Coating knowledge: Discussion on the factors affecting the powder loading rate of powder coating

The key points are as follows: [Abstract] the principle of electrostatic spraying of powder coating is introduced, the factors influencing the powder loading rate are analyzed, and the technological conditions to improve the powder loading rate are put forward [Key words] powder coating; powder loading rate; process parameters; electrostatic spraying; factor powder coating has the characteristics of high production efficiency, excellent film performance, good ecological environment protection and outstanding economy, which are widely valued by the world Powder coating grows at a rate of more than 10% every year, especially in the late 1990s in China, many powder coating manufacturers have emerged Under the premise of ensuring the appearance and mechanical properties of the powder coating, the powder coating manufacturer shall, Paint agent, top 10 Chinese wall paint brands Recommended introduction: interior wall paint and exterior wall paint can achieve beautiful, clean and pleasant effects, but the effects in different environments are different, so the color of the paint will be different There are ten brands of Chinese paint, ten brands of global paint, ten brands of Chinese wall paint, and ten brands of Chinese paint, Famous trademark of Chinese paint and coating In private rooms, most of us choose according to our own personality, personal hobbies and living habits The younger generation will choose the interior wall paint with rich colors and bright colors, while the older ones will have some working experience Home of coatings: [Abstract] the principle of electrostatic spraying of powder coating is introduced, the factors influencing powder loading rate are analyzed, and the technological conditions for improving powder loading rate are proposed [Key words] powder coating; powder loading rate; process parameters; electrostatic spraying; factor powder coating has the characteristics of high production efficiency, excellent film performance, good ecological environment protection and outstanding economy, which are widely valued by the world Powder coating grows at a rate of more than 10% every year, especially in the late 1990s in China, many powder coating manufacturers have emerged Under the premise of ensuring the appearance and mechanical properties of powder coating, the most concerned problem of powder coating manufacturers is the consumption of powder coating per unit profile, that is, the production cost Therefore, the powder coating rate has become a common concern of both manufacturers and users 1 Electrostatic spraying principle of powder coating electrostatic spraying of powder coating is to use the principle of high-voltage electrostatic corona electric field to connect the high-voltage negative electrode (generally 60-100kv) to the metal spray cup and the pole pin at the head of the spray gun, and the sprayed workpiece is grounded to form a positive electrode, so as to form a strong electrostatic field between the spray gun and the workpiece As the compressed air of carrier gas, when the powder coating is sent from the powder supply barrel to the spray cup and pole pin of the spray gun through the powder pipe, because it is connected with the high-voltage negative pole to generate corona discharge, a dense negative charge is generated near it, which makes the powder with the negative charge enter the static electric field with high electric field strength, under the double action of the static electric power and the driving force of carrier gas, The powder flies evenly to the surface of the grounded workpiece to form a thick and even powder layer, which is then heated and solidified to become a coating The powder loading rate of powder coating generally refers to the coverage efficiency of powder spraying From the spraying mechanism, it can be seen that the main adsorption force of electrostatic spraying is electrostatic power, and the powder loading rate mainly depends on the number of charged powder particles According to Coulomb's law, in a certain period of time, the charged amount of powder coating particles has the following relationship: therefore, improving the charged ability of powder particles can improve the powder loading rate of powder coating 2 Factors affecting powder coating rate 2.1 powder particle size from formula (1), it can be seen that the charge amount of powder is directly proportional to the square of powder particle size, increasing the charge amount of powder particle size, increasing the powder loading rate, on the contrary, reducing the powder particle size, reducing the charge amount of powder, decreasing the powder loading rate Therefore, in the production process of powder coating, the powder coating with small particle size (10 μ m) should be reduced as much as possible; however, the particle size of the powder should not be too large, the particle size is too large, the appearance quality of the coating film is reduced, and the orange peel is serious It is also possible that the gravity of the large particle powder exceeds the aerodynamic force and electrostatic force, and the powder coating has fallen down in the flight process because the gravity effect does not reach the workpiece surface, On the contrary, the powder loading rate decreased Therefore, the control of powder particle size is one of the key problems to control the quality of powder coating Figure 1 shows the particle size distribution of the epoxy polyester hybrid ch-08 powder coating The laser particle size distribution instrument is used for detection, and the spraying effect is good, and the powder loading rate is high It can be seen from Figure 1 that the particle size of powder coating suitable for electrostatic spraying is 20-90 μ M 2.2 the dielectric constant can be seen from formula (1): the electric charge of the powder is directly proportional to the dielectric constant of the powder Choosing the coating component with higher dielectric constant can increase the electric charge of powder particles, greatly improve the powder adsorption and powder loading rate 2.2.1 powder coating is mainly composed of epoxy powder, polyester powder and other high molecular compounds, which have high dielectric constant, so its Coulomb force (electrostatic force) is large, and its powder loading rate is high However, due to its relatively expensive price, some powder manufacturers reduce the cost of raw materials, add too many fillers, reduce the ratio of pigment to base, and greatly reduce the powder loading rate in order to meet the needs of market competition Table 1 shows the formula of ch-08 powder coating After several years of production inspection, it has good application effect and high powder loading rate 2.2.2 application and storage conditions of powder coating: compared with solvent coating, the coating film is easy to appear slight orange peel Therefore, many powder coating manufacturers in order to pursue the smooth surface of the workpiece, in the allowed range of powder particle size, try to reduce the particle size of the powder coating, so as to increase its leveling and achieve better coating effect But the finer the powder, the easier it is to absorb moisture The moisture absorption (moisture content) of powder coating directly affects the dielectric constant of powder Slight moisture absorption will affect its charged performance, reduce the powder loading rate, affect the fluidity and film-forming performance of the powder, so that the coating film is not smooth, or even difficult to absorb on the workpiece, the coating film will produce bubbles, pinholes and gun plugging and other disadvantages; serious moisture absorption of the powder will agglomerate, unable to carry out electrostatic spraying Therefore, in order to improve the powder loading rate, the following measures can be taken: (1) the compressed air purification system can be used only when the moisture content of the compressed air is reduced as much as possible through the secondary filtration and absorption device; (2) pay attention to the relative humidity of the air at the powder spraying site Every 30% change in the relative humidity is equivalent to two orders of magnitude change in the resistivity of the powder Especially in the areas with high relative humidity in the south, the qualified manufacturers suggest to install dehumidification air conditioner in the powder room; (3) keep the air circulation in the warehouse, and the powder coating packing box should be placed on the board on the isolated ground, with the stacking height no more than 4 layers 2.3 spraying process conditions 2.3.1 static voltage it can be seen from formula (1): the electric charge of powder coating is directly proportional to the electric field strength e, so increasing the static voltage and the electric charge of powder is conducive to the improvement of powder loading rate Through production test, the relationship between static voltage and adhesion of powder is shown in Figure 2 It can be seen from Figure 2 that the adhesion of powder increases rapidly with the increase of static voltage When it reaches 90KV, the change of adhesion is not obvious, so it is suitable to control the powder spraying voltage at 60 ~ 90KV in production 2.3.2 when the distance between the spray gun and the workpiece is determined by the electrostatic pressure, the electric field strength is inversely proportional to the distance between the poles When the distance between the spray gun and the workpiece is too short, spark discharge will occur; if the distance is too long, the powder loading rate will be reduced The relationship between spray gun distance and breakdown voltage is shown in Figure 3 It can be seen from the figure that when the static voltage is controlled at 60 ~ 90KV, the electrostatic spraying distance is more appropriate between 250 ~ 350mm 3 Conclusion: the powder loading rate is a technical index determined by many factors The powder spraying process is not only a fixed parameter, each manufacturer has its own enterprise standard In addition to the main factors discussed above, there are also some other factors, such as the surface shape of spraying workpiece, the type of spray gun, the performance of recovery system, etc., which will affect the powder loading rate and need to be explored and studied in production Liu Hong Liu Zhengyao [focus on WeChat official account "paint net"; pay attention to surprise, scan code to see if your husband is selling paint.. "Exchange network: 92525666] coatings home is focused on coatings, diatom mud, paint and coatings, coating technology, fire retardant coatings news information and coatings, diatom mud, paint and coatings, coating technology, fire retardant coatings decoration knowledge and decoration effect map.