Silica particulates

Details Silica particulates Silica particulates

1999-03-19

2001-03-06

Mulcahy, Peter D. (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

At least one aryl ring which is part of a fused or bridged...

C524S492000, C524S493000, C524S573000, C524S574000

Reexamination Certificate

active

06197875

ABSTRACT:

This invention relates to silica particulates, in particular precipitated silica particulates.
It is well known to use particles of silica as a reinforcing filler material for elastomeric and rubbery materials. Thus they have been used as a white reinforcing filler in elastomers, for example those used in the manufacture of vehicle tires. As with any filler material, the silica must be easy to handle and to formulate. One of the problems with silica in powder form is that it tends to form a dust. Apart from the environmental difficulties that this leads to, this dust formation tends to hinder the incorporation of the filler since it gives it a low apparent density. In addition, rubber mixing requires very accurate metering techniques for which powdery fillers are often unsuitable. This is because of the difficulty of pouring them.
It is possible to overcome problems of dusting by shaping the filler material into a granule or the like but such granules often are difficult to disperse adequately in the elastomer and the degree of reinforcement ultimately obtained is quite often lower than would be obtained using the same quantity of filler in powder form.
It is known in this art that if a filler is to provide optimum re-inforcing properties it must be present in the elastomer matrix in a form which is both as finely divided as possible and as homogenously distributed as possible. It will be appreciated that these requirements are somewhat incompatible. Accordingly, there is a need to provide silica particles which are finely divided but which can be homogenously distributed throughout the elastomer without significant dusting.
It has surprisingly been found that silica particles which have been treated with a polymer oil jelly (POJ) eliminate, or generally reduce, the problems of dusting without causing a deterioration of the other properties of the resulting elastomer. Indeed the resulting elastomer may possess various technical advantages. In particular, it has been found that the treated particles possess a higher density. Also the incorporation of the treated particles in the elastomer gives rise to a somewhat reduced viscosity in the uncured elastomer while at the same time reducing abrasion losses. Further the treated particles can be incorporated more quickly into the elastomer, thus resulting in shorter mixing times and, in consequence, less power.
According to the present invention there is provided the particulate silica which has been treated with a polymer oil jelly.
Polymer oil jellies are materials obtained by mixing an oil extender with a thermoelastic polymer to form a substantially homogenous blend.
Typically, the oil extender is a mineral oil, for example a naphthenic process oil. Preferred thermoelastic polymers are copolymers of ethylene, propylene and, optionally, a diene, for example with an ethylene content of 60 to 90% by weight more particularly 60 to 75% by weight while the propylene content is 10 to 35%, particularly 20 to 30%, by weight with the remainder (if any), preferably 2 to 10% by weight diene. Specific polymers include those with the following (a) ethylene 68.5%, propylene 27% and ENB 4.5%, (b) ethylene 70.5%, propylene 25% and ENB 4.5% and (c) ethylene 72.5%, propylene 25% and hexadiene 2.5%. Typical dienes include hexadiene and ENB (ethylidenenorbornene). Generally the oil extender will predominate and will typically account for 80%, for example 85 to 95%, by weight of the composition with the copolymer representing up to 50% by weight, for example from 5 to 15% by weight. In one embodiment, the polymer represents about 6.5% by weight of the POJ, the remainder being oil. Suitable polymer oil jellies for use in the present invention include those disclosed in GB-A-1430768.
The amount of polymer oil jelly used to treat the silica particles can vary within quite wide limits although, generally, the POJ is used in an amount from 2.5 to 40%, typically 5 to 30%, particularly 5 to 20% preferably from 10 to 20% and more preferably from 10 to 15%, by weight based on the weight of the silica. Use of an amount from, say, 10 to 15% by weight is generally sufficient to reduce the tendency to dust very significantly without adversely affecting any properties of the elastomer into which the particles are introduced.
The incorporation of the POJ into the silica particles can be achieved quite simply by mixing the two components together while the POJ is sufficiently fluid. In general, a temperature of at least 50° C. is required for this purpose. The upper temperature is not particularly critical but, in general, too high a temperature can give rise to discolouration. A general range is, therefore, 50 to 110° C. with a preferred range being from 60 to 90° C., especially about 80° C. In a preferred embodiment the POJ is preheated to the desired temperature. The silica particles are placed in a mixer and then the POJ added gradually. Mixing is generally complete in, say, five minutes.
The present invention is applicable to all types of precipitated silicas. While the present invention is particularly applicable to silica powders, the invention is also applicable to silicas in the form of granules, beads or spherules such as micro pearls. They are advantageously dispersable precipitated silica particulates. The silica can be in the form of a powder, spherical beads or granules generally having a CTAB (cetyl trimethyl ammonium bromide) specific surface [determined in accordance with French NFT standard 45007] of 60 to 240 m
2
/g, for example 90 to 180 m
2
/g, in particular 130 to 170 m
2
g, and a BET specific surface (determined by the Brunauer—Emmet—Teller method, described in The Journal of the American Chemical Society, vol 60, page 309 (February 1938) and corresponding to French NFT standard 45007 (November 1987)) of 70 to 250 m
2
/g, for example 100 to 190 m
2
/g, in particular 140 to 180 m
2
/g″. The silica may also have a CTAB specific surface of 100 to 240 m
2
/g in particular 140 to 200 m
2
/g, especially about 160 to 165 m
2
/g. They can also have a high ultrasonic desegregation factor (obtained following the procedure described in, for example WO95/09128). The silica will generally have a mean particle size of at least 60 &mgr;m, generally at least 80 &mgr;m and preferably from 100 to 300, especially 150 to 300, &mgr;m. Typical silica which can be used include those disclosed in EP-A-520862, WO95/09127 and WO95/09128.
Thus the silica used in the present invention can be silica prepared using a particular chemical process, for example for reacting a silicate with an acidifying agent as in EP-A-520862.
The median diameter after ultrasonic deagglomeration (Ø
50
) and the ultrasonic deagglomeration factor (F
D
), along with the pore size distribution which are mentioned in these patent specifications and which are suitable for the particles of silica used in the present invention are those measured before treatment with POJ.
The initial granulometry of the silica used has in general a great importance: The most preferred silicas have a mean particle size of at least 60 &mgr;m, preferably of at least 80 &mgr;m and in particular of at least 100 &mgr;m. The improvement from a dusting standpoint is usually the highest with silicas showing a mean particle size from 100 to 300 &mgr;m.
As indicated above, such particulate silicas are typically used for incorporation in natural of synthetic elastomers and rubbers and especially, elastomers used to manufacture vehicle tires and shoe soles. Such elastomers include butadiene polymers such as styrene-butadiene rubber and neoprene elastomers. Typically the silica is present in an amount from 25 to 150, for example from 40 to 100, parts per 100 parts, by weight of the elastomer.
One might expect that the suppression of dust could be achieved using oil. However, it has been found that the same dust suppression effect can be achieved using a smaller quantity of POJ than that of oil.


REFERENCES:
patent: 5306766 (1994-04-01), Omura et al.
patent: 5403570 (1995-04-01), Chevallier et al.
patent: 5561269 (

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