What is the humidity requirement in the printing and packaging workshop

What is the humidity requirement in the printing and packaing workshop?

According to the requirements of standardized standards, the environment of the printing workshop should be constant temperature and constant humidity, which not only helps to prevent paper deformation and improves the overprinting accuracy of products, but also ensures the printing adaptability of ink. But in fact, due to different climatic conditions in different regions and different investment in the printing workshop environment, it is difficult for most manufacturers to ensure the constant temperature and humidity of the workshop environment, which brings some practical difficulties and process failures to printing production.

The effect of temperature and humidity changes on paper
The water content of paper changes with the change of ambient temperature and humidity. The water absorption and water loss ability of paper is related to its own properties, structure and raw materials. Generally speaking, the higher the density of the paper, the longer the fiber, 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% to 7%. In the process of transportation, storage and printing of paper, the water content will increase or decrease with different environments. This often harmful for the production.

1 Paper absorbs water

Since the temperature and humidity of the paper itself is lower than the ambient temperature and humidity, in order to achieve a balance with the environment, the paper must absorb moisture from the air, resulting in a decrease in the density around the paper, an increase in the fiber gap, and the deformation of the paper in the form of "lotus leaf". Ups and downs warping.

The difficulty brought by this kind of deformed paper to the printing is: for the machine with the hem type front gauge, it is difficult to enter the front gauge due to the undulating paper mouth. The consequence is that the side gauges are not drawn in place and the overprinting is not allowed. Even the paper will directly enter the printing unit over the front gauge, resulting in failures such as crushing the printing plate and the blanket; for the top-swing front gauge, when the raised part of the paper enters the front gauge, it will collide with the front gauge tongue and pad pressing piece. , causing the paper to be out of place and affecting the overprinting accuracy. At the same time, the paper drag is slightly uneven, which also brings certain difficulties to Feida to separate the paper normally.

This kind of change of paper can be solved by normal air-drying method for offset paper, but for coated whiteboard paper above 250g/m2, it is difficult to air-dry the paper.

Our solution is: try to use paper produced in the same climate area as our factory, stack the cut paper into the workshop a few days in advance, let it have a process of adapting to the workshop environment, strictly control the moisture of the layout during the printing process, The semi-finished products are neatly stacked.

2 Paper loses water

Water loss of paper will cause shrinkage and form "tight edge", that is, the middle is concave (or raised), and the four sides are raised (or sunk). After the impression cylinder, the stress is released unevenly, and it is easy to wrinkle, which makes the product scrapped. In addition to the above methods, we also close the doors and windows and install curtains to ensure that the temperature and humidity of the workshop are not too low. When loading paper, rub and press the cardboard.

Therefore
1. The optimal working environment temperature of the printing workshop is 18 to 23 degrees Celsius, and the relative humidity is 55% to 65%.

2. A relatively stable humidity is an important part of the production of the printing workshop, which can ensure the stable humidity of the workshop and reduce the occurrence of problems such as paper deformation, inaccurate overprinting and static electricity.