Corrugated cartons are made of hydrophilic fibers and are extremely sensitive to environmental humidity: in high-humidity environments, moisture absorption causes the corrugations to collapse and the compressive strength to drop sharply. Water loss in a dry environment causes the cardboard to become brittle and the flap to break. Therefore, water content is not a static index, but a dynamic control target that runs through the whole link of base paper procurement → storage → production → finished product storage. The moisture content of corrugated cardboard has a direct impact on its quality and performance. If the water content is not properly controlled, it will lead to a series of malfunctions.
I. Faults Caused by Moisture Content
Faults caused by excessive moisture content
When the moisture content of corrugated cardboard is too high, the following faults may occur:
Reverse corrugation, edge delamination of the paper on the double-sided machine, severe cracks in the longitudinal cutting knife edge, damage to the corrugation, uneven corrugation formation, and obvious unglued stripes (dry stripes) on the corrugated cardboard.
Faults caused by insufficient moisture content
When the moisture content of corrugated cardboard is too low, the following faults may occur:
Severe cracks appear on the longitudinal cutting edge, corrugation cracks, wavy deformation, and uneven corrugation formation.
Faults caused by uneven moisture distribution
Uneven moisture distribution can also cause the following faults in corrugated cardboard:
Wrinkling on the surface and at the top of the corrugation, corrugation folding, longitudinal warping of the corrugated cardboard, lateral warping of the corrugated cardboard, S-shaped (composite) warping of the corrugated cardboard, and uneven corrugation formation.
II. Main Factors Affecting the Moisture Content of Corrugated Cardboard (Boxes)
The factors influencing moisture content can be systematically classified into three dimensions: raw materials, production processes, and environmental conditions. Among them, multiple factors interact with each other:
Raw material factors
- Paper raw material delivery moisture content: According to national standards, it should be 9% to 12% (some literature indicates 6% to 10% or 7% to 14%, but the mainstream is 9% to 12%); If the moisture content of the raw paper entering the factory exceeds the standard (such as > 14% or even up to 18%), it will directly lead to a high moisture content of the cardboard.
- Paper raw material fiber structure and glue properties: The fibers of core paper/corrugated paper are loose, or the starch adhesive has poor viscosity, both of which can easily cause the moisture content of the paperboard to increase after absorbing moisture.
Production process factors
- Preheating and drying control: Insufficient preheating temperature of the drum and improper adjustment of the wrap angle will result in uneven evaporation of moisture; low temperature in the drying section and high vehicle speed will lead to insufficient drying and higher moisture content.
- Glue amount: Corn starch adhesive contains a lot of water, the greater the glue amount, the higher the final water content of cardboard.
- Equipment operation parameters: Vehicle speed fluctuations, insufficient steam pressure (ideally 0.9-1.2 MPa), and condensate accumulation due to clogged steam traps all interfere with the water balance.
Environmental factors
- Production workshop temperature and humidity: A high-temperature and high-humidity environment accelerates the moisture absorption of the paperboard; a low-temperature and dry environment will exacerbate the loss of moisture.
- Storage and circulation environment: The relative humidity of the raw paper storage room should be ≤ 40%; The compressive strength of finished cartons will drop sharply in an environment with 80%RH and above 30℃.
The moisture content of corrugated cardboard directly affects its stiffness, bonding strength and compressive performance: if it is too high, it will be soft, cause the box to collapse, expose the corrugations and warp. If it is too low, it will become brittle and break, have longitudinal cutting cracks, and have poor folding endurance. The complexity of its control stems from the coupled influence of multiple links, including the state of the base paper, steam temperature, paste ratio, vehicle speed regulation and workshop environment, etc.
III. Main Approaches to Moisture Control of Corrugated Cardboard
Corrugated cardboard is made of fiber base paper and is extremely sensitive to temperature and humidity: excessive humidity can cause it to absorb moisture, soften and experience a sudden drop in strength. Excessive drying is brittle and easy to crack, which seriously affects the compression and folding resistance. Therefore, moisture control is not only a process step but also a key quality red line to ensure the safety of packaging.
① Strict control at the source of raw paper
- Factory inspection: According to GB13023-91 or GB/T 462-2008 standard, the moisture content should be 9%-12% (some standards are relaxed to 6%-10% or 8%±2%).
- Storage management: Set up an independent warehouse with a temperature of 15–20℃ and a relative humidity of ≤ 30%–40%. Stack vertically, keep the ground dry, and avoid outdoor storage.
② Precise temperature control (core method)
- Single-sided machine preheating roller: By adjusting the angle of the movable paper guide roller (increase/decrease the preheating area) or activating the spray device, the moisture content of the base paper can be dynamically balanced.
- Three-stage heating of the dryer: Each group of heating plates is equipped with an independent pressure reducing valve, with a temperature target of 160-180℃ (corresponding to steam pressure of 0.9-1.4MPa), ensuring that gelatinization and dehydration are completed simultaneously.
- Drain system maintenance: The drain of the drain valve should reach 2-3 times of the condensate, and the sewage inspection should be carried out every week to prevent preheating failure.
③ Precise management of paste and glue application volume
- Paste preparation: Strictly control the water volume and viscosity (50-60 seconds for single-sided machine, about 100 seconds for double-sided machine), use the new paste on the same day;
- Glue application amount adjustment: Control the thickness of the glue application by adjusting the gap between the glue application roller and the glue scraping roller (0.2-0.25mm) and the gap between the glue application roller and the corrugating roller (0.1-0.2mm), to avoid "thin paste with fast penetration → high water content" or "thick paste → uneven curing".
④ Dynamic Adaptation of Equipment Operating Parameters
- Vehicle speed adjustment: When the moisture content is too high, the speed is reduced to extend the drying time; when the moisture content is too low, the speed is increased to reduce the preheating contact time;
- Overbridge observation method (experience assistance) : The single-sided cardboard is stacked in positive ∞ font, indicating that the water matching between the base paper and the tile paper is good;
- Cooling section optimization: If the cooling section is too short, it is prone to water retention. Local blowing can be supplemented to accelerate the dissipation.
⑤ Environmental and Transportation Protection
- Production Workshop: Temperature and humidity should be stable (e.g. 18 ± 3℃, 35 ± 5% RH), with good ventilation;
- Transportation Protection: For high-humidity scenarios (such as seafood transportation), anti-water treatment technologies such as PE film coating, aluminum foil composite, AKD immersion or nano coating can be adopted to ensure that the Cobb value is ≤ 15 g/m² (60s).
The moisture content of corrugated cardboard has a significant impact on its quality and performance. Controlling the moisture content of corrugated cardboard is one of the key factors for ensuring its quality. During the production process, it is necessary to strictly control the moisture content of the base paper, reasonably set the temperatures of the preheating rollers and drying equipment, and take other effective control measures to ensure that the moisture content of the corrugated cardboard is within the standard range, thereby avoiding various malfunctions caused by moisture content.
Guangdong Shiteng Wisdom Technology Co., Ltd.
