Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Reexamination Certificate
2002-06-17
2003-05-13
Koslow, C. Melissa (Department: 1755)
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
C106S453000, C023S3130FB, C264S118000, C264S141000
Reexamination Certificate
active
06562120
ABSTRACT:
FIELD OF INVENTION
The present invention relates to the manufacture of pigment granules, for example iron oxide and chromium oxide pigments.
BACKGROUND
Metal oxides, such as iron oxides or chromium oxides, are used in the pigmentation of, among other things, cement and concrete products (e.g. paving slabs and blocks), paints, plastics, toners and inks, chelants, catalysts, and also in a variety of magnetic, medical, and pharmaceutical applications. Such metal oxide pigments have traditionally been used in the form of a powder.
Powdered metal oxide pigments, such as iron oxide and chromium oxide pigments, are dusty, giving rise to health hazards and making storage and handling difficult. Also, the powders are not free flowing and so cannot readily be conveyed through pipes, which readily become blocked by the powder; furthermore the poor flowing properties of powders makes it hard to meter them using auger screws to ensure the correct proportion of pigment to base material (e.g. concrete).
Similar problems are known in other industries, e.g. in the animal feedstuff industry, and such problems have been solved to a substantial extent by granulating the product. It is readily apparent that such solutions can be applied to the field of pigments to solve the above problems. For example, it has been proposed in FR-A-2 450 273 to granulate carbon black pigment used in the pigmentation of paper and cement and concrete; here it should be understood that carbon black gives rise to an even greater dusting problem than iron oxides since the granule size of carbon black powders is much smaller than that of iron oxide powders but also carbon black suffers from an additional problem of floating on the base material, which makes incorporation into the base material difficult. According to FR-A-2 450 273, the twin problems of dusting and poor incorporation are solved by mixing carbon black with at least 30% water and optionally also a wetting or dispersing agent in an amount of 0.5 to 12% and preferably 5 to 10% (based on the amount of the carbon black) and subjecting the resulting mixture to compression forces in a pearlising machine to form pearls or granules. Depending on the nature and operation of the pearlising machine, the compression forces can be substantial.
In contrast to FR-A-2 450 273, EP-B-0 268 645 requires that no compression forces are applied to pigments during the formation of pigment granules for use in colouring of concrete and cement. This may be achieved by an agglomeration technique, e.g. by means of rotating pan or drum granulising machines, which merely bring individual pigment particles into contact with each other in the presence of water and a binder (e.g. lignin sulphonate), whereupon the particles adhere to each other, i.e. they coalesce, to form the required granules. Alternatively pigment granules may be formed by spray drying a mixture of the pigment, water and a binder and commercially it is the spray drying method that is used. Both methods, however, require the presence of a considerable amount of binders to ensure that the pigment particles adhere to one another. If made by pan or drum pelletising machines, it may be necessary to dry the granules to a commercially acceptable water content below 4.2% water.
In U.S. Pat. No. 4,277,288, it has been proposed to manufacture pigment granules by forming a fluidised bed of pigment powder and adding into the bed an organic liquid or wax as a binder to promote granulation. A surfactant is also added.
U.S. Pat. No. 5,484,481 discloses a process for the granulation of pigments for use in dyeing cement and concrete involving compacting pigment powders in the presence of a binder to form flakes, breaking up the flakes and pelletising the ground flakes using known techniques, e.g. using rotating pans or drums, which would involve the application of water and a binder to the ground flakes.
However, the granulation of pigments must meet another criterion not required in other industries where pelletisation is common, e.g. the animal feed stuff industry, namely the requirement that any pigment granules must be capable of being readily dispersed in the base material to colour it uniformly since if they did not readily disperse, they would give rise to streaks or pockets of colour, which detract from the appearance of the final product. Thus granules should be able to be dispersed in the base material while at the same time should be sufficiently coherent and robust that they do not break down into powder again during storage or handling.
The manufactures of coatings (whether liquid or dry) require that pigments contain as few unnecessary additives as possible and it would therefore be desirable to be able to produce pigments with substantially reduced amounts of binders and, if possible, even to eliminate such additives.
It has generally been thought indispensable commercially to use one or more binders (other than water or other material that is or can be removed after the formation of the granule) in the manufacture of pigment granules to give the granules strength to resist being broken up into powder during handling and storage and to promote the dispersion of these granules in their end use.
It is an object of the present invention to manufacture pigment granules that both readily disperse in the base medium and also are robust and have a reduced liability to dusting, i.e. to being broken down into powder. It is a further object of the present invention to provide a process of manufacturing robust and readily dispersible pigment granules without the use of substantial quantities of binder.
DISCLOSURE OF THE INVENTION
According to the present invention, there is provided a process for the preparation of low dusting, free flowing granules of at least one pigment, said at least one pigment being selected from the group consisting of iron oxides, chromium oxides, cobalt blues, mixed metal oxides, carbon blacks, titanium oxides, or mixtures thereof, which process comprises mixing said at least one pigment with water to form a mixture having a dough-like consistency, extruding the mixture through at least one die to form extruded granules, thereby also compacting the mixture, and drying the extruded granules, so that the final water content of the granules is less than substantially 5%.
The action of forcing the material through a die during the extrusion process exerts a substantial compaction on the individual pigment particles, thereby increasing the strength of the granules.
Surfactants and/or binders may be added to the extrusion dough, although any binder used is preferably of the type that also has some surfactant properties. Examples of suitable binders/dispersants are Borresperse NA, Ultrazine NA, Pexol 2000, Dresinate 214, Dispex N40, Narlex LD31, Suparex DP CC002. Surfactants (e.g. anti-flocculants or wetting agents), such as sodium alkylbenzene sulphonates, also make suitable additives, as they can provide some incidental binding action, as well as improving the dispersion properties in the end use.
The water content of the dough mixture is critical to:
forming a stable granule
preventing the extruded granules from fusing to one another
producing discrete granules rather than just a long ribbon.
but the optimum water content can readily be determined for any pigment composition by simple trial and error.
The damp mixture is fed to a compression device whereby the mixture is forced through holes in a die, which is preferably a perforated plate or screen. This can be achieved by the action of a screw pushing the mixture through the die or by the action of a moving blade or a roller (or similar pushing device) wiped over the die and thereby compressing the mixture through the die.
Typically the extruder holes would be between 0.3 mm and 4 mn in diameter, but could be smaller or larger.
The extruded granules are dried (e.g. in a tray drier, band dryer, fluidised bed dryer etc) and may then be screened to remove fines and/or oversized granules, which latter can arise either because they are too long or because individ
Dunker Peter
Emery Peter Robin
McAualay Joseph Hugh
Cronin Michael J.
Elementis UK Limited
Koslow C. Melissa
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