CS209563B1 - Process for preparing fine mica with fractions for pearlescent pigments and apparatus for carrying out the process - Google Patents

Abstract

The dry pre-ground flake mica is wet-floured and ground by stirring in a wooden tub so that it contains as few ground fine particles below 5 µm and coarser particles above 100 to 150 µm as possible. The wet-ground mica is sorted in several stages of hydrocyclones in combination with a screen separator, where the upper limit of particle size above 50 µm is separated. The lower limit of particles below 5 µm is separated in a continuous sedimentation centrifuge with a mass number of revolutions. The upper limit of particle size above 20 µm is separated in a continuous sedimentation centrifuge with a lower number of revolutions. The coarse fraction is either used for the production of pigments with a metallic luster or is returned to grinding. The ground fine fraction is set aside in a sedimentation tank and can be used as fillers in the production of paints, varnishes and plastics. The separated water is returned to the process.

Description

The invention relates to a process for producing fine mica for pearlescent pigments and to an apparatus for carrying out the process. It is generally known that mica milling itself is a very unpretentious and problematic process, which consists in the perfect cleavage of mica according to the bottom area and, on the other hand, considerable strength and flexibility in other directions. This means that mica has a pronounced tendency to split according to cleavage, while the scales formed are less difficult to reduce. In the case of minerals of this type, it is common for the reduction of the particles to be accompanied by the formation of large amounts of very fine fractions. In no case can the grinding process be controlled in such a way that sorting is not necessary. The industrially most important mica is muscovite - light potassium mica and phlogophit magnesium-potassium. Muscovite for particularly excellent optical properties and low iron content has been selected as a carrier for the manufacture of pearlescent pigments based on mica, titanium dioxide, bismuth oxychloride and ferric oxide. Experimental tests have shown that only wet ground and sorted mica is suitable for the manufacture of pearl pigments.

Dry milled mica in impact mills and micronisers is absolutely unsuitable for the production of pearl pigments because it has no smooth surface and the edges of the particles are frayed and yet contains a significant amount of milled fine particles below 5 μ® which are ineffective in pearl luster.

Wet milling is carried out in wooden wheel mills, bar-lined drum mills, or by mixing thick mica slurry in wooden vats.

The mica particles should have a retained plenary structure of approximately 0.4 to 0.8 μια thickness and a high quality platelet shape with a smooth surface without sharp edges to achieve a high gloss. The particle size should range from approximately 5 to 150 μηι, the most convenient fraction for pearlescent pigments is a fraction of 10 to 40 μηι and should not contain finer: particles below 5 μπι, which reduce pigment shine and mirror reflection.

For the production of pearlescent pigments and their application to consumers, it is most desirable to produce three fractions of mica whose upper and lower limits are approximately in the following ranges: 5 to 20 μπι is a very fine mica, suitable for silk gloss pearlescent pigments, fine 10 to 50 μπι mica is used for most pearlescent pigments with universal use, more or less with metallic luster, and coarser mica, whose fraction ranges from 20 to 150 μm, which is exclusively used for pearlescent pigments with metallic luster, Proper distribution The particle size is determined by the method and conditions of the wet milling and the decisive influence on the quality of the pearlescent pigment. For the manufacture of pearlescent pigments, mica may be used immediately after sorting in a slurry or after drying.

As can be seen, the quality requirements of ground and screened mica for the manufacture of pearl pigments are very strict and achieving the desired quality is not a simple process. The technology of fine sorted mica has not been solved in the Czech Republic and there is practically nothing known about the ways of mica abroad.

The essence of the method and apparatus for preparing fine mica for pearlescent pigments is that the dry pre-milled flake mica is flaked and milled with water in a slurry form in a wooden vat for a certain period of time so as to obtain as many μπι particles and CO as possible. grinding fine particles below 5 µm, while maintaining the correct particle thickness, preferably below 0.5 µπι. The mica sorting at the upper limit of 40 to 60 μ, preferably 50 μπι, is carried out by three stages of consecutive hydrocyclones having a diameter of approximately 120 mm, 70 mm and 40 mm in a closed circuit, each time period. First sorting is performed on the largest hydrocyclones and gradually on smaller hydrocyclones. The remaining small residue of particles larger than 50 μηι is separated on a sieve screen with a mesh size of 40 to 60 μηι. A continuous sedimentation centrifuge with a maximum speed is used to sort the mica at the lower limit, roughly below 5 to 10 μη. In order to completely separate the finely divided fines, this process must be repeated two to three times. This process yields fractions of approximately 5 to 50 μm and particles above 50 μm are returned to the milling or can be used in the coarser fraction. Such mica is suitable for the production of pearlescent pigments with more or less metallic sheen. For the production of silk gloss pearlescent pigments, it is necessary to prepare mica in an even finer form, in the range of 5 to 20 μηι. To produce this very fine mica, a continuous sedimentation centrifuge with a lower and maximum speed is used for the upper and lower sorting limits. For very sharp separation of larger and smaller particles it is necessary to repeat the process two to three times in a row.

By this process, it is possible to obtain three fractions in roughly these ranges of 5 to 20 μηι, 5 to 50 μηι, 20 to 150 μm, which are sufficient basis for the production of almost all pearlescent pigments produced.

The progress achieved by the invention is that in this way the desired fineness and thickness of the mica particles for producing pearlescent pigments is achieved. The stacked grinding and sorting equipment works with good performance and short sorting time.

In the wooden grinding vat 1, the wet mica is slurried, the ground mica is discharged into the ground mica container 2, where it is diluted to a concentration of 2 to 10% (preferably 5%) and pumped by a pressure centrifugal pump to hydrocyclones Ja, fine the portion is fed to the container 6 or 2, the coarse portion being returned to the wooden milling vat 1. This cycle is repeated successively on the hydrocyclones 4b, on the hydrocyclones Jp. from here the screened fraction goes through, the screen separator into the bin of the sorted semi-product 6, a small residue of larger particles is returned to the wooden grinding vat 1. The sorted fraction on the hydrocyclones is pumped via pump J through the overflow vessel 8 to a continuous sedimentation centrifuge 2 · The sorted product is pumped through a hydrolysis pump 11. The screened fine fraction from the continuous sedimentation centrifuge 2 goes to the sedimentation tank 12 where water is separated and returned to the process. In the case of sharper separation from ground fines, the thickened fraction from the reservoir 10 after dilution with water is pumped through the pump 7 to the overflow vessel 8 for a continuous sedimentation centrifuge 2. This process is repeated two to three times.

Examples

Example 1 '

Weigh 80 kg dry pre-milled mica into a wooden grinding vat of approx. Approximately 50 L of water is then added and the aqueous mica slurry is stirred for 10 hours. The ground mica in the form of a thick slurry is discharged into a storage tank, where it is diluted with water to 5% concentration. With a pressure centrifugal pump, the diluted mica slurry is pumped to two stages of successive hydrocyclones. After the separation of almost all particles above 50 μιη, a portion of the mica slurry is transferred from the second stage of the hydrocyclone through a safety screen to a sorted stock. The coarse fraction of hydrocyclones is returned to milling or used for pearlescent products with a coarser structure. The sorted hydrocyclone slurry is pumped into the sorted semifinished product reservoir by means of a pump into the overflow vessel and from there it goes by gravity to a continuous sedimentation centrifuge at maximum speed. The thickened slurry from the centrifuge is discharged to the bin of the sorted product and is pumped there after dilution with water to the pearl pigment production plant. The fine fraction with ground fines goes to the sedimentation tank where it is separated from the water and can be used as fillers in the production of paints, varnishes and plastics. The separated water is returned to the production process. The screened mica contains particles ranging in size from 3 to 50 µm, the average particle thickness being 0.48 to 0.55 µm ·

Example 2

Same as Example 1 except that the mica was milled for 16 hours and the screening was carried out on hydrocyclones in three stages. The screened mica for hydrocyclones is separated from the milled fine particles on a continuous sedimentation centrifuge at a maximum speed of two times. The product obtained contains a fraction of 6 to 43 μin with an average particle thickness of 0.38 to 0.43 μι ».

Example 3

The same as Example 1, except that the mica is ground instead of 10 hours and 12 hours and the separation of the milled fine particles is carried out on a continuous sedimentation centrifuge at maximum speed three times in succession. The screened mica contains particles in the range of 8 to 75 μι », the average particle thickness of 0.43 to 0.48 μιη.

Example 4

Same as Example 1, except that ground mica is not screened on hydrocyclones, but sorting is only performed on a continuous sedimentation centrifuge with a maximum number of revolutions. The cycle is repeated twice. The screened mica contains particles of 6 to 120 pit, the average particle thickness is 0.48 to 0.50 μιη.

Example 5

The same as Example 2, except that a continuous sedimentation centrifuge with a lower number of rotations is used instead of hydrocyclones instead of hydrocyclones. A fraction having a particle size of 6 to 17 μι »and 17 to 62 μιη is obtained, the average particle thickness being 0.40 to 0.46 μη

Claims (2)

high / climbing object Process for preparing fine mica of pearlescent pigment fractions, characterized in that the dry pre-milled flake mica is decomposed in a slurry form and milled by stirring in a wooden grinding vat, the diluted slurry is then screened on hydrocyclones in combination with a sieve screen. separate particles above 40 to 50 μ, ιη and very fine particles below 5 to 20 μ.ηι, preferably 10 μ, ιη are separated on a continuous sedimentation centrifuge. Device for carrying out the method according to claim 1, characterized in that it consists of a wooden grinding tub (1), a mica storage tank (2) which is connected by a pressure centrifugal pump (3) with three stages of hydrocyclones (4a, 4b). , 4c), a sieve sorter (5), a container for the sorted semi-product (6), which is connected by a pump (7) via a overflow time (S) to a continuous sedimentation centrifuge (9), from a sorted product container (10) , pumps (11) and. sedimentation tanks (12).