| Ultraviolet(UV)curable cathodic electrophoretic coating is one kind of water-based environmental coating,which has the advantages,such as high throwing power,uniform film and low loss of raw materials.Due to application of UV curing technology,it avoids defects of high temperature curing for raditional cathodic electrophoretic coatings.At present,the researchs on UV-cured cathodic electrophoretic coatings mainly focuse on exploring the dynamic behavior during UV curing and reducing the water content of the wet film after flash-off,as well as improving the appearance of the coatings.In view of this,this paper innovatively designed several novel crosslinkers,systematically studied their effect on the photocuring behavior and basic physical and chemical properties of the coating.At the same time,the effects of different fluorine-containing matrix resins and novel microgel structure on the water content of the wet film after flash-off were also explored,and a novel UV curable cathodic electrophoretic coating with anti-smudge and hydrophobic properties were designed.The details from following several aspects are as follows:(1)Correlation between the chain length and side groups of photocrosslinkers and the photocuring kinetics and other physicochemical properties of UV curable cathodic coatings were studied.In this paper,three novel photoinitiated crosslinkers(M1,M2 and M3)containing soft and hard segment structures were synthesized.A novel UV curable cathodic coatings with different chain length and side groups was obtained by using the prepared polyacrylate bearing double bond as the matrix resin.Photo-DSC,TGA and other tests showed that the chain lengths and side groups on structure of photocrosslinking had little effect on the photoinitiation efficiency,but it had a significant regulation effect on the double bond conversion rate.The compatibility of the system containing the rigid chain structure deteriorated,which in turn leads to a relatively rough surface.A flexible segment would reduce hardness of the coating.All the modified coatings had excellent properties such as high adhesion,good flexibility,impact resistance and corrosion resistance.(2)Study on the correlation between photocrosslinking kinetics and other physicochemical properties of hyperbranched structured photocrosslinkers and UV curable cathodic coatings.The photoinitiator crosslinker was synthesized by the norbornene dianhydride and phthalic anhydride modifying hyperbranched polyester(HBPE).The modified compounds was prepared with terminal double bonds to carboxyl groups in the molar ratio of 6:6,3:9 and 9:3.Then,the prepared double bond polyacrylate as a matrix resin to synthesize a UV curable cathodic coatings with different hyperbranched structures.The samples were characterized by Photo-DSC,TGA and other tests.The results showed that the photocuring kinetics was mainly controlled by the double bond content,and have less influence on different hyperbranched structures.In addition,the enhanced of hyperbranched carboxyl group content,and made the particle size of the dispersion decrease.Hyperbranched structures with a high vinyl content can improve the thermal stability of the coating.(3)Correlation between the water content of the paint film and the comprehensive performance of the coating based on the hyperbranched microgel and UV-cured cathodic electrophoretic coating.In this paper,a novel microgel structure based on hyperbranched polymer was designed and synthesized for UV curable cathodic coatings.Then,the prepared double bond polyacrylate as a matrix resin to synthesized a UV-cured new cathode coating containing with different amounts of microgels.The samples characterized by calculation of water content of wet film,TGA and tensile tests.The results showed that the microgel content was increased,the water content of the paint film was decreased,but the overall performance of the coating was deteriorated.It is necessary to balance the addition amount of the microgel,the water content of the paint film after flashing,and the coating property in electrophoretic deposition.The increasing the amount of microgel made the water absorption of the modified coating decreased from 5.74%to 0.94%,and made the thermal stability decreased.Their elongation at break increased from 37.04%to 88.18%and the tensile strength increased from3.44 MPa to 6.82 MPa.However,it decreased the compatibility and the flexibility of coating,and the gloss was decreased from 92~o to 16.3~o.(4)The comprehensive performance study of the change of water content of the film after flash curing of the UV-cured fluoropolyacrylate-based cathodic electrophoretic coating and the anti-smudge property of the cured coating.For the first time,a novel UV-curable anti-smudge electrophoretic coating was prepared by using the prepared double-bond fluoropolyacrylate as the matrix resin and dipentaerythritol pent-/hex-acrylic acid(5-Acl)as the crosslinking agent.After calculation and analysis of wet film moisture content,XPS,contact angle,etc.,it showed that 5-Acl can increase the moisture of the paint film after flashing,but it can improve the overall performance of the coating.There is a need to balance the content of the cross-linking agent,the water content of the paint film after flashing,and the coating properties.The static contact angles of water,diiodomethane and hexadecane on them were 96.5±3~o,70.5±2~o and 32±2~o,respectively.The sliding angle of droplet increased and decreased with the droplet volume and surface tension.After the abrasion test,the fluorine atom content of the coating surface decreased from 14.49% to 8.37%,and far above the theoretical value.The water droplets,pump oils,cooking oils,toners,and waterborne epoxy paints can easily slid away from coatings without leaving visible traces.The oily pen marking surface shrinks and was discontinuous,indicating that the coating had excellent self-cleaning and anti-smudge.They had impact resistance,abrasion resistance,good flexibility and excellent corrosion resistance.(5)The comprehensive properties of the UV-curable polyurethane-based cathodic electrophoretic coating after the flashing of the paint film and the hydrophobicity of the coating.For the first time,a novel UV-curable fluorine-containing polyurethane-based cathodic electrophoretic coating was prepared by preparing a fluoropolyether alcohol half-end as a polyurethane prepolymer and grafting hydroxyethyl methacrylate into a double bond.After calculation and analysis of wet film moisture content,XPS,contact angle,etc.,it was shown that the moisture content of the paint film after flashing was reduced due to the inclusion of perfluoropolyether alcohol in the structure.And the low water content coating after flashing has excellent overall performance.A certain amount of heat contributes to the migration of low surface energy fluorosis.The average water absorption of the coating was2.82%,and water droplets fell off the surface of the coating without leaving traces,indicating that the coating had excellent hydrophobicity but poor stain resistance.At the same time,the coatings passed tests such as impact,bending,adhesion,and harsh chemical resistance. |
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