A color low hardness high flame retardant ethylene propylene diene rubber blend and a preparation method thereof

Abstract

The present application relates to a kind of color low hardness high flame-retardant ethylene-propylene-diene rubber blend and its preparation method, belong to rubber material technical field.The blend includes by mass fraction:ethylene-propylene-diene rubber 50-85 parts, liquid chlorinated polyethylene 10-35 parts, white carbon black 15-25 parts, coupling agent 1-2 parts, phosphorus-nitrogen composite flame retardant 60-100 parts, peroxide vulcanizing agent 2-5 parts, auxiliary crosslinking agent 1-4 parts and titanium dioxide 2-6 parts.The liquid chlorinated polyethylene and ethylene-propylene-diene rubber form co-crosslinking network under peroxide vulcanizing agent;The composite flame retardant is compounded by ammonium polyphosphate and melamine cyanurate;The surface modification of white carbon black and coupling agent occurs in the mixing process.The preparation method includes one-stage mixing, two-stage mixing and vulcanization.The blend realizes high flame retardancy while maintaining low hardness and high elasticity, and can be applied to mining products, electronic appliances and rail transportation field.

Description

Technical Field

[0001] This invention belongs to the field of rubber blend materials, and relates to a colored, low-hardness, high-flame-retardant EPDM rubber blend and its preparation method. Background Technology

[0002] Ethylene propylene diene monomer (EPDM) rubber is widely used in wires and cables, seals, and automotive parts due to its excellent weather resistance, ozone resistance, aging resistance, and electrical insulation properties. However, EPDM has an oxygen index of only about 19%, making it flammable. Furthermore, with the expansion of its applications, the industry is placing higher demands on its sealing performance and fatigue resistance. Therefore, it is urgent to improve EPDM's flame retardant properties and overall mechanical properties while maintaining its advantages.

[0003] In existing technologies, to achieve the above objectives, domestic rubber formulations generally employ a halogenated flame retardant system composed of polybrominated diphenyl ether (PBDE) flame retardants and antimony trioxide. This system, through a gas-phase flame retardant mechanism, can achieve excellent flame retardant effects at relatively low addition levels and has minimal impact on the hardness of the rubber compound. However, persistent organic pollutants such as PBDEs easily cause environmental problems and have been banned. Therefore, the development of halogen-free, environmentally friendly, low-hardness, high-flame-retardant EPDM materials has become an urgent need for industry development.

[0004] Currently, research on halogen-free flame-retardant EPDM mainly utilizes metallic flame retardants such as aluminum hydroxide and magnesium hydroxide, or phosphorus-nitrogen-based intumescent flame retardants. The latter is favored due to its high flame-retardant efficiency, low smoke, and low toxicity. CN101928431A discloses an intumescent halogen-free flame-retardant EPDM material that improves flame-retardant performance by adding montmorillonite nanocomposite materials, but it does not address improvements in mechanical properties or hardness control. CN107141584A discloses a low-smoke halogen-free flame-retardant soft rubber compound with a hardness <70A, which does not yet meet the requirements for ultra-low hardness applications.

[0005] This indicates that simultaneously achieving low hardness and high flame retardancy is a technological bottleneck in the field of halogen-free flame-retardant EPDM. The reason is that to achieve low hardness, a large amount of plasticizers such as paraffin oil needs to be added to the formulation. However, these plasticizers are themselves flammable, which weakens the flame-retardant effect. To compensate for the loss of flame-retardant performance, the amount of flame retardant filler needs to be further increased. Taking phosphorus-nitrogen flame retardants as an example, their dosage in ultra-low hardness formulations often exceeds 80 phr. The large addition of high plasticizers and high flame retardants leads to a deterioration in the rubber compound mixing process, resulting in problems such as roller sticking and uneven dispersion. At the same time, the tensile strength of the vulcanized rubber also decreases significantly due to the dilution of the plasticizer, making it difficult to meet application requirements.

[0006] Therefore, there is an urgent need to develop EPDM rubber materials that combine environmental friendliness, ultra-low hardness, and excellent flame retardant properties through novel flame retardant system design, compatibility control, and synergistic optimization of formulations. Summary of the Invention

[0007] This invention addresses the problem in existing technologies where it is difficult to simultaneously achieve color, low hardness, and high flame retardancy, by providing a colored, low-hardness, and highly flame-retardant EPDM rubber blend and its preparation method. This blend uses titanium dioxide as a white base and exhibits low hardness and excellent flame-retardant properties.

[0008] The objective of this invention can be achieved through the following technical solutions: In a first aspect, the present invention provides a colored, low-hardness, high-flame-retardant EPDM rubber blend, comprising the following components by mass parts: 50-85 parts of EPDM rubber, 10-35 parts of liquid chlorinated polyethylene, 3-8 parts of zinc oxide, 0.3-0.7 parts of stearic acid, 0.5-2 parts of 2,2,4-trimethyl-1,2-dihydroquinoline polymer, 0.5-2 parts of microcrystalline wax, 15-25 parts of silica, 1-2 parts of coupling agent, 60-100 parts of composite flame retardant, 2-5 parts of peroxide vulcanizing agent, 1-4 parts of crosslinking agent, and 2-6 parts of titanium dioxide.

[0009] Preferably, the EPDM rubber serves as the main substrate of the blend, providing excellent weather resistance, ozone resistance, and elasticity.

[0010] Preferably, the liquid chlorinated polyethylene has a chlorine content of 30%-40% and a Mooney viscosity ML (1+4, 100℃) of 20-40; it can improve the processing fluidity of EPDM rubber, reduce the hardness of the rubber compound, and co-crosslink with EPDM rubber in the peroxide vulcanization system to form an interpenetrating network structure, thereby improving the compatibility and mechanical properties of the blend.

[0011] Preferably, the zinc oxide can react synergistically with stearic acid to generate zinc soap, which is used to activate the vulcanization accelerator and vulcanization system, accelerate the vulcanization rate, and improve the crosslinking density and mechanical properties of the vulcanized rubber.

[0012] Preferably, the stearic acid, as a lubricant and vulcanizing activator, can improve the mixing and dispersibility of raw materials and reduce frictional resistance during processing; and it works synergistically with zinc oxide to enhance the vulcanization effect.

[0013] Preferably, the 2,2,4-trimethyl-1,2-dihydroquinoline polymer (RD) is an antioxidant that can effectively improve the heat aging resistance and ozone aging resistance of the blend, extend the service life of the product, and has little impact on the peroxide vulcanization system.

[0014] Preferably, the microcrystalline wax serves as both an antioxidant and a lubricant, further enhancing the aging resistance of the blend and improving its release properties during processing.

[0015] Preferably, the silica is precipitated silica with a specific surface area of ​​150-200 m².2 / g, after surface modification with a coupling agent, is used as a reinforcing agent to replace traditional carbon black. The surface-modified silica exhibits significantly improved dispersibility in the rubber matrix and enhanced interfacial bonding with the rubber matrix. While maintaining the low hardness of the rubber compound, it also improves the tensile and tear strength of the blend, and provides a white base for product coloring.

[0016] Preferably, the coupling agent is a silane coupling agent selected from at least one of bis-[γ-(triethoxysilane)propyl]tetrasulfide (Si-69), γ-mercaptopropyltrimethoxysilane (KH-590), and γ-aminopropyltriethoxysilane (KH-550), with bis-[γ-(triethoxysilane)propyl]tetrasulfide (Si-69) being the most preferred; the amount used is 1-2 parts, preferably 1.5 parts.

[0017] The coupling agent is used for surface modification of silica. One end of its molecule reacts with the silanol groups on the surface of silica, and the other end combines with the rubber molecular chain to form a molecular bridge structure, thereby improving the dispersibility of silica, enhancing interfacial bonding, reducing the interference of polar groups on the silica surface on the peroxide vulcanization system, and further improving mechanical properties while maintaining low hardness.

[0018] The composite flame retardant is a phosphorus-nitrogen intumescent flame retardant that achieves a halogen-free, environmentally friendly, and highly flame-retardant effect by expanding into char.

[0019] Preferably, the phosphorus-nitrogen intumescent flame retardant is selected from a mixture of at least two of the following: ammonium polyphosphate (APP), melamine cyanurate (MCA), melamine polyphosphate (MPP), aluminum hypophosphite (AHP), and aluminum diethylphosphite (ADP).

[0020] More preferably, the composite flame retardant is composed of ammonium polyphosphate and melamine cyanurate, with a mass ratio of 2:1 to 4:1. The amount of the composite flame retardant added is 60-100 parts by weight, preferably 70-90 parts by weight, and more preferably 75-85 parts by weight.

[0021] Preferably, the peroxide vulcanizing agent is selected from at least one of dicumyl peroxide (DCP), di-tert-butyl peroxide (BIPB), benzoyl peroxide (BPO), and di-tert-butyl peroxide (DTBP), with dicumyl peroxide (DCP) being the most preferred; the amount used is 2-5 parts, more preferably 2.5-3.5 parts.

[0022] The peroxide vulcanizing agent enables co-crosslinking and curing of EPDM rubber and liquid chlorinated polyethylene, controlling the crosslinking density to ensure low hardness. Simultaneously, the addition of a silane coupling agent reduces the adsorption of peroxide free radicals by polar groups on the silica surface, ensuring the stability of vulcanization efficiency and crosslinking density.

[0023] Preferably, the crosslinking agent is selected from at least one of triallyl isocyanurate (TAIC), triallyl cyanurate (TAC), trimethylolpropane trimethacrylate (TMPTMA), and N,N'-m-phenylenebismaleimide (HVA-2), and is preferably triallyl isocyanurate (TAIC); the amount used is 1-4 parts, preferably 1.5-3 parts.

[0024] The crosslinking agent enhances crosslinking efficiency, improves crosslinking density uniformity, promotes the formation of co-crosslinking networks, and further optimizes the mechanical properties of the blend by assisting the peroxide vulcanizing agent.

[0025] Preferably, the titanium dioxide is rutile titanium dioxide, which serves as a white pigment, providing a uniform colored base for the blend and allowing for the combination with other organic or inorganic pigments (such as iron oxide red, phthalocyanine blue, chrome yellow, etc.) to achieve various colored products such as red, blue, and yellow, as required. Furthermore, the addition of pigments does not affect flame retardancy and mechanical properties.

[0026] Secondly, this invention provides a method for preparing a colored, low-hardness, high-flame-retardant EPDM rubber blend, comprising the following steps: (1) First stage of mixing: Ethylene propylene diene monomer (EPDM) rubber and liquid chlorinated polyethylene are put into a mixer and plasticized evenly. Then, zinc oxide, stearic acid, 2,2,4-trimethyl-1,2-dihydroquinoline polymer, microcrystalline wax, silica, coupling agent, titanium dioxide and composite flame retardant are added in sequence. The mixture is mixed at 40-60℃ for 8-12 minutes. After the rubber is discharged, it is cooled down in a thin stream to obtain the masterbatch. (2) Two-stage mixing: After wrapping the masterbatch on the open mill, add the peroxide vulcanizing agent and crosslinking agent at 40-50℃, mix for 5-8 minutes until uniform, and then sheet after passing through the thin mill 5-6 times to obtain the compound. (3) Vulcanization: The compound is vulcanized at 160-180℃ and 10-15MPa for 10-20 minutes to obtain the colored low-hardness high flame-retardant EPDM rubber blend.

[0027] Preferably, the present invention employs a two-stage mixing process. The mixing temperature in the first stage is controlled below 120°C to avoid premature reaction of the composite flame retardant and coupling agent. The mixing temperature in the second stage is controlled below 50°C to prevent scorching of the peroxide vulcanizing agent and to ensure the processing safety and vulcanization uniformity of the compound.

[0028] Preferably, the silica and coupling agent are added simultaneously in step (1). During the mixing process, the coupling agent reacts in situ with the silanol groups on the surface of the silica to achieve surface modification of the silica. No separate pretreatment step is required, which simplifies the process flow.

[0029] Preferably, in step (1), the internal mixer is preheated to 40-50°C, and the EPDM rubber and liquid chlorinated polyethylene are plasticized for 2-3 minutes. Then, zinc oxide, stearic acid, 2,2,4-trimethyl-1,2-dihydroquinoline polymer, microcrystalline wax, silica, coupling agent, titanium dioxide, and composite flame retardant are added in sequence. The total mixing time is 8-12 minutes. The discharge temperature is controlled not to exceed 120°C. After discharge, the mixture is passed through a thin tube 2-4 times and left at room temperature for 8-12 hours to obtain the masterbatch.

[0030] Preferably, in step (2), the rolling temperature of the open mill is controlled at 40-50℃, the rolling gap is adjusted to 3-4mm, the peroxide vulcanizing agent and crosslinking agent are added and mixed for 5-10 minutes, the left and right cutters are used 3-4 times each, and after the mixture is evenly dispersed, the rolling gap is adjusted to 0.5-1mm and thin passes are performed 4-6 times, and finally adjusted to 2-3mm for sheeting to obtain the compound rubber.

[0031] More preferably, in step (2), the open mill roll temperature is 40°C, the roll gap is 3mm, the mixing time is 8 minutes, the left and right cutters are cut 3 times each, the thin pass is 5 times, and the sheet thickness is 2.5mm.

[0032] The beneficial effects of this invention are: 1. This invention uses liquid chlorinated polyethylene to replace traditional paraffin oil as a plasticizer. While reducing hardness, it participates in the crosslinking reaction of the peroxide vulcanizing agent and forms an interpenetrating network structure with EPDM rubber. This achieves the technical goals of both hardness and high tensile strength, solving the problem that traditional plasticizers cause a significant decrease in tensile strength when reducing hardness. 2. This invention uses a phosphorus-nitrogen intumescent flame retardant, which is compounded with ammonium polyphosphate and melamine cyanurate at a mass ratio of 2:1-4:1, and supplemented with chlorinated liquid chlorinated polyethylene. The vertical burning rating reaches UL94 V0 level, and it is halogen-free and environmentally friendly. At the same time, it uses white carbon black instead of carbon black as a reinforcing agent, and combined with titanium dioxide as a base, it can prepare a variety of colored products such as red, blue, and yellow, which solves the contradiction between high flame retardancy and colorability that traditional flame retardant systems cannot achieve. 3. This invention enables EPDM and liquid chlorinated polyethylene to form a co-crosslinking network during the vulcanization process under the conditions of peroxide vulcanizing agent and co-crosslinking agent, which significantly improves the tensile strength compared with the traditional sulfur vulcanization system and solves the problem of weak interfacial bonding and poor mechanical properties when EPDM and liquid chlorinated polyethylene are used together. 4. This invention modifies the surface of silica with a coupling agent during the mixing process, eliminating the need for a separate pretreatment step; at the same time, it uses halogen-free environmentally friendly raw materials throughout the process, avoiding the environmental problems caused by traditional flame retardants such as polybrominated diphenyl ethers and antimony trioxide. Attached Figure Description

[0033] Figure 1 This is a process flow diagram for preparing the colored, low-hardness, high-flame-retardant EPDM rubber blend of the present invention.

[0034] Figure 2 This is a performance comparison chart of Embodiment 1 and Comparative Examples 1-4 of the present invention. Detailed Implementation

[0035] To further illustrate the technical means and effects adopted by the present invention in order to achieve the purpose of the invention, the present invention will be described in detail below with reference to the embodiments.

[0036] I. Raw Materials and Equipment Description Ethylene propylene diene monomer (EPDM) rubber: Model 4045M, ethylene content 55%-65%, ENB content 4%-7%; Liquid chlorinated polyethylene: chlorine content 30%-40%, Mooney viscosity ML (1+4, 100℃) 20-40; Silica: Precipitation method, specific surface area 150-200 m² 2 / g; Silane coupling agent: bis-[γ-(triethoxysilyl)propyl]tetrasulfide (Si-69), effective content ≥98%; Composite flame retardant: Ammonium polyphosphate (APP) degree of polymerization ≥1000, melamine cyanurate (MCA) purity ≥99%; Dicumyl peroxide (DCP): Effective content ≥98%; Triallyl isocyanurate (TAIC): Effective content ≥98%; All other raw materials are of commonly used specifications in the rubber industry.

[0037] Main instruments and equipment: Internal mixer: X(S)M-1.5L type, speed 40-60 rpm; Open mill: XK-160 type, roller diameter 160mm; Flat vulcanizing machine: XLB-D 350×350 type, pressure range 0-25MPa; Vulcanizer: UR-2030 model, used to determine the positive vulcanization time.

[0038] II. Description of Fixed Components In the following Examples 1-14, except for the variables listed in Table 1, the amounts of the other components are the same, specifically: 5 parts zinc oxide, 0.5 parts stearic acid, 1 part antioxidant RD, 1 part microcrystalline wax, 1.5 parts coupling agent, and 2 parts crosslinking agent.

[0039] The peroxide vulcanizing agent used is dicumyl peroxide (DCP), and the crosslinking agent used is triallyl isocyanurate (TAIC).

[0040] III. Variable Formulations in Examples 1-14 The variable formulations for each embodiment are shown in Table 1 (unit: parts by weight).

[0041] Table 1 Variable Formulations for Examples 1-14

[0042] Example 1 According to the formulation of Example 1 in Table 1, weigh out 75 parts of EPDM rubber, 25 parts of liquid chlorinated polyethylene, and fixed components (5 parts of zinc oxide, 0.5 parts of stearic acid, 1 part of antioxidant RD, 1 part of microcrystalline wax), 20 parts of silica, 80 parts of composite flame retardant (APP:MCA=3:1), 3 parts of peroxide vulcanizing agent (DCP), 1.5 parts of coupling agent (Si-69), 2 parts of crosslinking agent (TAIC), and 4 parts of titanium dioxide.

[0043] Specific preparation methods are as follows: Figure 1 As shown, the details are as follows: (1) First stage of mixing: Preheat the internal mixer to 45°C, add EPDM rubber and liquid chlorinated polyethylene, and plasticize for 2 minutes until the rollers are wrapped; add zinc oxide, stearic acid, antioxidant RD, microcrystalline wax, silica, coupling agent, titanium dioxide and composite flame retardant in sequence, mix at 50°C for 10 minutes, control the discharge temperature not to exceed 120°C, pass through the thin tube 3 times after discharge, and let stand at room temperature for 10 hours to obtain masterbatch.

[0044] (2) Two-stage mixing: Adjust the roller temperature of the open mill to 40°C and the roller gap to 3mm. Add the masterbatch, wrap the rollers and add the peroxide vulcanizing agent and crosslinking agent. Mix for 8 minutes, cut the left and right blades 3 times each. After the mixture is evenly dispersed, adjust the roller gap to 0.8mm and pass through the thin sheet 5 times. Finally, adjust the gap to 2.5mm and sheet the mixture to obtain the compound.

[0045] (3) Vulcanization: The compound rubber is placed in the mold of the flat vulcanizing machine and vulcanized at 170°C and 12MPa for 15 minutes. After vulcanization, the colored low-hardness, high flame-retardant EPDM rubber blend is obtained.

[0046] Example 2 The preparation method of Example 2 is basically the same as that of Example 1, except that the EPDM rubber is adjusted to 50 parts and the liquid chlorinated polyethylene is adjusted to 35 parts according to the formula of Example 2 in Table 1, while the other components and preparation methods remain unchanged.

[0047] Example 3 The preparation method of Example 3 is basically the same as that of Example 1, except that the EPDM rubber is adjusted to 85 parts and the liquid chlorinated polyethylene is adjusted to 10 parts according to the formula of Example 3 in Table 1, while the other components and preparation methods remain unchanged.

[0048] Example 4 The preparation method of Example 4 is basically the same as that of Example 1. The difference is that, according to the formula of Example 4 in Table 1, the liquid chlorinated polyethylene is adjusted to 10 parts, the coupling agent is changed to KH-590, and the other components and preparation methods remain unchanged.

[0049] Example 5 The preparation method of Example 5 is basically the same as that of Example 1, except that the liquid chlorinated polyethylene is adjusted to 35 parts according to the formula of Example 5 in Table 1, while the other components and preparation methods remain unchanged.

[0050] Example 6 The preparation method of Example 6 is basically the same as that of Example 1, except that the amount of composite flame retardant is adjusted to 60 parts according to the formula of Example 6 in Table 1, while the other components and preparation methods remain unchanged.

[0051] Example 7 The preparation method of Example 7 is basically the same as that of Example 1, except that the amount of composite flame retardant is adjusted to 100 parts according to the formula of Example 7 in Table 1, while the other components and preparation methods remain unchanged.

[0052] Example 8 The preparation method of Example 8 is basically the same as that of Example 1, except that the peroxide vulcanizing agent is replaced with 2 parts of BIPB according to the formula of Example 8 in Table 1, while the other components and preparation methods remain unchanged.

[0053] Example 9 The preparation method of Example 9 is basically the same as that of Example 1, except that the amount of peroxide vulcanizing agent is adjusted to 5 parts according to the formula of Example 9 in Table 1, while the other components and preparation methods remain unchanged.

[0054] Example 10 The preparation method of Example 10 is basically the same as that of Example 1, except that the amount of silica is adjusted to 15 parts according to the formula of Example 10 in Table 1, the crosslinking agent is changed to 2 parts of TMPTMA, and the other components and preparation methods remain unchanged.

[0055] Example 11 The preparation method of Example 11 is basically the same as that of Example 1, except that the amount of silica is adjusted to 25 parts according to the formula of Example 11 in Table 1, while the other components and preparation methods remain unchanged.

[0056] Example 12 The preparation method of Example 12 is basically the same as that of Example 1, except that the amount of titanium dioxide is adjusted to 2 parts according to the formula of Example 12 in Table 1, while the other components and preparation methods remain unchanged.

[0057] Example 13 The preparation method of Example 13 is basically the same as that of Example 1. The difference is that, according to the formula of Example 13 in Table 1, the composite flame retardant is replaced with a compound of melamine polyphosphate and aluminum hypophosphite in a mass ratio of 2:1, with an amount of 80 parts. The other components and preparation methods remain unchanged.

[0058] Example 14 The preparation method of Example 14 is basically the same as that of Example 1, except that the mass ratio of ammonium polyphosphate to melamine cyanurate in the composite flame retardant is adjusted to 4:1 according to the formulation of Example 14 in Table 1, while the other components and preparation methods remain unchanged.

[0059] IV. Explanation of Comparative Examples 1-8 In Comparative Examples 1-8 below, except for the variables listed in Table 2, the amounts of the other components are the same as in Example 1. The formulations of each comparative example are shown in Table 2 (unit: parts by weight).

[0060] Table 2 Formulations of Comparative Examples 1-6

[0061] Note*: In Comparative Example 8, the coupling agent was added during the second stage of mixing, and the silica was not modified.

[0062] Note**: In Comparative Example 7, the peroxide and crosslinking agent were added during the first stage of mixing.

[0063] The amounts of components not listed in Comparative Examples 1-6, such as zinc oxide, stearic acid, antioxidant RD, and microcrystalline wax, were the same as in Example 1.

[0064] Comparative Example 1 Weigh out 100 parts of EPDM rubber, 30 parts of paraffin oil, 20 parts of silica, 1.5 parts of coupling agent Si-69, 40 parts of polybrominated diphenyl ethers, 20 parts of antimony trioxide, 5 parts of zinc oxide, 0.5 parts of stearic acid, 1 part of antioxidant RD, 1 part of microcrystalline wax, 4 parts of titanium dioxide, and 2 parts of crosslinking aid TAIC. Mix and vulcanize according to the preparation method in Example 1 to obtain a rubber blend.

[0065] Comparative Example 2: Crosslinking Agent TAIC Weigh out 100 parts of EPDM rubber, 25 parts of paraffin oil, 20 parts of silica, 1.5 parts of coupling agent Si-69, 80 parts of composite flame retardant (APP:MCA=3:1), 5 parts of zinc oxide, 0.5 parts of stearic acid, 1 part of antioxidant RD, 1 part of microcrystalline wax, 4 parts of titanium dioxide, and 2 parts of crosslinking agent TAIC. Mix and vulcanize according to the preparation method in Example 1 to obtain a rubber blend.

[0066] Comparative Example 3 Weigh out 75 parts of EPDM rubber, 25 parts of liquid chlorinated polyethylene, 20 parts of carbon black, 80 parts of composite flame retardant (APP:MCA=3:1), 5 parts of zinc oxide, 0.5 parts of stearic acid, 1 part of antioxidant RD, 1 part of microcrystalline wax, 4 parts of titanium dioxide, and 2 parts of crosslinking agent. Mix and vulcanize according to the preparation method of Example 1 to obtain a rubber blend.

[0067] Comparative Example 4 Weigh out 75 parts of EPDM rubber, 25 parts of liquid chlorinated polyethylene, 20 parts of silica, 1.5 parts of coupling agent Si-69, 80 parts of composite flame retardant (APP:MCA=3:1), 5 parts of zinc oxide, 0.5 parts of stearic acid, 1 part of antioxidant RD, 1 part of microcrystalline wax, and 4 parts of titanium dioxide. After a first-stage mixing according to the preparation method of Example 1, add 1.5 parts of sulfur, 1 part of accelerator CZ, and 0.5 parts of accelerator TMTD in the second-stage mixing. After thinning, sheet the mixture and vulcanize it at 170°C and 12MPa for 15 minutes to obtain the rubber blend.

[0068] Comparative Example 5 Weigh out 75 parts of EPDM rubber, 25 parts of liquid chlorinated polyethylene, 20 parts of silica, 1.5 parts of coupling agent Si-69, 80 parts of composite flame retardant (APP:MCA=1:1), 5 parts of zinc oxide, 0.5 parts of stearic acid, 1 part of antioxidant RD, 1 part of microcrystalline wax, 4 parts of titanium dioxide, and 2 parts of crosslinking agent TAIC. Mix and vulcanize according to the preparation method in Example 1 to obtain a rubber blend.

[0069] Comparative Example 6 Weigh out 75 parts of EPDM rubber, 25 parts of liquid chlorinated polyethylene, 20 parts of silica, 1.5 parts of coupling agent Si-69, 80 parts of composite flame retardant (APP:MCA=5:1), 5 parts of zinc oxide, 0.5 parts of stearic acid, 1 part of antioxidant RD, 1 part of microcrystalline wax, 4 parts of titanium dioxide, and 2 parts of crosslinking agent TAIC. Mix and vulcanize according to the preparation method in Example 1 to obtain a rubber blend.

[0070] Comparative Example 7 (One-Stage Mixing Method) Weigh out 75 parts of EPDM rubber, 25 parts of liquid chlorinated polyethylene, 20 parts of silica, 1.5 parts of coupling agent Si-69, 80 parts of composite flame retardant (APP:MCA=3:1), 5 parts of zinc oxide, 0.5 parts of stearic acid, 1 part of antioxidant RD, 1 part of microcrystalline wax, 4 parts of titanium dioxide, 3 parts of peroxide vulcanizing agent DCP, and 2 parts of crosslinking agent TAIC.

[0071] The preparation method is as follows: (1) Mixing: Preheat the internal mixer to 45°C, add EPDM rubber and liquid chlorinated polyethylene, and plasticize for 2 minutes until the rollers are wrapped; add zinc oxide, stearic acid, antioxidant RD, microcrystalline wax, silica, coupling agent, titanium dioxide, composite flame retardant, peroxide vulcanizing agent and crosslinking agent in sequence, mix at 50°C for 10 minutes, control the discharge temperature not to exceed 120°C, pass through the thin sheet 3 times after discharge, and then sheet to obtain the compound rubber.

[0072] (2) Vulcanization: The compounded rubber is placed in the mold of a flat vulcanizing machine and vulcanized at 170°C and 12MPa for 15 minutes to obtain the rubber blend.

[0073] Comparative Example 8 (no in-situ modification, coupling agent added later) Weigh out 75 parts of EPDM rubber, 1 part of liquid chlorinated polyethylene, 20 parts of silica, 80 parts of composite flame retardant (APP:MCA=3:1), 5 parts of zinc oxide, 0.5 parts of stearic acid, 1 part of antioxidant RD, 1 part of microcrystalline wax, 4 parts of titanium dioxide, 3 parts of peroxide vulcanizing agent DCP, 2 parts of crosslinking agent TAIC, and 1.5 parts of coupling agent Si-69.

[0074] The preparation method is as follows: (1) First stage of mixing: Preheat the internal mixer to 45°C, add EPDM rubber and liquid chlorinated polyethylene, and plasticize for 2 minutes until the rollers are wrapped; add zinc oxide, stearic acid, antioxidant RD, microcrystalline wax, silica, titanium dioxide and composite flame retardant in sequence, mix at 50°C for 10 minutes, control the discharge temperature not to exceed 120°C, pass through the thin tube 3 times after discharge, and let stand at room temperature for 10 hours to obtain masterbatch (silica was not surface modified).

[0075] (2) Two-stage mixing: Adjust the roller temperature of the open mill to 40°C and the roller gap to 3mm. Add the masterbatch, add coupling agent, peroxide vulcanizing agent and crosslinking agent after wrapping the roller. Mix for 8 minutes, cut the left and right blades 3 times each. After the mixture is evenly dispersed, adjust the roller gap to 0.8mm and pass through the thin sheet 5 times. Finally, adjust it to 2.5mm and sheet the rubber to obtain the compound.

[0076] (3) Vulcanization: The compounded rubber is placed in the mold of the flat vulcanizing machine and vulcanized at 170℃ and 12MPa for 15 minutes to obtain the rubber blend.

[0077] V. Performance Testing The performance of the rubber blends obtained in Examples 1-14 and Comparative Examples 1-8 was tested using the following methods: Tensile strength and elongation at break: tested according to GB / T 528 standard, with a tensile speed of 500 mm / min; Shore A hardness: Tested according to GB / T 531 standard, reading in 3 seconds; Vertical flammability rating: Tested according to UL94 standard, with a test piece thickness of 1.6 mm.

[0078] The test results are shown in Table 3.

[0079] Table 3 Performance test results of Examples 1-14 and Comparative Examples 1-8

[0080] Results Analysis As can be seen from the test results in Table 3, the performance comparison between Example 1 and Comparative Examples 1-4 is as follows: Figure 2 As shown, Example 1 is a preferred embodiment of the present invention, with a Shore A hardness of 42A, a tensile strength of 8.2 MPa, an elongation at break of 410%, a vertical flammability rating of UL94 V0, and a white color (which can be colored). This formulation achieves excellent mechanical properties and flame retardant properties while maintaining low hardness.

[0081] (1) Compared with Comparative Example 1, under the same flame retardant rating (V0), the hardness of Example 1 decreased by 6A and the tensile strength increased by 49.09%. Moreover, Example 1 uses a halogen-free environmentally friendly flame retardant, avoiding the environmental problems caused by traditional flame retardants such as polybrominated diphenyl ethers and antimony trioxide.

[0082] (2) Compared with Comparative Example 2, liquid chlorinated polyethylene can reduce hardness by 10A, improve flame retardancy rating from V1 to V0, and increase tensile strength by 32.2%. This proves that liquid chlorinated polyethylene can not only be used as a plasticizer, but also achieve synergistic improvement in hardness, flame retardancy and strength through co-crosslinking with EPDM rubber and its own flame retardant properties.

[0083] (3) Compared with Comparative Example 3, the combination of silica and coupling agent in Example 1 reduced the hardness by 4A and achieved colorization, proving that the combination of silica and coupling agent used in this invention is irreplaceable in achieving colorization and maintaining low hardness.

[0084] (4) Compared with the sulfur vulcanization of Example 1 and Comparative Example 4, it can be seen that the peroxide vulcanizing agent increases the tensile strength of the product by 34.4%, which proves that the peroxide vulcanizing agent is the key to realizing the co-crosslinking of EPDM rubber and liquid chlorinated polyethylene, forming an interpenetrating network structure and improving mechanical properties.

[0085] (5) In Example 2, the amount of EPDM rubber was 50 parts, with a hardness of 35A, a tensile strength of 6.8 MPa, and a flame retardancy rating of V0. In Example 3, the amount of EPDM rubber was 85 parts, with a hardness of 48A, a tensile strength of 8.6 MPa, and a flame retardancy rating of V0. This shows that within the range of 50-85 parts of EPDM, low hardness and V0 flame retardancy can be achieved, but the tensile strength increases with the increase of EPDM content.

[0086] (6) In Example 4, the amount of liquid chlorinated polyethylene was 10 parts, with a hardness of 45A, a flame retardant rating of V1, and a tensile strength of 7.5 MPa; in Example 5, the amount of liquid chlorinated polyethylene was 35 parts, with a hardness of 38A, a tensile strength of 7.2 MPa, and a flame retardant rating of V0. This indicates that the flame retardant performance decreases when the amount of liquid chlorinated polyethylene is less than 15 parts, and the tensile strength decreases significantly when the amount is more than 30 parts. The preferred amount of liquid chlorinated polyethylene is 20-30 parts.

[0087] (7) In Example 6, the composite flame retardant dosage was 60 parts, with a hardness of 39A and a tensile strength of 8.5 MPa, but the flame retardant rating was V1; in Example 7, the composite flame retardant dosage was 100 parts, with a hardness of 46A and a tensile strength of 7.6 MPa, and the flame retardant rating remained V0. This indicates that when the amount of flame retardant is less than 70 parts, the V0 flame retardant effect cannot be achieved, and when it is more than 90 parts, the hardness is too high and the strength decreases. The preferred amount of flame retardant is 70-90 parts.

[0088] (8) In Example 8, the amount of peroxide vulcanizing agent DCP was 2 parts, and its hardness was 40A and tensile strength was 7.1 MPa; in Example 9, the amount of peroxide vulcanizing agent DCP was 5 parts, and its hardness was 45A and tensile strength was 7.5 MPa. This shows that when the amount of peroxide vulcanizing agent DCP is less than 2.5 parts, the crosslinking is insufficient and the strength is low; when it is more than 4 parts, there is over-crosslinking and the strength decreases. The preferred amount of peroxide vulcanizing agent DCP is 2.5-3.5 parts.

[0089] (9) In Example 10, the amount of silica used was 15 parts, and its hardness was 40A and its tensile strength was 7.4 MPa; in Example 11, the amount of silica used was 25 parts, and its hardness was 47A and its tensile strength was 8.5 MPa. This shows that increasing the amount of silica used can improve the strength, but the hardness also increases accordingly. The preferred amount of silica used is 18-22 parts.

[0090] (10) In Example 12, the amount of titanium dioxide used was 2 parts, the hardness was 41A, the tensile strength was 8.3 MPa, and the color changed from white to translucent white. This shows that the amount of titanium dioxide used has little effect on mechanical properties and can be adjusted within the range of 2-6 parts according to the whiteness requirements.

[0091] (11) Compared with Comparative Examples 5 and 6, Examples 13 and 14 achieved a flame retardant rating of V0 when the APP:MCA ratio was 2:1 to 4:1; while when the APP:MCA ratio was 1:1 in Comparative Example 5 and 5:1 in Comparative Example 6, the flame retardant rating dropped to V1. This indicates that the ratio of APP to MCA must be controlled within the range of 2:1 to 4:1 to obtain excellent flame retardant effect.

[0092] (12) The rubber blends obtained in Examples 1-14 are white or translucent white, indicating that the present invention uses titanium dioxide as a white base and can further add other organic or inorganic pigments (such as iron oxide red, phthalocyanine blue, chrome yellow, etc.) to achieve various colored products such as red, blue, and yellow, according to actual needs. Experimental verification shows that adding 1-5 parts of colored pigment does not affect the flame retardant properties of the present invention, proving that the present invention has good color adaptability.

[0093] (13) Compared with Example 1, Comparative Example 7 adopted a one-stage mixing method, in which all components were added to the internal mixer at once. Due to the long-term mixing of the peroxide vulcanizing agent at high temperature, some scorching occurred, the Mooney viscosity of the mixed rubber increased to 85, the processing safety was poor, and the tensile strength decreased from 8.2 MPa to 6.8 MPa, a decrease of 17.1%. This proves that the two-stage mixing process of the present invention, which involves adding fillers and flame retardants in one stage and adding vulcanizing agents at low temperature in two stages, can effectively prevent scorching, ensure uniform dispersion of vulcanizing agents, and improve mechanical properties and processing safety.

[0094] (14) Compared with Example 1, Comparative Example 8 uses the coupling agent addition method, that is, silica and coupling agent are added separately, and the coupling agent is added during the second stage of mixing. Because the coupling agent failed to fully react with silica during the mixing process, the surface modification of silica was incomplete, the dispersibility was poor, the interfacial bonding was weak, and the tensile strength decreased from 8.2 MPa to 7.0 MPa, a decrease of 14.6%. This proves that the surface modification process of the present invention, which uses silica and coupling agent to be added simultaneously, can enable the coupling agent to fully react with silica, achieve uniform dispersion of silica and interfacial enhancement, and significantly improve the reinforcing effect.

[0095] In summary, this invention successfully prepared a colored, low-hardness, and highly flame-retardant EPDM rubber blend by using EPDM rubber and liquid chlorinated polyethylene, combined with a phosphorus-nitrogen intumescent flame retardant and a peroxide vulcanization system, and by adding a coupling agent to modify the surface of silica. This blend exhibits a Shore A hardness of 35-45A, a tensile strength ≥8MPa, and a vertical flammability rating reaching UL94 V0. Its excellent overall performance makes it suitable for wide applications in mining products, electronics, and rail transportation.

[0096] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A colored, low-hardness, high-flame-retardant EPDM rubber blend, characterized in that, By mass, it includes the following components: 50-85 parts of EPDM rubber, 10-35 parts of liquid chlorinated polyethylene, 3-8 parts of zinc oxide, 0.3-0.7 parts of stearic acid, 0.5-2 parts of 2,2,4-trimethyl-1,2-dihydroquinoline polymer, 0.5-2 parts of microcrystalline wax, 15-25 parts of silica, 1-2 parts of coupling agent, 60-100 parts of composite flame retardant, 2-5 parts of peroxide vulcanizing agent, 1-4 parts of crosslinking agent, and 2-6 parts of titanium dioxide.

2. The colored, low-hardness, high-flame-retardant EPDM rubber blend according to claim 1, characterized in that, The chlorine content of the liquid chlorinated polyethylene is 30%-40%.

3. The colored, low-hardness, high-flame-retardant EPDM rubber blend according to claim 1, characterized in that, The silica mentioned is precipitated silica with a specific surface area of ​​150-200 m². 2 / g.

4. The colored, low-hardness, high-flame-retardant EPDM rubber blend according to claim 1, characterized in that, The coupling agent is a silane coupling agent selected from at least one of bis-[γ-(triethoxysilyl)propyl]tetrasulfide, γ-mercaptopropyltrimethoxysilane, and γ-aminopropyltriethoxysilane.

5. The colored, low-hardness, high-flame-retardant EPDM rubber blend according to claim 1, characterized in that, The composite flame retardant is a phosphorus-nitrogen intumescent flame retardant selected from at least two of ammonium polyphosphate, melamine cyanurate, melamine polyphosphate, aluminum hypophosphite, and aluminum diethylphosphite.

6. The colored, low-hardness, high-flame-retardant EPDM rubber blend according to claim 3, characterized in that, The composite flame retardant is composed of ammonium polyphosphate and melamine cyanurate, with a mass ratio of 2:1 to 4:

1.

7. The colored, low-hardness, high-flame-retardant EPDM rubber blend according to claim 1, characterized in that, The peroxide vulcanizing agent is selected from at least one of dicumyl peroxide, di-tert-butyl cumyl peroxide, benzoyl peroxide, and di-tert-butyl peroxide; the co-crosslinking agent is selected from at least one of triallyl isocyanurate, triallyl cyanurate, trimethylolpropane trimethacrylate, and N,N'-m-phenylenebismaleimide.

8. A method for preparing a colored, low-hardness, high-flame-retardant EPDM rubber blend according to any one of claims 1 to 7, characterized in that, Includes the following steps: (1) First stage of mixing: Ethylene propylene diene monomer (EPDM) rubber and liquid chlorinated polyethylene are put into a mixer and plasticized evenly. Then, zinc oxide, stearic acid, 2,2,4-trimethyl-1,2-dihydroquinoline polymer, microcrystalline wax, silica, coupling agent, titanium dioxide and composite flame retardant are added in sequence. The mixture is mixed at 40-60℃ for 8-12 minutes. After the rubber is discharged, it is cooled down in a thin stream to obtain the masterbatch. (2) Two-stage mixing: After wrapping the masterbatch on the open mill, add the peroxide vulcanizing agent and crosslinking agent at 40-50℃, mix for 5-10 minutes until uniform, and then sheet after passing through the thin mill 4-6 times to obtain the compound. (3) Vulcanization: The compound is vulcanized at 160-180℃ and 10-15MPa for 10-20 minutes to obtain the colored low-hardness high flame-retardant EPDM rubber blend.

9. The preparation method according to claim 8, characterized in that, In step (1), the internal mixer is preheated to 40-50°C. First, EPDM rubber and liquid chlorinated polyethylene are plasticized for 2-3 minutes, and then each component is added in sequence. The silica and coupling agent are added at the same time. The total mixing time is 8-12 minutes. The discharge temperature is controlled to be ≤120°C. After discharge, the rubber is passed through a thin tube 2-4 times and left at room temperature for 8-12 hours to obtain the masterbatch.

10. The preparation method according to claim 8, characterized in that, In step (2), the rolling temperature of the open mill is controlled at 40-50℃, the rolling gap is adjusted to 3-4mm, the peroxide vulcanizing agent and crosslinking agent are added and mixed for 5-10 minutes, the left and right cutters are used 3-4 times each, and after the mixture is evenly dispersed, the rolling gap is adjusted to 0.5-1mm and thin passes are made 4-6 times. Finally, the gap is adjusted to 2-3mm and the sheet is made to obtain the compound rubber.

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