MXPA99011650A - Method for preparing a silica suspension in a vulcanisable silicon matrix to form elastomers - Google Patents

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.

Description

PROCESS OF PREPARING A SUSPENSION OF SILICA IN A MATRIX OF VULCANIZABLE SILICONE, TO FORM ELASTOMERS TECHNICAL FIELD: The field of the invention is that of silicone elastomers obtainable by polyaddition, and where the main components are siliconized polymers and fillers. More precisely, the present invention is related to the preparation of an intermediate product useful for obtaining these silicone elastomers, and constituted by a reinforced filler suspension in a polyorganosiloxane carrying Si-alkenyl functional groups, preferably Si-Vi susceptible to react by polyaddition with the SiH crosslinker functional groups of another POS.

PREVIOUS TECHNIQUE: Reinforcing and non-reinforcing fillers are distinguished in silicone rubbers.

The most commonly used reinforcing fillers are preferably pyrogenic silicas having a BET surface > 50 m2 / g. These have their reinforcing effect on the one hand to their morphology and on the other hand to the hydrogen bonds that are formed between the silanol groups on the surface of the silicas (3-4.5 SiOH / mm2 groups) and the polyorganosiloxane chains (POS) These interactions between the filler and the polymer increase the viscosity and modify the behavior of the polymer in the vicinity of the solid surface of the charges. On the other hand, the bonds between the polymers and fillers improve the mechanical properties, but they can also cause a damaging premature hardening ('structuring') of the elastomer precursor compositions.The non-reinforcing fillers have an extremely weak interaction with the polymer These are, for example, chalk, quartz powder, diatomaceous earth, mica, kaolin, aluminas or iron oxides, which frequently increase the viscosity of the unvulcanized precursors of the elastomers, as well as shore and hardness. modulus of elasticity of the latter.

The silicone elastomers may also contain, inter alia, catalysts, inhibitors, crosslinkers, pigments, anti-adhesion agents, pificants and adhesion promoters. These elastomers vulcanizable by polyaddition and also referred to as RTV elastomers, are formed prior to vulcanization by casting, extrusion, calendering or compression molding, by injection or by transfer. The silicone compositions vulcanizable in elastomers, by polyaddition at room temperature or at higher temperatures (generally <200 ° C), are conventionally packaged in the form of two component systems, ie they comprise two parts packed separately and before be mixed at the time of employment. In two-component systems, one of the components comprises the catalyst of the polyaddition reaction. This catalyst is preferably of a platinic nature. It can be, for example, a platinum complex such as that prepared from chloroplatinic acid and divinyl-1,3-tetramethyl-l, 3-3-disiloxane, according to the North American patent P 3 814 730 (Karstedt's catalyst). ). Other platinum complexes are described in the US patents USP 3159601, 3 159 662 and 3 220 972. This component, which includes the catalyst, can also comprise only one of the type I POS with Si-alkenyl cross-linking functional groups. Si-vinyl preference, or only of type II POS with SiH crosslinking functional group. In general, POS of type I and POS of type II comprise at least two Si-Vi and SiH groups respectively per molecule, preferably in position a,?; at least one of the two must comprise at least three crosslinking functional groups per molecule. The compositions comprise in a known manner the POS of type I and II, a platinum catalyst of crosslinking by polyaddition and a platinum inhibitor which allow the compositions to be cured not more than once from the packaging and mixed, eventually before they have been heated slightly. Examples of inhibitors are polyorganosiloxanes, advantageously cyclic, substituted with at least one alkenyl group, tetramethylvinyltetrasiloxane which is particularly preferred, - pyridine, phosphines and organic phosphites, unsaturated amides, alkylated maleates, and acetylenic alcohols ( see French Patent FR-B-1 528 464 and FR-A-2 372 874). Such compositions may also be presented in the form of single component systems that are not vulcanized more than after they have been heated. The preparation of the concentrated suspensions (in paste form) of reinforcing silicas in vinyl silicone oils, intended to produce vulcanizable elastomers by reaction of a polyhydrogenated crosslinking molecule such as a POS with the vinylated oil (SiH / SiVi addition), is widely used in the domain of silicone elastomers. The most known reinforcing particulate fillers are based on silica, but substances such as TiO2 A1203, kaolin, for example, can also be used in certain cases. These reinforcing fillers have a specific BET surface area of at least 50 m2 / g up to, in general, 400 m2 / g. These are ultra-fine powders that can be dispersed in silicone oils, preferably SiVi. This dispersion imposes problems of mixing the powder charge with the oil, and must be monitored particularly to obtain a uniform distribution of the charges in the suspension. Another difficulty to overcome is related to the rheology of prepared suspensions. In fact, it is clear that the introduction into the silicone oil of a pulverulent particulate filler with a very low granulometry necessarily leads to a notable increase in viscosity. However, this characteristic, although it accompanies the obtaining of good mechanical properties for the silica elastomers comprising the suspension as a raw material, is detrimental for handling and for shaping the suspension of the silicone compositions containing them. It is in fact more convenient to manipulate for the molding, extrusion or shaping, the fluid compositions that easily lend themselves to pumping, flow or mixing with functional additives, among others. The problem considered here can then be summarized as the search for a technical compromise between specifications, a priori antinomic, for suspensions of fine particulate fillers in siliconized oils, namely: fine distribution of the particles in the silicone matrix - homogenization of the dispersion - adaptation of the rheology of the suspension to the manipulation constraints (processing capacity) - mechanical properties of the RTV silicone elastomers. The French patent application No. 2 320 324 deals with this problem and describes a homogeneous distribution process in polyorganosiloxanes with a strongly dispersed active load of BET specific surface area of at least 50 m2 / g, this process being characterized in that the load is treated during incorporation, in the presence of water, by a modifying agent or compatibilizing agent of the silazane type, with hexamethyldisilazane being particularly preferred. The other compatibilizing agents mentioned are trimethylsilane, trimethylchlorosilane, trimethylethoxysilane, triorganosilylated mercaptans, triorganosilane acylates or triorganosilylated amines. According to this procedure described in this previous application, a polydimethylsiloxane-α, β-trimethylsiloxy is mixed with hexamethyldisilazane (HMDZ) and with water. Once this mixture is homogenized, the silica is incorporated in the form of particles and mixed until a homogeneous mixture is obtained. Heating is then carried out at 130 ° C to remove excess HMDZ and water by devolatilization. Allow to cool and check after measuring the viscosity of the suspension obtained, that this is relatively high, which surely confers high mechanical properties to the elastomers that can be prepared from this suspension, but that proves to be redhibitory on the plane of handling in an industrial context. This treatment of compatibilization of silica with silicone oil can be described as 'early' since the HMDZ is present from the contact of the reinforcing silica with this silicone oil.The compatibilization treatment is a means of delaying or preventing the reaction between the surface of a reinforcing filler and a siloxane polymer.This interaction causes the use of a structuring and results in the loss of aptitude of these mixtures for transformation.The processes of preparation of suspension of reinforcing silica are also known. in silicone oils, in which the treatment of the compatibilization with the help of hexamethyldisilazane intervenes after the incorporation of the silica in the silicone oil.This mode of treatment is here qualified as 'late'. This provides relatively fluid suspensions that may have a tendency to structure over time. In certain cases, the suspensions formed may have a certain tendency to thixotropy. This is not without the absence of undesirable consequences at the moment of the transformation and manipulation of these suspensions, mainly for their stirring or mixing. In any case, it has been found that, whatever the rheological qualities of the suspensions obtained by late treatment with MHDZ, the final mechanical properties of the elastomers prepared from said suspensions are perfectible (hardness, resistance to rupture, elongation to rupture, resistance to tearing). In particular, these do not reach the level of those found in the case of early treatment. By way of illustration this type of compatibilization treatment can be mentioned European Patent Application No. 0 462 032 which describes a process for the preparation of a paste that can be used mainly in vulcanizable compositions by polyaddition reaction and thus enable the production of elastomers silicone. According to this method, it is injected continuously and simultaneously, in a twin-screw extruder, into at least four different sites: - at least one POS SiVi oil, water, silica, a liquid polysilazane under normal temperature and temperature conditions. pressure (HMDZ). 'The silica is injected after the oil and the water upstream of the HMDZ, however there is no mixing, on the one hand, between the HMDZ and the water and, on the other hand, between the HMDZ and the silica, before the introduction of the HMDZ.

U.S. Patent No. 4,785,047 discloses a mixed treatment of compatibilization, on the border between the early and late treatments evoked above. This patent relates more precisely to a process for the preparation of transparent silicone elastomers. This document describes the pumpable, lube compositions formed by silicon-loaded suspensions treated with HMDZ, in silicone oils bearing or not functional cross-linking groups by polyaddition (SiH / SiVi). The problem indicated above in this patent is different from that of the prior art presented at the beginning. The purpose here is to first obtain the transparent elastomers and, in order to do so, to test the counterbalancing of the harmful effect on the transparency of the silicic charge by means of a treatment highly favored by the HMDZ. According to the process that is the object of this patent, a part of the silicone oil is first mixed with all the water and the silica, but only with a fraction of the HMDZ that systematically represents more than 15% by dry weight in relation to silica, namely 34% and 26% in the examples.

After the homogenization of this first mixture, the remaining HMDZ is incorporated and mixed thereto. The devolatilization treatment is then carried out for 1 hour at 150 ° C and under reduced pressure. The remainder of the silicone oil PDMS and PDMS a, γ-diVi is finally mixed for 1 hour at room temperature. The vulcanizable and transparent silicone suspension, obtained, has a viscosity comprised between 200 and 10,000 Pa.s. at 25 ° C. This technical proposal may sooner or later provide a solution to the problem of transparency but it proves to be unsatisfactory as regards the viscosity of the suspension and its handling.

BRIEF DESCRIPTION OF THE INVENTION: 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 charge in particulate form, treated with the aid of a compatibilizing agent, in a silicone oil, this being useful suspension as a raw material for the production of compositions vulcanizable by polyaddition in the RTV elastomer. This process must be satisfied according to the following loads: uniformity and homogenization of the distribution of the load in the siliconized oil, - optimization of the dispersion, the suspension drains well (without flow threshold) and viscosity adapted to handling and transformation of the suspension, - mechanical properties of the elastomers of an acceptable level. Another essential objective of the invention is to provide a process for preparing a suspension with reinforcing filler / silicone oil for RTV elastomers, which is simple to put into operation, economical and applicable on an industrial scale. Another essential objective of the invention is to provide a process for obtaining a silicone composition vulcanizable by polyaddition to form an RTV elastomer and comprising as a constituent the suspension as obtained by the process previously considered. These objectives, among others, are achieved by the present invention which relates to a process for preparing a suspension of a particulate filler, preferably silicic, in a material formed by a silicone oil comprising: polyorganosiloxanes (POS) of type ( I) carriers of Si-alkenyl functional groups - preferably Si-Vinyl -, adapted to react with the SiH cross-linking functional groups of a type II POS, - optionally the POS of type (II) carrying cross-linking functional groups Si- H adapted to react with the Si-alkenyl functional groups of POS (I), - and optionally POS of type (III) other than POS (I) and (II), said suspension being mainly usable to produce silicone compositions vulcanizable by polyaddition, this process is of the kind of those in which the particulate filler is treated with the help of a compatibilization agent (AC), characterized in that it consists essentially of introducing the compatibilization agent (AC), in the preparation medium: • by one part, before and / or substantially simultaneously with the presence of at least a part of the silicone oil used with at least part of the particulate filler used, this introduction of AC is operated once or several times by a fraction of AC corresponding to a proportion of less than or equal to 8%, preferably 5%, and more preferably still, to 3% by dry weight in relation to the total particulate charge; • and on the other hand, after this is put in the presence of POS / load. It is the merit of the inventors to have shown, after numerous investigations and experiments, that it would be advisable, in a totally surprising and unexpected way, to incorporate the compatibilizing agent (for example the HMDZ) before and after the mixing of the reinforcing filler. preferably, silicic, with the silicone oil (preferably type (I) SiVi), with the condition according to which, the fraction of the AC compatibilizing agent introduced before the POS / charge mixture, corresponds to at least 5% by weight of the total reinforcing load. These original and advantageous modalities make it possible to obtain suspensions endowed with rheological qualities and with an appropriate visco-elastic behavior. In effect, these suspensions do not have the flow threshold or a very weak threshold that is not detrimental to the applications. This considerably favors its start-up. In particular, they have a stable fluidity over time and adapted to handling and transformation operations, such as pumping, routing, mixing, shaping, molding, extrusion, etc. One of the main interests of the invention is that this experience on the plane of rheology does not exist to the detriment of the final mechanical properties of the crosslinked elastomer. In this way the technical commitment is achieved.

On the other hand, the methodology considered allows to obtain good homogeneous dispersions of the particulate charge in the oil. In addition, this methodology does not significantly complicate the process, which is simple to put into operation and inexpensive.

DETAILED DESCRIPTION OF THE INVENTION: According to one of these preferred embodiments of operation, the process according to the invention consists essentially of: * 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 constituted by silica 1 to 20 parts by weight of the compatibilizing agent (AC), selected from the silazanes, taken alone or as a mixture between them, preferably between the disilazanes, hexamethyldisilazane associated or not with divinyltetramethyldisilazane, which are particularly preferred; * reacting, preferably under stirring, * heating the obtained mixture, choosing a pressure / temperature pair such that a devolatilization of at least a part of the water and the volatile elements takes place; * cool the mixture if necessary. In other words, the process according to the invention allows access to a control of the viscosity of the suspension always maintaining an acceptable level, if not improving the mechanical properties of the final elastomer obtained from the suspension. The mixing is carried out with the aid of known and appropriate devices. It can be for example: mixers of internal mixing arms mixer planetary mixers with paddles in the form of plowshare double-shaft mixers with or against rotary mixers continuous extruders or other discontinuous or continuous devices. The mixing operation is carried out at normal temperature and pressure and preferably under inert atmosphere (N2). It is also convenient that under these conditions, the silicone oil, the water but also the compatibilizing agent are in the liquid form to facilitate mixing. The preferably silicic reinforcing filler represents from 10 to 50% by weight of the suspension. In practice, this load is of the order of 30 ± 10%. Advantageously, the proportion of compatibilizing agent introduced at a first time is at most equal to 8% of the reinforcing filler (and for example comprised between 1 and 3% of the reinforcing filler, preferably between 1 and 2%. In part, it can be stated that the total amount of compatibilizing agent AC is preferably between 5 and 30% of the silicic load, preferably between 10 and 20% The proportions of the AC agent introduced before and after mixing of charge / oil are respectively (5-25), preferably (10-20%).

In order to define more precisely, however this is not limiting, the preferred mode of operation of the process according to the invention, it can be indicated that it comprises the following steps: it is mixed, preferably under an inert gas atmosphere (for example N2), all or part of the silicone oil, water and all or part of the particulate silica, with a first fraction of CA comprised between 1 and 3% by dry weight in relation to the silica, is incorporated into the mixture a second fraction of AC representing between 10 and 15% by dry weight of the silica, - if necessary, the silicone oil and silica residues are added, preferably reacting by continuing the mixture, devolatilizing, preferably under an atmosphere of Inert gas (for example N2), the devolatilized mixture is allowed to cool and the suspension is possibly supplemented with the remains of the silicone oil.

According to a first particular embodiment of the implementation of the process of the invention, this comprises the following steps: 1 - proceeds to the homogenization of a mixture comprising the silicone oil, water and the first fraction of AC - preferably HDMZ , 2 - the particulate filler, preferably silica, is progressively added to the mixture obtained in 1, 3 - the mixture is continued, 4 - the second fraction of AC is incorporated progressively into the mixture obtained in 3 - preferably HMDZ The mixture is continued, 6 - is devolatilized, preferably by heating to a temperature >; 100 ° C. In step 1 of this first embodiment, there is a choice between the following three alternatives, among others: a) either all the oil and all the silica and the starting fraction of CA are put into operation, b) either all the oil is put into operation, a part of the silica and the starting fraction of AC, c) or all the silica, a part of the oil and the starting fraction of AC is put into operation. According to a second particular embodiment of the implementation of the process of the invention, the latter comprises the following steps: 1 '- proceeds to the homogenization of silicone oil and water 2'- is progressively incorporated into the mixture obtained in 1 , the particulate filler, preferably the silica, and simultaneously the first fraction of AC, preferably HMDZ; 3 - the mixture is continued, 4 - progressively incorporated into the mixture obtained in 3, the second fraction of AC, preferably HMDZ, 5 - the mixture is continued, 6 - is devolatilized, preferably by heating to a temperature > 100 ° C.

The characteristic of this second modality is linked to the fact that a co-addition of the particulate reinforcing filler and its compatibilizing agent is proceeded. It is thus possible to imagine a pre-mixing of these two constituents or alternatively a concomitant introduction of these. The progressive incorporation of stage 2 'can be carried out continuously or fractionally. According to a variant of this second embodiment, 1"- the silicone oil is charged, 2" - the particulate filler, preferably the silica, the first filtrate fraction is incorporated progressively and simultaneously in the oil. AC, preferably HMDZ, and water 3 - the mixture is continued, 4 - progressively incorporated into the mixture obtained in 3, the second fraction of AC, preferably HMDZ, 5 - the mixture is continued, 6 - is devolatilized, preferably by heating to a temperature > 100 ° C According to an advantageous arrangement of the invention corresponding to the case in which the reinforcing filler is silica and the AC agent of HMDZ, a sufficient amount of HMDZ is put into operation so that the proportion of the surface of the the portion Si (Me) 3 is > to 1 portion Si (Me) 3 per mm2, and preferably comprised between 1 and 2 Si (Me) 3 portions per mm2. According to a third embodiment of putting the invention into operation, the process involved is characterized: ß because the first fraction of AC is totally or partially replaced by at least one start-up auxiliary, chosen between the molecules and the associations of molecules: able to interact with the particulate charge, in particular with silicon in the case where it is a siliceous load to the detriment of the bonds or hydrogen bonds that this particulate charge maintains mainly between its own atoms and / or with those of silicone oil; - and apt to be eliminated from the preparation medium by devolatilization; B and because it is carried out in such a way that this operating aid is in the presence of water in the preparation medium. According to this third mode of operation, it is preferable that the start-up aid is easily removable from the preparation means. For this purpose, it is interesting that it lends itself well to elimination by devolatilization, for example by heating under vacuum or under gas stream. Under these conditions, it is clear that low molecular weight molecules will be preferred, as an operating aid. Advantageously, the operating auxiliary of the group comprising: the silazanos is chosen, with the HMDZ being preferred; the difunctional or preferably monofunctional hydroxylated siloxanes; - the amines, preferably the ammonia and / or the alkylamines, with diethylamine being particularly preferred; organic acids, with formic and / or acetic acids being preferred; - And their mixtures.

As indicated at the beginning, the products more particularly selected as operating aid are those endowed with a small molecular weight. This is verified mainly for the abovementioned amines and organic acids. In the case of products put into operation in the process according to the invention, it can be indicated that, for the silicone oil, linear or cyclic but above all linear polydiorganosiloxanes will be chosen preferably. As regards the POS (I), it will be polydiorganosiloxane oil carrying Si-alkenyl, particularly Si-vinyl, in and / or at the ends of the chain. In practice, mention may be made, for example, of the α, α-divinyl polydialkyl (methyl) siloxane. Preferably, the POS (I) used for the preparation of the suspension is a vinylated POS (I), carrying at least two SiVi portions per molecule, preferably at least three per molecule, when the POS (II) does not include more than two SiH portions per molecule. POS (II) is chosen from polyorganohydrogensiloxanes comprising at least two SiH moieties per molecule, preferably at least three when the POS (I) does not include more than two SiVi per molecule. In practice, mention may be made, for example, of the polyalkyl (methyl) hydrogenosiloxane or even the hydrogenated branched POSs, which include tri or tetrafunctional portions and SiH carrying portions. The POS (III) can be a polydiorganosiloxane, such as a polyalkyl preferably polydimethylsiloxane with trimethylsilylated ends. Preferred silicone oils (I, II, III) comprise essentially R2SiO portions, the symbols R representing identical or different, (cyclo) alkyl groups of 1 to 4 carbon atoms optionally halogenated, the aryl groups optionally substituted or halogenated. As the groupings: alkyl: Mention may be made mainly of the methyl, ethyl, propyl and butyl groups, - halogenated alkyl: there can be mentioned 3,3-trifluoropropyl, cycloalkyl: cyclohexyl, aryl: the group may be mentioned phenyl. Preferably, at least 85% of the R groups represent methyl groups.

The silica used in the process according to the invention is a reinforcing silica where the specific surface area is preferably between 50 and 400 m2 / g. These silicas can be precipitated silicas, but combustion silicas are generally used. The fact that silica is preferred does not exclude the use of other known types of reinforcing fillers. AC is preferably a silazane and more preferably still a disilazane. It is a liquid product under normal conditions of temperature and pressure (23 ° C - 760 mmHg). The viscosity of the suspension is one of the determining parameters that govern the process according to the invention. Thus, according to an advantageous provision of the latter: an alkenylated silicone oil, preferably vinylated, is introduced into operation, comprising at least two Si-alkenyl groups per molecule, preferably each located at one end of the chain and of dynamic viscosity at 25 ° C, less than or equal to 250 Pa.s, preferably at 100 Pa.s and more preferably still at 10 Pa.s, a silica of specific surface is chosen BET comprised between 50 and 400 m2 / g and of mixing conditions such that the dynamic viscosity at 25 ° C, of the suspension is less than or equal to 300 Pa.s, preferably at 250 Pa.s and more preferably still at 200 Pa. s.

INDUSTRIAL APPLICATION: The vocation of the reinforced filler / silicone oil suspension prepared according to the invention is to be used in the preparation of liquid or pasty silicone compositions, vulcanizable by polyaddition preferably, in silicone elastomer RTV in the ambient atmosphere at normal temperature or Higher temperature. Thus, according to these aspects, the present invention relates to a process for obtaining a silicone composition vulcanizable by polyaddition, characterized in that it consists in mixing the following products: A - a suspension that is prepared according to the process as defined above, B - one or several POS (I) as defined above, C - one or more POS (II) as defined above, D - possibly one or several POS (III), as defined above, used as diluent (s) E - a catalyst system comprising a catalyst, preferably of a platinic nature, and optionally an inhibitor or retarder. According to a first variant of this process: the composition is produced, in the form of a system of two components Ci and C2 intended to be brought into contact with each other to produce an elastomer crosslinked by polyaddition between the POS (I) and (II), and it is done in such a way only one of the parts Ci or C2 contains the catalyst D, and eventually one or the other of the POS (I) and (II). According to a second variant of this process for the preparation of vulcanizable liquid compositions, a single-component system is made to crosslink in ambient air and / or under the effect of temperature. These vulcanizable precursor compositions of elastomers can 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 possible additives F can also be constituted by pigments, anti-adhesion agents, plasticizers or rheology modifiers, stabilizers or adhesion promoters. The following examples illustrate: the preparation of reinforcing filler suspensions in silicone oils according to the invention, > the application of these suspensions as a raw material for the production of two component compositions and vulcanizable in RTV silicone elastomers > as well as the evaluation of the viscoelastic properties of the suspensions and the mechanical properties of the crosslinked elastomers obtained from said suspensions.

Two embodiments for putting the process of the invention into operation are given in the examples. The latter also comprise the comparative examples of preparation of the suspensions according to the prior art, according to the modalities of compatibilization treatment of the "late" type and of the "early" type.

EXAMPLES COMPARATIVE EXAMPLE 1: LATE TREATMENT In a 1.5-liter mixer, 750 g of polydimethylsiloxane (PDMS) oil are introduced, dialysed viscosity of 0.6 Pa.s and 21 g of water. After the homogenization, 321 g of a combustion silica characterized by its specific surface area of 300 m2 / g are added in portions in 70 minutes. After 120 minutes of mixing, 66 g of hexamethyldisilazane are added over 90 minutes. 60 minutes later a heating phase begins in the course of which the mixture is placed under a stream of nitrogen (250 l / h) when the temperature reaches 80 ° C; the heating continues until reaching approximately 155 ° C, temperature that is maintained during 2 h. After cooling, 43 g of vinylated oil are added and the suspension is homogenized. Starting from this suspension, a part A and a part B are formulated. Part A contains: 90.6 g of the suspension, 1.58 g of the PDMS oil a, Δ-dyninylated, described, 5.48 g of a PDMS a, ß -dihydrogenated oil whose titre is 1.9 meq of SiH per gram of oil, 2.35 g of a PDMS polyhydrogenated oil of viscosity of 30 mPa.s, with a titre of 1.6 meq of SiH per gram of oil. Part B contains: 11 g of the suspension 29 g of PDMS oil a, DIVINYL described above, 9.77 g of a PDMS a, DIVINATED oil whose titre is 0.05 meq Vi per gram oil, 70 PL a Karstedt catalyst dosed at 12% platinum 90 μl divinyltetramethyldisiloxane 140 μl tetravinyltetramethylcyclotetrasiloxane.

Parts A and B are mixed in the proportion of 100 to 10 and after the cessation of bubbling, 2 mm thick plates of elastomers are prepared. These moldings are vulcanized in a ventilated oven for 1 hour at 150 ° C. The samples needed for measuring the mechanical properties are cut out in these vulcanized elastomer plates.

EXAMPLE 2: EARLY TREATMENT The preceding example is reproduced except that here one starts by loading the 750 g of PDMS oil a,? -divinilado, the 21 g of water and 66 g of hexamethyldisilazane. After 10 minutes of agitation, the silica is incorporated in portions in 30 minutes; the mixture is continued for an additional 120 minutes before starting the heating phase which is the same as described above. The suspension is formulated as in example 1.

Comparative properties of the suspensions and vulcanized elastomers according to examples 1 and 2 The viscosity of the suspensions is measured by means of a dynamic rheometer equipped in a conical-plane geometry. The complex viscosity is taken at 1 Hz under 1 Pa as representative of the viscoelastic behavior of the suspensions. The mechanical properties are measured according to the standards in force: DIN 53505 for the measurement of the hardness, AFNOR T46002 for the measurements of rupture.

In the case of example 1, the viscosity is low but the breaking properties of the elastomer are modest. In the case of example 2, the best rupture properties are noted, but at the cost of an important viscosity.

EXAMPLE 3: TWO-TIME TREATMENT In a 100 1 arm mixer, 40 kg of a -? - divinylated oil of viscosity of 2 Pa.s, 0.27 kg of hexamethyldisilazane and 0.27 kg of water are introduced. After homogenization, 16.2 kg of a combustion silica characterized by its specific surface area of 200 m2 / g are added in portions in 100 minutes. After 60 minutes of mixing, 1.9 kg of hexamethyldisilazane are added in 60 minutes. 120 minutes later, a heating phase begins, in the course of which the mixture is placed under a stream of nitrogen (30 m 3 / h); the heating continues until reaching approximately 140 ° C, temperature that is maintained for 2 hours. The suspension is then allowed to cool. Starting from this suspension, part A and part B are formulated. Part A contains: 427 g of the suspension. 10 g of a PDVM poly viscosity oil of 0.4 Pa.s whose titre is 0.11 meq Vi per gram of oil. oil with viscosity trimethyl endings of 0.1 Pa.s. 26.5 g of a PDMS a,? -dihydrogenated oil whose titre is 1.9 meq of SiH per gram of oil. 11.3 g of a PDMS polyhydrogenated oil with a viscosity of 30 mPas whose titre is 1.6 meq SiH per gram of oil. Part B contains: 180 g of the suspension 20 g of the methyl-terminated oil described 250 μl of a Karstedt catalyst dosed with 12% platinum, 1 ml of tetravinyltetramethylcyclotetrasiloxane. The parts A and B are mixed in the proportion of 100 to 10 parts and after the completion of the bubbling the samples necessary for the measurement of the mechanical properties are prepared as explained for the comparative examples 1 and 2.

EXAMPLE 4: TWO-TIME TREATMENT WITH REAGENT CODING The previous example is reproduced except that here the 40 kg of PDMS a,? -divinillated oil and the 0.27 kg of water are loaded first. After 10 minutes of agitation, the silica is incorporated in portions in 120 minutes simultaneously to 0.27 kg of hexamethyldisilazane, which is distributed according to the silica portions. At the termination of this phase of coaddition of silica and hexamethyldisilazane, the process is continued as described above. The suspension is formulated as in example 3.

Properties of the suspensions and the vulcanized elastomers according to examples 3 and 4 The viscosity of the suspensions is measured by means of a dynamic rheometer equipped in a conical-plane geometry. The complex viscosity is taken at 1 Hz under 1 Pa and the threshold voltage for which the elastic and viscous modules are equal, and representative of the viscoelastic behavior of the suspensions. The mechanical properties are measured according to the standards in force.

Examples 3 and 4 show that the elastomers prepared from the oil / silica suspensions obtained according to the invention have a rheology with a low flow threshold and moderate viscosity. This very favorable rheological behavior is accompanied by excellent resistance to tearing.

EXAMPLE 5: TWO-TIME TREATMENT FOR HEXAMETILDISILAZAN Preparing the suspension In a 7 1 arm mixer, 2120 g of a mixture of α, α-deionized oils of viscosity of 1.5 Pa.s, 12.6 g of water and 12.6 g of hexamethyldisilazane are introduced. After the homogenization, 765 g of a combustion silica characterized by its specific surface area of 200 m2 / g are added in portions in 110 minutes. 80 g of hexamethyldisilazane are then added in 60 minutes. 120 minutes later a heating phase begins in which the mixture is placed under vacuum when the temperature reaches 70 ° C; the heating continues until reaching approximately 150 ° C, temperature that is maintained during 1 h. It is then cooled under a stream of nitrogen ("250 l / h) and the apparatus is emptied. Starting from this suspension, part A and part B are formulated. Part A contains: 946.7 g of the suspension 42.7 g of a α, β-dihydrogenated oil with a titre of 1.9 meq SiH per gram of oil 10.7 g of a polyhydrogenated oil with a titre of 1.6 meq SiH per gram of oil Part B contains: 22 g of the suspension 20 g of a,? -divinilado oil whose titre is 0.15 meq Vi per gram of oil 58 g of a a,? -divinilado oil whose title is 0.05 meq of Vi per gram of oil 140 μl of a catalyst of Karstedt dosed with 10% of platinum 0.15 g of diviniltetramethyldisiloxane 0.35 g of tetravinyltetramethylcyclotetrasiloxane. The parts A and B are mixed in the proportion of 100 to 10 parts and after the cessation of the bubbling, the necessary samples for the measurement of the mechanical properties are prepared.

EXAMPLE 6: TREATMENT WITH FIRST ACID PHASE The preceding example is reproduced, except that the 12.6 g corresponding to the first portion of hexamethyldisilazane are replaced with 3.6 g of formic acid. All other operations are conducted as described above. The suspension is formulated as in example 5.

EXAMPLE 7: TREATMENT WITH FIRST BASIC PHASE Example 5 is repeated, except that here the 12.6 g corresponding to the first portion of hexamethyldisilazane are replaced with 4.2 g of ammonia with 32% ammonia titre. All other operations are conducted as described above. The suspension is formulated as in example 5.

EXAMPLE 8: EVALUATION OF THE COMPARATIVE PROPERTIES OF THE SUSPENSIONS OF EXAMPLES 5 TO 7 The viscosity of the suspensions is measured by means of a dynamic rheometer equipped in a conical-plane geometry. They are taken as representative of the viscoelastic behavior of the suspensions: - the complex viscosity and its elastic and viscous components at 1 Hz under 1 Pa the threshold voltage for which the elastic and viscous moduli are equal. The mechanical properties are measured according to the standards in force.

Example 5 Example 6 Example 7 base acid Complex viscosity 41 38 42 Elasticity rate 0.68 0.65 0.73 Flow threshold < 1 < 1 < 1 Hardness Shore A 28 35 32 Elongation to rupture 700 400 610 Resistance to rupture 6.8 6.3 8.0 Resistance to tearing 29 21 23 It is easily observed that the rheological behavior of the suspensions is in all three cases typical of a product that flows well and that these suspensions allow the realization of elastomers with good mechanical properties.

Claims (11)

1. A process for preparing a suspension of a particulate filler, preferably silicic, in a material formed by a silicone oil comprising: polyorganosiloxanes (POS) of type (I) carrying functional groups Si-alkenyl - preferably Si-Vinyl - , adapted to react with the SiH crosslinking functional groups of a type II POS, possibly the POS of type (II) carrying Si-H crosslinking functional groups adapted to react with the Si-alkenyl functional groups of the POS (I), and optionally POS of type (III) different from POS (I) and (II), said suspension being mainly usable to produce silicone compositions vulcanizable by polyaddition, this process is of the kind of those in which the particulate filler is treated with the aid of a compatibilization agent (AC), characterized in that it consists essentially of introducing the compatibilization agent (AC), into the preparation medium n: • on the one hand, before and / or substantially simultaneously with the presence of at least a part of the silicone oil used with at least a part of the particulate filler used, this introduction of AC is operated in one or several times for a fraction of AC corresponding to a proportion of less than or equal to 8%, preferably 5%, and more preferably still, to 3% by dry weight in relation to the total particulate charge; • and on the other hand, after this is put in the presence of POS / load.

2. Process according to claim 1, characterized in that it consists essentially of: * 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 constituted by silica 1 to 20 parts by weight of the compatibilization agent (AC), selected from the silazanes, taken alone or as a mixture between them, preferably between the disilazanes, hexamethyldisilazane associated or not with divinyltetramethyldisilazane, which are particularly preferred; letting react, preferably under stirring, heating the obtained mixture, choosing a pressure / temperature pair in such a way that a devolatilization of at least a part of the water and the volatile elements takes place; cool the mixture if necessary.

3. Process according to claim 1 6 2, characterized in that: all or part of the silicone oil, water and all or part of the particulate silica is mixed with a first fraction of CA comprised between 1 and 3% by dry weight with respect to To the silica, a second fraction of AC is added to the mixture, which represents between 10 and 15% by dry weight of the silica, if necessary, the remains of the silicone oil and the silica are added, it is allowed to react preferably continuing the mixture The mixture is devolatilized, the devolatilized mixture is allowed to cool, and the suspension is eventually supplemented with the residues of the silicone oil.

4. Process according to claim 3, characterized in that: 1 - homogenization of a mixture comprising the silicone oil, water and the first fraction of AC - preferably HDMZ, 2 - is progressively added to the particulate filler, preferably the silica, to the mixture obtained in 1, 3 - the mixture is continued, 4 - progressively incorporated into the mixture obtained in 3, the second fraction of AC - preferably HMDZ - 5 - the mixture is continued, 6 - is devolatilized , preferably by heating to a temperature > 100 ° C.

5. Process in accordance with the • 10 claim 3, characterized in that: 1 '- the silicone oil and water 2' are homogenized - the particulate filler, preferably the silica, is incorporated progressively into the mixture obtained in 1, and simultaneously the first fraction of AC, preferably HMDZ; 3 - the mixture is continued, 4 - progressively incorporated into the mixture 20 obtained in 3, the second fraction of AC, preferably HMDZ, 5 - the mixture is continued, 6 - is devolatilized, preferably by heating to a temperature > 100 ° C.

6. Process according to claim 3, characterized in that: 1"- the silicone oil is charged, 2" - the particulate filler, preferably the silica, the first fraction of AC, is incorporated progressively and simultaneously in the oil, preferably HMDZ, and water 3 - the mixture is continued, 4 - the mixture obtained in 3 is incorporated progressively, the second fraction of AC, preferably HMDZ, 5 - the mixture is continued, 6 - is devolatilized, preferably by heating at a temperature > 100 ° C.

7. Process according to any of claims 1 to 6, characterized: > because the first fraction of AC is replaced totally or partially by at least one auxiliary put into operation, chosen between the molecules and the associations of molecules: able to interact with the particulate charge, in particular with silicon in the case where it is of a siliceous charge to the detriment of the hydrogen bonds or bridges that this particulate charge maintains mainly between its own atoms and / or those of the silicone oil; - and apt to be eliminated from the preparation medium by devolatilization; and because it is done in such a way that this • 10 start-up auxiliary is in the presence of water in the preparation medium.

8. Process according to claim 7, characterized in that the operating auxiliary of the group comprising is chosen. • the silazanos, with HMDZ being preferred; the difunctional or preferably monofunctional hydroxylated siloxanes; 20 - amines, preferably ammonia and / or alkylamines, with diethylamine being particularly preferred; organic acids, with formic and / or acetic acids being preferred; 25 and its mixtures.

9. Process of compliance with any of • claims 1 to 8, characterized in that: an alkenylated silicone oil, preferably vinyl, is introduced which comprises at least two Si-alkenyl groups per molecule, preferably each located at one end of the chain, and of viscosity dynamic at 25 ° C, less than or equal to 250 Pa.s, preferably at 100 Pa.s and more preferably still at 10 Pa.s, • 10 a silica of specific surface BET between 50 and 400 m2 / g and The mixing conditions are such that the dynamic viscosity at 25 ° C of the suspension is less than or equal to 300 Pa.s, preferably at 250 Pa.s and more preferably still 15 to 200 Pa.s

10. Process for obtaining a silicone composition vulcanizable by polyaddition, characterized in that it consists in mixing the following products: A- the suspension as prepared according to the process as defined in any of claims 1 to 9; B - one or more POS (I) as defined in claim 1, C - one or several POS (II) as defined in claim 1, D - possibly one or more POS (III), such as are defined in claim 1, useful (s) as diluent (s), E - a catalyst system comprising a catalyst, preferably of platinic nature, and optionally an inhibitor.

11. Process according to claim 10, characterized in that: the composition is produced in the form of the system of two components Ci and C2 intended to be brought into contact with one another to produce an elastomer crosslinked by polyaddition between the POS (I) and (II), and because it is done in such a way that only one of the parts Ci or C2 contains the catalyst D and possibly one or the other of the POS (I) (II).