[Chinese Packaging Network News] Friends working in the corrugated box industry often face a recurring problem from customers: "Why is the box so soft?" This issue is really frustrating and challenging to solve. The base paper used in corrugated cardboard is hydrophilic, meaning it naturally absorbs moisture from the air. During the rainy season or in high humidity conditions, the cardboard can absorb moisture from the air, causing it to become soft. This can lead to customer complaints, returns, fines, and even compensation. As a result, solving the issue of softening cardboard has become a top priority for corrugated box manufacturers.
First, the moisture resistance of paper and board
Raw paper and corrugated paper, especially corrugated medium, are highly absorbent. Prolonged exposure to moist air increases the water content, significantly reducing the lateral crushing strength. When relative humidity reaches 85%, the ring crush strength can drop by as much as 60%.
Solution
It is recommended to use a base paper with better waterproof and moisture-resistant properties, particularly when using a pitted surface. To test the waterproof effect, you can measure the surface water absorption using a Káble test. If the surface water absorption is below 50 g/m² (60 seconds), it indicates a better waterproof performance. If you don't have testing equipment, simply sprinkle a few drops of water on the cardboard or corrugated paper, wait 60 seconds, and check if the paper surface shows any discoloration after drying. If not, it suggests good water resistance.
To improve the surface water resistance of the paper, paper mills usually increase the amount of waterproofing agents in the surface sizing starch solution during the papermaking process. Since these agents are costly, the water-repellent base paper tends to be more expensive than regular base paper, with price differences ranging from 50 to 100 yuan per ton. The lower the grammage, the higher the cost. Therefore, corrugated box manufacturers should communicate with their customers and consider adjusting prices accordingly.
Second, the production process of corrugated boards
The main way to prevent softening is to choose quality materials, followed by optimizing the production process. Excess moisture is the key factor that causes softening. Therefore, during the manufacturing and processing of corrugated boxes, it's important to remove as much moisture as possible.
Solution:
Keep the base paper warehouse isolated from external influences as much as possible, avoiding damp air from entering freely. Installing a dehumidifier in the warehouse can help maintain a relative humidity level below 65%.
When the base paper is stored, it may absorb moisture from the air. Before running the machine, increase the preheating angle on the dryer. If this doesn’t work well, reduce the speed and increase the steam pressure.
Increasing the powder content in the paste and reducing the glue amount can help lower the moisture content of the box. Increasing the borax ratio also improves the feel and strength of the corrugated board.
Reduce the number of stacked boards on the conveyor belts and slow down the speed, especially after the corrugated board has been fully dried.
Third, storage environment
After the cardboard is off-line, it should be allowed to release any remaining moisture to avoid condensation caused by temperature differences. The storage area for cardboard or boxes should remain well-ventilated. Cardboard should never be placed directly on the ground—use pallets instead. Ensure there is enough space between stacks to allow for proper ventilation and heat dissipation.
It is recommended to use wooden pallets, which can absorb moisture from the ground and are suitable in size for corrugated boxes. Keeping the storage area ventilated and using protective wrapping films can effectively reduce and isolate the effects of weather-related softening.
Many manufacturers have started using dehumidifiers. If the warehouse humidity can be kept below 65%, the hardness of the cardboard will significantly improve.
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