White or gray spots sometimes appear on the surface of the composite film. This occurs easily in the production process of the job where the full-print ink is printed and compounded with the aluminized film. The main reasons are as follows.
(1) The surface tension of the ink is low, resulting in poor coating effect of the adhesive and uneven sizing, so that the adhesion force between the ink layer and the aluminum plating layer and the closeness between the layers may vary, resulting in plating. The reflective effect of the surface of the aluminum layer is also strong and weak, visually forming white or gray spots.
(2) The hiding power of the ink is not strong or the leveling property is poor, resulting in uneven covering (especially white ink and light yellow ink). In areas with poor coverage, the color of the aluminized layer penetrates through the ink.
(3) The adhesive concentration is too high, the viscosity is too large, and it is easy to reversely stick the ink to the glue liquid, so that the color of the printing layer changes. At the same time, if the viscosity of the adhesive is too large, the fluidity is not good, which can easily cause uneven sizing, affect the reflective performance of the surface of the aluminum plating layer, and cause spots.
(4) The ink and adhesive do not match, making the adhesive's penetrating performance to the ink not good.
(5) The composite film is not completely dried and the solvent is not fully evaporated, resulting in too much residual solvent in the adhesive, some of the ink layer is dissolved and glazing, thus forming spots, and many tiny bubbles are formed after the aging.
(6) The quality of the aluminized film itself is poor, and there are more light-transmitting spots. After the compounding, the reflectance of the aluminized layer is different, forming spots.
(7) The temperature of the drying tunnel (especially the first drying tunnel) is too high, which causes the surface glue to dry too fast and the surface is conjunctiva; when the internal solvent vaporizes in the second and third drying tunnels, it breaks the surface of the glue. The film, squeezed out of the adhesive, exposes the ink, causing uneven thickness of the adhesive layer, resulting in spots.