Gravure complex problems (below)

Third, on the "tunneling" phenomenon in the composite process The so-called "tunneling" phenomenon generally refers to the appearance of transverse stripes in composite products, especially at the two ends of the material. This wrinkle is flat with a composite substrate, and another kind of bulge forms a "tunnel." In the raised part of the wrinkles, the composite layer separates and does not stick. This phenomenon has many in the two-layer compounding. The three-layer compounding of BOPP/AL/PE mentioned in the letter has resulted in one more compounding process and more opportunities. The reasons for this phenomenon are generally the following:
1. Substrate Tension Problems In the dry composite process, after one of the two rolls of different substrates is coated with adhesive, they are laminated together by heat roller compaction. Therefore, the tension of these two different substrates is critical to the tension relationship of the finished product after compounding. In general, the tension of the two substrates in the composite is not adapted, one of which is too large and the other is too small. When the composite film is tight, it does not seem to show anything. After compounding, the original tension A substrate that is too large must shrink, and its shrinkage is significantly greater than that of a substrate with less original tension, which causes relative displacement and wrinkles. Taking BOPP and aluminum foil compounding as an example, after BOPP is coated with glue, it is heated in a drying tunnel. If the tension of the unwinding coil is relatively large, it is pulled tightly and heated again, and it is bound to stretch. However, the tension of aluminum foil cannot be as large as BOPP, and the elongation is small. Therefore, once cooled after being compounded, BOPP shrinks, produces wrinkles, and the aluminum foil bulges and a "tunnel" appears horizontally. Of course, this example uses a more extreme example.
In fact, the composite of another substrate, such as vacuum aluminized film, or PE and CPP film, as long as the unwinding tension of the two substrates is not well, will have this situation. There are two ways to solve this problem. One is to adjust the unwinding tension of the two substrates so that they can adapt to each other. The dry laminating machine is often equipped with a roll tension regulating device made of a magnetic powder brake, which is designed for such use. The second is to properly reduce the temperature of the drying tunnel. Since the substrate with large deformation is dried in the drying tunnel, the higher the temperature, the higher the elongation of the membrane, the greater the deformation, and the more severe the shrinkage after cooling. Of course, this method must take into account the problem of residual solvent, and the lower the temperature, the better.
2. There are several aspects to this problem of adhesive bonding. 1 Select the applicable adhesive. The solids content of the main polyurethane adhesive is 35% or 50%, and the solid content of the curing agent is 75%. In order to adapt to high-speed dry composite processes, high solids and low viscosity are now used. However, low-viscosity adhesives are often divided into smaller amounts and have little cohesion. It must wait until it cures and crosslinks to form a macromolecular structure to achieve the desired adhesion. However, when the composite is initially compounded, the initial adhesive force is small and the adhesive strength is insufficient. Therefore, when a substrate shrinks, relative displacement occurs between the upper and lower two different substrates, ie, wrinkles appear and "tunneling" occurs. Therefore, the choice of adhesives with high solids content, low viscosity, but high initial tack is the preferred method to solve this problem. - Suitable coating amount. One of the factors affecting the coating market is the anilox roller used for gluing. The thickness of the anilox roller and the depth of the mesh directly affect the amount of adhesive it can carry. The second is the preparation of glue solution, the control of glue concentration. Each glue liquid supplier should have a detailed formulation ratio and method description. The third is to pay attention to the hardness and pressure of the rubber roller, the angle and pressure of the blade. In general, plastic/plastic compound, plastic/aluminum compound, whether the compound is based on large-area printing, or non-printing blanks, 2.0~5.0g/m2 of glue is necessary, gluing The amount should not be too low. Too low, seemingly to save the cost, the actual compound is not strong, but to give up. Of course, it is not necessary to apply too much glue. Within a certain range, the fastness is proportional to the amount of glue, but after a certain degree, it is disproportionate.
3. Compounding Winding Tension Problem Winding tension is too small to be coiled tightly, compounding relaxation phenomena, and providing shrinkage to the substrate to be shrunk. This phenomenon is most noticeable at both ends of the composite product, and the middle portion is often firm, but the parts exposed to both ends are wrinkled due to uneven shrinkage. The solution is simple, as close as possible to close. The tension of the winding is large, the roll is compacted and compacted, and no relaxation occurs. Even if there is some tension in the inside, the initial tack is insufficient, but the possibility of shrinkage is smaller when the knit film is pressed. When the adhesive is cross-linked and cured during curing, the initial test tack is greatly increased, and the relative displacement between the composite substrates. It also loses its survival conditions so that wrinkles do not appear.
four. After the aluminized film is left for a period of time, the ink printed on the aluminized film and the sputtered aluminum powder will fall off. We have not encountered this problem in production. The printing on the aluminized film is generally printed on the non-sprayed aluminum surface. If the ink printed on the non-sprayed aluminum surface and the lead powder sprayed on the other surface are peeled off, there may be a problem with the stability of the film itself. Sometimes the antistatic agent in the film leaks out and there may be similar conditions. It is difficult to put forward valuable opinions because they do not understand the actual situation. We once sprayed aluminum into the vacuum chamber after BOPP printing, that is, the aluminum was painted on the ink surface, and no similar situation was encountered. It is recommended that the printing factory check the surface wetting tension on both sides of the film. The sprayed aluminum surface should reach a certain surface wet tension, and the printed surface should also reach a qualified surface wet tension, so that the fastness of aluminum spray and printing can be guaranteed.

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