The color of the product can attract customers and give the product a different kind of added value. People distinguish gray into 50 levels. However, many people think that black is the darkest color. Such customers have put forward higher requirements for color matching personnel and masterbatch manufacturers of modification enterprises.

Deep black plastics have gained a reputation in recent years, and plastic formulators are looking for increasing levels of blackness in their end products. Deep blacks are becoming more prominent in the auto industry, especially as black interiors are getting darker.

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Car interiors tend to use darker components. In consumer electronics, brands are using deep black exteriors to add value to their products.

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Mobile phones, desktop computers, laptops, including other high-end wearables and home appliances are getting darker.

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The purpose of this is to give a visual and tactile look that is consistent with a high-quality brand image. Deep black plastic, with a smooth surface, was also used to replace the black finish.

Where did the black come from?

Carbon black: the black of the black

The black stuff around us most likely contains carbon black. Carbon black is a highly engineered microscopic form of carbon. It is found in our clothes, wires, printing inks, rubber products, tires and all types of black plastic. In addition to imparting black color, carbon black can improve product performance. It can be used to increase the conductivity of materials and protect products from environmental stresses such as degradation caused by UV light.

The black color in plastics can be attributed to the presence of carbon black, so calling for a deeper black requires understanding what it does. Deep blacks are said to have more blackness, a complex result of a number of factors:

• Surface area

•structure

• The degree of dispersion of carbon black

Therefore, choosing the correct carbon black is the most important for the production of black plastic with high blackness. Manufacturers must select a carbon black for a specific designed high-value application, and a suitable carbon black needs to deliver the properties and performance benefits of higher blackness.

The recipe method to make black darker

A balance must be maintained between the competing goals of plastic formulation. Blackness, mechanical properties and cost-effectiveness must be carefully balanced. For a durable black plastic formulation, the following interrelated factors must be considered:

• Particle size and structure

• Surface area

• UV stability/protection

• Good dispersibility and/or ease of masterbatch dilution

• Excellent surface smoothness

• Physical and chemical cleanability

• Polymer compatibility

1. Particle size and structure

Particle size is a fundamental property that affects carbon black performance. Smaller particles absorb more visible light, which in turn results in greater blackness. Smaller particles also improve weatherability and increase electrical conductivity.

On the other hand, small particles increase viscosity. A more highly branched agglomerate structure is relatively easier to disperse, but also results in higher viscosity.

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2. Surface area

Another important property, also closely related to particle size, is surface area. Smaller particles have a smaller surface area per unit of carbon black. If carbon black has a higher surface area, it can use lower additions to achieve the required blackness.

The higher surface area also means that the carbon black has a finer fineness, and finer carbon blacks generally cost more, however, the additions are also lower. Lower additions can offset higher costs, resulting in the most economical solution. Carbon blacks with high surface areas require the use of higher mixing energies for enhanced dispersion.

3. UV stability/protection

Plastic parts that endure long-term sun exposure can absorb ultraviolet (UV) radiation. UV radiation can cause color changes, mechanical degradation and chalking. Carbon black absorbs some UV radiation and dissipates it as heat, thereby helping to protect the polymer.

The addition of suitable UV stabilizers can further increase the weatherability of the polymer. UV resistance ensures that blackness can be maintained for longer in harsh conditions.

4. Easy to disperse or simple masterbatch dilution

Incomplete dispersion results in the formation of carbon black agglomerates on the micrometer scale. The presence of agglomerates means that the carbon black particles are not completely separated and the full coloring potential is not realized. Manufacturers often increase the amount of carbon black added to make up for the lack of color strength. These aggregates also act as entrapments that deteriorate the mechanical properties of the polymer system.

When blending, choose carbon black with good dispersibility. When using masterbatch, ensure good dilutability to achieve uniform pigment dispersion.

5. Physical and chemical purity

Using the correct amount of carbon black and dispersing it well is completely futile if the carbon black contains a lot of physical impurities. Low levels of impurities are unavoidable in carbon black due to the presence of residues in carbon black. However, residue levels must be controlled to a few ppm. In order to achieve high blackness, make sure that the residual concentration of carbon black is below 20ppm.

Dispersion is also affected by the salt in the carbon black. The goal is that low ash carbon black should be used. Store carbon black in a clean, dry and dust-free environment to avoid contamination.

6. Excellent surface flatness

Surface smoothness is closely related to both dispersibility and physical purity. Evenly dispersed pigments exhibit a smooth surface appearance which helps improve the black appearance of polymer products. Using carbon black with very low residues helps prevent surface defects caused by the resulting inclusions.

7. Polymer compatibility

Always make sure that the carbon black you choose is compatible with your polymer system. Common grades are compatible with all common polymers, but may not provide the high performance in specific applications. Specialty grades provide excellent performance in such applications. Consult the carbon black manufacturer about whether a certain grade is suitable for your formulation.

Carbon Black Addition: Direct Blend or Masterbatch?

Typical plastic formulations include thermoplastic polymers mixed with various additives. The choice of a polymer such as PC, PA, PE or ABS depends on the desired mechanical properties and end application. Additives improve the physical and chemical properties of the matrix resin. Commonly used additives include:

• Antioxidants

• UV-stabilizer

•pigment

Additives impart specific physical and chemical properties to plastics. Plastic blending is the process of mixing polymers with additives in the molten state and giving sufficient shear. Mixing occurs as the polymer is dosed through the feeder and hopper.

An alternative to plastic blending is to use masterbatches. A masterbatch is a concentrate of pigments and additives added to a carrier. The carrier resin is filled with pigments and additives during heating, then cooled and cut into pellets. In use, the masterbatch and matrix resin particles are premixed as they are fed into the extruder. Final mixing is carried out by the screw of the extruder.

Masterbatches allow plastic processors to economically color raw polymers with greater uniformity. Plastic blending processes are prone to colorant agglomeration and insufficient dispersion. Masterbatches help processors deal with these issues. The use of masterbatches also helps reduce inventory, as fewer grades of polymer need to be stored.

The right choice of carbon black

Carbon black must be uniformly dispersed in the polymer to avoid occlusion formation. Occlusions may sacrifice the mechanical properties of the final product. Undispersed agglomerates can also cause surface chalking, which reduces gloss and blackness of the plastic. Masterbatch is the best way to achieve uniform dispersion. High energy mixing in a twin screw extruder will help to uniformly disperse the masterbatch in the matrix polymer.

An alternative way to avoid high mixing is to use a carbon black with a more branched agglomerate structure. A branched agglomerate structure can be identified by the absorption number (OAN).

So our conclusion is:

In direct blending, the viscosity of the system is lower than that of the masterbatch system.

In low viscosity systems, higher structured carbon blacks should be used for better dispersion

When choosing carbon black, there are many options. The above key points may help to achieve high blackness in deep black polymers. You can reduce product development time by working with an experienced pigment manufacturer.