Compression and tensile stretch resistant low sheet resistance self-healing flexible transparent conductive film and method of manufacture

Abstract

The application discloses a low-resistance self-healing flexible transparent conductive film and a manufacturing method thereof. The flexible substrate surface of the conductive film is provided with micro-nano scale grid interconnected grooves, the grooves are filled with a solid conductive layer, the upper layer is filled with a liquid conductive material and an encapsulation layer. The manufacturing method comprises the following steps: firstly, obtaining a flexible substrate with a grid interconnected groove structure; secondly, filling the grooves with a conductive slurry by using an electric field; thirdly, solidifying to form a solid conductive layer; fourthly, filling the upper layer with a liquid conductive material to form a liquid conductive layer; and finally, encapsulating to complete the preparation of the conductive film. When external pressure or stretching is applied to the conductive film, micro cracks are generated in the solid conductive layer material, the upper layer liquid conductive material is filled in the cracks in a self-healing manner without delay, and the stable conduction is maintained. Meanwhile, the line width and arrangement of the grid interconnected grooves are controlled to realize the regulation of the transparency, and the conductive film has the advantages of high conductivity, high transparency, strong environmental adaptability, strong pressure resistance, strong stretchability and long service life.

Description

Technical Field

[0001] The present invention belongs to the field of micro-nano manufacturing technology, and particularly relates to a compression-resistant and stretch-resistant low-square-resistance self-healing flexible transparent conductive film and a manufacturing method thereof. Background Art

[0002] The flexible electronics industry is developing rapidly, with a surge of flexible electronic products, including flexible displays, flexible solar cells, and flexible sensors, entering the market. In many applications, core components must possess both excellent conductivity for efficient signal transmission and high light transmittance to meet the visibility requirements of displays and touch panels. Therefore, flexible transparent conductive films, combining flexibility, high transparency, and high conductivity, are at the core of the development of many flexible optoelectronic products. Their manufacture has become a critical issue in the flexible electronics field, and cannot be underestimated.

[0003] Traditional conductive films, such as metal films, while offering excellent conductivity, suffer from drawbacks such as high rigidity and opacity, making them difficult to adapt to the demands of emerging flexible electronic devices. Indium tin oxide (ITO) is the most widely used alternative. ITO not only offers excellent conductivity and high visible light transmittance, but also boasts a mature and reliable film-forming technology and subsequent etching and patterning process, making it the mainstream material for the development of transparent conductive films. However, ITO transparent conductive films are brittle and prone to cracking when subjected to stress. Therefore, the development of flexible transparent conductive films with excellent mechanical bending properties has become a research hotspot.

[0004] Although flexible conductive films have promoted the development and application of flexible electronic skin and flexible displays to a certain extent, in actual application, flexible electronic devices are often squeezed, collided, scratched, and collided, which inevitably cause mechanical damage such as cracks to the conductive film, affecting the conductive performance. In view of this, the internal self-healing property of the conductive film becomes the key to solving this problem. This property means that the conductive film self-heals without delay after being damaged, maintains low square resistance, and ensures the continuous transmission of electrical signals. Therefore, the internal self-healing of the conductive film has become a hot topic of current research. At present, the manufacturing process system of flexible transparent conductive films has also shown a diversified trend, covering a variety of technologies such as electrospinning, magnetron sputtering, and vapor deposition; however, they all face difficulties such as complex process technology and high equipment costs, which have limited the large-scale manufacturing and widespread application of flexible transparent conductive films.

[0005] In summary, the flexible electronics industry is in urgent need of high-performance conductive films, yet existing materials and processes present numerous challenges. Therefore, there is a pressing need for a low-sheet-resistance, self-healing, flexible, transparent conductive film that is both compressive and tensile-resistant, capable of achieving internal self-healing without delay and maintaining low sheet resistance under both compressive and tensile conditions. Such a conductive film has the potential to overcome the limitations of existing flexible devices, opening up a new development path for the flexible electronics industry and addressing the urgent need for high-performance conductive films in diverse applications, from foldable phones and smart wearables to flexible sensors.

[0006] The invention patent application with publication number CN107527675A discloses a flexible conductive film and a preparation method thereof, including a conductive layer and a liquid metal layer covering the conductive layer, wherein the conductive layer is a carbon nanotube layer, a metal conductive layer or a metal oxide conductive layer. When the conductive layer is damaged or defective, the liquid metal has fluidity and can repair the damage to the conductive layer. The invention directly applies the liquid metal layer on the conductive layer, which does not have the characteristic of adjusting transparency, and the preparation process is conventional spraying, and the process performance has the problem of unstable performance. Summary of the Invention

[0007] In order to overcome the defects of the above-mentioned prior art, the purpose of the present invention is to provide a low-square-resistance self-healing flexible transparent conductive film and a manufacturing method that are resistant to compression and tension. An electric field is used to drive a conductive paste to fill the pre-imprinted grid interconnect grooves with a conductive paste, which is solidified to form a solid conductive layer. The liquid conductive paste is then filled by scraping to form an upper liquid conductive layer. Finally, a flexible base material is spin-coated to encapsulate the conductive film. This film, which is a composite of upper and lower conductive materials, has an upper layer that can heal itself without delay and fill the microcracks in the lower layer due to its fluidity, maintaining stable conduction, and has good compressive resistance and stretchability. At the same time, the transparency of the film can be flexibly adjusted by controlling the size of the grooves, and it has the advantages of high conductivity, stronger environmental adaptability, and longer life.

[0008] In order to achieve the above object, the technical solution adopted in the present invention is:

[0009] A low-square-resistance self-healing flexible transparent conductive film that is resistant to compression and stretching includes a flexible substrate. The surface of the flexible substrate has grooves interconnected by micro-nanoscale grids. The grooves are filled with two layers of conductive materials. The lower layer is a solid conductive layer formed by conductive materials, and the upper layer is a liquid conductive material. The liquid conductive material and the solid conductive layer can coexist stably. When microcracks are generated in the solid conductive layer of the lower layer under various external deformations, the liquid conductive material in the upper layer can self-heal and fill the microcracks generated in the solid conductive layer without delay due to its fluidity to maintain stable conduction; an encapsulation layer is provided on the surface of the groove.

[0010] The material of the flexible substrate includes polydimethylsiloxane, polyimide or polyester.

[0011] The conductive material includes gold, silver paste, or metal nanowire / carbon-based flexible polymer doped with metal nanowires.

[0012] The liquid conductive material is liquid metal or liquid conductive gel, and the liquid metal includes gallium indium tin alloy.

[0013] A method for manufacturing a compression-resistant and stretch-resistant low-square-resistance self-healing flexible transparent conductive film comprises the following steps:

[0014] The first step is to prepare the nanoimprint mold and flexible substrate: using photolithography to prepare an imprint mold with a surface-protruding micro-nanoscale grid interconnected structure; spin coating to form a flexible substrate material with a micron-level thickness, and place a conductive substrate underneath the flexible substrate material;

[0015] The second step is to prepare the micro-nanoscale grid interconnected groove structure: pressing the imprint mold onto the flexible substrate material, drying and completely curing the flexible substrate material, and then peeling off the imprint mold to obtain a flexible substrate with micro-nanoscale grid interconnected grooves;

[0016] The third step is the preparation of a solid conductive layer: Under the assistance of an electric field, a conductive material is filled into the groove of the flexible substrate and solidified to form a solid conductive layer;

[0017] Step 4: Preparation of liquid conductive layer: Using a doctor blade coating method, liquid conductive material is again filled onto the solid conductive layer in the groove to form a liquid conductive layer;

[0018] The fifth step is packaging: using spin coating, a transparent packaging layer is generated on the surface of the liquid conductive material, and the upper liquid conductive material is encapsulated in the groove to complete the preparation and packaging of the self-healing flexible transparent conductive film.

[0019] The micro-nanoscale grid interconnected grooves are adjusted in line width and arrangement to achieve regulation of the transparency of the conductive film.

[0020] The third step is specifically as follows: injecting liquid conductive material into the conductive nozzle, connecting alternating current between the conductive substrate and the conductive nozzle, allowing the electric field force to act, and filling the conductive material into the groove of the flexible substrate. Moving the conductive nozzle, controlling the filling amount of the conductive material, ensuring that the conductive material is filled to other predetermined groove positions, heating and drying it to solidify, and completing the preparation of the solid conductive layer.

[0021] The thickness of the solid conductive layer is 5-50 μm.

[0022] The liquid conductive material is scraped to a thickness of 5-50 μm.

[0023] The transparent encapsulation layer is made of PDMS and has a thickness of 20-80 μm.

[0024] The flexible substrate material includes polydimethylsiloxane, polyimide or polyester.

[0025] The imprinting mold is a silicon wafer having a convex structure after etching.

[0026] The conductive substrate is a rigid substrate glass with conductive nanomaterials deposited on the surface, and the conductive nanomaterials include indium tin oxide or gold.

[0027] The conductive material includes gold, silver paste, or metal nanowire / carbon-based flexible polymer doped with metal nanowires.

[0028] The liquid conductive material is liquid metal or liquid conductive gel, and the liquid metal includes gallium indium tin alloy.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] (1) The surface of the flexible substrate of the present invention has a micro-nanoscale grid interconnected groove structure. By adjusting the line width and arrangement of the protruding structure of the nanoimprint mold, such as the density, the size of the grid interconnected grooves of the flexible substrate can be flexibly controlled to ensure the transparency of the conductive film.

[0031] (2) If microcracks are generated in the solid conductive layer of the lower layer of the present invention due to external influences, the liquid conductive material provided in the upper layer has fluidity and can heal and fill the microcracks generated in the solid conductive layer 7 without delay to maintain stable conduction.

[0032] (3) In the present invention, when preparing the solid conductive layer, the conductive paste is filled into the groove of the flexible substrate with the assistance of the electric field force, and solidified to form a solid conductive layer. The advantage or principle of the electric field force is that the liquid conductive material usually has a high surface energy, and thus cannot achieve complete filling in the micro-nano scale grid groove. With the assistance of the electric field force, the liquid conductive material can be completely filled into the micro-nano scale groove; thus, the process is simple and ingenious.

[0033] In summary, the present invention adjusts the transparency of the conductive film by changing the groove line width and arrangement of the surface of the imprint mold; under the action of external pressure and tension, the lower solid conductive material produces microcracks, and the upper liquid conductive material, due to its strong fluidity, automatically heals without delay and fills the microcracks caused by large stress to maintain low square resistance, thereby achieving high conductivity; during preparation, the electric scraping method can achieve the perfect filling of high surface energy liquid conductive material into the grooves of the micro-nano grid structure, and realize the large-area scraping forming of the transparent conductive film structure. Therefore, the present invention has a simple process and strong operability. The resulting conductive film has high conductivity, high transmittance, and is compressible and stretchable, which expands the application prospects of conductive films in the field of flexible electronics. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Schematic diagram of the structure of the imprinting mold and the flexible substrate.

[0035] Figure 2 Schematic diagram of the nanoimprint groove process on a flexible substrate.

[0036] Figure 3 It is a structural schematic diagram of a flexible substrate with a groove structure and a conductive substrate.

[0037] Figure 4 Schematic diagram of the filling process of the lower solid conductive layer slurry.

[0038] Figure 5 Schematic diagram of the structure after the lower layer of solid conductive material is solidified.

[0039] Figure 6 Schematic diagram of the filling process of the upper layer of liquid conductive material.

[0040] Figure 7 Schematic diagram of the structure after the upper layer of liquid conductive material is filled.

[0041] Figure 8 This is a schematic diagram of the structure after the conductive film packaging is completed.

[0042] Figure 9 Schematic diagram of the working mechanism of the present invention under pressure and tension conditions.

[0043] Figure 10 Schematic diagram of the three-dimensional structure of the product prepared by the present invention.

[0044] Figure 11 Schematic diagram comparing the compressive performance of the conductive film of the present invention and that of a common conductive film.

[0045] In the figure: flexible base material 1; imprinting mold 2; groove 2'; conductive substrate 3; flexible base 4; conductive nozzle 5; conductive material 6; solid conductive layer 7; scraper 8; liquid conductive material 9. DETAILED DESCRIPTION

[0046] The preparation process of the present invention will be described in detail below with reference to the schematic diagram.

[0047] Reference Figure 3-Figure 8, including a flexible substrate 4, the surface of the flexible substrate 4 has grooves 2' with micro-nanoscale grid interconnection. By adjusting the line width and arrangement of the grooves 2', such as density, the size of the flexible substrate grid interconnection grooves can be flexibly controlled to ensure the transparency of the conductive film; the grooves 2' are filled with two layers of conductive material, the lower layer is a solid conductive layer 7 formed by a conductive material 6, and the upper layer is a liquid conductive material 9. The liquid conductive material 9 and the solid conductive layer 7 can coexist stably for a long time. When microcracks are generated in the solid conductive layer 7 of the lower layer under various deformations such as external impact, stretching, torsion, and folding, the liquid conductive material 9 on the upper layer will automatically heal the microcracks generated by the solid conductive layer 7 without delay due to its fluidity to maintain stable conduction. An encapsulation layer is provided on the surface of the groove 2'.

[0048] The material of the flexible substrate 4 includes polydimethylsiloxane, polyimide or polyester.

[0049] The conductive material 6 includes gold or silver paste, or a flexible polymer doped with metal nanowires / carbon, or liquid metal; the liquid metal includes bismuth indium tin alloy.

[0050] The liquid conductive material 9 is liquid metal or liquid conductive gel, and the liquid metal includes gallium-indium-tin alloy.

[0051] A method for manufacturing a compression-resistant and stretch-resistant low-square-resistance self-healing flexible transparent conductive film comprises the following steps:

[0052] Step 1: Preparation of nanoimprint mold and flexible substrate: Figure 1 As shown, an imprint mold 2 with a micro-nanoscale grid interconnected structure with surface protrusions is prepared by photolithography and etching technology; low surface energy treatment is performed to facilitate demolding after subsequent imprinting is completed; a layer of flexible base material 1 with a thickness of micrometer level is spin-coated by a glue spreader, and a conductive substrate 3 is placed under the flexible base material 1. The conductive substrate 3 is a rigid substrate glass with a conductive nanomaterial deposited on the surface, and the conductive nanomaterial is indium tin oxide or gold.

[0053] Step 2: Preparation of micro-nanoscale grid interconnected groove structure: Figure 2 As shown, an imprint mold 2 treated with low surface energy is pressed onto a flexible substrate material 1 with a certain amount of pressure. The imprint mold 2 is a silicon wafer with a convex structure after etching. The ambient temperature is adjusted to a temperature condition at which the flexible substrate material 1 can be cured using an oven. After the flexible substrate material 1 is completely cured, the imprint mold 2 is peeled off to obtain a flexible substrate 4 with micro-nanoscale grid-interconnected grooves, as shown in FIG. Figure 3 shown.

[0054] Step 3: Preparation of solid conductive layer: Figure 4As shown, a liquid silver paste is prepared in advance as the conductive material 6, which is injected into the storage cavity of the conductive nozzle 5. An alternating current is connected between the conductive substrate 3 and the conductive nozzle 5. At this time, the electric field force takes effect, and the conductive material 6 is filled into the groove 2' of the flexible substrate 4. At the same time, the conductive nozzle 5 is moved to control the filling amount of the conductive material 6 to ensure that the conductive material 6 can be accurately and efficiently filled into other predetermined grooves 2'. After filling, it is heated and dried, and solidified to complete the preparation of the solid conductive layer 7. The thickness of the solid conductive layer is 40μm. Figure 5 shown.

[0055] Step 4: Preparation of liquid conductive layer: Figure 6 As shown, a liquid conductive layer is prepared by scraping, and a liquid conductive material 9 is directly scraped on the solidified conductive material layer 7 with a scraper 8, and filled into the upper layer of the groove 2' of the flexible substrate 4. After filling, the residual material on the surface of the flexible substrate is wiped off to form a liquid conductive layer. The scraping thickness of the liquid conductive material 9 is 40μm, and the liquid conductive material 9 is a gallium indium tin alloy, such as Figure 7 shown.

[0056] Step 5: Encapsulation: After completing the filling of the upper and lower layers of conductive materials, spin-coat the flexible base material on the surface of the film. By controlling the spin-coating speed, a transparent encapsulation layer with a thickness of 30 μm is generated. The upper layer of liquid conductive material 9 is encapsulated in the groove to complete the preparation and encapsulation of the self-healing flexible transparent conductive film. Figure 8 shown.

[0057] The self-healing flexible transparent conductive film obtained by the present invention has good conductive stability; the composite form of the upper and lower conductive materials has good compressive resistance and stretchability. Figure 9 As shown in FIG. 1 , when external pressure and tension act on the conductive film, microcracks are generated in the lower solid conductive layer 7, and the upper liquid conductive material 9 heals and fills the cracks without delay to maintain stable conduction; Figure 10 As shown, it is a three-dimensional schematic diagram of the prepared transparent conductive film. The grooves interconnected by the micro-nanoscale grid on the flexible substrate 4 are filled with upper and lower layers of different conductive materials. The transmittance of the conductive film can be adjusted by regulating the size and arrangement of the grooves.

[0058] Reference Figure 11 As can be seen from the figure, the self-healing flexible transparent conductive film of the present invention has stronger compressive resistance than ordinary conductive films. The resistance of ordinary conductive films increases sharply under 5.1 MPa, while the structure of the present invention increases the compressive resistance to 17.5 MPa.

Claims

1. A low-square-resistance self-healing flexible transparent conductive film that is resistant to compression and tension, characterized in that: The flexible substrate (4) comprises a surface of the flexible substrate (4) having an embedded micro-nanoscale grid-interconnected groove (2'), the groove (2') being filled with two layers of conductive material, the lower layer being a solid conductive layer (7) formed by a conductive material (6), and the upper layer being a liquid conductive material (9), the liquid conductive material (9) and the solid conductive layer (7) being able to coexist stably, and when microcracks are generated in the solid conductive layer (7) under various external deformations, the liquid conductive material (9) in the upper layer can self-heal the microcracks generated by the solid conductive layer (7) without delay due to its fluidity to maintain stable conduction, and an encapsulation layer is provided on the surface of the groove (2'); the liquid conductive material (9) and the solid conductive layer (7) are constrained inside the embedded micro-nanoscale grid-interconnected groove (2') to achieve the compressive resistance of the flexible conductive film; The thickness of the solid conductive layer (7) is 40 μm; The coating thickness of the liquid conductive material (9) is 40 μm; The solid conductive layer (7) is formed by filling the conductive material (6) into the groove (2') of the flexible substrate (4) with the assistance of the electric field force, and solidifying. Specifically, the liquid conductive material (6) is injected into the conductive nozzle (5), an alternating current is connected between the conductive substrate (3) and the conductive nozzle (5), the electric field force acts, and the conductive material (6) is filled into the groove (2') of the flexible substrate (4), the conductive nozzle (5) is moved, the filling amount of the conductive material (6) is controlled, and the conductive material (6) is ensured to be filled into other predetermined grooves (2') positions, and the conductive material (6) is heated and dried to solidify, thereby completing the preparation of the solid conductive layer (7); The liquid conductive material (9) is formed by filling the solid conductive layer (7) in the groove (2') with the liquid conductive material (9) by means of scraping.

2. The compression- and tension-resistant, low-square-resistance, self-healing, flexible transparent conductive film according to claim 1, characterized in that: The material of the flexible substrate (4) includes polydimethylsiloxane, polyimide or polyester.

3. The compression- and tension-resistant, low-square-resistance, self-healing, flexible transparent conductive film according to claim 1, characterized in that: The conductive material (6) includes gold, silver paste, or a flexible polymer doped with metal nanowires / carbon.

4. The compression- and tension-resistant, low-square-resistance, self-healing, flexible transparent conductive film according to claim 1, characterized in that: The liquid conductive material (9) is liquid metal or liquid conductive gel, and the liquid metal includes gallium indium tin alloy.

5. The method for manufacturing a compression-resistant and tensile-resistant low-square-resistance self-healing flexible transparent conductive film according to claim 1, characterized in that: The following steps are involved: Step 1: Preparation of nanoimprint mold and flexible substrate: using photolithography technology to prepare an imprint mold (2) with a surface-convex micro-nanoscale grid interconnected structure; spin coating to generate a flexible substrate material (1) with a thickness of micrometer level, and placing a conductive substrate (3) under the flexible substrate material (1); Step 2: Preparation of a micro-nanoscale grid interconnected groove structure; pressing the imprint mold (2) onto the flexible substrate material (1), drying and completely curing the flexible substrate material (1), and then peeling off the imprint mold (2) to obtain a flexible substrate (4) having micro-nanoscale grid interconnected grooves; Step 3: Preparation of a solid conductive layer (7); Under the assistance of an electric field force, the conductive material (6) is filled into the groove (2') of the flexible substrate (4), and solidified to form a solid conductive layer (7); Step 4: Preparation of a liquid conductive layer; using a scraping method, the liquid conductive material (9) is again filled onto the solid conductive layer (7) in the groove (2') to form a liquid conductive layer; Step 5: Encapsulation: Using a spin coating method, a transparent encapsulation layer is generated on the surface of the liquid conductive material (9), and the upper layer of liquid conductive material (9) is encapsulated in the groove (2'), thereby completing the preparation and encapsulation of the self-healing flexible transparent conductive film.

6. The method for manufacturing a compression- and tension-resistant, low-square-resistance, self-healing, flexible transparent conductive film according to claim 5, characterized in that: The micro-nanoscale grid-interconnected grooves (2') are used to adjust the line width and arrangement of the grooves (2') to achieve regulation of the transparency of the conductive film.

7. The method for manufacturing a compression- and tension-resistant, low-square-resistance, self-healing, flexible transparent conductive film according to claim 5, characterized in that: The imprinting mold (2) is a silicon wafer having a convex structure after etching; The conductive substrate (3) is a rigid substrate glass with a conductive nanomaterial deposited on the surface, and the conductive nanomaterial includes indium tin oxide or gold.

8. The method for manufacturing a compression- and tension-resistant, low-square-resistance, self-healing, flexible transparent conductive film according to claim 5, wherein: The flexible substrate material (1) comprises polydimethylsiloxane, polyimide or polyester; The transparent encapsulation layer is made of PDMS and has a thickness of 20-80 μm; The conductive material (6) includes gold or silver paste, or a flexible polymer doped with metal nanowires / carbon; The liquid conductive material (9) is liquid metal or liquid conductive gel, and the liquid metal includes gallium indium tin alloy.

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