U.S. patent application number 10/103837 was filed with the patent office on 2002-10-03 for process for preparing a silica suspension in a curable silicone in order to form elastomers.
Invention is credited to Canpont, Dominique, Plantier, Andre, Pouchelon, Alain.
Application Number | 20020143082 10/103837 |
Document ID | / |
Family ID | 9508601 |
Filed Date | 2002-10-03 |
United States Patent
Application |
20020143082 |
Kind Code |
A1 |
Canpont, Dominique ; et
al. |
October 3, 2002 |
Process for preparing a silica suspension in a curable silicone in
order to form elastomers
Abstract
The invention concerns the preparation of a silica suspension in
a silicon fluid, said suspension being used to produce silicon
vulcanisable by polyaddition (RTV elastomers). The problem which
the invention aims to solve is that of finding a technical
compromise between the rheological and mechanical properties of the
final RTV. The invention solves the problem by providing a method
for preparing a silica suspension treated with hexamethyldisilazane
(HMDZ) in a silicon fluid with siloxyl Si-Vinyl function,
characterised in that it consists essentially in introducing HMDZ
in the preparation medium, before and/or substantially while
bringing at least part of the silicon fluid prepared with at least
part of the particulate filler used, said introduction being
carried out once or several times for a HMDZ fraction corresponding
to a proportion not more than 8% by dry weight with respect to the
total silica charge and after bringing together the POS and the
filler.
Inventors: |
Canpont, Dominique;
(Oullins, FR) ; Plantier, Andre; (Saint-Prim,
FR) ; Pouchelon, Alain; (Meyzieu, FR) |
Correspondence
Address: |
Norman H. Stepno
BURNS, DOANE, SWECKER & MATHIS, L.L.P.
P.O. Box 1404
Alexandria
VA
22313-1404
US
|
Family ID: |
9508601 |
Appl. No.: |
10/103837 |
Filed: |
March 25, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10103837 |
Mar 25, 2002 |
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09446676 |
Mar 24, 2000 |
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6391944 |
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09446676 |
Mar 24, 2000 |
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PCT/FR98/01319 |
Jun 23, 1998 |
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Current U.S.
Class: |
523/212 |
Current CPC
Class: |
C08G 77/20 20130101;
C08K 9/06 20130101; C08L 83/04 20130101; C08K 3/36 20130101; C08G
77/06 20130101; C08G 77/12 20130101; C08K 9/06 20130101; C08L 83/04
20130101; C08L 83/04 20130101; C08L 83/00 20130101; C08L 2666/54
20130101 |
Class at
Publication: |
523/212 |
International
Class: |
C08K 009/06 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 24, 1997 |
FR |
97/08171 |
Claims
1. Process for preparing a suspension of a particulate, preferably
siliceous, filler in a material formed by a silicone oil
comprising: polyorganosiloxanes (POS fluids) of type (I) which
carry Si-alkenyl--preferably Si-vinyl--functional groups capable of
reacting with the Si--H crosslinking functional groups of a POS
fluid of type II, optionally, POS fluids of type (II) which carry
Si--H crosslinking functional groups capable of reacting with the
Si-alkenyl functional groups of the POS fluids (I), and/or,
optionally, POS fluids of type (III) which differ from the POS
fluids (I) and (II), the said suspension being able to be used, in
particular, for producing silicone compositions that can be cured
by polyaddition, this process being of the kind of those in which
the particulate filler is treated with the aid of a compatibilizing
agent or compatibilizer (CA), characterized in that it essentially
consists in introducing some compatibilizer (CA) into the
preparation mixture: on the one hand, before and/or substantially
simultaneously with the contacting of at least part of the silicone
oil employed with at least part of the particulate filler used,
this CA introduction taking place in one or more steps for a CA
fraction corresponding to a proportion of at most 8%, preferably at
most 5% and even more preferably at most 3% by dry weight with
respect to the total particulate filler; and, on the other hand,
after this POS/filler contacting.
2. Process according to claim 1, characterized in that it
essentially consists: in mixing: 100 parts by weight of silicone
oil 0 to 5 parts by weight of water 20 to 80 parts by weight of
particulate filler consisting of silica 1 to 20 parts by weight of
compatibilizer (CA) selected from silazanes taken by themselves
alone or as a mixture thereof, preferably from disilazanes,
hexamethyldisilazane which may or may not be combined with
divinyltetra-methyldisilazane being particularly preferred; in
leaving the above to react, preferably with stirring, in heating
the mixture obtained, choosing a pressure/temperature pair so that
at least some of the water and of the volatile elements undergoes
devolatilization; if necessary, in cooling the mixture.
3. Process according to claim 1 or 2, characterized in that: all or
some of the silicone oil, the water and all or some of the
particulate siliceous filler are mixed with a first CA fraction of
between 1 and 3% by dry weight with respect to the silica, a second
CA fraction, representing between 10 and 15% by dry weight of
silica, is incorporated into the mixture, optionally, the rest of
the silicone oil and the rest of the silica are added, the mixture
is allowed to react, preferably by continuing the mixing, the
mixture is devolatilized, optionally, the devolatilized mixture is
allowed to cool and, optionally, the suspension is completed with
the rest of the silicone oil.
4. Process according to claim 3, characterized in that: 1. a
mixture comprising the silicone oil, the water and the first
CA--preferably HMDZ--fraction is homogenized, 2. the particulate
filler, preferably silica, is gradually added to the mixture
obtained at 1, 3. the mixing is continued, 4. the second
CA--preferably HMDZ--fraction is gradually incorporated into the
mixture obtained at 3, 5. the mixing is continued, 6. the mixture
is devolatilized, preferably by heating to a
temperature.gtoreq.100.degree. C.
5. Process according to claim 3, characterized in that: 1'. the
silicone oil and the water are homogenized, 2'. the particulate
filler--preferably silica--and, at the same time, the first
CA--preferably HMDZ--fraction are gradually incorporated into the
mixture obtained at 1, 3. the mixing is continued, 4. the second
CA--preferably HMDZ--fraction is gradually incorporated into the
mixture obtained at 3, 5. the mixing is continued, 6. the mixture
is devolatilized, preferably by heating to a
temperature.gtoreq.100.degree. C.
6. Process according to claim 3, characterized in that: 1". the
silicone oil is introduced, 2". the particulate filler--preferably
silica--together with the first CA--preferably HMDZ--fraction and
the water are gradually and simultaneously incorporated into the
oil, 3. the mixing is continued, 4. the second CA--preferably
HMDZ--fraction is gradually incorporated into the mixture obtained
at 3, 5. the mixing is continued, 6. the mixture is devolatilized,
preferably by heating to a temperature.gtoreq.100.degree. C.
7. Process according to any one of claims 1 to 6, characterized in
that the first CA fraction is replaced, completely or partly, with
at least one processing aid chosen from molecules and combinations
of molecules: capable of interacting with the particulate filler,
particularly with silicon if a siliceous filler is used, to the
detriment of the hydrogen bonds that this particulate filler
establishes especially between its own atoms and/or with those of
the silicone oil, and capable of being removed from the preparation
mixture by devolatilization, and in that actions are taken to
ensure that this processing aid is in the presence of water in the
preparation mixture.
8. Process according to claim 7, characterized in that the
processing aid is chosen from the group comprising: silazanes, HMDZ
being preferred; difunctional, or preferably monofunctional,
hydroxylated siloxanes; amines, preferably ammonia and/or
alkylamines, diethylamine being particularly preferred; organic
acids, formic and/or acetic acids being preferred; and mixtures
thereof.
9. Process according to any one of claims 1 to 8, characterized in
that an alkenylated--preferably vinylated--silicone oil comprising
at least two Si-alkenyl groups per molecule, each preferably
located at one end of the chain, and having a dynamic viscosity at
25.degree. C. not exceeding 250 Pa.s, preferably not exceeding 100
Pa.s and more preferably still not exceeding 10 Pa.s, is employed,
and in that a silica having a BET specific surface area of between
50 and 400 m.sup.2/g and mixing conditions such that the dynamic
viscosity at 25.degree. C. of the suspension does not exceed 300
Pa.s, preferably does not exceed 250 Pa.s, and more preferably
still does not exceed 200 Pa.s, are chosen.
10. Process for obtaining a silicone composition that can be cured
by polyaddition, characterized in that it consists in mixing the
following products: A--a suspension as prepared according to the
process as defined in any one of claims 1 to 9, B--one or more POS
fluids (I), as defined in claim 1, C--one or more POS fluids (II),
as defined in claim 1, D--optionally, one or more POS fluids (III),
as defined in claim 1, useful as diluent(s), E--a catalytic system
comprising a catalyst, preferably of the platinum kind, and,
optionally, an inhibitor.
11. Process according to claim 10, characterized in that the
composition is produced in the form of a two-component system
comprising parts C.sub.1 and C.sub.2 which are intended to be
brought into contact with each other in order to produce an
elastomer crosslinked by polyaddition between the POS fluids (I)
and (II) and in that care is taken to ensure that only one of the
parts, C.sub.1 or C.sub.2, contains some catalyst D and,
optionally, one or other of the POS fluids (I) and (II).
Description
TECHNICAL FIELD:
[0001] The field of the invention is that of silicone elastomers
which can be obtained by polyaddition and the main components of
which are silicone polymers and fillers.
[0002] More specifically, the present invention relates to the
preparation of an intermediate product useful for obtaining these
silicone elastomers and consisting of a suspension of a reinforcing
filler in a polyorganosiloxane carrying Si-alkenyl--preferably
Si--Vi--functional groups capable of reacting by polyaddition with
the SiH crosslinking functional groups of another POS.
PRIOR ART
[0003] A distinction may be made between reinforcing and
non-reinforcing fillers in silicone rubbers.
[0004] The most widely used reinforcing fillers are preferably
pyrogenic silicas having a BET surface area>50 m.sup.2/g. They
owe their reinforcing effect firstly to their morphology and
secondly to the hydrogen bonds which form between the silanol
groups on the surface of the silicas (3-4.5 SiOH groups/mm.sup.2)
and the polyorganosiloxane (POS) chains. These interactions between
the filler and the polymer increase the viscosity and modify the
behaviour of the polymer near the solid surface of the fillers.
Moreover, the bonds between polymers and fillers improve the
mechanical properties but may also cause prejudicial premature
curing ("structuring") of the precursor compositions of the
elastomers.
[0005] Non-reinforcing fillers interact extremely weakly with the
silicone polymer. These are, for example, chalk, quartz powder,
diatomaceous earth, mica, kaolin, aluminas or iron oxides. Their
effect is often to increase the viscosity of the uncured precursors
of the elastomers, as well as the Shore hardness and the modulus of
elasticity of these precursors.
[0006] Silicone elastomers may also contain, inter alia, catalysts,
inhibitors, crosslinking agents, pigments, antiblocking agents,
plasticizers and adhesion promoters.
[0007] These elastomers, curable by polyaddition and also called
RTV elastomers, are formed, before curing, by casting, extrusion,
calendering, or compression, injection or transfer moulding.
[0008] Silicone compositions made of elastomers, which can be cured
by polyaddition at room temperature or at higher temperatures
(generally <200.degree. C.), are conventionally packaged in the
form of two-component systems, that is to say comprising two parts
which are packaged separately and have to be mixed at the time of
use.
[0009] In two-component systems, one of the components comprises
the catalyst for the polyaddition reaction. This catalyst is
preferably of the platinum kind. It may, for example, be a platinum
complex like the one prepared from chloroplatinic acid and
1,3-divinyl-1,1,3,3-tetramethyl- disiloxane, according to U.S. Pat.
No. 3,814,730 (Karstedt catalyst). Other platinum complexes are
described in U.S. Pat. Nos. 3,159,601, 3,159,662 and 3,220,972.
[0010] This component including the catalyst may also comprise only
one of the POS fluids of type I having Si-alkenyl, preferably
Si-vinyl, crosslinking functional groups or only one of the POS
fluids of type II having an SiH crosslinking functional group.
[0011] Generally, the POS fluids of type I and the POS fluids of
type II comprise at least two Si--Vi and SiH groups per molecule,
respectively, preferably in the .alpha. and .omega. positions on
the chain: at least one of the two having to comprise at least
three crosslinking functional groups per molecule.
[0012] These compositions comprise, in a known manner, POS fluids
of type I and II, a platinum catalyst for crosslinking by
polyaddition and a platinum inhibitor allowing the compositions to
cure only once they have been removed from the package and mixed
together, optionally after they have been heated slightly.
[0013] As examples of inhibitors, mention may be made of:
[0014] polyorganosiloxanes, advantageously cyclic
polyorganosiloxanes, substituted with at least one alkenyl,
tetramethylvinyltetrasiloxane being particularly preferred,
[0015] pyridine,
[0016] organic phosphines and phosphites,
[0017] unsaturated amides,
[0018] alkylated maleates
[0019] and acetylenic alcohols (cf. FR-B-1,528,464 and
FR-A-2,372,874).
[0020] Such compositions may also be in the form of one-component
systems which cure only after having been heated.
[0021] The preparation of concentrated suspensions (pastes) of
reinforcing silicas in vinyl silicone oils, these suspensions being
intended to produce elastomers that can be cured by the reaction of
a polyhydrogenated crosslinking molecule such as a POS with the
vinyl silicone oil (SiH/SiVi addition), is widespread in the field
of elastomers.
[0022] The commonest reinforcing particulate fillers are based on
silica, but substances such as TiO.sub.2, Al.sub.2 O.sub.3 and
kaolin, for example, may also be used in certain cases.
[0023] These reinforcing fillers have a BET specific surface area
of at least 50 m.sup.2/g, and generally up to 400 m.sup.2/g. These
are ultrafine powders which may be dispersed in silicone,
preferably SiVi, oils. This dispersion causes problems when mixing
some of the pulverulent filler with the oil and particular care
must be taken in order to obtain a uniform distribution of the
fillers in the suspension.
[0024] Another difficulty to be overcome is associated with the
rheology of the suspensions prepared. This is because it is clear
that introducing a pulverulent particulate filler of very small
particle size into the silicone oil necessarily causes an
appreciable increase in the viscosity. However, this
characteristic, although it accompanies the achievement of good
mechanical properties for the silicon elastomers comprising the
suspension as raw material, is prejudicial to the handling and
forming of the suspension and of the silicone compositions
containing the suspension. It is in fact more convenient, for
moulding, extrusion or forming, to handle fluid compositions which
readily lend themselves, inter alia, to pumping, flowing or mixing
with functional additives.
[0025] The problematic considered here may therefore be summarized
as how to find a technical compromise between a priori antinomic
specifications for the suspensions of fine particulate fillers in
silicone oils, namely: fine distribution of particles in the
silicone matrix--uniformity of the dispersion--suitability of the
rheology of the suspension to the handling constraints
(processibility)--mechanical properties of the RTV silicone
elastomers.
[0026] French Patent Application No. 2,320,324 falls within this
problematic and describes a process for a homogeneous distribution
in polyorganosiloxanes of a highly disperse active filler of BET
specific surface area of at least 50 m.sup.2/g, this process being
characterized in that the filler is treated during incorporation,
in the presence of water, by a modifier or compatibilizer of the
silazane type, hexamethyldisilazane being particularly preferred.
The other compatibilizers mentioned are trimethylsilane,
trimethylchlorosilane, trimethylethoxysilane, triorganosilyl
mercaptans, triorganosilyl acylates or triorganosilyl amines.
According to this process, described in this prior application, an
.alpha., .OMEGA.-trimethylsiloxy polydimethylsiloxane with
hexamethyldisilazane (HMDZ) and with water. Once this mixture has
been homogenized, some particulate silica is incorporated into it
and mixing is continued until a homogeneous mixture is obtained.
Next, the mixture is heated to 130.degree. C. in order to remove
the excess HMDZ and water by devolatilization. It is left to cool
and, after measuring the viscosity of the suspension obtained, it
is found that the latter is relatively high, which, of course,
gives the elastomers capable of being prepared from this suspension
good mechanical properties, but which proves to be unacceptable
from a handling standpoint in an industrial context. This
compatibilization treatment of the silica with the silicone oil may
be termed "early" since the HMDZ is present as soon as the
reinforcing silica is brought into contact with this silicone
oil.
[0027] The compatibilization treatment is a means of retarding or
preventing reaction between the surface of a reinforcing filler and
a siloxane polymer. This interaction causes what is called
structuring and as a result the conversion of these mixtures is
more difficult.
[0028] Processes for preparing a suspension of reinforcing silica
in silicone oils are also known, in which the compatibilization
treatment with the aid of hexamethyldisilazane is carried out after
the silica has been incorporated into the silicone oil. This method
of treatment is termed here "late". It provides relatively fluid
suspensions which may have a tendency to structure over time. In
certain cases, the suspensions formed may have a certain tendency
to be thixotropic. This is not without having undesirable
consequences when converting and handling these suspensions,
especially when degassing them. Nevertheless, it may be stated
that, whatever the rheological properties of the suspensions
obtained by late HMDZ treatment, the final mechanical properties of
the elastomers prepared from the said suspensions are perfectible
(hardness, tensile strength, elongation at break, tear strength).
In particular, they do not reach the level of those found in the
case of early treatment.
[0029] By way of illustration of this type of compatibilization
treatment, mention may be made of European Patent Application No.
0,462,032 which describes a process for preparing a paste which can
be used especially in compositions that are curable by a
polyaddition reaction and which thus allows silicone elastomers to
be obtained. According to this process, the following are injected,
continuously and simultaneously, into a twin-screw extruder, at at
least four different points:
[0030] at least one SiVi POS oil,
[0031] water,
[0032] silica,
[0033] a liquid polysilazane under normal temperature and pressure
conditions (HMDZ).
[0034] The silica is injected downstream of the water and of the
oil and upstream of the HMDZ without, however, there being any
mixing, between the HMDZ and water on the one hand and between the
HMDZ and the silica on the other, before introduction of HMDZ.
[0035] U.S. Pat. No. 4,785,047 discloses a hybrid compatibilization
treatment, at the boundary between the early and late treatments
mentioned above. This patent relates more specifically to a process
for preparing transparent silicone elastomers. This document
describes pumpable liquid compositions formed from suspensions of
HMDZ-treated siliceous filler in silicone oils which may or may not
carry polyaddition-crosslinking functional groups (SiH/SiVi). The
problematic presented in this patent is different from that of the
prior art presented above. In this case it is in fact more one of
obtaining transparent elastomers and, in order to do so, of trying
to counteract the deleterious effect of the siliceous filler on the
transparency by a very substantial HMDZ treatment. According to the
process forming the subject of that patent, part of the silicone
oil is firstly mixed with all of the water and all of the silica,
but only with a fraction of the HMDZ representing systematically
more than 15% by dry weight with respect to the silica, namely 34%
and 26% in the examples.
[0036] After this first mixture has been homogenized, the remaining
HMDZ is incorporated and mixed into the latter.
[0037] Next, the devolatilization treatment is carried out for 1
hour at 150.degree. C. and under reduced pressure.
[0038] Finally, the rest of the PMDS silicone oil and the
.alpha.,.omega.-diVi PDMS silicone oil are mixed for 1 hour at room
temperature.
[0039] The transparent curable silicone suspension obtained has a
viscosity lying between 200 and 10,000 Pa.s at 25.degree. C.
[0040] This technical proposal may possibly provide a solution to
the transparency problem, but it proves to be unsatisfactory with
regard to the viscosity of the suspension and to its handling.
BRIEF SUMMARY OF THE INVENTION
[0041] In such a technical context, one of the essential objectives
of the present invention is to provide a process for preparing a
suspension of a particulate filler, treated with the aid of a
compatibilizer, in a silicone oil, this suspension being able to be
used as a raw material for the production of RTV elastomer
compositions that can be cured by poplyaddition.
[0042] This process has to meet the following specification:
[0043] the distribution of the filler in the silicone oil must be
uniform and homogeneous,
[0044] the dispersion must be optimal,
[0045] the suspension must flow well (no flow threshold) and the
viscosity must be suitable for handling and converting the
suspension,
[0046] the mechanical properties of the elastomers must be of an
acceptable level.
[0047] Another essential objective of the invention is to provide a
process for preparing a reinforcing filler/silicone oil suspension
for RTV elastomers which is simple to employ, inexpensive and able
to be applied on an industrial scale.
[0048] Another essential objective of the invention is to provide a
process for obtaining a silicone composition, curable by
polyaddition in order to form an RTV elastomer and comprising, as a
constituent element, the suspension as obtained by the intended
process above.
[0049] These objectives, among others, are achieved by the present
invention which relates to a process for preparing a suspension of
a particulate, preferably siliceous, filler in a material formed by
a silicone oil comprising:
[0050] polyorganosiloxanes (POS fluids) of type (I) which carry
Si-alkenyl--preferably Si-vinyl--functional groups capable of
reacting with the Si--H crosslinking functional groups of a POS
fluid of type II,
[0051] optionally, POS fluids of type (II) which carry Si--H
crosslinking functional groups capable of reacting with the
Si-alkenyl functional groups of the POS fluids (I),
[0052] and/or, optionally, POS fluids of type (III) which differ
from the POS fluids (I) and (II),
[0053] the said suspension being able to be used, in particular,
for producing silicone compositions that can be cured by
polyaddition,
[0054] this process being of the kind of those in which the
particulate filler is treated with the aid of a compatibilizing
agent or compatibilizer (CA),
[0055] characterized in that it essentially consists in introducing
some compatibilizer (CA) into the preparation mixture:
[0056] on the one hand, before and/or substantially simultaneously
with the contacting of at least part of the silicone oil employed
with at least part of the inarticulate filler used, this CA
introduction taking place in one or more steps for a CA fraction
corresponding to a proportion of at most 8%, preferably at most 5%
and even more preferably at most 3% by dry weight with respect to
the total particulate filler;
[0057] and, on the other hand, after this POS/filler
contacting.
[0058] It is to the credit of the inventors that they have
demonstrated, after extensive research and many experiments, that
it is surprisingly and unexpectedly appropriate to incorporate the
compatibilizer (for example HMDZ) before and after the reinforcing,
preferably siliceous filler has been mixed with the silicone oil,
(preferably of SiVi type (I)), as long as the fraction of
compatibilizer CA introduced before POS/filler mixing corresponds
to less than 5% by weight of the total reinforcing filler.
[0059] These novel and advantageous provisions make it possible to
obtain suspensions having suitable rheological properties and
suitable viscoelastic behaviour. This is because these suspensions
do not have a flow threshold, or have a very low threshold which is
not prejudicial to the applications. This considerably improves
their processing.
[0060] In particular, they have a fluidity which is stable over
time and suitable for the handling and conversion operations, such
as pumping, transferring, mixing, forming, moulding, extrusion,
etc.
[0061] One of the major advantages of the invention is that this
attainment from the rheology standpoint is not to the detriment of
the final mechanical properties of the crosslinked elastomer. The
technical compromise is achieved.
[0062] Moreover, the methodology adopted makes it possible to
obtain good homogeneous dispersions of the particulate filler in
the oil. In addition, this methodology does not significantly
complicate the process, which remains simple and inexpensive to
implement.
DETAILED DESCRIPTION OF THE INVENTION
[0063] In accordance with one of these preferred methods of
implementation, the process according to the invention essentially
consists:
[0064] in mixing:
[0065] 100 parts by weight of silicone oil
[0066] 0 to 5 parts by weight of water
[0067] 20 to 80 parts by weight of particulate filler consisting of
silica
[0068] 1 to 20 parts by weight of compatibilizer (CA) selected from
silazanes taken by themselves alone or as a mixture thereof,
preferably from disilazanes, hexamethyldisilazane which may or may
not be combined with divinyltetra-methyldisilazane being
particularly preferred;
[0069] in leaving the above to react, preferably with stirring,
[0070] in heating the mixture obtained, choosing a
pressure/temperature pair so that at least some of the water and of
the volatile elements undergoes devolatilization;
[0071] if necessary, in cooling the mixture.
[0072] In other words, the process according to the invention makes
it possible to control the viscosity of the suspension while at the
same time maintaining the mechanical properties of the final
elastomer obtained from the suspension at an acceptable level, or
even improving this level.
[0073] The mixing is carried out with the aid of known and suitable
devices. These may be, for example:
[0074] arm mixers
[0075] internal mixers
[0076] planetary mixers
[0077] ploughshare mixers
[0078] corotating or counterrotating twin-shaft mixers
[0079] continuous extruder-mixers
[0080] or other continuous or batch devices.
[0081] The mixing operation is carried out at normal temperature
and pressure and preferably in an inert atmosphere (N.sub.2).
Moreover, under these conditions the silicone oil, the water but
also the compatibilizer are in liquid form in order to make the
mixing easy.
[0082] The reinforcing, preferably siliceous, filler represents
from 10 to 50% by weight of the suspension. In practice, this
filler is of the order of 30.+-.10%.
[0083] Advantageously, the proportion of compatibilizer introduced
in a first step is at most equal to 8% of the reinforcing filler
(and, for example, between 1 and 3% of the reinforcing filler,
preferably between 1 and 2%). Moreover, it may be pointed out that
the total amount of compatibilizer CA is preferably between 5 and
30% of the siliceous filler, preferably between 10 and 20%.
[0084] The proportions of compatibilizer AC introduced before and
after filler/oil mixing are (5-25), preferably (10-20%),
respectively.
[0085] In order to define more precisely the preferred method of
implementing the process according to the invention, without
however this being limiting, it may be pointed out that the process
comprises the following steps:
[0086] all or some of the silicone oil, the water and all or some
of the particulate siliceous filler are mixed with a first CA
fraction of between 1 and 3% by dry weight with respect to the
silica,
[0087] a second CA fraction, representing between 10 and 15% by dry
weight of silica, is incorporated into the mixture,
[0088] optionally, the rest of the silicone oil and the rest of the
silica are added,
[0089] the mixture is allowed to react, preferably by continuing
the mixing,
[0090] the mixture is devolatilized, preferably in an inert-gas
atmosphere (eg. N.sub.2),
[0091] optionally, the devolatilized mixture is allowed to cool
[0092] and, optionally, the suspension is completed with the rest
of the silicone oil.
[0093] According to a first particular practical implementation of
the process of the invention, it comprises the following steps:
[0094] 1. a mixture comprising the silicone oil, the water and the
first CA--preferably HMDZ--fraction is homogenized,
[0095] 2. the particulate filler, preferably silica, is gradually
added to the mixture obtained at 1,
[0096] 3. the mixing is continued,
[0097] 4. the second CA--preferably HMDZ--fraction is gradually
incorporated into the mixture obtained at 3,
[0098] 5. the mixing is continued,
[0099] 6. the mixture is devolatilized, preferably by heating to a
temperature.gtoreq.100.degree. C.
[0100] In step 1 of this first practical implementation, a choice
is made between, inter alia, the following three alternatives:
[0101] a) either all the oil and all the silica, as well as the
initial CA fraction, are used,
[0102] b) or all the oil, part of the silica and the initial CA
fraction are used,
[0103] c) or all the silica, part of the oil and the initial CA
fraction are used.
[0104] According to a second particular practical implementation of
the invention, it comprises the following steps:
[0105] 1'. the silicone oil and the water are homogenized,
[0106] 2'. the particulate filler--preferably silica--and, at the
same time, the first CA--preferably HMDZ--fraction are gradually
incorporated into the mixture obtained at 1,
[0107] 3. the mixing is continued,
[0108] 4. the second CA--preferably HMDZ--fraction is gradually
incorporated into the mixture obtained at 3,
[0109] 5. the mixing is continued,
[0110] 6. the mixture is devolatilized, preferably by heating to a
temperature.gtoreq.100.degree. C.
[0111] The characteristic of this second method is associated with
the fact that the process involves the co-addition of the
particulate reinforcing filler and its compatibilizer. It is
therefore conceivable to make a preblend of these two constituents,
or, alternatively, to introduce them concomitantly. The gradual
incorporation in step 2' may be carried out continuously or in
stages.
[0112] According to a variant of this second practical method of
implementation,
[0113] 1". the silicone oil is introduced,
[0114] 2". the particulate filler--preferably silica--together with
the first CA--preferably HMDZ--fraction and the water are gradually
and simultaneously incorporated into the oil,
[0115] 3. the mixing is continued,
[0116] 4. the second CA--preferably HMDZ--fraction is gradually
incorporated into the mixture obtained at 3,
[0117] 5. the mixing is continued,
[0118] 6. the mixture is devolatilized, preferably by heating to a
temperature.gtoreq.100.degree. C.
[0119] According to one advantageous provision of the invention,
corresponding to the case in which the reinforcing filler is silica
and the compatibilizer CA is HMDZ, a sufficient amount of HMDZ is
used for the content of Si(Me).sub.3 units on the surface of the
silica to be .gtoreq.1 Si(Me).sub.3 unit per mm.sup.2 and
preferably between 1 and 2 Si(Me).sub.3 units per mm.sup.2.
[0120] According to a third method of implementing the invention,
the process to which it relates is characterized:
[0121] in that the first CA fraction is replaced, completely or
partly, with at least one processing aid chosen from molecules and
combinations of molecules:
[0122] capable of interacting with the particulate filler,
particularly with silicon if a siliceous filler is used, to the
detriment of the hydrogen bonds that this particulate filler
establishes especially between its own atoms and/or with those of
the silicone oil,
[0123] and capable of being removed from the preparation mixture by
devolatilization,
[0124] and in that actions are taken to ensure that this processing
aid is in the presence of water in the preparation mixture.
[0125] In accordance with this third method of implementation, it
is preferable for the processing aid to be readily removable from
the preparation mixture. For this purpose, it is beneficial for it
to be easily removed by devolatilization, for example by heating in
a vacuum or in a gas stream. Under these conditions, it is clear
that, as processing aid, molecules of low molecular weight will be
preferred.
[0126] Advantageously, the processing aid is chosen from the group
comprising:
[0127] silazanes, HMDZ being preferred;
[0128] difunctional, or preferably monofunctional, hydroxylated
siloxanes;
[0129] amines, preferably ammonia and/or alkylamines, diethylamine
being particularly preferred;
[0130] organic acids, formic and/or acetic acids being
preferred;
[0131] and mixtures thereof.
[0132] As indicated above, the products more particularly selected
as processing aids are those having a low molecular weight. This
proves to be the case especially for the amines and the organic
acids mentioned above.
[0133] With regard to the products employed in the process
according to the invention, it may be pointed out that, in the case
of the silicone oil, linear or cyclic, but more especially linear,
polydiorganosiloxanes will preferably be chosen.
[0134] With regard to the POS fluids (I), these will be
polydiorganosiloxane oils carrying an Si-alkenyl, particularly an
Si-vinyl, group in and/or at the ends of the chain. In practice,
mention may be made, for example, of
.alpha.,.omega.-divinyl-terminated polydialkyl (methyl) siloxanes.
Preferably, the POS (I) used for preparing the suspension is a
vinyl POS (I) carrying at least two SiVi units per molecule,
preferably at least three per molecule, when the POS (II) contains
only two SiH units per molecule.
[0135] As regards the POS (II), this is chosen from
polyorganohydrogenosiloxanes comprising at least two SiH units per
molecule, preferably at least three, when the POS (I) comprises
only two SiVi units per molecule. In practice, mention may be made,
for example, of polyalkyl(methyl)hydrogenosiloxanes or else
branched hydrogenated POS fluids having trifunctional or
tetrafunctional units and units carrying SiH.
[0136] The POS (III) may be a polydiorganosiloxane such as a
polyalkylsiloxane, preferably a polydimethylsiloxane, having
trimethylsilyl end groups.
[0137] The preferred silicone oils (I, II, III) essentially
comprise R.sub.2SiO units, the symbols R, which may be identical or
different, representing C.sub.1-C.sub.4 (cyclo)alkyls which may or
may not be halogenated, or aryl groups, which may or may not be
substituted or halogenated.
[0138] By way of groups:
[0139] alkyl: mention may especially be made of methyl, ethyl,
propyl and butyl groups,
[0140] haloalkyl: mention may be made of 3,3-trifluoropropyl,
[0141] cycloalkyl: mention may be made of cyclohexyl,
[0142] aryl: mention may be made of the phenyl group.
[0143] Preferably, at least 85% of the groups R represent methyl
groups.
[0144] The silica used in the process according to the present
invention is a reinforcing silica whose specific surface area is
preferably between 50 and 400 m/g. These silicas may be
precipitated silicas, but more generally fumed silicas are
employed. The fact that silica is preferred does not exclude making
use of other types of known reinforcing filler.
[0145] The CA is preferably a silazane and even more preferably a
disilazane. This is a product which is liquid under standard
temperature and pressure conditions (23.degree. C./760 mmHg).
[0146] The viscosity of the suspension is one of the key parameters
which govern the process according to the invention. Thus, in
accordance with one advantageous provision of the latter:
[0147] an alkenylated--preferably vinylated--silicone oil
comprising at least two Si-alkenyl groups per molecule, each
preferably located at one end of the chain, and having a dynamic
viscosity at 25.degree. C. not exceeding 250 Pa.s, preferably not
exceeding 100 Pa.s and more preferably still not exceeding 10 Pa.s,
is employed,
[0148] a silica having a BET specific surface area of between 50
and 400 m.sup.2/g and mixing conditions such that the dynamic
viscosity at 25.degree. C. of the suspension does not exceed 300
Pa.s, preferably does not exceed 250 Pa.s and more preferably still
does not exceed 200 Pa.s, are chosen.
[0149] Industrial Application
[0150] The purpose of the reinforcing filler/silicone oil
suspension prepared in accordance with the invention is for it to
be used for obtaining liquid or pasty silicone compositions made of
RTV silicone elastomer, which compositions can be cured, preferably
by polyaddition, in the ambient atmosphere and at a normal
temperature or at a higher temperature.
[0151] Thus, according to another of these aspects, the present
invention relates to a process for obtaining a silicone composition
that can be cured by polyaddition, characterized in that it
consists in mixing the following products:
[0152] A--a suspension as prepared according to the process as
defined above,
[0153] B--one or more POS fluids (I), as defined above,
[0154] C--one or more POS fluids (II), as defined above,
[0155] D--optionally, one or more POS fluids (III), as defined
above, useful as diluent(s),
[0156] E--a catalytic system comprising a catalyst, preferably of
the platinum kind, and, optionally, an inhibitor or retarder.
[0157] According to a first variant of this process:
[0158] the composition is produced in the form of a two-component
system comprising parts C.sub.1 and C.sub.2 which are intended to
be brought into contact with each other in order to produce an
elastomer crosslinked by polyaddition between the POS fluids (I)
and (II),
[0159] and care is taken to ensure that only one of the parts,
C.sub.1 or C.sub.2, contains some catalyst D and, optionally, one
or other of the POS fluids (I) and (II).
[0160] According to a second variant of this process for preparing
curable liquid compositions, a one-component system is produced
which is intended to be crosslinked in the ambient air and/or under
the effect of temperature.
[0161] These curable compositions, which are precursors of
elastomers, may also comprise one or more functional additives F
such as, for example, a non-reinforcing filler formed by chalk,
quartz powder, diatomaceous earth, mica, kaolin, aluminas or iron
oxides. These optional additives F may also consist of pigments,
antiblocking agents, plasticizers or rheology modifiers,
stabilizers or adhesion promoters.
[0162] The examples which follow illustrate:
[0163] the preparation of suspensions of reinforcing filler in
silicone oils in accordance with the invention,
[0164] the application of these suspensions as raw material for
obtaining two-component curable compositions made of RTV silicone
elastomers,
[0165] and the evaluation of the viscoelastic properties of the
suspensions and the mechanical properties of the crosslinked
elastomers obtained from the said suspensions.
[0166] Two methods of implementing the process of the invention are
given in the examples. The latter also comprise comparative
examples for preparing suspensions in accordance with the prior art
using compatibilization treatment methods of the "late" type and of
the "early" type.
EXAMPLES
Comparative Example 1: Late Treatment
[0167] Introduced into a 1.5 l arm mixer are 750 g of
.alpha.,.omega.-divinyl-terminated PolyDiMethylSiloxane (PDMS) oil
having a viscosity of 0.6 Pa.s and 21 g of water. After
homogenization, 321 g of a fumed silica, characterized by its
specific surface area of 300 m.sup.2/g, are added in portions over
70 minutes. After mixing for 120 minutes, 66 g of
hexamethyldisilazane are added over 90 minutes. A heating phase
starts 60 minutes later, during which, when the temperature reaches
80.degree. C., the mixture is placed in a stream of nitrogen (250
l/h); the heating continues until reaching approximately
155.degree., a steady temperature which is maintained for 2 h.
After cooling, 43 g of the vinyl-terminated oil are cooled and the
suspension homogenized.
[0168] Starting from this suspension, a part A and a part B are
formulated.
[0169] Part A contains:
[0170] 90.6 g of the suspension;
[0171] 1.58 g of the .alpha.,.omega.-divinyl-terminated PDMS oil
described;
[0172] 5.48 g of an .alpha.,.omega.-dihydrogeno PDMS oil containing
1.9 meq SiH per gram of oil
[0173] 2.35 g of a polyhydrogeno PDMS oil having a viscosity of 30
mPa.s, containing 1.6 meq SiH per gram of oil.
[0174] Part B contains:
[0175] 11 g of the suspension;
[0176] 29 g of the .alpha.,.omega.-divinyl-terminated PDMS oil
described above;
[0177] 9.77 g of an .alpha.,.omega.-divinyl-terminated PDMS oil
containing 0.05 meq Vi per gram of oil;
[0178] 70 .mu.l of a Karstedt catalyst containing 12% platinum;
[0179] 90 .mu.l of divinyltetramethyldisiloxane;
[0180] 140 .mu.l of tetravinyltetramethylcyclotetra-siloxane.
[0181] Parts A and B are mixed in a ratio of 100 to 10 and, after
degassing, 2 mm thick plaques of elastomers are prepared. The
mouldings are cured in a ventilated oven for 1 hour at 150.degree.
C. The test pieces necessary for measuring the mechanical
properties are cut from these plaques of cured elastomer.
Example 2: Early Treatment
[0182] The previous example is repeated except that the process
starts with the mixer being charged with 750 g of
.alpha.,.omega.-divinyl-termin- ated PDMS oil, 21 g of water and 66
g of hexamethylsisilazane [sic]. After stirring for 10 minutes, the
silica is incorporated in portions over 30 minutes; the mixing is
continued for a further 120 minutes before starting the heating
phase, which is the same as above.
[0183] The suspension is formulated as in Example 1.
[0184] Comparative Properties of the Suspensions and of the Cured
Elastomers According to Examples 1 and 2
[0185] The viscosity of the suspensions is measured by means of a
dynamic rheometer with a cone/plate geometry. The complex viscosity
at 1 Hz and at 1 Pa is taken as being representative of the
viscoelastic behaviour of the suspensions.
[0186] The mechanical properties are measured according to the
standards in force:
[0187] DIN 53505 for the hardness measurement
[0188] AFNOR T46002 for the breaking measurements.
1 Dynamic Shore A Stress at Elongation viscosity hardness break at
break Pa .multidot. s pts MPa % Example 1 13 38 6.1 390 Example 2
3000 35 6.9 560
[0189] In the case of Example 1, the viscosity is low but the
breaking properties of the elastomer are moderate. With regard to
Example 2, this has better breaking properties, but at the price of
having a high viscosity.
Example 3: Two-Step Treatment
[0190] Introduced into a 100 l arm mixer are 40 kg of
.alpha.,.omega.-divinyl-terminated oil having a viscosity of 2
Pa.s, 0.27 kg of hexamethyldisilazane and 0.27 kg of water. After
homogenization, 16.2 kg of a fumed silica characterized by its
specific surface area of 200 m.sup.2/g are added in portions over
100 minutes. After 60 minutes of mixing, 1.9 kg of
hexamethyldisilazane are added over 60 minutes. A heating phase is
started 120 minutes later, during which the mixture is placed in a
stream of nitrogen (30 m.sup.3/h); the heating continues until
reaching approximately 140.degree., a steady temperature which is
maintained for 2 h. The suspension is then left to cool.
[0191] Starting from this suspension, a part A and a part B are
formulated.
[0192] Part A contains:
[0193] 427 g of the suspension;
[0194] 10 g of a polyvinyl PDMS oil having a viscosity of 0.4 Pa.s,
containing 0.11 meq Vi per gram of oil;
[0195] 25 g of trimethyl-terminated oil having a viscosity of 0.1
Pa.s;
[0196] 26.5 g of an .alpha.,.omega.-dihydrogeno PDMS oil,
containing 1.9 meq SiH per gram of oil;
[0197] 11.3 g of a polyhydrogeno PDMS oil having a viscosity of 30
mPa.s, containing 1.6 meq SiH per gram of oil.
[0198] Part B contains:
[0199] 180 g of the suspension;
[0200] 20 g of the methyl-terminated oil described;
[0201] 250 .mu.l of a Karstedt catalyst containing 12%
platinum;
[0202] 1 ml of tetravinyltetramethylcyclotetra-siloxane.
[0203] Parts A and B are mixed in a ratio of 100 to 10 and, after
degassing, the test pieces necessary for measuring the mechanical
properties are prepared as explained in Comparative Examples 1 and
2.
Example 4: Two-Step Treatment with Coaddition of the Reactants
[0204] The previous example is repeated except that the mixer is
firstly charged with 40 kg of .alpha.,.omega.-divinyl-terminated
PDMS oil and 0.27 kg of water. After stirring for 10 minutes, the
silica is incorporated in portions over 120 minutes at the same
time as 0.27 kg of hexamethyldisilazane, which is divided according
to the portions of silica. After this phase of silica and
hexamethyldisilazane coaddition, the process is continued as
previously.
[0205] The suspension is formulated as in Example 3.
[0206] Properties of the Suspensions and of the Cured Elastomers
According to Examples 3 and 4
[0207] The viscosity of the suspensions is measured by means of a
dynamic rheometer with a cone/plate geometry. The complex viscosity
at 1 Hz and at 1 Pa and the threshold stress, for which the elastic
and viscous moduli are equal, are taken as being representative of
the viscoelastic behaviour of the suspensions.
[0208] The mechanical properties are measured according to the
standards in force.
2 Dynamic Threshold Shore A Tear viscosity stress hardness strength
Pa .multidot. s Pa pts N/mm Example 3 165 25 34 21 Example 4 150 1
36 18
[0209] Examples 3 and 4 show that the elastomers prepared from the
oil/silica suspensions obtained in accordance with the invention
have a rheology with a very low flow threshold and a moderate
viscosity. This very favourable rheological behaviour is
accompanied by excellent tear strength.
Example 5: Two-Step Treatment by Hexamethyldisilazane
[0210] Preparation of the Suspension
[0211] Introduced into a 7 l arm mixer are 2120 g of a mixture of
.alpha.,.omega.-divinyl-terminated oils having a viscosity of 1.5
Pa.s, 12.6 g of water and 12.6 g of hexamethyldisilazane. After
homogenization, 765 g of a fumed silica characterized by its
specific surface area of 200 m.sup.2/g are added in portions over
110 minutes. Then, 80 g of hexamethyldisilazane are added over 60
minutes. A heating phase starts 120 minutes later, during which,
when the temperature reaches 70.degree. C., the mixture is placed
under vacuum; the heating continues until reaching approximately
150.degree. C., a steady temperature which is maintained for 1 h.
The mixture is then cooled in a stream of nitrogen (.apprxeq.250
l/h) and the apparatus is drained.
[0212] Starting from this suspension, a part A and a part B are
formulated.
[0213] Part A contains:
[0214] 946.7 g of the suspension;
[0215] 42.7 g of an .alpha.,.omega.-dihydrogeno oil, containing 1.9
meq SiH per gram of oil;
[0216] 10.7 g of a polyhydrogeno oil, containing 1.6 meq SiH per
gram of oil.
[0217] Part B contains:
[0218] 22 g of the suspension;
[0219] 20 g of an .alpha.,.omega.-divinyl-terminated oil,
containing 0.15 meq Vi per gram of oil;
[0220] 58 g of an .alpha.,.omega.-divinyl-terminated oil,
containing 0.05 meq Vi per gram of oil;
[0221] 140 .mu.l of a Karstedt catalyst containing 10%
platinum;
[0222] 0.15 g of divinyltetramethyldisiloxane;
[0223] 0.35 g of tetravinyltetramethylcyclotetra-siloxane.
[0224] Parts A and B are mixed in a ratio of 100 to 10 and, after
degassing, the test pieces necessary for measuring the mechanical
properties are prepared.
Example 6: Treatment with an Acid First Step
[0225] The previous example is repeated except that the 12.6 g
corresponding to the first hexamethyldisilazane portion are
replaced with 3.6 g of formic acid. All the other operations are
carried out as previously.
[0226] The suspension is formulated as in Example 5.
Example 7: Treatment with a Base First Step
[0227] Example 5 is again repeated, except that the 12.6 g
corresponding to the first hexamethyldisilazane portion are
replaced with 4.2 g of aqueous ammonia containing 32% ammonia. All
the other operations are carried out as previously.
[0228] The suspension is formulated as in Example 5.
Example 8: Evaluation of the Comparative Properties of the
Suspensions of Examples 5 to 7
[0229] The viscosity of the suspensions is measured by means of a
dynamic rheometer with a cone/plate geometry. The following are
taken as being representative of the viscoelastic behaviour of the
suspensions:
[0230] the complex viscosity and its elastic and viscous components
at 1 Hz and at 1 Pa;
[0231] the threshold stress for which the elastic and viscous
moduli are equal.
[0232] The mechanical properties are measured according to the
standards in force.
3 Acid Base Example 5 Example 6 Example 7 Complex viscosity 41 38
42 Elasticity factor 0.68 0.65 0.73 Flow threshold <1 <1
<1 Shore A hardness 28 35 32 Elongation at break 700 400 610
Tensile strength 6.8 6.3 8.0 Tear strength 29 21 23
[0233] It may readily be seen that the rheological behaviour of the
suspensions is, in the three cases, typical of a product which
flows well and that these suspensions allow elastomers to be
produced with good mechanical properties.
* * * * *