The Influence and Countermeasures of Paper Shrinkage Change in Cigarette Box UV Printing

The Influence and Countermeasures of Paper Shrinkage Change in Cigarette Box UV Printing

In recent years, as commercial competition has intensified, in order to expand the market, merchants hope to increase the attractiveness of products and achieve anti-counterfeiting effects through the beautiful design and exquisite craftsmanship of product outer packaging. This has promoted the continuous development of printing and decoration technology, and the industry's packaging quality and design exquisiteness have also improved.

In order to improve the production cycle and production capacity, printing factories use UV printing for such products when they produce and process large-scale long-term products (such as cigarette packaging, daily necessities toothpaste boxes, etc.), because UV printing uses ultraviolet light to dry In this way, the printed matter is dried in a short time and then undergoes subsequent processing. The paper must undergo a high-temperature baking process during the printing process of the printing press. When the printed paper is baked, it will cause paper moisture loss and paper fiber The shrinkage under high temperature will cause the paper to be deformed (shrink the length and width dimensions), which will seriously affect the accuracy of the product post-processing procedure and reduce the product pass rate.

　　 How to deal with the problem of paper deformation? Due to the characteristics of the paper fiber and the direction of the paper grain, the size of the paper change during the product printing process is directly related to the direction of the paper fiber. Normally, it is: the direction of the paper fiber changes greatly, and the longitudinal direction changes less. Under normal circumstances, the law of change is that the larger the size of the paper, the larger the size of the paper, the larger the error will be. If you pay attention to the characteristics of product overprinting to determine the direction of the paper silk grain and adjust the size of the paper change, you can also reduce the difficulty of post-processing.

　　 According to the requirements of the packaging product structure, some processing techniques are necessary procedures, such as die cutting, indentation, etc. Some products have hot stamping, concave-convex, partial screen printing and other processes due to design or customer requirements. At this time, the deformation of the printing paper will have a serious impact on the quality of these post-press processing techniques. Directly lead to the inaccuracy of the nesting during the processing of these processes, which reduces the qualification rate of the product and affects the cost of product materials. Since UV printing, paper deformation has always been a key problem that many manufacturers want to solve.

　　In order to control the deformation of the paper, many manufacturers use protective film to protect the product during the process to reduce the change of the paper caused by the moisture absorption and release of the paper when the product is to be processed. This method can play a certain role in a certain sense, but it can only control the printing within a certain range after the off-machine change. There are many human influence factors, so there are certain risks.

　　 Such as: when workers wrap the protective film, the result of the film may be different depending on the person, and the protective effect of the film may be different. Furthermore, after the printed product is cooled down, there is a restoration process. If the protection is not the same, it will affect the restoration of different differences and deformation of the printed product, which will increase the difficulty of post-processing overprinting.

　　 After long-term data analysis of similar products in different regions, we have obtained the following solutions:

　　Solution One, pre-press typesetting

According to the different paper grain directions and deformation laws when the product is typeset, the product typesetting spacing is increased before printing, and the gap between the shrinkage caused by the product printing process and the post-press reduction is placed in the imposition spacing to achieve control of the product. The variation error of the whole machining process is within the controllable range. The controllable range refers to the overprinting and processing accuracy range during the production and processing of processing equipment, tools and plates in the post-processing process (including the error range of overprinting accuracy required by processes such as bronzing, die cutting, and concave-convex).

　　The specific treatment method is the Yunnan cigarette label product Hongmeichun. The imposition size is 520*730mm, and the number of impositions is 3 and 5 horizontally. The 730mm changes greatly due to the paper texture. The design pattern and box-shaped structure of this cigarette pack must be arranged horizontally, and the hot stamping of the hot stamping pattern plum blossom requires a high overprint accuracy (the error must be below 0.20mm> so the deformation of the paper seriously affects the product quality.

　　 Assuming that we measured that the printed product is under normal conditions, the paper reduction data after printing is 0.5-0.7mm horizontally and 0.15-0.25mm vertically. In this way, we can perform targeted enlargement of the spacing between 3 horizontally arranged products during typesetting. When enlarging, it is required to adjust based on the center line. The enlargement distance is determined according to the distance between the post-processing overprinting position and the center line. .

　　 The plum blossom as shown in the picture is difficult to overprint, and the two plum blossom patterns are at different positions from the center line. According to the ratio calculation, the two plum blossoms are enlarged at 0.15mm on the left and 0.3mm on the right. A total of 0.45mm is magnified, and 0.45mm is subtracted from 0.5-0.7mm of the number of changes in the off-machine of the printed product, so that there is only a variation error of about 0.25mm. Usually, the processing accuracy of our post-processing equipment is about 0.2mm. At the same time, there is an overprinting error space of about 0.15mm in the post-processing printing plate (hot stamping plate, concave-convex plate and die-cutting plate), so that after removing the positive and negative errors, the quality of the post-processing process can be fully met.

This solution is suitable for dry climate areas, such as the Northwest, Northeast, North China and Yunnan-Guizhou Plateau. Due to geographical and climatic factors, general printing companies do not install a central adjustment system, and cannot manage the production workshop with constant temperature and humidity, and cannot control printing. The moisture absorption and release stability of the product during processing. Special attention is paid to the fact that, when adopting, it is necessary to perform random inspections on the printing change data to find out the corresponding enlarged data. This requires relatively high technical and operational precision for the staff.

　　Program 2: Process Control Method

Strictly control the unevenness of moisture release and moisture absorption caused by the products during the printing process, and control the printing processing baking temperature according to the different moisture content of the paper incoming materials to ensure that all printed products are controlled to release moisture relatively evenly during the printing process to ensure a constant temperature and constant printing process environment Wet, strengthen the protection and control of the printed product process. The upper and lower moisture absorption and reduction are uniform, and the law and time of moisture absorption and reduction during the printed product process are measured. The protection method of the production environment with central air-conditioning is different from the environmental protection method of production without central air-conditioning.

Option 2 is suitable for areas in East China, Central China, and South China. These regions have hot climates and high relative humidity in the air. The printed products absorb moisture quickly during the processing process, and generally large and medium printing companies have installed central air conditioners to control the temperature of the production workshop. humidity. Of course, solution one can also be adopted, especially for products with poor paper quality (such as gray-bottomed cardboard), which has a large error due to the coarse change of the paper fiber.

　　 The above-mentioned scheme is one of the experiences that the author summed up from the long-term experience of solving related quality problems in the printing process in the production examples. Of course, there is still technical space for discussion for the reference of the same industry.

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