In recent years, as business 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 superb technology of product outer packaging. This promotes the continuous development of printing decoration technology, and the industry's product packaging quality and design exquisiteness have also increased.
In order to improve the production cycle and production capacity, printing factories mostly use UV printing for these products in order to improve the production cycle and production capacity of long-term products of large-scale business (such as cigarette packaging, daily necessities toothpaste boxes, etc.), because UV printing uses ultraviolet light to dry In this way, the printed matter can be dried in a short time and then processed afterwards. 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 fibers. Shrinkage at high temperature, thus deforming the paper off-machine (reducing the length and width size), seriously affecting the accuracy of the post-processing process of the product and reducing the production pass rate.
How to deal with the problem of paper deformation? Due to the characteristics of paper fibers and the direction of paper grains, the law of paper changes during product printing and processing is directly related to the direction of paper fibers. Normally: the direction of the fiber along the paper changes greatly, and the direction of the longitudinal grain changes little. Normally, the change rule is that the larger the paper size is, the smaller the change error will be. If you pay attention to the characteristics of product overprinting to determine the direction of the paper grain and adjust the size of the paper change, it can also reduce the difficulty of post-processing.
According to the packaging product structure requirements, some processing techniques are necessary processes, such as die cutting and indentation. Some products have processes such as bronzing, bumps, local screen printing and processing due to design or customer requirements. At this time, the deformation of the printing paper will seriously affect the quality of these post-press processing techniques. Directly lead to the inaccurate set of these technologies during processing to reduce the product qualification rate and affect the product material cost. Since UV printing, paper deformation has been a focus problem that many manufacturers want to solve.
In order to control the deformation of the paper, many manufacturers use a protective film to protect the product to reduce the paper changes caused by the moisture absorption and dehumidification of the paper when the product is to be processed. This method can play a certain role in a certain sense, but this can only control the printing within a certain range after the change of the machine, there are many artificial influencing factors, so there are certain risks.
For example, when a worker coats a protective film, the result of the film may be different due to different people, and the protection effect achieved is different. In addition, there is a reduction process after the printed product is cooled after being off the machine. If the protection is not the same, it will affect the recovery of the printed product. The difference is different and the deformation is different, which increases the difficulty of post-processing overprinting.
After long-term data analysis of similar products in different regions after deformation, we have come up with the following solutions:
Scheme one, prepress layout processing
That is, when the product is typeset, according to the different paper grain directions and deformation rules, the product typesetting spacing is incrementally processed before printing, and the gap between shrinkage and post-press reduction caused by the product printing process is placed in the imposition spacing to achieve control of the product. The variation error of the entire processing process is within the controllable range. The controllable range refers to the range of overprinting and processing accuracy during the production and processing of post-processing processes such as processing equipment, tools, and plates (including bronzing, die-cutting, bumping and other process requirements, overprinting accuracy error range).
The specific processing method is such as the Hongmeichun, a tobacco label product in Yunnan, the imposition size is 520 * 730mm, the number of impositions is 3 horizontal and 5 vertical, and 730mm changes greatly due to the direction of the paper grain. The cigarette pack design pattern and box-shaped structure must be arranged horizontally. The bronzing of the hot stamping pattern plum blossom requires high overprinting accuracy (the error must be below 0.20mm> so the paper deformation seriously affects the quality of the product.
Suppose we have measured that under normal conditions of printing, 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 the three products in the horizontal row during typesetting. During enlargement, the center line should be adjusted, and the enlargement distance is determined according to the distance of the post-processing overprint position from the center line. .
As shown in the figure, the plum blossom is difficult to overprint, and the positions of the plum blossoms on both sides are different from the center line. Based on the ratio calculation, the magnification ratio of the two plum blossoms is set to 0.15mm on the left and 0.3mm on the right. The total magnification is 0.45mm, and the number of printed machine changes 0.5-0.7mm minus 0.45mm, so that there is only a change error of about 0.25mm, usually the processing accuracy range of our post-processing equipment is about 0.2mm. At the same time, there is also an overprint error space of about 0.15mm in the post-processed printing plates (hot stamping, embossed and die-cut plates), so that the positive and negative errors can be completely removed to meet the quality requirements of the post-processing technology.
This solution is suitable for areas with dry climates, such as the northwest, northeast, north China, and Yunnan-Guizhou plateau areas. Due to geographical and climatic factors, general printing companies do not install a central adjustment system, and they cannot manage the temperature and humidity of the production workshop, and cannot control The stability of the product in the process of moisture absorption and dehumidification. In particular, it is necessary to analyze the change data of the printing to find the corresponding enlarged data when using it. This requires relatively high technical and operational precision requirements for the staff.
Option 2: Process control method
Strictly control the unevenness of moisture release and moisture absorption caused by the products in the printing process. According to the different moisture content of the paper materials, master the baking temperature of the printing process to ensure that all the printed products are controlled to be relatively even during the printing process. Wet, strengthen the protection of the printing process and control the absorption and reduction of moisture absorption up and down uniformly, measure the law and time of moisture reduction and reduction in the printing process, Handle the production arrangements of the front and back processes, shorten the processing cycle of the front and back processes and reduce the process of moisture absorption. The production environment with a central air-conditioning protection method is different from the environmental protection method without a central air-conditioning production.
Option 2 is suitable for areas in East China, Central China and South China, where the climate is hot, the relative humidity in the air is high, the printing products absorb moisture and restore quickly during processing, and generally large and medium-sized printing enterprises are equipped with central air conditioning to control the temperature of the production workshop. humidity. Of course, the first option can also be used, especially for some products with poor paper quality (such as gray bottom cardboard), the error due to the rough change of the paper fiber is large.
The above program is one of the experiences I have summed up to solve the related quality problems in the production example for a long time in the printing process. Of course, there is still a technical space to discuss for the reference of the same industry.
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