When we want to prepare a cake, we must first draw up the list of ingredients. It would be a problem to start kneading the mixture immediately and realize only during the process that you have forgotten an essential element for the recipe. Even worse, if we even discover that the house lacks what we need. We could then try to replace it with another ingredient, but the result would still be uncertain, with the risk of wasting precious time and making a mess. Here, the world of plastic coloring works just like pastry: before getting to work to create a project, you need to check that you have all the ingredients and that they are suitable for combining with each other. In fact, not all pigments are created equal. The use of organic pigments or inorganic pigments can give a very different result depending on the polymer with which they are mixed and the final product you want to make.
Are organic pigments natural?
Before starting, it is necessary to make a distinction on a topic that often causes confusion. Defining an organic or inorganic pigment has nothing to do with distinguishing between natural pigments and synthetic pigments. The doubt arises from the fact that the term “organic” is often mistakenly used as a synonym for “natural”, but this is not quite the case. In fact, both organic and inorganic pigments are extracted from naturally occurring products and are artificially synthesized in the laboratory. Indeed, precisely for an economic reason, it is often organic pigments that are made in test tubes, as materials of natural origin originate from limited sources and are often at the center of ethical debates.
Difference Between Organic Pigments and Inorganic Pigments
The main difference between organic pigments and inorganic pigments lies in the presence of carbon atoms within the molecules that compose them. Organic pigments in ancient times were extracted from living matter which is, in fact, composed of carbon (yes, that’s right, people also contain it). Plant roots and tree bark, flowers, shells, animal derivatives such as squid ink and murex purple, contain precious coloring elements. On the other hand, inorganic pigments placed their origin in minerals, such as rocks, limestone, soil, metals. Just think of the red of iron oxide or the blue of lapis lazuli. In the modern economy, however, things have changed a bit. As mentioned, mainly for an economic and ethical issue, and there is a tendency to synthesize all these pigments directly in the laboratory, especially with regard to organic pigments.
Organic or inorganic pigments? Which ones to choose for your plastic 
Of course, the different composition of the molecules of an organic element compared to an inorganic one also involves different properties. On the one hand, organic pigments are brighter and can be dosed in smaller quantities, but they are also more susceptible to exposure to bad weather and light. In contrast, inorganic pigments are less conspicuous, but have better resistance to light, water, and heat. Resistance to high temperatures is also different, with organic pigments running the greatest risk of “burning”. In addition to this, the phenomenon of color migration is much lower in inorganic pigments, unlike organic pigments which have a tendency to migrate. For these reasons, it is very important to know the properties of the pigments you want to use in your product, in order to correctly meet the needs of the application market.
Incompatibility: the case of warpage
The compatibility between the chemistry of a pigment and the chemistry of a specific polymer is never obvious and can even vary with the percentage of dosage. Working with materials science means taking all variants into account from the beginning of an item’s design, because even the slightest variation could result in unexpected reactions. For example, organic pigments such as blue phthalocyanines can alter the degree of crystallization of the plastic causing a phenomenon known as warpage, i.e. distortions and cracks forming during the cooling phase of the molded product. Thus, it may happen that you print a piece of different colors and everything seems to be fine. Then, when it comes to the blue color, the plastic is deformed and you have to rack your brains to solve the problem, wasting a lot of time in production.
Pigment leveling and other solutions
In reality, a solution exists for (almost) everything. Although organic pigments have a significant impact on the crystallisation behaviour of polymers, leading to issues such as warpage, the positive effects of a nucleating agent can compensate for distortion, smoothing out the behaviour of coloured plastics. This phenomenon, known as “pigment leveling”, is an allied solution against stress deformations and cracks. This can speed up the industrial process, reducing the need for continuous machine adjustments and the production of waste. As far as the formulation of a stable color, perhaps both bright and resistant to bright UV rays, is concerned, it is not a completely impossible task. A masterbatch suitable for the request can be made in the laboratory by creating the right mix of organic and inorganic pigments, perhaps with the addition of some special additives. In the end, with colors, the one who knows how to be more creative wins, even in finding solutions.
Organic pigments or inorganic pigments? That is the question!
Do you have a product design project in mind or do you want to make a plastic item, but you still have some doubts about the best pigments to use? Don’t worry, we’ll help you! Our colouring technicians will help you study a formula suitable for your process.
