Special-shaped high-temperature-resistant hard polyimide foam and preparation method thereof

Abstract

The invention discloses special-shaped high-temperature-resistant hard polyimide foam and a preparation method thereof. The preparation method comprises the following steps: preparing foamable precursor powder from aromatic dianhydride and diamine; placing the precursor powder in a simple mold, then placing the simple mold in an autoclave, carrying out heating and pressurizing foaming, and carrying out preliminary curing to form an incompletely crosslinked polyimide foam blank with certain strength; the method comprises the following steps: peeling and cutting a blank to obtain flat-plate-level foam with a certain thickness, placing the flat-plate-level foam on the surface of a lower mold of a foam product forming mold with a specific shape surface, covering the upper mold or coating a vacuum bag, placing the flat-plate-level foam in a high-temperature oven, and forming the foam product by setting the descending rate or vacuum degree of an upper mold plate of the mold and simultaneously heating. The hard polyimide foam arc plate with a specific shape surface is obtained. According to the method disclosed by the invention, the curved-surface special-shaped rigid polyimide foam is prepared by introducing a mold or a vacuum high-temperature heating mode, so that the rapid forming of the special-shaped curved-surface rigid polyimide foam is realized, and the application range of a foam material is widened.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer material preparation, and particularly relates to a special-shaped high-temperature resistant rigid polyimide foam and a preparation method thereof. Background Art

[0002] At present, sandwich composite material technology has become one of the most important means of lightweighting structural materials. Common sandwich core materials include silica aerogel insulation tiles, honeycombs, foams, etc. The insulation tiles are brittle and have limited mechanical properties; FRP honeycombs, aluminum honeycombs, etc. are subject to the limitations of high-temperature node glues; PMI foams, PU foams, etc. have limited mechanical strength in high-temperature environments above 200°C due to their own structure and physical properties; and the limitations of the core material's high-temperature performance directly restrict its molding matching with the high-temperature resistant composite material skin, which has become a bottleneck factor in improving the temperature resistance of sandwich structures. Polyimide foam material is an important type of polymer foam material. This type of foam material has excellent flame retardant properties, outstanding high temperature resistance, and excellent low-temperature brittleness resistance. It has been widely used as a heat insulation and noise reduction material abroad. Rigid polyimide foam material is a type of polyimide foam, which can be used as a sandwich material in an environment with high requirements for high temperature strength. At present, based on the end-capped RTM resin method, high-temperature resistant rigid foam materials with good high-temperature resistance, good antioxidant properties, high closed-cell rate, and the ability to maintain good compressive strength can be prepared.

[0003] However, most equipment products are components with a certain curvature or multiple curvatures, and the core material used in the above components should be of a special shape. In most cases, curved materials with a small curvature can be processed into special-shaped foams by flat plate processing. For foam products with large curvature and large curvature, there are two preparation processes, namely, processing after the special-shaped foam is formed; directly forming the flat-plate foam and then processing to obtain the desired foam. At present, there are the following problems in the special-shaped foam forming process: the special-shaped foam foaming process has problems such as poor cell stability, difficulty in controlling cell uniformity, severe cracking during the foaming process, and low yield rate. Moreover, the foam contains a thick skin after forming, and still needs to be processed into the desired shape. Direct processing of the flat-plate foam has the following problems: (1) high manufacturing cost and extremely low material utilization rate; (2) the internal foaming of the insulation material is uneven, which makes it difficult to control the uniformity of the foam of thick foam products and the product qualification rate is low, which will limit the use of rigid polyimide foam as a sandwich core material. Summary of the invention

[0004] The technical problem solved by the present application is: to overcome the shortcomings of the prior art, to provide a method for preparing a special-shaped rigid polyimide foam material by high-temperature hot pressing and shaping, to achieve rapid prototyping of rigid polyimide foam with complex surfaces, the method having the advantages of simple operation, high preparation efficiency, and high material utilization rate, and the prepared special-shaped rigid polyimide foam material is resistant to high temperatures and has good antioxidant properties, can maintain good compressive strength at high temperatures, and is suitable for composite sandwich structures.

[0005] The technical solutions provided by this application are as follows:

[0006] In a first aspect, a method for preparing a special-shaped high-temperature resistant rigid polyimide foam is disclosed, comprising:

[0007] S1: Preparing precursor powder of high temperature resistant rigid polyimide foam;

[0008] S2: placing the precursor powder in a mold, and then placing it in an autoclave, heating and pressurizing it for foaming to perform preliminary curing, cooling it, and releasing the pressure to obtain an incompletely cross-linked polyimide foam blank;

[0009] S3: cutting the incompletely cross-linked polyimide foam blank into flat-plate-level foam, bringing one side of the flat-plate-level foam into contact with the preformed surface, heating the flat-plate-level foam for curing and cross-linking, and gradually pressing the flat-plate-level foam toward the preformed surface.

[0010] In S2, the parameters of heating and pressurizing foaming are: pressure 0.01-0.3 MPa, temperature 240-350° C., and foaming time 8-24 h.

[0011] In S2, during the heating and pressurizing foaming process, a programmed temperature control method is adopted, firstly the temperature is raised to 250-280°C and kept constant for 1-3 hours, then 275-300°C and kept constant for 1-3 hours, then 300-325°C and kept constant for 1-3 hours, and then the temperature is lowered to room temperature for 1-3 hours.

[0012] In S3, the temperature at which the board-level foam is heated is 310-400°C.

[0013] During the heating process of S3, the mold and the foam need to be preheated first, the preheating temperature is 310-330°C, and the preheating time is 1-3 hours; after the preheating is completed, the flat-plate-level foam is heated, cured and cross-linked, and gradually pressed and fitted toward the preformed surface, and the heating procedure is as follows: heating to 320-350°C and keeping the temperature constant for 1-3 hours, 350-370°C and keeping the temperature constant for 2-4 hours, 390-400°C and keeping the temperature constant for 4-6 hours, and cooling to room temperature for 1-4 hours;

[0014] Step S3 includes two methods, namely:

[0015] The first type: in the above S3, after one side of the flat-plate-level foam is in contact with the preformed surface, the flat-plate-level foam is heated and shaped to complete curing and cross-linking, and the flat-plate-level foam is gradually pressed toward the preformed surface, including: the lower template surface is the preformed surface of the product, one side of the flat-plate-level foam is in contact with the lower template surface, the upper template surface is in contact with the side of the flat-plate-level foam away from the lower template, and after the upper mold, the lower mold and the flat-plate-level foam are preheated to the initial temperature of the heating process, the upper template descends to gradually press the flat-plate-level foam toward the preformed surface; the upper template descends at a rate of 0.1mm / 5min to 1mm / 3min. This process relies on the upper template's own gravity to press down, and when the pressure of the upper template on the flat-plate-level foam is its own gravity, the upper template stops pressing down; the gravity of the upper template ensures that one side of the flat-plate-level foam is completely in contact with the lower template surface.

[0016] The second type: in S3, after one side of the flat-level foam is brought into contact with the preformed surface, the flat-level foam is heated and shaped to complete curing and cross-linking, and at the same time, the flat-level foam is gradually pressed toward the preformed surface, including: the lower template surface is the preformed surface of the product, one side of the flat-level foam is in contact with the lower template surface, a vacuum bag is put on the outside of the integral component formed by the flat-level foam and the lower template, and vacuum is pumped to -0.02~0.5MPa and maintained for 0.5~1h, and then vacuumed to -0.05~-0.08MPa and maintained for 1~3h; and then vacuumed to -0.09~-0.1MPa to make the flat-level foam completely fit with the lower template surface of the mold, and finally heat and pressure are maintained for 0.5~5h.

[0017] The thickness of the flat-plate-grade foam is not greater than 22 mm.

[0018] This patent controls the heating and pressurizing foaming conditions in step S2 to obtain an incompletely cross-linked polyimide foam blank with a certain degree of cross-linking. After the incompletely cross-linked polyimide foam blank is processed into a flat-plate-level foam, it is further cross-linked through step S3. Through the condition control of step S3, the flat-plate-level foam has better shapeability and can be formed into a curved surface with a larger curvature.

[0019] In step S2, the temperature in the heating and pressurizing foaming conditions is lower than the foaming temperature of conventional high-temperature resistant rigid polyimide foam, so that the polyimide foam blank is in an incompletely cross-linked state. In the subsequent step S3, it can be shaped faster and can produce greater deformation; the later temperature of the heating stage of step S3 is higher than the conventional polyimide foam foaming temperature and higher than the glass transition temperature of the flat-level foam, so that the shapeability of the flat-level foam is improved.

[0020] In the S1, a precursor powder of a high-temperature resistant rigid polyimide foam is prepared, including: adding an aromatic dianhydride to a polar solvent, then adding a measured end-capping agent and a fatty alcohol, adding a diamine after complete reaction, and reacting at a temperature of 50 to 70°C for 0.5 to 3 hours to obtain a solution A; the amount of the fatty alcohol is 2 to 6 times the amount of the aromatic dianhydride; the amount of the aromatic dianhydride and the anhydride group in the end-capping agent to the amine group in the diamine is 1:1.1 to 1; then adding a foam stabilizer with a mass fraction of 0.5% to 10%, stirring for 0.5 to 3 hours to obtain a precursor solution, drying the obtained precursor solution to remove part of the solvent, and then crushing to obtain a foamable precursor powder.

[0021] The aromatic dianhydride includes one or a combination of 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride, 2,3,3',4'-benzophenone tetracarboxylic dianhydride, bisphenol A type diphenyl ether dianhydride or 2,3',4,4'-biphenyl tetracarboxylic dianhydride;

[0022] The diamine includes one or a combination of 1,4-p-phenylenediamine, 1,3-m-phenylenediamine, 4,4-'diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-bis(3-aminophenoxy)benzophenone, 4,4'-bis(3-aminophenoxy)diphenyl sulfone, 1,3-bis(4'-aminophenoxy)benzene or 2,2'-bis[4-(4-aminophenoxyphenyl)]propane.

[0023] The polar solvent is one or a combination of tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide or N-methylpyrrolidone;

[0024] The fatty alcohol includes methanol or ethanol;

[0025] The end-capping agent is 5-norbornene-2,3-dianhydride or a mixture of 5-norbornene-2,3-dianhydride and 4-phenylacetylene phthalic anhydride;

[0026] The foam stabilizer is one or a combination of AK8805 or DC-193.

[0027] In a second aspect, a special-shaped high-temperature-resistant rigid polyimide foam is provided, which is prepared according to any of the above-mentioned methods for preparing a special-shaped high-temperature-resistant rigid polyimide foam.

[0028] The density of the special-shaped high temperature resistant rigid polyimide foam is 80-350 kg / m 3 The closed porosity is 90-99%, and the thermal conductivity is 0.035-0.042 W·m -1 ·K -1 , the room temperature compressive strength is 1.2~16MPa.

[0029] In summary, this application at least includes the following beneficial technical effects:

[0030] (1) The present invention discloses a method for preparing a special-shaped high-temperature resistant rigid polyimide foam, which belongs to the technical field of preparing high-molecular polyimide foam materials, and specifically comprises the following steps: preparing a foamable precursor powder by using aromatic dianhydride and diamine; placing the precursor powder in a simple mold, and then placing it in an autoclave, heating and pressurizing it for foaming, and initially curing it to form an incompletely cross-linked polyimide foam blank with a certain strength; peeling and cutting the blank to obtain a flat-plate foam of a certain thickness, and then placing it on the surface of a lower mold of a foam product forming mold with a specific shape, covering it with an upper mold or covering it with a vacuum bag, and placing it in a high-temperature oven, and obtaining a rigid polyimide foam arc plate with a specific shape by setting the descending rate or vacuum degree of the upper mold plate of the mold and heating it at the same time. The method of the present invention prepares a rigid foam with a special curved surface by introducing a mold or a vacuum high-temperature heating method, thereby realizing the rapid molding of a rigid polyimide foam with a special curved surface and broadening the application range of the foam material.

[0031] (2) The present invention provides a method for preparing a special-shaped rigid polyimide foam material through a high-temperature hot pressing shaping process, thereby realizing the rapid molding of rigid polyimide foam with complex surfaces. The method has the advantages of simple operation, high preparation efficiency, low cost, and high material utilization.

[0032] (3) The present invention completes the process of fully cross-linking the foam plastic in the subsequent high-temperature hot-pressing shaping step, thereby reducing the temperature of the hot bending process and improving the molding efficiency.

[0033] (4) The method for preparing the special-shaped rigid polyimide foam material provided by the present invention has the following characteristics: the obtained special-shaped polyimide foam has uniform surface quality, high compressive strength and low thermal conductivity. When the foam density reaches 100kg / m 3 When the foam is compressed, its strength reaches more than 1MPa, and it can be used as the core material of sandwich structures with corresponding shapes, greatly broadening the application scope of current polyimide foam materials. DETAILED DESCRIPTION

[0034] In order to make the objectives, technical solutions and advantages of the present invention more clear, the embodiments disclosed in the present invention are described in further detail below.

[0035] The present application discloses a method for preparing a special-shaped high-temperature resistant rigid polyimide foam, comprising the following steps:

[0036] Step (1), adding aromatic dianhydride to a polar solvent, then adding a measured end-capping agent and fatty alcohol, after complete reaction, adding diamine, reacting at a temperature of 50 to 70°C for 0.5 to 3 hours to obtain solution A; the amount of fatty alcohol is 2 to 6 times the amount of aromatic dianhydride; the amount of aromatic dianhydride and the anhydride group in the end-capping agent to the amine group in the diamine is 1:1.1 to 1; then adding a foam stabilizer with a mass fraction of 0.5% to 10%, stirring for 0.5 to 3 hours to obtain a precursor solution, drying the obtained precursor solution to remove part of the solvent, and then crushing to obtain a foamable precursor powder.

[0037] The aromatic dianhydride includes one or a combination of 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride, 2,3,3',4'-benzophenone tetracarboxylic dianhydride, bisphenol A type diphenyl ether dianhydride or 2,3',4,4'-biphenyl tetracarboxylic dianhydride;

[0038] The diamine includes one or a combination of 1,4-p-phenylenediamine, 1,3-m-phenylenediamine, 4,4-'diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-bis(3-aminophenoxy)benzophenone, 4,4'-bis(3-aminophenoxy)diphenyl sulfone, 1,3-bis(4'-aminophenoxy)benzene or 2,2'-bis[4-(4-aminophenoxyphenyl)]propane.

[0039] The polar solvent is one or a combination of tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide or N-methylpyrrolidone;

[0040] The fatty alcohol includes methanol or ethanol; the end-capping agent is 5-norbornene-2,3-dianhydride or a mixture of 5-norbornene-2,3-dianhydride and 4-phenylacetylene phthalic anhydride;

[0041] The end-capping agent is 5-norbornene-2,3-dianhydride or a mixture of 5-norbornene-2,3-dianhydride and 4-phenylacetylene phthalic anhydride;

[0042] The foam stabilizer is one of AK8805 or DC-193 or a combination of several thereof.

[0043] Step (2), placing the precursor powder obtained in step (1) in a simple mold, and then putting it into an autoclave, heating and pressurizing it for foaming, initially curing it to form a rigid polyimide foam blank with a certain strength and not completely cross-linked, cooling it, and releasing the pressure to obtain a rigid polyimide foam blank.

[0044] The heating and pressurized foaming parameters are as follows: pressure 0.01-0.3 MPa, heating process is program temperature control, 240-350°C, and the total foaming time is 4-24h.

[0045] Step (3) peeling and cutting the incompletely cross-linked rigid polyimide foam blank to obtain a flat-plate foam of a certain thickness, and then placing it on the surface of the lower mold of a foam product forming mold with a specific shape, covering it with an upper mold or covering it with a vacuum bag, placing it in a high-temperature oven, setting the descending rate of the upper mold plate of the mold or controlling the vacuum degree, and simultaneously heating and shaping it by program and completing curing and cross-linking to obtain a special-shaped rigid polyimide foam with a specific shape. The shaping temperature is staged and the shaping temperature is 310 to 400°C.

[0046] The thickness of the incompletely cross-linked rigid polyimide foam blank is not more than 22mm; the thickness of the mold is usually greater than 10mm, and the shape of the lower mold template is the product shape; when the mold is used for shaping, the descending rate of the upper mold template is 0.1-1mm / 5min; when the vacuum bag is used for shaping, the specific process parameters are as follows: first evacuate to -0.02-0.5MPa and maintain for 0.5-1h, then evacuate to -0.05-0.08MPa and maintain for 1-3h; then evacuate to -0.09-0.1MPa to make the foam blank completely fit with the surface of the lower mold of the mold, and finally keep the temperature and pressure for 0.5-2h, cool down and release the pressure to remove the foam product.

[0047] According to a second aspect of the present invention, there is provided a special-shaped high-temperature-resistant rigid polyimide foam, which is prepared by the above-mentioned preparation method.

[0048] Preparation Example

[0049] Preparation of foamable RTM process resin:

[0050] RTM1: In a three-necked flask equipped with an agitator and a condenser, add 1400 g of tetrahydrofuran, 570 g of ethanol, and then add 728 g of 2,3',4,4'-biphenyltetracarboxylic anhydride, 375 g of 5-norbornene-2,3-dianhydride, raise the temperature to 65°C and continue the reaction for 3 hours, then add 445 g of 1,3-m-phenylenediamine, mix for 2 hours, and then add 20 g of AK8805 to obtain a precursor solution, remove the solvent, and then dry it in an environment of 240°C, then crush it with a high-speed crusher, pass it through a 300-mesh sieve, and set it aside.

[0051] RTM2: In a three-necked flask equipped with an agitator and a condenser, add 1000 g of tetrahydrofuran, 340 g of methanol, and then add 880 g of 2,3',4,4'-biphenyltetracarboxylic anhydride and 830 g of 5-norbornene-2,3-dianhydride. Heat to 65°C and continue the reaction for 3 hours. Then add 490 g of 1,3-m-phenylenediamine and 320 g of 1,3-bis(4'-aminophenoxy)benzene. After mixing for 2 hours, add 15 g of AK8805 to obtain a precursor solution. Remove the solvent, then dry it in an environment of 240°C, and then crush it with a high-speed crusher, pass it through a 300-mesh sieve, and set it aside.

[0052] RTM3: In a three-necked flask equipped with a stirrer and a condenser, add 1260g of tetrahydrofuran, 552g of ethanol, 882g of α-isomeric biphenyl dianhydride and 495g of 4-phenylethynyl phthalic anhydride, raise the temperature to 65°C and continue the reaction for 3h, then add 432g of 1,3-m-phenylenediamine, continue stirring for 2h, then add 18g of AK8805 to obtain a precursor solution, then remove the solvent, then dry in an environment of 240°C, then crush with a high-speed crusher, pass through a 300-mesh sieve, and set aside.

[0053] Example 1

[0054] A total of 2 kg of the above-mentioned resin powder RTM1 is placed in a simple mold, and then the mold is placed in a high-temperature pressure tank. N2 is flushed back and forth three times to remove oxygen, and then N2 is filled in and pressurized to 0.075 MPa. The temperature is raised to 260°C and kept constant for 1 hour, 280°C for 1 hour, 300°C for 2 hours, and then cooled for 2 hours. Then the pressure is released to normal pressure and taken out to obtain an incompletely cross-linked polyimide foam blank.

[0055] The polyimide foam blank was peeled and cut to obtain a 12 mm thick flat-plate foam, which was then placed on the lower mold surface of an arc-shaped foam product molding mold, covered with an upper mold, and placed in a high-temperature oven. The mold and the foam were first preheated to 310°C for 1 hour, and then the upper mold of the mold was set to descend at a rate of 1 mm / 3 min, and the temperature was raised to 320°C for 1 hour, 350°C for 3 hours, 390°C for 5 hours, and then cooled for 2 hours. The mold was taken out and demoulded to obtain an arc-shaped hard polyimide foam. The obtained polyimide foam material had a density of 100 kg·m -3 , thickness 10mm, compression strength 1.28MPa, thermal conductivity 0.032W·m -1 ·K -1 .

[0056] Example 2

[0057] A total of 2 kg of the above-mentioned resin powder RTM1 is placed in a simple mold, and then the mold is placed in a high-temperature pressure tank. N2 is flushed back and forth three times to remove oxygen, and then N2 is filled in and pressurized to 0.10 MPa (the density of the incompletely cross-linked polyimide foam blank obtained in Example 1 is higher), the temperature is raised to 260°C and kept at a constant temperature for 1 hour, 280°C and kept at a constant temperature for 1 hour, 300°C and kept at a constant temperature for 2 hours, and then the temperature is lowered for 2 hours, and then the pressure is released to normal pressure and taken out to obtain an incompletely cross-linked polyimide foam blank.

[0058] The polyimide foam blank was peeled and cut to obtain a 12 mm thick flat-plate foam, which was then placed on the lower mold surface of an arc-shaped foam product molding mold, covered with an upper mold, and placed in a high-temperature oven. The mold and the foam were first preheated to 310°C for 1.5 hours, and then the upper mold of the mold was set to descend at a rate of 0.5 mm / 5 min, and the temperature was raised to 320°C for 1 hour, 350°C for 3 hours, and 390°C for 5 hours. The temperature was lowered for 2 hours, the mold was taken out, and demolding was performed to obtain an arc-shaped hard polyimide foam. The obtained polyimide foam material had a density of 130 kg·m -3 , thickness 11mm, compression strength 1.8MPa, thermal conductivity 0.035W·m -1 ·K -1 .

[0059] Example 3

[0060] A total of 2 kg of the above-mentioned resin powder RTM1 is placed in a simple mold, and then the mold is placed in a high-temperature pressure tank. N2 is flushed back and forth three times to remove oxygen, and then N2 is filled in and pressurized to 0.25 MPa (the density is higher than that of the incompletely cross-linked polyimide foam blank obtained in Example 1). The temperature is raised to 260°C and kept at a constant temperature for 1 hour, 280°C and kept at a constant temperature for 1 hour, 300°C and kept at a constant temperature for 2 hours, and then cooled for 2 hours, and then the pressure is released to normal pressure and taken out to obtain an incompletely cross-linked polyimide foam blank.

[0061] The polyimide foam blank was peeled and cut to obtain a 12 mm thick flat-plate foam, which was then placed on the lower mold surface of an arc-shaped foam product molding mold, covered with an upper mold, and placed in a high-temperature oven. The mold and the foam were first preheated to 310°C for 2 hours, and then the upper mold of the mold was set to descend at a rate of 0.5 mm / 5 min, and the temperature was raised to 320°C for 1.5 hours, 350°C for 3.5 hours, and 390°C for 6 hours. The temperature was lowered for 2 hours, the mold was taken out, and demolding was performed to obtain an arc-shaped rigid polyimide foam. The obtained polyimide foam material had a density of 300 kg·m -3 , thickness 11mm, compression strength 13.5MPa, thermal conductivity 0.040W·m -1 ·K -1 .

[0062] Example 4

[0063] A total of 2 kg of the above-mentioned resin powder RTM1 is placed in a simple mold, and then the mold is placed in a high-temperature pressure tank. N2 is flushed back and forth three times to remove oxygen, and then N2 is filled in and pressurized to 0.075 MPa. The temperature is raised to 260°C and kept constant for 1 hour, 280°C for 1 hour, 300°C for 2 hours, and then cooled for 2 hours. Then the pressure is released to normal pressure and taken out to obtain an incompletely cross-linked polyimide foam blank.

[0064] The polyimide foam blank was peeled and cut to obtain a 12 mm thick flat-plate foam, which was then placed on the lower mold surface of an arc-shaped foam product molding mold, covered with a vacuum bag, and placed in a high-temperature oven. The mold and the foam were first preheated to 310°C for 1.5 hours, first vacuumed to -0.04MPa, heated to 320°C and kept constant for 1 hour, then vacuumed to -0.06MPa, heated to 350°C and kept constant for 3 hours, then vacuumed to -0.09MPa, heated to 390°C and kept constant for 5 hours, cooled for 2 hours, and the mold was taken out and demoulded to obtain an arc-shaped hard polyimide foam. The obtained polyimide foam material had a density of 110 kg·m -3 , thickness 10.5mm, compression strength 1.3MPa, thermal conductivity 0.033W·m -1 ·K -1 .

[0065] Example 5

[0066] A total of 2 kg of the above-mentioned resin powder RTM2 was placed in a simple mold, and then the mold was placed in a high-temperature pressure tank. N2 was flushed back and forth three times to remove oxygen, and then N2 was filled in and pressurized to 0.075 MPa. The temperature was raised to 260°C and kept constant for 1 hour, 280°C for 1 hour, 300°C for 2 hours, and then cooled for 2 hours. Then the pressure was released to normal pressure and the mold was taken out to obtain an incompletely cross-linked polyimide foam blank.

[0067] The polyimide foam blank was peeled and cut to obtain a 12 mm thick flat-plate foam, which was then placed on the lower mold surface of an arc-shaped foam product molding mold, covered with an upper mold, and placed in a high-temperature oven. The mold and the foam were first preheated to 310°C for 1.5 hours, and then the upper mold of the mold was set to descend at a rate of 0.5 mm / 5 min, and the temperature was raised to 320°C for 1 hour, 350°C for 3 hours, and 390°C for 5 hours. The temperature was lowered for 2 hours, the mold was taken out, and demolding was performed to obtain an arc-shaped hard polyimide foam. The obtained polyimide foam material had a density of 130 kg·m -3 , thickness 10mm, compression strength 1.6MPa, thermal conductivity 0.035W·m -1 ·K -1 .

[0068] Example 6

[0069] A total of 2 kg of the above-mentioned resin powder RTM3 was placed in a simple mold, and then the mold was placed in a high-temperature pressure tank. N2 was flushed back and forth three times to remove oxygen, and then N2 was filled in and pressurized to 0.05 MPa. The temperature was raised to 280°C and kept constant for 1 hour, 300°C for 1 hour, 320°C for 2 hours, and then cooled for 2 hours. Then the pressure was released to normal pressure and taken out to obtain an incompletely cross-linked polyimide foam blank.

[0070] The polyimide foam blank was peeled and cut to obtain a 12 mm thick flat-plate foam, which was then placed on the lower mold surface of an arc-shaped foam product molding mold, covered with an upper mold, and placed in a high-temperature oven. The mold and the foam were first preheated to 330°C for 1.5 hours, and then the upper mold of the mold was set to descend at a rate of 0.5 mm / 5 min, and the temperature was raised to 350°C for 1 hour, 370°C for 3 hours, 400°C for 5 hours, and then cooled for 2 hours. The mold was taken out and demoulded to obtain an arc-shaped hard polyimide foam. The obtained polyimide foam material had a density of 180 kg·m -3 , thickness 10mm, compression strength 2.9MPa, thermal conductivity 0.035W·m -1 ·K -1 .

[0071] Comparative Example 1

[0072] A total of 2 kg of the above-mentioned resin powder RTM1 is placed in a simple mold, and then the mold is placed in a high-temperature pressure tank. N2 is flushed back and forth three times to remove oxygen, and then N2 is filled in and pressurized to 0.075 MPa. The temperature is raised to 260°C and kept constant for 1 hour, 280°C for 1 hour, 300°C for 2 hours, 320°C for 2 hours, 350°C for 2 hours, 390°C for 3 hours, and then cooled for 2 hours. Then the pressure is released to normal pressure and taken out to obtain a fully cross-linked polyimide foam blank.

[0073] The polyimide foam blank was peeled and cut to obtain a 12 mm thick flat-plate foam, which was then placed on the lower mold surface of an arc-shaped foam product molding mold, covered with an upper mold, and placed in a high-temperature oven. The mold and foam were first preheated to 330°C for 1 hour, and then the upper mold of the mold was set to descend at a rate of 0.6 mm / 3 min, and the temperature was raised to 350°C and kept constant for 4 hours, 390°C and kept constant for 6 hours, and then cooled for 2 hours. The mold was taken out and demoulded to obtain an arc-shaped hard polyimide foam. The obtained polyimide foam material had a density of 105 kg·m -3 , thickness 10.5mm, compression strength 1.08MPa, thermal conductivity 0.034W·m -1 ·K -1 .

[0074] Compared with Example 1, the entire heating process is 25 hours, which is 10 hours longer than that of Example 1.

[0075] Comparative Example 2

[0076] A total of 2 kg of the above-mentioned resin powder RTM1 is placed in a simple mold, and then the mold is placed in a high-temperature pressure tank. N2 is flushed back and forth three times to remove oxygen, and then N2 is filled in and pressurized to 0.2 MPa. The temperature is raised to 260°C and kept constant for 1 hour, 280°C for 1 hour, 300°C for 2 hours, 320°C for 2 hours, 350°C for 2 hours, 390°C for 3 hours, and then cooled for 2 hours. Then the pressure is released to normal pressure and taken out to obtain a fully cross-linked polyimide foam blank.

[0077] The polyimide foam blank was peeled and cut to obtain a 15 mm thick flat-plate foam, which was then placed on the lower mold surface of an arc-shaped foam product molding mold, covered with an upper mold, and placed in a high-temperature oven. The mold and foam were first preheated to 330°C for 2 hours, and then the upper mold of the mold was set to descend at a rate of 0.3 mm / 5 min, and the temperature was raised to 350°C and kept constant for 4 hours, 390°C and kept constant for 6 hours, and then cooled for 2 hours. The mold was taken out and demolded, but an arc-shaped rigid polyimide foam with good adhesion was not obtained (there was a gap of 0.5 to 2 mm between the foam board and the mold). The density of the obtained polyimide foam material was 220 kg·m -3 , average thickness 14mm, compression strength 2.0MPa, thermal conductivity 0.037W·m -1 ·K -1 .

[0078] By comparing the embodiment with comparative examples 1 and 2, it can be clearly determined that: in comparative example 2, the fully cross-linked polyimide foam with a larger density cannot be directly subjected to curved surface forming; in comparative example 1, the fully cross-linked polyimide foam with a smaller density can be formed into a preformed surface, but it takes too long. The preparation method of the present patent can perform curved surface forming on flat-plate-level foams with different densities (including flat-plate-level foams with a larger density, and the density of the flat-plate-level foams that can be formed can reach 300kg / m 3 ), and can more quickly obtain a special-shaped high-temperature resistant rigid polyimide foam with a predetermined profile surface.

[0079] The present invention has been described in detail above in conjunction with specific implementations and exemplary examples, but these descriptions cannot be understood as limiting the present invention. Those skilled in the art understand that, without departing from the spirit and scope of the present invention, a variety of equivalent substitutions, modifications or improvements may be made to the technical solution of the present invention and its implementation methods, all of which fall within the scope of the present invention. The scope of protection of the present invention shall be subject to the attached claims.

[0080] The contents not described in detail in the specification of the present invention belong to the common knowledge of those skilled in the art.

Claims

1. A method for preparing a special-shaped high-temperature resistant rigid polyimide foam, characterized in that: include: S1: Preparing precursor powder of high temperature resistant rigid polyimide foam; S2: placing the precursor powder in a mold, and then placing it in an autoclave, heating and pressurizing it for foaming to perform preliminary curing, cooling it, and releasing the pressure to obtain an incompletely cross-linked polyimide foam blank; S3: cutting the incompletely cross-linked polyimide foam blank into flat-plate-level foam, bringing one side of the flat-plate-level foam into contact with the preformed surface, heating the flat-plate-level foam for curing and cross-linking, and gradually pressing the flat-plate-level foam toward the preformed surface.

2. The method for preparing a special-shaped high-temperature resistant rigid polyimide foam according to claim 1, characterized in that: In S2, the parameters of heating and pressurizing foaming are: pressure 0.01-0.3 MPa, temperature 240-350° C., and foaming time 4-24 h.

3. The method for preparing a special-shaped high-temperature resistant rigid polyimide foam according to claim 2, characterized in that: In S2, during the heating and pressurizing foaming process, a programmed temperature control method is adopted, firstly the temperature is raised to 250-280°C and kept constant for 1-3 hours, then 275-300°C and kept constant for 1-3 hours, then 300-325°C and kept constant for 1-3 hours, and then the temperature is lowered to room temperature for 1-3 hours.

4. The method for preparing a special-shaped high temperature resistant rigid polyimide foam according to claim 1, characterized in that: In S3, the temperature at which the board-level foam is heated is 310-400°C.

5. The method for preparing a special-shaped high temperature resistant rigid polyimide foam according to claim 4, characterized in that: During the heating process of S3, the mold and the foam need to be preheated first, the preheating temperature is 310-330°C, and the preheating time is 1-3 hours. After the preheating is completed, the flat-plate-level foam is heated, cured and cross-linked, and gradually pressed and fitted toward the preformed surface. The heating procedure is as follows: heat to 320-350°C and keep the temperature constant for 1-3 hours, 350-370°C and keep the temperature constant for 2-4 hours, 390-400°C and keep the temperature constant for 4-6 hours, and cool to room temperature for 1-4 hours.

6. The method for preparing a special-shaped high temperature resistant rigid polyimide foam according to claim 1, characterized in that: In S3, after one side of the flat-plate-level foam is brought into contact with the preformed surface, the flat-plate-level foam is heated and shaped to complete curing and cross-linking, and the flat-plate-level foam is gradually pressed toward the preformed surface, including: The lower template surface is the pre-molding surface of the product. One side of the flat-grade foam contacts the lower template surface, and the upper template surface contacts the side of the flat-grade foam away from the lower template. After the upper mold, the lower mold and the flat-grade foam are preheated as a whole to the initial temperature of the heating process, the upper template descends to gradually press the flat-grade foam toward the pre-molding surface; the upper template descends at a rate of 0.1 mm / 5 min to 1 mm / 3 min.

7. The method for preparing a special-shaped high temperature resistant rigid polyimide foam according to claim 1, characterized in that: In S3, after one side of the flat-plate-level foam is brought into contact with the preformed surface, the flat-plate-level foam is heated and shaped to complete curing and cross-linking, and the flat-plate-level foam is gradually pressed toward the preformed surface, including: The lower template surface is the preformed surface of the product. One side of the flat-level foam is in contact with the lower template surface. A vacuum bag is put on the outside of the integral component formed by the flat-level foam and the lower template. The vacuum is pumped to -0.02~0.5MPa and maintained for 0.5~1h. The vacuum is then pumped to -0.05~-0.08MPa and maintained for 1~3h. The vacuum is then pumped to -0.09~-0.1MPa to make the flat-level foam completely fit with the lower template surface of the mold. Finally, the heat and pressure are maintained for 0.5~5h.

8. The method for preparing a special-shaped high temperature resistant rigid polyimide foam according to claim 1, characterized in that: The thickness of the flat-plate-grade foam is not greater than 22 mm.

9. A special-shaped high temperature resistant rigid polyimide foam, characterized in that: The foam is prepared according to the method for preparing a special-shaped high-temperature-resistant rigid polyimide foam according to any one of claims 1 to 8.

10. The special-shaped high temperature resistant rigid polyimide foam according to claim 9, characterized in that: The density of the special-shaped high temperature resistant rigid polyimide foam is 80-350 kg / m 3 The closed porosity is 90-99%, and the thermal conductivity is 0.035-0.042 W·m -1 ·K -1 , the room temperature compressive strength is 1.2~16MPa.