Paint protection film has a coating and a glue layer. These two layers of structure are mostly obtained through the coating process. Some factories use TPU base film to be directly coated on both sides, and some use coating to directly coat the TPU film and glue. The PET film is then transferred to the TPU film.

If PET glue is applied and then transferred, then due to the low surface energy of the PET film, the PET film usually needs to be corona treated during the coating process to improve the surface adhesion of the PET film.

1. Corona principle

High-frequency and high-voltage electricity is applied to the treatment device to cause corona discharge, producing small and dense purple-blue sparks. Various plasmas generated after air ionization are accelerated under the action of strong electric field, thereby impacting the plastic products in the processing device.

The energy of these plasma particles is generally several to tens of electron volts, which is close to the chemical bond energy of plastic molecules. Therefore, it can induce the breakage of chemical bonds of plastic surface molecules and cause degradation, increasing surface roughness.

During corona discharge, a large amount of ozone is also produced. Ozone is a strong oxidant that oxidizes molecules on the surface of plastics to produce carbonyl compounds, peroxide compounds, etc. In addition, corona treatment can also remove oil, water vapor and dirt. After the above-mentioned physical and chemical modifications, the wettability and adhesion of the plastic surface can be significantly improved.

2. Three different corona methods

1. On the film production line

It is commonly known as hot film treatment, which is the most common form of treatment. Since the polymer molecules are processed before they have completed crystallization, the treatment effect is strong, but it is generally only suitable for film treatment that will be reprocessed immediately (such as printing, coating or lamination). The processing device is arranged behind the film cooling and shaping section and before the winding device.

2. Performed on the film reprocessing line

Commonly known as cold film treatment, the quality of this form of treatment is also related to the experience of the film. If the film is stored for a long time after production, a large amount of precipitated additives will adhere to the surface of the film, and the processing quality will deteriorate. When choosing this method, attention should also be paid to whether electric sparks may cause ignition of the solvent used. The processing device is installed before the printing (or coating, laminating) device.

3. A combination of the above two forms

That is, it is processed first on the film production line, and then processed a second time on the film reprocessing line. It is suitable for films with poor quality during the first treatment, or films that have been stored for a long time after the first treatment and the treatment effect has faded a lot.

3. Advantages of thin film corona:

1. A wide range of processing materials can be used for polyethylene, polypropylene, polyvinyl chloride, polyamide, polyester, polycarbonate, fluoroplastics, and various corresponding copolymers;

2. The processing time is short and the speed is fast, and can be processed on the production line;

3. Simple operation and easy control;

4. Corona treatment only involves a very shallow area of ​​the plastic surface, generally only on the order of nanometers, and basically does not affect the mechanical properties of the product;

5. No waste liquid discharge, basically no environmental pollution.