Discussion on Inaccurate Overprint of Paper

Paper is a kind of material containing variability of plant fibrous tissue. It has the function of moisture absorption and moisture release. When the moisture in the air is constantly changing, it will adjust to the humidity of the air. When the air humidity is higher than the moisture content of the paper, it will absorb moisture in the air and expand and elongate; otherwise, it will release moisture and shorten the contraction to achieve a relative balance with the environment.
Offset offset printing is based on the principle of immiscibility between oil and water. Therefore, the post-press sheet generally stretches, and shrinkage becomes shorter. In order to eliminate such failures, the relevant printing process is discussed:
1. Try to use cross-filaments when printing. The paper has horizontal and vertical threads. In the papermaking part of the papermaking process, as the pulp (vegetable fiber) flows perpendicularly to the moving screen, the fibers are suddenly accelerated and most of them are linked along the direction of movement of the wire mesh, forming what we call The vertical and horizontal thread. The plant fibers in the paper are all hollow translucent tubes. We can vividly say that the long main direction of the fiber itself is what we call longitudinal warp, and the direction of the fiber and fiber gap is a transverse warp.
The experimental results show that the cohesive force of the fiber itself is greater than the binding force (mainly hydrogen bonding force) between fibers. After the paper is wet, the telescopic extension in the longitudinal direction is smaller than that in the horizontal direction, which is approximately 1:2. Therefore, overprinting products must consider the deformation of the paper's vertical and horizontal threads. Therefore, when printing, make the longitudinal twist direction of the paper parallel to the axis of the drum, and the same batch of printing paper should be consistent in the direction of the strand.
2. Overprinting water (commonly known as water pressure). In the case that printing paper is not well controlled, in order to prevent the paper from elongating in printing, Fang Wang can be used to overprint the clean water first, so that the paper can be adapted to the printing requirements, and then the printing color can be started. This method does not solve overprinting. Have a certain role.
3. Control the printing plate surface moisture. Moisture in the printing plate. The moisture content of the printing plate is a key factor in controlling the stretching of the paper. The moisture of the plate is transmitted to the paper by a cloth, and the larger the plate surface moisture, the greater the expansion and contraction. Therefore, the smaller the control of the water content of the layout, the better, especially when printing 80 g of offset paper.
4. Pull the plate to lengthen the plate. Generally monochrome machine in the third, four-color printing process, two-color machine in the second printing process, the image of the paper has a longer stretch, resulting in overprinting is not allowed. This is because the PS plate material has good ductility and can be stretched by the plate-pulling machine so that the image on the plate plate and the image on the paper sheet can be evenly stretched to make the overprinting accurate.
Most small and medium-sized printing and repairing companies in China generally do not have air-conditioning equipment. Most of the measures are to sprinkle some water around the machine to increase the air humidity. For non-network printing products that do not require high printing, the spray nozzle can be used to spray water directly on the paper edge and then printed on the machine; for the workshop with high humidity, the cut paper is best covered with a plastic cover to prevent moisture from becoming longer; If you are printing in the second printing, you can use the method of borrowing lines to compensate for the image's flexibility.
In general, there are many processing methods that can solve the problem of over-printing and lead to overprinting. As long as the discussion and management of the printing process are strengthened, it can generally be solved.