Preparation method and application of environment-friendly high-temperature-resistant hard rubber

Abstract

The invention discloses a preparation method of environment-friendly high-temperature-resistant hard rubber, which comprises the following steps: by taking natural rubber as a substrate, adding carbon black, white carbon black and barium sulfate for reinforcement, plasticizing by using naphthenic oil, adding a peroxide vulcanizing agent, a co-crosslinking agent, an activating agent, a silane coupling agent, a macromolecular resin modifier and an anti-aging agent for mixing, and performing high-temperature vulcanization molding, thereby obtaining the environment-friendly high-temperature-resistant hard rubber. The high-temperature-resistant hard rubber is prepared. Natural rubber is adopted as a matrix, and a peroxide vulcanization system and the co-crosslinking agent are synergistically modified, so that the rubber material has high hardness, high strength, excellent thermal aging stability and low compression set, and has wide application value in the industrial field; and the composite material is particularly suitable for the fields of steel pipeline liners, high-temperature-resistant die and clamp gaskets, medium-high-temperature environment sealing elements and the like of industrial fluid transmission systems which need structural support, compression resistance, bearing resistance, small temperature-resistant deformation and reliable sealing.

Description

Technical Field

[0001] This invention relates to the field of polymer materials, specifically to a method for preparing and applying an environmentally friendly high-temperature resistant rigid adhesive. Background Technology

[0002] As the power density of electric motors in new energy vehicles continues to increase, the working environment of their suspension systems and battery pack buffer structures is becoming increasingly harsh. Actual measurement data shows that the local temperature inside the battery compartment can reach over 150℃, accompanied by frequent thermal cycling and mechanical vibration. Traditional rubber damping components are prone to aging, cracking, and rebound failure under such combined stress, directly affecting the safety and service life of the entire vehicle. Similarly, in the application of high-speed railway bridge bearings, materials are required not only to have high load-bearing capacity but also to maintain dimensional stability under temperature variations ranging from -40℃ to +80℃ to avoid cumulative structural displacement caused by thermal expansion and contraction. Currently, the elastomers used for high-temperature structural components mainly include silicone rubber (VMQ), fluororubber (FKM), and polyurethane (PU). Among them, silicone rubber has excellent temperature resistance (up to 200–250℃), but its hardness is difficult to exceed 70A and its mechanical strength is low (tensile strength <10 MPa), making it unsuitable for load-bearing structures; fluororubber is expensive (≥200,000 yuan / ton) and difficult to process, so it is mainly used in extreme corrosive environments; polyurethane generally has problems such as poor heat resistance (Tg <100℃) and easy hydrolysis.

[0003] In contrast, modified rigid rubber based on natural rubber offers advantages such as low raw material cost, mature processing, and excellent mechanical properties. However, its heat resistance has long been limited by the stability of the crosslinking system. Currently, natural rubber-based rigid rubber is widely used in vibration damping and sealing applications, but its heat resistance is generally below 120℃, mainly due to the thermal instability of polysulfide bonds in the sulfur vulcanization system. These bonds break and rearrange at temperatures above 100℃, leading to degradation of the crosslinking network, manifested as decreased tensile strength and increased compression set. Especially under dynamic loads or long-term static pressure conditions, the material is prone to creep relaxation, severely affecting sealing reliability and structural support capacity, making it difficult to simultaneously meet the comprehensive requirements of high modulus, low creep, and wide temperature range adaptability. Therefore, there is an urgent need to develop a novel rigid rubber composition and its controllable preparation method that can maintain the processing advantages of natural rubber while possessing excellent high-temperature resistance, high hardness, and good stability.

[0004] The macroscopic properties of rubber materials essentially depend on the structural characteristics of their three-dimensional cross-linked network. Traditional sulfur vulcanization mainly forms flexible, long polysulfide bonds, which, while imparting a certain degree of dynamic flexibility, suffer from poor thermodynamic stability and are prone to β-fracture at high temperatures. In contrast, peroxide-induced C–C cross-links have higher bond dissociation energies (~370 kJ / mol), significantly improving the network's heat resistance threshold. However, relying solely on peroxide vulcanization often leads to increased material brittleness. To address this, the introduction of functional co-crosslinking agents (such as TAIC) can construct rigid bridging structures between crosslinking points, increasing crosslinking density and enhancing segment rigidity through the aromaticity of isocyanurate rings, thus achieving a synergistic optimization of "high strength + moderate toughness." Simultaneously, by regulating the filler-rubber interface interaction through silane coupling agents, stress can be effectively transferred, and microcrack propagation can be suppressed. Furthermore, while adding large amounts of fillers (such as carbon black and barium sulfate) to increase modulus can improve hardness, it often causes processing difficulties, uneven dispersion, and stress concentration, ultimately reducing tear strength and fatigue life. Therefore, maintaining good mechanical integrity while achieving high hardness has become a key technical challenge restricting the development of high-performance hard rubber. In the preparation of highly filled hard rubber, excessively high filler content often leads to a sharp increase in rubber viscosity, causing excessive load on the internal mixer, poor heat dissipation, and even premature scorching. Furthermore, if the coupling agent (such as Si-69) is not added within the appropriate temperature window, it will be difficult to complete the condensation reaction with the surface of silica, resulting in a significant reduction in the reinforcing effect.

[0005] Therefore, developing a preparation process that combines good processing rheology, controllable vulcanization behavior, and high repeatability is key to achieving large-scale production of high-quality hard rubber. Summary of the Invention

[0006] To achieve the above technical objectives, this invention provides a method for preparing an environmentally friendly high-temperature resistant rigid adhesive, comprising the following preparation steps: (1) Natural rubber, reinforcing filler, hardening filler and silane coupling agent are put into a mixer in a predetermined weight ratio and mixed at 140-150℃ for 3-5 minutes. The mixture is then discharged and cooled to obtain masterbatch. (2) Transfer the masterbatch to the open mill, heat it to above 70°C, add plasticizer and mix, continue to heat it to no more than 100°C, then cool it to 60°C, add peroxide vulcanizing agent, co-crosslinking agent, vulcanization accelerator, activator, polymer resin modifier and antioxidant, mix evenly and then pass through the thin sheet 3-7 times to obtain the compound; (3) Let the compounded rubber stand for more than 4 hours, cut it into pieces, place it in a preheated mold, and mold it into a raw rubber sheet with a thickness of 3 mm. Then, vulcanize it at 150-180℃ for 30-60 minutes to obtain the hard rubber.

[0007] Furthermore, the vulcanization temperature is 160℃ and the vulcanization time is 60 min.

[0008] Furthermore, based on 100 parts by weight of natural rubber, the amounts of each component are as follows: 60-90 parts of reinforcing filler, 10-30 parts of hardening filler, 1-3 parts of silane coupling agent, 5-15 parts of plasticizer, 3-6 parts of peroxide vulcanizing agent, 1-4 parts of co-crosslinking agent, 0.5-3 parts of vulcanization accelerator, 1-3 parts of activator, 1-3 parts of antioxidant, and 5-15 parts of polymer resin modifier.

[0009] Further, the product is characterized by the following proportions of each component, based on 100 parts by weight of natural rubber: 80 parts of reinforcing filler, 20 parts of hardening filler, 6 parts of plasticizer, 6 parts of peroxide vulcanizing agent, 3 parts of co-crosslinking agent, 1 part of vulcanization accelerator, 2 parts of activator, 1 part of silane coupling agent, 1 part of antioxidant, and 6 parts of polymer resin modifier.

[0010] Furthermore, the reinforcing filler is at least one of carbon black or silica; the hardening filler is barium sulfate; and the plasticizer is naphthenic oil.

[0011] Further, the peroxide vulcanizing agent is one of DCP, BIPB, or DBPH; the co-crosslinking agent is TAIC or TMPTMA; the vulcanization accelerator is diphenylguanidine DPG; the activator is active magnesium oxide or active zinc oxide; the silane coupling agent is one of sulfur-containing silanes; and the antioxidant is IPPD or RD.

[0012] Furthermore, the peroxide vulcanizing agent is DCP; the co-crosslinking agent is TAIC; the vulcanization accelerator is DPG; the activator is activated magnesium oxide; the silane coupling agent is Si-69; and the antioxidant is RD.

[0013] Furthermore, the polymer resin modifier is one or more of petroleum resin, phenolic resin, engineering resin, or bio-based resin.

[0014] Furthermore, the polymer resin modifier is one or more of the following: C5 petroleum resin, C9 petroleum resin, DCPD petroleum resin, linear alkylphenol resin, nitrile-modified phenolic resin, methyl phenolic resin, polyimide, benzoxazine resin, epoxy resin powder, hydrogenated rosin glycerol ester, lignin derivative, or vegetable oil-based polymer.

[0015] Furthermore, the polymer resin modifier is one or more of polyimide resin, C9 petroleum resin, or linear alkylphenol resin SP-1068.

[0016] The environmentally friendly high-temperature resistant rigid rubber prepared by the above method has a Shore hardness ≥85D, tensile strength ≥18 MPa, and heat distortion temperature ≥150℃ after vulcanization.

[0017] The rigid adhesive provided by this invention has high hardness and rigidity, excellent high temperature resistance and good mechanical retention rate, and can be used in the fields of steel pipe lining in industrial fluid transmission systems, high temperature mold and fixture gaskets, and sealing components in medium and high temperature environments.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) High-filler reinforcement system: By introducing reinforcing and hardening fillers (carbon black + silica + barium sulfate) and polymer resin modifiers (such as C9 petroleum resin and phenolic resin), the crosslinking density and modulus are effectively improved. The resulting product has a Shore hardness of ≥85D, which is higher than that of ordinary rubber materials. It is suitable for components such as seals and gaskets that require high structural strength.

[0019] (2) Excellent mechanical strength and high temperature resistance: Si-69 coupling agent achieves excellent mechanical strength and prevents debonding failure at high temperature. Peroxide vulcanizing agent plus co-crosslinking agent constructs a stable C-C crosslinking network with high thermal decomposition temperature. Combined with heat-resistant resin (such as phenolic resin, benzoxazine, polyimide) and active magnesium oxide and other stabilizing agents, it significantly improves thermal aging stability and is suitable for vibration damping components in vibration environment.

[0020] (3) The “two-stage” mixing process is adopted: the filler and coupling agent are first dispersed efficiently in the internal mixer, and then sensitive additives are added in the low-temperature section of the open mill to avoid the risk of scorching, ensure the uniform distribution of the vulcanization system, and make the process highly controllable and suitable for industrial continuous production.

[0021] (4) The hard rubber composition provided by the present invention is free of halogens, heavy metal catalysts and toxic aromatic amines in the whole formula. It uses environmentally friendly plasticizers (naphthenic oil replaces aromatic oil) and low VOC release additives. Through scientific formula design and optimized process control, it achieves the three major goals of detoxification, high performance and industrialization. It has broad market prospects and industrialization value in the application of natural rubber-based materials in medium and high temperature structures. Detailed Implementation

[0022] 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.

[0023] The rubber performance testing method used in this invention is as follows: 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.

[0024] 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.

[0025] Tensile strength: Measured according to GB / T528-2009 Determination of tensile stress-strain properties of vulcanized rubber or thermoplastic rubber.

[0026] Hot air aging performance: The test was conducted according to GB / T 3512-2014 "Accelerated aging and heat resistance test of vulcanized rubber or thermoplastic rubber in hot air". The sample was placed in a 150℃ forced air aging chamber and heated for 72 hours. After being taken out, it was left to stand under standard conditions for 24 hours, and then its tensile properties were measured. The tensile strength retention rate was not less than 80%, which indicates that the material has excellent heat aging stability.

[0027] Example 1 The rigid adhesive provided in this example is prepared according to the following steps: (1) In a 2 L internal mixer, add 100 parts by weight of natural rubber and plasticize for 1 min. Then add 50 parts of carbon black N330, 30 parts of silica, 20 parts of barium sulfate and 1 part of Si-69 in batches. Heat to 145℃ and mix for 4 min to obtain masterbatch. (2) The masterbatch is transferred to a two-roll mill and heated to above 70°C. 6 parts naphthenic oil are added and mixed. The temperature is then raised to no more than 100°C and cooled to 60°C. 6 parts DCP, 3 parts TAIC, 1 part diphenylguanidine, 2 parts magnesium oxide, 4 parts C9 petroleum resin, 2 parts SP-1068 and 1 part antioxidant RD are added and mixed evenly. After thin-pass treatment 5 times, the mixed rubber is sheeted out. (3) Let the compounded rubber stand for more than 4 hours, cut it into pieces, place it in a preheated mold, and mold it into a raw rubber sheet with a thickness of 3 mm. Then, vulcanize it at 160°C for 60 minutes to obtain the hard rubber.

[0028] 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. 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.

[0029] 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 peroxide vulcanization and vulcanization accelerator, silane coupling agent, and polymer resin modifier 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 entire vulcanization network. Subsequent introduction of components that alter rheology and interfaces (such as Si-69) can reduce interference from these "post-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 under high humidity conditions before dehumidification. When the vulcanization accelerator is added first, it quickly complexes with the already dispersed activator to form an active vulcanization intermediate, shortening the dispersion of vulcanization time. This 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.

[0030] 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.

[0031] 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 polymer modified 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.

[0032] After performance testing, the hard plastic prepared in this embodiment has a hardness of 88D, a tensile strength of 14.6 MPa, an elongation at break of 120%, a heat distortion temperature (HDT, 0.45 MPa) of 158℃, and a tensile retention rate of 88% after hot air aging (150℃×72h).

[0033] Comparative Example 1: The vulcanization system consisting of 6 parts DCP and 3 parts TAIC was replaced with 9 parts sulfur. Other experimental conditions and processes were the same as in Example 1. The test results showed that although the initial strength was similar, the tensile retention rate was only 65% ​​after aging at 150°C, and slight cross-linking network degradation occurred, indicating that the peroxide system is more suitable for high-temperature applications.

[0034] Comparative Example 2: No polymer resin modifier was added. Other experimental conditions and processes were the same as in Example 1. The test results showed that the hardness decreased to 82 D and the heat distortion temperature decreased to 142℃, indicating that the resin modifier made a significant contribution to improving hardness and heat resistance.

[0035] As can be seen from the above examples and comparative analyses, this invention significantly improves the hardness, modulus, and thermal dimensional stability of rubber materials by rationally selecting reinforcing fillers, hardening fillers, and polymer resin modifiers, combined with a peroxide vulcanization system. By optimizing the mixing and vulcanization process, early crosslinking is avoided, ensuring uniform dispersion of each component, and obtaining high-quality products with stable performance and good appearance, a new type of hard rubber material with high hardness, high temperature resistance, and environmental safety has been successfully prepared. Its comprehensive performance is significantly better than that of traditional formulations, and it has good prospects for industrial application.

[0036] Although the above embodiments have described the present invention and its implementation in detail, it should be noted that for those skilled in the art, any changes, modifications, substitutions, combinations, simplifications, etc., made to the corresponding conditions without departing from the technical principles of the present invention should be considered as equivalent substitutions, and these improvements should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing an environmentally friendly high-temperature resistant rigid adhesive, characterized in that, The preparation steps include the following: (1) Natural rubber, reinforcing filler, hardening filler and silane coupling agent are put into a mixer in a predetermined weight ratio and mixed at 140-150℃ for 3-5 minutes. The mixture is then discharged and cooled to obtain masterbatch. (2) Transfer the masterbatch to the open mill, heat it to above 70°C, add plasticizer and mix, continue to heat it to no more than 100°C, then cool it to 60°C, add peroxide vulcanizing agent, co-crosslinking agent, vulcanization accelerator, activator, polymer resin modifier and antioxidant, mix evenly and then pass through the thin sheet 3-7 times to obtain the compound; (3) Let the compounded rubber stand for more than 4 hours, cut it into pieces, place it in a preheated mold, and mold it into a raw rubber sheet with a thickness of 3 mm. Then, vulcanize it at 150-180℃ for 30-60 minutes to obtain the hard rubber.

2. The method for preparing rigid adhesive according to claim 1, characterized in that, Based on 100 parts by weight of natural rubber, the amounts of each component are as follows: 60-90 parts reinforcing filler, 10-30 parts hardening filler, 1-3 parts silane coupling agent, 5-15 parts plasticizer, 3-6 parts peroxide vulcanizing agent, 1-4 parts co-crosslinking agent, 0.5-3 parts vulcanization accelerator, 1-3 parts activator, 1-3 parts antioxidant, and 5-15 parts polymer resin modifier.

3. The method for preparing rigid adhesive according to claim 1, characterized in that, Based on 100 parts by weight of natural rubber, the amounts of each component are as follows: 80 parts reinforcing filler, 20 parts hardening filler, 6 parts plasticizer, 6 parts peroxide vulcanizing agent, 3 parts co-crosslinking agent, 1 part vulcanization accelerator, 2 parts activator, 1 part silane coupling agent, 1 part antioxidant, and 6 parts polymer resin modifier.

4. The method for preparing rigid adhesive according to claim 1, characterized in that, The reinforcing filler is at least one of carbon black or silica; the hardening filler is barium sulfate; and the plasticizer is naphthenic oil.

5. The method for preparing rigid adhesive according to claim 1, characterized in that, The peroxide vulcanizing agent is one of dicumyl peroxide (DCP), bis(tert-butylperoxy)dibenzyl ether (BIPB), or 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane (DBPH); the co-crosslinking agent is one of triallyl isocyanurate (TAIC) or trimethylolpropane trimethacrylate (TMPTMA); the vulcanization accelerator is diphenylguanidine (DPG); the activator is active magnesium oxide or active zinc oxide; the silane coupling agent is one of sulfur-containing silanes; and the antioxidant is N-isopropyl-N′-phenyl-p-phenylenediamine (IPPD) or 2,2,4-trimethyl-1,2-dihydroquinoline polymer (RD).

6. The method for preparing rigid adhesive according to claim 1, characterized in that, The peroxide vulcanizing agent is DCP; the co-crosslinking agent is TAIC; the vulcanization accelerator is DPG; the activator is active magnesium oxide; the silane coupling agent is Si-69; and the antioxidant is RD.

7. The method for preparing rigid adhesive according to claim 1, characterized in that, The polymer resin modifier is one or more of petroleum resin, phenolic resin, engineering resin, or bio-based resin.

8. The method for preparing rigid adhesive according to claim 1, characterized in that, The polymer resin modifier is one or more of polyimide resin, C9 petroleum resin, or linear alkylphenol resin SP-1068.

9. An environmentally friendly, high-temperature resistant rigid adhesive, characterized in that, The rigid rubber prepared according to the method described in claims 1-8 has a Shore hardness ≥85D, a tensile strength ≥18 MPa, and a heat distortion temperature ≥150℃ after vulcanization.

10. The method according to claims 1-9, characterized in that, The rigid adhesive can be used in the lining of steel pipes in industrial fluid transmission systems, gaskets for high-temperature molds and fixtures, and sealing components for medium and high-temperature environments.