Composite membrane is a kind of separation membrane, which is composed of microporous membrane or ultrafiltration membrane as supporting layer and covered with dense homogeneous membrane with thickness of 0.1-0.25 μ m as barrier layer. Sometimes white or gray spots appear on the surface of the composite film, which is easy to appear in the production process of full-length ink printing and composite with aluminum coating. The main reasons are as follows.
(1) The surface tension of the ink is low, resulting in the poor coating effect of the adhesive and uneven glue, so the bonding force and the tightness between the ink layer and the aluminum coating will be different, so the reflective effect of the aluminum coating surface is also strong or weak, forming white or gray spots visually.
(2) Ink covering power is not strong or poor leveling, resulting in uneven covering (especially white ink and light yellow ink). In the place where the covering effect is not good, the color of the aluminum coating will penetrate through the ink.
(3) If the adhesive concentration is too high and the viscosity is too high, it is easy to reverse the ink into the glue, which changes the color of the printing layer. At the same time, if the viscosity of the adhesive is too large, the fluidity will be poor, which is easy to cause uneven gluing, affect the reflective performance of the aluminum coating surface and produce spots.
(4) Ink and adhesive do not match, so that the permeability of the adhesive on the ink is not good, there is rejection phenomenon, will also produce spots.
(5) The drying of the composite film is not complete and the solvent volatilization is not enough, resulting in too much residual solvent in the adhesive, part of the ink layer is dissolved and polished, thus forming spots, and when serious, many tiny bubbles will be formed after aging.
(6) The quality of the aluminized film is poor, and there are many light transmission points. After compounding, due to the different reflectivity of the aluminum coating, spots are formed.
(7) The temperature of the drying channel (especially the first drying channel) is too high, which leads to the surface glue drying too fast and the surface conjunctiva; when the internal solvent gasifies in the second and third drying channels, it will break through the film on the surface, squeeze up the adhesive and expose the ink, resulting in uneven thickness of the adhesive layer, resulting in spots.
The above is the common problem of compound film spots, if you have any questions and good suggestions, welcome to contact the manufacturer of bate packaging which focuses on flexible packaging. www.dgbpk.com