Halogen-free intumescent flame retardant applied to conveyor belt as well as preparation method and application of halogen-free intumescent flame retardant

Abstract

The invention discloses a preparation method of a halogen-free intumescent flame retardant applied to a conveyor belt, and the preparation method comprises the following steps: S1, adjusting the pH value of a formaldehyde solution to 7-9, adding melamine powder, and carrying out a first heating reaction to obtain a trihydroxymethyl melamine solution; s2, polyvinyl alcohol is added into deionized water for stirring and heating treatment, and a polyvinyl alcohol solution is obtained; adding boron nitride and a silane coupling agent into the polyvinyl alcohol solution for second heating reaction, and adjusting the pH value to 4-6 to obtain a second mixed solution; and S3, mixing the second mixed solution and the trihydroxymethyl melamine solution, and carrying out a third heating reaction to obtain the halogen-free intumescent flame retardant applied to the conveyor belt. The flame retardant provided by the invention belongs to a halogen-free and low-toxicity three-in-one intumescent flame retardant, is applied to a flame-retardant rubber material for a conveying belt, has good compatibility with a rubber matrix and small influence on mechanical properties of the rubber matrix, and improves the flame retardance and durability of the rubber material.

Description

Technical Field

[0001] This invention belongs to the field of intumescent flame retardant technology, specifically relating to a halogen-free intumescent flame retardant for use in conveyor belts, its preparation method, and its application. Background Technology

[0002] Conveyor belts, as key equipment in high-risk scenarios such as mining, chemical, and power industries, must possess flame retardancy, wear resistance, and weather resistance, with flame retardancy and safety being paramount. Traditional intumescent flame retardants present numerous problems in practical applications, including: their high addition levels (typically 20%–30%) easily lead to the deterioration of the mechanical properties of the base materials (such as rubber and plastics), manifested as a decrease in tensile strength and mechanical properties; the acid source components, such as ammonium polyphosphate (APP), exhibit significant moisture absorption and hydrolysis issues, causing the flame retardant system to degrade in humid environments; simultaneously, poor compatibility during processing easily leads to uneven dispersion or premature decomposition, and the char layer structure is prone to collapse at extreme high temperatures, resulting in a sharp drop in flame retardant efficiency. Furthermore, while traditional halogenated flame retardants offer high flame retardant efficiency, the toxic substances such as dioxins and hydrogen halides released during combustion seriously threaten the ecological environment and human safety. Halogen-free intumescent flame retardants represent a new direction for the future development of conveyor belt flame retardancy.

[0003] Halogen-free intumescent flame retardants (HF-IFR) utilize the synergistic effect of acid, carbon, and gas sources to form a dense, expanded char layer upon heating. This layer isolates heat and oxygen, achieving highly efficient flame retardancy while generating only low-toxicity fumes, significantly reducing the risk of secondary disasters. Current research on HF-IFR technology largely focuses on phosphorus-nitrogen synergistic systems, such as the combination of ammonium polyphosphate and melamine. While this system can reduce toxic smoke release, it faces two major bottlenecks: highly efficient flame retardants like red phosphorus are prone to moisture absorption and oxidation, posing a risk of combustion and explosion during processing, and leaving residual phosphine gas; to balance flame retardancy and mechanical properties, excessive charring agents are often added, leading to deterioration of the rubber compound's flowability and causing delamination or uneven thickness during conveyor belt calendering. Some technologies attempt to improve dispersibility through nano-modification, but insufficient surface treatment of the flame retardant still fails to suppress migration during the high-temperature vulcanization stage. Melamine's decomposition temperature (250~350℃) matches the processing temperature of common polymers, avoiding the risk of thermal decomposition during processing. Furthermore, its low smoke and low toxicity (combustion products are CO2, H2O, and a small amount of nitrogen-containing gas) comply with environmental regulations. Moreover, its water resistance, char layer strength, and processing dispersibility can be further improved through surface coating or compounding with chitin and metal oxides. These advantages make melamine a key choice for balancing flame retardancy, durability, and cost-effectiveness in conveyor belts. Further research is urgently needed on composite systems formulated with melamine as the core component of intumescent flame retardants to overcome the aforementioned bottlenecks.

[0004] Therefore, developing a novel halogen-free intumescent flame retardant that imparts high flame retardancy to materials without reducing their thermal stability is of great significance and value. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a halogen-free intumescent flame retardant for conveyor belts, its preparation method, and its application. The prepared flame retardant integrates a char source, an acid source, and a gas source, belonging to a "three-in-one" intumescent flame retardant. Trimethylolmelamine is used as the gas source in the flame retardant. Polyethylene is compounded with boron nitride and a silane coupling agent to form a nitrogen-silicon synergistic system, constructing a BO-Si cross-linked structure. A silicon-boron composite system is used as the char source. Through the synergistic effect of the acid source, char source, and gas source, a dense porous char layer is formed when heated, preventing the rubber products used in conveyor belts from contacting the fire source, thereby exerting a flame-retardant effect.

[0006] The primary objective of this invention is to provide a method for preparing a halogen-free intumescent flame retardant for use in conveyor belts, the method comprising the following steps: After adjusting the pH of the formaldehyde solution to 7-9, S1 adds melamine powder, stirs evenly, and then carries out the first heating reaction to obtain a trimethylol melamine solution. S2 adds polyvinyl alcohol to deionized water and stirs and heats it until it is completely dissolved to obtain a polyvinyl alcohol solution; boron nitride and silane coupling agent are added to the polyvinyl alcohol solution at the same time, stirred evenly and subjected to a second heating reaction. After the reaction is completed, it is cooled to room temperature to obtain a first mixed solution; the pH value of the first mixed solution is adjusted to 4-6 to obtain a second mixed solution. S3 mixes the second mixed solution and the trimethylol melamine solution, stirs them evenly, and carries out a third heating reaction to obtain a halogen-free intumescent flame retardant for use in conveyor belts.

[0007] Specifically, the mass ratio of formaldehyde solution to melamine powder in step S1 is (1-3):1.

[0008] Specifically, in step S1, the reaction temperature of the first heating reaction is 60-70°C, and the reaction time is 10-30 min.

[0009] Specifically, in step S2, the mass ratio of polyvinyl alcohol, boron nitride, silane coupling agent, and deionized water is (1-3):(3-5):(1-2):11; the silane coupling agent is any one of γ-aminopropyltriethoxysilane, γ-(2,3-epoxypropoxy)propyltrimethoxysilane, or γ-(methacryloyloxy)propyltrimethoxysilane.

[0010] Specifically, the reaction temperature of the stirring and heating treatment in step S2 is 80-90°C; the reaction temperature of the second heating reaction is 80-90°C, and the reaction time is 10-30 min.

[0011] Specifically, in step S3, the volume ratio of the second mixed solution to the trimethylol melamine solution is 1:1.

[0012] Specifically, in step S3, the reaction temperature of the third heating reaction is 50–70°C, and the reaction time is 0.5–2 h.

[0013] The second objective of this invention is to provide a halogen-free intumescent flame retardant for use in conveyor belts, obtained by the above method.

[0014] The third objective of this invention is to provide an application of the halogen-free intumescent flame retardant as described above in flame-retardant rubber materials for conveyor belts.

[0015] Specifically, the components and proportions of the flame-retardant rubber material for the conveyor belt are as follows by weight: 5-15 parts of halogen-free intumescent flame retardant for the conveyor belt, 50 parts of natural rubber, 35 parts of butadiene rubber, 15 parts of styrene-butadiene rubber, 10-15 parts of plasticizer, 50-60 parts of carbon black, 4 parts of zinc oxide, 2 parts of stearic acid, 3 parts of antioxidant, 2-5 parts of N-cyclohexyl-2-benzothiazole sulfenamide, 0.5 parts of dibenzothiazole disulfide, and 2 parts of sulfur.

[0016] Compared with the prior art, the present invention has the following beneficial technical effects: (2) This invention develops a novel halogen-free intumescent flame retardant. Trimethylol melamine is prepared by reacting formaldehyde aqueous solution and melamine; then, by compounding polyethylene with boron nitride and silane coupling agent, a nitrogen-silicon synergistic system is formed, and a BO-Si crosslinked structure is constructed; trimethylol melamine is compounded with a mixed solution mainly composed of polyethylene to form an intumescent flame retardant. When applied to flame-retardant rubber materials for conveyor belts, the rubber materials exhibit both high flame retardancy and material durability. (3) The flame retardant prepared by this invention integrates carbon source, acid source and gas source into one, and belongs to the "three-in-one" intumescent flame retardant; Trimethylolmelamine is used as the gas source in the flame retardant. Under the action of the gas source, the intumescent flame retardant expands to form a foam layer, releasing a large amount of non-flammable CO2, H2O and a small amount of nitrogen-containing gas, which plays a role in inhibiting the spread of fire source; Polyethylene is compounded with boron nitride and silane coupling agent to form a nitrogen-silicon synergistic system and construct a BO-Si cross-linked structure; and the silicon-boron composite system is used as the carbon source; Through the synergistic effect of acid source, carbon source and gas source, a dense porous carbon layer is formed when heated, which prevents the rubber products used for conveyor belts from contacting the fire source, thereby playing a flame retardant role; In addition, the properties of boron nitride reduce the dynamic friction coefficient of rubber products and reduce the wear of conveyor belts, and the silane coupling agent improves the dispersion of boron nitride in rubber; (3) The preparation method of this invention is simple and environmentally friendly. The flame retardant prepared is halogen-free and naturally non-toxic. When applied to rubber materials, it does not produce harmful substances and can give the rubber materials a good flame retardant effect with a small amount added. Moreover, the flame retardant can be well dispersed in the rubber matrix, has good similarity with rubber, has little impact on the mechanical properties of rubber, avoids the deterioration of the mechanical properties of the matrix material, and significantly improves the heat insulation and oxygen barrier efficiency of rubber products. It solves the problems of uneven dispersion and high-temperature char layer collapse of traditional flame retardants. The process of this invention is simple and suitable for harsh industrial scenarios. Detailed Implementation

[0017] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention. Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by those skilled in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing specific embodiments only and is not intended to limit the present invention.

[0018] The sources of some of the raw materials used in the embodiments and comparative examples of this invention are as follows: melamine was purchased from Shanghai Ebi Chemical Reagent Co., Ltd.; silane coupling agent was purchased from Shandong Jinli Chemical Co., Ltd.; boron nitride was purchased from Beijing Deco Island Gold Technology Co., Ltd.; formaldehyde solution was a 37% formaldehyde aqueous solution; polyvinyl alcohol was a 99% polyvinyl alcohol solid; unless otherwise stated, all other raw materials were commercially available.

[0019] Example 1 Preparation of halogen-free intumescent flame retardants for use in conveyor belts S1 first adjusts the pH of the formaldehyde solution to 8 by slowly adding 0.1 mol / L sodium hydroxide solution. Then, melamine powder is added to the formaldehyde solution at a mass ratio of 1:1. After stirring evenly, the solution is heated at 65°C for 20 minutes until it becomes clear, thus obtaining a trimethylol melamine solution. S2 is prepared by weighing polyvinyl alcohol, boron nitride, γ-aminopropyltriethoxysilane (silane coupling agent KH-550), and deionized water in a mass ratio of 1:3:1:11. First, polyvinyl alcohol is added to the deionized water and heated at 90°C for 10 minutes with stirring to ensure complete dissolution, yielding a polyvinyl alcohol solution. Then, boron nitride and silane coupling agent KH-550 are simultaneously added to the polyvinyl alcohol solution, stirred evenly, and subjected to a second heating reaction at 90°C for 20 minutes. After the reaction is complete, the solution is cooled to room temperature to obtain a first mixed solution. The pH of the first mixed solution is adjusted to 5 using 0.1 mol / L hydrochloric acid to obtain a second mixed solution. S3 mixes the second mixed solution and the trimethylol melamine solution at a volume ratio of 1:1, stirs them evenly, and then heats them at 60°C for 1 hour before cooling them at room temperature. The solution gradually transforms into a gel form, thus obtaining the halogen-free intumescent flame retardant for conveyor belts prepared in Example 1.

[0020] Preparation of flame-retardant rubber materials for conveyor belts The halogen-free intumescent flame retardant prepared above was added to the flame-retardant rubber formulation for conveyor belts. The components and proportions of the flame-retardant rubber formulation for conveyor belts are as follows by mass: The following components are used in conveyor belts: 10 parts of halogen-free intumescent flame retardant, 50 parts of natural rubber, 35 parts of butadiene rubber, 15 parts of styrene-butadiene rubber, 15 parts of plasticizer, 55 parts of carbon black N330, 4 parts of zinc oxide, 2 parts of stearic acid, 3 parts of antioxidant, 3 parts of accelerator N-cyclohexyl-2-benzothiazole sulfenamide, 0.5 parts of accelerator dibenzothiazole disulfide, and 2 parts of vulcanizing agent sulfur. The specific steps include: adding 10 parts of halogen-free intumescent flame retardant, 50 parts of natural rubber, 35 parts of butadiene rubber, and 15 parts of styrene-butadiene rubber to a mixer and mixing evenly; slowly adding 10 parts of plasticizer, 50 parts of carbon black N330, 4 parts of zinc oxide, 2 parts of stearic acid, and 3 parts of antioxidant, and then mixing for 10-20 minutes; adding 3 parts of accelerator N-cyclohexyl-2-benzothiazole sulfenamide, 0.5 parts of accelerator dibenzothiazole disulfide, and 2 parts of vulcanizing agent sulfur to the above system in batches; mixing for 6-10 minutes; uniformly sheeting the compound and letting it stand; and then vulcanizing the cooled compound at 160℃ / 15MPa for 10 minutes on a vulcanizing machine to obtain the flame-retardant rubber material for conveyor belts prepared in Example 1.

[0021] Example 2 Preparation of halogen-free intumescent flame retardants for use in conveyor belts S1 first adjusts the pH of the formaldehyde solution to 7 by slowly adding 0.1 mol / L sodium hydroxide solution. Then, melamine powder is added to the formaldehyde solution at a mass ratio of 3:1. After stirring evenly, the solution is heated at 70°C for 15 minutes until the solution becomes clear, thus obtaining a trimethylol melamine solution. S2 is prepared by weighing polyvinyl alcohol, boron nitride, γ-(2,3-epoxypropoxy)propyltrimethoxysilane (silane coupling agent KH-560), and deionized water in a mass ratio of 3:5:2:11. First, polyvinyl alcohol is added to the deionized water and heated at 80°C for 20 minutes with stirring to ensure complete dissolution, yielding a polyvinyl alcohol solution. Then, boron nitride and silane coupling agent KH-560 are simultaneously added to the polyvinyl alcohol solution, stirred evenly, and subjected to a second heating reaction at 80°C for 30 minutes. After the reaction is complete, the solution is cooled to room temperature to obtain a first mixed solution. The pH of the first mixed solution is adjusted to 4 using 0.1 mol / L hydrochloric acid to obtain a second mixed solution. S3 mixes the second mixed solution and the trimethylol melamine solution at a volume ratio of 1:1, stirs them evenly, and then heats them at 70°C for 0.5 hours before cooling them at room temperature. The solution gradually transforms into a gel form, thus obtaining the halogen-free intumescent flame retardant for conveyor belts prepared in Example 2.

[0022] Preparation of flame-retardant rubber materials for conveyor belts The halogen-free intumescent flame retardant prepared above was added to the flame-retardant rubber formulation for conveyor belts. The components and proportions of the flame-retardant rubber formulation for conveyor belts are as follows by mass: The following components are used in conveyor belts: 10 parts of halogen-free intumescent flame retardant, 50 parts of natural rubber, 35 parts of butadiene rubber, 15 parts of styrene-butadiene rubber, 15 parts of plasticizer, 55 parts of carbon black N330, 4 parts of zinc oxide, 2 parts of stearic acid, 3 parts of antioxidant, 3 parts of accelerator N-cyclohexyl-2-benzothiazole sulfenamide, 0.5 parts of accelerator dibenzothiazole disulfide, and 2 parts of vulcanizing agent sulfur. The specific steps include: adding 10 parts of halogen-free intumescent flame retardant, 50 parts of natural rubber, 35 parts of butadiene rubber, and 15 parts of styrene-butadiene rubber to a mixer and mixing evenly; slowly adding 15 parts of plasticizer, 55 parts of carbon black N330, 4 parts of zinc oxide, 2 parts of stearic acid, and 3 parts of antioxidant, and then mixing for 10-20 minutes; adding 3 parts of accelerator N-cyclohexyl-2-benzothiazole sulfenamide, 0.5 parts of accelerator dibenzothiazole disulfide, and 2 parts of sulfur vulcanizing agent to the above system in batches; mixing for 6-10 minutes; uniformly sheeting the compound and letting it stand; and then vulcanizing the cooled compound at 160℃ / 15MPa for 10 minutes on a vulcanizing machine to obtain the flame-retardant rubber material for conveyor belts prepared in Example 2.

[0023] Example 3 Preparation of halogen-free intumescent flame retardants for use in conveyor belts S1 first adjusts the pH of the formaldehyde solution to 9 by slowly adding 0.1 mol / L sodium hydroxide solution. Then, melamine powder is added to the formaldehyde solution at a mass ratio of 2:1. After stirring evenly, the solution is heated at 60°C for 30 minutes until the solution becomes clear, thus obtaining trimethylol melamine solution. S2 is prepared by weighing polyvinyl alcohol, boron nitride, γ-(methacryloyloxy)propyltrimethoxysilane (silane coupling agent KH-570), and deionized water in a mass ratio of 2:4:1:11. First, polyvinyl alcohol is added to the deionized water and heated at 85°C for 20 minutes with stirring to ensure complete dissolution, yielding a polyvinyl alcohol solution. Then, boron nitride and silane coupling agent KH-570 are simultaneously added to the polyvinyl alcohol solution, stirred evenly, and subjected to a second heating reaction at 85°C for 20 minutes. After the reaction is complete, the solution is cooled to room temperature to obtain a first mixed solution. The pH of the first mixed solution is adjusted to 5 using 0.1 mol / L hydrochloric acid to obtain a second mixed solution. S3 mixes the second mixed solution and the trimethylol melamine solution at a volume ratio of 1:1, stirs them evenly, and then heats them at 60°C for 1.5 hours before cooling them at room temperature. The solution gradually transforms into a gel form, thus obtaining the halogen-free intumescent flame retardant for conveyor belts prepared in Example 3.

[0024] Preparation of flame-retardant rubber materials for conveyor belts The halogen-free intumescent flame retardant prepared above was added to the flame-retardant rubber formulation for conveyor belts. The components and proportions of the flame-retardant rubber formulation for conveyor belts are as follows by mass: The following components are used in conveyor belts: 10 parts of halogen-free intumescent flame retardant, 50 parts of natural rubber, 35 parts of butadiene rubber, 15 parts of styrene-butadiene rubber, 10 parts of plasticizer, 60 parts of carbon black N330, 4 parts of zinc oxide, 2 parts of stearic acid, 3 parts of antioxidant, 5 parts of accelerator N-cyclohexyl-2-benzothiazole sulfenamide, 0.5 parts of accelerator dibenzothiazole disulfide, and 2 parts of vulcanizing agent sulfur. The specific steps include: adding 15 parts of halogen-free intumescent flame retardant, 50 parts of natural rubber, 35 parts of butadiene rubber, and 15 parts of styrene-butadiene rubber to a mixer and mixing evenly; slowly adding 10 parts of plasticizer, 60 parts of carbon black N330, 4 parts of zinc oxide, 2 parts of stearic acid, and 3 parts of antioxidant, and then mixing for 10-20 minutes; adding 5 parts of accelerator N-cyclohexyl-2-benzothiazole sulfenamide, 0.5 parts of accelerator dibenzothiazole disulfide, and 2 parts of vulcanizing agent sulfur to the above system in batches; mixing for 6-10 minutes; uniformly sheeting the compound and letting it stand; and then vulcanizing the cooled compound at 160℃ / 15MPa for 10 minutes on a vulcanizing machine to obtain the flame-retardant rubber material for conveyor belts prepared in Example 3.

[0025] Comparative Example 1 The preparation of rubber materials for conveyor belts differs from that in Example 1 in that the halogen-free expanded flame retardant prepared in Example 1 is not added. The rubber formulation for conveyor belts contains the following components and proportions by weight: 50 parts natural rubber, 35 parts butadiene rubber, 15 parts styrene-butadiene rubber, 10 parts plasticizer, 50 parts carbon black N330, 4 parts zinc oxide, 2 parts stearic acid, 3 parts antioxidant, 2 parts accelerator N-cyclohexyl-2-benzothiazole sulfenamide, 0.5 parts accelerator dibenzothiazole disulfide, and 2 parts sulfur vulcanizing agent. The specific steps include: adding 50 parts of natural rubber, 35 parts of butadiene rubber, and 15 parts of styrene-butadiene rubber to a mixer and mixing them evenly; slowly adding 10 parts of plasticizer, 50 parts of carbon black N330, 4 parts of zinc oxide, 2 parts of stearic acid, and 3 parts of antioxidant, and then mixing for 10-20 minutes; adding 2-5 parts of accelerator N-cyclohexyl-2-benzothiazole sulfenamide, 0.5 parts of accelerator dibenzothiazole disulfide, and 2 parts of vulcanizing agent sulfur to the above system in batches; mixing for 6-10 minutes; uniformly sheeting the compound and letting it stand; and then vulcanizing the cooled compound at 160℃ / 15MPa for 10 minutes on a vulcanizing machine to obtain the conveyor belt rubber material prepared in Comparative Example 1.

[0026] Comparative Example 2 The preparation of conveyor belt rubber materials differs from that in Example 1 in that the halogen-free expanded flame retardant prepared in Example 1 is replaced with a boron nitride compounded silane coupling agent flame retardant.

[0027] The conveyor belt rubber formulation contains the following components and proportions by weight: 10 parts boron nitride compounded silane coupling agent, 50 parts natural rubber, 35 parts butadiene rubber, 15 parts styrene-butadiene rubber, 10 parts plasticizer, 50 parts carbon black N330, 4 parts zinc oxide, 2 parts stearic acid, 3 parts antioxidant, 2 parts accelerator N-cyclohexyl-2-benzothiazole sulfenamide, 0.5 parts accelerator dibenzothiazole disulfide, and 2 parts sulfur vulcanizing agent. The specific steps include: adding 50 parts of natural rubber, 35 parts of butadiene rubber, and 15 parts of styrene-butadiene rubber to a mixer and mixing them evenly; slowly adding 10 parts of plasticizer, 50 parts of carbon black N330, 4 parts of zinc oxide, 2 parts of stearic acid, and 3 parts of antioxidant, and then mixing for 10-20 minutes; adding 2-5 parts of accelerator N-cyclohexyl-2-benzothiazole sulfenamide, 0.5 parts of accelerator dibenzothiazole disulfide, and 2 parts of vulcanizing agent sulfur to the above system in batches; mixing for 6-10 minutes; uniformly sheeting the compound and letting it stand; and then vulcanizing the cooled compound at 160℃ / 15MPa for 10 minutes on a vulcanizing machine to obtain the conveyor belt rubber material prepared in Comparative Example 2.

[0028] Comparative Example 3 The preparation of conveyor belt rubber materials differs from that in Example 1 in that the halogen-free expanded flame retardant prepared in Example 1 is replaced with a conventional aluminum hydroxide flame retardant.

[0029] The conveyor belt rubber formulation contains the following components and proportions by weight: 10 parts aluminum hydroxide flame retardant, 50 parts natural rubber, 35 parts butadiene rubber, 15 parts styrene-butadiene rubber, 10 parts plasticizer, 50 parts carbon black N330, 4 parts zinc oxide, 2 parts stearic acid, 3 parts antioxidant, 2 parts accelerator N-cyclohexyl-2-benzothiazole sulfenamide, 0.5 parts accelerator dibenzothiazole disulfide, and 2 parts sulfur vulcanizing agent. The specific steps include: adding 50 parts of natural rubber, 35 parts of butadiene rubber, and 15 parts of styrene-butadiene rubber to a mixer and mixing them evenly; slowly adding 10 parts of plasticizer, 50 parts of carbon black N330, 4 parts of zinc oxide, 2 parts of stearic acid, and 3 parts of antioxidant, and then mixing for 10-20 minutes; adding 2-5 parts of accelerator N-cyclohexyl-2-benzothiazole sulfenamide, 0.5 parts of accelerator dibenzothiazole disulfide, and 2 parts of vulcanizing agent sulfur to the above system in batches; mixing for 6-10 minutes; uniformly sheeting the compound and letting it stand; and then vulcanizing the cooled compound at 160℃ / 15MPa for 10 minutes on a vulcanizing machine to obtain the conveyor belt rubber material prepared in Comparative Example 3.

[0030] Performance testing The conveyor belt rubber materials prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to performance tests according to the following methods: Oxygen index was tested using an FTAⅡ limiting oxygen index tester from PL Corporation (UK) according to ASTM D2863-08 standard. Mechanical properties were tested using a DXLL-5000 electronic tensile testing machine from Shanghai Dengjie Machinery Equipment Co., Ltd., at a tensile rate of 25 mm / min and an experimental temperature of 25℃. Hardness testing was conducted according to national standard GB / T 531.1-2008; tensile properties were tested according to national standard GB / T-528-2009; tear resistance was tested according to national standard GB / T-529-2008; dynamic friction coefficient testing was conducted according to national standard GB / T-40721-2021; DIN abrasion volume testing was conducted according to national standard GB / T-9867-2008; and flame retardancy testing was conducted according to national standard GB / T-10107-2008.

[0031] The performance test results of the rubber materials prepared in Examples 1-3 and Comparative Examples 1-3 are shown in Table 1: Table 1 As shown in Table 1, the halogen-free intumescent flame retardant of this invention exhibits significant improvements in environmental safety, flame retardant efficiency, and mechanical durability when applied to conveyor belt rubber materials. In terms of mechanical properties, compared to Comparative Example 1 (without flame retardant), the tensile strength of Examples 1-3 all showed a slight decrease. Example 2 showed the smallest performance decrease, at only 9.8%, while Comparative Example 3 showed the largest decrease, at 17.5%. This is because the added aluminum hydroxide was not well dispersed in the rubber compound, forming stress concentration points and thus reducing tensile strength. This is also evidenced by the poor tear strength of Comparative Example 3. The kinetic friction coefficient of rubber decreased with increasing flame retardant content, indicating that boron nitride not only acts as a carbon source to inhibit rubber combustion but also reduces the rubber's friction coefficient. Comparing various formulations with added flame retardants, the mechanical properties of the halogen-free intumescent flame retardant prepared according to this invention are superior to those with other flame retardants. This is because the prepared halogen-free intumescent flame retardant has good compatibility with rubber, can be well dispersed in the rubber matrix, and has little impact on rubber properties. As shown in Example 2, when 10 parts of the flame retardant are added to the rubber formulation, the tensile strength decreases by only 9.8%, and the limiting oxygen index increases to 22.1%. Furthermore, the processing temperature has good compatibility with the polymer, solving problems such as uneven dispersion and high-temperature char layer collapse associated with traditional flame retardants. In terms of flame retardant performance, the oxygen index of the flame retardants prepared in Examples 1-3 of this invention is significantly higher than that of commercially available flame retardants. This is because the inert gases such as nitrogen and ammonia released by the thermal decomposition of the flame retardant prepared according to this invention not only dilute combustible gases but also synergize with acid and carbon sources to form a dense, porous char layer, which can significantly improve heat insulation and oxygen barrier efficiency. Simultaneously, the oxygen index increases with the increase in the amount of flame retardant used. This invention optimizes the flame retardant addition amount to 10%~20% through multiple experiments, so that the prepared rubber material has both high flame retardancy and material durability, while avoiding the deterioration of the mechanical properties of the matrix material.

[0032] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing a halogen-free intumescent flame retardant for use in conveyor belts, characterized in that, The preparation method includes the following steps: After adjusting the pH of the formaldehyde solution to 7-9, S1 adds melamine powder, stirs evenly, and then carries out the first heating reaction to obtain a trimethylol melamine solution. S2 adds polyvinyl alcohol to deionized water and stirs and heats it until it is completely dissolved to obtain a polyvinyl alcohol solution; boron nitride and silane coupling agent are added to the polyvinyl alcohol solution at the same time, stirred evenly and subjected to a second heating reaction. After the reaction is completed, it is cooled to room temperature to obtain a first mixed solution; the pH value of the first mixed solution is adjusted to 4-6 to obtain a second mixed solution. S3 mixes the second mixed solution and the trimethylol melamine solution, stirs them evenly, and carries out a third heating reaction to obtain a halogen-free intumescent flame retardant for use in conveyor belts.

2. The method according to claim 1, characterized in that, The mass ratio of formaldehyde solution to melamine powder in step S1 is (1-3):

1.

3. The method according to claim 1, characterized in that, In step S1, the reaction temperature of the first heating reaction is 60-70°C, and the reaction time is 10-30 min.

4. The method according to claim 1, characterized in that, In step S2, the mass ratio of polyvinyl alcohol, boron nitride, silane coupling agent, and deionized water is (1-3):(3-5):(1-2):11; the silane coupling agent is any one of γ-aminopropyltriethoxysilane, γ-(2,3-epoxypropoxy)propyltrimethoxysilane, or γ-(methacryloyloxy)propyltrimethoxysilane.

5. The method according to claim 1, characterized in that, The reaction temperature of the stirring and heating treatment in step S2 is 80-90°C; the reaction temperature of the second heating reaction is 80-90°C, and the reaction time is 10-30 min.

6. The method according to claim 1, characterized in that, In step S3, the volume ratio of the second mixed solution to the trimethylol melamine solution is 1:

1.

7. The method according to claim 1, characterized in that, The reaction temperature of the third heating reaction in step S3 is 50-70℃, and the reaction time is 0.5-2h.

8. A halogen-free intumescent flame retardant for use on conveyor belts, obtained by the method of any one of claims 1 to 7.

9. The application of a halogen-free intumescent flame retardant as described in claim 8 in flame-retardant rubber materials for conveyor belts.

10. The application according to claim 9, characterized in that, The flame-retardant rubber material for conveyor belts comprises the following components and proportions by weight: 5 parts of halogen-free intumescent flame retardant for conveyor belts, 50 parts of natural rubber, 35 parts of butadiene rubber, 15 parts of styrene-butadiene rubber, 10-15 parts of plasticizer, 50-60 parts of carbon black, 4 parts of zinc oxide, 2 parts of stearic acid, 3 parts of antioxidant, 2-5 parts of N-cyclohexyl-2-benzothiazole sulfenamide, 0.5 parts of dibenzothiazole disulfide, and 2 parts of sulfur.

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