Plasma is a gaseous substance that is completely or partially ionized, containing atoms, molecules, and ions in metastable and excited states, with roughly equal amounts of electrons, positive ions, and negative ions, meaning that its total positive and negative charges are the same. Therefore, it is called plasma, and after the three states of solid, liquid, and gas, it is called the fourth state of matter.

Principles of Plasma Processing

During plasma treatment, a special ionized gas (composed of ions, electrons, ion clusters, and central particles) bombards the surface of the material. The high-energy plasma (0-20eV) provides sufficient energy to the polymer chains (0-10eV) to break the chemical bonds of the polymer surface molecular chains, resulting in a series of physical and chemical changes.

Vacuum plasma treatment

The principle of low-temperature plasma treatment mainly includes three aspects

Firstly, the plasma surface cleaning effect. Due to the fact that plasma is generated by gas glow discharge in a vacuum chamber, it contains many "active" components, including high-energy electrons in high-speed motion, atoms and molecules in ionized states caused by ionization, neutral atoms, molecules, atomic clusters in activated states, and unreacted atoms and molecules. These "active" components can remove static electricity, dust, and oil impurities from the surface of the material, thoroughly cleaning the surface and greatly improving the surface performance of the material;

Secondly, plasma surface activation. Generally speaking, the energy of the "active" components in plasma is relatively high, with the electron energy in high-speed motion ranging from a few to tens, which is greater than the molecular bonding energy in polymer materials such as resins (between a few to tens). Therefore, it can destroy the chain groups in polymer molecules and form some free radicals. Plasma particles from different gas sources will undergo some chemical changes with the material surface, corresponding to the introduction of different polar groups. For example, oxygen plasma treatment introduces oxygen-containing groups, nitrogen or ammonia plasma introduces nitrogen-containing groups, etc., thereby increasing the surface activity of the material;

Thirdly, the plasma surface etching effect. The high-energy "active" components in the plasma strongly bombard the surface of the material and undergo relatively complex physical changes, producing strong etching effects, removing some unstable bonding layers on the surface, increasing the surface roughness and roughness, which is conducive to improving the overall stability of the composite material surface.

Principle of corona treatment

The principle of corona treatment is to apply high-frequency and high-voltage electricity to the electrode, creating a strong electric field on both sides of the electrode that ionizes the nearby air. The various plasmas generated after ionization are accelerated and impact the materials inside the treatment device under the action of the electric field, increasing the surface roughness of the materials. Discharge also generates a large amount of ozone, which is a strong oxidant that can oxidize the materials, producing a large number of polar groups (usually carboxyl and hydroxyl groups) and increasing the surface energy of the materials.

Corona treatment

The difference and connection between plasma treatment and corona treatment

In most cases, plasmas are divided into high-temperature plasmas and low-temperature plasmas based on temperature. Low temperature plasma is mainly generated by accelerating the impact of electrons, ions, or high-energy neutral particles through methods such as electric field, light, high-energy radiation, high-energy radiation, or high temperature. Low temperature plasma used for material surface modification mainly includes arc discharge, corona discharge, glow discharge, dielectric barrier discharge, atmospheric glow discharge, and other discharge methods depending on the discharge mode. Each discharge method has its own discharge characteristics and applicable conditions.

Simply put, corona discharge belongs to low-temperature plasma discharge. Corona discharge is a weak and unstable discharge that occurs when the electric field around the electrode is extremely uneven and the pressure is high. By changing the electrode structure, stable discharge under atmospheric pressure can be achieved, but the ionization degree of the obtained plasma is small, the power is low and unstable, and it is easy to convert into arc discharge.

Below are two aspects to understand the differences and connections between plasma treatment and corona treatment

Shape of processed material

The common corona treatment equipment is to apply high-frequency voltage between ceramic electrodes and metal rollers, and ionize the air in the middle gap area to generate plasma. Due to the existence of discharge gaps, corona treatment has certain limitations on the thickness of the treated material, generally around 0-5mm. Therefore, corona treatment is commonly used to treat thin film materials, thin plates, fabrics, etc.

Plasma processing equipment can be made into different types of devices according to different discharge structures, and there are almost no restrictions on the properties of the materials being processed. Whether it is thin films, sheets, or shaped parts, there are almost suitable plasma processing equipment that can meet them.

Treatment effect

Generally speaking, the gas ionized by corona treatment is mainly air, and the plasma discharge formed by corona discharge is weak and uneven, resulting in low efficiency in the generation of plasma and active particles; So corona discharge is only suitable for applications that do not require high electron energy and electron density, and for products that do not require high adhesive strength, such as fabrics, plastic films, plastics, etc. The production cost is not high, but the effect is very good.

Plasma treatment can introduce almost all types of gases in terms of process gas selection, and the ionization degree of plasma equipment is generally higher than that of corona equipment, which means that the plasma density is higher, and the plasma treatment effect is relatively better, and the uniformity of plasma treatment is also better than that of corona treatment.

The above is a brief introduction to the differences and connections between corona treatment and plasma treatment. Overall, the principles of plasma treatment and corona treatment for modifying materials are the same. They both achieve the goal of changing material properties by generating low-temperature plasma and physical and chemical reactions on the material surface. The difference between corona treatment and plasma treatment equipment is that the principle of generating plasma is different, resulting in slight differences in the applicable materials and treatment effects.