Three Major Challenges in the Use of Solvent-Free Adhesives and Their Solutions
- Solvent-free adhesives, developed in the 1970s, can reduce energy consumption, improve production efficiency, enhance product quality and lower overall production costs in film lamination.
- Because they contain no solvents, solvent-free adhesives support environmental protection and clean production and are attracting growing attention in flexible packaging.
- In solvent-free lamination with PE film as the inner layer and thickness below 45 µm, a curing temperature above 40°C tends to significantly increase the coefficient of friction of the final laminate; the solution is to reduce coating weight while lowering curing temperature without compromising lamination quality.
- In lamination of metallized materials, especially VMPET, metallized-layer transfer causes insufficient peel strength in the final laminate and is particularly pronounced in solvent-free lamination; adjusting the adhesive formulation can minimize the probability of transfer.
Solvent-free adhesives are a technology developed in the 1970s. Using solvent-free adhesives to laminate films can reduce energy consumption, improve production efficiency, enhance product quality and lower overall production costs. Because they contain no solvents, they are conducive to environmental protection and clean production, and are therefore attracting increasing attention from professionals in the flexible packaging industry. However, there are also many challenges to be solved in their use.
Challenge One: Significant Impact on the Slip Properties of PE Films
In the solvent-free lamination process, for laminate structures with a PE film as the inner layer (especially when the PE film thickness is <45 µm), the coefficient of friction tends to increase significantly when the curing temperature exceeds 40°C. This is mainly because: during the blown film extrusion of PE film, under the condition of the same amount of slip agent added, the thinner the PE film, the less slip agent per unit area; in the solvent-free lamination stage, the higher the curing temperature, the more vigorous the molecular movement of the slip agent, which migrates into the solvent-free adhesive layer and reacts with it, resulting in greater consumption of the slip agent and causing the coefficient of friction of the final laminated product to increase.
Solution: On the premise of ensuring lamination quality, reduce the coating weight and at the same time lower the curing temperature.
Challenge Two: Insufficient Peel Strength of Metallized Materials
In the lamination of metallized materials (especially VMPET), the most common problem is the transfer of the metallized layer, which results in insufficient peel strength of the final laminate, and this is particularly pronounced in the solvent-free lamination process. There are many reasons for the transfer of the metallized layer, including the metallized material, the lamination process, and the inherent characteristics of the solvent-free adhesive itself. Considering solely from the perspective of the solvent-free adhesive.
Solution: By adjusting the adhesive formulation, minimize the probability of metallized layer transfer.
Challenge Three: Dissolution with Certain Inks
In the solvent-free lamination process, the phenomenon of the adhesive dissolving the ink occasionally occurs, especially with certain inks made from dyes.
Solution: This can be alleviated by controlling the solvent-free lamination process, but at the same time, solvent-free adhesive manufacturers need to communicate with ink suppliers in order to provide effective research solutions.
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