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High Jetness Plastics: The “Secret” to Make Blacks Blacker

SpecialChem – Oct 9, 2019


High Jetness Plastics: The “Secret” to Make Blacks Blacker

Blacks are Getting Blacker

Color has long been used by marketing specialists to position their offering as a superior quality product to attract consumers and in some cases to charge a premium price. People tend to think of gray as having “50 shades” but most consider black to be just black. Product design specialists believe that people associate a deeper black with higher quality.

In this context, deep-black plastics have gained popularity in recent years. Plastic formulators are looking for ever-increasing jetness in their finished product. Deep black is becoming more prominent in the automotive industry. The ever-popular black exteriors are turning blacker.

  • Car interiors are also showing more jet-black components. In consumer electronics, brands are using deep-black exteriors to add value to their offerings.
  • Cell phones, tablets, laptops, other high-end portable devices and home appliances are turning a deeper shade of black.

The aim is to impart a look and feel that is consistent with the high-quality brand image. Deep-black plastics, with a smooth surface finish, are also being used to displace black surface coatings.

Carbon Black: The “Black” in Black

Most things black, around us, are likely to contain carbon black. Carbon black is a highly-engineered, microscopic form of carbon. It is present in our clothes, shoes, toys, wires, printing inks, rubber goods, tires and all types of black plastics. Besides imparting a black color, carbon black can enhance the performance of a product. It can be used to add electrical conductivity to materials and to protect products from environmental stresses such as degradation from ultraviolet radiation.

Car interiors are also showing more jet-black components

The black color in plastics is attributable to the presence of carbon black, thus the quest for a deeper black must begin with examining its role. Deeper blacks are said to have more “jetness”. Jetness is a complex function of:

  • Surface area
  • Structure, and
  • Degree of dispersion of carbon black

Therefore, choosing the right carbon black is of utmost importance in the production of high jetness, black plastics. Manufacturers must choose a carbon black specifically designed for use in high-value applications. A suitable carbon black has the properties and performance advantages to deliver higher jetness.

The “Secret” to Make Blacks Blacker

A balance must be struck between competing objectives in plastics formulation. Jetness, retention of mechanical properties and cost-effectiveness must be carefully balanced. For the formulation of a durable, jet-black plastic the following interrelated factors must be considered:

  • Particle size and structure
  • Surface area
  • UV stability / protection
  • Excellent dispersion and/or easy masterbatch dilutability
  • Superior surface smoothness
  • Physical and chemical cleanliness
  • Polymer compatibility

Particle Size and Structure

Particle-size is the fundamental property that affects the performance of carbon black. Smaller particles absorb more visible light which leads to greater jetness. Smaller particles also improve weatherability and increase conductivity.

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

Particle Size and Structure
Particle Size and Struture

Surface Area

Another important property, closely related to particle size, is the surface area. Smaller particles have higher surface area per unit mass of carbon black. Carbon blacks, with a higher surface area, require lower loading to achieve the desired jetness.

Higher surface area is also an indicator of the fineness of carbon black.

Finer carbon blacks generally cost more but require lower loading. The lower loading may offset the high cost, resulting in the most economical solution. Carbon black with higher surface area requires increased mixing energy for dispersion.

UV Stability / Protection

Plastic parts that endure long term exposure to sunlight can absorb ultraviolet (UV) radiation. UV radiation can cause color change, degradation of mechanical properties, and chalking. Carbon blacks absorb some of that UV radiation and dissipate that energy as heat, thereby helping to protect the polymer.

The addition of suitable UV-stabilizers can further increase polymer weatherability. UV resistance ensures that jetness is retained for a longer period under harsh conditions.

Ease of Dispersion or Easy Masterbatch Dilutability

Incomplete dispersion leads to the formation of micro-scale carbon black agglomerates. The presence of agglomerates means that the carbon black particles are not fully separated and the full-color potential has not been realized. Producers often increase the carbon black loading to compensate for this lack of color development. These agglomerates also act as inclusions which deteriorate the mechanical properties of the polymer system.

Select a carbon black with good dispersibility when compounding.
When using a masterbatch, ensure that it has good dilutability for uniform pigment dispersion.

Physical and Chemical Cleanliness

Using the right amount of carbon black and dispersing it well can all be undone if the carbon black contains a high level of physical impurities. Low levels of impurities are generally unavoidable in carbon blacks due to the presence of residue. The residue level, however, must be on the scale of a few parts per million (ppm). To achieve high jetness, ensure that the carbon black has a level of residue lower than 20 ppm (45 microns).

Dispersion is also impacted by the salts in carbon black. The aim should be to use low ash carbon blacks. Store the carbon black in a clean, dry and dust-free environment to avoid contamination.

Superior Surface Smoothness

Surface smoothness is closely related to both dispersion and physical cleanliness. The uniformly dispersed pigment shows a smooth surface finish which helps enhance the jet-black appearance of polymer products. Using carbon blacks with very low residue levels helps to prevent surface imperfections caused by the resulting inclusions.

Polymer Compatibility

Always ensure that the carbon black you choose is compatible with your polymer system. General grades work with all common polymers but may not deliver high performance in specific applications. Specialized grades deliver superior performance in such applications. Consult the manufacturer about the suitability of a grade to your formulation.

Incorporating Carbon Black into Polymers: Plastic Compounding or Masterbatches?

Appliances with High JetnessA typical plastic formulation consists of a thermoplastic polymer mixed with various additives. The choice of a polymer such as PC, PA, PE or ABS depends on the desired mechanical properties and end-usage. Additives enhance the physical and chemical properties of the base polymer. Commonly used additives include:

The additives impart specific physical and chemical properties to the plastic. Plastic compounding is the process of mixing the polymer, in molten state, with suitable additives and sufficient shear. The mixing occurs as the polymer is dosed through feeders and hoppers.

An alternate approach to plastic compounding is the use of masterbatches. A masterbatch is a concentrated mixture of pigments and additives incorporated into a carrier resin. The carrier resin is loaded with the pigment and additives in a heat process, then cooled and cut into granules. During use, the masterbatch is premixed with granules of the host polymer as it is fed into the machine. The final mixing is performed by the screw in the extrusion part of the machine.

Masterbatches allow plastic processors to color raw polymers economically and with greater uniformity. The plastic compounding process is prone to colorant clumping and inefficient dispersion. Masterbatches help the processors in dealing with these issues. The use of masterbatches also helps reduce inventory as fewer grades of polymer need to be stocked.

Choosing the Right Carbon Black for Your System

Carbon black must be evenly dispersed in the polymer to avoid the formation of inclusions. Inclusions can compromise the mechanical properties of the final product. The undispersed agglomerates may also cause pips on the surface reducing the gloss and jetness of the plastic.

Masterbatches are the best route to achieve an even dispersion. High energy mixing in a twin-screw mixer can help evenly disperse the masterbatch into the host polymer.

An alternate approach, which avoids high energy mixing, is the use of a carbon black with a more branched aggregate structure. A branched aggregate structure is identifiable by a high oil absorption number (OAN).

In direct compounding, the viscosity of the system is lower than that of a masterbatch system. In low viscosity systems, a higher-structure carbon black should be used for better dispersion.

There are many choices when it comes to selecting a carbon black. The key points presented above can help you achieve high jetness in deep-black polymers. You can reduce product development time by partnering with an experienced pigment manufacturer. Consult a development specialist to maximize your chances of success.

Birla Carbon’s Raven® High Jetness Carbon Blacks

Raven Carbon Black by Birla Carbon Today, thermoplastics is a very complex market. A fresh approach to product development is necessary to meet new processing challenges. Birla Carbon, a leading manufacturer of carbon blacks, has evolved a cooperative approach towards product development. They work in close collaboration with manufacturers to shorten the time from the laboratory to the finished product. The approach has been successfully demonstrated by developing customized products for various customers.

Carbon black’s physical properties determine its level of performance. Birla Carbon’s exacting standards help maintain key product properties. The size of particles and aggregates, purity and final product form are precisely controlled. These standards help produce products that meet strict colloidal specifications. Birla Carbon has designed specialty products to meet specific market requirements for high-performance polymers.

Birla Carbon’s high color Raven® blacks are designed for exceptional color and physical properties. These products offer high jetness, UV protection and viscosity control. Specialized solutions dramatically improve the function of carbon black in engineering plastics.

Birla Carbon’s most recent new product series for applications requiring very high jetness will be featured at the K Fair. These products are particularly designed keeping both color and processability in mind. Because of their unique combination of surface area and structure, they are easy to disperse and hence provide excellent jetness. With this Raven product series, OEMs can achieve the deep-black color and high gloss desired for their automotive, electronics and appliance applications.

Get in touch with an applications expert from Birla Carbon. Their expert advice can shorten the path to a solution for your specific challenge. 

Find out Birla Carbon's Carbon Blacks Product Range:

 »  Explore Carbon Black Technology Center by Birla Carbon!

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