In the production process of white cardboard boxes, precise control of the cardboard's moisture content is crucial to preventing warping. Due to its surface coating, white cardboard exhibits different absorbency and dehydration characteristics compared to ordinary cardboard. If the moisture content is unbalanced, uneven fiber expansion and contraction can directly lead to edge warping, central depression, or overall distortion of the white cardboard box, severely impacting its appearance and functionality. Therefore, a systematic moisture content control system must be established, encompassing the entire chain, including raw material inspection, environmental temperature and humidity control, printing process adaptation, adhesive management, stacking optimization, finished product storage protection, and dynamic monitoring and adjustment.
Raw material inspection is the first line of defense in moisture content control. The coating process of white cardboard alters its hygroscopicity, and differences in coating thickness and material between different suppliers can lead to varying moisture content sensitivities. Before production, the moisture content of each batch of raw paper must be tested to ensure it is balanced with the humidity of the workshop environment, preventing chain reactions in subsequent processing caused by excessively high or low moisture content in the raw paper. For example, if the moisture content of the base paper is lower than the ambient humidity, it is prone to absorbing moisture and expanding during production; conversely, it may dehydrate and shrink, both of which can lead to warping.
Stable ambient temperature and humidity are crucial to preventing cardboard from absorbing or dehydrating. The temperature and humidity in the printing workshop and the white cardboard box forming workshop must be kept in dynamic equilibrium to avoid drastic changes in cardboard moisture content due to environmental fluctuations. High temperature and low humidity environments accelerate the evaporation of moisture from the cardboard surface, and the different evaporation rates of the fiber layers under the coating can easily create stress differences, causing warping; low temperature and high humidity environments may cause the cardboard to absorb moisture and expand overall. By installing an intelligent temperature and humidity control system, combined with air conditioning, dehumidifiers, and humidifiers, maintaining the workshop environment within a suitable range can effectively reduce passive changes in cardboard moisture content.
Adapting the printing process requires balancing ink drying and cardboard protection. The surface coating of white cardboard has relatively low ink absorption; therefore, ink viscosity and printing pressure must be controlled during printing to prevent ink buildup that leads to slow surface drying and subsequently increases in localized moisture content. Simultaneously, drying equipment parameters need to be optimized to ensure rapid ink drying without overheating the cardboard, preventing fiber shrinkage due to high-temperature dehydration. For example, combining infrared drying with hot air circulation can balance drying efficiency and cardboard protection.
The selection and management of laminating adhesive directly affects the moisture balance of the cardboard. When laminating white cardboard with corrugated cardboard, the solid content, coating amount, and penetration of the adhesive must be strictly matched. High-solids-content adhesives have low moisture content, which reduces moisture absorption by the cardboard; however, insufficient coating may lead to weak adhesion. Low-solids-content adhesives, while having strong adhesion, can easily cause cardboard deformation due to moisture penetration. Therefore, it is necessary to determine the optimal adhesive formulation and coating parameters through experiments to ensure uniform adhesive coverage and controllable moisture penetration. Furthermore, the drying speed of the adhesive must be synchronized with the production rhythm to avoid cardboard shrinkage due to excessively rapid drying or moisture absorption due to excessively slow drying.
Optimizing the stacking method can balance the moisture distribution of the cardboard. Freshly laminated white cardboard boxes have a high moisture content; if stacked directly, the bottom boxes will deform under pressure, while the top boxes will evaporate moisture too quickly. A "cross-stacking" method is used, where adjacent cardboard box surfaces face perpendicularly, promoting air circulation and balancing the evaporation rate of moisture between layers. Simultaneously, breathable partitions are placed between stacked layers to prevent direct contact between the boxes, reducing localized deformation due to gravity.
Protecting the finished product storage environment is crucial for long-term stability. White cardboard boxes are sensitive to humidity; storage warehouses must be equipped with moisture-proof facilities, such as moisture-proof films and dehumidifiers, to prevent the boxes from absorbing moisture and expanding. Sealed packaging is required during transportation to prevent rain or humid air intrusion. If customers do not use the white cardboard boxes immediately upon receipt, they should be instructed to store them in a dry, well-ventilated area to avoid prolonged exposure that could lead to moisture content fluctuations.
Dynamic monitoring and adjustment are the core of closed-loop control. By installing humidity sensors on the production line, changes in cardboard moisture content are monitored in real time, and process parameters are dynamically adjusted based on ambient temperature and humidity data. For example, when the sensor detects high cardboard moisture content, the drying temperature can be automatically increased or the drying time extended; when the moisture content is low, the hot plate temperature can be reduced or the preheating time shortened. This data-driven adjustment model ensures that the moisture content of the cardboard remains within a reasonable range, fundamentally avoiding warping issues and improving the production quality and stability of white cardboard boxes.
