November 1, 2012

Ultrasonic dispersion of organic pigment particles

I continue to stumble into methods that have the potential to improve the handling of paint. In 1989 BASF (one of the big paint manufacturers in this world) filed patent 4929279 in which an invention is contained to improve the dispersion of pigment particles by irradiating it with ultrasonic waves. The optimal frequency range is between 40 Kilohertz and 2 Megahertz. These can be generated with relatively simple and low cost devices that use very little energy and are commercially available, more in particular with pond foggers... Below you see one of those.

Ultrasonic pond fogger

They are available in types that have a 40 mm diameter which tightly fits into a PVC or PE tube (I've tried this before for a different purpose). These babies produce 1.7 Megaherz, which is inside the preferred frequency range the patent suggests. Not sure if they will function in paint, since they were built to make a fine fog (in the jacuzzi) from clean water, but I'll give it a try anyway. The problem would be the particles in paint which will clog to the ceramic plate, making it too heavy, as a result of which it becomes too hot and stops working. But as the ceramic disk becomes heavier, the frequency also drops, which probably will make it work precisely in the frequency range that was claimed to be necessary...

So all that needs to be done now is to find a way to protect the ceramic disk from paint that accumulates on it (for which I already have an idea... :D).

But there may is more to structured particle dispersion in the patent. One particular way to use devices that generate ultrasonic waves, is attaching them to a ship's hull. It causes debris to depart from the ship's body, somewhat similar to ultrasonic cleaners that some airbrush artists use. What happens when a polluted object is radiated with ultrasonic waves? From approximately 20 Kiloherz and upwards, organic matter (tissue) starts to disintegrate. When this occurs it is separated from materials that have a stronger (more solid) structure, which is why ultrasonic cleaning works so well.

A higher the ultrasonic frequency will disintegrate stronger structures. This is why for a specific purpose the frequency range has to be tuned with care. Applying waves within the frequency range as is mentioned in BASF's patent will cause pigment particles to unclog from each other, which will make them float in the solvent as smaller clusters of particles or even single particles. The result of this is that the paint becomes easier to spray because it flows better, while coverage is better. Less layers of finely distributed particles will have the same visual effect as more layers of paint consisting of more coarse clusters of pigment particles.

A note and side-track: It does not matter how energy is induced - ultrasonic waves, electrical-, magnetic- or light-waves, the effect on the material onto which the radiation is applied is the same. So beside ultrasonic generators there are also other means to affect the dispersion level in liquids. The higher effectiveness of spraying less paint may not be important to the airbrush trade, but be more useful when large surfaces are painted. Painting a Boeing 747's upper half of the fuselage and its tail section, on average requires approximately 500 liters of paint, which represents a weight of over 500 kilograms. Each kilogram on their air-crafts costs airline companies 10,000 Euro in annual operation. Paints with better particle dispersion could make a significant difference there.

Heaps of testing to do in time to come. Stay informed and visit this blog regularly.