Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Reexamination Certificate
1999-08-13
2001-01-16
Green, Anthony (Department: 1755)
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
C546S037000
Reexamination Certificate
active
06174361
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
The present invention is described in the German priority application No. 198 36 714.7 filed Aug. 13, 1998, which is hereby incorporated by reference as is fully disclosed herein.
BACKGROUND OF THE INVENTION
The present invention relates to a particularly environment-friendly and economic process for preparing transparent N,N′-dimethylperylene-3,4,9,10-tetracarboxylic diimide pigments for pigmenting materials of high molecular mass.
The pigmentation of automotive finishes, especially the metallic finishes, requires pigments which, with high transparency and a pure hue, produce strongly colored and highly lustrous coatings. The paint concentrates (millbases) and the paints themselves must be of low viscosity and should not exhibit any pseudoplasticity. A further requirement is for very good fastness properties, especially weather fastness.
N,N′-Dimethylperylene-3,4,9,10-tetracarboxylic diimide (dimethyl-perylimide), as an organic red or chestnut pigment (C.I. Pigment Red 179, C.I.No. 71130), has been in use for a long time, and both transparent and hiding forms of the pigment are known. Depending on the production conditions, red or chestnut-colored pigments are obtained. The following processes are described for its production:
DE-B-21 53 087 (GB-A-1 370 433) describes the reaction of perylene-3,4,9,10-tetracarboxylic dianhydride with monomethylamine at from 120 to 150° C. using high concentrations of the dianhydride. The crude dimethylperylimide pigments obtained in the condensation are isolated, dried and then converted to the final pigment form by an intensive grinding and kneading operation with salt followed by renewed drying. Following each stage of the process the pigment is isolated, so that there are large amounts of wastewater produced. However, the process does not yield a transparent dimethylperylimide pigment suitable for use in metallic finishes. DE-B-2 504 481 describes a process for producing transparent dimethylperylimide pigments by condensing perylene-3,4,9,10-tetracarboxylic dianhydride with at least 4 times the molar amount of monomethylamine. The excess monomethylamine is separated from the pigment suspension by filtration and can be distilled off from the mother liquor using steam. The filtration of the methylamine-containing suspension causes considerable technical problems, since because of its severe odor monomethylamine must not be allowed to pass into the environment. An additional distillation unit is required for working up the methylamine-containing mother liquor. Transparent pigments are obtained only in high dilution.
EP-A-0208 266 discloses the production of a hiding dimethylperylimide pigment. In this process, dry, finely divided, crude dimethylperylimide pigment with a particle size of less than 0.04 &mgr;m are subjected to a recrystallizing grinding process in a mill or disperser in the presence of an organic solvent, and the dimethylperylimide pigment is subsequently isolated.
EP-A-0 088 392 describes a process for producing transparent dimethylperylimide pigments by reacting peracid with at least 4 times the molar amount of monomethylamine. The excess monomethylamine has to be liberated from the mother liquor using sodium hydroxide solution and separated off by distillation. This produces considerable amounts of salts which load the wastewater.
EP-A-0 318 022 describes a process for preparing hiding dimethylperylimide pigments by reacting peracid with at least 2 times the molar amount of monomethylamine. The crude pigment obtained after the condensation is ground on a stirred ballmill and then finished with solvents. It is not possible to obtain transparent pigments by the condensation, beadmilling and finishing conditions described therein.
SUMMARY OF THE INVENTION
There was a need to prepare transparent dimethylperylimide pigments in a simple and environmentally unobjectionable manner.
It has been found that transparent dimethylperylimide pigments having advantageous coloristic and rheological properties can be prepared in a simple and ecologically unobjectionable manner from crude dimethylperylimide pigments by beadmilling at high energy density if surfactants and/or pigment dispersants are added no later than at the beadmilling stage.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention provides a process for preparing N,N′-dimethylperylene-3,4,9,10-tetracarboxylic diimide, utilizing the reaction of perylene-3,4,9,10-tetracarboxylic dianhydride with monomethylamine, which comprises employing at least 2 times the molar amount of monomethylamine per mole of perylene-3,4,9,10-tetracarboxylic dianhydride and at least 3 times the amount by weight of water based on the weight of the dianhydride, conducting the reaction at a temperature from 50 to 200° C., removing unreacted monomethylamine by distillation, subjecting the resulting crude pigment to wet grinding in a liquid, aqueous or aqueous-organic medium in a stirred ballmill which is operated with a power density of more than 1.5 kW per liter of milling space and a stirrer tip speed of more than 12 m/s under the action of grinding media having a diameter of less than or equal to 0.9 mm, and isolating the pigment obtained, with the proviso that at any desired point during the process, but no later than during wet grinding, one or more additives from the group consisting of pigment dispersants and surfactants are added.
The perylene-3,4,9,10-tetracarboxylic dianhydride can be employed in dry form or as the presscake.
The process of the invention is preferably conducted using from 5 to 12 times the amount by weight of water, in particular from 6 to 9 times the amount by weight of water, based on the weight of the dianhydride. It is preferred to employ from 3 to 10 times the molar amount, in particular from 3 to 8 times the molar amount, of monomethylamine per mole of dianhydride. The monomethylamine is preferably added in aqueous solution but can also be introduced in gaseous form.
The monomethylamine is judiciously added at a temperature between 0 and 80° C., preferably between 20 and 60° C. The reaction of the dianhydride with the monomethylamine takes place at a temperature between 50 and 200° C., preferably between 90 and 180° C., under superatmospheric pressure if desired. After the end of the reaction, excess monomethylamine is distilled off, advantageously at atmospheric pressure and up to a temperature of about 100° C. at the distillation bridge. Although it is advantageous to remove all of the excess monomethylamine prior to the grinding process, it is also possible to remove the monomethylamine later on—for example, after the grinding process, or only when the pigment is isolated.
The monomethylamine removed by distillation can be used again for a subsequent condensation reaction.
If desired, prior to wet grinding and/or prior to filtration, neutralization is carried out with a little acid in order to eliminate nuisance odors.
The coarsely crystalline crude perylene pigment obtained from the synthesis is either isolated and then sent, or sent directly, to a wet grinding stage for the purpose of fine division.
The production of these pigments in accordance with the invention requires a high level of grinding action, which is achieved through the use of specific embodiments of a stirred ballmill. Examples of such mills that are suitable for grinding to the required efficiency are those designed for continuous and batchwise working, having a cylindrical or hollow-cylindrical milling chamber in horizontal or vertical construction and the capacity to be operated with a specific power density of more than 1.5 kW per liter of milling space, their stirrer tip speed being more than 12 m/s. The constructional design ensures that the high level of grinding energy is transferred to the millbase. Examples of mills suitable for this purpose are described in DE-C 3 716 587. If the grinding intensity of the mill is too low, the good properties according to the invention, especially the high transparency and color strength and outstanding
Boehmer Martin
Urban Manfred
Weber Joachim
Clariant GmbH
Green Anthony
Hanf Scott E.
Jackson Susan S.
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