This method is used to determine the color characteristics of paper and cardboard, including the reflection factor, the internal reflection factor and the tristimulus reflection factor. Suitable for samples that do not contain fluorescent dyes, the testing process includes measurement under a CIE1964 colorimetric system using a photoelectric integration Colorimeter. In order to improve the accuracy of the test, the dyed specimen should be calibrated using a standard plate that is close to the color of the specimen. The measurement results involve parameters such as color coordinates, luminosity index, chromaticity index and hue angle.
Purpose and Scope of Application
Objective: The purpose of this method was to accurately determine the color characteristics of paper and cardboard, including the reflectance factor (R), the internal reflection factor (R internal reflection) and the tristimulus reflection factor (R_x, R_y, R_z). These indicators can describe the color performance of paper and cardboard under light conditions in detail, involving parameters such as lightness, chromaticity and hue, and provide a basis for color management and quality control.
Scope of application: This method is suitable for paper and cardboard specimens without fluorescent dyes. For dyed specimens, it is recommended to use a standard plate that is close to the color of the specimen for calibration to improve the accuracy of the test. This ensures the accuracy of the test results, especially when working with samples with close colors, and avoids errors due to color differences.
definition
Reflection Factor (R) – The ratio of the radiant flux reflected by an object under a given condition to the radiant flux reflected by a fully reflected diffuser, expressed as a percentage. This metric measures the ability of an object's surface to reflect light.
Internal reflectance factor (R-internal reflection) – the measured value at which the reflectance factor reaches a stable value when the thickness of the specimen reaches a certain level. This indicates the internal reflective properties of the specimen.
Tristimulus reflectance factor (R_x, R_y, R_z) – the reflectance factor measured in CIE1964 supplemented with a standard chromaticity system to describe the color behavior of paper at different wavelengths of light. This system is measured based on the value of the color matching function defined in CIE1964.
CIE1964 Chromaticity System – A chromaticity system prescribed by CIE1964 that describes color using specific color matching function values (x, y, z), also known as a chroma system with a 10-degree field of view.
Tristimulus Values – represent the three original stimuli required for the experimental light to achieve color matching in the chromaticity system, which are denoted by X, Y, Z, and are used to calculate the specific properties of the color.
Color coordinates – Coordinates that describe the color of an object and are used to express the position of the color in the chromaticity diagram.
ELAB Chromatic System – The CIE1976 recommended color space and color aberration formula, including the L*a*b* color space, which is used to represent the lightness (L'), red-green axis (a*), and yellow-blue axis (b*) of a color, as well as to calculate chromatic aberration (ΔE).
Luminosity Index (L') – A luminosity value representing the color of an object, with an L' value of 0 indicating black (no light reflection) and an L' value of 100 indicating white (total optical reflection).
Chromaticity Index (a*, b*) – describes the degree of red-green (a*) and yellow-blue (b*) of a color. A positive value indicates a reddish caste, and a negative value indicates a greenish cast. A positive value of b* indicates a yellowish tinge, and a negative value indicates a bluish bias.
Chroma (C) – The purity or saturation of an object's color, which indicates the intensity of the color.
Hue angle (h) – The angle at which the color is within a 360-degree range, indicating the type of color. 0 degrees is red, 90 degrees is yellow, 180 degrees is green, and 270 degrees is blue.
Instruments & Equipment
Photoelectric integral Colorimeters are used to determine tristimulus reflectance factors (R_x, R_y, R_z). The instrument should comply with the relevant spectral characteristics standards to ensure the accuracy and reliability of the measurements.
Working Standards: For near-white paper patterns, use a white standard plate for calibration; For dyed paper patterns, calibration is performed using standard plates of similar colors. All standards must be calibrated regularly to ensure the accuracy of the test results.
Preparation of specimens
Sampling is carried out according to standard methods to ensure the representativeness and consistency of the specimen.
Cut a 150mm x 75mm rectangular specimen from the sheet of paper, no less than 10 pieces. Ensure that the total thickness of the specimen meets the requirements for reflectance stability and is protected against contamination or unwanted effects of light and thermal radiation.
Test procedure
Calibrate the scale and zero point of the photointegrated Colorimeter using a standard plate and a black barrel to ensure that the instrument is in the correct working condition prior to testing.
The protective layer of the specimen is removed, the specimen is placed on the test hole, and the tristimulus reflex factor of the topmost specimen is determined. Measure at least 5 pieces of each sample, flip the sample stack after testing one side, and repeat the measurement of the other side.
How to calculate and present the results of the test
The tristimulus values X, Y, Z of the specimen are calculated from the measured values and further data analysis and result representation are performed as needed.
summary
Paper and cardboard colorometry evaluates color properties by means of a reflection factor and a tristimulus reflex factor. This method is particularly suitable for specimens that do not contain fluorescent dyes, and ensuring accuracy requires proper specimen preparation and instrument calibration. By using a photoelectric integrator and a CIE1964 colorimetric system, the color of paper and cardboard can be described in detail, including lightness, chromaticity, and hue. Accurate measurements help ensure color consistency in paper product production and quality control.
