Talking about the Cause Analysis and Troubleshooting of Die Cutting Dark Line Burst
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In the post-press processing of paper packaging, die-cutting and indentation are an important process. The die-cutting plate is formed into a certain shape on a die-cutting machine by using a die-cutting plate arranged by a steel knife and a steel wire. The grooves or the grooves for bending are commonly referred to as dark lines. The quality requirements for dark lines are suitable for wide and narrow, clear and full, not bursting, and well formed. Burst is a relatively common quality problem. The reasons are various, some are more intuitive, some are more subtle. This article tries to analyze from the following aspects.
Improper pressure
1. There are foreign objects in the dark line of the bottom plate, which causes the sudden increase of dark line pressure to be the common cause of bursting. It is also the most destructive cause. It often breaks the dark line as a whole, resulting in product scrapping, but it is also more intuitive, easy to judge and solve, as long as it is cleaned up in time. Foreign objects can be eliminated. In this regard, in the die-cutting process, the bottom plate should be cleaned to prevent foreign matter from entering the die-cutting machine, ensuring smooth operation of the nip.
2. The running version, that is, the die-cut version or the bottom plate. The steel wire is often pressed against the edge of the dark line groove, causing a large area of dark line to burst, and is mainly concentrated on the dark line in the same direction. When you find this, you should immediately re-upgrade and lock the die-cut and the master.
3. According to the requirements of the die-cutting process, different steel wires should be used for different papers, as well as different thicknesses of the bottom plate and different dark line groove widths. If they do not match, it is easy to cause dark lines to burst. The following is a commonly used calculation method for your reference.
(1) Die-cut jam
Let A: the thickness of the bottom paper, B: the width of the dark line, C: the thickness of the cardboard, D: the thickness of the steel, then:
D≥C;
A≤C;
B=(C×1.5)+D
(2) Die cut corrugated cardboard
Let A: the thickness of the bottom paper, B: the width of the dark line, C: the thickness of the corrugated board (cable), D: the thickness of the steel line, E: the thickness of the corrugated board after flattening, then:
D≥E;
A≤E;
B=(E × 2)+D
Generally speaking, in the case of ensuring that the dark line does not burst, the dark line groove should be as narrow as possible, so that the dark line is full and easy to bend, and the product is formed well, especially for PET paper, the dark line groove is narrower than the general product, but the dark line The slot is too narrow, which may cause the dark line to burst.
Improper surface treatment of printed products
1. Effect of embossing
The embossing process is an emerging surface finishing process in recent years, which presses a paper with a patterned steel roll and a hard wool roll to press the desired grain on the surface of the paper. The embossing process was initially limited to the pages of greeting cards, desk calendars and books, and was gradually adopted by paper packaging products. The use of the embossing process enhances the appearance of the product, but it also has a certain negative impact on the post-packaging process. First, the greater pressure during embossing (usually 3 to 8 MPa) makes it easy to produce a certain amount of paper. Deformation, resulting in inaccurate pressure or unevenness; second, it is easy to cause dark line burst, because the paper is strongly squeezed by the pattern steel roller and wool roller, the surface will be damaged to varying degrees, especially when the pattern roller has sharp texture At the same time, the surface of the paper will be stabbed. If the dark line is pressed against the stab position when the die is cut, a burst will be formed when the bend is made. To avoid such problems, first of all, when designing the pattern, avoid using small points and very thin lines, because it is very sharp on the pattern steel roller, it is easy to damage the surface of the paper, forming a burst; secondly, embossing The pressure should be moderate. If it is a sheet-fed product, you can grind the wool roller to make the pattern completely replicate on the wool roller to achieve the desired effect with less pressure. If it is a card, you can lick the paper first. Embossing, because after the paper is smashed, the paper becomes thicker and softer, the plasticity is improved, and it is easy to press out the clear lines.
2. Effect of oil polishing
After the surface of the paper is oiled and polished, the varnish solidifies into a mirror surface on the surface of the paper, and the elongation is extremely small, and the indentation is easily bent to cause a burst. In this regard, the paper can be dampened or softened or used directly on the back of the paper by the melter.
Improper selection of process and materials
1. Paper grain effect
In the papermaking process, the paper fibers are arranged in a uniform direction due to the oscillation of the device, which forms the directionality of the paper, and this characteristic of the paper has a great influence on printing and post-processing. Practice has proved that, in the die-cutting, if the direction of the indented steel wire and the paper fiber is perpendicular, the paper fiber is radially destroyed, the dark wire is easily bent, formed well, and the angle is small; if the indentation steel wire is parallel to the paper fiber direction, the paper is If the horizontal direction is not damaged, the dark line is not easy to bend, and the shape is rounded, and the angle is large, which is easy to break for the outer layer of the paper. This directionality of paper has little effect on the die-cutting of sheet-fed products, but it is not well formed, but it is not easy to break the line, but it has a greater impact on the card-card products. If it is not handled well, it will not be formed. Well, it is easy to explode, mainly because the dark lines of parallel paper lines burst at different positions, while the other direction does not explode. In order to avoid such problems, it is necessary to stipulate that the paper and the lining of the lining are perpendicular to each other when the process is formulated. It is not parallel. If it has already appeared, it is only by humidifying the paper and widening the dark line or increasing the steel. The knife arc is used to make up.
2. Die cutting problem
Die-cutting is the basis of die-cutting work. If you improperly handle some creases, it will also cause a burst.
For example, in the post-processing finishing process of packaging, film coating is a relatively common process. The main material is biaxially oriented polypropylene film (BOPP), which has very good tensile strength and tensile strength of 130Mpa in both vertical and horizontal directions. Above, it is generally not easy to burst, but if there is a slight gap, it will easily burst from the notch. Therefore, if the die cutter is damaged during the die cutting, or if the indentation line is cut, there is a burr. That is, the BOPP film is damaged at the dark line or the knife line interface, and the BOPP film cannot be stressed when the dark line is bent, which may cause a burst.
In short, the die cutter and the die cut line at the dark line should avoid the knife edge and the interface, and try to make the arc angle or a steel knife to form once.
3. Material quality problem
There is a problem with the quality of the material, and it is easy to cause the dark line to burst. If the water content of the paper is too low and the paper becomes brittle, it will easily cause the dark line to burst.
In order to avoid the burst caused by material quality problems, paper should be used selectively with low surface strength paper, recycled paper and sandwich paper; for BOPP film, prevent sun exposure and long-term storage, and avoid the decrease of tensile strength.
The above only lists the common causes of the dark line bursting of paper. In fact, there are other reasons. This requires careful observation and careful thinking in actual operation to eliminate the dark line bursting fault.