Difficulties in the Bonding process of metal-effect powder coatings

China Coatings Online News:
Metal powder coating manufacturing process mainly has the following preparation methods:
1)
extrusion method:
that is, before extrusion, flaky metal pigments are treated like other pigments, and then mixed with all other raw materials. The disadvantage is that, with the exception of special formulations, the vast majority of metal pigments are crushed during extruse.
2)
dry mixing method:
simple, economical, most domestic manufacturers use this method, however, due to the good conductivity of metal pigments, so that the construction performance of coatings is very poor, for example, metal pigment separation, spray gun short circuit and so on. Also because the metal pigment is only loosely mixed in the base powder, it is an isolated part of the entire coating. Dry mixing method, the addition of metal pigments in 1.5%-6% or so, such as too much is not easy to spray.
3)
a special
mixing procedure is included in the Bonding French Bonding process. This special procedure is used to solve the attachment problem between the base powder and the metal pigment, so that the metal pigment is connected with the base powder, the pigment in the formulation added quantity: 1% to 20%.
The earliest Bonding equipment are developed and produced by foreign companies, because of its high price, domestic equipment suppliers powder coating production enterprises generally use dry mixing or domestic bonding equipment, with the continuous efforts of domestic suppliers, domestic equipment in the process has made considerable progress, but compared with imported equipment, Bonding process still has the following needs to improve:
1. Precisely control the temperature of the raw material.
2. The temperature of the raw materials in the mixing pot should be the same.
stability and repeatability of the process.
In addition to the choice of Bonding equipment, in the manufacture and construction of metal effect powder coatings, there are still the following problems to be solved:
(1) powder coatings with a small variety of metal pigments, small selection range, poor performance That is, aluminum and silver powder pigments, pearlescing pigments, copper and gold powder pigments and other metal pigments (e.g. nickel powder, stainless steel powder, etc.). Each type of metal pigment also contains a lot of color products, through the powder manufacturer's formulation design, applied to the powder coating, it makes the powder colorful, greatly enriched the variety and decoration of the powder coating.
due to the properties of the metal pigments themselves, there are fewer types of metal pigments that can meet the needs of high performance, and now only weather-resistant grade pearlesic powders and a small number of aluminum powders can meet limited high-end needs. In aluminum powder, because of the livelyness of aluminum pigments, easy to react with water and alkaline substances, such as in accordance with the standards of the construction industry, mortar experiments and detergents and other experiments are not passable, so that the construction powder coating metal effect is very poor, and paint gap is large, which also makes powder coatings in many construction projects can not compete with in particular. Therefore, a small number of foreign aluminum powder suppliers after research and development launched weather-resistant aluminum powder, aluminum powder particles after a number of parcels (acrylic resin and silicon dioxide), improve its chemical resistance, after testing in powder coating applications, most can meet the requirements of the building, but fine-grained metal pigments, in the unstable mixing process, easy to produce fragmentation, resulting in performance decline. The advantages of pearl powder is that the pearl pink phase is more, good chemical resistance, the disadvantage of metal texture is not strong, compared to aluminum powder gap is too large. Pearl powder selection is also more demanding, must be through a special package of weather-resistant level products, which many domestic manufacturers ignore the requirements in this regard, the industrial-grade pearl powder applied to ultra-weather-resistant products, bringing quality hazards.
material limitations make the development of metal-effect powder coatings somewhat hindered. But the good news is that many material suppliers continue to innovate in technology development, coupled with more innovative production processes, these problems have been solved.
(2) the state of metal pigments and substrates in the production process isDry mixing process or incomplete binding process, will cause the base powder and metal pigment part and complete separation, pigment dispersion in the base powder uneven, spray sample when the color effect is affected by voltage, atomization and powder output, small samples and production mixture between the large difference, resulting in instability of the formula. Also because the conductivity of metal pigments is higher than resin, metal pigment additions can not be too much, plus the amount of about 1.5-6%, such as too much is not easy to spray, resulting in a lot of effects can not be made, limiting the use of powder coatings.
So improving the efficiency of the Bonding process is the direction of the major manufacturers are committed to the development, stable production process is used to solve the problem of the adhesion between the base powder and the metal pigment, so that the metal pigment and the base powder linked together. Let the metal pigment has the same charged properties as the resin, and through the design of the formula, break through the limit of the amount of metal pigment, add the amount in the formula: 1% to 20%, the real can be comparable with the paint.
(3) metal effect powder coating in the customer's construction instabilityThe materials industry uses powder coatings mainly aluminum profiles, ceilings and curtain wall panels, aluminum profiles have four sides to be sprayed and the length is generally about 6 meters, and the ceiling and curtain wall panel area is large, which increases the uncertainty of spraying, especially the metal effect of powder coatings, due to the color difference between metal pigments and base powder, it is easy to cause the following problems:
1) aluminum profile four The color of each surface and the head and the middle color is not consistent, we call it "yin and yang surface"
2) ceiling or curtain wall board, between the two boards or the middle of a board and the color is not the same as around, we call the "hair flower or cloud class phenomenon"
3) spraying when the surface of the plate becomes rough, similar to the sand surface, especially in the corner area.
4) after the customer's 1 or 2 levels of recycling system, the color difference between recycled powder and new powder is large, customers themselves can not add new powder or directly use recycled powder.
, all three problems are related to metal pigments, so through the choice of formula and process, improve the disadvantages of metal pigments, to completely solve the problem of writing.
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