Selecting Carbon Black for Paints, Coatings and Inks

    Adding carbon black (CB) particles to elastomeric polymers is essential to the

successful industrial use of rubber in many applications, and the mechanical reinforcing effect of CB in rubber has been

studied for nearly 100 years. Despite these many decades of investigations, the origin of stiffness enhancement of elastomers

from incorporating nanometer-scale CB particles is still debated. It is not universally accepted whether the interactions

between polymer chains and CB surfaces are purely physical adsorption or whether some polymer–particle chemical bonds are

also introduced in the process of mixing and curing the CB-filled rubber compounds. We review key experimental observations

of rubber reinforced with CB, including the finding that heat treatment of CB can greatly reduce the filler reinforcement

effect in rubber. The details of the particle morphology and surface chemistry are described to give insights into the nature

of the CB–elastomer interfaces. This is followed by a discussion of rubber processing effects, the influence of CB on

crosslinking, and various chemical modification approaches that have been employed to improve polymer–filler interactions

and reinforcement. Finally, we contrast various models that have been proposed for rationalizing the CB reinforcement of


    Natural rubber composite has been continuously developed due to its advantages such as a good combination of strength and

damping property. Most of carbon black (CB)/Natural Rubber (NR) composite were used as material in tyre industry. The

addition of CB in natural rubber is very important to enhance the strength of natural rubber. The particle loading and

different structure of CB can affect the composite strength. The effects of CB particle loading of 20, 25 and 30 wt% and the

effects of CB structures of N220, N330, N550 and N660 series on tensile property of composite were investigated. The result

shows that the tensile strength and elastic modulus of natural rubber/CB composite was higher than pure natural rubber. From

SEM observation the agglomeration of CB aggregate increases with particle loading. It leads to decrease of tensile strength

of composite as more particle was added. High structure of CB particle i.e. N220 resulted in highest tensile stress. In fact,

composite reinforced by N660 CB particle shown a comparable tensile strength and elastic modulus with N220 CB particle. SEM

observation shows that agglomeration of CB aggregates of N330 and N550 results in lower stress of associate NR/CB composite.

    Carbon black is a highly engineered form of carbon widely used in paints as paint carbon black, coatings and inks to achieve a spectrum ranging from gray to deep

black. Over the time, the properties of carbon black pigment have been modified to achieve required properties in the final

product, such as increased tinting strength, improved the level of jetness or blue undertone and conductivity.

    Explore the different carbon black production processes and the properties to consider while selecting the right carbon

black for your formulations.

    Properties and End-uses of Carbon Black

    Carbon black is used in many products and articles we use and see around us on a daily basis, such as: rubbers, plastics,

coatings, tires, ink carbon clack.

    Thus, the requirements for the carbon black are different for each application and influence the specific properties in

the final application.

    For the coating carbon blacks market,

there is a wide range of carbon black grades available. This can make it difficult to choose the most suitable carbon black

for your final application. For example, when aiming for automotive paint with a blue undertone, the carbon black of choice

will have a high jetness. However, normally these types of carbon black grades are the most difficult to disperse correctly

into the desired particle size.

    The carbon black producers are addressing these issues by developing specialty carbon black grades that have been

surface-modified and/or are pre-treated to overcome these difficulties.

    How Carbon Black is Produced?

    The properties of the carbon black are influenced by the method of preparation. The different processes used for

channel carbon black production are discussed below.

    Furnace Black Process: It is the most common method which uses (aromatic) hydrocarbon oil as the raw material. Due to its

high yield and possibility to control the particle size and structure, it is most suitable for mass production of carbon


    In the reactor the conditions (e.g. pressure and temperature) are controlled to provide a number of reactions. The most

important reactions include: particle nucleation, particle growth, aggregate formation. Water injection rapidly reduces the

temperature and ends the reaction. The primary particle size and structure of the carbon black is controlled by tuning the

conditions in the reactor and the time allowed before the reaction is quenched.

    Thermal Black Process: It is the most common method used for carbon black production after the furnace black process. It

is a discontinuous or cyclical process.

    This process uses natural methane gas as raw material. When the natural gas is injected into the furnace at an inert

atmosphere, the gas decomposes into carbon black and hydrogen. The carbon black produced using this method has the largest

particle size and the lowest degree of aggregates or structure. Due to the nature of the raw material, this carbon black is

the purest form available on the industrial scale.

    Channel Process: This process uses partially combusted fuel which is brought into contact with H-shaped channel steel. It

is not the most used method anymore because of its:

    The benefit of this process is that it provides carbon black with a lot of functional groups.

    Acetylene Black Process: This process uses acetylene gas as raw material. It produces mainly high structure and higher

crystallinity, making this type of carbon black suitable for electric conductive applications.

    Lampblack Process: It is the oldest industrial process for making carbon black. It uses mineral/vegetable oils as its raw


    Recovered Carbon Black from End-of-life Tires

    Recovered carbon black or (r)CB is a fast-expanding market. Recovered high purity carbon black is obtained through the pyrolysis process of end-of-life tires. The importance of

companies in the production and use of recovered carbon black is three-fold:

    The growing global problems arising with end-of-life tires (ELT)

    Companies shifting strategy to fulfill the targets ensuring a green economy

    Price changes of regular carbon black due to fluctuations in oil pricing

    Depending on the composition, the content of carbon black in tires can be up to 30%. Next to carbon black, the tires



    Rubber processing additives



    Fillers such as silica

    The amount of silica depends on the type of tire, for example winter or summer tire, racing tire, or tire for

agricultural vehicles, and will not be separated from the carbon black during the pyrolysis process, which will result in

higher ash content.

    In a typical car tire, up to 15 different types of conductive

carbon black
s can be used, each attributing to the different properties required. This blend of

environmental carbon blacks will then also be the make-up of

the final (r)CB composition. Besides tires, other sources that can be used are rubber conveyor belts or other technical

rubber products.

    The main differences in the properties of recovered carbon black are:

    The ash content is higher for (r)CB caused by the fillers being used in tire production.

    A blend of rubber carbon black properties as a result of the

carbon black used in the tire.

    Residual hydrocarbons on the carbon black surface, depending on the quality of the pyrolysis process.

    To understand how the properties of (r)CB influence the final applications and to know which

plastic carbon black is used in which category, we need to

understand the fundamental differences between the available carbon blacks.


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