Study On Preparation And Performance Of Waterborne UV Curable Non-isocyanate Polyurethane Coatings

At present,polyurethane(PU)is one of the most widely used polymer materials because of its excellent comprehensive performance.It has been widely used in various industries.Among them,coating is a very important application field of polyurethane,but the raw material of polyurethane-isocyanate and the raw material of isocyanate-phosgene both are highly toxic substances,which will cause serious harm to the environment and human health,and can not meet the more and more demand to environmental protection of our country.Non-isocyanate polyurethane is synthesized without the use of isocyanate.Therefore,it has attracted extensive attention from scholars at home and abroad.Solvent based coatings usually contain large amounts of organic solvents such as benzene.This kind of organic solvent is not only flammable and explosive,will seriously pollute the environment,harm to human health due to its volatilization.Furthermore,volatilization of organic solvents is also a serious waste of resources.However,waterborne coatings can be diluted with water because its solvent is water and exhibit low VOCs.Therefore,waterborne coatings have become the development trend for the industry.Moreover,UV curable coatings exhibit obvious advantages such as fast drying,energy saving,environmental protection.As the consciousness of huan environmental protection increase,the requirements for environmental protection of coatings are becoming stricter.As a kind of environmentally friendly coatings,UV curable cotings have broad application prospects.In this work,the following research work has been done:(1)Using itaconic acid as the source of unsaturated double bond,a series of UVcurable non-isocyanate polyurethanes with high acid value and low hydroxyl value were synthesized by two-step method.The first step is to make ethylene carbonate with moderate price and yield react with different aliphatic diamines(1,2-ethanediamine,1,4-butanediamine,1,6-hexanediamine)to form a series of non-isocyanate polyurethane(NIPU)monomers.The ends of these NIPU monomers are two hydroxyl groups,and their structure was measured through nuclear magnetic resonance.The second step is the melt polyester polycondensation.The prepared NIPU monomers were reacted with itaconic acid to form a series of UV curable non-isocyanate polyurethanes(NIPUs)with high acid value and low hydroxyl value.The structures of these UV curable NIPUs were characterized by NMR and chemical analysis.The results show that each UV curble NIPU molecular chain contains more than two C=C double bonds on average which theoretically indicates that the prepared UV curable NIPUs can be used as the main resin in the UV curable coatings..(2)The stable polymer emulsion was obtained by neutralizing UV curable NIPU with high acid value and low hydroxyl value.Then,the polymer emulsion as the main resin of waterborne UV curable coating,was mixed with photoinitiator DMPA and promoter triethanolamine to prepare waterborne UV curable NIPU coating.The gel content,mechanical properties,thermal stability and coating properties(adhension,flexibility,pencil hardness,water resistance,solvent resistance)of the prepared waterborne UV curable NIPU coatings were characterized.The results show that the gel contents of three waterborne UV-cured NIPU coatings were very high,which indicated that the unsaturated double bond in the itaconic acid exhibit high UV curable activity.Moreover,UV-cured NIPU-B coating has excellent mechanical properties,thermal stability and coating properties due to its high crosslinking dendsity and suitable aliphatic diamine in the NIPU-B molecular chain.It is proved that the prepared UV curable NIPUs with high acid value and low hydroxyl value can be used as the main resins in the UV curable coatings.NIPU-B as the main resin of the UV curable system has a very broad potential application,such as UV curable inks,cotings and adhesives.