Discussion on the application of powder coatings and metal powder coatings in the field of construction

Abstract: The industry standards and development status of powder coatings for construction at home and abroad are reviewed, and some problems in the application of metallic effect powder coatings on aluminum profiles and curtain walls are mainly reported
.

One is to solve the chemical resistance of the coating film, especially the acid and alkali resistance.

The second is to solve the problem of spraying on the yin and yang surface and the surface blooming

Because powder coatings do not contain organic solvents at all, they have low VOC (volatile organic compounds) emissions during curing, and have become one of the most environmentally friendly coating systems
.

Compared with liquid paints, powder coatings have advantages in environmental protection and performance.

Powder coatings first developed in Europe in the 1960s, and did not rise in China until the 1980s.

In addition to anti-corrosion and weather resistance, powder coatings also have good aesthetics and decoration

Metal powder coating manufacturing process

(1) Extrusion method: Before extrusion, the flake metallic pigment is treated similarly to other pigments, and then mixed with all other raw materials
.
The disadvantage is that in addition to special formulations, most of the metal pigments will be crushed during the extrusion process
.

(2) Dry blending method: simple and economical.
Most domestic manufacturers use this method.
However, due to the good conductivity of metal pigments, the chargeability of the coating is weakened and the construction performance deteriorates, for example, separation of metal pigments, spray guns Short circuit and so on
.
Also because the metallic pigment is only loosely mixed in the base toner, it is an isolated component in the entire paint
.
In the dry blending method, the amount of metallic pigment added is about 1.
5 -6%, if too much, it is not easy to spray
.

(3) Bonding method: The bonding process includes a special mixing procedure.
This special procedure is used to solve the adhesion problem between the base powder and the metal pigment, so that the metal pigment and the base powder are connected together.
The pigment is added in the formula Quantity: 1%～20%
.

2.

Powder coatings for building have the same excellent weather resistance and chemical resistance as ordinary fluorocarbon paints, as well as their own unique advantages.
The comparison is as follows:

In addition, it should be emphasized to compare the environmental protection and safety characteristics between the two, especially in the construction process, because powder coating has no VOC emissions, its harm to construction personnel is far less than paint
.
It also makes the construction safer and reduces the possibility of solvent burning and explosion
.

3.

Comparing these standards, Qualicoat's certification system registration is relatively complete, which respectively certifies the process of the profile factory and the coating products of the powder coating manufacturer
.

At present, Qualicoat has passed more than 500 powder certifications, and there are only two paint systems.

However, the domestic Qualicoat certification is still concentrated in Level 1 and Level 2
.
Qualicoat Class3 certification is not much, because the powder of Qualicoat Class3 is a fluorocarbon system
.

Except for some large powder factories in China, it is rarely involved.
This requires our engineers and technicians to make more efforts in raw material development and formulation design
.
As a pioneer in architectural powder coatings, TIGER has become the only powder coating supplier in China that has obtained QUALICOAT's 1, 2, and 3 level certificates
.

b.
Some main performance requirements of metallic effect powder coatings for construction:

4.
Difficulties in manufacturing and construction of metallic effect architectural powder coatings and solutions

a) There are not many types of metallic pigments for architectural powder coatings, the selection range is small, and the performance is poor
.
There are many varieties of metallic pigments used in powder coatings, which are roughly divided into four categories
.
Namely aluminum and silver powder pigments, pearlescent pigments, copper-gold powder pigments and other metal pigments (such as nickel powder, stainless steel powder, etc.
)
.

Each type of metallic pigment also contains products with many hues.
After being applied to powder coatings, it makes the powder colorful, which greatly enriches the variety and decoration of powder coatings
.

There are fewer types of metal pigments that can meet the needs of construction, and now only weather-resistant pearlescent powder and a small part of aluminum powder are available
.
The choice of pearl powder is also more demanding, and it must be a weather-resistant product that has been specially wrapped
.

The advantage of pearlescent powder is that there are more pearlescent pink phases, good chemical resistance, but the disadvantage is that the metal texture is not strong, and the gap is too large compared to aluminum powder
.

In terms of aluminum powder, due to the active nature of aluminum pigments, it can easily react with water and alkaline substances.
According to the standards of the construction industry, mortar experiments and detergent experiments cannot pass.
Poor, the gap with paint is large, which also makes powder coatings unable to compete with it in many construction projects
.

Therefore, a few foreign aluminum powder suppliers have developed weather-resistant aluminum powder through research and development.
The aluminum powder particles have been wrapped (acrylic resin + SiO2) for many times to improve their chemical resistance.
After the powder coating application test, it can fully meet the architectural requirements.
Request
.

b) State instability of metallic pigments and base powders

Because the base powder and the metallic pigment are completely independent (see the right picture below)
.
The dry mixing method currently used in China, due to the limitation of equipment, the pigment is unevenly dispersed in the base powder.
The color effect of the sample plate is affected by the voltage, atomization and powder output.
The difference between the sample and the production mixture is large, resulting in The formulation is unstable
.

Also because the conductivity of metallic pigments is higher than that of resins, the amount of metallic pigments cannot be added too much, and the amount added is about 1.
5-6%.
If too much, it is not easy to spray, resulting in many effects that cannot be formulated, which limits the use of powder coatings.

.

The bonding process includes a special mixing process.
This special process is used to solve the adhesion problem between the base powder and the metal pigment, so that the metal pigment and the base powder are joined together (see the picture below on the left).
Let the metal pigment have the same resin The same charging performance, breaking through the limitation of the amount of metal pigments, the addition amount in the formula: 1% to 20%
.

c) The instability of metallic effect powder coatings applied by customers

The powder coatings used in the building materials industry are mainly aluminum profiles, ceilings and curtain wall panels.
Aluminum profiles need to be sprayed on four sides and the length is generally about 6 meters, while the ceiling and curtain wall panels have a larger area
.

This all increases the uncertainty during spraying, especially for powder coatings with metallic effects, due to the color difference between the metallic 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, we call it "yin and yang side"
.

2) The color of the ceiling or curtain wall panel is different between two panels or between the middle of a panel and the surroundings.
We call this "flowering or cloud phenomenon"
.

3) The surface of the board becomes rough during spraying, which resembles a sand-grained surface, especially at the corners
.

4) After the customer's level 1 and 2 recycling system, the color difference between the recycled powder and the new powder is large, and the customer cannot add new powder or directly use the recycled powder
.

To sum up, these four problems are all related to metallic pigments, so through the choice of formula and process, to improve the disadvantages of metallic pigments, these problems can be completely solved
.

1) Manufacturing process: Through extrusion and bonding processes, the problem of dispersion of metallic pigments and base powders is solved
.
In the extrusion method, due to the high shear of the extruder, the pigment is destroyed, so special metal pigments must be selected, such as the powdersafe system of ECKART
.

The bonding process, through the selection of equipment and program settings, while retaining the metal effect to the greatest extent possible, the metallic pigment and the base powder are bonded together as much as possible
.

Through these two processes, the roughening and blooming caused by the accumulation of metallic pigments during spraying can be effectively solved
.

2) Formulation selection: including the choice of base powder, metal pigments, and dispersing aids
.

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

The choice of metallic pigments is the soul of the formula.
Two points need to be paid attention to:

1.
The color of the metallic pigment should be as consistent with the base powder as possible to reduce the color difference, which will effectively avoid the yin and yang surface and the phenomenon of cloudiness;

2.
It is the metal pigment that must meet the standard to meet the requirements of the building standard.
If the mortar experiment test is cumbersome, you can quickly detect whether the metal pigment meets the chemical resistance requirements through chemical reagents such as 10% hydrochloric acid and 5% NAOH
.

The chemical reagent droplets are dropped on the powder coating sample plate at a certain concentration.
After the required time is reached, the sample plate is rinsed with water to visually observe the surface where the reagent has been dropped, and compare the loss of aluminum powder
.

The choice of dispersant is the highlight of the entire formula.
An effective dispersant can stabilize the manufacturing process and improve the dispersion and charging performance during spraying
.
The icing on the cake for the entire recipe design
.

3) Strengthen inspection:

The purpose of the inspection is to verify the stability of the metallic-effect powder coatings, find defects in advance, and reduce the chance of customers recurring problems
.
Usually by imitating the customer's site conditions, such as verifying the charging performance of the paint and the color stability after recycling
.

It is also possible to visually observe the bonding effect between the metallic pigment and the base powder by comparing the particle size or electron microscope
.
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 architectural powder coatings, with the increasing global requirements for environmental protection and the continuous improvement of people’s living standards, the application of powder coatings has gradually expanded, and the pace of market development has accelerated, especially for powder coatings with metallic effects.
Due to its brilliant effects and environmental protection characteristics, market demand is expected to be high
.

Of course, there are still some areas that need to be improved and optimized.
I think with the dedicated efforts of the technical engineers of the majority of powder coating companies, the metallic effect architectural powder coatings will surely become a bright star in the architectural coatings industry
.