Preparation And Property Of Aluminum Pigments Encapsulated By Organic And Inorganic Composite Films

Flaky aluminum pigments are widely used in paint and printing ink industry due to their uniquely metallic effect and"flop-effect". In order to enhance the anti-corrosion propert and improve the compatibility with resin, the surface of aluminum pigments was modified by acrylate resin single layer, acrylate and silica double layers and acrylate composited with silica layer, respectively.Hydroxyl acrylic resin encapsulated aluminum pigments were prepared by adsorption of the resin on the surface of Al particles via hydrogen-bond, which has been pre-prepared by free radical polymerization of methal methacrylate (MMA), ethyl acrylate (EA), n-butyl acrylate (BA), acrylic acid (AA)and methacrylate -2 - hydroxy ethyl (2-HEMA). Effects of absorption conditions on the property of aluminum pigments were investigated. The results show that when the mass of aluminum pigments is 1.5 g and mass of resin more than 2.0 g, the hydroxyl acrylic resin film can be well-formed on the surface of aluminum pigments after at least 2h adsorption under the temperature of 50℃. The film can improve the anti-corrosion property of aluminum pigments and their compatibility with resin without reducing their metallic appearance. However, the hydrogen-bond between hydroxyl acrylic resin and aluminum pigments is very weak and easily to be destroyed.In order to enhance the binding force between encapsulated layer and aluminum pigments, polyacrylate (PA) and SiO2 double-layer encapsulated aluminum pigments (PA/SiO2/Al) were prepared via sol-gel method and in-situ polymerization. Firstly, aluminum pigments were encapsulated with a layer containing vinyl group activated silica using VTES and TEOS as precursors through sol-gel method. The second layer was then formed on the surface of aluminum pigments by free radical copolymerization of MMA, MA and C=C group of VTES in the presence of benzoyl peroxide (BPO). Effects of in-situ polymerization conditions on the morphology, the metallic appearance, the anti-corrosion property and the compatibility of aluminum pigments were also investigated. It was found that when the mass of aluminum pigments is 1.5 g, the mass of monomers is 0.7 g, the temperature is 85℃and the reaction time is 4~6 hrs, the as-prepared PA/SiO2/Al shows good dispersion in coating. The weight loss of PA/SiO2/Al from coating is almost 0 after peeling-off test under high temperature and humidity. The compatibility of PA/SiO2/Al with resin was improved resulting in stronger binding between layers and aluminum pigments. The L-value of coating containing PA/SiO2/Al is just 6.67 lower than that of raw aluminum pigments, indicating that encapsulation has less effect on the metallic appearance of aluminum pigments. Furthermore, there is no change in L-value of coating before and after dipping the sample in acid medium of (pH=1) for 24 hrs, revealing that the PA/SiO2/Al presents good anti-corrosion. Fourier transformation infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis proved that SiO2 and PA successfully encapsulated on the surface of aluminum pigments in turns.In order to simplify the encapsulation process and minimize the loss of metallic luster of aluminum pigments, organic-inorganic hybrid encapsulated aluminum pigments were further developed using siloxane groups modified acrylate resin and TEOS as precursors. Firstly, Siloxane groups modified acrylate resin Poly (Methyl methacryalte-n-Butyl acrylate-Vinyl trieth oxysilane (PMBV) was formed by co-polymerization of MMA, BA and VTES. When nBA:nMMA:nVTES=2:2:1, the amount of Initiator is 3% of total monomers, the reaction temperature is 110℃and the reaction time is more than 3 hrs, the conversion rate is up to 92.5%, and the product of polymerization is colorless and transparent with Molecular Weight of 3700 and Molecular weight distribution of 2.056. Outcomes of FTIR, nuclear magnetic resonance of H element (1H NMR), nuclear magnetic resonance of C element (13C NMR) and differential scanning calorimentry (DSC) analysis of resin demonstrate that VTES, MMA and BA copolymerized with each other instead of self-polymerized. The content of silicon in PMBV is about 3.89% according to the result of colorimetry. Then the hydrolysis-condensation product of PMBV and TEOS was studied by atomic force microscopy(AFM), FTIR, thermo gravimetric(TG)and nuclear magnetic resonance of Si element (29Si NMR). The results show that hydrolysis products of PMBV and TEOS have self-condensed and co-condensed with each other simultaneously in ethanol media to form homogeneous and transparent organic-inorganic hybrid materials. Variable angle XPS analysis shows that the contents of Si, O and C element have relationship with the thickness of hybrid films, indicating that the siloxane groups and the silicon have co-condensed with hydroxyl groups on the surface of aluminum in the hydrolysis - condensation process.PMBV composited with SiO2 encapsulated aluminum pigments (PMBV-SiO2/Al) were prepared by hydrolysis and condensation of PMBV and TEOS on the surface of pigments via sol-gel method using ammonia as catalyst and ethanol/H2O as dispersion media. FTIR, TG and XPS analysis of encapsulated aluminum pigments reveal that when the mass of aluminum pigments is 1.5 g, the amounts of ammonia and H2O are 3 mL and 3 mL respectively, the total amount of PMBV and TEOS is 13.1mmol(molars of Si), and the ratio of PMBV to TEOS is 1:0.45~1(molars of Si),PMBV and TEOS can form uniform and compact organic-inorganic hybrid layer on the surface of aluminum pigments. The as-prepared aluminum pigment shows good anti-corrosion and compatibility with resin. It is useful to enhance the corrosion resistance of PMBV-SiO2/Al by increase the amount of TEOS, which means that the anti-corrosion property of PMBV-SiO2/Al largely depends on SiO2. And the comparison of anti-corrosion of a variety of aluminum pigments also verifies this conclusion. Lightness value test shows L-value of PMBV-SiO2/Al decrease 0.24, stating clearly that the organic - inorganic hybrid film maintained the metallic appearance of aluminum pigments well. Peeling test demonstrates that the adhesion of PMBV-SiO2/Al in coating has been enhanced compared with that of raw aluminum pigments, which means the compatibility of PMBV-SiO2/Al with resin has been improved. However, the compatibility of PMBV-SiO2/Al is slightly poorer than that of PA/SiO2/Al.