Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
1999-08-13
2002-08-20
Le, Hoa T. (Department: 1773)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C427S212000, C427S221000, C428S407000
Reexamination Certificate
active
06436538
ABSTRACT:
This invention relates to a collection of loose composite plateletlike particles comprising a core and at least one coating layer consisting essentially of a compound having from 60 to 95% by weight of carbon and from 5 to 25% by weight of nitrogen, the balance to 100% being selected from elements of the group consisting of hydrogen, oxygen and sulfur, as well as to processes for the manufacture thereof, to polymer compositions containing it, and to the use thereof as effect pigments.
Effect (or luster) pigments are reflective flat particles that show at least partly specular reflection of the incident light. In a surface painted with effect pigments, for example, the effect pigment particles in the paint usually orient themselves substantially parallel to the surface, so that the colored paint surface when illuminated by a fixed white light source shows a luster effect and may appear in different colors according to the angle at which it is viewed and the nature of the effect pigment. A high-quality coloured effect pigment should impart highly saturated colors to the medium in which it is incorporated at all viewing angles. An optically variable pigment should also have a large difference in color between different viewing angles (high goniochromaticity).
The visual difference between two colors is best reflected by the &Dgr;E* value in the L*a*b* color system (CIE-LAB 1986). Different types of effect pigments are able to impart effects to varying degrees; for example, simple metal particles, for example aluminium flakes, mainly produce differences in brightness (high &Dgr;L*), which in combination with transparent colored pigments leads to the so-called metallic flop effect.
In effect pigments, color is mainly produced by interference of light. Such pigments are particles that have been coated with a thin layer of a colorless or colored substance; the color effect depends on the thickness of the coating layer and may manifest itself both in the brightness (L*) and in the hue (H*). The goniochromaticity arises because the optical path length of the reflected beam is different at different angles to the surface.
Interference pigments can be prepared from any known plate-like particles, for example from plate-like organic or inorganic colored pigments, such as &bgr;-copper phthalocyanine, 3,4,9,10-perylenetetracarboxylic acid diimides, fluororubins or &agr;-Fe
2
O
3
, from metal flakes, such as aluminium, copper or bronze flakes, or from silicatic particles.
However, the demands made of pigments are constantly increasing, so that the conventional effect pigments are unable fully to meet today's high expectations, particularly in high-quality applications such as automotive lacquers. For example, many effect pigments which would be desirable from the point of view of hue often exhibit inadequate light or weather stability, and many interference pigments are lacking chroma (C*, saturation) and opacity.
In many cases, too, the mechanical strength of the effect pigments is not satisfactory. For example upon dispersion into an ink or paint composition, the coatings may break or peel off, leading to insatisfactory coloristics. This happens particularly with flat, smooth coatings which are desirable for coloristic reasons. Another problem is that it is very difficult to make relatively thick coatings without forming agglomerates, thus impairing the optical properties.
The preparation of fine black pigments through oxydative pyrolysis at 200-350° C. of acrylonitrile-based polymer particles treated with an adhering aminosiloxane is disclosed in JP-63/142066-A. This process leads to an uniformly shaped black powder, which contains only traces of nitrogen and does not produce any luster effect or goniochromaticity.
DD 238 994 discloses organophilic colored fillers consisting of small clay or kaolin particles (Ø≦2 &mgr;m) embedded in a matrix based on conducting polymers, which are obtained by calcination of a ceramic mass of clay and a polymer such as acrylonitrile at a temperature between 150° C. and 50° C. below the clay's decomposition point. Yet, these composite fillers are of brown to black color, without any luster effect or goniochromaticity, and their components are not arranged regularly.
DD 238 993 discloses organophilic colored fillers consisting of small clay or kaolin particles (Ø<2 &mgr;m) embedded in a matrix containing amorphous carbon, which are obtained by calcination of a ceramic mass of clay and a polymer such as acrylonitrile at a temperature above the clay's decomposition point. Additional components such as mica may be contained in amounts up to 20% by weight. Yet, these composite fillers are of brown to black color, without any luster effect or goniochromaticity, and their components are not arranged regularly.
U.S. Pat. No. 5,322,561 relates to conductive flaky pigments, the conductive coating of which consists of a metal oxide pigment layer doped with additional metal oxide particles and containing interdispersed carbon black particles. The color is however black to pale and silvery grey, with quite a low chroma.
U.S. Pat. No. 3,087,827 discloses the deposition of carbon onto a TiO
2
layer from hydrocarbons, fatty acids, fats or soaps at 700-1000° C. The carbon fills into the minute spaces between the TiO
2
particles, even when deposited at the end of the process. Total absence of oxygen is required in order to avoid undesirable soot or particulate carbon formation. Moreover, the products are insatisfactory light stable as is known from U.S. Pat. No. 5,501,731.
U.S. Pat. No. 5,271,771 discloses carbon-containing effect pigments which are obtained through simultaneous deposition of carbon and a metal on a plate-like substrate, and subsequent redox reaction between the metal oxide in the pigment's undercoat and the metal in the pigment's topcoat, together with precipitation of carbon, at high temperatures under reducing conditions. It is however not possible to deposit the carbon-containing layer without altering the system's optical properties.
Dark effect pigments are known from DE-OS 195 02 231, which are coated with soot embedded in or overlaid with titanium oxide. They are obtained by coating a plateletlike core mechanically with soot particles, precipitating thereon titanium hydroxide and a metallic reducing agent, and pyrolizing the obtained composite at about 500-1000° C. under inert conditions. The chroma is somewhat improved but at the detriment of the lightness which is much too low.
U.S. Pat. No. 4,076,551 discloses pigments coated with a metal hydroxide or bismuth oxychloride layer and carbon black particles incorporated therein. Example 3 discloses a blue mica/TiO
2
interference pigment coated with 3% of carbon black and 0.73% Al
2
O
3
, which exhibits a strong dark blue powder color with a lively blue shimmer and may be heated to 300° C. for 40 minutes without any gloss or color change. However, the amount of carbon which can be fixed is limited and depends on the pigment's available surface area. For mica flakes, it does not exceed about 15 mg/m
2
, the carbon in excess remaining in suspension and affecting the luster. In addition, it is very difficult to disperse the carbon black in aqueous media, and the coating is irregular, so that the color and the goniochromaticity do not meet today's requirements to a satisfactory extent.
U.S. Pat. No. 5,501,731 claims that some of above lacks may be solved by coating plateletlike silicatic substrates with carbon-containing metal compounds (such as Cr
III
acac
3
) and compounds of the formula [(CH
2
O)
1-6
]
x
(such as sugars or starch), and then decomposing the carbon-containing compounds on the surface of the substrate particles under oxygen-excluding conditions. Very smooth coatings can allegedly be obtained when the decomposition takes place from the gas phase. However, this process leads to coatings containing high amounts of a metal—the ratio Cr/C is 0.92 in example 1 and 1.50 in example 2. Consequently, it is only suitable for very thin layer
Bujard Patrice
Herren Fritz
Schulthess Adrian
Takahashi Ryuichi
Takeshita Kimiya
Ciba Specialty Chemicals Corporation
Crichton David R.
Le Hoa T.
LandOfFree
Nitrogen doped carbon-coated effect pigments and their... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Nitrogen doped carbon-coated effect pigments and their..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Nitrogen doped carbon-coated effect pigments and their... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2905940