Synthesis And Performance Study Of Two-Component Polyurethane Coatings

At present,the polyurethane coating market is still dominated by solvent-based twocomponent polyurethane coatings,which are widely used in clothing and footwear,civil construction,municipal engineering,rail transportation,coastal port equipment protection and other fields,but also for the high-end industrial anti-corrosion coating field,with excellent protection and decorative effect.As environmental awareness increases,solventbased polyurethane coatings will be gradually replaced,but high strength,high performance solvent-based polyurethane coatings still have market value.Therefore,the aim of this paper is to study the influence of various factors on coating performance in two-component polyurethane coatings;to synthesise the optimum ratio of polyurethane coatings with excellent performance;and to conduct a cross-sectional comparison study with wet-curing polyurethane coatings.In this paper,a series of wet-cured polyurethane coatings(MCPU)with different isocyanate index(R-value)were firstly synthesised using isophorone diisocyanate(IPDI),polyether diol(N-220)and polyether triol(N-330)as monomers.It was found that the tensile strength of the coating films increased from 2.3 MPa to 6.6 MPa and the strain at break decreased from 693% to 295% as the R-value increased;the contact angle on the surface of the MCPU films gradually decreased and the water resistance decreased;the thermal stability of the coating films first increased and then decreased.The mechanical properties of the coating were significantly improved by the addition of nano-silica.Then,a series of two-component polyurethane prepolymers with different isocyanate index(R-value)and different molar ratios of two polyether polyols were synthesised using isophorone diisocyanate(IPDI),polyether diol(N-220)and polyether triol(N-330)as monomers.The two-component polyurethane-polyurea coatings(PUU)with a total R value of 1.1 were then prepared by reacting with a curing agent component consisting of4,4’-submethyl-bis(2-chloroaniline)(MOCA)and polyethertriol(N-330).The relationship between PUU coating film properties and R-value and polyol molar ratio was investigated.It was found that as the R value increased,the tensile strength of the two-component polyurethane-polyurea film increased from 0.79 MPa to 2.70 Mpa and the strain at break decreased from 813% to 307%;the water contact angle decreased and the water resistance of the coating film decreased;the pencil hardness gradually increased and the wear resistance of the coating improved.As the molar ratio of polyether diol and polyether triol increased,the tensile strength of the coating decreased from 3.25 MPa to 0.73 MPa and the strain at break increased from 352.46% to 484.22%;the water contact angle of the coating film increased significantly,and when the molar ratio of the two polyether alcohols reached 3:1,the contact angle was the largest and the water resistance was the best;the adhesion of the PUU coating film continued to improve as the molar ratio increased.The cross-sectional shape of the PUU film changed from flat and smooth to a rough plane with obvious folds and tear patterns,and the thermal stability of the coating film improved.The compound defoamer composed of silicone defoamer and Ca O can effectively solve the problem of coating foaming,with the best effect of 0.8～1% addition;the addition of inorganic filler nano-silica obviously improves the mechanical strength of the coating film;the catalyst stannous octanoate has the best effect within 0.7～1.1% mass fraction,which not only improves the reaction rate of the system,reduces the reaction time,but also leaves sufficient drying time for the film formation.The catalyst was added within 0.7～1.1%to improve the reaction rate,reduce the reaction time and leave sufficient drying time.Two-component polyurethane coatings have obvious advantages over one-component polyurethanes.Short curing time;mechanical properties can be adjusted according to requirements;excellent hydrophobic properties of the film surface and water resistance;strong adhesion to the substrate.