Faults and Countermeasures in the Composite Process of Aluminum Foil and Aluminum Coating

In recent years, due to the poor oxygen permeability of PP, water permeability of PET, poor ink adhesion and color difference migration of PE, high tensile elongation, easy wrinkling, and difficulty in overprinting, most PVC is toxic. If PVC is used, high-frequency heat sealing is required, and the film often breaks. PT has poor tear resistance and may shrink, decrease strength, or become brittle at high temperatures. Packaging materials have the aforementioned different defects, and AL and aluminum plated film have become the most frequently used and fashionable substrates at present. However, during the processing and composite process of AL and aluminum plated thin films, slight carelessness may lead to quality issues. The most common composite products have quality problems such as "spots" and "white spots", which are more likely to occur than quality problems in plastic/plastic, aluminum/plastic, or aluminum/paper composite processing. This is a headache for many flexible packaging manufacturers. In response to this malfunction, the author was invited to conduct serious research on the quality issues that occurred in the aluminum coating composite processing of color printing and ink factories in Hangzhou and Wenzhou, Zhejiang, Wuxi and Jiangyin in Jiangsu, Zhengzhou and Xinxiang in Henan, and to systematically introduce the causes and solutions for reference by packaging and printing colleagues.

1、 Aluminum coated composite products produce "spots" phenomenon

After the aluminum coating is compounded, obvious white or gray spots are produced, which are most common in the process of full plate ink printing and lamination. There are three main reasons for these spots:

1. The quality of the aluminum coating itself is poor, and the coating is easy to peel off and the aluminum coating and rolling film are uneven, especially when the adhesive is applied, resulting in dense or scattered white spots of varying sizes after lamination. The adhesion strength of ink and adhesives on their surfaces varies, and the adhesion strength between the ink layer and the coating is low at the point of spots (spots caused by uneven dispersion of ink or adhesives), resulting in poor interlayer tightness; The plating layer without spots has significantly transferred and the interlayer tightness is good. The strength of reflection through the aluminum plating layer forms white spots or gray spots, and the depth of the spots is closely related to the ink coverage and glue application amount, especially the smoothness of the glue. Good covering power, light spots; Good adhesive leveling and uniform coating with few white spots; On the contrary, there are many spots and severe white spots.

2. The ink itself has poor tightness and poor covering power. After the printing film is coated with adhesive, the ink layer is infiltrated by ethyl acetate in the adhesive, and some of it is dissolved. After composite, the ink layer/adhesive layer is easily infiltrated and damaged by the solvent of the adhesive system, resulting in color differences, forming so-called spots.

3. The quality of the adhesive is poor. This is not about the adhesive itself, but rather the poor adhesion of this adhesive to the aluminum plating layer, especially for the uneven adhesive when it is combined with OPP printing film and BOPP printing film and aluminum plating film, the performance of this adhesive is more obvious. Mainly due to the high surface tension, poor coating performance, and uneven application of adhesive, this adhesive causes the phenomenon of "spots". At the same time, this type of adhesive generally has a high initial adhesion and poor solvent release. After ripening, due to the influence of residual solvents, its strength is actually not as good as the initial adhesion. After the printing film is compounded, the ink layer may be soaked by residual solvents and may also produce spots. When this type of adhesive is used at high speed on mesh rolls with 150 threads or more, it produces