The abnormality of the solventless composite process in flexible packaging is usually caused by objective factors such as paper, film, ink, adhesive, machine equipment, and subjective factors such as temperature, pressure, speed, amount of glue, and customer use. According to the actual application of the adhesive in the composite process, the causes and treatment methods of several common anomalies are summarized. I hope to bring some technical references to the manufacturers that use solvent-free composite processes.
Aluminum Plating Transfer Phenomenon:
The aluminized film not only has the characteristics of a plastic film, but also replaces the aluminum foil to some extent, thereby improving the grade of the product and having a relatively low cost. However, in the production process, the problem of transfer of the aluminized layer often occurs, which leads to a decrease in the peeling strength of the composite film, which degrades the performance of the product, and may even affect the quality of the package contents.
The root cause of the aluminum plating transfer is that the bonding force between the aluminum plating layer and the substrate is less than the bonding force between the aluminum plating layer and the glue layer, resulting in a decrease in the overall peeling strength of the composite film, so that the aluminum plating layer is largely separated from the substrate to the glue layer. The phenomenon of migration.
At present, most of the aluminized films used are VMCPP and VMPET, and the corresponding composite membrane structures include OPP/VMCPP, PET/VMCPP, and PET/VMPET. In practical applications, the most prone to problems is PET composite VMPET, because it is often used in the middle layer composite. This is because, as an aluminized substrate, CPP and PET have great differences in tensile properties. PET has a large rigidity and can be compounded with a material that is also extremely rigid, in the process of curing the adhesive, due to The presence of cohesive force can easily cause damage to the adhesion of the aluminized layer, thereby causing migration of the aluminized layer.
Main Reasons And Treatment Methods:
(1) The amount of glue applied is too large. The amount of sizing should be appropriate, and the amount of sizing is too small, which will undoubtedly result in a small composite fastness and easy peeling; however, the amount of sizing is too large to cause volatility and dryness. Secondly, the amount of applied glue is large, the curing time is long, and the penetration effect on the aluminum plating layer is strong. Therefore, according to the substrate and use, after a small test to determine the reasonable process parameters, choose a reasonable amount of glue.
(2) Poor ripening conditions, mainly due to excessive curing temperature. Controlling the curing time and appropriately reducing the curing temperature can reduce the transfer of aluminum plating.
(3) The proportion of glue mixing is not correct. Reducing the ratio of curing agent can improve the transfer of aluminum plating within a certain range. The specific method is to reduce the amount of curing agent when the working glue is mixed, so that the crosslinking reaction degree of the main agent and the curing agent is reduced, thereby reducing the film. The brittleness allows it to maintain good flexibility and stretchability to control the transfer of the aluminized layer.
(4) The adhesive selection is not correct. Use a suitable or special adhesive. When using a composite aluminized film, do not use an adhesive with too low viscosity because the low-viscosity binder has a small molecular weight and weak inter-molecular force. The strong molecular activity easily penetrates into the aluminum plating to affect the adhesion of the aluminum plating. ,
(5) The quality of the substrate itself is poor. Change the adapted substrate.
(6) If the operating tension is too large, the aluminum alloy film will be pulled to cause elastic change, resulting in transfer. The tension is controlled, and the tension must be controlled when the aluminum is unwound. The reason is that the aluminized film stretches under tension and produces elastic deformation. The aluminized layer is correspondingly easy to loosen and the adhesion is relatively reduced.
(7) Excessive solvent excessive destruction of aluminum plating, because the aluminum plating layer of the aluminized film is relatively thin, it is inevitable that there will be some pinholes, and the residual solvent penetrates into the aluminum plating layer to destroy the aluminum layer to cause aluminum plating transfer.
