| At present,commercial vehicle coatings in our country are mainly solvent-based coatings,especially topcoats with relatively high decorative properties.Pushed by the trend of advocating ecological civilization and environmental protection in the whole world,as well as the policy call of the construction of beautiful China since the 19 th Congress,it is imperative for the automotive industry to pay more attention to waterborne paint,and the demand for waterborne paint by users will increase explosively.Therefore,the development of waterborne paint for commercial vehicles has become a hot research topic in the recent years in China.Compared with passenger cars,commercial vehicle coatings have their own characteristics,and their surface decoration requirements are relatively low.The bottom surface of commercial vehicle coatings is integrated with waterborne automotive coatings.Because of its combination of primer corrosion resistance and high decorative finish,and one-time coating,it is simple in process,safe and environmentally friendly,and is well received by users.It is currently a research hotspot in the field of anti-corrosion protective coatings.However,the high anti-corrosion and high decorative properties of coatings are often contradictory,and it is difficult to obtain both.At the same time,the application research of commercial vehicle waterborne topcoat will lay a foundation for the comprehensive waterborne topcoat in the future.This thesis mainly studies the high gloss and salt fog resistance of the waterborne paint film and the influence of the coating process on the heat rash,sagging and oil pit of the surface during the coating process of the waterborne automotive topcoat.The thesis is divided into four parts:The first part is the introduction of the domestic and foreign automotive coatings market and technical application.It describes in detail the waterborne progress of automotive coatings in China,and focuses on the current situation and existing problems of commercial automotive waterborne coatings in China.At last,the research purpose,content and innovation of this paper are summarized.In the second part,a theoretical method for the calculation of the glossiness of waterborne paint with high gloss is reported.The theoretical glossiness of waterborne coatings can be calculated from the specular reflectance R of coatings by Fresnel formula based on the refractive index of various materials.The theoretical calculation method has been verified by a large number of practical samples.The results show that the refractive index of waterborne paint is additive if the resin has good compatibility.As long as the surface of the paint film is smooth and flat,the calculated value of the glossiness at 20 degrees and 60 degrees is very consistent with the measured value.The theoretical calculation method can guide the design of high gloss waterborne paint products and improve the formula test efficiency.In the third part,a novel one-coat waterborne automotive paint with high gloss and good salt fog resistance property is reported.The effects of different kinds of resins and antirust pigments,different amounts of driers,crosslinking agent,and coating process on salt spray resistance,gloss and early hardness of the paint film are studied.The molecular structure of the resin and paint film are characterized by Fourier transform infrared spectroscopy,and the effects of different drying processes on the crosslinking and curing of the paint film are compared and analyzed by thermogravimetric method.The results show that when the dosage of the drier is 0.4%,the fineness of the paste below 10 ?m,the application viscosity about 30 s,and baking above 80? for 20 minutes,salt spray resistant time of the prepared paint film under the conditions is exceeding 504 hours,gloss more than 80°,hardness up to HB after placing for 48 hours.It was increased for dryness of paint film by adding 1.5% crosslinking agent XL701 when temperature lower than 10 °C in winter.The fourth part studies the influence of the coating process on the heat rash,sagging and oil pit of the surface during the coating process of the waterborne automotive topcoat.In this paper,modified waterborne alkyd resin is physically blended with waterborne acrylic resin to prepare two-component waterborne topcoat.The effects of viscosity and application film thickness of waterborne paint on the heat rash,sagging and oil pit of waterborne automotive topcoat are discussed.The results show that: the degree of heat rash on the surface of the paint film can be reduced by controlling the film thickness and the curing agent dose.Reducing the film-forming thickness or increasing the viscosity of the paint can reduce the sagging of the waterborne automobile finish paint.Adding an appropriate amount of defoaming agent can reduce the oil pockets of the film,but adding too much will make the surface of the paint film worse.Proper addition of leveling agent and wetting agent can avoid the generation of oil pockets of the paint film. |
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