Studies of UV-cationic hybrid system and its application in inkjet solder resist
Inkjet printing is a relatively novel non-contact printing technology and has broad development prospects with its high efficiency,economy and environmental features in solder resist process.In this study,the curing speed,adhesion,and hardness of UV cured coating were compared,and 3,4-epoxycyclohexylformate-3',4'-epoxycyclohexylmethyl ester(TTA-21)as the cationic monomer for the hybrid system was selected from five commercially available cationic monomers.The TTA-21/1,6-hexanediol diacrylate(HDDA)hybrid system with a mass ratio of 2∶3 was selected as the research object,and its reaction conversion rate,curing degree,thermal performance,thermal stability,and the application of the prepared ink in solder resist were studied.The research results showed that:(1)Under LED illumination,both free radical and cationic components underwent polymerization reactions.The reaction rate of the free radical system was faster and the conversion rate of the reaction was higher.The reaction rate of cationic system was slow and the conversion rate was relatively low.Continuous light exposure in a short period of time could not significantly improve the conversion rate of cationic system.Under photothermal dual curing,the degree of reaction between cationic epoxy ring opening polymerization and free radical double bond addition reaction increased,and the curing process was more thorough.(2)The cured products of the hybrid system had two phases,but the thermogravimetric curve showed only one weight loss curve,indicating that the hybrid system may form an interpenetrating cross-linked network structure after LED heating and baking.There was a certain microphase separation structure between the epoxy component and the acrylic component,which enhanced the overall performance of the cured film.(3)The application study showed that the prepared qualified solder resist ink had the viscosity of 8-14 mPa·s(45 ℃),the surface tension of around 22 mN/m,and the particle size range of 135-150 nm.Its solvent resistance,acid and alkali resistance,and solder resistance could all meet the requirements of solder resist ink.
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