DE1592845B - Process for the continuous production of zinc chromate pigments - Google Patents

Description

1 5S2 845

mix compounds in solid phase at room temperature from reactants that were previously only available at room temperature could be reacted in solution. Both the chemical composition as well as the purity of the pigments produced in this way are from all points of view Satisfactory, their grindability is similar to that of the product made by wet means, and their oil absorbency is better than that of the previously known products; their grain size, Color and its moisture content can be determined with the help of the feed ratio of the starting components can be adjusted at will. The pigments obtained do not contain any soluble salts; accordingly are the weather and corrosion resistance of those made from these pigments Colors considerably larger than those of mineral paints made with the help of known processes became. The energy consumption of the process is very low. The system can be used in a continuous Operation can be easily regulated, instrumented and automated.

No liquid phase is used in the method according to the invention; therefore, on devices to dissolve the solid components and to warm up, stir and transport the solutions, also the filtering and washing processes, which require an extremely high amount of energy and drying can be dispensed with. The lack of corrosive solutions increases the price and reduces the wear and tear on the devices.

The particular advantages of the method according to the invention can be seen from comparative experiments, those with the zinc tetroxychromate produced according to the invention and with conventional zinc tetroxychromate, produced by the wet process.

In these tests, the friability of the pigments was tested in the attritor. In addition, the Corrosion-inhibiting effect in the aerosol salt mist chamber at 35 ° C for 250 hours, in the steam chamber at 35 ° C for 250 hours, in the steam chamber at 35 ° C during 750 hours, in distilled water at 24 ° C for 1000 hours and in an industrial environment 6 weeks exposure tested.

As a result of these tests has been shown that the Zinktetroxychromat produced with the inventive method a / ₀ shorter Verreibzeit comprising than the known Zinktetroxychromat by about 35 ° and that the corrosion inhibition effect in both the steam chamber and upon immersion in distilled water and in the exposure in an industrial setting was better than the conventional zinc tetroxychromate. The test results in the aerosol salt mist chamber were the same.

The content of water-soluble chromium oxide is in the zinc tetroxychromate produced according to the invention by about 50 to 70% lower than the known produced zinc tetroxychromate.

The process according to the invention is illustrated in more detail by the examples below. The drawing Figure 2 is a process diagram of Example 2.

example 1

To produce zinc tetroxychromate, 71 g of ZnO and 17 g of CrO _{3 are} fed into a hammer mill with a vertical axis and high rotational speed. A constant temperature of about 60 ° C. is set by thermostatting, and the grinding process is started. By a rotor arranged above the distribution head is water vapor at 50 ° / ₀ sodium excess, based on ίο the stoichiometric amount is introduced into the mill. The reaction gives 100 g of powder paints, ie the conversion is practically 100% · 90.4% of the product has a grain size between 1 and 40 μ. on.

Example 2

Zinc tetroxychromate is produced on a large scale according to the ■ scheme shown in the drawing. The solid zinc oxide 1 and the solid chromium oxide 2 are removed from the container I in Form of the solid powder mixture 3 fed into the grinding device II. This grinder is expediently a hammer mill with high rotational speed. That from air 8 and water vapor 9 im Mixture IV produced mixture 4 is also blown into the grinding device II. From the Grinding device II, with the release of heat of reaction, the solid powder paint 5 and the Mixture 6 of powder and air.

The powder paint 7 is deposited from the mixture 6 in the cyclone III. The air 8 is from the Cyclone III introduced into the mixer IV, the air being mixed with the water vapor 9.

The known wet method and the known semi-wet method are the same as in Example 2 compared to an industrial process in which 101 zinc tetroxychromate Powder paint can be produced. The results of the economic feasibility analysis are presented in the summarized in the table below.

Daily turnover of material in t

liquid

Cloudy ....

Powder ...

gas

Steam ...
All in all,

Wet
proceedings

266

145

515
1120

Half wet. proceedings

28

424

54

34

540 1173

Dry process (according to the invention)

Energy expenditure per day

Thermal energy,
10 ° Kcal / day .. 43 37

% 2575 2216

Electric
energy

kWh / day ..

917
166

504 91

33 12 1.3

46 100

1.3 100

552 100

1 sheet of drawings

Claims (2)

1 2. the grinding speed, the grain fineness of the solid Claims · Components and the intensity of the touch of the components reacting with one another are increased. The grinding is done in the presence of Process for the continuous production of 5 water vapor carried out. Zinc chromate pigments, characterized by this knowledge is surprising because zinc oxide is characterized by the fact that zinc oxide together with and chromium oxide in the presence of water vapor, chromium oxide in one of the composition of the end product, which is not desired or only to a limited extent, corresponds to the composition of the end product react and the product forms a coarse-metric ratio through dry grinding io granular turbidity. However, if allowed to react according to the invention, the solid components being brought into contact with the dry mixture of the two components in steam at the same time, in the presence of steam, being produced. Zinkchromatpigmente strength in virtually 100 _^0/0 sales. 2. The method according to claim 1, characterized in that the invention relates to a method draws that the solid components with a 15 for the continuous production of zinc chromate gas circulation grinding device ground be pigments, which is characterized in that the. Zinc oxide together with chromium oxide in one of the Composition of the desired end product corresponding stoichiometric ratio 20 dry grinding reacts, with the solid Components are brought into contact with water vapor at the same time. The invention relates to a method for continuous According to an advantageous embodiment of the lent production of zinc chromate pigments, which in the process according to the invention can use the solid the solid phase is carried out. 25 components during grinding except with water Up to now, zinc chromate pigments could only be mixed with hydrogen sulfide, sulfur dioxide, of discontinuous wet processes from salt, carbon dioxide, acetic acid vapor or their mixtures solutions or suspensions are produced. see be brought into contact. Because of the disadvantages of the known processes, the process according to the invention is advantageous one endeavors, however, to find methods which are carried out at 3 ° in a gas circulation grinding device. smaller amounts of material worked than the previous leads. known wet processes and the pigment color obtained in continuous die as grist Devices can be carried out. Advantageously before removing it from the system For this reason the so-called "semi-wet" was classified, in particular with the help of one in the continuous process for the production of 35 device built-in sieves. Zinc tetroxychromate worked out. In this process, the solid oxides to be converted and the obtained will drive higher solution and suspension pigment paint grist can expediently with the help Concentrations applied than in the wet-a carrier gas are transported, the drive, and also the concentration of the millbase obtained is obtained by powder deposition. Pigment suspension is larger. 4 ° The carrier gas cleaned from the powder can be fed into the However, no procedure has been found so far. System can be returned. which would have enabled the sizing prior to deriving from the grind during manufacture Zinc chromate pigments to completely dispense with the use of the device and the transport with the aid of the carrier liquid phase. gases can also take place at the same time. The invention is based on the object of providing a 45 As a carrier gas for the water vapor with which the To make process accessible through the zinc-solid components during the grinding in Chromate pigments can be brought in without the use of a liquid touch, advantageously air Medium can be produced. It is known to be used. that in comminution processes by grinding products that have an unsatisfactory grain size Solid phase materials and mixtures of materials 50 may be mixed with fresh reactants chemical processes can be worked up again at temperatures below. 100 ⁰ C, which otherwise not or only if the mechanical-chemical process heat is generated, otherwise not or only at higher temperatures, which could affect the quality of the product, or only at higher temperatures , take place. With this previously known mechanical 55 it can be cooled. If necessary, the grinding-induced chemical processes can, however, be heated on the device - primarily to trigger the conversion related to the amount of material used - ■ also be heated,
low, the amount of cleavage surfaces formed, with the help of the method according to the invention, that is, the new active centers, low and the following pigments can be produced very advantageously. Possibility of mixing the components 60:
limited. Such procedures have therefore become ν · ,,. _u * r- n, cv η au r \ Manufacture of pigments on an industrial scale Z.nktetroxychromat CrO ₃ · 5 ZnO · 4 H ₂ O drive not previously used. Zmktrioxychromat. . CrO ₃ • 4 ZnO • 3 H ₂ O According to the invention it has now been found that a zinc yellow in all colors in an effective manner mechanically induced chemi- 65 tons 4 CrO ₃ -4 ZnO-K ₂ O- cal process for the production of zinc chromate- ² Pigments from oxides without using a The method according to the invention has numerous liquid medium can be carried out if benefits on. It enables the production of marital