The attached paper discusses how objective color measurement helps manufacturers monitor material quality, additive loading, oxygen scavenger concentration, thermal degradation, and process stability, while also explaining why haze measurements should be performed on representative bottle-wall cutouts rather than directly on preforms.
1. Color Measurement Provides an Early Indicator of Process Variation
Changes in CIELAB color values (L*, a*, b*), ΔE, and Yellowness Index can reveal resin variation, additive loading changes, oxygen scavenger concentration differences, dryer performance issues, and thermal degradation before these conditions become visible in finished bottles. As a result, color measurement serves as both a quality-control and process-monitoring tool.
2. L* and Yellowness Trends Can Be Valuable Process-Control Parameters
Many manufacturers utilize L* measurements to monitor oxygen scavenger loading consistency and Yellowness Index or b* values to identify thermal degradation, drying issues, and process instability. Trending these measurements over time often reveals process drift before it results in customer-visible defects or off-spec production.
3. Measure Color on Preforms and Haze on Bottle-Wall Cutouts
Color and haze evaluate different optical properties and should be measured using different sample types. Preforms are the preferred sample for transmission color measurement, while haze measurements should be performed on representative bottle-wall cutouts. This approach improves measurement repeatability, aligns with ASTM D1003 Procedure B methodology, and provides better correlation to final package appearance.
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Color is one of the most important quality attributes in PET packaging because it directly influences consumer perception, brand consistency, and product appearance. However, color measurement of PET preforms is often misunderstood. Manufacturers frequently use color data not only to verify appearance, but also to monitor material quality, oxygen scavenger loading, thermal degradation, dryer performance, and overall process stability.
This white paper explains the fundamentals of color measurement for transparent and translucent PET preforms, including recommended measurement practices, key color metrics such as CIELAB, ΔE, and Yellowness Index, and how color data can be used as an effective process-control tool. The paper also clarifies the important distinction between color and haze measurements, explaining why preforms are typically measured for color while haze evaluations are best performed on representative bottle-wall cutouts. Together, these concepts provide a practical framework for improving quality control, reducing variation, and maintaining consistent package appearance.
Download the full document below to learn more.
To learn more about Color and Color Science in industrial QC applications, click here: Fundamentals of Color and Appearance
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