The amount of glue applied is insufficient or uneven

Insufficient or uneven amount of glue due to insufficient amount of glue produced by the white spot can be observed in the composite machine. In the dry composite process, the coated adhesive must be able to fill the bumps and bumps on the surface of the ink and film to avoid appearance defects such as obvious white spots.When the water-based adhesive dry composite is used to produce lightweight packaging products, the economic coating amount of water-based adhesive is 1.8 ~ 2.2g/m2, and the working concentration is 42% (the working concentration of different brands of water-based adhesive may vary), and the number of lines is 180 lines/inch, and the depth of the mesh hole is 32μm.Due to the large opening degree of the net hole on the roller, if the surface of the roller is worn, it will have a more obvious impact on the amount of glue. Therefore, in the dry composite process of water-based adhesives, the operator should often detect the actual amount of glue applied by the roller to avoid insufficient amount of glue applied due to excessive wear of the roller.

In addition, the uniformity of the amount of water-based adhesive is also a very key factor, if the coating is not uniform, there will inevitably be a small amount of local glue, resulting in white spots. Therefore, we should pay special attention to the following two issues:

①The assembly of the scraper should be flat and straight, without distortion, and the Angle and pressure of the scraper should be adjusted appropriately to ensure uniform scraping effect;

②During normal production, the scraper should keep the left and right strings to avoid the wear of the rubber roller in a fixed position.

Poor level of glue

Because water-based adhesives are not like solvent-based adhesives, they can achieve a better leveling effect under the action of their own gravity and surface tension after coating, so when coating water-based adhesives, it is necessary to use a flattening roller to flatten the adhesive. The speed, pressure and surface cleanliness of the flattening roller are related to the leveling effect of the water-based adhesive, and the rotation direction of the flattening roller should be opposite to the compound direction, otherwise the flattening effect cannot be achieved, and the speed should be slightly higher than the compound speed.

The leveling effect of the water-based adhesive is also affected by the surface tension of the coated film. Since the surface tension of the water-based adhesive is obviously higher than that of the solvent-based adhesive, the surface tension of the ink on the coated film is required to be not less than 38mN/m, otherwise the water-based adhesive will automatically shrink after coating and cannot be continuously formed. Therefore, the operator should pay attention to the detection of the surface tension of the coated film. In addition, if the surface of the coated film is not clean, adhering to substances with low surface tension, etc., it will reduce the leveling performance of the adhesive liquid, and will also produce a fault similar to the printing of "shrinkage holes", which is manifested as "pitting" on the composite film.

The net hole of the roller is blocked

In the dry composite of solvent-based adhesives, there are generally two kinds of clog in the mesh holes of the roller. One is that the two-component adhesive is deposited at the corners of the mesh holes of the roller, which cannot be transferred out, and the cross-linking curing occurs over time, making the mesh holes shallow; Second, when high concentration adhesive is coated with a high wire number roller in a high temperature environment, due to the rapid volatilization of ethyl acetate, poor transfer of adhesive liquid and thus blocking the mesh hole, which is somewhat similar to the "dry plate" phenomenon caused by the rapid volatilization of organic solvents in the printing process.

When using water-based adhesive for dry composite, in order to prevent the plug of the roller mesh, the scraper should be loosened during shutdown, and the roller should be soaked in the adhesive to keep rotating. If the mesh hole of the adhesive roller is blocked, it must be cleaned with organic solvents such as butyl ketone. If the shape of the net hole of the roller is not suitable, it is also easy to cause the plug of the net hole, but this blockage occurs gradually. The net hole of the coating roller used in the dry composite of water-based adhesives is shallow and the opening is large, so that the contact area between the water-based adhesive and the film substrate can be as large as possible, which is conducive to improving the coating effect and drying efficiency. We generally use 180 lines/inch four-corner flat-bottom embossing rollers or 200 lines/inch four-corner flat-bottom connected embossing rollers, or electric carving rollers with smaller internal angles and larger grooving, it is not recommended to use four-corner pyramid embossing rollers, because the latter has a larger internal Angle of the mesh hole, poor release of adhesive liquid, easy to block the mesh hole, and the appearance of the film in the production of rigid composite is very good. However, after the production of thousands of meters or nearly 10,000 meters, there will be white glue spots, and the detection will find that the amount of glue has been relatively insufficient.