As a core component of food packaging, the moisture-proofing of the inner surface of food paper tubes is directly related to the shelf life and safety of food. Because paper tubes are composed of multiple layers of paper, their fiber structure is highly absorbent. Inadequate moisture-proofing of the inner surface can lead to food caking, mold, and quality degradation. Therefore, improving the moisture-proofing of the inner surface through process optimization is crucial for extending food shelf life.
Surface coating is a fundamental method for moisture-proofing the inner surface of food paper tubes. Applying a continuous moisture-proof coating to the inner surface of the paper tube creates a physical barrier that blocks water vapor penetration. Commonly used coating materials include thermoplastic resins such as polyethylene (PE) and polypropylene (PP), as well as thermoset materials such as epoxy resin and polyurethane. These coatings must be non-toxic, odorless, chemically resistant, and certified for food contact safety. Coating is typically applied by roller or spray coating to ensure uniform coverage of the inner surface of the paper tube and avoid localized defects that could lead to moisture-proofing failure.
In addition to traditional coatings, new nanocomposite coating technologies are increasingly being applied to food paper tubes. Nanomaterials such as silica and zinc oxide have high surface area and strong hygroscopicity. Dispersing them in a coating can significantly improve moisture-proofing performance. Nanocoatings not only form a dense physical barrier but also capture water molecules through chemical adsorption, achieving a dual moisture-proofing effect. Furthermore, nanocoatings enhance the mechanical strength of the paper tube, reducing damage to the coating caused by impact during transportation, and further improving moisture-proof stability.
For high-humidity environments or long-term storage requirements, the inner wall of food paper tubes often utilizes a multi-layer composite structure. By combining the moisture-proof coating with high-barrier materials (such as aluminum foil and EVOH), a gradient moisture-proof system can be created. For example, an inner layer of nanocoating, a middle layer of aluminum foil, and an outer layer of regular paper can effectively block water vapor while controlling costs. The composite process must ensure strong bonding between the layers to prevent delamination that could degrade moisture-proof performance.
The moisture-proof treatment of the inner wall of food paper tubes also requires coordinated optimization of the processing technology. During the winding process, the smoothness of the paper tube's inner wall must be controlled to avoid uneven coating thickness caused by surface irregularities. Furthermore, drying process parameters must be optimized to prevent cracks or bubbles from forming during the curing process. For example, using staged temperature control—pre-drying at a low temperature to remove solvents followed by high-temperature curing to form a dense coating—can significantly improve moisture-proofing.
The impact of ambient temperature and humidity on the moisture-proofing performance of food paper tubes cannot be ignored. In high-temperature and high-humidity environments, paper tube fibers absorb moisture and expand, potentially causing the coating to crack or detach. Therefore, moisture-proofing treatments must be designed to adapt to environmental conditions. For example, hygroscopic additives can be added to the coating. When the humidity rises, the additives absorb excess moisture and maintain the coating's structure. When the humidity drops, the additives release moisture, preventing cracking due to shrinkage. This dynamic adjustment mechanism can significantly improve the moisture-proofing performance of paper tubes in various environments.
The effectiveness of moisture-proofing treatments on the inner wall of food paper tubes must be rigorously tested and verified. Common testing methods include moisture permeability testing, moisture absorption testing, and simulated environmental aging tests. The moisture permeability test measures the amount of water vapor that permeates the paper tube per unit time to evaluate its moisture-proof performance. The moisture absorption rate test uses a weighing method to measure the amount of water absorbed by the paper tube under specific humidity conditions. The simulated environmental aging test exposes the paper tube to high temperature and high humidity to observe how its moisture-proof performance changes over time. These testing methods ensure that the moisture-proof treatment of food paper tubes meets actual usage requirements.
