If it is a hard spot protective film, if it is a bubble, you can see it carefully if you have it before you compound it. This is caused by the production process and other reasons when producing the PET protective film, and cannot be further processed. If you have a dedicated test tool, the thickness of the bubble point is not the same as elsewhere.
There are many reasons for the hard spots (pre-transportation, during production, subsequent processing, etc.) If the previous film is all right, then you must pay attention to the smoothness of the roller during the subsequent processing. You can touch the roller with your hand Smoothness. If the hardness of the rubber pressure roller is too large, the air pressure of the pressure roller can be adjusted appropriately. There is also the cause of impurities brought into the roller, which is often ignored.https://www.pe-protectionfilm.com/