Highly-Structured Silica Having a Low Water Uptake, Preparation Method Thereof and Uses of Same

Abstract

The invention relates to a highly-structured precipitated silica having a low water uptake and high dispersibility in different pasty or solid matrices or media, elastomers or silicon, and to the preparation method thereof. The invention also relates to the use of said silica, for example, as a reinforcing filler in matrices based on elastomers (clear or semi-clear for shoe soles), in silicon matrices (in particular, for the coating of electric cables), as a filler and/or support and/or vehicle in different compositions (food compositions, cosmetic compositions, pharmaceutical compositions, compositions for the production of paints or paper, compositions for the production of porous membrane separators for batteries) or as a thickening agent in toothpastes.

Description

EXAMPLES 1-3

Model Opaque Toothpaste

sorbitol (Neosorb 70/70 (Roquette Freres)) 45
polyethylene glycol PEG 1500     5
sodium saccharinate              0.2
sodium fluoride                  0.08
sodium monofluorophosphate       0.72
water                            24.2
abrasive silica (Tixosil 63, sold by Rhodia) 10
silica of the invention          7
titanium dioxide                 1
spearmint flavoring              1
foaming agent (30% in water):    5
Texapon Z 95 P (Cognis)

Measurement of the Viscosity of a Dentifrice Formulation

The viscosity is determined on a tube of paste with a diameter of 25 mm at predetermined periods at 37° C. after preparation of the paste.

The measurement equipment used is a Brookfield RVT viscometer equipped with a Helipath device. The TE spindle is used at 5 rpm (revolutions per minute). The measurement is carried out in a downward direction after 90 seconds.

Example 1

14 000 g of water and 450 g of a 236 g/l (as SiO₂ equivalent) aqueous sodium silicate solution were introduced into a reactor equipped with a system for regulating the temperature and pH and with a system for stirring with a 3-bladed propeller, the SiO₂/Na₂O ratio by weight (Rw) of the sodium silicate used being 3.46.

After starting to stir (250 revolutions per minute), the vessel heel thus formed was heated to 95° C. and the pH was brought to 7.5, over 11 minutes, by addition of an 80 g/l aqueous sulfuric acid solution (mean flow rate of 61 g per minute).

Once the pH of 7.5 was reached, 3045 g of a 236 g/l (as SiO₂ equivalent) aqueous sodium silicate solution (Rw=3.46) were added continuously at a constant flow rate of 35 grams per minute (duration of addition: 87 minutes) while maintaining the pH of the medium at a value equal to 7.5 (to within about 0.1 pH unit) by addition to the medium of an 80 g/l aqueous sulfuric acid solution with a flow rate controlled according to the change measured for the pH of the medium. Taking stock, 3383 g of the sulfuric acid solution were added to the medium, which corresponds to a mean flow rate of 40 grams of sulfuric acid solution added per minute.

After the period of addition of 87 minutes, the addition of silicate was halted and addition of acid was continued until the pH of the reaction mixture had stabilized at 3.6. Maturing was carried out by leaving the solution to stir for 5 minutes.

The slurry obtained was subsequently filtered and washed on a flat filter and then the cake obtained, the loss on ignition of which is 80.5%, was disintegrated mechanically at a pH of 5.5 and was then dried by rotary atomization.

The physicochemical characteristics of the unmilled dry silica obtained are as follows:

• • pH: 5.9
  • median particle diameter: 80 μm
  • median diameter after ultrasound: 31.0 μm
  • % greater than 51 μm after ultrasound: 18.6
  • Na₂SO₄ content: 1.6% by weight (with respect to the total weight of the material in the dry state)
  • CTAB specific surface: 133 m²/g
  • BET specific surface: 143 m²/g
  • DOP oil uptake: 305 ml/100 g
  • loss on ignition at 1000° C.: 6.5%
  • residual water content after 2 hours at 105° C.: 3.9%
  • water uptake: 5.8%
  • transmission: 80% at a refractive index of 1.460
  • packing density (PD): 0.27 g/ml
  • viscosity of the model toothpaste after 4 weeks: 250 mPa·s

Example 2

The operations described in comparative example 1 are repeated, the dried product being milled so as to obtain a median particle diameter of 10 μm.

The physicochemical characteristics of the milled dry silica obtained are as follows:

• • pH: 5.9
  • median particle diameter: 10 μm
  • median diameter after ultrasound: 7 μm
  • % greater than 51 μm after ultrasound: 1.0
  • Na₂SO₄ content: 1.6% by weight (with respect to the total weight of the material in the dry state)
  • CTAB specific surface: 133 m²/g
  • BET specific surface: 143 m²/g
  • DOP oil uptake: 315 ml/100 g
  • loss on ignition at 1000° C.: 7%
  • residual water content after 2 hours at 105° C.: 4.4%
  • water uptake: 5.9%
  • transmission: 80% at a refractive index of 1.460
  • packing density (PD): 0.1 g/ml
  • viscosity of the model toothpaste after 4 weeks: 325 mpa·s

Example 3

14 000 g of water and 630 g of a 236 g/l (as SiO₂ equivalent) aqueous sodium silicate solution were introduced into a reactor equipped with a system for regulating the temperature and pH and with a system for stirring with a 3-bladed propeller, the SiO₂/Na₂O ratio by weight (Rw) of the sodium silicate used being 3.46.

After starting to stir (250 revolutions per minute), the vessel heel thus formed was heated to 95° C. and the pH was brought to 7.5, over 11 minutes, by addition of an 80 g/l aqueous sulfuric acid solution (mean flow rate of 61 g per minute).

Once the pH of 7.5 was reached, 3600 g of a 236 g/l (as SiO₂ equivalent) aqueous sodium silicate solution (Rw=3.46) were added continuously at a constant flow rate of 48 grams per minute (duration of addition: 75 minutes) while maintaining the pH of the medium at a value equal to 7.5 (to within about 0.1 pH unit) by addition to the medium of an 80 g/l aqueous sulfuric acid solution with a flow rate controlled according to the change measured for the pH of the medium. Taking stock, 3975 g of the sulfuric acid solution were added to the medium, which corresponds to a mean flow rate of 53 grams of sulfuric acid solution added per minute.

After the period of addition of 90 minutes, the addition of silicate was halted and addition of acid was continued until the pH of the reaction mixture had stabilized at 3.4. Maturing was carried out by leaving the solution to stir for 5 minutes.

The slurry obtained was subsequently filtered and washed on a flat filter and then the cake obtained, the loss on ignition of which is 86%, was disintegrated mechanically at a pH of 5 and was then dried by rotary atomization.

The physicochemical characteristics of the unmilled dry silica obtained are as follows:

• • pH: 5.3
  • median particle diameter: 65 μm
  • median diameter after ultrasound: 22 μm
  • % greater than 51 μm after ultrasound: 3.3
  • Na₂SO₄ content: 1.0% by weight (with respect to the total weight of the material in the dry state)
  • CTAB specific surface: 182 m²/g
  • BET specific surface: 185 m²/g
  • DOP oil uptake: 340 ml/100 g
  • loss on ignition at 1000° C.: 6.5%
  • residual water content after 2 hours at 105° C.: 3.9%
  • water uptake: 5.7%
  • transmission: 85% at a refractive index of 1.460
  • packing density (PD): 0.18 g/ml
  • viscosity of the model toothpaste after 4 weeks: 615 mPa·s

Example 4

14 000 g of water and 450 g of a 236 g/l (as SiO₂ equivalent) aqueous sodium silicate solution were introduced into a reactor equipped with a system for regulating the temperature and pH and with a system for stirring with a 3-bladed propeller, the SiO₂/Na₂O ratio by weight (Rw) of the sodium silicate used being 3.46.

After starting to stir (250 revolutions per minute), the vessel heel thus formed was heated to 98° C. and the pH was brought to 7.5, over 11 minutes, by addition of an 80 g/l aqueous sulfuric acid solution (mean flow rate of 61 g per minute).

Once the pH of 7.5 was reached, 3150 g of a 236 g/l (as SiO₂ equivalent) aqueous sodium silicate solution (Rw=3.46) were added continuously at a constant flow rate of 35 grams per minute (duration of addition: 90 minutes) while maintaining the pH of the medium at a value equal to 7.5 (to within about 0.1 pH unit) by addition to the medium of an 80 g/l aqueous sulfuric acid solution with a flow rate controlled according to the change measured for the pH of the medium. Taking stock, 3510 g of the sulfuric acid solution were added to the medium, which corresponds to a mean flow rate of 39 grams of sulfuric acid solution added per minute.

After the period of addition of 90 minutes, the addition of silicate was halted and addition of acid was continued until the pH of the reaction mixture had stabilized at 3.4. Maturing was carried out by leaving the solution to stir for 5 minutes.

The slurry obtained was subsequently filtered and washed on a flat filter and then the cake obtained, the loss on ignition of which is 86.4%, was disintegrated mechanically at a pH of 4.3 and was then dried by rotary atomization.

The dried silica was subsequently milled using a classifier hammer mill.

The physicochemical characteristics of the silica in the powder form obtained are as follows:

• • pH: 4.6
  • mean particle size: 12 μm
  • Na₂SO₄ content: 0.25% by weight (with respect to the total weight of the material in the dry state)
  • CTAB specific surface: 166 m²/g
  • BET specific surface: 170 m²/g
  • DOP oil uptake: 365 ml/100 g
  • loss on ignition at 1000° C.: 5%
  • residual water content after 2 hours at 105° C.: 2.5%
  • ater uptake: 5.8%
  • packing density (PD): 0.08 g/ml

Claims

1-14. (canceled)

15. A precipitated silica exhibiting: a CTAB specific surface of 140 to 230 m2/g,a DOP oil uptake of greater than 300 ml/100 g,a water uptake of less than 6% and preferably of greater than 3%,a pH of 3.5 to 7.5,a level of residual anion, expressed as sodium sulfate, of less than or equal to 2%, anda mean particle size or a median particle diameter of less than 30 μm.

16. A precipitated silica according to claim 15, exhibiting: a CTAB specific surface of 145 to 185 m2/g,a DOP oil uptake of 315 to 450 ml/100 g,a water uptake of less than 6% and greater than 3%,a pH of 4 to 7,a level of residual anion, expressed as sodium sulfate, of less than or equal 1.5%, anda mean particle size or a median particle diameter of between 30 μm and 20 mm.

17. A precipitated silica according to claim 16 exhibiting: a CTAB specific surface of 150 to 185 m2/g,a DOP oil uptake of greater than 320 to 400 ml/100 g,a water uptake of greater than or equal to 4% and of less than or equal to 5.8%,a pH of 4 to 6, anda level of residual anion, expressed as sodium sulfate, of less than or equal to 1%.

18. A precipitated silica according to claim 17, exhibiting: a CTAB specific surface of 150 to 180 m2/g,a DOP oil uptake of 340 to 380 ml/100 g, anda level of residual anion, expressed as sodium sulfate, of less than or equal to 0.5%,

19. The silica as claimed in claim 1, having a mean particle size or a median particle diameter of less than 30 μm, preferably of less than 20 μm, in particular of between 5 and 15 μm, especially between 8 and 13 μm.

20. The silica as claimed in claim 15, having a mean particle size or a median particle diameter of between 30 μm and 20 mm.

21. The silica as claimed in claim 15, having a median particle diameter, after deagglomeration under ultrasound, of at most 35 μm, optionally of at most 25 μm.

22. The silica as claimed in claim 15, having a BET specific surface such that the BET-CTAB difference is at most 30 m2/g, optionally at most 10 m2/g.

23. The silica as claimed in claim 15, having a packing density of at most 0.3 g/ml, optionally of 0.04 to 0.3 g/ml.

24. The silica as claimed in claim 15, in the form of a powder.

25. A process for the preparation of a silica as claimed in one claim 15, comprising the following stages: (a) producing a starting vessel heel with a temperature of between 80 and 100° C., optionally of greater than or equal to 90° C., comprising water and a silicate, with a concentration of silicate in said vessel heel, expressed as SiO2 equivalent, being less than or equal to 15 g/l;(b) adding, at a temperature of between 80 and 100° C., optionally 90 and 100° C., an acidifying agent to bring the pH of the medium to a value of between 7 and 8, optionally between 7.3 and 7.7 to form a medium;(c) in the medium thus produced in stage (b), carrying out, at a temperature of between 80 and 100° C., optionally between 90 and 100° C., a simultaneous addition of a silicate and of an acidifying agent, with a respective amounts of silicate and of acidifying agent added over time being specifically chosen so that, throughout the duration of the addition: the pH of the reaction medium remains between 7 and 8 and optionally between 7.2 and 7.8; andthe concentration of silicon in the medium, expressed as SiO2 equivalent, remains less than or equal to 35 g/l;(d) adding, at a temperature of between 80 and 100° C., optionally between 90 and 100° C., an acidifying agent to the medium obtained on conclusion of stage (c) so as to bring the medium to a pH of between 3 and 6.5 to obtain an aqueous silica dispersion;(e) filtering the aqueous silica dispersion obtained in stage (d) in order to obtain a filtration cake;(f) drying the filtration cake produced on conclusion of the stage (e), optionally washing it beforehand; and(g) optionally milling or micronizing the silica obtained on conclusion of stage (f), wherein the filtration cake exhibits, prior to the drying of it in stage (f), a loss on ignition at 1000° C. of greater than 82%, optionally of 84 to 88%.

26. Shoe soles comprising a silica as defined in claim 15.

27. A matrix based on silicone(s) comprising a silica as defined in claim 15 as reinforcing filler.

28. A carrier for liquids comprising a silica as defined in claim 15.

29. A dentifrice composition in the paste or gel form comprising a silica as defined in claim 15 as a thickening agent.

30. Battery separators comprising a silica as defined in claim 15.