Mixing and dispersion, complementary processes

Octaviano Fernandez*

On this occasion we want to consider, in a clear way, the causes why in Mexico and Latin America it is difficult to effectively carry out the research in the factory, necessary for the development of new or better coatings and inks.

To do effective research and development it is necessary to have the ability to recreate the production process of the plant faithfully in the testing laboratories, a process that is not really very complex. Still, most factories fail to reproduce such scenarios when trying to develop new products or improve and modify existing ones.

Many of the manufacturers of coatings and inks have testing laboratories, in which they have very important measuring instruments for research and development. These instruments are mostly used to measure physical or appearance properties, which although important, only allows to verify if the products that are being tested can fall within the quality parameters that are needed or, in other cases, to verify that the products have the necessary physical attributes to be used.

The problem is that they do not have the necessary instrumentation to reproduce the entire industrial process involved in the production of a coating or ink, and evaluate a new component in the formulation or modification of the process, activities corresponding to research and development. In these two activities, the ability to emulate production processes must be considered.

The production process of a coating or an ink is composed of several sub-processes, such as dispersion, grinding, dosing, packaging, etc. Two of them are extremely important when we talk about research and development: dispersion and grinding, because in them lies most of the secret of production.

It is in the inability to simulate these two processes, where the reason why for many coatings and ink factories it is impossible to do proper research and development is evident.

Clarification of concepts
There is a lot of confusion in the middle about the difference between scattering and mixing or shaking.  The goals of both are very different. Dispersion goes beyond mixing or stirring, the mechanical power needed to achieve dispersion is much higher than that needed to mix

Most of the pigments, additives and raw materials used in the formulation of coatings and inks require to disperse from peripheral speeds of between 18 and 25 m/s. The peripheral velocity is that reached at the edge of the dispersion discs.

In the process equipment it is very easy to reach these speeds necessary for dispersion (18 to 25 m / s), because the sizes of the discs combined with the rpm facilitate the tasks, in such a way that it is very easy to create the effect of the donut, which is the sign that the greatest possible mechanical power is being transferred to the grinding base.

See the following example:
Assume that you have a production disperser with the following characteristics:
Disperser disc diameter : 200mm
Arrow revolutions : 2300rpm

The formula for calculating peripheral velocity is as follows: v = π·d·n
60
V= Peripheral speed
π = 3,141.....
d= Diameter of the disc in meters
n= arrow revolutions at rpm

Therefore if we follow the above formula: (π)3.1416 x (d) 0.20 x (n) 2300
60

the resulting peripheral velocity would be 24.08 m/s.

These conditions are very easy to achieve in almost any coatings or inks plant in the process part, the problem lies in the laboratory, since most of these do not have the appropriate technology to produce these conditions.

Different are the reasons why this happens, the most common is that in the laboratory it is about imitating the process with equipment with the same amount of revolutions per minute; that is, if in process you have a disperser that reaches 3,500 RPM, in the laboratory you have another that reaches the same 3,500 RPM, without taking into account that what needs to be imitated are the peripheral speeds not the RPM.

The following example tries to illustrate what happens when only RPMs are taken into account in the laboratory to simulate the process.

Example of a 3,500 RPM laboratory equipment

Disperser disc diameter : 30mm
Arrow revolutions : 3500rpm

Using the formula to obtain the peripheral speed it will be possible to observe that only a speed of 5.49m / s is achieved, which only allows mixing the ingredients, but never dispersing them.

To be able to imitate the dispersion process in the laboratory it is necessary to have an apparatus that allows to reach much higher peripheral speeds (18 to 25 m / s), to calculate the type of device that is needed it is necessary to go to process and get the range of peripheral speeds with which it is working, that is achieved using the formula presented above.

Disperser disc diameter : 30mm
Arrow revolutions : 15500rpm

(π )3.1416 x (d)0.030 x (n)15500
60

The resulting peripheral velocity would be 24.34 m/s

This indicates that it is necessary to have the ability to increase the RPM to very high levels so that with the size of the disk it is possible to reach the peripheral speeds necessary to make a dispersion as at the production level.

Some considerations
To be able to simulate the dispersion process, you would have to have the ability in the laboratory to be able to run tests at very high peripheral speeds.
If it is not possible to test new additives, pigments and other ingredients because it cannot generate the right conditions for them to reach their best development, how can we talk about research and development?

Many of the ingredients used in the manufacture of coatings and inks need to be dispersed at high speeds in order to give their best development. All coating factories have the capacity at the production level to generate these conditions, the problem lies at the laboratory level, where due to the type of equipment used, the ideal conditions (18 to 25m / s) in which these materials reach their best performance and consequently you can not see all the benefits they provide.

That is why it is frequently observed in the middle, formulas that are not modified for years, comments such as, that additive to me did not work, and so on. Could it be that the advances in the industry are very slow that for this reason a formula cannot be improved in eight years? Could it be that an additive can work for one company in a particular product and in another company in the same product not? Or, is it really that technology is not available to adequately test the technological advances that arise day by day and from which companies should continuously benefit to improve their products or reduce their costs?

The answer to the above questions is obvious. It is possible to do research and development of new products, as long as we have in the test laboratories the necessary and appropriate instruments to reliably reproduce the production process. An attitude of openness to changes and knowledge of new technology will lead us to achieve this goal, which will allow us to obtain important economic benefits, as well as offer customers more and better products and have an industry that globally we need.

*Exacolor