Study On Bonding Process Of Metallic Powder Coating

Powder coating is a new type coating without solvent.It characterizes by no solvent,zero pollution,environmental protection,energy saving and resource recycling.Its share in coating industry increases year by year.In recent years,functional powder coating has attracted more and more attention.It can be used not only in automobiles,household appliances,metal door,etc.but also in high grade arts and crafts with satisfactory adornment.The key process to make the metallic powder coating in industry is bonding,which makes the metallic pigment particles and the powder coating particles be bonded with each other.The purpose of this technology is to ensure no separation between the metallic pigment particles and the powder coating particles,the uniformity and consistency of metallic pigments in the coatings,the recyclability of the overspray powder.At present,the main bonding process of metallic powder coating in industry is thermo bonding.This method has a large defect,since it needs to control quite precise temperature and time.In the process,if the temperature is too high or the time is too long,the all powders are easy to agglomerate and wasted.Similarly,if the temperature is too low or the time is too short,the process also cannot produce qualified metallic powder coatings.To overcome the disadvantages of the thermo bonding,based on the main raw materials powder coatings,metallic pigment aluminum powders,polyvinyl alcohol(PVA).This study developed a new type of bonding technology which made the powder coatings particles and metallic aluminum pigment particles bond with each other at normal temperature.That is to say,we can process metallic powder coatings at normal temperature.This technology can avoid a series of complicated problems in the traditional industry.Thus,we call this technology cold bonding,compared with the thermo bonding technology.This study tested four different cold bonding methods to prepare the metallic powder coatings.They are high-speed mixing,the improved mixing,jet mixing and the wet-air fluidization.The three former methods are similar and the jet mixing method has the best effect.Further researches in jet mixing show that different glue formulas(PVA glue and extra water)have influence on the bonding effect.When the PVA glue is 0.75 g with no extra water,the difference of the aluminum content between the sample deposited on the test panel and the original sample is minimal(4.29%),the bonding effect is the best.The wet-air fluidization method can be divided into two steps to complete,metal aluminum flakes were firstly coated with polyvinyl alcohol(PVA)glue and then treated in the wet-air fluidized bed with coating powders to achieve their bonding.The influencing factors of wet-air fluidization method,e.g.the relative humidity and flow rate of fluidized gas,fluidization time were investigated.Within the scope of testing range,the optimal bonding effect is achieved when the fluidized gas was saturated wet air,the fluidization time was 10 min and the flow rate was 0.5 L/min.In this paper,the cold bonding method that we studied can reduce the difference of metal aluminum content to about 5% between before and after spraying,which is comparable to the effect of the thermo bonding method.This cold bonding method can improve the production of the metallic effect powder coating,meet the increasing market demand,and expand the application field.It has a huge market potential.