Thin Paper Printing Process

Keywords: thin paper printing moisture content of paper, relatively speaking, 65 g/m2 paper called thin paper. Thin paper in the printing process due to the paper moisture content, tensile strength, thickness, hardness and opacity and other factors, prone to wrinkles, dirt, overprint and other phenomena. Combining my experience in thin paper printing, I discussed and analyzed this printing process from several aspects including paper drying, paper feeding, wetting, inking, printing pressure, and paper collection.
First, before the paper is printed, the paper should be hung and humidity controlled to balance the moisture content of the paper, thereby reducing the paper deformation in the printing process. Because of the change in the moisture content of the paper, it will cause the paper to stretch and shorten, resulting in curls, wrinkles, flounces or tight edges. Thin paper is more sensitive to the moisture content of the paper.
The water content of paper and the relative humidity of air are not in a straight line but change in a sigmoid shape. At high humidity or low humidity, relative humidity changes have a greater impact on the moisture content of the paper. Therefore, printing at moderate temperatures is advantageous.
The printing shop should strictly control the relative humidity. Dry paper, printing workshops can take the following measures: 1. Configuration of air conditioners, humidifiers and other equipment; 2. Close the windows, hanging curtains; 3. Sealed semi-finished products and finished products with plastic film.
According to the printability of paper, the table lists the reasonable temperature and humidity control ranges for reference.

Since offset printing is based on the immiscible principle, the printing process inevitably wets the printing plate, so the moisture content of the paper is a variable.
Therefore, the conditional printing plant can make the relative humidity of the paper-making workshop 8% to 15% higher than that of the printing shop. In this way, the paper will lose part of its moisture when it enters the printing shop, and absorbs some moisture during the printing process. Since the change of the moisture content of the paper has a hysteresis effect on the change of the relative humidity, the water content of the paper in the printing process is basically unchanged, so that the paper size is kept stable, which is conducive to the smooth progress of the printing process.
Under normal circumstances, you can also use the current method of printing. This method reduces the paper's environmental impact on paper in the process of transportation and storage. It is easy and effective.
Second, the stable, accurate and continuous delivery of paper is an important condition for guaranteeing the smooth progress of printing. Because of the low stiffness of the tissue, it can bring difficulties to the delivery and delivery of the tissue, and the printing speed can be appropriately reduced. Take the Roland RZK-3B1/1E type BB machine as an example, the printing speed is controlled at 5000-6000 sheets/hour.
Before the paper is printed on the machine, the paper should be repeatedly shaken, knocking the papers that stick together up and down, and the presence of air between the papers is a prerequisite for the smooth separation of the paper.
In the process of paper feeding, the control of air volume is the key. To adjust the size of suction and blowing, the distribution of air flow should follow the principle of symmetry. For thin paper printing, the air blowing volume should not be too large, otherwise the rear edge of the paper can be blown up easily, which brings certain difficulties to the pressure of the paper blowing nozzle. The loose paper mouthpiece is suitable for blowing the top 5- 8 sheets of paper. Pay attention to adjust the angle and distance of the paper nozzle, so that the paper between the two nozzles is always in the state of tension. The paper nozzle is 6~8mm away from the paper stack. The position of the tablet or brush should not be too far away. Otherwise, some papers will not be pressed, causing double sheets.
Paper does not allow relative sliding on the paperboard. The force of paper advancement comes from friction. Since the thin paper itself is light in weight, it is possible to appropriately increase the pressure on the paper by the pressure roller, but be careful that if the pressure of the two pressure rollers is not equal, the paper may be skewed. In addition, two pieces of pressure paper are added to the front of the conveying plate to effectively control the folding angle of the paper.
The paper feed teeth should be carefully adjusted and frequently maintained. Since the tensile strength of thin paper is small, it should be ensured that the pressure of the tusks is consistent and flexible. It is recommended to clean and lubricate once every two months to remove paper hair, paper dust, etc., to ensure the ability to pick paper.
Third, inking and wetting Because of the low opacity of thin paper, if the amount of ink is too large, overprinting will occur, affecting the reading effect. The amount of ink below should not be too large. It is best to use a quick-drying ink or add a suitable amount of desiccant to prevent dirt.
Thin paper is sensitive to changes in water content and should be wetted with alcohol. Alcohol has small surface tension and is volatile. It can effectively reduce the amount of water on the surface of the printing plate and change the wetting state of the paper, thereby reducing the paper deformation and ensuring the overlay accuracy. In the RZK3B1/1E machine operation instructions, the alcohol concentration is preferably controlled at 8% to 15%. However, in practice, we have found that low alcohol concentration results in high water content, more foam in fountain solution, and poor printing results. So we control the alcohol concentration at about 30%.
Fourth, the printing pressure to take into account the problem of printing, the roller pressure is not too large, graphic and clear, ink does not appear on the line.
Fifth, in the process of receiving and delivering paper, faults that are prone to occur include: picking up dirt and missing paper.
Since the tissue has a low basis weight and is easy to float at the time of delivery, it is necessary to control the amount of paper collected. And pay attention to observe the position of the paper falling on the delivery. If the paper is falling behind, you should lift the delivery table properly and adjust the timing of the collection teeth to make the paper fall flat on the delivery table. (Zhang Xingrong Nanjing Aide Printing Co., Ltd.)