Matting agent for UV varnishes

1. A UV coating material, comprising:

a surface-modified silicon dioxide particle,

wherein at least a part of the silicon dioxide particle is coated with an organopolysiloxane which is a polyoxyalkylene-modified siloxane derivative of the formula (I)

wherein

R 1 and/or R 7 =R 2 or [R 4 ] w —[R 5 ] x —[R 6 ] y —R 8 ,

R 2 =R 3 or ≠R 3 stands for identical or different alkyl radicals or alkylene radicals having 1 to 24 carbon atoms or optionally substituted phenyl radicals having up to 24 carbon atoms,

R 4 =a divalent radical of the formula O, NH, NR 2 , S or a radical of the formula (OSi(CH 3 ) 2 ) u , where

u=1 to 200,

R 5 =identical or different alkyl radicals or alkylene radicals having 1 to 24 carbon atoms, or

C n H 2n-f R 2 f —R 4 —C m H 2m-g R 2 g , where

f=0 to 12,

g=0 to 12,

n=1 to 18,

m=1 to 18,

R 6 =O—(C 2 H 4-a R 2 a O) b (C c H 2c O) d , where

a=0 to 3,

b=0 to 100,

c=2 to 12,

d=0 to 100,

the sum (b+d)=1 to 200,

and the sequence of the individual polyoxyalkylene segments (C 2 H 4-a R 2 a O) b and (C c H 2c O) d is arbitrary, or

R 6 =O e —C h H 2h —C i H 2i-j R 9 j , where

e=0,

h=0 to 24,

i=0 to 24,

j=1 to 3,

and R 9 in each case is a divalent radical of the formula O, a hydroxyl group, a radical of the formula C h1 H 2h or a radical of the formula C k H 2k-l (OH) l , where

k=0 to 24 and

l=1 to 3,

R 8 =a hydrogen radical or a monovalent organic radical, if y is 1, it being necessary for there to be at least one hydrogen radical per molecule, or is an OH group or a monovalent organic radical, with y=0, there being at least one OH group per molecule,

v=0 to 200,

w=1,

x=1,

y=0 or 1,

z=1 to 200,

and the sum (w+x+y)=2 or 3.

2. The UV coating material of claim 1 , wherein the silicon dioxide particle is a precipitated silica, a fumed silica, a semigel, or a silica gel.

3. The UV coating material of claim 1 ,

wherein the surface-modified silicon dioxide particle has a d 50 of from 1 to 50 μm, a DBP of from 100 to 600 g/100 g, a C content of from 1% to 20% by weight, or a combination thereof.

4. The UV coating material of claim 1 ,

wherein the UV coating material has a refractive index of n D 20=1.4000 to 1.5000,

the UV coating material comprises 5% by weight of the surface-modified silicon dioxide particle, and

a transmittance of the UV coating material is at least 20% improved over an otherwise identical coating material comprising 5% by weight of a reference silicon dioxide treated with a polyethylene wax and not with the surface-modified silicon dioxide particle.

5. The UV coating material of claim 1 , wherein the organopolysiloxane has a polyether excess of from 5% to 50% by weight.

6. The UV coating material of claim 1 , wherein the UV coating material is a clear coating material or a pigmented coating material.

7. The UV coating material of claim 1 , further comprising:

a binder based on a reactive monomer, based on a reactive oligomer, or based on both.

8. The UV coating material of claim 1 , comprising:

from 3% to 30% by weight of the organopolysiloxane-modified silicon dioxide particle; of at least one component selected from the group consisting of a photoinitiator, a flow control agent, an antioxidant, a pigment, a microcrystalline wax, an organic solvent, and water; or of both the organopolysiloxane-modified silicon dioxide particle and the at least one component.

9. A process for preparing the UV coating material of claim 1 , the process comprising:

contacting a dried silicon dioxide, a suspension of silicon dioxide, or a filter cake with at least one organopolysiloxane comprising a multiple bond.

10. The process of claim 9 , comprising:

reacting an alkali metal silicate solution with an acidifier, further adding an acidifier to set a pH of from 7 to 2, to obtain a silicon dioxide suspension,

isolating precipitated solid from the silicon dioxide suspension by filtration, and

drying the solid by slow drying or rapid drying to obtain a dried silicon dioxide, such that the dried silicon dioxide has a residual moisture content of less than 10%,

treating the dried silicon dioxide with an organopolysiloxane comprising a multiple bond,

or a combination thereof.

11. The process of claim 9 , wherein a content of the organopolysiloxane is from 0.5% to 30% by weight, and -the organopolysiloxane comprises a carbon-carbon double bond, a carbon-carbon triple bond, or both.

12. The process of claim 10 , further comprising: resuspending the precipitated solid isolated by filtration with water, sulphuric acid, or a mixture of water and sulphuric acid, then

adding to the suspension a surface-modifying organopolysiloxane comprising a carbon-carbon double bond, a carbon-carbon triple bond, or both, and

drying the resulting suspension.

13. The process of claim 10 , further comprising:

admixing and intimately mixing the dried silicon dioxide with a surface-modifying organopolysiloxane comprising a carbon-carbon double bond, a carbon-carbon triple bond, or both.

14. The process of claim 13 , further comprising:

further mixing the dried silicon dioxide and the organopolysiloxane for 0-2 h, heat treating the dried silicon dioxide and the organopolysiloxane at from 20 to 150° C.,

or both.

15. The process of claim 9 , further comprising:

grinding surface-modified silicon dioxide, separating off dried silicon dioxide particles having a diameter of more than 50 μm, or both.

16. The process of claim 9 , further comprising:

simultaneously grinding and surface-modifying, in a milling apparatus, a silicon dioxide, a semigel, or a silica gel.

17. The process of claim 16 , wherein the milling apparatus employs a milling gas with a pressure of ≦4 bar (abs), a temperature of less than or equal to 180° C., or both.