Plastic is pigmented by incorporating pigments, which are insoluble colorants, directly into the plastic material during the manufacturing process. This differs from dyes, which are soluble and work by dissolving into the plastic. The choice between dye and pigment depends on the type of plastic being used.
Types of Pigments Used in Plastics
Many different types of pigments are used to color plastics, offering a wide range of colors and properties. Some common examples include:
- Organic Pigments: These are carbon-based pigments, often offering bright, vibrant colors. However, they can be less resistant to fading from UV light compared to inorganic pigments.
- Inorganic Pigments: These pigments are derived from minerals and often provide better lightfastness and heat resistance. Examples include titanium dioxide (white), iron oxides (reds, yellows, browns), and carbon black (black).
The Pigmentation Process
The process of adding pigment to plastic typically occurs during the compounding or mixing stage. Pigments are carefully dispersed within the molten plastic resin using specialized equipment such as:
- High-shear mixers: These mixers create intense shearing forces that break down pigment agglomerates and promote even distribution throughout the plastic.
- Extruders: These machines melt and mix the plastic resin and pigments, creating a homogeneous mixture ready for further processing.
The amount of pigment added will affect the intensity of the final color. Precise control of pigment concentration is critical to achieve consistent and accurate color reproduction.
Choosing the Right Pigment
The selection of a pigment depends on several factors:
- Type of Plastic: Different plastics have varying compatibility with pigments. Some pigments may migrate or cause discoloration in certain plastics.
- Desired Color: The choice of pigment will, of course, depend on the final color required.
- Performance Requirements: Factors such as lightfastness, heat resistance, chemical resistance, and cost need to be considered.
Reference Integration: As noted in the provided reference, "Plastic colorants are chemical compounds used to color plastic. Those compounds come in a form of dyes and pigments. The type of a colorant is chosen based on the type of a polymeric resin, that needs to be colored. Dyes are usually used with polycarbonates, polystyrene and acrylic polymers." This highlights the importance of selecting the appropriate colorant (dye or pigment) based on the plastic resin. Pigments are the key component for coloring many types of plastic, as highlighted in the process descriptions above.
