A method for preparing hard rubber

Abstract

This invention discloses a method for preparing hard rubber. Reinforcing agents and activators are added to natural rubber in a specific ratio. A plasticizer is added during the drying process. The mixture is heated to remove moisture and improve flowability, then cooled to 60°C to lock in the oil. A vulcanization accelerator, vulcanizing agent, silane coupling agent, and polymer resin are then added and mixed. The mixture is then plasticized and vulcanized to obtain a final product. The reinforcing agents include clay, talc, light calcium carbonate, carbon black, silica, and barium sulfate. The plasticizer is naphthenic oil, the vulcanization accelerator is diphenylguanidine, and the polymer resin is high-styrene resin. Adding the plasticizer and heating the mixture ensures uniform dispersion of the reinforcing agents and activators. Cooling the mixture before adding the vulcanizing agent and vulcanization accelerator avoids the risk of crosslinking during the mixing stage. Plasticization homogenizes the silane coupling agent, reinforcing agent, activator, vulcanizing agent, vulcanization accelerator, and polymer resin, significantly improving heat transfer efficiency, reducing under-vulcanization / over-vulcanization gradients, and resulting in more uniform crosslinking density. This method can be applied in specialized engineering fields such as aerospace and automotive.

Description

Technical Field

[0001] This invention provides a method for preparing hard rubber, which relates to the field of polymer materials. Background Technology

[0002] In recent years, with the increasing demands on material performance from industrial automation, transportation and high-performance equipment, high-performance hard rubber, as a material with high hardness and excellent chemical stability at room temperature, has gradually expanded its application from traditional seals and rubber rollers to aerospace, automotive and engineering machinery fields.

[0003] HG / T 3954-2007 specifies that rubber compounds for conveying and tension rollers must have a tensile strength greater than 35 MPa, an elongation at break greater than 350%, and a hardness greater than 75. For extrusion and immersion rollers, the rubber compounds must, after immersion in strong acids and alkalis at 90°C for 3 days, exhibit a reduction in hardness, tensile strength, and elongation at break not exceeding 5 degrees, 15%, and 20%, respectively. Traditional adhesive materials often struggle to simultaneously meet multiple requirements, including high strength, excellent interfacial bonding, and resistance to heat aging.

[0004] Natural rubber has poor mechanical properties, and carbon black is an effective reinforcing filler. However, its dark color limits the applications of the finished products. To manufacture lighter-colored products, silica and kaolin are often added, but the reinforcing effect is minimal, and excessive addition of silica and kaolin can negatively impact the physical properties of the products. Some researchers have modified natural rubber with high-styrene resin. High-styrene resin contains approximately or more than 85% styrene, and its high Tg glassy hard phase forms dispersed "hard micro-regions / physical crosslinking points" in the natural rubber matrix, significantly restricting the movement of cis-1,4-polyisoprene segments, effectively increasing modulus and hardness. Simultaneously, the modified system exhibits increased viscosity and interfacial friction, and the two-phase structure causes localized high shear and stronger hysteresis, leading to increased viscous dissipation and faster temperature rise during processing. While traditional natural rubber can achieve high tear strength and fatigue resistance under sulfur vulcanization conditions, the introduction of polysulfide bonds also results in poor heat aging resistance. Peroxide vulcanization often leads to short crosslinks and a lack of slippage ability, resulting in insufficient mechanical properties of the rubber compound. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, this invention provides a method for preparing hard rubber, characterized by comprising the following preparation steps:

[0006] (1) In a mixer, add natural rubber, reinforcing agent and activator in proportion and stir until well mixed;

[0007] (2) When the temperature of the mixture exceeds 70°C, add plasticizer and stir. Heat the mixture to no more than 100°C and then cool it to 60°C. Add vulcanization accelerator and vulcanizing agent, then add silane coupling agent and functional polymer material and stir to mix well.

[0008] (3) Pour the mixture out and transfer it to the open mill for thin-pass treatment 3-7 times. Then press the mixture into a rectangle with a thickness of 3mm. Store it at room temperature for more than 4 hours before vulcanization. Set the vulcanization temperature and vulcanization time. Preheat the mold first, and then put the cut rubber sheet into the mold to obtain a hard rubber product.

[0009] Furthermore, the vulcanization temperature is 160℃ and the vulcanization time is 60 min.

[0010] Further, by weight, natural rubber is 80-120 parts, reinforcing agent is 20-80 parts, plasticizer is 3-10 parts, vulcanization accelerator is 0.5-1.4 parts, vulcanizing agent is 20-70 parts, silane coupling agent is 1-10 parts, and functional polymer material is 1-20 parts.

[0011] Further, by weight, the components are: 100 parts natural rubber, 40-70 parts reinforcing agent, 6 parts plasticizer, 1 part vulcanization accelerator, 29-49 parts vulcanizing agent, 1-7 parts silane coupling agent, and 3-10 parts functional polymer materials.

[0012] Furthermore, the vulcanizing agent is sulfur, the vulcanization accelerator is diphenylguanidine, and the activator is one or more of magnesium oxide and zinc oxide.

[0013] Furthermore, the reinforcing agent is one or more of the following: clay, talc, light calcium carbonate, carbon black, precipitated silica, or barium sulfate.

[0014] Furthermore, the silane coupling agent is one of sulfur-containing silanes, preferably silicon 69.

[0015] Furthermore, the functional polymer material is one or more of natural resins, petroleum-based resins, synthetic resins, lignin derivatives, or inorganic carbon materials.

[0016] Furthermore, the functional polymer material is one or more of the following: terpene resin, rosin resin, damask resin, petroleum resin, phenolic resin, polyterpene resin, cashew nut shell oleoresin, alkaline lignin, high-styrene resin, coumarone resin, or carbon fiber.

[0017] The high-performance hard rubber provided by this invention can be used in the preparation of pipe linings.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] (1) Natural rubber is the core matrix of the hard rubber system. Its excellent elasticity and mechanical strength provide a basis for subsequent vulcanization and crosslinking. The introduction of accelerators and active oxides effectively improves the shortcomings of traditional sulfur vulcanization in terms of heat aging resistance. It not only increases the crosslinking density, but also significantly improves the temperature resistance and fatigue resistance, becoming an important technical path for hard rubber formulation innovation.

[0020] (2) The application of reinforcing agents has significant advantages in improving mechanical properties and reducing production costs. By using interface modification measures such as silane coupling agents, the reinforcing effect of fillers can be fully utilized to form a uniform and continuous stress transmission network.

[0021] (3) The introduction of softeners such as naphthenic oil and functional polymer materials plays a key regulatory role in improving the processing performance of rubber compounds, reducing the oil absorption value of fillers, and coordinating the interaction between various components, providing greater design space and process flexibility for formulation design.

[0022] (4) The synergistic effect between the components significantly improves the overall performance of hard rubber, achieving a balance between high hardness, high rigidity and excellent resistance to media, and meeting the requirements of high-quality rubber rollers in HG / T 3954-2007. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention.

[0024] The rubber performance testing method used in this invention is as follows:

[0025] Stress at constant elongation refers to the stress value that a material experiences or transmits when it is stretched to a fixed elongation ratio (strain) and kept constant during a tensile test. It describes "stress under a fixed elongation state".

[0026] Elongation at break refers to the percentage of relative elongation a material undergoes from its initial length to its fracture length during a tensile test. It is a key indicator characterizing the ductility (toughness / stretchability) of a material.

[0027] Hardness: The Shore hardness test was performed. The Shore hardness test method is GB / T531.1-2008 Test Method for Indentation Hardness of Vulcanized Rubber or Thermoplastic Rubber, Part 1.

[0028] Tensile strength: Measured according to GB / T528-2009 Determination of tensile stress-strain properties of vulcanized rubber or thermoplastic rubber.

[0029] Media resistance test: Weigh the rubber sample to be tested and immerse it thoroughly in different solvents. Place the sample in an oven at a specific temperature according to the test requirements for 7 days. After immersion, remove the rubber sample, wash it with deionized water, and air dry it on filter paper (1-3 hours) or in an oven. Finally, weigh the sample and calculate the rate of change in mass.

[0030] ,

[0031] Where M0 is the mass of the sample before immersion, and M1 is the mass of the sample after immersion.

[0032] Test conditions: 40% sulfuric acid (85℃*7 days), 20% hydrochloric acid (50℃*7 days), 40% sodium hydroxide (85℃*7 days), 70% phosphoric acid (85℃*7 days).

[0033] Example 1

[0034] The rubber provided in this embodiment is prepared according to the following steps:

[0035] (1) In a 2 L internal mixer, add 100 parts by weight of natural rubber and mix for 1 min. Add 10 parts by weight of silica and 4 parts by weight of magnesium oxide and stir for 2 min. Add 20 parts by weight of carbon black N660 and stir for 5 min. Add 10 parts by weight of barium sulfate in two batches and stir for 2 min each time.

[0036] (2) When the temperature of the mixture exceeds 70°C, add 6 parts by weight of naphthenic oil in 3 batches and stir for 2 min each time. Transfer the mixture to a 5 L internal mixer, heat to 100°C and then cool to 60°C. Add 1 part by weight of diphenylguanidine and 30 parts by weight of sulfur and stir for 2 min. Add 1 part by weight of silicon 69 and 3 parts by weight of high styrene resin and stir for 2 min.

[0037] (3) Pour the mixture out and transfer it to the open mill for thin-pass treatment 7 times. Then press the mixture into a rectangle with a thickness of about 3 mm. Store it at room temperature for at least 4 hours before vulcanization. Set the vulcanization temperature to 160℃ and the vulcanization time to 60 min. Preheat the mold first, then put the cut rubber sheet into the mold. After the time is up, take out the sample and perform relevant performance tests.

[0038] Step (2) The mixture is heated to 70°C to bake the rubber, which enhances the movement of natural rubber molecular chain segments, reduces internal friction, and lowers Mooney viscosity, which is conducive to dispersing reinforcing agents and activators. After adding the plasticizer naphthenic oil, the naphthenic oil can be accelerated to penetrate into the rubber molecular chain, further reducing the intermolecular forces, softening the rubber compound and reducing viscosity.

[0039] Raising the temperature to approximately 100°C (close to the boiling point of water) significantly promotes the diffusion and evaporation of moisture introduced by the rubber compound and inorganic fillers (such as barium sulfate, magnesium oxide, and silica) through moisture absorption, dispersing residual low-boiling substances. Simultaneously, the higher temperature enhances the movement of rubber molecular chains, allowing the naphthenic oil to soften denser or locally crystalline regions more thoroughly, resulting in a more uniform internal oil distribution. This reduces the subsequent "soft outside, hard inside" gradient and promotes the uniform distribution of activators to form active species.

[0040] Lowering the temperature to 60℃ serves several purposes. First, it "locks" the already infiltrated naphthenic oil within the rubber compound, reducing the migration of free oil during subsequent settling. Second, 60℃ is below the effective activation zone of the vulcanization accelerator. Adding the vulcanization accelerator, vulcanizing agent, silane coupling agent, and high-styrene resin sequentially at a lower temperature significantly reduces the risk of crosslinking during the mixing stage. This allows for preferential uniform dispersion of the vulcanization system at the lower temperature, avoiding early vulcanization during the high-temperature, high-shear stage and ensuring the consistency of the vulcanization network throughout the system. Subsequent introduction of components that alter rheology and interfaces (Si69, high-styrene resin) can reduce interference from these "added components" on the accelerator / sulfur dispersion. Third, silanes are highly reactive and sensitive to moisture and temperature. Adding them at a lower temperature in the later stages reduces the ineffective preferential hydrolysis / self-condensation of the silane coupling agent in the high-humidity environment before dehumidification. At this point, the vulcanization accelerator, added first, rapidly complexes with the already dispersed activator. The formation of an active vulcanization intermediate shortens the dispersion of vulcanization time and avoids adverse side reactions or "competitive adsorption" between the silane coupling agent and the vulcanization accelerator and activator at high temperatures, thus improving the effective coupling between the silane coupling agent and silica. Fourthly, adding the silane coupling agent too early will change the surface energy of the particles, which may promote "wetting-adhesion-re-agglomeration". Adding the silane coupling agent after the vulcanization system is formed is beneficial for filler dispersion. High-styrene resin will also increase the rigidity and viscosity of the system. If added too early, it will increase the difficulty of dispersing the subsequent vulcanization accelerator / sulfur / silane coupling agent, which is prone to "local enrichment" and "agglomeration", resulting in uneven vulcanization and performance dispersion. If added too early, it will also cause the mixture to heat up during mixing, which will increase the risk of early crosslinking when added to the vulcanization system later. High-styrene resin is added in the later stage after the vulcanization accelerator / sulfur has been evenly dispersed and the silane coupling agent has also taken the lead. Only a short mixing time is needed to achieve uniformity.

[0041] In step (1), the reinforcing agent with strong adsorption capacity is first dispersed well, which is conducive to the uniform dispersion of the substances added later in the mixing process in step (2). After the vulcanization accelerator is added, it quickly complexes with the already dispersed activator to form an active vulcanization intermediate, thus shortening the dispersion of vulcanization time.

[0042] In step (3), before the chemical reaction has started, the roller gap is set very small to generate high shear stress, which further disperses the filler agglomeration that may still exist in the early mixing, so that the reinforcing agent can achieve a finer dispersion scale and improve the reinforcing efficiency. The thin-pass treatment provides an opportunity for secondary homogenization, reducing the "local enrichment" and uneven adsorption caused by the subsequent vulcanization system, silane coupling agent, and high styrene resin. Moreover, the chemical coupling of silane coupling agent and hydroxyl-containing fillers such as silica requires a relatively high temperature to be significantly promoted, but the thin-pass treatment can significantly improve the contact probability and surface activation degree of the filler through forced contact, interface renewal and moderate frictional heat generation, which provides more effective contact sites for the coupling reaction during subsequent hot vulcanization. The thin-pass treatment also helps the resin to form a more stable micro-distribution and phase state in the rubber matrix, reducing phase separation and weak interfacial areas. In step (3), pressing the mixture into a 3 mm thick sheet has good heat transfer efficiency in flat vulcanization. Allowing the rubber chains to rest for 4 hours allows them to return to a more thermodynamically balanced entangled state, reducing residual deformation and uneven shrinkage in the vulcanized parts. During this resting period, plasticizers, accelerators, and vulcanizing agents also undergo slow diffusion and interfacial redistribution, thus reducing the risk of short-term oil spraying / blooming and resulting in more consistent hardness and tensile stress within the sheet. For systems containing silane coupling agents and silica, the coupling reaction is time-dependent. A 4-hour resting period provides a window for diffusion and interfacial rearrangement, allowing more coupling precursors to contact and react more completely during subsequent hot vulcanization, improving wet grip resistance, dynamic fatigue resistance, and other properties.

[0043] Example 2

[0044] The rubber provided in this embodiment is prepared according to the following steps:

[0045] (1) In a 2 L internal mixer, add 100 parts by weight of natural rubber and mix for 1 min. Add 10 parts by weight of talc powder and 2 parts by weight of magnesium oxide and stir for 2 min. Add 40 parts by weight of carbon black N660 and stir for 5 min. Add 10 parts by weight of barium sulfate in two batches and stir for 2 min each time.

[0046] (2) When the temperature of the mixture exceeds 70°C, add 6 parts by weight of naphthenic oil in 3 batches and stir for 2 min each time. Transfer the mixture to a 5 L internal mixer, heat to 100°C and then cool to 60°C. Add 1 part by weight of diphenylguanidine and 30 parts by weight of sulfur and stir for 2 min. Add 1 part by weight of silicon 69 and 10 parts by weight of high styrene resin and stir for 2 min.

[0047] (3) Pour the mixture out and transfer it to the open mill for thin-pass treatment 4 times. Then press the mixture into a rectangle with a thickness of about 3 mm. Store it at room temperature for at least 4 hours before vulcanization. Set the vulcanization temperature to 160℃ and the vulcanization time to 60 min. Preheat the mold first, then put the cut rubber sheet into the mold. After the time is up, take out the sample and conduct relevant performance tests.

[0048] Example 3:

[0049] The rubber provided in this embodiment is prepared according to the following steps:

[0050] (1) In a 2 L internal mixer, add 100 parts by weight of natural rubber and mix for 1 min. Add 10 parts by weight of clay, 1 part by weight of magnesium oxide and 1 part by weight of zinc oxide and stir for 2 min. Add 10 parts by weight of carbon black N660 and stir for 5 min. Add 40 parts by weight of barium sulfate in two batches and stir for 2 min each time.

[0051] (2) When the temperature of the mixture exceeds 70°C, add 6 parts by weight of naphthenic oil in 3 batches and stir for 2 min each time. Transfer the mixture to a 5 L internal mixer, heat to 100°C and then cool to 60°C. Add 1 part by weight of diphenylguanidine and 45 parts by weight of sulfur and stir for 2 min. Add 1 part by weight of silicon 69 and stir for 2 min.

[0052] (3) Pour the mixture out and transfer it to the open mill for thin-pass treatment 7 times. Then press the mixture into a rectangle with a thickness of about 3 mm. Store it at room temperature for at least 4 hours before vulcanization. Set the vulcanization temperature to 160℃ and the vulcanization time to 60 min. Preheat the mold first, then put the cut rubber sheet into the mold. After the time is up, take out the sample and conduct relevant performance tests.

[0053] Example 4:

[0054] The rubber provided in this embodiment is prepared according to the following steps:

[0055] (1) In a 2 L internal mixer, add 100 parts by weight of natural rubber and mix for 1 min. Add 10 parts by weight of light calcium carbonate, 1 part by weight of magnesium oxide and 1 part by weight of zinc oxide and stir for 2 min. Add 10 parts by weight of carbon black N660 and stir for 5 min. Add 40 parts by weight of barium sulfate in two batches and stir for 2 min each time.

[0056] (2) When the temperature of the mixture exceeds 70°C, add 6 parts by weight of naphthenic oil in 3 batches and stir for 2 min each time. Transfer the mixture to a 5 L internal mixer, heat to 100°C and then cool to 60°C. Add 1 part by weight of diphenylguanidine and 45 parts by weight of sulfur and stir for 2 min.

[0057] (3) Pour the mixture out and transfer it to the open mill for thin-pass treatment 7 times. Then press the mixture into a rectangle with a thickness of about 3 mm. Store it at room temperature for at least 4 hours before vulcanization. Set the vulcanization temperature to 160℃ and the vulcanization time to 60 min. Preheat the mold first, then put the cut rubber sheet into the mold. After the time is up, take out the sample and conduct relevant performance tests.

[0058] Example 5:

[0059] The rubber provided in this embodiment is prepared according to the following steps:

[0060] (1) In a 2 L internal mixer, add 100 parts by weight of natural rubber and mix for 1 min. Add 10 parts by weight of silica, 1 part by weight of magnesium oxide and 1 part by weight of zinc oxide and stir for 2 min. Add 20 parts by weight of carbon black N660 and stir for 5 min. Add 10 parts by weight of barium sulfate in two batches and stir for 2 min each time.

[0061] (2) When the temperature of the mixture exceeds 70°C, add 6 parts by weight of naphthenic oil in 3 batches and stir for 2 min each time. Transfer the mixture to a 5 L internal mixer, heat to 100°C and then cool to 60°C. Add 1 part by weight of diphenylguanidine and 30 parts by weight of sulfur and stir for 2 min. Add 1 part by weight of silicon 69 and 3 parts by weight of high styrene resin and stir for 2 min.

[0062] (3) Pour the mixture out and transfer it to the open mill for thin-pass treatment 7 times. Then press the mixture into a rectangle with a thickness of about 3 mm. Store it at room temperature for at least 4 hours before vulcanization. Set the vulcanization temperature to 160℃ and the vulcanization time to 60 min. Preheat the mold first, then put the cut rubber sheet into the mold. After the time is up, take out the sample and conduct relevant performance tests.

[0063] Comparative Example 1:

[0064] The rubber provided in this comparative example is prepared according to the following steps:

[0065] (1) In a 2 L internal mixer, add 100 parts by weight of natural rubber and mix for 1 min. Add 10 parts by weight of silica and 4 parts by weight of magnesium oxide and stir for 2 min. Add 20 parts by weight of carbon black N660 and stir for 5 min. Add 10 parts by weight of barium sulfate in two batches and stir for 2 min each time.

[0066] (2) When the temperature of the mixture exceeds 70°C, stir for 2 min. Add 6 parts by weight of naphthenic oil in 3 portions and stir for 2 min each time. Transfer the mixture to a 5 L internal mixer, heat to 100°C and then cool to 60°C. Add 1 part by weight of diphenylguanidine and 30 parts by weight of sulfur and stir for 2 min. Add 3 parts by weight of high styrene resin and stir for 2 min.

[0067] (3) Pour the mixture out and transfer it to the open mill for thin-pass treatment 4 times. Then press the mixture into a rectangle with a thickness of about 3 mm. Store it at room temperature for at least 4 hours before vulcanization. Set the vulcanization temperature to 160℃ and the vulcanization time to 60 min. Preheat the mold first, then put the cut rubber sheet into the mold. After the time is up, take out the sample and conduct relevant performance tests.

[0068] Comparative Example 2:

[0069] The rubber provided in this comparative example is prepared according to the following steps:

[0070] (1) In a 2 L internal mixer, add 100 parts by weight of natural rubber and mix for 1 min. Add 10 parts by weight of silica and 4 parts by weight of magnesium oxide and stir for 2 min. Add 20 parts by weight of carbon black N660 and stir for 5 min. Add 10 parts by weight of barium sulfate in two batches and stir for 2 min each time.

[0071] (2) When the temperature of the mixture exceeds 70°C, add 6 parts by weight of naphthenic oil in 3 batches and stir for 2 min each time. Transfer the mixture to a 5 L internal mixer, heat to 100°C and then cool to 60°C. Add 1 part by weight of diphenylguanidine and 30 parts by weight of sulfur and stir for 2 min. Add 1 part by weight of silicon 69 and stir for 2 min.

[0072] (3) Pour the mixture out and transfer it to the open mill for thin-pass treatment 4 times. Then press the mixture into a rectangle with a thickness of about 3 mm. Store it at room temperature for at least 4 hours before vulcanization. Set the vulcanization temperature to 160℃ and the vulcanization time to 60 min. Preheat the mold first, then put the cut rubber sheet into the mold. After the time is up, take out the sample and conduct relevant performance tests.

[0073] Comparative Example 3

[0074] The rubber provided in this comparative example is prepared according to the following steps:

[0075] (1) In a 2 L internal mixer, add 100 parts by weight of natural rubber and mix for 1 min. Add 10 parts by weight of silica and 4 parts by weight of magnesium oxide and stir for 2 min. Add 20 parts by weight of carbon black N660 and stir for 5 min. Add 10 parts by weight of barium sulfate in two batches and stir for 2 min each. Add 6 parts by weight of naphthenic oil in three batches and stir for 2 min each. Add 1 part by weight of diphenylguanidine and 30 parts by weight of sulfur and stir for 2 min. Add 1 part by weight of silicon 69 and 3 parts by weight of high styrene resin and mix and stir for 2 min.

[0076] (2) Pour the mixture out and transfer it to the open mill for thin-pass treatment 7 times. Then press the mixture into a rectangle with a thickness of about 3 mm. Store it at room temperature for at least 4 hours before vulcanization. Set the vulcanization temperature to 160℃ and the vulcanization time to 60 min. Preheat the mold first, then put the cut rubber sheet into the mold. After the time is up, take out the sample and perform relevant performance tests.

[0077] The performance test results of the above embodiments and comparative examples are shown in Table 1.

[0078] Table 1

[0079]

[0080] As shown in Table 1, in Comparative Example 3, the high-styrene resin or silane coupling agent was directly mixed with other additives and added to the natural rubber without regard to the order of addition. Comparative Examples 1 and 2, unlike Comparative Example 3, underwent dehumidification and cooling after the addition of reinforcing agents and activators. Furthermore, the addition of the high-styrene resin and silane coupling agent was placed after the addition to the vulcanization system, improving the dispersion of the vulcanization system and preventing premature cross-linking, thus increasing the elongation at break. Compared to Comparative Example 1, which only added high-styrene resin, and Comparative Example 2, which only added silicon 69, the hard rubber prepared in Example 1 showed increased hardness and elongation at break, as well as increased tensile strength. This is mainly because the high-styrene resin has a high benzene ring content in its molecular chain, resulting in a regular and rigid molecular structure (the benzene ring is a rigid group that restricts molecular chain rotation), good compatibility with the rubber matrix, and, due to the presence of butadiene segments, similar polarity to natural rubber and styrene-butadiene rubber. When filled into rigid rubber, its rigid molecular chains can interweave in the rubber network to form a "rigid support skeleton", which greatly improves the Shore hardness and tensile stress (the stress required for a material to reach a certain deformation) of the rubber compound, making it more difficult for rigid rubber to deform under stress and meeting the rigidity requirements of structural components.

[0081] As can be seen from the data in Examples 3 and 4, the hard rubber prepared by adding magnesium oxide and zinc oxide synergistically exhibits good tensile properties while maintaining hardness. This is mainly because zinc oxide and magnesium oxide are added simultaneously. Among them, ZnO, as a strong activator, usually accelerates the main vulcanization rate and may increase the final crosslinking density, thereby improving the hardness, tensile stress, and rigidity of the vulcanizate, reducing the problem of excessive hardness and decreased elasticity caused by excessive MgO, and balancing hardness and toughness.

[0082] Example 5, based on Example 1, adds a synergistic system of magnesium oxide and zinc oxide, increasing the crosslinking density and improving the hardness, tensile stress, and elongation at break of the vulcanizate. Due to the later addition of high-styrene resin and silane coupling agent, Examples 1 and 5 reduce the ineffective preferential hydrolysis / self-condensation of the silane coupling agent in the high-humidity environment before dehumidification, avoiding adverse side reactions or "site-competing" adsorption between the silane coupling agent and vulcanization accelerators and activators at high temperatures. This improves the effective coupling between the silane coupling agent and silica. Therefore, the resulting adhesive material shows no significant quality change after prolonged immersion in strong acids and alkalis at high temperatures, with no significant reduction in hardness, tensile strength, or elongation at break.

[0083] The rigid rubber of this invention exhibits a mass change rate of no more than 1% after prolonged immersion in strong acids and alkalis at high temperatures. It can also be used as a lining in pipelines transporting high-pressure corrosive gases, or as a lining in high-pressure reactors or high-pressure storage tanks containing corrosive media such as strong acids, strong alkalis, and salt solutions. Alternatively, it can be used as an isolation sleeve for the shaft seal / drive shaft seal of a stirring device in high-pressure reactors containing corrosive media such as strong acids, strong alkalis, and salt solutions.

Claims

1. A method for producing a hard rubber, characterized by, It comprises the following preparation steps: (1) in an internal mixer, natural rubber and reinforcing agent, activator are added in proportion and stirred uniformly; (2) when the temperature of the mixture exceeds 70℃, plasticizer is added and stirred, and the mixture is heated to not more than 100℃ and then cooled to 60℃, vulcanization accelerator, vulcanizing agent, silane coupling agent and functional polymer material are added and stirred uniformly; (3) the mixture is poured out and moved to an open mill for thin pass processing 3-7 times, then the mixture is pressed into a long rectangle with a thickness of 3 mm, stored at room temperature for more than 4 h, and then vulcanized, the vulcanization temperature and time are set, the mold is preheated, and the cut rubber plate is placed in the mold to obtain a hard rubber product; The functional polymer material is high styrene resin, the activator is magnesium oxide and zinc oxide, and the silane coupling agent is silicon 69. The natural rubber is 80-120 parts, the reinforcing agent is 20-80 parts, the plasticizer is 3-10 parts, the vulcanization accelerator is 0.5-1.4 parts, the vulcanizing agent is 20-70 parts, the silane coupling agent is 1-10 parts, and the functional polymer material is 1-20 parts by weight.

2. The method of claim 1, wherein the step of mixing the rubber and the filler is performed at a temperature of 100°C or higher. The vulcanization temperature is 160℃, and the vulcanization time is 60 min.

3. The method of claim 1, wherein the step of mixing the rubber and the filler is performed at a temperature of 100°C or higher. The natural rubber is 100 parts, the reinforcing agent is 40-70 parts, the plasticizer is 6 parts, the vulcanization accelerator is 1 part, the vulcanizing agent is 29-49 parts, the silicon 69 is 1-7 parts, and the functional polymer material is 3-10 parts by weight.

4. The method of claim 1, wherein the step of mixing the rubber and the filler is performed at a temperature of 100°C or higher. The vulcanizing agent is sulfur, and the vulcanization accelerator is diphenyl guanidine.

5. The method of claim 1, wherein the step of mixing the rubber and the filler is performed at a temperature of 100°C or higher. The reinforcing agent is one or more of clay, talc, light calcium carbonate, carbon black, white carbon black or barium sulfate.

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