Study On The Preparation And Performance Of UV Delayed Curing Adhesive

Ultraviolet（UV）light curing technology has many advantages of fast curing speed,the absense of volatile solvents,low VOC emission,energy saving,environmental protection and many more,which has developed rapidly and has many applications in transportation,construction,packaging,labeling and many other fields in the past ten years.However,the development and application of UV curing technology is limited owing to UV curing technology have many disadvantages,such as limited curing depth,dark-coloured materials,application problems in opaque substrates.For adhesives,due to the adhered substrate is opaque in most application scenarios where the light penetration is inhibited,which cannot initiate photopolymerization at the interface between two substrates.Therefore,how to solve the effective light curing of photocurable adhesives between opaque substrates has important research significance and application value in the field of UV curing adhesives.In this paper,two types of one-component UV delayed curing adhesives were prepared by choosing the types of photoinitiators and matrix resin,which can be applied for bonding between opaque substrates,apply a layer of adhesive on the surface of the substrate,after UV irradiation,which cannot quickly induce photopolymerization,and requires a long induction period,with rapid complete reaction following the induction period.This operating approach could provide enough time effectively and predictably to achieve the purpose of initial fixation between bonded substrates,following achieve curing completely by post-curing mechanisms in a short time.The specific research content is divided into the following two parts:（1）A series of one-component UV curing epoxy adhesive with delayed curing properties was prepared by matrix resin of epoxy acrylate（EA）,1,6-hexanediol diacrylate（HDDA）,epoxy（E51）,joining the Pentaerythritol-3-mercaptopropionate（SH4）as curing agent.Especially we use the photobase generator together with photosensitizer ITX（isopropyl-thioxane）asthephotoinitiatorsystemandusing2,2,6,6-tetramethylpiperidine-1-oxy radical（TEMPO）as radical inhibitor to inhibite free radicals generated by photosensitizers after UV irradiation.The delayed curing properties and mechanical properties of the adhesive system with different component proportions were studied by tensile shear test.The thermal mechanical properties and thermal properties of the cured adhesive were characterized by dynamic thermomechanical analyzer（DMA）,differential scanning calorimetry（DSC）and thermogravimetric analyzer（TGA）.The results show that,with the quality ratio of epoxy acrylate,1,6-hexanediol diacrylate and epoxy resin E51 reacts with sulfhydryl groups to form a cross-linked network was 30:30:40,and adding 1wt%of photobase generator TBD?HBPH₄,after UV irradiation for 20 s,the adhesive coated on stainless steel substrate can provide at least 2 min delayed curing window,the adhesive can produce a certain initial bond strength within 20 min,realizing the fixation between the two substrates.At room temperature for 3 h,the initial bonding strength of the adhesive is 0.71MPa.The tensile shear strength of UV adhesive can reach 4.32 MPa after fully cured at 80℃for 2 h.And the initial thermal decomposition temperature is more than 290℃,which has good thermal stability.（2）A series of one-component UV curing epoxy adhesive with delayed curing properties was prepared by mixing bisphenol A type epoxy resin with different kinds of epoxy active diluents at certain stoichiometric ratios and adding sulfonium salt as photoinitiator.The delayed photocuring properties and mechanical properties of adhesive systems with different reactive and photoacid generator diluents were studied by tensile shear test.The thermomechanical properties and thermal properties of the adhesive systems were investigated by dynamic thermomechanical analyzer（DMA）,differential scanning calorimetry（DSC）and thermogravimetric analyzer（TGA）.And the viscosity was measured by rheometer to reflect the storage performance of the adhesive system.The results show that,with 25 wt%of trimethylolpropanetriglycidylether（EP3）as active diluent,after UV irradiation for 10 s,the adhesive coated on stainless steel substrate can provide about 3 min delayed curing window,to complete the bonding operation between the substrate,and the adhesive can produce a certain initial bond strength within 10 min,realizing the fixation between the two substrates.After fully cured,the tensile shear strength of the adhesive can reach 3.42 MPa,which has good bonding properties.With adjusting the content of active diluent in the system,the delayed curing time of the adhesive can be effectively controlled from 2 min to 20 min.The results of TGA show that the adhesive has good thermal stability and the initial thermal decomposition temperature is more than 300℃.In addition,the adhesive system can be stored at least 90 d at a temperature of 50℃.Therefore,it is demons-trated that the single-component photocurable adhesives prepared in this paper have the characteristics of delayed curing and can be applied to the adhesion between opaque substrates.At the same time,they have good adhesion strength and storage stability at room temperature.The application prospect is broad.