Talking about the problem of paper crease after printing
2019-11-23 15:07:18
When the climate is dry, the problem of collapsing cracks (also known as “bend ribs†or “burstsâ€) that are plagued by users of coated paper will increase. To explain this issue, we must start with the composition of coated paper. Coated paper is composed of wood pulp and paint. Wood pulp is what we call wood fiber (needle pulp/long fiber, broad-leaf pulp/staple fiber). Wood fiber has water hardness, and it becomes brittle, and water absorbs soft and tough. characteristic. This feature is well verified. We take a small tree branch from a living tree and perform a bending test. Generally the branches that have just been removed have a strong toughness at the time of bending and are difficult to break at one time. If the branches are dried, they are air-dried. Losing water can easily break it. The coated paper, which uses fibers as its main raw material, also inherits its characteristics. In China, summer temperatures are high and rainfall is high. The relative humidity of the environment is high, and the paper maintains its original toughness. However, in winter, the temperature and precipitation decrease, the relative temperature of the environment decreases, and the paper easily loses water and becomes brittle. This is the main problem in the production of crevice bursts. the reason.
Knowing the cause of the problem, we can solve it when we encounter such problems, namely controlling the moisture content of the paper. The paper's moisture content is basically controlled at 4% to 6%. After production, it is rapidly packaged with leaching kraft paper to prevent water loss. During the printing process, the temperature and humidity of the storage and processing plant environment were not controlled, and the water that was opened when the package was opened before printing was lost during storage. In the process of printing and printing, printing ink and coating oil need to be accelerated by hot air, infrared, UV light and other methods. At this time, the water in the paper is lost more and more, if the paper is not directly processed by folding, There will be a problem of collapsing bursts. The following is a brief introduction of several remedies for this problem, for your reference.
Rewetting treatment: replenish the paper before folding. Double-sided printing products: If it is rotary printing, the temperature of the oven is adjusted during the drying process to prevent the paper from losing too much water. Another can be used to increase the humidity of the environment, such as water spray around the workshop and the paper roll, etc., to adjust the humidity of the paper, and spray near the sample at the same time, directly fill the water samples.
Single-sided printing products: The back of the water can be used, the effect is more obvious. Once there was a printing factory using a copper plate gravure printing machine, after the single-sided printing roll, automatic bag making machine, automatic folding forming a small package bag, there is a break at the folding point, after the back of the water process, the yield A substantial increase.
Boxed products: After the indentation, use a damp cloth to wipe the folds.
Folding, indentation process Adjust the folding process to reduce the folding pressure as much as possible to ensure that the printed sample can be formed.
According to the requirements of the die cutting process, different steel wires, different thicknesses of the bottom plate, and different bottom mold groove widths should be selected for different papers. If the related process does not match, it is easy to cause a crack in the fold. The following is a common calculation method for your reference.
B=[C×1.5]+D
Among them, B-indentation bottom die groove width; C-paper thickness; D-steel wire thickness and D≥C; A≤C;
When indenting a thick paper or a box product, the width of the bottom mold groove is enlarged as much as possible, and the indentation pressure is appropriately reduced. Although the indentation line is not very clear, the molding will not be very clear and look good, but the problem of bursting can be avoided or mitigated.
The selection of paper filaments is very important when the paper is folded. At present, most coated papers on the market are made by high-speed paper machines on the web, in both directions (longitudinal: parallel to the paper filaments, horizontal: perpendicular to the paper filaments). There is also a certain difference in nature, and the vertical folding resistance of paper is relatively better than that of the transverse direction. Therefore, it is recommended to select the folding line and the direction of vertical direction of the paper web as much as possible during the folding process.
The above is a summary of the analysis and processing methods of the cracks in the mouth of the printing factory masters and experts during work learning. In addition, different customers choose papers of different grades according to different requirements of their products, and it is also very important to avoid and mitigate such problems.
Knowing the cause of the problem, we can solve it when we encounter such problems, namely controlling the moisture content of the paper. The paper's moisture content is basically controlled at 4% to 6%. After production, it is rapidly packaged with leaching kraft paper to prevent water loss. During the printing process, the temperature and humidity of the storage and processing plant environment were not controlled, and the water that was opened when the package was opened before printing was lost during storage. In the process of printing and printing, printing ink and coating oil need to be accelerated by hot air, infrared, UV light and other methods. At this time, the water in the paper is lost more and more, if the paper is not directly processed by folding, There will be a problem of collapsing bursts. The following is a brief introduction of several remedies for this problem, for your reference.
Rewetting treatment: replenish the paper before folding. Double-sided printing products: If it is rotary printing, the temperature of the oven is adjusted during the drying process to prevent the paper from losing too much water. Another can be used to increase the humidity of the environment, such as water spray around the workshop and the paper roll, etc., to adjust the humidity of the paper, and spray near the sample at the same time, directly fill the water samples.
Single-sided printing products: The back of the water can be used, the effect is more obvious. Once there was a printing factory using a copper plate gravure printing machine, after the single-sided printing roll, automatic bag making machine, automatic folding forming a small package bag, there is a break at the folding point, after the back of the water process, the yield A substantial increase.
Boxed products: After the indentation, use a damp cloth to wipe the folds.
Folding, indentation process Adjust the folding process to reduce the folding pressure as much as possible to ensure that the printed sample can be formed.
According to the requirements of the die cutting process, different steel wires, different thicknesses of the bottom plate, and different bottom mold groove widths should be selected for different papers. If the related process does not match, it is easy to cause a crack in the fold. The following is a common calculation method for your reference.
B=[C×1.5]+D
Among them, B-indentation bottom die groove width; C-paper thickness; D-steel wire thickness and D≥C; A≤C;
When indenting a thick paper or a box product, the width of the bottom mold groove is enlarged as much as possible, and the indentation pressure is appropriately reduced. Although the indentation line is not very clear, the molding will not be very clear and look good, but the problem of bursting can be avoided or mitigated.
The selection of paper filaments is very important when the paper is folded. At present, most coated papers on the market are made by high-speed paper machines on the web, in both directions (longitudinal: parallel to the paper filaments, horizontal: perpendicular to the paper filaments). There is also a certain difference in nature, and the vertical folding resistance of paper is relatively better than that of the transverse direction. Therefore, it is recommended to select the folding line and the direction of vertical direction of the paper web as much as possible during the folding process.
The above is a summary of the analysis and processing methods of the cracks in the mouth of the printing factory masters and experts during work learning. In addition, different customers choose papers of different grades according to different requirements of their products, and it is also very important to avoid and mitigate such problems.
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