In printing production, paper is one of the most demanding materials for the environment. Because the paper is a porous structural material composed of plant fibers supplemented with various excipients, it has strong hydrophilicity. If the ambient temperature and humidity are not well controlled, the paper will be deformed and affect normal printing. Therefore, maintaining proper ambient temperature and humidity is the key to improving the quality of paper printing and improving production efficiency.
Data collection: the effect of temperature and humidity on paper size
We sampled and tested four kinds of commonly used papers in two production workshops, and obtained different types and sizes of papers in different temperature and humidity environments. The specific changes of the dimensions are shown in Tables 1 to 4. .
Through the analysis of the data listed in Tables 1 to 4, we found that no matter what kind of paper is placed in different temperature and humidity environments, it will cause abnormalities in paper size reduction or enlargement, but different papers have different temperature and humidity. . As shown in the ordinary 71g/m2 plain aluminized paper in workshop 2 in Table 1, the lateral dimensions of the paper measured by three samplings are reduced, especially the paper collected in the workshop environment with temperature and humidity of 21 °C / 35% after 72 hours. The horizontal size is reduced by 1.5mm; the same type of paper in workshop 1 is only collected in the case of temperature and humidity of 25 ° C / 55% after entering the workshop for 24 hours, the lateral increase is 0.2mm, and the water content is slightly increased. In the two sampling tests where the ambient temperature and humidity were 27 ° C / 55% and 27 ° C / 52%, respectively, although the moisture content of the paper was reduced, the size did not change. The sub-grain aluminized paper in Table 2, only after entering the workshop 2 for 24 hours, the paper collected under the environment of temperature and humidity of 26 ° C / 40%, the lateral size is reduced by 1 mm, and the other humidity is not less than 50%. The paper size obtained did not change. The single-sided coated paper in Table 3 has no change in the paper size measured by the temperature and humidity of 25 ° C / 40%, and the others have different degrees of increase, measured in a temperature and humidity environment of 22 ° C / 60%. The horizontal size of the paper even rose by 2.5mm. The waterproof coated paper in Table 4 has no change in the paper size measured when the temperature and humidity in the workshop 1 is 22 ° C / 45%, and the other is reduced or enlarged, but the variation is significantly smaller than that of the single-sided coated paper.
Don't underestimate the change of 1~2mm. For high-volume imprinting products, it can affect the final printing quality. Of course, different papers are not sensitive to the environment. Ordinary coated paper is more hydrophilic than waterproof coated paper and aluminized paper, but paper that is less sensitive to moisture, especially in different environments, especially humidity. When placed in an environment, it will also cause changes in the size of the paper, but the length of time that causes the same change will be different, and these subtle changes are enough to affect the overprinting of the printed product.
Analysis: Reasons for temperature and humidity affecting paper size
The reason why temperature and humidity affect the paper size is because the paper fiber is porous and hydrophilic, and is very sensitive to water. The temperature and humidity of the environment change slightly, and the moisture content of the paper changes. Generally, the water content of the paper increases as the relative humidity increases, and accordingly the paper size becomes larger, and the lateral change generally increases. Conversely, as the relative humidity decreases, the paper moisture content decreases, and accordingly the paper size is reduced. The dimensional stability of the paper has a lot to do with the suitability of the print and the suitability of the registration. Especially for products with multi-color overprinting, the paper size changes greatly, which will result in inaccurate product overprinting, resulting in defective products and waste products. Therefore, the dimensional change of the paper due to the change of temperature and humidity is one of the most important issues affecting product quality. In addition, changes in paper moisture content can also cause changes in other properties of the paper. If the water content increases, the tensile strength and surface strength of the paper decrease; if the water content is too low, the paper becomes brittle and hard, and the phenomenon of electrostatic charge is more likely to occur during printing.
Experience: Suitable temperature and humidity environment for different papers
Through these years of work experience and repeated experimental observations, some experiences can be drawn: the suitable humidity of printed aluminum-plated paper prints is between 45% and 60%, and the storage environment humidity of coated paper is 40% to 50%. It is more suitable. Of course, this is not absolute. It is necessary to adjust the ambient humidity while ensuring that the raw materials are stable. Because some raw materials are too high or too low in water to affect the printing effect, it is necessary to dry or humidify in advance.
In summary, the temperature and humidity control of the printing workshop, especially the humidity control, is an important issue that cannot be ignored. Keeping the humidity of the workshop stable within a reasonable range is one of the requirements of the printing process. When selecting heating equipment, it is recommended to use the direct heating method in the workshop, and install the temperature and humidity meter at the appropriate position in the workshop to monitor the ambient temperature and humidity, and adjust accordingly according to the situation. It should be emphasized that after the holidays are returned (after a period of work stoppage), the humidity and temperature of the printing workshop should be adjusted three hours in advance to start printing more quickly. Of course, the temperature and humidity requirements for printing different prints are not exactly the same. We need to adjust them according to the suitability of different papers in the printing process. These require us to repeatedly demonstrate and experiment in the printing process. In short, no matter what print data is inseparable from the accumulation and analysis of various types of data in the process.
The above content is selected from the 8th issue of “ Printing Technology †of Keyin Media in 2016. For more journal content, please pay attention to the journal channel .
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