In the dry season, due to moisture, the corners and bursts of color boxes during die cutting, bonding and packaging often plague many packaging and printing companies. Next, let's take a look at how senior technicians deal with such problems.
One. cause
1 Improper pressure leads to burst 1.1 There is foreign matter in the indentation groove of the bottom plate, which causes a sharp increase in pressure during die cutting. This is a common cause of bursting in production and is also a destructive cause. It will break the dark line as a whole and cause the product to be scrapped.
1.2 The running version, that is, the die-cut version or the bottom version, makes the steel line fall outside the indentation groove. The burst caused by this reason is mainly concentrated on the dark line in the same direction, because the cutter or the indentation knife does not cooperate closely with the wooden formwork, and it deflects under pressure.
1.3 The selection of the thickness of the steel wire and the width of the bottom groove of the indentation does not match the paper material. According to the requirements of the die-cutting process, different steel wires should be used for different papers, as well as different thicknesses of base plates and different widths of dark wire grooves. If they do not match, it is easy to cause dark wire burst.
2 Burst caused by die-cutting plate production process
2.1 Improper handling of the position of the steel wire when making the die-cut version or burrs when the steel wire is cut off. If the product has been surface-treated during die cutting, for example, covered with film. The burrs left on the steel wire during die cutting will damage the tensile strength of the surface film, and the film will not burst when the product is molded, and it will burst.
2.2 Steel knife at the dark line The steel wire has a knife edge and an interface. Due to the unevenness of the interface, tearing will occur during die cutting.
2.3 When the sponge pad of the crimping knife is improperly positioned, the crimping burst phenomenon will occur. If the crimping knife is deformed or damaged, the crimping burst will also occur.
2.4 Whether the combination of knife and thread on the knife mold is reasonable. Especially in the design, the thickness of the paper is not taken into consideration, the knife and the line cannot be effectively avoided in the overlap, and interference occurs during the molding, so that the force is excessively concentrated there and a burst occurs.
3 Material quality issues
3.1 The moisture content of the paper is too low and the paper becomes brittle. This phenomenon occurs more frequently in winter. Due to the cold and dry weather in winter, the relative humidity in the air is low, which will directly affect the moisture content of the cardboard, causing the cardboard to break after crimping. Between -14%);
3.2 The biaxially oriented polypropylene film of the paper lamination material has a slight gap, which causes a decrease in the tensile strength. Laminating is a relatively common method of surface treatment of paper. The main material is BOPP film. If the BOPP film is damaged before die cutting, it will cause the BOPP film to be forced to cause bursting after bending after die cutting. The bursting of the film only occurs in the film layer, and it will extend along the bursting direction with the addition of the force point. The bottom paper does not burst, which means that it has nothing to do with the paper. problem.
3.3 The paper orientation is wrong. During die cutting, if the indentation steel wire is perpendicular to the paper fiber direction, and the paper fiber is damaged radially, the dark line is easy to bend, the shape is good, and the angle is small; if the indentation steel wire is parallel to the paper fiber direction, the paper is not in the transverse direction When damaged, the dark lines are not easy to bend, and are formed into rounded corners with large angles. They have a large supporting force on the outer layer of the paper and are easily broken. The directionality of the paper has little effect on the die-cutting of single-sheet paper products, but the forming is not good, but it is not easy to burst the line, but it has a greater impact on the card-mounted card products. Well, it is also easy to burst the line, mainly because the dark lines of parallel paper lines burst at different positions, but the other direction does not burst.
3.4 The corrugated configuration is too high. The bursting strength and transverse compressive strength of the base paper are one of the influencing factors. If the fold resistance of the inner paper is too low, it may easily cause burst.
3.5 The mold is used for too long. In the die-cutting, the die-cutting plate will loosen after a long period of use, causing the die-cutting tool to bounce during the die-cutting process, causing the cardboard crimping line to burst. Due to the long-term use of the rubber pad, the unevenness of the rubber pad causes the pressure line to burst.
two. Process improvement
(1) If there is a burst caused by foreign objects in the indentation groove, the sampling inspection shall be strengthened during production, and it shall be controlled to 200 samples. This question is relatively intuitive and easy to judge. It is necessary to clean up foreign objects in time to keep the bottom plate clean.
(2) If you find out that this is the case, you should immediately re-release the version, and lock the die-cut version and the bottom version.
(3) There is a common calculation method for the burst caused by the mismatch between the thickness of the steel wire and the thickness of the indentation groove and the material:
Die-cut cardboard
Let A: the thickness of the bottom paper, B: the width of the dark line slot, C: the thickness of the jammed paper, D: the thickness of the steel wire, then: D≥C; A≤C; B = (C × 1.5) + D
Die-cut corrugated cardboard
Let A: the thickness of the backing paper, B: the width of the dark line groove, C: the thickness of the corrugated cardboard (card-mounted tile), D: the thickness of the steel wire, E: the thickness of the corrugated cardboard after flattening, then it should be: D≥E; A≤E ; B = (E × 2) + D
(4) If the steel wire on the die-cutting plate has burrs or cutting edges, the burrs or cutting edges of the indentation knife can be rounded with a grinding wheel or file or the thick knife can be replaced. If two thin pieces of knife are used in combination, the effect is better.
(5) When making die-cutting plates, the dark lines should be made into rounded corners or a steel knife at one time.
(6) When the pressure line burst occurs due to the improper position of the sponge strip, you can use a sponge pad to stick to the mold's crimping knife to help destroy the corrugation at the cardboard crimping line to solve the burst phenomenon, but the use of The sponge pad should not be too soft, and should use a harder guard.
(7) For the moisture content of paper, the cardboard should be produced and die-cut in time after it comes out. It is not easy to store it for too long, reducing the effect of relative humidity on the moisture content of the cardboard. For the cardboard with a low moisture content, you can apply water on the cardboard to reduce the bursting phenomenon .
(8) For the burst caused by the inaccuracy of the register, do a forming action after the register and pre-fold it for a 180-degree test to visually check whether the indentation line is offset.
(9) The mold should be checked frequently, and if the knife is loose, it should be repaired or remade in time.
(10) The improvement plan for the burst caused by the paper thread direction is:
a. The direction of the color box without paper is perpendicular to the main forming line, which is convenient for forming.
b. The tile direction of the two-layer color box should be perpendicular to the paper direction, so that the color box molding has stiffness.
c. Mounting three layers (tile type) can adjust the wire direction according to the configuration of the tile plate.
(11) Burst improvement plan due to the toughness and folding resistance (configuration) of paper:
a. The toughness and folding resistance of paper depends mainly on the content of wood pulp during papermaking. The higher the wood pulp, the more long fibers that make up the paper, the better the toughness and folding resistance, and vice versa.
b. The higher the requirements for bursting resistance and box pressure, the higher the corrugated configuration, and the higher the requirements for the facing paper. At this time, toughness and folding resistance are needed; the worse the corrugated configuration, the higher the requirements for the facing sheet reduce;
c. The company also needs to purchase a testing device to test the raw paper when feeding, not only to decompose the grammage and whiteness.
(12) The improvement plan of burst caused by the quality of the membrane:
a. Replace the raw materials of the film;
b. Change the film feeding direction;
c. Modify the die-cutting knife version, extend it at the joint of the knife and the U-shaped corner, and the pressure line at the plane hole should be raised by 0.5mm-0.7mm to reduce the buffering force when folded;
(13) Improvement plan for material thickness and ruler angle.
a. For different materials, the R angle of the knife mold must be greater than the thickness of the material when it is designed;
b. The matching position of the knife and the line and the plane hole must not conflict or interfere during molding, and reasonable avoidance is required, especially when the corrugated product is formed, the main line and the tile direction are likely to burst when the corrugated product is formed.
c. We have to work towards a low gram weight and a high configuration, and we cannot simply pursue a high configuration.
three. Environmental factors and various standards
(1) The temperature in the workshop is kept balanced
(2) Control of water content when mounting paper (18 ± 3)
(3) Appropriate moisture content product during die cutting (18 ± 3)
(4) Pressure adjustment of the die-cutting machine (the bottom paper breaks 70% and the rest needs to be filled with the bottom paper)
(5) Width and thickness of die-cutting scribe line (paper flattened thickness × 1.5 = scribe line width)
(6) Inspection of die-cutting die (visual inspection, steel ruler, vernier caliper)
(7) Techniques during molding
a. Fold the main line of the gluing box by 180 degrees.
b. The fold of the upper and lower rocking covers should be greater than 135 degrees.
c. The secondary line should be folded more than 135 degrees.
d. Corrugated board should be folded 90 degrees.
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