In the laminating process, flexible packaging manufacturers sometimes encounter such a phenomenon: when using a common type of polyurethane adhesive composite polyethylene film, when the finished film is just off the machine, the peeling strength can still meet the requirements, and after entering the drying room, the curing is completed. The intensity is greatly reduced, or it is easy to open and break the bag for a while. Laminating manufacturers often think that it is a problem of glue. In fact, the cause of this phenomenon is generally caused by the precipitation of additives such as slip agents in the film.
We know that in the production process, most of the additives such as heat stabilizers, antioxidants, anti-adhesive agents, and opening slip agents are added to prevent adhesion and easy processing. Since the additive is added instead of being grafted on the PE molecule, after the film is processed, the additive will migrate out from the surface of the inner membrane of the film as time passes and the temperature changes. A closer look reveals a thin layer of powder or waxy substance that can be wiped off by hand. The longer the time, the more the migration, which reduces the bond strength.
The effect of the auxiliary agent in the PE film on the composite strength of the adhesive is generally a slip agent such as erucamide or oleic acid amide. In general, the thicker the film, the more slip agent per unit area. Practice has shown that when the thickness of the polyethylene film exceeds 60 μm, the phenomenon of precipitation of the additive is greatly increased. This is because, under the same specific surface area, as the thickness of the film increases, the amount of the additive contained therein increases accordingly. When the content of the additive in the film exceeds a certain amount, the properties of the lamination film are affected. The content of the slip agent (ppm) in the film × film thickness (μm) = 2200-26000, coupled with a reasonable production process, can make the composite product have a certain peel strength, and can make the composite film have enough Slippery. When the slip agent content (ppm) × film thickness (μm) exceeds 26,000, the problem of a large drop in peel strength due to the precipitation of the slip agent may occur due to the lamination of the ordinary polyurethane adhesive.
In the case of the same amount of sizing, the content of the slip agent is high, and the peel strength of the film exceeding the product of 26,000 is drastically lowered. Of course, the amount of sizing will be large, but it will increase the cost. If you use additive-resistant glue, it may not have any effect. Because this gel contains ingredients that contain the slip agent, the effect of the slip agent can be avoided.
Polyethylene film is used as a heat-sealing material for flexible packaging. The amount of slip agent in the raw material is critical to the composite peel strength, openness, slip and heat seal strength. If this is ignored, quality will be produced. The accident caused the loss. Therefore, flexible packaging manufacturers should pay attention to the selection of polyethylene film.
One must understand the content of slip agent in polyethylene film, some manufacturers may provide it to you, and some manufacturers do not provide it as a technical secret. Therefore, at this time, it is necessary to use a common type of polyurethane adhesive film to be careful, first do a small test or simply use the auxiliary rubber to avoid the quality problem caused by the excessive content of the slip agent.
The second is to detect the surface tension of the polyethylene film, because if the film is precipitated by the slip agent, the surface tension will not meet the lamination requirements, which requires re-sparking. The precipitated wax will volatilize at the high temperature of the spark, so that the composite strength will not be affected.
The third is to choose a suitable adhesive, because for the film with high content of slip agent, only these special glue can overcome the precipitation of the slip agent and avoid the quality problem caused by precipitation.
The fourth is to understand the setting of the curing temperature. Generally, the aging should be carried out under low temperature conditions to avoid the precipitation of high temperature of the slip agent. The composite membrane of the lower machine should be sent to the curing chamber as soon as possible, and the composite film should be heated at 40 ° C to 50 ° C to melt and level the uncured adhesive, eliminate the small bubbles and white spots, and continue to mature for 48 hours. Achieve satisfactory bond strength.
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