Multi-color injection molding process for smart wearable devices

Abstract

The present application relates to the technical field of material processing, and discloses a multi-color injection molding process for intelligent wearable equipment, which comprises the following steps: preparing hard granules by melt extruding polybutylene terephthalate resin and epoxy-containing styrene-acrylonitrile copolymer; preparing soft granules by mixing thermoplastic polyurethane elastomer and amino-terminated hyperbranched polyamide-ester auxiliary; laser etching the hard skeleton bonding surface to form microtexture; and using segmented speed control in the second injection molding, using the shear friction heat generated by high-speed pulse injection to activate the epoxy-amine chemical cross-linking reaction at the interface. The present application realizes the firm combination of hard and soft materials without adhesives through the synergistic mechanism of rheological matching and in-situ chemical bonding, significantly improves the bonding strength and moisture and heat aging resistance of the interface, simplifies the process flow, and is suitable for the precision manufacturing of intelligent wearable equipment.

Description

Technical Field

[0001] This invention relates to the field of materials processing technology, specifically to a multi-color injection molding process for smart wearable devices. Background Technology

[0002] Smart wearable devices typically consist of a rigid shell and a soft wristband or overlay to balance structural support for internal electronic components with tactile comfort during wear. Polybutylene terephthalate (PBT) is often used as the rigid skeleton material due to its excellent mechanical strength and dimensional stability, while thermoplastic polyurethane elastomer (TPU) is often chosen as the soft overlay material due to its good flexibility and abrasion resistance. Achieving a strong bond between these two dissimilar materials at the interface during two-color injection molding is crucial for ensuring product quality.

[0003] However, because PBT is a crystalline polymer with a rapid cooling crystallization rate, and differs from TPU in melt polarity and shrinkage rate, effective intermolecular diffusion and entanglement are difficult to achieve under conventional injection molding processes, resulting in insufficient interfacial bonding strength. Existing solutions primarily rely on the physical design of the mold structure, specifically designing macroscopic mechanical interlocking structures such as undercuts, through holes, or deep grooves on the surface of the rigid skeleton. While this physical bonding method provides some tensile strength, it does not form chemical bonds at the microscopic interface. During long-term use of smart wearable devices, the difference in thermal expansion coefficients between the two materials due to the corrosive effects of human sweat and changes in environmental temperature and humidity can create internal stress differences, leading to loosening of the mechanical interlocking points and the formation of microscopic gaps at the interface. This can result in problems such as product delamination, delamination, or dirt accumulation.

[0004] Another common method to enhance bonding strength is to introduce an intermediate layer process. This involves spraying a primer or adhesive onto the surface of the rigid skeleton after injection molding, followed by a soft plastic overlay. While this method improves adhesion, it adds drying and spraying steps, prolonging the production cycle. Furthermore, the introduced organic solvents pose a risk of volatile organic compound (VOC) emissions, making it difficult to meet increasingly stringent environmental and health safety standards. In addition, some commercially available chemical modification methods, while improving compatibility by adding compatibilizers, often require sacrificing the modulus or heat resistance of the matrix material, and effective interfacial reactions are difficult to complete within the extremely short cooling time of injection molding. Therefore, developing an injection molding process that achieves high-strength, aging-resistant bonding between PBT and TPU without using adhesives or sacrificing the material's intrinsic properties is a pressing technical challenge for the industry. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a multi-color injection molding process for smart wearable devices, which solves the problems of low interfacial bonding strength, poor environmental aging resistance, and complex production processes caused by existing two-color injection molded products of polybutylene terephthalate and thermoplastic polyurethane elastomer relying on mechanical interlocking or adhesive bonding processes.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a multi-color injection molding process for smart wearable devices, comprising the following steps: S1, Preparation of the first component: Polybutylene terephthalate resin, epoxy-containing styrene-acrylonitrile copolymer and antioxidant are mixed in proportion, and melt extruded and granulated at 230 degrees Celsius to 245 degrees Celsius to obtain rigid skeleton granules; S2, Preparation of the second component: Thermoplastic polyurethane elastomer, amino-terminated hyperbranched polyamide-ester additive and antioxidant are mixed in proportion and extruded and granulated under low temperature shear mode of 180 degrees Celsius to 205 degrees Celsius to obtain soft coated granules. S3, Mold preparation: Laser etching is performed on the area corresponding to the hard-soft interface in the first injection mold to form a micro-texture. S4, First Injection Molding: The first component is injected into the mold and cooled to obtain a hard skeleton with micro-texture on the surface; S5, Second Injection Molding: The second component is injected into the cavity. The injection process adopts segmented speed control. The first segment uses low-speed injection to fill the flow channel and non-contact interface area. When the melt front reaches the hard skeleton texture area, it switches to the second segment of high-speed pulse injection. The shear friction heat is used to activate the epoxy-amine chemical crosslinking reaction at the interface. After holding pressure and cooling, multi-color injection molded products are obtained.

[0007] By adopting the above technical solution, this invention solves the problem of bonding dissimilar materials by utilizing the matching mechanism between polymer rheological properties and interfacial chemical reaction kinetics. The specific mechanism of action is as follows: Firstly, the micro-filling mechanism is based on the shear-thinning effect. The terminal amino-terminated hyperbranched polyamide-ester additive introduced in the second component has a highly branched spherical three-dimensional structure with low intermolecular entanglement. During the low-speed stage of injection molding flow, the melt maintains a high viscosity, preserving laminar flow and preventing gas entrainment. When the melt enters the bonding interface and switches to high-speed injection, the high shear rate induces the hyperbranched polymer to orient, and the system exhibits significant shear-thinning behavior, resulting in a decrease in apparent viscosity. This low-viscosity melt can penetrate deep into the micro-texture of the rigid skeleton surface, increasing the contact area between the two phases and eliminating interfacial micropores.

[0008] Secondly, the in-situ chemical bonding mechanism is based on shear-thermal activation. High-speed injection generates high-frequency shear friction between the melt and the rough microtextured surface, converting mechanical energy into heat energy. This leads to a local temperature increase at the interface, exceeding the activation energy threshold of the chemical reaction. Under these conditions, the epoxy groups on the hard framework surface undergo ring-opening addition reactions with the terminal amino groups in the soft material: the terminal amino groups act as nucleophiles, attacking the carbon atoms of the epoxy ring, opening the epoxy structure and forming covalent bonds, generating a three-dimensional cross-linked network at the interface. This chemical bonding, combined with the physical anchoring effect of the microtexture, significantly improves the interfacial bonding strength and environmental aging resistance.

[0009] Preferably, in the first component, the polybutylene terephthalate resin comprises 92.0 to 98.0 parts by weight, the epoxy-containing styrene-acrylonitrile copolymer comprises 1.5 to 7.5 parts by weight, and the antioxidant comprises 0.1 to 1.0 parts by weight; in the second component, the thermoplastic polyurethane elastomer comprises 92.0 to 96.5 parts by weight, the amino-terminated hyperbranched polyamide-ester additive comprises 3.0 to 7.5 parts by weight, and the antioxidant comprises 0.1 to 1.0 parts by weight.

[0010] By adopting the above technical solution, a reasonable component ratio ensures a balance between the mechanical properties of the matrix material and the interfacial reactivity. A moderate epoxy component content guarantees sufficient crosslinking point density without affecting crystallization performance; a moderate hyperbranched amine component content balances rheological modification effects with precipitation control on the material surface.

[0011] Preferably, the preparation method of the epoxy-containing styrene-acrylonitrile copolymer in step S1 includes: using xylene as a solvent, adding a mixed solution of styrene, acrylonitrile, glycidyl methacrylate and an initiator dropwise to the reaction system at 125°C to 140°C to carry out a free radical copolymerization reaction, and drying after devolatilization after the reaction is completed; the copolymer has an epoxy equivalent of 265 g / mol to 435 g / mol and a weight-average molecular weight of 5200 to 8800.

[0012] By adopting the above technical solution, the specific molecular weight range endows the copolymer with good dispersibility in the matrix and the ability to migrate to the surface; the limited epoxy equivalent provides a suitable density of reactive groups, avoiding interfacial embrittlement caused by excessive crosslinking density.

[0013] Preferably, the preparation method of the terminal amino hyperbranched polyamide-ester additive in step S2 includes the following sub-steps: Step 1: Heat diisopropanolamine to melt, add succinic anhydride in batches, and carry out polycondensation reaction at 145°C to 150°C until the acid value of the system drops below 10 mg potassium hydroxide per gram to obtain the terminal hydroxyl intermediate. Step 2: Cool the system and add isophorone diisocyanate dropwise to the hydroxyl-terminated intermediate. Control the reaction temperature to not exceed 100 degrees Celsius and maintain the temperature to obtain the isocyanate-terminated prepolymer. Step 3: Further cool the system, add diamine compounds dropwise to the prepolymer, carry out the end-capping reaction at 40°C to 60°C, and remove volatiles under vacuum to obtain the final product.

[0014] By employing the above technical solution, a hyperbranched polymer with a specific core and shell structure was constructed. The flexible core composed of diisopropanolamine and succinic anhydride provides thermal stability; isophorone diisocyanate serves as a rigid connecting arm to enhance heat resistance and deformation resistance; and externally grafted diamine compounds provide highly reactive terminal amino groups, ensuring stability and interfacial reaction efficiency at processing temperatures.

[0015] Preferably, the specific parameters for segmented speed control in step S5 are as follows: the speed of the first segment low-speed injection is 15 mm / s to 25 mm / s; the speed of the second segment high-speed pulse injection is 180 mm / s to 280 mm / s; and the switching point is set at the position where the second injection melt just contacts the interface of the rigid skeleton after flowing through the runner and gate.

[0016] By adopting the above technical solution, the first stage of low-speed injection prevents the melt from undergoing thermal degradation and gas streaks due to excessive shearing in the flow channel system; the second stage of high-speed injection concentrates the release of shear heat in the interface region, providing the enthalpy required for the chemical reaction, while avoiding performance degradation caused by excessive overall heating time of soft materials.

[0017] Preferably, in step S3, the microtexture is a non-inverted structure with a surface roughness Ra of 3.2 micrometers to 6.0 micrometers, an average width RSm of 50 micrometers to 100 micrometers, and the texture direction forms an angle of 45 degrees to 90 degrees with the flow direction of the second injection melt.

[0018] By adopting the above technical solution, specific texture parameters and directions increase melt flow resistance and enhance the shear friction heating effect. The non-inverted structure eliminates interference from mechanical interlocking, facilitates demolding, and ensures that the interface strength mainly comes from chemical bonding.

[0019] This invention provides a multi-color injection molding process for smart wearable devices. It offers the following advantages: 1. This invention introduces epoxy-containing components and amino-terminated hyperbranched components into a rigid polybutylene terephthalate (PET) matrix and a flexible thermoplastic polyurethane elastomer, respectively, and utilizes the shear friction heat generated by high-speed injection molding to initiate an in-situ interfacial chemical reaction. This process forms a high-density covalent cross-linked network at the interface, which, combined with the physical anchoring effect of the microtexture, significantly improves the bonding strength between dissimilar materials, effectively solving the problems of weak interfacial bonding and easy delamination in traditional physical insert injection molding.

[0020] 2. The interfacial chemical bonding mechanism constructed in this invention exhibits excellent resistance to environmental aging. Compared to physical bonds that rely solely on mechanical interlocking, covalent bonding effectively resists hydrolysis under humid and hot conditions and thermal stress damage caused by differences in thermal expansion coefficients. After undergoing high-temperature and high-humidity aging and thermal shock tests, the product still maintains a high interfacial retention rate, meeting the structural reliability requirements of smart wearable devices for long-term use in contact with human sweat and in complex outdoor temperature and humidity environments.

[0021] 3. This invention utilizes the shear-thinning properties of terminal amino-terminated hyperbranched polyamide-ester additives in conjunction with a segmented injection rate process to achieve efficient filling and reaction control of micro-textures. The viscosity drop effect induced by high-speed pulse injection allows the melt to deeply wet the micron-level texture structure, eliminating interfacial porosity defects. Simultaneously, this process eliminates the need for primer treatment and adhesive bonding, avoiding the emission of volatile organic compounds, simplifying the manufacturing process, and improving production efficiency and product yield. Attached Figure Description

[0022] Figure 1 This is a graph showing the relationship between the apparent viscosity and shear rate of the soft material of the present invention. Figure 2 A comparison diagram of melt temperature at the flow channel and interface under different processes of the present invention; Figure 3 The results of the damp heat aging test of the present invention are shown in the figure; where (a) is a comparison of peel strength and (b) is a comparison of strength retention rate. Detailed Implementation

[0023] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0024] To achieve the above objectives, the present invention provides the following technical solution: The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0025] Polybutylene terephthalate (PBT) resin, intrinsic viscosity 1.0 dL / g, CAS No. 26062-94-2.

[0026] Thermoplastic polyurethane (TPU) elastomer, polyether type, Shore hardness 85A.

[0027] Succinic anhydride, purity ≥99.0%, CAS No. 108-30-5.

[0028] Diisopropanolamine, purity ≥98.0%, CAS No. 110-97-4.

[0029] Isophorone diisocyanate (IPDI), purity ≥99.0%, CAS No. 4098-71-9.

[0030] Ethylenediamine, purity ≥99.5%, CAS No. 107-15-3.

[0031] 1,6-Hexanediamine, purity ≥99.0%, CAS No. 124-09-4.

[0032] Antioxidant 1010, CAS No. 6683-19-8.

[0033] Preparation Example 1: This preparation example provides an ethylenediamine-based hyperbranched polyamide-ester, comprising the following steps: 139.8 parts by weight of diisopropanolamine were added to a reaction vessel equipped with a mechanical stirrer, nitrogen gas delivery tube, thermometer and water separator, and heated to 90°C to melt it; Under nitrogen protection, 100.1 parts by weight of succinic anhydride were added in three portions. After stirring evenly, the temperature was raised to 145°C and the reaction was carried out for 2.5 hours until no more water was generated and the acid value of the system dropped to 8.5 mg KOH / g, thus obtaining the terminal hydroxyl intermediate. The system was cooled to 80°C, and 222.3 parts by weight of isophorone diisocyanate were slowly added dropwise. The dropping rate was controlled to maintain the reaction temperature at no more than 90°C. After the addition was completed, the reaction was kept at the temperature for 1.5 hours to obtain the isocyanate-terminated prepolymer. Cool the reaction system to 40°C, slowly add 120.2 parts by weight of ethylenediamine, stir vigorously and maintain the temperature between 40-50°C, and react for 2.0 hours; After the reaction was completed, unreacted ethylenediamine and volatiles were removed by vacuum rotary evaporation at 120℃ and -0.09MPa. After cooling, a pale yellow glassy solid was obtained, with an amine value of 195 mgKOH / g and a branching degree of 0.58.

[0034] Preparation Example 2: This preparation example provides a hexamethylenediamine-based hyperbranched polyamide-ester, comprising the following steps: 146.5 parts by weight of diisopropanolamine were added to a reaction vessel equipped with a mechanical stirrer, nitrogen gas delivery tube, thermometer and water separator, and heated to 90°C to melt it. Under nitrogen protection, 100.1 parts by weight of succinic anhydride were added in three portions. After stirring evenly, the temperature was raised to 150°C and the reaction was carried out for 3.0 hours until no more water was generated and the acid value of the system dropped to 6.2 mg KOH / g, thus obtaining the terminal hydroxyl intermediate. The system was cooled to 85°C, and 244.5 parts by weight of isophorone diisocyanate were slowly added dropwise. The dropping rate was controlled to maintain the reaction temperature at no more than 95°C. After the addition was completed, the reaction was kept at the temperature for 1.5 hours to obtain the isocyanate-terminated prepolymer. Cool the reaction system to 45°C, slowly add 232.4 parts by weight of 1,6-hexanediamine, stir vigorously and maintain the temperature between 45-55°C, and react for 2.5 hours; After the reaction was completed, unreacted 1,6-hexanediamine and volatiles were removed by vacuum rotary evaporation at 125℃ and -0.09MPa. After cooling, a pale yellow glassy solid was obtained, with an amine value of 172 mgKOH / g and a branching degree of 0.63.

[0035] Preparation Example 3: This preparation example provides a hexamethylenediamine-based hyperbranched polyamide-ester, comprising the following steps: 153.2 parts by weight of diisopropanolamine were added to a reaction vessel equipped with a mechanical stirrer, nitrogen gas delivery tube, thermometer and water separator, and heated to 90°C to melt it; Under nitrogen protection, 100.1 parts by weight of succinic anhydride were added in three portions. After stirring evenly, the temperature was raised to 150°C and the reaction was carried out for 3.5 hours until no more water was generated and the acid value of the system dropped below 5.0 mg KOH / g, thus obtaining the terminal hydroxyl intermediate. The system was cooled to 90°C, and 255.6 parts by weight of isophorone diisocyanate were slowly added dropwise. The dropping rate was controlled to maintain the reaction temperature at no more than 100°C. After the addition was completed, the reaction was kept at the temperature for 2.0 hours to obtain the isocyanate-terminated prepolymer. The reaction system was cooled to 50°C, and 267.3 parts by weight of 1,6-hexanediamine were slowly added dropwise. The mixture was stirred vigorously and the temperature was maintained between 50-60°C for 3.0 hours. After the reaction was completed, unreacted 1,6-hexanediamine and volatiles were removed by vacuum rotary evaporation at 130℃ and -0.09MPa. After cooling, a yellow glassy solid was obtained, with an amine value of 155 mgKOH / g and a branching degree of 0.68.

[0036] Preparation Example 4: This preparation example provides a styrene-acrylonitrile-glycidyl methacrylate copolymer, comprising the following steps: In a reactor equipped with a reflux condenser, a constant pressure dropping funnel, a mechanical stirrer and nitrogen protection, 120 parts by weight of xylene were added, and the temperature was raised to 135°C and kept under reflux. 35 parts by weight of styrene, 10 parts by weight of acrylonitrile, 55 parts by weight of glycidyl methacrylate (GMA) and 4.0 parts by weight of di-tert-butyl peroxide (DTBP) were mixed evenly to prepare a mixed monomer solution. The mixed monomer solution was added dropwise to the reactor at a uniform rate over 3.0 hours, while maintaining the temperature at 135-140℃ during the addition process; After the addition was complete, the reaction was kept at the temperature for 1.0 hour, and then 0.5 parts by weight of di-tert-butyl peroxide was added within 30 minutes, and the reaction was kept at the temperature for another 2.0 hours to improve the monomer conversion rate. After the reaction was complete, the temperature was raised to 180℃, and the solvent and unreacted monomers were removed under a vacuum of -0.095 MPa. The material was then discharged, cooled, and pulverized to obtain the solid copolymer SAG-1. The weight-average molecular weight was measured to be 5200, and the epoxy equivalent was 265 g / mol.

[0037] Preparation Example 5: This preparation example provides a styrene-acrylonitrile-glycidyl methacrylate copolymer, comprising the following steps: In a reactor equipped with a reflux condenser, a constant pressure dropping funnel, a mechanical stirrer and nitrogen protection, 120 parts by weight of xylene are added, and the temperature is raised to 125°C and kept under reflux. 52 parts by weight of styrene, 15 parts by weight of acrylonitrile, 33 parts by weight of glycidyl methacrylate (GMA) and 1.5 parts by weight of di-tert-butyl peroxide (DTBP) were mixed evenly to prepare a mixed monomer solution. The mixed monomer solution was added dropwise to the reaction vessel at a uniform rate over 3.5 hours, while maintaining the temperature at 125-130℃ during the addition process. After the addition was complete, the reaction was kept at the temperature for 1.5 hours, and then 0.3 parts by weight of di-tert-butyl peroxide (dissolved in a small amount of xylene) was added within 30 minutes, and the reaction was kept at the temperature for another 2.0 hours. After the reaction was completed, the temperature was raised to 180℃, and the solvent and unreacted monomers were removed under a vacuum of -0.095MPa. The material was then discharged, cooled, and pulverized to obtain the solid copolymer SAG-2. The weight-average molecular weight (Mw) was measured to be 8800, and the epoxy equivalent was 435 g / mol.

[0038] Example 1: This embodiment provides a multi-color injection molding process for smart wearable devices, including the following steps: (1) Preparation of the first component (rigid skeleton material): 96.0 parts by weight of polybutylene terephthalate resin, 3.5 parts by weight of epoxy-containing styrene-acrylonitrile copolymer obtained in Preparation Example 4 and 0.5 parts by weight of antioxidant 1010 are mixed evenly and melt-extruded into granules in a twin-screw extruder. The extrusion temperature is controlled at 230-240℃ to obtain rigid skeleton granules; (2) Preparation of the second component (soft coating material): 95.0 parts by weight of polyether thermoplastic polyurethane elastomer, 4.5 parts by weight of medium molecular weight end-amino hyperbranched polyamide-ester additive obtained in Preparation Example 2 and 0.5 parts by weight of antioxidant 1010 are mixed evenly and granulated in a twin-screw extruder in low-temperature shear mode. The extrusion temperature is controlled at 180-195℃ to obtain soft coating granules. (3) Mold preparation: A two-color rotary mold is used to laser etch the cavity surface corresponding to the hard-soft interface in the first injection molding mold to form a non-inverted grid texture. The surface roughness Ra is measured to be 4.5 micrometers, the average width RSm of the texture contour unit is 75 micrometers, and the texture direction is perpendicular to the melt flow direction of the second injection. (4) First injection molding: The first component is injected into the mold at a barrel temperature of 245°C and a mold temperature of 70°C. The injection speed is 50 mm / s. After cooling for 20 seconds, a hard skeleton with micro-texture on the surface is obtained. (5) Second injection molding: Rotate the mold and inject the second component into the cavity at a barrel temperature of 205°C. The injection process is divided into two stages: the first stage fills the flow channel and the non-contact interface area, with an injection speed of 20 mm / s; when the melt front reaches the hard skeleton texture area, immediately switch to the second stage high-frequency pulse injection, increase the injection speed to 220 mm / s, hold pressure of 45 MPa, hold pressure time of 5 seconds, and eject after cooling for 25 seconds.

[0039] Example 2: This embodiment provides a multi-color injection molding process for smart wearable devices, including the following steps: (1) Preparation of the first component (rigid skeleton material): 98.0 parts by weight of polybutylene terephthalate resin, 1.5 parts by weight of epoxy-containing styrene-acrylonitrile copolymer obtained in Preparation Example 4 and 0.5 parts by weight of antioxidant 1010 are mixed evenly and melt-extruded into granules in a twin-screw extruder. The extrusion temperature is controlled at 230-240℃ to obtain rigid skeleton granules; (2) Preparation of the second component (soft coating material): 96.5 parts by weight of polyether-type thermoplastic polyurethane elastomer, 3.0 parts by weight of the low molecular weight terminal amino hyperbranched polyamide-ester additive obtained in Preparation Example 1 and 0.5 parts by weight of antioxidant 1010 are mixed evenly and granulated in a twin-screw extruder in low-temperature shear mode. The extrusion temperature is controlled at 180-195℃ to obtain soft coating granules. (3) Mold preparation: The interface area of ​​the first injection molding mold is laser etched to form a random sand texture. The surface roughness Ra is measured to be 3.2 micrometers and the average width RSm of the texture contour unit is 50 micrometers. (4) First injection molding: The first component is injected into the mold at a barrel temperature of 240°C and a mold temperature of 60°C. The injection speed is 40 mm / s. After cooling for 15 seconds, a rigid skeleton is obtained. (5) Second injection molding: Rotate the mold and inject the second component into the cavity at a barrel temperature of 200°C. The first stage low-speed filling speed is 15 mm / s. When the melt contacts the interface texture area, switch to the second stage high-speed injection, increase the speed to 180 mm / s, hold pressure of 40 MPa, hold pressure time of 4 seconds, and eject after cooling for 20 seconds.

[0040] Example 3: This embodiment provides a multi-color injection molding process for smart wearable devices, including the following steps: (1) Preparation of the first component (rigid skeleton material): 92.0 parts by weight of polybutylene terephthalate resin, 7.5 parts by weight of the low epoxy content styrene-acrylonitrile copolymer obtained in Preparation Example 5 and 0.5 parts by weight of antioxidant 1010 are mixed evenly and melt-extruded into granules in a twin-screw extruder. The extrusion temperature is controlled at 235-245℃ to obtain rigid skeleton granules; (2) Preparation of the second component (soft coating material): 92.0 parts by weight of polyether-type thermoplastic polyurethane elastomer, 7.5 parts by weight of high molecular weight end-amino hyperbranched polyamide-ester additive obtained in Preparation Example 3 and 0.5 parts by weight of antioxidant 1010 are mixed evenly and granulated in a twin-screw extruder in low-temperature shear mode. The extrusion temperature is controlled at 190-205℃ to obtain soft coating granules. (3) Mold preparation: The interface area of ​​the first injection molding mold is deeply etched to form a high-density mesh texture. The surface roughness Ra is measured to be 6.0 micrometers and the average width RSm of the texture contour unit is 100 micrometers. (4) First injection molding: The first component is injected into the mold at a barrel temperature of 250°C and a mold temperature of 80°C. The injection speed is 60 mm / s. After cooling for 25 seconds, a rigid skeleton is obtained. (5) Second injection molding: Rotate the mold and inject the second component into the cavity at a barrel temperature of 210°C. The first stage low-speed filling speed is 25 mm / s. When the melt contacts the interface texture area, switch to the second stage high-speed injection, increase the speed to 280 mm / s, hold pressure of 60 MPa, hold pressure time of 6 seconds, and eject after cooling for 30 seconds to obtain a two-color injection molded product.

[0041] Example 4: This embodiment provides a multi-color injection molding process for smart wearable devices, including the following steps: (1) Preparation of the first component (rigid skeleton material): 95.0 parts by weight of polybutylene terephthalate resin, 4.5 parts by weight of the low epoxy content styrene-acrylonitrile copolymer obtained in Preparation Example 5 and 0.5 parts by weight of antioxidant 1010 are mixed evenly and extruded to obtain rigid skeleton granules. (2) Preparation of the second component (soft coating material): 94.0 parts by weight of polyether thermoplastic polyurethane elastomer, 5.5 parts by weight of medium molecular weight end-amino hyperbranched polyamide-ester additive obtained in Preparation Example 2 and 0.5 parts by weight of antioxidant 1010 are mixed evenly and granulated by low temperature extrusion to obtain soft coating granules. (3) Mold preparation: The surface roughness Ra of the textured area of ​​the mold interface is 5.0 micrometers, and the texture direction is at a 45° angle to the flow direction; (4) First injection molding: Process conditions are the same as in Example 1; (5) Second injection molding: The second component is injected into the cavity at a barrel temperature of 205°C. The first stage low-speed filling speed is 20 mm / s; the second stage interface activation injection speed is 250 mm / s, the holding pressure is 50 MPa, and the two-color injection molded product is obtained after cooling and solidification.

[0042] Comparative Example 1: Compared to Example 1, the differences are as follows: the first component (rigid skeleton material) does not contain epoxy-containing styrene-acrylonitrile copolymer, and only uses polybutylene terephthalate resin and antioxidants; the second component (soft coating material) does not contain amino-terminated hyperbranched polyamide-ester additives, and only uses polyether-type thermoplastic polyurethane elastomer and antioxidants. All other raw material ratios, molds, and process parameters are the same.

[0043] Comparative Example 2: Compared to Example 1, the difference lies in that the terminal amino hyperbranched polyamide-ester additive in the second component (soft coating material) is replaced with an equal amount of linear 1,6-hexanediamine (a small molecule amine). All other aspects are the same.

[0044] Comparative Example 3: Compared to Example 1, the difference lies in that: in the second injection molding process, a low injection speed (20 mm / s) is maintained throughout, and the high-frequency pulse acceleration in the second stage is not performed. Everything else is the same.

[0045] Comparative Example 4: Compared to Example 1, the difference lies in that the bonding interface area of ​​the first injection molding die is a smooth mirror surface (Ra<0.1 micrometers) and has not undergone laser etching texture processing. All other aspects are the same.

[0046] Comparative Example 5: Compared to Example 1, the difference is that the first component (rigid skeleton material) does not contain epoxy-containing styrene-acrylonitrile copolymer (SAG-1), but is replaced with an equal amount of pure polybutylene terephthalate resin. All other aspects are the same.

[0047] Comparative Example 6: The difference from Example 1 is that the additives used in the second component (soft coating material) are replaced with the terminal hydroxyl intermediate (ungrafted amine hyperbranched polymer) obtained in Preparation Example 1. All else is the same.

[0048] Comparative Example 7: The difference from Example 1 is that the second injection molding process uses high-speed injection (220 mm / s) throughout, including the runner filling stage. Everything else is the same.

[0049] Test Example 1: This test aims to verify the rheological behavior of the soft coating material (second component) in the embodiments at different shear rates, and in particular to confirm whether the hyperbranched polymer system has the expected nonlinear shear thinning effect.

[0050] Experimental subjects: Sample A: Soft coated granules prepared in Example 1.

[0051] Sample B: Pure thermoplastic polyurethane elastomer granules (blank control).

[0052] Sample C: Granules prepared in Comparative Example 2.

[0053] The samples to be tested (sample A, sample B and sample C) were placed in a vacuum oven and dried at 80°C for 4 hours to remove moisture.

[0054] A Rosand RH7 dual-column capillary rheometer was selected, and the barrel temperature was set to 205℃ and kept constant.

[0055] The dried sample is added to the barrel, preheated at a constant temperature for 5 minutes, and then compacted to remove air from the material.

[0056] Set the shear rate scan range to 10. 2 s -1 Up to 2×10 5 s -1 Data on shear stress and apparent viscosity at different shear rates were collected.

[0057] Each sample was tested three times under the same conditions, and the arithmetic mean was taken as the final test result.

[0058] The experimental data are shown in Table 1: Table 1: Apparent viscosity data of samples at different shear rates Shear rate (s⁻¹) Sample A (Example 1) Sample B (pure TPU) Sample C (Comparative Example 2) 100 785.4 821.2 412.5 200 712.8 765.9 398.1 500 589.3 680.4 365.2 1,000 452.1 592.6 340.8 2,000 285.6 510.3 321.4 5,000 85.2 425.8 298.7 10,000 32.4 360.5 285.9 50,000 12.8 215.1 240.3 100,000 8.5 155.4 210.6 200,000 5.1 112.7 185.2 in conclusion: According to Table 1 and Figure 1 Data shows significant differences in the rheological behavior of the samples. Sample B exhibits the pseudoplastic characteristics of a conventional polymer melt, with viscosity decreasing gradually with increasing shear rate. Sample C has a significantly lower initial viscosity than samples A and B, indicating that linear small-molecule amines produce a plasticizing effect under low shear. This low viscosity state can easily cause unstable filling or overflow during the injection molding runner transport stage. Sample A maintained a relatively high viscosity (785.4 Pa·s @ 100 s) in the low shear rate range. -1 The values ​​are close to those of pure thermoplastic polyurethane elastomer matrix, indicating that under these conditions, the hyperbranched polymer molecules maintain a contractile conformation, do not undergo deentanglement, and the terminal amino groups are in a shielded state, without reducing the matrix viscosity.

[0059] Entering the high shear rate range (>2000s) -1 After 10,000 s, sample A showed the largest decrease in apparent viscosity. -1 At that time, the viscosity of sample A decreased to 32.4 Pa·s, lower than that of samples B (360.5 Pa·s) and C (285.9 Pa·s). This shear-sensitive characteristic confirms that the hyperbranched structure undergoes deformation and orientation under high-frequency shear stress, resulting in reduced intramolecular friction. This characteristic is consistent with the process design of Example 1: during the second high-speed pulse stage, the decrease in material viscosity allows the melt to penetrate into the microtexture (Ra 4.5 μm) of the mold surface, providing conditions for the generation of micro-frictional heat; at the same time, the molecular chain extension caused by high shear helps to expose the terminal amino groups to the phase interface, promoting chemical reactions.

[0060] Test Example 2: A K-type thermocouple probe with a diameter of 0.5 mm (measuring point A) is pre-embedded in the center of the interface bonding area after the first rigid skeleton is formed, so that the tip of the probe contacts the root of the texture on the skeleton surface; a thermocouple probe of the same specification (measuring point B) is pre-embedded 20 mm after the gate of the second jet channel.

[0061] Install the mold onto the two-color injection molding machine, connect the data acquisition instrument, and set the sampling frequency to 1000Hz.

[0062] The second injection molding was performed according to the parameter conditions of Example 1 (segmented speed change + texture), Comparative Example 3 (low speed throughout + texture), Comparative Example 4 (segmented speed change + smooth surface) and Comparative Example 7 (high speed throughout + texture).

[0063] Record the temperature changes at measuring points A and B during the injection molding process, and extract the highest peak temperature for each molding cycle.

[0064] Each set of parameters was run 10 times continuously. The data from the first 3 times was discarded, and the average value of the last 7 times was taken.

[0065] The experimental data are shown in Table 2: Table 2: Records of peak melt temperatures at the flow channel and interface under different process conditions Test group Set the barrel temperature (°C) Measuring point B: Peak temperature at the flow channel inlet (°C) Measuring point A: Peak temperature of the interface region (°C) Example 1 205 212.4 268.7 Comparative Example 3 205 206.1 209.8 Comparative Example 4 205 214.2 221.5 Comparative Example 7 205 243.6 275.2 in conclusion: According to Table 2 and Figure 2 Data shows that process parameters and mold surface condition have different effects on the local temperature of the melt. In Example 1, the temperature at measuring point B (flow channel) was 212.4℃, close to the set barrel temperature, indicating that there was little shear heat accumulation during the low-speed filling stage, and the melt was within the processing temperature range. The temperature at measuring point A (interface) was 268.7℃, 63.7℃ higher than the barrel temperature. This temperature rise originated from the shear friction and viscous dissipation of the melt flowing at high speed across the micro-textured surface, and the temperature value reached the activation conditions for the interfacial chemical reaction.

[0066] In Comparative Example 3, the temperature at measuring point A was 209.8℃, showing little difference from measuring point B. The low-flow-rate melt exhibited insufficient shear stress on the textured surface, preventing the formation of localized high temperatures. In Comparative Example 4, the temperature at measuring point A was 221.5℃. The smooth mold surface exhibited low frictional resistance, resulting in limited temperature rise from high-speed injection, failing to reach the temperature required for interfacial reaction. In Comparative Example 7, the temperature at measuring point A was 275.2℃, but the temperature at measuring point B reached 243.6℃, ​​indicating that the melt generated significant shear heat during the runner stage before entering the cavity, increasing the risk of thermal degradation of the base material. The parameter settings in Example 1, while controlling the runner melt temperature, also increased the interfacial region temperature.

[0067] Test Example 3: The injection molded products prepared in Example 1 and Comparative Examples 1, 2, 3, 5, and 6 were selected as test subjects.

[0068] At the junction of hard and soft materials in the product, a scalpel is used to scrape off the soft material layer that is close to the surface of the hard skeleton. The sampling depth is controlled within 0.2 mm to obtain an interface layer sample.

[0069] The sample was dried in a vacuum oven until constant weight was achieved, and the initial weight was recorded as follows. Each sample weighs approximately 0.2g.

[0070] The sample was immersed in a flask containing 50 mL of N,N-dimethylformamide (DMF) and extracted by reflux in an oil bath at 80 °C for 24 hours.

[0071] After extraction, the sample was filtered through a 200-mesh stainless steel screen, and the residual solids were collected and washed three times with ethanol.

[0072] The residual solid was dried in a vacuum oven until constant weight, and the residual weight was recorded as follows. .

[0073] According to the formula ; Calculate the gel content.

[0074] Each group of samples was tested in parallel 5 times, and the arithmetic mean was taken.

[0075] The experimental data are shown in Table 3: Table 3: Solvent extraction gel content test results of interfacial layer samples in each group Sample source Initial weight (g) Residual weight (g) Gel content (%) Remark Example 1 0.2452 0.1746 71.2 The residue is a continuous network of hard membrane. Comparative Example 1 0.2388 0.0019 0.8 The solution is clear and almost completely dissolved. Comparative Example 2 0.2514 0.0412 16.4 The residue was in the form of broken flocculent material. Comparative Example 3 0.2405 0.0137 5.7 Very little residue Comparative Example 5 0.2336 0.0028 1.2 Almost completely dissolved Comparative Example 6 0.2471 0.0035 1.4 Almost completely dissolved in conclusion: Table 3 shows that the solvent resistance of the interface materials varies among the groups. The gel content of the sample in Example 1 was 71.2%, indicating that the polymer segments at the interface had formed a three-dimensional network structure that could not be dissolved by DMF, confirming that the epoxy groups on the hard adhesive side and the hyperbranched amine groups on the soft adhesive side under thermal activation conditions under chemical cross-linking.

[0076] The gel content of Comparative Examples 1, 5, and 6 was all below 1.5%, which is within the experimental error range. These three groups of samples lacked reaction auxiliaries, epoxy acceptors, or amine donors, resulting in no chemical bonding at the interface and complete dissolution of the thermoplastic polyurethane matrix in the solvent. Comparative Example 3 had a gel content of 5.7%, indicating that under low-speed injection conditions throughout the process, the interfacial shear heat was insufficient to overcome the activation energy, resulting in a low degree of chemical crosslinking. Comparative Example 2 had a gel content of 16.4%, lower than Example 1, indicating that the linear diamine had lower functionality and was easily encapsulated by the matrix, resulting in a lower crosslinking network density than the hyperbranched polymer system.

[0077] Test Example 4: The two-color injection molded products prepared in Examples 1-4 and Comparative Examples 1-7 were placed in a constant temperature and humidity environment of 23±2℃ and 50±5%RH for 24 hours.

[0078] Using a water jet cutting device, a 20mm wide strip sample was cut from the central area of ​​the product, preserving the interface between the hard and soft materials. Five parallel samples were prepared for each group.

[0079] The specimen is mounted onto a universal testing machine equipped with a 90-degree peeling fixture.

[0080] The rigid skeleton part of the specimen is fixed on the horizontal sliding test table, and the soft covering part is clamped in the tensile fixture above.

[0081] The tensile speed was set to 50 mm / min for testing. The average load during the peeling process was recorded, and the value was calculated according to the formula (peel strength = average load / sample width).

[0082] After the test, examine the damaged surface and determine the damage mode (interface damage, cohesive damage, or mixed damage).

[0083] The experimental data are shown in Table 4: Table 4: Results of 90° peel strength test and failure modes of samples in each group Group Average peel strength (N / cm) Standard deviation (SD) Destruction Mode Example 1 54.2 1.8 Cohesive destruction of the soft rubber matrix (100%) Example 2 41.5 2.1 Mixed destruction (with a tendency towards cohesion) Example 3 56.8 2.4 Cohesive destruction of the soft rubber matrix (100%) Example 4 48.3 1.9 Cohesive breakdown of the soft rubber matrix (95%) Comparative Example 1 3.6 0.5 Interface damage (smooth separation) Comparative Example 2 18.9 3.2 Mixed damage (local adhesion) Comparative Example 3 12.4 1.1 Interface destruction Comparative Example 4 6.7 0.4 Interface destruction Comparative Example 5 4.2 0.6 Interface destruction Comparative Example 7 38.6 5.8 Mixed failure (accompanied by bubble defects) in conclusion: Table 4 shows that peel strength is affected by chemical composition and process parameters. Examples 1, 3, and 4 exhibit peel strengths exceeding 45 N / cm, with the primary failure mode being cohesive failure of the soft adhesive matrix, indicating that the interfacial bonding strength is higher than the bulk yield strength of the thermoplastic polyurethane material. Comparative Example 1, relying on physical adhesion, achieved a peel strength of 3.6 N / cm, with a smooth detachment at the interface. Comparative Example 5, lacking the epoxy component on the hard adhesive side, achieved a peel strength of 4.2 N / cm, demonstrating that unilateral chemical modification failed to achieve effective adhesion.

[0084] Regarding process parameters, the peel strengths of Comparative Example 3 (low speed) and Comparative Example 4 (smooth interface) were 12.4 N / cm and 6.7 N / cm, respectively. Due to the lack of shear-friction thermal activation conditions, the degree of interfacial chemical reaction was low. In terms of additive structure, Comparative Example 2 used a straight-chain diamine, with a peel strength of 18.9 N / cm, lower than Example 1. The density of interfacial crosslinking points formed by straight-chain molecules was lower than that of the hyperbranched polymer system, and small molecules were prone to migration.

[0085] Comparative Example 7 (high-speed throughout) showed a peel strength of 38.6 N / cm, but with a large standard deviation (5.8) and accompanying bubble defects. High-speed shearing throughout resulted in melt overheating and degradation, affecting the uniformity of the material's internal structure. Example 1 employed segmented injection rate control, achieving high bonding strength while maintaining stable mechanical properties.

[0086] Test Example 5: Two-color injection molded products prepared in Example 1 and Comparative Examples 1, 2, 3 and 7 were selected and cut to prepare standard peel test samples, 10 samples in each group, which were divided into control group and aging group.

[0087] The control group samples were subjected to a 90-degree peel strength test, and the initial peel strength was recorded.

[0088] The aging group samples were placed in a constant temperature and humidity test chamber, with the temperature set at 85℃ and the relative humidity at 85%.

[0089] Maintain the test conditions for 168 hours, with the sample suspended in the air to ensure uniform contact with the humid and hot air.

[0090] Remove the sample and allow it to stand in a standard environment (23℃, 50%RH) for 24 hours to allow the temperature and humidity to reach equilibrium.

[0091] The treated samples were subjected to a 90-degree peel strength test, and the strength retention rate was calculated as (strength after aging / initial strength × 100%).

[0092] The experimental data are shown in Table 5: Table 5: Comparison of peel strength before and after damp heat aging test Group Initial peel strength (N / cm) Peel strength after aging (N / cm) Strength retention rate (%) Damage Mode Change Example 1 54.2 48.6 89.7 Still a cohesive destruction Comparative Example 1 3.6 0.2 5.6 Automatic interface delamination Comparative Example 2 18.9 11.4 60.3 Transform into interface destruction Comparative Example 3 12.4 4.1 33.1 Complete interface destruction Comparative Example 7 38.6 26.5 68.7 Mixed destruction in conclusion: According to Table 5 and Figure 3 Data shows that a humid and hot environment affects the interfacial strength of different bonding mechanisms. In Example 1, after 168 hours of aging treatment, the peel strength decreased from 54.2 N / cm to 48.6 N / cm, with a retention rate of 89.7%, and the failure mode remained cohesive failure of the soft rubber matrix. The chemical cross-linking network formed by the in-situ reaction at the interface has chemical stability and can resist moisture penetration and hydrolysis; the bonding layer did not degrade.

[0093] In Comparative Example 1, the strength of the physical bond interface decreased to 0.2 N / cm after aging, with a retention rate of 5.6%, and the sample interface delaminated. Moisture penetration into the interfacial micro-gaps caused TPU to absorb moisture and swell, leading to the failure of the physical anchoring points. The retention rate of Comparative Example 2 was 60.3%, lower than that of Example 1. The cross-linked network constructed by the linear amine system had low density, and the linear molecular chain segments relaxed under high temperature and high humidity conditions, allowing water molecules to diffuse to the interfacial bonding points and trigger hydrolysis.

[0094] Comparative Example 3, due to its low degree of interfacial chemical reaction, experienced a strength reduction to 4.1 N / cm after aging, with a retention rate of 33.1%. Comparative Example 7, with a retention rate of 68.7%, suffered from thermal degradation of the matrix material caused by high-speed shearing throughout the process, which reduced the material's hydrolysis resistance. Microscopic defects generated during processing accelerated the breakdown of the interfacial layer. Example 1 demonstrates that high-density chemical bonding and controlled process parameters can improve the long-term stability of the product.

[0095] Test Example 6: The materials and process conditions of Example 1, Comparative Example 2 and Comparative Example 7 were selected and production verification was carried out on the same two-color injection molding machine.

[0096] Each set of parameters is used for 100 consecutive injection molding cycles, and all injection products are collected to establish a sample library.

[0097] Inspect the appearance of the product under a D65 standard light source and record the yellowing of the gate and runner ends, silver streaks or flow marks on the surface, and overflow at the parting line.

[0098] A 50x optical microscope was used to inspect the microstructure of the gate area to confirm the presence of tiny bubbles or carbonized black spots.

[0099] Count the number of defective samples of each type, and calculate the yield rate and the occurrence rate of each individual defect.

[0100] The experimental data are shown in Table 6: Table 6: Appearance Quality Statistics for Each Group After 100 Continuous Production Runs Group Total number of samples (number of samples) Scorching and yellowing rate (%) Flow mark / air mark rate (%) Overflow / Randomness (%) Overall yield rate (%) Example 1 100 0.0 2.0 1.0 97.0 Comparative Example 2 100 1.0 5.0 18.0 76.0 Comparative Example 7 100 11.0 23.0 4.0 62.0 in conclusion: Table 6 shows that the matching degree between material rheological properties and process parameters affects processing quality. Example 1 achieved an overall yield of 97.0%, with no scorching or yellowing, and minimal flow marks and overflow. During the flow channel transport stage, the hyperbranched polymer maintained the matrix viscosity, suppressing low-shear turbulence and gas entrainment; segmented injection rate control reduced shear heat accumulation before the melt entered the cavity, preventing material thermal degradation.

[0101] Comparative Example 7 showed a scorching and yellowing rate of 11.0% and a flow mark / gas streak rate of 23.0%. The high injection speed throughout the process caused the melt to undergo continuous strong shearing within the runner. Viscous dissipation led to a temperature rise exceeding the thermal decomposition temperature of TPU and additives, resulting in degradation products and volatile gases forming yellowing and silver streaks on the product surface. The high filling speed caused the melt to generate jet streams, and uneven cooling resulted in flow marks.

[0102] Comparative Example 2 had a overflow rate of 18.0%, higher than other groups. Linear-chain small-molecule amines plasticize and reduce the viscosity of the TPU matrix at low shear rates. If the initial viscosity of the melt is too low during the initial filling stage, it is easy to squeeze into the mold parting line gap during the holding pressure stage, forming flash. Example 1 utilizes the viscosity retention characteristics of hyperbranched structures under low shear to ensure the stability of the injection molding process.

[0103] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A multi-color injection molding process for smart wearable devices, characterized in that, Includes the following steps: S1. Polybutylene terephthalate resin, epoxy-containing styrene-acrylonitrile copolymer and antioxidant are mixed in proportion and melt-extruded and granulated at 230-245℃ to obtain rigid skeleton granules. S2. Thermoplastic polyurethane elastomer, amino-terminated hyperbranched polyamide-ester additive and antioxidant are mixed in proportion and extruded and granulated under low temperature shear mode of 180-205℃ to obtain soft coated granules. S3. Laser etching is performed on the area in the first injection molding die corresponding to the hard-soft interface to form a micro-texture. S4. First injection molding: The first component is injected into the mold and cooled to obtain a hard skeleton with micro-texture on the surface. S5. Second injection molding: The second component is injected into the mold cavity, and the injection process uses segmented speed control. The first stage uses low-speed injection to fill the flow channel and the cavity area before the melt reaches the bonding interface; When the melt front reaches the hard skeleton texture area, the process switches to the second stage of high-speed pulse injection, using shear friction heat to activate the epoxy-amine chemical crosslinking reaction at the interface. After holding pressure and cooling, multi-color injection molded products are obtained.

2. The multi-color injection molding process for a smart wearable device according to claim 1, characterized in that, The weight ratios of the rigid skeleton granules and the soft coated granules are as follows: Rigid skeleton granules: 92.0-98.0 parts of polybutylene terephthalate resin, 1.5-7.5 parts of epoxy-containing styrene-acrylonitrile copolymer, and 0.1-1.0 parts of antioxidant; The soft coated granules consist of 92.0-96.5 parts of thermoplastic polyurethane elastomer, 3.0-7.5 parts of amino-terminated hyperbranched polyamide-ester additive, and 0.1-1.0 parts of antioxidant.

3. The multi-color injection molding process for a smart wearable device according to claim 1, characterized in that, The preparation method of the epoxy-containing styrene-acrylonitrile copolymer in step S1 includes: Using xylene as a solvent, a mixed solution of styrene, acrylonitrile, glycidyl methacrylate and an initiator was added dropwise to the reaction system at 125-140℃ to carry out a free radical copolymerization reaction. After the reaction was completed, the product was obtained by devolatilization and drying. The copolymer has an epoxy equivalent of 265-435 g / mol and a weight-average molecular weight of 5200-8800.

4. The multi-color injection molding process for a smart wearable device according to claim 1, characterized in that, In the raw materials for preparing the epoxy-containing styrene-acrylonitrile copolymer, the weight ratio of the monomers is: 35-52 parts styrene, 10-15 parts acrylonitrile, and 33-55 parts glycidyl methacrylate.

5. The multi-color injection molding process for a smart wearable device according to claim 1, characterized in that, The preparation method of the terminal amino hyperbranched polyamide-ester additive in step S2 includes the following sub-steps: Diisopropanolamine is heated to melt, and succinic anhydride is added in batches. Polycondensation reaction is carried out at 145-150℃ until the acid value of the reaction mixture drops below 10mgKOH / g to obtain the terminal hydroxyl intermediate. The hydroxyl-terminated intermediate is cooled down, and isophorone diisocyanate is added dropwise to the hydroxyl-terminated intermediate. The reaction temperature is controlled to not exceed 100°C, and the reaction is maintained at this temperature to obtain an isocyanate-terminated prepolymer. The isocyanate-terminated prepolymer is further cooled, and a diamine compound is added dropwise to the prepolymer. The end-capping reaction is carried out at 40-60°C, and the volatiles are removed under vacuum to obtain the final product.

6. The multi-color injection molding process for a smart wearable device according to claim 5, characterized in that, The diamine compound is ethylenediamine or 1,6-hexanediamine; the resulting terminal amino hyperbranched polyamide-ester additive has an amine value of 155-195 mgKOH / g and a branching degree of 0.58-0.

68.

7. The multi-color injection molding process for a smart wearable device according to claim 1, characterized in that, In step S3, the microtexture is a non-inverted structure with a surface roughness Ra of 3.2-6.0 micrometers, an average width RSm of 50-100 micrometers for the texture contour unit, and the texture direction forms an angle of 45-90 degrees with the flow direction of the second melt injection.

8. The multi-color injection molding process for a smart wearable device according to claim 1, characterized in that, In step S5, the specific parameters for the segmented speed control are as follows: The initial low-speed injection rate is 15-25 mm / s; The second high-speed pulse injection speed is 180-280 mm / s; The switching point is set as: the time when the second jet of melt just comes into contact with the interface between the hard skeleton and the flow channel and the gate.

9. The multi-color injection molding process for a smart wearable device according to claim 1, characterized in that, In step S5, the process conditions for the second injection molding also satisfy: The barrel temperature is 200-210℃, the holding pressure is 40-60 MPa, and the holding time is 4-6 seconds.

10. The multi-color injection molding process for a smart wearable device according to claim 1, characterized in that, In step S4, the process conditions for the first injection molding are: barrel temperature of 230-250℃, mold temperature of 60-80℃, and injection speed of 40-60 mm / s.

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