Brightness Enhancement Film Research Articles

Manufacture of brightness enhancement films (BEFs) by ultraviolet (UV) irradiation and their applications for organic light emitting diodes (OLEDs)

By ultraviolet (UV) irradiation, brightness enhancement films (BEFs) have been successfully manufactured with UV-curable polymers and applied for organic light emitting diodes (OLEDs). With BEFs, either green OLEDs (BEF/ITO glass/NPB (30 nm)/Alq 3 (65 nm)/LiF (0.5 nm)/Al (100 nm)) or white OLEDs (BEF/ITO glass/TAPC (40 nm)/mCP:Os:Firpic mixture (weight ratio = 82:17:1; 25 nm)/BCP (15 nm)/Alq 3 (30 nm)/LiF (0.5 nm)/Al(150 nm)) exhibit better electroluminescent performances than those without BEFs. In case of green OLEDs, the luminance and electroluminescent yield with 45° compound BEFs are, respectively, 1.51-fold and 1.42-fold (at 9 V, 60 mA/cm 2) larger than those without BEFs. In case of white OLEDs, moreover, the luminance and electroluminescent yield with 45° compound BEFs are, respectively, 1.28-fold and 1.21-fold (at 9 V, 16 mA/cm 2) larger than those without BEFs.

Design guidance of backlight optic for improvement of the brightness in the conventional edge-lit LCD backlight

An edge-lit backlight as a surface illuminator in the liquid crystal display achieves high brightness illumination with the light-condensing optic, composed of lamps, a light guide plate, a reflection film, a diffuse film, and a brightness enhancement film (BEF). This paper dealt with a technique to improve the brightness of a LCD backlight by increasing the light-condensing efficiency of an existing BEF. First, the technique was proposed; the efficiency of a BEF can be improved by a proper shaping of the angular luminance of lights entering the BEF. Then, its validness was experimentally proved with investigation of the brightness change of a test monitor backlight, varying the angular shape of the incident light to a BEF by adjusting the scattering power of both a diffuse film and an ink material printed on a light guide plate. It was revealed that the improvement range of the brightness by the proposed technique is about 5–9%.

Simulations of pixel moirés in the liquid crystal display with image processing technique

The objective of this paper is to simulate the pixel moirés arising in the liquid crystal display with an image processing technique. The LCD panel and the backlight can be regarded as the micro shutter arrays and the surface illuminator, respectively. The RGB shutters have the spatial periodicity and the illumination lights condensed by a brightness enhancement film (BEF) also have the spatial periodicity depending on the prismatic structure size and orientation of a BEF. Pixel moirés become visible when the spatially aliased periods and amplitudes of illumination lights exceed certain critical values. Avoidance of pixel moirés in the liquid crystal display is a design problem related with choice of prism pitch and orientation of a BEF. In this study an image processing algorithm which can predict the pixel moirés arising in the liquid crystal display was devised, and prediction accuracy was investigated. As a design example, optimal values of prism pitch and orientation of a new BEF having relatively large pitches, 150–200 μm were tried to be found with a devised simulator, and simulation results were discussed.

P‐115: Broad Band Selective Reflection from a Single Cholesteric Liquid Crystal Layer with a Helical Pitch Gradient and its Applications

AbstractWe have succeeded in obtaining broadband selective reflection over the entire visible spectrum from a single cholesteric liquid crystal layer with a helical pitch gradient. The broadband cholesteric layer is applied to brightness enhancement films for LCD, to decorative films with metallic reflection, and to IR shielding films. The decorative film and the IR shielding film are immune to radio wave for telecommunication.

Measurement of the mechanical properties of brightness enhancement films (BEFs) for LCDs by optical interferometry

The brightness enhancement film (BEF) is one of the important components in the liquid crystal displays (LCDs). Since the thicknesses of BEFs are very less, it increases the difficulty to measure their mechanical properties. In this paper, we successfully propose a methodology by combining the micro tensile test and optical interferometry to characterize Young’s moduli and Poisson’s ratios of BEFs. In addition, the thermal and hygrothermal effects on the mechanical properties of BEFs were also investigated. The finite element analysis (FEA) was utilized to verify the precision of our proposed methodology. The results show that Young’s moduli of BEFs are influenced by temperature and humidity whereas Poisson’s ratios of BEFs are less influenced by temperature and humidity.

Analysis and fabrication of a prism film with roll-to-roll fabrication process

A prism-based brightness enhancement film (BEF), has been investigated through computer-aided optical analysis and experiments in this study. The prism film was fabricated on a 100 microm thick PET film substrate using roll-to-roll (R2R) process with UV curable resins of different refractive indices. The results from both optical analysis and experiments showed that resins with higher refractive indices have better on-axis luminous gain. The prism structures fabricated on the substrate achieved a replication rate of 97.54% in this study. Compared with the 3M BEF, the prism films developed in this study are improved in on-axis luminous gains when the refractive index of the resin is higher than 1.53.

Dependence of the gain factor of the reflective polarizer on the configuration of optical sheets

The correlation between the optical performance of the reflective polarizer, which is a key optical component for the brightness enhancement of the liquid crystal display (LCD), and the configuration of optical sheets was investigated in a direct‐lit CCFL (cold‐cathode fluorescent lamp) backlight. The optical gain of the reflective polarizer, the polarization state of the light emitted from each film, and the loss factor for the polarization conversion process occurring in the lower part of the backlight were determined using a phenomenological approach for the polarization recycling process. The present study suggests that the correlation between the optical performance of the brightness enhancement films and the backlight configuration should be carefully considered in the optimization of the backlight structure.

Improvement of the outcoupling efficiency of an organic light-emitting device by attaching microstructured films

In this paper, we present and analyse the optical characteristics, such as spectral shift, CIE coordinates, viewing angle dependence, luminous current efficiency and luminous power efficiency, of an organic light-emitting device (OLED) with a commercial diffuser film or a brightness-enhancement film (BEF) attached. Compared to a planar green OLED, the luminous current efficiencies of the OLED with an attached diffuser film or BEF increase by 29% and 23%, respectively. The overall luminous power efficiencies are enhanced by 28% and 7%. Compared to the planar green device, we observe blue shifts at different viewing angles when microstructured films are attached, which is the evidence that the waveguiding modes are being extracted. In our planar OLED, the peak wavelength blue shifts and the full width at the half maximum (FWHM) decrease with increasing viewing angles due to the microcavity effect. When the diffuser is attached, the spectral peak has a constant blue shift (6nm) compared to that of the planar OLED. On the other hand, in the BEF case, the spectral shift depends on the viewing angle (2–12nm blue shifts from 0 to 80°). This is due to the different operating principles (scattering and redirected light) of the diffuser and BEF. Since the transmittance spectra of both the diffuser film and the BEF are flat over the visible range, it is suitable for lighting applications by using white OLED. When attaching the films on a commercial white OLED, the luminous current efficiencies of the OLED with an attached diffuser film or BEF increase by 34% and 31%, respectively. The overall luminous power efficiencies are enhanced by 42% and 8%.

Geometric optics analysis on light transmission and reflection characteristics of metallic prism sheets

Light transmission and reflection characteristics of metallic prism sheets are investigated based on a geometric optics approach. An analytic method is presented for finding the radiant intensity profiles of light transmitted through and reflected by a single metallic prism sheet for an incident light with arbitrary radiant intensity profile. With a simple interaction model between adjacent prism sheets, the analysis method for a single prism sheet is generalized for analyzing prism sheet layers composed of several prism sheets. Light transmission and reflection characteristics of a single prism sheet and prism sheet layers are compared. It is seen that the metallic prism sheet can be appropriately applicable to transflective devices or brightness enhancement film for liquid crystal displays.

L-7: Late-News Paper: Novel Polymerisable Liquid Crystalline Acrylates for the Manufacturing of Ultrathin Optical Films

Newly developed polymerisable nematic liquid crystalline materials in the Paliocolor® family with medium and high birefringence (0.16 and 0.20, respectively) are described. They enable the manufacturing of optical films, such as retardation films, brightness enhancement films and color filters, with superior quality and extremely reduced thickness by using coating techniques.

7.3: Novel Structure of Carbon Nanotubes Backlight Unit

A novel structure of carbon nanotubes backlight unit (CNT-BLU) was introduced to improve the uniformity. From the calculation and experimental verification, large improvement on uniformity can be observed. Benefiting from these important results, the new planar backlight technology has chances to proceed to mass production and reduce the cost of optical films such as diffuser and/or brightness enhancement film. Based on the structure, the printed CNT-BLU has the potential to replace traditional backlight technology because of it's good properties like the simple processes, easy to large scale, low surface Temp and Hg-free…etc.

47.2: The Characteristics of LCD Module with Two‐dimensionally Integrated Fluorescent Lamp for TV Applications

AbstractA 32 inch Two‐dimensionally Integrated Fluorescent Lamp (TIFL), the largest size in the world, has been developed at the first time. It is integrated into a backlight unit without using double brightness enhancement film (DBEF). The luminance of a TIFL backlight unit is 12500 nits at 140 watts of power consumption and its luminous efficacy is 55 lumens/watt at very high correlated color temperature. The color coordinate is 0.261/0.287 on the LCD. The usage of TIFL simplifies backlight assembly process and removes expensive optical sheets. As a result, LCD TVs employing TIFL will rapidly expand its market share in the large size TV application.

Polymer films derived from aligned and polymerised reactive liquid crystals

The principles and methods of fabricating thin polymer films with particular optical properties via the process of in-situ photopolymerisation of reactive liquid crystals are described. The optical properties of these films are described in terms of their retardation profile. Some possible applications, such as compensation films for improving the viewing angle of a TN-TFT liquid crystal display are discussed. A novel way of combining the properties of a quarter wave foil and a compensation film for a broad band cholesteric brightness enhancement film is also described.

Technology transfer in a diversified, Global Manufacturing Company

Technology transfer is one manifestation of a corporate culture of innovation at 3M that includes elements of reward and recognition, emphasis on communication and a toleration of mistakes as learning experiences, not occasions for punishment. Within this context, the company's microreplication technology offers an example of what can be accomplished. The technology involves making microscopic changes to the surface of materials, which influence their behavior. It was developed in the 1960s to produce the lightweight and inexpensive plastic fresnel lenses that made possible the first economical overhead projectors for classroom and business use. Since then, many additional applications have been discovered. These include brightness-enhancement films for laptop computer screens, brighter reflective materials for highway safety, super-abrasives for microfinishing of precision metal parts and even a mechanical fastener for disposable diapers. Many additional applications are anticipated as the company's scientists continue to refine their understanding of the technology.