According to the requirements of standardized standards, the environment of the offset printing workshop should be constant temperature and constant humidity, which not only helps prevent paper deformation, improves the accuracy of product overprinting, but also ensures the printing suitability of the ink. But in fact, due to the different climatic conditions in different regions, companies invest in the environment of offset printing workshops differently, which makes it difficult for most manufacturers to guarantee the constant temperature and constant humidity of the offset printing workshop environment, which brings some practical difficulties and process failures to offset printing production. 1. The effect of temperature and humidity changes on paper The water content of the paper changes with the change of environmental temperature and humidity, and the paper's water absorption and water loss ability is related to its own nature, structure and raw materials. Generally speaking, the higher the density of the paper, the longer the fiber and the higher the sizing degree, the lower the water content, otherwise the opposite. The water content of the paper produced by the paper mill is usually 5% to 7%. During the transportation, storage and printing of paper, the water content will increase or decrease with different environments. This change in water content will affect offset printing. It is often harmful and useless. 1. Paper absorbs water Because the temperature and humidity of the paper itself is lower than the environmental temperature and humidity, in order to achieve the balance with the environment, the paper must absorb moisture from the air, which causes the density around the paper to decrease, the fiber gap increases, and the paper deforms to show "lotus edge" Undulating warping. The difficulty of this deformed paper for offset printing is: For the machine with a hem type front gauge, it is difficult to enter the front gauge due to the undulation of the paper gripper. The operator must increase the pressure of the pressed paper to achieve the purpose. The consequence is that the side rule pull paper is not in place and the overprint is not accurate. Even the paper will go over the front gauge and enter the printing unit directly, and the printing plate, blanket, etc. will be damaged; for the swing-up front gauge, the convex part of the paper When entering the front gauge, it will collide with the paper tongue and pad of the front gauge, which will cause the paper to not be in place and affect the accuracy of overprinting. At the same time, the paper is slightly uneven, which also makes Feida difficult to separate the paper normally. This change of paper can be solved by the normal paper drying method for offset paper, but for coated whiteboard paper above 250g / m2, the paper drying is difficult to work. Our solution is: try to use paper produced in the same region as the factory's climate, stack the cut paper into the offset printing workshop a few days in advance, let it have a process to adapt to the workshop environment, and strictly control the moisture of the plate during the printing process , Neatly stack semi-finished products. 2. Paper loses water The loss of paper will cause shrinkage and form a "tight edge", that is, a concave (or convex) in the middle, and the four sides are raised (or down). When printing this paper, it is difficult to separate the paper, and second, when it enters After imprinting the cylinder, the stress is unevenly released, and it is easy to wrinkle, which makes the product scrapped. In addition to the above methods, we also closed doors and windows and installed curtains to try to ensure that the temperature and humidity of the workshop are not too low. When loading paper, feed and rub the board. Second, the influence of temperature on ink The viscosity and fluidity of the ink change with temperature. The higher the temperature, the lower the viscosity and the greater the fluidity. This characteristic of the ink has a great relationship with the production process and the quality of the print. The performance is: the appropriateness of the viscosity directly affects the transfer of the ink, the firmness of the imprint, the amount of ink penetration and the gloss of the printed product. If the fluidity is too small, the ink will not spread smoothly and unevenly, resulting in unevenness of the ink color on the same printing surface. If the fluidity is too large, the imprint will not be transferred accurately. Not bright, reducing the print quality. And there is a close relationship between the viscosity and fluidity of the ink, while increasing the viscosity of the ink, it will reduce its fluidity, otherwise the opposite. It can be seen that, according to temperature changes, correct adjustment of the viscosity and fluidity of the ink is important for printing. In the cold winter, our factory had the following two process failures due to the low temperature. 1. The temperature is too low, and the ink is not adjusted properly, causing ghosting failure. When printing under the condition of 8-10 ℃, because the fluidity of the ink is too small, we added a large amount of No. 6 ink, which greatly reduced the viscosity of the oil, and the ink formed floating ink on the printing plate and transferred The water supply roller, after the water roller rotates for one week, is inked in the blank of the printing plate. As a result, the ink roller and the water roller supply ink to the printing plate at the same time, forming a special type of ghost image. Later, the temperature picked up, the car wash was refilled, and the ghosting problem was eliminated. 2. The temperature is too low, the viscosity of the ink is too large, and the production is forced to stop. In mid-to-late January, the temperature dropped suddenly, and the temperature was generally -25 ~ -27 ℃. Although the workshop had heating supply, the temperature at night was only 5 ℃. Under such operating conditions, it is difficult to properly adjust the ink viscosity and fluidity so that it has good printability. Adding various auxiliary agents to reduce the viscosity of the ink, it is necessary to increase its fluidity, which will lead to excessive fluidity process failure. When printing a batch of color printing jobs during the night shift, we put the ink that had been pre-heated on the side of the heater into the ink fountain, and added an appropriate amount of debonding agent and No. 6 ink, but the ink became hard again within half an hour. Because the temperature is too low, the internal cohesion of the ink increases, the activity of the oil molecules weakens, and the dispersion force decreases, which makes the ink not easy to break the wire. During printing, the imprint gripping force is not enough to overcome the combined force of the adhesion and peeling force of the blanket to the paper. , So the paper is stuck on the blanket. Although we have taken measures to reduce printing pressure, replace blankets, and reduce printing speed, we still cannot eliminate the fault and have to stop production. The next day, after the workshop temperature rose, there was no more paper sticking to the blanket, and production returned to normal. In summary, changes in temperature and humidity have a significant impact on offset printing production. It is recommended that qualified manufacturers try to improve the current status of the offset printing workshop, and provide a relatively stable temperature and humidity environment for offset printing to ensure normal production. Foundation Makeup Brush,Professional Brush Set,12Pcs Brush Set,12Pcs Brush Set DONGGUAN YACAI COSMETICS CO.,LTD. , https://www.yacaicosmetic.com
The influence of temperature and humidity on the quality of offset printing in the printing workshop