1. The initial viscosity of the adhesive itself is insu […]
1. The initial viscosity of the adhesive itself is insufficient, and the cohesion is too small
The tunneling effect caused by this reason is to solve the problem by improving the quality of the adhesive. Today’s adhesives are developing towards high solid content and low viscosity. This is to meet the needs of large-scale and high-speed dry laminating machines and use less diluents, thereby reducing the emission of organic solvents to the atmosphere and reducing environmental pollution. The need to reduce production costs.
In the past, a 20% low solid content operating solution was generally used. If the glue amount is 4g/㎡ dry basis, the total glue solution amount is 20g/㎡. Of the total amount of 20g, organic solvents account for 16g, which becomes a gas and is discharged into the air during drying. On the one hand, it pollutes the environment; on the other hand, it is wasted and the cost increases. At present, most of the operating solutions with high solid content of 30%~35% are used, and some are even as high as 45%. Similarly, the amount of glue is 4g/㎡ dry basis, and the amount of glue coating is reduced to 13g/㎡ or 9g/㎡. The amount of organic solvents is much less than the previous ones, and the advantages are obvious.
However, the low-viscosity adhesive has a small molecular weight and often has little cohesion. It must be cured and cross-linked to form a macromolecular structure before it has an ideal adhesive force. The initial adhesion is very small when it is just compounded. Insufficient adhesion. When a substrate is about to shrink, it is easy to produce relative displacement between the two substrates, causing wrinkles or "tunnels". This must start with the synthesis of adhesives, and produce products with low viscosity and high solid content with low viscosity and large initial viscosity. As a manufacturer of aluminum foil bags, this product should be selected among many adhesives to ensure the quality of the product.
Of course, if the tension control of the equipment is very precise and the operation technology is excellent, the initial adhesion of the adhesive is very low and there will be no wrinkle or "tunnel" problems. For example, many solvent-free laminating machines in China are using solvent-free When the adhesive is produced, the initial adhesion is very low, less than 0.2N/15mm, but it will not produce wrinkles or "tunnels".
2. The winding tension is too small and the winding is not tight
There is relaxation after compounding, which provides the possibility of shrinking the substrate to be shrinked. Therefore, when the two or three substrates are combined, the winding tension should be large, so that it can be rolled tightly and compacted, so that it does not appear to relax. If this can be achieved, even if the tension is uneven and the initial adhesion is insufficient, wrinkles will not appear. Because it is placed in the curing chamber under the rolled and compacted state to allow the adhesive to be fully cross-linked and cured, the adhesion is greatly improved, and there will be no relative displacement between the two substrates. Therefore, no matter what the reason, it is always beneficial to increase the winding tension after compounding. However, it is necessary to prevent the "indentation" phenomenon caused by the loose core and the tight outer ring.