Synthesis And Application Of Functional Polyester For Laminated Tin-free Steel

Polymer laminated tin-free steel is a technology that plastic film is laminated on the steel by high temperature and pressure. It has been applied for replacing conventional polymer coated steel in food packaging, household building and automobile industry. Compared with the conventional polymer coated steel, polymer laminated tin-free steel has the characteristics of high corrosion resistance, deep draw ability and easy decoration. The production technology was simplified by ignoning thermal dry process. This technology is solvent free, thus it is environmentally friendly. Bi-axis-oriented polyethylene terephthalate film is often used as a laminating material in industry because of its excellent comprehensive properties, such as gas barrier, good mechanical, flexibile and non-toxic properties. However, the film is difficult to be laminated on tin-free steel due to its relatively high melting temperature and rigid molecular chains, which greatly limits the application of the film in the industry of polymer laminated tin-free steel. In this paper, the main aims are to improve the surface energy, thermal properties and interfacial property of polyester film used as laminating material instead of coating resin. So, polyester film was modified by copolymerization and the structure and the properties of laminating film were studied. First, the non-ionic polyester was synthesized base on acid and glycol modified PET.The structures and properties of the polyester were characterized. Then the polyester was made into film and corona treatment was used to improve the film surface energy for laminating material.Furthermore, the properties of the laminated steel were investigated. Base on the synthesis process of non-ionic polyester, ionic polyesters were prepared via introducing ionic monomer copolymerization. An ionic polyester was selected to make film based on its structures and properties. New technique was applied in making ionic polyester film because of its special physical properties. The laminated steel was prepared without surface treatment and the interfacial bonding strength of the materials were analyzed.The Poly(ethylene terephthalate-co-neopentyl terephthalate-co-ethylene isophthalate-co-neopentyl isophthalate)(PENIT) polyester was prepared via method of direct esterification and polycondensation. The PENIT polyester was made into film by biaxial oriented stretching production line. Corona treatment was used to improve the film surface energy for laminating material. The key technological conditions were ascertained in the esterification and polycondensation process such as the catalyst, stabilizer, temperature and time. The structures and thermal properties of the polyesters are characterized by proton nuclear magnetic resonance(1H-NMR), thermogravimetry analysis(TG), differential scanning calorimeter(DSC), wide-angle X-ray diffraction(WAXD) and polarized optical microscopy(POM). Meanwhile, peel strength and crystallinity of the polyester film are also measured at various lamination temperatures.The results show that the copolyester had similar thermal stability and intrinsic viscosity with PET. However, the inclusion of NPG and IPA monomers reduced the crystallization ability of the copolyester. After corona discharge treatment, the surface energy of PENIT film increased from 37.2 m J/m2 to 51.4 m J/m2. The corona treated PENIT film had good bonding strength with TFS under proper temperature.The effect of corona discharge treatment on the film was investigated by ATR-FTIR, XPS, SEM and AFM. The decaying behaviors of corona films were studied by measuring contact angle and XPS. Base on mechanism of corona treatment on polyester film surface, the bonding mechanism between film and TFS was analyzed.This thesis first presents another route to prepare laminated material. A lasting surface energy polyester was obtained by introducing ionic monomer copolymerization. The third comonomer is isophthalic acid-5-sulphonic acid sodium, and the fourth is 1, 4-butanediol or polyethylene glycol. Base on synthesis process of PENIT polyester, the poly(ethylene terephthalate-co-1,4-butylene terephthalate-co-ethylene isophthalate sodiosulfonate-co-1,4-butylene isophthalate sodiosulfonate) polyester(PEBST) and poly(ethylene terephthalate-co-ethylene isophthalate sodiosulfonate-co-polyethylene glycol) polyester(PEPST) were prepared. The structures and thermal properties of the polyesters were characterized by proton nuclear magnetic resonance(1H-NMR), thermogravimetry analysis(TG), differential scanning calorimeter(DSC), rheological and surface energy test. It is found that the surface energy of the polyesters increased significantly due to introduction of ionic monomer and the fourth monomer improved the processability of polyesters effectively. The ratio of mononers can control the melting point of polyester. The PEPST laminating film was made by industrial biaxial oriented stretching production line. New film forming process was applied to match its special physical properties. In order to mimic the change of crystallinity in actual film tensile process, the non-isothermal cold crystallization kinetics of the PEPST polyester was studied. At an appropriate lamination temperature, the laminating material has a good peel strength without the need of surface treatment.