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Soft packaging manufacturers sometimes encounter this phenomenon in the laminating process. When using ordinary polyurethane adhesives to compound polyethylene films, the peel strength can still meet the requirements when the complex film is released from the machine. However, the intensity is greatly reduced, or for a period of time, it is easy to open and break the bag. The laminating manufacturers often think that it is a problem of glue, and actually causes this phenomenon. In general, it is caused by precipitation of additives such as slip agents in the film.
We know that in the production process of films, most of them add additives such as heat stabilizers, antioxidants, anti-adhesive agents, and open-slip additives, so as to prevent adhesion and facilitate processing. Because additives are added, rather than grafted onto the PE molecules, the additive migrates out of the membrane's inner membrane surface as time passes and temperature changes. Careful observation will reveal that it is a thin layer of powdery or waxy material that can be wiped off by hand. The longer the time, the more the amount of migration, so that the bond strength is reduced.
The influence of the additives in the PE film on the composite strength of the adhesive is generally smoother, such as erucamide, oleic amide and the like. In general, the thicker the film, the more slip agent per area. Practice shows that when the polyethylene film thickness exceeds 60 μm, the phenomenon of additive precipitation will be greatly increased. This is because with the same specific surface area, as the thickness of the film increases, the amount of additives contained therein increases accordingly. After the additive content in the film exceeds a certain amount, the film properties will be affected. The content of slip agent in the film (ppm) × film thickness (μm) = 2200-26000, coupled with a reasonable production process, can make the composite product not only have a certain peel strength, but also can make the composite film have enough Slippery. When the slip agent content (ppm) × film thickness (μm) exceeds 26,000 or more, laminating with an ordinary polyurethane adhesive may cause a problem that the peel strength is greatly reduced due to the precipitation of the slip agent.
In the case of the same sizing amount, the slip agent content is high, and the film peel strength with a product of more than 26,000 is greatly reduced. Of course, the amount of sizing will be large, but it will increase the cost. However, if you use anti-adhesive glue, it may not have any effect. Because this glue contains ingredients that contain slip agents, the effect of slip agents can be avoided.
Polyethylene film as a heat-sealing material for flexible packaging, the amount of the slip agent in the raw material, is critical to the composite peel strength, opening, slip properties and heat seal strength, if you ignore this, will produce quality Loss caused by accident. Therefore, manufacturers of flexible packaging must pay attention to the use of polyethylene film.
One of them is to understand the content of lubricant in polyethylene film. Some manufacturers may take the initiative to provide it to you, and some manufacturers do not provide it as a technical secret. Therefore, at this time, it is necessary to be careful with the ordinary type polyurethane adhesive laminating film, first to do the next test or simply use the anti-adhesive agent to avoid the quality problem caused by the excessive content of the slip agent.
Secondly, the surface tension of the polyethylene film should be tested because if the film is precipitated with a slip agent, the surface tension cannot reach the laminating requirement. This requires a new electric discharge treatment. The precipitated wax will evaporate at the high temperature of the electric spark, so that it will not affect the composite strength.
The third option is to choose a suitable adhesive, because for films with high levels of slip agent, only these special glues can overcome the release of the slip agent and avoid quality problems caused by precipitation.
Fourth, we must understand the aging temperature setting. In general, aging should be performed at a low temperature in order to avoid exacerbation of the high temperature of the lubricant. The composite membrane of the next machine should be sent to the curing chamber as soon as possible, and the composite film should be heated at 40°C-50°C to melt and level the uncured adhesive, eliminating small bubbles and white spots. After 48 hours of continuous maturation Achieve satisfactory adhesion strength.
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