Water loss of paper will cause shrinkage and form "tight edges", that is, the middle is concave (or convex) and the four edges are tilted (or down). When printing this kind of paper, it is difficult to separate the paper, and the second is that when it enters impression cylinder, the stress is unevenly released and it is easy to wrinkle, which makes the product scrapped. Therefore, before printing, the paper should be piled into the printing workshop to make it have a process of adapting to the workshop environment, so that its temperature and humidity can reach a balance with the workshop environment; Or install temperature and humidity adjustment equipment in the paper warehouse, so that the paper is consistent with the environmental temperature and humidity of the printing workshop. In the printing process, strictly control the moisture in the layout and neatly stack the semi-finished products.
3. Influence of temperature and humidity on ink
The viscosity and fluidity of ink will change with the change of temperature. The higher the temperature, the smaller the viscosity and the greater the fluidity. The smaller the humidity, the faster the volatile drying of ink, and the greater the humidity, the slower the volatile drying of ink. This characteristic of ink has a great relationship with the production process and the quality of printed matter, which is shown as follows: whether the viscosity is appropriate or not directly affects the transfer of ink, the firmness of imprint, the penetration of ink and the gloss of printed matter. The fluidity is too small, which will make the ink spread unsmooth and uneven, resulting in uneven ink color on the same printing surface; Excessive fluidity will make the imprint unable to be transferred accurately, and the graphic level is not clear, the ink color is not full, and the color is not bright, which reduces the quality of printed products. There is a close relationship between the viscosity and fluidity of ink. While increasing the viscosity of ink, it will reduce its fluidity, and vice versa. It can be seen that it is very important for printing to correctly adjust the viscosity and fluidity of ink according to the temperature change. In cold winter, if the temperature is too low, the following two process failures will easily occur.
(1) When printing at the temperature of 8-10℃, the viscosity of the ink is greatly reduced due to the small fluidity of the ink, and a large amount of ink blending oil is added, so that the ink forms floating ink on the image and text of the printing plate, which is transferred to the water roller, and the water roller writes ink on the blank of the printing plate after one revolution, and as a result, the ink roller and the water roller supply ink to the printing plate at the same time, forming a special ghost, and the ghost distance is exactly the circumference of the water roller.
(2) If the temperature is too low, the ink viscosity will be too high, so it is difficult to adjust the ink viscosity and fluidity correctly to make it have good printability. At this time, if various auxiliaries are added to reduce the viscosity of ink, it is bound to increase its fluidity, which will lead to printing process failure. Because the temperature is too low, the internal cohesion of the ink increases, the molecular activity of the oil is weakened, and the dispersion force is reduced, which makes the ink not easy to be broken by drawing. In printing, the clamping force of embossing teeth is not enough to overcome the resultant force of the adhesive force and peeling force of the blanket to the paper, so the paper is stuck to the blanket, which leads to the failure of normal production.
