Common Questions and Key Factors of Black Masterbatches

The materials that make up the black masterbatch are: A. carbon black; B. carbon black carrier; C. carbon black wetting agent; D. carbon black dispersant; E. other processing aids.

According to the international classification, there are more than 30 varieties in China, which are mainly divided into two categories: rubber and non-rubber.

Among the carbon blacks for rubber, it is mainly wear-resistant carbon black, which can effectively improve the wear resistance of rubber tires; among non-rubber carbon blacks, there are only a few kinds of carbon blacks that can really be used as black masterbatches.

The channel carbon black is the most widely used in plastics, mainly due to its rich source, high purity and small particle size. Among them, it is divided into high-pigment carbon black (particle size 9-17mm), medium-pigment carbon black (particle size 18-25mm) and low-pigment carbon black (particle size 26-37mm).

Due to the different varieties of carbon black, the price varies greatly. Due to its own multi-activity, carbon black particles rarely exist as primary particles, and almost all exist as agglomerated particles with a certain range of particle sizes.

The carrier is the substance that carries the carbon black. Generally, the raw material used in plastic products will be used as the carrier. The black masterbatch produced in this way has good compatibility with plastic raw materials.

For instance, PS (polystyrene) plastic products, the black masterbatch carrier used is PS. For polyethylene plastic products, the carrier is polyethylene. However, LDPE (high pressure polyethylene) is generally used because LDPE has the strongest carbon black bearing capacity and good processability.

While HDPE and LLDPE can only produce low concentration black masterbatch. For PP (polypropylene) plastic products, only black masterbatches with PP and LDPE as carriers can be used while HDPE, LLDPE and other plastics cannot be used as carriers, mainly considering the weak compatibility which will cause PP to become brittle. There are also black masterbatches with recycled materials as carriers.

EVA is generally chosen as general-purpose carriers, and other vinyl elastomers are chosen for more advanced carriers, with less odor.

The specific gravity of carbon black is about 2g/cm³. Due to the small particle size of carbon black, the apparent density is very small, which is fluffy and light. For smooth processing, the carbon black must first be wetted. The choice of wetting agent is critical.

In order to reduce costs, there are not a few companies that use a lot of products such as white oil or paraffin, which will seriously affect the strength of the processed products.

There are two types of organic dispersants and inorganic dispersants. High-grade black masterbatch uses organic dispersant, mainly used for plastic products with high environmental requirements, such as drip irrigation products.

Low-grade black masterbatches use inorganic dispersants, commonly calcium carbonate. It can be judged from the masterbatch packaging: using only half a bag of 25kg means inorganic dispersant; using a full bag means organic dispersant. The use of inorganic dispersants can greatly reduce the cost of black masterbatch, but it is fatal that calcium carbonate has the effect of accelerating the aging of plastic products.

In addition, calcium carbonate inhibits flame retardants to a certain extent. Therefore, black masterbatch containing calcium carbonate cannot be added to general flame retardant materials, such as flame retardant thermoplastic elastomers.

Yes. A smooth process requires the correct selection of antioxidants, internal lubricants, external lubricants, modifiers and antistatic agents etc.

There are three types: single screw method, twin screw method and kneader mixing method.

Single-screw method: After mixing the material with a mixer, it is granulated by a single-screw extruder. Generally, the concentration of carbon black is 18-20%. The process is out of date and the environmental conditions of the production site are poor. It is an eliminated process.

At present, some enterprises use the reciprocating single-screw mixing extruder. In this model, the screw rotates and moves back and forth at the same time, and there are pins on the barrel, so the effect of mixing and dispersing is very good.

Twin-screw method: After mixing the materials with a mixer, the twin-screw extruder is used to make strands or water rings for granulation. Due to the limited mixing capacity of the twin-screw machine itself, the concentration of carbon black in the masterbatch is generally 25-32%.

Kneader mixing method: After mixing the material with a kneader, it is fed into a twin-screw extruder from a feeder, and granulated through a water ring or underwater. The concentration of the masterbatch is generally 40-45%.

Yes. The kneader mixing method improves the carrying capacity of the carrier to the carbon black, and the carbon black can enter the carrier more uniformly.

In terms of dyeing plastic products, black masterbatch only needs 0.6%-0.8%, it will be extremely black, and it will not be darker even if you add more.

According to the test data, if the products used outdoors in Xinjiang need to rely on black masterbatch for anti-aging, they only need to use high-quality black masterbatch (not the kind that uses recycled materials as a carrier, white oil wetting, calcium carbonate dispersion, etc.) , the content of carbon black in the product reaches 2-2.5%, that is: in every 100 kg of raw materials, there are 5-6 parts (weight) of masterbatch containing 40% of carbon black, which plays a far more important role than any anti-aging product. , the product life can reach more than 10 years.

This is why drip irrigation products, water delivery products, and communication cable products are all black. Besides, carbon black has a special contribution to the increase of product strength and conductivity.

In actual production, about 2 parts of black masterbatch are generally used, and then anti-aging additives are added to reduce product cost by using the synergistic effect of anti-aging and carbon black to prevent aging.

For flame retardant modified plastics or thermoplastic elastomers, adding 2% of black masterbatch is usually not enough, and it is generally added to about 5%.

In addition, the life of outdoor use also determine the appropriate reduction of the amount of black masterbatch. The premise is that carbon black must form a continuous phase in the product, that is, there is a carbon black "film" to protect the plastics.

If too little black masterbatch is added, the carbon black phase (that is, the part with high concentration of small pieces) is discontinuous in the product. At the boundary between the phases, the plastic molecules are the most fragile, and are directly attacked by ultraviolet light to accelerate the oxygen aging reaction. In this case carbon black acts as an impurity in the product which worsen the quality.

Good quality black masterbatch has gloss and moderate hardness. An oily appearance means too much oil, and a dim appearance means that the carrier is recycled material or excessive calcium carbonate.

If it is chewed with teeth, "soft and brittle" stands for a good quality of  black masterbatch. Ultrasoft means too much organic dispersant; soft and loose means that the carbon black concentration is low and contains more calcium carbonate; too brittle means that the carbon black content is too high, or the carrier is recycled.

The protruding small tip indicates that the product processing equipment has limited ability to disperse the masterbatch, and the agglomerated particles of carbon black in the masterbatch cannot be uniformly sheared. The black masterbatch with a lower concentration should be used; or the masterbatch has too much calcium carbonate and too much white oil is extruded under high pressure by single-screw or twin-screw machines to form small rigid blocks that cannot be dispersed. If the surface is concave, it is caused by the volatilization of small molecular substances in the masterbatch, indicating that there is too much white oil.

To be comprehensive. First of all, if the fineness of calcium carbonate in the black masterbatch is 1000 meshes and the content is within 10%, it is a good choice for products without outdoor exposure, and the price is low. The appearance of the product has good gloss, the carbon black is evenly dispersed during processing, the blackness is not affected, and the impact on the strength of the product is small.

If the fineness of calcium carbonate is lower than 1000 mesh, the gloss may be dull, the surface may be rough, and the strength of the product will decrease. If the amount of 1000 mesh calcium carbonate exceeds 10%, the surface of the product will be dull and gray, the blackness will be insufficient, and the strength of the product will decrease.

Secondly, it is not good to contain calcium carbonate in any outdoor products that have anti-aging requirements, depending on the service life of the product, whether to use it or not. Finally, using this type of black masterbatch requires an equipment of high shear capacity.

The higher content of carbon black means that the dispersion is more difficult, and the requirements for the shearing capacity of the equipment are also increased. It is necessary to configure a screw with a large aspect ratio, a mixing section and a wear-resistant screw, which depends on the equipment.

For equipment with good mixing effect, using masterbatch with high concentration of carbon black, the added quantity is small, which saves money. For equipment with limited mixing capacity, the use of masterbatch with high carbon black concentration results in uneven dispersion and prominent pitting, resulting in a high rejection rate, which is not worth the loss. It is possible the production is not normal when using the masterbatch with 40% carbon black content, but after switching to 35%, the effect is very good.

This is related to the storage and processing of black masterbatch. The carbon black for plastics produced in China, regardless of high pigment, medium pigment or low pigment, has the problem of high oxygen content up to 3-8% as per relevant data reports. This directly affects the oxidative aging of the carrier during the processing and storage of the masterbatch. Once such aging occurs, it will directly lead to premature aging of the products using the masterbatch in the future. The oxidation induction period test fully proves this. In order to avoid and alleviate this phenomenon, adding an appropriate amount of anti-aging agent is the best choice to ensure the quality of black masterbatch.

For this kind of masterbatch, wear-resistance is the first. It has a certain anti-aging effect and poor dyeing ability. Its price is very cheap. The main point is that the equipment shoud be extremely wear-resistant.

Immediately after adding it into the equipment, the current increases, the torque increases, the plastic processing temperature is increased, the fluidity is still poor and the product is difficult to color.

Black masterbatches are produced using carbon black. The difficult-to-dispersion properties of carbon black is always a headache for color masterbatch manufacturers. The dispersion of high-load black masterbatches produced using single or twin screw extruders is very poor. When the end user mixes or molds these black masterbatches, it performs only slightly better than carbon black, but the results are just as unsatisfactory. To achieve a stable high dispersion, a high-quality shear mixer must be used to compound carbon blacks. With sufficient strength, mixers can fully mix the carbon black and base resin together. The type of carbon black used also affects dispersibility. The smaller the carbon black particles, the harder it is to disperse.

The second factor that determines the quality of black masterbatches is the covering power, and this factor is especially important for masterbatches used in scrap or recycled polymers, where the role of black is to cover other colors in the scrap material. Large particle carbon black has poor tinting ability and is not easy to cover all other colors in the lower layer. As a result, the final product only gets a deviated color. The ability to correctly select a carbon black with a high tinting power to cover the existing color during the melting process is the so-called covering power.

The third factor that determines the quality of black masterbatch is rheology and flow. If a color masterbatch itself has good dispersion, but it cannot flow into the material to be molded, the production effect is not ideal. In general, primer resins used to produce masterbatches have higher rheological properties. To save costs, some masterbatch producers use reusable materials, scrap or recycled materials as resin carriers. The flow properties of the masterbatches produced in this way will be significantly reduced, and if the rheology is not good, the mold will have trouble with cycle times and surface handling. It is worth noting that if the dispersion and rheology are not high, some end users will compensate by increasing the dilution ratio, but this approach will only increase the cost of using the masterbatch. Masterbatches with minimal dilution ratios produce uniform, well-dispersed blacks.

Compatibility is the fourth factor that determines the quality of black masterbatch. If the masterbatch is produced from chips or recycled material, it may contain contaminants or other non-meltable polymers. This can cause unforeseen, unmanageable troubles, wasting the end consumer's time and materials. At this time, primer resin can be used to produce high-quality color masterbatch, and the masterbatch has good compatibility during the melting process. High quality masterbatches can be produced using LLDPE, LDPE, HDPE, PP, PS, SAN, PA and other materials. Special polymeric masterbatches are available if engineering grades and stringent physical properties are specified. Several international large-scale color masterbatch manufacturers are conducting research to produce the so-called "global universal" color masterbatch. These masterbatches are widely compatible with other raw materials, have good rheology, and can be used flexibly.

One of the main manifestations of stability is a stable carbon black ratio. If the percentage of carbon black fluctuates, then the amount of masterbatch that needs to be melted is not the same, and it is impossible to produce the same shade of product. Some final producers have reported that the required dilution ratio usually varies by 5-8% during the production process, which is obviously unacceptable. Meanwhile, other factors such as the fluidity and dispersion of the injected melt should be consistent too.

The last factor that determines the quality of black masterbatch is the lightness and darkness of the color. There are various carbon black types on the market that can be used for coloring masterbatches, but the colors and prices of each type are also very different. Large particle carbon blacks have lower coloration and different undertones than small particle carbon blacks. Large particle masterbatches are suitable for applications such as waste bag film production, but are not suitable for production of products that focus on aesthetics, such as TV signs or where UV protection is required such as agricultural films or external pipes. For these products, only the more expensive small particle carbon blacks are used. In addition, low transparency is also a characteristic of small particle carbon blacks.