Liquid crystal writing device

Abstract

The application discloses a liquid crystal writing device, which comprises a first conductive layer, a liquid crystal layer, a second conductive layer and a substrate layer arranged in sequence, wherein the liquid crystal layer comprises a liquid crystal polymer network, and a plurality of cells for containing liquid crystal molecules are distributed in the liquid crystal polymer network, and the size of each cell is between 0.6 and 1 microns. The liquid crystal writing device can display white ink.

Description

Technical Field

[0001] This application relates to the field of liquid crystal film technology, and in particular to a liquid crystal writing device. Background Technology

[0002] Liquid crystal writing devices (LCDs) offer advantages such as eye protection, dust-free operation, and convenience, making them promising for the education market. Typically, an LCD writing device comprises a first transparent conductive layer, a liquid crystal layer, a second transparent conductive layer, and a substrate layer, arranged sequentially. Its working principle utilizes the bistable nature of liquid crystals to display and / or erase written content on the LCD writing pad.

[0003] Specifically, when the liquid crystal writing device is in a ready-to-write state, the liquid crystal molecules are in a transmissive state to visible light, and the device does not display content, instead displaying the color of the base layer (such as black). During writing, the user applies external pressure to the liquid crystal layer, causing the pressured liquid crystal molecules to deflect. These deflected molecules reflect light within a specific wavelength range, thus displaying the writing. When the user needs to erase the writing, a voltage is applied to the liquid crystal layer through the first and second transparent conductive layers, causing the liquid crystal molecules to deflect and return to a transmissive state to visible light, thus erasing the writing.

[0004] Existing writing devices typically display only a single color—green, blue, or red—and cannot display white. However, these colors differ from the black-on-white writing style commonly used in teaching and office settings, making them inconvenient for users. Summary of the Invention

[0005] The main purpose of this application is to propose a liquid crystal writing device that aims to solve the problem that existing writing devices often display only a single green, blue, or red color, but cannot display white.

[0006] To achieve the above objectives, this application proposes a liquid crystal writing device, comprising a first conductive layer, a liquid crystal layer, a second conductive layer and a substrate layer disposed sequentially. The liquid crystal layer comprises a liquid crystal polymer network, wherein a plurality of cell cells for accommodating liquid crystal molecules are distributed in the liquid crystal polymer network, and the size of each cell is between 0.6 and 1 μm.

[0007] Preferably, the liquid crystal polymer network is prepared by polymer monomers through ultraviolet polymerization or thermal polymerization.

[0008] Preferably, the polymer monomer includes at least one multifunctional compound, the functional groups of which are used to react with other polymer monomers to reduce the cell size of the formed liquid crystal polymer network.

[0009] Preferably, the multifunctional compound includes dipentaerythritol hydroxypentaacrylate.

[0010] Preferably, the multifunctional compound includes pentaerythritol tetraacrylate.

[0011] Preferably, the multifunctional compound includes tetraethoxypentaerythritol tetraacrylate.

[0012] Preferably, the polymer monomers include 0-20% of dipentaerythritol hydroxypentaacrylate, 0-20% of pentaerythritol tetraacrylate, 0-20% of bisphenol A diacrylate ethoxylate, and 0-20% of polyethylene glycol diacrylate.

[0013] Preferably, the polymer monomers include 0-8% dipentaerythritol hydroxypentaacrylate, 0-8% pentaerythritol tetraacrylate, 0-15% bisphenol A diacrylate, 0-15% polyethylene glycol diacrylate, and 0-10% isobornyl acrylate.

[0014] Preferably, the liquid crystal polymer network further includes a plurality of spacers disposed between the first conductive layer and the second conductive layer.

[0015] Preferably, the liquid crystal polymer network further includes a chiral agent that matches the liquid crystal.

[0016] Compared with the prior art, the beneficial effects of the technical solution of this application are as follows: by setting the cell size of the liquid crystal polymer network between 0.6 and 1 μm, on the one hand, the liquid crystal polymer network can effectively bind the liquid crystal; on the other hand, the liquid crystal molecules in the planar state can achieve a thickness that reflects natural light across the entire wavelength range, thereby enabling the writing on the liquid crystal writing device to appear white. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of an embodiment of the liquid crystal writing device of this application;

[0018] Figure 2A for Figure 1 A schematic diagram of the structure of a liquid crystal polymer network according to an embodiment;

[0019] Figure 2B for Figure 1 A schematic diagram of another embodiment of the liquid crystal polymer network;

[0020] Figure 2C for Figure 1 A schematic diagram of another embodiment of a liquid crystal polymer network. Detailed Implementation

[0021] The solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments in this application, and not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0022] It should be understood that, unless the context requires otherwise, the term "comprising" is interpreted throughout the specification and claims as open-ended and encompassing, meaning "including, but not limited to." In the description of the specification, terms such as "one embodiment," "some embodiments," "exemplary embodiment," "example," "specific example," or "some examples" are intended to indicate that a particular feature, structure, material, or characteristic associated with that embodiment or example is included in at least one embodiment or example of this application. The illustrative representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific feature, structure, material, or characteristic may be included in any suitable manner in any one or more embodiments or examples.

[0023] Additionally, it should be noted that when describing the elements and embodiments thereof in this application, the articles “a,” “an,” “the,” and “the” are intended to indicate the presence of one or more elements; unless otherwise stated, “multiple” means two or more; the terms “comprising,” “including,” “containing,” and “having” are intended to be inclusive and indicate that additional elements may exist besides those listed; the terms “first,” “second,” “third,” etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or order of formation.

[0024] The polygons used in this specification are not strictly defined; they can be approximate triangles, rectangles, trapezoids, pentagons, or hexagons, etc. They may have minor deformations due to tolerances, and may include chamfers, fillets, curved edges, and other variations.

[0025] As early as the 18th century, scientists, while determining the melting point of organic compounds, discovered that cholesterol benzoate crystals melted into a turbid liquid when heated to 145°C (melting point). Upon further heating to 178.5°C (clearing point), the turbid liquid suddenly transformed into an isotropic, clear liquid. Within the temperature range between the melting point and the clearing point, cholesterol benzoate exists in an intermediate phase, distinct from isotropic liquids. Further research revealed that many compounds can exhibit intermediate phases, in which substances possess strong anisotropic physical characteristics while simultaneously exhibiting fluidity like ordinary fluids. Therefore, such intermediate phases are called liquid crystal phases, and substances capable of exhibiting liquid crystal phases are called liquid crystals.

[0026] Liquid crystals are widely used in various fields due to their dielectric anisotropy, birefringence, and electro-optic effects. For example, this application proposes a liquid crystal writing device.

[0027] Please see Figure 1 , Figure 2A , Figure 2B and Figure 2C In one embodiment, the liquid crystal writing device includes a first conductive layer 100, a liquid crystal layer 200, a second conductive layer 300, and a substrate layer (not shown) disposed sequentially. The liquid crystal layer 200 includes a liquid crystal polymer network 320, in which a plurality of unit cells for accommodating liquid crystal molecules are distributed (e.g., ...). Figure 2A 321 in the middle, Figure 2B 322 in the middle, Figure 2C (323 in the middle).

[0028] Here, the first conductive layer 100 and the second conductive layer 300 can be selected as transparent electrode layers or light-shielding electrode layers, and their light transmittance is not limited. In a preferred embodiment, the materials of the first conductive layer 100 and the second conductive layer 300 include indium tin oxide (ITO). The substrate layer has a photoresist function and can be selected as black or colored. When the liquid crystal writing device is a blackboard for teaching, the substrate layer is preferably a black photoresist layer. For ease of description, the following embodiments are illustrated using a black photoresist layer as the substrate layer.

[0029] The liquid crystal polymer network 320 can be prepared by selecting a nematic liquid crystal, a chiral agent (not shown), a spacer (not shown), and a UV-polymerizable monomer. Preferably, the liquid crystal has a birefringence between 0.14 and 0.18, a clearing point less than 130°C, and a melting point higher than -30°C. It is readily understood that, in an optional embodiment, the liquid crystal material used to prepare the liquid crystal polymer network 320 can also be a cholesteric liquid crystal, and the monomer material can also be a thermally polymerizable monomer. In a specific embodiment, the monomer material can be prepared first, and then the raw materials, including the liquid crystal and the monomer material, can be thoroughly mixed and then pressed to uniformly distribute the liquid crystal between the first conductive film 100 and the second conductive film 300. Then, UV adhesive is cured by UV irradiation to form a polymer-dispersed liquid crystal. The number of unit cells in the liquid crystal polymer network 320 is related to factors such as the size of the liquid crystal handwriting device and the monomer material concentration, and is not specifically limited here. The spacer is placed between the first conductive layer 100 and the second conductive layer 300, serving as the skeleton of the liquid crystal layer 200 and providing support, so that the cross-sectional size of the liquid crystal layer 200 is uniform. The size of the spacer can be set based on the size of the liquid crystal writing device, the specific application scenario, etc.

[0030] In this embodiment, the working principle of the liquid crystal writing device is as follows:

[0031] When the liquid crystal writing device is in its initial state, the liquid crystal layer 200 is capable of scattering and / or transmitting incident light (not shown). That is, in the absence of a zero electric field, the incident light is scattered and / or transmitted through the liquid crystal layer 200 and illuminates the substrate layer. Some of the light is reflected at the surface of the substrate layer, and the reflected light (not shown) passes through the liquid crystal layer 200 again and is scattered and / or transmitted. At this time, the liquid crystal writing device displays the color of the substrate layer (e.g., black).

[0032] When the liquid crystal writing device is in writing mode, the user applies pressure to the liquid crystal layer 200 using a writing tool (e.g., a writing pen), causing some liquid crystal molecules within the liquid crystal layer 200 to deflect under pressure (see...). Figure 1 The liquid crystal molecules 330 that are deflected and the liquid crystal molecules 310 that are not deflected have their long axes basically parallel to the plane of the substrate layer, presenting a planar state. They can selectively reflect light of a specific wavelength range, so that the liquid crystal writing device can display a specific color (such as green), that is, display handwriting.

[0033] When it is necessary to erase the written marks, the first conductive layer 100 and the second conductive layer 300 are activated and a voltage is applied to create an electric field in the liquid crystal layer 200. Under the influence of the electric field, the liquid crystal molecules are deflected, and the liquid crystal layer 200 re-enters a state capable of scattering and / or transmitting incident light. The liquid crystal writing device then displays the base layer color again, and the written marks are erased.

[0034] It is worth mentioning that, to increase the stability of the liquid crystal writing device, the planes of the first conductive layer 100, the liquid crystal layer 200, and the second conductive layer 300 are substantially parallel to the plane of the substrate layer. The size of the unit cell in the liquid crystal polymer network 320, that is, along the direction substantially perpendicular to the substrate layer, is the maximum diameter of the unit cell (e.g., ...). Figure 2A , Figure 2B and Figure 2C (Diameter indicated by the middle arrow).

[0035] Studies have shown that when the cell size is set between 0 and 0.05 μm, the liquid crystal polymer network 320 has a strong binding ability on the liquid crystal molecules, restricting the flow of the liquid crystal and preventing the liquid crystal molecules from freely flipping within the cell, resulting in thin and dark handwriting. When the cell size is set between 0.05 and 0.6 μm, the handwriting will appear as a single color; when the cell size is set between 0.6 and 1 μm, the cell size is larger, and the liquid crystal can be better bound. The planar liquid crystal reaches a certain thickness within the cell, which can reflect natural light across the entire wavelength range, making the handwriting appear white.

[0036] In this embodiment, to enable the liquid crystal writing device to display white text, the cell size is preferably between 0.6 and 1 μm.

[0037] In one embodiment, the polymer monomer includes at least one multifunctional compound whose functional groups react with other polymer monomers to reduce the cell size of the formed liquid crystal polymer network 320. Thus, the cell size in the liquid crystal polymer network 320 can be controlled by adjusting the composition / content of the multifunctional compound.

[0038] In an optional embodiment, the multifunctional compound may be dipentaerythritol hydroxypentaacrylate, pentaerythritol tetraacrylate, or tetraethoxypentaerythritol tetraacrylate.

[0039] In one specific embodiment, the polymer monomers include 0-20% of dipentaerythritol hydroxypentaacrylate, 0-20% of pentaerythritol tetraacrylate, 0-20% of bisphenol A diacrylate ethoxylate, and 0-20% of polyethylene glycol diacrylate.

[0040] Here, dipentaerythritol hydroxypentaacrylate has a molecular structure containing five acrylate groups and one unesterified hydroxyl group attached to the molecular backbone of dipentaerythritol. Dipentaerythritol hydroxypentaacrylate can be used as a photocurable monomer, which can be rapidly cured under ultraviolet light and used as an adhesive; it can also be copolymerized with other monomers to prepare polymer materials with special properties, thereby improving the mechanical, thermal, and optical properties of the materials.

[0041] Pentaerythritol tetraacrylate has a molecular structure containing four acrylate groups attached to four hydroxymethyl groups of pentaerythritol. This structure gives it high reactivity, enabling it to undergo free radical polymerization under the action of an initiator to form a cross-linked polymer. Pentaerythritol tetraacrylate can be used as a monomer in UV-curable coatings to improve the hardness, abrasion resistance, chemical resistance, and weather resistance of the coatings; it can also be used in the preparation of adhesives to improve the adhesive strength and curing speed; and it can be used as a crosslinking agent to mix with other materials to prepare high-performance composite materials, enhancing the mechanical properties, heat resistance, and water resistance of the composite materials.

[0042] Ethylene oxide bisphenol A diacrylate contains two acrylate groups in its molecular structure, linked to the phenolic hydroxyl groups of bisphenol A via an ethoxy group. Ethylene oxide bisphenol A diacrylate exhibits excellent adhesion, low shrinkage, good chemical resistance, heat resistance, water resistance, and abrasion resistance, as well as a favorable balance of hydrophilicity and hydrophobicity. It can be used as a photoresist, solder resist ink, photopolymer, adhesive, and coating.

[0043] Structurally, polyethylene glycol diacrylate (PEG) is obtained by esterification of the hydroxyl groups at both ends of polyethylene glycol with acrylic acid. The middle segment is polyethylene glycol, with acrylate groups attached to both ends. This structure gives PEG diacrylate both the properties of polyethylene glycol, such as good water solubility and biocompatibility, and the reactivity of acrylate groups, allowing it to polymerize under the influence of light or an initiator to form a cross-linked polymer.

[0044] In this embodiment, dipentaerythritol hydroxypentaacrylate, as a multifunctional compound, absorbs light of a specific wavelength in the presence of a photoinitiator (such as benzoin ethers, benzophenones, etc.), exciting the photoinitiator molecules to an excited state, which then undergo cleavage to generate free radicals. Taking benzoin ether as an example, under ultraviolet light irradiation, it cleaves to generate benzoyl free radicals and benzyloxy free radicals, which can initiate the polymerization reaction of dipentaerythritol hydroxypentaacrylate. The free radicals generated during the initiation stage react with the carbon-carbon double bonds in the dipentaerythritol hydroxypentaacrylate molecule to form new free radicals. These new free radicals then continue to react with the carbon-carbon double bonds of other dipentaerythritol hydroxypentaacrylate molecules, causing the polymer chain to grow continuously. For example, after one free radical adds to a dipentaerythritol hydroxypentaacrylate molecule, the resulting active center of the free radical attracts the carbon-carbon double bonds of another dipentaerythritol hydroxypentaacrylate molecule for addition, and so on, resulting in rapid growth of the polymer chain.

[0045] Thus, increasing the component / content of dipentaerythritol hydroxypentaacrylate can increase the polymer chain density and reduce the cell size in the liquid crystal polymer network 320. Similarly, for pentaerythritol tetraacrylate, which is also a multifunctional compound, increasing the component / content of pentaerythritol tetraacrylate can also increase the polymer chain density and reduce the cell size in the liquid crystal polymer network 320.

[0046] It is worth mentioning that, in an optional embodiment, pentaerythritol tetraacrylate can be replaced with tetraethoxypentaerythritol tetraacrylate. Its molecular structure can be considered as the product obtained by the esterification reaction of the four hydroxyl groups of pentaerythritol with acrylic acid, with each hydrogen atom on the hydroxyl group being replaced by an ethoxy group. Specifically, the molecular structure of tetraethoxypentaerythritol tetraacrylate contains four acrylate groups and four ethoxy groups. The acrylate groups impart photocuring reactivity, while the ethoxy groups improve the flexibility and solubility of the molecule. It features good flexibility, low viscosity, and high reactivity, while also possessing good scratch resistance and solvent resistance. It can be used in photocuring reactions for UV polymerization of various unsaturated systems such as UV coatings and UV adhesives. Similar to pentaerythritol tetraacrylate, for tetraethoxypentaerythritol tetraacrylate, which is also a multifunctional compound, increasing the component / content of tetraethoxypentaerythritol tetraacrylate can also increase the polymer chain density and reduce the cell size in the liquid crystal polymer matrix 320.

[0047] In this embodiment, the components / contents of dipentaerythritol hydroxypentaacrylate, pentaerythritol tetraacrylate, bisphenol A diacrylate ethoxylate, and polyethylene glycol diacrylate are all configured between 0% and 20%, which allows the cell size in the liquid crystal polymer network 200 to be between 0.6 and 1 μm, thereby enabling the liquid crystal writing device to display white text.

[0048] In another specific embodiment, the polymer monomers include 0-8% of dipentaerythritol hydroxypentaacrylate, 0-8% of pentaerythritol tetraacrylate, 0-15% of bisphenol A diacrylate, 0-15% of polyethylene glycol diacrylate, and 0-10% of isobornyl acrylate.

[0049] Here, the molecular structure of isobornyl acrylate includes an acrylate moiety and an isobornyl moiety. The acrylate moiety contains a carbon-carbon double bond and an ester group. The carbon-carbon double bond has high reactivity and can undergo various reactions such as addition and polymerization. The ester group serves as a bridge connecting the acrylate moiety and the isobornyl group, while also imparting a certain degree of polarity and chemical stability to the molecule. The isobornyl moiety is based on a bicycloheptane skeleton, with a hydrogen atom attached to the 2-carbon position and methyl groups attached to the 1, 7, and 7-carbon positions, respectively. The isobornyl group is a large, nonpolar group with significant steric hindrance, which gives the isobornyl acrylate molecule unique physical and chemical properties, such as reducing intermolecular forces in the polymer chain and improving the polymer's solubility, flexibility, and water resistance.

[0050] Isobornyl acrylate possesses characteristics such as high activity, high hardness, low shrinkage, low viscosity, high boiling point, low surface tension, high glass transition temperature, low chromaticity, high refractive index, and good hydrophobicity. It can be used as a reactive diluent in radiation-cured coatings to reduce viscosity, improve application performance, and enhance coating leveling. It can also be used in the manufacture of adhesives, improving their adhesion to certain materials.

[0051] In this embodiment, the components / contents of dipentaerythritol hydroxypentaacrylate are configured between 0% and 8%, pentaerythritol tetraacrylate between 0% and 8%, bisphenol A diacrylate ethoxylate between 0% and 15%, polyethylene glycol diacrylate between 0% and 15%, and isobornyl acrylate between 0% and 10%. This allows the cell size in the liquid crystal polymer network to be between 0.6 and 1 μm, enabling the liquid crystal writing device to display white text.

[0052] It should be noted that the technical solutions of the various embodiments of this application can be combined with each other, but only if they can be implemented by those skilled in the art. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed in this application.

[0053] The above description is only a part or preferred embodiment of this application. Neither the text nor the drawings should limit the scope of protection of this application. All equivalent structural transformations made using the content of this application's specification and drawings under the overall concept of this application, or direct / indirect applications in other related technical fields, are included within the scope of protection of this application.

Claims

1. A liquid crystal writing device, characterized in that, It includes a first conductive layer, a liquid crystal layer, a second conductive layer and a substrate layer arranged in sequence. The liquid crystal layer includes a liquid crystal polymer network, in which a plurality of unit cells for accommodating liquid crystal molecules are distributed, and the size of each unit cell is between 0.6 and 1 μm.

2. The liquid crystal writing device as described in claim 1, characterized in that, The liquid crystal polymer network is formed by polymer monomers through ultraviolet polymerization or thermal polymerization.

3. The liquid crystal writing device as described in claim 2, characterized in that, The polymer monomer includes at least one multifunctional compound, the functional groups of which are used to react with other polymer monomers to reduce the cell size of the formed liquid crystal polymer network.

4. The liquid crystal writing device as described in claim 3, characterized in that, The multifunctional compound includes dipentaerythritol hydroxypentaacrylate.

5. The liquid crystal writing device as described in claim 3, characterized in that, The multifunctional compound includes pentaerythritol tetraacrylate.

6. The liquid crystal writing device as claimed in claim 3, characterized in that, The multifunctional compound includes tetraethoxypentaerythritol tetraacrylate.

7. The liquid crystal writing device as claimed in claim 2, characterized in that, The polymer monomers include 0-20% dipentaerythritol hydroxypentaacrylate, 0-20% pentaerythritol tetraacrylate, 0-20% bisphenol A diacrylate, and 0-20% polyethylene glycol diacrylate.

8. The liquid crystal writing device as claimed in claim 2, characterized in that, The polymer monomers include 0-8% dipentaerythritol hydroxypentaacrylate, 0-8% pentaerythritol tetraacrylate, 0-15% bisphenol A diacrylate, 0-15% polyethylene glycol diacrylate, and 0-10% isobornyl acrylate.

9. The liquid crystal writing device according to any one of claims 1-8, characterized in that, The liquid crystal polymer network further includes a plurality of spacers disposed between the first conductive layer and the second conductive layer.

10. The liquid crystal writing device according to any one of claims 1-8, characterized in that, The liquid crystal polymer network also includes a chiral agent that matches the liquid crystal.

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