Claims
- 1. In the process for preparation of improved iron oxide black pigments by the reaction of aromatic nitro compounds with metallic iron of form finely divided pigment which is predominantly Fe.sub.3 O.sub.4, the improvement comprising heating the finely divided uncoated Fe.sub.3 O.sub.4 pigment to a temperature of 400.degree. C. to 750.degree. C. under a non oxidizing atmosphere.
- 2. Process according to claim 1 wherein the non-oxidizing atmosphere contains water vapor.
- 3. Process according to claim 1 wherein the finely divided pigment is heated from 2 minutes to 5 hours.
- 4. Process according to claim 1 wherein the heating is carried out continuously in a rotary tubular furnace.
- 5. Process according to claim 1 wherein after heating the pigment is cooled to below 100.degree. C. while still under the non-oxidizing atmosphere.
Priority Claims (1)
| Number |
Date |
Country |
Kind |
| 3620333 |
Jun 1986 |
DEX |
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BACKGROUND OF THE INVENTION
This application is a continuation of application Ser. No. 059,492, filed Jun. 8, 1987, now abandoned.
The present invention relates to new, color-intensive, blue-tinged iron oxide black pigments obtained by the nitrobenzene reduction process and to an improved process for the preparation of iron oxide black pigments by the reaction of aromatic nitro compounds with metallic iron, optionally with the addition of control chemicals, to produce pigments consisting predominantly of Fe.sub.3 O.sub.4.
Iron oxide black pigments may be prepared by various processes. According to U.S. Pat. No. 4,173,624 and GB No. 15 349 53 those pigments may be prepared by the reaction of iron salts with alkalies. Once major disadvantage of this process is that it results in the formation of a quantity of neutral salts equivalent to the quantity of alkalies put into the process. The reductive calcination of iron compounds as disclosed in GB No. 1 575 337 has the disadvantage of forming calcination gases.
The reduction of FeOOH or Fe.sub.2 O.sub.3 with reducting gases such as hydrogen at elevated temperatures has been described in U.S. Pat. No. 4,631,089. The produre required for dealing with hydrogen or combustible gases at elevated temperatures is, however, expensive.
The reaction of iron scrap in atmospheric oxygen in a slightly acid medium as described in U.S. Pat. No. 4,123,501 and has the disadvantage of low reaction velocities.
Lastly, the preparation of iron oxide pigments by the reaction of aromatic nitro compounds with iron to form aromatic amine by-products and iron oxide pigments is disclosed in DE-C 703 416, DE-C 551 255 and DE-C 518 929.
Yellow (.alpha.-FeOOH), red (.alpha.-Fe.sub.2 O.sub.3) or black (Fe.sub.3 O.sub.4) iron oxide pigments may be obtained, depending on the nature and quality of the iron used (granules, cast turnings) and on the control chemicals.
The starting material used for the production of iron oxide black pigments by the so-called nitrobenzene process are aromatic nitro compounds such as nitrobenzene and metallic iron. The metallic iron is in most cases iron turnings as this is the least expensive form of iron. The particle size is controlled by varying the process parameters, using control chemicals and suitable choice of the qualities of iron. Very finely divided pigments obtained by this process have, however, such a pronounced brown tinge that they cannot be used as iron oxide black pigments. These pigments have color value deviations of more than one unit in the .DELTA.b*-value .DELTA.(B*.gtoreq.+1), based on the Trade product Bayferrox 320.
No color intensive iron oxide pigments which are neutral or blue tinged in color of the kind preferred by the lacquer and building industry have heretofore been obtained by the nitrobenzene reduction process.
It is therefore an object of the present invention. to provide an iron oxide black pigment produced by the nitrobenzene reduction process which does not have the disadvantages described above and therefore fulfils the requirements of a black pigment.
These requirements are fulfilled by the iron black pigments according to this invention.
The present invention produces improved iron oxide black pigments which have a blue tinge but do not have the objectionable brown tinge of pigments produced by the known nitrobenzene process. The improved pigments, which are also a part of the present invention, are produced from conventional iron oxide black pigments obtained by the nitrobenzene reduction process by a tempering or heating of such pigments at an elevated temperature for a period of time sufficient to remove the objectionable brown tinge.
US Referenced Citations (3)
| Number |
Name |
Date |
Kind |
| 4358431 |
Brunn et al. |
Nov 1982 |
|
| 4491619 |
Biermann et al. |
Jan 1985 |
|
| 4631089 |
Rademachers et al. |
Dec 1986 |
|
Continuations (1)
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Number |
Date |
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| Parent |
59492 |
Jun 1987 |
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Patent Grant
4966641
