The Synthesis Of The Special Polyester For Bopet Film And The Study On Pilot Test Of Film Preparation

The biaxially oriented optical polyethylene terephthalate film(BOPET)is a matrix material for functional films in liquid crystal display,optical protective film and high performance optical labels.Compared to traditional BOPET,advanced optical BOPET displays a excellent optical performance(eg,transmittance?92%,haze<1%),high strength,wide temperature range and good barrier properties.However,synthesis of raw resin material and manufacturing technology of this kind of high performance optical film have been lagging behind in China,which hinder the development of optical functional film industry.Although most of the polyesters are currently made in China,the synthesis of optical polyester is still in its infancy.Moreover,the lack of literatures makes it more challenging in synthesis of optical polyesters.As a semi-crystalline polyester,PET would crystallize when heated and stretched.Optical performance can also be affected by crystallization.Additionally,catalysts critically influences the optical performance,thermal properties and crystallization of polyester.In this work,we improved the synthesis technology of polyester based on the catalyst and molecular structure design.The optimal process was carried out in industrial production line.Firstly,the ethylene glycol antimony / ?-Al OOH composite catalyst was prepared to replace ethylene glycol antimony catalyst which leads to a gray color,low luminousness and high haze of the polyester.The active ?-Al OOH was prepared by hydrolysis of basic aluminum acetate.And the hydrolysis process was studied by Fourier transform infrared spectroscopy(FT-IR),X-ray diffraction(XRD),aluminum magnetism(27Al NMR)and particle size analysis.The results shows basic aluminum acetate ionizes Al30([Al30O8(OH)56(H2O)24] 18+)coordination ion and a small amount of Al(H2O)6 3+.The final hydrolyzates are [(H2O)4Al(?-OH)(H2O)4] 4 +,?-Al OOH and Al(OH)3.The catalytic effect and mechanism were investigated by using glycol antimony / ?-Al OOH composite catalyst to catalyze the synthesis of poly(ethylene terephthalate-co-ethylene isophthalate)(PEIT).In the first step,?-Al OOH reacts with ethylene glycol to produce aluminum glycolate.Then,aluminum glycolate coordination centers catalyze the condensation process.The combination of ethylene glycol antimony and ?-Al OOH improve the catalytic efficiency and reduce the polyester polycondensation time.Compared with ethylene glycol antimony catalyst,the ethylene glycol antimony / ?-Al OOH composite catalyst reduce the polycondensation time by 18.6% and effectively reduce the diethylene glycol content in the polyester.The catalyst also change the end structure of the polyester,and affect the rheological properties,crystallinity and optical properties of the polyester.The ethylene glycol antimony / ?-Al OOH composite catalyst can reacts with the carboxyl and hydroxyl end groups of the polyester after the catalytic polycondensation reaction,producing alkoxy antimony,aluminum alkoxide and terminal carboxylate complexes.These new terminal structures have strong nucleation ability which change the crystallinity and affect the optical properties of polyester.As a result,the transmittance of PEIT reach 90.46%.The new terminal structures also hinder the thermal motion of the polyester molecular chain,which affects the rheological properties and increase the melting point and the glass transition temperature of the polyester.Based on the above study,poly(ethylene terephthalate-co-ethylene isosorbide terephthalate)(PEIST)and poly(ethylene terephthalate-co-ethylene isomannide terephthalate)(PEIMT)have been synthesized through the isosorbide and isomannide modified poly(ethylene terephthalate),respectively.For the polymerization,ethylene glycol antimony and ?-Al OOH were chosed as composite catalyst.The difference in thermal,optical and crystallization properties between PEIST and PEIMT was disclosed by differential scanning calorimetry(DSC),POM,XRD and ultraviolet-visible spectroscopy.The results showed that PEIST and PEIMT possessed excellent thermal performance.Furthermore,the haze and crystallization ability of these two copolyester decrease with increasing isosorbide and isomannide during the polymerization process.However,isosorbide and isomannide only slightly influenced the optical properties.Due to the difference in color stability,the degree of yellowing increased with the amount of isosorbide and isomannide.The absorbance of blue-violet visible light led to the decrease of light transmittance of the two copolyesters.Compared with PEIST,PEIMT possessed superior color stability and better optical performance.However,the haze of PEIMT should be further decreased.For further decreasing the haze of PEIMT,Isophthalic acid and 1,4-cyclohexanedicarboxylic acid were introduced during the synthesis of PEIMT,respectively.The obtained products had been denoted as PEIIT and PEICT,respectively.The characterization results suggested that the crystallization ability of the two copolyesters decreased with the amount of the fourth monomers content.Furthermore,the light transmittance would also increase.When the degree of yellowing achieved a certain degree,the light transmittance would decrease.It should be noted that the quaternary copolymerization could greatly reduce the haze of the copolyesters,and the haze of PEIIT and PEICT copolyesters was reduced to zero.However,compared with the PEIIT,PEICT showns higher melting point under the same content of the fourth monomers.More over,PEICT would achieve the zero haze when using the fewer fourth monomer.The pilot tests and biaxial tensile experiment have been done for the PEICT with optimal optical performance.The obtained polyester chips and optical BOPEICT membrane met the specifications of commercial optical polyesters and membranes.