A thermochromic polyamide fiber and a method for preparing the same

Abstract

The present application belongs to the technical field of functional fiber and smart textile preparation, and relates to a thermochromic polyamide fiber and a preparation method thereof. The preparation method adopts a melt spinning process, and the spinning raw material comprises a polyamide resin component, a thermochromic microcapsule component and a rheological modifier component. The thermochromic microcapsule has a core-shell structure, the core layer is an organic thermochromic material, the shell layer is melamine, and a silica coating layer is further arranged on the surface of the shell layer, and the silica coating layer is combined with the shell layer through a covalent bond. The rheological modifier is a rare earth ion organic complex. The rare earth ion organic complex is a lanthanide series rare earth ion organic complex or a cerium series rare earth ion organic complex. The thermochromic polyamide fiber is prepared by the preparation method. The present application can improve the heat resistance and shear resistance of the thermochromic microcapsule, improve the rheological behavior of the polyamide melt, effectively protect the mechanical strength and color change function of the fiber while reducing the thermal damage of the microcapsule in the spinning process.

Description

Technical Field

[0001] This invention belongs to the field of functional fiber and smart textile preparation technology, and relates to a thermochromic polyamide fiber and its preparation method. Background Technology

[0002] Thermochromic polyamide fibers are a class of smart fibers capable of reversible color changes with temperature, showing broad application prospects in fields such as body temperature monitoring, smart clothing, anti-counterfeiting labels, and high-temperature early warning. Preparing functional fibers by melt-blending thermochromic materials with polyamide is an effective way to obtain smart fibers with sensitive color-changing response and wash resistance. However, the melt-spinning temperature of polyamide is relatively high, and the shear rate in the screw and spinneret areas is large, which places extremely high demands on the heat resistance and shear strength of the added thermochromic materials.

[0003] Currently, thermochromic functions are mostly achieved through microencapsulation technology to protect the sensitive color-changing core material. Melamine is a commonly used microcapsule shell material, which has high cross-linking density and good thermal stability. However, the shell itself is brittle and is prone to cracking under high temperature and high shear spinning conditions, which leads to core material leakage and loss of color-changing function. Therefore, improving the structural stability of microcapsules in the polyamide melt spinning process is the key to achieving industrialization.

[0004] Patent application CN116236985A uses KH560 in-situ modified epoxy resin as the wall material. The prepared microcapsule wall material has a dense structure, but the glass transition temperature of epoxy resin is relatively low. Under the high-temperature processing conditions of polyamide melt spinning, it is easy to soften and it is difficult to continuously provide effective protection for the core material.

[0005] Patent application CN117619285A improves the impact resistance of microcapsules by constructing a "rigid inside and flexible outside" double-layer polyurea shell structure, but the heat resistance of its flexible outer shell layer is limited, and the structure is still prone to damage under the dual effects of high temperature and high shear during the spinning process.

[0006] Patent application CN121023667A utilizes the Pickering effect of SiO2 nanoparticles to form a stable oil-in-water emulsion, prepares a polyurea / silica hybrid wall material through interfacial polymerization, and encapsulates the phase change core material n-octadecane within it; however, this scheme is a one-step bulk construction process starting from microcapsule preparation, which has high process control requirements, and is mainly developed for phase change material core materials. For thermochromic core material systems with higher protection requirements, there is still room for further improvement in the protective effect.

[0007] Currently, there are few reports on the use of thermochromic microcapsules in polyamide melt spinning. Most thermochromic polyamide products introduce the thermochromic material onto the surface of fibers or fabrics through finishing processes such as coating and printing. The very few thermochromic fibers prepared using melt spinning processes use polypropylene as the matrix. Since the spinning temperature of polypropylene is much lower than that of polyamide, the microcapsules can meet the processing requirements without modification, and the related technology cannot be directly transferred to polyamide spinning systems. While finishing methods are simple, they suffer from poor abrasion and wash resistance, easily affecting the fabric's hand feel and breathability, and failing to achieve uniform bulk color change, thus limiting the product's application range and service life.

[0008] Therefore, it is necessary to provide a thermochromic polyamide fiber and its preparation method to effectively improve the structural stability of thermochromic microcapsules during polyamide melt spinning, while ensuring the comprehensive performance of the fiber, so as to solve the technical problems existing in the prior art. Summary of the Invention

[0009] The purpose of this invention is to solve the problems existing in the prior art and to provide a thermochromic polyamide fiber and its preparation method.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0011] A method for preparing thermochromic polyamide fiber, comprising a melt spinning process, wherein the spinning raw materials include a polyamide resin component, a thermochromic microcapsule component, and a rheology modifier component;

[0012] The thermochromic microcapsule has a core-shell structure. The core layer is an organic thermochromic material, the shell layer is melamine, and the shell surface is also provided with a silica coating layer. The silica coating layer and the shell layer are bonded by covalent bonds, resulting in high interfacial bonding strength. It can be directly adapted to existing mature melamine-based thermochromic microcapsule products without the need to redevelop the core material encapsulation process.

[0013] The 5% thermal weight loss temperature of thermochromic microcapsules is 317-332℃;

[0014] The rheology modifier is a rare earth ion organic complex; the rare earth ion organic complex is a lanthanide rare earth ion organic complex or a cerium-based rare earth ion organic complex, which can effectively broaden the processing window of polyamide melt spinning and improve the operational stability of the production process.

[0015] In the spinning raw materials, the mass of the rheology modifier is 0.5wt%-5wt% of the mass of the polyamide resin;

[0016] The temperature of each zone of the screw in melt spinning is 210-240℃. Specifically, the screw in melt spinning has five zones: zone 1 is 215-225℃, zone 2 is 230-238℃, zone 3 is 236-240℃, zone 4 is 238-240℃, and zone 5 is 238-240℃.

[0017] This invention addresses two key aspects. First, it incorporates a silica coating layer with high rigidity and heat resistance onto the thermochromic microcapsules. This coating layer simultaneously increases the thermal decomposition temperature and shear resistance of the microcapsules. Furthermore, the covalent bonding between the silica coating layer and the shell strengthens the interfacial bonding, further enhancing the thermal decomposition temperature and shear resistance. Second, it adds a rheology modifier to the spinning raw material. This modifier weakens the hydrogen bonding between polyamide molecular chains, reduces the apparent viscosity of the polyamide melt, and improves the melt's rheological behavior. This, in turn, helps lower the spinning temperature or reduce internal frictional heat during processing, thereby minimizing thermal damage to the thermochromic microcapsules and ensuring the fiber's color-changing function. These two strategies work together to guarantee the fiber's excellent color-changing function and overall performance.

[0018] In the existing technology for preparing polyamide fibers, the spinning temperature is generally high. For example, the spinning temperature of patent application CN103147158A is above 260℃ (screw temperature is 260±2℃ in zone 1, 266±2℃ in zone 2, and 260±6℃ in zones 3, 4, and 5), the spinning temperature of patent application CN110820079A is 250-295℃, the spinning temperature of patent application CN201010237604.X is 245-265℃, the spinning temperature of patent application CN201210483226.2 is 252-255℃, the spinning temperature of patent application CN202111357991.5 is 255-285℃, and the spinning temperature of patent application CN201710131351.X is 250-320℃. This invention reduces the spinning temperature to below the level of existing technologies (210-240℃) by adding an appropriate amount of rheology modifier. At the same time, the spinning temperature does not exceed the initial decomposition temperature of the thermochromic microcapsules. This can minimize the thermal damage to the thermochromic microcapsules during melt spinning and ensure the color-changing function of the fiber.

[0019] As a preferred technical solution:

[0020] The preparation steps of the thermochromic polyamide fiber and the thermochromic microcapsules described above are as follows:

[0021] (a) Melamine-coated organic thermochromic material microcapsules are dispersed in a mixture of ethanol and water, and the pH is adjusted to alkaline (7.5-11) with ammonia solution. The melamine-coated organic thermochromic material microcapsules have a core-shell structure, with the core layer being an organic thermochromic material and the shell layer being melamine.

[0022] (b) Add silane coupling agent to carry out pretreatment reaction to introduce active groups on the surface of melamine-coated organic thermochromic material microcapsules, provide reaction sites for subsequent covalent bonding between silica coating layer and shell layer, and strengthen the interfacial bonding between the two layers.

[0023] (c) The silica precursor is slowly added dropwise to the reaction system at a rate of 0.5 mL / min using an injection pump to carry out the hydrolysis and polycondensation reaction (stirring can be carried out during the reaction, and the stirring speed is 500 rpm). A silica modified layer is formed on the surface of the melamine-coated organic thermochromic material microcapsules. The inorganic components are uniformly and densely deposited on the surface of the microcapsules through in-situ hydrolysis and polycondensation. The reaction conditions are mild and can effectively protect the activity of the internal organic thermochromic core material.

[0024] (d) After the reaction was completed, the microcapsules were centrifuged, washed (in ethanol and 0.1 wt% ammonia solution in sequence) and vacuum dried (100 °C, 4 h) to obtain thermochromic microcapsules.

[0025] In the method for preparing thermochromic polyamide fiber as described above, in step (a), the average particle size of the melamine-coated organic thermochromic material microcapsules is 2-3 μm; and in the mixture of ethanol and water, the volume ratio of ethanol to water is 3-4:1.

[0026] In the preparation method of thermochromic polyamide fiber as described above, in step (b), the silane coupling agent is γ-aminopropyltriethoxysilane (KH-550); the amount of silane coupling agent is 2-10 wt% of the mass of melamine-coated organic thermochromic material microcapsules; the temperature of the pretreatment reaction is 40-100℃, and the time is 1-6 h.

[0027] In the preparation method of thermochromic polyamide fiber as described above, in step (c), the silica precursor is tetraethyl orthosilicate (TEOS); the amount of silica precursor is 5-20 wt% of the mass of melamine-coated organic thermochromic material microcapsules; the pH value of the alkaline conditions is 7.5-11.0; the temperature of the hydrolysis-condensation reaction is 10-100℃, and the time is 12-48 h.

[0028] The method for preparing thermochromic polyamide fibers as described above uses an organic thermochromic material that is an organic three-component system composed of a leuco dye, a color developer, and a solvent.

[0029] In the method for preparing thermochromic polyamide fiber as described above, the rheology modifier is one or more of lanthanum acetate, lanthanum butanetetracarboxylate, lanthanum stearate, lanthanum citrate, lanthanum trimellitate, lanthanum pyromellitic tetracarboxylate, cerium stearate, cerium butanetetracarboxylate, and cerium citrate.

[0030] The method for preparing thermochromic polyamide fiber as described above uses polyamide 6 (PA6), polyamide 66 (PA66), or polyamide 56 (PA56) as the polyamide resin.

[0031] In the above-described method for preparing thermochromic polyamide fibers, the mass of the thermochromic microcapsules in the spinning raw material is 4wt%-7wt% of the mass of the polyamide resin.

[0032] The method for preparing thermochromic polyamide fiber as described in any of the above claims is as follows: the spinning raw material is melt-blended and granulated in a twin-screw extruder to obtain a blend. Blending first can achieve uniform dispersion of thermochromic microcapsules, rheology modifier and polyamide resin, ensuring the uniformity of various properties of the final fiber. Then, the blend is melt-spun, and after stretching and winding, thermochromic polyamide fiber is obtained.

[0033] The melt blending temperature of the twin-screw extruder is 210-240℃, the screw speed is 100-250rpm, the spinning speed of melt spinning is 1000-3000m / min, and the draw ratio is 1-3 times.

[0034] The present invention also provides a thermochromic polyamide fiber, which is prepared by the method for preparing a thermochromic polyamide fiber as described in any of the preceding claims;

[0035] In thermochromic polyamide fibers, the rupture rate of thermochromic microcapsules is less than 5%; the tensile strength of thermochromic polyamide fibers is ≥3.5cN / dtex, the color difference value ΔE before and after thermochromic change is >5, the fiber has excellent water resistance, the color-changing function can still be stably maintained after multiple washes, and the original soft hand feel and breathability of polyamide fibers can be maintained.

[0036] Beneficial effects:

[0037] (1) The present invention improves the rigidity and heat resistance of thermochromic microcapsules by setting a silica coating layer on the surface of thermochromic microcapsules, enhances their structural stability in the high temperature and high shear environment of polyamide melt spinning, reduces the risk of core material leakage, and ensures the color-changing function of the fiber.

[0038] (2) This invention improves the rheological behavior of polyamide melt by adding rare earth ion organic complexes as rheology modifiers to spinning raw materials, reduces the temperature requirements of spinning processing, further reduces the damage of thermal stress to thermochromic microcapsules, and improves the operability of spinning process.

[0039] (3) The rare earth ion organic complex used in this invention can form reversible coordination bonds with polyamide molecular chains. While improving melt processing performance, it can also form physical cross-linking points after fiber curing, reducing the mechanical property loss caused by the destruction of molecular chain hydrogen bonds and ensuring the mechanical strength of thermochromic polyamide fibers. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the thermochromic microcapsule in Example 1; wherein, 1-core layer, 2-shell layer, 3-silica coating layer;

[0041] Figure 2 The TGA (thermogravimetric analysis) curves are shown for the thermochromic microcapsules and pure microcapsules (melamine-coated organic thermochromic material microcapsules) in Example 1. Detailed Implementation

[0042] The present invention will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0043] The following are the test methods for the relevant performance indicators in each embodiment and comparative example:

[0044] Rupture Rate: There is currently no unified national or industry standard for determining the rupture rate. This invention uses a scanning electron microscope statistical counting method for determination. The sample is cut into cross-sectional slices with a thickness of 10-15 μm along the perpendicular fiber axis using a cryo-microtome. After being sputter-coated with gold, the slices are placed on the sample stage of a scanning electron microscope and observed under an accelerating voltage of 5-8 kV and a magnification of 3000-5000x. At least 10 fiber cross-sectional fields of view are randomly selected, and the total number of microcapsules is not less than 100. Cracks or breaks in the shell, voids remaining after leakage of the core material, or irreversible collapse and deformation of the capsule wall are all considered ruptures. The rupture rate is calculated by multiplying the ratio of the number of ruptured microcapsules to the total number of microcapsules by 100%, and the average value of the 10 fields of view is taken as the test result.

[0045] Tensile strength: determined in accordance with GB / T 14344-2022 "Test Method for Tensile Properties of Chemical Fiber Filaments".

[0046] Color difference ΔE before and after thermochromic color change: The color difference was measured according to the instrument measurement method in Clause 6.1 of GB / T 21898-2023 "Textile Color Representation Methods". The CIELAB color difference formula was used for evaluation, referring to GB / T 3978-2008 "Standard Illuminators and Geometric Conditions", GB / T 3979-2008 "Methods for Measurement of Object Colors" and GB / T 7921-2008 "Uniform Color Space and Color Difference Formula". The test temperature before color change was 20℃, and the test temperature after color change was 36℃.

[0047] Washing: Perform the washing procedure as specified in GB / T 12490-2014 "Textiles - Tests for color fastness to household and commercial washing".

[0048] The embodiments of this invention disclose specific manufacturers and brand information of the relevant substances. This content is only intended to fully disclose the technical solution, enabling those skilled in the art to understand, reproduce, and verify the technical effects of this invention. It is an exemplary description of the implementation methods and not a limitation on the scope of protection of this invention. Those skilled in the art should understand that, without departing from the core technical concept and substantive technical solution of this invention, similar equivalent raw materials produced by other manufacturers can be used to implement this invention. Such equivalent substitutions and conventional modifications all fall within the scope of protection of this invention, and the protection boundary of this invention should not be limited based on the specific manufacturers and brand information recorded in the embodiments.

[0049] Example 1

[0050] A method for preparing thermochromic polyamide fibers, the specific steps of which are as follows:

[0051] (1) Preparation of materials;

[0052] Melamine-coated organic thermochromic material microcapsules: Manufacturer: Dongguan Qiansebian New Material Co., Ltd., Brand: TSSB Blue-35 Degrees, Average particle size: 2μm;

[0053] A mixture of ethanol and water: the volume ratio of ethanol to water is 4:1;

[0054] Silane coupling agent: KH-550;

[0055] Silica precursor: TEOS;

[0056] Polyamide resin: PA6, manufactured by Guangdong Hengshenmeida New Material Co., Ltd., brand name Bringt RV 2.4;

[0057] Rheology modifier: Lanthanum stearate, manufactured by Gaomi Hanbang New Material Technology Co., Ltd., brand name HBL-101;

[0058] (2) Preparation of thermochromic microcapsules;

[0059] (a) Disperse melamine-coated organic thermochromic material microcapsules in a mixture of ethanol and water, and adjust the pH value to 9;

[0060] (b) A silane coupling agent was added for pretreatment at 60°C for 2 hours to introduce active groups onto the surface of the melamine-coated organic thermochromic material microcapsules; wherein the amount of silane coupling agent was 5 wt% of the mass of the melamine-coated organic thermochromic material microcapsules.

[0061] (c) A silica precursor is slowly added dropwise to the reaction system to carry out a hydrolysis-condensation reaction at a temperature of 25°C for 24 hours, forming a silica-modified layer on the surface of the melamine-coated organic thermochromic material microcapsules; wherein the amount of silica precursor used is 10 wt% of the mass of the melamine-coated organic thermochromic material microcapsules.

[0062] (d) After the reaction was completed, the microcapsules were separated, washed and dried to obtain thermochromic microcapsules;

[0063] like Figure 1 As shown, the thermochromic microcapsules prepared have a core-shell structure. The core layer 1 is an organic thermochromic material, which is an organic three-component system composed of a leuco dye, a color developer, and a solvent. The shell layer 2 is melamine, and the surface of the shell layer 2 is also provided with a silica coating layer 3.

[0064] like Figure 2 As shown, the 5% thermal weight loss temperature of the thermochromic microcapsules is 328℃, which is significantly higher than that of the melamine-coated organic thermochromic material microcapsules.

[0065] (3) Preparation of thermochromic polyamide fibers;

[0066] Polyamide resin, thermochromic microcapsules and rheology modifier are melt-blended and granulated in a twin-screw extruder to obtain a blend. The blend is then melt-spun, and after stretching and winding, thermochromic polyamide fiber is obtained.

[0067] The rheology modifier accounts for 2 wt% of the polyamide resin mass, and the thermochromic microcapsules account for 5 wt% of the polyamide resin mass. The melt blending temperature of the twin-screw extruder is 210-240℃, and the screw speed is 200 rpm. The temperature of each zone of the melt spinning screw is 210-240℃. Specifically, the melt spinning screw has five zones: zone 1 is 218℃, zone 2 is 235℃, zone 3 is 238℃, zone 4 is 240℃, and zone 5 is 240℃. The spinning speed is 2500 m / min, and the draw ratio is 2.5.

[0068] The final thermochromic polyamide fiber had a rupture rate of 3.8% for the thermochromic microcapsules; a tensile strength of 4.2 cN / dtex; a color difference ΔE of 6.7 before and after thermochromic changes; and a color difference ΔE of 5.9 after 10 washes.

[0069] Comparative Example 1

[0070] A method for preparing polyamide fibers differs from Example 1 only in that the rheology modifier is caprolactam.

[0071] In the final polyamide fiber, the rupture rate of the thermochromic microcapsules was 18.6%; the tensile strength of the polyamide fiber was 2.4 cN / dtex; the color difference ΔE before and after thermochromic change was 3.2; and the color difference ΔE before and after thermochromic change was 1.8 after 10 water washes.

[0072] Compared with Example 1, Comparative Example 1 showed a significantly higher microcapsule rupture rate and a marked deterioration in fiber breaking strength and color-changing properties. This is because caprolactam, as a small-molecule plasticizer, can only irreversibly weaken the hydrogen bonding between polyamide molecular chains. Although it can slightly reduce melt viscosity, it cannot form physical cross-linking points after cooling and solidification to compensate for the loss of hydrogen bonds, resulting in a significant decrease in fiber strength. At the same time, its viscosity reduction is limited and cannot effectively broaden the processing window or significantly reduce the spinning temperature. Microcapsules still rupture in large numbers under high temperature and high shear conditions, and core material leakage directly leads to a significant deterioration in fiber color-changing properties.

[0073] Comparative Example 2

[0074] A method for preparing polyamide fibers differs from Example 1 only in that the rheology modifier is ethylene glycol.

[0075] In the final polyamide fiber, the rupture rate of the thermochromic microcapsules was 21.3%; the tensile strength of the polyamide fiber was 2.1 cN / dtex; the color difference ΔE before and after thermochromic change was 2.8; and the color difference ΔE before and after thermochromic change was 1.5 after 10 water washes.

[0076] Compared with Example 1, Comparative Example 2 showed a greater degree of performance degradation. This is because ethylene glycol and the polyamide matrix have a large difference in polarity and limited compatibility, making them prone to phase separation and precipitation during processing, forming defect points inside the matrix. At the same time, ethylene glycol can only irreversibly break hydrogen bonds and cannot form coordination crosslinks. Under the dual effects, the mechanical strength of the fiber further decreases, and the plasticizing and viscosity-reducing effect is weaker than that of rare earth complexes. The microcapsule rupture rate is higher, and the loss of fiber color change performance is more severe.

[0077] A comparison of Example 1, Comparative Example 1, and Comparative Example 2 shows that common rheology modifiers (e.g., caprolactam, ethylene glycol, propylene glycol, butanediol, polyethylene glycol, dodecyl lactam, benzoate, stearamide, etc.) can lead to a certain degree of decrease in fiber strength. This invention selects rare earth ion organic complexes as rheology modifiers. By adding appropriate proportions, it can not only lower the spinning temperature and prevent the rupture of thermochromic microcapsules, but also ensure that the spun thermochromic polyamide fibers have good mechanical strength. This is because rare earth ions have unique empty orbitals and strong coordination ability, easily forming reversible coordination bonds with carbonyl oxygen or amide nitrogen on the polyamide molecular chain. This coordination weakens the hydrogen bonding between polyamide molecular chains in the melt state, making it easier for the molecular chains to align during melt spinning. After the filaments cool and solidify, the coordination bonds can reform stable physical cross-linking points, acting as a kind of "molecular anchor" to fix the oriented molecular chain structure, thereby reducing the decrease in mechanical properties caused by hydrogen bond disruption. Therefore, rare earth ion organic complexes can maintain or even enhance the mechanical strength of fibers to the maximum extent while reducing processing temperature.

[0078] Example 2

[0079] A method for preparing thermochromic polyamide fibers, the specific steps of which are as follows:

[0080] (1) Preparation of materials;

[0081] Melamine-coated organic thermochromic material microcapsules: Manufacturer: Dongguan Qiansebian New Material Co., Ltd., Brand: TSSB Blue-35 Degrees, Average particle size: 2μm;

[0082] A mixture of ethanol and water: the volume ratio of ethanol to water is 3:1;

[0083] Silane coupling agent: KH-550;

[0084] Silica precursor: TEOS;

[0085] Polyamide resin: PA6, manufactured by Guangdong Hengshenmeida New Material Co., Ltd., brand name Bringt RV 2.4;

[0086] Rheology modifier: a mixture of lanthanum stearate (manufacturer: Gaomi Hanbang New Material Technology Co., Ltd., brand name: HBL-101) and cerium stearate (manufacturer: Shanghai Aichun Biotechnology Co., Ltd., brand name: A614152329) in a mass ratio of 1:1;

[0087] (2) Preparation of thermochromic microcapsules;

[0088] (a) Disperse melamine-coated organic thermochromic material microcapsules in a mixture of ethanol and water, and adjust the pH value to 8.5;

[0089] (b) A silane coupling agent was added for pretreatment at 50°C for 3 hours to introduce active groups onto the surface of the melamine-coated organic thermochromic material microcapsules; wherein the amount of silane coupling agent was 3 wt% of the mass of the melamine-coated organic thermochromic material microcapsules.

[0090] (c) A silica precursor is slowly added dropwise to the reaction system to carry out a hydrolysis-condensation reaction at a temperature of 40°C for 18 hours, forming a silica-modified layer on the surface of the melamine-coated organic thermochromic material microcapsules; wherein the amount of silica precursor used is 7 wt% of the mass of the melamine-coated organic thermochromic material microcapsules.

[0091] (d) After the reaction was completed, the microcapsules were separated, washed and dried to obtain thermochromic microcapsules;

[0092] The prepared thermochromic microcapsules have a core-shell structure. The core layer is an organic thermochromic material, which is an organic three-component system composed of a leuco dye, a color developer, and a solvent. The shell layer is melamine, and the surface of the shell layer is also provided with a silica coating layer.

[0093] The 5% thermal weight loss temperature of the thermochromic microcapsules is 328℃;

[0094] (3) Preparation of thermochromic polyamide fibers;

[0095] Polyamide resin, thermochromic microcapsules and rheology modifier are melt-blended and granulated in a twin-screw extruder to obtain a blend. The blend is then melt-spun, and after stretching and winding, thermochromic polyamide fiber is obtained.

[0096] The rheology modifier accounts for 2.5 wt% of the polyamide resin, and the thermochromic microcapsules account for 4 wt% of the polyamide resin. The melt blending temperature of the twin-screw extruder is 210-240℃, and the screw speed is 200 rpm. The temperature of each zone of the melt spinning screw is 210-240℃. Specifically, the melt spinning screw has five zones: zone 1 is 215℃, zone 2 is 230℃, zone 3 is 236℃, zone 4 is 238℃, and zone 5 is 238℃. The spinning speed is 3000 m / min, and the draw ratio is 2.

[0097] The final thermochromic polyamide fiber had a rupture rate of 4.5% for the thermochromic microcapsules; a tensile strength of 3.8 cN / dtex; a color difference ΔE of 6.1 before and after thermochromic changes; and a color difference ΔE of 5.3 after 10 washes.

[0098] Example 3

[0099] A method for preparing thermochromic polyamide fibers, the specific steps of which are as follows:

[0100] (1) Preparation of materials;

[0101] Melamine-coated organic thermochromic material microcapsules: Manufacturer: Dongguan Qiansebian New Material Co., Ltd., Brand: TSSR Red -35 degrees, Average particle size: 2μm;

[0102] A mixture of ethanol and water: the volume ratio of ethanol to water is 4:1;

[0103] Silane coupling agent: KH-550;

[0104] Silica precursor: TEOS;

[0105] Polyamide resin: PA6, manufactured by Guangdong Hengshenmeida New Material Co., Ltd., brand name Bringt RV 2.4;

[0106] Rheology modifier: Lanthanum acetate, manufactured by Zibo Rongruida Powder Materials Factory, brand name La(AC)3·5H2O;

[0107] (2) Preparation of thermochromic microcapsules;

[0108] (a) Disperse melamine-coated organic thermochromic material microcapsules in a mixture of ethanol and water, and adjust the pH value to 10;

[0109] (b) A silane coupling agent was added for pretreatment at 80°C for 4 hours to introduce active groups onto the surface of the melamine-coated organic thermochromic material microcapsules; wherein the amount of silane coupling agent was 8 wt% of the mass of the melamine-coated organic thermochromic material microcapsules.

[0110] (c) A silica precursor is slowly added dropwise to the reaction system to carry out a hydrolysis-condensation reaction at a temperature of 60°C for 36 hours, forming a silica-modified layer on the surface of the melamine-coated organic thermochromic material microcapsules; wherein the amount of silica precursor used is 15 wt% of the mass of the melamine-coated organic thermochromic material microcapsules.

[0111] (d) After the reaction was completed, the microcapsules were separated, washed and dried to obtain thermochromic microcapsules;

[0112] The prepared thermochromic microcapsules have a core-shell structure. The core layer is an organic thermochromic material, which is an organic three-component system composed of a leuco dye, a color developer, and a solvent. The shell layer is melamine, and the surface of the shell layer is also provided with a silica coating layer.

[0113] The 5% thermal weight loss temperature of the thermochromic microcapsules is 332℃;

[0114] (3) Preparation of thermochromic polyamide fibers;

[0115] Polyamide resin, thermochromic microcapsules and rheology modifier are melt-blended and granulated in a twin-screw extruder to obtain a blend. The blend is then melt-spun, and after stretching and winding, thermochromic polyamide fiber is obtained.

[0116] The rheology modifier is 0.5 wt% of the polyamide resin, and the thermochromic microcapsules are 6.5 wt% of the polyamide resin. The melt blending temperature of the twin-screw extruder is 210-240℃, and the screw speed is 250 rpm. The temperature of each zone of the melt spinning screw is 210-240℃. Specifically, the melt spinning screw has five zones: zone 1 is 225℃, zone 2 is 235℃, zone 3 is 240℃, zone 4 is 240℃, and zone 5 is 240℃. The spinning speed is 2750 m / min, and the draw ratio is 2.5.

[0117] The final thermochromic polyamide fiber had a rupture rate of 3.2% for the thermochromic microcapsules; a tensile strength of 4.3 cN / dtex; a color difference ΔE of 6.5 before and after thermochromic changes; and a color difference ΔE of 5.8 after 10 washes.

[0118] Comparative Example 3

[0119] A method for preparing polyamide fiber differs from Example 3 only in that: in step (3), the mass of the rheology modifier is 0.4 wt% of the mass of the polyamide resin.

[0120] In the final polyamide fiber, the rupture rate of the thermochromic microcapsules was 12.5%; the tensile strength of the polyamide fiber was 3.3 cN / dtex; the color difference ΔE before and after thermochromic change was 3.8; and the color difference ΔE before and after thermochromic change was 2.9 after 10 water washes.

[0121] Compared with Example 3, Comparative Example 3 showed a significantly increased microcapsule rupture rate and a marked deterioration in fiber color-changing properties. Although the tensile strength still met the standard, it decreased. This is because when the amount of rheology modifier is too low, it is insufficient to effectively weaken the hydrogen bonding between polyamide molecular chains. The melt viscosity remains high, making low-temperature spinning impossible. As a result, a large number of microcapsules still rupture in the high-temperature, high-shear environment, leading to a significant decrease in the color-changing function. At the same time, the amount of rare earth complex is insufficient, resulting in too few physical cross-linking points formed by reversible coordination. The reinforcing effect cannot be fully utilized, thus the fiber tensile strength also decreases to some extent.

[0122] Example 4

[0123] A method for preparing thermochromic polyamide fibers, the specific steps of which are as follows:

[0124] (1) Preparation of materials;

[0125] Melamine-coated organic thermochromic material microcapsules: Manufacturer: Tianjinli New Material Technology Co., Ltd., Brand: Red RTP3040, Average particle size: 3μm;

[0126] A mixture of ethanol and water: the volume ratio of ethanol to water is 3:1;

[0127] Silane coupling agent: KH-550;

[0128] Silica precursor: TEOS;

[0129] Polyamide resin: PA66, manufactured by Shenma Industrial Co., Ltd., grade FYR 3.4;

[0130] Rheology modifier: Lanthanum stearate, manufactured by Gaomi Hanbang New Material Technology Co., Ltd., brand name HBL-101;

[0131] (2) Preparation of thermochromic microcapsules;

[0132] (a) Disperse melamine-coated organic thermochromic material microcapsules in a mixture of ethanol and water, and adjust the pH value to 7.5;

[0133] (b) A silane coupling agent was added for pretreatment at 40°C for 1 hour to introduce active groups onto the surface of the melamine-coated organic thermochromic material microcapsules; wherein the amount of silane coupling agent was 2 wt% of the mass of the melamine-coated organic thermochromic material microcapsules.

[0134] (c) A silica precursor is slowly added dropwise to the reaction system to carry out a hydrolysis-condensation reaction at a temperature of 10°C for 12 hours, forming a silica-modified layer on the surface of the melamine-coated organic thermochromic material microcapsules; wherein the amount of silica precursor used is 5 wt% of the mass of the melamine-coated organic thermochromic material microcapsules.

[0135] (d) After the reaction was completed, the microcapsules were separated, washed and dried to obtain thermochromic microcapsules;

[0136] The prepared thermochromic microcapsules have a core-shell structure. The core layer is an organic thermochromic material, which is an organic three-component system composed of a leuco dye, a color developer, and a solvent. The shell layer is melamine, and the surface of the shell layer is also provided with a silica coating layer.

[0137] The 5% thermal weight loss temperature of the thermochromic microcapsules is 324℃;

[0138] (3) Preparation of thermochromic polyamide fibers;

[0139] Polyamide resin, thermochromic microcapsules and rheology modifier are melt-blended and granulated in a twin-screw extruder to obtain a blend. The blend is then melt-spun, and after stretching and winding, thermochromic polyamide fiber is obtained.

[0140] The rheology modifier accounts for 5 wt% of the polyamide resin mass, and the thermochromic microcapsules account for 4.5 wt% of the polyamide resin mass. The melt blending temperature of the twin-screw extruder is 210-240℃, and the screw speed is 100 rpm. The temperature of each zone of the screw in melt spinning is 210-240℃, specifically, the temperature of zone 1 is 225℃, the temperature of zone 2 is 238℃, the temperature of zone 3 is 240℃, the temperature of zone 4 is 240℃, the temperature of zone 5 is 240℃, the spinning speed is 2000 m / min, and the draw ratio is 3.

[0141] The final thermochromic polyamide fiber had a rupture rate of 4.9% for the thermochromic microcapsules; a tensile strength of 3.5 cN / dtex; a color difference ΔE of 6.2 before and after thermochromic change; and a color difference ΔE of 5.2 after 10 washes.

[0142] Comparative Example 4

[0143] A method for preparing thermochromic polyamide fiber differs from Example 4 only in that a silane coupling agent is not added in step (b).

[0144] The 5% thermal weight loss temperature of the thermochromic microcapsules is 286℃.

[0145] In the final thermochromic polyamide fiber, the rupture rate of the thermochromic microcapsules was 16.3%; the tensile strength of the thermochromic polyamide fiber was 3.2 cN / dtex; the color difference ΔE before and after thermochromic change was 3.3; and the color difference ΔE before and after thermochromic change was 2.4 after 10 water washes.

[0146] Compared with Example 4, the 5% thermal weight loss temperature of the thermochromic microcapsules in Comparative Example 4 was significantly lower. This is because without the addition of silane coupling agent, the silica coating layer and the shell layer cannot be covalently bonded, and the interfacial bonding between the two layers is weak. This further leads to a significant increase in the microcapsule rupture rate and a significant decrease in the fiber color-changing performance.

[0147] Example 5

[0148] A method for preparing thermochromic polyamide fibers, the specific steps of which are as follows:

[0149] (1) Preparation of materials;

[0150] Melamine-coated organic thermochromic material microcapsules: Manufacturer: Tianjinli New Material Technology Co., Ltd., Brand: Blue RTP8040, Average particle size: 3μm;

[0151] A mixture of ethanol and water: the volume ratio of ethanol to water is 4:1;

[0152] Silane coupling agent: KH-550;

[0153] Silica precursor: TEOS;

[0154] Polyamide resin: PA56, manufactured by Shanghai Kaisai Biotechnology Co., Ltd., brand name E-1273;

[0155] Rheology modifier: cerium stearate, manufactured by Shanghai Aichun Biotechnology Co., Ltd., brand name A614152329;

[0156] (2) Preparation of thermochromic microcapsules;

[0157] (a) Disperse melamine-coated organic thermochromic material microcapsules in a mixture of ethanol and water, and adjust the pH value to 11;

[0158] (b) A silane coupling agent was added for pretreatment at 100°C for 6 hours to introduce active groups onto the surface of the melamine-coated organic thermochromic material microcapsules; wherein the amount of silane coupling agent was 10 wt% of the mass of the melamine-coated organic thermochromic material microcapsules.

[0159] (c) A silica precursor is slowly added dropwise to the reaction system to carry out a hydrolysis-condensation reaction at a temperature of 100°C for 48 hours, forming a silica-modified layer on the surface of the melamine-coated organic thermochromic material microcapsules; wherein the amount of silica precursor used is 20 wt% of the mass of the melamine-coated organic thermochromic material microcapsules.

[0160] (d) After the reaction was completed, the microcapsules were separated, washed and dried to obtain thermochromic microcapsules;

[0161] The prepared thermochromic microcapsules have a core-shell structure. The core layer is an organic thermochromic material, which is an organic three-component system composed of a leuco dye, a color developer, and a solvent. The shell layer is melamine, and the surface of the shell layer is also provided with a silica coating layer.

[0162] The 5% thermal weight loss temperature of the thermochromic microcapsules is 317℃;

[0163] (3) Preparation of thermochromic polyamide fibers;

[0164] Polyamide resin, thermochromic microcapsules and rheology modifier are melt-blended and granulated in a twin-screw extruder to obtain a blend. The blend is then melt-spun, and after stretching and winding, thermochromic polyamide fiber is obtained.

[0165] The rheology modifier accounts for 5 wt% of the polyamide resin mass, and the thermochromic microcapsules account for 7 wt% of the polyamide resin mass. The melt blending temperature of the twin-screw extruder is 210-240℃, and the screw speed is 200 rpm. The temperature of each zone of the melt spinning screw is 210-240℃. Specifically, the melt spinning screw has five zones: zone 1 is 220℃, zone 2 is 235℃, zone 3 is 240℃, zone 4 is 240℃, and zone 5 is 240℃. The spinning speed is 1500 m / min, and the draw ratio is 3.

[0166] The final thermochromic polyamide fiber had a rupture rate of 2.1% for the thermochromic microcapsules; a tensile strength of 3.6 cN / dtex; a color difference ΔE of 7.3 before and after thermochromic changes; and a color difference ΔE of 6.6 after 10 washes.

[0167] Comparative Example 5

[0168] A method for preparing polyamide fiber differs from Example 5 only in that: in step (3), the mass of the rheology modifier is 7 wt% of the mass of the polyamide resin.

[0169] In the final polyamide fiber, the rupture rate of the thermochromic microcapsules was 7.8%; the tensile strength of the polyamide fiber was 2.2 cN / dtex; the color difference ΔE before and after thermochromic change was 6.9; and the color difference ΔE before and after thermochromic change was 6.1 after 10 water washes.

[0170] Compared with Example 5, Comparative Example 5 showed a severe deterioration in fiber breaking strength, a significant increase in microcapsule rupture rate, and a slight decrease in fiber color-changing properties. This is because excessive rheology modifier dosage excessively weakens the hydrogen bonding between polyamide molecular chains, leading to a significant decrease in melt strength and making the fibers prone to breakage and filament drift during spinning. Simultaneously, excessive rare earth ion organic complexes aggregate in the matrix, forming stress concentration points. The fluctuation in spinning tension exacerbates the mechanical damage to the microcapsules, causing the rupture rate to rebound and increase. Furthermore, the reformation of coordination bonds is insufficient to fully compensate for the excessive loss of hydrogen bonds. These multiple factors combined result in a significant decrease in fiber strength to an unacceptable level, and the fiber color-changing properties also slightly deteriorate due to increased microcapsule breakage.

Claims

1. A method for preparing thermochromic polyamide fibers, employing a melt spinning process, characterized in that, The spinning raw materials include polyamide resin components, thermochromic microcapsule components, and rheology modifier components; The thermochromic microcapsules have a core-shell structure, with the core layer being an organic thermochromic material and the shell layer being melamine. The surface of the shell layer is also covered with a silica coating layer, which is covalently bonded to the shell layer. The 5% thermal weight loss temperature of thermochromic microcapsules is 317-332℃; The rheology modifier is a rare earth ion organic complex; the rare earth ion organic complex is a lanthanide rare earth ion organic complex or a cerium-based rare earth ion organic complex. In the spinning raw materials, the mass of the rheology modifier is 0.5wt%-5wt% of the mass of the polyamide resin; The temperature of each zone of the screw in melt spinning is 210-240℃.

2. The method for preparing thermochromic polyamide fiber according to claim 1, characterized in that, The preparation steps of thermochromic microcapsules are as follows: (a) Melamine-coated organic thermochromic material microcapsules are dispersed in a mixture of ethanol and water, and the pH is adjusted to alkaline. The melamine-coated organic thermochromic material microcapsules have a core-shell structure, with the core layer being an organic thermochromic material and the shell layer being melamine. (b) A silane coupling agent is added for pretreatment to introduce active groups on the surface of melamine-coated organic thermochromic material microcapsules; (c) A silica precursor is added dropwise to the reaction system to carry out a hydrolysis and polycondensation reaction, forming a silica-modified layer on the surface of melamine-coated organic thermochromic material microcapsules; (d) After the reaction is complete, the microcapsules are separated, washed and dried to obtain thermochromic microcapsules.

3. The method for preparing thermochromic polyamide fiber according to claim 2, characterized in that, In step (a), the average particle size of the melamine-coated organic thermochromic material microcapsules is 2-3 μm; in the mixture of ethanol and water, the volume ratio of ethanol to water is 3-4:

1.

4. The method for preparing thermochromic polyamide fiber according to claim 2, characterized in that, In step (b), the silane coupling agent is γ-aminopropyltriethoxysilane; the amount of silane coupling agent is 2-10 wt% of the mass of the melamine-coated organic thermochromic material microcapsules; the temperature of the pretreatment reaction is 40-100℃ and the time is 1-6h.

5. The method for preparing thermochromic polyamide fiber according to claim 2, characterized in that, In step (c), the silica precursor is tetraethyl orthosilicate; the amount of silica precursor used is 5-20 wt% of the mass of the melamine-coated organic thermochromic material microcapsules; the pH value under alkaline conditions is 7.5-11.0; the temperature of the hydrolysis-condensation reaction is 10-100℃, and the time is 12-48h.

6. The method for preparing a thermochromic polyamide fiber according to claim 1, characterized in that, Organic thermochromic materials are organic three-component systems consisting of leuco dyes, color developers, and solvents.

7. The method for preparing thermochromic polyamide fiber according to claim 1, characterized in that, The rheology modifier is one or more of lanthanum acetate, lanthanum butanetetracarboxylate, lanthanum stearate, lanthanum citrate, lanthanum trimellitate, lanthanum pyromellitictetracarboxylate, cerium stearate, cerium butanetetracarboxylate, and cerium citrate.

8. The method for preparing thermochromic polyamide fiber according to claim 1, characterized in that, In the spinning raw materials, the mass of thermochromic microcapsules is 4wt%-7wt% of the mass of polyamide resin.

9. A method for preparing a thermochromic polyamide fiber according to any one of claims 1 to 8, characterized in that, The preparation process of thermochromic polyamide fiber is as follows: the spinning raw material is melt-blended and granulated in a twin-screw extruder to obtain a blend, and then the blend is melt-spun, stretched and wound to obtain thermochromic polyamide fiber. The melt blending temperature of the twin-screw extruder is 210-240℃, the screw speed is 100-250rpm, the spinning speed of melt spinning is 1000-3000m / min, and the draw ratio is 1-3 times.

10. A thermochromic polyamide fiber, characterized in that, It is prepared by the method for preparing thermochromic polyamide fiber as described in any one of claims 1 to 9; In thermochromic polyamide fibers, the rupture rate of thermochromic microcapsules is less than 5%; the tensile strength of thermochromic polyamide fibers is ≥3.5cN / dtex, and the color difference value ΔE before and after thermochromic change is >5.

Images