Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Reexamination Certificate
2002-03-25
2003-07-08
Koslow, C. Melissa (Department: 1755)
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
C106S403000, C106S415000, C106S456000
Reexamination Certificate
active
06589331
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to flake shaped, metal oxide coated soft iron pigments.
2. Background Art
Colored effect pigments that display a metallic luster have been the object of intense research and development efforts for many years because of their special optical qualities, particularly because of their brilliancy. Effect pigments are pigments of a flake shape that display a direct reflection and only little scattering. In addition to reflection properties, they may also display interference properties and must be oriented in a preferred direction by a method based on the given application. The special feature of all applications that are pigmented with effect pigments is the pronounced angle-dependence of the optical appearance. The particle size of effect pigments considerably exceeds that of coloring pigments. The preferred particles that find the most application have sizes between 5 and 50&mgr; and a diameter-to-thickness ratio of 30-150. Flakes with a diameter up to 250&mgr; are used in a few fields of application. The conceptions regarding the ideal shape of metallic effect pigments, in practice, are based on the so-called “silver dollar”, a largely spheroidal aluminum flake that has few scattering centers. The present invention describes effect pigments that have the layer sequence metal oxide—iron—metal oxide. In the category of the metal oxide coated iron pigments only few developments have become known to date. They are essentially concerned with iron pigments that display temper colors. The term temper colors refers to interference reflection phenomena that result from the oxidation of the surface of metal particles. Known metal pigments that display temper colors are the superficially oxidized brass pigments that are on the market in various shades of color depending on the thickness of the oxide film.
DE 4419 741 describes iron pigments that display temper colors. The colored effect pigments with a metallic luster are produced by atomizing molten iron, grinding the resulting granular iron, and subsequently heating the flake shaped particles to 200-500° C. in the presence of atmospheric oxygen. When heated in air, an oxide layer forms on the surface of the iron particles and temper colors appear in the color tones gold, red violet and blue. The production of colored iron pigments with metallic luster is described very similar in EP 673980. There, too, granular iron is first produced by atomizing molten iron. Subsequent wet grinding of the granular iron and subsequent heating of the ground products at 350° C. produce the temper colors gold, copper, violet and blue in that order. The sequence of colors requires a time period of only 1-4 minutes. The shortcomings of iron pigments with temper colors and the method of their production are manifold. The most significant shortcoming is the low reproducibility of the color hues. Even a slight change in the thickness of the iron oxide coating is enough to produce different interference reflection colors, and the oxide layer that is produced by oxidation of the iron surface is also not conclusively defined regarding its composition (Fe
2
O
3
/Fe
3
O
4
). Since pure iron in a fine distribution reacts pyrophoric, the difficulties in adjusting discrete color hues become greater as the particle size of the iron flakes decreases. EP 673980 thus describes only the production of relatively large iron flakes with temper colors (70-80% of the particles are between 100-300&mgr;). Further deficits of the described methods for producing the above iron-based effect pigments already result in the atomizing step. When molten iron is atomized, the granular iron is obtained relatively large-grained and with not very homogeneously distributed particle sizes. Since a particle size range of 5-50&mgr; is preferred in effect pigments, the iron particles that are produced by atomizing must not only be deformed but also reduced in size. This is very expensive. Furthermore, the reactivity of the iron flakes significantly increases with their reduction in size.
In view of the difficulties involved in the production of suitable iron substrates and their susceptibility to oxidization, a number of developments in the past have dealt with the metal oxide coating of corrosion and oxidization resistant special steel flakes. Special steel or “stainless steel” refers to iron alloys with 18-30% Cr, 0-8% Ni, also Mo, Cu, V and C. Stainless steel flakes are on the market for applications in heavy corrosion proofing. Even though iron is the main component of the special steel flakes—which frequently results in the catchy but misleading term iron flakes—developments in metal oxide coatings of special steel or stainless steel flakes are not in competition with the object of the present invention. The reasons are as follows: special steel alloys have different optical constants than iron. Since the optical constants of the reflector material largely determine the overall optical appearance of the pigments, one must distinguish between special steel and iron. Special steel furthermore lacks the ductility of iron, which is why usually only relatively thick flakes with little coverage are available for coatings.
Special steel flakes, in contrast to iron flakes, are for the most part produced by metal-cutting processes. Lastly, special steel lacks the ferromagnetism that is characteristic for iron and which represents the cause for the orientability of metal oxide coated iron flakes with the aid of an external magnetic field. The applications that deal with the coating of special steel or stainless steel flakes are listed below, to complete the picture:
DE 41 043 10.3 describes oxide-coated flake shaped pigments that are produced wet-chemically by coating stainless steel flakes with iron oxide and titanium oxide. The pigments display a steel gray or black gray body color and interference colors. The production of titanium dioxide coated stainless steel flakes is described similarly in JP 10/110 113. WO 00/43 457 describes the production of Fe
2
O
3
, TiO
2
and ZrO
2
coated effect pigments, the metallic core material is preferably composed of titanium, tantalum, zircon, stainless steel or Hastelloy (a nickel alloy).
Alternative methods for producing metal oxide coated iron pigments by PVD methods and subsequent reduction in size of the films that are prepared in the vacuum are conceivable. However, so far no products with the layer sequence metal oxide—iron—metal oxide (“three-layer combo” with iron reflector layer) have become known that are produced according to this method. The high cost would likely conflict with an implementation of this concept on an industrial scale.
From this follows that the development of effect pigments on the basis of iron depends to a significant degree on making suitable metal substrates available. Of the pigment developments described so far, none is able to meet the requirements in the decorative and functional fields.
SUMMARY OF THE INVENTION
It was the object of the present invention to develop novel, colorful effect pigments with metallic luster for decorative and functional fields of application. The novel pigments were intended to stand out by their brilliancy and their orientability with the aid of an external magnetic field. They were to have a high covering power and particle sizes preferably in the range of 5-36&mgr;. The novel pigments were furthermore supposed to be stable in slightly alkaline conditions, as they are found in many water lacquers.
This object was met with the use of highly pure reduced carbonyl iron powder, which is commercially available in a spherical particle shape and narrow particle size distribution in various particle sizes from 1-10&mgr; (suppliers: BASF AG, Ludwigshafen, or ISP, Wayne, N.J.) This powder, which is mechanically soft and ductile because of its purity, is gently ground and subsequently subjected to the oxide coating. The oxide coating may take place via wet-chemical deposition processes or via CVD methods in the fluidize
Greiwe Klaus
Henglein Frank
Ostertag Werner
Trummer Stefan
Browdy and Neimark , P.L.L.C.
Eckart GmbH & Co. KG
Koslow C. Melissa
Manlove Shalie
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