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Manufacturers of transparent plastics know all too well that haze can present challenges in achieving the desired outcomes. Too much scattering of the transmitted light produces a cloudy appearance that impacts consumer quality perceptions of quality and buying decisions. As a result, upholding consistent quality requires sophisticated tools that accurately and scientifically quantify color and haze.

Spectrophotometers inspect these attributes objectively, providing numerical values to compare. These devices help eliminate product appearance variations so you can regularly and effectively meet consumer expectations for quality.

Choose the Right Color Spectrophotometer

Benchtop spectrophotometers are ideal for measuring color and ensuring uniformity in plastic products. To ensure consistency, manufacturers should measure points across the entire range of production.

Using a spectrophotometer to measure the color of transparent sheet plastic offers several benefits, such as:

• Accurate data: Spectrophotometers provide reliable color data that reflects its actual color.
• Repeatability: These instruments provide a repeatable way to measure color, minimizing errors and facilitating consistent color throughout production.
• Standard compliance: HunterLab's spectrophotometers follow industry standards for color measurement, ensuring consistency across the supply chain.

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.

The use of plastic bottles in liquid packaging first became popular in the 1950s and 1960s. Today, plastic's cost-effectiveness, durability and recyclability have made it the go-to material for bottles among most major companies. Throughout the manufacturing of these bottles, it is vital that processors maintain accurate coloration. Any product entering the sales market should be uniform and consistent, down to the label and the packaging. This level of precision calls for specialized tools — and HunterLab provides them.

The Power of Spectrophotometers 

When you need to measure the color of plastic bottles, spectrophotometers offer the most objective and precise results. A spectrophotometer measures how light reflects off the bottle and uses those measurements to produce a numerical value in line with some of the most well-known color indices. 

Spectrophotometers make it easy for any brand to streamline its coloration practices and increase product consistency. Their use can translate to major benefits in:

• Brand identity: Plastic bottles can be manufactured in almost any color, so many brands produce their bottles using a unique pigment combination to set them apart. Coloring bottles consistently allows you to establish your own look that consumers will begin to recognize over time, even before they see the label.

• Consumer satisfaction: Changes in any part of your product or its packaging — including a significant color departure — can signal to loyal consumers that your product has changed in some way. By keeping your colors consistent, you can put consumers at ease and ensure they stay with your brand instead of choosing a competitor. 

The Yellowness Index from ASTM International provides a measurable standard for assessing the yellowness in white or light-colored materials, such as plastics. This standard determines the degree of yellowness present, allowing companies to perform quality control processes to maintain product consistency. The test uses a spectrophotometer to quantify the color measurement.

The APHA color system is the most common measurement scale for measuring yellowness in liquids. It serves industries ranging from chemical production to pharmaceutical development.

Materials That Require Yellowness Observations

Various plastics require yellowness observations due to the changes these materials undergo in processing. These plastics include:

• Polyvinyl chloride (PVC)
• Polycarbonate (PC)
• Purified terephthalic acid (PTA)
• Polyethylene terephthalate (PET)

Yellowness appears in PET due to oxidation. With the increasing use of recycled PET (rPET), manufacturers must measure color to counter yellowness and determine the correct ratio of optical brighteners required to mitigate it.

What Is the Yellowness Index?

The Yellowness Index (YI) measures yellowness due to product changes. The ASTM E313 Yellowness Index is the most common method for determining yellowness in materials like plastics. The standard gives defined indices for measuring the shift from ideal white. It is calculated according to the following formula:

YI = (100CxX - CzZ)/Y

The X, Y, and Z variables are CIE Tristimulus values, which express color and how it is perceived. Cx and Cz depend on the illuminant and observer. During calculations, users choose the values for these coefficients from a table to correspond with spectrophotometer settings. The ASTM E313 combines the calculations into a single value, defining the yellowness amount in a sample. The lower the number, the less yellow the material is.

The YI value is commonly reported as the difference in yellowness between a product sample and the original or reference, designated as delta YI (∆YI).

Plastic bottles are the standard packaging for many products, from juice, soda, and condiments to laundry detergent. That means you need yours to stand out. Color can play a major role in differentiating your brand and increasing your products' appeal, especially when it's consistent. Here's what you need to know about measuring color in plastic bottles.

1. Consistent Color Builds Consumer Trust

Sight is one of the first senses we use when shopping. Color is essential in the decision-making process of potential buyers, even if they don't realize it. When you go to the store, you look for what's familiar to you. So do your customers. By creating and distributing a product with consistent coloration and packaging, you signal to everyone that you care about the appearance, presentation and effects of your offerings from one batch to the next.

2. Plastic Bottle Color Is Part of Your Brand Identity

When you create a color formula that's different enough from everyone else's, your plastic bottles can set your brand apart. Loyal customers will begin to associate that color with your name over time. If the color changes, many will wonder if what's inside the bottle is different, too.

At HunterLab, we've spent more than 70 years becoming experts in the field of color measurement and observing how product coloration affects consumer preferences. We've learned that color is vital in every aspect of product marketing, from the product itself to all its packaging. We've produced solutions that enable manufacturers to measure color accurately in many products, including plastic bottles. 

What Influences the Color of Plastic?

Plastic is known for its versatility. The material can be molded and colored in almost any way — and the color is baked into the plastic itself, so it has little chance of fading or changing once it's been cured. Still, some factors may change the way your plastic bottles look in stores, such as:

• Light: At its core, color measurement is about assessing how light interacts with an object to produce the color we perceive. Different types of light can make colors on the same object appear differently to the human eye.
• Opacity: Just as plastic can be made into any color, it can come in various opacities. From completely opaque to clear and transparent, differences in translucence will change the way your bottles' color is perceived.
• Gloss: Gloss is a measure of an object's reflectance, which more or less refers to how shiny something is. A glossier piece of plastic is more reflective, which affects the appearance of the color underneath.

A spectrophotometer is the best way to measure the color of opaque and transparent pellets. The color measurement solution enables you to maintain color consistency to meet industry standards and improve the pellets' appearance.

Measure Pellets With the Right Equipment

When measuring the color of opaque and transparent pellets, it is essential to utilize a spectrophotometer that considers opaqueness and transparency. Spectrophotometers that measure reflectance are well-suited for evaluating both opaque and transparent pellets.

Prepare Your Samples

A standard procedure needs to be implemented when preparing and presenting samples. Having procedures that everyone follows helps limit any inconsistencies between samples to ensure more accurate results. Consider developing a repeatable sample preparation method for repeated results.

Maintain Industry Standards When Measuring