High static stiffness rubber mix and method of making and use thereof

Abstract

This invention belongs to the field of polymer composite materials technology, specifically relating to a high static stiffness compound, its preparation method, and its application. The high static stiffness compound comprises the following raw materials in parts by weight: a rubber matrix comprising 55-60 parts of EPDM rubber, 20-25 parts of high-styrene rubber, and 20 parts of chlorinated butyl rubber; a reinforcing component comprising 100-110 parts of carbon black and 40 parts of silica; a composite hardening component comprising 17.5-21 parts of phenolic resin, 10-15 parts of engineering plastic powder, and 1.2-1.5 parts of curing agent; and additives comprising 5-6 parts of silane coupling agent, 10-12 parts of plasticizer, 2 parts of stearic acid, 5 parts of zinc oxide, 1.5 parts of sulfur, 3.3 parts of accelerator, and 3.5 parts of antioxidant. The compound of this invention exhibits high static stiffness and creep resistance. This invention also provides its preparation method and application.

Description

Technical Field

[0001] This invention belongs to the field of polymer composite materials technology, specifically relating to high static stiffness compound rubber, its preparation method and application. Background Technology

[0002] Rubber materials are widely used due to their excellent elasticity. However, in many industrial scenarios (such as heavy equipment gaskets, high-performance sealing strips, protective components, etc.), not only elasticity is required, but also the ability of the material to resist deformation in the initial stage of stress, that is, high static stiffness, in order to ensure structural stability and precision.

[0003] In existing technologies, the main methods for improving the hardness and stiffness of rubber include: 1. Add high reinforcing fillers: such as using large amounts of fumed silica, carbon black, etc., but excessive filling can easily lead to a decrease in the toughness of the rubber compound and make processing difficult.

[0004] 2. Use high-styrene resin or phenolic resin: as a hardening agent, it can effectively improve the modulus, but may affect dynamic fatigue performance.

[0005] 3. Through structural design: For example, the multi-layer composite structure (quartz powder layer, neoprene rubber layer, etc.) used in Chinese Patent Publication No. CN221892719U is used to improve the overall performance, but the process is complicated.

[0006] Furthermore, maintaining a certain level of toughness (tear resistance) while reducing compression set under high hardness is a continuous goal pursued in this field. For example, Chinese patent application publication number CN104761910A utilizes a specific combination of raw rubber and metal compounds to reduce compression set while maintaining high hardness. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a high static stiffness compound that exhibits high static stiffness while also possessing good toughness and creep resistance. This invention also provides its preparation method and applications.

[0008] The high static stiffness compound of the present invention comprises the following raw materials in parts by weight: The rubber matrix comprises 55-60 parts of ethylene propylene diene monomer (EPDM), 20-25 parts of high styrene rubber (HSR), and 20 parts of chlorinated butyl rubber (CIIR). Ethylene propylene diene monomer (EPDM) rubber offers excellent resistance to ozone, weathering, heat aging, and chemical media, making it the preferred primary rubber for track pads; high-styrene rubber, as a rigid hardening phase, effectively improves static stiffness; chlorinated butyl rubber provides excellent airtightness, damping, and good adhesion to metal / concrete, and also helps improve weather resistance.

[0009] The reinforcing component contains 100-110 parts of carbon black and 40 parts of silica. Carbon black provides good reinforcement, thermal conductivity, and moderate elasticity, which is key to ensuring that dynamic heat generation is not too high; fumed silica is preferred, providing high reinforcement and hardness, and its surface silanol groups help improve the adhesion of rubber compounds under wet and slippery conditions.

[0010] The composite hardening component contains 17.5-21 parts of phenolic resin, 10-15 parts of engineering plastic powder, and 1.2-1.5 parts of curing agent; Phenolic resin provides a chemically rigid network; engineering plastic powder consists of physically rigid particles, whose high Tg provides long-lasting high-temperature stiffness and creep resistance; the curing agent activates the crosslinking reaction of phenolic resin, improving network efficiency.

[0011] The additives include 5-6 parts of silane coupling agent, 10-12 parts of plasticizer, 2 parts of stearic acid, 5 parts of zinc oxide, 1.5 parts of sulfur, 3.3 parts of accelerator, and 3.5 parts of antioxidant.

[0012] Silane coupling agents strongly bridge silica and rubber molecules, significantly reducing dynamic heat generation and improving fatigue resistance; plasticizers improve the processing fluidity of highly filled rubber compounds and balance hardness; zinc oxide is active zinc oxide, which acts as an activator to improve crosslinking efficiency and thermal stability.

[0013] Preferably, the ethylene content of the EPDM rubber is >60wt%, and the ENB content is less than 3.0wt%; the high-styrene rubber is a butadiene-styrene copolymer with a styrene content of 60wt%-70wt%.

[0014] Preferably, the carbon black is one or a blend of two of N550 or N660, and the silica is fumed silica with a specific surface area of ​​155-195 m². 2 / g.

[0015] Preferably, the engineering plastic powder is polyphenylene oxide (PPO) with a particle size of 10-30 μm; the engineering plastic powder is surface modified with a coupling agent. If the particle size is too coarse (>50 μm), it may become a stress concentration point, leading to premature cracking; if it is too fine (<5 μm), it is prone to agglomeration, making dispersion difficult and causing a surge in costs.

[0016] The specific steps for surface modification of engineering plastic powder are as follows: Mix silane coupling agent (KH550) or titanate coupling agent, anhydrous ethanol and water in a volume ratio of 1:10:1, stir to obtain hydrolysate, add engineering plastic powder that has been vacuum dried at 80℃ for 4h to remove moisture to the hydrolysate and disperse at 40-80℃ for 2-4h, then filter, wash with ethanol 2-3 times, vacuum dry at 70℃, and sieve to obtain the final product.

[0017] Preferably, when using engineering plastic powder and phenolic resin, the engineering plastic powder and phenolic resin are pre-dispersed first.

[0018] Phenolic resins with a medium softening point of 95-110℃ are preferred. If the softening point is too low, it will easily cause the rollers to stick during processing, while if the softening point is too high, it will be difficult to disperse.

[0019] Phenolic resins with high hydroxymethyl content (>9%) are preferred, as they have higher activity and react more fully with rubber.

[0020] Phenolic resin, as a reactive hardener, forms a rigid secondary bond network with rubber during vulcanization. It is the core of improving static stiffness without significantly impairing elasticity. Alkyl phenolic resin (such as tert-butyl phenolic resin and octyl phenolic resin) is preferred because it has better compatibility with rubber (especially EPDM) and the alkyl segments can provide a certain degree of toughness.

[0021] Preferably, the curing agent is hexamethylenetetramine (HMT), the silane coupling agent is silicon 69 or KH550, and the plasticizer is one or both of naphthenic oil or paraffin oil.

[0022] Preferably, the accelerator is a combination of TMTD and MBTS; the antioxidant is a combination of 4020 and RD. TMTD provides a rapid and flat crosslinking platform, while MBTS works synergistically with TMTD to ensure scorch safety. The antioxidant provides highly efficient resistance to thermo-oxidative aging.

[0023] The method for preparing the high static stiffness compound of the present invention includes the following steps: (1) Add some plasticizer to the engineering plastic powder, and then pre-disperse it with phenolic resin in a high-speed mixer to obtain a paste; (2) Add EPDM rubber, high styrene rubber and chlorinated butyl rubber to internal mixer A, plasticize evenly, then add carbon black, silica, silane coupling agent, zinc oxide, stearic acid, remaining plasticizer and antioxidant, mix to 150-155℃, discharge and cool to obtain a first section of masterbatch. (3) Add the first stage of masterbatch to internal mixer B, raise the temperature to 110-120℃, add the paste, and mix at 120-130℃ for 3-5 minutes to obtain the second stage of compound. The mixing temperature of 120-130℃ is higher than the softening point of rubber, which is conducive to shear transmission, but much lower than the glass transition temperature of engineering plastics, to ensure that the engineering plastic particles remain in a hard solid state. If the temperature is too high, the engineering plastic particles will soften and deform and stick together under shear, forming putty-like clumps, which will lead to dispersion failure. At this temperature, sufficient mechanical energy and sufficient mixing time (3-5 minutes) are required to break up any possible pre-agglomerates and distribute each hard particle evenly into the rubber matrix.

[0024] (4) Put the two-stage compound into the internal mixer C, raise the temperature to 90-100℃, add the curing agent, then raise the temperature to 130-140℃ and mix for 2-3 minutes, then add the accelerator and sulfur and mix. After the temperature drops below 100℃, discharge the compound into the open mill, re-mill and sheet it to obtain the final product.

[0025] Preferably, in step (1), the mass ratio of engineering plastic powder to plasticizer is 100:(15-30), and the pre-dispersion temperature is 85-100℃.

[0026] The high static stiffness compound described in this invention is used to manufacture railway rail cushioning pads.

[0027] Compared with the prior art, the beneficial effects of the present invention are: Phenolic resin melts and flows at the vulcanization temperature, undergoing a grafting reaction with rubber molecules to form a robust, pervasive "chemically rigid network" in the rubber compound. This network forms the chemical foundation for the stiffness of the compound in this invention. Engineering plastic powder, uniformly dispersed as micron-sized solid particles during compounding, acts as infusible "physically rigid particles," embedded in the rubber-phenolic resin matrix like "micro-skeletons." Through physical resistance, it directly and efficiently enhances modulus and hardness, while exhibiting excellent resistance to high-temperature deformation. The two work synergistically to form a dual-network structure of "chemical network + physical skeleton," achieving a "1+1>2" hardening effect and dimensional stability, and improving creep resistance.

[0028] The compound of this invention achieves a significant improvement in static stiffness through the addition of composite hardening components; the composite rubber matrix design retains necessary toughness and tear resistance while maintaining high stiffness. The reasonable formulation design, feeding sequence, and multi-stage mixing method of this invention solve the problems of uneven mixing and high heat generation in high-filler rubber compounds. Detailed Implementation

[0029] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments.

[0030] Unless otherwise specified, all raw materials used in the examples were commercially available.

[0031] EPDM rubber: Keltan ® 5260, ethylene content 62wt%, Mooney viscosity ML(1+4) 125℃ is 55, ENB content 2.3wt%.

[0032] High-styrene rubber: styrene content 65wt%.

[0033] The silica is fumed silica produced by the fumed silica process, with a specific surface area of ​​175 m². 2 / g.

[0034] Engineering plastic powder: PPO, with a particle size of 10-30μm, D50=20μm, and a number average molecular weight of 25000.

[0035] The phenolic resin is tert-butylphenolic resin 2402.

[0036] The surface modification steps for PPO powder are as follows: Silane coupling agent KH550, anhydrous ethanol, and water were mixed in a volume ratio of 1:10:1 and stirred to obtain a hydrolysate. PPO powder that had been vacuum dried at 80°C for 4 hours to remove moisture was added to the hydrolysate and dispersed at 60°C for 3 hours. Then, it was filtered, washed three times with ethanol, vacuum dried at 70°C, and sieved to obtain modified PPO.

[0037] The specific formulations of the examples and some comparative examples are shown in Table 1 (all components in Table 1 correspond to parts by mass).

[0038] Table 1 Formulations of Examples and Comparative Examples 1-2

[0039] The preparation methods of high static stiffness compound rubber in Examples 1-3 include the following steps: (1) Add naphthenic oil to surface-modified PPO powder, and then pre-disperse it with phenolic resin in a high-speed mixer to obtain a paste; the mass ratio of PPO powder to naphthenic oil is 100:15. (2) Add EPDM rubber, high styrene rubber, and chlorinated butyl rubber to internal mixer A, and plasticize them evenly. Then add carbon black, silica, silicon 69, zinc oxide, stearic acid, remaining naphthenic oil, antioxidant 4020 and RD, and mix them to 155°C. Discharge the rubber and cool it to obtain a first section of masterbatch. (3) Put the first stage of masterbatch into internal mixer B, raise the temperature to 115°C, add the paste, and mix at 125°C for 5 minutes to obtain the second stage of compound. (4) Put the two-stage compound into the internal mixer C, raise the temperature to 95°C, add the curing agent, then raise the temperature to 135°C and mix for 3 minutes, then add the accelerator TMTD and MBTS, sulfur and mix. After the temperature drops to below 100°C, discharge the compound into the open mill, re-mill and sheet it to obtain the final product.

[0040] Comparative Example 1 The preparation method of the compound rubber includes the following steps: (1) Add EPDM rubber, high styrene rubber, and chlorinated butyl rubber to internal mixer A, plasticize evenly, then add carbon black, silica, silicon 69, zinc oxide, stearic acid, plasticizer naphthenic oil, antioxidant 4020 and RD, mix to 155℃, discharge and cool to obtain a first section of masterbatch. (2) Put a section of masterbatch into internal mixer C, raise the temperature to 95°C, then raise the temperature to 135°C and mix for 3 minutes. Then add accelerator TMTD and MBTS, sulfur and mix. After the temperature drops below 100°C, discharge the rubber to the open mill, re-mill and sheet it to obtain the final product.

[0041] Comparative Example 2 The preparation method of the compound rubber includes the following steps: (1) Add EPDM rubber, high styrene rubber and chlorinated butyl rubber to internal mixer A, plasticize evenly, then add carbon black, silica, silicon 69, zinc oxide, stearic acid, plasticizer naphthenic oil and antioxidant, mix to 155°C, discharge and cool to obtain a first section of masterbatch. (2) Put the first stage of masterbatch into the internal mixer B, raise the temperature to 115°C, add phenolic resin, and mix at 125°C for 5 minutes to obtain the second stage of compound. (3) Put the two-stage compound into the internal mixer C, raise the temperature to 95°C, add the curing agent, then raise the temperature to 135°C and mix for 3 minutes, then add the accelerator and sulfur and mix. After the temperature drops to below 100°C, discharge the compound into the open mill, re-mill and sheet it to obtain the final product.

[0042] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that the PPO powder used was not surface modified, and the preparation method of the compound was the same as that in Example 1.

[0043] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that the PPO particle size used is 40-60μm, D50=50μm, and the PPO modification and compound preparation methods are the same as in Example 1.

[0044] Comparative Example 5 The difference between Comparative Example 5 and Example 1 is that the average particle size of the PPO used is 1-5 μm, D50=3 μm, and the PPO modification and compound preparation methods are the same as in Example 1.

[0045] Comparative Example 6 The difference between Comparative Example 6 and Example 1 is that the engineering plastic powder used is PA6, with a particle size of 10-30 μm, D50=20 μm, and a number-average molecular weight of 25000. The PA6 modification and compound preparation methods are the same as in Example 1. During the compounding process in step (3), the PA6 particles soften, then deform and stick together, forming clay-like lumps, resulting in dispersion failure and failure to obtain a two-stage compound with uniform components.

[0046] Comparative Example 7 The difference between Comparative Example 7 and Example 1 is that the EPDM rubber used is Keltan. ®9950, ethylene content 44wt%, Mooney viscosity ML(1+4) 125℃ 60, ENB content 9.0wt%. The PPO modification and compound preparation method is the same as in Example 1.

[0047] Comparative Example 8 The difference between Comparative Example 8 and Example 1 is that the high-styrene rubber used has a styrene content of 23.5 wt%. The PPO modification and compound preparation methods are the same as in Example 1.

[0048] Performance testing The performance test results of the compound rubbers obtained in Examples 1-3 and Comparative Examples 1-8 are shown in Table 2.

[0049] Table 2 Performance Test Tables for Examples and Comparative Examples

[0050] As can be seen from Table 2, the overall performance of the embodiments of the present invention is significantly better than that of the comparative examples.

[0051] In terms of static stiffness and hardness, the hardness of Examples 1-3 was higher than that of the comparative example. In particular, Example 2 achieved the ultimate hardness by increasing the amount of PPO and resin, proving that the composite hardening component can significantly improve hardness. Tensile stress is a core indicator of static stiffness. The tensile stress of Examples 1-3 was far greater than that of the comparative example, proving that the "physical + chemical" dual-network stiffening effect is optimal.

[0052] Compared with Example 1, Comparative Example 1 did not add composite hardening components and relied solely on filler reinforcement. As a result, the hardness and tensile stress were significantly reduced, and the static stiffness was insufficient. The heat aging hardness retention rate decreased significantly, the compression set increased significantly, and the high-temperature creep resistance was poor. The dynamic stiffness ratio increased significantly, the fatigue temperature rise increased significantly, the dynamic and static stiffness balance was poor, and the overall performance was far lower than that of Example 1.

[0053] Compared with Example 1, Comparative Example 2 lacks PPO rigid particles and relies solely on phenolic resin for hardening. Its tensile stress is lower than that of Example 1, and its static stiffness improvement is limited. Its compression set is increased, and its dynamic stiffness ratio and fatigue temperature rise are both inferior to those of Example 1, indicating that the lack of a physical rigid phase cannot achieve the optimal high static stiffness effect.

[0054] Compared to Example 1, the PPO powder in Comparative Example 3 was not surface-modified, and its static properties (hardness, 100% tensile stress) were basically the same as those in Example 1, indicating that the lack of modification did not affect the static stiffness of the material. However, the dynamic properties, interfacial bonding, and aging resistance showed a significant decrease: the tear strength was significantly reduced, indicating insufficient interfacial bonding between the rubber and PPO; the dynamic stiffness ratio increased, the fatigue temperature rise increased, the interfacial friction increased, and the dynamic stability deteriorated; the heat aging hardness retention rate and compression set were slightly worse, resulting in reduced long-term reliability. This proves that surface coupling modification of PPO can improve interfacial bonding, dynamic properties, and fatigue life.

[0055] Compared with Example 1, the PPO particle size of Comparative Example 4 is too coarse, which causes stress concentration and uneven dispersion, resulting in a significant decrease in tensile stress, hardness, and tear strength, an increase in dynamic stiffness ratio, an increase in fatigue temperature rise, an increase in compression set, and a significant deterioration in high static stiffness and creep resistance.

[0056] Compared with Example 1, the PPO particles in Comparative Example 5 are too fine and prone to agglomeration, resulting in decreased reinforcement efficiency, reduced tensile stress, hardness, and tear strength, increased dynamic temperature rise, and poorer dynamic and static stiffness balance, thus failing to achieve the comprehensive performance of Example 1.

[0057] Compared with Example 1, Comparative Example 7 uses EPDM with low ethylene and high ENB content. The rubber matrix has insufficient rigidity and heat resistance, significantly reduced hardness and tensile stress, decreased heat aging retention rate, increased compression set, increased dynamic temperature rise, and its static stiffness and aging resistance are inferior to those of Example 1.

[0058] Compared with Example 1, the high-styrene rubber of Comparative Example 8 has too low styrene content, insufficient matrix rigidity, and significantly reduced static stiffness (stress at constant elongation and hardness). Its high-temperature creep resistance, heat aging retention rate, and dynamic stiffness ratio are all significantly worse, making it impossible to achieve the design goal of high static stiffness.

Claims

1. A high static stiffness compound, characterized in that, The raw materials include the following parts by weight: The rubber matrix comprises 55-60 parts of EPDM rubber, 20-25 parts of high-styrene rubber, and 20 parts of chlorinated butyl rubber. The reinforcing component contains 100-110 parts of carbon black and 40 parts of silica. The composite hardening component contains 17.5-21 parts of phenolic resin, 10-15 parts of engineering plastic powder, and 1.2-1.5 parts of curing agent; The additives include 5-6 parts of silane coupling agent, 10-12 parts of plasticizer, 2 parts of stearic acid, 5 parts of zinc oxide, 1.5 parts of sulfur, 3.3 parts of accelerator, and 3.5 parts of antioxidant.

2. The high static stiffness compound according to claim 1, characterized in that, Ethylene propylene diene monomer (EPDM) rubber has an ethylene content >60wt% and an ENB content <3.0wt%; high-styrene rubber is a butadiene-styrene copolymer with a styrene content of 60wt%-70wt%.

3. The high static stiffness compound according to claim 1, characterized in that, The carbon black is one or a blend of two of N550 or N660; the silica is fumed silica with a specific surface area of ​​155-195 m². 2 / g.

4. The high static stiffness compound according to claim 1, characterized in that, The engineering plastic powder is polyphenylene ether with a particle size of 10-30μm; the engineering plastic powder is surface modified with a coupling agent.

5. The high static stiffness compound according to claim 4, characterized in that, When using engineering plastic powder and phenolic resin, the engineering plastic powder and phenolic resin should be pre-dispersed first.

6. The high static stiffness compound according to claim 1, characterized in that, The curing agent is hexamethylenetetramine, the silane coupling agent is silicon 69 or KH550, and the plasticizer is one or both of naphthenic oil or paraffin oil.

7. The high static stiffness compound according to claim 1, characterized in that, The accelerator is a combination of TMTD and MBTS; the antioxidant is a combination of 4020 and RD.

8. A method for preparing a high static stiffness compound according to any one of claims 1-7, characterized in that, Includes the following steps: (1) Add some plasticizer to the engineering plastic powder, and then pre-disperse it with phenolic resin in a high-speed mixer to obtain a paste; (2) Add EPDM rubber, high styrene rubber and chlorinated butyl rubber to internal mixer A, plasticize evenly, then add carbon black, silica, silane coupling agent, zinc oxide, stearic acid, remaining plasticizer and antioxidant, mix to 150-155℃, discharge and cool to obtain a first section of masterbatch. (3) Put the first stage of masterbatch into the internal mixer B, raise the temperature to 110-120℃, add the paste, and mix at 120-130℃ for 3-5 minutes to obtain the second stage of compound. (4) Put the two-stage compound into the internal mixer C, raise the temperature to 90-100℃, add the curing agent, then raise the temperature to 130-140℃ and mix for 2-3 minutes, then add the accelerator and sulfur and mix. After the temperature drops below 100℃, discharge the compound into the open mill, re-mill and sheet it to obtain the final product.

9. The method for preparing high static stiffness compound according to claim 8, characterized in that, In step (1), the mass ratio of engineering plastic powder to plasticizer is 100:(15-30), and the pre-dispersion temperature is 85-100℃.

10. An application of the high static stiffness compound according to any one of claims 1-7, characterized in that, Used to manufacture rail cushioning pads.

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