GB/T 37946.2-2025 in English

Standard Revision Background and Technological Evolution

GB/T 37946.2-2025, the second part of a series of standards for testing methods for organic light-emitting materials, is a major upgrade and improvement to the 2019 edition. This revision integrates the content of GB/T 37945-2019 and GB/T 37946-2019, reflecting the enhanced requirements and technological advancements for thermal performance testing of materials in the organic light-emitting display industry.

With the rapid development of OLED display technology, the impact of the thermal properties of organic light-emitting materials on device life and stability has become increasingly prominent. The new standard adds three key sections: melting point testing, glass transition temperature testing, and high-temperature aging testing, and refines the detailed requirements for thermal stability testing, providing a more comprehensive technical basis for material R&D and quality control.

Detailed Explanation of Thermal Stability Testing

Thermal stability testing utilizes thermogravimetric analysis (TGA), which assesses the thermal decomposition characteristics of a material by measuring the mass change of a sample under programmed temperature conditions. The standard requires that the sensitivity of the thermobalance should be no less than ±10μg, and the purge air volume should be controlled within the range of 5mL/min~200mL/min.

During the test, the sample must be ground into a uniform powder and tested at a heating rate of 10°C/min within the temperature range of 50°C to 700°C. Key test results include the temperature at which 5% weight loss occurs and other typical weight loss percentages.

Melting Point Test Method

The melting point is determined using differential scanning calorimetry (DSC), which measures the temperature dependence of the heat flow difference between the sample and a reference sample. The standard requires the use of a differential scanning calorimeter certified according to JJG936 and an analytical balance with a 0.1mg resolution.

Sample preparation requirements are extremely strict: the sample should be a uniform powder, weighed 2mg-5mg with an accuracy of ±0.1mg, and three samples should be taken in parallel. During the test, special care should be taken to prevent sample spillage and contamination of the crucible and instrument furnace.

The melting point is determined using the tangent method: a tangent line is drawn at the intersection R1 of the vertical curve at the peak of the derivative curve of the melting peak and the melting point curve. The melting point is determined at R2, the intersection of the extrapolated tangent line with the starting baseline.

Glass Transition Temperature Test

The glass transition temperature (Tg) is a key parameter measuring the transition from a glassy to a highly elastic state in organic materials and is crucial to the thermal stability of OLED devices. This test also utilizes the DSC method, but requires two heating cycles.

The first heating cycle is conducted at a rate of 5°C/min-20°C/min, allowing the sample to melt before rapidly cooling. The second heating is carried out at a slower rate of 1°C/min to 10°C/min, heating to 30°C above the extrapolated end temperature. The glass transition temperature is defined as the intersection of the extrapolated tangent line of the starting baseline and the tangent line at the inflection point of the curve.

Innovation in High-Temperature Aging Test

The new high-temperature aging test added to the new standard simulates the stability of the material in a high-temperature environment during actual use. The test needs to be carried out in an ISO Class 7 clean environment or above, using special equipment such as an organic sublimation purification device and a heat-resistant vacuum glass tube.

The aging conditions are in the temperature range of 200°C to 500°C and the time range of 24h to 300h, which can be adjusted according to the properties of the material. During the test, it is necessary to regularly observe the color change of the material, and subsequent tests such as main substance content analysis are required after the aging is completed.

Implementation suggestions and precautions

When implementing the new standard, special attention should be paid to the following aspects:

Instrument Calibration and Maintenance: All testing instruments must be regularly calibrated in accordance with relevant JJG regulations to ensure the accuracy and comparability of test results. In particular, thermal balances and differential scanning calorimeters have high sensitivity requirements and require the establishment of strict calibration procedures.

Sample Preparation Standardization: The uniformity of sample grinding, sampling accuracy, and sample loading method will all affect test results. It is recommended to establish standardized sample preparation operating procedures to ensure comparability of test results between different laboratories.

Environmental Control: Controlling the temperature and humidity of the test environment is important for the stability of the results. In particular, humidity has a significant impact on the test results of certain organic materials, and strict control of environmental conditions is required.

Data Interpretation Standardization: A unified interpretation method is required for determining characteristic temperatures such as melting point and glass transition temperature. Inter-laboratory comparison is recommended to ensure consistency in data interpretation.

Technology Development Trends and Outlook

With the rapid development of flexible OLED display technology, higher requirements are being placed on the thermal performance of organic light-emitting materials. Further refinement of testing methods may be required in the future, including:

1. Adding testing methods for the thermal properties of materials in a bent state

2. Developing thermal stability testing methods for a higher temperature range (e.g., above 800°C)

3. Establishing an evaluation method for the correlation between material thermal properties and device lifespan

4. Improving a quantitative evaluation system for changes in material properties after high-temperature aging

The implementation of GB/T 37946.2-2025 will strongly promote technological progress and quality improvement in my country's organic light-emitting materials industry, providing solid technical support for the development of the OLED display industry.