After testing with the heat sealing tester, there was a leakage of the heat sealing edge. The core solution is to first investigate the human factors in the testing operation and sample preparation, then optimize the heat sealing process parameters, and finally verify the adaptability of the material itself. The specific steps can be gradually solved according to the following steps to ensure that the treatment plan is operable and targeted.
Step 1: Eliminate non process errors in testing operations and sample preparation
This is the most easily overlooked link and a priority direction for investigation to avoid misjudging process or material issues due to operational problems.
Check if the sample preparation is standardized
The cutting and pretreatment of heat sealed samples directly affect the sealing effect. Firstly, confirm whether the sample cutting is smooth. If there are burrs, gaps, or uneven thickness on the heat sealed edge, it will cause uneven stress and heating during heat sealing, resulting in small gaps and leakage; Next, check if the surface of the sample is clean. If there is residual dust, oil, or moisture, it will block the fusion bonding between the heat sealing layers and damage the integrity of the seal. At this point, it is necessary to use high-precision cutting tools to cut the sample again, ensuring that the heat sealed edge is smooth and free of burrs, and wipe the surface of the sample with a dust-free cloth before testing.
Verify whether the testing operation meets the standards
Key confirmation of the operation details of the heat sealing tester: firstly, whether the heat sealing pressure is evenly applied. If the heat sealing head of the instrument is tilted, worn, or the pressure setting does not fully cover the heat sealing area, it will cause local sealing failure; The second is whether the control of heat sealing time is precise. If the contact time of the pressure head is too short or too long during manual operation, it will affect the sealing effect; The third is whether the leakage detection method after testing is standardized, such as whether the pressure values and holding time of negative pressure method and positive pressure method comply with relevant standards (such as GB/T15171, ASTMF2054), to avoid "false leakage" caused by improper detection methods.
Step 2: Optimize the heat sealing process parameters
If leakage still occurs after excluding operational and sample issues, it is necessary to focus on adjusting the parameters of the three elements of heat sealing (temperature, pressure, time), which is the core means of solving heat sealing leakage.
Adjust the heat sealing temperature
Temperature is the key factor determining the degree of melting of the heat sealing layer. When the temperature is too low, the heat sealing layer material cannot fully melt, and molecular level fusion cannot be formed between the two thin films. Relying solely on pressure bonding can easily result in gaps that are not tightly sealed; If the temperature is too high, it will cause degradation and coking of the heat sealing layer material, damage the material structure, and form pinholes or brittle cracks.
Optimization method: The gradient heating test method is used to gradually increase the temperature at intervals of 5 ℃ based on the existing temperature (such as from 120 ℃ to 150 ℃), while maintaining the same pressure and time. After each test, leakage detection is carried out to find the lowest effective temperature that can achieve leak free sealing and avoid material damage caused by high temperature.
Optimize heat sealing pressure
The function of pressure is to ensure that the melted heat sealing layer fully contacts and adheres, eliminating interlayer air. When the pressure is insufficient, the molten material cannot bond tightly, and there are small gaps between the layers, which can become leakage channels; Excessive pressure can squeeze out too much molten material, causing the heat sealed edge to become thinner, the strength to decrease, and even resulting in holes.
Optimization method: Based on the determined effective temperature, gradually adjust the pressure at intervals of 0.1 MPa (such as increasing from 0.2 MPa to 0.5 MPa), observe the heat sealing edge state under different pressures, and select a pressure value with a smooth heat sealing edge, no extruded material, and no leakage.
Adjust the heat sealing time
The duration of the melting and fusion process of the heat sealing layer is determined by time and needs to be matched with temperature and pressure. The time is too short, and the pressure is stopped before the heat sealing layer is completely melted, resulting in insufficient sealing strength; If the time is too long, it will exacerbate the thermal degradation of the material.
Optimization method: Under the determined temperature and pressure parameters, extend the heat sealing time at intervals of 0.5s (such as from 1s to 3s), and find the shortest time that meets the sealing requirements through testing, balancing efficiency and sealing quality.
Step 3: Verify the compatibility of the heat sealing material
If there is still a leakage problem after optimizing the process parameters, the adaptability and quality of the material itself need to be considered.
Check the compatibility of the heat sealing layer material
The melting temperature and properties of heat sealing layers made of different materials (such as PE, CPP, EVA) are different. If the two layers of heat sealing materials in the composite film do not match, or if the thickness of the heat sealing layer is too thin (usually recommended to be ≥ 20 μ m), it will result in poor sealing effect. For example, when heat sealing PE film and CPP film, the intersection range of their melting temperatures should be selected as the heat sealing temperature, otherwise it is easy to have one side fully melted and the other side not melted.
Identify material quality defects
Check if there are any quality issues with the material itself, such as impurities or crystal dots in the heat sealing layer, or defects such as pinholes or uneven thickness in the film, which can directly lead to leakage points after heat sealing. At this point, it is necessary to contact the material supplier, provide testing data, change batches or adjust the material formula.
Step 4: Record and solidify the optimal parameters
After solving the leakage problem, it is necessary to record and archive the final heat sealing temperature, pressure, and time parameters, and conduct multiple repeated tests to verify the stability of the parameters, form a standardized heat sealing process plan, and avoid similar problems in subsequent testing or production.