Preparation And Application Of Star Polyester For High Solid Low Viscosity Two-component Polyurethane Coatings

The traditional solvent-based two-component polyurethane coatings（2K-PU）display excellent properties and have been widely used as wood and industrial coatings.However,these coatings have some disadvantages including high viscosities,high organic solvent contents,as well as high VOC emissions,which could not meet the requirements of environmental protection regulations.Therefore,this topic developed novel mothods to synthesize star-shaped hydroxyl resins,then reduced the viscosity of the resin system and prolonged the pot life of the 2K-PU by mixed glycidyl ether compounds and the polyether polyol,then optimized coating formulations such as diluents,leveling auxiliaries,defoaming auxiliaries,etc.to prepare high-solids 2K-PU wood coatings with excellent performance,and the conclusions are as follows:（1）A core molecule carrying hydroxyl groups was synthesized by secondary amine reacted with an alcohol amine,then reacting with the unit glycidyl ether to offer a star-shaped hydroxyl resin（SHP-1）with a secondary hydroxyl group.The number average molecular weights of these resins were ranged from 913 to 1390 with 1.55-1.75 of the PDI indexes,the resin viscosity of the 100%solids content was low to 1160 mPa.s.The molecular structure was characterized by infrared（FTIR）and nuclear magnetic resonance（¹H NMR）spectroscopy.The effects of the types and additions of the starting materials including anhydride,alcohol amine and monoglycidyl ether on the viscosities and properties of the resins were investigated.It was found that the resin with irregular molecular structure display lower viscosity and similar film hardness than that of resin with regular molecular structure.Compared with the aromatic unit glycidyl ether,the viscosity resin with the aliphatic glycidyl ether is lower,and the viscosity of the modified product of C₁₂ glycidyl ether is the lowest.The film prepared from the series of star-shaped hydroxy resins has good thermal stability and excellent performance.（2）A compound with a primary hydroxyl group was prepared with caprolactone ring-open reacting with and 1,2-propanediol and then ring-opening with trimethylolpropane triglycidyl ether to prepare a star resin with a secondary hydroxyl group（SHP-2）catalysted by the cationic catalyst,the number molecular weight of SHP-2 is range of 696 and 869,the PDI index is between 1.15 and 1.14,the viscosity with 100%solid content is low to 1,660mPa.s.The molecular structure was characterized by FTIR and ¹H NMR.The effects of long-chain primary alcohol categorigies and the ratio of caprolactone to 1,2-propanediol on the viscosities and properties of the resin were investigated.It was found that the viscosities of the series of star-shaped hydroxy resins decreased with the increase of the length and molecular weight of the primary carbon chain,and the SHP-3-7 prepared with dodecyl alcohol had a viscosity low to 1160 mPa.s,while the viscosity of SHP-3-1 prepared with n-hexanol is up to 6000 mPa.s,and with decreasing the amount of primary alcohol,increasing the content of caprolactone and 1,2-propanediol,the viscosity of SHP-3 rapidly increase,and the hardness also increase accordingly.（3）Two kinds of star-shaped hydroxy resins were modified with TMPGE and N303 to decrease the low viscosities and prolong the pot life of 2K-PU.The curing agent types and the optimal ratioes are preferred.The prepared high-solid 2K-PU wood coating has a 70%of the solid contents,330 g/L of the VOC with 17 mPa.s of the applied viscosity,and display high coating hardness up to 3H,as well as excellent chemical resistance and thermal stability.