15

2020

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01

Issues with Pigment Carbon Black in Plastic Applications

　　The impact of the basic properties of pigment carbon black—such as primary particle size, structure, porosity, and surface functional groups—on the performance of plastics can be summarized as follows:
　　The primary particle size of pigment carbon black is small (with a large specific surface area).
　　(1) Can enhance the blackness of carbon black;
　　(2) Can enhance the coloring power of carbon black;
　　(3) Can enhance the UV resistance of carbon black;
　　(4) Can improve the electrical conductivity of carbon black;
　　(5) Can increase the viscosity of plastics;
　　(6) Reduce the dispersibility of carbon black;
　　(7) Increase the water absorption of carbon black and plastic.
　　If the dispersion and stability of pigment carbon black fail to meet application requirements, it will directly affect the performance of plastic products. Common issues include:
　　(1) “Flocculation,” “reagglomeration,” and “aggregation” are common dispersion problems frequently encountered in pigment pastes. These issues arise from Brownian motion between carbon black pigment particles. Achieving ideal dispersion depends on advancements in dispersion equipment, the application of additives, and the use of other relevant technologies.
　　(2) Poor dispersion of the pigment paste leads to reduced blackness in plastic products, causing them to appear more brownish and with poor gloss. These issues can be addressed by intensifying the dispersion process; alternatively, they can be resolved by adjusting the amount of carbon black added; or by increasing the mixing time and improving the mixing conditions.
　　(3) The high viscosity of plastics is often associated with an excessive addition of carbon black. Moreover, a high addition level may cause the plastic to overheat. Excessive temperature can trigger adverse reactions in thermosensitive polymers, leading to system overheating and the formation of gel. It can also degrade the dispersion quality of pigment carbon black and compromise the stability of the system. Therefore, reducing the amount of carbon black added or maintaining an appropriately controlled temperature can help lower the likelihood of these issues occurring.
　　Carbon black pigment serves as a coloring agent, an ultraviolet-resistant aging inhibitor, and an antistatic agent for plastics. With the development of the plastics industry, the use of carbon black in plastics has been steadily increasing—from ordinary everyday plastic products to high-end engineering plastics—all of which rely on carbon black. Although the amount used is relatively small, carbon black significantly influences the performance of plastics. Consequently, the performance requirements for carbon black used in plastics have become increasingly stringent. Different plastic products intended for different applications have varying requirements for carbon black properties. To reduce the cost of plastics, the amount of carbon black used must be maximized as much as possible; however, the performance and type of grinding equipment will have a crucial impact on the dispersion of carbon black. Different plastics demand different levels of dispersion.
　　In many cases, insufficient performance of plastics can be directly attributed to inadequate dispersion of carbon black. For plastic products such as cable jackets and optical fibers, the level of carbon black dispersion must reach a much higher standard. For plastics with extremely high performance requirements, thorough dispersion of carbon black is crucial. If the dispersion level of pigment carbon black can be maximized, it will enable plastics to achieve superior specifications in terms of color, hue, viscosity, gloss, stability, and extrusion characteristics.

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