High-Performance Inorganic Pigments for Improved Paints and Coatings
Paints and coatings producers face challenges in meeting more demanding product specifications, increasing regulatory requirements, logistics and production issues, and attaining sustainability targets.
A class of pigments known as Complex Inorganic Color Pigments (CICPs) address these issues and allow paints and coatings producers to develop, produce, and market differentiated products for specialty applications.
Colorant classification systems can be broken down many different ways. Pigments fall broadly into two classifications; organic and inorganic. In general, the organic pigments provide bright chromatic colors with variable, but inherently limited heat-stability,
chemical resistance, opacity, and overall durability.
Inorganic pigments provide higher stability, durability, and opacity- but with a smaller range of less chromatic colors than the organic pigments.
The CICPs bridge that performance difference with the durability of standard inorganic pigments while having bright colors that rival the organic pigment offerings. Many of the advantages of the CICPs can be explained by the terms in “CICP”.
Complex refers to that they are not based on single oxides, but are multiple metals in a single oxide structure and are locked in place during high-temperature calcination in a kiln at usually over 800°C. Inorganic since they do not have any organic functional groups that can degrade.
They can also be thought of a ‘ceramic’ in nature. Color because they are not white like titanium dioxide or other fillers. They selectively absorb wavelengths of light to give the impression of color.
Pigment as opposed to dye. They are discrete, inert particles that will not dissolve in organic solvents or resins like a dye colorant would. For example, instead of a single oxide like iron oxide or chromium oxide, CICPs would be made by intimately mixing the iron and chromium oxides, and then calcining them at about 1000C.
At these temperatures the metal ions move randomly and are no longer a physical mixture of iron and chromium, but are a new chemical compound with distinct color and other properties. In this case an Iron Chromium(III) pigment that is black in color and known as CI Pigment Brown 29. This pigment class is also an example of a color pigment that has other properties.
PBr29 pigments are dark in color, but reflect the near infrared wavelengths of sunlight- so dark materials left in the sun stay cooler. This an example of how CICPs bring together color and function into highperformance pigments.
The inorganic chemistry, high-temperature calcination and controlled processing give these pigments properties that chemists and paint formulators desire in a pigment. During the calcination step, the pigments are fully oxidized and made inert so that they won’t change color or degrade.
The pigments heat stability at high temperatures gives them good stability in oven-cured systems and durability in high heat coatings, along with general stability. This stability
extends to the pigments being inert to acids and bases, and solvent attack. The stability also makes them pass a number of regulatory requirements for sensitive applications like FDA food contact applications.
When exposed to UV light, the pigments generally have good absorption properties to protect resin and substrates from the damaging effects of the sun. The UV light that is absorbed is dissipated as heat and not as destructive free radicals that can attack resins and organic materials.
While the material off the kiln has usually been sintered into large particles, CICPs for
coatings are processed to have an average particle size between 0.5 and 1.5 microns for most pigments. Along with these useful and controlled particle sizes, the surface area of the pigments is relatively low for low resin-demand, and high gloss.
While bright, chromatic colors are a strength of the CICPs, their interaction with light beyond the visible wavelengths (400-700nm) in the near infrared (700- 2500nm) give them properties that improve materials sustainability. Only half of the sun’s energy is
in the visible part of the spectrum. Outside of a few percent in the highly damaging UV (295-400nm), the other roughly half of the sun’s energy is in the invisible IR spectrum.
All black pigments absorb in the visible for dark aesthetically pleasing colors, and standard pigments continue to absorb in the IR, contributing to the reason why black colors get hot
under the sun. Some CICP black pigments, specifically the Iron Chromium(III) Oxide (CI Pigment Brown 29), absorb in the visible for the black color, but in the invisible IR, they reflect away the sun’s energy.
While a standard black, like carbon black, has a Total Solar Reflectance (TSR) of only 5%, a CICP IR Black will reflect 25-30% (TSR) of the sun’s energy. This means that IR Black materials will stay cooler than standard black materials. A white material will always be the coolest, but for many applications, there is a preference for darker colors.
When used in building products like roof coatings, the advantage of IR Black pigments has been acknowledged by regulatory and energy companies as one strategy to reduce not just
overall energy used for cooling, but reducing peak energy demand in hot afternoons- a key to keeping energy grids stable.
Besides the CI Pigment Brown 29 pigment chemistry that is the basis for the IR Black technology, there are a wide range of CICPs based on titanium, cobalt, and a number of other metal oxides. Some of the best known and most impactful follow.
Cobalt Blues and Greens
Cobalt Aluminate blue (CI Pigment Blue 28) is a bright red-shade blue that is well known from artist color palettes, but finds use in a number of different coatings systems. The Cobalt Chromium(III) Aluminate (CI Pigment Blue 36) are green-shade blues with high tint
strength and excellent weatherability.
They come in a wide range of colors from navy blue to teal shades. The Cobalt Titanate greens (CI Pigment 50) are bright green shades that find use when standard chromium
oxide (CI Pigment Green 17) isn’t chromatic enough. By modifying the cobalt greens with some lithium, a turquoise shade can be produced.
Titanate Yellows and Browns
These pigments can be thought of as ‘doped’ or modified titanium dioxide. By the inclusion of different metals in the calcination step, different colors can be produced. A Nickel Antimony Titanate (CI Pigment Yellow 53) is a green shade of yellow that is less chromatic than Bismuth Vanadate (CI Pigment Yellow 184), but with higher heat stability and excellent weathering.
The Chromium(III) Antimony Titanate (CI Pigment Brown 24) is a red-shade yellow
with excellent weathering and high-opacity. And by making a Manganese Antimony Titanate (CI Pigment Yellow 164) a heat stable and iron-free dark brown pigment can be made.
CICP Black Pigments
Besides IR Black pigments, a number of black CICP pigments are available. The Copper Chromite (CI Pigment Black 28) pigments are the standard for highperformance
elevated-temperature and ultimate in high-durability coatings. The Manganese Ferrite
(CI Pigment Black 26) pigments are stable to 600C and are chromium free.
The Chrome(III) Iron Nickel (CI Pigment Black 30) are high-temperature stable blacks for glass enamel applications.
NTP Yellow and RTZ Orange
Two newer classes of CICPs are the NTP (Niobium Tin Pyrochlore) Yellow and the RTZ (Rutile Tin Zinc) high performance pigments. The NTP Yellow (CI Pigment Yellow 227) and the RTZ Orange (CI Pigment Yellow 216) are brighter and more chromatic than standard
CICPs like the titanate yellows. They approach the shades of high-performance organic yellow pigments and make excellent replacements for Chrome Yellow (CI Pigment Yellow 34).
Uses of CICPs in Coatings
Due to the color, opacity, and inertness of the CICPs, they can be used in a wide range of coatings systems. Their properties make them especially suited for use in a number of systems.
High-temperature coatings used in industrial and automotive applications. The CI Pigment Black 28 pigments in general and the CI Pigment Black 26 is a used in automotive applications where formulations don’t contain chromium in any form.
The cobalt blue and greens, along with the titanate yellows provide chromatic colors that survive when other organic or inorganic pigments fail. Coil and extrusion coatings are a major use of CICPs due to their color stability both in processing and also in weathering especially compared to organic pigment tints with white. CICPs provide the color for
the fluoropolymer systems that have 40 year warrantees.
The key pigments are:
• CI Pigment Black 28- Highly durable with good control of color in tints,
• CI Pigment Brown 29- The CICP IR Black for use in building products,
• CI Pigment Blue 28 & Blue 36- Bright chromatic blues with long term stability,
• CI Pigment Brown 24 and Yellow 53: Titanate yellows used in masstone of for stable yellow pastel tints,
• CI Pigment Green 50: Brighter and more chromatic than chromium oxide green, for branding colors.
The Ntp Yellow and Rtz Orange- Bright Colors for Signature Buildings and Accents
Powder coatings can use the same pigments as highheat along with coil and extrusion coatings applications. CICPs can be used in the latest generations of highly durable AMMA 2605 coatings for durable color.
The CI Pigment Brown 24 and CI Pigment Yellow 53 provide heat-stable red-shade and green-shade yellows when organic yellow pigments degrade and change color. There continues to be research done in expanding the performance of the CICP class of pigments.
Improved versions are being developed to address regulatory concerns, increase sustainability, and improve colors increasing the overall highly-durable color-space.
CICPs may not be the most appropriate pigment for every application, but they are a critical tool for paint and coatings chemists and formulators to have on their bench for when all other options have failed and the ultimate in pigment performance or added functionality are required.
Mark Ryan – Market and Product Manager
The Shepherd Color Company
Sena Şahin – Sales Responsible
Color & More Kimyasal Hammaddeler Satış ve Pazarlama A.Ş.
