Liquid filling bag issues rarely appear on the bag surface; they mostly manifest in the sealing edge, nozzle welding area, and pouring experience. The three most common feedbacks from buyers are leakage after transportation, sealing edge cracking during drop tests, and inconsistent pouring speed when pouring out. Each of these issues has its own priority for evaluation and can be confirmed with a small quantity during the sample stage. Below, we will explain the key points for verification in the circulation, sealing, and pouring stages.
Why do liquid filling bags often fail at the sealed edge first?
The liquid in the bag is pressed against the entire bag body by its own weight, and the bottom seal is subjected to this pressure over time. At the folded pleat area of the bottom, multiple layers of film must be sealed simultaneously. The outer layer may block heat, while the inner layer may not be properly welded. Although the surface appears as a continuous seal, there may be an unsealed channel inside, leading to leakage that often occurs several days after filling. Widening the seal, extending the heat sealing time, or avoiding the most stressed corner areas can reduce the risk, but ultimately, the seal strength and leak detection tests are necessary to confirm.
How to design drop testing to closely simulate real-world distribution?
Drop testing should be closely aligned with real-world distribution conditions to be meaningful. The drop height, landing angle, surface material, and liquid level all affect the results. The difference between a flat drop and an angled drop can be significant. An effective approach is to make the drop direction similar to actual logistics conditions, repeating drops at angles commonly encountered during courier sorting or handling. Use samples filled to the actual shipping liquid level. Conduct leak detection after each drop, as this is more reliable than simply checking for ruptures, since some bags may appear intact but start leaking the next day. Refer to the following for more details. ASTM D4169 Transportation performance testing methods, serving as the basis for designing drop test procedures.
Troubleshooting Order for Sealing Leaks and Leakage
To troubleshoot leaks, narrow down the issue step by step rather than replacing materials immediately. First, determine whether the leak is from the sealing edge or the suction nozzle: wipe the bag dry and let it sit to observe where the leakage occurs; then cut into the seal area to check for material inclusion, bubbles, or folds. Common causes include liquid from the filling process coming into contact with the sealing area, insufficient sealing edge width, and weak weld points on the suction nozzle. If you suspect a problem with the seal integrity, you can use ASTM F2096 This type of coarse leak detection method is used for confirmation, then decide whether to adjust parameters or change the structure. The differences in bag types such as suction bag can be referred to. Nozzle Bag Product Classification。
Poor pouring experience, where is the problem likely to occur?
When the flow is uneven, it’s usually because the intake of air can’t keep up with the liquid discharge. As liquid is poured out, air must simultaneously enter the bag. If the opening can only accommodate one direction at a time, the liquid flow will be intermittent. Bags with small openings and large capacities are most prone to this fluctuation. Bags that rely on squeezing and those that rely solely on gravity for pouring feel completely different. As the bag is used, it gradually softens, and the actual effect of the opening changes during pouring. Adding an air vent, enlarging the opening, or switching to a squeeze-type design may all be helpful. The choice depends on how the bag is lifted.
Sample Confirmation Checklist: What to Check and What to Measure
Sample making should revolve around the previous three steps, following a fixed checklist to run through the process, rather than relying on personal feeling to judge.
- Fill and seal the product according to the actual speed of the production line, then observe after one day whether the bottom seal of the bag is leaking.
- Perform leakage testing after each drop according to the shipping liquid level and common angles.
- Pour the actual contents into another container, record the pouring time and whether there is any fluctuation in speed.
- Test the seal by repeatedly opening and closing the lid several times, checking the engagement between the suction nozzle threads and the seal.
Only samples that pass all four tests are worth proceeding with.
When should the nozzle bag structure be replaced?
When the contents are thick, require complete emptying, or contain large particles, a spout bag structure is often not cost-effective. High-viscosity contents flow slowly through small-diameter openings, while larger diameters can cause splashing. Products requiring complete emptying tend to leave residue around the spout. Large particles may also clog the opening. These requirements are better suited for wide-mouth flat-bottom bags or rigid containers, and are not suitable for all liquids. Compare accordingly. Liquid Beverage Packaging Solutions Determine based on the common forms in the list.
Conclusion
Treat the liquid filling bagging process as three simultaneous validations: the sealing edge must withstand long-term pressure from the liquid’s weight, the bag body must endure real-world drop impacts during distribution, and the discharge must allow air to enter and liquid to exit. Conduct small-scale trials using actual product contents, real shipping liquid levels, and actual line speeds, recording the results as data to determine the structure. The specific structure will vary depending on the product and sales environment, and should be based on the trial data. Refer to the following for guidance. Refill Pump Bag for Dish Soap This common supplementary form is for comparison.
Common Questions
The height and number of times for the bagging drop test should be determined based on specific requirements.
Drop testing for liquid-filled pouches should be determined based on actual distribution conditions rather than using a fixed height. First, identify the most common logistics method: express delivery sorting, pallet stacking, or in-store delivery, as each has different drop heights and angles. In terms of frequency, it is recommended to perform multiple drop tests on the same specification and conduct leakage checks after each test. A single successful test does not guarantee stability for the entire batch. You can use transportation testing methods such as ASTM D4169 to develop the test plan, and then validate it with actual packaging.
Check the bottom seal first when the bag cracks during drop testing.
First, check the heat seal at the bottom pleat area of the bag, not the surface material. At the corner where multiple layers of film overlap, the outer layer may block heat while the inner layer is not properly welded, causing the bag to tear here first during a drop impact. Next, check if liquid was trapped in the sealing area during filling. When troubleshooting, compare the sealing width, heat sealing parameters, and filling level together, and confirm with a leak test. This usually helps identify the root cause before modifying the structure.
Can a zipper and a valve be made on the same liquid filling bag?
Yes, but the location and cost should be considered. A zipper allows for multiple accesses, while a spout offers better control when pouring. Both are commonly found together in large-capacity or frequently re-filled refills, such as those with zippers.Large Capacity Beverage Packaging BagsThe challenge lies in the fact that both functional components take up space on the bag surface and need to avoid the filling and sealing areas, making the bag design more complex. Single-dose refill packs are usually not equipped with a zipper, while products intended for long-term storage and repeated use are more suitable for having both features.
During the sample stage, which data should be checked to determine if the sealing is applicable?
Prioritize checking the data on seal leakage and edge strength. Leakage can be confirmed through static observation and leak detection; strength can be tested by resealing the edge after a drop. Filling speed is often overlooked; manually sealed products may have weak seals due to air bubbles on high-speed lines. Recording these three items as data is more suitable as a basis for acceptance than relying solely on the appearance of sample bags.