Yellowish or grey in color or with yellow streaks:

  PET film, especially after being rolled into a reel, is yellow or gray in color. It can be seen with the naked eye. If there are yellow bars, the film must be unfolded or observed under light. Or spread it on a white backing for better identification.

  Reason analysis: gel point, yellow point, black point" is the same reason, yellowing is due to poor thermal oxidative stability of the resin, or more air entering the extruder. When the resin is thermally oxidized to generate a large amount of acetaldehyde , because acetaldehyde reduces antimony trioxide to antimony, causing the film (resin) to turn gray. The appearance of yellow bars is mostly after replacing the filter or after replacing the resin. The reason is that there may be air entering during the replacement. People, or some resins stay in the machine for too long, causing some resins to turn yellow, and these yellowed resins cannot be fully mixed with normal melting and plasticizing after they are formed, so yellow strips appear.

  The adhesive strength of printing, compounding and aluminizing is not enough:

  For printing, compounding, and vacuum aluminizing box bonding strength, self-adhesive tapes are usually used for testing. There are three kinds of conditions: full peeling, partial peeling and no peeling. The first two are insufficient drilling strength.

  Reason analysis: The bonding strength of PET film, ink and mink mixture is subject to the surface tension of PET film. The surface tension of the untreated PET film is 42~48N/S, which cannot meet the adhesive strength requirements with the ink adhesive. Therefore, some measures such as corona treatment should be taken to improve the surface tension in the production, so that it reaches more than 55N/cm.