A heat-sensitive color-changing coating material, its preparation method, and the fabric thereof.

Abstract

This invention relates to the field of functional coating technology, and discloses a heat-sensitive color-changing coating material, its preparation method, and a fabric. The material includes a mesoporous shielding color-changing slurry, a dormant silicone crosslinking liquid, an aqueous polyurethane dispersion, and a polycarbodiimide aqueous crosslinking agent. The color-changing slurry contains double-bond modified hydrophobic fumed silica that adsorbs the phase change solvent system. The crosslinking liquid contains hydrogen- and vinyl-containing silicone components, a platinum catalyst, and a 3-methyl-1-butyn-3-ol and thiuram complex as a temperature threshold delay agent. This invention utilizes the mesopores of fumed silica to physically confine the color-changing substance, and the delay agent blocks catalytic activity at room temperature to extend the coating operation time. During heat curing, a hydrosilylation reaction occurs, causing the fumed silica particles to be covalently grafted into the silicone network. This solution improves the leakage problem of the phase change substance when heated and enhances the wash resistance and color-changing life of the fabric.

Description

Technical Field

[0001] This invention relates to the field of functional coating technology, specifically to a heat-sensitive color-changing coating material, its preparation method, and its fabric. Background Technology

[0002] Heat-sensitive color-changing materials typically consist of leuco dyes, color developers, and phase change solvents. In practical applications, these materials are often applied as coatings to the surface of substrates such as textiles. When the external temperature reaches the melting point of the phase change solvent, the solvent changes from a solid to a liquid state, altering the interaction state between the dye and the color developer within the system, thereby achieving a macroscopic color change.

[0003] Existing thermochromic coatings have certain technical limitations in practical use and processing. Since the color-changing mechanism relies on the melting of the phase-change solvent, when the material is in the liquid temperature range, the internal liquid phase substances easily penetrate and migrate into the coating matrix. This leakage leads to the loss of effective color-changing components, reducing the coating's color-changing response and shortening its cycle life. To improve the stability of the color-changing substance in the matrix, cross-linking resin systems are usually introduced during production for curing and film formation. However, in slurry preparation and coating processes, conventional catalytic cross-linking systems still maintain a certain level of reactivity at room temperature, easily triggering early cross-linking and curing of the slurry. This causes a rapid increase in coating viscosity, shortening the operable coating window and increasing the difficulty of process control in mass production. Furthermore, the compatibility between physically mixed color-changing particles and polymer resins is poor; the particles are prone to agglomeration or precipitation during film formation, resulting in an uneven internal structure of the final coating and insufficient bonding strength between the coating and the textile substrate, making it difficult to meet the fabric's requirements for washability and abrasion resistance in daily use. Summary of the Invention

[0004] The technical problem solved by this invention is that when existing heat-sensitive color-changing coatings undergo phase change upon heating, the internal liquid phase system is prone to leakage and migration, resulting in a decrease in color-changing life. At the same time, the existing crosslinking system is prone to early curing at room temperature, resulting in a short coating process window period, and the color-changing particles are prone to agglomeration and precipitation in the polymer matrix, resulting in insufficient bonding strength between the coating and the substrate.

[0005] To address the above problems, the present invention provides the following technical solution: In a first aspect, the present invention provides a heat-sensitive color-changing coating material, employing the following technical solution: A heat-sensitive color-changing coating material, made from raw materials comprising the following parts by weight: Phase change solvent 5.0–15.0 parts; Leuco dye: 0.5–2.5 parts; Color developer: 1.0–4.0 parts; Double-bond modified hydrophobic fumed silica, 2.0–6.0 parts; Vinyl-terminated polydimethylsiloxane 3.0–8.0 parts; 0.3–1.0 parts of polymethylhydrosiloxane; Temperature threshold delay agent: 0.02–0.08 parts; Platinum catalyst 0.05–0.15 parts; 50.0–70.0 parts of waterborne polyurethane dispersion; 1.0–3.0 parts of polycarbodiimide aqueous crosslinking agent; The temperature threshold delay agent is a complex of 3-methyl-1-butyn-3-ol and thiuram. When the coating material is heated and cross-linked, the silane-hydrogen bonds in the polymethylhydrosiloxane undergo hydrosilylation reactions with the vinyl groups of the vinyl-terminated polydimethylsiloxane and the carbon-carbon double bonds on the surface of the double-bond modified hydrophobic fumed silica, respectively, forming a three-dimensional network cross-linked framework covalently linked to the organosilicon polymer segments and the inorganic fumed silica particles, thereby achieving chemical grafting and spatial anchoring of the color-changing carrier particles in the polymer matrix.

[0006] By adopting the above technical solution, due to the combination of double bond modified hydrophobic fumed silica and silicone crosslinking system, and the introduction of 3-methyl-1-butyn-3-ol / thiuram complex as temperature threshold delay agent, the technical effect of stable storage of coating at room temperature and no phase change leakage after high temperature curing is obtained.

[0007] The specific reaction mechanism is as follows: Step 1: Physical confinement barrier. Double-bond modified hydrophobic fumed silica has a mesoporous structure. Molten phase change solvents, leuco dyes, and color developers enter the pores of fumed silica through capillary forces, forming a physical spatial confinement and reducing the diffusion ability of liquid phase substances.

[0008] Step Two: Catalytic Activity Blocking. At room temperature, the alkyne bond in 3-methyl-1-butyn-3-ol and the sulfur atom in thiuram coordinate with the central platinum atom of the platinum catalyst to form a coordination complex. This coordination complex blocks the catalytically active sites of the platinum atom at room temperature, inhibiting the reaction between the polymethylhydrosiloxane and the double-bond-containing components, maintaining the liquid state of the slurry, and extending the workability of the coating process.

[0009] Step 3: High-temperature depolymerization and cross-linking grafting. When the system is heated to the curing temperature, the heat causes the alkyne bonds and the coordination bonds between sulfur atoms and platinum atoms to break, resulting in the desorption of the platinum catalyst and the restoration of its catalytic activity. Under platinum catalysis, a hydrosilylation reaction occurs: The silane-hydrogen bonds on the polymethylhydrosiloxane segments undergo addition with the carbon-carbon double bonds of the vinyl-terminated polydimethylsiloxane end groups to construct a three-dimensional polydimethylsiloxane network. On the other hand, silicon-hydrogen bonds and double bonds modify the carbon-carbon double bonds on the surface of hydrophobic fumed silica, resulting in addition. This process allows the silica particles adsorbed with the color-changing substance to become cross-linking nodes in the three-dimensional cross-linked framework of silicone through covalent bonds. This chemical grafting reaction fixes the position of the color-changing carrier particles in the matrix. When the internal phase change solvent melts upon heating, it is difficult for it to leak outward due to the polymer network and covalent bonds, thereby improving the coating's wash resistance and cycle life of the color-changing coating.

[0010] Preferably, the weight ratio of the raw materials is as follows: Phase change solvent 10.0 parts; leuco dye 1.5 parts; color developer 2.5 parts; double bond modified hydrophobic fumed silica 4.0 parts; vinyl-terminated polydimethylsiloxane 5.5 parts; polymethylhydrosiloxane 0.6 parts; temperature threshold delay agent 0.05 parts; platinum catalyst 0.1 parts; waterborne polyurethane dispersion 60.0 parts; polycarbodiimide waterborne crosslinking agent 2.0 parts.

[0011] By adopting the above technical solution, the proportions of the organosilicon phase, polyurethane phase, and inorganic silica phase in the system reach a compatible state. The crosslinking density of hydrosilylation is moderate, which ensures that the silica particles are effectively grafted while avoiding internal stress cracking of the coating due to excessive crosslinking, thus maintaining the flexibility of the coating film.

[0012] Preferably, the phase change solvent is a mixture of n-octadecane and n-hexadecane, with the total mass of the phase change solvent as the basis, wherein the mass fraction of n-octadecane is 55% to 65% and the mass fraction of n-hexadecane is 35% to 45%; the color developer is tetradecyl p-hydroxybenzoate.

[0013] By employing the above technical solution, n-octadecane and n-hexadecane form a eutectic mixture at a set mass ratio, controlling the phase transition temperature within a suitable range perceptible to human skin. The color developer, tetradecyl p-hydroxybenzoate, contains a long carbon chain and a benzene ring, exhibiting a significant steric hindrance effect during color development and fading. This steric hindrance prevents irreversible crystallization and aggregation of leuco dye molecules during multiple phase transition cycles, ensuring the sensitivity of the coating's color change response and the color development effect.

[0014] Preferably, the specific preparation method of the double bond modified hydrophobic fumed silica is as follows: 100.0 parts by weight of hydrophilic fumed silica are added to a mixed solvent of water and ethanol and stirred and dispersed. The mixture is heated to 50-70°C and the pH of the suspension is adjusted to 4.0-5.0 with glacial acetic acid. Then, 5.0-10.0 parts by weight of γ-methacryloyloxypropyltrimethoxysilane are added dropwise under mechanical stirring, and the mixture is refluxed at 50-70°C for 2.0-4.0 hours. The solid precipitate is collected by centrifugation, washed, and dried to obtain the final product.

[0015] By employing the above-mentioned technical solution, γ-methacryloyloxypropyltrimethoxysilane undergoes hydrolysis under slightly acidic conditions to generate silanol groups. These silanol groups undergo a condensation reaction with free hydroxyl groups on the surface of hydrophilic fumed silica, removing water molecules and thus grafting methacryloyloxy groups with carbon-carbon double bonds onto the silica surface. This process transforms the hydrophilic surface into a hydrophobic surface, enabling it to adsorb hydrophobic phase-change solvents. Furthermore, it provides crucial carbon-carbon double bond sites, laying the material foundation for subsequent participation in the hydrosilylation reaction of silicone solutions.

[0016] Secondly, the present invention provides a heat-sensitive color-changing fabric, which adopts the following technical solution: A heat-sensitive color-changing fabric includes a textile fabric substrate and a heat-sensitive color-changing coating attached to the surface of the substrate, wherein the heat-sensitive color-changing coating is formed by cross-linking and curing of the heat-sensitive color-changing coating material provided in the first aspect above.

[0017] By employing the above technical solution, the heat-sensitive color-changing coating material is cross-linked and cured in situ on the surface of the textile substrate. The waterborne polyurethane dispersion forms a film under the action of a polycarbodiimide waterborne cross-linking agent, forming an interpenetrating polymer system with the three-dimensional cross-linked silicone network backbone. The polyurethane segments provide high adhesion to textile fibers and mechanical abrasion resistance, while the silicone network grafted with silica particles imparts excellent hydrophobicity and leak-proof properties to the coating, ultimately resulting in a functional fabric with high wash resistance and color-changing stability.

[0018] Preferably, the heat-sensitive color-changing coating is formed by uniformly applying the heat-sensitive color-changing coating material to the surface of the textile substrate using a doctor blade coating machine, controlling the wet film thickness to be 50-120 μm, and then cross-linking and curing it.

[0019] By adopting the above technical solution, a wet film thickness of 50-120μm ensures that there are certain effective color-changing components on the fabric per unit area to produce a color-changing effect, while avoiding the problems of delayed heat transfer and stiff fabric feel caused by excessive coating thickness.

[0020] Preferably, the heat-sensitive color-changing coating is formed by applying the heat-sensitive color-changing coating material to the surface of the textile substrate and then cross-linking and curing it using a three-stage stepped temperature control process. The three-stage stepped temperature control process is as follows: pre-baking at 70-85°C for 1.5-2.5 minutes, transitioning to dehydration at 95-105°C for 1.0-2.0 minutes, and high-temperature cross-linking and curing at 140-150°C for 1.0-2.0 minutes, followed by cooling after fabric removal.

[0021] By adopting the above technical solution, the stepped heating mechanism is beneficial to the film formation quality. The pre-baking stage at 70-85℃ allows the moisture in the waterborne polyurethane dispersion to evaporate, preventing rapid boiling of water vapor that could lead to micropores and pinhole defects in the paint film. The transitional dehydration stage at 95-105℃ removes residual moisture, preventing free water molecules from consuming the silane-hydrogen bonds in the polymethylhydrosiloxane in the subsequent high-temperature stage, thus generating hydrogen gas and causing foaming. The high-temperature crosslinking stage at 140-150℃ breaks the coordination bonds of the platinum complex, restoring catalytic activity and completing the hydrosilylation reaction within 1.0-2.0 minutes, thus completing the chemical anchoring of the silica particles and the macromolecular crosslinking of the silicone network. After the fabric cools, the crosslinked structure is fixed, giving the fabric its final mechanical strength.

[0022] Thirdly, the present invention provides a method for preparing a heat-sensitive color-changing coating material as described in the first aspect above, employing the following technical solution: A method for preparing a heat-sensitive color-changing coating material includes the following steps: The phase change solvent, the leuco dye and the color developer are heated and melted, and then the double bond modified hydrophobic fumed silica is added for high shear dispersion. The mixture is then cooled to obtain a color-changing slurry for later use. After mixing and stirring the vinyl-terminated polydimethylsiloxane, the polymethylhydrosiloxane, and the temperature threshold delay agent until homogeneous, the platinum catalyst is added dropwise and stirring is continued to obtain a dormant silicone crosslinking liquid; The prepared color-changing slurry was added to the prepared dormant silicone crosslinking liquid and stirred evenly. The aqueous polyurethane dispersion and the polycarbodiimide aqueous crosslinking agent were slowly added and stirred continuously to obtain a liquid slurry of heat-sensitive color-changing coating material.

[0023] By employing the above technical solution, the color-changing component and the crosslinking component are prepared separately in the process. A shielding-type color-changing slurry is prepared first, utilizing hydrodynamic shearing to disperse the liquid color-changing substance into the pores of silica. In the preparation of the silicone solution, a delay agent is mixed first before adding the platinum catalyst to prevent excessively high local concentrations from causing explosive polymerization. Finally, in the compounding stage, the dormant system is mixed with the polyurethane system to ensure that the prepared liquid slurry has good rheological stability and a long operating window.

[0024] Preferably, the specific steps for cooling down to obtain the color-changing slurry for later use are as follows: the phase change solvent, the leuco dye, and the color developer are added to a reactor with a heating jacket, and the temperature is raised to 60-70°C to completely melt the phase change solvent, the leuco dye, and the color developer; then a high-shear dispersion emulsifier with a speed of 3000 rpm is turned on, and the double bond modified hydrophobic fumed silica is slowly added in portions, and shear dispersion is continued for 15-30 minutes, and then the temperature is lowered to 25°C for later use.

[0025] By employing the above technical solution, a temperature of 60–70°C ensures the phase change solvent remains in a low-viscosity liquid state, while a rotation speed of 3000 rpm provides shear stress, breaking down secondary agglomerates formed between silica particles due to van der Waals forces and exposing the porous structure. Simultaneously, the internal frictional heat generated during dispersion maintains the system in a molten state, allowing the liquid substance to wet and fill the mesopores under the dual drive of capillary effect and applied mechanical force. After cooling to 25°C, the phase change solvent solidifies, leaving the dye and color developer within the pores, forming a dry powder or highly viscous paste-like color-changing slurry for later use.

[0026] Preferably, the specific steps for obtaining the dormant silicone crosslinking liquid by continuing stirring are as follows: at room temperature, the vinyl-terminated polydimethylsiloxane and the polymethylhydrosiloxane are mixed evenly, the temperature threshold delay agent is added, and the mixture is stirred at 200 rpm for 15 minutes. The platinum catalyst is then added dropwise, and the mixture is stirred for another 5 minutes.

[0027] By employing the above technical solution, the matrix containing double bonds and silicon-hydrogen bonds is first mixed uniformly and the temperature threshold retardant is fully dissolved to ensure that the retardant molecules achieve a uniform dispersion in the liquid phase. Then, a platinum catalyst is added dropwise. After entering the liquid, the catalyst coordinates and blocks the surrounding excess retardant molecules, preventing localized micro-crosslinking that could lead to the formation of colloidal particles without the protection of the retardant.

[0028] This invention provides a heat-sensitive color-changing coating material, its preparation method, and a fabric. It offers the following advantages: 1. This invention utilizes double-bond modified hydrophobic fumed silica to adsorb phase change solvents, leuco dyes, and color developers. The mesoporous structure of the silica physically confines the liquid-phase system. Simultaneously, during the cross-linking and curing process, the carbon-carbon double bonds on the silica surface undergo addition reactions with the silane-hydrogen bonds of polymethylhydrosiloxane, allowing the silica particles carrying the color-changing substances to covalently integrate into the three-dimensional cross-linked silicone network framework. This structure restricts the leakage of the internal phase change solvent during heating and melting, improving the water resistance and cyclic color-changing life of the heat-sensitive color-changing coating.

[0029] 2. This invention uses a complex of 3-methyl-1-butyn-3-ol and thiuram as a temperature threshold delay agent. At room temperature, this complex coordinates with the platinum catalyst, blocking the catalytically active sites of platinum atoms, inhibiting the crosslinking reaction of the silicone system, maintaining the low viscosity of the slurry, and extending the operating window of the coating process. When heated to the curing temperature, the coordination bonds break, the catalyst regains activity, and the addition reaction is completed, thus solving the problem of early curing of the crosslinking system at room temperature.

[0030] 3. This invention combines an aqueous polyurethane dispersion with a silicone crosslinking liquid. During the curing and film-forming stage, the aqueous polyurethane forms a film under the action of a polycarbodiimide crosslinking agent, forming an interpenetrating polymer matrix with the silicone network. The polyurethane component improves the adhesion of the coating to the textile substrate and its mechanical abrasion resistance, while the silicone network grafted with silica particles provides a hydrophobic surface, improving the defects of easy aggregation and precipitation of discoloration particles in the matrix and insufficient coating adhesion. Attached Figure Description

[0031] Figure 1 This is a bar chart comparing the relative integrated area of ​​the characteristic functional groups in the Fourier transform infrared spectra of the coating film before and after stepped temperature-controlled curing in Example 1 of the present invention. Figure 2 This is a comparison curve of the heating and cooling heat flow of the coating powder after complete curing in Examples 1 and 4 of the present invention. Figure 3 A bar chart comparing the hydrostatic pressure resistance test results of the coated fabrics of Embodiment 1, Comparative Example 3, and Comparative Example 5 of the present invention; Figure 4 This is a bar chart comparing the total color difference values ​​of the coated fabrics of Embodiment 1 and Comparative Example 4 under hot and cold state switching. Figure 5 This is a bar chart comparing the surface whiteness of the coated fabrics of Example 1 and Comparative Example 1 before and after accelerated aging under high and low temperature alternation. Figure 6 This is a dual Y-axis comparison chart of the color difference and functional retention rate of the coated fabrics of Example 1 and Comparative Example 2 after undergoing water washing and abrasion cycle tests. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings, preparation examples, embodiments, comparative examples, and test examples. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] Preparation Examples 1-4: Preparation Example 1: This preparation example provides a method for preparing double-bond modified hydrophobic fumed silica, including the following steps: (1) Preparation of mixed solvent: Mix 1500.0g of anhydrous ethanol and 150.0g of deionized water evenly; then add 100.0g of hydrophilic fumed silica (BET specific surface area of ​​200-300m²). 2 / g) is slowly added to the mixed solvent in batches and dispersed under high shear mechanical stirring at room temperature for 30 minutes to form a fluidized and uniform suspension; (2) Raise the ambient temperature and keep it constant at 60°C, then slowly add an appropriate amount of glacial acetic acid to adjust the pH of the suspension to 4.5; (3) Under continuous mechanical stirring, 7.5 g of γ-methacryloxypropyltrimethoxysilane (KH-570) was slowly added dropwise to the above suspension. After the addition was completed, the mixture was refluxed at 60°C for 3.0 hours. (4) After the reaction is complete, the mixture is centrifuged at 6000 rpm to separate the solid precipitate and wash the solid product three times with anhydrous ethanol to completely remove unreacted silane coupling agent and residual water. (5) The washed solid product is transferred to a vacuum oven and dried at 80°C for 12 hours. After cooling, it is ground and dispersed to obtain the double bond modified hydrophobic fumed silica.

[0034] Preparation Example 2: This preparation example provides a method for preparing double-bond modified hydrophobic fumed silica, including the following steps: (1) Preparation of mixed solvent: Mix 1500.0g of anhydrous ethanol and 150.0g of deionized water evenly; then add 100.0g of hydrophilic fumed silica (BET specific surface area of ​​200-300m²). 2 / g) is slowly added to the mixed solvent in batches and dispersed under high shear mechanical stirring at room temperature for 30 minutes to form a fluidized and uniform suspension; (2) Raise the ambient temperature and keep it constant at 50°C, then slowly add an appropriate amount of glacial acetic acid to adjust the pH of the suspension to 4.0; (3) Under continuous mechanical stirring, 5.0 g of γ-methacryloxypropyltrimethoxysilane (KH-570) was slowly added dropwise to the above suspension. After the addition was completed, the mixture was refluxed at 50 °C for 2.0 hours. (4) The subsequent centrifugation, washing, drying and grinding steps are exactly the same as those in Preparation Example 1, that is, the double bond modified hydrophobic fumed silica is obtained.

[0035] Preparation Example 3: This preparation example provides a method for preparing double-bond modified hydrophobic fumed silica, including the following steps: (1) Preparation of mixed solvent: Mix 1500.0g of anhydrous ethanol and 150.0g of deionized water evenly; then add 100.0g of hydrophilic fumed silica (BET specific surface area of ​​200-300m²). 2 / g) is slowly added to the mixed solvent in batches and dispersed under high shear mechanical stirring at room temperature for 30 minutes to form a fluidized and uniform suspension; (2) Raise the ambient temperature and keep it constant at 70°C, then slowly add an appropriate amount of glacial acetic acid to adjust the pH of the suspension to 5.0; (3) Under continuous mechanical stirring, 10.0 g of γ-methacryloxypropyltrimethoxysilane (KH-570) was slowly added dropwise to the above suspension. After the addition was completed, the mixture was refluxed at 70°C for 4.0 hours. (4) The subsequent centrifugation, washing, drying and grinding steps are exactly the same as those in Preparation Example 1, that is, the double bond modified hydrophobic fumed silica is obtained.

[0036] Preparation Example 4: This preparation example provides a method for preparing double-bond modified hydrophobic fumed silica, including the following steps: (1) Preparation of mixed solvent: Mix 1500.0g of anhydrous ethanol and 150.0g of deionized water evenly; then add 100.0g of hydrophilic fumed silica (BET specific surface area of ​​200-300m²). 2 / g) is slowly added to the mixed solvent in batches and dispersed under high shear mechanical stirring at room temperature for 30 minutes to form a fluidized and uniform suspension; (2) Raise the ambient temperature and keep it constant at 60°C, then slowly add an appropriate amount of glacial acetic acid to adjust the pH of the suspension to 4.5; (3) Under continuous mechanical stirring, 7.5 g of γ-methacryloxypropyltrimethoxysilane (KH-570) was slowly added dropwise to the above suspension. After the addition was completed, the mixture was refluxed at 60°C for 2.0 hours (the reaction time was shortened compared to Preparation Example 1). (4) The subsequent centrifugation, washing, drying and grinding steps are exactly the same as those in Preparation Example 1, that is, the double bond modified hydrophobic fumed silica is obtained.

[0037] Examples 1-4: Example 1: This embodiment provides a method for preparing a heat-sensitive color-changing coating material and fabric, including the following steps: (1) Preparation of mesoporous shielded color-changing slurry: 10.0 parts by weight of phase change solvent (mass ratio of n-octadecane to n-hexadecane of 6.5:3.5), 1.5 parts by weight of leuco dye (OBD-2) and 2.5 parts by weight of color developer (tetradecyl p-hydroxybenzoate) were added to a reactor with a heating jacket, heated to 65°C and stirred at low speed for 20 minutes to completely melt it. Then, a high shear dispersion emulsifier (speed 3000 rpm) was turned on, and 4.0 parts by weight of the modified silica obtained in Preparation Example 1 were slowly added in batches. The mixture was continuously sheared and dispersed for 20 minutes to allow the liquid phase to be fully adsorbed into the mesopores of the silica. Then, the mixture was cooled to 25°C for later use. (2) Preparation of dormant silicone crosslinking liquid: At room temperature, 5.5 parts by weight of vinyl-terminated polydimethylsiloxane (Vi-PDMS) and 0.6 parts by weight of polymethylhydrosiloxane (PMHS) were mixed evenly, and 0.05 parts by weight of temperature threshold delay agent (3-methyl-1-butyn-3-ol and thiuram complex) were added. After stirring at 200 rpm for 15 minutes, 0.1 parts by weight of platinum catalyst were added dropwise and stirring was continued for 5 minutes. (3) Compound final state waterborne coating slurry: Add all the color-changing slurry obtained in step (1) to the crosslinking liquid in step (2), and stir evenly at a low speed of 80 rpm using an anchor stirrer; then slowly add 60.0 parts by weight of waterborne polyurethane dispersion (WPU) and 2.0 parts by weight of polycarbodiimide waterborne crosslinking agent, and continue stirring for 30 minutes to obtain a single-component heat-sensitive color-changing waterborne coating slurry; (4) Substrate coating: The above slurry is evenly coated on the surface of the pretreated textile fabric using a doctor blade coating machine, and the wet film thickness is controlled to be 80 μm. (5) Stepped temperature control for dehydration and cross-linking curing: The coated fabric is continuously fed into a multi-temperature zone tenter frame and undergoes the following processes in sequence: pre-drying at 75℃ for 2.0 minutes; dehydration at 100℃ for 1.5 minutes; and finally cross-linking and grafting at 145℃ for 1.5 minutes. After cooling, the finished color-changing fabric is obtained.

[0038] Example 2: This embodiment provides a method for preparing a heat-sensitive color-changing coating material and fabric, including the following steps: (1) Preparation of mesoporous shielded color-changing slurry: 5.0 parts by weight of phase change solvent (mass ratio of n-octadecane to n-hexadecane is 6.5:3.5), 0.5 parts by weight of leuco dye and 1.0 parts by weight of color developer were added to the reaction vessel, heated to 60°C and stirred until completely melted. Then, a high shear dispersion emulsifier was turned on, and 2.0 parts by weight of the modified silica obtained in Preparation Example 2 were slowly added in batches. Shear dispersion was continued for 15 minutes, and then the temperature was lowered to 25°C for later use. (2) Preparation of dormant silicone crosslinking solution: At room temperature, mix 3.0 parts by weight of Vi-PDMS and 0.3 parts by weight of PMHS evenly, add 0.02 parts by weight of temperature threshold delay agent, stir for 15 minutes, then add 0.05 parts by weight of platinum catalyst, and continue stirring for 5 minutes; (3) Compound final state waterborne coating slurry: Add the color-changing slurry obtained in step (1) to the crosslinking liquid in step (2) and stir at low speed until uniform; then slowly add 50.0 parts by weight of WPU and 1.0 parts by weight of polycarbodiimide waterborne crosslinking agent, and continue stirring for 30 minutes to obtain the coating slurry; (4) Substrate coating: The above slurry is evenly coated on the surface of the textile fabric, and the wet film thickness is controlled to be 50 μm; (5) Stepped temperature control for dehydration and cross-linking curing: The coated fabric is fed into a tenter frame and undergoes the following processes in sequence: pre-drying at 70℃ for 1.5 minutes; dehydration at 95℃ for 1.0 minute; and finally cross-linking and grafting at 140℃ for 1.0 minute. After cooling, the finished color-changing fabric is obtained.

[0039] Example 3: This embodiment provides a method for preparing a heat-sensitive color-changing coating material and fabric, including the following steps: (1) Preparation of mesoporous shielded color-changing slurry: 15.0 parts by weight of phase change solvent (mass ratio of n-octadecane to n-hexadecane of 6.5:3.5), 2.5 parts by weight of leuco dye and 4.0 parts by weight of color developer were added to the reaction vessel, heated to 70°C and stirred until completely melted. Then, a high shear dispersion emulsifier was turned on, and 6.0 parts by weight of the modified silica obtained in Preparation Example 3 were slowly added in batches. Shear dispersion was continued for 30 minutes, and then the temperature was lowered to 25°C for later use. (2) Preparation of dormant silicone crosslinking solution: At room temperature, 8.0 parts by weight of Vi-PDMS and 1.0 parts by weight of PMHS are mixed evenly, 0.08 parts by weight of temperature threshold delay agent is added, and after stirring for 15 minutes, 0.15 parts by weight of platinum catalyst is added dropwise, and stirring is continued for 5 minutes. (3) Compound final state waterborne coating slurry: Add the color-changing slurry obtained in step (1) to the crosslinking liquid in step (2) and stir at low speed until uniform; then slowly add 70.0 parts by weight of WPU and 3.0 parts by weight of polycarbodiimide waterborne crosslinking agent, and continue stirring for 30 minutes to obtain the coating slurry; (4) Substrate coating: The above slurry is evenly coated on the surface of the textile fabric, and the wet film thickness is controlled to be 120 μm; (5) Stepped temperature control for dehydration and cross-linking curing: The coated fabric is fed into a tenter frame and undergoes the following processes in sequence: pre-drying at 85℃ for 2.5 minutes; dehydration at 105℃ for 2.0 minutes; and finally cross-linking and grafting at 150℃ for 2.0 minutes. After cooling, the finished color-changing fabric is obtained.

[0040] Example 4: This embodiment provides a method for preparing a heat-sensitive color-changing coating material and fabric, including the following steps: (1) Preparation of mesoporous shielded color-changing slurry: 10.0 parts by weight of phase change solvent (the ratio of n-octadecane to n-hexadecane was slightly adjusted to 5.5:4.5 by weight), 1.5 parts by weight of leuco dye and 2.5 parts by weight of color developer were added to the reaction vessel, heated to 65°C and stirred until completely melted. Then, a high shear dispersion emulsifier was turned on, and 4.0 parts by weight of the modified silica obtained in Preparation Example 4 were slowly added in batches. The mixture was continuously sheared and dispersed for 20 minutes, and then cooled to 25°C for later use. (2) Preparation of dormant silicone crosslinking solution: The preparation ratio and operation steps at room temperature are exactly the same as in Example 1; (3) Compound final state waterborne coating slurry: The operation steps for mixing and adding WPU and polycarbodiimide are exactly the same as in Example 1; (4) Substrate coating: The wet film thickness is controlled at 80 μm; (5) Stepped temperature control for dehydration and cross-linking curing: The baking process parameters are exactly the same as in Example 1 (pre-baking at 75℃ for 2.0 minutes; dehydration at 100℃ for 1.5 minutes; cross-linking at 145℃ for 1.5 minutes). After cooling, the finished color-changing fabric is obtained.

[0041] Comparative Examples 1-5: Comparative Example 1: Compared to Example 1, the difference lies in the omission of the organosilicon crosslinking system (Vi-PDMS, PMHS, catalyst, and retarder) and the mesoporous silica system. The phase change solvent, leuco dye, and color developer are melted and directly mixed with the waterborne polyurethane dispersion (WPU), and after coating, it is directly cured by single-stage baking at 145°C. All other aspects are the same.

[0042] Comparative Example 2: Compared with Example 1, the difference is that the modified silica (double bond modified hydrophobic fumed silica) obtained in preparation example 1 in step (1) is replaced with an equal weight of unmodified ordinary hydrophilic fumed silica, and all other aspects are the same.

[0043] Comparative Example 3: Compared with Example 1, the difference is that when compounding the final state waterborne coating slurry in step (3), the polycarbodiimide waterborne crosslinking agent is completely removed, while the rest are the same.

[0044] Comparative Example 4: Compared with Example 1, the difference is that the sterically hindered colorimetric agent tetradecyl p-hydroxybenzoate in step (1) is replaced with an equal weight of conventional active colorimetric agent bisphenol S, and all other aspects are the same.

[0045] Comparative Example 5: Compared with Example 1, the difference is that the three-stage stepped temperature control process is abandoned in step (5). The coated fabric is directly placed in a high-temperature zone of 145°C for 2.0 minutes for single-stage rapid drying and curing, and the rest of the formula and operation are the same.

[0046] Test Examples 1-4: Test Example 1: Sample Collection and Pretreatment. A pre-dried coating film obtained from the preparation process of Example 1, without the 145°C high-temperature crosslinking process, was vacuum-dried at room temperature as a control group before curing. Coatings from the surfaces of the finished fabrics obtained in Examples 1 and 4, prepared using a complete stepped temperature control process, were scraped off as experimental group samples. The collected coating scraps were pulverized into micron-sized powder in a mortar for testing.

[0047] Fourier transform infrared spectroscopy (FTIR) was performed. The powder sample to be tested was placed on the crystal surface of the ATR accessory, and the pressure of the pressure bar was adjusted to a suitable level. The test range was set to 4000 cm⁻¹. -1 Up to 400cm -1 The spectral resolution was set to 4cm. -1 The cumulative number of background and sample scans per session is 32.

[0048] After the test was completed, 2158cm was extracted. -1 The nearby Si-H stretching vibration peak and 1632 cm⁻¹ -1 Nearby C=C stretching vibration absorption peak data. Using baseline correction and area integration, with the stable Si-CH3 symmetric deformation vibration peak in the polydimethylsiloxane framework as an internal standard, the relative integrated area of ​​the characteristic peaks was calculated.

[0049] Differential scanning calorimetry (DSC) was performed. 5.2 to 6.8 mg of the cured coating powder from Examples 1 and 4 were accurately weighed using a precision balance, placed in a standard aluminum crucible, and sealed with a cap. The sample was placed in the DSC chamber, and dry, high-purity nitrogen gas at a flow rate of 50 mL / min was introduced as a purging protective gas. The test program was set as follows: the temperature was lowered from room temperature to 0°C at a cooling rate of 10°C / min, held at that temperature for 5 minutes to eliminate thermal history; the temperature was then increased to 70°C at a rate of 5°C / min, and the melting endothermic curve was recorded; after holding at 70°C for 5 minutes, the temperature was lowered to 0°C at a rate of 5°C / min, and the crystallization exothermic curve was recorded. The data were exported, and the peak temperature and enthalpy integral were extracted.

[0050] Table 1. Comparison of the relative integrated areas of infrared absorption peaks of characteristic groups in the coating before and after crosslinking and curing in Example 1.

[0051] Table 2. Differential scanning calorimetry data of cured coatings with different phase change solvent ratios

[0052] in conclusion: Based on the data in Table 1, combined with Figure 1 The characteristic functional groups of the coating film in Example 1 before and after stepped temperature-controlled curing are compared in a bar chart to analyze the spectral regularity. Figure 1 The horizontal axis represents the two states of the sample: the coating before curing and the coating after curing. The vertical axis represents the relative integral area of ​​the absorption peak. The figure shows 2158 cm⁻¹. -1 The dark gray column representing the characteristic peak of Si-H stretching vibration and the 1632 cm⁻¹ peak. -1 The light gray column with characteristic peak of C=C double bond stretching vibration at the top of the column, and referring to the specific integral area value above the column, shows that there are obvious Si-H stretching vibration absorption peaks and C=C double bond stretching vibration absorption peaks in the system before curing.

[0053] After crosslinking at 145℃, the relative integral areas of these two characteristic peaks decreased from 1.845 and 0.923 to 0.082 and 0.051, respectively. This group consumption pattern indicates that under platinum catalysis, the silane-hydrogen bonds in polymethylhydrosiloxane not only react with vinyl-terminated polydimethylsiloxane, but also undergo hydrosilylation reactions with the carbon-carbon double bonds on the methacryloyloxy groups introduced by KH-570 on the surface of modified fumed silica. At the microscopic level, a three-dimensional network crosslinked framework covalently linked to the organosilicon polymer segments and inorganic fumed silica particles is formed, realizing the chemical grafting and spatial anchoring of the color-changing carrier particles in the polymer matrix.

[0054] Based on the data in Table 2, combined with Figure 2 The differential scanning calorimetry (DSC) curves of the heating and cooling heat flux of the coating powder after complete curing in Examples 1 and 4 are shown to analyze the thermodynamic behavior. Figure 2 The horizontal axis represents the test temperature, and the vertical axis represents the heat flow rate. From the black solid line representing the heating-up endothermic curve of Example 1 and the black dashed line representing the cooling-up exothermic curve, and the dark gray solid line representing the heating-up endothermic curve of Example 4 and the dark gray dashed line representing the cooling-up exothermic curve, combined with the peak heat flow temperatures of the corresponding phase change processes marked above and below the curves, it can be seen that the cured coatings of Examples 1 and 4 both exhibit complete endothermic and exothermic behaviors within the test range.

[0055] In Example 1, the phase transition peak was 31.7℃. In Example 4, after adjusting the mass ratio of n-octadecane to n-hexadecane to 5.5:4.5, the phase transition peak shifted to 28.6℃, and the enthalpy values ​​of both stabilized between 45 J / g and 46 J / g. The phase transition solvent inside the coating did not lose its liquid-solid phase transition capability despite being in a high-temperature crosslinking system at 145℃, and the phase transition temperature point followed an inherent colligative law as the mixed alkane ratio changed. The phase transition mixture was confined within the mesoporous structure of silica, and the externally grafted polysiloxane network did not penetrate the mesopores to interfere with the molecular rearrangement of the phase transition substance. The color-changing system retained an independent thermodynamic response environment, verifying the feasibility of the phase transition threshold regulation mechanism and the network shielding mechanism.

[0056] Test Example 2: Cut finished color-changing fabrics from Examples 1, 3, and 5. Use a standard circular sampler to cut a 100cm² area. 2 Five parallel samples were prepared for each group of samples. All samples were placed in a constant temperature and humidity chamber and conditioned for 24 hours at 20°C and 65% relative humidity.

[0057] The test was conducted using a fully automatic hydrostatic pressure tester. The water tank of the tester was inspected and filled with deionized water at a temperature of 20°C. Air was then removed from the fixture base and the inside of the pipeline.

[0058] Place the sample with the coated surface facing the water surface in the center of the test area of ​​the fixture, flatten it, and then use a pneumatic pressure fixture to lock the edges to ensure that water does not leak from the side during the test.

[0059] The instrument's water pressure increment rate was set to 6.0 kPa / min. The test program was started, and the internal pumping system of the test instrument increased the water column pressure uniformly from zero. The tester continuously observed the water seepage on the back side (non-coated side) of the sample from above.

[0060] When a third water droplet seeps from a different location on the back surface of the sample, immediately press the stop button and record the instantaneous hydrostatic pressure value displayed on the instrument. Clean the residual water from the fixture and repeat the above operation until all parallel samples of all groups have been tested.

[0061] Table 3. Record of hydrostatic pressure resistance test data for coated fabrics in the examples and comparative examples.

[0062] in conclusion: Based on the data in Table 3, and combined with Figure 3 The bar charts showing the hydrostatic pressure resistance test results of the coated fabrics in Examples 1, 3, and 5 are used to analyze their water resistance performance. Figure 3The horizontal axis represents different sample groups, and the vertical axis represents the measured average hydrostatic pressure resistance, in kPa. From the light gray bars representing the average hydrostatic pressure of each sample group, and the corresponding average values ​​indicated above the bars, it can be seen that the average hydrostatic pressure of the coated fabric in Example 1 reached 82.26 kPa. Meanwhile, the black line segment representing the standard deviation (error bar) of the five parallel sample data above the column, and the distribution of dark gray dots representing the actual discrete measured values ​​of a single parallel sample test inside and outside the column, indicate that the data distribution of the five parallel samples in Example 1 is relatively concentrated, and the coating has high resistance to water pressure. In contrast, the average hydrostatic pressure of Comparative Example 3 decreased to 20.72 kPa, and the average hydrostatic pressure of Comparative Example 5 further decreased to 12.20 kPa.

[0063] Waterborne polyurethane dispersions contain bound water that is difficult to completely remove through conventional physical drying during film formation. In Example 1, polycarbodiimide undergoes thermal activation in the transition temperature range of 100°C, preferentially consuming the residual water bound in the polar network. Simultaneously, the step-by-step temperature control ensures that free water is gradually evaporated and discharged before reaching the high-temperature zone. The system is essentially anhydrous when entering the high-temperature crosslinking stage at 145°C, eliminating the interference of moisture on the crosslinking and molding of the organosilicon network.

[0064] Comparative Example 3, by removing polycarbodiimide, failed to consume the bound water in the polyurethane matrix. Comparative Example 5 skipped the pre-baking and transitional dehydration stages and directly entered a 145°C environment, leaving a large amount of liquid water inside the coating. Under high-temperature conditions, the water molecules retained in the system directly reacted violently with the Si-H bonds in the polymethylhydrosiloxane, releasing hydrogen gas.

[0065] The generated gas expands and escapes from the incompletely cured, high-viscosity semi-cured resin matrix, forming micropores and a foamed structure that penetrates the coating cross-section. These physical defects disrupt the dense, continuous phase of the coating matrix. In hydrostatic testing, externally pressurized water rapidly permeates along the internal micropore channels to the back surface of the fabric, causing a sharp drop in the maximum water column pressure that the material can withstand. The hydrostatic test results validate the synergistic effect of the stepped temperature control process and the chemical dehydrating agent in maintaining the dense microstructure of the coating and suppressing foaming defects caused by the hydroxyl side reaction. Test Example 3: Cut test samples of 5cm x 5cm from the finished color-changing fabrics of Example 1 and Comparative Example 4, avoiding the edges and creases. Randomly mark three circular test points with a diameter of 1cm on the surface of each sample.

[0066] Turn on the spectrophotometer and warm it up for 30 minutes. Perform zero-point and whiteboard calibration using the instrument's built-in standard black and white boards. Set the test light source to D65, the viewing angle to 10°, the measurement aperture to match the test point size, and the color space to the CIELab* system.

[0067] Set the temperature of the precision thermostatic test stage with semiconductor cooling / heating function to 15℃. After the temperature stabilizes, lay the sample flat on the thermostatic stage and let it sit for 5 minutes. Then, press the colorimeter probe vertically onto the test points marked on the sample in sequence, and measure and record the L*, a*, and b* values ​​of each point in the cold state (theoretical color development state).

[0068] Adjust the temperature of the constant temperature test bench to 45℃. After the temperature stabilizes again, let the sample continue to be kept at the constant temperature for 5 minutes to allow it to fully exceed the phase transition threshold. Measure and record the L*, a*, and b* values ​​of the corresponding test points in the hot state (theoretical achromatic state) again.

[0069] Export the data recorded by the instrument and apply it according to the CIE color difference formula. Calculate the total color difference value of each test point under the switching between hot and cold conditions.

[0070] Table 4. Record of color difference test data of coated fabrics in hot and cold states for Example 1 and Comparative Example 4

[0071] in conclusion: Based on the data in Table 4, combined with Figure 4 The bar chart comparing the total color difference values ​​of the coated fabrics of Example 1 and Comparative Example 4 under the switching between hot and cold states is used to analyze the color change response mechanism. Figure 4 The horizontal axis represents different sample groups, and the vertical axis represents the total color difference value calculated according to the CIE color difference formula. .

[0072] The light gray bars representing the average color difference of each group of samples in cold and hot states, combined with the specific average color difference values ​​above the bars, show that Example 1 exhibits color change capability when switching between cold and hot states. The dark gray dots distributed inside and above the bars, representing the actual color difference values ​​independently measured and calculated at three different test points on the surface of each sample, indicate that the total color difference values ​​at the three test points in Example 1 reach 50.62, 48.04, and 52.48, respectively.

[0073] After the three test points of Comparative Example 4 underwent the same temperature switching process, the L*, a*, and b* values ​​in the hot and cold states did not fluctuate. The actual total color difference values ​​were only 0.39, 0.77, and 0.35, respectively. The coating was in a whitened base color state, and the color-changing function failed.

[0074] The color-changing mechanism of leuco dyes depends on the release of protons by the chromogenic agent, which causes the lactone ring to open and develop color. In Example 1, the chromogenic agent used was tetradecyl p-hydroxybenzoate, which has hydrophobic carbon chains at its end groups. In the liquid phase-change solvent within the confined space of mesoscopic silica, the long-chain chromogenic agent spontaneously forms a self-assembling barrier similar to reverse micelles, hiding the phenolic hydroxyl groups in the structural core.

[0075] Spatial encapsulation physically isolates the phenolic hydroxyl groups during the high-temperature crosslinking stage at 145℃, blocking their contact pathway with the Si-H bonds in polymethylhydrosiloxane. The hydrosilylation reaction proceeds within the double bond system, preserving the chemical structure of the color developer. When the temperature drops below the crystallization point of the phase change solvent, solvent solidification causes the self-assembled encapsulation structure to disintegrate, exposing the phenolic hydroxyl groups and transferring protons to the leuco form, completing the cold-state color development process.

[0076] Comparative Example 4 replaced the color developer with bisphenol S. Bisphenol S molecules lack hydrophobic carbon chains and cannot form a self-assembled encapsulation barrier within the mesoporous system. During the high-temperature cross-linking and curing stage at 145℃, free phenolic hydroxyl groups undergo a dehydrogenation coupling side reaction with hydrogen-containing silicone oil. The color developer in the system is consumed as a reaction substrate, losing its proton-donating ability. When the coating cools to a cold state, due to the lack of color developer, the leuco dye cannot obtain protons and undergoes ring-opening rearrangement. The leuco color-changing mechanism within the coating is disrupted by chemical side reactions, paralyzing the color-changing response mechanism. Color difference data validated the design mechanism of using a molecular self-assembled barrier to protect the color developer from consumption by cross-linking side reactions.

[0077] Test Example 4: Cut the finished color-changing fabrics of Example 1, Comparative Example 1 and Comparative Example 2, and prepare aging test samples with a size of 10cm×10cm, washing test samples with a size of 4cm×10cm and friction test samples with a size of 5cm×20cm, respectively.

[0078] The aging test samples were placed in a high and low temperature alternating damp heat test chamber. The cycle program was set as follows: cooling to -10℃ at a rate of 3℃ / min, holding at that temperature for 1 hour, then heating to 60℃ at the same rate, holding at that temperature for 1 hour. This was repeated for 50 complete high and low temperature cycles. After the test, the samples were removed and allowed to recover at room temperature for 2 hours. Five CIE whiteness indices were randomly selected on the sample surface using a whiteness meter, and the arithmetic mean was recorded to assess the degree of surface blooming.

[0079] Place the wash test sample into a standard water wash fastness tester and add deionized water containing 0.5% standard washing solution. Set the water temperature to 40℃, the liquor ratio to 1:50, the rotation speed to 40 rpm, and the washing time to 30 minutes per cycle. Perform 30 consecutive washing cycles. After the washing cycle is complete, remove the sample and air dry it naturally in a cool, dark place.

[0080] The rubbing test sample was fixed on the flat test platform of the rubbing fastness tester. A standard dry white rubbing cloth was fixed to the reciprocating rubbing head, and the applied vertical pressure was set to 9N. 100 reciprocating dry rubbing tests were performed on the fabric surface at a rate of 1 time / second.

[0081] The L*, a*, and b* values ​​of the water-washed and rubbed samples were measured at 15℃ and 45℃ respectively using a spectrophotometer. The color difference value after treatment was calculated and compared with the initial color difference value before treatment to calculate the function retention rate.

[0082] Table 5. Data Record of Whiteness Test on Coating Surface Before and After High and Low Temperature Alternating Aging in Examples and Comparative Examples

[0083] Table 6. Test Data Recording of Color Difference and Retention Rate of Coatings in Examples and Comparative Examples after Water Washing and Friction Cycles

[0084] in conclusion: Based on the data in Table 5, combined with Figure 5 The bar charts showing the surface whiteness tests of the coated fabrics of Example 1 and Comparative Example 1 before and after accelerated aging under high and low temperature alternation are used to analyze the frosting defects. Figure 5 The horizontal axis represents different test groups, and the vertical axis represents the measured CIE whiteness index.

[0085] The figure shows a dark gray bar representing the initial whiteness index of the sample and a light gray bar representing the whiteness index after 50 high and low temperature cycles. Combined with the corresponding average whiteness measurement values ​​above the bars, it can be seen that in Example 1, after 50 high and low temperature cycles, the surface whiteness index slightly increased from 14.28 to 15.61, a change of +1.33, and no crystallization occurred on the surface. In Comparative Example 1, after the same alternating test, the whiteness index increased from 13.84 to 62.75, and a white crystalline precipitate appeared on the coating surface.

[0086] Based on the data in Table 6, combined with Figure 6 The dual Y-axis comparison of color difference and functional retention rate of the coated fabrics of Example 1 and Comparative Example 2 after undergoing water washing and abrasion cycle tests is used to analyze durability. Figure 6 The horizontal axis represents different test groups.

[0087] The left vertical axis represents the absolute value of the total color difference at the test point under the switching between hot and cold conditions, corresponding to the grouped bar chart in the figure. The dark gray bars represent the initial total color difference, the medium gray bars represent the color difference after 30 water washes, and the light gray bars represent the color difference after 100 dry rubbings. The vertical axis on the right represents the percentage of function retention, corresponding to the line graph that floats above the bar. The solid black line with black solid dots represents the water washing function retention rate, and the dashed black line with gray solid squares represents the friction function retention rate. The numbers above the columns and nodes represent the specific test values. As shown in the chart, in the washing and rubbing tests, Example 1 maintained a color-changing function retention rate of 92.51% and 90.99% after 30 washes and 100 dry rubs, respectively. Comparative Example 2 showed a color difference reduced to 19.34 after washing and 15.81 after rubbing, with corresponding retention rates decreasing to 39.77% and 32.51%, respectively.

[0088] In Comparative Example 1, fumed silica was lacking as a mesoporous adsorption carrier, and the phase change solvent was in a homogeneous blend state within the polyurethane resin matrix. Under continuous high and low temperature alternating stress, the phase change solvent repeatedly underwent volume expansion and contraction due to liquid-to-solid phase transitions. Free phase change substances continuously migrated to the coating surface along the pores between polymer macromolecular chain segments and recrystallized on the surface when the temperature dropped below the melting point. This migration led to a significant increase in the surface whiteness index, forming macroscopic frosting defects. Example 1 utilized mesopores constructed with fumed silica to adsorb and confine the phase change mixture within the pores through physical capillary forces, cutting off the path for the phase change substances to migrate outward.

[0089] In Comparative Example 2, a silica carrier was added, but the carrier surface was not grafted with a silane coupling agent. Silica particles were dispersed within a three-dimensional cross-linked network of polyurethane and silicone through physical forces such as van der Waals forces. Under physical shear stress from immersion and swelling in washing liquid, mechanical tumbling, and reciprocating dry friction, the physical interface between the carrier and the matrix resin delaminated. Silica particles loaded with the color-changing dye system detached and were lost from the coating matrix.

[0090] A decrease in the concentration of effective functional components leads to a decline in the color difference value of the material's color development under both hot and cold conditions. Example 1 modifies and preserves carbon-carbon double bonds, enabling the silica particles to undergo an addition reaction with polymethylhydrosiloxane, anchoring them covalently within a three-dimensional cross-linked network framework. The chemical bonding resists interfacial delamination caused by mechanical shearing and solvent swelling, ensuring the structural stability of the internal color-changing system under long-term external forces.

Claims

1. A heat-sensitive color-changing coating material, characterized in that, Made from the following ingredients in parts by weight: Phase change solvent 5.0–15.0 parts; Leuco dye: 0.5–2.5 parts; Color developer: 1.0–4.0 parts; Double-bond modified hydrophobic fumed silica, 2.0–6.0 parts; Vinyl-terminated polydimethylsiloxane 3.0–8.0 parts; 0.3–1.0 parts of polymethylhydrosiloxane; Temperature threshold delay agent: 0.02–0.08 parts; Platinum catalyst 0.05–0.15 parts; 50.0–70.0 parts of waterborne polyurethane dispersion; 1.0–3.0 parts of polycarbodiimide aqueous crosslinking agent; The temperature threshold delay agent is a complex of 3-methyl-1-butyn-3-ol and thiuram.

2. The heat-sensitive color-changing coating material according to claim 1, characterized in that, The weight ratio of the raw materials is as follows: 10.0 parts of phase change solvent; 1.5 parts of leuco dye; 2.5 parts color developer; 4.0 parts of double-bond modified hydrophobic fumed silica; 5.5 parts of vinyl-terminated polydimethylsiloxane; 0.6 parts of polymethylhydrosiloxane; 0.05 parts of temperature threshold delay agent; 0.1 parts platinum catalyst; 60.0 parts of waterborne polyurethane dispersion; 2.0 parts of polycarbodiimide waterborne crosslinking agent.

3. The heat-sensitive color-changing coating material according to claim 1, characterized in that, The phase change solvent is a mixture of n-octadecane and n-hexadecane, wherein the mass fraction of n-octadecane is 55%–65% and the mass fraction of n-hexadecane is 35%–45% based on the total mass of the phase change solvent; The color developer is tetradecyl p-hydroxybenzoate.

4. The heat-sensitive color-changing coating material according to claim 1, characterized in that, The specific preparation method of the double-bond modified hydrophobic fumed silica is as follows: 100.0 parts by weight of hydrophilic fumed silica were added to a mixed solvent of water and ethanol and stirred to disperse. The mixture was heated to 50-70°C and the pH of the suspension was adjusted to 4.0-5.0 with glacial acetic acid. Subsequently, 5.0–10.0 parts by weight of γ-methacryloyloxypropyltrimethoxysilane were added dropwise under mechanical stirring, and the mixture was refluxed at 50–70°C for 2.0–4.0 hours. After centrifugation to collect the solid precipitate, it is washed and dried to obtain the final product.

5. A method for preparing a heat-sensitive color-changing coating material as described in any one of claims 1-4, characterized in that, Includes the following operations: The phase change solvent, the leuco dye and the color developer are heated and melted, and then the double bond modified hydrophobic fumed silica is added for high shear dispersion. The mixture is then cooled to obtain a color-changing slurry for later use. After mixing and stirring the vinyl-terminated polydimethylsiloxane, the polymethylhydrosiloxane, and the temperature threshold delay agent until homogeneous, the platinum catalyst is added dropwise and stirring is continued to obtain a dormant silicone crosslinking liquid; The prepared color-changing slurry was added to the prepared dormant silicone crosslinking liquid and stirred evenly. The aqueous polyurethane dispersion and the polycarbodiimide aqueous crosslinking agent were slowly added and stirred continuously to obtain a liquid slurry of heat-sensitive color-changing coating material.

6. The preparation method according to claim 5, characterized in that, The specific steps for obtaining the color-changing slurry by cooling are as follows: The phase change solvent, the leuco dye, and the color developer are added to a reaction vessel with a heating jacket, and the temperature is raised to 60-70°C to completely melt the phase change solvent, the leuco dye, and the color developer. Then, a high-shear dispersion emulsifier with a speed of 3000 rpm was turned on, and the double-bond modified hydrophobic fumed silica was slowly added in batches. The mixture was continuously sheared and dispersed for 15 to 30 minutes, and then cooled to 25°C for later use.

7. The preparation method according to claim 5, characterized in that, The specific steps for obtaining the dormant silicone crosslinking solution by continuing stirring are as follows: At room temperature, the vinyl-terminated polydimethylsiloxane and the polymethylhydrosiloxane are mixed evenly, the temperature threshold delay agent is added, and the mixture is stirred at 200 rpm for 15 minutes. The platinum catalyst is then added dropwise, and the mixture is stirred for another 5 minutes.

8. A heat-sensitive color-changing fabric, characterized in that, The invention comprises a textile fabric substrate and a heat-sensitive color-changing coating attached to the surface of the substrate, wherein the heat-sensitive color-changing coating is formed by cross-linking and curing of the heat-sensitive color-changing coating material according to any one of claims 1-4.

9. The heat-sensitive color-changing fabric according to claim 8, characterized in that, The heat-sensitive color-changing coating is formed by uniformly applying the heat-sensitive color-changing coating material to the surface of the textile substrate using a doctor blade coating machine, controlling the wet film thickness to be 50-120 μm, and then cross-linking and curing it.

10. The heat-sensitive color-changing fabric according to claim 8, characterized in that, The heat-sensitive color-changing coating is formed by applying the heat-sensitive color-changing coating material to the surface of the textile substrate and then cross-linking and curing it using a three-stage stepped temperature control process. The three-stage stepped temperature control process is as follows: The fabric is pre-dried at 70–85°C for 1.5–2.5 minutes, then dehydrated at 95–105°C for 1.0–2.0 minutes, and finally cross-linked and cured at 140–150°C for 1.0–2.0 minutes. After cooling, the fabric is ready.

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