Preparation,structure And Properties Of Cathodic Electrodeposition Coatings Based On Waterborne Polyurethanes Containing Hydrophobic Side Chain

As a kind of environmental friendly materials,waterborne polyurethanes possess several advantages such as non-toxic,flame retardant and pollution-free properties,and are often used as coating or adhesive in furniture,mobile phones and flexible substrates,etc.The cathodic electrophoretic coating process has the advantages of high material utilization rate,low pollution,high automation and the ability to coating complex workpiece,etc.Cationic waterborne polyurethane(CWPUs)cathodic electrophoretic coating exhibit extensive prospects because of its excellent performance.Due to the obvious deficiencies of poor water resistance and low surface hardness prevalent in CWPUs,hydrophobic modification of CWPUs has been actively studied in recent years.Therefore,with the purpose of increasing crosslinking density and introducing low surface energy components,a series of CWPUs cathodic electrophoretic coatings with hydrophobic structures were designed and synthesized by introducing the octadecyl side chain,branched polydimethylsiloxane side chain,and hydrophobic modified eloxite nanotubes.This work does not only promote the development of polyurethane industry,but also have important scientific research values.The specific research work of this paper was as follows:1.Hydroxyl-terminated cationic waterborne polyurethane was synthesized(HCWPUs)by using N-MDEA as hydrophilic chain extender,and the chemical structure of HCWPUs was confirmed by FTIR.The optimal formula of HCWPUs was as follows: N-MDEA content,NCO/OH mole ratio and neutralization degree were 7.5 wt.%,0.90 and 100 %,respectively.The optimal HCWPUs exhibited excellent emulsion stability and smooth cathodic electrophoretic paint film with a pencil hardness of 3H,adhesion force of 1 grade,and good water resistance.HCWPUs/NWBI cathodic electrophoretic coating was prepared by mixing HCWPUs with non-ionic waterborne blocked polyisocyanate(NWBI).NWBI had no adverse effects on emulsion performance and paint film appearance of HCWPUs/NWBI cathodic electrophoretic coating,and the film hardness,adhesion force,water resistance and solvent resistance were significantly improved.When the NWBI content was 7 wt.%,the paint film pencil hardness was over 6 H and the number of acetone wiping times was more than 200 times.2.A series of CWPUs cathodic electrophoretic coatings containing octadecyl side(CWPUs-G)were synthesized by using monoglyceride 1-octadecanoate(GMS)as hydrophobic modified component.When the content of GMS content was 15 wt.% or less,CWPUs-G emulsion had good stability and the appearance was milky white with blue light.When the GMS content was more than 15 wt.%,the emulsion with milky white appearance showed poor stability.Ocadecyl side chains do not affect the light transmittance of CWPUs-G film,and could enrich on the surface of the film.The CWPUs-G cathodic electrophoretic paint film with increased degree of phase separation of soft and hard segments,exhibited smooth surface,excellent adhesion force,flexibility,impact resistance,improved hydrophobicity,and reduced water absorption ratio.The introduction of HCWPUs/7wt%NWBI further improved the performance of the CWPUs-G cathodic electrophoretic coating with the pencil hardness of the paint film increased from HB to 3 H,and the adhesion force,flexibility and impact resistance maintained good level.3.Using branched aminoethyl aminopropyl polydimethylsiloxane(BAEAPS)as hydrophobic modified component,a series of cationic waterborne polyurethane cathodic electrophoretic coatings with different BAEAPS contents(CWPUs-Si)were synthesized.The chemical structure and elemental composition were confirmed by FTIR and XPS.When the content of BAEAPS was 9 wt.% or less,the emulsion stability of CWPUs-Si cathodic electrophoretic coatings was excellent.Polydimethylsiloxane side chian showed obvious enrichment in the film surface of CWPUs-Si,with the increasing of BAEAPS content,the phase separation of soft and hard segments in CWPUs-Si enhanced,and the film surface morphology varied from micron scale random wrinkle to sub-micron or nanoscale dimension random wrinkle,which could significantly reduce the surface energy and water absorption ratio and promote water contact angle,Tg,storage modulus E’.When the BAEAPS content was increased to 9 wt.%,CWPUs-Si9 electrophoretic paint film possessed smooth appearance,excellent adhesion force,flexibility and impact resistance with pencil hardness increasing to HB,water contact angle increasing to 106.4 °,and water absorption decreasing to 3.05 %.4.Using methoxy-terminated branched aminoethyl aminopropyl polydimethylsiloxane(MEO-BAEAPS)as hydrophobic modified component,a series of cationic waterborne polyurethane cathodic electrophoretic coatings with different MEO-BAEAPS contents(CWPUs-MSi)were synthesized.The chemical structure and elemental composition were confirmed by FTIR and XPS.The emulsion stability of CWPUs-MSi cathodic electrophoretic coatings with BAEAPS content under 9 wt.% was excellent.Polydimethylsiloxane side chain showed obvious enrichment in the film surface of CWPUs-MSi,with the increasing of MEOBAEAPS content,the phase separation of soft and hard segments in CWPUs-MSi enhanced,and the film surface morphology CWPUs-MSi varied from micron scale irregular folds to submicron or nanoscale dimension irregular folds,which could significantly reduce the surface energy and water absorption ratio,promote water contact angle,Tg and storage modulus E’.When MEO-BAEAPS content was increased to 9 wt.%,CWPUs-MSi9 electrophoretic paint film possessed smooth appearance,excellent adhesion force,flexibility and impact resistance with pencil hardness increasing to 1 H,water contact angle increasing to 110.2 °,and water absorption decreasing to 3.3 %.5.A series of cathodic electrophoretic coatings with double hydrophobic side-chain cationic waterborne polyurethane(CWPUs-MSi G)were synthesized by using 5 wt.% of MEOBAEAPS and a series amount GMS as hydrophobic modified components.CWPUs-MSi G cathodic electrophoretic coating had good emulsion stability when GMS content was 11 wt% or less.Both MEO-BAEAPS and GMS were significantly enriched on the film surface of CWPUs-MSi G.With the increasing of GMS content,the phase separation degree of hard and soft phases in CWPUs-MSi G film increased,and the surface morphology showed irregular folds at the sub-micron or nanometer scale.Although the content of GMS had no effect on the water contact angle,the water absorption decreased obviously.Introducing two components hydrophobic modified POS@HNTs into CWPUs-MSi G5 for the preparation of CWPUsMSi G5/POS@HNTs cathodic electrophoretic coating,the POS@HNTs further improved the performance of CWPUs-MSi G5,such as increased water contact angle increased,decreased water absorption ratio,and increased pencil hardness.Moreover,all of the cathode electrophoresis paint electrophoresis paint film possessed smooth and transparent appearance,excellent adhesion force,flexibility and impact resistance.