Process for fine division of organic pigments

Details Process for fine division of organic pigments Process for fine division of organic pigments

2001-10-05

2003-06-24

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

06582508

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention describes an environment-friendly and economic process for fine division of organic pigments.
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, as described for example in DE-A-27 42 575, or pigmentary dispersants or other additives are used in order to achieve specific effects, as described for example in EP-A-0 666 288 or in EP-A0 574 790.
In order to convert a crude pigment into the pigment or prepigment form, a variety of fine division processes are known, examples being acid pasting (reprecipitation from solvents, particularly acids), salt kneading, dry grinding, and wet grinding processes. Combinations of these techniques are also described. U.S. Pat. No. 3,607,336 describes an acid pasting process for fine division, in which the pigment is dissolved in sulfuric acid and precipitated in turbulent flow. The process is accompanied by the production of large amounts of dilute acid, which must either be emitted into the wastewater or regenerated at expense.
DE-A-27 42 575 describes a process of fine division by dry grinding without salt; as in the case of any dry grinding process, the environment is burdened by the dust and noise produced. Mill vibrations have to be damped by means of complex constructional measures.
U.S. Pat. No. 5,919,299 describes a combination of dry grinding in the presence of salt with subsequent acid swelling. The described advantage of the reduced amount of salt at the dry grinding stage necessitates the second step of acid swelling, in the course of which large amounts of acid are produced, which together with the still considerable amounts of salt must be emitted into the wastewater or recovered at expense, and so make the process uneconomic.
EP-A-0 678 559 describes a fine division process without the use of salt. This advantage comes, however, at the expense of a two-stage process, namely a combination of dry and wet grinding. As a result, the process becomes time-consuming, cost-intensive and hence uneconomic. In the case of the wet grinding process, the use of grinding media leads inevitably to abrasion and thus to the incorporation of extraneous substances into the product.
U.S. Pat. No. 6,013,126 describes a salt kneading process in the presence of fatty acids. In the course of the salt kneading, large amounts of salt and solvents are obtained which either burden the environment or have to be recovered, at expense.
With the mechanical fine division processes known to date, the largest part of the energy is converted into heat and only a fraction of the energy introduced is used effectively for grinding. When grinding media such as beads are used, abrasion occurs and thus the product is contaminated by extraneous substances. The scaleup of new products from the laboratory to the industrial scale is often complicated and may cause difficulties, since the introduction of the mechanical energy, the transmission of the energy for effective grinding, the energy lost through heat production, and the necessary heat dissipation, for example, depend greatly on the geometries and sizes of the apparatus, and so are also factors codetermining the economics of the process at the industrial scale.
SUMMARY OF THE INVENTION
It was an object of the present invention to develop a universally applicable, cost-effective, technically reliable, and economic process for fine division of organic pigments, said process being combinable if desired with the measures known in connection with the preparation of pigments, such as the use of solvents, pigmentary and nonpigmentary dispersants, or other auxiliaries; permitting unproblematic scaleup; and removing the possibility of contamination by extraneous substances.
It has been found that the object of the invention may be achieved, surprisingly, through the use of a microjet reactor.
The present invention provides a process for the fine division of pigments which comprises spraying a coarsely crystalline crude pigment and/or a poorly dispersible prepigment in suspension form 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 suspension 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.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Pigment fine division in accordance with the invention requires a high grinding and dispersing action. This is brought about by spraying the suspensions used into the reactor chamber under a pressure of at least 50 bar, preferably at least 500 bar, in particular from 500 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 in principle be configured as a two-jet, three-jet or multijet reactor, preference being given to a two-jet configuration. In the 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.
In one particularly preferred embodiment of the process of the invention, the suspension jets are sprayed against one another frontally through two opposed nozzles by means of a high-pressure pump.
The temperatures of the supplied suspensions are situated appropriately in the range from −50 to +250° C., preferably between 0 and 180° C., particularly from 0 to 100° C., especially between 10 and 80° C. It is also possible to operate under pressure at above the boiling point of the liquid 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. Additio

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