Self-healing Coating for Touch Screen and Its Preparation Method

Abstract

The present application provides a self-healing coating for a touch screen and a preparation method thereof. The self-healing coating is formed by curing a sol formed by konjac glucomannan and POSS-modified nano-silica. The content of the POSS-modified nano-silica decreases from the surface to the inside of the self-healing coating. Moreover, the self-healing coating is a multi-layer stacked structure formed by sequentially coating sols containing different concentrations of the POSS-modified nano-silica on the surface of the touch screen and curing. The content of the POSS-modified nano-silica on the surface layer of the self-healing coating is relatively high, which can provide more active sites such as amino groups and hydroxyl groups, serving as "anchor points" for dynamic hydrogen bonds or dynamic chemical bonds, improving the repair strength of the damaged interface and enhancing the repair efficiency.

Description

Technical Field

[0001] This application belongs to the technical field of touchscreens, and more specifically, relates to a self-healing coating for touchscreens and a preparation method thereof. Background Art

[0002] The use of electronic touchscreen products is currently very popular. During daily use, touchscreens are easily scratched by sharp objects, resulting in scratches of varying depths, which affect the appearance and user experience. Generally, when a scratch on a touchscreen occurs, it gradually spreads from the surface layer to the inner layer of the touchscreen. Therefore, the scratches on the surface layer are usually wider and more severely damaged; as the scratches gradually spread to the inner layer, the scratches are dispersed by stress to form finer and less severe cracks.

[0003] Currently, there are already self-healing coatings for touchscreens that can repair the generated scratches under a certain mechanism, thereby extending the service life of the touchscreens. However, the repair effect on scratches is not very ideal. After the touchscreen is self-healed, the previously scratched marks can still be seen at the original scratch positions, but the scratched marks are significantly faded. It can be seen that there is still room for improvement in the repair strength of the existing self-healing coatings for scratches. Summary of the Invention

[0004] The purpose of the embodiments of this application is to provide a self-healing coating for touchscreens and a preparation method thereof, so as to solve the technical problem of insufficient scratch repair strength of touchscreens existing in the prior art.

[0005] To achieve the above purpose, the technical solution adopted in this application is: to provide a self-healing coating for touchscreens, the self-healing coating is formed by curing a sol formed by konjac glucomannan and POSS-modified nano-silica, wherein the content of the POSS-modified nano-silica decreases from the surface to the inside of the self-healing coating; the self-healing coating is a multi-layer stacked structure formed by successively coating sols containing different concentrations of the POSS-modified nano-silica on the surface of the touchscreen and curing.

[0006] In one embodiment, the self-healing coating is formed by curing three layers of sols, and a graphene layer with a thickness of 10 - 15 nanometers is coated between every two adjacent cured sols; in the order from the surface to the inside of the self-healing coating, the concentrations of the POSS-modified nano-silica contained in the three layers of sols before curing are 6 g / L, 4 g / L, and 2 g / L respectively, and the thicknesses of the three layers of sols after curing are 50 microns, 30 microns, and 20 microns respectively.

[0007] In one embodiment, the self-healing coating further includes PAMAM-modified nano-silica, and the content of the PAMAM-modified nano-silica decreases from the surface to the inside of the self-healing coating.

[0008] According to another aspect of the present invention, the present invention further provides a method for preparing a self-healing coating for a touch screen, comprising:

[0009] Adding an appropriate amount of konjac glucomannan powder into deionized water and stirring evenly, and then dividing the formed konjac glucomannan solution into multiple portions;

[0010] Grafting POSS onto the surface of nano-silica to obtain POSS-modified nano-silica;

[0011] Sequentially adding different contents of POSS-modified nano-silica to the prepared multiple portions of konjac glucomannan solution, thereby obtaining multiple portions of mixed sols with sequentially increasing concentrations of POSS-modified nano-silica;

[0012] Sequentially coating the multiple portions of mixed sols on the surface of the same touch screen in the order of sequentially increasing concentrations of POSS-modified nano-silica and preliminarily curing to form a multi-layer stacked structure;

[0013] Making the mixed sol cure to form a self-healing coating through a drying and UV curing process.

[0014] In one embodiment, grafting POSS onto the surface of nano-silica to obtain POSS-modified nano-silica, comprising:

[0015] Adding nano-silica powder into deionized water and performing ultrasonic cleaning to remove impurities and bubbles on the surface of the nano-silica;

[0016] Adding nano-silica into a tetrahydrofuran solvent and stirring evenly to form a silica dispersion;

[0017] Dissolving a silane coupling agent in a tetrahydrofuran solvent to form a uniform silane coupling agent solution;

[0018] Dissolving a POSS monomer in a tetrahydrofuran solvent, and synchronously adding it to the silica dispersion together with the silane coupling agent solution, stirring and reacting at 70 °C for 4 - 6 hours and then drying.

[0019] In one embodiment, when grafting POSS onto the surface of nano-silica to obtain POSS-modified nano-silica, the feeding mass ratio of the nano-silica to the POSS is 1.2:1.

[0020] In one embodiment, the konjac glucomannan solution is divided into three portions, and POSS-modified nano-silica is sequentially added to the three portions of konjac glucomannan solution, so that the concentrations of POSS-modified nano-silica in the three portions of mixed sols are 2 g / L, 4 g / L, and 6 g / L respectively;

[0021] Coating multiple portions of the mixed sol on the surface of the touch screen in the order of increasing POSS-modified nano-silica concentration, including:

[0022] First, coat a layer of sol containing POSS-modified nano-silica with a concentration of 2 g / L on the touch screen. After preliminary curing, coat a layer of graphene layer;

[0023] Then, coat a layer of sol containing POSS-modified nano-silica with a concentration of 4 g / L on the touch screen. After preliminary curing, coat a layer of graphene layer;

[0024] Then, coat a layer of sol containing POSS-modified nano-silica with a concentration of 6 g / L on the touch screen. After preliminary curing, coat a layer of graphene layer;

[0025] Finally, through the drying and UV curing processes, the three-layer mixed sol is cured to form a self-healing coating. In the order from the surface to the inside of the self-healing coating, the thicknesses of the three-layer mixed sol after curing are 50 microns, 30 microns, and 20 microns in sequence, and the thickness of the graphene layer is 10 - 15 nanometers.

[0026] In one embodiment, the graphene layer is coated and formed through the following steps:

[0027] Disperse graphene in deionized water, add sodium dodecyl sulfate as a surfactant, form a dispersion through ultrasonic treatment, and then spray to form a film layer with a thickness of 10 - 15 nanometers.

[0028] In one embodiment, the following steps are further included:

[0029] Graft PAMAM onto the surface of nano-silica to obtain PAMAM-modified nano-silica. Add different amounts of PAMAM-modified nano-silica to the prepared multiple portions of konjac glucomannan solution in sequence, so that in each portion of the konjac glucomannan solution, the mass ratio of POSS-modified nano-silica to PAMAM-modified nano-silica is 1:1.

[0030] In one embodiment, the following step is further included: adding nanosilver wires to the konjac glucomannan solution.

[0031] The beneficial effects of the self-healing coating for the touch screen provided in this application are as follows: Compared with the prior art, the self-healing coating for the touch screen provided in this application is formed by curing a sol formed by konjac glucomannan and POSS-modified nano-silica, and the content of the POSS-modified nano-silica decreases from the surface to the inside of the self-healing coating. In this way, the content of the POSS-modified nano-silica on the surface layer of the self-healing coating is relatively high, which can provide more active sites such as amino groups and hydroxyl groups, serving as the "anchoring points" of dynamic hydrogen bonds or dynamic chemical bonds, improving the repair strength of the damaged interface and enhancing the repair efficiency. In addition, the high concentration of POSS-modified nano-silica can also increase the mechanical properties and wear resistance of the surface layer of the self-healing coating. The cracks in the inner layer are relatively slight, so the concentration of POSS-modified nano-silica can be relatively low, and the concentration of konjac glucomannan can be relatively high, so as to maintain a relatively high light transmittance and toughness, inhibit the cracks from continuing to expand to deeper positions, thereby enhancing the repair strength of the scratches on the touch screen and greatly improving the problem that obvious traces still exist after the relatively serious scratches in the prior art are repaired. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of this application, the following will briefly introduce the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings in the following description are only some embodiments of this application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0033] Figure 1 It is a schematic flow chart of the preparation method of the self-healing coating for the touch screen provided in the embodiment of this application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] In order to make the technical problems, technical solutions and beneficial effects to be solved by this application clearer, the following further details this application in conjunction with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not used to limit this application.

[0035] Now, the self-healing coating for the touch screen provided in the embodiment of this application will be described. The self-healing coating for the touch screen is an ultra-thin coating coated and cured on the surface of a traditional touch screen, which can undergo a chemical reaction when scratched, thereby self-repairing the scratches and extending the service life of the touch screen. Specifically, the self-healing coating for the touch screen is formed by curing a sol formed by konjac glucomannan and POSS-modified nano-silica, and the content of the POSS-modified nano-silica decreases from the surface to the inside of the self-healing coating.

[0036] Konjac glucomannan, also known as KGM, is a natural high-molecular-weight soluble dietary fiber. It is a high-molecular-weight heteropolysaccharide composed of glucose and mannose residues with a molecular ratio of 1:(1.6 - 1.7) polymerized through β-1,4 glycosidic bonds to form the main chain, and containing β-1,3 branches and acetyl groups. Konjac glucomannan is a water-soluble non-ionic polysaccharide with various unique physical and chemical properties such as water solubility, water retention and thickening, stability, suspension, gelation, adhesion, and film formation.

[0037] POSS (cage-shaped polyhedral oligomeric silsesquioxane) is an organic-inorganic hybrid molecule with a special structure, with a molecular size of 1 - 3 nanometers. Its inner part is a cage-shaped inner shell composed of an alternating inorganic skeleton of Si-O-Si, and the outer layer is surrounded by an organic group, such as an amino group, an aldehyde group, etc. The organic groups on the outside of POSS can react with various groups, so it is often used as a modifier to improve the properties of polymer materials. And POSS-modified silica uses silica as a rigid core, with POSS molecules grafted on the surface to form an organic-inorganic hybrid interface. Specifically, the surface of nano-silica is rich in hydroxyl groups (-OH), about 4 - 8 hydroxyl groups per square nanometer; the cage-shaped silicon-oxygen skeleton (Si-O-Si) of the POSS molecule can be modified with organic functional groups (such as hydroxyl groups, amino groups or epoxy groups), and the vertex positions of the cage-shaped three-dimensional structure (such as the T8 type) of the POSS molecule contain reactive silicon hydroxyl groups (Si-OH). The silicon hydroxyl groups (Si-OH) of POSS and the hydroxyl groups (-OH) on the surface of nano-silica are combined through hydrogen bonds, which can reduce the aggregation of nano-silica; on the other hand, the silicon-oxygen groups of POSS (such as Si-O-R) hydrolyze to form silanols (Si-OH) in an aqueous environment, which can undergo a condensation reaction with the hydroxyl groups on the surface of nano-silica to directly form Si-O-Si covalent bonds; in addition, POSS has a cage-shaped polyhedral structure (such as T8, T10, T12), and its silicon-oxygen skeleton (Si-O-Si) can also be bonded to the hydroxyl groups (-OH) on the surface of nano-silica through a silane coupling reaction, thus forming a three-dimensional network.

[0038] Amino groups, aldehyde groups, etc. on the surface of nano-silica grafted and modified with konjac glucomannan and POSS are combined through dynamic covalent bonds to form a reversible crosslinked network; when the temperature is higher than 40 °C, the molecular chain movement ability is enhanced, promoting dynamic reorganization, enabling the molecular chains broken at the previously scratched areas to move and reorganize, and the organic groups exposed by POSS react with the hydroxyl groups of the surrounding free konjac glucomannan to form new crosslinking points, realizing the self-healing function. Second, the hydroxyl groups of konjac glucomannan form multiple hydrogen bonds with the hydroxyl groups on the surface of nano-silica and the organic side chains of POSS (such as amino groups). When the coating is damaged, the hydrogen bonds are broken, but under temperature stimulation, such as heating to 40 °C, the molecular chain movement ability of konjac glucomannan is enhanced, and the broken hydrogen bonds are dynamically reorganized through the reorientation of hydroxyl groups with hydroxyl groups / amino groups. Functional groups such as amino groups on the surface of POSS-grafted nano-silica can serve as hydrogen bond anchoring points to promote the formation of new hydrogen bonds at the damaged interface, realizing the self-healing of the coating, and the high specific surface area of nano-silica provides more hydrogen bond binding sites, accelerating the repair efficiency.

[0039] In particular, the content of the POSS-modified nano-silica decreases from the surface of the self-healing coating towards the inside. For example, the self-healing coating of the touch screen can be specifically divided into three layers. The surface layer of the self-healing coating is formed by curing a mixed sol with a concentration of 6 g / L of POSS-modified nano-silica; the middle layer of the self-healing coating is formed by curing a mixed sol with a concentration of 4 g / L of POSS-modified nano-silica; and the innermost layer of the self-healing coating is formed by curing a mixed sol with a concentration of 2 g / L of POSS-modified nano-silica. In this way, the content of the POSS-modified nano-silica decreases from the surface of the self-healing coating towards the inside. As we know, when the sliding marks on the touch screen are generated, they gradually spread from the surface layer to the inner layer of the touch screen. Therefore, the scratches on the surface layer are usually wider and more severely damaged; as the scratches gradually spread to the inner layer, the scratches are dispersed by stress to form finer and less severe cracks. If all components of the entire self-healing coating are uniformly distributed in the thickness direction, then when encountering relatively severe scratches, the self-healing coating may have insufficient repair strength for repairing the relatively severe scratches on the surface layer, while the self-healing coating is relatively easy to repair the relatively fine cracks in the deep layer. Therefore, we specifically reduce the content of the POSS-modified nano-silica in the self-healing coating from the surface of the self-healing coating towards the inside. In this way, the concentration of the POSS-modified nano-silica on the surface layer of the self-healing coating is relatively high, which can provide more active sites such as amino groups and hydroxyl groups, serving as the "anchor points" of dynamic hydrogen bonds or dynamic chemical bonds, improving the repair strength of the damaged interface and enhancing the repair efficiency. In addition, the high-concentration POSS-modified nano-silica can also increase the mechanical properties and wear resistance of the surface layer of the self-healing coating. The cracks in the inner layer are relatively minor, so the concentration of the POSS-modified nano-silica can be relatively low, and the concentration of konjac glucomannan can be relatively high, so as to maintain relatively high light transmittance, toughness and adhesion, and inhibit the cracks from continuing to expand to deeper positions.

[0040] The present invention forms a self-healing coating by curing a sol formed by konjac glucomannan and POSS-modified nano-silica, and the content of the POSS-modified nano-silica decreases from the surface of the self-healing coating towards the inside. In this way, the content of the POSS-modified nano-silica on the surface layer of the self-healing coating is relatively high, which can provide more active sites such as amino groups and hydroxyl groups, serving as the "anchor points" of dynamic hydrogen bonds or dynamic chemical bonds, improving the repair strength of the damaged interface and enhancing the repair efficiency. In addition, the high-concentration POSS-modified nano-silica can also increase the mechanical properties and wear resistance of the surface layer of the self-healing coating. The cracks in the inner layer are relatively minor, so the concentration of the POSS-modified nano-silica can be relatively low, and the concentration of konjac glucomannan can be relatively high, so as to maintain relatively high light transmittance and toughness, inhibit the cracks from continuing to expand to deeper positions, thereby enhancing the repair strength of the scratches on the touch screen and greatly improving the problem that obvious traces still exist after repairing relatively severe scratches in the prior art.

[0041] In one embodiment, the self-healing coating is a multi-layer stacked structure formed by successively coating sols containing the POSS-modified nano-silica with different concentrations on the surface of the touch screen and curing. In the actual manufacturing process, multiple portions of sols containing konjac glucomannan and POSS-modified nano-silica are pre-prepared, and the difference between each portion of the sol lies in the different concentrations of the POSS-modified nano-silica. Then, in the order of increasing concentration of the POSS-modified nano-silica, the sols are successively coated on the surface of the touch screen, so as to obtain a self-healing coating in which the content of the POSS-modified nano-silica gradually decreases from the surface to the inside. By adopting this structure and the corresponding batch-by-batch coating method, the operation is simple and the manufacturing cost is relatively lower.

[0042] In one embodiment, the self-healing coating is formed by curing three layers of sols, and a graphene layer with a thickness of 10 - 15 nanometers is coated between every two adjacent cured sols; in the order from the surface to the inside of the self-healing coating, the concentrations of the POSS-modified nano-silica contained in the three layers of sols before curing are 6 g / L, 4 g / L, and 2 g / L respectively, and the thicknesses of the three layers of sols after curing are 50 microns, 30 microns, and 20 microns respectively.

[0043] In the actual operation process, three portions of sols are pre-prepared, and the concentrations of the POSS-modified nano-silica in the three portions of sols are 2 g / L, 4 g / L, and 6 g / L respectively. First, a sol containing the POSS-modified nano-silica with a concentration of 2 g / L is coated on the touch screen, and after preliminary curing, a graphene layer is coated; then, a sol containing the POSS-modified nano-silica with a concentration of 4 g / L is coated on the touch screen, and after preliminary curing, a graphene layer is coated; then, a sol containing the POSS-modified nano-silica with a concentration of 6 g / L is coated on the touch screen, and after preliminary curing, a graphene layer is coated; finally, the three-layer mixed sol can be cured to form a self-healing coating through drying and UV curing processes. In this way, in the order from the surface to the inside of the self-healing coating, the thicknesses of the three-layer mixed sol after curing are 50 microns, 30 microns, and 20 microns in sequence; the thickness of the graphene layer is 10 - 15 nanometers.

[0044] By coating a layer of graphene layer between two adjacent layers of solidified sol, graphene, as a two-dimensional material, can form a continuous film through solution spraying, thereby combining with the sol solidified layer. The graphene layer can provide conductivity and mechanical support, improving the sensitivity and durability of the touch screen. Moreover, the hardness of the graphene layer is greater than that of the solidified sol. Therefore, such a self-healing coating forms a "soft-hard-soft" alternating structure. The graphene layer can inhibit the crack propagation of the self-healing coating during sliding, reducing the interlayer stress concentration. In particular, the layered structure of graphene can inhibit the longitudinal propagation of cracks deeper, thereby extending the service life.

[0045] Specifically, the thickness of the graphene layer is 10 - 15 nanometers. When the thickness of the graphene layer exceeds 20 nanometers, the light transmittance significantly decreases (<85%), which may affect the screen display effect. While a 10 - 15 nanometer graphene layer can not only meet the requirements of the touch screen for conductivity but also improve the fracture toughness, maintaining a good mechanical strengthening effect, and effectively preventing crack propagation across layers through the two-dimensional sheet structure.

[0046] Furthermore, in the order from the surface to the inside of the self-healing coating, the thicknesses of the three layers of solidified sol are 50 microns, 30 microns, and 20 microns respectively. In this way, not only does the outermost layer have the highest content of POSS-modified nano-silica, but also the thickest thickness; while the innermost layer has the lowest content of POSS-modified nano-silica and the thinnest thickness, further realizing the optimization of the gradient change of the content of POSS-modified nano-silica in the self-healing coating, making the POSS-modified nano-silica distributed as much as possible in the outer layer of the self-healing coating, increasing the repair ability and effect of the surface layer of the self-healing coating.

[0047] In one embodiment, the self-healing coating further includes PAMAM-modified nano-silica, and the content of the PAMAM-modified nano-silica decreases from the surface to the inside of the self-healing coating. Polyamidoamine (PAMAM) dendrimer is a colorless to light yellow transparent liquid and does not affect the light transmittance of the touch screen. Using nano-silica as a carrier, the dendritic polyamidoamine (PAMAM) is grafted onto its surface through covalent bonds to form a stable composite structure. The terminal amino or carboxyl group of PAMAM reacts with the hydroxyl group (-OH) on the surface of silica to achieve chemical anchoring. The dendritic molecules of PAMAM provide a high density of functional groups (such as amino groups, amide groups), which can significantly increase the reaction sites on the surface of silica and serve as the anchoring points for dynamic hydrogen bonds, promoting the rapid reorganization of konjac glucomannan molecular chains at the damaged interface and improving the repair efficiency.

[0048] Specifically, the content of PAMAM-modified nano-silica decreases from the surface to the inside of the self-healing coating. Similarly, the self-healing coating of the touch screen can be specifically divided into three layers, and the three sub-layers are formed by curing a mixed sol of PAMAM-modified nano-silica and konjac glucomannan with different concentrations. In this way, the content of PAMAM-modified nano-silica decreases from the surface to the inside of the self-healing coating. The concentration of PAMAM-modified nano-silica on the surface layer of the self-healing coating is relatively high, which can provide more active sites such as amino groups and hydroxyl groups, serving as "anchoring points" for dynamic hydrogen bonds or dynamic chemical bonds, improving the repair strength of the damaged interface, enhancing the repair efficiency, and also increasing the mechanical properties and wear resistance of the surface layer of the self-healing coating.

[0049] According to another aspect of the present invention, the present invention further provides a method for preparing a self-healing coating for a touch screen, comprising the following steps:

[0050] Add an appropriate amount of konjac glucomannan powder to deionized water and stir evenly, and then divide the formed konjac glucomannan solution into multiple portions;

[0051] Graft POSS onto the surface of nano-silica to obtain POSS-modified nano-silica;

[0052] Sequentially add different amounts of POSS-modified nano-silica to the prepared multiple portions of konjac glucomannan solution to obtain multiple portions of mixed sols with sequentially increasing concentrations of POSS-modified nano-silica;

[0053] Coat the multiple portions of mixed sols on the surface of the same touch screen in the order of sequentially increasing concentration of POSS-modified nano-silica and preliminarily cure to form a multi-layer stacked structure;

[0054] Cure the mixed sol to form a self-healing coating through a drying and UV curing process.

[0055] Specifically, take an appropriate amount of konjac glucomannan powder and add it to deionized water and stir evenly to form a konjac glucomannan sol. Divide the obtained konjac glucomannan sol into multiple portions, for example, it can be divided into three portions, stored in three storage buckets respectively, denoted as storage bucket No. 1, storage bucket No. 2, and storage bucket No. 3.

[0056] Graft POSS onto the surface of nano-silica. In a corrosion-resistant reaction kettle, add nano-silica powder and POSS powder according to a mass ratio of 1.2:1. Use ethanol as the solvent to disperse POSS and nano-silica powder in the solvent, with a solid-liquid ratio of 1:15. Add a silane coupling agent (such as KH550, with a dosage of 3-5% of the mass of silica), adjust the pH to 4-5, and stir and react at 70 °C for 4-6 hours to form Si-O-Si covalent bonds. After the reaction is completed, the POSS-modified silica can be dried in a vacuum drying oven.

[0057] Add the dried POSS-modified silica to the obtained konjac glucomannan sol. The concentration of POSS-modified silica added to each portion of konjac glucomannan sol is different, and the finally obtained mixed sols are arranged in ascending order of the concentration of POSS-modified silica. For example, the obtained konjac glucomannan sol is divided into three portions and stored in three storage barrels respectively, denoted as storage barrel No. 1, storage barrel No. 2, and storage barrel No. 3. Add a predetermined amount of POSS-modified silica to the three storage barrels in sequence, so that the concentrations of POSS-modified silica in storage barrel No. 1, storage barrel No. 2, and storage barrel No. 3 are 2 g / L, 4 g / L, and 6 g / L respectively.

[0058] Coat the multiple portions of mixed sols on the surface of the same touch screen in ascending order of the concentration of POSS-modified nano-silica. For example, first coat a mixed sol with a predetermined thickness and a concentration of POSS-modified nano-silica of 2 g / L on the touch screen surface and preliminarily cure it; then coat a mixed sol with a predetermined thickness and a concentration of POSS-modified nano-silica of 4 g / L on the touch screen surface and preliminarily cure it; finally, coat a mixed sol with a predetermined thickness and a concentration of POSS-modified nano-silica of 6 g / L on the touch screen surface.

[0059] After the coating of the mixed sol is completed, first place the touch screen in a vacuum drying oven for preliminary drying, and then use an ultraviolet curing process to cure the mixed sol coated on the touch screen surface to form a self-healing coating.

[0060] In other embodiments, the number of coating layers of the mixed sol on the touch screen can also be two, four, or other numbers.

[0061] The self-healing coating of the touch screen prepared by the above method has a decreasing content of POSS-modified nano-silica from the surface to the inside of the coating. In this way, the content of POSS-modified nano-silica on the surface layer is relatively high, which can provide more active sites such as amino groups and hydroxyl groups, serving as the "anchoring points" of dynamic hydrogen bonds or dynamic chemical bonds, improving the repair strength of the damaged interface and enhancing the repair efficiency. In addition, the high concentration of POSS-modified nano-silica can also increase the mechanical properties and wear resistance of the surface layer of the self-healing coating. The cracks in the inner layer are relatively slight, so the concentration of POSS-modified nano-silica can be relatively low, and the concentration of konjac glucomannan can be relatively high, so as to maintain a relatively high light transmittance, toughness and adhesion, inhibit the cracks from continuing to expand to deeper positions, thereby enhancing the repair strength of the touch screen scratches and greatly improving the problem that obvious traces still exist after the relatively serious scratches in the prior art are repaired. By adopting the above-mentioned batch coating method, a self-healing coating with a gradient distribution of silica concentration can be obtained through simple operation, and the manufacturing cost is relatively lower, without the need for expensive equipment and complex professional operations.

[0062] In one embodiment, grafting POSS onto the surface of nano-silica to obtain POSS-modified nano-silica includes:

[0063] Adding nano-silica powder into deionized water and performing ultrasonic cleaning to remove impurities and bubbles on the surface of nano-silica;

[0064] Adding nano-silica into tetrahydrofuran solvent and stirring evenly to form a silica dispersion;

[0065] Dissolving a silane coupling agent in tetrahydrofuran solvent to form a uniform silane coupling agent solution;

[0066] Dissolving POSS monomer in tetrahydrofuran solvent, and synchronously adding it to the silica dispersion together with the silane coupling agent solution, stirring and reacting at 70 °C for 4-6 hours and then drying.

[0067] Specifically, in the grafting modification process of POSS and silica, dispersing nano-silica powder in deionized water and then performing ultrasonic cleaning to remove impurities and bubbles on the surface of silica particles. In addition, the nano-silica can also be activated with an acid solution to expose more hydroxyl groups on the nano-silica and enhance the subsequent reaction activity. After the treatment is completed, the nano-silica powder is dried by a dryer to remove moisture.

[0068] Then prepare a reaction kettle, add tetrahydrofuran solvent into the reaction kettle, and then disperse the pretreated nano-silica in the tetrahydrofuran solvent, and the solution can be stirred by a stirring device to form a silica dispersion.

[0069] Then dissolve the silane coupling agent in a tetrahydrofuran solvent to form a uniform silane coupling agent solution. For example, if KH550 is used, the dosage is 3-5% of the mass of silicon dioxide.

[0070] Dissolve the POSS monomer in a tetrahydrofuran solvent and synchronously add it to the silicon dioxide dispersion together with the silane coupling agent solution. Adjust the pH of the mixed solution to 4-5 and stir and react at 70 °C for 4-6 hours to graft POSS onto the surface of nano-silicon dioxide. Finally, put the nano-silicon dioxide modified by POSS grafting into a vacuum drying oven for drying.

[0071] In the above grafting modification process, a tetrahydrofuran solvent is used as a single graft coupling agent. A polar solvent (such as tetrahydrofuran) can improve the compatibility of POSS and the silane coupling agent, and the grafting rate is relatively high.

[0072] In one embodiment, in the step of grafting POSS onto the surface of nano-silicon dioxide to obtain POSS-modified nano-silicon dioxide, the feeding mass ratio of nano-silicon dioxide to POSS is 1.2:1. After POSS grafting modification, more active sites of silicon dioxide can be exposed. The hydroxyl groups of konjac glucomannan form multiple hydrogen bonds with the hydroxyl groups on the surface of nano-silicon dioxide and the organic side chains (such as amino groups) of POSS. When the coating is damaged, the hydrogen bonds break, but under temperature stimulation, such as heating to 40 °C, the molecular chain movement ability of konjac glucomannan is enhanced, and the broken hydrogen bonds are dynamically reorganized through the reorientation of hydroxyl groups with hydroxyl groups / amino groups to achieve self-repair. When the feeding mass ratio of nano-silicon dioxide to POSS is 1.2:1, the comprehensive number of active sites of the hydroxyl groups on the surface of nano-silicon dioxide and the organic side chains of POSS is relatively large, and the effect of rapid self-repair of scratches is relatively ideal.

[0073] In one embodiment, the konjac glucomannan solution is divided into three portions, and POSS-modified nano-silicon dioxide is added to the three portions of konjac glucomannan solution in sequence, so that the concentrations of POSS-modified nano-silicon dioxide in the three mixed sols are 2 g / L, 4 g / L, and 6 g / L respectively;

[0074] The multiple mixed sols are coated on the surface of the touch screen in the order of increasing concentration of POSS-modified nano-silicon dioxide, including:

[0075] First, coat a sol containing POSS-modified nano-silicon dioxide with a concentration of 2 g / L on the touch screen, and then coat a graphene layer after preliminary curing;

[0076] Then coat a sol containing POSS-modified nano-silicon dioxide with a concentration of 4 g / L on the touch screen, and then coat a graphene layer after preliminary curing;

[0077] Then, a sol with a concentration of 6 g / L containing POSS-modified nano-silica is coated on the touch screen. After preliminary curing, a graphene layer is coated again.

[0078] Finally, through drying and UV curing processes, the three-layer hybrid sol is cured to form a self-healing coating. In the order from the surface to the inside of the self-healing coating, the thicknesses of the three-layer hybrid sol after curing are 50 microns, 30 microns, and 20 microns in sequence, and the thickness of the graphene layer is 10 - 15 nanometers.

[0079] In this way, the surface layer contains a relatively high concentration of POSS-modified nano-silica, which can repair relatively severe surface scratches and improve wear resistance and mechanical strength; the concentration of POSS-modified nano-silica in the middle layer is the second highest, which can repair relatively slight scratches, and as the content of konjac glucomannan increases, the toughness is improved, and it can inhibit the scratches from continuing to spread towards the deep layer; the concentration of POSS-modified nano-silica in the innermost layer is the lowest, and the content of konjac glucomannan is the highest, so that the base of the self-healing coating maintains a relatively high light transmittance and toughness. Secondly, in the order from the surface to the inside of the self-healing coating, the thicknesses of the three-layer sol after curing are 50 microns, 30 microns, and 20 microns respectively. In this way, not only the content of POSS-modified nano-silica in the outermost layer is the highest, but also the thickness is the thickest; while in the innermost layer, the content of POSS-modified nano-silica is the lowest, and the thickness is the thinnest, thereby further optimizing the gradient change of the content of POSS-modified nano-silica in the self-healing coating, making POSS-modified nano-silica distributed as much as possible in the outer layer of the self-healing coating, and increasing the repair ability and effect of the surface layer of the self-healing coating.

[0080] In addition, by coating a graphene layer between two adjacent cured sols, as a two-dimensional material, graphene can form a continuous film through solution spraying, and thus combine with the sol cured layer. The graphene layer can provide conductivity and mechanical support, and can improve the sensitivity and durability of the touch screen; moreover, the hardness of the graphene layer is greater than that of the cured sol, so such a self-healing coating forms a "soft-hard-soft" alternating structure. The graphene layer can inhibit the crack propagation of the self-healing coating during sliding friction and reduce the interlayer stress concentration. In particular, the layered structure of graphene can inhibit the longitudinal propagation of cracks towards deeper depths, thereby extending the service life.

[0081] Particularly, the thickness of the graphene layer is 10 - 15 nanometers. When the thickness of the graphene layer exceeds 20 nanometers, the light transmittance significantly decreases (<85%), which may affect the screen display effect. While a graphene layer with a thickness of 10 - 15 nanometers can not only meet the requirements of the touch screen for conductivity, but also improve the fracture toughness, maintain a good mechanical strengthening effect, and effectively prevent crack propagation across layers through the two-dimensional sheet structure.

[0082] In one embodiment, the graphene layer is formed by coating through the following steps:

[0083] Disperse graphene in deionized water, add sodium dodecyl sulfate as a surfactant, form a dispersion through ultrasonic treatment, and then spray to form a film layer with a thickness of 10 - 15 nanometers.

[0084] As an anionic surfactant, the hydrophobic end (dodecyl chain) of sodium dodecyl sulfate is adsorbed on the graphene surface through van der Waals forces, and the hydrophilic end (sulfate group) extends into the water, forming a double electric layer (enhanced Zeta potential), effectively inhibiting the stacking of graphene sheets through π-π bonds or agglomeration through van der Waals forces. Through ultrasonic dispersion treatment, the dispersion of single-layer or few-layer graphene is achieved. The ultrasonic atomization spraying technology can be used to precisely control the droplet size, making the film layer thickness uniform. The 10 - 15 nm film layer has both high transparency (visible light region > 90%) and excellent conductivity (sheet resistance < 100 Ω / sq). In one embodiment, the method for preparing the self-healing coating of the touch screen further includes the following steps:

[0085] Graft PAMAM onto the surface of nano-silica to obtain PAMAM-modified nano-silica. Add different contents of PAMAM-modified nano-silica to multiple prepared konjac glucomannan solutions in sequence, such that the mass ratio of POSS-modified nano-silica to PAMAM-modified nano-silica in each konjac glucomannan solution is 1:1.

[0086] Specifically, while grafting POSS onto the surface of nano-silica to obtain POSS-modified nano-silica, PAMAM can be simultaneously grafted onto the surface of nano-silica to obtain PAMAM-modified nano-silica. Then, both POSS-modified nano-silica and PAMAM-modified nano-silica are added to the konjac glucomannan solution. In each portion of the konjac glucomannan solution, the masses of POSS-modified nano-silica and PAMAM-modified nano-silica are the same. That is to say, in the konjac glucomannan solution with a lower concentration of added POSS-modified nano-silica, the concentration of added PAMAM-modified nano-silica is also lower; while in the konjac glucomannan solution with a higher concentration of added POSS-modified nano-silica, the concentration of added PAMAM-modified nano-silica is also higher. The terminal amino groups of PAMAM (polyamidoamine dendrimer) can achieve rapid self-healing through dynamic covalent bonds (such as imine bonds), and in the scratch experiment, the PAMAM grafting system can complete the repair at room temperature. In addition, the dendritic structure of PAMAM can adsorb more nano-silica particles to form a multi-level dispersion network, increasing the fracture toughness of the coating by 15%. This ensures that the surface layer of the self-healing coating always has more active sites relative to the inner layer, which can serve as the "anchor points" for dynamic hydrogen bonds or dynamic chemical bonds, improving the repair strength at the damaged interface, enhancing the repair efficiency, and also increasing the mechanical properties and wear resistance of the surface layer of the self-healing coating.

[0087] In one embodiment, the following steps are further included: adding silver nanowires to the konjac glucomannan solution. Specifically, after dissolving konjac glucomannan in deionized water to form a konjac glucomannan solution, silver nanowires are added to the konjac glucomannan solution. On the one hand, this can increase the conductivity of the subsequent formed self-healing coating of the touch screen and improve the touch sensitivity of the touch screen; on the other hand, silver nanowires also have certain antibacterial properties, so that the formed self-healing coating of the touch screen also has certain antibacterial properties, becoming a multifunctional composite coating.

[0088] Example

[0089] A preparation method of a self-healing coating for a touch screen is prepared by the following steps:

[0090] Add an appropriate amount of konjac glucomannan powder to deionized water and stir evenly to form a konjac glucomannan solution, then add silver nanowires to the konjac glucomannan solution, and divide the solution into three equal portions;

[0091] Add nano-silica powder to deionized water and perform ultrasonic cleaning to remove impurities and bubbles on the surface of nano-silica; then add nano-silica to tetrahydrofuran solvent and stir evenly to form a silica dispersion; dissolve the silane coupling agent in tetrahydrofuran solvent to form a uniform silane coupling agent solution; dissolve POSS monomer and PAMAM monomer in tetrahydrofuran solvent according to a mass ratio of 1:1, and synchronously add them to the silica dispersion with the silane coupling agent solution. The feeding mass ratio of nano-silica to POSS is 1.2:1. After stirring and reacting at 70 °C for 4 - 6 hours, dry to obtain POSS and PAMAM mixed-modified nano-silica;

[0092] Add different contents of the mixed-modified nano-silica to the three prepared konjac glucomannan solutions in sequence, so that the concentrations of the mixed-modified nano-silica in the three mixed sols are 2 g / L, 4 g / L, and 6 g / L respectively;

[0093] Coat the three mixed sols on the surface of the same touch screen in the order of increasing concentration of the mixed-modified nano-silica and preliminarily cure them into a three-layer stacked structure;

[0094] Make the mixed sol cure to form a self-healing coating through drying and UV curing processes.

[0095] Three samples are prepared in the above manner, denoted as sample a, sample b, and sample c respectively. A commercially available touch screen with a self-healing coating is used as a control sample. Under the environment of 25 °C and 45% humidity, under the action of the same scratch force (scratched with a 500 g weight), the scratch depth is 10 - 15 μm, and the single scratch repair effect, repair time required, scratch depth before and after repair, scratch repair rate, and roughness before and after repair are recorded. In addition, all samples are subjected to 150 scratch-repair cycle tests, the light transmittance (visible light band) after 150 repairs is recorded, and the light transmittance retention rate is calculated. The results are shown in Table 1 below:

[0096] Table 1 Self-healing performance test data of three samples and the control sample

[0097]

[0098] In summary, the present application provides a self-healing coating for a touch screen. The self-healing coating is formed by curing a sol formed by konjac glucomannan and POSS-modified nano-silica. The content of the POSS-modified nano-silica decreases from the surface to the inside of the self-healing coating. In this way, for the surface layer with relatively severe scratches, the self-healing strength and efficiency are improved by the relatively high concentration of POSS-modified nano-silica, and at the same time, the mechanical properties and wear resistance of the surface layer are improved. For the inner layer with slight cracks, the concentration of konjac glucomannan is relatively higher, so as to maintain relatively high light transmittance, toughness and adhesion, and inhibit the cracks from continuing to expand to deeper positions. The self-healing coating of the touch screen is formed by curing a mixed sol containing konjac glucomannan with different concentrations by batch coating, which has simple operation and low cost.

[0099] The above are only the preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A self-healing coating for a touch screen, characterized in that, The self-healing coating is formed by curing a sol formed by konjac glucomannan and POSS-modified nano-silica, wherein the content of the POSS-modified nano-silica decreases from the surface to the inside of the self-healing coating, and the self-healing coating is a multi-layer stacked structure formed by sequentially coating sols containing different concentrations of the POSS-modified nano-silica on the surface of the touch screen and curing them.

2. The self-healing coating for a touch screen according to claim 1, wherein, The self-healing coating is formed by curing three layers of sols. A graphene layer with a thickness of 10-15 nanometers is coated between every two adjacent cured sols. According to the order from the surface to the inside of the self-healing coating, the concentrations of the POSS-modified nano-silica contained in the three layers of sols before curing are 6 g / L, 4 g / L, and 2 g / L respectively, and the thicknesses of the three layers of sols after curing are 50 microns, 30 microns, and 20 microns respectively.

3. The self-healing coating for a touch screen according to claim 1 or 2, characterized in that The self-healing coating further includes PAMAM-modified nano-silica, and the content of the PAMAM-modified nano-silica decreases from the surface to the inside of the self-healing coating.

4. A method for preparing a self-healing coating for a touch screen, characterized in that, Including: Adding an appropriate amount of konjac glucomannan powder to deionized water and stirring evenly, and then dividing the formed konjac glucomannan solution into multiple portions; Grafting POSS onto the surface of nano-silica to obtain POSS-modified nano-silica; Sequentially adding different contents of POSS-modified nano-silica to the prepared multiple portions of konjac glucomannan solution to obtain multiple portions of mixed sols with sequentially increasing concentrations of POSS-modified nano-silica; Sequentially coating the multiple portions of mixed sols on the surface of the same touch screen in the order of sequentially increasing concentration of POSS-modified nano-silica and preliminarily curing to form a multi-layer stacked structure; Making the mixed sol cure to form a self-healing coating through a drying and UV curing process.

5. The preparation method of the self-healing coating for a touch screen according to claim 4, characterized in that, Grafting POSS onto the surface of nano-silica to obtain POSS-modified nano-silica, including: Adding nano-silica powder to deionized water and performing ultrasonic cleaning to remove impurities and bubbles on the surface of the nano-silica; Adding nano-silica to a tetrahydrofuran solvent and stirring evenly to form a silica dispersion; Dissolving a silane coupling agent in a tetrahydrofuran solvent to form a uniform silane coupling agent solution; Dissolving a POSS monomer in a tetrahydrofuran solvent, synchronously adding it to the silica dispersion together with the silane coupling agent solution, stirring and reacting at 70 °C for 4-6 hours, and then drying.

6. The preparation method of the self-repairing coating for a touch screen according to claim 5, characterized in that, When grafting POSS onto the surface of nano-silica to obtain POSS-modified nano-silica, the feeding mass ratio of nano-silica to POSS is 1.2:

1.

7. The preparation method of the self-healing coating for a touch screen according to claim 4, characterized in that, The konjac glucomannan solution is divided into three portions, and POSS-modified nano-silica is sequentially added to the three portions of konjac glucomannan solution so that the concentrations of POSS-modified nano-silica in the three portions of mixed sols are 2 g / L, 4 g / L, and 6 g / L respectively; The sequentially coating the multiple portions of mixed sols on the surface of the touch screen in the order of sequentially increasing concentration of POSS-modified nano-silica includes: First, a sol with a concentration of 2 g / L containing POSS-modified nano-silica is coated on the touch screen. After preliminary curing, a graphene layer is coated again. Next, a sol with a concentration of 4 g / L containing POSS-modified nano-silica is coated on the touch screen. After preliminary curing, a graphene layer is coated again. Then, a sol with a concentration of 6 g / L containing POSS-modified nano-silica is coated on the touch screen. After preliminary curing, a graphene layer is coated again. Finally, through the drying and UV curing processes, the three-layer mixed sol is cured to form a self-healing coating. In the order from the surface to the inside of the self-healing coating, the thicknesses of the three-layer mixed sol after curing are 50 microns, 30 microns, and 20 microns in sequence, and the thickness of the graphene layer is 10 - 15 nanometers.

8. The preparation method of the self-healing coating for the touch screen according to claim 7, wherein, The graphene layer is formed by coating through the following steps: Graphene is dispersed in deionized water, and sodium dodecyl sulfate is added as a surfactant. After forming a dispersion through ultrasonic treatment, a film layer with a thickness of 10 - 15 nanometers is sprayed.

9. The preparation method of the self-healing coating for a touch screen according to any one of claims 4-8, characterized in that, It also includes the following steps: PAMAM is grafted onto the surface of nano-silica to obtain PAMAM-modified nano-silica. Different amounts of PAMAM-modified nano-silica are sequentially added to multiple prepared konjac glucomannan solutions, such that in each konjac glucomannan solution, the mass ratio of POSS-modified nano-silica to PAMAM-modified nano-silica is 1:

1.

10. The preparation method of the self-healing coating for the touch screen according to claim 9, characterized in that, It also includes the following steps: Nano silver wires are added to the konjac glucomannan solution.

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