Pigments are important elements within paints, coatings and inks, and are added to impart colour, bulk or a desired physical/chemical property for wet or dry film. Quality pigment is not just seen as an ‘ideal’, but a necessity. Paints, coatings and inks contribute to consumers all over the world to personalise their business, homes and products, and without proper dispersion the colour will not hold up.
What are pigments?
Pigments are insoluble powders, either finely ground natural or synthetic which impart colour when added to paints and coating formulations. The dry pigment is dispersed in liquid material and stabilised using resin to minimise agglomeration, a phenomenon where pigments containing water and solvent form “lumps”.
There are two types of pigment:
Despite being around for centuries, these types of pigments are used less frequently due to the weaker colour strength. And with the colour supplied through minerals and metals, they are quite simple in their chemical structure. However, organic pigments do not disperse as easily and form clumps of pigment particles (agglomerates).
Inorganic pigments on the other hand, are also known as ‘synthetic pigments’ as they are formulated in labs and manufactured through the chemical process of oxidation. They are commonly used for paints, plastics, synthetic fibres and ink. Anywhere which is needed to provide opacity.
Why are pigments dispersed?
In their powdered form, pigments have large agglomerates, which needs to be reduced. And there are a number of benefits for reducing the overall size:
- Maximise colour efficiency
- Prevent settling of particles
- Achieve the desired colour
- Achieve same particle result every time
Overall, there are four aspects to the dispersion process:
- Deagglomeration– breaking down the agglomerates through crushing and mechanical shearing
- Wetting– Involves replacing the air and moisture between the pigment particles with a pigment dispersing agent or binding solution
- Distribution– depending on the viscosity, the pigment is equally dispersed through the binder system
- Stabilisation– to prevent reagglomerating, the pigment is stabilised through the addition of additives
Good quality dispersions lead to high quality colour and strength, and this is an important factor when it comes to colouring. The quality and performance of the pigment however can be measure by the following:
Colour Strength– When choosing the pigment, colour strength has to be considered. The higher the colour strength, the less pigment is required to achieve a certain shade depth. When pigment dispersion is used successfully, it results in a high level of colour consistency. So, to consistently achieve great colour strength, the correct size particles during dispersion will help hugely during this process.
Heat Resistance– During testing, colour is assessed during various temperature intervals, to which the colour sample in question is evaluated. This is because, at higher temperatures, pigments become more soluble, resulting in shading. Typically, with the exception of yellow iron oxide, inorganic pigments have an enhanced heat stability compared to organic pigments.
Weather Stability– There can be many different factors which result in colouring being suitable for outdoor use, such as, binder type, pigment concentration, titanium dioxide, what stabilisers used and the outdoor performance required. If outdoor colouring is required, it needs to be selected for its weather resistance characteristics. Weather stability is also closely linked to light fastness – pigments need to be chosen which does not fade over time.
Productivity– To be productive, the colour needs to be able to spread over large surface areas whilst the quality is not compromised. One of the best ways to achieve this is through excellent concentration of colour pigments.
So, are you searching for quality pigment? Get in contact with us to find out more on our pigment dispersions and what we can do for you. If you are wondering why colour is so important, have a look at our other blog.