Technologies toward flexible liquid‐crystal displays

Abstract— Several leading technologies for flexible liquid‐crystal displays have been developed recently at ERSO. The roll‐to‐roll compatible techniques, polymer‐added liquid crystal, have been applied on a film‐like substrate. A flexible black‐and‐white cholesteric liquid‐crystal display was also implemented by photo‐induced phase separation. Color filters placed on a plastic substrate by a low‐temperature manufacturing process was successfully fabricated. A novel design of a wide‐viewing‐angle color plastic LCD was also proposed.     

Thin flexible photosensitive cholesteric displays

Abstract— A novel optically addressable, flexible bistable cholesteric liquid‐crystal display (ChLCD) is presented. These displays utilizeazo‐binaphthalene photosensitive chiral dopants that undergo photo‐isomerization upon exposure to light. The isomerization results in a change in the pitch of the cholesteric liquid crystal (ChLC), which enables the creation of inherently high‐resolution light‐weight displays that are optically written. The displays can be photo‐addressed without patterned electrodes or complex addressing schemes. Capitalizing on the dynamic pitch and the bistability of photosensitive ChLCDs, the display is switched with a single pulse at a specific single voltage to drive the region of the display with a shorter pitch to the focal‐conic texture and the region of the display with a longer pitch to the planar texture. Once in the different textures, the display can hold an image indefinitely regardless of ambient lighting. As such, these displays are a natural fit for badges, shelf‐labels, and point‐of‐sale cards. In this paper, the photosensitive properties of an encapsulated display system in comparison to an unencapsulated display system is discussed. Properties such a photosensitivity, thermal relaxation, and electro‐optical response are studied and reported. In addition, a flexible optically addressable ChLCD is developed and demonstrated.     

Roll‐to‐roll manufacturing considerations for flexible,cholesteric liquid‐crystal display (Ch‐LCD) media

Abstract— Roll‐to‐roll methods and equipment to manufacture a bistable, passively driven display media on a flexible substrate have been developed. Using continuous coating techniques and equipment, cholesteric liquid‐crystal droplets in a gelatin binder and a dark layer are simultaneously coated onto laser‐etched‐patterned transparent ITO conductors on a polymeric web. Second conductors are printed with a UV‐curable polymer thick‐film ink over the active display layers, followed by slitting and chopping to complete the manufacture of display media in a full roll‐to‐roll mode. Segmented‐ and matrix‐display media can be generated using these techniques. This paper will focus on the manufacturing considerations for producing matrix‐display media.     

Large‐area black/white bistable cholesteric liquid‐crystal display and the thermal‐addressing system

Abstract— A 3‐m‐length black/white bistable cholesteric liquid‐crystal display was made by a roll‐to‐roll process and the display area is 25 × 300 cm. The black/white performance was made by black nano‐pigment and blended ChLC droplets with different wavelengths. It was written by a thermal‐addressing system, realizing high resolution and low cost.     

Color displays and flexible displays using quick‐response liquid‐powder technology for electronic paper

Abstract— Color displays and flexible displays that use electronic liquid powder have been developed. Novel types of color displays using either a colored powder or a color filter are discussed. We have also developed a flexible display with low‐cost substrate films with a high‐throughput roll‐to‐roll manufacturing method. These technologies enable a QR‐LPD to be widely used as an electronic‐paper display.     

An effective way to achieve full color cholesteric liquid crystal displays with single liquid crystal mixture and layer

Two‐step ultraviolet exposure method to achieve flexible color cholesteric LCD with single liquid crystal mixture and layer was proposed. The first step for polymer wall formation via photo‐polymerization induced phase separation and second step for color rendering with the photo‐sensitive chiral dopant were independently carried out without the interference of ultraviolet reaction using proper band‐pass filer. This display has good color performance and mechanical stability, which can be also driven by simplified driving circuit so that it would be a substantive solution for color flexible displays.     

Single‐substrate encapsulated cholesteric LCDs: Coatable,drapable, and foldable

Abstract— The first ever, reflective cholesteric liquid‐crystal displays (ChLCDs) on single textile substrates made with simple coating processes have been developed. A novel approach for fabrication of ultra‐thin encapsulated ChLCDs with transparent conducting polymers as bottom and top electrodes will be reported. These displays are fabricated from the bottom‐up by sequential coating of various functional layers on fabric materials. Encapsulation of the cholesteric liquid‐crystal droplets in a polymer matrix and the mechanical flexibility of the conducting polymers allow for the creation of durable and highly conformable textile displays. The development and status of this next‐generation display technology for both monochrome and multicolor cholesteric displays will be discussed.     

Full‐color transflective cholesteric LCD with image‐enhanced reflector

Abstract— A full‐color bistable transflective cholesteric liquid‐crystal display (Ch‐LCD) was demonstrated by using an imbedded image‐enhanced reflector (IER) on top of each transmissive subpixel. The RGB colors were achieved by patterning conventional color filters on a black‐and‐white Ch‐LCD. In addition, the IER on top of each transmissive subpixel provides similar paths for the transmissive backlight and the reflected ambient light. A simple transflective Ch‐LCD was demonstrated.     

A novel field‐sequential blue‐phase‐mode AMLCD

Abstract— Through the realization of a blue‐phase‐mode (hereinafter, the operational mode of liquid crystal having a blue phase is referred to as a blue‐phase mode), a display using an improved field‐sequential method was confirmed to be capable of display at a frame rate of 180 fps (field frequency of 540 Hz) or higher. Under this condition, an image without annoyance caused by color breakup was obtained. Moreover, a novel field‐sequential AMLCD integrated with a scan driver by combining the liquid‐crystal‐display (LCD) technology using blue phase and oxide‐semiconductor technology has been developed.     

A single‐substrate multicolor cholesteric liquid‐crystal display prepared through ink‐jet printing

Abstract— Ink‐jet printing was used to prepare a single‐substrate multicolor cholesteric liquid‐crystal (Ch‐LC) display incorporating three Ch‐LCs exhibiting different reflective wavelengths. A room‐temperature low‐vacuum chemical‐vapor‐deposition process was developed for coating a thin polymer film onto the Ch‐LC so that the top electrode could be coated onto the Ch‐LC layer. Herein, the successful operation of such a 10.4‐in. QVGA Ch‐LC display at 40 V will be described.     

Full‐color photo‐addressable electronic paper using cholesteric liquid crystals and organic photoconductors

Abstract— Full‐color photo‐addressable electronic paper using cholesteric liquid crystals and organic photoconductors was developed. The electronic paper is comprised of two stacked photo‐addressable elements displaying blue/green and red images, respectively. Each photo‐addressable element was independently controlled by two different color‐addressing lights. Furthermore, blue and green images were selectively switched by one organic photoconductor using the threshold characteristics of cholesteric liquid crystals. A highly reflective polymer‐dispersed cholesteric liquid‐crystal (PDCLC) layer was obtained by a new formation process based on the sol‐gel transition behavior of a gelatin matrix and an agar overcoat layer. The PDCLC layer had a close‐packed honeycomb‐like monolayer structure with a flat surface. The A6‐sized prototype had paper‐like features and showed full‐color bistable images instantly written with a viewer‐type writing apparatus.     

Novel transmissive color filter using cholesteric liquid crystal with wide viewing angle

Abstract— A new design for a cholesteric liquid‐crystal (CLC) color filter has been devised. Since this system absorbs no light, it uses backlight energy very efficiently. When CLCs of this type with an expanded selective reflection band are combined with light sources with sharp RGB emission peaks, such as LEDs, it is possible to reduce the dependence of color shift on viewing angle and make more efficient use of light.     

Deformed nanostructure of photo‐induced biaxial cholesteric films and their application in VA‐mode LCDs

Abstract— Novel biaxial retardation films made from photo‐induced deformed cholesteric liquid‐crystal (LC) nanostructures using reactive mesogen mixtures (RMMs) for a viewing‐angle compensation of vertically aligned liquid‐crystal displays (VA‐LCDs) was developed. The deformed cholesteric LC nanostructure has been observed by X‐ray‐diffraction (XRD) measurement. The birefringence of the film was described well by our optical model based on a form birefringence theory. The VA‐LCDs with photo‐induced biaxial cholesteric films have excellent viewing‐angle properties.     

Reflective cholesteric displays: From rigid to flexible

Abstract— Bistable reflective cholesteric liquid‐crystal displays are low‐power displays that are suitable for a variety of applications ranging from signage to high‐resolution electronic books. Recent advancements have included higher brightness, full color, black and white from a single layer, and lighting solutions. Cholesteric displays also lend themselves to simple integration into flexible materials since they may be coated and printed. We have developed reflective cholesteric displays on thin flexible plastic substrates, as well as other unconventional substrates such as paper and drapable fabrics. This paper serves as a review for recent advances in the cholesteric‐display technology at Kent Displays.     

Auto‐calibration of drive condition for cholesteric liquid crystal displays

Dynamic drive scheme (DDS) is known widely as passive matrix addressing that obtains both high‐speed re‐writing and a high contrast ratio in the field of cholesteric liquid crystal displays (LCDs). However, DDS has a serious problem in that the proper drive condition is very narrow and it is largely influenced by individual differences in LCDs that arise during their production. We have developed a new auto‐calibration system that adjusts both the contrast ratio and color balance automatically using capacitances of effective pixels and temperature compensation models that utilize the physical properties of cholesteric LCDs. We have managed to optimize the driving conditions between 5 and 35 °C with this method, and obtained both stable and high‐quality color images where the reflectance is 36%, contrast ratio is 8, and NTSC ratio is 20%. This auto‐calibration system has been able to greatly improve the production yield of cholesteric LCDs and made it possible to make practical use of cholesteric LCDs.     

Flexible hybrid substrates of roll‐to‐roll manufacturing for flexible display application

A flexible hybrid substrate was developed and demonstrated for roll‐to‐roll (R2R) manufacturing. Layer‐by‐layer misalignment can be well controlled within 5 µm. Top‐gate amorphous InGaZnO thin‐film transistor was fabricated on the flexible hybrid substrate by R2R process for the first time. A 4.3‐in. segment‐type reflective Electro‐Phoretic Display (EPD) display was also demonstrated to show the R2R capability of flexible substrates.     

Current status and future prospect of in‐cell‐polarizer technology

Abstract— A thin‐crystalline‐film (TCF) polarizer has been developed which can be used internally in liquid‐crystal‐display cells. Based on this material, a manufacturing process has been developed for the fabrication of monochrome LCDs with internal polarizers. A new TCF polarizer material and coating equipment, developed to realize a high‐performance color TFT‐LCD, are discussed.     

Optical design and roll‐to‐roll fabrication process of microstructure film for wide viewing LCDs

We have developed a new microstructure film for wide viewing liquid crystal displays (LCDs). By attaching it to the surface of a conventional LCD, the viewing angle characteristics of LCD has drastically improved without causing a blur of the frontal image and a decrease in the contrast ratio under bright ambient light conditions. This film can be applied to various LC modes including twisted nematic and multidomain vertical alignment by changing its internal micrometer‐size 3D structure. Further, this film can be mass‐produced efficiently by self alignment roll‐to‐roll process.     

Development of a high‐resolution RGBW flexible display using a white organic light‐emitting diode with microcavity structure and that of a side‐roll touch panel

In this study, white organic electroluminescent devices with microcavity structures were developed. A flexible high‐resolution active‐matrix organic light‐emitting diode display with low power consumption using red, green, blue, and white sub‐pixels formed by a color‐filter method was fabricated. In addition, a side‐roll touch display was developed in combination with a capacitive flexible touch screen.