The double-sided tape used for car stickers is generally a composite material such as reflective film, so the arching of such materials is a common problem, which is actually a tunnel phenomenon. Generally, it means that the laminated product has horizontal stripes, especially at both ends of the material. This kind of streak is one kind of cladding substrate flat, and the other kind of protrusion forms a "tunnel", and the cladding layer is separated in the convex part, and there is no adhesion.

This phenomenon occurs in two-layer lamination, such as PP adhesive, car body sticker, cold lamination film, etc., and three layers such as spray-painted reflective film and double-sided tape, one more lamination, more opportunities to appear.

The reasons for the tunnel phenomenon (arching) generally include the following:

1. The unwinding tension of the substrate

The dry lamination process is to coat one of two rolls of different substrates with adhesive, then heat and dry them and roll them together to laminate them together. Therefore, the tension of the two different substrates affects the finished product after lamination. tension is crucial. Generally speaking, the tension of the two substrates during lamination does not match, one is too large and the other is too small. Since each film roll is taut during lamination, it seems that nothing can be seen. After lamination, The substrate with too much tension is bound to shrink, and its shrinkage is obviously larger than that of the original substrate with low tension, which causes relative displacement and wrinkles.

Take an example: BOPP is laminated with aluminum foil. After BOPP is glued, it is heated in the drying tunnel. If the unwinding tension is large, it will be pulled tighter, and then heated, it will be stretched and deformed. However, the tension of aluminum foil cannot be as large as that of BOPP, and the elongation is small. Therefore, once cooled after lamination, BOPP shrinks, causing wrinkles, aluminum foil bulges, and "tunnels" appear in the transverse direction. In fact, no matter whether it is vacuum aluminized film and paper, or PVC and paper, PE and CPP film, as long as the unwinding tension of the two substrates is not well matched, this will happen.

2. The problem of water loss and shrinkage of the substrate

If the base material is release paper, it will lose water and shrink after drying in the drying tunnel. According to experience, it will shrink by 8-15mm/1285mm. Paper with high water content will shrink more. If it returns to a humid environment after lamination, it will cause dimensional changes and cause the tunnel to fold.

3. The adhesive force of the adhesive

1. Incorrect use of adhesive. Generally, the solid content of the commonly used adhesive for lamination is 50%. In order to adapt to the high-speed dry lamination process, the practice of high solid content and low viscosity is now mostly used. However, low-viscosity adhesives tend to have smaller molecular weights and less cohesion. Ideal adhesion can only be achieved when they are cross-linked and solidified into a macromolecular structure. However, the initial adhesion when just laminating is very small and the adhesion is insufficient. Therefore, when one substrate shrinks, there will be relative displacement between the upper and lower two different substrates, that is, wrinkles and "tunnels" will appear.

2. The uneven coating of the car film will also cause the car sticker to bulge.

Fourth, the winding tension problem of lamination and slitting

The tension of lamination, slitting and winding is too small, the roll is not tight, and the lamination is loose, which provides the possibility of shrinkage for the substrate to be shrunk. This phenomenon is more obvious at both ends of the laminated product, often the middle part is firm, but the exposed parts of the two ends are wrinkled due to uneven shrinkage.