Temperature-controlled color-changing leather and method for manufacturing the same

Abstract

The present application relates to the field of leather, and more particularly to a temperature-controlled color-changing leather and a preparation method thereof, comprising a leather layer and a buffer layer, a color-changing layer and a protective layer arranged in sequence on the leather layer; the color-changing layer comprises the following raw materials in parts by weight: modified polyurethane resin 100-120 parts, water-based polycarbonate 15-25 parts, color-changing microcapsules 15-30 parts, heat-conducting filler 2-5 parts, aziridine 1-2 parts, silicone oil 2-3 parts, antioxidant 0.3-0.8 parts, leveling agent 0.2-0.5 parts, thickening agent 0.5-1.5 parts, phase solvent 3-5 parts and dispersant 0.5-1 part. The gradient design of each layer structure, the toughening modification of the material and the strengthening of the microcapsule shell layer solve the core technical problems of poor bending resistance, easy breakage of microcapsules and low production efficiency of the existing temperature-controlled color-changing leather.

Description

Technical Field

[0001] This invention relates to the field of leather, and more specifically, to a temperature-controlled color-changing leather and its preparation method. Background Technology

[0002] Thermochromic leather is a functional leather that exhibits a reversible color change in response to temperature variations. It is widely used in fashion bags, footwear, automotive interiors, and smart wearables. Current thermochromic leather production typically employs a coating method, where a mixture of thermochromic powder, heat-sensitive colorant, and phase change material is applied to the leather surface to achieve the color change in response to temperature. However, existing technologies still have the following limitations: Poor color uniformity: The thermochromic powder is prone to agglomeration in the resin matrix, and the phase change medium is prone to macroscopic migration during the coating curing process, resulting in local color spots on the coating; at the same time, the coating has poor thermal conductivity and uneven temperature field distribution, which further aggravates the problem of asynchronous color change.

[0003] Short lifespan: Existing temperature-controlled color-changing leather typically only lasts for 4,000-8,000 reversible color changes. The main reason is that the microcapsule wall material is prone to rupture during repeated thermal expansion and contraction, leading to leakage of the color-changing components; at the same time, electron transfer type color-changing materials are prone to degradation and failure under long-term oxidative conditions.

[0004] Slow response speed: The low thermal conductivity of the polymer resin coating (approximately 0.1-0.3 W / m·K) results in delayed heat conduction, long color change response time, and negatively impacts user experience. Summary of the Invention

[0005] The purpose of this invention is to provide a thermochromic leather with a gradient structure in each layer, good material toughness, and reinforced microcapsule shell, which solves the core technical problems of poor bending resistance, easy damage to microcapsules, and low production efficiency in existing thermochromic leathers. While maintaining excellent thermochromic properties, it also improves mechanical properties, processing efficiency, and environmental performance.

[0006] Another objective of this invention is to provide a method for preparing temperature-controlled color-changing leather, which has a reasonable curing process, short production cycle, and low energy consumption.

[0007] The technical problem solved by this invention is achieved by the following technical solution.

[0008] On one hand, embodiments of the present invention provide a temperature-controlled color-changing leather, comprising a leather layer and a buffer layer, a color-changing layer, and a protective layer sequentially disposed on the leather layer; The color-changing layer comprises the following raw materials by weight: 100-120 parts modified polyurethane resin, 15-25 parts waterborne polycarbonate, 15-30 parts color-changing microcapsules, 2-5 parts thermally conductive filler, 1-2 parts aziridine, 2-3 parts silicone oil, 0.3-0.8 parts antioxidant, 0.2-0.5 parts leveling agent, 0.5-1.5 parts thickener, 3-5 parts compatibilizer, and 0.5-1 part dispersant; The buffer layer comprises the following raw materials by weight: 100-110 parts of waterborne polyurethane, 0.3-0.5 parts of aziridine, 0.5-1.5 parts of thickener, and 0.5-1 parts of wetting and dispersing agent; The protective layer is a polyurethane varnish.

[0009] In some embodiments of the present invention, the method for preparing the modified polyurethane resin includes the following steps: (1) Synthesis of polyurethane prepolymer: Polytetrahydrofuran ether diol, isophorone diisocyanate and dimethylolpropionic acid are mixed and reacted at 80-85℃ until the NCO content reaches the theoretical value. (2) Introduction of side chain pyridine ligand: 4-hydroxypyridine was added to the reaction system of (1) and reacted at 60°C for 2-3 hours; (3) Neutralization and emulsification: Triethylamine is added and the reaction is carried out for 30-40 minutes. Then, the reaction system is dispersed in deionized water containing ethylenediamine under high-speed shear and emulsified for 30-40 minutes. (4) Metal coordination crosslinking: Add zinc acetate and stir for 1-1.5 hours to obtain an aqueous polyurethane dispersion with a solid content of 35-40%, which is the modified polyurethane resin. In some embodiments of the present invention, the modified polyurethane resin comprises the following raw materials in parts by weight: 100-110 parts of polytetrahydrofuran ether diol, 45-50 parts of isophorone diisocyanate, 8-10 parts of dimethylolpropionic acid, 5-10 parts of 4-hydroxypyridine, 6-8 parts of triethylamine, 1-2 parts of ethylenediamine, and 2-6 parts of zinc acetate. In some embodiments of the present invention, the method for preparing the color-changing microcapsules includes the following steps: Methyl stearate and methyl palmitate are mixed and heated until melted. Thermochromic powder and thermosensitive colorant are added and stirred at 60-65℃ until completely dispersed to obtain core material mixture. The core material mixture is mixed with the polyurethane prepolymer to obtain the oil phase; SDS and PVA are dissolved in deionized water to obtain the aqueous phase; the oil phase is added to the aqueous phase and subjected to high-speed shearing for 5-10 minutes to obtain the emulsion. Transfer the emulsion to a reaction vessel, heat it, add a mixture of ethylenediamine and water dropwise, and continue the reaction for 1.5-2 hours; Adjust the pH of the reaction system to 6.5-7.0, purge with nitrogen to remove oxygen, add methyl methacrylate, butyl acrylate and potassium persulfate, and react for 3-4 hours under a nitrogen atmosphere; after cooling to room temperature, centrifuge, wash and spray dry to obtain color-changing microcapsules. In some embodiments of the present invention, the color-changing microcapsules comprise, by weight, the following raw materials: 30-40 parts methyl stearate, 10-15 parts methyl palmitate, 5-10 parts thermochromic powder, 1-3 parts thermosensitive colorant, 30-40 parts polyurethane prepolymer, 1-2 parts SDS, 1-3 parts PVA, 1-2 parts ethylenediamine, 6-10 parts methyl methacrylate, 4-6 parts butyl acrylate, and 0.1-0.3 parts potassium persulfate.

[0010] In some embodiments of the present invention, the method for preparing the thermally conductive filler includes the following steps: Vacuum-dried h-BN nanosheets and antimony-doped tin oxide were added to anhydrous ethanol and ultrasonically dispersed evenly. Then, hydrolyzed silane solution was added and the mixture was stirred for 4-5 hours. After centrifugation, washing, drying, grinding and sieving, the thermally conductive filler was obtained.

[0011] On the other hand, embodiments of the present invention provide a method for preparing temperature-controlled color-changing leather, comprising the following steps: S1 uses artificial leather or genuine leather as the base layer and performs plasma treatment on the surface of the base layer. S2, after mixing the raw materials of the buffer layer evenly, a buffer layer slurry is obtained. The buffer layer slurry is coated on the surface of the base layer after step S1, pre-drying at 50-60℃ for 2-3 minutes, treating under hot air at 80-90℃ for 2-3 minutes, and cooling to room temperature to obtain the buffer layer. S3, mix all the raw materials of the color-changing layer evenly to obtain the color-changing paste, coat the color-changing paste on the surface of the buffer layer, and dry it in a multi-temperature zone oven to obtain the color-changing layer; S4. After curing at room temperature for 24-48 hours, apply polyurethane varnish to the surface of the color-changing layer and cure at 60-80℃ for 5-8 minutes to obtain the temperature-controlled color-changing leather.

[0012] In some embodiments of the present invention, the coating thickness of the buffer layer slurry is 20-40 μm, and the thickness of the buffer layer is 5-15 μm.

[0013] In some embodiments of the present invention, the coating thickness of the color-changing layer slurry is 20-30 μm, and the thickness of the color-changing layer is 10-15 μm.

[0014] In some embodiments of the present invention, the thickness of the protective layer is 3-5 μm.

[0015] Compared with the prior art, the embodiments of the present invention have at least the following advantages or beneficial effects: The temperature-controlled color-changing leather provided by this invention features a buffer layer between the leather layer and the color-changing layer. This buffer layer uses highly elastic waterborne polyurethane as a matrix to form an elastomer structure. By controlling the dry film thickness of the buffer layer to 5-15 μm and the dry film thickness of the color-changing layer to 10-15 μm, the buffer layer can effectively absorb and disperse stress during leather bending, stretching, or embossing, avoiding stress concentration or direct stress acting on the brittle color-changing layer. This significantly inhibits the formation of microcracks while protecting the integrity of the color-changing microcapsules.

[0016] The color-changing layer provided by this invention avoids macroscopic phase separation of the components during the coating curing process by encapsulating thermosensitive color-changing powder, heat-sensitive colorant, and phase change material in nanoscale microcapsules. The nanoscale microcapsules achieve molecular-level dispersion in the resin matrix, eliminating color spots caused by micro-agglomeration. Furthermore, the color-changing microcapsules employ a polyurethane-acrylate double-shell structure, with the second shell being a copolymer of methyl methacrylate and butyl acrylate, achieving a balance between shell hardness and toughness. This structure reduces the breakage rate of the microcapsules during coating, embossing, and long-term bending, ensuring the long-lasting stability of the leather's color-changing function.

[0017] The addition of modified boron nitride thermally conductive filler improves the thermal conductivity of the color-changing layer, ensuring a uniform temperature field distribution and eliminating asynchronous color changes caused by temperature differences. Combined with the thermal conductivity of the elastic buffer layer, the color-changing response time can be shortened.

[0018] Modified polyurethane resin has a synergistic effect through chemical crosslinking and metal-ligand coordination physical crosslinking. Chemical crosslinking ensures that the material remains solid at high temperatures; the metal-ligand coordination bonds undergo partial reversible dissociation at 40-60℃, which moderately reduces the matrix modulus and enhances the mobility of chain segments, thereby effectively releasing the volume stress generated by the phase transition of microcapsules, preventing microcapsule rupture, and extending the service life of the color-changing layer.

[0019] The temperature-controlled color-changing leather preparation method provided by this invention uses a process that combines low-temperature pre-drying and high-temperature hot air treatment for the buffer layer, which completes film formation and drying within 2-3 minutes. The protective layer is cured with hot air at 60-80℃ for 3-5 minutes, which is seamlessly connected with the drying process of the color-changing layer, realizing the one-time molding of the three-layer structure, which greatly reduces the production cycle and energy consumption. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0021] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to specific embodiments.

[0022] On one hand, embodiments of the present invention provide a temperature-controlled color-changing leather, comprising a leather layer and a buffer layer, a color-changing layer, and a protective layer sequentially disposed on the leather layer; The color-changing layer comprises, by weight, the following raw materials: 100-120 parts modified polyurethane resin, 15-25 parts waterborne polycarbonate, 15-30 parts color-changing microcapsules, 2-5 parts thermally conductive filler, 1-2 parts aziridine, 2-3 parts silicone oil, 0.3-0.8 parts antioxidant, 0.2-0.5 parts leveling agent, 0.5-1.5 parts thickener, 3-5 parts compatibilizer, and 0.5-1 part dispersant; The buffer layer comprises, by weight, the following raw materials: 100-110 parts of waterborne polyurethane, 0.3-0.5 parts of aziridine, 0.5-1.5 parts of thickener, and 0.5-1 parts of wetting and dispersing agent; The protective layer is a polyurethane varnish. The polyurethane varnish is an aliphatic polyurethane dispersion, which may be Bayhydrol UH 2558 (Covestro), Lacper 4527 (Wanhua Chemical), or Daotan VTW 1262.

[0023] The buffer layer serves as a modulus transition and stress buffer, the color-changing layer provides temperature-controlled color change and heat conduction, and the protective layer provides scratch resistance, weather resistance, and abrasion resistance.

[0024] The functions of each ingredient in the buffer layer are as follows: Waterborne polyurethane, the main film-forming substance, has high elasticity and an elongation at break of >500%. As a flexible matrix, it absorbs bending stress and prevents cracks from propagating to the discoloration layer.

[0025] Aziridine, a crosslinking agent, improves water resistance and interlayer adhesion while maintaining flexibility, and avoids embrittlement caused by over-curing.

[0026] Thickeners adjust the viscosity of the buffer layer slurry to meet the coating process requirements (20-40μm wet film thickness) and prevent sagging.

[0027] Wetting and dispersing agents reduce surface tension, improve the wettability of the slurry on the leather substrate, and ensure uniform spreading without pinholes.

[0028] Compatibilizers improve polymer compatibility; options include block polyether-polycarbonate copolymers, BYK-9076 (a copolymer containing pigment affinity groups), or Tego Dispers 760W.

[0029] Dispersants to prevent sedimentation and agglomeration include BYK-190 (an acrylate copolymer containing pigment affinity groups), Disperbyk-2015, or Tego Dispers 755W.

[0030] The effects of each ingredient in the color-changing layer are as follows: Modified polyurethane resin, through pyridine-zinc metal coordination modification, can construct a dynamic cross-linked network that combines high strength with a certain degree of self-healing ability; it also provides an encapsulation and fixation effect for microcapsules.

[0031] Waterborne polycarbonate, with its toughening effect, forms an interpenetrating network (IPN) with modified polyurethane, significantly improving the coating's flexibility and reducing brittleness. The modified polyurethane provides a rigid framework and functional coordination crosslinking, while the waterborne polycarbonate provides a flexible phase.

[0032] Color-changing microcapsules contain phase change materials (methyl stearate / methyl palmitate) and thermochromic powder. When the temperature changes, the phase change materials melt / crystallize, causing the color-changing powder to develop / decolorize, thus achieving reversible temperature-controlled color change.

[0033] The thermally conductive filler, h-BN (high thermal conductivity, insulation) and ATO (antimony-doped tin oxide, thermally conductive and antistatic), is uniformly dispersed after silane modification to accelerate heat transfer to the microcapsules and improve the color change response speed.

[0034] Aziridine reacts with the carboxyl groups on the polyurethane molecular chain to form a cross-linked network, improving its water and solvent resistance.

[0035] Silicone oil reduces the coefficient of friction on the coating surface, improves the smoothness of the feel, and also improves scratch resistance to a certain extent.

[0036] Antioxidants prevent the thermal and oxidative aging of polyurethane, extending the service life of leather, and especially protecting the organic dyes in the color-changing microcapsules. Preferably, the antioxidant is Irganox 1010 or Irganox 1076.

[0037] Leveling agents reduce the surface tension of coatings, eliminate defects such as orange peel and pinholes, and ensure a uniform appearance of the color-changing layer. Leveling agents are polyether-modified polydimethylsiloxane, acrylates, or fluorocarbon compounds, and can be BYK-333, BYK-346, or TegoGlide 450.

[0038] Thickeners control the viscosity of the slurry, adapting it to the coating process (20-30μm wet film), and preventing sedimentation and sagging. Thickeners can be polyurethane associative thickeners (HEUR), alkali-swellable acrylates (ASE / HASE), or cellulose ethers, and can be RM-8W, RM-2020, or BYK-420.

[0039] In some embodiments of the present invention, the method for preparing the modified polyurethane resin includes the following steps: (1) Synthesis of polyurethane prepolymer: Polytetrahydrofuran ether diol, isophorone diisocyanate and dimethylolpropionic acid are mixed and reacted at 80-85℃ until the NCO content reaches the theoretical value. (2) Introduction of side chain pyridine ligand: 4-hydroxypyridine was added to the reaction system of (1) and reacted at 60°C for 2-3 hours; (3) Neutralization and emulsification: Triethylamine is added and the reaction is carried out for 30-40 minutes. Then, the reaction system is dispersed in deionized water containing ethylenediamine under high-speed shear and emulsified for 30-40 minutes. (4) Metal coordination crosslinking: Add zinc acetate and stir for 1-1.5 hours to obtain an aqueous polyurethane dispersion with a solid content of 35-40%, which is the modified polyurethane resin. In some embodiments of the present invention, the modified polyurethane resin comprises, by weight, the following raw materials: 100-110 parts of polytetrahydrofuran ether diol, 45-50 parts of isophorone diisocyanate, 8-10 parts of dimethylolpropionic acid, 5-10 parts of 4-hydroxypyridine, 6-8 parts of triethylamine, 1-2 parts of ethylenediamine, and 2-6 parts of zinc acetate. Polytetrahydrofuran ether diol serves as the soft segment component, providing flexibility and low-temperature performance; isophorone diisocyanate serves as the hard segment component, providing strength and weather resistance; dimethylolpropionic acid, as a hydrophilic chain extender, introduces carboxyl groups into the system, imparting water dispersibility to the resin and providing reaction sites for subsequent aziridine crosslinking; 4-hydroxypyridine, with side chain functionalization, introduces pyridine coordinating groups for forming metal coordination crosslinks with zinc acetate; triethylamine forms salts with carboxyl groups, achieving water dispersibility of the resin; ethylenediamine extends the molecular chain, increases molecular weight, and enhances film-forming properties; zinc acetate provides Zn²⁺. + It forms coordination bonds with pyridine nitrogen atoms to construct a dynamic reversible cross-linked network, endowing the coating with self-healing ability and high toughness.

[0040] In some embodiments of the present invention, the method for preparing the color-changing microcapsules includes the following steps: mixing methyl stearate and methyl palmitate, heating to melt, adding thermochromic powder and thermosensitive colorant, and stirring at 60-65°C until completely dispersed to obtain a core material mixture; The core material mixture was mixed with the polyurethane prepolymer to obtain the oil phase; SDS and PVA were dissolved in deionized water to obtain the aqueous phase; the oil phase was added to the aqueous phase and subjected to high-speed shearing for 5-10 minutes to obtain the emulsion; the emulsion was transferred to a reactor, heated, and a mixture of ethylenediamine and water was added dropwise, and the reaction was continued for 1.5-2 hours; the pH of the reaction system was adjusted to 6.5-7.0, nitrogen gas was purged to remove oxygen, methyl methacrylate, butyl acrylate and potassium persulfate were added, and the reaction was carried out under a nitrogen atmosphere for 3-4 hours; after cooling to room temperature, the mixture was centrifuged, washed, and spray-dried to obtain the color-changing microcapsules. In some embodiments of the present invention, the color-changing microcapsules, by weight, comprise the following raw materials: 30-40 parts methyl stearate, 10-15 parts methyl palmitate, 5-10 parts thermochromic powder, 1-3 parts thermosensitive colorant, 30-40 parts polyurethane prepolymer, 1-2 parts SDS (sodium dodecyl sulfate), 1-3 parts PVA (polyvinyl alcohol), 1-2 parts ethylenediamine, 6-10 parts methyl methacrylate, 4-6 parts butyl acrylate, and 0.1-0.3 parts potassium persulfate.

[0041] Methyl stearate and methyl palmitate are the main components of the phase change core material. As a binary eutectic system, it has a melting point of 25-35℃, during which a solid-liquid phase transition occurs, triggering discoloration. Thermochromic powder and thermosensitive colorant form a color development system. When the temperature changes, the phase change material melts, and the polarity / acidity / alkalinity of the environment changes, which leads to the reversible combination / separation of the colorant and the color developer, thus achieving a color change.

[0042] The polyurethane prepolymer, as the precursor of the first shell, reacts with ethylenediamine to form a polyurea-polyurethane shell, providing basic coating and mechanical strength. SDS + PVA act as emulsifiers and protective colloids, stabilizing the emulsion and controlling the microcapsule particle size distribution. Ethylenediamine acts as a shell curing agent, reacting with the polyurethane prepolymer to form a dense first shell. Methyl methacrylate and butyl acrylate are the second shell monomers, which copolymerize to form an acrylate shell. MMA provides hardness and BA provides toughness, forming a hard-soft copolymer shell that improves compressive strength while maintaining toughness.

[0043] Potassium persulfate acts as a free radical initiator, initiating the copolymerization of MMA and BA to form a second shell.

[0044] In some embodiments of the present invention, the preparation method of the thermally conductive filler includes the following steps: adding vacuum-dried h-BN nanosheets and antimony-doped tin oxide to anhydrous ethanol and ultrasonically dispersing them evenly; then adding hydrolyzed silane solution and stirring the reaction for 4-5 hours; centrifuging, washing, drying, grinding and sieving to obtain the thermally conductive filler.

[0045] h-BN nanosheets, also known as hexagonal boron nitride nanosheets, have high thermal conductivity and electrical insulation, and construct thermally conductive pathways in the morphology layer. Antimony-doped tin oxide (ATO) is thermally conductive and antistatic, aiding in thermal conduction while preventing static electricity buildup.

[0046] Silane coupling agents improve the compatibility of inorganic powders with polyurethane matrices, enhance dispersibility, and reduce agglomeration.

[0047] On the other hand, embodiments of the present invention provide a method for preparing temperature-controlled color-changing leather, comprising the following steps: S1 uses artificial leather or genuine leather as the base layer and performs plasma treatment on the surface of the base layer. S2, after mixing the raw materials of the buffer layer evenly, a buffer layer slurry is obtained. The buffer layer slurry is coated on the surface of the base layer after step S1, pre-drying at 50-60℃ for 2-3 minutes, treating under hot air at 80-90℃ for 2-3 minutes, and cooling to room temperature to obtain the buffer layer. S3, mix all the raw materials of the color-changing layer evenly to obtain the color-changing paste, coat the color-changing paste on the surface of the buffer layer, and dry it in a multi-temperature zone oven to obtain the color-changing layer; The drying parameters in the multi-zone oven are as follows: First zone: 50-60℃, 3-5 minutes (low temperature pre-drying); Second zone: 70-80℃, 2-3 minutes (medium temperature drying); Third zone: 85-90℃, 1-2 minutes (high temperature setting).

[0048] S4. After curing at room temperature for 24-48 hours, apply clear polyurethane varnish to the surface of the color-changing layer and cure at 60-80℃ for 5-8 minutes to obtain the temperature-controlled color-changing leather.

[0049] The coating thickness of the buffer layer slurry is 20-40 μm, and the thickness of the buffer layer is 5-15 μm. The coating thickness of the color-changing layer slurry is 20-30 μm, and the thickness of the color-changing layer is 10-15 μm. The thickness of the protective layer is 3-5 μm.

[0050] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0051] Example 1 1. Preparation of modified polyurethane resin (1) Synthesis of polyurethane prepolymer: Polytetrahydrofuran ether diol, isophorone diisocyanate, and dimethylolpropionic acid were mixed and reacted at 80-85℃. The NCO content was measured every 30 minutes: about 1g of sample was added to 20mL of di-n-butylamine-toluene solution (0.2 mol / L), shaken for 30 minutes, and titrated with 0.1 mol / L HCl. The reaction was stopped when the NCO content reached the theoretical value of 4.8±0.2%. (2) Introduction of side-chain pyridine ligand: 4-hydroxypyridine was added to the reaction system of (1) and reacted at 60°C for 2.5 hours; (3) Neutralization and emulsification: Triethylamine was added and the reaction was carried out for 40 minutes. Then, the reaction system was dispersed in deionized water containing ethylenediamine under high-speed shear and emulsified for 30 minutes. (4) Metal coordination crosslinking: Add zinc acetate and stir for 1.5 hours to obtain an aqueous polyurethane dispersion with a solid content of 35%, which is the modified polyurethane resin.

[0052] The raw material formula is as follows: 100 parts of polytetrahydrofuran ether diol, 45 parts of isophorone diisocyanate, 8 parts of dimethylolpropionic acid, 5 parts of 4-hydroxypyridine, 6 parts of triethylamine, 1 part of ethylenediamine, and 2 parts of zinc acetate.

[0053] 2. Preparation of color-changing microcapsules Methyl stearate and methyl palmitate are mixed and heated until melted. Thermochromic powder and thermosensitive colorant are added and stirred at 60-65℃ until completely dispersed to obtain core material mixture. The core material mixture was mixed with the polyurethane prepolymer to obtain the oil phase; SDS and PVA were dissolved in deionized water to obtain the aqueous phase; the oil phase was added to the aqueous phase and subjected to high-speed shearing for 10 minutes to obtain the emulsion. Transfer the emulsion to a reaction vessel, heat it, add a mixture of ethylenediamine and water dropwise, and continue the reaction for 1.5-2 hours; The pH of the reaction system was adjusted to 6.5-7.0, nitrogen gas was purged to remove oxygen, methyl methacrylate, butyl acrylate and potassium persulfate were added, and the reaction was carried out under a nitrogen atmosphere for 4 hours. After cooling to room temperature, the mixture was centrifuged, washed and spray-dried to obtain color-changing microcapsules.

[0054] The formula is as follows: 35 parts methyl stearate, 13 parts methyl palmitate, 8 parts thermochromic powder, 2 parts thermosensitive colorant, 35 parts polyurethane prepolymer, 1.5 parts SDS, 2 parts PVA, 1.5 parts ethylenediamine, 8 parts methyl methacrylate, 5 parts butyl acrylate, and 0.2 parts potassium persulfate.

[0055] 3. Preparation of thermally conductive fillers Vacuum-dried h-BN nanosheets and antimony-doped tin oxide were added to anhydrous ethanol and ultrasonically dispersed evenly. Then, hydrolyzed silane solution was added and the mixture was stirred for 4-5 hours. After centrifugation, washing, drying, grinding and sieving, the thermally conductive filler was obtained.

[0056] The mass ratio of h-BN nanosheets to antimony-doped tin oxide is 1:1.

[0057] 4. Preparation of temperature-controlled color-changing leather S1 uses artificial leather as a base layer and performs plasma treatment on the surface of the base layer. S2, after the raw materials of the buffer layer are mixed evenly, a buffer layer slurry is obtained. The buffer layer slurry is coated on the surface of the base layer after step S1, pre-drying at 50-60℃ for 3 minutes, treating with hot air at 80-90℃ for 3 minutes, and cooling to room temperature to obtain a buffer layer. The coating thickness of the buffer layer slurry is 40μm, and the thickness of the buffer layer is 15μm.

[0058] S3. Mix all the raw materials of the color-changing layer evenly to obtain a color-changing slurry. Coat the color-changing slurry onto the surface of the buffer layer and dry it in a multi-temperature zone oven to obtain a color-changing layer. The coating thickness of the color-changing slurry is 30 μm and the thickness of the color-changing layer is 15 μm.

[0059] The drying parameters in the multi-zone oven are as follows: First zone: 55℃, 5 minutes (low temperature pre-drying); Second zone: 75℃, 3 minutes (medium temperature drying); Third zone: 85℃, 2 minutes (high temperature setting).

[0060] S4. After curing at room temperature for 24-48 hours, a clear polyurethane varnish is applied to the surface of the color-changing layer, and then cured at 60-80℃ for 8 minutes to obtain the temperature-controlled color-changing leather. The thickness of the protective layer is 5μm.

[0061] The sources of each raw material in Example 1 are shown in Table 1.

[0062] Table 1

[0063] Example 2 The difference from Example 1 is that the modified polyurethane resin formulation is as follows: 110 parts of polytetrahydrofuran ether diol, 45 parts of isophorone diisocyanate, 8 parts of dimethylolpropionic acid, 5 parts of 4-hydroxypyridine, 6 parts of triethylamine, 1 part of ethylenediamine, and 2 parts of zinc acetate.

[0064] The remaining raw materials, proportions, and preparation methods are the same as in Example 1.

[0065] Example 3 The difference from Example 1 is that the modified polyurethane resin formulation is as follows: 100 parts of polytetrahydrofuran ether diol, 50 parts of isophorone diisocyanate, 10 parts of dimethylolpropionic acid, 10 parts of 4-hydroxypyridine, 8 parts of triethylamine, 2 parts of ethylenediamine, and 6 parts of zinc acetate.

[0066] The remaining raw materials, proportions, and preparation methods are the same as in Example 1.

[0067] Example 4 The difference from Example 1 is that the formulation of the color-changing microcapsules is as follows: 30 parts methyl stearate, 10 parts methyl palmitate, 5 parts thermochromic powder, 1 part thermosensitive colorant, 30 parts polyurethane prepolymer, 1 part SDS, 1 part PVA, 1 part ethylenediamine, 6 parts methyl methacrylate, 4 parts butyl acrylate, and 0.1 parts potassium persulfate.

[0068] The remaining raw materials, proportions, and preparation methods are the same as in Example 1.

[0069] Example 5 The difference from Example 1 is that the formulation of the color-changing microcapsules is as follows: 40 parts methyl stearate, 15 parts methyl palmitate, 10 parts thermochromic powder, 3 parts thermosensitive colorant, 40 parts polyurethane prepolymer, 2 parts SDS, 3 parts PVA, 2 parts ethylenediamine, 10 parts methyl methacrylate, 6 parts butyl acrylate, and 0.3 parts potassium persulfate.

[0070] The remaining raw materials, proportions, and preparation methods are the same as in Example 1.

[0071] Example 6 The difference from Example 1 is that the mass ratio of h-BN nanosheets to antimony-doped tin oxide is 1:2.

[0072] The remaining raw materials, proportions, and preparation methods are the same as in Example 1.

[0073] Example 7 The difference from Example 1 is that the mass ratio of h-BN nanosheets to antimony-doped tin oxide is 2:1.

[0074] The remaining raw materials, proportions, and preparation methods are the same as in Example 1.

[0075] Example 8 The difference from Example 1 is that the thickness of the buffer layer is 5 μm; the thickness of the color-changing layer is 10 μm; and the thickness of the protective layer is 3 μm.

[0076] The remaining raw materials, proportions, and preparation methods are the same as in Example 1.

[0077] Example 9 The difference from Example 1 is that the thickness of the buffer layer is 10 μm; the thickness of the color-changing layer is 12 μm; and the thickness of the protective layer is 4 μm.

[0078] The remaining raw materials, proportions, and preparation methods are the same as in Example 1.

[0079] Comparative Example 1 The difference from Example 1 is that water-based polyurethane is used instead of modified polyurethane resin in the color-changing layer raw material, while the other raw materials, proportions and preparation methods are the same as in Example 1.

[0080] Comparative Example 2 The difference from Example 1 is that no thermally conductive filler is added to the color-changing layer raw material; instead, an equal amount of modified polyurethane resin is used. The remaining raw materials, proportions, and preparation methods are the same as in Example 1.

[0081] Comparative Example 3 The difference from Example 1 is that no buffer layer is set, and the color-changing layer paste is directly applied to the leather layer. The other raw materials, proportions and preparation methods are the same as those in Example 1.

[0082] Comparative Example 4 The difference from Example 1 is that no buffer layer is set, and the color-changing layer paste is directly coated on the leather layer. In addition, water-based polyurethane is used instead of modified polyurethane resin in the color-changing layer raw material, while the other raw materials, proportions and preparation methods are the same as in Example 1.

[0083] Experimental Example The temperature-controlled color-changing leather prepared based on the examples and comparative examples was tested according to the following methods, and the results are shown in Tables 2 and 3.

[0084] 1. Bending resistance test Test standard: GB / T 12586-2003 "Determination of flexural strength of leather"; Testing equipment: Bally type leather flexural endurance tester; Test conditions: ambient temperature: 23±2℃, relative humidity 50±5%; low temperature: -10±2℃; Sample size: 70mm × 45mm; Folding angle: 22.5°; Folding frequency: 100 times / minute; Judgment criteria: Observe whether cracks, crazing, or peeling appear on the coating surface, and record the number of bends when the first crack appears. The target of the example is 200,000 cycles at room temperature without cracking and 10,000 cycles at low temperature without cracking.

[0085] 2. Coating elongation at break test Test standard: GB / T 528-2009 "Determination of tensile stress-strain properties of vulcanized rubber or thermoplastic rubber"; Testing equipment: Universal testing machine; Sample preparation: Peel the coating off the leather substrate and cut it into dumbbell shapes (Type I, total length 115mm, gauge length 25mm). Tensioning speed: 500 mm / min; Test environment: 23±2℃, relative humidity 50±5%; Judgment criteria: Record the elongation at the time of fracture of the specimen and take the average value of 5 specimens.

[0086] 3. Microcapsule breakage rate test Test method: Microscopic counting method; Testing equipment: Optical microscope (400-1000x magnification); Sampling method: Take microcapsule powder samples before coating, and take samples from the leather coating after coating (freeze-section or solvent dissolution and separation). Statistical method: The total number of microcapsules and the number of broken microcapsules were counted before and after coating. The breakage rate was calculated as (number of broken microcapsules / total number of microcapsules) × 100%. At least 500 microcapsules were counted for each sample, and the results were repeated 3 times and the average value was taken.

[0087] Judgment criteria: Microcapsule wall rupture, core material leakage, or capsule collapse is considered as damage.

[0088] 4. Color change response time test Test method: Hot plate contact method; Testing equipment: constant temperature hot plate (accuracy ±0.5℃), stopwatch, colorimeter or visual inspection; Test procedure: Place the leather sample (50mm×50mm) in a constant temperature environment at 25℃ for equilibration for 30 minutes. Quickly transfer it to a constant temperature hot plate at 35℃ (or directly heat it from the 25℃ environment), and record the time required from contact with the hot plate to complete color change (visual or ΔE≥90% change).

[0089] Number of repetitions: Each sample was tested 5 times, and the average value was taken.

[0090] 5. Color-changing effect retention rate test Test method: Thermal cycling aging method; Testing equipment: constant temperature and humidity chamber, colorimeter; Test conditions: Cycle the sample between 25℃ and 35℃, holding each temperature for 10 minutes, and test the color difference value after every 100 cycles; Judgment criterion: Color change effect retention rate = (color difference ΔE after cycling / initial color difference ΔE) × 100%.

[0091] 6. Coating adhesion test Test standard: GB / T 9286-1998 "Cross-cut test for paints and varnishes"; Testing equipment: cross-cut tester (1mm tooth spacing), 3M tape (type 600); Test procedure: Use a cross-cutting tool to cut 10×10 1mm×1mm squares on the coating surface, adhere with tape, and then peel off vertically. Judgment criteria: Grade 0: The cut edges are completely smooth with no peeling; Grade 1: There is slight peeling at the intersection of the cuts, with a peeling area ≤5%.

[0092] Table 2

[0093] Table 3

[0094] Tables 2 and 3 show that the synergistic effect of the buffer layer and the modified resin increases the flexural life from 26,000 cycles to over 200,000 cycles (an increase of approximately 669%); the buffer layer effectively disperses stress, reducing the microcapsule breakage rate from 16.2% to 2.4% (a reduction of 85%); the thermally conductive filler shortens the response time from 7.5 seconds to 4.3 seconds (a reduction of 43%); and the gradient drying process shortens the curing time from over 24 hours to less than 30 minutes.

[0095] The embodiments described above are some, but not all, embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A temperature-controlled color-changing leather, characterized in that, It includes a leather layer and a buffer layer, a color-changing layer, and a protective layer sequentially disposed on the leather layer; The color-changing layer comprises the following raw materials by weight: 100-120 parts modified polyurethane resin, 15-25 parts waterborne polycarbonate, 15-30 parts color-changing microcapsules, 2-5 parts thermally conductive filler, 1-2 parts aziridine, 2-3 parts silicone oil, 0.3-0.8 parts antioxidant, 0.2-0.5 parts leveling agent, 0.5-1.5 parts thickener, 3-5 parts compatibilizer, and 0.5-1 part dispersant; The buffer layer comprises the following raw materials by weight: 100-110 parts of waterborne polyurethane, 0.3-0.5 parts of aziridine, 0.5-1.5 parts of thickener, and 0.5-1 parts of wetting and dispersing agent; The protective layer is a polyurethane varnish.

2. The temperature-controlled color-changing leather according to claim 1, characterized in that, The preparation method of the modified polyurethane resin includes the following steps: (1) Synthesis of polyurethane prepolymer: Polytetrahydrofuran ether diol, isophorone diisocyanate and dimethylolpropionic acid are mixed and reacted at 80-85℃ until the NCO content reaches the theoretical value. (2) Introduction of side-chain pyridine ligand: 4-hydroxypyridine was added to the reaction system of (1) and reacted at 60°C for 2-3 hours; (3) Neutralization and emulsification: Triethylamine is added and the reaction is carried out for 30-40 minutes. Then, the reaction system is dispersed in deionized water containing ethylenediamine under high-speed shear and emulsified for 30-40 minutes. (4) Metal coordination crosslinking: Add zinc acetate and stir for 1-1.5 hours to obtain an aqueous polyurethane dispersion with a solid content of 35-40%, which is the modified polyurethane resin.

3. The temperature-controlled color-changing leather according to claim 2, characterized in that, The modified polyurethane resin, by weight, comprises the following raw materials: 100-110 parts of polytetrahydrofuran ether diol, 45-50 parts of isophorone diisocyanate, 8-10 parts of dimethylolpropionic acid, 5-10 parts of 4-hydroxypyridine, 6-8 parts of triethylamine, 1-2 parts of ethylenediamine, and 2-6 parts of zinc acetate.

4. The temperature-controlled color-changing leather according to claim 1, characterized in that, The method for preparing the color-changing microcapsules includes the following steps: Methyl stearate and methyl palmitate are mixed and heated until melted. Thermochromic powder and thermosensitive colorant are added and stirred at 60-65℃ until completely dispersed to obtain core material mixture. The core material mixture is mixed with the polyurethane prepolymer to obtain the oil phase; SDS and PVA are dissolved in deionized water to obtain the aqueous phase; the oil phase is added to the aqueous phase and subjected to high-speed shearing for 5-10 minutes to obtain the emulsion. Transfer the emulsion to a reaction vessel, heat it, add a mixture of ethylenediamine and water dropwise, and continue the reaction for 1.5-2 hours; Adjust the pH of the reaction system to 6.5-7.0, purge with nitrogen to remove oxygen, add methyl methacrylate, butyl acrylate and potassium persulfate, and react for 3-4 hours under a nitrogen atmosphere; after cooling to room temperature, centrifuge, wash and spray dry to obtain color-changing microcapsules.

5. The temperature-controlled color-changing leather according to claim 4, characterized in that, The color-changing microcapsules, by weight, comprise the following raw materials: 30-40 parts methyl stearate, 10-15 parts methyl palmitate, 5-10 parts thermochromic powder, 1-3 parts thermosensitive colorant, 30-40 parts polyurethane prepolymer, 1-2 parts SDS, 1-3 parts PVA, 1-2 parts ethylenediamine, 6-10 parts methyl methacrylate, 4-6 parts butyl acrylate, and 0.1-0.3 parts potassium persulfate.

6. The temperature-controlled color-changing leather according to claim 1, characterized in that, The method for preparing the thermally conductive filler includes the following steps: Vacuum-dried h-BN nanosheets and antimony-doped tin oxide were added to anhydrous ethanol and ultrasonically dispersed evenly. Then, hydrolyzed silane solution was added and the mixture was stirred for 4-5 hours. After centrifugation, washing, drying, grinding and sieving, the thermally conductive filler was obtained.

7. A method for preparing temperature-controlled color-changing leather as described in any one of claims 1-6, characterized in that, Includes the following steps: S1 uses artificial leather or genuine leather as the base layer and performs plasma treatment on the surface of the base layer. S2, after mixing the raw materials of the buffer layer evenly, a buffer layer slurry is obtained. The buffer layer slurry is coated on the surface of the base layer after step S1, pre-drying at 50-60℃ for 2-3 minutes, treating under hot air at 80-90℃ for 2-3 minutes, and cooling to room temperature to obtain the buffer layer. S3, mix all the raw materials of the color-changing layer evenly to obtain the color-changing paste, coat the color-changing paste on the surface of the buffer layer, and dry it in a multi-temperature zone oven to obtain the color-changing layer; S4. After curing at room temperature for 24-48 hours, apply polyurethane varnish to the surface of the color-changing layer and cure at 60-80℃ for 5-8 minutes to obtain the temperature-controlled color-changing leather.

8. The method for preparing temperature-controlled color-changing leather according to claim 7, characterized in that, The coating thickness of the buffer layer slurry is 20-40μm, and the thickness of the buffer layer is 5-15μm.

9. The method for preparing temperature-controlled color-changing leather according to claim 7, characterized in that, The coating thickness of the color-changing slurry is 20-30μm, and the thickness of the color-changing layer is 10-15μm.

10. The method for preparing temperature-controlled color-changing leather according to claim 7, characterized in that, The thickness of the protective layer is 3-5 μm.

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