| Light diffusing film is the essential optical thin film in the LCD display module and is usually applied to light-fixture billboard,outdoor display screen and LCD to homogenize light from the light sources. Currently, the major methods of preparing light diffusing film are coating and extrusion blending method, while the research of adopting multilayer co-extrusion method is less. Since the light diffusing film made by multilayer co-extrusion can solve dusting and scaling-off, and reduce the use amount of light diffusing agent compared with monolayer light diffusing film with saving cost, this article researched light diffusing film based on Polyethylene terephthalate(PET) by multilayer co-extrusion.In this paper, LLDPE/PET multilayer co-extrusion light diffusing film were prepared first so as to research the influence of content of light diffusing agent, stretching method and extension ratio on the transmittance and haze of light diffusing film; meanwhile, morphology of PET thin films was analyzed by SEM. The results showed that, the particle diameter of dispersing phase enlarged with the increase of the concentrations of LLDPE, while the transmittance of film without stretching reduced and haze increased. After biaxial drawing, the morphology of dispersed phase deviated from sphere, the transmittance of multilayer light diffusing film was increased and haze decreased gradually. However, the decrease tendency of haze was less than multilayer light diffusing film. When the concentrations of LLDPE occupied 8wt% of light diffusing layer, the transmittance of multilayer light diffusing film(177?m) prepared was 87.4% and its haze was84.42%. The LLDPE/PET light diffusing film prepared by multilayer co-extrusion method could increase transmittance while keeping the haze at higher value; meanwhile, its use amount of light diffusing agent was 50% lower than multilayer light diffusing film.Secondly, organosilicon/PET multilayer co-extrusion light diffusing film were prepared to research the influence of extension ratio, screw speed ratio, extrusion temperature, rotating rate and temperature of cooling roller, tackifying PET on the transmittance and haze of light diffusing film. The results showed that, the transmittance of multilayer light diffusing film increased firstly and reduced later with the increase of the ratio of biaxial drawing; when the extension ratio was excessive, the surface of the film would form spherical micro-structure, which caused the reduction of the transmittance and increase of haze. Meanwhile, the increase of extrusion temperature at middle layer, decrease of the thickness ration of light diffusion layer and middle layer, improvement of the rotating rate of cooling roller and lowering of temperature of cooling roller could increase transmittance and decrease of haze. When the content of organosilicon occupies10wt% of light diffusion layer, screw speed ratio was 110:80,temperature of cooling roller was 25 ? and the revolving speed of cooling roller was 1.4m/min, the transmittance of organosilicon/PET multi-layer light diffusing film(160?m) after 2.5 multiple biaxial drawing was 81.2% and its haze was 93.24%. After tackifying the PET at light diffusion layer by 1wt% chain extender, the screw speed of main extruder had wider adjustment range, which was more beneficial to the preparation of multilayer co-extrusion light diffusing film.Thirdly, it prepared PP/PET multilayer co-extrusion light diffusing film to research the influence of content as well as particle size of light diffusing agent, compatilizer content and extension ratio on the light transmittance as well as haze of light diffusing film. The results showed that, the addition of 2.5wt%PP-g-MAH could improve the compatibility of PET resin and dispersion phase, refine disperse particle size. With the increase of biaxial drawing multiple, the transmittance of light diffusing film increased firstly and then tended to constant while the haze decreased gradually. When the biaxial drawing multiple increased to 3 times, the morphology of dispersed phase deviated from sphere and the change of degree of sphericility wasthe major reason causing the variation of transmittance and haze. When the screw speed ratio was 110:80, and the content of PP-g-MAH and PP occupied 12wt% of light diffusion layer, the transmittance of PP/PET multilayer light diffusing film(210?m) after 2 multiple biaxial drawing was 78.2% and its haze was 93.33%.At last, the PMMA/PET coating light diffusing film was prepared for comparing the multilayer co-extrusion light diffusing film with coating light diffusing film. The research results showed that, the transmittance decreased while haze increased with PMMA content increasing. When the content of PMMA occupied 23wt% of coating layer, the transmittance of film was 90.1% and its haze was 87.03%.Compared with the PMMA/PET light diffusing film prepared by coating,the PP/PET light diffusing film and organosilicon/PET light diffusing film prepared by multilayer co-extrusion has higher haze but lower transmittance. |
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