High-density polymethacrylimide foam and preparation method thereof

Abstract

The invention discloses high-density polymethacrylimide foam and a preparation method of the high-density polymethacrylimide foam. The foam is prepared from the following raw materials in parts by weight: 40-160 parts of methacrylic acid; 0 to 80 parts of methacrylonitrile; 0.1 to 6 parts of a third monomer; 0.04 to 5 parts of an initiator; 6-10 parts of a cross-linking agent; 0.5-10 parts of a foaming agent; and 4-10 parts of core-shell rubber nanoparticles. According to the method, methacrylic acid and methacrylonitrile are adopted as main monomers, high-performance PMI foam can be prepared, the use amount of a foaming agent does not need to be greatly reduced, the crosslinking degree and toughness of the PMI foam can be improved by adding the allyl ester crosslinking agent containing double bonds and the core-shell rubber nanoparticles, and the high-density and tough PMI foam can be obtained; the problem that the utilization rate is low due to the fact that a resin plate is not transparent and cannot be foamed is solved, and the problems that foam density is uneven and high-temperature stability is insufficient are also solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer material preparation, and particularly relates to a high-density polymethacrylimide foam and a preparation method thereof. Background Art

[0002] Under the same density condition, compared with various existing foam plastics, polymethacrylimide (PMI) foam plastics have the highest strength and stiffness and the best heat resistance, and are ideal core layer materials for high-performance sandwich structure composite materials. They are widely used in the fields of aerospace, rail transit, medical bed boards, lightweight automobiles, etc.

[0003] The applications of PMI foam in aerospace ground equipment are mainly adapters, lightweight covers, etc. Their performance requirements are high, and high-density PMI foam with a density of 200 - 400 kg / m 3 is required to have the properties of light weight and high strength, certain toughness, and be suitable for the processes of machining and mid-temperature compression molding of composite fiber cloth prepregs. If polyurethane foam is used, under the same density condition, its room temperature compression strength is only 1 / 2 of that of PMI foam. If the density of the foam is increased to meet the strength requirements, it will lead to overweight of the components; its mid-temperature compression strength is only 1 / 5 of that of PMI foam, and it is not suitable for the requirements of the mid-temperature prepreg compression molding process.

[0004] To obtain high-density PMI foam, it is generally achieved by reducing the blowing agent. However, a large number of experiments have proved that the blowing agent in the system cannot be significantly reduced or even not added at all. Our research shows that when preparing PMI foam with a density of 150 kg / m 3 by reducing the blowing agent, white spots will appear on the resin surface during the process of the polymer turning transparent; to obtain higher-density foam, as the amount of the blowing agent is further reduced, there will be more opaque substances on the surface of the resin plate, and even opaque substances will appear inside, which will affect the utilization rate of the resin plate, and even cannot foam normally, and the surface of the foam plate will crack severely, resulting in scrapping. Therefore, to obtain high-density foam, the blowing agent cannot be significantly reduced, and first, it is necessary to ensure that the resin plate is completely and normally transparent.

[0005] By controlling the maximum foaming temperature and foaming ratio of the transparent resin plate, high-density PMI foam plates can also be obtained. However, due to a large amount of blowing agent residue in the system, such foam plates have insufficient dimensional and density stability in a high-temperature environment. For the long-term high-temperature post-treatment carried out to make up for this deficiency, there are also obstacles. The foam volume will expand, resulting in a decrease in density, and it cannot meet the process and use requirements of ground equipment.

[0006] Without reducing the blowing agent, by adding allyl ester crosslinkers containing double bonds, only the crosslinking degree of the system can be partially improved, and the density of PMI foam can be increased to a limited extent; however, if an excessive amount of allyl ester crosslinkers is added, it will cause the surface or interior of the resin plate to be opaque to varying degrees. In severe cases, the plate cannot be foamed normally, resulting in scrapping. The addition of a large amount of allyl ester crosslinkers also leads to an imbalance between crosslinking and foaming speeds during the foaming process of the resin plate, and significant density differences are likely to exist inside and outside the foam sheet material; moreover, the PMI foam obtained in this way is too brittle, the tensile fracture elongation rate is reduced, and the impact resistance is decreased, making it prone to cracking in a dynamic stress environment during product use.

[0007] We unexpectedly found that by adding polybutadiene-polyacrylate core-shell rubber nanoparticles, the crosslinking degree of the system can be further improved, the foam density can be controlled, and the density uniformity of the foam board can be enhanced; moreover, the toughness of PMI foam is increased, and the impact resistance is improved while the modulus remains unchanged. This additional crosslinked structure containing nanoparticles enhances the high-temperature rigidity of the foam board, preventing the secondary foaming of small molecule blowing agents in the system during high-temperature tempering, ensuring the density uniformity and stability of PMI foam sheets. Summary of the Invention

[0008] The purpose of the present invention is to provide a high-density polymethacrylimide foam and its preparation method to solve the deficiencies of the prior art, thereby solving the technical problem that the prior art cannot stably prepare high-density PMI foam.

[0009] The purpose of the present invention is achieved by the following technical solutions:

[0010] A high-density polymethacrylimide foam is prepared from the following raw materials in parts by weight:

[0011] 40 - 160 parts of methacrylic acid;

[0012] 0 - 80 parts of methacrylonitrile;

[0013] 0.1 - 6 parts of the third monomer;

[0014] 0.04 - 5 parts of initiator;

[0015] 6 - 10 parts of crosslinker;

[0016] 0.5 - 10 parts of blowing agent;

[0017] 4 - 10 parts of core-shell rubber nanoparticles;

[0018] Minor auxiliaries.

[0019] The crosslinking agent is an acrylate containing double bonds, and is selected from any one of allyl methacrylate, allyl acrylate, isobornyl acrylate, 2-hydroxyethyl methacrylate, and pentaerythritol triacrylate.

[0020] Preferably, the initiator is a combination of benzoyl peroxide, lauroyl peroxide, dicarbonate peroxide, tert-butyl peroxybenzoate, azobisisobutyronitrile (AIBN), azodiisooctanenitrile (ABVN), tert-amyl peroxybenzoate, methyl ethyl ketone peroxide, and cyclohexanone peroxide. Among them, the mass ratio of the four initiators of benzoyl peroxide, lauroyl peroxide, dicarbonate peroxide, and tert-butyl peroxybenzoate is in the range of (1.5 - 2.5):(2 - 3):(2.7 - 3.7):(1 - 2).

[0021] Preferably, the high-density polymethacrylimide foam is a fine-pore foam with a pore size of 90 - 220 μm, and the foaming agent is a combination selected from formamide, tert-butanol, isopropanol, azodicarbonamide, sodium bicarbonate, n-pentane, and isopentane. Among them, the mass ratio of formamide, tert-butanol, and isopropanol is in the range of (6 - 8):(2 - 4):(1 - 3).

[0022] Preferably, the core-shell rubber is selected from polybutadiene-polyacrylate core-shell rubber, nitrile rubber-polyacrylate core-shell rubber, natural rubber-polyacrylate core-shell rubber, and chloroprene rubber-polyacrylate core-shell rubber nanoparticles. The core components are mainly polybutadiene rubber, nitrile rubber, natural rubber, chloroprene rubber, etc., and the shell components are acrylate esters.

[0023] The present invention also discloses a preparation method of a high-density polymethacrylimide foam, which is characterized by including the following steps:

[0024] S1. According to parts by weight, methacrylic acid and methacrylonitrile are added with an initiator, a crosslinking agent, a foaming agent, core-shell rubber nanoparticles, and other reagents, and mixed evenly to obtain a mixed solution;

[0025] S2. The mixed solution is poured into a mold, and free radical polymerization is carried out at a temperature of 30 - 55 °C to obtain a prepolymer resin plate;

[0026] S3. The prepolymer resin plate is subjected to pretreatment, demolding, and post-treatment to obtain a foamable resin plate; wherein, the pretreatment and post-treatment are carried out according to the following method: the prepolymer resin plate is heated to 50 - 70 °C and maintained for 4 - 8 h, then heated to 75 - 95 °C and maintained for 4 - 6 h, and finally heated to 100 - 115 °C and maintained for 2 - 5 h;

[0027] S4. Heat-expand the foamable resin sheet to obtain high-density polymethacrylimide foam; wherein, the heat expansion is carried out according to the following method: first heat the foamable resin sheet to 125-140 °C and hold for 2.5-4.5 h, then raise the temperature to 145-165 °C and hold for 40-60 min, then raise the temperature to 170-185 °C and hold for 45-60 min, and finally raise the temperature to 190-220 °C and hold for 1-3.5 h;

[0028] S5. Carry out post-treatment of high-temperature tempering on the high-density polymethacrylimide foam, and the post-treatment of high-temperature tempering is carried out according to the following method: heat the foam board to 120-140 °C and hold for 3-5 h, then raise the temperature to 150-180 °C and hold for 3-6 h, and then raise the temperature to 185-205 °C and hold for 5-8 h.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] The preparation method of the high-density polymethacrylimide foam provided by the present invention does not require a large reduction in the amount of foaming agent in the system to ensure the normal transparency of the resin sheet. By adding an appropriate amount of allyl ester cross-linking agent, the cross-linking degree of the system is partially increased. At the same time, an appropriate amount of polybutadiene-polyacrylate core-shell rubber nanoparticles is added, which has the functions of both increasing the cross-linking degree and enhancing the toughness, ensuring that the cross-linking degree of the final resin sheet is moderate, the foaming board can be normally foamed, the foaming temperature and foaming ratio do not need to be restricted, and the target density is achieved; the foam board can undergo high-temperature tempering for a long time, and the density is stable without decrease; and the comprehensive performance is excellent, and the toughness is significantly improved. The high-density polymethacrylimide foam prepared by the present invention has good machinability and mechanical properties, and good high-temperature dimensional and weight stability, improved toughness, and necessary impact resistance, making the high-density polymethacrylimide foam product meet the application requirements of ground equipment. Detailed implementation mode

[0031] In order to make the purpose, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below. It should be understood that the specific implementation modes described herein are only used to explain the present invention and are not used to limit the present invention.

[0032] A high-density polymethacrylimide foam provided by the present invention is prepared from the following raw materials in parts by weight:

[0033] 40-160 parts of methacrylic acid;

[0034] 0-80 parts of methacrylonitrile;

[0035] 0.1-6 parts of the third monomer;

[0036] Initiator: 0.04 - 5 parts;

[0037] Crosslinking agent: 6 - 15 parts;

[0038] Foaming agent: 0.5 - 10 parts;

[0039] Core - shell rubber nanoparticles: 4 - 10 parts;

[0040] Secondary auxiliary agent: 0.2 - 3 parts.

[0041] The functions of the main raw materials of the high - density polymethacrylimide foam provided by the present invention are further described as follows:

[0042] In the present invention, the main monomers are selected as methacrylic acid (MAA) and methacrylonitrile (MAN), which can achieve stable copolymerization to prepare high - performance PMI foam. In the embodiments of the present invention, the mass ratio of the main monomers is preferably MAA:MAN=(1 - 1.4):(0.8 - 1.2), and white PMI foam is obtained.

[0043] In the present invention, the dosage of the foaming agent is not excessively reduced. Based on the formulation with a density of 150 kg / m 3 The crosslinking degree of the system is improved by adding allyl ester crosslinking agents. The allyl ester structure contains two double bonds, which can participate in the crosslinking of the molecular chains of the system, effectively improving the crosslinking degree of the system, increasing the melt strength of the copolymer, increasing the resistance to cell expansion during the foaming process, reducing the foaming ratio, and thus increasing the density of the PMI foam. Appropriate addition of acrylate crosslinking agents can effectively increase the density of the PMI foam, and can also significantly improve the compressive strength, tensile strength and shear strength of the PMI foam, and the thermal stability is also improved to a certain extent.

[0044] By adding an appropriate amount of allyl ester crosslinking agent, when the high - temperature foaming reaches the specified density range, the temperature inside and outside the foam board gradually decreases. Due to the pressure difference in the system, the excess foaming agent cannot completely turn into gas and generate bubbles. Part of it will still remain in the polymer in the form of low - molecular dissolved substances, and another part will be stored in the cells in the form of gas with a certain pressure. When undergoing long - time high - temperature tempering treatment, due to the increased crosslinking degree, the resistance to cell expansion increases, and the cells cannot continue to expand. This ensures the high - temperature dimensional and density stability of the foam board.

[0045] However, the allyl ester crosslinking agent cannot be added excessively. When the addition amount is 1.2 parts, the resin board is normally transparent. By partially restricting the foaming temperature, a density of 150 kg / m 3PMI foam boards of about [specific value], but there are serious problems of internal and external density differences, and the high-temperature dimensional and density stability of the foam are insufficient; when increased to 4 times, there are opaque white substances on the surface layer and edges of the resin board, which need to be partially cut off. For the remaining resin board, by limiting the foaming temperature, the density of the foam board can be increased to 240 kg / m 3 , and the internal and external density differences are improved; when increased to 6 times, there are more opaque white substances on the surface layer of the resin board, and more parts need to be cut off. For the remaining resin board, it is foamed by restricting the foaming temperature, and the density of the foam board can barely be increased to 360 kg / m 3 , but the comprehensive utilization rate is relatively low; when increased to 8 times, the resin board cannot be normally transparent, the volume of the white substances is too large, and the resin board cannot be foamed, resulting in scrapping.

[0046] Research shows that when the dosage of allyl ester cross-linking agent is increased to 1.5 - 7 parts, cutting off the opaque part of the resin board and foaming with a transparent resin board can obtain a foam board with a density range of 200 - 300 kg / m 3 of the foam board, but the utilization rate of the resin board is low, and the density uniformity of the foam board is poor; and although the density of the foam board has increased, the comprehensive performance and thermal stability are still insufficient, the brittleness is enhanced, and the impact resistance decreases. While the PMI foam required for ground equipment needs to reach a maximum density of 400 kg / m 3 or above, and it is required to have good density uniformity, high-temperature stability and impact resistance in a dynamic environment. Simply adding allyl ester cross-linking agent cannot meet the requirements.

[0047] We innovatively add an appropriate amount of polybutadiene-polyacrylate core-shell rubber nanoparticles. There are physical and chemical interactions between the rubbery core and the plastic-like thin shell of the particles, which are closely combined. The addition amount is 0.5 - 5 parts, which will not have an adverse impact on the polymerization and foaming processes. Combining with allyl esters can further improve the cross-linking degree of the system and simultaneously improve the flexibility of the foam.

[0048] The polyacrylate shell of the rubber particles can enhance the stability of the particles and improve the compatibility of the particles in the PMI raw material mixture and the foamable copolymer, and improve the dispersibility and binding force of the particles in the PMI material. For polyacrylate, in the foamable copolymer of PMI, at high temperature, some of the side-chain ester bonds are hydrolyzed to form carboxyl groups, and then the carboxyl groups can react with the side-chain carboxyl groups of the PMI resin at high temperature to form anhydrides, or react with nitrile groups to form imides. Thus, the chemical combination between the shell polymer and the PMI resin is achieved, and the cross-linking degree of the PMI system is improved, which is beneficial to controlling the foaming density and making the internal and external density uniformity of the foam board better. The groups and mechanisms of this cross-linking reaction are different from those of allyl acrylate cross-linking agents. The complementarity of the two cross-linking systems makes the cross-linking and foaming processes of the resin more balanced, avoiding problems such as too fast foaming, foam cracking, and uneven cell structure caused by the imbalance between the two.

[0049] The mechanism by which such nanoparticles enhance the toughness of the foam material is different from that of adding plasticizers, and it will not cause a decrease in the heat-resistant temperature of the foam material or a decrease in the modulus of the foam material. The core of the above-mentioned rubber particles is rubbery polybutadiene, which has a large deformation ability and elasticity. The core-shell rubber and the PMI resin are phase-separated, and the rubber-phase particles play a role in stress concentration. When the PMI foam is subjected to external forces, especially impact, these particles pull the two surfaces of the crazes, causing the crazing expansion to terminate here, and at the same time leading to the formation of more crazes, absorbing and consuming more energy, and enhancing the toughness and impact resistance of the PMI foam.

[0050] In summary, in this application, methacrylic acid and methacrylonitrile are used as the main monomers, without reducing the amount of the foaming agent in the system. By adding an appropriate amount of allyl ester cross-linking agent and polybutadiene-polyacrylate core-shell rubber, the cross-linking degree of the system is appropriate, and a normal-polymerization transparent resin that can be normally foamed and a high-density PMI foam can be obtained. The high-density PMI foam prepared in this way improves the material utilization rate, has good density uniformity and high-temperature stability, better comprehensive performance, enhanced toughness, enhanced impact resistance, avoids the risk of cracking of the foam product in the application environment, enables the high-density PMI foam product to have the necessary performance, and meets the application requirements of ground equipment.

[0051] The following further illustrates the component ratios and preparation methods of the high-density polymethacrylimide foam provided by the present invention through specific examples.

[0052] Example 1

[0053] The following components in parts by weight are used: 60 parts of methacrylic acid, 50 parts of methacrylonitrile, 1.2 parts of acrylamide, 0.08 part of initiator, 1.2 parts of allyl methacrylate, 4 parts of foaming agent, 0.8 part of secondary auxiliary agent. After mixing evenly, it is poured into a mold and sealed, and free radical polymerization is carried out in a 36°C constant temperature water bath for about 7 days to obtain a transparent prepolymer resin plate. After pre-treatment and post-treatment, foaming is carried out, and the highest foaming temperature is 220°C, obtaining a PMI foam board with a density of 150 ± 35 kg / m 3 The comprehensive performance is tested after high-temperature tempering.

[0054] Example 2

[0055] Use the following components in parts by weight: 60 parts of methacrylic acid, 50 parts of methacrylonitrile, 1.2 parts of acrylamide, 0.08 part of initiator, 1.2 parts of allyl methacrylate, 4 parts of foaming agent, 1.5 parts of core-shell rubber nanoparticles, 0.8 part of secondary auxiliary agent. After mixing evenly, pour it into a mold and seal it. Carry out free radical polymerization in a 36°C constant temperature water bath for about 7 days to obtain a transparent prepolymer resin plate. After pre-treatment and post-treatment, carry out foaming. The highest foaming temperature is 220°C to obtain a PMI foam board with a density of 200 ± 26 kg / m 3 and test the comprehensive performance after high-temperature tempering.

[0056] Example 3

[0057] Use the following components in parts by weight: 60 parts of methacrylic acid, 50 parts of methacrylonitrile, 1.2 parts of acrylamide, 0.08 part of initiator, 1.8 parts of allyl acrylate, 4 parts of foaming agent, 2.0 parts of core-shell rubber nanoparticles, 0.8 part of secondary auxiliary agent. After mixing evenly, pour it into a mold and seal it. Carry out free radical polymerization in a 36°C constant temperature water bath for about 7 days to obtain a transparent prepolymer resin plate. After pre-treatment and post-treatment, carry out foaming. The highest foaming temperature is 220°C to obtain a PMI foam board with a density of 243 ± 23 kg / m 3 and test the comprehensive performance after high-temperature tempering

[0058] Example 4

[0059] Use the following components in parts by weight: 60 parts of methacrylic acid, 50 parts of methacrylonitrile, 1.2 parts of acrylamide, 0.08 part of initiator, 2.4 parts of allyl acrylate, 4 parts of foaming agent, 2.5 parts of core-shell rubber nanoparticles, 0.8 part of secondary auxiliary agent. After mixing evenly, pour it into a mold and seal it. Carry out free radical polymerization in a 36°C constant temperature water bath for about 7 days to obtain a transparent prepolymer resin plate. After pre-treatment and post-treatment, carry out foaming. The highest foaming temperature is 220°C to obtain a PMI foam board with a density of 286 ± 18 kg / m 3 and test the comprehensive performance after high-temperature tempering.

[0060] Example 5

[0061] Use the following components in parts by weight: 60 parts of methacrylic acid, 50 parts of methacrylonitrile, 1.2 parts of acrylamide, 0.08 part of initiator, 3.6 parts of allyl methacrylate, 4 parts of foaming agent, 3.4 parts of core-shell rubber nanoparticles, 0.8 part of secondary auxiliary agent. After mixing evenly, pour it into a mold and seal it. Carry out free radical polymerization in a 36°C constant temperature water bath for about 7 days to obtain a transparent prepolymer resin plate. After pre-treatment and post-treatment, carry out foaming. The highest foaming temperature is 220°C to obtain a PMI foam board with a density of 354 ± 15 kg / m 3 and test the comprehensive performance after high-temperature tempering.

[0062] Example 6

[0063] Use the following components in parts by weight: 60 parts of methacrylic acid, 50 parts of methacrylonitrile, 1.2 parts of acrylamide, 0.08 part of initiator, 4.2 parts of allyl methacrylate, 4 parts of foaming agent, 4 parts of core-shell rubber nanoparticles, 0.8 part of secondary auxiliary agent. After mixing evenly, pour it into a mold and seal it. Carry out free radical polymerization in a 36°C constant temperature water bath for about 7 days to obtain a transparent prepolymer resin plate. After pre-treatment and post-treatment, carry out foaming. The highest foaming temperature is 220°C, and a PMI foam board with a density of 420±12 kg / m 3 is obtained. After high-temperature tempering, the comprehensive performance is tested.

[0064] Example 7

[0065] Use the following components in parts by weight: 60 parts of methacrylic acid, 50 parts of methacrylonitrile, 1.2 parts of acrylamide, 0.08 part of initiator, 7.0 parts of allyl acrylate, 4 parts of foaming agent, 0.8 part of secondary auxiliary agent. After mixing evenly, pour it into a mold and seal it. Carry out free radical polymerization in a 36°C constant temperature water bath for about 7 days to obtain a transparent prepolymer resin plate. After pre-treatment and post-treatment, carry out foaming. The highest foaming temperature is 220°C, and a PMI foam board with a density of 310±22 kg / m 3 is obtained. After high-temperature tempering, the comprehensive performance is tested.

[0066] Example 8

[0067] Use the following components in parts by weight: 60 parts of methacrylic acid, 50 parts of methacrylonitrile, 1.2 parts of acrylamide, 0.08 part of initiator, 7.0 parts of core-shell rubber nanoparticles, 4 parts of foaming agent, 0.8 part of secondary auxiliary agent. After mixing evenly, pour it into a mold and seal it. Carry out free radical polymerization in a 36°C constant temperature water bath for about 7 days to obtain a transparent prepolymer resin plate. After pre-treatment and post-treatment, carry out foaming. The highest foaming temperature is 220°C, and a PMI foam board with a density of 268±30 kg / m 3 is obtained. After high-temperature tempering, the comprehensive performance is tested.

[0068] Repeat the above examples to prepare enough high-density polymethacrylimide foam. Take the high-density polymethacrylimide foam prepared in Examples 1-8 for performance parameter testing. The test data are shown in Table 1.

[0069] Table 1 Performance test data of high-density polymethacrylimide foam

[0070]

[0071] As can be seen from Table 1, in Example 1 of the present invention, no core-shell rubber nanoparticles were added, and the resulting product was a conventional PMI foam with very poor density stability. In Examples 2 to 6, an appropriate amount of allyl esters and core-shell rubber nanoparticles were added, resulting in an increase in density, an improvement in density stability, and a significant improvement in performance. Among them, the toughness was also improved, and the elongation at break reached up to 2.8%. With the increase in core-shell rubber nanoparticles, the dosage of allyl esters can be moderate, and the crosslinking degree of the system will not be excessive. The density uniformity, stability, comprehensive performance, and toughness of the prepared high-density PMI foam are significantly improved. Both the compression modulus and the tensile modulus are maintained without decrease. In this way, the PMI foam can withstand long-term high-strength compression loads and fully meet the application requirements of ground equipment.

[0072] To further verify the superiority of the allyl esters and core-shell rubber nanoparticles selected in the present invention, we also conducted Examples 7 and 8. In Example 7, 7 parts of allyl acrylate were added alone. Although a transparent resin was obtained and it could be normally foamed to a density of 310 kg / m 3 , the density stability of the foam board was poor. Although the compression strength had approached the strength of 350 kg / m 3 , the tensile strength and modulus both decreased, approaching the strength and modulus of 260 kg / m 3 . The elongation at break was only 1.2%, indicating that the crosslinking degree of the system was very high, the compression strength was enhanced, but the brittleness increased, the toughness decreased significantly, and the impact resistance decreased. After verification by customers, such materials could not withstand high-pressure impacts and would fracture.

[0073] Comparing with Example 8, when 7 parts of core-shell rubber nanoparticles were added alone, a foam with a density of 268 kg / m 3 was obtained through normal transparency and foaming. However, the density stability was even worse, indicating that compared with allyl acrylate, allyl acrylate had a stronger ability to increase the crosslinking degree with the same amount of core-shell rubber nanoparticles. The comprehensive performance showed that the compression strength had increased, approaching the strength of 286 kg / m 3 , the tensile strength had increased significantly, approaching the strength of 350 kg / m 3 , and the elongation at break reached 3.0%, indicating that the core-shell rubber nanoparticles could increase the crosslinking degree of the system and more effectively improve the toughness of the system.

[0074] With the effective interaction of the two, appropriate ratios can be used to prepare high-density PMI foams of various density models, with good density uniformity and stability, excellent comprehensive performance, and improved toughness.

[0075] It can be seen that the present invention avoids the drawbacks of the system becoming opaque due to excessive reduction of the blowing agent or the instability of the performance and density of the foam board caused by controlling the foaming temperature and size. Innovatively, acrylate and core-shell rubber nanoparticles are selected, combining the advantages of both to improve the crosslinking degree of the system, enhance the comprehensive performance, and at the same time improve the toughness of the system, enhance the impact resistance, and effectively prepare high-performance high-density PMI foam, which can meet the application requirements of high-demand ground equipment.

[0076] Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications to these embodiments once they know the basic creative concept. Therefore, the appended claims are intended to be construed to include the preferred embodiments as well as all changes and modifications falling within the scope of the present invention. Obviously, those skilled in the art can make various changes and variations to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these modifications and variations.

Claims

1. A high-density polymethacrylimide foam, characterized in that: Prepared from the following raw materials in parts by weight: 40-160 parts of methacrylic acid; Methacrylonitrile 0-80 parts; 0.1 to 6 parts of the third monomer; Initiator 0.04-5 parts; 6-10 parts of cross-linking agent; 0.5-10 parts of foaming agent; 4 to 10 parts of core-shell rubber nanoparticles; Secondary additives: 0.2-3 parts.

2. The high-density polymethacrylimide foam according to claim 1, characterized in that: The crosslinking agent is an acrylate containing a double bond, and is selected from any one of allyl methacrylate, allyl acrylate, isobornyl acrylate, hydroxyethyl methacrylate, and pentaerythritol triacrylate.

3. The high-density polymethacrylimide foam according to claim 1, characterized in that: The initiator is a combination of dibenzoyl peroxide, dodecyl peroxide, peroxydicarbonate, tert-butyl perbenzoate, azobisisobutyronitrile (AIBN), azobisisoheptanenitrile (ABVN), tert-amyl perbenzoate, methyl ethyl ketone peroxide, and cyclohexanone peroxide.

4. The high-density polymethacrylimide foam according to claim 1, characterized in that: The foaming agent is a combination selected from formamide, tert-butyl alcohol, isopropyl alcohol, azodicarbonamide, sodium bicarbonate, n-pentane and isopentane.

5. The high-density polymethacrylimide foam according to claim 1, characterized in that: The core-shell rubber is selected from polybutadiene-polyacrylate core-shell rubber, nitrile rubber-polyacrylate core-shell rubber, natural rubber-polyacrylate core-shell rubber, and chloroprene rubber-polyacrylate core-shell rubber nanoparticles. The core component is mainly polybutadiene rubber, nitrile rubber, natural rubber, and chloroprene rubber, and the shell component is polyacrylate.

6. The high-density polymethacrylimide foam according to claim 1, characterized in that: The secondary auxiliary agent includes a retarder and a release agent. The retarder is any one of p-methoxyphenol, hydroquinone, 2,5-di-tert-butylhydroquinone, and p-benzoquinone; the release agent is an organic silicone release agent, specifically including methyl silicone oil, ethyl silicone oil, methyl hydrogen silicone oil, and hydroxy silicone oil.

7. The method for preparing high-density polymethacrylimide foam according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1. According to the weight ratio, methacrylic acid, methacrylonitrile, an initiator, a crosslinking agent, a foaming agent, core-shell rubber nanoparticles and other reagents are added, and mixed to obtain a mixed solution; S2. The mixture is poured into a mold and subjected to free radical polymerization at a temperature of 30 to 55 ° C to obtain a prepolymerized resin plate; S3. The prepolymer resin plate is subjected to pretreatment, demoulding, and posttreatment to obtain a foamable resin plate; wherein the pretreatment and posttreatment are implemented as follows: the prepolymer resin plate is heated to 50-70°C and maintained for 4-8 hours, then heated to 75-95°C and maintained for 4-6 hours, and finally heated to 100-115°C and maintained for 2-5 hours; S4. heating and foaming the foamable resin plate to obtain a high-density polymethacrylimide foam; wherein the heating and foaming is carried out according to the following method: first heating the foamable resin plate to 125-140°C and maintaining it for 2.5-4.5 hours, then heating it to 145-165°C and maintaining it for 40-60 minutes, then heating it to 170-185°C and maintaining it for 45-60 minutes, and finally heating it to 190-220°C and maintaining it for 1-3.5 hours; S5. The high-density polymethacrylimide foam is subjected to high-temperature tempering post-treatment, and the high-temperature tempering post-treatment is implemented as follows: the foam board is heated to 120-140°C and maintained for 3-5 hours, then heated to 150-180°C and maintained for 3-6 hours, and then heated to 185-205°C and maintained for 5-8 hours.

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