Coated pearlescent pigments with SiO2 and cerium oxide

• US 20060042509A1
• Filed: 08/26/2005
• Published: 03/02/2006
• Est. Priority Date: 08/26/2004
• Status: Active Grant

• Current Assignee: Eckart GmbH (Eckart)
• Original Assignee: ECKART GmbH & Co. KG (Susanne Klatten, MBA)
• Inventors: Schmidt, Ulrich, Henglein, Frank, Kaupp, Gunter, Kruger, Peter
• Granted Patent: US 7,413,599 B2
• Time in Patent Office: Days
• US Class Current: 106/415
• CPC Class Codes: C01P 2004/88 Thick layer coatings
• CPC Class Codes: C09C 1/0015 Pigments exhibiting interference colours, e.g. transparent platelets of appropriate thinness or flaky substrates, e.g. mica, bearing appropriate thin transparent coatings
• CPC Class Codes: C09C 1/0021 comprising a core coated with only one layer having a high or low refractive index
• CPC Class Codes: C09C 2200/102 the core consisting of glass or silicate material like mica or clays, e.g. kaolin
• CPC Class Codes: C09C 2200/401 Inorganic protective coating
• CPC Class Codes: C09C 2200/407 Organosilicon materials, e.g. silanes, silicones
• CPC Class Codes: C09C 2200/408 comprising additional functional groups, e.g. –NH2, -C=C- or -SO3

Abstract

The invention relates to pearlescent pigments with a platelet-shaped substrate comprising metal oxide and having a first and a second protective layer, said metal oxide having a refractive index of greater than 1.8, there being on the platelet-shaped substrate a first protective layer comprising cerium oxide and/or cerium hydroxide and a second protective layer of SiO₂, applied to which is an organic chemical aftercoat comprising at least one silane having at least one functional bond group and at least one silane without a functional bond group, it being possible for metal oxide layers other than cerium oxide and SiO₂ to be disposed between the first and the second protective layer. The invention further relates to a process for preparing these pigments, and to the use thereof.

Claims

1. A pearlescent pigment with a platelet-shaped substrate comprising metal oxide and having a first and a second protective layer, said metal oxide having a refractive index of greater than 1.8, there being on the platelet-shaped substrate a first protective layer comprising cerium oxides, cerium hydroxide, or a mixture thereof and

a second protective layer of SiO₂, applied to which is an organic chemical aftercoat comprising at least one silane having at least one functional bond group and at least one silane without a functional bond group, it being possible for metal oxide layers other than cerium oxide and SiO₂ to be disposed between the first and the second protective layer.

2. The pearlescent pigment as claimed in claim 1, wherein the organic chemical aftercoat is joined covalently to the SiO₂ layer.

3. The pearlescent pigment as claimed in claim 1, wherein the SiO₂ content of the pigment is 0.5% to 8% by weight, based on the total weight of the pigment.

4. The pearlescent pigment as claimed in claim 1, wherein the silane without a functional bond group is an alkylsilane.

5. The pearlescent pigment as claimed in claim 1, wherein the silane without a functional bond group has the structural formula (II)

(R¹—

X-[A-Y]_n—

B)_(4-z)Si(OR²)_z  

 

(II)

where

n=1 to 100;

z is an integer from 1 to 3;

R¹ is straight- or branched-chain alkyl having 1 to 12 carbon atoms, which may be substituted by halogens;

an aryl having 6 to 12 carbon atoms;

or an aryl having 6 to 12 carbon atoms, which is substituted by alkyl having 1 to 6 carbon atoms, halogen atoms, or a combination thereof;

R² is straight- or branched-chain alkyl having 1 to 6 carbon atoms;

A and B independently of one another are a divalent group consisting of straight- or branched-chain alkylene having 1 to 12 carbon atoms;

an arylene having 6 to 12 carbon atoms;

or an arylene having 6 to 12 carbon atoms, which is substituted by alkyl having 1 to 6 carbon atoms, halogen atoms, or a combination thereof; and

X and Y independently of one another are O or S.

6. The pearlescent pigment as claimed in claim 5, wherein R¹ and R² are selected independently of one another from the group consisting of methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, phenyl, biphenylyl, naphthyl, and mixtures thereof.

7. The pearlescent pigment as claimed in claim 5, wherein A and B are selected independently of one another from the group consisting of ethylene, propylene, 1-butylene, 2-butylene, phenylene, phenylene substituted by alkyl having 1 to 6 carbon atoms, and mixtures thereof.

8. The pearlescent pigment as claimed in claim 5, wherein the silanes may be are present in pure form with a defined n or in mixtures with different n.

9. The pearlescent pigment as claimed in claim 1, wherein the at least one functional bond group is selected from the group consisting of acrylate, methacrylate, vinyl, amino, cyanate, isocyanate, epoxy, hydroxyl, thiol, ureido, carboxyl groups, and mixtures thereof.

10. The pearlescent pigment as claimed in claim 1, wherein the silane having at least one functional bond group is an aminosilane.

11. The pearlescent pigment as claimed in claim 1, wherein the fraction of cerium is 0.05% to 3.0% by weight, based in each case on the total weight of the pigment.

12. The pearlescent pigment as claimed in claim 1, wherein the fraction of the organic chemical aftercoat is between 0.1% and 6% by weight, based on the total weight of the pigment.

13. The pearlescent pigment as claimed in claim 1, wherein the first protective layer further comprises SiO₂.

15. The pearlescent pigment as claimed in claim 1, wherein the platelet-shaped substrate comprises one or more metal oxide layers.

16. The pearlescent pigment as claimed in claim 1, wherein disposed between the first protective layer and the second protective layer of SiO₂ there are disposed further layers.

17. The pearlescent pigment as claimed in claim 1, wherein the platelet-shaped substrate is selected from the group consisting of oxide coated mica flakes, oxide coated glass flakes, oxide coated alumina flakes, oxide coated SiO₂ flakes, bismuth oxychloride flakes, pure TiO₂ flakes, and mixtures thereof, wherein the oxide coating comprises a layer of TiO₂;

a layer of iron oxide;

a first layer of TiO₂ and a second layer of iron oxide;

or a first layer of iron oxide and a second layer of TiO₂.

18. The pearlescent pigment as claimed in claim 1, wherein the substrate comprises a layer of TiO₂.

33. An article provided with a coating comprising pearlescent pigment as claimed in claim 1.

34. The article as claimed in claim 33, which is a vehicle body or an architectural facing.

35. The pearlescent pigment as claimed in claim 4, wherein the alkylsilane is applied using an alkylsilane having the formula R_(4-z)Si(X)_z, R being a substituted or unsubstituted, unbranched or branched alkyl chain having 10 to 22 carbon atoms, X being a halogen group, an alkoxy group, or a combination thereof, and z being an integer from 1 to 3.

36. The pearlescent pigment as claimed in claim 11, wherein the fraction of cerium is 0.1% to 1.0% by weight, based in each case on the total weight of the pigment.

37. The pearlescent pigment as claimed in claim 12, wherein the fraction of the organic chemical aftercoat is between 0.4% and 2% by weight, based on the total weight of the pigment.

38. The pearlescent pigment as claimed in claim 15, wherein the one or more metal oxide layers comprise tin oxide.

39. The pearlescent pigment as claimed in claim 15, wherein the platelet-shaped substrate is calcined.

40. The pearlescent pigment as claimed in claim 16, wherein the further layers comprise metal oxide layers.

14. (canceled)

19. A process for preparing a pearlescent pigment comprising the following steps:

(a) suspending platelet-shaped substrate comprising metal oxide in a liquid phase, said metal oxide having a refractive index of greater than 1.8,

(b) applying a layer comprising cerium oxide, cerium hydroxide, or a mixture thereof to said platelet-shaped substrate,

(c) optionally applying one or more metal oxide layers to the pigment coated in step (b),

(d) applying an SiO₂ layer to the pigment coated in step (b) or step (c), and

(e) modifying the surface of the SiO₂ layer with an aftercoat comprising at least one silane having at least one functional bond group and at least one silane without a functional bond group.

20. The process as claimed in claim 19, wherein the liquid phase in step (a) comprises a predominant fraction of organic solvent.

21. The process as claimed in claim 19, wherein the layer comprising cerium oxide, cerium hydroxide, or a mixture thereof in step (b) is applied using cerium compounds that are soluble in organic solvent.

22. The process as claimed in claim 19, wherein the SiO₂ layer in step (d) is applied with addition of tetraalkoxysilane to the pigment coated in step (b) or (c), with optional addition of water.

23. The process as claimed in claim 22, wherein the tetraalkoxysilane is selected from the group consisting of tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane, tetrabutoxysilane, and mixtures thereof.

24. The process as claimed in claim 19, wherein additionally in step (d) nitrogen-containing bases are added.

25. The process as claimed in claim 19, wherein the SiO₂ layer in step (e) is subjected to organic chemical surface modification in a liquid phase having a predominant fraction of organic solvent.

26. The process as claimed in claim 19, wherein the pigments coated in step (b) or step (c) are suspended in step (d) in water or in a predominantly aqueous medium and the SiO₂ layer is applied using aqueous silicate solutions such as waterglass.

27. The process as claimed in claim 26, wherein the pigments coated with an SiO₂ layer are taken up in a liquid phase having a predominant fraction of organic solvent and are subsequently subjected to organic chemical surface modification.

28. The process as claimed in claim 19, wherein the organic solvent is ethyl acetate, alcohols, such as methanol, ethanol, n-propanol, isopropanol, n-butanol, 2-methylpropanol, 2-methoxypropanol or butyl glycol, or mixtures thereof.

29. The process as claimed in claim 19, wherein at least one silane having at least one functional bond group is a monomer.

30. The process as claimed in claim 19, wherein at least one silane having at least one functional bond group is a silane which has been prehydrolyzed to an extent of not more than 50%.

41. The process as claimed in claim 20, wherein the predominant fraction of organic solvent comprises less than 50% by weight of water.

42. The process as claimed in claim 21, wherein the cerium compounds are selected from the group consisting of cerium(III) acetate, cerium(III) octoate, cerium(III) acetylacetonate, cerium(III) nitrate, cerium(III) chloride, and mixtures thereof.

43. The process as claimed in claim 21 further comprising the addition of water.

44. The process as claimed in claim 30, wherein at least one silane having at least one functional bond group is a nonprehydrolyzed silane.

31. (canceled)

32. (canceled)