U.S. patent application number 11/062091 was filed with the patent office on 2005-06-23 for precipitated silica used as reinforcing filler for elastomers.
Invention is credited to Chevallier, Yvonick, Cochet, Philippe, Fourre, Patrick.
Application Number | 20050135985 11/062091 |
Document ID | / |
Family ID | 9507207 |
Filed Date | 2005-06-23 |
United States Patent
Application |
20050135985 |
Kind Code |
A1 |
Chevallier, Yvonick ; et
al. |
June 23, 2005 |
Precipitated silica used as reinforcing filler for elastomers
Abstract
The invention relates to a novel process for the preparation of
precipitated silica which can be used as a reinforcing filler for
elastomers. The invention also relates to novel precipitated
silicas in the form of powder, granules or, preferably,
substantially spherical beads, these silicas being characterized in
that they have a BET specific surface of between 185 and 250
m.sup.2/g, a CTAB specific surface of between 180 and 240
m.sup.2/g, and a pore distribution such that the pore volume V2
made up of the pores with a diameter of between 175 and 275 .ANG.
represents less than 50% of the pore volume V1 made up of the pores
with diameters of less than or equal to 400 .ANG., a pore volume
(V.sub.d1), made up of the pores with a diameter of less than 1
.mu.m, of greater than 1.65 cm.sup.3/g, a fineness value (F.V.) of
between 70 and 100 .ANG., and a content of fines (.tau..sub.f),
after deagglomerability with ultrasound, of at least 50%.
Inventors: |
Chevallier, Yvonick;
(Fontaines Saint-Martin, FR) ; Cochet, Philippe;
(Lyon, FR) ; Fourre, Patrick; (Lyon, FR) |
Correspondence
Address: |
Rhodia Inc.
CN 7500
259 Propect Plains Road
CRANBURY
NJ
08512
US
|
Family ID: |
9507207 |
Appl. No.: |
11/062091 |
Filed: |
February 18, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11062091 |
Feb 18, 2005 |
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10233722 |
Sep 3, 2002 |
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10233722 |
Sep 3, 2002 |
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09230309 |
Jul 23, 1999 |
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6468493 |
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Current U.S.
Class: |
423/335 ;
423/339 |
Current CPC
Class: |
C01P 2004/50 20130101;
C01P 2004/61 20130101; C08K 2201/003 20130101; C08K 3/36 20130101;
C01P 2004/62 20130101; B82Y 30/00 20130101; C08K 2201/002 20130101;
Y10T 428/2982 20150115; C01P 2006/11 20130101; C01P 2004/32
20130101; C01P 2006/16 20130101; C01P 2006/14 20130101; C09C 1/30
20130101; C08K 7/26 20130101; C08K 2201/006 20130101; C01P 2006/22
20130101; C01P 2006/12 20130101; C01P 2006/17 20130101; C08K
2201/005 20130101; C01B 33/193 20130101; C01P 2004/64 20130101;
C08K 7/18 20130101; C01P 2004/51 20130101; C01P 2006/19 20130101;
C08K 3/36 20130101; C08L 21/00 20130101 |
Class at
Publication: |
423/335 ;
423/339 |
International
Class: |
C01B 033/12 |
Foreign Application Data
Date |
Code |
Application Number |
May 26, 1997 |
FR |
97/06369 |
Claims
1-26. (canceled)
27. A precipitated silica, having: a BET specific surface of
between 185 and 250 m.sup.2/g, a CTAB specific surface of between
180 and 240 m.sup.2/g, a pore distribution and pore volumes V1, and
V2, such that the pore volume V2 made up of pores with a diameter
of between 175 and 275 .ANG. represents less than 50% of the pore
volume V1 made up of pores with diameters of less than or equal to
400 .ANG., a pore volume (V.sub.d1), made up of pores with a
diameter of less than 1 .mu.m, of greater than 1.65 cm.sup.3/g, a
fineness value (F.V.) of between 70 and 100 .ANG., and a content of
fines (.tau..sub.f), after deagglomerability with ultrasound, of at
least 50%.
28. A silica according to claim 27, having a pore distribution such
that the ratio V2/V1 is not more than 0.45.
29. A silica according to claim 27, wherein the pore volume
(V.sub.d1) is at least 1.70 cm.sup.3/g.
30. A silica according to claim 29, wherein the pore volume
(V.sub.d1), is between 1.70 and 1.80 cm.sup.3/g.
31. A silica according to claim 27, having a fineness value (F.V.)
of between 80 and 100 .ANG..
32. A silica according to claim 27, having a median diameter (+50),
after deagglomerability with ultrasound, of less than 8.5
.mu.m.
33. A silica according to claim 32, wherein the median diameter
(.phi..sub.50), is between 5 and 7 .mu.m.
34. A silica according to claim 27, having an ultrasound
deagglomerability factor (F.sub.D) of greater than 5.5 ml.
35. A silica according to claim 34, wherein the ultrasound
deagglomerability factor (F.sub.D) is greater than 9 ml.
36. A silica according to claim 27, having a pore volume (V3), made
up of pores with a diameter of between 100 and 300 .ANG., of at
least 0.82 cm.sup.3/g.
37. A silica according to claim 27, having a total pore volume
(TPV) of greater than 3.0 cm.sup.3/g.
38. A silica according to claim 37, wherein the total pore volume
(TPV) is of between 3.1 and 3.4 cm.sup.3/g.
39. A silica according to claim 27, having a packed filling density
(PFD) of greater than 0.28.
40. A silica according to claim 27, having an oil absorption value
DOP of between 230 and 330 ml/100 g.
41. A silica according to claim 27, being in the form of
substantially spherical beads with an average size of at least 80
.mu.m.
42. A silica according to claim 27, being in the form of powder
with an average size of at least 15 .mu.m.
43. A silica according to claim 27, being in the form of granules
at least 1 mm in size.
44. A reinforcing filler for elastomers, comprising a silica as
defined in claim 27.
Description
[0001] The present invention relates to a novel process for the
preparation of precipitated silica, in particular precipitated
silicas in the form of powder, substantially spherical beads or
granules, and to their application in reinforcing elastomers.
[0002] It is known that precipitated silica has long been used as a
white reinforcing filler in elastomers.
[0003] However, as with any reinforcing filler, it is convenient
for it to be manipulable, on the one hand, and especially for it to
be readily incorporated in mixtures, on the other hand.
[0004] It is known, in general, that in order to obtain the optimum
reinforcing properties imparted by a filler, this filler should be
present in the elastomer matrix in a final form which is both as
finely divided as possible and distributed as homogeneously as
possible. However, such conditions can only be achieved provided
that, on the one hand, the filler has a very good capacity to be
incorporated in the matrix during mixing with the elastomer
(incorporability of the filler) and to become disintegrated or
deagglomerated in the form of a very fine powder (disintegration of
the filler) and provided that, on the other hand, the powder
obtained from the above mentioned disintegration process can
itself, in turn, be dispersed fully and homogeneously in the
elastomer (dispersibility of the powder).
[0005] Furthermore, for reasons of mutual affinity, silica
particles have an annoying tendency, in the elastomer matrix, to
agglomerate together. These silica/silica interactions have the
harmful consequence of limiting the reinforcing properties to a
level substantially lower than that which could theoretically be
achieved if all the silica/elastomer interactions liable to be
created during the mixing operation were effectively obtained (this
theoretical number of silica/elastomer interactions being, as is
well known, directly proportional to the external surface area of
the silica used).
[0006] In addition, such silica/silica interactions tend, in the
raw state, to increase the stiffness and the consistency of the
mixtures, thus making them more difficult to use.
[0007] These drawbacks are encountered in particular in the case of
silicas with a relatively high specific surface area, which,
furthermore, generally do not have very good reinforcing
properties.
[0008] The problem arises of providing fillers which, while having
a relatively high specific surface area, show a satisfactory
dispersibility in elastomers and good reinforcing properties.
[0009] The aim of the present invention is to avoid the
abovementioned drawbacks and to solve the problem mentioned
above.
[0010] With this aim, the invention proposes a novel process for
the preparation of precipitated silica, of the type comprising the
reaction of a silicate with an acidifying agent, whereby a
suspension of precipitated silica is obtained, followed by
separation and drying of this suspension, characterized in
that:
[0011] the precipitation is carried out in the following way:
[0012] (i) an initial stock solution is formed containing at least
some of the total amount of the silicate used in the reaction and
at least one electrolyte, the concentration of silicate (expressed
as SiO.sub.2) in the said initial stock solution being between 50
and 60 g/l,
[0013] (ii) the acidifying agent is added to the said stock
solution until a pH value of between 7 and 8.5 for the reaction
medium is obtained,
[0014] (iii) the acidifying agent is added to the reaction medium
along with, where appropriate, simultaneously, the remaining amount
of the silicate,
[0015] the separation comprises a filtration and washing operation
using a filter equipped with a means of compacting,
[0016] a suspension having a solids content of less than 17% by
weight is dried by spraying.
[0017] It has thus been found that a certain, relatively low,
concentration of silicate, expressed as SiO.sub.2 in the initial
stock solution, combined with the use of a filter equipped with a
means of compacting, preferably at a low compacting pressure, and
with a suitable solids content of the suspension to be dried
constitute important conditions for giving the products obtained
their good properties.
[0018] It should be noted, in general, that the process concerned
is a process for the synthesis of precipitation silica, i.e. an
acidifying agent is reacted, under specific conditions, with a
silicate.
[0019] The choice of acidifying agent and of silicate is made in a
manner which is well known per se.
[0020] It may be recalled that a strong inorganic acid, such as
sulphuric acid, nitric acid or hydrochloric acid, or an organic
acid, such as acetic acid, formic acid or carbonic acid, is
generally used as acidifying agent.
[0021] The acidifying agent can be dilute or concentrated; its
normality can be between 0.4 and 8 N, for example between 0.6 and
1.5 N.
[0022] In particular, when the acidifying agent is sulphuric acid,
its concentration can be between 40 and 180 g/l, for example
between 60 and 130 g/l.
[0023] It is moreover possible to use, as silicate, any common form
of silicate, such as metasilicates, disilicates and advantageously
an alkali metal silicate, in particular sodium or potassium
silicate.
[0024] The silicate can have a concentration, expressed as silica,
of between 40 and 330 g/l, for example between 60 and 300 g/l, in
particular between 60 and 250 g/l.
[0025] In general, sulphuric acid is used as acidifying agent and
sodium silicate is used as silicate.
[0026] When sodium silicate is used, it generally has an
SiO.sub.2/Na.sub.2O weight ratio of between 2 and 4, for example
between 3.0 and 3.7.
[0027] As more particularly regards the preparation process of the
invention, the precipitation is carried out in a specific manner
according to the following steps.
[0028] A stock solution which comprises silicate and an electrolyte
is first formed (step (i)). The amount of silicate present in the
initial stock solution advantageously represents only some of the
total amount of silicate used in the reaction.
[0029] According to an essential characteristic of the preparation
process of the invention, the concentration of silicate in the
initial stock solution is between 50 and 60 g of SiO.sub.2 per
litre. Preferably, this concentration is between 55 and 60 g/l.
[0030] The initial stock solution comprises an electrolyte. The
term electrolyte is understood here in its normal accepted meaning,
i.e. it means any ionic or molecular substance which, when in
solution, decomposes or dissociates to form ions or charged
particles. As electrolyte, mention may be made of a salt from the
group of salts of alkali metals and alkaline-earth metals, in
particular the salt of the metal of the starting silicate and of
the acidifying agent, for example sodium chloride in the case of
the reaction of a sodium silicate with hydrochloric acid, or,
preferably, sodium sulphate in case of the reaction of a sodium
silicate with sulphuric acid.
[0031] If the electrolyte used is sodium sulphate, its
concentration in the initial stock solution is preferably between
12 and 20 g/l, in particular between 15 and 20 g/l.
[0032] The second step consists in adding the acidifying agent to
the stock solution of composition described above (step (ii)).
[0033] This addition, which entails a corresponding decrease in the
pH of the reaction medium, is carried out until a pH of between 7
and 8.5 is reached; in particular between 7 and 8, for example
between 7.5 and 8.
[0034] Once the desired pH has been reached, the third step (step
(iii)) is then carried out.
[0035] In the (preferred) case of an initial stock solution
comprising only some of the total amount of silicate used in the
reaction, a simultaneous addition of acidifying agent and of the
remaining amount of silicate is carried out in step (iii).
[0036] This simultaneous addition is preferably carried out such
that the pH is constantly equal (to within .+-.0.2) to the value
reached after step (ii).
[0037] In general, in a subsequent step, an additional amount of
acidifying agent is added to the reaction medium, preferably until
a pH of between 4 and 6, in particular between 4.5 and 5.5, is
obtained in the reaction medium.
[0038] In this case, it may be advantageous, after this addition of
an additional amount of acidifying agent, to carry out a maturation
of the reaction medium, it being possible for this maturation to
last, for example, from 1 to 30 minutes, in particular from 2 to 15
minutes.
[0039] In the case of an initial stock solution comprising the
total amount of the silicate used in the reaction, an addition of
acidifying agent is carried out in step (iii), preferably until a
pH of between 4 and 6, in particular between 4.5 and 5.5, is
obtained in the reaction medium.
[0040] In this case, it may again be advantageous, after step
(iii), to carry out a maturation of the reaction medium, it being
possible for this maturation to last, for example from 1 to 30
minutes, in particular from 2 to 15 minutes.
[0041] The temperature of the reaction medium is generally between
68 and 98.degree. C.
[0042] According to a variant of the invention, the reaction is
carried out at a constant temperature, preferably between 75 and
95.degree. C.
[0043] According to another (preferred) variant of the invention,
the temperature at the end of the reaction is higher than the
temperature at the start of the reaction: thus, the temperature at
the start of the reaction is preferably maintained at between 68
and 80.degree. C., and is then increased, preferably to a value of
between 80 and 98.degree. C., and is maintained at this value until
the end of the reaction.
[0044] After the steps which have just been described, a silica
broth is obtained, which is then separated (liquid/solid
separation).
[0045] According to another essential characteristic of the
preparation process of the invention, the said separation comprises
a filtration and washing operation using a filter equipped with a
means of compacting, the compacting pressure preferably being
low.
[0046] This filter can be a belt filter equipped with a roller
which ensures compacting.
[0047] However, preferably, the separation comprises a filtration,
a washing and then a compacting operation, using a filter press; in
general, the pressure at the end of the filtration is between 3.5
and 6.0 bar, for example between 3.8 and 4.5 bar; in a very
advantageous manner, the said compacting is carried out by
introduction of air at a pressure of less than 4.5 bar, in
particular between 3.8 and 4.3 bar, for 20 to 40 seconds, for
example for about 30 seconds.
[0048] The suspension of precipitated silica thus recovered (filter
cake) is then spray-dried.
[0049] According to one characteristic of the preparation process
of the invention, this suspension should have, immediately before
it is spray-dried, a solids content of less than 17% by weight.
This solids content is preferably between 14.5 and 16.5% by
weight.
[0050] It should be noted that, after the filtration, dry material,
for example, silica in accordance with the invention in pulverulent
form, can also be added to the filter cake, in a subsequent step of
the process.
[0051] The drying can be carried out using any suitable type of
atomizer, in particular a turbine, nozzle, liquid-pressure or
twin-fluid atomizer.
[0052] It should be noted that the filter cake is not always under
conditions which allow spraying, in particular on account of its
high viscosity. In a manner which is known per se, the cake is
subjected, in this case, to a crumbling operation. This operation
can be carried out by passing the cake through a colloidal- or
ball-type mill. The crumbling is generally carried out in the
presence of an aluminium compound, in particular sodium aluminate,
and preferably in the presence of an acidifying agent as described
above (in the latter case, the aluminium compound and the
acidifying agent are advantageously added simultaneously). The
crumbling operation makes it possible in particular to lower the
viscosity of the suspension to be subsequently dried.
[0053] According to a preferred embodiment of the invention, the
drying is carried out using a nozzle atomizer. The precipitated
silica which can be obtained in this case is advantageously in the
form of substantially spherical beads, preferably with an average
size of at least 80 .mu.m, for example at least 100 .mu.m.
[0054] After the drying operation, a step of grinding can be
carried out on the recovered product. The precipitated silica which
can then be obtained is generally in the form of a powder,
preferably with an average size of at least 15 .mu.m, in particular
between 15 and 60 .mu.m, for example between 20 and 45 .mu.m.
[0055] The ground products with the desired particle size can be
separated from any non-conforming products by means, for example,
of vibrating screens with appropriate mesh sizes, and the
non-conforming products thus recovered can then be sent for
grinding.
[0056] Similarly, according to another embodiment of the invention,
the drying operation is carried out using a turbine atomizer. The
precipitated silica which can be obtained in this case can be in
the form of a powder, preferably with an average size of at least
15 .mu.m, in particular between 30 and 150 .mu.m, for example
between 45 and 120 .mu.m.
[0057] Lastly, the dried product (dried in particular by a turbine
atomizer) or ground product as indicated above can, according to
another embodiment of the invention, be subjected to an
agglomeration step.
[0058] The term agglomeration is understood here to refer to any
process which makes it possible to bind together finely divided
objects in order to bring them into the form of objects of larger
size with greater mechanical strength.
[0059] These processes are, in particular, direct compression, wet
granulation (i.e. with the use of a binder such as water, silica
slurry, etc.), extrusion and, preferably, dry compacting.
[0060] When the latter technique is used, it may prove to be
advantageous, before carrying out the compacting, to de-aerate
(this operation also known as predensification or degassing) the
pulverulent products so as to remove the air included therein and
ensure more uniform compacting.
[0061] The precipitated silica which can be obtained according to
this embodiment of the invention is advantageously in the form of
granules, preferably with a size of at least 1 mm, in particular
between 1 mm and 10 mm.
[0062] After the agglomeration step, the products can be calibrated
to a desired size, for example by screening, and then packaged for
their future use.
[0063] The precipitated silica powders, and the beads, obtained by
the process according to the invention thus offer the advantage,
inter alia, of allowing simple, effective and economical access to
granules as mentioned above, in particular by standard shaping
operations such as, for example, granulation or compacting, without
these operations entailing any degradations liable to mask, or even
destroy, the good intrinsic properties associated with these
powders or these beads, as may be the case in the prior art using
standard powders.
[0064] Other subjects of the invention consist of novel
precipitated silicas which, while having a high specific surface
area, nevertheless show satisfactory dispersibility and good
reinforcing properties, and in particular which, when used as
reinforcing fillers for elastomers, give these elastomers good
rheological and mechanical properties.
[0065] In the account which follows, the BET specific surface is
determined according to the Brunauer-Emmet-Teller method described
in "The Journal of the American Chemical Society", Vol. 60, page
309, February 1938 and corresponding to standard NF T 45007
(November 1987).
[0066] The CTAB specific surface is the external surface area
determined according to standard NF T 45007 (November 1987)
(5.12).
[0067] The DOP oil absorption value is determined according to
standard NF T 30-022 (March 1953) using dioctyl phthalate.
[0068] The packed filling density (PFD) is measured according to
standard NF T 30-042.
[0069] The pH is measured according to ISO standard 787/9 (pH of a
5% suspension in water).
[0070] The pore volumes given are measured by mercury porosimetry;
each sample is prepared as follows: each sample is predried for 2
hours in an oven at 200.degree. C. then placed in a test container
within 5 minutes of removal from the oven and is degassed under
vacuum, for example using a rotary vane pump; the pore diameters
are calculated by means of the Washburn relationship, with a
contact angle theta equal to 1400 and a surface tension gamma equal
to 484 dynes/cm (Micromeritics 9300 porosimeter).
[0071] The fineness value (FV) represents the median radius of the
intra-aggregate pores, i.e. the radius of pores to which the pore
surface S.sub.0/2 corresponds, measured by mercury porosimetry
(S.sub.0 is the surface area provided by all the pores of diameter
greater than or equal to 100 .ANG.).
[0072] The dispersibility of the silicas according to the invention
is quantified by means of measuring the fines content
(.tau..sub.f), i.e. the proportion (by weight) of particles less
than 0.3 .mu.m in size, after deagglomerability with ultrasound,
carried out according to the dispersibility test described
below.
[0073] In this test, the silica's dispersibility is measured by
means of a particle size measurement, (by sedimentation), carried
out on a silica suspension which has been deagglomerated beforehand
by ultra-sonication. The ultrasound deagglomerability (or
dispersibility) is carried out using a Vibracell Bioblock sonicator
(600 W) equipped with a probe 19 mm in diameter. The particle size
measurement is taken using a Sedigraph granulometer (sedimentation
in the field of gravity+scanning with a beam of X-rays).
[0074] 4 grams of silica are weighed into a sample tube (of volume
equal to 75 ml) and are made up to 50 grams by addition of
deionized water: an aqueous suspension containing 8% silica is thus
produced, which is homogenized for 2 minutes by magnetic stirring.
The deagglomerability (dispersibility) with ultrasound is then
performed as follows: with the probe immersed over a depth of 4 cm,
the output power is adjusted so as to obtain a power needle
deflection indicating 20%. The deagglomerability is carried out for
210 seconds.
[0075] The particle size measurement is then carried out using a
Sedigraph granulometer. For this, speed of vertical scanning of the
cell by the beam of X-rays is first adjusted to 918, which
corresponds to a maximum size analysed of 85 .mu.m. Deionized water
is circulated in the said cell, then the electrical zero and the
mechanical zero of the paper recorder are adjusted (this adjustment
being performed with the "100%" potentiometer of the recorder at
the maximum sensitivity). The paper recorder pen is placed at the
point representing the initial size of 85 .mu.m. The deagglomerated
silica suspension, which has optionally been cooled beforehand, is
then circulated in the cell of the Sedigraph granulometer (the
particle size analysis being carried out at 30.degree. C.) and the
analysis then begins. The analysis stops automatically once a size
of 0.3 .mu.m is reached (about 45 minutes). The content of fines
(.tau..sub.f), i.e. the proportion (by weight) of particles smaller
than 0.3 .mu.m in size, is then calculated.
[0076] This content of fines (.tau..sub.f), or content of particles
smaller than 0.3 .mu.m in size, is proportionately larger the
higher the dispersibility of the silica.
[0077] In certain cases, the dispersibility (and deagglomerability)
of the silicas according to the invention can also be quantified by
means of a specific deagglomerability test.
[0078] The deagglomerability test is carried out according to the
following procedure:
[0079] the cohesion of the agglomerates is assessed by a particle
size measurement (by laser scattering), carried out on a suspension
of silica deagglomerated beforehand by means of ultra-sonication;
the deagglomerability of the silica (rupture of the objects from
0.1 to a few tens of microns) is thus measured. The
deagglomerability with ultrasound is carried out using a Vibracell
Bioblock sonicator (600 W) equipped with a probe 19 mm in diameter.
The particle size measurement is carried out by means of laser
scattering on a Sympatec granulometer.
[0080] 2 grams of silica are weighed into a sample tube (height: 6
cm and diameter: 4 cm) and are made up to 50 grams by addition of
deionized water: an aqueous suspension containing 4% silica is thus
produced, which is homogenized for 2 minutes by magnetic stirring.
The deagglomerability with ultrasound is then performed as follows:
with the probe immersed over a depth of 4 cm, the output power is
adjusted so as to obtain a power dial needle deflection indicating
20%. The deagglomerability is carried out for 420 seconds. The
particle size measurement is then carried out after a known volume
(expressed in ml) of the homogenized suspension has been introduced
into the cell of the granulometer.
[0081] The value of the median diameter .phi..sub.50 which is
obtained is proportionately smaller the larger the silica's
deagglomerability. The ratio (10.times. volume of suspension
introduced (in ml))/optical density of the suspension detected by
the granulometer is also determined (this optical density is about
20). This ratio indicates the content of particles smaller than 0.1
.mu.m in size which are not detected by the granulometer. This
ratio, known as the ultrasound deagglomerability factor (FD), is
proportionately higher the larger the silica's
deagglomerability.
[0082] A novel precipitated silica is now proposed, according to
the invention, this silica being characterized in that it has:
[0083] a BET specific surface of between 185 and 240 m.sup.2/g,
[0084] a CTAB specific surface of between 180 and 240
m.sup.2/g,
[0085] a pore distribution such that the pore volume V2 made up of
the pores with a diameter of between 175 and 275 .ANG. represents
less than 50% of the pore volume V1 made up of the pores with
diameters of less than or equal to 400 .ANG.,
[0086] a pore volume (V.sub.d1), made up of the pores with a
diameter of less than 1 .mu.m, of greater than 1.65 cm.sup.3/g,
[0087] a fineness value (F.V.) of between 70 and 100 .ANG.,
[0088] a content of fines (.tau..sub.f), after deagglomerability
with ultrasound, of at least 50%, preferably of at least 55%.
[0089] The silica according to the invention has a relatively large
specific surface. Its BET specific surface is between 185 and 250
m.sup.2/g, preferably between 195 and 225 m.sup.2/g, in particular
between 200 and 220 m.sup.2/g; its CTAB specific surface is between
180 and 240 m.sup.2/g, preferably between 185 and 220 m.sup.2/g, in
particular between 190 and 205 m.sup.2/g.
[0090] It generally has a BET specific surface/CTAB specific
surface ratio ranging between 1.0 and 1.2, i.e. a low
microporosity.
[0091] One of the characteristics of the precipitated silica
according to the invention lies in the pore volume distribution,
and in particular in the distribution of the pore volume which is
generated by the pores with diameters of less than or equal to 400
.ANG.. The latter volume corresponds to the working pore volume of
the fillers used in the reinforcement of elastomers. Analysis of
the porograms shows that, in this case, the silica according to the
invention has a pore distribution such that the pore volume made up
of the pores with a diameter of between 175 and 275 .ANG.
represents less than 50%, in particular not more than 45%,
especially between 25 and 45%, of the pore volume made up of the
pores with diameters of less than or equal to 400 .ANG..
[0092] The silica according to the invention has a pore volume
(V.sub.d1), made up of the pores with a diameter of less than 1
.mu.m, of greater than 165 cm.sup.3/g; this pore volume is
preferably at least 1.70 cm.sup.3/g, in particular between 1.70 and
1.80 cm.sup.3/g.
[0093] Preferably, its pore volume (V3), made up of the pores with
a diameter of between 100 and 300 .ANG., is at least 0.82
cm.sup.3/g, in particular at least 0.85 cm.sup.3/g; it is usually
at least 0.86 cm.sup.3/g.
[0094] It generally has a total pore volume (TPV) of greater than
3.0 cm.sup.3/g, for example between 3.1 and 3.4 cm.sup.3/g.
[0095] Its fineness value (F.V.) is between 70 and 100 .ANG.,
preferably between 80 and 100 .ANG., for example between 82 and 98
.ANG..
[0096] The silica according to the invention thus has specific
porosity characteristics.
[0097] Furthermore, and this is one of the essential
characteristics, it has a very satisfactory dispersibility. Thus,
it has a fines content (.tau..sub.f), or content of particles less
than 0.3 .mu.m in size, after deagglomerability with ultrasound, of
at least 50%, preferably of at least 55%; this content can be, for
example, at least 60%.
[0098] In general, its ultrasound deagglomerability factor
(F.sub.D) is greater than 5.5 ml, in particular greater than 9 ml
or even 13 ml.
[0099] The silica according to the invention can have a median
diameter (.phi..sub.50), after deagglomerability with ultrasound,
of less than 8.5 .mu.m, in particular between 5 and 7 .mu.m.
[0100] The pH of the silica according to the invention is usually
between 6.0 and 7.5, in particular between 6.3 and 6.9.
[0101] Its packed filling density (PFD) is generally greater than
0.26, in particular greater than 0.28; it is, for example, at least
equal to 0.30.
[0102] The silica according to the invention has an oil absorption
value DOP usually ranging between 230 and 330 ml/100 g, preferably
between 240 and 300 ml/100 g.
[0103] It can be in the form of powder, granules or,
advantageously, in the form of substantially spherical beads.
[0104] The silica powders according to the invention preferably
have an average size of at least 15 .mu.m; this size is, for
example, between 15 and 60 .mu.m (in particular between 20 and 45
.mu.m) or between 30 and 150 .mu.m (in particular between 45 and
120 .mu.m).
[0105] They make it possible to obtain a good compromise between
implementation/mechanical properties in the vulcanized state. They
also constitute preferred precursors for the synthesis of granules
as mentioned later.
[0106] The substantially spherical beads according to the invention
preferably have an average size of at least 80 .mu.m.
[0107] According to certain variants of the invention, this average
bead size is at least 100 .mu.m, for example at least 150 .mu.m; it
is generally not more than 300 .mu.m and is preferably between 100
and 270 .mu.m. This average size is determined according to
standard NF X 11507 (December 1970) by dry-packing and
determination of the diameter corresponding to a cumulative
screening residue of 50%.
[0108] Such a silica in the form of substantially spherical,
advantageously solid, homogeneous beads, which produce very little
dust and are of good flowability, has a very satisfactory
dispersibility and good reinforcing properties. Such a silica also
constitutes a preferred precursor for the synthesis of powders and
granules according to the invention.
[0109] Such a silica in the form of substantially spherical beads
constitutes a very advantageous variant of the invention.
[0110] The dimensions of the granules according to the invention
are preferably at least 1 mm, in particular between 1 and 10 mm,
along the axis of their largest dimension (length).
[0111] The said granules can be in very diverse forms. For example,
mention may be made in particular of cylindrical, parallelepipedal,
pastille and platelet forms or of extrudate forms with circular or
multilobed cross-section.
[0112] The silicas according to the invention, in particular in
powder, substantially spherical bead or granule form, are
preferably prepared according to the preparation process in
accordance with the invention and described above.
[0113] The silicas according to the invention or prepared by the
process according to the invention find a particularly advantageous
application in the reinforcement of natural or synthetic
elastomers. While having a fairly high specific surface, they have
a satisfactory dispersibility and good reinforcing properties, in
particular when compared with silicas of the prior art with an
identical or similar surface area. Furthermore, they generally have
reinforcing properties that are comparable to or even better than
those of highly dispersible silicas, this being the case for
smaller amounts of silicas according to the invention used in
elastomers.
[0114] The examples which follow illustrate the invention without,
however, limiting its scope.
EXAMPLE 1 (COMPARATIVE)
[0115] The following ingredients:
[0116] 333 litres of aqueous sodium silicate (65.degree. C.) having
an SiO.sub.2/Na.sub.2O weight ratio equal to 3.45 and a density at
20.degree. C. equal to 1.230
[0117] 667 litres of aqueous solution (20.degree. C.) containing
11.2 kg of Na.sub.2SO.sub.4 are introduced into a stainless-steel
reactor fitted with an impeller stirring system and heating via a
jacket.
[0118] The concentration of silicate, expressed as SiO.sub.2, in
the initial stock solution is thus 78 g/l. The mixture is then
brought to a temperature of 70.degree. C. while stirring is
continued. Dilute sulphuric acid with a density at 20.degree. C.
equal to 1.050 is then introduced therein, at a flow rate of 9.2
l/min, until a pH (measured at its temperature) equal to 8.0 is
obtained in the medium. The reaction temperature is 70.degree. C.
during the first 25 minutes; it is then brought from 70 to
94.degree. C. over about 10 minutes and then maintained at
94.degree. C. until the end of the reaction.
[0119] Aqueous sodium silicate of the type described above is then
introduced (i.e. when the pH of the reaction medium has reached a
value of 8.0), at a flow rate of 2.5 l/min, and sulphuric acid,
also of the type described above, is introduced simultaneously, at
a flow rate adjusted such that the pH of the reaction medium during
the period of introduction is constantly equal to 8.0.+-.0.1. After
40 minutes of simultaneous addition, the introduction of the sodium
silicate is stopped and introduction of the dilute acid is
continued for about 10 minutes, so as to bring the pH of the
reaction medium to a value equal to 5.2. After this introduction of
acid, the reaction broth obtained is kept stirring for 5
minutes.
[0120] The total reaction time is 100 minutes.
[0121] A precipitated silica broth or suspension is thus obtained,
which is then filtered and washed using a filter press with
vertical plates, the said plates being equipped with a deformable
membrane allowing the filter cake to be compressed by introduction
of air under pressure; the precipitated silica broth is first
filtered, the pressure at the end of filtration being 5.6 bar; the
cake formed is then washed with water, after which it is compacted
by introduction of air at a pressure of 6.4 bar for 2 minutes.
[0122] The cake obtained is then fluidized by mechanical and
chemical action (simultaneous addition of sulphuric acid and of an
amount of sodium aluminate corresponding to an Al/SiO.sub.2 weight
ratio of 0.28%). After this crumbling operation, the resulting
broth, with a pH equal to 6.2 and a loss on ignition equal to 82.0%
(thus a solids content of 18.0% by weight), is atomized using a
nozzle atomizer.
[0123] The characteristics of the silica Al obtained in the form of
substantially spherical beads are thus as follows:
1 BET specific surface 240 m.sup.2/g CTAB specific surface 200
m.sup.2/g pore volume V1 represented by the 1.03 cm.sup.3/g pores
of d .ltoreq. 400 .ANG. pore volume V2 represented by the 0.31
cm.sup.3/g pores of 175 .ANG. .ltoreq. d .ltoreq. 275 .ANG. ratio
V2/V1 30% pore volume (V.sub.d1) made up of the 1.64 cm.sup.3/g
pores of d < 1 .mu.m fineness value (F.V.) 76 .ANG. pore volume
V3 represented by the 0.85 cm.sup.3/g pores of 100 .ANG. .ltoreq. d
.ltoreq. 300 .ANG. total pore volume (TPV) 3.16 cm.sup.3/g PFD 0.33
oil absorption value DOP 256 ml/ 100 g pH 6.6 average particle size
220 .mu.m
[0124] The silica Al is subjected to the dispersibility test as
defined previously in the description: it has a fines content
(.tau..sub.f), i.e. a proportion of particles less than 0.3 .mu.m
in size, after deagglomerability with ultrasound, of 30%.
[0125] The silica Al is subjected to the deagglomerability test as
defined previously in the description: after deagglomerability with
ultrasound, it has a median diameter (.phi..sub.50) of 12.0 .mu.m
and an ultrasound deagglomerability factor (F.sub.D) of 3.0 ml.
EXAMPLE 2 (COMPARATIVE)
[0126] The following ingredients:
[0127] 280 litres of aqueous sodium silicate (65.degree. C.) having
an SiO.sub.2/Na.sub.2O weight ratio equal to 3.45 and a density at
20.degree. C. equal to 1.230
[0128] 720 litres of aqueous solution (20.degree. C.) containing
16.5 kg of Na.sub.2SO.sub.4 are introduced into a stainless-steel
reactor fitted with an impeller stirring system and heating via a
jacket.
[0129] The concentration of silicate, expressed as SiO.sub.2, in
the initial stock solution is thus 65 g/l. The mixture is then
brought to a temperature of 70.degree. C. while stirring is
continued. Dilute sulphuric acid with a density at 20.degree. C.
equal to 1.050 is then introduced therein, at a flow rate of 7.7
l/min, until a pH value (measured at its temperature) equal to 8.0
is obtained in the medium. The reaction temperature is 70.degree.
C. during the first 25 minutes; it is then brought from 70 to
94.degree. C. over about 10 minutes and then maintained at
94.degree. C. until the end of the reaction.
[0130] Aqueous sodium silicate of the type described above is then
introduced (i.e. when the pH of the reaction medium has reached a
value of 8.0), at a flow rate of 2.1 l/min, and sulphuric acid,
also of the type described above, is introduced simultaneously, at
a flow rate adjusted such that the pH of the reaction medium during
the period of introduction is constantly equal to 8.0.+-.0.1. After
40 minutes of simultaneous addition, the introduction of the sodium
silicate is stopped and introduction of the dilute acid is
continued for about 10 minutes, so as to bring the pH of the
reaction medium to a value equal to 5.2. After this introduction of
acid, the reaction broth obtained is kept stirring for 5
minutes.
[0131] The total reaction time is 100 minutes.
[0132] A precipitated silica broth or suspension is thus obtained,
which is then filtered and washed using a filter press with
vertical plates, the said plates being equipped with a deformable
membrane allowing the filter cake to be compressed by introduction
of air under pressure; the precipitated silica broth is first
filtered, the pressure at the end of filtration being 5.6 bar; the
cake formed is then washed with water, after which it is compacted
by introduction of air at a pressure of 6.6 bar for 2 minutes.
[0133] The cake obtained is then fluidized by mechanical and
chemical action (simultaneous addition of sulphuric acid and of an
amount of sodium aluminate corresponding to an Al/SiO.sub.2 weight
ratio of 0.28%) After this crumbling operation, the resulting
broth, with a pH equal to 6.2 and a loss on ignition equal to 82.0%
(thus a solids content of 18.0% by weight), is atomized using a
nozzle atomizer.
[0134] The characteristics of the silica A2 obtained in the form of
substantially spherical beads are thus as follows:
2 BET specific surface 214 m.sup.2/g CTAB specific surface 190
m.sup.2/g pore volume V1 represented by the 1.01 cm.sup.3/g pores
of d .ltoreq. 400 .ANG. pore volume V2 represented by the 0.46
cm.sup.3/g pores of 175 .ANG. .ltoreq. d .ltoreq. 275 .ANG. ratio
V2/V1 46% pore volume (V.sub.d1) made up of the 1.68 cm.sup.3/g
pores of d < 1 .mu.m fineness value (F.V.) 91 .ANG. pore volume
V3 represented by the 0.85 cm.sup.3/g pores of 100 .ANG. .ltoreq. d
.ltoreq. 300 .ANG. total pore volume (TPV) 3.11 cm.sup.3/g PFD 0.32
oil absorption value DOP 256 ml/ 100 g pH 6.6 average particle size
215 .mu.m
[0135] The silica A2 is subjected to the dispersibility test as
defined previously in the description: it has a fines content
(.tau..sub.f), i.e. a proportion of particles less than 0.3 .mu.m
in size, after deagglomerability with ultrasound, of 42%.
[0136] The silica A2 is subjected to the deagglomerability test as
defined previously in the description: after deagglomerability with
ultrasound, it has a median diameter (.phi..sub.50) of 9.0 .mu.m
and an ultrasound deagglomerability factor (F.sub.D) of 4.5 ml.
EXAMPLE 3
[0137] The following ingredients:
[0138] 275 litres of aqueous sodium silicate (65.degree. C.) having
an SiO.sub.2/Na.sub.2O weight ratio equal to 3.45 and a density at
20.degree. C. equal to 1.230
[0139] 825 litres of aqueous solution (20.degree. C.) containing
18.2 kg of Na.sub.2SO.sub.4 are introduced into a stainless-steel
reactor fitted with an impeller stirring system and heating via a
jacket.
[0140] The concentration of silicate, expressed as SiO.sub.2, in
the initial stock solution is thus 58 g/l. The mixture is then
brought to a temperature of 74.degree. C. while stirring is
continued. Dilute sulphuric acid with a density at 20.degree. C.
equal to 1.050 is then introduced therein, at a flow rate of 7.6
l/min, until a pH (measured at its temperature) equal to 7.7 is
obtained in the medium. The reaction temperature is 74.degree. C.
during the first 25 minutes; it is then brought from 74 to
94.degree. C. over about 10 minutes and then maintained at
94.degree. C. until the end of the reaction.
[0141] Aqueous sodium silicate of the type described above is then
introduced (i.e. when the pH of the reaction medium has reached a
value of 7.7), at a flow rate of 2.1 l/min, and sulphuric acid,
also of the type described above, is introduced simultaneously, at
a flow rate adjusted such that the pH of the reaction medium during
the period of introduction is constantly equal to 7.7.+-.0.1. After
40 minutes of simultaneous addition, the introduction of the sodium
silicate is stopped and introduction of the dilute acid is
continued for about 10 minutes, so as to bring the pH of the
reaction medium to a value equal to 5.2. After this introduction of
acid, the reaction broth obtained is kept stirring for 5
minutes.
[0142] The total reaction time is 98 minutes.
[0143] A precipitated silica broth or suspension is thus obtained,
which is then filtered and washed using a filter press with
vertical plates, the said plates being equipped with a deformable
membrane allowing the filter cake to be compressed by introduction
of air under pressure; the precipitated silica broth is first
filtered, the pressure at the end of filtration being 5.6 bar; the
cake formed is then washed with water, after which it is compacted
by introduction of air at a pressure of 4 bar for 30 seconds.
[0144] The cake obtained is then fluidized by mechanical and
chemical action (simultaneous addition of sulphuric acid and of an
amount of sodium aluminate corresponding to an Al/SiO.sub.2 weight
ratio of 0.28%). After this crumbling operation, the resulting
broth, with a pH equal to 6.2 and a loss on ignition equal to 83.7%
(thus a solids content of 16.3% by weight), is atomized using a
nozzle atomizer.
[0145] The characteristics of the silica Pi obtained in the form of
substantially spherical beads are thus as follows:
3 BET specific surface 216 m.sup.2/g CTAB specific surface 192
m.sup.2/g pore volume V1 represented by the 0.97 cm.sup.3/g pores
of d .ltoreq. 400 .ANG. pore volume V2 represented by the 0.34
cm.sup.3/g pores of 175 .ANG. .ltoreq. d .ltoreq. 275 .ANG. ratio
V2/V1 35% pore volume (V.sub.d1) made up of the 1.73 cm.sup.3/g
pores of d < 1 .mu.m fineness value (F.V.) 87 .ANG. pore volume
V3 represented by the 0.86 cm.sup.3/g pores of 100 .ANG. .ltoreq. d
.ltoreq. 300 .ANG. total pore volume (TPV) 3.15 cm.sup.3/g PFD 0.30
oil absorption value DOP 295 ml/ 100 g pH 6.6 average particle size
190 .mu.m
[0146] The silica P1 is subjected to the dispersibility test as
defined previously in the description: it has a fines content
(.tau..sub.f) i.e. a proportion of particles less than 0.3 .mu.m in
size, after deagglomerability with ultrasound, of 57%.
[0147] The silica P1 is subjected to the deagglomerability test as
defined previously in the description: after deagglomerability with
ultrasound, it has a median diameter (.phi..sub.50) of 5.2 .mu.m
and an ultrasound deagglomerability factor (F.sub.D) of 14.4
ml.
EXAMPLE 4
[0148] The following ingredients:
[0149] 275 litres of aqueous sodium silicate (65.degree. C.) having
an SiO.sub.2/Na.sub.2O weight ratio equal to 3.45 and a density at
20.degree. C. equal to 1.230
[0150] 825 litres of aqueous solution (20.degree. C.) containing
18.2 kg of Na.sub.2SO.sub.4 are introduced into a stainless-steel
reactor fitted with an impeller stirring system and heating via a
jacket.
[0151] The concentration of silicate, expressed as SiO.sub.2, in
the initial stock solution is thus 58 g/l. The mixture is then
brought to a temperature of 75.degree. C. while stirring is
continued. Dilute sulphuric acid with a density at 20.degree. C.
equal to 1.050 is then introduced therein, at a flow rate of 7.6
l/min, until a pH (measured at its temperature) equal to 7.7 is
obtained in the medium. The reaction temperature is 75.degree. C.
during the first 25 minutes; it is then brought from 75 to
94.degree. C. over about 10 minutes and then maintained at
94.degree. C. until the end of the reaction.
[0152] Aqueous sodium silicate of the type described above is then
introduced (i.e. when the pH of the reaction medium has reached a
value of 7.7), at a flow rate of 2.1 l/min, and sulphuric acid,
also of the type described above, is introduced simultaneously, at
a flow rate adjusted such that the pH of the reaction medium during
the period of introduction is constantly equal to 7.7.+-.0.1. After
40 minutes of simultaneous addition, the introduction of the sodium
silicate is stopped and introduction of the dilute acid is
continued for about 10 minutes, so as to bring the pH of the
reaction medium to a value equal to 5.2. After this introduction of
acid, the reaction broth obtained is kept stirring for 5
minutes.
[0153] The total reaction time is 98 minutes.
[0154] A precipitated silica broth or suspension is thus obtained,
which is then filtered and washed using a filter press with
vertical plates, the said plates being equipped with a deformable
membrane allowing the filter cake to be compressed by introduction
of air under pressure; the precipitated silica broth is first
filtered, the pressure at the end of filtration being 4 bar; the
cake formed is then washed with water, after which it is compacted
by introduction of air at a pressure of 4 bar for 30 seconds.
[0155] The cake obtained is then fluidized by mechanical and
chemical action (simultaneous addition of sulphuric acid and of an
amount of sodium aluminate corresponding to an Al/SiO.sub.2 weight
ratio of 0.28%). After this crumbling operation, the resulting
broth, with a pH equal to 6.2 and a loss on ignition equal to 83.7%
(thus a solids content of 16.3% by weight), is atomized using a
nozzle atomizer.
[0156] The characteristics of the silica P2 obtained in the form of
substantially spherical beads are thus as follows:
4 BET specific surface 200 m.sup.2/g CTAB specific surface 190
m.sup.2/g pore volume V1 represented by the pores 1.03 cm.sup.3/g
of d .ltoreq. 400 .ANG. pore volume V2 represented by the 0.49
cm.sup.3/g pores of 175 .ANG. .ltoreq. d .ltoreq. 275 .ANG. ratio
V2/V1 48% pore volume (V.sub.d1) made up of the 1.80 cm.sup.3/g
pores of d < 1 .mu.m fineness value (F.V.) 93 .ANG. pore volume
V3 represented by the 0.87 cm.sup.3/g pores of 100 .ANG. .ltoreq. d
.ltoreq. 300 .ANG. total pore volume (TPV) 3.32 cm.sup.3/g PFD 0.31
oil absorption value DOP 280 ml/ 100 g pH 6.6 average particle size
210 .mu.m
[0157] The silica P2 is subjected to the dispersibility test as
defined previously in the description: it has a fines content
(.tau..sub.f), i.e. a proportion of particles less than 0.3 .mu.m
in size, after deagglomerability with ultrasound, of 62%.
[0158] The silica P2 is subjected to the deagglomerability test as
defined previously in the description: after deagglomerability with
ultrasound, it has a median diameter (.phi..sub.50) of 5.4 .mu.m
and an ultrasound deagglomerability factor (F.sub.D) Of 10.0
ml.
EXAMPLE 5
[0159] The following ingredients:
[0160] 262 litres of aqueous sodium silicate (65.degree. C.) having
an SiO.sub.2/Na.sub.2O weight ratio equal to 3.45 and a density at
20.degree. C. equal to 1.230
[0161] 858 litres of aqueous solution (20.degree. C.) containing
18.7 kg of Na.sub.2SO.sub.4 are introduced into a stainless-steel
reactor fitted with an impeller stirring system and heating via a
jacket.
[0162] The concentration of silicate, expressed as SiO.sub.2, in
the initial stock solution is thus 55 g/l. The mixture is then
brought to a temperature of 75.degree. C. while stirring is
continued. Dilute sulphuric acid with a density at 20.degree. C.
equal to 1.050 is then introduced therein, at a flow rate of 7.25
l/min, until a pH (measured at its temperature) equal to 7.7 is
obtained in the medium. The reaction temperature is 75.degree. C.
during the first 25 minutes; it is then brought from 75 to
94.degree. C. over about 10 minutes and then maintained at
94.degree. C. until the end of the reaction.
[0163] Aqueous sodium silicate of the type described above is then
introduced (i.e. when the pH of the reaction medium has reached a
value of 7.7), at a flow rate of 1.9 l/min, and sulphuric acid,
also of the type described above, is introduced simultaneously, at
a flow rate adjusted such that the pH of the reaction medium during
the period of introduction is constantly equal to 7.7.+-.0.1. After
40 minutes of simultaneous addition, the introduction of the sodium
silicate is stopped and introduction of the dilute acid is
continued for about 10 minutes, so as to bring the pH of the
reaction medium to a value equal to 5.2. After this introduction of
acid, the reaction broth obtained is kept stirring for 5
minutes.
[0164] The total reaction time is 101 minutes.
[0165] A precipitated silica broth or suspension is thus obtained,
which is then filtered and washed using a filter press with
vertical plates, the said plates being equipped with a deformable
membrane allowing the filter cake to be compressed by introduction
of air under pressure; the precipitated silica broth is first
filtered, the pressure at the end of filtration being 5.6 bar; the
cake formed is then washed with water, after which it is compacted
by introduction of air at a pressure of 4 bar for 30 seconds.
[0166] The cake obtained is then fluidized by mechanical and
chemical action (simultaneous addition of sulphuric acid and of an
amount of sodium aluminate corresponding to an Al/SiO.sub.2 weight
ratio of 0.28%). After this crumbling operation, the resulting
broth, with a pH equal to 6.2 and a loss on ignition equal to 83.5%
(thus a solids content of 16.5% by weight), is atomized using a
nozzle atomizer.
[0167] The characteristics of the silica P3 obtained in the form of
substantially spherical beads are thus as follows:
5 BET specific surface 215 m.sup.2/g CTAB specific surface 197
m.sup.2/g pore volume V1 represented by the 1.02 cm.sup.3/g pores
of d .ltoreq. 400 .ANG. pore volume V2 represented by the 0.27
cm.sup.3/g pores of 175 .ANG. .ltoreq. d .ltoreq. 275 .ANG. ratio
V2/V1 26% pore volume (V.sub.d1) made up of the 1.72 cm.sup.3/g
pores of d < 1 .mu.m fineness value (F.V.) 83 .ANG. pore volume
V3 represented by the 0.86 cm.sup.3/g pores of 100 .ANG. .ltoreq. d
.ltoreq. 300 .ANG. total pore volume (TPV) 3.14 cm.sup.3/g PFD 0.30
oil absorption value DOP 285 ml/ 100 g pH 6.6 average particle size
210 .mu.m
[0168] The silica P3 is subjected to the dispersibility test as
defined previously in the description: it has a fines content
(.tau..sub.f), i.e. a proportion of particles less than 0.3 .mu.m
in size, after deagglomerability with ultrasound, of 55%.
[0169] The silica P3 is subjected to the deagglomerability test as
defined previously in the description.
[0170] After deagglomerability with ultrasound, it has a median
diameter (.phi..sub.50) of 6.4 .mu.m and an ultrasound
deagglomerability factor (F.sub.D) Of 9.1 ml.
[0171] The characteristics of the silicas prepared in Examples 1 to
5 above, as well as those of a commercial silica, in the form of
powder and granules, sold by the company PPG Industries, in this
case HI-SIL.RTM. 2000 (reference A3), and those of the silica
(reference MP1) in the form of substantially spherical beads,
prepared in Example 12 of patent application EP-A-0,520,862
(Application No. 92401677.7), are collated in Table I below.
6 TABLE I A1 A2 A3 MP1 P1 P2 P3 S.sub.BET (m.sup.2/g) 240 214 239
170 216 200 215 B.sub.CTAB (m.sup.2/g) 200 190 212 160 192 190 197
V1 (cm.sup.3/g) 1.03 1.01 1.07 0.90 0.97 1.03 1.02 V2 (cm.sup.3/g)
0.31 0.46 0.20 0.55 0.34 0.49 0.27 V2/V1 (%) 30 46 19 61 35 48 26
Vd1 (cm.sup.3/g) 1.64 1.68 1.93 1.80 1.73 1.80 1.72 F.V. (.ANG.) 76
91 76 120 87 93 83 .gamma..sub.f (%) 30 44 29 78 57 56 55 V3
(cm.sup.3/g) 0.85 0.85 0.88 0.77 0.86 0.87 0.86 TPV (cm.sup.3/g)
3.16 3.11 2.70 3.00 3.15 3.32 3.14 PFD 0.33 0.32 0.32 0.28 0.30
0.31 0.30 DOP (ml/100 g) 256 256 295 276 295 280 285 pH 6.6 6.6 6.8
6.7 6.6 6.6 6.6 Average size (.mu.m) 220 215 * 260 190 210 210
.phi..sub.50 (.mu.m) 12.0 9.0 12.9 4.3 5.2 10.0 6.4 F.sub.D (.mu.m)
3.0 4.5 2.0 6.5 14.4 5.4 9.1 *not measured
EXAMPLE 6
[0172] This example illustrates the use and behaviour of silicas
according to the invention and of silicas not in accordance with
the invention, in an industrial rubber formulation.
[0173] The following formulation is used (the parts are expressed
by weight):
7 S.B.R. rubber .sup.(1) 103 B.R. rubber 1220 .sup.(2) 25 silica 70
(80 in the case of MP1) ZnO .sup.(3) 2.5 stearic acid 2 6PPD
.sup.(4) 1.9 CBS .sup.(5) 1.7 DPG .sup.(6) 2 sulphur .sup.(7) 1.4
silane X50S .sup.(8) 12.8 .sup.(1)Styrene/butadiene copolymer in
solution of the type BUNA 1955S25, sold by the company Bayer
.sup.(2)Polybutadiene polymer of the type B.R. 1220, sold by the
company Shell .sup.(3)Rubber-quality zinc oxide
.sup.(4)N-(1,3-Dimethylbutyl)-N'-phenyl-p-phenylenedi- amine sold
by the company Akzo .sup.(5)N-Cyclohexyl-2-benzothiazy- l
sulphenamide .sup.(6)Diphenylguanidine .sup.(7)Vulcanizing agent
.sup.(8)Silica/rubber coupling agent, on carbon black support, sold
by the company Degussa
[0174] The formulations are prepared in the following way, in two
stages:
[0175] Stage 1
[0176] The following ingredients are introduced, in this order and
at the times indicated in brackets (the temperature increasing
gradually from 60 to 160.degree. C.) into an internal mixer
(Banbury type):
[0177] S.B.R. and B.R. 1220 (to)(60.degree. C.),
[0178] 2/3 of the amount of silica and the X50S (to +1 nm),
[0179] the remainder (1/3) of the silica and the stearic acid
(t.sub.0+2 nm).
[0180] The mixer is unloaded (dropping of the mixture) when the
chamber temperature reaches 160.degree. C.
[0181] Stage 2
[0182] The mixture obtained after Stage 1 is reintroduced into the
internal mixer (t.sub.0') at 60.degree. C. (the temperature then
rising gradually).
[0183] The active ZnO and the 6PPD are then introduced (t.sub.0'+30
s).
[0184] The mixer is unloaded (dropping of the mixture) when the
chamber temperature reaches 160.degree. C. The mixture is then
introduced into a cylinder mixer, maintained at 40.degree. C., in
order to be calendered therein. The CBS, the DPG and the sulphur
are introduced into this mixer.
[0185] After homogenization and three fine screenings, the final
mixture is calendered in the form of sheets 2.5 to 3 mm in
thickness.
[0186] The test results are as follows:
[0187] 1--Rheological Properties
[0188] The measurements are taken on the crude formulations at
170.degree. C.
[0189] The apparatus used to carry out the measurements is a
Monsanto 100 S rheometer.
[0190] The results are given in Table II below.
8 TABLE II A1 A2 A3 MP1 P1 P2 P3 Min. torque (in. lb) 27 25 32 18
21 19 21 Max. torque (in. lb) 85 82 84 76 78 77 80
[0191] The formulations obtained from the silicas according to the
invention (P1, P2, P3) give:
[0192] lower values than those of the formulations prepared from
the silicas A1, A2 and A3,
[0193] values not far from those of the formulation obtained from
the silica MP1.
[0194] This reflects a great ease of implementation of the mixtures
prepared from the silicas according to the invention, in particular
as regards the extrusion and calendering operations often carried
out during the manufacture of elastomeric compositions (reduced
energy cost to prepare the mixture, greater ease of injection
during mixing, less swelling at the die during extrusion, less
shrinkage on calendering, etc.).
[0195] 2--Mechanical Properties
[0196] The measurements are taken on the vulcanized
formulations.
[0197] The vulcanization is obtained by maintaining the
formulations at 150.degree. C. for 40 minutes.
[0198] The following standards were used:
[0199] (i) tensile tests (moduli, tensile strength)
[0200] NF T 46-002 or ISO 37-1977 (DIN 53 504)
[0201] (ii) tear strength tests
[0202] NF T 46-007 (notched at 0.5 mm)
[0203] The results obtained are given in Table III below.
9 TABLE III A1 A2 A3 MP1 P1 P2 P3 100% Modulus 4.8 4.5 3.9 3.0 3.3
3.0 3.2 (MPa) 300% Modulus 12.5 13.5 12.4 14.7 14.5 13.7 13.8 (MPa)
300% Modulus/ 2.6 3.0 3.2 4.7 4.4 4.6 4.3 100% Modulus Tensile 13.0
17.5 17.1 19.4 19.5 20.2 19.6 strength (MPa) Tear strength 33.0
32.7 30.5 36.7 41.1 42.6 37.3 (kN/M)
[0204] These results show that the silicas according to the
invention afford very good mechanical properties.
[0205] On the one hand, the silicas according to the invention lead
to low 100% moduli, which is proof of good dispersibility of the
silica, and to fairly high 300% moduli, which is proof of a high
density of silica/rubber interactions. Furthermore, they lead to a
high 300% modulus/100% modulus ratio, i.e. a very good compromise
between these two moduli, which is proof of a good reinforcing
effect.
[0206] On the other hand, the high reinforcing power of the silicas
according to the invention is also confirmed by the high values
obtained for the tensile strength and the tear strength.
[0207] The silicas according to the invention thus impart a higher
level of performance to all of the mechanical properties.
[0208] 3--Dynamic Properties
[0209] The measurements are taken on the vulcanized
formulations.
[0210] The vulcanization is obtained by maintaining the
formulations at 150.degree. C. for 40 minutes. The results
(illustrating the susceptibility to heating) are given in Table IV
below (the lower the values, the lower the susceptibility to
heating). The apparatus used for carrying out the measurements is
indicated.
10 TABLE IV A1 A2 A3 MP1 P1 P2 P3 Internal heating 111 92 101 84 89
84 88 (.degree. C.) .sup.(1) 70.degree. C. tan 0.14 0.14 0.16 0.14
0.13 0.13 0.13 delta .sup.(2) .sup.(1) Goodrich flexometer .sup.(2)
Instron viscoelasticimeter
[0211] The susceptibility to heating obtained using the silicas
according to the invention is fairly low.
[0212] In particular, it is less than that observed with the
silicas A1, A2 and A3 which have a specific surface of the same
order.
[0213] It is close to that observed with the silica MP1 which has a
much lower specific surface; the tan delta is even lower than that
observed with the latter silica.
* * * * *