Corona treatment of plastic film

(1) Corona treatment is a technique that utilizes the electric field generated by high-frequency and high voltage in specific shaped electrode gaps to discharge thin films or other materials, forming certain polar groups on the surface of the treated material. Improve the surface tension of the processed material, thereby enhancing the smoothness of printing or composite.

(2) At present, there are three main types of methods for corona treatment in China: ① inductive capacitive type; ② Crystal type; ③ Thyristor type.

Inductive capacitance type has a large volume, high noise, and poor performance, which has tended to be phased out.

The transistor type has small size, low noise, simple production, and convenient repair. The disadvantage is low power, which is the most widely used type in China.

Thyristor type, with high power, fast processing speed, and good performance, can meet the requirements of large and medium-sized equipment, high and medium speed equipment. The corona device attached to the imported BOPP film production equipment also requires this type of device. However, the equipment is expensive and uneconomical. However, for wider and thicker processing areas or those that require fast processing speed and high surface tension, this type of device is still preferred.

The electrode forms for corona treatment mainly include knife shaped, strip shaped, and needle shaped. In addition to the corona treatment device itself, electrode gap, environmental conditions, temperature, and time also have a significant impact on the treatment effect.

The discharge frequency is closely related to the electrode gap. When the frequency is determined, excessive or small electrode gaps can cause energy loss and affect the treatment effect. If the frequency is 20kHz, the gap is about 8mm. If the frequency decreases, the gap should be appropriately reduced.

The environmental gas conditions during corona treatment also have a significant impact on the treatment effect. When treated in air, oxygen, or carbon dioxide gas, the effect is basically the same. The initial tension increases quickly, about 10 seconds, and the tension can reach over 40mN/m. But as time increases, the tension basically does not increase. When treated in nitrogen, helium, argon, and chlorine, the situation is different. In practical applications, it is generally treated in air. Only when there are special requirements, consider handling in a certain gas.

The temperature and time of corona treatment are generally below 75 ℃. The higher the temperature, the more significant the change in surface tension. As for time, within a certain range, the longer the time, the better the effect. In practical work, if the processing effect cannot meet the requirements, the processing speed can be appropriately reduced and the processing time can be extended.

After corona treatment of thin films, the shelf life should not be too long. Generally, the surface tension of the most treated film shows a certain downward trend within 7-10 days. Afterwards, it entered a relatively stable stage, but after 1-3 months, the tension decreased again. The film should be stored in a dry and clean place.