The contamination on candy packaging seals is mostly caused by powder getting into the wrong place, not due to insufficient strength of the film. This issue is particularly noticeable with sour candies and powdered snacks. Sugar powder is fine, acidic, and prone to moisture absorption and clumping. Once it falls into the sealing area, the seal does not completely stick; instead, it sticks most of the way, leaving a small channel. This is not visible during visual inspection, but leakage occurs after transportation and pressure. Therefore, the focus of on-site investigation should be on material dispensing, static electricity, and cleanliness in the sealing area. Below is a step-by-step guide on how to investigate, how to make improvements, and how to verify the results.
Key Points
- Sealing contamination is often caused by powder fallout. Check the material discharge height and the material barrier first, then check the parameters.
- Static can affect sealing, film conveying, and opening simultaneously, so the operating condition of the ionizer should be checked separately.
- Acceptance must consider both strength and integrity, and samples must be retained throughout the entire operational period.
Why are sour candies and sugar powders particularly prone to causing sealing contamination?
Three mechanisms deliver the powder to the sealing zone. The first is gravity rebound, where coarse particles hit the flow of material and bounce up against the inner walls of the bag above the loading line. The second is electrostatic attraction, which becomes more pronounced with finer sugar powder. Charged particles tend to adhere to the nearest surface, and the moving film surface happens to be that surface. The third is post-filling migration, where during the movement of the bag from the filling station to the sealing station, if there is vibration, the powder redistributes and moves upward.
The proportion of these three components varies in different formulas. Products coated with surface powder, mixed with acid powder and sugar powder, produce much more loose dust compared to coated granulated sugar. On the same production line, sealing is stable for one specification, but becomes leaky when switching to another specification. This is usually due to a change in dust quantity, not equipment failure.
Contaminated seals may exhibit symptoms such as discoloration, deformation, leakage, or reduced sealing effectiveness.
Contamination-related failure rarely manifests as a complete seal crack. More commonly, the seal appears continuous but can be felt as small hard spots when peeled apart, or there may be a darkened appearance in certain sections with incomplete fusion. Another manifestation is gradual moisture absorption of the contents even when the package is intact, due to the narrow channel, which is not detectable by sight or touch. It can only be inferred through weight loss or changes in texture.
| Performance | More likely causes | Check what first |
|---|---|---|
| Cracks, localized darkening | Sugar powder or sugar crystals trapped | Cutting height, distance from sealing line to material surface |
| Good appearance but contents are damp | Fine channels exist | Integrity Check, Sealing Knife Cleanliness Status |
| The batch is sometimes good and sometimes bad. | Static or dust accumulation varies with operation fluctuations | Ion wind, electrostatic measurement, frequency of blade cleaning |
| Performance drops suddenly after changing specifications | Dust quantity and bulk density have changed | Are the filling parameters shared across different specifications? |
On-site inspection should be carried out in what order?
- First, open the seal of the failed bag to determine whether it is due to powder contamination or insufficient temperature, as the two issues require completely different handling approaches.
- Record the location of defective bags within the production batch to determine whether they occurred during the start-up phase, stable operation phase, or the closing phase.
- Check the cutting height, the distance between the material surface and the sealing line, and whether the purging before sealing is effective.
- Check or measure the static condition in the workshop and confirm the operating status of the ionizer.
- Monitor the cleanliness of the sealing blade during one production cycle to determine an appropriate cleaning schedule.
- If the issue persists even after all the above factors are stable, consider adjusting the sealing parameters or changing the sealing layer structure.
Static electricity and moisture absorption can lead to a variety of secondary issues.
Static electricity not only attracts sugar powder to the sealing area but also causes the film surfaces to stick together, leading to unstable film movement and difficulty in opening the bag. Operators often have to manually push the film, which in turn brings more powder into the sealing zone. Once sugar powder absorbs moisture, it becomes sticky and clumps together, forming a coating on the sealing blade. This coating affects heat transfer and leaves marks on the surface of the bags in subsequent steps.
These two issues combined can also affect the friction coefficient, resulting in the bags not moving properly or suddenly slipping on the packaging machine. The relationship between the friction coefficient and the anti-stick agent is itself an independent troubleshooting direction. If both film abnormalities and seal contamination occur simultaneously, it is recommended to investigate the friction coefficient and anti-stick agent application.Machine Friction ConditionInclude all items in the inspection rather than focusing only on the sealing knife.
What can be modified on the equipment and molds?
Most modifications do not require changing materials. Installing a dust shield or reducing the outlet opening can minimize powder spillage. Lowering the outlet height can significantly reduce rebound. Adding an ion wind or low-pressure blowing before sealing can remove floating powder above the material surface. For the sealing blade, the key is to establish a fixed cleaning schedule and record it, rather than cleaning it only when it appears dirty.
If the product line also produces specifications with different shapes and higher dust levels, such as freeze-dried sugar blocks, the bag type and opening position will also affect the powder drop point, and you can refer to the following.Windowed Vacuum-Sealed Candy BagThe opening and spacing of this type of bag should be compared with the reference, but the exact positions still need to be tested on the actual machine at our factory.
How should acceptance and sample retention be carried out?
Acceptance should consider both strength and integrity simultaneously, not just strength. Peel tests can detect hard spots and dark sections, but they cannot identify fine leaks, so leakage testing according to integrity methods is still required. Reference can be made to dye penetration methods. ASTM F1929It specifies the testing conditions and evaluation methods. When in actual use, it should be implemented after confirming the applicable scope based on the product specifications of the factory.
Sample retention should be conducted by shift and production time periods, rather than only retaining the first batch at startup. Sealing issues often accumulate over time with operation, and only samples covering the entire operational period can reveal trends. Retention should also record sealing parameters and cleaning actions at the same time points, otherwise it will be impossible to determine the source of differences during subsequent reviews.
Conclusion
Contamination of sour candy and sugar powder snacks during sealing should first be checked along the powder path, then consider parameters and materials. Adjusting the filling height, blocking mechanism, and ion wind are the three adjustments with the lowest cost and usually the most effective; after the sealing blade cleaning cycle is fixed, the variation between batches will be significantly reduced. When reorganizing the bag type and opening position, you can refer to the following.Candy Snack Packaging SolutionsThe overall bag shape logic, then return to the specific product and confirm based on actual measurements from the factory’s machines.
Common Questions
Sugar powder falling into the sealing area, can increasing the sealing temperature press it down?
It’s not necessarily the case, and it often makes the problem more hidden. Increasing the temperature may make the seal appear smoother, but the powder remains trapped inside, and the channel is not eliminated—it’s just harder to detect visually. The correct sequence is to first reduce the powder landing points, then confirm whether the sealing parameters match the window of the structure. If wrinkles appear on the film surface or the edges of the seal become brittle after increasing the temperature, it indicates that the temperature has exceeded the normal range.
In workshops with high static electricity, is the contamination during sealing more severe?
The effect is usually more noticeable, especially for products with fine sugar powder. Charged particles actively adhere to the film surface and equipment surfaces, not only falling in the sealing area but also affecting film movement and opening. First, confirm whether the ion wind device is functioning properly and correctly aligned with the material surface. Then observe the change in sealing failure rate before and after controlling static electricity for the same batch of products, using data to determine the extent of static influence.
When inspecting packaging bags for sour candy, what should be focused on?
Focus on the peeling condition in the sealing area and consistency within the batch, rather than just the appearance. Sampling should cover the start-up section, stable section, and end section. After peeling, check for hard spots, darkened sections, or areas with poor fusion. If the appearance is normal but there are signs of moisture absorption in the contents, further integrity testing is required. Record the sealing parameters and cleaning actions at each sampling point for traceability.
Why does the same sealing parameter work normally in the morning but not in the afternoon?
The most common cause is the gradual accumulation of sugar powder on the sealing blade, which alters heat transfer. This layer reduces the actual temperature reaching the sealing surface, resulting in decreased effectiveness despite unchanged parameters. Second, fluctuations in workshop temperature and humidity throughout the day affect the adhesion and electrostatic properties of the sugar powder. The solution is to establish a fixed cleaning schedule and record it, while also incorporating workshop temperature and humidity into daily records, rather than repeatedly adjusting temperature compensation.