Particle size carbon black pigments

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. 

Black pigments. Carbon blacks are organic pigments produced by partial combustion of petroleum products or natural gas. The particle size and intensity of blackness depends on the process and the raw materials used. For example, carbon black pigment prepared from vegetable oils or coal-tar distillates are inferior in color and opacity compared with the high carbon blacks prepared from the petroleum products or natural gas. 

The use of carbon black pigmentation/stabUization in thermoplastics for external exposure is widely applicable but has to be undertaken with care since it increases radiant heat absorption and hence the possibility of distortion. The type, particle size and degree of dispersion of the carbon are important for optimum efficacy. Additions in the order of 1-3% are generally sufficient for this purpose but in rubbers, where the carbon black also has a reinforcing function, considerably more is used. Other pigments have varying effects, an example being iron oxide which protects polyolefins yet catalyses the decomposition of PVC. 

Carbon black pigments include furnace black, lamp black, acetylene black and channel black. Carbon black has a primary particle size of 5 0 nm and a specific surface area of 40-600 m g (27). 

In general white pigments give better reflectance in the 300-400 nm region than coloured pigments. Metal powders are sometimes used but they can be active and act as randomly placed mirrors in the matrix. The most effective screener is Carbon Black and here the efficiency depends on the t)qje, concentration and particle size of the pigment. Various types include Furnace Black (17-70nm), Lamp Black (50-90 nm). Thermal Black (150-500 nm) and Acetylene Black (35-50 nm). 

Carbon black pigments are classified into six classes lamp black, furnace black, thermal black, acetylene black, channel black and gas black. They all differ in their typical properties such as particle size, jetness, undertone and surface chemistry. 

Black Pigments. The only black pigment used to an appreciable extent in inks is carbon black It is used in newsprinting, pubHcation, commercial and packaging printing therefore, in large quantities. Black pigments ate offered in fluffy or beaded forms and in a variety of particle sizes and physical properties. 

The aimual worldwide production of carbon blacks, which iaclude a large variety of carbonaceous products, was estimated to be around six million metric tons ia 1994. More than 90% of this pigment is consumed by the mbber iadustries, ia particular, by the tire iadustry as a reinforcing agent. The rest (- 500, 000 t) is used for coloring plastics, printing inks, and paints. Particle size of carbon blacks varies from 5 to 500 p.m and can be controlled by the process conditions and feedstock (see Carbon, carbon black). 

Carbon black (soot). It is obtained by the incomplete combustion of natural gas or liquid hydrocarbons. The particle size of carbon black is very small its applications are mainly in rubber industry (to strengthen and reinforce rubber) and also as a pigment in the preparation of inks, etc. 

Carbon black includes several forms of artificially prepared carbon, such as furnace black, channel black, lamp black, and animal charcoal. It is a finely divided form of carbon consisting of particles of extremely fine size. It is obtained by partial combustion (in 50% required air) of vapors of heavy oil fraction of crude oil in a furnace or by thermal cracking of natural gas. Carbon black is used in many abrasion-resistant rubber products including tire treads and belt covers. It also is used in typewriter ribbons, printing inks, carbon paper, and paint pigments. It also can be an absorber for solar energy and UV radiation. 

The top curve in Figure 8 applies to pigments with a high absorption index k and low refractive index rt (e.g., carbon black) and shows that the optimal particle size lies below a given limit. 

The light absorption coefficient of black pigments determines their optical quality. Their color intensity and hiding power depend on the particle size and particle size distribution. The most important black pigments are carbon blacks, iron oxides (Section 3.1.1), and mixed metal oxides (Section 3.1.3). 

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