High jetness in paints and coatings

Jet black and carbon black are both black colors, but they have different origins, uses, and appearances.
 

Jetness is often measured using light microscopy to assess macro-dispersion. Assessing micro-dispersion, however, is not quite as straightforward via electron microscopy. Fortunately, we can use color as an indirect measure. When developing a mixing protocol or new formulation, we can characterize dispersion by measuring:
 

• jetness,
• blue tone, and
• gloss of injection molded parts

Tint strength is also a good indicator of the hiding power that the pigment is delivering under a given set of processing conditions. Specific measurements, such as the Mc value can be used to assess the jetness of a black pigment or coating. As the undertone of a black color has an impact on the visual assessment, the hue-dependent degree of blackness is calculated as follows¹:
 

Here, Mc = hue-dependent degree of blackness

 

High jetness vs. low jetness

The difference lies in the depth and quality of the black color.
 

• High jetness: Describes a deep, rich black.
• Low jetness: Indicates a less intense, possibly grayish or brownish-black.
  
   

Jetness vs. color depth
 

• Jetness: It is a subset of color depth, specifically focused on the richness of black.
• Color depth: This is a broader term that can apply to any color, describing its intensity or saturation.
  
   

Jetness vs. gloss

Both properties contribute to the overall appearance, but they are distinct.
 

• Jetness: It refers to the perceived depth and quality of a black color. It is characterized by its richness, intensity, and often, a bluish undertone.
• Gloss: It is an optical property that is defined as the ability of a surface to reflect light in a specular direction as described in Figure 1. A high-gloss finish reflects light more intensely, while a low-gloss finish appears more matte or dull. If the gloss trap remains closed all the reflected and scattered light would be part of the detected light. Therefore, the jetness measured in this case would be lower.
   

Figure 1: Diffuse and Specular Reflections of Light on Plane Surfaces²

Jetness vs. coverage

• Jetness: It is concerned with the color's appearance.
• Coverage: It refers to a paint's ability to hide or obscure the underlying surface. A high-coverage paint requires fewer coats to achieve a uniform color.
  
   

High jetness paint vs. matte finishes

• High jetness paint: A high-jetness paint can be either glossy or matte, depending on its formulation.
• Matte finishes: They have a low-gloss appearance, reducing reflectivity.
  
   

High jetness paint vs. opacity

• High jetness: It relates to the depth and quality of black.
• Opacity: It refers to a paint's ability to block light from passing through.

Several factors can influence the jetness of a black pigment or coating. Some of the factors are summarized here.

 

Pigment selection

For thermoplastic products, carbon black is a popular choice for achieving deep, jet-black colors. Smaller carbon black particles offer excellent color intensity while maintaining cost-effectiveness.

The oil adsorption number (OAN) indicates the carbon black's structural complexity. A higher OAN suggests easier dispersion, leading to improved color performance. However, fully realizing the color potential of carbon black, especially finer grades, can be challenging in demanding applications.

It is crucial to ensure the carbon black is thoroughly dispersed within the thermoplastic matrix. This optimizes color performance and other properties like surface finish, UV protection, and gloss. This micro-dispersion requires complete de-agglomeration and uniform distribution of the carbon black particles (as illustrated in Figure 2).
 

Figure 2: Carbon Black Dispersion in Polymer Matrix³

Agglomeration and color development

When carbon black aggregates are not fully separated (Figure 3a), it indicates a high degree of agglomeration and limits the realization of the full-color potential. As we move from left to right, an increase in the aggregate population (as individual entities) leads to improved micro-dispersion. This is crucial for achieving full-color development (jetness and blue tone).

While particle size is the primary driver of color development, structure plays a secondary role. High jetness applications require carbon black with a small particle size or high surface area. However, high surface area carbon blacks are inherently more difficult to disperse compared to those with medium or lower surface areas.

Figure 3 demonstrates the correlation between jetness (a), blue tone (b), and surface area. As anticipated, finer carbon blacks deliver deeper jetness and a bluer undertone. These relationships are observed across various resin systems, including SAN, PP, PC, PA, and ABS. Therefore, understanding the challenges associated with dispersing and processing these materials is essential for maximizing color performance, which will be explored in the following sections.
 

Figure 3: Higher Surface Area Carbon Blacks Deliver Jetter Color and a Bluer Undertone (Shaded Area Shows Color Performance of High Color and Piano Blacks)⁴

Dispersion process

The high surface area of carbon blacks used for high jetness applications makes achieving effective dispersion challenging. The mixing process involves several variables that must be optimized, including:
 

• screw speed,
• throughput, and
• equipment type

Increasing screw speed promotes carbon black dispersion, while higher throughput can hinder it. The choice of equipment varies, with twin screw extruders offering versatility due to their unique screw configuration and modular design. For highly loaded masterbatch systems, Farrell Continuous Mixers (FCMs) are efficient and produce high-quality masterbatch materials.

A well-dispersed carbon black requires good dispersion at both the macro and micro levels.
 

• Macro-dispersion is visible and crucial for surface finish aesthetics.
• Micro-dispersion is essential for optimal color performance. For a specific carbon black and resin/polymer combination, enhancing micro-dispersion leads to increased blackness. Complete micro-dispersion involves both distributive and dispersive dispersion, which means full deagglomeration down to the aggregate level.

Aggregates are the fundamental units of carbon black, as illustrated in the accompanying micrograph. Good dispersion is attributed to concurrent distribution and dispersive mixing (Figure 4).
 

Figure 4: Conceptual Mixing Process³

Dispersion and compounding

Achieving full dispersion in a polymer matrix requires both time and energy. A specific time/energy ratio must be determined for each product. This helps to balance production efficiency with performance.

Twin screw extruders, continuous mixers, and kneaders are widely used in the coatings and plastics industry for compounding carbon black.
 

• Twin screw extruders often dominate plastic compounding due to their well-established technology, scalability, and adaptable design. This accommodates various resin chemistries and formulations.
• Farrell Continuous Mixers (FCMs) are efficient and produce high-quality masterbatch materials due to their counter-rotating non-intermeshing rotors, large free-volume chamber, and internal temperature control. This is for highly loaded masterbatch and temperature-sensitive resin systems.
• Kneaders, such as those manufactured by Buss, utilize simultaneous rotation and axial oscillation of the screw shaft. This creates a homogeneous shear field for mixing.

To achieve optimal compounding results, process variables like screw and barrel profiles, feeding configurations, residence time, temperature profiles, and throughput must be understood and adjusted for each machine and compound system combination.

 

Formulation

Masterbatch compounding is an effective method for improving carbon black dispersion and achieving the desired color performance. This approach complements proper resin selection and optimal carbon black loading. Generally, increasing carbon black loading raises masterbatch viscosity, subjecting carbon black agglomerates to greater shear forces. Incorporating specialized additives compatible with carbon black can further enhance wettability and dispersion.

 

Base color

The underlying color of the substrate can influence the perceived jetness of the black coating. A lighter base color can enhance the contrast and make the black appear deeper.

 

Film thickness
 

The thickness of the coating can affect its opacity and the overall perception of the black color. A thicker film can provide a more intense black.

 

The application technique can influence the perceived jetness of paint. Proper application ensures that the pigment is evenly distributed, and the desired color depth is achieved. Here are some common techniques:
 

• Spray application: Often used for large surfaces due to its efficiency and ability to achieve a smooth, even finish.
• Roller application: Suitable for smaller areas and can provide a textured finish if desired.
• Brush application: Ideal for detailed work and can achieve a more traditional or handcrafted look.
  
   

Market applications of high jetness paints & coatings

High jetness paints are primarily used in applications where a deep, rich black color is desired. Here are some common applications:
 

• Automotive coatings: Used for exterior and interior components, such as the body, trim, and wheels.
• Consumer electronics: Applied to smartphones, tablets, laptops, and other devices to enhance their aesthetic appeal.
• Industrial coatings: Used in various industries, including aerospace, construction, and packaging, for components requiring a deep black finish.
• Luxury goods: Applied to high-end products like watches, jewelry, and furniture to add a touch of sophistication.

Select commercial carbon black grades available in our database for various coatings market applications:

 

Techniques for incorporating high jetness pigments in paints & coatings

High jetness pigments, primarily carbon black, are essential for achieving deep black colors. The specific type of carbon black, its particle size, and its surface properties can significantly impact the resulting jetness.

High jetness pigments are typically incorporated into coatings through the following processes:

 

• Dispersion: The pigment is dispersed in a liquid medium to create a uniform suspension.
• Mixing: The pigment dispersion is mixed with other components of the coating, such as binders, solvents, and additives.
• Application: The formulated coating is applied to the desired surface using appropriate techniques (e.g., spraying, rolling, brushing).
• Curing: The coating is allowed to dry and cure, forming a solid film with the desired jetness.