Packaging Quality Issue & Solutions XVI

答：

The flexible packaging with an aluminum coating undergoes repeated rubbing and compression during transportation. As a result, invisible through-hole pinholes appear on the coating or aluminum foil layer, causing a significant decline in barrier performance..

Solution:

1. Abrasion Resistance Test: According to GB/T 41347-2022 "Test Methods for Abrasion Resistance of Flexible Packaging Materials", a rubbing test instrument is used to simulate the actual rubbing and folding compression behavior through the combined motion of the direct drive axis and the rotating axis. The standard provides 5 rubbing modes (long stroke 2700 times/900 times/270 times/20 times, short stroke 20 times), and the rubbing frequency is 45 times per minute. After rubbing, the sample is subjected to pinhole counting or gas barrier comparison tests to quantify the abrasion resistance performance. The test can be conducted by the Flex durability tester (https://www.linktesting.org/4261.html/gelbo-tester-rct-02/)
2. Comparison of barrier performance before and after rubbing: Using an gas permeability tester or a water vapor permeability tester, the barrier performance changes of the sample before and after rubbing are tested respectively. The barrier performance attenuation rate is the core indicator for evaluating the anti-rubbing ability of the coating/aluminum foil layer. The test can be conducted by the Differential pressure gas permeability tester (https://www.linktesting.org/3852.html/gas-permeability-tester-gtc-203h/)
3. Pinhole counting method: After rubbing, the sample is placed on a backlight table for visual counting of the number of pinholes, or the staining and penetration method is used to enhance the visibility of the pinholes, and the number of pinholes on each sample is counted (the standard requires controlling it within 5 to 50 per sheet to ensure the validity of the test).The test can be conducted by the aluminum pinhole tester (https://www.linktesting.org/993.html/aluminum-foil-pinhole-tester-ltzk-02/)

答：

Products such as milk powder, puffed snacks, and pharmaceutical granules that are sensitive to humidity may absorb moisture and form lumps, become softer in texture, or have their active ingredients degraded during the shelf life due to insufficient water vapor barrier properties. The water vapor transmission rate (WVTR) is the core quantitative indicator for measuring the moisture barrier performance of flexible packaging.

Solution:

1. Cup-type weight gain/weight loss test: According to GB/T 1037-2021 "Determination of Water Vapor Transmission Properties of Plastic Films and Sheets - Cup-type Weight Gain and Weight Loss Method", a combination of moisture permeability cup, constant temperature and humidity box, and analytical balance is used. In the weight gain method, desiccant is placed in the moisture permeability cup, and the water vapor transmission rate is calculated based on the weight increment of the cup body; in the weight loss method, water is used as the medium, and the water vapor transmission rate is calculated based on the weight reduction. This method is applicable to films or sheets with a WVTR of no less than 2 g/(m²·24h).
2. Data stability determination: The weighing interval is 24, 48 or 96 hours. The test is terminated when the difference in weight increments between two consecutive measurements is no more than 5%. The stable data are then used to calculate the WVTR.The test can be conducted by the water vapor transmission rate tester (https://www.linktesting.org/3610.html/wvtr-water-vapor-transmission-rate-testerwtc-203h/)

答：

Although the average peel strength of the soft packaging composite film is qualified, local delamination and layering still occur during actual use. The reason is that the adhesive coating is uneven or the curing process is incomplete, resulting in abnormally low peel strength in certain areas. Just looking at the single average value cannot reveal such "hidden weak points".

Solution:

1. Full-process collection and analysis of peel curves: Conduct T-type peel tests using a tensile testing machine, simultaneously collecting the force-displacement curve instead of merely taking the average peel force. Analyze whether the curve is stable (plateau-like), whether there are sawtooth oscillations (uneven coating) or step-like fluctuations (local delamination).
2. Key indicators extraction: In addition to the average peel force, focus on extracting the minimum peel force and the fluctuation range of peel force. If the minimum peel force is much lower than the average value, or if the fluctuation amplitude exceeds the average value ± 20%, it indicates the presence of a local weak bonding area.
3. Destruction form determination: After the peel is broken, observe the fracture surface to distinguish between interface destruction (separation of the adhesive layer and the substrate), cohesive destruction (breakage of the adhesive layer itself), and substrate tearing. Different destruction forms correspond to different process problems.The test can be conducted by the automatic tensile tester (https://www.linktesting.org/7007.html/automatic-tensile-tester-xlw-500n/).

答：

The test values for the heat sealing strength of the packaging bag were qualified, but the seal still broke during filling, dropping or transportation impact. The reason is that the heat sealing strength only reflects the static tensile force and cannot reflect the energy absorption capacity of the seal under dynamic impact. Even if the heat sealing strength is high, if the seal material is brittle, it will still break during the impact.

Solution:

1. Heat sealing failure test: According to the patented method, a tensile testing machine is used to stretch the heat-sealed sample at a speed of 280 - 320 mm/min. The stretching force-displacement curve is recorded, and the area of the curve is calculated, which represents the failure energy of the heat-sealed area (in joules). The failure energy comprehensively reflects the strength and toughness of the seal, and is more capable of predicting the performance under dynamic impact compared to a single heat sealing strength.The test can be conducted by the automatic tensile tester (https://www.linktesting.org/7007.html/automatic-tensile-tester-xlw-500n/) & the simulation instrument heat seal tester(https://www.linktesting.org/891.html/heat-seal-tester-lth-h3/)
2. Failure extension of the heat sealing area: The extension at the time of failure is simultaneously recorded (in mm). A low extension indicates that the seal is brittle, even if the strength value meets the standard, the impact resistance may still be insufficient.
3. Multi-site sampling verification: Samples are taken from the side, back, top, and bottom heat-sealed areas of the packaging bag to ensure the consistency of the heat sealing performance in each sealing area, avoiding a weak sealing area at the periphery becoming the starting point of impact damage.

答：

When soft packaging films or sheets are subjected to impacts from heavy objects falling or from hard objects during transportation and handling, they may suffer through-type ruptures. The drop weight impact performance reflects the material's resistance to damage under free-fall impact. It differs from the force application method of the pendulum impact and is an important indicator for evaluating the film's resistance to dynamic impact. Approximately 30% of plastic packaging quality accidents are directly related to incomplete or missing performance tests. Drop weight impact is often a neglected testing blind spot.

Solution:

1. Drop dart impact test: Using a drop dart testing instrument, in accordance with GB/T 9639 or ASTM D1709, the film sample is clamped in a circular fixture, and a specified mass of the drop dart is released to freely fall and impact the sample from the set height. The drop dart mass (in grams) at which 50% of the samples are damaged is determined by the step method (Method A or Method B) to quantify the material's impact resistance toughness.The test can be conducted by the falling dart impact tester(https://www.linktesting.org/856.html/ltmc-a-falling-dart-impact-tester/)
2. Verification of low-temperature drop dart impact: For frozen food packaging, the sample is pre-treated at -18℃ before conducting the drop dart impact test to evaluate whether the film's impact resistance under the low-temperature brittle state meets the requirements for cold chain transportation.
3. Data statistics and determination: The drop dart impact test usually requires at least 20 valid samples for step method statistics. The larger the drop dart mass, the better the material's impact resistance performance. The results are matched and evaluated with the product's transportation drop height and the weight of the contents.