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, characterized 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.

1 - 11 . (canceled)  
     
     
         12 . Process for preparing a suspension of a particulate filler in a material formed by a silicone oil comprising: 
 polyorganosiloxanes (POS fluids) of type (I) which carry Si-alkenyl 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 suspension being able to be used for producing silicone compositions that can be cured by polyaddition,    this process being one in which the particulate filler is treated with the aid of a compatibilizing agent or compatibilizer,    the process comprising introducing a compatibilizer into a mixture of silicone oil and particulate filler:    after contacting of at least part of the silicone oil employed with at least part of the particulate filler used, this compatibilizer introduction optionally taking place in a first step for a compatibilizer fraction corresponding to a proportion of at most 8% by dry weight with respect to the total particulate filler.    
     
     
         13 . Process according to  claim 12 , comprising: 
 mixing a total of:    100 parts by weight of silicone oil,    0 to 5 parts by weight of water,    20 to 80 parts by weight of particulate filler comprising silica; and    1 to 20 parts by weight of compatibilizer selected from silazanes or a mixture of silazanes;    leaving the above to react,    heating the mixture obtained at a pressure and temperature so that at least some of the water and of the volatile elements undergoes devolatilization; and,    if necessary, cooling the mixture.    
     
     
         14 . Process according to  claim 12 , wherein a first compatibilizer fraction is replaced, completely or partly, with at least one processing aid, wherein the at least one processing aid is different from the first compatibilizer fraction and is selected from molecules or combinations of molecules which are capable of interacting with the particulate filler, to the detriment of the hydrogen bonds that this particulate filler establishes between its own atoms and/or with those of the silicone oil, and are capable of being removed from the preparation mixture by devolatilization, and said processing aid is in the presence of water in the preparation mixture.  
     
     
         15 . Process according to  claim 14 , wherein the processing aid is selected from: 
 silazanes;    difunctional, or monofunctional, hydroxylated siloxanes;    amines;    organic acids; or    mixtures thereof.    
     
     
         16 . Process according to  claim 12 , wherein the silicone oil is an alkenylated silicone oil comprising at least two Si-alkenyl groups per molecule and having a dynamic viscosity at 25° C. not exceeding 250 Pa·s, the particulate filler comprises a silica having a BET specific surface area of between 50 and 400 m 2 /g and the mixing conditions are such that the dynamic viscosity at 25° C. of the suspension does not exceed 300 Pa·s.  
     
     
         17 . (canceled)  
     
     
         18 . Process according to  claim 35 , wherein the silicone composition is produced in the form of a two-component system comprising parts C 1  and C 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 only one of the parts, C 1  or C 2 , contains some catalyst B and, optionally, one or the other of the POS fluids (I) and (II).    
     
     
         19 . Process according to  claim 12 , wherein said particulate filler is a siliceous filler.  
     
     
         20 . Process according to  claim 12 , wherein said Si-alkenyl functional groups are Si-vinyl groups.  
     
     
         21 . Process according to  claim 12 , wherein said compatibilizer fraction corresponds to a proportion of at most 5% by dry weight with respect to the total particulate filler.  
     
     
         22 . Process according to  claim 12 , wherein said compatibilizer fraction corresponds to a proportion of at most 3% by dry weight with respect to the total particulate filler.  
     
     
         23 . Process according to  claim 13 , wherein said silazanes or said mixture of silazanes are disilazanes.  
     
     
         24 . Process according to  claim 13 , wherein said silazanes or said mixture of silazanes comprises hexamethyldisilazane, optionally combined with divinyltetra-methyldisilazane.  
     
     
         25 . Process according to  claim 14 , wherein said molecules or combinations of molecules are capable of interacting with silicon.  
     
     
         26 . Process according to  claim 15 , wherein said silazanes comprise hexamethyldisilazane.  
     
     
         27 . Process according to  claim 15 , wherein said amines are ammonia and/or alkylamines.  
     
     
         28 . Process according to  claim 15 , wherein said organic acids are formic acid and/or acetic acid.  
     
     
         29 . Process according to  claim 16 , wherein said alkenylated silicone oil is vinylated silicone oil.  
     
     
         30 . Process according to  claim 16 , wherein said at least two Si-alkenyl groups are located at one end of the molecule chain.  
     
     
         31 . Process according to  claim 16 , wherein said silicone oil has a dynamic viscosity at 25° C. not exceeding 100 Pa·s.  
     
     
         32 . Process according to  claim 16 , wherein said silicone oil has a dynamic viscosity at 25° C. not exceeding 10 Pa·s.  
     
     
         33 . Process according to  claim 16 , wherein said dynamic viscosity at 25° C. of the suspension does not exceed 250 Pa·s.  
     
     
         34 . Process according to  claim 16 , wherein said dynamic viscosity at 25° C. of the suspension does not exceed 200 Pa·s.  
     
     
         35 . Process for obtaining a silicone composition that can be cured by polyaddition, the process comprising: 
 (a) preparing a suspension (A) comprising a particulate filler and a silicone oil, wherein the suspension is prepared in a process comprising introducing a compatibilizer after contacting of the silicone oil and filler, wherein the introduction of the compatibilizer is preformed in a first step for a compatibilizer fraction corresponding to a proportion of at most 8% by dry weight with respect to the total particulate filler;    wherein the suspension (A) is comprised of polyorganosiloxanes (POS fluids) of type (I) which carry Si-alkenyl 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 of type (I), and/or optionally POS fluids of type (III) which differ from the POS fluids (I) and (II), and    (b) mixing suspension (A) with a catalytic system (B) comprising a catalyst and optionally an inhibitor.