Study On Preparation And Coating Properties Of UV-curable Cationic Waterborne Polyurethane

Cationic waterborne polyurethane has a broad market prospect in the fields of coatings,leather,textiles and paper making for a large number of positive charges in its main chain.At present,due to the shortcomings of complex technology and poor emulsion stability,cationic waterborne polyurethanes have relatively few applications and research reports,especially the research on light-curing polyurethane emulsifiers.In view of the current research situation,a one-step synthesis of polyurethane prepolymer was carried out in this paper,which was then terminated with pentaerythritol triacrylate and neutralized with acetic acid to obtain a series of cationic self-emulsifying photocurable polyurethane.On this basis,a series of cationic photocurable polyurethane emulsifiers were synthesized by changing the formula,and used as a reactive emulsifier to emulsify the oily UV curable resin.Finally,modified by nano-alumina to enhance the abrasion resistance of the light-cured coating.Firstly,a series of self-emulsifying cationic light-curing polyurethanes with different linear and branched structures and MDEA content were prepared from polylactide（PLA）,N-methyldiethanolamine（MDEA）,trihydroxy branched monomer（T01）,isophorone diisocyanate（IPDI）,methacrylate（HEA）,pentaerythritol triacrylate（PETA）etc.The structure was characterized by FTIR and ¹H-NMR.The effects of neutralization degree,MDEA content,branched structure on the stability,and properties of light-cured cationic waterborne polyurethane emulsion were systematically studied.The results show that with the increase of neutralization degree and MDEA content,the stability of the dispersion increases,the particle size decreases,and the hydrophilicity of the photocurable polyurethane increases after the introduction of branched structure.When the MDEA content is 6 wt.%and the neutralization degree is 90%,the dispersion has the best performance.The thermal storage at 60℃is normal for 15 days,the viscosity is 23.6 m Pa·s,and the average particle size is 229.5nm.The curing process of the coating was monitored by FTIR.The results showed that when the photoinitiator 1173 content was 3 wt.%,the C=C conversion rate tended to be stable after curing for 45 s at 40m W/cm²ultraviolet light intensity.The C=C conversion rate of the coating decreases with the increase of MDEA content.When the MDEA content is 5 wt.%linear structure,the C=C conversion rate reaches 91.47%.After introducing the branched structure,the C=C conversion rate of the coating decreases.The physical and media resistance properties of the cured coating were tested,and the results showed that with the increase in neutralization degree and MDEA content,the hydrophilicity of the coating increased and the media resistance property decreased.Secondly,based on the self-emulsifying photocurable polyurethane acrylate,a series of photocurable polyurethane acrylate emulsifiers were prepared by changing the raw material ratio.The effects of IPDI drop acceleration,end-capping temperature,amount of polymerization inhibitor and end-capping agent on the reaction were studied.The results showed that the suitable reaction conditions were:IPDI drop acceleration was 1.5 m L/min,end-capping temperature was 70℃,polymerization inhibitor dosage was 6 wt‰,and end-capping agent HEA:PTEA was 7:3.The polymer structure was characterized by FTIR and¹H-NMR,and the results showed that the expected product was successfully synthesized.The particle size and stability of the emulsion were studied using laser particle size analyzer,thermal storage and high-speed centrifugation.The results show that the introduction of branched structure,increasing the degree of neutralization,the content of MDEA and emulsifier can increase the stability of the emulsion.Compared with the linear structure emulsifier,the amount of emulsifier dropped from 50%to about 30%after adding branched structure.When the neutralization degree is 120%,MDEA/PLA is 3/1,and T01:PLA is 1:6,the emulsifier emulsifies the commercial polyurethane R03 with a mass ratio of 3:7 to obtain a stable emulsion.The thermal energy storage at 60℃is stable for more than 60 days,the average particle size is 0.68μm,and it is centrifuged at 3000 r/min for 15 min.FTIR was used to monitor the curing process of the paint film.The results showed that when the photoinitiator 1173 content was 3 wt.%,the C=C conversion rate tended to be stable after curing for 60 s at 40 m W/cm²ultraviolet light intensity.The double bond conversion rate increases with the increase in the amount of emulsifier.After adding branched structure,the performance of the paint film is significantly enhanced.The hardness of the paint film prepared by emulsifier PUAE-B5 emulsified R03 is 3H,the adhesion is 0-1 grade,and it has excellent media resistance.PUAE-B5 can be compounded with commercial polyurethane R03 and R09 to control the performance of its light-cured paint film,and the hardness of the paint film can be adjusted between B～3H.Finally,KH-570 was used to modify nano-alumina with different crystal forms.The grafting amount of KH-570 and the stability of nano-alumina were characterized by FTIR,sedimentation experiment and centrifugation.The results showed that the grafting amount of KH-570 and the stability of nano-alumina suspension increased first and then decreased with the increase of KH-570 content.When the KH-570content is 0.7 wt.%,the grafting amount is the highest,and the nano-alumina suspension is the most stable.A steel wool abrasion tester,FTIR and ultraviolet spectrophotometer were used to study the abrasion resistance,double bond conversion and light transmittance of the cured coating.The results show that with the increase of nano-alumina content,the abrasion resistance of the coating first improved and then decreased,and the double bond conversion rate and light transmittance decreased.When the contents of modifiedα-Al₂O₃andγ-Al₂O₃are 1.00 wt.%and 0.75 wt.%,respectively,the coating performance is optimal.The coating is scratched by steel wool for 4000 times under a pressure of 25.5 k Pa,and the coating hardness is up to 5 H,Adhesion is 0～1 grade,and has excellent resistance to acid and alkali,alcohol resistance,water resistance,high adhesion and other properties,the light transmittance in the 700 nm band is 90.29%and 97.75%.