Common Plastic Injection Molding Materials and How They Are Colored

Color plays a crucial role in the design and functionality of plastic products. It enhances aesthetic appeal and brand identity, helping products stand out in the market and align with brand colors. Additionally, color serves functional purposes, such as color coding for safety and efficiency or providing UV protection to extend the lifespan of products exposed to sunlight.

Coloring Before the Injection Molding Process

Pre-colored Resins: Pre-colored resins are polymers that are mixed with pigments during the manufacturing process, resulting in a material that is already colored before it reaches the injection molding stage. This preparation involves integrating colorants into the polymer matrix to achieve a uniform and consistent color throughout the material. One of the key advantages of using pre-colored resins is that they eliminate the need for additional color mixing during molding, ensuring precise color matching and reducing the risk of color variation in high-volume production runs. This consistency makes pre-colored resins an ideal choice for applications where uniformity and reliability are critical.

Coloring During the Injection Molding Process

Masterbatch: Masterbatch, also known as color masterbatch or pigment preparation, is a specialized polymer material designed for coloring plastics. It is composed of three main components: pigments or dyes, carriers, and additives. The pigments, which can be organic (such as phthalocyanine red, phthalocyanine blue, and azo red) or inorganic (such as titanium dioxide and carbon black), are highly concentrated and uniformly distributed within a resin carrier. This creates a pigment concentration with superior coloring power compared to the pigment alone. During processing, a small amount of masterbatch is mixed with uncolored resin to achieve the desired color and pigment concentration in the finished product.

The carrier is usually made of the same resin as the product to ensure compatibility and flowability. A dispersant is added to help the pigments disperse evenly, preventing clumping. This dispersant should have a lower melting point than the resin and good compatibility with both the resin and the pigments. Common dispersants include low-molecular-weight polyethylene wax and stearates. While masterbatch typically doesn’t contain additional additives, unless specifically requested by clients, it can include functional agents like flame retardants, brighteners, antimicrobials, antistatic agents, and antioxidants, enhancing the properties of the final product.

Dry Pigments: Dry pigments are finely ground particles used to color plastics directly. While they offer a broad range of colors, using them can be challenging due to potential dispersion issues and the need for precise mixing techniques. Dry pigments are often used in specialty applications where unique colors or effects are required. Proper handling and processing are essential to achieve uniform color and avoid contamination.

Coloring After the Injection Molding Process

Painting and Coating: Painting and coating involve applying a layer of color or finish to molded parts to enhance their appearance and functionality. Techniques such as spray painting, dipping, and electroplating are commonly used to achieve additional color, complex patterns, and textures. These methods not only enhance aesthetics but also provide protective layers that can increase durability and resistance to environmental factors. By offering the ability to create intricate finishes, painting and coating allow manufacturers to produce visually appealing products that stand out in the market.