SERINA TRADING

If it's not bad enough that our paint industry's in a slump, the TiO2 price goes into orbit too. Why? I've no idea. Some producers say it is due to poor capacity planning, others, strong demand (really?) and some say higher input costs.

Then there are those who admit they want to "restore margins". What I do know is the producers are calling the shots. The customers are so punch-drunk with all the increases, they hardly resist anymore!

So, although you thought your formulations were already extended to the limit, you are forced to have a relook at TiO2 extenders to reduce costs.

Everyone is on the bandwagon suggesting extenders – so which one is the best?

The reason that rutile TiO2 is the best opacifier by far revolves around two issues:

  • The higher the refractive index, the better the light scattering or refraction. Rutile TiO2 has by far the highest refractive index of all the white pigments. It is 2.7 compared to 2.55 for anatase TiO2 or 1.6 for calcium carbonate.
  • Secondly, the peak of the scattering power of a pigment is at half the wavelength of light (450nm). Rutile TiO2 with a particle size of 0.22u has been optimised to sit exactly on this peak.

These two factors put rutile TiO2 head and shoulders above other white pigments, which is why it is so difficult to replace completely!

Good as it is, you still need other white particles to separate the TiO2 particles in the paint film. If the titanium particles are too close together, they overlap. This crowding reduces the number of possible light scattering sites, hence reducing opacity.

To avoid crowding, we need to use fillers or extenders to separate the TiO2 particles from each other. This is called spacing.

However there are so many extenders to chose from, each with its own strengths and weaknesses. For example:

Calcium carbonate
Kaolin
Calcined kaolin
Talc
Silica
Hollow spheres
Barium sulphate
Alumina trihydrate
Entrapped air
TiO2-coated calcium carbonate
Cheaper grades of TiO2

Which one is best though? Well it depends on many factors like particle size, refractive index and oil absorption. Not to mention your formulation, PVC*, cost factors and how well it is extended already.

*PVC = Pigment Volume Concentration  

The answer is to test them.

You've probably been offered so many TiO2 extenders lately that you feel a bit daunted by the whole thing. How to start evaluating them given that you have many different paint formulations?

To help with this problem, I am going to suggest an easy step-by-step approach which you can follow to find the best extender for your own application.

The better extenders will be those with a similar particle size to the TiO2 particles. This is best explained with a diagram like this:


Since the TiO2 particles are 0.22 microns, the first step to sort out your TiO2 extender possibilities would be to:

  1. Discard anything with a mean particle size (D50) above 1 micron

Extenders with particles bigger than a micron are too big to space the TiO2 efficiently. With lots of paint grades and formulations to choose from, I suggest that you

  1. Start with the paint formulation that is under the most cost pressure

This is the paint grade that will benefit most from your cost reduction efforts. Before doing any TiO2 substitution, you should first check if this formulation is being properly dispersed in the factory.

  1. Compare the grind of a factory sample with a lab-prepared sample

You could save on TiO2 just by making sure your dispersion is correct! You may need to mill a bit longer or adjust the dispersant. Then cut back on TiO2 to get the same result as before.

Now bring out the TiO2 extenders you plan to test. For a quick screening you should

  1. Make a 20% TiO2 substitution with each extender in the chosen formulation

This will sort out the men from the boys! When you check the paint's properties you will easily see which extender has potential and which doesn't. Then it is time to

  1. Do a costing exercise on the good ones

By now your eyes should start shining when you work out the possible savings. It should be easy enough to choose the best TiO2 extender based on performance and cost savings. The final step of course is to

  1. Tweek the addition rate of the extender for best results

Then go on and roll it out to your other formulations (that's the real slog, I know).

It's a simple approach but it gives you a way to get started and get saving. Hope this helps and best of luck!

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SERINA TRADING

PO Box 1549
Sun Valley
7985 Cape Town
SOUTH AFRICA

Tel: +27 21 785 2081
Fax: +27 21 785 2863

 

Contact: Jenny Jay
ATSC. Ph.D (Chemistry)
Email: jenny@kaolin.co.za
Managing Director