Cholesteric liquid crystal devices

Abstract

To improve a cholesteric liquid crystal device which is also called a writing tablet.SOLUTION: A cholesteric liquid crystal device has an optical response opposite to that of the prior art. The liquid crystal device takes advantage of a unique and unusual effect in cholesteric liquid crystals, where pressure applied to the device with a pointed stylus without applying a voltage creates a transmissive texture in contrast to the planar texture of the prior art.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present disclosure relates to a cholesteric liquid crystal pressure-sensitive device.

Background Art

[0002] To replace paper with a simple, low-cost, reusable alternative device, Kent Displays Inc. developed the BOOGIE BOARD® writing tablet (see U.S. Patents No. 6,104,448 and No. 8,139,039 incorporated by reference). As shown in Figure 1, the BOOGIE BOARD® writing tablet technology utilizes the unique properties of cholesteric liquid crystals, with the liquid crystal material appropriately sandwiched between two substrates 3 and 4. The front substrate 3 is flexible to form the writing surface (Figures 1-3). In the prior art BOOGIE BOARD® writing tablet, the liquid crystal is initially a substantially translucent texture known as a focal conic texture 2, which allows the user to see the device's light-absorbing background material, typically provided by a dark-colored back substrate 4 or a coating or layer 24 on the back substrate. By applying moderate local pressure to the writing surface using an object 8, the focal conic texture changes to a reflective texture known as a planar texture 9. The color of the planar texture 9 is determined by the pitch length of the cholesteric liquid crystal. For example, writing on a writing tablet device having a black light-absorbing background material and a cholesteric liquid crystal with a pitch length adjusted to green (550 nm) produces green writing or marks 10 that contrast with the black surrounding area 7 of the rest of the writing device where no pressure is applied. The image is erased to form a blank page by initializing the writing device to a semi-transparent or focal conic texture. To do this, a button on the writing tablet is pressed, and a voltage 25 is applied accordingly to transparent electrodes 5 and 6 on the inner surface of the substrate (see, for example, U.S. Patent No. 10,558,065 incorporated by reference). Both the focal conic texture and the planar texture are stable and do not require voltage to maintain their texture. The only voltage used is an erase voltage pulse applied to the electrodes that transitions all liquid crystal layers, including the planar texture of marks 10, to a focal conic texture.

[0003] A drawback of the BOOGIE BOARD® writing tablet is that it can only write reflective lines or marks on darker, light-absorbing background materials without applying voltage during writing. This is because, in conventional technology, the pressure applied to a cholesteric liquid crystal writing tablet can only drive the tablet to a reflective planar texture. As a result, to maximize the contrast of conventional writing tablets, the choice of light-absorbing background materials is limited to colors and tones that have a considerable amount of light absorption. This set of conditions limits the types of contrast combinations possible between the planar mark and the translucent surrounding area. Furthermore, in this mode in which the BOOGIE BOARD® writing tablet operates, it is not possible to create dark lines or marks with a white, reflective surrounding area without applying voltage, and therefore it cannot mimic writing on a typical paper notebook, notepad, or whiteboard. In a more general sense, it is impossible to perform dark writing on a light background material using this mode, known as Mode B. In an attempt to overcome these limitations, in U.S. Patent No. 8,139,039, Schneider et al. proposed applying a small continuous voltage to a typical writing tablet initialized to a planar reflective texture while applying local pressure to the writing surface to convert the cholesteric liquid crystal from a planar texture to a more transmissive texture (known as mode A). However, the need to apply a constant voltage throughout the entire writing process is a significant drawback, negating one of the most important advantages of bistable cholesteric liquid crystals, which form images without the use of voltage. Therefore, Schneider et al.'s technique was commercially useful for partially erasing images rather than writing images. [Overview of the project]

[0004] This disclosure describes for the first time a liquid crystal device in which applied pressure drives the liquid crystal into a translucent texture, in contrast to the color-reflective planar textures of the prior art, and does so without applied voltage. Dark marks or writing of the translucent texture can be made where pressure is applied, thereby creating a peripheral portion of the reflective texture where no pressure is applied. Even black writing with a white peripheral portion, which was previously impossible, is possible. The liquid crystal device comprises a liquid crystal layer containing a cholesteric liquid crystal material disposed between a first substrate and a second substrate. There are two optional first and second conductive layers. The first conductive layer is disposed between the first substrate and the liquid crystal layer, and the second conductive layer is disposed between the second substrate and the liquid crystal layer. The first substrate and the first conductive layer, when it is the front substrate, are transparent and flexible, while the second substrate and the second conductive layer, when it is the back substrate, can be transparent, translucent, or opaque depending on the desired background. By applying one or more appropriate voltage pulses to both conductive layers, the cholesteric liquid crystal is initialized into a reflective texture.

[0005] Localized pressure applied to a first substrate, such as by a stylus or the tip of a fingernail, generates a mark or writing on the device of a translucent texture in contrast to a reflective texture present where no pressure is applied. The image includes a mark formed from the translucent texture, which allows light to pass through the liquid crystal layer and be partially or almost completely absorbed by the light-absorbing background material. There is a surrounding area where no pressure is applied, and this surrounding area includes the reflective texture. As defined herein and used throughout this disclosure, a reflective texture is not entirely reflective, and a translucent texture is not entirely translucent. A reflective texture allows some light to pass through and some light to be reflected. A translucent texture is a texture that allows some incident light to pass through and weakly scatters it. A reflective texture reflects substantially more light than the light weakly scattered by a translucent texture. A light-absorbing background material can be seen through a translucent texture. Therefore, if the back substrate is black, localized pressure will produce a dark mark that contrasts with the color of the reflective texture of the rest of the device (the surrounding area) where no pressure is applied, and the color of the surrounding area depends on the pitch length of the cholesteric liquid crystal. The dark mark contains transmissive liquid crystal, for example, allowing the underlying black substrate to be seen through the liquid crystal layer. In one example, the surrounding area may be called bright and the mark may be called dark relative to each other. Naturally, this is only because the mark contrasts with the surrounding area, and does not require a high level of brightness in the surrounding area or a high level of darkness in the mark. When using a colored light-absorbing background material, both the mark and the surrounding area may appear as the selected color. The colored light-absorbing background material does not need to be a uniform color, and for example, it can include a pattern, grid, or display image behind the light-absorbing background material or behind it.

[0006] To completely erase the image, an appropriate voltage pulse is applied to the conductive layer, driving the cholesteric liquid crystal across the entire writing surface, including the previously pressurized area, to create a reflective texture.

[0007] When a liquid crystal device is completely erased, the cholesteric liquid crystal material becomes a reflective texture across the entire writing surface or screen. This can be referred to as the initial texture of the liquid crystal device or the initialized liquid crystal device.

[0008] In one embodiment, the user is positioned near a first substrate or front substrate to which pressure is applied, and a light-absorbing background material absorbs light passing through the liquid crystal layer. The light-absorbing background material and a second substrate or back substrate are further from the user than the front substrate. In one embodiment, the second substrate may be flexible. The user can turn the device over while remaining in the same position, and the user can apply pressure to the second substrate, in which case the user is closer to the second substrate than to the first substrate. In this disclosure, the term “substrate” is used collectively to include not only the main material of the film bulk but also any coatings or treatments on their surfaces.

[0009] Turning to a general first aspect of the present disclosure, the liquid crystal device comprises a first substrate and a second substrate spaced apart from each other, wherein the first substrate is transparent and flexible. A liquid crystal layer is disposed between the first substrate and the second substrate. The liquid crystal layer comprises a cholesteric liquid crystal material. The cholesteric liquid crystal material is configured to form an image by allowing pressure to be applied to the first substrate by a user without the application of voltage, thereby changing at least a portion of the cholesteric liquid crystal material from a reflective texture to a translucent texture.

[0010] Referring here to a specific feature of the first embodiment, the liquid crystal device comprises a light-absorbing background material that absorbs light passing through the liquid crystal layer. In another specific feature, the light-absorbing background material consists of a coating or layer on a second substrate. In yet another feature, the light-absorbing background material is opaque or translucent. Furthermore, the light-absorbing background material may comprise a second substrate that is opaque or translucent.

[0011] Another feature is that the second substrate is flexible, and pressure applied to the second substrate by the user changes at least a portion of the cholesteric liquid crystal material from a reflective texture to a translucent texture.

[0012] In another feature, the liquid crystal device comprises a first conductive layer disposed between a first substrate and a liquid crystal layer, and a second conductive layer disposed between a second substrate and a liquid crystal layer. In particular, the liquid crystal device may include an electronic circuit configured to apply an erase voltage to the first and second conductive layers, wherein the electronic circuit is an integral part of the liquid crystal device. A further variation is a combination of the liquid crystal device of the first embodiment and a separate erase device not permanently connected to the liquid crystal device, wherein the separate erase device comprises an electronic circuit configured to apply an erase voltage to the first and second conductive layers. In another feature, the image is erased by applying a voltage to the conductive layers to make the cholesteric liquid crystal material a reflective texture. In yet another feature, there is a cell gap between the first and second conductive layers, ranging in size from about 2 microns to about 4 microns.

[0013] Another characteristic is that the cholesteric liquid crystal material contains cholesteric liquid crystals dispersed in a polymer.

[0014] Another feature is that the liquid crystal device comprises a second liquid crystal layer laminated on top of the liquid crystal layer. In particular, the second liquid crystal layer is sandwiched between conductive layers. Another feature is that the liquid crystal device may comprise at least one intermediate substrate disposed between the liquid crystal layer and the second liquid crystal layer. Yet another feature is that the second liquid crystal layer comprises a second cholesteric liquid crystal material, and the cholesteric liquid crystal material and the second cholesteric liquid crystal material have opposite chiralities. Another feature is that the second liquid crystal layer comprises a second cholesteric liquid crystal material, and the cholesteric liquid crystal material and the second cholesteric liquid crystal material have different pitch lengths. In another feature, the liquid crystal device comprises a third conductive layer disposed between the intermediate substrate and the second liquid crystal layer, and a fourth conductive layer disposed between the second substrate and the second liquid crystal layer.

[0015] Other features relate to erasing the liquid crystal device by bending the device in various ways. In this context, the liquid crystal device comprises a first conductive layer disposed between a first substrate and a liquid crystal layer, and a second conductive layer disposed between a second substrate and a liquid crystal layer. In one feature, the image is partially or completely erased by bending caused by rolling or scrolling the liquid crystal device. In another feature, the image is partially or completely erased by bending caused by shaking or flapping the liquid crystal device. Another feature is that the image is partially or completely erased by bending caused by twisting the liquid crystal device. Another feature is that the image is partially or completely erased by bending caused by crumpling the liquid crystal device. Another feature is that the image is partially or completely erased by bending caused by removing the liquid crystal device from contact with an object.

[0016] Furthermore, the liquid crystal device may include a stylus for applying pressure.

[0017] In a second embodiment, the liquid crystal device comprises a first substrate and a second substrate spaced apart from each other, wherein the first substrate is flexible and transparent. A liquid crystal layer is disposed between the first substrate and the second substrate. The liquid crystal layer includes a cholesteric liquid crystal material. The liquid crystal device includes a light-absorbing background material that absorbs light passing through the liquid crystal layer. The cholesteric liquid crystal material allows the user to apply pressure to the first substrate without applying voltage to form a dark, pressure-applied mark, thereby making the surrounding areas where no pressure is applied appear bright.

[0018] Referring to a specific feature of the second embodiment, the liquid crystal device comprises a first conductive layer disposed between a first substrate and a liquid crystal layer, and a second conductive layer disposed between a second substrate and a liquid crystal layer. In another feature, the liquid crystal device comprises an electronic circuit configured to apply an erase voltage to the first and second conductive layers. The electronic circuit is an integral part of the liquid crystal device. Another feature is a combination of the liquid crystal device of the second embodiment and a separate erase device that is not permanently connected to the liquid crystal device. The separate erase device comprises an electronic circuit configured to apply an erase voltage to the first and second conductive layers.

[0019] In another feature of the second embodiment, the second substrate is flexible, and pressure applied to the second substrate by the user causes at least a portion of the cholesteric liquid crystal material to change from a reflective texture to a translucent texture.

[0020] While the above "Summary of the Disclosure" broadly describes the embodiments of the Disclosure, please understand that the following "Detailed Description" provides a more detailed explanation of the embodiments of the Disclosure and presents specific embodiments that should not be construed as necessary limitations of the Invention as broadly defined in the claims. Many additional features, advantages, and a better understanding of the Disclosure should be derived from the accompanying drawings and the following "Detailed Description". [Brief explanation of the drawing]

[0021] [Figure 1] A cross-sectional view of a typical prior art writing tablet showing drawing and erasing operations. [Figure 2] A front view of one form of the typical prior art writing tablet of FIG. 1 showing drawing and erasing operations. [Figure 3] A front view of another form of the typical prior art writing tablet of FIG. 1 showing drawing and erasing operations. [Figure 4] A cross-sectional view of the liquid crystal device of the present disclosure showing drawing and erasing operations. [Figure 5] A front view of one form of the liquid crystal device of FIG. 4 showing drawing and erasing operations. [Figure 6] A front view of another form of the liquid crystal device of FIG. 4 showing drawing and erasing operations. [Figure 7] A front view of the liquid crystal device of the present disclosure showing erasing by bending the device in various ways. [Figure 8A] A cross-sectional view of an embodiment having two stacked layers of cholesteric liquid crystal material. [Figure 8B] A front view of an embodiment having two stacked layers of cholesteric liquid crystal material.

Mode for Carrying Out the Invention

[0022] Figures 4 to 6 show cross-sections of a liquid crystal device 26 comprising a flexible first substrate or front substrate 3 and an optionally flexible second substrate or back substrate 4, not proportional to actual size. The first substrate 3 and the second substrate 4 are spaced apart from each other. A liquid crystal layer 27 is placed between the first substrate and the second substrate. The liquid crystal layer 27 contains cholesteric liquid crystal material. The front substrate 3 is transparent. The back substrate 4 can be transparent, or it can be translucent, opaque, or multicolored to function as a light-absorbing background material. An optional light-absorbing background material 24 absorbs light passing through the liquid crystal layer 27. The light-absorbing background material 24 can be coated or laminated onto the back substrate 4. If the back substrate 4 is light-absorbing, the separate light-absorbing background material 24 may be omitted. An optional second conductive layer 5 and an optional first conductive layer 6 are spaced apart, with a cholesteric liquid crystal layer 27 placed between them. The first conductive layer 6 is placed between the first substrate 3 and the liquid crystal layer 27, and the second conductive layer 5 is placed between the second substrate 4 and the liquid crystal layer 27. There is a cell gap or distance between the spaced-apart first conductive layer 6 and the second conductive layer 5 (or between adjacent substrates if no conductive layer is used). A spacer having a size approximating the cell gap is placed within the cell gap. In particular, the cell gap has a size in the range of about 2 microns to about 4 microns, most specifically about 2 microns. In one example, the first conductive layer 6 and the second conductive layer 5 can be adjacent to the liquid crystal layer 27, and more specifically, they can be formed as two coatings, one on the first substrate 3 and the other on the second substrate 4.

[0023] As would be understood by those skilled in the art upon considering the present disclosure, the liquid crystal device 26 is not limited by the presence or absence of a polymer layer or other material in the liquid crystal layer 27, or by the material present or absent between the liquid crystal layer 27 and the first conductive layer 6 or between the liquid crystal layer 27 and the second conductive layer 5, or by the material between the first conductive layer 6 and the first substrate 3 or between the second conductive layer 5 and the second substrate 4, or by the presence or absence of material on the outer surfaces of the first substrate 3 and the second substrate 4, and encompasses all these variations. The first conductive layer 6 disposed adjacent to the first substrate 3 can also be transparent, and the second conductive layer 5 disposed adjacent to the second substrate 4 can be transparent, translucent, or opaque. The conductive layers 5 and 6 may or may not be the same as each other and may or may not be patterned.

[0024] In the embodiments shown in FIGS. 4 to 6, the writing surface of the liquid crystal device 26 is on the front (first) substrate 3, and the first substrate is closer to the user compared to the back (second) substrate 4. The first substrate 3 may have various layers thereon, such as an antiglare coating and a scratch-resistant coating. On the other hand, the user can turn the liquid crystal device over while remaining in the same position and write on the second substrate 4 as the writing surface closer to the user compared to the first substrate 3. In the turned-over liquid crystal device 26, when writing on the second substrate 4, the light absorption layer may be rearranged on the other side of the liquid crystal layer 27 (i.e., the side farther from the user compared to the liquid crystal layer). This may be a permanent design or a temporary design, such as when using a removable light-absorbing background material 24 that can be moved from one substrate to the other.

[0025] The cholesteric liquid crystal material of the liquid crystal layer 27 is initially a reflective texture 29, and when viewed from the front, the screen or writing surface of the liquid crystal device 26 appears as a reflective color determined by the pitch of the cholesteric liquid crystal, in combination with the reflection spectra of layer 4 and the light-absorbing background material 24 (Figure 4, top and Figure 5). The liquid crystal device 26 is designed so that local deformation caused by pressure applied to the front substrate 3 by an external object 8 deforms the front substrate 3, changing at least a portion of the cholesteric liquid crystal texture from a reflective texture 29 to a translucent texture 28. A mark 31 containing the region of liquid crystal material of the translucent texture 28 is generated (Figure 6). There is a surrounding area 30 that is not subjected to pressure, consisting of one or more regions of the reflective liquid crystal material 29 for forming an image (Figure 4, middle and bottom, and Figure 6). This process does not require the application of voltage to create an image, and the formation of the translucent texture is a phenomenon that has not been used in liquid crystal devices to the best of the inventors' knowledge, which is of great significance. The translucent texture 28 generated by the local deformation remains even after the deformation is complete, allowing more ambient light to pass through the deformation region, i.e., the liquid crystal region including the mark 31, than passes through the surrounding portion 30 of the reflective texture to which no pressure has been applied. The light passing through the translucent texture 28 is absorbed and / or reflected by layers 4 and / or 24.

[0026] While we do not wish to be bound by theory, studies of the transmissive texture 28 using polarized light microscopy have shown similarities to classical focal conic textures, although they are not necessarily identical. The light-absorbing background material 24 absorbs most of the light passing through the transmissive texture 28 region of the liquid crystal layer 27 under localized pressure. The undeformed area of ​​the display screen or writing surface (periphery 30) remains a reflective texture 29 (appearing bright), reflecting some of the ambient light according to the circular polarization characteristics of the cholesteric liquid crystal of the planar texture. The non-bright or dark mark 31 contrasts with the bright peripheral region 30. The result when the liquid crystal device is viewed from the front is a visible mark 31 that contrasts with the peripheral region 30 (Figure 6). The mark 31 may be black, or it may be a color or hue that contrasts with the planar texture of the peripheral region 30.

[0027] For example, if a transparent back substrate 4 is provided with an optional black light-absorbing background material 24 and the pitch length of the cholesteric liquid crystal is adjusted to be green, the resulting front view of the device will have more or less black marks 31 (dark marks) and a green surrounding area 30 around the marks 31 (Figure 6). The black light-absorbing background material 24 absorbs most of the light passing through the area of ​​the translucent texture 28 of the liquid crystal layer 27 to which localized pressure is applied.

[0028] More specifically, cholesteric liquid crystals in a liquid crystal layer can be initialized into a reflective texture. This reflective texture is formed by several or all of the cholesteric liquid crystal domains having a helical axis orientation distribution substantially perpendicular to the plane of the substrate, enabling selective light reflection according to Bragg's law, well known in the prior art of liquid crystal materials. This configuration is often called a planar texture. Localized pressure applied to the device surface by a stylus or other object transforms the substantially bright reflective texture into a translucent texture only in the area where the localized pressure is applied. The translucent texture partially transmits light, allowing it to interact with the opposite layer of the device. This translucent texture is similar to, but not identical to, a focal conic texture. In a focal conic texture, some or most of the cholesteric liquid crystals along the helical axis of the domain are distributed in a more random orientation, allowing more light to pass through the transition region and scatter, and be absorbed and / or reflected by a light-absorbing background material on the back of the liquid crystal layer away from the writing surface (see U.S. Patent No. 6,104,448 incorporated herein by reference). Ambient light interacts differently with both the reflective and transmissive textures, producing an image with good contrast. The image remains permanent until the device is partially or completely erased.

[0029] Object 8 can be a stylus, a fingernail, or any force-generating entity capable of causing local deformation of the front substrate 3. Object 8 can be a solid object, but as a force-generating entity, it can be a local pressure caused by a liquid jet or gas jet. The liquid crystal layer 27 may contain cholesteric liquid crystals dispersed in the polymer, with or without additives.

[0030] While we do not wish to be bound by theory, nor do we understand that the inventor does not need to explain the mechanism behind the invention, the effect of applying localized pressure to the front substrate 3 that changes the cholesteric liquid crystal from a reflective texture to a transmissive texture is, surprisingly, the opposite of that of the prior art. It should be noted that this effect can be produced using the exact same cholesteric liquid crystal disclosed in the prior art (see, for example, U.S. Patent No. 8,228,301). However, this effect can be produced by either changing the polymer formulation of the polymer dispersed in the cholesteric liquid crystal dispersion (see Example 1) or by adding a non-reactive additive such as mineral oil to the prior art dispersion material (Example 2). In both formulations of Examples 1 and 2, this effect occurs when the distance between the first substrate or front substrate 3 and the second substrate or back substrate 4 is in the range of about 2 μm to about 4 μm. In some cases, this effect is enhanced by increasing the surface energy of the substrate surface closest to the cholesteric liquid crystal material. For example, modified forms can be created in UV / ozone substrate surface treatments that increase the substrate surface energy. Those skilled in the art should be able to modify the features of the examples without excessive experimentation to arrive at other cholesteric liquid crystal materials or devices having the same properties as those described in the claims of this disclosure. Modified forms of the formulations in Examples 1 and 2 may be produced, for example, by using different initiators, crosslinkers, monomers, cholesteric liquid crystal compounds, or nematic liquid crystal compounds. For example, modifications can be made to the formulations intended to increase contrast or change linewidth while remaining within the scope of this disclosure. By using various processing conditions, such as curing irradiance and curing time, devices having the properties described in this disclosure can be obtained. These changes in composition, structure, and processing create systems that respond differently to different types of forces. Local compressive forces result in a translucent texture contrasting with the reflective surrounding areas.While we do not wish to be bound by theory, it is thought that polymer morphology and / or plasticizing effects of non-reactive materials can influence the rheological behavior of liquid crystals, thus allowing them to flow differently depending on the applied force and rearrange into different textures when they relax after the flow has ended.

[0031] In one embodiment, conductive layers 5 and 6 may be connected to an electronic circuit 33 configured to create a new, complete page for writing on again by applying an appropriate voltage pulse V2 (Figures 4 and 5) that refreshes the entire device to an initial reflective texture 29 (i.e., erases the entire visible area, screen, or writing surface). The electronic circuit 33 does not need to be permanently attached to the device. For example, the electronic circuit 33 may be a separate unit from the liquid crystal device, with the liquid crystal device periodically electrically engaging when erasure is desired (see U.S. Patent No. 9,651,813 incorporated herein by reference). The voltage profile required to drive the cholesteric liquid crystal to a reflective or planar texture follows the well-known electro-optical transition mechanism of cholesteric liquid crystals (see U.S. Patents No. 5,437,811 and 5,453,863 incorporated herein by reference). The appropriate voltage pulses or pulse sequences supplied by the erase circuit 33 to drive the cholesteric liquid crystal into a reflective or planar texture are sufficient to erase the written image and refresh or initialize the device. It is not necessary to apply a constant voltage to maintain the reflective or transmissive texture, as in the embodiments described above.

[0032] In another embodiment, the liquid crystal layer is configured such that appropriate mechanical bending of the liquid crystal device 26 initializes the cholesteric liquid crystal material to a reflective texture 29 and erases the written image, allowing the liquid crystal device 26 to be reused. In this regard, the device comprises a first conductive layer and a second conductive layer on either side of the liquid crystal layer, so that erasing can still be performed electronically. The act of bending the liquid crystal device provides an alternative way to erase the liquid crystal device instead of applying a voltage. When the device is erased by bending, the conductive layer is bent along with the rest of the device. This is also possible if one attempts to write on the liquid crystal device 26 (after or otherwise) and attempts to erase the liquid crystal device by applying a voltage. The left side of Figure 7 shows a schematic front view of the liquid crystal device 26 including a light-transmitting mark 31 and a bright reflective texture on the surrounding portion 30 around the mark 31. The right side of Figure 7 shows the liquid crystal device in its initial state, with the entire writing surface exhibiting a reflective texture.

[0033] By applying various bending modes to a liquid crystal device in a written state, complete erasure of an image can be achieved. Complete erasure of a reflective texture utilizes the ripple of bending stress moving across the flexible device. Figure 7 shows various ways of bending a liquid crystal device for erasure, changing the liquid crystal device from a state with writing or a mark 31 on a translucent texture with a peripheral portion 30 of reflective texture around the mark (left figure) to a state where the entire writing surface of the device 26 is initially a reflective texture 29 (right figure). For example, the liquid crystal device 26 can be bent by holding it with both hands and bending it (bend and erase 35). In another example, the liquid crystal device 26 may be bent by shaking the device until erasure is achieved (shake and erase 36). If the substrate is sufficiently thin, the liquid crystal device 26 can be bent inward and / or outward to bend the entire device area, enabling useful applications such as rolling, erasing writing or drawing when rolled inward and outward (roll and erase 37). Bending across the liquid crystal device area can also be achieved by peeling the flexible device away from the object it is in contact with (peel off and erase 38). There are many other examples of substrate bending that can be used to achieve complete erasure, such as torsion, twisting, and even crumpling (39).

[0034] The erase sensitivity can also be adjusted. This means that the erase process may require completing one to several cycles of a selected bending mode. Again, this depends on the application. For example, in "peel and erase" applications, complete erasure can be achieved on the first attempt to remove the flexible device from the surface to which it is attached. On the other hand, in other applications, several bends or oscillations may be required to completely erase the liquid crystal device, which is desirable to prevent accidental erasure.

[0035] The multilayer liquid crystal device 26 may be flexible if it is designed to be erased by bending, for example. Naturally, this does not prevent the liquid crystal device from having non-flexible elements, as long as this does not hinder erasure by bending the multilayer liquid crystal device. In one example, the back substrate may be a thicker element that allows for less bending of the multilayer liquid crystal device, but is still thick enough to allow erasure by bending. The sides of the liquid crystal device may be sealed in ways known to those skilled in the art, including but not limited to sealing gaskets and laser singulation. For example, such sealing prevents delamination when the liquid crystal device is bent to erase. In another example, the liquid crystal device may have a non-flexible frame or bezel, but still allow bending for erasure. On the other hand, the liquid crystal device 26 may be partially non-flexible, for example, if it is not designed to use bending for erasure.

[0036] Embodiments of the laminated liquid crystal layers are shown in Figures 8A and 8B. In this structure, two or more layers of cholesteric liquid crystal material (a first liquid crystal layer 11 and a second liquid crystal layer 12) are laminated and may share one common transparent intermediate substrate 13 that is flexible. Alternatively, the intermediate substrate 13 can be replaced with two optically coupled flexible transparent or translucent substrates. The front surface of the first substrate 3 serves as a flexible writing surface, while the back substrate of the light-absorbing layer 24 or the second substrate 4 and an optional coating function as a background material depending on the reflective / absorbent properties of their combined effect. The laminated device comprises conductive layers 18, 19, 20, and 21. The first conductive layer 18 is positioned between the first substrate 3 and the liquid crystal layer 11, the second conductive layer 19 is positioned between the intermediate substrate 13 and the liquid crystal layer 11, the third conductive layer 20 is positioned between the intermediate substrate 13 and the second liquid crystal layer 12, and the fourth conductive layer 21 is positioned between the second substrate 4 and the second liquid crystal layer 12. The liquid crystal layer 11 is positioned in the cell gap between the conductive layers 18 and 19, and the second liquid crystal layer 12 is positioned in the cell gap between the conductive layers 20 and 21. The cholesteric liquid crystal material of the first liquid crystal layer 11 and the second liquid crystal layer 12 is designed such that local pressure applied by a moving or stationary object 8 causes local deformation in the front substrate 3 and the intermediate substrate(s) 13, changing the reflective texture 40, 32 of both liquid crystal layers 11 and 12, which are not subjected to pressure, to the translucent texture 14, 15 in the areas where local pressure is applied. The regions of the translucent textures 14 and 15 may or may not be the same. The regions of the translucent textures 14 and 15, as well as the regions of the planar textures 40 and 32, are stable even without an electric field. The reflective textures 40 and 32 are inherent to the cholesteric liquid crystal material and have a reflective color that depends on their pitch length, and the reflective color is influenced by any color of layer 4 and the light-absorbing background material 24 observed when viewed from the front (Figure 8B). The mark 17 formed by the translucent texture contrasts with the bright mixed color of the reflective color regions of reflective texture 40 and reflective texture 32, shown by the peripheral portion 16 of the reflective texture in Figure 8B.If the texture is transparent, regions 14 and 15 allow the second substrate 4 and / or any light-absorbing background material 24 to be seen. The reflected color of the reflective (e.g., planar) texture 40 in the first liquid crystal layer 11 blends with the reflected color of the reflective (e.g., planar) texture 32 in the second liquid crystal layer 12 and is further influenced by the colors from the layers below the liquid crystal layer 12, such as displays, patterns, etc. (e.g., the colored light-absorbing background material 24). The regions of the reflective textures 40 and 32 are regions that are not pressed down and no pressure is applied. Another example is when the light-absorbing background material 24 is a translucent layer. The stacked multilayer liquid crystal device may be flexible. This does not prevent the use of non-flexible elements or components in the device, as described above for the liquid crystal device 26.

[0037] The advantage of this type of structure is that by combining the optical properties of multiple layers, it is possible to achieve effects that are difficult or impossible with a single layer. For example, the first liquid crystal layer 11 and the second liquid crystal layer 12 may contain cholesteric liquid crystals having the same pitch length (same color) but opposite chirality, resulting in a total reflectance exceeding 50%, which is the theoretical limit for a single layer. The first liquid crystal layer 11 and the second liquid crystal layer 12 may have different colors that are additionally mixed, providing colors that cannot be achieved with a single layer alone. For example, a liquid crystal device comprising a blue first liquid crystal layer 11 and a yellow second liquid crystal layer 12, when it has a reflective texture, provides a broader wavelength range that is close to the appearance of a white background material, which is desirable in certain applications, through the additional mixing of these colors. The presence of conductive layers 18, 19, 20, and 21 allows for the application of appropriate voltages provided by electronic erase circuits 22 and 23, which convert all of the first liquid crystal layer 11 and the second liquid crystal layer 12, including the previously written areas of the translucent textures 14 and 15, into reflective textures, thereby initializing the device as described in Figure 4. The erase circuits 22 and 23 do not need to be part of the stacked liquid crystal device, but can be part of a separate erase device that is not permanently attached to the stacked liquid crystal device. [Examples]

[0038] This disclosure presents specific embodiments, which should not be used in any way to limit the subject matter defined in the claims. [Examples]

[0039] • Raw materials and preparation of mixture A A composition containing the following components, namely 0.39 (w / w)% Irgacure 819 (purchased from IGM resins), 2.23 (w / w)% methyl methacrylate, 4.60 (w / w)% bisphenol A ethoxylate diacrylate, 6.16 (w / w)% di(ethylene glycol) 2-ethylhexyl ether acrylate, and 0.66 (w / w)% 2-hydroxyethyl methacrylate (all purchased from Sigma-Aldrich), was vortex-mixed in a brown vial. To this vial, 18.82 (w / w)% MDA-00-3506 nematic liquid crystal and 66.97 (w / w)% MDA-01-1955 cholesteric liquid crystal (both obtained from Merck) were added. A clear solution was obtained using mechanical stirring. 0.2 (w / w)% of 2 μm plastic spacers (purchased from Nanomicro) were added to this mixture and dispersed by ultrasound. The components are based on the total weight of the composition.

[0040] • Liquid crystal device manufacturing Transparent 5-mil polyethylene terephthalate (PET) film and transparent 7-mil PET film were treated with UV ozone and coated with AGFA conductive polymer PEDOT:PSS S300 to obtain sheet resistances of 150 Ω / sq to 800 Ω / sq. Mixture A was laminated between these films with the conductive polymer side adjacent to the mixture. Lamination conditions were set to achieve a cell gap of approximately 2 μm. The reactive mixture was cured through the 5-mil substrate using a UV lamp. After curing, the PET on the opposite side of the cured surface was coated with black ink.

[0041] • LCD device operation A 50Vrms square wave, well-known in the art, was applied to the device at 20Hz to drive the liquid crystal to its initial reflective state. When direct pressure was applied to the transparent 5-mil PET side using an object, the reflectivity of the deformed area decreased, forming a transmissive mark on the liquid crystal layer with higher transmittance through the cholesteric liquid crystal material layer than the undepressed reflective portion of the display screen. The black ink layer absorbed the light passing through the mark, creating contrast with the surrounding area, which is the reflective texture of the undeformed region. A 50Vrms square wave was applied at 20Hz to refresh the device and return it to its initial reflective texture. [Examples]

[0042] • Raw materials for mixture B A composition containing the following components, namely 0.47 (w / w)% Irgacure 651 (IGM resins), 19.25 (w / w)% methyl methacrylate, 3.47 (w / w)% trimethylolpropane triacrylate, and 0.40 (w / w)% lauryl methacrylate (all purchased from Sigma-Aldrich), was vortex-mixed in a brown vial. 14.86 (w / w)% MDA-00-3506 and 55.90 (w / w)% MDA-01-1955 (both from Merck), along with 0.94 (w / w)% 4 μm plastic spacer (Nanomicro) and 4.71% mineral oil (CVS brand), were added. This mixture was further mixed ultrasonically for 20 minutes.

[0043] • Liquid crystal device manufacturing Transparent 5-mil polyethylene terephthalate (PET) film and transparent 7-mil PET film were treated with UV ozone and coated with AGFA conductive polymer PEDOT:PSS S300 to obtain sheet resistances of 150 Ω / sq to 800 Ω / sq. Mixture B was laminated between these films with the conductive polymer side adjacent to the mixture. Lamination conditions were set to achieve a cell gap of approximately 4 μm. The reactive mixture was cured using a UV lamp adjacent to the 5-mil substrate and through the 5-mil substrate. After curing, the PET on the opposite side of the cured surface was coated with black ink.

[0044] • LCD device operation A 50Vrms square wave was applied to the device at 20Hz to drive the liquid crystal to its reflective state. When direct pressure was applied to the transparent 5 mil PET side using an object, the reflectivity of the deformed area decreased, and the light transmittance through the cholesteric liquid crystal material layer increased, forming a dark mark, which is a translucent texture, on the liquid crystal layer. The black ink layer absorbed the light passing through the liquid crystal of the mark, creating contrast with the surrounding area, which is a reflective texture in the undeformed area. A 50Vrms square wave was applied at 20Hz to refresh the device and return it to its initial reflective texture.

[0045] Many modifications and variations will become apparent to those skilled in the art upon reading the above disclosure. Therefore, it should be understood that the present invention may be implemented in ways other than those specifically illustrated and described within the scope of the attached claims. [Explanation of symbols]

[0046] 2...Semi-transparent texture or focal conic texture, 3...First substrate or front substrate, 4...Second substrate or back substrate, 5...Transparent electrode or second conductive layer, 6...Transparent electrode or first conductive layer, 7...Black surrounding area, 8...Object, 9...Reflective texture or planar texture, 10...Mark, 11...First liquid crystal layer, 12...Second liquid crystal layer, 13...Intermediate substrate, 14...Transparent texture, 15...Transparent texture, 16...Surrounding area, 17...Mark, 18...First conductive layer, 19...Second conductive layer, 20...Third conductive layer, 21... 4th conductive layer, 22...erasure circuit, 23...erasure circuit, 24...light-absorbing background material or light-absorbing layer, 25...voltage, 26...liquid crystal device, 27...liquid crystal layer, 28...transparent texture, 29...reflective texture or reflective liquid crystal material, 30...surrounding area, 31...mark, 32...reflective texture or planar texture, 33...electronic circuit or erase circuit, 35...bend to erase, 36...shake to erase, 37...roll up to erase, 38...peel to erase, 39...crumple, 40...reflective texture or planar texture, V2...voltage pulse

Claims

1. A first substrate and a second substrate arranged at a distance from each other, wherein the first substrate is flexible and transparent, A liquid crystal layer containing a cholesteric liquid crystal material is disposed between the first substrate and the second substrate. A liquid crystal device comprising, A liquid crystal device in which the cholesteric liquid crystal material is configured such that, without applying a voltage, pressure is applied to the first substrate by a user, thereby changing at least a portion of the cholesteric liquid crystal material from a reflective texture to a transmissive texture and forming an image.

2. The liquid crystal device according to claim 1, further comprising a light-absorbing background material that absorbs light passing through the liquid crystal layer.

3. The liquid crystal device according to claim 2, wherein the light-absorbing background material is composed of a coating or layer on the second substrate.

4. The liquid crystal device according to claim 2, wherein the light-absorbing background material is opaque or translucent.

5. The liquid crystal device according to claim 2, wherein the light-absorbing background material is composed of the opaque or translucent second substrate.

6. The liquid crystal device according to claim 1, wherein the second substrate is flexible, and pressure applied to the second substrate by the user causes at least a portion of the cholesteric liquid crystal material to change from the reflective texture to the transmissive texture.

7. The liquid crystal device according to claim 1, comprising a first conductive layer disposed between the first substrate and the liquid crystal layer, and a second conductive layer disposed between the second substrate and the liquid crystal layer.

8. The liquid crystal device according to claim 7, comprising an electronic circuit configured to apply an erase voltage to the first conductive layer and the second conductive layer, wherein the electronic circuit is an integral part of the liquid crystal device.

9. A combination of a liquid crystal device according to claim 7 and a separate erase device that is not permanently connected to the liquid crystal device, A combination wherein the separate erasing device comprises an electronic circuit configured to apply an erasing voltage to the first conductive layer and the second conductive layer.

10. The liquid crystal device according to claim 7, wherein the image is erased by applying a voltage to the conductive layer that makes the cholesteric liquid crystal material the reflective texture.

11. The liquid crystal device according to claim 7, wherein the cell gap between the first conductive layer and the second conductive layer is in the range of about 2 microns to about 4 microns in size.

12. The liquid crystal device according to claim 1, wherein the cholesteric liquid crystal material comprises cholesteric liquid crystal dispersed in a polymer.

13. The liquid crystal device according to claim 1, further comprising a second liquid crystal layer laminated on the aforementioned liquid crystal layer.

14. The liquid crystal device according to claim 13, comprising at least one intermediate substrate disposed between the liquid crystal layer and the second liquid crystal layer.

15. The liquid crystal device according to claim 13, wherein the second liquid crystal layer comprises a second cholesteric liquid crystal material, and the cholesteric liquid crystal material and the second cholesteric liquid crystal material have opposite chiralities.

16. The liquid crystal device according to claim 13, wherein the second liquid crystal layer comprises a second cholesteric liquid crystal material, and the cholesteric liquid crystal material and the second cholesteric liquid crystal material have different pitch lengths.

17. The liquid crystal device according to claim 14, further comprising a third conductive layer disposed between the intermediate substrate and the second liquid crystal layer, and a fourth conductive layer disposed between the second substrate and the second liquid crystal layer.

18. The liquid crystal device according to claim 7, wherein the image is partially or completely erased by bending caused by rolling or winding the liquid crystal device.

19. The liquid crystal device according to claim 7, wherein the image is partially or completely erased by bending caused by shaking or flapping the liquid crystal device.

20. The liquid crystal device according to claim 7, wherein the image is partially or completely erased by bending caused by twisting the liquid crystal device.

21. The liquid crystal device according to claim 7, wherein the image is partially or completely erased by bending caused by crumpling the liquid crystal device.

22. The liquid crystal device according to claim 7, wherein the image is partially or completely erased by bending that occurs when the liquid crystal device is removed from contact with an object.

23. The liquid crystal device according to claim 1, comprising a stylus for applying the aforementioned pressure.

24. A first substrate and a second substrate arranged at a distance from each other, wherein the first substrate is flexible and transparent, A liquid crystal layer containing a cholesteric liquid crystal material disposed between the first substrate and the second substrate, A light-absorbing background material that absorbs light transmitted through the liquid crystal layer and A liquid crystal device comprising, A liquid crystal device in which the cholesteric liquid crystal material allows a user to apply pressure to the first substrate without applying voltage, thereby forming a dark, pressure-applied mark, and the surrounding area where no pressure is applied appears bright.

25. The liquid crystal device according to claim 24, comprising a first conductive layer disposed between the first substrate and the liquid crystal layer, and a second conductive layer disposed between the second substrate and the liquid crystal layer.

26. The liquid crystal device according to claim 25, comprising an electronic circuit configured to apply an erase voltage to the first conductive layer and the second conductive layer, wherein the electronic circuit is an integral part of the liquid crystal device.

27. A combination of the liquid crystal device described in claim 25 and a separate erase device that is not permanently connected to the liquid crystal device, A combination wherein the separate erasing device comprises an electronic circuit configured to apply an erasing voltage to the first conductive layer and the second conductive layer.

28. The liquid crystal device according to claim 24, wherein the second substrate is flexible, and pressure applied to the second substrate by the user causes at least a portion of the cholesteric liquid crystal material to change from a reflective texture to a transmissive texture.

Images