Coating technology: application of special effect pigments in powder coatings

Powder coating is widely used in Europe, America and Asia Pacific market because of its high efficiency and durability The innovation of coating technology has opened up a new market for powder coating and has been applied more widely Powder coating can be used in high light, low light, flat light and metal texture finish, and the color is not limited Br > special search effect pigments can create unique and dazzling visual effects for powder coatings In fact, they are suitable for all resin systems Many of them can also be used in outdoor durable coatings and industrial coatings Br > advantages of powder coatings br > br > new option: powder coatings do not emit VOC during curing, which makes them replace more traditional solvent based and water-based coatings Br > high efficiency: powder coating has high efficiency because of its composition: 100% solid, little or no waste It does not require a solvent collection system When necessary, the spray booth can be built in a relatively small space Moreover, because the transfer and curing equipment can be switched, the liquid coating system can be easily replaced by powder coating system Replacement of the liquid transfer system requires a certain amount of cost, but: this can quickly recover the investment by improving efficiency Br > durability: powder coating is more resistant to acid rain and ultraviolet light than liquid coating They have good weather resistance, durability, stone impact resistance and scratch resistance They have been effectively applied to those products that need durability, such as: building board, office furniture, outdoor equipment, home appliances, children's toys, bicycles, car tires, motorcycles Br > special effect pigment for powder coating br > special effect pigment is more and more widely used in powder coating Because it is not only convenient to use, safe and reliable, but also has good decorative effect, it gradually occupies a certain market share of metal pigments in the powder coating industry Br > the largest market of effect pigments is in building coatings, including aluminum building panels and curtain wall panels Gray metallic hue: the most commonly used hue in this application field This kind of tone can be obtained by combining black or gray powder coating with white pearlescent pigment for external use Mica effect pigments: aluminum powder pigments are cheaper and more durable substitutes Metallic pigments need to be coated with another varnish to increase durability and reduce light loss Mica effect pigments do not need another coat of varnish Because of its own chemical inertia Br > pigment and resin mixture br > effect pigment can not be mixed with powder resin by extrusion, grinding and classification, which is a traditional melting mixing process Because this kind of technology will cause the pigment to be broken, which will reduce or even disappear the pearlescent effect of the pigment, the dry mixing technology or bonding technology should be used Br > dry mixing process: specially developed for the treatment of easily broken pigments It uses a P / K drum mixer, a low shear mixer or a mechanical mixer (a henshel machine at low speed) to mix the powder coating and the effect pigment together Uniform pearlescent resin mixture is used to prepare powder coating Bonding process: the resin is heated to a little higher than the softening point, and then mixed with the effect pigment The pigment adheres to the resin to form a whole Br > dosage br > in order to produce metal effect in dry mixing process, the dosage of effective pigment usually accounts for 3% ~ 5% of powder coating The concentration of effective pigment in the bonding process can also be increased Some users use very low concentration search effect pigments (such as 0.25% - 1.0%) as toners The amount of effective pigment depends on the user's requirements Br > effect pigments can be mixed with transparent colorants to obtain different colors Effect pigments should be avoided with opaque pigments or fillers Because these pigments will affect the effect of pigment search Most of the commercialized powder coatings are not transparent, so they can't be dry mixed with effect pigments In these cases, the larger the size of pigment, the better the effect If possible, the powder coating can be processed in two steps to obtain a brighter appearance: first, spray an opaque layer of pigment, partially cure; then disperse the effect pigment in the transparent powder, fully cure, and obtain a deep effect coating Br > Application br > powder coating: the fastest growing surface coating in the coating industry It is very important to understand the shortcomings of current powder coatings This section will briefly introduce some technical problems existing in the use of effect pigments in powder coatings, so as to be solved by powder coating equipment suppliers Researchers are also developing products that can further improve the appearance quality of paint films Br > at present, there are two types of powder coating system: Corona spraying method and friction charged spraying method In order to improve the application effect of the effect pigment in the powder coating, the two coating methods require the effect pigment to be bonded with resin Corona spraying method is more commonly used The application of triboelectric spraying method is less, which is used to paint the parts with complex geometry In the process of corona spraying, in order to transfer the powder coating to the coated object, it is necessary to let the coating pass through an electrostatic field, the coating is negatively charged, and then attached to the coated object with positive electricity Although the dry mixture of powder coating looks uniform, mica effect pigment is inert and is not easy to be charged And whether the powder can be charged: the key to the success of powder coating Br > because mica based search effect pigments are not easy to be charged, they are easy to be separated from those charged search paints in the process of spraying on the coated objects This difference in the charge capacity leads to a decrease in the transfer efficiency of pearlescent pigments In other words, in the process of spraying, some of the uncharged pearlescent pigments fall into the collection system, which will cause many problems The most obvious result: uneven or speckled paint The non charged pearlescent pigment may also accumulate in the bending nozzle, accumulate into a large lump, and then spray on the coated object If this happens, the concentration of pearlescent pigment on the coated object will change constantly, which makes it impossible to get stable film in the daily production operation Br > in addition, if the composition of powder coating is constantly changing when it is used, the concentration of pigment sprayed out is different from the initial concentration of powder, which can not be recycled, so the coating manufacturer has to discard a part of powder, thus affecting the economy of powder coating But: if the effect pigment and resin are bonded together, the above disadvantages can be avoided, and can be recycled or recycled BR> control of current or voltage in corona coating process: very important In most cases, in order to get the ideal spraying effect, the voltage should not be greater than 80kV Higher voltage will cause back ionization This happens in the process of electrostatic spraying, the accumulation of charged powder particles is excessive, and the amount of powder deposited on the substrate is limited The rest of the powder sprayed on the board will be repelled by the powder coating which has been painted in front, forming shrinkage cavity Br > researchers are constantly striving to improve the efficiency of existing spraying technology For example, the future of powder paste technology for automobile varnish is very good In this system, the powder resin is dispersed in water, which improves the flow and leveling of the powder system, and the coating effect is as smooth as the liquid coating The relationship between particle size and performance of br > powder coatings br > fluidization performance of powder coatings affects its application and coating effect If the pigment is used in the composition, the fluidization degree will change with the flow characteristics of the pigment Larger particle size effect pigments will not gather together, shake the packaging container, good liquidity This means that the pigment will not affect the overall fluidization, and will not affect the powder in the hopper and transmission system The larger the particle size of the effect pigment is, the better the effect is in the corona coating process Br > fine or ultra-fine pigments in the powder are easy to agglomerate It can be found that the flake like pigments will stick together, which reduces the efficiency of fluidization and transport system The poor fluidization effect of powder coating will lead to the fluctuation of powder amount through the spray gun When a large mass of powder falls on the coating, it will cause the uneven film On the contrary, the fluidization is too good, the ultra-fine material will be separated from the powder and eliminated through the pipeline, thus affecting the final appearance of the paint film Br > conclusion br > with the increase of the amount of powder coating, the amount of effective pigment also increases Researchers are constantly striving to develop new products and improve the technical level of powder coating.