| The synthetic conditions of polyurethane elastomer(PUE) were optimized via orthogonal design using half- prepolymerization.PU coating was modified by nanoparticles. The effects of nano-CaCO3 on the mechanical properties and corresponding dynamic mechanical properties were studied.The properties of PU coating were reinforced via adding pigments and fillers with different structures.Surface defects of the coating film were solved by various additives.Finally,Higher-class PU stone chip-resistant underbody coating was prepared,with wider temperature range of resultful damping and higher loss tangent.Firstly,the preparing processes of PUE were investigated.A liquefacient MDI and polytetrahydrofuran(PTMG) were used as the starting materials,and 1,4-butanediol(BDO) was used as chain extender.The optimal synthetic conditions of PUE were determined as follows:PTMG:MDI=4:6(mass ratio),pouring once as charging method,T=85℃,t=2～3h, -NCO%=6.5%(ultimate),R=1.15.Under this condition,properties of PUE were shown as follows:tensible strength of 4.67MPa,tear strength of 18.92kN/m,shore A hardness of 70, breaken elongation of 484.28%.Temperature range of resultful damping(tanδ＞0.25)was in the range of 5～105℃,and tanδmax was 0.35.Secondly,PU coating was modified by adding nano-CaCO3 and the optimal disperse conditions were obtained.When ingredient B of PU coating was used as dispersion medium,the best adding amount of nano-CaCO3 in the range of 6～8wt%was obtained by the mixed dispersion method(ball mill 6h after ultrasonic dispersion 40min).PU coating with nano-CaCO3 showed higher performance than that of coating without nano-CaCO3, and its tensile strength(5.33MPa) was improved by 14.1%,tear strength(24.82kN/m) was raised by 31.2%,shore A hardness(74)was enhanced by 5.8%,elongation at break (422.98%) was decreased a little.Temperature range of resultful damping(tanδ＞0.25) was in the range of -40～- 120℃which was widen by 60%,and tanδmax(0.43) was increased by 22.8%.Thirdly,The effects of pigments and fillers on properties of PU coating were studied via orthogonal design.Color paste was then obtained from the dispersion mixture by adding 14～16wt%chromic oxide,8～11wt%precipitated baryta,4～7wt%glass flake, 14～17wt%titanic oxide and 2～5wt%saponite.Under this condition,mechanical properties of PU coating was improved,and the glass transition temperature shifted to higher temperature with loss tangent rising.Furthermore,two loss peaks combined into one.In comparison with PU coating without pigments and fillers,the properties of this kind of coating were enhanced.Its tensible strength(8.72MPa) was improved by 63.2%,tear strength(20.32 kN/m) was decreased a little,shore A hardness(78) was raised by 5.8%, although its elongation at break(223.46%) was reduced,it still can meet the index. Temperature range of resultful damping(tanδ＞0.25) was in the range of -15～100℃,and tanδmax was 0.42.Moreover,the surface defects of the coating film,such as lower solidifying,air bubble and sinkhole,were decreased by adding catalyst(0.03wt%DBTDL),antibubbling agent(0.2～0.7wt%BYK-141) and levelling agent(1～2wt%BYK-306).Finally,PU stone chip-resistant coating with wider temperature range of resultful damping and higher loss tangent was prepared.It consisted of half- prepolymer(A) and color paste(B),then it was applied with general spray gun.Panels were sprayed with EP resin as electrocoating.And then,stone chip-resistant coating was sprayed on the steels to a thickness of 200μm.At last,the stone chip test was Carried out using VDA- 508 stone chip test equipment.The test surface was bombarded ten times with 500g steel shots,at a pressure of 0.3MPa.The rating scale of PU stone chip-resistant coating was two.Therefore, it was approved that the obtained PU stone chip-resistant coating showed higher performance than domestic T-5H coating.It met the request of stone chip-resistant,and it can be widely used as stone chip-resistant underbody coating for motorcar,tank,armored car and so on.
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