Guide to Overcoming Color Challenges in Plastic Manufacturing

Plastic manufacturing has grown significantly since the 1950s, surpassing that of any other material. Today, plastics see use in markets ranging from automotive to goods packaging to food and beverage production. Plastic color is and will continue to be pivotal as the primary determinant by which consumers judge product quality and desirability, yet accurately quantifying it comes with unique challenges.

Common Challenges in Plastic Color Measurement

Typical plastic color measurement challenges include the following.

Natural Yellowing

Virgin plastic resins naturally yellow during processing as a result of oxidation. Additional yellowing can occur with age or exposure to ultraviolet rays. To achieve clear or almost clear end products, manufacturers must add optical brighteners that fluoresce on the blue side of the visible spectrum to negate the yellowness. That translates into almost all plastic goods containing at least some percentage of optical brighteners. As a result, these materials inherently fluoresce and introduce more complexity to achieving the desired clarity and visual chromatic qualities.

Regulatory Pressures

Government entities worldwide are passing ever-stricter regulations on the percentage of post-consumer recycled plastic that must be used in new plastic production to prioritize a more circular economy. An increase in the amount of recycled plastic used causes a corresponding rise in the amount of optical brighteners and other additives in feedstock that manufacturers must adjust for.

These challenges make accurate color measurements even more pivotal since one variation in the input can substantially impact the outcomes.

ESG Initiatives

In addition to governmental action, modern plastics manufacturers are feeling similar pressures from their stakeholders. Consumers, employees, and investors alike increasingly call for more sustainable practices and transparency in environmental impact.

To account for these pressures, many companies enact Environmental, Social, and Governance (ESG) initiatives that help achieve the six principles of a more circular economy. These pillars include minimizing waste, maximizing resources, saving energy, and reducing carbon footprint.

How to Resolve Color Measurement Challenges in Plastics

Fortunately, there are several steps you can take to resolve color measurement challenges with plastics production.

1. Conform to Standards

Knowing whether your color and spectral data fall within acceptable tolerances starts with quantifying the results you want. Best practices for establishing desirable color and spectral data include defining your color standards and conforming to established globally accepted testing methodologies.

Color scales, scores, and indices are an objective, scientific tool for communicating color through numeric expressions. These values serve as a shared language for determining the precise color of a raw material or end product. Common color scales, scores, and indices in the plastics industry include:

• Yellowness Index (YI)
• CIE Y
• Hunter L, a, b
• CIE L*, a*, b*
• ASTM E313 Whitness/Yellowness
• ISO 11475 Whiteness Index
• ISO 17223 Yellowness Index

Conforming to global standards is also essential to ensuring consistent measurement approaches and results integrity. For example, measuring the color of plastic pellets involves following the ASTM D6290-19 standards for testing methodology. Part of this framework encourages measuring large sample areas for higher accuracy and greater repeatability. Both help support manufacturers in achieving desired color outcomes while reducing waste and complying with regulations.

2. Measure Regularly

One primary way to overcome color measurement challenges in plastics is to implement frequent measuring. Capturing data at each production stage yields actionable insights about which practices and processes may be altering colors. 

For example, clarity is essential for those manufacturing transparent plastics. Measuring raw plastic pellets helps manufacturers understand how much yellowness exists in their feedstock so they have a scientific basis for the amount of optical brighteners they need to add for transparency. Getting the blend right at the first process step lessens the potential for rework and scrap, supporting ESG goals of reducing waste and maximizing resources.

Similarly, plastic production often involves the inclusion of other chemicals, like plastic colorants, flow additives, and heat additives. Precision dosing of these expensive additives is crucial since too little can influence performance, too much increases costs, and both can impact color. Manufacturers can quantify chromatic data as production processes occur to identify where discrepancies arise. That enables faster resolution to limit the scope of any issues, reducing defective products and excess energy consumption that leads to higher carbon footprints.

Consistent color measurement satisfies four of the six cornerstones of a plastics circular economy, empowering companies with more confidence in their ESG programs. It also helps support compliance with government mandates by enabling manufacturers to achieve repeatable results with recycled resins and blends.

3. Use the Most Accurate Color Measurement Solution

Spectrophotometers are the answer to accuracy, repeatability, and consistency in quantifying plastic color and spectral data. These solutions measure transmittance and reflectance light to allow comparison against your tolerances and industry-recognized scales and indices. This comparison enables manufacturers to control color quality across production lines, manufacturing facilities, masterbatches, and suppliers for enhanced compliance, waste reduction, and stakeholder reporting and accountability.

Many styles are available to meet diverse needs and enhance efficiency, including handheld and benchtop spectrophotometers.

A portable unit empowers you to measure color in the field. These lightweight devices are ideal for capturing data directly on the production floor or in a supplier's facility to ensure conformance with tolerances. For example, the MiniScan EZ 4500L from HunterLab offers exceptional convenience, generous storage, and an unrivaled device agreement for consistency.

Benchtop models enable accurate measurement for quality assurance at every color workflow. Capture data in just seconds on opaque, nonuniform surfaces like safety cones with a spectrophotometer like ColorFlex L2. This option delivers objective spectral and color information to document tolerance conformance or quantify differences so you can better investigate their root cause.

The compact Agera is perfect for those who use recycled plastic pellets as a raw material since it contains UV-controllable LED illumination. Measure pellet color for consistency when developing masterbatches to mitigate the risk of color variations while supporting regulatory compliance, quality, repeatability, and ESG goals.

UltraScan PRO offers both transmittance and reflectance measurements and provides a spectral range of 350 nanometers to 1,050 nanometers — the full CIE visible range plus near infrared (NIR). This equipment can simultaneously measure haze for improved efficiency and drive value in applications like ophthalmic lens manufacturing, where clarity and color are paramount for visibility.

Trust HunterLab for Plastic Color Measurement Solutions

HunterLab has been synonymous with the plastic industry's most dependable and accurate color measurement solutions for more than seven decades. Over the past 70-plus years, we've brought manufacturers color spectrophotometers they can trust for their quality assurance and color consistency needs. Our devices offer exceptional inter-instrument agreement and more built-in features and value than any others available, making them the first choice of quality labs for today's best brands.

Request a quote on your preferred option or talk with our team to find the best solution for your application.