In the dry season, due to moisture, many packaging and printing enterprises are often troubled by the explosion angle and burst of color boxes in the process of die cutting, bonding and packaging. Next, let's take a look at how senior technicians deal with this kind of problem.
1、 Cause
1. Burst due to improper pressure
1.1 there are foreign matters in the indentation groove of the bottom plate, resulting in a sharp increase in pressure during die cutting. This is a common and destructive cause of burst in production. It will break the dark line as a whole and cause the product to be scrapped.
1.2 run plate, that is, the die-cutting plate or base plate is in position, so that the steel wire falls on the outside of the indentation groove. The burst caused by this reason is mainly concentrated on the dark line in the same direction, because the cutter or indentation knife does not fit closely with the wood formwork, resulting in deflection under pressure.
1.3 the selection of steel wire thickness and indentation bottom groove width does not match the paper material. According to the requirements of die-cutting process, different steel wires, baseplates with different thickness and different dark wire slot widths should be selected for different papers. If they do not match, it is easy to cause the dark wire to burst.
2. Bursting caused by die-cutting plate making process
2.1 When making die-cutting plate, the position of steel wire is handled improperly or burr is left when steel wire is cut off. In die-cutting, if the product has surface treatment, such as film coating. Some burrs left on the steel wire during die cutting will damage the pull-up strength of the surface film. When the product is formed, the film cannot be stressed, and it will burst.
2.2 the steel knife and steel wire at the dark line have knife edge and interface. Because the interface is not smooth, tearing will occur during die cutting.
2.3 when the sponge pad of the wire pressing knife is not properly positioned, the wire pressing will burst, and the deformation and damage of the wire pressing knife will also cause the wire pressing to burst.
2.4 whether the matching of knife and line on the knife die is reasonable. In particular, the paper thickness is not considered in the design, the knife and line cannot be effectively avoided in the overlapping, and the interference occurs during forming, resulting in excessive stress concentration and burst.
3. Material quality problems
3.1 the water content of the paper is too low and the paper becomes brittle. This phenomenon often occurs in winter. Due to the dry and cold weather in winter and low relative humidity in the air, it will directly affect the moisture content of the paperboard, resulting in the fracture of the paperboard after pressing. Generally, the moisture content of the base paper is controlled at the upper limit (8% - 14%);
3.2 the biaxially oriented polypropylene film of paper coating material has a slight notch, resulting in the reduction of tensile strength. Film covering is a common paper surface treatment method. Its main material is BOPP film. If BOPP film is damaged before die-cutting, BOPP film will not be stressed and burst when bending after die-cutting. The bursting of the film only occurs in the film layer. With the adjustment of the force point, it will extend along the bursting direction, and the paper at the bottom layer does not burst, which indicates that it has nothing to do with the paper. If the film is not broken, the paper has nothing to do with the film, and there is a problem with the paper.
3.3 paper orientation is incorrect. During die cutting, if the indentation steel line is perpendicular to the direction of paper fiber and destroys the paper fiber radially, the dark line is easy to bend, good forming and small angle; If the indentation steel line is parallel to the fiber direction of the paper and the paper is not damaged in the transverse direction, the dark line is not easy to bend, form into rounded corners, have a large angle, and have a large supporting force for the outer layer of the paper, which is easy to break. This directionality of paper has little impact on the die cutting of sheet fed products. It is just that the forming is not good, but it is not easy to burst, but it has a great impact on the card mounting products. If it is not handled well, it is not only bad, but also easy to burst, mainly because the dark lines parallel to the paper grain burst at different positions, but not in the other direction.
3.4 the corrugated configuration is too high. The bursting strength and transverse ring crush strength of base paper are one of the influencing factors. If the folding resistance of the lining paper is too low, it will easily lead to bursting.
3.5 the mold is used for too long. In die-cutting, after the die-cutting plate is used for a long time, the line pressing knife will loosen, resulting in the line pressing knife bouncing up in the process of die-cutting, resulting in the bursting of paperboard line pressing. Due to the long-term use of the rubber pad, the uneven rubber pad causes the pressure line to burst.
2、 Process improvement
(1) For the burst caused by foreign matters in the indentation groove, strengthen the sampling inspection during production and control it to 200 pieces for sampling inspection once. This problem is more intuitive and easy to judge. Clean up the foreign matters in time and keep the bottom plate clean
(2) If it is found that the plate is running, it shall be re loaded immediately, and the die-cutting plate and base plate shall be locked.
(3) There is a common calculation method for burst caused by mismatch between steel wire thickness, indentation bottom groove thickness and material:
Die cutting paper jam
If a: thickness of backing paper, B: width of dark wire slot, C: thickness of paper jam, D: thickness of steel wire, then: D ≥ C; A≤C； B=(C × 1.5)+D
Die cut corrugated board
If a is the thickness of the backing paper, B is the width of the dark wire slot, C is the thickness of the corrugated board (clamping tile), D is the thickness of the steel wire, and E is the thickness of the corrugated board after flattening, there should be: D ≥ E; A≤E； B=(E × 2)+D
(4) If there are burrs or cutting edges on the steel wire on the die-cutting plate, the burr or cutting edge of the indentation elimination tool can be rounded with a grinding wheel or file or replaced with a thick knife. If two thin knives are used together, the effect is better
(5) When making the die-cutting plate, the dark line should be made into an arc angle or a steel knife at one time.
(6) When the pressure line burst occurs due to the improper position of the sponge rubber strip, the sponge pad can be pasted next to the pressure line knife of the die to help destroy the corrugated at the paperboard pressure line, so as to solve the burst phenomenon. However, the sponge pad used should not be too soft, and its own hard protective strip should be used.
(7) For the water content of paper, die cutting shall be produced in time after the paperboard comes out, which is not easy to store for a long time, so as to reduce the impact of relative humidity on the moisture content of paperboard. For paperboard with low moisture content, water can be coated on the paperboard to reduce the burst phenomenon.
(8) For the burst caused by inaccurate overprinting, do the forming action after overprinting and pre fold 180 degrees to test, and visually check whether the indentation line is offset.
(9) The mold shall be checked frequently. If the knife is loose, it shall be repaired or remade in time.
(10) The improvement scheme for bursting caused by the problem of paper wire direction is as follows:
a. The silk direction of the color box without paper mounting shall be perpendicular to the forming main line to facilitate forming.
b. The tile direction of the color box mounted on two layers should be perpendicular to the paper direction, so that the color box can be formed with stiffness.
c. Mounting three layers (tile plate type) can adjust the wire direction according to the configuration of tile plate.
(11) Improvement scheme for bursting caused by paper toughness and folding resistance (configuration):
a. The toughness and folding resistance of paper mainly depend on the content of wood pulp during papermaking. The higher the wood pulp, the more long fibers constitute the paper, the better the toughness and folding resistance, and vice versa.
b. The higher the requirements for burst resistance and box pressure, the higher the corrugation configuration will be, and the higher the requirements for face paper. At this time, a surface sheet with good toughness and folding resistance is required; The worse the corrugated configuration, the lower the requirements for the relative surface tension;
c. The company also needs to purchase a testing equipment to test the raw paper during feeding. It can not only decompose the gram weight and whiteness.
(12) Improvement scheme for bursting caused by membrane quality:
a. Replace the raw materials of the film;
b. Change the paper direction of the upper film;
c. Modify the die-cutting blade plate, extend it at the knife joint and U-shaped angle, and lift the pressing line at the aircraft hole by 0.5mm-0.7mm to slow down the buffer force during folding;
(13) Improvement scheme of material thickness and ruler angle.
a. For different materials, the R angle of the die must be greater than the thickness of the material;
b. The matching position of knife, line and aircraft hole shall not conflict or interfere during forming, and shall be avoided reasonably. In particular, when the main line and tile are in the same direction during forming, it is very easy to burst.
c. We should work towards low gram weight and high configuration, and we can't blindly pursue high configuration.
3、 Environmental factors and standards
(1) The temperature in the workshop is balanced
(2) Control of water content during paper mounting (18 ± 3)
(3) Appropriate moisture content during die cutting (18 ± 3)
(4) Pressure adjustment of die-cutting machine table (70% of the base paper is broken, and the rest needs to be broken)
(5) Width and thickness of die cutting scribed line (thickness of paper flattened) × 1.5 = scribed line width)
(6) Inspection of die cutting tool (visual inspection, steel ruler, vernier caliper)
(7) Molding technique
a. The main line that needs to be pasted should be folded 180 degrees.
b. The folding of the upper and lower swing covers shall be greater than 135 degrees.
c. The secondary line shall be folded more than 135 degrees.
d. The corrugated board should be folded back 90 degrees