Why Do Corrugated Boxes Get Damp?
Corrugated boxes are widely used packaging products, serving as the backbone of transportation packaging. In addition to protecting goods, facilitating storage and transportation, they also enhance the visual appeal of products and serve promotional purposes. However, corrugated boxes primarily consist of cellulose, semi-cellulose, lignin, etc., indicating a strong hydrophilic nature and high moisture absorption capacity.
The compressive strength of damp corrugated boxes significantly decreases, and in conditions approaching 99.99% humidity, boxes may even experience disintegration and collapse. Therefore, environmental humidity has a substantial impact on the performance of corrugated boxes, with high humidity directly threatening their functionality. In areas where corrugated boxes are stored or where a large quantity of goods is packaged using corrugated boxes, humidity needs to be controlled within a reasonable range.
Excessive moisture content in corrugated boxes can cause changes in their shape, adhesive hydrolysis, and a direct reduction in compressive strength, burst strength, and aesthetic appeal. Due to their high moisture absorption, corrugated boxes can directly absorb moisture from the air, leading to an increase in their own moisture content. When controlling environmental humidity, it is advisable to avoid using desiccants because corrugated boxes themselves have high moisture absorption properties and can act as an alternative “desiccant.” In some cases, the moisture absorption capacity of corrugated boxes may even exceed that of the desiccants.
During such situations, efforts should be made to use:
- Mechanical equipment, especially in large warehouses, to enhance ventilation. Ventilation facilitates moisture dispersion and prevention, and large warehouses should ensure mechanical ventilation. However, ventilation should be avoided during damp and humid weather.
- Dehumidifying equipment. Dehumidifiers can effectively control environmental humidity continuously for extended periods, making them indispensable for moisture prevention in storage. They can work well during humid and damp weather, providing cost-effective solutions compared to air conditioning. They can also be combined with fresh air systems, creating a dual-function system for ventilation and dehumidification.
- Additionally, the more layers a corrugated box has, the better its moisture resistance. For instance, a 7-layer corrugated box has better moisture resistance and compressive strength than 5-layer or 3-layer boxes. In areas with high humidity, especially in the southern regions, corrugated boxes with more layers may be necessary.
How to Prevent Moisture in Corrugated Boxes
- Adding waterproof resins during the paperboard manufacturing process ensures that water droplets will not penetrate the surface of the paperboard within 5 minutes. Starch paste often incorporates a significant amount of waterproof additives, such as urea-formaldehyde resin, melamine-formaldehyde resin, polyvinyl alcohol-acetaldehyde resin, etc. However, waterproof additives are relatively expensive and may cause issues such as peeling during the production process.
- Hydrophobic corrugated boxes, also known as waterproof corrugated boards, involve coating low-surface-energy substances such as polylactic acid (PLA), polyolefin, polycarbonate, polyamide, polyester, and molten paraffin. This changes the material’s roughness and surface morphology. After being soaked in water, hydrophobic corrugated boards form water droplets on the surface, allowing water to slide off without penetrating the interior of the paperboard. Hydrophobic treatment is cost-effective and suitable for packaging dry powder items, especially powders that tend to clump after absorbing water. Hydrophobic corrugated boards do not significantly reduce compressive strength before dew evaporation, effectively protecting the goods.
- Waterproof (coated) corrugated composite paperboard, also known as waterproof or moisture-proof corrugated paperboard, has a surface that remains nearly impermeable to water for an extended period but loses its waterproofing ability when immersed in water. Waterproof corrugated paperboards are typically used for curtain coatings, where molten synthetic resins or wax mixtures are applied to the surface to form a resin or wax film. If necessary, a double-sided coating can also be used.
Five Major Testing Standards for Qualified Paper Boxes
Circular compressive strength test
This test evaluates the functionality of paperboard under pressure, serving as a crucial indicator of corrugated box strength. The radial compressive strength of paperboard affects the edge compressive strength of corrugated paperboard, which, in turn, significantly influences the overall compressive strength of the paper box.
Moisture content inspection
Moisture content refers to the percentage of water in the original paper or paperboard, expressed as a percentage. Moisture content has a significant impact on the strength of the box. Therefore, it is one of the main reasons for three severe defect inspection items in paper box testing. This testing method uses the drying method.
Tensile strength, breaking length, and elongation test
Tensile strength refers to the pulling force that paper or paperboard can withstand per unit area. Breaking length is related to tensile strength, and the larger the tensile strength, the greater the breaking length. Elongation is the ratio of the increase in length to the original length when paper or paperboard is stretched until it breaks.
Folding resistance test
Folding resistance refers to the logarithm of the number of double-foldings required for a sample of standard width to crack under certain conditions. It is an indicator of the fatigue resistance of the paper to folding in the machine direction and one of the basic mechanical properties of paper, indicating its ability to resist repeated folding.
Paper and paperboard puncture strength test
This test measures the pressure at which uniform increases in pressure are applied to paper or paperboard. It interplays with tensile strength, elongation, and tear strength.