Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Reexamination Certificate
2000-08-28
2002-11-26
Green, Anthony J. (Department: 1755)
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
C106S412000, C106S413000, C106S496000, C106S497000, C106S498000, C106S502000
Reexamination Certificate
active
06485558
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a process for the preparation of an organic colorant composition in granular form, comprising wax-coated organic pigments.
When prepared, organic pigments are generally obtained in the form of powders. Powders comprise very small particles and therefore give rise to a great deal of dust. Dust development leads to the contamination of apparatuses, plants and products, so that expensive and time-consuming cleaning work has to be carried out especially when changing products. Consequently, the pigment processors require the provision of pigment forms which do not produce dust.
For use, pigments must be dispersed in the application medium. If the pigments are present as powder, the dispersing is generally effected with the introduction of a considerable amount of energy, for example for the use of twin-screw extruders in the coloring of plastics. Pigments which are present in a predispersed form are therefore advantageous for the application.
JP 10-251533 describes quinacridone pigments which are brought into a predispersed form by wax coating via an isobutanol finish. The wax-coated quinacridone pigments, which have a particle size of from about 0.05 to 0.3 &mgr;m, are used in the form of a powder and thus have the disadvantage of developing dust.
DE-A1-29 40 156 and WO 92/07912 describe processes for the preparation of low-dust, free-flowing pigment granules by using a fluidized-bed method. Blowing air through the pigment powder produces a fluidized bed or fluidized pigment powder, which is sprayed with an aqueous solution, dispersion or emulsion of a granulating assistant.
In another process (DE 39 35 815 C2), the pigment is sprayed with a wax dispersion in a mixer-granulator. These processes have the disadvantage that the pigment is not present in a predispersed form advantageous for subsequent use, since the surface of the pigment particles is only incompletely coated with the wax or the assistant. In addition, it is not possible to fluidize every powder pigment to give a fluidized bed (Powder Technology 57, 127-133 (1989)), so that this method cannot be generally used.
Said processes have the disadvantage that either a predispersed but dust-producing pigment powder (JP 10-251 533) or pigment granules which do not produce dust but are not sufficiently predispersed are prepared. Moreover, the known processes for the preparation of a pigment form which does not produce dust start from prepared pigment powder and therefore give rise to additional operations, which increase the cost.
SUMMARY OF THE INVENTION
It is the object of the present invention to provide a process for the preparation of dustless, flowable and readily dispersible organic pigments, which requires no additional process steps compared with the preparation of the corresponding pigment powder.
It has been found that the disadvantages mentioned in the prior art are surprisingly overcome by spray-drying organic pigments which have been coated with a wax or polymer layer during a finish process to be carried out in the pigment preparation.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention relates to a process for the preparation of readily dispersible pigment granules, which comprises adding a wax or waxy polymer to an organic pigment during the finish process in an organic or aqueous organic medium, removing the organic solvent of said organic or aqueous organic medium and spraydrying an aqueous suspension of the pigment. Said aqueous suspension may be obtained by steam distillation or washing out with water.
During the finish process, the pigment particles are brought into intimate contact with the wax or waxy polymer. After removal of the solvent by steam distillation, a sprayable aqueous solution is obtained. Nevertheless, it may be expedient to filter the suspension prior to the spray-drying and to remove any salts present by washing and to stir the press cake obtained by the filtration again to give a sprayable suspension. In an expedient procedure for washing out with water, the solid is filtered off and is washed solvent-free with water, and the press cake obtained thereby is diluted with water to give a sprayable suspension.
As a result of the spray-drying, on the one hand, granulation to a suitable particle size is achieved without the coating of the pigment particles with the wax or polymer, achieved during the solvent finish, being damaged. On the other hand, the drying and milling required in the preparation of pigment powders are avoided.
The pigment granules according to the invention have a mean particle diameter of from 0.05 to 5 mm. Granules having particle diameters in the range from 0.1 to 2 mm are particularly preferred. Owing to their generally spherical shape, the granules are flowable and hence readily meterable. Because of their size and weight, the granules produce very little dust.
Suitable organic pigments are, for example, azo pigments, such as monoazo, disazo, naphthol and metal complex pigments, as well as polycyclic pigments, such as isoindolinone and isoindoline pigments, anthanthrone, thioindigo, quinophthalone, anthraquinone, dioxazine, phthalocyanine, quinacridone, perylene, perinone, diketopyrrolopyrrole and azomethine pigments.
Waxes do not have a standard chemical definition and form a group of substances with identical or similar application properties, characterized by particular physical properties. Thus, the term “wax” designates a number of natural or synthetically obtained substances which as a rule have the following properties: kneadable at 20° C., solid to brittly hard, coarse to finely crystalline, translucent to opaque, but not glassy; melting without decomposition above 40° C., relatively low viscosity and nonthread-drawing slightly above the melting point, highly temperature-dependent consistency and solubility, polishable under slight pressure (cf. Ullmanns Encyklopätdie der technischen Chemie [Ullmann's Encyclopedia of Industrial Chemistry], Volume 24, 4th Edition, 1983, pages 1-49, Verlag Chemie, Weinheim and Römpps Chemie-Lexikon [Römpp's Chemistry Lexicon], Volume 6, 8th Edition, 1988, page 463, Franck'sche Verlagshandlung).
Preferred waxes are: natural waxes, such as vegetable waxes, e.g. carnauba wax and candellila wax, and animal waxes, e.g. beeswax, modified natural waxes, such as, for example, paraffin waxes, microwaxes, semisynthetic waxes, such as, for example, montan ester waxes, or fully synthetic waxes, such as polyolefin waxes, e.g. polyethylene and polypropylene waxes, polyethylene glycol waxes, cycloolefin copolymer waxes, amide waxes, such as, for example, N,N′-distearylethylenediamine, and chlorine- or fluorine-containing polyolefin waxes or polyethylene-polytetrafluoroethylene wax mixtures.
Polyolefin waxes and polyolefin waxes containing polar groups and formed by subsequent oxidation of the polyolefin wax, by a graft reaction with monomers containing carboxyl, carboxylic ester, carboxylic anhydride or hydroxyl groups or by copolymerization of an olefin and a monomer containing carboxyl, carboxylic ester, carboxylic anhydride or hydroxyl groups, are particularly preferred.
Suitable polymers are relatively high molecular weight compounds which have a waxy character and were preferably prepared by polycondensation or polyaddition processes, for example thermoplastic polyester, epoxide, styrene/acrylate copolymer, styrene/butadiene copolymer and cycloolefin copolymer resins, such as, for example, ®Topas.
In order to have sufficient solubility at elevated temperature in organic solvents, the polymers generally have a number average molecular weight ({overscore (M)}
n
) of up to 20,000. Waxes having a number average molecular weight ({overscore (M)}
n
) of up to 10,000 are preferred, those having a number average molecular weight ({overscore (M)}
n
) of up to 5000 being particularly preferred. The drop point of the waxes used according to the invention or the softening temperature of the polymers is preferably in the range from 60 to 180° C.,
Metz Hans Joachim
Ohleier Heinfred
Clariant GmbH
Green Anthony J.
Silverman Richard P.
LandOfFree
Process for the preparation of pigment granules does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for the preparation of pigment granules, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for the preparation of pigment granules will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2922057