Synthesis And Properties Of Amino Resin/Silica Modified Waterborne Polyurethane Coating

Waterborne polyurethane(WPU)coating is an environmentally friendly coating that uses water as a dispersion medium.The composition of WPU does not contain volatile organic solvents and has the advantages of safety,non-toxicity,and low VOCs.However,traditional one-component WPU needs to introduce sufficient hydrophilic groups on the molecular backbone and reduce the rigidity of the molecular structure to ensure that the WPU has good dispersion in water,which leads to the disadvantages of mechanical properties,water resistance and heat resistance of the WPU coating.In order to overcome the above shortcomings,this article mainly makes the following work(1)One kind of hydroxyl-terminated waterborne polyurethane(HWPU)with internal cross-linking structure is synthesized by toluene diisocyanate(TDI80),poly(1,4-butylene adipate)(PBA1000),trimethylolpropane(TMP),2,2-bis(hydroxymethyl)butyric acid(DMBA)and neopentyl glycol(NPG).The effect of R value,DMBA content,NPG content,TMP content on the stability of HWPU emulsion and the properties of HWPU coating were studied.The results show that when the R value is 0.85,DMBA content is 4.5 wt%,NPG content is 8.5 wt%,and TMP content is 5.0 wt%,a HWPU emulsion with particle size of 65 nm,translucent appearance and good stability was prepared.The pencil hardness of the HWPU coating is HB,the adhesion is 0 level,the impact strength is above 50 kg·cm,temperature of the extrapolated onset is 254°C,and the water absorption rate is 8.09%.(2)One kind of silica crosslinking modified HWPU was prepared by the hydrolysis and condensation process of TEOS and KH560 in HWPU as well as the reaction of epoxy group and carboxyl group.When the content of KH560 is 1wt% and the content of TEOS is 3?7wt%,the modified emulsion is stable.The pencil hardness of silica modified HWPU coating has a slightly increase.Temperature of the extrapolated onset achieves to 271 ?,water absorption rate reduces to 5.10?6.28%,and the minimum water contact angle is 74.1 °.(3)One kind of crosslinking modified HWPU was prepared by using Cymel325.Through the reaction of alkoxy groups on Cymel325 with hydroxyl and carboxyl groups on HWPU,a high degree crosslinking is build in HWPU coating.When the content of Cymel325 is 30wt%,the pencil hardness of the modified coating significantly improves to 3H,the impact strength reduces to 42kg·cm,the adhesion level is 1,temperature of the extrapolated onset increases to 268?;the water absorption rate of the coating decreases significantly to 2.94%(4)One kind of HWPU which modified simultaneously with 1wt% KH560,5wt% TEOS and 30wt% Cymel325 was prepared.The modified coating maintains good mechanical properties and water resistance.The temperature of the extrapolated onset is further increased to 279°C.Moreover,the surface of the coating is smooth and flat,without defects such as bubbles.