Carbon black | technical paper Dr Natalie Harris of Birla Carbon examines the properties of
different carbon blacks and provides useful advice on selecting the best products for particular plastics applications
How to get the best from carbon black
Carbon blacks fi nd use in a variety of plastics markets. Applications include colour concentrates, fi bres, conductive compounds, pipes, and wire and cables. Each market segment presents challenges in terms of the carbon black properties that are required to meet the desired performance needs. This paper will discuss the fundamental carbon
black properties. Emphasis will be placed on under- standing the relationship between performance requirements for a specifi c application and the impor- tant carbon black properties. It will also discuss the selection criteria for carbon black grades. There are a large number of commercially carbon
black products available and the selection process can become overwhelming. For any carbon black application the specifi c
performance needs have to be understood. Such requirements could cover appearance (mass-tone, tint and gloss), UV protection and electrical conductivity (conductive, antistatic /dissipative or insulative). The ability to meet any or all of these performance param- eters is extremely dependent on the correct selection of a carbon black. Achieving adequate dispersion of the pigment is also important via optimized mixing methods.
The user should have a good understanding of the impact of carbon black properties on end performance. For this reason the four fundamental properties of carbon black will be discussed. These include fi neness, structure, porosity and surface treatment. Non-funda- mental properties relating to cleanliness and physical form will also be introduced. Understanding this property-performance relationship is key to “getting the best out of a product”. Then main section headers for this paper are: 1)
Fundamental properties; 2) Dispersion of carbon black; 3) Performance needs in plastics; and, 4) Application requirements.
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Fineness/Particle size distribution Increases: Color, tint, conductivity, UV protection, vehicle demand & viscosity. Lowers: Dispersability
Structure/Aggregate size and shape distribution Slightly reduces: Color & tint. Increases: Electrical conductivity, vehicle demand & viscosity. Increases: Dispersability
Higher porosity Increases: Electrical conductivity, vehicle demand & viscosity. Enables: Reduced loading in conductive applications
Higher Surface Functionality Improves: Vehicle wetting. Reduces: Viscosity of liquid systems. Lowers: Electrical conductivity
Figure 1: Carbon black fundamental properties and impact on performance parameters
1) Fundamental properties The fundamental properties of carbon black are particle size distribution, aggregate size and shape distribution, pore size distribution and surface activity distribution. These are shown in Figure 1 along with their relation- ship to performance properties. Empirical measurements such as surface area, tint
strength and oil absorption are most typically used to describe and specify carbon blacks. In addition to fundamental properties, the physical form (degree of agglomeration; powder or bead form) and non-black constituents (ash, residue, sulphur etc) can play important roles in performance. Particle size refers to the spherical areas of the
rotational paracrystalline domain within the carbon black aggregates. Mean particle size for furnace products typically range from 8 nm to 100 nm. The particle size distribution is the single most important property for infl uencing the degree of blackness or jetness with smaller particle sizes/higher surface area
November 2013 | COMPOUNDING WORLD 37
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