Organic vs. Inorganic Pigments

Ink is a major part of the printing process… it’s what creates the intricate designs on packaging and allows us to understand the product and its intended use. Without ink, the packaging world would be a dull place!

There are 3 basic components to ink. First is pigment, which is the solid component to ink. The pigment does not dissolve in the vehicle, but rather is suspended in it. Pigments are where we get the actual color of the ink. The vehicle is next, and it is the liquid component to the ink. Depending on the type of vehicle that is used it helps determine the stiffness, drying rate, adhesion, gloss, and rub resistance of the ink. It can be a combination of resins that help bind the pigment to the substrate or solvents. Lastly, are any additives needed.

Let’s look at the coloring agent of the ink – our pigments. There are two broad categories – inorganic and organic pigments. Organic pigments contain carbon atoms which form strong stable chemical bonds and are always present in animal, vegetable, and synthetic organic chemistry. Organic pigments are usually bright, pure, light in weight and rich in tinting strength.

Inorganic pigments tend to be dry ground minerals. They contain metals and are often opaque, while most organic pigments are considered transparent. Titanium dioxide, on the left, is one of the most widely used inorganic pigments and is used extensively in packaging applications. Another example would be aluminum, seen here on the right, which is used to create metallic inks. Bronze is also used as a metallic ink. Inorganic pigments offer great lightfastness, or resistance to fade after being exposed to light for an extended period of time.

Organic pigments are created in labs using carbon chemistry. These pigments are created by combining 2 colorless liquids to precipitate a pigment from the reaction. Once a pigment is precipitated out, the remaining salts are rinsed out with water. This results in a presscake that contains about 60% water. With flexographic inks, the presscake is dispersed into the vehicle, while with lithographic inks the water must be removed by binding the pigment to oil instead and the water is flushed away. The inks created from organic pigments are transparent and their lightfastness varies.

When it comes to deciding whether to use an organic or inorganic pigment, the following must be determined: (1) if the opaqueness of the pigment is a driving attribute, (2) the vibrancy of color is the key criteria, and (3) if its ability to withstand light and weather is paramount. Organic pigments tend to generate brighter and richer colors than inorganic pigments. However, organic pigments are usually more prone to fading or being destroyed when they’re exposed to sunlight and harsh chemicals than are their inorganic counterparts. Many organic pigments, when applied in a single layer, are incapable of generating a surface coat that will completely hide the undercoat, while inorganic pigments are generally more opaque.

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