Graphene leather capable of sensing temperature and developing color and preparation method thereof

Abstract

The invention belongs to the technical field of graphene, and particularly relates to graphene leather capable of realizing temperature-sensitive color development and a preparation method of the graphene leather. As the graphene heating functional layer adopts the high-thixotropic silver paste, the printed circuit pattern is clear in edge, uniform in thickness and extremely high in consistency with the designed pattern; and a clear interface is formed between a silver paste circuit and leather fibers, and improper penetration is avoided. And the circuit resistance value consistency is excellent (the deviation is controlled within + / -5%), so that rapid, uniform and stable planar heating can be realized after the graphene heating layer is connected, and the local overheating hidden danger is perfectly eliminated. According to the present invention, the natural texture and the soft touch feeling of the leather are maintained while the efficient and safe heating performance with the visual color developing function is achieved.

Description

Technical Field

[0001] This invention belongs to the field of graphene technology, specifically relating to a temperature-sensitive color-changing graphene leather and its preparation method. Background Technology

[0002] In recent years, flexible heating materials have been increasingly widely used in automotive seats, smart wearables, and home textiles. Currently, the mainstream flexible heating elements on the market are mainly based on two types of substrates: one type is plastic films, represented by polyethylene terephthalate (PET) and polyimide (PI). Although these films have good insulation and temperature resistance, they are relatively hard and lack flexibility. They are prone to making noise when bent or in contact with the human body, affecting user comfort. Moreover, their plastic texture is difficult to coordinate with high-end interior materials such as leather and fabrics, and they are mostly used in concealed designs. The other type is fabric materials, represented by polyester and non-woven fabrics. Their flexibility is improved, but their material strength is relatively weak. They are prone to deformation and wear after long-term use, and their surface texture is difficult to meet consumers' expectations for a high-end luxury feel, thus limiting their application scenarios.

[0003] Furthermore, existing heating materials generally lack the ability to intuitively display the heating area, requiring users to typically perceive the heating status through touch, without providing immediate visual feedback. Therefore, there is an urgent need to develop a new type of heating material that combines a good tactile feel, excellent material performance, and the ability to display the heating area in real time and intuitively, in order to meet users' dual needs for comfort and functionality. Summary of the Invention

[0004] (a) Technical problems to be solved

[0005] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a temperature-sensitive color-developing graphene leather and its preparation method. The prior art directly applies the planar electrode printing process to leather, but the leather surface has pores and fiber gaps of 0.5-2μm. The present invention solves the technical problems of uneven silver paste penetration, which is caused by the easy accumulation of silver paste in the pores and insufficient silver paste coverage at the fiber protrusions.

[0006] (II) Technical Solution

[0007] In a first aspect, the present invention provides a temperature-sensitive color-developing graphene leather, comprising: a bottom protective layer, a graphene heating functional layer, and an upper color-developing protective layer stacked from bottom to top.

[0008] The bottom protective layer includes a fiber substrate layer and a first waterproof adhesive layer disposed on the fiber substrate layer;

[0009] The graphene heating functional layer includes a graphene conductive film, and a silver paste wire printed with high thixotropic silver paste is provided on the lower surface of the graphene conductive film. The graphene conductive film and the silver paste wire are electrically connected. The silver paste wire is connected to a terminal, which is used to connect to a power line. The graphene heating functional layer is bonded and fixed to the bottom protective layer with the side provided with the silver paste wire through a first waterproof adhesive layer.

[0010] The upper color-developing protective layer includes a leather substrate layer, a second waterproof adhesive layer on the lower surface of the leather substrate layer, and a thermochromic coating on the upper surface of the leather substrate layer. The thermochromic coating can change color according to its own temperature changes. The upper color-developing protective layer is fixed to the graphene heating functional layer through the second waterproof adhesive layer, so that the thermochromic coating can change color in response to the temperature change caused by the heating of the graphene conductive film.

[0011] Optionally, the high thixotropic silver paste is made from the following raw materials in the indicated mass percentages: 68%-72% flake silver powder, 10%-15% polyurethane resin, 2.0%-3.5% fumed silica nanoparticles, and the balance being a mixed solvent, wherein the mixed solvent is a compound of cyclohexanone and dimethyl ester (DBE).

[0012] Optionally, a first adhesive mesh layer is further laminated between the first waterproof adhesive layer and the graphene heating functional layer; and a second adhesive mesh layer is further laminated between the second waterproof adhesive layer and the graphene heating functional layer.

[0013] Optionally, in the bottom protective layer, the fiber substrate layer is selected from at least one of polyester, nylon and non-woven fabric materials;

[0014] Both the first waterproof adhesive layer and the second waterproof adhesive layer are made of hot melt adhesive that can be heat-pressed.

[0015] Optionally, the thermochromic coating is made from the following raw materials: an aqueous polyurethane emulsion, microcapsules encapsulating a first color developer, and a second color developer;

[0016] The microcapsule comprises an outer shell and a core material encapsulated within the outer shell, wherein the outer shell is urea-formaldehyde resin;

[0017] The core material comprises a low-melting-point phase change material and a blue powdery solid dispersed in the low-melting-point phase change material; the blue powdery solid is formed by co-crystallization of crystal violet lactone and a first color developer; the first color developer is bisphenol A, and the second color developer is 2,4-dinitrophenol.

[0018] Optionally, the thermochromic coating is composed of: 50-55 wt% aqueous polyurethane emulsion, 35-45 wt% microcapsules and 5-10 wt% second color developer, wherein the solid content of the aqueous polyurethane emulsion is 35-45%.

[0019] In a second aspect, the present invention provides a method for preparing the temperature-sensitive color-developing graphene leather described in the first aspect, comprising the following steps:

[0020] S1. A first waterproof adhesive layer is laminated onto the fiber substrate layer to obtain the bottom protective layer;

[0021] S2. Terminals are set on the first waterproof adhesive layer of the bottom protective layer. High thixotropic silver paste is used to print silver paste wires connecting the terminals. Then, graphene conductive ink is coated in the area between the silver paste wires. After curing, a graphene heating functional layer that is in ohmic contact with the silver paste wires is formed. The layer is then dried to cure the graphene conductive ink into a graphene conductive film.

[0022] S3. A second waterproof adhesive layer is laminated on the lower surface of the leather substrate layer, and a thermochromic coating is applied to the upper surface of the leather substrate layer to obtain the upper color-developing protective layer.

[0023] S4. The upper color-developing protective layer is combined with the graphene heating functional layer through the second waterproof adhesive layer to obtain the temperature-sensitive color-developing graphene leather.

[0024] Optionally, in step S2, the method for preparing the highly thixotropic silver paste includes the following steps:

[0025] S21. Dissolve thermoplastic polyurethane resin in a mixed solvent composed of cyclohexanone and dimethyl bis(BE) dicarboxylic acid to form a carrier solution.

[0026] S22. Add flake silver powder to the carrier solution and disperse it to form a conductive paste;

[0027] S23. Add fumed silica nanoparticles to the above conductive slurry, and then grind them to form a three-dimensional network structure of fumed silica in the slurry.

[0028] S24. Vacuum degassing and maturation treatment is performed on the ground slurry.

[0029] Optionally, in step S3, the method for preparing the thermochromic coating includes the following steps:

[0030] S31. Crystal violet lactone and bisphenol A are dissolved in anhydrous ethanol, cooled, and crystallized to form a uniform composite crystal; by filtration, washing and vacuum drying, a blue powdery solid is obtained.

[0031] S32. The blue powdery solid is dispersed in a molten low-melting-point phase change material as an oil phase, which is emulsified in an aqueous phase to form an emulsion; urea and formaldehyde are mixed to prepare urea-formaldehyde resin, which undergoes a condensation reaction in the emulsion to form a transparent shell on the surface of the oil droplets in the emulsion; microcapsules are obtained by filtration, washing, and vacuum drying.

[0032] S33. Disperse the microcapsules and 2,4-dinitrophenol in an aqueous polyurethane solution and stir until uniform to form a coating slurry;

[0033] S34. The coating slurry is applied to the upper surface of the leather substrate layer and cured to form a thermochromic coating.

[0034] (III) Beneficial Effects

[0035] This invention uses genuine leather or high-performance synthetic leather as the surface material that comes into contact with the user, fundamentally solving the problems of traditional plastic heating films, such as their stiff texture, tendency to produce abnormal noises, and the mediocre feel and insufficient strength of fabric-based materials. The final product exhibits the soft touch, luxurious appearance, and excellent durability unique to natural leather, and can be seamlessly integrated into application scenarios with demanding material requirements, such as automotive interiors, high-end home furnishings, and luxury clothing.

[0036] This invention creatively endows heating materials with visual capabilities by applying a thermochromic coating to the leather surface. During the heating process, temperature changes in the heated area drive a noticeable color change in the coating, providing users with clear and intuitive visual indications. Users can remotely confirm whether the heating system is activated, its operating status, and the extent of the heated area without touching the surface, greatly enhancing the product's user-friendliness, safety, and technological appeal.

[0037] The graphene heating functional layer of this invention has the advantages of high electrothermal conversion efficiency, uniform heating, and stable performance. Its double protective system, consisting of a TPU waterproof layer and protective cloth / leather on both the top and bottom sides, not only provides robust mechanical protection for brittle conductive circuits (such as copper foil and silver paste) and the graphene film, preventing damage from bending and compression, but also endows the product with excellent waterproof, moisture-proof, and aging-resistant properties, significantly extending its service life.

[0038] Because this invention uses highly thixotropic silver paste, the printed circuit patterns have clear edges, uniform thickness, and extremely high consistency with the design. Under a microscope, a clear interface is formed between the silver paste circuit and the leather fibers, with no improper penetration. The circuit resistance is extremely consistent (deviation controlled within ±5%), thus enabling rapid, uniform, and stable planar heating after the graphene heating layer is connected, perfectly eliminating the risk of localized overheating. The product of this invention achieves efficient, safe heating performance with intuitive color development while maintaining the natural texture and soft touch of leather. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the structure of the temperature-sensitive color-developing graphene leather of Embodiment 1 of the present invention;

[0040] Figure 2 This is a schematic diagram of the graphene heating functional layer in Embodiment 1 of the present invention.

[0041] Figure label:

[0042] 1: Fiber substrate layer;

[0043] 2: First waterproof adhesive layer;

[0044] 3: First adhesive mesh layer;

[0045] 4: Graphene heating functional layer;

[0046] 5: Second adhesive mesh layer;

[0047] 6: Second waterproof adhesive layer;

[0048] 7: Leather substrate layer;

[0049] 8: Temperature-sensitive color-changing coating. Detailed Implementation

[0050] To better explain and facilitate understanding of the present invention, the present invention will be described in detail below through specific embodiments.

[0051] The high thixotropic silver paste of the present invention is made from the following raw materials in the indicated mass percentages: 68%-72% flake silver powder, 10%-15% polyurethane resin, 2.0%-3.5% fumed silica, and 15%-20% cyclohexanone and a mixed solvent of dimethyl ester (DBE).

[0052] The roles of each raw material in the high thixotropic silver paste of this invention are explained below:

[0053] The flake-shaped silver powder serves as the conductive component of the circuit, with a content of 68%-72%. A flake structure, rather than a spherical one, is chosen because the flake-shaped silver powder is more easily oriented under shear force, forming a highly efficient conductive layer, and is better locked into the three-dimensional network when stationary. A content below this range results in insufficient conductivity, while a content above this range impairs the rheological properties of the slurry.

[0054] The thermoplastic polyurethane resin, comprising 10%-15% of the adhesive skeleton and film-forming material, forms a viscous carrier after dissolving in a solvent. This resin possesses excellent natural adhesion to both the leather substrate layer and the TPU underlayer protective layer. It encapsulates silver powder and, upon curing, forms a strong, flexible film layer, ensuring the bonding strength between the circuitry and the substrate, as well as its bending resistance.

[0055] The fumed silica, comprising 2.0%-3.5%, is key to achieving high thixotropy. These extremely fine nanoparticles are interconnected in the slurry via hydrogen bonds and van der Waals forces, forming a three-dimensional network structure. This network is strong enough to prevent silver powder sedimentation and slurry flow when at rest; when subjected to the shear force of the printing squeegee, the network is instantly disrupted, the viscosity drops sharply, and the slurry flows level and passes through the screen; once the shear force disappears, the network rapidly rebuilds, causing the slurry to immediately return to its solid state, fixing it to the leather surface and preventing further penetration.

[0056] The cyclohexanone and dimethyl ester (DBE) mixture, with a solvent content of 15%-20%, serves to dissolve the polyurethane resin, adjust the initial viscosity of the slurry, and control the drying speed. Cyclohexanone ensures complete resin dissolution, while the slow-drying DBE prevents the screen from drying out during printing, ensuring process stability.

[0057] The principle of graphene-heated leather temperature-sensing color development in this invention is as follows: At low temperatures (below the melting point of the core material), the colorless dye and the color developer react to form a blue powdery solid, meaning the reaction causes the microcapsules to exhibit the first color, blue. When the leather is heated to above 40°C, the core material absorbs heat and melts into a liquid, instantly dissolving and releasing the colorless dye from the blue powdery solid. The released dye diffuses through the liquid medium, penetrates the micropores of the outer shell, enters the leather coating matrix, and encounters the more acidic color developer 2,4-dinitrophenol in the matrix, undergoing a rapid color development reaction to generate the second color, red. This process causes the blue inside the microcapsules to fade, and the entire capsule displays a striking red, thus achieving a clear and intuitive visual alarm for a specific temperature threshold.

[0058] In other words, this invention mixes the microcapsules with an adhesive to form a slurry, and then uses screen printing to print a warning symbol on a predetermined area on the back of the car seat leather. At room temperature, the symbol is blue. When the seat heating system malfunctions or overheats locally, causing the temperature of that area to exceed 45°C, the symbol color quickly changes from blue to red, proactively and conspicuously alerting the driver or passengers to the risk of overheating, thus elevating traditional passively heated leather into a smart interactive interface with safety warning capabilities.

[0059] Example 1

[0060] The method for preparing graphene-heated leather in this embodiment includes the following steps:

[0061] S1. Select non-woven fabric as the fiber substrate layer, and laminate a TPU film on its upper surface as the first waterproof adhesive layer by hot pressing; laminate a first adhesive mesh layer on the upper surface of the first waterproof adhesive layer to form the bottom protective layer, which provides an ideal smooth and strong adhesion substrate for subsequent circuit printing.

[0062] S2. Terminals are set on the first adhesive mesh layer of the bottom protective layer. High thixotropic silver paste is used to print silver paste wires connecting the terminals. Then, graphene conductive ink is coated in the area between the silver paste wires. After curing, a graphene heating functional layer that is in ohmic contact with the silver paste wires is formed. After drying, the graphene conductive ink is cured to form a graphene conductive film.

[0063] The highly thixotropic silver paste is cured under ultraviolet light for 30-60 seconds after printing, thereby forming conductive wires with extremely uniform width and thickness. This ensures consistent resistance in the transition region from the copper foil to the graphene film, avoiding localized overheating at the connection points.

[0064] The high thixotropic silver paste of this embodiment is made from the following raw materials in the indicated weight percentages: 70% flake silver powder, 13% polyurethane resin, 3% fumed silica nanoparticles, and 14% mixed solvent. The mixed solvent is a mixture of cyclohexanone and dimethyl ester (DBE). Its preparation method is as follows:

[0065] S21. In a light-proof, sealed stirred container, add a mixed solvent of cyclohexanone and DBE. Slowly add granular thermoplastic polyurethane resin at 300 rpm. Continue stirring at 500 rpm for 80 minutes until the resin is completely dissolved, forming a homogeneous, transparent, and bubble-free viscous carrier solution.

[0066] S22. At a stirring speed of 300 rpm, evenly add the micron-sized flake silver powder to the carrier solution in three batches. After each addition, wait until the silver powder is completely wetted by the liquid before adding the next batch. This process aims to avoid loss of silver powder due to dust and to prevent it from agglomerating into hard, difficult-to-break particles. After all the silver powder has been added, continue stirring at a stirring speed of 700 rpm for 40 minutes. The goal of this stage is to initially break up the agglomerates of silver powder, allowing it to be largely encapsulated by the resin solution, forming a preliminary conductive paste matrix.

[0067] S23. Slowly add fumed silica nanoparticles at a rotation speed of 400 rpm. After addition, transfer the slurry to a three-roll mill for processing. Adjust the roller gap of the three-roll mill sequentially to 50 μm, 25 μm, and 15 μm, allowing the slurry to pass through the mill 3 times, 2 times, and 2 times respectively under these conditions. Under the strong shear force, the aggregates of fumed silica nanoparticles are completely broken up, constructing a homogeneous and stable three-dimensional network structure.

[0068] S24. The paste is then transferred to a vacuum degassing tank and maintained at a vacuum of -0.095 MPa for 18 minutes to thoroughly remove air bubbles entrained during stirring and grinding. The presence of air bubbles severely affects the quality of the printed pattern and the continuity of the circuitry. The degassed silver paste is then placed in a sealed container and allowed to mature at room temperature (25±3℃) and in the dark for at least 24 hours.

[0069] S3. A TPU waterproof layer is laminated onto the lower surface of the leather substrate layer as a second waterproof adhesive layer to enhance its structural stability and prevent moisture intrusion; a second adhesive mesh layer is then laminated onto the lower surface of the second waterproof adhesive layer. A thermochromic coating is applied to the upper surface of the leather substrate layer using a spraying process, thus forming an upper color-changing protective layer. This thermochromic coating can display or change color with temperature changes.

[0070] The thermochromic coating of this embodiment is composed of 53 wt% aqueous polyurethane emulsion, 40 wt% microcapsules, and 7 wt% second color developer, and its preparation method is as follows:

[0071] S31. One part by weight of the colorless dye crystal violet lactone and three parts by weight of the first color developer bisphenol A are dissolved together in an appropriate amount of anhydrous ethanol. The solution is heated and stirred in a 60°C water bath until fully dissolved. Under a cooling rate of 1°C per minute and stirring conditions, crystallization occurs, forming uniform composite crystals. By filtration, washing, and vacuum drying, a blue powdery solid is obtained, which is then ground and sieved to a particle size of less than 10 micrometers.

[0072] S32. Disperse 10 parts by weight of the blue powdery solid evenly into 50 parts by weight of molten paraffin core material with a melting point of 45°C to form a suspended oil phase. Dissolve 5 parts by weight of sodium dodecyl sulfate (SDS) emulsifier in 200 parts by weight of deionized water at 50°C and stir to form an aqueous phase. Slowly pour the oil phase into the aqueous phase at 10,000 rpm and continuously shear for 5 minutes to form a stable oil-in-water (O / W) emulsion. At this point, the emulsion droplets contain the blue powdery solid.

[0073] S33. At 50°C, the above emulsion was transferred to a three-necked flask, and the pH of the emulsion was adjusted to 3.5. A urea-formaldehyde resin prepolymer prepared by mixing 15 parts by weight of urea and 20 parts by weight of 37% formaldehyde solution was slowly added dropwise to the emulsion. The reaction was carried out at a stirring speed of 300 rpm for 4 hours. During this period, the urea-formaldehyde resin underwent a condensation reaction at the emulsion droplet interface, forming a dense polymer shell that encapsulated the paraffin core containing blue powdery solids. After the reaction was completed, the mixture was naturally cooled to room temperature, filtered, washed three times with deionized water, and finally vacuum dried at 40°C for 24 hours to obtain free-flowing microcapsule powder that appeared as blue spheres under a microscope.

[0074] S34. Use 40 parts by weight of waterborne polyurethane as a film-forming binder. Dissolve 5 parts by weight of 2,4-dinitrophenol strong acid color developer in 20 parts by weight of ethanol, then add it to the waterborne polyurethane and stir thoroughly to ensure uniform dispersion. Slowly add 30 parts by weight of the above microcapsule powder to the above mixture and stir at 500 rpm for 15 minutes to ensure that the microcapsules are uniformly dispersed and not damaged, forming a slurry to be coated.

[0075] S35. The paste is printed onto the seat cushion of the car seat using a screen printing process. The wet film thickness is controlled to be approximately 90 μm. The coated leather is then dried at 60°C for 5 minutes to allow the water-based polyurethane to form a film, firmly fixing the microcapsules and colorant to the leather surface.

[0076] S4. The upper color-developing protective layer is combined with the graphene heating functional layer through its second adhesive mesh layer.

[0077] By hot pressing, the adhesive between the layers is melted to form a strong overall sandwich structure, and finally the temperature-sensitive color-changing graphene leather of this embodiment is obtained.

[0078] This embodiment presents a smart effect of dynamic color switching. At low temperatures (<45°C), the coating displays blue due to the reaction of crystal violet lactone within the microcapsules with bisphenol A. When the temperature reaches and exceeds the 45°C threshold, the core material melts, and crystal violet lactone is released into the coating matrix, reacting with the pre-distributed strong acidic second color developer, 2,4-dinitrophenol, to generate a red product. The entire process achieves a striking and reversible color transition from blue to red, providing a clear warning effect and rich information hierarchy.

[0079] Example 2

[0080] The preparation method of the high thixotropic silver paste in this embodiment includes the following preparation steps:

[0081] S21. In a light-proof, sealed container, add the mixed solvent of cyclohexanone and DBE, and the polyurethane resin. Stir at 500 rpm for 60 minutes until the resin is completely dissolved. Then, add the polyamide wax slurry and shear at 1500 rpm at 40-50°C for 10 minutes. This helps to fully activate the thixotropic network of the polyamide wax and disperse it evenly in the resin solution, forming a paste-like matrix.

[0082] S22. Slowly add flake silver powder at 400 rpm. After adding all the powder, increase the speed to 600 rpm and stir for 20 minutes to form a conductive paste matrix.

[0083] S23. Slowly add fumed silica at 400 rpm. After addition, transfer the slurry to a three-roll mill. Gently pass it through twice with a small roller gap of 20 μm. The purpose of this step is to utilize the shearing force of the rollers to efficiently interweave and composite the hydrogen-bonded network of the fumed silica nanoparticles with the crystalline network of the activated polyamide wax, forming a stable, binary synergistic thixotropic structure.

[0084] S24. The ground slurry is vacuum degassed at -0.095 MPa for 15 minutes. Subsequently, it is allowed to stand and mature at a constant temperature of 35°C for 36 hours. This gentle heat treatment process helps the polyamide wax network reach its final thermodynamic stability in the slurry system.

[0085] The other steps are the same as in Example 1.

[0086] Comparative Example 1

[0087] The conductive silver paste used in this comparative example employs commercially available MG Chemicals 840 series conductive epoxy resin. The conductive phase is a mixture of micron / nano silver flakes, and the resin is a low-viscosity epoxy resin.

[0088] Circuit printing was performed on leather substrates from the same batch and with the same processing parameters using the same screen printing equipment and process parameters.

[0089] It can be observed that after printing, traditional silver paste cannot cure quickly and remains fluid on the surface of the first adhesive mesh layer of the underlying protective layer for a period of time. It exhibits significant penetration and accumulation in the gaps between the nonwoven fabric fiber substrate layers, while the coverage is too thin or even breaks appear at the fiber protrusions. The cured circuit lines have rough edges and uneven thickness, resulting in large resistance dispersion (±15% or more) across the entire heating area. During heating, obvious localized overheating (accumulation areas) and low-temperature areas (weak points) occur, resulting in poor heating uniformity and a risk of burnout with long-term use.

[0090] Comparative Example 2

[0091] The core material of the microcapsules in this comparative example comprises the colorless dye crystal violet lactone and the first color developer bisphenol A, both dissolved or dispersed in a paraffin solvent with a melting point of 45°C. The outer shell is urea-formaldehyde resin formed by in-situ polymerization. The initial color of the microcapsules is blue.

[0092] The coating slurry is prepared as follows: 30 parts by weight of the above-mentioned ordinary thermochromic microcapsule powder are directly added to the base material composed of 40 parts by weight of waterborne polyurethane and 20 parts by weight of deionized water. The mixture is stirred at 500 rpm for 15 minutes to ensure that the microcapsules are evenly dispersed, forming the slurry to be coated.

[0093] The difference from Example 1 is that this coating slurry lacks the second color developer, 2,4-dinitrophenol.

[0094] Using the same screen printing process as in the previous example, the paste was printed onto the same automotive seat leather surface, with the wet film thickness controlled to be approximately 90 μm. It was then dried in an oven at 60°C for 5 minutes to allow the waterborne polyurethane to form a film, thus fixing the microcapsules onto the leather surface.

[0095] At low temperatures, the color reaction within the microcapsules of this comparative example coating produces a blue hue. When the temperature exceeds the melting point of the core material, the paraffin melts, and the color reaction within the microcapsules is reversibly terminated due to spatial separation of the reactants, causing the blue color to gradually fade and ultimately revealing the leather base color or the transparent color of the microcapsule shell. This comparative example cannot provide, for instance, the clear, dynamic visual signal of escalating from one alert state to a higher alert state, as in Example 1.

[0096] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A type of graphene leather capable of temperature-sensitive color development, characterized in that, It includes: a bottom protective layer, a graphene heating functional layer, and an upper color-developing protective layer stacked from bottom to top; The bottom protective layer includes a fiber substrate layer and a first waterproof adhesive layer disposed on the fiber substrate layer; The graphene heating functional layer includes a graphene conductive film, and a silver paste wire printed with high thixotropic silver paste is provided on the lower surface of the graphene conductive film. The graphene conductive film and the silver paste wire are electrically connected. The silver paste wire is connected to a terminal, which is used to connect to a power line. The graphene heating functional layer is bonded and fixed to the bottom protective layer with the side provided with the silver paste wire through a first waterproof adhesive layer. The upper color-developing protective layer includes a leather substrate layer, a second waterproof adhesive layer on the lower surface of the leather substrate layer, and a thermochromic coating on the upper surface of the leather substrate layer. The thermochromic coating can change color according to its own temperature changes. The upper color-developing protective layer is fixed to the graphene heating functional layer through the second waterproof adhesive layer, so that the thermochromic coating can change color in response to the temperature change caused by the heating of the graphene conductive film.

2. The temperature-sensitive color-changing graphene leather according to claim 1, characterized in that, The high thixotropic silver paste is made from the following raw materials in the indicated mass percentages: 68%-72% flake silver powder, 10%-15% polyurethane resin, 2.0%-3.5% fumed silica nanoparticles, and the balance being a mixed solvent, wherein the mixed solvent is a compound of cyclohexanone and dimethyl ester (DBE).

3. The temperature-sensitive color-changing graphene leather according to claim 1, characterized in that, A first adhesive mesh layer is further laminated between the first waterproof adhesive layer and the graphene heating functional layer; a second adhesive mesh layer is further laminated between the second waterproof adhesive layer and the graphene heating functional layer.

4. The temperature-sensitive color-changing graphene leather according to claim 1, characterized in that, In the underlying protective layer, the fiber substrate layer is selected from at least one of polyester, nylon and non-woven fabric materials; Both the first waterproof adhesive layer and the second waterproof adhesive layer are made of hot melt adhesive that can be heat-pressed.

5. The temperature-sensitive color-changing graphene leather according to claim 1, characterized in that, The thermochromic coating is made from the following raw materials: water-based polyurethane emulsion, microcapsules encapsulating a first color developer, and a second color developer; The microcapsule comprises an outer shell and a core material encapsulated within the outer shell, wherein the outer shell is urea-formaldehyde resin; The core material comprises a low-melting-point phase change material and a blue powdery solid dispersed in the low-melting-point phase change material; the blue powdery solid is formed by co-crystallization of crystal violet lactone and a first color developer; the first color developer is bisphenol A, and the second color developer is 2,4-dinitrophenol.

6. The temperature-sensitive color-changing graphene leather according to claim 5, characterized in that, The thermochromic coating is composed of 50-55 wt% waterborne polyurethane emulsion, 35-45 wt% microcapsules and 5-10 wt% second color developer, wherein the solid content of the waterborne polyurethane emulsion is 35-45%.

7. A method for preparing temperature-sensitive color-developing graphene leather as described in any one of claims 1-6, characterized in that, Includes the following steps: S1. A first waterproof adhesive layer is laminated onto the fiber substrate layer to obtain the bottom protective layer; S2. Terminals are set on the first waterproof adhesive layer of the bottom protective layer. High thixotropic silver paste is used to print silver paste wires connecting the terminals. Then, graphene conductive ink is coated in the area between the silver paste wires. After curing, a graphene heating functional layer that is in ohmic contact with the silver paste wires is formed. The layer is then dried to cure the graphene conductive ink into a graphene conductive film. S3. A second waterproof adhesive layer is laminated on the lower surface of the leather substrate layer, and a thermochromic coating is applied to the upper surface of the leather substrate layer to obtain the upper color-developing protective layer. S4. The upper color-developing protective layer is combined with the graphene heating functional layer through the second waterproof adhesive layer to obtain the temperature-sensitive color-developing graphene leather.

8. The method according to claim 7, characterized in that, In S2, the preparation method of the high thixotropic silver paste includes the following steps: S21. Dissolve thermoplastic polyurethane resin in a mixed solvent composed of cyclohexanone and dimethyl bis(BE) dicarboxylic acid to form a carrier solution. S22. Add flake silver powder to the carrier solution and disperse it to form a conductive paste; S23. Add fumed silica nanoparticles to the above conductive slurry, and then grind them to form a three-dimensional network structure of fumed silica in the slurry. S24. Vacuum degassing and maturation treatment is performed on the ground slurry.

9. The method according to claim 7, characterized in that, The method for preparing the thermochromic coating includes the following steps: S31. Crystal violet lactone and bisphenol A are dissolved in anhydrous ethanol, cooled, and crystallized to form a uniform composite crystal; by filtration, washing and vacuum drying, a blue powdery solid is obtained. S32. The blue powdery solid is dispersed in a molten low-melting-point phase change material as an oil phase, which is emulsified in an aqueous phase to form an emulsion; urea and formaldehyde are mixed to prepare urea-formaldehyde resin, which undergoes a condensation reaction in the emulsion to form a transparent shell on the surface of the oil droplets in the emulsion; microcapsules are obtained by filtration, washing, and vacuum drying. S33. Disperse the microcapsules and 2,4-dinitrophenol in an aqueous polyurethane solution and stir until uniform to form a coating slurry; S34. The coating slurry is applied to the upper surface of the leather substrate layer and cured to form a thermochromic coating.

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