Polarizing diffuser film, method for producing polarizing diffuser film, and liquid crystal display device comprising polarizing diffuser film

Abstract

Disclosed is a film having polarization selectivity and diffusibility, and a means for easily producing the film. The polarizing diffuser film is composed of substantially one kind of crystalline resin having an intrinsic birefringence of not less than 0.1, has a total light transmittance to visible light of 50-90%, a transmission haze to visible light of 15-90% and a transition polarization degree to visible light of 20-90%.

1 . A polarizing diffuser film made of substantially one kind of crystalline resin having an intrinsic birefringence of 0.1 or more, wherein the film has:
 a total light transmittance to visible light of 50-90%,   a transmission haze to visible light of 15-90%, and   a transmission polarization degree to visible light degree of 20-90%.   
     
     
         2 . The polarizing diffuser film according to  claim 1 , wherein:
 the film has a crystallinity of 8-40%,   bright portions and dark portions are observed in a polarization microscopy image of the film observed under crossed Nicol polarizers, the polarization microscopy image taken by irradiating the film with polychromatic light,   the bright portion and the dark portion are made up of substantially the same composition,   the bright portions have major axes which are substantially parallel to one another, and   the bright portions have higher crystallinity and degree of orientation than the dark portions.   
     
     
         3 . The polarizing diffuser film according to  claim 1 , wherein:
 the film has a crystallinity of 8-40%,   bright portions and dark portions are observed in a polarization microscopy image of the film under crossed Nicol polarizers, the polarization microscopy image taken by irradiating the film with polychromatic light,   the bright portion and the dark portion are made up of substantially the same composition,   the bright portions have major axes which are substantially parallel to one another,   where a Raman spectrum is measured at 0.5 μm intervals along a 5 μm-long line passing through the bright portion and dark portion in a cross section of the film substantially parallel to the major axes of the bright portions by irradiation with a light beam with 514.5 nm wavelength by argon ion laser with an argon ion laser Raman spectrophotometer, and then half-value widths of peaks near 1730 cm −1  in the respective Raman spectra are plotted against distance from the measurement start point, at least one of the half-value width differences between adjacent local maximum peak and local minimum peak in the plot is 0.2 cm −1  or more, and   where a Raman spectrum is measured at 0.5 μm intervals along a 5 μm-long line passing through the bright portion and dark portion in a section of the film substantially parallel to the major axes of the bright portions by irradiation with two different polarized light beams with 514.5 nm wavelength by argon ion laser with an argon ion laser Raman spectrophotometer, one linearly polarized in parallel to the major axes of the bright portions and the other linearly polarized perpendicularly to the major axes of the bright portions, and then Raman band intensity ratios (Ip/Iv) (where Ip is an intensity of a band near 1615 cm −1  in the Raman spectrum for the light linearly polarized in parallel to the major axes of the bright portions, and Iv is an intensity of a band intensity near 1615 cm −1  in the Raman spectrum for the light linearly polarized perpendicular to the major axes of the bright portions) are plotted against distance from the measurement start point, at least one of the band intensity ratio differences between adjacent local maximum peak and local minimum peak in the plot is 0.03 or more.   
     
     
         4 . The polarizing diffuser film according to  claim 1 , wherein:
 the film has a crystallinity of 8-40%,   the film is a uniaxially stretched film made of crystalline resin having an intrinsic birefringence of 0.1 or more,   the film has a transmission haze to visible light of 20-90% at 100 μm film thickness,   a bright-dark structure is observed in a TEM image of a cross section of the film cut perpendicular to the stretching direction of the film (imaged area is 0.1 μm in film thickness direction and has an area of 45 μm 2 ), and   bright portions and dark portions in the bright-dark structure are made up substantially the same composition.   
     
     
         5 . The polarizing diffuser film according to  claim 2 , wherein the film has a molecular orientation ratio-correction (MOR-c) at 100 μm film thickness of 1.2-7 as measured with a microwave molecular orientation analyzer. 
     
     
         6 . The polarizing diffuser film according to  claim 3 , wherein the film has a molecular orientation ratio-correction (MOR-c) at 100 μm film thickness of 1.2-7 as measured with a microwave molecular orientation analyzer. 
     
     
         7 . The polarizing diffuser film according to  claim 4 , wherein in a binarized image of the bright-dark structure, the area ratio of the bright portions is 6-80%. 
     
     
         8 . The polarizing diffuser film according to  claim 1 , wherein the film has a transmission polarization degree at 100 μm film thickness of 30-90%. 
     
     
         9 . The polarizing diffuser film according to  claim 2 , wherein the film has a crystallinity of 8-30%. 
     
     
         10 . The polarizing diffuser film according to  claim 1 , wherein the crystalline resin is selected from the group consisting of polyester resins, aromatic polyetherketone resins, and liquid crystalline resins. 
     
     
         11 . The polarizing diffuser film according to  claim 10 , wherein the crystalline resin is polyethylene terephthalate resin. 
     
     
         12 . The polarizing diffuser film according to  claim 1 , wherein the film has a light condensable surface shape on at least one surface thereof. 
     
     
         13 . The polarizing diffuser film according to  claim 12 , wherein the light condensable surface shape is a surface shape of the polarizing diffuser film itself, or a shape of a resin layer on the polarizing diffuser film. 
     
     
         14 . The polarizing diffuser film according to  claim 12 , wherein the light condensable surface shape is selected from the group consisting of one-dimensional prisms, two-dimensional prisms, and microlenses. 
     
     
         15 . A method of manufacturing a polarizing diffuser film according to  claim 1 , comprising:
 producing a crystallized sheet by heating an amorphous sheet made of crystalline resin having an intrinsic birefringence of 0.1 or more; and   substantially uniaxially stretching the crystallized sheet.   
     
     
         16 . The method according to  claim 15 , wherein the step of producing a crystallized sheet includes heating the amorphous sheet at temperature T which satisfies the following Inequality (1) until crystallinity of the sheet reaches 3% or higher.
     Tc− 30 °≦CT<Tm− 10° C.  Inequality (1)
   
       where Tc is a crystallization temperature of the crystalline resin, and Tm is a melting temperature of the crystalline resin. 
     
     
         17 . The method according to  claim 15 , wherein the crystallized sheet has a transmission haze to visible light of 7-70%, and a crystallinity of 3-20%. 
     
     
         18 . A liquid crystal display device comprising in order:
 (A) a surface light source for a backlight of a liquid crystal display;   (B) at least one optical device and/or air gap;   (C) the polarizing diffuser film according to  claim 1 ; and   (D) a liquid crystal panel which includes a liquid crystal cell sandwiched between two or more polarizing plates.   
     
     
         19 . The liquid crystal display device according to  claim 18 , wherein the polarizing diffuser film is arranged adjacent to the liquid crystal panel. 
     
     
         20 . The liquid crystal display device according to  claim 19 , wherein the polarizing diffuser film also serves as a light source-side protective film for the polarizing plates of the liquid crystal panel. 
     
     
         21 . The liquid crystal display device according to  claim 18 , wherein a polarized-light reflection axis of the polarizing diffuser film is directed in substantially the same direction as an absorption axis of the polarizing plate arranged at the light source-side of the liquid crystal panel.