Preparation of powder coatings with aluminum profiles for outdoor use

Zhang Jianfei, Chen Yubin, Tian Yongfeng, North Coatings Industry Research and Design Institute
Resum
introduced the formulation, production process and performance indicators of powder coatings for outdoor aluminum profiles, and discussed various factors affecting coating performance.
1, introduction
in the environmental issues are increasingly concerned today, the world's paint production VOC content control more and more strict. Powder coatings because of its low pollution, high environmental protection, high utilization rate and so on, in the industrial coatings industry accounted for a growing proportion

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metal profiles are widely used in the construction industry because of their excellent durability, decoration and process molding. Aluminum profiles, because of their good processing performance, light weight and so on, accounting for more than 80% of the amount of metal profiles, powder coatings in the application of aluminum profiles has been rapidly growing.
powder coating spray aluminum profile, compared with anode oxidation, electrophoresis coating surface treatment methods, water and air pollution and energy consumption significantly reduced,
coating mechanical properties such as hardness, wear resistance, impact resistance and other indicators are greatly improved, service life than ordinary anode aluminum profile is 1 times higher, and rich colors, more reflect the diversity and individuality of the building.
At present, powder electrostectrical spraying has become a hot spot in the surface coating of aluminum profiles in China, and the combination of powder spraying and thermal transfer technology will make them more fashionable, so that powder spraying profiles have more room for development.
2, preparation of aluminum profile powder coatings
2.1 Raw materials
isocyanate trisornate glycerides (TGIC), end-oxycodone polyester resin, hydroxyamide (HAA), titanium white powder, ultra-fine sulphate, sabbath, leveling agent GLP588, luminescent agent BLC701, polyethylene wax, anti-light, ultraviolet agent, antioxidant, etc.
2.2 Production equipment
MIX-5 premixer, EX30 twin screw extruder, air-cooled track-type chip crusher, ACM-2 vertical grinder (ACM grinding), high-voltage electrostature spraying equipment, etc.
2.3 Production process
a general powder coating preparation process: premixed, high-temperature melt extrusion and crushing.
2.4 Base Formula for Aluminium Profile Powder Coatings
Table 1 for Aluminum Profile Powder Coatings.
2.5 Aluminum profile powder coating performance
aluminum profile powder coating performance test results can be found in Table 2.
3, results and discussion
3.1 end of the choice of pyride polyester resin
as aluminum profile powder coating, not only with excellent weather resistance and physical mechanical properties, but also have good decorative properties.
This allows the selected polyester resin to take into account the leveling and reactive properties, i.e. low melting viscosity and suitable Tg, so that we can get a comprehensive performance of excellent aluminum profile powder coating. The test results for the performance of powder coatings prepared in different specifications of polyester resins can be found in Table 3.
from Table 3, the specifications of polyester resins have a greater impact on the performance of the prepared powder coatings. Tg of resin is very important for the storage stability and crushing of powder coatings, and when Tg is low, the prepared powder coatings are easy to condense when stored, affecting the use.
viscosity of polyester resin directly affects the appearance of the coating film. Because the leveling process of powder coatings is different from oily coatings, this requires the choice of polyester resin, under the premise of meeting mechanical properties, melting viscosity as low as possible, so as to facilitate the preparation of a flat appearance of the coating film.
3.2 curing agents
Usually, the varieties of curing agents used in weather-resistant polyester powder coatings are mainly TGIC and HAA. With HAA-cured polyester powder coating in baking curing to release water and other small molecular compounds, coating is easy to produce pores and other ills.
, the coating appearance and various properties of polyester powder coatings cured with TGIC are relatively good. The test results for coating properties prepared with 2 curing agents are available in Table 4.
aluminum profile with powder coating on the appearance of higher requirements, so generally choose TGIC with end-based polyester resin as the main film-forming substances. Figures 1 to 2 are the reactions of end-to-end pyride polyester resins to TGIC and HAA.
3.3 Pigment selection
Since aluminum profile powder coatings are weather-resistant coatings for outdoor use, in addition to heat-resistant pigment varieties, light resistance is required to reach 7 to 8 (8 best), weather resistance to 4 to 5 (5 best).
is not suitable for the selection of poor weather resistance of sharp titanium-type titanium dioxide powder and easily powdered calcium carbonate and other fillers, taking into account the coating requirements have a good appearance, can not choose a large amount of oil-absorbing fillers, such as talcum powder, mica powder. Finally, ultra-fine nihilite sulfate and gold-redstone titanium dioxide were selected as the filler parts of aluminum profile powder coating.
3.4 Additive Selection
Additives are an important part of powder coating formulations and, although they are used in small quantities, their effect on powder coating and coating properties cannot be ignored. In some cases, additives play a decisive role.
3.4.1 leveling agent
leveling agent is the role of powder coating melt flow usually on the surface to form a very thin single molecular layer, in order to reduce surface pressure, overcome the hole and other ills.
Taking into account the weather resistance of the coating film, the 503 series of leveling agents can not be selected for epoxy resin as the carrier, the general leveling agent GLP588 is SiO2 dispersed acrylates leveling agent, its active ingredient is polyacrylate and dispersion carrier SiO2. The effect of leveling agent dosage on the appearance of the coating film can be found in Table 5.
the test results show that when there is no leveling agent or leveling agent dosage is too small, the coating film has a shrink hole, with the increase of leveling agent dosage, the appearance of the coating film is better, but when the leveling agent dosage exceeds 1.5%, the coating film resistance is poor, so the final selected leveling agent dosage is 1.0% to 1.5% of the total powder.
3.4.2 anti-light
in powder coatings, the anti-light of the coating film is mainly divided into physical and chemical de-lighting 2 kinds. In general, physical anti-light agents can provide 20% to 70% (60 degrees) of film gloss, while chemical anti-lighting can reach less than 10%.
, the anti-lighting agent used as aluminum profiles is generally a physical anti-lighting agent, which in turn occupies the main market with a variety of modified wax-type anti-lighting agents.
wax-type anti-lighting agent can not only reduce the film gloss, but also improve the scratch resistance of the coating film. However, when the use is too high, there will be a series of ills such as powder sticking, storage stability and so on. Therefore, it is very important to choose the right anti-light agent. The following questions should be considered in the selection of anti-light agents.
(1) matching with film-forming substances: coating film de-lighting is caused by the presence of incompatible substances in the system, so different resin systems should be paired with different types of anti-lighting agents.
(2) coating appearance: Due to the high leveling requirements of aluminum profile powder coatings, caution is required for detergents that contain active ingredients. If the amount of use is too high, the film orange grain is heavier, and even appear wrinkled, sanding phenomenon.
(3) on the mechanical properties of the coating film: different models of anti-light agents on the mechanical properties of the coating film is affected, especially reflected in the impact resistance of the coating film. The use of anti-light agent is too high, which will cause the film resistance to shock is good and the reverse punch is not good phenomenon.
3.4.3 Other additives
As an aluminum profile powder coating for outdoor use, it is necessary to add the appropriate amount of UV absorbers, antioxidants, etc. to the formulation.
polyethylene wax can help improve the scratch resistance of the coating film, but its yellowing resistance is poor, for light aluminum profile powder coating, while improving the scratch resistance of the coating film should also consider the film's yellowing resistance.
4, conclusion
developed aluminum profile powder coating production process is stable, in line with the design of aluminum profile coating appearance and performance requirements, product performance leading domestic. If the product can be further popularized and applied in the market, it is of great significance to promote the development of domestic aluminum profiles and technological progress.
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