The basic solution to the most popular offset over

The basic solution to inaccurate offset overprint

offset lithography is based on the principle that oil and water are immiscible. Therefore, after printing, the paper will generally lengthen, while the shrinkage will become shorter, which is rare. In order to eliminate this kind of fault, this paper discusses the relevant printing technology

1. Try to use horizontal grain when printing. Paper can be divided into horizontal grain and vertical grain. In the papermaking process, because the pulp (plant fiber) flows vertically to the moving silk, the fibers are suddenly accelerated, and most of them will be connected along the moving direction of the silk, forming what we call vertical and horizontal grain. The plant fibers in the paper are hollow and translucent tubes. We can vividly say that the length direction of the fiber itself is what we call the longitudinal grain, and the direction of the gap between the fiber and the fiber is the transverse grain. The experimental results show that the cohesion of the fiber itself is greater than the bonding force between the fibers (mainly hydrogen bond force). The paper concrete pressure testing machine always needs a lot of friction. After being damped, the expansion and contraction in the longitudinal grain direction is smaller than that in the horizontal grain direction, and the two are roughly 1:2. Therefore, the deformation relationship between the vertical and horizontal grain of the paper must be considered for products with more accurate overprint. Therefore, when printing, make the longitudinal grain direction of the paper parallel to the roller axis. What are the differences between domestic and imported experimental machines: and the grain direction of the same batch of printing paper should be consistent

2. Overprint clear water (commonly known as water pressing). When the printing paper is not easy to master, in order to prevent the paper from stretching during printing, the method of overprinting once with clear water can be adopted to make the paper adapt to the printing requirements, and then start printing color. This method has a certain effect on solving the inaccurate overprinting

3. Control the moisture content of the printing plate. The moisture content of the printing page is the key factor to control the paper expansion and contraction. The moisture content of the page is transferred to the paper through the blanket. The greater the moisture content of the page, the greater the expansion and contraction. Therefore, the smaller the moisture of the layout, the better, especially when printing 80g double offset paper

4. Use a plate drawing machine to stretch the printing plate. Generally, the monochrome machine is in the third and fourth color printing process, and the two-color machine is in the second printing process. The image on the paper is stretched and enlarged, resulting in inaccurate overprint. This is because PS plates have good ductility, which can be lengthened by an economical commercial production machine through plate drawing, so that the printing plate image can be stretched evenly with the image on the paper to make overprint accurate

paper is a kind of material containing changeable plant fiber tissue. It has the function of moisture absorption and moisture release. When the moisture in the air is constantly changing, it will adjust and balance with the air humidity. When the air humidity is higher than the moisture contained in the paper, it will absorb the moisture in the air and expand and elongate; On the contrary, if these tables and files are lost, they will release water and shrink and shorten, so as to achieve a relative balance with the environmental humidity