1. Characteristics of carbon black
1. Blackness and particle size
The blackness is directly related to the particle size of carbon black. The smaller the particle size, the larger the specific surface area and the higher the blackness of carbon black. This is because although the primary particles have been fused into primary aggregates, their specific surface still works. If the primary particles are fine, the specific surface area of ​​the aggregates is larger. The displayed color is darker and has better UV protection. Since the fine particle carbon black has a higher light absorption rate than the coarse particle carbon black, the coloring power is stronger. However, when the particle size is reduced, since blue light is preferentially absorbed, the hue becomes brownish. The fine primary particles give carbon black a larger specific surface area, while increasing the difficulty of dispersion. Generally, surface treatment can adjust wettability and improve dispersion.
2. Structure
Carbon black particles not only exist in the form of primary particles, but also sinter into agglomerates during production. This aggregate is composed of primary particles through chemical bonding. In the process of coagulation, carbon black composed of a large number of branched primary aggregates is called high-structure carbon black. The carbon black composed of primary aggregates with fewer chain branches is called low-structure carbon black.
3. Surface chemistry
The production method of carbon black differs in its surface chemical properties. The carbon black surface has different oxygen-containing functional groups (such as carboxyl group, lactone group, phenol group, carbonyl group, etc.). Generally, carbon black with high oxygen-containing functional groups has high volatile content, good color tone adjustability, and high fluidity. After the carbon black sample is heated to 825 ± 25oC, the carbon black volatile content is expressed as a percentage weight loss. The more carbon black oxygen-containing genes, the greater the volatile content.
4. Hygroscopicity and density
Carbon black is a substance with a large surface area, so it has certain hygroscopicity. The moisture absorption of carbon black is mainly determined by the surface area. Measures can be strengthened, especially during packaging, storage and transportation to reduce the hygroscopicity of the product. Because the high moisture content (hygroscopicity) will cause trouble for the processing process, special packaging is required for certain varieties of carbon black. Powdered pigmented carbon black or granular pigmented carbon black used in a given plastic blend depends on the type of dispersion and the characteristics of the resin, but the processing ability is also an important factor. Most current dispersion equipment can exert shear force , Enough to disperse the particles evenly.
Second, the application of carbon black in the plastics industry
Prior to selection, its use must be determined, for example for coloring, UV protection, or electrical conductivity.
1. Carbon black for coloring
Pigment carbon black can generally color plastics better. Pigment carbon black can be selected according to the coloring characteristics or physical and chemical properties. The choice of coloring carbon black varieties is basically determined by the blackness that the finished product must achieve. Use extremely fine pigmented carbon black to achieve particularly high-blackness coloring; PE garbage bags, plastic bags, cable materials and other products need only medium-level blackness, and can use carbon black varieties with low specific surface area and high structure When plastics are toned, small errors in carbon black weighing and batching will cause significant color difference. Therefore, it is advisable to use low-pigment carbon blacks with larger particle sizes and poor coloring power, so that the amount of carbon black can be slightly Large, the weighing error is relatively small, and has the advantages of better dispersion and lower price. For gray plastics, the use of fine-grained carbon black tends to appear brownish gray, while the use of coarse-grained pigmented carbon black produces a blueish gray. Compared with other organic pigments, carbon black has better performance in addition to its difficulty in dispersion. The scientific blending amount of carbon black can provide better antistatic or electrical conductivity.
Carbon black is basically non-toxic, but it is relatively easy to fly and pollute, so it is often used in the form of masterbatch for the plastics industry, which eliminates pollution and improves the dispersion of carbon black in plastics. Carbon black is used as a pigment for plastics. The commonly used dosage forms are powder and granular. Granular carbon black is less flying, but it is more difficult to disperse, so powder carbon black is used in plastic coloring.
2. Application of UV protection
One of the uses of carbon black in the plastics industry is to prevent ultraviolet light aging. Because carbon black has high light absorption, it can effectively prevent plastics from being oxidized and degraded by sunlight. The role of carbon black as an ultraviolet light stabilizer in plastics is: converting light energy into heat energy; protecting the plastic surface from radiation of a certain wavelength; intercepting atomic groups to produce an anti-aging effect, thereby preventing catalytic degradation. Ultraviolet rays are particularly harmful to polyolefins. Tests have shown that when the concentration of carbon black with a certain fineness is 2%, perfect ultraviolet shielding can be achieved. The protective effect of carbon black on the 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, because of the increased surface area, its ability to absorb light or block light is increased, so the UV protection is enhanced, but the particle size is less than 20nm, and its protection tends to the same level, because the particle size is too small Scattering is reduced, and the light going forward threatens the stability of the polymer. The structure is lower, that is, when the aggregate size is smaller, the geometric volume of the aggregate is smaller, which will enhance the protection of the polymer. This is also the reason why the carbon black with a lower structure is darker. The surface of carbon black contains more oxygen groups, that is, when the volatile content is higher, it can eliminate the genes generated when the polymer is decomposed, so the protective effect is also enhanced.
3. Application of HunterLab color measuring instrument (coloring intensity measuring instrument) in carbon black
1. Influence of surface characteristics
When measuring color matching, gloss and surface flatness have the greatest influence on color difference. When light hits an uneven surface, it produces reflection, scattering and absorption on the surface. The rough surface has large scattering and less reflection and absorption, so the human eye's reaction gloss is low, while the high-gloss coating surface is flat, the reflection is large, and the scattering is small. The human eye is particularly sensitive to gloss and the gloss is high. From the economic considerations of actual production, we choose the matting agent with the appropriate particle size according to the application. It determines the amount of matting agent. Generally, the more matting agent is used, the lower the gloss. The HunterLab colorimeter (0o / 45o or 45o / 0 o) is particularly sensitive to black and white gloss. Taking high-pigment carbon black as an example, when the gloss drops from 20 to 10, the △ E will differ by about 1 (measured with 0o / 45 o similar to the human eye), while other brands of colorimeters measure the same blackboard, △ E The error is within 0.3. When the gloss of other colors changes within ± 1.0 degrees, △ E is generally within the allowable error range. Of course, the high temperature resistance of the pigment and the baking time and temperature in the production will also have a greater impact on △ E, which is a problem that needs to be particularly careful in actual production.
2. Desktop and portable equipment are available
Desktop colorimeter LabScan XE and the new portable colorimeter MiniScan EZ, they have their unique advantages, the test results remain consistent with the human eye, MiniScan EZ is lightweight, easy to carry, can directly measure and read data, can also be connected to a computer Output data. Especially in the production line or when communicating with customers, it can give full play to its advantage of portability.
Outdoor Misting Cooling System
High Pressure Misting System,Anti-drip Hose For Irrigation,Drip Irrigation Sprinkler,Garden Irrigation Sprinkler
ZHEJIANG HAOCHUAN RUBBER &PLASTIC CO.,LTD , https://www.zjhaochuan.com