Optical Compensation Film Research Articles

Light control using a double-stacked liquid crystal cell with enhanced viewing angle–blocking performance

In the future, there will be technological challenges between providing entertainment to passengers and eliminating driver distractions to ensure safety. Viewing angle control technologies for automotive display panels depending on each mode are required to integrate and provide both entertainment and advanced driver assistance system functions because watching videos while driving is regulated in most countries. In automotive display panels, unique electro-optical characteristics are required to control blocking or transmission only from the driver's direction while always being well observed from the passenger's direction. In this study, we developed a viewing angle control technology using double-stacked twisted nematic liquid crystal (TN-LC) films with excellent light-blocking performance only in the driver's direction over wide polar angle ranges in the privacy mode. By configuring the two TN-LC films in ordinary-ray mode and the other in the extraordinary-ray mode, the light could be completely blocked in the privacy mode, whereas it remained well transmitted in the normal mode in a specific left direction. Moreover, using double-stacked TN-LC films, light leakage at high polar angles in the privacy mode can be completely eliminated even without an optical compensation film, which is typically used to eliminate light leakage at high polar angles. Electro-optical films based on polarization optics are potential candidates for accelerating the growth of infotainment in self-driving cars.

Amorphous Blue Phase III: Structure, Materials, and Properties.

Blue phases (BPs) have a frustrated structure stabilized by chirality-dependent defects. They are classified into three categories: blue phase I (BPI), blue phase II (BPII), and blue phase III (BPIII). Among them, BPIII has recently attracted much attention due to its elusive amorphous structure and high-contrast electro-optical response. However, its structure has remained unelucidated, and the molecular design for stabilizing BPIII is still unclear. We present the following findings in this review. (1) BPIII is a spaghetti-like tangled arrangement of double-twist cylinders with characteristic dynamics. (2) Molecular biaxiality and flexibility contribute to stabilize BPIII. (3) BPIII exhibits submillisecond response, high contrast, and wide-viewing angle at room temperature without surface treatment or an optical compensation film. It was free from both hysteresis and residual transmittance. The electro-optical effects are explained in relation to the revealed structure of BPIII. Finally, we discuss the memory effect of a polymer network derived from the defects of BPIII.

Optical Z-Plate Compensation Film Manufactured by In-Plane Stretching Process to Improve Display Quality of OLEDs

Optical Z-Plate Compensation Film Manufactured by In-Plane Stretching Process to Improve Display Quality of OLEDs

Design of optical compensation film for improving the optical performance of organic light emitting diodes

The organic light emitting diode (OLED) display is one of the most promising devices among next-generation information displays because of the advantage of optically clear self-emitting characteristics. Nevertheless, in the conventional OLED display device, the luminous efficiency is increased by using a metal electrode having a high reflectance in the cell, but due to the reflection characteristic in the cell from the incident of external light, the dark characteristic is deteriorated and the contrast characteristic is dramatically reduced. In order to overcome this disadvantage, we propose an optical configuration consisting of a polarizer, quarter-wave plate (QWP), and C-plate for wide-band and wide-view performance, which mean high contrast in visual wavelength range and viewing angle in terms of polar and azimuthal angles while maintaining the transmittance characteristics of OLED when external light is incident. To designing an optimized optical configuration, the phase differences of light were calculated with trigonometric method and polarization characteristics were analyzed using a Poincaré sphere when passing through each optical film. To verify the optical performance of the proposed optical configuration, we applied it to OLED devices through experiments, as a result we confirmed that optical performance could be improved in terms of wide-band and wide-view without disturbing with the transmittance of OLED device.

Optical compensation schemes for elimination of off-axis color difference in a light control film based on dichroic dyes

We report optical compensation schemes for eliminating off-axis light leakage and color differences when a dichroic dye-based light control film is applied to a display panel. When a vertically aligned dichroic dye (VA-Dye) film without an optical compensation film is applied to the display panel, the light emitted from the display panel can be completely blocked on the upward and downward sides because the absorption axes of the dichroic dye molecules and top polarizer are perpendicular to each other. However, light leakage occurred in the diagonal direction because of the deviation in the angle between the absorption axes. To eliminate off-axis light leakage and off-axis color differences, we present three approaches for optical compensation. First, we optimized the positive biaxial + B plate by controlling its Nz value such that the off-axis color difference could be significantly reduced. Next, we employed optical compensation films using + B/negative C (-C) and positive A (+A)/positive C (+C) configurations. These designed configurations using commercially available films exhibited a significant reduced off-axis color difference as well as the elimination of light leakage in oblique directions when the VA-Dye film was applied to the display panel.

Effect of propionyl group on birefringence and wavelength dispersion of propionylated cellulose acetate optical compensation films

Propionylated cellulose acetate (PCA) with different propionyl substitution degrees (DSPr) was synthesized, and the corresponding optical films were prepared by solution casting. The birefringence and its wavelength dispersion of PCA films stretched at 10 °C above and below the glass transition temperature (Tg) with different draw ratios (DR) were studied. The introduction of propionyl group at different substitution sites present different contribution to birefringence and its wavelength dispersion. The propionyl group at C-2 and C-3 sites have a larger positive orientation birefringence with stronger normal wavelength dispersion, while that at the C-6 site shows a smaller negative orientation birefringence with weaker normal wavelength dispersion compared with the acetyl group. Compared with CA film, the introduction of the propionyl group weakens the orientation birefringence of PCA film. With the increase of DSPr from 0.023 to 0.303, the occurrence of propionyl substitution only at the C-6 site turns to C-2, C-3 and C-6 sites and the wavelength dispersion of in-plane birefringence (Δnin) decreases. When DSPr is further increased to 0.537, the Δnin and out-of-plane birefringence (Δnth) of PCA films at different DR show a very weak wavelength dispersion with the relative horizontal curves. Current results indicate that when the substitution degree of the propionyl group and acetyl group is suitable, the wavelength dispersion of PCA film can be eliminated.

Light control using vertically aligned dichroic dye films for windshield antireflection in automotive displays.

A vertically aligned dichroic dye (VA-Dye) film, whose absorption axis is perpendicular to that of its substrates, was laminated on a display panel in which the absorption axis of the top polarizer was set to 0°. In the vertical viewing angle of the display panel, the absorption axes of the top polarizer and dichroic dye are at right angles to each other, and, so, the light emitted from the display panel can be blocked. In the horizontal viewing angle of the display panel, the absorption axes of the top polarizer and dichroic dye are parallel to each other so that the light emitted from the display panel can be transmitted. Based on these polarization optics, we achieved complete elimination of light emitted in the upward or downward direction of the display panel, while the light emitted to the left and right is transmitted. We also added a designed optical compensation film using a positive biaxial (+B) retarder to the VA-Dye film so that the light emitted in the upward and downward directions of the display panel could be blocked in a wide viewing angle range (not only in the vertical direction, but also in the diagonal direction). The display panel using the VA-Dye film with the +B retarder showed excellent optical performance, such as significantly lower transmittance over a wide viewing angle range in the upward direction and relatively higher transmittance compared to that of a reference panel without the VA-Dye film. In addition, the VA-Dye film can be manufactured with a lower thickness, easier fabrication, and lower cost when compared with other technologies.

(Digital Presentation) Electro-Oxidative Trimerization of Catechol to Hexahydroxytriphenylene Using a Flow Microreactor

Due to their unique spectroscopic and geometric features, discotic liquid crystals (DLCs) have a variety of possible applications, including optical compensation films for liquid crystal displays, organic semiconductors for electronic devices, organic light-emitting diodes (OLEDs), and organic photovoltaic cells (OPVs).The most basic molecular structure of DLC is that of a triphenylene core surrounded by alkoxy and acyloxy groups. Even today, triphenylene with 2,3,6,7,10,11-hexaalkoxy and acyloxy groups is considered to be a common structural motif of DLC, and is undergoing rapid development. Until the 1990s, many studies had been reported on the synthesis of these hexasubstituted triphenylenes by trimerization of 1,2-disubstituted benzenes, but these protocols were not practical industrially due to the limitation of substituents, lack of reproducibility, the need for strict temperature control at -80°C, and poor solubility of reagents. Hence, today, the introduction of alkyl or acyl groups into 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP) has become a common synthetic strategy for hexasubstituted triphenylene. Therefore, HHTP is an important starting material for the synthesis of various types of hexasubstituted triphenylene.HHTP was conventionally synthesized by oxidative trimerization of 1,2-dimethoxybenzene followed by demethylation of the resulting hexamethoxytriphenylene. However, this method required the use of at least a stoichiometric amount of sulfuric acid, which generated a large amount of waste acid. Therefore, the development of more efficient methods, such as trimerization of 1,2-dihydroxybenzene (catechol) to HHTP, has been actively studied in recent years. Kobori et al. synthesized HHTP in 70-76% yield by oxidative trimerization of catechol using FeCl3 as an oxidant. However, the HHTP product was contaminated with Fe impurities, which was undesirable for the application of DLC in the display and semiconductor industries. Furthermore, this protocol includes a reduction step of peroxidized HHTP (quinone), which accounts for 40-60% of the total HHTP yields. Some other protocols do not use metal reagents, but they use 60-80 wt% H2SO4 aq., which result in a large amount of waste acid.On the other hand, we have recently developed an efficient method for aromatic C,C-coupling reactions by electrochemical oxidation in a flow microreactor. In this synthetic method, peroxidation of the products can be avoided by controlling the residence time in the reactor. In addition, electrochemical oxidation can be carried out without the use of oxidants or catalysts. Thus, this synthetic method has many features to overcome the drawbacks of conventional methods.In this study, we have successfully carried out the electro-oxidative trimerization of catechol in a flow microreactor to synthesize HHTP efficiently without the need for metallic reagents and reduction procedures.As a result, HHTP was obtained in 20% yield using 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) as a solvent. The results showed that the radical cations of catechol, which were generated on the anode surface, proceeds C,C-coupling in HFIP. On the other hand, the yield decreased to 4% or 0% when HFIP/H2O mixed solvents were used. DFT calculation suggested that the proton dissociation equilibrium of catechol intermediate greatly affects the reaction mechanism. We calculated the pK a values of catechol intermediate in each HFIP/H2O solvent composition, and discussed the effect of H2O contamination on the HHTP yield. Figure 1

Photopolymerisable liquid crystals for additive manufacturing

Liquid crystals are often regard as a fourth state phase of matter alongside solids, liquids and gases. It has been estimated that one out of every ten new synthetic compounds is a liquid crystal, mainly due to the fact that liquid crystals have been used in Liquid Crystalline Displays (LCDs) for over 50 years. Liquid crystals, often referred to as mesogens, exhibit an unique range of ordered mesophases with anisotropic physical properties, such as optical, magnetic and dielectric anisotropy, for example. These highly anisotropic properties and the ability of liquid crystals to self-organize on surfaces, has led to them being, are used in a wide range of non-LCD applications. These applications include photochromics, pressure sensitive paints, optical retarders and optical compensation films, etc. Highly crosslinked, anisotropic polymer networks, derived from photopolymerisable liquid crystals, so-called reactive mesogens (RMs), have enabled solution-fabricated organic light-emitting diodes (OLEDs), organic field-effect transistors (OFETs) and organic photovoltaic devices (OPVs) for plastic electronics. This review will be focus on the relatively recent application of liquid crystals, i.e., the 3D/4D printing of reactive mesogens and subsequent polymerization to form anisotropic polymer networks in advanced additive manufacturing applications. It will highlight the challenges of the synthesis and use of new liquid crystalline materials in 3D/4D printing for additive manufacturing applications. It will show how the study of the successful development of design strategies for the synthesis of novel liquid crystals for flat panel displays is inspiring the development of novel photopolymerisable liquid crystals for additive manufacturing. It is intended that this review will serve to inspire chemists, with little or no knowledge of liquid crystals, or liquid crystal chemists, to design and synthesize new liquid crystals for 3D/4D printing. Photopolymerisable liquid crystals (reactive mesogens) with advanced functional aromatic cores and two photoreactive endgroups are used to fabricate stimulus-responsive liquid crystalline elastomers (LCEs) using 3D/4D printing techniques, such as fused-deposition modeling (FDM), direct ink writing (DIW), digital light-processing (DLP) and two-photon polymerization (2PP). Reactive mesogens represent a highly promising class of advanced functional for new types of actuators, sensors, soft robotics, drug delivery systems, energy-absorbing and reinforced devices, etc., primarily due to their liquid crystalline properties, such as anisotropic swelling, high elastic modulus and sensitive actuation. • Stimulus-responsive photopolymerisable liquid crystals (PLCs) for additive manufacturing. • Structure-property discussion for PLCs with advanced aromatic cores and photoreactive endgroups. • 3D/4D printing PLCs for application in smart devices (actuators, sensors, soft robotics, etc). • Highly promising PLCs due to anisotropic swelling, high elastic modulus and sensitive actuation.

Colorless polyimides derived from 1S,2S,4R,5R-cyclohexanetetracarboxylic dianhydride, self-orientation behavior during solution casting, and their optoelectronic applications

A novel cycloaliphatic monomer for polyimides (PI), 1S,2S,4R,5R-cyclohexanetetracarboxylic dianhydride (H′-PMDA) is proposed in this work. H′-PMDA shows high polymerizability with various diamines in contrast to its isomer, i.e., conventional hydrogenated pyromellitic dianhydride (H-PMDA) and leads to highly flexible and colorless PI films with very high Tg's. In particular, the combinations with rigid structures of diamines give rise to PIs with significantly decreased coefficients of thermal expansion (CTE) owing to high extents of in-plane chain orientation induced by thermal imidization, whereas the H-PMDA-based counterparts do not. The decreased CTE reflects structural rigidity/linearity of the H′-PMDA-based diimide units as supported by liquid crystallinity observed in the corresponding model compound. Solution casting of a chemically imidized PI derived from H′-PMDA and 2,2′-bis(trifluoromethyl)benzidine (TFMB) results in a lower CTE than that of the thermally imidized counterpart, suggesting the presence of a self-orientation phenomenon during solvent evaporation. The mechanism is proposed in this work. H′-PMDA/TFMB and its copolymer systems can be useful as plastic substrates in image display devices and/or novel coating-type optical compensation films.

Bistable cholesteric liquid crystal light shutter with multielectrode driving.

An electrically activated bistable light shutter that exploits polymer-stabilized cholesteric liquid crystal film was developed. Under double-sided three-terminal electrode driving, the device can be bistable and switched between focal conic and homeotropic textures with a uniform in-plane and vertical electrical field. The transparent state with a transmittance of 80% and the opaque/scattering state with a transmittance of 13% can be realized without any optical compensation film, and each can be simply switched to the other by applying a pulse voltage. Also, gray-scale selection can be performed by varying the applied voltage. The designed energy-saving bistable light shutter can be utilized to preserve privacy and control illumination and the flow of energy.

Triphenylene-based discotic liquid crystals: recent advances

Since the early work of Chandrasekhar and his co-workers on hexaesters of benzene published in 1977, discotic liquid crystals (DLCs), in particular, triphenylene-based DLC materials have been investigated intensively, especially over the last decade. The first successful commercialisation of triphenylene-based DLCs has been accomplished in Fuji ‘Wide-View’ optical compensation films. DLCs represent a broad well understood class of soft matter which possess the ability to self-organise into highly anisotropic and ordered structures such as columns that function not only as organic anisotropic semiconductors, but also contribute to the development of new smart materials in the field of organic electronics for many device applications such as photovoltaic devices, light-emitting diodes, field-effect transistors, memory elements, and sensors. Over the last 35 years, more than 1000 triphenylene derivatives have been synthesised and investigated starting from structure-properties to structure-device performance relationships. The very first review by Cammidge and Bushby followed by Kumar summarised the chemistry and physical properties of triphenylene-based discotics up to 2003. In this review, progress in the research of triphenylene DLC materials since 2004 is comprehensively outlined.

Colorless polyimides with low coefficient of thermal expansion derived from alkyl-substituted cyclobutanetetracarboxylic dianhydrides

Alkyl-substituted cyclobutanetetracarboxylic dianhydrides (CBDAs) were synthesized by photo-dimerization of alkyl-substituted maleic anhydrides to obtain novel colorless polyimides (PIs). Dimethyl-substituted CBDA (DM-CBDA) showed much higher polymerizability with various diamines than conventional cycloaliphatic tetracarboxylic dianhydrides and led to high molecular weights of PI precursors. Polyaddition of non-substituted CBDA and trans-1,4-cyclohexanediamine (t-CHDA) was completely inhibited by salt formation in the initial reaction stage. The use of DM-CBDA allowed the formation of a homogeneous/viscous PI precursor solution by overcoming the salt formation problem. The prominent substituent effect probably reflects how the methyl substituents of DM-CBDA contributed to increasing the salt solubility. Some of the thermally imidized DM-CBDA-based systems simultaneously possessed non-coloration, low coefficient of thermal expansion (CTE), very high Tg exceeding 300 °C and very low dielectric constant. Copolymerization was very effective for improving the solubility of DM-CBDA-based PIs. The copolyimide cast films prepared via chemical imidization displayed a further decreased CTE without sacrificing other target properties, suggesting that the present materials can be useful as plastic substrates in display devices. The mechanism of self-chain orientation behavior during solution casting is also discussed. A potential application of the copolyimide systems as optical compensation film materials in liquid crystal displays is proposed. © 2013 Society of Chemical Industry.

Solution‐processable colorless polyimides derived from hydrogenated pyromellitic dianhydride with controlled steric structure

AbstractThis work presents novel colorless polyimides (PIs) derived from 1R,2S,4S,5R‐cyclohexanetetracarboxylic dianhydride (H″‐PMDA). Isomer effects were also discussed by comparing with PI systems derived from conventional hydrogenated pyromellitic dianhydride, that is, 1S,2R,4S,5R‐cyclohexanetetracarboxylic dianhydride (H‐PMDA). H″‐PMDA was much more reactive with various diamines than H‐PMDA, and the former led to PI precursors with much higher molecular weights. The results can be explained from the quite different steric structures of these isomers. The thermally imidized H″‐PMDA‐based films were colorless regardless of diamines because of inhibited charge‐transfer interaction. In particular, the H″‐PMDA/4,4′‐oxydianiline system simultaneously achieved a very high Tg exceeding 300 °C, high toughness (elongation at break > 70%), and good solution processability. In contrast, the H‐PMDA‐based counterparts were essentially insoluble. The outstanding solubility of the former probably results from disturbed chain stacking by its nonplanar steric structure. An advantage of chemical imidization process is also proposed. In some cases, a copolymerization approach with an aromatic tetracarboxylic dianhydride was effective to improve the thermal expansion property. The results suggest that the H″‐PMDA‐based PI systems can be promising candidates for novel high‐temperature plastic substrate materials in electronic paper displays. A potential application as optical compensation film materials in liquid crystal displays (LCD) is also proposed in this work. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

44.2 WITHDRAWN: 44.3: WITHDRAWN: 44.4: Flexible LCDs Fabricated with a Slit Coater

AbstractA homogeneously aligned liquid crystal layer can be assembled on a film substrate using a slit coater. Flexible twisted nematic and in‐plane switching LCDs with such a liquid crystal layer are demonstrated. The production time of this method is expected to be several tens of minutes shorter than that of the conventional method since it does not require an alignment film. This method can also be used to fabricate photovoltaic cells and optical compensation films.

TN-LCD 광학보상을 위한 Biaxial Film의 이론적 해석

In this paper, we have studied on the optimal design of the optical compensation film for the TN-LCDs. To have wide viewing angle panels, several methods such as multi-domain method, optical path method, and phase compensation method have been proposed. Among these methods, this paper focused on the phase compensation method. In the phase compensation method, the phase retardation generated from the optical birefringence for the off-axis incident is compensated by using optical films with refractive anisotropy. To compensate the phase retardation of the TN-LCDs, we have proposed design concept for the biaxial optical films and analyzed the optical performance for the proposed structures. The calculation of the dynamic motion of the liquid crystals was based on the Ericksen-Leslie theory and the optical performance of the TN-LCD was calculated from the Extended Jones Matrix Method. From the results, we have confirmed that the optical characteristics of the TN-LCDs with the biaxial films have been improved considerably compared with the TN-LCDs compensated by the combination of the uniaxial films.

Optical Compensation Film for FPD Produced by Liquid Crystalline Monomer

Optical Compensation Film for FPD Produced by Liquid Crystalline Monomer

광경화성 액정과 비반응성 네마틱 액정 혼합 필름의 분자 배향 및 광학 특성

Reactive mesogen인 광경화성 액정은 광반응에 의해 분자들이 네트워크 구조를 형성하여 초기 액정 분자들의 배향을 유지한 상태로 필름을 만들 수 있다. 광경화성의 reactive mesogen과 광반응 그룹이 없는 네마틱 액정을 혼합하여 경화 전과 후의 액정 혼합물의 배향을 비교하였고, 비반응성 네마틱 액정의 양과 온도에 따른 액정필름의 복굴절 변화를 조사하였다. 네마틱 액정의 양에 따라 복굴절이 다른 필름을 얻을 수 있어 reactive mesogen을 이용한 광학 보상필름 응용 가능성을 확인하였다.

P‐160: Improvement of the Contrast Ratio in Twisted Nematic LCD

AbstractMainly due to the twisted directors near surface in dark state, the decreased contrast ratio of TN mode has been observed. Here we describe the investigation of the contrast ratio of twist nematic liquid crystal display (TN‐LCD) with an optical compensation film, WV‐film, by using computational simulation and suggest new method to improve the contrast ratio significantly. Our results indicated that by optimizing the pitch of liquid crystal with chiral dopant, the contrast ratio was improved about 20%, but the reverse twisted region of the liquid crystal occurs. By adopting twisted WV‐Film, the contrast ratio was increased about 19% without the reverse twisted region.

A single‐cell‐gap transflective liquid‐crystal display using different pretilt angles in transmissive and reflective regions

Abstract— A single‐cel l‐gap transflective liquid‐crystal display with two types of liquid‐crystal alignment based on an in‐plane‐switching structure is proposed. The transmissive region is almost homeotropically aligned with the rubbed surfaces at parallel directions while the reflective region has a homeotropic liquid‐crystal alignment. For every driving voltage for a positive‐dielectric‐anisotropy nematic liquid crystal, the effective cell‐retardation value in the transmissive region becomes larger than that in the reflective region because of optical compensation film which is generated by low‐pretilt‐angle liquid crystal in the transmissive region. Under the optimization of the liquid‐crystal cell and alignment used in the transmissive and reflective areas, the transmissive and reflective parts have similar gamma curves. An identical response time in both the transmissive and reflective regions and a desirable viewing angle for personal portable displays can also be obtained.