Plastics : Detailed explanation of color in plastics

Basic methods of coloring plastics:

Color carriers:

• Masterbatch (concentrated color pellets)
• Liquid color
• Pre-colored compounds
• Direct powder pigments

A masterbatch is a concentrated mixture of pigments, additives, or other ingredients that are encapsulated in a carrier resin. It's used to color or modify the properties of plastics during manufacturing, allowing for more precise and efficient processing compared to using raw pigments or additives directly.

Direct powder pigments are pure, raw colorants in powder form that are added directly to materials like plastics, paints, or inks without any carrier system or pre-dispersion. They are the basic coloring materials in their natural state before being processed into other forms like masterbatches.

Timing of color adding: 

• During molding/extrusion
• During compounding
• During raw material production

Compounding is the process of mixing and melting different plastic materials and additives together to create a new plastic material with specific properties. It combines base resins with additives, colorants, or other materials to enhance or modify the final plastic's characteristics.

Types of colorants:

Pigments (Solid particles):

• Don't dissolve in plastic
• More heat stable
• Better opacity

Examples:

• Titanium dioxide (white)
• Carbon black
• Iron oxide (reds/browns)
• Ultramarine blue

Dyes (Dissolve in plastic):

• Dissolve completely
• Better clarity
• Brighter colors
• Less heat stable

Common issues:

Processing problems:

• Uneven color distribution
• Color streaking
• Specks and spots
• Burning/degradation
• Color shifting

Color streaking is a manufacturing defect where uneven lines or bands of color appear in a plastic product, caused by poor dispersion or mixing of colorants in the material. It looks like unwanted stripes or swirls in the finished product.

Color shifting is when the color of a plastic product appears to change or vary under different viewing angles or lighting conditions, often occurring as an unintended defect during manufacturing due to inconsistent mixing, improper processing temperatures, or material stress.

Quality Issues:

• Batch-to-batch variation
• Weather resistance
• Light fastness
• Migration/bleeding

Important factors:

Processing temperature:

• Different colors need different temperatures
• Some pigments affect processing
• Heat history matters
• Degradation risks

Material compatibility:

• Not all colorants work in all plastics
• Different loading levels needed
• Chemical compatibility
• Processing effects

Color testing:

Visual Methods:

• Color comparison
• Light box viewing
• Visual standards
• Defect inspection

Technical Methods:

• Spectrophotometer testing
• Color measurement
• Opacity testing
• Dispersion testing

A spectrophotometer is a device that measures how materials reflect or absorb light across different wavelengths. In quality control, it's used to precisely measure and verify colors to ensure consistency and accuracy in manufacturing.

Dispersion testing evaluates how well colorants (like pigments) are distributed throughout a material. It checks if the color particles are broken down and spread evenly in the plastic, with no clumps or uneven areas.

Special Considerations:

Food Contact:

• FDA approved colorants
• Migration testing
• Safe pigments
• Regular testing

Outdoor Use:

• UV stability
• Weather resistance
• Color fastness
• Heat stability

Cost Factors:

Material Costs:

• Pigment/dye prices
• Loading levels
• Waste rates
• Quality needs

Pigments are insoluble color particles that remain intact in the material they color. 

Dyes, on the other hand, are soluble colorants that dissolve into the material they color.

Processing Costs:

• Setup time
• Cleaning time
• Scrap rates
• Quality control

Common Applications:

Consumer Products:

• Brand colors
• Aesthetic appeal
• Durability needs
• Cost constraints

Industrial applications:

• Color coding
• UV protection
• Heat management
• Identification

Packaging:

• Brand identity
• Product protection
• Consumer appeal
• Regulatory compliance