Nacreous pigments having improved light fastness, their preparation and use

• US 4,565,581 A
• Filed: 12/27/1982
• Issued: 01/21/1986
• Est. Priority Date: 12/24/1981
• Status: Expired due to Fees

• Current Assignee: Merck Patent GmbH (Merck & Co., Inc.)
• Original Assignee: Merck Patent GmbH (Merck & Co., Inc.)
• Inventors: Bernhard, Horst
• Primary Examiner(s): Williams, Howard S.
• Application Number:
  US06/453,048
• Time in Patent Office: 1,121 Days
• Field of Search: 106/308 B, 106/291, 106/309, 106/DIG. 3, 427/214, 427/218, 427/219, 428/363, 428/404
• US Class Current: 106/417
• CPC Class Codes: C01P 2004/20 extending in two dimensions, e.g. plate-like
• CPC Class Codes: C01P 2004/84 one phase coated with the other
• 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 1/0051 comprising a stack of coating layers with alternating low and high refractive indices, wherein the first coating layer on the core surface has the 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 2200/301 Thickness of the core
• CPC Class Codes: C09C 2200/401 Inorganic protective coating
• CPC Class Codes: C09C 2220/106 comprising only a drying or calcination step of the finally coated pigment
• CPC Class Codes: Y10S 106/03 Mica
• CPC Class Codes: Y10T 428/2911 Mica flake
• CPC Class Codes: Y10T 428/2993 Silicic or refractory material containing [e.g., tungsten oxide, glass, cement, etc.]

Abstract

Nacreous pigments having improved light fastness are based on mica platelets coated with titanium dioxide and, optionally other additional metal oxides. These pigments carry an additional thin manganese oxide layer. The pigments are prepared in a process wherein mica is coated in aqueous suspension with one or more titanium dioxide hydrate layers and, optionally, with further metal oxide layers, mixed with the titanium dioxide hydrate or separately therefrom, and then is washed, dried and calcined. The process further comprises precipitating an additional layer of manganese hydroxide onto the base pigment, either directly after coating with the titanium dioxide hydrate and/or metal oxide layers or after the calcination thereof. The flakes are the washed, dried and calcined.

The new pigment can be used for pigmenting plastics, lacquers, paints and cosmetics, inter alia.

Claims

1. Nacreous pigments having improved light fastness comprising mica platelets whose surfaces are coated with a layer comprising titanium dioxide and which are coated with a thin top layer comprising manganese oxide, wherein the amount of manganese oxide is about 0.05-0.5% by weight, relative to total pigment weight.

2. Nacreous pigments of claim 1 wherein at least one metal oxide layer also contains about 0.1-20 wt. % of SiO₂.

3. Nacreous pigments of claim 2, comprising alternating layers of TiO₂ and tin oxide.

4. Nacreous pigments of claim 1 wherein the TiO₂ is in the rutile form.

5. Nacreous pigments of claim 1 comprising alternating layers of TiO₂ and tin oxide.

6. Nacreous pigments of claim 1 wherein the mica platelets are 5-200 μ

m in diameter.

7. Nacreous pigments of claim 1 further comprising a metal oxide other than TiO₂ in said layer comprising TiO₂.

8. Nacreous pigments of claim 1 further comprising at least one other layer of metal oxide other than TiO₂.

9. A process for preparing nacreous pigments having improved light fastness and comprising mica platelets whose surfaces are coated with a layer comprising titanium dioxide and which are coated with a thin top layer comprising manganese oxide, wherein the amount of manganese oxide is about 0.05-0.5% by weight, relative to total pigment weight,

comprising, coating the mica platelets in aqueous suspension by precipitating thereon at least one titanium dioxide hydrate layer and subsequently precipitating a top layer of manganese hydroxide onto the resultant coated platelets;

and then washing, drying and calcining the coated platelets,

wherein the precipitation of titanium-containing layers is achieved by suspending mica platelets in an aqueous solution of a pH of about 0.5-5, heating the solution to about 50°

-100°

C., adding a soluble titanium salt thereto and maintaining the solution pH substantially constant; and

, in any titanium layers also comprising another metal oxide, simultaneously adding a soluble salt of the cation of said other oxide to the solution whereby the metal cation is also precipitated; and

wherein the manganese precipitation is effected by adjusting a suspension of said platelets to a pH above 3 and a temperature of 50°

-100°

C., and then adding to the suspension a manganese salt and maintaining the pH value at an essentially constant value.

10. A process of claim 9 wherein the precipitation of manganese hydroxide is preceded by washing, drying and calcining of the pigments coated with TiO₂.

11. A process of claim 10 wherein the pigments are coated with TiO₂ and other metal oxides.

12. A process of claim 9 wherein the precipitation of manganese hydroxide follows directly after the last coating step with TiO₂ or other metal oxide.

13. A process of claim 9, wherein the titanium dioxide hydrate is precipitated such that TiO₂ is obtained in the rutile form after calcination.

14. A process of claim 9 wherein SiO₂ is coprecipitated in the formation of one or more of the metal oxide layers by adding a soluble silicate salt to the solution, and wherein said one or more metal oxide layers contains about 0.1-20 wt. % of SiO₂.

15. A process of claim 9 wherein the manganese hydrate is precipitated from a solution of a Mn(II) salt.

16. A process of claim 9 wherein the nacreous pigments further comprise a metal oxide other than TiO₂ in said layer comprising TiO₂ and wherein said process further comprises including in at least one TiO₂ layer another metal oxide by coprecipitating the corresponding hydrated metal oxide along with the hydrated titanium dioxide.

17. A process of claim 9 wherein the nacreous pigments further comprise at least one other layer of metal oxide other than TiO₂ and wherein said process further comprises coating said pigments with at least one separate metal oxide layer comprising a metal oxide other than TiO₂ by separately precipitating thereon the corresponding hydrated metal oxide.

18. In a composition comprising a base ingredient and a pearlescent pigment based on TiO₂ coated mica flakes, the improvement wherein the mica flakes have surfaces coated with a layer comprising titanium dioxide and which are coated with a thin top layer comprising manganese oxide.

19. A composition of claim 18 wherein the base ingredient is a plastic, lacquer, paint or toiletry formulation.

20. A composition of claim 18 wherein said mica flakes further comprise a metal oxide other than TiO₂ in said layer comprising TiO₂.

21. A composition of claim 18 wherein said mica flakes further comprise at least one other layer of metal oxide other than TiO₂.