Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Reexamination Certificate
2001-10-05
2003-03-25
Green, Anthony J. (Department: 1755)
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
C106S412000, C106S494000, C106S495000, C106S496000, C106S497000, C106S498000, C241S005000, C241S015000, C241S018000, C241S024100
Reexamination Certificate
active
06537364
ABSTRACT:
BACKGROUND OF THE INVENTION
Organic pigments have been known for a long time and have acquired great industrial importance for pigmenting high molecular mass organic materials such as paints, plastics or printing inks. At the synthesis stage, the pigments are often obtained in the form of coarsely crystalline crude pigments which at that stage do not meet the technical requirements. They must first be subjected to a process of fine division which brings about a reduction in particle size. This is commonly followed by a heat treatment, in order to obtain pigments meeting the technical requirements, or pigment dispersants or other additives are used in order to achieve specific effects, as described for example in EP-A-0 807 668.
In order to convert a crude pigment into pigmentary or prepigment form, a variety of fine division processes are known, examples being acid pasting (reprecipitation from solvents, particularly acids), dry grinding, and wet grinding processes. In the course of the dry and wet grinding techniques, grinding media cause abrasion and so lead to foreign substances being carried into the product.
U.S. Pat. No. 3,607,336 describes an acid pasting process. The pigment is dissolved in sulfuric acid and precipitated in turbulent flow. The turbulent flow precipitation is disclosed to produce a finer particle than was hitherto possible with the conventional precipitation variants.
EP-A-0 075 182 describes an acid pasting process that uses polyphosphoric acid as the solvent.
EP-A-0 737 723 describes a process for precipitating pigments from solutions in polar solvents and aqueous alkali.
SUMMARY OF THE INVENTION
It is an object of the present invention to develop a universally applicable and industrially reliable process for the fine division of organic pigments by precipitation, which prevents the possibility of contamination by foreign substances and produces especially fine particles with a particularly narrow size distribution.
It has been found that the object of the invention may be achieved, surprisingly, through the use of a microjet reactor.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention provides a process for the fine division of pigments which comprises dissolving one or more coarsely crystalline crude pigments in a solvent and precipitating them with a liquid precipitation medium by spraying the pigment solution and the precipitation medium through nozzles to a point of conjoint collision in a reactor chamber enclosed by a housing in a microjet reactor, appropriately via one or more pumps, preferably high-pressure pumps, a gas or an evaporating liquid being passed into the reactor chamber through an opening in the housing for the purpose of maintaining a gas atmosphere in the reactor chamber, especially at the point of collision of the jets, and where appropriate of effecting cooling as well, and the resulting pigment suspension and the gas or the evaporated liquid being removed from the reactor through a further opening in the housing by means of overpressure on the gas entry side or underpressure on the product and gas exit side.
Crude pigment fine division in accordance with the invention requires intensive, rapid, uniform, and reproducible mixing of the precipitation medium with the pigment solution. This is brought about by spraying the solution of the pigment that is used and the precipitation medium into the reactor chamber under a pressure of at least 10 bar, preferably at least 50 bar, in particular from 50 to 5000 bar.
In order to prevent material wear on the inner surfaces of the housing, the collision point is shifted into the material-remote gas space. By “material-remote” here is meant that, in the vicinity of the collision point of the jets, a gas atmosphere is maintained by means of the introduced gas or evaporating liquid. This means that the collision point at which the jets impinge on one another is not sited on a vessel wall or on a pipe wall. This prevents the material wear that would occur at the point where cavitation takes place on material walls. Cavitation occurs particularly when using high pressures, especially at pressures above 3000 bar. Moreover, the colliding jets are not braked by the gas atmosphere prior to their collision, as would be the case, for example, if they had to pass through a liquid.
The material of the nozzles should be as hard and thus low-wearing as possible; examples of suitable materials include ceramics, such as oxides, carbides, nitrides or mixed compounds thereof, with preference being given to the use of aluminum oxide, particularly in the form of sapphire or ruby, although diamond is also particularly suitable. Suitable hard substances also include metals, especially hardened metals. The bores of the nozzles have diameters of less than 2 mm, preferably less than 0.5 mm and in particular less than 0.4 mm.
The microjet reactor may be configured as a two-jet, three-jet or multijet reactor, preference being given to a two-jet configuration. In a case of an arrangement with two jets, the jets preferably strike one another frontally (180° angle between the jets); in the case of a three-jet arrangement, an angle of 120° between the jets is appropriate. The jets advantageously may be mounted in a device which can be adjusted to the point of conjoint collision. As a result of these different embodiments it is possible, for example, to realize different volume ratios of the pigment solution to the precipitation medium which are required for the precipitation. For example, the pigment solution may be sprayed to a point of conjoint collision through 1, 2 or more nozzles, preferably through one nozzle, and independently thereof the precipitation medium may be sprayed to the same point through 1, 2 or more nozzles, preferably through 1, 2 or 3 nozzles.
In one particularly preferred embodiment of the process of the invention, the pigment solution and the precipitation medium are sprayed against one another frontally through two opposed nozzles by means of two high-pressure pumps. A further particularly preferred embodiment of the process of the invention is a three-jet reactor in which, for example, by means of a high-pressure pump the pigment solution is sprayed to the point of conjoint collision through one nozzle and by means of a second high-pressure pump the precipitation medium is sprayed to the same point through two nozzles.
The nozzle of the pigment solution and that of the precipitation medium may have different diameters. The nozzle through which the precipitation medium is sprayed appropriately has a diameter which is from 0.2 to 5 times, preferably from 0.3 to 3 times, that of the nozzle through which the pigment solution is sprayed.
The temperatures of the supplied pigment solution and of the precipitation medium are situated appropriately in the range from −50 to 250° C., preferably between 0 and 190° C., particularly between 0 to 170° C. It is also possible to operate under pressure at above the boiling point of the pigment solution or of the precipitation medium.
Where necessary, the introduced gas or the evaporating liquid that is used to maintain the gas atmosphere in the inside of the housing may be used for cooling. Additionally, an evaporating cooling liquid or a cooling gas may be introduced into the reactor chamber by way of an additional bore in the housing. The aggregate state of the cooling medium may be conditioned by temperature and/or pressure. The medium in question may comprise, for example, air, nitrogen, carbon dioxide or other, inert gases or liquids having an appropriate boiling point under increased pressure. It is possible here for the transition of the cooling medium from the liquid to the gaseous state to take place in the reactor itself by virtue of the fact that heat released in the course of the precipitation brings about the change in aggregate state. It is also possible for the evaporative cooling of an expanding gas to be utilized for cooling. The housing enclosing the reactor chamber may also be constructed in such a way that it is thermostatable
Brychcy Klaus
Dietz Erwin
Schnaitmann Dieter
Unverdorben Leonhard
Weber Joachim
Bisulca Anthony A.
Clariant GmbH
Green Anthony J.
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