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1. WO2020200164 - A SELECTIVELY ERASABLE LIQUID CRYSTAL WRITING BOARD

Document

Description

Title of Invention 0001   0002   0003   0004   0005   0006   0007   0008   0009   0010   0011   0012   0013   0014   0015   0016   0017   0018   0019   0020   0021   0022   0023   0024   0025   0026   0027   0028   0029   0030   0031   0032   0033   0034   0035   0036   0037   0038   0039   0040   0041   0042   0043   0044   0045   0046   0047   0048   0049   0050   0051   0052   0053   0054   0055   0056   0057   0058   0059   0060   0061   0062  

Claims

1   2   3   4   5   6   7   8   9   10   11   12   13   14   15   16   17   18  

Drawings

1   2   3   4   5   6  

Description

Title of Invention : A selectively erasable liquid crystal writing board

Field of the Invention

[0001]
The invention relates to the technical field of liquid crystal applications, in particular to a selectively erasable liquid crystal writing board.

Background of the Invention

[0002]
At present, in the fields of education, business and the like, the application of liquid crystal writing boards becomes wider and wider, and the continuous development of liquid crystal writing board technologies and the updating and replacement of products are promoted on the performance requirements of liquid crystal writing boards. The first generation of writing boards is a digital board, which requires expensive production equipments, and its writing cannot be precisely controlled. Along the rapid development of the display technologies, the second generation of writing boards with a capacitance screen is generated, where a touch operation is realized through static electricity of a human body and thus the control is sensitive. However, the screen touch operation cannot be carried out after gloves are worn. Even if a professional stylus is used, fine operation cannot be carried out and writing experience is not ideal. As the third generation, flexible liquid crystal writing boards have highly improved performances. Based on the pressure sensitive technology, the stroke weigh difference can be changed by controlling the pressure of a pen point during writing or drawing, and drawing effect and writing consistency of the writing boards is close to that of the paper. Moreover, ever lack of a professional stylus, the colorful writing can be realized by a pencil or other hard objects. The flexible liquid crystal writing boards belong to active display without a backlight source and polarizers, therefore difficulty of production process and cost are greatly reduced and monochrome and multicolor display can be realized.
[0003]
At present, most of commercial liquid crystal writing boards are whole screen erased, which greatly limits their application in the huge education market. In theory, the selectively erasing technique is to re-orientate liquid crystal molecules from a reflective state to a weak scattering state in a selected area.
[0004]
The most common methods are the following three methods: 1, compressing the thickness of liquid crystal layer to increase partial electric field intensity; 2, heating liquid crystals to their clear point and then cooling down to room temperature to eliminate writing; 3, using a electrode matrix by etching ITO conductive film into rows, where upper and lower ITO conductive films are vertically arranged to form a matrix and intersection points can be erased by the control of a driving device. Method 1 has the problems of darkening along time, large erasing force, erasing trace residue and the like; method 2 has slow heat transfer rate, danger of scalding and large energy consumption; and method 3 has the disadvantages of high cost, erasing trace residue, misoperation and the like. Moreover, during them, only method 1 realized productization in occasions where a low erasing quality is required, such as a child graffiti drawing board.
[0005]
In conclusion, the current market has no selectively erasing technologies which can be applied to large-size writing boards, and technological breakthrough is the key to the wide use of liquid crystal writing boards in education.
[0006]
Summary of the Invention
[0007]
The purpose of the present invention is to solve the above technical problems in the prior art, and disclose a liquid crystal writing board capable of realizing selectively erasing. The erasing operation is concise and convenient, the cost is low, and no erasing trace residue exists.
[0008]
The technical scheme of the present invention is as follows:
[0009]
A selectively erasable liquid crystal writing board, wherein the liquid crystal writing board comprises: a first substrate, a first conductive layer, a functional layer, a liquid crystal layer, a second transparent conductive layer and a second transparent substrate stacked in sequence, wherein an external electric field can be applied to the selectively erasable liquid crystal writing board via the first conductive layer and the second transparent conductive layer, wherein upon application of an external mechanical pressure on a selected area of the liquid crystal writing board, the fractional voltage across the functional layer in the selected area is reduced, and the fractional voltage across the liquid crystal layer in the selected area is increased to reach a threshold voltage required to switch the liquid crystal molecules in the liquid crystal layer to a desired state.
[0010]
In a preferred embodiment, the functional layer comprises polymers mixed with conductive particles.
[0011]
In a preferred embodiment, the functional layer comprises a composite polymer layer coated with plurality of isolated first conductive islands on the side facing the first conductive layer, wherein the composite polymer layer is substantially uniformly separated from the first conductive layer using spacers.
[0012]
In a preferred embodiment, the spacing between the first conductive layer and the composite polymer layer is between 1μm and 50μm.
[0013]
In a preferred embodiment, the isolated first conductive islands are comprised of closely arranged conductive patches with shapes of triangles, rectangles, squares, circles, diamonds, parallelograms, trapezoids, other regular or irregular polygon or combinations thereof.
[0014]
In a preferred embodiment, the relative dielectric constant of the composite polymer layer is between 20 and 200.
[0015]
In a preferred embodiment, the thickness of the composite polymer layer is between 30μm and 500μm.
[0016]
In a preferred embodiment, the composite polymer layer comprises a polymer host and nanoparticle dopants of high dielectric constants.
[0017]
In a preferred embodiment, the polymer is one or more selected from the group of polyethylene, polymethyl methacrylate, polyvinyl chloride, polycarbonate, polyvinylidene fluoride, urea-formaldehyde resin, unsaturated polyester resin, polytetrafluoroethylene and polyimide.
[0018]
In a preferred embodiment, the material of the nanoparticle dopants is one or more selected from the group of silver, carbon nanotubes, conductive carbon powder, nickel and barium titanate.
[0019]
In a preferred embodiment, the functional layer further comprises plurality of isolated second conductive islands on the side facing the liquid crystal layer.
[0020]
In a preferred embodiment, the functional layer comprises a polymer layer and a plurality of hollow microspheres dispersed in the polymer layer.
[0021]
In a preferred embodiment, the hollow microspheres have a diameter of 20μm-150μm.
[0022]
In a preferred embodiment, the first conductive layer and the second transparent conductive layer are one or more selected from the group of ITO, graphene, nano-silver and other metal conductive layers.
[0023]
In a preferred embodiment, the liquid crystal layer comprises a polymer and liquid crystals dispersed in the polymer.
[0024]
In a preferred embodiment, the liquid crystal layer further comprises a plurality of spacers dispersed in the polymer.
[0025]
In a preferred embodiment, the liquid crystals are cholesteric liquid crystals.
[0026]
In a preferred embodiment, the functional layer is disposed between the liquid crystal layer and the second transparent conductive layer.
[0027]
The selectively erasable liquid crystal writing board of the present invention has advantages of a convenient and simple erasing operation, low cost, and no erasing trace residue.

Brief Description of the Drawings

[0028]
The present invention will become more apparent by the description of embodiments thereof with reference to the attached drawings in which:
[0029]
FIG. 1 is a schematic view illustrating the cross-section of a selectively erasable liquid crystal writing board according to the first embodiment of the present invention;
[0030]
FIG. 2 is a schematic view illustrating the cross-section of a selectively erasable liquid crystal writing board according to the second embodiment of the present invention;
[0031]
FIG. 3 is a schematic view illustrating the cross-section of a selectively erasable liquid crystal writing board according to the third embodiment of the present invention;
[0032]
FIG. 4 is a top view of the electrode layer in a selectively erasable liquid crystal writing board according to the second and the third embodiments of the present invention;
[0033]
FIG. 5 is a schematic view illustrating the possible shapes of electrodes in the electrode layer according to the second and third embodiments of the present invention;
[0034]
FIG. 6 is a schematic view illustrating the cross-section of a selectively erasable liquid crystal writing board according to the fourth embodiment of the present invention.

Detailed Description of the Invention

[0035]
In the following description, for the purpose of explanation so as to have a comprehensive understanding of the invention, numerous specific details are disclosed, however, it is obvious to those skilled in the art, that the invention can be implemented without these specific details. In other embodiments, well-known structures and devices are shown in block diagrams in the invention. The exemplary embodiments are merely illustrative of the invention, rather than limiting the scope of the present invention being defined by appended claims thereof.
[0036]
Embodiment 1
[0037]
As shown in FIG. 1, the selectively erasable liquid crystal writing board of this embodiment includes a first substrate 10, a first conductive layer 20, a functional layer 30, a liquid crystal layer 40, a second transparent conductive layer 50, and a second transparent substrate 60 stacked in sequence, where an external electric field can be applied to the selectively erasable liquid crystal writing board via the first conductive layer 20 and the second transparent conductive layer 50. When an external mechanical pressure is applied on a selected area of the liquid crystal writing board, the thickness of the functional layer 30 in the selected area is reduced, which causes decreasing of the fractional voltage across the functional layer 30 and increasing of the fractional voltage across the liquid crystal layer 40 in the selected area to reach a threshold voltage required to switch the liquid crystal molecules in the liquid crystal layer to a desired state, which is an erasing state in this case.
[0038]
In this embodiment, the functional layer 30 is a pressure sensitive conductive film. When a force is applied to a selected area from outer side of the second transparent substrate 60 that is locally deformable, the second transparent substrate 60 in the area is bent, causing the resistivity of the functional layer 30 in the area to be reduced due to extrusion. When a certain electric field is applied between the first conductive layer 20 and the second transparent conductive layer 50, since the resistivity of the functional layer 30 is reduced, the fractional voltage across the functional layer 30 is also reduced, while the fractional voltage across the liquid crystal layer 40 is increased, causing the voltage applied to the liquid crystal molecules in the liquid crystal layer 40 of the selected area reaches a threshold value. As a result, the liquid crystal molecules in the selected area are rotated (i.e., the orientation of the liquid crystal molecules is changed from the reflective state to the scattering state. ) to achieve selectively erasing in the area. When the liquid crystal writing board requires whole screen erasing, an external driving circuit 70 applies a larger voltage than the threshold value through the whole screen between the first conductive layer 20 and the second transparent conductive layer 50.
[0039]
In this embodiment, the functional layer 30 may be a thin film composed of a single material or a thin film composed of two or more substances, for example, the pressure sensitive conductive film is comprised of polymers mixed with conductive particles. In this case, part of conductive particles along the electric field direction will contact each other due to the elastic deformation of the functional layer 30 upon the external mechanical pressure, causing the resistivity of the functional layer in the area to be decreased. But not limited thereto, any material whose resistance value can be changed by external pressure can be used.
[0040]
In this embodiment, the functional layer 30 may be disposed between the liquid crystal layer 40 and the second transparent conductive layer 50, as long as the transmittance of the functional layer 30 meets the requirement.
[0041]
In this embodiment, the first conductive layer 20 and the second transparent conductive layer 50 are one or more selected from the group of ITO, graphene, nano-silver, and other conductive materials. The first conductive layer 20 may be transparent or opaque. The liquid crystal layer 40 includes a polymer and liquid crystals dispersed in the polymer. Preferably, the liquid crystal layer 40 further comprises a plurality of spacers dispersed in the polymer to define the thickness of the liquid crystal layer 40. In this embodiment, the liquid crystals are preferably cholesteric liquid crystals.
[0042]
Embodiment 2
[0043]
The same technical features as the first embodiment will not described any more in this embodiment. As shown in FIG. 2, the functional layer 30 in this embodiment includes a composite polymer layer 31 coated with plurality of isolated first conductive islands 32 on the side facing the first conductive layer 20, where the composite polymer layer 31 is substantially uniformly separated from the first conductive layer using spacers 33.
[0044]
In this embodiment, the spacing between the first conductive layer and the composite polymer layer is between 1μm and 50μm. More preferably, the spacing is between 8μm and 20μm, such as 8μm, 12μm and 20μm. In this embodiment, the shape of the spaces 33 is sphere, but not limited thereto, the spacers 33 may also have a shape of pillar or other shapes.
[0045]
In this embodiment, when a press force is applied to a selected area from outer side of the second transparent substrate 60 of locally deformable, the corresponding area of the second transparent substrate 60 is bent, and thus part of the first conductive islands 32 in the area will be pressed down and contact the first conductive layer 20 across the spacers 33 to realize a electrical connection. As a result, the fractional voltage across the functional layer 30 in the area is reduced, while the fractional voltage across the liquid crystal layer 40 is increased, causing the voltage applied to the liquid crystal molecules in the liquid crystal layer 40 of the selected area to reach a threshold value. Therefore, the liquid crystal molecules in the selected area are rotated (i.e., the orientation of the liquid crystal molecules is changed from the reflective state to the scattering state. ) to achieve selectively erasing in the area. When the liquid crystal writing board requires whole screen erasing, an external driving circuit 70 applies a larger voltage than the threshold value through the whole screen between the first conductive layer 20 and the second transparent conductive layer 50.
[0046]
In this embodiment, preferably, the composite polymer layer 31 contains a high dielectric constant material, thus further decreasing the driving voltage of the liquid crystal writing board. The relative dielectric constant of the composite polymer layer 31 is between 20 and 200. In this case, the liquid crystal layer 40 and the composite polymer layer 31 are equivalent to two capacitors in series by neglecting the resistive effect, therefore the fractional voltage across the liquid crystal layer 40 is positively related to the capacitance value of the composite polymer layer 31. When the capacitance value is increased along with the dielectric constant of the composite polymer layer, the fractional voltage across the liquid crystal layer is also increased, which is more favorable for the threshold voltage to be reached. The film thickness of the composite polymer layer 31 is between 30μm and 500μm. In this embodiment, the composite polymer layer 31 includes a polymer host and nanoparticle dopants of high dielectric constants. Preferably, the polymer is one or more selected from the group of polyethylene (PE) , polymethyl methacrylate (PMMA) , polyvinyl chloride (PVC) , polycarbonate (PC) , polyvinylidene fluoride (PVDF) , urea-formaldehyde resin (UF) , unsaturated polyester resin (UP) , polytetrafluoroethylene (PTFE) , polyimide (PI) , and the like. The material of the nanoparticle dopants is one or more selected from silver, carbon nanotubes, conductive carbon powder, nickel and barium titanate.
[0047]
In this embodiment, the first conductive islands 32 form a pattern, such as a figure, a word or others. Preferably, the first conductive islands 32 may be an array of square patches arranged closely and independently to one another. As shown in the FIG. 4, for example, the square electrodes may have a side length of 0.5 mm to 10mm, and the spacing between adjacent square patterns is between 50μm and 200μm. But not limited thereto, for example, as shown in FIG. 5, the shape of the first conductive islands 32 may also be triangles, rectangles, squares, circulars, diamonds, parallelograms, trapezoids, regular hexagon, regular octagon, other regular or irregular polygons, or their combination, whose size is between 1μm and 10mm. The patterns of the first conductive islands 32 may be appropriately set according to the specific dimensions of the selectively erasable liquid crystal writing board. In this embodiment, if the first conductive islands have a same shape, the area according to these first conductive islands can be regarded as the smallest erasing unit. During a selectively erasing process, when any part of one erasing unit or multiple erasing units is pressed, the writing on the whole part of that erasing unit or the multiple erasing units will be erased.
[0048]
In this embodiment, for example, the composite polymer layer 31 has a film thickness of 30μm, a dielectric constant of 30, a resistivity of more than 1010Ω·cm, and a black color. A silver electrode is evaporated on the lower surface of the composite polymer layer and is etched to form first conductive islands 32 which have an array of 10mm*10mm square electrodes with a spacing of 0.2mm. The second transparent substrate 60 employs a transparent flexible PET of 180μm thickness. The spacing between the first conductive layer 20 and the composite polymer layer 31 is supported by spherical spacers with a diameter of 20μm and a density of 5/mm 2. In preparation process of this embodiment, the spacers are sprayed on the first substrate 10 with the first conductive layer 20 after cleaned, where the first substrate 10 is glass and the first conductive layer 20 is ITO film. Next the liquid crystal layer 40 is disposed between the composite polymer layer 31 and the second transparent substrate 60, and then is processed into a film by a roll pressing method. Then the whole thing is bonded to the first substrate 10 with the first conductive layer 20 formed before to make a final sample. After applied 150V square wave voltage between the first conductive layer and the second transparent conductive layer, a selected area is pressed, and the writing completely disappears without residue, so as to meet the design requirement.
[0049]
Embodiment 3
[0050]
The same technical features as the second embodiment will not described any more in this embodiment. The difference is that the functional layer 30 in this embodiment also includes plurality of isolated second conductive islands 34 located on the side facing the liquid crystal layer 40, as shown in FIG. 3.
[0051]
In this embodiment, the second conductive islands 34 can be arranged in a same pattern as the first conductive islands 32, or they can be arranged in a correspondingly way or in a staggered manner, so long as the selectively erasing function of the invention can be realized.
[0052]
In this embodiment, when a press force is applied to a selected area from outer side of the second transparent substrate 60 of locally deformable, the corresponding area of the second transparent substrate 60 is bent, and thus part of the first conductive islands 32 in the area will be pressed down and contact the first conductive layer 20 across the spacers 33 to realize the electrical connection. As a result, the fractional voltage across the functional layer 30 in the area is reduced, while the fractional voltage across the liquid crystal layer 40 is increased, causing the voltage applied to the liquid crystal molecules in the liquid crystal layer 40 of the selected area to reach a threshold value. The liquid crystal molecules in the selected area are rotated (i.e., the orientation of the liquid crystal molecules is changed from the reflective state to the scattering state. ) to achieve selectively erasing in the area. When the liquid crystal writing board requires whole screen erasing, an external driving circuit 70 applies a larger voltage than the threshold value through the whole screen between the first conductive layer 20 and the second transparent conductive layer 50.
[0053]
In this embodiment, for example, the composite polymer layer 31 has a film thickness of 50μm, a dielectric constant of 45, a resistivity of more than 1010 Ω·cm, and a black color. A silver electrode is evaporated on both surfaces of the composite polymer layer and is etched to form the first conductive islands 32 and the second conductive islands 34 which have an array of 10mm*10mm square electrodes with a spacing of 0.2mm. The second transparent substrate 60 employs a transparent flexible PET of 180μm thickness. The spacing between the first conductive layer 20 and the composite polymer layer 31 is supported by pillar spacers with a diameter of 70μm and a height of 12μm. The pillar spacers are regularly arranged and have a space of 5mm with each other. In preparation process of this embodiment, the liquid crystal layer 40 is disposed between the composite polymer layer 31 and the second transparent substrate 60, and then is processed into a film by a roll pressing method. Then the whole thing is bonded to the first substrate 10 with the first conductive layer 20 formed before to make a final sample, where the first substrate 10 is glass and the first conductive layer 20 is ITO. After applied 100V square wave voltage between the first conductive layer and the second transparent conductive layer, a selected area is pressed, and the writing completely disappears without residue, so as to meet the design requirement.
[0054]
With respect to the second embodiment, the second conductive islands 34 with a same pattern in corresponding positions as the first conductive islands 32 is added in this embodiment, which helps further reducing of the fractional voltage across the functional layer 30 and increasing of the fractional voltage across the liquid crystal layer 40 during a selectively erasing process, to achieve a better partial erasing effect than the second embodiment.
[0055]
Embodiment 4:
[0056]
The same technical features as the first embodiment will not described any more in this embodiment. The difference is that the functional layer 30 in this embodiment comprises a polymer layer 301 and a plurality of hollow microspheres 302 dispersed in the polymer layer 301, as shown in FIG. 6. Preferably, the hollow microspheres 302 have a diameter of 20μm-150μm.
[0057]
In this embodiment, the functional layer 30 is an elastic film, where a force is applied to a selected area from outer side of the second transparent substrate 60, causing the second transparent substrate 60 in the area to be bent and the thickness of the functional layer 30 in the area to be reduced due to extrusion. When a certain voltage is applied between the first conductive layer 20 and the second transparent conductive layer 50, since the film thickness of the functional layer 30 in a selected area is decreased after pressed, the fractional voltage across the functional layer 30 is reduced, while the fractional voltage across the liquid crystal layer 40 is increased, causing the voltage applied to the liquid crystal molecules in the liquid crystal layer 40 of the selected area reaches a threshold value. As a result, the liquid crystal molecules in the selected area are rotated (i.e., the orientation of the liquid crystal molecules is changed from the reflective state to the scattering state. ) to achieve selectively erasing in the area. When the liquid crystal writing board requires whole screen erasing, an external driving circuit 70 applies a larger voltage than the threshold value through the whole screen between the first conductive layer 20 and the second transparent conductive layer 50.
[0058]
In this embodiment, the material composed of the functional layer 30 may be a single-substance film with excellent elastic deformation properties, and has good thickness recovery performance after being pressed; or an elastic film formed by mixing two or more substances. But not limited thereto, the functional layer can use any material whose thickness can be changed by an external pressure and recovered or nearly recovered to the original shape right after the pressure is released.
[0059]
The principle of the selectively erasable liquid crystal writing board of this embodiment of the present invention is that: the composite polymer layer and the liquid crystal layer can be equivalent to a series circuit, where the fractional voltage across the liquid crystal layer in a selected area reaches the threshold voltage when a large enough voltage is applied to all layers, to achieve the erasing of the writing in the selected area. Typically, the substrate of a liquid crystal writing board is PET material, which has a much larger fractional voltage than that of the liquid crystal layer. In order to erasing, an extremely large voltage is required, which makes it difficult to implement this selectively erasing function. By disposing the pressure sensitive conductive film, the elastic layer or improving the dielectric constant of the composite polymer layer in the present invention, the selectively erasing voltage can be successfully reduced to a safe range. The equivalent circuit of the general thin film can adopt series-parallel equivalent effects of the resistance capacitor. Since the dielectric constant of the composite polymer layer in the present invention is very large and the resistance effect can be neglected, the liquid crystal layer and the composite polymer layer are equivalent to two capacitors in series. As a result, the fractional voltage across the liquid crystal layer is positively related to the capacitance value of the composite polymer layer. As the dielectric constant of the composite polymer layer increases along with the capacitance value, the fractional voltage on the liquid crystal layer increases. When the dielectric constant of the composite polymer layer reach a certain value, ever low driving voltage applied to all layers can be used to change the phase state of the liquid crystals.
[0060]
It is to be noted here that the present invention achieves the objectives primarily either by adjusting the resistance or thickness of the functional layer, or by adjusting the dielectric constant of the composite polymer layer. But not limited thereto, two or more above parameters can be adjusted simultaneously, as long as the design concepts consistent with the present invention are both achievable.
[0061]
The functional layer and the liquid crystal layer in the present invention are relatively independent where the parameters are more easily adjusted, to achieve optimal driving effect, convenient operation, low cost and no erasing trace residue, and avoid the problems of vigorously erasing, erasing trace residue, high cost, writing dimmed, and slow response in other selectively erasing methods.
[0062]
While several particular exemplary embodiments have been described above in detail, the disclosed embodiments are considered illustrative rather than limiting. Those skilled in the art will readily realize that alternatives, modifications, variations, improvements, and substantial equivalents are possible without substantially departing from the novelty spirits or scope of the present disclosure. Thus, all such alternatives, modifications, variations, improvements, and substantial equivalents are intended to be embraced within the scope of the present disclosure as defined by the appended claims.

Claims

[Claim 1]
A selectively erasable liquid crystal writing board, comprising: a first substrate, a first conductive layer, a functional layer, a liquid crystal layer, a second transparent conductive layer and a second transparent substrate stacked in sequence, wherein an external electric field can be applied to the selectively erasable liquid crystal writing board via the first conductive layer and the second transparent conductive layer, wherein upon application of an external mechanical pressure on a selected area of the liquid crystal writing board, the fractional voltage across the functional layer in the selected area is reduced, and the fractional voltage across the liquid crystal layer in the selected area is increased to reach a threshold voltage required to switch the liquid crystal molecules in the liquid crystal layer to a desired state.
[Claim 2]
The selectively erasable liquid crystal writing board of claim 1, wherein the functional layer is comprised of polymers mixed with conductive particles.
[Claim 3]
The selectively erasable liquid crystal writing board of claim 1, wherein the functional layer comprises a composite polymer layer coated with plurality of isolated first conductive islands on the side facing the first conductive layer, wherein the composite polymer layer is substantially uniformly separated from the first conductive layer using spacers.
[Claim 4]
The selectively erasable liquid crystal writing board of claim 3, wherein the spacing between the first conductive layer and the composite polymer layer is between 1μm and 50μm.
[Claim 5]
The selectively erasable liquid crystal writing board of claim 3, wherein the isolated first conductive islands are comprised of closely arranged conductive patches with shapes of triangles, rectangles, squares, circles, diamonds, parallelograms, trapezoids, other regular or irregular polygon or combinations thereof.
[Claim 6]
The selectively erasable liquid crystal writing board of claim 3, wherein the relative dielectric constant of the composite polymer layer is between 20 and 200.
[Claim 7]
The selectively erasable liquid crystal writing board of claim 3, wherein the thickness of the composite polymer layer is between 30μm and 500μm.
[Claim 8]
The selectively erasable liquid crystal writing board of claim 3, wherein the composite polymer layer comprises a polymer host and nanoparticle dopants of high dielectric constants.
[Claim 9]
The selectively erasable liquid crystal writing board of claim 8, wherein the polymer is one or more selected from the group of polyethylene, polymethyl methacrylate, polyvinyl chloride, polycarbonate, polyvinylidene fluoride, urea-formaldehyde resin, unsaturated polyester resin, polytetrafluoroethylene and polyimide.
[Claim 10]
The selectively erasable liquid crystal writing board of claim 8, wherein the material of the nanoparticle dopants is one or more selected from the group of silver, carbon nanotubes, conductive carbon powder, nickel and barium titanate.
[Claim 11]
The selectively erasable liquid crystal writing board of claim 3, wherein the functional layer further comprises plurality of isolated second conductive islands on the side facing the liquid crystal layer.
[Claim 12]
The selectively erasable liquid crystal writing board of claim 1, wherein the functional layer comprises a polymer layer and a plurality of hollow microspheres dispersed in the polymer layer.
[Claim 13]
The selectively erasable liquid crystal writing board of claim 12, wherein the hollow microspheres have a diameter of 20μm-150μm.
[Claim 14]
The selectively erasable liquid crystal writing board of claim 1, wherein the first conductive layer and the second transparent conductive layer are one or more selected from the group of ITO, graphene, nano-silver and other conductive materials.
[Claim 15]
The selectively erasable liquid crystal writing board of claim 1, wherein the liquid crystal layer comprises a polymer and liquid crystals dispersed in the polymer.
[Claim 16]
The selectively erasable liquid crystal writing board of claim 15, wherein the liquid crystal layer further comprises a plurality of spacers dispersed in the polymer.
[Claim 17]
The selectively erasable liquid crystal writing board of claim 15, wherein the liquid crystals are cholesteric liquid crystals.
[Claim 18]
The selectively erasable liquid crystal writing board of claim 1, wherein the functional layer is disposed between the liquid crystal layer and the second transparent conductive layer.

Drawings

[ Fig. 1]  
[ Fig. 2]  
[ Fig. 3]  
[ Fig. 4]  
[ Fig. 5]  
[ Fig. 6]