Surface-modified precipitated silicas

1. A lacquer, comprising:

a surface-modified precipitated silica having a polymer on a surface thereof;

wherein the polymer used to surface modify the said surface-modified silica is a polyorganosiloxane or a modified polyorganosiloxane;

wherein the polymer is a polyorganosiloxane having the following structure:

wherein

Y=—OH, —OR or

Y=H 5 C 2 —O—(C 2 H 4 O) m —, H 7 C 3 —O—(C 3 H 6 O) m — or

R=alkyl,

R 2 =alkyl,

R 3 =alkyl,

a=0-100, b is >/=1 to 100=0-100, c=0-100, d is >/=1 to 100=0-100,

m=0-100 and k=0-100; or

wherein the polymer is a polyorganosiloxane having the following structure:

wherein

R 1 is a methyl radical or

and a sum of the units a=0 to 100, the sum of the units b=0 to 15, the ratio of methyl to alkoxy radicals for the radicals R 1 being less than 50:1 and b being ≧1 if a=0, and a≧5 if b=0.

2. The lacquer of claim 1 , wherein the surface-modified silica satisfies the following requirement:

a particle distribution d50 is 1-50 μm,

an oil absorption DBP is 100-600 g/100 g, and

a C content is 1-20%.

3. The lacquer of claim 1 , wherein the surface-modified silica has a Sears number V 2 <25 ml/5 g.

4. The lacquer of claim 3 , wherein the surface-modified silica has a particle distribution d50 of from 1 to 40 μm.

5. The lacquer of claim 3 , wherein the surface-modified silica has an oil absorption DBP of from 200 to 500 g/100 g.

6. The lacquer of claim 3 , wherein the surface-modified silica has a C content of from 1 to 10%.

7. The lacquer of claim 1 , wherein a uncoated silica of said surface-modified silica and said surface modified-silica are the same; and wherein said reference silica is coated with a polyethylene wax.

8. A process for preparing a lacquer according to claim 1 , comprising:

obtaining a surface-modified, hydrophobicized precipitated silica by

a) precipitating an alkali metal silicate solution with an acidifier under weak acidic to alkaline conditions,

b) further adding an acidifier to set a pH of from 7 to 2, to give a silica suspension,

c) isolating the precipitated solid by filtration, thereby obtaining a precipitated silica, and

d) drying the precipitated silica such that a residual moisture content is less than 10%,

e) treating the silica suspension or the precipitated silica with a polymer to obtain said surface-modified precipitated silica, the amount and the nature of the polymer being chosen such that the modified precipitated silica improves a transmission of a clear coating material, having a refractive index of n D 20=1.4492 and containing 5% by weight of this modified precipitated silica, by at least 20%, in comparison to said clear coating material containing 5% by weight of a reference precipitated silica treated with a polyethylene wax,

and

adding said surface-modified, hydrophobicized precipitated silica to a lacquer formulation.

9. The process as claimed in claim 8 , wherein 0.5-30% by weight of a polyorganosiloxane or a modified polyorganosiloxane is added to the silica suspension adjusted in step b) to a pH of 7-2.

10. The process of claim 8 , wherein the treatment in step e) is carried out for 1 to 30 minutes and with stirring.

11. The process of claim 8 , wherein step e) is carried out in a silica suspension; and wherein the temperature of the silica suspension in step e) is 20-100° C.

12. The process as claimed in claim 8 , wherein the precipitated silica isolated by filtration in accordance with step c) and optionally washed with deionized water is resuspended with water or sulfuric acid or with a mixture of water and sulfuric acid; and subsequently in step e) 0.5-30% by weight of a polyorganosiloxane or a modified polyorganosiloxane is added to the silica suspension and the resulting suspension is dried, to obtain said surface-modified silica.

13. The process of claim 11 , wherein the drying after step e) takes place such that the product has a residual moisture content of less than 10%.

14. The process of claim 11 , wherein the temperature of the silica suspension in step e) is 20-100° C.

15. The process as claimed in claim 8 , wherein after step d) 0.5-30% by weight of polyorganosiloxane or a modified polyorganosiloxane is added in step e) to the silica and the two are intimately mixed.

16. The process of claim 15 , wherein the addition in step e) is carried out with a duration of from 0 to 120 minutes and with mixing.

17. The process of claim 16 , wherein the silica and the polyorganosiloxane or the modified polyorganosiloxane are mixed for 0-2 h more.

18. The process of one of claims 15 , wherein the temperature of the mixture in step e) is 20-150° C.

19. The process of one of claim 8 , further comprising f) grinding after the surface-modified precipitated silica has been dried.

20. The process of claim 19 , wherein after the surface-modified silica has been dried or after or during the grinding in step f) particles having a diameter of more than 50 μm are separated off.

21. The lacquer of claim 1 , wherein the surface-modified silica imparts improved transmission in relation to a reference precipitated silica treated with polyethylene wax, said reference precipitated silica having the following properties:

ACEMATT ® OK

Features and test methods

Units

412

Loss on drying

%

6

2 h at 105° C.

in accordance with DIN EN ISO 787-2

Loss on ignition based on dried substance

%

13

2 h at 1000° C.

in accordance with DIN EN ISQ 3262-1

pH

—

6

5% in water

in accordance with DIN EN ISO 787-0

Sulfate content as SO 4

%

1

IR spectroscopy

Degussa method

Particle size

μm

mean value (TEM)

3

D50 value (laser diffraction)

6.0

Surface treatment

Organic

Tapped density

g/l

130

unsieved

in accordance with DIN EN ISO 787-11

Density

g/cm 3

1.9

in accordance with DIN EN ISO 787-10

Oil number

g/100 g

220

in accordance with DIN EN ISO 787-5

SiO 2 content based on ignited substance

%

98

in accordance with DIN EN ISO 3262-19.