Polarizing diffuser film, method for producing polarizing diffuser film, and liquid crystal display device comprising polarizing diffuser film
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%, and wherein
a bright-dark structure having dark portions and bright portions dispersed in the dark portions is observed in a TEM image of a first cross section of the film which imaged area has a thickness of 0.1 μm in film thickness direction and has an area of 45 μm 2 , and
the bright portions and dark portions in the bright-dark structure are made of substantially the same composition and have different crystallinity from each other.
2. The polarizing diffuser film according to claim 1 , wherein:
the film is a uniaxially stretched film made of the substantially one kind of crystalline resin, and
a bright-dark structure having dark portions and bright portions dispersed in the dark portions is also observed in a TEM image of a second cross section of the film cut perpendicular to the stretching direction of the film which imaged area has a thickness of 0.1 μm in film thickness direction and has an area of 45 μm 2 ).
3. The polarizing diffuser film according to claim 2 , wherein
in a binarized image of the bright-dark structure in the second cross section of the film, the area ratio of the bright portions is 6-80%.
4. The polarizing diffuser film according to claim 1 , 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.
5. The polarizing diffuser film according to claim 1 , wherein the film has a transmission polarization degree at 100 μm film thickness of 30-90%.
6. The polarizing diffuser film according to claim 1 , wherein the film has a crystallinity of 8-40%.
7. 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.
8. The polarizing diffuser film according to claim 1 , wherein the crystalline resin is polyethylene terephthalate resin or polyethylene naphthalate resin.
9. The polarizing diffuser film according to claim 1 , wherein the film has a light condensable surface shape on at least one surface thereof.
10. The polarizing diffuser film according to claim 9 , 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.
11. The polarizing diffuser film according to claim 9 , wherein the light condensable surface shape is selected from the group consisting of one-dimensional prisms, two-dimensional prisms, and microlenses.
12. 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.
13. The method according to claim 12 , 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° C.≦ T<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.
14. The method according to claim 12 , wherein the crystallized sheet has a transmission haze to visible light of 7-70%, and a crystallinity of 3-20%.
15. 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.
16. The liquid crystal display device according to claim 15 , wherein the polarizing diffuser film is arranged adjacent to the liquid crystal panel.
17. The liquid crystal display device according to claim 16 , wherein the polarizing diffuser film also serves as a light source-side protective film for the polarizing plates of the liquid crystal panel.
18. The liquid crystal display device according to claim 15 , 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.
19. The polarizing diffuser film according to claim 1 , wherein:
the first cross section of the film is a cross section of the film cut parallel to a reflection axis of the film, and
the bright portions have major axes which are substantially parallel to one another.
20. The polarizing diffuser film according to claim 1 , wherein:
the film is a uniaxially stretched film made of the substantially one kind of crystalline resin, and
the first cross section of the film is a cross section of the film cut parallel to the stretching direction of the film.