Formulator’s Corner Formulating with Pigments – Part 2

By Charles Lubbers , Garrett Gebhardt

For many consumers, a trip to the in-store paint chip aisle can lead to indecisiveness, as choosing the “just­ right” color to reflect the personality and mood for a space can be a challenge. Even though many consumers experience doubt when trying to choose the perfect hue, formulators must confidently select the colors they will offer to the marketplace, while also offering a range of finishes and performance features consumers demand for today’s paints: high hiding, paint plus primer, low voe, scrub and stain resistance, light stability, and more. The technology behind colorants does much more than just deliver color. Part 1 in this series on pigments (Coatings Tech, 11 (10) October 2014) focused on the different families and chemistries of pigments and how these impact key properties, such as lightfastness, durability, opacity, and chroma. Equally important for the formulator is the knowledge of how to transform those pigments into a usable form for their application, which is the focus of Part 2.

Unfortunately, there is no such thing as a true “uni­versal colorant” to deliver the needed performance in all applications and vehicles. Liquid dispersions are the most common means of reliably delivering color in coat­ings and graphic arts applications. Although pigments may be applied directly to the substrate in applications such as stamped concrete, often the goal of such appli­cations is to deliver a mottled or irregular appearance rather than a uniform surface. In most applications, pigments are handled in a liquid form for both ease of use and consistent color delivery. Dispersions for archi­tectural coatings perform as part of a full-color palette available through in-store dispensing systems or in-plant tinting.

A similar palette is utilized in graphic arts for spot color printing, while a smaller CMYK (cyan-magenta­ yellow-black) set is used in most other print applica­tions. Consistent strength and color batch-to-batch is critical in all applications. In paints, the color delivery must also be consistent across the various tint base­lines, with strengths ranging from pastels to deep tones. Properties of pigment dispersions vary widely by tar­geted application. Dispersions used in waterborne architec­tural coatings can differ greatly from those used in aque­ous stains, solventborne coatings, or today’s UV-curable coatings and inks. While the traditional ethylene-glycol­based canister colorant may deliver excellent performance in numerous latex emulsions and alkyd house paints, it will generally fall short in industrial coatings.