Pearlescent pigments

Details Pearlescent pigments Pearlescent pigments

2003-01-31

2004-04-13

Koslow, C. Melissa (Department: 1755)

Compositions: coating or plastic

Materials or ingredients

Pigment, filler, or aggregate compositions, e.g., stone,...

C106S416000, C106S417000, C106S418000, C106S419000, C106S450000, C106S455000, C106S461000, C106S479000, C106S480000, C106S481000

Reexamination Certificate

active

06719837

ABSTRACT:

The present invention relates to pearlescent pigments based on substrates coated with one or more layers of nitrides or oxynitrides, to methods for the production of such pigments and to their use in plastics, paints, coatings, powder coatings, inks, printing inks, glasses, ceramic products, agriculture foils, for lasermarking of papers and plastics and in cosmetic formulations.
The pearlescent pigments that are used and prepared according to this invention are at least partially transparent pigments with an angle-dependent optical effect.
Absorption pigments without any substrates based on nitrides or oxynitrides are well known. A good overview over these substances can be found in Marchand et al. “Nitrides and Oxynitrides: Preparation, Crystal Chemistry and Properties,”
Journal of the European Ceramic Society
, 8 (1991), p 197-213. It is characteristic for these pigments that through the variation of the metal oxides or mixed oxides and/or a variation in the N/O ratio a wide range of the color spectrum can be covered. These pigments are synthesized by simply mixing the metal oxides together with a mineralizer and subsequently heating this mixture under an ammonia gas atmosphere.
Titanium nitride coated substrates used as conductive pigments and produced in a fluidized bed reactor are disclosed in EP-A 0 401 141. Here, substrate particles were to be made conductive by a coating with titanium nitride. To achieve this, mica powder is coated via CVD in a fluidized bed apparatus at a constant temperature. As reactants a titanium halide and ammonia, mixed with an inert gas such as argon, are used.
Titanium oxynitride coated SiO
2
platelets are disclosed in WO2000/17277. In this application TiO
2
/SiO
2
-flakes are reduced with a metal under a non-reductive atmosphere at high temperatures using a metal halide as accelerator. The resulting product consists of titanium oxynitride-coated SiO
2
platelets and titanium suboxide coated SiO
2
platelets. Titanium nitride and oxynitride layers made according to this technology have turned out to be non-continuous and consequently showing brownish to olive colors. These rather unattractive colors were already described in the examples of WO 2000/17277.
It was therefore an object of the present invention to provide pigments with a great variety of different masstones which combine an attractive angle dependant interference phenomenon with the absorption color, therewith extending the range of pearlescent pigments based on substrates coated with nitrides/oxynitrides. Upon further study of the specification and appended claims, further objects and advantages of this invention will become apparent to those skilled in the art.
The present invention now provides new kinds of pigments which are based on nitride, respectively, oxynitride layers on substrates. These pigments are based on substrates coated with a selectively absorbing layer.
Surprisingly, a pearlescent pigment has now been found, which is based on substrates coated with one or more layers, characterized in that at least one layer is selectively light absorbing and consists of a nitride and/or oxynitride with the proviso that layers of titanium nitride or titanium oxynitride are excluded.
Preferably the synthesis of the new pigments is divided into two steps. The first step is the synthesis of a precursor and the second a conversion process carried out in a furnace. The new pigments can be produced in conventional static ovens, belt kilns or rotary kilns. However, a better product with less agglomerates and faster reaction rates is obtained in fluidized bed reactors.
The precursor is preferably produced in an aqueous precipitation process such as described for example in U.S. Pat. Nos. 3,087,828, 3,087,829, DE-A 19 59 998, DE-A 20 09 566, DE-A 22 14 545, DE-A 22 44 298, DE-A 23 13 331, DE-A 25 22 572, DE-A 31 37 808, DE-A 31 37 809, DE-A 31 51 343, DE-A 31 51 354, DE-A 31 51 355, DE-A 32 11 602, DE-A 32 35 107, WO 93/08237 and EP-A 0 763 573. Halide, carbonate, oxalate, chloride, oxychloride or alcoholate solutions are used to precipitate oxides, respectively, mixed oxides onto substrates. The reaction parameters such as temperature, pH, agitation velocity and reactor geometry are optimized to yield a flat continuous layer of insoluble oxides and/or hydroxides on the substrates. The mixed oxides are coprecipitated onto the substrates following an analogous process. For example, solutions of the different metal salts are mixed and then slowly added in the reactor to coat the substrate.
A wide range of precursors can also be synthesized using dopant ions, such as silicon, vanadium, chromium, aluminum, cerium, neodymium, praseodymium, sulfur, selenium, cobalt, nickel, zinc and phosphate ions, coprecipitated into the oxide respectively hydroxide layers. The dopants can be used to create color effects (like rare earth, vanadium, or cobalt ions) as well as for the control of grain growth (like SiO
2
or aluminum oxide) during the subsequent reaction with the reaction gas, such as ammonia. Advantageously this process does not need mineralizers or other reactive gases.
In the second step the precursors obtained in the above first step are converted into nitrides/oxynitrides. The precursors to be converted are calcined, for example, in a conventional static oven, belt kiln or rotary kiln. However, a better product with less agglomerates and faster reaction rates is obtained in a fluidized bed reactor. This process can be performed batchwise or continuously. A suitable mixture of gases consists of at least one inert and one reaction gas. Examples of useful reaction gases are N
2
, or N
2
/H
2
, but preferably ammonia. Further examples of converting to nitrides are shown in U.S. Pat. No. 5,246,493 and the above-cited Marchand article. Suitable inert gases are Ar, H
2
/CO/N
2
, N
2
(at lower reaction temperatures). The gas composition may vary from >0 to 100 vol.-%, preferably from 20 to 80 vol.-% of reaction gas in inert gas.
The temperature is maintained during calcinations, for example, at a fluidized bed temperature at 700 to 1250° C., preferably 800° C. to 1100° C. The conversion from oxides/mixed oxides to nitrides/oxynitrides is carried out depending on the different parameters, such as gas flow rates, reaction time or temperature profiles. The longer the reaction time the higher the nitride-to-oxynitride ratio. Consequently the reaction time determines the obtained structure of the compound. The color and the color strength of compounds is associated to a specific structure; thus, it is preferred that the reaction time is well controlled. In addition, for the same reason, temperature control is desirable.
In order to maintain the almost ideal conditions prevalent in a homogeneous fluidized bed in comitercurrent/cocurrent contacting special devices may be used. Instabilities like formation of channels or of bubbles in the bed are instantly destroyed by vibrations or agitating facilities.
If the reaction with the reaction gas, preferably ammonia, is not carried out to full completeness, mixtures of phases can be obtained including gradient of phase concentration through the layer thickness. These incompletely reacted products can be advantageous with respect to a desired color shade.
Suitable substrates which can be used in the present invention as base material, include, for example, spherical or platelet-shaped substrates, especially preferred are natural micaceous iron oxide (for example as in WO 99/48634), synthetic and doped micaceous iron oxide (for example as in EP-A 0 068 311), mica (muscovite, phlogopite, fluorophlogopite, synthetic fluorophlogopite, talc, kaolin), basic lead carbonate, flaky barium sulfate, SiO
2
, Al
2
O
3
, TiO
2
, glass, ZnO, ZrO
2
, SnO
2
, BiOCl, chromium oxide, BN, MgO flakes, Si
3
N
4
, graphite, pearlescent pigments (including those which react under the fluidized bed conditions to nitrides, oxynitrides or by reduction to suboxides etc.) (for example EP-A 9 739 066, EP-A 0 948 571, WO 99/61529, EP-A 1 028 146, EP-A 0 763 573, U.S. Pat. No. 5,858,078

Affiliated with

Also associated with

Rating

Pearlescent pigments does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Pearlescent pigments, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Pearlescent pigments will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3272062