Analysis of die-cutting dark line burst and troubleshooting

In the post-press processing of paper packaging, die-cutting and indentation is an important process. It is to cut the substrate into a certain shape on a die-cutting machine by means of a die-cutting plate lined with a steel knife and steel wire. Press marks or groove marks for bending, groove marks for bending are commonly called dark lines. The quality requirements for dark lines are wide and narrow, suitable for clarity, fullness, no burst, and good molding. Burst is a relatively common quality problem. The causes are various, some are intuitive and some are hidden. This article tries to analyze from the following aspects.

First, the pressure is not proper

1. There are foreign objects in the dark line of the bottom plate, which causes the sharp increase in dark line pressure to be a common cause of bursting, and it is also the most destructive cause. It often causes the entire dark line to break, causing the product to be scrapped, but it is also more intuitive and easy to judge and solve, as long as the foreign matter is cleared in time to eliminate the malfunction. In this regard, in the process of die-cutting, it is necessary to ensure that the bottom plate is clean and foreign matter is prevented from entering the die-cutting machine, ensuring that the press-fitting part works smoothly.

2. The running version, ie die-cut version or bottom version, makes the steel wire often pressed against the edge of the dark trough, causing a large area of ​​dark lines to burst, and is mainly concentrated on dark lines in the same direction. When this happens, you should immediately re-publish and lock the die-cut version and the bottom plate.

3. According to the requirements of the die-cutting process, different steel wires, different thicknesses of the original plate, and different dark line groove widths should be selected for different papers. If it does not match, it can easily cause the dark line to burst. The following is a common calculation method for your reference.

(1) Die-cut cardboard

Let A: shade thickness B: dark groove width C: jam thickness D: steel thickness should have: D ≥ C; A ≤ C; B = (C × 1.5) + D

Second, improper surface treatment of printed products

1. The effect of embossing

The embossing process is an emerging surface finishing process in recent years. It presses the paper through a patterned steel roller and a hard wool roller to emboss the required lines on the surface of the paper. The embossing process was initially limited to the front pages of greeting cards, desk calendars, and books, and was gradually adopted by paper packaging products. The use of the embossing process enhances the decorative appearance of the product, but it also has a negative impact on the post-packaging process. First, the greater pressure during embossing (usually at 3 to 8 MPa) makes it easy to produce certain paper. Deformation, resulting in inaccurate pressure embossing or die-cutting position; Second, it is easy to cause the dark line burst, because the paper is subjected to the strong compression of the pattern steel roller and the wool roller, the surface will be subject to different degrees of damage, especially when the pattern roller has a sharp line At the same time, the surface of the paper will be punctured. If the dark line is pressed against the puncture site when it is die-cut, it will burst when it is bent. Therefore, it is necessary to avoid the use of small points and very thin lines, because it is very sharp on the patterned steel roller, it is easy to damage the surface of the paper, forming a burst; Second, the pressure on the embossing should be moderate, if it is a sheet of paper products, you can more A roll of wool is used to make the pattern completely replicated on the roller and the desired effect is achieved with less stress.

2. The effect of oil polishing

After the surface of the paper has been oiled and polished, the varnish solidifies into a mirror surface on the surface of the paper. The elongation is extremely small, and the creasing of the indentation can easily cause bursting. To do this, you can make the paper wet or soft, or use a gluing machine to apply water to the back of the paper.

Third, improper selection of processes and materials

1. Effect of paper pattern

In the papermaking process, the paper fibers are aligned in a uniform direction due to the oscillation of the apparatus, which forms the directionality of the paper. This characteristic of the paper has a great influence on printing and post-processing. Practice has proved that, when die-cutting, if the indentation steel wire is perpendicular to the direction of the paper fiber, and the fiber of the paper is destroyed radially, the dark line is easy to bend, the molding is good, and the angle is small; if the indentation steel wire is parallel to the paper fiber direction, the paper is If the transverse direction is not damaged, the dark lines are not easily bent, and they are formed into rounded corners. The angle is large, and the external force of the paper is large and easily broken. This directionality of the paper has little effect on the die-cutting of sheet-fed products, but it is not well formed, but it is not easy to burst. In order to avoid such problems, it is necessary to specify that the paper lines and the lined paper lines are perpendicular to each other when the process is being developed. If it has already appeared, it can only be compensated by humidifying the paper and widening the dark line or increasing the curvature of the steel knife.

2. Die Making Problems

Die-cutting is the basis for die-cutting work. If some of the creases are improperly handled, it can also lead to popping. For example, in the post-processing and finishing process of packaging, the film is a relatively common process. The main material is the biaxially oriented polypropylene film (BOPP). Its tensile strength is very good, and its longitudinal and transverse tensile strength is Above 130Mpa, under normal circumstances it is not easy to burst, but if there is a slight gap, it will easily burst from the gap. Therefore, in the production of die-cutting plates, if the die-cutting knife is damaged or burrs are left when the indentation line is cut off, that is, the BOPP film is damaged at the dark line or at the cutter wire interface, and the BOPP film cannot be subjected to stress when the dark line is bent. Cause burst.

In short, the cutting knife and die cutting line at the dark line should avoid the knife edge and the interface. Try to make a round angle or a steel knife to shape once.

3. Material quality issues

Material quality problems, but also easily lead to dark lines burst, such as paper water content is too low, the paper becomes brittle, it is easy to cause the dark line burst.
To avoid bursting caused by material quality problems, paper, paper with low surface strength, recycled paper and sandwich paper should be used selectively. For BOPP film, it is necessary to prevent sun exposure and long-term storage to avoid the decrease of tensile strength.