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What is the principle of plasma treatment of plastic parts?
Author:Original Click :1743 Date: 2021-03-18

1. The concept of surface energy There is surface energy on the surface of an object, and each material is different. The unit of surface energy is dyne. The larger the dyne value, the higher the surface energy, the lower the value, and the lower the dyne value. The general coating and Bonding, the reason for the poor bonding force is the low surface energy (provided that the surface is clean), and the approximate dyne value is only in the range of 10-30. Under such surface energy conditions, it is not suitable for bonding and coating. , Only when the dyne value is higher than 40-50 is more suitable for bonding and coating; There are two ways to reflect and measure the surface energy of an object: 1. Use a dyne pen to measure. The dyne pen is similar to an oil-based pen. It is a liquid drawn directly on the surface of the object. Each dyne value corresponds to a dyne pen. The dyne pens are distinguished by model. , If you use No. 40 dyne strokes, the traces on the painting will shrink and deform quickly, then the surface energy must be less than 40. We weigh it according to the speed of the shrinkage. If the shrinkage is fast, we will use the No. 30 test again. The effect is that if the No. 30 does not shrink within 1 minute and is evenly flat, then the surface energy must be greater than 30 dyne. If we want to test accurately, we can use No. 33 and No. 32 to test again, because we are in What may be needed when processing the product is that the dyne value exceeds a certain value, so we require the dyne value to exceed 60 dyne, then use 60 dyne to test directly after processing; 2. The simpler dyne test is to measure the drip angle. The dyne value of water is 72. If the surface energy of the object exceeds 70, then the water drip angle is generally less than 10 degrees, and the wettability to water will be very high. Great. Two, there are two factors that affect the surface coating and bonding effect 1. The characteristics of the workpiece itself are mainly reflected by the surface energy. The lower the surface energy of the material, the worse the coating effect and bonding; 2. The properties of the coating such as glue and ink are determined; for example, glue, epoxy glue, acrylic glue, then each glue has its own molecular structure, chemical groups and chemical bonds. Since each glue can bond with the material so firmly in the process of bonding, it also has a series of reactions with the surface of the workpiece. The main chemical reaction is the chemical reaction of bonding and adhesion. There are very complex chemical reactions, such as: chemical bond recombination, group bonding, bonding, cross-linking, substitution and other reactions; so in the process of bonding and coating, whether the chemical properties of the coating material are comparable to the workpiece The role of absorption or mutual affinity is very important. If our glue or coating material and the workpiece itself repel each other, then no matter how high our surface energy is, it will not work. Of course, this situation is more common. Sometimes we For workpieces treated with oxygen plasma, there are a lot of oxygen free radicals on the surface of the workpiece. There are three types of glues like ABC. The nature of the glue itself determines that glue A prefers to affinity with oxygen free radicals, while B and C are not compatible with oxygen free. On the contrary, it has affinity for hydrogen radicals, so it is certain that the bonding of A will be better, while the bonding of B and C will be relatively poor. If the workpiece is treated with hydrogen plasma, the bonding of B and C may be better, and A It will be worse, which is why we use different plasma atmospheres to process the workpiece, so as to achieve different effects; 3. Material classification The surface energy is determined by the molecular structure and characteristics of the material itself; Classification of materials: divided into polar materials and non-polar materials. Polar materials are also called polar materials. Most of them are organic compounds. All the polymer compounds we come into contact with are polar materials; polar materials. The strength is the hydrophilicity and wettability of the material; the specific is what we call the surface energy, the strong polarity is the good hydrophilicity, good wettability, and high surface energy, 40 or even 70 dyne or more, so the adhesion And coating effect is better, on the contrary, poor polarity means hydrophilicity, poor wettability, low surface energy, 10-20 dyne, that is, the material we say is very inert and low surface energy, so it is not suitable for coating And bonding Non-polar materials are also called non-polar materials, such as ceramics, pure silica glass, etc. Most of them are based on the chemical composition of inorganic salts. Their molecular structure is stable, without chemical bonds and free charges, low surface energy, and hydrophilic. Poor wettability, especially difficult during coating and bonding, requiring special materials or glue;  Fourth, the origin and principle of plasma treatment Now that we know the classification of materials and surface energy, how can we improve the surface energy of the object and workpiece? High surface energy is suitable for coating and bonding, and low surface energy is not suitable for bonding and coating. The surface energy of the object and workpiece can be improved, and it can be suitable for coating and bonding, so there is a plasma surface treatment process, which can generate some radical groups, free charges, functional groups, etc. on the surface of the workpiece through plasma. So that the surface energy of the object and the workpiece is increased, and the dyne value is increased, which is suitable for bonding and coating; For example, the oxygen that we pass into the vacuum chamber is oxygen, then the oxygen plasma generated by the ionization of oxygen is composed of more complicated microscopic ions such as oxygen atoms, oxygen ions, electrons, neutrons, and protons, and these are charged during processing. The particles will accelerate and decelerate under the influence of electric field force, and the movement is irregular. Because the direction of our electric field is changing and the direction of the force is constantly changing, the processing process will have acceleration, deceleration, collision, absorption, etc. Particle motion forms, objects and workpieces are composed of CHON and other elements. The chain structure of carbon chain exposed to the outermost layer will also be participated by these accelerated particles through collisions, reactions, etc., and new groups are formed, there are The chemical bond breaks and reorganizes, then at this time the outermost molecular level of the workpiece surface is treated by the oxygen plasma, and the treated workpiece surface will change from the original poor polarity to good polarity with more free radicals. With more free charge, the surface energy will be greatly improved, which is suitable for bonding and coating; Five, the function and role of plasma treatment Plasma treatment has three functions, each of which has a specific purpose: 1: Clean; 2: Activation; 3: Etching; While we are using plasma to process the workpiece, all three effects are taking place, so which one we need most and which one is the most important is what we need to consider; 1: Clean; It is possible that the surface of some workpieces is originally dirty, such as the release agent on the surface of the injection molded part, the residual glue on the surface of the glass, etc. Sometimes the release agent cannot be observed with the naked eye, but it does exist. Then we need to perform plasma treatment to remove the contaminants. Clear away, so that the surface of the workpiece is itself, which is cleaning; there are two ways to clean: one is a chemical reaction, such as a polymer compound of CHO, we use oxygen plasma, O+C=CO+CO2, O+2H=H2O and other materials that react to produce meteorology are taken away by the vacuum pump. The second is physical impact. The particles have a certain kinetic energy and energy under the control of electric field force, which tells the impact of the surface of the workpiece, some small particles may be It is cleared; but the particles are so small that we can't imagine, so he can only hit things smaller than him, so they are all meteorological things and will not cause damage to the surface of the workpiece; 2: Activation; The main principle of activation is mentioned above, so every glue system and coating coating has its favorite groups. For example, the acrylic glue system in the glue has carboxyl groups, which have an affinity for carboxyl groups. We have two kinds of coatings: A and B. A prefers hydroxyl groups, so we put the surface of the object through plasma treatment to allow the hydroxyl groups to exist on the surface of the workpiece. At this time, when we coat the material A on the surface of the workpiece, the bonding force is very good; if We coat the processed workpiece with B paint at the same time, it may not be effective and easy to fall off; so the concept of activation is to introduce corresponding functional groups, groups, chemical bonds (such as positive or negative charges), etc., Therefore, in addition to our treatment process, there are also coating materials related; for example, when some workpieces are recoated, the effect of our treatment with oxygen is good, but the effect of treatment with argon is not good. This is the principle; 3: Etching; When two objects are in contact, they have a surface area, and the distance between the two points is the closest in a straight line. When two objects are in contact, if both are smooth, then the contact surface is the smallest. If the two objects are very rough, a mountain topography is formed. , Then when these two objects are in close contact, their contact surface will be greatly enlarged, so our etchback is based on this principle. For example, we sometimes have a process of roughening before bonding and coating. , That's it, but our plasma surface treatment is to make the amount of etchback to be the smallest. Its morphology is molecular-level etchback, which cannot be observed with the naked eye, so we can't see whether the surface of the workpiece is damaged. If you perform SEM Scanning with an electron microscope, you can see their processing effect; Six, the characteristics of plasma treatment Under normal circumstances, plasma treatment will have three treatment effects at the same time and affect each other; but according to the difference of the access atmosphere and workpiece, one of the three treatment effects will be absolutely dominant, and the other will be auxiliary; Because organic materials are very different, some even pure materials are divided into different labels, and the chemical properties are different according to the amount of mixed substances. Many also incorporate some glass fiber, ceramic powder, waste, primer, etc., so This leads to great changes in the characteristics of the material, so the specific plasma process needs to be tested at this time. Sometimes we use N gas to treat the effect very well. A little bit of new mixed fillers in the material, then it may be N gas The treatment effect is not good, and you may have to change to another atmosphere to deal with; In addition, plasma treatment has a certain timeliness. On-duty treatment is used on duty. Because the charge and free radicals on the surface of the workpiece are polar, they may react with free particles in the air to cancel each other and ablate. Therefore, plasma treatment is Time-sensitive, the specific time-sensitive length is also different according to different materials, the same PE, PS, due to different labels, better treated PE, placed for half a year, the effect is still very good, modified PE can only be placed 1 Day, the effect is very poor the next day, it needs to be processed again in order to achieve the desired effect; Therefore, the types of materials provided by your company and the corresponding processing parameters and timeliness are not ascertainable. We can only provide a reference parameter and timeliness in general, and specific on-site tests are required to verify;

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