What is corona discharge?
Date: Aug 23 2024 From: Star Color
1、 Definition of corona dischargeCorona refers to the phenomenon of partial discharge occurring on the surface of a charged body in a gas or liquid medium. This phenomenon often occurs around high-voltage wires and near the tips of charged bodies, producing substances such as ozone and nitrogen oxides during the process.
In the printing industry, corona treatment is an important surface treatment technology, especially on non absorbent substrates, which often requires corona treatment to increase surface tension and improve the adhesion of printing ink. It has a significant effect on improving printing quality and effectiveness.
2、 Development of corona dischargeThe phenomenon of corona discharge was first observed in the late 19th century, when scientists noticed that under high voltage, the air near sharp objects would emit a flickering light, which is called corona discharge. In 1901, French scientist H W. Geitel first proposed the concept of using corona discharge to alter the surface characteristics of objects. Subsequently, some scientists and engineers began researching and developing corona treatment technology.
At the beginning of the 20th century, corona treatment technology began to be applied in the printing industry to improve the wetting and adhesion of ink on paper surfaces. The initial corona discharge equipment was relatively simple, used low voltage, and had limited treatment effect. With the continuous deepening of scientific research and engineering practice, corona discharge equipment has been improved and optimized, and the treatment effect has been significantly improved.
In the second half of the 20th century, with the widespread application of new materials such as plastics and coatings, corona discharge technology has also been further developed. The design of corona equipment is more precise, and the control of corona voltage is more accurate, which can adapt to the processing needs of different materials. At the same time, the application areas of corona treatment technology have also expanded to packaging, labeling, printed circuit boards, optical devices, and other fields.
What is corona discharge?
3、 The principle of corona treatmentThe principle of corona treatment is to use high-frequency high voltage to discharge on the treated plastic surface, generating low-temperature plasma. These plasmas enter the surface of the processed material through electric shock and permeation, disrupting its molecular structure and subsequently oxidizing and polarizing the surface molecules that have been treated.
The strong oxidants such as ozone generated during the corona process can also oxidize the surface molecules of the material, producing polar functional groups, thereby increasing the surface roughness and wettability of the material, and improving its adhesion to printing materials such as ink and glue.
Plastic sheet corona discharge
4、 The process of corona dischargeIn corona treatment, a strong electric field is formed by applying a high voltage (usually several thousand volts) to the corona electrode. The electric field causes nearby gas molecules to be affected by the electric field force, resulting in displacement of electrons and positive ions.
Electron release and ionization: When the electric field strength near the tip or acute angle of the corona electrode exceeds the ionization energy of molecules in the gas, electrons will be released from the tip or acute angle. These electrons have enough energy to leave the electrode surface and ionize surrounding gas molecules. This forms a plasma region that includes electrons, positive ions, and neutral molecules.
Space charge region: Due to the generation of electrons and positive ions, a space charge region is formed in the plasma region. Electrons have negative charges, while positive ions have positive charges. Their presence creates a local electric field in the plasma region.
Air ionization and corona discharge: When the electric field strength in the gas near the corona electrode exceeds the breakdown electric field strength of the gas molecules, the gas molecules will undergo ionization process, further releasing electrons and positive ions, forming more plasma. The formation of these plasma regions and space charge regions leads to the occurrence of corona discharge. The electrons and positive ions generated during corona discharge will move at high speed, collide with surrounding gas molecules, and produce various chemical and physical effects.
Generating surface effect: The electrons and positive ions released by corona discharge have an impact on the surface of the treated material. They can change the chemical state of the material surface, generate oxides, increase surface energy, and improve wettability and adhesion.
The process of corona discharge
5、 Application of corona treatmentIn the printing industry, corona treatment is widely used for surface treatment of various materials such as plastic films and glass. By corona treatment, the adhesion, wettability, hydrophilicity, and oleophilicity of these materials can be significantly improved, thereby enhancing printing quality and effectiveness.
For example, conducting corona treatment before printing plastic film can help ink adhere better to the surface of the film, reducing fading and delamination; Performing corona treatment before printing on metal plates can enhance the adhesion between the coating and the substrate, making the coating more uniform and firm.
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