High-Performance Inorganic Pigments

High-Performance Inorganic Pigments for Advanced Paints and Coatings Paint and coating manufacturers face challenges in meeting more demanding product specifications, increasing regulatory requirements, logistical and production issues, and achieving sustainability goals. Complex Inorganic Color Pigments (CICP) address these issues, enabling paint and coating manufacturers to develop, produce, and market differentiated products for specific applications. Dye category classification systems can be organized in many different ways. Pigments are generally divided into two classes: organic and inorganic. Organic pigments provide various bright chromatic colors but inherently have limited heat stability, chemical resistance, opacity, and overall durability. Inorganic pigments offer higher stability, durability, and opacity but have less chromatic color variety than organic pigments. CICPs close this performance gap by combining the bright colors that rival organic pigments with the durability of standard inorganic pigments. The advantages of CICPs can be explained through the terms in "CICP." Complex: They consist of multiple metals calcined at temperatures above 800°C and existing within a single oxide structure. Inorganic: They have no degradable organic functional groups and can also be thought of as a 'ceramic' found in nature. Color: They are not white like titanium dioxide or other fillers. They selectively absorb wavelengths of light to produce color impression. Pigment: They are discrete, inert particles that do not dissolve in organic solvents or resins, unlike what a dye would do. For example, instead of a single oxide like iron oxide or chromium oxide, CICPs are created by mixing iron and chromium oxides and then calcining them at approximately 1000°C. At these temperatures, metal ions move randomly; they are no longer a physical mixture of iron and chromium. A new chemical compound with different colors and other properties. In this case, it is an Iron Chromium(III) pigment, which is black in color and also known as CI Pigment Brown 29. This pigment class is also a class of a color pigment with other properties. PBr29 pigments are dark in color but reflect near-infrared wavelengths of sunlight. This allows dark-colored materials left in the sun to remain cooler. This example is a good illustration of how color and function are combined in CICPs in high-performance pigments. Inorganic chemistry, through high-temperature calcination and controlled processing, enables chemists and color engineers to impart the properties they desire in a pigment. During the calcination step, pigments become completely oxidized and are rendered inert to prevent color change or deterioration. The high-temperature heat stability of pigments provides them with overall stability, good stability for oven-cured systems, and durability in high-temperature coatings. This stability extends to the pigments being inert to solvents, acids, and bases. Additionally, it allows them to pass a series of regulations for sensitive applications such as FDA food contact applications. Pigments typically have the ability to absorb light well when exposed to UV light to protect the resin and substrate from the harmful effects of the sun. The UV light absorbed is dissipated as heat rather than destructive free radicals that can attack resins and organic materials. While material exiting the kiln typically sinters in large particles, CICPs for coatings are processed to have an average particle size between 0.5 and 1.5 microns. In addition to these convenient and controlled particle sizes, the surface area of pigments is relatively low and adequate for low resin demand and high gloss. While bright, chromatic colors are a strength of CICPs, their interaction with light beyond visible wavelengths (400-700 nm) in the near-infrared (700-2500 nm) gives them properties that increase material sustainability. Only half of solar energy is in the visible part of the spectrum. Except for a few percent in the extremely harmful UV (295-400 nm), the other roughly half of solar energy is in the invisible IR (Infrared Reflectance) spectrum. For aesthetically pleasing dark colors, all black pigments absorb visible light and standard pigments continue to absorb light in the IR, causing black colors to heat up in the sun. Some CICP black pigments, particularly Iron Chromium(III) Oxide (CI Pigment Brown 29), absorb the visible for black color but reflect solar energy in the invisible IR. While a standard black such as carbon black has only 5% TSR (Total Solar Reflectance), a CICP IR Black will reflect 25-30% of solar energy (TSR). This means that IR Black materials will remain cooler than standard black materials. A white material will always provide the most cooling, but for many applications darker colors are preferred. When used in building products such as roof coatings, IR Black pigments are accepted by regulators and energy companies not only as a strategy to reduce total energy used for cooling but also to reduce peak energy demand on the hottest afternoons. (The key to keeping energy use constant) CI Pigment Brown 29, the foundation of IR Black technology, has a wide range of CICP products based on its chemistry as well as titanium, cobalt, and a series of other metal oxides. This product is one of the most well-known and most effective products.  

Cobalt Blues and Greens

Cobalt Aluminate blue (CI Pigment Blue 28) is a bright blue with red undertones well-known in artists' color palettes but has applications in a number of different coating systems. Cobalt Chromium(III) Aluminate (CI Pigment Blue 36) is a blue with green undertones offering high color strength and excellent weatherability. They have a wide color range from navy to turquoise tones. Cobalt Titanate greens (CI Pigment 50) are bright green tones that can be used when standard chromium oxides (CI Pigment Green 17) are not sufficiently chromatic. By mixing cobalt greens with a small amount of lithium, a turquoise tone can be produced.

Titanate Yellows and Browns

These pigments can be thought of as 'doped' or modified titanium dioxide. Different colors can be produced by incorporating different metals into the calcination step. Nickel Antimony Titanate (CI Pigment Yellow 53) is a yellow with a greenish tone that is less chromatic than Bismuth Vanadate (CI Pigment Yellow 184) but has higher heat stability and excellent weatherability. Chromium(III) Antimony Titanate (CI Pigment Brown 24) is a yellow with a reddish tone offering excellent weatherability and high opacity. And Manganese Antimony Titanate (CI Pigment Yellow 164) is a heat-resistant, iron-free dark brown pigment.

CICP Black Pigments

In addition to IR Black pigments, many black CICP pigments exist. Copper Chromite (CI Pigment Black 28) pigments are the standard in high-performance, high-temperature coatings with excellent durability. Manganese Ferrite (CI Pigment Black 26) pigments are stable up to 600°C and are chromium-free. Chromium(III) Iron Nickel (CI Pigment Black 30) pigments are blacks with very high temperature resistance for glass enamel applications.

NTP Yellow and RTZ Orange

Two new CICP classes, NTP (Niobium Tin Pyrochlore) yellows and RTZ (Rutile Tin Zinc) oranges, are high-performance pigments. NTP Yellows (CI Pigment Yellow 227) and RTZ Oranges (CI Pigment Yellow 216) are brighter and more chromatic than standard CICPs like titanate yellows. They approach the tones of high-performance organic yellow pigments and can be used as replacements for Chromium Yellows (CI Pigment Yellow 34).

Uses of CICPs in Coatings

CICPs can be used in a wide range of coating systems because of their colors, opacity, and inertness. Their properties additionally make them suitable for use in a wide variety of applications. They can be used in high-temperature-resistant coatings such as industrial and automotive applications. Generally, CI Black 28 and CI Black 26 pigments are used in automotive applications where formulations contain no chromium whatsoever. Cobalt blues and greens, together with titanate yellows, provide surviving chromatic colors when other organic or inorganic pigments fail. Aluminum/steel coil and extrusion coatings represent a significant area of use for CICPs, particularly compared to light-shaded organic pigment tones, both because of problems during processing and their color stability against weathering. CICPs also provide colors for 40-year-warranty fluoropolymer resin-based paint systems. Key pigments are: • CI Pigment Black 28 - Extremely durable with good color control in color tones, • CI Pigment Brown 29 - 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 for stable yellow pastel tones, • CI Pigment Green 50 - Unique pigments that are brighter and more chromatic than chromium oxide green.  

NTP Yellow and RTZ Orange - Bright Colors for Signature Buildings and Accents

In powder coatings, high-temperature-resistant pigments can be used as in aluminum/steel coil and extrusion coatings. CICPs can be used for long-lasting colors in the latest generation, highly durable, AAMA 2605 certified coatings. While organic yellow pigments degrade and change color, CI Brown 24 and CI Yellow 53 Pigments provide heat-resistant yellows with reddish and greenish tones. Research continues to expand the performance of the CICP pigment class. New versions are being developed to address regulatory concerns, increase sustainability, and generally improve colors by expanding the high-durability color range. CICPs may not be the most suitable pigment for every application, but when all other options have failed, when maximum pigment performance or additional functionality is required, they are critical products that paint and coating chemists and color engineers must have on their benches.     Mark Ryan Market and Product Manager The Shepherd Color Company   Sena Şahin Sales Manager Color & More Chemical Raw Materials Sales and Marketing Inc.