TiO2 remains the costliest part of making paint. If it isn’t price increases from suppliers to worry about, our weak currency makes it even worse!
When the TiO2 price goes up, production costs go up. However these often can’t be passed on to already cash-strapped customers.
So, although you thought your paint formulations were already extended to the limit, you have no choice but to have a re-look at TiO2 extenders.
Everyone is on the bandwagon suggesting extenders. How do we decide which one is best? This is the topic we are exploring today.
The reason that rutile TiO2 is the best opacifier by far, is due to two factors:
- Firstly, the peak of the light scattering power of a pigment is at half the wavelength of light (550nm). Rutile TiO2 with a particle size of 0.27u (270nm), has been optimised to sit exactly on this peak.
- Secondly, the higher the refractive index of the material, 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 1.63 for calcium carbonate, as shown in this graph:
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 reduce crowding, we need to use smaller fillers or extenders. Only when these materials approach the size of TiO2, are they be able to separate the TiO2 particles effectively. This is called spacing.
However, there are many extenders to choose from, each with its own strengths and weaknesses. Some example are:
Ground calcium carbonate
Precipitated calcium carbonate
Kaolin
Calcined kaolin
Talc
Hollow spheres
Barium sulphate
Alumina trihydrate
Entrapped air
Engineered white pigments, like FP440
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’d like to suggest an easy step-by-step approach which you can follow to find the best extender for your own application.
The better extenders are usually those with a particle size below 1u. This diagram shows why small particles space TiO2 better than large ones:
With thanks to Huntsman article (now out of print)
Since the TiO2 particles are around 0.27u in size, the first step to screen your extenders would be to:
1. Discard anything with a mean particle size (D50) above 1 micron
Particles larger than a micron are too big to space the TiO2 efficiently, as you can see above. One exception is where the extender already contains some TiO2, like in our engineered white pigment, FP440 which has D50=1u.
With many paint grades and formulations to choose from, I suggest that you
2. 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 whether this formulation is being properly dispersed in the factory.
3. 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 in Matt paints (above critical PVC), I suggest you
4. Make a 15% 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.
For Silk paints (below cPVC), we suggest a 10% replacement instead, to minimise any negative impact on gloss and sheen levels. Then it is time to:
5. 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:
6. Tweak 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.
Remember if TiO2 is in short supply and you can replace even 5% with an extender, then you can make 5% more paint volume with the same amount of TiO2 (see our suggestion below).
Of course you can also consider using no TiO2 at all. For example, by downloading our TiO2-free paint formulation. This approach only really works if you plan to start a new range. If you compare TiO2 with no-TiO2, the TiO2 formula will win every time, for reasons given above.
Hope this helps and best of luck in these challenging times.
(Dr) Jenny Jay
Managing Director, SERINA TRADING
P.S. I suggest you include the following in your screening. Contact us for free samples.
FP-440 – 1u engineered white pigment
IOKAL ULTRAFINE – 0.75u calcium carbonate
If you are short of time and staff, you can always just replace 3 – 5% of the TiO2 in all of your formulations with our white pigment FP-440. At this low level, your risk is low. You shouldn’t see any difference in the performance of your paint and you will make some savings. Then you can optimise later for maximum savings when you have the time to do so!