U.S. patent application number 10/486573 was filed with the patent office on 2005-02-10 for method of preparing silicas, silicas with specific pore-size and/or particle-size distribution, and the uses thereof, in particular for reinforcing polymers.
Invention is credited to Valero, Remi.
Application Number | 20050032965 10/486573 |
Document ID | / |
Family ID | 8866658 |
Filed Date | 2005-02-10 |
United States Patent
Application |
20050032965 |
Kind Code |
A1 |
Valero, Remi |
February 10, 2005 |
Method of preparing silicas, silicas with specific pore-size and/or
particle-size distribution, and the uses thereof, in particular for
reinforcing polymers
Abstract
The invention relates to a novel method of preparing silicas and
to highly-structured silicas having the following characteristics:
a specific surface area CTAB (SCTAB) of between 40 and 525 m2/g; a
specific surface area BET (SBET) of between 45 and 550 m2/g; an
object size distribution width Ld ((d84-d16)/d50), which is
measured by XDC particle size analysis after deagglomeration with
ultrasound, of at least 0.91; and a pore-size distribution such
that ratio V(d5-d50)/V(d5-d100) is at least 0.66. The invention
also relates to the use of said silicas as polymer reinforcing
fillers.
Inventors: |
Valero, Remi; (Lyon,
FR) |
Correspondence
Address: |
Jean-Louid Seugnet
Rhodia Inc
Intellectual Property Dept
259 Prospect Plains Road CN 7500
Cranbury
NJ
08512-7500
US
|
Family ID: |
8866658 |
Appl. No.: |
10/486573 |
Filed: |
February 11, 2004 |
PCT Filed: |
August 13, 2002 |
PCT NO: |
PCT/FR02/02872 |
Current U.S.
Class: |
524/493 ;
423/335 |
Current CPC
Class: |
C01P 2006/16 20130101;
C01P 2004/51 20130101; Y02E 60/10 20130101; C01P 2006/80 20130101;
A61K 2800/412 20130101; C01P 2006/90 20130101; C01P 2004/61
20130101; C01P 2006/17 20130101; A61Q 11/00 20130101; C01B 33/193
20130101; C08K 3/36 20130101; C01P 2006/12 20130101; Y10T 428/2982
20150115; C01P 2006/14 20130101; A61K 8/25 20130101; H01M 50/431
20210101; C01P 2004/32 20130101; C08K 3/36 20130101; C08L 21/00
20130101 |
Class at
Publication: |
524/493 ;
423/335 |
International
Class: |
C08K 003/34; C01B
033/12 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 13, 2001 |
FR |
01/11001 |
Claims
1-51. (Canceled)
52. A process for preparing silica, comprising the reaction of a
silicate with an acidifying agent whereby a silica suspension is
obtained, followed by the separation and the drying of this
suspension, said reaction of the silicate with the acidifying agent
being carried out according to the following successive steps: (i)
forming an aqueous stock having a pH of between 2 and 5; (ii)
adding simultaneously silicate and acidifying agent to the said
stock in such a way that the pH of the reaction mixture is
maintained between 2 and 5; (iii) stopping the addition of the
acidifying agent, while continuing to add silicate into the
reaction mixture until a pH value of the reaction mixture of
between 7 and 10, is obtained; (iv) adding simultaneously silicate
and acidifying agent to the reaction mixture in such a way that the
pH of the reaction mixture is maintained between 7 and 10; and (v)
stopping the addition of the silicate, while continuing to add the
acidifying agent into the reaction mixture until a pH value of the
reaction mixture of less than 6 is obtained.
53. The process according to claim 52, wherein a maturing step is
carried out between step (iii) and step (iv).
54. The process according to claim 52, wherein a maturing step is
carried out after step (v).
55. The process according to claim 52, wherein, in step (v), the
addition of the silicate is stopped, while continuing to add the
acidifying agent into the reaction mixture until a pH value of the
reaction mixture of between 3 and 5.5 is obtained.
56. The process according to claim 52, wherein, between step (iii)
and step (iv), acidifying agent is added to the reaction mixture,
the pH of the reaction mixture after this addition being between 7
and 9.5.
57. The process according to claim 52, wherein the entire reaction
between the silicate and the acidifying agent is carried out
between 70 and 95.degree. C.
58. The process according to claim 52, wherein the entire reaction
between the silicate and the acidifying agent is carried out at a
constant temperature.
59. The process according to claim 52, wherein step (i) comprises
the addition of acidifying agent to water so as to obtain a pH
value of the stock thus formed of between 2 and 6.
60. The process according to claim 52, wherein step (i) comprises
the addition of acidifying agent to a water+silicate mixture so as
to obtain a pH value of the stock thus formed of between 2 and
6.
61. The process according to claim 52, wherein step (i) comprises
the addition of acidifying agent to a stock containing preformed
silica particles at a pH of greater than 7 so as to obtain a pH
value of the stock thus formed of between 2 and 6.
62. The process according to claim 52, wherein the drying is
carried out by spray drying.
63. The process according to claim 52, wherein the separation
comprises a filtration carried out by means of a filter press.
64. The process according to claim 62, wherein the drying is
carried out by means of a nozzle spray dryer.
65. The process according to claim 52, wherein the separation
comprises a filtration carried out by means of a vacuum filter.
66. The process according to claim 62, wherein the drying is
carried out by means of a turbine spray dryer.
67. A silica, having: a CTAB specific surface area (S.sub.CTAB) of
between 40 and 525 m.sup.2/g; a BET specific surface area
(S.sub.BET) of between 45 and 550 m.sup.2/g; a size distribution
width L.sub.d ((d84-d16)/d50) of objects measured by XDC particle
size analysis after ultrasonic disintegration of at least 0.91, and
a pore volume distribution such that the ratio
V.sub.(d5-d50)/V.sub.(d5-d100) is at least 0.66.
68. The silica according to claim 67, wherein the size distribution
width L.sub.d of objects is of at least 0.94.
69. The silica according to claim 67, wherein the ratio
V.sub.(d5-d50)/V.sub.(d5-100) is at least 0.68.
70. The silica according to claim 67, wherein the size distribution
width L.sub.d ((d84-d16)/d50) of objects measured by XDC particle
size analysis after ultrasonic disintegration, is of at least 1.04,
and the pore volume distribution such that the ratio
V.sub.(d5-d50)/V.sub.(d5-d100) is at least 0.71.
71. The silica according to claim 67, having, after ultrasonic
disintegration, a median diameter (.O slashed..sub.50S) of less
than 8.5 .mu.m.
72. The silica according to claim 67, having, after ultrasonic
disintegration, a median diameter (.O slashed..sub.50M) of less
than 8.5 .mu.m.
73. The silica according to claim 67, having a rate of
disintegration, denoted by a, measured in the test referred to as
ultrasonic disintegration in pulsed mode, at 100% power of a 600
watt probe, of at least 0.0035 .mu.m.sup.-1.min.sup.-1.
74. A silica, having: a CTAB specific surface area (S.sub.CTAB) of
between 40 and 525 m.sup.2/g; a BET specific surface area
(S.sub.BET) of between 45 and 550 m.sup.2/g; and a pore
distribution width ldp of greater than 0.70.
75. The silica according to claim 74, having a size distribution
width L.sub.d ((d84-d16)/d50) of objects, measured by XDC particle
size analysis after ultrasonic disintegration, of at least
0.91.
76. The silica according to claim 74, having, after ultrasonic
disintegration, a median diameter (.O slashed..sub.50S) of less
than 8.5 .mu.m.
77. The silica according to claim 74, having, after ultrasonic
disintegration, a median diameter (.O slashed..sub.50M) of less
than 8.5 .mu.m.
78. The silica according to claim 74, having a rate of
disintegration, denoted by .alpha., measured in the test referred
to as ultrasonic disintegration in pulsed mode, at 100% power of a
600 watt probe, of at least 0.0035 .mu.m.sup.1.min.sup.1.
79. A silica, having: a CTAB specific surface area (S.sub.CTAB) of
between 40 and 525 m.sup.2/g; a BET specific surface area
(S.sub.BET) of between 45 and 550 m.sup.2/g; a size distribution
width L'.sub.d ((d84-d16)/d50) of objects smaller than 500 nm,
measured by XDC particle size analysis after ultrasonic
disintegration, of at least 0.95; and a pore volume distribution
such that the ratio V.sub.(d5-d50)/V.sub.(d5-d100) is at least
0.71.
80. The silica according to claim 69, having the ratio
V.sub.(d5-d50)/V.sub.(d5-d100) of at least 0.73.
81. A silica, having: a CTAB specific surface area (S.sub.CTAB) of
between 40 and 525 m.sup.2/g; a BET specific surface area
(S.sub.BET) of between 45 and 550 m.sup.2/g; a size distribution
width L'.sub.d ((d84-d16)/d50) of objects smaller than 500 nm,
measured by XDC particle size analysis after ultrasonic
disintegration, of at least 0.90; and a pore volume distribution
such that the ratio V.sub.(d5-d50)/V.sub.(d5-d100) is at least
0.74.
82. The silica according to claim 70, wherein the size distribution
width L.sub.d of objects of at least 1.04 and the size distribution
width L'.sub.d of objects smaller than 500 nm is of at least
0.95.
83. The silica according to claim 77, wherein, after ultrasonic
disintegration, the median diameter (.O slashed..sub.50S) is of
less than 8.5 .mu.m, in particular less than 6.0 .mu.m.
84. The silica according to claim 79, having, after ultrasonic
disintegration, a median diameter (.O slashed..sub.50M) of less
than 8.5 .mu.m.
85. The silica according to claim 79, having a rate of
disintegration, denoted by .alpha., measured in the test referred
to as ultrasonic disintegration in pulsed mode, at 100% power of a
600 watt probe, of at least 0.0035 .mu.m.sup.-1.min.sup.-1.
86. The silica according to claim 67, having a (Sears
number.times.1000)/(BET specific surface area (S.sub.BET)) ratio of
less than 60.
87. The silica according to claim 67, having an object size such
that the mode of the particle size distribution measured by XDC
particle size analysis after ultrasonic disintegration satisfies
the following condition: XDC mode
(nm).gtoreq.(5320/S.sub.CTAB(m.sup.2/g))+8.
88. The silica according to claim 67, having a pore volume
(V.sub.80) formed by the pores having a diameter of between 3.7 and
80 nm of at least 1.35 cm.sup.3/g.
89. The silica according to claim 67, wherein the CTAB specific
surface area (S.sub.CTAB) is of between 60 and 330 m.sup.2/g; and
the BET specific surface area (S.sub.BET) of between 70 and 350
m.sup.2/g.
90. The silica according to claim 67, wherein the CTAB specific
surface area (S.sub.CTAB) is of between 90 and 230 m.sup.2/g.
91. The silica according to claim 67, wherein the BET specific
surface area (S.sub.BET) is of between 110 and 270 m.sup.2/g.
92. The silica according to claim 67, having a
(S.sub.BET-S.sub.CTAB).gtor- eq.5 m.sup.2/g.
93. The silica according to claim 67, having a
(S.sub.BET-S.sub.CTAB)<5- 0 m.sup.2/g.
94. The silica according to claim 67, being in the form of
approximately spherical beads having a mean size of at least 80
.mu.m.
95. The silica according to claim 67, being in the form of a powder
having a mean size of at least 15 .mu.m.
96. The silica according to claim 67, being in the form of granules
having a mean size of at least 1 mm.
97. A reinforcing filler for polymers, comprising a silica as
defined in claim 67.
98. A reinforcing filler in a natural rubber, comprising a silica
as defined in claim 67.
99. A shoe sole comprising a silica as defined in claim 67.
100. The shoe sole according to claim 99, further comprising
monoethoxydimethylsilylpropyl tetrasulphide.
Description
[0001] The present invention relates to a novel process for
preparing silica, to silicas having a particular particle size
distribution and/or a particular pore distribution, especially in
the form of powder, of approximately spherical beads or of
granules, and to their applications, such as the reinforcement of
polymers.
[0002] It is known to employ white reinforcing fillers in polymers,
particularly in elastomers, such as for example precipitated
silica.
[0003] It is an object of the invention to provide, in particular,
an alternative filler for polymer compositions, having a typical
characteristics, also providing them with a highly satisfactory
compromise of properties, in particular as regards their mechanical
and dynamic properties, without impairing their Theological
properties.
[0004] The invention firstly provides a novel process for preparing
silica, of the type comprising the reaction of a silicate with an
acidifying agent whereby a silica suspension is obtained, followed
by the separation and the drying of this suspension, characterized
in that the reaction of the silicate with the acidifying agent is
carried out according to the following successive steps:
[0005] (i) an aqueous stock having a pH of between 2 and 5 is
formed;
[0006] (ii) silicate and acidifying agent are added simultaneously
to the said stock in such a way that the pH of the reaction mixture
is maintained between 2 and 5;
[0007] (iii) the addition of the acidifying agent is stopped, while
continuing to add silicate into the reaction mixture until a pH
value of the reaction mixture of between 7 and 10 is obtained;
[0008] (iv) silicate and acidifying agent are added simultaneously
to the reaction mixture in such a way that the pH of the reaction
mixture is maintained between 7 and 10; and
[0009] (v) the addition of the silicate is stopped, while
continuing to add the acidifying agent into the reaction mixture
until a pH value of the reaction mixture of less than 6 is
obtained.
[0010] Thus, it has been found that the succession of particular
steps, in particular the presence of a first simultaneous addition
of acidifying agent and silicate in an acid medium at pH between 2
and 5 and of a second simultaneous addition of acidifying agent and
silicate in a basic medium of pH between 7 and 10, constitute
important conditions for giving the products obtained their
particular characteristics and properties.
[0011] The acidifying agent and the silicate are chosen in a manner
well known per se.
[0012] As acidifying agent, a strong mineral acid, such as
sulphuric acid, nitric acid or hydrochloric acid, or an organic
acid, such as acetic acid, formic acid or carbonic acid, will in
general be used.
[0013] The acidifying agent may be dilute or concentrated; its
normality may be between 0.4 and 36N, for example between 0.6 and
1.5N.
[0014] In particular, in the case in which the acidifying agent is
sulphuric acid, its concentration may be between 40 and 180 g/l,
for example between 60 and 130 g/l.
[0015] However, as silicate, it is possible to use any standard
form of silicates such as metasilicates, disilicates and,
advantageously, an alkali metal silicate, especially sodium or
potassium silicate.
[0016] The silicate may have a concentration (expressed as
SiO.sub.2 content) of between 40 and 3-30 g/l, for example between
60 and 300 g/l, in particular between 60 and 260 g/l.
[0017] In general, sulphuric acid will generally be employed as the
acidifying agent, and sodium silicate as silicate.
[0018] If sodium silicate is used, this is generally present with
an SiO.sub.2/Na.sub.2O weight ratio of between 2.5 and 4, for
example between 3.2 and 3.8.
[0019] With regard more particularly to the preparation process of
the invention, the reaction between the silicate and the acidifying
agent takes place in a very specific manner according to the
following steps.
[0020] Firstly, an aqueous stock having a pH of between 2 and 5 is
formed.
[0021] Preferably, the stock formed has a pH of between 2.5 and 5,
especially between 3 and 4.5; this pH is, for example, between 3.5
and 4.5.
[0022] This initial stock may be obtained by addition of acidifying
agent to water so as to obtain a pH value of the stock between 2
and 5, preferably between 2.5 and 5, especially between 3 and 4.5,
and for example between 3.5 and 4.5.
[0023] It may also be obtained by addition of acidifying agent to a
water+silicate mixture so as to obtain this pH value.
[0024] It may also be prepared by addition of acidifying agent to a
stock containing preformed silica particles at a pH of less than 7,
so as to obtain a pH value between 2 and 5, preferably between 2.5
and 5, especially between 3 and 4.5 and for example between 3.5 and
4.5.
[0025] The stock formed in step (i) may optionally include an
electrolyte. However, it is preferable for no electrolyte to be
added during the preparation process, in particular in step
(i).
[0026] The term "electrolyte" is understood here in its normally
accepted meaning, that is to say it means any ionic or molecular
substance which, when it is in solution, decomposes or dissociates
to form ions or charged particles. As electrolyte, mention may be
made of a salt of the group of alkali-metal and alkaline-earth
metal salts, especially the salt of the metal of the initial
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 the case of the reaction of
a sodium silicate with sulphuric acid.
[0027] The second step (step (ii)) consists of a simultaneous
addition of acidifying agent and of silicate in such a way (in
particular with such flow rates) that the pH of the reaction
mixture is maintained between 2 and 5, preferably between 2.5 and
5, especially between 3 and 4.5, for example between 3.5 and
4.5.
[0028] This simultaneous addition is advantageously carried out in
such a way that the pH value of the reaction mixture is always
equal (to within .+-.0.2) to that reached at the end of the initial
step (i).
[0029] Next, in a step (iii), the addition of the acidifying agent
is stopped, while continuing to add silicate into the reaction
mixture so as to obtain a pH value of the reaction mixture of
between 7 and 10, preferably between 7.5 and 9.5.
[0030] It may then be advantageous for the reaction mixture, just
after this step (iii) and therefore just after the addition of
silicate has been stopped, to undergo a maturing step, especially
at the pH obtained after step (iii), and in general with stirring;
this maturing step may, for example, last 2 to 45 minutes, in
particular from 5 to 25 minutes, and preferably includes neither
addition of acidifying agent nor addition of silicate.
[0031] After step (iii) and the optional maturing step, acidifying
agent and silicate are again simultaneously added in such a manner
(in particular with such flow rates) that the pH of the reaction
mixture is maintained between 7 and 10, preferably between 7.5 and
9.5.
[0032] This second simultaneous addition (step (iv)) is
advantageously carried out in such a way that the pH value of the
reaction mixture is always equal (to within .+-.0.2) to that
achieved after the preceding step.
[0033] It should be noted that it is possible, between step (ii)
and step (iv), for example between, on the one hand, the optional
maturing step following step (iii) and, on the other hand, step
(iv), to add acidifying agent to the reaction mixture, the pH of
the reaction mixture after this addition of acidifying agent being,
however, between 7 and 9.5, preferably between 7.5 and 9.5.
[0034] Finally, in a step (v), the addition of the silicate is
stopped, while continuing to add acidifying agent into the reaction
mixture so as to obtain a pH value of the reaction mixture of less
than 6, preferably between 3 and 5.5, in particular between 3 and
5, for example between 3 and 4.5.
[0035] It may then be advantageous, after this step (v) and
therefore just after stopping the addition of acidifying agent, for
the reaction mixture to undergo a maturing step, especially at the
pH obtained after step (v), and in general with stirring; this
maturing step may last, for example, from 2 to 45 minutes, in
particular from 5 to 20 minutes, and preferably includes no
addition of acidifying agent nor addition of silicate.
[0036] The reaction vessel in which the entire reaction between the
silicate and the acidifying agent takes place is usually fitted
with suitable stirring equipment and with suitable heating
equipment.
[0037] The entire reaction between the silicate and the acidifying
agent is generally carried out between 70 and 95.degree. C., in
particular between 75 and 90.degree. C.
[0038] According to a variant of the invention, the entire reaction
between the silicate and the acidifying agent is carried out at a
constant temperature, usually between 70 and 95.degree. C., in
particular between 75 and 90.degree. C.
[0039] According to another 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 (for example
during steps (i) to (iii)) at between 70 and 85.degree. C., and
then the temperature is increased, preferably up to a value between
85 and 95.degree. C., at which value it is maintained (for example
during steps (iv) and (v)) until the end of the reaction.
[0040] After the steps that have just been described, a silica
slurry is obtained, which is then separated (by liquid-solid
separation).
[0041] The separation used in the preparation-process according to
the invention usually comprises filtration followed, if necessary,
by washing. The filtration is carried out using any suitable
method, for example by means of a filter press, a band filter or a
vacuum filter.
[0042] The silica suspension thus recovered (the filter cake) is
then dried.
[0043] This drying may be carried out using any means known per
se.
[0044] Preferably, the drying is spray drying. For this purpose,
any suitable type of spray dryer may be used, especially a turbine,
nozzle, liquid-pressure or two-fluid type spray dryer. In general,
when the filtration is carried out by means of a filter press, a
nozzle spray dryer is used, and when the filtration is carried out
by means of a vacuum filter, a turbine spray dryer is used.
[0045] It should be noted that the filter cake is not always under
conditions allowing spray drying, especially because of its high
viscosity. In a manner known per se, the cake is then subjected to
a disintegration operation. This operation may be carried out
mechanically, by passing the cake through a colloidal-type mill or
a ball mill. The disintegration is generally carried out in the
presence of an aluminium compound, in particular sodium aluminate,
and optionally in the presence of an acidifying agent, as described
above (in the latter case, the aluminium compound and the
acidifying agent are generally added simultaneously). The
disintegration operation makes it possible in particular to lower
the viscosity of the suspension to be subsequently dried.
[0046] When the drying is carried out by means of a nozzle spray
dryer, the silica that can then be obtained is usually in the form
of approximately spherical beads.
[0047] After the drying, a milling step may then be carried out on
the recovered product. The silica that can then be obtained is
generally in the form of a powder.
[0048] When the drying is carried out by means of a turbine spray
dryer, the silica that can then be obtained may be in the form of a
powder.
[0049] Finally, the product, dried (especially by a turbine spray
dryer) or milled as indicated above, may optionally be subjected to
an agglomeration step which consists, for example, of direct
compression, wet granulation (that is to say with the use of a
binder such as water, a silica suspension, etc.), extrusion or,
preferably, dry compacting. When the latter technique is used, it
may prove opportune, before carrying out the compacting operation,
for the pulverulent products to undergo de-aeration (an operation
also called predensification or degassing) so as to remove the air
included in the products and to ensure that they are more uniformly
compacted.
[0050] The silica that can then be obtained by this agglomeration
step is generally in the form of granules.
[0051] The silica powders, like the silica beads, obtained by the
process according to the invention thus offer the advantage inter
alia of obtaining granules in a simple, effective and economic
manner, especially by conventional forming operations, such as for
example granulation or compacting, without these operations causing
any degradation liable to mask, or even destroy, the good intrinsic
properties that these powders or these beads have, as may be the
case in the prior art when processing conventional powders.
[0052] The preparation process according to the invention makes it
possible in particular to obtain silicas more of the
precipitative-silica type which, on the one hand, are highly
structured and non-friable and, on the other hand, generally have a
high dispersibility in polymers, give the latter a very
satisfactory compromise of properties, in particular as regards
their dynamic and mechanical properties (especially a good
reinforcing effect and very good abrasion resistance), without
impairing their Theological properties. The silicas obtained
preferably have a particular particle size distribution and/or pore
distribution.
[0053] The silicas that can be obtained by the process of the
invention constitute one of the aspects of the present
invention.
[0054] Further objects of the invention consist of novel silicas,
more of the precipitated-silica type, which are highly structured
and possess a specific particle size distribution and/or a
particular pore distribution; furthermore, they generally have good
dispersibility in polymers, give the latter a very satisfactory
compromise of properties, in particular as regards their dynamic
properties (especially a reduction in the strain energy dissipation
(low Payne effect), low hysteresis losses at high temperature
(especially a reduction in tan .delta. at 60.degree. C.) without
impairing their rheological properties (and therefore without
impairing their processability/formability (for example, a lower
green viscosity for the same specific surface area)) and possess
good mechanical properties, in particular a good reinforcing
effect, especially in terms of moduli, and very good abrasion
resistance, hence improved wear resistance in the case of finished
articles based on the said polymers.
[0055] In the description that follows, the BET specific surface
area is determined using the Brunauer-Emmet-Teller method described
in "The Journal of the American Chemical Society", Vol. 60, page
309, February 1938 and corresponding to the International Standard
ISO 5794/1 (Appendix D).
[0056] The CTAB specific surface area is the external surface area
determined according to the NF T 45007 (November 1987) (5.12)
standard.
[0057] The DOP oil uptake is determined according to the NF T
30-022 (March 1953) standard using dioctyl phthalate.
[0058] The pH is measured according to the ISO 787/9 standard (the
pH of a 5% suspension in water).
[0059] The XDC particle size analysis method, using centrifugal
sedimentation, by which, on the one hand, the size distribution
widths of silica objects and, on the other hand, the XDC mode
illustrating its size of objects were measured, is described
below.
[0060] Equipment Needed:
[0061] BI-XDC (Brookhaven Instrument X Disc Centrifuge) centrifugal
sedimentation particle size analyser sold by Brookhaven Instrument
Corporation;
[0062] 50 ml tall form beaker;
[0063] 50 ml graduated measuring cylinder; P1 1500 watt Branson
ultrasonic probe, with no endpiece, 13 mm in diameter;
[0064] deionized water;
[0065] ice-filled crystallizer;
[0066] magnetic stirrer.
[0067] Measurement Conditions:
[0068] DOS 1.35 version of the software (supplied by the
manufacturer of the particle size analyser);
[0069] fixed mode;
[0070] rotation speed;
[0071] duration of the analysis: 120 minutes;
[0072] density (silica): 2.1;
[0073] volume of the suspension to be sampled: 15 ml.
[0074] Preparation of the Specimen:
[0075] add 3.2 g of silica and 40 ml deionized water to the tall
form beaker;
[0076] put the beaker containing the suspension in the ice-filled
crystallizer;
[0077] immerse the ultrasonic probe in the beaker;
[0078] disintegrate the suspension for 16 minutes using the 1500
watt Branson probe (used at 60% of maximum power);
[0079] after the disintegration, put the beaker on a magnetic
stirrer.
[0080] Preparation of the Particle Size Analyser:
[0081] turn the apparatus on and leave to heat for 30 minutes;
[0082] rinse the disc twice with deionized water;
[0083] introduce 15 ml of the specimen to be analysed into the disc
and start the stirring;
[0084] enter into the software the above-mentioned measurement
conditions;
[0085] make the measurements;
[0086] when the measurements have been taken:
[0087] stop the disc rotating;
[0088] rinse the disc several times with deionized water;
[0089] stop the apparatus.
[0090] Results
[0091] In the apparatus register, record the values of the 16 wt %,
50 wt % (or median) and 84 wt % let-through diameters and the value
of the mode (the derivative of the cumulative particle size curve
gives a frequency curve the abscissa of the maximum of which
(abscissa of the main population) is called the mode).
[0092] The size distribution width L.sub.d of objects, measured by
XDC particle size analysis, after ultrasonic disintegration (in
water), corresponds to the (d84-d16)/d50 ratio in which dn is the
size for which n % of particles (by weight) have a size smaller
than that size (the distribution width L.sub.d is therefore
calculated from the cumulative particle size curve taken in its
entirety).
[0093] The size distribution width L'.sub.d of objects smaller than
500 nm, measured by XDC particle size analysis, after ultrasonic
disintegration (in water), corresponds to the (d84-d16)/d50 ratio
in which dn is the size for which n % of particles (by weight),
with respect to the particles smaller in size than 500 nm, have a
size smaller than that size (the distribution width L'.sub.d is
therefore calculated from the cumulative particle size curve
truncated above 500 nm).
[0094] In addition, using this centrifugal sedimentation XDC
particle size analysis method, it is possible to measure a
weight-average size of the particles (that is to say of the
secondary particles or aggregates), denoted d.sub.w, after
dispersion, by ultrasonic disintegration, of the silica in water.
The method differs from that described above by the fact that the
suspension formed (silica+deionized water) is disintegrated, on the
one hand, for 8 minutes and, on the other hand, using a 1500 watt
1.9 cm VIBRACELL ultrasonic probe (sold by Bioblock) (the probe
being used at 60% of maximum power). After analysis (sedimentation
for 120 minutes), the weight distribution of particle sizes is
calculated by the software of the particle size analyser. The
weight-average geometrical mean of the particle sizes (Xg according
to the nomenclature of the software), denoted d.sub.w, is
calculated by the software from the following equation: 1 log d w =
1 n m i log d i / 1 n m i ,
[0095] m.sub.i being the mass of all of the objects in the class of
size d.sub.i.
[0096] The pore volumes given are measured by mercury porosimetry;
each specimen is prepared as follows: each specimen is predried for
2 hours in an oven at 200.degree. C. and then placed in a test
container within 5 minutes following its removal from the oven and
vacuum-degassed, for example using a rotary vane pump; the pore
diameters (AUTOPORE III 9420 Micromeritics porosimeter) are
calculated by the Washburn equation with a contact angle .theta. of
140.degree. and a surface tension .gamma. of 484 dynes/cm (or
N/m).
[0097] V.sub.(d5-d50) represents the pore volume formed by the
pores of diameters between d5 and d50 and V.sub.(d5-d100)
represents the pore volume formed by the pores of diameters between
d5 and d100, dn here being the pore diameter for which n % of the
total surface area of all the pores is formed by the pores of
diameter greater than that diameter (the total surface area of the
pores (S.sub.0) may be determined from the mercury intrusion
curve).
[0098] The pore distribution width ldp is obtained by the pore
distribution curve, as indicated in FIG. 1, i.e. the pore volume
(in ml/g) as a function of the pore diameter (in nm): the
coordinates of the point S corresponding to the principal
population, namely the values of the diameter X.sub.S (in nm) and
the pore volume Y.sub.S (in ml/g), are recorded; a straight line of
the equation Y=Y.sub.S/2 is plotted; this straight line cuts the
pore distribution curve at two points A and B on either side of
X.sub.S, the abscissae (in nm) of points A and B being X.sub.A and
X.sub.B, respectively; the pore distribution width pdw is equal to
the ratio (X.sub.A-X.sub.B)/X.sub.S.
[0099] In some cases, the dispersibility (and disintegratability)
of the silicas according to the invention may be quantified by
means of specific disintegration tests.
[0100] One of the disintegration tests is carried out according to
the following protocol:
[0101] The cohesion of the agglomerates is assessed by a particle
size measurement (using laser diffraction) carried out on a
suspension of silica ultrasonically disintegrated beforehand; in
this way, the disintegratability of the silica (the break-up of
objects from 0.1 to a few tens of microns) is measured.
[0102] The ultrasonic disintegration is carried out using a
Bioblock Vibracell sonifier (600-W) fitted with a 19 mm diameter
probe. The particle size measurement is carried out by laser
diffraction on a SYMPATEC particle size analyser.
[0103] Weighed in a pillbox (height: 6 cm and diameter: 4 cm) are 2
grams of silica to which 50 grams of deionized water are added: an
aqueous suspension containing 4% silica, which is homogenized for 2
minutes by magnetic stirring, is thus produced. Next, the
ultrasonic disintegration is carried out as follows: with the probe
immersed over a length of 4 cm, the output power is adjusted so as
to obtain a deflection of the needle of the power dial indicating
20%. The disintegration is carried out for 420 seconds. Next, the
particle size measurement is taken after a known volume (expressed
in ml) of the homogenized suspension has been introduced into the
container of the particle size analyser.
[0104] The value of the median diameter .O slashed..sub.50S (or
Sympatec median diameter) that is obtained is smaller the higher
the disintegratability of the silica. It is also possible to
determine the (10.times.volume of suspension (in ml)
introduced)/(optical density of the suspension detected by the
particle size analyser) ratio may also be determined (this optical
density is around 20). This ratio is indicative of the content of
particles of a size of less than 0.1 .mu.m, which particles are not
detected by the particle size analyser. This ratio is called the
ultrasonic Sympatec disintegration factor (F.sub.DS).
[0105] Another disintegration test is carried out according to the
following protocol:
[0106] The cohesion of the agglomerates is assessed by a particle
size measurement (using laser diffraction) carried out on a
suspension of silica ultrasonically disintegrated beforehand; in
this way, the disintegrability of the silica (break-up of objects
from 0.1 to a few tens of microns) is measured. The ultrasonic
disintegration is carried out using a Bioblock VIBRACELL sonifier
(600 W), used at 80% of maximum power, fitted with a 19 mm diameter
probe. The particle size measurement is carried out by laser
diffraction on a Malvern Mastersizer 2000 particle size
analyser.
[0107] 1 gram of silica is weighed in a pillbox (height: 6 cm and
diameter: 4 cm) and deionized water is added to bring the weight to
50 grams: an aqueous suspension containing 2% silica, which is
homogenized for 2 minutes by magnetic stirring, is thus produced.
Ultrasonic disintegration is then carried out for 420 seconds.
Next, the particle size measurement is taken after all of the
homogenized suspension has been introduced into the container of
the particle size analyser.
[0108] The value of the median diameter .O slashed..sub.50M (or
Malvern median diameter) that is obtained is smaller the higher the
disintegratability of the silica. It is also possible to determine
the (10.times.blue laser obscuration value)/(red laser obscuration
value) ratio. This ratio is indicative of the content of particles
smaller in size than 0.1 .mu.m. This ratio is called the Malvern
ultrasonic disintegration factor (F.sub.DM).
[0109] A disintegration rate, denoted .alpha., may be measured by
means of another ultrasonic disintegration test, at 100% power of a
600 watt probe, operating in pulsed mode (i.e.: on for 1 second/off
for 1 second) so as to prevent the ultrasonic probe from heating up
excessively during the measurement. This known test, forming the
subject matter for example of Application WO 99/28376 (see also
Applications WO 99/28380, WO 00/73372 and WO 00/73373), allows the
variation in the volume-average size of the particle agglomerates
to be continuously measured during sonification, according to the
indications given below. The set-up used consists of a laser
particle size analyser (of the MASTERSIZER S type sold by Malvern
Instruments: He--Ne laser source emitting in the red at a
wavelength of 632.8 nm) and of its preparation station (Malvern
Small Sample Unit MSX1), between which a continuous flux stream
treatment cell (Bioblock M72410) fitted with an ultrasonic probe
(600 watt VIBRACELL-type 12.7 mm sonifier sold by Bioblock) was
inserted. A small quantity (150 mg) of silica to be analysed is
introduced with 160 ml of water into the preparation station, the
rate of circulation being set at its maximum. At least three
consecutive measurements are carried out in order to determine,
using the known Fraunhofer calculation method (Malvern 3$$D
calculation matrix), the initial volume-average diameter of the
agglomerates, denoted d.sub.v[0]. Sonification (pulsed mode: on for
1 s/off for 1 s) is then applied at 100% power (i.e. 100% of the
maximum position of the tip amplitude) and the variation in the
volume-average diameter d.sub.v[t] as a function of time t is
monitored for about 8 minutes, a measurement being taken
approximately every 10 seconds. After an induction period (about
3-4 minutes), it is observed that the inverse of the volume-average
diameter 1/d.sub.v[t] varies linearly, or substantially linearly,
with time t (disintegration steady state). The rate of
disintegration .alpha. is calculated by linear regression from the
curve of variation of 1/d.sub.v[t] as a function of time t in the
disintegration steady state region (in general, between 4 and 8
minutes approximately); it is expressed in
.mu.m.sup.-1.min.sup.-1.
[0110] The aforementioned Application WO 99/28376 describes in
detail a measurement device that can be used for carrying out this
ultrasonic disintegration test. This device consists of a closed
circuit in which a stream of particle agglomerates in suspension in
a liquid can circulate. This device essentially comprises a
specimen preparation station, a laser particle size analyser and a
treatment cell. Setting to atmospheric pressure, within the
specimen preparation station and the actual treatment cell, makes
it possible for the air bubbles that form during sonification (i.e.
the action of the ultrasonic probe) to be continuously removed. The
specimen preparation station (Malvern Small Sample Unit MSX1) is
designed to receive the silica specimen to be tested (in suspension
in the liquid) and to make it circulate around the circuit at the
preset speed (potentiometer-maximum speed about 3 l/min) in the
form of a stream of liquid suspension. This preparation station
simply consists of a receiving container which contains the
suspension to be analysed and through which the said suspension
flows. It is equipped with a variable-speed stirring motor so as to
prevent any sedimentation of the particle agglomerates of the
suspension, a centrifuge mini-pump is designed to circulate the
suspension in the circuit; the inlet of the preparation station is
connected to the open air via an opening intended to receive the
charge specimen to be tested and/or the liquid used for the
suspension. Connected to the preparation station is a laser
particle size analyser (MASTERSIZER S) whose function is to
continuously measure, at regular time intervals, the volume-average
size d.sub.v of the agglomerates, as the stream passes, by a
measurement cell to which the recording means and the automatic
calculation means of the particle size analyser are coupled. It
will be briefly recalled here that laser particle size analysers
make use, in a known manner, of the principle of light diffraction
by solid objects in suspension in a medium whose refractive index
is different from that of the solid. According to the Fraunhofer
theory, there is a relationship between the size of the object and
the angle of diffraction of the light (the smaller the object the
larger the angle of diffraction). In practice, all that is required
is to measure the quantity of diffracted light for various angles
of diffraction in order to be able to determine the size
distribution (by volume) of the specimen, d.sub.v corresponding to
the volume-average size of this distribution
d.sub.v=.SIGMA.(n.sub.id.sub.i.sup.4)/.SIGMA.(n.sub.-
id.sub.i.sup.3) where n.sub.i is the number of objects of the class
of size or diameter d.sub.i). Finally, a treatment cell fitted with
an ultrasonic probe is inserted between the preparation station and
the laser particle size analyser, the said cell being able to
operate in continuous or pulsed mode and intended to continuously
break up the particle agglomerates as the stream passes. This
stream is thermostatically controlled by means of a cooling circuit
placed, within the cell, in a jacket surrounding the probe, the
temperature being controlled, for example, by a temperature probe
immersed in the liquid within the preparation station.
[0111] The Sears number is determined using the method described by
G. W. Sears in the article in Analytical Chemistry, Vol. 28, No.
12, December 1956 entitled "Determination of specific surface area
of colloidal silica by titration with sodium hydroxide".
[0112] The Sears number is the volume of 0.1M sodium hydroxide
solution needed to raise the pH of a 10 g/l silica suspension in a
200 g/l sodium chloride medium from 4 to 9.
[0113] To do this, 400 grams of sodium chloride are used to prepare
a 200 g/l sodium chloride solution acidified to pH 3 with a 1M
hydrochloric acid solution. The weighings are performed by means of
a Mettler precision balance. 150 ml of this sodium chloride
solution are delicately added to a 250 ml beaker into which a mass
M (in g) of the specimen to be analysed, corresponding to 1.5 grams
of dry silica, has been introduced beforehand. Ultrasound is
applied for 8 minutes to the dispersion obtained (Branson 1500 W
ultrasonic probe; 60% amplitude, 13 mm diameter), the beaker being
in an ice-filled crystallizer. The solution obtained is then
homogenized by magnetic stirring, using a bar magnet having
dimensions of 25 mm.times.5 mm. A check is made that the pH of the
suspension is less than 4, if necessary by adjusting it using a 1M
hydrochloric acid solution. Next, a 0.1M sodium hydroxide solution
is added at a rate of 2 ml/min by means of a Metrohm titrator pH
meter (672 Titroprocessor, 655 Dosimat) precalibrated using pH 7
and pH 4 buffer solutions. (The titrator pH meter was programmed as
follows: 1) Call up the "Get pH" program- and 2) Introduce the
following parameters: pause (wait time before the start of
titration): 3 s; reactant flow rate: 2 ml/min; anticipation
(adaptation of the titration rate to the slope of the pH curve):
30; stop pH: 9.40; critical EP (sensitivity of detection of the
equivalence point): 3; report (parameters for printing the
titration report): 2, 3 and 5 (i.e. creation of a detailed report,
list of measurement points and titration curve)). The exact volumes
V.sub.1 and V.sub.2 of sodium hydroxide solution added in order to
obtain a pH of 4 and a pH of 9, respectively, are determined by
interpolation. The Sears number for 1.5 grams of dry silica is
equal to ((V.sub.2-V.sub.1).times.1- 50)/(SC-M), where:
[0114] V.sub.1: volume of 0.1M sodium hydroxide solution at
pH.sub.1=4;
[0115] V.sub.2: volume of 0.1M sodium hydroxide solution at
pH.sub.2=9;
[0116] M: mass of the specimen (in g);
[0117] SC: solids content (in %).
[0118] The pore distribution width may possibly be also illustrated
by the parameter W/FI determined by mercury porosimetry. The
measurement is carried out using PASCAL 140 and PASCAL 440
porosimeters sold by ThermoFinnigan, operating in the following
manner: a quantity of specimen between 50 and 500 mg (in the
present case 140 mg) is introduced into a measurement cell. This
measurement cell is installed in the measurement unit of the
PASCAL-140 apparatus. The specimen is then vacuum-degassed for the
time needed to achieve a pressure of 0.01 kPa (typically around 10
minutes). The measurement cell is then filled with mercury. The
first part of the mercury intrusion curve Vp=f(P), where Vp is the
mercury intrusion volume and P is the applied pressure, for
pressures of less than 400 kPa, is determined using the PASCAL 140
porosimeter. The measurement cell is then installed in the
measurement unit of the PASCAL 440 porosimeter, the second part of
the mercury intrusion curve Vp=f(P) for pressures between 100 kPa
and 400 MPa being determined using the PASCAL 440 porosimeter. The
porosimeters are used in PASCAL mode so as to permanently adjust
the rate of mercury intrusion according to the variations in the
intrusion volume. The rate parameter in PASCAL mode is set to 5.
The pore radii Rp are calculated from the pressure values P using
the Washburn equation, assuming that the pores are cylindrical,
choosing a contact angle .theta. of 140.degree. and a surface
tension .gamma. of 480 dynes/cm (or N/m). The pore volumes Vp are
relative to the mass of silica introduced and are expressed in
cm.sup.3/g. The signal Vp=f(Rp) is smoothed by combining a
logarithmic filter ("smooth dumping factor" filter parameter
F=0.96) and a moving-average filter ("number of points to average"
filter parameter f=20). The pore size distribution is obtained by
calculating the derivative dVp/dRp of the smooth intrusion curve.
The fineness index FI is the pore radius value (expressed in {dot
over (a)}ngstroms) corresponding to the maximum of the pore size
distribution dVp/dRp. The mid-height width of the pore size
distribution dVp/dRp is denoted by W.
[0119] The number of silanols per nm.sup.2 of surface area is
determined by grafting methanol onto the surface of the silica.
Firstly, 1 gram of raw silica is put into suspension in 10 ml of
methanol, in a 110 ml autoclave (Top Industrie, reference
09990009). A bar magnet is introduced and the autoclave,
hermetically sealed and thermally insulated, is heated to
200.degree. C. (40 bar) on a magnetic stirrer, heating for 4 hours.
The autoclave is then cooled in a cold water bath. The grafted
silica is recovered by settling and the residual methanol is
evaporated in a stream of nitrogen. Finally, the grafted silica is
vacuum dried for 12 hours at 130.degree. C. The carbon content is
determined by an elemental analyser (NCS 2500 analyser from CE
Instruments) on the raw silica and on the grafted silica. This
quantitative determination is carried out on the grafted silica
within the three days following the end of drying--this is because
the humidity of the air or heat may cause hydrolysis of the
methanol grafting. The number of silanols per nm.sup.2 is then
calculated using the following formula:
N.sub.SiOH/nm.sub..sup.2=[(% C.sub.g-%
C.sub.r).times.6.023.times.10.sup.2-
3]/[S.sub.BET.times.10.sup.18.times.12.times.100]
[0120] where % C.sub.g: percent mass of carbon present on the
grafted silica;
[0121] % C.sub.r: percent mass of carbon present on the raw
silica;
[0122] S.sub.BET: BET specific surface area of silica (in
m.sup.2/g).
[0123] According to a first variant of the invention, a novel
silica will now be proposed which is characterized in that it
possesses:
[0124] a CTAB specific surface area (S.sub.CTAB) of between 40 and
525 m.sup.2/g;
[0125] a BET specific surface area (S.sub.BET) of between 45 and
550 m.sup.2/g;
[0126] a size distribution width L.sub.d ((d84-d16)/d50) of objects
measured by XDC particle size analysis after ultrasonic
disintegration of at least 0.91, in particular at least 0.94,
and
[0127] a pore volume distribution as a function of the size of the
pores such that the ratio V.sub.(d5-d50)/V.sub.(d5-d100) is at
least 0.66, in particular at least 0.68.
[0128] The silica according to this variant of the invention
possesses, for example:
[0129] a size distribution width L.sub.d ((d84-d16)/d50) of objects
measured by XDC particle size analysis after ultrasonic
disintegration of at least 1.04; and
[0130] a pore volume distribution as a function of the size of the
pores such that the ratio V.sub.(d5-d50)/V.sub.(d5-d100) is at
least 0.71.
[0131] This silica may have a ratio V.sub.(d5-d50)/V.sub.(d5-d100)
of at least 0.73, in particular at least 0.74. This ratio may be at
least 0.78, especially at least 0.80 or even at least 0.84.
[0132] A second variant of the invention consists of a novel silica
characterized in that it possesses:
[0133] a CTAB specific surface area (S.sub.CTAB) of between 40 and
525 m.sup.2/g;
[0134] a BET specific surface area (S.sub.BET) of between 45 and
550 m.sup.2/g; and
[0135] a pore distribution width ldp of greater than 0.70, in
particular greater than 0.80, especially greater than 0.85.
[0136] This silica may have a pore distribution width ldp of
greater than 1.05, for example greater than 1.25 or even greater
than 1.40.
[0137] The silica according to this variant of the invention
preferably possesses a size distribution width L.sub.d
((d84-d16)/d50) of objects measured by XDC particle size analysis
after ultrasonic disintegration, of at least 0.91, in particular at
least 0.94, for example at least 1.0.
[0138] Also proposed, according to a third variant of the
invention, is a novel silica characterized in that it
possesses:
[0139] a CTAB specific surface area (S.sub.CTAB) of between 40 and
525 m.sup.2/g;
[0140] a BET specific surface area (S.sub.BET) of between 45 and
550 m.sup.2/g;
[0141] a size distribution width L'.sub.d ((d84-d16)/d50) of
objects smaller than 500 nm, measured by XDC particle size analysis
after ultrasonic disintegration, of at least 0.95; and
[0142] a pore volume distribution as a function of the size of the
pores such that the ratio V.sub.(d5-d50)/V.sub.(d5-d100) is at
least 0.71.
[0143] This silica may have a ratio V.sub.(d5-d50)/V.sub.(d5-d100)
of at least 0.73, in particular at least 0.74. This ratio may be at
least 0.78, especially at least 0.80 or even at least 0.84.
[0144] A fourth variant of the invention consists of a novel silica
characterized in that it possesses:
[0145] a CTAB specific surface area (S.sub.CTAB) of between 40 and
525 m.sup.2/g;
[0146] a BET specific surface area (S.sub.BET) of between 45 and
550 m.sup.2/g;
[0147] a size distribution width L.sub.d ((d84-d16)/d50) of objects
smaller than 500 nm, measured by XDC particle size analysis after
ultrasonic disintegration, of at least 0.90, in particular at least
0.92; and
[0148] a pore volume distribution as a function of 25 the size of
the pores such that the ratio V.sub.(d5-d50)/V.sub.(d5-d100) is at
least 0.74.
[0149] This silica may have a ratio V.sub.(d5-d50)/V.sub.(d5-d100)
of at least 0.78, especially at least 0.80 or even at least
0.84.
[0150] In the silicas according to the invention (that is to say
those in accordance with one of the four variants of the
invention), the pore volume provided by the coarsest pores usually
represents the largest proportion of the structure.
[0151] The silicas may have both an object size distribution width
L.sub.d of at least one 1.04 and an object size (smaller than 500
nm) distribution width L'.sub.d of at least 0.95.
[0152] The size distribution width L.sub.d of objects of the
silicas according to the invention may in certain cases be at least
1.10, in particular at least 1.20; it may be at least 1.30, for
example at least 1.50 or even at least 1.60.
[0153] Likewise, the object size (smaller than 500 nm) distribution
L'.sub.d of the silicas according to the invention may be, for
example, at least 1.0, in particular at least 1.10 and especially
at least 1.20.
[0154] Preferably, the silicas according to the invention possess a
particular surface chemistry such that they have a (Sears
number.times.1000)/(BET specific surface area (S.sub.BET)) ratio of
less than 60, preferably less than 55, for example less than
50.
[0155] The silicas according to the invention generally have a
high, and therefore a typical object size which may be such that
the mode of their particle size distribution measured by XDC
particle size analysis after ultrasonic disintegration (in water)
satisfies the condition: XDC mode (nm).gtoreq.(5320/S.sub.CTMB
(m.sup.2/g))+8, or even the condition: XDC mode (in
nm).gtoreq.(5320/S.sub.CTAB (m.sup.2/g))+10.
[0156] The silicas according to the invention may possess, for
example, a pore volume (V.sub.80) formed by the pores having
diameters between 3.7 and 80 nm of at least 1.35 cm.sup.3/g, in
particular at least 1.40 cm.sup.3/g or even at least 1.50
cm.sup.3/g.
[0157] The silicas according to the invention preferably have a
satisfactory dispersibility in polymers.
[0158] Their median diameter (.O slashed..sub.50S), after
ultrasonic disintegration, is in general less than 8.5 .mu.m; it
may be less than 6.0 .mu.m, for example less than 5.5 .mu.m.
[0159] Likewise, their median diameter (.O slashed..sub.50M), after
ultrasonic disintegration, is in general less than 8.5 .mu.m, it
may be less than 6.0 .mu.m, for example less than 5.5 .mu.m.
[0160] They may also possess a rate of disintegration, denoted by
.alpha., measured in the test referred to previously as ultrasonic
disintegration in pulsed mode, at 100% power of a 600 watt probe,
of at least 0.0035 .mu.m.sup.-1.min.sup.-1, in particular at least
0.0037 .mu.m.sup.-1.min.sup.-1.
[0161] The silicas according to the invention may have an
ultrasonic disintegration factor (F.sub.DS) of greater than 3 ml,
in particular greater than 3.5 ml, especially greater than 4.5
ml.
[0162] Their ultrasonic disintegration factor (F.sub.DM) may be
greater than 6, in particular greater than 7, especially greater
than 11.
[0163] The silicas according to the present invention may have a
weight-average particle size, measured by XDC particle size
analysis after ultrasonic disintegration, d.sub.w, of between 20
and 300 nm, especially between 30 and 300 nm, for example between
40 and 160 nm.
[0164] In general, the silicas according to the present invention
also have at least one, or even all, of the following three
characteristics:
[0165] a particle size distribution such that
d.sub.w.gtoreq.(16,500/S.sub- .CTAB)-30;
[0166] a porosity such that W/FI.gtoreq.-0.0025 S.sub.CTAB+0.85;
and
[0167] a number of silanols per unit area,
N.sub.SiOH/nm.sub..sup.2, such that
N.sub.SiOH.sub..sup.2.ltoreq.-0.027 S.sub.CTAB+10.5.
[0168] According to one embodiment, the silicas according to the
invention generally have:
[0169] a CTAB specific surface area (S.sub.CTAB) of between 60 and
330 m.sup.2/g, in particular between 80 and 290 m.sup.2/g;
[0170] a BET specific surface area (S.sub.BET) of between 70 and
350 m.sup.2/g, in particular between 90 and 320 m.sup.2/g.
[0171] Their CTAB specific surface area may be between 90 and 230
m.sup.2/g, especially between 95 and 200 m.sup.2/g, for example
between 120 and 190 m.sup.2/g.
[0172] Likewise, their BET specific surface area may be between 110
and 270 m.sup.2/g, especially between 115 and 250 m.sup.2/g, for
example between 135 and 235 m.sup.2/g.
[0173] According to another embodiment, the silicas according to
the invention generally have:
[0174] a CTAB specific surface area of between 40 and 380
m.sup.2/g, in particular between 45 and 280 m.sup.2/g; and
[0175] a BET specific surface area of between 45 and 400 m.sup.2/g,
in particular between 50 and 300 m.sup.2/g.
[0176] Their CTAB specific surface area may be between 115 and 260
m.sup.2/g, especially between 145 and 260 m.sup.2/g.
[0177] Likewise, their BET specific surface area may be between 120
and 280 m.sup.2/g, especially between 150 and 280 m.sup.2/g.
[0178] The silicas according to the present invention may have a
certain microporosity; thus, the silicas according to the invention
usually are such that (S.sub.BET-S.sub.CTAB).gtoreq.5 m.sup.2/g, in
particular .gtoreq.15 m.sup.2/g, for example .gtoreq.25
m.sup.2/g.
[0179] This microporosity is not in general too great: the silicas
according to the invention are generally such that
(S.sub.BET-S.sub.CTAB)<50 m.sup.2/g, preferably <40
m.sup.2/g.
[0180] The pH of the silicas according to the invention is usually
between 6.3 and 7.8, especially between 6.6 and 7.5.
[0181] They possess a DOP oil uptake that varies, usually, between
220 and 330 ml/100 g, for example between 240 and 300 ml/100 g.
[0182] They may be in the form of approximately spherical beads
with a mean size of at least 80 .mu.M.
[0183] This mean size of the beads may be at least 100 .mu.m, for
example at least 150 .mu.m; it is in general at most 300 .mu.m and
preferably lies between 100 and 270 .mu.m. This mean size is
determined according to the NF X 11507 (December 1970) standard by
dry screening and determination of the diameter corresponding to a
cumulative oversize of 50%.
[0184] The silicas according to the invention may also be in the
form of powder having a mean size of at least 15 .mu.m; for
example, it is between 15 and 60 .mu.m (especially between 20 and
45 .mu.m) or between 30 and 150 .mu.m (especially between 45 and
120 .mu.m).
[0185] They may also be in the form of granules having a size of at
least 1 mm, in particular between 1 and 10 mm, along the axis of
their largest dimension (length).
[0186] The silicas according to the invention are preferably
prepared by the preparation process according to the invention and
described above.
[0187] The silicas according to the invention or those prepared by
the process according to the invention find particularly useful
application in the reinforcement of natural or synthetic
polymers.
[0188] The polymer compositions in which they are used, especially
as reinforcing filler, are in general based on one or more polymers
or copolymers, in particular one or more elastomers, especially
thermoplastic elastomers, preferably having at least one glass
transition temperature between -150 and +300.degree. C., for
example between -150 and +20.degree. C.
[0189] As possible polymers, mention may be made of diene polymers,
in particular diene elastomers.
[0190] For example, it is possible to use polymers or copolymers
derived from aliphatic or aromatic monomers comprising at least one
unsaturated group (such as especially ethylene, propylene,
butadiene, isoprene and styrene), polybutyl acrylate, or blends
thereof; mention may also be made of silicone elastomers,
functionalized elastomers (for example those functionalized by
functional groups capable of reacting with the surface of the
silica) and halogenated polymers. Polyamides may be mentioned.
[0191] The polymer (or copolymer) may be a bulk polymer (or
copolymer), a polymer (or copolymer) latex or a solution of a
polymer (or copolymer) in water or in any other suitable dispersing
liquid.
[0192] As diene elastomers, mention may be made, for example, of
polybutadienes (BR), polyisoprenes (IR), butadiene copolymers,
isoprene copolymers, or blends thereof, and in particular
styrene-butadiene copolymers (SBR, especially emulsion
styrene-butadiene copolymers ESBR or solution styrene-butadiene
copolymers SSBR), isoprene-butadiene copolymers (BIR),
isoprene-styrene copolymers (SIR), styrene-butadiene-isoprene
copolymers (SBIR) and ethylene-propylene-diene terpolymers
(EPDM).
[0193] Mention may also be made of natural rubber (NR).
[0194] The polymer compositions may be sulphur-vulcanized
(vulcanisates are then obtained) or crosslinked, especially by
peroxides.
[0195] In general, the polymer compositions furthermore include at
least one coupling (silica/polymer) agent and/or at least one
covering agent; they may also include inter alia an
antioxidant.
[0196] It is possible in particular to use, as coupling agents,
what are called "symmetrical" or "asymmetrical", polysulphide-based
silanes, these being given as non-limiting examples; mention may
more particularly be made of bis((C.sub.1-C.sub.4)alkoxyl
-(C.sub.1-C.sub.4)alkylsilyl(C.sub.1- -C.sub.4)alkyl polysulphides
(especially disulphides, trisulphides or tetrasulphides) such as,
for example, bis(3-(trimethoxysilyl)propyl) polysulphides or
bis(3-(triethoxysilyl)propyl) polysulphides. Mention may also be
made of monoethoxydimethylsilylpropyl tetrasulphide.
[0197] The coupling agent may be pregrafted onto the polymer.
[0198] It may also be employed in the free state (that is to say
not pregrafted) or grafted onto the surface of the silica. The same
applies to the optional covering agent.
[0199] The use of a silica according to the invention or a silica
prepared by the process according to the invention may allow the
quantity of coupling agent to be employed in reinforced polymer
compositions to be substantially reduced, for example by around
20%, while maintaining a substantially identical compromise of
properties.
[0200] The coupling agent may optionally be combined with a
suitable "coupling activator", that is to say a compound which,
when mixed with this coupling agent, increases the effectiveness of
the latter.
[0201] The proportion by weight of silica in the polymer
composition may vary over quite a wide range. Usually it represents
from 20 to 80%, for example 30 to 70%, of the quantity of
polymer(s).
[0202] The silica according to the invention may advantageously
constitute all of the inorganic reinforcing filler, and even all of
the reinforcing filler, of the polymer composition.
[0203] However, at least one other reinforcing filler, such as in
particular a commercial highly dispersible silica such as, for
example, Z1165 MP or Z1115 MP, a treated precipitated silica (for
example one "doped" using a cation such as aluminium), or another
inorganic reinforcing filler such as, for example, alumina, or even
an organic reinforcing filler, especially carbon black (optionally
covered with an inorganic layer, for example with silica), may
optionally be combined with this silica according to the invention.
The silica according to the invention therefore preferably
constitutes at least 50%, or even at least 80%, by weight of all of
the reinforcing filler.
[0204] Mention may be made, as non-limiting examples, of finished
articles based on the polymer compositions described above
(especially those based on the abovementioned vulcanisates), shoe
soles (preferably in the presence of a coupling (silica/polymer)
agent), floor coverings, gas barriers, fire-retarding materials and
also engineering components such as cable car wheels, seals for
domestic electrical appliances, seals for liquid or gas pipes,
seals for brake systems, sheaths or ducts, cables and drive
belts.
[0205] In the case of shoe soles, it is possible to use,
advantageously in the presence of a coupling (silica/polymer)
agent, polymer compositions based, for example, on natural rubber
(NR), polyisoprene (IR), polybutadiene (BR), styrene-butadiene
copolymer (SBR) and butadiene-acryonitrile copolymer (NBR).
[0206] For the engineering components, it is possible to use, for
example in the presence of a coupling (silica/polymer) agent,
polymer compositions based, for example, on natural rubber (NR),
polyisoprene (IR), polybutadiene (BR), styrene-butadiene copolymer
(SBR), polychloroprene, butadiene-acrylonitrile copolymer (NBR),
hydrogenated or carboxylated nitrile rubber, isobutylene-isoprene
copolymer (IIR), halogenated (especially brominated or chlorinated)
butyl rubber, ethylene-propylene copolymer (EPM),
ethylene-propylene-diene terpolymer (EPDM), chlorinated
polyethylene, chlorosulphonated polyethylene, epichlorohydrin
rubber, silicones, fluorocarbon rubber and polyacrylates.
[0207] The silicas according to the invention or those prepared by
the process according to the invention may also be employed as a
catalyst support, as an absorbent for active materials (in
particular a support for liquids, for example those used in food,
such as vitamins (vitamin E), choline chloride), as a
viscosity-modifying, texturing or anti-clumping agent, as an
element for battery separators, or as an additive for dentrifices
or for paper.
[0208] The following examples illustrate the invention without,
however, limiting the scope thereof.
EXAMPLE 1
[0209] 10 litres of purified water were introduced into a 25 litre
stainless steel reactor. The solution was heated to 80.degree. C.
The entire reaction was carried out at this temperature. 80 g/l of
sulphuric acid were introduced, with stirring (350 rpm, propeller
stirrer), until the pH reached a value of 4.
[0210] Simultaneously introduced into the reactor over 35 minutes
were a sodium silicate solution (having an SiO.sub.2/Na.sub.2O
weight ratio of 3.52) having a concentration of 230 g/l at a rate
of 76 g/min and sulphuric acid, having a concentration of 80 g/l,
at a rate set so as to maintain the pH of the reaction mixture at a
value of 4. After the 30th minute of addition, the stirring rate
was increased to 450 rpm.
[0211] At the end of 35 minutes of simultaneous addition, the
introduction of acid was stopped when the pH reached a value of 9.
The flow of silicate was then also stopped. The mixture was then
matured for 15 minutes at pH 9. At the end of maturing, the
stirring rate was reduced to 350 rpm.
[0212] Next, the pH was taken to pH 8 by introducing sulphuric
acid. A new simultaneous addition was carried out for 40 minutes
with a sodium silicate flow rate of 76 g/min (the same sodium
silicate as in the case of the first simultaneous addition) and a
flow rate of sulphuric acid, with a concentration of 80 g/l,
regulated so as to maintain the pH of the reaction mixture at a
value of 8.
[0213] After this simultaneous addition, the reaction mixture is
taken to a pH of 4 by sulphuric acid having a concentration of 80
g/l. The mixture is matured for 10 minutes at pH 4. 250 ml of
flocculant FA 10 (polyoxyethylene having a molar mass of
5.times.10.sup.6 g) at 1% were introduced after the 3rd minute of
the maturing.
[0214] The slurry was filtered and washed under vacuum (16.7%
solids content). After dilution (13% solids content), the cake
obtained was mechanically broken up. The resulting slurry was spray
dried by means of a turbine spray dryer.
[0215] The characteristics of the silica P1 obtained were then the
following:
[0216] CTAB specific surface area: 221 m.sup.2/g;
[0217] BET specific surface area: 240 m.sup.2/g;
[0218] V.sub.(d5-d50)/V.sub.(d5-d100): 0.74;
[0219] Width L.sub.d (XDC): 1.62;
[0220] Pore distribution width ldp: 1.42;
[0221] Width L'.sub.d (XDC): 1.27;
[0222] Sears number.times.1000/BET specific surface area: 42.9;
[0223] XDC mode: 39 nm;
[0224] Pore volume V.sub.80: 1.69 cm.sup.3/g;
[0225] .O slashed..sub.50S (after ultrasonic disintegration): 4.8
.mu.m;
[0226] F.sub.DS: 4.6 ml;
[0227] .alpha.: 0.00626 .mu.m.sup.-1.min.sup.-1;
[0228] d.sub.w: 79 nm;
[0229] W/FI: 0.62;
[0230] N.sub.SiOH/nm.sub..sup.2: 3.90.
EXAMPLE 2
[0231] 9.575 kg of purified water and 522 g of sodium silicate
(SiO.sub.2/Na.sub.2O weight ratio of 3.55) with a concentration of
235 g/l were introduced into a 25 litre stainless steel reactor.
The solution was heated to 80.degree. C. The entire reaction was
carried out at this temperature. Sulphuric acid, with a
concentration of 80 g/l, was introduced, with stirring (300 rpm,
propeller stirrer), until the pH reached a value of 4 (615 g of
acid introduced).
[0232] Simultaneously introduced into the reactor over 40 minutes
were a sodium silicate solution (having an SiO.sub.2/Na.sub.2O
weight ratio of 3.55) having a concentration of 235 g/l at a rate
of 50 g/min and sulphuric acid, having a concentration of 80 g/l,
at a rate set so as to maintain the pH of the reaction mixture at a
value of 4.
[0233] At the end of 40 minutes of simultaneous addition, the
introduction of acid was stopped when the pH reached a value of 9.
The flow of silicate was then also stopped. The mixture was then
matured for 15 minutes at pH 9 at 80.degree. C.
[0234] Next, the pH was taken to pH 8 by introducing sulphuric acid
over 2 minutes. A new simultaneous addition was carried out for 60
minutes with a sodium silicate flow rate of 76 g/min (the same
sodium silicate as in the case of the first simultaneous addition)
and a flow rate of sulphuric acid, with a concentration of 80 g/l,
regulated so as to maintain the pH of the reaction mixture at a
value of 8.
[0235] After this simultaneous addition, the reaction mixture is
taken to a pH of 4 over 5 minutes by sulphuric acid having a
concentration of 80 g/l. The mixture is matured for 10 minutes at
pH 4.
[0236] The slurry was filtered and washed under vacuum (5.5% cake
solids content). After dilution (12% solids content), the cake
obtained was mechanically broken up. The resulting slurry was spray
dried by means of a turbine spray dryer.
[0237] The characteristics of the silica P2 obtained were then the
following:
[0238] CTAB specific surface area: 182 m.sup.2/g;
[0239] BET specific surface area: 197 m.sup.2/g;
[0240] V.sub.(d5-d50)/V.sub.(d5-100): 0.76;
[0241] Width L'.sub.d (XDC): 1.12;
[0242] Pore distribution width ldp: 1.26;
[0243] Width L'.sub.d (XDC): 0.90;
[0244] XDC mode: 57 nm;
[0245] Pore volume V.sub.80: 1.40 cm.sup.3/g;
[0246] .O slashed..sub.50S (after ultrasonic disintegration): 4.1
.mu.m;
[0247] F.sub.DS: 4.0 ml.
EXAMPLE 3
[0248] 10 litres of sodium silicate (SiO.sub.2/Na.sub.2O weight
ratio of 3.55) with a concentration of 10 g/l were introduced into
a 25 litre stainless steel reactor. The solution was heated to
80.degree. C. The entire reaction was carried out at this
temperature. Sulphuric acid, with a concentration of 80 g/l, was
introduced, with stirring (300 rpm, propeller stirrer), until the
pH reached a value of 4 (615 g of acid introduced).
[0249] Simultaneously introduced into the reactor over 40 minutes
were a sodium silicate solution (having an SiO.sub.2/Na.sub.2O
weight ratio of 3.55) having a concentration of 230 g/l at a rate
of 50 g/min and sulphuric acid, having a concentration of 80 g/l,
at a rate set so as to maintain the pH of the reaction mixture at a
value of 4.
[0250] At the end of 40 minutes of simultaneous addition, the
introduction of acid was stopped when a pH of 8 was reached.
[0251] A new simultaneous addition was carried out for 60 minutes
with a sodium silicate flow rate of 50 g/min (the same sodium
silicate as in the case of the first simultaneous addition) and a
flow rate of sulphuric acid, with a concentration of 80 g/l, set so
as to maintain the pH of the reaction mixture at a value of 8.
[0252] After this simultaneous addition, the reaction mixture is
taken to a pH of 4 over 4 minutes by sulphuric acid having a
concentration of 80 g/l. The mixture is matured for 10 minutes at
pH 4.
[0253] The slurry was filtered and washed under vacuum (13.7% cake
solids content). After dilution (11.2% solids content), the cake
obtained was mechanically broken up. The resulting slurry was spray
dried by means of a turbine spray dryer.
[0254] The characteristics of the silica P3 were then the
following:
[0255] CTAB specific surface area: 228 m.sup.2 .mu.g;
[0256] BET specific surface area: 245 m.sup.2 .mu.g;
[0257] V.sub.(d5-d50)/V.sub.(d5-d100): 0.76;
[0258] Width L.sub.d (XDC): 1.48;
[0259] Pore distribution width ldp: 1.98;
[0260] Width L'.sub.d (XDC): 1.16;
[0261] XDC mode: 42 nm;
[0262] Pore volume V.sub.80: 1.48 cm.sup.3/g;
[0263] .O slashed..sub.50S (after ultrasonic disintegration): 4.4
.mu.m;
[0264] F.sub.DS: 4.3 ml.
EXAMPLE 4
[0265] 12 litres of a sodium silicate solution (SiO.sub.2/Na.sub.2O
weight ratio of 3.5) with a concentration of 10 g/l were introduced
into a 25 litre stainless steel reactor. The solution was heated to
80.degree. C. The entire reaction was carried out at this
temperature. Sulphuric acid, with a concentration of 80 g/l, was
introduced, with stirring (300 rpm, propeller stirrer), until the
pH reached a value of 8.9.
[0266] Simultaneously introduced into the reactor over 15 minutes
were a sodium silicate solution (having an SiO.sub.2/Na.sub.2O
weight ratio of 3.5) having a concentration of 230 g/l at a rate of
76 g/min and sulphuric acid, having a concentration of 80 g/l, at a
rate set so as to maintain the pH of the reaction mixture at a
value of 8.9. Thus, a sol of scarcely aggregated particles was
obtained. The sol was withdrawn and rapidly cooled using a copper
coil through which cold water circulates. The reactor was rapidly
cleaned.
[0267] 4 litres of purified water were introduced into the 25 litre
reactor. Sulphuric acid, having a concentration of 80 g/l, was
introduced until the pH reached a value of 4. A simultaneous
addition of the cold sol with a flow rate of 195 g/min and
sulphuric acid, having a concentration of 80 g/l, with a flow rate
allowing the pH to be set to 4, was carried out over 40 minutes. A
maturing step lasting 10 minutes was carried out.
[0268] After 40 minutes of simultaneous sol/sulphuric acid
addition, there was a simultaneous addition, over 20 minutes, of
sodium silicate with a flow rate of 76 g/min (the same sodium
silicate as in the case of the first simultaneous addition) and
sulphuric acid with a flow rate of 80 g/l set so as to maintain the
pH of the reaction mixture at a value of 4. After the 20 minutes,
the flow of acid was stopped when a pH of 8 was obtained.
[0269] A new simultaneous addition was carried out for 60 minutes
with a sodium silicate flow rate of 76 g/min (the same sodium
silicate as in the case of the first simultaneous addition) and a
flow rate of sulphuric acid, with a concentration of 80 g/l, set so
as to maintain the pH of the reaction mixture at a value of 8. The
stirring rate was increased when the mixture became very
viscous.
[0270] After this simultaneous addition, the reaction mixture is
taken to a pH of 4 over 5 minutes by sulphuric acid having a
concentration of 80 g/l. The mixture is matured for 10 minutes at
pH 4.
[0271] The slurry was filtered and washed under vacuum (15% cake
solids content). After dilution, the cake obtained was mechanically
broken up. The resulting slurry was spray dried by means of a
turbine spray dryer.
[0272] The characteristics of the silica P4 were then the
following:
[0273] CTAB specific surface area: 230 m.sup.2/g;
[0274] BET specific surface area: 236 m.sup.2/g;
[0275] V.sub.(d5-d50)/V.sub.(d5-d100): 0.73;
[0276] Width L.sub.d (XDC): 1.38;
[0277] Pore distribution width ldp: 0.67;
[0278] Width. L'.sub.d (XDC): 1.14;
[0279] XDC mode: 34 nm;
[0280] Pore volume V.sub.80: 1.42 cm.sup.3/g;
[0281] .O slashed..sub.50S (after ultrasonic disintegration): 3.8
.mu.m;
[0282] F.sub.DS: 4.6 ml.
EXAMPLE 5
[0283] 10 litres of a sodium silicate solution (SiO.sub.2/Na.sub.2O
weight ratio of 3.48) with a concentration of 5 g/l were introduced
into a 25 litre stainless steel reactor. The solution was heated to
80.degree. C. Sulphuric acid, with a concentration of 80 g/l, was
introduced, with stirring (300 rpm, propeller stirrer), until the
pH reached a value of 4.2.
[0284] Simultaneously introduced into the reactor over 30 minutes
were a sodium silicate solution (having an SiO.sub.2/Na.sub.2O
weight ratio of 3.48) having a concentration of 230 g/l at a rate
of 75 g/min and sulphuric acid, having a concentration of 80 g/l,
at a rate set so as to maintain the pH of the reaction mixture at a
value of 4.2.
[0285] After 30 minutes of simultaneous addition, the introduction
of acid was stopped when the pH reached a value of 9. The flow of
silicate was then also stopped. A maturing step was carried out for
15 minutes at pH 9, while progressively increasing the temperature
(over 15 minutes) from 80 to 90.degree. C., at which value the rest
of the reaction was carried out.
[0286] Next, the pH was brought to pH 8 by introducing sulphuric
acid having a concentration of 80 g/l. There was then a new
simultaneous addition, carried out over 50 minutes, of sodium
silicate at a rate of 76 g/min (the same sodium silicate as in the
first simultaneous addition) and of sulphuric acid, with a
concentration of 80 g/l, at a rate set so as to maintain the pH of
the reaction mixture at a value of 8.
[0287] After this simultaneous addition, the reaction mixture is
taken to a pH of 4 by sulphuric acid having a concentration of 80
g/l. The mixture is matured for 10 minutes at pH 4.
[0288] The slurry was filtered and washed under vacuum (19.6% cake
solids content). After dilution (10% solids content), the cake
obtained was mechanically broken up. The resulting slurry was spray
dried by means of a turbine spray dryer.
[0289] The characteristics of the silica P5 obtained were then the
following:
[0290] CTAB specific surface area: 135 m.sup.2/g;
[0291] BET specific surface area: 144 m.sup.2 .mu.g;
[0292] V.sub.(d5-d50)/V.sub.(d5-d100): 0.76;
[0293] Width L.sub.d (XDC): 1.52;
[0294] Pore distribution width ldp: 2.65;
[0295] Width L'.sub.d (XDC): 0.92;
[0296] Sears number.times.1000/BET specific surface
[0297] area: 49.3;
[0298] XDC mode: 57 nm;
[0299] Pore volume V.sub.80: 1.12 cm.sup.3/g;
[0300] .O slashed..sub.50S (after ultrasonic disintegration): 5.9
.mu.m;
[0301] d.sub.w: 159 nm;
[0302] W/FI: 1.47;
[0303] N.sub.SiOH/nm.sub..sup.2: 5.20.
EXAMPLE 6
[0304] Three polymer compositions were prepared:
[0305] one containing highly dispersible precipitated silica Z1165
MP, sold by Rhodia, having a density of 2.1 g/cm.sup.3, and a
coupling agent (reference composition R1);
[0306] the other two each containing silica prepared in Example 4
and a coupling agent (compositions C1 and C2).
[0307] Silica Z1165 MP had the following characteristics:
[0308] CTAB specific surface area: 160 m.sup.2/g;
[0309] Width L.sub.d (XDC): 0.56; Pore distribution width ldp:
0.50;
[0310] Width L'.sub.d (XDC): 0.56;
[0311] XDC mode: 41 nm;
[0312] Pore volume V.sub.80: 1.12 cm.sup.3/g;
[0313] .O slashed..sub.50S (after ultrasonic disintegration)<6
.mu.m;
[0314] .alpha.: 0.0049 .mu.m.sup.-1.min.sup.-1;
[0315] d.sub.w: 59 nm;
[0316] W/FI: 0.39;
[0317] N.sub.SiOH/nm.sub..sup.2: 8.10.
1TABLE 1 (compositions in parts by weight) Composition R1
Composition C1 Composition C2 SBR.sup.(1) 100 100 100 Silica
Z1165MP 50 0 0 Silica of 0 50 50 Example 4 Silane Si69.sup.(2) 4 4
6.25 Diphenylguanidine 1.45 1.45 1.45 Stearic acid 1.1 1.1 1.1 Zinc
oxide 1.82 1.82 1.82 Antioxidant.sup.(3) 1.45 1.45 1.45
Sulphenamide.sup.(4) 1.3 1.3 1.3 Sulphur 1.1 1.1 1.1
.sup.(1)Solution-synthesized styrene-butadiene copolymer (BUNA VSL
5525-0 type) not oil-extended; .sup.(2)Filler/polymer coupling
agent (sold by Degussa); .sup.(3)N-(1,3-dimethylbutyl)-N'-phenyl--
p-phenylenediamine; .sup.(4)N-cyclohexyl-2-benzothiazyl
sulphenamide (CBS).
[0318] Composition C1 contained a quantity of coupling agent
identical to that of reference composition R1. Composition C2
contained an optimized quantity of coupling agent with regard to
the specific surface area of the silica used (Example 4).
[0319] The compositions were prepared by thermomechanically working
the elastomers in an internal mixer (of the Brabender type) having
a volume of 75 cm.sup.3, in two steps, with a mean blade speed of
50 revolutions/minute until a temperature of 120.degree. C. was
obtained, these steps being followed by a finishing step carried
out on an external mixer.
[0320] The vulcanization temperature was chosen to be 170.degree.
C. The vulcanization conditions for the compositions were tailored
to the vulcanization rates of the corresponding compounds.
[0321] The properties of the compositions are given below, the
measurements having been carried out (on the vulcanized
compositions) according to the following standards and/or
methods:
[0322] Vulcanization Properties (Rheological Properties)
[0323] (Green properties--Rheometry at 170.degree. C., t=30
minutes)
[0324] NF T 43015 standard.
[0325] A Monsanto 100 S rheometer was used especially for the
measurement of the minimum torque (C.sub.min) and the maximum
torque (C.sub.max).
[0326] Ts2 corresponded to the time over which it was possible to
monitor the mixture; the polymer mixture cured after Ts2 (start of
vulcanization).
[0327] T90 corresponded to the time it took for the mixture to
undergo 90% vulcanization.
[0328] Mechanical Properties (of the Compositions Vulcanized at
170.degree. C.)
[0329] Tensile properties (moduli): NF T 46002 standard
[0330] The x % moduli corresponded to the stress measured at a
tensile strain of x %.
2TABLE 2 Vulcanization Composition R1 Composition C1 Composition C2
Cmin (in .multidot. lb) 10 21 14 Ts2 (min) 3.1 2.1 3.1 T90 (min)
29.4 42.0 36.4 C.sub.max (in .multidot. lb) 91 97.5 103 Mechanical
10% modulus 0.95 1.3 1.05 (MPa) 100% modulus 3.6 4.0 4.6 (MPa) 200%
modulus 9.5 9.8 12.2 (MPa)
[0331] It may be seen that compositions C1 and C2 containing a
silica according to the invention exhibit a useful compromise of
properties compared with that of reference composition R1.
[0332] Despite the unoptimized vulcanization conditions,
composition C1 led to a more pronounced reinforcement in terms of
moduli than reference composition R1.
[0333] The adjustment in coupling agent content made in the case of
composition C2 results in a vulcanization rate comparable to that
of reference composition R1; in addition, composition C2 has moduli
(in particular, 100% and 200% moduli) very much higher than those
obtained with reference composition R1.
EXAMPLE 7
[0334] 10 litres of a sodium silicate solution (SiO.sub.2/Na.sub.2O
weight ratio of 3.53) with a concentration of 5 g/l were introduced
into a 25 litre stainless steel reactor. The solution was heated to
80.degree. C. Sulphuric acid, with a concentration of 80 g/l, was
introduced, with stirring (300 rpm, propeller stirrer), until the
pH reached a value of 4.2.
[0335] Simultaneously introduced into the reactor over 35 minutes
were a sodium silicate solution (having an SiO.sub.2/Na.sub.2O
weight ratio of 3.53) having a concentration of 230 g/l at a rate
of 50 g/min and sulphuric acid, having a concentration of 80 g/l,
at a rate set so as to maintain the pH of the reaction mixture at a
value of 4.2.
[0336] After 35 minutes of simultaneous addition, the introduction
of acid was stopped when the pH reached a value of 9. The flow of
silicate was then also stopped. A maturing step was carried out for
15 minutes at pH 9, while progressively increasing the temperature
(over 15 minutes) from 80 to 90.degree. C., at which value the rest
of the reaction was carried out.
[0337] Next, the pH was brought to pH 8 by introducing sulphuric
acid having a concentration of 80 g/l. There was then a new
simultaneous addition, carried out over 50 minutes, of sodium
silicate at a rate of 50 g/min (the same sodium silicate as in the
first simultaneous addition) and of sulphuric acid, with a
concentration of 80 g/l, at a rate set so as to maintain the pH of
the reaction mixture at a value of 8.
[0338] After this simultaneous addition, the reaction mixture is
taken to a pH of 4 by sulphuric acid having a concentration of 80
g/l. The mixture is matured for 10 minutes at pH 4.
[0339] The slurry was filtered and washed under vacuum (16.8% cake
solids content). After dilution (10% solids content), the cake
obtained was mechanically broken up. The resulting slurry was spray
dried by means of a turbine spray dryer.
[0340] The characteristics of the silica P6 obtained were then the
following:
[0341] CTAB specific surface area: 170 m.sup.2/g;
[0342] BET specific surface area: 174 m.sup.2/g;
[0343] V.sub.(d5-d50)/V(d.sub.5-d100): 0.78;
[0344] Width L.sub.d (XDC): 3.1;
[0345] Pore distribution width ldp: 1.42;
[0346] Width L'.sub.d (XDC): 2.27;
[0347] Sears number.times.1000/BET specific surface area: 50.6;
[0348] XDC mode: 41 nm;
[0349] Pore volume V.sub.80: 1.38 cm.sup.3/g;
[0350] .O slashed..sub.50S (after ultrasonic disintegration): 4.3
.mu.m;
[0351] F.sub.DS: 3.7 ml;
[0352] .alpha.: 0.00883 .mu.m.sup.-1.min.sup.-1;
[0353] d.sub.w: 98 nm;
[0354] W/FI: 0.78;
[0355] N.sub.SiOH/nm.sub..sup.2: 4.40.
EXAMPLE 8
[0356] Introduced into a 2000 litre reactor were 700 litres of
industrial water. This solution was heated to 80.degree. C. by
direct injection heating of steam. Sulphuric acid, with a
concentration of 80 g/l, was introduced, with stirring (95 rpm),
until the pH reached a value of 4.
[0357] Simultaneously introduced into the reactor over 35 minutes
were a sodium silicate solution (having an SiO.sub.2/Na.sub.2O
weight ratio of 3.52) having a concentration of 230 g/l at a rate
of 190 l/hour and sulphuric acid, having a concentration of 80 g/l,
at a rate set so as to maintain the pH of the reaction mixture at a
value of 4.
[0358] After 35 minutes of simultaneous addition, the introduction
of acid was stopped when the pH reached a value of 8. There was
then a new simultaneous addition, carried out over 40 minutes, of
sodium silicate at a rate of 190 l/hour (the same sodium silicate
as in the first simultaneous addition) and of sulphuric acid, with
a concentration of 80 g/l, at a rate set so as to maintain the pH
of the reaction mixture at a value of 8.
[0359] After this simultaneous addition, the reaction mixture is
taken to a pH of 5.2 by sulphuric acid having a concentration of 80
g/l. The mixture is matured for 5 minutes at pH 5.2.
[0360] The slurry was filtered and washed in a filter press (22%
cake solids content). The cake obtained was broken up by adding a
quantity of sodium aluminate corresponding to an Al/SiO.sub.2
weight ratio of 0.3%. The resulting slurry was spray dried by means
of a nozzle spray drier.
[0361] The characteristics of the silica obtained P7 in the form of
approximately spherical beads were then the following:
[0362] CTAB specific surface area: 200 m.sup.2/g;
[0363] BET specific surface area: 222 m.sup.2/g;
[0364] V.sub.(d5-d50)/V.sub.(d5-d100): 0.71;
[0365] Width L.sub.d (XDC): 1.0;
[0366] Pore distribution width ldp: 1.51;
[0367] Width L'.sub.d (XDC): 0.93;
[0368] Sears number.times.1000/BET specific surface area: 31.5;
[0369] XDC mode: 34 nm;
[0370] Pore volume V.sub.80: 1.44 cm.sup.3/g;
[0371] Mean particle size: >150 .mu.m;
[0372] .O slashed..sub.50S (after ultrasonic disintegration): 4.8
.mu.m;
[0373] F.sub.DS: 5.4 ml;
[0374] .O slashed..sub.50M (after ultrasonic disintegration): 5.0
.mu.m;
[0375] F.sub.Dm: 11.5;
[0376] .alpha.: 0.00566 .mu.m.sup.-1.min.sup.-1;
[0377] d.sub.w: 68 nm;
[0378] W/FI: 0.70;
[0379] N.sub.SiOH/nm.sub..sup.2: 4.50.
EXAMPLE 9
[0380] Introduced into a 2000 litre reactor were 700 litres of
industrial water. This solution was heated to 78.degree. C. by
direct steam injection heating. Sulphuric acid, with a
concentration of 80 g/l, was introduced, with stirring (95 rpm),
until the pH reached a value of 4.
[0381] Simultaneously introduced into the reactor over 35 minutes
were a sodium silicate solution (having an SiO.sub.2/Na.sub.2O
weight ratio of 3.52) having a concentration of 230 g/l at a rate
of 190 l/hour and sulphuric acid, having a concentration of 80 g/l,
at a rate set so as to maintain the pH of the reaction mixture at a
value of 4.
[0382] After 35 minutes of simultaneous addition, the introduction
of acid was stopped when the pH reached a value of 8. There was
then a new simultaneous addition, carried out over 40 minutes, of
sodium silicate at a rate of 190 l/hour (the same sodium silicate
as in the first simultaneous addition) and of sulphuric acid, with
a concentration of 80 g/l, at a rate set so as to maintain the pH
of the reaction mixture at a value of 8.
[0383] After this simultaneous addition, the reaction mixture is
taken to a pH of 5.2 by sulphuric acid having a concentration of 80
g/l. The mixture is matured for 5 minutes at pH 5.2.
[0384] The slurry was filtered and washed in a vacuum filter (18%
cake solids content). The cake obtained was broken up mechanically
using industrial water (10% of water added with respect to the
cake) by adding a quantity of sodium aluminate corresponding to an
Al/SiO.sub.2 weight ratio of 0.3%. The resulting slurry was spray
dried by means of a turbine spray drier.
[0385] The characteristics of the silica obtained P8 were then the
following:
[0386] CTAB specific surface area: 194 m.sup.2/g;
[0387] BET specific surface area: 212 m.sup.2/g;
[0388] V.sub.(d5-d50)/V.sub.(d5-100): 0.75;
[0389] Width L.sub.d (XDC): 1.11;
[0390] Pore distribution width ldp: 0.83;
[0391] Width L'.sub.d (XDC): 4.29;
[0392] Sears number.times.1000/BET specific surface area: 34.9;
[0393] XDC mode: 47 nm;
[0394] Pore volume V.sub.80: 1.37 cm.sup.3/g;
[0395] .O slashed..sub.50S (after ultrasonic disintegration): 5.9
.mu.m;
[0396] .alpha.: 0.00396 .mu.m.sup.-1.min.sup.-1.
EXAMPLE 10
[0397] Two polymer compositions were prepared:
[0398] one containing highly dispersible precipitated silica Z1165
MP, sold by Rhodia (the characteristics of which were mentioned in
Example 6), and a coupling agent (reference composition R2);
[0399] the other containing silica prepared in Example 8 and a
coupling agent (composition C3).
3TABLE 3 (compositions in parts by weight) Composition R2
Composition C3 BR.sup.(1) 70 70 SBR.sup.(2) 15 15 NBR.sup.(3) 15 15
Silica Z1165MP 50 0 Silica of 0 50 Example 8 SILQUEST A1891.sup.(4)
1 1 Liquid paraffin.sup.(5) 10 10 Stearic acid 1.5 1.5 Zinc oxide 3
3 Polyethylene 3 3 glycol.sup.(6) TBBS.sup.(7) 1 1 TBzTD.sup.(8)
0.6 0.6 Sulphur 1.5 1.5 .sup.(1)Polybutadiene (KOSYN KBR01 type);
.sup.(2)Solution-synthesized styrene-butadiene copolymer (BUNA VSL
5025 type) not oil-extended; .sup.(3)Butadiene-acrylonitrile
copolymer (KRYNAC 34-50 type); .sup.(4).gamma.-Mercaptopropyltri-
ethoxysilane filler/polymer coupling agent (sold by Crompton);
.sup.(5)PLASTOL 352 (sold by Exxon); .sup.(6)PEG 4000 type (sold by
Huls); .sup.(7)N-tert-butylbenzothiazyl sulphenamide;
.sup.(8)Tetrabenzylthiuram disulphide.
[0400] The compositions were prepared by thermomechanically working
the elastomers in an internal mixer (Banbury type) having a volume
of 1200 cm.sup.3. The initial temperature and the speed of the
rotors were set so as to achieve drop temperatures of the compounds
of about 120.degree. C. This step was followed by a finishing step
carried out on an external mixer at temperatures below 110.degree.
C. This phase allowed the vulcanization system to be
introduced.
[0401] The vulcanization temperature was chosen to be 160.degree.
C. The vulcanization conditions for the compositions were tailored
to the vulcanization rates of the corresponding mixtures.
[0402] The properties of the compositions are given below, the
measurements having been carried out according to the following
standards and/or methods:
[0403] Vulcanization Properties (Rheological Properties)
[0404] (Green properties--Rheometry at 160.degree. C., t=30
minutes)
[0405] NF T 43015 standard.
[0406] A Monsanto 100 S rheometer was used especially for the
measurement of the minimum torque (C.sub.min) and the maximum
torque (C.sub.max).
[0407] Ts2 corresponded to the time over which it was possible to
monitor the mixture; the polymer mixture cured after Ts2 (start of
vulcanization).
[0408] T90 corresponded to the time it took for the mixture to
undergo 90% vulcanization.
[0409] Mechanical Properties (of the Compositions Vulcanized at
160.degree. C.)
[0410] Tensile properties (moduli, tensile strength and elongation
at break): NF T 46002 standard
[0411] The x % moduli corresponded to the stress measured at a
tensile strain of x %.
[0412] Tear strength: NF T 46007 (method B) standard.
[0413] Shore A hardness: ASTM D2240 standard; the value in question
is measured 15 seconds after application of the force.
[0414] Abrasion resistance: DIN 53516 standard; the measured value
is the abrasion loss: the lower the loss, the better the abrasion
resistance.
4 TABLE 4 Vulcanization Composition R2 Composition C3 Cmin (in
.multidot. lb) 22 28 Ts2 (min) 0.8 1.4 T90 (min) 3.3 2.8 C.sub.max
(in .multidot. lb) 96 95 Mechanical 10% modulus (MPa) 0.8 0.8 100%
modulus (MPa) 2.8 3.1 300% modulus (MPa) 9.0 8.9 Tensile strength
11.9 12.8 (MPa) Elongation at break 377 418 (%) Tear strength 68 73
(No. 10 notch) (kN/m) Shore A hardness 68 70 (pts) Abrasion loss
(mm.sup.3) 36 29
[0415] It may be seen that composition C3 containing a silica
according to the invention exhibits a particularly beneficial
compromise of properties compared with that of reference
composition R2.
[0416] While still having a vulcanization rate comparable to that
of reference composition R2 and moduli similar to those of
reference composition R2, composition C3 possesses a tensile
strength, an elongation at break, a tear strength and a Shore
hardness that are superior to those of reference composition R2.
Above all, composition C3 has an abrasion resistance very much
higher than reference composition R2: the abrasion loss is thus
reduced by almost 20%.
EXAMPLE 13
[0417] Three polymer compositions were prepared:
[0418] one containing highly dispersible precipitated silica Z1165
MP, sold by Rhodia (the characteristics of which were mentioned in
Example 6), and a coupling agent (reference composition R3);
[0419] the other two containing silica prepared in Example 8 and a
coupling agent (composition C4), or silica prepared in Example 9
and a coupling agent (composition C5).
5TABLE 5 (compositions in parts by weight) Composition R3
Composition C4 Composition C5 SBR.sup.(1) 103 103 103 BR.sup.(2) 25
25 25 Silica Z1165MP 80 0 0 Silica of 0 80 0 Example 8 Silica of 0
0 80 Example 9 TESPT.sup.(3) 6.4 8.0 7.7 Stearic acid 2.0 2.0 2.0
Zinc oxide 2.5 2.5 2.5 Antioxidant.sup.(4) 1.9 1.9 1.9 DPG.sup.(5)
1.5 1.8 1.8 CBS.sup.(6) 2.0 2.0 2.0 Sulphur 1.1 1.1 1.1
.sup.(1)Solution-synthesized styrene-butadiene copolymer (BUNA VSL
5025-1 type), oil-extended (37.5% by weight); .sup.(2)Polybutadiene
(BUNA CB24 type sold by Bayer); .sup.(3)Filler/polymer coupling
agent: bis(3-(triethoxysilyl)prop- yl tetrasulphide (sold by
Degussa under the name Si69);
.sup.(4)N-1,3-dimethylbutyl-N-phenyl-para-phenylenediamine
(SANTOFLEX 6-PPD sold by Flexsys); .sup.(5)Diphenylguanidine
(VULKACIT D sold by Bayer); .sup.(6)N-cyclohexyl-2-benzothiazyl
sulphenamide (SANTOCURE sold by Flexsys).
[0420] Each of the three compositions was prepared in three
successive phases. The first two phases, carried out in an internal
mixer, allowed thermomechanical working at high temperature until a
maximum temperature of about 150.degree. C. was obtained. They were
followed by a third mechanical working phase carried out on
cylinders at temperatures below 110.degree. C. The latter phase
allowed the vulcanization system to be introduced.
[0421] The mixer employed for the first two phases was an internal
mixer of the Brabender type, with a capacity of 70 cm.sup.3. The
initial temperature and the speed of the rotors were set each time
so as to achieve drop temperatures of the compound close to
150.degree. C. The first step made it possible to incorporate the
elastomers (at to), the silica (divided introduction, 2/3 then 1/3)
with the coupling agent (at t.sub.0+2 min), then with the DPG (at
t.sub.0+4 min) and finally the stearic acid (at t.sub.0+6 min).
After discharge from the mixer (compound drop at t.sub.0+7 min),
followed by compound cooling (temperature below 100.degree. C.) and
reintroduction (at t'.sub.0) into the internal mixer (the
temperature then progressively rising), a second step in this mixer
made it possible, by a thermomechanical treatment, to improve the
dispersion of the silica and of its coupling agent in the
elastomeric matrix. During this step, the zinc oxide and the
antioxidant were incorporated (at t'.sub.0+1 min).
[0422] After discharge from the mixer (compound drop at t'.sub.0+4
min) followed by cooling of the compound (temperature below
100.degree. C.), the third phase made it possible to introduce the
vulcanization system (sulphur and CBS). It was carried out on a
cylinder mixer preheated to 50.degree. C. The duration of this
phase was between 5 and 20 minutes.
[0423] After homogenization and finish passes, each final compound
was calendered in the form of sheets 2-3 mm in thickness.
[0424] The vulcanization temperature was chosen to be 160.degree.
C. The vulcanization conditions for the compositions were tailored
to the vulcanization rates of the corresponding compounds.
[0425] The properties of the compositions are given below, the
measurements having been carried out according to the standards
and/or methods indicated in Example 10. The dynamic properties (of
the compositions vulcanized at 160.degree. C.), such as the tan
.delta. at 60.degree. C., were determined on a METRAVIB VA3000
viscoelasticimeter, according to the ASTM D5992 standard, with a 4%
prestrain and a frequency of 10 Hz (sinusoidal wave).
6 TABLE 6 Composition Composition Composition Vulcanization R3 C4
C5 Cmin (dN .multidot. m) 25 33 27 Ts2 (min) 3.9 3.8 4.1 T90 (min)
14.2 16.3 15.2 C.sub.max (dN .multidot. m) 71 76 75 Mechanical 10%
modulus 0.6 0.7 0.6 (Mpa) 100% modulus 2.4 2.8 2.9 (Mpa) 200%
modulus 6.4 7.4 7.2 (Mpa) Shore A 62 67 67 hardness (pts) Abrasion
loss 72 56 58 (mm.sup.3) Dynamic tan.delta. (60.degree. C.) 0.121
0.113 0.100
[0426] It may be seen that compositions C4 and C5 each containing a
silica according to the invention exhibit a particularly beneficial
compromise of properties compared with that of reference
composition R3.
[0427] While still having a vulcanization rate comparable to that
of reference composition R3, compositions C4 and C5 possess moduli
and a Shore hardness higher than those of reference composition R3.
Above all, compositions C4 and C5 exhibit a much higher abrasion
resistance than reference composition R3: the abrasion loss is thus
reduced by about 20%. Finally, compositions C4 and C5 possess a
lower tan .delta. at 60.degree. C. than reference composition R3,
it also proving to be particularly beneficial in the case of the
properties of finished articles based on these compositions C4 or
C5.
* * * * *