Definition
Thermal stickers are disposable temperature indicator devices based on the color-changing characteristics of heat-sensitive materials. It is typically composed of a substrate, a heat-sensitive chromic layer, and a protective layer that visually indicates the temperature state when the ambient temperature reaches or exceeds its specific nominal temperature, undergoing significant and often irreversible changes in its appearance. It is not a continuous measuring instrument, but a threshold-based temperature monitoring tool.
Principle
The core working principle of temperature sensitive tapes is based on physical or chemical changes in heat-sensitive materials. Common heat-sensitive materials include liquid crystals, molten compounds, or mixtures that undergo solid-phase chemical reactions. When the temperature reaches a specific phase change temperature or reaction temperature of the material, the microstructure or chemical state of the material changes, resulting in a change in its absorption or reflection characteristics in the visible light band, which is macroscopically manifested as the color changing from one state (such as white) to another state (such as black). This process is often irreversible, resulting in a permanent record of temperatures exceeding set thresholds.
Measurement method
The measurement of temperature patches is a qualitative or semi-quantitative threshold judgment. The method of use is to stick the temperature sticker tightly on the surface of the object to be measured. Conduct experiments or process monitoring. Observe the color state of the temperature sticker. If the color changes (e.g., from light to dark), it indicates that the temperature of the measurement point has reached or exceeded the rated response temperature of the temperature sticker during the monitoring period. The record result is "Yes/No" or "Overtemperature/Not Overtemperature". Some products are designed with multiple temperature threshold points, which can be roughly judged by observing the discoloration in different areas.
Influencing factors
The accuracy of the indication of a thermosensitive patch is affected by various factors. Ambient temperature and its duration are critical factors, and the rated temperature must be reached and maintained for sufficient time to complete the adequate discoloration reaction. The thermal contact of the tested surface, such as whether it is tightly adhesive, whether there are voids or insulation, can affect the heat transfer efficiency. The measured object with different heat capacity and thermal conductivity may cause a difference between the indicated temperature and the actual core temperature of the object. Additionally, environmental factors such as mechanical stress, chemical corrosion, and strong light exposure (particularly UV light) can also interfere with heat-sensitive materials or affect color interpretation. Storage conditions are just as important as expiration date, and improper storage can cause drift in its rated response temperature.
Applications
Due to their simplicity, low cost and passive characteristics, temperature sensitive patches have a wide range of uses in many industrial and scientific research fields. In the electrical and electronic industry, it is used to monitor overheating of circuit boards, transformers, or power supply equipment during operation or testing. In the field of materials handling and chemical processes, it is used to monitor whether the surface temperature of reactors, conveyor pipelines or storage tanks exceeds safe limits. In the aerospace sector, it can be used to monitor the temperature exposure history of components in specific tests. In food logistics and warehousing, certain models can be used to indicate whether a disruption has occurred in the refrigerated chain. In scientific experiments, it is also often used to assist in confirming whether the expected temperature change has occurred locally in the equipment.
Selection considerations
Choosing the right temperature sensitive patch requires a comprehensive consideration of multiple parameters. The primary parameter is the response temperature, which should be selected according to the monitoring target temperature threshold, and pay attention to the nominal accuracy range of the product (e.g., ±1°C or ±2°C). The response time should be in line with the demand, i.e. the time it takes for the temperature to reach a threshold to a noticeable discoloration. The color-changing contrast should be high enough for easy identification. The adhesive's properties need to be appropriate to the surface material being tested (e.g., metal, plastic, coating) and surface cleanliness and curvature, taking into account the humidity of the operating environment, the presence of oil or vibration. For situations where multiple temperature points need to be monitored, a multi-point temperature sensing patch can be selected. In addition, it is necessary to confirm the certification of the product and whether it meets the requirements of relevant industry standards or specifications.