Several common causes of white spots in the dry compounding process of water-based adhesives!

The amount of glue is insufficient or uneven
the white spot caused by the insufficient amount of glue can be observed when the composite machine is lowered. In the dry composite process, the coated adhesive must be able to fill the ink and the surface of the film bump, in order to avoid the appearance of obvious white spots and other defects. When using water-based adhesive dry compound to produce lightweight packaging products, the economic coating volume of water-based adhesive is 1.8 to 2.2g/m2, the working concentration is 42% (the working concentration of different brands of water-based adhesive may vary), the general number of lines is 180 lines / inch, mesh depth of 32 m of coating rollers for . Due to the large opening of the mesh on this coating roller, if the surface of the coating roller wear, it will have a more obvious impact on the amount of glue applied. Therefore, in the process of water-based adhesive dry compounding, operators should often detect the actual amount of glue applied to the roller, to avoid excessive wear of the glue roller resulting in insufficient amount of glue.
addition, the uniformity of the amount of water-based adhesive coating is also a very critical factor, if the coating is not uniform, there will inevitably be a small amount of local adhesive, resulting in white spots. Therefore, we should pay special attention to the following two problems:
(1) scraper assembly should be straight, can not be distorted, and should be the scraper angle and pressure adjustment appropriate to ensure the same scraper effect
; Lue fluid leveling is poor
because the water-based adhesive is not like solvent-based adhesive, after coating can achieve a better leveling effect under the effect of its own gravity and surface pressure, so when applying water-based adhesive, 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 composite direction, otherwise the flattening effect will not be achieved, and its speed should be slightly higher than the composite speed.
the leveling effect of water-adhesives is also affected by the surface stress of the coated film. Because the surface tensor of the water-based adhesive is significantly higher than the solvent-based adhesive, it is required that the surface tensor of the ink on the coating film is not less than 38mN/m, otherwise the water-based adhesive will automatically contract after coating, can not be continuously filmed. Therefore, operators should pay attention to the coating film surface stress detection.
In addition, if the surface of the coated film is not clean, adhere to the low surface pressure of the material, etc. , will reduce the smoothing performance of the glue, but also will produce a similar to the printing "shrink hole" failure, as shown in the composite film appears "point".
Coating roller mesh cavitation
In solvent-based adhesive dry compound, the glue roller mesh cavitation is generally two kinds of clogging, one is two-component adhesive deposited in the corner of the coating roller mesh, can not be transferred out, with the occurrence of crosslinking over time Curing and shallowing of the mesh, and second, when using high-wire number coating rollers to coat high-concentration adhesives in high-temperature environments, due to ethyl acetate volatilization too fast, poor fluid transfer thus clogging the mesh, which is somewhat similar to the printing process due to the rapid evaporation of organic solvents caused by the "dry version" phenomenon.
When using a water-based adhesive for dry compounding, in order to prevent blockage of the coating roller mesh, loosen the scraper during shutdown and keep the coating rollers in the adhesive. If the adhesive roller mesh is blocked, it must be cleaned with organic solvents such as butyl ketones.
if the shape of the mesh of the glue roller is not suitable, it is easy to cause the mesh blockage, but this blockage occurs gradually. Water-based adhesive dry composite use of the coating roller shallow, large opening, so that the water-based adhesive and film substrate between the largest possible contact area, is conducive to improve the coating effect and drying efficiency. We generally use 180-wire/inch four-corner flat-bottomed embossed rollers or 200-wire/inch four-corner flat-bottomed connected embossed rollers, or electric carving rollers with smaller inner corners and larger grooves, and do not recommend the use of four-corner pyramid-shaped embossed rollers. Because the latter's net hole inner corner is larger, the release of the glue is poor, easy to clog the mesh, the appearance of the film just composite production is very good, but the production of thousands of meters or nearly 10,000 meters after the appearance of white dot adhesive spots, at this time the detection will find that the amount of glue has been relatively inadequate.
In addition, when re-using the two-component water-based adhesive, we should grasp the degree of its utilization and the proportion of the addition of old glue, because this will not only directly affect the peeling strength of the composite products, but also will make the transfer of water-based adhesive worse, and even cause the glue roller mesh blockage, which will produce white spots.
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