Study On Preparation And Application Of Silicone Modified Polyester Waterborne Polyurethane

In recent years,the increasing environmental awareness promotes the transformation of solvent-based polyurethane to water-based polyurethane in various fields.The application of waterborne polyurethane(WPU)as water-based ink binders in food packaging and printing field are more widely used.However,WPU ink binders exhibit poor properties in water resistance,thermal stability and adhesion performance on plastic films.In order to solve those problems,the organic silicon is used to modify WPU,preparing modified WPU ink binder with excellent properties.Polycaprolactone diol(PCL),isophorone diisocyanate(IPDI)and dimethylol propionic acid(DMPA)as the main raw materials,a type of waterborne polyurethane(WPU)was prepared by using acetone prepolymer dispersion method and phase inversion process.On this basis,a series of WPU modified by silane coupling agent and polysiloxane respectively were prepared.(1)The effect of feeding stage of silane coupling agent on WPU stability was investigated.It showed that the reaction was difficult to control and easily produced gel by modification at prepolymer stage owing to the strong reactivity of amine.Thus,a mass of solvent was added into prepolymer to reduce the viscosity and removed it via rotary evaporation.Nevertheless,the reaction kept stable and the WPU emulsion had a good stability in modification at emulsification stage.Therefore,the modification at emulsification stage was favorable to the emulsion stability of WPU.(2)Diffrent kinds of silane coupling agent were utilized to modify WPU.The effect of3-aminopropyltriethoxysilane(KH-550)and N-(2-aminoethyl)-3-aminopropyltriethoxysilane(KH-791),on the property of WPU by adding at emulsification stage was investigated.It was found that the property of WPU modified with KH-791 was better than KH-550.Due to the modification with KH-791 and chain extension,molecular weight of polymer increased,and further developed into more branched and cross-linking network,producing WPU with the excellent water resistence,thermostability and adhesion.And then he effect of KH-791 content on the property of WPU was investigated.The result showed the increase in KH-791 content improved the thermostability,water resistance,wetting ability on PET films,the cross-linking density and cohesion strength of WPU film.The hydrolytic hydroxyl of alkoxy group in side chain can react with the active group on PET surface,which improved the adhesion and peel strength on PET films.However,when the KH-791 content was too large,the cross-linking density and cohesive strength of WPU were too high,and the mechanical performance decreased,which would lead to the decrease of peel strength and water resistance.When content of KH-791 was 3wt%,WPU had the highest adhesion strength on PET film,and exhibited excellent water resistance and thermostability.(3)Polydimethylsiloxane(PDMS)was utilized to modify WPU.The effect of the molecular weight(Mn)of PDMS on the performance of WPU was investigated.Result showed that as the Mn of PDMS increased,the degree of microphase separation increased,the emulsion particle size became larger and the stability became worse.In addition,the mechanical properties and peel strength on PET film decreased.However,the surface free energy and water absorption of film decreased significantly.Considering the above consequences,when the Mn of PDMS was 1000,properties of WPU were the optimum.Finally,the effects of PDMS content on the WPU was investigated.The results showed that with increasing the content of PDMS(Mn=1000),the initial decomposition temperature of WPU film increased from 164.6 ? to 198.7 ?,and the water absorption decreased from11.4 % to 5.0 %.And the wetting properties of WPU on PET films improved while the adhesion and peel strength improved slightly and then declined.When the content of PDMS was 4wt%,the WPU exhibited excellent good water resistance,thermostability and adhesion.(4)On the basis of the above researches,waterborne polyurethane modified by KH-791 and PDMS was used to prepare water-based polyurethane ink.And the ink had excellent water resistance and thermostability.The adhesion on PET film was increased from 87% to 100%and 96%,respectively.