Colorimeter controls batch color difference in plastic and rubber films.

This article primarily discusses how to use a colorimeter to control color variations in the production of plastic and rubber films. It explains the working principle of a colorimeter, which involves converting colors into numerical values represented by three parameters: L, a, and b, and then calculating the color difference. The article also lists several key factors that influence color, such as raw materials and process parameters. It then introduces a control process, from setting standards and tolerances to standardizing measurements and correcting issues. Finally, it highlights practical considerations, such as the impact of film gloss and transparency on measurements. Overall, the approach emphasizes using objective data-driven methods to stabilize product color and improve quality.

Introduction

In the continuous production of plastic and rubber films, batch-to-batch color consistency is a key measure of product quality and process stability. Color deviations not only affect product appearance but can also suggest fluctuations in raw materials, process parameters, or equipment status. The use of colorimeters for objective and quantitative color control has become a standard practice in modern industry to ensure the stability of product color batches. This paper aims to explore the application principles, key parameters and implementation methods of colorimeters in this field.

Principle of chromatic aberration measurement

Colorimeters quantify color information into digital signals by simulating the standard observer's perception of color. Its core principle is based on the standard chromaticity system established by the International Illumination Commission (CIE). The instrument typically uses a standard light source such as D65 or C to illuminate the sample, receive the reflected light through the detector, and calculate the coordinate value of the sample in a specific color space.

The most commonly used color space is the CIE L*a*b* (CIELAB) system. Among them, L* represents luminosity, a* represents red-green chromaticity, and b* represents yellow-blue chromaticity. The overall difference between the two colors, known as chromatic aberration (ΔE), can be calculated by the following formula:

ΔE = √[(ΔL*)² + (Δa*)² + (Δb*)²]

Among them, ΔL*, Δa*, and Δb* represent the differences between the L*, a*, and b* values of the standard sample and the batch sample, respectively. More complex chromatic aberration formulas, such as CIE94 or CIEDE2000, introduce weighting factors to better match the human eye's visual perception.

Key influencing factors

There are many factors affecting the color difference of plastic and rubber film batches, which can be summarized as follows:

Raw material fluctuations	Pigments, resins, additives, etc. performance differences between batches.
Process parameters change	Such as extrusion temperature, pressure, traction speed, cooling conditions, etc.
Device status	Mold wear, screw cleanliness, heating element aging, etc.
Measurement conditions	Sample preparation, instrument calibration, measurement aperture, light source selection, etc.

Control the implementation process

To establish an effective color aberration control system, it is necessary to follow a systematic process:

Establish standards	Determine the standard color plate that is approved by all parties and measure its standard Lab* value.
Set tolerances	Agree with the customer according to the product requirements to set the acceptable maximum ΔE value.
Standardized measurements	Unified sampling position, number of sample stacks, instrument calibration frequency and measurement mode.
Data analysis	Continuously record data, analyze chromatic aberration trends, and correlate them with process parameters.
Corrective prevention	When ΔE exceeds the limit, initiate the investigation procedure and adjust the relevant factors.

Application Notes

In practical applications, it is necessary to pay attention to the influence of the characteristics of the film itself on the measurement. For example, the transparency of the film, surface gloss, texture, and the presence of optical brighteners can significantly affect the measurement results. For high-gloss or transparent films, a comprehensive evaluation may be required using different measurement modes that include specular light (SCI) and excluded specular light (SCE). In addition, the flatness of the sample and the backing conditions (e.g., using a whiteboard or blackboard) must be strictly uniform to ensure data comparability.

Epilogue

Using colorimeters to quantify and control the batch color difference of plastic and rubber films is an important step from empirical judgment to data-driven quality management. By understanding measurement principles, controlling key variables, and implementing standardized processes, manufacturers can effectively reduce color fluctuations, improve product consistency, and meet the market's continuous demand for high-quality appearance. Continuous monitoring and data analysis also provide a reliable basis for process optimization.

References

1. Introduction: Refer to the general principles of polymer material processing quality control.
2. Principle of color aberration measurement: According to the official definition of CIELAB color space and color aberration formula in the CIE publication.
3. Key Influencing Factors and Control Process Section: Integrates guidelines for color quality control from multiple industry standards.
4. Application Considerations: Cites specialized technical literature on the impact of material optical properties on color measurement.