What surface treatment does BOPP synthetic paper need before printing?

BOPP synthetic paper usually needs surface treatment before printing to improve its surface tension, enhance the adhesion of the ink and printing effect. The common surface treatment methods include corona treatment and flame treatment, but corona treatment is widely used because of its simplicity and good treatment effect.

Corona treatment

Corona treatment is by applying high frequency and high voltage electricity to the surface of the film to make its corona discharge and produce small and dense sparks. These sparks ionize the air and form a low-temperature plasma, which accelerates the impact on the surface of the film under the action of a strong electric field, causing the chemical bond of the plastic surface molecules to break, generating free radicals, and then oxidizing and cross-linking with oxygen in the air, resulting in polar groups on the surface of the film and increasing the surface roughness. At the same time, the corona treatment process will also produce ozone, ozone as a strong oxidizing agent can further oxidize the plastic surface molecules, improve the surface tension.

The specific process of corona treatment includes the following steps:

1.Equipment preparation: Corona treatment system is composed of corona roller and press roller, electrode plate, exhaust system, electrical control part, etc. Corona rolls are usually made of high temperature and ozone resistant silicone rubber or special polyurethane elastomers.

2.Applying voltage: high frequency and high voltage is applied between the corona roller and the electrode plate to produce corona discharge.

3.Processing film: BOPP synthetic paper through the corona roll and the gap between the electrode plate, by the impact of low temperature plasma and ozone oxidation, the surface performance is improved.

4.Exhaust cooling: the ozone and heat generated during the treatment process are discharged through the exhaust system, and the corona roller is cooled by the water cooling cooling system.

Factors affecting corona treatment effect

1.Electrode type: Compared with single electrode, double electrode can produce higher treatment value at the same energy consumption, and can reduce the attenuation of surface tension and electrostatic induction on the film surface during storage.

2.Film temperature: As the film temperature increases, the surface treatment value will increase accordingly. Therefore, the surface treatment effect of the film can be improved by adjusting the set temperature of the preheating roll or the temperature of the film at the exit of the transverse pull.

3.Line speed: Different line speeds will affect the time the film stays between the plates, thus affecting the corona treatment effect. In general, the electrode voltage needs to increase as the production line speed increases.

4.Electrode exhaust air volume: The opening degree of the electrode exhaust valve will affect the size of the film surface treatment value. The larger the exhaust air volume, the smaller the surface treatment value; Conversely, the smaller the exhaust air volume, the greater the surface treatment value. However, it should be noted that too little exhaust air will lead to too high ozone concentration, which will adversely affect the environment and equipment.

5.Surface material: The surface tension of polypropylene homopolymer and copolymer will be significantly different after the same corona treatment. In addition, the surface coating of smoothing agent or antistatic agent will also affect the corona treatment effect.

6.Plate gap: The size of the plate gap has a certain effect on the corona treatment effect. If conditions permit, minimize the distance between the corona roller and the electrode plate to improve the processing degree.

To sum up, corona treatment of BOPP synthetic paper before printing is an effective means to improve its surface properties and improve the printing effect. Through reasonable adjustment of processing parameters and equipment conditions, the ideal surface treatment effect can be obtained.