Abstract: Differential coating and gluing changed the coating state of the adhesive from spot coating to surface coating, thereby relatively expanding the bonding area of the material and increasing the bonding strength. When the bonding strength is met, the amount of sizing can be reduced, thereby reducing the compounding cost, and also reducing the probability of problems in the composite product.
At present, 70% of the problems in the composite process are related to the gluing method. For example, the appearance of aluminized film composites is not good, the aluminization transfer phenomenon of aluminized film composite products, the transparency of transparent film composites is not good, the solvent residue is too high, and cooking bags are broken.
The gluing method we use on the dry compound machine is generally called scraper gluing. This sizing method requires relatively high coordination of the working fluid concentration, viscosity, and line number of the anilox roller, and it is difficult to find regular operating experience. Because the viscosity of the adhesive produced by each manufacturer is not the same, the viscosity of the working fluid changes with the concentration, ambient temperature, and the length of use. In particular, the viscosity of water-based glue is susceptible to the influence of ambient temperature, and the change is greater. And many problems in composite products are related to the poor coordination of the three.
In the production process, once we find that the bonding strength of the composite film is low or the appearance is not good, we often increase the coating amount, so that there can be more dry basis when the hot-pressing compounding and high temperature curing are carried out later, so that During secondary leveling, it makes up for the defect of poor initial coating state. However, a series of quality problems such as increased costs, excessive residual solvents, composite transfer of aluminized films, and incomplete drying and curing have been brought along, and excessive coating sometimes reduced the bonding strength.
Differential coating and sizing can improve these phenomena.
1.Differential coating and gluing method (gum coating or kiss coating method)
On the coating machine, we use a large number of differential coating methods (also known as anastomotic coating or kiss coating). The so-called differential coating method sizing is to form a reverse or forward speed difference between the running film and the surface of the rotating anilox roll, and adjust the coating amount by adjusting this speed difference. At the same time, the line contact in the traditional blade coating and gluing method was changed to a bonding with a certain contact area, that is, the kiss coating method. Of course, in the differential coating process, for high-precision coating, such as automotive glass film, film, metal film and other high-precision coating, there are 3-roller, 5-roller, or even 7-roller differential coating mechanisms. But for the requirements of our composite film products, the single-roller differential coating shown in the figure can fully meet the requirements, and the coating state has been greatly improved.
In this way, the uneven spot-shaped coating formed on the film by the conventional doctor blade sizing becomes a relatively smooth surface coating.
Because the coating state of the adhesive is changed from spot coating to planar coating, the bonding area of the material is relatively enlarged, and the bonding strength is also increased. Because we all know that the most effective way to increase the bonding strength is to increase the bonding area. In this way, compared with the traditional squeegee sizing, under the same sizing amount, the bonding strength will be relatively enhanced, or when the bonding strength is met, the sizing amount can be reduced, thereby reducing the compounding cost and Reduce the chance of problems with composite products.
The differential coating and gluing method can also use a working solution with a higher concentration than the blade coating and gluing method, which can further reduce the compounding cost.
Due to the change of the coating state, the pressure of the composite pressing roller can also be appropriately reduced, so that the hot pressing is changed to the laminating direction, which can reduce the deformation of the film and make the composite product more flat. Because under the action of tension, the high temperature and high pressure contact point of the composite heat roller is the main deformation point of the film.
Application of differential coating and gluing method on dry composite equipment
The structure of the differential coating machine and the dry laminating machine we are using is only one unwinding station. Some multifunctional coating machines are themselves compound machines with compound stations. At present, there are already large-scale color printing plants using this type of differential coating and gluing dry-drying machine. The author has also done corresponding experiments on the coating machine, and the effect is indeed beyond imagination, especially the composite of transparent film and aluminum plating.
The emerging solvent-free compounding is actually a sizing method for differential coating. Solvent-free compounding can achieve better bonding strength with a smaller sizing amount than dry compounding. My personal understanding is that the coating state of the adhesive is changed to make the coating of the adhesive more Even and flat, enlarge the bonding area. Therefore, a small amount of sizing is used to achieve a good bonding effect.
Conversely, if the coating state of the solvent-free adhesive is uneven, such a low sizing amount is estimated to be insufficient for the bonding strength. And if the coating state of the solvent-based adhesive reaches the coating level of the solvent-free composite equipment, the solvent-based adhesive can also use a much smaller amount of glue than the current one to produce a good bonding effect. Therefore, it is not that the adhesive strength of the solvent-free adhesive is stronger than that of the solvent-based adhesive, but that the difference is caused by the difference in the state of the glue applied by the glue application method.
There are also solvent-free composite aluminized films, which occasionally have poor appearance, but generally do not have aluminum transfer. It is also because its gluing amount is only a few grams, and if the existing dry laminating machine, the gluing amount of the aluminized film composite is also reduced to such a small amount (not considering the appearance), I want to aluminize The layers are also not transferred. In order to achieve a good appearance, we have to increase the glue amount to nearly 3g / ㎡ to solve the problem, which will increase the probability of aluminum coating transfer. At the same time, the transparency of the transparent bag or the transparent part is not high, and the glue lines and spots are directly related to the glued state.
Differential glue can also reduce compounding costs by at least 30%. In addition to greatly reducing the sizing amount, differential coating can also use a working solution with a higher concentration than the existing sizing method (40% ~ 45%), which can save a part in the solvent. Because the sizing amount is significantly reduced, in addition to reducing the solvent residue, you can also increase the vehicle speed appropriately, improve production efficiency, and reduce the occurrence of problem products.
And if the differential coating and gluing method is combined with the newly emerging two-component waterborne polyurethane adhesive, compared with the current compound cost, it is estimated that the cost per ton of adhesive can be reduced by 6000 ~ 8000 yuan . Because the performance of the two-component water-based polyurethane adhesive can completely replace the existing solvent-based adhesives (water-cooked).
Third, the conclusion
According to the information obtained so far, the application of the differential glue method can greatly improve the quality of composite products and reduce the cost of composite products.