Coloring pigment and method of manufacture

Details Coloring pigment and method of manufacture Coloring pigment and method of manufacture

1996-02-07

1998-04-14

Bell, Mark L.

Compositions: coating or plastic

Materials or ingredients

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

106457, 106459, 423138, 423151, 423152, C09C 124

Patent

active

057387176

DESCRIPTION:

BRIEF SUMMARY
This invention relates to colouring pigment, more particularly black or red colouring pigment, such as may be used in paints, rubber, concrete, plastics and various other materials and compositions, and a method of manufacturing such a colouring pigment.
High quality black colouring pigment is conventionally made by chemical precipitation of ferrous and ferric salts. The processes used, with some variations and improvements, are mostly based on the Penninman Zoph process as disclosed in U.S. Pat. No. 1327061. These are wet processes which require considerable expertise and control to produce a good quality pigment with a minimum of red, yellow and green contamination. From the black pigment produced, red pigments can be obtained by further processing.
Substantial capital investment in plant is involved and relatively high production costs so that the pigment produced by these conventional processes is expensive to buy.
A lower quality black colouring pigment is produced at lower cost by processing natural minerals, for example mined magnetite, carbon and other organic material, or inorganic materials such as bones. A poorer level of colouring, tinting strength and weathering ability is a characteristic of these pigments, resulting from the high content of undesirable elements in, and the unsuitable physical characteristics of, the minerals or materials used.
It is an aim of the present invention to provide a colouring pigment which is of better colour and tinting strength than this lower quality pigment and is not as costly to produce as the pigments obtained by chemical precipitation.
According to one aspect the present invention consists in colouring pigment made from a synthetic magnetite produced by oxidation of ferrous mill scale and reduced to a particle size such that preferably at least 95% of the product does not exceed 20 microns.
Typically at least 85% of the particle size of the product should not be more than 10 microns.
Ferrous mill scale for use in the production of the synthetic magnetite, being a waste product, is not costly. A ready source of ferrous mill scale is from the rolling of iron or steel billets but it may be obtained from other iron or steel plant sources as well.
Oxidised ferrous mill scale suitable for use in the manufacture of the pigment is commercially available,
A typical analysis of a synthetic magnetite made from ferrous mill scale and commercially available is:


______________________________________ Total Iron as Fe 71.27% Iron Oxide as FeO 5.30% Magnetite as Fe.sub.3 O.sub.4 87.40% Hematite as Fe.sub.2 O.sub.3 5.18% K.sub.2 O 0.05% Na 0.05% CaO 0.49% MgO 0.11% SiO.sub.2 0.62% A1.sub.2 O.sub.3 0.28% Mn.sub.3 O.sub.4 0.39% Cr.sub.2 O.sub.3 0.08% ______________________________________
The particle size of the colouring pigment affects the tinting strength of the colouring pigment, the smaller the particle size the greater the tinting strength. The higher the percentage of particles that does not exceed 10 microns the better the tinting strength that can be achieved. Ideally 100% of the pigment is reduced to a particle size not exceeding 10 microns.
The colouring pigment may be black. This is produced when temperatures in the manufacture of the pigment are kept low, preferably below 40.degree. C. It is desirable that unoxidised iron should be kept to a maximum amount of 0.5% to avoid introducing a browning tint into the pigment which reduces the black quality of the pigment.
For the best quality black, apart from having a typical analysis of 95-99.5% oxides of iron, the molecular ratio of the synthetic magnetite should be 0.9 to 1.1:1, being defined as: ##EQU1## A molecular ratio of this order ensures that there is little or no haemetite inclusion in the synthetic magnetite to reduce the denseness of the black colour achieved.
It is possible to achieve a black colouring pigment in accordance with the invention which has very little red, green or yellow contamination so that it provides an intense black with a distinctive blue background,

REFERENCES:
patent: 0127350 (1872-05-01), Hughes
patent: 1327061 (1920-01-01), Penniman, Jr. et al.
patent: 1848660 (1932-03-01), Renkwitz
patent: 4123501 (1978-10-01), Kohler et al.
patent: 4139398 (1979-02-01), Pellizzon et al.
patent: 4299635 (1981-11-01), Dickerson
patent: 4432803 (1984-02-01), Hitzrot, Jr.
patent: 4966641 (1990-10-01), Westerhaus et al.
patent: 4990189 (1991-02-01), Weise et al.
Levin et al. Phase Diagrams for Ceramists pp. 38 & 39 (1964).
Encyclopedia of Chemical Technology, vol. 17, pp. 795-798 (1982).

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