Method of preparing silicas, silicas with specific pore-size and/or particle-size distribution, and the uses thereof, in particular for reinforcing polymers

Abstract

The invention relates to a novel method of preparing silicas and to highly-structured silicas having the following characteristics: a specific surface area CTAB (SCTAB) of between 40 and 525 m2/g; a specific surface area BET (SBET) of between 45 and 550 m2/g; an object size distribution width Ld ((d84−d16)/d50), which is measured by XDC particle size analysis after deagglomeration with ultrasound, of at least 0.91; and a pore-size distribution such that ratio V(d5−d50)/V(d5−d100) is at least 0.66. The invention also relates to the use of said silicas as polymer reinforcing fillers.

1 - 51 . (Canceled)  
     
     
         52 . A process for preparing silica, comprising the reaction of a silicate with an acidifying agent whereby a silica suspension is obtained, followed by the separation and the drying of this suspension, said reaction of the silicate with the acidifying agent being carried out according to the following successive steps: 
 (i) forming an aqueous stock having a pH of between 2 and 5;    (ii) adding simultaneously silicate and acidifying agent to the said stock in such a way that the pH of the reaction mixture is maintained between 2 and 5;    (iii) stopping the addition of the acidifying agent, while continuing to add silicate into the reaction mixture until a pH value of the reaction mixture of between 7 and 10, is obtained;    (iv) adding simultaneously silicate and acidifying agent to the reaction mixture in such a way that the pH of the reaction mixture is maintained between 7 and 10; and    (v) stopping the addition of the silicate, while continuing to add the acidifying agent into the reaction mixture until a pH value of the reaction mixture of less than 6 is obtained.    
     
     
         53 . The process according to  claim 52 , wherein a maturing step is carried out between step (iii) and step (iv).  
     
     
         54 . The process according to  claim 52 , wherein a maturing step is carried out after step (v).  
     
     
         55 . The process according to  claim 52 , wherein, in step (v), the addition of the silicate is stopped, while continuing to add the acidifying agent into the reaction mixture until a pH value of the reaction mixture of between 3 and 5.5 is obtained.  
     
     
         56 . The process according to  claim 52 , wherein, between step (iii) and step (iv), acidifying agent is added to the reaction mixture, the pH of the reaction mixture after this addition being between 7 and 9.5.  
     
     
         57 . The process according to  claim 52 , wherein the entire reaction between the silicate and the acidifying agent is carried out between 70 and 95° C.  
     
     
         58 . The process according to  claim 52 , wherein the entire reaction between the silicate and the acidifying agent is carried out at a constant temperature.  
     
     
         59 . The process according to  claim 52 , wherein step (i) comprises the addition of acidifying agent to water so as to obtain a pH value of the stock thus formed of between 2 and 6.  
     
     
         60 . The process according to  claim 52 , wherein step (i) comprises the addition of acidifying agent to a water+silicate mixture so as to obtain a pH value of the stock thus formed of between 2 and 6.  
     
     
         61 . The process according to  claim 52 , wherein step (i) comprises the addition of acidifying agent to a stock containing preformed silica particles at a pH of greater than 7 so as to obtain a pH value of the stock thus formed of between 2 and 6.  
     
     
         62 . The process according to  claim 52 , wherein the drying is carried out by spray drying.  
     
     
         63 . The process according to  claim 52 , wherein the separation comprises a filtration carried out by means of a filter press.  
     
     
         64 . The process according to  claim 62 , wherein the drying is carried out by means of a nozzle spray dryer.  
     
     
         65 . The process according to  claim 52 , wherein the separation comprises a filtration carried out by means of a vacuum filter.  
     
     
         66 . The process according to  claim 62 , wherein the drying is carried out by means of a turbine spray dryer.  
     
     
         67 . A silica, having: 
 a CTAB specific surface area (S CTAB ) of between 40 and 525 m 2 /g;    a BET specific surface area (S BET ) of between 45 and 550 m 2 /g;    a size distribution width L d  ((d84−d16)/d50) of objects measured by XDC particle size analysis after ultrasonic disintegration of at least 0.91, and    a pore volume distribution such that the ratio V (d5−d50) /V (d5−d100)  is at least 0.66.    
     
     
         68 . The silica according to  claim 67 , wherein the size distribution width L d  of objects is of at least 0.94.  
     
     
         69 . The silica according to  claim 67 , wherein the ratio V (d5−d50) /V (d5−100)  is at least 0.68.  
     
     
         70 . The silica according to  claim 67 , wherein 
 the size distribution width L d  ((d84−d16)/d50) of objects measured by XDC particle size analysis after ultrasonic disintegration, is of at least 1.04, and    the pore volume distribution such that the ratio V (d5−d50) /V (d5−d100)  is at least 0.71.    
     
     
         71 . The silica according to  claim 67 , having, after ultrasonic disintegration, a median diameter (Ø 50S ) of less than 8.5 μm.  
     
     
         72 . The silica according to  claim 67 , having, after ultrasonic disintegration, a median diameter (Ø 50M ) of less than 8.5 μm.  
     
     
         73 . The silica according to  claim 67 , having a rate of disintegration, denoted by a, measured in the test referred to as ultrasonic disintegration in pulsed mode, at 100% power of a 600 watt probe, of at least 0.0035 μm −1 .min −1 .  
     
     
         74 . A silica, having: 
 a CTAB specific surface area (S CTAB ) of between 40 and 525 m 2 /g;    a BET specific surface area (S BET ) of between 45 and 550 m 2 /g; and    a pore distribution width ldp of greater than 0.70.    
     
     
         75 . The silica according to  claim 74 , having a size distribution width L d  ((d84−d16)/d50) of objects, measured by XDC particle size analysis after ultrasonic disintegration, of at least 0.91.  
     
     
         76 . The silica according to  claim 74 , having, after ultrasonic disintegration, a median diameter (Ø 50S ) of less than 8.5 μm.  
     
     
         77 . The silica according to  claim 74 , having, after ultrasonic disintegration, a median diameter (Ø 50M ) of less than 8.5 μm.  
     
     
         78 . The silica according to  claim 74 , having a rate of disintegration, denoted by α, measured in the test referred to as ultrasonic disintegration in pulsed mode, at 100% power of a 600 watt probe, of at least 0.0035 μm 1 .min 1 .  
     
     
         79 . A silica, having: 
 a CTAB specific surface area (S CTAB ) of between 40 and 525 m 2 /g;    a BET specific surface area (S BET ) of between 45 and 550 m 2 /g;    a size distribution width L′ d  ((d84−d16)/d50) of objects smaller than 500 nm, measured by XDC particle size analysis after ultrasonic disintegration, of at least 0.95; and    a pore volume distribution such that the ratio V (d5−d50) /V (d5−d100)  is at least 0.71.    
     
     
         80 . The silica according to  claim 69 , having the ratio V (d5−d50) /V (d5−d100)  of at least 0.73.  
     
     
         81 . A silica, having: 
 a CTAB specific surface area (S CTAB ) of between 40 and 525 m 2 /g;    a BET specific surface area (S BET ) of between 45 and 550 m 2 /g;    a size distribution width L′ d  ((d84−d16)/d50) of objects smaller than 500 nm, measured by XDC particle size analysis after ultrasonic disintegration, of at least 0.90; and    a pore volume distribution such that the ratio V (d5−d50) /V (d5−d100)  is at least 0.74.    
     
     
         82 . The silica according to  claim 70 , wherein the size distribution width L d  of objects of at least 1.04 and the size distribution width L′ d  of objects smaller than 500 nm is of at least 0.95.  
     
     
         83 . The silica according to  claim 77 , wherein, after ultrasonic disintegration, the median diameter (Ø 50S ) is of less than 8.5 μm, in particular less than 6.0 μm.  
     
     
         84 . The silica according to  claim 79 , having, after ultrasonic disintegration, a median diameter (Ø 50M ) of less than 8.5 μm.  
     
     
         85 . The silica according to  claim 79 , having a rate of disintegration, denoted by α, measured in the test referred to as ultrasonic disintegration in pulsed mode, at 100% power of a 600 watt probe, of at least 0.0035 μm −1 .min −1 .  
     
     
         86 . The silica according to  claim 67 , having a (Sears number×1000)/(BET specific surface area (S BET )) ratio of less than 60.  
     
     
         87 . The silica according to  claim 67 , having an object size such that the mode of the particle size distribution measured by XDC particle size analysis after ultrasonic disintegration satisfies the following condition: XDC mode (nm)≧(5320/S CTAB (m 2 /g))+8.  
     
     
         88 . The silica according to  claim 67 , having a pore volume (V 80 ) formed by the pores having a diameter of between 3.7 and 80 nm of at least 1.35 cm 3 /g.  
     
     
         89 . The silica according to  claim 67 , wherein the CTAB specific surface area (S CTAB ) is of between 60 and 330 m 2 /g; and 
 the BET specific surface area (S BET ) of between 70 and 350 m 2 /g.    
     
     
         90 . The silica according to  claim 67 , wherein the CTAB specific surface area (S CTAB ) is of between 90 and 230 m 2 /g.  
     
     
         91 . The silica according to  claim 67 , wherein the BET specific surface area (S BET ) is of between 110 and 270 m 2 /g.  
     
     
         92 . The silica according to  claim 67 , having a (S BET −S CTAB )≧5 m 2 /g.  
     
     
         93 . The silica according to  claim 67 , having a (S BET −S CTAB )<50 m 2 /g.  
     
     
         94 . The silica according to  claim 67 , being in the form of approximately spherical beads having a mean size of at least 80 μm.  
     
     
         95 . The silica according to  claim 67 , being in the form of a powder having a mean size of at least 15 μm.  
     
     
         96 . The silica according to  claim 67 , being in the form of granules having a mean size of at least 1 mm.  
     
     
         97 . A reinforcing filler for polymers, comprising a silica as defined in  claim 67 .  
     
     
         98 . A reinforcing filler in a natural rubber, comprising a silica as defined in  claim 67 .  
     
     
         99 . A shoe sole comprising a silica as defined in  claim 67 .  
     
     
         100 . The shoe sole according to  claim 99 , further comprising monoethoxydimethylsilylpropyl tetrasulphide.