Plasma surface treatment machine is a process equipment used for surface treatment pretreatment. It has functions such as increasing surface tension, fine cleaning, removing static electricity, and activating surfaces. It is widely used in glass, metal, cable, rubber, plastic, paste box, paste box, and rubber surface modification treatment.

Principle of action of plasma surface treatment machine

Plasma surface treatment machine can be understood as a device that generates plasma, and the principle of action of plasma surface treatment machine is the principle of action of plasma.

There are many types of particles in plasma, and the properties of each particle are also different. Research has shown that electrons are the main ones reacting on the surface of materials, followed by metastable particles. When plasma impacts the surface of a material, in addition to transferring its own energy to surface molecules, it also causes surface etching, causing molecules of gas or other substances adsorbed on the surface to leave the surface. Some particles, especially electrons and metastable particles, may also undergo self sputtering. Some particles, especially electrons and metastable particles, may penetrate the surface of the material to a depth of up to one. After the molecules inside the surface of the material are impacted, the electron layer is excited and undergoes electron transitions, while causing sputtering and radiation. Shallow electrons may also escape to the space above the surface of the material.

The energy of plasma particles is generally several to tens of electron volts, while the bond energies of common chemical bonds in polymer materials are shown in Table 1. From this, it can be seen that the energy of the vast majority of particles in the plasma is slightly higher than these chemical bond energies, indicating that the plasma has sufficient energy to cause various chemical bonds within the polymer to break or recombine, manifested in the degradation of macromolecules, reactions between material surfaces and foreign monomers under the action of plasma, and the presence of electrons, excited state molecular atoms, free radicals, photons and other particles, which makes the system have rich chemical activity.

The energy of plasma can act on the surface of materials through light radiation, neutral molecular flow, and ion flow. Neutral particles in a plasma system will transfer energy to the material by continuously bombarding the solid surface.

There are many different types of reactions during the plasma surface treatment process, which may generate free radicals on the surface, introduce functional groups, cause surface erosion, form cross-linked structural layers, and etching effects. It should be pointed out that these effects are generally not singular, often with certain effects being dominant and several effects coexisting. And it is precisely these processes that determine the effectiveness of plasma surface treatment.

The main forms of action of plasma surface treatment machines

1. The generation of surface free radicals

Plasma surface treatment can effectively generate a large amount of free radicals in the surface layer of polymer materials. Whether it is inert gas plasma or active gas plasma, as long as it comes into contact with polymer materials for a short time of tens of seconds to a few minutes, this effect is very obvious. Taking O2 and other ions as examples, the specific process is roughly shown in the following formula, in which there must be many active species.

O2→Hv+e+02++O2+O2*+Og+L

Hv is the ultraviolet light emitted by plasma radiation, and O2 * represents excited oxygen molecules. These active species in the plasma react with the surface of polymer materials to generate some free radicals. In addition, the ultraviolet radiation generated during plasma discharge can also produce free radicals, which is caused by the penetrating radiation of ultraviolet radiation that triggers the formation of free radicals.

2. Formation of surface functional groups and cross-linking layers

Free radicals can add specific functional groups to the surface of polymer materials activated by plasma treatment. For example, amino groups generated by the action of H2, N2, NH3, and plasma can be introduced into the surface of polymers.

By plasma surface treatment, specific functional groups are introduced onto the surface of polymer materials, resulting in a completely different surface state from the original properties.

The gases used in plasma treatment, whether they are non oxidizing gases such as helium and ammonia, or oxidizing gases such as oxygen, will form hydrophilic groups on the surface through contact with air due to the residual free radicals. The occurrence of free radicals is the result of the interaction between charged particles such as electrons, ions, and neutral particles in the plasma, and the ultraviolet radiation emitted by the plasma also plays a significant role. Generally, plasma surface modification is the result of the combined action of physical, chemical, and photochemical factors, rather than the result of a single factor. Moreover, the surface treated with plasma will continue to undergo a considerable amount of post reaction with oxygen and other media in the atmosphere not only during treatment, but also during treatment. The introduction of specific functional groups on the surface of activated materials is a characteristic of plasma chemical treatment.

The most important aspect in the surface reaction between plasma and polymer materials, closely related to practicality such as wetting and adhesion, is the generation of oxygen-containing functional groups. Although polymer materials have different structures, the same chemical structure is formed on the surface after plasma treatment. This indicates that inert gases have a greater ability to crosslink the outermost 2-3 layers of polymer materials, especially helium plasma, which has a high diffusion rate and the ability to transfer high energy to the surface through ion neutralization mechanism. Therefore, surface layer crosslinking occurs before oxidation reaction, and the surface structure formed after crosslinking is basically similar.

3. Formation of etched and roughened surfaces

The physical effects of charged particles such as electrons, ions, and excited state groups in plasma on the surface of materials can be easily observed. That is to say, electronic, ionic and other functional groups all have a certain amount of kinetic energy. When they strike the surface of polymer materials, due to the fact that most polymers are carbon atoms or structures containing other heteroatoms, they will produce a sputtering etching effect on the material surface, which has a significant modification effect on its structure, producing some volatile and unstable compounds accompanied by surface functionalization.

When treated with reactive gas plasma, pollutants or low molecular compounds attached to the surface of the material are removed from the surface by reacting with chemically activated groups in the plasma, resulting in surface irregularities and changes in the shape of the material surface. An increase in surface roughness is beneficial for bonding, leading to an increase in bonding strength.

In summary, the principle of plasma surface treatment machine relies on the action of plasma on the surface of the product (plasma groups include positive ions, negative ions, free radicals, and various active groups), which can remove trace pollutants and impurities on the surface; This process also produces etching, which can roughen the surface of the sample, forming many fine pits and increasing the roughness ratio of the sample surface, thereby improving the adhesion and wetting performance of the solid surface.