1: Composition of Black Masterbatch
The materials used to compose black masterbatch include: A. Carbon black; B. Carbon black carrier; C. Carbon black wetting agent; D. Carbon black dispersing agent; E. Other processing aids.
2: Types of Carbon Black used in Black Masterbatch
According to international classification, there are more than 30 varieties in China, which are mainly divided into two categories: rubber use and non-rubber use. The main type of carbon black used in rubber is wear-resistant carbon black, which can effectively improve the wear resistance of rubber tires; for non-rubber use, only a few types of carbon black can truly serve as black masterbatch.
The channel process carbon black is the most widely used in plastics, mainly because of its abundant source, high purity, and small particle size. It can be further divided into high-pigment carbon black (particle size 9-17 mm), medium-pigment carbon black (particle size 18-25 mm), and low-pigment carbon black (particle size 26-37 mm).
Due to the different types of carbon black, there is a large difference in price. Carbon black particles rarely exist in their native particle form due to their inherent activity, and almost all exist as agglomerated particles with a certain range of particle sizes.
3: What is Carbon Black Carrier?
The carrier is the substance that carries the carbon black. Generally, the carrier material used is the same as the raw material used for plastic products. This creates a black masterbatch with good compatibility with the plastic raw material. For example, for PS (polystyrene) plastic products, the carrier for black masterbatch used is PS. For polyethylene plastic products, the carrier is polyethylene.
However, generally, LDPE (high-density polyethylene) is used as the carrier, as it has the strongest ability to carry carbon black and good processing performance. Other polyethylenes such as HDPE and LLDPE can only produce low-concentration black masterbatch. For PP (polypropylene) plastic products, only black masterbatch with PP and LDPE as carriers can be used, but not those with HDPE, LLDPE, or other plastics as carriers. Of course, there are also black masterbatches that use recycled materials as carriers.
4: Why does carbon black need a wetting agent?
Carbon black has a density of about 2g/cm and appears fluffy and lightweight due to its small particle size. To facilitate processing, carbon black must first be wetted. The choice of wetting agent is crucial. Many companies use products such as white oil or paraffin to reduce costs, but this can severely affect the strength of the processed products.
5: What dispersants are used for carbon black masterbatches?
Dispersants are mainly divided into two categories: organic and inorganic dispersants. High-end black masterbatches use organic dispersants, mainly for plastic products with high environmental requirements, such as drip irrigation products. Low-end black masterbatches use inorganic dispersants, commonly with calcium carbonate. You can judge from the packaging of the masterbatch. If only half a bag is used for 25 kg, it is definitely an inorganic dispersant; if the bag is full, it is a black masterbatch using an organic dispersant. The use of inorganic dispersants can greatly reduce the cost of black masterbatches, but calcium carbonate has a fatal effect on accelerating the aging of plastic products.
6: Does black masterbatch need processing aids?
Of course, it does. Smooth processing requires the correct selection of antioxidants, internal lubricants, external lubricants, modifiers, and antistatic agents.
7: What are the processing methods for black masterbatches?
There are three processing methods: single-screw method, twin-screw method, and intensive mixing method.
The single-screw method: After mixing the materials with a mixer, the single-screw extruder is used to pull the strip granules. Generally, the carbon black concentration is 18-20%. This is an outdated process with poor production site environmental conditions and has been eliminated, although some newly established small factories may still use this method for processing.
The twin-screw method: After mixing the materials with a mixer, the twin-screw extruder is used to pull the strip or underwater pelletize. Due to the limited mixing capacity of the twin-screw extruder itself, the carbon black concentration in the masterbatch is generally 25-32%.
The intensive mixing method: After mixing the materials with a mixer, they are kneaded in the intensive mixer, then fed into the twin-screw extruder by a feeder, and pelletized by underwater or underwater cutting. The carbon black concentration in the masterbatch is generally 40-45%.
8: Does the processing method affect the performance of the masterbatch?
Yes, it does. Among them, the compounding method can improve the carrier's ability to carry carbon black, and at the same time, carbon black can enter the carrier more uniformly. By taking advantage of the compounding machine's mechanical kneading advantage, the particles that have agglomerated are broken up, greatly reducing the agglomeration particle size of the carbon black particles in the masterbatch, and the particle diameter and distribution of the carbon black in the masterbatch are uniform, which cannot be replaced by the other two methods.
9: In which aspects should black masterbatches have outstanding performance?
In terms of coloring plastic products, black masterbatches only need 0.6%-0.8% to be extremely black, and adding more will not make it darker. According to experimental data, if products used outdoors in Xinjiang need to rely on black masterbatches for anti-aging, as long as high-quality black masterbatches are used (instead of recycled materials as carriers, white oil for wetting, calcium carbonate for dispersion, and other black masterbatches).
When the carbon black content in the product reaches 2-2.5%, that is, for every 100 kilograms of raw materials, there are 5-6 parts (by weight) of masterbatch containing 40% carbon black, its effect far exceeds any anti-aging product, and the product life can reach more than 10 years.
This is why drip irrigation products, water supply products, and communication cable products are all black. In addition, carbon black has special contributions to the increase in product strength and enhancement of conductivity.
10: It seems that not as many parts of black masterbatch are used in actual production?
That's right. In actual production, generally only about 2 parts of black masterbatch are used, and anti-aging agents are added to utilize the synergistic effect of anti-aging and carbon black to reduce product costs. In addition, the length of time the product is used outdoors and the required product life also determine the appropriate reduction in the amount of black masterbatch used, provided that the carbon black must form a continuous phase in the product, that is, the plastic is protected by a carbon black "film".
If too little black masterbatch is added, the carbon black phase (i.e., the part with high concentration of small pieces) is not continuous in the product. At the boundary between the phases, the plastic molecules are the most fragile and are directly hit by ultraviolet light, accelerating the oxidation reaction. At this time, carbon black in the product is like an impurity and is better off not being added. When the boundary between the phases is less than 280mm, it can avoid ultraviolet light damage and the product is safe.