Carbon black pigments plastics applications

In the past decades, the rapidly expanding automobile industry has required increasing numbers of tires, black pigmented plastics and black paints with various characteristics. This has led not only to the development of new rubber grades, but also to the development of new carbon blacks required by refined application processes and to the development of a new and better manufacturing process, the furnace-black-process. This process allows the production of nearly all types of car-... 

U.S. consumption of carbon black in 1988 by various market sectors is shown in Table 6. About 90% of total consumption is in the mbber industry and 69% for tires. About 10% is consumed for other automotive products and 11% for rubber products unrelated to the automotive industry. The automotive industry accounts for 79% of consumption. Pigment applications account for about 10% of consumption, most of this for plastics and printing inks. Western Europe consumes 74% in tires and other automotive products and almost 20% in other industrial mbber products. Pigment applications in Western Europe and Japan are 5—6% of consumption. 

Besides their two main uses as reinforcing fillers and pigments, small amounts of carbon blacks are used by the electrical industry to manufacture dry cells, electrodes, and carbon brushes. Special blacks are used to give plastics antistatic or electrical conduction properties. Another application is the UV stabilization of polyolefins [4.31]. 

Conductivity in plastic coatings is achieved through the use of a conductive pigment, most often conductive carbon black. Conductivities of the order of 1 Mfl/cm2 are required for effective transfer efficiencies of subsequent topcoat applications. Without the use of a conductive primer, plastics in themselves would not be conductive, and hence would be very unreceptive to topcoat transfer efficiencies of greater than 20 percent. 

The term carbon black describes a group of industrial carbons created through the partial combustion or the thermal decomposition of hydrocarbons. Carbon black is unique in that it possesses the smallest particle size and highest oil absorption among the commercially available pigments for plastics. These characteristics help explain carbon black s excellent color strength, cost-effectiveness, and ultraviolet (UV) performance and place it as the most widely used black pigment for thermoplastic applications. 

The aim of this chapter is to provide an understanding of how carbon black particle size and shape translate into dispersion quality and other performance attributes in plastics applications. While this chapter focuses on carbon black s effectiveness as a pigment, some attention will also be paid to some of the other plastics performance properties it influences, such as stability against UV radiation, effects on mechanical properties, and electrical conductivity. At its conclusion, this chapter will help the reader select an appropriate carbon black grade for specific plastics applications. 

In addition to jetness, plastics pigmented with carbon blacks typically exhibit color undertones. Undertone in black plastics appears as a distinct blue or brown-to-orange undertone, depending on the particle size of the carbon black used. In general, in full-shade, black molded applications, fine-particle-size carbon blacks impart a bluer tone. This behavior reverses itself in tints. Large-particle-size carbon blacks impart bluer undertone. Note that the effects of fillers, polymers, and dispersion can alter the typical behavior described above. Tint strength is the relative ability of the carbon black to darken a resin colored with chromatic pigments. 

Freshly collected carbon black has an extremely low bulk density of 20-60 g To facilitate handling and further processing by the customer, it must be compacted. Densification by put gassing , a process by which the carbon black is conducted over porous, evacuated drums, is the weakest form of compacting which allows the carbon black to retain its powdery state [4.16]. This form of compacting is used for certain pigment blacks for the paint, ink and plastic applications in which good dispersibility must remain. 

Abrasion. Resistance to abrasion is adequate for many applications including footwear and can be improved hy addition of reinforcing pigments (hard clay, silicas, carbon blacks) and through use of added plastic materials such as polystyrene or polyolefins. Abrasion resistance is reduced by oils, seme resins and large-particle fillers. It is also improved with Increased molecular weight of the polymer (Table III). 

Carbon black is much more widely used in the rubber industry, which accounts for 93% of its sales, than in plasties. Special grades have nevertheless found a number of niche applications in the plastics industry, as a way to increase the electrical conductivity of plastics and promote electrostatic dissipation, as a black pigment, and as a way of improving weathering ability. 

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