Abstract: This article summarizes the industry standards and development status of powder coatings for construction at home and abroad, and focuses on reporting some difficulties in the application of metal effect powder coatings on aluminum profiles and curtain walls.

One is to solve the problem of chemical resistance, especially acid and alkali resistance, of the coating film. General metal aluminum powder pigments cannot meet its requirements, only those that have undergone special treatment can meet the requirements, but the price is relatively expensive.

The second is to solve the problem of spray coating on both positive and negative surfaces, as well as surface discoloration. Especially for formulas with high content of metallic pigments, large color differences, and strong metallic feel, there are more problems. This article explores these two issues.

Introduction to Manufacturing Process and Characteristics of Metal Powder Coatings

Powder coatings, due to their complete absence of organic solvents, have low emissions of volatile organic compounds (VOCs) during curing and have become one of the most environmentally friendly coating systems.

Compared to liquid paint, powder coatings have advantages in environmental protection and performance. In recent decades, powder coatings have rapidly developed as a new technology in the coating industry.

Powder coatings first developed in Europe in the 1960s and did not rise in China until the 1980s, but now the annual usage of powder coatings in China has surpassed that in Europe.

Powder coating not only has anti-corrosion and weather resistance, but also has good aesthetic and decorative properties. Manufacturing process of metal powder coating

Extrusion method: Prior to extrusion, the flake metal pigment is treated similarly to other pigments and then mixed with all other raw materials. The disadvantage is that, except for special formulations, the vast majority of metal pigments will be crushed during the extrusion process.

Dry mixing method: simple and economical, most domestic manufacturers use this method. However, due to the good conductivity of metal pigments, the electrical charge of the coating is weakened, and the construction performance is deteriorated, such as separation of metal pigments, short circuit of spray guns, etc. Due to the fact that metallic pigments are only loosely mixed in the base powder, they are isolated components throughout the entire coating. Dry mixing method, the amount of metal pigment added is 1.5– About 6%, if too much, it will not be easy to spray.

(3) Bonding method: The bonding process includes a special mixing procedure This special program is used to solve the adhesion problem between the base powder and the metal pigment, allowing the metal pigment to bond with the base powder. The amount of pigment added in the formula is 1% to 20%.

2. Introduction to the types and characteristics of architectural powder coatings, as well as performance comparison with fluorocarbon paints

Powder coatings for construction have excellent weather resistance, chemical resistance, and unique advantages similar to ordinary fluorocarbon paints. The comparison is as follows:

In addition, it should be emphasized to compare the environmental and safety characteristics between the two, especially during the construction process. Due to the absence of VOC emissions, powder coating poses much less harm to construction personnel than paint. It also makes construction safer and reduces the possibility of solvent combustion and explosion.

3. Introduction to Relevant Standards and Certification of Building Powder Coatings

a. Due to the characteristics of powder coatings, weather resistant powder coatings have their own unique reference standards and certifications. In the construction powder coating industry, we generally divide them into four levels, corresponding to equivalent products. Below is an example of TIGER's products.

Comparing these standards, Qualicoat's certification system registration is relatively complete, which certifies the processes of profile factories and the coating products of powder coating manufacturers.

At present, Qualicoat has passed over 500 powder certifications, with only 2 paint systems. Therefore, powder coatings have great potential in the aluminum industry.

But currently, Qualicoat certification in China is still focused on Level 1 and Level 2. There are not many certifications for Qualicoat Class3 yet, because the powder of Qualicoat Class3 is a fluorocarbon system.

Except for some large powder factories in China, there are few involved, which requires our engineering and technical personnel to make more efforts in raw material development and formula design. TIGER, as a pioneer in architectural powder coatings, has become the only powder coating supplier in China to obtain all QUALICOAT level 1, 2, and 3 certificates. b. Some main performance requirements for metal effect powder coatings for construction: 4. Manufacturing and construction difficulties of metal effect building powder coatings, solutions

a) There are not many types of metal pigments used in architectural powder coatings, with a limited selection range and poor performance.

There are many varieties of metal pigments used for powder coatings, which are generally divided into four categories. Aluminum silver powder pigment, pearl pigment, copper gold powder pigment, and other metal pigments (such as nickel powder, stainless steel powder, etc.).

Each type of metal pigment contains many colors of products, which, when applied to powder coatings, make the powder colorful and greatly enrich the variety and decorative properties of powder coatings. There are fewer types of metal pigments that can meet the needs of construction, and now only weather resistant pearl powder and a small amount of aluminum powder are available. The selection of pearl powder is also quite strict, it must be a weather resistant product that has been specially wrapped.

The advantages of pearl powder are that there are more pearl pink colors and good chemical resistance, but the disadvantages are that the metallic texture is not strong and the difference compared to aluminum powder is too large. In terms of aluminum powder, due to the reactivity of aluminum pigments, they are prone to react with water and alkaline substances. According to the standards of the construction industry, mortar experiments and detergent experiments cannot pass. In recent years, the metal effect of building powder coatings has been poor, with a large gap compared to paint, which also makes powder coatings unable to compete with them in many construction projects.

So a few foreign aluminum powder suppliers have developed weather resistant aluminum powder, which has been wrapped multiple times on aluminum powder particles (acrylic resin+SiO2) to improve its chemical resistance. After testing in powder coating applications, it can fully meet the requirements of construction. b) The instability of the state between metallic pigments and base powders is due to the complete independence of the base powder and metallic pigments (as shown on the right in the figure below). The dry mixing method currently used in China, due to equipment limitations, causes uneven dispersion of pigments in the base powder, and the color effect is affected by voltage, atomization, and powder output when spraying the sample. The difference between the sample and the production mixture is large, resulting in unstable formula.

Due to the higher conductivity of metal pigments compared to resins, the amount of metal pigment added should not be too much, with a dosage of 1.5; About 6%, if too much, it will be difficult to spray, resulting in many effects that cannot be formulated and limiting the use of powder coatings. The bonding process involves a special mixing procedure This special program is used to solve the adhesion problem between the base powder and the metal pigment, connecting the metal pigment with the base powder (see left in the figure below). It gives the metal pigment the same electrical properties as the resin, breaking through the limitation of the amount of metal pigment. The addition amount in the formula is 1% to 20%.

c) Metal effect powder coatings are mainly used in the unstable building materials industry for customer construction. Powder coatings are mainly used for aluminum profiles, ceilings, and curtain wall panels. Aluminum profiles have four sides that need to be sprayed and are generally about 6 meters long, while ceilings and curtain wall panels have larger areas.

This increases the uncertainty during spraying, especially for powder coatings with metallic effects. Due to the color difference between the metal pigment and the base powder, it is easy to cause the following problems: 1) The color of the four sides of the aluminum profile and the color of the material head are inconsistent with the middle color, which we call“ The Yin Yang aspect;. 2) Ceiling or curtain wall panels, where the color between two panels or the middle and surrounding areas of one panel is different, we call it“ The phenomenon of blooming or cloudy spots;. 3) During spraying, the surface of the board becomes rough, resembling a sandblasted surface, especially at the corners. 4) After passing through the customer's 1st and 2nd level recycling systems, there is a significant color difference between the recycled powder and the new powder, making it impossible for the customer to add new powder or directly use the recycled powder. In summary, these four issues are all related to metal pigments, so by selecting formulas and processes to improve the drawbacks brought by metal pigments, these problems can be completely solved. 1) Manufacturing process: Solve the dispersion problem of metal pigments and base powders through extrusion and bonding processes. Due to the high shear of the extruder, the pigment is damaged in the extrusion method, so it is necessary to choose specially treated metal pigments, such as ECKART's powdersafe system.

Craftsmanship involves selecting equipment and setting programs to maximize the retention of metallic effects while bonding metallic pigments and base powders together as much as possible.

These two processes can effectively solve the problem of roughness and discoloration caused by the accumulation of metal pigments during spraying. 2) Formula selection: including the selection of base powder, metal pigment, and dispersing agent.

Reasonable design and manufacturing of base powder is one of the key points of the entire formula, which stabilizes the manufacturing process through the ratio of resin, curing agent, and additives.

The selection of metallic pigments is the soul of the formula, and two points need to be noted:

1. The color of the metal pigment should be consistent with the base powder as much as possible to reduce color difference, which can effectively avoid the phenomenon of yin-yang surface and flower cloud spots;

2. Metal pigments must meet the requirements of building standards. If the mortar test is complicated, chemical reagents such as 10% hydrochloric acid and 5% NaOH can be used to quickly detect whether the metal pigment meets the chemical resistance requirements. Chemical reagent droplets are dropped onto a powder coating sample at a certain concentration. After reaching the required time, the sample is rinsed with water and the surface where the reagent drips is visually observed to compare the loss of aluminum powder. The selection of dispersant is the highlight of the entire formula. An effective dispersant can stabilize the manufacturing process, improve the dispersibility and electrical performance during spraying. Add icing on the cake to the entire formula design. 3) Strengthen inspection:

The purpose of inspection is to verify the stability of metal effect powder coatings, detect defects in advance, and reduce the probability of customers encountering problems again. Generally, by imitating the on-site conditions of customers, such as verifying the electrical performance of coatings and the color stability after recycling.

The bonding effect between metal pigments and base powder can also be observed intuitively by comparing particle size or electron microscopy. The method varies from person to person, and it is important to stabilize the manufacturing process through convenient and fast testing methods.

5. Conclusion

Due to the excellent comprehensive performance of building powder coatings, with the increasing global demand for environmental protection and the continuous improvement of people's living standards, the application field of powder coatings has gradually expanded, and the pace of market development has accelerated. Especially for metal effect powder coatings, due to their dazzling effects and environmentally friendly characteristics, the market demand is expected to be high.

Of course, there are still some areas that need improvement and optimization. I believe that with the dedicated efforts of technical engineers in powder coating enterprises, metal effect building powder coatings will become a shining star in the building coating industry.