Environment-friendly foaming TPU + PU inflation-free composite tire and preparation method thereof

Abstract

The invention belongs to the technical field of polymer composite tire materials and tire preparation, and discloses an environment-friendly foamed TPU + PU inflation-free composite tire and a preparation method thereof, a TPU tire top is optimized by a composite modifier and is matched with an anti-aging component, and the wear resistance and the anti-aging performance are excellent; the PU foaming layer is subjected to process regulation and control, the buffer performance is stable, the static load resistance is high, and the problems of cracking, uneven abrasion and the like are not prone to occurring after long-term use; regular air supply maintenance is not needed, extra cost in the using process is reduced, safety risks caused by maintenance negligence are avoided, the running reliability of a vehicle is improved, and the overall service life of the tire is prolonged; multi-performance balance is achieved through collaborative optimization of the structure and materials, the TPU tire top adopts the composite pattern design of the transverse drainage lines, the longitudinal anti-skid lines and the annular noise reduction grooves, and the drainage and anti-skid functions and the noise reduction effect are considered at the same time; the PU foaming layer is regulated and controlled by a modified reinforcing component and a composite foaming agent, the elasticity and the structural strength are synergistically improved, and the buffering and damping effect is close to that of a high-quality pneumatic tire.

Description

An environmentally friendly foamed TPU+PU airless composite tire and its preparation method Technical Field

[0001] This invention belongs to the field of polymer composite tire materials and tire preparation technology, specifically an environmentally friendly foamed TPU+PU airless composite tire and its preparation method. Background Technology

[0002] Tires are load-bearing and cushioning components in vehicle operation. Their structure and material system directly affect driving stability, service life and maintenance frequency. Existing tire products mainly include pneumatic tires and solid tires. Pneumatic tires rely on internal air pressure to maintain their support capacity, while solid tires mainly rely on the material itself to provide load-bearing and cushioning.

[0003] While pneumatic tires offer good elasticity and cushioning, they are prone to leaks and even blowouts due to punctures, aging, or abnormal tire pressure. They also require regular inflation and maintenance. Solid tires, on the other hand, avoid leaks but are typically heavier, have weaker cushioning, and produce more noticeable vibrations and noise. Furthermore, a single material structure makes it difficult to simultaneously achieve wear resistance, static load resistance, and long-term stability. Existing pneumatic tire solutions also suffer from insufficient bonding stability between the TPU top and PU foam layer and the rim, as well as poor uniformity in the foam layer structure.

[0004] Therefore, existing pneumatic tires still have shortcomings in balancing structural stability, material synergy, and low maintenance requirements, especially in terms of the reliability of the interface bonding between the TPU top, PU foam layer, and wheel hub, as well as the consistency of foam layer molding, which still need further improvement. Summary of the Invention

[0005] The purpose of this invention is to provide an environmentally friendly foamed TPU+PU airless composite tire and its preparation method, so as to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing an environmentally friendly foamed TPU+PU airless composite tire, comprising the following specific steps: preferably, in the wheel hub modification stage, an aluminum alloy or reinforced nylon wheel hub is selected, and 3-4 staggered inverted trapezoidal annular grooves are machined on the outer circumferential surface of the wheel hub by CNC machining, and bidirectional staggered oblique anti-skid teeth are machined on the inner wall of the grooves; subsequently, a three-step composite treatment process of laser micro-etching, plasma activation, and silane coupling agent anchoring is adopted. Laser micro-etching uses pulsed laser to form uniform micron-level rough texture on the outer circumferential surface of the wheel hub and in the grooves, and the texture is distributed in a honeycomb pattern. During plasma activation, a mixed gas with an argon and oxygen volume ratio of 3:1 is introduced, and the processing time is controlled at 70-80s and the power at 120-140W to activate the surface of the wheel hub, remove oil and impurities, and increase the content of active groups such as hydroxyl and carboxyl groups on the surface; the laser spot size is controlled at 50-80μm to ensure the uniformity and consistency of the micron texture and avoid local textures being too dense or too sparse, which would affect the mechanical interlocking effect with the PU foam layer.

[0007] The silane coupling agent anchoring process involves immersing the activated wheel hub in a 2%-3% (w / w) KH-550 silane coupling agent ethanol solution for 15-20 minutes. After removal, the wheel hub is dried in sections in an oven at 110-130℃ and cooled to room temperature for later use. The coupling agent molecular bridging enhances the chemical adhesion between the wheel hub and the PU foam layer.

[0008] Preferably, in the TPU premixing stage, thermoplastic polyurethane elastomer particles with a Shore hardness of 86-89A are used as the base material, and a composite modification system is added according to the mass percentage ratio relative to the TPU base material. The composite modification system includes a composite wear-resistant modifier composed of 1.8%-3.2% nano-alumina and 0.8%-1.2% aramid short fibers, combined with 0.6%-0.9% hindered phenolic anti-aging agent, 0.9%-1.1% polysiloxane lubricant, 0.4%-0.5% carbon fiber reinforcement, and 0.3%-0.5% TPU-PU graft copolymer. An interface compatibilizer is used to improve the interfacial compatibility between TPU and PU. The above raw materials are put into a high-speed mixer and a staged mixing process is adopted. First, the mixture is premixed at a low speed of 500-600 r / min and 80-90℃ for 8-10 min to ensure that the modifier is evenly dispersed in the TPU base material. Then, the speed is increased to 900-1000 r / min and the temperature is maintained at 85-90℃ for high-speed dispersion for 7-10 min to ensure that the particle size of the modifier is ≤3μm, thereby improving the wear resistance, tear strength and processing fluidity of the TPU raw material. At the same time, the compatibilizer is used to pre-adapt the PU foam layer.

[0009] After modification, the TPU raw material has a tear resistance of ≥80kN / m, which can prevent tires from tearing and breaking due to impact from foreign objects during driving.

[0010] Preferably, in the toe-forming stage, the premixed TPU raw material is fed into a twin-screw extruder, employing a segmented temperature and pressure control process. The feeding section temperature is 165-170℃, the compression section temperature is 182-188℃, the melting section temperature is 192-198℃, and the die head section temperature is 188-192℃. The screw speed is 35-45 r / min, and the die head pressure is controlled at 12-15 MPa. The extrusion forms an annular toe-forming preform. The twin-screw extruder has a screw length-to-diameter ratio of 40:1 to ensure that the TPU raw material is fully melted and sheared within the barrel, avoiding uneven performance after toe-forming due to insufficient melting. Subsequently, the preform is fed into a dual-die system. The cavity-co-forming mold adopts an integrated molding process of hot pressing, vacuum adsorption and biaxial stretching. The hot pressing temperature is controlled at 170-180℃, the pressure is 8-10MPa, and the vacuum degree is -0.085~-0.09MPa. The tread pattern and inner fixing holes are formed in one step. The tread forming is a composite structure composed of transverse drainage patterns, longitudinal anti-slip patterns and annular noise reduction grooves. 44-46 stepped fixing holes are uniformly formed on the inner side of the tire top for mechanical interlocking with the PU foam layer. After molding, the TPU tire top is placed in a constant temperature cooling box at 62-68℃ for gradient cooling for 60 minutes, and then transferred to an annealing furnace at 40-50℃ for 30 minutes to eliminate internal stress from processing.

[0011] Preferably, in the PU premixing stage, PU foaming raw materials are configured according to a weight ratio to form a raw material system with synergistic optimization of elasticity and structural strength. The raw material system consists of isocyanate components, polyol components, a composite catalyst, modified nano-montmorillonite, and a composite environmentally friendly foaming agent, with the ratio of isocyanate component: polyol component: composite catalyst: modified nano-montmorillonite: composite environmentally friendly foaming agent = 1:1.2:0.03:0.05:0.08. The composite catalyst is a mixture of amine catalyst, organometallic catalyst, and delayed catalyst in a mass ratio of 2:1:0.5, controlling the foaming reaction rate and uniformity. The nano-montmorillonite is pretreated with silane coupling agent KH-560 to enhance its elasticity and structural strength. It exhibits strong compatibility with the PU matrix and incorporates 0.2%-0.3% carbon fiber microfilaments. The composite environmentally friendly foaming agent is a mixture of HCFC-free physical foaming agent and chemical foaming agent at a weight ratio of 3:1. The above raw materials are fed into a high-speed shear mixer and subjected to low-temperature mixing, vacuum degassing, and secondary dispersion processes. The speed is controlled at 1600-1900 r / min, the temperature at 22-24℃, and the mixing time at 3.5-4.5 min. Vacuum degassing is performed simultaneously during the mixing process. After mixing, the mixture is allowed to stand for 1 min and then subjected to secondary vacuum degassing to ensure the consistency of the density and cushioning performance of the PU foam layer, while also adapting to the material characteristics of the TPU tire top.

[0012] Preferably, the cavity positioning stage employs a dual-positioning coaxial positioning fixture combining electromagnetic adsorption and mechanical limiting. This fixture coaxially positions the cooled and annealed TPU tire top and the pre-treated wheel hub, with the wheel hub concentrically positioned at the inner center of the TPU tire top. The fixture's electromagnetic adsorption force fixes the position, while its annular mechanical limiting ring assists in positioning, ensuring a uniform annular gap between the outer circumference of the wheel hub and the inner surface of the TPU tire top. Elastic sealing end caps are installed at both ends of the TPU tire top to form a closed cavity. The cavity undergoes secondary vacuum degassing, while the cavity temperature is controlled at 25-28°C to remove air and moisture from inside the cavity.

[0013] Preferably, in the casting and curing stage, the premixed PU foaming material is injected into the sealed cavity via a metering pump, employing a three-stage gradient pressure casting process. In the initial casting stage, when the injection volume reaches 30% of the cavity volume, the pressure is controlled at 0.3-0.4 MPa. In the intermediate filling stage, when the injection volume increases from 30% to 90% of the cavity volume, the pressure is increased to 0.6-0.7 MPa to ensure the material is uniformly filled into the stepped fixing holes on the inner side of the TPU tire top and the annular groove of the wheel hub, forming a mechanically fitted structure. In the final pressure replenishment stage, when the injection volume increases from 90% to 100% of the cavity volume, the pressure is reduced to 0.5-0.6 MPa for pressure replenishment and filling, eliminating pressure at the end of the cavity. Dead corners; After casting, a segmented and temperature-controlled curing process is adopted to achieve the synergistic curing of TPU tire top and PU foam layer. In the initial curing stage, it is left to stand in an environment of 26-29℃ for 30 minutes to allow the PU foam material to fully foam and initially cross-link. In the gradient temperature curing stage, it is transferred to a constant temperature oven and heated to 62-68℃ at a heating rate of 5℃ / h. The oven temperature on the TPU tire top side is controlled at 65-68℃, and the temperature of the PU foam layer center is controlled at 62-65℃, and the temperature is maintained for 70-80 minutes. In the synergistic cooling stage, it is naturally cooled to room temperature, so that the PU foam layer and TPU tire top and wheel hub form an integrated structure of mechanical interlocking, chemical bonding and molecular bridging.

[0014] Preferably, in the post-processing stage, the positioning fixture and sealing end cap are removed, and a CNC grinding machine is used to grind off excess PU foam overflow from the tire edge. After grinding, the tire edge is chamfered, and then plasma is used to lightly treat the tire surface to remove surface impurities. In the aging stabilization treatment stage, the tire is placed in a constant temperature and humidity environment of 50°C and 60% for 48 hours of low-temperature aging stabilization treatment, and then transferred to a room temperature environment for 24 hours to eliminate internal stress generated during the curing process. The multi-dimensional core performance testing stage adopts national standards. Alternatively, the TPU tire crown undergoes abrasion resistance testing as specified by industry standards, with a wear volume ≤70mm³; static load resistance is verified by permanent deformation ≤2.5% after bearing 1.5 times the rated load for 24 hours and unloading for 30 minutes; PU foam layer closed-cell rate ≥96%, peel strength ≥1.8MPa; tire crown subsidence under rated load is 9-11mm, and driving noise ≤63dB; additionally, an interfacial shear strength test is added, with an interfacial shear strength ≥1.2MPa, ensuring that the product meets design requirements, thus obtaining the finished tire.

[0015] This invention also provides an environmentally friendly foamed TPU+PU airless composite tire, prepared using the above-mentioned method, comprising a wheel hub, a PU foam layer, and a TPU toe cap, forming an integrated composite structure with mechanical interlocking, chemical bonding, and molecular bridging. The wheel hub is made of aluminum alloy or reinforced nylon, with multiple staggered inverted trapezoidal annular grooves on its outer circumference. The inner wall of the grooves has bidirectional staggered oblique anti-skid teeth. The outer circumference of the wheel hub and the grooves have a modified layer formed by a three-step composite treatment of laser micro-etching, plasma activation, and silane coupling agent anchoring. The TPU toe cap is made of thermoplastic polyurethane elastomer, with stepped fixing holes on the inner side that interlock with the PU foam layer, and a composite tread pattern composed of transverse drainage patterns, longitudinal anti-skid patterns, and annular noise reduction grooves on the outer side. The PU foam layer fills the space between the wheel hub and the TPU toe cap, forming a mechanical interlock with the wheel hub through the annular grooves and anti-skid teeth, and a mechanical interlock with the TPU toe cap through the fixing holes.

[0016] The beneficial effects of this invention are as follows: 1. This invention, by adopting a non-inflatable composite structure consisting of a TPU top, a PU foam layer, and a rim, enables the tire to form stable support without relying on internal air pressure, thereby avoiding the performance degradation of traditional pneumatic tires under conditions of puncture, leakage, and abnormal tire pressure. Simultaneously, by setting the TPU top as a wear-resistant load-bearing layer and the PU foam layer as a buffer support layer, the tire maintains its non-inflatable characteristics while also ensuring wear resistance, cushioning performance, and static load resistance, thus improving the problems of solid tires being too heavy, having insufficient cushioning, and offering low user comfort. Furthermore, by adding wear-resistant modifying components, anti-aging components, and reinforcing components to the TPU material, and coordinating with the stable foaming molding of the PU foam layer, the tire can maintain good structural integrity and operational stability under long-term alternating load conditions, thereby reducing the need for routine maintenance such as inflation, lowering the frequency of maintenance during use, and helping to extend the overall service life of the tire.

[0017] 2. This invention achieves a more balanced overall performance of the tire through the coordinated design of the tire crown structure, foam layer material, and rim material. Specifically, by incorporating lateral drainage grooves, longitudinal anti-skid grooves, and annular noise-reducing grooves on the outer side of the TPU tire crown, the tire simultaneously provides drainage, anti-skid protection, and reduced rolling noise during driving, thereby enhancing its adaptability to different road conditions. By introducing modified reinforcing components into the PU foam layer and using a composite environmentally friendly foaming agent for foam control, the foam layer maintains good structural strength and closed-cell uniformity while forming an elastic support structure, thus enabling the tire to combine cushioning and shock absorption capabilities with load-bearing stability. The use of aluminum alloy or reinforced nylon rims allows the rims to meet connection and support requirements while maintaining a lighter weight, thus reducing the overall tire assembly weight. Furthermore, gradient cooling and low-temperature aging stabilization treatment reduce the accumulation of internal stress after molding, resulting in less vibration and smoother tire operation during use.

[0018] 3. This invention constructs a composite connection system combining mechanical interlocking, chemical bonding, and molecular bridging, enabling a relatively stable interfacial bond between the wheel hub, PU foam layer, and TPU tire top. Specifically, by setting staggered inverted trapezoidal annular grooves and bidirectional staggered oblique anti-skid teeth on the outer circumference of the wheel hub, the mechanical interlocking effect between the wheel hub and the PU foam layer is increased. By sequentially performing laser micro-etching, plasma activation, and silane coupling agent anchoring treatments on the wheel hub surface, the surface activity and interfacial bonding conditions of the wheel hub are improved. Simultaneously, by adding a TPU-PU graft copolymer interfacial compatibilizer during the TPU premixing stage and employing gradient pressure casting and segmented temperature-controlled curing processes during the casting and curing stage, the interfacial transition between the PU foam layer and the TPU tire top and wheel hub is more complete, thereby improving the bonding strength between the components. Furthermore, by performing vacuum degassing and secondary dispersion treatment on the PU foam raw material, the internal pore distribution of the foam layer is made more uniform, reducing molding defects such as voids and local collapse, which is beneficial to improving the structural stability and overall reliability of the tire during long-term use. Attached Figure Description

[0019] Figure 1 is an overall flowchart of the preparation method of the present invention; Figure 2 is a flowchart of the surface modification treatment of the wheel hub substrate of the present invention. Detailed Implementation

[0020] The technical solutions of 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.

[0021] As shown in Figures 1 and 2, this embodiment of the invention provides a method for preparing an environmentally friendly foamed TPU+PU airless composite tire, including the following specific steps: In the wheel hub modification stage, an aluminum alloy or reinforced nylon wheel hub is selected. Three to four staggered inverted trapezoidal annular grooves with a depth of 4.5-5.5 mm and a width of 9.5-10.5 mm are machined on the outer circumference of the wheel hub using CNC machining. The grooves have bidirectional staggered oblique anti-slip teeth with a tooth height of 1.2-1.4 mm and a tooth pitch of 2.8-3.2 mm. These bidirectional staggered oblique anti-slip teeth significantly increase the mechanical engagement force with the PU foam layer. CNC machining uses carbide cutting tools, with a cutting speed controlled at 1500-2000 r / min and a feed rate of 50-80 mm / min to ensure the dimensional accuracy of the grooves and the structural integrity of the anti-slip teeth, avoiding machining burrs that could affect the subsequent interlocking effect with the PU foam layer.

[0022] Subsequently, a three-step composite treatment process was adopted, consisting of laser micro-etching, plasma activation, and silane coupling agent anchoring. Laser micro-etching uses pulsed laser to form uniform micron-level rough textures on the outer circumference of the wheel hub and in the grooves, with a roughness Ra=1.4-1.6μm. The textures are distributed in a honeycomb pattern, which increases the surface specific surface area. The laser scanning path adopts a spiral superposition scanning, with an overlap rate of 30%-40% between adjacent scanning trajectories, to avoid localized missed etching or excessively dense texture overlap, and to ensure the uniformity of the modified layer on the wheel hub surface.

[0023] The pulsed laser has a power of 60-70W, a frequency of 20kHz, and a scanning speed of 300mm / s. During the plasma activation process, a mixed gas with an argon-oxygen volume ratio of 3:1 is introduced. The processing time is controlled at 70-80s and the power at 120-140W. This activates the wheel hub surface, removing oil and impurities while increasing the content of active groups such as hydroxyl and carboxyl groups on the surface. The mixed gas flow rate is controlled at 10-15L / min to ensure sufficient contact between the gas and the wheel hub surface, avoiding problems such as incomplete activation due to too low a flow rate and surface damage due to too high a flow rate.

[0024] The silane coupling agent anchoring process involves immersing the activated wheel hub in a 2%-3% (w / w) KH-550 silane coupling agent ethanol solution for 15-20 minutes. After removal, it is placed in an oven at 110-130℃ for segmented drying, first pre-drying at 80℃ for 15 minutes, then constant-temperature drying at 120℃ for 15 minutes, and finally cooling to room temperature for use. Through molecular bridging of the coupling agent, the chemical adhesion between the wheel hub and the PU foam layer is improved.

[0025] The ethanol solution contains 95% ethanol by volume. The pH of the solution is adjusted to 4.5-5.5 using deionized water to promote the hydrolysis of the silane coupling agent and improve the molecular bridging efficiency.

[0026] In the TPU premixing stage, thermoplastic polyurethane elastomer (TPU) particles with a Shore hardness of 86-89A are used as the base material. This TPU elastomer is a polyester-type thermoplastic polyurethane with a tensile strength ≥35MPa and an elongation at break ≥500% (tested at 23℃), balancing wear resistance and elastic recovery, suitable for tire top applications. A composite modification system is added according to the mass percentage relative to the TPU base material. The composite modification system contains a composite wear-resistant modifier composed of 1.8%–3.2% nano-alumina and 0.8%–1.2% aramid short fibers. The nano-alumina particle size is 50-80nm, the aramid short fiber length is 0.8-1.2mm, the nano-alumina purity is ≥99.5%, and the aramid short fiber diameter is 10-15μm. The carbon fiber reinforcement has a length of… The material has a thickness of 1-3 mm and a diameter of 5-8 μm to ensure uniform dispersion of the reinforcing components in the TPU matrix, fully leveraging its wear-resistant and reinforcing properties. It is combined with 0.6%-0.9% hindered phenolic anti-aging agent (type 1010), 0.9%-1.1% polysiloxane lubricant, 0.4%-0.5% carbon fiber reinforcing agent, and 0.3%-0.5% TPU-PU graft copolymer interface compatibilizer to improve the interfacial compatibility between TPU and PU. The polysiloxane lubricant uses methylphenyl polysiloxane with a viscosity of 500-1000 mPa·s (25℃), improving the processing fluidity of the TPU raw material without affecting the interfacial compatibility with the PU foam layer. This anti-aging agent can capture free radicals generated during TPU processing and use, inhibiting thermal oxidative degradation and extending the tire's service life in complex outdoor environments.

[0027] The pretreatment process is as follows: Nano-montmorillonite and 1%-2% KH-560 silane coupling agent are stirred and mixed at 80-90℃ for 30-40 minutes, and then dried at 105-110℃ for 2 hours to remove moisture and complete the coupling agent grafting.

[0028] The above raw materials are put into a high-speed mixer and a staged mixing process is adopted. A vertical high-speed mixer is selected, and the stirring blades are of the blade type with a gap of ≤5mm between the blades and the inner wall of the barrel to ensure that the modifier and TPU base material are quickly and evenly mixed and avoid local agglomeration. First, the mixture is premixed at a low speed of 500-600r / min and 80-90℃ for 8-10min to make the modifier evenly dispersed in the TPU base material. Then, the speed is increased to 900-1000r / min and the temperature is maintained at 85-90℃ for high-speed dispersion for 7-10min to ensure that the particle size of the modifier is ≤3μm, thereby improving the wear resistance, tear strength and processing fluidity of the TPU raw material. At the same time, the PU foam layer is adapted in advance by using a compatibilizer.

[0029] Nitrogen gas is introduced during the mixing process for protection, with a flow rate of 5-8 L / min, to prevent the TPU base material and modifier from oxidizing and degrading during high-temperature mixing, thus ensuring the stability of the raw material performance.

[0030] In the toe crown forming stage, premixed TPU raw materials are fed into a twin-screw extruder, employing a segmented temperature and pressure control process. The feed section temperature is 165-170℃, the compression section temperature is 182-188℃, the melt section temperature is 192-198℃, and the die head section temperature is 188-192℃. The screw speed is 35-45 r / min, and the die head pressure is controlled at 12-15 MPa. The extrusion forms a ring-shaped toe crown preform with an inner diameter 44-46 mm larger than the outer diameter of the wheel hub, with a pre-filled PU foam layer. The blank is then fed into a dual-cavity co-forming mold, employing an integrated hot-pressing, vacuum adsorption, and biaxial stretching molding process to enhance the toughness of the tire top. The hot-pressing temperature is controlled at 170-180℃, the pressure at 8-10MPa, and the vacuum degree at -0.085~-0.09MPa, forming the tread pattern and inner fixing holes in one step. The surface roughness of the mold cavity Ra≤0.8μm is achieved, and nitriding treatment is used to enhance wear resistance. The clearance between the mold cavity and the blank is 0.1-0.2mm to ensure clear tread pattern formation.

[0031] The tread is a composite structure consisting of lateral drainage patterns, longitudinal anti-skid patterns, and annular noise-reducing grooves. The lateral drainage patterns are 2.2-2.8 mm deep and 8.5-9.5 mm apart, the longitudinal anti-skid patterns are 2.8-3.2 mm deep and 13-14 mm apart, and the annular noise-reducing grooves are 2 mm wide, 1.5 mm deep, and 30 mm apart, balancing drainage, anti-skid, and noise reduction performance. 44-46 stepped fixing holes are uniformly formed on the inner side of the tread top, with a diameter of 6-7 mm and a depth of 8-10 mm. The hole openings have a 1 mm chamfer for a stronger mechanical fit with the PU foam layer. The fixing holes are equidistantly distributed along the circumference of the inner side of the TPU tread top, with a central angle deviation of ≤0.5° between adjacent fixing holes, ensuring uniform force distribution during the mechanical fit between the PU foam layer and the tread top after filling.

[0032] After molding, the TPU toe cap is placed in a constant temperature cooling box at 62-68℃ for gradient cooling for 60 minutes at a cooling rate of 5℃ / 10min. Then it is transferred to an annealing furnace at 40-50℃ for 30 minutes to eliminate internal stress during processing and improve the dimensional stability of the toe cap.

[0033] In the PU premixing stage, PU foaming raw materials are configured according to a weight ratio to form a raw material system with synergistic optimization of elasticity and structural strength. This raw material system consists of isocyanate components, polyol components, a composite catalyst, modified nano-montmorillonite, and a composite environmentally friendly foaming agent. The isocyanate component is diphenylmethane diisocyanate (MDI-100), and the polyol component is polyether polyol with a molecular weight of 2000-3000. The polyether polyol is polypropylene glycol with a hydroxyl value of 56±2 mgKOH / g, ensuring a balance between crosslinking density and elasticity in the PU foaming reaction. The combination of these two components can simultaneously achieve optimal performance in PU foaming. The elasticity and structural strength of the U-shaped foam layer; isocyanate component: polyol component: composite catalyst: modified nano-montmorillonite: composite environmentally friendly foaming agent = 1:1.2:0.03:0.05:0.08; the composite catalyst is composed of amine catalyst, organometallic catalyst and delayed catalyst in a mass ratio of 2:1:0.5, which controls the foaming reaction rate and uniformity, and avoids pore defects caused by excessively fast foaming in the early stage; the sodium bicarbonate particle size is controlled at 1-5μm to ensure uniform decomposition rate during foaming, avoid large pores inside the PU foam layer due to excessively large particles, and ensure the density of the foam layer.

[0034] Triethylenediamine was selected as the amine catalyst, stannous octoate was selected as the organometallic catalyst, and dimethylcyclohexylamine was selected as the delayed catalyst. Triethylenediamine rapidly initiates the foaming reaction, stannous octoate accelerates the crosslinking of PU molecular chains, and dimethylcyclohexylamine slows down the later stage of the reaction. The three catalysts work synergistically to avoid structural defects in the foamed layer caused by asynchronous foaming and crosslinking.

[0035] Nano-montmorillonite is pretreated with silane coupling agent KH-560 to enhance its compatibility with the PU matrix. At the same time, 0.2%-0.3% carbon fiber microfilaments are added to further improve the structural strength and elastic stability of the foam layer. The composite environmentally friendly foaming agent is made by compounding HCFC-free physical foaming agent (cyclopentane) and chemical foaming agent (sodium bicarbonate) in a weight ratio of 3:1, which takes into account both foaming efficiency and environmental protection, and improves the closed-cell rate of the foam layer. The carbon fiber microfilaments have a length of 0.5-1.0 mm and a diameter of 7-10 μm, and the surface oxidation treatment is used to improve the wettability with the PU matrix.

[0036] The above raw materials are put into a high-speed shear mixer and subjected to low-temperature mixing, vacuum degassing, and secondary dispersion processes. The rotation speed is controlled at 1600-1900 r / min, the temperature at 22-24℃, and the mixing time at 3.5-4.5 min. During the mixing process, a vacuum degassing is performed simultaneously at a vacuum degree of -0.08 to -0.09 MPa for 1.5-2.5 min. After mixing, the mixture is allowed to stand for 1 min, and then a second vacuum degassing is performed at a vacuum degree of -0.09 to -0.095 MPa for 1-2 min to remove air bubbles from the raw materials. This ensures the consistency of the density and cushioning performance of the PU foam layer and adapts to the material characteristics of the TPU toe cap, achieving material synergy.

[0037] The density of the PU foam layer is controlled between 0.45 and 0.55 g / cm³, which is achieved by adjusting the amount of composite foaming agent and the foaming pressure to ensure that the cushioning and shock absorption effect is close to that of a high-quality pneumatic tire.

[0038] The crosslinking density of the PU foam layer is controlled at 1.2-1.5 mmol / cm³, which is achieved by adjusting the reaction ratio of isocyanate and polyol and the curing process, ensuring a long-term balance between the elasticity and structural stability of the foam layer.

[0039] The mixing sequence is as follows: first add the polyol component, modified nano-montmorillonite and carbon fiber microfilaments, and mix at low speed for 2 minutes; then add the composite catalyst and composite environmentally friendly foaming agent, and continue mixing for 1 minute; finally add the isocyanate component, start high-speed shear mixing to ensure that each component reacts fully.

[0040] The cavity positioning stage employs a dual-positioning coaxial positioning fixture combining electromagnetic adsorption and mechanical limiting to improve positioning accuracy and avoid foaming defects caused by positioning deviations. The cooled and annealed TPU tire top and the pre-treated wheel hub are coaxially positioned, with the wheel hub concentrically placed at the center of the inner side of the TPU tire top. The fixture's electromagnetic adsorption force (500-600N) fixes their positions, while the fixture's annular mechanical limiting ring (gap ≤0.1mm) assists in positioning, ensuring a uniform annular gap of 22-23mm between the outer circumference of the wheel hub and the inner side of the TPU tire top. This gap corresponds to the designed thickness of the PU foam layer, preventing uneven gaps from causing stress imbalance in the foam layer. The dimensional tolerance of the annular gap is controlled at ±0.2mm, monitored in real-time by a displacement sensor built into the fixture to ensure a uniform PU foam layer thickness and prevent uneven local stress.

[0041] Four displacement sensors are evenly arranged around the circumference of the tooling ring limit ring. The distance between the monitoring point and the inner side of the TPU tire top is ≤1mm. The sampling frequency is 10Hz. The sensor provides real-time feedback on the gap size deviation and triggers fine adjustment.

[0042] The auxiliary positioning sequence is as follows: First, place the wheel hub inside the TPU tire top, then activate the mechanical limit ring to clamp and position it with a clamping force of 300-400N. Next, activate the electromagnetic adsorption to keep it fixed. The adsorption continues until the casting and curing are completed to avoid positioning deviation.

[0043] Elastic sealing end caps made of silicone rubber are installed at both ends of the TPU mold top to meet sealing requirements and form a closed cavity. The silicone rubber sealing end caps have a Shore hardness of 50-60 degrees and a compression set of ≤8% (70℃×24h) to ensure the cavity sealing performance and prevent material leakage during casting. The cavity is then subjected to secondary vacuum degassing at a vacuum degree of -0.09~-0.095MPa for 12-14 minutes, while the cavity temperature is controlled at 25-28℃. Constant temperature degassing avoids temperature fluctuations affecting foaming, removes air and moisture from inside the cavity, and prevents defects such as pores, voids, and delamination during foaming, ensuring the integrity of the foam layer and the interface bonding effect.

[0044] In the casting and curing stage, the premixed PU foam material is injected into the sealed cavity through a metering pump. The flow rate of the metering pump is 55-75 mL / s, and the metering accuracy is ±0.5 mL / s. A three-stage gradient pressure casting process is adopted. The metering pump is a gear-type metering pump. The casting port is set to 3-4 evenly distributed on the side of the sealed cavity, with an angle of 90° between adjacent casting ports, to ensure that the PU foam material fills the cavity quickly and evenly.

[0045] During the initial pouring stage, when the injection volume reaches 30% of the cavity volume, the pressure is controlled at 0.3-0.4 MPa to ensure the material smoothly fills the bottom of the cavity and avoids impacting the wheel hub and TPU top. During the intermediate filling stage, when the injection volume increases from 30% to 90% of the cavity volume, the pressure is increased to 0.6-0.7 MPa to ensure the material is evenly filled into the stepped fixing holes inside the TPU top and the annular groove of the wheel hub, forming a mechanically fitted structure. During the final pressure replenishment stage, when the injection volume increases from 90% to 100% of the cavity volume, the pressure is reduced to 0.5-0.6 MPa for pressure replenishment, eliminating dead corners at the end of the cavity and preventing material shortages. After pouring, a segmented, temperature-controlled curing process is used to achieve coordinated curing of the TPU top and the PU foam layer. The initial curing stage is carried out in an environment of 26-29℃. After standing for 30 minutes, the PU foam material is allowed to fully foam and initially cross-link, avoiding over-foaming that could lead to elasticity failure. During the gradient temperature curing stage, the material is transferred to a constant temperature oven, where the temperature is increased to 62-68℃ at a rate of 5℃ / h, with a control accuracy of ±0.5℃ / h. Precise regulation is achieved through the oven's PID temperature control system, ensuring consistent co-curing of TPU and PU. The oven temperature on the TPU top side is controlled at 65-68℃, and the temperature at the center of the PU foam layer is controlled at 62-65℃. This temperature is maintained for 70-80 minutes to achieve deep cross-linking and curing, improving bonding strength and structural stability. The temperature accuracy for segmented temperature control is ±1℃, with real-time temperature monitoring via built-in thermocouples to ensure consistent co-curing of TPU and PU, preventing interface bonding defects caused by temperature deviations.

[0046] The thermocouple on the top of the TPU tire is embedded in the mold cavity wall 3mm from the contact surface of the tire top. The thermocouple in the center of the PU foam layer is inserted into the preset position of the foam layer through the reserved hole in the cavity to ensure that the temperature monitoring accurately reflects the actual curing environment.

[0047] During the synergistic cooling stage, the tire is naturally cooled to room temperature at a rate of ≤5℃ / h. Forced air cooling is used, with the wind speed controlled at 1-2m / s. Uniform heat dissipation prevents the tire from cooling too quickly in certain areas and generating internal stress, thus ensuring the stability of the integrated structure. This allows the PU foam layer to form an integrated structure with mechanical interlocking, chemical bonding, and molecular bridging with the TPU tire top and wheel hub.

[0048] In the post-processing stage, the positioning fixture and sealing end cap are removed, and a CNC grinding machine is used to grind the excess PU foam material on the tire edge. The grinding accuracy is ±0.08mm, the grinding speed of the CNC grinding machine is 3000-4000r / min, and a diamond grinding wheel with a grit size of 80-120 mesh is selected. Air cooling is used during the grinding process, with a wind speed of 0.8-1.2m / s, to prevent the PU foam layer from softening and deforming due to high temperature.

[0049] After grinding, the tire edges are chamfered at a 45° angle and 1mm width to ensure the tire dimensions meet vehicle installation standards. Then, the tire surface is lightly treated with plasma at a power of 80-100W for 30 seconds to remove surface impurities and improve surface smoothness. The plasma treatment uses argon as the working gas at a flow rate of 8-12L / min to avoid oxidation of the tire surface caused by air, while also improving surface cleanliness and aging resistance for subsequent use.

[0050] The aging and stabilization process involves placing the tire in a constant temperature and humidity environment of 50℃ and 60% for 48 hours for low-temperature aging and stabilization, followed by 24 hours of resting at room temperature to eliminate internal stress generated during the curing process and improve structural stability and dimensional accuracy. The humidity control accuracy is ±3%RH, which is dynamically adjusted by the humidity sensor in the constant temperature and humidity chamber to ensure stable and optimized tire performance during the aging process.

[0051] The multi-dimensional core performance testing adopts plastic performance testing methods specified by national or industry standards. The TPU tire top undergoes abrasion resistance testing, with abrasion volume ≤70mm³; static load resistance is verified by withstanding 1.5 times the rated load for 24 hours and unloading for 30 minutes, with permanent deformation ≤2.5%; PU foam layer closed-cell rate ≥96%, peel strength ≥1.8MPa; tire top subsidence under rated load is 9-11mm, and driving noise ≤63dB; at the same time, an interface shear strength test is added, with an interface shear strength ≥1.2MPa, ensuring that the product meets the design requirements, thus obtaining the finished tire.

[0052] This invention also provides an environmentally friendly foamed TPU+PU airless composite tire, prepared using the above-mentioned method, comprising a wheel hub, a PU foam layer, and a TPU toe cap, forming an integrated composite structure with mechanical interlocking, chemical bonding, and molecular bridging; the wheel hub is made of aluminum alloy or reinforced nylon, with multiple staggered inverted trapezoidal annular grooves on its outer circumference, and bidirectional staggered oblique anti-skid teeth on the inner wall of the grooves; the outer circumference of the wheel hub and the grooves are provided with a modified layer formed by a three-step composite treatment of laser micro-etching, plasma activation, and silane coupling agent anchoring; the TPU toe cap... Made of thermoplastic polyurethane elastomer, the inner side has stepped fixing holes that fit into the PU foam layer, and the outer side has a composite tread pattern consisting of transverse drainage patterns, longitudinal anti-slip patterns, and annular noise reduction grooves. The PU foam layer fills the space between the wheel hub and the TPU tire top, forming a mechanical fit with the wheel hub through annular grooves and anti-slip teeth, and a mechanical fit with the TPU tire top through fixing holes. It also forms a chemical bond with the wheel hub and TPU tire top through a modified layer. The closed-cell rate of the PU foam layer is ≥96%, and the peel strength at the junction of the three is ≥1.8MPa and the interfacial shear strength is ≥1.2MPa.

[0053] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0054] 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 method for preparing an environmentally friendly foamed TPU+PU airless composite tire, characterized in that, The specific steps include: In the wheel hub modification stage, aluminum alloy or reinforced nylon wheel hubs are selected, and the outer circumferential surface of the wheel hub is machined to form staggered inverted trapezoidal annular grooves and bidirectional staggered oblique anti-slip teeth located on the inner wall of the annular grooves. Then, the outer circumferential surface of the wheel hub is sequentially subjected to laser micro-etching, plasma activation, and silane coupling agent anchoring treatment. In the TPU premixing stage, thermoplastic polyurethane elastomer is selected as the tire top base material, and wear-resistant modification components, anti-aging components, lubricating components, reinforcing components, and interface compatibility components are added. A staged mixing process is then used to obtain the TPU premix. In the toe crown forming stage, the TPU premix is ​​extruded to form an annular toe crown blank, and then a TPU toe crown is formed using an integrated molding process of hot pressing, vacuum adsorption, and biaxial stretching. The outer side of the TPU toe crown forms a tread pattern, and the inner side forms stepped fixing holes. In the PU premixing stage, isocyanate components, polyol components, composite catalysts, modified reinforcing components, and composite environmentally friendly foaming agents are configured according to weight ratio, and PU foaming premix is ​​obtained by low-temperature mixing, vacuum degassing, and secondary dispersion processes. The composite environmentally friendly foaming agent is formed by compounding HCFC-free physical foaming agents and chemical foaming agents. In the cavity positioning stage, the TPU toe crown and the modified wheel hub are coaxially positioned using a coaxial positioning fixture, forming an annular cavity between them. In the casting and curing stage, the PU foam premix is ​​injected into the annular cavity, and a PU foam layer is formed between the wheel hub and the TPU tire top using a gradient pressure casting process and a segmented temperature-controlled curing process. In the post-treatment stage, the cured tire is cleaned and subjected to low-temperature aging stabilization treatment to obtain an environmentally friendly foamed TPU+PU airless composite tire.

2. The method for preparing an environmentally friendly foamed TPU+PU airless composite tire according to claim 1, characterized in that, In the wheel hub modification stage, 3-4 staggered inverted trapezoidal annular grooves are formed by machining, and the bidirectional staggered oblique anti-slip teeth are set on the inner wall of the annular grooves; the plasma activation uses a mixed gas of argon and oxygen, and the silane coupling agent anchoring is carried out by soaking in KH-550 silane coupling agent ethanol solution and then drying in sections.

3. The method for preparing an environmentally friendly foamed TPU+PU airless composite tire according to claim 2, characterized in that, In the TPU premixing stage, the toe cap base material is thermoplastic polyurethane elastomer particles with a Shore hardness of 86-89A; the wear-resistant modification component includes nano-alumina and aramid short fibers; the anti-aging component is a hindered phenolic anti-aging agent; the lubricating component is a polysiloxane lubricant; the reinforcing component is a carbon fiber reinforcing agent; and the interface compatibility component is a TPU-PU graft copolymer interface compatibility agent.

4. The method for preparing an environmentally friendly foamed TPU+PU airless composite tire according to claim 3, characterized in that, During the top forming stage, the tread pattern consists of transverse drainage patterns, longitudinal anti-skid patterns, and annular noise reduction grooves, and the stepped fixing holes are spaced apart along the inner circumferential side of the TPU top.

5. The method for preparing an environmentally friendly foamed TPU+PU airless composite tire according to claim 4, characterized in that, In the PU premixing stage, the modified reinforcing components include modified nano-montmorillonite and carbon fiber microfilaments; the HCFC-free physical foaming agent is cyclopentane, the chemical foaming agent is sodium bicarbonate, and the weight ratio of the HCFC-free physical foaming agent to the chemical foaming agent is 3:

1.

6. The method for preparing an environmentally friendly foamed TPU+PU airless composite tire according to claim 5, characterized in that, In the PU premixing stage, the polyol component, modified nano-montmorillonite and carbon fiber microfilaments are first mixed, then the composite catalyst and composite environmentally friendly foaming agent are added, and finally the isocyanate component is added. During the mixing process, vacuum degassing is performed once, and after the mixing is completed, a second vacuum degassing is performed.

7. The method for preparing an environmentally friendly foamed TPU+PU airless composite tire according to claim 6, characterized in that, In the cavity positioning stage, the coaxial positioning fixture uses a combination of electromagnetic adsorption fixation and mechanical limiting assistance to achieve coaxial positioning of the TPU tire top and the wheel hub; in the casting and curing stage, the gradient pressure casting process includes an initial filling stage, a middle expansion stage, and a final compensation stage.

8. The method for preparing an environmentally friendly foamed TPU+PU airless composite tire according to claim 7, characterized in that, In the post-processing stage, surface cleaning is performed using plasma treatment, and low-temperature aging stabilization is performed using a constant temperature and humidity environment. After the treatment is completed, the wear resistance of the TPU tread top, the tire's static load resistance, the closed-cell rate of the PU foam layer, the peel strength, the tread top sinking, the driving noise, and the interfacial shear strength are tested.

9. An environmentally friendly foamed TPU+PU airless composite tire, characterized in that, The environmentally friendly foamed TPU-PU airless composite tire is prepared using the method described in claims 1-8, comprising a wheel hub, a PU foam layer, and a TPU top; the wheel hub is made of aluminum alloy or reinforced nylon, with staggered inverted trapezoidal annular grooves and bidirectional staggered oblique anti-skid teeth on its outer circumference, and a modified layer formed by laser micro-etching, plasma activation, and silane coupling agent anchoring treatment on its outer circumference; the TPU top is located on the outside of the wheel hub, with stepped fixing holes on its inner side that fit into the PU foam layer, and a tread pattern on its outer side; the PU foam layer fills the space between the wheel hub and the TPU top, and the PU foam layer is formed by curing a polyurethane foam system containing HCFC-free physical foaming agent and chemical foaming agent.

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