A micro-porous silica gel material based on supercritical foaming and a preparation method thereof

Abstract

The application discloses a kind of microporous silica gel materials based on supercritical foaming and preparation method thereof, microporous silica gel material includes the following raw materials by weight parts, silicone rubber 100 parts, active zinc oxide 1~3 parts, modified nano-silica 20~40 parts, vulcanizing agent 2~4 parts, vulcanization accelerator 2~4 parts;The modifier of modified nano-silica is cage polysilsesquioxane containing silicon hydroxyl structure, microporous silica gel material is prepared by the steps of premixing-re-mixing-pre-vulcanization-supercritical foaming-re-vulcanization setting-irradiation sterilization, the tensile strength of microporous silica gel material can reach 5.8~6.9MPa, after foaming, pore shape is uniform, bubble hole is not broken, average pore size is between 50~60 microns, mechanical property is strong, flame-retardant grade reaches V-1 above, after high-energy electron beam irradiation of microporous silica gel material, material is not seen abnormal change.

Description

Technical Field

[0001] This invention relates to the field of microporous silica gel material production technology, and in particular to a microporous silica gel material based on supercritical foaming and its preparation method. Background Technology

[0002] Supercritical foamed microporous silicone materials possess excellent thermal insulation properties due to their porous structure. However, compared to solid materials, microporous materials exhibit lower mechanical strength. To improve the mechanical strength of microporous silicone materials, a certain amount of reinforcing filler, such as silica (including fumed silica or precipitated silica), is added. However, excessive silica filler content significantly increases the processing difficulty of the compound. Moreover, reinforcing fillers are prone to agglomeration during processing. Agglomeration and uneven dispersion of reinforcing fillers within the material result in poor cell quality during silicone foaming, such as excessively large cell size differences, uneven cell size, and obvious cell merging. These cell defects, including excessively large cell size differences and uneven cell size, can lead to uneven stress distribution among the cells during use, causing stress concentration and reducing the mechanical properties of the microporous silicone material.

[0003] Therefore, in the preparation and production process of supercritical foamed microporous silicone materials, how to prevent the agglomeration of reinforcing fillers inside the material, improve the uniformity of the cells, and avoid excessive differences in cell size has become a challenge in improving the mechanical properties of supercritical foamed microporous silicone materials. Summary of the Invention

[0004] Based on the shortcomings of the existing technology, the present invention aims to provide a microporous silicone material based on supercritical foaming and its preparation method. By improving the reinforcing filler, the problem of agglomeration of the reinforcing filler in silicone rubber is solved, the uniform cell structure of the silicone foam material after supercritical foaming is obtained, and the mechanical properties of the microporous silicone material are improved.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0006] A microporous silicone material based on supercritical foaming, comprising the following raw materials by weight: 100 parts silicone rubber, 20-40 parts modified nano silica, 1-3 parts active zinc oxide, 2-4 parts vulcanizing agent, and 2-4 parts vulcanization accelerator.

[0007] The activated zinc oxide is obtained by activating zinc oxide powder, and the activation steps are as follows:

[0008] Take 100 parts of zinc oxide powder and use an air jet mill to perform air jet milling treatment on the zinc oxide powder. After air jet milling, zinc oxide powder with a particle size of 1-5 micrometers is obtained. Add 10 parts of a pre-prepared mixture of acetic acid and ethanol to the zinc oxide powder and disperse it in a ball mill for 2-4 hours at a speed of 20-50 rpm to obtain a mixed zinc oxide slurry. Place the above zinc oxide slurry in a high-pressure steam pot, introduce high-pressure steam, and cook it in a sealed, tumbling manner for 4-8 hours. Then, depressurize the high-pressure steam pot and simultaneously introduce steam and nitrogen at a volume ratio of 1:1 to heat and purge the zinc oxide slurry for 1-2 hours to remove ethanol and residual acetic acid from the zinc oxide slurry. Place the zinc oxide slurry after removing ethanol and residual acetic acid in a muffle furnace and calcine it at 300-400℃ for 2-4 hours to obtain calcined zinc oxide powder. Cool it naturally in the muffle furnace and sieve it through a 1500-2500 mesh nylon screen to obtain active zinc oxide.

[0009] The modified nano-silica is prepared through the following steps:

[0010] S1: Dry the silica in a vacuum oven at 100~150°C to constant weight. Mix the dried silica with dehydrated toluene in a mass ratio of 1:(5~10) to obtain the first mixture.

[0011] S2: Under nitrogen protection, a modifier containing a cage-like polysilsesquioxane with a silanol structure is added to the first mixture. The amount of modifier is 5-10 wt% of the amount of silica. The mixture is ultrasonically vibrated at a temperature of 30-40°C. After mixing, 0.5-2 wt% of catalyst is added based on the weight of silica. The system is heated to 90-110°C and refluxed at this temperature for 5-12 hours. After the reaction is completed, the suspension is filtered to obtain filtered silica.

[0012] S3: Filtered silica is washed 3-4 times with anhydrous ethanol to remove toluene solvent and catalyst, and then vacuum dried at 80-90℃ to constant weight to obtain dried silica.

[0013] S4: After being ground, dried silica is sieved through a 1000-2500 mesh nylon sieve to obtain modified nano silica;

[0014] The silicone rubber is one of methyl vinyl silicone rubber and phenyl silicone rubber;

[0015] In step S1, the silica is fumed silica with a particle size of 20-50 nm and a specific surface area of ​​200-300 m² / g.

[0016] In step S2, the modifier is one of trisilyl phenyl cage polysilsesquioxane or trisilyl isooctyl cage polysilsesquioxane.

[0017] Furthermore, in the step of activating zinc oxide, the air pressure of the air jet mill is 0.4~0.6MPa.

[0018] Furthermore, in the step of activating zinc oxide, the mixture of acetic acid and ethanol is prepared at a weight ratio of 1:(10~20).

[0019] Furthermore, in the step of activating zinc oxide, the internal pressure of the high-pressure steam pot is 1.5~2.5MPa, and the high-pressure steam pot is kept at a temperature of 110~130℃ after heating.

[0020] Further, in step S1, the dehydrated toluene is prepared by the following method: molecular sieves are placed in toluene solvent, and ultrasonic vibration is performed on the solvent at a temperature of 30~40℃ for 1~2 hours. After mixing, the mixture is filtered to obtain dehydrated toluene with a water content of 100~200ppm.

[0021] Further, in step S2, the catalyst is one or both of triethylamine or dibutyltin dilaurate.

[0022] Furthermore, the vulcanizing agent is one or more of dicumyl peroxide, benzoyl peroxide, and tert-butyl peroxide.

[0023] Furthermore, the vulcanization accelerator is one or more of dicyclohexylsulfenamide, diphenylguanidine, 2-mercaptophenylprophiazole, or cadmium carbamate.

[0024] This invention provides a method for preparing microporous silica materials based on supercritical foaming, comprising the following steps:

[0025] Step 1, premixing: Take 100 parts of silicone rubber and 20-40 parts of modified nano silica according to the ratio, mix them in a mixer for 20-40 minutes to obtain a mixture, and let the mixture stand at room temperature for 3-5 days;

[0026] Step 2, remixing: Add 2-4 parts of vulcanizing agent, 1-3 parts of active zinc oxide, and 2-4 parts of vulcanization accelerator to the mixture according to the formula. Mix in an internal mixer for 15-30 minutes, then start vacuuming. During the vacuuming process, continue mixing for 15-30 minutes, and control the internal pressure below 1000Pa. After maintaining this for 2-4 hours, discharge the material to obtain the remixed material. Let the remixed material stand at 4-10℃ for 1-2 days before preparing it for use.

[0027] Step 3, pre-vulcanization: The mixed materials are injected into the mold using a rubber injection molding machine. The mold temperature is raised to 110~125℃, and the pressure inside the mold is increased to 8~16MPa. The vulcanization time is 120~250s. Then, the mold is depressurized to normal pressure and cooled rapidly to obtain a pre-vulcanized product with a fixed shape and a preliminary cross-linked three-dimensional structure.

[0028] Step 4, supercritical foaming: supercritical fluid is introduced into the mold, and the mold is heated to 80~110℃ and pressure 15~30MPa for 20~60min. The pressure inside the mold is rapidly reduced to atmospheric pressure within 1~2s. The pressure reduction rate is such that the expansion of saturated gas is triggered, resulting in a vulcanized product with a uniform and stable internal cell structure.

[0029] Step 5, Re-curing and Shaping: Rapidly raise the mold temperature to 135~150℃ to completely vulcanize the foamed silicone. During the re-curing process, continuously evacuate the mold to maintain a low vacuum of 0.03~0.05MPa inside the mold. The curing time is 30~60min to obtain microporous silicone material.

[0030] Step 6, Irradiation sterilization: The prepared microporous silica material is sterilized by high-energy electron beam irradiation under nitrogen protection. The high-energy electron beam irradiation dose is controlled at 15~20 kGy and the irradiation time is 3~6s to obtain sterilized microporous silica material.

[0031] Furthermore, in step four, the supercritical fluid is a mixture of carbon dioxide and nitrogen, with a volume ratio of nitrogen to carbon dioxide of 1:4.

[0032] The present invention has the following beneficial effects:

[0033] This invention utilizes supercritical silica foaming to produce microporous silica materials. Leveraging the superior properties of silica, it achieves the lightweight and thermal insulation requirements of microporous silica materials. In traditional foaming processes, the instability of the silica matrix-bubble interface often leads to uneven cell size distribution and cell collapse. However, by introducing modified nano-silica, interfacial tension is reduced and heterogeneous nucleation sites are provided, significantly optimizing the foam structure. The modified nano-silica is modified by grafting cage-like polysilsesquioxanes containing silanol groups onto the surface of silica. This achieves carbon dioxide-philic group modification of nano-silica with cage-like polysilsesquioxanes, enhancing its dispersibility and interfacial compatibility in the silica matrix, thereby promoting the formation of uniform cell structures, inhibiting cell merging, and improving... The introduction of the cage-like structure of the polysilsesquioxane further improves the mechanical properties of silicone, ensuring the stability of the silicone pores during foaming. This results in microporous silicone materials with high mechanical strength, excellent thermal stability, and superior flame retardancy. Simultaneously, the introduction of activated zinc oxide fills the cavities within the cage-like structure of the polysilsesquioxane, further anchoring the cage-like structure and improving its stability. This addresses the issue of insufficient hardness in microporous silicone materials after the introduction of the cage-like structure, thus synergistically improving the mechanical strength of the material. Furthermore, activated zinc oxide further enhances the high-temperature resistance and UV resistance of the microporous silicone material.

[0034] This invention relates to a microporous silicone material. During the mixing process, no small-molecule structure control agents such as hydroxyl silicone oil are added, thus avoiding the generation of volatile small molecules during the mixing process. As a result, the internal structure of the silicone material avoids problems such as uneven cell structure or even cell structure rupture caused by the diffusion and migration of residual volatile small molecules during the foaming process, which is common in traditional silicone foaming processes.

[0035] This invention uses supercritical fluid as a physical foaming agent to avoid the residue problem of traditional chemical foaming agents, thus improving the safety performance of microporous silicone materials. Attached Figure Description

[0036] Figure 1 This is a SEM schematic diagram of the internal cross-section of the microporous silicone material in Embodiment 1 of the present invention.

[0037] Figure 2 This is a schematic SEM image of the internal cross-section of the microporous silicone material in Embodiment 2 of the present invention.

[0038] Figure 3 This is a SEM image of the internal cross-section of the microporous silicone material in Comparative Example 1 of the present invention.

[0039] Figure 4 This is a SEM image of the internal cross-section of the microporous silicone material in Comparative Example 2 of the present invention.

[0040] Figure 5 This is a SEM image of the internal cross-section of the microporous silicone material in Comparative Example 3 of the present invention.

[0041] Figure 6 This is a SEM image of the internal cross-section of the microporous silicone material in Comparative Example 4 of this invention. Detailed Implementation

[0042] The present invention will be further described in detail below with reference to embodiments. It should also be understood that the following embodiments are only for further illustration of the present invention and should not be construed as limiting the scope of protection of the present invention. The specific mass, reaction time, temperature, process parameters, etc., in the examples are merely examples within a suitable range. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention.

[0043] The activation steps for preparing activated zinc oxide are as follows:

[0044] 100 parts of zinc oxide powder were subjected to air jet milling at a pressure of 0.5 MPa to obtain zinc oxide powder with a particle size of 1-5 micrometers. Ten parts of a pre-prepared mixture of acetic acid and ethanol (weight ratio 1:15) were added to the zinc oxide powder and dispersed in a ball mill for 4 hours at a speed of 20 rpm to obtain a mixed zinc oxide slurry. This slurry was then placed in a high-pressure steam boiler and high-pressure steam was introduced to create a high-pressure steam... After the internal pressure of the pot reaches 2MPa, it is heated simultaneously and kept at 120℃ for 8 hours under sealed tumbling and steaming conditions. Then, the pressure of the high-pressure steam pot is released, and water vapor and nitrogen are simultaneously introduced at a volume ratio of 1:1 to heat and purge the zinc oxide slurry for 2 hours to remove ethanol and residual acetic acid from the zinc oxide slurry. The zinc oxide slurry after the removal of ethanol and residual acetic acid is placed in a muffle furnace and calcined at 300℃ for 4 hours to obtain calcined zinc oxide powder. The powder is then naturally cooled in the muffle furnace and sieved through a 2500-mesh nylon sieve to obtain active zinc oxide.

[0045] Preparation of modified nano-silica A:

[0046] S1: Dry 50g of silica (fumed silica with a particle size of 20~50nm and a specific surface area of ​​200~300m² / g) in a vacuum oven at 120°C to constant weight. Mix the dried silica with 250g of dehydrated toluene to obtain 300g of the first mixture.

[0047] S2: Under nitrogen protection, 5g of trisilyl alcohol phenyl cage-shaped polysilsesquioxane modifier was added to the first mixture. The mixture was ultrasonically vibrated at 35°C. After mixing, 1g of triethylamine catalyst was added, the system was heated to 100°C, and refluxed at this temperature for 8 hours. After the reaction was completed, the suspension was filtered to obtain filtered silica.

[0048] S3: The filtered silica was washed three times with anhydrous ethanol to remove toluene solvent and catalyst, and then vacuum dried at 90°C to constant weight to obtain dried silica.

[0049] S4: Dry silica, after being ground, is sieved through a 1000~2500 mesh nylon sieve to obtain modified nano silica, which is labeled as modified nano silica A.

[0050] Dehydrated toluene was prepared by the following method: molecular sieves were placed in toluene solvent, and the solvent was ultrasonically mixed at 40°C for 2 hours. After mixing, the mixture was filtered to obtain dehydrated toluene with a water content of 137 ppm.

[0051] Preparation of modified nano silica B: Same as modified nano silica A, except that the modifier is trisilyl isooctyl cage polysilsesquioxane, and the catalyst is 0.25g of dibutyltin dilaurate, that is, the amount of catalyst is 0.5wt%.

[0052] Preparation of modified nano silica C: Same as modified nano silica A, except that the modifier is hydroxyl silicone oil and the catalyst is 1g of triethylamine catalyst, that is, the amount of catalyst is 1wt%.

[0053] Example 1:

[0054] A microporous silica material based on supercritical foaming, comprising, by weight, the following raw materials: 100 parts phenyl silicone rubber, 30 parts modified nano-silica A, 3 parts benzoyl peroxide, 1 part active zinc oxide, and 3 parts diphenylguanidine. The preparation method of the microporous silica material is as follows:

[0055] Step 1, Premixing: Phenyl silicone rubber and modified nano silica A are mixed in a mixer for 30 minutes to obtain a mixture. The mixture is then left to stand at room temperature for 3 days.

[0056] Step 2, remixing: Add benzoyl peroxide, active zinc oxide and diphenylguanidine to the mixture according to the ratio. Mix in a mixer for 30 minutes, then start vacuuming. During the vacuuming process, continue mixing for 30 minutes while controlling the internal pressure at 1000Pa. After maintaining this pressure for 4 hours, discharge the material to obtain the remixed material. Let the remixed material stand at 10℃ for 2 days before preparing it for use.

[0057] Step 3, pre-vulcanization: The mixed materials are injected into the mold using a rubber injection molding machine. The mold temperature is raised to 120°C, the pressure inside the mold is increased to 15MPa, and the vulcanization time is 200s. Then, the mold is depressurized to normal pressure and cooled rapidly to obtain a pre-vulcanized product with a fixed shape and a preliminary cross-linked three-dimensional structure.

[0058] Step 4, supercritical foaming: Supercritical fluid is introduced into the mold. The supercritical fluid is a mixture of carbon dioxide and nitrogen, and the volume ratio of nitrogen to carbon dioxide is 1:4. The mold is heated to 100°C and immersed for 60 minutes under a pressure of 18MPa. The pressure inside the mold is rapidly reduced to atmospheric pressure within 1 second. The pressure reduction rate is such that the expansion of saturated gas is triggered, resulting in a vulcanized product with a uniform and stable internal cell structure.

[0059] Step 5, Re-curing and Shaping: The mold temperature is rapidly increased to 150℃ to fully vulcanize the foamed silicone. During the re-curing process, the mold is continuously evacuated to maintain a low vacuum of 0.04MPa inside the mold. The curing time is 60 minutes to obtain microporous silicone material.

[0060] Step 6, Irradiation sterilization: The prepared microporous silica material is sterilized by high-energy electron beam irradiation under nitrogen protection. The high-energy electron beam irradiation dose is controlled at 15 kGy and the irradiation time is 5s to obtain sterilized microporous silica material.

[0061] The microporous silicone material obtained in Example 1 was cut open, and its internal cross-section was scanned using a desktop scanning electron microscope (COXEM, model EM-30+, Korea). (Refer to...) Figure 1 As shown, the microporous silicone material exhibits uniform pore shape, no pore rupture, and an average pore diameter of 60 micrometers after foaming.

[0062] The performance test results of the prepared microporous silica gel material are as follows:

[0063] The tensile strength of the material was measured using a universal testing machine (Shimadzu Corporation, Japan, model AGX-100 plus), and was 6.9 MPa.

[0064] The flame retardancy rating of the material was determined in a horizontal and vertical combustion test chamber in accordance with the national standard GB / T 2408-2008, and the result was V-0.

[0065] No abnormal changes were observed in the material after it was irradiated with a high-energy electron beam.

[0066] Example 2:

[0067] A microporous silica material based on supercritical foaming comprises, by weight, the following raw materials: 100 parts of methyl vinyl silicone rubber, 40 parts of modified nano silica B, 3 parts of dicumyl peroxide, 1 part of active zinc oxide, and 3 parts of 2-mercaptophenylprophiazole. The preparation method of the microporous silica material is the same as in Example 1.

[0068] The microporous silicone material obtained in Example 2 was cut open, and its internal cross-section was scanned using a desktop scanning electron microscope (COXEM, model EM-30+, Korea). (Refer to...) Figure 2 As shown, the microporous silicone material exhibits uniform pore shape, no pore rupture, and an average pore diameter of 50 micrometers after foaming.

[0069] The microporous silica material prepared has the following performance test results: tensile strength of 5.8 MPa, flame retardancy rating of V-1, and no abnormal changes were observed in the material after high-energy electron beam irradiation.

[0070] Comparative Example 1:

[0071] A microporous silica material based on supercritical foaming comprises, by weight, the following raw materials: 100 parts phenyl silicone rubber, 30 parts unmodified silica, 3 parts benzoyl peroxide, 5 parts hydroxyl silicone oil (structure control agent), 1 part active zinc oxide, and 3 parts diphenylguanidine. The preparation method of the microporous silica material is the same as in Example 1.

[0072] The microporous silicone material obtained in Comparative Example 1 was cut open, and its internal cross-section was scanned using a desktop scanning electron microscope (COXEM, model EM-30+, South Korea). Figure 3 As shown, the microporous silicone material exhibits uneven pore shape, ruptured cells, and an average pore diameter of 40 micrometers after foaming.

[0073] The microporous silica material prepared has the following performance test results: tensile strength of 4.3 MPa, flame retardancy rating of V-2, and white frost on the surface of the material after high-energy electron beam irradiation.

[0074] Comparative Example 2:

[0075] A microporous silica material based on supercritical foaming comprises the following raw materials in parts by weight: 100 parts of phenyl silicone rubber, 30 parts of modified nano silica C, 3 parts of benzoyl peroxide, 1 part of active zinc oxide, and 3 parts of diphenylguanidine. The preparation method of the microporous silica material is the same as in Example 1.

[0076] The microporous silicone material obtained in Comparative Example 2 was cut open, and its internal cross-section was scanned using a desktop scanning electron microscope (COXEM, model EM-30+, South Korea). Figure 4 As shown, the microporous silicone material has a uniform pore shape after foaming, but the pores ruptured.

[0077] The microporous silica material prepared has the following performance test results: tensile strength of 5.2 MPa, flame retardancy rating of V-2, and no abnormal changes were observed in the material after high-energy electron beam irradiation.

[0078] Comparative Example 3:

[0079] A microporous silica material based on supercritical foaming is the same as in Example 1, except that in the preparation method of the microporous silica material, only carbon dioxide is used as the supercritical fluid.

[0080] The microporous silicone material obtained in Comparative Example 3 was cut open, and its internal cross-section was scanned using a desktop scanning electron microscope (COXEM, model EM-30+, South Korea). Figure 5 As shown, after the microporous silicone material was foamed, although no cell rupture occurred, the pore shape was dense but the cells were generally small, with an average pore diameter of 25 micrometers, and there were many differences in size between cells.

[0081] The microporous silica gel material prepared has the following performance test results: tensile strength of 7.2 MPa, flame retardancy rating of V-2, and no abnormal changes were observed in the material after high-energy electron beam irradiation.

[0082] Comparative Example 4:

[0083] A microporous silica material based on supercritical foaming is the same as in Example 1, except that in the preparation method of the microporous silica material, only nitrogen is used as the supercritical fluid.

[0084] The microporous silicone material obtained in Comparative Example 4 was cut open, and its internal cross-section was scanned using a desktop scanning electron microscope (COXEM, model EM-30+, South Korea). Figure 6 As shown, after the microporous silicone material was foamed, although no cell rupture occurred, the pores were dense but generally small, with an average pore diameter of 28 micrometers, and there were many differences in size between the cells.

[0085] The microporous silica material prepared has the following performance test results: tensile strength of 6.3 MPa, flame retardancy rating of V-2, and no abnormal changes were observed in the material after high-energy electron beam irradiation.

[0086] Comparative Example 5:

[0087] A microporous silicone material based on supercritical foaming, similar to Example 1, except that the silicone rubber in its raw material is pure methyl silicone rubber.

[0088] The microporous silica material prepared has the following performance test results: tensile strength of 5.5 MPa, flame retardancy rating of V-1, and slight yellowing after being irradiated by high-energy electron beam.

[0089] In Examples 1 and 2 of this invention, the tensile strength of the microporous silica material reaches 5.8-6.9 MPa. After foaming, the pore shape is uniform, the pores do not rupture, and the average pore diameter is between 50 and 60 micrometers. This indicates that the present invention uses a cage-like polysilsesquioxane containing a silanol structure as a modifier to graft cage-like polysilsesquioxane with a three-dimensional structure onto the surface of silica. This achieves carbon dioxide-philic group modification of nano-silica by cage-like polysilsesquioxane, greatly enhancing its dispersibility and interfacial compatibility in the silica matrix, thereby promoting the formation of a uniform cell structure. The introduction of the cage-like structure of the cage-like polysilsesquioxane significantly improves... The mechanical structural properties of microporous silicone materials were improved by introducing activated zinc oxide. Activated zinc oxide fills the cavity of the cage-like structure of the polysilsesquioxane, further anchoring the cage-like structure and improving its stability. This addresses the problem of insufficient hardness in microporous silicone materials after the introduction of the cage-like structure, which increases elasticity. Furthermore, it synergistically improves the mechanical strength properties of microporous silicone materials. Compared to Comparative Examples 1 to 4, the flame retardant rating improved from V-2 to V-1 or V-0, demonstrating good flame retardant effect. No abnormal changes were observed after high-energy electron beam irradiation.

[0090] In Comparative Example 1 of this invention, the use of unmodified silica as a filler in the microporous silica material leads to uneven dispersion of silica within the silica, resulting in uneven cell structure after foaming. Furthermore, during the mixing process, small-molecule structure control agents such as hydroxyl silicone oil inevitably generate small molecules during bonding, and the diffusion and migration of residual volatile small molecules cause uneven cell structure or even cell structure rupture. After the material is irradiated with a high-energy electron beam, the small-molecule structure control agents can easily diffuse and migrate from the interior of the material, causing a white frost to form on the surface of the microporous silica material, which affects the use of the microporous silica material.

[0091] In Comparative Example 2 of this invention, modified nano-silica modified with a conventional structure control agent is used as a filler for microporous silica material. After foaming, the pores are uniform. However, during the re-curing and setting process, it is difficult to withstand continuous low vacuum re-curing. Consequently, the foam material has insufficient structural strength during the re-curing and setting process, resulting in pore rupture.

[0092] In this invention, comparative examples 3 to 4 show that under nitrogen foaming conditions, the growth of foam cells is limited. After adding carbon dioxide, the cell size increases to a certain extent. This is because the solubility of carbon dioxide is significantly higher than that of nitrogen. After a sufficient amount of mixed gas enters the matrix, carbon dioxide gas nucleates and grows, and the foam is rapidly formed after foaming. However, whether using nitrogen or carbon dioxide, the pore size is relatively small.

[0093] In Comparative Example 5 of this invention, pure methyl silicone rubber was used instead of phenyl silicone rubber in the raw materials. The resulting microporous silicone material met the requirements in terms of strength, pore shape, and other properties. However, after the material was irradiated by a high-energy electron beam, it turned slightly yellow, indicating that pure methyl silicone rubber was not good for the weather resistance of the prepared microporous silicone material, which limited its application in outdoor and other weather-resistant applications.

[0094] The above embodiments merely illustrate implementation methods of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. A microporous silica gel material based on supercritical foaming, characterized in that, By weight, it includes the following raw materials: 100 parts silicone rubber, 1-3 parts active zinc oxide, 20-40 parts modified nano silica, 2-4 parts vulcanizing agent, and 2-4 parts vulcanization accelerator. The activated zinc oxide is obtained by activating zinc oxide powder, and the activation steps are as follows: Take 100 parts of zinc oxide powder and use an air jet mill to perform air jet milling treatment on the zinc oxide powder. After air jet milling, zinc oxide powder with a particle size of 1-5 micrometers is obtained. Add 10 parts of a pre-prepared mixture of acetic acid and ethanol to the zinc oxide powder and disperse it in a ball mill for 2-4 hours at a speed of 20-50 rpm to obtain a mixed zinc oxide slurry. Place the above zinc oxide slurry in a high-pressure steam cooker, introduce high-pressure steam, and cook it in a sealed, tumbling manner for 4-8 hours. Then, depressurize the high-pressure steam cooker and simultaneously introduce steam and nitrogen at a volume ratio of 1:1 to heat and purge the zinc oxide slurry for 1-2 hours to remove ethanol and residual acetic acid from the zinc oxide slurry. Place the zinc oxide slurry after removing ethanol and residual acetic acid in a muffle furnace and calcine it at 300-400℃ for 2-4 hours to obtain calcined zinc oxide powder. Cool it naturally in the muffle furnace and sieve it through a 1500-2500 mesh nylon screen to obtain active zinc oxide. The modified nano-silica is prepared through the following steps: S1: Dry the silica in a vacuum oven at 100~150°C to constant weight. Mix the dried silica with dehydrated toluene at a mass ratio of 1:5~10 to obtain the first mixture. S2: Under nitrogen protection, a modifier containing a cage-like polysilsesquioxane with a silanol structure is added to the first mixture. The amount of modifier is 5-10 wt% of the amount of silica. The mixture is ultrasonically vibrated at a temperature of 30-40°C. After mixing, 0.5-2 wt% of catalyst is added based on the weight of silica. The system is heated to 90-110°C and refluxed at this temperature for 5-12 hours. After the reaction is completed, the suspension is filtered to obtain filtered silica. S3: Filtered silica is washed 3-4 times with anhydrous ethanol to remove toluene solvent and catalyst, and then vacuum dried at 80-90℃ to constant weight to obtain dried silica. S4: After being ground, dried silica is sieved through a 1000-2500 mesh nylon sieve to obtain modified nano silica; The silicone rubber is one of methyl vinyl silicone rubber and phenyl silicone rubber; In step S1, the silica is fumed silica with a particle size of 20-50 nm and a specific surface area of ​​200-300 m² / g. In step S2, the modifier is one of trisilyl phenyl cage polysilsesquioxane or trisilyl isooctyl cage polysilsesquioxane.

2. The microporous silica gel material based on supercritical foaming according to claim 1, characterized in that, In the activation step of active zinc oxide, the air pressure of the air jet mill is 0.4~0.6MPa.

3. The microporous silica gel material based on supercritical foaming according to claim 1, characterized in that, In the activation step of active zinc oxide, the mixture of acetic acid and ethanol is prepared at a weight ratio of 1:10~20.

4. The microporous silica gel material based on supercritical foaming according to claim 1, characterized in that, In the activation step of active zinc oxide, the internal pressure of the high-pressure steam pot is 1.5~2.5MPa, and the high-pressure steam pot maintains a temperature of 110~130℃ after heating.

5. The microporous silica gel material based on supercritical foaming according to claim 1, characterized in that, In step S1, the dehydrated toluene is prepared by the following method: molecular sieves are placed in toluene solvent, and ultrasonic vibration is performed at a solvent temperature of 30~40℃ for 1~2 hours. After mixing, the mixture is filtered to obtain dehydrated toluene with a water content of 100~200ppm.

6. The microporous silica gel material based on supercritical foaming according to claim 1, characterized in that, In step S2, the catalyst is one or both of triethylamine or dibutyltin dilaurate.

7. The microporous silica gel material based on supercritical foaming according to claim 1, characterized in that, The vulcanizing agent is one or more of dicumyl peroxide, benzoyl peroxide, and tert-butyl peroxide.

8. The microporous silica gel material based on supercritical foaming according to claim 1, characterized in that, The vulcanization accelerator is one or more of dicyclohexylsulfenamide, diphenylguanidine, 2-mercaptophenylprophiazole, or cadmium carbamate.

9. A method for preparing a microporous silica gel material based on supercritical foaming as described in any one of claims 1 to 8, characterized in that, Includes the following steps: Step 1, premixing: Take 100 parts of silicone rubber and 20-40 parts of modified nano silica according to the ratio, mix them in a mixer for 20-40 minutes to obtain a mixture, and let the mixture stand at room temperature for 3-5 days. Step 2, remixing: Add 2-4 parts of vulcanizing agent, 1-3 parts of active zinc oxide, and 2-4 parts of vulcanization accelerator to the mixture according to the formula. Mix in an internal mixer for 15-30 minutes, then start vacuuming. During the vacuuming process, continue mixing for 15-30 minutes, and control the internal pressure below 1000Pa. After maintaining this for 2-4 hours, discharge the material to obtain the remixed material. Let the remixed material stand at 4-10℃ for 1-2 days before preparing it for use. Step 3, pre-vulcanization: The mixed materials are injected into the mold using a rubber injection molding machine. The mold temperature is raised to 110~125℃, and the pressure inside the mold is increased to 8~16MPa. The vulcanization time is 120~250s. Then, the mold is depressurized to normal pressure and cooled rapidly to obtain a pre-vulcanized product with a fixed shape and a preliminary cross-linked three-dimensional structure. Step 4, supercritical foaming: supercritical fluid is introduced into the mold, and the mold is heated to 80~110℃ and pressure 15~30MPa for 20~60min. The pressure inside the mold is rapidly reduced to atmospheric pressure within 1~2s. The pressure reduction rate is such that the expansion of saturated gas is triggered, resulting in a vulcanized product with a uniform and stable cell structure inside. Step 5, Re-curing and Shaping: Rapidly raise the mold temperature to 135~150℃ to completely vulcanize the foamed silicone. During the re-curing process, continuously evacuate the mold to maintain a low vacuum of 0.03~0.05MPa inside the mold. The curing time is 30~60min to obtain microporous silicone material. Step 6, Irradiation sterilization: The prepared microporous silica material is sterilized by high-energy electron beam irradiation under nitrogen protection. The high-energy electron beam irradiation dose is controlled at 15~20 kGy and the irradiation time is 3~6s to obtain sterilized microporous silica material. In step four, the supercritical fluid is a mixture of carbon dioxide and nitrogen.

10. The method for preparing a microporous silica gel material based on supercritical foaming according to claim 9, characterized in that, In step four, the volume ratio of nitrogen to carbon dioxide is 1:4.

Images