Carbon Black Unveiled: Driving Excellence in the Coatings Industry

Carbon Black Unveiled: Driving Excellence in the Coatings Industry

Carbon black is a material that is produced by the incomplete combustion of coal tar, vegetable matter, or petroleum products and by ethylene cracking processes. It is a very versatile and widely used material in various industries. The bulk of carbon black is dedicated to rubber applications. Next to that, approximately 10% of the global carbon black output finds it’s applications as a pigment, UV stabilizer, antistatic, and conductive agent in various industries such as plastics, inks, and coatings applications.

Explore the evolution of carbon black, from ancient history to modern high-performance pigments and understand it’s crucial role in coatings. Discover the various manufacturing processes giving carbon black it’s key properties and learn about sustainability initiatives shaping the future of carbon black and the coatings and ink industry.

The History of Carbon Black in Coatings and Inks

Prehistoric people that were decorating cave walls used pigments and spit or fat as a binding medium. The pigments used were predominantly earth pigments such as iron oxide-based minerals and calcite, complemented by carbon black originating from burning of wood (charcoal) or other animal or plant-based materials.

rubber

                           Charcoal horse drawings Chauvet cave - France

Ancient Chinese and Egyptian civilizations employed carbon black mixed with biobased substances to create dyes and inks, whereas in Egypt it was also used in the preparation of cosmetics. The distinctive dark cosmetic applied to the eyebrows, eyelashes and the perimeter of the eye used by the ancient Egyptians was called kohl[1]. Originally, black kohl consisted mainly of galena ore (lead sulfide, PbS) while it has been made plausible that later in history kohl consisted of carbon black[1,2].

Later the Greeks and the Romans developed methods to obtain larger quantities of carbon black by burning oils in specially designed furnaces. This method may be considered as an early form of the lamp black process.

The invention of the printing press in the 15th century and the geographical spread of these devices from the 15th – 17th century marked the start of an era of mass communication and significantly increased the demand for carbon black.

The development of new technologies and accelerated growth of various industries during the Industrial Revolution boosted the demand for carbon black and it was during this period that an alternative production method, the channel black process was developed. The channel black process allowed mass production of carbon black. The increased economy of scale considerably reduced costs, making carbon black more accessible and affordable.

The 20th century saw the development of the furnace black process, involving the combustion of petroleum derivatives in a furnace and later becoming the dominant method of production, as well as the acetylene black process, relying on thermal decomposition instead of combustion.

Manufacturing and properties

As outlined in the previous section several methods to produce carbon black are available[3]. The relevant ones for coatings and inks being the furnace black process, gas black process and the lamp black process. These processes all rely on the incomplete combustion of hydrocarbons in the presence of oxygen under controlled conditions. Next to these processes the carbon black may undergo surface treatment.

  • Lamp Black

The Lamp black process involves a tank that holds the liquid raw material, aromatic oils based on petroleum or coal, situated under a fireproof hood. The incomplete combustion can be controlled by the gap between the tank and the hood. Lamp Blacks feature relatively large primary particles and a wide primary particle size distribution.

The lamp black process

                               The lamp black process

  • Gas and Channel Black

The Channel Black process was a process, where gas was burned beneath channels filled with cooling water.

In the Gas Black process, developed by Degussa chemist Harry Kloepfer in 1934 a hydrogen containing carrier gas is pumped over hot creosote[4,5]. The evaporated part of the creosote is burned incompletely, and the formed carbon black is deposited on water-cooled rollers. The process is still in use by Orion Engineered Carbons (OEC) to produce specialty carbon blacks that feature excellent fineness and a very narrow primary particle size distribution.

The gas black process

                              The gas black process

Even though channel blacks show some similar properties to gas blacks, they should not be confused with the latter and more recent.

  • Furnace Black

The Furnace Black process is the predominant process used to produce carbon black. In this process, the raw liquid material, heavy aromatic oils from coal or petroleum, is fed through nozzles into a flame of hot air and natural gas and decomposed by thermal oxidation at high temperatures. The Furnace Black process allows for variability in the raw materials and process parameters. The versatility of this process allows the production of a wide range of carbon blacks having different properties.

The furnace black process
                                  The furnace black process

Compared to the high-quality products produced by the gas black method, the furnace black process even allows the production of deep black products with reduced oil absorption and after treatment, such as for instance OEC’s fine particle size specialty carbon blacks, COLOUR BLACK FW 310 & FW 255 and medium particle size NEROX® 600 & 510.

  • Surface treatment

Carbon black primary particles are spherical and consist of paracrystalline carbon layers. On the particle surface, the free valences are saturated by different organic groups, which are crucial to the interaction between the Specialty Carbon Black particles and other coating components. To make the particle surface more polar, carbon blacks are oxidized. This treatment elevates the number of oxygen-containing groups, particularly carboxyl groups and reduces the carbon black’s particular pH value.

For coating and ink applications, the surface treatment serves multiple purposes. It improves the interaction with polar solvents and binders, thereby giving the carbon black improved dispersibility, lower mill base viscosity, better pigment stabilization and higher blackness or jetness. A fine example is NEROX® 600, exhibiting high jetness and gloss in industrial water-based coatings whilst offering lower mill base viscosity and higher flocculation stability compared to conventional Gas and Furnace Blacks.

Zooming in on Carbon Black

Commercially available carbon black is supplied in the form of finely divided black beads or powder. Naturally the carbon black particles are not present in isolated form. They form aggregates by chemical bonding of their primary particles. Depending on the production method, the primary particles may have particle sizes ranging from a few nanometers up to almost 100 nanometers and a broad or small particle size distribution. It is the primary particle size of carbon black that determines the coloristic properties of the coatings.

The aggregates, usually a few hundred nanometers in size, are generally the smallest dispersible units of the powder. The degree of aggregation is also known as “structure” for which oil absorption is a gauge. Similar to the surface chemistry of the carbon black particles, the structure of carbon blacks also relates to physical paint properties.

The aggregates further join through van der Waals forces to form agglomerates, ultimately resulting in the carbon black supplied as powder, beads or pellets.

carbon black

Carbon Black in coatings

Specialty Carbon Blacks are used in paints and coatings for mass tone coloration, tinting of white and coloured coatings and for transparent coloration[6]. For mass tone coloration of high quality solvent-borne coatings, the use of fine particle sized oxidized Gas Blacks, COLOUR BLACK FW 2 and FW 200 and oxidized Furnace Blacks is preferred. For reasons of pH stability, untreated fine particle sized Gas, f.i. COLOUR BLACK FW 285, and Furnace Blacks, f.i. COLOUR BLACK FW 171, are also used in water-borne coatings. Some high-quality furnace blacks, especially surface treated NEROX® 510 & 600 as well as COLOUR BLACK FW 255 & COLOUR BLACK FW 310 are very suitable for both solvent- and water based industrial- and automotive coatings offering high jetness and bluish undertone.

The proper choice of carbon black grade strongly depends on the formulator’s desired properties of the coating and the limitations of the processing methods.

Although oxidized carbon blacks have been found in most cases to have less tendency to flocculate than untreated ones, carbon blacks require stabilisation by means of wetting and dispersing additives. The choice of additives is usually facilitated by guidelines from the additive supplier.

The higher structured carbon blacks, though easier to disperse, will have a more pronounced viscosity increasing effect than less structured carbon blacks and may impart limitations on the pigment loading.

carbon black

Colour properties

For mass tone black coating formulations, a decrease in mean primary particle size of carbon black and of the aggregates leads to an increase in blackness or jetness, a measure of the intensity of a colour sensation. Hence the jetness of a coating follows the general trend of Gas black / Furnace black > Lamp black. The surface appearance of the hue has a bluish undertone with decreasing particle size, which enhances the visual blackness. Surface treatment is another parameter. Oxidization will increase the jetness and the bluish undertone of the hue.

Another important factor in the sensation of a black colour is the gloss of a coating. Gloss has a major influence on the “black perception” of an observer. Although there are some exceptions, the general observation is that the higher the gloss, the higher the jetness.

For tinting applications, the color strength also increases with decreasing primary particle size. The colour sensation however, contrary to mass tone formulations, is no longer bluish but moves to a brownish undertone upon decreasing primary particle size. Coarser particles will generate a more bluish tone of the tinted coating formulation.

For transparent coatings the hue follows the same trend as for tinted coating formulations. Finer particle size carbon black will reduce the transparency of the coating compared to coarser particles but will generate more brownish hue than coarser particles that will show a more bluish undertone.

carbon black

Various other properties

The vital role carbon black plays in the coatings and in ink industry is not only due to its unique coloristic properties.  Carbon black also enhances the durability and stability of coatings and inks. It’s resistance to light, heat and chemical exposure makes it an extremely versatile pigment that ensures the durability of the coatings formulated with it. Carbon black is also used to improve the UV resistance of coatings. As an example, oxidized gas blacks are used in the automotive industry, not only to impart a deep black color to the coating but also to absorb UV radiation and thereby limiting the loss of gloss and fading of the coating.

In applications such as antistatic coatings or conductive inks carbon blacks can be used to enhance the conductivity of the coating or ink. The conductive properties of carbon black can be achieved through careful control of structure and particle size. Untreated Furnace grades with high structure are known to give the best properties in this regard.

Addressing Sustainability Challenges with Carbon Black

In response to growing environmental concerns, a demand for environmentally sustainable carbon black is emerging and some alternative eco-friendly technologies focused on feedstock and production methods are being explored.

The use of renewable and recovered oils from, for instance recycled end of life tires as well as the use of bio-sourced methane are promising options regarding feedstock as well as innovations in production, such as yield improvement and reducing process CO2 emissions, contribute to a route heading towards sustainable carbon black. These are not empty phrases. Recently Orion Engineered Carbons announced the launch of a grade of carbon black made of 100% bio-circular feedstock that are not in competition with food/feed production and are therefore not part of a food-feed-fuel competition[7].

Supporting your formulation challenges

Tracing the evolution from ancient pigments to modern engineered forms, we have explored the diverse manufacturing processes of carbon black and its key features, with an emphasis on the pivotal role of carbon black in coating and inks.

At Safic-Alcan we are dedicated to sustainable solutions. In close co-operation with Orion Engineered Carbons our qualified sales engineers can offer you a wealth of product information. Our technical experts are here to support you, always ensuring you to streamline innovative and sustainable solutions for your coating formulations.

To discover more, visit our online catalog or reach out to us or your regular contact in at Safic-Alcan.

References

(1) McMullen, R.L.; Dell’Acqua, G.; Cosmetics 2023, 10, 71. https://doi.org/10.3390/cosmetics10030071

(2) Riesmeier, M.; Keute, J.; Veall, M.A.; Borschneck, D.; Stevenson, A. Garnett, A.; Williams, A.; Ragan, M.; Devièse, T.  Sci. Rep. 2022, 12, 5932

(3) “Specialty carbon blacks for industrial coatings, Technical Information 1458”, Company publication of Orion Engineered Carbons GmbH, Frankfurt, 2023

(4) https://history.evonik.com/en/inventions/carbon-blacks

(5) Kloepfer, H. Process for the Preparation of Active Carbon Black, US Patent, 1943 2,307,050

(6) “Specialty carbon blacks in modern coating systems”, Company publication of Orion Engineered Carbons GmbH, Frankfurt, 2017

(7) https://orioncarbons.com/orion-s-a-launches-bio-circular-printex-nature-35-for-ink-applications/, 2024

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