Composite adhesive, method of preparing the same, and display device

Abstract

The application relates to the technical field of high polymer materials, in particular to a composite adhesive, a preparation method thereof and a display device. The composite adhesive is used for a reflective display module, has conductivity, and comprises polyurethane and a polymer modifier; the mass ratio of the polyurethane to the polymer modifier is (15:1) to (5:1), and the glass transition temperature of the polymer modifier is above 75 DEG C. The composite adhesive is prepared by compounding the polyurethane and the polymer modifier in a specific ratio, and the glass transition temperature of the polymer modifier is controlled to be above 75 DEG C, so that the mechanical properties of the composite adhesive are effectively improved, and the hardness and strength of the adhesive film formed by the composite adhesive are enhanced.

Description

Technical Field

[0001] This application belongs to the field of polymer materials technology, and in particular relates to a composite adhesive, its preparation method, and a display device. Background Technology

[0002] Electronic paper does not require a backlight; it relies on reflecting external light to display images. For example... Figure 1 As shown, the main structure of electronic paper includes an indium tin oxide layer 01, an ink layer 02, a conductive adhesive layer 03, and a TFT substrate 04, which are stacked sequentially. The conductive adhesive layer 03 serves as the structure connecting the core functional layer ink layer 02 and the TFT substrate 04, and its mechanical properties directly affect the overall reliability of the electronic paper.

[0003] In existing technologies, polyurethane emulsions are commonly used adhesives in electronic paper due to their excellent bonding properties, elasticity, and chemical resistance. However, existing polyurethane emulsions suffer from insufficient hardness, leading to stringing at the cut edges during laser cutting. This stringing not only affects the smoothness and aesthetics of the cut edges but can also interfere with subsequent assembly processes, reducing production efficiency. Furthermore, due to insufficient film hardness, air bubbles easily form at the edges of the film after high-temperature storage. These air bubbles not only affect the appearance quality of the electronic paper but also damage the integrity of its internal structure, impacting its structural stability and display effect, ultimately reducing product reliability and lifespan. Summary of the Invention

[0004] The purpose of this application is to provide a composite adhesive, its preparation method, and a display device to solve the technical problem of insufficient hardness of polyurethane emulsion films in the prior art.

[0005] Meanwhile, embodiments of this application also provide a reflective display module and a display device.

[0006] To achieve the above-mentioned objectives, the technical solution adopted in this application is as follows: In a first aspect, embodiments of this application provide a composite adhesive. The composite adhesive of this application embodiment is used in a reflective display module and has conductivity; the composite adhesive comprises polyurethane and a polymer modifier. The mass ratio of polyurethane to polymer modifier is (15:1) to (5:1), and the glass transition temperature of polymer modifier is above 75℃.

[0007] The composite adhesive of this application is formulated by blending polyurethane and a polymer modifier in a specific ratio, and controlling the glass transition temperature of the polymer modifier to be above 75°C. The polyurethane and polymer modifier form a blend system, with polymer modifier molecules intertwined and interpenetrating with polyurethane molecules to form an interpenetrating network structure. Polyurethane provides good flexibility and toughness to the composite adhesive, while polymer modifier molecules have higher rigidity compared to polyurethane molecules. In this application's composite adhesive, rigid chain segments are embedded and support the flexible network, enhancing mechanical properties. This interpenetrating network structure effectively resists external stress, inhibits molecular chain slippage, and limits excessive chain movement at high temperatures, effectively improving the mechanical properties of the composite adhesive, enhancing the hardness and strength of the adhesive film formed by the composite adhesive, and reducing stringing during laser cutting of the cured adhesive film. Simultaneously, the adhesive film formed by the composite adhesive of this application also exhibits good mechanical properties at high temperatures, effectively reducing air bubbles generated at the film edges after storage at high temperatures such as 70°C. This effectively improves the quality of products using the composite adhesives of the present application embodiments. For example, when the composite adhesives of the present application embodiments are applied to electronic paper, they effectively improve the flatness and aesthetics of the electronic paper, increase assembly efficiency and yield, reduce air bubbles at the edges of the electronic paper, improve the internal structural integrity and display effect of the electronic paper, improve product reliability, and extend product life.

[0008] Secondly, embodiments of this application provide a method for preparing a composite adhesive. The method for preparing a composite adhesive according to embodiments of this application includes the following steps: The solvent, polyurethane, and polymer modifier are first mixed to obtain modified polyurethane; The modified polyurethane and conductive filler are mixed a second time to obtain a composite adhesive.

[0009] The mass ratio of polyurethane to polymer modifier is (15:1) to (5:1), and the glass transition temperature of polymer modifier is above 75℃.

[0010] The composite adhesive preparation method of this application involves mixing polyurethane and a polymer modifier in a specific ratio, and controlling the glass transition temperature of the polymer modifier within a specific range. The polyurethane is modified by the polymer modifier, resulting in a composite adhesive with good mechanical properties, high strength, and high hardness. The composite adhesive prepared by this method maintains good stability and interfacial adhesion even at high temperatures. When applied to precision electronic devices such as electronic paper, it significantly improves the flatness of these devices, increases assembly efficiency and yield, and reduces the risk of delamination and bubble expansion due to thermal stress during long-term use. Furthermore, the preparation method of this application involves fewer steps, easier control of process parameters, and high production efficiency, making it suitable for industrial production.

[0011] Thirdly, embodiments of this application provide a reflective display module. The reflective display module of this application includes a transparent conductive layer, an electrophoretic functional layer, and a thin-film transistor substrate. The electrophoretic functional layer and the thin-film transistor substrate are bonded together by a conductive adhesive layer, wherein the conductive adhesive layer is prepared from the composite adhesive described above.

[0012] The conductive adhesive layer made with the composite adhesive in this application embodiment has excellent mechanical properties, high hardness, and high strength. This reduces the stringing phenomenon at the cutting edges during laser cutting, improves the flatness after cutting, and increases the efficiency of subsequent assembly processes. When the conductive adhesive layer softens significantly during storage, the material in the conductive adhesive layer, especially at the edges, flows, easily causing the conductive adhesive layer to peel off from the electrophoretic functional layer and / or the thin-film transistor substrate, resulting in bubbles. This greatly affects the structural integrity and display effect of the reflective display module. However, the conductive adhesive layer made with the composite adhesive in this application embodiment still maintains good hardness even at high temperatures such as 70°C. This means that even after storage at high temperatures such as 70°C, bubbles are less likely to form at the edges of the conductive adhesive layer in the reflective display module, effectively improving the structural integrity of the reflective display module, improving the display effect, widening the applicable temperature range of the reflective display module, and extending the service life of the reflective display module.

[0013] Fourthly, embodiments of this application provide a reflective display device. The reflective display device of this application includes the reflective display module described above.

[0014] Based on the flat structure, good mechanical reliability of the interlayer structure and good high-temperature stability of the reflective display module described above, the reflective display device of this application embodiment can achieve a longer service life, more stable display quality and a wider range of applications. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0016] Figure 1 This is a schematic diagram of the structure of an electronic paper; Figure 2 This is a schematic diagram of the structure of conductive particles in the conductive adhesive layer of electronic paper; where... Figure 2 In the diagram, 'a' represents the structure of conductive particles in the conductive adhesive layer and the TFT substrate. Figure 2 b in the diagram represents the structure of the conductive particles in the conductive adhesive layer, the ink layer, and the TFT substrate. Figure 3 This is a schematic diagram showing the bubbles formed on the electronic paper of Comparative Example B1 after high-temperature storage. Figure 3 In the diagram, 'a' represents a schematic diagram of the electronic paper in Comparative Example B1 after high-temperature storage. Figure 3 In the image, b is a micrograph of the edge bubbles on the electronic paper of Comparative Example B1 after high-temperature storage; Figure 4 These are schematic diagrams of electronic paper after high-temperature storage in Examples B1 to B3, wherein... Figure 4 In the diagram, 'a' represents a schematic diagram of the electronic paper after high-temperature storage in Example B2. Figure 4 b in the figure is a schematic diagram of the electronic paper after high-temperature storage in Example B3; Figure 4 c in the figure is a schematic diagram of the electronic paper after high-temperature storage in Example B1; Figure 5 These are schematic diagrams illustrating the electronic paper display effects of Comparative Example B1, Example B3, Example B9, and Example B17; wherein, Figure 5 In the diagram, 'a' represents a schematic representation of the electronic paper display effect in Comparative Example B1. Figure 5 b in the figure is a schematic diagram of the electronic paper display effect in embodiment B3; Figure 5 c in the figure is a schematic diagram of the electronic paper display effect in embodiment B9; Figure 5 In the diagram, d represents the electronic paper display effect of embodiment B17; Figure 6 These are schematic diagrams illustrating the electronic paper display effects of Examples B11, B15, B13, B16, and B12; wherein, Figure 6 In the diagram, 'a' represents a schematic representation of the electronic paper display effect in Example B11. Figure 6 In the diagram, b is a schematic representation of the electronic paper display effect in Example B15; Figure 6 c in the figure is a schematic diagram of the electronic paper display effect in embodiment B13; Figure 6 In the diagram, d represents the electronic paper display effect of embodiment B16; Figure 6 In this diagram, 'e' represents a schematic representation of the electronic paper display effect in Example B12. Figure 7 These are schematic diagrams illustrating the display effects of electronic paper under low-temperature conditions in Examples B16, B13, B11, B12, and B15; wherein, Figure 7 In the diagram, 'a' represents a schematic representation of the electronic paper display effect in Example B16. Figure 7 b in the figure is a schematic diagram of the electronic paper display effect in embodiment B13; Figure 7 c in the figure is a schematic diagram of the electronic paper display effect in embodiment B11; Figure 7 In the diagram, d represents the electronic paper display effect of embodiment B12; Figure 7 In this diagram, 'e' represents the electronic paper display effect of embodiment B15. Figure 8 This is a schematic diagram illustrating the display effect of the B14 electronic paper at 51°C and 0°C; wherein, Figure 8 In the figure, 'a' is a schematic diagram of the display effect of the electronic paper in Example B14 at 51°C; Figure 8 In the figure, b is a schematic diagram of the display effect of the electronic paper in Example B14 at 0°C. Detailed Implementation

[0017] To make the technical problems, technical solutions, and beneficial effects of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0018] In this application, the term "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0019] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can both mean: a, b, c, a~b (i.e., a and b), a~c, b~c, or a~b~c, where a, b, and c can be single or multiple.

[0020] It should be understood that in the various embodiments of this application, the order of the above processes does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0021] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms "a" and "the" as used in the embodiments of this application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0022] The weights of the relevant components mentioned in the embodiments of this application can refer not only to the specific content of each component, but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this application is within the scope disclosed in the embodiments of this application. Specifically, the mass in the embodiments of this application can be a well-known unit of mass in the chemical industry, such as µg, mg, g, or kg.

[0023] The terms "first" and "second" are used for descriptive purposes only, to distinguish objects, such as substances, from one another, and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. For example, without departing from the scope of the embodiments of this application, "first XX" may also be referred to as "second XX," and similarly, "second XX" may also be referred to as "first XX." Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of that feature.

[0024] To address the technical problem of insufficient hardness in existing polyurethane emulsion films, this application proposes the following technical solution.

[0025] In a first aspect, embodiments of this application provide a composite adhesive. The composite adhesive of this application embodiment is used in a reflective display module and has conductivity; the composite adhesive comprises polyurethane and a polymer modifier. The mass ratio of polyurethane to polymer modifier is (15:1) to (5:1), and the glass transition temperature of polymer modifier is above 75℃.

[0026] The composite adhesive of this application embodiment is formulated by compounding polyurethane and a polymer modifier in a specific ratio, and controlling the glass transition temperature of the polymer modifier to be above 75°C. The polyurethane and polymer modifier form a blend system, with polymer modifier molecules intertwined and interpenetrating with polyurethane molecules to form an interpenetrating network structure. The rigid segments of the polymer modifier are embedded in and support the flexible polyurethane network, effectively optimizing the overall mechanical properties of the composite adhesive, resulting in a significant enhancement of its hardness and strength. This performance improvement brings significant benefits to the products and processes using the composite adhesive of this application embodiment. Firstly, the cured adhesive film is less prone to stringing during laser cutting, effectively ensuring neat and smooth processing edges, thereby improving the efficiency of subsequent assembly processes and product yield.

[0027] Furthermore, existing adhesive films tend to soften and become more fluid at high temperatures. This fluidity creates new interfaces within the film, leading to easy peeling between the film and the adhesive, and consequently, air bubbles at the bonded edges. The composite adhesive of this application produces a film that exhibits excellent mechanical properties at room temperature and good thermal stability. Its hardness and other mechanical properties are also significantly improved at high temperatures, preventing air bubbles from forming at the film edges even under storage conditions such as 70°C, effectively maintaining the integrity of the material structure. This improved mechanical performance of the composite adhesive effectively enhances the quality of products using it. In particular, when applied to precision devices such as electronic paper, the composite adhesive effectively improves the flatness and aesthetics of the electronic paper, while effectively preventing edge air bubbles, strengthening interlayer bonding, and significantly improving the internal structural integrity and display stability of the product.

[0028] In some embodiments, the mass ratio of polyurethane to polymer modifier can be (12:1) to (5:1). In exemplary cases, the mass ratio of polyurethane to polymer modifier can be typical but not limiting mass ratios such as 12:1, 11:1, 10:1, 9:1, 8:1, 7:1, 6:1, and 5:1, or any mass ratio between any two values. Increasing the content of polymer modifier can significantly improve the hardness and high-temperature stability of the adhesive film, but it is difficult to effectively solve the problems of stringing and bubbling, and it can easily lead to brittleness of the adhesive film, decreased adhesion, and even the risk of delamination. Controlling the mass ratio of polyurethane to polymer modifier within this range can effectively improve the mechanical properties of the adhesive film, such as hardness, to suppress processing defects, while maintaining good interfacial adhesion properties.

[0029] In some embodiments, based on the total mass of the composite adhesive as 100%, the polyurethane content in the composite adhesive of this application embodiment can be 19.5%~37%, and in exemplary examples it can be 20%~35% or 20%~30%. In exemplary examples, the polyurethane content can be typical but not limiting contents such as 19.5%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, and 37%, or any content between any two values. Increasing the polyurethane content can improve the flexibility and interfacial bonding of the adhesive film formed after the composite adhesive has cured. However, if the polyurethane content is too high, the rheological properties of the composite adhesive will decrease, the coating processing performance will deteriorate, and uneven coating or insufficient adhesive may occur. Reducing the polyurethane content effectively improves the flowability and coating performance of the composite adhesive. However, excessively low polyurethane content makes it difficult to form a continuous and dense film structure, resulting in insufficient film cohesion and a tendency to crack and delaminate, thus affecting the reliability of the final product. By controlling the polyurethane content within this range, combined with the synergistic effect of the polymer modifier content and glass transition temperature, the hardness and strength of the composite adhesive are effectively improved while ensuring suitable flexibility and processing performance. This reduces the occurrence of interlayer cracking or poor adhesion due to the embrittlement of the composite adhesive, thereby further improving the long-term reliability of products using the composite adhesive of this application under complex working conditions.

[0030] In some embodiments, the average molecular weight of the polyurethane can be 15-30 kDa (where kDa refers to kilodaltons). In exemplary cases, the average molecular weight of the polyurethane can be typical but not limiting values ​​such as 15 kDa, 20 kDa, 25 kDa, and 30 kDa, or any value between two of these. It should be noted that the average molecular weight in the embodiments of this application refers to the number-average molecular weight. When the molecular weight of the polyurethane is low, the composite adhesive has good flowability and is easy to process, but the cohesive strength and durability of the cured film are insufficient. When the molecular weight of the polyurethane is high, the mechanical strength and toughness of the film are significantly improved, but the increased viscosity may lead to a decrease in coating uniformity. By controlling the average molecular weight of polyurethane within this range, sufficient chain length can be provided to form effective inter-chain entanglement and physical cross-linking points, further promoting the formation of a stable cross-linking network in the composite adhesive. This further improves the mechanical properties and heat resistance of the cured composite adhesive film, such as hardness and toughness. At the same time, it effectively adjusts the viscosity and flowability of the composite adhesive, improves processing performance, and enhances the uniformity and integrity of the composite adhesive film formed by coating and lamination. This significantly improves the mechanical strength and heat resistance of the cured film, such as hardness and toughness. On the other hand, it avoids the problem of excessively high viscosity and poor flowability caused by excessively long molecular chains.

[0031] In some embodiments, based on the total mass of the composite adhesive as 100%, the content of the polymer modifier in the composite adhesive of this application embodiment can be 1.7% to 7.2%, optionally 2% to 7%, or 2% to 5%. In exemplary examples, the content of the polymer modifier can be typical but not limiting contents such as 1.7%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, and 7.2%, or any content between any two values. When the content of the polymer modifier is low, the adhesive film formed by the cured composite adhesive of this application embodiment has good flexibility and adhesion, but insufficient hardness and high-temperature stability, making it difficult to completely solve the problems of stringing and bubbles. When the content of the polymer modifier is high, the rigidity, hardness, and high-temperature deformation resistance of the adhesive film are significantly enhanced, which can effectively suppress the processing defects of the adhesive film, but it will lead to increased brittleness of the adhesive film and reduced toughness and adhesion. By controlling the content of the polymer modifier within this range, and combining the synergistic effect of the polymer modifier's glass transition temperature and the polyurethane content, the strength of the composite adhesive is further improved. Simultaneously, the stability of the composite adhesive under high-temperature environments is enhanced, effectively reducing the formation of bubbles at the adhesive film edges, increasing the bonding force between the composite adhesive and the interface, and reducing the risk of delamination at the adhesive interface. In particular, it reduces excessive softening of the composite adhesive and the formation of bubbles at the adhesive film edges under high-temperature environments, thus improving the stability of the adhesive under high-temperature conditions.

[0032] In some embodiments, the polymer modifier includes at least one selected from polyacrylate, epoxy resin, polyimide, and urea-formaldehyde resin. These polymer modifiers have high strength and good compatibility with polyurethane, forming a blend system with polyurethane to create a stable cross-linked network at the molecular level. This significantly improves the mechanical properties of the composite adhesive, such as strength and hardness, while maintaining excellent flexibility and heat resistance.

[0033] In some embodiments, the polyacrylate includes at least one selected from polymethyl methacrylate, butyl acrylate, acrylic acid, and hydroxyethyl acrylate. In further embodiments, the average molecular weight of the polyacrylate can be 50-100 kDa. In exemplary examples, the average molecular weight of the polyacrylate can be typical but not limiting molecular weights such as 50 kDa, 60 kDa, 70 kDa, 80 kDa, 90 kDa, and 100 kDa, or any molecular weight between any two values. When polyacrylate is used as a polymer modifier, its molecular weight has a significant impact on the performance of the composite adhesive. When the molecular weight of the polyacrylate is small, it has good compatibility with polyurethane, is easy to disperse and mix, and has strong chain segment mobility, which can improve the initial flowability and wettability of the composite adhesive system to the substrate; however, when the molecular weight of the polyacrylate is small, its contribution to improving the hardness and high-temperature stability of the adhesive film is relatively weak, and the mechanical strengthening effect of the adhesive film is not significant. When the molecular weight of polyacrylate is large, the polyacrylate molecular chains are longer and more rigid, enabling it to form a strong interpenetrating network with polyurethane more effectively, greatly improving the mechanical strength, hardness, and heat resistance of the film. However, an excessively large molecular weight of polyacrylate can reduce the compatibility between polyacrylate and polyurethane, making it difficult to disperse the polyacrylate uniformly and increasing the viscosity of the composite adhesive, thus increasing the difficulty of coating and affecting the uniformity of film formation. By controlling the molecular weight of polyacrylate within this range, combined with parameters such as the content of polyacrylate, the rheological properties of the composite adhesive can be effectively improved. While ensuring that the composite adhesive has good flowability and processing performance, the rigidity-enhancing effect of polyacrylate can be fully utilized, further improving the mechanical strength of the film formed by the composite adhesive in the embodiments of this application.

[0034] In some embodiments, the glass transition temperature of the polymer modifier can be 75~115°C. In exemplary examples, the glass transition temperature of the polymer modifier can be a typical but not limiting temperature such as 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, 110°C, 115°C, or any temperature between any two values.

[0035] High glass transition temperature polymer modifiers maintain a rigid glassy state at room temperature and even high temperatures up to 70°C. As a skeleton embedded in the polyurethane network, they significantly improve the hardness and creep resistance of the adhesive film at both room and high temperatures, thereby inhibiting laser cutting and fiber formation and edge bubble generation at high temperatures. However, excessively high glass transition temperatures may lead to decreased compatibility between the modifier and the polyurethane matrix, increasing the brittleness of the adhesive film at low temperatures (0°C) or room temperature, resulting in reduced interfacial adhesion. Controlling the glass transition temperature of the polymer modifier within this range further improves the hardness and strength of the cured composite adhesive film, reduces the softening and deformation of the cured film at high temperatures, reduces brittleness, improves adhesion, and further enhances the interlayer bonding between the film and the adhesive. Controlling the glass transition temperature of the polymer modifier within this range, combined with the synergistic effect of the polyurethane content and the polymer modifier, further improves the heat resistance and structural stability of the composite adhesive, enabling it to maintain excellent adhesion performance even at high temperatures.

[0036] Understandably, the glass transition temperature of polymer modifiers can be tested using the methods specified in ISO 11357-2 and ASTM D3418.

[0037] In some embodiments, the composite adhesive of this application further includes conductive fillers and solvents. The solvent may include at least one of water or an organic solvent, including at least one of ethanol, acetone, butanone, and ethyl acetate. When water is used as the solvent, the composite adhesive of this application forms an aqueous dispersion system, effectively improving the dispersibility of the conductive filler, enhancing the conductivity selectivity of the composite adhesive, and reducing the emission of volatile organic compounds, thus exhibiting environmental friendliness, safety, and non-toxicity. When an organic solvent is used, it effectively improves the solubility and film-forming properties of the polyurethane and polymer modifier, further promoting the formation of a uniform, dense, continuous, and defect-free high-quality adhesive film, improving the integrity of the bonding interface, and enhancing the structural stability of precision components using the composite adhesive of this application.

[0038] In some embodiments, based on the total mass of the composite adhesive as 100%, the solvent content in the composite adhesive of this application embodiment can be 32% to 68.1%. In exemplary examples, the solvent content can be typical but not limiting contents such as 32%, 33%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, and 68%, or any content between any two values. The solvent content affects the processing performance and final film quality of the composite adhesive. When the solvent content is high, it can significantly reduce the viscosity of the system, improve fluidity, make the composite adhesive easier to coat and level, and better penetrate into porous or complex structured substrates; however, the amount of solvent required to evaporate during the curing process is large, which prolongs the drying time, increases energy consumption, and easily leads to a large shrinkage rate of the adhesive film due to uneven solvent evaporation or residue, resulting in pinholes or defects inside the adhesive film. When the solvent content is low, the curing speed is fast and the shrinkage rate is small; however, the viscosity of the composite adhesive system is high, the fluidity is poor, which easily causes coating difficulties and uneven spreading, thereby affecting the uniformity of the adhesive film and the interfacial adhesion. By controlling the solvent content within this range, the rheological properties of the composite adhesive can be further optimized, the uniformity and integrity of the coated or laminated film can be improved, and the interfacial bonding strength can be enhanced.

[0039] In some embodiments, the conductive filler may include at least one of the following: a metallic conductive filler, a carbon-based conductive filler, a conductive polymer, and a ceramic conductive filler. Specifically, the metallic conductive filler may include at least one of silver, gold, and copper; the carbon-based conductive filler may include at least one of graphene, carbon nanotubes, and graphite; the conductive polymer may include a polyaniline-polypyrrole composite; and the ceramic conductive filler may include at least one of zinc oxide and barium titanate.

[0040] In some embodiments, the particle size of the conductive filler can be 200~2000 nm, optionally 500~1000 nm. In exemplary embodiments, the particle size of the conductive filler can be typical but not limiting particle sizes such as 200 nm, 500 nm, 1000 nm, 1500 nm, 2000 nm, or any particle size between any two values.

[0041] In some embodiments, the content of conductive filler can be 5% to 30%. In exemplary embodiments, the content of conductive filler can be typical but not limiting contents such as 5%, 10%, 15%, 20%, 25%, 30%, or any content between any two values.

[0042] When the composite adhesive in the embodiments of this application is used as an adhesive for electronic paper, such as Figure 1As shown, the conductive adhesive layer 03 connects the ink layer 02 and the TFT substrate 04. The TFT substrate 04 includes multiple electrodes 041, and the ink layer 02 includes multiple arrayed ink microcapsules 021, each containing charged pigment particles. The core principle of electronic paper display lies in precisely controlling the movement of the charged pigment particles within the ink microcapsules 021 using an electric field. When a voltage is applied to the electrodes 041 of the TFT substrate 04, the charged pigment particles within the ink microcapsules 021 move under the influence of the electric field. Similarly, when a voltage is applied to the electrodes 041 of the TFT substrate 04, pigment particles with different charges within the ink microcapsules 021 move under the influence of the electric field. By controlling the direction and magnitude of the electric field at different positions of the electrodes 041, the arrangement and combination of the pigment particles change, thereby presenting the desired black-and-white or color patterns on the surface, achieving image and text display. To reduce crosstalk between adjacent electrodes, achieve precise electric field control, improve display resolution and contrast, and enhance clarity, the conductive adhesive layer 03 needs to have good conductivity along the thickness direction and good insulation along the direction perpendicular to the thickness.

[0043] Polyurethane is an insulating material with a volume resistivity (ρ) as high as 10⁻⁶. 12 Ω·cm. When conductive fillers are added to polyurethane, at low filler content, the volume resistivity is higher than that of pure polyurethane with increasing filler content, but the change is not significant. This is mainly because when the amount of conductive filler is small, the conductive pathway has not yet been formed, and the insulating layer formed by the organic groups or oil film on the surface of the conductive particles increases the potential barrier between the conductive particles, resulting in a slight increase in the volume resistivity of the conductive particle + polyurethane material compared to the pure polyurethane material. However, as the amount of conductive filler continues to increase, the volume resistivity begins to decrease. When the content of conductive filler increases to a certain range, the volume resistivity of the composite material decreases sharply, from 10 Ω·cm. 13 Ω·cm decreased to 10 4 The Ω·cm was reduced by approximately eight orders of magnitude. By controlling the content and particle size of the conductive filler within this range, and combining parameters such as the thickness of the conductive adhesive layer, the composite adhesive of this application embodiment is applied to electronic paper, resulting in the following structure of the ink layer 02, conductive adhesive layer 03, and TFT substrate 04 in the electronic paper. Figure 2 As shown, where, Figure 2 In the diagram, 'a' represents a schematic representation of the conductive particles and the TFT substrate. Figure 2Figure 'b' shows a schematic diagram of the conductive particle structure in the ink layer 02, TFT substrate 04, and conductive adhesive layer 03. The conductive adhesive layer 03 includes conductive particles 031. In the direction parallel to the TFT substrate 04, the distance between conductive particles 031 is greater than 10 nm, and there is no electrical conductivity between the conductive particles 031. Therefore, the conductive adhesive layer 03 has poor conductivity in the direction parallel to its plane. However, the distance between conductive particles 031 and the ink layer 02, and between conductive particles 031 and the TFT substrate 04, is less than 10 nm, or the conductive particles 031 are in contact with the ink layer 02 and the TFT substrate 04 respectively. This results in good conductivity of the conductive adhesive layer 03 along its thickness direction, giving the composite adhesive of this embodiment good Z-axis conductivity. When applied to electronic paper, it can effectively improve the clarity and contrast of the display.

[0044] In some embodiments, the composite adhesive of this application may further include a surface tension modifier and / or an antifoaming agent. The content of the surface tension modifier may be 0.1% to 5%, and the content of the antifoaming agent may be 0.1% to 5%. In exemplary embodiments, the content of the surface tension modifier may be a typical but non-limiting content such as 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, or any content between any two values; the content of the antifoaming agent may be a typical but non-limiting content such as 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, or any content between any two values. The surface tension modifier can effectively improve the wetting and spreading ability of the composite adhesive on the substrate, and improve the uniformity of the coating film and the interfacial adhesion; the antifoaming agent can effectively suppress the generation and residue of bubbles during stirring, dispersion and coating, and further improve the density and electrical performance stability of the adhesive film. In exemplary embodiments, the surface tension modifier may include a polysiloxane leveling and wetting agent.

[0045] In some embodiments, the composite adhesive of this application may further include a crosslinking agent. In a further embodiment, the content of the crosslinking agent may be 0.1% to 5%. In exemplary examples, the content of the crosslinking agent may be typical but not limiting contents such as 0.1%, 0.5%, 1%, 2%, 3%, 4%, and 5%, or any content between any two values. By adding a crosslinking agent and controlling the content of the crosslinking agent within this range, the crosslinking density and network structure of the composite adhesive are further improved, thereby improving thermal stability, mechanical strength, and resistance to environmental aging. The defoamer may include silicone-based defoamers; the crosslinking agent may include polymeric carbodiimide crosslinking agents.

[0046] In some embodiments, by combining the polyurethane content and molecular weight, as well as the fillers and conductive fillers in the polymer modifiers of the above embodiments, the performance of the composite adhesive of this application embodiments is further optimized. For example, the pH value of the composite adhesive of this application embodiments can be 6-8, and the viscosity can be 20-500 cps. In the exemplary example, the pH value of the composite adhesive of this application embodiments can be typical but not limiting values ​​such as 6, 6.5, 6.7, 6.8, or any value between any two; the viscosity can be typical but not limiting viscosities such as 20 cps, 50 cps, 100 cps, 150 cps, 200 cps, 250 cps, 300 cps, 350 cps, 400 cps, 450 cps, 500 cps, or any viscosity between any two values. The higher the glass transition temperature, the stronger the material's resistance to temperature deformation, which can improve high-temperature bubbles and their high-temperature deformation delamination. Controlling the glass transition temperature of the composite adhesive within this range further enhances the strength of the adhesive film formed by the composite adhesive, reduces brittleness, and allows the film to exhibit good overall performance over a wide temperature range. Controlling the pH value of the composite adhesive within this range effectively reduces the risk of corrosion to the bonded materials. Controlling the viscosity of the composite adhesive within this range ensures good rheological properties, making it suitable for various precision coating processes such as screen printing, spraying, and dispensing, and improving coating uniformity.

[0047] In some embodiments, when the cured adhesive film of this application has a thickness of 20 μm and a length and width of 50 mm × 50 mm, the current when a 1V voltage is applied to both sides of the adhesive film at 0-50°C can be 20-300 μA, preferably 100-300 μA. In exemplary examples, the current value can be 20 μA, 50 μA, 100 μA, 150 μA, 200 μA, 250 μA, or 300 μA. In further embodiments, the current when a 1V voltage is applied to both sides of the adhesive film at room temperature can be 100-300 μA. Figure 1 As shown, when the conductivity of the conductive adhesive layer 03 is low, the charged pigment particles in the ink microcapsules 021 cannot move sufficiently under the action of the electric field, resulting in low display clarity of the electronic paper. Conversely, when the conductivity of the conductive adhesive layer 03 is too high, crosstalk occurs between different electrodes 041 in the TFT substrate 04, leading to blurred pattern edges. The conductivity of polyurethane increases with increasing temperature. In this embodiment, by adding conductive fillers of specific content and particle size range to the composite adhesive, the adhesive film exhibits suitable conductivity under low temperatures such as 0°C and high temperatures of 50~70°C, thereby further improving the display effect of the electronic paper using the composite adhesive of this embodiment at different temperatures.

[0048] Secondly, embodiments of this application provide a method for preparing a composite adhesive. The method for preparing a composite adhesive according to embodiments of this application includes the following steps: S01: The solvent, polyurethane, and polymer modifier are subjected to a first mixing treatment to obtain modified polyurethane; S02: The modified polyurethane and conductive filler are mixed for a second time to obtain a composite adhesive.

[0049] The mass ratio of polyurethane to polymer modifier is (15:1) to (5:1), and the glass transition temperature of polymer modifier is above 75℃.

[0050] The composite adhesive of this application is prepared by blending polyurethane with a polymer modifier having a glass transition temperature of not less than 75°C, and controlling the mass ratio of polyurethane to polymer modifier within a specific range. The resulting composite adhesive exhibits excellent performance in terms of mechanical strength, overall hardness, and dimensional and interfacial stability at high temperatures. The prepared composite adhesive maintains good stability and interfacial adhesion performance even at high temperatures. Using this composite adhesive in the assembly of precision electronic devices such as electronic paper not only effectively ensures the surface flatness of the devices, improves assembly efficiency and product yield, but also significantly suppresses interfacial delamination and bubble growth problems caused by long-term thermal cycling, thereby improving the long-term reliability of precision electronic devices such as electronic paper.

[0051] The composite adhesive, polyurethane, polymer modifier, conductive filler, and solvent in the composite adhesive preparation method of this application are the same as those mentioned above, and will not be repeated here.

[0052] Step S01: The solvent, polyurethane, and polymer modifier are mixed in a first mixing process to promote thorough mixing between the polyurethane and the polymer modifier, thereby obtaining modified polyurethane.

[0053] In some embodiments, the polyurethane in the preparation method of this application can be derived from a polyurethane emulsion, and the polymer modifier can be derived from a polymer modifier emulsion. Step S01 may include: performing a first mixing treatment on the polyurethane emulsion and the polymer modifier emulsion to obtain modified polyurethane.

[0054] In some embodiments, the solid content of the polyurethane emulsion can be 39% to 40%, and the viscosity can be 20 to 500 cps. In exemplary cases, the solid content of the polyurethane emulsion can be typical but not limiting contents such as 39%, 39.2%, 39.5%, 39.8%, and 40%, or any content between any two values; the viscosity of the polyurethane emulsion can be typical but not limiting viscosities such as 20 cps, 50 cps, 100 cps, 150 cps, 200 cps, 250 cps, 300 cps, 350 cps, 400 cps, 450 cps, and 500 cps, or any viscosity between any two values. Controlling the solid content and viscosity of the polyurethane emulsion within this range further improves the flowability of the polyurethane emulsion, enhances the mixing uniformity of the polyurethane and polymer modifier in the first mixing treatment, and further improves the rheological properties of the composite adhesive.

[0055] In some embodiments, the pH of the polyurethane emulsion can be 6 to 8. Controlling the pH of the polyurethane emulsion within this range helps maintain its dispersion stability.

[0056] In some embodiments, the polyurethane emulsion solvent may include water or an organic solvent. The organic solvent in the polyurethane emulsion solvent may be the organic solvent used in the composite adhesive described above, and will not be elaborated further here.

[0057] In some embodiments, the solid content of the polymer modifier emulsion can be 39% to 40%, and the viscosity can be 50 to 300 cps. In exemplary examples, the solid content of the polymer modifier emulsion can be typical but not limiting contents such as 39%, 39.2%, 39.5%, 39.8%, and 40%, or any content between any two values; the viscosity of the polymer modifier emulsion can be typical but not limiting viscosities such as 50 cps, 100 cps, 150 cps, 200 cps, 250 cps, and 300 cps, or any viscosity between any two values. Controlling the solid content and viscosity of the polymer modifier emulsion within this range further improves the uniformity of the polymer modifier in the first mixing treatment, thereby enhancing the uniformity of the composite adhesive.

[0058] In some embodiments, the pH value of the polymer modifier emulsion can be 7-9, and the solvent of the polymer modifier emulsion can include water or an organic solvent. The organic solvent in the polymer modifier emulsion can be the organic solvent used in the composite adhesive described above, and will not be elaborated further here.

[0059] In some embodiments, the first mixing treatment can be stirring, with a stirring speed of 300-500 r / min and a mixing time of 1-2 hours. Controlling the stirring speed and time within this range promotes thorough mixing of the polyurethane and polymer modifier to form a homogeneous blend system.

[0060] In some embodiments, the mass ratio of polyurethane emulsion to polymer modifier emulsion can be (5:1) to (10:1), preferably (5:1) to (6:1). In some embodiments, the mass ratio of polyurethane emulsion to polymer modifier emulsion can be a typical but not limiting mass ratio of 5:1, 6:1, 7:1, 8:1, 9:1, or 10:1, or any mass ratio between any two values. By controlling the mass ratio of polyurethane emulsion to polymer modifier emulsion within this range, combined with the solid content of polyurethane emulsion and polymer modifier emulsion, the ratio of polyurethane and polymer modifier in the composite adhesive can be adjusted, further improving the strength and hardness of the composite adhesive after curing.

[0061] Step S02: In step S02, the modified polyurethane and conductive filler are subjected to a second mixing treatment to promote the full dispersion of the conductive filler in the modified polyurethane, thereby obtaining a composite adhesive.

[0062] In some embodiments, the conductive filler may be dispersed to form a suspension before the second mixing treatment, and the suspension containing the conductive filler may be subjected to a second mixing treatment with modified polyurethane to further promote the dispersibility of the conductive filler.

[0063] In some embodiments, the second mixing treatment can be stirring, with a stirring rate of 800-1000 r / min and a mixing time of 2-3 hours. Controlling the stirring speed and time of the second mixing treatment within this range further promotes thorough mixing of the modified polyurethane and conductive filler, thereby further improving the conductivity stability of the composite adhesive.

[0064] In some embodiments, based on the total amount of raw materials of the composite adhesive being 100%, the raw materials of the composite adhesive in this application embodiment include the following components: Polyurethane emulsion 50%~90%; Polymer modifier emulsion 5%~20%; Conductive filler content: 5%~30%.

[0065] In the example, the amount of polyurethane emulsion added can be a typical but non-limiting value such as 50%, 60%, 70%, 80%, or 90%, or any value between any two values. The amount of polymer modifier emulsion added can be a typical but non-limiting value such as 5%, 10%, 15%, or 20%, or any value between any two values. By controlling the content of polyurethane emulsion, polymer modifier emulsion, and conductive filler within this range, and combining parameters such as the solid content in the polyurethane emulsion and polymer modifier, the content of polyurethane, polymer modifier, and conductive filler in the resulting composite adhesive can be controlled, thereby further improving the mechanical properties of the composite adhesive, increasing the hardness and strength of the adhesive film formed after curing, and enhancing the Z-axis conductivity of the composite adhesive.

[0066] In some embodiments, after the second mixing step, a third mixing treatment is further performed with at least one of the surface tension modifier, defoamer, and crosslinking agent and the composite adhesive. The surface tension modifier, defoamer, and crosslinking agent improve the rheological properties of the composite adhesive and enhance coating uniformity.

[0067] Thirdly, embodiments of this application provide a reflective display module. The reflective display module of this application includes a transparent conductive layer, an electrophoretic functional layer, and a thin-film transistor substrate. The electrophoretic functional layer and the thin-film transistor substrate are bonded together by a conductive adhesive layer, wherein the conductive adhesive layer is prepared from the composite adhesive described above.

[0068] The reflective display module of this application uses a conductive adhesive layer formed by the aforementioned composite adhesive. Based on the excellent mechanical strength and high hardness of the conductive adhesive layer made by the composite adhesive, it significantly suppresses the stringing phenomenon generated at the cutting edge during laser cutting, thereby improving the flatness of the cut surface and facilitating smooth subsequent assembly processes. This effectively improves the assembly efficiency and yield of the reflective display module. Simultaneously, this conductive adhesive layer exhibits good stability under high-temperature storage conditions, effectively suppressing the formation of bubbles at the edges, thereby effectively ensuring the structural integrity of the reflective display module, improving its display quality, and extending the device's lifespan.

[0069] In some embodiments, the reflective display module can be electronic paper, wherein the transparent conductive layer can be an ITO layer, that is, an indium tin oxide film layer, and the electrophoretic functional layer can also be called an ink layer, which includes multiple microcapsules containing charged pigment particles.

[0070] In some embodiments, the thickness of the conductive adhesive layer can be 2-30 μm, preferably 5-10 μm. In exemplary examples, the thickness of the conductive adhesive layer can be typical but not limiting thicknesses such as 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, 25 μm, and 30 μm, or any thickness between any two. By controlling the thickness of the conductive adhesive layer within this range, and combining the content and particle size of the conductive filler in the conductive adhesive layer, the spacing between the conductive particles in the conductive adhesive layer is made greater than 10 nm, and the conductivity of the conductive adhesive layer along the thickness direction can be 10. -4 ~10 -7 The conductive adhesive layer has good Z-axis conductivity (S / m). This effectively optimizes the display effect of the reflective display module in the embodiments of this application.

[0071] Fourthly, embodiments of this application provide a reflective paper display device. The reflective display device of this application includes the reflective display module described above.

[0072] Based on the flat structure, good mechanical reliability of the interlayer structure and good high-temperature stability of the reflective display module described above, the reflective display device of this application embodiment can achieve a longer service life, more stable display quality and a wider range of applications.

[0073] In order to enable those skilled in the art to clearly understand the above-described implementation details and operations of this application, and to significantly demonstrate the advancements of the composite adhesive, its preparation method, and the display device in the embodiments of this application, the following examples illustrate the above technical solutions.

[0074] Example A1 This embodiment provides a composite adhesive. The composite adhesive includes a polyurethane emulsion, a polymer modifier, and a conductive filler. The contents of the polyurethane emulsion, polymer modifier, and conductive filler are shown in Table 1. The polymer modifier is polymethyl methacrylate, and the conductive filler includes silver powder and carbon nanotubes.

[0075] The method for preparing the composite adhesive in this embodiment includes the following steps: Step S01: Take the polyurethane latex and polymethyl methacrylate latex shown in Table 1, add them to the reaction vessel, and perform the first mixing treatment to obtain modified polyurethane. The polyurethane latex has a solid content of 40.1%, a viscosity of 96 cps, a pH value of 6.8, and a molecular weight of 20 kDa; the polymethyl methacrylate latex has a glass transition temperature of 95℃, a solid content of 35%, a viscosity of 250 cps, and a pH value of 8. The first mixing treatment conditions are: stirring at a stirring speed of 500 r / min and a temperature of 25℃ for 1.5 hours.

[0076] Step S02: Take 10g of carbon nanotubes and slowly add them to the reaction vessel for the second mixing treatment. The carbon nanotubes have a length of 0.5~50μm and a diameter of 8-15nm. The conditions for the second mixing treatment are stirring and dispersing at a stirring speed of 900r / min and a temperature of 25℃ for 2.5 hours.

[0077] Step S03: Slowly add the surface tension modifier, defoamer, and crosslinking agent to the reactor for a third mixing treatment to obtain the composite adhesive of this embodiment. The surface tension modifier is a polysiloxane-based leveling and wetting agent, with an addition amount of 2.73 g; the defoamer is an organosilicon-based defoamer, with an addition amount of 0.35 g; and the crosslinking agent is a polymeric carbodiimide crosslinking agent, with an addition amount of 0.71 g. The conditions for the third mixing treatment are: stirring and dispersing at a stirring speed of 500 r / min for 30 minutes.

[0078] Examples A2 to A9 Examples A2 to A9 each provide a composite adhesive. The composite adhesives of Examples A2 to A9 and their preparation methods are basically the same as those of the composite adhesive of Example A1, except that: 1. The amount of polymer modifier (polymethyl methacrylate) added to the composite adhesives of Examples A2 to A9 is shown in Table 1.

[0079] 2. The glass transition temperature of the polymethyl methacrylate contained in the composite adhesive of Example A7 is 75°C.

[0080] 3. The glass transition temperature of the polymethyl methacrylate contained in the composite adhesive of Example A8 is 115°C.

[0081] 4. The glass transition temperature of the polymethyl methacrylate contained in the composite adhesive of Example A9 is 120°C.

[0082] Table 1

[0083] Example A10 This embodiment provides a composite adhesive comprising a polyurethane emulsion, a polymer modifier, and a conductive filler. The contents of the polyurethane emulsion, polymer modifier, and conductive filler are shown in Table 1. The polymer modifier is polymethyl methacrylate, and the conductive filler is silver powder. The preparation method of this composite adhesive is as follows: Step S01: Take 80g of polyurethane emulsion and 20g of polymethyl methacrylate emulsion, add them to a reaction vessel, and perform a first mixing treatment to obtain modified polyurethane. The polyurethane and polymethyl methacrylate used in this embodiment are the same as those used in Example A1. The first mixing treatment conditions in this embodiment are: stirring and mixing for 2 hours at a stirring speed of 500 r / min and a temperature of 25°C.

[0084] Step S02: Take 20g of silver powder and slowly add it to the reaction vessel for the second mixing treatment. The conditions for the second mixing treatment are: stirring and dispersing for 3 hours at a stirring speed of 1000r / min and a temperature of 25℃.

[0085] Step S03: Slowly add the surface tension modifier, defoamer, and crosslinking agent to the reactor for a third mixing treatment to obtain the composite adhesive of this embodiment. The surface tension modifier is a polysiloxane-based leveling and wetting agent, with an addition amount of 2.73 g; the defoamer is an organosilicon-based defoamer, with an addition amount of 0.35 g; and the crosslinking agent is a polymeric carbodiimide crosslinking agent, with an addition amount of 0.71 g. The conditions for the third mixing treatment are: stirring and dispersing at a stirring speed of 500 r / min for 30 minutes.

[0086] Examples A11 to A17 Examples A11 to A17 each provide a composite adhesive. The composite adhesives of Examples A11 to A17 and their preparation methods are basically the same as those of the composite adhesive of Example A10, except that the polymethyl methacrylate content, the type and content of conductive fillers in the composite adhesives of Examples A11 to A17 are shown in Table 2.

[0087] Table 2

[0088] Note: The particle size of the silver powder in Table 2 is 0.3~1.15μm; the diameter and length of the carbon nanotubes are the same as those of the carbon nanotubes in Example A1.

[0089] Comparative Example A1 This comparative example provides a composite adhesive. This comparative example composite adhesive is essentially the same as the composite adhesive of Example A1, except that it does not contain polymethyl methacrylate.

[0090] Comparative Example A2 This comparative example provides a composite adhesive. The composite adhesive of this comparative example is essentially the same as the composite adhesive of Example A1, except that the glass transition temperature of the polymethyl methacrylate in this comparative example composite adhesive is 70°C.

[0091] The types and amounts of raw materials used in the composite adhesives of Comparative Examples A1 to A2 are shown in Table 1.

[0092] Example B1 This application provides a reflective display device (i.e., electronic paper). The reflective display device includes a transparent conductive layer, an electrophoretic functional layer, a conductive adhesive layer, and a thin-film transistor substrate stacked sequentially. The conductive adhesive layer is prepared by thermosetting the composite adhesive of Example A1, and the thickness of the conductive adhesive layer is 20 μm.

[0093] Examples B2 to B17, Comparative Examples B1 to B2 Examples B2 to B17 and Comparative Examples B1 to B2 each provide a reflective display device. The difference between the reflective display devices of Examples B2 to B17 and Comparative Examples B1 to B2 and the reflective display device of Example B1 is as follows: the conductive adhesive layer of the reflective display device of Example B2 is made from the composite adhesive of Example A2; the conductive adhesive layer of the reflective display device of Example B3 is made from the composite adhesive of Example A3, and so on, with the conductive adhesive layer of the reflective display device of Example B17 being made from the composite adhesive of Example A17. The conductive adhesive layer of the reflective display device of Comparative Example B1 is made from the composite adhesive of Comparative Example A1, and the conductive adhesive layer of the reflective display device of Comparative Example B2 is made from the composite adhesive of Comparative Example A2.

[0094] Performance evaluation (1) Mechanical property investigation The conductive adhesive layers in Examples B1 to B17, Comparative Examples B1 and B2 were subjected to adhesive film performance tests. After storage at high temperature for 24 hours, bubbles were observed on the adhesive film surface. The results are as follows: Figure 3 , Figure 4 As shown in Table 3.

[0095] Table 3

[0096] like Figure 3 As shown, when no polymer modifier is added to the composite adhesive, numerous air bubbles appear at the edges of the conductive adhesive layer after high-temperature storage of the electronic paper, leading to poor electronic paper display. Figure 4 As shown, when a polymer modifier is added to the composite adhesive, air bubbles are significantly reduced, effectively improving the display effect of electronic paper. For example, Figure 4 As shown in Figure a, when the amount of polymethyl methacrylate added is 5g, the number of bubbles decreases, with only a few bubbles at the edges; as shown in Figure a. Figure 4As shown in b, when the amount of polymethyl methacrylate (PMMA) added is 12g, the number of bubbles is significantly reduced, with only a few micro-bubbles at the edge of the conductive adhesive layer; while when the amount of PMMA added is 20g, there are no visible bubbles at the edge of the conductive adhesive layer. As shown in Table 3, in the electronic paper with conductive adhesive layers prepared using the composite adhesives of Examples A4 to A9, there are no visible bubbles at the edge. Although there are also no visible bubbles in the electronic paper using the composite adhesive of Example A9, the glass transition temperature of PMMA is too high, which causes the bonding temperature of the conductive adhesive layer to rise above 100°C during electronic paper processing, posing a risk of burns during operation. In addition, the temperature resistance of the capsule layer does not reach 120°C, and excessively high temperatures can easily damage the capsules in the electrophoretic functional layer (capsule layer), thus affecting the quality of the electronic paper. This indicates that the composite adhesive of this application embodiment, by adding a polymer modifier and controlling the content of the polymer modifier and the glass transition temperature within a specific range, effectively improves the mechanical properties of the composite adhesive and increases the hardness and strength of the adhesive film formed by the composite adhesive. When the composite adhesive of this application embodiment is applied to electronic paper, it effectively improves the display effect of electronic paper, broadens the applicable temperature range of electronic paper, and improves the durability of electronic paper.

[0097] (2) Electrical performance test The composite adhesives from Examples A1 to A17, Comparative Examples A1 and A2 were used to prepare test films with a thickness of 20 μm and dimensions of 50 mm x 50 mm. The conductivity in the parallel direction and the Z-axis direction (the thickness direction of the test film), as well as the current at room temperature and 0°C, were tested. The results are shown in Tables 2 and 3. The display effect of the electronic paper in each of the above examples and comparative examples was also examined, and the results are as follows: Figure 5 As shown.

[0098] The test method for the current in the conductive adhesive layer is as follows: A 50mm*50mm test membrane with a thickness of 20μm was fabricated. The upper and lower electrodes were fixed at a voltage of 15V. The current between the upper and lower electrodes was measured using a Keithley 5.5-digit 6485 picoammeter.

[0099] As shown in Table 2, the composite adhesive of this application embodiment has good Z-axis conductivity and the current values ​​are similar under normal temperature and low temperature conditions. This indicates that the composite adhesive of this application embodiment has stable conductivity over a wide temperature range, which effectively improves the display effect of electronic paper in low temperature environments.

[0100] Display performance evaluation: The display effects of the electronic paper in Examples B1 to B17, Comparative Examples B1 and B2 were examined at different temperatures, and the results are as follows: Figures 5 to 8 As shown. Among them, Figures 5 to 8In the electronic paper display, "T" indicates the displayed temperature. For example, T=000 in the figure indicates that the display is at 0℃, and T=051 indicates that the display is at 51℃. "15V" indicates that the driving voltage is 15V, and "100" indicates that the driving time is 100 seconds.

[0101] like Figure 5 As shown, in Comparative Example B1, Example B3, and Example B9, the electronic paper displays images with high contrast and clear edges at 47°C. However, in Example B17, due to the excessively high Z-axis conductivity in the conductive adhesive layer, crosstalk occurs between adjacent electrodes in the TFT substrate, resulting in blurred edges on the electronic paper display.

[0102] As shown in Table 2, Figure 6 and Figure 7 As shown, the test films of the composite adhesives in Examples B11 and B12 exhibited current values ​​ranging from 55 to 200 μA at both room temperature and 0°C. The electronic papers in Examples B11, B12, and B15 all demonstrated good display performance at high temperatures of 41-42°C and low temperatures of -2°C to -3°C. In the test film of Example A13, the current value of the 1V test film at room temperature was 60 μA, and the current value at 0°C was 5 μA, indicating a lower current value at 0°C. While the electronic paper of Example B13 displayed clearly at around 40°C, the images and text were blurry at a low temperature of -4°C. Similarly, the test film of Example A16 had a lower current value, and while the electronic paper of Example B16 displayed clearly at around 40°C, the images and text were blurry at a low temperature of around 0°C.

[0103] like Figure 8 As shown, the electronic paper in Example B14 exhibits good display performance under both high and low temperature conditions, with clear image display and high contrast.

[0104] When the conductivity of the conductive adhesive layer in electronic paper is low, the charged pigment particles in the electrophoretic functional layer cannot move sufficiently under the influence of the electric field, resulting in low display clarity. When the conductivity of the conductive adhesive layer in electronic paper is too high, interference occurs between different electrodes in the thin-film transistor substrate, leading to blurred pattern edges. The conductivity of the conductive adhesive layer increases with increasing temperature. This application's embodiments effectively optimize the conductivity of the conductive adhesive layer by controlling the conductive filler content in the composite adhesive within a specific range, combined with parameters such as the particle size of the conductive filler, thereby improving the display effect of electronic paper.

[0105] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A composite adhesive, used in a reflective display module, having conductivity, characterized in that, The composite adhesive includes polyurethane and a polymer modifier; The mass ratio of the polyurethane to the polymer modifier is (15:1) to (5:1), and the glass transition temperature of the polymer modifier is above 75°C.

2. The composite adhesive as described in claim 1, characterized in that, The glass transition temperature of the polymer modifier is 75~115℃.

3. The composite adhesive as described in claim 1, characterized in that, The polymer modifier includes at least one of polyacrylate, epoxy resin, polyimide, and urea-formaldehyde resin.

4. The composite adhesive as described in claim 3, characterized in that, The polyacrylate has an average molecular weight of 50-100 kDa, and the polyacrylate includes at least one of polymethyl methacrylate, butyl acrylate, acrylic acid, and hydroxyethyl acrylate.

5. The composite adhesive according to any one of claims 1-4, characterized in that, The average molecular weight of the polyurethane is 15~30kDa.

6. The composite adhesive according to any one of claims 1-4, characterized in that, The viscosity of the composite adhesive is 20~500 cps.

7. The composite adhesive according to any one of claims 1-4, characterized in that, The current of the cured adhesive film is 20~300μA at 1V.

8. The composite adhesive according to any one of claims 1-4, characterized in that, The composite adhesive further includes conductive fillers and solvents, and based on 100% of the total mass of the composite adhesive, the composite adhesive comprises the following components: Polyurethane 19.5%~37%; Polymer modifier 1.7%~7.2%; Conductive filler 5%~30%; Solvent content: 32%~68.1%.

9. The composite adhesive as described in claim 8, characterized in that, The conductive filler includes at least one of the following: metal conductive filler, carbon-based conductive filler, conductive polymer, and ceramic conductive filler; The particle size of the conductive filler is 200~2000nm.

10. A method for preparing a composite adhesive, characterized in that, Includes the following steps: The polyurethane and polymer modifier are first mixed to obtain modified polyurethane; The modified polyurethane is mixed with conductive filler in a second mixing process to obtain a composite adhesive. The mass ratio of the polyurethane to the polymer modifier is (15:1) to (5:1), and the glass transition temperature of the polymer modifier is above 75°C.

11. A reflective display module, comprising a transparent conductive layer, an electrophoretic functional layer, and a thin-film transistor substrate stacked sequentially, wherein the electrophoretic functional layer and the thin-film transistor substrate are bonded together by a conductive adhesive layer, characterized in that, The conductive adhesive layer is prepared by the composite adhesive of any one of claims 1-9 or by the composite adhesive prepared by the preparation method of claim 10.

12. The reflective display module as described in claim 11, characterized in that, The thickness of the conductive adhesive layer is 2~30μm.

13. A reflective display device, characterized in that, Includes the display module as described in any one of claims 11-12.

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