Interpreting ISO 2469: A Global Universal Standard for Diffuse Reflectance Properties of Pulps, Papers and Boards

In the papermaking, printing and related industrial chains, the optical properties of pulps, papers and boards directly determine product quality, application adaptability and market competitiveness. As a core optical index, the uniformity and accuracy of diffuse reflectance measurement are crucial. ISO 2469, a special standard developed by the International Organization for Standardization (ISO), provides a unified paradigm for the measurement of diffuse reflectance related to such products worldwide, and is an important basis for industry quality control, trade and technological research and development. This article will comprehensively interpret ISO 2469 from the aspects of standard foundation, development history, core content, practical applications and important significance, helping industry practitioners deeply understand its value and application points.

TÔI. Basic Cognition of ISO 2469 Tiêu chuẩn

1.1 Core Positioning of the Standard
ISO 2469 is fully titled “Giấy, board and pulps — Measurement of diffuse radiance factor (diffuse reflectance factor)”. It belongs to the fields of Pulps (85.040) and Paper and Board (85.060) in the International Classification for Standards (ICS), and corresponds to Paper (Y32) in the Chinese Standard Classification. The core goal of this standard is to standardize the measurement methods of diffuse radiance factor for various pulps, papers and boards, ensure the comparability and reliability of measurement results between different laboratories, enterprises and countries, and eliminate technical barriers for industry quality control and global trade.

1.2 Definition of Core Terms
To understand ISO 2469, it is first necessary to clarify the key terms defined by it, which is the basis for the implementation of the standard. The core terms include:
•Radiance factor: The ratio of the radiance of a surface element in a specific direction to that of a perfect diffuse reflector, which is a basic parameter for measuring the reflectivity of materials.
•Diffuse radiance factor: The ratio of the radiance of a material under diffuse illumination and normal detection conditions to that of a perfect diffuse reflector, which is also the core index focused on by ISO 2469.
•Intrinsic diffuse radiance factor: The diffuse radiance factor of a layer or pad of material thick enough to be opaque, which can avoid the interference of material thickness on measurement results and better reflect the inherent optical properties of the material itself.

II. Development History of ISO 2469 Tiêu chuẩn

Since its release, ISO 2469 has always kept pace with the technological development and market demand of the papermaking industry, and has undergone many revisions and improvements to gradually improve measurement accuracy and applicability. The evolution of its successive versions is as follows:
1.TRONG 1977, ISO 2469:1977 was released for the first time, establishing the basic framework for the determination of diffuse reflectance factor of paper, board and pulp, and providing the industry with the first unified measurement standard.
2.TRONG 1994, ISO 2469:1994 was released, optimizing the measurement method and clarifying the basic requirements for test equipment. Đồng thời, Technical Corrigendum 1 (ISO 2469:1994/Cor 1:1998) was released to correct detailed problems in practice.
3.TRONG 2007, ISO 2469:2007 was released, further refining the measurement process, clarifying the specific requirements for sample handling and environmental control, and improving the stability of measurement results.
4.TRONG 2014, ISO 2469:2014 was released, referencing more relevant international standards (such as CIE lighting standards and other papermaking industry measurement standards), improving the measurement requirements for fluorescent whitening agent materials, and clarifying the specific specifications for instrument calibration.
5.TRONG 2024, ISO 2469:2024 was officially released. As the latest version, it further optimizes the measurement paradigm, adapts to the development of digital and intelligent measurement equipment, strengthens the connection with the global metrological system, and becomes an important foundation for the industry to move towards optical precision and quality digitalization.
Ngoài ra, this standard is widely adopted worldwide. Many countries have formulated their own corresponding national standards based on ISO 2469, such as the British BS ISO 2469 series, the Korean KS M ISO 2469 series, and the French NF ISO 2469:2014, forming a global unified measurement system.

III. Analysis of the Core Content of ISO 2469

The core content of ISO 2469 revolves around “the uniformity and accuracy of measurement”, covering measurement principles, instrument requirements, sample handling, calibration procedures, result expression and other aspects. It is applicable to all types of pulps, papers and boards, including materials containing fluorescent whitening agents.

3.1 Measurement Principle
The standard adopts the core principle of diffuse illumination and normal detection, đó là, simulating a specific light source (such as CIE illuminant C, D65, vân vân.) to diffusely irradiate the sample, detecting the reflected radiance of the sample in the vertical direction, and then comparing it with the radiance of a perfect diffuse reflector to calculate the diffuse radiance factor. For materials containing fluorescent whitening agents, it is necessary to adjust the ultraviolet content of the instrument illumination to be consistent with the fluorescent reference standard of the selected CIE light source to ensure the accuracy of measurement results.
Đồng thời, the standard specifies two key measurement geometries: d/0° (diffuse illumination, 0° viewing angle) and 0°/d (0° illumination, diffuse viewing angle), and precisely defines the integrating sphere geometry to adapt to the measurement needs of different types of samples.

3.2 Instrument Requirements
ISO 2469 puts forward clear requirements for the technical parameters of measurement instruments (mainly reflectometers and spectrophotometers), the core of which includes:
•Spectral characteristics: It shall meet specific wavelength requirements. Ví dụ, when measuring ISO brightness, the dominant wavelength is 457 nm and the half-wave width is 44 nm to ensure that the spectral response matches human vision.
•Geometric conditions: It shall meet the d/0° or 0°/d geometric requirements. The diameter of the integrating sphere and the diameter of the test hole shall comply with the standard provisions (such as the integrating sphere diameter of 150mm and the test hole diameter of 32mm), and a gloss absorber shall be provided to eliminate the specular reflection light of the test sample.
•Calibration requirements: Instruments shall be calibrated regularly. Calibration shall be based on relevant standards such as ISO 4094, and first-class, second-class and third-class international reference standards (IR1, IR2, IR3) shall be used for quantity transmission to ensure measurement accuracy.
Ví dụ, equipment such as Datacolor Elrepho 1000 spectrophotometer and WSB-3A intelligent digital whiteness meter all meet the instrument requirements of ISO 2469 and can be used for the measurement work specified by the standard.

3.3 Sample Handling and Test Procedures
The standard puts forward strict requirements for the sampling, preparation and handling of samples to avoid the interference of the samples themselves on the measurement results. The core procedures are as follows:
•Sample sampling: Representative samples shall be taken in accordance with relevant standards (such as GB/T 450, GB/T 740), avoiding watermarks, dust and obvious paper defects.
•Sample preparation: Cut the sample into the specified size (chẳng hạn như 75 mm × 150 mm) to form a sample stack. The number of layers shall be thick enough to reach an opaque state (to ensure the accuracy of the measurement of the intrinsic diffuse radiance factor). Protective paper sheets shall be attached to the top and bottom of the sample stack to avoid contamination.
•Environmental control: Samples shall avoid high-temperature and high-humidity pretreatment, and can be subjected to temperature and humidity treatment as required (such as specified in GB/T 10739) to ensure a stable test environment.
•Test process: After the instrument is preheated, calibrate it with non-fluorescent reference standards and fluorescent reference standards, then test the top sample of the sample stack in turn, record no less than 10 test results, and calculate the average value and standard deviation.

3.4 Calibration and Reference Standards
Calibration is the key to ensuring the accuracy of measurement results. ISO 2469 clarifies a three-level reference standard system. The purpose and calibration requirements of each level of standard are as follows:
•First-class International Reference Standard (IR1): Calibrated by international standardization laboratories, it serves as the benchmark for quantity transmission.
•Second-class International Reference Standard (IR2): Calibrated by standardization laboratories based on IR1, it is divided into non-fluorescent and fluorescent types, which are used to calibrate the photometric scale of reference instruments in authorized laboratories and adjust the ultraviolet content of instruments respectively.
•Third-class International Reference Standard (IR3): Calibrated by authorized laboratories based on IR2, it is also divided into non-fluorescent and fluorescent types, which are used to calibrate instruments in test laboratories and adjust the ultraviolet level of sample irradiation.
Ngoài ra, the standard also specifies the calibration requirements for working standards. Working standards shall be calibrated through IR3 and used for daily instrument calibration and testing to ensure measurement consistency.

3.5 Result Expression and Abnormal Value Handling
Measurement results are expressed as diffuse radiance factor (percentage), which shall be accurate to the specified precision (such as ISO brightness accurate to 0.5%). Đồng thời, parameters such as average value and standard deviation shall be reported. If the measurement difference between the two sides of the sample exceeds the specified range (chẳng hạn như 0.5%), the results of the two sides shall be reported separately; if the difference is within the allowable range, the average value of the two sides can be reported.
For abnormal values, the standard specifies handling methods to ensure the reliability of measurement results. Đồng thời, it is required to indicate any deviation from the standard in the test report, as well as factors that may affect the results (such as instrument type, environmental conditions, vân vân.).

IV. Practical Application Scenarios of ISO 2469

As a basic measurement standard in the papermaking industry, ISO 2469 has application scenarios throughout the entire industrial chain of pulp production, paper manufacturing, printing and processing, quality inspection, and extends to related supporting fields.

4.1 Quality Control in Papermaking Enterprises
For pulp, paper and board production enterprises, ISO 2469 is the core basis for quality control. By following the standard to measure the diffuse reflectance properties of products, enterprises can accurately control key indicators such as product whiteness and opacity, ensure the consistency of products from different batches, and avoid affecting market reputation due to quality fluctuations. Ví dụ, when producing cultural paper, it is necessary to control the whiteness of the paper through standard measurement to ensure the printing effect; when producing packaging

our product GA-5011 Paper Whiteness Tester meets this standard.

GA-5011 Paper Whiteness Tester
Tổng quan:
White/Brightness tester is to determine the whiteness, yellowness, color and color difference of the object, but also can determine the opacity of paper, transparency, light scattering coefficient, light absorption coefficient and ink absorption value.Widely used in papermaking, in, gốm sứ, công nghiệp hóa chất, textile printing and dyeing, vật liệu xây dựng, grain, salt and other industries.

Equipment function:
1.Measure the reflected color and color difference of the object, which can be displayed or printed: diffuse reflection factors Rx, Ry, Rz, stimulus values Y10, X10, Z10, chromaticity coordinates X10, Y10, Z10;Lightness L *, Một * chromaticity, b *, chroma C * ab, hue Angle h * ab, dominant wavelength lambda d, excited purity, Pe Δ E * ab color, brightness difference Δ L *, chroma difference Δ ab, poor tonal Δ h C * * ab, hunter system L, a and b.
2.The ISO brightness (blue light whiteness R457) and Z whiteness (Rz) can be measured to measure the fluorescence whiteness generated by emission of fluorescent substances in the fluorescence whitening samples.
3.CIE whiteness (Gantz whiteness W10 and color TW10) was measured.
4.Measure the whiteness of ceramics.
5.Measure the whiteness of building materials and non-metallic minerals.
6.Measure hunter whiteness WH.
7.Measure yellow YI.
8.OP of opacity of test sample
9.Measure the transparency T of the sample
10.The light scattering coefficient S of the sample was measured
11.Measure the light absorption coefficient A of the sample.
12.Measure ink absorption value.

Test standards：
ISO 2469 Giấy, Board and Pulp — Determination of Diffuse reflectance Factors
ISO 2470 Paper and Board — Determination of Whiteness (Diffuse/vertical method)
ISO 2471 Paper and Board — Determination of Opacity (paper backing) — Diffuse reflectance Method
ISO 9416 “Determination of Light Scattering and Light Absorption Coefficients of Paper” (Kubelka-Munk)
ISO 11475 “Determination of CIE Whiteness for Paper and Cardboard, D65/10 (outdoor Daylight)”
GB/T 7973 Determination of Diffuse Reflection Factors of Paper, Board and Pulp (Diffuse/vertical Method)
GB/T 7974 “Determination of Brightness (Whiteness) of Paper, Board and Pulp”
GB/T 7975 “Determination of Color of Paper and Board (Diffuse reflectance method)”
GB/T 24288 — Determination of Main Wavelength and Excitation Purity of Paper and Board — D65/10 Diffuse reflectance Method
GB/T 10339 “Determination of Light Scattering and Light Absorption Coefficients of Paper, Board and Pulp”
GB/T 8424.2 Instrumental Evaluation Method for Relative Whiteness of Textile Color Fastness Test
GB/T 13173.14 “Test Method for Surfactant Detergents — Determination of Whiteness of Powder Detergents”
GB/T 8424.1 General Principles for The Determination of Surface Colors for Color Fastness Tests of Textiles
Paper and Board — Determination of CIE Whiteness, D65/10 (outdoor Daylight)
GB/T 1543 “Determination of Opacity of Paper and Board (Paper Backing)”
GB/T 6688 “Instrumental Method for the Determination of Relative Strength and Chromatic Aberration of Dyes”
GB/T 13025.2 General Test Methods for Salt Industry, Determination of Whiteness
GB/T 2913 test Methods for Whiteness of Plastics
GB/T 5950 Measurement Method for Whiteness of Building Materials and Non-metallic Mineral Products
GB/T 3979 Measurement method of Object Color
GB/T 8424.3 Calculation of Color Difference for Textile Color Fastness Test
GB/T 2679 – Determination of Paper Transparency
GB/T 9338 instrument Method for The Determination of Relative Whiteness of Fluorescent Brighteners
GB/T 11186 Measurement Method of Coating Film Color
GB/T 9984.5 “Test Method for Sodium tripolyphosphate for Industry — Determination of Whiteness”
GB/T 22427.6 Determination of Starch Whiteness
GB/T 13835.7 Test Method for Whiteness of Rabbit Hair Fiber
GB/T 12911 “Determination of Ink Absorbability of Paper and Cardboard”
GB/T 4739 “Method for Determination of Colorimetry for Ceramic Pigments for Daily Use”
GB/T 11942 Measurement Method for Chromaticity of Colored Building Materials
QB/T 2789 general Test Method for Cosmetics Color tristimulus Value and Color difference △E* Determination
QB/T 1503 “Method for Determination of Whiteness of Ceramics for Daily Use”
Test Method for Plastic Yellow Index HG/T 3862
Fz-t50013 test Methods for Whiteness of Cellulose Chemical Fibers – Blue Ray Diffuse Reflection Factor Method

Main performance parameters
1. The instrument has novel appearance and compact structure, and advanced circuit design effectively ensures the accuracy and stability of measurement data.
2. The instrument simulates D65 illumination.CIE 1964 supplementary chroma system and CIE 1976 (L* A * B *) chromatic space chromatic aberration formula were used.
3. The instrument adopts D/O illumination to observe the geometric conditions.The diameter of the diffuse ball is 150mm, the diameter of the test hole is 30mm, and the light absorber is provided to eliminate the influence of the specular reflection of the sample.
4. LCD module with large screen and high pixels is adopted to display measurement and statistical results in Chinese with prompts for operating steps. Friendly man-machine interface makes the operation of the instrument simple and convenient
5. The instrument adds a printer and adopts imported thermal printing movement, no need to use ink and ribbon, no noise when working, fast printing speed and other characteristics
6. The instrument is equipped with standard RS232 interface, which can communicate with microcomputer software
7. The instrument is protected by power off, and the calibration data will not be lost after power off
8. Can store 9 reference samples.

Technical Specification