Atmospheric State
Environmental conditions in a print shop or warehouse are measured by the amount of water vapor present in the air relative to the maximum possible amount at that temperature. When low relative humidity occurs, typically below thirty five percent, the dry air begins to strip moisture from the hygroscopic paper fibers. This leads to a rapid loss of water from the edges of the paper stacks.
The resulting imbalance in moisture causes the fibers to shrink at different rates.
Dimensional Change
Paperboard curls and warps as the edges become shorter than the center of the sheet. This physical distortion makes it difficult for the feeders on a printing press to pick up the sheets reliably. It also affects the registration of the colors because the sheet size is no longer consistent.
In extreme cases, the board becomes brittle and cracks when it is folded or creased.
Static Accumulation
Dry air acts as an insulator, allowing static electricity to build up on the surface of the moving web or sheets. This charge causes the substrate to stick to the machinery or other sheets, leading to jams and production delays. Low relative humidity also increases the risk of dust attracting to the board surface, which can ruin the print quality.
Humidification systems are used to keep the air within a safe range for processing.
