Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Reexamination Certificate
2002-04-01
2003-09-09
Koslow, C. Melissa (Department: 1755)
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
C423S633000
Reexamination Certificate
active
06616747
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a process for producing granular hematite particles, and more particularly, to a process for producing granular hematite particles having a high purity, a small equilibrium water content and a reduced oil absorption in an industrially and economically useful manner.
The granular hematite particles produced according to the process of the present invention are useful as red-based color iron oxide pigments for paints, colored resins, printing inks, cosmetics, building materials or the like.
Granular hematite particles exhibit a red color varying from light red to deep red and, therefore, have been extensively used as red-based color iron oxide pigments for producing paints, colored resins, printing inks and cosmetics by mixing the pigments with vehicle or resin, or for producing building materials by mixing the pigments with cement, concrete, asphalt, etc.
Since the hue and particle size of the granular hematite particles have a close relationship with each other, various granular hematite particles having different colors varying from light red to deep red have been produced by appropriately controlling the particle size thereof. The granular hematite particles having a larger particle size tend to exhibit a deeper hue. For example, the granular hematite particles having an average particle diameter of not more than 0.2 &mgr;m, e.g., 0.05 to 0.2 &mgr;m, exhibit a light red color, while those having an average particle diameter of 0.4 to 0.6 &mgr;m exhibit a deep red color. In addition, the granular hematite particles having an average particle diameter of from more than 0.2 to less than 0.4 &mgr;m exhibit a half-tone color between light red and deep red.
In recent years, from industrial and economical viewpoints, it has been strongly required to produce granular hematite particles, i.e., red-based color iron oxide pigments having a high quality and excellent properties using inexpensive materials without use of any specific device such as autoclave.
Hitherto, the red-based color iron oxide pigments have been typically produced (i) by passing an oxygen-containing gas through a suspension containing ferrous hydroxide obtained by reacting an aqueous ferrous sulfate solution with an aqueous alkali hydroxide solution such as aqueous sodium hydroxide solution while keeping the suspension at a pH value of 4.5 to 6.5 and a temperature of 65 to 90° C. to form magnetite particles; subjecting the thus obtained magnetite particles to filtration, water-washing and drying; and then heat-treating the magnetite particles at a temperature of 450 to 800° C. (for example, Japanese Patent Publication (KOKOKU) No. 49-35520(1974), etc.), (ii) by producing hematite particles in an aqueous solution; and subjecting the thus obtained hematite particles to filtration, water-washing and then drying (for example, Japanese Patent Publication (KOKOKU) Nos. 35-1224(1960) and 38-9852(1963), Japanese Patent Application Laid-Open (KOKAI) Nos. 49-73400(1974), 51-8193(1976) and 2001-200177, etc.); or the like.
At present, it has been strongly required to produce granular hematite particles having a high purity, a smaller equilibrium water content and a more reduced oil absorption in an industrially and economically useful manner. However, any of the above conventional methods fails to produce granular hematite particles fulfilling these properties in an industrial and economical methord.
Namely, the method described in Japanese Patent Publication (KOKOKU) No. 49-35520(1974) is disadvantageous from industrial and economical viewpoints since the aqueous solution containing expensive alkali hydroxide such as sodium hydroxide is used as the raw material.
In Japanese Patent Publication (KOKOKU) No. 35-1224(1960), there is described the method of producing hematite particles by preparing an aqueous iron nitrate solution by using non-pyrite particles and an aqueous nitric acid solution; heating the resultant aqueous iron nitrate solution from which residues are removed, at a temperature of not less than 50° C., especially, 135 to 250° C. in a closed pressure reaction vessel; and then rapidly cooling the solution. Thus, this method requires the use of the pressure reaction vessel, i.e., autoclave.
In Japanese Patent Publication (KOKOKU) No. 38-9852(1963), there is described the method of producing hematite particles in an aqueous solution by continuously introducing a gaseous oxidant into an acidic ferrous salt solution having a pH value of 4 to 5 in the presence of iron materials in an autoclave. Thus, this method also requires the use of the pressure reaction vessel, i.e., autoclave. Further, in this KOKOKU, it is described that “the red ferric oxide produced by the present method was &agr;-type iron oxide, and as a result of the analysis, it was confirmed that products obtained at a reaction temperature of 95° C. were Fe
2
O
3
.½H
2
O while those obtained at a reaction temperature of 120° C. were Fe
2
O
3
”. Thus, in this method, the hematite particles produced under ordinary pressure exhibit a low purity.
In Japanese Patent Application Laid-Open (KOKAI) No. 49-73400(1974), there is described the method of producing hematite particles by passing an oxygen-containing gas through an aqueous ferrous salt solution in the presence of seed crystals and metal iron. In this method, although no specific device such as autoclave is used, the obtained hematite particles contain as impurities &agr;-FeOOH in an amount of about 15% or less.
In Japanese Patent Application Laid-Open (KOKAI) No. 51-8193(1976), there is described the method of producing hematite particles by adding to an aqueous ferrous salt solution, as an alkali component, alkali hydrogen carbonate solely in an equivalent amount or more based on acid radical, or as an alkali component, alkali hydrogen carbonate and alkali carbonate in combination with alkali hydroxide such that the total alkali content is not less than an equivalent amount based on the acid radical and the alkali hydroxide content is not more than an equivalent amount based on the acid radical; and subjecting the resultant solution to oxidation reaction at a pH value of 7 to 11 and a temperature of from 65° C. to the boiling point. Although no specific device such as autoclave is used, since expensive alkali carbonate is used as the aqueous alkali solution, this method is not advantageous from industrial and economical viewpoints. Furthermore, in this KOKAI, it is described that “as a result of X-ray analysis, it was confirmed that most of the products were hematite”. Thus, the description means that the hematite particles produced by this method still contain impurities.
In Japanese Patent Application Laid-Open (KOKAI) No. 2001-200177, there is described the method of producing iron oxide red pigments having an excellent chroma by passing an oxygen-containing gas through an aqueous iron chloride solution at a temperature of 70 to 100° C. in the presence of iron materials and hematite seed crystals to obtain reddish brown precipitates containing granular hematite particles as a main component, wherein hematite produced by reacting dilute nitric acid with the iron materials at a temperature of not less than 90° C. is used as the hematite seed crystals. In this KOKAI, there are described no teachings and suggestions concerning improvements in purity, equilibrium water content and the like.
As a result of the present inventors' earnest studies, it has been found that by passing an oxygen-containing gas through an aqueous ferrous nitrate solution at a temperature of 80 to 90° C. in the presence of iron materials and hematite seed crystals to form reddish brown precipitates containing granular hematite particles as a main component; subjecting the obtained reddish brown precipitates to filtration, water-washing and drying; and then heat-treating the reddish brown precipitates in air at a temperature of 450 to 900° C., the obtained granular hematite particles can exhibit a high purity, a small equilibrium water content and a reduced o
Koslow C. Melissa
Manlove Shalie A.
Toda Kogyo Corporation
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