Flame-retardant antistatic polyurea repair material and its application in repair of mining devices

Abstract

The application discloses a flame-retardant antistatic polyurea repairing material and application thereof in repairing of mining devices, and belongs to the technical field of high polymer repairing materials for mining. The flame-retardant antistatic polyurea repairing material is a two-component polyurea mixed material, and the two-component polyurea material comprises component A and component B; the component A is an MDI type isocyanate prepolymer; and the component B comprises amino-terminated polyether, m-phenylenediamine, a fast-reaction type aromatic chain extender, a tertiary amine catalyst, a reaction type phosphorus-nitrogen flame retardant, a nano wear-resistant filler, a flame-retardant synergist, conductive carbon black, conductive fiber, an antistatic additive, a silane coupling agent, a latent catalyst, an antioxidant and a defoaming agent. The application can be used for repairing of mining conveyor belts, mining conveying pipelines, hydraulic support back-up plates, mining motor housings and middle troughs of scraper conveyors, so as to solve the problems of slow curing, insufficient early strength performance and substandard flame-retardant antistatic performance of the existing mining repairing materials.

Description

Technical Field

[0001] This invention relates to the field of polymer repair materials for mining, specifically to flame-retardant and antistatic polyurea repair materials and their application in the repair of mining equipment. Background Technology

[0002] In mining production systems, equipment such as mining conveyor belts, conveying pipelines, hydraulic support side plates, and scraper conveyor troughs are subjected to harsh working conditions of high wear, high corrosion, and high impact for extended periods. They also face flammable and explosive environmental risks, making them highly susceptible to damage, cracking, corrosion, and other malfunctions. If not repaired in time, these issues can lead to production interruptions or even safety accidents.

[0003] Patent CN120118265A discloses a castable polyurethane material formulation and its application process in conveyor belt repair. The castable polyurethane material formulation includes: 100 parts of component A; 8-20 parts of component B; 5-25 parts of component C; 0.5-10 parts of component D; and 102-106 parts of component E. Component C is a flame retardant, specifically expandable graphite powder; and component D is an antistatic liquid. The application process of the castable polyurethane material in conveyor belt repair includes the following steps: 1. Grinding the damaged area of ​​the conveyor belt to be repaired; 2. Applying component E; 3. Mixing components A, B, C, and D together; 4. Pouring and leveling the mixed mixture; 5. Surface curing occurs within fifteen minutes, and the required curing time is sixty minutes. This invention offers the following advantages: it meets the requirements of MT / T113-1995, can be cast in one piece, and its curing speed, physical properties, and adhesion can meet the needs of various types of on-site repairs of coal mine conveyor belts. While cast-type polyurethane can achieve rapid curing, it requires specialized casting equipment, strict control of ambient temperature and humidity before construction, poor adaptability to high humidity and dust conditions underground, and a long waiting time for complete curing after construction, resulting in limited repair efficiency.

[0004] Due to the special nature of mining operations, daily downtime for maintenance is very short, averaging between 2 and 4 hours. The methods described above generally suffer from insufficient adhesion strength between the repair layer and the substrate, limited wear resistance and tear resistance, resulting in a short service life after repair. Frequent maintenance increases upkeep costs and downtime. While ordinary polyurea materials cure quickly, they lack early strength and have low initial strength, requiring a long curing period before being put into use. Furthermore, their flame retardant and antistatic properties are difficult to meet mining safety standards such as GB 12476.1-2013 "Electrical Apparatus for Combustible Dust Environments - Part 1: General Requirements" and GB 24763-2009 "Flame Retardant Performance and Test Methods for Mining Conveyor Belts," posing a safety hazard of static electricity accumulation and potential fire or explosion in the flammable and explosive environment of mines.

[0005] Therefore, developing a rapid repair material that combines early strength, flame retardancy, and antistatic properties to achieve in-situ rapid repair of mining equipment is a core technical problem that urgently needs to be solved in the field of mining equipment operation and maintenance. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by providing a flame-retardant and antistatic polyurea repair material and its application in the repair of mining equipment, thereby solving the problems of slow curing, insufficient early strength, and substandard flame-retardant and antistatic properties of existing mining repair materials.

[0007] The technical solution adopted in this invention is as follows.

[0008] Component A is an MDI-type isocyanate prepolymer (amino-terminated polyether is a compound system of polyetheramine D2000 and T5000) accounting for 30% to 40% of the total mass of the polyurea material. The components of component B, by mass percentage of the total polyurea material, are as follows: Component B comprises, by mass percentage of the following components: amino-terminated polyether 25%–35%, m-phenylenediamine 5.5%–9.5%, fast-reacting aromatic chain extender 1%–2.5%, tertiary amine catalyst 0.05%–0.2%, reactive phosphorus-nitrogen flame retardant 5%–10%, nano-wear-resistant filler 5%–8%, flame retardant synergist 1.5%–3%, conductive carbon black 2%–5%, conductive fiber 1%–2%, antistatic agent 0.5%–1.5%, silane coupling agent 1%–1.8%, latent catalyst 0.1%–0.4%, antioxidant 0.1%–0.8%, and defoamer 0.05%–0.15%. The amino-terminated polyether is a compound system of polyetheramines D2000 and T5000; the fast-reacting aromatic chain extender is methylcyclohexanediamine; the tertiary amine catalyst is triethylenediamine; the latent catalyst is dibutyltin dilaurate; the reactive phosphorus-nitrogen flame retardant is aluminum diethylphosphinate; the flame retardant synergist is antimony trioxide; the nano-wear-resistant filler is a compound system of nano-alumina and nano-silica; the silane coupling agent is KH550 silane coupling agent; the antistatic agent is a quaternary ammonium salt cationic surfactant; and the latent catalyst is dibutyltin dilaurate.

[0009] Its beneficial effects are: 1. Using MDI-type isocyanate prepolymer and polyetheramine D2000 / T5000 compound system as polyurea core raw material, a highly elastic molecular chain structure is constructed to ensure that the material maintains excellent mechanical properties such as tensile strength ≥18MPa and elongation at break ≥400% even after the addition of flame retardant and antistatic components, making it suitable for fatigue conditions of dynamic operation of conveyor belts.

[0010] 2. By combining reactive phosphorus-nitrogen flame retardant (aluminum diethylphosphonate) with inorganic expandable flame retardant filler (magnesium hydroxide / aluminum hydroxide compound) and antimony trioxide synergist, a highly efficient flame retardant effect with a limiting oxygen index ≥28% is achieved; the reactive flame retardant is covalently bonded to the polyurea molecular chain, avoiding the problem of reduced material elasticity caused by traditional additive flame retardants, and forming a dense carbon layer during combustion to inhibit flame spread.

[0011] The compound filler fully utilizes the high hardness of nano-alumina to significantly enhance the wear resistance of the repair layer. It also leverages the hydrogen bonds formed between the hydroxyl groups on the surface of nano-silica and polyurea molecules to strengthen the interfacial bonding between the filler and the polyurea matrix, preventing filler detachment during long-term friction. The particle size of the compound filler is controlled at 50-100nm, ensuring uniform dispersion within the polyurea material without affecting the flowability or density of the coating during spraying. This guarantees a smooth repair layer surface and reduces the adhesion and frictional damage caused by mineral particles.

[0012] A composite conductive system consisting of conductive carbon black and conductive fibers, combined with quaternary ammonium salt-type antistatic additives, is employed to maintain a stable surface resistivity of 10 Ω·cm by optimizing filler particle size and dispersion process. 6 -10 9 Within the Ω range, it effectively releases static charge; it ensures wear resistance of ≤0.08cm³ / 1.61km, balancing safety and durability.

[0013] 3. Add silane coupling agent KH550 to promote chemical bonding between polyurea material and conveyor belt rubber matrix, improve interfacial tensile shear strength ≥3MPa, and prevent repair layer peeling or cracking.

[0014] 4. Rapid Curing and Safe Construction. This prepolymer, modified with short-chain polypropylene glycol, retains the high reactivity of MDI while improving compatibility with component B, allowing for rapid reaction with component B and providing a foundation for the material's early strength performance. Precise dosage control of dibutyltin dilaurate catalyst, combined with a fast-reacting aromatic chain extender to accelerate the addition reaction rate of amino groups and isocyanates, and a tertiary amine catalyst to lower the activation energy and shorten the gel time, synergistically enables the polyurea material to complete early cross-linking within a short time after spraying, enhancing the early strength of the repair layer and achieving early strength without causing spray gun clogging. It surface dries within 3 minutes and reaches over 60% of its maximum strength after 25-30 minutes of heat preservation curing, meeting the time requirements for rapid in-situ repair in underground mines. Furthermore, the curing process releases no harmful volatile substances, complying with mining environmental safety requirements.

[0015] As a preferred technical solution, the conductive carbon black is acetylene black.

[0016] As a preferred technical solution, the conductive fiber is conductive carbon fiber.

[0017] As a preferred technical solution, amino-terminated polyether is compounded from polyetheramine D2000 and T5000 at a weight ratio of 1:1.2 to 1.8. By compounding polyetheramine D2000 and T5000 at a weight ratio of 1:1.2 to 1.8, the molecular weight distribution and molecular chain flexibility of the amino-terminated polyether can be precisely controlled. This allows the polyurea material to maintain excellent elasticity (elongation at break ≥400%) while increasing tensile strength to ≥20MPa and tear strength to ≥50kN / m, thereby enhancing its resistance to dynamic loads and impact wear in devices such as mining conveyor belts and scraper conveyor troughs.

[0018] This formulation optimizes the viscosity characteristics of component B, ensuring excellent spray flow when mixed with component A. This prevents issues like nozzle clogging or uneven coating thickness during application, guaranteeing the uniformity and density of the repair layer. Furthermore, this molecular weight blending system enhances the compatibility of the material with flame-retardant and antistatic components, preventing performance fluctuations caused by uneven filler dispersion.

[0019] As a preferred technical solution, the nano wear-resistant filler is a composite system of nano alumina and nano silica, in which nano alumina accounts for 60% to 70% of the total mass of the nano wear-resistant filler and nano silica accounts for 30% to 40%.

[0020] By blending nano-alumina and nano-silica at a mass ratio of 60%–70%:30%–40%, the high hardness (Mohs hardness 9) of nano-alumina can be fully utilized to improve the wear resistance of the repair layer, resulting in a wear resistance of ≤0.06cm³ / 1.61km, far superior to ordinary polyurea repair materials. It utilizes the abundant hydroxyl groups on the surface of nano-silica to form a stable hydrogen bond network with the polyurea molecular chains, enhancing the interfacial bonding strength between the filler and the polyurea matrix and preventing filler detachment under long-term friction or impact loads. It can also optimize the packing density and dispersibility of the nano-filler, ensuring uniform distribution of the filler within the polyurea matrix without affecting the material's spray flowability and coating density, guaranteeing a smooth and flat repair layer surface, reducing the adhesion and wear of mineral particles, and extending the service life of the repair device.

[0021] As a preferred technical solution, the antioxidant is 1010 antioxidant. 1010 antioxidant is a highly efficient hindered phenolic antioxidant. The hindered phenolic groups in its molecular structure can effectively capture free radicals generated by oxidation reactions in polyurea materials during long-term use, inhibiting molecular chain breakage and cross-linking aging, and improving the thermal stability and weather resistance of the material.

[0022] In response to the harsh working conditions of dampness, high temperature and oxidation corrosion in underground mines, adding 1010 antioxidant at a mass ratio of 0.5% to 1% of component B can enable the repair material to retain tensile strength ≥85% and elongation at break ≥80% after accelerated aging at 80℃ for 1000 hours, thus extending the service life of the repair layer of mining equipment.

[0023] The antioxidant has good compatibility with the flame retardant, conductive filler and chain extender components in this invention, and will not interfere with the flame retardant, antistatic properties and rapid curing characteristics of the material.

[0024] Adding antioxidant 1010 delays material aging, while silicone defoamer eliminates air bubbles during construction, ensuring a continuous and dense repair layer. The curing process releases no harmful volatile substances, meeting the safety requirements for mining environments.

[0025] As a preferred technical solution, the defoamer is a polyether-modified siloxane defoamer.

[0026] The use of silicone defoamers effectively eliminates microbubbles generated during the mixing and spraying of polyurea materials, preventing defects such as pores and pinholes from forming inside or on the surface of the repair layer, ensuring a continuous and dense structure. The silicone defoamer exhibits excellent compatibility with the polyurea matrix and its functional components, and will not negatively affect the material's flame retardancy, antistatic properties, or mechanical strength. The repair layer effectively blocks the penetration of moisture, dust, and corrosive media in the mining environment, preventing accelerated corrosion or wear caused by pores in the repaired area.

[0027] As a preferred technical solution, component A is a modified MDI prepolymer prepared by reacting 4,4'-diphenylmethane diisocyanate (MDI-100) and polypropylene glycol (PPG-1000) at a mass ratio of 3:1-1.3 at 70-80℃ for 2-3 hours, and the NCO content of the prepolymer is controlled to be 20%-22%.

[0028] The application of any of the above-mentioned flame-retardant and antistatic polyurea repair materials in the repair of mining equipment is characterized in that: the flame-retardant and antistatic polyurea repair material is used to spray an elastic and dense layer onto the damaged surface of the mining equipment.

[0029] As a preferred technical solution, the mining equipment includes a mining conveyor belt, a mining conveying pipeline, a hydraulic support side guard plate, a mining motor housing, and a scraper conveyor central trough. Detailed Implementation

[0030] Example 1. A flame-retardant and antistatic polyurea repair material, characterized in that: the repair material is a two-component polyurea mixture, comprising component A and component B.

[0031] Component A is an MDI-type isocyanate prepolymer (amino-terminated polyether is a compound system of polyetheramine D2000 and T5000) accounting for 30% to 40% of the total mass of the polyurea material. Component B comprises the following components at a percentage of the total mass of the polyurea material: amino-terminated polyether 25%–35%, m-phenylenediamine 5.5%–9.5%, fast-reacting aromatic chain extender (methylcyclohexanediamine) 1%–2.5%, tertiary amine catalyst (triethylenediamine) 0.05%–0.2%, reactive phosphorus-nitrogen flame retardant (aluminum diethylphosphinate) 5%–10%, nano-wear-resistant filler 5%–8%, and flame retardant synergist (…). Antimony trioxide 1%–3%, conductive carbon black 2%–5%, conductive fiber 1%–2%, antistatic additive (quaternary ammonium salt cationic surfactant) 0.5%–1.5%, silane coupling agent (KH550 silane coupling agent) 1%–1.8%, latent catalyst (dibutyltin dilaurate) 0.1%–0.4%, antioxidant (quaternary ammonium salt cationic surfactant) 0.1%–0.8%, defoamer 0.05%–0.15%; The amino-terminated polyether is a compound system of polyetheramine D2000 and T5000; the fast-reacting aromatic chain extender is methylcyclohexanediamine; the tertiary amine catalyst is triethylenediamine; the latent catalyst is dibutyltin dilaurate; the reactive phosphorus-nitrogen flame retardant is aluminum diethylphosphinate; the flame retardant synergist is antimony trioxide; the nano-wear-resistant filler is a compound system of nano-alumina and nano-silica; the silane coupling agent is KH550 silane coupling agent; the antistatic agent is a quaternary ammonium salt cationic surfactant; the latent catalyst is dibutyltin dilaurate; the conductive carbon black is acetylene black; and the conductive fiber is conductive carbon fiber.

[0032] Specifically, in this embodiment, component A is an MDI-type isocyanate prepolymer: 30%; Component B consists of: 35% amino-terminated polyether (polyetheramine D2000 and T5000 compounded in a 1:1 mass ratio), 9.5% m-phenylenediamine, 2.5% methylcyclohexanediamine, 0.2% triethylenediamine, 8% aluminum diethylphosphinate, 6% nano-alumina and nano-silica (compounded in a 3:2 mass ratio), 2% antimony trioxide, 2% acetylene black, 1% conductive carbon fiber, 0.5% quaternary ammonium salt cationic antistatic agent, 1% KH550 silane coupling agent, 0.1% dibutyltin dilaurate, 0.1% antioxidant, and 0.1% defoamer.

[0033] The antioxidant is 1010 antioxidant. The defoamer is a polyether-modified siloxane defoamer. The quaternary ammonium salt cationic surfactant is specifically dodecyl dimethyl benzyl ammonium chloride. This cationic quaternary ammonium salt can gradually migrate to the surface of the polyurea coating, adsorb trace water molecules in the environment to form a continuous conductive water film, and form a synergistic effect with the three-dimensional intrinsic conductive network constructed by conductive carbon black and conductive carbon fibers, stabilizing the surface resistivity of the material and adapting to the requirements of continuous release of static charge in the high humidity environment of underground mines. The modified MDI prepolymer is prepared by reacting 4,4'-diphenylmethane diisocyanate (MDI-100) and polypropylene glycol (PPG-1000) at a mass ratio of 3:1 at 70°C for 2 hours. The NCO content of the prepolymer is controlled at 20%.

[0034] After heating components A and B to 55°C, they are mixed in a mass ratio and transported to the spray gun through a high-pressure airless spraying device. The mixture is then evenly sprayed onto the worn and damaged surface of the pre-polished mining conveyor belt. The total thickness of the coating is controlled to be 2-3 mm. After the coating is completed, it is surface dry in 2 minutes. After curing at 28°C for 25 minutes, the strength of the repair layer reaches 63% of the maximum strength and can be put into use directly.

[0035] Example 2. This example differs from Example 1 in that the components are calculated as a percentage of the total mass of the polyurea material: Component A consists of 40% MDI-type isocyanate prepolymer; Component B consists of: 25% amino-terminated polyether (polyetheramine D2000 and T5000 compounded in a mass ratio of 1:1.8), 5.5% m-phenylenediamine, 1% methylcyclohexanediamine, 0.05% triethylenediamine, 10% aluminum diethylphosphinate, 5% nano-alumina and nano-silica (compounded in a mass ratio of 3:2), 3% antimony trioxide, 5% acetylene black, 2% conductive carbon fiber, 1.5% quaternary ammonium salt cationic antistatic agent, 1.5% KH550 silane coupling agent, 0.3% dibutyltin dilaurate, 0.1% antioxidant, and 0.05% defoamer.

[0036] Example 3. This example differs from Example 1 in that the components are calculated as a percentage of the total mass of the polyurea material: Component A consists of 33% MDI-type isocyanate prepolymer; Component B consists of: 32% amino-terminated polyether (a blend of polyetheramine D2000 and T5000 in a mass ratio of 1:1.2), 8% m-phenylenediamine, 1.8% methylcyclohexanediamine, 0.1% triethylenediamine, 7% aluminum diethylphosphinate, 7% nano-alumina and nano-silica (a blend in a mass ratio of 7:3), 2% antimony trioxide, 3% acetylene black, 1.5% conductive carbon fiber, 1% quaternary ammonium salt cationic antistatic agent, 1% KH550 silane coupling agent, 0.2% dibutyltin dilaurate, 0.3% antioxidant, and 0.1% defoamer.

[0037] The performance parameters of the materials in Examples 1-3 and ordinary polyurea materials are compared as follows: A conventional two-component polyurea material (without flame retardant or antistatic modification, and generally poor early strength performance) was selected as a control group. The performance of the flame-retardant and antistatic polyurea repair materials in Examples 1-3 was tested, and the comparison of various parameters is shown in the table below:

[0038] The performance comparison is as follows: 1. Early strength performance advantage: As can be seen from the 1-hour and 3-hour compressive strength data, the early strength performance of the mining polyurea repair material of this invention far exceeds that of ordinary polyurea. The 1-hour compressive strength of ordinary polyurea is only 2.1 MPa, which is difficult to meet the immediate load-bearing requirements of rapid mine repair; while the materials in Examples 1-3 all have a 0.5-hour compressive strength exceeding 15 MPa, a 3-hour compressive strength exceeding 26 MPa, and a 24-hour strength close to or slightly higher than the final strength of ordinary polyurea. This material enables the repaired parts of mining equipment, roadways, etc., to reach a safe load-bearing strength in a short time, significantly shortening downtime for repair and improving mine production efficiency.

[0039] 2. Flame retardant performance advantages: Ordinary polyurea has an oxygen index of only 22.3% and a vertical burning rating of V-2, making it a flammable material that cannot meet the high flame retardant requirements of underground mines; the material of this invention, through the synergistic effect of reactive phosphorus-nitrogen flame retardants and antimony trioxide, has an oxygen index exceeding 31% and a vertical burning rating of V-0. It burns without dripping or open flame spread, effectively suppressing the risk of fire and meeting the flame retardant safety standards for mining materials.

[0040] 3. Advantages in antistatic properties: Ordinary polyurea has a volume resistivity as high as 1.5×10⁻⁶. 12 Ω·cm, belonging to insulating materials, easily accumulates static electricity and causes sparks; the material of this invention, through synergistic modification with conductive carbon black, conductive fibers and antistatic additives, reduces the volume resistivity to 10. 6 With a capacitance of Ω·cm, it can quickly discharge static charge, avoid safety hazards caused by static accumulation, and meet the anti-static safety requirements of underground mines.

[0041] 4. Mechanical and wear-resistant properties: The tensile strength of the material of this invention is slightly higher than that of ordinary polyurea. Although the elongation at break is slightly reduced, it still remains above 460%, exhibiting excellent resistance to deformation. The wear resistance is far superior to that of ordinary polyurea, with wear loss only about 40% of that of ordinary polyurea. This can significantly improve the service life of the repaired parts, reduce the number of repeated repairs, and lower the maintenance costs of mines.

[0042] Example 4. This example differs from Example 1 in that the components are calculated as a percentage of the total mass of the polyurea material: Component A is MDI-type isocyanate prepolymer: 38%; Component B consists of: 28% amino-terminated polyether (a blend of polyetheramine D2000 and T5000 in a mass ratio of 1:1.5), 6% m-phenylenediamine, 1.2% methylcyclohexanediamine, 0.15% triethylenediamine, 9% aluminum diethylphosphinate, 6% nano-alumina and nano-silica (a blend in a mass ratio of 7:3), 1.5% antimony trioxide, 4% acetylene black, 1.2% conductive carbon fiber, 0.8% quaternary ammonium salt cationic antistatic agent, 1.8% KH550 silane coupling agent, 0.4% dibutyltin dilaurate, 0.8% antioxidant, and 0.15% defoamer. The total mass percentage of all components in this embodiment is 100%. The modified MDI prepolymer was prepared by reacting 4,4'-diphenylmethane diisocyanate (MDI-100) and polypropylene glycol (PPG-1000) at a mass ratio of 3:1 at 80°C for 3 hours. The NCO content of the prepolymer was controlled to be 22%.

[0043] Repairing the middle trough of a mine scraper conveyor using the above-mentioned materials is characterized by the following steps: Surface pretreatment: Sandblasting is used to completely remove rust, scale, and oil from the surface to be repaired in the central tank. The surface is then wiped with anhydrous ethanol to remove residual dust and oil, ensuring it is clean and dry. A solvent-free epoxy primer is sprayed and dried with a hot air gun, ensuring a surface moisture content of ≤1%, and cured for 25 minutes. Component A is heated to 60℃ and component B to 55℃. The mixture of components A and B is sprayed three times using a spraying device, with a spraying pressure controlled at 18MPa, a single spray thickness of 1.0mm, and a 10-minute interval between adjacent sprays. The repair area is then covered with a cotton blanket and kept warm for 30 minutes to complete the repair. The entire repair process is completed within 2 hours.

[0044] After the repair was completed, the surface resistivity of the central tank stabilized at 10. 6 ~10 9 With a safety range of Ω, it effectively releases static charge, avoiding mining safety risks caused by static electricity accumulation; its wear resistance is 0.03cm³ / 1.61km, superior to ordinary repair materials, and can withstand the friction and impact of ore particles for a long time, extending the service life of the central trench by 2 times; its interfacial tensile shear strength is 3.5Pa, ensuring a strong bond between the repair layer and the central trench substrate, with no peeling or cracking under frequent dynamic loads; it surface dries within 3 minutes and achieves over 60% of its maximum strength after repair, with rapid curing characteristics. Combined with optimized construction steps, the entire repair process can be controlled within 2 hours, allowing for immediate use after repair; significantly reducing equipment downtime and improving mine production efficiency.

[0045] Example 5. This example differs from Example 4 in that the components are calculated as a percentage of the total mass of the polyurea material: Component A is MDI-type isocyanate prepolymer: 36%; Component B consists of: 29% amino-terminated polyether (a blend of polyetheramine D2000 and T5000 in a mass ratio of 1:1.6), 7% m-phenylenediamine, 2% methylcyclohexanediamine, 0.08% triethylenediamine, 6% aluminum diethylphosphinate, 8% nano-alumina and nano-silica (a blend in a mass ratio of 3:2), 2.5% antimony trioxide, 2.5% acetylene black, 1.8% conductive carbon fiber, 1.2% quaternary ammonium salt cationic antistatic agent, 1.2% KH550 silane coupling agent, 0.25% dibutyltin dilaurate, 0.4% antioxidant, and 0.07% defoamer. The modified MDI prepolymer is prepared by reacting 4,4'-diphenylmethane diisocyanate (MDI-100) and polypropylene glycol (PPG-1000) in a mass ratio of 3:1 at 80°C for 3 hours. The NCO content of the prepolymer is controlled at 22%.

[0046] A 1.2m × 0.4m wear area with a wear depth of 2mm appeared on the surface of a fabric-core conveyor belt for an iron ore mine. Local longitudinal tears caused by falling ore were also observed, with a depth of 4mm. Repair was performed using a polyurea material with the aforementioned components. The method includes the following steps: Step 1: Surface Pretreatment Select a damaged area on the conveyor belt surface as the repair area and remove the aging layer and debris. Step 2: Interface Activation Treatment Spray rubber interface activator onto the repair area and let it stand for 5 minutes to form an active reaction layer; apply filler to the longitudinal tear on the conveyor belt surface and smooth it out. Step 3: Primer application Apply the primer, dry it with a hot air blower, and cure it for 25 minutes; Step 4: Polyurea spraying The polyurea material is sprayed onto the surface of the active reaction layer several times. The polyurea material is introduced into the flame retardant system and the antistatic system. There is an 8-minute interval between two consecutive sprays. During the interval, the previous coating layer is checked for defects such as bubbles and sagging. If there are any, they are repaired in time with a scraper to finally form a polyurea repair layer. Step 5: Constant temperature curing The repair area is covered with an electric heating blanket and kept warm for 25 minutes at a temperature of 70°C. After the heating blanket is removed, the in-situ repair of the repair area is completed. The ambient temperature during repair is 15°C and the relative humidity does not exceed 80%. The conveyor belt is a steel cord rubber conveyor belt or a fabric rubber conveyor belt.

[0047] In step 1, a high-pressure water gun can be used to rinse the surface of the damaged area to remove debris and aging layer. The surface of the repair area is then polished to make it smooth, and a hot air blower is used to dry the polished surface until the moisture content is ≤1%. Specifically, during surface pretreatment, the surface of the damaged area is cleaned to remove dust, gravel particles, and oil. Then, an angle grinder with a diamond grinding disc is used to polish the damaged area to remove the aged adhesive layer, debris, and oxide layer. The polishing area extends 50mm beyond the edge of the damage, and the surface roughness is controlled at Ra25μm after polishing. Finally, a hot air gun (temperature 60℃) is used to dry the polished surface for 20 minutes to ensure that the surface moisture content is ≤1%.

[0048] During the interface activation treatment, a rubber interface activator is uniformly sprayed onto the dried surface at a spraying amount of 30 g / m².

[0049] The activator is allowed to fully penetrate the rubber surface and form an active reaction layer, ensuring that the interfacial adhesion strength with the subsequent primer and polyurea materials is increased by more than 30%. The longitudinal tear on the conveyor belt surface is then filled with filler and smoothed.

[0050] The rubber interface activator comprises, by weight percentage, 3% silane coupling agent (KH-550), 15% nitrile rubber resin, 1% dibutyltin dilaurate, 0.5% antioxidant RD, and the remainder being ethyl acetate. This activator effectively wets the surface of the conveyor belt rubber substrate, opens the rubber molecular chains, and simultaneously forms stable chemical bonds with subsequent primer materials and polyurea layers, significantly improving interfacial adhesion strength. It also possesses excellent weather resistance and anti-aging properties, making it suitable for the complex environments of non-coal mines with high temperatures, high humidity, and high dust levels, ensuring long-term stable adhesion of the repair layer.

[0051] The filler is a two-component filler material composed of polyurethane elastomer, carbon black reinforcing agent, crosslinking agent, and silane coupling agent. Specifically, the mass percentages of each component are as follows: polyurethane elastomer 65%, carbon black reinforcing agent 15%, diphenylmethane diisocyanate (MDI) crosslinking agent 6%, silane coupling agent KH-560 1.5%, and antioxidant RD 0.5%. This filler has a well-balanced composition. The polyurethane elastomer provides excellent elasticity and adhesion; the carbon black reinforcing agent enhances the filler's abrasion and tear resistance; the crosslinking agent improves the structural stability after curing; the silane coupling agent optimizes the interfacial bonding with the conveyor belt rubber substrate and subsequent coatings; and the antioxidant extends the filler's anti-aging life in mining environments, enabling it to effectively fill longitudinal tears on the conveyor belt surface and form a smooth transition base layer with the surrounding substrate, providing favorable conditions for subsequent primer and polyurea layer application.

[0052] For the primer application, a solvent-free epoxy primer compatible with the rubber activation layer and polyurea material is selected. It is applied evenly to the activated surface using a toothed scraper, with a coating amount controlled at 120g / ㎡, ensuring complete coverage of the damaged area and a 20mm perimeter, forming a dense transition layer with a thickness of 20μm. The surface drying time of the epoxy primer is 25 minutes; the hot air blower temperature must be controlled at 50℃. The primer is a solvent-free epoxy primer, comprising, by weight, 25% polyamide curing agent, 10% propylene oxide butyl ether, 0.5% 2-methylimidazole, 1% fumed silica, 0.3% anti-settling agent, and the remainder being bisphenol A epoxy resin. The hot air blower should be kept at least 30cm away from the primer surface, blowing evenly over the repaired area to prevent uneven heating; the auxiliary drying time is until the primer surface reaches a state of "not sticky to the touch and without drips". Keep the hot air blower at least 30cm away from the primer surface and blow it evenly over the repair area to prevent uneven heating. The drying time should be based on the primer surface reaching a state where it is "not sticky to the touch and free of drips".

[0053] During polyurea spraying, component A is heated to 60℃ and component B to 55℃, then sprayed using a spraying machine. The spraying pressure is adjusted to 15MPa, and the spraying is performed in three coats: the first coat is 1mm thick, with a 10-minute cooling interval; the second coat is 1mm thick, for a total thickness of 2mm; the repair layer extends 40mm beyond the damaged edge. The edges are beveled for a smooth transition.

[0054] Post-treatment and constant temperature curing: Immediately after the third spraying, cover the repair area with a flexible electric heating blanket (500W) and set the temperature to 70℃ for 25 minutes. After the insulation period, allow it to cool naturally to room temperature. Use 80-grit sandpaper to sand the edges of the repair layer to ensure a height difference of ≤0.5mm with the original conveyor belt surface. If defects such as pinholes or bubbles exist, use polyurea repair agent for touch-up treatment.

[0055] Through a gradient-interval spraying and isothermal curing process, the polyurea repair layer reaches 65% of its maximum strength after curing. The repair layer's hardness, measured with a Shore A hardness of 75 and a tensile strength of 15.9 MPa, was tested using a portable bond strength tester, yielding a bond strength of 3.8 MPa. Its flame retardant and antistatic properties meet mining safety requirements, with an oxygen index ≥30% and a surface resistivity ≤10 Ω·cm. 8 Ω; Taber abrasion test was conducted, and the abrasion amount was less than 38mg / 1000 rpm; tear strength test showed a value of 15.9kN / m, fully meeting the conveyor usage conditions; the entire repair process was completed within 2 hours, and the equipment could be put into use immediately after repair; significantly reducing equipment downtime and improving mine production efficiency. No tear propagation or repair layer peeling issues occurred after 24 months of use.

[0056] Example 6. This example differs from Example 4 in that the components are calculated as a percentage of the total mass of the polyurea material: Component A is MDI-type isocyanate prepolymer: 32%; Component B consists of: 34% amino-terminated polyether (a blend of polyetheramine D2000 and T5000 in a mass ratio of 1:1.8), 9% m-phenylenediamine, 2.2% methylcyclohexanediamine, 0.12% triethylenediamine, 5% aluminum diethylphosphinate, 5.5% nano-alumina and nano-silica (a blend in a mass ratio of 7:3), 1.8% antimony trioxide, 3.2% acetylene black, 1.4% conductive carbon fiber, 0.6% quaternary ammonium salt cationic antistatic agent, 1.6% KH550 silane coupling agent, 0.15% dibutyltin dilaurate, 0.35% antioxidant, and 0.08% defoamer. The modified MDI prepolymer is prepared by reacting 4,4'-diphenylmethane diisocyanate (MDI-100) and polypropylene glycol (PPG-1000) in a mass ratio of 3:1 at 80°C for 3 hours. The NCO content of the prepolymer is controlled at 22%.

[0057] A longitudinal tear measuring 3.0m in length and 0.4m in width, with a tear depth of 4mm, appeared on a fiber-core conveyor belt in an underground coal mine. The aforementioned polyurea material was used for repair. The repair method includes the following steps: Step 1: Surface Pretreatment Select a damaged area on the surface of the conveyor belt as the repair area. Use a high-pressure water gun to wash away the surface debris of the damaged part of the repair area and remove the aging layer and debris. Grind the surface of the repair area to make it flat and use a hot air blower to dry the surface of the ground repair area until the moisture content is ≤1%. The conveyor belt is a steel wire rope core rubber conveyor belt or a fabric core rubber conveyor belt. Step 2: Interface Activation Treatment Spray the rubber interface activator onto the repair area and let it stand for 5-8 minutes to form an active reaction layer; apply filler to the longitudinal tear on the conveyor belt surface and smooth it out; Step 3: Primer application Apply the primer, dry it with a hot air blower, and cure it for 25 minutes; Step 4: Polyurea spraying The polyurea material is sprayed onto the surface of the active reaction layer several times. The polyurea material is introduced into the flame retardant system and the antistatic system. There is a 10-minute interval between two consecutive sprays. During the interval, the previous coating layer is checked for defects such as bubbles and sagging. If there are any, they are repaired in time with a scraper to finally form a polyurea repair layer. Step 5: Constant temperature curing The repair area is covered with an electric heating blanket and kept warm for 30 minutes at a temperature of 75°C. After the heating blanket is removed, the in-situ repair of the repair area is completed. The ambient temperature during the repair is 30°C and the relative humidity does not exceed 80%.

[0058] Specifically, in step 1, the working pressure of the high-pressure water gun needs to be controlled at 9MPa. During the rinsing process, local ventilation equipment should be turned on to avoid the risk of slipping due to the accumulation of sewage and debris. For grinding, an explosion-proof angle grinder should be used, equipped with a dust mask and goggles. Dust should be collected through a negative pressure dust collection device to prevent the concentration from exceeding the standard. For drying, an explosion-proof hot air gun should be used, with a temperature ≤80℃, to ensure that the surface moisture content is ≤1% and to avoid contact with flammable and explosive substances. The grinding area should extend 100mm beyond the edge of the damage, and the surface roughness should be Ra50μm.

[0059] In step 2, before spraying the rubber interface activator, confirm that the gas concentration is <0.5%, control the spraying amount to 40g / ㎡, and maintain ventilation to prevent the accumulation of volatiles; apply the filler with an anti-static scraper, smoothing it without bubbles or depressions. In step 3, an antistatic scraper is used to apply the primer, with a base coat amount of 160g / ㎡ and a base coat thickness of 30μm; the temperature of the explosion-proof hot air blower is 50℃, and the distance from the surface is ≥30cm. The condition of the primer is monitored in real time until it is "not sticky to the touch and has no drips" to meet the curing requirements of extended humidity in the well. In step 4, the polyurea spraying equipment is explosion-proof. Specifically, component A is heated to 70°C and component B is heated to 55°C to ensure that the material maintains good fluidity in the underground environment. The spraying pressure is controlled at 20MPa, the atomization is uniform and there is no splashing, the thickness of a single spray does not exceed 1.0mm, and the cumulative thickness reaches 3mm to meet the requirements of wear resistance and tear resistance. During spraying, the equipment is kept 50cm away from the repair area, and the equipment moves at a uniform speed to avoid local coatings being too thick or too thin. Continuous ventilation is used to prevent the accumulation of atomized particles. When the polyurea material is cooling, the step of placing a fiber reinforcement mesh on the surface of the polyurea material is also included.

[0060] In step 5, the electric blanket is an explosion-proof electric blanket with a power of 800W and a heat preservation temperature of 70℃. It is monitored by a dedicated person to prevent electrical sparks. The entire process is equipped with a gas monitoring device. Work must be stopped immediately if the gas concentration exceeds 0.5%. Construction personnel must wear anti-static clothing, and open flames and non-explosion-proof equipment are strictly prohibited to ensure safety during underground operations. The entire in-situ repair time shall not exceed 2 hours.

[0061] The components of the rubber interface activator, by weight percentage, include 5% silane coupling agent (KH-550), 15% nitrile rubber resin, 1% dibutyltin dilaurate, 1% antioxidant RD, and the remainder is ethyl acetate.

[0062] The primer is a solvent-free epoxy primer, which, by mass ratio, comprises 35% polyamide curing agent, 15% propylene oxide butyl ether, 0.5% 2-methylimidazole, 3% fumed silica, 0.8% anti-settling agent, and the remainder is bisphenol A epoxy resin. The fiber reinforcement mesh is an ultra-high molecular weight polyethylene (UHMWPE) fiber reinforcement mesh. UHMWPE fibers possess outstanding abrasion resistance (wear amount is only 1 / 5 that of glass fibers) and excellent impact resistance, significantly reducing frictional loss between the mine conveyor belt and the ore; its good flexibility allows it to closely conform to irregular damaged areas on the conveyor belt surface, ensuring full bonding between the repair layer and the substrate; furthermore, this fiber is resistant to chemical corrosion, has low water absorption, maintains stable performance in humid underground environments, has no risk of hydrolysis, and is suitable for long-term use in mines. The entire repair process takes no more than 2 hours.

[0063] Through a gradient-interval spraying and isothermal curing process, the polyurea repair layer achieved 72% of its maximum strength after curing. The hardness of the repair layer was tested using a Shore A hardness tester, reaching 82, with a tensile strength of 18.5 MPa. The bond strength between the repair layer and the conveyor belt body was tested using a portable bond strength tester, yielding a result of 3.8 MPa. The flame retardant and antistatic properties meet mining safety requirements, with an oxygen index ≥30% and a surface resistivity ≤10 Ω·cm. 8 Ω; Taber abrasion test was conducted, and the abrasion amount was less than 30mg / 1000 rpm; tear strength test was conducted, and the value reached 16.7kN / m, which fully meets the conditions for conveying use; the entire repair process was completed within 2 hours, and the equipment can be put into use immediately after repair; it significantly reduces equipment downtime and improves mine production efficiency; the conveyor belt has not experienced tear expansion or repair layer peeling problems in 24 months of use.

Claims

1. A flame-retardant and antistatic polyurea repair material, characterized in that: The repair material is a two-component polyurea mixture, which includes component A and component B. Component A is an MDI-type isocyanate prepolymer comprising 30% to 40% of the total mass of the polyurea material; Component B comprises the following components in the total mass percentage of the polyurea material: amino-terminated polyether 25%–35%, m-phenylenediamine 5.5%–9.5%, fast-reacting aromatic chain extender 1%–2.5%, tertiary amine catalyst 0.05%–0.2%, reactive phosphorus-nitrogen flame retardant 5%–10%, nano-wear-resistant filler 5%–8%, flame retardant synergist 1.5%–3%, conductive carbon black 2%–5%, conductive fiber 1%–2%, antistatic agent 0.5%–1.5%, silane coupling agent 1%–1.8%, latent catalyst 0.1%–0.4%, antioxidant 0.1%–0.8%, and defoamer 0.05%–0.15%. The amino-terminated polyether is a compound system of polyetheramines D2000 and T5000; the fast-reacting aromatic chain extender is methylcyclohexanediamine; the tertiary amine catalyst is triethylenediamine; the latent catalyst is dibutyltin dilaurate; the reactive phosphorus-nitrogen flame retardant is aluminum diethylphosphinate; the flame retardant synergist is antimony trioxide; the nano-wear-resistant filler is a compound system of nano-alumina and nano-silica; the silane coupling agent is KH550 silane coupling agent; the antistatic agent is a quaternary ammonium salt cationic surfactant; and the latent catalyst is dibutyltin dilaurate.

2. The flame-retardant and antistatic polyurea repair material according to claim 1, characterized in that: The conductive carbon black is acetylene black.

3. The flame-retardant and antistatic polyurea repair material according to claim 1, characterized in that: The conductive fiber is a conductive carbon fiber.

4. The flame-retardant and antistatic polyurea repair material according to claim 1, characterized in that: The amino-terminated polyether is a blend of polyetheramine D2000 and T5000 in a weight ratio of 1:1.2 to 1.

8.

5. The flame-retardant and antistatic polyurea repair material according to claim 1, characterized in that: The nano wear-resistant filler is a composite system of nano alumina and nano silica, in which nano alumina accounts for 60% to 70% of the total mass of the nano wear-resistant filler and nano silica accounts for 30% to 40%.

6. The flame-retardant and antistatic polyurea repair material according to claim 1, characterized in that: The antioxidant is 1010 antioxidant.

7. The flame-retardant and antistatic polyurea repair material according to claim 1, characterized in that: The defoamer is a polyether-modified siloxane defoamer.

8. The flame-retardant and antistatic polyurea repair material according to claim 1, characterized in that: The modified MDI prepolymer was prepared by reacting 4,4'-diphenylmethane diisocyanate and polypropylene glycol at a mass ratio of 3:1-1.3 at 70-80℃ for 2-3 hours. The NCO content of the prepolymer was controlled to be 20%-22%.

9. The application of the flame-retardant and antistatic polyurea repair material according to any one of claims 1-8 in the repair of mining equipment, characterized in that: The flame-retardant and antistatic polyurea repair material is used to spray onto the damaged surface of mining equipment to form an elastic and dense layer.

10. The application of the flame-retardant and antistatic polyurea repair material as described in claim 9 in the repair of mining equipment, characterized in that: The mining equipment includes a mining conveyor belt, a mining conveying pipeline, a hydraulic support side guard plate, a mining motor housing, and a central trough for the scraper conveyor.

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