Wave-absorbing rubber and method for preparing the same

Abstract

The application discloses a wave-absorbing rubber and a preparation method thereof, and the preparation method comprises the following steps: S1, mixing a first wave-absorbing agent, a first coupling agent, a first lubricant and a first solvent to obtain a first mixture, and sequentially performing ball milling, filtering and drying on the first mixture to obtain a first modified wave-absorbing agent; mixing a second wave-absorbing agent, a thermoplastic phenolic resin, a curing agent, a second coupling agent and a second solvent to obtain a second mixture, and sequentially performing stirring, filtering and drying on the second mixture to obtain a second modified wave-absorbing agent; S2, uniformly mixing polyether polyurethane, polyester polyurethane, a second lubricant, a plasticizer, a reinforcing agent, a crosslinking agent, the first modified wave-absorbing agent and the second modified wave-absorbing agent to obtain a wave-absorbing rubber compound; S3, performing calendering on the wave-absorbing rubber compound to obtain a green rubber sheet; and S4, performing heating and pressurizing vulcanization on the green rubber sheet to obtain the wave-absorbing rubber.

Description

Technical Field

[0001] This invention relates to the field of microwave absorbing rubber technology, and in particular to a microwave absorbing rubber and its preparation method. Background Technology

[0002] Microwave-absorbing rubber is a functional composite material made by adding microwave-absorbing agents (such as magnetic solid powders like carbonyl iron powder) to a rubber or thermoplastic elastomer matrix. Microwave-absorbing rubber can convert electromagnetic waves into heat or other energy through electrical or magnetic losses, thus absorbing most or all of the electromagnetic waves. It can be used as a radar stealth medium and is widely applied in military stealth, microwave devices, and electromagnetic shielding for electronic communications.

[0003] Since microwave absorbing rubber is generally used in outdoor environments such as high temperature and humidity, marine salt spray, acidic salt spray, and low temperature and dryness, the environmental resistance requirements for microwave absorbing rubber are relatively high. It cannot peel off, rust (i.e., the microwave absorbing agent in the microwave absorbing rubber rusts), peel, or corrode. At the same time, microwave absorbing rubber may be used at different temperatures, and sometimes it needs to be repeatedly bent back and forth during use. It cannot be torn or damaged during use. Therefore, microwave absorbing rubber needs to have high mechanical strength in both high and low temperature environments. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing microwave absorbing rubber. The microwave absorbing rubber prepared by this method not only meets the requirements for microwave absorption performance, but also has good mechanical properties under normal temperature, high temperature and low temperature conditions.

[0005] This invention provides a method for preparing microwave absorbing rubber, comprising the following steps: S1: Mix the first microwave absorber, the first coupling agent, the first lubricant and the first solvent to obtain a first mixture. Then, ball mill, filter and dry the first mixture in sequence to obtain a first modified microwave absorber. The second microwave absorber, thermoplastic phenolic resin, curing agent, second coupling agent and second solvent are mixed to obtain a second mixture. The second mixture is then stirred, filtered and dried in sequence to obtain a second modified microwave absorber. S2: Mix polyether polyurethane, polyester polyurethane, second lubricant, plasticizer, reinforcing agent, crosslinking agent, first modified microwave absorbing agent and second modified microwave absorbing agent evenly to obtain microwave absorbing compound; S3: Calender the microwave absorbing compound to obtain a raw rubber sheet; S4: The raw rubber sheet is heated and pressurized for vulcanization to obtain microwave absorbing rubber.

[0006] In one feasible embodiment, both the first and second microwave absorbers are carbonyl iron powders, the particle size of the first microwave absorber is larger than that of the second microwave absorber, and the iron content of the first microwave absorber is greater than that of the second microwave absorber.

[0007] In one feasible embodiment, the first absorbing agent has a particle size of 4.5~10μm and an iron content >99.5%; the second absorbing agent has a particle size of 2.8~3.5μm and an iron content >97.5%.

[0008] In one feasible manner, the mass parts of each component in the first mixture are as follows: 100 parts of the first microwave absorber, 0.5-2 parts of the first coupling agent, 0.2-1 parts of the first lubricant, and 50-70 parts of the first solvent. The mass fractions of each component in the second mixture are as follows: 100 parts of the second microwave absorber, 5-10 parts of thermoplastic phenolic resin, 5-15 parts of curing agent, 1-3 parts of the second coupling agent, and 50-70 parts of the second solvent.

[0009] In one feasible manner, the first lubricant is a fatty acid salt, and the first solvent is ethanol; The second solvent is a mixture of acetate and ethanol, wherein the acetate includes one or more of methyl acetate, ethyl acetate, and butyl acetate, and the mass ratio of the acetate to the ethanol is (1~1.5):1.

[0010] In one feasible approach, the ball milling parameters for the first mixture are: a ball-to-material ratio of 1:3 to 1:5, a ball milling speed of 20 to 40 rpm / min, and a ball milling time of 12 to 24 h.

[0011] In one feasible embodiment, the mass parts of each component in the microwave absorbing compound are as follows: 50-100 parts of polyether polyurethane, 10-30 parts of polyester polyurethane, 1-3 parts of second lubricant, 5-15 parts of plasticizer, 0.5-13 parts of reinforcing agent, 3-8 parts of crosslinking agent, 50-100 parts of first modified microwave absorbing agent, and 300-350 parts of second modified microwave absorbing agent.

[0012] In one feasible manner, the second lubricant comprises one or more of paraffin wax and stearate; The plasticizer includes one or more of phthalates and dioctyl sebate; The reinforcing agent comprises 5-10 parts of fumed silica and / or 0.5-3 parts of hydroquinone dihydroxyethyl ether; The crosslinking agent comprises 2-5 parts of a primary crosslinking agent and 1-3 parts of a secondary crosslinking agent. The primary crosslinking agent is BIPB, and the secondary crosslinking agent comprises one or more of TDI and TAIC.

[0013] In one feasible manner, the vulcanization parameters of the raw rubber sheet are: vulcanization temperature 130-170℃, vulcanization pressure 10-15 MPa, and vulcanization time 10-30 min.

[0014] The present invention also provides a microwave absorbing rubber, which is made by the microwave absorbing rubber preparation method described above.

[0015] The method for preparing microwave-absorbing rubber provided by this invention has the following advantages: 1. Polyurethane is used as the matrix material. The polyurethane matrix has good adhesion properties, making it easy to bond during use and preventing the microwave absorbing rubber from falling off during use.

[0016] 2. By combining two polyurethane materials, polyether polyurethane and polyester polyurethane, and adding additives, the microwave absorbing rubber exhibits good mechanical properties under normal temperature, high temperature, and low temperature conditions.

[0017] 3. By modifying the first microwave absorber, a first modified microwave absorber is obtained. This improves the affinity between the first microwave absorber and the polyurethane matrix, allowing the first microwave absorber to disperse better within the polyurethane matrix. This is beneficial for improving the high and low temperature resistance of the microwave-absorbing rubber. Furthermore, ball milling alters the morphology of the first microwave absorber, resulting in a lower density, less space occupied within the polyurethane matrix, and less impact on the polymer chains of the polyurethane matrix, thus improving the flexibility and elongation of the microwave-absorbing rubber. By modifying the second microwave absorber, a second modified microwave absorber is obtained. This improves the affinity between the second microwave absorber and the polyurethane matrix, allowing the second microwave absorber to disperse better within the polyurethane matrix. This is beneficial for improving the high and low temperature resistance of the microwave-absorbing rubber. Moreover, surface coating of the second microwave absorber improves its corrosion resistance. Detailed Implementation

[0018] The specific embodiments of the present invention will be described in further detail below. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention. The terms "first," "second," "third," "fourth," etc. (if present) in the specification and claims of the present invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0019] Microwave-absorbing rubber is a functional composite material made by adding microwave-absorbing agents to rubber or thermoplastic elastomers as the matrix. Currently, silicone rubber, EPDM rubber, and single polyurethane rubber are commonly used as matrix materials. Among them, silicone rubber has poor mechanical strength and is easily torn; EPDM rubber has poor low-temperature resistance and is prone to brittle fracture at low temperatures, and its adhesion and corrosion resistance are also poor, making the patches prone to rusting (i.e., the microwave-absorbing agent in the matrix rusts); while polyurethane rubber generally uses cast polyurethane elastomers, which have high mechanical strength at room temperature but poor flexibility and are easily broken, and their flexibility is even worse at low temperatures.

[0020] To address the aforementioned technical problems, this invention provides a method for preparing microwave-absorbing rubber, comprising the following steps: S1: Mix the first microwave absorber, the first coupling agent, the first lubricant and the first solvent to obtain a first mixture. Then, ball mill, filter and dry the first mixture in sequence to obtain a first modified microwave absorber. The second microwave absorber, thermoplastic phenolic resin, curing agent, second coupling agent and second solvent are mixed to obtain a second mixture. The second mixture is then stirred, filtered and dried in sequence to obtain a second modified microwave absorber. S2: Mix polyether polyurethane, polyester polyurethane, second lubricant, plasticizer, reinforcing agent, crosslinking agent, first modified microwave absorbing agent and second modified microwave absorbing agent evenly to obtain microwave absorbing compound; S3: Calender the microwave absorbing compound to obtain a raw rubber sheet; S4: The raw rubber sheet is heated and pressurized for vulcanization to obtain microwave absorbing rubber.

[0021] In step S1 above, the first microwave absorber undergoes two modifications: Firstly, ball milling alters its morphology, changing it from an onion-like granular surface to a lamellar and serrated structure. The modified absorber has a larger specific surface area and lower density, occupying less space within the polyurethane matrix and having less impact on the polyurethane polymer chains, thus improving the flexibility and elongation of the microwave-absorbing rubber. Secondly, the first coupling agent generates polar functional groups (silanol groups, Si-OH) through hydrolysis in the first solvent, which are then grafted onto the surface of the first absorber. This enhances the affinity between the absorber and the polyurethane matrix (silanol groups can react with the isocyanate groups of the polyurethane matrix), allowing for better dispersion of the absorber within the polyurethane matrix and improving the high and low temperature resistance of the microwave-absorbing rubber. The first lubricant reduces the significant heat generated during ball milling, preventing excessive reaction upon heating. In this process, ball milling of the first mixture not only alters the appearance of the first microwave absorber but also ensures that all substances in the first mixture are mixed uniformly. Filtration of the first mixture removes excess first solvent.

[0022] In step S1 above, the second microwave absorber undergoes two modifications: Firstly, the second coupling agent generates polar functional groups (Si-OH) through hydrolysis with the second solvent, which are then grafted onto the surface of the second microwave absorber. This improves the affinity between the second microwave absorber and the polyurethane matrix, allowing the second microwave absorber to disperse better within the polyurethane matrix and enhancing the high and low temperature resistance of the absorbing rubber. Secondly, thermoplastic phenolic resin coats the surface of the second microwave absorber and cures it under the action of a curing agent, forming a resin coating layer on the surface of the second microwave absorber. This not only improves the corrosion resistance of the second microwave absorber (the second microwave absorber alone rusts in a neutral salt spray chamber after about 24 hours, while after being coated with phenolic resin, it can rust after 96 hours), but also further enhances the affinity between the second microwave absorber and the polyurethane matrix. The filtration of the second mixture removes excess second solvent.

[0023] In step S2 above, polyurethane is used as the matrix material. The polyurethane matrix has good adhesion properties, making it easy to bond during use and preventing the microwave-absorbing rubber from falling off. Simultaneously, a combination of polyether polyurethane and polyester polyurethane is used. Polyether polyurethane has good low-temperature resistance, while polyester polyurethane has good high-temperature resistance. Combined with additives (secondary lubricant, plasticizer, reinforcing agent, etc.), the microwave-absorbing rubber exhibits good mechanical properties under normal temperature, high temperature, and low temperature conditions.

[0024] In one embodiment, in step S1 above, both the first and second microwave absorbing agents are carbonyl iron powder, with the first microwave absorbing agent having a larger particle size than the second microwave absorbing agent, and the first microwave absorbing agent having a higher iron content than the second microwave absorbing agent. This allows the first and second microwave absorbing agents to have good absorption effects on electromagnetic waves of different frequencies, thereby enabling the microwave absorbing rubber to have good absorption effects on electromagnetic waves of different frequencies, and improving the absorption range of the microwave absorbing rubber for electromagnetic waves of different frequencies. Of course, in other embodiments, the first and second microwave absorbing agents can also be other substances, such as iron powder, carbon powder, alloy powder, etc.

[0025] In one embodiment, the particle size of the first absorbing agent is 4.5~10μm, and the iron content of the first absorbing agent is >99.5%; the particle size of the second absorbing agent is 2.8~3.5μm, and the iron content of the second absorbing agent is >97.5%.

[0026] In one embodiment, in step S1 above, the mass fractions of each component in the first mixture are as follows: 100 parts of the first microwave absorber, 0.5-2 parts of the first coupling agent, 0.2-1 parts of the first lubricant, and 50-70 parts of the first solvent. The first coupling agent can be a silane coupling agent, specifically KH560 silane coupling agent. The first lubricant is a fatty acid salt, specifically one or more of calcium stearate and zinc stearate. The first solvent is ethanol.

[0027] The mass fractions of each component in the second mixture are as follows: 100 parts of the second microwave absorber, 5-10 parts of thermoplastic phenolic resin, 5-15 parts of curing agent, 1-3 parts of the second coupling agent, and 50-70 parts of the second solvent. The thermoplastic phenolic resin can be grade 2123, and the synthetic monomers are phenol and formaldehyde, with a phenol to formaldehyde mass ratio of 1:(0.75-0.85) and a free phenol content of 0.5%-1.5%. The curing agent is the same as that used for the thermoplastic phenolic resin, such as hexamethylenetetramine. The second coupling agent can be a silane coupling agent, specifically KH560 silane coupling agent. The second solvent is a mixture of acetate and ethanol, wherein the acetate includes one or more of methyl acetate, ethyl acetate, and butyl acetate, and the mass ratio of acetate to ethanol in the second solvent is (1~1.5):1.

[0028] In one embodiment, in step S1 above, the ball milling parameters of the first mixture are: ball-to-material ratio of 1:3 to 1:5, ball milling speed of 20 to 40 rpm / min, and ball milling time of 12 to 24 h.

[0029] The drying conditions for the first mixture are: drying at 70℃~80℃ for 4~6 hours.

[0030] As one implementation, in step S1 above, the stirring conditions for the second mixture are: stirring in a disperser at a speed of 300~600 rpm / min for 12~24 hours.

[0031] The drying conditions for the second mixture are: drying at 70℃~80℃ for 4~6 hours.

[0032] In one embodiment, in step S2 above, the mass parts of each component in the microwave absorbing compound are as follows: 50-100 parts of polyether polyurethane, 10-30 parts of polyester polyurethane, 1-4 parts of the second lubricant, 5-15 parts of plasticizer, 0.5-13 parts of reinforcing agent, 3-8 parts of crosslinking agent, 50-100 parts of the first modified microwave absorbing agent, and 300-350 parts of the second modified microwave absorbing agent.

[0033] The polyether polyurethane can be in the following quantities: 50 parts, 60 parts, 70 parts, 80 parts, 90 parts, 100 parts, etc., or any combination thereof. The polyester polyurethane can be in the following quantities: 10 parts, 15 parts, 20 parts, 25 parts, 30 parts, etc., or any combination thereof. The second lubricant can be in the following quantities: 1 part, 1.5 parts, 2 parts, 2.5 parts, 3 parts, 3.5 parts, 4 parts, etc., or any combination thereof; preferably, the second lubricant is in the following quantities: 1-3 parts. The plasticizer can be in the following quantities: 5 parts, 8 parts, 10 parts, 12 parts, 15 parts, etc., or any combination thereof. The reinforcing agent can be in the following quantities: 0.5 parts, 1 part, 5 parts, 10 parts, 13 parts, etc., or any combination thereof. The crosslinking agent can be in the following mass percentages: 3 parts, 4 parts, 5 parts, 6 parts, 7 parts, 8 parts, etc., or any combination thereof. The first modified microwave absorbing agent can be in the following mass percentages: 50 parts, 60 parts, 70 parts, 80 parts, 90 parts, 100 parts, etc., or any combination thereof. The second modified microwave absorbing agent can be in the following mass percentages: 300 parts, 310 parts, 320 parts, 330 parts, 340 parts, 350 parts, etc., or any combination thereof.

[0034] The polyether polyurethane can be a low-temperature resistant compounded polyether polyurethane. The soft segment of the compounded polyether polyurethane molecular chain can be polytetrahydrofuran ether diol (PTMEG), the hard segment can be 4,4-diphenylmethane diisocyanate (MDI), and the chain extender can be α-allyl glycerol ether; specifically, Covestro's product with the brand name 9370AU can be used. Of course, other types of polyether polyurethane can also be used.

[0035] Polyester polyurethane can be a high-temperature resistant compounded polyester polyurethane. The soft segment of the compounded polyester polyurethane molecular chain can be polyethylene phthalate diol, the hard segment can be 4,4-diphenylmethane diisocyanate (MDI), and the chain extender can be 1,4-butanediol (BDO); ​​specifically, Covestro's product with the brand name 460 can be used. Of course, polyester polyurethane can also be other types of polyester polyurethane.

[0036] The second lubricant includes one or more of paraffin wax and stearates.

[0037] Plasticizers include one or more of phthalates and dioctyl sebate (DOS), wherein phthalates include dioctyl phthalate (DOP).

[0038] There are two types of reinforcing agents: one is fumed silica, also known as white carbon black, with a mass fraction of 5-10 parts; the other is hydroquinone dihydroxyethyl ether (HQEE), with a mass fraction of 0.5-3 parts. The two reinforcing agents can be added separately or together in different proportions.

[0039] The crosslinking agent comprises 2-5 parts of a primary crosslinking agent and 1-3 parts of a secondary crosslinking agent. The primary crosslinking agent is BIPB (1,4-bis(tert-butylperoxy)diisopropylbenzene), and the secondary crosslinking agent comprises one or more of TDI (toluene diisocyanate) and TAIC (tracene propyl isocyanurate).

[0040] As one implementation method, step S2 described above can specifically be: 1. Heat the open mill to about 35℃~45℃, then spray the surface with a release agent. After the release agent has completely evaporated, add polyether polyurethane and polyester polyurethane to the open mill and mix for 3~5 minutes. Then add the second lubricant and plasticizer, mix for 3~5 minutes in the open mill, then add the crosslinking agent and reinforcing agent. After mixing back and forth in the open mill for 10~15 minutes, the masterbatch is obtained.

[0041] 2. Dry the masterbatch (e.g., dry in an oven at 60°C for 30 minutes) to remove any remaining moisture. Then, spray a release agent onto the surface of the open mill, turn on the cooling water circulation system of the open mill, and adjust the temperature of the open mill to 15°C~25°C. Then, add the masterbatch, the first modified microwave absorber, and the second modified microwave absorber to the open mill, mix and disperse for 10~15 minutes, and tumble back and forth more than 10 times to complete the mixing process and obtain the microwave absorbing compound.

[0042] As one implementation method, the above-mentioned step S3 can specifically be: Let the microwave-absorbing compound stand at room temperature for more than 4 hours, then turn on the open mill and heat it to 35℃~45℃. Spray a release agent on the surface and then re-roll the microwave-absorbing compound. Adjust the roller gap to a suitable gap (depending on the product thickness, for example, 0.3~0.5mm), and calender the microwave-absorbing compound through the rollers. Control the calendering thickness by adjusting the roller speed to obtain a raw rubber sheet of a certain thickness.

[0043] As one implementation method, in step S4 above, the vulcanization parameters of the raw rubber sheet are: vulcanization temperature 130-170℃, vulcanization pressure 10-15Mpa, and vulcanization time 10-30min.

[0044] As one implementation method, the above-mentioned step S4 can specifically be as follows: Cut the calendered raw rubber sheet into the required size (e.g., 200*200mm), place it in the mold frame, set the temperature of the vulcanizing machine to 130-170℃, the pressure to 10-15Mpa, and the vulcanization time to 10-30min. After one or two venting cycles, heat and pressurize to vulcanize into microwave-absorbing rubber of a certain specification.

[0045] This invention also provides a microwave absorbing rubber, which is made using the microwave absorbing rubber preparation method described above.

[0046] Example 1 A microwave absorbing rubber, by mass parts, comprises the following raw materials: 90 parts polyether polyurethane, 10 parts polyester polyurethane, 1 part lubricant A (stearate), 1 part lubricant B (paraffin), 3 parts plasticizer A (DOP), 5 parts plasticizer B (DOS), 5 parts reinforcing agent A (fumed silica), 3 parts main crosslinking agent (BIPB), 2.5 parts co-crosslinking agent A (TAIC), 80 parts first modified microwave absorbing agent, and 350 parts second modified microwave absorbing agent.

[0047] The specific preparation steps of the microwave absorbing rubber are as follows: (1) Modification of microwave absorbers 100 parts of carbonyl iron powder (iron content > 99.5%) with a particle size of 4.5~10μm, 1 part of silane coupling agent, 0.5 parts of fatty acid salt, and 60 parts of ethanol were mixed to obtain a first mixture. The first mixture was then ball-milled, filtered, and dried sequentially to obtain a first modified microwave absorber. The ball-milling parameters for the first mixture were: ball-to-material ratio of 1:3, ball milling speed of 30 rpm / min, and ball milling time of 18 h. The drying conditions were: drying at 80℃ for 4 h.

[0048] 100 parts of carbonyl iron powder (iron content > 97.5%) with a particle size of 2.8~3.5μm, 8 parts of thermoplastic phenolic resin, 10 parts of curing agent hexamethylenetetramine, 2 parts of silane coupling agent, 30 parts of ethyl acetate, and 30 parts of ethanol were mixed to obtain a second mixture. The second mixture was then stirred, filtered, and dried sequentially to obtain a second modified microwave absorber. The stirring conditions for the second mixture were: stirring at 400 rpm / min in a disperser for 16 hours. The drying conditions were: drying at 80℃ for 4 hours.

[0049] (2) Mixing process Heat the open mill to about 40°C, then spray a release agent onto the surface. After the release agent has completely evaporated, add 90 parts of polyether polyurethane and 10 parts of polyester polyurethane to the open mill and mix for 4 minutes. Then add 1 part of lubricant A (stearate), 1 part of lubricant B (paraffin), 3 parts of plasticizer A (DOP), and 5 parts of plasticizer B (DOS). After mixing in the open mill for 4 minutes, add 3 parts of primary crosslinking agent (BIPB), 2.5 parts of co-crosslinking agent A (TAIC), and 5 parts of reinforcing agent A (fumed silica). After mixing back and forth in the open mill for 10 minutes, the masterbatch is obtained.

[0050] The masterbatch is dried to remove any remaining moisture. Then, a release agent is sprayed onto the surface of the open mill, the cooling water circulation system of the open mill is turned on, and the temperature of the open mill is adjusted to 20°C. The masterbatch, 80 parts of the first modified microwave absorber, and 350 parts of the second modified microwave absorber are then added to the open mill, mixed and dispersed for 12 minutes, and tumbled back and forth more than 10 times to complete the mixing process and obtain the microwave absorbing compound.

[0051] (3) Calendering process The above-mentioned microwave-absorbing compound was left at room temperature for more than 4 hours. Then, the open mill was turned on and the temperature was raised to 40°C. A release agent was sprayed on the surface and then the microwave-absorbing compound was turned over. The roller gap was adjusted to a suitable gap (depending on the product thickness). The microwave-absorbing compound was calendered through the rollers, and the calendering thickness was controlled by adjusting the roller speed to obtain a raw rubber sheet of a certain thickness.

[0052] (4) Vulcanization process Cut the calendered raw rubber sheet into the required size and place it in the mold frame. Set the temperature of the vulcanizing machine to 150℃, the pressure to 12Mpa, and the vulcanization time to 20min. After one or two venting cycles, heat and pressurize to vulcanize into microwave-absorbing rubber of a certain specification.

[0053] Example 2 A microwave absorbing rubber, by mass parts, comprises the following raw materials: 90 parts polyether polyurethane, 10 parts polyester polyurethane, 1 part lubricant A (stearate), 3 parts lubricant B (paraffin), 5 parts plasticizer A (DOP), 3 parts reinforcing agent B (HQEE), 5 parts main crosslinking agent (BIPB), 1.5 parts co-crosslinking agent A (TAIC), 100 parts first modified microwave absorbing agent, and 330 parts second modified microwave absorbing agent.

[0054] The preparation steps of the microwave absorbing rubber in Example 2 (including the preparation steps of the first modified microwave absorbing agent and the second modified microwave absorbing agent) are the same as those in Example 1, and will not be repeated here.

[0055] Example 3 A microwave absorbing rubber, by mass parts, comprises the following raw materials: 70 parts polyether polyurethane, 30 parts polyester polyurethane, 1 part lubricant A (stearate), 3 parts lubricant B (paraffin), 5 parts plasticizer A (DOP), 5 parts reinforcing agent A (fumed silica), 3 parts reinforcing agent B (HQEE), 3 parts main crosslinking agent (BIPB), 1 part co-crosslinking agent B (TDI), 50 parts first modified microwave absorbing agent, and 350 parts second modified microwave absorbing agent.

[0056] The preparation steps of the microwave absorbing rubber in Example 3 (including the preparation steps of the first modified microwave absorbing agent and the second modified microwave absorbing agent) are the same as those in Example 1, and will not be repeated here.

[0057] Comparative Example 1 A microwave absorbing rubber, by mass parts, comprises the following raw materials: 100 parts polyester polyurethane, 1 part lubricant A (stearate), 1 part lubricant B (paraffin), 3 parts plasticizer A (DOP), 5 parts main crosslinking agent (BIPB), 1 part co-crosslinking agent B (TDI), 40 parts first modified microwave absorbing agent, and 390 parts second modified microwave absorbing agent.

[0058] The preparation steps of the microwave-absorbing rubber in Comparative Example 1 (including the preparation steps of the first modified microwave-absorbing agent and the second modified microwave-absorbing agent) are the same as those in Example 1, and will not be repeated here.

[0059] The raw material formulations of the microwave absorbing rubber in Examples 1-3 and Comparative Example 1 are shown in the table below: The microwave absorbing rubbers of Examples 1-3 and Comparative Example 1 were subjected to the following tests: Tensile strength: Tested according to GB / T 528-2009 standard for determination of tensile stress-strain properties of vulcanized rubber or thermoplastic rubber. Among them, each microwave absorbing rubber was tested for tensile strength according to the above standard in its original state (without high temperature aging and low temperature freezing), after high temperature aging (aging at 150℃ for 4 hours), and after low temperature freezing (freezing at -55℃ for 4 hours).

[0060] Elongation at break: Tested according to GB / T 528-2009 Standard for Determination of Tensile Stress-Strain Properties of Vulcanized Rubber or Thermoplastic Rubber. Specifically, the elongation at break of each microwave-absorbing rubber was tested according to the above standard in its original state (without high-temperature aging and low-temperature freezing), after high-temperature aging (aging at 150℃ for 4 hours), and after low-temperature freezing (freezing at -55℃ for 4 hours).

[0061] Tear strength: Tested in accordance with GB / T 529-2008 standard for determination of tear strength of vulcanized rubber or thermoplastic rubber.

[0062] Salt spray resistance: Tested according to the national military standard GJB.150.11A-2009.

[0063] High temperature and high humidity resistance: Tested according to the national military standard GJB.150.9A-2009.

[0064] Areal density: Weigh a microwave-absorbing rubber sheet with dimensions of 100mm in length, 100mm in width, and 0.5mm in thickness. Divide the weight by the surface area to obtain the areal density. The unit of areal density is kg / m³. 2 .

[0065] Electromagnetic performance (maximum absorption peak): Tested according to the national military standard GJB-2038A.

[0066] It should be noted that when conducting mechanical property tests on the microwave absorbing rubber (including tensile strength, elongation at break, and tear strength), a 2mm thick microwave absorbing rubber sheet is used; when conducting tests on the microwave absorbing rubber's resistance to salt spray, high temperature and humidity, areal density, and electromagnetic properties, a 0.5mm thick microwave absorbing rubber sheet is used.

[0067] The test results are shown in the table below: Analysis of the table above shows that the microwave-absorbing rubber in Example 1 exhibits the best overall performance in terms of mechanical strength, environmental resistance, and electromagnetic properties. Specific analysis is as follows: (1) Matrix material: Comparative Example 1 uses pure polyester polyurethane as matrix material, and the low temperature elongation at break of Comparative Example 1 is only 4%; Example 1 uses a mixture of two polyurethanes, and its low temperature elongation at break reaches 60%; This is because polyester polyurethane has good mechanical strength, but poor low temperature performance, while polyether polyurethane has slightly worse mechanical strength than polyester polyurethane, but because its molecular chain is more flexible, it has better low temperature performance. Adding a small amount of polyester polyurethane to the polyether polyurethane matrix can take into account both high and low temperature performance.

[0068] (2) Lubricant: In each example and comparative example, the lubricant generally consists of two components. One component acts as a release agent, such as stearic acid. The long-chain alkyl groups of stearic acid cover the surface of rubber molecules, reducing intermolecular friction and decreasing the viscosity of the mixture. The carboxyl groups (-COOH) form an adsorption layer on the surface of the metal roller, blocking the direct contact between the polar groups of polyurethane and the metal, significantly reducing the sticking to the roller and the mold. The other component is paraffin wax, which is composed of alkanes of different molecular weights consisting of carbon and hydrogen. Paraffin wax has a lubricating effect on rubber, making the rubber compound easier to calender, extrude, and demold, thus improving the appearance of the finished product. Comparing Examples 1, 2, and 3, Examples 2 and 3 added too much lubricant B. Since the lubricant does not participate in the crosslinking reaction and does not provide mechanical properties, but occupies the volume of the microwave absorber and blocks the affinity between the microwave absorber and the rubber, it will reduce the tensile strength of the rubber. Therefore, only a small amount of lubricant B needs to be added.

[0069] (3) Plasticizer: Plasticizers are generally substances such as phthalates, with dioctyl phthalate (DOP) being the most commonly used. In Comparative Example 1, Example 2 and Example 3, the low-temperature elongation at break of the rubber was still insufficient even with the addition of this plasticizer alone. Therefore, dioctyl sebate (DOS) was added in Example 1. DOS is an aliphatic diester with outstanding cold resistance, which is several times that of DOP. It also has heat resistance. When 5 parts of DOS were added in Example 1, the low-temperature elongation of the rubber was significantly increased to 60%. Under these conditions, the rubber was not easily broken and had good flexibility.

[0070] (4) Crosslinking agent: The main crosslinking agent is generally peroxide, and the co-crosslinking agent can be TDI or TAIC. In Comparative Example 1, the main crosslinking agent is the main component, with a small amount of co-crosslinking agent TDI added. After the polyurethane rubber is crosslinked with BIPB peroxide, the remaining active groups are crosslinked with TDI. However, TDI can only be used to extend the chain by reacting the hydroxyl groups in the raw rubber molecules. It can be seen that the microwave absorbing rubber in Comparative Example 1 has general heat resistance, and the tensile strength after aging is only 3.3 MPa. In Example 3, the amount of main crosslinking agent is reduced, and the tensile strength is even lower, only 2.5 MPa. Therefore, in Example 1, two crosslinking agents are used in synergy: 3 parts of main crosslinking agent and 2.5 parts of co-crosslinking agent. Excessive use of primary crosslinking agent increases crosslinking density but reduces elongation. Therefore, the amount of primary crosslinking agent is reduced and replaced with a partial co-crosslinking agent (TAIC). TAIC molecules have three highly reactive allyl double bonds. Free radicals generated by peroxides readily add to the double bonds of TAIC, generating stable free radicals. These free radicals can then react efficiently with the free radicals of polyurethane macromolecules to form a polymer-TAIC-polymer crosslinking network structure. The crosslinking bonds formed by TAIC are mainly thermally stable C-C bonds. This network is more stable at high temperatures, less prone to breakage or recombination, reducing factors that degrade rubber properties at high temperatures. Therefore, Example 1 shows the highest tensile strength of 5.5 MPa.

[0071] (5) Conclusion: Based on the comparison between Example 1 and Comparative Example 1 in the table above, Example 1, which uses a mixture of two types of rubber matrices, exhibits better low-temperature performance, preventing the microwave absorbing rubber from becoming brittle at -55℃. The high-temperature performance of Example 1 was further improved through a reasonable primary and secondary crosslinking agent system and the selection of reinforcing agents. Powder modification of the two microwave absorbing agents improved the affinity between the absorbing agents and the matrix, further enhancing the mechanical properties of the microwave absorbing rubber. A comparison of electromagnetic properties revealed that the modified powder had a lower absorption peak, indicating a stronger electromagnetic shielding effect. Of course, the ball-milled modified powder also greatly contributes to the mechanical properties of the rubber, allowing it to maintain a certain degree of flexibility at low temperatures.

[0072] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing microwave-absorbing rubber, characterized in that, Includes the following steps: S1: Mix the first microwave absorber, the first coupling agent, the first lubricant and the first solvent to obtain a first mixture. Then, ball mill, filter and dry the first mixture in sequence to obtain a first modified microwave absorber. The second microwave absorber, thermoplastic phenolic resin, curing agent, second coupling agent and second solvent are mixed to obtain a second mixture. The second mixture is then stirred, filtered and dried in sequence to obtain a second modified microwave absorber. S2: Mix polyether polyurethane, polyester polyurethane, second lubricant, plasticizer, reinforcing agent, crosslinking agent, first modified microwave absorbing agent and second modified microwave absorbing agent evenly to obtain microwave absorbing compound; S3: Calender the microwave absorbing compound to obtain a raw rubber sheet; S4: The raw rubber sheet is heated and pressurized for vulcanization to obtain microwave absorbing rubber.

2. The method for preparing microwave-absorbing rubber as described in claim 1, characterized in that, Both the first and second microwave absorbers are carbonyl iron powders. The particle size of the first microwave absorber is larger than that of the second microwave absorber, and the iron content of the first microwave absorber is greater than that of the second microwave absorber.

3. The method for preparing microwave-absorbing rubber as described in claim 2, characterized in that, The first microwave absorbing agent has a particle size of 4.5~10μm and an iron content of >99.5%; the second microwave absorbing agent has a particle size of 2.8~3.5μm and an iron content of >97.5%.

4. The method for preparing microwave-absorbing rubber as described in claim 1, characterized in that, The mass fractions of each component in the first mixture are as follows: 100 parts of the first microwave absorber, 0.5-2 parts of the first coupling agent, 0.2-1 parts of the first lubricant, and 50-70 parts of the first solvent; The mass fractions of each component in the second mixture are as follows: 100 parts of the second microwave absorber, 5-10 parts of thermoplastic phenolic resin, 5-15 parts of curing agent, 1-3 parts of the second coupling agent, and 50-70 parts of the second solvent.

5. The method for preparing microwave-absorbing rubber as described in claim 1, characterized in that, The first lubricant is a fatty acid salt, and the first solvent is ethanol; The second solvent is a mixture of acetate and ethanol, wherein the acetate includes one or more of methyl acetate, ethyl acetate, and butyl acetate, and the mass ratio of the acetate to the ethanol is (1~1.5):

1.

6. The method for preparing microwave-absorbing rubber as described in claim 1, characterized in that, The ball milling parameters for the first mixture are: ball-to-material ratio of 1:3 to 1:5, ball milling speed of 20 to 40 rpm / min, and ball milling time of 12 to 24 h.

7. The method for preparing microwave-absorbing rubber as described in claim 1, characterized in that, The mass fractions of each component in the microwave absorbing compound are as follows: 50-100 parts of polyether polyurethane, 10-30 parts of polyester polyurethane, 1-3 parts of second lubricant, 5-15 parts of plasticizer, 0.5-13 parts of reinforcing agent, 3-8 parts of crosslinking agent, 50-100 parts of first modified microwave absorbing agent, and 300-350 parts of second modified microwave absorbing agent.

8. The method for preparing microwave-absorbing rubber as described in claim 1, characterized in that, The second lubricant includes one or more of paraffin wax and stearate; The plasticizer includes one or more of phthalates and dioctyl sebate; The reinforcing agent comprises 5-10 parts of fumed silica and / or 0.5-3 parts of hydroquinone dihydroxyethyl ether; The crosslinking agent comprises 2-5 parts of a primary crosslinking agent and 1-3 parts of a secondary crosslinking agent. The primary crosslinking agent is BIPB, and the secondary crosslinking agent comprises one or more of TDI and TAIC.

9. The method for preparing the microwave-absorbing rubber according to any one of claims 1-8, characterized in that, The vulcanization parameters for the raw rubber sheet are: vulcanization temperature 130-170℃, vulcanization pressure 10-15Mpa, and vulcanization time 10-30min.

10. A microwave-absorbing rubber, characterized in that, It is made using the method for preparing microwave-absorbing rubber as described in any one of claims 1-9.

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