In industrial production, it is often necessary to add a new production process on the basis of the original process due to product characteristics, upgrading process, etc., to meet the requirements of increasing product reliability and process rationality. Of course, when adding a new process, it is necessary to understand the characteristics of the new process, and if necessary, adjust the production line appropriately according to its characteristics, in order to play the role of the new process, make better use of the new process, and meet the needs of actual production.
Plasma treatment process is an emerging process with a wide range of applications. However, no matter which industry it is used in, the principles and precautions of plasma process are basically the same. It is just that different products have different processing purposes. The process parameters are different. The following is a brief introduction to the principle of plasma cleaning, the generation of timeliness after treatment, the reasons for the decline of treatment effects and the precautions in actual production:
1. The principle of plasma cleaning
1. Decompose the absorbed atoms and molecules on the surface of the material to clean the surface of the material;
2. The energy of particles in low-temperature plasma is generally about a few to ten electron volts, which is greater than the binding energy of polymer materials (a few to ten electron volts). The photon energy also has several electron volts, which can break many organic large The chemical bonds of molecules form new bonds, generating free radicals such as =CO, -OH, HOO-, -CN, =CS and -COOH, which are easy to graft or polymerize with other materials, and improve the chemical reaction activity of surface molecules;
3. The surface molecules of the broken bond react with particles in the air to form a large number of polar groups, and the material changes from non-polar to polar, thereby improving the activity of the surface of the material;
4. The continuous bombardment of heavy particles will (reactively) etch the surface of the material, resulting in many micropores, increasing the surface roughness of the material, enhancing the surface energy, increasing the contact surface between surface molecules and other materials, and enhancing infiltration ；
5. The surface of the newly processed material has a certain electrostatic charge and has a certain electrostatic attraction ability, and so on.
2. The generation of timeliness after treatment and the reasons for the decline of treatment effect
In practical applications, the effect of plasma treatment on material modification is not lasting. As time goes by, part of the treatment effect will gradually lose. This phenomenon is called the timeliness or aging of plasma treatment. The mechanism of the timeliness of plasma treatment is very complex, mainly caused by the dynamic reorganization of the surface of the material.
1. After plasma treatment, active groups are introduced into the surface of the material to increase the surface energy of the material, but this state is not stable. In order to reduce the surface free energy, the molecular chain will freely rotate or migrate freely, so that the active groups will gradually turn to adjacent molecules or groups, or even inside the material, so that the system tends to stabilize and the surface activity is reduced;
2. Long-term storage makes the active surface adsorb various impurities and cause the surface energy to decrease;
3. The material contains one or more polymers and a variety of small molecule additives, such as low antioxidants, plasticizers, antistatic agents, lubricants, colorants, pigments and stabilizers, etc., with the prolonged storage time Or increase in temperature leads to increased mobility of molecular chains. On the one hand, surface active bonds are moved away from the surface or quickly recombined. On the other hand, some additives will migrate from the inside of the material to the surface. The higher the temperature, the greater the mobility, which affects the surface of the material. can. The longer the storage time, the higher the storage temperature, or the higher the content of certain additives (such as slip agents), the greater the change in its surface energy;
4. The surface is subjected to external forces (such as friction) to cause part of the surface molecules to fall off or recombine, and the surface roughness decreases, resulting in a decrease in surface energy, and so on.
In short, the timeliness of plasma processing is mainly affected by the type of processing gas, processing parameters, the chemical composition of the processed material, the crystalline structure, and the storage environment of the processed material.
3. Precautions after plasma treatment
In actual production, after the surface of the material is treated, it must be ensured that the surface is clean, not worn, and the storage temperature should not be high, and printing, spraying or gluing and other processes should be implemented as soon as possible to avoid the degradation of the treatment effect and the deterioration of the surface adaptability of the material.
Matters needing attention in actual operation:
1. Plasma treatment is nano-level treatment. The effects of cleaning, activation and etching only occur on the surface of the material, about a few to tens of nanometers, so the treated surface cannot be wiped, and physical friction will cause some surface molecules. Falling off or compounding, the surface roughness decreases, resulting in a decrease in surface energy;
2. The product after plasma treatment cannot be baked at high temperature or placed in a place where the temperature is too high. Too high temperature will cause the free rotation or free migration of molecular chains on the surface to be processed, and accelerate the active groups to turn to adjacent molecules or groups. , Which leads to accelerated decline in the treatment effect.
3. The treated surface cannot be cleaned with active liquids such as alcohol or acetone. Active liquids such as alcohol will directly react with the active groups on the surface to be treated to reduce the active groups and accelerate the decline of the treatment effect.
4. Based on the above basic principles, in actual production, you should also be careful not to directly touch the treated surface with your hands, so as to avoid friction, hand sweat, oil stains, etc., which may cause damage to the treated surface.
In summary, plasma treatment is nano-level cleaning and activation, which has a good effect on the removal of microscopic dirt and the activation of the surface of the material without changing the original performance of the material.
The treated surface does not need other treatments, and can be directly subjected to printing, bonding and other processes.
If other treatments are carried out after the plasma treatment, it will cause the opposite effect, leading to the decline of the treatment effect of the treated surface. If the product quality requirements are high or the surface of the substrate is seriously polluted, it is usually necessary to add alcohol wiping or ultrasonic cleaning before the plasma process to achieve better results.