A gradient heterogeneous interface layer, a fiber-reinforced rubber composite structure and a preparation method and application thereof

Abstract

This invention belongs to the field of polymer composite materials technology, specifically relating to a gradient heterogeneous interface layer, a fiber-reinforced rubber composite structure, its preparation method, and its application. The gradient heterogeneous interface layer for fiber-reinforced rubber composite structures provided by this invention includes a polymer substrate and nanoscale rigid particles dispersed in the polymer substrate. Along the thickness direction, the gradient heterogeneous interface layer is divided into an inner and an outer side. The concentration of nanoscale rigid particles decreases gradually from the inner side to the outer side of the gradient heterogeneous interface layer, and the average concentration of nanoscale rigid particles in the inner quarter-thickness region of the gradient heterogeneous interface layer is at least 1.5 times the average concentration of nanoscale rigid particles in the outer quarter-thickness region. The gradient heterogeneous interface layer provided by this invention can significantly improve the fatigue resistance of fiber-reinforced rubber composite structures while maintaining interfacial adhesion strength.

Description

Technical Field

[0001] This invention belongs to the field of polymer composite materials technology, specifically relating to a gradient heterogeneous interface layer, a fiber-reinforced rubber composite structure, its preparation method, and its application. Background Technology

[0002] At the moment of aircraft landing, the tire bead area fits tightly with the rim and withstands strong impact and lateral force. The stress concentration at the interface between the fiber cord layer and the rubber matrix in this area is prominent. The durability of the interface under dynamic shear and repeated flexing is directly related to tire safety and is a key factor in the design of aircraft tires.

[0003] Currently, industrial applications commonly employ RFL impregnation and the addition of high-volume reinforcing fillers to the interfacial transition layer to enhance interfacial modulus and rigidity, thereby achieving initial bond strength. However, while a uniform, high-filler system can improve rigidity, it leads to decreased interfacial flexibility and insufficient stress dispersion. Under cyclic dynamic loads, it struggles to effectively dissipate strain energy, causing localized stress concentrations that induce and propagate microcracks, ultimately resulting in interfacial debonding and delamination failure.

[0004] In summary, existing technologies struggle to balance interface rigidity, adhesive strength, and dynamic compliance. Summary of the Invention

[0005] The purpose of this invention is to provide a gradient heterogeneous interface layer, a fiber-reinforced rubber composite structure, its preparation method and application. The gradient heterogeneous interface layer provided by this invention can significantly improve the fatigue resistance of the fiber-reinforced rubber composite structure while maintaining the interfacial adhesion strength.

[0006] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a gradient heterogeneous interface layer for fiber-reinforced rubber composite structures, comprising a polymer substrate and nanoscale rigid particles dispersed in the polymer substrate; the gradient heterogeneous interface layer is divided into an inner side and an outer side along the thickness direction, the concentration of the nanoscale rigid particles decreases gradually from the inner side to the outer side of the gradient heterogeneous interface layer, and the average concentration of nanoscale rigid particles in the inner quarter thickness region of the gradient heterogeneous interface layer is at least 1.5 times the average concentration of nanoscale rigid particles in the outer quarter thickness region.

[0007] Preferably, the raw materials for preparing the polymer substrate include polymers, including natural rubber and / or isoprene rubber; the weight-average molecular weight of the polymer is greater than 1 × 10⁻⁶. 5 g / mol.

[0008] Preferably, the nanoscale rigid particles are nanoparticles with functionalized surfaces, the nanoparticles including nano-silica and / or carbon nanotubes, and the functionalized groups used in the modification include at least one of epoxy groups, mercapto groups, and unsaturated double bond groups that can chemically react with the polymer matrix or vulcanization system.

[0009] This invention provides a fiber-reinforced rubber composite structure, comprising a plywood layer, a gradient heterogeneous interface layer, and a rubber layer stacked sequentially; the gradient heterogeneous interface layer is the gradient heterogeneous interface layer described in the above technical solution, wherein the inner surface of the gradient heterogeneous interface layer is in contact with the plywood layer, and the outer surface is in contact with the rubber layer.

[0010] Preferably, the fiber cords in the fabric layer are polyamide fiber cords.

[0011] Preferably, the raw materials for preparing the rubber layer include a raw rubber component, which includes one or more of natural rubber, butadiene rubber, and styrene-butadiene rubber.

[0012] This invention provides a method for preparing the fiber-reinforced rubber composite structure described above, comprising the following steps: The rubber-impregnated cord is impregnated with interface layer slurries of varying concentrations, from highest to lowest, according to the concentration of nanoscale rigid particles. Each concentration gradient interface layer slurry includes at least two types of interface layer slurries with different concentrations of nanoscale rigid particles. After each impregnation, the cord is pre-dried, and after the final pre-drying, it is dried to obtain an initial gradient heterogeneous interface layer on the surface of the rubber-impregnated cord. Then, a rubber layer semi-finished product is bonded to the surface of the initial gradient heterogeneous interface layer, followed by pre-compression and co-vulcanization to obtain the fiber-reinforced rubber composite structure.

[0013] Preferably, the concentration difference of nanoscale rigid particles in the interface layer slurry of adjacent concentration gradients is at least 5 wt%; the pre-drying temperature is 45~60℃; the drying temperature is 50~80℃, and the drying temperature is greater than the pre-drying temperature.

[0014] This invention provides the application of the fiber-reinforced rubber composite structure described in the above technical solution or the fiber-reinforced rubber composite structure prepared by the preparation method described in the above technical solution in fiber-reinforced rubber products.

[0015] The present invention provides a tire, wherein the tire bead comprises the fiber-reinforced rubber composite structure described in the above technical solution or the fiber-reinforced rubber composite structure prepared by the preparation method described in the above technical solution.

[0016] This invention provides a gradient heterogeneous interface layer for fiber-reinforced rubber composite structures, comprising a polymer substrate and nanoscale rigid particles dispersed in the polymer substrate. The gradient heterogeneous interface layer is divided into an inner and an outer side along its thickness direction. The concentration of the nanoscale rigid particles decreases gradually from the inner side to the outer side of the gradient heterogeneous interface layer, and the average concentration of nanoscale rigid particles in the inner quarter-thickness region of the gradient heterogeneous interface layer is at least 1.5 times the average concentration of nanoscale rigid particles in the outer quarter-thickness region. In this invention, the polymer substrate is a continuous phase mainly composed of a molecular chain entanglement network, and the nanoscale rigid particles form a dispersed phase in the polymer matrix and are non-uniformly distributed along the thickness direction of the gradient heterogeneous interface layer, decreasing gradually from the inner side to the outer side. Compared with the prior art, the present invention has the following beneficial effects: By constructing a nanoscale rigid particle concentration gradient distribution, the present invention enables the gradient heterogeneous interface layer to have modulus gradient characteristics in the thickness direction, which can effectively disperse dynamic shear stress, avoid stress concentration, and thus inhibit the initiation and propagation of microcracks; The present invention uses a polymer matrix mainly based on physical entanglement, which endows the gradient heterogeneous interface layer with good flexibility and energy dissipation capability. While maintaining the interfacial bonding strength, it significantly improves the fatigue resistance of fiber-reinforced rubber composite structures under repeated flexural deformation, which can meet the reliability requirements of high-end products such as aircraft tires under complex service conditions.

[0017] This invention provides a fiber-reinforced rubber composite structure, comprising a ply layer, a gradient heterogeneous interface layer, and a rubber layer stacked sequentially. The gradient heterogeneous interface layer is the same as described in the previous technical solution, with its inner surface in contact with the ply layer and its outer surface in contact with the rubber layer. The fiber-reinforced rubber composite structure provided by this invention improves the shear fatigue resistance of the ply layer-rubber layer interface, making it suitable for high-end rubber products with extremely high safety requirements, such as aircraft tires.

[0018] This invention provides a method for preparing the fiber-reinforced rubber composite structure described in the above technical solution. This invention employs a multi-layer impregnation coating process, and by controlling parameters such as slurry concentration, number of impregnations, pre-drying, and drying conditions, it can achieve precise construction of gradient structures at the micrometer scale. The process flow is compatible with existing rubber industrial impregnation production lines and has good prospects for industrial implementation.

[0019] In summary, the gradient heterogeneous interface layer and fiber-reinforced rubber composite structure provided by this invention have controllable structure and simple preparation process. They are suitable for key parts that bear dynamic loads, such as aircraft tire bead, and can also be extended to other high-end fiber-reinforced rubber products, with significant economic and social benefits. Attached Figure Description

[0020] Figure 1A schematic diagram of the longitudinal section structure of the tire provided by the present invention; Figure 2 A schematic diagram of the gradient heterogeneous interface layer provided by the present invention; In the diagram: 100 - tread, 200 - sidewall rubber, 300 - gradient heterogeneous interface layer, 400 - belt layer, 500 - carcass ply, 600 - rim, 310 - first layer, 320 - second layer, 330 - third layer. Detailed Implementation

[0021] This invention provides a gradient heterogeneous interface layer for fiber-reinforced rubber composite structures, comprising a polymer substrate and nanoscale rigid particles dispersed in the polymer substrate; the gradient heterogeneous interface layer is divided into an inner side and an outer side along the thickness direction, the concentration of the nanoscale rigid particles decreases gradually from the inner side to the outer side of the gradient heterogeneous interface layer, and the average concentration of nanoscale rigid particles in the inner quarter thickness region of the gradient heterogeneous interface layer is at least 1.5 times the average concentration of nanoscale rigid particles in the outer quarter thickness region.

[0022] In this invention, unless otherwise specified, all raw materials / components used in the preparation are commercially available products well known to those skilled in the art.

[0023] The gradient heterogeneous interface layer for fiber-reinforced rubber composite structures provided by this invention includes a polymer substrate. In this invention, the polymer substrate is a high molecular weight polymer substrate. The polymer substrate constitutes a continuous phase primarily composed of a physically entangled network of molecular chains. In this invention, the raw materials for preparing the polymer substrate preferably include polymers. The polymer preferably includes natural rubber and / or isoprene rubber. The weight-average molecular weight of the polymer is preferably greater than 1 × 10⁻⁶. 5 g / mol. This invention optimizes the weight-average molecular weight of the polymer, thereby giving the polymer high entanglement properties and imparting good flexibility and stress dispersion ability to the gradient heterogeneous interface layer without relying on high chemical crosslinking density.

[0024] In this invention, the raw materials for preparing the polymer substrate preferably also include additives, which preferably include carbon black N660, carbon black N375, aromatic oil, 1-3 parts of stearic acid, 3-5 parts of zinc oxide, accelerator NOBS, accelerator DZ, co-crosslinking agent HV-268, binder A, anti-scorching agent CTP, and insoluble sulfur.

[0025] The gradient heterogeneous interface layer for fiber-reinforced rubber composite structures provided by this invention comprises nanoscale rigid particles dispersed in a polymer substrate. In this invention, the nanoscale rigid particles form a dispersed phase in the polymer matrix. The gradient heterogeneous interface layer is divided into an inner side and an outer side along the thickness direction. The nanoscale rigid particles form a dispersed phase in the polymer matrix and are non-uniformly distributed along the thickness direction of the gradient heterogeneous interface layer. The concentration of the nanoscale rigid particles decreases gradually from the inside to the outside of the gradient heterogeneous interface layer, and the average concentration of nanoscale rigid particles in the inner quarter thickness region (starting from the inner surface and accounting for one-quarter of the total thickness region) of the gradient heterogeneous interface layer is at least 1.5 times the average concentration of nanoscale rigid particles in the outer quarter thickness region (starting from the outer surface and accounting for one-quarter of the total thickness region); more preferably, the average concentration of nanoscale rigid particles in the inner third thickness region (starting from the inner surface and accounting for one-third of the total thickness region) of the gradient heterogeneous interface layer is at least 1.5 times the average concentration of nanoscale rigid particles in the outer third thickness region (starting from the outer surface and accounting for one-third of the total thickness region), and more preferably 1.5 to 2.5 times.

[0026] In this invention, the average concentration of nanoscale rigid particles in different regions of the gradient heterogeneous interface layer is the percentage of the mass of nanoscale rigid particles in that region relative to the mass of the raw materials used to prepare the polymer matrix, namely natural rubber and / or isoprene rubber.

[0027] In this invention, along the thickness direction of the gradient heterogeneous interface layer, the nanoscale rigid particles in the gradient heterogeneous interface layer are sequentially divided into three regions with progressively decreasing average concentrations from the inner surface to the outer surface: a first region (starting from the outer surface, occupying one-third of the total thickness), a second region (occupying one-third of the total thickness between the first and second regions), and a third region (starting from the outer surface, occupying one-third of the total thickness). The average concentration of nanoscale rigid particles in the first region is 1.75 times that in the second region. The average concentration of nanoscale rigid particles in the first region is 2.5 times that in the third region. In this invention, the average concentration of nanoscale rigid particles in the first region is preferably 45-55 wt%, and in some embodiments it can be 50 wt%. The average concentration of nanoscale rigid particles in the second region is preferably 30-40 wt%, and in some embodiments it can be 35 wt%. The average concentration of nanoscale rigid particles in the third region is preferably 15-25 wt%, and in some embodiments it can be 20 wt%.

[0028] This invention constructs a concentration gradient so that the gradient heterogeneous interface layer exhibits higher rigidity and modulus on the inner side (closer to the fiber layer, or the carcass ply in the tire bead), which facilitates good stress transfer with the RFL treatment layer; while on the outer side (closer to the rubber layer, or the sidewall rubber in the tire bead), it exhibits lower rigidity, maintaining compliance with the rubber matrix. When the interface layer is subjected to dynamic shear stress, the stress is gradually dispersed along the thickness direction, avoiding stress concentration at a single interface, thereby inhibiting the initiation and propagation of microcracks and improving the fatigue resistance of the interface layer.

[0029] In this invention, the nanoscale rigid particles are preferably surface-functionalized nanoparticles. The use of surface-functionalized nanoparticles enhances their interfacial bonding with the polymer matrix, preventing agglomeration during processing and allowing the particles to participate in cross-linking reactions during vulcanization, forming a stable interfacial bond. The nanoparticles preferably include nano-silica and / or carbon nanotubes, more preferably nano-silica, and most preferably silica. The silica can be fumed silica. The functionalized groups preferably contain at least one of epoxy, mercapto, and unsaturated double bond groups capable of chemically reacting with the polymer matrix or vulcanization system. In a specific embodiment of this invention, the nanoscale rigid particles can be surface-hydrophobically modified silica, specifically silane coupling agent-modified silica. The silane coupling agent used in the silane coupling agent-modified silica can be KH-560. The silane coupling agent-modified silica is preferably KH-560-modified silica.

[0030] In this invention, the preparation process of the gradient heterogeneous interface layer of the fiber-reinforced rubber composite structure does not employ the mechanical plasticizing process that leads to a significant reduction in molecular weight. This invention uses polymers with high entanglement properties (weight-average molecular weight greater than 1 × 10⁻⁶). 5 (g / mol polymer) can impart good flexibility and stress dispersion to the gradient heterogeneous interface layer without relying on high chemical crosslinking density.

[0031] This invention provides a fiber-reinforced rubber composite structure, comprising a plywood layer, a gradient heterogeneous interface layer, and a rubber layer stacked sequentially. The gradient heterogeneous interface layer is the same as described in the previous technical solution, with its inner surface in contact with the plywood layer and its outer surface in contact with the rubber layer. In this invention, along the thickness direction of the gradient heterogeneous interface layer, from the inner interface adjacent to the plywood layer to the outer interface adjacent to the rubber layer, the local concentration of the nanoscale rigid particles decreases in a gradient manner.

[0032] like Figure 2As shown, the fiber-reinforced rubber composite structure provided by the present invention includes a ply layer. In the present invention, the ply layer is a tire carcass ply layer. The ply layer can be obtained by vulcanizing impregnated ply fabric. The impregnated ply cord is preferably a fiber cord treated with resorcinol-formaldehyde-latex impregnation. The fiber cord in the ply layer is preferably a polyamide fiber cord, and in the embodiment, it can be nylon 66 cord, with a preferred linear density of 1400 dtex / 2.

[0033] like Figure 2 As shown, the fiber-reinforced rubber composite structure provided by the present invention includes a gradient heterogeneous interface layer disposed on the outer surface of the fabric layer. The inner surface of the gradient heterogeneous interface layer is in contact with the fabric layer.

[0034] like Figure 2 As shown, the fiber-reinforced rubber composite structure provided by the present invention includes a rubber layer disposed on the outer surface of the gradient heterogeneous interface layer. In the present invention, the rubber layer is a sidewall rubber. The raw materials for preparing the rubber layer preferably include a raw rubber component, and the orthogonal component includes one or more of rubber, butadiene rubber, and styrene-butadiene rubber. In the embodiments of the present invention, the rubber layer adopts a sidewall rubber formulation.

[0035] In this invention, the sidewall rubber preferably comprises the following raw materials by weight: 50-60 parts natural rubber, 40-50 parts butadiene rubber, 40-45 parts N660 carbon black, 6-8 parts aromatic oil or environmentally friendly processing oil, 1-3 parts zinc oxide, 1-2 parts stearic acid, 2-3 parts antioxidant 4020, 1-2 parts antioxidant RD, 1.5-2 parts microcrystalline wax, 2-3 parts tackifying resin, 1.5-2 parts sulfur, 1.2-1.5 parts accelerator CBS, and 0.1-0.2 parts scorching inhibitor CTP.

[0036] This invention provides a method for preparing the fiber-reinforced rubber composite structure described above, comprising the following steps: The rubber-impregnated cord is sequentially impregnated with interface layer slurries of varying concentrations, from highest to lowest, according to the concentration of nanoscale rigid particles. Each concentration gradient interface layer slurry includes at least two types of interface layer slurries with different nanoscale rigid particle concentrations. After each impregnation, pre-drying is performed, followed by a final pre-drying after the last impregnation and then final drying. This process yields an initial gradient heterogeneous interface layer on the surface of the rubber-impregnated cord. Then, a semi-finished rubber layer is bonded to the surface of the initial gradient heterogeneous interface layer, followed by pre-compression and co-vulcanization to obtain the fiber-reinforced rubber composite structure.

[0037] In this invention, the impregnated cord is preferably a fiber cord treated with resorcinol-formaldehyde-latex (RFL). The method for preparing the impregnated cord preferably includes impregnating the fiber cord with resorcinol-formaldehyde-latex followed by drying to obtain the impregnated cord.

[0038] In this invention, the impregnation solution (RFL solution) used for the resorcinol-formaldehyde-latex impregnation treatment preferably comprises the following components in parts by weight: 1.5-1.9 parts resorcinol, 2.5-2.7 parts 35-37 wt% formaldehyde solution, 0.05-0.1 parts sodium hydroxide, 14-14.3 parts natural rubber latex, 25-30 parts butadiene-pyridine latex, 2-2.6 parts 25-28 wt% ammonia, and 15-48.4 parts water. The preferred method for preparing the impregnation solution includes: dissolving resorcinol in water, adding formaldehyde solution and sodium hydroxide, and pre-reacting for 6 hours; then adding natural rubber latex, butadiene-pyridine latex, and ammonia, stirring and diluting to a solid content of 20%, and aging for 24 hours before use. In this invention, the impregnation treatment preferably involves impregnating the cord in an impregnation machine with the RFL solution, followed by drying and heat treatment to obtain the impregnated cord. The drying temperature is preferably 120~150℃; the drying time is preferably 2~5 min. The heat treatment temperature is preferably 200~220℃; the heat treatment time is preferably 1~2 min.

[0039] This invention achieves a gradient distribution of nanoscale rigid particles through a multi-layer impregnation coating process. The invention involves impregnating a resin-impregnated cord with an interface layer slurry containing a high concentration of nanoscale rigid particles, pre-drying it to form an inner layer, and then impregnating it with an interface layer slurry containing a low concentration or no particles, pre-drying it to form an outer layer. By controlling the pull-up speed of each impregnation, the solid content of the interface layer slurry, and the degree of pre-drying between layers (pre-drying temperature and time), and finally drying (controlling the drying temperature and time), partial intermixing of the inner and outer layers occurs at the interface, thereby constructing a gradient heterogeneous interface layer on the surface of the resin-impregnated cord with a decreasing particle concentration from the inside out.

[0040] In this invention, the concentration difference of nanoscale rigid particles in the interface layer slurry of adjacent concentration gradients is preferably at least 5 wt%, more preferably 5 to 20 wt%, and even more preferably 10 to 15 wt%, to ensure that a measurable concentration gradient can be formed after multilayer coating.

[0041] In this invention, the interface layer slurries of each concentration gradient preferably include a first interface layer slurry, a second interface layer slurry, and a third interface layer slurry. The raw materials for preparing the interface layer slurries preferably include wet-process silica. The wet-process silica is preferably prepared from surface-hydrophobically modified silica and natural rubber latex. Specifically, the surface-hydrophobically modified silica is silane coupling agent-modified silica. The silane coupling agent used in the silane coupling agent-modified silica can be KH-560. Preferably, the silane coupling agent-modified silica is KH-560-modified silica.

[0042] In this invention, the dry rubber content (i.e., solid content) of the natural rubber latex is preferably 40-60 wt%, and in the embodiments it can be 50 wt% or 60 wt%. In this invention, the mass percentage of the surface-hydrophobically modified silica in the dry rubber latex is preferably 15-55%, preferably 15-25 wt%, 30-40 wt%, or 45-55 wt%, and in the embodiments it can be 20%, 35%, or 50%.

[0043] In this invention, the concentration of nanoscale rigid particles in the interface layer slurries of each concentration gradient is expressed as a percentage of the mass of surface-hydrophobic modified silica used in the preparation of the wet-process silica adhesive to the mass of the dry natural rubber latex. Preferably, the mass of surface-hydrophobic modified silica used in the first interface layer slurry used in the preparation of the wet-process silica adhesive is 45-55 wt% of the dry natural rubber latex, and in this example, it can be 50 wt%. Preferably, the mass of surface-hydrophobic modified silica used in the second interface layer slurry used in the preparation of the wet-process silica adhesive is 30-40 wt% of the dry natural rubber latex, and in this example, it can be 35 wt%. Preferably, the mass of surface-hydrophobic modified silica used in the third interface layer slurry used in the preparation of the wet-process silica adhesive is 15-25 wt% of the dry natural rubber latex, and in this example, it can be 20 wt%.

[0044] In this invention, the interface layer slurry preferably comprises the following raw materials in parts by weight: 100 parts of wet-process silica, 20-30 parts (preferably 25 parts) of carbon black N660, 10-20 parts (preferably 15 parts) of carbon black N375, 1-3 parts (preferably 2 parts) of aromatic oil, 1-3 parts (preferably 2 parts) of stearic acid, 3-5 parts (preferably 4 parts) of zinc oxide, 0.5-2 parts (preferably 1 part) of accelerator NOBS, 0.5-2 parts (preferably 1 part) of accelerator DZ, 0.5-2 parts (preferably 1 part) of co-crosslinking agent HV-268, 0.5-2 parts (preferably 1 part) of binder A, 0.1-1 parts (preferably 0.5 parts) of anti-scorching agent CTP, and 1-3 parts (preferably 2.5 parts) of insoluble sulfur IS-60. The interface layer slurry preferably further includes an organic solvent, the amount of which is based on preparing the wet-process silica adhesive into a solution of 10-20 wt% (preferably 15 wt%). The organic solvent may be toluene.

[0045] In this invention, the preferred method for preparing the wet-process silica adhesive includes the following steps: dispersing silica in a silane coupling agent treatment solution for modification treatment to obtain surface-hydrophobic modified silica; mixing the surface-hydrophobic modified silica, lecithin emulsion, and coagulating enzyme to obtain a surface-hydrophobic modified silica aqueous dispersion; mixing the surface-hydrophobic modified silica aqueous dispersion with natural rubber latex and allowing it to stand and solidify to obtain the wet-process silica adhesive.

[0046] This invention involves dispersing silica in a silane coupling agent treatment solution for modification, resulting in surface-hydrophobic modified silica. In this invention, the silane coupling agent treatment solution comprises a silane coupling agent, ethanol, and water, wherein the silane coupling agent can be KH-560. The water can be deionized water. The preferred mass percentages of the silane coupling agent, ethanol, and water in the silane coupling agent treatment solution are 10%, 80%, and 10%, respectively. The preferred mass ratio of silica to the silane coupling agent is 4-6:1, and in some examples, it is 5:1. The preferred temperature for the modification treatment is 50-60°C, and the preferred time is 8-10 hours. The modification treatment is carried out under stirring. After the modification treatment, the obtained solid product is preferably washed alternately with ethanol and water and then dried to obtain the surface-hydrophobic modified silica. The number of alternating washes is 1-3 times. The drying is preferably vacuum drying, and the preferred temperature for vacuum drying is 40-50°C.

[0047] After obtaining surface-hydrophobically modified silica, the present invention mixes the surface-hydrophobically modified silica, lecithin emulsion, and coagulating enzyme to obtain an aqueous dispersion of surface-hydrophobically modified silica. In the present invention, the lecithin emulsion preferably comprises lecithin and water, and the mass concentration of lecithin in the lecithin emulsion is preferably 0.05~0.1 g / mL. The mass ratio of silica to lecithin in the lecithin emulsion is preferably 40~60:1, more preferably 50~55:1. The mass ratio of silica to coagulating enzyme is preferably 450~500:1. The present invention does not have special requirements for the specific implementation method of the mixing.

[0048] A surface-hydrophobic modified silica aqueous dispersion is obtained; the surface-hydrophobic modified silica aqueous dispersion is mixed with natural rubber latex and allowed to stand and solidify to obtain silica wet-process adhesive. In this invention, the dry rubber content of the natural rubber latex is preferably 40-60 wt%, and in the examples it can be 50 wt%. The mass percentage of the surface-hydrophobic modified silica in the dry rubber latex is preferably 15-55%, more preferably 15-25 wt%, 30-40 wt%, or 45-55 wt%, and in the examples it can be 20%, 35%, or 50%. In this invention, the standing solidification time is preferably 12-15 h. After the standing solidification is completed, the obtained solid product is dried to obtain the silica wet-process adhesive. The drying is preferably carried out in a forced-air drying oven, and the drying temperature is preferably 100-120℃.

[0049] In this invention, the preferred method for preparing the interface layer slurry includes: softening wet-process silica adhesive and dissolving it in an organic solvent to obtain an adhesive solution; mixing the adhesive solution, carbon black N660, carbon black N375, aromatic oil, stearic acid, zinc oxide, and binder A to obtain a mixture; grinding and mixing accelerator NOBS, accelerator DZ, co-crosslinking agent HV-268, anti-scorching agent CTP, and insoluble sulfur IS-60, and finally adding them to the mixture, stirring evenly, and allowing it to stand to degas to obtain the interface layer slurry.

[0050] This invention involves sequentially impregnating the PVC-coated cord with interface layer slurries of varying concentrations, from highest to lowest, according to the concentration of nanoscale rigid particles. Each concentration gradient of interface layer slurry includes at least two different concentrations of nanoscale rigid particles. Pre-drying is performed after each impregnation, followed by a final pre-dry after the last impregnation, and then final drying. Preferably, the PVC-coated cord is impregnated with a first interface layer slurry, then pre-dried, then impregnated with a second interface layer slurry, then pre-dried again, then impregnated with a third interface layer slurry, then pre-dried again, and finally dried. The impregnation time is preferably 5-15 seconds, and in some embodiments, 10 seconds. After each impregnation, the cord is preferably pulled out at a uniform pulling speed of 0.3-0.5 m / min. The pre-drying is preferably carried out in a forced-air drying oven. The temperature of the pre-drying (including the first, second, and third pre-drying) is preferably 45-60°C, and in some embodiments, 50 or 60°C. The pre-drying time (including first pre-drying, second pre-drying, and third pre-drying) is preferably 10-20 minutes. The drying temperature is preferably 50-80°C, and in this embodiment, it can be 70°C. The drying time is preferably 30-40 minutes. This invention, through pre-drying and drying (controlling temperature and time), allows the solvent between layers to evaporate slowly, promoting partial intermixing between layers. This allows the solvent in each layer to evaporate and form partially mixed regions between layers, creating a gradient heterogeneous interface layer with decreasing silica concentration from the inside out. By controlling the pre-drying and drying temperature and time, this invention can adjust the degree of interlayer mixing, thereby controlling the steepness of the gradient distribution.

[0051] After obtaining an initial gradient heterogeneous interface layer on the surface of the impregnated cord, the present invention further describes the following steps: a rubber layer semi-finished product is bonded to the surface of the initial gradient heterogeneous interface layer, and then pre-pressed and co-vulcanized sequentially to obtain the fiber-reinforced rubber composite structure.

[0052] In this invention, the semi-finished rubber layer can be a sidewall rubber semi-finished product. The sidewall rubber semi-finished product preferably comprises the following components by weight: 50-60 parts natural rubber, 40-50 parts butadiene rubber, 40-45 parts N660 carbon black, 6-8 parts aromatic oil or environmentally friendly processing oil, 1-3 parts zinc oxide, 1-2 parts stearic acid, 2-3 parts antioxidant 4020, 1-2 parts antioxidant RD, 1.5-2 parts microcrystalline wax, 2-3 parts tackifying resin, 1.5-2 parts sulfur, 1.2-1.5 parts accelerator CBS, and 0.1-0.2 parts scorch inhibitor CTP.

[0053] In this invention, the preferred method for preparing the sidewall rubber semi-finished product includes: adding natural rubber and butadiene rubber to a mixer for plasticizing, then sequentially adding N660 carbon black, aromatic oil or environmentally friendly processing oil, zinc oxide, stearic acid, antioxidant 4020, antioxidant RD, microcrystalline wax, and tackifying resin for mixing, and after discharge, cooling and sheeting on a two-roll mill to obtain a first-stage compound. After the first-stage compound has rested, sulfur, accelerator CBS, and scorch inhibitor CTP are added to the two-roll mill, mixed evenly, and then sheeted to obtain the uncured sidewall rubber semi-finished product.

[0054] In this invention, the pre-pressing is preferably performed using a calendering roller or a bonding machine. The pre-pressing pressure is preferably 0.2~0.5 MPa. This invention eliminates air between interfaces through pre-pressing, achieving good physical adhesion. In this invention, the co-vulcanization is preferably performed on a flat vulcanizing machine. The co-vulcanization conditions preferably include: vulcanization temperature preferably 135~150℃, which can be 140℃ in the example; vulcanization pressure preferably 10~30 MPa, which can be 25 MPa in the example; and vulcanization time preferably 15~40 min, which can be 30 min in the example.

[0055] This invention provides the application of the fiber-reinforced rubber composite structure described in the above-described technical solution, or the fiber-reinforced rubber composite structure prepared by the preparation method described in the above-described technical solution, in fiber-reinforced rubber products. In this invention, the fiber-reinforced rubber product can be a fiber-rubber composite component in an aircraft tire that bears dynamic loads. The fiber-reinforced rubber product can be a tire bead. The fiber-reinforced rubber composite structure provided by this invention improves the shear fatigue resistance of the cord-rubber interface, making it suitable for high-end rubber products with extremely high safety requirements, such as aircraft tires.

[0056] like Figure 1 As shown, this invention provides a tire, wherein the tire bead comprises the fiber-reinforced rubber composite structure described in the above-described technical solution or the fiber-reinforced rubber composite structure prepared by the preparation method described in the above-described technical solution. The tire provided by this invention is an aircraft tire.

[0057] To further illustrate the present invention, the technical solutions provided by the present invention are described in detail below with reference to embodiments, but these should not be construed as limiting the scope of protection of the present invention. The natural rubber latex used in the embodiments of the present invention has a dry rubber content of 60 wt% and is selected from Hainan Natural Rubber Industry Group Co., Ltd.; the silica is fumed silica with a specific surface area of ​​approximately 200 m². 2 / g, selected from German company, CE; silane coupling agent KH-560 (γ-glycidyl etheroxypropyltrimethoxysilane), selected from Nanjing Shuguang Chemical Group; nylon 66 cord (specification 1400dtex / 2), selected from Shenma Industry Co., Ltd.; other rubber additives are all commercially available industrial products.

[0058] Example 1 Preparation of wet-process silica sizing agent: 100g of silane coupling agent KH-560 was prepared into a surface treatment solution. The solution composition, by mass percentage, was: 10% KH-560, 80% ethanol, and 10% deionized water. 500g of silica was dispersed in the above treatment solution and stirred at 60℃ for 8 hours. After the reaction, the silica was washed three times alternately with ethanol and deionized water, and then vacuum dried at 50℃ to constant weight to obtain surface-hydrophobically modified silica.

[0059] Add 10g of lecithin to 200mL of deionized water and stir at high speed to disperse evenly, thus obtaining a lecithin emulsion. Add the above surface-modified silica to the lecithin emulsion, stir to disperse evenly, then add 1g of coagulating enzyme and continue stirring for 30min to obtain a surface-hydrophobic modified silica aqueous dispersion.

[0060] A surface-modified hydrophobic silica aqueous dispersion was mixed with natural rubber latex containing 1000g of dry rubber (dry rubber content 60 wt%), and slowly stirred for 30 min until the system became a viscous paste. The mixture was transferred to a stainless steel tray, allowed to stand and solidify for 12 hours, and then dried in a 120℃ forced-air drying oven to constant weight to obtain silica / natural rubber wet-process co-precipitated rubber, i.e., silica wet-process rubber.

[0061] In this embodiment, by adjusting the amount of surface-hydrophobic modified silica added, 200g, 350g, and 500g of surface-hydrophobic modified silica were added to natural rubber latex containing 1000g of dry rubber, respectively, to prepare silica wet-process rubber with a surface-hydrophobic modified silica content of 20%, 35%, and 50% of the dry rubber mass, respectively, which are denoted as 20% wet-process rubber, 35% wet-process rubber, and 50% wet-process rubber.

[0062] The above-mentioned wet-process precipitated silica rubber was lightly mixed on an open mill under the following conditions: roll temperature 40-50℃, roll gap 1mm, rotation speed 30-50 r / min, and mixing time 3-5 min. High temperatures and prolonged shearing were avoided throughout the mixing process to preserve the original molecular weight and entangled structure of the natural rubber to the greatest extent possible.

[0063] Preparation of gradient heterogeneous interface layer slurries: Using 20%, 35%, and 50% wet-process slurries as the matrix, three different concentrations of silica with different hydrophobic surface modifications were prepared according to the formulations shown in Table 1. The preparation method was as follows: Silica wet-process slurries were softened by passing them through a two-roll mill, then chopped and added to toluene. The mixture was heated and stirred to dissolve, resulting in a 15% silica wet-process slurry. Then, according to the formulation directions in Table 1, carbon black N660, carbon black N375, aromatic oil, stearic acid, zinc oxide, and binder A were added sequentially to the slurry, and the mixture was stirred at high speed until uniformly dispersed. Finally, insoluble sulfur IS-60, accelerator NOBS, accelerator DZ, co-crosslinking agent HV-268, and anti-scorching agent CTP were pre-ground into fine powder and added last at a temperature below 40℃. The mixture was stirred for 10 minutes and allowed to stand to remove bubbles before use.

[0064] Table 1. Gradient Heterogeneous Interface Layer Slurry Formulation (Unit: Parts by Mass)

[0065] Preparation of RFL-impregnated cord: Nylon 66 1400 dtex / 2 cord was subjected to RFL impregnation. The impregnation solution formulation, by weight, was: resorcinol 1.9 parts, 37% formaldehyde solution 2.7 parts, sodium hydroxide 0.1 parts, natural rubber latex 14.3 parts, butadiene-pyridine latex 30 parts, 28 wt% ammonia water 2.6 parts, and water 48.4 parts. The preparation method was as follows: resorcinol was dissolved in water, 37% formaldehyde solution and sodium hydroxide were added, and the mixture was pre-reacted for 6 hours; then natural rubber latex, butadiene-pyridine latex and ammonia water were added, and the mixture was stirred and diluted to a solid content of 20%, and then cured for 24 hours before use. The cord was impregnated with RFL solution in an impregnation machine, dried at 150℃ for 2 minutes, then heat-treated at 220℃ for 1 minute, and then wound up for use.

[0066] Preparation of the gradient heterogeneous interface layer slurry: The RFL impregnated cord, which was wound up and ready for use, was first impregnated in slurry H (high silica concentration) for 10 seconds, and then pulled out at a uniform speed of 0.5 m / min. It was then dried in a 60℃ hot air drying oven for 10 minutes to allow the solvent to evaporate and form the inner layer. Then, the cord was again impregnated in slurry M (medium silica concentration) for 10 seconds, and then pulled out at a uniform speed of 0.5 m / min. The intermediate layer is formed by drying in a 60℃ hot air drying oven for 10 minutes. Finally, the cord is immersed in slurry L (low silica concentration) for 10 seconds and pulled out at a uniform speed of 0.5 m / min. A stepped temperature-increasing drying process is adopted: first, it is dried at 50℃ for 20 minutes, and then the temperature is increased to 70℃ for 30 minutes to allow the solvent between the layers to evaporate slowly, promote the inter-layer mixing, and form an initial gradient heterogeneous interface layer with decreasing silica concentration from the inside to the outside.

[0067] Preparation of Sidewall Rubber Semi-finished Product: The sidewall rubber semi-finished product comprises the following components by weight: 60 parts natural rubber, 40 parts butadiene rubber, 45 parts N660 carbon black, 8 parts aromatic oil, 3 parts zinc oxide, 2 parts stearic acid, 2 parts antioxidant 4020, 1 part antioxidant RD, 1.5 parts microcrystalline wax, 2 parts tackifying resin, 1.5 parts sulfur, 1.2 parts accelerator CBS, and 0.1 parts scorch inhibitor CTP. The preparation method is as follows: Natural rubber and butadiene rubber are added to a mixer for plasticizing. Then, N660 carbon black, aromatic oil, zinc oxide, stearic acid, antioxidant 4020, antioxidant RD, microcrystalline wax, and tackifying resin are added sequentially for mixing. After discharge, the mixture is cooled and sheeted on a two-roll mill to obtain a partial compound. After a section of the compounded rubber has been left to stand, sulfur, accelerator CBS and anti-scorching agent CTP are added to the open mill. After being mixed evenly, the mixture is sheeted out to obtain the uncured tire sidewall rubber semi-finished product.

[0068] Vulcanization of the composite structure: The cords with the initial gradient heterogeneous interface layer are cut to a suitable size and bonded to the unvulcanized sidewall rubber semi-finished product. Strict direction control is maintained during bonding: the outer side of the gradient heterogeneous interface layer (i.e., the side of the last impregnated slurry L) is in contact with the surface of the sidewall rubber semi-finished product. A pre-pressure of 0.2~0.5 MPa is then applied using a calendering roller or bonding machine to remove air from the interface and achieve good physical adhesion. After bonding, co-vulcanization is performed on a flat vulcanizing machine under the following conditions: temperature 135~150℃, pressure 10~30MPa, time 15~40min. In this embodiment, the preferred vulcanization conditions are: temperature 140℃, pressure 25MPa, time 30min. The resulting fiber-rubber composite structure sample is designated as Example 1.

[0069] Comparative Example 1: Using the exact same raw materials, formulation, and preparation process as Example 1, the only difference was that only slurry M (medium silica concentration, 35% wet-process adhesive) was used for single-layer impregnation coating, with three impregnations to construct a homogeneous interface layer with a silica concentration of 35%, the thickness of which was equivalent to the total thickness of the three layers in Example 1. The remaining steps were the same as in Example 1, and a comparative sample was prepared, designated as Comparative Example 1.

[0070] Comparative Example 2: The same RFL impregnated cord, sidewall rubber semi-finished product, composite structure bonding method and vulcanization process as Example 1 were used. The only difference was that the distribution direction of silica concentration in the gradient heterogeneous interface layer was opposite to that in Example 1, that is, a reverse gradient heterogeneous interface layer with silica concentration gradually increasing from the inside to the outside was constructed.

[0071] Specifically, the RFL impregnated cord is first immersed in slurry L for 10 s, then pulled out at a uniform speed of 0.5 m / min, and dried in a hot air drying oven at 60℃ for 10 min to form a low silica concentration inner layer on the outside of the RFL impregnated layer; then it is immersed in slurry M for 10 s, pulled out at a uniform speed of 0.5 m / min, and dried at 60℃ for 10 min to form a medium silica concentration intermediate layer; finally, it is immersed in slurry H for 10 s, pulled out at a uniform speed of 0.5 m / min, and dried using a stepped temperature-increasing drying process: first dried at 50℃ for 20 min, then heated to 70℃ for 30 min to form a high silica concentration outer layer.

[0072] The outer side of the resulting reverse gradient heterogeneous interface layer, namely the high-precision silica slurry H layer, is in contact with the surface of the sidewall rubber semi-finished product. Subsequently, bonding, pre-compression, and co-curing are performed according to the method described in Example 1 to obtain a comparative sample, designated as Comparative Example 2. Dynamic adhesive fatigue performance testing was conducted according to GB / T 39639 "Test Method for Dynamic Adhesive Performance of Impregnated Cords and Ropes". The test conditions were: temperature 80℃, frequency 13Hz, dynamic displacement amplitude ±2mm (tensile-compression reciprocating mode). The number of fatigue cycles at which visible debonding or delamination occurred was recorded. Five parallel samples were tested for each formulation, and the average value was taken.

[0073] The test results show that the dynamic fatigue lives of the five samples prepared in Example 1 were 48,200, 43,700, 46,500, 42,800, and 45,900 cycles, respectively, with an average of 45,420 cycles and a standard deviation of ±2,100 cycles. The dynamic fatigue lives of the five samples prepared in Comparative Example 1 were 25,100, 22,300, 21,800, 24,500, and 23,200 cycles, respectively, with an average of 23,380 cycles and a standard deviation of ±1,450 cycles. The dynamic fatigue lives of the five samples prepared in Comparative Example 2 were 19,800, 17,600, 18,900, 17,100, and 19,000 cycles, respectively, with an average of 18,480 cycles and a standard deviation of ±1,100 cycles.

[0074] Test results show that, compared with Comparative Example 1 which uses a homogeneous interface layer, Example 1 using the gradient heterogeneous interface layer of the present invention has a dynamic fatigue life that is improved by about 94%, indicating that the particle concentration gradient distribution constructed by the present invention can effectively disperse dynamic shear stress, inhibit the initiation and propagation of interface microcracks, and significantly improve the fatigue resistance of the interface layer; compared with Comparative Example 2, Example 1 has a dynamic fatigue life that is improved by about 145%, indicating that the gradient heterogeneous interface layer with decreasing silica concentration from the inside to the outside can significantly improve the dynamic adhesion stability between RFL impregnated cord and sidewall rubber; while the reverse gradient structure allows the high silica concentration layer to directly contact the sidewall rubber, which easily forms an interface region with high rigidity and obvious stress concentration, which is not conducive to adhesion retention under dynamic load.

[0075] As can be seen from the above embodiments, the present invention addresses the current technical status of the interface layer between the fiber cord and the rubber matrix, which suffers fatigue failure and interface debonding due to stress concentration under periodic dynamic loads. It provides a gradient heterogeneous interface layer with a gradient structure, its composite structure, and preparation method, which can significantly improve its fatigue resistance while maintaining the interfacial bonding strength.

[0076] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A gradient heterogeneous interface layer for fiber-reinforced rubber composite structures, characterized in that, It includes a polymer substrate and nanoscale rigid particles dispersed in the polymer substrate; the gradient heterogeneous interface layer is divided into an inner side and an outer side along the thickness direction, the concentration of the nanoscale rigid particles decreases from the inner side to the outer side of the gradient heterogeneous interface layer, and the average concentration of nanoscale rigid particles in the inner quarter thickness region of the gradient heterogeneous interface layer is at least 1.5 times the average concentration of nanoscale rigid particles in the outer quarter thickness region.

2. The gradient heterogeneous interface layer according to claim 1, characterized in that, The raw materials for preparing the polymer substrate include polymers, including natural rubber and / or isoprene rubber; the weight-average molecular weight of the polymer is greater than 1 × 10⁻⁶. 5 g / mol.

3. The gradient heterogeneous interface layer according to claim 1, characterized in that, The nanoscale rigid particles are nanoparticles with functionalized surfaces. The nanoparticles include nano-silica and / or carbon nanotubes. The functionalized groups include at least one of epoxy groups, mercapto groups, and unsaturated double bond groups that can chemically react with the polymer matrix or vulcanization system.

4. A fiber-reinforced rubber composite structure, characterized in that, It includes a fabric layer, a gradient heterogeneous interface layer and a rubber layer stacked in sequence; the gradient heterogeneous interface layer is the gradient heterogeneous interface layer according to any one of claims 1 to 3, wherein the inner surface of the gradient heterogeneous interface layer is in contact with the fabric layer and the outer surface is in contact with the rubber layer.

5. The fiber-reinforced rubber composite structure according to claim 4, characterized in that, The fiber cords in the fabric layer are polyamide fiber cords.

6. The fiber-reinforced rubber composite structure according to claim 4, characterized in that, The raw materials for preparing the rubber layer include raw rubber components, which include one or more of natural rubber, butadiene rubber, and styrene-butadiene rubber.

7. The method for preparing the fiber-reinforced rubber composite structure according to any one of claims 4 to 6, characterized in that, Includes the following steps: The rubber-impregnated cord is impregnated with interface layer slurries of varying concentrations, from highest to lowest, according to the concentration of nanoscale rigid particles. Each concentration gradient interface layer slurry includes at least two types of interface layer slurries with different concentrations of nanoscale rigid particles. After each impregnation, the cord is pre-dried, and after the final pre-drying, it is dried to obtain an initial gradient heterogeneous interface layer on the surface of the rubber-impregnated cord. Then, a rubber layer semi-finished product is bonded to the surface of the initial gradient heterogeneous interface layer, followed by pre-compression and co-vulcanization to obtain the fiber-reinforced rubber composite structure.

8. The preparation method according to claim 7, characterized in that, The concentration difference of nanoscale rigid particles in the interface layer slurry of adjacent concentration gradients is at least 5 wt%; the pre-drying temperature is 45~60℃; the drying temperature is 50~80℃, and the drying temperature is greater than the pre-drying temperature.

9. The application of the fiber-reinforced rubber composite structure according to any one of claims 4 to 6 or the fiber-reinforced rubber composite structure prepared by the preparation method according to claim 7 or 8 in fiber-reinforced rubber products.

10. A tire, characterized in that, The tire bead comprises the fiber-reinforced rubber composite structure as described in any one of claims 4 to 6 or the fiber-reinforced rubber composite structure prepared by the preparation method described in claim 7 or 8.

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