form of balls or beads. These beads are essentially spherical.
The silica beads of the invention have a mean particle size of at least 80 &mgr;m.
In one preferred embodiment of the invention, this mean particle size is at most 300 &mgr;m. In other embodiments of the invention, the mean particle size is greater than 100 &mgr;m, in particular 150 &mgr;m and preferably ranges from 100 to 250 &mgr;m. This mean particle size is determined according to the standard NF X 11507 (December 1970) by dry screening and measuring the corresponding diameter on a cumulative residue of 50%.
Another characteristic of the silica beads of the invention is their BET surface. The BET specific surface area is determined by the BRUNAUER-EMMET-TELLER method described in
Journal of the American Chemical Society,
Vol. 60, page 309 (February 1938) and by the standard NFT 45007 (November 1987) (5.11.2).
The BET specific surface is at most 130 m
2
/g according to the first embodiment of the invention. It ranges from 100 to 130 m
2
/g in the second embodiment and is less than 100 m
2
/g in the third embodiment.
According to particular variants of the invention, in the first embodiment the BET surface is less than 100 m
2
/g and in the first and third embodiments, this specific surface is at most 95 m
2
/g, typically is less than 50 m
2
/g and in particular ranges from 60 to 90 m
2
/g.
The silica beads of the invention have a total pore volume of at least 1.6 cm
3
/g and more preferably at least 1.8 cm
3
/g.
It may, in particular, be greater than 2 and preferably ranges from 2.4 to 3.3 cm
3
/g. Specifically referring to said second embodiment, it is equal to at most 3.3 cm
3
/g, this upper limit being preferred in the first and third embodiments.
The pore volumes provided herein are measured by mercury porosimetry, the pore diameters being calculated by the WASHBURN equation with a contact angle of theta=130° and a surface tension of gamma=484 dynes/cm.
The porosity measurements are carried out on materials dried at 150° under a pressure of 1 Pa. The porosities given relate to pores having diameters ranging from 10&mgr; to 0.001&mgr;.
An important property of the silica beads of the invention is their density. Typically, their fill density in the packed state (DRT) is at least 0.28 and may be as high as 0.37.
In the embodiment of the invention, the density of the beads is higher than 0.32, more particularly is at least 0.33 and thus may range from 0.33 to 0.37.
This density is measured by the standard NFT No. 030100.
Another characteristic of the silica beads of the invention is their oil uptake, DOP. It typically is at most 270 ml/100 g.
According to the embodiments of the invention, the DOP uptake is at most 250 ml/100 g, more particularly 215 ml/g, specifically in the second embodiment, and it may, for example, range from 180 to 215 ml/100 g.
The DOP uptake is determined by the NFT Standard 30-022 (March '53) using dioctylphthalate.
An additional property of the silica beads of the invention is their CTAB specific surface area. Typically, this is at most 130 m
2
/g, more particularly is equal to or less than 100 m
2
/g and preferably is equal to or less than 90 m
2
/g.
The CTAB surface is the external surface area determined by the NFT Standard 45007 (5.12) (November 1987).
In another embodiment of the invention, the silica beads display a BET/CTAB surface ratio ranging from 0.9 to 1.2.
The process of the preparation of the silica beads described above will now be more fully described.
The process is characterized by two specific principal stages: precipitation and drying.
It will be appreciated that the process of the invention is one for the synthesis of precipitated silica, i.e., one in which an acidifying agent is reacted with a silicate.
The acidifying agent and the silicate are selected in known manner. In general, a strong inorganic acid, such as sulfuric acid, nitric acid or hydrochloric acid, or an organic acid, such as acetic acid, formic acid, carbonic acid, is used.
With respect to the silicate, any common form of silicates may be used, such as metasilicates, disilicates and, advantageously, an
Burns Doane Swecker & Mathis L.L.P.
Griffin Steven P.
Johnson Edward M.
Rhone-Poulenc Chimie
LandOfFree
Precipitated silica beads does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Precipitated silica beads, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Precipitated silica beads will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2528642