Corrugated boxes are a core material in the logistics and packaging industries. Their moisture-proofing properties directly impact their service life and the safety of their contents. In humid environments, untreated cartons are susceptible to moisture absorption, leading to reduced strength, deformation, and even mold. Scientific moisture-proofing techniques can significantly extend the lifespan of cartons by physically or chemically blocking moisture penetration.
Surface sizing is a fundamental process for moisture-proofing corrugated boxes. By spraying a sizing agent during the paper drying phase, a dense waterproof film is formed on the surface of the corrugated box, preventing water droplets from penetrating within five minutes. Common sizing materials include rosin glue, paraffin wax, and synthetic resins. These materials fill the gaps between paper fibers, reducing surface energy and thus minimizing moisture absorption. Glued cartons maintain structural stability in short-term humid environments, preventing compressive strength loss due to moisture absorption. They are particularly suitable for packaging dry powdered goods or products that frequently move in and out of cold storage.
Laminated paper lamination technology achieves effective moisture-proofing by laminating a plastic film onto the surface of the corrugated box. This process uses a cast film machine to evenly coat plastic particles, such as polyethylene, onto the surface of paper, creating a continuous waterproof layer. The resulting coated cartons are not only oil- and moisture-resistant but can also be sealed through heat sealing. Despite the higher cost, their excellent barrier properties make them a preferred solution for packaging items such as seafood and fruits and vegetables in high-humidity environments. Furthermore, the coating enhances the cartons' abrasion resistance, reducing surface damage during transportation and indirectly extending their service life.
Hydrophobic corrugated cardboard achieves moisture resistance through a coating with a low-surface-energy material. This process utilizes a hydrophobic agent, such as polylactic acid, polyolefin, or molten paraffin, applied to the cardboard face paper. This coating causes water droplets to roll off the surface, similar to a lotus leaf, rather than penetrating the fibers. This treatment is cost-effective and minimizes the impact on the carton's recyclability. It is suitable for packaging powders that easily clump after absorbing water or for goods requiring cold chain transportation. Once removed from cold storage, hydrophobic-treated cartons effectively resist moisture intrusion caused by condensation on the wall, maintaining stable compressive strength.
Water-repellent corrugated cardboard uses a curtain coating process to form a resin or wax film on the cardboard surface, making it virtually impermeable to water even after prolonged contact. This process involves evenly applying a molten synthetic resin or wax mixture to the corrugated cardboard surface, creating a dense barrier layer. Water-repellent boxes are often used to package products such as salted and frozen foods that are exposed to moisture for extended periods. The soft wax layer also prevents scratches on high-finish items such as furniture and pianos.
Adding a water-repellent agent to the corrugated paste is a key process for improving the moisture resistance of corrugated boxes. By adding a high-molecular-weight polymer to the starch adhesive, it replaces the hydroxyl groups in the starch molecules, creating a more water-resistant adhesive layer. This treatment effectively prevents collapse of boxes in humid environments due to moisture absorption and emulsification along the corrugated paste lines, making it particularly suitable for cold chain logistics or high-humidity warehousing. Cardboard boxes treated with the water-repellent agent maintain their structural integrity when stored in cold storage or humid environments, significantly extending their service life.
The surface lamination process involves applying a plastic film, such as polypropylene, to the surface of a carton and bonding it with adhesive under heat and pressure to create a strong, waterproof layer. The laminated carton not only offers excellent moisture-proof properties, but also enhances resistance to friction and contamination, making it less susceptible to cracking when folded. This process is particularly suitable for products such as aquatic products and electronic instruments, which require a tight seal. Although laminated cartons are difficult to recycle, their superior protective properties still make them a key player in the high-end packaging market.
The vent design is an innovative solution to the problem of heat vapor absorption. For products like beer that generate heat during packaging, condensation easily forms inside the carton, reducing its compressive strength. Perforations in the carton's side label promote air circulation and reduce water vapor accumulation. This design maintains the carton's moisture-proof properties while effectively preventing structural failure caused by excessive internal humidity, further extending the carton's lifespan.
