Discussion on the quality control of powder coating products

As an environmentally friendly coating material developed in recent decades, powder coating has the advantages of high coating efficiency, good protection and decoration, so as to achieve sustained and rapid development.

With the rapid increase in powder coating manufacturers and powder coating production, the application field of powder coating continues to expand, the competition between powder coating manufacturers is becoming more and more fierce, and powder coating users have higher and higher requirements for the quality of coating products, so more stringent requirements are put forward for the product quality control of powder coatings. The author talks about the quality control of powder coatings, combined with the actual situation of the company's production of powder coatings for many years, for the reference of peers.

1.The production principle of powder coating

The production of powder coating is to add solid materials such as resin, curing agent, pigment, filler and additives to the mixer according to the formula amount without using solvents or water and other media, and then input the extruder into the extruder for melting and mixing after full mixing and dispersion; Then press into thin sheets on the tablet cooler, cool and crush into thin sheets, and then crush by air classification grinding and then cyclone separation, the separated coarse powder is screened by the vibrating screen to obtain the finished product, and the fine powder is recovered through the bag filter, the whole production process is a physical process, basically there is no chemical reaction.

2. Factors influencing product quality

2.1 Stability of the formulation

The quality of raw materials is the basic condition to ensure the quality of powder coating products, so the technical indicators of raw materials, such as resin gelling time, softening point, and reactive functional group technical indicators, must be regularly spot-checked to ensure product quality and customer needs. The principle of powder coating formula design is not only to ensure product quality to adapt to the cruel market competition, but also to comprehensively consider the cost of each raw material in the formula, but do not use shoddy, or even replace outdoor product formula with indoor powder coating formula, deceive users, and cause adverse effects; At the same time, it is also necessary to make the formula stable and continuous, and control the quality of the same batch or different batches of powder coating products.

2.2 Production process control

The production process of powder coating is a physical mixing process, and the purpose of pre-mixing is to mix powdered materials such as resins, pigments, fillers, additives and so on in a dry state. Create conditions for melt extrusion and obtain better dispersion effect. If you mix it at will, or even manually stir and mix, it will cause the instability of the formula and the quality of the powder will decrease; Extrusion is the core process of powder production, which has a decisive impact on the quality of powder, the mixing effect of the extruder is not good, which will affect the gloss of the product, and the leveling will also become poor, and there will be uneven color mixing, local gelatinization, the formation of plate particles and other drawbacks; The main purpose of grinding is to make the particle size distribution of the powder suitable for electrostatic spraying.

2.3 Particle size of powder coatings

Powder coating suitable for electrostatic spraying, its particle size is better between 10~90μm. The particle size of powder coating is an important indicator of the quality of powder coating, and the leveling, powder rate and stability of powder coating products are related to powder particle size, therefore, controlling powder particle size is the key issue of powder coating quality.

The particle size control of powder coating suitable for electrostatic spraying is 20~90 μm, and the customer is satisfied with the powder quality after use.

2.4 Powder coating fluidization effect

The powder with good fluidity is easy to fluidize during use, it appears very fluffy, and has a water-like effect, from the powder supply barrel to the spray gun, the powder is transported lightly, and the powder comes out of the nozzle and atomizes well, and there is no agglomeration or spitting powder. The fluidity test of powder coating is guided by the Selier fluidity test method, that is, a certain amount of powder sample (about 250g) is weighed and placed in a cylindrical plastic container with a porous bottom plate with a diameter of 100mm; Compressed air is introduced from the bottom of the multi-well plate at a rate of 200 L/h to fluidize the powder, and the mass of the powder flowing out within 30 s is determined, and the fluidity of the powder can be calculated according to the following formula:

Where: the mass of the outgoing powder in m —30 s, g; H0 — the height of the powder in the container when it is not aired, mm; H1 — The height of the powder in the container when the fluidization is stable, mm.

2.5 Mechanical properties and others

Powder coating manufacturers usually test the following indicators: gloss, film thickness, color difference, impact, cupping, pencil hardness, adhesion, flexibility, etc., in order to test the quality of powder coating products and ensure that the products meet the needs of customers.

3. Conclusion

There are many influencing factors for the quality of powder coating, and sometimes a variety of factors are intertwined, resulting in problems in the quality of spraying products, so to improve the quality of powder coating products, it is necessary to continuously explore and summarize in production practice, pay attention to all aspects of the production process, establish a sound product quality management system, and improve product quality. At the same time, good powder coating products must also cooperate with good spraying process conditions to produce ideal spraying products.