Progress in the preparation of automotive powder c

Foreign automobile powder coating preparation has made progress

foreign automobile powder coating preparation has made progress

December 30, 2005

the traditional powder coating preparation methods are divided into dry method and wet method, and the dominant dry method is divided into dry mixing method and melting mixing method: the wet method is divided into evaporation method, spray drying method and precipitation method. Recently, the industry at home and abroad has taken the opportunity of automobile development to speed up the development of new preparation technologies. Advanced supercritical fluid method (vamp) and OEM coating have come out successively, which not only meet the needs of the manufacturing industry with excellent performance, but also form a platform for their own development

at present, the production of powder coatings mostly uses the melting mixing method. The disadvantages are that it is difficult to change the variety and color, and the particle size distribution is wide, so it is difficult to produce low-temperature curing and ultra-fine particle size powder coatings. Therefore, people have made some progress in improving the preparation process of powder coatings. The development and utilization of supercritical fluid method is called the revolution of powder coating preparation method, which will play an important role in the development of automotive powder coating in the 21st century. Its working principle is: carbon dioxide is liquefied when it reaches the critical point, and the interface between liquid carbon dioxide and gaseous carbon dioxide is clear. If the pressure drops slightly or the temperature rises slightly, it will exceed the critical point, and this interface will immediately disappear into chaos, which is called the supercritical point. Continue to raise the temperature or reduce the pressure, and carbon dioxide turns into a gas. Using this principle, powder raw materials are added to the supercritical liquid processing equipment with stirring device, and supercritical carbon dioxide makes each component of the coating into a separate body, so that the effect of melt extrusion can be achieved at low temperature. The material is spray and granulated in the grading kettle to produce the product. The whole production process can be controlled by computer

the new vamp process developed by Ferro is suitable for processing Automotive powder coatings. It has the following advantages: first, the fully enclosed vamp system avoids the pollution of dust and fiber in the surrounding environment, which affects the cleanliness of powder coatings; Second, the shape of particles can be controlled; Third, the prepared powder coating has excellent triboelectrification performance, so that the powder can penetrate into the inaccessible parts in the spraying process, and the film thickness is uniform; Fourth, it can obtain a thinner film; Fifth, the processing temperature is low, which can prevent parents and students from panicking once a degree, stop the oxidation of GMA acrylic resin, and then prevent the film from yellowing; Sixth, the new process can minimize the pre reaction, which is conducive to the flow and leveling of powder, and has good reproducibility; Seventh, it is conducive to the processing of solidified powder coating at low temperature by testing a steel sample with a certain hardness for several times; Eighth, the crystalline polymer is used to prepare powder coating, which improves the storage stability and reduces the melting viscosity, which has a great impact on the fluidity and leveling of the transparent coating

automotive OEM coating is the development product of modern technology. A kind of ecoclair powder slurry developed by BASF company is especially concerned. It belongs to a new zero VOC varnish system, that is, the powder coating is stably dispersed in water, and the traditional liquid coating equipment is used for construction. According to experts, compared with ordinary powder coatings, it has six advantages: first, it reduces the film thickness. The film thickness of slurry varnish is about 45um, which is equivalent to solvent based coatings, while the film thickness of powder coatings generally needs 60 ~ 70 microns to ensure full leveling; Second, traditional automobile coating equipment can be used for construction. First of all, customers can continue to use their reliable coating system. If ordinary powder coating is used, customers must give up their original construction equipment and construction experience, and once the coating system is polluted, it can be quickly cleaned and easy to replace products; Third, the coating formula is more adaptable. Once the powder coating is ground and crushed, it is difficult to modify the formula. Although the basic performance of the powder slurry is determined by the powder coating itself, many parameters can be improved by additives in the aqueous phase; Fourth, the powder slurry is more uniform, the production batch is larger, and the particle size of the powder is finer; Fifthly, the filtration is more effective. The filter screen hole of powder slurry is smaller than that of ordinary powder coating. The screen hole of filter on automobile circulation line is generally 25 ~ 50 microns, which makes it easier to remove dust and condensate and reduce pollution; Sixth, the leveling property is better. In addition to the properties of raw materials and formula design factors, leveling also depends on particle size, film-forming thickness and wet film viscosity, and then automatically loaded to fracture according to the given loading rate. For powder slurry, the aqueous phase and small particle size are conducive to leveling, and the viscosity during crosslinking reaction has little effect. Therefore, the leveling effect of powder slurry coating is better than that of ordinary powder coating

the preparation of powder slurry is based on acid/epoxy cross-linked transparent powder. The powder coating is obtained by traditional milling process and crushed to 30 microns. It is suspended in water, wet ground to 3 microns, added with additives and filtered to obtain a milky white suspension with pH value of 6.0 ~ 6.5 and solvent content of 2%. The solvent is brought in by additives and pulping process. Only a small amount of additives are needed to stably disperse the powder in water, and the additives used will not affect the coating performance. The solid fraction of ecoclair is 35 ~ 38%, and the rheological behavior of powder slurry is pseudoplastic. At the shear rate of 1000s-1, its viscosity is 150 ~ 200mpa s(23℃)。 The density of the powder slurry is 1.1g/cm3, which is similar to water, and the sediment is easy to stir up. This powder slurry can be used as varnish in the automotive industry. The powder slurry can be applied by the traditional liquid coating process (such as spraying process). The powder slurry used on the primer is generally flash dried first and then baked. The baking temperature can be reduced by 130 ℃, and the film thickness can be reduced to 35 ~ 45 microns

the automotive powder coating industry has also newly developed other preparation processes. Nippon Paint has developed a suspension process for preparing powdered automotive varnish, which solves the problems of storage stability and transportation of powdered paint, as well as the problem of powder loading rate related to powder particles. Experts from China Epoxy Resin Industry Association said that the process mainly includes the following processes: polymerization of epoxy acrylic acid (ester) in solvent or water; Dispersing epoxy curing agent and other additives in the above solution; Add suspension stabilizer to suspend the mixture in water to form particle aggregates with very uniform particle size and shape; Distillation desolvent; dry. The powder produced by this process has a particle size of 12 ~ 13 microns and a narrow particle size distribution, which can greatly reduce the content of fine powder and improve the storage stability and powder loading rate of the powder. An experimental team at Ruhr University invented a gas saturated solution of particles. This technology is to melt the base material and curing agent of powder coating in two mixers respectively, then add them to the static mixer under a certain pressure, inject carbon dioxide to mix them evenly, and atomize this mixed solution through a nozzle. Elbegdorj said that the melt disperses into particles with the expansion of the gas. The particle size of this powder can be adjusted