Study On Ultraviolet Aging Resistance Of Polycarbonate Transparent Parts With Silicone Coatings/TiO₂ Films

Polycarbonate?PC?has excellent optical and mechanical properties,but it is easily influenced by UV radiation,friction and wear and other service environment,which result in performance degradation and limit its service safety and service life.Preparation of organic,inorganic and hybrid coatings on PC surfaces can ensure intrinsic performance of PC and add new functions at same time,which make PC parts meet the increasingly complex service environment.This has a certain academic significance and engineering value.In this paper,the PC surface was pretreated by shortwave ultraviolet?UVC?.The chemical sol-gel method and the physical magnetron sputtering technique were combined to prepare the silicone coating and the inorganic TiO₂ film on the PC surface.The effects of UVC pretreatment on the PC structure and PC/silicone coating adhesion were investigated.And the photo-degradation and adhesion failure behavior of PC/silicone coating/TiO₂ thin film system under UV irradiation were analyzed to study its UV aging resistance.The main work includes:1.The mechanism and effect of UVC pretreatment on the adhesion of PC/silicone coatings were studied.The results showed that: The adhesion performance increased first and then decreased with the prolongation of UVC pretreatment time.The reason was that PC surface produced hydroxyl,carboxyl and other polar groups in the early stage of UVC pretreatment.It increased chemical bonding between the substrate and the coating at the interface and enhanced the adhesion.As the pretreatment time was further prolonged,the PC surface produced a low-molecular-weight degradation thin layer,which was easy to break away from the PC substrate with silicone coating and resulted in a decrease in adhesion.2.The UV aging resistance of PC/silicone coatings was investigated.The results showed that: Silicone coatings did not degrade under UV irradiation and have no significant effect on the UV aging behavior of PC substrates.It was due to the Si-O bond in the silicone coating was strong and could not be destroyed and allowed the passage of ultraviolet light and oxygen molecules.The UV aging resistance of PC/silicone coating was slightly improved after UVC pretreatment.The reason was that PC substrate and silicone coating was more closely after UVC pretreatment.This could reduce the infiltration of oxygen at the interface and delay the UV aging process.At the same time,the stress caused by the aging of the ultraviolet aging was reduced and the adhesion failure of PC/silicone coating was delayed.3.The effect of TiO₂ film on the UV aging resistance of PC/silicone coating was discussed.The results showed that: The structure of inorganic TiO₂ film was dense and it could hinder the infiltration of oxygen.At the same time,the UV absorption capacity of TiO₂ could reduce the UV light acting on the PC surface.Therefore,TiO₂ film could obviously improve the UV aging resistance of PC substrate and delay the adhesion failure.The structure of the silicone coating was stable and did not degrade with the inorganic TiO₂ film under UV irradiation.It protected the PC substrate as an intermediate layer and also played a role in the mechanical transition between the PC substrate and the inorganic TiO₂ film.