Light Diffuser Plates for LCD-TV Backlight Systems

Transcription

1 Light Diffuser Plates for LCD-TV Backlight Systems Sumitomo Chemical Co., Ltd. IT-Related Chemicals Research Laboratory Akiyoshi KANEMITSU Takashi SAKAMOTO Hironobu IYAMA A lighting system called direct type is usually employed for backlight systems in large size LCD-TVs. With this type of backlight system, a diffuser plate has to be mounted in order to blur the images of CCFLs and to hold several thin optical films. We have developed diffuser plates with properties which are specially optimized for this type of backlight system, and have released them onto the market. In this report, the properties that are required for diffuser plates and our R&D activity will be described. Fig. 1-a) Fig. 1-b) TV set (/1 k unit) LCD TV PDP Projection TV % 9% 8% 7% 6% 5% 4% 3% 2% 1% % " 4" 49" 33" 37" 3" 32" 26" 29" 21" 25" 16" 2" 15" a) by each system b) by size (only LCD TV) Fig. 1 Worldwide development of the number of TV set [Quoted from reference 1) and 2)]

2 Fig. 2 Fig. 3-a mm Fig. 3-b Fig. 4 a) Photo of the CCFLs in the backlight unit (w/o diffuser plate) Fig. 3 Fig. 4 Basic function of the light diffuser plate (CCFL = Cold Cathode Fluorescent Lamp) Light diffuser plate CCFLs Reflector b) Photo of the CCFLs in the backlight unit (with diffuser plate) Diffusion film LC panel DBEF Prism film Typical configuration of the direct type backlight system Light Guide Plate Laptop PC ( ~ 17") Wedge structure Monitor (15 ~ 23") 4 ~ 12mm Light Diffuser Plate Television (2" ~ over 1") 1.5 ~ 3mm Fig. 2 2mm.7mm Typical configuration of backlight systems for various types of liquid crystal displays Mie Fig. 5

3 Diffusion factor ; D (B7 + B2) / 2 D = 1 B5 B = I / cos 9 +9 Collimated incident ray Incident ray Fig. 5 Calculated Mie scattering diagrams of two particles with different refractive indices. n of matrix is1.5, n of particle is 1.55 and 1.6 for black line and blue line, respectively I 5 I 2 Transmitted scattering profile Mie Tt D JIS Fig. 6 Fig. 7 Fig. 82 D % Intensity Fig Fig. 7 I Angle (deg.) An example of the transmitted scattering profile of a diffuser plate and the definition of Diffusion Factor (D) Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Sample Tt % Higher transmittance and higher diffusivity = Higher luminance with higher uniformity Some examples of Tt-D balance curve obtained from some particles with various diameters and refractive indices

4 2 Sample A Sample B Sample B Uniformity ( ) Particle I Particle II Luminance (cd/m 2 ) Sample A Sample B Sample A Sample B Fig. 9 Some examples of the luminance performance using a model backlight unit Fig Incident angle = Diffuser plate CCFL Sample A ; Tt= 55%, D = 9, Sample B ; Tt= 65%, D = 6. DA > DB Transmitted scattering diagrams of two different diffuser plates with different Tt and D Mie Fig Incident angle = 4 Sample AB Fig. 1Sample A Sample B Sample A Fig. 1 Sample B Sample A ; Tt = 55%, D = 9, No CCFL image was observed. Luminance 63 cd/m 2 Sample B ; Tt = 65%, D = 6, Some CCFL images were observed. Luminance 635 cd/m 2 The images of the CCFLs observed through Sample A plate and B plate 4Table 1

5 Fig. 4 mm UVCON Fig. 11 Fig. 11 Fig. 12 Log (surface resistance) Conventional method Improved method Intensity of light CCFL Hg-lamp wave length [nm] Fig. 12 Exposure time (hr) Hg lamp exposure test for the diffuser plates with different types of anti-static treatment Chromaticity x hr 5 hr 1 hr 15 hr 2 hr Fig. 11 Exposure time Sample α Sample β PC Some examples of the UV (Hg lamp) exposure test results for various kind of base resin with different additives Fig. 4 Fig. 13 RM4 3)

6 RM8XS Major size of the LCD TV inch 3inch 37inch 45inch 65inch RM8XS RM8XS Sumitomo Light Diffuser Plate Fig. 13 RM4 RM41 RM7XX : Put onto the market RM8X 24.9 RM8XS 25.2 The history of our development of diffuser plates for LCD-TVs Fig %5 37 Shift of plate center (mm) Fig. 14 Time after the lamps turned on (hr) RM8XS (2mmt) PMMA based material (2mmt) PC (2mmt) RM7X (2mmt) Curl behavior of diffuser plates under illumination of CCFLs in backlight unit. Moisture adsorption ; RM8XS =.1%, PC =.4%, PMMA = 1.9%, RM7X =.3% Table 1 General properties of our diffuser plate Test Item Thickness Unit mm Method Light Transmittance % JIS K 7361 Haze % JIS K 7163 Gloss % JIS Z 8741 Diffusion factor % SCC method Tensile Strength MPa JIS K 7113 Tensile Elongation % JIS K 7113 Tensile Modulus GPa JIS K 7113 Flexural Strength MPa JIS K 723 Notched Izod Impact Strength kj/m 2 JIS K 711 Heat Distortion Temperature (18.6kg) C JIS K 727 Scratch Hardness (pencil method) JIS K 56 Surface Resistivity Ω JIS K 6911 Coefficient of Linear Expansion / C JIS K 7197 RM8XS 2 RM81S = 55 RM82S = 6 RM83S = 65 RM84S = / 7 RM81S = 93 RM82S = 76 RM83S = 59 RM84S = H 1 9~

7 a) Sample C (2mmt) 8 RM8XS Fig mm 25mm RM8XS b) RM84S (2mmt) 26 inch TV set. 16 hours later, after being kept in the chamber of which temperature was 5 C and humidity was 8%. 81 C 83 C 84 C Fig. 15 Example of Mura test result 75 C 79 C Fig. 15Sample C RM8XS Fig C 77 C Distribution of the maximum temperature (Size of backlight unit = 46inch, Chamber temperature = 55 C) Fig RM8XS 8 8 Fig C 3hr 9 C 3hr 24mm Test method 15mm PC RM83S2T RM83S1.5T PC RM83S1.5T < Specimen size > Width : 25mm Thickness : 1.5mmT, 2mmT Bending displacement was measured Heat resistant grade Heat resistant grade RM83S2T Heat distortion test performed at 8 degree and 9 degree

8 LED Fig. 18 flux flux 1 Fig. 19 Fig. 19-a) 6 Fig. 19-b) PET Fig. 19-a) Fig. 19-c) Luminance (cd/m 2 ) 8 Fig. 18 Fig. 19 1% 99% 96% 9% Reflector RM83 Diffuser film Prism film Light Source 1% 3% 6% Flux measurement of the 2 inch size LCD TV backlight system a) b) c) Luminance (cd/m 2 ) Angle (degree) Angle (degree) Angle (degree) Diffuser plate Diffuser plate / Diffuser film Luminance (cd/m 2 ) Diffuser plate / Diffuser film / Prismatic film Luminance profiles of three different types of optical film components

9 1) 26,,, BP (26), p.97 2) 26,,, BP (26), p.36 3),,,,, 22-II, 15 (22) PROFILE Akiyoshi KANEMITSU Hironobu IYAMA Takashi SAKAMOTO