The importance of temperature and humidity control in the printing shop
We are a big printing company in Shenzhen China . We offer all book publications, hardcover book printing, papercover book printing, hardcover notebook, sprial book printing, saddle stiching book printing, booklet printing,packaging box, calendars, all kinds of PVC, product brochures, notes, Children's book, stickers, all kinds of special paper color printing products, game cardand so on.
For more information please visit
http://www.joyful-printing.com. ENG only
http://www.joyful-printing.net
http://www.joyful-printing.org
email: info@joyful-printing.net
Paper or paperboard used for temperature packaging printing should be properly controlled in paper storage, which often affects its performance due to improper storage. 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. The paper expands after it absorbs water, and 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 are reduced, 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 paper.
During the entire packaging production process, the paper is taken out of the warehouse, cut, printed and formed, and transferred from one workshop to another. At this time, it is necessary to consider the possible change of temperature and humidity due to the change of space, resulting in Changes in paper properties.
(1) The storage should 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, making the paper brittle and fragile. , there is a tight edge phenomenon. Therefore, the paper should be stored close to the environment.
(2) Due to the difference in temperature and humidity in the printing workshop due to changes in the surrounding environment, the paper should be humidity-treated before being put into printing, especially sheetfed. When a single sheet of paper is unpacked, the water content cannot be the same as the temperature and humidity of the printing workshop. It should be humidity-treated to make the water content of the paper uniform and consistent with the temperature and humidity of the printing workshop.
There are usually three ways to adjust the offset sheet of paper:
(a) Hanging and adjusting the humidity in the printing workshop or in the air-drying room similar to the temperature and humidity of the printing workshop.
(b) Humidification treatment is carried out between the air-laid papers which are 6%-8% higher than the relative humidity of the printing workshop.
(c) The paper should be humidified first in a damp place, and then the water balance should be made in the printing workshop or in the air-drying room similar 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 some equipment and venues are needed. 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, the paper should be sent to the printing workshop for conditioning 24 hours before the printing, so that the moisture contained in the paper is compatible with the temperature and humidity of the printing workshop.
In this way, the overprinting accuracy can be ensured and the quality of the printed product can be improved. In addition, the humidity control measures of the web and the sheet of paper are different. The web is wrapped in paper rolls (such as cow paper packaging), 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) The temperature and humidity control of the printing workshop is the control of the whole process of printing. Some printers only pay attention to the temperature and humidity control of the 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 stable processing environment, so that the paper products can be processed "all the way". Otherwise, when the printed matter enters the dry and cold post-press processing workshop from the printing workshop with temperature and humidity control, the front printing is good. The paper, cardboard, and paperboard are processed in a carton type, and the edges of the paper may be broken, and the whiteness may be a problem, resulting in great waste in production. When developing a series of plans for individual procurement, warehouse management and production environment control, the printing company should fully consider the impact of small links on overall production and product quality, be global, manage in place, create a good production environment, and improve production. quality.
The influence of ambient temperature and humidity on offset printing 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 to prevent paper deformation, improves the overprinting precision of the product, but also ensures the printing suitability of the ink. However, due to the different climatic conditions in different regions, the investment environment of the offset printing workshop is different, which makes it difficult for most manufacturers to ensure the constant temperature and constant humidity of the offset printing workshop environment, which brings some practical difficulties and process failures to the offset printing production.
The influence 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 capacity of paper is related to its own nature, structure and raw materials. In general, 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 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. It is often harmful and unhelpful.
Paper water absorption: Since 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 a decrease in the density around the paper, an increase in the fiber gap, and a deformation of the paper. ", the four sides are undulating.
The difficulty of this deformed paper for offset printing is that for the hem-type front gauge machine, it is difficult to enter the front gauge due to the undulation of the paper crevices. In order to achieve the purpose, it is necessary to increase the pressure of the pressure plate, which has the consequence that The side gauge is not in place and the overprint is not allowed. Even the paper will go through the front gauge and directly enter the printing unit to break the printing plate, blanket and other faults.
For the front pendulum type, when the convex portion of the paper enters the front gauge, it collides with the front gauge tongue and the pad press, causing the paper to be out of position, which affects the overprinting accuracy. At the same time, the paper drags a little high and low, which also brings difficulties to Feida's normal separation of paper. This change in paper can be solved by the normal paper-washing method for offset paper, and it is difficult for paper-coated paper of 250 g/m2 or more to be effective.
Our solution is to use as much paper as possible in the same climate as our factory, and put the cut paper into the offset shop a few days in advance, so that it has a process to adapt to the workshop environment, and strictly control the moisture in the printing process. , neatly stacked semi-finished products.
Loss of water on paper: shrinkage of paper will cause shrinkage, forming a "tight edge", that is, a concave (or convex) in the middle, and four sides (or under the valgus). When the paper is printed, it is difficult to separate the paper. When it enters the impression cylinder, the stress is released unevenly, which is easy to wrinkle and the product is scrapped. In addition to the above methods, we also close the doors and windows to install curtains, try to ensure that the temperature and humidity of the workshop is not low. When loading paper, knock on the board paper.
Because the temperature is too low, the internal cohesive force of the ink increases, the activity of the oil molecules is weakened, and the discrete force is reduced, so that the ink is not easily broken by the drawing. When printing, the embossing force of the embossing is insufficient to overcome the adhesion of the blanket to the paper and the peeling force. Therefore, a problem occurs in that the paper is stuck on the blanket. Despite the measures to reduce printing pressure, replace blankets, and reduce printing speed, it is still impossible to eliminate the problem and stop production. The next day, after the temperature of the workshop rose, there was no problem with the paper sticky blanket and the production returned to normal.
In summary, temperature and humidity changes do have a significant impact on offset printing. It is recommended that qualified manufacturers try to improve the status quo of the offset printing workshop and provide a relatively stable temperature and humidity environment for the offset printing to ensure normal production.