What is the difference between Carbon Black and
In today's world our consumption of Carbon Blacks
registers approx.6 800 000 t.
The majority are used in rubber
applications, hence the name "Rubber Blacks". Only approx. 550 000t belong
to the group of Pigment Blacks.
This group of pigment is produced under pigment relevant
production conditions. On the contrary to the Rubber-Black production, the
feedstock is based only on specific hydro carbons with low sulphur
The particle size of Pigment Blacks is the main parameter
for adjusting the shade of black in the application. So this should be
kept in mind as a production parameter as well as the morphology, called
structure, expressed in DBP absorption, and the surface chemistry
expressed in pH value and/or volatile content, determined by over 950? .
As aforementioned, the particle size of Pigment Blacks
determines the colouristic behaviour. The rule - the smaller the particle
size the darker the application - can be transferred to all applications
and to all coating systems. We find products for the coating and inkjet
industry which are approx. 11nm means 11?, mill-micron up to typical
tinting Pigment Black which are approx. 100nm, near by Titandioxyide.
To effectively disperse and stabilise, especially the
fine particle size Pigment Blacks, it is necessary to apply, in addition,
a specific surface treatment for the black pigment.
This is done by an
after-treatment, based on oxidation, to increase the amount of functional
groups, mainly COOH-groups. Oxidised Pigment Blacks are easy to find in
the wide production list of the Pigment Black producers: Volatile content
is higher and the pH-Value is lower, when compared with the basic
pigments. The longer the production time for these pigments the more
expensive the price, although the performances are better.
Water-based coatings show the highest increase of all
environmentally friendly coatings. In particular, automotive paint and
repair paint producers face the problem of producing like shades in
coatings based on binders like PE/CAB, 2C-Acrylics, NC-comb.,
thermoplastic acrylics, special PE and water based Acrylics and PU
systems. To attain the same blackness in all mentioned paints is a real
For water-based base-coats we need small particle size
Pigment Blacks as well, if possible, the one which we use in solvent born
coatings or similar. But there is a big difference in terms of the wetting
power of the binders.
Is it possible to disperse the pigment in selected solvent
born resin with or without small amounts of wetting agents. However,
it is essential in waterbased coatings to use special wetting agents
in large proportions. It is also necessary to recognise that the Pigment
Black can differ. As mentioned above we have a high density of chemical
groups on the surface of the oxidised Pigment Black particle, along
with a higher acidity of the pigment. Such pigment black particles require
a higher amount of amines to neutralise and to adjust a required pH
value of approx.8. For water based coatings, non oxidised Pigment Blacks
can be used as an economical alternative.
The important factor for success in terms of colour and stabilisation
is the type and the amount of wetting agent. There are a wide range
of wetting agents which work well. In regards to the amount required,
as a guideline 75 to 100% wetting agent, active substance calculated
on fine particle size Pigment Black. Pigments with larger particles
requires less than that.
Pigment Black concentration in the mill base is also
influenced by the particle size of the Black. 15% to 20 % Pigment Black
for the mill base is possible.
In the final paint, depending on the
thickness of the paint film layer, between 5% and 10% calculated on resin
solid are usual.
For industrial applications, fine Pigment Blacks as
mentioned above, are not necessary. Particle sizes of approx.25 nm are
sufficient to fulfil the request from paint users. Dispersion,
stabilisation and costs are significantly more favourable compared to the
fine particle Pigment Blacks.
Powder coatings are much more 'user-friendly' with
This is because the dispersing energy in the extruders
are considerably higher than in other dispersing equipment and once well
dispersed there is no space for re-agglomeration or flocculation.
rule concerning particle size and blackness applies for powder coatings
The difference in after-treated Pigments and non treated
is often quite small. We regularly do not find any difference in
Blackness, it is only the undertone which can change. Fine particle
oxidised Pigment Blacks (13nm) produce a bluish undertone which actually
makes the onlooker believe that the coating is more black. Only 1% Pigment
Black is necessary to produce a powder coating with good hiding power and
with less influence on the levelling of the coating.
For tinting purposes large particle size Pigment Blacks,
like Lamp Black are easy to handle because of there relatively low tinting
Can we use Pigment Blacks in UV-curing systems?
not easy to produce deep black UV -coatings with Pigment Blacks. The main
barrier is the particle size.
In the literature you find formulations
including 25nm-Pigment Black, oxidised and combined with specific high
reactive accelerators and selected acrylic resins. That's the limit
insofar as blackness concerns. Better colouristic results are obtainable
by using Aniline Blacks.
Pigment Blacks with larger particle sizes
which are after-treated, are a good option only for black coatings and
UV-curing printing inks.
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