Factors influencing powder coating loading rate

Powder coating is a solid powder coating composed of solid resin, pigment, filler and additives, etc., which is mostly used for anti-corrosion construction.

Compared with ordinary solvent-based coatings and water-based coatings, the dispersion medium of solvent-based coatings is different, the dispersion medium of solvent-based coatings is organic solvent, the dispersion medium of water-based coatings is water, and the dispersion medium of powder coatings is air.

Since powder coatings basically do not contain organic solvents, they are environmentally friendly coatings, and they have been vigorously promoted in the field of environmental protection. In addition to the characteristics of environmental protection, powder coatings also have the advantages of reusability and high comprehensive utilization.

The principle of electrostatic spraying is to use the high-voltage electrostatic corona electric field to connect the high-voltage negative electrode on the metal deflector mark at the head of the spray gun, and the sprayed workpiece is grounded to form a positive electrode, so that a strong electrostatic electric field is formed between the spray gun and the workpiece.

When the powder coating is sent from the powder supply barrel to the deflector rod of the spray gun through the powder pipe as the compressed air used as the carrying gas, due to the corona discharge generated by the high-voltage negative electrode connected to the deflector rod, a dense negative charge is generated near it, so that the powder is negatively charged and enters the electrostatic field with high electric field strength.

Under the dual action of electrostatic force and carrier gas, the powder evenly flies to the surface of the grounded workpiece to form a uniform powder layer, which is then heated and solidified into a durable coating film.

Good powder coating is very easy to spray, spraying 1-3 guns can cover the substrate, less secondary recovery powder, high work efficiency.

Poor powder coating is not easy to powder, spray 3-5 guns to cover the substrate, secondary recovery powder is more, and the work efficiency is low. By recycling and then constructing, the comprehensive utilization rate of good powder coating can reach 99%.

For powder coating, we must not ignore the importance of the first-time powder rate. The powder coating rate generally refers to the powder coating coverage, under the premise of ensuring the appearance and mechanical properties of the powder coating film, the amount of powder coating consumed per unit profile, that is, the production cost.

Therefore, the powder loading rate of powder coating is a very important factor, and it is a technical index determined by a variety of factors. So how can you improve the powder coating rate?

1. Control the particle size distribution of powder coating, the narrower the better

Because the particle size of the powder coating is related to the charge charge, the larger the particle size, the greater the charge charge, if the particle size distribution of the powder coating is uneven, there will be a large particle size to reach the surface of the sprayed object first, and the small particle size will arrive or can not arrive, so that the powder rate is reduced at one time, and it is easy to appear the appearance quality problem of the paint film.

Therefore, it is necessary to control the particle size of the powder coating within a certain range, not too big nor too small, each enterprise will formulate its own standards according to the needs of downstream customers, and the general particle size is about 40-50μm.

2. Increase the resin content

Among the components of powder coatings, resin, as a polymer compound, has the highest dielectric constant, and pigments, fillers and other dielectric constants are low.

If there are more substances in the powder coating with a higher dielectric constant, the powder rate will be increased when spraying, but it will also increase the cost, and the coating company needs to configure the resin content according to customer needs.

3. Reasonable choice

Pigment and filler fineness and dispersion have a lot to do with powder loading. Pigments and fillers with uniform fineness and good dispersion can improve the primary powder rate.

4. Indispensable conductive additives

Conductive additives can make powder particles carry more charge, so it is necessary to pay attention to the addition of conductive additives in the formulation design.

Especially for parts such as groove dead corners, due to the weak power line of the Faraday effect, the powder particles with more charge can reach the surface of the workpiece by their own force, thus improving the powder loading rate of these parts.

5. Spraying process conditions

Due to the difference between the climate between the north and the south, and the different temperature and humidity characteristics in winter and summer, it will affect the powder rate to some extent, so it is necessary to design a relatively stable temperature and humidity, a relatively clean spraying environment, a relatively stable voltage, a more appropriate spraying spacing, a suitable air pressure, and a good grounding of the workpiece.

6. Suitable spray gun

The primary powder rate is related to the type of spray gun, the process parameters, the shape of the workpiece, and the spraying method. Many companies only pay attention to the maximum powder output of the spray gun, in fact, the compressed air output and air pressure increase, the powder output can be increased.

However, it is a question whether the high-voltage electrostatic generator can charge so much powder. In the case of spray guns, dense powders block each other's path to charging, leaving the powder behind uncharged, or charged, with very little charge.

From the point of view of the spraying process, when the coating surface reaches electrostatic equilibrium, the powder particles that come behind and the particles on the coating surface will repel each other, and even fall against the opposite movement of ionization, and be recovered by the recovery equipment.

Therefore, the amount of powder output should be measured according to the charged capacity of the spray gun, and whether the powder is fully charged should be considered, and according to the shape of the sprayed workpiece, according to repeated experiments.

In addition, if the workpiece has grooves, grooves, sharp corners, small holes and other shapes, it will produce Faraday shielding phenomenon, and the sprayed coating will be very thin and leak the bottom.