In the process of manufacturing and use, there are many factors that affect the deformation of the paper. The physical and chemical characteristics of the pulp, the beating situation, the choice of chemicals and fillers, the papermaking performance, the equipment status of the paper machine, and the water gain and loss during use will all affect The size of the paper changes. Here we only discuss the dimensional changes caused by the loss of moisture during the transportation and printing of finished paper.
Paper is mainly composed of cellulose, and cellulose is a very hydrophilic substance, which has strong water absorption and dehydration. During the storage, transportation and printing of paper, changes in the water content of the paper due to changes in temperature and humidity cause expansion and contraction. The main reasons for paper size changes caused by paper moisture changes are: When the paper moisture changes, the single fibers that make up the paper can absorb water expansion or lose water shrinkage, changing the shape of the entire fiber, which causes the paper size to change; there is hydrogen inside the paper Bonding, when the paper absorbs or loses moisture, the role of hydrogen bonding is strengthened or weakened, causing the fibers to tighten or push apart.
The changes in the shape of the fibers inside the paper due to the loss of water will eventually lead to changes in the size of the paper, which will adversely affect the printing. When the moisture content of the paper is too large, the binding force between the fiber, filler and rubber in the paper is easy to decrease, which will affect the surface strength of the paper, resulting in the occurrence of undesirable phenomena such as dusting and lint after printing. The occurrence of powder loss and hair loss reduces the hardness and stiffness of the edge of the paper, and it is easy to cause the problem of unstable positioning during paper feeding, resulting in misregistration. If the moisture content of the paper is too low, the paper will have poor elasticity, and the dot print will easily expand during printing, resulting in a large dot expansion rate.
Therefore, the paper should not be printed under high humidity conditions that are not suitable for its water content, but should be printed under medium humidity, which is conducive to the guarantee of overprint accuracy. In order to keep the moisture content of the paper uniform on the entire paper surface, and to adapt to the temperature and humidity of the printing workshop, at the same time, in order to reduce the sensitivity of the paper to the environmental humidity and improve the stability of the paper size, it is generally necessary to take Certain measures.
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