The main properties of carbon black

Chemical properties

The production process of carbon black is different, the chemical properties of the surface are also different. The true surface area of most carbon blacks is greater than the geometric surface area calculated from the particle size. This is due to the presence of many micropores on the surface of carbon black, especially carbon black with a particle size of less than 25nm.

According to analysis, groups such as phenolic, quinone, and carboxyl groups can be detected on the surface of carbon black. The concentration of these acidic groups is particularly high on the surface of gas black and furnace black. The pyrone structure can be detected in furnace black, which determines the basic nature of furnace black. Volatile content can judge the concentration of surface functional groups, and can also measure the polarity of carbon black. In addition, due to the large surface area of carbon black, it is easy to absorb moisture in the volatile environment, so special attention should be paid to moisture absorption during transportation, storage and use of carbon black.

Most of them are geometric studies that explore the contact of conductive particles. The theory believes that the greater the amount of carbon black, the greater the density of carbon black particles or aggregates of carbon black particles in a dispersed state, the smaller the average distance between the particles, and the higher the probability of mutual contact. The more conductive paths formed by the aggregates of black particles. The greater the polarity of the blend system composed of polymers of different polarities and carbon black, the greater the critical volume fraction of carbon black, which means that the conductivity of the system decreases, because the surface of carbon black contains strong polar groups. The polarity of the matrix is large, and the effect is enhanced. At this time, the strength increases, but it hinders the aggregation of the conductive particles themselves, resulting in poor conductivity. However, in a blend system composed of a multi-component matrix resin and carbon black, due to the different polarities of different matrixes, the filled carbon black will cause segregation. At this time, the conductivity depends on the concentration and distribution of the carbon black particles in the segregation phase. The state also depends on the proportion of the segregation phase polymer.

Blackness

Blackness refers to the intensity of black appearance that carbon black has. When carbon black is used for coloring, the blackness is mainly based on the absorption of light. For a specific concentration of carbon black, the finer the carbon black, the higher the degree of light absorption. In addition to the light absorption inside the carbon black, the blackness is also affected by light scattering with a brightening effect due to the geometric structure of the particle surface, which will reduce the blackness. As the particle size decreases, the degree of light scattering decreases. Only for very fine carbon black, increasing the concentration of carbon black can increase the blackness. For coarse carbon black, the degree of light scattering, which is the dominant factor, increases as the number of carbon black increases, but the blackness decreases accordingly.

Tinting intensity

Color strength can be understood as the effect of counteracting the whitening ability of white pigments. The color strength also increases with the decrease of the particle size and structure of the primary particles.

Tone

The degree of light scattering of "carbon black particles" decreases as the particle size decreases. In addition to affecting the brightness enhancement effect, it also affects the color tone. The reasons are as follows: 　When light can pass through a colored layer whose main color is black, short-wave The scattering effect of blue light is stronger than that of long-wave red light. The finer the carbon black, the more pronounced this effect. The red light component has a smaller loss due to scattering, so the depth into the colored layer is greater. The blue light is scattered strongly overall, and the scattering in the opposite direction, that is, behind is also strong, so it is reflected from the colored layer again. When observing the reflection process, the bluish tint colored by fine carbon black will give people the feeling of higher blackness. If the carbon black is coarse, it will show a brown hue accordingly. When observing the transmission process, the hue relationship of the same colored layer (incompletely transparent film) is just the opposite. As the particle size decreases, the blue light with strong scattering will pass through the colored layer to a smaller depth, that is, the blue light will pass through the colored layer. From the layer to the other side, the composition is less, and it comes out from the other side. Therefore, due to the lack of blue light component on the side of observation, the colored layer exhibits a brown hue when observed during transmission. When using titanium dioxide to adjust the gray (gray hue), the situation is similar to observing the coloring of the main color during transmission. The light is scattered back and forth in the white pigment in the plastic sheet containing the black pigment. The smaller the particle size of carbon black, It will make the blue light scatter stronger in the visible light, so more of the rest of the red light will be transmitted through, showing a yellowish gray. On the contrary, when coloring, use coarse-grained carbon black, especially for larger lamps. Black, you get a bluish shade of gray.

Dispersion

The finer the pigment black, the more contact points between the carbon black aggregates, and as a result, the stronger the cohesion between them. When the pigment black is mixed into the material, the uniform distribution of the initial carbon black starts, the work to be done for the dispersion It will be large to separate the carbon black particles and finally achieve the highest blackness and coloration. Compared with high-structure carbon black, low-structure carbon black is more likely to reach a high concentration, but it requires greater dispersing power during the dispersion process. The dispersibility of carbon black is affected by the degree of structure. Because high-structure carbon black has good dispersibility, its color strength is naturally stronger.

When powdered carbon black is used, there will be a problem of dispersion and headaches. Therefore, masterbatch or slurry can be used.

The price of prefabricated carbon black is higher than that of pure pigment black. However, if the advantages of clean process, high efficiency and low technical investment are taken into account, carbon black preparations have their value.

Light stability

Light will aging plastics, especially the ultraviolet rays in the sun will accelerate the aging of plastics. The use of organic UV absorbers and antioxidants can extend the life. However, pigment black is still considered the best UV stabilizer.

As an ultraviolet light absorber, pigment black is mainly used to extend the outdoor service life of plastic products.

The small particle size carbon black (20 nm) with a concentration of 0.5% has almost the same photoprotection effect as the 2% relatively coarse particle size carbon black (95 nm).

Food contact

All coloring pigments related to daily necessities stipulated by the Food Sanitation Law, including pigments, must meet the specified purity standards. First of all, these standards stipulate the content of heavy metals in general pigments, the solubility of its components in 0.1N hydrochloric acid (the same as the acidity of gastric juice), and the content of aromatic ammonia. Then, a special purity standard for carbon black was formulated, and this standard differs from country to country.