Toughened phenolic resin foam sealant for deep high-stress environments and its preparation process

Abstract

This invention relates to the field of composite material technology and discloses a toughened phenolic resin foam sealant for deep high-stress environments and its preparation process. The process includes raw material pretreatment, matrix and additive premixing, main mixing, curing agent addition and final mixing, foaming and curing, and post-treatment. By using a toughened phenolic resin matrix composed of silicone-modified phenolic resin and carboxyl-terminated nitrile rubber, the flexibility and heat resistance of the resin system are improved, enabling it to adapt to deformation and maintain structural integrity under deep high-stress environments, thereby enhancing the long-term sealing reliability and durability of the sealant. Through the combined use of physical and chemical foaming agents, they work synergistically during the curing process to form a uniform, fine, and stable closed-cell structure to adapt to complex sealing interfaces, reducing the material's density and water absorption tendency, and improving its sealing stability under high pressure differential environments.

Description

Technical Field

[0001] This invention relates to the field of composite material technology, specifically to a toughened phenolic resin foam sealant for deep high-stress environments and its preparation process. Background Technology

[0002] Phenolic resin is a synthetic resin formed by the condensation polymerization of phenol and formaldehyde under the action of a catalyst. According to engineering properties, it is divided into thermoplastic and thermosetting types. It has the characteristics of resistance to weak acids and alkalis, heat resistance and stable mechanical properties. It is insoluble in water but soluble in organic solvents such as acetone and alcohol.

[0003] Currently, in the field of sealing materials used in deep, high-stress environments, traditional phenolic resin sealants suffer from insufficient flexibility and heat resistance, making it difficult to adapt to deformation under long-term high stress, resulting in a decline in sealing reliability and durability.

[0004] Therefore, a toughened phenolic resin foam sealant for deep high-stress environments and its preparation process are proposed to solve the above problems. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a toughened phenolic resin foam sealant for deep high-stress environments and its preparation process, solving the problem mentioned in the background art that traditional phenolic resin sealants are difficult to adapt to deformation under long-term high stress, leading to a decrease in sealing reliability and durability.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a preparation process for a toughened phenolic resin foam sealant for deep high-stress environments, comprising the following steps: Step 1: Raw material pretreatment. Place the reinforcing filler in an oven at 100-120℃ and dry for 2-4 hours to remove adsorbed water. Disperse the corrosion-resistant filler by mechanical stirring at 300-500r / min for 0.5-1 hours. Step 2: Premix the matrix and additives. Add the toughening phenolic resin matrix, coupling agent and half the weight of reinforcing filler to a high-speed mixer and mix for 20-40 minutes at 60-80℃ and 500-800r / min to obtain the premixed compound. Step 3: Main mixing. Transfer the premixed rubber compound to a planetary mixer, and add the remaining reinforcing filler, flame retardant, corrosion-resistant filler and composite foaming agent in sequence. Mix for 30-60 minutes under vacuum of -0.08 to -0.1 MPa and stirring speed of 100-300 r / min. Step 4: Adding and final mixing of curing agent. Add curing agent to the mixture from Step 3 and mix for 15-30 minutes under vacuum of -0.08 to -0.1 MPa and stirring speed of 50-150 r / min to obtain a uniform sealant paste. Step 5: Foaming and Curing. Inject the sealant paste into the mold and place it in a hot press. First, raise the temperature from room temperature to 80-100℃ at a rate of 2-5℃ / min and hold for 20-40 minutes for pre-foaming. Then, raise the temperature to 140-160℃ at a rate of 3-8℃ / min and hold for 1-3 hours under a pressure of 5-10MPa for curing. Step 6: Post-processing. Remove the molded part along with the mold from the hot press, allow it to cool naturally to below 60°C, then demold it. Place it in an oven at 120-140°C for post-curing treatment for 4-8 hours to obtain toughened phenolic resin foam sealant. In step four, the curing agent needs to be pre-crushed and passed through a 100-200 mesh sieve before being added; the final mixing process is divided into two stages. In the first stage, the mixture is carried out at normal pressure and a speed of 80-120 r / min for 8-15 minutes. In the second stage, the vacuum is drawn to above -0.09 MPa and the mixture is carried out at a speed of 40-80 r / min for 7-15 minutes.

[0007] Preferably, in step one, the drying process is carried out under a nitrogen atmosphere, and the mechanical stirring and dispersion process is carried out in a dispersion vessel equipped with a high-speed shear head, with a shear rate of 1000-2000 r / min.

[0008] Preferably, in step two, the temperature of the inner wall of the mixing chamber of the high-speed mixer is controlled at 65-75°C, and half the weight of the reinforcing filler needs to be pre-wetted manually with the coupling agent in a separate container for 5-10 minutes before being added.

[0009] Preferably, in step three, the order in which the materials are added is as follows: First, add the remaining reinforcing filler and mix for 10-20 minutes. Then, add the flame retardant and corrosion-resistant filler and mix for 10-20 minutes. Finally, slowly and evenly sprinkle the composite foaming agent while stirring and continue mixing for 10-20 minutes. The planetary mixer has a revolution speed of 30-60 r / min and a rotation speed of 60-120 r / min.

[0010] Preferably, in step four, the curing agent needs to be pre-crushed and passed through a 100-200 mesh sieve before being added; The final mixing process is divided into two stages. In the first stage, the mixture is carried out at atmospheric pressure and a speed of 80-120 r / min for 8-15 minutes. In the second stage, the vacuum is evacuated to above -0.09 MPa and the mixture is carried out at a speed of 40-80 r / min for 7-15 minutes.

[0011] Preferably, in step five, a layer of release agent is pre-coated on the inner surface of the mold cavity; the closing pressure of the hot press is controlled at 1-3 MPa during the pre-foaming stage, and is gradually increased to 5-10 MPa during the process of heating to the curing temperature.

[0012] Preferably, in step five, the foaming and curing process is carried out in a multi-layer hot press with programmable temperature and pressure control, and the mold cavity depth is 1.5-2.5 times the design thickness of the final product, so that it has sufficient foaming space.

[0013] Preferably, in step six, the temperature rise procedure for the post-curing treatment is as follows: Increase the temperature from room temperature to 80°C at a rate of 1-2°C / min, hold for 1 hour, and then increase it to 120-140°C at a rate of 0.5-1°C / min.

[0014] Toughened phenolic resin foam sealant for deep, high-stress environments is made from the following raw materials in parts by weight: 100 parts toughening phenolic resin matrix, 5-15 parts composite foaming agent, 8-20 parts curing agent, 20-50 parts reinforcing filler, 1-5 parts coupling agent, 3-10 parts flame retardant, and 5-15 parts corrosion resistant filler.

[0015] Preferably, the toughened phenolic resin matrix is ​​a blend of silicone-modified phenolic resin and carboxyl-terminated nitrile rubber, wherein the mass ratio of silicone-modified phenolic resin to carboxyl-terminated nitrile rubber is 100:10 to 100:30. The composite foaming agent is composed of a physical foaming agent and a chemical foaming agent in a mass ratio of 1:1 to 1:3. The physical foaming agent is microencapsulated azodicarbonamide with a particle size of 10-30 μm, and the chemical foaming agent is a mixture of sodium bicarbonate and citric acid in a mass ratio of 1:0.5 to 1:1. The curing agent is hexamethylenetetramine and benzoxazine resin; The reinforcing filler is a composite of silicon carbide whiskers and aramid pulp, wherein the diameter of the silicon carbide whiskers is 0.2-1.0 μm and the aspect ratio is 20-50, the fiber length of the aramid pulp is 0.5-3 mm, and the mass ratio of the silicon carbide whiskers to the aramid pulp is 1:0.2 to 1:0.8. The coupling agent is a mixture of silane coupling agent KH-550 and titanate coupling agent NDZ-201, with a mass ratio of 1:0.5 to 1:1.5. The flame retardant is a composite of red phosphorus and aluminum hydroxide, wherein the red phosphorus coating rate is 85%-95%, the aluminum hydroxide particle size D50 is 2-5μm, and the mass ratio of the two is 1:2 to 1:4. The corrosion-resistant filler is a mixture of flake mica powder and nano silica. The flake mica powder has a particle size of 300-800 mesh, and the nano silica has a particle size of 20-50 nm. The mass ratio of the two is 1:0.1 to 1:0.3.

[0016] Preferably, the sealant has a compressive strength of 18-25 MPa, a water absorption rate of ≤3%, an oxygen index of ≥32%, and a mass change rate of ≤1.5% after soaking in 10% NaOH and 10% H2SO4 at 25°C for 168 h.

[0017] Compared with the prior art, the present invention provides a toughened phenolic resin foam sealant for deep high-stress environments and its preparation process, which has the following beneficial effects: 1. In this invention, by using a toughened phenolic resin matrix composed of a blend of organosilicon-modified phenolic resin and carboxyl-terminated butadiene-acrylonitrile rubber, the flexibility and heat resistance of the resin system are improved, enabling it to adapt to deformation and maintain structural integrity under deep high-stress environments, thereby enhancing the long-term sealing reliability and durability of the sealant.

[0018] 2. In this invention, physical foaming agents and chemical foaming agents are used in combination and work synergistically during the curing process to form a uniform, dense and stable closed-cell structure. This not only gives the sealant excellent compressible resilience to adapt to complex sealing interfaces, but also reduces the density and water absorption tendency of the material, and improves its sealing stability under high pressure differential environment.

[0019] 3. In this invention, the comprehensive performance of the product is enhanced by adding reinforcing fillers and composite flame retardants. The reinforcing fillers improve the compressive strength and creep resistance. The composite flame retardants synergistically form char and provide heat and oxygen insulation during combustion, giving the sealant good flame retardant properties, thereby meeting the multiple stringent requirements for material mechanical properties, durability and fire safety under deep high stress environment. Detailed Implementation

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0021] Example 1: Preparation process of toughened phenolic resin foam sealant for deep high-stress environments, including the following steps: Step 1: Raw material pretreatment. Place the reinforcing filler in an oven at 100℃ and dry for 2 hours to remove adsorbed water. Disperse the corrosion-resistant filler by mechanical stirring at 300r / min for 0.5 hours. Step 2: Premix the matrix and additives. Add the toughening phenolic resin matrix, coupling agent and half the weight of reinforcing filler to a high-speed mixer and mix for 20 minutes at 60°C and 500 r / min to obtain the premixed compound. Step 3: Main mixing. Transfer the premixed rubber compound to a planetary mixer, and add the remaining reinforcing filler, flame retardant, corrosion-resistant filler and composite foaming agent in sequence. Mix for 30 minutes under vacuum of -0.08MPa and stirring speed of 100r / min. Step 4: Adding and final mixing of curing agent. Add curing agent to the mixture from Step 3 and mix for 15 minutes under vacuum of -0.08MPa and stirring speed of 50r / min to obtain a uniform sealant paste. Step 5: Foaming and curing. Inject the sealant paste into the mold and place it in a hot press. First, raise the temperature from room temperature to 80°C at a rate of 2°C / min and hold for 20 minutes for pre-foaming. Then, raise the temperature to 140°C at a rate of 3°C / min and hold for 1 hour under a pressure of 5MPa for curing. Step 6: Post-processing. Remove the molded part along with the mold from the hot press, let it cool naturally to below 60°C, then demold it. Place it in an oven at 120°C for post-curing treatment for 4 hours to obtain toughened phenolic resin foam sealant. In step four, the curing agent needs to be pre-crushed and passed through a 100-mesh sieve before being added; The final mixing process is divided into two stages. In the first stage, the mixture is carried out at atmospheric pressure and a speed of 80 r / min for 8 minutes. In the second stage, the vacuum is evacuated to above -0.09 MPa and the mixture is carried out at a speed of 40 r / min for 7 minutes.

[0022] In step one, the drying process is carried out under a nitrogen atmosphere, and the mechanical stirring and dispersion process is carried out in a dispersion vessel equipped with a high-speed shear head, with a shear rate of 1000 r / min.

[0023] In step two, the temperature of the inner wall of the mixing chamber of the high-speed mixer is controlled at 65°C, and half the weight of the reinforcing filler needs to be pre-wetted manually with the coupling agent in a separate container for 5 minutes before being added.

[0024] In step three, the order in which the materials are added is as follows: First, add the remaining reinforcing filler and mix for 10 minutes. Then, add the flame retardant and corrosion-resistant filler and mix for 10 minutes. Finally, slowly and evenly sprinkle the composite foaming agent while stirring and continue mixing for 10 minutes. The planetary mixer has an orbital speed of 30 r / min and a rotational speed of 60 r / min.

[0025] In step five, a layer of release agent is pre-coated on the inner surface of the mold cavity; the closing pressure of the hot press is controlled at 1MPa during the pre-foaming stage, and is gradually increased to 5MPa during the process of heating to the curing temperature.

[0026] In step five, the foaming and curing process is carried out in a multi-layer hot press with programmable temperature and pressure control. The mold cavity depth is 1.5 times the design thickness of the final product, so that it has sufficient foaming space.

[0027] In step six, the temperature rise procedure for the post-curing treatment is as follows: The temperature was increased from room temperature to 80°C at a rate of 1°C / min, held for 1 hour, and then increased to 120°C at a rate of 0.5°C / min.

[0028] Toughened phenolic resin foam sealant for deep, high-stress environments is made from the following raw materials in parts by weight: The mixture comprises 100 parts toughening phenolic resin matrix, 5 parts composite foaming agent, 8 parts curing agent, 20 parts reinforcing filler, 1 part coupling agent, 3 parts flame retardant, and 5 parts corrosion-resistant filler.

[0029] The toughened phenolic resin matrix is ​​a blend of silicone-modified phenolic resin and carboxyl-terminated butadiene-acrylonitrile rubber, wherein the mass ratio of silicone-modified phenolic resin to carboxyl-terminated butadiene-acrylonitrile rubber is 100:10. The composite foaming agent is composed of a physical foaming agent and a chemical foaming agent in a mass ratio of 1:1. The physical foaming agent is microencapsulated azodicarbonamide with a particle size of 10μm, and the chemical foaming agent is a mixture of sodium bicarbonate and citric acid in a mass ratio of 1:0.5. The curing agent is hexamethylenetetramine and benzoxazine resin; The reinforcing filler is a composite of silicon carbide whiskers and aramid pulp, wherein the diameter of the silicon carbide whiskers is 0.2 μm and the aspect ratio is 20, the fiber length of the aramid pulp is 0.5 mm, and the mass ratio of silicon carbide whiskers to aramid pulp is 1:0.2. The coupling agent is a mixture of silane coupling agent KH-550 and titanate coupling agent NDZ-201, with a mass ratio of 1:0.5. The flame retardant is a complex of red phosphorus and aluminum hydroxide, wherein the red phosphorus has a coating rate of 85%, the aluminum hydroxide has a particle size D50 of 2μm, and the mass ratio of the two is 1:2. The corrosion-resistant filler is a mixture of flake mica powder and nano silica. The flake mica powder has a particle size of 300 mesh, and the nano silica has a particle size of 20 nm. The mass ratio of the two is 1:0.1.

[0030] The sealant has a compressive strength of 18.5 MPa, a water absorption rate of ≤3%, an oxygen index of ≥32%, and a mass change rate of ≤1.5% after soaking in 10% NaOH and 10% H2SO4 at 25℃ for 168 h.

[0031] Example 2: Preparation process of toughened phenolic resin foam sealant for deep high-stress environments, including the following steps: Step 1: Raw material pretreatment. Place the reinforcing filler in an oven at 110℃ and dry for 3 hours to remove adsorbed water. Disperse the corrosion-resistant filler by mechanical stirring at 400r / min for 0.75 hours. Step 2: Premix the matrix and additives. Add the toughening phenolic resin matrix, coupling agent and half the weight of reinforcing filler to a high-speed mixer and mix for 30 minutes at 70℃ and 650r / min to obtain the premixed compound. Step 3: Main mixing. Transfer the premixed rubber compound to a planetary mixer, and add the remaining reinforcing filler, flame retardant, corrosion-resistant filler and composite foaming agent in sequence. Mix for 45 minutes under vacuum of -0.09MPa and stirring speed of 200r / min. Step 4: Adding and final mixing of curing agent. Add curing agent to the mixture from Step 3 and mix for 22 minutes under vacuum of -0.09 MPa and stirring speed of 100 r / min to obtain a uniform sealant paste. Step 5: Foaming and curing. Inject the sealant paste into the mold and place it in a hot press. First, raise the temperature from room temperature to 90°C at a rate of 3.5°C / min and hold for 30 minutes for pre-foaming. Then, raise the temperature to 150°C at a rate of 5.5°C / min and hold for 2 hours under a pressure of 7.5MPa for curing. Step 6: Post-processing. Remove the molded part along with the mold from the hot press, allow it to cool naturally to below 60°C, then demold it. Place it in an oven at 130°C for post-curing treatment for 6 hours to obtain toughened phenolic resin foam sealant. In step four, the curing agent needs to be pre-crushed and passed through a 150-mesh sieve before being added; the final mixing process is divided into two stages. In the first stage, the mixture is mixed at 100 r / min for 11 minutes under normal pressure. In the second stage, the vacuum is drawn to above -0.09 MPa and the mixture is mixed at 60 r / min for 11 minutes.

[0032] In step one, the drying process is carried out under a nitrogen atmosphere, and the mechanical stirring and dispersion process is carried out in a dispersion vessel equipped with a high-speed shear head, with a shear rate of 1500 r / min.

[0033] In step two, the temperature of the inner wall of the mixing chamber of the high-speed mixer is controlled at 70°C, and half the weight of the reinforcing filler needs to be pre-wetted manually with the coupling agent in a separate container for 7.5 minutes before being added.

[0034] In step three, the order in which the materials are added is as follows: First, add the remaining reinforcing filler and mix for 15 minutes. Then, add the flame retardant and corrosion-resistant filler and mix for 15 minutes. Finally, slowly and evenly sprinkle the composite foaming agent while stirring and continue mixing for 15 minutes. The planetary mixer's revolution speed is 45 r / min and its rotation speed is 90 r / min.

[0035] In step five, a layer of release agent is pre-coated on the inner surface of the mold cavity; the closing pressure of the hot press is controlled at 2MPa during the pre-foaming stage, and is gradually increased to 7.5MPa during the process of heating to the curing temperature.

[0036] In step five, the foaming and curing process is carried out in a multi-layer hot press with programmable temperature and pressure control. The mold cavity depth is 2.0 times the design thickness of the final product, so that it has sufficient foaming space.

[0037] In step six, the temperature rise procedure for the post-curing treatment is as follows: The temperature was increased from room temperature to 80°C at a rate of 1.5°C / min, held for 1 hour, and then increased to 130°C at a rate of 0.75°C / min.

[0038] Toughened phenolic resin foam sealant for deep, high-stress environments is made from the following raw materials in parts by weight: The mixture comprises 100 parts toughening phenolic resin matrix, 10 parts composite foaming agent, 14 parts curing agent, 35 parts reinforcing filler, 3 parts coupling agent, 6 parts flame retardant, and 10 parts corrosion resistant filler.

[0039] The toughened phenolic resin matrix is ​​a blend of silicone-modified phenolic resin and carboxyl-terminated butadiene-acrylonitrile rubber, wherein the mass ratio of silicone-modified phenolic resin to carboxyl-terminated butadiene-acrylonitrile rubber is 100:20. The composite foaming agent is composed of a physical foaming agent and a chemical foaming agent in a mass ratio of 1:2. The physical foaming agent is microencapsulated azodicarbonamide with a particle size of 20μm, and the chemical foaming agent is a mixture of sodium bicarbonate and citric acid in a mass ratio of 1:0.75. The curing agent is hexamethylenetetramine and benzoxazine resin; The reinforcing filler is a composite of silicon carbide whiskers and aramid pulp, wherein the diameter of the silicon carbide whiskers is 0.6 μm and the aspect ratio is 35, the fiber length of the aramid pulp is 0.75 mm, and the mass ratio of silicon carbide whiskers to aramid pulp is 1:0.5. The coupling agent is a mixture of silane coupling agent KH-550 and titanate coupling agent NDZ-201, with a mass ratio of 1:1.0. The flame retardant is a complex of red phosphorus and aluminum hydroxide, wherein the red phosphorus has a coating rate of 90%, the aluminum hydroxide has a particle size D50 of 3.5 μm, and the mass ratio of the two is 1:3. The corrosion-resistant filler is a mixture of flake mica powder and nano silica. The flake mica powder has a particle size of 550 mesh, and the nano silica has a particle size of 35 nm. The mass ratio of the two is 1:0.2.

[0040] The sealant has a compressive strength of 22.7 MPa, a water absorption rate of ≤3%, an oxygen index of ≥32%, and a mass change rate of ≤1.5% after soaking in 10% NaOH and 10% H2SO4 at 25℃ for 168 h.

[0041] Example 3: Preparation process of toughened phenolic resin foam sealant for deep high-stress environments, including the following steps: Step 1: Raw material pretreatment. Place the reinforcing filler in an oven at 120℃ and dry for 4 hours to remove adsorbed water. Disperse the corrosion-resistant filler by mechanical stirring at 500r / min for 1 hour. Step 2: Premix the matrix and additives. Add the toughening phenolic resin matrix, coupling agent and half the weight of reinforcing filler to a high-speed mixer and mix for 40 minutes at 80℃ and 800r / min to obtain the premixed compound. Step 3: Main mixing. Transfer the premixed rubber compound to a planetary mixer, and add the remaining reinforcing filler, flame retardant, corrosion-resistant filler and composite foaming agent in sequence. Mix for 60 minutes under vacuum of -0.1MPa and stirring speed of 300r / min. Step 4: Adding and final mixing of curing agent. Add curing agent to the mixture from Step 3 and mix for 30 minutes under vacuum of -0.1MPa and stirring speed of 150r / min to obtain a uniform sealant paste. Step 5: Foaming and curing. Inject the sealant paste into the mold and place it in a hot press. First, raise the temperature from room temperature to 100°C at a rate of 5°C / min and keep it at that temperature for 40 minutes for pre-foaming. Then, raise the temperature to 160°C at a rate of 8°C / min and keep it at 10MPa for 3 hours for curing. Step 6: Post-processing. Remove the molded part along with the mold from the hot press, allow it to cool naturally to below 60°C, then demold it. Place it in an oven at 140°C for post-curing treatment for 8 hours to obtain toughened phenolic resin foam sealant. In step four, the curing agent needs to be pre-crushed and passed through a 200-mesh sieve before being added; the final mixing process is divided into two stages. In the first stage, the mixture is stirred for 15 minutes at 120 r / min under normal pressure. In the second stage, the vacuum is drawn to above -0.09 MPa and the mixture is stirred for 15 minutes at 80 r / min.

[0042] In step one, the drying process is carried out under a nitrogen atmosphere, and the mechanical stirring and dispersion process is carried out in a dispersion vessel equipped with a high-speed shear head, with a shear rate of 2000 r / min.

[0043] In step two, the temperature of the inner wall of the mixing chamber of the high-speed mixer is controlled at 75°C, and half the weight of the reinforcing filler needs to be pre-wetted manually with the coupling agent in a separate container for 10 minutes before being added.

[0044] In step three, the order in which the materials are added is as follows: First, add the remaining reinforcing filler and mix for 20 minutes. Then, add the flame retardant and corrosion-resistant filler and mix for 20 minutes. Finally, slowly and evenly sprinkle the composite foaming agent while stirring and continue mixing for 20 minutes. The planetary mixer has an orbital speed of 60 r / min and a rotational speed of 120 r / min.

[0045] In step five, a layer of release agent is pre-coated on the inner surface of the mold cavity; the closing pressure of the hot press is controlled at 3MPa during the pre-foaming stage, and is gradually increased to 10MPa during the process of heating to the curing temperature.

[0046] In step five, the foaming and curing process is carried out in a multi-layer hot press with programmable temperature and pressure control. The mold cavity depth is 2.5 times the design thickness of the final product, so that it has sufficient foaming space.

[0047] In step six, the temperature rise procedure for the post-curing treatment is as follows: The temperature was increased from room temperature to 80°C at a rate of 2°C / min, held for 1 hour, and then increased to 140°C at a rate of 1°C / min.

[0048] Toughened phenolic resin foam sealant for deep, high-stress environments is made from the following raw materials in parts by weight: The mixture comprises 100 parts toughening phenolic resin matrix, 15 parts composite foaming agent, 20 parts curing agent, 50 parts reinforcing filler, 5 parts coupling agent, 10 parts flame retardant, and 15 parts corrosion resistant filler.

[0049] The toughened phenolic resin matrix is ​​a blend of silicone-modified phenolic resin and carboxyl-terminated butadiene-acrylonitrile rubber, wherein the mass ratio of silicone-modified phenolic resin to carboxyl-terminated butadiene-acrylonitrile rubber is 100:30. The composite foaming agent is composed of a physical foaming agent and a chemical foaming agent in a mass ratio of 1:3. The physical foaming agent is microencapsulated azodicarbonamide with a particle size of 30μm, and the chemical foaming agent is a mixture of sodium bicarbonate and citric acid in a mass ratio of 1:1. The curing agent is hexamethylenetetramine and benzoxazine resin; The reinforcing filler is a composite of silicon carbide whiskers and aramid pulp, wherein the diameter of the silicon carbide whiskers is 1.0 μm and the aspect ratio is 50, the fiber length of the aramid pulp is 3 mm, and the mass ratio of silicon carbide whiskers to aramid pulp is 1:0.8. The coupling agent is a mixture of silane coupling agent KH-550 and titanate coupling agent NDZ-201, with a mass ratio of 1:1.5. The flame retardant is a composite of red phosphorus and aluminum hydroxide, wherein the red phosphorus has a coating rate of 95%, the aluminum hydroxide has a particle size D50 of 5 μm, and the mass ratio of the two is 1:4. The corrosion-resistant filler is a mixture of flake mica powder and nano silica. The flake mica powder has a particle size of 800 mesh, and the nano silica has a particle size of 50 nm. The mass ratio of the two is 1:0.3.

[0050] The sealant has a compressive strength of 20.3 MPa, a water absorption rate of ≤3%, an oxygen index of ≥32%, and a mass change rate of ≤1.5% after soaking in 10% NaOH and 10% H2SO4 at 25℃ for 168 h.

[0051] Comparative Example 1: The difference between this comparative example and Example 1 is that the blend of silicone-modified phenolic resin and carboxyl-terminated nitrile rubber was not used in this comparative example.

[0052] Comparative Example 2 differs from Example 1 in that no composite foaming agent was added during the preparation process of this comparative example.

[0053] Comparative Example 3 differs from Example 1 in that no composite of silicon carbide whiskers and aramid pulp was added during the preparation process of this comparative example.

[0054] Comparative Example 4 differs from Example 1 in that no composite material of red phosphorus and aluminum hydroxide was added during the preparation process of this comparative example.

[0055] The performance of the toughened phenolic resin foam sealants for deep high-stress environments prepared in Examples 1-3 and Comparative Examples 1-4 was tested. The test items and test methods are as follows: Compression strength test: The test was conducted using a universal testing machine. The sample size was a Φ25mm×25mm cylinder, and the compression rate was 2mm / min.

[0056] Water absorption test: After drying the sample to constant weight in an oven at 50℃, immerse it in distilled water at 25℃ for 24 hours, take it out, blot the surface moisture with filter paper, weigh it, and calculate the percentage increase in mass.

[0057] Oxygen Index Test: In a nitrogen-oxygen mixture, the minimum oxygen concentration required for a sample to burn continuously for 3 minutes over a length of 50 mm is determined.

[0058] Corrosion resistance test: The sample was immersed in 10% NaOH solution and 10% H2SO4 solution, kept at 25°C for 168 hours, then removed, rinsed with deionized water and dried to constant weight. The rate of change of mass was calculated to evaluate the acid and alkali corrosion resistance.

[0059] Quantitative characterization of cell structure and closed-cell rate: The cross-section of the sample was observed using a scanning electron microscope, and the average diameter and distribution of the cells were statistically analyzed using image analysis software; the closed-cell rate was determined using the volume expansion method.

[0060] Density and dimensional stability test: The apparent density of the molded product was determined and the foaming ratio was calculated; after the sample was placed in an 80°C oven for 168 hours, its linear dimensional change rate was measured to evaluate heat shrinkage.

[0061] High-temperature compression creep and stress relaxation test: Simulating a deep high-stress environment, a constant load of 30% of the room temperature compressive strength was applied to the sample in a 120℃ constant temperature chamber for 168 hours, and the creep strain was recorded; after unloading, the sample was allowed to stand for 24 hours, and the residual strain was measured and the rebound rate was calculated.

[0062] Cyclic compression fatigue test: The specimen was subjected to strain-controlled cyclic compression test at room temperature, i.e., strain amplitude 20%, frequency 5Hz, and number of cycles 10. 4 After the test, the sample was left to stand for 1 hour, and its compression permanent deformation rate was measured. Then, its compression strength retention rate was tested again.

[0063] High pressure differential sealing performance verification test: The sealant was molded into an annular gasket of specified size and placed between a pair of standard flat flanges. The initial seal was formed by uniformly tightening the bolts to the specified preload stress of 50MPa. Nitrogen pressure of 5MPa was applied and maintained for 24 hours. The leakage rate of the system was monitored using a leak detector. Subsequently, three thermal cycles from -20℃ to 120℃ were performed, and the leakage rate was tested again.

[0064] The test data of the toughened phenolic resin foam sealants prepared in Examples 1-3 and Comparative Examples 1-4 are recorded in Tables 1-3 below: Table 1: Table 2: Table 3: By comparing and analyzing the data in Tables 1-3, it can be seen that the toughened phenolic resin foam sealant prepared using the processes in Examples 1-3 has superior overall performance compared to the sealant prepared using the processes in Comparative Examples 1-4. This indicates that the present invention, by using a toughened phenolic resin matrix composed of a blend of silicone-modified phenolic resin and carboxyl-terminated nitrile rubber, improves the flexibility and heat resistance of the resin system, enabling it to adapt to deformation and maintain structural integrity under deep high-stress environments, thereby enhancing the long-term sealing reliability and durability of the sealant. Furthermore, the combined use of physical and chemical foaming agents synergistically enhances the sealant's performance during the curing process. The process creates a uniform, fine, and stable closed-cell structure, which not only endows the sealant with excellent compressible resilience to adapt to complex sealing interfaces, but also reduces the material's density and water absorption tendency, improving its sealing stability under high pressure differential environments. By adding reinforcing fillers and composite flame retardants, the overall performance of the product is synergistically enhanced. The reinforcing fillers improve compressive strength and creep resistance; the composite flame retardants synergistically form char and provide heat and oxygen insulation during combustion, giving the sealant good flame retardant properties, thus enabling it to meet the multiple stringent requirements for material mechanical properties, durability, and fire safety under deep high stress environments.

[0065] By comparing and analyzing the relevant data in Tables 1-3, it can be seen that the toughened phenolic resin foam sealant prepared by the preparation process provided by the present invention has low water absorption, excellent flame retardancy and good resistance to media corrosion while maintaining appropriate compressive strength.

[0066] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0067] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A preparation process for toughened phenolic resin foam sealant for deep high-stress environments, characterized in that: Includes the following steps: Step 1: Raw material pretreatment. Place the reinforcing filler in an oven at 100-120℃ and dry for 2-4 hours to remove adsorbed water. Disperse the corrosion-resistant filler by mechanical stirring at 300-500r / min for 0.5-1 hours. Step 2: Premix the matrix and additives. Add the toughening phenolic resin matrix, coupling agent and half the weight of reinforcing filler to a high-speed mixer and mix for 20-40 minutes at 60-80℃ and 500-800r / min to obtain the premixed compound. Step 3: Main mixing. Transfer the premixed rubber compound to a planetary mixer, and add the remaining reinforcing filler, flame retardant, corrosion-resistant filler and composite foaming agent in sequence. Mix for 30-60 minutes under vacuum of -0.08 to -0.1 MPa and stirring speed of 100-300 r / min. Step 4: Adding and final mixing of curing agent. Add curing agent to the mixture from Step 3 and mix for 15-30 minutes under vacuum of -0.08 to -0.1 MPa and stirring speed of 50-150 r / min to obtain a uniform sealant paste. Step 5: Foaming and Curing. Inject the sealant paste into the mold and place it in a hot press. First, raise the temperature from room temperature to 80-100℃ at a rate of 2-5℃ / min and hold for 20-40 minutes for pre-foaming. Then, raise the temperature to 140-160℃ at a rate of 3-8℃ / min and hold for 1-3 hours under a pressure of 5-10MPa for curing. In step five, a layer of release agent is pre-coated on the inner surface of the mold cavity, and the closing pressure of the hot press is controlled at 1-3 MPa during the pre-foaming stage, and is gradually increased to 5-10 MPa during the process of heating to the curing temperature. In step five, the foaming and curing process is carried out in a multi-layer hot press with programmable temperature and pressure control. The mold cavity depth is 1.5-2.5 times the design thickness of the final product, so that it has sufficient foaming space. Step 6: Post-processing. Remove the molded part along with the mold from the hot press, allow it to cool naturally to below 60°C, then demold it. Place it in an oven at 120-140°C for post-curing treatment for 4-8 hours to obtain toughened phenolic resin foam sealant. The toughened phenolic resin foam sealant comprises: 100 parts toughened phenolic resin matrix, 5-15 parts composite foaming agent, 8-20 parts curing agent, 20-50 parts reinforcing filler, 1-5 parts coupling agent, 3-10 parts flame retardant, and 5-15 parts corrosion resistant filler. The toughened phenolic resin matrix is ​​a blend of organosilicon-modified phenolic resin and carboxyl-terminated butadiene-acrylonitrile rubber, wherein the mass ratio of organosilicon-modified phenolic resin to carboxyl-terminated butadiene-acrylonitrile rubber is 100:10 to 100:

30. The composite foaming agent is composed of a physical foaming agent and a chemical foaming agent in a mass ratio of 1:1 to 1:

3. The physical foaming agent is microencapsulated azodicarbonamide with a particle size of 10-30 μm, and the chemical foaming agent is a mixture of sodium bicarbonate and citric acid in a mass ratio of 1:0.5 to 1:

1. The curing agent is hexamethylenetetramine and benzoxazine resin; The reinforcing filler is a composite of silicon carbide whiskers and aramid pulp, wherein the mass ratio of silicon carbide whiskers to aramid pulp is 1:0.2 to 1:0.

8. The flame retardant is a composite material of red phosphorus and aluminum hydroxide coated with the other two in a mass ratio of 1:2 to 1:

4. In step four, the curing agent needs to be pre-crushed and passed through a 100-200 mesh sieve before being added; the final mixing process is divided into two stages. In the first stage, the mixture is carried out at normal pressure and a speed of 80-120 r / min for 8-15 minutes. In the second stage, the vacuum is drawn to above -0.09 MPa and the mixture is carried out at a speed of 40-80 r / min for 7-15 minutes.

2. The preparation process of the toughened phenolic resin foam sealant for deep high-stress environments according to claim 1, characterized in that: In step one, the drying process is carried out under a nitrogen atmosphere, and the mechanical stirring and dispersion process is carried out in a dispersion vessel equipped with a high-speed shear head, with a shear rate of 1000-2000 r / min.

3. The preparation process of the toughened phenolic resin foam sealant for deep high-stress environments according to claim 1, characterized in that: In step two, the temperature of the inner wall of the mixing chamber of the high-speed mixer is controlled at 65-75℃, and half the weight of the reinforcing filler needs to be pre-wetted manually with the coupling agent in a separate container for 5-10 minutes before being added.

4. The preparation process of the toughened phenolic resin foam sealant for deep high-stress environments according to claim 1, characterized in that: In step three, the order in which the materials are added is as follows: First, add the remaining reinforcing filler and mix for 10-20 minutes. Then, add the flame retardant and corrosion-resistant filler and mix for 10-20 minutes. Finally, slowly and evenly sprinkle the composite foaming agent while stirring and continue mixing for 10-20 minutes. The planetary mixer has a revolution speed of 30-60 r / min and a rotation speed of 60-120 r / min.

5. The preparation process of the toughened phenolic resin foam sealant for deep high-stress environments according to claim 1, characterized in that: In step six, the temperature rise procedure for the post-curing treatment is as follows: Increase the temperature from room temperature to 80°C at a rate of 1-2°C / min, hold for 1 hour, and then increase it to 120-140°C at a rate of 0.5-1°C / min.

6. A toughened phenolic resin foam sealant for deep high-stress environments, prepared by the preparation process of the toughened phenolic resin foam sealant for deep high-stress environments according to any one of claims 1-5, characterized in that: Made from the following parts by weight of raw materials: 100 parts toughening phenolic resin matrix, 5-15 parts composite foaming agent, 8-20 parts curing agent, 20-50 parts reinforcing filler, 1-5 parts coupling agent, 3-10 parts flame retardant, and 5-15 parts corrosion resistant filler.

7. The toughened phenolic resin foam sealant for deep high-stress environments according to claim 6, characterized in that: The toughened phenolic resin matrix is ​​a blend of organosilicon-modified phenolic resin and carboxyl-terminated butadiene-acrylonitrile rubber, wherein the mass ratio of organosilicon-modified phenolic resin to carboxyl-terminated butadiene-acrylonitrile rubber is 100:10 to 100:

30. The composite foaming agent is composed of a physical foaming agent and a chemical foaming agent in a mass ratio of 1:1 to 1:

3. The physical foaming agent is microencapsulated azodicarbonamide with a particle size of 10-30 μm, and the chemical foaming agent is a mixture of sodium bicarbonate and citric acid in a mass ratio of 1:0.5 to 1:

1. The curing agent is hexamethylenetetramine and benzoxazine resin; The reinforcing filler is a composite of silicon carbide whiskers and aramid pulp, wherein the diameter of the silicon carbide whiskers is 0.2-1.0 μm and the aspect ratio is 20-50, the fiber length of the aramid pulp is 0.5-3 mm, and the mass ratio of the silicon carbide whiskers to the aramid pulp is 1:0.2 to 1:0.

8. The coupling agent is a mixture of silane coupling agent KH-550 and titanate coupling agent NDZ-201, with a mass ratio of 1:0.5 to 1:1.

5. The flame retardant is a composite of red phosphorus and aluminum hydroxide, wherein the red phosphorus coating rate is 85%-95%, the aluminum hydroxide particle size D50 is 2-5μm, and the mass ratio of the two is 1:2 to 1:

4. The corrosion-resistant filler is a mixture of flake mica powder and nano silica. The flake mica powder has a particle size of 300-800 mesh, and the nano silica has a particle size of 20-50 nm. The mass ratio of the two is 1:0.1 to 1:0.

3.

8. The toughened phenolic resin foam sealant for deep high-stress environments according to claim 6, characterized in that: The sealant has a compressive strength of 18-25 MPa, a water absorption rate of ≤3%, an oxygen index of ≥32%, and a mass change rate of ≤1.5% after soaking in 10% NaOH and 10% H2SO4 at 25°C for 168 h.

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