Basic Research Of Supercritical Carbon Dioxide Assisted Varnish Spraying Process

In the field of coating,a large number of volatile organic compounds are used which can cause environment pollution and risk to human health.The state had started to limit the using of these solvents.Supercritical carbon dioxide is a kind of green solvent.It can be used to replace the volatile organic compounds when is used in coating spraying process and protect the environment.In this paper,through measuring the infrared spectrum and viscoaverage molecular weight of resin,the influence of supercritical carbon dioxide on resin was investigated.A spraying device was built which could add supercritical carbon dioxide into the coating.Different varnishes were used to explore the spraying effect.Fluent was used to auxiliary verification.The specific research contents are as follows:(1)Infrared spectrum and intrinsic viscosity of phenolic resin and chlorinated polyvinyl chloride resin were measured to explore if supercritical carbon dioxide could influence the resin properties.The results showed that under the condition of 55 °C,10 MPa,supercritical carbon dioxide treatment of 5h,Through measuring infrared spectrum,supercritical carbon dioxide didn't change the resin functional groups.Through measuring viscosity average molecular weight,supercritical carbon dioxide didn't change the viscosity average molecular weight.Therefore,supercritical carbon dioxide didn't change resin's properties.(2)On the basis of literature research,the experimental equipment was set up.Using phenolic varnish,vinyl perchloride varnish and nitrocellulose varnish,the influence of temperature,pressure,spraying distance(Distance between the spraying gun and the base plate)and varnish content(Varnish content of varnish and supercritical carbon dioxide mixure)on spraying effect was studied.Varnish content had significant effect on the size of coating droplets.With increasing of varnish content during spraying,the average diameter of coating droplets increased significantly.Pressure had some effect on the size of coating droplet.As the pressure increased,the size of coating droplet decreased.Temperature and spraying distance had little influence on the size of coating droplet.With increasing of temperature and spraying distance,droplet size decreased slightly.Through orthogonal test,phenolic varnish,vinyl perchloride varnish,nitrocellulose varnish's minimum coating droplet were 79.26 ?m?62.94 ?m?65.47 ?m,respectively.(3)Phenolic varnish and nitrocellulose varnish's coating film obtained from coating spraying process could pass GB/T1733-93 water resistance test.Phenolic varnish and vinyl perchloride varnish's coating film could pass GB/T9286 grid method.According to GB/T6739-2006,the hardness of phenolic varnish,vinyl perchloride varnish and nitrocellulose varnish were determined to be 3B,6B and HB,respectively.(4)Spraying process was simulated by Fluent.The independent variables is temperature,pressure,varnish content and nozzle diameter.The dependent variable is diameter of coating droplets.The results showed that diameter of coating decreased with increasing of temperature,pressure and increased with increasing of varnish content and nozzle diameter.