Study On The Effect Of Reactive Diluents On The Performance Of Radiation-curable Pressure-sensitive Adhesives

As one of the important types of adhesives,pressure-sensitive adhesives（PSAs）are widely used in industrial manufacturing and daily life because of their good bonding performance,ease to use and peel.Under the national strategy of reducing pollution and carbon emissions,radiation-curing PSAs have become one of the main development directions of PSAs due to their high efficiency,energy saving,no VOCs emission and excellent overall performance.Radiation-cured PSAs,curing by ultraviolet（UV）light or electron beam（EB）,mainly consist of oligomers,reactive diluents and photoinitiators.In recent years,the effect of oligomer on the performance of PSAs has been widely investigated,while the influence of reactive diluent on the performance of radiation-curable PSAs are seldom studied.The reactive diluents have an important influence on the wettability,curing process and cross-linking degree of radiation-curable materials.Therefore,in this study the effect of the functionalities and structures of reactive diluents on the curing rate,adhesion performance,high thermal resistance and other performance of two kinds of PSAs cured through UV and EB were investigated.The first part focuses on the effect of functionalities and structures of reactive diluents on the performance of UV-curable PSAs.A series of PSAs using urethane acrylate（PUA）as the main resin were prepared by changing the types of reactive diluent,photoinitiator addition and UV irradiation dose.The gel content,double bond conversion,glass transition temperature（T_g）,rheology,contact angle,adhesive properties and thermal resistance of the PSAs were characterized by using photo-differential scanning calorimetry（Photo-DSC）,dynamic thermomechanical analysis（DMA）,rotational rheometer,optical contact angle meter and universal testing machine systems.The results of the study show that with the increase of the functional degree of the reactive diluent,the degree of cross-linking and holding power of the PSAs are significantly improved,but the peel strength and tack of the PSAs decreased.The reactive diluents with flexible structures such as long alkyl chains and ether bonds reduce the cohesion and surface energy of PSAs,thus leading to a decrease in the three main adhesive properties（peel strength,tack,holding power）and thermal resistance;the reactive diluents containing five-membered oxygen rings and benzene rings caused slightly reduction of the cohesion of PSAs,increased the surface energy,and have less effect on the peel strength of PSAs;but significantly reduce the thermal resistance.The reactive diluent with hydroxyl and bridge ring structure can increase the cohesion and surface energy of PSAs,which effectively improves the three major adhesive properties and thermal resistance.The second part studied the effect of reactive diluent structure on the performance of EB-cured PSAs.The double bond conversion rate,adhesive properties,elastic modulus and thermal resistance of the PSAs were characterized by total reflection Fourier infrared（FIR）spectroscopy,universal testing machine and atomic force microscopy（AFM）systems.The results show that the reactive diluents with flexible structures such as long alkyl chains and ether bonds significantly reduce the EB cure rate,peel strength and tack of PSAs.the reactive diluents containing hydroxyl groups,bridge rings and other structures can improve the EB cure rate of PSAs,and reactive diluents with hydroxyl groups can improve the three major adhesive properties of PSAs.The reactive diluents containing five-membered oxygen heterocycles,benzene rings have less effect on the EB cure rate and adhesion properties of PSAs.By comparing the performance of EB-cured and UV-cured PSAs,it is found that EB-cured PSAs have higher cohesion and cross-linking,and exhibit better holding power,more than 300%,and better thermal resistance,more than 20°C.The third part further develops research on radiation-curable antistatic PSAs.The effect of the addition of antistatic agents on antistatic properties and other performance of radiation-curable PSAs was investigated based on the results of the first two parts.The surfactant type antistatic agent is more compatible with the PSAs than the ionic liquid type,and the antistatic properties is improved.However,the peel strength of the PSAs with s surfactant type antistatic agent was significantly reduced.The addition of reactive diluents with a five-membered oxygen heterocyclic structure can improve the antistatic properties of the PSAs,the surface resistance of this kind of PSAs can be reduced to 10¹⁰Ωwhen the amount of antistatic agent added is only0.5 wt.%.The thermal effect accompanying the UV curing process helps the surfactant type antistatic agent to migrate to the surface of the PSAs,so the antistatic properties of UV-cured PSAs is better than that of EB-cured PSAs.