| Acrylic polymers have been widely used as sensitive-pressure adhesive (PSA) because of their good film-forming property, excellent oxidation resistance and high transparency. More importantly, it is easy to design the performance of acrylic polymers by controlling the molecular structure. At present, more and more attention is paid to emulsion polymerization in the PSAs industry. However, there exists some weaknesses in adjusting the molecular microstructure and preparing composite latex for conventional emulsion polymerization. Miniemulsion polymerization possesses great potential in preparing composite latex with refined microstructure owing to its special nucleation mechanism, namely monomer droplet nucleation.In this dissertation, miniemulsion polymerization using reactive surfactant and cosurfactant was conducted. And a systematic study of the miniemulsion polymerization was carried out. Then, tackifier/acrylic composite latex was prepared through miniemulsion polymerization by using hydrogenated rosin (HR), terpene resin (TR) and petroleum resin (PR) as tackifiers. And the composite latex PSAs were also cured with a better hold tack. At the same time, the acrylic latex PSA with wide molecular weight distribution (WMD) was prepared by in-situ two-step miniemulsion polymerization. The ball tack,180°peel strength and hold tack were enhanced simultaneously. Main research contents and results are listed as following.Firstly, stable acrylic miniemulsion latex was synthesized by using butyl acrylate (BA),2-ethylhexyl acrylate (2-EHA) and methyl methacrylate (MMA) as main comonomers, methacrylic acid (MAA) as functional monomer, allyloxy nonylphenol ethoxylates ammonium sulfate (DNS-86) and steary methacrylate (SMA) as reactive surfactant and cosurfactant respectively. Effects of ultrasound time, the type and content of surfactant and cosurfactant on the miniemulsion polymerization and latex film properties were studied. The difference of kinetics between miniemulsion and conventional emulsion polymerization was also discussed. The latex was characterized by dynamic light scattering (DLS) and Fourier transform infrared spectroscopy (FT-IR). The results showed that the droplet size reached a balanced state of fission and fusion when ultrasound time was300seconds. DNS-86and SMA were incorporated in the polymer chain via covalent bonds, and the miniemulsion system with DNS-86/SMA as the (co)surfactant had better water resistance and wettability for non-polar materials compared to the counterpart using conventional (co)surfactant. The Zeta potential of the latex with DNS-86/SMA system reached-43.8mV, which meant a good stability. And the water absorption rate decreased from26.2wt%to8.3wt%.Secondly, tackifying modification for acrylic miniemulsion was carried out by using various tackifiers. Effects of the type of tackifiers on latex stability and the wettability for non-polar surface were studied. Mechanical properties of the PSAs were also investigated. The composite latex and corresponding latex film were characterized by DLS, GPC and DSC. The results showed that among these tackifiers, HR was the best tackifier for the latex, while PR was the worst one. When the HR content was5wt%, the monomer conversion was97.6%, coagulation rate was less than0.09%, Zeta potential reached-49.6mV, and the composite latex had an excellent stability. Interface failure occurred during the mechanical property test, and9#ball tack,8.6N/25mm180°peel strength,79h hold tack were obtained. DSC results indicated that HR had a good compatibility with acrylic copolymer, and reduced the glass transition temperature of HR/acrylic composite latex film. GPC test revealed that some residual rosin acid in HR could play a role of chain transfer agent and inhibitor, and hence reduced the molecular weight of the copolymer.Thirdly, pre-miniemulsion which contained not HR (MH) and contained HR (ML) was prepared respectively, and emulsion polymer with wide molecular weight distribution (MWD) was synthetized by in-situ two-step miniemulsion polymerization. Effect of the MH:ML(mass ratio) in emulsion polymer on the mechanical properties of the PSAs was studied. When the MH:ML was25:75, the ball tack reached12#,180°peel strength was9.4N/25mm, and the hold tack exceeded24h, indicating that the mechanical properties achieved relatively high levels. In the meantime, the mechanical properties of PSAs with in-situ wide MWD were superior to that of PSAs with wide MWD obtained by blending method. |
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