Preparation And Properties Of Waterborne Polyurethane For Laminating Adhesive

At present,the laminating adhesive used in domestic flexible packaging is mainly solvent-based polyurethane（PU）,which contains a large amount of volatile organic compounds（VOC）and hazardous air pollutants（HAP）.It not only pollutes the environment,but also affects the physical and mental health of workers.Meanwhile,the comprehensive cost is high.Therefore,it does not meet the development direction of the flexible packaging industry.Based on the background,solvent-based polyurethane（PU）must be replaced by environmentally friendly waterborne polyurethane（WPU）.However,the water resistance,transferability,mechanical properties and thermal stability of WPU products are not good in domestic,which limits its application in the field of flexible packaging laminating adhesive.This paper aims to solve these problems and explore WPU in laminating adhesives field with excellent overall performance.In this paper,the appropriate monomer formulation is explored firstly,and then the multi-component copolymerization,nanoparticle modification,and silicone modification are explored to prepare WPU films for laminating adhesive.Firstly,six kinds of WPU emulsions were synthesized by using polypropylene glycols with two molecular weight（PPG1000,PPG2000）and three diisocyanates（HDI,IPDI,TDI）.These emulsions were coated on BOPET release base film,then different series of WPU/BOPET composite films and WPU films were prepared.By analyzing their properties,the preferred monomer and compounding system were chosen.Then multi-component copolymerization was carried out to confirm the preferred formulation.Finally,in order to further improve the performance of these emulsions and films,nano-SiO₂,PDMS and GAPD are used for modification.Fourier transform infrared spectrometer（FTIR）,X-ray diffractometer（XRD）,differential scanning calorimeter（DSC）,scanning electron microscope（SEM）,universal tensile testing machine,thermal gravimetric analysis（TGA）,ultraviolet spectrophotometer are employed to characterize the chemical structure,aggregation state,surface morphology,mechanical properties,thermal stability properties and optical properties of WPU films.In addition,the peel strength between WPU/BOPET composite films was also researched.The results indicate that:HDI-WPU and IPDI-WPU films have good transmittance under visible light,up to 91.81%and 89.74%.IPDI-WPU and TDI-WPU films have higher tensile strength,up to 9.66 MPa and 11.86 MPa.When DMPA content is 6%,the initial R value is 2.0,total R value is 1.2 and the degree of neutralization is 100%,the overall performance of WPUfilms is the best.When the molar ratio of HDI/IPDI is 2:8,the mechanical properties and water resistance of WPU films are good,and the peeling strength of the WPU/BOPET composite films is small,just is 0.25 N/cm.The WPU films have basically met the demand of WPU laminating adhesive.The modification of WPU with nano-SiO₂ can improve the mechanical and thermal properties of WPU films.When the content of nano-SiO₂ is 6%,the mechanical properties are optimal.At that time,the tensile strength and the elongation are respectively23.76 MPa and 470.50%while T_5%and T_10%increase to 256.3℃and 281.3℃,respectively.The modification of PDMS and GAPD can further improve the mechanical properties and thermal properties of WPU films.When the PDMS and GAPD contents are 3%,the tensile strength of the WPU films are25.61 MPa and 19.14 MPa,respectively.At the same time,T_5%increases to 264.9℃and253.1℃,respectively,T_10%increases to 293.8℃and 282.9℃,respectively.The water absorption rates are 8.95%and 9.81%,respectively.The peel strength of WPU/BOPET composite films is as low as 0.14 N/cm and 0.19 N/cm,respectively.Compared to unmodified films,the transmittance under visible light is up to 89.62%and 90.17%,respectively.The modified WPU films have excellent comprehensive performance,which are expected to be used as a laminating adhesive in high-end commodity flexible packaging.