Influence of temperature and humidity in the hotte

The influence of environmental temperature and humidity on offset printing

according to the requirements of standardized standards, the environment of offset printing workshop should be constant temperature and humidity, which is not only conducive to preventing paper deformation, improving product overprint accuracy, but also ensuring the printability of ink. But in fact, due to the different climatic conditions in various regions and the different investment of enterprises in the environment of offset printing workshop, most manufacturers are difficult to ensure the constant temperature and humidity of the environment of offset printing workshop, which brings some practical difficulties and process failures to offset printing production

first, the influence of temperature and humidity changes on paper

the water content of paper changes with the change of environmental temperature and humidity. The water absorption and loss capacity of paper are related to its own properties, structure, raw materials and other factors. Generally speaking, the higher the density of paper, the longer the fiber and the higher the sizing degree, the lower the water content, otherwise the opposite. The water content of paper produced by paper mills is usually 5% - 7%. In the process of paper transportation, storage and printing, the water content will increase or decrease with different environments. This change in water content is often harmful to offset printing

1. Paper absorbs water. Because the temperature and humidity of the paper itself is lower than the ambient temperature and humidity, in order to achieve the balance with the environment, the paper must absorb moisture from the air, resulting in the density around the paper is reduced, the fiber gap is increased, the paper deformation is "lotus leaf edge", and the four sides are undulating and warping. The difficulty this deformed paper brings to offset printing is that for the machine with a pendulum front gauge, it is difficult to enter the front gauge due to the undulation of the paper in its mouth. In order to achieve the purpose, the operator is bound to increase the pressure on the paper, resulting in the side gauge pulling paper is not in place and overprint is not accurate. As for other aluminum alloy terminals that do not have the same performance as AA (8000) series conductor aluminum alloy, even the paper will cross the front gauge and directly enter the printing unit, resulting in the failure of rolling the printing plate and blanket; For the up swinging front gauge, when the paper convex part

enters the front gauge, it collides with the front gauge stop paper tongue and pad pressing sheet, resulting in the paper not in place, affecting the overprint accuracy. At the same time, the paper drag is slightly uneven, which also makes it difficult for Feida to separate the paper normally. This change of paper can be solved by normal paper drying for offset paper, but for coated white board with more than 250G/m2, paper drying is difficult to work. Our solution is: try to use the paper produced in the same climate area as our factory, 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, strictly control the moisture of the layout in the printing process, and stack the semi-finished products neatly

2. The paper loses water. Water loss of the paper will cause shrinkage and form a "tight edge", that is, the middle is concave (or convex), and the four sides are cocked (or crouched). When this kind of paper is printed, it is difficult to separate the paper, and the second is that when it enters the embossing cylinder, the stress is released unevenly, which is very easy to wrinkle and scrap the product. In addition to the above methods, we also close the doors and windows and install door curtains to try to ensure that the temperature and humidity in the workshop are not low. When loading paper, knead and press the paperboard

second, the effect of temperature on ink

the viscosity and fluidity of ink change with the change of temperature. The higher the temperature, the smaller the viscosity and the greater the fluidity. This characteristic of ink has a great relationship with the production process and print quality, which is manifested as: 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 print. If the fluidity is too small, the ink will not spread smoothly and evenly, resulting in uneven ink color on the same printing surface; If the fluidity is too large, the imprint cannot be transferred accurately, the picture and text level is not clear, the ink color is not full, and the color is not bright, which reduces the print quality. 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, electromechanical, accessories, sheet metal, boards, sensors and so on are on the contrary. It can be seen that it is important for printing to correctly adjust the viscosity and fluidity of ink according to temperature changes. In cold winter, the following two process failures occurred in our factory due to low temperature

1. The temperature is too low and the ink is improperly adjusted, resulting in ghosting failure. When printing at 8-10 ℃, because the fluidity of the ink is too small, we add a large amount of No. 6 inking oil, which greatly reduces the viscosity of the oil. The ink forms a floating ink on the printing plate and transfers it to the water supply roller. After the water roller rotates for a week, it inks on 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 ghosting. The ghosting distance from the actual impression is just the circumference of the water roller. Later, the temperature rose, the car was washed and inked again, and the ghosting fault was eliminated

2. The temperature is too low, the viscosity of the ink is too large, and the production is forced to stop. In the middle and late January of one year, the temperature plummeted, and the temperature was generally -25~-27 ℃. Although there was heating supply in the workshop, the temperature at night was only 5 ℃. Under such operating conditions, it is difficult to correctly adjust the viscosity and fluidity of the ink to make it have good printability. Adding various auxiliary agents to reduce the viscosity of the ink is bound to increase its fluidity, which will lead to process failures with excessive fluidity. During the night shift printing of a batch of color printing activities, our enterprises producing single component products are increasing day by day. We add the ink that has been softened by baking in advance beside the heating to the ink bucket, and add an appropriate amount of debonding agent and No. 6 inking oil, but within half an hour, the ink hardens again. Because the temperature is too low, the internal cohesion of the ink increases, the activity of oil molecules decreases, and the dispersion force decreases, which makes the ink difficult to pull and break. During printing, the holding force of the embossing teeth is not enough to overcome the combined force of the adhesive force and stripping force of the blanket on the paper, so the failure of the paper sticking to the blanket occurs. Although we have taken measures to reduce the printing pressure, replace the blanket and reduce the printing speed, we still can't eliminate the fault and have to stop production. There should be no obvious eccentricity between the head and the counterbore. After the temperature in the workshop rises, there is no paper sticking to the blanket, and the production returns to normal

to sum up, temperature and humidity changes do have a significant impact on offset printing production. It is suggested that qualified manufacturers should try their best to improve the current situation of offset printing workshop and provide an environment with relatively stable temperature and humidity for offset printing to ensure normal production

source: packaging and printing