The sealing part appears to be in good condition, but after a few days, it started to leak. How can we solve this problem?
答：
The common cause is that particles or droplets of the contents (such as powder, sauce, debris) are mixed in the sealing area, preventing the upper and lower heat-sealed layers from fully melting together, thus forming tiny leakage channels.
Solution:
Before sealing, add dust removal or liquid absorption devices (such as brushes, negative pressure adsorption) to reduce the risk of material clamping.
Select anti-pollution heat sealing materials (such as specific formulations of PE or co-extruded films), and even with minor foreign substances, effective sealing can still be achieved.
Adjust the heat sealing process: appropriately extend the heat sealing time, lower the temperature, and utilize the melt's fluidity to fill the gaps between the particles. Use the heat seal tester to find the best sealing parameter combination https://www.linktesting.org/891.html/heat-seal-tester-lth-h3/.
The frozen packagings tend to crack or the sealing parts break when exposed to low temperatures.
答：
The fundamental cause is the insufficient cold resistance of the material. Ordinary polyethylene (PE) becomes brittle at low temperatures, with its flexibility and impact resistance decreasing; moreover, excessive heat sealing causes the material at the sealing edge to become thinner and leads to stress concentration, which makes it prone to breaking when frozen.
Solution:
Switch to cold-resistant and toughening materials, such as metallocene polyethylene (mPE), EVA or POE blended modified materials, to enhance the low-temperature impact resistance.
Optimize the heat sealing parameters: Reduce the heat sealing pressure and temperature to prevent the sealing area from being overly compressed and becoming too thin. Use the heat seal tester to find the best sealing parameter combination https://www.linktesting.org/891.html/heat-seal-tester-lth-h3/.
How to quickly determine whether the sealing performance is qualified? Are there any simple on-site detection methods?
答：
The negative pressure method (bubble method) is commonly used at the factory site. The packaging bag is immersed in water, and the vacuum is applied to the interior of the sealed container. If there are continuous bubbles emerging, the location where the bubbles appear is the leakage point.
Solution:
In addition, the following methods can also be combined for verification:
Positive pressure blasting method: Inflate and pressurize the packaging, test the bursting strength, and quantitatively evaluate the sealing strength. Use position pressure sealing tester to find the best sealing parameter combination https://www.linktesting.org/1225.html/intelligent-sealing-instrument-mfy-06s/
Transport simulation test: Place the packaging on a vibration table to simulate the transportation process, and then test the sealing performance. This can expose fatigue leaks caused by rubbing and vibration.
The corners of the blister packaging (such as fast food boxes) are always not sealed properly. How to solve?
答：
The poor sealing at the corner is usually caused by two reasons:
The sealing plate shape does not match: The flat soldering iron cannot cover the corner transition area of the plastic packaging box, resulting in a blind area for heat sealing.
Uneven thickness of the tray: The wall thickness at the corners of the thin-walled plastic packaging box is relatively thin, resulting in uneven pressure distribution during heat sealing.
Solution:
Change the flat heat-sealing soldering iron to an irregular-shaped one (such as hourglass-shaped or wing-shaped), so that the corners can also receive sufficient heat and pressure.
By using the floating pressure head technology, the thickness deviation is automatically compensated to ensure consistent pressure throughout.
When designing the blister packaging box, avoid using right-angle corners and instead use rounded corners for a smooth transition, which can reduce stress concentration.
The biscuit packaging was clearly sealed properly, but it became damp and soft after several months. Why?
答：
This phenomenon is due to insufficient barrier properties of the packaging material, rather than failure of the seal. Common causes include:
The water vapor transmission rate (WVTR) of the material is too high, allowing external moisture to slowly seep into the packaging.
The interlayer of the composite film peeled off (split), causing the barrier layer (such as aluminum foil, EVOH) to fail and moisture to penetrate through the split interface.
Solution:
Re-calculate the required WVTR based on the product shelf life, and select high-barrier materials such as aluminum foil composite film or aluminum oxide/silicon oxide evaporation film.
For high-fat dried fruits, the inner layer material should be made of EVOH co-extruded film to prevent the erosion of the composite adhesive by the oil, which could cause delamination.
When the products enter the factory, strict tests are conducted on the WVTR and composite strength of the films, and accelerated aging tests are carried out under simulated temperature and humidity conditions to verify the results. Use the WVTR tester to complete the QC test for raw material (https://www.linktesting.org/3610.html/wvtr-water-vapor-transmission-rate-testerwtc-203h/)
