Discussion of powder coating de-lighting technology

Introduction: Powder coating as a new type of environmental protection paint, with its excellent characteristics, has become the world's most promising paint. This paper analyzes the principle of de-lighting of powder coatings and discusses the factors affecting the de-lighting.Since the 1970s, with the development of industry, solvent-based coating of air pollution has become the focus of international attention, powder coating with its complete solvent-free, can be converted into coating film, and coating efficiency, protection and decoration of good characteristics, to adapt to the coating industry to save resources and energy, reduce environmental pollution and improve efficiency and other aspects of the requirements, by the world's widespread attention, so as to achieve rapid development . In the past, high-gloss bright paint with its bright colors, bright and other advantages by consumers love; However, with the continuous improvement of people's living standards, weather-resistant low-light powder coating usage shows a larger upward trend, consumers feel the high-gloss bright paint film after the reflective more serious, harmful to the human eye; High-grade varnish coating, with its natural, noble, elegant, attracted the vast number of consumers, the surface of the varnish coating can hide slight paint film defects, so that the appearance of uniform, welcomed by paint manufacturers, medium and low gloss coatings in the future paint market will attract more and more attention. To explore the influence factors of powder coating luster has some guiding significance for the production and use of powder coating.
, the principle of
, coating film gloss (%) is an important indicator for decorative coatings. Gloss is the ability of the surface of an object to reflect light when it is projected on the surface of an object, and is measured by a photoelectrometer in production. The basic principle of powder coating de-lighting is to use various means to destroy the smoothness of the coating, increase the microscopic roughness of the coating surface, reduce the reflectivity of the coating surface to light, powder coating de-lighting has physical and chemical methods. Physical anti-light added anti-light agent, so that the coating in the film-forming process, the surface produces uneven, increase the scattering of light and reduce reflection; Chemical de-lighting is obtained by introducing structures or substumps in coatings that absorb light, such as polypropylene things.
, the main factors affecting the luster of powder coatings
1. The particle size of the powder coating
the surface gloss of the object is closely related to the roughness of the surface of the object, and the diffuse scattering, reflection, scattering and refraction of light to the surface of the object produce the appearance of de-lighting. The larger the particles, the higher the surface microscopic roughness, the better the de-lighting efficiency, but the particle size of the powder can not be too large, otherwise, the appearance of the coating film quality decline, orange peel serious, and the gravity of large particles of powder more than aerodynamic and static electricity, powder coating has not reached the surface of the work piece has fallen, so that the powder rate is reduced. Suitable for electrostitive spray powder coating, particle size control in 20 to 90um is more suitable.
2. Anti-lighting agent addition
anti-light agent is added to the powder coating formula can reduce the film gloss additives, commonly used in metal soap, wax and functional fine materials, mainly through the anti-light agent and film-forming materials between the poor compatible and produce a de-lighting effect. With CH08 powder coating as the object, the addition of a curing agent and coating film gloss relationship is shown in Figure 1.
As can be seen from Figure 1, in a certain range, increase the amount of anti-light agent, the gloss of the coating film decreased, but when the amount of anti-light agent more than 6% but make the gloss slightly increased, the amount of digestive agent in about 7% is more ideal.
3. Filler varieties
Filler de-lighting effect is to use fillers to destroy the flatness of the coating film, resulting in a rough surface. Based on ch08 (epoxy polyester hybrid) product formulation, we examined the light-reducing properties of common filler titanium white powder, precipitated niobium sulfate, Lid powder, and light calcium carbonate, the results of which can be found in Table 1.
can be found in Table 1, the de-lighting performance of the filler sequence is: titanium white powder >secreted radon sulfate> Lide powder> lightweight calcium carbonate. Fillers generally account for 20 to 30% of the overall paint quality, filler additions too much will make the coating surface granulated, seriously affecting the performance of the coating film.
4. Powder coating mixing
The mixed powder method refers to the use of a similar but different reaction activity of this feature, at least 2 powders mixed to achieve the purpose of de-lighting. The results of the mixed test of Hansen Bond and St. Union's 2 companies epoxy polyester powder coatings are below Table 2.
differences in reaction activity or the higher the temperature difference that causes crosslinking, the lower the film gloss. Different manufacturers of polyester resin melt viscosity, reaction activity is different, different ratio of the powder between the surface stress is difficult to achieve the same, so the flatness of the coating film is affected, gloss changes, or even loss of light. However, the use of this method to put into production in large quantities is unlikely, the production process is difficult to control, easy to cause pinholes, shrink holes and other ills.
5. The curing temperature and time of the coating film
Take the CH-08 powder coating curing process as an example, the curing temperature and time and the gloss relationship of the coating film are shown in Figure 2 and Figure 3, respectively.
can be seen from Figure 2: When the leveling temperature is below 120 degrees C, the coating film is basically non-glossy; The gloss rises rapidly above 120 degrees C, reaching 65% at 130 degrees C, reflecting a better leveling effect. For CH-08 high-gloss coatings, the curing temperature requirements of about 180 degrees C can meet the requirements. From Figure 3: Proper extension of curing time helps to increase the gloss of the coating film, after 160s to reach a good leveling state, continue to extend the curing time, gloss change is not obvious. In production, it is hoped that the leveling time is shorter, energy saving, curing time is reduced, and production is increased. In order to obtain a good level appearance and improve gloss, the suspension chain rate needs to be adjusted, and the line speed of ch-08 powder coating spray line is 4.5 to 5.5m /m in, which can meet the requirements of coating thickness and curing process.
Three, conclusion
affect the luster of powder coatings many factors, in addition to the main factors discussed above, there are other methods such as synthetic acid and high acid polyester resin, acrylic series anti-light resin, high-performance anti-light curing agent varieties and other preparation powder coatings to achieve the goal of de-glossing, to meet the growing demand of the market. As soon as possible to develop a good anti-light effect, wide range of anti-light, coating durability, good price and cheap new anti-light curing agent and anti-light resin to prepare low-light, lightless powder coating products, to find a convenient, economical and effective way to eliminate light, is the preparation of low-light powder coating 1 important subject.
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