The Complete Guide to Transparent Plastic Preform Color Measurement

Transparent plastic preforms are essential for companies that manufacture goods like beverages, edible oils, and intermediate chemicals like alcohols and glycols to form the container for the end product. The color of these preforms is equally vital, helping determine the final product's appearance and its impact on consumers' acceptance, buying decisions, and perceptions of quality. 

Beyond influencing your customers, color consistency keeps manufacturing costs under control, since alterations can lead to waste. All cement the importance of color measurement at every stage of production to uphold quality assurance (QA) throughout the supply chain, from raw materials to finished goods.

The Challenges With Color Consistency in Transparent Plastic Preforms

Multiple factors can impact the appearance of transparent plastic preforms, from raw material variations to processing conditions and physical characteristics. All present specific challenges to overcome to achieve consistency and the desired appearance.

Variability in Raw Materials

Variability in raw materials is a frequent challenge for every plastics manufacturer, as well as producers who rely on plastic preforms.

Global regulatory bodies and consumers are embracing sustainability, leading to higher demand for the inclusion of more recycled polyethylene terephthalate (rPET). With this rising expectation comes new challenges, since rPET often contains high amounts of optical brightening agents (OBAs) to overcome yellowing. Every delivery of raw materials typically differs in that composition, making color measurement crucial to managing rPET variations successfully. Quantifying color at this stage empowers scientific, objective, and data-driven decisions to uphold aesthetics, quality, and performance.

Other challenges include variations in the amount and type of additives and pigments that can influence the final color. Additionally, contaminants like dust or residual color from previous runs may lead to alterations in appearance or clarity.

Physical Preform Properties

Transparent plastic preforms naturally present measurement challenges due to their physical properties.

Preform shapes and specifications represent the first difficulty. Contoured surfaces and variations in thickness inherently impact cooling rates, which can lead to alterations in color consistency. Inaccurate sample presentation can further influence measurement accuracy.

Additionally, transparent plastic preforms are susceptible to haze that affects color perception. This cloudy appearance is often caused by microparticles embedded within the plastic, which causes light to scatter when it interacts with the sample.

How Spectrophotometry Addresses the Challenges

Spectrophotometry is the most accurate and objective way to quantify color in transparent plastic preforms. Top-rated spectrophotometers solve the issues of manual visual evaluations — observer fatigue, error-prone assessments, and variabilities in surroundings that can affect how we perceive appearance.

Specialized Design for Transparent, Contoured Surfaces

This equipment provides scientific, numerical color data through specialized optical geometries and controlled lighting by measuring transmittance — the intensity of light at specific wavelengths within the visible spectrum that passes through the sample. Operators can then compare the readouts against established scales and indices, such as the Yellowness Index, to ensure the preform falls within acceptable tolerances, promoting consistent and repeatable results.

Higher rPET Content Without Guesswork

Tight color control with spectrophotometry is also how brands increase rPET without sacrificing appearance. When you have objective color data within seconds, you can raise recycled content while protecting appearance. Capture color measurement during incoming to set OBA dosing from data, not estimates. Using the same approach for in-process assessment and final inspection also helps identify alterations faster to uphold your quality control (QC) and support color consistency, even across different sites and suppliers.

The World's Best Spectrophotometers for Color Measurement of Transparent Plastic Preforms

HunterLab manufactures two industry-leading spectrophotometric solutions for color measurement in transparent plastic preforms, each engineered for the precise data you need for stringent QA and QC.

Vista — the Industry's Gold Standard

HunterLab's Vista spectrophotometer is the gold standard for color data capture in transparent plastic preforms. This innovative device drives efficiency in manufacturing with:

• Intelligent sample-presentation design: Vista boasts a modular sample handling system that promotes quick, accurate sample presentation. A preform holder accessory is available to further support correct positioning.
• Simultaneous haze measurement: This spectrophotometer simultaneously quantifies color and haze with a single push of the button and provides outcomes within 5 seconds.
• Exceptional value: Vista is a long-lasting, feature-rich, and cost-effective solution with the lowest total cost of ownership of our solutions.
• Connectivity options: USB and Ethernet connections make it fast and easy to print, stream, or export data to streamline QA/QC documentation.
• User-friendly operation: Intuitive touch screen navigation and one-touch standardization reduce training needs and save time.

UltraScan VIS — the Versatile QA Lab Workhorse

The UltraScan VIS is a versatile appearance control solution for even the busiest QA labs, especially if your production line handles more than transparent plastic preforms. With optical geometries that can capture measurements via both transmittance and reflectance, this equipment is compatible with transparent, translucent, and opaque samples alike.

Additionally, UltraScan VIS delivers:

• Color data readouts in less than 5 seconds and the ability to capture haze for high-throughput operations.
• Exceptional inter-instrument agreement (IIA) for superior confidence in result accuracy.
• Full visible-spectrum capabilities, plus automated UV calibration and control for actionable insight into OBA data.
• Automatic lens switching when transitioning between small- and large-area viewing for superior efficiency.
• Compatibility with HunterLab preform holder accessories for both transmittance and reflectance measurements to simplify accurate sample presentation.

Best Practices for Spectrophotometry in Transparent Plastic Preform Color Measurement

The following tips help manufacturers like you implement spectrophotometry with minimal disruption and maximum support for success.

Prepare and Present Samples Accurately

Accurate sample presentation is critical to getting correct appearance data, especially when dealing with preforms' challenging physical attributes. Establish clear protocols for sample handling and preparation so that they remain consistent across users, production lines, and facilities. Using specially designed accessories that help properly position samples for presentation is also best to support accurate color and haze data.

Standardize and Maintain Your Spectrophotometer Regularly

Standardizing the spectrophotometer sets the photometric scale. Always follow the manufacturer's instructions for standardization to help ensure your equipment performs as expected. Determine when operators should standardize according to your workflows — some companies institute the process at shift changes, while others may want to conduct it more frequently or when sample types change.

While the best-rated spectrophotometers are typically low-maintenance devices, adhering to any schedules or recommendations provided in the user's manual will help keep the equipment in peak condition.

Build Color Checks Into Every Process While Supporting Sustainability

The potential for inconsistencies that affect downstream quality and brand acceptance can occur at every manufacturing stage, from raw material quality to processing conditions. As a result, it's best to implement strict color QC measures throughout your operations. Doing so empowers you to catch any alterations where and when they occur so you can devise strategies to mitigate costly rework and waste.

Beyond waste reduction, regular color checks further support sustainability by limiting your business's carbon footprint. With fewer corrections needed to achieve consistent, repeatable quality, your business maximizes resource use and diminishes emissions associated with rework. 

Choose HunterLab Spectrophotometers for Transparent Preform Color Excellence

As the originator of measuring color for appearance's sake, HunterLab has led the industry for over 70 years. Our top-rated spectrophotometers help the world's leading brands maintain color consistency, achieve quality standards, and support a more circular economy. Each device we manufacture also includes our legendary customer support, empowering long-term value and ongoing color excellence.

Connect with our color measurement experts online to request a quote for your preferred equipment or for help identifying the best spectrophotometer to meet your needs.