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Reasonable control of temperature and humidity when storing paper products
2019-02-25
 
Paper is a highly hydrophilic material. Changes in the moisture content of the paper can cause the paper to become deformed and become brittle, causing inaccurate overprinting of the printed matter and breakage during the forming process of the paper. Changes in ambient temperature and humidity are the main factors affecting the moisture content of the paper. The paper not only absorbs moisture during contact with the paper, but also absorbs moisture from the moist air and drains it into the dry air. When the paper absorbs water, it expands, the linear size and area in all directions increase, and the mechanical strength decreases. The paper shrinks after dehydration, and the linear size and area in all directions shrinks, becoming stiff and brittle. Therefore, to control the change in paper properties, it is necessary to control the moisture content of the paper and control the temperature and humidity of the environment in which the paper is placed.
 
Throughout the printing process, paper is taken from the warehouse, cut, printed, and post-pressed, and transferred from one workshop to another. At this time, it is necessary to consider the possible changes in temperature and humidity due to the change of space. This results in a change in paper properties.
(1) Warehouse
In storage, pay attention to the conditions of paper storage, and control the temperature and humidity of the warehouse environment. If the paper is under high humidity, it will absorb the surrounding moisture and curl and deform, and the ruffle will appear. If the paper is stored in a very dry environment, it will cause the water in the paper to be dispersed and the paper will become brittle and brittle. , there is a tight edge phenomenon. Therefore, the paper should be stored close to the environment.
(2) Printing workshop
Due to the difference in temperature and humidity due to changes in the surrounding environment, the paper should be subjected to humidity conditioning before being printed, especially for sheetfed paper. When the sheet of paper is unpacked, the water content cannot be the same as the temperature and humidity of the printing workshop. It is necessary to carry out the humidity control treatment to make the water content of the paper uniform and consistent with the temperature and humidity of the printing workshop.
There are usually three methods for adjusting the offset sheet of paper: 1 hanging in the printing workshop or in the drying room close to the temperature and humidity of the printing workshop; 2 drying paper at 6%-8% higher than the relative humidity of the printing workshop. The humidity is treated separately; 3 the paper is first humidified in a damp place, and then the water is balanced between the printing workshop or the air-drying paper which is close to the temperature and humidity of the printing workshop to make the water content of the paper uniform. Comparing these three methods, the latter two methods work well, but require some equipment and venue. Due to the limited conditions, most of the printing factories in China currently use the first method, which is usually called the natural humidity control method. If the paper is stored in an environment without temperature and humidity control, at least 24 hours before the printing, the paper should be sent to the printing workshop for humidity control, so that the moisture contained in the paper is compatible with the temperature and humidity of the printing workshop. In order to ensure the accuracy of overprinting and improve the quality of printed products.
In addition, the web and the sheet of paper have different humidity control measures. The web is wrapped in paper rolls (such as kraft paper), and its outer packaging can protect the moisture content of the web inside from the external environment humidity. Only open the outer packaging before the machine is installed.
(3) Postpress processing workshop
Temperature and humidity control is the control of the entire process of printing. Some printers only pay attention to the temperature and humidity control of the printing workshop, but ignore the temperature and humidity control of the finishing shop. The printing workshop is equipped with corresponding air conditioners, humidifiers and other devices to ensure the stability of the printing workshop environment. The post-press processing workshop should also adopt the same method to ensure the stability of the processing environment, in order to make the paper products processing "all the way smoothly." Otherwise, when the printed matter enters the dry and cold post-pressing workshop from the printing workshop with temperature and humidity control, the front printed paper, cardboard, and cardboard will be broken, exposed, etc. when the carton forming process is performed. The problem is a huge waste of production.



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