Definition of carbon black:
Carbon black is a highly dispersed black powdery material produced by incomplete combustion of hydrocarbons (hydrocarbons). It is composed of carbon elements. Its microcrystals have quasi-graphite structure and concentric orientation. Its "particles" are composed of melts with nearly spherical or other irregular shapes.
Use of carbon black:
The use of pigmented carbon black in different industries is different, but the most important role is to play two roles, coloring and ultraviolet protection applications.
1. Pigmented carbon black is more advantageous in coloring
Pigmented carbon black can generally be better colored to plastics. Pigmented carbon black can be selected according to its coloring characteristics or physical and chemical properties. The selection of the types of carbon black for coloring is basically determined by the blackness of finished products. With very fine pigmented carbon black, it can finish the coloring with high blackness requirement.
PE garbage bags, plastic bags, cable materials and other products need only moderate blackness, can be used with low specific surface area, high structure carbon black varieties;
Small errors in carbon black weighing and proportioning will lead to obvious color difference when plastics are tinted. Therefore, it is advisable to use low-pigmented carbon black with larger particle size and poor coloring power, so that the amount of carbon black can be slightly larger, the weighing error is relatively small, and it has the advantages of better dispersion and lower price.
Compared with other organic pigments, carbon black has better properties except that it is difficult to disperse. The scientific amount of carbon black can provide better antistatic or conductivity. Pigment carbon black is basically non-toxic, so it is often used in the plastic industry in the form of color masterbatch, which can eliminate pollution and improve the dispersion of carbon black in plastics.
Application of ultraviolet protection
One of the applications of carbon black in plastic industry is anti-ultraviolet aging. Because carbon black has high absorbance, it can effectively prevent the photooxidation degradation of plastic caused by sunlight. As an ultraviolet stabilizer, carbon black plays an important role in plastics: converting light energy into heat energy; protecting the surface of plastics from certain wavelength of radiation; intercepting atomic clusters to produce anti-aging effect, thus preventing catalytic degradation. Ultraviolet radiation is particularly harmful to polyolefins. It has been proved that the perfect ultraviolet shielding effect can be achieved when the concentration of carbon black of certain fineness is 2%.
The protective effect of carbon black on ultraviolet aging of plastics depends on the particle size, structure and surface chemistry of carbon black.
When the particle size of carbon black is small, the protection of ultraviolet radiation is enhanced because of the increase of surface area and its ability to absorb or shade light. However, when the particle size is less than 20 nm, the protection of carbon black tends to the same level. The reason is that when the particle size is too small, the reverse scattering decreases, and the continued forward light will threaten the stability of polymer.
When the size of aggregates is small, the protective effect of aggregates on polymers will be enhanced because of their smaller geometrical volume, which is also the reason why the carbon black with lower structure is black.
There are more oxygen groups on the surface of carbon black, that is to say, when the volatility is high, the genes produced during polymer decomposition can be eliminated, so the protective effect is enhanced.