Paper is a material with strong water absorption. Poor humidity control can cause paper deformation, resulting in phenomena such as ruffled edges and tight edges, leading to a decrease in paper quality. If the humidity is too low, it can cause problems such as paper fragility and decreased flexibility. If the humidity is too high, it will cause a decrease in strength, and the paper will be soft and easily rotten. In order to maintain appropriate humidity and ensure the quality of paper, it is necessary for paper mills to use humidifiers.

The moisture content of paper varies with changes in environmental temperature and humidity, and the ability of paper to absorb and lose water is related to its own properties, structure, and raw materials. Generally speaking, the higher the density of paper, the longer the fibers, and the higher the degree of sizing, the lower the moisture content. Otherwise, the opposite is true. The moisture content of paper produced by paper mills is usually 5% to 7%. During the transportation, storage, and printing process of paper, its moisture content may increase or decrease with different environments. This change in moisture content is often harmful to offset printing.

1. Paper absorbs water

Due to the fact that the temperature and humidity of the paper itself are lower than the ambient temperature and humidity, in order to achieve balance with the environment, the paper must absorb moisture from the air, resulting in a decrease in density around the paper, an increase in fiber gaps, and deformation of the paper into a "lotus leaf edge" with undulating and warped edges. The difficulty that this deformed paper brings to offset printing is that for machines with bottom edge front gauges, due to the undulating waves of the paper, it is difficult to enter the front gauge. In order to achieve the goal, the operator must increase the pressure on the paper sheet, causing the side gauge to pull the paper improperly and the printing to be inaccurate. Even if the paper passes over the front gauge and directly enters the printing unit, it may cause faults such as crushing the printing plate and blanket

2. Paper dehydration

Paper loss of water can cause shrinkage, forming a "tight edge", where the middle is concave (or convex) and the four sides are raised (or folded). This type of paper is difficult to separate during printing, and when it enters the embossing cylinder, the stress is not evenly released, making it prone to wrinkling and product scrap. In addition to the above methods, we also close doors and windows and install door curtains to ensure that the temperature and humidity in the workshop are not too low. When loading paper, we rub and press the board paper.