Preparation And Characterization Of Water-borne Acrylics Resin Coating And Its Application As Automotive Topcoats

A series of rigid rules of environmental protection and industries limitations have been formulated, resulting by that people become more and more aware of environmental problems. In coating industry, in order to reduce the emission of volatile organic compound (VOC), environmental coatings (water-borne coating, high solid coating and powder coating) are slowly but resolutely replacing solvent-borne coating. Among the three kinds of environmental coatings, water-borne coating is primary because it has similar spraying process with solvent-borne coating and its dispersion medium, water, is cheap and without any pollution. However, the properties of water-borne coating can not be referred as good comparing to solvent-borne coating, especially its poor water resistance. These limit its applications in fields with high requirements such as automobile decoration and ship protection. Therefore, it values a lot to develop water-borne coating with good bulk properties and water resistance,especially water-borne acylic resin coating which is of high gloss, good wheather resistance and adhesion.Two approaches were designed to improve properties of water-borne acrylic resin coating. The first one was that acrylic resin with dense structure was prepared by radical solution copolymerization between vinyl monomers and self-made functional monomer (ACE), which was firstly synthesized by ring-opening reaction of Glycidyl ester of VERSATIC acid (E10) owning huge non-polar side group, with AA. The conversion of E10 was highest When the reaction was taken in following condition: E10/AA = 1.2, 90℃×4h. The viscosity of ACE-WA resin coating with 20wt% ACE was the lowest, 23.75Pa.s. It was shown that the properties of ACE-WA resin coating were improved comparing to unmodified WA resin coating. Properties of curing film of ACE-WA resin coating with 15wt% ACE with curing agent Luwipal 066 when curing at 140℃×30min were best: bending strength=2mm, hardness=4H, adhesion=level 0, impact strength=50kg.cm, gloss(60°)=130, water resistance=3d.Another approach was that acrylic resin mixed with star and linear structures was prepared by radical solution copolymerization between vinyl monomers and self-made functional monomer (BBA), which was firstly synthesized by transesterification of pentaerythritol with acetoacetate tert-butyl diazoacetate(t-BBA). The aim of the approach was to reduce the viscosity of acrylic resin, increase its water solubility, and improve properties of its curing film base on star polymer. Polymerization temperature/time and initiator amount/time were studied to gurantee the conversion of monomers. Through univariate formula design, chain transfer agent amount, hard/soft monomers ratio, vinyl monomers and BBA content have been studied according to the viscosity and transmittance of BBA-WA resin and properties of its curing film. Synthesis of BBA-WA resin coating with best properties of curing film were prepared in the following condition: 110℃, 7h, BPO 1.4 wt %,chain transfer agent 1.2 wt %, BBA 15wt%, AA 7 wt %, n-BA 40 wt %, St 12 wt %. The corresponding curing condition was curing agent Luwipal 066 40wt%, 140℃, 30min. The best properties are bending strength=2mm, hardness=3H, adhesion=level 0, impact strength=50kg.cm, gloss (60°) =120, water resistance=5d.The reaction of BBA as a vinyl monomer was demonstrated by FT-IR, 1H-NMR and 13C-NMR. The viscosity of modified acrylic resin coatings reduced and their transmittance increased. GPC, DSC, TG/DTG, and SEM were applied to characterize modified acylic resin and its curing film. There are som advantages of modified acylic resin coating comparing to unmodified one. Some of these advantages were an increase in the crosslinking density, improvement in film toughness, hardness and gloss.