Precipitated silica and paper industry/other applications thereof

Abstract

Precipitated silica specifically useful in the paper industry and in particular in paper-coating applications for inject printing, is characterized by an uptake of DOP oil lower than 260 ml/100 g, a pore volume (V d25 ) of greater than 0.8 ml/g formed by pores having a diameter of less than 25 nm, a CTAB specific surface area of greater than 280 m 2 /g.

1 .- 23 . (canceled) 
   
   
       24 . A precipitated silica, which comprises:
 an uptake of DOP oil of less than 260 ml/100 g,   a pore volume (V d25 ), formed by pores having a diameter of less than 25 nm, of greater than 0.8 ml/g, and   a CTAB specific surface area of greater than 280 m 2 /g.   
   
   
       25 . The precipitated silica as defined by  claim 24 , having an uptake of DOP oil of less than 240 ml/100 g. 
   
   
       26 . The precipitated silica as defined by  claim 24 , having a pore volume (V d25 ), formed by pores having a diameter of less than 25 nm, of greater than 0.9 ml/g. 
   
   
       27 . The precipitated silica as defined by  claim 24 , having a CTAB specific surface area of greater than 300 m 2 /g. 
   
   
       28 . The precipitated silica as defined by  claim 24 , having a BET specific surface area of greater than 450 m 2 /g. 
   
   
       29 . The precipitated silica as defined by  claim 24 , having a pore diameter (d p ), for pores with a diameter of less than 25 nm, taken at the maximum of the distribution of pore size by volume, of less than 12.0 nm. 
   
   
       30 . The precipitated silica as defined by  claim 24 , having an aluminum content of less than 2,800 ppm. 
   
   
       31 . The precipitated silica as defined by  claim 24 , having a median particle size (d50) of at most 20 μm. 
   
   
       32 . The precipitated silica as defined by  claim 24 , which comprises:
 an uptake of DOP oil of less than 205 ml/100 g,   a pore volume (V d25 ), formed by pores having a diameter of less than 25 nm, of at least 0.95 ml/g,   a CTAB specific surface area ranging from 330 to 400 m 2 /g,   a BET specific surface area of greater than 510 m 2 /g,   a pore diameter (d p ), for pores with a diameter of less than 25 nm, taken at the maximum of the distribution of pore size by volume, of less than 12.0 nm, and   a median particle size (d50) ranging from 6 to 10.5 μm.   
   
   
       33 . An aqueous suspension of precipitated silica, which comprises al least one precipitated silica as defined by  claim 24 . 
   
   
       34 . A method for preparing a precipitated silica as defined by  claim 24 , comprising reacting a silicate with an acidifying agent to obtain a suspension of precipitated silica and then separating and drying this suspension, wherein the reaction of the silicate with the acidifying agent is carried out according to the following successive steps:
 (i) forming an initial stock comprising a part of the total amount of the silicate employed in the reaction, the concentration of silicate (expressed as SiO 2 ) in said initial stock ranging from 10 to 50 g/l, and the temperature of said initial stock ranging from 40 to 65° C.,   (ii) adding acidifying agent and the remaining amount of the silicate to said stock simultaneously, for 20 to 150 minutes, the ratio of the amount of silicate added (expressed as SiO 2 )/amount of silicate present in the initial stock (expressed as SiO 2 ) being greater than 5:
 a) either at constant flow rates resulting, upon completion of such simultaneous addition, in a reaction medium pH value ranging from 3.5 to 8.5, 
 b) or at a flow rate of acidifying agent adjusted such as to maintain the reaction medium pH at a value which is constant and ranges from 3.5 to 8.5, 
   (iii) in the event that the reaction medium pH value at the end of step (ii) is greater than 6.0, adding acidifying agent to the reaction medium for 3 to 25 minutes, to provide a reaction medium pH value ranging from 3.5 to 6.0, and   (iv) maintaining the reaction medium obtained at the end of the preceding step stirred for 5 to 60 minutes.   
   
   
       35 . The method as defined by  claim 34 , which comprises, between step (i) and step (ii), the following step (i′):
 (i′) adding acidifying agent to said stock for 5 to 30 minutes, until a reaction medium pH value ranging from 3.5 to 8.5 is obtained.   
   
   
       36 . The method as defined by  claim 34 , wherein the concentration of silicate (expressed as SiO 2 ) in said initial stock ranges from 15 to 45 g/l. 
   
   
       37 . The method as defined by  claim 34 , wherein no electrolyte is added in step (i). 
   
   
       38 . The method as defined by  claim 34 , wherein the separation comprises filtration, followed by disintegration of the filtration cake obtained at the end of the filtration, a carboxylic acid being mixed with or added to said cake before or during the disintegration operation. 
   
   
       39 . The method as defined by  claim 34 , wherein the precipitated silica obtained at the end of the drying step is milled or micronized. 
   
   
       40 . A precipitated silica prepared by the method as defined by  claim 34 . 
   
   
       41 . An aqueous suspension of precipitated silica, which comprises at least one precipitated silica as defined by  claim 40 . 
   
   
       42 . A filler or coating for paper, comprising a suspension of precipitated silica as defined by  claim 24 . 
   
   
       43 . A coating slip for paper for inkjet printers, which comprises a precipitated silica as defined by  claim 24 . 
   
   
       44 . A method for improving the printing qualities of paper, which comprises including as filler material for such paper, a precipitated silica as defined by  claim 24 . 
   
   
       45 . A coating filler for thermal paper, a filler for the bulk of the paper, a liquid support, a solid support, optionally a catalyst support, an absorbing agent and/or odor masker, a desiccating agent, an additive for inks, a beer or wine clarifier and/or stabilizer, an anti-caking agent, a matting agent, an additive for paint, an anti-blocking agent or an anti-slip agent, for chromatography, for the adsorption of liquid or of gas, optionally in cigarette filters, a battery separator or a gelling agent for sulfuric acid, comprising the precipitated silica as defined by  claim 24 . 
   
   
       46 . The precipitated silica as defined by  claim 27 , having a CTAB specific surface area of greater than 350 m 2 /g. 
   
   
       47 . The precipitated silica as defined by  claim 28 , having a BET specific surface area of greater than 540 m 2 /g. 
   
   
       48 . The precipitated silica as defined by  claim 30 , having an aluminum content of less than 200 ppm. 
   
   
       49 . The precipitated silica as defined by  claim 31 , having a medium particle size (d50) ranging from 3.5 to 12 μm.